What is MIM

Metal powder injection molding (MIM) is a new molding technology developed by the combination of powder metallurgy and polymer injection molding. MIM is a kind of molding technology which is made by mixing binder and metal powder into a specific mold. It is especially suitable for mass production of small, complex shape and large amount of metal products, especially the precision metal parts with complex structure, small volume and special requirements. It is difficult to process with traditional processing methods and the processing cost is high. Metal powder injection molding can reduce the processing cost.

The production process of MIM products is: powder + binder → mixing → granulation → injection molding → degreasing (MIM degreasing furnace) → sintering (MIM sintering furnace) → subsequent treatment → forming products. In the process of producing MIM cemented carbide parts, improper material selection and operation control may cause defects in cemented carbide parts. How to avoid such defects?

1. Powder selection. In addition to meeting the basic requirements of particle size distribution and particle size, MIM cemented carbide powder metallurgy also requires that the purity of the powder should be high, and the powder with impurities should not be selected. If the powder is mixed with sulfur, phosphorus, silicon and other elements, these substances will form pores during the sintering process, resulting in product defects.

   
   

   
   

2. Feedstock production. The cemented carbide powder needs proper binder in mixing. When mixing, the cemented carbide powder and binder should be fully mixed. In the mixing process, the temperature must be strictly controlled to avoid the volatilization and uneven distribution of the binder, so that the mixture has good rheological property and viscosity value after being made into feedstock, so as to avoid defects in the later links.

3. The link of forming green part. This is also a key link in the production of cemented carbide parts. In order to avoid product defects, it is necessary to pay attention to the reasonable control of mold temperature, feeding amount, injection pressure, packing pressure, packing time and injection speed in the injection process, so as to effectively avoid the defects of injection green body.

4. Debinding process. In the process of debinding, if the temperature of debinding furnace is too fast, the crack defects of cemented carbide parts will be caused. The method of gradual temperature rising can be used to debined.

5. Sintering process. Because of the high density of cemented carbide, the product is easy to deform due to its own gravity during liquid phase sintering. Appropriate supporting device can be used. For larger products, the material with the same shrinkage rate can be selected as the support plate. In addition, the sintering time of liquid phase should be shortened as much as possible.