The size change of plastic parts is essentially caused by different shrinkage degrees of plastic. All operations with variable material temperature, mold, pressure and production cycle will lead to the change of product size, especially PP, PE, nylon, etc. with large crystallinity. The main reasons to dimensional change of injection molding are as follows:

1. Machine

1) If the plasticizing capacity is insufficient, the machine with large plasticizing capacity should be selected.

2) If the feeding is unstable, check whether the voltage of the machine fluctuates, whether the components of the injection system are worn or whether there are problems with the hydraulic valve.

3) If the screw speed is unstable, check whether the motor is faulty, whether the screw and barrel are worn, whether the hydraulic valve is stuck, and whether the voltage is stable.

4) The temperature is out of control, the proportional valve and the total pressure valve are not working normally, and the back pressure is unstable.

2. Mold

1) To have enough mold strength and rigidity, cavity material to use wear-resistant materials.

2) the first mock exam is not required when the size accuracy is very high.

3) Ejection system, gating system and cooling system should be set reasonably to ensure the stability of production conditions.

3. Plastics

1) The mixture of new material and recycled material should be consistent.

2) The drying conditions should be consistent and the particles should be uniform.

3) The influence of shrinkage on dimension accuracy is fully considered in material selection.

4. Processing:

1) Plastic processing temperature is too low, should raise the temperature, because the higher the temperature, the smaller the size shrinkage.

2) For crystalline plastics, mold temperature should be lower.

3) The molding cycle should be stable and not undulate.

4) The feeding amount, that is, the injection amount, should be stable.