Plastic Injection Molding

Defects can be costly! Especially in the production process. Here is a small insight into some common defects in injection molding.

    1. Burn Marks:

The occurrence of a blackened edge near the end of the cavity-filling process

Causes	Solution
Incorrect Injection Speed	Reduce and regulate the injection speed
High Resin Temperature	Examine and monitor the resin temperature regularly
Incorrect Venting and Gating	Make the needed corrections in the design to place the Venting and Gates at the right place
Wearing of Screw and Barrel	Regularly replace the Screw and Barrel to avoid complete wear and tear

 

  2. Surface Delamination:

Delamination in injection molding refers to a defect where thin layers or flakes appear on the surface of the molded part, which can often be peeled off.

Causes	Solution
Contamination of plastic resin	Proper storage of the resin
Mold temperature too low	Temperature and Cooling Time has to be monitored
Excessive Moisture	Appropriately dry materials before molding to remove moisture.

 

 3. Vaccum Voids:

Trapped air pockets are known as air voids or vacuum voids

Causes	Solution
Low injection pressure	Proper Venting and gating Proper Packing Pressure Optimized cooling

 

  4. Discoloration:

When the finished plastic product is a different colour than it is supposed to be.

Causes	Solution
New product made from leftover pellets from the previous production.	Not using the leftover pellets from the previous running of machining
Residual material stuck in the nozzle or mould due to low pressure.	Regular removal of any excess colour and residual material

 

5. Warping:

Warping occurs when different parts of a product cool and solidifies unevenly during plastics processing.

Causes	Solution
Premature cooling rates	Make the cooling process gradual Adjust the mould temperature

 

6. Flash:

The thin layer of plastic forms when two different mold surfaces meet to create a boundary.

Causes	Solution
Low clamp force	Regulate clamp force at the control
Gap within the mold	Make sure excess injection is not done
Incorrect Injection parameters	Monitoring of the injection process at every run of the machine

  

7. Sink Marks:

Sink marks are slight depressions or irregularities that appear during the cooling and solidification phase of injection molding.

Causes	Solution
Incorrect Melt Temperature	Adjust the melting resin within the recommended temperature
High mold temperature	Use of the right temperature
Low Pack and Hold time	Ensure the gates are solidified

 

Conclusion:

The mentioned imperfections, as well as additional ones, could lead to financial losses if manufacturers do not prevent them. The most important ones are the ones already pointed out. Preventing these issues from happening is the sole method to guarantee a seamless production process.