Application Of Injection Molding Process In Automotive Plastic Parts
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.
Fourthly, according to the characteristics of automobile complex plastic parts, the drive form of the injection molding machine and the design of the mold clamping mechanism are currently used hydraulically mechanically or fully hydraulically. Institutional injection molding machine. After many years of efforts, Terry Machinery Co., Ltd. broke through the traditional constraints and developed a mechanical structure with two-plate clamping and direct compression and composite clamping.
The advantage of this structure is that its open stroke is far greater than the hydraulic toggle clamp structure, at least more than 2 times, to meet the production needs of large automotive plastic parts (such as bumpers, dashboards, etc.). Secondly, the mode locking uses four composite oil cylinders to lock synchronously, and the large-tonnage smooth clamping is realized with a small flow rate. The clamping force can be higher than the hydraulic toggle clamp structure with the same tonnage. Accurately guarantee the precision of molding composite surfaces of large-scale complex plastic parts of automobiles.
Fifth, because the cavity surface of auto parts is very complex, the injection molding machine must consider its particularity when designing, and configure some special function programs: such as multi-group core pulling function, timing control function, injection molding machine matching mold changing device function , matching pick-up robot device features. These special features have obvious advantages in producing automotive plastic parts. For example, in order to shorten the production cycle, this type of injection molding machine is used to automatically remove the large-scale plastic product parts after the mold is ejected by the pick-up robot, and the multi-group pull cores make the large-scale plastic products steadily integrated. Out, no whitening or cracking. At present, most of the robots used in this injection molding system are 3-axis pick-up robots and 6-axis pick-up robots.