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October 24, 2002

3 Min Read
MIM heads to the mold

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Through the RPM 2000 process, this green MIM blank has been machined and will be hardened to serve as a mold cavity insert.

Dennis Crounse Sr. once bid $30,000 to make a mold that he knew would cost at least $80,000 to build, just to test a theory he had: “That no matter how low we bid, the Chinese will bid lower,” says Crounse, owner of TechniMold Tool Inc. (Cary, IL). In the end, the mold shop in China gave the customer the mold and charged only for the parts.

“We’re never going to beat the Chinese in labor,” says Crounse. “We have to find a better way.” That way, he became convinced, was to use MIM to build cores/cavities for the molding of plastic parts. It would be faster and cheaper than conventional molds, he knew, and thus more competitive.

For seven years he worked to perfect the process, finally obtaining a patent last year. He calls it Rapid Production of Molds (RPM 2000). The process begins with a digital CAD representation to generate the core and cavity. The core and cavity models are then fitted into a die pocket, from which a green (unsintered) core and cavity are generated using fine metal powders premixed with a binder. Both core and cavity are then debound and sintered. A secondary operation on the core/cavity molds fits them into a mold base. “Once I have my masters, I can mold as many cores and cavities as I need,” Crounse says.

The advantage of RPM 2000, says Crounse, is that the process results in a hardened mold at a fraction of the cost of traditional methods. The amount of time that can be saved depends on the complexity of the cores and cavities. “When you talk multiples, I can cut the time in half,” he adds.

A variation on the process is one in which Crounse uses MIM to mold a block, or blank, with the approximate dimensions of a tool insert, and then directly machines the cores and cavities on that block. “The MIM material is about three times easier to cut than aluminum and will yield the same corresponding savings,” he says. “The big difference is that subsequent processing produces a hardenable tool steel part that lasts 10 times longer than an aluminum tool.”

Crounse says that this variation is more precise than molding the cores and cavities because the cores and cavities are being directly cut into the MIM material block instead of relying on the compounded tolerance capabilities of another process.

TechniMold is licensing its RPM 2000 technology to other companies interested in adopting this method for making molds. Crounse notes that the technology is best suited for smaller, more complex molded parts.

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Figures 1-3. Through the RPM 2000 process, cavity inserts are machined from a MIM blank, which are subsequently hardened and incorporated into a mold base.

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Figures 4-6. A core insert is machined in the same process as the cavity.

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Figure 7. A fully hardened cavity insert with a fully hardened MIM part formed from the mold.

Figure 8. A fully hardened core insert with ejector pins as it has been incorporated into a mold base.

Figure 9. In another RPM 2000 process that's said to be better for producing multicavity tools, a master core or cavity insert developed, around which core and cavity inserts are molded. Pictured here is the master core, formed using the DTM process.

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Figure 10. The master is compared to the fully hardened insert.

Contact information
TechniMold Tool Inc., Cary, IL
Dennis Crounse Sr.; (847) 639-4226
[email protected]

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