Analysis of the Process Flow and Key Technologies in Metal Injection Molding

Metal Injection Molding (MIM), as an advanced technology that integrates plastic injection molding and powder metallurgy, has become a key process in high-end manufacturing due to its advantages of "complex molding + mass production." The process involves four core stages, each relying on breakthroughs in critical technologies to achieve the unity of high precision and high performance in products.

The core process of MIM is a closely interlinked and indispensable cycle. The first step involves feedstock preparation, where metal fine powder (1-20μm, such as stainless steel or titanium alloy powder) is mixed with thermoplastic binders (resin + plasticizer + lubricant) in a ratio of approximately 8:2. Through high-temperature stirring by a twin-screw extruder, the metal powder is uniformly dispersed to avoid agglomeration, ultimately forming feedstock with excellent flowability—the foundation for subsequent molding.  The second step is injection molding, which utilizes a modified plastic injection machine to inject the feedstock into precision molds under temperatures of 150-200°C and pressures of 50-150MPa, producing a "green body" with the exact shape of the final product. At this stage, precise parameter control is essential to prevent defects such as material shortage or air bubbles.  The third step is debinding, which removes the binder from the green body: solvent debinding quickly dissolves some of the binder, while thermal debinding gradually volatilizes the remaining components through a temperature gradient of 1-5°C/h. Combining both methods prevents deformation and cracking of the green body, ultimately yielding a "brown body."  The final step is sintering, where the brown body is placed in an inert gas or vacuum environment and heated to 80%-90% of the metal's melting point (e.g., 1350-1450°C for stainless steel), held at this temperature for 2-4 hours. This promotes the diffusion and fusion of powder particles, causing uniform shrinkage of 10%-25% in the product. Shrinkage allowances must be pre-designed in the mold to achieve a dense final product.

The core guarantee for the stability of the MIM process lies in key technologies. First is the control of feedstock uniformity. If the powder and binder are not mixed evenly, it will lead to variations in product strength. By adopting "stepwise mixing" (pre-mixing the powder with part of the binder first, then adding the remaining components), combined with real-time monitoring via near-infrared spectroscopy, the powder distribution deviation can be controlled within 5%.  Next is the prevention of deformation during debinding. A low-viscosity solvent is used to accelerate binder leaching, while the green body is fixed with supports. During thermal debinding, the temperature is increased according to the binder decomposition temperature gradient, balancing efficiency and stability.  Finally, there is the control of sintering precision. Through "constant-temperature sintering + segmented cooling," the product density is ensured to reach over 95% of the theoretical density. A uniform temperature field inside the sintering furnace, combined with graphite fixtures, allows the dimensional accuracy to be maintained within ±0.5%.

Nowadays, MIM technology has been widely applied in fields such as automotive sensor housings, medical dental implants, and consumer electronics 5G filters. It not only addresses the challenges of machining complex structural components but also increases material utilization rates to over 95%, becoming a key driver in advancing precision manufacturing.