When troubleshooting shear heat issues on molded parts, I would start with the nozzle tip on the injection machine. Make sure your nozzle tip orifice is around 75-85% of the sprue-bushing orifice. Then, check to make sure there is nothing hindering the flow of plastic through the runner system. You may need an overflow tab to reduce the chance of cold slugs getting into the gate areas and causing the material to shear even further. Then finally, check your gate dimensions.
You should again be approximately 75-85% of the nominal wall thickness to ensure good flow into the part. If the resin you are running is sensitive to jetting, you may want to bounce the material entering the gate off a wall or a sturdy boss to deflect flow. In addition, I would check the water flow to the mold. Ensure you have enough cooling water to maintain an even temperature across the tool.
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