What is the fundamental reason for molding shrinkage?

1, Material essential properties
The essential properties of materials are one of the fundamental foundations for forming shrinkage. The physical and chemical properties of different materials vary greatly, and these differences directly affect their behavior during the molding process. For example, thermoplastic materials have flowability after heating and melting, but will experience shortening during the cooling and solidification process due to the rearrangement and shrinkage of molecular chains; During the processing of metal materials, dimensional changes may also occur due to the effects of plastic deformation and elastic recovery. In addition, performance indicators such as thermal expansion coefficient, elastic modulus, and yield strength of materials are also key factors determining the degree of forming shrinkage.
2, Forming process conditions
The molding process conditions have a direct and significant impact on molding shrinkage. The setting of process parameters such as temperature, pressure, and time directly affects the flowability and curing rate of materials, thereby determining the final size and shape of the molded parts. For example, in the injection molding process, if the injection temperature is too high and the material melt flowability is too strong, the shrinkage rate increases after cooling; Insufficient injection pressure may lead to incomplete material filling, resulting in under injection and dimensional deviation. In addition, mold design, cooling system layout, and post-treatment processes (such as annealing, aging, etc.) are also important factors affecting molding shrinkage.
3, Die design and manufacturing accuracy
As a key tool in the molding process, the design and manufacturing accuracy of molds directly affect the dimensional stability and shape accuracy of the molded parts. Unreasonable mold design, such as improper selection of parting surfaces and insufficient demolding slope, can increase the risk of molding shrinkage. Meanwhile, machining errors, assembly clearances, and wear during the mold manufacturing process can also lead to unstable dimensions of the molded parts. Therefore, improving the precision of mold design and manufacturing is one of the effective ways to reduce molding shrinkage.
4, Environmental factors and operational level
Environmental factors such as temperature and humidity can also have a certain impact on molding shrinkage. For example, during molding operations in high temperature and high humidity environments, the material will expand after absorbing moisture, and will experience greater shrinkage after cooling and solidification. In addition, the skill level and experience accumulation of operators are also important factors affecting the formation of short shrinkage. Skilled operators can accurately control process parameters, promptly identify and solve problems, thereby reducing the risk of molding shrinkage.
5, Theoretical analysis and numerical simulation
In order to gain a deeper understanding of the fundamental causes of molding shrinkage and find effective solutions, theoretical analysis and numerical simulation have become important research methods. By establishing constitutive models, heat conduction models, and flow models of materials, it is possible to simulate the flow, heat transfer, and solidification behaviors of materials during the molding process, and predict the size and shape changes of molded parts. These simulation results can not only provide guidance for process optimization, but also help researchers gain a deeper understanding of the mechanism of forming shrinkage.