This technical information has been contributed by
Miller Precision Manufacturing Industries
Patented Threaded Inserts Designed to Thrive in Heavy-Duty Applications
Fredserts are available as standard components in several sizes and materials.
Photo courtesy of Miller Precision Manufacturing Industries (www.millerprecision.com).
You may not have heard of the “Fredsert,” a unique threaded insert patented by the General Dynamics Corporation more than a decade ago. Fredserts were initially designed for the U.S. Marine Corps Expeditionary Fighting Vehicle (EFV) by an engineer named Fred Wheeler, who designed the product to meet a variety of application-specific demands. Among the design objectives were a water-tight seal; solid locking to prevent back-out; corrosion resistance in extended saltwater exposure; and the ability to be easily removed and replaced in the field. Today, the American-made Fredserts are manufactured by Miller Precision Manufacturing Industries, Inc., of Ottoville, Ohio. As their use expands to various other applications, nearly 4,000 of the threaded inserts are incorporated into each EFV, according to company representatives.
The Fredsert is reported to have simplified vehicle design, improved producibility, and reduced program logistical costs. It is self-tapping, utilizing a design and installation method that facilitates self-locking and eliminates the need for a mechanical locking procedure subsequent to installation. According to representatives of General Dynamics, the self-locking feature of the Fredsert mitigates logistical problems, as a damaged insert can be removed simply by backing it out and installing a new one. But in-the-field removal and replacement of commercial inserts, such as Keenserts and Rosans, drives up logistical costs, they say, because the inserts must be drilled out due to their mechanical locking mechanisms.
Company representatives say that Fredsert technology has fostered new attachment concepts that reduce the total number of fasteners. By introducing flexibility in vehicle assembly operations, the design reduces assembly costs. And by drastically simplifying the removal and replacement of inserts in the field, Fredserts are reported to have reduced logistical support costs.
Geometrically, the Fredsert effectively combines a tapered thread profile, full thread engagement, cutting flutes, and a flanged head—characteristic features that provide friction fit and material compression to reliably lock a Fredsert in place. The Fredsert was designed, company representatives say, “to resist vibration, tensile loading, and shear loading in the most demanding heavy-duty applications.”
The Fredsert (www.Fredsert.com) offers a number of unique features. For example, rather than permanently locking into place, it has a patented geometry that causes it to “break away” at approximately 80 percent of the recommended installation torque value. As a result, it can be quickly and easily removed and replaced using the same equipment. Other commercially available inserts, however, can only be removed by drilling them out and, in some cases, re-tapping to the next largest tap size, company representatives say. This can be especially difficult if the insert is installed in a large structure or a tight enclosure because access and rigidity are limited.
The Fredsert combines a tapered thread profile and 100 percent thread engagement with cutting flutes and a flanged head to create a friction fit with material compression to reliably lock the threaded insert in place.
Photo courtesy of Miller Precision.
Another differentiator is that titanium Fredserts, as well as those made from stainless steel, are available as a standard product. Titanium Fredserts reportedly provide weight savings of 40 percent versus stainless steel inserts of the same size. But titanium inserts from other major insert manufacturers “are either not an option or they are quoted at an extremely high price and long lead time,” according to company representatives.
Another benefit of the threaded inserts is that they create a 100 percent watertight seal without the use of a thread locking agent, such as Loctite. The combination of a tapered thread profile, 100-percent thread engagement, and a flanged head is said to result in a “perfect” seal on the OD thread of the insert. “Blind” Fredserts also provide a watertight seal on the ID thread because the ID thread bore doesn't break through the bottom of the insert.
Potential applications of the Fredsert, which the company calls “next generation threaded insert technology,” include automotive engine blocks and castings; pneumatic and hydraulic fittings; and agricultural equipment, as well as aircraft, military vehicle, and ship and submarine components.
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