Metal powder injection molding (MIM) is a new powder metallurgy near net shape forming technology formed by introducing modern plastic spray molding technology into the field of powder metallurgy to promote the development and upgrading of private economy. The basic technological process is as follows: first, the solid powder is evenly mixed with the organic binder, and after granulation, it is injected into the mold cavity with a spray forming machine under the state of heating and plasticization (~150 ℃), and then the binder in the formed billet is removed by chemical or thermal decomposition methods, and finally the final product is obtained by sintering and densification. Compared with traditional technology, it has the characteristics of high precision, uniform organization, excellent performance and low production cost. Its products are widely used in electronic information engineering, biological medical devices, office equipment, automobiles, machinery, hardware, sports equipment, watch industry, weapons, aerospace and other industrial fields. Therefore, it is generally believed that the development of this technology will lead to a revolution in parts forming and processing technology, which is known as "the hottest parts forming technology today" and "the forming technology of the 21st century".
parmatech company in California, USA, invented it in 1973. In the early 1980s, many countries in Europe and Japan also invested a lot of energy in the research of this technology, which has been rapidly promoted. Especially in the mid-1980s, this technology ultrasonic vibration machining technology has achieved rapid development since its industrialization, increasing at an alarming rate every year. So far, more than 100 companies in more than 10 countries and regions such as the United States, Western Europe and Japan are engaged in the product development, research and sales of this process technology. Japan is very competitive and outstanding. Many large companies have participated in the promotion of MIM industry, including Pacific metal, Mitsubishi steel, Kawasaki iron, Kobe Steel, Sumitomo mining, Seiko Epson, Datong special steel, etc. At present, Japan has more than 40 companies specializing in MIM industry, and the total sales value of its MIM industrial products has already surpassed Europe and directly followed the United States. So far, more than 100 companies around the world have been engaged in the product development, research and sales of this technology. Therefore, MIM technology has become the most active frontier technology field in the new manufacturing industry. It is regarded as a pioneering technology in the world's metallurgical industry and represents the main direction of powder metallurgy technology development MIM technology.
metal powder spray molding technology is a product of the penetration and intersection of many disciplines, such as plastic molding technology, polymer chemistry, powder metallurgy technology and metal materials. By using molds to spray molding blanks and rapidly manufacturing structural parts with high density, high precision and three-dimensional complex shapes through sintering, it can quickly and accurately materialize design ideas into products with certain structural and functional characteristics, And can directly mass produce parts, which is a new change in the manufacturing technology industry. This process technology not only has the advantages of less conventional powder metallurgy processes, no cutting or less cutting, high economic benefits, but also overcomes the shortcomings of traditional powder metallurgy products, uneven materials, low mechanical properties, difficult to form thin-walled, complex structures, especially suitable for mass production of small, complex and special requirements of metal parts. Process flow binder → mixing → spray forming → degreasing → sintering → post-treatment
powder metal powder
the particle size of metal powder used in MIM process is generally 0.5~20 μ m； Theoretically, the finer the particles are, the larger the specific surface area is, and it is easy to form and sinter. The traditional powder metallurgy process uses more than 40 μ M thick powder. The function of organic adhesive is to bond metal powder particles, so that the mixture can be heated in the ejector barrel with rheology and lubricity, that is to say, it is the carrier that drives the powder flow. Therefore, the choice of adhesive is the carrier of the whole powder. Therefore, the selection of adhesion and tension is the key to the whole powder spray molding. Requirements for organic adhesives:
1 Less dosage and less adhesive can make the mixture have better rheology;
2. No reaction. In the relevant information, Jinan new era Gold Testing Instrument Co., Ltd. will introduce to you that there is no chemical reaction with metal powder in the process of removing the adhesive;
3. Easy to remove, no carbon remains in the products. The mixture evenly mixes the metal powder with the organic adhesive to make various raw materials become the mixture for spray molding. The uniformity of the mixture directly affects its fluidity, thus affecting the spray molding process parameters, as well as the density and other properties of the final material. The process of spray forming is consistent with that of plastic spray forming in principle, and its equipment conditions are basically the same. In the spray molding process, the mixture is heated into rheological plastic materials in the ejector barrel, and injected into the mold under appropriate spray pressure to form a blank. The microstructure of the spray formed blank should be uniform, so that the product can shrink evenly in the sintering process. The organic adhesive contained in the blank must be removed before sintering. This process is called extraction. The extraction process must ensure that the adhesive is gradually discharged from different parts of the blank along the micro channels between the particles without reducing the strength of the blank. The removal rate of binder generally follows the diffusion equation. Sintering can make porous degreased blanks shrink to densify into products with certain structure and properties. Although the properties of products are related to many process factors before sintering, in many cases, the sintering process has a great and even decisive impact on the microstructure and properties of the final products. Post treatment for parts with precise size requirements, necessary post-treatment is required. This process is the same as the heat treatment process of conventional metal products.
characteristics of MIM process comparison between MIM process and other processing processes
the particle size of raw powder used by MIM is μ m. The particle size of raw powder in traditional powder metallurgy is mostly μ m。 The high density of the finished product of MIM process is due to the use of fine powder. MIM process has the advantages of traditional powder metallurgy process, and the high degree of freedom in shape can not be achieved by traditional powder metallurgy. Traditional powder metallurgy is limited to the strength and filling density of the mold, and the shape is mostly two-dimensional cylindrical The traditional precision casting drying process is an extremely effective technology for making products with complex shapes. In recent years, the finished products with slit and deep hole can be completed with the aid of ceramic core. However, due to the strength of ceramic core and the limitation of the fluidity of casting liquid, this process still has some technical difficulties. Generally speaking, this process is more suitable for manufacturing large and medium-sized parts, while MIM process is more suitable for small and complex shape parts. Compare the project manufacturing process MIM process traditional powder metallurgy process powder particle size（ μ m) Relative density (%) product weight (g) less than or equal to 400 grams 10-hundreds product shape three-dimensional complex shape two-dimensional simple shape mechanical properties advantages and disadvantages MIM process and traditional powder metallurgy method comparison die casting process is used in aluminum and zinc alloys and other materials with low melting point and good casting liquid fluidity. Due to the limitation of materials, the strength, wear resistance and corrosion resistance of the products of this process are limited.
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