Metal injection molding is the production process that resolves the conflict between geometric complexity and production volume in metal component manufacturing. Machining can achieve very complex geometries but becomes expensive at volume as the time per part does not reduce significantly with scale. Die casting can handle high volumes but is limited to relatively simple geometries and is restricted to non-ferrous alloys. Metal injection molding sits at the intersection of these constraints: it produces complex geometries, works with a wide range of alloys including stainless steel and titanium, and its per-part cost falls substantially as volume rises and tooling investment is amortised.
The Process That Makes It Possible
Metal injection molding begins with a feedstock consisting of fine metal powder blended with a thermoplastic binder into a flowable compound. This feedstock is injected into a steel mould at elevated temperature and pressure, filling the cavity to produce a “green” part that holds the shape of the mould. The green part undergoes debinding to remove the binder, typically through a combination of solvent and thermal processing, followed by sintering in a controlled atmosphere furnace at temperatures approaching the alloy’s melting point.
During sintering, the metal powder particles bond and the part densifies to approximately 95-99% of theoretical density depending on the alloy and process conditions. The part shrinks by a predictable amount, typically 15-20% linear, and this shrinkage is accounted for in the mould dimensions so the finished part meets its specified dimensions.
When Metal Injection Molding Is the Right Process
Metal injection molding is the appropriate process when:
The part is small (typically under 100 grams, though larger parts are possible), has complex three-dimensional geometry, and is required in volumes of at least several thousand per year.
The material is a metal alloy that can be reduced to fine powder and sintered to full density, including stainless steels, low-alloy steels, titanium alloys, and specialty alloys.
The dimensional tolerances required are achievable through the MIM process, typically ?0.3% to ?0.5% of nominal dimension for standard production, with tighter tolerances achievable through secondary operations.
“Singapore’s position in precision manufacturing depends on mastering the processes that produce what competitors cannot,” said EDB Chief Executive Chng Kai Fong. Metal injection molding at the standard required for medical devices and precision instruments is one of those processes.
Cost Structure of Metal Injection Molding
The cost structure of MIM is characterised by high tooling cost relative to simple machining operations and low variable cost per part at volume. Tooling for a MIM component typically costs from S$15,000 to S$50,000 depending on part complexity and the number of cavities in the mould. At volumes of ten thousand parts per year and above, this tooling investment is amortised rapidly against the low per-part production cost.
For designers considering MIM, the question is not whether the tooling cost is large in absolute terms but whether the total cost of ownership over the production life of the part, including tooling amortised across the volume, is lower than the alternative manufacturing route.
Quality and Traceability
Production under an ISO 13485 quality management system means that every metal injection molded part lot is traceable from the finished component back to the raw materials and process records. This traceability is required for medical device components and is standard practice at AMT for all production.
AMT Metal Injection Molding
AMT produces metal injection molded components from its Singapore facility for high-volume and complex part applications in medical devices, industrial equipment, and precision instruments. Their MIM capability spans from design feasibility through tooling, process qualification, and series production.