Understanding Metal Injection Molding (MIM) Technology: A Comprehensive Guide

Metal Injection Molding (MIM), a precision manufacturing technology that integrates plastic injection molding and powder metallurgy, has become a core solution for manufacturing micro-precision parts due to its advantages of "one-time molding of complex structures + high-efficiency mass production." To understand this technology, the key lies in mastering the logical chain of four core processes: material preparation, injection molding, debinding, and sintering.

Material preparation is the "foundation" of MIM technology, and its core is creating a "feed" material that combines fluidity and plasticity. First, metal powders with a particle size of 5-20 micrometers (such as stainless steel or titanium alloys) are selected. The finer the powder, the higher the precision of the final part. Then, the metal powder is mixed with a thermoplastic binder (such as polyethylene or paraffin wax) in a ratio of approximately 9:1, and uniform dispersion is achieved through high-temperature melting and shearing stirring. This feed retains the essential properties of metal while possessing the flow characteristics of plastic, laying the foundation for subsequent molding.

Injection molding is the key to "shaping," sharing similar principles with plastic injection molding but requiring even higher precision. The feedstock is fed into an injection molding machine and injected at high speed into the cavity of a precision mold at a temperature of 150-200℃ and a pressure of 10-100MPa. The mold needs to be customized according to the part structure, with an inner wall precision of 0.005 mm. This ensures that after the feedstock cools and solidifies, it replicates complex structures such as labyrinthine runners and micro-grooves. The dimensions of the molded blank (called the "green blank") are close to the final part, with only sintering shrinkage allowance.

The degreasing process is the core of "impurity removal and purification," aiming to remove the binder from the green blank. Since direct high-temperature removal can easily cause cracking of the green blank, it is usually carried out in two steps: first, 70%-90% of the volatile binder is removed by solvent or low-temperature heating, and then the remaining binder is removed by medium-temperature heating. The temperature is controlled at 200-600℃ throughout the process, and the holding time is adjusted according to the thickness of the part. After degreasing, a "brown blank" is obtained, which consists only of a metal powder skeleton and has low strength, requiring careful handling.

Sintering is the final step of "quality improvement molding." The brown billet is fed into a sintering furnace and held for several hours at a temperature 100-200°C below the metal's melting point (typically 1350-1400°C for stainless steel). At this high temperature, the surface of the metal powder particles melts and fuses together, causing the billet volume to shrink by 15%-25%, ultimately forming a metal part with a density exceeding 95%, exhibiting mechanical properties comparable to forgings. After sintering, subsequent processing such as polishing and heat treatment can be performed as needed.

This complete "powder-material-shape-material" process enables MIM (Mechanical Injection Molding) to achieve high-precision mass production of complex parts. Its core advantages lie in a material utilization rate exceeding 95% and a dimensional tolerance of ±0.1%, perfectly balancing precision and efficiency.