To complete the intensive processing of automotive instrumentation structural parts, it is very important to master the scene environment of plastic parts molding, such as the trend of temperature, pressure, time, and molecular structure, and the trend of fiber filler and its molecular crystallization in automotive plastic part during molding, all of which will affect the specification accuracy of automotive instrumentation structural parts. The shrinkage and shaking of automotive instrumentation structural parts caused by the molding environment is the root cause of specification deviation of automotive instrumentation structural parts.
First, is the influence of formwork temperature. The temperature in the processing and forming of automotive instrumentation structural parts has a great influence on the product specification accuracy, especially the temperature of the formwork. Mold temperature is based on the trend and crystallinity of molten polymer, which directly affects the shrinkage of products, and then leads to specification deviation. For amorphous resin, the mold temperature is high, the solution cools slowly, the molecules have enough relaxation time, the crystallization tends to be more complete, the crystallinity is high, and the shrinkage rate increases. For crystalline resin, in the whole process of automotive instrumentation structural parts processing, high mold temperature can reduce the post-shrinkage and make the product specification stable. If the mold temperature is low, the cooling is fast, and the molecular structure of the solution is frozen and cleaned, it is not easy to crystallize, the volume change is small, and the product shrinkage is small. However, the low mold temperature increases the post-shrinkage of the product and prolongs the shrinkage time, so it is not easy to stabilize the specifications of automotive instrumentation structural parts. It is a sensitive factor in the whole crystallization process, and the crystallization rate can differ several times when the temperature difference is 1℃. Uneven or unstable mold temperature will immediately affect the crystallinity, and then the products processed by Automotive Instrumentation Structural Parts will shrink, resulting in specification deviation.
Second, is the influence of injection pressure. The change of injection pressure leads to a bulge in product size. With other process parameters unchanged, increasing injection pressure can improve the melt filling activity, increase the active length, speed up the filling speed, make the product compact, and reduce the shrinkage, but it is easy to produce orientation stress. When the pressure is low, the product cannot be fully compacted and the shrinkage rate increases.
Third, is the influence of holding pressure. Maintaining pressure plays an important role in stabilizing the product size. During the processing of automotive instrumentation structural parts, increasing the pressure holding can supplement and compact the shrinkage of in-mold products and reduce the shrinkage rate. However, if the holding pressure is too high, the residual stress will increase when the product is molded, causing deformation or cracking, which will affect the product size.
Fourthly, the influence of injection time. Before the gate is closed, the shorter the injection time, the larger the shrinkage rate and the larger the change range of shrinkage rate. When the injection time reaches or exceeds the solidification time of the gate, even if the injection time is prolonged, the quality and shrinkage of the products processed by Automotive Instrumentation Structural Parts will not change again. Injection time control is closely related to the designed gate thickness, which controls the gate closing time to a great extent.
Fifth is the influence of holding time. The longer the holding time, the more favorable the melt is for plastic filling and compaction. The higher the processing density of automotive instrumentation structural parts, the smaller the shrinkage. When the gate is coagulated and sealed, the holding pressure will not revive the shrinkage reduction of the processed products of automotive instrumentation structural parts, and too long a holding pressure will prolong the molding cycle.