Injection molding defect-shrinkage
Shrinkage is a common defect in injection molding, which manifests as local depressions or size reduction on the surface of plastic products. It not only affects the appearance of the product, but may also reduce its functionality.
The following will analyze the reasons of injection shrinkage from four aspects and provide specific solutions.
1. Injection molding machine. Insufficient clamping force causes flash and may also cause shrinkage. Check the clamping system.
2. Injection mold. The design of plastic products should keep the wall thickness uniform to ensure consistent shrinkage. The temperature control system of the mold should ensure that the temperature of each section is uniform. For thin-walled parts, the temperature should be raised to ensure that the molten plastic flows smoothly in the mold cavity. For thick-walled parts, the mold temperature should be lowed. The gate should be opened symmetrically and preferably opened on the thick-walled part.
3. Plastic material. Crystalline plastics shrink more severely than amorphous plastics, and the amount of material should be appropriately increased during processing.
4. Injection molding. The barrel temperature is too high, and the volume change is large. For plastic with poor fluidity, the temperature should be appropriated increased to ensure fluidity. Adjusting the injection molding process parameter can reduce shrinkage defects. For example, reduce the injection speed and extend the holding time.
