Main types of casting process

The main process of casting includes metal melting, model making, pouring solidification and demoulding cleaning. The main materials used for casting are cast steel, cast iron, casting nonferrous alloys (copper, aluminum, zinc, lead, etc.).

Casting process can be divided into sand casting process and special casting process.

Folding special casting process


Special casting processes include centrifugal casting, low pressure casting, differential pressure casting, pressurized casting, plaster casting, ceramic casting and so on.

Pressure casting

Pressure casting refers to the casting process of molten metal under the action of other external forces (without gravity). The broad sense of pressure casting includes die casting and vacuum casting, low pressure casting, centrifugal casting, etc. The narrow sense of pressure casting refers to die casting machine metal mold pressure casting, referred to as die casting. These casting processes are the most commonly used and the lowest price in the nonferrous metal casting at present.

Metal mold casting

Metal mold casting is a modern technology of hollow casting mold made of metal (heat-resistant alloy steel, ductile iron, heat-resistant cast iron, etc.).

Metal mold can be either gravity casting or pressure casting. The metal mold can be used repeatedly. Each time the molten metal is poured, a casting is obtained. The life is long and the production efficiency is high. Metal mold casting not only has good dimensional accuracy and smooth surface, but also has higher strength and less damage than sand mold under the condition of pouring the same liquid metal. Therefore, in the mass production of non-ferrous metals in medium and small castings, as long as the melting point of the casting material is not high, generally preferred metal mold casting. However, metal mold casting also has some drawbacks: because heat-resistant alloy steel and the manufacture of hollow cavities on it are more expensive, so the metal mold costs a lot, but overall and die-casting mold costs are much cheaper than. For small batch production, the cost of the mold apportioned to each product is obviously too high, generally unacceptable. Because the metal mold is limited by the mold material size and cavity processing equipment, casting equipment capacity, so it also appears powerless to the particularly large castings. As a result, metal mold casting is seldom used in small batch and large piece production. In addition, although the metal mold used heat-resistant alloy steel, but the heat resistance is still limited, generally used in aluminum alloy, zinc alloy, magnesium alloy casting, copper alloy casting has been less used, but less used in ferrous metal casting.

Die-casting


Die casting is a metal mold die casting on the die casting machine, which is the highest production efficiency casting technology at present.

Die casting machine is divided into two types: hot chamber die casting machine and cold chamber die casting machine. Hot-chamber die-casting machine has high degree of automation, less material loss and higher production efficiency than cold-chamber die-casting machine. However, due to the heat resistance of the machine, it can only be used in the production of zinc alloy, magnesium alloy and other low melting point materials. Nowadays aluminum alloy die castings widely used 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 liquid metal fills the cavity under high pressure and high speed, and forms and solidifies under high pressure. The shortcomings of die casting are that the air in the cavity is bound to be trapped in the inner part of the casting inevitably during the filling process of the liquid metal under high pressure and high speed, thus forming the subcutaneous pores. It is not suitable for heat treatment. Zinc alloy die castings should not be sprayed (but can be painted). Otherwise, when the internal pores of the casting are heated by the above treatment, the casting will be deformed or bubbled due to thermal expansion. In addition, the machining allowance of die castings should also be smaller, generally around 0.5mm, which can not only reduce the weight of the castings, reduce the amount of cutting to reduce costs, but also avoid penetrating the surface of the dense layer, expose subcutaneous pores, resulting in scrap of the workpiece.


Melt mold casting


Lost wax casting, now called investment casting, is a kind of casting technology with little or no cutting. It is an excellent casting technology in the foundry industry, and it is widely used. It is not only suitable for casting of various types and alloys, but also for producing castings with higher dimensional accuracy and surface quality than other casting methods. Even castings which are difficult to be cast by other casting methods are complex, high temperature resistant and difficult to be processed. Investment casting can be used for casting.

Investment casting is developed on the basis of wax pattern casting in ancient times. As an ancient civilized country, China is one of the countries that used this technology earlier. As far back as centuries BC, the ancient working people in China created this lost wax casting technology, which was used to cast clocks, tripods and utensils with various fine patterns and characters, such as the Chunqiu Zeng Hou Yi tomb plate. The pedestal of the grave of Zeng Houyi is a series of intertwined dragons, which are interlaced at the top and bottom to form a multi-layer moire pattern in the middle. These patterns are difficult to be made by ordinary casting technology, but the paraffin wax casting technology can be used to make them without strength and easy to carve. The exquisite Zeng Hou Yi tomb tray can be obtained by carving the same paraffin material as the tray of Zeng Hou Yi tomb, and then adding pouring system, coating, dewaxing and pouring.


The modern investment casting method was applied in industrial production in 1940s. The development of jet engines at that time required the manufacture of complex shapes, precise sizes and surfaces such as blades, impellers and nozzles.