In response to Nils Aksel Ruud, Brock Hinzmann wrote:
>I am also very interested in your experiences with Rapid Tooling. I have been
>told that injection molded parts must hold to tolerances of plus or minus
>0.0002 inch (0.005 millimeter), but that Keltool and RapidTool (DTM process)
>generally allow only 0.005 inch (0.127 mm). Although Keltool and RapidTool are
>capable of producing at least 10,000 parts, are such parts accurate enough for
>your application? Since the requirements for each application may vary, you
>might explain your application when you respond.
Unrealistic expectations may be more of a factor in the acceptance of
tooling via RP&M than a mismatch between capabilities and true
requirements. Ask yourself:
1) Do I really need plus or minus 0.0002 inch (0.005 millimeter)?
You do not need these close tolerances on most parts. On a few parts you
may need plus or minus 0.0002 inch but only on a few critical dimensions
and not on the entire part.
2) Is plus or minus 0.0002 inch realistic for a production injection mold?
No. The accuracy of CNC is generally overstated and even if the tool were
perfect, you would have to control the temperature to plus or minus 1.7
degrees C to maintain plus or minus 0.0002 inch on a ten inch dimension.
3) Can I hold plus or minus 0.0002 inch on an injection molded part?
Even if the tool were perfectly accurate, holding plus or minus 0.0002 inch
on the part is unrealistic.
Dr. Carl Deckard
Assistant Professor of Mechanical Engineering
P.O. Box 340921
Clemson South Carolina 29634-0921
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