1、 Overview& nbsp; There are many process methods for making metal materials into required products, such as casting, forging, extrusion, rolling, drawing, stamping, cutting, powder metallurgy, and so on. Among them, casting is the most basic and commonly used process& nbsp; & nbsp; Casting is the process of injecting molten metal into a hollow mold made of high-temperature resistant materials and condensing it to obtain the desired shape of the product. The resulting product is a casting& nbsp; & nbsp; Casting can be divided into ferrous metal casting (including cast iron, cast steel) and non-ferrous metal casting (including aluminum alloy, copper alloy, zinc alloy, magnesium alloy, etc.) based on the material of the casting& nbsp;& nbsp; & nbsp; Casting can be divided into sand casting and metal casting according to the material of the casting mold& nbsp; & nbsp; Casting can also be divided into gravity casting and pressure casting according to the pouring process of molten metal. Gravity casting refers to the process of injecting molten metal into a mold under the influence of the Earth's gravity, also known as casting. Generalized gravity casting includes sand casting, metal casting, investment casting, lost foam casting, mud casting, etc; The narrow meaning of gravity casting specifically refers to metal mold casting. Pressure casting refers to the process of injecting molten metal into the mold under the action of other external forces (excluding gravity). According to the magnitude of pressure, it is further divided into high-pressure casting (die casting) and low-pressure casting& nbsp; & nbsp; Sand casting is a traditional casting process that uses sand as the main molding material to make molds. Sand molds generally use gravity casting, and low-pressure casting, centrifugal casting, and other processes can also be used when there are special requirements. Sand casting has a wide range of adaptability, including small and large parts, simple and complex parts, single parts, and large batches. A mold used for sand casting, usually made of wood, commonly known as a wooden mold. In addition, sand molds have higher fire resistance than metal molds, so materials with higher melting points such as copper alloys and black metals also use this process more frequently. However, sand casting also has some shortcomings: because each sand mold can only be poured once, the mold is damaged after obtaining the casting and must be reshaped, so the production efficiency of sand casting is relatively low; Due to the overall soft and porous nature of sand, the dimensional accuracy of sand castings is lower and the surface is also rougher.  & nbsp; Metal mold casting is a modern process that uses heat-resistant alloy steel to make hollow casting molds for casting. Metal molds can be either gravity cast or pressure cast. The metal mold can be reused multiple times, and with each pouring of molten metal, one casting is obtained, resulting in a long lifespan and high production efficiency. Metal mold castings not only have good dimensional accuracy and smooth surface, but also have higher strength and are less prone to damage compared to sand mold castings when pouring the same metal liquid. Therefore, when producing medium and small castings of non-ferrous metals in large quantities, as long as the melting point of the casting material is not too high, metal mold casting is generally preferred. However, metal mold casting also has some shortcomings: because heat-resistant alloy steel and the processing of hollow cavities on it are relatively expensive, the cost of metal mold molds is not expensive, but overall, compared to the cost of die-casting molds, it is much cheaper. For small-scale production, the mold cost allocated to each product is significantly too high and generally not easy to accept. Due to the limitations of mold material size, cavity processing equipment, and casting equipment, metal molds are not suitable for the production of particularly large castings. In small-scale and large-scale production, metal mold casting is generally not used. In addition, although metal mold molds use heat-resistant alloy steel, their heat resistance is still limited, and they are generally used for casting aluminum alloys, zinc alloys, and magnesium alloys. They are less commonly used in copper alloy casting, and less commonly used in black metal casting& nbsp;& nbsp;  & nbsp; Die casting is a metal mold pressure casting process carried out on a die casting machine, which is currently the most efficient casting process. Die-casting machines are divided into two categories: hot chamber die-casting machines and cold chamber die-casting machines. The hot chamber die-casting machine has a high degree of automation, less material loss, and higher production efficiency than the cold chamber die-casting machine. However, due to the limitations of the machine's heat resistance, it can only be used for the production of low melting point materials such as zinc alloy and magnesium alloy castings. The widely used aluminum alloy die castings nowadays can only be produced on cold chamber die casting machines due to their high melting point. The main characteristic 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 disadvantage of die castings is that during the process of filling the cavity under high pressure and high speed, the air in the cavity is inevitably trapped inside the casting, forming subcutaneous pores. Therefore, aluminum alloy die castings are not suitable for heat treatment, and zinc alloy die castings are not suitable for surface spraying (but can be painted). Otherwise, during the above treatment and heating, the internal pores of the casting will expand and cause deformation or bubbling of the casting. In addition, the mechanical cutting allowance for die-casting parts should also be smaller, usually around 0.5mm, which can reduce the weight of the casting, reduce the cutting amount to reduce costs, and avoid penetrating the surface dense layer, exposing subcutaneous pores, and causing the workpiece to be scrapped.2、 Comparison of commonly used casting methodsAmong the commonly used casting methods, sand casting technology has the strongest adaptability, lower equipment and casting costs, and is widely used. Currently, sand casting accounts for about 80% to 90% of the total production of castings in the world. However, in specific situations, such as thin-walled parts, precision casting, or mass production, special casting often exhibits unique advantages. The characteristics and applicability of commonly used casting methods are shown in Table 2-5. & nbsp; Table 2-5; Characteristics and applicability of commonly used casting methods project Sand castingMetal mold castingPressure castingLow-pressure castingcentrifugal casting Investment castingFull mold castingContinuous castingCasting characteristicstexture of materialVarious alloysMainly non-ferrous alloysNon-ferrous alloyVarious alloysVarious alloysVarious alloysVarious alloysVarious alloysSizeVarious sizesMainly for small and medium-sized itemsMedium and small piecesMedium and small piecesVarious sizesMainly small itemsVarious sizesVarious sizesstructurecomplexcommonlyMore complexMore complexcommonlycomplexMore complexsimple3、 The Development Trend of Casting Technology  & nbsp; With the rapid development of science and technology, especially the widespread application of computers, the casting industry is transforming from labor-intensive to high-tech, and developing from mechanization and automation to intelligence. Traditional processes and materials are gradually being replaced by new processes and materials& nbsp;（1） Application of Computers1. Computer Aided Process Planning (CAPP); Computer technology has been widely applied in developed countries, such as simulating the flow field, temperature field, stress field, solidification structure, etc. during the filling process, optimizing the design of casting pouring position, pouring system, riser, etc., as well as calculating and optimizing parameters such as pouring temperature, pouring time, and mold temperature.2. Automatic control and detection of the casting process; In recent years, the control and detection of casting processes have formed automated processing technologies at different levels, from single machine to system, from rigidity to flexibility, and from simplicity to complexity. By replacing discrete components with integrated circuits and replacing relays with programmable control, automatic control of casting equipment and even the entire production line can be achieved.Real time monitoring or adaptive control of various process parameters has been applied to monitoring the performance of molding sand and sand treatment process, furnace material ratio and smelting quality, casting performance, and working conditions of molding lines. Effectively improving casting quality and production efficiency.Flexible units (FMCs) such as die-casting and machine modeling have been developed and applied, which can quickly replace molds or templates without stopping according to predetermined process plans within a specified range, achieving production of multiple varieties and batches. Various types of operating machines with motion functions similar to human arms, as well as industrial robots that can be automatically controlled, reprogrammed, and multifunctional, are being further developed and expanded in application. The Computer Integrated Manufacturing System (CIMS) is also under development& nbsp;（2） Application of Advanced Manufacturing Technology1. Precision Casting Technology; With the increasing demand for blank accuracy in industrial production, high-efficiency, high compactness, and precision casting technologies have been further improved and expanded in application, such as high-pressure molding, air impact molding, self hardening sand molding, and special casting technologies such as die casting, investment casting, and full mold casting. Die casting and full mold casting are developing rapidly, and die-casting machines are becoming larger. Car doors can now be cast as a whole. The advantages of full mold casting in producing castings with nearly no surplus and complex shapes, as well as green production, have gradually emerged.  & nbsp; 2. Rapid prototyping technology; This is a forming technology that uses various methods such as laser solidification, laser sintering, or melt deposition to quickly stack materials such as resin, plastic, wax, or metal to obtain products. Figure 2-2-43 shows the working principle of using a laser beam to scan the photosensitive resin and solidify it layer by layer for rapid prototyping. This technology has been used in casting production to produce wax molds, molds, shells, cores, etc.  Figure 2-2-43 Laser Rapid Prototyping （3） Metal melting  & nbsp; Large scale cupola is developing towards hot air, water cooling, large tonnage and continuous smelting. The small cupola is developing towards the direction of further improving the quality of molten iron, mainly by strengthening preheating air supply, oxygenation air supply and dehumidification air supply. In mass production and the production of important castings, the use of cupola electric furnace duplex melting is increasing. In addition, the induction furnace is gradually replacing the cupola, and the electric furnace melting will tend to be multi furnace body with single power supply for melting and insulation to reduce energy consumption. The purification and strengthening technology of materials will be further developed, such as vacuum melting and pouring, outside furnace refining, strengthening inoculation, directional crystallization, and rapid solidification& nbsp;（4） Styling materials  & nbsp; At present, clay sand wet casting is widely used for medium and small castings both domestically and internationally. Due to its mature process, low cost, strong process adaptability, and high production capacity, it will still be the main molding method for a considerable period of time in the future. Dry sand has long been phased out abroad and replaced with self hardening sand.  & nbsp; Resin sand has good formability, simple process, high recycling rate of old sand, and good surface quality of castings. It has been widely used in core making and is recognized as the direction of future development. However, due to the presence of harmful substances such as formaldehyde and phenols in the resin, which pollutes the environment, higher strength resins are currently being developed to reduce their dosage.  & nbsp; Water glass sand, which is suitable for the production of steel castings, has great development prospects as a green casting process with less and no pollution. Its poor collapsibility and low recycling rate of old sand have been overcome, and its application is gradually expanding. There are tens of millions of tons of discarded old sand in China every year, so using high-quality raw sand and improving the recycling rate of old sand are still important issues for reducing costs and achieving green casting.