Manufacturing complex metal parts can be difficult with most casting methods—creating the die is costly and the process requires a lot of fail-safes to ensure the liquid metal fills the mold and solidifies properly. Recent years have seen the rise of an alternative, though: metal injection molding (MIM), a form of powder metallurgy that promises high-quality products with lower costs. Many industries are turning to MIM as the answer to manufacturing challenges—why?
Metal injection molding is similar to other powder metallurgy processes, but it starts with a different feedstock composed of fine metal powder and a plastic/wax binding material. This feedstock is heated and injected into the mold, producing a metal and plastic “green” part. A multi-stage process removes the binder via thermal or chemical treatment, and the results are sintered to join the metal particles. After sintering, the products are about 95-98% as dense as the bulk metal, which may be further improved on.
Applications of MIM
Within the past few decades, the market for MIM parts has steadily grown and is projected to grow further. MIM parts are often small, complex and mass-produced components where dimensional specifications must be met with high accuracy; this includes extremely thin walls and fine details such as threading or identification marking. This includes application in electronics, firearms, medical equipment and the aerospace and automotive industries.
MIM is limited to small feedstock injections, and the tools and molds are more expensive upfront. However, compared to competing methods, MIM is more economical overall for high-volume production of small metal parts with complex geometries, a niche that nonetheless has high demand—some components that can be produced through MIM are impossible to create otherwise. Sintering also works at about 90% of the material’s actual melting temperature, making it valuable for alloys with prohibitively high melting points. Additionally, little to no machining is required for the final product, saving considerably on material costs, and the injection process essentially combines multiple stages into one.