(1) Mold The manufacturing accuracy of each part of the mold is the most important factor that affects the dimensional accuracy of the part. In addition, molds after long-term use are often deformed or loosened due to molding pressure (such as injection pressure, clamping force, etc.), which is also one of the causes of part errors.

The structure of the mold will also affect the dimensional accuracy of the plastic parts. Some dimensions of the plastic part can be directly controlled by the mold size, and are not affected by the movable part of the mold, such as the lateral size of the injection molded part; while other dimensions cannot be directly determined by the mold size, but are affected by the movable part of the mold, such as the opening The mold direction spans the size of the mold parting surface, side hole size, etc.

(2) Plastic materials Different plastic materials have their own standard shrinkage rate. Materials with a small shrinkage rate (such as polycarbonate) have very small product dimensional errors, and it is easy to ensure dimensional accuracy. The same material, different production batch numbers, the shrinkage rate will also be affected by errors.

(3) Molding process Changes in molding process conditions (such as temperature, pressure, time, speed, etc.) directly cause material shrinkage, which ultimately affects the dimensional accuracy of plastic parts.

In view of the above reasons, the dimensional accuracy of plastic parts should be reasonably determined, and a lower accuracy level should be used as much as possible. The dimensions of different parts on the plastic parts are treated differently. For the free dimensions without tolerance requirements on the plastic part drawings, it is recommended to adopt the 7-level accuracy level in the standard.

The processing surface quality of the mold is the main factor that affects the surface quality of the plastic part. Generally, the molding surface quality of molds is 1 to 2 grades higher than that of plastic parts. Transparent plastic parts require the same processing surface quality of the core and cavity. However, the molding process conditions sometimes have an impact on the surface quality of the plastic parts. For example, the temperature of the molding resin is too low, which may cause vibration and flow lines when the plastic melt flows, and eventually cause defects on the surface of the plastic parts. Therefore, in actual operation, the surface quality of plastic parts can also be improved by adjusting the temperature of the resin and the mold temperature.