WELDING &CUTTING PROCESS

WHAT WE ARE GOING TO DISCUSS

Welding

Welding process

Arc Welding

Gas Welding

Resistance Welding

Cutting

Cutting process

Thermal & Metallurgical consideration in Welding & Cutting

WELDING

• Welding is a process of joining two metal pieces as a result of significant diffusion of the atoms of the welded pieces into the joint (weld) region. Welding is carried out by heating the joined pieces to melting point and fusing them together (with or without filler material) or by applying pressure to the pieces in cold or heated state.

ADVANTAGES OF WELDING Strong and tight joining; Cost effectiveness; Simplicity of welded structures design; Welding processes may be mechanized and

automated.DISADVANTAGES OF WELDING

Internal stresses, distortions and changes of micro-structure in the weld region;

Harmful effects: light, ultra violate radiation, fumes, high temperature.

WELDING

APPLICATIONS OF WELDING Buildings and bridges structures; Automotive, ship and aircraft constructions; Pipe lines; Tanks and vessels; Railroads; Machinery elements.

WELDING

WELDING PROCESSES

• Carbon Arc Welding;• Shielded Metal Arc Welding (SMAW);• Submerged Arc Welding (SAW);• Metal Inert Gas Welding (MIG, GMAW);• Tungsten Inert Gas Arc Welding (TIG, GTAW);• Electro slag Welding (ESW);• Plasma Arc Welding (PAW);

Arc welding

• Spot Welding (RSW);• Flash Welding (FW); • Resistance Butt Welding (UW) ;• Seam Welding (RSEW);

Resistance Welding (RW);

• Oxyacetylene Welding (OAW);• Ox hydrogen Welding (OHW);• Pressure Gas Welding (PGW);

Gas Welding (GW);

• Forge Welding (FOW);• Cold Welding (CW);• Friction Welding (FRW);• Explosive Welding (EXW);• Diffusion Welding (DFW);• Ultrasonic Welding (USW);

Solid State Welding (SSW);

Thermit Welding (TW);

Electron Beam Welding (EBW);

Laser Welding (LW).

WELDING PROCESSES

ARC WELDING• Arc welding is a welding process, in which heat is

generated by an electric arc struck between an electrode and the work piece. Electric arc is luminous electrical discharge between two electrodes through ionized gas.

Any arc welding method is based on an electric circuit consisting of the following parts:

• Power supply (AC or DC);• Welding electrode;• Work piece;• Welding leads (electric cables) connecting the electrode

and work piece to the power supply.

ARC WELDING

• When a long join is required the arc is moved along the joint line. The front edge of the weld pool melts the welded surfaces when the rear edge of the weld pool solidifies forming the joint.

• When a filler metal is required for better bonding, filling rod (wire) is used either as outside material fed to the arc region or as consumable welding electrode, which melts and fills the weld pool. Chemical compositions of filler metal is similar to that of work piece.

• Molten metal in the weld pool is chemically active and it reacts with the surrounding atmosphere. As a result weld may be contaminated by oxide and nitride inclusions deteriorating its mechanical properties. Neutral shielding gases (argon, helium) and/or shielding fluxes are used for protection of the weld pool from atmospheric contamination. Shields are supplied to the weld zone in form of a flux coating of the electrode or in other forms

ARC WELDING

• Types of weld joints are shown in the figure:

ARC WELDING

• Carbon Arc Welding;• Shielded Metal Arc Welding (SMAW);• Submerged Arc Welding (SAW);• Metal Inert Gas Welding (MIG, GMAW);• Tungsten Inert Gas Arc Welding (TIG, GTAW);• Electro slag Welding (ESW);• Plasma Arc Welding (PAW);

METHODS OF ARC WELDING

CARBON ARC WELDING (CAW) Carbon Arc Welding (CAW) is a welding process, in

which heat is generated by an electric arc struck between an carbon electrode and the work piece. The arc heats and melts the work pieces edges, forming a joint.Carbon arc welding is the oldest welding process.If required, filler rod may be used in Carbon Arc Welding. End of the rod is held in the arc zone. The molten rod material is supplied to the weld pool. Shields (neutral gas, flux) may be used for weld pool protection depending on type of welded metal.

METHODS OF ARC WELDING

METHODS OF ARC WELDING

SHIELDED METAL ARC WELDING (Stick welding, Manual metal arc welding)

• Shielded metal arc welding uses a metallic consumable electrode of a proper composition for generating arc between itself and the parent work piece. The molten electrode metal fills the weld gap and joins the work pieces.The electrodes are coated with a shielding flux of a suitable composition. The flux melts together with the electrode metallic core, forming a gas and a slag, shielding the arc and the weld pool. The flux cleans the metal surface, supplies some alloying elements to the weld, protects the molten metal from oxidation and stabilizes the arc. The slag is removed after Solidification.

• This is the most popular welding process capable to produce a great variety of welds.

METHODS OF ARC WELDING

METHODS OF ARC WELDING

SUBMERGED ARC WELDINGSubmerged Arc Welding is a welding process, which utilizes a bare consumable metallic electrode producing an arc between itself and the work piece within a granular shielding flux applied around the weld.The arc heats and melts both the work pieces edges and the electrode wire. The molten electrode material is supplied to the surfaces of the welded pieces, fills the weld pool and joins the work pieces.Since the electrode is submerged into the flux, the arc is invisible. The flux is partially melts and forms a slag protecting the weld pool from oxidation and other atmospheric contaminations.

METHODS OF ARC WELDING

METHODS OF ARC WELDING

METAL INERT GAS WELDING (Gas Metal Arc Welding)

• Metal Inert Gas Welding is a arc welding process, in which the weld is shielded by an external gas (Argon, helium, CO2, argon + Oxygen or other gas mixtures).

• Consumable electrode wire, having chemical composition similar to that of the parent material, is continuously fed from a spool to the arc zone. The arc heats and melts both the work pieces edges and the electrode wire. The fused electrode material is supplied to the surfaces of the work pieces, fills the weld pool and forms joint.

• Due to automatic feeding of the filling wire (electrode) the process is referred to as a semi-automatic. The operator controls only the torch positioning and speed

METHODS OF ARC WELDING

METHODS OF ARC WELDING

TUNGSTEN INERT GAS ARC WELDING (Gas Tungsten Arc Welding)

• Tungsten Inert Gas Arc Welding is a welding process, in which heat is generated by an electric arc struck between a tungsten non-consumable electrode and the work piece.The weld pool is shielded by an inert gas (Argon, helium, Nitrogen) protecting the molten metal from atmospheric contamination.

• The heat produced by the arc melts the work pieces edges and joins them. Filler rod may be used, if required.

• Tungsten Inert Gas Arc Welding produces a high quality weld of most of metals. Flux is not used in the process.

METHODS OF ARC WELDING

METHODS OF ARC WELDING

ELECTROSLAG WELDING• Electroslag Welding is a welding process, in which the heat is

generated by an electric current passing between the consumable electrode (filler metal) and the work piece through a molten slag covering the weld surface.Prior to welding the gap between the two work pieces is filled with a welding flux. Electroslag Welding is initiated by an arc between the electrode and the work piece (or starting plate). Heat, generated by the arc, melts the fluxing powder and forms molten slag. The slag, having low electric conductivity, is maintained in liquid state due to heat produced by the electric current.

• The slag reaches a temperature of about 3500°F (1930°C). This temperature is sufficient for melting the consumable electrode and work piece edges. Metal droplets fall to the weld pool and join the work pieces.

• Electroslag Welding is used mainly for steels.

METHODS OF ARC WELDING

METHODS OF ARC WELDING

PLASMA ARC WELDING• Plasma Arc Welding is the welding process utilizing heat

generated by a constricted arc struck between a tungsten non-consumable electrode and either the work piece (transferred arc process) or water cooled constricting nozzle (non-transferred arc process).

• Plasma is a gaseous mixture of positive ions, electrons and neutral gas molecules.

• Transferred arc process produces plasma jet of high energy density and may be used for high speed welding and cutting of Ceramics, steels, Aluminum alloys, Copper alloys, Titanium alloys, Nickel alloys.

• Non-transferred arc process produces plasma of relatively low energy density. It is used for welding of various metals and for plasma spraying (coating). Since the work piece in non-transferred plasma arc welding is not a part of electric circuit, the plasma arc torch may move from one work piece to other without extinguishing the arc.

METHODS OF ARC WELDING

METHODS OF ARC WELDING

GAS WELDING (GW)• Gas Welding is a welding process utilizing heat of the

flame from a welding torch. The torch mixes a fuel gas with Oxygen in the proper ratio and flow rate providing combustion process at a required temperature. The hot flame fuses the edges of the welded parts, which are joined together forming a weld after Solidification. The flame temperature is determined by a type of the fuel gas and proportion of oxygen in the combustion mixture: 4500°F - 6300°F (2500°C - 3500°C). Depending on the proportion of the fuel gas and oxygen in the combustion mixture, the flame may be chemically neutral (stoichiometric content of the gases), oxidizing (excess of oxygen), carburizing (excess of fuel gas).

Filler rod is used when an additional supply of metal to weld is required. Shielding flux may be used if protection of weld pool is necessary. Most of commercial metals may be welded by Gas Welding excluding reactive metals (titanium, zirconium) and refractory metals (tungsten, molybdenum).

Gas Welding equipment: • Fuel gas cylinder with pressure regulator;• Oxygen cylinder with pressure regulator;• Welding torch;• Blue oxygen hose;• Red fuel gas hose;• Trolley for transportation of the gas cylinders.

GAS WELDING (GW)

GAS WELDING (GW)

The most popular methods of Gas Welding are: • Oxyacetylene Welding (OAW)• Oxyhydrogen Welding (OHW)• Pressure Gas Welding (PGW)

METHODS OF GAS WELDING

OXYACETYLENE WELDING (OAW)Oxyacetylene Welding is a Gas Welding process using a combustion mixture of acetylene (C2H2) and oxygen (O2) for producing gas welding flame. Oxyacetylene flame has a temperature of about 6000°F (3300°C). Combustion of acetylene proceeds in two stages:

1. Inner core of the flame. C2H2 + O2 = 2CO + H2

2. Outer envelope of the flame: CO + H2 + O2 = CO2 + H2O

Acetylene is safely stored at a pressure not exceeding 300 psi (2000 kPa) in special steel cylinders containing acetone. Outside of cylinder acetylene is used at a absolute pressure not exceeding 30 psi (206 kPa). Higher pressure may cause explosion.

METHODS OF GAS WELDING

OXYHYDROGEN WELDING (OHW)Oxyhydrogen Welding is a Gas Welding process using a combustion mixture of Hydrogen (H2) and oxygen (O2) for producing gas welding flame.

Oxyacetylene flame has a temperature of about 4500°F (2500°C).Combustion reaction is as follows:2H2 + O2 = 2H2O

Oxyhydrogen Welding is used for joining metals with low melting points, like aluminum, magnesium, etc.

METHODS OF GAS WELDING

PRESSURE GAS WELDING (PGW)Pressure Gas Welding is a Gas Welding, in which the welded parts are pressed to each other when heated by a gas flame.

The process is similar to Resistance Butt Welding. Pressure Gas Welding does not require filler material. Pressure gas welding is used for joining pipes, rods, railroad rails

METHODS OF GAS WELDING

RESISTANCE WELDING • Resistance Welding is a welding process, in which

work pieces are welded due to a combination of a pressure applied to them and a localized heat generated by a high electric current flowing through the contact area of the weld. Heat produced by the current is sufficient for local melting of the work piece at the contact point and formation of small weld pool (”nugget”). The molten metal is then solidifies under a pressure and joins the piecesResistance Welding (RW) is used for joining vehicle body parts, fuel tanks, domestic radiators, pipes of gas oil and water pipelines, wire ends, turbine blades, railway tracks.

AC electric current (up to 100 000 A) is supplied through copper electrodes connected to the secondary coil of a welding transformer.

The following metals may be welded by Resistance Welding:

Low carbon steels - the widest application of Resistance Welding

Aluminum alloys Medium carbon steels, high carbon steels and Alloy

steels (may be welded, but the weld is brittle)

RESISTANCE WELDING

• Spot Welding (RSW)• Flash Welding (FW) • Resistance Butt Welding (UW)• Seam Welding (RSEW)

The most popular methods of Resistance Welding are

RESISTANCE WELDING

SPOT WELDING (RSW)• Spot Welding is a Resistance Welding (RW) process, in

which two or more overlapped metal sheets are joined by spot welds. The method uses pointed copper electrodes providing passage of electric current. The electrodes also transmit pressure required for formation of strong weld.Diameter of the weld spot is in the range 1/8” - 1/2” (3 - 12 mm).Spot welding is widely used in automotive industry for joining vehicle body parts.

METHODS OF RESISTANCE WELDING

METHODS OF RESISTANCE WELDING

FLASH WELDING (FW)• Flash Welding is a Resistance Welding (RW) process,

in which ends of rods (tubes, sheets) are heated and fused by an arc struck between them and then forged (brought into a contact under a pressure) producing a weld. The welded parts are held in electrode clamps, one of which is stationary and the second is movable. Flash Welding method permits fast (about 1 min.) joining of large and complex parts. Welded part are often annealed for improvement of toughness of the weld.Steels, Aluminum alloys, Copper alloys, Magnesium alloys, Copper alloys and Nickel alloys may be welded by Flash Welding. Thick pipes, ends of band saws, frames, aircraft landing gears are produced by Flash Welding.

RESISTANCE BUTT WELDING (UW)• Resistance Butt Welding is a Resistance Welding (RW)

process, in which ends of wires or rods are held under a pressure and heated by an electric current passing through the contact area and producing a weld.The process is similar to Flash Welding, however in Butt Welding pressure and electric current are applied simultaneously in contrast to Flash Welding where electric current is followed by forging pressure application.Butt welding is used for welding small parts. The process is highly productive and clean. In contrast to Flash Welding, Butt Welding provides joining with no loss of the welded materials.

METHODS OF RESISTANCE WELDING

SEAM WELDING (RSEW)• Seam Welding is a Resistance Welding (RW)

process of continuous joining of overlapping sheets by passing them between two rotating electrode wheels. Heat generated by the electric current flowing through the contact area and pressure provided by the wheels are sufficient to produce a leak-tight weld. Seam Welding is high speed and clean process, which is used when continuous tight weld is required (fuel tanks, drums, domestic radiators).

METHODS OF RESISTANCE WELDING

High welding rates; Low fumes; Cost effectiveness; Easy automation; No filler materials are required; Low distortions.

ADVANTAGES OF RESISTANCE WELDING

High equipment cost; Low strength of discontinuous welds; Thickness of welded sheets is limited - up to

1/4” (6 mm);

DISADVANTAGES OF RESISTANCE WELDING

CUTTINGWhen ordering metal, most people specify a particular size and shape of the material, and the processes employed to ensure that the raw metal meets this specification are varied and broadly flexible. Since metal is, by definition, extremely tough and therefore difficult to cut, a range of devices and measures have had to be developed, each of which is the best option for a particular type of metal or desired shape. Often, small sections of the metal will need to be removed, in order to make holes for screws, bolts and so on.The most basic means of cutting metal are based upon manual tools, which is to say smaller cutting devices which can be operated by hand.For jobs which are too large or deal with materials which are too robust to make manual metal cutting a practical proposition, machine cutting has to be applied, and this comes in various different forms

• Welding or burning technologies work by the application of heat to the surface of the metal, bringing it up to a temperature at which it will soften and then break along a carefully delineated line

• Oxy-Fuel Cutting• Plasma Arc Cutting (PAC) • Laser Beam Cutting (LBC)• Water Jet

CUTTING PROCESS

OXY-FUEL CUTTING • Oxy-fuel cutting is a cost-effective method of plate edge

preparation for bevel and groove welding. It can be used to easily cut rusty and scaled plates and only requires moderate skill to produce successful results. The oxy-fuel gas cutting process creates a chemical reaction of oxygen with the base metal at elevated temperatures to sever the metal. The necessary temperature is maintained by a flame from the combustion of a selected fuel gas mixed with pure oxygen.

• The process is based on the rapid formation of iron oxide which occurs when a high-pressure pure oxygen stream is introduced into the cutting envelope. The iron is quickly oxidized by the high purity oxygen and heat is liberated by this reaction

CUTTING PROCESS

OXY-FUEL CUTTING • The oxygen stream and combusted gas transport the molten

oxide away and the metal in its path burns, producing a narrow cut known as a kerfs. Continued iron oxide formation requires large volumes of oxygen to be delivered to the cut zone at a controlled preset pressure. The intense heat produced by this reaction sustains the cutting process and the production of the cut.

• Common oxy-fuel cutting applications are limited to carbon and low alloy steel. These materials can be cut economically, and the setup is quick and simple. For manual oxy-fuel gas cutting there is no electric power requirement and equipment costs are low. Materials from 1/16in (1.6mm) to 4in (102mm) thick are commonly cut using manual oxy-fuel gas cutting. Materials 12in (0.3m) and greater in thickness are successfully severed using machine cutting.

CUTTING PROCESS

PLASMA ARC CUTTING (PAC) • Plasma Arc Cutting (PAC) severs metal by melting a localized

area of the material with a constricted electric arc that removes the molten material with a high velocity jet of hot ionized gas.

• The PAC process can be used to cut any electrically conductive metal if its thickness and shape permit full penetration by the plasma jet. Because the PAC process can be used to cut nonferrous materials, and is faster than oxy-fuel cutting with ferrous material less than three inches thick, it is the most economical alternative for many industrial applications.

• PAC equipment is available for cutting a wide range of material thicknesses, and precision plasma can produce laser-like quality cuts in some applications for significantly lower equipment and operating costs.

CUTTING PROCESS

LASER BEAM CUTTING (LBC) • Laser Beam Cutting (LBC) is a thermal cutting process that

utilizes highly localized melting or vaporizing to sever metal with the heat from a beam of coherent light, usually with the assistance of a high-pressure gas. An assist gas is used to remove the melted and volatilized materials from the beam path. Both metallic and non-metallic materials can be cut by the laser beam process. The output beam is often pulsed to very high peak powers in the cutting process, increasing the travel speed of the cutting operation.

• The two most common types of industrial lasers are carbon dioxide (CO2) and neodymium-doped yttrium aluminum garnet (Nd:YAG). A CO2 laser uses a gaseous medium to produce the lasing action while the Nd:YAG use a crystalline material. CO2 lasers are commercially available in powers up to 6kW and Nd:YAG systems are available up to 6kW.

CUTTING PROCESS

LASER BEAM CUTTING (LBC) • Done by mechanized equipment, laser cutting delivers

highly reproducible results with narrow kerfs width, minimal heat-affected zone and little-to-no distortion. The process is flexible, easy to automate and offers high cutting speeds with excellent cut quality. Equipment costs are high but are becoming lower as resonator technology becomes less expensive

CUTTING PROCESS

WATER JET• The remaining type of technology used to cut metal

accurately is erosion technology. This is technology which mimics the effect of water upon metal in the natural environment, but does so at a highly accelerated rate. Water jet cutting is particularly useful since it doesn’t rely on the creation of heat to cut through the metal, and can therefore be used on metal which may be sensitive to the effects of heat. A water jet cutter slices through the metal using a highly concentrated jet of water or, on occasion, water with the addition of an abrasive substance.

CUTTING PROCESS

THERMAL & METALLURGICAL CONSIDERATION IN WELDING & CUTTING

• Thermal considerations for welding, temperature distribution, Analytical analysis, heating & cooling curves. Metallurgical consideration of weld, HAZ and Parent metal, micro & macro structure. Solidification of weld and properties.

TEMPERATURE DISTRIBUTION IN WELDING `The welding temperature distributions in the HAZ were

measured using K-type thermocouples in similar and dissimilar thin butt-welded joints which experienced one-pass GTAW welding process. Three dimensional finite element simulations were also implemented to predict the temperature distributions throughout the plates using ABAQUS software. Comparison between experimental and simulation results reveals very good agreement. The results provide good evidence for prediction of the HAZ microstructure considering the fact that the thermocouples have been attached very closely to the weld line, and provide objective cooling slopes

• Methods for characterizing and interpreting cooling curves are reviewed. Procedures discussed include visual inspection; the calculation of various critical cooling rates, times and temperatures; the integration of areas under the cooling curve or cooling rate curve; the use of the Grossman quench severity factor; and, more recently, the use of quench factor analysis to relate cooling curve behavior to the physical properties of quenched pieces.

• The objective of this paper is to provide a general review of the approaches to cooling curve analysis published to date. Both strengths and shortcomings of techniques are discussed.

ANALYTICAL ANALYSIS OF HEATING AND COOLING CURVE

HEAT EFFECTED ZONE AND PARENT METAL

• During the fabrication of a large diameter pressure vessel out of 18 Ni maraging steel by manual TIG welding, micro cracks were noticed at the heat-affected zone (HAZ)/parent metal interface. The location of these cracks was very different from those reported at the fusion zone/HAZ I interface due to “constitutional liquation”. Extensive optical metallographic, scanning electron microscopy and energy dispersive X-ray analyses were carried out to identify the cause for the occurrence of these cracks. It is inferred from the experimental results that the micro segregation of titanium and nickel due to repeated thermal cycling during multipass welding led to the formation of TiC/Ti(CN) and stable austenite film on the grain boundaries. Under severe thermal stresses developed during welding, microvoids generated at the interface of TiC/Ti(CN) inclusions and austenite and further propagated intergranularly due to the premature failure of the austenite films.

REFRENCES• http://www.substech.com/dokuwiki/doku.php?id=classific

ation_of_welding_processes• http://www.substech.com/dokuwiki/doku.php?id=principle

s_of_arc_welding&DokuWiki=2f9f7c9a8ffd6dfab462772528d7dec0

• http://www.substech.com/dokuwiki/doku.php?id=gas_welding_gw

• http://www.substech.com/dokuwiki/doku.php?id=resistance_welding_rw

• http://www.praxair.com/industries/welding-and-metal-fabrication/cutting-processes

• http://www.castlemetalseurope.com/blog/different-forms-processes-metal-cutting/

Compiled by Abdul Ahad (D-13-IN-02)abdulahad2693@gmail.com