Machining Methods

Characteristics and differences of various castings

Gravity casting refers to the process in which the molten metal is injected into the mold under the influence of the earth's gravity, also known as casting.Gravity casting refers to the process in which the molten metal is injected into the mold under the influence of the earth's gravity, also known as casting.

1. Casting can also be divided into gravity casting and pressure casting according to the casting process of molten metal. Gravity casting refers to the process in which the molten metal is injected into the mold under the influence of the earth’s gravity, also known as casting. Gravity castings  in a broad sense includes sand casting, metal casting, investment casting, mud casting, etc .; narrow sense gravity casting refers specifically to metal casting. Pressure casting refers to the process in which the molten metal is injected into the mold under the action of other external forces (without gravity). Pressure casting in a broad sense includes pressure casting and vacuum machining castings, low pressure casting, centrifugal casting, etc. of die casting machine; narrow sense pressure casting refers to metal die casting of die casting machine, referred to as die casting. Xudong Precision Casting Factory has long been engaged in gravity casting of sand and metal molds. These casting processes are currently the most commonly used in non-ferrous metal casting, and are also the cheapest.

2. Sand casting is a traditional casting process that uses sand as the main molding material to make castings. Sand casting is generally gravity casting, and low pressure casting, centrifugal casting and other processes can also be used when there are special requirements. The adaptability of sand casting is very wide, small parts, large parts, simple parts, complex parts, single parts, large quantities can be used. Moulds used for sand casting were formerly made of wood, commonly known as wood molds. In order to change the disadvantages of wood molds such as deformation and damage, Xudong Precision Casting Factory changed all the aluminum alloy molds or resin molds with high dimensional accuracy and long service life, except for the sand castings produced in a single piece. Although the price has increased, it is still much cheaper than the mold for metal mold casting. In small batches and large parts production, the price advantage is particularly prominent. In addition, sand molds are more refractory than metal molds, so materials with higher melting points such as copper alloys and ferrous metals also use this process. However, sand casting also has some shortcomings: because each sand casting can only be poured once, the casting mold is damaged after the casting is obtained, and it must be re-shaped, so the production efficiency of sand casting is low; and because the overall nature of the sand is soft It is porous, so the dimensional accuracy of sand castings is low and the surface is rough. However, Xudong Precision Casting Factory has accumulated many years of technical accumulation, which has greatly improved the surface condition of sand castings, and its effect after shot blasting is comparable to that of metal castings.

3. Metal mold casting is a modern process for making hollow molds for casting using heat-resistant alloy steel. The metal mold can be either gravity casting or pressure casting. The metal mold can be used repeatedly for many times. Each time a metal liquid is poured, a casting is obtained. The service life is very long and the production efficiency is very high. Metal castings not only have good dimensional accuracy and smooth surface, but also in the case of pouring the same metal liquid, the strength of the castings is higher than that of sand molds, and it is less likely to be damaged. 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 casting is generally preferred. However, metal mold casting also has some shortcomings: because the processing of heat-resistant alloy steel and making hollow cavities on it is relatively expensive, the cost of metal molds is expensive, but the overall cost is lower than that of die casting molds. too much. For small batch production, the cost of the mold allocated to each product is obviously too high and is generally not easy to accept. And because the metal mold is limited by the size of the mold material and the capacity of the cavity processing equipment and casting equipment, it is also powerless for particularly large castings. Therefore, in small batches and large parts production, metal casting is rarely used. In addition, although the metal mold adopts heat-resistant alloy steel, the heat resistance is still limited. It is generally used for the casting of aluminum alloys, zinc alloys, and magnesium alloys. It has been rarely used in copper alloy casting, and it is used for ferrous metal casting. Even less. The metal molds of Xudong Precision Casting Factory are all designed and manufactured by themselves, so they can provide customers with cheap and applicable high-quality molds in a more timely manner.

4. Die-casting is metal die-casting performed on a die-casting machine and is currently the most efficient casting process. Die casting machines are divided into hot chamber die casting machines and cold chamber die casting machines. 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, due to the heat resistance of the machine parts, it can only be used for the production of castings with low melting point materials such as zinc alloys and magnesium alloys. . Aluminum alloy die castings widely used today can only be produced on cold chamber die casting machines due to their high melting point. The main feature of die casting is that the molten metal fills the cavity under high pressure and high speed, and is formed and solidified under high pressure. The disadvantage of die casting is that because the molten metal fills the cavity under high pressure and high speed, it is inevitable The air in the mold cavity is wrapped inside the casting to form pores under the skin, so aluminum alloy die castings should not be heat treated, and zinc alloy die castings should not be sprayed on the surface (but can be painted). Otherwise, when the pores inside the casting are heated by the above treatment, they will expand due to heat and cause the casting to deform or blister. In addition, the mechanical cutting allowance of die castings should also be smaller, generally around 0.5mm, which can not only reduce the weight of the casting, reduce the amount of cutting processing to reduce costs, but also avoid penetrating the dense surface layer and exposing the subcutaneous pores, resulting in The workpiece is scrapped.

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