1. Metal powder. The particle size of the metal powder used in the MIM process is generally 0.5-20μm; theoretically, the finer the particle, the larger the specific surface area, and it is easy to form and sinter. The traditional powder metallurgy process uses coarser powder larger than 40μm.
2. Organic adhesive. The role of organic adhesive is to bond metal powder particles, so that the mixture has rheology and lubricity when heated in the barrel of the injection machine, that is, the carrier that drives the powder to flow. Therefore, the choice of adhesive is the key to the entire powder injection molding. Requirements for organic adhesives: ①Small amount, that is, using less adhesive can make the mixture produce better rheology; ②No reaction, no chemical reaction with metal powder in the process of removing the adhesive Reaction; ③Easy to remove, no carbon remains in the product. Necessary post-processing for debonding and sintering of mixed binder metal powder granulation injection molding
3. Kneading and granulation. During kneading, the metal powder and the organic binder are uniformly blended to adjust the rheology to be suitable for injection molding. The uniformity of the mixture directly affects its fluidity, thus affecting the injection molding process parameters and even the density and other properties of the final material. The scraps and waste products produced during the injection molding process can be re-crushed, pelletized, and recycled.
4. Injection molding. The process of this step is the same as the plastic injection molding process in principle, and the equipment conditions are basically the same. In the injection molding process, the mixture is heated in the barrel of the injection machine into a plastic material with rheological properties, and injected into the mold under appropriate injection pressure to form a blank. The density of the injection molded blank should be uniform in the microscopic view, so that the product shrinks uniformly during the sintering process. Controlling injection temperature, mold temperature, injection pressure, holding time and other forming parameters is essential to obtain a stable green body weight. It is necessary to prevent the separation and segregation of the components in the injection material, otherwise it will cause the size to be out of control and distortion and be scrapped.
5. Debonding. The organic binder contained in the blank must be removed before sintering. This process is called debonding. The debonding process must ensure that the adhesive is gradually discharged from different parts of the blank along the tiny channels between the particles without reducing the strength of the blank. After solvent extraction of part of the adhesive, the remaining adhesive must be removed by thermal debonding. When debonding, control the carbon content and reduce the oxygen content in the blank.
6. Sintering. Sintering is carried out in a sintering furnace with a controlled atmosphere. The high density of MIM parts is achieved through high sintering temperature and long sintering time, thereby greatly improving and improving the mechanical properties of the part materials.
7. Post-processing. For parts with more precise size requirements, necessary post-processing is required. This process is the same as the heat treatment process of conventional metal products.