Poly-Cast solves “thin wall” processing issues through innovative tool design & delivers 100% quality check for leak detection.on Tuesday, June 21, 2016
Summary: A U.S. based manufacturer of sterility process validation and monitoring instruments came to Poly-Cast with a unique problem. They had recently developed a self-contained biological indicator for testing sterility but their current supplier was having problems producing good parts. The engineering team from Poly-Cast investigated and was able to identify a number of problems with the tooling design and mechanical sequencing which were causing the failures.
Backstory: Poly-Cast was introduced to the client by a Manufacturer’s Rep who was calling on both companies. When hearing of the client’s issue the Rep felt Poly-Cast would be the best resource for the client. He knew Poly-Cast was experienced with the production of thin wall parts like the indicator vial and so put the two companies in touch. After a few conversations by phone, Dan Leedom (President of Poly-Cast) chose to travel to the customer’s location with a member of his engineering team to help the client determine the next best step; they eventually decided to move the tool to Poly-Cast in Tigard for additional testing.
Problem: The Poly-Cast engineering team identified three specific problems: first, the current tool design was flawed due to an improper mechanical sequence which caused core shift during the filling process and produced parts with non-concentric walls. Second, the gate geometry was causing the part to fill incorrectly; and third, there was a problem concerning the cooling of the parts.
Solution: Processing parts with thin walls can be very tricky, but Poly-Cast has an excellent track record for solving thin wall issues. Our first objective was to help our client get their product to market, so we transferred the existing tool from the client’s current supplier, and by making adjustments to the injection mold mechanical sequencing, we were able to produce enough good parts for a suitable bridge inventory. Once our client’s immediate inventory needs were met, we went to work on a more permanent solution by designing and building a new tool. We rectified the core shift issue by incorporating a mechanical sequence designed specifically for an 8 cavity tool. We corrected the cooling problem by re-routing the water jackets, and we optimized the gate to obtain the best possible resin flow.
Outcome: Once the new tool was qualified and the process documented, Poly-Cast was able to supply our client with good and reliable parts. The combination of the mechanical sequencing we developed and the gate geometry we chose produced concentric parts with uniform thin walls. The cooling configuration we incorporated helped to reduce the cycle time, saving the client money. We were also able to automate the production of these parts due to the gate location we chose, saving the client even more money per part. Our automation design also had a serendipitous effect. The vacuum system for grabbing the parts out of the mold also served as a leakage test for the vial; sophisticated sensors were mounted on the end-of-arm and if a vacuum delta was detected, the part was immediately rejected.
Reflection: This was a challenging problem to solve. Our customer had been convinced by their previous supplier the processing problems were due to the number of cavities in the tool – too many working parts. Our first task was to run the tool ourselves to determine if this was the case. In a way, they were correct. Because of the mistakes made with the mechanical sequencing and the cooling issues, the tool was almost impossible to run. Even after making some major adjustments to the sequencing, we could only successfully produce parts from 4 cavities. The decision to build a new tool was based on the need to have 8 working cavities in order to meet production demands. This decision also gave us the opportunity to correct the gate location as well as the cooling problems. It was during our qualification process of the new tool when we noticed the propensity for microscopic holes to be created at the gate geometry. Since our goal was to ship parts with a 0% failure rate, we began looking for an answer. It was during one of our weekly engineering meetings that we came up with the innovative solution of using the vacuum to grab the part and simultaneously detect leaks.