Injection Molding Defects and How to Avoid Them

one of PTMS’ plastic injection molded parts

Plastic injection molding is one of the best methods for manufacturing parts. The benefits include operation automation, size and shape flexibility, fast production speed, and high efficiency. In addition, products from injection molding are usually precise in size. However, a number of injection molding defects continue to pose a threat to the products’ quality.

Here, we discuss some injection molding parts defects and what can be done to avoid them.

Warping

Warping is a molding defect that appears when different components of the plastic part unevenly shrink. During the cooling phase of the molding process, uneven shrinkage may put stress on parts causing twisting or bending. Usually, the cause of warpage is the cooling process that happens rapidly.

How to avoid it?

By lowering the temperature of the plastic material or mold and by ensuring the cooling process is lengthy enough to prevent uneven stresses, it’s possible to prevent warping.

Burns

During injection, the overheated resin in the mold or trapped air may cause burns. Increased plastic injection speeds or excessive heat may lead to overheating, causing the resin to burn. Burns may appear as brown or black colored spots on the surface or edge of the part.

How to avoid them?

Decrease the injection speed to limit the risk of an air trap, lower the mold and melt temperature to prevent overheating, and reduce the mold cycle time so that resin and trapped air doesn’t have time to overheat.

a power connector

Flow lines

Also known as flow marks, flow lines are lines that are commonly caused by a variation in the cooling speed of the molten plastic as it flows through the mold. They might be a little different in color than the remaining piece and typically appear in a wavy pattern.

While flow lines don’t usually affect the integrity of the piece, they can be unacceptable in certain products such as high-end frames for glasses.

How to avoid them?

To avoid flow lines, increase the pressure and injection speed to ensure the materials fill the mold before cooling. To keep the flow rate consistent and increase wall thickness, you can also try rounding the mold’s corners.

Get perfect plastic injection molding services at a reasonable price from PTMS

As the best plastic injection mold maker in China, PTMS has invested in auto-injection machines for all their production equipment. This improves their competitive molding price and reduces their labor cost, allowing them to offer high-quality injection molding services at lower prices.

Reach out to them directly for more information!

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