Metal Injection Molding (MIM) is a new powder metallurgy forming technology developed on the basis of plastic injection molding. It was invented by Dr. Wiech of Parmatech Company in California, USA, in 1973. It is a technology combining mold injection molding and rapid sintering technology to manufacture high-precision shaped and complex structural parts. MIM manufacturing process is a multi-disciplinary and interdisciplinary technology, including polymer chemistry, powder metallurgy, plastic molding manufacturing and metal materials science. The process uses metal powder as raw material, and can conduct multi-level component optimization design in combination with product performance and technical indicators. The injection molding machine is used to manufacture precision components with complex structure, which is more suitable for mass production and manufacturing. The process mainly includes: mixing of metal powder and resin binder, injection molding, ablation degreasing, and high-temperature sintering.
The main advantages of MIM manufacturing process include: excellent product organization and performance, low cost of mass production, short production cycle, and the ability to realize the overall forming and manufacturing of complex cavity structure. The binder is the core technology of the MIM manufacturing process, which determines the advantages and disadvantages of the entire process, and can increase the fluidity of the powder to improve the injection ability and structure the overall shape of complex products. At present, the binders used in the MIM manufacturing process mainly include the following systems: paraffin based system, oil-based system, polyaldehyde based system, water-soluble system, gel water-based system, acrylic based system and thermosetting resin system, etc, Paraffin-based (PW) system is the most widely used binder. The MIM manufacturing process is similar to the investment, which is more suitable for the forming and manufacturing of thin-walled structural parts to achieve near-net forming. The dimensional tolerance of parts can reach ± 0.1%~± 0.3%, and the material utilization rate can reach more than 92%. Due to the high fluidity of metal powder, it is more suitable for the synthesis of parts with complex shapes and high dimensional accuracy requirements [56 – 58]. Compared with traditional investment casting and machining, MIM manufacturing process has lower mass manufacturing cost, shorter production and manufacturing cycle, and more obvious market competitiveness. It has been widely used in manufacturing missile tail, warhead, shaped cover, circuit control fuze and other parts in the aerospace field. In terms of mass manufacturing of small and complex precision components, it has more cost advantages and faster product manufacturing reaction speed than investment casting.