Stud Welding

Record it: attach a fastener to a plate without drilling through it. Sketch a ship's deck and mark why a hole is unacceptable.

Measure a steel round bar offcut standing in for the stud. Calculate its area, πr², in square millimetres.

Mild steel yields around 250 N/mm². Multiply by your area to predict the force the stud itself could carry. Record the prediction.

A 10 mm stud is welded in roughly 0.5 s at about 1000 A. Multiply out the energy at 25 V and note how small the total is.

A manual fillet of the same size takes several seconds. Write down the ratio — stud welding is fast because the arc is short, not because it is hot.

Use the battery spot welder to attach a strip to a coupon. This stands in for the stud weld: a short, machine-timed, single-shot joint.

Clamp and pull with the force meter until failure. Record the peak force and compare it with your step 3 prediction, scaled for area.

Record the rule from industrial practice: a sound stud weld bends the stud rather than breaking the joint. The joint is meant to be stronger than the fastener.

Clamp a round bar in the vice and bend it 30 degrees. The bend is the acceptance test used on real stud welds — the joint must survive it.

Draw the ring that surrounds the stud during welding. It contains the pool, shapes the collar of expelled metal and shields the arc from air.

Measure the collar of any welded joint you have available. That ring of expelled metal is the visible evidence that the whole face fused, not just the rim.

Record them: lift (arc gap), time, and plunge. Every stud weld is those three numbers, exactly as a spot weld is current, time and force.

Short does not mean harmless. A stud weld lasts a fraction of a second and delivers hundreds or thousands of amperes while it does. The flash is bright enough to cause arc eye from a single cycle, and because it is over before you can look away, protection has to be on before the trigger, not after the first one surprises you.

The stud is a projectile if the weld fails. A misfire can eject the stud from the gun. Never point a stud gun at anyone, including yourself, and keep the ferrule seated.

In this blueprint the spot welder and the vice are the hazards. Expelled molten metal from the spot weld, and a bar under bending load in a vice that can spring when it releases. Glasses on, and keep your face out of the plane of the bend.

US 2,191,494, “Stud welder”, Edward F. Nelson, filed 5 July 1938, granted 27 February 1940. Nelson worked at the New York Navy Yard, and the process was developed to solve a naval problem: fastening wooden decking, cable runs and equipment to steel decks and bulkheads without drilling holes that would have to be sealed and would weaken the plate.

The mechanism is a controlled retreat. The gun presses the stud onto the plate, then lifts it by a fraction of a millimetre to strike an arc across the gap. Both the stud's end face and a matching disc of the plate melt. A spring then plunges the stud into the pool, which freezes almost instantly because the surrounding cold steel is an enormous heat sink. Total elapsed time is measured in milliseconds — and the whole cross-section is fused, which is why the joint outlives the stud.

Two families came out of it. Drawn-arc stud welding, the patent's own method, uses a ceramic ferrule and suits studs from about 3 to 25 mm. Capacitor-discharge stud welding, developed later, dumps a charged capacitor bank through a small ignition tip in one to three milliseconds — so fast that the far side of a thin sheet shows no mark at all. That is how a stainless appliance panel gets its internal mounting studs without any visible blemish on the show face.

Where it ended up. Structural steel shear studs on composite floor decks, insulation pins in ductwork, fixing studs in car bodies, and the mounting bosses inside almost every metal appliance you own. It is one of the most-used welding processes in the world and one of the least-noticed, precisely because a good stud weld looks like nothing happened.