The traditional die casting process is mainly composed of four steps, or called high pressure die casting. These four steps, which include mold preparation, filling, injection, and sanding, are the basis of various modified die casting processes. During the preparation process, a lubricant is sprayed into the mold cavity. In addition to helping to control the temperature of the mold, the lubricant can also help to release the casting. The mold can then be closed and the molten metal is injected into the mold at a high pressure ranging from 10 to 175 mpa. When the molten metal is filled, the pressure is maintained until the casting solidifies. The push rod then pushes out all the castings, and since there may be more than one cavity in a mold, multiple castings may be produced in each casting process. The process of falling sand requires separation of the residue, including the mold opening, runner, gate, and flitter. This process is usually done by extruding the casting with a special dressing die. Other methods of sand removal include sawing and sanding. If the gate is fragile, you can beat the casting directly, which can save labor. Excess moulds can be reused after melting. The usual yield is about 67 percent
High pressure injection causes the mold to be filled very quickly, so that the molten metal fills the entire mold before any part solidifies. In this way, surface discontinuities can be avoided even in thin wall sections that are difficult to fill. However, this can also cause air retention, since it is difficult to escape when filling the mold quickly. this problem can bee reduced by placing vents on the parting line, but even very sophisticated processes can leave holes in the center of the casting. Most die casting can be done by secondary machining to complete some structures that cannot be completed by casting, such as drilling, polishing.g
Water-based lubricants, called emulsions, are the most commonly used type of lubricant due to health, environmental, and safety concerns. Unlike solvent-based lubricants, it does not leave byproducts in the casting if the minerals in the water are removed using a suitable process. If the water is not treated properly, minerals in the water can cause surface defects and discontinuities in the casting. There are four main types of water-based lubricants: water mixed with oil, oil mixed with water, semi-synthetic and synthetic. Water-oil lubricants are best because when using lubricants, the water deposits the oil and cools the surface of the mold by evaporation, which can help release the mold. Typically, this type of lubricant has a ratio of 30 parts water to 1 part oil. In extreme cases, the ratio can reach 100:1
Oils that can be used as lubricants include heavy oils, animal fats, vegetable fats, and synthetic fats. The heavy residual oil is relatively viscous at room temperature, while it becomes thin film at high temperature in die casting process. The emulsion viscosity and thermal properties can be controlled by adding other substances to the lubricant. These include graphite, aluminum and mica. Other chemical additives prevent dust and oxidation. Emulsifiers can be added to water-based lubricants so that oil-based lubricants, including soap, alcohol, and ethylene oxide, can be added to the water
For a long time, commonly used solvent-based lubricants include diesel and gasoline. They facilitate the casting to come out. However, small explosions occur during each die casting process, which causes carbon to accumulate on the cavity walls. Solvent-based lubricants are more homogeneous than water-based lubricants
