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newSchoolWorks.com › VoTechWorks › Transportation › Auto Body & Collision › Externship / Worksite Placement › Lesson 2
TRN-AUTO25-08 · Lesson 2 · 120 clock hours · lab

Applied Collision Repair Tasks — Metal, Welding, and Structural Work

Objective. The student will complete assigned metal straightening, MIG/squeeze-type resistance welding, and bolt-on or structural panel replacement tasks on customer vehicles to the quality level accepted by the shop supervisor.

⚠ 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.

Applied Collision Repair Tasks — Metal, Welding, and Structural Work

During your externship you move from the classroom to the shop floor, where every repair decision affects a real customer's vehicle. The tasks in this phase — metal straightening, MIG and resistance welding, and structural panel replacement — are the core competencies tested by both the I-CAR ProLevel and ASE B-series credentials. Work carefully, log everything, and ask your journeyman supervisor before you are unsure, not after.

Dollying, Hammering, and Stud-Welding Dent Repair

Metal straightening begins with reading the damage. Walk around the panel and identify the high spots (stretched or rolled metal above the body line) and low spots (pushed-in areas). The goal is to move metal back toward its original shape without thinning or work-hardening it beyond recovery.

Hammer-on-dolly is used to raise a low spot: hold the dolly directly behind the low area and strike on top of the dolly contact point. The rebound energy raises the metal. Hammer-off-dolly is used to lower a high spot: position the dolly slightly away from the hammer strike so the surrounding metal is supported while the high point is tapped down. Alternate between techniques as the panel approaches alignment.

Stud welding (drawn arc stud welding) is the preferred method when the back side of a panel is inaccessible. Weld steel studs or pins to the low area, then use a slide hammer or pulling bar to draw the dent out incrementally. Remove studs by twisting with pliers after pulling, then file or grind flush. Wear a welding helmet rated for the arc, leather gloves, and flame-resistant clothing during any arc welding operation.

Log every vehicle by its Repair Order (RO) number, the task you performed, the time you spent, and your supervisor's initials before the end of the shift. An incomplete log entry cannot be verified and will not count toward your evaluation.

Replacing Bolt-On and Welded Structural Panels

Before cutting or drilling anything, look up the OEM body repair manual or the applicable I-CAR repair procedure for the exact year, make, and model. Repair procedures specify factory weld locations, weld types, metal grades (including high-strength steel or advanced high-strength steel), seam sealer locations, and anti-corrosion treatment requirements. Never guess at weld count or location on a structural component.

Bolt-on panels (hoods, doors, fenders) are removed by unbolting at the hinge or mounting points. Capture shim locations and note gap measurements before removal so the new panel can be aligned to the same fit.

Welded structural panels — quarter panel sections, uni-rails (front or rear frame rails on unitized bodies), rocker panels, and similar components — require sectioning or full replacement. The procedure typically follows these stages:

1. Establish the correct vehicle dimensions using a tram gauge or electronic measuring system before any cuts are made. Verify against OEM or industry dimension specifications.

2. Cut at OEM-approved sectioning locations only. Use a cut-off disc on an angle grinder; keep the cut straight and minimize heat.

3. Remove factory spot welds using a spot-weld drill bit or cutter. Count the factory welds and match that count with plug welds on the replacement panel.

4. Fit the new panel, re-measure, and clamp. Dimensions must be within the tolerance stated in the repair procedure before welding begins.

5. Perform plug welds (MIG) or squeeze-type resistance spot welds at the marked locations. Match the weld diameter and spacing to factory specifications.

6. Apply seam sealer per the OEM specification at all seams that were originally sealed. Allow proper cure time before priming.

7. Apply weld-through primer or cavity wax to enclosed sections as specified to restore corrosion protection.

MIG and Squeeze-Type Resistance Spot Welding

MIG (Metal Inert Gas) plug welding is the shop standard for replacing factory spot welds on steel panels. Use the wire diameter, shielding gas mixture, and voltage/wire-speed settings recommended for the metal thickness you are welding. On high-strength steel (HSS) or advanced high-strength steel (AHSS), follow OEM heat input guidance carefully — excessive heat destroys the engineered strength of these materials.

Squeeze-type resistance spot welding (STRSW) replicates factory spot welds most closely and is the preferred method when the OEM procedure specifies it and panel access allows. Set the machine's pressure, current, and weld time to match the combined metal thickness per the machine manufacturer and I-CAR guidelines.

Welding PPE is non-negotiable: auto-darkening welding helmet (appropriate shade for the process), leather welding gloves, flame-resistant jacket or sleeves, and safety glasses under the helmet. Remove or cover flammable materials in the work area. Keep a fire extinguisher within reach. Follow the shop's lockout/tagout procedures when setting up or servicing welding equipment.

Measuring Panel Fit

After welding, verify that gaps and flushness meet OEM body specifications before the supervisor approves the repair. Use a tram gauge for diagonal measurements across the opening, or an electronic measuring system if the shop has one. Both diagonal measurements should be equal within the OEM tolerance. Check door, deck lid, or hood gaps with a gap gauge or ruler for uniform spacing. Record your final measurements in the field log next to the RO number.

Field Log and Supervisor Evaluation

Your supervisor rates each completed task as Needs Assistance, Meets Standard, or Exceeds Standard on the employer skills checklist. You must receive Meets Standard or better on at least 80 percent of rated tasks in this externship phase to remain on track for a passing employer evaluation. If you receive a Needs Assistance rating, ask your supervisor for specific feedback the same day and request a re-evaluation opportunity on the next appropriate vehicle.

Key terms10

Hammer-on-dollyA metal-straightening technique where the dolly is held directly behind the low spot and the hammer strikes over the same point, using rebound to raise the metal.
Hammer-off-dollyA metal-straightening technique where the dolly supports the panel away from the hammer strike, allowing high spots to be knocked down while surrounding metal is braced.
Stud welding (drawn arc)A process that arc-welds a steel stud or pin to the surface of a panel so a slide hammer or pulling bar can draw out a dent from the accessible side.
Plug weldA MIG weld made through a drilled hole in the top layer of metal, fusing it to the layer beneath; used to replicate factory spot welds during panel replacement.
Squeeze-type resistance spot welding (STRSW)A welding process that uses clamping pressure and electrical current to fuse overlapping metal layers, closely replicating the OEM factory spot-weld.
SectioningReplacing only a portion of a structural panel by cutting at OEM-approved locations rather than removing the entire panel assembly.
Tram gaugeA measuring tool with two adjustable pointers on a bar used to compare diagonal or length dimensions across a vehicle opening or structural section.
Uni-railA front or rear frame rail that is integrated into the unitized (unibody) structure of the vehicle, providing primary crash-load management.
Seam sealerA flexible, adhesive compound applied to panel seams and lap joints to prevent moisture intrusion and corrosion after structural repairs.
Repair Order (RO) numberA shop-assigned identifying number for each customer vehicle job; used to track work performed, parts, labor, and technician accountability.

Worked examples4

1. You remove a factory spot-welded rear quarter panel section and count 28 factory spot welds along the sectioning joint. The OEM procedure says to match factory weld count. How many plug welds must you make on the replacement panel at that joint?
  1. Identify the required weld count from the OEM procedure: match factory count = 28 welds.
  2. Count the drilled plug-weld holes you have prepared in the replacement panel flange.
  3. Confirm: 28 holes prepared = 28 plug welds required.
  4. After welding, verify each hole is fully fused; a missed hole reduces weld count below the OEM specification.
Answer: 28 plug welds must be made at that joint to match the factory specification.
2. After fitting a replacement uni-rail, you take two diagonal tram-gauge measurements across the front structure. Measurement A (left-front to right-rear reference point) reads 43 1/4 inches. Measurement B (right-front to left-rear reference point) reads 43 9/16 inches. What is the difference, and is this within a typical ±3 mm (approximately 1/8 inch) OEM tolerance?
  1. Convert both measurements to a common fraction with denominator 16: Measurement A = 43 4/16 in; Measurement B = 43 9/16 in.
  2. Subtract: 43 9/16 − 43 4/16 = 5/16 inch difference.
  3. Convert 5/16 inch to millimeters: 5/16 × 25.4 = 7.9 mm.
  4. Compare to tolerance: 7.9 mm is greater than 3 mm.
  5. Conclusion: The structure is not within tolerance; additional pulling or adjustment is required before welding.
Answer: The difference is 5/16 inch (approximately 7.9 mm), which exceeds a ±3 mm tolerance. The rail position must be corrected before welding.
3. A door opening has an OEM specified uniform gap of 5 mm around the door perimeter. You measure the gap at four points: top = 5 mm, front = 4 mm, bottom = 6 mm, rear = 5 mm. Which points are outside a ±1 mm allowable variation from the 5 mm target, and by how much?
  1. Allowable range: 5 mm ± 1 mm = 4 mm to 6 mm.
  2. Top: 5 mm — within range.
  3. Front: 4 mm — at the lower limit (borderline acceptable at exactly 4 mm, but note for monitoring).
  4. Bottom: 6 mm — at the upper limit (borderline acceptable at exactly 6 mm, but note for monitoring).
  5. Rear: 5 mm — within range.
  6. Conclusion: No point exceeds ±1 mm from the 5 mm target; all four readings fall within the 4–6 mm allowable band. However, the 2 mm spread from front (4 mm) to bottom (6 mm) is at the maximum allowable variation and should be reported to the supervisor.
Answer: All four gap readings are within the ±1 mm tolerance (range: 4–6 mm), but the full 2 mm spread between the tightest and loosest points is at the limit and should be flagged to the supervisor for approval.
4. You are drilling out factory spot welds on a rocker panel flange. The flange has two layers of 0.8 mm steel. Your spot-weld cutter should not penetrate the second (inner) layer. What is the combined thickness of both layers, and why does knowing this matter when setting cutter depth?
  1. Calculate combined thickness: 0.8 mm + 0.8 mm = 1.6 mm total.
  2. The spot-weld cutter must cut through the first layer (0.8 mm) and into the weld nugget without going deeper than ~1.6 mm so the inner layer is not damaged.
  3. Set the cutter stop or control drilling pressure so penetration does not exceed the outer-layer thickness of 0.8 mm into the material.
  4. Damaging the inner (structural) layer creates additional repair work and may compromise the replacement flange fit.
Answer: Combined thickness is 1.6 mm. Knowing this allows you to limit cutter depth to the outer layer (~0.8 mm) so the inner structural layer is preserved and the replacement panel seats correctly.
In class: Under journeyman direction, perform dollying, hammering, and stud-welding dent repair on assigned panels; log each vehicle RO number, task performed, time spent, and supervisor initials in the field log at the end of each shift. · Replace at least one bolt-on or welded structural component (quarter panel section, uni-rail, or similar) following the OEM or I-CAR repair procedure for that vehicle; record the vehicle year/make/model and the reference procedure used. · Assist with or independently perform sectioning, plug-welding, and seam-sealing on a replacement panel; measure and verify panel fit using a tram gauge or electronic measuring system before the supervisor approves the repair.
Materials: Shop MIG welder and consumables, squeeze-type resistance spot welder, hammer-and-dolly set, stud welder, tram gauge or electronic measuring system, angle grinder with cut-off and flap discs, I-CAR repair procedures (vehicle-specific), OEM body repair manuals accessed via the shop's OEM information subscription, student field log
Check: Supervisor rates each completed task on the employer skills checklist (scale: Needs Assistance / Meets Standard / Exceeds Standard); student must receive Meets Standard or better on at least 80 percent of rated tasks in this phase to remain on track for a passing employer evaluation.

Practice check8

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

Non-Structural Analysis and Damage Repair (ASE B3 / I-CAR Metal)
1. When using the hammer-on-dolly technique, where is the dolly positioned relative to the hammer strike?
Structural Analysis and Damage Repair (ASE B4 / I-CAR Structural)
2. Before cutting a welded structural panel for sectioning, which action is most critical?
Welding and Cutting (I-CAR / ASE B4)
3. Which welding process most closely replicates OEM factory spot welds and is preferred when the repair procedure specifies it and access allows?
Structural Analysis and Damage Repair (ASE B4 / I-CAR Structural)
4. Why is it especially important to follow OEM heat input guidelines when welding advanced high-strength steel (AHSS)?
Painting and Refinishing / Structural Repair (ASE B2/B4 / I-CAR)
5. After MIG plug welding a replacement quarter panel, which step must be completed before priming to restore corrosion protection at enclosed seams?
Safety and Environmental Compliance (I-CAR / ASE General)
6. A student performing stud-weld dent repair must wear which minimum PPE during the arc-welding steps?
Structural Analysis and Damage Repair (ASE B4 / I-CAR Structural)
7. When counting spot welds to drill out on a factory flange, what determines how many plug welds the technician must make on the replacement panel at the same joint?
Workplace and Professional Skills (Externship Evaluation)
8. A student's employer skills checklist shows 15 rated tasks: 11 rated Meets Standard, 2 rated Exceeds Standard, and 2 rated Needs Assistance. What percentage of tasks received Meets Standard or better, and does this meet the 80 percent threshold?
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