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    Die casting process


    Traditional die-casting process is mainly composed of four steps, or high-pressure die-casting. These four steps include mold preparation, filling, injection and falling sand, which are also the basis of various modified die-casting processes. During the preparation process, it is necessary to spray lubricant into the mold cavity. In addition to helping to control the temperature of the mold, lubricants can also help mold release. The mold can then be closed and molten metal can be injected into the mold under high pressure, which is in the range of about 10 to about 175 MPa. When the molten metal is filled, the pressure will be maintained until the casting solidified. Then putter will launch all the castings, because there may be more than one mold cavity, so each casting process may produce multiple castings. The process of falling sand needs to separate the residue, including the mold opening, runner, gate and flash. This process is usually done by squeezing the casting through a special dressing die. Other sand removal methods include sawing and grinding. If the gate is relatively fragile, you can directly beat castings, this can save manpower. Excess die can be reused after melting. The typical yield is about 67%.
    High-pressure injection results in a very fast filling of the mold, so that the molten metal fills the entire mold before any part is solidified. In this way, surface discontinuities can be avoided even in thin-walled portions that are difficult to fill. However, this can also result in air entrapment because the air is hard to escape when filling the mold quickly. This problem can be reduced by placing the vent on the parting line, but even a very delicate process leaves holes in the center of the casting. Most die-castings can be completed by secondary processing some can not be completed by casting the structure, such as drilling, polishing.
    After the sand is finished, defects can be checked, the most common defects include stagnation (pouring dissatisfaction) and cold scar. These defects may be due to mold or molten metal temperature is not enough, mixed with metal impurities, too little vent, too much lubricant and other causes. Other defects include porosity, shrinkage, thermal cracking, and flow marks. Flow marks are marks left on the surface of the castings by gate defects, sharp corners or excessive lubricant.
    Water-based lubricants, called emulsions, are the most commonly used types of lubricants for health, environmental and safety reasons. Unlike solvent-based lubricants, if the minerals in the water are removed by a suitable process, they do not leave by-products in the casting. If the process of treating water is improper, minerals in the water can cause casting surface defects and discontinuities. There are four main types of water-based lubricants: water-based oil, oil-water, semi-synthetic and synthetic. Water-lubricated lubricants are the best because when water is used, the water cools the surface of the mold by evaporation while depositing the oil, which can help with mold release. Normally, this type of lubricant is mixed in a ratio of 30 parts water to 1 part oil. In extreme cases, this ratio can reach 100: 1.