Look for MIM In Gun Parts

Expect more penetration of the metal injection molding (MIM) process into the firearms’ components business. MIM offers an opportunity to create precise net shape parts at significant cost savings over machining and other metal-forming processes.

One example is a rear sight used on sporting and military rifles such

This gun sight is a MIM award winner.

as the AR-15, M4, and M16 models, which received an award of distinction in this year’s design competition held by the Metal Powder Industries Federation.  Made by Megamet Solid Metals (Earth City, MO) for Yankee Hill Machine Co., the nickel steel MIM part has tight  tolerances and a complex geometry requiring an elaborate tool design. The sight allows the shooter to target objects at ranges up to 200 yards by using the larger aperture, and to target objects at longer ranges by flipping the sight down and using the smaller aperture. The part is made to a density of 7.5 g/cm3 and has an as-sintered ultimate tensile strength of 55,000 psi. Savings over investment casting are pegged at 40%. Secondary operations are limited to tapping and nitride finishing.

On Wednesday, ATW Companies (Warwick, RI) acquired Metalform  (New Britain, CT)  a gun magazine manufacturing firm. That’s significant because ATW owns Parmatech, the company that invented MIM in the 1970s. ATW is beefing up capacity at its Parmatech Proform operation in Rhode Island, and has set defense and firearms as a key growth market. To date, MIM has made minimal penetration into firearms applications, mostly for niche areas such as the Megamet gun sight.

The acquisition of Metalform’s deep-drawing, stamping, and pistol magazine fabrication capabilities supports ATW’s vertical integration into the rapidly growing firearms and defense industries. Among Metalform’s top products are 38 caliber, 45 caliber, and 9 mm magazines, supplied to many top firearms industry companies.  “Metalform will be joining a strong firearms and defense team with expertise in a variety of technologies, including precision CNC machining, MIM, laser cutting, precision metal tubing, and stamping,” says Tracy MacNeal, ATW’s director of business development. ATW companies serve nearly all the major firearms players.

In the MIM process very fine metal powder is mixed with a plastic binder that allows the mixture to flow in  injection molding machines that are specially fitted with wear-resistant screws and barrels.  In a departure from steps taken in plastics injection molding, the parts then go into equipment that removes the binder. Then the remaining structure is sintered, eliminating voids. Part of the considerable art in MIM is developing materials and debinding technologies that minimize distortion and maximize part strength, a critical factor for firearms components.

The technology has improved dramatically in recent years partly due to the entrance of major technology players such as BASF, which is the leading supplier of metal powders.

About Doug Smock

Former Chief Editor at Plastics World and Senior Technical Editor Design News
Defense, Design, Injection Molding, Metal Injection Molding, North America, Powder Metal ,

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