The essence of high-pressure casting (abbreviated as die casting) is the method of filling the cavity of a die casting mold (die casting mold) with liquid or semi liquid metal at a higher speed under high pressure, and forming and solidifying under pressure to obtain castings.
High pressure casting is a casting method in which molten alloy liquid is poured into a pressure chamber to fill the cavity of a steel mold at high speed, and the alloy liquid solidifies under pressure to form a casting. The main characteristics that distinguish high-pressure die casting from other casting methods are high pressure and high speed Metal liquid fills the mold cavity under pressure and crystallizes and solidifies at higher pressures, commonly ranging from 15-100 MPa Metal liquid fills the mold cavity at high speed, usually between 10-50 meters per second, and some can even exceed 80 meters per second (the linear speed of the mold cavity introduced through the internal gate - the internal gate speed). Therefore, the filling time of the metal liquid is extremely short, about 0.01-0.2 seconds (depending on the size of the casting), and the mold cavity can be filled.
Advantages of high-pressure casting
1. High dimensional accuracy of castings,; Good surface smoothness, generally equivalent to grades 5-8
2. The strength and hardness are relatively high, and the strength is generally increased by 25-30% compared to sand casting
3. Stable size, good interchangeability, capable of die-casting thin-walled and complex castings
4. The machine has high productivity, for example, the domestically produced J-III3 horizontal cold air die-casting machine can die cast 600-700 times on average in eight hours, and the small hot chamber die-casting machine can die cast 3000-7000 times on average every eight hours
5. Die casting molds have a long lifespan, with a pair of die casting molds and die cast bell alloys having a lifespan of several hundred thousand times, or even millions of times; Easy to achieve mechanization and automation
6. Die-casting parts have the advantages of high precision in size and smooth surface. They are generally used directly without mechanical processing or with very small processing volume, which not only improves metal utilization but also reduces a lot of processing equipment and working hours
Disadvantages of high-pressure casting
1. Due to the high filling speed and unstable flow state of liquid metal in the mold cavity during die casting, the general die casting method is adopted, which is prone to the formation of pores and poor elongation inside the casting, and cannot be subjected to heat treatment
2. Difficulty in die-casting complex castings with internal concavity and convexity
3. Small batch production is not suitable because the manufacturing cost of die-casting molds is high, the production efficiency of die-casting is high, and small batch production is not economical
4. The cost of equipment and molds is high