Due to the unique characteristics of the
plastic parts of the complex parts of the automobile, the injection molding needs to fully consider the following factors: the drying treatment of the materials, the new requirements of the glass fiber reinforced materials on the screw, the driving form and the clamping structure. Wait.
First, when the commonly used resin materials such as automobile bumpers and instrument panels are modified resins such as modified PP and modified ABS, the resin materials have different hygroscopicity to meet the moisture content requirements during molding (general requirements ≤ 0.2) %), the resin raw material must be subjected to hot air drying or dehumidifying drying before entering the pre-plastic metering of the injection molding machine.
The modified PP (PPEPDM) resin has low hygroscopicity and is generally used in a hot air dryer at 80-100 ° C for 2-3 h. The modified ABS (PCABS) has strong hygroscopicity, and is subjected to dehumidifying and drying treatment using a dehumidifying dryer before molding drying. We have fully considered the function of the dehumidification drying system in the design of automotive complex plastic parts forming systems.
Secondly, the plastic parts for automotive use in China are basically glass-reinforced plastic products. Compared with the resin containing chopped glass fiber reinforced plastics, the material and structure of the screw for the injection molding machine without glass fiber reinforced plastic parts are Larger difference. When designing the injection molding machine, attention should be paid to the alloy material of the screw barrel and the special heat treatment process to ensure its corrosion resistance and strength.
Third, because the auto parts are different from conventional products, its cavity surface is very complicated, the force is not equal, the stress distribution is uneven, and the processing capability required by it is mainly considered in the design. The processing capability of the injection molding machine is reflected in both the clamping force and the injection molding capacity (expressed in terms of 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, otherwise the mold parting surface will be separated to produce a 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 clamping is the clamping force (or clamping force) KN of the injection molding machine; P cavity is the average pressure of the cavity, MPa, related to the structure shape, precision requirements and the number of cavities per model, etc. The range is generally between 25-40 MPa; F is the mold cavity, and the horizontal overlap projection area CM3 of the runner and the feed port. In order to ensure reliable mold clamping, the process clamping force during injection molding must be less than the rated clamping force of the injection molding machine. The maximum theoretical injection volume of the injection molding machine is matched with the clamping force of the injection molding machine. It is the injection capacity of the injection molding machine with the polystyrene (PS) as the reference resin before leaving the factory.
Fourth, according to the characteristics of complex plastic parts of automobiles, the driving form of the injection molding machine and the design of the clamping mechanism are hydraulic hydraulic or full hydraulic hydraulic elbows, or direct compression clamping at the center. Institutional injection molding machine. After years of hard work, Tairui Machinery Co., Ltd. has broken through the traditional constraints and developed a mechanical structure of two-plate clamping direct compression and compound clamping. The advantage of this structure is that its mold opening stroke is far greater than the hydraulic toggle joint clamping structure, at least 2 times, to meet the production needs of large plastic parts (such as bumpers, instrument panels, etc.). Secondly, the clamping mode is synchronously locked by four composite cylinders, and the large-tonnage smooth clamping is realized with a small flow rate, and the clamping force can be higher than that of the hydraulic torsion clamping structure of the same tonnage. The precision of the molded composite surface of large and complex plastic parts of automobiles is fully guaranteed.
Fifth, due to the complexity of the cavity surface of auto parts, the injection molding machine should be designed with special features in mind, such as multiple sets of core functions, timing control functions, and mold changing device functions. , supporting the function of the pick-up robot device. These special features are very advantageous in the production of automotive plastic parts. For example, in the production process of the bumper with this type of injection molding machine, in order to shorten the production cycle, the large-sized plastic parts after the mold opening and ejection are automatically taken out by the picking robot, and the plurality of sets of cores make the large plastic products smooth and flat. Out, there will be no whitening or cracking. At present, most of the three-axis pick-up robots we use in this injection molding system use a 6-axis pick-up robot.
