Injection molding continues to make the manufacturing process for various plastic parts more efficient and cost effective. This is what makes it popular and why companies are looking for reputable custom plastic injection molders to partner with. However, sometimes plastic parts do not turn out exactly as they should. There are several potential reasons behind defects in plastic injection molded components.

What are the common reasons behind plastic part defects?

custom plastic injection molderThe very technical and complex process of injection molding a wide range of plastic parts leaves miniscule room for error that would cause potentially very costly defects. The errors range from small defects to more serious ones, which is why you should always choose a reliable company to partner with. Here are the most common reasons behind defects:

Mold design & improper maintenance

The majority of defects due to improper maintenance or poor mold design fall into four specific categories:

  • Short shot: This defect happens when there is not enough plastic in the mold for proper formation of the part.
  • Drag marks: Some parts come out of the mold with scratches on them. This probably means there are issues with draft angles or the ejector system. The reason is faulty design that requires replacement.
  • Warping: If the components come out warped or distorted, there might be a problem with the cooling system. When the plastic is improperly cooled, it tends to warp.
  • Jetting: Jetting happens when a single line of plastic cools too slowly or too quickly to all the other plastic surrounding it. This is usually caused by poor mold design and requires the creation of a new mold.

Resins & additives

Some of the most common issues that stem from using inappropriate resin or additives include:

  • Marks: Moisture is the most likely culprit for a plastic injection molded component that has silver marks near the injection area. This means that the resin was stored in a moist environment.
  • Embedded debris: If there are any foreign materials on the parts after molding, this is likely due to the injection mold barrel being unclean prior to beginning the molding. Also, the resin itself could contain impurities that have contaminated it.
  • Delamination: This problem causes a surface layer of flaky resin. Again, the most likely reason for this is moisture or another contaminant prior to the injection.
  • Streaks: If you notice color streaks throughout the part, it is probably due to improper mixing of either dyes or resins. Colorants require uniform blending in order to create a solid color.

Resin processing

Once the resin is injected into a mold, it undergoes additional processing. Some of the defects that can occur during this stage are:

  • Degradation: This issue results from the resin losing a portion of its flexibility or durability.
  • Stress cracks: Another name for this defect is stress crazing, and it happens after overexposing resin to high temperatures.
  • Flow marks: This represents wavy lines or resin discoloration due to slow injection of the material, which causes faster-than-necessary cooling of the product.
  • Burn marks: If the resin remains in the mold for too long, or if there is insufficient ventilation in the mold – the part will burn, leaving visible marks.
  • Blistering: This fault occurs when the resin either suffers extreme heat or improper cooling.

Which custom plastic injection molder should I hire?

custom plastic injection moldersThere are numerous other reasons, both simple and complex, that can lead to a defect in a plastic injection molded component. That is why you should partner with a dependable plastic molder in the United States who will carefully design your plastic part applying important considerations and ensure all the important factors that could affect the process are under control. That is why you should turn to Wunder Mold.

We are your reputable manufacturer of a wide range of high-quality parts through plastic injection molding. We listen to your needs and concerns, apply your input when designing your part, and then move on to manufacture it using our efficient and cost-effective process. This is how we ensure you receive a durable, long-lasting, and dependable part. Call us at (707) 448-2349 or send us an email to