Since the first quarter of 1988, Pratt & Whitney (P&W), a Division of United Technologies
Corporation (UTC), has been involved in the development for the use of rapid prototyping
technologies that use a "layer-by-Iayer" building approach. Based on over 4 1/2 years
experience with Stereolithography, this paper will address three aspects of our experience
including: Implementation, Current Operations, and Future PlansMechanical Engineerin

Aubin, Richard F.

English

Since the first quarter of 1988, Pratt &amp; Whitney (P&amp;W), a Division of United Technologies
Corporation (UTC), has been involved in the development for the use of rapid prototyping
technologies that use a &quot;layer-by-Iayer&quot; building approach. Based on over 4 1/2 years
experience with Stereolithography, this paper will address three aspects of our experience
including: Implementation, Current Operations, and Future PlansMechanical Engineerin

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Richard F. AubinUnited Technologies/Pratt & Whitney400 Main Street MS 118-38East Hartford, CT 06108Phone 203-565-9073A CASE STUDY IN RAPID PROTOTYPINGINTRODUCTION:Since the first quarter of 1988, Pratt & Whitney (P&W), a Division of United TechnologiesCorporation (UTC), has been involved in the development for the use of rapid prototypingtechnologies that use a "layer-by-Iayer" building approach. Based on over 4 1/2 yearsexperience with Stereolithography, this paper will address three aspects of our experienceincluding: Implementation, Current Operations, and Future Plans.BACKGROUND:Component parts for gas turbine engines are required to function in environments that areunlike any other industry, with combustor temperatures reaching 2,500 degrees F., and pullloads on our 1st blades reaching 50,000 gls. However, manufacturing these parts isaccomplished using conventional methods that are similar to other industries.Conventional methods for prototype fabrication, small batch production and manufacturingprocess development have relied on drawings, hard tooling, numerical control programming,complex machining and/or extensive hand work. These approaches are typically characterizedby long lead-time, high cost and multiple iterations to achieve desired results.There are many organizations today, that continue to employ these methods, but before theycan make the transition into the new era of rapid prototyping, they must recognize that theyare out of step with the current environment. Without feeling the need to change, the "BoiledFrog Phenomenon" is likely to occur.The Boiled Frog:This phenomenon is based on a classical experiment in biology. A frog which is placed in apan of cold water but which still has the freedom to jump out can be boiled if the temperaturechange is gradual, for it is not aware of the barely detectable changing heat threshold. Incontrast, a frog dropped in a pot of boiling water will immediately jump out: it has felt theneed to survive. In a similar vein, organizations and managers that are insensitive to graduallychanging environments, are likely to become "boiled frogs"; they act in ignorant bliss ofenvironmental triggers and eventually are doomed to failure.174Richard AubinUnited Technologies/Pratt & WhitneyIMPLEMENTATION:Up until 1988, P&W was deeply involved in conventional prototyping methods. We had anextensive investment in CAD/CAM equipment and trained personnel, but still had to "iterate"at the expense of extended lead times and increased costs. However, unlike the frog, we feltthe water getting warm before it was too late.Along came an opportunity to "beta test" a new technology called Stereolithography (SLA)from 3D Systems Inc., of Valencia, California. Although faced with many unknowns andassociated risks, we decided to get involved, and acquired 2 "beta machines" in January -February 1988. One SLA machine with a 9-inch part building capacity was located at ourfacility in West Palm Beach, Florida, while the second one was located at our manufacturingfacility in East Hartford, Connecticut.We were fortunate to have extensive resources in computer modeling hardware and software,and experienced people proficient in its use. Initially, we used floppy disks to transport thecomputer models from the CAD systems to SLA, but learned quickly that complex computermodels were very large in size. By using our shop computer network system (ethernet), weare now able to download computer models directly to the SLA machine.To increase the exposure of this new technology and to demystify its operation, we gavewalking tours and presentations to:• Managers - So they understood its potential "fit" for their requirements,• Engineers - So they understood the computer modeling requirements, e.g., bases &supports,.. Mfg. Shop - So they could understand its capabilities and how to get access.We soon felt that we were a "tours-r-us" operation, but it paid off. Shortly, we were buildinga large variety of prototype objects and identified many tangible and intangible benefits.One of the most significant tangible benefits was the identification of design errors early in thedesign process. Because SLA was so fast and relatively inexpensive to produce a prototype ascompared to traditional methods, engineers were given more latitude to improve their designs,so design quality was enhanced prior to reaching manufacturing. In the past, too many designflaws were uncovered after the manufacturing departments made the tooling and the parts,investing time and resources only to find out they did the "wrong part right." By working outthese errors before involving manufacturing, we can better align our shop resources to doingthe "right part right."Joel Mokyr, Professor of Economics and History at Northwestern University and author ofhis recently published book titled, The Lever Of Riches, states: "Technological progress hasbeen one ofthe most potent forces in history in that it has provided society with what175Richard F. AubinUnited Technologies/Pratt & Whitneyeconomists call a 'free lunch, ' that is, an increase in output that is not commensurate with theincrease in effort and cost necessary to bring it about." There have been several occasionswhere, as a result of rapid prototyping, we have had a taste of this ''free lunch."Another tangible benefit was the improvement in communications among design engineers,and between engineering and manufacturing personnel because they now had a physical objectto use instead of a sketch or drawing that was subject to interpretation.On the intangible benefits side, the SLA process provided an incentive and reward mechanismto our engineers to learn and use computer solid modeling that for more than just "prettypictures". By generating computer models of their design ideas, they would be rewarded withthe satisfaction of possessing a physical prototype in return.Although considered intangible, our engineers were thus enabled to "think-out-loud", meaningthat they were now able to generate physical objects directly from their computer modelsquickly and inexpensively. A new degree of enthusiasm resulted in the engineering communityas a result of this new capability that essentially kept them "fresh" instead of growing "stale"while waiting for the hardware to arrive.Further, engineers were now receptive to change by incorporating suggested improvementsfrom peers and from manufacturing personnel.Needless to say, these benefits provided significant time and cost savings.By the end of the first year of using SLA, we recognized the value of working together withother "beta test companies". Collectively, we worked and shared ideas to improve accuracyand surface finish. We also identified errors in the SLA process, and provided suggestions forimprovement by submitting enhancement proposals to 3D Systems. Eventually, theseenhancements were manifested in later revisions of the software, so mutual benefit wasrealized as a result of team-playing.With a few "free lunches" under our belt, we finished the first year with some valuable lessonslearned, and unlike the "boiled frog," we found ourselves rewarded by being sensitive to ourchanging environment.After beta testing the early version of the SLA device, we were given another opportunity.This time, 3D Systems was offering their larger SLA machine for beta test, that had a 20-inchpart building capacity. This gave P&W the capability to build larger prototype objects; weproceeded without hesitation.Having recognized the benefits of working with other companies throughout the beta testingprograms, P&Wand the other beta test companies took the initiative to establish the SLA usersgroup. This group was comprised of all users of SLA for the purpose of providing a forumfor technical information exchange among the SLA users community. Through this forum,176Richard F. AubinUnited Technologies/Pratt & Whitneycompanies share lessons learned, and identify strategies to improve their output. P&Wprovided leadership to this group by chairing this organization from its inception through itsfirst year.Internally, P&W decided to expand its rapid prototyping capabilities, and share its lessonslearned with our sister divisions of UTC by establishing what we called an "Express PrototypeConsortium." This consortium served as a vehicle for technology transfer with: Carrier,Hamilton Standard, Otis Elevator, Pratt & Whitney Canada, Sikorsky Aircraft, and UnitedTechnologies Automotive.CURRENT OPERATIONS:Currently, our operation in East Hartford has grown to include a total of 4 SLA machines andthrough the benefits of economies of scale, we are able to be responsive to the prototypingdemands of our entire corporation. Last year, 1990, over 1,600 prototypes were processed atour East Hartford facility.We see this activity in several basic areas:.. Design VerificationAs previously mentioned, there is great value in identifying design errors priorto manufacturing involvement. Improving designs by "iterating in plastic" ismuch more effective in time and cost than by conventional manufacturingtechniques which iterate in "hard tooling.".. Manufacturing Producibility StudiesRapid prototyping is one of the key facilitators of integrated productdevelopment or concurrent engineering. Our manufacturing shops can get anearlier startup on process development by having a replica of a part to use toprove out tooling and fixturing while the actual real parts are being produced.For example, while investment castings are being processed, plastic replicas canbe used in the manufacturing environment to ensure proper fixturing and toolingfor final machining. When the actual parts arrive, the machining process isalready up and ready... Prototype Parts For Test And Conversion To Other MaterialsOccasionally, the plastic object can serve directly as a prototype in a test wherethe physical properties of the plastic can suffice. Techniques to convert theplastic object to other plastic materials having improved physical properties arealso commonly available in industry through injection molding processes. Andlastly, investment castings can be generated in a fraction of the time through theuse of temporary tooling.177Richard F. AubinUnited Technologies/Pratt & Whitneyit Research and Development EffortsTo date our biggest limitation with the photo-curable resins has been accuracyand surface finish. Our focus therefore has been to improve the process stepswhich affect them. We have learned that all variables in the total process mustbe considered, including: computer modeling preparation, hardware andsoftware development, materials, and post-processing.Additional activities we have pursued include development relationships with resin suppliers toimprove the basic resins themselves for less shrinkage, distortion, and better surface finish.Because of the benefits we realized from beta testing Stereolithography, we are currentlyinvolved in the beta testing of new emerging technologies:it Selective Laser Sintering (SLS), from DTM Corporation of Austin, Texas. This is aprocess that uses the heat of a C02 laser to sinter powdered materials in a layer-by-Iayertechnique. The materials offered include wax and poly carbonate plastic.it Fused Deposition Modeling (FDM) from Stratasys Inc., of Minneapolis, Minnesota. Thisis a process that uses a heated extruder mechanism to deposit thin layers of wax or nylon-like plastic materials.Both technologies build prototype objects directly from computer models, and each has itsadvantages; however, because of beta testing and non disclosure agreements, furtherinformation is prohibited at this time and is best derived directly from the companiesdeveloping the technologies.Finally, we are actively involved in several rapid prototyping consortia with academiaincluding MIT, and the University of Texas.FUTURE PLANS:As you have seen, we have been very active players in the Stereolithography field. We lookforward to improvements in that field as it improves and in other technologies that we arehearing about in this conference. We feel strongly that continued development is essential toimprove the accuracy and surface finish for prototype objects and to come closer to the "real"physical properties of "production-like parts. "As leaders in the application of rapid prototyping, we can't wait for these developments tomature. Although much can be done unilaterally and internally, more can be accomplished bypro-actively working with the manufacturers of rapid prototyping technologies, other users,and academia to drive development in the direction for maximum benefit to industry.The next "free lunch" just may evolve through dedicated continuous improvement.178

A Case Study in Rapid Prototyping

https://repositories.lib.utexas.edu/bitstream/2152/64397/2/1992-20-Aubin.pdf

A Case Study in Rapid Prototyping

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