The mold is specially designed, and the casting will remain in the moving part when the mold is opened. In this way, the push rod of the movable part will push out the casting. The push rod is usually driven by the pressure plate, which will drive all the push rods at the same time with the same force accurately to ensure that the casting will not be damaged. When the casting is pushed out, the pressure plate shrinks and retracts all the push rods to prepare for the next die casting. Because the casting is still in a high temperature state when it is demoulded, only when the number of push rods is enough can the average pressure on each push rod be small enough to avoid damaging the casting. But the push rod will still leave traces, so it must be carefully designed so that the position of the push rod will not affect the casting operation too much.
Other parts in the mold include core slide plate, etc. Core is a part used to drill holes or holes in castings. They can also be used to add details to castings. There are three main types of cores: fixed, movable and loose. The direction of the fixed cores is parallel to the direction in which the castings leave the mold, and they are either fixed or permanently connected to the mold. The movable core can be arranged in any direction except the demoulding direction. Before opening the mold after solidification of the casting, the movable core must be taken out of the mold cavity by using a separation device. The slider is very close to the moving core, and the biggest difference is that the slider can be used to make inverted concave surfaces. Using cores and sliders in die casting will greatly increase the cost. Loose cores, also known as take-out blocks, can be used to make complex surfaces, such as threaded holes. Before each cycle begins, it is necessary to manually install the slider and then push it out together with the casting. Then take out the loose core. The loose core is the most expensive core, because it requires a lot of labor to manufacture and will increase the cycle time.
The discharge port is usually thin and long (about 0. 13mm), so the molten metal can be cooled quickly and the waste can be reduced. There is no need to use riser in die casting process, because the pressure of molten metal is very high, which can ensure continuous flow from the gate into the mold.
Due to the temperature, the most important material characteristics of the mold are thermal shock resistance and flexibility. Other characteristics include hardenability, machinability, hot cracking resistance, weldability, usability (especially for large molds) and cost. The service life of the mold directly depends on the temperature of molten metal and the time of each cycle. The die used for die casting is usually made of hard tool steel. Because cast iron can't bear huge internal pressure, the mold is expensive, which also leads to high mold opening cost. Metals die-cast at higher temperatures require harder alloy steel.
The main defects in die casting process include wear and erosion. Other defects include thermal cracking and thermal fatigue. When defects appear on the surface of the mold due to excessive temperature change, thermal cracks will appear. However, after too many times of use, the defects on the surface of the mold will produce thermal fatigue.