Metal Powder Injection Molding is a new near-net molding technology formed by the introduction of modern plastic injection molding technology into the field. The basic process is to first mix the solid powder with organic binder evenly after granulation and injected into the mold cavity with injection molding machine at 150C under heated plasticized state to solidify the molding, and then remove the binder from the molding bad by chemical or thermal decomposition method, and finally get the final product by sintering and densification. Compared with the traditional process, MIM has high precision, uniform organization, excellent performance, low production cost, etc. Its products are widely used in electronic information engineering, biological medical devices, office, automotive, machinery, hardware, sports equipment, watch industry, weapons and aerospace and other industrial fields. It is widely believed that the development of this technology will lead to a revolution in the technology of forming and processing of parts and is known as the hottest technology of forming parts today and the forming technology of the 21st century.

 

MIM technology was invented by the United States California Parmatech company in 1973 in the early eighties many countries in Europe and Japan have also invested great efforts to start researching the technology and make it rapidly promoted, especially in the mid-eighties the technology to achieve industrialization since the most rapid development of production has been increasing at an alarming rate every year. So far, the United States, Western Europe, Japan and other more than a dozen countries and regions have more than a hundred companies engaged in the process technology product development, development and sales work. Many large companies are involved in the promotion and application of the MIM process, including Pacific Metals, Mitsubishi Steel, Kawasaki Steel, Kobe Steel, Sumitomo Mining, Seiko Epson, Daido Special Steel, etc. At present, there are more than forty companies specializing in MIM industry in Japan, and the total value of sales of MIM products has long surpassed that of Europe and directly caught up with the United States.

 

MIM technology has become the most active frontier technology field in the new manufacturing industry, which is the pioneering technology in the world metallurgical industry and represents the main direction of technology development. Metal powder injection molding technology is a product of the penetration and intersection of plastic molding technology, polymer chemistry, process science and science and other multidisciplinary products using the mold can be injected into the molded blanks and through sintering rapid manufacturing of high-density, high-precision three-dimensional complex shape of structural parts can quickly and accurately materialize the design ideas with certain structural and functional characteristics of the product and can be directly mass-produced parts is a manufacturing technology industry. A new change in the manufacturing technology industry. The process technology not only has the advantages of conventional process less, no cutting or less cutting, high economic efficiency and overcome the traditional process products uneven material, low mechanical properties, thin-walled molding difficulties, complex structure and other shortcomings, especially suitable for mass production of small, complex and special requirements of metal parts.

 

1. The process flow of MIM is a metal powder binder a mixing an injection molding a degreasing a sintering a post-treatment. Metal powder MIM process used in the metal powder particle size is generally 0.520um. theoretically the finer the particles, the greater the specific surface area is also easier to shape and sintering, while the traditional process uses a coarser powder than 40um.

 

2. organic binder organic binder is the role of bonding metal powder particles so that the mixture in the injection machine barrel after heating with rheology and lubricity that the binder is driven by the powder flow carrier. Therefore, the choice of binder is the key to the entire powder injection molding. The requirements of the organic binder for O less amount of binder with less binder can make the mixture produce better rheology @ not react in the process of removing the binder and the metal powder does not have any chemical reaction 3 easy to remove in the product without residual carbon.

 

3. mix the metal powder and organic binder evenly mixed together to make a variety of raw materials into injection molding with a mixture. The uniformity of the mixture directly affects its fluidity and thus the injection molding process parameters as well as the density and other properties of the final material.

 

4. injection molding This step of the process is the same as the plastic injection molding process in principle, and the conditions are basically the same. In the injection molding process, the mixture is heated into a plastic material with rheological properties in the barrel of the injection machine and injected into the mold under the appropriate injection pressure to form the bad. The injection molded material should be uniform in appearance so that the product will shrink uniformly during the sintering process.

 

5. extraction molding bad before sintering must remove the organic binder contained in the bad also the process is called extraction. Extraction process must ensure that the binder from different parts of the blank along the tiny channel between the particles gradually discharge without reducing the strength of the bad. The exclusion rate of the binder generally follows the diffusion equation.

 

6. sintering can make the porous degreasing bad shrinkage densification into a certain organization and properties of the product. Although the performance of the product and the sintering process before many factors related to but in many cases the sintering process on the final product of the metallographic organization and performance has a great or even decisive influence.

 

7. post-treatment for the size requirements of the more precise parts need to carry out the necessary post-treatment. This process is the same as the process of conventional metal products.

 

MIM Process Characteristics and Comparison with Other Processing Processes

MIM use of raw material powder particle size in 215um while most of the traditional raw material powder particle size in 50100um MIM process of the finished product density is high relative density of 9598 while the traditional powder metallurgy process relative density is only 8085 mainly because the MIM process using microfine powder MIM product weight is usually less than 400 grams of traditional powder metallurgy product weight of ten to hundreds of grams MIM The product shape of MIM can be three-dimensional complex shape traditional powder metallurgy product shape is usually two-dimensional simple shape.MIM process has the advantages of the traditional process and its high degree of freedom of shape is not achieved by the traditional process. Traditional powder metallurgy process is affected by the mold strength and filling density molding shape is mostly two-dimensional cylindrical shape. The traditional precision casting desiccation process is an effective technology for making complex shape products. In recent years, the use of ceramic cores can assist in the manufacture of slits and deep holes, but there are still some technical difficulties in the process due to the limitations of the core strength and liquid flow. Generally speaking, the process is more suitable for manufacturing large and medium-sized parts, and more suitable for manufacturing small parts with complex shapes by MIM process. Die-casting process for aluminum and zinc alloys and other low melting point, good liquid flow of the material the process of the product because of the material limitations of its strength, wear resistance, corrosion resistance are certain limits. Precision casting process although in recent years the accuracy and complexity of its products have been improved, but still compared to the dewaxing process and MIM process. Powder forging is an important development that has been applied to the mass production manufacturing of connecting rods. However, in general, the cost of engineering and the life of the die are still issues that need to be further addressed. The traditional process has improved its machining capability by automation and has made great progress in terms of effectiveness and accuracy, but the basic procedure is still inseparable from the step-by-step machining of turning, planing, milling, grinding, drilling and polishing to complete the shape of the part. The processing accuracy of the method is much better than other processing methods but because of the low effective utilization of material and the completion of its shape is limited by the tool and some parts can not be completed with. On the contrary, MIM can effectively use the material without restriction for small, difficult shape of the manufacture of precision parts MIM process is relatively low cost and high efficiency has a strong competitive edge MIM technology is not competing with traditional machining methods but to make up for the technical deficiencies or defects of traditional machining methods can not be produced MIM technology can play its part in the field of traditional machining methods to produce parts. MIM technology can play its specialty in the field of parts made by traditional machining methods.

 

Technical Advantages of the MIM Process in the Manufacture of Components

 

The injection molding process technology can mold highly complex structural parts using an injection machine to inject the product grossly to ensure that the material fully fills the mold cavity, which also ensures the realization of the highly complex structure of the part. In the past, the traditional processing technology of making individual components and then assembled into components can be considered when using MIM technology to integrate into a complete single part greatly reducing the number of steps to simplify the processing procedures.

 

1.MIM and other metal processing methods compared to the high dimensional accuracy of the product does not require secondary processing or only a small amount of finishing. Injection molding process can be directly formed thin-walled, complex structural parts product shape has been close to the final product requirements part size tolerance is generally maintained at about +0.1 +0.3 especially for reducing the processing costs of difficult to carry out carbide to reduce the processing losses of precious metals is particularly important.

 

2. The product microstructure is uniform, high density and good performance in the pressing process due to the friction between the mold wall and powder and powder and powder makes the pressing pressure distribution uneven, which also leads to the pressing of the gross bad in the microstructure is not uniform so that it will cause the pressing powder metallurgy parts in the sintering process shrinkage is not uniform so have to reduce the sintering temperature to reduce this effect so that the product porosity, material The mechanical properties of the products are seriously affected by poor denseness and low density. On the contrary, the injection molding process is a fluid molding process, the presence of the adhesive guarantees the uniform arrangement of the powder, thus eliminating the non-uniformity of the microstructure of the gross bad, thus enabling the density of the sintered product to reach the theoretical density of the material. In general, the density of pressed products can only reach a maximum of 85 of the theoretical density. high denseness of the product can increase the strength, ductility, ductility, electrical and thermal conductivity to improve magnetic properties.

 

3. High efficiency easy to achieve high volume and large-scale production MIM technology using metal molds and engineering plastics injection molding tooling life is comparable. Due to the use of metal molds MIM is suitable for high volume production of parts. As the use of injection molding machine product blanks greatly improve production efficiency to reduce production costs and injection molding product consistency, repeatability and thus provide a guarantee for high-volume and large-scale industrial production.

 

4.Wide range of applicable materials wide range of applications iron-based low-alloy high-speed steel stainless steel gram valve alloy carbide can be used for injection molding of a wide range of materials in principle, any high-temperature casting powder materials can be manufactured by the MIMT process into parts, including the traditional manufacturing process of difficult-to-machine materials and high melting point materials. In addition, MIM can also be used to make any combination of alloys that will be molded into parts according to customer requirements for material formulation research. Injection molding products have been applied to all areas of the national economy has a broad market prospect.

5. MIM process using micron-level fine powder can accelerate sintering shrinkage can help improve the mechanical properties of the material to extend the fatigue life of the material and can improve the resistance, stress corrosion resistance and magnetic properties.

 

Application Areas of MIM Technology

1.Computer and its auxiliary facilities such as printer parts, magnetic cores, firing pin pins, drive parts, etc.

2. Tools such as drills, bits, nozzles, gun drills, spiral cutters, punches, sockets, wrenches, electrical tools, hand tools, etc.

3.Household appliances such as cases, watch chains, electric toothbrushes, scissors, fans, golf heads, jewelry chain rings, ball point pen clamps, cutting tool tips and other parts

4. Medical machinery parts such as orthodontic frames, scissors, tweezers, etc.

5. Military parts such as missile tail, gun parts, warheads, drug type cover, fuze parts, etc.

6. Electrical parts electronic packaging micro motor, electronic parts, sensor parts, etc.

7. Machinery parts such as cotton loosening machines, textile machines, edge-rolling machines, office machinery, etc.

8.Automobile and marine parts such as clutch inner ring, fork set, distributor set, valve guide, synchronous Yi, airbag parts, etc.

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