Metal Injection Molding is a green technology that reduces waste compared to traditional manufacturing processes like 5 axis CNC machining. The process also eliminates toxic fumes and requires no chlorine or wax based materials.
The MIM process begins with a finely milled metal powder. This material is combined with binders and lubricants. Once the exact recipe is determined for each individual design, compounding can begin.
1. Versatility
MIM is an excellent production process for components that are difficult to efficiently manufacture using other methods. This includes complex small parts with tight tolerances, such as internal/external threads, miniaturization, and identity marking.
In MIM, metal powder is mixed with what's called a binder to create a feedstock for injection into the part mold. The feedstock is injected through gates (typically tab, tunnel, or jump) into the part cavity. Once sintering is complete, the binder is removed in a low-temperature debinding oven.
A good MIM design will minimize the number of gates and gating locations to keep costs down. Part designers should also consider draft angles and corner radii for optimum moldability and avoid features like sharp corners or transitions from thick to thin.
2. High-volume production
The MIM process is well-suited for high-volume production of small, geometrically complex metal parts. It is particularly beneficial for medical devices, which require tightly configured metal components.
The MIM production process starts with a blend of fine metal powders mixed with what's known as the binder to form a “feedstock” for injection molding. The feedstock is then injected into the part mold and then placed into a low temperature debinding oven where the binder is vaporized.
Afterward, the part is subjected to a sintering process that allows the metal particles to fuse together and eliminate surface pores. The result is a net-shape metal component that has mechanical properties that are comparable to those of wrought metal. As with any production method, however, it's important to design the product for the process from the start in order to maximize its benefits.
3. Cost-effectiveness
MIM is a cost-effective solution for producing parts that would be too expensive to fabricate using other methods. This includes parts with a high number of features and complex geometries.
The MIM process starts with metal powders mixed with binders to form a feedstock mixture. This is injected into the part mold to create the desired shape. The molded part, called a green part, is then cooled and removed from the mold. Binder removal is referred to as debinding and then the part is thermally processed, or sintered, in an atmosphere or vacuum furnace. This removes any remaining binder and fuses the metal particles together to eliminate surface pores and achieve a dense solid.
Sintered parts can be treated just like forging or casting metal parts, and can be welded, soldered, blued, hardened, tempered, polished, ground and drilled. This makes MIM a highly scalable manufacturing process requiring only one up-front investment in tooling to produce millions of parts.
4. Flexibility in piece geometry
MIM parts are very precise, and tolerances can be tighter than those produced by other manufacturing processes. In-process inspections using coordinate measuring machines (CMM) and optical comparators help ensure that dimensional specifications are met.
This enables manufacturers to produce intricate metal components at a high rate without the time and expense associated with machining. These benefits can be particularly valuable in the medical industry, where complex shapes and tight tolerances are critical for the safety and reliability of load-bearing orthopedic implants.
Intricate Nitinol components, for example, require precise geometry and a strong, durable alloy with excellent biocompatibility. MIM is able to meet these demands by producing intricate parts at high volume cost effectively.
5. Dimensional stability
MIM parts are dimensionally stable, similar to parts produced by investment casting and discrete machining. They can be used where tight tolerances and complex geometries are critical.
MIM components shrink isotropically during the sintering process, which eliminates surface pores by fusing the metal particles together. This gives a denser solid that is very close to the design dimensions.
Compounding is the key to controlling shrinkage and ensuring quality over time. It is critical to choose a manufacturing recipe that works for your specific alloy selection and part geometry. For example, choosing a nickel-based or cobalt-chrome alloy with FDA and biocompatibility approval will ensure your finished MIM part is suitable for medical use.
