Rapid Tooling Research

Prof Phill Dickens

Professor of Manufacturing Technology
De Montfort University
Leicester
LE1 9BH
UK

Professor Phil Dickens has been involved in rapid prototyping and manufacturing since 1990. He has led UK government missions on rapid prototyping to Japan and has been a member of a similar mission to the USA. He is a past member of the Advisory committee of SME/RPA. He has also been involved in organising several conferences and seminars on rapid prototyping and manufacturing. Professor Phill Dickens has recently moved from the University of Nottingham to De Montfort University to take the position of Professor of manufacturing technology. He will be continuing the work on rapid tooling and is now starting work on the next generation of machines for rapid manufacturing.

Rapid Tooling Research

Introduction

This paper has been prepared as a general overview of the research into rapid tooling during the last few years. It is not meant to be a comprehensive list of all the organizations or all of the activities or publications. It is intended to give a flavour of the work. In producing this overview many of the organizations are included and apologies are given now for those that are not. The overview is split into three main sections: Research topics, Organizations, and finally tables linking these together.

Research Topics

Cast Tools

Investment cast tool steel inserts have been used to manufacture production tools for injection moulding (Denton and Jacobs, 1994). Cast tools for die-castings have also been successfully produced (Litsey and Dzugen, 1998). However, it has been shown that it is very difficult to maintain reasonable tolerances with cast tooling (Almond et. al., 1997). The main problem with investment cast tools is generally not the surface roughness which can be very good, but distortion of the casting as it contracts on cooling. There may be some benefit in casting tools where the distortion can be controlled or where finish machining is used.

Conformal Cooling Channels

Work at MIT showed that it was possible to reduce cycle times for injection moulding by up to 37% (Sachs et. al., 1997) and similar work with electroformed tooling has given reductions of about 40% (McDonald, 1998). This use of conformal cooling channels is likely to be the major benefit of rapid tooling rather than reduced lead times or costs.

EDM Electrodes

EDM electrodes was one of the first areas to receive attention for rapid tooling and a significant amount of work has been done in this area (Killander, 1996). Electrodes made from Zirconium Diboride using selective laser sintering have indicated that they have very good performance in terms of erosion rate and wear rate (Stucker et. al. 1997). Electrodes made by copper plating SL models have been used successfully for finishing cuts (Arthur et. al. 1996). However, these electrodes had thin coatings of around 0.175mm and could not be used as roughing electrodes. More recent work has showed that increasing the copper thickness to 0.5mm allows the electrodes to be successfully used for roughing (Yang et. al. 1998).

Electrodes made by electroforming copper into SL cavities have shown they can be used successfully for roughing cuts (Ippolito et. al. 1996). However, problems occur when trying to electroplate into narrow slots. This produces flaws in the copper, which lead to premature failure of the electrodes (Yarlagadda et. al., 1998).

Electroformed Tooling

One of the most successful combinations has been a nickel shell and ceramic backing to produce small to large tools (Wise, 1997). This has mostly been used in combination with Stereolithography but some workers have also used FDM models (Greul et. al., 1995).

Jet plating was used to manufacture a tooling cavity but it was difficult to control the height (Dover et. al., 1996).

Graded Materials

Shape Deposition Manufacturing has been used to make an injection-moulding tool that has different materials within the structure (Fessler et al., 1997). Along with conformal cooling channels graded materials will be the other major benefit of making tools by adding layers of material. It is likely that this will become one of the major research areas of the future.

Laminated Tooling

Although most laminated tooling is made with metal sheets some large tools have been made from polystyrene sheets (Cheol et. al., 1996). Most tools are made with sheets that have the profile cut at 90 degrees. This is mainly to reduce costs and programming times. However, beveled edges produce a much better surface finish on the tool (Walczyk and Hardt, 1996).

Laminated tools have been used successfully in production for moulding hundreds of thousands of polyurethane parts. Tools made by this technique compared favorably in terms of cost and lead times with cast or machined tools (Dickens, 1996).

Large tools have been made for injection moulding glass fibre filled polyamide (Dormal et. al., 1998) or for sheet metal forming, but problems occur with tearing of sheets when the tool is not finished (Muller and Enzmann, 1998).

Initial work has shown that bonding is not necessary for laminated tooling, even for high-pressure applications like die-casting of aluminium (Soar and Dickens, 1997; Soar and Dickens, 1998). Research was undertaken to evaluate various bonding techniques for aluminium laminated tooling. A number of adhesives showed good results (Walczyk & Dolar 1997).

The latest development is a prototype machine for making laminated tools. This is based at Toyota Technological Institute (Himmer, et. al. 1998). This machine bonds the laminates with laser spot welding. Both halves of the sheet metal forming tools are produced simultaneously. The current method of doing this causes problems in bonding the top half of the tool.

It is likely that laminated tooling will become more important over the next few years, especially for large tools.

Patterns

All of the commercial rapid prototyping systems have been used to manufacture patterns for sand casting. These have generally worked very well and a good example of this is with the Disamatic Green sand casting process (Levinson and Moos, 1997).

Powder Tooling

The easiest way to make tools with powder is to cast a highly filled resin against a master pattern. Powders with 10% by volume resin have successfully made tools for moulding plastic parts (Greaves and Vawter, 1998).

As well as injection moulding of plastics, Keltool inserts have been successfully used for die casting of several hundred parts, (Litsey and Dzugen, 1998) as have tools made by the RapidTool process (Reinhart et. al., 1998). The normal material for die-casting applications is H13, which is very resistant to heat cracking, which is the normal method for these tools to fail. Metal powders that have been infiltrated with copper have poor resistance to heat cracking under these conditions. Although cracking occurs after just a few parts it is still possible to use the tool provided the witness marks on the castings can be accepted. Obviously, cracking will become severe and parts of the tool will start to break away.

It has been shown that it is possible to manufacture tools by casting powders as in the Keltool process but have only 0.1% shrinkage (Noguchi and Nakagawa, 1997). A variation of this technique has been used with slip casting of powders. This also gave lower shrinkage rates (Ainsley and Hon, 1996). Work at Rensselaer has resulted in the manufacture of tools by using an adaptation of the gel casting technique for ceramics (Rock et. al., 1996).

Selective laser sintering has produced most of the tools that have been made directly from powder (Badrinarayan and Barlow, 1994) with inserts infiltrated with epoxy for short runs or copper for production runs (Barlow et. al., 1996). A direct metal powder produced by Electrolux has been used successfully for injection moulding of plastics (Nyrhila, 1996). EOS GmbH now markets this.

An alternative powder technique is to fuse particles together with a high power laser (Klocke et. al., 1996) and without doubt the most impressive tool produced so far is that from Krupp. This tool was intended for forging steel parts (Peterseim and Luck, 1997).

Sprayed Tools

The strength of sprayed metal tooling is normally a big problem. However, it has been shown that the mechanical properties of these shells can be significantly improved (Fussell et. al., 1994). One way to improve the mechanical properties of sprayed shells is to simultaneously shot peen the material as it is deposited (Gotzsche-Larsen, 1997).

SLS Direct Tools

Tools made directly by the SLS process from plastic powder have required extensive finishing to enable release of the plastic parts (Venus and van de Crommert, 1996).

Stereolithography Tooling

Stereolithography tools have been used to manufacture waxes for investment casting but one of the problems is the slow cooling rate (Male et. al., 1996).

Research conducted under the European Action on Rapid Prototyping (EARP) has shown that tools made directly in the Stereolithography machine perform better for injection moulding than tools made by any other RP process (Roberts and Ilston, 1998). This research showed that there is a significant difference in the surface roughness of moulds produced by different RP techniques. Further work has shown that improving the surface roughness by polishing then increases tool life. (Blair and Colton, 1998).

Over 500 polypropylene parts have been successfully moulded into Stereolithography tools (Rahmati and Dickens, 1997). Research has indicated that moulding of Delrin or Polypropylene into Stereolithography tools has little effect on the mechanical properties of the parts (Jayanathi et. al., 1997). However, moulding of polyamide has given quite different results with Young's Modulus being higher and elongation at break being much less in Stereolithography tools (Dusel, et. al., 1998). This has been explained as being due to different amounts of crystallinity with non-crystalline materials having greater mechanical properties and crystalline materials having high tensile and flexural strength but lower impact strength (Dawson, 1998).

Silica filler has been used in SL resins to give better abrasion resistance and a higher modulus (Taft, et. al., 1997), an alternative route is being developed which uses liquid crystal resins that have a higher glass transition temperature (Chartoff, et. al., 1998).

The main reason that it is possible to inject plastic into Stereolithography tools is the low thermal conductivity of the resin which is 0.21 W/mK, compared to 45 W/mK for Tool Steel. In metal tools the heat transfer rate is high and so the plastic is trying to freeze before the cavity is filled. To overcome this requires high injection pressures and high injection speeds. With Stereolithography inserts the heat transfer rate is much lower and so the pressures and injection speeds can be greatly reduced. However, the big disadvantages with Stereolithography inserts is the much lower mechanical strength and the long cycle times due to lower thermal conductivity. This then leads to an optimum temperature at which parts should be ejected from the tool cavity (Hopkinson and Dickens, 1998).

Electroplating the surfaces of the Stereolithography inserts has been suggested as a way of improving abrasion resistance and also reducing hot spots in the tool cavity. (Jacobs, 1997).

Tolerances

One of the main problems with Rapid Tooling techniques at the moment is the inability to hold tight tolerances, especially on larger tools. Jacobs has shown that when tools are produced by a process which involves the tool material changing from a liquid to a solid then this usually has an associated shrinkage of the material. The variation in the accuracy is directly proportional to the amount of shrinkage (Jacobs, 1998). A modified version of this prediction model produced by Jacobs determines the tolerances for a number of rapid tooling techniques (Mueller, 1998).

Organizations

3D Systems (3D)
Tools made directly by Stereolithography have indicated reasonable tool life for injection moulding of plastics (Jacobs, 1997).

Alcoa
Some work has been undertaken to improve the mechanical properties of shells produced by metal spraying (Fussell et. al., 1994).

Bavarian Laser Centre (BLZ)
Lasers have been used to manufacture tools by either powder sintering or laser ablation (Coremans et. al., 1996).

BIBA
A number of Rapid Tooling routes have been assessed for manufacturing prototype sheet metal parts (Muller and Enzmann, 1998).

Buckinghamshire College (Bucks)
Tool cavities for injection moulding have been manufactured by electroforming onto SL models (Dover et. al., 1996). Various tooling techniques have been assessed for producing waxes for investment casting (Male et. al., 1996).

CEMCOM Corp. (CEM)
Electroformed nickel shells have been backed with ceramic to produce injection-moulding tools that have good performance and tool life (Wise, 1997).

Clemson University (Clem)
Filled Stereolithography resins with Silica have been used to manufacture tools for injection moulding (Taft et. al., 1997).

CRIF
Laminated tools for injection moulding have been made, ranging from small to large cavities (Dormal et. al., 1998).

Danish Technological Institute (DTI)
Tools made by simultaneous metal spraying and shot peening perform much better than conventional sprayed tooling (Gotzsche-Larsen, 1997). Patterns for the Disamatic Green sand casting process have been successfully manufactured with Stereolithography (Levinson and Moos, 1997).

Delphi Interior & Lighting Systems (Delphi)
Injection moulding tools have been successfully manufactured and run using a highly filled resin. (Greaves and Vawter, 1998).

De Montfort University
Laminated tools have been used successfully for die-casting aluminium parts. It appears that it is not always necessary to bond these laminates even for applications as extreme as these (Soar and Dickens, 1998). There appears to be an optimum temperature at which plastic parts should be ejected from Stereolithography tools (Hopkinson and Dickens, 1998).

Dupont Somos
The mechanical properties of plastic parts have been investigated when Stereolithography tools were used for injection moulding plastics (Jayanathi et. al., 1997).

Electrolux Rapid Development (Electro)
A low melting point material has been developed by Electrolux which is now used commercially in the SLS machines marketed by EOS GmbH (Nyrhila, 1996).

EMTEC
Investment casting of H13 tool steel has produced successful tools for die casting (Litsey and Dzugen, 1998).

ExpressTool (Exp)
The accuracy of tooling, where there is a change in the material state from liquid to solid is dependent on the magnitude of shrinkage (Jacobs, 1998).

Electroformed tooling with conformal cooling channels have resulted in cycle time reductions of around 40% (McDonald, 1998).

Ford Motor Company (Ford)
The earliest reported work on manufacturing investment cast tooling with the use of sacrificial RP models showed that tool steel inserts could be made (Denton and Jacobs, 1994).

Fraunhofer (IFAM)
Injection moulding tools have been successfully manufactured by electroforming directly onto FDM models (Greul et. al., 1995).

Fraunhofer IPT (IPT)
The Controlled Metal Build-up process has been used to manufacture tools for injection moulding of rubber parts (Klocke et. al., 1996).

Institutet for Verkstadsteknisk Forskning (IVF)
Several techniques for manufacturing EDM electrodes have been analysed. Tools made by the RapidTool process have also been investigated (Killander, 1996).

KruppEntwicklungszentrum (Krupp)
Under a European project Krupp managed to produce a forging tool in tool steel which was almost 100% dense (Peterseim and Luck, 1997).

MIT
Conformal cooling channels in injection-moulding tools have been produced by 3D printing (Sachs et. al., 1997).

New Jersey Institute of Technology (NJIT)
Stereolithography models, which have been electroplated with a 0.5mm copper coating, have been used successfully as roughing electrodes for EDM (Yang et. al., 1998).

PERA
Tools for injection moulding of plastics have been produced by investment casting with RP models as sacrificial patterns (Almond et. al., 1997).

Plynetics Express Corporation (Plyn)
Models have been produced which predict the tolerances of parts made with rapid tooling processes (Mueller, 1998).

Politecnico di Torino (Pol Tor)
EDM electrodes have been manufactured by electroforming copper into RP cavities (Ippolito et. al., 1996).

Queensland University of Technology (QUT)
Electroforming, onto Stereolithography models has made EDM electrodes. These electrodes have then been used for machining steel (Yarlagadda et. al., 1998).

Rensselaer Polytechnic Institute (RPI)
A variety of cutting techniques have been investigated which are capable of providing beveled edges on sheets for laminated tools (Walczyk and Hardt, 1996) as have various bonding techniques for laminated tooling (Walczyk & Dolar, 1997). A powder moulding technique similar to freeze casting has been developed to manufacture metal tools (Rock et. al., 1996).

Rapid Prototyping & Manufacturing Institute - Georgia Institute of Technology (RPMI)
It has been shown that improving the service finish of Stereolithography moulds by polishing gives greater tool life (Blair and Colton, 1998) and that injection moulding of plastic into Stereolithography tools results in different mechanical properties than when steel tools are used (Dawson, 1998).

Stanford University (Stan)
Tools for injection moulding have been manufactured by SDM. These tools have different materials in certain locations (Fessler et al., 1997).

Swiss Federal Institute of Technology (Swiss)
A standard method of assessing tool performance has been developed (Karapatis et. al., 1997).

Technische Universitat Munchen (TUM)
Tools for die-casting have been made by the RapidTool process and have been used successfully even though cracking occurs after just a few shots (Reinhart et. al., 1998).

University of Dayton (U of Day)
New liquid Crystal resins have been developed which have higher glass transition temperatures and these may prove particularly useful for injection moulding tools (Chartoff et. al., 1998).

University of Liverpool (U of Liv)
Tooling has been made by slip casting stainless steel powders (Ainsley and Hon, 1996).

University of Nottingham (U of Nott)
EDM electrodes manufactured by copper plating SL models have been successfully used as finishing electrodes (Arthur et. al. 1996). Stereolithography tooling has been used successfully to mould polypropylene (Rahmati and Dickens, 1997). Laminated tool has been used in production for moulding polyurethane parts at Ford (Dickens, 1996) and for die-casting of aluminium (Soar and Dickens, 1997).

University of Rhode Island (U of RI)
Manufacturing of EDM electrodes from Zirconium Diboride using selective laser sintering has indicated low wear rates and high erosion rates (Stucker et. al., 1997).

University of Stuttgart (U of Stutt)
Mechanical properties of plastic parts moulded in Stereolithography tools have been analysed and simulation used to predict properties (Dusel et. al., 1998).

University of Sunderland (U of Sun)
Injection moulding into a variety of materials such as silicon rubber or direct SLS tools has produced plastic parts (Venus and van de Crommert, 1996).

University of Texas (U of Tex)
Some of the early work on tools made by selective laser sintering indicated the potential of this technique (Badrinarayan and Barlow, 1994). SLS inserts have been infiltrated with either epoxy resin or copper (Barlow et. al., 1996).

University of Tokyo (U of Tokyo)
Laminated tools were first researched at University of Tokyo and have resulted in a prototype machine (Himmer et. al., 1998). Tools were made for injection moulding by casting metal powders against an RP master (Noguchi and Nakagawa, 1997).

University of Utah (U of Utah)
Large laminated tools made from polystyrene have been used to manufacture composite structures (Cheol et. al., 1996).

University of Warwick (U of W)
Injection moulding tools were made by a number of rapid prototyping processes and then evaluated in terms of their performance and tool life (Roberts and Ilston, 1998).

Upfront Technologies (Upfront)
Keltool inserts have been successfully used to die cast several hundred aluminium parts (Litsey and Dzugen, 1998).

References

Ainsley, C. And Hon, K.K.B. 1996, 'Slip casting as a Rapid Tooling process', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 12 - 14 Aug 1996, ISSN 1053-2153, p167-174.

Almond, H., Steel, S., Dickens, P.M., Wykes, C., 1997, 'The accuracy of RP models for investment casting of injection mould tool inserts', Proc. of Rapid Tooling & Manufacture -Scandinavian Conference & Exhibition, Nov. 12 -13 1997, Danish Technological Institute, Aarhus, Denmark.

Arthur, A., Dickens, P.M., Bocking, C., Cobb, R., 1996, 'Wear & Failure Mechanisms for SL EDM Electrodes', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 12 -14 Aug 1996, ISSN 1053-2153, p175-189.

Badrinarayan, B. And Barlow, J.W., 1994, 'Manufacture of injection moulds using SLS', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 8 -10 Aug 1994, ISSN 1053-2153, p371-378.

Barlow, J.W., Beaman, J.J., Balasubramanian, B., 1996, 'A rapid mould making system: material properties and design considerations', Rapid Prototyping Journal, Vol. 2, No. 3, 1996, p4-15.

Blair, B.M., Colton, J.S., 1998, 'Processing of stereolithography plastics to improve surface finish' Proc. of 3D Systems North American Stereolithography user Group mtg., March 1 -5 1998, San Antonio, Texas.

Chartoff, R., Ullett, J.S., Schultz, J.W., 1998 'New high temperature SLA resins for rapid plastic tooling', Proc. of 3D Systems North American Stereolithography user Group mtg., March 1 -5 1998, San Antonio, Texas.

Cheol, H. L., Gaffney, T.M., Thomas, C.L., 1996, 'Soft Tooling for low production manufacturing of large structures', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 12 -14 Aug 1996, ISSN 1053-2153, p207-214

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Dawson, K., 1998, 'The effect of rapid tooling on final product properties', Proc. of 3D Systems North American Stereolithography user Group mtg., March 1 -5 1998, San Antonio, Texas.

Denton, K.R. and Jacobs, P.F. 1994, 'QuickCastTM & Rapid tooling: A case history at Ford Motor Company', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 8 -10 Aug 1994, ISSN 1053-2153, p154-174.

Dickens, P.M., 1996, 'Laminated Tooling for Moulding Polyurethane parts', Proc. Rapid Prototyping & Manufacturing 96 Conf., April 23 -25 1996, Dearborn, MI, SME.

Dormal, T., Dam, J-L., Baraldi, U., 1998, 'A new technology for the manufacturing of large prototype injection moulds: LLCC', Proc. of 7th European Conference on Rapid Prototyping & Manufacturing, July 7 -9 1998, Aachen, Germany, Ed. by Campbell, R.I., p327-335.

Dover, S.J., Rennie, A.E.A., Bennett, G.R., 1996, 'Rapid Prototyping using electrodeposition of copper', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 12 -14 Aug 1996, ISSN 1053-2153, p191-198.

Dusel, K.-H., Esch, J., Eyerer, P., Luck, T., 1998, 'Rapid Tooling simulation and applications of the injection moulding process', Proc. of 7th European Conference on Rapid Prototyping & Manufacturing, July 7 -9 1998, Aachen, Germany, Ed. by Campbell, R.I., p375-383.

Fessler, J., Nickel, A., Link, G., Prinz, F., 1997, 'Functional Graded Metallic prototypes through Shape Deposition Manufacturing', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 11 -13 Aug 1997, ISSN 1053-2153, p521-528.

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Rahmati, S. and Dickens, P.M., 1997 'Stereolithography injection mould tool failure analysis', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 11 -13 Aug 1997, ISSN 1053-2153, p295-305.

Reinhart, G., Fahrer, J., Breitinger, F., 1998, 'Rapid tooling process chains based on SLS', Proc. of 7th European Conference on Rapid Prototyping & Manufacturing, July 7 -9 1998, Aachen, Germany, Ed. by Campbell, R.I., p351-359.

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Sachs, E., Allen, S., Guo, H., Banos, J., Cima, M., Serdy, J., Brancazio, D., 1997 'Progress on Tooling by 3D Printing; Conformal Cooling, Dimensional Control, Surface Finish and Hardness', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 11 -13 Aug 1997, ISSN 1053-2153, p115-123.

Soar, R.C. and Dickens P.M., 1997 'Deflection and prevention of ingress within laminated tooling for pressure die-casting', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 11 -13 Aug 1997, ISSN 1053-2153, p307-315.

Soar, R.C. and Dickens, P.M., 1998 'The use of laminated tooling for the production of prototype pressure die-cast tools', Proc. TCT'98 Conf., 13 - 14 Oct. 1998, Nottingham.

Stucker, B., Bradley, W., Eubank, P.T., Norasetthekul, S., Bozkurt, B., 1997 'Zirconium Diboride/Copper EDM Electrodes from Selective Laser Sintering', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 11 -13 Aug 1997, ISSN 1053-2153, p257-265.

Taft, D., Ogale, A., Paul, F., Hunt, E., Ahzi, S., 1997, 'Silica filled resins for SLA Tools', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 11 -13 Aug 1997, ISSN 1053-2153, p341-348.

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Walczyk, D and Dolar, N. 1997 'Bonding Methods for laminated tooling', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 11 -13 Aug 1997, ISSN 1053-2153, p211-221.

Walczyk, D and Hardt, E. 1996, 'Recent Developments in profiled edge lamination dies for sheet metal forming', Proc. Solid Freeform Fabrication Symposium, Austin, Texas, 12 -14 Aug 1996, ISSN 1053-2153, p215-226.

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