1. Selection of Parting Surface
The parting surface is the surface in a mold used to separate the moving mold and the fixed mold. Its selection directly affects the mold's structural design, the demolding of plastic products, and the molding quality. When selecting the parting surface, the following principles should be followed: First, ensure smooth demolding of the plastic product; the parting surface should be selected at the maximum contour of the plastic product. Second, facilitate mold processing and manufacturing; the parting surface should be as flat as possible to reduce the processing of complex curved surfaces. Third, consider the appearance quality of the plastic product, avoiding leaving parting line marks on the appearance surface. Finally, combine the injection molding process requirements to ensure that the molten plastic can uniformly fill the cavity.
2. Consideration of Shrinkage Rate
Plastics shrink during the molding process due to cooling and solidification. Different types of plastics have different shrinkage rates, and even for the same type of plastic, the shrinkage rate is affected by molding process parameters, product shape, and size. In mold design, the shrinkage rate of the plastic must be accurately considered, and the dimensions of the molded parts must be enlarged and calculated to ensure that the final dimensions of the plastic product meet the design requirements. Typically, shrinkage rate data provided by the plastic supplier should be consulted before design, and appropriate adjustments should be made based on actual production experience.
3. Mold Strength and Stiffness Calculation
During injection molding, the mold is subjected to the impact of high-pressure molten plastic. Therefore, the mold must possess sufficient strength and stiffness to prevent deformation or damage during use. For critical mold components, such as the mold plate, core, and cavity, strength and stiffness calculations are required. Strength calculations primarily ensure that the parts do not fracture under stress, while stiffness calculations control the deformation of the parts within allowable limits, avoiding impacts on the dimensional accuracy and demolding of the plastic products due to deformation. During calculation, appropriate mechanical models and material parameters should be selected for analysis based on the actual stress conditions of the mold.