The die-casting mold consists of two parts, a cover part and a movable part, and the part which is combined is called a parting line. In hot chamber die casting, the covered portion has a gate, while in cold chamber die casting, it is an injection port. Molten metal can enter the mold from here, and the shape of this part matches the injection chamber in the hot chamber die casting or the injection chamber in the cold chamber die casting. The movable part usually includes a push rod and a flow path, and the so-called flow path is a passage between the gate and the cavity through which the molten metal enters the cavity. The cover portion is usually attached to the fixed platen or the front platen, and the movable portion is attached to the movable platen. The cavity is divided into two cavity inserts which are separate components that can be removed or mounted relatively easily from the mold by bolts.
The mold is specially designed to 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, and it will accurately drive all the push rods with the same amount of force, so as to ensure that the casting is not damaged. When the casting is pushed out, the platen shrinks and all the pushers are retracted, ready for the next die casting. Since the castings are still at a high temperature during demolding, only the number of push rods is sufficient to ensure that the average pressure on each of the push rods is small enough to not damage the casting. However, the putter still leaves traces, so it must be carefully designed so that the position of the putter does not have too much impact on the operation of the casting.
Other components in the mold include core slides and the like. The core is the part used to open or open the casting and they can also be used to add detail to the casting. There are three main types of cores: fixed, active and loose. The direction of the stationary core is parallel to the direction in which the castings come out of the mold, either fixed or permanently attached to the mold. The movable core can be arranged in any direction other than the direction of the escape, and the movable core must be taken out of the cavity by means of a separating device before the casting is solidified and the mold is opened. The slider and the movable core are very close, the biggest difference is that the slider can be used to make an inverted surface. The use of cores and sliders in die casting adds significant cost. Loose cores, also known as take-up blocks, can be used to make complex surfaces such as threaded holes. Before each cycle begins, the slider needs to be manually installed and finally pushed out with the casting. Then take out the loose core. A loose core is the most expensive core because it requires a lot of labor to make it, and it increases cycle time.
The discharge port is usually thin and long (about 0.13 mm), so the molten metal can be cooled quickly to reduce waste. It is not necessary to use a riser in the die casting process because the molten metal has a high pressure and can be continuously flowed into the mold from the gate.
Due to temperature, the most important material properties for the mold are thermal shock resistance and softness. Other features include hardenability, machinability, thermal crack resistance, weldability, and usability (especially for large molds). And the cost. Die life depends directly on the temperature of the molten metal and the time of each cycle. Molds for die casting are usually made of hard tool steel, because cast iron cannot withstand large internal pressures, so the mold is expensive, which also leads to high mold opening costs. Metals die cast at higher temperatures require the use of harder alloy steels.
The main defects that can occur during the die casting process include wear and erosion. Other defects include hot cracking and thermal fatigue. When the surface of the mold is too large due to temperature changes, thermal cracking occurs. When the number of uses is too large, defects occurring on the surface of the mold may cause thermal fatigue.