Secondary Operations with MIM
Since the tolerance average for the metal injection molding process falls within ±0.3%, many parts are sintered to final dimensions; however, if tighter tolerances are required for a certain feature, a secondary operation can be performed. MIM materials can be machined, tapped, drilled, broached, sized, ground, or welded like their wrought counterparts. MIM components can also be hot isostatically pressed and heat treated to improve strength, hardness, and wear resistance. And because MIM typically limits a part’s interconnected porosity to less than 0.2%, standard coloring and plating techniques can be applied without the need for special surface preparation.
It is especially important to discuss material specifications with your component fabricator because the need for secondary operations does increase component cost. Selecting the right material for your component can reduce the need for or number of secondary operations.
Metal injection molding allows for a number of secondary operations, including the following:
A sintered part is forced to conform to a rigid mandrel or substrate and in doing so the body is slightly deformed to match the substrate. This provides additional control for dimensional tolerances. Coining is also used to improve flatness.
All common machining operations can be applied to MIM components. Machining is often performed to add threads, undercuts, grooves, or other special features that would be difficult or expensive to accommodate in the tooling.
MIM components utilize the same heat treatment operations as their wrought counterparts to increase material properties, such as quench and tempering. In some cases, heat treatment is included within the cooling cycle or by use of a properly designed post-sintering cycle.
Hot isostatic pressing is a process that utilizes elevated temperature and isostatic gas pressure to eliminate non-surface-connected porosity and increase density in metals. In most cases this increases the part to 100% of theoretical density and imparts the associated improved mechanical improvements accordingly. This improves the material’s mechanical properties and, potentially, workability.
Carbon is important to attaining high strengths in steels. A high surface hardness is attained with carbon surface additions using a heating cycle with an atmosphere containing a high carbon potential.
Like other metallic components, MIM components are joined by welding, brazing, or even adhesive techniques.
Surface treatments such as polishing, coating, painting, cleaning, anodizing, plating, sealing, and laser glazing can all be applied to MIM components.
Learn more about designing with metal injection molding from Metal Injection Molding: A Comprehensive MIM Design Guide by Randall M. German, FAPMI.