In the design of plastic injection mold, it is necessar […]
In the design of plastic injection mold, it is necessary to reduce the shrinkage according to the shrinkage of different materials, while the die-casting mold basically has no shrinkage, and the product size will be as large as the mold cavity size; the biggest difference between the two types of mold is the injection, the gate of the die-casting mold is different from the injection mold, and the high pressure of splitting cone is needed to decompose the material flow. The material channel and feed port of die-casting die are generally much larger than that of plastic, so it is difficult to modify. Especially for aluminum alloy die-casting die, piston injection is used to fill the cavity of the die, and the material handle is very large, while the plastic die is a screw injection of injection molding machine, which is a small hole. The injection speed of the die-casting die is fast, usually a section of injection pressure, the injection pressure of the die-casting die is large, so the template needs to be relatively thicker to prevent deformation. Plastic mold is usually injected in several sections to keep pressure. The die-casting mold is two plate mold (I haven't seen three plate die-casting mold for the moment). Different product structures of plastic mold are different. Three plate mold is common. The number and sequence of mold opening match the mold structure. We usually do not use square thimble and cylinder for die casting die, Inclined pin (high temperature and good solution fluidity) is easy to jam, which leads to unstable die production The first runner is different. The runner of the die-casting die is wider. The feeding area should be calculated according to the size and weight of the product. Generally, the width and thickness should not exceed the thickness of the product meat (75%). There is only one feeding mode of the die-casting die, which is different from the plastic mold, and it can use point feeding, submerged rubber port (or submerged thimble), bull point feeding and large water port direct feeding.
The core of die casting die does not need to be quenched, because the temperature in the die cavity is more than 700 degrees during die casting. Therefore, each molding is equivalent to quenching once, and the die cavity will become more and more hard. The general injection mold should be quenched to above hrc52, and the general cavity of the die-casting mold should be nitrided to prevent the alloy from sticking to the cavity. Because the corrosion of the die-casting mold is relatively large, some customers also require the outer surface of the mold to be blue treated. At the same time, the parting surface matching requirements of die-casting mold are higher, because the alloy fluidity is much better than plastic. It will be very dangerous for the material flow of high temperature and high pressure to fly out of the parting surface; compared with injection mold, the mating clearance of the movable mating part of die-casting mold (such as core pulling slider) is larger, and the high temperature of die-casting process will cause thermal expansion, and if the clearance is too small, the mold will be stuck. No matter what kind of mold, when injecting, the gas in the sealed cavity is compressed and cannot be discharged, which will lead to the phenomenon of insufficient feeding or burning of the product. Generally, the injection mold can be discharged by means of thimble, parting surface, etc., and the die-casting mold must be provided with an exhaust slot and a slag collecting bag (to collect the cold material head).