Case Study: Internal Latch
Process: Metal injection molding
Materials: MIM-4140 low-alloy steel
Density: 7.5 g/cc minimum
Hardness: 48–53 HRC
End Use and Function
This component, made from a low-alloy steel, is an internal latch that drives a subassembly for the telescoping feature of the collapsible stock on MCX and MPX rifles. The innovation behind this component comes from the complex geometry and tight print tolerances that require a refined metal injection molding process to produce precise and functional parts.
Both the diameter and perpendicularity of the through hole in relation to the profile of the slot at the other end are critical for functionality. Those features, as well as the overall length of the latch, make this a challenging part to mold with no distortion in the finished product. The part is sintered near-net shape, requiring only a reaming operation to achieve the tight ± 0.02 mm (± 0.001 inch) tolerance on the through hole, in addition to several other minimal secondary operations. By controlling factors such as gate location, injection velocity, hold pressure, and barrel temperature, the MIM process was utilized in a way that repeatedly produces quality parts in the final assembly.
This component was designed for MIM as a result of many design sessions with the customer, which highlights the need to find a fabricator early in your design process. Due to the irregular geometry of the part, it would be extremely challenging and expensive to try to manufacture this component via traditional methods. The MIM process allows this part to be produced with no metal waste in a cost-effective manner.