Case Study: Rotor

Process: Metal injection molding
Hardness: 27 HRC
Density: 7.5 g/cm³
Tensile Strength: 900 MPa (130,500 psi)
Yield Strength: 730 MPa (106,000 psi)

2012 Grand Prize: Rotor
2012 Grand Prize: Rotor

End Use and Function

A compact, lightweight, hand-emplaced munition device with extensive design and qualification requirements including cost efficiency and control. Parts had to be as close to net-shape as possible.

Fabrication

The intricate design is demonstrated by its four holes on two perpendicular planes, two angled slots with square corners, and numerous internal and external radii, flats, slots, and cutouts. All of these features require very tight tolerances: 0.00635 cm (0.0025 in.) to 0.0127 cm (0.005 in.). Moreover, the square bottom-hole could only be formed by via metal injection molding (MIM) because prior attempts with other fabrication processes, including machining, proved unsuccessful. It is estimated that the machined version of the part could cost as much as five times that of the MIM design. The rotor is made to a density of 7.5 g/cm³ and has an ultimate tensile strength of 900 MPa (130,500 psi), yield strength of 730 MPa (106,000 psi), a 6% elongation, and 27 HRC hardness.

Results

  • MIM is the ideal process for developing this extremely complex and multi-functional device at tight tolerances at a high production volume without risking the accuracy and reliable functionality of the rotor.
  • Cost effective part, whereas casting and machining were not considered as options due to extensive costs.