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Common Injection Molding Defects and How to Prevent Them

Common Injection Molding Defects and How to Prevent Them

A single mold defect can cause serious product quality issues and increase the expenses of injection molding. It can impact the aesthetics and performance of a product and even put users’ safety at risk. Here are some common injection molding defects and how to prevent them.

Flow Lines

The rate at which material cools throughout the mold can differ, creating a pattern of wavy lines on narrower sections of a part. Ring-shaped bands may also appear near the entry points of molten material. Although the component can still retain its integrity, its final appearance may be undesirable.

Flow lines can be prevented by increasing the injection speed, material temperature, or pressure. Corners of a mold, where wall thickness increases, can be rounded. You can also increase the distance between the mold gates and coolant, so material cools more slowly.


Warping is an uneven shrinking of parts. It can put a great deal of stress on parts, causing bending or twisting. A part that is warped may not lie flat as it was intended to.

Warping is often caused by rapid cooling. Therefore, a longer, more gradual cooling process can help prevent it, as can lowering the material or mold temperature in the injection molding machine. Using a material that’s less prone to shrinking can help, while more uniform symmetry and wall thickness can add stability as well.


Delamination is when thin layers of material separate or peel off on the part surface. It can reduce a component’s strength. Contaminated base materials, such as resin pellets that don’t properly bond together, most often cause this.

To prevent delamination, increase the temperature of the mold. The material can also be pre-dried to avoid excessive moisture. Avoiding contamination during resin storage and handling is important. Redesigning the mold to reduce the need for release agents can be preventative as well.

Mold Design Problems

Poor mold design can cause a short shot, or when the molten material doesn’t fill the entire mold cavity. After, for example, plastic injection molding, the part is incomplete. This can create aesthetic and functional problems. A short shot can be prevented by widening channels or gates to improve flow (a thinner base material can help here too), or increasing injection speed, pressure, or mold temperature. If trapped air is the problem, add air vents or enlarge the existing ones.

A flash is an excess of molding material at the edge of a part. Since material has flowed outside the flow channels, it can cause a serious defect. The mold may need to be completely redesigned to fix this. Increasing plate clamping force can keep material within the flow channel. Material flow can also be improved by adjusting injection pressure, mold temperature, and ventilation.

Top Injection Molding Manufacturers Can Prevent Defects

Laszeray Technology, LLC offers metal injection molding and a plastic injection molding service with in-house design of molding tools. All tooling is maintained and repaired on-site. Our commitment to quality is a benefit to rapid prototyping and advanced product development. To learn more, call us today at 440-582-8430.

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