Metal powder injection molding

1.MIM the process
MIM process: metal powder + binder →mixing→ injection molding → degreasing →sintering → Post-processing.
(1) metal powder
MIM process used in metal powder particle size is generally 0.5 ~ 20μm. In theory, the finer particles, surface area the more, so more easy molding and sintering. The traditional powder metallurgy process is used more than 40μm of thick powder.
(2) organic binder
The role of the organic binder bonding metal powder particles, so that the mixture after heated in the injection machine barrel has rheology and lubricity, which adhesive is to bring the carrier of powder flow. Therefore, the binder of choice is the key to the powder injection molding. The requirements of the organic binder as follows: ① use less, use less binder mixture can produce a better rheology; ② does not react in the process of removing the binder and metal powder can not afford any chemical reaction; ③ easy to remove, no residue within the carbon in the products.
(3) mixing
The metal powder and organic binder evenly blended together to make a variety of raw materials into injection molding mixture. Uniformity of the mixture directly affect their mobility, thus affecting the injection molding process parameters and the final material density and other properties.
(4) Injection Molding
This step process and plastic injection molding process is the same in principle, the equipment is basically the same conditions. In the injection molding process, injection machine barrel in the mixture is heated into a rheological properties of plastic materials and, where appropriate under pressure into the injection mold, molding the rough. Injection molding blank should be uniform in appearance, so that the products uniform shrinkage during the sintering process.
(5) extraction of rough shape
In the blank must be removed before sintering contained within the organic binder, the process is called extraction. Extraction process must ensure that the different parts of the binder from the rough along the small channel between the granule gradually passed, without reducing the strength of rough. Binder elimination rate generally follows the diffusion equation.
(6) sintered
Make the porous sintered density of the fat into a blank contract and properties of certain products. Although the performance of products and many of the processes before sintering factors, but in many cases, the final sintering process on microstructure and properties of products have a great or even decisive impact.
(7) post-processing
Size requirements for the more sophisticated parts, the need for the necessary post-processing. This process with the conventional metal heat treatment processes the same.
2.MIM process characteristics and comparison with other processing:
MIM powder particle size of raw materials used in the 2 ~ 15μm, while the traditional powder metallurgy raw material powder particle size mostly in the 50 ~ 100μm; MIM process finished, high-density, relative density of 95% to 98%, while the conventional powder metallurgy process is relatively density of only 80% to 85% (mainly due to fine powder using MIM technology); MIM products typically weigh less than 400 grams, the weight of conventional powder metallurgy products from ten to several hundred grams; MIM product complex three-dimensional shape can be shape, the traditional powder metallurgy products are usually two-dimensional shape of a simple shape. MIM process has the advantages of conventional powder metallurgy process, and its shape is the traditional powder metallurgy high degree of freedom can not be achieved. By conventional powder metallurgy process intensity and the mold filling density, forming mostly two-dimensional cylindrical shape.
Casting off the traditional dry process production of complex shapes as a product of the effective techniques used in recent years supporting ceramic core can complete the slit, the manufacture of deep hole, but by casting liquid ceramic core strength and liquidity constraints, the process there are still some technical problems. In general, the process manufacturing large and medium-sized parts is more appropriate for small parts manufacturing complex shapes MIM process is more suitable places.
Aluminum and zinc die-casting process for the low melting point alloys, cast of good material fluid flow, the process of the product due to material constraints, strength, wear resistance, corrosion resistance, there is a certain limit. MIM technology can process the raw material is more.
Although in recent years, casting process and the accuracy of its products have increased in complexity, but still less than the dewaxing process and MIM process. Powder forging is an important development, has been applied to rod volume manufacturing. But in general, the cost of forging and heat treatment project in the life of the mold is still a problem, yet to be resolved.
By conventional machining process automation to enhance its processing capacity, effectiveness and accuracy in the great progress, but the basic process is still tied up with the gradual process (car, plane, milling, grinding, drilling, polishing, etc.) to complete the processing of part shape. Precision machining method is far superior to other processing methods, but because the efficient use of materials is low, and its shape is subject to the completion equipment and tools, machining some parts can not be completed. On the contrary, MIM materials can be used effectively, without limitation, for small, difficult shape manufacturing of precision parts, MIM process is more mechanical processing, its low cost and high efficiency, has a strong competitive edge.
MIM technology is not competitive with traditional processing methods, but to make up for the traditional processing methods are technically inadequate or can not produce defects. MIM technology can be produced in the traditional processing methods on the field of play to its strengths parts.
Source:http://www.mhcmp.com