Advantages and Process Flow of MIM

MIM is the abbreviation of Metal Injection Molding. Metal powder injection molding technology is the product of the penetration and intersection of plastic molding technology, polymer chemistry, powder metallurgy technology and metal materials science. There is a very practical explanation about MIM: design metal parts like plastic injection parts; Utilizing the advantages of rapid replication by plastic injection, metal parts are formed by injection molding, and then made into metal solid parts through the thermal process.

Although MIM is formed by metal powder, it cannot be separated from plastic. Injection molding pellets are composed of metal powder and plastic, which mainly plays the role of adhesion and lubrication. Through the coating effect of plastic, the wear of metal powder on the screw is greatly reduced, and the fluidity of injection melt is increased, which makes metal injection possible.

Ⅰ. Six advantages make MIM focus:

(1) Structural parts capable of forming highly complex structures

Traditional metal processing generally refers to the processing of metal plates into products through turning, milling, planing, grinding, drilling, boring, etc; Due to the technical cost and time cost, this kind of product is difficult to achieve complex structure. MIM uses the injection molding machine to inject the product blank to ensure that the material is fully filled with the mold cavity, which also ensures the realization of the high complex structure of the part.

(2) The product has uniform microstructure, high density and good performance

Generally, the density of pressed products can only reach 85% of the theoretical density; The product density obtained by MIM technology reaches more than 96%.

(3) High efficiency, easy to realize mass and large-scale production

The life of metal mold used by MIM technology is equivalent to that of engineering plastic injection molding tool mold. Due to the use of metal molds, MIM is suitable for mass production of parts.

(4) Wide range of applicable materials and wide application fields

Iron base, low alloy, high speed steel, stainless steel, valve alloy, hard alloy, etc. are all suitable for MIM forming.

(5) Substantial saving of raw materials

Generally, the utilization rate of metal formed by metal processing is relatively low. For example, the utilization rate of raw materials for the metal shell of LeTV MAX mobile phone is less than 10%, and most of the aluminum alloy becomes debris. MIM can greatly improve the utilization rate of raw materials, which is 100% in theory.

(6) MIM process uses micron-sized fine powder

It can not only accelerate the sintering shrinkage, help improve the mechanical properties of the material, extend the fatigue life of the material, but also improve the resistance to stress corrosion and magnetic properties.

ⅠⅠ. Process Flow of MIM:

1. Mixing and granulation

Mixing is to mix metal powder and organic adhesive evenly to make various raw materials become the mixture for injection molding. Granulation is to extrude the mixture into granules. The particle size of metal powder used in MIM process is generally 0.5~20 μ m。 Theoretically, the finer the particle, the larger the specific surface area, and the easier it is to form and sinter. The role of organic binder is to bond metal powder particles, so that the mixture has rheological and lubricating properties after heating in the barrel of the injection machine, that is, the binder is the carrier that drives the powder flow. Therefore, the selection of binder is the key to the whole powder injection molding. Common adhesives include PP, PE, EVA, PEG and POM.

2. Injection molding

This kind of injection molding is not different from ordinary metal injection molding, but the screw is required to be more wear-resistant.

3. Degreasing (also called extraction)

Before sintering, the organic binder contained in the blank must be removed. This process is called extraction. The extraction process must ensure that the binder 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.

4. Sintering

Sintering can make the porous degreased blank shrink and densify into products with certain structure and properties. Although the properties of the products are related to many process factors before sintering, in many cases, the sintering process has a great or even decisive impact on the microstructure and properties of the final products.

5. Secondary treatment

For parts with relatively precise size requirements, necessary post-processing is required. This process is the same as the heat treatment process of conventional metal products. Precision CNC is the most popular process for secondary treatment.