The characteristics and differences of various precision castings

1. Precision 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 of pouring molten metal into a mold under the action of the earth's gravity, also known as casting. Generally speaking, gravity casting includes sand casting, metal casting, investment casting, clay casting and so on. In a narrow sense, gravity casting refers to metal casting. Pressure casting refers to the process in which molten metal is injected into the mold under other external forces (not including gravity). Generally speaking, pressure casting includes pressure casting, vacuum casting, low pressure casting, centrifugal casting and so on. Die casting in a narrow sense refers to die casting of metal molds by die casting machine, referred to as die casting.
2. Sand casting is a traditional casting process that uses sand as the main molding material to make molds. Gravity casting is generally used for sand molds. Low pressure casting and centrifugal casting can also be used for special requirements. Sand casting has wide adaptability, and can be used for small, large, simple, complex, single-piece, and large-scale use. The molds used for sand casting were previously made of wood, called wooden molds. In addition, sand molds have higher fire resistance than metal molds, so materials with high melting points, such as copper alloys and ferrous metals, also use technology. However, sand casting also has some shortcomings: because each sand mold can only be poured once, the mold is damaged after casting and must be reshaped. The production efficiency of sand casting is low; because the sand mold is soft and porous as a whole, sand casting has low dimensional accuracy and rough surface.
3. Lost foam casting is a modern technology of hollow casting made of heat-resistant alloy steel. The metal mold can be cast by gravity or pressure. The metal mold can be reused. Once the molten metal is poured, castings can be obtained with long service life and high production efficiency. Metal castings not only have good dimensional accuracy and smooth surface, but also have higher strength than sand castings when pouring the same molten metal and are not easily damaged. Therefore, in the mass production of small and medium-sized non-ferrous metal castings, metal casting is the first choice for casting. However, permanent mold casting also has some disadvantages: because the heat-resistant alloy steel and the cavity made on it are very expensive, the metal mold is very expensive, but the overall cost is much cheaper than the die-casting mold. For small batch production, the mold cost allocated to each product is obviously too high and generally unacceptable. In addition, due to the limitations of mold size and cavity processing equipment and casting equipment capabilities, it seems that it cannot be used for a long time. Therefore, aluminum alloys, magnesium alloys, zinc alloys, magnesium alloys, zinc alloys, magnesium alloys, and zinc alloy castings used in small batches, large batches, and mass production are rarely used.

4. Die-casting is metal die-casting on a die-casting machine, which 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 degree of automation of the hot chamber die casting machine is higher than that of the cold chamber die casting machine, with less material loss and high production efficiency. However, due to the limitation of heat resistance of parts, it can only be used for casting and production of low melting point materials, such as zinc alloy and magnesium alloy. The aluminum alloy die castings that are widely used today can only be produced on cold chamber die casting machines because of the high melting point. The main feature of die casting is that molten metal fills the cavity under high pressure, and then forms and solidifies under high pressure. The disadvantage of die-casting is that cavity air is inevitably wrapped in the casting, forming subcutaneous pores. Therefore, aluminum alloy die-casting is not suitable for heat treatment, and zinc alloy die-casting is not suitable for surface spraying (but spraying). Otherwise, when the pores in the casting are heated by the above treatment, the casting will be deformed or blistered due to thermal expansion. Therefore, the machining allowance of die castings is relatively small, generally about 0.5 mm, which can reduce the weight of castings and reduce surface spraying (but spraying). Otherwise, when the pores in the casting are heated as described above, the pores in the casting will be deformed or blistered due to the heat.