Currently, Rick Finnie is working on a thermoplastic injection molded part (M.R. Mold & Engineering is also known for its expertise in liquid silicone rubber (LSR) molds). The product is a secure lock box for the medical industry that requires tamper proofing.
"The door is a highly visible part, so a direct sprue gate couldn't be used, which would be the usual choice," explains Finnie. "The second choice was to put the gate at the end of the door, but that would have required a 10-inch runner, so we had concerns with a side edge gate. There were just a lot of issues so we chose to have Kruse Analysis do a filling analysis for us."
Initially Finnie thought the gate location he chose was "a terrible location" but the wall thickness at that site allowed the part to fill without flow or knit lines. The analysis also showed that the gate and sprue were freezing before the part was fully packed. Finnie's team redesigned the gate and sprue.
Additionally, the customer had added a tamper-proof feature onto the side walls that resulted in portions of the wall being .250 thick. "That was problematic because the analysis showed probably sink marks and a cycle time of 60-plus seconds," Finnie comments. "We went back to our customer and suggested they make design changes to eliminate the thick wall sections. They improved the design and Kruse re-ran the analysis. With the simulation results, we were able to shave 15 seconds off the cycle time."
Kruse did a warp analysis because the part looked as if that might be a problem and Finnie was in the middle of building this tool. "We needed to know at that point if what we expected would happen during molding process would actually happen."
Finnie was also concerned that the gate in the middle of the part might result in part warpage. "We needed to know at that point if what we predicted would happen during the molding process would actually happen. Some part warpage is to be expected but we wanted to use the analysis to determine how severe it might be," added Finnie. "Kruse did a warpage analysis, and results showed that warpage would be well within tolerance."
Finnie notes that in his experience with Kruse Analysis, Torsten Kruse is extremely knowledgeable in plastics and the injection molding process from his years of working at Arburg. "That's key to Torsten's expertise in performing material processing flow analysis," he adds, noting that he was in a Sigmasoft users group with Kruse when one thing became very apparent: "If you've never molded a plastic part you have no business operating this software."
Sigmasoft calculates a multi-stage analysis in which you can tell the software to run the analysis 25 simulated cycles while performing a thermal analysis of the steel to see what happens within each cycle. For example, an analysis of a 1-minute cycle vs. a 45-second cycle, will enable us to see how hot the steel will get when you put 400-degree plastic into the mold every 45 seconds.
"The software allows you to pick as many cycles as you want, and at some point the steel will reach a steady state. But, if you don't know how to operate an injection molding machine, you'll never get it right," comments Finnie. "Anybody can punch numbers in and come out with an answer, but it's a bogus answer. Torsten puts in accurate information to get accurate results."
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