Overview: key criteria for selecting MIM technology

The MIM strengths of complex shapes, smaller sizes, and large production volumes have found numerous applications in firearms, watches, hand tools, surgical tools, orthodontic brackets, automotive engine parts, electronic packages, cutting tools, and sporting devices.

Figs. 11 and 12 illustrate a number of MIM examples.

Key criteria for selecting Metal Injection Moulding technology

Fig. 11 (a) An example of a PIM component with a combination of thick and thin sections (component courtesy of Advanced Materials Technologies); (b) An example of an undercut moulded into this PIM cemented carbide nozzle body (component courtesy of Retco Tool); (c) PIM pepper grinder that illustrates the use of coring to reduce mass and decrease wall thickness; (d) Stiffening ribs on the interior of a housing (component courtesy of MoldMasters); (e) A simple web to stiffen and link two regions in a PIM component

 

Key criteria for selecting Metal Injection Moulding technology

Fig. 12 Examples of MIM parts showing the geometric attributes favored in production

 

To summarise this quick guide, the criteria for identifying a MIM candidate are captured in a few key considerations [1, 8]:

  • Mass/volume
    MIM is excellent at reducing fabrication costs for components where much material loss would occur in machining or grinding
  • Quantity
    Tooling and set-up costs are difficult to justify for low production quantities, so MIM works best when annual production quantities exceed 20,000 per year
  • Material
    MIM is most attractive for designs that use hard to machine materials such as titanium, stainless steel, and nickel alloys
  • Complexity
    MIM is best applied to complex geometries, it works best on components that require multiple axes for indexing in machining
  • Performance
    If performance is important, then the high density in MIM generates properties that usually are competitive
  • Surface finish
    The surface roughness reflects the initial particle size, yet controlled textures are possible at almost no cost penalty, unlike competitive processes
  • Tolerances
    MIM tends to have a high cost from secondary operations if tight tolerances are required, the as-sintered tolerances are probably on ± 0.3%
  • Assembly
    Benefits arise when multiple parts can be consolidated into a single piece to save on inventory and assembly costs
  • Blemishes
    MIM has inherent blemishes that must be located in noncritical positions or removed after fabrication; examples include gates marks, ejector pin marks, or parting lines
  • Novel compositions
    MIM can form novel material combinations that are difficult via traditional processes, for example laminated or two-material structures or mixed metal-ceramic materials for wear applications.

 

Metal injection moulding leads to outstanding success when the design anticipates MIM fabrication and invites expert participation.

Review by an advisor knowledgeable with MIM invariably leads to lower costs, better quality, longer mould life, and good reconciliation between intended function and the MIM process attributes.

Many materials are available via MIM, but a few are dominant. When the material is difficult to machine, such as tool steels, titanium, nickel alloys, or stainless steel, then the net-shape aspect of MIM is most beneficial.

Component geometric features need not be sacrificed for MIM, but there are certain geometric characteristics where the technology is most successful.

The properties attainable via MIM vary between production sites; however, the many properties converge to the range customarily found in engineering handbooks. Now we are seeing new MIM materials, custom designed for the process. These include laminated (hard-soft, magnetic-nonmagnetic, and conductive-insulator) structures, foamed metals, and hollow objects. These options propel MIM into areas where there are few alternative technologies.

 

Continue to next page: References

 

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  • Bosch Advanced Ceramics: Driving ceramic Additive Manufacturing for series production with Lithoz
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  • Playing the long game: The story of Binder Jetting, and ExOne’s view on a rapidly evolving technology landscape
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  • Advanced Powder Injection Moulding process developments presented at Euro PM2020
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