Metal mold casting is a modern technology of hollow casting mold made of metal (heat resistant alloy steel, nodular cast iron, heat resistant cast iron, etc.).
The metal mold can be cast by gravity or pressure. The metal mold can be repeatedly used for many times, and each time molten metal is poured, a casting is obtained, so that the service life is long, and the production efficiency is high. Metal mold castings not only have good dimensional accuracy and smooth surface, but also have higher strength than sand mold castings and are less prone to damage under the condition of pouring the same molten metal. Therefore, in mass production of non-ferrous metal medium and small castings, as long as the melting point of the casting material is not too high, metal mold casting is generally preferred. However, the metal mold casting also has some disadvantages: because the heat-resistant alloy steel and the processing of the hollow cavity made on it are relatively expensive, the metal mold is expensive, but the overall cost is much lower than that of the die casting mold. For small batch production, the die cost allocated to each product is obviously too high to be generally accepted. And because the metal mold is limited by the size of the mold material and the capacity of the cavity processing equipment and the casting equipment, there is nothing that can be done for particularly large castings. Therefore, metal mold casting is rarely used in small batch and large-size production. In addition, although the metal mold uses heat-resistant alloy steel, its heat-resistant ability is still limited. It is generally used for casting aluminum alloy, zinc alloy and magnesium alloy. It has been less used in copper alloy casting and even less used in ferrous metal casting.
Die casting
Die casting is a metal mold pressure casting on a die casting machine and is currently the casting process with the highest production efficiency.
Die casting machines are divided into two types: hot chamber die casting machines and cold chamber die casting machines. Hot-chamber die-casting machines have high degree of automation, less material loss and higher production efficiency than cold-chamber die-casting machines. However, due to the restriction of heat resistance of parts, they can only be used for the production of castings of low melting point materials such as zinc alloy and magnesium alloy at present. 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 characteristics of die casting are that the molten metal fills the cavity under high pressure and high speed, and then forms and solidifies under high pressure. The disadvantages of die casting are: because the air in the cavity is inevitably entrapped inside the casting to form subcutaneous pores during filling the cavity under high pressure and high speed, aluminum alloy die casting is not suitable for heat treatment and zinc alloy die casting is not suitable for surface spraying (but can be painted). Otherwise, the internal air holes of the casting will encounter thermal expansion and cause deformation or bubbling of the casting when heated by the above treatment. In addition, the machining allowance for die castings should also be made smaller, generally about 0.5mm, which can not only reduce the weight of the castings, reduce the machining amount to reduce the cost, but also avoid penetrating through the dense layer of the surface, exposing subcutaneous pores and causing the workpiece to be scrapped.