DN Staff

August 20, 2001

3 Min Read
7 reasons for using self-clinching fasteners

Permanently installed in an assembly, self-clinching fasteners provide strong threads in metal sheets too thin to be tapped, and have enabled the development of many thin-metal designs that otherwise would not be possible.

As an example, design requirements for orthogonal chassis construction usually are satisfied by bent tabs and relief slots, brackets and hardware, or welding. However, each of these methods to produce right-angle assemblies has been known to exhibit performance or production drawbacks.

In enclosures where EMI is a concern, the "holes" created when bent tabs are used can impact negatively on desired shielding. Welding tabs is an extra production step, and plating and finish problems can occur. Where right-angle brackets are used for mounting, a variety of additional necessary hardware includes attaching screws, washers, lockwashers, and nuts, which tend to hamper assembly time and increase parts inventory.

Here are some of the typical reasons design engineers specify self-clinching fasteners (whether right- angle clinch or other types):

  1. Self-clinching fasteners are often the most practical and effective joining method for thin-metal assemblies (the fasteners are designed for permanent installation in metal sheets or panels as thin as 0.020 inch/0.51 mm).

  2. The fasteners are relatively small (even miniature types are available) and require less "real estate" for attachment, which meets smaller, lighter packaging requirements of today's designs, especially those applications in the electronics industry.

  3. Once installed, self-clinching fasteners do not loosen and will not fall out, which ensures that delicate internal circuitry is protected from hardware damage.

  4. The fasteners eliminate the need to stock, use, or handle additional hardware (such as washers, lock washers, loose nuts, or bolts); accompanying thread-forming screws leave no metal residue.

  5. Self-clinching fasteners can accelerate end-product assembly, because hardware installation is usually performed during fabrication instead of during final production.

  6. Self-clinching fasteners allow for component disassembly for service or other reasons.

  7. In those cases where nuts and screws for completing final attachment cannot be reached after a component is assembled, self-clinching fasteners (specified for installation during the initial fabrication process) can simplify and expedite component mounting and assembly operations.

Using right-angle fasteners on this electronic enclosure cut the total number of fasteners in half and cut assembly time from 1.5 hours to 15 minutes.

Installation procedures. Regardless of fastener type or variation, all self-clinching fasteners are installed by pressing them into place in a properly sized drilled or punched hole. This pressing or squeezing process causes displaced panel material to cold flow into a specially designed annular recess in the shank or pilot of the fastener, 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 the mating screw or nut.

The advantages of self-clinching fasteners multiply when a fastener can function as a right-angle attachment point.

Material compatibility. Designers should keep in mind that the fastener material must be compatible with the panel or sheet material. In addition, the fastener hardness must be greater than the hardness of the panel material into which it is installed. A general rule of thumb is that the fastener should be at least 20 points HRB greater than the panel or sheet material hardness. (Punched holes will produce an increased hardness around the mounting hole.)

Individual application requirements will largely direct design engineers to specific self-clinching fastener types, which traditionally fall into one of four primary categories: nuts, studs, spacers/standoffs, or panel fasteners.

Regardless of self-clinching fastener type or variation, all demonstrate conformance to principles of Design For Manufacture and Assembly from the outset of a component's design through to its final assembly.

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