In 1939, Ted Nelson, founder of Nelson Stud Welding Inc., worked at the Mare Island naval shipyard that built naval vessels. Frustrated at how long it took to weld the required steel bolts onto the steel plate, Nelson developed a technology whereby the operator could instantaneously weld the bolt without having to weld around its circumference. The resulting weld was stronger than welds produced by other arc welding processes.
“Ted Nelson ended up receiving a citation because he saved millions of man hours during the war,” says Douglas Phillips, director of product management, equipment, Nelson Stud Welding Inc.
Today, Nelson Stud Welding is a global manufacturer of stud fasteners and welding equipment with headquarters in Elyria, Ohio, and manufacturing sites in Germany and China. It has customers in multiple industries, including industrial, automotive, construction, military and nuclear.
About the stud
Similar to MIG welding, stud welding is an arc welding process in which the stud, or fastener, is joined to a base metal. The studs are typically threaded or unthreaded bolts or similar-shaped parts. The whole process is completed in milliseconds.
“That’s why they call it split second fastening,” Phillips says.
The two general types of stud welding are drawn arc stud welding and capacitor discharge (CD) stud welding.
With drawn arc stud welding, the operator uses a weld tool, or gun, to place the stud against the base metal. When triggered, an electric solenoid in the gun lifts the stud to a pre-set height off the base metal. The drawn arc melts the base of the stud and the base metal, creating a molten pool. The gun then forces the stud down into the molten pool and the molten material is held in place with a ceramic ferrule until the weld is formed.
Drawn arc stud welding typically welds studs from 1/4 in. up to 1 in. dia. Material must be 1/8 in. or thicker.
For CD stud welding, capacitors are charged to a predetermined setting on the power supply. When triggered, the stored energy is discharged and the burst of electricity creates the molten pool. The gun pushes the stud down into the molten pool. CD studs have a special tip on the end that is consumed during the weld.
With its low heat generation, CD stud welding is used for very thin sheet metal and coated materials and typically welds studs up to 3/8 in. dia.
Short-cycle stud welding is similar to drawn arc stud welding, but happens over a shorter time period of 20 ms to 30 ms. It is also for thin sheet metal and is used almost exclusively in industrial and automotive applications. It is typically used for small-diameter studs less than 1/2 in.
Nelson also offers gas arc stud welding, which is used for more exotic materials, such as aluminum. Studs are typically up to around 1/2 in. dia.
Stud welding is fast, reliable and accurate. The resulting weld is stronger than the surrounding base metal or the stud. The area around the stud is flat and clean, and because welds can be achieved on only one side, the reverse side is not damaged. One-sided stud welding also means greater design versatility.
Fewer manufacturing steps are required because there is no through-hole preparation. No through hole also means leak resistance, reduced corrosion problems and structural integrity of the workpiece.
To perform stud welding, all the operator has to do is position the stud into the gun, press the gun to the base metal and pull the trigger. A certified welder is not required.
However, another benefit of stud welding is in robotic applications, which is why stud welding has been used in the automotive industry for 50 years. Today, hundreds of studs are inside every vehicle that are used for grounding for the electrical system, routing wire harnesses and hanging trim, among other uses.
One of the bigger pushes in stud welding equipment over the last couple of years is that manufacturers are designing battery supplies into their welders.
“A lot of companies are taking advantage of the automotive industry’s revolutionary battery designs,” Phillips says. “This is opening up a whole new level of potential for industrial equipment. There is a big trickle-down factor for that battery design.”
Nelson has also developed the Arc Charger power source. This welder allows operators to plug into 120-V power supply to run the welder instead of the typical 3-phase, 480-V power supply or a larger generator.
“Mounting antennas on top of water towers or installing seating in stadiums are good examples,” Phillips says. “Any construction project or outdoor installation where there is no industrial power available would be good application for the Arc Charger.”
Tried and true
Along with these newer developments, stud welding has incorporated other technologies over the past 20 years.
“Stud welding has changed quite a bit since the beginning, especially over the last two decades,” Phillips says. “People are continually trying to reduce the size and weight of the equipment and make it more energy efficient.”
Inverter-type power supplies are high-frequency switching devices that allow very precise control of the weld arc and reduce the weight of the equipment dramatically. A typical transformer rectifier unit that weighs 500 lbs. would be about 80 lbs. as an inverter.
One of the main benefits of lighter weight equipment is portability. The lighter and easier it is to move the equipment around, the more attractive it is to users in construction and shipbuilding markets.
Another benefit of using an inverter is its energy efficiency and ability, therefore, to reduce electricity bills. On a transformer rectifier unit, the transformer has to charge up and create a magnetic field for it to transform the voltage and the current. It takes energy to create that magnetic field.
“Just by turning the welder on, you’re using up energy,” Phillips says. “Inverters only use energy while they are welding, and the idle currents are extremely low. You can save up to 30 to 40 percent a year using an inverter over a trans-rec unit.”
This energy savings comes in industrial applications where the equipment is consistently running for long periods.
Another benefit integrated into the equipment is the precise control of the weld arc. Process monitoring measures the weld current and arc voltage to verify that the welds are being made correctly. Inverter-based welding can sense changes, such as variation in input voltage, and can compensate for them on the fly. This ensures the process uses the correct current and time for the stud actually being welded.
Other design improvements over the years include making stud welding equipment safer. On modern equipment, users can take advantage of a series of interlocks that prevent accidental triggering.
Also, automated stud welding has implemented several new designs to safeguard both the equipment and operators. Safety Level D and Category 4 relays and safety circuits ensure that all motion and electrical energy in the welding process provide the maximum protection.
Another big change that occurred is the advent of servo-electric weld tools instead of solenoid and spring-driven tools, or weld guns.
Servo drives in stud welding have been around for about 10 to 15 years with the technology becoming refined over the past decade, according to Phillips.
“The high-tech products being developed are all servo-driven,” he says. “The advantage of the servo-electric drive is it allows you to program some of the movement parameters without making mechanical adjustments. Also, servo-electric means a closed-loop control system so it delivers the exact same motion and speed every time. This compensates for wear and tear in the motion of the device where the solenoid spring wears out and slows over time.”