Threaded Hardware Offers Fastening Options for Metal and Plastic Components

NASA Tech Briefs, Jul 2004 by Ross, Skip

Permanently installed threaded hardware provides a reliable attachment in most fastener installations.

PennEngineering Fastening Technologies, Danboro, Pennsylvania

For every challenge that may arise when attaching metal or plastic components, a hardware solution usually can be found. When permanently installed threaded hardware is specified as a solution to provide strong, reliable, and reusable threads in an assembly, users can further gain production and performance benefits over and above the method's intrinsic value in attachment.

Whether the application is for fastener installation in thin metals, nonductile materials, or plastics, a wide variety of styles and types of threaded hardware is available to meet the need.

* Threaded Fasteners for Thin Metals. Ideal for thin-metal designs, self-clinching fasteners can be utilized in sheets too thin to tap, and can serve as superior threaded alternatives to extruded/tapped or stamped threads. There are dozens of types and thousands of variations, including free-running, self-locking, floating, and blind hole fasteners.

Self-clinching hardware typically is made from steel, stainless steel, or aluminum, and will install permanently in metal sheets as thin as 0.020''/0.51mm. These fasteners can eliminate a need for washers, lock washers, and nuts for final attachment of components. Since they become an integral part of an assembly in which they are installed and reduce the amount of hardware to handle and inventory, self-clinching fasteners promote quicker product assembly and reduced costs. High volumes can be installed automatically.

Their installation is accomplished by pressing the fastener into place in a properly sized drilled or punched hole. This process causes displaced sheet material to cold flow into a specially designed annular recess in the shank or pilot of the fastener, permanently locking the fastener in place. A serrated clinching ring, knurl, ribs, or hex head prevents the fastener from rotating in the metal when tightening torque is applied to mating hardware.

For instances in which there is access from only one side ("blind" applications), blind threaded inserts can provide a solution. Installation is performed from the accessible "front" side of workpieces as thin as 0.010''/0.25mm. With inaccessibility no longer an obstacle for fastener installation, aluminum, brass, steel, or stainless steel blind threaded inserts prove especially helpful in tubing and extrusion applications.

An added advantage with blind threaded inserts is that during their installation, several thin sheets of dissimilar materials can be assembled and then final components can be attached. This capability eliminates any need to perform spot welding or other secondary operations, saving production steps, time, and cost.

* Threaded Fasteners for Non-Ductile Materials. Broaching fasteners are among the hardware solutions for componentto-board, board-to-board, and board-to-chassis fastening applications. These will install permanently in all types of printed circuit boards, as well as in components made from acrylics or polycarbonates. They are offered in a variety of types, sizes, and finishes. Their use eliminates the need for washers, lock washers, nuts, and other excess hardware.

Popular styles include broaching nuts with permanent threads for board mounting or component attachment; threaded or unthreaded standoffs for stacking or spacing, and flare-mounted standoffs for greater pullout performance; threaded studs for use as solderable connectors or as permanently mounted mechanical fasteners with external threads; all-metal standoffs featuring a spring action to hold a PC board securely without screws or threaded hardware; and one-piece board-mount screw assemblies with captive screws for easy mounting and removal of PC boards.

* Threaded Fasteners for Plastics. All-metal inserts (brass, stainless steel, or aluminum) for attaching plastic components offer a practical advantage over permanently bonded adhesives or rivets by enabling the subsequent repeated disassembly and reassembly of components. Types include ultrasonic/heat staking threaded inserts, which are installed ultrasonically or with a thermal press; molded-in threaded inserts installed during the molding process; and press-in threaded inserts, which are installed by pressing them into premolded or drilled holes.

Because every application is different, consulting an experienced hardware manufacturer as a partner early in the design process is recommended. This can help ensure proper fastener selection and pave the way to arrive at custom solutions, where appropriate.

This article was written by Skip Ross, Technology Research Manager at PennEngineering® Fastening Technologies, Danboro, PA; Tel: 215-766-8853; Fax: 215-766-0143; www.pennfast.com.