Self Clinching Technology

How It Works

Self clinching fasteners require two features to properly secure themselves to a metal panel – an undercut and displacers that move material into the undercut. This displacement is driven by the installation of the fastener. Take a clinch nut (or press nut) for example. It uses knurls as displacers while the ramped shank creates an undercut and serves as a pilot within a panel hole.

During installation, the knurls are the first feature to touch the outer surface of the panel. They must move material out of the way for the barrel to seat completely on the panel. Using the proper installation equipment and force, the material is guided into the undercut. Post-installation, the shank will now have to displace the material again in order to fall out of the panel, which requires forces similar to those associated with install.

The specific self clinching features often change based on the fastener type. While the clinch nut uses knurls as displacers and a ramped shank as an undercut, many standoffs simply use the head as a displacer and a square undercut where the barrel meets the head. Some larger studs use large, coarse ribs to fill a trapezoidal undercut since there is more material to move, favoring energy efficient displacement.

Schematic comparing undercut volume and displacer volume of a self-clinching nut

Advantages & Limitations

Self clinching technology is a very secure and strong fastening solution for a variety of metals and sheet thicknesses. It minimizes loose parts like nuts and washers that otherwise would be necessary to complete a fastened joint, and installation is fast and consistent when using the proper equipment and procedure. Most cost savings come from reduced time and energy spent in production at scale with improvements in quality and consistency.

The greatest limitation of self clinching fasteners is the cost associated with the installation equipment and more expensive parts. While there are a wide variety of applications in which self clinching is a valuable solution, more time is spent developing the features required for materials of different hardness, ductility, for sheets of different thicknesses, and for corrosive environments. Given the production volume required to offset the investment in installation equipment, this can limit the versatility of self-clinching parts.

Comparison showing how self-clinching can overcome some limitations of weld nuts

Properties comparison of weld nuts and self clinching technology.

Self clinching requires ductile metals to function properly – a material that commonly sees welding as a valid solution to putting threads in a panel. The equipment is simpler, the parts are simpler and typically cheaper, and innovations in laser welding have greatly improved the quality in dimensionally smaller applications. Nonetheless, energy usage is greater and additional time is required to allow welded joints to cool. Weld spatter can also cause quality problems that jeopardize an assembly if it isn’t caught during production, and where welding requires similar metals to function properly, self clinching can work with a variety of dissimilar metals.

To read more about the tradeoffs between self clinching and welding, visit "An Alternative to Welding."

Common Applications

While self clinching is limited to metal applications, it provides the opportunity to use corrosion-resistant coatings that remain intact upon install. This is useful for marine environments with temperature and humidity concerns. Mass production of automotive, telecom, medical, and consumer electronics parts can benefit from using self clinching fasteners over alternative attachment technologies, especially as innovations in conductive fasteners continue to grow.