How to Avoid Defects in Injection Molding

When fast approaching deadlines and material availability concerns are at hand, the last thing a customer wants to deal with is an order to inject molded parts into a product that has defects. These quality issues can take many forms, which is why it is necessary to work with a molder that is well-versed in the common issues that can arise during production.

How to Avoid Defects in Injection Molding
How to Avoid Defects in Injection Molding

Defect 1: Blush

One of the most common injection molding defects is blush, which is the cloudy discoloration that may be found around injection gates or throughout the molded part of the blush. While this defect gets its name from the discoloration that occurs, the issue it causes is more than an aesthetic defect. Blushing can indicate a weakened molded structure, warning injection molders that their component may perform poorly when used with a new or modified blush.

There are several different potential causes for gate blush, which is why it is important to collaborate with experts who can verify each stage of manufacturing. For example, improperly sized gates paired with incorrect material types may result in blushing easily, but by adjusting the relative thickness of the molded part or by adjusting the molding nozzle diameter, the molding process can return to proper working order in the case of a broken or destroyed piece of material, such as a broken or destroyed piece of material that is not properly molded or is not properly used. Furthermore, factors such as incorrect melting temperatures or poorly positioned gates are other easily remedied reasons for blushing.

Defect 2: Flash

“Flash” is another common injection molding defect. This defect can occur when material leaks into the parting line (the split between mold halves), across a hole, or into a side feature to form a thin region of undesired plastic. Flash can be the result of too much pressure during the molding cycle, an undersized injection molding machine, tool wear/damage, or an improperly designed or built tool. A professional will know the difference.

Defect 3: Sink

Sink marks occur when the inner material of a molded part shrinks and pulls the outer surface wall inward. This defect leads to material depressions that impact the functionality of some molded components.

The easiest way to avoid sinks is through designs with inconsistent wall thickness. The second way to avoid sinks is to gate them into the thickest section of the part so that you can continue to pump material in as it cools. The third method of avoiding sinks is to develop a disciplined process to determine the proper pack pressure and pack time.

Defect 4: Burns

Burning, also known as dieseling, typically appears as a black or rust-colored discoloration on the edge or surface of a molded plastic part. Burn marks don’t affect part integrity unless the plastic is burned to the extent of degradation.

Trapped air is the most common reason for overheating during the custom injection molding process. This is useful for molders that utilize larger gas vents during manufacturing to allow air to escape as necessary. To avoid air becoming trapped in the first place, it can also be useful to reduce the injection speeds of the molding material. Tool vents can wear and hob inward, which reduces their effectiveness. A professional can help determine how to diagnose and fix the problem.

Avoid Injection Molded Part Defects by Working with the Best

By utilizing their time-tested industry knowledge, molding experts can detect and eliminate everything from minor surface defects to extreme defects that compromise overall product functionality. V1 PLASTIC is one of the most dependable injection molding experts, and as such, we can produce parts that are free from the most common defects listed above, as well as detect and solve rarer defects before they are delivered to customers.

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