Best describes the reason why MIM works
time：2020-05-06Views：283 Author：Best Seiko
The MIM process combines the flexibility of injection molding design with the high strength and integrity of precision metals to achieve low-cost solutions for highly complex geometric parts. The MIM process is divided into four unique processing steps (mixing, forming, degreasing, and sintering) to realize the production of parts, and the surface treatment is determined according to the product characteristics. The fine metal powder with mixed particles less than 20µ is mixed with the thermoplastic and paraffin binder in the exact proportion. The volume of metal powder and binder is about 60:40. The mixing process is carried out in a special mixing device, which is heated to a certain temperature to melt the binder. In most cases, mechanical mixing is used until the metal powder particles are evenly coated with a binder and cooled to form particles (called raw materials), which can be injected into the mold cavity. The equipment and technology of injection molding are similar to injection molding. The granular raw material is fed into the machine to be heated and injected into the mold cavity under high pressure to form a green part. After cooling, the mold is only melted under a condition of about 200°C (full fusion with the metal powder). The whole process can be carried out. The mold can be designed as multi-cavity to improve productivity. The cavity size is designed to be 20% more than metal parts to compensate for shrinkage during sintering. The shrinkage change of each material is precise and known. Degreasing Degreasing is the process of removing binder from molded parts. This process is usually completed in several steps. Most of the binder is removed before sintering, and the remaining part can support the parts to enter the sintering furnace. Degreasing can be accomplished by a variety of methods, the solvent extraction method is commonly used. The degreased parts are semi-permeable, and the residual binder is easily volatilized during sintering. The sintered and degreased parts are put into a furnace controlled by high temperature and high pressure. The part is slowly heated under the protection of the gas to remove the residual adhesive. After the binder is completely removed, the part is heated to a very high temperature, and the voids between the particles disappear due to the fusion of the particles. The part shrinks directionally to its design size and transforms into a dense solid. For most materials, the typical sintered density is theoretically greater than 97%. The high sintered density makes the product performance similar to forged materials. Surface treatment According to specific needs, some parts may need surface treatment after sintering. Heat treatment can improve the physical properties of metals. Electroplating and painting can be applied to high-density materials. Provide welding or cooling treatment technology.