Common Problems and Solutions of Injection Mold Trial (2)

  • Jun 21,2022

Warping of plastic parts


--> Characteristics of injection molded part defects

The shape of injection molded part similar to the cavity, but it is a twisted version.


--> Possible cause of the problem

1) Excessive internal stress in the injection molded part cause bending.

2) Mold filling is slow.

3) Insufficient plastic in the cavity.

4) Plastic temperature is too low or inconsistent.

5) Injection molding is too hot during ejection.

6) Insufficient cooling or inconsistent temperature of moving and fixed molds.

7) Unreasonable structure of injection molded parts.


--> Solution

1) Decrease the injection pressure.

2) Decrease screw forward time.

3) Increase cycle time (especially the cooling time).

4) Increase injection speed.

5) Increase the plastic temperature.

6) Use the cooling device.

7) Increase suitable cooling time or improve cooling condition, or try to keep the temperature of moving mold & fixed mold the same.

8) Improve the structure of the plastic part according to the actual situation.



Plastic parts are not fully filled


--> Characteristics of injection molded part defects

The injection molding process is incomplete because the mold cavity is not filled with plastic or the injection molding process lacks certain details.


--> Possible cause of the problem

1) Insufficient injection speed.

2) Plastic shortage.

3) The screw leaves no screw pad at the end of the stroke.

4) Running time change.

5) Injection cylinder temperature is too low.

6) Insufficient injection pressure.

7) The nozzle part is sealed.

8) The heater outside the nozzle or cylinder does not work.

9) Injection time is too short.

10) Plastic sticks to the wall of hopper.

11) Injection molding machine capacity is too small.

12) Mold temperature is too low.

13) Anti-rust oil that does not clean the mold.

14) The backstop ring is damaged, and the melted plastic has a backflow phenomenon.


--> Solution

1) Increase injection speed.

2) Check the amount of plastic in the hopper.

3) Check that the injection stroke is set correctly, change if necessary.

4) Check the non-return valve if weared or cracked.

5) Check for stable operation.

6) Increase melted plastic temperature.

7) Increase back pressure.

8) Check the nozzle hole for foreign objects or unplasticized plastic.

9) Check all heater casings with an ammeter to verify correct energy output.

10) Increase screw forward time.

11) Increase the cooling capacity in the throat area of the hopper, or reduce the temperature in the rear area of the injection cylinder.

12) Use a larger injection machine.

13) Properly increase the mold temperature.

14) Clean up the rust inhibitor in the mold.

15) Check or replace the backstop ring.




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