An Overview Of Rapid Prototyping Technologies In Manufacturing

Transcription

1 An Overview Of Rapid Prototyping Technologies In Manufacturing Dr. A. Dolenc Institute of Industrial Automation Helsinki University of Technology July 24, 1994 Abstract This document overviews a new class of manufacturing processes generally known as Rapid Prototyping Techniques or Technologies (RPT) that build parts by adding material on a layer-by-layer basis, in contrast to conventional methods that remove material. We discuss their basic principles, data transfer, applications, and compare them with their conventional counterparts. Otakaari 1, FIN Espoo, Finland. Tel: Fax: (Internet): ado@mail.cs.hut.fi. 1

2 Contents 1 About This Document 5 2 What Is Rapid Prototyping? 5 3 Overview Of Some Processes Stereolithography :::::::::::::::::::::::::::::::: Solid ground curing ::::::::::::::::::::::::::::::: Selective laser sintering ::::::::::::::::::::::::::::: Laminated object manufacturing ::::::::::::::::::::::::: A short comparison ::::::::::::::::::::::::::::::: 11 4 DatatransfertoRPT Constraints on the model ::::::::::::::::::::::::::::: 14 5 RPT In Manufacturing Toolings ::::::::::::::::::::::::::::::::::::: 18 6 RPT In Industrial Design 18 7 RPT In Medical Applications 18 8 RPT vs conventional technologies 20 9 Conclusions Acknowledgements 21 2

3 List of Figures 1 A schematic drawing of an SLA. ::::::::::::::::::::::::: 7 2 A schematic drawing of a SOLIDER process. :::::::::::::::::: 8 3 A schematic drawing of an SLS process. ::::::::::::::::::::: 9 4 A schematic drawing of a LOM process. ::::::::::::::::::::: 10 5 A scenario between designer and manufacturer. ::::::::::::::::: 12 6 The state transitions of a parametric surface model. ::::::::::::::: 13 7 The typical scenario of data preparation. ::::::::::::::::::::: 13 8 A correct triangulation :::::::::::::::::::::::::::::: 14 9 Incorrect triangulations. ::::::::::::::::::::::::::::: Correct vs. incorrect slices. ::::::::::::::::::::::::::: Changes in the requirements for the manufacturing industry. :::::::::: Development time vs. development costs. :::::::::::::::::::: Obtaining medical models from scanned images. :::::::::::::::: RPT vs conventional technologies. :::::::::::::::::::::::: 20 3

4 List of Tables 1 Other Stereolithography-based processes. :::::::::::::::::::: 7 2 A short comparison of some RP processes. ::::::::::::::::::: 11 4

5 1 About This Document This document has two versions, a printed version and an electronic version. The printed version is obtained using LAT E X, and converted to PostScript using dvips. The compressed PostScript file can be obtained via anonymous ftp at sauna.cs.hut.fi ( ) in /pub/rp-ml/rp.ps.z. The electronic version is obtained using latex2html 1. It may happen that both versions are not updated simultaneously. Observe that some differences are bound to exist between both versions. Take, for instance, a link to another document. Whereas in the electronic version it suffices to have only the link, in the printed version, it is replaced by a description of the contents of the other document. 2 What Is Rapid Prototyping? The past decade has witnessed the emergence of new manufacturing technologies that build parts on a layer-by-layer basis. Using these technologies, manufacturing time for parts of virtually any complexity is measured in hours instead of days, weeks, or months; in other words, it is rapid. The first commercial process was presented at the AUTOFACT show in Detroit (US) in November 1987, by a company called 3D Systems, Inc. At that time, the process was very inaccurate and the choice of materials was limited. Therefore, the parts obtained where considered prototypes. Like in software engineering, a prototype is something to look at, servesas a basis for discussion but cannot be used for anything serious, i.e. in a production environment. Since then, Rapid Prototyping Technologies (RPT) have taken enormous strides. Nowadays, there are over 30 processes some of which are commercial, while others are under development in research laboratories 2. The accuracy has improved significantly, and the choice of materials is relatively large, to the extent that the term prototype is becoming misleading; the parts are more and more frequently being used for functional testing or to derive tools for pre-production testing. It is very likely that a new term, or one of the numerous other expressions that are floating around, will replace it in the future 3. It is true that rapid prototyping (notice the lowercase) can be achieved using conventional methods such as NC milling and hand carving. However, the term RP is normally reserved for the new technologies that build parts by adding material instead of removing it. In order to regard RP in the right perspective, one would need to compare it with the conventional methods. Unfortunately, this is beyond the scope of the present work. I will explain, though, to the best of my ability, the strategic importance of RP and describe in some detail some of the processes that will be referenced later A survey dated May 1993 by Wohlers Associates includes 34 processes out of which 11 are commercial with approximately 525 machines sold worldwide. 3 Personally, I favour the expression Rapid Prototyping&Manufacturing (RPM). 5

6 3 Overview Of Some Processes All the processes described in this Section take as input a 3D model and a set of parameters that are process-dependent. The model to be manufactured is sliced by a set of parallel planes. The space between two adjacent slices is called a layer. The component of the process where the part is built is called the workspace. Although the processes described here can differ significantly, e.g. by the use of materials other than photopolymers, the underlying theme is the same; they all build parts on a layerby-layer basis. Such processes are generally known as Layered Manufacturing Techniques or Technologies (LMT). These technologies are changing at a quick pace, and the information contained herein may become quickly outdated. For our purposes, it is not important that they be described in great detail. More information can be found in other sources [13, 14, 16, 21, 24,?]. 3.1 Stereolithography Our first example of RPT is the Stereolithography apparatus (SLA) (Figure 1), developed and commercialized by 3D Systems, Inc. (US). A short explanation on how the process operates is as follows. Initially, the elevator is located at a distance from the surface of the liquid equal to the thickness of the first, bottom-most layer. The laser beam will scan the surface following the contours of the slice. The interior of the contour is then hatched using a hatch pattern. The liquid is a photopolymer that when exposed to the ultra-violet (uv) laser beam solidifies or is cured. The elevator is moved downwards, and the subsequent layers are produced analogously. Fortunately, the layers bind to each other. Finally, the part is removed from the vat, and the liquid that is still trapped in the interior is usually cured in a special oven. The laser beam that solidifies the liquid is the HeCd-laser shown in the upper-left corner of Figure 1. A second, HeNe-laser is used to ensure that the surface of the liquid is in the correct location. The sweeper 4 breaks the surface tension, ensures that a flat surface is obtained, and minimizes the processing time of each layer. Because the part is built in a liquid environment, and because the interior of the part still contains liquid polymer, it may be necessary to add support structures to increase the rigidity of the part, and to avoid overhangs from sinking to the bottom of the platform or from floating freely in the vat. The support structures are usually removed manually after the part is taken away from the platform. Scanning time depends on the geometry of the contours, hatch patterns, the speed of the laser, and the recoating time (i.e. the time taken to place a layer of photopolymer over the last solidified layer). The SLA is not the only process based on Stereolithography. Table 1 lists other organizations that commercialize processes based on the same principles. 4 Not present in the low-end model of the SLA-family. 6

7 HeCd-laser Lenses Mirror Elevator Sweeper Liquid polymer HeNe-laser Platform FIGURE 1. A schematic drawing of an SLA. Organization Country Product CMET (Mitsubishi) Japan SOUP 600, 850 D-MEC (JSR/Sony) Japan SCS 1000HD Laser 3D France SPL 1000, 5000 EOS GmbH Germany STEREOS 400, 600 Teijin Seiki Co. Japan Soliform 300, 500 TABLE 1. Other Stereolithography-based processes. 7

8 3.2 Solid ground curing The SOLIDER system was developed and commercialized by Cubital Ltd. (Israel). It also uses a photopolymer, sensitive to uv-light. It is, however, a significantly different process (see Figure 2). UV-lamp + shutter Mask plate cleaner Polymer spreader Residual polymer Wax spreader Wax cooling plate Milling head Electrical charging Mask development Mask erasure Liquid polymer (current layer) Wax Platform FIGURE 2. A schematic drawing of a SOLIDER process. The first difference concerns the vat: it moves horizontally as well as vertically. The horizontal movements take the workspace to different stations in the machine. The second difference concerns the light source: instead of using a laser beam, a uv-lamp (mercury) is used to flood the chamber and expose and solidify the entire layer at once. This avoids the need for post-curing the parts. To select the areas that should be cured, a mask is built on a glass plate, and subsequently, erased after begin used. The mask is built using a process similar to the one used in laser printers. The glass plate with the mask is placed between the lamp and the surface of the workspace. The third difference is that the parts are built surrounded by wax, eliminating the need for support structures 5. Once a layer has been exposed to the uv-lamp, the un-cured areas those areas filled with residual, liquid polymer are replaced by wax. This is done by wiping away the residual polymer and applying a layer of wax. The wax is hardened by a cold metal plate, and 5 On the other hand, one must de-wax the part. This can be done even with a dish washer, if the geometry of the part permits. 8

9 subsequently, the layer is milled to the correct height. The milling station also allows for layers to be removed, i.e. an undo operation is possible. The new layer of polymer is applied when the workspace moves from the milling station back to the exposure chamber. The latest improvements announced by Cubital are the ability to change the size of the workspace and an additional uv-lamp. 3.3 Selective laser sintering The University of Texas at Austin developed a method for sintering powder materials. The process is depicted in Figure 3. Instead of a liquid polymer, powders of different materials are CO2 Laser Optics Scanning Mirrors Powder Leveling Roller Unsintered Powder Workpiece Part Cylinder and Powder Bed Powder Cartridge Feedding/Collecting System FIGURE 3. A schematic drawing of an SLS process. spread over a platform by a roller. A laser sinters selected areas causing the particles to melt and then solidify. Unlike the processes mentioned above where there is only one phase transition, in sintering there are two: from solid to fluid, back to solid again. Processes that behave in this way 9

10 are generally known as selective laser sintering (SLS) processes. The materials being used or investigated include plastics, wax, metals, and coated ceramics. It is hoped that parts made of materials other than plastics with the required mechanical properties can be made using such processes. Like the SOLIDER system, there is no need for support structures, because the surrounding powder supports the parts being built. The process developed at Austin is being commercialized by DTM Corp. Recently, EOS GmbH has introduced to the market a process that operates under the same principles. 3.4 Laminated object manufacturing Helysis developed and commercialized a system that cuts and binds foils as illustrated in Figure 4. The undersurface of the foil has a binder that when pressed and heated by the roller causes it to Laser Ra Mirror Heated Roller Optic head Feeder Platform Collector FIGURE 4. A schematic drawing of a LOM process. 10

11 glue to the previous foil. The foil is cut by a laser following the contour of the slice. To help the removal of the excess material once the parts have been built, the exterior of the slice is hatched, as opposed to fluid-based processes (e.g. the SLA process), where the interior is hatched. The thickness of the foil is not constant. Therefore, a sensor (not shown in the Figure) measures the current foil thickness, and the model is sliced accordingly. 3.5 A short comparison From the user s point-of-view, the major aspects taken into consideration in chosing when and how to obtain a part are: time, cost, and functionality. Regarding RPT, none of the processes excel in all respects; each process has restrictions imposed by costs, accuracy, materials, geometry, and size. Table 2 6 is a short summary of the differences between the processes discussed in the previous Sections. The comparison is not complete, in that various other important aspects are not included, e.g. the price of the equipment, maintenance costs, and material costs. Process SLA 250 SOLIDER 5600 SLS 2000 LOM 1015 Company 3D Systems, Inc. Cubital Ltd. DTM Corp. Helisys Max. part size (mm) ( height) Layer thickness 0:1 0:9 0:05 0:15 0:13 0:005 0:05 (min/max; mm) Speed (vertical) dependent dependent Part geometry Part geometry layers/hour 10 mm/hour Accuracy 0:2mm :1% (all directions) 0:05 0:25mm 0:127mm Thermoplastics Photocurable Photocurable (PVC, nylon, Paper, nylon, Materials resins resins, wax ABS/SAN), polyester wax TABLE 2. A short comparison of some RP processes When the part does not fit in the workspace of the machine, acceptable results have been obtained by splitting the model in parts, building the parts separately, and then binding them together. Regarding the software tools and data exchange formats, the lowest common denominator is triangulated models represented in STL format. All vendors supply software tools to verify, correct, and slice the models. However, the software architecture and the quality of the tools varies considerably. Data transfer is now covered in the next Section. 6 This Table was compiled from an internal report of the INSTANTCAM project [3]. 11

12 4 Data transfer to RPT As mentioned earlier, speed is one of the most distinguishing features of RPT when compared to conventional methods. In fact, in many cases, the use of RPT can only be justified if the part can be obtained quickly. Quite often, though, the limiting factor is the time spent preparing the data. Once the data is correct, manufacturing time is known and relatively fast. Figure 5 sketches a typical scenario. The designer delivers the model to the manufacturer using surface Designer Error Description or the Part Manufacturer 3D Model FIGURE 5. A scenario between designer and manufacturer. mail or by electronic means. The model will usually be represented in some neutral format, e.g. VDAFS [27], IGES [25], or STL [1], or in some native format when both have access to the same CAD system. The model is then verified for correctness and converted to a suitable form if possible. The manufacturer is faced with the following problems: Is the model correct? If not, what is the nature of the mistakes and can they be corrected locally? If the mistakes cannot be corrected locally, how can one describe them to the designer? RP machines are not yet commonplace and the physical distance between the designer and the manufacturer plays a role in delivery time due to difficulties and delays in communication. Besides, the manufacturing costs are directly related to the amount of work spent preparing the data and the actual building of the part. The former can represent as much as 2=3 of the total costs. Therefore, any software tool that can minimize the number of times the designer and the manufacturer need to communicate or make their communication more efficient is beneficial. In a nutshell, these are problems related to data transfer. A closer look at how parametric surface models 7 are transferred will give us a better understanding of the problems. Figure 6 depicts the state transitions of interest undertaken by a model from the moment it is sent by the designer until it is manufactured. All the state transitions in the diagram are possible. For instance, one can take slices from medical imaging systems and interpolate intermediary slices that are subsequently used in a LMT process. In this case, a 3D model is never evaluated 7 Henceforth referred to as models. 12

13 Model in Internal, Native Format of Application Programs Facetted Model in Neutral Format (e.g. STL) a + - Sliced Model +b- LMT Process + c - Surface Model in Neutral Format (e.g. IGES or VDAFS) FIGURE 6. The state transitions of a parametric surface model. (path b+b,). On the other hand, some processes cannot effectively handle sliced models or 2 1 D models therefore, a faceted model is created and then sliced again (path b+a,a+b,). 3 The reason is that in some cases it is important to be able to position the model arbitrarily in the workspace of the machine, and this cannot be done with sliced models. The typical scenario is shown in Figure 7. A 3D CAD system a surface or solid modeller CAD System a - a + a - a + a - Verifier/ Corrector Process dependent a + Slicer b - LMT Process FIGURE 7. The typical scenario of data preparation. is used for creating the model. The most common step that follows is facetting the model. The current de facto data exchange standard for representing faceted models is called STL [1]. This format requires significant redundancy and is restricted to triangles. Normally, each vendor supplies the software tools for verifying the correctness of the model, generate process-dependent data, and to perform the slicing of faceted models. The format for representing the slices is proprietary. There is a trend for LMT vendors to develop interfaces based on slicing surface 13

14 models together with major CAD vendors. One of the objectives is to eliminate the need for always generating intermediary, faceted models. Therefore, the interest in correctly slicing models for LMT is growing. 4.1 Constraints on the model As mentioned above, data transfer between CAD systems and RP processes is mainly based on data exchange formats capable of representing faceted models. The current de facto standard is the STL format [1] which allows one to represent triangulated models, i.e. each facet is a triangle. FIGURE 8. A correct triangulation In order for models to be correctly manufactured they must represent a collection of one or more non-intersecting solids. The manufacturer hopes to receive well-behaved STL-files such as the one outlined in Figure 8. In a correct STL-file, each triangle has exactly one neighbour along each edge, and triangles are only allowed to intersect at common edges and vertices. Under these conditions, it is possible to distinguish precisely the inside from the outside of the model. Unfortunately, quite often incorrect faceted models are used. The mistakes can be numerous (Figure 9). The models can contain gaps due to missing facets, facets may intersect at incorrect locations, the same edge may be shared by more than two facets, etc. Special cases of these errors may occur that require separate treatment, e.g. overlapping facets (coplanar facets whose intersection results in another facet). The reasons for such errors are related to the application that generated the faceted model, the application that generated the original 3D CAD model, and the user. Many STL interfaces in CAD systems fail to inform the user that the result is not correct and problems remain undetected until the manufacturer attempts to process the model. Errors in the model can interfere with the building process. For instance, if a slice contains a gap when the internal structure of the slice is built, stray vectors might be created (Figure 10). The possibility of this happening is great, due to the fact, that the tool in this case is a laser 14

15 Gap FIGURE 9. Incorrect triangulations. beam of small diameter (approximately 0:2mm in an SLA), and the distance between the hatch lines may be likewise apart 8. These stray vectors damage the resulting part and possibly other parts being built in the same platform. The internal structure is process-dependent and is usually Contour of the slice Hatch pattern Stray vectors FIGURE 10. Correct vs. incorrect slices. proprietary information. Therefore, the internal structures used in practice will probably differ from the ones shown in Figure 10, but they all require simple, non-intersecting contours to be successfully created. These, in turn, can only guaranteed to be obtained if the original model is correct, i.e. a solid. 8 Not all processes use a laser beam but similar problems may occur with other processes. 15

16 5 RPT In Manufacturing RPT can be useful to anyone who manufactures a product or needs a physical object. To illustrate the strategic importance of RPT, we will use, as an example, the manufacturing industries. Figure 11 [26] illustrates how the requirements for the manufacturing industries have changed over the past three decades. One partner in the INSTANTCAM project markets appliances in Number of Variants Product Lifetime Product Complexity Required Delivery Time FIGURE 11. Changes in the requirements for the manufacturing industry. 10 countries. The same product family may have 6 different motors and 4 different technical features. The different technical features can be simple such as different materials, plugs, or colors, or complex such as differences in the internal housing. These differences are needed in order to attend to specific needs of users or to differenciate oneself from the competition. In addition, product lifetimes are becoming shorter, forcing a design group to develop new products whithin a shorter time. During the development process, one is frequently faced with the choice of either extending the development time or increasing the resources in order to meet the deadlines. Under these circumstances, time to market has been identified as a key factor in profitability; it is the development time and not the cost that is critical for the results (Figure 12 [18]). 16

17 DEVIATION Product Lifetime: 5 Years Extending development time by about 6 months Increasing development costs by about 50% 5% DECREASED PROFITS 30% FIGURE 12. Development time vs. development costs. This scenario requires changes on how a product is developed. Different groups design, engineering, marketing, production must cooperate more closely towards a common goal and work concurrently. The goal must be clear to everyone involved, and if cooperation is to be effective, it is essential to avoid communication problems. RPT allows a physical model to be available as soon as a 3D CAD model is ready. The physical model is a perfect communication tool; if a picture is worth a thousand words, then a physical model is worth a thousand pictures. In addition, parts produced via RPT are more and more frequently being used for functional tests and for obtaining tools that can be used for pre-series production tests. In this way, errors can be found at an earlier stage when changes are not so costly. Requirements can be refined and better understood leading to better products that meet the market demands. It has been estimated that using RPT effectively, the development time for toolings can be reduced by half. Another important aspect is the cost of introducing changes in the design of a product. In this respect, development of a physical product does not differ from software development: the cost of introducing changes increases significantly as one reaches the final stages of development. RPT can be an effective means for evaluating a design before costly committments are made, commitments that affect manufacturing costs and, ultimately, the final cost of the product. Again, the analogy holds: prototype software is developed for the same reason! However, Rapid Prototyping cannot be used effectively by product developers that do not use a 3D CAD system to create a model of the product. 17

18 5.1 Toolings The ideal situation is the ability to build any part with any material. Clearly, this is not yet possible, but there is relief in sight. Soligen s DSPC process is capable of producing ceramic shells, and is now in beta testing [21, 29]. Two Institutes of the Fraunhofer Gesellschaft in Germany, the Institute for Manufacturing Engineering and Automation (IPA, Stuttgart, Germany) and the Institute for Applied Material Research (IFAM, Bremen, Germany), are developing a process they call Multiphase Jet Solidification which can build plastic, metallic, and ceramic parts [12]. Another exciting project is being carried out at the Carnegie-Mellon University (USA) where a process capable of building composite parts is being developed [11]. The properties offered by RPT part are sufficiently good nowadays to enable the production of prototype toolings by using a process chain. A well-established method is vaccum casting. From the RPT model, one obtains a silicon mould from which approximately 20 parts can be made in Epoxy or investment casting wax. Various process chains have been reported in the literature [19, 15]. Each one has limitations concerning the geometry of the part, precision, number of parts that can be manufactured, and materials that can be obtained in the final part. In addition, some process chains, such as QuickCast, are restricted to a certain RP process. 6 RPT In Industrial Design When comparing industrial design applications to the manufacturing of toolings, the role of dimensional accuracy is not as significant as the quality of the surface. It should be clear to the reader by now that parts made via LMT exhibit a staircase effect. This effect can be minimized by choosing a suitable building direction, but rather often this is done at the expense of building time and costs. The staircase effect can be addressed in several ways. Firstly, good software tools can help minimize the problem [5]. Secondly, post-treatment can be applied, and in this case, the part is usually polished. Finally, the processes can be improved to virtually eliminate the problem. For instance, the technology developed by Laser 3D [2] can use a layer thickness as low as 0:015mm resulting in parts with no noticable staircase effect to the naked eye. Soligen claims that their process can also eliminate the staircases using different principles. 7 RPT In Medical Applications Applying RPT in the medicine is a new and exciting field. Many applications have become possible due to the convergence of three distinct technologies, namely Medical Imaging, Computer Graphics and CAD, and RPT. Computer-Assisted Tomography (CT) and Magnetic Resonance Imaging (MRI) provide high resolution images of internal structures of the human body, e.g. bone structures and organs. Once 18

19 these images have been processed by suitable software tools, it is possible to transfer the result to a RP process and obtain a physical part, called a medical model. Figure 13 depicts this process. Images (pixmaps) Image Processing Toolbox Edge Detection RP-specific Data Generation Contours, Internal vectors, Support structures RP Process Contours Physical Part FIGURE 13. Obtaining medical models from scanned images. Together, these technologies provide doctors and surgeons with a new tool physical models of human internal structures to better plan and prepare complex surgeries. If the surgeries can be carried out more successfully, less costs associated to post-operative treatment are expected, in addition to reduced risks, reduced patient suffering, and improvements in the quality of the results. Another recent application has been the manufacturing of a human chromosome 9. In this case, a chromosome was depleted of DNA by enzymatic digestion, leaving just the scaffold. Markers where introduced to serve as reference points for the 3D reconstruction. Next, EM photographs of tilted series from 0 o to 60 o, with steps of 3 o, were taken. A 3D CAD model containing triangles was obtained from the pictures, and a physical model was then built. Chromosomes are extremely complex. Several visualization techniques are used to understand their structure, including electron microscopic tomography, hidden line removal, stereo projections, and animations. Physical models, though, may become an indispensible tool for researches in the field. 9 A description of this episode can be found through the World Wide Web at in the document chromosome.html. It contains color photographs and videos of the model, and the original pictures of the chromosome. 19

20 8 RPT vs conventional technologies RPT does not and will not replace completely conventional technologies such NC and highspeed milling, or even hand-made parts. Rather, one should regard RPT as one more option in the toolkit for manufacturing parts. Figure 14 depicts a rough comparison between RPT and milling regarding the costs and time of manufacturing one part as a function of part complexity 10.Itis Costs Time LMT NC milling High-speed milling Complexity Complexity FIGURE 14. RPT vs conventional technologies. assumed, evidently, that the part can be manufactured by either technology such that the material and tolerance requirements are met. The axis have no values; these are company dependent. RPT offers clear advantages when more than one copy of a complex part must be made. Out of context, part complexity cannot be defined precisely, but it certainly contains the following ingredients: model size, wall height and thickness, and the ratio between these two, total number of surfaces in the CAD model, tolerance requirements, type of CAD system used to generate tool paths, and so on. Again, what is, and what is not, a complex part varies, to some extent, from one company to another. Concerning material requirements, it is clear that when using milling one can always obtain directly a part with the desired mechanical properties. This is usually the choice when manufacturing production toolings. But, as mentioned earlier, using a chain of processes that includes a RPT part, it is many times possible to obtain, indirectly, the same results in a shorter period of time. 9 Conclusions It is impossible to cover all aspects of these relatively new manufacturing processes without being brief at times. The reader should browse the literature to overcome the obvious limitations of this work. More important, though, is their effective introduction in the current working practices of companies. It is clear that these technologies, when applied correctly, can bring benefits in the form of better products in shorter lead times, and at reduced costs. 10 The original figure is part of an unpublished report of the INSTANTCAM project. 20

21 10 Acknowledgements I was introduced to RPT while participating in the INSTANTCAM project, an European Consortium of partners from both industry and research centers. A lot of material presented here was derived from reports of that project. I am very gratefull to these partners, particularly Hans Müller (BIBA, Germany), Ulrich Reetz (Black&Decker GmbH, Germany), Bent Mieritz and Karsten L. Jensen (the Danish Technological Institute, Denmark), Reidar Hovtun (NTH-SINTEF Production Engineering, Norway), and my collegue Ismo Mäkelä. The schematic drawings of the processes were made available by Joakim Simons and Benjamin Sederholm from the Mechanical Engineering Department of our Institute. At HUT, we received the financial support of TEKES. References [1] 3D Systems, Inc. Stereolithography Interface Specification, July [2] A.-L. Allanic, C. Médard, and P. Schaeffer. Stereophotolithography: A Brand New Machinery. In Solid Freeform Fabrication Symposium, pages University of Texas at Austin, August Austin, Texas, USA. [3] V. Burguete. LMT Processes Comparison. Technical report, Instituto Superior Técnico, Available from the author. Address: Av. Rovisco Pais 1, P-1096 Lisboa Codex, Portugal. [4] Cubital Ltd., 13 Ha Sadna St., Industrial Zone North, Raanana 43650, Israel. Cubital Facet List Syntax Guide. [5] A. Dolenc. Software Tools for Rapid Prototyping Technologies in Manufacturing. PhD thesis, Helsinki University of Technology, October Published in ACTA POLY- TECHNICA SCANDINAVICA, Mathematics and Computer Science Series No. 62. [6] A. Dolenc and I. Mäkelä. LEAF: A Data Exchange Format for LMT Processes. In Third International Conference on Rapid Prototyping, pages , Dayton, Ohio USA, June [7] A. Dolenc and I. Mäkelä. Optimized Triangulation of Parametric Surfaces. In Adrian Bowyer, editor, Computer-aided Surface Geometry and Design (Mathematics of Surfaces IV), number 48 in The Institute of Mathematics and its Applications Conference Series, pages Clarendon Press (Oxford), The Conference took place at Bath University (UK) in September An improved version of this work can be found in [5]. [8] A. Dolenc and I. Mäkelä. Slicing Procedures for Layered Manufacturing Techniques. Computer-Aided Design, 26(2): , February This article is a subset of [5]. 21

22 [9] A. Dolenc, I. Mäkelä, and R. Hovtun. Better Software for Rapid Prototyping with IN- STANTCAM. In G. L. Olling and F. Kimura, editors, Human Aspects in Computer Integrated Manufacturing, pages North-Holland, Also available as Technical Report TKO-B66 from the Helsinki University of Technology. [10] R. J. Donahue and R. S. Turner. CAD Modeling and Alternative Methods of Information Transfer for Rapid Prototyping Systems. In National Conference on Rapid Prototyping, pages University of Dayton and EMTEC, June Dayton, OH, USA. [11] D. Dutta, N. Kikuchi, P. Papalmbros, F. Prinz, and L. Weiss. Project MAXWELL: Towards Rapid Realization of Superior Products. In H. L. Marcus, J. J. Beaman, J. W. Barlow, D. L. Bourell, and R. H. Crawford, editors, Solid Freeform Fabrication Symposium, pages University of Texas at Austin, August Austin, Texas, USA. [12] M. Geiger, W. Steger, M. Greul, and M. Sindel. Multiphase Jet Solidification. EARP Newsletter, (3):8, January This Newsletter is published by the EARP Project and printed at the Danish Technological Institute (Århus, Denmark). [13] P. F. Jacobs, editor. RAPID PROTOTYPING & MANUFACTURING: Fundamentals of Stereolithography. SME, [14] K. L. Jensen. Desktop manufacturing, the next Industrial Revolution. Technical report, Danish Technological Institute, Teknologiparken, DK-8000 Aarhus, Denmark, This document contains a rather complete technical description of all RP processes, including some efforts that never reached the market. It was, though, no longer updated after [15] K. L. Jensen and R. Hovtun. Making Electrodes for EDM with Rapid Prototyping. In Third International Conference on Rapid Prototyping, pages , Dayton, Ohio USA, June [16] J. P. Kruth. Material Incress Manufacturing by Rapid Prototyping Techniques. In Annals of CIRP, volume 40/2, pages , [17] I. Mäkelä and A. Dolenc. Some efficient procedures for correcting triangulated models. In H.L.Marcus,J.J.Beaman,J.W.Barlow,D.L.Bourell,andR.H.Crawford,editors,Solid Freeform Fabrication Symposium, pages University of Texas at Austin, August Austin, Texas, USA. [18] McKinsey&Co. Various sources are cited. Apparently, this is part of a study conducted by McKinsey&Co. The Figure was kindly supplied by Mr. Ulrich Reetz (Black&Decker),

23 [19] T. H. Pang and P. F. Jacobs. StereoLithography 1993: QuickCast TM. In Solid Freeform Fabrication Symposium, pages University of Texas at Austin, August Austin, Texas, USA. [20] S. J. Rock and M. J. Wozny. A Flexible File Format for Solid Freeform Fabrication. In H. L. Marcus, J. J. Beaman, J. W. Barlow, D. L. Bourell, and R. H. Crawford, editors, Solid Freeform Fabrication Symposium Proceedings, pages The University of Texas at Austin, September [21] E. Sachs, M. Cima, P. Williams, D. Brancazio, and J. Cornie. Three Dimensional Printing: Rapid Tooling and Prototypes Directly from a CAD Model. Transactions of the ASME, 114: , [22] X. Sheng and B. E. Hirsch. Triangulation of trimmed surfaces in parametric space. Computer-Aided Design, 24(8): , August [23] X. Sheng and U. Tucholke. On triangulation surface model for SLA. In Second International Conference on Rapid Prototyping, pages , Dayton, Ohio USA, June A better version of this paper was published in [22]. [24] Technical Insights, Inc., PO Box 1304, Fort Lee, NJ , USA. Rapid Prototyping: Strategic Technology for Product Development Success, Winter [25] U.S. Department of Commerce, National Bureau of Standards, Gaithersburg, MD 20899, USA. Initial Graphics Exchange Specification (IGES) Version 4.0, June [26] VDMA. The Figures where found by Mr. Ulrich Reetz (Black&Decker) in a brochure, [27] Verband der Automobilindustrie e.v. (VDA), Westendstrasse 61, D-6000 Frankurt am Main, Germany. VDA Surface Interface, version 2.0, January [28] L. E. Weiss, E. L. Gursoz, F. B. Prinz, P. S. Fussel, S. Mahalingam, and E. P. Patrick. A Rapid Tool Manufacturing System Based on Stereolithography and Thermal Spraying. Manufacturing Review, 3(1):40 48, March [29] J. Yoo, M. J. Cima, S. Khanuja, and E. M. Sachs. Structural Ceramic Components by 3D Printing.InH.L.Marcus,J.J.Beaman,J.W.Barlow,D.L.Bourell,andR.H.Crawford, editors, Solid Freeform Fabrication Symposium, pages University of Texas at Austin, August Austin, Texas, USA. 23