How to Use Self-Clinching Fasteners on Stainless Steel

Engineers routinely turn to self-clinching (SC) fasteners when they need a practical way to put threads in thin-metal sheets. The permanently installed fasteners reduce hardware and promote thinner and lighter designs. But when working with stainless steel sheets and parts, engineers have to make some difficult choices. Knowing more about SC fasteners can simplify those decisions.

Self-clinching basics
In general, SC fasteners are forcefully pressed into properly sized holes during installation. This forces some of the sheet material to cold flow into a specially designed annular recess in the shank or pilot of the fastener, permanently locking it to the sheet. (Cold flow is when a metal is deformed by force rather than temperature.) After installation, the reverse side of the sheet remains flush and smooth, and a mating screw completes final component attachment.

As a rule, SC fasteners should be used whenever components must be readily replaced and where loose nuts and hardware can’t be reached, such as on an inaccessible side of a metal sheet. SC fasteners can be installed during metal fabrication and can simplify and expedite subsequent component mounting and assembly, even when done in the field.

A prevalent misconception is that all stainless SC fasteners will work in all stainless-steel sheets. But the relative hardnesses of the SC fasteners and sheets are critical because the fasteners must be harder than the sheets.

The metal around the mounting hole can undergo work hardening when the hole is created if the punch tool is dull. This raises the hardness in the area around the hole and will lead to improper installation of self-clinching fasteners because the metal will not flow as predicted.

One solution is to use a special anvil with a raised ring during installation. It helps displace the stainless-steel sheet material and ensures the fastener’s annular groove gets filled.