Stud welding fuses the entire end of a metal stud to a base metal in a fraction of a second by drawing an arc or dumping a capacitor charge through the joint. It is a one-shot fastening process: load a stud in the gun, press it against the work, pull the trigger, and you have a welded fastener with no drilling, tapping, or back-side access. The two methods you will shop for are drawn-arc, for heavier studs into structural plate, and capacitor-discharge (CD), for small studs onto thin or finished sheet.
This page explains how arc stud welding works, the difference between drawn-arc and CD, the equipment you actually need, the base metal limits for each method, and how AWS D1.1 and C5.4 define a sound stud weld. Note up front that the dent-pulling “stud welder” sold for auto body work is a different tool entirely: it tacks a small pin or pull-tab to a panel so you can yank a dent with a slide hammer, and it has nothing to do with the fastening process described here. Stud welding is hot work that produces arc flash, fume, and spatter, and the information below is general process guidance, not a substitute for the equipment manufacturer’s instructions or the governing code. Qualify and test to the applicable standard before any load-bearing work.
What Stud Welding Is
Stud welding (sometimes called arc stud welding, or by the AWS designation SW) attaches a fastener, a threaded stud, a headed shear connector, a pin, a standoff, or an insulation pin, to a base metal by fusing the whole contact end of the stud at once. There is no fillet around the stud and no separate filler rod. The stud itself is the consumable, and the joint is a full cross-section fusion weld between the stud base and the plate.
That full-section bond is why a welded stud is strong in tension and shear straight out of the gun. A properly welded 3/4 inch shear stud develops the strength of the stud shank, which is the whole point of using welded studs to make a steel beam act compositely with a concrete slab. The process is fast, repeatable, and leaves the back side of the plate unmarked when done within the right thickness range, so it shows up anywhere a fastener has to go onto one accessible side of a part.
You see stud welding in steel-frame construction (shear connectors on floor beams, which tie into the same composite-action detailing covered in column base plate welding), in shipbuilding and bridge work, on switchgear and electrical enclosures, on appliance and HVAC panels, and on stainless trim and architectural panels where a visible fastener head would be ugly.
How the Arc Forms the Weld
Both methods share the same basic idea: create a brief, intense heat source at the stud-to-plate interface, melt both faces, and bring them together so they solidify as one. They differ in how the arc is established and how long it burns.
Drawn-Arc Stud Welding
Drawn-arc is the heavier-duty method and the one used for structural studs. The sequence inside the gun is automatic once you pull the trigger:
- The gun presses the stud against the work, and a ceramic ferrule (a one-time ring that surrounds the stud base) sits against the plate.
- The gun energizes the circuit and lifts the stud a short distance off the plate, drawing an arc. This is the “drawn arc.”
- The arc burns for a set weld time, typically in the range of tenths of a second for larger studs, melting the stud end and forming a molten pool in the base metal.
- The gun plunges the stud down into the pool, the current cuts off, and the two molten faces solidify together.
- You snap the spent ferrule off, and a fillet of expelled metal rings the base of the stud.
The ferrule does real work. It concentrates the arc, contains the molten pool, shields it from air, and shapes the metal that gets pushed out into that ring fillet. For studs above about 5/16 inch, a shielding gas or a flux load in the stud tip is often added on top of the ferrule for cleaner welds. Drawn-arc handles studs from roughly 1/4 inch up through about 1-1/4 inch diameter, which is the range that covers headed shear connectors and structural attachments.
Because drawn-arc puts a real heat pulse into the plate, it needs base metal with enough thickness to take it. A long-standing rule of thumb keeps the plate at least one-third to one-fifth of the stud diameter so you neither burn through nor mark the back side. The manufacturer’s data for the specific stud and machine is the real authority on minimum thickness.
Capacitor-Discharge Stud Welding
CD is the thin-sheet, small-stud method, and it works on a different physical idea. Instead of drawing an arc over tenths of a second, a CD welder charges a capacitor bank and releases the whole charge through the joint in a few thousandths of a second.
The CD stud has a small pointed tip on its weld end. When the stud contacts the work and the charge fires, that tip vaporizes almost instantly, which ignites the arc. The full discharge then melts the mating faces and the spring-loaded gun drives the stud home, all inside a few milliseconds. There is no ferrule and no flux. The weld is so fast that very little heat soaks into the base metal.
That speed is the entire advantage. CD welds small studs, generally 1/4 inch and under, onto thin sheet without burning through and without leaving a heat mark, discoloration, or distortion on the back side. It is the method for stainless appliance panels, electrical enclosures, signage, and architectural sheet where the visible face has to stay clean. It is not the method for heavy structural studs, where you need the sustained energy of a drawn-arc weld.
There are two common CD variants: contact (or initial-gap) CD, where the stud rests on the work and fires, and gap CD, where the gun holds the stud slightly off the surface and accelerates it as the charge releases. Both finish in milliseconds.
| Drawn-Arc | Capacitor-Discharge (CD) | |
|---|---|---|
| How the arc starts | Stud lifts off plate to draw an arc | Tip on stud end vaporizes to ignite the arc |
| Weld time | Tenths of a second | A few thousandths of a second |
| Stud size range | Roughly 1/4 in to 1-1/4 in | Small studs, generally 1/4 in and under |
| Ferrule | Required (ceramic, one per weld) | None |
| Base metal thickness | Needs heavier plate (heat soaks in) | Works on thin and finished sheet |
| Back-side mark | Possible on thin material | Minimal to none |
| Typical use | Shear studs, structural, shipbuilding | Enclosures, appliance panels, trim |
Equipment You Need
A stud welding setup is built around the gun, the power source, and the consumable studs. The pieces differ between the two methods.
For drawn-arc, you need a stud welding power source sized for the largest stud you will run (these are high-current DC units, and the bigger the stud, the more current and the bigger the cables), a drawn-arc gun with the lift-and-plunge mechanism, a chuck and foot or leg assembly sized to the stud, the matching ceramic ferrules, and the studs themselves. Equipment from the established stud welding makers (Nelson Stud Welding and Image Industries among them) lists the current, time, and cable requirements per stud diameter, and you size the system to the studs you are placing rather than guessing.
For CD, the power source is smaller because the energy comes from a capacitor bank rather than sustained mains current, so CD units are lighter and draw far less from the wall during a weld. You need the CD gun, a charging supply, and CD-type studs with the ignition tip already formed on the weld end. CD studs are not interchangeable with drawn-arc studs: the tip geometry is part of how the weld initiates.
Across both methods the consumables matter as much as the machine. The studs are mill products with a defined base geometry, the ferrules are matched to the stud diameter and shape, and using the wrong ferrule or a damaged stud base gives you a bad weld. AWS C5.4, Recommended Practices for Stud Welding, is the reference that ties equipment, stud design, and technique together, and it is worth having on hand if you are setting up a stud welding operation.
Base Metals and What Welds Well
Carbon and low-alloy steel studs onto steel plate are the bread-and-butter combination and the easiest to weld. Stainless steel studs weld well by both methods, with CD being common for stainless because it keeps the heat-affected zone tiny and avoids discoloring a finished surface. Aluminum studs can be stud welded, but aluminum needs its own setup: drawn-arc aluminum stud welding typically runs with shielding gas, and the parameters differ from steel. As with any aluminum structural work, the governing standard there would be AWS D1.2, Structural Welding Code, Aluminum, rather than the steel code.
A few base-metal realities hold across the board:
- The base metal must be clean at the weld spot. Mill scale, paint, galvanizing, rust, and oil all interfere with a sound stud weld. Grind or clean to bright metal.
- Galvanized and coated base metal is weldable but adds variability and fume. The coating burns off in the arc, which can leave porosity, so test and adjust.
- Plate thickness sets the method. Thin or finished sheet pushes you to CD. Heavier plate where you want a full-strength structural stud points you to drawn-arc.
- Dissimilar combinations (a stud of one alloy onto a different base metal) need to be proven by test, not assumed.
When the visible face of a thin panel cannot show any sign of the weld, CD is the answer, the same logic that drives fastener choice in thin-gauge and finish work generally.
Code, Qualification, and Testing
For anything load-bearing, the weld is only as good as the qualification and inspection behind it. On structural steel, the governing document in the United States is AWS D1.1, Structural Welding Code, Steel, and stud welding lives in its own clause: Clause 9 (Stud Welding) in current D1.1 editions (D1.1:2020 and later), which was Clause 7 in pre-2020 editions. That clause covers the studs, the application qualification, the workmanship, and the testing.
The defining production check for stud welds is the bend test, and it is refreshingly direct. A welded stud is bent about 30 degrees off vertical, by striking it with a hammer or pushing it with a bending bar or pipe, and a sound weld bends without any cracking at the weld or in the heat-affected zone. A bad weld snaps off or cracks at the base. Because the bent stud is acceptable for use if it passes (you do not have to straighten it for many applications, and it can often be left bent or straightened per the code), the bend test is a usable production tool, not just a destructive coupon test.
AWS D1.1 also requires proving the setup before production. At the start of a shift, or when the operator, equipment, or setup changes, you weld test studs and bend-test them to confirm the procedure is producing sound welds before any studs go onto the actual structure. For visual acceptance, a good drawn-arc stud shows a full, uniform fillet of flash all the way around the base. A stud with flash missing on one side was welded with the gun off-axis or with the arc shielded unevenly, and it is suspect.
If you are placing shear studs or structural attachments and need to understand where these requirements sit in the broader code, the AWS D1.1 structural welding code guide lays out the clause structure and qualification framework that the stud welding clause plugs into. None of this is optional on a real structure: undocumented, untested stud welds have no place in load-bearing work, and the engineer of record or the inspection authority sets the actual acceptance criteria for your job.
Safety Notes
Stud welding is an arc process, so the standard welding hazards apply. The arc throws ultraviolet and infrared radiation, so eye and skin protection rated for the current is required even though the arc is brief. Drawn-arc welds at high current produce real arc flash and spatter, and the expelled flash around the ferrule is hot. CD welds are fast and lower-energy but still produce an arc and a flash, and the vaporized ignition tip puts metal fume into the air.
Treat it as hot work. Clear combustibles from the area, control fume with ventilation or extraction, and follow the same arc-welding personal protective equipment, electrical safety, and fume practices that govern any arc process, in line with OSHA 29 CFR 1910 Subpart Q (Welding, Cutting, and Brazing) and ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes. The high cable currents on a drawn-arc system make cable condition and connection integrity a real safety item, not a formality. Inspect leads, keep connections tight, and do not run a damaged gun or cable.
Common Stud Welding Problems
Stud snaps off in the bend test. The weld did not fuse fully. Causes include too little weld time or current for the stud size, a dirty or coated base metal, a short or weak arc from incorrect plunge, or a moisture-loaded ferrule. Clean to bright metal, reset parameters to the stud manufacturer’s data, and re-test.
Flash missing on one side of the stud base. The gun was held off perpendicular, or the ferrule was not seated flat against the plate. Hold the gun square to the surface and make sure the ferrule sits flush before firing.
Burn-through or back-side marking on thin sheet. Too much heat for the base metal thickness, which usually means drawn-arc was used where CD belonged, or the plate is below the minimum thickness for that stud. Switch to a CD setup for thin or finished sheet, or move to thicker base metal.
Porosity at the weld. Coating (galv, paint, plating) or contamination burning into the molten pool, or a wet ferrule. Clean the base metal and keep ceramic ferrules dry, since they absorb moisture and gas the weld if stored in damp conditions.
Inconsistent welds across a run. Worn or wrong-size chuck, sloppy stud-to-chuck contact, cable connections loosening under high current, or supply voltage sag. Tighten and inspect the consumable path from chuck to ground, and confirm the power source is not being starved.
For the wider process family this fastening method sits beside, the resistance and spot welding guide covers spot, seam, and projection welding, which join sheet metal through current, time, and pressure rather than a drawn or discharged arc.