AUTOGRAPHS

Producing Mold Positives in a Day

Jason Force, a Design Engineer for Cantada (Sarasota, FL) began working on an interesting project where he was required to study subsonic flight characteristics on a few projectile components. To begin with, Jason needed to produce mold positives for the symmetric projectile prototypes he was to investigate.

“I had ZoomRP.com build two components. One of the components was designed with half-sections of the shapes I needed, and was used to define the parting plane. The other component was built with full shapes to complete the other half of the mold,” he said. There are also variations of two different patterns in the parts. One pattern is cast in ZA-12, which is a higher strength zinc-aluminum alloy. That part becomes an insert for the other pattern type, which is cast in a variation of lead alloys.

He went on to use refractory clay to make the mold negatives, and then used aluminum and lead alloys, which are gravity cast into the molds. Casting pressures for gravity molding is ultra-light. This allowed for minor surface imperfections from the ZoomRP process to rarely translate to the final cast product.

“Since the RP process is relatively inexpensive, it was extremely cost effective to include an array of similar parts with different parameters in the same mold.” He added that, “Because one component is an insert, I can mix-and-match to experiment with a wide parameter set.”

Jason designed the parts himself using Alibre as his solid modeling program, which offers standard CAD tools. He saved the CAD files into STL files. ZoomRP.com had no problem with the export files used for production. The process is simple to complete, and can all be done online. The material Jason decided on was ZoomRP’s HD Blue Polyjet. “The part was delivered from ZoomRP.com “as-fabbed” with no finishing whatsoever,” Jason said. “I did very little additional blast finishing before the parts were used for molding. I left only one section unfinished and it performed just as well as the finished sections,” he said. Jason’s parts measured about 3-inches by 3-inches by 0.7-inches. Specific tolerances were not so important on this project as much as surface finish was because the final products are resized in a die.

According to Jason, the things that he liked most about using ZoomRP.com was that it was inexpensive for the final components, that the HD Blue process had a good to best surface finish, that the company offered great turnaround times, and they didn’t attempt to do unnecessary finishing. “Another company I worked with actually sanded off some of the details I needed on the product,” he said. “And two different companies only offered single-sided finishing, which was actually worse than unfinished for my particular purposes, because it changed the dimensions of only one half of the mold.”

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