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Welding

Another way

By Gretchen Salois

Above: Suppliers to the auto industry are often required to resistance weld fasteners to high strength steel stampings.

Expertise, coupled with the right equipment setup, ensures strong projection weld results

April 2020 - Resistance welding, long viewed as a stepchild in the family of welding, is finally gaining the attention and respect it deserves by manufacturers of metal parts, says Tom Snow, chairman of T. J. Snow Co. Inc.

This is especially true in applications such as resistance projection welding of nuts and studs to the high-strength steel alloys now being used in the automotive industry to reduce weight.

Founded in 1905, The Ohio Nut & Bolt Co., Berea, Ohio, advises customers on resistance welded fasteners and produces a wide selection of styles, which include parts designed to be either spot welded or projection welded. Spot welding can be done successfully with a rocker arm-type resistance welder, whereas projection-welded nuts and studs are best attached with a vertical action press-type machine.

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By choosing the proper weld nut design and a large enough welder, it is possible to resistance projection weld threaded nuts to heavy gauge fabrications.

When it won business with customers in the transportation equipment industry, Metal Solutions Inc., based in Vandergrift, Pennsylvania, was required to projection weld various nuts and studs in both carbon and stainless steel, as well as perform standalone spot welding.

“Projection welding was a new venture for us as this was yet to be in our wheelhouse,” recalls Robert Geer, vice president of Metal Solutions. “I contacted Buckeye Fasteners after seeing their company name on one of the drawings.”

After speaking with Larry Kelly, business development manager at Buckeye Fasteners, Geer worked with Kelly and Ron Foreman to determine how to approach projection welding. “These folks did test samples, then began doing small production runs for us until we made the decision to purchase our own welder,” Geer says.

Buckeye Fasteners is the distribution arm of Ohio Nut & Bolt, which in turn is both a vendor and a customer of Chattanooga, Tennessee-based T. J Snow, which makes, services and consults on resistance welding machinery.

Both T. J. Snow and Ohio Nut & Bolt offer lab services to analyze the type and size of resistance welding machine that would work best. Successfully welding fasteners to high-strength steels requires close attention to three main variables of the process: current, weld time and forging force.

Traditional single-phase AC and the more modern three-phase Mid Frequency Direct Current (MFDC) machines are available for welding samples. In addition, several sizes of Capacitor Discharge (CD) resistance welding machines reside in T. J. Snow’s lab. CD resistance welding technology has many benefits, including a greatly reduced heat-affected zone.

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Resistance projection welding is an ideal way to attach fasteners to a sheet metal stamping with the proper nut design, electrodes and welding machine.

To avoid getting weld splatter in the threads of a projection-welded fastener, it’s important to select a welder with a high kilovolt-amperes (KVA) rating so that weld time (current flow) can be minimized. It’s also advisable to use the proper type of resistance welding electrodes.

Metal Solutions purchased a remanufactured 100 KVA press-type spot welder from T. J. Snow. Snow started with a heavy based older unit, stripped it down and upgraded it with new parts, added an Entron programmable controller that holds 40 weld schedules, and a Koolant Koolers water recirculator and chiller, according to Geer.

Geer performed his due diligence by requesting quotes from other welding machinery builders but “I liked the idea of a heavier remanufactured model,” he says.

Customized setup

Over the years, T. J. Snow has served as its customers’ welding engineer. “Resistance welding has often been considered a ‘black art’ and companies that did not have an expert on staff have produced automotive parts with weak welds,” which in turn will cause “expensive recalls,” Tom Snow says.

“Depending on the application, we’re able to determine the right fit,” says Jeff Morgan, applications engineer at T. J. Snow. “We recently sold a CD resistance welding machine to a Tier 1 customer welding fasteners to ultra-high-strength steel (over 1,400 Megapascals). To ensure we’ve picked the right setup, we welded samples of the materials the customer works with regularly.”

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Above: Projections of a weld nut. Below: A nut welding application performed by T. J. Snow Co. Inc.

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Foreman, resistance weld technician and weld department manager at Ohio Nut & Bolt, says, “T. J. Snow’s machinery and rebuilds are for all types of people, including those not familiar with the control unit of a resistance welder.”

Ohio Nut & Bolt also recommends different types of fasteners if needed for a customer’s application. Customers request help in understanding how to perform certain welding jobs to get the best result, Foreman says.

“Many times I can have the customer [film] the welding process and I see the problem watching the welding. I make suggestions to fix the weld and they start experiencing good welds. If I notice the welder is too large or too small for that application, I contact T. J. Snow for help. They respond quickly, which helps satisfy our customers.”

Ohio Nut & Bolt sells fasteners across at least 5,000 distinct customers each year. “We sell to a few larger tiered customers, but the majority of our customers are smaller specialty shops and job shops that work in the automotive industry,” Foreman says.

Those smaller shops rely on Foreman’s years of experience in recommending the best nut or stud for their applications. “A customer might want to use a stud with a ring projection, but if the fastener does not need to be air- or liquid-tight, it’s often better to choose a part with three sausage-shaped projections,” he says. “With multiple projections, they get a stronger bond rather than trying to weld all the way around the head with a ring projection.”

By using recommendations about the correct fastener size, shape and projection type, Ohio Nut’s customers are able to apply the technology to both thick and thin materials. And as more and more companies express interest in automating processes, special nut feeders are often added to the machines to speed up production.

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Metal Solutions operator welding nuts for a panel frame. It is important to use a vertical-action press-type welder instead of a rocker arm design.

Training and technology

Customers come to T. J. Snow for training as well as machinery. Josh Garmon oversees service and training, which he says have evolved over the last 10 to 15 years.

“Weld controls in particular have changed and we’ve had to adapt our [training] class to account for that, as well as for changing metallurgy,” Garmon says. “Our classes last one day and start with the basics. The goal of the seminar is to expose trainees to specific topics they’ll come across while on the job.”

Both T. J. Snow and Ohio Nut & Bolt belong to the Resistance Welding Manufacturing Alliance, a standing committee of the American Welding Society that promotes use of the process. The alliance has introduced a Certified Resistance Welding Technician designation, which is awarded to applicants who pass a subject matter exam.

Ohio Nut & Bolt’s Foreman underwent T. J. Snow’s training, which he found very practical for everyday activities. “For example, if you lower the pressure on the electrode tip, the instructor explains what will happen, and then you learn about the overall operation. You find out the different things you can do to avoid common problems,” Foreman says.

T. J. Snow’s instructors are themselves field service technicians who work at the plant level on a daily basis. “They know what you need to learn and leave out what will go over your head,” Garmon says. “Instead of just teaching theory, they often use war stories from service calls to illustrate a point.” FFJ

Sources

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