Metal powder injection molding

Metal powder injection molding technology (MIM) is a new near net forming technology of powder metallurgy, which introduces modern plastic injection molding technology into the field of powder metallurgy.

Characteristics of metal powder injection molding process
The technology of metal powder injection molding is the product of the combination of plastic molding technology, polymer chemistry, powder metallurgy technology and metal materials. It can be used to mold the blank and make high density, high precision, three-dimensional complex shape structural parts by vacuum sintering furnace. It can quickly and accurately materialize the design idea into a certain structure and function It is a new revolution in manufacturing technology industry that the products with characteristics can be directly produced in batches.
Metal powder injection molding technology not only has the advantages of less conventional P / M process, no cutting or less cutting, high economic benefits, but also overcomes the disadvantages of traditional P / M process products, uneven materials, low mechanical properties, difficult to form thin-walled and complex structures, especially suitable for mass production of small, complex and special metal parts.
Technological process binder → mixing → injection molding → vacuum degreasing → vacuum sintering → post treatment.

MIM Debinding Sintering Furnace

Powder Metal
The particle size of metal powder used in MIM process is generally 0.5 ~ 20 μ m; theoretically, the finer the particle is, the larger the specific surface area is, and it is easy to form and sinter.
However, the traditional powder metallurgy process uses coarser powder larger than 40 μ M.

Organic Adhesive
The function of organic adhesive is to bond metal powder particles, so that the mixture heated in the barrel of injection machine has rheological and lubricity, that is to say, the carrier that drives the powder flow. Therefore, the choice of adhesive is the carrier of the whole powder. Therefore, the key to the whole powder injection molding is to select the adhesive and pull. Requirements for organic adhesives:
1. Less dosage and less adhesive can make the mixture produce better rheological property;
2. No reaction, no chemical reaction with metal powder in the process of removing adhesive;
3. Easy to remove, no carbon remained in the product.

Mixture
The metal powder and the organic adhesive are mixed uniformly, so that various raw materials can be used as the mixture for injection molding. The uniformity of the mixture directly affects its fluidity, thus affecting the injection molding process parameters, as well as the density and other properties of the final material. The process of injection molding in this step is consistent with that of plastic injection molding in principle, and the equipment conditions are basically the same. In the process of injection molding, the mixture is heated into a plastic material with rheological property in the barrel of the injection machine, and is injected into the mold under the appropriate injection pressure to form the blank. The microstructure of the injection molding blank should be uniform, so that the product can contract uniformly in the vacuum sintering process.

Extraction
The organic binder contained in the blank must be removed before vacuum 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 channel between the particles without reducing the strength of the blank. The removal rate of binder generally follows the diffusion equation. Vacuum sintering can make the porous debinding blank shrink to densification and become a product with certain structure and properties. Although the properties of the products are related to many process factors before sintering, in many cases, the vacuum sintering process has a great, even decisive influence on the microstructure and properties of the final products.