There are an estimated 700,000 components in a Boeing 737NG, with more than 7,000 of these planes built to date. Many of these parts are produced via traditional manufacturing methods that require die-casting and value-added processes – machining, metal finishing, plating.
Metal injection molding (MIM) technology provides an alternative, and often better, processing method for the huge quantity of fasteners, screws, seatbelt components, wing flap screw seals, bushings, and dozens of areospace components. These important aerospace components are candidates for cost savings, weight savings, durability improvements, and enhanced cosmetic appearance by using MIM.
Appropriate manufacturing process
Aerospace designers have specified MIM for key aircraft components since the 1980s, but MIM hasn’t attracted large number of users. Now, designers searching for better ways to ensure quality while saving money are turning to MIM technology. And, with more than 49,000 aircraft projected to be manufactured by 2026, there’s tremendous component volume that MIM could support.
Just as composite fiber has replaced aluminum in fuselage and wing structures, and ceramics have replaced key engine components, MIM is replacing smaller, traditional metal components. A net-shape molding process for producing solid metal parts, MIM combines the design freedom of plastic injection molding with superior material properties near that of wrought metals.
MIM mixes metal powder with a thermoplastic binder and is molded into a cavity. The molded part is thermally processed (sintered), removing the binder while producing a net-shaped, high-density component. Because it’s a molding process, it can produce an almost limitless array of highly complex three-dimensional geometries in many different metal alloys.
Traditionally, aerospace manufacturers have used powdered metallurgy (PM), plastic molding, and precision machining smaller part designs, but a comparison reveals several advantages when using MIM.
MIM parts have greater metal density and 3x the fatigue strength of PM parts. A MIM processed part has the tensile strength of the original material. Also, PM parts are limited to 2D features while MIM allows complex aerospace geometry including undercuts, holes perpendicular to the main axis, and precise 3D features.
MIM is often better than precision machining aerospace components because of weight. Often, excess material is left in the part to save machining time and removal cost, retaining excess weight. In contrast, MIM parts incorpote many features incorporated into the tooling with excess material cored out, saving part weight, manufacturing time, material, and money in the final component cost.
MIM is superior to plastic components because MIM parts are conductive, magnetic, strong, stiff, chemically resistant, and can operate at temperatures far higher than the melting range of most polymers.
Good part candidates
MIM should be considered as a cost-reducing technology when part production quantities are more than 10,000 pieces, are an appropriate size range, have complex shape, and require material performance, and necessitate reduced cost. MIM almost always has a cost advantage where the shape complexity is beyond the range of the other manufacturing processes previously described.
MIM is not a large part process. Parts measuring 3" in all directions or smaller and weighing 25g or less are the best MIM candidates. Combining multiple parts into a single component (assembly) is often possible with MIM to eliminate screws, adhesive bonding, soldering, and welding while reducing weight and cost of multiple components.
Shape complexity is an area where MIM is strongest. MIM is often specified for components ranging from 20 specifications (dimensions, locations, surface finish, material density, etc.) on the design drawing to more than 250 specifications. Surface finish flexibility allows everything from matte stainless steel to highly polished surface finishes and color. Almost everything cosmetically and practically possible is available when specifying MIM.
Lightweighing, a long-term aircraft design goal, can be achieved with MIM.
Smith Metal Products http://www.smithmetals.com
About the author: Jim Beyer is an account manager at Smith Metal Products and can be reached at 651.257.3143 or firstname.lastname@example.org.