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Metal Injection Molding (MIM) ProcessMetal injection molding (MIM) offers a manufacturing capability for producing complex shapes in large quantities. The process utilizes fine metal powders (typically less than 20 micrometers) which are custom formulated with a binder (various thermoplastics, waxes, and other materials) into a feedstock which is granulated and then fed into a cavity (or multiple cavities) of a conventional injection molding machine. After the “green” component is removed, most of the binder is extracted by thermal or solvent processing and the rest is removed as the component is sintered (solid-state diffused) in a controlled-atmosphere furnace. The MIM process is very similar to plastic injection molding and high-pressure die casting, and it can produce much the same shapes and configuration features. However, it is limited to relatively small, highly complex parts that otherwise would require extensive finish machining or assembly operations if made fromany other metal-forming process.
The advantages of the metal injection molding process lie on its capability to produce mechanical properties, nearly equivalent to wrought materials, while being a net-shape process technology with good dimensional tolerance control. Metal injection molded parts offer a nearly unlimited shape and geometric-feature capability, with high production rates possible through the use of multi-cavity tooling.
Process Overview
When to Use MIM?MIM is an established, highly evolved metal-forming technology, producing intricate components that go into a great variety of end products in countless industries. But, as is true with all metal-forming technologies, MIM is not suited for every application, all the time.
To help you understand exactly where MIM emerges as the ideal fit for component fabrication, in this section we offer some general guidelines to use in assessing whether your part is a candidate for the metal injection molding process. You’ll also find some straightforward comparisons between MIM and alternative technologies that will provide further data for your assessment. Finally, we offer a comprehensive, though not exhaustive, listing of the range of materials that are being used in the production of MIM parts.
General GuidelinesWhat makes a particular component an ideal candidate for fabrication via MIM? We break down our guidelines into four basic areas: complexity, size, production volume, and final properties.
ComplexityMIM offers the same design freedom as plastic injection molding. The more geometrically complex a part is, the more solid the rationale for manufacturing it via the MIM process. Parts may include cross holes, angle holes, internal threads, irregular shapes, splines, undercuts, side holes or grooves, complex contours, orcantilevers.
Parts that would usually be made by assembling multiple components can be designed as a single MIM part. Some parts that could not be fabricated via any other process can be made through MIM. A Complexity that would be cost prohibitive to do via multiple machining operations or by casting and then finishing can be achieved cost effectively through MIM processing.
SizeIn general, the weight range MIM parts tend to fall within is 0.1 to 250 grams, although above 100 grams the high cost of the extremely fine powders used in the process begins to neutralize MIM’s cost advantages, unless the complexity is extreme. The Parts should have wall thicknesses not less than .13 mm (.005 in.) and not more than 12.7 mm (.5 in.). Due to material flow limitations, the distance from gate to the farthest point on the part should be around four inches. MIM part tolerances are nominally ±0.3%–0.5%, although tighter tolerances can be achieved in some cases if deemed essential.
Production VolumeMedium to high volumes of 10, 000 to 2, 000, 000 parts annually are typically needed in order to be able to amortize costs associated with tooling and start-up engineering. The best economic advantages are achieved at the highest quantities, due to the benefits of larger material purchases, multi-cavity tooling, and dedicated production units.
Final PropertiesMIM fabrication is ideal where near-full density, high impact toughness, fracture toughness, and fatigue and corrosion resistance are required. And if non-standard material properties are required, these can be developed with new alloy systems.
MIM is appropriate for materials that are difficult to machine, materials with multi-phase microstructures, or high work-hardening materials. And it delivers a high-quality surface finish (32 rms or better) and cleaner feature detail than investment casting.
Technology ComparisonsThere is a place for each of the traditional metal-forming processes: each has its own strong suits as well as its limitations. But wherever a component fabrication choice exists between MIM and one or more of the other processes, it pays to see how they stack up in a head-to-head comparison.
MIM vs. Conventional PM
MIM vs. Machining
MIM vs. Investment Casting
Materials RangeThe Metal Injection Molding industry can manufacture an extremely wide variety of metal alloy compositions for use in your application. The alloy families shown below make up a broad representation of the spectrum of alloys which can be/have been produced for various applications. If you do not see the exact alloy or alloy family shown on our extensive list in which you have interest, please contact your supplier in order to see if the alloy or a substitute alloy is available. Working closely with your supplier will enable you to find the best solution for your application.
The most common alloy families are:Iron, low-alloy steels, stainless steels
Other alloysAluminum alloys, bio-compatible alloys, carbides, ceramics, cobalt-based alloys, controlled-expansion alloys, copper and copper alloys, hard metals, heavy-metal alloys, magnetic alloys (soft and hard), nickel-based alloys, precious metals, reactive metals, shape-memory alloys, specialty alloys, titanium and titanium alloys, tool steels.
Specification
Parameter | MIM | PM | CNC Machining | Investment Casting |
---|---|---|---|---|
Density | 98% | 88% | 100% | 98% |
Tensile Strength | High | Low | High | High |
Elongation | High | Low | High | High |
Hardness | High | Low | High | High |
Complexity | High | Low | High | Medium |
Surface Finish | High | Medium | High | Medium |
Production Volumes | High | High | Low | Medium |
Range of Materials | High | High | High | Medium-High |
Cost | Medium | Low | High | Medium |
Advabtage OF PM