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Sheet metal fastening, no nuts required
Supply chain crunch brings hardware challenges to the fore for metal fabrication shops
- By Tim Heston
- September 15, 2021
- Article
- Assembly and Joining
2021’s supply chain challenges have led to some absurd realities, proving that even the smallest ripple can grow into waves of disruption. According to one representative at a major contract metal fabricator based in the upper Midwest, the company experienced major project delays not due to sheet metal shortages or even labor challenges. Weld nuts, it turned out, were to blame.
“You don’t want things to grind to a halt because of a $10-per-thousand weld nut sitting on a boat in the ocean.” So said Larry Fey, Wood Dale, Ill.-based director of sales for the manufacturing division at fastener supplier Optimas Solutions.
Some fabricators make smart use of punch press lance-and-form tools, which allows certain components to simply clip together. Other fab shops still use machine screws, but they’ve reduced the need for nuts. In-turret tapping heads can cold-form threads into sheet metal, and extrude-and-tap strategies can insert threads into sheet metal too thin to accept threads.
Other fab shops use the helix thread-form approach, which replaces the nut with a helix formed into the sheet metal itself. Punch machine OEMs, Mate, Wilson, and others offer thread form tools. For its part, Optimas manufactures the screws and supplies helix thread form tools through a licensing agreement with Industrias LOTU S.A. in Spain and its U.K.-based subsidiary, High Torque Engineering Ltd. Called the High Torque Fastening System, the tool can be supplied as a tool on a stamping press or a form tool on a CNC punch.
The fastener supplier has licensed a technology that eliminates the need for a nut for certain sheet metal fastening applications. “The technology eliminates the whole process of procuring a nut. Manufacturers don’t need to engineer the nut, nor do they have to store it.”
The technology isn’t new. Regardless, with the demand boom and supply chain choke of 2021, fabricators have renewed interest in ways to simplify fastening. And eliminating the need for the weld (or cold-formed) nut is one way to achieve that simplification.
When the screw’s threads mate with the helix form in the sheet metal, they create a secure connection. With the High Torque Fastening System, the mated material (that is, the sheet without the helix form) can be up to 2.5 mm thick.
Like any technology, the High Torque fastening system does have a few drawbacks, the most significant of which involves vibration endurance. “If the assembly will experience a lot of vibration at the mating area,” Fey said, “the fastener could loosen. Manufacturers need to take that into consideration when designing parts.”
Optimas has worked with manufacturers to determine how much vibration the fastening system can withstand in specific applications. Some manufacturers use an expansion clip under the helix-formed sheet metal. The clip doesn’t require a special tool or machine to insert, but of course it does add some assembly labor. Assemblers (and, potentially, repair personnel after the product is in use) also need access to the underside of the assembled joint.
Fey said that in many cases companies choose to use clips for fastening areas that require it—ones that, for example, will endure significant vibration during use—but then rely only on the simple helix form to secure the remaining screws.
Such fastening technology fits into a larger conversation about the time-consuming and mistake-prone nature of fastening in the fab shop. The most obvious is using the wrong hardware. “You have to worry about people pulling a nut with the wrong thread,” Fey said. “It’s hard to see the difference between an M4 and M6 when you’re looking at them.”
Shops mitigate these problems through 5S in hardware insertion and assembly, making it difficult or impossible for the operator to reach for the wrong nut. Automated nut feeding, be it at the insertion press or welder, can help matters too. Fab shops also talk with design engineers or customers about standardizing hardware. If a product has just one kind of hardware, there’s less chance for a mismatch. It can also make inventory management much easier.
Another issue with nuts is the masking they require before painting or powder coating. A shop might have a fully automated laser cutting and bending cell, but it probably still employs someone to mask all exposed hardware manually. A mistake in masking can lead to paint getting into the nut’s threads, which leads to problems in final assembly or, worse, quality issues at the customer.
“You don’t want to get paint into the threads, which can cause cross-threading or incorrect threading between the fastener and the nut,” Fey said.
Fastening is a process ripe for simplification, and the first step is to standardize hardware to just one or a handful of sizes that fit all material grades and thicknesses. Some applications can go a step further and cut the number of hardware pieces in half—by eliminating the nut.
The helix technology doesn’t change the physics of sheet metal. “For instance, when you’re mating two pieces of sheet metal, you need to make sure they’re compatible with each other,” Fey explained. “So, you don’t want steel fastened to aluminum, which could create corrosion between the two materials.”
Again, fastening machine screws to a formed helix in the sheet metal can withstand only so much vibration when in use. But with no nuts required, the sheet metal can flow from forming (where a form tool on a stamping press or CNC punch creates the helix) to bending; powder coating; and assembly, where assemblers can use a standard power hand tool to drive the helix-threaded screws. The helix form has no “threads,” at least in the traditional sense, for paint or coating to become trapped and wreak havoc on fastening integrity. Hence, there’s no need to mask.
Most important, especially amid the supply chain choke of 2021, production isn’t hindered by a delay in nut shipments. Nuts don’t cost much, but if they’re sitting on a containership when they should be on the factory floor, they can be incredibly expensive.
About the Author
Tim Heston
2135 Point Blvd
Elgin, IL 60123
815-381-1314
Tim Heston, The Fabricator's senior editor, has covered the metal fabrication industry since 1998, starting his career at the American Welding Society's Welding Journal. Since then he has covered the full range of metal fabrication processes, from stamping, bending, and cutting to grinding and polishing. He joined The Fabricator's staff in October 2007.
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The Fabricator is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The Fabricator has served the industry since 1970.
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