Plastic Injection Molding Defects and Solutions

Injection molding is the most widely used method for plastic injection molding, and how can we solve problems in the process?


Plastic Injection Mold

There are many common plastic processing methods, such as injection molding, hollow molding, compression molding or rotational molding, etc., and we specialize in "Injection Molding".

Among all plastic molding methods, Injection Molding is the most widely used method for plastic processing.

Injection Molding is to introduce thermoplastic plastic or thermosetting plastic into the heating cylinder of the injection molding machine. After it is completely melted, the pressure of the plunger or screw generates heat energy and frictional heat energy, and then injects it into the mold cavity of the closed mold. After waiting for solidification, the mold can be opened to take out the finished product. 
This processing technology can derive other production methods depending on materials, mechanical design and product requirements.

▲ Plastic Injection Molding Process - Flushing Pipeline

In addition to processing procedures, different resin materials have various suitable uses, they also have corresponding process adjustments and mold design methods. Therefore, controlling the product manufacturing process is not an easy task.

The following is a list of several common injection molding defects and solutions based on our experience for your reference:

Injection molding defects and solutions
Defects Causes Solutions
Weld Lines Two or more resin flow paths collide into each other. 1. Increase resin temperature.
2. Increase injection speed.
3. Increase hold pressure.
4. Add vent holes.
5. Add overflow well.
Short Shots 1. Low material viscosity.
2. Narrow gate or runner.
1. Increase resin temperature.
2. Increase injection speed.
3. Enlarge gate or runner.
4. Add vent holes.
Sink Marks 1. Design issue.
2. Resin is not cool and cure properly.
1. Optimize mold and product design.
2. Increase hold pressure and time.
Flow Line Resin solidifies at different rates, often occurring near the gate. 1. Increase injection speed and pressure.
2. Enlarge gate size.
Surface Delamination 1. Resin contamination
(ex: mix with other resin).
2. Resin stick to the mold surface
1. Replace resin.
2. Increase mold temperature.
3. Reduce injection speed and resin temperature.
Warping 1. Uneven thickness.
2. Design issue.(ex: undercut)
1. Increase hold time and pressure.
2. Increase cooling time.
3. Modify mold.
Jetting Resin set cold before the cavity filled. 1. Change gate location.
2. Reduce the injection pressure and velocity.
3. Increase resin and mold temperature.
Burn marks 1. Near the gate or runner.
Resin temperature is too high.
2. End of filling part.
Injection speed too high or gas can not get out.
1. Reduce resin temperature and process time.
2. Reduce injection speed at the end or improve vent.
Flash 1. Injection speed or pressure too high.
2. Mold damage.
3. Mold is not clamped properly.
1. Reduce injection speed and pressure.
2. Modify mold.
3. Increase clamp pressure.
Void Gas trap inside the product. 1. Reduce injection speed.
2. Increase hold pressure and time.
3. Increase gate size.

We hope that this information can help you understand injection molding better. 
If you have any other process control, mold design or other questions, please feel free to contact us.

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Resin Process - The Importance of Temperature Control 

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