structure
The parting surface, pressing direction of the injection mold and the structure, layout and size of the casting system directly affect the flow direction, density distribution, pressure-preserving and shrinking action and molding time, which have a great influence on shrinkage and directionality.

Molding process conditions

The molding conditions such as the temperature, injection pressure and holding time of the injection mold have a great influence on the shrinkage of the plastic parts. The temperature of the injection mold is high, the melt cools slowly, the density is high, and the shrinkage is large. Especially for crystalline plastics, because of its large volume change, its shrinkage is larger, and the uniform temperature distribution of the injection mold also directly affects the size and directionality of the shrinkage of each part of the plastic part. The injection pressure is high, the viscosity of the melt is small, the elastic recovery is large after demolding, and the shrinkage is reduced. The shrinkage time is long and the shrinkage is small.

Since the shrinkage rate is not a fixed value, but fluctuates within a certain range, the change of the shrinkage rate will cause the dimensional change of the plastic part. Therefore, the design of the injection mold should be based on the shrinkage range of the plastic, the wall thickness of the plastic part, the shape, and the feed. The port form, size, and position forming factors are considered to determine the shrinkage rate of each part of the plastic part. For plastic parts with high precision, plastics with small fluctuation range of shrinkage should be selected, and there is room for mold repair. After the test, the injection molds are gradually corrected to meet the requirements of plastic parts size and precision.

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