During injection molding, temperature, pressure, time and other technological parameters must be strictly controlled in accordance with the technological requirements.And the molding cycle must be consistent ,and it cannot be changed at will. If the injection pressure is too low, the pressure holding time is too short, the mold temperature is too low or uneven, the temperature at the barrel and nozzle is too high, and the cooling of the plastic parts is insufficient, that will lead to the shape size of the injection molded parts is not stable.
Under normal circumstances, it is useful to overcome the problem of injection molded parts size instability when using of higher injection pressure and injection speed, appropriate extension of mold filling and pressure holding time,and improving the mold temperature and material temperature.
The shrinkage of molding materials has a great influence on the dimensional accuracy of injection molded parts. If the precision of molding equipment and mold is very high, but the shrinkage rate of molding raw materials is very large, it is difficult to ensure the dimensional accuracy of plastic parts.
Therefore, it is necessary to consider the shrinkage of the raw material fully after molding on the size of the precision of plastic parts. For the selection of raw materials, the range of shrinkage can not be greater than the requirements of dimensional accuracy of injection molded parts.
The structural design and manufacturing accuracy of the mold directly affect the dimensional accuracy of the injection molded parts. In the process of injection molding, if the rigidity of the mold is insufficient or the molding pressure in the mold cavity is too high, the mold will be deformed and the size of the plastic parts will be unstable.
Therefore, in the design of the mold,it should design enough mold strength and rigidity, control of processing accuracy strictly. And mold cavity material should use wear-resistant materials. The best is cavity surface heat treatment and cold hardening treatment.