Shenzhen Alu Rapid Prototype Precision Co., Ltd.

Metal Injection Molding (MIM) is a hybrid manufacturing process that blends the precision of plastic injection molding with the strength of powder metallurgy. It enables the high-volume production of small, complex metal parts with intricate shapes and excellent mechanical properties, often at a lower cost than traditional machining for such components. MIM is ideal for parts under 100 grams, like gears, surgical tools, or firearm components, and can achieve densities up to 99% of solid metal.

How Does the Process Work?

The MIM process involves four main stages: feedstock preparation, injection molding, debinding, and sintering. Here's a step-by-step breakdown:

1.Feedstock Preparation: Fine metal powders (typically 1–20 micrometers in size) are mixed with a binder system, usually polymers like wax and polypropylene, to form a viscous "feedstock." This mixture behaves like a non-Newtonian fluid, allowing it to flow under pressure while holding shape once cooled. The metal can be stainless steel, titanium, or other alloys, making up about 60% of the volume.

2.Injection Molding: The feedstock is heated to a semi-liquid state and injected into a precision mold (similar to plastic injection molding) at high pressure (up to 100 MPa). The mold cools rapidly, solidifying the part into a "green" state—a fragile, binder-held shape that mirrors the final design. This step allows for complex features like threads, thin walls (down to 0.1 mm), or detailed textures in a single operation.

3.Debinding: The green part undergoes debinding to remove most of the binder, leaving a porous "brown" part (about 40% air by volume). This is done via solvent extraction, thermal heating (up to 500°C), catalytic processes, or a combination. The result is a brittle but handleable structure, often with some initial shrinkage.

4.Sintering: The brown part is heated in a controlled furnace (e.g., 1,350–1,400°C for stainless steel) under a protective atmosphere or vacuum. This causes the metal particles to bond via diffusion and capillary forces, densifying the part to near-full solidity (96–99% density) and shrinking it by about 15–20% in each dimension. Optional liquid-phase sintering can enhance bonding by partially melting the particles.

After sintering, optional post-treatments like heat treating, plating, or machining refine the part to meet tolerances (typically ±0.3%) and surface finishes (as low as 1 μm Ra).

Materials and Applications

Common materials include stainless steels (e.g., 17-4 PH), low-alloy steels, titanium, and superalloys. Binders are temporary and fully removed. MIM excels in industries like medical (implants), automotive (gears), and consumer electronics (hinges), producing net-shape parts that minimize waste.

Advantages and Limitations

MIM offers design freedom for complex geometries, high production rates, and material efficiency, but it's best for high volumes (thousands of parts) due to tooling costs. It's less suitable for very large parts (>20 cm) or low-quantity runs.