Welding and cutting in the new millennium - esab.de · submerged arc welding, gas-tung-sten arc...

A welding review published by The Esab Group Vol. 54 No. 1–2 1999

Welding and cutting in the new millennium

Svetsaren No.1–2 1999

Contents Vol. 54 No. 1–2 1999Challenges for welding consumables for the newmillenniumImportant trends for materials development challenges the development of consumables andprocesses.

From prototype to integrated production system10 years of research and development results in theTHOR ArcWeld production system — a system forthe automatic programming of welding robots.

Welding duplex chemical tankers the ESAB wayA review ot the production of chemical tankers atFactorías Vulcano S.A in Spain.

Consumables for welding modified 9 Cr-1 Mo steelA comparison between modified and conventionalcreep-resistant ferritic steels and the consumablesto be used.

Laser welding catalytic converters — a complete success for AP Torsmaskiner AB, SwedenLarge-scale production of laser-welded componentfor vehicles.

Consumables for welding high strength steelsThe use of high strength steels increases the needfor new welding consumables

Cutting systems in an environmental contextThe environmental issues have become an increas-ingly important point on the agenda when it comesto the design of cutting systems

New ESAB OK Tubrod 15.13 for robot welding atFincantieriThe future success of the European Union projectfor Fully Automatic Ship Production ultimately de-pends on the performance of cored wires when itcomes to optimising productivity.

Stubends & Spatter

Laser welding — A mature process technology withvarious application fieldsThe possible applications for laser welding in themanufacturing industries will be more or less unlimited.

Energy efficiency in weldingLower energy costs give better economy and environmental effects with the choice of the rightequipment.

Effect of interpass temperature on properties ofhigh-strength weld metalsThe microstructure of high-strength weld metals becomes sensitive to variations in the interpass temperature in multirun welds.

“The technology of tomorrow” has already been implemented at BORSIG in GermanyInstalling the new technologies for adaptive weldingand automatic robotic oxy-fuel cutting at BORSIG’sheavy-duty plant has clearly increased productivity.

Increasing availabilityWith modern cutting systems it is possible to unifymachine investment and to cut workpiece idle timesdramatically.

Fabricators pleased with increased submerged arcproductivity from cored wiresSAW with cored wires gives great benefits directlyfrom improved welding economy due to an increaseddeposition rate converted to higher travel speed

Welding and cutting beyond the year 2000Major trends and conclusions from a gas-relatedpoint of view

Modern MIG welding power sourcesFeatures of modern power source technology.

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Articles in Svetsaren may be reproduced without permission but with an acknowledgement to Esab.

PublisherBertil Pekkari

EditorLennart Lundberg

Editorial committeeKlas Weman, Lars-Göran Eriksson, Johnny Sundin, Johan Elvander, Dag Jacobsen,

Jerry Uttrachi, Stan Ferree, Ben Altemühl, Nils-Erik Andersen, Susan Fiore

AddressEsab AB, Box 8004, S-402 77 Göteborg, Sweden

Internet addresshttp://www.esab.se

E-mail: [email protected]

Printed in Sweden by Skandia-Tryckeriet, Göteborg

A welding review published by The Esab Group No. 1–2 • 1999

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The Friction Stir Welding process isbeing used for the welding of fuel tanksin the Boeing Delta space rockets.

Nya Svetsaren 1, 1999. 1999-07-01 10.15 Sidan 2

Svetsaren No.1–2 1999 3

Arc welding was invent-ed around 100 years agoand, at least during thepast 50 years, it hasbeen the main fabrica-tion method for struc-tures made of steel andother metallic materials.There are several arcwelding processes,which means that thereare many possible waysto optimise the weldingoperation. With many ofthe methods, the me-

chanisation of the pro-cess is possible and thiscan decrease the cost ofwelding. With the largenumber of consumablesavailable, the flexibilityrequired to achieve ap-propriate properties inthe welded joint is veryhigh.The potential for adjusting thechemical composition of the weldmetal is almost unlimited. By us-ing different flux systems, weldingcharacteristics such as drop trans-fer, arc stability and the fluidity

of the molten metal can be con-trolled.

However, to maintain profit-ability, industry must always lookfor ways of improving and ration-alising working processes. Aswelding is such a central processfor many fabricators, the weldingoperation has been the focalpoint for many of the improve-ments which have been madeover the years. These improve-ments can be categorised intothree main groups:

developments in designdevelopment of welding pro-cessesdevelopments in materials.

Of course, these developmentscannot be seen in isolation but

Challenges for welding consumables for the new millennium

by Lars-Erik Svensson and Johan Elvander, Esab AB, Göteborg, Sweden

Figure 1. The relative use of different welding processes, measured in the form of weld metal consumption.


4 Svetsaren No.1 1999

are interrelated. In order to dis-cuss possible future develop-ments, it may, however, be helpfulto make this division.

Design developments fall out-side the scope of this paper, but itcan be briefly stated that, withthe introduction of high-speedcomputers, finite element calcula-tions of critical details in a struc-ture have become a standardtool, helping to optimise the con-struction significantly. Althoughdesign is traditionally conserva-tive, due to the major conse-quences of a failure, there is defi-nitely a trend towards utilisingmaterials such as higher strengthsteels or aluminium to producelighter structures with a highload-carrying capacity. In thiscontext, it must be realised thatone of the controlling factors indesign is fatigue, which is a limit-ing factor for the use of high-strength steels.

With the development ofmechanised welding, it is moreadvantageous to use fillet weldingrather than butt welding. To im-plement this, the development ofthe welding processes took placeprimarily from 1930 and onwards.The most common processes likesubmerged arc welding, gas-tung-sten arc welding and gas-metalarc welding were all developedmore than 50 years ago. Theyhave been further refined withthe aid of sophisticated electroniccomponents in power sources,elaborate handling devices likecolumns and booms and seamsensors. Many of the methods arenow fully automated. The produc-tivity of the processes has alsobeen increased by a number ofmodifications. The best exampleis probably submerged arc weld-ing, where productivity can be in-creased by using multi-wire sys-tems or by feeding metal powderinto the weld pool. In gas-metalarc welding, the use of coredwires has led to an increase inproductivity. Here, too, modifica-tions to the process, as in RapidArc and Rapid Melt, have ac-quired some degree of popularity.

In parallel with the develop-ments in productivity, consum-ables have also been developedto meet new and higher require-

ments. Three different situationshave been encountered;

higher strength and impacttoughness as well as enhancedcorrosions resistance is de-sired to match the develop-ment of steel,higher impact toughness atlower temperatures is neededfor structures operating inharsh environments to main-tain strength and toughnessfor welds deposited with high-er productivity (which gener-ally means higher heat inputand coarser microstructures).

Arc welding has been estab-lished for many years as the lead-ing joining process. In certain ap-plications, other processes haveacquired increasing popularity. Inthe automotive industry in partic-ular, many other joining process-es, such as adhesives and laserwelding, have taken over fromtraditional arc welding. In mostother circumstances, arc weldingis still the leading process, despitethe fact that many other process-es have been developed. In recentyears, two other processes, laserwelding and friction stir welding,have been introduced and devel-oped to such an extent that theycan be regarded as realistic chal-lengers to arc welding. The bene-fits to the user of these processesare that they are often performedin just one or two passes, even forrelatively thick material, and thatthe distortion of the plates is verysmall, resutling in far less workfor rectification. The drawbacksare the large investment costs andthe need for much closer fit-up ofthe plates. In the case of laserwelding, special grades of plateare needed and, in the case offriction stir welding, the supple-mentary equipment for handlingthe plates is quite extensive. Inthe large research projects thathave been run or are still in pro-gress and in which these process-es are being evaluated, otherdrawbacks have also been noted.The ductility of laser welds is usu-ally lower than that found in arcwelds and, due to the very highcooling rates, martensite is oftenformed both in the heat affectedzone and in the weld metal. Fric-tion stir welding is still very much

more at the development stageand has only been used commer-cially for welding aluminium, withvery promising results. It is stillnot known whether it will be pos-sible to use this process for steelson a larger scale.

Process developmentThe relative use of differentwelding consumable types, meas-ured in terms of weld metal con-sumption, for welding structuralsteel between 1975 and 1996 isshown in Figure 1. The figureshows the development for threeregions: Western Europe, theUSA and Japan.

The use of covered electrodeshas been replaced by methodsproducing higher productivity.MIG/MAG welding, using solidwires, has captured the largestmarket shares. The consumptionof tubular wire was less than 5%for many years, but, during thelast few years, it has increasedmarkedly and is now almost 10%.This consumption is expected tocontinue to increase rapidly.

The decrease in the use of cov-ered electrodes is expected to beless dramatic in the years tocome, although some further de-crease can still be foreseen. Thegrowth of tubular wires will thenbe due in part to a change in pro-cess from covered electrodes, butit will mainly result from the re-placement of solid wires with tu-bular wires.

The major change which is cur-rently taking place is the increas-ing use of welding robots andother forms of mechanisation.This trend is particularly strong incountries with high labour costs,but another, equally importantfactor is the difficulty involved infinding qualified welders who arewilling to perform manual weld-ing. It has, in fact, been found thatthe wear and tear experienced bywelders, especially when weldingwith semi-automatic processes,can be quite high. To address thissituation, two possible methodscan be considered: either fullymechanise the operation or intro-duce another method which im-poses less weight on the welder’sarms and shoulders. The secondmethod has sometimes been


Svetsaren No.1 1999 5

used. One example of this comesfrom Norway where, in a particu-lar application, MMA weldingwith high-recovery covered elec-trodes replaced semi-automaticwelding. It was actually foundthat productivity was not reducedbut was instead enhanced. Thelesson to be learned here is thatthere are several ways of achiev-ing high productivity. High flex-ibility and a careful analysis ofthe different options is most like-ly to promote the optimum choi-ce, which will in turn lead to max-imised productivity.

Environmental questions haveattracted increasing interest inmodern society. The demand formore environmentally-friendlyoperations has been stepped up— in the welding industry andother areas. Esab has played anactive part in improving the situ-ation with regard to the impacton the environment from manyparts of its operations. Detailsabout Esab’s environmental ac-tivities can be found in (1). Anew report describing further im-provements will be issued in1999.

The main welding process inFigure 1 is MIG/MAG weldingwith solid wire. This is not sur-prising, due to the combination offlexibility, productivity and qual-ity the method offers. The latestdevelopments here are related tothe packaging system. For appli-cations with high duty cycles, theintroduction of Marathon Pacwas a major improvement. Mara-thon Pac has been further refinedand is now made of recyclablematerial. Using a special system,the wire always comes outstraight, producing extremely lowfriction in the wire conduit. Witha new and improved design, 12 mlong wire conduits are used.When starting, only the free wireneeds to be accelerated, therebyreducing the wear on the driverollers. The straight wire is a ma-jor benefit in different situationswhen the wire has to be posi-tioned carefully (e.g. welding innarrow gaps) or when welding inthin plate, for example. When us-ing robot welding, joint trackingis critical and the straight wiremakes this much more accurate.

The most important benefit ofMarathon Pac is, however, the op-portunity to increase productivity.The number of bobbin changes isreduced significantly, repairs andrejects are reduced and it is pos-sible to run unmanned shifts dur-ing the night.

Further improvements on thepackaging side are expected. Atpresent, Marathon Pac is avail-able in two sizes. The serial con-nection of several MarathonPacs, to reduce the number ofchanges, has also been testedwith promising results.

The most important factor fora fabricator using robotic weldingis that the robot can run continu-ously. This in turn leads to re-quirements being imposed on theequipment and consumables, to-gether with high and consistentquality to create the conditionsnecessary for problem-free oper-ation.

For the wires at a robot weld-ing station, feedability and easeof arc striking are essential prop-erties. The new robotic wire,PZ6105R, from Filarc is one ex-ample of this development.

Most robots are designed forsolid wires, but they can be chan-ged relatively simply to coredwires and the different parametersettings that are needed. The ad-vantages of metal cored wirescompared with solid wires arethe higher welding speeds thatcan be attained, the improvementin penetration and the reductionin spatter.

As soon as a robot is installed,the handling time is more or lessconstant, independent of thechoice of process. So, the onlyway to increase productivity stillfurther is to increase the weldingspeed (e.g. use of cored wires).The higher and broader penetra-tion in fillet welds produces a



larger safety margin for the con-struction and the opportunity forwider tolerances in the fit-up.There are also discussions aboutwhether it is possible to take ac-count of the penetration whencalculating the throat thickness.This would add a further benefitto the cored-wire process andwould also be a significant cost-reduction factor. Another impor-tant factor is the bead shape,which is much smoother for thecored-wire process. The transitionbetween the weld metal and thebase material is also muchsmoother with cored wires, some-thing that is very important forconstructions subjected to fluctu-ating loads. The low spatter re-duces the need for post-cleaningto a minimum, thereby enablingwelded parts to be immediatelytransported to the next link inthe manufacturing chain.

There are some further devel-opment in the MAG process(twin-arc MAG and tandemMAG) which may be of signifi-cant interest for the future. Intwin-arc MAG, two wires are fedinto the same torch and connect-ed to a sophisticated power sour-ce. The wires have the same volt-age, but different feeding rates.By pulsing, disturbances betweenthe arcs are avoided. This processproduces extremely high deposi-tion rates. The process has alsobeen tested with metal coredwires (PZ 6105R and OK Tubrod14.13) with good results.

Submerged arc welding hashad a fairly stable share of themarket over the years. It is ahigh-productivity process and theapplications are therefore oftenassociated with heavy industry. Anumber of improvements havebeen made for even higher pro-ductivity, such as increasing thenumber of welding wires. Onerelatively new development in-volves using a tubular wire in-stead of a solid wire. This increas-es the deposition rate, improvesthe penetration profile andmakes the adaptation of chemicalcomposition much easier. Theprocess is now being further op-timised, with the joint develop-ment of the cored wire and theflux, to provide a better process.One further example of develop-

ment within this field is the useof a cold wire, which is fed separ-ately but in synchronised form,into the weld pool. This featureboth increases productivity sig-nificantly and helps to cool theweld, thereby preventing exces-sive grain growth. A patent forthis process has now been filedby Esab.

In the future, it is expectedthat, in the case of assemblywelding, especially for heavyequipment, covered electrodeswill still be used. The use of tubu-lar wires will increase significant-ly, especially in Europe. Tubularwires will replace covered elec-trodes, as well as solid wires tosome extent. The main develop-ments will be seen in tubular andsolid wires, particularly in con-nection with mechanised welding.For the technically most ad-vanced fabricators, sophisticatedmethods like laser welding willbe introduced. For fabricatorswho cannot invest the very largeamount of money required for la-sers, advanced methods like twin-arc MIG, which is still based onrelatively conventional powersources, but with advanced soft-ware, could be one possible wayof increasing productivity. How-ever, the majority of fabricatorsare small and medium-sized en-terprises and, as a result, conven-tional welding methods will stillbe used. Productivity will then beobtained from using more effi-cient consumables.

Developments in struc-tural steelThe large advance in terms of theweldability of structural steelscame with the introduction of thethermo-mechanically (TM) pro-cessed steels at the beginning ofthe 1980s. Compared with the tra-ditional normalised steels, thenew steels had a much leanercomposition, for the same yieldstrength. The carbon content inparticular was reduced and thestrength was obtained from finergrain size and increased disloca-tion density. Sometimes, acceler-ated cooling was used, adding ex-tra strength as the steel trans-formed to bainite rather than fer-rite.

In addition to the lower carboncontent, the quality of the steelswas improved significantly by areduction in the impurity element(sulphur and phosphorus) con-tent.

It is difficult to envisage a simi-lar major development in steels inthe near future. Slow and contin-uous improvements will probablybe made to TM steels — in termsof their impact properties, for ex-ample — and they may find newapplications, but, as there willprobably be no major changes,there will be no need to makeany significant changes to theconsumables used for weldingthese steels.

In the new European standardEN 10 113-3, TM steels with yieldstrengths of up to 460 MPa arespecified. TM steels can now beproduced at many steelworks.What might differ between sup-pliers is the combination of platethickness and yield strength thatcan be delivered. Many of thesteels supplied with yieldstrengths of up to approximately500 MPa are made using the TMprocess. For the highest strengthlevels in this range, the produc-tion process is determined by theplate thickness. For thinner pla-tes, the TM process can be used,but for heavier plates it is neces-sary to use quenching and tem-pering to obtain the properties.Above approximately 500 MPa,all steels are of the QT type.These steels are also of high qual-ity, with a low impurity contentand good weldability. However,with increasing strength levelsand increased thickness, more al-loying is needed, making preheat-ing necessary.

A trend that has continued forsome years involves using steelsof higher strength. The advantageof this is obvious; structures canbe made with thinner plates, re-ducing the weight and therebyimproving the opportunity forhigher loads. It should be notedthat there are situations in whicha structure cannot take advantageof thinner plates, such as whenbuckling, stiffness or fatiguestrength is the design criterion.

High-strength steels are com-monly defined as steels with a



yield strength of more than 350MPa.These steels now have foundtheir way into many areas of con-struction. In several new spectac-ular bridge constructions, TMsteels with yield strengths of 420or 460 MPa have been used. Oneexample is the Great Belt bridgein Denmark which was built dur-ing the mid-1990s and recentlywent into operation. Part of thebridge is made in the form of asteel suspension bridge, usingsome 80,000 tonnes of steel. Halfthis amount is accounted for byTM steels, with a yield strength of420 MPa. Details of the buildingof this bridge are presented in(2).

Another example from thebridge sector, in which a veryhigh-strength QT steel is used, isthe world’s largest suspensionbridge, the 1,990 m long Akashibridge in Japan. The constructionof this bridge was completed in1997 and the bridge is now in op-eration. In the box girders of thisbridge (comprising hundreds oftonnes of the steel), a very high-strength steel, HT780, with a yieldstrength of more than 780 MPawas used. It is particularly inter-esting to note that this steel onlyneeded less than 50°C of preheat-ing, despite its high strength, dueto the elaborate alloying tech-nique, combined with the quench-ing and tempering technique (3).

Examples of applications forhigh-strength steels with yieldstrengths of up to around 500MPa include standard structuralsteelworks, excavator equipment,pipelines, cranes, roof support inmines and, of course, offshoreconstructions.

Steels of higher strength suchas 690 MPa are used for trailersfor heavy haulage work, cranes

with a high lifting capacity, dump-er bodies and so on. For steelswith even higher strength (900MPa and above), typical applica-tions include penstocks, conveyorsystems and mobile bridges.

For steels with a yield strengthof 350-450 MPa, there are usuallyvery few welding problems. Theproblems that can arise here in-clude low toughness in the weldmetals, often associated with in-creased nitrogen content, due tothe use of too long an arc. If low-hydrogen consumables are used,hydrogen cracking is very rarely aproblem. If it arises, it is relatedto the welding of heavy plates.Solidification cracking may occurin very special circumstances, butit should generally pose no prob-lems. Impact toughness in high-dilution welds, such as one-sidedwelding with only one bead, cansometimes be low. This is, howev-er, often due to some incompat-ibility between the base metaland the consumable.

It is not until steels with a yieldstrength of 600 MPa or above areused that welding may becomesomewhat problematic and re-quire more caution. The steels areused in demanding applications,requiring good toughness at lowtemperatures in many cases. Inthis case, two problems may oc-cur. The first involves finding aweld metal with a yield strengthhigher than that of the steel andat the same time possessing goodimpact toughness. There are anincreasing number of consum-ables with these properties, butthere may still be problems whenit comes to combining high pro-ductivity and good mechanicalproperties. This is discussed inmore detail in the paper by L-ESvensson in this issue.

The second problem is relatedto hydrogen cracking. With thesteel developments that have tak-en place, including a lean alloyingcontent, the weldability of thesteels has been increased. In par-ticular, the need for preheatinghas been reduced dramatically.This is especially true of steels oflower strength, such as 350–500MPa steels. For these steels, theweld metals are also lean in alloy-ing content and do not requirepreheating. However, when itcomes to the high-strength steels,the situation is more complicated.The only way to increase thestrength of these weld metals is toincrease alloying. The advancedprocessing routes used for thesteels can naturally not be ap-plied to the weld metal. So, in asituation in which there is lesshardenability in the HAZ than inthe weld metal, there may be sev-eral reasons why hydrogen crack-ing would be more likely to occurin the weld metal. Preheatingmust then be prescribed to pro-tect the weld metal rather thanthe HAZ of the parent plate. Thisis a somewhat new situation and,although fabricators have learnthow to handle it, there is a lack offundamental knowledge aboutweld metal hydrogen crackingwhich must be remedied.

One solution that might appearto an attractive means of resolv-ing this situation is a further re-duction in hydrogen content fromthe consumables. Developmentsin which the hydrogen content ofthe weld metals has been reducedhave already been in progress formany years. As was noted in aprevious paper (4), hydrogen con-tents as specified in Table 1 havebeen obtained as a result of in-tensive research and develop-ment during the past decade.

There are several reasons forbelieving that the rate at whichthis downward trend will contin-ue will be slower in the futurethan it has been in the past. It willbe increasingly difficult to makefurther reductions from the verylow levels that have already beenachieved. The hydrogen contentcan be reduced by a number ofmeasures. Unfortunately, thesechanges often tend to have a neg-ative effect on other properties,

Consumable type Hydrogen content Comments(ml/100 g weld metal)

Basic covered electrodes 5 3 ml for special types

Tubular wires,basic or metal cored < 5

Tubular wires, rutile < 10 often < 5

Submerged arc fluxes < 5

Table 1. Hydrogen content of different consumables.



such as welding characteristics.So, a further reduction in hydro-gen will lead to consumableswhich are less attractive to thewelder. This factor has to be tak-en seriously and evaluatedagainst the benefits of a furtherreduction in the hydrogen con-tent. Another important factor ishow accurately the measurementof hydrogen content can be made.Investigations have shown thatthe error is around 0.5–1.0 ml/100g weld metal for the gas chroma-tography method. The relative er-ror at, say, 2 ml hydrogen/100 gweld metal is then 25-50%. Itmust be noted here that the largeerrors are not due to the analyti-cal equipment but instead to vari-ations in the specimen prepara-tion phase.

Apart from hydrogen stemmingfrom the consumable, there areother sources of hydrogen, such asthe surrounding atmosphere, thebase material or dirt and oil onthe plate and joint surfaces.

So, the amount of hydrogen inthe weld pool can differ from thehydrogen content specified by theelectrode manufacturer. Natural-ly, the hydrogen content of theconsumable is also affected bythe possible moisture absorption.Although low moisture absorp-tion electrodes have been devel-oped, some absorption alwaystakes place. This can be avoidedby using vapour-tight packaging,like Esab’s VacPac. In this kind ofpackaging, the electrodes arekept in the same condition aswhen they were manufactureduntil the package is opened.

To benefit fully from the devel-opment of steels, to increase pro-

ductivity during welding, system-atic investigations need to bemade, partly to be able better todefine the preheating necessaryfor safe welding, but also in orderpossibly to develop the weld met-als still further with the aim ofmaking them crack-resistant whi-le maintaining the mechanicalproperties.

Developments in heat-resistant steelsThe steels which are traditionallyused for high-temperature appli-cations within the petrochemicalindustry or the power generatingindustry can broadly be classifiedinto two groups. One group, spec-ified in EN 10 028-2 Steels forpressure purposes, with specifiedelevated temperature properties,contains those steels commonlyfound in high-temperature powerplants. In this standard, there arefirst four unalloyed quality steels,with a yield strength varying from235 to 355 MPa. The properties ofthese steels are specified up to400°C. For use at higher tempera-tures, steels alloyed with molyb-denum and chromium are used.The simplest steel is only alloyedwith about 0.3% molybdenum.The most common steels are al-loyed with either 1.25Cr-0.5Mo or2.25Cr-1Mo. These steels havetheir tensile properties specifiedup to 500°C. The maximum oper-ating temperature is 565°C. Thecreep properties, given as refer-ence in the standard, are specifiedup to 600°C for a 2.25Cr-1Mosteel (10 CrMo 9-10).

There are a number of sugges-tions on how to modify the

2.25Cr-1Mo steel in particular.The most frequent suggestionsare to increase the chromiumcontent, so that the typical com-position would be 3Cr-1Mo in-stead, and to add vanadium. Theaddition of vanadium increasesthe high-temperature strength ef-fiectively, but the cracking risk inthe HAZ is increased.

Consumables for welding thesesteels have much the same com-position as the parent material.The microalloying elements vana-dium and niobium are on a lowerlevel than they are in the steel,thereby reducing the creepstrength of the weld metals some-what. Since the microstructure ofthe weld metal is bainitic, theprior austenite grain boundariesare preserved and may be a sour-ce of embrittlement. In general,the welded joint is annealed afterwelding, to improve toughnessand reduce residual stresses. Incommon with other similar mi-crostructures, the weld metals cansuffer from two types of embrit-tlement. During annealing, whichtypically takes place at 690°C,carbides can precipitate on theprior austenite grain boundariesand this can lead to lower tough-ness. This is called irreversibleembrittlement, as it is difficult toremove the carbides. At lowertemperatures, typically 400-500°C,reversible embrittlement may oc-cur. This is due to the segregationof impurity elements, like phos-phorus, to the prior austenitegrain boundaries. This processmay take place either during slowcooling through the critical tem-perature regime or if the con-struction is operating at this tem-perature, as is common in theprocess industry, for example.

To prevent reversible embrit-tlement, it is important that thephosphorus content is reduced tothe absolute minimum. The de-gree of segregation and embrittle-ment is also influenced by otherelements and formulae have beendeveloped to help control thepermissible content of variouselements. The best-known of the-se formulae is the Bruscato X-factor (5).

For more demanding applica-tions, steels with higher alloyingcontents are used. The steel with

Alloy Minimum preheating Max interpass Post-weldtemperature °(C) temperature °(C) heat treatment (°C)

0.5 Mo 75 250 600-650(t > 15 mm) (t > 30 mm)

1Cr-0.5 Mo 100 300 650-750(t > 15 mm) (all thickness)

2.25Cr-1Mo 200 350 700-750(t > 15 mm) (all thickness)

9Cr-1 Mo 200 350 700-770(all thickness) (all thickness)

12Cr-1Mo 350 450 intercooling to 125-150(all thickness) PWHT 700-770

Table 2 Preheating, interpass and post-weld heat treatment temperatures for Cr-Mosteels. Based on draft for standard “Welding of ferritic steels”.



the highest alloying content inthis group is 12Cr-1Mo steel.However, most interest in recentyears has focused on steels withabout 9% chromium-1% molyb-denum, where large-scale devel-opments have taken place.

About 20 years ago, work be-gan in the US on the develop-ment of a steel of the 9Cr-1Motype, with high-temperature char-acteristics like those of a 12Cr-1Mo steel but far better weldabil-ity. Another aim was to be able toincrease the operating tempera-ture of power plants to around600°C, thereby significantly in-creasing efficiency. The modifica-tion from the original 9Cr-1Mosteel lies primarily in the additionof vanadium, niobium and nitro-gen. This modified steel has al-ready found a number of applica-tions, mainly in the form of pipes.

Developments in this field arerapid. There are suggestions fornew steel compositions, like 9Cr-2Mo, or to replace molybdenumwith tungsten. The aim here is

further to improve the creepproperties. These developmentswill call for the further develop-ment of weld metals. It is expect-ed that, if the 9Cr type of steelcontinues to increase, by beingused in the petrochemical indus-try, for example, this will be oneof the most intensive and inter-esting area of materials develop-ment in the years to come.

The weldability of Cr-Mo steelsis limited and weldability deteri-orates as the alloying content in-creases. Preheating and post-weldheat treatment are required tovarying degrees for many of thesteels. A summary of the recom-mendations for welding thesesteels is given in Table 2. For allsteels, consumables with matchingproperties (and often very similarchemistry) exist, for all the com-mon processes. Note that 12Cr-1Mo is an exception. This alloy isnot welded using high-productivi-ty methods. However, consum-ables for welding 9Cr-1Mo modi-fied steels are still being devel-

oped. Some of the characteristicsof these weld metals are detailedin the paper by E-L Bergqvist inthis issue.

Developments in stain-less steelThe use of stainless steels hasbeen increasing worldwide for along time and this trend is expect-ed to continue. Apart from thecommon grades, significant devel-opments have taken place when itcomes to new grades with im-proved characteristics (see Table3). Ferritic-austenitic duplex andsuperduplex, as well as superaus-tenitic steel, have been devel-oped. One of the important driv-ing forces behind the develop-ment of new stainless steel hasbeen the need to improve charac-teristics in chloride-containingenvironments. This harsh environ-ment gives rise to both pittingand stress corrosion cracking.

These types are now beingused in increasing tonnages in theoil and gas industry, in the pulpand paper industry, in other typesof process industry and in appli-cations such as chemical tankers,for example.

Information about some auste-nitic, duplex, superduplex andsuperaustenitic steels is given inTable 3.

The welding of stainless steel iswell established and a range ofconsumables suitable for all thecommon welding processes isavailable.

There is a fairly extensive rangeof consumables for welding du-plex steels using all the differentwelding processes. Representativeexamples are given in Table 4. Atthe present time, it appears thatthe development of the family ofduplex steels has slowed downand that modifications are beingmade to existing types rather thandeveloping new steels. The use ofduplex and super-duplex steelscan be expected to increase stead-ily in the years to come.

Duplex materials are especiallysuitable in environments wherethere is a risk of stress corrosioncracking — in other words, envi-ronments which frequently con-tain chloride. Even the highest-alloyed duplex steels are, howev-

Steel type Chemical composition (%) Tensile PREproperties (N/mm2)

C Cr Ni Mo N Others Rp0.2 Rm *)

AusteniticsASTM 304L 0.02 18.5 9.5 - - 205 520 19ASTM 316L 0.02 17.0 11.5 2.7 - 205 500 27UNS NO8904 0.01 20.0 25.0 4.5 - Cu 220 500 36

Super-austeniticsUNS S31254 0.01 20.0 18.0 6.2 0.20 Cu 300 650 43UNS S32654 0.01 24.2 17.9 7.2 0.45 Cu 430 750 55

DuplexUNS S31803/S32205 0.02 22 5.5 3.0 0.18 480 680 35

SuperduplexUNS S32750 0.02 25 7.0 4.0 0.28 540 780 42

*) PRE = %Cr + 3.3%Mo + 16%N

Consumables Weld metal chemical Tensile FN PRE Impact composition (%) properties toughness

(N/mm2) –60°C (J)

C Cr Ni Mo N Rp0.2 Rm

OK 67.55 0.03 22.0 9.0 3 0.17 645 800 30-45 35 65OK 68.55 0.03 25.5 9.5 4 0.25 700 900 30-50 43 45

Table 3. Examples of stainless steels, with typical compositions and properties.

Table 4 Duplex weld metals for MMA. The composition of the weld metals isrepresentative of other welding processes as well.



er, susceptible to crevice corro-sion in certain conditions (highertemperatures, de-aerated water,very high chloride content). Towithstand seawater environments,like the North Sea, with a chlo-ride content of around 21,000ppm, the steels need to be im-proved still further.

Alongside the development ofthe duplex and super-duplex, afamily of steels, known as super-austenitic steels, was developed.Some examples of these steels aregiven in Table 3. In typical cases,they contain around 20% chromi-um, 18% nickel, 6% molybdenumand 0.2% nitrogen. Chromiumand molybdenum produce excel-lent corrosion characteristics, whi-le nitrogen stabilises the austeniteand reduces the risk of sigmaphase formation during welding.The advantage of these steels isthat they have better ductility andimpact strength than the duplexand super-duplex steels. The yieldstress of super-austenitic steels is,however, lower than that of du-plex steels (of the order of 350MPa). The corrosion resistance ofthese super-austenitic steels ismore or less the same as that ofthe super-duplex steels, as isshown by the similar PRE values(Table 3).

In order to comply with ex-tremely rigorous corrosion re-quirements, the super-austeniticsteels have been improved stillfurther. Examples of steels withhigher PRE values include Alloy31 from VDM and 654 SMO fromAvestaSheffield. These materialsare generally included amongstainless steels, but they aresometimes on the borderline ofnickel-based alloys.

Super-austenitic steels are notwelded with consumables of thesame type, as it is not possible toobtain sufficiently high PRE val-ues with these weld metals. Theprincipal problems are caused bythe molybdenum content. Molyb-denum segregates heavily duringsolidification and the areas whichare poor in molybdenum have afar lower PRE value than theparent metal. Nor is it possible tocompensate for the molybdenumwith other alloying elements, asthis leads to a significant risk of

intermetallic phase precipitation.Consumables of the nickel-basetype are used to weld these steels.The most common type is Ni-21Cr 9 Mo 3 Nb, which is used formost welding processes. Potentialproblems with this compositionare hot cracking and the precipi-tation of intermetallic phases. Toavoid this, a low heat input andlow interpass temperature shouldbe used and dilution should berestricted. A better choice may beto use the recently developed al-loy Ni-23 Cr 16 Mo instead (6).

Very recently, the developmentof stainless steels for offshore ac-tivities has taken a different rou-te. For cost-saving reasons, anddue to increasing experience ofthe corrosion potential of the me-dia that are transported, there isan initiative to develop so-calledsuper-martensitic steels and weldmetals. These steels, which have arange of composition of around10-13 % Cr, 2-4% Ni and 0-6%Mo, all with an extremely lowcarbon content, are now the sub-ject of intensive research and de-velopment programmes. More in-formation on these steels is pre-sented in the paper by L Karlssonin this issue.

Another trend that has emer-ged relatively recently is the at-tempt to improve the weldabilityof steels at the lower end of thestainless steel range, namely steelwith a chrome content of around10-12 %. These steels are interest-ing for use in the transport sector.

The most popular method forwelding stainless steel is manualmetal arc, followed by MIG usingsolid wires. However, with solidwires, there is a greater risk ofweld defects, such as lack of fu-sion. Cored wires, which have re-cently been developed for manyof the common stainless steel gra-des, improve this situation signifi-cantly. Productivity is enhancedby about 30% and spatter is sig-nificantly reduced. Cored wireshave been developed for bothdownhand and out of positionwelding.

Developments in aluminiumAluminium is finding more wide-spread use in most engineering

structure segments. The new high-speed ferries for Stena Line bet-ween Sweden and Denmark andacross the Irish Sea are good ex-amples of the way aluminium isbeing utilised to obtain a lighterweight to permit either a higherload-carrying capacity or fasterspeeds. However, the use of alu-minium has also made it neces-sary to redesign the ferry con-struction.

The advantages of aluminiumas an engineering metal are obvi-ous; it is a light and yet compara-tively strong material, with rela-tively good corrosion. It is alsoenvironmentally-friendly, in thatit is recyclable. There are alsosome drawbacks to aluminium;the lower Young’s modulusmakes it less stiff, the high ther-mal expansion coefficient induceshandling problems during weld-ing and straightening operationsand large amounts of energy arerequired for the production ofraw aluminium.

The drawbacks to aluminiummentioned above, combined withother things, like the loss ofstrength in the heat affected zoneduring welding, are making de-sign and fabrication in aluminiumdifferent from that in steel.

The difference compared withsteel can be clearly seen whenwelding aluminium. At present,the principal technical problemsassociated with the welding of al-uminium are

solidification cracks in theweld metalliquation cracks in the heat af-fected zonepore formation andstrength reduction in the heataffected zone

Both solidification and liqua-tion cracks are thought to be duein the main to the occurrence ofintermetallic phases with a low-melting temperature at the grainboundaries. Alloys with a widesolidification range are the mostsusceptible to cracking. Thismeans that it is the hardenablealloys, to which zinc or copperhave been added, which are mostsusceptible to cracking. Some al-loys also contain lead, therebyincreasing the risk of cracking.Solidification cracks can beavoided by selecting silicon-



alloyed consumables. It has alsobeen demonstrated that silicon-alloyed consumables reduce therisk of liquation cracks in hard-enable Al-Mg-Si alloys, probablybecause the solidification tem-perature of the weld metal islower than that of the parentmetal and any cracks thereforehave time to heal before stress iscreated across the joint. In thesolid-solution strengthening al-loys, mainly alloyed with magne-sium, it is those with a low mag-nesium content that are the mostsusceptible to cracking. Howev-er, many alloys, in particular thenon-hardnable ones, but also thehardenable magnesium-siliconalloys, have very good weldabil-ity.

Pores in aluminium welds areusually caused by hydrogen frommoisture. There is a very greatdifference in the solubility of hy-drogen between the molten andthe solid state. So, when solidifi-cation of the weld metal occurs,there is large supersaturation ofhydrogen. The hydrogen is thenprecipitated as pores. To keep thepore formation to a minimum,the hydrogen content must beminimised. All sources of hydro-gen (i.e. the shielding gas, parentmetal and consumables) must beclosely controlled. Recent investi-gations (7) have shown that thematerial in the gas hoses has amajor influence on the moisturecontent. Hoses made from PVCor rubber give off moisture in lar-ge quantities and must be flushedwith gas for perhaps 10 minutesafter they have been idle forsome time. Hoses made from PEor PTFE have a much lowermoisture pick-up and the time forflushing can consequently be re-duced.

Higher heat input is anotherway to improve the situation, as itgives the hydrogen longer tomove out of the weld pool. How-ever, despite these actions, it isdifficult completely to suppresspore formation.

The reduction in strengtharound a weld in aluminium al-loys is inevitable, except for alloysin the untreated or room-tempe-rature-aged condition. This loss ofstrength is due to recovery andrecrystallisation in deformation-

hardened alloys and precipitationcoarsening and dissolution in age-hardened alloys. To compensatefor the strength reduction, severalstrategies are used. Most fre-quently, welds are placed in lowstress areas. Other methods in-clude locally increasing the thick-ness of material. Heat-treatablealloys can, in principle, be givenrenewed heat treatment (solutiontreatment and ageing) to restorethese properties, but this ap-proach naturally involves manypractical difficulties.

Aluminium is almost exclusive-ly welded using MIG or TIG.There is a wide range of consum-ables for welding aluminium, ei-ther pure aluminium or solidsolution-hardened alloys. Thewelding wires are mainly alloyedwith magnesium or, in the case ofcertain alloys, silicon. Modifica-tions to the Al-Mg-system aremade by adding manganese invarying amounts, to increase thestrength still further.

The addition of titanium or zir-conium, to act as grain refiners, isalso quite common. However, thedevelopment of new alloys forwelding wires is relatively slow,probably reflecting the demandfrom the market.

ConclusionsThe most important trends whenit comes to materials develop-ment and which will challenge thedevelopment of consumables are:

improved productivity forcommonly used steelsincreased use of steel with im-proved properties

For consumables, future develop-ments will focus on

tubular wires, for both structu-ral and stainless steelsnew consumables with im-proved high-temperaturecharacteristicsnew consumables with im-proved corrosion propertiesthe development of consum-ables with an even lower hy-drogen content, but also animproved understanding ofweld metal hydrogen crackingmechanisms

On the process side, the followingtrends are anticipated:

high-productivity systems

About the authorLars-Erik Svensson, PhD, is man-ager of the Esab Central Labora-tories in Gothenburg. He has wor-ked for more than 15 years withwelding metallurgy, focusing pri-marily on unalloyed and low-alloy-ed steels. He has published onebook and more than 25 papers onthe microstructure and propertiesof welds.

Johan Elvander, M. Sc, (Materialseng.) joined Esab AB in 1982 aftergraduating from The Royal Insti-tute of Technology in Stockholm.He started as development engi-neer for stick electrodes and nowholds a position as head of Re-search & Development, businessarea Consumables in Europe.

better software for processcontrolmore consumables suitable formechanisation

References1 Esab Environmental Report 1997

2 F. Rouvillian, High strength steel in amajor bridge construction over theGreat Belt Svetsaren, V 49, 1, p 15, 1995

3 H. Mabuchi, Recent progress in structu-ral steels for building and bridges, ISIJ,no 159, Feb 1996

4 A Backman, Development within mate-rials technology - Consumables in the21st century, Svetsaren, V 49, 1, p 4,1995

5 R Bruscato, Temper Embrittlement andCreep Embrittlement of 2 ºCr-1 MoShielded Metal-Arc Weld Deposits,Welding Journal, 49, p 148-s, 1970

6 L Karlsson, S L Andersson, S Rigdaland T Huhtala, New Ni-base consum-ables for welding of highly alloyedstainless steels, Proc Stainless steels ’96,Dusseldorf/Neuss, June 3-5, 1996

7 Aga AB, O Runnerstam, private com-munication



Close to 10 years of re-search and developmentare culminating in thefirst industrial productin the shape of theTHOR ArcWeld pro-duction system, a systemfor the automatic pro-gramming of welding robots, integrating theentire process from theimport of CAD data tothe execution of robotprograms.During the past year, the R&Dcompany AMROSE A/S inOdense in Denmark has beencollaborating with Ib AndresenIndustri A/S in Langeskov inDenmark in the EU projectknown as TOMATO. The aim of

the project has been to transferthe advanced robot technology(developed by AMROSE in closecollaboration with Odense SteelShipyard Ltd.) to other metal in-dustries.

The first working prototype ofa robotic production system con-trolled by AMROSE technologywas successfully built and in-stalled at Odense Steel ShipyardLtd. in 1994–95 and it is still beingused in the daily production ofship assemblies.

The TOMATO project has fo-cused on developing the userinterface and adapting the techni-cal functionalities in order to en-sure that the system meets thedemands imposed by companiesin the metal industry for a flex-ible production system.

An internal demonstration ofTHOR ArcWeld at Ib AndresenIndustri was scheduled for the

end of 1998 and AMROSE willbe ready to introduce the systemto the rest of the industry duringthe first half of 1999.

The robot works continuallyThe joint venture between thetwo companies in the TOMATOproject has resulted in the iden-tification of a series of technicalsuccess criteria for the introduc-tion of THOR ArcWeld at a man-ufacturing company.

The immediate advantage ofoff-line programming is that therobot can keep working, whilethe programming is handled onoffice computers.

With CAD data as the startingpoint, it is possible to generate ageometrical model of a work celland workpiece. Subsequently, acollision-free trajectory is calcu-lated for the welding robot in in-

by Charlotte Hybschmann Jacobsen and Michael Wehner Rasmussen,AMROSE A/S, Denmark

From prototype to integrated production system

Robot arc welding of industrial mixer at Ib Andresen Industri.



tegration with the workpiece ma-nipulator.

The fact that the programmingitself does not demand valuableon-line time makes the robot-wel-ding of small series profitable.Using sensory equipment, real-time corrections can be made tothe welding process, thereby en-suring high weld quality which inturn reduces the post-processingtime.

Finally, costs are minimized forexpensive precision fixtures whichare only made to compensate forthe traditional inability of robotsto compensate for the incorrectposition of the weld groove.

Customer’s own systemThe system has been developedwith a view to incorporating it inthe customer’s daily productionflow; from the construction de-partment to the shop floor.

It is important that the systemrequires as little individual adap-tation as possible—which is alsothe case when it comes to theinterface with the customer’sCAD and robot systems. The cus-tomer must be able to continueusing his own CAD system forthe design of the workpieceswhich are going to be welded. Atthe same time, THOR ArcWeldgenerates robot programs directlyfor the robot system, which thecustomer then uses in production.

The program is modular in de-sign and has an internal languagefor application developmentwhich ensures very simple adap-tation to different customers andapplications. The system is de-signed in such a way that it canwork with workpiece modelsfrom 90% of all “mid-range”CAD systems. In the same way,the system makes it possible togenerate robot programs for dif-ferent robot controllers (e.g. MO-TOMAN, CONOSS and HIRO-BO).

Joint, seam and runTHOR ArcWeld covers the entirecycle of operations for a work-piece — from 3D CAD drawings(which are imported into the sys-tem) to complete robot programswhich are executed through a sys-tem-integrated computer on the

shop floor. THOR ArcWeld alsocontains instructions for the robotoperator to mount workpieceparts during the production pro-cess, for example.

In THOR ArcWeld, any givenweld is split up into its individualelements: joint, seam and run.

Using these elements ensuresthe greatest possible control ofthe automation process. This re-sults in maximum flexibility in theadjustment of welding require-ments to different workpiecetypes. From heavy workpieces,such as a car lifting platform,which demand weld seams withhigh durability, to workpieces,such as industrial mixers, whichdemand visually high weld qual-ity. Using the CAD model as thestarting point, THOR ArcWeldautomatically identifies the fol-lowing three basic elements ofthe welds:

Joints between platesSeams which are placed onthe jointsRuns which make up theseams

The automatic process whichtakes the workpiece from onestep to another is based on custo-mer-defined rules which can sub-sequently be modified and adapt-ed as required.

Between each step of the auto-matic process, it is possible manu-ally to adjust data and therebydeviate from the set rules.

The user operates in a graphi-cal environment which displaysthe workpiece, the robot and thework cell, plus any positionersand fixtures. The user can contin-uously monitor the automaticprocess in the graphical windowand is able at all times to inter-vene with data adjustments.

The real worldOn the basis of actual workingprocedures at IAI, the followingcase illustrates the facilities ofTHOR ArcWeld.

The company receives an orderfor a number of items. Each itemconsists of both robot-welded pla-tes and plates which must be bentbefore being welded onto the al-ready welded parts of the item.

The construction departmentdraws the particular workpiece ina 3D CAD program, whereaftergeometrical data is imported intoTHOR ArcWeld.

The CAD model is enriched bywelding data which is indepen-dent from the place and methodof production (i.e. whether theworkpiece is welded manually orby a robot).

A so-called assembly tree isbuilt. The assembly tree specifiesthe order of assembly for the var-ious parts of the workpiece.

The user specifies joints be-tween plates; seams and runs arethen generated automatically.

The interaction of THOR

A view of the virtual robot work cell in THOR ArcWeld.



ArcWeld with a customer-adapt-ed process database may havespecified that outer corner jointsshould be welded vertically, ifpossible. From this information,the program calculates how thepositioner must move the work-piece between welding jobs withrespect to the overall weldingprocess.

Anchor points are specified.These must be taken into accountbefore the welding process is in-itiated. The anchor points aresubsequently converted intorobot-controlled sensings.

It is possible to enter noteswhich can be read on the shopfloor. An example of this is a notespecifying that one in every ten ofa certain type of weld mustundergo quality control. Thismessage will then appear on thecomputer screen on the shopfloor after every tenth executionof the welding program.

Further work with the work-piece is then transferred to therobot programmer.

The work cell in which theworkpiece is going to be weldedis then chosen. Apart from a ro-bot and its environment, the workcell also consists of a manipulatorand a fixture.

A task tree must be set up. Asopposed to the assembly tree,the job graph reflects the orderand type of tasks to be executedon the workpiece on the shopfloor. The jobs which make upthe job graph are very varied:from robot welding and sensingto messages to the work-cell op-

erator about the placement ofworkpiece parts and performingquality control.

In principle, THOR ArcWeldcan automatically translate thelist of weld seams into a completerobot program, but, in reality,some manual adjustment of theautomatically generated data isrequired.

When the robot programmer issatisfied, he releases the program.The workcell operator can nowdownload the program to therobot controller.

Before the robot is activated, itis possible to play back the simula-tion and thereby obtain a compre-hensive view of the entire process.

The workpiece is mounted asspecified on the computer screenand the robot program is started.

There is direct interaction bet-ween the system and the robotduring the entire production pro-cess.

The robot operator monitorsthe messages on his screen andthe robot automatically stopswhen a new workpiece part needsto be placed in the positioner.The robot does not start againuntil it is actively re-started.

Later versions will include areport tool in which various sta-tistical data, such as the numberof workpieces and welded metres,the welding speed and the num-ber of stops, will be collected andpresented in a report.

The maths insideA non-traditional mathematicalapproach, combined with inspi-

ration from the latest researchresults in the field of ArtificialPotential methods, led the AM-ROSE team to create a new andhighly-efficient robotics con-cept.

This new robotics concept in-cludes mathematical techniquesfrom the field of molecular dy-namics. In this case, mathematicalmodels enable the computationof the motion of atoms and mole-cules under the influence of at-tractive and repulsive forces.

Tweaking the formalism a lit-tle, the scientists turned the forcesacting between atoms in natureinto artificial forces, in a comput-er model which actively controlthe movements of robots.

The artificial forces are chosento encourage the robot to movetowards its target area and thereperform its task (e.g. weld), whileat the same time avoiding colli-sions between the robot, theworkpiece and the surroundings.The attractive forces can be visu-alised as rubber bands that dragthe robot towards its goal. In thesame way, the repulsive forcescan be seen as springs that pushthe robot away from obstacles inthe environment.

Artificial forces are not fullyadequate when high-precisioncontrol over the robot tool isneeded. In the THOR motioncomputations, the tool centrepoint is tied to a frame of refer-ence that moves according to thespecifications of the task. In thisway, the tool is dragged along bythe moving frame with the exactrequired (high-precision) motion.

About the authorsCharlotte Hybschmann Jacobsenhas a masters degree in molecularbiology. She is in charge of userinterface design and documenta-tion of the AMROSE products.

Michael Wehner Rasmussen has amasters degree in internationalmarketing, and he is responsiblefor the commercialisation of theadvanced robot technology deve-loped by AMROSE.

Principles from molecular dynamics are used to generate robot motion.


Factorías Vulcano S.A,Vigo, is a medium size ship-yard in the north of Spainproducing an extensiverange of civil and maritimeproducts, including chemi-cal carriers in both carbonand duplex stainless steel.Currently, the yard is final-ising the construction ofThe Primo, a duplex chemi-cal tanker for the Swedishshipping company Initia.The fabrication, from theindoor panel lines down tothe final outdoor block assembly, is characterisedby wide scale use of ESABwelding solutions with a keyrole for ESAB OK Tubrodcored wires. This article reviews the production ofchemical tankers at Vulca-no. Special attention is focussed on the role ofFCAW.

AcknowledgementWe would like to thank FactoríasVulcano for their excellent co-operation in preparing this arti-cle. A special word of thank weaddress to Ramón Pérez Vázqu-ez, Production Manager, JesúsFernández Iglesias, Steel SupplyManager, and Javier Peréz, Weld-er Foreman. Their openness hascontributed greatly to this article.In addition, we compliment ourspanish Esab colleagues José LuisSastre, Carmen Herrero and JoséMaría Fernández Vidal on thegreat marketing success achievedat Factorías Vulcano.

IntroductionThe title “Welding duplex chemi-cal tankers the Esab way”, is per-haps a bit over-ambitious, but it isrightly chosen in the sense thatFactorías Vulcano apply ourwelding solutions in practicallyevery stage of the fabrication pro-cess of chemical tankers. Theshipyard has made intelligent useof ESAB’s capability to serve as atotal supplier for stainless steelfabrication, selecting dependableand productive consumable/equipment combinations forpractically all fabrication steps.The yard possesses a high level ofpractical welding knowledge, pro-viding a solid basis for, sometimesdifficult, but often fruitful techni-cal discussions between our com-panies. Over the years, the co-operation in developing and im-plementing new techniques hasdeveloped such that today we feelwe can rightfully claim that Esab’s mission statement to be“the preferred partner for weld-ing and cutting” is fully valid forthis shipyard.

This article presents a bird-eye-view on the fabrication of chemi-cal tankers in duplex stainlesssteel at Factorías Vulcano. Avoid-ing too much technical detail, itwill step by step discuss the fabri-cation process as well as theESAB welding solutions that havebecome established. The FCAWwith rutile cored wires is empha-sised, because it plays a key role inthe fabrication and because theseproducts are relatively new for du-plex stainless steel welding.

Factorías VulcanoStarting out with the repair ofrailway engines in 1919, FactoríasVulcano widened their capabil-ities to what they are today; a fullscale fabricator of civil and mari-time constructions. Today’s prod-uct range comprises civil engi-neering products like boilers, ma-rine fresh water generators, re-fuse incinerators and sewagetreatment plants, whereas theshipbuilding segment fabricatescontainer ships, refrigerated ves-sels and chemical carriers.


Welding duplex chemical tankersthe ESAB way

Wide scale application of ESAB welding solutions atFactorías Vulcano S.A., Spain

By Ben Altemühl, Svetsaren editor, interviewing Factorías Vulcano production management.


stainless steel assembly work in-volves the joints numbered 1,connecting the prefabricateddeck plates to construct the tankfloor. Here Factorías Vulcano ap-ply a combination of manualFCAW on ceramic backing stripfor single sided root passes andSAW for the filling layers. ESABOK Tubrod 14.37 has been select-ed as the FCAW consumable, be-cause of its capabilities for down-hand work. With it’s slow freez-ing, fluid slag, it is designed toweld at high travel speed givinghigh productivity (Figure 3). Itgives good penetration and, afterslag removal, the back side of theroot requires no grinding orbrushing. The ceramic backingstrips to be used with this productrequire a rectangular groove toaccommodate the slag and to pro-mote a good bead appearance.OK 14.37 is welded in 85%Ar/15%CO2 gas protection, a mix-ture applied at Factorías Vulcanofor all FCAW (stainless and car-bon steel). Here, and for all otherFCAW, the yard uses simplisticrectifiers without the need forpulsing.

SAW filling is done with theESAB wire/flux combination OK16.86/OK Flux 10.93, a combina-tion widely applied in duplexstainless steel fabrication, andwith an excellent reputation. Theflux is a low-hydrogen, non-alloy-ing, basic agglomerated type(AWS: SA AF 2 DC). OK Autrod16.86 is of the 23Cr-9Ni-3Mo typealloyed with 0.15%N to obtain aweld metal with sufficiently over-matching mechanical properties, agood austenite/ferrite balance,and excellent corrosion resistancewhen welding standard UNS

In 1990 the company com-menced a three year plan to re-structure and modernise the ship-yard, involving a 1200M Pesetasinvestment. What results today isa modern medium-size shipyardwith advanced FORANCAD/CAM design facilities, anESAB NUMOREX NXB9000under water plasma cutting instal-lation connected to the CAD/CAM system. Also, a panel fabri-cation line with two ESAB A6-LAE1250-TAC1000 submergedarc welding machines, mechan-ised welding stations for stiffenerattachment and various systemsfor mechanised SAW and FCAWapplied in sub-assembly and finalassembly. The yard lay-out guar-antees an efficient flow of workthrough production. Along withthe modernisation, the yard im-plemented the ISO 9001 qualityassurance system. Together withan orderbook of specialised pro-jects that reaches well into thenext century, the yard is well posi-tioned to compete in today’s de-manding market.

Construction of chemi-cal tankers at FactoríasVulcanoAlthough fabricated out of twocompletely different base materi-als, carbon steel and duplex stain-less steel, the construction of

chemical tankers at Factorías Vul-cano takes place according to es-tablished, modern shipbuildingpractices involving panel fabrica-tion, the construction of sub-sec-tions, the assembly of block sec-tions, and the final connecting ofblock sections in the dock. Weshall focus on the role of duplexstainless steel cored wires. Sincethese are applied primarily in thedock assembly, we describe thefabrication of The Primo in re-versed order.

Figure 1 gives a schematic viewof a 16000DWT chemical carrierfrequently built by Vulcano, andvery much resembling the Primo.The vessel has 12 tanks in duplexstainless steel and two small tanksserving for storage of cleaningwaste. Parts in duplex stainlesssteel are highlighted in red. Verti-cal assembly welds are indicatedwith yellow dots.

Figure 2 shows the Primosomewhere half way during theassembly of the chemical cargotanks. Prefabricated sections arehighlighted with individualcolours and all assembly weldsare visualised by yellow lines,numbered 1 to 9, and described inthe margin.

For a good understanding ofthe construction, we recommendto first have a look at Figure 4. Itshows the next block section tobe assembled, comprising a decksection and tank assembly, thecorrugated bulkheads. As such, itwill be turned and placed in theconstruction. The yellow lines inFigure 2 may, therefore, indicateready welds or welds to be madewhen the next block section hasbeen positioned.

The first step in the duplex


Figure 1: Top-side view of a chemical tanker with 12 duplexstainless steel tanks. Yellow dots in the magnification representvertical assembly welds.

Figure 3: Root pass in deck joint withOK Tubrod 14.37 seen from above.


S31803 types of duplex stainlesssteel. Vulcano use ESAB A2 Mul-titrac SAW machines, guided byrails attached parallel to thejoints. The same machine-consu-mable solution is used all overthe yard, providing a dependablewelding method in many produc-tion steps (see later).

The same method as describedfor the tank floors is used for theconnection of the tank floor tothe carbon steel hull of the bot-tom (2), be it with 309L typewelding consumables. The flux-cored wire for welding the root pass on ceramic strip is OK Tubrod 14.22, also a rutiletype for all positional use, where-as the wire/flux combination applied for filling is OK Autrod16.53/OK Flux 10.93.

The next assembly step in-volves the placement of the twoside wall sections to the bottomof the vessel where first the car-bon steel parts are connected, fol-lowed by weld type number 3between subsequent block sec-tions. Basically, this is the sametype of joint as between the cor-rugated bulkheads (6), but weld-ed with a slight angle. It is a V-joint welded vertically-up, manu-ally or mechanised with rail-trackequipment, with OK Tubrod

14.27. This rutile cored wire withfast freezing slag system is by farthe most productive solution formaking these kinds of assemblywelds, with deposition rates thatreach up to 3kg/h. Single-sidedroot passes are again made on ce-ramic backing strips with a rec-tangular groove

Assembly welds type 4 and 5connect the tank walls to the tankfloor. Both types are treated assemi-positional welds, primarilyperformed with FCAW. Rootpasses are welded on rectangularceramic strips in the case of weld4 and on cylindric ceramics in thecase of weld 5. The back side ofweld 5 has poor accessibility dueto the geometry of the construc-tion. SMAW with ESAB OK67.50, an established acid- rutileelectrode for standard duplexgrades, was found to provide themost practical and secure solutionfor sealing the root.

The next fabrication step con-cerns the placement of the thirdprefabricated block section com-prising a deck section and a crossof longitudinal and transversetank walls; the corrugated bulk-heads. This section can be seenisolated, and upside down, in Fig-ure 4. The prefabrication of thiscomponent will be described later.

After turning and positioning

this section between the sidewalls of the ship, a number of as-sembly welds remain to be made.

Assembly welds type number 6are the ones indicated with yel-low dots in figure 1. They connectthe corrugated longitudinal bulk-head with the previous tank sec-tion, and the transverse bulk-heads with the corrugated partsattached perpendicular to theside walls. The welding methodand consumable used are exactlythe same as described for weldtype number 3 (OK Tubrod14.27), but the welding position istruly vertical-up.

To obtain optimal weldingeconomy, Factorias Vulcano applymechanised welding with railtrack systems for the filler layers.Figure 5 shows a typical exampleof a vertical assembly weld madein this way. Deposition ratesamount to 3kg/h when calculatedat 100% duty cycle, which is high-ly productive for this kind of un-avoidable assembly welds.

Assembly weld 7, between cor-rugated bulkheads and the tankfloor, is carried out manually, be-cause the geometry of the joint istoo complicated to allow mechan-isation (Figure 6). Moreover, theroot gap may show misalign-ments, requiring the welder tomanually build-up the root with avarying number of beads. OK Tubrod 14.27 proves to be a ver-satile and dependable consum-able for this kind of demandingwork. Root passes are made al-most twice as fast as with stickelectrodes, using cylindrical ce-ramic backing, with excellent ab-lity to compensate for misalign-ment of the joint.


Figure 4: Fabrication of a block section consisting of a tank cover with verticalcorrugated walls in duplex stainless steel.

Figure 5: Vertical weld between corru-gated tank walls; mechanised weldedwith OK Tubrod 14.27


Connection between corrugated bulkheads and tank floor

Position: PC/2GRoot: FCAW with OK Tubrod 14.27,manually welded onto cylindricceramic backing.Filling: FCAW with OK Tubrod 14.27,welded manually.


1

Figure 2: Principal dock assembly welds in d

Tank floor frompre-fabricated plates.

Position: PA/1GRoot & 1st pass: FCAW with OKTubrod 14.37, welded manually ontoceramic backing strip.Filling: SAW with OK Autrod 16.86/OK Flux 10.93

4 Connection between verticaltank wall and angled side wall

Position: PC/2GRoot: FCAW withOK Tubrod 14.27,welded manuallyonto ceramicbacking strip.Filling: FCAW withOK Tubrod 14.27,welded manually .

3

6

Connection between corrugated bulkheads andbetween tank side walls

Position: PF/3GRoot: FCAW with OK Tubrod 14.27,welded manually onto ceramicbacking stripFilling: FCAW with OK Tubrod 14.27,welded manually.

72 Connection between tank floor and carbon steel hull

Position: PA/1GRoot & 1st pass: FCAW with OKTubrod 14.22, welded manually ontoceramic backing strip.Filling: SAW with OK Autrod 16.53/OK Flux 10.93

5 Connection between angled side wall and tank floor

Position: PC/2GMulti-layer T-joint; full penetration.FCAW with OK Tubrod 14.27,manually.Sealing: SMAW with OK67.50

1

2

3

3

6

5

74

89

9

9


Connection between corrugated bulkheads and tankcover

Position: PC/2GRoot: FCAW with OK Tubrod 14.27,manually welded onto cylindricceramic backing.Filling: FCAW with OK Tubrod 14.27,welded manually.

elds in duplex stainless steel

8

9 Connection between tank cover and between tank covers and side walls

Position: PA/1GRoot & 1st pass: FCAW with OKTubrod 14.37, manually welded ontoceramic backing strip.Filling: FCAW with OK Tubrod 14.37

3

4

Assembly weld 8, connecting asmall, extending part of the cor-rugated bulkhead to the deck ofthe subsequent tank section, isdone in a semi-overhead positionwith exactly the same weldingprocedure. OK Tubrod 14.27 isone of the best cored wires avail-able for overhead work, becausethe stiff, fast freezing slag pre-vents sagging of the weld metal.

The last step in the assemblyprocess involves the connectionof the tank cover (weld type 9).This is done in the downhand po-sition with OK Tubrod 14.37(root passes on rectangular ce-ramic backing strips.

SubassemblyGoing back to Figure 4, it can beseen that this prefabricated blocksection consists of two major parts;the tank cover and a cross of twocorrugated bulkheads placed per-pendicular to the tank cover.

Starting with the tank top, it isclear that it is composed of a great number of plates. The smallyellow lines represent weldsmade indoor on the panel lines(described later) to form thepanels out of which the deck iscomposed. The thick yellow lines

are the pre-assembly welds con-necting the panels to form thetank cover. They are made ac-cording to exactly the same weld-ing procedure as described forthe tank floor in Figure 2 (weldtype 1). FCAW is used for theroot and first pass (OK Tubrod14.37 on rectangular ceramicbacking strip) and SAW (OK Au-trod16.86/ OK Flux 10.93) is usedfor filling and capping.

The sketch of Figure 7 de-scribes the basic component ofthe corrugated bulkheads. Assuch, they are supplied by thesteel fabricator, bent to the rightgeometry with welds connectingthe three areas of increasing platethickness. To form a completelongitudinal bulkhead nine weldsare required. Figure 8 shows thefabrication of these welds. Againthe combination of OK Tubrod14.37 on ceramic backing for theroot pass and OK Autrod 16.86/OK Flux 10.93 is applied for thefilling layers.

Two pre-assembly welds re-main to form the block section.The transverse corrugated bulk-heads are connected to the longi-tudinal ones by means of K-jointswelded mechanised in vertical-up

Figure 6: Attachment of a vertical corrugated tank wall to the tank floor; manuallywith OK Tubrod 14.27 (PC position).

Plate thickness

24 mm 15 mm18 mm

19Svetsaren No.1 1999

Figure 7: Corrugated wall segment as purchased from the steel works.


position with OK Tubrod 14.27using cylindrical ceramic backingto allow fast root pass deposition.The cross of bulkheads created inthis way is attached to the tankcover in PB position with OK Tu-brod 14.27 using the same weld-ing procedure as applied in thedock assembly for weld type 7.

Panel fabricationPanel fabrication is carried out in-doors on a panel fabrication linewith two ESAB A6-LAE1250-TAC1000 submerged arc weldingmachines. Panels for the tankfloor, the tank cover and for theside walls of the tanks are all pre-fabricated according to the samewelding procedure. The number ofplates comprising a panel varies.

At the moment of our visit,there was no duplex fabricationin progress, so we describe the

welding procedure by means ofthe sketch in figure 9a. Duplexplates are bevelled to a Y-jointwith a land of 4mm and posi-tioned on the panel line with aminimal root gap. To avoid con-tamination of the duplex materi-al, AISI 316L plates are placedbetween the duplex plates andthe carbon steel rollers of thepanel line.

SAW with OK Autrod 16.86and OK Flux 10.93 is applied forthe complete joint. The first layeris carried out with a tandem sys-tem; the two filling layers withsingle-wire SAW. After completingthe above, the panels are turnedand sealed with single wire SAW.

At this moment, Factorias Vul-cano are experimenting with anew ESAB solution aiming atsingle-sided welding of the pan-els, which would provide a sub-


The ESAB OK Tubrod series of cored wires for standardduplex stainless steel consist of an all-position type, OK Tubrod 14.27 and one for downhand use, OK Tubrod 14.37.They provide fabricators with optimal welding characteris-tics and productivity for manual or mechanised welding.

OK Tubrod 14.27 is a very versatile consumable, suitedfor truly all welding positions, including pipe welding incombination with the TIG process for rooting. Very fastvertical-down welding of fillet welds is possible for partsthat allow to be attached without secure root penetration.Many fabricators standardise on this type only, when themajority of the work involves positional welding.

Both types have very clear advantages compared withMMA and GMAW, reviewed below.

Advantages over MMA• higher productivity in general due to higher duty cycle• productivity for positional welding almost 3 times

higher through increased deposition rates• very economic deposition of root passes, with less

welder skill needed• no stub-end waste and therefore higher efficiency

Advantages over GMAW• up to 150% higher productivity in positional welding• excellent performance with conventional power sour-

ces; no expensive pulsed arc equipment needed.• use of normal 80%Ar/20%CO2 shielding gas; use of

expensive high Ar mixtures is avoided. Fabricatorshave an option to standardise on one gas when weld-ing both unalloyed and stainless steels.

• less oxydation of weld surface due to protective action of slag

• no grinding or sealing needed for the back side of rootpasses

• easy parameter setting

ESAB OK Tubrod rutile cored wires for duplex stainless steel

Product dataClassifications

AWS A5.22: OK Tubrod 14.27 E2209T1-1/E2209T1-4OK Tubrod 14.37 E2209T0-1/E2209T0-4

ApprovalsOK Tubrod 14.27 ABS, Controlas, DNV, GL, LR,

RINA, TÜV OK Tubrod 14.37 DNV, GL, LR, TÜV

All weld metal composition (weight %)OK Tubrod 14.27 OK Tubrod 14.37C: ≤0.03 C: ≤0.03Si: 0.50-0.90 Si: 0.60-1.00Mn: 0.50-1.00 Mn: 0.70-1.20Cr: 21.0-23.0 Cr: 21.0-23.0Ni: 8.0-10.0 Ni: 8.0-11.0Mo: 2.75-3.25 Mo: 2.75-3.25N: 0.11-0.17 N: 0.10-0.16P: ≤0.025 P: ≤0.035S: ≤0.025 S: ≤0.025

FN: 30-50 FN: 30-50

Mechanical properties in Ar/CO2OK Tubrod 14.27 14.37

Rp0.2% (MPa) ≥500 ≥480Rm (MPa) ≥690 ≥690A5d (%) ≥25 ≥25ISO-V –20°C (J) ≥60 ≥40

Shielding gas: Ar/CO2 or CO2

Polarity: DC+

stantial time saving. Successfultests have been carried out with abacking rail filled with fine grainOK Flux 10.93 enabling to depos-it a good quality root pass that re-quires no sealing (Figure 9b). Ap-plication of this system, however,requires an investment in stain-less steel rollers, because it doesnot allow protection of the du-plex material in the way utilisedpresently. The feasibility studyhas not yet been completed.

Steel grade and mecha-nical propertiesAll duplex stainless steel used forthe construction of the Primo ispurchased from Avesta under thebrand name Avesta 2205. It is astandard, molybdenum alloyedgrade.

Mechanical properties of thewelds are overmatching with all



Figure 8: Welding of a corrugatedbulkhead. Root (below) made withFCAW; filling and capping with SAW.

Figure 9a: Double sided SAW panelfabrication.

Figure 9b: Single-sided SAW panelfabrication. Root pass on gutter filledwith fine grain OK FLUX 10.93

ESAB consumables used for thisproject. The Ferrite number ofthe weld is required to be bet-ween 25–70 which is a normal re-quirement for duplex stainlesssteel welding, and sufficientlywide for construction practice.The Ferrite number is checked bymeans of a representative se-quence of weld samples in vari-ous stages of the construction, us-ing the same welding procedureand consumables as for the actualwelds. From the same samples,confirmation of mechanical prop-erties are obtained.

Preheating is not applied, al-though a minimal temperature of16ºC is prescribed; sufficient toavoid condensation under themild climatic conditions of the re-gion. The interpass temperature islimited to a maximum of 150ºC.

Appendix I shows a full WPSfor OK Tubrod 14.27 prescribingthe manual or mechanised assem-bly welding in PF position, as de-scribed in Figure 2 (weld type 6).It contains useful information forreaders that have become inter-ested in this product, as well as afree lesson in welding terminolo-gy in the rich and beautiful Span-ish language.

To concludeWhen having the privilege of vis-iting this modern, yet cosy ship-yard in Galicia, I fell at homefrom the start, enjoying the warmand open atmosphere I encoun-tered. It was very rewarding tosee that Esab’s commitment to be

a total supplier works out so wellat Factorías Vulcano, and that ourproducts are being applied to thefull satisfaction of the yard.

To avoid leaving behind theimpression that it is fun to be aneditor for Svetsaren, I will refrain

from describing the short boattrip across a beautiful bay, afterthe interview, to the small familyrestaurant where I received valu-able lessons in seafood dining.“Disfrutaba de toda forma y undía regresaré”.

Figure 10: Welding Procedure Specifications.


22 Svetsaren No.1–2 1999

To meet the demands ofthe power generating industry with its aim ofincreasing steam temper-atures and pressures, thedevelopment of morecreep-resistant ferriticsteels started in the mid-1970s. Ferritic steels werepreferred to austeniticsteels because of theirlower coefficient of ther-mal expansion and theirhigher resistance to ther-mal shock (1). Of thesesteels, the modified 9%Cr1%Mo steel known asP91/T91 or, in Europe, asX10CrMo VNb9-1, hasbeen used in a wide rangeof industrial applications.As Table 1 shows, theroom-temperature strengthof the modified variant issuperior to that of theconventional variant.In addition to improved room-temperature tensile strength, themodified variant also has in-creased creep strength, lowerductile-to-brittle transition tem-peratures and higher upper-shelfenergy. The improved mechanicalproperties are explained by smalldifferences in the chemical com-position consisting of controlledamounts of Nb, N and V in theP91 steels, see Table 2.

P91 is primarily used in nor-malised and tempered condition.During heat treatment, a fine dis-persion of Nb(C, N) and M23C6is precipitated. Through the mech-anism of precipitation strengthen-ing, this gives rise to the enhancedmechanical properties.

P91 is generally used in steampiping, headers and super heaterpiping where the advantages overconventional CrMo steels can beused either for weight reductionsor to permit an increase in operat-ing temperature. Arav and vanWortel (2) made a comparison ofthe pipe-wall thickness requiredfor different creep-resistant mate-rials in certain operating conditionsand demonstrated that the wallthickness can be reduced by three-quarters if P91 is chosen instead of2 1/4Cr1Mo steel (Figure 1).

Welding is one of the most es-sential fabrication processes forcomponent manufacture. Theweldability of P91 steels is verygood. Due to the high alloyingcontent, a relatively high preheat-ing temperature (200-350°C)must be used. The exact choice ofpreheating temperature also de-pends on the material thicknessand the amount of restraint. Alow hydrogen content is naturallynecessary and only the basic typeof consumables should thereforebe used.

When designing a welded com-ponent, it is important to considernot only the mechanical proper-ties of the base material but inparticular the strength and prop-erties of the weldments. For com-ponents designed for high-tempe-rature service, the creep proper-ties must be regarded as central.

Consumables and welding modified 9 Cr-1 Mo steel

by Eva-Lena Bergquist, Esab AB, Göteborg, Sweden

Steel grade Rp (MPa) Rm (MPa) A5 (%)

conventional 9Cr-1Mo (P9) min 205 min 415 min 30

X10CrMoVNb9-1 min 415 min 585 min 20(P91)

Steel grade C Si Mn P S Cr Mo Ni Nb V Al N

P9 max 0.25- 0.30- max max 8.0- 0.9-0.15 1.00 0.60 0.025 0.025 10.0 1.10

P91 0.08- 0.20- 0.30- max max 8.0- 0.85- max 0.06- 0.18- max 0.03-0.12 0.50 0.60 0.02 0.01 9.5 1.05 0.40 0.10 0.25 0.04 0.07

Table 2. The specified chemical composition of conventional 9Cr-1Mo (denotedP9) compared with the composition of P91 (X10CrMoVNb9-1). (wt%).

Table 1. Mechanical properties of modified and conventional 9Cr-1Mo steel.

Figure 1. Comparison of the wall thick-ness required for different creep-resis-tant materials. Assumed operating con-ditions 250 bar and 600°C. Note the lar-ge reduction in wall thickness which ispossible when P91 steel is chosen.From Arav and van Wortel (2).

21/4 Cr1Mo

X20

347H

P91



As a result, this paper will discussthe creep properties of weld-ments in P91steels and the waythey are affected by the weldingprocedure, post-weld heat treat-ment and consumable composi-tion. There is also a brief discus-sion of the impact strength of P91type weld metals.

Weldment creep propertiesSeveral investigations haveshown that, when creep tests areconducted across a welded jointin X10CrMoVNb9-1, creep frac-ture occurs mainly in the heat af-fected zone (HAZ) and only

rarely in the weld metal. A softzone that forms at the outer re-gion of the HAZ, the so calledType IV zone (this denominationis based on a weldment crackingmode model made by Shuller etal.(3)), is a matter of great con-cern. In this zone, the tempera-ture has not been high enough toreturn the alloy carbides into so-lution. Instead, carbide coarsen-ing takes place and this minimisesthe precipitation strengthening(4). The effect is apparent as ahardness minimum. Figure 2shows the typical hardness profileof a weldment in modified 9Cr-1Mo steel (5).

In addition, the temperature inthis zone is just enough to austen-itise the material, but it is nothigh enough to cause any signifi-cant grain growth. So, consider-able grain refinement will con-tribute still further to reducingthe high-temperature creepstrength.

The reduction in creepstrength due to this creep weakzone has been examined in sever-al investigations. Creep strengthreductions of approximately 20-30% have been reported (1), (2),(7). A recent investigation atTNO (6), using isostress creeptests, i.e. creep testing at constantstress with varying temperature,demonstrated creep rupture lifetimes almost one order of magni-tude lower for weldments com-pared with parent material (Fig-ure 3).

The creep-weak zone is verynarrow. The limited width of thezone leads to macroscopicallylow ductility in the type IV frac-tures. Figure 4 illustrates the dif-ferences in the elongation of basematerial and cross-weld speci-mens as obtained by TNO (6).

As so many of the creep prop-erties of weldments are con-trolled by this creep-weak zone,it is relevant to ask whether thiszone can be removed or madeless harmful in some way. The re-maining part of this section willdeal with the influence of thewelding process, the post-weldheat treatment and the composi-tion of the welding consumable.

Provided that fusion welding isemployed, the Type IV zone willalways be present, irrespective ofwelding process. It is inevitablethat there always will be a zonethat is exposed to the criticaltemperature range. The widthand the distance of this zonefrom the fusion boundary may,however, vary. In this case, thewelding process will only have anindirect influence, through theheat input and the cooling rate. Ahigher heat input will lead to awider zone, which will be placedfurther away from the fusion line.Recent investigations indicatethat a wider zone is more detri-mental to creep properties than athinner one. So, very high heat

Figure 2.Typical hardness profile of a weldment in modified 9Cr-1Mo steel (afterreference (5)). Note the hardness minimum appearing in the outer part of the HAZ.WM=weld metal; C=coarse grain zone; F=fine grain zone.

Figure 3.Time to rupture of isostress (100MPa) cross-weld creep tests in X10CrMoVNb9-1 as a function of testing temperature. This illustrates the reduction in creepstrength in the weldments compared with the base material. The welds were produ-ced with submerged arc welding. From reference (6).



inputs should be avoided whenwelding P91 steels. However, asyet it is not possible to specify anupper limit for the heat input.

A typical post-weld heat treat-ment temperature for P91 steelis 750–760°C. As can be under-stood from the mechanism thatcauses the soft zone, post-weldheat treatment in this regiondoes not “cure” the loss of creepstrength.

A couple of unconventionalpre- or post-weld heat treatmentroutines have been proposed, butnone has yet proved to be usefulfor industrial applications.

From the discussion of TypeIV cracking in the preceding par-agraph, it might be thought, whenthe subject is examined from acreep point of view, that thechemical composition of the weldmetal is of less interest. This is,however, not the case. The chem-ical composition affects the creepstrength of the weld metal and,because of the stress redistribu-tion mechanisms that are activat-ed in a creep-loaded weld, thecreep lifetime of the Type IVzone is also affected. Too strong aweld metal will lead to a concen-tration of creep strain in theweakest area, i.e. the Type IVzone. Moreover, when deformed,a weld metal that is weaker thanthe parent metal will attempt toshed load onto the adjacent re-gion and thereby induce a TypeIV failure. So, the optimum solu-tion is probably to aim at weldmetal creep strength in the samerange as that of the parent mate-rial.

The Nb, V and N content ofthe consumables has been shownto be important for the weld met-al creep properties, just as it isfor the creep properties of theparent metal. The role of theseelements is the same, namely toform and stabilise carbides andnitrides. The importance of thethree elements is clearly shownin Figure 5 which is a comparisonbetween an electrode of standardOK 76.98 composition and an ex-perimental electrode (8). Thestandard electrode shows clearlybetter creep strength than theexperimental one, which is leanerin its composition.

Weld metal toughnessThe weld metal toughness may bethought to be irrelevant in assem-blies designed for operation inthe temperature range of 500-600°C, since this is definitely far

in excess of the temperaturerange at which brittle fracturecould occur. However, the com-ponents may very well also bestressed at ambient temperatureduring testing or start-up, for ex-

Figure 4. Creep elongation of the base material and cross-weld samples at differenttest temperatures. The low elongation in the cross-weld samples is due to the effectof the Type IV fracture. Isostress creep testing at 100 MPa. Welds were producedwith manual metal arc welding. From reference (6).

Nb (wt%) V (wt%) N (wt%)

OK 76.98 0.056 0.197 0.051experimental 0.020 0.142 0.028

Figure 5.Creep strength of cross-weld specimen welded with different consumables.This illustrates the importance of having the correct amount of microalloying elements.



ample. To minimise the risk ofbrittle fracture in these situations,a minimum toughness average forweld metal of 47J (minimum sin-gle value of 38J) at 20°C has re-cently been introduced in the Eu-ropean specification EN1599:1997.

Esab’s product programmecurrently offers two consumablechoices for welding P91— oneMMA welding electrode desig-nated OK 76.98 and one solidwire called OK Tigrod 13.38. Thetypical impact values of theseproducts are all well above theEN 1599 requirements, see Table3. Furthermore, a cored wire/fluxcombination is currently underdevelopment, but it has not yetbeen fully tested and validated.

It has already been mentionedthat the welding process in itselfhas no influence on the creepstrength of weldments in P91. Inthe case of impact toughness,however, the choice of processmay be significant. The highesttoughness is normally achievedusing GTAW, while flux processessuch as MMA and SAW producelower toughness values. It hasbeen suggested that the reasonfor this is varying oxygen content.An oxygen content of less than100-200 ppm may be reachedwith GTAW procedures, whileMMA and SAW will producetypical oxygen contents in therange of 400-800 ppm.

On many occasions, it is wise tomake the composition of a weld-ing consumable as similar to theparent steel type as possible. Forthe modified 9%Cr-1%Mo steel,

however, it was realised at an ear-ly stage that adjustments to theniobium and nickel content werecrucial to obtain acceptabletoughness values. Compared withthe parent steel, the Nb contenthas to be lowered. However, asstated above, the Nb is essentialfor satisfactory creep resistanceand cannot be totally excluded.The Nb content in the Esab con-sumables is therefore limited to0.04-0.08%, seeTable 4.

The Ni content, on the otherhand, is higher in the weld metalthan in the parent material. Theaddition of Ni lowers the so-cal-led Ac1 temperature. This canhave both a positive and a nega-tive effect on the toughness, de-pending on how much it is low-ered. The positive aspects includethe fact that an Ac1 temperaturethat is closer to the PWHT tem-perature improves the responseto tempering, which has a benefi-cial effect on the toughness. Italso minimises the risk of residualdelta ferrite. Delta ferrite isthought to lower the creep resis-tance and may also have a detri-mental effect on toughness. How-ever, an excessive amount of Nimay lower the Ac1 to a level thatis exceeded by the upper end ofthe PWHT temperature range,causing austenite to form, whichwill in turn be transformed intountempered martensite. Untem-pered martensite has a negativeeffect on the impact toughness.Due to these factors, the nickelcontent in the Esab consumablesis controlled in the range shownin Table 4.

Further developmentThere is strong environmentaland economic pressure to in-crease the thermal efficiency ofpower stations still further, there-by leading to a steady increase insteam temperatures and pres-sures. Alloying with W, Cu and/orNi has produced a range of newsteel variants with even highercreep strength than X10CrMoVNb9-1. The effect of welding thesematerials has not yet been thorough-ly investigated, but some resultsindicate that the effect is similarto that in X10CrMoVNb9-1.

References(1) H. Cerjak, E.Letofsky. “The effect of

welding on the properties of advanced9-12%Cr steels.” Proceedings fromInternational conference on weldingtechnology, materials and materialstesting, fracture mechanics and qualitymanagement, 1997.

(2) F. Arav, J.C. van Wortel. “Propertiesand application of the modified 9Crsteel T91/P91.” Stainless Steel Europe,April 1995.

(3) H.J. Schuller, L.Hagn, A. Woitscheck.“Risse im Schweissnachtberrich vonFormstucken aus Heissdampfleitungen– Werkstoffuntersuchungen.” VGBKraftwerkstech, vol 54 1974.

(4) A.J. Tack, C.W. Thomas. “The high tem-perature properties of weldments increep resistant steel.” Proceedingsfrom IIW Asian Pacific welding con-gress, 1996.

(5) M. De Witte. “T91/P91 base materialand weldments.” Laborelec report.

(6) J.C. van Wortel, F. Arav. “Investigationsinto the properties of modified 9Crsteel for high temperature applica-tions”. TNO report no: T91 94-30.

(7) K. Bell. “An analysis of publishedcreep rupture data for modified 9Crsteel weldments”. TWI report no598/1997.

(8) H. Theofel. “Untersuchung einer artglei-chen Schweissverbindung fur 9%Cr1%Mo-Sthähle unter besonderer Beruck-sichtigung des Langzeitkriechverhal-tens.” Staatliche Materialprufunganstalt,Universität Stuttgart,AIF-Nr 9300.

Product Rp0.2 Rm A5 (%) KV (J) at 20°C(MPa) (MPa)

OK 76.98 650 760 18 70

OK Tigrod 13.38 690 785 20 200

EN 1599 requirement min 415 min 585 min 17 min. average 47

Table 3. Mechanical properties of OK 76.98 and OK Tigrod 13.38. Typical values.

Product C Si Mn P S Cr Ni Mo V Nb N

OK 76.98 0.08- 0.2- 0.4- max max 8.0- 0.4- 0.85- 0.15- 0.04- 0.030-0.13 0.5 1.0 0.02 0.02 10.0 1.0 1.10 0.30 0.08 0.070

OK Tigrod 13.38 0.08- 0.20- 0.35- max max 8.6- 0.6- 0.85- 0.18- 0.04- 0.030-0.12 0.50 0.60 0.010 0.010 9.3 0.9 1.05 0.25 0.08 0.070

Table 4. Specified composition for OK 76.98 and OK Tigrod 13.38.

About the authorsEva-Lena Bergquist graduatedfrom Bergsskolan in Filipstad inSweden in 1986. She spent thefollowing ten years working pri-marily on failure analyses atSAAB Automobile and later atABB STAL AB. In 1997, she joi-ned Esab and is now a researchengineer at the Central Labora-tories in Göteborg.



Since the beginning ofthe 1990s, laser weldinghas been an acceptedmethod in the automo-tive industry for weldingvehicle bodies and body-work components. VolvoCars opened the doorfor this technology whenit began using lasers toweld the roof joints ofthe 850 model, currentlythe S70 and V70 model.The method has nowbecome state of the artand a number of otherlarge car manufacturers,like BMW, Mercedes,VW and Audi, now per-form similar welding.However, the giants inthe automotive industryare not the only oneswho use laser welding.

The large-scale production oflaser-welded components for ve-hicles has also developed. In thesmall town of Torsås in Smålandin Sweden, AP Automotive Sys-tem Torsmaskiner AB has beeninvolved in the professional laserwelding of catalytic converters forthe automotive industry for thepast five years.

AP Torsmaskiner AB, as thecompany is generally known, isone of the leading suppliers ofmanifolds and catalytic convert-ers to the European automotiveindustry. The company’s product

programme previously also in-cluded silencers. Major customersinclude Volvo, VW, Ford and Mitsubishi. Production is highlyautomated and, at the 1998/99year-end, it included some 50 in-dustrial robots for conventionalwelding.

Hans Nyström works as a pro-ject leader with project planningfor new production and, at thesame time, he is responsible forwelding at AP Torsmaskiner AB.He was involved at the very startwhen laser welding was first in-troduced and he tells a fascinat-ing story about the arrival of laserwelding in Torsås.

He described the successful la-ser welding of catalytic convertersfor the automotive industry at aseminar for the Swedish lasergroup within Sweden’s Engineer-ing Industries.

“It all began in the autumn of1992,” says Hans Nyström. “It wasdecided that we would start pro-ducing what is known as a ‘stam-

ped muffler’, patented by ourowners AP Parts in Toledo in theUSA. This silencer was designedfor the Volvo 960.”

Success vital“The ‘shell’ would be joined to-gether using laser welding. Thiswas a wonderful opportunity forus to introduce an entirely newwelding method,” Hans contin-ues. “The machine was to be a 6kW CO2 laser. Some capacity wasleft over on this machine and sowe decided to laser weld the cata-lytic converters, because we hadjust received an order for a cata-lytic converter for the Volvo 850.No sooner said than done. We de-signed the first catalytic converterfor laser welding.

Test welding was done at Per-mascand AB in Ljungaverk ontheir 1.5 kW CO2 laser. The ma-terial in the catalytic converterwas ferritic stainless W1.4512 andtwo plates, 1.5 mm thick, were go-ing to be joined using lap joints.

Laser welding catalytic converters— a complete success for

AP Torsmaskiner AB, Swedenby Hans Engström MSc, Lic Eng, Luleå, Sweden

AP Torsmaskiner AB’s main products are manifolds and catalytic converters forthe automotive industry.



One question which wouldhave a decisive effect on futuredevelopments was the structureof the weld metal. We started toweld with argon as the shieldinggas. It became clear that the welddepth was not sufficient. The re-sults were improved when wechanged to helium and and theweld metal analysis was perfect!The catalytic converter projectcould continue.”

Laser welding cell fromthe USAThe laser welding machine wasbuilt by LMI, a company just eastof Minneapolis in the USA. Theenergy source in the machine is aTrumpf 6 kw turbolaser, buteverything else was built by LMI.The equipment has three axeswith two welding stations and thelaser beam is switched from onestation to the other via a moving,indexing mirror.

Hans Nyström goes on to ex-plain that, in September 1993, aso-called run-off took place atLMI. At that time, the welded ob-ject was the silencer that was go-ing to be produced for the Volvo960. It consisted of six “shells“made of ferritic, stainless sheetsteel which were put together —four were 0.5 mm and two 1.0mm. In addition, two of them (0.5

mm) were aluminium-plated. Itemerged that laser welding thismaterial combination was notwithout its problems as largenumbers of pores developed. Themain reason for this was found tobe a kind of dry oil which wasused when the plates were pres-sed and which still remained insuch quantities that it made laserwelding impossible. This problemwas eventually solved, however.

Training is important“Training is an extremely impor-tant parameter,” Hans continues.“Two operators were selected fortwo weeks of training on this ma-chine. One week was spent at oursister company in Granger in theUSA, where a similar productwas produced on similar ma-chines. The other week was spentat LMI in connection with the so-called run-off. This subsequentlyproved to have a very importanteffect on our production when itcame to the handling, mainte-nance and service of the equip-ment.

Commissioning the cat-alytic converter — a to-tal success“Just like the commissioning ofany new machinery and equip-ment, the commissioning processof the shell silencer was associat-ed with some problems,” Hansexplains.

“Material problems with the si-lencer now emerged in the formof an excessive amount of thepreviously-mentioned dry oilwhich was left after pressing theplates. We have now sorted outthis problem for the most part,but it recurred from time to timeas production continued. Otherproblems of different kinds whichresulted in stoppages were causedby the laser. Otherwise, every-thing functioned almost perfect-ly.”

So how did the commissioningprocess of the catalytic convertergo? “It went fantastically well!All that was needed was a minoradjustment after the ‘startingshot’ was fired!

“I have never been involved insuch a smooth commissioningprocess,” Hans Nyström contin-

ues — and he has 30 years’ expe-rience of production engineering.“Production and the system bothfunctioned very well until a shorttime ago when we were forced toreplace both the turbines in thelaser. It had then been in opera-tion for 17,000 hours.“

Useful experience —money to be saved“Yes, we have certainly learned agreat deal from this installation,“Hans Nyström adds.

“In our view, the design of thecross-flow which keeps dirt anddust away from the focusing opticcould be improved. We think thatfar more resources should be in-vested here.

“When it comes to the supplyof shielding gas, there is scope forany number of new ideas,” Hanssays. “It has become clear that thedesign of the gas nozzle is veryimportant. Its position and theway the shielding gas is directedat the welding point are just asimportant. We have seen that thisaffects the gas flow, the weldingspeed and the weld quality. Sothere is money to be saved here.”

A precise fit, top-class clean-ness and consistent quality are vi-tal in the material that is going to

Hans Nyström has every reason to bepleased with the laser welding of thesecatalytic converters. The commissio-ning process went smoothly and pro-duction functions perfectly.

The laser welding cell comes fromLMI in the USA and is equipped witha 6 kW Trumpf CO2 laser. The cell hastwo stations and they weld alternately.The parts of the catalytic converter(the shell and the inserts) are fixed inplace using hydraulic fixtures whichclamp round the catalytic converter.The weld joint is a lap joint which iswelded at 3.5 m/minute.



be welded if the results are to besatisfactory.

Stable fixtures — moderate force“Stable fixtures are essential forsecure fixation. However, thereare some limits when it comes tothe gaps between the plates whenlap joints are performed. Somecare must be taken in terms of thetension in the plates. If the jointsare too tight, pores will be pro-duced as some gas forms betweenthe plates. These pores can thenform because these gases can onlyescape via the molten pool.

“So make sure the gap is one-to two-tenths of a millimetrewide!”

However, with smaller materialthicknesses than those mentionedabove, other rules may apply, ac-cording to Hans Nyström, as heconcludes his presentation.

Hans Nyström’s description isan excellent example of the kindof things that can happen when anew technology like laser weldingis introduced into production. Itis essential to be in control of allthe parameters, otherwise prob-lems can occur. However, in theright conditions, laser welding is ahighly productive and reliablewelding method, the use of whichis now increasing sharply in man-ufacturing industry.

Hans Nyström and his col-leagues at AP Torsmaskiner ABin Torsås are now examining newapplications for laser welding!

AP Automotive System TorsmaskinerAB is a leading supplier of manifoldsand catalytic converters to the Euro-pean automotive industry. The compa-ny is situated in Torsås in the south-eastern part of the County of Små-land, not far from the well-known“kingdom of glass”, where some ofthe world’s leading glassworks, such asOrrefors and Kosta, are located. Inthe past, the company also producedsilencers, but these operations havenow been transferred to another com-pany within the AP Automotive Sys-tems Group in the Netherlands.

The company has around 450 em-ployees and turnover in 1998 totalledsome SEK 750 million.

AP Automotive System Torsma-skiner AB’s most important customeris Volvo Car Corporation but majororders have also been received fromVW and Ford, necessitating the instal-lation of completely new productionlines which are currently being com-missioned.

The company is expanding verysharply. In 1998 it produced 200,000

catalytic converters and 760,000 mani-folds. By the year 2000, these figureswill have risen to 300,000 and2,000,000 units respectively. The largeorders from VW and Ford will ac-count for most of this increase in pro-duction. The number of employees isalso increasing sharply and the workforce already totals around 500.

As a result of this expansion, turn-over will double in the space of twoyears.

For several years, the company wasa member of the AP Parts Group,with its headquarters in Toledo in theUSA. However, in December 1997, itchanged owners when Questor in theUSA purchased the group.

AP Torsmaskiner AB, as the com-pany is generally known, is now partof AP Automotive Systems Inc.

The AP Automotive SystemsGroup has a total of around 3,000 em-ployees. Its largest customers are GMand Ford, while Volvo dominates inEurope.

About the authorHans Engström is acting Head ofthe Division of Materials Proces-sing at Luleå University of Tech-nology, Luleå, Sweden. He hasbeen actively involved in the R&Dof laser materials processing since1981 and has worked in severalareas, such as laser surface modifi-cation, systems and welding. Formany years, he has also headed thelaser group at the university. Inaddition, he had been activelyinvolved in the successful intro-duction and progress of the LaserGroup at the Association of Swe-dish Engineering Industries, as theeditor of the group membershipjournal, Laser News.

AP Automotive System Torsmaskiner AB



For many years, therehas been a desire to in-crease the use of highstrength steels in differ-ent applications. Obvi-ously, by increasing thestrength of the steel,thinner, more economi-cal solutions can becreated. There are cur-rently many examples ofwelded structures madefrom steels with a yieldstrength of up to 690MPa. Although verythin plates are used inmany cases in these con-structions, resulting in alow risk of brittle frac-ture, there are also somelarge types of construc-tion, such as submarines,in which thick plates areused.

In these heavy plate structures,the risk of brittle fracture hasbeen assessed thoroughly, usingconventional impact toughnesstesting, fracture mechanics testingand detonation tests. It is general-ly believed that a steel with high-er strength also requires greatertoughness, compared with a lowerstrength steel.

There are several lines of de-velopment which increase theneed for new welding consum-ables with a strength level of 690MPa and above. The first is thewider use of 690 MPa steels (1).For most applications, there is arequirement for weld metalstrength which overmatches the

strength of the base metal. Forthe 690 MPa grade of steel, thereare few consumables which over-match the strength of the steel,while still meeting the toughnessrequirements. Instead, matchingweld metals are used. This hasraised the question of the structu-ral integrity of these joints, as it isthought that the weld metal haslower toughness than the steel.Research programs which are ad-dressing this problem are current-ly in progress. In this context, asecond line of development canalso be seen. Apart from lookingfor overmatching weld metals,there is also a call from fabrica-tors to use more high productivityprocesses for welding these steels,mainly cored wires and sub-merged arc welding. Some resultsof investigations in this field hasbeen dealt with in this paper.

The second line of develop-ment is to enhance the yieldstrength to make it even higherthan 690 MPa. Steels with a yieldstrength of 900, 1,000 and 1,100MPa and good impact toughnessare currently available on themarket. The applications for thesesteels include mobile cranes, con-veyor systems and roof supports.These steels are currently weldedwith undermatching consumablesand the welds therefore have tobe placed in low-stress sections.There is also a drive towards theuse of heavy plates with thesevery high strengths. The need forhigher strength consumables isthen likely to increase.

In this paper, consumables pro-ducing weld metals with a yieldstrength of 690 MPa and abovehas been presented. The mechani-cal properties of different weldingprocedures has been given andthe relationship between strengthand impact toughness has beendiscussed. Firstly, however, a gen-

eral presentation of the relation-ship between microstructure andmechanical properties will bemade.

Microstructure and me-chanical propertiesIn order to understand the rela-tionship between microstructureand mechanical properties, sometypical microstructures from weldmetals with different yieldstrengths are shown in Figure 1.All the micrographs were takenin the last deposited bead, in or-der to avoid the influence of heattreatment from subsequently de-posited beads. The microstructurein the last deposited bead is, how-ever, generally only part of thetotal microstructure of a weldedjoint. When multipass welding isused, the weld metal contains anumber of beads, each of whichcontains a number of subzones inwhich the weld metal has beenreheated to different peak tem-peratures. This produces a com-plex pattern of zones which mayhave different properties. Fur-thermore, the welding procedurealso influences the size and pro-portions of the various zones, aswell as the microstructure withineach zone.

So, the mechanical propertiesof different weld metals must becompared with great care. Themicrostructure,which is depen-dent on the chemical compositionand cooling conditions, is just onefactor which influences the me-chanical properties. The weldingprocedure, including the number,size and placement of beads, isjust as important. In the case ofmanual welding, the welder him-self then can have a major influ-ence.

Despite these difficulties, somegeneral conclusions on the effect

Consumables for welding highstrength steels

by Lars-Erik Svensson, Esab AB, Göteborg, Sweden



of microstructure on mechanicalproperties can be drawn. In Fig-ure 1a, the three most typical mi-crostructural constituents areseen: allotriomorphic ferritealong the prior austenite grainboundaries, Widmanstätten sideplates and acicular ferrite. Theweld metal is of the basic typeand therefore has a relatively lowcontent of non-metallic inclu-sions. The percentage of the vari-ous constituents varies with the

alloying content and cooling rateof the weld metal. As a very gen-eral rule of thumb, a weld metalwith this type of appearance willhave a yield strength (YS) of ap-proximately 450–550 MPa and anultimate tensile strength (UTS) of600–700 MPa. The ductility, meas-ured as A5, is about 25% and thearea reduction at fracture (Z) isapproximately 70%. All these val-ues are just guidelines and willvary with the precise conditions

in which the weld metal was de-posited.

Two main mechanisms areavailable for strengthening a low-alloyed C-Mn weld metal: grainrefinement and solid solutionhardening. Particle dispersionhardening should be possible toapply in principle, but it generallyleads to unacceptably low impacttoughness. Grain refinement isachieved by making the alloymore hardenable, so that thetransformations occur at a lowertemperature. As a result, a largeramount of the fine-grained acicu-lar ferrite can be formed. If theamount of alloying content iseven higher, bainite or martensiteis formed.

Acicular ferrite is the mostproblematic constituent to con-trol. The exact mechanisms whichare involved in the formation ofthis phase are still not under-stood.

Figure 1b shows a weld metalwith a YS of approximately 690MPa, a UTS of around 900 MPa,a ductility of 20% and a reduc-tion in area of about 60%. Thisweld metal is alloyed with nickel,chromium and molybdenum, in-creasing the contribution by solid

Figure 1 Micrographs illustrating the variation in the microstructure of weld metals with various strength levels(a) a weld metal with a yield strength of 450–550 MPa containing allotriomorphic ferrite, Widmanstätten ferrite and acicular

ferrite(b) a weld metal with a yield strength of 690 MPa, with a mixture of acicular ferrite, bainite and martensite in the microstructure(c) a weld metal with a yield strength of around 900 MPa, with a microstructure consisting of a mixture of bainite and marten-

site.

Product Process Chemical composition (%) Mechanical properties

C Mn Ni Cr Mo Rp0.2 Rm KV-40°C(MPa) (MPa) (J)

OK 75.75 MMA 0.06 1.6 2.1 0.35 0.4 755 820 70OK Autrod 13.43/OK Flux 10.62 SAW 0.1 1.3 2.2 0.6 0.5 700 795 75OK Tubrod 14.03 MCW 0.07 1.6 2.3 - 0.6 740 min 740-900 47OK Tubrod 15.27 FCW 0.06 1.6 2.5 - - 750 800 80

(at -50°C)PZ 6148 FCW 0.06 1.6 2.2 0.5 0.5 690 min 770-900 50

(at -50°C)OK Autrod 13.29 GMAW 0.06 1.3 1.2 0.3 0.2 750 820 40

(at -30°C)OK Autrod 13.31 GMAW 0.1 1.7 1.9 0.35 0.5 850 890 60

(at -20°C)OK 75.78 MMA 0.04 2.1 3.1 0.5 0.6 920 965 80PZ 6149 FCW 0.09 1.7 2.3 1.0 0.5 890 950

Table 1. Summary of consumables for welding steels with a yield strength of 690 MPa or above.



solution hardening to strength.For the most part, however,strength is increased by an in-crease in the proportion of low-temperature transformation phas-es. The allotriomorphic ferritealong the prior austenite grainboundaries has essentially van-ished, as has the Widmanstättenferrite. The microstructure nowconsists of a mixture of acicularferrite, bainite and martensite.

Figure 1c shows a weld metalessentially comprising bainite andmartensite, with a YS of 900 MPa,a UTS of about 1,000 MPa, a duc-tility of 18% and a reduction inarea of around 55%.

These examples show that it ispossible, at least to some extent,to connect mechanical propertiesto microstructure. However, thereare some points that should bediscussed in greater detail. Thefirst is the tensile properties. Theyare generally measured with lon-gitudinal tensile bars with a 10mm gauge diameter. Normally,this means that many zones aresampled and the mechanical dataare an average of the individualvalues in these zones. However, incertain situations, smaller sizespecimens are used, sampling few-er zones. In very special situations,depending on the exact weldingprocedure, more or less fullyweld-normalised microstructurescan be sampled, thereby produc-ing far lower strength than if thefull weld metal structure had beenexamined. This risk is particularlygreat for weld metals of lowerstrength. For higher strengthwelds, the difference in propertiesbetween the different zones di-minishes, due to the higher hard-enability of the alloys. This can besubstantiated by the hardnessvariations from the face to theroot through the three types ofweld metal from Figure 1. This isshown in Figure 2. Needless tosay, the weld metals have differenthardnesses, but the variation inhardness along each line is moreinteresting. As can be seen, thereis less scatter in the harder alloys,which means that there is lessvariation between different zonesfor these alloys. Consequently,they are less sensitive to tensiletest specimen size.

The variation in hardness bet-ween different zones also has aneffect on what is perhaps themost important property for weldmetals, namely impact toughness.It is far more difficult to give anumber to the impact toughnessfor the three types of alloy in Fig-ure 1 than to the tensile proper-ties, as the impact toughness iseven more process dependent.

The factors which control im-pact toughness are difficult topresent clearly and briefly. Thebasic microstructure naturally hasa major influence as a result ofgrain size dependence: a finergrain size produces higher impacttoughness. When lower tempera-ture transformation products,such as bainite and martensite,appear on a larger scale in the

Process Consumable Heat input Plate Mechanical Comments(kJ/mm) thickness properties

(mm)

MMA OK 75.75 2.7 40 908 MPa UTS PWHT 31 J/-55°C 600°C/1.6 h

MMA OK 75.78 1.5 15 1028 MPa UTS 3G position53 J/-60°C

FCAW PZ 6148 1.2 30 942 MPa UTS 3G position56 J/-40°C

FCAW PZ 6149 1.5 30 955 MPa UTS*) 1G position50 J/-50°C

MCW OK Tubrod 14.03 1.2 16 819 MPa UTS*)65 J/-40°C

SAW 13.43/10.62 2.6 30 851 MPa UTS 1G position75 J/-40°75 J/-40°

*) Tensile strength in transverse tensile test.

Table 2. Summary of some welding procedures using consumables for weldinghigh strength steels. The results of the mechanical tests relate to the weld metal,unless otherwise stated.

Figure 2 Hardness development through the three weld metals in Figure 1. The dif-ference in hardness reflects the difference in strength. The variation in hardnessalong the line of measurement reflects the sensitivity of each weld metal to the heatgenerated by subsequent passes.

VICKERS HARDNESS



microstructure, impact toughnessis generally reduced. To obtain anacceptable impact toughness forthese phases, other measures

must be taken, such as using avery low carbon content. Increas-ing the addition of alloys to in-crease strength usually reduces

impact toughness, with the excep-tion of nickel, which tends to in-crease it. It is usually claimed thatincreased strength results in a re-duction in impact toughness, butthis depends on the mechanismthat is responsible for the in-crease in strength. Impact tough-ness also depends on the size ofnon-metallic inclusions. This is de-termined by the basicity of theslag system (or oxygen potentialof the gas) and the heat input.Recently, the effect of minor ele-ments on impact toughness hasattracted a great deal of interest.There are also factors such as em-brittling elements like nitrogenand the actual welding processalso appears to have some influ-ence. Processes with higher pro-ductivity may have a somewhatlower impact toughness. Howev-er, many details relating to the in-fluence of the above factors asso-ciated with toughness have notbeen clarified.

Figure 3 Impact toughness at –40°C, measured at several positions across a weldedjoint. The plate on the left-hand side was wrought while the right-hand plate wascast.

Figure 4 Graph showing the relationship between yield strength and impact toughness for weld metals with a yield strength ofmore than 690 MPa. This illustrates that high impact toughness values can be obtained for high strength weld metals using several welding processes.

Yield strength (MPa)

Impa

ct t

ough

ness

at

–40°

C (

J)



In very rough terms, it can beassumed that a weld metal likethe one in Figure 1a has an im-pact toughness at –40°C of 150 J,the one in Figure 1b 100 J andthe one in Figure 1c 50 J. Due tothe greater homogeneity of themicrostructure of the higher al-loyed weld metals, they have farless scatter in terms of impacttoughness.

Welding steels with ayield strength of 690 MPa In this section, consumables forwelding steels with a yieldstrength of 690 MPa will be pre-sented. Some results from differ-ent welding procedures will alsobe shown.

Table 1 gives details of theEsab range of consumables forwelding high strength steels. Thechemical compositions and me-chanical properties relate to allweld metal. It should be notedthat the two last consumables aredesigned for welding steels ofeven higher strength.

A number of welding proce-dures in which these consumableshave been used are presented inTable 2, together with the resultsof mechanical testing. As can beseen, the welding proceduresspan quite a large field, in termsof both heat input and platethickness. A parameter which isnot given in Table 2 but is still im-portant is the preheating andinterpass temperatures used dur-ing welding. A preheating tem-perature of 100–150°C was gener-ally used for all thicknesses. Thisprevented hydrogen cracking. Inthe case of modern quenched andtempered steels with a low car-bon content, the main risk whenit comes to hydrogen cracking liesin the weld metal. So the choiceof preheating temperature shouldnot be based on the compositionof the steel. Unfortunately, thereare as yet no formulae or graphi-cal methods that provide reliableguidelines for the avoidance ofweld metal hydrogen cracking. Inorder to find suitable preheatingtemperatures, more elaboratemethods, such as a Tekken test,should be used.

As can be seen from Table 2,high tensile strengths were found

in the weld procedures. In gener-al, when it came to the transversetensile tests, fracture was found inthe base material. However, theremight be a problem in situationsin which the consumables onlygive a slight overmatching to 690MPa in an all weld metal test. Thereason for this is that the weldmetal, which is created by mixingthe consumable and the base ma-terial under the influence of thecooling conditions dictated by thewelding procedure, does not usu-ally increase very much instrength, unless large amounts ofalloying elements are picked upfrom the base material. The basematerial, which has a specifiedminimum yield strength of 690MPa, has a much higher yieldstrength in practice. It is not un-common for the steel to have ayield strength which is 100–150MPa higher than the minimumspecified value. Naturally, thesesteels also have a higher ultimatetensile strength. So, even withweld metals which should nomi-nally overmatch the strength ofthe steel, fracture may take placein the weld metal in a transversetensile test.

What is particularly encourag-ing when it comes to the weldingprocedures in Table 2 are thegood values for impact toughnesswhich were measured in the weldmetals. Figure 3 shows a plot ofthe impact toughness at –40°C forvarious positions across a weld-ment in steels with a yieldstrength of 690 MPa. In this par-ticular case, which relates to theFCAW procedure using PZ 6148,the welding was done betweentwo plates, one rolled and onecast. As can be seen, there is a de-crease in toughness from the basematerial via the HAZ to the weldmetal. This picture is often foundfor welds in 690 MPa steels, irre-spective of the consumable orwelding procedure. The impacttoughness of the weld metal isgood, but it is slightly lower thanin the HAZ.

A large number of test weldshave been prepared in order tostudy the connection between thestrength and impact toughness ofweld metals. A summary of thisconnection is presented in Figure 4,

which presents data for sub-merged arc, manual metal arc andflux cored arc weld metals. Theyield strength of the weld metalsvaried from about 650 MPa toabove 1,000 MPa. A clear trendcan be seen — an increase inyield strength produces a de-crease in impact toughness. Ascan also be seen, weld metalsfrom manual metal arc weldinghave a slightly higher impacttoughness than submerged arcweld metals.

ConclusionsWelding steels with a specifiedminimum yield strength of 690MPa is possible using most of thecommon arc welding processes.There are high productivity pro-cesses for welding these steels,mainly cored wires and submer-ged arc welding. There is a rangeof consumables that will provideboth the strength and impacttoughness to match the base ma-terial properties. To avoid hydro-gen cracking in the weld metal, apreheating temperature of125–150°C should be used; thelower temperature is applicablefor thin plates and a low level ofrestraint. One particular problemis the actual yield strength of thedelivered base materials, which isoften far higher than the specifiedminimum yield strength. The weldmetals normally overmatch thesteel, but, as the yield strength ofthe weld metal increases, a de-crease in impact toughness isseen. This then indicates that aconsumable with slight over-matching properties should be se-lected for each case.

About the authorLars-Erik Svensson, PhD, is man-ager of the Esab Central Labora-tories in Gothenburg. He has worked for more than 15 yearswith welding metallurgy, focusingprimarily on unalloyed and low-alloyed steels. He has publishedone book and more than 25 paperson the microstructure and proper-ties of welds.



The most commonlyused cutting technolo-gies are shown in Figure1. The cutting ranges fordifferent materials andplate thicknesses aregiven, together with therecommended maxi-mum thicknesses for thecutting processes andthe energy level/am-peres in question. In ad-dition to this informa-tion, current usagelargely depends on theaccuracy that can be ob-tained and this is illus-trated in Figure 2.

During the past 30 years, the en-vironmental issues associatedwith thermal cutting have at-tracted steadily increasing atten-tion. Around 1960, plasma cut-ting was virtually unknown andlaser cutting had not been in-vented. Oxy-fuel cutting wastriggering some degree of envi-ronmental discussion, mainly asa result of the very high Nx-Oycontent found in connection withcutting. At this time, the industryin general took no special opera-tor precautions against dust andfumes. The increased use of cut-ting as one of the means of op-timising steel designs and, in par-ticular, the increasing focus onoperator comfort in general inNorthern Europe during theyears that followed virtuallykicked off a new comfort busi-ness programme, based to a verylarge degree on the increasingawareness of the health hazardsassociated with dust, fumes and

gases, noise, radiation and ergo-nomics in general.

Dust, fumes and gasesThe first steps when it came toremoving the health risks posedby dust, fumes and gases focusedon oxy-fuel cutting and werebased on national regulations, inparticular those in Germany andScandinavia. The result was thetypical cutting table with fumeextraction, divided into compart-ments, so that the position of thetorch controls the compartmentfrom which extraction is active(Fig. 3).

Over the years, this type of in-stallation has been improved interms of design and functionalityand is now thought to deal veryeffectively with the environmentinside current production facil-ities, provided that the upkeep

Fig. 2. The most commonly quoted accuracies for different cutting pro-cesses. Each process designation isplaced in the middle of the respectivegraph area. HyDefinition Plasma isthe proprietary designation belong-ing to Hypertherm, Inc., courtesyHypertherm Plasmatechnik GmbHand corresponding to the term fine-beam plasma referred to in this doc-ument.

Cutting systems in an environmental context

by Dipl.-Ing. Klaus Decker, ESAB-HANCOCK GmbH, Karben, Germany

Fig. 1. Cutting ranges for different thermal cutting processes, cutting process withenergy level/amperes vertical, plate thicknesses horizontal, legend incl. max. platethickness in mm in text, courtesy Rainer Schäfer ESAB-HANCOCK GmbH.



and verification of the function isperformed correctly.

This type of installation is usedfor oxy-fuel and dry-plasma cut-ting and the actual process deter-mines the extraction volume tobe used, the normal range being4,000-8,000 m3/h for a compart-ment length of 500-1,000 mm andtable widths of up to 4,000 mm.

Whereas the interior environ-ment was catered for very effec-tively by these measures, the pol-lution from the extraction funnelinto the surroundings was han-dled using a coarse separator anda traditional cyclone, in combina-

tion with a funnel height whichwas decided from case to case.Expressed in figures, this type offunnel extraction can typically ac-commodate a dust content in theregion of 50 mg/m3 and upwardswith an aerosol type of particlesize, although the actual analysisdepends on the type of materialand the cutting process.

At the present time, this typeof installation works satisfactorilyin many environments. With in-creasing urbanisation, however,neighbourhood pollution is agrowing problem. Special cy-clones like that shown in Figure 3and special filter systems (Fig. 4)can create solutions in which theairborne pollution from dust intothe surroundings is 5 mg/m3 andless. There is no question that thecall for these systems will in-crease, in particular when parti-cles originate from the cutting ofstainless types of material.

Dry-plasma cutting was re-ferred to explicitly above as op-posed to water-plasma cutting, aprocess which is far better in theenvironmental context than thedry-plasma process, as the cuttingtakes place with the plate andplasma jet under water, eventhough the energy input is rela-tively high. It is performed withspecial water tables with rapidoperating level control. As re-gards dust, fumes and gases andeven noise levels, water-plasmacutting is very advantageous. Toput it bluntly, practically every-thing stays in the water and re-quires only something like aonce-a-year clean-out of the resi-due from the bottom of the table,while the water can be disposedof as harmless through the regu-lar sewage system.

The obvious process advan-tage, as seen from an environ-mental viewpoint, is accompaniedby the advantages of high cuttingspeed and improved precisiondue to water cooling. Markingmust, however, take place on thedry plate before cutting and thewater level operations reduceproductivity, in particular forsmall plate formats.

With regard to dust, fumes andgases, laser cutting by and largecalls for environmental measureswhich are very similar to those

described for oxy-fuel and dry-plasma cutting. The volume ofhazardous gases and dust is, how-ever, small, due to the cutting gas-es that are used and the very nar-row kerf.

Noise and radiationWhereas the previous paragraphconcluded that many environ-mental problems have been sol-ved, the situation is somewhatdifferent when it comes to thenoise and radiation problems as-sociated with dry-plasma and la-ser cutting. In both cases, thepractical and, at the same time,somewhat drastic solution ap-pears to be to “encapsulate” thecutting installation from the sur-rounding environment, as well asfrom the operator. This is not aseasy as it might look at first sight.Isolation during ongoing cuttingexcludes the traditional handlingof plates and cut parts and willundoubtedly reduce productivityto some degree, even if large in-vestments are made to facilitatethese operations. The situationwhen it comes to handling underthese circumstances represents amajor future challenge for whichthe present state of the art in cut-ting systems is not fully prepared.This issue will be touched uponagain in a subsequent paragraph.

To give just one example. Inmany cases, fine-beam plasmacutting is currently an alternativeto laser cutting as illustrated byFigure 2. The typical noise level isaround or above 100 dBA (dis-tance of one metre). It is not es-pecially practical to encapsulatethe torch and beam, but it can bedone and will reduce the noiselevel to below 85 dBA. The indus-try is, however, not particularlywilling to accept such a solutionas it will increase upkeep costsand generally make cutting morecostly because the operator is un-able to watch the cutting processand also because the effectivecutting field for a given machinesize is reduced.

One solution to the problemcould be a separate building forthe installation with remote oper-ation facilities for the cutting op-eration and to some extent alsofor loading and unloading. This is

Fig. 3. Special cyclone with double diptubes operates with very high centrifu-gal action and produces a maintenan-ce-free filtration efficiency of 99.5% ata particle size of 5 mm (principle).

Fig. 4. Filter solution able to pro-vide a very high degree of cleanli-ness for cutting table extractioninto the surrounding environ-ment.



undoubtedly a very costly solu-tion and one with reduced pro-ductivity.

Another solution could be toadapt the process to water-plas-ma operation. This would call fora water table, an air muffleraround the torch and a largercutting power source to providethe increased energy that is need-ed for under-water cutting. Alsoa solution which calls for high in-vestments and has inherent fea-tures that will reduce productiv-ity. To the knowledge of the au-thor, none of the solutions has sofar actually been put into opera-tion.

Ergonomics in generalThe development of controls forCNC cutting has brought about ageneral improvement in ergo-nomics. Just consider the follow-ing examples – marking equip-ment, automatic nesting, automat-ic cutting bridges, colour monitorfacilities, automatic height con-trol, flame control and monitor-ing by sensors and advanced pro-gramming facilities.

In the case of cutting installa-tions, ergonomic improvementsworth mentioning include auto-matic plate alignment, tables withtransport facilities for the out-loading of parts and double ta-bles, roller bed arrangements,special overhead cranes, specialarrangements for easy slag re-moval, all features that have hel-ped to reduce the heavy physicalwork and the man-hours used permetre cut.

Development targetsProductivity in the broadest senseof the word is the driving forcewhen it comes to selecting the de-velopment targets for the cuttingprocess as applied in cutting in-stallations. This focuses attentionon the operations that are neededafter cutting, as a result of a moreor less perfect cutting perfor-mance. In plain terms, the an-swers to quality issues such as ac-curacy, freedom from dross,squareness and bevel quality.

In the case of different cuttingprocesses, we find different com-binations of answers to thesequality issues.

At the present time, dross-freeand accurately-cut parts are basi-cally regarded as the major targetsto aim for, because the cost asso-ciated with dross removal by post-processing cut parts is consider-able, as is the lack of precision forwelding operations that, more of-ten than not, follows after cutting.

Another productivity issuewhich has a direct bearing on thenature of the cutting process isthe minimising of process down-time due to wear to torch tips,electrodes and nozzles. Systemsfor monitoring, surveillance andfast and precise exchange modesare in demand for all processes.

It is also relevant to mentionthe constant design attention thatmust be paid to the interactionbetween the aforementioned de-velopment of controls and thecorresponding electrical and me-chanical design of cutting ma-chines, as regards their dynamicresponse to rapid movementswith up to five degrees of free-dom. A very high degree of dy-namic response is an absoluteprerequisite for realising the po-tential advantages offered by anysophisticated cutting process.

Finally, modern IT develop-ments, utilised correctly with ad-vanced sensor technology, havemade great advances in diagnos-tic systems possible. This trendwill continue and lead to furtherimprovements relating to preven-tive upkeep to minimise down-time, to secure fast troubleshoot-ing and provide input for qualitysurveillance.

Water plasmaIn order to reduce the post-pro-cessing of cut parts and also toobtain higher cutting speeds atreduced energy consumption, the-re is a move towards cutting withoxygen, O2, instead of nitrogen,N2 (Fig. 5).

Investigations appear to indi-cate that the running costs, interms of the consumption of gas,energy and consumables, end upat the same cost level, whereasthe use of O2 improves the dross-free range of plate thickness andpermits a 40% increase in cuttingspeed in 12 mm steel plate. forexample. As the energy that isneeded is lower as a result of theexothermic reactions with O2 insteel, changing to O2 increasesthe possible plate thickness for agiven size of power source.

When it comes to the precisionand accuracy that can be ob-tained, it is likely that water-plas-ma cutting, no matter which gas isused, will lose its foothold tosome degree and laser cutting willbe preferred. In the case of newinstallations, it will be possible totake the special precautions thatare needed to operate a laser-cut-ting installation, while paying dueconsideration to its environmen-tal implications. This will be tou-ched upon at a later stage.

Laser and dry plasmaThe dry processes have the inher-ent advantage of being dry, whichmeans that they do not need awater table, a considerably moreexpensive arrangement than a

Fig. 5. Cutting speeds versus plate thickness for MS for water-plasma cutting withO2 and N2 respectively.

Cutting speeds N2 /O2

Cutting Speed N2

Cutting Speed O2Plate thickness (mm)

Sp

eed

(m/m

in)



comparable table arrangementfor a dry process. What is more,handling cutting with water tablestakes time and introduces otherdisadvantages like those touchedupon earlier.

However, the dry processesalso have inherent disadvantageswhen it comes to the environ-mental issues of noise and, partic-ularly in the case of laser, radia-tion. As has already been said,the use of laser cutting will in-crease as a result of reduceddross appearance, greater accura-cy and the higher productivitythat can be obtained with dry cut-ting tables.

The author believes that thiswill take place, although the actu-al cutting speed for laser versusplasma-water at the present time,for 20 mm MS, for example, is 1m/min compared with 3 m/min.

For shipyards in particular,when they invest in new cuttingfacilities, it will be attractive tochange to laser and it will alsothen be possible to handle the en-vironmental issues in the idealmanner. In short, this will resultin the complete removal of theoperator and other manual activ-ities from the installation site anda change to complete reliance onremote control, remote handlingand remote surveillance. For thesupplier and designer of thesecutting installations, there is stillsome way to go before all the fa-cilities for the programming andsurveillance of the relevant cut-ting parameters are available, butit is thought that this will be thetrend in development as far as la-ser is concerned. While this is be-ing implemented, we shall prob-ably see the development of thelaser technique towards copingwith thicker material while main-taining the level of precision. Thecurrent standard is 25–30 mm forMS. The double-focus techniqueis one way of achieving this.

Finally, it is worth noting thatlaser cutting lends itself to inter-esting precision jobs such as con-tour cutting, with or without bev-el, in one operation on two-dimensional or three-dimensionalworkpieces, also including thecutting of small holes, with orwithout chamfers. Figures 6 and 7

illustrate this development in la-ser cutting.

At present, fine-beam plasmacutting has potential for thin pla-te cutting which can be furtherexploited when the appropriatesolutions for reducing or avoidingthe inherent noise level are intro-duced.

Fine-beam plasma cutting isvery attractive investment-wise,as compared with laser cutting,for a number of applications whe-re the highest precision is notnecessary (compare with Fig. 2).At the same time, it is to be ex-pected that, within the foresee-able future, fine-beam plasma willincrease in capability from thepresent maximum 20 mm thick-ness up to a maximum of 50 mm,both figures referring to MS.

SummaryOver the years, environmental is-sues have become an increasinglyimportant point on the agendawhen it comes to the design ofcutting systems. The current tech-nology, its productivity merits anddeficiencies are briefly described,as they relate to present and up-

coming environmental issues inthe fields of dust, fume and gases,noise, radiation and ergonomicsin general. With that as the start-ing point, a discussion of the out-look for improvements–the waysand means of establishing im-proved environmental conditions,while paying due consideration toproductivity, as seen through theeyes of a manufacturer of cuttingsystems, featuring a horizonstretching into the next millenni-um–is presented.

Fig. 6. An S-axis laser-cutting head which is fully programmable.

Fig. 7. A modern laser-cutting installation for large plate formats with screeningfrom radiation.

About the author:

Klaus Decker, Dipl.-Ing. is Managing Director of ESABCUTTING SYSTEMS.



Esab Italy contribute tothe success of robotwelding at the Monfal-cone yard, as part of itsextensive service to theyard.

The Monfalcone yard is the loca-tion for FASP, the European Un-ion project for Fully AutomaticShip Production. The experiencethat is acquired here will enableEuropean shipyards to buildcompetitively in terms of cost andtime in relation to yards in theFar East.

Overall view of massiverobot welding installationThe state-owned Monfalconeyard specialises in large luxurycruise vessels. The fabricationprocedures are conventional; pla-te cutting and bending, panel line,plate assembly to panels, followedby the build-up of sections and fi-nal hull construction.

When it comes to FASP, Fin-cantieri is in the process of refin-ing each stage to achieve thehighest possible level of automa-tion.

Robot welding for shipsThis represents a step-up frommechanisation methods which in-volve GMAW processes fordownhand and vertical-up welds.

The traditional role of robotsfor welding industrial products,often aided by workpiece manip-ulation, has to be re-thought, be-cause shipbuilding robots have towork over considerable distancesacross and along panel lines. Whilethis is not easy, linear positioningon this scale is well within the capability of current technology.

The other essential factor forrobot welding is consistency inthe fit-up of plates, profiles andso forth on panels. In this context,

the skills of the Monfalcone yardhave been very useful.

The “robot-friendly”cored wireAs a major supplier of SAW con-sumables at Monfalcone, Esabwas well placed to give advice.The yard naturally had an openchoice of cored wires from suppli-ers worldwide. Optimum resultsrequired:

Rutile type to conform withestablished shipbuilding weld-ing practiceUse of CO2 gas for economyGood feedability to minimisestoppagesPositional capability to handlefillet welds in PB/2F andPF/3F≠ positions with fullpenetrationWide parameter box to avoidcritical setting of welding cur-rent, voltage and wire speedHighest possible productivity

To satisfy these requirements, itwas agreed to base the new wireon the FILARC PZ6113 type ofrutile flux-cored wire, as thiswould meet all the above require-ments. This was proven with ro-bots, and for shipbuilding, in both1.2 and 1.6 mm sizes.

With application support fromEsab cored wire development,Esab Italy presented the new OKTubrod 15.13 to the yard for eval-uation. This joint helped to rein-force the well-established posi-

tion of Esab Italy as a weldingsupplier to the Monfalcone yard.

Tests and subsequent produc-tion proved that OK Tubrod15.13 met all the requirements.

It is truly robot-friendly!The yard is currently obtaining

experience from the supply ofcored wires from a 200–235 kgMarathon Pac, thus avoidingdowntime for changing spools.Wire feeding at distances of up to20 m is compatible with the longcolumns on which shipbuildingrobots are mounted.

The future success of FASP,and indeed all robot welding forshipyards, ultimately depends onthe performance of cored wireswhen it comes to optimising pro-ductivity.

In this context, Esab’s market-ing organisations, will definitelybe adding many new advantages.

New ESAB OK Tubrod 15.13 for robot welding at Fincantieri

Report by Ferruccio Mariani, ESAB Italy

About the authorFerruccio Mariani joined ESABin 1991 as product manager forFCWs and SAW products.He had previously worked for 17years at Ansaldo ABB in Milan inItaly, firstly as a welding supervi-sor at the Nuclear Welding Dept.and later as a welding engineerwith responsibility for procedurequalifications and welder trainingactivities. His current position atESAB SALDATURA in Italy isconsumables marketing manager.



ESAB has sold two sets of Fric-tion Stir Welding (FSW) equip-ment to Sapa in Sweden. Sapa isa leading aluminium extruder andfabricator of aluminium products.With this investment, Sapa willalso be able to include the pro-duction and welding of large pro-files and panels in its business.

The first ESAB SuperStir™system Sapa purchased fromESAB is equipped with doublewelding heads. The machine willbe used to manufacture parts forthe automobile industry. This is abreakthrough for FSW in the au-tomotive industry. The secondESAB SuperStir™ machine willbe used for the production of lar-ge panels and heavy profiles witha welding length of up to 14.5metres. This machine has threewelding heads, which means thatit is possible to weld from twosides of the panel at the sametime, or to use two weldingheads, positioned on the sameside of the panel, starting at the

centre of the workpiece andwelding in opposite directionsfrom one another. Using thismethod, the productivity of theFSW installation is substantiallyincreased.

Sapa is a member of theGränges Group, which employs4,500 people in 12 countries andis one of the world’s largest pro-ducers of extruded aluminiumprofiles. Sapa, Skandinaviska Alu-minium Profiler AB, is the Swed-ish subsidiary company with 1,400employees and a turnover of SEK2.1 billion. In Sweden, Sapa hasthe leading position with a mar-ket share of more than 50%.

ESAB was the only weldingequipment manufacturer to joinThe Welding Institute (TWI) asan original R&D contributor todevelop the Friction Stir Weldingprocess in 1992. ESAB decided tomarket the process under thename of ESAB SuperStir™ andsupplied its first commercial FSWmachine to Marine Aluminium of

Norway in the autumn of 1996.To date, upwards of 120,000 me-tres of weld have been performedwithout defects. Since then,ESAB has also delivered fourFSW systems to The BoeingCompany in the United States,which uses the equipment to pro-duce components for the Deltafamily of rockets, used for launch-ing communications satellites.

The Friction Stir Welding methodThe friction generated by a rotat-ing tool, in combination with highpressure, plasticises (softens) thesurrounding material and the tooltransports material using a closedkeyhole technique. Welds can bemade in any position using single-pass or double-sided techniques.The process requires no specialsurface preparation before weld-ing, such as machining or etching.As no melting occurs, no fillermaterial or shielding gas is used,the joints are free from distortionand porosity, have no lack of fu-sion and do not change their ma-terial composition. Another ad-vantage of FSW is that it is nowpossible to weld aluminium alloyswhich could previously not bewelded, with excellent results.Moreover, this is a very environ-mentally-sound method, as thereis no spatter, no toxic fumes andno noise during welding.

The method is ideal for theproduction of ships, offshore plat-forms, railway carriages andbridges and for applications with-in the automotive and process in-dustries.

Complete production programmeESAB, the world’s leading com-pany in welding and cutting, isnow also the world leader when itcomes to the production of equip-ment for Friction Stir Welding.ESAB can offer a number of dif-ferent SuperStir™ systems forworkpieces ranging from verysmall up to 10x30 metres for ap-plications of all kinds.

Additional information isavailable from:ESAB Welding Equipment ABAttn: Lars-Göran ErikssonPhone: +46 584 81160Fax: +46 584 411721Email: [email protected]

Two ESAB SuperStir™ machines go to Sapa

Stub-ends&Spatter



Esab Welding Equipment in Swe-den is delivering pipe-weldingequipment to a pipe mill in Indo-nesia. The pipe mill will producelongitudinal welded pipes within24-42“ (610-1,067 mm) in lengthsof between 20-40’ (6-12.3 m).

After pressing the plate to pro-duce a pipe, the pipe is fedthrough a fixture for continuousCO2 tack welding externally. Thepipe is then placed on a carriage,turned 180° , and internal weldingtakes place when the pipe entersa 13-metre long boom with athree-electrode, submerged arcwelding head.

External three-electrode weld-ing follows, with a fixed weldinghead and the pipe moving on acarriage. The internal weldingequipment includes a specially-built, compact three-wire SAWhead, a wire feeder, AC powersources, a wire drum table, a TVmonitoring system and a controlpanel.

The welding process is one-pool welding with AC on all elec-trodes. The wire-feed motors are

placed in the rear end of theboom and the wire is pushedthrough wire conduits to thewelding head. Joint tracking issupervised by the operators fromthe TV monitoring system by ad-justing the pipe in relation to thewelding head.

The external welding equip-ment includes a floor-mountedcolumn and boom, a motorisedslide cross, a three-wire weldinghead, a laser joint-tracking sys-tem, AC power sources, a fluxhandling system and a controlpanel.

The three-electrode systemfeatures special narrow weldingnozzles for one-pool welding.Each electrode can be adjustedon three axes using slides andscales for accurate set-up at dif-ferent plate thicknesses. Automat-ic joint tracking is achieved by alaser camera and servo slides ontwo axes.

The control system for thewelding is an integrated part ofthe centralised product trackingcontrol system, in which eachpipe is individually trackedthroughout the manufacturingprocess.

In principle, the welding con-trol panels at each welding sta-tion are based on a PLC, wherethe operator can supervise theprocess.

Welding parameters are pro-grammed centrally and fed toeach PLC via the computer net-work. The operator’s task will beto key in individual pipe numbersand supervise the process.

After welding is completed, allthe parameters, together with anydeviations and the individual pipenumber, will be fed back to thecentral computer system.

When Esab designed this newpipe-welding equipment, the aimwas to create a flexible modular-ised system, which could be incor-porated in existing booms, car-riers and pipe carriages at differ-ent customer facilities.

Ray Hoglund, chief executive ofESAB Group worldwide, an-nounces the opening of the com-pany’s headquarters in Duluth,Ga., a suburb of Atlanta.

“We chose the Atlanta area be-cause of its quality of life, world-class airport, international recog-nition and reputation as one ofthe top 10 cities in which to es-tablish a global headquarters,“said Hoglund.

Joining Hoglund at ESABGroup is Frank Engel, who willserve as the company’s chief fi-nancial officer. Engel was previ-ously chief financial officer forESAB Welding & Cutting Prod-ucts. Hoglund has also promotedtwo other ESAB employees topositions at the company’s head-quarters. Anders Backman hasbeen appointed group vice-presi-dent for welding consumablesand Mart Tiismann has been ap-pointed group vice-president forwelding equipment. Both previ-ously worked for ESAB Europe.

ESAB Group manages thecompany’s operations in NorthAmerica, South America, Europeand Asia. The company’s goal isto improve its global leadershipposition by developing an inter-national approach, which is basedon the strength of its national andregional teams.

The company’s new address is:ESAB Group, 2180 SatelliteBoulevard, Suite 375, Duluth, GA,30097. The phone number is (678) 475 5100 and the fax num-ber is (678) 475 5101.

New multi-wire SAW equipment for the longitudinal

welding of pipes

ESAB Group establishesworldwide

headquartersin Atlanta



Esab Welding & Cutting Productshas acquired AlcoTec Wire Com-pany, located in Traverse City,Michigan, USA. AlcoTec was pur-chased from Aluminium Compa-ny of America (ALCOA) and Al-uminium Technology Corpora-tion. It is the only fully-integratedaluminium wire producer in theUSA.

“AlcoTec is the technologicalleader and the world’s largestproducer of aluminium weldingwire,” says Ray Hoglund , chiefexecutive of Esab worldwide.“Not only is AlcoTec the fore-most expert in the production ofaluminium welding wire, it alsoconsistently brings innovations tothe applications engineering sideof the business. The acquisition ofthe company will enable Esab tostrengthen its commitment to theresearch and development of alu-minium filler metals, buildingupon our history of product inno-vation.”

Aluminum fabrication is in-creasing in a variety of industries,including aerospace, automotive,bridges, military, railways, recrea-tion, shipbuilding, trucking andutilities. Design engineers andfabricators like the unique char-acteristics of high strength andlow weight aluminium has to of-fer.

AlcoTec currently employs 130people. Brothers Bruce and SteveAnderson, who are partners inAluminum Technology Corpora-tion, will continue to manage theday-to-day operations at AlcoTec.

“This is an important acquisi-tion for Esab,” said Nigel Smith,chief executive of Charter, theparent company of The EsabGroup. “The complementary na-ture of AlcoTec’s leading positionin aluminium wire will furtherstrengthen Esab’s position as theglobal market leader in welding.”

Robotic welding is characterisedby high duty cycles, often withhigh welding currents, and by fre-quent stop/starts. In addition, ahigh and especially consistentweld quality is required. This plac-es demands on the welding con-sumable that can not fully be metby standard wire products likesolid and cored wires developedfor semi-automatic MIG welding.

FILARC PZ6105R is a metal-cored wire optimised for roboticwelding by means of feedability,dependable starting and a wellbalanced welding performance. Itis suited for single- and multi-lay-er fillet and butt welds in the PAand PB position.

Improved feedabilityA optimised wire finish and opti-mal coiling ensures constant deliv-ery in long liners, while avoidingfeeding problems due to contami-nation of liners and contact tips. Itis available in FILARC Mara-

ClassificationsAWS A5.18-93: E70C-6M H4~EN 758-97: T 42 4 M M 3 H5

Shielding gasAr/15–25%CO2EN 439: M21

Weld metal composition [%]C: 0.03–0.07 P :≤0.025Si: 0.60–0.90 S: ≤0.025Mn: 1.40–1.80

Deposition data in: Ar/CO2I Vwire Dep. rate[A] [m/min] [kg/h]150 3.5 2.1250 7.0 4.2350 12.1 7.2450 18.5 11.2Diameter: 1.4 mmStickout: 20 mm

All weld metal mechanical propertiesTensile strength, Rm [MPa]: 510-600Yield strength, Re [MPa]: ≥420Elongation, A5 [%]: ≥22Impact value,Av (ISO-V) –40°C [J]: ≥47

Esab acquiresAlcoTec

Currentand

polarity

DC +

Approvals(Pending)

TÜVDB

DNVABSGLLRBV

EN 758Hydrogen

class

H5

Positions

thonPac bulk packaging to avoiddowntime from coil changing.

Dependable starting and a stable arcThe special formulation providesa reliable calm arc ignition withminimal spatter, and reduced riskof wire burn-back. Improved cur-rent transfer assures a stable arcand a very low spatter level alongthe weld.

ProductivityPZ6105R comes in B 1.4mm, themost versatile size for most robotwelding equipment. Above a levelof 250A, it provides excellentweldability and optimal produc-tivity, up to very high currents. Awide range of fillet sizes can becovered.

Smooth weld appearanceFlat fillet welds with good tie-inand penetration favour the ap-pearance and fatigue performanceof robot welded workpieces.

FILARC PZ6105RThe robot-friendly cored wire


The Oscar Kjellberg Award

Professors Göran Alpsten andJan-Olof Sperle have been award-ed the 1999 Oscar Kjellberg GoldMedal for their many years ofwork in the field of fatigue andthe anti-fatigue design of steelstructures. The medals were pre-sented by Bertil Pekkari, Presi-dent of the Swedish WeldingCommission at its spring meeting.

Göran Alpsten, M. Eng, and Dr.Techn , was involved in the pro-duction of Construction WeldingStandards and was chairman of aworking group for the anti-fatiguedesign of welded joints. He hasbeen active in a number of majorprojects that utilise advancedwelded constructions, includingGloben athletics arena in Stock-holm and the Öresund Fixed Linkbetween Sweden and Denmark.

Jan-Olof Sperle, M. Eng, hasalso been working on the prob-lems of fatigue. In his doctoralthesis, entitiled “High strengthsteel for light weight structures”,fatigue-related issues play an im-portant part. Dr, Sperle has beenthe Swedish representative on theIIW Fatigue Committee since1975.

The Kjellberg Gold Medal is theSwedish Welding Commission’smost prestigious award. It was established in the memory of Oscar Kjellberg, inventor of thecoated welding electrode andfounder of ESAB. According tothe rules, the Kjellberg Awardmay be given to individuals whohave made major contributions tothe benefit of welding and relateddisciplins. It was presented for thefirst time in 1941 and has beenpresented on four occasions, in1944, 1992, 1994 and 1995.

One of Esab Norway’s largestand oldest customers has de-signed and manufactured a trulyunique steel/glass structure whichis going to protect the ruins of acathedral from the 13th centuryin Hamar in Norway. The struc-ture is a tubular framework com-prising some 4,500 pieces of pip-ing which have been welded to-gether with complicated joints. Inall, around 1,000 different geome-tries have been calculated for the-se pipe ends. In addition, some3,000 attachment points for glasshave been welded, about 1,700 ofwhich were different.

Are we entitled to ”manipulate”the workings of history and nature?The structure has created someheated discussions and headlinesin Norway. Should ruins really beenclosed? Are they not part ofthe landscape and, as such, shouldthey not be allowed to stay asthey are and perhaps crumble inpeace? Opinions differed on the-se points, but the Norwegian Cen-tral Board of National Antiqui-ties decided that the ruins shouldbe enclosed. Because, since themid-19th century, it has restoredthe ruin extensively, but it stillfeared that the brickwork wouldsoon collapse as a result of ero-sion. This takes place primarily asa result of frost erosion and con-stant fluctuations around 0°Cshould therefore be avoided. En-closing the ruin makes it possible

to control the temperature andkeep it above freezing point allyear round.

Since the construction workwas completed, the negative criti-cism has stopped, however. “In-credible but true. A real success!The first impression of the glassbuilding was fantastic.” “Buildingsomething new is the only way tospotlight the historical. Inside, theruin appears as something mag-nificent and unexpected.” “Thecontrast between the new and theold has enabled something of a‘resurrection’ to take place.” The-se are just some of the manycomments that have been heardsince the work was completed.

Esab’s contribution will be partof the futureAB Esab in Larvik in Norwaysupplied all the consumables forthe construction and the custom-er naturally also uses a fair num-ber of ESAB machines in his pro-duction process. The constructionin itself is unique, as all the steelstructures fitted together perfect-ly during assembly, thereby dem-onstrating that all the previousproduction processes had beenperformed correctly. As a result,the customer is extremely satis-fied with his own and his suppli-ers’ performance in this complexproject. It is pleasing for Esab tobe able to contribute to such adeserving cause, an attempt topreserve this unique building forposterity.


Esab Norway helping to save history



The utilisation of laserwelding in manufactur-ing industries has in-creased rapidly duringthe last few decades andcan be regarded as amore or less maturetechnique. During weld-ing, the very high powerdensity in the focal pointevaporates the materialand causes a narrow,deep entry hole whichmoves through theworkpiece as the beamis moved. This is knownas ”key-hole” deep pen-etration welding [Fig. 1].During welding, an inertgas (normally helium ornitrogen) flows througha nozzle to the work-piece surface in order toprevent oxidation.

The most common laser for highpower welding is the carbon diox-ide laser (CO2 laser). This laseremits light with a wavelength of10.6 µm. The laser gas mixtureused in CO2 lasers consists main-ly of helium, to ensure the remov-al of generated heat, carbon diox-ide, the laser-active medium, andnitrogen, in which a gas dischargecreates the energy necessary forexcitation. The CO2 laser is espe-cially cost-effective when used forthe high-speed welding of com-paratively thin-walled structureslike car bodies. The disadvantage

of this type of laser is that it re-quires a sophisticated system todistribute the laser beam to theworkpiece. This also means thatthe work stations are not as flex-ible as they might be. The qualityof the beam is also reduced if it isnecessary to transfer the laserbeam via many mirrors.

The other dominant lasersource is the Nd:YAG laser. Thistype of laser has a wavelengththat is ten times shorter(1064nm) than that of the CO2laser. The laser-active medium,neodymium (Nd3+-ions), is lo-cated in a solid crystal made upof yttrium-aluminium-garnet andis usually rod-shaped. The opticalexcitation in pulsed lasers (p-lasers) generally occurs bymeans of krypton flash-lamps,whereas krypton arc lamps areused in continuous-wave highpower lasers (cw-lasers). Theprincipal advantage comparedwith CO2 lasers is that the light

from the Nd:YAG can be trans-mitted to the workpiece by opti-cal fibres and can therefore bemore easily integrated into a lar-ge variety of systems.

However, the development ofmore flexible and efficient lasersis continuing and in recent yearswe have seen new products, suchas diode-pumped Nd:YAG lasersor direct-acting diode lasers, start-ing to be used in commercial pro-duction.

This article will present a num-ber of laser welding applications.Naturally, from the author’s pointof view, several examples havebeen taken from the automotiveindustry, but, to highlight the vari-ous opportunities presented bylaser processing, some exampleswill also deal with micro technol-ogy welding, as well as the weld-ing of plastic components. At theend, some examples of new pro-cess development are also re-viewed.

Laser weldingA mature process technology with

various application fieldsby Johnny K Larsson, MSc, Volvo Car Corporation, Sweden

Figure 1.The principle of “key-hole” deep penetration welding.

High intensity beam(power P)

Molten pool

Key-hole

Depth of weldpenetration (d)

Speed oftravel (V)

Melted zonewith (w)



Automotive applicationsSome of the keywords in automo-tive manufacturing today arequality, flexibility, high productiv-ity and cost effectiveness. Laserwelding appears to meet all theserequirements and the proof canbe found in the impressive num-ber of lasers already in operationtoday at automotive companies.

Roof laser welding can bemore or less regarded as state ofthe art among automotive manu-facturers and some European carmanufacturers will now be men-tioned, simply to illustrate howwell-established the laser weldingprocess is.

VolvoVolvo started roof laser weldingin series production in connectionwith the introduction of the 850model in early 1991. The reasonfor choosing laser welding for theroof of the 850 was the strengthrequirements for the upper roofrail, a crucial part of the Volvosystem known as SIPS (Side Im-pact Protection System). As a re-sult, the roof rail had to be de-signed as a closed section [Fig. 2].

This restricted the opportunityto join the roof to the rest of thebody to either adhesive bondingor laser welding. Both conceptswere evaluated in early proto-

types and the test results indicat-ed that the laser would be superi-or. When it came to both productrequirement fulfilment and thereliability and environmental as-pects in production terms, the la-ser welding technique emerged asthe winner.

The installation at the Ghentplant consists of a 6 kW CO2 la-ser, a five-axis gantry robot and abeam delivery system includingfive mirrors, the last of which is ofthe parabolic, focusing type.Three different, easily exchange-able laser welding heads with ad-jacent focusing alternatives areincluded. The welding speed isaround 5.5 m/min, a prerequisitionin order to correspond to the sta-tion cycle time.

The fixation of the sheets inthis overlap joint (0.8mm uncoat-ed to 0.8mm 8µm electro-galvani-zed steel) was associated withmajor difficulties, as one of thesheets was part of a closed beamsection with no access for a sta-tionary backing fixture. The prob-lem was finally solved with theaid of a Pressure Roller Device(PRD). This consists of a copperwheel mounted on the laser headand featuring adaptive z-compen-sation through the telescopic ac-tion of the laser head. The wheelsqueezes the sheets together witha point force of about 250N andguarantees at the same time thatthe focal point is located in theoptimum position vis-à-vis theworkpiece. The welding is thencarried out using helium, at 30l/min, as the shielding gas.

As laser welding cells for carbody manufacture represent aconsiderable investment cost, Vol-vo had to investigate cost reduc-tion potential when the decisionwas made to start production ofthe 850 model at the SwedishTorslanda Plant as well in thesummer of 1994. The main objec-tive for the new laser welding sta-tion was to ensure cost optimiza-tion without undermining the ex-perience acquired from the earli-er Ghent installation. This has re-sulted in a far more simple andflexible robot system using two125 kg standard robots and twoZeiss telescopic tubes for thebeam guidance system, instead ofthe very dedicated gantry robot

Figure 2. Typical joint geometry for roof laser welding. Roof welding being perfor-med on the Volvo S70 model at the production plant in Ghent in Belgium.

Figure 3. Flexible laser welding cell at the Volvo Torslanda Plant in Gothenburg.

Laser weld



[Fig. 3]. The capital investmentfor this system is approximately25% lower than that of a conven-tional gantry robot, but it hasproduced satisfactory results interms of weld quality and up-time.

When the new Volvo S80 wasintroduced in the spring of 1998,the Torslanda cell had to be equ-ipped with a second laser sourceof 6 kW in order to meet capacityrequirements, as both this modeland the S70 (formerly the 850)were manufactured in mixed pro-duction on the same assemblyline. This means that both sidesare now being welded simultane-ously, whereas the previous pro-cess solution welded one side at atime. The length of the seam weldon each side of the car body isapproximately 1.4 metres for sa-loon models and 2.3 metres forestates. The two welding cells inGhent and Torslanda have so farproduced more than 1,000,000 carbodies. This represents a record

of 4,000,000 metres of continuouslaser beam welded joints.

BMWWhen it launched its latest 5 Se-ries model, BMW presented laserwelding as extensive as 11 metreson each car body and 12,000 me-tres of laser welding is performedevery day at the Dingolfing Plant.

Two 5 kW CO2 lasers, eachconnected to an industrial robot,perform roof to uni-side weldingutilizing Zeiss telescopic tubesand a roller device with a pres-sure force of 700N to minimizethe gap between the parts thatare being welded. The welding isdone intermittently (10 weldstitches/side) at a speed of 5m/min. This welding operation ex-tends from the roof to the rearcross-member joint [Fig. 4]. Forquality assurance purposes, the“Jurca” system has been intro-duced. This system monitors plas-ma radiation and plasma temper-ature.

At a sub-assembly station, twomore 5 kW CO2 lasers weld thedashboard panel. In the first op-eration, the lower cowl is weldedcontinuously to the firewall. Aclosure panel (upper cowl) isloaded on top to create the closedcowl section. This is welded con-tinuously utilizing both laserswith adherent robots to make twoweld lines in parallel to avoid dis-tortion. This sub-assembly repre-sents about 4.5 m of continuouswelding and contributes greatlyto the improved torsional stiff-ness of this car body model.

For the assembly of the trunklid, BMW utilizes the so-called“beam-trap” technique. If the la-ser beam has an S-polarized sha-pe, it is possible to focus it on thejoint by reflection. This techniquealso offers the advantage that theparts to be welded are less sensi-tive to positioning accuracy. Theouter trunk lid consists of twoparts, an upper and a lower one,which are welded together using

Figure 4. Extensive car body laser welding of the BMW 5 Series model.

Laser: 2 Trumpf TLF 5000 TurboRobot: 2 KUKA IRB761 with

Zeiss tubes for beam guidance

Material: Roof: ZStE 220BH, t=0.75mm ~V-1343Uniside: St14 ZE75/0, t=0.85mm ~V-1157Cross-member: ZstE 260BH,t=0.65mm ~V-1341

Weld speed: 5 m/min, 10 welds per side

Laser: Trumpf 2kWRobot: Gantry typeMaterial: St14 ZE75/0, t=0.75 ~V-1157

Laser: 2 Trumpf TLF 5000 TurboRobot: 2 KUKA IRB761 with Zeiss

tubes for beam guidanceMaterial: Firewall: St14 ZE75/75 ~V-1157

Cowl lower: ZstE 300BHCowl upper: ZstE 300BH ZE75/0



this technique. The welding isperformed by a 2 kW CO2 laseroperating in a gantry robot sys-tem. For the firewall and trunk-lid applications, a seam trackingsystem must be utilized.

FordAt Ford’s Cologne Plant, the roofof the Scorpio estate model iswelded to the sides of the bodyusing an Nd:YAG laser. The 2 kWlaser produces the beam througha fibre-optic delivery system tothe welding nozzle, which is fittedon an industrial robot. The weld-ing nozzle has a guide roller fittedto it, which runs parallel to thewelding optics. This guide rollersqueezes the panels together inthe region of the focal point ofthe laser beam with a pro-grammed clamping force, whilekeeping the focal point positionconstant. By employing this lasertechnology, Ford claims that theroof channels can be made small-er in the roof seam area, whichwould not have been possible us-ing resistance spot welding. In ad-dition, the stiffness and seal tight-ness are enhanced through thecontinuous joint, while noise gen-eration and sealant operationsare reduced.

AudiAt present, both Audi and VWuse Nd:YAG for roof laser weld-ing. Audi does this on the A3 andA4 Series models manufacturedin Ingolstadt, whereas the compa-ny is still using the CO2 tech-nique for the equivalent weldingwork on the A6 models producedin Neckarsulm. At the Audi In-golstadt Plant, 1,800 cars are pro-duced every day. A4 and A3 mod-els are produced on three parallelbody assembly lines.

The first line began operatingin 1994. The A4 limousine modelis assembled here, utilizing a 2kW Nd:YAG laser for welding,with a second for back-up. Theapplication is the vertical weldingof the C-pillar (150 mm) andtransversal welding in the “Q-glass” opening. Both applicationsare performed as overlap welds inelectro-galvanized coated sheetswith a welding speed of 2 m/min.

On line two, the A4 limousine

and A4 Avant (estate model) areproduced in mixed production.For the Avant model, the applica-tion is roof to uni-side welding; 60weld stitches are made on eachside, representing a total weldlength of 1.6 metres. The reasonfor choosing stitch welding is toavoid distortion in the car body.A specific welding sequence isused for the same reason. As theamount of welding is higher inthis cell compared with the previ-ous one, two 2 kW Nd:YAG la-sers operate in parallel to weldthe roofs of the Avant modelsand the C-pillars and Q-glassopenings of the limousines. Athird laser is used as back-up inthe event of equipment break-down. In this cell, power monitor-ing is used as a quality controlmeasurement; the effective pow-er at the workpiece is not allowedto drop below 1450W. The cycletime on both lines is 83 seconds.

The third and most recent linewas inaugurated in 1996 in con-junction with the launch of thenew Audi A3 Coupé. Also in thiscell, two 2 kW lasers work in par-allel with a third laser as back-up.The application here is also roofwelding, but with a slight differ-ence compared with the A4Avant. In the area between theA- and B-pillars, stitch welding isutilized with 19 stitches with alength of 15–20 mm on each side.For the rear part of the roof, con-tinuous welding is performed. Thetotal weld length is 1,075 mm oneach side and the material thick-ness is 0.9 mm for the uni-sideand 0.8 mm for the roof. Bothcomponents are electro zinc-coa-ted. The welding speed is 1.6m/min, which means that the cy-cle time is a little longer com-pared with the other two lines —88 seconds. For quality assurance,the monitoring system developedby LaserZentrum Hannover isused. It supervises the power,weld length and the gap betweensheets.

In all the cells, “CORGON18”is used as the shielding gas, 20l/min. This is a gas mixture of18% CO2 and 82% Ar. As bothparts to be welded are zinc-coa-ted, it has been necessary to de-velop and use a cross-jet to pro-tect the nozzle from any back

spatter of evaporating zinc. Avail-ability in the Audi Ingolstadt la-ser cells is said to be close to99%.

VolkswagenVolkswagen introduced Nd:YAGlaser welding in connection withthe launch of the new Passatmodel. Production at the Emdenand Mosel plants utilizes 2 kWsystems. As both the roof paneland the uni-side are made of zinc-coated steel, VW has chosen notto make a conventional overlapweld in order to avoid zinc spat-ter and unstable welding condi-tions. Instead, the weld is posi-tioned at the edge of the roofpanel, which means that, apartfrom avoiding the above-mentio-ned welding problems, the weldspeed can be considerably in-creased. This means that thewelding which is performed with-out using shielding gas (the sameas in the case of the Ford Scor-pio) can be done at a speed of5–6 m/min, whereas the corre-sponding figure for normal over-lap welding would be approxi-mately 3 m/min. To be able toperform this edge welding, aseam-tracking system (Scout-sen-sor) had to be introduced. Thecontributions from laser weldingare said to be improvements instrength, quality and precision.Moreover, the increased stylingand design freedom is also men-tioned.

One of the main reasons whyVW chose to invest in theNd:YAG technology was a desirealso to be able to weld inside thecar body. This is now being uti-lized as some variants of the Pas-sat models are equipped with arear seat back panel to improvethe torsional stiffness of the car.Due to the flexibility offered bythe robot-mounted welding noz-zle with integrated fibre optics, itis possible to intermittently per-form this fairly complex weldingprocedure and still maintain ac-ceptable weld quality.

RenaultAt the Sandouville plant, Renaulthas now started to investigate thethree-dimensional laser weldingof complete car bodies. This in-



Accurate positioning using expensive external fixation devices

Step Time Accuracyper step after each step

1. Accurate positioning using expensive tools 10 s ±1µm2. Laser welding 0.1 s ±1µm3. Removal of the tools 0.5 s ±3µm (final)

Total 10.6 s ±3µm (final)

Laser adjustment method

Step Time Accuracyper step after each step

1. Rough positioning using simple tools 1 s ±3µm2. Laser welding 0.1 s ±5µm3. Removal of the tools 0.5 ±6µm4. Laser manipulation 0.5–1.0 s ±0.3µm (final)

(closed loop with computer vision)Total 2.1–2.6 s ±0.3µm (final)

volves the four- and five-doorversions of the Laguna model.The application is stitch weldingin the windscreen opening. Nine60 mm long welds connect theroof and the windscreen cross-member. Furthermore, threewelds on each side, ranging bet-ween 50-100 mm in length, attachthe uni-side to the inner part ofthe A-post. Welding is facilitatedas all the parts are uncoated apartfrom the body uni-side. The inter-mittent method of welding in theA-pillar area is used to avoidwelding three sheet layers. TwoNd:YAG lasers offering 3 kW atthe workpiece are used, togetherwith 600 µm fibres for beam de-livery. The welding nozzles are at-tached to two robots and equip-ped with a roller fixture, which,with the support of a pneumaticcylinder, produces a point pres-sure of 250N in order to minimizethe gap between the sheets. Thefocal length is 200 mm and“CARBON45”, the standardshielding gas for arc welding pro-cedures at the plant, is used forlaser welding as well. The cycletime is 45 seconds, which requiresa welding speed of 4–5 m/min. Byintroducing a cross-jet function,the service life of the protectiveglass for the focusing lens hasbeen increased from 100 to 1,000hours.

Micro technologyLaser micro-processing has

grown to become a mature tech-nology for many parts in the elec-tronics industry. It has not onlyreplaced conventional technolo-gies but, as a result of the rede-sign of product parts dedicated tothe new technology, it has alsoenabled improved product qual-ity and new products. The lowcost of ownership, the reliabilityof the equipment, the high yieldof the process, combined with thehigh accuracy and flexibility, havemade the laser a very valuabletool.

Laser spot welding is an ac-cepted technology in the elec-tronics industry. Every manufac-turer of TV and computer moni-tor tubes uses this technology forthe assembly of the electron gun.Typically, 150 tiny laser welds, ap-plying pulsed Nd:YAG lasers andfibre beam delivery systems, areused to sub-assemble the cath-odes, the electron optic grids andlenses and, finally, to assemblethe gun. It would be true to saythat the quality of modern TVpicture tubes could not be real-ized without laser spot welding.The weld reject figure has im-proved from 0.1% for resistancewelding to only 0.002% for laserwelding. Rigorous demands areimposed on the accuracy of theindividual sub-assemblies. An ac-curacy in the order of 3-5 µm forthe critical dimensions can be ob-tained in mass production utiliz-ing laser spot welding.

Together with a continuingtrend towards miniaturisation,new products that require micronand sub-micron accuracy in massproduction are being designed.Because laser welding involvesthe introduction of heat into theproduct, if only to a very limitedextent, thermo-mechanical defor-mation and displacement have tobe considered at the design pha-se, so that they can be utilized inlaser adjustment operations. Sev-eral thermo-mechanical mecha-nisms are known to produce bothbending and shortening in a part.In this way, it would be possibleto manipulate several degrees offreedom in a product that ismounted on the structure. Usingthis new technology of laser ma-

Figure 5: Some micro-technologyapplications utilizing pulsed Nd:YAGlaser welding.a) Micro-wire connection, with a wirediameter of 40 µmb) Soldering frame with a copper-to-copper joint produced with a laserweld width of 0.1 mmc) Holder of a vibration quartz with aweld width of 0.05 mm

Table 1.The influence of laser adjustment on accuracy and processing time.



nipulation for the adjustment ofparts, elaborate positioning pro-cedures using expensive, compli-cated tools can be replaced bysimple tools and the final accura-cy will be produced by laser ad-justment [Table 1].

It is clear that laser processingin the electronics industry has be-come a mature technology and alarge number of parts can only bemanufactured using this technol-ogy [Fig. 5]. Using solid state la-sers with high beam quality, it ispossible to create weld sizes inthe 100 µm range. By adaptingthe beam geometry and pulseshape for each individual weldingapplication, it is possible to mini-mize the distortion as well as thecontamination of the welded part.

Welding plasticsThe application of lasers hascreated new opportunities in thewelding of thermoplastic compo-nents, which until now has pri-marily been performed usingultrasonic or vibration welding.For this area of application,Nd:YAG and diode lasers, offer-ing radiation near a wavelengthof 1 µm, are suitable for use be-cause of the absorption character-istics of plastic materials. Theseabsorption characteristics in thematerials to be welded are veryimportant when using laser. Theabsorption and thereby the pene-tration depth of the radiation is afunction of the laser beam andmaterial composition. Plastic ma-terials absorb the CO2 radiationin the surface layer and cause thevaporisation of the material. TheNd:YAG and diode radiationpenetrates into the polymer sam-ple and produces a melting vol-ume which is necessary for thewelding process. The absorptionproperties can be influenced bythe content of pigment in theplastic material. So black partscan be welded together, becausebeing black to the eye differsfrom being black or absorptivefor the laser.

Virtually all thermoplastic ma-terials can be laser welded. Thejoining of two different materialsis possible if the material combi-nation is weldable, i.e. the tem-perature ranges in which the ma-

terials are liquid must overlap.Fluorinated and temperature-resistant materials can be weldedwith lasers, as well as PMMA andABS, or plastic to metal. In acombination of increasing inter-est to the automotive industry,TPEs can easily be joined withthermoplastics using laser radia-tion [Fig. 6].

A keyless entry product has ablack keypad overlap-weldedonto the black case [Fig. 7]. Thekeypad is coloured with a pig-ment transparent to laser radia-tion, while carbon is used as theabsorptive pigment for the case.Welding these keyless entry casesis the first example in which thelaser is being used in an industrialapplication. Laser welding waschosen because the keypad is thefinal part of the assembly and iswelded after all the electronic cir-cuits are mounted. Other weldingprocesses would have led to in-creased scrap rates. Ten diode la-sers with an output power of 30W each are used to perform thewelding process and the weldingspeed is in the range of 5 m/min.

Using the laser also permits ex-cellent quality control of the weldseam during production. Modernelectronics and sensor technologyprovide the means for on-linemonitoring and process control of

Figure 8: Principal layout of a diode laser bar for an HPDL.

Figure 6: Diode laser welded speci-mens of TPE/thermoplastics.

Figure 7: Laser welded polymer keycasing with integrated electronic com-ponents.



the melt zone temperature duringthe welding process. The exacttemperature needed for the mate-rial can be maintained by control-ling the laser power with the tem-perature signal obtained from themeasurement. The temperaturecontrol unit can be integratedinto the optical head and guaran-tees reproducible and constantquality in the weld seam, inde-pendent of material inhomogene-ity resulting from previous pro-cessing steps.

Future developmentsHigh Power Diode Lasers(HPDL)High power diode lasers usuallyhave wavelengths of between 790and 980 nm. Compared with CO2and solid state lasers, HPDLscannot be focused down to acomparable spot size, due to thehigher beam divergence and lackof coherence between the individ-ual diode emitters. The diver-gence parallel to the diode arrays(called the slow axis) is about 10°(full angle), whereas the diver-gence perpendicular or vertical tothe diode arrays (called the fastaxis) is up to 50° (full angle). Dueto this divergence astigmatism,special optics are used to com-pensate and, owing to the poorbeam quality, short focal lengthfocusing optics are used to obtaina reasonable focused spot.

A single diode bar currentlyproduces about 30 W, althoughwith future developments it ishoped to raise the power to 50 W.A typical bar is 0.120.621.0 mmin size [Fig. 8]. Output powers inthe kilowatt range can be pro-duced by stacking bars togetherto form an array or stack. A stackwith an output power of 1 kW isapproximately the same size as ashoe box [Fig. 9]. The beam froma 1.4 kW HPDL can be focuseddown to a spot size of about 1.5mm23 mm, which gives a powerdensity of about 52104 W/cm2.Diode lifetime is expected to bein excess of 10,000 hours and nomaintenance will be required,apart from cleaning the focusingoptic.

At present, there are only afew installations of HPDLs in in-dustry for materials processing

purposes. The most interestingones are used to weld plastics,solder small components and forsurface treatment, in particularfor hardening and cladding.

Due to the low power densitywhich is produced, only heat con-duction welding has so far beenpossible. Initial tests in Germanyshow that a 1.4 kW HPDL canbutt weld 0.8 mm mild steel usinga 50 mm focal length optic and aprocessing speed of 1 m/min. TheHPDL can also weld zinc-coatedmaterials. Another area of inter-est is the conduction fillet weld-ing of 1 mm thick stainless steelwhich produces a cosmetically ex-cellent weld. The laser welding ofaluminium is also expected toundergo improvements. With theHPDLs with an 800 nm wave-length, aluminium shows good

absorption. All over the world,large-scale efforts are now beingmade to improve the beam qual-ity of diode lasers in order to ex-tend the use of this type of laserto other “difficult-to-weld” appli-cations.

Plasma Arc Augmented LaserWeldingOne interesting approach is tocombine a Nd:YAG laser of fairlylow power with a plasma weldingtorch equipment, the so-calledPALW technique (PALW = Plas-ma Arc Augmented Laser Weld-ing) [Fig. 10].

This will increase the level ofefficiency, making the price of asystem of this kind favourable.The plasma is directed into thelaser keyhole using the laser plas-ma. A cross-section through aweld of this kind shows the deeppenetration effect of the laser,combined with the wide weldbead of the plasma. Geometry ofthis kind is favourable from theautomotive crashworthiness anddurability point of view. As alarger volume of melted materialis produced, the positioning bet-ween the sheets to be welded canbe less precise.

Double focus weldingThe hybrid techniques, like theabove-mentioned PALW or lasers

Figure 9: 1 kW high power diodelaser.

Figure 10: PALW (Plasma Arc Augmented Laser Welding), featuring a combinedplasma torch and Nd:YAG laser set-up.

0.6 mm fibreGas and powersupply

Weldingheadwith fl=120 mm

Crossjet nozzle

Pressurefinger Plasma torch

Plasma

Nd: YAG

PALW



combined with MIG or TIGtorches, generally result in fairlybulky arrangements, which limitthe accessibility of the weldinghead. To obtain similar results, i.e.extremely deep penetration and abroader weld seam, different op-tical arrangements can be used tosplit and focus the laser beam ontwo (or even more) spots. Thisdouble focus or twin spot tech-nique is now being evaluated atmany laser laboratories world-wide and it has so far producedsome promising results in connec-tion with welding aluminium, forexample.

RemoteLaser WeldingUtilizing what is designated as“Remote Laser Welding (RLW)”[Fig. 11], deep penetration weld-ing can be accomplished over lar-ge areas and from a distancegreater than 1 metre, using a slabdischarge CO2 laser. The beam issteered over ± 20° by galvo mir-rors and the focal length can bechanged over 600 mm. This sys-tem can produce five spot welds asecond. Furthermore, each of the-se spot welds can be performed ina complex pattern, which increas-es the volume of the molten ma-terial, by oscillating or wobblingthe beam. This enhances thestrength and accommodates gaps.

The rapid welding, in combina-tion with the fact that the remotewelding system is less expensivethan a laser robot, results in adramatic reduction in the cost ofeach spot weld.

SummaryThe large number of laser weld-ing applications described in thisarticle clearly indicates that thelaser is regarded as an acceptedand mature processing tool forassembly operations. The advan-tages of laser welding include thehigh processing speed, resultingin a narrow heat affected zoneand almost no distortion in thefinished part. This contactlessmethod is also easy to robotize,which is a necessity if it is intend-ed for use in high volume produc-tion, in the automotive and elec-tronics industries, for example.Moreover, the high quality weldcan be controlled on-line usingvarious integrated monitoringsystems, developed especially forlaser welding.

With the on-going process de-velopment described at the endof the article, the possible appli-cations for laser welding in themanufacturing industries will bemore or less unlimited. In fact, forsome applications, no alternativejoining method can be found.

Figure 11: Principle of the remote welding technique.

About the author

Johnny K Larsson graduated fromthe Lund Institute of Technologyin Sweden in 1975. After spendingeight years as an engineer in theheavy truck industry, he joinedVolvo Cars in 1986. Since then, hehas been responsible for the R&Dprogramme at the Body Engineer-ing Department, covering areassuch as materials technology, join-ing methods, structural analysisand simulations.

In recent years, he has focused histechnical skills on joining technol-ogies for current and future carbody concepts and is therefore act-ing as project manager for a num-ber of activities in this field withinthe company. He is also involvedin different EUCAR and interna-tional projects dealing with joiningtechniques.

Through the years, Mr Larsson hasbecome a well-known person onthe international scene and hasserved as session chairman at nu-merous automotive and laser con-ferences such as FISITA, ISATA,NOLAMP and so on. He also con-tributes to the continuing educa-tion of European automotive engi-neers through his involvement inorganizations like EUROMOTORand ELA (European Laser Acade-my).

Mr Larsson holds a number oftrust positions in the SwedishWelding Commission and in theSwedish Association for Laser Ap-plications in the Manufacturing In-dustry, among others.

Over the years, Mr Larsson haspresented a number of technicalpapers focusing on the innovativeresearch work performed withinthe Volvo Group.

I therefore foresee a rapid in-crease in industrial laser weldingand I can promise that what is de-scribed here should actually beregarded as the “tip of the ice-berg” of what is to come.



Energy costs have oftenbeen disregarded as aminor part of the totalwelding cost. This articledemonstrates that poorpower source efficiencyconsumes unnecessaryamounts of extra energy,leading to costs whichcan be avoided by choos-ing the right equipment.

When it comes to the weldingprocess, there are major differ-ences in the energy consumptionof the welding methods. In addi-tion to the energy costs, the heatinput is a welding parameter ofgreat significance for the metal-lurgical effects and thermal dis-tortion.

We also have to consider theenvironmental effects of the un-necessary electricity consump-tion, the heat generation and thewaste of our common resources.Other aspects related to the useof electric energy are also dis-cussed, including the problems as-

sociated with electromagneticcompatibility (EMC) and the pos-sible harmful effects of electro-magnetic fields for human beings.

Power sourcesTypical efficiency values for arcwelding power sources are 75–85%. This means that, for a loadof 500 A/40 V, the losses can be inthe range of 3–6 kW. The valuedepends on the type of powersource that is used. Inverters aresmaller and they also have lesspower loss than traditional ma-chines, see Fig. 1.

Normal welding is not continu-ous and the arc time factor has tobe taken into account when cal-culating the energy costs. Duringthe time when it is switched onbut not in use, the equipment hasopen circuit losses. The old rotat-ing welding converter could haveopen circuit losses of more than 1kW, large MMA welding ma-chines 300–400 W, while the mod-ern inverter power sources per-haps have no more than 50 W.

If the power source is designedcorrectly, all the losses are dissi-pated without too great an in-

crease in temperature in the sen-sitive parts, i.e. insulation materialor semiconductors. If the internalcooling surfaces are clogged upwith dust and dirt, the tempera-ture increases and shortens theservice life of the equipment. It isalso important from a safetypoint of view to avoid overheat-ing. A breakdown in the insula-tion between the primary andsecondary windings in the trans-former may enable the mainsvoltage to reach the welding cir-cuit. If the secondary circuit is notconnected to earth, this would behazardous to the welder.

When choosing a power sourcefor industrial welding, high effi-ciency is obviously an importanteconomic factor. Even if the en-ergy cost is just part of the totalwelding cost, it can be highenough to justify the extra invest-ment cost required for energy-saving equipment. The lossesfrom several machines in a work-shop also contribute by helping toincrease the temperature in anenvironment that is perhaps al-ready too hot.

The dimensioning of theelectrical installation depends onthe total need for power but alsoon the power factor. The powerfactor is important when it comesto calculating the apparent powerand the size of the fuses. Inverterpower sources that have manygood properties do not necessari-ly have a high power factor. Ifthey are equipped with a PowerFactor Correction (PFC) circuit,the power factor is increased andthe necessary fuse size can be re-duced.

If the welding transformer hasa poor power factor, this indicatesa phase shift that can be im-proved by phase compensatingcapacitors. The power factor ofinverters mainly depends on adistortion in the shape of the cur-rent, a deviation from the sine

Energy efficiency in weldingby Klas Weman, ESAB Welding Equipment AB, Laxå, Sweden



wave. In this case, the above-men-tioned PFC circuit is a possibleway of helping to improve thepower factor.

If the necessary welding energyis used at short intervals, as it is inresistance welding, for example,the mains must be able to deliverhigh electric power. This is com-parable with the effect of a lowpower factor — the size of thefuses and the total cost of theelectrical installation increasesand can be high in comparisonwith the real need for electric en-ergy as measured in kWh.

Electrical and magneticnoiseSemiconductors in welding recti-fiers and inverters cause distur-bances of higher frequency inboth the mains and welding cir-

cuits. The highest frequenciesmake electrical noise that caninterfere with radio communica-tions, computers or other electri-cal equipment. The lower fre-quency ripple in the welding cir-cuit must be filtered in such away that it does not affect thewelding properties. The currentripple of inverter power sourcesis of such an amplitude and fre-quency (20–100 kHz) that a riskof interaction with the weldermust be taken into consideration.The experts are discussing whether there is a risk of certaintypes of cancer. The magneticfield can also produce heating ef-fects. Using a simple test devel-oped by the author, it was pos-sible to measure the rate of in-crease in temperature by one de-gree Celsius a minute on a metal

Fig. 2. Total energy per metre needed for some different welding methods (4 mmsteel plate). Power losses from the equipment are included in the calculation.

About the authorsKlas Weman, MSc, is involved withPower Technology Developmentat ESAB Welding Equipment ABin Laxå, Sweden, and is an associa-te professor at the WeldingTechnology Department at theRoyal Institute of Technology inStockholm, Sweden. ProfessorWeman has broad-based experien-ce of the R&D of arc equipment,power sources and welding proces-ses.

Joakim Hedegård (b. 1961), Licen-tiate of Technology, has been wor-king for nearly ten years in thearea of welding, mainly with edu-cation and applied research pro-jects. He is a former productmanager at ESAB and AssistantTechnical Secretary to the SwedishWelding Commission and willsoon be joining the Swedish Insti-tute for Metals Research as pro-gramme manager for the JoiningTechnology Centre.

plate (simulating an implant) clo-se to a welding cable. The highwelding current which is commonin resistance welding can inter-fere with the function of pace-makers.

Choice of welding methodOne interesting point is to studythe welding methods with regardto their need for energy. In addi-tion to the cost of energy, theheat input is an important weld-ing parameter. Too much heat in-put into the joint will reduce theimpact strength and introducethermal stress and distortion inthe workpiece. More recent weld-ing methods can achieve highwelding speeds and low heat in-put. The diagram in Fig. 2 shows acomparison between differentwelding methods. The total ener-gy for a one-metre long weld iscalculated. It is interesting to seethat, in spite of the low efficiencyof lasers, laser welding can com-pete effectively with traditionalmethods like MMA. As a rule ofthumb, the welding methods withthe highest energy density usuallyhave the lowest heat input.

Fig. 1. Energy consumption per year for different types of MMA-welding powersource. The differences depend on different efficiency and open circuit losses.

Ene

rgy

cons

ump

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Actual welding current, (A)Converter

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AbstractHigh-strength weld metals fre-quently have a microstructureconsisting of martensite or a mix-ture of martensite and acicularferrite. The alloying of the weldmetal has to be designed so thatsufficient hardenability to gener-ate the required microstructureduring cooling is obtained. It hasbeen observed that the yieldstrength of such alloys can exhibitconsiderable variation in therange of 700-950 MPa for thesame consumable electrode. Thework presented here reveals onereason for these variations — thatthe cooling curve of the weld isclose to the limit of hardenabilityof the material. This means thatthe microstructure obtained be-comes sensitive to variations inthe interpass temperature in mul-tirun welds.

IntroductionMaking a high-strength steel us-ing a variety of well-establishedstrengthening mechanisms is astraightforward procedure.Achieving toughness, which is theability of the metal to absorb en-ergy during fracture, is far moredifficult. The essence of most al-loy design is to obtain a reason-able compromise betweenstrength and toughness.

Unlike wrought steels, weldscannot usually be processed toenhance the microstructure andproperties once the joint is com-pleted. Many welds that are usedfor structural steels cannot evenbe heat treated after deposition.As a result, there are limitationsto the maximum strength that canusefully be exploited. A high-strength weld is therefore cur-rently limited to a yield stress ofabout 900 MPa for most practicalcircumstances.

Untempered microstructurescapable of resisting deformation

at such large stresses are basedon martensite or on mixtures ofmartensite/bainite/acicular ferrite.The alloys must therefore containa sufficient content of austenite-stabilising elements consistentwith the hardenability required toavoid other phase transforma-tions. At the same time, the car-bon concentration must be mini-mised to avoid excessive hardnesswhen the weld is deposited. So,elements such as manganese,nickel, chromium and molybde-num are added as they improvehardenability and yet do not ex-cessively strengthen the steel. Atypical weld metal compositionfor manual metal arc welding istherefore:Fe-0.05C-0.5Si-1Mn-3Ni-0.5Cr-0.5Mo wt%with a strength of about 900 MPaand a Charpy notch toughness at–60°C of about 60 J.

It has been found that the me-chanical properties of this andsimilar higher strength welds arevariable, even though the chemi-cal composition of the depositdoes not change (1). In particular,the yield strength can vary (150MPa), whereas the ultimate ten-sile strength does not vary asmuch. This is unsatisfactory fromthe customer’s point of view andindeed for the electrode manufac-turer who has to supply elec-trodes to specification.

The purpose of the presentwork was to investigate the vari-ability in the mechanical proper-ties of these high-strength welddeposits.

Experimental detailsWeld specificationsAn experimental weld (multirunMMA) was fabricated accordingto ISO 2560 using a 20 mm thickplate filled with 30 runs (threebeads per layer). An interpasstemperature of 250°C was used.

This configuration causes little di-lution of the weld metal, therebypermitting the accurate isolationand measurement of weld metalproperties. Welding was per-formed at 24 V, 180 A and a heatinput of 1kJ/mm. The nominalcomposition data for the weld areshown in Table 1.

Mechanical testingTwo tensile specimens and 20Charpy-V impact specimens weremachined. Prior to tensile testing,the specimens were degassed at250°C for 16 hours. The impactspecimens were tested at four dif-ferent temperatures and fivespecimens were tested at eachtemperature. The test tempera-tures were +20°C, 0°C, –20°C,–40°C and –60°C.

Specimens for microscopySpecimens for light microscopywere produced by hot mountingthe weld material in bakelite. Fol-lowing grinding and polishingdown to a 1 µm diamond grit fin-ish, the samples were etched with2% nital.

Transmission electron micros-copy samples were made from cy-lindrical rods with a diameter of 3mm machined from sections ofweld metal. The final prepara-tions were performed using atwin jet electropolisher at ambi-ent temperature and a potentialof 50V. The electropolishing solu-tion comprised 5% perchloricacid, 10% glycerol and 85% etha-nol (Brammar, 1965). Imagingwas performed in a Philips 400STtransmission electron microscopeoperating at 120 kV.

Effect of interpass temperature onproperties of high-strength weld metals

by Mike Lord, Gill Jennings and Every, Great Britain

C Mn Si Cr Mo Ni

05 2.0 0.3 0.4 0.6 3.0

Table 1 Concentration (in weight%)of the major alloying elements in theexperimental weld.



Figure 1. Dark-field optical micro-graph showing little resolvable detail.

Rp0.2 Rm A5 (%) Z (%) Impact toughness (J)(MPa) (MPa)

+20°C 0°C –20°C –40°C –60°C872 922 22 67 102 95 87 79 64

Figure 2. TEM micrograph showingthe bainitic microstructure of the weldmetal.

Figure 3. Electron diffraction patternshowing ferrite and austenite spots inan approximate Kurdjumov-Sachsorientation.

DilatometryA Thermecmastor Z thermo-mechanical simulator was used tostudy the phase transformationsoccurring within the weld metalas a function of the applied cool-ing rates. The transformationswere monitored using laser dila-tometry. Specimens for use in thesimulator were machined into cyl-inders with a length of 12 mmand a diameter of 8 mm. A holewith a diameter of 5 mm was dril-led along the central length of thespecimens, the reduction in mate-rial volume producing more accu-rate data. Heating the specimenswas effected via an induction coiland cooling was similarly con-trolled using a combination of in-duction coil heating and jets ofhelium quenching gas.

In the production of a continu-ous cooling transformation(CCT) curve, the specimens wereaustenitised at 1,200°C for 10minutes in order to reduce the ef-fect of the austenite microstruc-ture before each specific coolingcycle was applied.

ResultsMechanical testingThe results of the tensile and im-pact toughness tests are present-ed in Table 2.

MicrostructureLight microscopy has a resolutionof about 0.5 µm at most. Observa-tions revealed apparently plate-like features, but they were be-lieved to represent clusters of pla-tes which are much finer. The finestructure could not really be revealed and was not found tochange much with its positionwithin the multirun weld (Figure 1).

Thin foil observations usingtransmission electron microscopyrevealed a fine microstructurecomprising bainite plates with awidth of the order of 0.3 µm. A

typical TEM micrograph is shownin Figure 2. Electron diffractionproved the presence of retainedaustenite films between the bai-nitic ferrite plates. The crystallo-graphic orientation between theaustenite and adjacent ferrite wasfound to be consistent with thatexpected from a rational Kurdju-mov-Sachs (KS) relationship(Figure 3).

The alloy contains a fairly lowcarbon concentration, so the rea-dy observation of reasonablythick retained austenite filmsmight be considered surprising atfirst sight. However, carbon ispartitioned from the bainite afterit stops growing and this stabilisesthe austenite which is enriched incarbon (2). In fact, the observa-tion of these thick films can besafely taken to indicate the pres-ence of bainite, which in low-alloysteels can be difficult to distin-guish from martensite. Carbideprecipitation was never found inspite of extensive investigations.

Dilatometry to produce a CCTcurveFurther experiments using dila-tometry were conducted to verifythat the fine plates with interven-ing austenite represented bainiterather than martensite. If the ob-served transformation tempera-ture remains constant for differ-ent cooling rates, it can be con-cluded that the final microstruc-ture must be martensitic, sincethe martensite-start (Ms) temper-ature does not depend on thecooling rate for low-alloy steels(3). On the other hand, the tem-perature at which a detectablefraction of bainite forms does de-pend on the cooling rate, becausethe overall kinetics of the reac-tion can be described in terms ofa C curve on a continuous cool-ing transformation (CCT) dia-gram.

A CCT curve was produced bycooling specimens at various ratesranging from 100°C/s to 0.05°C/s.Figure 4 shows the experimentalCCT curve, along with the calcu-lated Ms temperature (4) and acalculated MMA weld bead cool-ing rate with an interpass temper-ature of 250°C (5) denoted ’250°CITP’.

Table 2. Results of mechanical testing.



The calculated weld bead cool-ing rate clearly cuts the CCT cur-ve beyond the limit of harden-ability in a region which shouldproduce a bainitic microstructure.TEM micrographs showed fineplates which confirm a displacivemechanism of transformation.These two curves intersect at aposition at which the gradient ofthe CCT curve is very large. Con-sequently, small variations in thecooling rate of the material coulddrastically alter the transforma-tion temperature and thereby theresultant mechanical properties.This hypothesis led to questionsconcerning the possible causes ofsuch variations. The problem wasapproached using a sophisticatedmethod of pattern recognition,known more generally as neuralnetwork analysis.

Neural network: themethodThere are difficult problems(such as welding) in which thegeneral concepts might be under-stood but which are not as yetamenable to rigorous mathemati-cal treatment. Most people are fa-miliar with regression analysiswhere data are best-fitted to aspecified relationship which isusually linear. The result is anequation in which each of the in-puts xj is multiplied by a weightwj. The sum of all such productsand a constant C then gives an es-timate of the output y =

It is well understood that thereare dangers in using such rela-tionships beyond the range of fit-ted data.

A more general method of re-gression is neural network analy-sis (6–9). As before, the inputdata xj are multiplied by weights,but the sum of all these productsforms the argument of a hyper-bolic tangent. The output y istherefore a non-linear function ofxj; the function which is usuallychosen is the hyperbolic tangentbecause of its flexibility. The ex-act shape of the hyperbolic tan-gent can be varied by altering theweights (Figure 5a). Further de-grees of non-linearity can be in-troduced by combining several ofthese hyperbolic tangents (Figure5b), so that the neural networkmethod is able to capture almostarbitrarily non-linear relation-ships. For example, it is wellknown that the effect of chromi-um on the microstructure ofsteels is quite different at largeconcentrations than in dilute al-loys. Standard regression analysiscannot cope with such changes inthe form of relationships.

One potential difficulty when itcomes to the use of powerful re-gression methods is the possibil-ity of overfitting data (Figure 6).For example, it is possible to pro-duce a neural network model fora completely random set of data.To avoid this difficulty, the ex-perimental data can be dividedinto two sets, a training dataset

and a test dataset. The model isproduced using only the trainingdata. The test data are then usedto check that the model behaveswhen presented with previouslyunseen data.

Neural network models inmany ways mimic human experi-ence and are capable of learningor being trained to recognise thecorrect science rather than non-sensical trends. Unlike human ex-perience, these models can betransferred readily between gen-erations and steadily developedto make design tools of lastingvalue. These models also imposea discipline on the digital storageof valuable experimental data,which may otherwise be lost withthe passage of time.

Figure 4 Experimental CCT curve.

Figure 6 A complicated model mayoverfit the data. In this case, a linearrelationship is all that is justified bythe noise in the data.

Figure 5 a) Three different hyperbolic tangent functions; the “strength” of eachdepends on the weights. (b) A combination of two hyperbolic tangents to produce amore complex model. Details about the methodology can be found in DavidMackay’s article in Mathematical Modelling of Weld Phenomena III.



Neural network structureWhile there are many varieties ofneural network, the type used inthis work can be expressed dia-gramatically as shown below. Inthis case, the network is com-posed of three “layers”. The firstlayer contains the model inputdata provided by the user, such ascompositional details (simply asnormalised values), the second“hidden” layer is an internal stageand describes the degree of com-plexity of the substructure of thenetwork. The third “output” layercontains the predicted value ofthe parameter in question whenrunning a calculation. Figure 7shows a simplified network withfive example input parameters.

The circles within the diagramare called nodes or units, so herethere are five “input nodes”. Thehidden layer comprises three hid-den nodes and the output layer issimply a single output node. Thenumber of nodes in the hiddenlayer limits the complexity of thepossible relationships betweenthe input and output nodes. Thelines connecting the nodes repre-sent mathematical functions per-formed on the values as they passfrom the input to the output lay-er. In this network, hyperbolic

tangent functions are utilised, asthey are always single valued, ex-hibit both near-linear and non-linear regions and are relativelyeasy to manipulate. When per-forming a “prediction” using aneural network, data are operat-ed on by a hyperbolic tangentfunction as they are passed bet-ween the input and hidden layers.This function is of the form:-

where xj are the normalised val-ues of the input variables, wij

(1)

are a set of “weights” associatedwith each input and hidden unitand ui

(1) are bias values analo-gous to constants found in linearregression.

The values hi are transferredfrom the hidden layer to the out-put layer via a second function ofthe form:–

where y is the value of the outputnode (e.g. yield strength), wi

(2)

are a second set of weights and u(2) is a further constant known asa ‘bias’.

The numerous weighting coef-ficients and constants (wij

(1), – ui

(1), wi(2) and u(2)) are required in

order to provide the flexibility to

calculate accurate output valuesfrom input data. At the heart ofthe neural network techniquethere are algorithms designed toevaluate these coefficients andconstants in order to produce sat-isfactory results.

Training the networkTraining involves repeatedly ex-posing the training algorithms todata for the network inputs (e.g.compositions) and, crucially, theoutput (e.g. yield stress). The datamust come from a database rele-vant to the particular applicationin question. The quality of thisdatabase determines, at least inpart, the final accuracy of the net-work predictions. The requiredsize of the database may vary de-pending on the complexity of theproblem that is being modelled.In general, the larger the amountof accurate data, the better thepredictions of the resulting net-work. The training algorithms re-fine the coefficients and variablesin the above equations by com-paring the predicted and actualoutput values of the output node.Through a complicated back-pro-pagation process, the computerprogram attempts to reduce thedifferences between predictedand actual values until they reachacceptably low levels. There is anadditional problem with “over-training”, which means that thenetwork can learn the examplesin the dataset too well and willthen be unable to predict valuesfor different unseen composi-tions. This is analogous with fit-ting a complicated curve to a setof points that lie on a straightline, where the experimental er-rors have been modelled into thenetwork rather than just thetrend. Using a number of differ-ent hidden nodes and training ona randomly-selected half of theavailable data, the best networkcan be picked to strike a balancebetween modelling real trendsand overtraining on noise in thedata. The second half of the data-set is used to compare the predic-tions of this trained network (Fig-ure 8). Ideally, plots of predictedversus measured values for boththe training and testing halves ofthe dataset should contain equaldegrees of scatter.

Figure 7 Graphical representation of a neural network. Some examples of inputnode parameters are also presented.



Two types of network were trai-ned on data from 770 welds drawnfrom a variety of sources, the firstgiving yield stress as an output, thesecond ultimate tensile strength(10). Nineteen input variableswere provided for each of thesewelds, fifteen of which were due toalloying elements, while the re-maining four were due to the heatinput, interpass temperature andtempering time and temperaturevalues if applicable.

A number of different net-works were trained and tested. Inthe case of the yield stress mod-els, the five best models werethen combined to create a “com-mittee”. A committee of net-works is superior to a single oneas, collectively, they should cap-ture the trends in the data moreeffectively. Each network withinthe committee was retrained onthe complete dataset to providegreater accuracy before commit-tee predictions were made. Simi-larly, a committee of four modelswas used in the predictions of ul-timate tensile strength.

Investigation of tensile strengtheffectsAs stated earlier, previous analy-ses of the weld microstructurehad provided little insight intothe cause of the observed varia-tions in strength. However, dila-tometer data in the form of aCCT curve had shown that typi-cal MMA measured cooling ratescould fall in a critical region. Thehardenability of the weld metalcaused plotted weld cooling rates

to fall close to the “nose” of thebainite curve in a region of par-ticularly high gradient. A calcula-tion of this kind indicated thatsmall variations in the weld cool-ing rate could considerably affectthe transformation temperature.It was thought likely that such avariation in the displacive trans-formation temperatures of thematerial would have a largeenough effect significantly to al-ter mechanical properties. Themajority of the transformationoccurring at a higher tempera-ture, for example, would lead to areduction in yield stress, as the ef-fects of diffusion on both carbonmobility and dislocations are tem-perature dependent.

Compositional variations alonecould not be held responsible forthe large variations in yieldstrength reported for this materi-

al. It would seem more plausibleto consider process parameters asbeing responsible. This rationaleeventually led to the identifica-tion of the interpass temperatureas a possible candidate for caus-ing the strength variations. Largejoints comprise many passes inorder to deposit the requiredamount of material. Welds underconstruction cool at a rate deter-mined by their environment, suchas the degree to which the sur-rounding material acts as a heatsink and the temperature of thosesurroundings. If the interpasstemperature is high, a subse-quently deposited bead will coolat a reduced rate which, it wassurmised, may be significantlylower, depending upon the tem-perature. The trained neural net-work as a research tool was nowuseful as it provided a means of

Figure 8 The similar appearance of both training and testing data graphs indicates a good balance between predicting trendsand modelling noise.

Figure 9 Predicted and measured yield and ultimate tensile strengths as afunction of interpass temperature.



testing this theory without havingto perform lengthy experimentswith real welds.

Predictions were made afterchoosing a range of interpasstemperatures. The results were sosignificant that it was decided toperform physical experiments inorder to test the predictions. Aseries of three welds, using thehigh-strength steel electrode,were produced with carefullymonitored interpass temperaturesof 50°C, 110°C and 250°C. The re-sults of the predictions and thetensile tests on the new welds arepresented in Figure 9.

There is a clearly predicted di-vergence in the yield stress andUTS of the weld metal as a func-tion of the interpass temperature,a divergence of approximately 1MPa per °C. A second feature ofthe predicted curves is the cross-ing over of yield stress and UTSpredictions below about 90°C.This is an example of situations inwhich caution should be exer-cised when using neural networkpredictions. The network clearlyhas no knowledge of the laws thatdetermine the behaviour of thesystem it is modelling and conse-quently the user must always en-sure that they make physical sense.

In this case, it is to be expectedthat the gap between yield stressand UTS reduces to a few MPa atinterpass temperatures approach-ing ambient temperatures. Theexperimental results clearly showa divergence in yield stress andUTS similar to that predicted. Inthis case, the yield stress modelappears to be more accurate, asthe UTS values appear to reduceas a function of interpass temper-ature, whereas the UTS networkpredicts a slight increase as afunction of interpass temperature.It is the yield stress values thatare of most interest, particularlyas they approach the UTS valuesat low interpass temperatures andfall off rapidly as this tempera-ture is increased. Conventionally,it is desirable to have the yieldstress to UTS ratio closer to 0.8in the interests of producing duc-tile failure in the event of thejoint being overloaded. This ratiois only realised at interpass tem-peratures of above 200°C. These

results provide a probable causefor the varying properties in weldmetals of these kinds. Historically,the interpass temperature has of-ten not been rigidly monitoredand it is clearly imperative withthis weld composition that pre-cautions are taken.

The results of these experi-ments have enabled a recommen-dation to be made detailing thestrict adherence to the specifiedinterpass temperature.

ConclusionsThere are three major conclu-sions that can be drawn from thiswork. By comparing transmissionelectron microscopy and diffrac-tion data with measurements oftransformation temperatures us-ing dilatometry, it has been pos-sible to prove that the high-strength weld cannot be fullymartensitic at the cooling ratestypical of welding. The micro-structure will instead consist of amixture of martensite and bainite,the latter consisting of bainiticferrite separated by carbon-enri-ched films of retained austenite.These methods are recommendedin circumstances where it is oth-erwise difficult to distinguish bai-nite and martensite (i.e. when themicrostructure is very fine andthe carbon concentration so smallthat carbide precipitation is pre-vented).

The second conclusion is thatdifficulties are to be expectedwith respect to the mechanicalproperties when the bainite andmartensite transformations occurat temperatures which are notmuch above the nominal inter-pass temperature. This is becausethe cooling rate of the weld bet-ween the bainite and martensitestart temperatures becomes verysensitive to the interpass temper-ature. Failure accurately to con-trol the interpass temperatureleads to large variations in themicrostructure and hence in themechanical properties.

Finally, a neural network mod-el has been shown to be reliablein predicting the effect of theinterpass temperature onstrength, both in terms of the ab-solute values and in the relativevariation in the yield and ultimate

tensile strengths. It is particularlyencouraging that the model pre-dicted that the difference bet-ween these two measurements ofstrength is a function of the inter-pass temperature.

AcknowledgementsThe author is grateful to theEPSRC and Dr Lars-Erik Svens-son. I would like to thank DrHarry Bhadeshia for his continu-ing support and enthusiasticsupervision. Finally, I would liketo acknowledge the financial sup-port of Magdalene College via itsgenerous scholarship.

References1 P. T. Oldland, C. W. Ramsay, D. K. Mat-

lock, D. L. Olson, Welding ResearchSupplement, April 1989, pp 158-167

2 H. K. D. H. Bhadeshia, Bainite inSteels, Institute of Materials, 1992, 154-157

3 R. Kumar, Physical Metallurgy of Ironand Steel, Asia Publishing House,1968,200-256

4 H. K. D. H. Bhadeshia, Metal Science,15, 1981, 175-180

5 L.-E. Svensson, B. Gretoft, H. K. D. H.Bhadeshia, Scand. J. Metallurgy,15,1986, 97-103

6 D. J. C. MacKay, Neural Computation,4, 3, 1992a, 415-447

7 D. J. C. MacKay, Neural Computation,4, 3, 1992b, 448-472

8 D. J. C. MacKay, Neural Computation4, 5, 1992c, 698-714

9 D. J. C. MacKay, Darwin College Jour-nal, Cambridge, 1993, 81

10 T. Cool, H. K. D. H. Bhadeshia, D. J. C.MacKay, Mat. Sci. Eng. A, 223, 1997,186-200

About the authorMike Lord graduated from Cam-bridge University with a degree inNatural Science, specialising inMaterials Science 1995. He thenjoined the Phase transformationresearch group in Cambridge to doa PhD. His subject was phasetransformations and properties ofhigh strength weld metals. Hiswork was sponsored by Esab andEPSRC. Mr Lord was awarded theGranjon prize 1998, Category 2 byIIW for his paper “Interpass tem-perature and the welding of strongsteels”. Mr Lord is presently work-ing at Gill Jennings and Every,training to become a British andEuropean Patent Attorney.



BORSIG (a companywithin Babcock-BorsigAG), a famous supplierof pressure vessels andheat exchangers for thechemical and petro-chemical industries, hasoptimized its weldingand cutting productionprocess by implement-ing fully-automated systems for submergedarc welding (SAW) andoxy-fuel cutting.

An advanced, fully-adaptiveSAW process is used at BORSIGfor butt welds of up to 120 mmin joint depth. The multi-layertandem SAW process is con-trolled by intelligent softwarewhich makes its own decisionsfor the complete welding opera-tion.

The holes for nozzle intersec-tions in the shell of the pressurevessel are cut by an industrial ro-bot. Off-line programming forcutting holes with constant weldbevel angles or constant joint vol-ume is performed using differentmacros.

The advanced welding and cut-ting systems are mounted on amulti-functional gantry whichtravels on rails. The gantry worksin conjunction with two anti-creep roller bed stations, see Fig-ure 1. This type of installation wasspecially designed by ESAB forthe requirements of the BORSIGproduct range.

Fig 1. – The multi-functional gantry in operation at BORSIG.

Fig 2. Typical configuration of a combined reformed and synthesis gas heat recovery system.

“The technology of tomorrow” has already been implemented at

BORSIG in Germanyby Dr. Ing Andreas Risch, Head of the Welding Engineering Dept. at

BORSIG GmbH, Germany, and Mr Bengt Ekelöf, Senior Project Manager at Esab Welding Equipment AB, Sweden



BORSIG productsAs one of the leading suppliers ofcomplete Process Gas Waste Heatrecovery systems and quenchcooling systems for the chemicaland petrochemical industries,BORSIG designs and fabricatesdifferent types of heat exchangerand pressure vessel.

The Quench Coolers are usedfor the rapid quenching of the gaseffluent from cracking furnaces inethylene plants. The main applica-tions for the Process Gas WasteHeat Recovery Systems are am-monia, methanol, hydrogen andcoal gasification plants.

Examples of components inthese systems, manufactured byBORSIG, include:

Process Gas Waste Heat Boil-ersHP Steam SuperheatersHT Shift Waste Heater Boil-ersBoiler Feed Water PreheatersGas/Gas Heat ExchangersSynloop Waste Heat BoilersSteam Drums

Fig 2 shows a typical configura-tion for a combined reformed andsynthesis Gas Heat Recovery Sys-tem.

Almost every pressure vesselor heat exchanger is a unique ap-plication, specially designed ac-cording to the requirements ofthe specific process or client spe-cifications.

All these applications involvehigh gas inlet temperatures (up to1,200°C), often accompanied byhigh process gas pressure up to300 bar, as well as the generationof high-pressure steam (up to 140bar).

Quality requirementsThe design and manufacture ofhigh-pressure equipment isstrictly regulated in worldwidepressure-vessel codes like AD,ASME, BS, Raccolta, Codap,Stoomwezen, IBR, JS, AS and soon. The production quality, andthe quality of the welding con-nections in particular, is very im-portant because of the criticaloperating conditions of the pres-sure vessels. Imperfections in thewelded zone are restricted to anabsolute minimum (mostly min.Group B according to ISO 5817or better).

Every pressure vessel contain-ing longitudinal or circumferen-tial joints in the shells or the inletand outlet sections is subjected tocomplete non-destructive testingsuch as magnetic particle or dyepenetrant checks, as well as 100%radiographic (RT) and/or ultra-sonic (UT) examination. Nozzlewelds are normally completelyexamined by UT.

Prior to weld production, aprocess qualification test (PQR),including intensive non-destructi-ve and mechanical testing, has tobe performed in order to verifythat the properties of all weldsmatch the requirements specifiedin the applicable codes and thebase materials. The process whichis going to be used in productionis restricted to the qualified rangeof the PQR when it comes tobase material group, thicknessrange, post-weld heat treatment

(PWHT), range of welding pa-rameters (e.g. pre-heating tem-perature, welding speed, voltage,amperage, interpass temperatureand so on).

Materials and weldingtechnologiesDue to the service conditions ofthe equipment that is going to bemanufactured, many differentsteels are used to manufacturethe pressure vessels and heat ex-changers. The following materialsare examples for the main parts(hull) of the above-mentionedpressure vessels:

High strength C steels (e.g.SA 516 Gr.70) for shells ofSteam Drums and WHBsC-0.5% Mo steels (e.g.15Mo3) for shells and nozzlesof Steam Drums and QuenchCoolersHigh strength, temperature-resistant steels (e.g. 15 NiCu-MoNb 5 or SA 302 Gr.B/Gr.C) for shells and nozzles ofSteam Drums, Process GasWHBs or Synloop WHBs(steam side)C-1.25% Cr-0.5% Mo steels(e.g. 13 CrMo 4-5) for shells ofWHBs (steam side) and forgas-inlet and gas-outlet sec-tions, tube sheets or forgedrings for process gas WHBs(gas side)C-2.25%Cr-1%Mo steels (e.g.10 CrMo 9-10) and C-3%Cr-1%Mo steels (10 CrMo 9-10

Fig 4. Waste Heat Boiler (WHB) for 270 MWe combined cycle coal gasificationpower plant.

Fig 3. Compact process WHB/SteamDrum unit for 1500 MTPD ammoniaplant.



mod.) for gas inlet sections,shell, tube sheets and nozzlesof synloop WHBs (gas side)

The above-mentioned or com-parable steels were welded tothemselves (e.g. shell-shell) orwere combined with one another(e.g. shell-tube sheet). The thick-ness of the shells for steam drumsand WHBs (steam side) generallyranges between 40 and 120 mm,the gas-inlet sections of synloopWHBs increase up to 250 mm.The diameter of the vessels candiffer from approx. 1,000 mm(e.g. quench coolers) to 3,000 mm(e.g. WHB). Typical applicationsare shown in Figs 3 and 4.

Due to the wall thickness andin order to meet the requiredmechano-technological proper-ties, most of the applications, es-pecially the higher alloyed steels,require pre-heating during weld-ing and cutting, as well as con-trolled energy input and restrict-ed interpass temperatures duringwelding operation.

In order to prevent cold crack-ing, the high strength steels needto be pre-heated to between 150and 250°C. Preheating within200–250° and 250–300°C is alsorequired for C-1.25%-Cr-1%Mo-and C-2.25%Cr-1%Mo steels.

For circumferential joints, a Upreparation with a weld bevel an-gle of 8° is normally used. Conesare welded to cylindrical parts us-ing a V-joint preparation (com-plete opening angle 50°). Nozzlewelds (set-in nozzle) were per-formed with a half-V preparation(weld bevel angle 30–40°). Themain welding technologies areGTAW and SMAW for the rootpass and SAW for the fill/cap lay-ers and back welding.

In order to optimize the pro-duction quality and the efficiencyof the welding operation, BOR-SIG has incorporated a largenumber of automated weldingand cutting processes in its pro-duction process.

Examples include fully-auto-mated, tube-to-tube sheet weld-ing for heat exchangers with com-puterised orbital GTAW weldingmachines (multi-layer TIG tech-nology with filler wire), automat-ed GTAW hot-wire overlay weld-ing for critical dissimilar joints,

GMAW robot welding of doublepipe Quench-Cooler elements, ro-bot welding of special stiffenersystems to thin tube sheet andCNC plasma or oxy-fuel cuttingof plates using CAD data andmacro-programming systems.

BORSIG’s criteria for thechoice of the advancedwelding and cutting systemsUp to the end of 1997, the sub-merged arc welding of circumfe-rential and longitudinal joints, aswell as the cutting of nozzle holesin shells and gas inlet/gas outletsections, was performed exclu-sively with operator-controlledwelding and cutting equipment.The quality of these operationswas therefore mainly influencedby the knowledge and experienceof the operators.

The use of CNC-controlledmachines which require absoluteprogramming is not suitable be-cause the actual geometry doesnot always correspond to thenominal geometry (base materialthickness, joint condition, accura-cy of shells, misalignments and soon) Additionally, pre-program-ming the bead placements for themulti-run sequence leads to a re-duction in efficiency due to theincrease in downtime.

So, more effective automationrequired the implementation ofintelligent and adaptive software

that makes its own decisions forthe entire operation. This wasverified in 1997 by installing thewelding gantry, including the ad-vanced ESAB ABW technologyfor the SAW process and the ro-bot cutting system which can beprogrammed off-line on a macrobase. Only the chosen type ofsoftware guarantees the flexibilitywhich is necessary in pressurevessel manufacturing which spe-cializes in client-oriented solu-tions.

The systemThe fully-automatic, multi-purpo-se gantry was developed byESAB and the project was real-ised in close co-operation withBORSIG engineers. All the ele-ments and programming unitswere designed with user orienta-tion as the starting point.

The gantry has a fully-automa-tic, laser-supported submerged-arc ESAB ABW welding system(see Fig 5), which works in con-junction with two 150-tonne roll-er bed systems equipped withanti-creep units. This permits thewelding of longitudinal seams upto 4,200 mm in length and cir-cumferential seams with a diame-ter of up to 3,500 mm.

The special narrow roller beddesign permits the rotation ofvessels with attached nozzles orflanges with a maximum projec-tion of 750 mm and a minimum

Fig 5. ABW tandem welding head with laser support optical sensor.



distance of 500 mm between twonozzles or attached parts respec-tively.

At wall thicknesses of up to120 mm, which covers 95% of allBORSIG applications, fully-auto-matic adaptive tandem weldingcan be performed. At thicknessesof up to 135 mm, mechanized tan-dem welding with the ESABABW head is possible. In theevent of thicker wall thicknessesof up to 250 mm, a second con-ventional single-wire weldinghead can be used.

In any case, all the automaticor semi-automatic operationswere controlled by the main con-trol PC, Fig. 6. Two 250-litre pres-sure tanks located at the base ofthe gantry automatically supplythe integrated continuous flux re-covery system with new flux.

Alternatively, different fluxesdepending on the procedure canbe supplied from the pressuretanks at the base. The flux systemis equipped with built-in electricalheaters. Minimum flux consump-tion is guaranteed by integral fluxsuction and circulation.

An industrial robot of theABB IRB 2400/S4 type, equippedwith a flame cutting (oxy-fuel)burner system, is mounted on a

carriage which is installed per-pendicular to another carriage atthe main horizontal boom of thegantry, Fig 7. Both carriages areinstalled as linear external robotaxes which are used to positionthe robot and, if required, as ad-ditional robot axes during cuttingoperations. The cutting of nozzleholes, programmed on an off-line,macro-supported basis, is possibleat wall thicknesses of up to 150mm.

The system permits the cuttingof holes with a diameter of up to1,500 mm. The maximum ratiobetween the hole cut-out and thediameter of the course is 0.68.This results in a minimum shelldiameter of 2,500 mm if a hole of1,500 mm is to be cut.

Additionally, the gantry can beused as a multi-functional plat-form for fitting and welding noz-zles and the other attachments tothe vessels. For this purpose, theplatform can be flexibly modifiedusing removable insulated floorplates. The whole gantry and theroller bed systems can be posi-tioned free on rails over a lengthof 45 m. All the main energy anddata transfer cables were installedunder the floor in cable chainscovered by movable floor plates.

The ESAB ABW adaptivejoint fill programThe ESAB ABW adaptive tan-dem welding system mounted onthe gantry can handle both cir-cumferential and longitudinalwelding in a fully-automatic jointfilling procedure. This is possiblethanks to the intelligent softwarein the system.

True measurement data fromthe joint profile measured by anoptical sensor during welding de-termine both the required level ofthe welding parameters on a con-

Fig 6. Main PC welding controller.

Fig 7. 6-axis robot oxy-fuel cutting system.

Fig 9. Principle of ABW. Curventadaption program.

Fig 8. Principle ABW weld speedadaption program.



tinuous basis, as well as the posi-tioning of related axes for track-ing and inter-run formation.

This means that both the beadsize and bead placement are con-trolled by the system software ina self-adaptive manner for all thefill layers including the cap.

The system software influencesthe following four fill parameters:

The weld speedThe currentThe bead placementThe number of beads in filland cap layers

This unique feature enablesABW to adapt the parameters tomatch deviations in the cross-sec-tional area and geometry alongthe entire joint line.

Each of the four fill parame-ters influenced by the ESABABW system software performsdifferent tasks in the adaptiveABW weld fill procedure.

The weld speed controls theamount of weld metal deposit-ed in different areas along thejoint line, Fig 8.The current controls both the

bead height and the amountof weld metal deposited in dif-ferent areas of the joint, Fig 9.The bead placement influenc-es the pattern of the inter-runformation in different areas ofthe joint.The selected number of beadsin each layer determines theinter-run penetration, the sha-pe of the actual joint bottomand the degree of weld fill.

The unique ESAB ABW weldtechnology is designed to givemanufacturers dealing with highquality butt welding a 100% auto-matic multi-layer technology,thereby enabling them to producea defect-free weld fill, even if thejoint geometry deviates from thenominal configuration.

The configuration of the ESABABW system was specially modi-fied according to BORSIG re-quirements for flexible produc-tion. The modified system canalso verify joints between shellsand thicker flanges (step on oneside near the weld), as well asjoints between shells and cones,with the automatic generation ofa smooth transitional contourbetween the two parts.

Registration and documentation of thewelding operationContinuous, fully-automatic, mul-ti-run tandem welding for manyhours with limited operator sur-veillance requires not only excel-lent man-machine communica-tion (MMC), Fig 10, during theweld fill operation, but also a re-port system which explains howthe work has been accomplished.

The ESAB ABW operatingsystem software installed at BOR-SIG includes a report system inwhich welding and positioningdata from the operation are regis-tered in two separate files – theWeld Report file and the Log file.

In the weld report, all the instal-lation parameters such as wiretype and wire dimension, flux typeand permissible interpass temper-atures are stored, together withthe specified process parameterssuch as welding voltage, weldingcurrent and welding speeds andtheir report, alarm and stop limits.

All the important events dur-

ing welding, such as start, stop(s),re-starts, exceeded report limitsand warnings for flux level, highor low interpass temperature, arestored in the weld report. All theevents are stored together withthe actual date, time, weld layer,weld bead and position in thejoint. Should the event be an ex-ceeded process parameter, theparameters at the time in ques-tion are also stored.

In the log file, the position andprocess parameters are continu-ously registered (every 20 mm). Anormal log file report for a thick-walled welding object could fill1,000 pages.

Robotic oxy-fuel cuttingof nozzle holesDue to the saddle contour of a tu-bular intersection in a cylindricalshell, the programming of thehole-cutting operation is mathe-matically complicated.

In order to simplify the program procedure, a computer-based, off-line programming system of the ARAC type is used.

Two macros verify the calcula-tion of the saddle contour andtransfer it to robot co-ordinates.Cuts with either a constant grooveopening or a constant weld vol-ume can be made. The operatoronly puts the following data intothe macro:

Shell diameterWall thicknessDiameter of the hole/shellintersectionAngle of the weld bevelCutting parameters (e.g. pre-heating time, gas parameters,cutting speed and so on)Off-set for position of the cut-out and the cut width.

After transferring the programfrom the off-line PC to the robotcontrol unit and putting the robotin the cutting position, a measur-ing program is started prior to theoperation.

A special measuring sensormounted at the burner tip per-forms a stepwise control of thesurface at the location of the cut-out in a test mode.

Deviations from an optimumcylindrical surface are correctedin the macro by setting an addi-

Fig 10. MMC system weld parametersetup.

Fig 11. Robot system in cutting ope-ration.



tional off-set in order to secure aconstant distance between bur-ner-tip and the metal surface oneach occasion. This is a vital func-tion for a good and reproduciblecutting result.

The cutting operation can bestarted by a special remote-con-trol unit, which has a user-friend-ly design for all the steps requiredduring cutting. The welding taperis cut in one pass, see Fig 11. Allthe gas parameters of all the fla-mes (pre-heating, stick-in andcutting flame) can be adjustedand changed at any time duringoperation using a digital gas mix-ture system.

Effect of the gantry in-stallation in productionImmediately after installation, itwas clear that the multi-purposegantry improved productivity, aswell as the quality level, very ef-fectively. After one year of suc-cessful operation with the system,it can be established that manysynergies are helping to increasethe efficiency of heavy vessel pro-duction.

The anti-creep function of thespecially-designed roller bed sys-tems produces important advan-tages during welding start-up andactual welding.

Since all the industrially manu-factured shells, rolled from plates,show deviations from an ideal cy-lindrical contour, it is impossibleto avoid creep in the vessels orvessel parts without this function.In the past, the adjustment of theconventional roller beds in orderto minimize creep required a gre-at deal of time (sometimes morethan one shift).

With the new system, the ves-sel only needs to be positioned onthe rollers and, after some rota-tions which are required for syn-chronization, its horizontal posi-tion remains stable within a rangeof ±1 mm. The special narrow de-sign of the roller beds in combi-nation with the anti-creep sensorsystem reduces the restrictions re-lating to nozzle positions to anabsolute minimum. This permitsmore flexibility in the pressurevessel design.

After a minimum of time for

calibration and parameter setting,the welding process can be start-ed directly. During welding, theoperator only supervises slag re-moval and visually checks theweld quality from the bottom(floor). Downtime is reduced toan absolute minimum – interrup-tions are normally only requiredif the filler wire (100 kg wirecoils) has to be renewed.

One of the most importantpoints is the improvement inquality, which is no longer influ-enced by the operator’s practicalexperience and knowledge.

Due to the adaptive weld fillfunctions in the ESAB ABW sys-tem, the repair rate has been re-duced dramatically in comparisonwith conventional semi-automaticSAW machines. After sufficientoperator training, only defect-freejoints have been produced.

Using the robot system to cutnozzle holes has significantly re-duced the number of workingsteps that were previously neces-sary.

It is no longer necessary tomark the cut-out contour on theshell surface. The downtime caus-ed by handling and positioningconventional mechanized cuttingmachines is avoided completely.Moreover, the effective cuttingtime has been reduced by half be-cause the cut-outs are performedin one step instead of the normaltwo (straight cut and angle cut asseparate operations).

Cutting is performed with highaccuracy when it comes to wallthicknesses of between 50 and150 mm. The maximum diameterdeviations for the cut-out are ±2 mm and the weld bevel anglediffers by no more than ±1°. Thishigh accuracy influences the fit-up of the nozzles and the follow-ing welding operation performedusing SAW nozzle welding ma-chines very positively.

Another very important pointis the human factor. Operatorsand welders are no longer ex-posed to high temperature radia-tion due to the required high pre-heating temperatures, because allthe fully-automatic operationscan be supervised from the floor.Moreover, if nozzle fit-up andnozzle welding or other opera-tions are performed from the

movable and flexible platform,the insulated floor plates protectthe fitters and welders.

The quality results producedby the fully-automatic weldingand cutting operation are not de-pendent on the operator’s practi-cal knowledge or his/her concen-tration. On the other hand, it hasbeen found to be advantageous ifexperienced SAW operators andcutters handle the system, be-cause of their “feeling” for theprocesses. Due to the user-orien-ted design of the process controlunits, only basic PC knowledge orbasic experience of CNC cuttingapplications are required.

ConclusionInstalling the new technologiesfor adaptive welding and auto-matic robotic oxy-fuel cutting atBORSIG’s heavy-duty plant hasclearly increased productivity.The high level of automation en-sures a high degree of flexibilitywith a simultaneous high level ofquality. Downtime is significantlyreduced compared with similarplants and this reduces the num-ber of hours spent on machining.

About the authorsIn 1995, Andreas Risch wasawarded a PhD at the Faculty ofMechanical/Welding Engineeringat the University of Technology inAachen. Since 1996, he has beenemployed at Deutsche BabcockBorsig AG (now Borsig GmbH),where he has been head of weld-ing engineering since 1997. In thiscapacity, he represents Borsig onevery issue relating to welding,metallurgy and materials research.He is also involved with the re-search and development of weld-ing technologies and is responsiblefor checking and monitoring sup-pliers.

Bengt Ekelöf is Senior ProductManager at Esab Welding Equip-ment AB in Sweden. He has beenwith Esab for many years and waspreviously a project engineer fo-cusing on fully-automated weldingsystems. Bengt Ekelöf was also re-sponsible for the patent for theABW system.



The objective of increas-ing machine availabilityis part of the specifica-tion for any new ma-chine under develop-ment. However, this ob-jective can only be real-ised if a range of impor-tant factors are takeninto consideration.

If the causes of machine down-time are analysed, it will soon beestablished that, apart from themachine itself, the machine oper-ator, the lack of properly trainedservice personnel and an inade-quate supply of replacement partsall affect downtime.

An increase in availability canonly be achieved by implement-ing a series of actions which takeaccount of the overall situation.

The foundations for high avail-ability are, of course, laid at themachine design stage.

Solutions that had been well-proven over a number of yearswere employed in the develop-ment of a range of medium ma-chines for the autogenous andplasma processes, as well as for anew range of laser machines. The-se solutions included the trackguidance system in the longitudi-nal direction and the latest engi-neering developments.

When selecting componentsfor both the new ranges, the em-phasis was placed on high reli-ability.

Universal, overall design con-cepts have a decisive effect onmachine availability. From themechanical design and the electri-cal system to the user interface,the ranges exhibit the same con-cepts and functions.

The kit system is designed in

such a way that individual mod-ules are used for various machinesizes, thereby minimising the vari-ation in parts for the completerange. The larger series this pro-duces does not simply result inmore cost-effective production,shorter delivery times and an im-proved supply of replacementparts. It also produces a generalimprovement in quality with alower failure rate. Reliable me-chanical construction and electri-cal components alone are not suf-ficient.

Controller technology, userinterface, machine operation andmaintenance also have a decisiveeffect on machine availability. In-correct operation, perhaps withserious consequences, and down-time can only be avoided if theoperator is in full control of hismachine.

Universal controller conceptsand operating structures for all

Fig. 1. New range of medium machines of modular design.

Increasing availabilityby Dipl.-Ing. Rainer Schäfer, Technical Manager at ESAB-Hancock, Germany



cutting technologies, togetherwith standardised and modularmachine-interface programming,facilitate worldwide service andtraining for our machines. Thecontinuation of this concept, andin particular the integration oftechnology-aided measures, suchas the automatic setting of pro-cess parameters using databasesor the integration of difficult pro-cess cycles with the controller, en-hance the user-friendliness of ourmachines, which is in turn reflect-ed in reduced downtime.

The use of these methods en-ables us noticeably to improvethe already high availability ofour machines.

This task will also be the sub-ject of on-going development andwill be included in the specifica-tion for each machine.

The market call for increasing-

ly narrow tolerances for cut parts,pledges of guaranteed quality andthe employment of high qualitycutting technology with lasers andwater jets make it necessary toaddress the quality requirementsfor machine tools.

Due to the high geometricalflexibility, laser-beam and water-jet cutting are the preferredmethods for the manufacture ofworkpieces with complicated sha-pes in intermediate quantitiesdown to the production of singleparts. The increasing demand inthis market segment can be large-ly traced to these considerationsand has led to a three- or five-axis module being needed forthese tools as a basic machine, de-pending on requirements. ESAB-HANCOCK has also respondedto this challenge and has broughta five-axis portal machine onto

the market, with a high-perfor-mance CO2 laser system.

Machine networking and inte-gration into the material flow at aproduction facility in economical-ly viable configurations representa market challenge for machinesand system suppliers.

ESAB-HANCOCK has dem-onstrated that these solutions arepossible. In 1996, five-axis plasmaand autogenous profile produc-tion centres were incorporatedinto the production facility at aKorean shipyard.

“Ready for the newworld of automation”It is wise not to lose sight of thisobjective. The automation of pro-duction cells and their integrationinto the production organisationleads to more and more complexnetworked systems.

In automation engineering,separate worlds are coming to-gether to form integral systems.Specialised technologies, such asPLCs and CNCs, mix with classi-cal data processing. Informationtechnology offers numerous waysforward. New and combined sys-tems offer improved rationalisa-tion potential, but they requirethorough personnel training.Relying on “learning by doing”results in acceptance problemsand start-up difficulties. The ad-vantages of these systems may in-clude:

Self-monitoring of the ma-chineDisplay of servicing pointsAutomatic process monitor-ingDetection of process errors,introduction of correctionroutines and so on

Fig. 2. Universal controller family with the same user guidance system.

Fig. 3. Setting process parameters on the NCE controller family.



Human interaction during production is reduced to a minimumInformation technology will notsimply influence complex systemsin the development of cutting ma-chines. “Stand-alone” systemsdown to the small-machine levelwill also be affected by informa-tion technology, offering the userscope for rationalisation. Devel-opments here are oriented to-wards process data optimisation,process monitoring and the earlydetection of tool wear. Thismakes the best use of machineperformance and guarantees uni-form production quality.

ESAB-HANCOCK has alsoset a benchmark here and pio-neered developments in this di-rection. Autogenous process mon-itoring systems for small and me-dium machines are our contribu-tion. The advantages of these ma-chines for the user are obvious.

The machines can be operatedin part without supervision andwithout the risk of producingscrap when a process error oc-curs.

More and more companies aredemanding productivity increasesand higher technical availabilityin their machines. A significantmarket requirement in this con-nection is preventive mainte-nance.

Here, too, information technol-ogy is offering us new ways toprepare cutting machines to meetthe market challenge. ESAB-HANCOCK is already offeringdiagnostic systems which supplydata for process monitoring, aswell as providing a foundation forfurther developments in preven-tive maintenance.

Modern CNC controllers fromESAB-HANCOCK contain thelatest in information technologywith DNC (Direct NumericalControl) interfaces ensuring thereliable data transfer of cuttingprograms from Windows hostcomputers to the CNC.

Modern communication tech-niques enable the visualisationand logging of current machinestatus and processing states viafeedback on DDE (DynamicData Exchange) servers to WIN-DOWS (in real time, the Micro-

Fig. 4. Laser cutting system with an automatic workpiece-changing table; pallet size 3m212m.

Fig. 5. CNC-controlled multi-axialhead for laser cutting.

Fig. 6. Burr-free cuts with the highestcut quality, without reworking the cutedges.



Fig. 7. Machine integration.

Fig. 8. Fully automatic submerged plasma cutting system with automatic loadingand unloading system.

Fig. 9. An easy-to-operate interface for software and hardware components enablesefficient data transfer between application components.

soft communications standard forprocess and production automa-tion enables easy operation andintegration with existing commu-nication networks).

Some examples showing thescope for rationalisation for theoperator of these systems are giv-en below.

The DDE report client moni-tors the DDE server and writesthe accumulated times, distancesand, where applicable, fault num-bers in an ACCESS database.This means not only that a stan-dardised output from the reportgenerator is possible, but also thatusers who have MS-ACCESSavailable can use the data for oth-er purposes and for their own ap-plications.

Concluding remarksThe market is demanding increas-ingly precise components withhigh quality cutting results, alongwith higher machine availability.These features constitute the mo-tivation for innovation amongmachine manufacturers and arehelping to move thermal cuttingcloser to the central point of pro-duction.

With modern cutting systems,it is possible to incorporate oper-ations which are normally carriedout by drilling and milling intothe cutting systems. The markingand surface cleaning processesare also being integrated in cut-ting systems. Depending on theprofile of machining require-



Fig. 12. The “Report Generator” pro-duces status reports with the followinginformation from the data gathered ina database:Date and timeProgram numberThe following from three processes:=> Number of tool activations => Processing times=> Path distances travelledFast travel (distance and time)Overall program running timeFault log

Fig. 10. The most varied connection methods to controllers are possible. No matter serial, telephone or Ethernet connections areused, the data is transferred reliably.

Fig. 11. The remote monitoring of machines enables an overview to be obtained ofthe machine status and quick interventions to be made when failures occur.

About the author

Rainer Schäfer graduated from uni-versity in 1984 with a master's de-gree in mechanical engineering.After having worked in areas in-cluding research and product devel-opment at Atlantik and Heyligen-stadt, he joined ESAB-Hancock in1995. He now has the title of Tech-nical Director and is responsible forR&FD mechanics and electronics.

ments, it is possible to unify ma-chine investment and to cutworkpiece idle times dramaticallyso that the cutting centre be-comes a profitable productiontool.



In Svetsaren 1-2/96, wededicated an article tosubmerged arc weldingwith special cored wiresdeveloped by ESAB,in which we discussedindustrial applicationsfrom Finland where themethod was pioneered.In the meantime, thetechnique has maturedand has been adoptedby fabricators acrossEurope. They benefitfrom productivity ad-vantages resulting from

higher deposition rates,as well as the avoidanceof plate edge bevelling,a smaller weld volumeand a reduced numberof layers. Before discuss-

ing industrial applica-tions from Germany, theNetherlands and theUnited Kingdom, theauthors re-introduce thetheme.

Fabricators pleased with increased submerged arc

productivity from cored wiresImproved welding technique has now matured

By Martin Gehring, ESAB GmbH, Solingen, and Shaun Studholme, ESAB UK Ltd.

Table 1: ESAB OK Tubrod cored wires for the submerged arc welding of normal-temperature and low-temperature steels.

Metal-cored AWSOK Tubrod 14.00S/OK Flux 10.71 CMn F7A2-EC1

Basic flux-coredOK Tubrod 15.00S/OK Flux 10.71 CMn F7A4-EC1OK Tubrod 15.24S/OK Flux 10.62 1Ni F8A6-EG-GOK Tubrod 15.25S/OK Flux 10.62 2.5Ni F7A8-ECNi2-Ni2



IntroductionSubmerged arc welding (SAW) iswidely recognised as a very pro-ductive welding process, offeringthe following advantages:

a high deposition rate due tothe use of high welding cur-rentsa high travel speeda reduced incidence of coldlaps and slag inclusionsa smooth weld surface withgood tie-inno spatter, no fumes

The productivity of SAW isfurther optimised with variantssuch as twin arc, tandem andmetal-powder addition, but thesemethods normally require large-scale investments in equipment.

The productivity of single-wireSAW can, however, be increasedsignificantly by substituting speci-ally-developed cored wires forsolid wires. In the majority of ap-plications, this requires no addi-tional financial expenditure as theexisting equipment is adequate.

Product rangeThe range of ESAB OK Tubrodcored wires for submerged arcwelding is reviewed in Table 1.

Both OK Tubrod 14.00S and15.00S are Grade 3 approved, incombination with OK Flux 10.71,by the major ship classificationsocieties, as well as TÜV and DB.

OK Tubrod 15.24S and 15.25Sare designed for low-temperatureapplications in offshore fabrica-tion, for example.They are usedin combination with OK Flux10.62.

Both OK Flux 10.71 and 10.62are basic agglomerated fluxes.

Single Wire Deposition Rate ComparisonOK Tubrod 15.00S + OK Flux 10.71

OK Autrod 12.20 (S2) + OK Flux 10.71

20

18

16

14

12

10

8

6

4

2

0

300

358

400

450

500

550

600

650

700

750

800

850

900

950

1000

kg/h

r

Current (A)

15.00S 2.4mm15.00S 3mm15.00S 4mm12.20 2.4mm12.20 3mm12.20 4mm

Figure 1. Deposition rate increase obtainable with cored wires for submerged arcwelding.

Figure 3. Fabrication of a cylinder forthe wood industry. Tube halves areattached to the inside of the cylinderwith the cored wire/flux combinationESAB OK Tubrod 14.00S/OK Flux10.81.

Figure 2. A single pass, double-sided I-joint made in 17 mm plate at 60 cm/min travel speed with the cored wire flux combina-tion ESAB OK Tubrod 15.00S/ESAB OK Flux 10.71. Plates were not bevelled before welding. Middle: Meyer Werft Papenburg.Right: SSW Fähr- und Spezialschiffbau GmbH.



Advantages of coredwireThe deposition rate of coredwires exceeds that of solid wiresof the same diameter by up to20% when welded with the samecurrent (Figure 1).

The resistance heating is high-er with cored wires, because thecurrent-conducting cross-sectionis concentrated in the sheath. Thehigher current density results in ahigher melt-off rate and therebya higher deposition rate. This ef-fect is even more pronouncedwith SAW than with gas-shieldedflux-cored arc welding, becausemuch higher welding currents areused.

In all the applications dis-cussed below, fabricators benefitdirectly from improved weldingeconomy due to an increaseddeposition rate converted to high-er travel speed.

Additional advantages, such asa reduction in weld volume, fewerbeads, the avoidance of plateedge bevelling, plus a wide rangeof welding currents which can be

used with the same diameter, aremore dependent on the specificapplication.

Industrial applicationsMeyer Werft, Papenburg & SSWFähr- und SpezialschiffbauGmbH, Bremerhafen, GermanyBoth yards, Meyer Papenburgand SSW (the former SeebeckWerft), changed from solid wiresto cored wires as the consumablefor the double-sided submergedarc welding of butt joints in platefields. Both use the same coredwire/flux combination OK Tubrod15.00S (4.0 mm)/OK Flux 10.71.In both cases, the single-headwelding of 17 mm thick plate isperformed.

In comparison with the previ-ous application with solid wire,the travel speed for a single-layer,double-sided weld went up to 60cm/min (see Figure 2).

In addition, it was no longernecessary to bevel the plate edges

Figure 4. Three hydraulic cylindersfabricated by Hydrowa installed on aNorwegian oil rig. The stroke of thecylinders is as high as 18 m.

Figure 5. Welding of a cylinder’s circumferential weld with OK Flux 10.71 and OK Tubrod 15.00S.

before welding, because of the se-cure penetration of the coredwire. Normally, the yards wouldgive the joint a Y-preparation.The avoidance of bevelling wascrucial to both yards, as it ac-counts for major cost savings.

KRAFFT-Walzen, Düren,GermanyKRAFFT fabricates rollers andcylinders for paper and textileplants. One of the welding jobsconsists of attaching tube halvesto the inside of rollers (see Figure3). The rollers are 2.9 m widewith a diameter of 1.5 m andhave a wall thickness of 5 mm.This was previously done usingSAW with solid wire.

After changing to OK Tubrod14.00S, the travel speed for weld-ing these fillet welds was in-creased by more than 100%, as aresult of the higher depositionrate and the use of a smaller thro-at size, which was made possibleby more secure penetration.



I U v HI(A) (V) (mm/min) (KJ/mm)

OK Flux 10.62/solid wire (1Ni/0.25Mo) 650 30 410 2.8OK Flux 10.62/OK Tubrod 15.24S (I) 650 30 410 2.8OK Flux 10.62/OK Tubrod 15.24S (II) 750 32 580 2.5

Procedure test results

Solid wire OK Tubrod 15.24S(I) (II)

No. of runs 25 20 25Arc time (min.) 35 29 (–21%) 27 (–27%)

Yield strength (MPa) 581 510 517Tensile strength (MPa) 646 588 587CVN (J) –40 69 159 166

–50 43 147 143

The total welding costs werereduced by 45%.

Hydrowa, Eindhoven, the NetherlandsHydrowa B.V. specialises in thedesign and fabrication of hydraul-ic cylinders with a length of up to22 m for a variety of industries in-cluding offshore, dredging, auto-motive and food (Fig. 4).

Recently, the company equip-ped its workshop with a newESAB submerged arc weldingstation consisting of a movableMKR 300 column and boom, astationary ESAB A2 MinimasterSAW automatic welder, an LAE1000 power source and twoESAB 10RTN manipulators.

With the new station, Hydrowaadopted submerged arc weldingwith cored wires to weld the cir-cumferential joints of hydrauliccylinders (Fig. 5). The automaticSAW equipment and the powersource are selected to handle cyl-inders with a diameter of 15 to400 cm . The SAW machine has amaximum current of 800A, feed-ing solid as well as cored wireswith a diameter of up to 4 mm.

The cored wire/flux combina-tion OK Tubrod 15.00S/OK Flux10.71, produces productivity ad-vantages over submerged arcwelding with solid wires.

First of all, OK Tubrod 15.00Swith a diameter of 3.0 mm can beapplied directly over a TIG-wel-ded root run without burning

through, because a welding cur-rent as low as 200A can be cho-sen, producing reduced penetra-tion and an excellent tie-in. Forthe same application, SAW withsolid wire requires a second layerwith GMAW before SAW can beused, because a 3 mm size solidwire requires a welding current ofat least 300A.

In addition, filling runs can beperformed with a welding currentof up to 600A with the same wiresize. In this case, Hydrowa bene-fits fully from the increased depo-sition rate from cored wire whichis converted to a travel speed of60–80 cm/min. As a 3 mm solidwire would produce 40–60 cm/min., there is a substantial im-provement in productivity.

Kværner Oil & Gas Limited,ScotlandWelding economy and integrityfor offshore fabrication was test-ed using a welding procedurequalification for OK Tubrod15.24S/OK Flux 10.62 in compari-son with an established proce-dure for solid wire SAW. Thewelding procedure involved a 1/2V-joint in 40 mm thick, grade50D plate.

Tests were done at the sameparameters as the existing proce-dure, but also at increased wel-ding current and travel speed,according to table 2.

Tested at the same parameters,thicker beads are deposited

40 mm45º

50D

1

SMAW root & hot passSolid & cored wire fill

Table 2. OK Tubrod 15.24S/OK Flux 10.62.Welding procedure qualification for offshore fabrication compared with SAW solid wire.

About the authorsMartin Gehring graduated in 1993as a Dipl.Ing. from the universityin Aachen. Since 1994, he has beenproduct manager for consumablesat Esab GmbH in Solingen in Ger-many and focuses primarily on thedesign of customer-specific sys-tems within SAW and on weldingusing solid wire and shielding gas.

Shaun Studholme, Product Manag-er, Cored Wires in Esab Group(UK) Ltd. He is responsible forcored wire marketing and is basedat Waltham Cross, UK.

because of the increased deposi-tion rate. The mechanical proper-ties show that this does not leadto loss of low-temperature tough-ness, whereas an arc time reduc-tion of 21% is obtained.

At a higher welding current,while selecting a travel speedgiving the required bead thick-ness, arc time is reduced by 27%.

Additional tests prove thatmechanical properties remainsatisfactory after stress relieving.Moreover, the combination OKFlux 10.62/OK Tubrod 15.24S isCTOD-tested, making it a veryinteresting option for more pro-ductive submerged arc welding inoffshore fabrication.



An important questionfor the welding and cut-ting industry relates tolikely developments be-yond the year 2000.Some major trends andconclusions are alreadyclear.

More cost-effective produc-tion is still the single most im-portant issue.Other strong driving forcesare quality assurance and glo-bal environmental protection.System approach. Cost versusthe performance and reliabil-ity of the entire productionchain. A low cost for individu-al parts does not automatical-ly lead to the lowest cost forthe system. Instead, it mightlead to sub-optimisation.A system is no stronger thanits weakest link. This empha-sises the importance of indi-vidual parts of the system.They could be gases. Theycould be filler metals. Theycould be power sources and soon. Improvements to individu-al parts must lead to the en-hancement of the perfor-mance and reliability of thesystem. If the performance ofindividual parts is too good,however, this could lead tounnecessary costs. “Fitness forpurpose” is therefore a keyexpression.Stronger focus on the end-user will increase the call foruser-friendly systems, as wellas the requirements relatingto personal health and safety.Increased use of new or im-proved materials. This also in-cludes surface-treated materi-

als. Improvements could in-clude lower weight, improvedmechanical properties or cor-rosion-resistance properties.

This will lead to suppliers ofequipment and different consum-ables more frequently offering in-dividual customer solutions. Sohow will gases and gas applica-tion know-how help to meet cus-tomer demands in the future?

System approachThere are many considerations acompany must take into accountwhen it comes to sharpening itscompetitive edge. The functionsand design of the product, itsquality, appearance, as well as itsimpact on the environment, haveto be weighed up against the cost.As if that were not be enough,the working environment, health

and safety and job satisfactionmust also be included in thepoints for consideration. The finalproduct and its features are in fo-cus, rather than the result of indi-vidual steps in the manufacturingprocess. This is a system or mod-ule approach. The result of oneoperation may strongly influencethe cost of performing a subse-quent operation. For example,high cutting quality may facilitatewelding. So, even if the cost of thecutting increases, the cost of thewelding may be reduced and thetotal cost of cutting and weldingcould be lowered. In a similarmanner, a system approach canbe broken down into a specificoperation. A welding process, forexample, should be optimisedfrom both cost and feature as-pects. Individual parts of the

70

444

18

56

644

18

12 Cost saving

Labour

Shielding gasFiller materialElectricity, water etc.

Base material etc.

Before change ofshielding gas

After change ofshielding gas

Figure 1. Example of how an increase in productivity (reduction in labour cost)produces a cost saving, even if the cost of the shielding gas increases.

Welding and cutting beyond the year 2000

by Kjell-Arne Persson, AGA AB, Sweden



welding system, like the shieldinggas, may have a critical effect onthe result, but they may have aminor effect on the cost. For ex-ample, if productivity can be in-creased by 20% using a shieldinggas that costs 50% more, the totaloperational cost could still besubstantially lower. The simplereason for this is that the cost ofthe gas only represents about 3%of the total cost. See Figure 1.

Optimised customer so-lution by the intelligentuse of industrial gases Knowledge of gases and their ef-fect on the cutting or weldingprocess is still limited among us-ers. In welding, knowledge ofshielding gases is often restrictedto the function of preventing airmaking contact with the arc andheated metal. This is one functionof many. The shielding gas alsohelps to produce good arc igni-tion, good arc stability for lowspatter levels, good and consistentpenetration for reliable results,good mechanical properties andcorrosion resistance by control-ling the oxidation rate and pick-up of carbon and nitrogen, for ex-ample, high-quality and consistentweld surface appearance, as wellas low fume and gas emissions.See Figure 2.

The influence of gases is not al-ways simple. In fact, in most cas-es, it is somewhat complicated.For example, the oxidising com-ponent (carbon dioxide and/oroxygen) that exists in someshielding gases is necessary forarc stabilisation. The most suit-able amount of oxidising compo-nent differs, however, for differ-ent materials. The MAG weldingof unalloyed or low-alloyed steelsrequires more oxidising compo-nent than the welding of stainlesssteels. In the MIG welding of alu-minium, no oxidising componentat all is required for arc stabilisa-tion. An unnecessarily high levelof oxidising component, on theother hand, gives rise to unwant-ed oxidation. This could involvesurface oxides but also oxide in-clusions. A balance must there-fore be struck between enoughoxidising component for arcstability and the lowest possible

oxidising component to avoid un-wanted oxidation. In fact, the ox-idising component also has an ef-fect on the surface tension whichin turn affects the possible weld-ing speed and the weld appear-ance. It also has an effect on theburn-off rate of alloying elementswhich will influence the mechani-cal properties.As can be seen, theinfluence of the shielding gas isvery complicated.Other gas-rela-ted examples include:

Addition of hydrogen to theshielding gas. In the TIG weld-ing of austenitic stainlesssteels, this increases penetra-tion and welding speed andthereby productivity. On theother hand, some materialsare sensitive to hydrogen be-cause it can be harmful andcause pore formation andeven cracking.Nitrogen additions can securecorrosion resistance in theTIG welding of duplex stain-less steels. In other materials,this does not produce any ad-vantages and might even beharmful by causing porosity orchanging material properties.The purity level of the cuttingoxygen has a strong effect oncutting speed in oxy-fuel cut-ting. High purity promoteshigh cutting speeds.

These are a few exampleswhich show that the behaviour ofthe system often depends on the

behaviour of its constituent partsbut also on the interaction bet-ween the different constituentparts. It is not only the propertiesof the shielding gas or the fillermaterial or the base material orthe power source alone which areimportant, it is the interactionbetween them that determinesthe performance of the system. Tocomplicate things still further, theperformance of the system de-pends to a very large extent onthe parameter settings. The opti-mum performance can only beobtained if all the information isknown — that is the properties ofthe individual parts, their interac-tion and how they depend on pa-rameter settings. One good exam-ple of this is RAPID PROCESS-ING™. It has made it possible toboost productivity substantiallywithout sacrificing penetration,reliability or weld appearance.

User-friendlinessThe working conditions of weld-ers and operators are often de-manding, hard, hot, and dirty. Ac-tion or equipment that will helpwelders and operators in theirwork, to facilitate their work, toimprove their health and safetyare therefore attracting more andmore attention. They can rangefrom the use of more lightweightequipment for easier and moreergonomic handling, or equip-ment that provides improved reli-

Figure 2. Areas in which the shielding gas has an effect on the welding result.



ability by producing fewer irritat-ing interruptions to equipmentwith built-in knowledge andequipment to improve health andsafety.

More gas-related examples in-clude:

Gas supply systems. A centralgas supply system reduces theneed to move heavy cylinders.It also increases safety. In caseof fire, no or at least fewer cyl-inders have to be moved awayto safer areas.Shielding gases that improvethe working environment byreducing fume and gas emis-sion.Gases that make it easier toset suitable process parame-ters and help to produce con-sistent behaviour.Gas delivery security. Deliveryof a gas to a customer at shortnotice or within a specifiedtime limit. The distributionform, compressed gas in cylin-ders or liquids, is less impor-tant for the customer as longas the gas is there and has theright quality. The customerpays for a function rather thana component.Early warning signals of gasleakage. Leakage that couldlead to harmful situations.Information booklets that areinstructive, like the “Factsabout” information series.

Global environmentThe impact on the global envi-ronment of gases in welding andcutting is mainly a result of theproduction and transportation ofthe gases. A gas like argon, whichis used in shielding gases, comesfrom the air and returns to the airunchanged. The energy requiredto separate the small amount of argon that exists in the air (< 1%), however, has a negativeimpact on the environment, asdoes the energy needed to trans-port it. The amount of energy thatis needed to separate air is mini-mised in the new and large air-separation plants. Fewer, largeplants, however, result in longertransportation. The transportationof liquid argon is comparativelylow in terms of energy consump-tion when compared with the

transportation of heavy cylinderscontaining compressed gas. Ef-forts are therefore being made tominimise energy consumption inair-separation plants, to use liquidtransportation as far as possibleand to locate filling stations sothat the liquid argon can be putinto cylinders as close to the cus-tomer as possible. Carbon dioxideis extracted from waste products,mainly from fermentation pro-cesses. It is therefore used “a sec-ond” time before it is spread inthe air.

Some examples of productsand applications which alreadymeet future requirements

MISON® shielding gases There are now a variety of MISON® shielding gases for dif-ferent welding processes, differ-ent materials and different pur-poses. Gases that can improveproductivity, contribute to lowspatter formation, produce con-sistent penetration, low surfaceslag formation and a good surfaceappearance, as well as improvingthe welders’ environment by re-ducing fume and ozone forma-tion.

RAPID PROCESSING™Know-how packages that boostproductivity mainly by increasingthe deposition rate. No or onlysmall investments in equipmentare required. Today there arepackages for welding unalloyedand low-alloyed steels, for weld-ing coated steels, for weldingstainless steels and for welding al-uminium.

New shielding gas mixturesNew shielding gas mixtures thatoptimise the MIG/MAG, TIG andlaser welding of “new” materials.

Materials that are finding in-creasing industrial use.

Some examples of “new” mate-rials are duplex stainless steels,martensitic or super-martensiticsteels and aluminium alloys.

AGA LASERLINE™ A complete range of gases andgas supply systems that producehigh performance in laser cuttingand in laser welding.

ODOROX®

Oxygen with a small additive thatproduces an unpleasant smell.This gives an early warning ofoxygen leakage. Fires in an at-mosphere of leaking oxygen arevery difficult to extinguish andcan lead to serious accidents. Ear-ly warning signals make it pos-sible to act before harmful situa-tions occur.

ConclusionThere will probably not be anydramatic changes in welding andcutting in the near future. When itcomes to industrial gases, the gas-es and gas application know-howwill be important in welding andcutting beyond the year 2000.This will probably be even moreimportant than it is at present,due to other improvements inbase metals, filler materials, pow-er sources, lasers and mechanisa-tion equipment. In particular,application knowledge or aknowledge of how to use gases inthe optimum manner will behighlighted still further in the future.

ODOROX® and MISON® areregistered trademarks

About the authorKjell-Arne Persson is R&D Man-ager for Manufacturing Industry.He graduated with an MSc in tech-nical physics from the Royal Insti-tute of Technology in Stockholmand has been working at AGA sin-ce 1980. He is involved in researchand development, first and fore-most within the fields of weldingand cutting.



This article gives a gen-eral overview of thetechnological develop-ment of semi-automaticwelding machines. Whenit comes to the state ofthe art, some modernhigh-tech equipment isused to exemplify thelatest technology.

Welding power sources have beengreatly influenced by the rapiddevelopments that have takenplace when it comes to powerelectronic components. The per-formance of the equipment is alsoa result of new control and com-munication technology.

Power sourcesThe main purpose of the powersource is to supply the systemwith suitable electric power. Fur-thermore, the performance of thepower source is of vital impor-tance to the welding process —the ignition of the arc, the stabil-ity of the transfer of the meltedelectrode material and theamount of spatter that is generat-ed. For this purpose, it is impor-tant that the static and dynamiccharacteristics of the power sour-ce are optimised for the weldingprocess.

Different types of powersourceStep-adjusted welding rectifierThis is the traditional and still themost common power source formanual MIG/MAG welding. Thevoltage setting is adjusted by con-necting a varying number ofwindings on the primary side ofthe transformer. The dynamic

Modern MIG welding powersources

by professor Klas Weman, ESAB Welding Equipment AB, Laxå, Sweden

Fig. 1. The new ESAB Aristo 320 and 450 MIG welding equipment.

Fig. 2. Static characteristics of a step-controlled MIG/MAG-welding power source.



properties are set using an induc-tor. Fig. 2 shows the static charac-teristics of a step-controlled weld-ing power source. It is importantthat there are a sufficient numberof voltage steps and that they areclose enough to enable the weld-er always to find the optimal volt-age setting.

Thyristor-controlled welding rectifier If the diodes in the secondaryrectifier are replaced by thyris-tors, it is possible to control theoutput voltage electronically. Un-fortunately, the speed of regula-tion is limited to the frequency ofthe mains and the dynamic prop-erties must also be mainly con-trolled by an inductor.

Inverter power source In the inverter, the mains ACvoltage is rectified and transistorsare used to produce a higher fre-quency in the range of 20-100kHz. This high frequency makes itpossible to reduce the size of thetransformer. The weight and sizeof the power source will thus bereduced and the efficiency will beincreased. Another major advan-tage is that a rapid electronic con-trol can be used to control boththe static and dynamic propertiesof the power source.

Traditional and newtechnologyElectronically-controlled behavi-

our is interesting. Earlier types ofpower source were designed andbuilt to be optimised for one ap-plication or welding method. Thenew technology makes it possibleto use the power source for dif-ferent methods and to optimisethe performance for each applica-tion. The function of the machinecan be divided into two indepen-dent parts — the electronic con-trol and the power package.

The welding properties are nolonger determined by the designof the machine but can be con-trolled electronically or by a com-puter. The high operating fre-quency of the inverter powersource increases the controlspeed and makes it possible toachieve optimal properties. It isalso possible to use pulsed arcwelding where short pulses cutoff every single droplet from theelectrode. This results in quitenew opportunities when weldingin aluminium and stainless steel,for example. The freedom to con-trol the machine in different waysmakes it possible to use it for dif-ferent welding methods, but it canalso be optimised for each indi-vidual choice of electrode diame-ter, shielding gas and materialquality.

Computer technologyAs in many other technical areas,the use of computers and com-puter controls is developing whenit comes to welding applications.The more sophisticated theequipment, the more developedthe technology — like that usedin advanced inverter powersources and control equipmentfor mechanised welding, for ex-ample. Even straightforward stan-dard equipment like power sourc-es and feed units can contain mi-crocomputer controls, somethingwhich can in fact be justified fromboth an economical and servicereliability point of view.

Adjusting the equipmentCommunication with the usercan be facilitated — but perhapsalso sometimes made more diffi-cult — by new technology. Itshould be a challenge for themanufacturers of welding equip-ment to create a simple and cle-

arly-defined user interface, whichstill allows all the necessary set-tings to be made.

Control of the weldingprocessIn order to affect the stability ofthe arc, inverters include facilitiesfor controlling the welding pro-cess. The welding properties arevery important to the welder andhis acceptance of the power sour-ce. As the power source itselfdoes not affect the properties, it is possible to have full control ofthe process by to have full controlof the process by the software.These programs are then inde-pendent of the power supply thatis used.

Communication betweenthe units As a result of developments, mi-crocomputers are currently usedin many different system compo-nents, such as power sources, wirefeed units and control boxes. Onepowerful means of communica-tion between these units is theuse of a standard communicationbus. ESAB have chosen the CANbus for this purpose. CAN standsfor Controller Area Network andwas originally developed for theautomotive industry by Boschand Intel.

In robot welding, the CAN busis used for communication bet-ween the welding equipment andthe robot control unit.

Improved immunity tointerferenceIn comparison with the analoguetechnique, the digital technique isnot sensitive to variations causedby voltage drops or other distur-bances. This guarantees that thevalues are reliable and are exactlythe same from one occasion tothe next. The CAN bus communi-cation between the different partsof the machine, together with animproved mechanical and electri-cal design (zone system), has alsoreduced the sensitivity to electri-cal noise. The CAN bus has theintelligence to re-transmit a mes-sage if it has not arrived in thecorrect way.

Fig. 3. Control box for the Aristo2000 welding machine. The slotfor the PC card is on the top left-hand side.



Control boxThe control box, see Fig. 3, is usedfor all man-machine communica-tion:

Setting the welding parame-tersChanging the welding methodMeasuring welding dataStoring parameter settings inthe memory

When used for MIG/MAGwelding, information about wiretype, electrode diameter and gasmixture is specified and the weld-ing properties are optimised forthis specific combination. Thevoltage is pre-set according to abuilt-in relationship with the wirefeed speed, a so-called synergyline. There is a database withmore than 175 synergy lines. Allyou need to do is enter a wirefeed speed. A preliminary voltageis then automatically selected bythe system.

PCMCIA cardA memory PC card (PCMCIA) isused to upgrade the software. Thecard can also be connected to aPC and be used for storing the library containing the user’s set-ting data.

The card can store all the weld-ing data that can be moved frommachine to machine, therebymaintaining weld quality.

If several machines are pro-grammed with welding data from

the same card, the weld result willbe exactly the same. This is idealif several machines are used forwelding similar objects.

MonitoringThe CAN bus can also be used tomonitor the welding process viaan external PC. In the Weldoc™WMS 4000 computer program,the user can supervise the weld-ing process and enter alarm lim-its. The system is also used forlogging and documentation andcan be included in the quality

control system at a company. Thiscomplies with the internationalquality standard ISO 9000/EN729.

ConclusionThe technological developmentof electronics and computer tech-nology is rapid and is having amajor influence on the develop-ment of welding equipment. Theinformation given here can beseen as a teaser about what mod-ern power source technology hasto offer.

Fig. 4. Screen appearance when using the WMS 4000 program to monitor the wel-ding process.

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Welding and cutting in the new millennium - esab.de · submerged arc welding, gas-tung-sten arc...

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Transcript of Welding and cutting in the new millennium - esab.de · submerged arc welding, gas-tung-sten arc...