Published ArticleOver the past few years, methods of layered manufacturing (LM) have advanced substantially to the point where they now provide vital strategic benefits to various organisations. One area of application where LM technologies have begun to reach a critical mass is in the development and production of high-performance tooling in different forming processes. With these tooling capabilities now available, the next challenge becomes the development of optimal process chains to minimise lead times and production costs, while still ensuring high quality of castings. The relevant issues that influence where a break-even point will be between different process chains and thereby also the point of selection between such optimal process chains according to different situations include among others:   the size of production runs,   part size and complexity, and  the cast materials involved.  This paper reflects some of the experiences gained from an investigation towards developing a set of generic rules (guidelines) for the design of optimal process chains for sand casting prototypes of automotive components using LM methods, and more specifically the 3D Printing process

Centner, T.

De Beer, N.

Dimitrov, D.

English

Central University Of Technology Free State - LibraryCUT, South Africa

PRODUCT AND PROCESS INNOVATIONS BY MEANS OF RAPIDTECHNOLOGIESD. DIMITROV, N. DE BEER and T. CENTNERLaboratory for Rapid Product Development, Department of Industrial Engineering,University of Stellenbosch, Stellenbosch, South AfricaABSTRACTOver the past few years, methods of layered manufacturing (LM) have advancedsubstantially to the point where they now provide vital strategic benefits to variousorganisations. One area of application where LM technologies have begun to reach acritical mass is in the development and production of high-performance tooling indifferent forming processes. With these tooling capabilities now available, the nextchallenge becomes the development of optimal process chains to minimise leadtimes and production costs, while still ensuring high quality of castings. The relevantissues that influence where a break-even point will be between different processchains and thereby also the point of selection between such optimal process chainsaccording to different situations include among others:• the size of production runs,• part size and complexity, and• the cast materials involved.This paper reflects some of the experiences gained from an investigation towardsdeveloping a set of generic rules (guidelines) for the design of optimal process chainsfor sand casting prototypes of automotive components using LM methods, and morespecifically the 3D Printing process.Keywords:Rapid Prototyping, Rapid Tooling, 3D Printing1. INTRODUCTIONRapid Prototyping (RP) technologies have over 15 years of history [1], in which timethey have expanded vastly. Some of them, like the Strereolithography, continue tokeep their market leadership, while others, like the Selective Ground Curing (SGC) orthe Laminated Object Manufacturing (LOM), disappeared from the market. In theirplace new technologies are emerging, bringing new advantages and coveringdifferent application areas. One of these technologies is the Three DimensionalPrinting (3DP) based on MIT’s (Massachusetts Institute of Technology) ink jetprinciple and utilised by Z-Corporation in a variety of printers. It is considered to beone of the most future oriented rapid prototyping systems. Classified as a typical“concept modeller”, a low-end system, it is spreading rapidly worldwide and withinonly three years it has become the third most widely used layered manufacturing(LM) equipment [2]. The selective use of different materials in combination with thehigh building speed and suitable post treatment techniques opened a wide field ofapplication for this technology - far beyond the original idea of generating designiterations. These applications include pattern making for investment, sand andvacuum casting as well as for bridge tooling, design aids for tooling equipment,reconstructive surgery aids and others.With the advent of each new avenue of application, it is however critical tounderstand exactly what the range of its capabilities are, in order to compare current50D. Dimitrov, N. De Beer and T. Centnerprocesses and techniques, or even future improvements. As its abilities becomeapparent, a set of process chains is spawned. Based on its inherent advantages anddrawbacks, each process chain will have specific situations where it will be moresuitable than the other.One such avenue of application that is considered in this paper is the production ofhigh-performance tooling in different forming processes. Several process chains havebeen developed [3] that utilise different combinations of materials and techniques.This paper deals with current research towards the building a set of generic rules(guidelines) for the design of optimal process chains for sand casting prototypes ofautomotive components using LM methods, and more specifically the 3D Printingprocess.2. DECIDING FACTORS FOR THE CHOICE OF PROCESS CHAINThe key indicators that determine which process chain is more suitable for a givensituation usually become apparent with time and experience. But with the growinginternational competition and shortened product lifetimes, companies are pressurisedto develop new abilities and process chains much sooner in order to be at the marketearlier with their innovative products than their competitors. In this regard, thedevelopment, maintenance and expansion of prototyping capability are veryimportant.It still remains a challenging task to identify optimal process chains for specificapplications, and therefore a framework or model for selecting the most suitableprocess chain needs to be developed. This model is to be based on a comparativebenchmarking study of capabilities of each process chain.The execution of benchmarking tests is a traditional practice and necessary for allkinds of high productive and capital-intensive equipment. The objective of thebenchmarking can however, differ substantially from case to case. In our case abenchmarking procedure was developed with the sole purpose to evaluate theperformance capabilities of process chains for sand casting prototypes of automotivecomponents. From the results of the benchmarking study, the individual abilities ofeach process will indicate its suitability and scope of application.3. RESEARCH APPROACH AND EXPERIMENTAL BASE3.1 Benchmarking approach and procedureBenchmark developmentThe benchmarking procedure involved the comparison between three differentprocess chains. The component (Figure 1) that was used for this comparison is atypical automotive component with robust features suitable for the sand castingprocess.Journal for New Generation Sciences: Volume 4 Number 151Figure 1: CAD image of component used in benchmarking study(a) (b)Figure 2: Benchmarking part indicating (a) split line and (b) split surfaceWith at least one undercut, the choice of positioning the split line was done withcareful consideration of the constraints associated with the sand casting procedures.The process chains that were compared during the benchmarking study were thefollowing:• ZCast™ Direct Pour (Shell Method)• Production Intent Casting, and• Fibreglass ToolingA short description of each process chain is given below.ZCast™ Direct Pour (Shell Method)In late 2002, Z Corporation introduced a new technology to address the prototypingneeds of the metal casting industry as well as end users seeking to rapidly producemetal prototype parts. This new technology, ZCast™ Direct Metal Casting, consistsof materials and processes that allow designers and engineers to 3D print mouldsand/or cores. These printed parts can then be used directly as a mould for pouringmetal. The ZCast™ process is revolutionary because it eliminates the patterncreation phase of the traditional sand casting process. As a result, the ZCast™process drastically reduces the time it takes to produce a casting from weeks to days[4]. The Shell Method was developed to reduce the cost of ZCast™ Direct Pourmethod and to increase the size of the casting envelope [5]. The process involves thedesign of basic parting lines and coring. A 3D mould shell approximately 25 mm thickusing ZCast 500 plaster-ceramic composite material is printed. If necessary, the shellis created with ribbing and backfilled with traditional foundry sand to facilitate addedstrength while minimising material cost. During this study, Z Corporation’s ZPrinter310 System was used to create the printed components.52D. Dimitrov, N. De Beer and T. CentnerProduction Intent CastingThis method is a combination of the zp102 plaster material for creating patterns, andZCast 500 material for creating cores. The process first involves designing foundrytooling as it would be designed for the production foundry process, includingcoreprints, offset partings, and clearances [5]. The pattern equipment is then printedwith the zp102 material, infiltrated with epoxy, and if necessary backfilled with a rigidplastic filler for added strength. If cores are required, they are produced using theZCast 500 material.Fibreglass ToolingThis process chain, like the previous two, begins from a CAD design with chosen splitline and core designs. As with the Shell Method, the Fibreglass Tooling methodrequires the development of the negative CAD image from its positive in order toobtain the CAD designs of the two mould halves. The pattern halves are then printedusing zp102 plaster material. Fibreglass material is applied to the split surface andsides of the mould. The positive fibreglass geometry is mounted to a wooden frame,and is used to create the subsequent sand moulds necessary for sand casting.Where cores are involved, patterns of the core geometry are printed using zp102material and are used to create core boxes.4. DISCUSSION OF RESULTSFigure 3 below shows some of the results that were obtained during selected stagesof each of the process chains. As with all LM technologies, each process chainbegins with a CAD image of the components that are to be printed using the ZPrinter310.Journal for New Generation Sciences: Volume 4 Number 153Figure 3: Selected results from steps in process chainsProcess ChainA. Shell Method B. Production IntentCastingC. Fibreglass Tooling1.CADDesign2.Printing,Infiltrationandpre-processing3.PostProcessing4.Tooling/Moulds5.MetalPouring&Machining54D. Dimitrov, N. De Beer and T. CentnerThe steps for creating negative CAD images from the positive designs turned out tobe more arduous than initially anticipated. Using ProEngineer, there are differentways to create a mould from a model. One way to create the mould is with using theProCast module of ProEngineer. A second approach is to define a split line manuallyand copy the surfaces from the original model to get the negative prints of the innerand outer part geometry. After that, the sp lit surface has to be created and thesurfaces have to be merged and filled to get a solid.The first method is quicker if the model has a simple split line, but as soon as the splitline contour becomes intricate, it becomes tedious to use the ProCast module ofProEngineer, and the second, manual procedure is followed. This is why, also in thiscase, it became necessary to use the second method in this study.The Shell Method has the least amount of steps in its process chain and is thereforethe quickest of the three. It is most suitable for low run mould production. Figure 3shows the resulting moulds that were obtained after printing the CAD models withZCast 500 material. The mould on the left has already been baked at 180ºC forapproximately 6 hours, and is ready for metal pouring.The step that took the longest for Production Intent Casting was the post processingrequired after printing the models. The models were printed over a period of twodays, while post processing took at least three days. It was a challenge to create agood surface finish in the deep pockets of the tool geometry, and this became thecause behind the extended post processing time. The tooling was finally created byenclosing the infiltrated and surface-prepared models with wood. These tools forsand casting are not as durable as conventional tooling – but with necessary care,and depending on the tool geometry, they should be able to produce several sandmoulds suitable for medium run mould production.The Fibreglass Tooling method on the other hand, provided sand cast tooling in linewith the quality of conventional tooling. The trade-off for obtaining this extended toollife was the time it took to create the tooling. Although this method, in comparison tothe other two methods, took the longest to produce, it can still be stated withconfidence that printing the model before overlaying with fibreglass considerablyreduces the time for creating the tooling when still compared to conventional patternand tool making.5. CONCLUSIONS AND OUTLOOKBased on the technological characteristics of the process chains as illustrated above,following evaluation remarks emphasising their applicability for making functionalparts in end use materials (or close equivalents) in the shortest time can be made:• The accuracy of the tooling produced is well within the required tolerances for thesand casting process.• Design (complex shapes) – in general greater ability to handle complex shapesand design features. Creating the CAD negatives should however not beunderestimated when the geometry and split line becomes more complex.• Materials – ZCast 500 material is at this stage restricted to use for casting onlynon-ferrous metals. Zp102 provides a sufficiently durable alternative for tooling ofmedium batch sizes. Gel-coated fibreglass meets the industry standard in terms ofquality and tool life.Journal for New Generation Sciences: Volume 4 Number 155• Part size – Size of tools is not restricted to only the build volume of the printer,since partitions can be assembled to create larger moulds and tools. Theassembly process should however be planned carefully, and noted that extra timeis spent on post processing.• Batch size – The Shell Method is suitable in general for small production runs, butideal for one-offs. Production Intent Casting is suitable, depending on partgeometry, for batch sizes in the region of 10-30 parts. Fibreglass Tooling batchsizes are in line with batch sizes available from conventional tooling.• Time saving – is substantial for Shell Method, since moulds are produced directlyfrom CAD data. The other two processes also provide substantial time savingcompared to conventional tooling methods.• Cost issues – not necessarily prime objective due to many additional, non-monetary advantages such as quality assurance, risk management and others.This summary as well as the case study data and analysis, presented in this paper,prove that the developed process chains have achieved the objective for a nicheapplication in the production of sand casting prototypes of automotive componentsusing LM methods, and more specifically the 3D Printing process.6. REFERENCES[1] Levy, G.N., Schindel, R., Kruth, J.P., 2003, Rapid Manufacturing and RapidTooling with Layer Manufacturing (LM) Tec hnologies, State of the Art and FuturePerspectives, Keynote Paper from the Annals of the CIRP Vol 52/2/2003, pp.1-23.[2] Wohlers, T., 2004, Wohlers Report - Rapid Prototyping and Tooling: State of theIndustry, Worldwide Progress Report, Fort Collins, Colorado.[3] Wohlers, T., 2002, New Developments and Trends in Rapid and HighPerformance Tooling, Proceedings from International Conference: WorldwideAdvances in Rapid and High-Performance Tooling, EuroMold 2002, Frankfurt,Germany.[4] Website: www.zcorp.com, ZCast Technology Overview.[5] Krouth, T.J., 2002, Foundry Tooling and Me tal Castings in Days, Proceedingsfrom International Conference: Worldwide Advances in Rapid and High-Performance Tooling, EuroMold 2002, Frankfurt, Germany.56D. Dimitrov, N. De Beer and T. Centner

Product and process innovations by means of rapid technologies

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Product and process innovations by means of rapid technologies

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