Pressure casting
Pressure casting refers to the process of injecting molten metal into the mold under the action of other external forces (excluding gravity). Pressure casting in a broad sense includes pressure casting, vacuum casting, low-pressure casting, centrifugal casting, etc; Narrow sense of pressure casting refers to the metal mold pressure casting of pressure casting machine, which is referred to as die casting for short. These casting processes are the most commonly used and the lowest relative price in nonferrous metal casting.
Metal mold casting
Metal mold casting is a modern technology of hollow mold for casting made of metal (heat-resistant alloy steel, nodular cast iron, heat-resistant cast iron, etc.).
The metal mold can be either gravity casting or pressure casting. The mold of metal mold can be used repeatedly. Each time the liquid metal is poured, a casting can be obtained. The service life is very long and the production efficiency is very high. The casting surface is not only more accurate, but also easier to be damaged than the metal mold when the casting size is not the same. Therefore, in the mass production of medium and small castings of non-ferrous metals, metal mold casting is generally preferred as long as the melting point of the casting material is not too high. However, metal mold casting also has some shortcomings: because the processing of heat-resistant alloy steel and hollow cavity on it are more expensive, the cost of metal mold is not cheap, but it is much cheaper compared with the cost of die-casting mold. For small batch production, the mold cost allocated to each product is obviously too high, which is generally not easy to accept. And because the mold of metal mold is limited by the size of mold material and the capacity of cavity processing equipment and casting equipment, it is powerless to do anything for particularly large castings. Therefore, metal mold casting is rarely used in small batch and large piece production. In addition, although the metal mold adopts heat-resistant alloy steel, its heat-resistant ability is still limited. It is generally used for the casting of aluminum alloy, zinc alloy and magnesium alloy. It has been less used in copper alloy casting, and less used in ferrous metal casting.
Die-casting
Die casting is the metal mold pressure casting on the die casting machine, which is the casting process with the highest production efficiency.
Die casting machines are divided into hot chamber die casting machines and cold chamber die casting machines. The hot chamber die casting machine has a high degree of automation, less material loss and higher production efficiency than the cold chamber die casting machine. However, restricted by the heat resistance of the parts, it can only be used for the casting production of low melting point materials such as zinc alloy and magnesium alloy. Nowadays, aluminum alloy die castings widely used can only be produced on cold chamber die casting machine because of their high melting point. The main feature of die-casting is that the liquid metal fills the cavity under high pressure and high speed, and forms and solidifies under high pressure. The disadvantage of die-casting parts is that during the process of filling the cavity under high pressure and high speed, the air in the cavity is inevitably clamped in the interior of the casting to form subcutaneous pores. Therefore, aluminum alloy die-casting parts should not be heat treated, and zinc alloy die-casting parts should not be sprayed with plastic (but can be painted). Otherwise, when the pores inside the casting are heated by the above treatment, they will encounter thermal expansion and cause deformation or bubbling of the casting. In addition, the machining allowance of die-casting parts should also be small, generally about 0.5mm, which can not only reduce the weight of castings and cutting amount to reduce costs, but also avoid penetrating the dense layer on the surface and exposing subcutaneous pores, resulting in scrapping of workpieces.