laminated object manufacturing for rapid tooling and patternmaking in foundry industry

Ž .Computers in Industry 39 1999 47–53

Laminated object manufacturing for rapid tooling andpatternmaking in foundry industry

Bernhard Mueller a,), Detlef Kochan b

a Formguss Dresden, Germanyb SFM, Dresden, Germany

Abstract

Ž .The laminated object manufacturing LOM process is an effective rapid prototyping technology with a variety ofapplication possibilities. Applying LOM in rapid tooling and patternmaking is especially advantageous because of the LOMobjects’ robustness, their wood-like properties and their comparably low material costs. Possible fields of application areshown in the following. Explicit application examples in sand casting, investment casting and ceramics processing show howa reduction of necessary process steps and cycle times can be achieved by the application of LOM models. To gain this thecontrol of the LOM objects’ accuracy and stability during different secondary processes is of decisive importance. q 1999Elsevier Science B.V. All rights reserved.

Ž .Keywords: Rapid prototyping; Rapid tooling and patternmaking; Foundry industry; Laminated object manufacturing LOM

1. Introduction

The new technologies of direct object generationŽfrom 3D CAD data rapid prototyping and manufac-

.turing keep belonging to the most important growthw xmarkets worldwide. According to Wohlers 1 the

1996 growth rate amounts more than 40% with amarket share of 80% for the United States. Specificadvantages and disadvantages characterize all intro-duced systems. Although all technologies proceed alayer-by-layer generation based on sliced 3D CADdata some considerable differences result from thephysical principles and the processed materials.

) Corresponding author. E-mail:[email protected]

Searching for the ideal process the following hasto be considered: like there is no universal process intraditional manufacturing technology there will benone in rapid prototyping either. Instead, it is impor-tant to select the best suited system by the user’sspecific demands.

Considering the dominating Rapid Prototypingapplication so far it can be assumed that all commer-cially available systems like stereolithography, lami-

Ž .nated object manufacturing LOM , fused depositionŽ . Ž .modeling FDM , selective laser sintering SLS , etc.

Ž w x.see Ref. 2 are suited for design checking pur-poses. Differences in benchmarking result from theapplication ranges of the processes for different sec-ondary operations. From that point of view the fol-lowing shows a deeper characterization of the advan-tages and application possibilities of the LOM pro-cess—without comparing or ranking all availablesystems.

0166-3615r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S0166-3615 98 00127-4

( )B. Mueller, D. KochanrComputers in Industry 39 1999 47–5348

2. Specific advantages of the LOM technology

Various advantages emerge from the peculiarityof the LOM process compared to other RP technolo-

w x Ž .gies 3–14 : a very low internal tensions of theLOM parts prevent distortion, shrinking and defor-

Ž .mation, b the parts have a high durability, lowŽ .brittleness and fragility, c very large parts can be

Žproduced by the LOM process 500=800=500. Ž .mmr20=30=20 in. , d LOM parts out of paper

have properties comparable to plywood—a typicalŽ .patternmaking material, e various organic and inor-

ganic materials with different chemical and mechani-cal properties for a whole variety of applications can

Žbe processed currently commercially available are. Ž .paper and plastic , f the parts are very well finish-

Ž .able, g LOM materials are non-toxic, non-reactiveŽ .and, therefore, easy to handle and dispose and h

material, machine and process costs are lower thanwith other RP systems what results in lower partcosts.

Some properties might be considered as disadvan-Ž .tages: a a high effort must be applied for decubing,

Ž .finishing and sealing the parts, b the control of theparts’ accuracy in the Z-dimension is relatively com-plicated for paper LOM parts due to a swelling effectŽ . w x Ž .‘Z growth’ 15 , c The part accuracy is limited

Ž .due to the comparably simple machine design, dmechanical and thermal material properties are inho-mogeneous due to the laminated structure of basic

Ž .material and adhesive and e the detail reproductionand durability of small part features is comparablylow.

Compared to other RP systems the advantages ofLOM predominate and the process gets more andmore popular with users. This is not least proven bythe fact that Helisys ranked the 15th fastest growing

w xhigh tech company in the US in 1995 10 .

3. Application range

The strength of the LOM technology is especiallyto be seen with large, compact models of complexgeometry with not too many fine details and under-cuts. In addition LOM models can be applied in allcases where traditionally wooden patterns are used.

In a lot of other fields of application LOM modelsare of equal value like other RP models. Generallyspoken almost all geometric objects can be generatedby the LOM process.

The application of LOM models is economicallyuseful not only for reasonably priced design modelsbut also for the generation of prototype and pre-seriestools and tool inserts for molding and die castingŽ . Žrapid tooling and for casting patterns rapid pat-

. w xternmaking 16 . Table 1 shows the main fields ofapplication and the way of using the LOM objects inthe particular case.

The economy of LOM application in foundryindustry is remarkably high where low volume com-plex metal parts need to be produced in very short

Žtime prototypes, pre-series and low volume series.production . Manual sand molding with a loose LOM

pattern is best suited for that type of application.For higher volume production resin plate patterns

and core boxes are required. A combined use ofŽLOM and traditional patternmaking LOM master

patterns for resin plate patterns and core boxes,.mounting of LOM pattern halves on wooden plates

might prove more economical than straight tradi-tional patternmaking.

Another deciding factor is if 3D CAD data areavailable and applicable. The generation of LOMobjects is based on a complete 3D CAD model. Theeffort for 3D design has to be considered in thedecision on the applicability of LOM. Especiallycasting patterns might be problematic in the CADmodeling process because of their draft angles andmany roundings. Compromises between LOM and

Žtraditional patternmaking e.g., subsequent modifica-tion of a LOM model with traditional methods to

.turn it into a complete casting pattern can solve thisproblem.

Another problem of decisive character for appli-cability and acceptance of LOM like of any other RPtechnology is the durability and wear resistance ofthe generated objects. Especially important for LOMapplication in tooling and patternmaking are:Ø heat resistance,Ø moisture resistance,Ø tensile and compressive strength andØ wear resistance.

The selection of an appropriate LOM material onthe one hand and of a suitable coating process on the

( )B. Mueller, D. KochanrComputers in Industry 39 1999 47–53 49

Table 1Fields of LOM application

Branch Process LOM model as Function of LOM models

Positives Negatives

Molding and plastics processing vacuum castingrRTV X master pattern for silicon moldinjection molding X master pattern for toolrtool insertblow molding X master pattern for toolrtool insertrotational molding X master pattern for rotational moldlaminating X laminating moldvacuum forming X vacuum forming mold

Foundry technology sand casting X pattern for sand moldinginvestment casting X master pattern for wax injection mold

X wax injection moldX master pattern for plaster mold

die casting X master pattern for dierdie insertpressure die casting X master pattern for dierdie insert

Ceramics industry low pressure X master pattern for plaster moldinjection molding X moldrmold insert

Architecturercivil engineering advertised objects X terrain models with buildingsdemonstration objects X reproductions of facades, sculptures etc.

Medicine reproductions of organs X reproductions of organs and bone structuresorthopedic surgery X master patterns for artificial limbs

other is important for that. Fortunately the variety ofLOM materials has increased lately—also due to theappearance of new vendors. In the meantime moreheat resistant materials, plastic and ceramic foils areavailable besides the classic paper materials. Surfaceimprovement currently reaches from wear resistantorganic coats to thin film technologies like titaniumnitrite or diamond-like carbon.

Certainly the know-how of the particular RP ser-vice provider still plays the most important role. Theappropriate, tailor-made solution for the particularcase decides on the application’s success or failure.

4. Examples from new fields of application

In the following some selected examples of LOMapplication in new fields are described in detail. Thefocus is set on the description of the technical solu-tion and the reached effects.

4.1. Sand casting

Ž .The cable sleeve Fig. 1 is a complex casting. Itsgeometry is sophisticated because of the wall thick-

Ž .ness of 3 mm 0.12 in. and less, exterior fins andthe required flatness of the sealing surface. The part

Žmeasures about 330=140=70 mm 13=5.5=.2.75 in. . The customer desired eight aluminum parts.

Ž .The 3D CAD model ProrENGINEER data wasŽ .processed for casting by adding draft angle 1.58 ,

Ž .roundings radius 2 and 3 mmr0.08 and 0.12 in.Ž .and shrinkage factor globally 1.0% and by simpli-

fying some features in arrangement with the cus-tomer.

The LOM model was generated on a LOM 1015with Helisys’ LPS paper. The LOM model wassanded and sealed as usual. The roundings betweenthe fins and the base plate proved to be too small forthe molding process. For this reason the pattern-maker enlarged the radius traditionally to 3 mmŽ .0.12 in. . In addition a reinforcement plate wasmounted onto the LOM pattern to ease its removalfrom the sand mold without damage. Afterwards aspecially developed wear and moisture resistant coat-ing was applied on the LOM pattern. The preparedpattern was available to the foundry after 1 1r2weeks.

The first three castings were hand-molded. Corre-sponding to the customer’s demands the gained sur-face quality was comparable to plaster casting or


Ž .Fig. 1. Application example ‘cable sleeve’ LOM pattern and aluminum casting .

investment casting due to the use of oil-bound facingsand. Dimensional accuracy was much better thanthe German DIN standards require for Sand CastingŽ .DIN 1688 part 1-GTA 15r5 . All castings keep to

Žthe much tighter tolerances of GTA 13 DIN 1680.part 2 .

Five more castings were molded in furane resinsand. This was done on the customer’s request toproduce the castings faster and lower priced. Thesurface quality of these parts was more typical forsand casting. The dimensional accuracy was compa-rable to that of the hand-molded castings.

Due to the surface sealing with the special coatingŽneither wear nor a part swelling visible and measur-

.able occurred in spite of the abrasive impact and themoisture content of the molding sand. For this reasonit can be assumed that a much higher number ofcastings could have been produced with the sameLOM pattern.

This way the customer received first metal parts 21r2 weeks after providing the CAD data. In compar-ison the first parts would have been ready after 4weeks going the traditional way. The pattern costswere reduced by 25% as well.

4.2. InÕestment casting

Ž .The axle bracket Fig. 2 is a typical pressure diecasting part used in the automotive industry. For

geometry checking in fitting tests five prototypes inŽ .series material aluminum casting were needed. The

lost wax process was selected to provide them.To reduce the effort for the wax injection tool a

LOM mold was used instead of a machined metaltool. Starting with the CAD data of the bracket thetool halves were designed. The location of the ejec-tor pins was already implemented into the CADmodel. After generating, finishing and sealing theLOM mold halves the tool was completed by ream-ering the ejector pin holes and setting bolts forscrewing the tool on.

After 2 1r2 weeks a functioning LOM wax injec-tion tool was created. Wax injection was done with

Ž .0.2 to 0.4 MPa at 708C 1608F . Thermal and pres-sure stress in the LOM tool and controlling thecooling process of the wax part were problematic.By applying a special surface coat on the tool therequired number of wax parts could be created in theLOM mold.

ŽThe wax parts with thin fins of just 3 mm 0.12.in. were handed over to the foundry. Aluminum

parts were created by the lost wax process. The thinwalls and long running distances were problematic.

All in all, castings were ready after 4 weeks.Choosing the described technology the foundry wasable to create such complex parts in this size for thefirst time.


Ž .Fig. 2. Application example ‘axle bracket’ LOM mold with injected wax pattern .

4.3. Ceramic part

ŽBecause of high stresses a conveying worm 25.mmr1 in. in diameter, 50 mmr2 in. long should be

made of ceramic. To produce green parts low pres-sure injection molding is a common process. The

Ž .worm’s geometry Fig. 3 did neither allow a divided

two-piece hard tool because of the undercuts of theworm’s pitch nor to screw the worm out of the toolbecause of machining allowances on the worm’s flatsides and the brittleness of the green part.

For this reason the decision was made to use aone-piece tool with flexible mold halves. Therefore,a LOM positive of the worm was created considering

ŽFig. 3. Application example ‘conveying worm’ LOM master pattern, silicon cushion with metal jacket and injected ceramic parts—green.and hardened .


the material shrinkage. This model was used tocreate a silicon cushion similar to those for RTV andvacuum casting of plastic parts. To absorb the rela-tively high pressures a metal jacket was placed aroundthe silicon cushion. The metal jacket was designed toserve as a universal tool for different worms ofsimilar size but with different pitches and designs.

This process ensured a removal of the injectedgreen parts from the mold without damage. Theceramic mixture was injected with a pressure ofabout 4 MPa at temperatures of about 70 to 808CŽ .160 to 1758F . The tool life of the silicon cushionwas between 30 and 50 injections with toleranceskept. Preparing the metal reinforced silicon tool in-cluding generation of a LOM positive took only 11r2 weeks. The costs of this one-piece tool werejust about 25 to 30% of a conventional steel tool.

5. Summary

Currently suitability for rapid tooling processeshas been an outstanding aspect when comparingdifferent RP technologies. The examples showed aremarkable suitability of LOM objects for certainapplications in foundry technology, especially for:Ž . Ž .a sand casting patterns, b wax injection molds for

Ž .investment casting and c master models for siliconŽmolding processes wax patterns for investment cast-

ing, plastic parts by vacuum casting and RTV, ce-ramic parts by low pressure injection molding, low

.melting zinc–aluminum partsAll these applications require a suitable surface

coating of the LOM objects with special materialsfor best pattern removal, durability and pattern life.

References

w x1 T. Wohlers, Rapid Prototyping State of the Industry: 1997Worldwide Progressive Report, Wohlers Associates, FortCollins, 1997.

w x2 D. Kochan, Solid Freeform Manufacturing, Advanced RapidPrototyping, Elsevier, Amsterdam, 1993.

w x3 D. Kochan, B. Mueller, Enhanced casting quality by im-

Ž . Ž .proved LOM patterns, Giesserei 84 13 1997 17–22, inGerman.

w x4 A. Chaudhry, Desktop manufacturing flavors, Computer-Ž . Ž .world 26 45 1992 81.

w x5 N.N., Laminated object manufacturing, Rapid PrototypingReport, The Newsletter of the Desktop Manufacturing Indus-

Ž . Ž .try 1 1 1991 1 and 6–8.w x6 M. Feygin, LOM system goes into production, in: Proceed-

ings of the Second International Conference on Rapid Proto-typing, Dayton, 1991.

w x7 N.N., Paper for laminated object manufacturing, Rapid Proto-typing Report, The Newsletter of the Desktop Manufacturing

Ž . Ž .Industry 1 2 1991 4–5.w x8 M. Feygin, B. Hsieh, Laminated object manufacturing

Ž .LOM : a simpler process, Proceedings of the Solid FreeformFabrication Symposium, Austin, 1991, pp. 123–130.

w x9 M.J. Tsenter, Utilization and application of laminated objectŽ .manufacturinge LOMe technology for prototyping and

production of plastic and metal components, Proceedings ofŽ . Ž .the AUTOFACT Conference, Chicago 2 1995 pp. 65–74.

w x Ž .10 J.L. Johnson Coordinator , Rapid prototyping: technologiesand application, Short Course Program, University of Cali-fornia, Los Angeles, 1996.

w x11 I. Berndt, H. Mettke, Diverse experiences with LOM andstereolithography process chains, Collected Paper of the 3rdInternational User Conference ‘Intelligent Production Sys-tems—Solid Freeform Manufacturing’, Dresden, 1995, pp.223–229, in German.

w x12 S. Au, P.K. Wright, A comparative study of rapid prototyp-ing technology, Proceedings of the ASME Winter AnnualMeeting, New Orleans, 1993, pp. 73–82.

w x13 D. Jayaram, A. Bagchi, C.C. Jara-Almonte, S. O’Reilly,Benchmarking of rapid prototyping systems—beginning toset standards, Proceedings of the Solid Freeform FabricationSymposium, Austin, 1994, pp. 146–153.

w x14 T.T. Wohlers, Chrysler compares rapid prototyping systems,Ž . Ž .Computer-Aided Engineering 11 10 1992 84–90.

w x15 B. Mueller, Coating of LOM sand casting patterns to im-prove their resistance to moisture and wear, Collected Papersof the VDG Information Symposium ‘Rapid Prototyping’,Paper III, Duesseldorf, 1997, in German.

w x16 D. Kochan, B. Mueller, From rapid prototyping to rapidmanufacturing—a survey of experiences with LOM in the

Ž . Ž .USA, Giesserei 84 11 1997 26–32, in German.

Bernhard Mueller was born in Ger-many in 1970. He has been to the Dres-

Ž .den University of Technology TUD ,Germany and to the California State

Ž .University, Long Beach CSULB , USA.In 1997, he graduated from TUD and

Ž .received the Dipl.-Ing. MSc degree inManufacturing Engineering. He is cur-rently employed as a Research Engineerat Formguss Dresden, Germany and isresponsible for the application of rapidprototyping in foundry work.


Detlef Kochan was born in Germany in1935. He received the Dr.-Ing. degree in1971 from the Industrial Manufacturingand Automation Faculty of the DresdenUniversity of Technology. Since 1970he has been an Associate Professor andsince 1975 a Full Professor for Manu-facturing TechnologyrCAM at the sameinstitute. In 1993, he founded the com-pany SFM—Gesellschaft zur SchnellenFertigung von Modellen. He is currentlymanager of this company, honorary

member of IFIP TC 5 and Chairman of GFaI LV Sachsen. Hisresearch interests are Intelligent Production System and SolidFreeform Manufacturing.

laminated object manufacturing for rapid tooling and patternmaking in foundry industry

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