This article discusses that by most measures, the last few months have been good for the rapid prototyping (RP) industry. Worldwide system sales continue to grow as the technology finds greater application in many countries, including Canada, Hong Kong, India, Italy, Malaysia, Taiwan, and the United Kingdom. During the same period, the rate at which RP-related Us patents were issued accelerated to more than one per week, according to a study by Chatham Research of Amherst, NH. In recent years, researchers have also been working on solid-form fabrication (SFF) techniques to construct prototype and production tooling, even for precision metal parts, an advance that would truly revolutionize the manufacturing industry. Of particular interest to manufacturing engineers is the continued evolution of rapid tooling (RT) technologies—methods to swiftly fabricate prototype and production—grade tooling for manufacturing processes such as plastic injection molding.
By Most Measures, the last 18 months have been good for the rapid prototyping (RP) industry.
Worldwide system sales continue to grow as the technology finds greater application in many countries, including Canada, Hong Kong, India, Italy, Malaysia, Taiwan, and the United Kingdom. During the same period, the rate at which RP-related U.S. patents were issued accelerated to more than one per week, according to a study by Chatham Research of Amherst, N.H.
The success of rapid prototyping-the fast physical modeling of digital designs—is no surprise. RP has brought marked changes to the process of product development. The use of RP models to evaluate a design's form, finish, and function early in the development cycle has greatly increased the speed at which better conceived, more finely focused products can be brought to market.
In recent years, researchers have also been working on solid-form fabrication (SFF) techniques to construct prototype and production tooling, even for precision metal parts, an advance that would truly revolutionize the manufacturing industry.
Another positive development for the industry is the recently established Global Alliance of RP Associations, an international group of 13 RP-related organizations dedicated to sharing RP information. Further evidence of maturation is an incipient movement to establish industry standards, an effort being championed by Kevin K. Jurrens, an engineer at the National Institute of Standards and Technology (NIST) in Gaithersburg, Md.
Needed steps toward market rationalization are starting to take place, as well. For example, RP industry leader 3D Systems of Valencia, Calif., acquired the stereolithography business of its European rival EOS GmbH of Munich and then negotiated a cross-licensing agreement with a Japanese competitor, Sony/ D-MEC Ltd. of Tokyo, for stereolithography technology.
But maturation of the RP business has also led to less positive developments. Though unit sales of RP equipment grew 34 percent in 1997, that is significantly lower than the 55-percent annual growth rate the industry averaged over the last six years, according to Terry Wohlers, president of Wohlers Associates Inc., a consulting firm based in Fort Collins, Colo., that tracks the RP business.
As 19 SFF system manufacturers fight for new business in a market that is probably not big enough to support them all, some companies have suffered poor revenue and profits. BPM Technology, the maker of the Personal Modeler, for example, folded last year. Helisys Inc. of Torrance, Calif., and Cubital Ltd. of Raanana, Israel, are reportedly in perilous positions and their management teams are looking toward acquisitions, mergers, or new investment opportunities.
Meanwhile, the heretofore burgeoning RP service bureau business hit a roadblock, as the price for outsourced models has dropped by as much as 50 percent. The business slowdown and the greater availability of used equipment due to company failures are affecting new systems sales, Wohlers said.
Another disappointment has been the relatively slow sales of concept modeling systems such as 3D Systems' Actua 2100, Genisys from Stratasys Inc. of Eden Prairie, Minn., and the high-speed Z402 system from Z Corp. of Somerville, Mass. The hope was that design engineers would flock to these lower-cost, office-friendly units. Instead, concerns about the reliability of the Actua 2100 and Genisys machines as well as high prices have kept sales of concept modelers in check. One bright spot in this area has been the realization that these machines will be useful in introducing the technology to new users. Cummins Engine Co. in Columbus, Ill., for instance, used an Actua system to educate its engineers about rapid prototyping before it justified the purchase of a high-end SLA-500 machine from 3D Systems.
Most industry observers believe that these unsettling problems are temporary. After all, the penetration of SFF technology into industry is still exceedingly modest and the pressures on industry to speed product development are only going to get worse. RP technology will eventually be more readily adopted as young engineers, steeped in modern digital design and engineering methods, gradually rise to positions in which they can exert control over product development processes.
Of particular interest to manufacturing engineers is the continued evolution of rapid tooling (RT) technologies- methods to swiftly fabricate prototype and production-grade tooling for manufacturing processes such as plastic injection molding (see "From CAD Art To Rapid Metal Tools," March 1997). Established RT approaches include epoxy tooling (3D Systems' 3D Keltool and Direct AIM, an area that now also includes a new aluminum-filled epoxy resin from Cubital) and Rapid-Tool from DTM Corp. of Austin, Tex.
But emerging rapid tooling approaches are starting to come on line as well, including technologies from CEMCOM in Baltimore, Dynamic Tooling in Fresno, Calif., Express Tool in Warwick, R.L, and Extrude Hone in Irwin, Pa. Beyond these examples are more speculative technologies like laser-engineered net shaping and cold-gas dynamic spraying. Much about these newer RT techniques is proprietary to the individual companies, and each comes with its own set of capabilities and limitations. None of them as yet offers consistently faster turnaround times than conventional tooling methods, the dimensional accuracy of CNC-machined tooling, nor much choice regarding material composition or maximum part size.
Still, if the technology can be successfully put to use, rapid tooling promises to be a great boon to the multibillion-dollar worldwide tooling industry.
Progress Toward Rapid Tooling
New RP-based technologies may bring faster turnaround to the billion-dollar tooling industry.
The Nickel-ceramic Composite (NCC) Tooling process from CEMCOM Corp. is aimed at fabricating "bridge" and short-run production tooling for plastic injection and compression molds. According to Sean Wise, director of research and development for CEMCOM, the NCC tooling technology has the potential to reduce the time needed to fabricate matched die sets by half.
Cemcom'S process uses plastic RP models as patterns for the fabrication of nickel-ceramic composite tooling that can withstand tens of thousands of cycles, he said. Nickel is electroformed directly against the RP pattern to create the tool geometry. The nickel shells are then coupled with a standard mold frame using CEMCOM's patented chemical bonded ceramic (CBC), which does not shrink, is very stiff, and has the same coefficient of thermal expansion as both nickel and steel. The near-net-shape process is particularly suited to components larger than 10 by 10 inches, Wise said. Accuracy is said to be on a par with that of the RP patterns. CEMCOM is looking to licensee NCC Tooling technology.
Little is Publicly Known about the PHAST (Prototype Hard and Soft Tooling), which was developed by Jim Tobin of Proctor & Gamble, and then licensed to Plynetics Express, a large service bureau in Schaumburg, Ill. The process is said to use a ceramic shell produced by coating an RP pattern with a ceramic slurry similar to investment casting slurries. The volume of the shell is filled with steel powder, consisting of about 50 percent steel and 50 percent air. "Copper material" is positioned above the powder metal and is infiltrated into the porous material during a furnace cycle.
Paul Vawter, President of Dynamic Tooling, has developed a rapid tooling technology he calls PolySteel. Using an RP model as a pattern, the process produces mold inserts that are 90 percent steel and 10 percent epoxy. The result are molds that are several times stronger than aluminum and significantly harder as well. The molds work well for prototyping glass-filled nylons, ABS, and wax patterns for investment casting. The process captures undercuts and can replicate small details, because the surface finish is a mirror image of the RP pattern. Aspect ratios of 8:1 are possible. Accuracy is ±0.001 to 0.002 inch per inch, mostly due to the pattern, he said. Repeatability is ±0.0005 inch.
Since PolySteel has very good thermal conductivity, injection- molding cycle times are similar to those for a machined steel mold, said Vawter. Current lead time is 5 to 10 days for inserts, and 10 to 15 days for molds and molded parts. Vawter said that he is looking to license the technology.
"We found many positive attributes to this new tooling process," said Tom Greaves, advanced manufacturing engineer for General Motors' Delphi Interior & Lighting Systems in Pontiac, Mich. Greaves' team used the PolySteel technology to mold 250 copies of a part, with dimensions of 1 by 3.75 by 6.5 inches, from polypropylene, ABS, and 30-percent-glass-filled nylon. "Features including high aspect ratios were included in the tool and did not require separate inserts," Greaves said. "Also, we did not see any erosion at the gate afterwards."
Vawter is also working on an RP-based powder metal forging process for making steel mold and die inserts. In the process, an RP model is used as a pattern for casting a new pattern in a special low-shrinkage ceramic material. After curing, the ceramic pattern is placed in an enclosure with very fine H13 or P20 steel powder, and applied heat and pressure consolidate the powder. Insert feature accuracies range from ±0.001 to 0.002 inch per inch.
Engineers from DTM Corp. have reportedly made major improvements to its RapidSteel process, a powder-metal technology intended to produce near-net-shape metal mold inserts for prototype or preproduction tooling applications. In RapidSteel Version 2.0, stainless steel powder replaces carbon-steel powder as the base metal, and a bronze infiltrant is used instead of copper. The binder system has also been modified. In addition, the process uses powders with smaller particles, which permits the formation of thinner (0.075-millimeter-thick) layers. Part shrinkage, meanwhile, has been cut from 4 percent to 0.2 percent.
With RapidSteel 2.0, the laser-sintered green mold inserts now go directly from the Sinterstation to the furnace, eliminating the previous polymer infiltration step. As a result, typical processing times have been cut in half, said a DTM spokesmen, who added that the redesigned process can make molds capable of producing as many as 150,000 plastic parts, or hundreds of aluminum, zinc, or magnesium parts.
"We feel that the process has been improved significantly," said Scott Schermer, project engineer for Dickten & Masch Manufacturing Co. in Nashotah, Wis. Schermer evaluated RapidSteel 2.0 on the custom molding company's year-old Sinterstation 2500 machine by molding test parts of Nylon-612 filled with 33 percent glass. "So far, we've run 300 shots with the new RapidSteel tools and have observed no wear at all." He added that the parts exhibit good quality detail, with large features all within 10 thousandths of an inch.
DTM's other rapid tooling development, Copper Polyamide technology, will allow short-run production (several hundred parts) in polyethylene, polypropylene, and ABS for functional testing and concept evaluation. In this case, the starting powder is a mixture of copper and nylon powder, which is then sintered into actual molds complete with cavities and core. No furnace processing is necessary, and the composite mold inserts are machinable. "For a relatively simple geometry with no slides or side cores, you can get tools in less than a week," Schermer said. "We did 150 shots with one mold and saw only a little wear around the gate area."
Copper Polyamide, part of DTM's RapidTool family of products, is currently in beta testing, said John Murcheson, DTM's president. He expects the process to reach the market in the third quarter of 1998.
Expresstool of Warwick, R. I., is working on two rapid tooling technologies, said Tom McDonald, the firm's president. The first is an electroforming process that takes advantage of conformal cooling channels, a previously difficult-to-accomplish technique that can help avoid hot spots in the mold. Cooling channels can also cut injection-mold cycle times by 10 to 20 percent. The electroforming process is now commercially available, according to McDonald. The other process, about which little is public so far, is described as a powder-metal technology that yields hard tooling of chromium. carbide, a cermet with hardness levels of 55 to 60 Rockwell C. This technique is not nearly as well developed as the electroforming process.
The electroforming process is being co-developed by Express Tool and Hasbro, Inc., of Pawtucket, R.I., said Paul Jacobs, vice president of technology for Express Tool. This process produces 1- to 2-mm-thick layers of nickel on a computer-numerical-control-machined graphite mandrel.
Jacobs said that graphite is the ideal mandrel for electroforming, since it machines easily and releases easily from the nickel shell. A key advantage of electroforming, he stressed, is that there is no shrinkage, so it results in very accurate core and cavity mold inserts. With conformal cooling lines in place, the nickel shell is backed with aluminum- filled epoxy. The high aluminum fraction helps heat conduction.
An advantage to this process is the ability to produce large parts. A disadvantage is that deep holes do not electroform well, but machined inserts can be welded to the shell. Mold life has been shown to be in excess of 200,000 shots with thermoplastics. No data have been released concerning the production of parts from glass-filled polymers.
In addition to Hasbro, Express Tool has formed strategic partnerships with Ford, Kodak, United Technologies Research Center-Automotive, and others to further develop these RT technologies.
The Prometal Rapidtooling System (RTS-300) is an SFF machine capable of creating steel molds and parts up to 10 by 12 by 12 inches in size, explained Mike Rynerson, R&D director at ExtrudeHone. It is based on the three-dimensional printing (3DP) technology developed by Professor Emanuel Sachs' 3DP Consortium at Massachusetts Institute of Technology in Cambridge, Mass. ExtrudeHone took an exclusive license to use 3DP to make metal parts and tooling. PRO METAL uses an electrostatic ink-jet printing head to deposit a liquid binder material onto powders, selectively hardening slices of an object layer by layer. Successive layers of powder are spread on top of the growing prototype as the process continues, until the object is complete. The unbound powder supports the object as it is constructed. The result is a green metal part that is then sintered in a furnace and finally infiltrated with secondary metal. Rynerson said the part shrinks 1.7 percent during sintering, but grows 0.2 percent during infiltration. Final part accuracy is said to be ±0.002 inch.
Rynerson said PROMETAL not only works with stainless or tool steel, but other materials as well. Applications include tooling for injection molding, vacuum forming, blow molding, lost-foam patterns, and direct fabrication of powder metal components. Prototype plastic injection molds have shown that PROMETAL tooling is capable of holding fine detail at injection pressures up to 30,000 pounds per square inch, and can survive well over 100,000 shots of glass-filled nylon.
ExtrudeHone's industrial partners include Amp Inc., Johnson & Johnson's Advanced Healthcare Systems, United Technologies, and Motorola, which ordered the first commercial (RTS-300) machine. The company has also been successful in garnering several government grants, Rynerson noted. ExtrudeHone has received $3 million from the Technology Research Program to research low-cost, high-performance tooling technology: a $1 million grant from the National Science Foundation to study remote (long-distance) manufacturing via digital data transmission: and $6 million in NIST Advanced Technology Program (ATP) money to work with General Motors' Saginaw (Mich.) division on advanced lost-foam casting processes.
"The ATP machine will have a 96-jet print head and a 300-mm-by-800-mm work space," said Sachs, who is also working on the project. He said its accuracy will be similar to its predecessor, adding that "maintaining low shrinkage is key." The machine, which itself will fit in an enclosure 1 meter by 0.5 m by 0.5 m, will be capable of processing 200 cubic centimeters of powder per minute. Sachs said that selective hardening, functionally gradient materials, and materials with controlled porosity will be investigated, as well as the use of nonmetals such as silicon carbide and tungsten carbide.
Optomec Design Co. of Albuquerque, N.M., has licensed the Laser Engineered Net Shaping (LENS) technology developed in recent years at the Department of Energy's Sandia National Laboratory in Albuquerque. The LENS process, which makes fully dense metal parts, injects metal powder into a pool of molten metal created by a focused laser beam as the substrate below is slowly moved to trace out the geometry of the desired part.
Using National Science Foundation, Department of Energy, and Ballistic Missile Defense Organization funding, as well as the services of former Sandia LENS researcher Dave Keicher, Optomec developed the DMD-RS-101 direct metal deposition research station, which can build objects as large as a 12-inch cube. Two of the $350,000- machines have been built; one is at Optomec, the other at Ohio State University in Columbus.
Similar technologies are being pursued at Stanford University in Palo Alto and at Los Alamos National Laboratory in New Mexico.
Cold Gas Dynamic Spray
A new Spray Deposition process, based on accelerating metal particles to high speeds with gas pressure and then spraying them on surfaces, is being studied by a research consortium, said Robert McCune, staff technical specialist at Ford. The consortium includes the National Center for Manufacturing Sciences in Ann Arbor, Mich., Ford Motor Co., GM, Pratt & Whitney, GE Aircraft Engines, TubalCain Co., and Flame Spray Industries. The process was developed by an Anatolii N. Papyrin-Ied team in the former Soviet Union (Papyrin is now at Penn State University in University Park). The cold gas dynamic spray process produces a dense, cold-worked metal deposit with low porosity, high hardness, and little oxidation, he said. "It deposits an incredibly good quality material," McCune said. "For example, we measured a Young's Modulus of 170 gigapascals. That's 85 percent of the handbook value."
In the process, the accelerated particles stay in the solid state, he explained. "The energy for softening and deformation comes from the kinetic energy of the particle, which can reach velocities ranging from 300 to 1200 meters per second." Deposition efficiencies of up to 70 to 80 percent have been attained. McCune said that the process can develop high residual compressive stress at the substrate surface.
So far, the researchers have tested the spray process with low-carbon steel powder with particles ranging from 1 to 50 microns in size. "This is an emerging technology that could take a prominent role in solid freeform fabrication," he said.