Case Study: Compression Frame

Process: Metal injection molding (MIM)

Material: MIM-420 stainless steel

Density: 7.7 g/cm³

Tensile Strength: 1,730 MPa (250,000 psi)

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End Use and Function

The compression frame is essential for holding and aligning the targeting drill guide during tarsometatarsal fusion.

Fabrication

The parts are produced using MIM-420 stainless steel in a single cavity open and shut mold with two slides. The first forms the rectangular opening. The second forms the two holes at a 60-degree angle on the opposite end of the frame. Hot isostatic pressing (HIP) is required to achieve an average density of 7.7 g/cm³. After HIP, an annealing process is performed prior to secondary operations. The parts are sized in a die with two slides, so that forces can be applied in perpendicular directions to the parts. A hole is drilled, and a countersink added. The frames are vacuum, heat treated, and tempered to meet a 40 HRC minimum hardness, and the frames are passivated prior to shipment.

Results

MIM was selected for net-shape manufacturing, high production volume, and cost reductions. The MIM process provided better material utilization, the so-called “buy to fly ratio”, as it achieves a net-shape part without processing scrap, where machining would have resulted in a volume of processing scrap that was greater than the part itself.