First of all, when commonly used resin materials such as bumpers and dashboards are modified resins such as modified PP and modified ABS, the resin materials have different hygroscopicity and meet the water content requirements during molding (general requirements ≤ 0.2 %)) The resin material must be hot air dried or dehumidified dried prior to entering the injection molding machine screw pre-mold metering.
The modified PP (PPEPDM) resin is less hygroscopic and generally uses a hot air dryer at 80-100°C for 2-3 hours. The modified ABS (PCABS) has a strong hygroscopicity. Before the molding and drying, the desiccant dryer is used for dehumidifying and drying. We have fully considered the function of the dehumidification and drying system in the design of automotive molding systems for complex plastic parts.
Secondly, at present, the domestic automotive plastic parts are basically glass-fiber-reinforced plastic products. Compared with the use of chopped glass fiber-reinforced resins, the material and structure of the screw of injection molding machines used to form glass fiber-reinforced plastic parts are not limited. Big difference. When the injection molding machine is designed, it is necessary to pay attention to the alloy material of the screw barrel and the special heat treatment process to ensure its corrosion resistance and strength.
Third, because the automotive parts and conventional products are different, its cavity surface is very complex, the stress is not equal, the stress distribution is uneven, in the design, it needs to consider its processing capacity. The processing capacity of the injection molding machine is reflected in the mold clamping force and the injection capacity (indicated by the maximum theoretical injection volume). When the injection molding machine is molding a product, the mold clamping force must be greater than the mold opening force generated by the mold cavity pressure, or the mold parting surface will be separated to generate flash.
The formula for determining the mold clamping force of the injection molding machine is as follows: P mold clamping ≥ P cavity × F/100. In the formula: P mold is the clamping force (or clamping force) KN of the injection molding machine; P cavity is the average cavity pressure, MPa, and the product structure shape, accuracy requirements and the number of cavity per model, etc. The range is generally between 25-40MPa; F is the mold cavity, and the horizontal overlap projection area CM3 of the runner and inlet.
In order to ensure a reliable clamping, injection molding process clamping force must be less than the injection molding machine rated clamping force. The maximum theoretical injection volume of the injection molding machine matches the tonnage of the mold clamping force of the injection molding machine. It is the injection capacity of the injection molding machine that is nominally based on polystyrene (PS) before delivery.