1. Introduction Injection molding is a very complex multi-factor coupling dynamic processing process. Each factor of the molding process has an important impact on the molding quality of the product. Forming shrinkage is one of the key factors affecting the quality of the product. There are many factors affecting the shrinkage of injection molded products, molding materials (including polymer molecular chain structure, crystallinity, mechanical properties, rheological properties, etc.), product structure (including product thickness, insert structure, etc.), process conditions (including injection Speed, holding pressure, dwell time, cooling time, etc.) and mold design (including gate location and quantity, cooling circuit distribution, etc.) all affect their shrinkage behavior. In this paper, the CAE method was used to study the effect of the change in thickness of the product on the lateral shrinkage (in the direction of flow) and the longitudinal shrinkage (vertical flow direction) of the injection molding.
2, simulation experimental conditions 2.1 experimental product structure and size simulation experiments used in the product structure shown in Figure 1, the product is a 36mm × 36mm square products, in order to study the effect of thickness on the injection molding shrinkage, in the thickness range of 0.8 ~ Within 4.0mm, a product is obtained for each 0.5mm increase in thickness, and the transverse shrinkage Sh (measured as the average of the shrinkage ratios of Sh1, Sh2, Sh3, etc.) and the longitudinal shrinkage Sz (Sz1, Sz2, Sz3, etc.) are measured. The average of the rates).
2.2 Process conditions and methods of the simulation experiment The experiment was carried out on two different materials for different thickness products, and the crystalline material PP and the amorphous material ABS were simulated. Each material was simulated by "filling + warping" according to common process conditions. The process conditions are shown in Table 1. The process conditions of the same material are used for articles of different thicknesses, and the gate location is shown in Figure 1. The "fill + warp" analysis was performed on each thickness of the product, and then the shrinkage ratios of six positions such as Sh1, Sh2, Sh3, Sz1, Sz2, and Sz3 as shown in FIG. 1 were measured, and Sh1 and Sh2 were taken. The average value of three of Sh3 and the like is the transverse shrinkage ratio Sh of the product, and the shrinkage ratio of three positions such as Sz1, Sz2, and Sz3 is the longitudinal shrinkage ratio Sz of the product.
3, simulation results and data processing using the product shown in Figure 1 and the process conditions in Table 1, using the "Flow + Warp" function of MoldFlow software to simulate the shrinkage of the product, as shown in Figure 2, shown in Figure 2 PP plastic, warpage of 1.4mm thickness of the product.
Using the result query function of MoldFlow in the simulation results, the shrinkage rates of the six positions shown in Fig. 1 were measured, and the shrinkage ratios of six positions such as Sh1, Sh2, Sh3, Sz1, Sz2, and Sz3 were obtained and recorded in the table. 2 Table 3.
According to the simulation results of the above different thickness parts, the MATAB software is used to perform the spline curve fitting method to fit the result data of the product shrinkage rate, which can be obtained as shown in Fig. 3 (crystalline material PP) and Fig. 4 (non The shrinkage curve of the different thickness products shown by the crystalline material ABS).
4. Summary It can be seen from the curves of Fig. 3 and Fig. 4 that whether it is a crystalline plastic or a non-crystalline plastic product, when the thickness of the product is different, the shrinkage rate of the product is greatly different, as the thickness of the product increases. Large, both the longitudinal shrinkage and the lateral shrinkage of the article are increasing. However, this tendency to increase is non-linear, but gradually decreases as the thickness increases, and the longitudinal shrinkage is slightly less than the transverse shrinkage.