Used in nearly every industry to make everything from plastic bottle caps to automotive door panels, injection molding is a truly versatile manufacturing process.

Injection molding requires precise technique, and without the proper knowledge and experience, manufacturers risk diminishing product quality as a result of molding defects. Luckily, various precautions and corrective actions can be taken to prevent these negative effects.

Below, we’ll delve into three common causes of molding defects and how to best avoid them.

Common Molding Defects and How to Avoid Them

Resin casting isolated on white

1. Blistering

Blisters are unintentionally raised or layered areas of a molded surface resulting from overheated tools. This can happen when the operating speed is too high, the cooling time is too low, or the heater is malfunctioning.

Corrective action: To avoid molding defects of this kind, check the cooling area and test the tool to identify any external sources that may be contributing to additional heat.

2.  Burn marks

These brown, black, or rust-colored surface degradations can be caused by either gas or air, depending on the application. Gas burns leave marks after excessive heating or heating parts too quickly, while air burns form as a result of overheating air that’s trapped in the mold.

Corrective action: Manufacturers can remedy burn marks by reducing operating speeds and mold and melt temperatures. Testing the tool’s ventilation and degassing systems will also help to achieve proper shot speed and temperature.

3. Color streaking

“Color streaking” refers to undesired changes in the material’s color as a result of improper mixing of the colorant with granules and can also be caused by colorant running low, revealing the material’s natural color.

Corrective action: Operators should check the colorant and granule mixture rate and ensure the colorant level in system feed is correct prior to operating.

Learn More

These are just a few of the different types of degradations that can occur during the injection molding process. To learn more about potential part defects, and to access our comprehensive guide on molding defect corrective actions, download the eBook, “Molding Defects, Causes, and Corrective Actions.”


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