How to solve the depression of injection molded parts?

How to solve the depression of injection molded parts?

Sometimes the processed injection products will show shrinkage and depression. What's the matter? What causes these situations?

1. Machine side

If the nozzle hole is too large, the melt will flow back and shrink, and the resistance will be too small and the amount of material will be insufficient.
If the clamping force is insufficient, the flash will also shrink. Check whether there is a problem with the clamping system.
If the amount of plasticization is insufficient, a machine with a large amount of plasticization should be used to check whether the screw and barrel are worn.
2. Mould

The design of the parts should make the wall thickness uniform and ensure consistent shrinkage.
The cooling and heating system of the mold must ensure that the temperature of each part is consistent.
The gating system must be unobstructed and the resistance must not be too large. For example, the size of the main runner, runner, and gate must be appropriate, the smoothness must be sufficient, and the transition zone must be arc-transitioned.
For thin parts, the temperature should be increased to ensure that the material is smooth, and for thick-walled parts, the mold temperature should be lowered.
The gate should be opened symmetrically, and should be opened in the thick wall part of the product as much as possible, and the volume of the cold slug well should be increased.
3. Plastic

Crystalline plastics shrink more than non-crystalline plastics. During processing, increase the amount of material appropriately, or add nucleating agents to the plastics to accelerate crystallization and reduce shrinkage depressions.

4. Processing

The temperature of the barrel is too high, and the volume changes greatly, especially the forehearth temperature. For plastics with poor fluidity, the temperature should be appropriately increased to ensure smoothness.
The injection pressure, speed, back pressure is too low, and the injection time is too short, so that the material volume or density is insufficient and the shrinkage pressure, the speed, the back pressure is too large, and the time is too long to cause flashing and shrinkage.
The feeding amount means that the injection pressure is consumed when the cushion is too large, and the amount is insufficient when the cushion is too small.
For parts that do not require precision, after the injection and holding pressure, the outer layer is basically condensed and hardened, and the sandwich part is still soft and can be ejected. The part is ejected early and allowed to cool slowly in air or hot water. The contraction is gentle and not so conspicuous without affecting the use.