Application Digest 7411

Small fasteners solve big assembly problems

Pat Kelly, Applications Engineering Manager,
Penn Engineering & Manufacturing Corp.

Size is one of the most significant design factors influencing the assembly of electronic components. Small components leave less room for fastening hardware. And as sheets get thinner, holding power can be jeopardized, unless engineers can find a different way to provide strong threads.

Universal assembly challenges also come into play in electronics. These include the need to disassemble components easily for service, and to re-attach them securely. Miniature self-clinching fasteners are designed to meet those challenges.

PEM miniature fasteners provide strong, reusable threads in sizes 0-80 through .25-28, and M2 through M6. Non-locking and self-locking types are available. They can be installed in sheets as thin as 0.020 inch (0.76 mm). By becoming a permanent part of the sheet, the fasteners eliminate loose hardware and allow easy disassembly of components.

Upon installation, the fastener's knurled collar completely embeds in the panel to prevent rotation of the fastener. The knurl's spin resistance greatly exceeds the torque that can be exerted by the self-locking feature.

When the collar is embedded in the panel, the undercut cavity beneath the collar fills with displaced panel material, thereby developing pushout resistance of as much as 420 lbs, depending on thread size and material. A dry-film lubricant applied to the fasteners provides the smooth, non-galling, prevailing torque performance necessary for reliable locking and reusability. The fasteners can achieve torque-out values as great as 110 lb-inches.

PEM miniature fasteners must be installed by a force applied through parallel surfaces. Proper installation is accomplished by pressing the fastener into a pre-drilled or punched hole, and the fastener provides immediate visual confirmation of installation.

Custom Molding Cuts Costs

Jerry Scrocco, Efson, Inc.

Design for assembly was a prime consideration when Siemens Energy & Automation, Inc., Alpharetta, GA, redesigned their rotary operating handle. The low-profile, door-mounted handle operates circuit breakers and power switches "through the door." These systems appear on the control panels of welding systems and other equipment.

Rapid prototyping techniques proved the design would work. Drawings and prototypes sent to several potential suppliers drew mixed reactions. Some shied away from the "critical tolerances" of the three glass-filled nylon parts. Others wanted unacceptable design modifications. Custom molding using a proprietary tooling program called "Master-Insert" enabled Efson, Inc. to quote the parts as designed and win the contract.

The parts are molded in 33% glass-filled nylon. After molding, hot stamping produces a contrasting color on the raised ON/OFF indicators.

In addition to three molded parts, the handle includes two metal camming plates and a locking lever. After installing the metal parts in the plastic shell, workers insert the rotary handle. A gentle, firm squeeze snaps the handle plate and cover together. Time savings achieved during assembly reduce in-place cost by more than half when compared to the previous die-cast zinc unit.

For application help on custom molding, call (910) 799-8200.