Functional Prototyping--Has the Future Arrived?

A faster, simpler, and less-costly method to produce complex ceramic molds for casting metal parts has been developed. It can help foundries to deliver a first article within days of receiving a purchase order.

YEHORAM UZIEL
Chief Executive Officer
Soligen, Inc.

Successfully launching a new product into today's competitive market depends on fast, efficient product development, coupled with quick and flexible manufacturing processes. Timing is essential--a delay of a few months can result in lost market share and may cause a potentially successful product to fail. Companies introducing new products must achieve a combination of efficient design, concurrent engineering, and just-in-time (JIT) production. Once a prototype of a new product has been market tested, the race is on to deliver it to the market before the competition shows up.

Computers have played a major role in expediting time-to-market for new products. Today's designers use sophisticated computer aided design (CAD) software to create designs on-screen, updating them easily when changes are required. Meanwhile, assembly has become increasingly automated through the use of computerized inventory control systems and assembly robots that can work around the clock and without human error.

The first step--design--and the last step--assembly--have been largely automated. The fabrication of parts remains the bottleneck in getting products to market quickly.

Casting is the most effective method for producing metal parts, in terms of both material use and labor cost. In comparison to other fabrication methods, casting allows fewer geometrical constraints, a wider variety of alloys, thin walls, and more. However, these advantages can be offset by the long lead time between purchasing and acceptance, which is a result of the need for a pattern to create the mold. The pattern design process often requires iterative trial and error prototyping since gating design, usually described as an art, is often based on empirical, mostly undocumented, experience.

The role of computers in foundries.
Computers could assist the foundryman in both designing gating and analyzing a design by simulating solidification. In some foundries, the pattern design is made on CAD and then converted to a drawing, which instructs the pattern or die maker. In these foundries, the same CAD data created to describe the pattern or mold can be used for simulating the solidification of the molten metal in the ceramic mold. However, the analysis can be costly in time and money. Except for extremely intricate parts--which require sophisticated gating design--such analysis may not justify the effort involved.

Functional prototyping
Competitive pressure induced by alternative fabrication methods attracted the foundry community to a newly-developed technology--rapid prototyping. In rapid prototyping, pioneered by 3D Systems, Inc. of Valencia, CA, a physical object is created directly from a CAD file. The actual process, called stereolithography, involves a laser solidifying liquid resin into solid plastic and forming, in successive layers, a three dimensional "print" of the part. Pattern makers view this technique as a method to create patterns, or sections of patterns, directly from a CAD file. If draft angles and parting lines are included in the pattern's CAD, plastic sections can be made and then incorporated into a pattern. Rapid prototyping can make either wax or plastic patterns that can be treated as a wax pattern substitute and then destroyed or melted out for each build.

The main roadblock in foundries for using rapid prototyping more extensively is the incompatibility of rapid prototyping to casting technology. Plastic patterns are not durable enough and have long-term dimensional instability (they may warp or distort as time goes by and internal stresses are relieved). For investment casting, plastic patterns do not dissolve easily and may crack the shells, and wax patterns made by laser sintering--which involves joining wax powder particles into a wax object using a laser beam--do not have the required accuracy and surface finish.

Direct Shell Production Casting
Direct shell production casting (DSPC) is a metalcasting process in which the ceramic shell--complete with integral cores--is manufactured automatically and directly from the designer's CAD file, and without tooling or patterns of any kind. It is a turn-key process that allows parts designed on a computer screen to be fabricated by simply pouring molten metal. It provides a complete solution, from customer's design data acceptance, through mold design and production.

DSPC creates the equivalent of ceramic shells made for investment casting by dipping a wax assembly into a ceramic slurry. Because DSPC eliminates the need for a wax pattern, and since there is no need for tooling or setup for creating the ceramic molds, DSPC truly combines the advantages of casting and computerized numerical control (CNC) machining in a unique process for fabricating metal parts.

The DSPC machine
The DSPC system consists of two pieces of equipment: a shell design unit (SDU) and a shell production unit (SPU). The SDU is a graphics workstation running specialized software that allows the geometry of a casting shell to be generated from a CAD file. The SPU then automatically fabricates the shell from raw materials.

Each turnkey DSPC machine, Expected to sell in the U.S. for about $300,000, will feature a 16 x 16 x 16 in. workspace volume, layers of 0.002 in. thick and 0.002 in. resolution. The DSPC molding shells can include several cavities, allowing more than one copy of a pan to be made at a time. The shells may also contain integral ceramic cores, allowing hollow parts to be made. The projected build rate will be 350 in3/hr, and the total build time for the entire workspace volume will vary from 9 to 20 hr, depending on the geometry of the shell design. The cost per molding shell is estimated to be between $250 and $2,500.

Internal mold surface finish is still a concern for developers. As the DSPC machine's resolution improves, the final part finish will improve. Methods by which the inside mold surfaces may be smoothed or coated to achieve improved part surface quality are currently being tested.

DSPC technology has the potential to create a structural change in the foundry industry, and conceivably to consolidate the sand, investment, and diecasting industries into one. Moreover, DSPC presents a breakthrough in the way that metal parts are designed and manufactured. In the near future, designs which have no geometrical constraints and do not require expensive tooling will be feasible. In addition, design changes will be easily incorporated.

Because DSPC is not subject to distortion, what you see on the computer screen is what you get as a ceramic mold. Drawing will not be needed, since the engineer will be able to send the CAD file via modem or network to the foundry and, within days, receive as many functional parts, ready for assembly, as he may need. The foundry, relieved from pattern or mold making will import the CAD file, design gating on screen and pour metal into the DSPC-made shell to form the near net shape part.

DSPC makes possible true just-in-time (JIT) production and concurrent engineering. Since no tooling or setup are required, it is a technology with the potential to produce parts at a cost that is almost independent of the quantity ordered, and to eliminate the distinction between prototype and production metal parts. DSPC will also help reduce inventories (since there is no cost advantage to fabricate parts in large quantities) and production turnaround time. Furthermore, when no machining is required, the cost of pans produced with DSPC will be determined primarily by the cost of the metal, rather than geometrical complexity. This new capability should have a tremendous impact on new product development and greatly simplify cost engineering and purchasing functions.

DSPC's initial applications are in low-volume manufacturing, such as prototyping of complex metal parts (whether or not these parts are intended to be produced with investment casting). In addition, DSPC is suitable for producing one-of-a-kind parts, as well as tooling for plastics molding and diecasting.

In only a few years, production rates and part quality will be high enough that DSPC could become more economical than investment casting for all parts and run sizes.

Later, DSPC is expected to achieve sufficient production rates and accuracy that it could displace other casting processes and CNC machining to become a dominant method for producing metal parts.

End of article


Sidebars

Why CAD is not more widely used in the foundry industry
In recent years Computer Aided Design (CAD) has become an essential tool for designing metal parts. CAD eliminates the manual drafting process, and allows the engineer to design more sophisticated parts with greater precision. However, the ultimate output of expensive software and computing power is a two-dimensional paper drawing. Foundries must interpret the part's design drawing into a pattern design, requiring shrinkage compensation, filleting of sharp comers, and the incorporation of draft angles and parting lines. Such modifications usually require tie foundry to regenerate the CAD file, making the customer CAD file of no use to the foundry. It is easier for the foundry engineer to mark the customer's drawing and forward it to the pattern or mold maker than to redo the CAD.

Background on Soligen
Soligen, Inc. was founded in 1991 to commercialize DSPC technology with the goal of providing the foundry industry with a rapid, tool-less process for creating metal parts. Last year, Soligen obtained the exclusive license to develop Three Dimensional Printing (30P) invented at the Massachusetts Institute of Technology, Cambridge, MA. The company's management team has extensive experience in the rapid prototyping industry.

Soligen, a company based in a new 10,000 square foot manufacturing facility in Northridge, CA, is presently focusing on the first-generation DSPC Alpha machines. Soligen's Alpha group consists of three members: Pratt & Whitney, Johnson & Johnson, and Sandia National Laboratories. The Alpha group is helping Soligen in commercializing DSPC technology by testing the concept in "real-life" environments. Feedback from the Alpha group helps Soligen to prioritize DSPC performance enhancements and test each software or hardware improvement. Several primary applications for these machines will be examined.

Richard Aubin, project manager at Pratt & Whitney, East Karford, CT, says: "We're excited about the direct shell production process because of its potential to compress lead time for investment castings. This is one of the few technologies that extends current manufacturing capabilities to fabricate parts and tooling that are not possible with conventional manufacturing methods. It is conceivable that with additional development this technology will dramatically change the way production parts are fabricated."

Soligen Ships First DSPC System
In January, the first alpha DSPC system was installed at Sandia National Laboratories in Albuquerque, NM. The installation of the first of three alpha units comes only seven months after the start of the engineering effort to commercialize the DSPC process.

DSPC has the potential for radically reshaping manufacturing. Using a three-dimensional technique--pioneered by MIT and under exclusive worldwide license to Soligen--to literally "print" the ceramic molds used to cast metal parts, Soligen's process can potentially reduce the longest lead time component of industrial manufacturing--fabrication of metal parts and tooling.

Printing ceramic molds directly from a computer-aided design (CAD) file allows manufacturers and design engineers to combine the benefits of investment casting with the quick turnaround time found in computer-numerical controlled (CNC) machining to create a new paradigm for metal parts production. Recognizing this, alpha partners signed up in mid-1992 to purchase early production versions of the DSPC system.

"We are very excited about Soligen's DSPC technology and are glad to be a participant in the alpha program," said Leif Gonnsen, system operator at Sandia. "DSPC could potentially have a very large impact on the way metal parts are made, and Sandia, with its commitment to helping U.S. industry develop leading-edge manufacturing technologies, will evaluate the technology seriously."

Soligen also announced that the company poured aluminum into the first ceramic mold generated by its DSPC system, producing a metal part.

Originally published in 1993 in Foundry Management & Technology