Case Study: Front Sight Base

Process: Metal injection molding
Surface Hardness: HRC 26–32
Materials: MIM-4605
Density: 7.5g/cc

Front Site Base
2016 Grand Prize: Front Site Base

End Use and Function

This front sight base is for an AR-15 rifle. The size of this component, which is much larger than the typical metal injection molded (MIM) part, as well as the complex geometry, presented a challenge for the MIM process. The part also needed to be extremely reliable and durable in aggressive environments.

Fabrication

The MIM-4605 low-alloy steel part is used on the AR-15 rifle. Part geometry was approached so as to allow the entire net shape to be formed with pass core shutoffs and slide action in the injection mold. Maintaining the shape geometry while reducing the need for post-sintering secondary operations was achieved through optimized molding parameters and part staging during sintering. The only secondary operation required is spreading the so-called “ears” at the base of the part that could not be fully supported on the sintering trays; all other part features meet the drawing specifications as sintered.

Results

  • The switch from a part machined from bar stock to a MIM part yielded savings of more than 30%.
  • Nearly entirely produced via MIM, which means this part produced almost zero metal scrap