Voids in plastic injected part

Voids are formed inside the wall of a part and can adversely affect the structural performance of the plastic injected part. Except in transparent parts, voids can be invisible to the naked eye. Voids are formed as a result of shrinkage of the molten core after the wall has solidified on the cooler mold surface. The shrinkage of the molten core cause the layers of material to pull away, forming an opening in the part or void. Here are some causes and solutions below for voids of plastic injected parts.

Higher melt temperature slow down the cooling rate of the polymer in the plasticinjection mold, causing higher shrinkage in the hotter core, leading to voids. Solutions: Lower melt temperatures can help reduce the formation of voids.

Injecting the material at high speeds raising melt temperature due to share heating can also cause overheating. Solutions: Low packing pressures will allow voids to form since there is not enough resistance applied on the core to prevent shrinkage.

A gate that freezes-off too soon will prevent material from filling out the cavity completely, causing the molten core to shrink. Solutions: Measuring gate seal time can indicate whether the cavity is full before the gate closes.

Small runner diameters will cool faster and hinder cavity filling, creating the potential for voids to form in the part. Solutions: Larger-diameter runners, such as full round, trapezoidal, and modified trapezoidal are recommended.

A cold mold will only enhance the formation of the skin surface long before the core cools sufficiently. As a result, the core forms more slowly and shrinks more. Solutions: Increasing plastic injection mold temperature slows down the cooling rate, and the formation of the skin prevents voids. Improvements can be made in mold cooling, such as the addition of bubblers, cooling pins, thermal pins, or steel inserts to drive out more heat from the part.

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