Metal Injection Molding Process
Process 1 to 3: Feedstock Preparation
The primary raw materials for MIM are metal powders and polymer. The blended powder mix is worked into the plastified binder at elevated temperature and the intermediate product is the so-called feedstock.
Process 4: Injection Molding Process
Feedstock is fed into the injection machine where the binding additives are melted to enable the metal powder to flow. After cooling to an acceptable temperature, the ‘green’ parts are ejected and removed from mold. The ‘green’ MIM parts are formed in an injection molding process equivalent to the forming of plastic parts.
Process 5: Debinding Process
The subsequent binder removal process serves to obtain parts with an interconnected pore network without destroying the shape of the components. This process commonly referred as “debinding” and it may be performed chemically or thermally. The choice of debinding method depends on the material being processed, required physical and metallurgical properties and chemical composition. The part is so called “brown part” after debinding process.
Process 6: Sintering Process
Sintering process leads to the elimination of most of the pore volume formerly occupied by the binder. As a consequence, MIM parts exhibit a substantial shrinkage as high as 15-20% during sintering and sintered density is approximately 98% of theoretical. If necessary, sintered MIM parts may be further processed by conventional metalworking processes like heat treatments or surface treatments, coining, machining, coating to achieve tighter tolerances or enhanced properties.