The dimensional change of plastic parts is essentially caused by the different degrees of shrinkage of the plastic. Any change in material temperature, mold, pressure, and production cycle will lead to changes in the size of the part, especially PP, PE, nylon, etc. with higher crystallinity. The main reasons are as follows:

1. Machine side:

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

(2) The supply is unstable. Check whether the voltage of the machine is fluctuating, whether the components of the injection system are worn or whether there is a problem with the hydraulic valve.

(3) The screw speed is unstable. It should be checked whether the motor is faulty, whether the screw and the 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 properly, and the back pressure is unstable.

2. Mold aspect:

(1) To have sufficient mold strength and rigidity, the cavity material should be made of wear-resistant material.

(2) When the dimensional accuracy is high, try not to adopt a multi-cavity form.

(3) The ejector system, pouring system and cooling system should be set up reasonably to ensure the stable production conditions.

3. Plastics:

(1) The mixing of new materials and recycled materials should be consistent.

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

(3) The influence of shrinkage rate on dimensional accuracy is fully considered when selecting materials.

4. Processing:

(1) If the plastic processing temperature is too low, the temperature should be increased because the higher the temperature, the smaller the dimensional shrinkage.

(2) For crystalline plastics, the mold temperature is lower.

(3) The molding cycle should be stable and should not be excessively fluctuating.

(4) The amount of feed, that is, the amount of shot glue should be stable.

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