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Case Study: 48-Cavity Mold with 1.7-million Shots

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During NPE2015, we showcased a 48-cavity mold to demonstrate the quality of mold that GSM can provide. We always strive to meet or exceed our customer standards sometimes that means providing our customers the basic but reliable “Chevy”. However, when needed, we can provide “Cadillac” quality tools. In this case, we needed a “Tesla” – highly efficient, fast, and easy to maintain. (Side note: We actually build tools for Chevy, Cadillac and Tesla vehicles.)

This tool is a high performance plastic injection mold that makes valves for oil filters. It is one of three identical molds that have been in production for over a million shots each. We started the project by analyzing both the part and previous tool and making some important design changes…

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The part was previously molded with the gate on the head of the part and the legs formed with two slides. We decided to lay the part down and ask for some part concessions to make the inside of the part round. Then, the legs could be formed in the cavity rather than the slides. We designed the mold to have the slides wear rather than the cavities. We went one step further and designed the slide cores to be easily replaced. This created the best possible solution for tool maintenance because, now, the tool does not need to be completely disassembled to re-seat the tool as wear occurs.

Lower Cost with Larger Processing Window
The next item we chose to do differently was to gate into a cold runner with a sub-gate. Gating directly into the part creates 48 different part processes when using a 48-drop hot-runner system. Our method created a larger process window that was not as temperature dependent as the 48-drop hot-runner and reduced the overall cost of the tool because we only needed 24-drops rather than 48-drops. We utilized a mini runner that feeds two parts per hot-runner drop but we designed the runner to be less than 20% of the part weight so that a closed loop system could be used at the injection molder. We were able to spend less tooling capital and provide the same outcome – full material utilization with a large process window.

Gate Changes for Longer Life
One of the challenges we faced was the material, which is a glass filled material. The glass will wear out the gate inserts if we did not pay proper attention to them. An open hot-runner drop reduced the hot-runner gate wear as compared to a normal pin-point drop. However, we still had sub-gates to contend with. Our solution was to create a double-sided replaceable gate insert that could be replaced from the parting line. Once the gates wear, we could flip the gate insert and start making new gate inserts without the tool being down. Two final modifications to the gate inserts were creating them out of D2 with a hardness of Rc60-62 and square sub-gates. The thought was the extra hardness would give us extra gate insert life and the square sub-gates allowed for a larger gate with less resin contact to the steel. The outcome – after 1.7-million shots, we have yet to replace the gate inserts and the process is still running smoothly.

Faster Cooling Equates to Faster Cycle Times
The final item we considered was cooling. A mold is a cooling fixture. The faster the mold can cool the part, the faster the mold cycle time is. A faster cycle time translates into better profitability. For this tool, we were able to design the water flow in such a way that the cavities had balanced cooling with lines close to the part, the gate inserts had water, each slide nose had water, and the mold base had water. The end outcome was a process that was 12% faster than the previous process. Over the course of millions of shots, that is a substantial increase in productivity.

Overall, this tooling project was a success. The tool has a much broader process that the previous tool, a faster cycle time, is easy to maintain, and the hot-runner cost less than the previous tool. Plus, the tool was built in China which allowed us to get the best value for our customer.

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Global Source Manufacturing

is a world class tool development and maintenance company based in Troy, Ohio with capabilities in the United States and China.

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Global Source Manufacturing
155 Marybill Drive | Troy, Ohio 45373
P: 937.242.6165
E: service@globalsource.us