Innovative manufacturing technologies for thedisassembly of consumer goods

E Uhlmann, F Elbing and J Dittberner*

Institute for Machine Tools and Factory Management, Technical University Berlin, Berlin, Germany

Abstract: Ecological harmless disposal of used technical consumer products will become mandatoryfor producers and importing companies. This disposal policy will focus on product and materialloops; used products will be disassembled and the parts and materials then recycled. Owing toenvironmental and legislative reasons, the importance of disassembly as a step in the process ofrecycling is steadily rising. The article presents developed technologies and tools for the disassemblyof consumer goods. The aim is to recover materials and reusable components within asemiautomatic pilot disassembly system. Different destructive processes were optimized todisassemble washing machines.

Keywords: ecological disposal, disassembly of consumer goods, recycling

1 INDUSTRIAL DISASSEMBLY

Not long ago, a product life started with assembly andended with disposal. Today, in times of increasingwaste quantity and decreasing natural resources, lifecycles are invented in which materials are reprocessedor reutilized and components are reused [1] (Fig. 1).Old technical consumer products are disassembled.These old products are called disassembly goods ordisassembly objects.

Disassembly is a major operation in the recycling ofused technical products, but disassembly is not ashighly automated as assembly yet. The standard of auto-mation for disassembling is still very low and thereforedismantling is often performed manually [2, 3]. Employ-ment is slow and cost intensive, especially in the highlyindustrialized parts of the world such as Europe. Hencerecycling is more economic by automated disassembly.On the other hand, the human worker is the most flexibletool available. When confronted with the high variety oftypes of technical product and the state that they are inafter use, it is clear that a large amount of informationhas to be considered when choosing disassembly tools,processes and strategies.

The conclusion is that flexibility and speed are twomain requirements for industrial disassembly. At theTechnical University Berlin the Collaborative Research

Centre 281 (CRC281) works on basics, tools and pro-cesses for disassembly as well as on its planning andimplementation. The objective is to increase the effective-ness and to minimize the costs of disassembly throughoptimized disassembly methods. It begins at the productplanning phase and does not end at the actual technicaldisassembly process. This paper presents a general intro-duction of the four project areas of the CRC281 andfocuses on the examinations of subproject dealing withthe development of processes and tools for the separa-tion of insoluble connections.

1.1 Collaborative Research Centre 281

Sustainability is a prerequisite for future development.Much research is carried out to obtain sustainabledesigning methods and manufacturing processes.Often, newly developed products are designed formaterial and product cycles, but these are futuretrends. Today there are products at the end of theirlife, which were not intended for reuse or reutilizationbut for disposal. They were not designed for disassemblyand, since disassembly is not necessarily the inversion ofassembly, innovative disassembly technologies have tobe found.

At the Technical University Berlin and the Berlin Uni-versity of Arts, the CRC281 disassembly factories for therecovery of resources from product and material cyclespromoted by the Deutsche Forschungsgemeinschaftinvestigates industrial disassembly. In 1995 the projectwas started and it was granted a final 3 year term in

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The MS was received on 6 October 2003 and was accepted after revisionfor publication on 28 April 2004.*Corresponding author: Institut fur Werkzeugmaschinen und Fabrikbe-trieb, Technische Universitat Berlin, Pascalstraße 8-9, D-10587 Berlin,Germany.

2003. It is a collaboration of nine institutes from twouniversities.

The centre is divided into four different project areas,which deal with different aspects of disassembly [4](Fig. 2). Each project area is divided into three to sixsubprojects, and 21 research engineers guide an overallof 16 subprojects.

Project area A, tools and processes, invents and opti-mizes single disassembly techniques and tools as well asa pilot disassembly system. Project area B deals withthe logistic problems of collection and distribution indisassembly and describes ways to implement the dis-assembly factory in the environment. Project area Cdetermines the value of a disassembly product andplans disassembly. Project area D designs disassembly-friendly products and facilitates disassembly. In thefollowing, an overview of the project areas is given.The Web pages www.sfb281.de contain more detailedinformation.

1.1.1 Tools and processes

In order to control and economically to optimize dis-assembly processes, a basic knowledge of these processesis required. Project area A delivers these elementary pro-cesses as well as tools, production facilities, informationand sensor systems for disassembly [4]. Within theresearch period 2001–2003 the goal of project area Awas to develop highly flexible, adaptable and modularprocesses and tool concepts for different life cyclescenarios. The research on cutting processes, informa-tion, sensor and disassembly systems had to be combined

and verified within a pilot disassembly system. The over-all focus is on advantages, disadvantages and restrictionsof processes and tools concerning flexibility, modularityand adaptability.

Challenges for further investigations of disassemblyprocesses and tools include fast, safe, ecological andeconomical disassembly of structural parts and materialsby destroying them. As an example the separation ofwashing machine housings is tested in order to achievefast access to valuable components.

New modular tools for manual and automated use aredeveloped to disconnect joints and to handle disassemblyobjects. This is realized by the generation of new actingsurfaces. Tools developed during the first and secondresearch periods are integrated into a modular construc-tion kit as functional units.

Further process and tool developments, e.g. desolder-ing, are related to non-destructive disassemblies in orderto preserve component quality for reuse. A concept forclamping technologies for disassembly combines clamp-ing and handling of different products. Within theproject area, a cleaning technology with laser and dryice blasting reuse and further use of disassemblyproducts is developed.

The life cycle unit collects life-cycle-related data inorder to support disassembly processes. Detailed infor-mation about product and component quality isavailable throughout the entire life cycle. Productinformation about the steering of disassembly and re-assembly are equally gathered.

The development of processes and tools, securitydirectives, information systems, effectors and sensors isthe first step in the direction of automation. The productarea is divided into six subprojects, which deal with theseparation of insoluble connections, shape-independentend effectors for non-destructive disassembly, flexibleclamping technology, protection of labour and safetyprecautions, cleaning technologies, sensor-guided pro-cesses and realization of a pilot disassembly system.Within the disassembly system the interplay of thedevelopments of the other subprojects is tested. Dis-assembly operations and sequences are put together

Fig. 1 Disassembly within a product’s life cycle

Fig. 2 Project areas of the CRC281

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and optimized. Disassembly objects are up-to-datewashing machines, used car engines and a disassembly-friendly washing machine designed in the project.

1.1.2 Logistics and urban development

It is necessary to integrate logistics, disassembly factoriesand urban structures in order to achieve closed productand material loops. Project area B develops logistical dis-assembly systems in close relation to the pilot-disassemblysystem of product area A, as well as other in-house logisticsystems. The object is to match external logistics with thelogistics of customers as well as with suppliers. Thisrequires a certain organization, which has to be designedand installed prior to realization [4]. Questions of collec-tion and storage of disassembly goods are answered,and procedures optimized. In addition, scenarios of thenecessary infrastructure are developed as well as methodsto integrate disassembly factories into urban or ruralenvironment. One emphasis is the disassembly-friendlyconstruction of the disassembly factory itself. The projectis divided into three subprojects which deal with theprocess-oriented development of logistical systems, thecreation of a regional network of disassembly factoriesand the interaction between disassembly factory and city.

1.1.3 Product evaluation and disassembly planning

A substantial requirement of disassembly is the investi-gation of the individual product. Planning and realiza-tion of disassembly facilities are strongly influenced byuncertainties, which result from usage of products. Tomeet resulting requirements the systems have to beflexible and offer an on-line control potential reachingfar further than any given system available today.

Information relevant for disassembly, such as experi-ence gained from previous efforts, general product infor-mation and the usage-related condition of the product,must be considered together. The disassembly processof an individual product cannot be precisely predictedahead of time and must be planned just prior to thestart of the process or even during the process. Thissituation results from different conditions in which a pro-duct may be dependent on the influence of usage.

Evaluation of disassembly relies heavily on the differ-ence between costs and benefits. On the side of costs it ismost important to give values to a wide range of differentitems such as emissions, resource consumption or socialcosts. To evaluate items as social costs, it becomesnecessary to find appropriate cost-accounting systems.As one result, the system found can help to improveexisting products and, additionally, the quality of newproducts.

Project area C is divided into three subprojects, whichdeal with methods of assessing recycling suitability andcomputer aided disassembly planning and control aswell as with the economic and ecological course ofaction [4].

1.1.4 Product design and ease of disassembly

Disassembly efficiency will be increased if design for easeof disassembly requirements such as reusable componentarchitecture or pure material use are met. Emphasis lieson joints. It is demanded not only that joints offeraccessibility for tools but also that they are easy to dis-assemble. The deduction of design criteria provides agreat deal of support for assessment during the designstage. To predict end-of-life product conditions, simula-tion tools are needed which require an information net-work that provides and receives information fromproducers, users and recyclers.

Project area D is divided into four subprojects for theproduct, with the selection, embodiment and arrange-ment of fasteners, with design guidelines for structuresand joining components, with simulation tools for adisassembly-adequate product design and with thedisassembly-oriented information–technological infra-structure [4].

2 SEPARATION OF INSOLUBLE

CONNECTIONS

Within project area A the subproject A1, separation ofinsoluble connections, develops processes and tools fordestructive disassembly [4, 5]. The task was approachedfrom two different points of view. One was the classifica-tion of components and joints. The other was thecategorization of existing manufacturing technologies.

Disassembly products consist of components andjoints. Components are made of sheets, poles or morecomplex workpieces. Joints are rivets, screws, welds orforming connections. Ideally, to disassemble a consumerproduct all joints have to be dismantled. Often this is notpossible. This may result from the connection itself aswith welded joints, or from external influences on itsuch as corrosion or damage.

These connections have to be destroyed and are calledinsoluble. Also it might prove more effective not to dis-mantle connected parts but partly to destroy one partto obtain fast access to downstream parts that may bereusable.

Plasma arc cutting, drilling, water jet cutting, abrasivecutting, splitting and shearing are examined, as well as acombination of these with a cryogenic pre-treatmentwith liquid nitrogen. One emphasis in the research lieson the minimization of side effects that might influencethe functionality of reusable parts. Some processesimplement forces on the parts to be disassembled andthus cause unwanted deformations. Other processescause a spray of sparks or material particles thatdamage or contaminate other parts and hence thenecessary reconditioning has to be extended. Anotheremphasis is to understand how to use the processesfor disassembly properly, in a way that is highly

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flexible and cost effective. Often these goals contradicteach other. Then a practicable compromise has to befound.

Some of the tested processes are integrated in the pilotdisassembly system. In it the first example for a disassem-bly object was a washing machine. There the first task forthe destructive processes was to open up the case of thewashing machine and to gain fast access to reusablecomponents such as the motor, the pump or the valveunit.

Most cases for washing machines are made of steel.Others are made of stainless steel, and a few of alumi-nium. The coatings used are enamel paints, dry lacquersor two-component lacquers. Thus different combina-tions of material and coating were used for the examina-tions. The goal is to cut sheets out of each wall of thehousing. The sheets have to be as large as possible toallow easy access to inner parts. Thus a frame is left tosupport the swinging system. In the process of openinga housing, long cuts have to be produced. Adequate pro-cesses for this purpose were plasma arc cutting, water jetcutting and abrasive cutting.

Inside a washing machine, other non-reusable partswere identified for destructive disassembly. Bars, wireand point-shaped connections were among these. It ispossible to destroy these parts and joints by plasma arccutting, water jet cutting and abrasive cutting, too. How-ever, compared with the small size of the object theycause a high amount of different emissions, sparks andby-products. Therefore dividing processes such as shear-ing and splitting were tested. A hydraulic blade cutterwas used to shear bars and wire. An adjusted chippinghammer splits screw heads and rivet heads from thebase bodies. Contrary to the other processes, theamount of used energy and the geometry of blades andacting effectors had to be optimized.

In the following, some of the various examinations onplasma arc cutting and water jet cutting are described.

2.1 Plasma arc cutting

For the disassembly of washing machines, specific dis-assembly sequences were elaborated for each type. Thewasher case is separated by means of plasma arc cuttingin such a way that a frame remains, to which the innercomponents are attached. The aim of this disassemblystep is to reach the inner components and assemblies asrapidly and cost-effectively as possible. A roboticplasma arc cutting device, PA-S 45 CNC by Kjellberg,Finsterwalde, Germany, was used. The installationworks with a transmitted plasma arc at cuttingamperages of 40–130A, a cutting voltage of 160V anda cutting power of 20 kW. In the course of technicalinvestigations, a qualitative gas analysis was carriedout as well as process optimization with regard to themaximum cutting speed and a completely cut-through

workpiece, minimum mechanical and thermal compo-nent damage and minimum removal particle mass [6].

The maximum cutting speed was obtained in experi-ments with the standard experimental set-up by Tagucci,during which the parameters (cutting amperage, cuttinggas, workpiece material and material thickness) werevaried. The cutting gases tested were air, Ar–H2 andAr–H2–N2. The maximum cutting speeds could beobtained with air. Irrespective of how rapid the cutwith air may be, there is a high emission of removalparticles. With increasing cutting amperage the maxi-mum cutting speed increases too. At a cutting averageof 125A a maximum cutting speed of 12m/min can beachieved. The cutting amperage and the cutting gaswith a minimum removal particle mass were determined.

Figure 3 displays the removal particlemass as a functionof the cutting amperage in the case of plasma arc cutting ofa workpiece similar to the washer case of the Bosch V454type. After optimization the particle emission duringplasma arc cutting of the washer case could be reducedby 95 per cent compared with the initial setting, whichemployed a cutting amperage of 125A and air as thecutting gas. The conclusion is that the removal particlemass is almost irrespective of the cutting speed in thecase of a defined separating cut and that it is only minimalwhen an Ar–H2 cutting gas and a cutting amperage of75A are applied. A disassembly time of 3min is calculatedfor the industrial disassembly of a complete washingmachine case if optimized parameters are applied duringthe separation of the four lateral walls of the washercase. After that, the assemblies and components can bedisassembled in a destruction-free manner.

Including the results of the above-described examina-tions the construction of the plasma arc plant and theperiphery were altered and integrated into a hybridpilot disassembly system. Owing to the high cuttingspeed, good automation and low cutting costs, plasmaarc cutting was used in the pilot disassembly system toopen washing machine cases from various suppliers.Further examinations took place on cutting poles andwires by plasma arc cutting.

2.2 Water jet cutting

A robotic abrasive water jet cutting device from IngersollRand, Bad Nauheim, Germany, was used for theexamination of water jet cutting in disassembly. Againmetallic materials were processed. The maximum work-ing pressure was 320MPa, the average abrasive massflow was 350 g/min and an abrasive garnet mesh 80was used.

The first focus is on the optimization of the maximumtraverse rate at which a workpiece is cut through. Depend-ing on the material and the workpiece thickness a modelwas built to predict the maximum traverse rate. Besidesthe material properties, the working distance, abrasive

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mass flow and the working pressure quantify the traverserate. It is highest at the maximum pressure and anabrasive mass flow of 350 g/min [7].

Another task of the investigations on water jet cuttingwas to determine and explain the jet properties, andparticularly the influence of the secondary jet on innercomponents and assemblies. If water jet cutting is usedfor three-dimensional machining, damages occurcaused by the primary and the secondary jet. Theprimary jet is the jet prior to machining and the second-ary jet exists behind the workpiece that is machined andceases in infinity or when striking inner components.Within disassembly the chances are high that the second-ary jet strikes an inner component or other assemblies.When the so-called secondary jet distance, the distancebetween the primary workpiece and inner components,is small, reusable parts are at risk of being damaged.Thus the objective is to minimize the energy of thesecondary jet and to predict its influence on othercomponents. The secondary distance is measured on astraight line, which runs vertically to the primary work-piece through the jet exit point.

With knowledge about the kerf geometry, it is possibleto predict the depth of the damage from the secondaryjet. Essentially, the damage of the inner componentsdepends on the traverse rate and the secondary jetdistance, which is the gap between the primary andsecondary workpieces. Ideally, the damage inflicted bythe secondary jet during cutting with the maximumtraverse rate is zero. Thus the traverse rate must beseen in relation to the maximum traverse of the primaryworkpiece. As the traverse rate becomes closer to themaximum value, the secondary jet energy decreasesand the possible damage is less.

The secondary jet spreads according to the same rulesas a primary water jet. As a result, it is possible to

minimize and predict the damage of inner components.With this knowledge, it is possible to set cutting strate-gies for disassembly, which avoid damage on reusablecomponents.

The abrasive water jet was integrated into the dis-assembly process of standard washing machines toopen the plastic lye container and to separate it fromthe washing cylinder made from stainless steel. Figure4 shows the disassembly stages of a washing machine.It starts with the opening of the case, followed by theseparation of the swinging system, which is then strippedfrom the weights, pump and motor. Afterwards thewater jet opens up the lye container and the washingcylinder is removed.

2.3 Conclusion

The possibilities of using destructive separating manu-facturing processes for the disassembly of old consumerproducts exist but are restricted. When used alone, thereis always a side effect that might affect reusable parts.Measures have to be taken to neutralize the side effects.It is possible to remove contamination by cleaning.Damage can be repaired. To save workers and the envir-onment from emissions, exhaust and filter systems haveto be installed. All these measures cause disassemblycosts to rise, either as a result of a more complex techni-cal and mechanical equipment or by increasing the timefor disassembly.

Another way to minimize those effects is to combinethe processes with another operation. Already cryogenicpre-treatment with liquid nitrogen has been tested. Bycooling material to a temperature of nearly �200 8C, itis possible to embrittle the material. Thus lower forcesoccur while cutting material and it is possible to increase

Fig. 3 Removal particle mass as a function of cutting amperage and cutting gas during plasma arc cutting of awashing machine case

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the cutting speed. The time to split a screw head from ascrew of 6 cm diameter was reduced from 8 to 3 s whilethe nitrogen application took about 2.5 s.

Another aim within the subproject is to let the workerin disassembly know which process is the best for a task.Therefore a process selection system (PSS) was devel-oped. All information about the examined processes ispooled in this system. The main objective of the selectionsystem is to help to identify the most efficient process fora specific disassembly operation. Thus, an existing dis-assembly plan was assumed. Therefore, there must beknowledge about which part can be reused and how togain access to it.

Figure 5 shows the environment in which the PSS isembedded. Industrial disassembly requires exact planningof the disassembly sequence for each product. For everysingle step of this sequence an adequate process has tobe determined. By linking the processes it is possible tofind the cheapest and fastest method for the wholesequence. The step is described by the kind of part,material, geometry, surface, further usability and its posi-tion.Within the PSS the information is compared with thecollected technological data. A matching disassemblyprocess is selected and written into the disassembly plan.In the following, the content and procedure of the PSS isdescribed in detail.

The first piece of information that the system needs iswhich part has to be worked on and its specific features.Then, a practical working sequence has to be established.The recycling purpose for disassembled parts has to bedefined. The user then has to decide which criterion,technological or economical, the output has to refer to.

Figure 1 shows the resulting selection sequence of thePSS. The single steps are described in the following.

As described above, it is possible to categorize the dis-assembly objects for destructive processing into sheets,joints and bars. Sheets are flat plates or formed three-dimensional formations such as housings or cases. Fordestructive processing, the planes that create such aformation are taken as single parts.

Because of the very wide variety of existing joints theyhave to be subdivided. The user has to choose between

Fig. 4 Disassembly stages of a washing machine

Fig. 5 Environment of the PSS (DOM, document objectmodel)

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point, plane and linear connections. A bar has smallcross-section compared with its length. Examples arepoles, springs and wires.

It is possible to choose between geometrical, topogra-phical and material features. The features are alreadycategorized according to the results of optimization ofthe researched processes. For example, sheets aresubdivided into sheets with thicknesses of 0.1–2.5mm,2.5–5mm and 5–10mm. Topographical features aremacroscopic surface features such as fins, ribs or holes.

The user chooses the appropriate working sequence,which is a contour, a straight line or a point. This relatesto the disassembly plan. Then, an enquiry is madewhether the operation has to be executed once or manytimes. It is significant for the selection if a housing isconnected to a supporting frame by 20 rivets or withone welding line, for example. The value of the part tobe disassembled is estimated. Is it a reusable part orintended only for utilization? Reusable parts are morevaluable. To gain high profit, disassembly processeshave to have little influence on inner parts in order tominimize rework and costs.

Within this selection step the user chooses betweendifferent scenarios. It depends on the location wherethe work takes place and on whether manual or auto-mated processes are preferred. The choice betweendifferent locations relates to whether the disassemblymachinery is used stationary or mobile. When mobilemachinery is used, not all researched processes areuseful due to their extent and complexity. In addition,it is possible to pre-select processes and tools alreadyexisting at the user’s location.

The user has the opportunity to specify the preferredcriteria for the resulting selection sheet. It is possible toselect whether the order of possible processes relates tothe costs or to the rate. This feature is important, forexample, if a single punctual connection has to bedestroyed. A user might be interested in knowingwhich is the fastest method. If there is no preferencebetween these two criteria, the system will arrange theprocesses according to the disassembly costs auto-matically.

In this selection step the user is given an output tablewith the variety of possible processes for the specifictask. The processes are according to the selected criteriaordered. Moreover, the table contains secondary infor-mation about safety precautions and occurring second-ary damage. The notes on safety give precautioninstructions to follow, e.g. whether an exhaust or gogglesare necessary. To summarize all prior selection steps thesheet additionally lists the given information.

3 OUTLOOK

The challenges for industrial disassembly are new life-cyclemanagement laws, a growing recycling and maintenance

industry, the handling of contamination and harmfulchemicals in recyclable products, and the reuse ofcomponents from recyclable products. An approach tothis field is made by the CRC281 disassembly factories.Focuses are on the disassembly of consumer goods andon the cleaning of components for reuse. The object isto develop processes and tools for fast and economical dis-assembly.

The described examinations show the independence ofwater jet cutting and plasma arc cutting from thematerial and working direction. The processes werecompared with other processes such as drilling, abrasivecutting, shearing, splitting and a self-developed strike-cutting tool. Plasma arc cutting is the most flexible andmost rapid process for the disassembly of metallicconsumer goods. Only when it comes to disassemblingnon-metallic components is water jet cutting even moreeffective; otherwise it is the second choice. The flexibilityof these processes is their main advantage. The main dis-advantage is the occurrence of only partly controllableand non-eliminable side effects. The approach of usingprocesses that only have high process forces as a sideeffect on the disassembly object is very promising. There-fore other processes will be combined with cryogenic pre-treatment. Also it is possible to use heat to lower thecohesion of a material. It is planned specifically to heatparts. This will be achieved by means of induction,friction, electricity, sound, flames, electric arc, etc. Inthe long run the examination will be the basis for thedevelopment of new destructive methods and self-destructing connections.

In addition the heating processes themselves will betested. The so-called melting processes belong to themanufacturing processes not yet examined.

All collected data and information will be added to thePSS. It will also be extended with information aboutnon-destructive disassembly techniques and tools.

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