Push-on plastic nuts and self-clinching sheet metal studs have each established a good track record when it comes to improving assembly productivity. But these two fastener types have traditionally run on different tracks. "They haven't been used together," says Jay McKenna, special products manager for PennEngineering Fastening Technologies.
PennEngineering, however, recently combined these two fastening approaches in a new product that lets users simply push a plastic hex nut, clip, or bracket onto the company's self-clinching studs.
The thread form used on these "X-Press Thread" studs has about twice the pitch of a conventional self-clincher. It also has a 60-40 configuration—a 60 percent slope in the on-direction and a 40 percent slope in the off-direction. Together, these features "make it easy to slide the nut on but hard to pull it off," says Brian Bentrim, one of the company's new product development engineers.
At the same time, the new threads still allow for easy removal of the nut or mating component. Users simply twist the nut off the stud. "In fact, it takes fewer turns to remove the nut due to the increase in pitch," Bentrim notes.
The X-Press thread form doesn't in itself qualify as cutting edge. In fact, McKenna freely acknowledges that one of PennEngineering's European customers, an automotive OEM, had for years been using a similar thread form on some of its welded studs, including those used to route fuel and brake lines. "That customer asked us to put the thread form on one of our self-clinching products," he says.
It's a combination that makes a lot of sense. As McKenna explains, that automotive OEM wanted to avoid the expense and hassle of welding fasteners onto sheet metal. "The same goes for many of our customers, not just those in automotive," he says. When coupled with in-die installation techniques, which insert the studs during the stamping process, the new self-clinchers can even reduce the total number of manufacturing steps.
While the desire for push-on nuts, clamps, and brackets mostly boils down to speed, push-on mating components do have a side benefit related to over-torque protection. "They're not really intended for applications where you want to develop a clamp-load as much as for applications where you want to avoid over-torquing," Bentrim says. These applications include routing of various fluid-handling lines, securing soft materials such as carpet, and fastening onto brittle materials that can break under the stress of over-tightened nuts.
PennEngineering has been supplying custom X-Press threaded studs in Europe for the past couple of years. This month, the company will offer X-Press threads on some of its self-clinching studs.
Initially, these studs will be available in a 5-mm diameter with thread lengths of 10, 15, 20, and 25 mm, and as custom sizes.