Metal injection molding can be traced back to the powder injection molding of ceramic spark plugs in the 1920s, and in the following decades, powder injection molding mainly focused on ceramic injection molding. It was not until 1979 that Parmatech Corporation's metal injection molding products won two awards, and Wiech and Rivers obtained patents respectively, that powder injection molding began to shift to metal injection molding as the mainstay. After Parmatech Corporation transferred some of their patents, MIM companies sprang up. In 1980, Wiech founded Witec Corporation, in 1982, Brunswick Corporation entered the MIM industry and acquired Witec Corporation, and then registered Omark Industries, Remington Military Products, Rocky Dental and other subsidiaries. In 1986, Japan's Nippon Seison Corporation introduced the Wiech process. In 1990, Israel's Metalor2000 Corporation introduced the Wiech process technology from Parmatech Corporation and established a MIM production line. After nearly 20 years of development, the global MIM product market value reached about 1 billion US dollars by 2003. Geographically, the United States accounted for 55%, followed by Europe and Japan. At present, there are more than 500 companies in the world engaged in the production and sales of metal injection molding products, and another 40 MIM powder suppliers and 20 MIM feedstock suppliers. According to statistics, the global MIM industry has a forming capacity of more than 700 injection molding machines, 500 furnaces and 300 mixers. Marko Maetzig analyzed the situation in Europe in detail. There are 120 companies and 30 research institutions engaged in MIM work in Europe, with 250 injection molding machines and an annual consumption of 1100 tons of feedstock. Of the MIM companies in Europe, 38% come from the traditional ceramic industry, 27% come from the plastic industry, 8% come from the traditional powder metallurgy and metal cutting industry, 5% come from the casting industry, and another 14% are newly established companies. Japan now has 20 to 30 MIM companies, and Japan's MIM market has shown a steady upward trend in recent years. Although it declined in 2001 compared to 2000, overall, its sales volume showed a steady growth trend.

MIM has experienced a rapid development path. Although MIM is attracting more and more attention, its industrial scale is still small compared to traditional processing technologies, and there is still great potential for development. The emerging MIM industry still needs us to take a series of efforts such as setting industrial standards, accelerating industrialization, improving the quality of practitioners, developing equipment and winning customers to develop and grow it. However, the development of MIM technology is still amazing and shows strong vitality. Figure 1.6 shows the MIM sales statistics and forecast for the past 15 years and the next 10 years. From the figure, it can be seen that the average annual growth rate of MIM sales in the 1990s reached 22%, and it is expected that the entire market will still increase by 20% to 30% in the next ten years. As the process continues to improve, the advantages of metal injection molding technology are gradually showing up, and it will be accepted by more and more industries and customers, and its market share is also rapidly increasing. Due to the huge market potential, many venture capital funds have also begun to get involved in the MIM industry. It can be foreseen that MIM will develop into one of the most promising component manufacturing technologies in the 21st century.

1-3 The development direction of metal injection molding technology

Metal injection molding technology uses fine powder and a large amount of binder, which makes its process and mechanism greatly different from the traditional powder metallurgy pressing/sintering process. There are many new basic theoretical and practical problems involved in powder/binder plastic body rheological behavior, feedstock stable flow filling mold cavity process prediction and control, physical and chemical mechanism and kinetics of binder removal from green body , Sintering loose powder aggregates to full densification etc. These basic theoretical and practical problems involve multiple disciplines such as powder science, sintering theory, polymer science, rheology, surface physical chemistry , Computer numerical simulation etc.

After more than 20 years of development , there are more than 500 companies and research institutions worldwide engaged in metal injection molding technology work , products have been applied to various industries , including aerospace , weapons , firearms , mobile communication products , automotive parts , office machine products , leisure products , precision mechanical parts , medical products , keys , electric tool parts , fiber optic communication products , bearing parts , clock parts etc . The material system is also very wide , including stainless steel , low alloy steel , tungsten alloy , titanium alloy , hard alloy , ceramic etc . But by the end of 2003 , The global MIM product market value was only 1 billion US dollars , much lower than various forecast numbers , and far from reaching a processing technology that can compete with machining , precision casting , pressing / sintering etc . The main reason is that the existing MIM technology is limited to the preparation of small size , low precision , low mechanical performance products and material systems by adding and removing a large amount of binder . At present , the existing metal injection molding technology in the international scope can only prepare products with a thickness of less than 10mm ( and mostly 5mm ) , low requirements for microstructure and mechanical properties , and dimensional accuracy of ±0.3% to 0.5% , such as high-speed steel , hard alloy , titanium alloy and ceramic tools , blades etc . There are several reasons for this . Due to the addition of a large amount of binder in the MIM process , the binder is removed after sintering similar to the loose sintering of traditional powder metallurgy . Fine powder must be used as raw material to meet the densification requirements , resulting in a significant increase in cost . For larger size products , if fine powder can only be used , there will be no competitiveness . At the same time , as the product size increases , the time required for debinding increases exponentially , and the probability of defects increases significantly . In addition , as the product size increases , the injection molding process time increases , and higher requirements are placed on the rheological properties of the binder , so that it can quickly bring the powder to different parts of the mold cavity . These are all factors that restrict the development of MIM technology to larger sizes . Therefore, MIM technology has been limited to smaller size products . For dimensional accuracy, due to the addition and removal of binder in the MIM process, sintered products experience a very large shrinkage rate (linear shrinkage rate of 10% to 20%) . At this time, various factors will affect dimensional accuracy, so it is necessary to establish a mathematical model of the influence of process parameters on dimensional accuracy, and establish a real-time monitoring system.

In addition, due to the multiple physical and chemical state changes of the powder/binder plastic body during the MIM process, different defects are easily introduced at different stages, so MIM technology is currently less used in materials and products with high mechanical performance requirements and defect sensitivity .

But in the market, the size range of various parts products required is generally greater than 10mm, and the minimum thickness is mostly between 10 and 30mm. If MIM products can reach a size range of 30mm, then MIM application fields will be greatly expanded, especially in firearms, automobiles, precision machinery and other fields, such as submachine guns, machine guns, artillery, automobile engines, mechanical arm parts etc . The ±0.3% to 0.5% dimensional accuracy of metal injection molding technology is better than that of precision casting products, but it lags behind powder metallurgy pressing/sintering machining. If it can be increased to ±0.1% to 0.05%, it will reach the dimensional accuracy of traditional powder metallurgy pressing/sintering process and approach machining. The level of product will also greatly expand the application field and vitality of MIM technology. On the other hand, although MIM has been applied to various material systems at present, in terms of market sales volume, most products are concentrated on low-alloy steel and stainless steel products with low mechanical performance requirements. Taking Japan's statistics as an example, in 2002, 67% of MIM products were low-alloy steel and stainless steel products, and only less than 15% were Ti alloys, high-speed steels, hard alloys and other defect-sensitive tool materials with high mechanical performance requirements. These tool materials are very difficult to process themselves and are very suitable for MIM objects, but because this type of material is sensitive to defects, traditional MIM processes easily introduce various defects in various process steps, making it so far MIM technology is rarely used in these materials. If defect-free and high-performance MIM technology can be developed, it will greatly expand the types of MIM materials and expand the market for MIM materials.

At present, some units abroad have also begun to pay attention to the limitations of existing MIM technology and have started research in some aspects. For example, France's Impace company has developed a new binderless MIM process called Quickset, which only requires 5% of the traditional MIM binder content, breaking through the quality and size limitations of traditional MIM products. Using this process with 74µm particle size powder can prepare products with a thickness of up to 20mm and a weight of up to 800g. The US Thermat company has developed a new PMIM process that uses different particle size powders to match each other, making the product size accuracy reach ±0.1%. The University of Pennsylvania in the United States is studying the MIM process of hard alloys, high-speed steels and ceramic tools. In addition, in terms of the combination of injection molding and other emerging advanced technologies, various work is also being carried out in the United States and Europe, such as the combination of injection molding technology and microwave sintering technology, mixed injection of various material systems, injection molding technology and microelectronics production technology The combination and introduction of highly automated control chemical production equipment.

In recent years, metal injection molding technology has mainly developed in two directions: expanding the applicable material system, and developing high-reliability production equipment that meets the unique binder and debinding technology. It is characterized by the following aspects:

Multi-directional expansion of the mim metal material system

Injection molding technology is a relatively ideal, economical forming method that can form close to the final required shape, and only requires a small amount or no subsequent processing after sintering. This has become more and more important in the industrial production and application of precision ceramics. In the production of precision ceramics, it is mainly applied to carbides, metal ceramics, inorganic non-metallic ceramics, oxide ceramics, intermetallic compounds, etc.

Take zirconia ceramic optical fiber ferrules as an example. The green body prepared by injection molding technology can greatly shorten the subsequent processing time. Since the green body formed in the mold cavity has a through-hole with a certain accuracy, the subsequent grinding process is reduced to one-third to one-fourth of the extrusion molding, thereby improving the production efficiency and greatly reducing the production cost.

Wear-resistant tool materials that have been developed include Co-based alloys, W-based alloys, hard alloys, Al2O3-30TiC composite cutting tool ceramics, mullite, SiC, Si3N4, etc. Injection molding is also applied to other materials, such as SiC/Al composites, tool steels, titanium alloys, non-magnetic hard alloys, W/Cu alloys, rare earth permanent magnetic materials, KOVAR alloys, etc.

Magnetic materials such as soft magnetic ferrites and bonded permanent magnets (such as NdFeB, SmCo, etc.) are another broad field of application of injection molding technology.

Diversity of binder and multi-channel of defatted technology

. Acetate ester as substrate, polyethylene glycol (peg) polymer as matrix and acrylic polymer as matrix, AGAR as the matrix numerous of binder system have further development and application. Computer aided control thermal degreasing and solvent degreasing technology, catalytic defatted technology, and freeze drying technology, microwave auxiliary drying technology was used in the study of binder skim. And the successful application of these techniques, on the one hand, greatly shorten the degreasing time (fromseveral days to a few hours). On the other hand has realized the control of polymer decomposition reaction of volatile products that generated in the process of degreasing, so as to more effectively eliminates the defects in the process of degreasing. 

The predictable, along with the further research, development and application of metal injection molding. In the near future, MIM technology will develop as an attractive net shaping preparation technology that parallel to machining, precision casting, pressing/sintering process. It will be known and accepted by more and more workpiece designer.