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newSchoolWorks.com › VoTechWorks › Transportation › Auto Body & Collision › Panel Repair and Replacement › Lesson 3
TRN-AUTO25-03 · Lesson 3 · 14.5 clock hours · lab

Stud Welding and Slide-Hammer Dent Pulling

Objective. Students will set up and operate a stud-welding dent-pulling system to extract panel damage from the outer surface without requiring backside access, then grind and clean studs to bare metal.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a certified examiner or master technician in the trade or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Stud Welding and Slide-Hammer Dent Pulling

Why This Method Matters

Many collision-damaged panels sit over closed cavities — door skins, quarter panels, and pillars — where reaching the backside to push the metal out is impossible without major disassembly. Stud-welding dent pulling solves this problem by attaching small steel studs directly to the outer surface of the damaged panel and then pulling the metal outward with a slide hammer or cross-bar puller. When done correctly, the technique moves metal precisely, reduces distortion, and leaves a surface that needs only minimal filler work.

How the System Works

A stud-welding gun (sometimes called a dent-puller gun or CD stud welder) uses a brief electrical arc — capacitor-discharge (CD) technology — to fuse a small steel stud to the panel surface in a fraction of a second. The weld is strong enough to transmit pulling force but shallow enough to avoid burn-through on thin automotive steel. After the stud is welded, you slide a slide hammer over it or clamp a cross-bar puller across several studs, then apply controlled outward force.

Ground connection placement is critical. The ground clamp must be attached to bare metal as close to the damage as practical — ideally within 12 inches. A poor ground causes weak welds, arc blow, or inconsistent stud attachment. If the panel has paint, you must clean a small spot to bare metal for the ground before beginning.

Setting Up the Stud Welder

Stud welders have adjustable heat (current) and, on some units, timing settings. Automotive outer panels are typically 18-gauge (approximately 1.2 mm) or 20-gauge (approximately 0.9 mm) steel. Thinner metal requires lower heat to prevent burn-through. Always consult the equipment manufacturer's chart before dialing in settings. A test weld on a scrap piece of the same gauge confirms the setup: a properly welded stud requires firm effort to snap off; a cold weld breaks at the base with almost no force; a hot weld burns through or leaves a crater.

Stud Placement Patterns

The placement pattern you choose controls how force is distributed across the damage:

Document every stud location in your lab log by sketching the panel, numbering each stud, and recording the pull sequence and result. This log is a required deliverable.

Pulling Technique

With a slide hammer, thread the hammer onto the stud, brace your non-dominant hand against the panel edge (never in the pull path), and deliver short, controlled strokes — not one violent yank. Watch for the metal to yield gradually. Over-pulling creates a high spot that is harder to correct than the original dent.

With a cross-bar puller, the bar spreads force across multiple studs simultaneously. This is preferred for wide, shallow damage. Hook the bar, apply steady tension by turning the central screw or using a ratchet, and stop frequently to re-assess the profile.

After Pulling: Stud Removal and Surface Prep

Once the dent is pulled to the desired level, each stud must be removed and the weld nugget ground flush:

1. Snap or twist the stud shank off by rocking it side to side.

2. Grind the remaining weld nugget flush using a die grinder fitted with a grinding stone. Keep the grinder moving to avoid creating a low or high spot. Do not use the die grinder like a file — feather across the weld in overlapping passes.

3. Follow with an angle grinder and flap disc if the panel needs broader leveling, but exercise caution on thin gauge steel.

4. Clean the area thoroughly with wax-and-grease remover and a tack cloth to remove grinding debris and any residual contaminants.

5. Apply guide coat (a thin, contrasting-color spray or powder) over the worked area. Block-sand lightly with a straight block. High and low spots will be revealed by where the guide coat remains or disappears. A properly repaired surface shows even guide-coat removal with no isolated dark spots.

The target final profile is within 1.5 mm of flat across the repaired area.

Safety Requirements

Stud welding produces UV arc flash, spatter, and heat. Wear a face shield (not safety glasses alone) whenever operating the stud gun. A leather apron protects against spatter burns. Gloves are required during grinding and welding operations. Grinding generates metal particles — keep bystanders clear and wear the face shield during all grinder use. Ensure adequate ventilation; do not operate in enclosed spaces without airflow. Inspect the stud gun power cable and connections before each use. If the equipment has any damaged insulation, tag it out and notify the instructor immediately.

Before connecting or adjusting the stud welder, verify the power switch is off. Never point the stud gun at anyone. Keep flammable materials away from the work area.

Key terms8

Capacitor-discharge (CD) stud welderA welding tool that releases a rapid burst of stored electrical energy to fuse a small steel stud to a panel surface in milliseconds, minimizing heat input and reducing the risk of burn-through on thin automotive steel.
Stud placement patternThe planned arrangement of welded studs across a dent area, chosen to distribute pulling force correctly for the shape of the damage — perimeter-to-center for wide dents, linear series for creases.
Slide hammerA hand tool with a weighted mass that slides along a shaft; threaded onto a welded stud, it delivers repeated outward impact force to pull dented metal back toward its original contour.
Cross-bar pullerA dent-pulling attachment that spans multiple studs and applies a broad, even pulling force across a wider area, preferred for shallow, large-diameter dents to avoid over-pulling a single point.
Ground connectionThe electrical return path for the stud welder, clamped to bare metal close to the damage; a poor or distant ground produces weak or inconsistent stud welds.
Guide coatA thin layer of contrasting-color spray or powder applied over a repaired surface and then lightly sanded to reveal high and low spots by showing where the coating is removed unevenly.
Weld nuggetThe small fused metal deposit left on the panel after a stud is snapped off; it must be ground flush with a die grinder to restore the panel surface before finishing.
Burn-throughA hole or severe crater melted into a panel when heat input from welding or grinding is excessive relative to the metal's thickness; it requires patch welding to repair and should be avoided by correct equipment settings.

Worked examples4

1. A shallow wide dent measures approximately 150 mm across and is centered on a door skin. You plan to place studs in three concentric rings — an outer ring of 8 studs, a middle ring of 5 studs, and a center group of 2 studs. In what order should you pull, and how many total pulls will you make?
  1. Identify the total stud count: 8 (outer) + 5 (middle) + 2 (center) = 15 studs, so 15 total pulls.
  2. For a wide shallow dent, pull the outer ring first to release tension at the perimeter and prevent locking the center low.
  3. Pull the middle ring second, working around the ring in sequence rather than pulling opposite studs alternately (which can cause waviness).
  4. Pull the two center studs last, using short strokes to avoid over-pulling.
Answer: 15 total pulls; sequence is outer ring first (8 pulls), middle ring second (5 pulls), center group last (2 pulls).
2. Your stud welder chart shows that 18-gauge steel (approximately 1.2 mm) requires a heat setting of 6 on a 1-to-10 scale, and 20-gauge steel (approximately 0.9 mm) requires a setting of 4. You are working on a panel stamped '20 GA.' What setting do you use, and why would using a setting of 6 be a problem?
  1. Read the panel specification: 20-gauge = approximately 0.9 mm, thinner than 18-gauge.
  2. Select the setting appropriate for 20-gauge: setting 4.
  3. At setting 6 (intended for thicker 18-gauge metal), the extra heat on 0.9 mm steel risks burn-through — creating a hole — and can distort the surrounding panel.
Answer: Use setting 4. Setting 6 would deliver excessive heat to the thinner 20-gauge panel, risking burn-through and added distortion.
3. After pulling and grinding stud remnants on a repair area, you apply guide coat and block-sand lightly. The guide coat is completely removed in a 40 mm circle at one location but remains fully intact in a 25 mm oval nearby. What do these two results tell you, and what is the corrective action for each?
  1. Where guide coat is fully removed in a circle, the metal is higher than the surrounding surface — a high spot. Corrective action: carefully work the high spot down using a body hammer and dolly or a planishing tool, then re-check with guide coat.
  2. Where guide coat remains intact in an oval, the metal is lower than the surrounding surface — a low spot. Corrective action: apply a thin coat of body filler or, if the low is small and shallow, re-pull or massage the metal upward, then re-check with guide coat.
  3. Re-apply guide coat and repeat the block-sand check after each correction until guide coat removes evenly across the entire repaired area.
Answer: The bare circle is a high spot (needs to be brought down); the intact oval is a low spot (needs to be built up or re-pulled). Each must be corrected and re-verified with guide coat until the profile is within 1.5 mm of flat.
4. A dent measures 3.8 mm deep at its lowest point before pulling. After the first pull sequence, a guide coat check shows the remaining low is 2.1 mm. After a second pull sequence it is 0.8 mm. Is the 0.8 mm result within the acceptance standard for this lab, and how much depth was removed by each pull sequence?
  1. First pull sequence removed: 3.8 mm − 2.1 mm = 1.7 mm of depth.
  2. Second pull sequence removed: 2.1 mm − 0.8 mm = 1.3 mm of depth.
  3. Compare the final measurement (0.8 mm) to the acceptance standard (within 1.5 mm of flat).
  4. 0.8 mm is less than 1.5 mm, so the result meets the standard.
Answer: First sequence removed 1.7 mm; second removed 1.3 mm. The final 0.8 mm remaining low is within the 1.5 mm acceptance standard — the repair passes.
In class: Instructor setup demo: ground connection placement, stud gun settings for steel gauge, single-pull and multi-stud serpentine sequence technique on a door skin. · Students pull a minimum of three distinct dent scenarios (shallow wide dent, sharp crease, edge ding) on practice panels, documenting stud placement pattern and pull sequence in a lab log. · After pulling, students grind stud remnants flush using a die grinder with a grinding stone, then clean with wax-and-grease remover and inspect with guide coat to verify final profile.
Materials: Stud-welding dent-pull kit, slide hammer, cross-bar puller, die grinder, grinding stones, wax-and-grease remover, tack cloths, guide-coat spray, 20-gauge and 18-gauge steel practice panels, angle grinder with flap disc, PPE: face shield, gloves, leather apron
Check: Lab log completed for all three pulls; final panel profile within 1.5 mm of flat confirmed by guide coat; no burn-through or added distortion; PPE worn throughout — observed by instructor.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

I-CAR ProLevel — Non-Structural Panel Repair
1. When using a stud-welding dent-pull system on a closed door skin, why is proper ground clamp placement critical?
I-CAR ProLevel — Non-Structural Panel Repair
2. For a wide, shallow dent, in what order should stud pulls be executed?
ASE B2 — Panel Repair and Replacement
3. A technician is preparing to stud-weld on a 20-gauge steel panel. Compared to an 18-gauge panel, the correct heat setting should be:
ASE B2 — Panel Repair and Replacement
4. After snapping off stud shanks, which tool and abrasive combination is most appropriate for grinding the weld nuggets flush with the panel surface?
I-CAR ProLevel — Non-Structural Panel Repair
5. Guide coat is applied to a repaired panel and lightly block-sanded. An oval area retains full guide coat while the surrounding panel shows even removal. This indicates:
I-CAR ProLevel — Workplace Safety
6. Which PPE item is specifically required when operating a stud welder because of the UV arc flash it produces?
I-CAR ProLevel — Non-Structural Panel Repair
7. A cross-bar puller is preferred over a single slide hammer for which type of damage?
I-CAR ProLevel — Workplace Safety
8. During a lab inspection, a student's stud gun power cable shows a section of cracked and missing insulation. The correct immediate action is to:
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