The essence of high pressure die casting (die casting for short) is a method that liquid or semi-liquid metal fills the cavity of die casting mold at high speed under the action of high pressure, and then forms and solidifies under pressure to obtain castings. Compared with other casting methods, die casting has the following three advantages: good product quality and high dimensional accuracy of castings, which are generally equivalent to 6~7 grades or even 4 grades; Good surface finish, generally equivalent to 5~8 grades; The strength and hardness are higher, the strength is generally 25~30% higher than that of sand casting, but the elongation is reduced by about 70%; Stable size and good interchangeability; Die-casting thin-walled complex castings. For example, the minimum wall thickness of zinc alloy die casting can reach 0.3mm； at present; Aluminum alloy castings can reach 0.5mm；; The minimum casting aperture is 0.7mm；; The minimum pitch is 0.75 mm, with high production efficiency and high machine productivity. For example, domestic J Ⅲ 3 horizontal cold air die casting machine can die cast 600 ~ 700 times in eight hours on average, and small hot chamber die casting machine can die cast 3000~7000 times in eight hours on average. Die-casting type has a long service life, and a pair of die-casting type and die-casting clock alloys can have a service life of hundreds of thousands or even millions of times; It is easy to realize mechanization and automation. Die casting parts have accurate dimensions, smooth surface and good economic benefits. Generally, it is used directly without mechanical processing, or the processing amount is very small, which not only improves the metal utilization rate, but also reduces a lot of processing equipment and working hours; The casting price is easy; Combined die casting can be used for other metal or nonmetal materials. Save assembly time and metal. Disadvantages of die casting Although die casting has many advantages, there are also some shortcomings to be solved. Such as: 1). Due to the high filling speed and unstable flow pattern of liquid metal during die casting, the castings are easy to produce blowholes and cannot be heat treated by ordinary die casting methods. 2) It is difficult to die-cast complex concave castings; 3) High melting point alloys (such as copper and ferrous metals) have short die-casting life; 4) Not suitable for small batch production. The main reasons are high manufacturing cost of die casting, high production efficiency of die casting machine and uneconomical small batch production.