Case Study: Stainless Steel Shaft Assembly

Process: Metal injection molding
Secondary processes: Laser welding, straightened, finish machined, and reamed
Material: MIM 17-4 PH stainless steel
Density: 7.5 g/cm³
Tensile Strength: 1,190 MPa
Yield Strength: 1,090 MPa
Hardness: 33 HRC

Stainless Steel Shaft Assembly
2014 Award of Distinction: Stainless Steel Shaft Assembly

End Use and Function

This component is a metal injection molded (MIM) shaft assembly used in a novel surgical instrument for passing sutures through difficult-to-reach tissue.

Fabrication

This part’s design is highly complex and, unlike most surgical tools, this instrument is single-use, so a precise fabrication process had to be developed that could be scaled up to deliver high volumes at low cost using MIM-17-4 PH stainless steel. That process involves molding the 178 mm (7 in.) shaft in two parts, laser welding them together, and then performing finish machining, ID reaming, heat treating, sand blasting, and passivation to achieve the tightly toleranced dimensions. The parts have a density of 7.5 g/cm³, an ultimate tensile strength of 1,190 MPa, a yield strength of 1,090 MPa, an elongation 6.0%, and an apparent hardness of 33 HRC.

Results

Using MIM to develop this part resulted in:

  • a part that is four-to-five times less expensive than Swiss CNC machining would have been.
  • considerable (90%) waste savings over Swiss CNC machining from steel rod stock.