At 12:45 PM 5/30/96 EDT, Terry Wohlers wrote:
>Has anyone experienced success at cast tooling? The idea is to use RP patterns
>to produce metal cores and cavities for injection mold tooling. Example
>approaches are rubber/plaster, sand, and investment casting. I know that Karl
>Denton, then at Ford, produced mold inserts for a wiper motor cover using 3D's
>QuickCast. Who else has been instrumental in advancing cast tooling?
As far as I see one of the biggest problem in investment cast tooling is
dimensional errors resulted from shrinkage of the alloy during its
solidification. There are three main approaches to solve this problem.
1- Measure dimensional error of cast part (mold core or cavity) and based on
that modify your CAD file to compensate for the shrinkage:
This procedure may require more than one iteration and it could be more
costly than using CNC machining.
2- Predict the shrinkage using a casting simulation software (solidification
modeling, FEA) and compensate the CAD files of the casting patterns
accordingly:
This is not an easy job to do. Whatever the accuracy of your modeling
software is, there are still a lot of error coming from prediction of
ceramic shell thickness, thermal properties of the ceramic shell, alloy
properties, metal pouring conditions and other external influences.
Soligen's direct ceramic shell fabrication technology can solve some of
these problems: You can closely control thickness and material properties of
the shell during fabrication. Even more you can "design" the shell based on
the solidification simulations...
Another example comes from The Edison Materials technology Center (EMTEC).
They managed a technology transfer program (20 parties were involved) in
which Pro/Cast solidification modeling software (from UES, Inc.) was used
to aid design of QuickCast patterns. Computed Tomography from ARACOR is used
for reverse engineering of the cast parts. The investment cast tool was
shown during the RP&M Exposition Dearborn, MI...
3- Closely control critical casting parameters (such as cooling rate and
alloy properties) to minimize or even eliminate the shrinkage:
Precision Castparts Corp. of Portland, OR uses their patented Thermally
Controlled Solidification (TCS) technology to minimize or eliminate surface
shrink. They recently made some experiments to adapt their technology into
investment cast tool production. They were also presenting one of the tools
made during the RP&M Expo...
Regards
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Erkut Negis
New Silkroad Int'l, Inc. Phone : (617) 730-9512
75 Saint Alphonsus St. #301 Fax : (617) 734-3128
Boston, MA 02120 E-Mail: enegis@lynx.neu.edu
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