Characteristics of metal casting, sand casting and die casting

Casting can also be divided into gravity casting and pressure casting according to the pouring process of liquid metal. Gravity casting refers to the process of injecting molten metal into the mold under the action of the earth’s gravity, also known as casting. Gravity casting in a broad sense includes sand casting, metal casting, investment casting, mud casting, etc.; gravity casting in a narrow sense specifically refers to metal casting. Pressure casting is a process in which liquid metal is injected into the mold under the action of other external forces (excluding gravity). The broad sense of pressure casting includes pressure casting and vacuum casting, low pressure casting, centrifugal casting, etc.; the narrow sense of pressure casting refers to the metal mold pressure casting of the pressure casting machine, which is called die casting for short.

Sand casting is a kind of traditional casting technology which takes sand as the main molding material to make the mold. Generally, gravity casting is used for sand mold, and low-pressure casting, centrifugal casting and other processes can be used when there are special requirements. Sand casting has a wide range of adaptability, small, large, simple, complex, single, mass can be used. The mold used for sand casting was usually made of wood, commonly known as wood mold. In order to change the defects of wood mold, such as easy to deform and damage, Xudong precision casting factory has changed all of them into aluminum alloy mold or resin mold with high dimensional accuracy and long service life, except for the single sand mold. Although the price has increased, it is still much cheaper than the mold used in metal mold casting. In small batch and large-scale production, the price advantage is particularly prominent. In addition, the fire resistance of sand mold is higher than that of metal mold, so the materials with higher melting point, such as copper alloy and ferrous metal, also use this process. However, there are some disadvantages of sand casting: because each sand casting can only be poured once, the mold is damaged after the casting is obtained, and must be reshaped, so the production efficiency of sand casting is low; and because the overall property of sand is soft and porous, the size accuracy of sand casting is low, and the surface is rough.

Metal mold casting is a modern technology of making hollow mold with heat-resistant alloy steel. The metal mold can be either gravity casting or pressure casting. The mold of the metal mold can be used repeatedly. Every time the liquid metal is poured, one casting can be obtained, which has a long service life and high production efficiency. The casting of metal mold not only has good dimensional accuracy and smooth surface, but also has higher strength and less damage than that of sand mold when pouring the same liquid metal. Therefore, in the mass production of small and medium-sized castings of non-ferrous metals, as long as the melting point of the casting material is not too high, metal mold casting is generally preferred. However, there are some disadvantages of metal mold casting: because heat-resistant alloy steel and the processing of making hollow cavity on it are relatively expensive, the mold cost of metal mold is not cheap, but the overall cost is much cheaper than that of die-casting mold.

Die casting is a kind of metal mould pressure casting on die casting machine, which is the most efficient casting technology at present. Die casting machine is divided into hot chamber die casting machine and cold chamber die casting machine. The hot chamber die casting machine has high degree of automation, less material loss and higher production efficiency than the cold chamber die casting machine. However, restricted by the heat-resistant ability of the parts, it can only be used for the production of low melting point materials such as zinc alloy and magnesium alloy at present. The main feature of die casting is that the metal liquid fills the cavity under high pressure and high speed, and forms and solidifies under high pressure. The disadvantages of die casting are: because the air in the cavity is inevitably trapped in the casting to form subcutaneous pores in the process of filling the cavity under high pressure and high speed, so the aluminum alloy die casting is not suitable for heat treatment, and the zinc alloy die casting is not suitable for surface treatment Spray (but spray). Otherwise, when the air hole in the casting is heated by the above treatment, it will encounter thermal expansion and cause the casting to deform or bubble. In addition, the machining allowance of die casting should be smaller, generally at 0. About 5mm, it can not only reduce the weight of the casting, reduce the amount of cutting to reduce the cost, but also avoid penetrating the surface dense layer, exposing the subcutaneous pores, resulting in the workpiece scrapping.

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