1. Introduction to MIM development: Metal Injection Molding (Metal Injection Molding, referred to as MIM) was invented in 1973 by Parmatech, California, which specializes in MIM technology research and product development. MIM is a combination of plastic injection molding technology, high A new near-net forming technology for metal parts in molecular science, powder metallurgy technology and metal materials science. This technology was poorly understood at the time. In the past, due to the lack of suitable powders and raw materials, the price was too high, the knowledge platform was incomplete, the technology was immature (long degreasing time, products are easily deformed, etc.), people did not understand and accept the market for a long time, and the production (including mold manufacturing) cycle was too long. Due to insufficient investment and other reasons, its development and application is relatively slow. In the mid-1980s, in order to solve the difficulties of MIM technology and promote the practical application of MIM technology, the United States formulated a high-level powder engineering plan, and the research content included 18 topics related to injection molding. Subsequently, Japan, Germany, etc. also actively carried out MIM development research. The guidance of the US government has accelerated the development of MIM technology. After decades of development, MIM technology has been rapidly developed due to the greatly improved powder output rate, reasonable binder design, and the appearance of advanced degreasing methods. With the deepening of MIM research, it has been industrialized by the early 1990s. After more than 20 years of hard work, MIM has become a fast-growing and promising new near-net forming technology in the international powder metallurgy field, and is known as one of the "international hot metal forming technology". 2. MIM process: MIM is a forming method that injects plastic mixture of metal powder and its binder into the model. It is to mix the selected powder with the binder uniformly (by weight ratio/volume ratio), and then granulate the mixture and then shape it for injection molding. The polymer imparts its viscous flow characteristics to the mix, which contributes to the uniformity of forming, cavity filling, and powder filling. After forming, the binder is removed and the defatted blank is sintered. Some sintered products may also need to be further densified, heat-treated or machined. Sintered products not only have the same complex shape and high precision as the products obtained by plastic injection molding, but also have physical, chemical and mechanical properties close to those of forgings. This process technology is suitable for mass production of metal parts with small, precise, complex three-dimensional shapes and special performance requirements. MIM technology consists of four main processes: ① powder and binder mixing and granulation; ② injection molding by injection molding machine; ③ select appropriate degreasing process for degreasing; ④ sintered parts to make them dense. 3. Advantages of MIM process: MIM technology, as a near-net forming technology for manufacturing high-quality precision parts, has unparalleled advantages in conventional powder metallurgy, machining and precision casting methods. 1. Can produce small metal parts with complex shapes (0.1-500g) like plastic products; Injection molding is a key technology that affects MIM. MIM's molding equipment, molds, and even injection cycle are very similar to injection. There is competition with several other forming technologies, such as sand casting, die casting and precision casting, and machining. MIM not only inherits the advantages of traditional powder metallurgy and plastic injection molding, but also breaks through the limitations of powder metallurgy in the shape of parts. The complexity of the shape increases and the cost competitive advantage of MIM increases. A good application of MIM is to manufacture small parts with complex shapes. Those parts that require other assembly and forming processes to be achieved by other production processes; 2. The parts of the parts are uniformly organized, with high dimensional accuracy and high relative density (≥95%) ); Because MIM is a mixed process of injection and powder sintering technology, the tolerance control capability is also a combination of the two. The usual injection tolerance range is ±0.3%～0.5%mm; the relative density can reach more than 95%; 3. The surface finish is good; the surface roughness after sintering is 0.2～1.6μm. This range is equivalent to the surface quality of the grinding process, and can be directly used in many occasions where the surface roughness is relatively low; 4. The product quality is stable, the production efficiency is high, and it is easy to achieve large-scale and large-scale production. 4. Application of MIM parts in automobiles: With the advancement of science and technology, the main direction of automobile development is energy saving, environmental protection, comfort, intelligence and light weight. As a near net forming process, MIM can not only obtain parts with high density, good mechanical properties and small surface roughness, but also produce parts with complex structures in large quantities and efficiently, generally do not need to continue finishing, parts The cost reduction has promoted the development of lightweight vehicles and reduced environmental pollution, thus attracting the attention of the automotive industry. Using MIM technology, tiny automotive parts can be designed as a whole or multiple components, and the MIM process is used for injection molding at a time, so that the parts can achieve the characteristics of miniaturization, integration, and low cost under the premise of satisfying performance. At the same time, parts with complex shapes such as external slots, external threads, cross holes, blind holes, stiffener plates, grooves and key pins can be manufactured. The automobile manufacturing industry is a big user of MIM. Typical uses are high temperature and high wear resistance engine parts and gearbox parts. Others are such as rod parts (cable joints), clutch inner rings, rocker arm inserts, shift forks Covers, distributor covers, car airbag parts, car lock parts, etc. China has become the world's largest automobile production and sales country, with automobile production accounting for about 30% of the world's total. The automobile industry occupies an important position in my country's economic development. As far as our country is concerned, the MIM market has gradually grown since 2000. In just a few decades, the domestic MIM market has shown a relatively strong development momentum. According to statistics, the domestic MIM market scale exceeded the 1 billion yuan mark in 2011 (approximately US$1 billion globally). By 2015, the market size was close to 5 billion yuan (approximately US$2 billion worldwide), and China’s MIM market has grown into a global market. An important part of the MIM market. At the same time, the powder metallurgy branch of China Steel Structure Association predicts that the size of my country's MIM market will exceed 7 billion yuan by 2018, and judges that my country's MIM market will still embrace high-speed development space in the future. The use of powder metallurgy products per car in the world is 14 kg in Europe, 16 kg in Japan, and 19.5 kg in the United States. The domestic automobile MIM product usage is only about 5 kg. It is foreseeable that driven by the continuous growth of automobile production, the future application of MIM products in the automobile industry will face a broader development space. 5. Summary of metal powder injection molding: With the continuous maturity of the MIM process and the rapid development of the automotive industry, the application of new processes and new materials is also constantly updated, and automotive consumers have put forward higher requirements for automobiles: safety , Comfort, environmental protection, etc., the number of parts on the car is very large. Under the development trend of energy saving, low emission and light weight of the car, more MIM parts will be applied to replace the traditional processing technology, which is also necessary It will inject new impetus into the transformation and innovation of the development of the automobile industry.