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Developments speed investment casting.

With roots in the "lost wax" process practiced since the Bronze Age, investment casting has been around a long time. Now the modern process, used to produce near-net shape metal parts ranging from turbine blades to golf club heads, is benefiting from such current technologies as CAD/CAM and rapid prototyping.

Researchers at government labs, universities, and in industry are integrating the new technologies, reducing the time needed to design parts and produce the ceramic molds used in the process from months to as little as one week.

At Sandia National Laboratories, Albuquerque, NM, for example, scientists Frank J Zanner and Michael C Maguire are heading up the FastCast program. The goal is to reduce the time needed to produce high-quality investment castings by integrating not only rapid prototyping but solid modeling and casting simulation technologies. The researchers are "trying to build a 'toolkit' that people can use to design investment cast parts quickly and right the first time," says Mr Zanner. The program will incorporate empirical knowledge about the finer points of investment casting--such as gating and risering to achieve desired solidification rates and casting microstructure--in a "knowledge base" that will be essentially transparent to users, he adds.

Working along the same lines is Soligen Inc, Northridge, CA, which is developing direct shell production casting (DSPC) technology based on a three-dimensional printing technique developed at Massachusetts Institute of Technology. Soligen's first alpha test unit was installed at Sandia earlier this year and has already been used to make parts. Two other alpha units also have been sold and shipped.

DSPC starts with a workstation and software that lets users generate a casting shell geometry directly from a CAD file of the part. A "tree" for casting multiple parts, complete with gates, runners, and pouring cup, is then designed on-screen.

The ceramic shell is built up layer by layer using three-dimensional printing. Proprietary software "slices" the design data into thin cross sections, and a print head similar to that of an ink-jet printer then sprays a binder on a thin layer of ceramic powder. Areas corresponding to the cross section are converted to solid ceramic, while unbound powder is removed and recycled.

The DSPC process can handle ceramic cores and lets users simulate casting on-screen to verify the shell design. Soligen says the process gets users "from art to part" in less than a week. In conventional investment casting, the tree would be fabricated by hand using wax, repeatedly dipped in ceramic slurry to form the mold, and fired to remove the wax before pouring. Time required to go from design to casting might range from about four weeks to several months.

3D Systems Inc, Valencia, CA, has developed another rapid prototyping process for investment casting, this one based on stereolithography. The Quickcast system uses "quasi-hollow" patterns created using stereolithography in conjunction with conventional investment casting techniques such as wax gating. The pattern is strong enough to withstand dipping to form the shell mold, but collapses on itself during firing of the shell at 1650F. The small amount of ash (30 micrograms/gram) left after the pattern burns out is removed, and the shell is ready for casting.

Quickcast is being used to make prototype parts at three foundries, and potential casting users can contact 3D Systems to have prototype patterns made using the process. The catch is that the parts must be cast by one of the three participating foundries.

For more information from Soligen Inc, circle 336. For more information from 3D Systems Inc, circle 337. For more information from Sandia, contact Frank J Zanner or Michael C Maguire; phone: 505/845-3085; fax: 505/845-3430.
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Copyright 1993 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Manufacturing Update
Publication:Tooling & Production
Date:Apr 1, 1993
Words:607
Previous Article:Dial in for high production machining, accuracy.
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