MIM (metal injection molding) is an advanced technology of metal forming which combine the advantage of plastic injection molding and conventional powder metallurgy technology (press sintered, precision casting, forging, stamping, machining). The main MIM steps are including Feedstock, Injection molding, Debinding, Sintering. In order to get the final metal part, post treatment will be necessary such as machining, sizing, blasting, polish, coating, heat treatment etc.
|Fine metal powder (particle size is about 0.5~20μm) combined with thermoplastic binders will be put into a special mixing equipment and heated to a certain degree the binder melt, stirring until the metal powder and binder are evenly mixed. Then it granulated into required materials called feedstock.|
|This process has the same principle as the plastic injection molding. Put the granulated feedstock into the injection machine where it will be heated and molded under high pressure. The part is called green part. This step will be repeated when mass production. The mold cavity is sized approximately 20% larger to compensate for shrinkage that takes place during sintering. The shrinkage changes is based on the used metal materials.|
|Before sintering, the binder must be removed in the molded part (green part). This process is debinding and part after it is called brown part. In this process, the binder should be discharged from particle gap and won’t reduce the part strength.|
|The brown part is put on the ceramic plate and placed into a high temperature, atmosphere-controlled furnace. The part is slowly heated in a protective atmosphere to drive out the remaining binder generally in 24 hours. Once the binders are evaporated, the part is heated to high temperature where the void space between the particle is eliminated as the particle fuse together. The part shrinks isotopically to its original dimensions and transforms into a dense solid. The sintered density is typically greater than 97% of theoretical for most materials. Sintering have critical influence to the metallurgical structure and performance of the final part.|
|For the need of real requirements, certain post treatment will be necessary to the sintered part. To improve physical properties, heat treatment can be done as on any metal materials. Any type of machining operation can be performed to achieve tolerances that are highly precise. Plating and coating can be readily applied due to the high material density. Surface finish such as magnetic grinding, polish, coating to make the appearance better.|