5 Injection Molding Errors and How to Resolve Them

If you’ve been inspired by the quality of injection molds in China, then you probably already have your own injection molding machine; or at least you’re looking to get one. You also probably did so to create your own products. That’s great! But injection molding is not simple.

Before the injection molds in China became the perfect plastic product creator, their manufacturers went through all the mistakes possible and found ways to resolve all of them.

If you want to have the perfect injection mold that China is known for, then you have to know all the common injection mold error you’ll encounter and how to solve them! Here they are:

Flow Lines

These are annoying streaks that show up after a cast is done. What’s worse is that these are usually in off-tone colors! This usually happens because of:

  • The bends and contours in a mold makes the plastic flow in different speeds.
  • Varying wall thickness slows down the injection speeds, which causes the plastic solidify at different speeds.

How to Resolve it

  1. Speed up the injection and up the pressure to fill all the cavities.
  2. Heat up the molten plastic and even the mold itself more so the plastic won’t cool down too fast.
  3. Round out the corners where the wall thickness changes so that the plastic won’t change speed and direction so much.

Sink Marks

These are small craters that usually appear in the thicker parts of a cast. In these areas, the cooling is a bit harder. When it doesn’t cool right, sink marks appear. The causes of this could be:

  • Not enough time to cool.
  • Cooling mechanism sucks.
  • Not enough pressure on the cavity.
  • High temperature at the gate.

How to Resolve it

  1. Lower the mold temperature.
  2. Increase holding pressure and time.
  3. Modify the mold to have less thick areas.

Vacuum Voids

These are pockets of air stuck near the surface of a cast. This usually happens when the molten plastic doesn’t solidify or when two halves of a cast aren’t put together properly.

How to Resolve it

  1. Switch to a plastic that is less thick.
  2. Increase holding pressure and time.
  3. Align the mold perfectly.
  4. Find the gate at the thickest part of the mold.

Surface Delamination

This is a condition where foreign materials get into the plastic and cause the surface layer to thin. At times, these look like coatings and can even be peeled off! This happens when the said foreign material and the plastic just don’t get along. Not only will it make the cast ugly, but it will make it weak as well!

How to Resolve it

  1. Dry and clean the plastic properly before injecting it.
  2. Heat up the mold.
  3. Smooth out the corners in the mold.
  4. Improve the ejection mechanism so that you don’t need to use much mold release agents.

Weld Lines

Even though these are named as “lines”, they are more like planes. These appear when two molten plastics meet and the way they bond is not smooth; a line appears to show where they were joined but in reality, there is a whole inconsistent plan underneath. Usually, this happens when the bond isn’t completed.

How to Resolve it

  1. Increase the heat of the mold and plastic as well as the injection speed.
  2. Redesign the mold so that the plastic will flow from only one source.
  3. Use a plastic that is less thick or has a lower melting point.

Key Takeaway

This is just half of the errors that you must master in order to the get the kind of injection molds that China and its companies make. Be patient and don’t be afraid to make mistakes. You’ll learn and, eventually, you won’t make mistakes anymore.

About the Author

Kathleen Calado – The IT girl next door who loves travel and photography. Passionate about make-ups and a frustrated dancer. Her dream is to travel all around the world and write a blog for every country that she visits.

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