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newSchoolWorks.com › VoTechWorks › Transportation › Auto Body & Collision › Welding for Auto Body & Collision Repair › Lesson 12
TRN-AUTO25-04 · Lesson 12 · 30 clock hours · lab

Integrated Welding Practical: Structural Panel Section and Documentation

Objective. Students will plan and execute a complete sectioning and replacement weld on a door skin or quarter-panel section using correct MIG or resistance spot welding processes, producing a repair order and passing all quality checks without instructor prompting.

⚠ 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.

Integrated Welding Practical: Structural Panel Section and Documentation

This lab lesson is your capstone welding exercise. You will plan, execute, document, and defend a complete sectioning and weld repair on a door skin or quarter-panel without step-by-step instructor guidance. The goal is to work the way a professional collision technician works: consult the OEM procedure, make sound process decisions, and produce work that meets industry quality standards.

Why Documentation Comes First

Before you pick up a tool, you write a repair plan. The repair order (RO) is a legal and business document. It records what was damaged, what process you selected, what materials you used, and the labor operations performed. Insurers, shop owners, and—in some cases—courts rely on accurate ROs. Your plan must specify:

Photograph the damage before touching it. Every subsequent major step—cut line marked, pieces fit, tack welds placed, final welds ground—gets a photo and a dated log entry. This habit protects you professionally and is standard practice in production shops.

Process Selection: MIG vs. Resistance Spot Welding

MIG plug welding is the most common substitute for factory resistance spot welds when resistance spot welding (RSW) equipment cannot reach a joint or when the OEM procedure calls for it. You drill a hole (typically 8 mm) in the top layer, clamp the pieces tightly, and fill the hole with a weld nugget that fuses to the backing layer.

Resistance spot welding uses copper electrodes to pass high current through the stacked panels, creating a nugget without a hole. Modern inverter-based RSW equipment can replicate factory spot welds in accessible locations and is preferred by many OEMs on high-strength steel (HSS) and advanced high-strength steel (AHSS) because it adds less heat to the surrounding metal.

Always check the OEM repair procedure before choosing. Some OEMs prohibit MIG on certain AHSS components because excess heat changes the metallurgy and reduces crash performance. The procedure excerpt you receive in this lab will tell you what is allowed.

Sectioning Joint Location

A sectioning joint must fall in an area that:

1. The OEM approves (check the procedure).

2. Is away from high-stress areas such as bends, character lines, and factory welds where possible.

3. Allows full access for welding from both sides if a butt joint is used, or overlaps adequately if a lap joint is specified.

For a door skin, the cut is almost always made at the hemmed flange at the bottom and the spot-weld line at the door frame perimeter. For a quarter-panel, sectioning locations vary widely by vehicle; never assume—read the procedure.

Fit-Up and Tacking

Poor fit-up is the most common cause of weld failure and distortion. Use clamps, sheet-metal screws, or Vise-Grips to pull the panel tight before tacking. A gap larger than the thickness of the thinner panel is generally unacceptable for a butt joint. Check alignment against body reference points before committing to final welds.

Tack every 25–50 mm around the joint, then fill in sections to distribute heat and minimize warpage. Skip-welding (stitch welding in a pattern that avoids sequential adjacent passes) keeps the panel from overheating in one zone.

Grinding and Inspection

Grind welds flush with an angle grinder and flap disc. Do not grind through the base metal—the weld should be flush, not recessed. Use a straightedge or your fingertip across the ground area to confirm. A weld that is proud by 0.5 mm will telegraph through body filler and paint.

The I-CAR visual inspection checklist covers: no cracks, no porosity holes, full fusion at the weld face, consistent nugget size and spacing for plug or spot welds, and no burn-through on adjacent panels.

For pull or peel testing on spot or plug welds, a minimum of two welds per joint are tested. A passing plug or spot weld pulls material from the parent metal (button pull-out) rather than separating at the weld interface.

Corrosion Protection

Safety in This Lab

Defending Your Work

During the structured walkthrough, you will answer three questions about your process choices. Typical questions probe why you chose MIG over RSW (or vice versa), why you placed the joint where you did, and how you verified weld quality before the instructor inspected. Review your log and photos before the walkthrough—they are your evidence.

Key terms9

Sectioning jointThe location where a damaged panel is cut and a replacement section is welded in; must be placed according to OEM-approved locations away from high-stress areas.
MIG plug weldA weld made by filling a pre-drilled hole in the top layer of stacked panels with weld metal that fuses to the backing layer, used as a substitute for factory resistance spot welds.
Resistance spot welding (RSW)A welding process that uses copper electrodes to pass high electrical current through stacked panels, creating a fused nugget without added filler metal; preferred by many OEMs on high-strength steels.
Weld-through primerA zinc-rich primer applied to bare metal mating surfaces before assembly; it survives welding heat and provides corrosion protection in areas inaccessible after the joint is closed.
Button pull-outThe desirable result of a pull or peel test in which the weld nugget remains intact and tears material from the parent metal, indicating full fusion and adequate weld strength.
Advanced high-strength steel (AHSS)Steel grades engineered for high tensile strength and energy absorption in crash structures; require special welding procedures because excessive heat can alter their metallurgical properties and reduce crash performance.
Skip welding (stitch welding pattern)A welding sequence that alternates weld positions around a joint rather than running sequential adjacent passes, distributing heat to minimize panel distortion and warpage.
Repair order (RO)A written document recording the damage found, repair operations planned and performed, materials used, and labor involved; serves as the legal and business record of the repair.
I-CAR quality checklistA structured inspection form developed by the Inter-Industry Conference on Auto Collision Repair listing visual and mechanical criteria that a completed weld repair must meet to be considered acceptable.

Worked examples4

1. You are planning MIG plug welds to replace eight factory resistance spot welds on a quarter-panel lap joint. The OEM procedure specifies 25 mm center-to-center spacing. What diameter hole should you drill, and how many plug welds will you place?
  1. Step 1 – Hole size: Industry standard for a MIG plug weld hole is approximately 8 mm (5/16 in) diameter in the top sheet. Use a step drill or hole punch to produce a clean, round hole.
  2. Step 2 – Weld count: The OEM procedure specifies replacing the same number of welds that were removed. Eight factory spot welds were present, so you place eight plug welds.
  3. Step 3 – Spacing check: 8 welds × 25 mm spacing = 175 mm minimum joint length to accommodate all welds at the specified pitch. Confirm the available joint length on the panel is at least 175 mm; if so, the plan is feasible.
  4. Step 4 – Record: Enter hole diameter (8 mm), weld count (8), and spacing (25 mm) on the repair order before beginning.
Answer: Drill 8 mm holes; place 8 plug welds at 25 mm center-to-center spacing along the lap joint.
2. After grinding your plug welds flush, you measure the ground surface and find one spot that is 1.2 mm below the surrounding panel surface. Is this acceptable, and what should you do?
  1. Step 1 – Evaluate: A ground surface that is recessed below the parent metal means you have ground through part of the base metal or the weld is under-filled. Either condition is not acceptable for a structural or cosmetic repair.
  2. Step 2 – Assess the cause: Check whether the weld itself was under-filled (insufficient wire feed or travel speed too fast) or whether over-grinding created the recess.
  3. Step 3 – Corrective action: If the weld metal is still present but low, you can add a small additional weld pass to build up the area, then re-grind carefully to flush. If base metal has been ground away significantly, consult your instructor—the repair may need to be re-evaluated.
  4. Step 4 – Recheck: After correction, use a straightedge across the surface; it should contact the weld area without rocking, indicating the surface is flush or within an acceptable tolerance for body filler to address.
Answer: A 1.2 mm recess is not acceptable; add weld material to bring the area flush with the panel surface, then re-grind carefully and re-inspect.
3. Your MIG welder has a wire feed speed set to deliver proper penetration on 0.8 mm (20-gauge) door skin steel. The shop floor supervisor asks you to weld a 1.6 mm (16-gauge) structural bracket with the same settings. Should you adjust, and why?
  1. Step 1 – Recognize the thickness difference: 1.6 mm is twice the thickness of 0.8 mm sheet. The same wire feed speed and voltage that give good fusion on 0.8 mm will likely produce a cold, under-penetrated weld on 1.6 mm.
  2. Step 2 – Adjustment needed: Increase wire feed speed and/or voltage to match the thicker material. Consult the welder manufacturer's settings chart (usually on the inside door of the welder) for the correct parameters for 1.6 mm steel with your wire diameter.
  3. Step 3 – Test weld: Run a test bead on scrap of the same thickness and visually inspect for good tie-in at the toes, no undercut, and consistent bead width before welding the actual part.
  4. Step 4 – Document: Record the adjusted settings (wire feed speed, voltage) on the repair order or lab log so the settings can be reproduced or reviewed.
Answer: Yes—increase wire feed speed and voltage to match the 1.6 mm material; verify with a test weld on scrap before welding the actual bracket.
4. You need to apply weld-through primer to a 150 mm × 80 mm mating flange before assembling the quarter-panel section. The can label states the product must be applied in a thin, even coat and allowed to dry before welding. You have 15 minutes before your scheduled weld start. Is 15 minutes likely sufficient for dry time, and what is the consequence of welding over wet primer?
  1. Step 1 – Check the label: Drying times for weld-through primers vary by brand but are typically in the range of a few minutes for surface dry under normal shop conditions. Read the specific product label to confirm.
  2. Step 2 – Assess 15 minutes: In most cases, 15 minutes at normal shop temperature (around 70 °F / 21 °C) is adequate for surface dry on a thin coat, but confirm with the product data sheet.
  3. Step 3 – Consequence of welding over wet primer: Solvents trapped in wet primer will vaporize explosively during welding, causing porosity (gas pockets) in the weld nugget. Porosity weakens the weld and is a visual inspection failure.
  4. Step 4 – Best practice: Apply the primer as early in the fit-up process as possible, keep the coat thin, and confirm it is dry to the touch before clamping and welding.
Answer: Fifteen minutes is generally adequate for a thin coat under normal shop conditions, but verify with the product label; welding over wet primer causes porosity that weakens the weld and fails inspection.

The math in this lesson1

Learners multiply 8 plug welds by 25 mm spacing to check minimum joint length for the section.
6.RP.3
In class: Students receive a damaged panel assembly and an OEM repair procedure excerpt; they independently write a step-by-step repair plan including process selection, joint location, weld count, and corrosion protection, then review the plan with the instructor before beginning. · Students execute the full repair—cut, fit, weld, grind flush, inspect, and apply weld-through primer to bare metal areas—documenting each step with photographs and entries in the lab log. · Instructor conducts a structured walkthrough: student verbally defends process choices while instructor applies pull-test or visual inspection to the completed welds; student self-scores against the I-CAR quality checklist before the instructor scores independently.
Materials: Damaged panel assemblies (door skin or quarter-panel from salvage), MIG welders, resistance spot welder, plasma cutter, angle grinder, body saw, weld-through primer, full PPE, OEM repair procedure excerpt, repair order forms, digital camera or smartphone, I-CAR quality checklist, lab log forms
Check: Repair order complete with all required fields; all welds pass I-CAR visual inspection checklist; pull or peel test passes on a minimum of two spot or plug welds per joint; student correctly answers three verbal defense questions—all four criteria must be met to pass.

Practice check8

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

I-CAR ProLevel – Structural panel repair and sectioning
1. According to standard industry practice, where must a sectioning joint on a quarter-panel be located?
ASE B-Series – Welding and cutting (B2/B5)
2. A pull or peel test on a MIG plug weld produces a 'button pull-out.' What does this result indicate?
I-CAR ProLevel – Steel and materials
3. Why do some OEM procedures prohibit MIG welding on certain advanced high-strength steel (AHSS) structural components?
I-CAR ProLevel – Corrosion protection
4. Weld-through primer is applied to mating flanges before assembly primarily to:
ASE B-Series – Welding and cutting
5. A student grinds a completed plug weld and finds the surface is 1.2 mm below the surrounding panel. The BEST next step is to:
I-CAR ProLevel – Safety and shop practices
6. Which of the following PPE items is required when operating an angle grinder during panel repair?
ASE B-Series – Welding and cutting
7. Skip welding (alternating weld positions around a joint) is used during panel sectioning primarily to:
I-CAR ProLevel – Structural panel repair and sectioning
8. During the verbal defense walkthrough, the instructor asks why you chose resistance spot welding instead of MIG plug welding for a specific joint. The BEST answer is:
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