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newSchoolWorks.com › VoTechWorks › Transportation › Auto Body & Collision › Frame Straightening and Structural Repair › Lesson 8
TRN-AUTO25-02 · Lesson 8 · 22 clock hours · lab

Structural Component Sectioning Procedures

Objective. Students will perform a structural rail section repair following OEM or I-CAR sectioning guidelines, including correct cut location, joint preparation, weld sequencing, and post-weld inspection.

⚠ 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.

Structural Component Sectioning: Why It Matters

When a collision damages a structural rail beyond straightening, the damaged section must be removed and replaced. This process is called sectioning. Done correctly, a sectioned rail restores the vehicle's original crash-energy management, geometry, and safety performance. Done incorrectly, it can create a point of weakness that fails in a future impact—or collapses before impact because the weld zone is brittle or poorly located.

Both I-CAR and original equipment manufacturers (OEMs) publish sectioning procedures specific to each vehicle and component. These documents specify exactly where cuts may and may not be made, what joint design to use, and the order in which welds are completed. Following these guidelines is not optional—it is the professional and ethical standard of care.

Finding the Correct Cut Location

Before picking up a cut-off wheel, consult the OEM repair manual or the applicable I-CAR sectioning guideline for the vehicle you are working on. The cut location is governed by three rules:

1. Avoid factory welds. Cutting through or immediately adjacent to a resistance spot weld or a factory MIG weld creates a heat-affected zone on top of an existing stress riser. Minimum clearance from any factory weld is specified in the procedure—commonly at least 25 mm (about 1 inch), but always defer to the published specification.

2. Avoid high-stress areas. Bends, kick-up zones, and areas near suspension mounting points concentrate stress. The procedure directs you to a relatively straight, flat section of rail where stress distribution is more uniform.

3. Match the replacement part. The service part is designed to be spliced at a specific location. Your cut on the vehicle must align with the corresponding end of the service part so joint fit-up is correct.

Mark your cut line with a paint marker or scribe, then call your instructor to verify the location before you cut. This step cannot be skipped.

Joint Design and Surface Preparation

The two most common joint types in rail sectioning are the butt joint with backing and the offset butt joint. The OEM or I-CAR procedure specifies which applies. Key preparation steps:

Weld Sequencing

Sequencing matters for two reasons: distortion control and structural integrity. The general rule is to tack-weld, check alignment, then complete welds in a balanced, alternating pattern rather than running one long bead all the way around.

For a typical sectioning procedure:

1. Place tack welds at four equally spaced points around the joint to hold alignment.

2. Measure alignment again with a straight edge or frame-measuring system. Adjust if necessary before committing to full welds.

3. Complete plug welds in the specified pattern, allowing each weld to cool briefly to prevent heat buildup that warps the metal.

4. Complete butt weld beads in segments, alternating sides when the joint is accessible from more than one side.

5. Do not weld continuously from one end to the other. Backstep or skip welding helps manage distortion.

Set the MIG welder to the manufacturer-recommended voltage and wire-feed speed for the gauge of steel you are welding. High-strength steel (HSS) and ultra-high-strength steel (UHSS) are common in modern rails. Do not use excessive heat. Overheating UHSS destroys its tensile properties and cannot be reversed by any shop process.

Post-Weld Inspection

After welding, the joint must pass both a visual and a dimensional inspection.

Visual: Each weld should show full fusion at the edges, a consistent profile with no undercut, and no porosity (pinholes). Grind only to the extent specified—over-grinding thins the metal.

Dimensional: Lay a straight edge along the rail. Check alignment at the joint in all planes. Use the shop's measuring system to confirm the rail is within the OEM's alignment tolerance. For most passenger vehicles this is ±2 mm from the datum specification. Record all measurements on the sectioning inspection form. The form is a quality-control record; fill it out completely and honestly.

Safety in the Sectioning Bay

Connecting to Your Credentials

I-CAR ProLevel assessments evaluate your ability to follow approved procedures, use correct techniques, and document your work—exactly what this lab practices. ASE B-series written exams test your knowledge of structural repair concepts, weld types, and inspection criteria. Both credentials reward technicians who understand why each step exists, not just how to perform it.

Key terms9

SectioningThe process of cutting out a damaged structural component section and replacing it with a new section joined at OEM- or I-CAR-specified locations, restoring structural integrity.
Weld-through primerA corrosion-inhibiting primer applied to metal surfaces before assembly that will be trapped inside a joint and inaccessible to conventional primer after welding.
Heat-affected zone (HAZ)The area of base metal surrounding a weld that has been altered in microstructure and strength by welding heat without actually melting.
High-strength steel (HSS) / Ultra-high-strength steel (UHSS)Steel grades used in modern vehicle structures whose elevated tensile strength depends on controlled manufacturing; excessive welding heat permanently degrades their properties.
Butt joint with backingA joint type in which two square-cut ends meet edge-to-edge and a strip of metal placed behind the joint supports the weld pool and ensures full penetration.
Plug weldA weld made through a drilled or punched hole in one layer of metal, fusing it to the layer beneath; used to replicate factory spot welds in sectioning procedures.
Weld sequencingThe specified order in which tack welds and full welds are placed to control heat distortion and maintain joint alignment throughout the welding process.
Sectioning inspection formA shop quality-control document on which the technician records cut location, weld placement, alignment measurements, and primer application to verify the repair meets specifications.
DatumA reference plane or point defined in the vehicle's dimension specifications from which all frame and structural measurements are taken to verify alignment.

Worked examples4

1. The OEM sectioning procedure states the cut must be at least 25 mm from the nearest factory spot weld. You measure and find the closest factory spot weld center is 38 mm from your proposed cut line. Is the cut location acceptable?
  1. Identify the minimum required clearance from the procedure: 25 mm from the factory weld center.
  2. Measure the actual distance from the proposed cut line to the nearest factory weld center: 38 mm.
  3. Compare: 38 mm ≥ 25 mm.
Answer: Yes. The proposed cut line is 38 mm from the factory weld, which exceeds the 25 mm minimum clearance. The location is acceptable, pending instructor verification.
2. After welding, you measure the rail with the shop's measuring system. The specification for the front rail at datum point A is 820 mm. Your measurement reads 817 mm. Is the repair within the ±2 mm tolerance?
  1. Determine the specification: 820 mm.
  2. Calculate the allowable range: 820 − 2 = 818 mm (minimum); 820 + 2 = 822 mm (maximum).
  3. Compare your measurement of 817 mm to the range 818–822 mm.
  4. 817 mm is less than 818 mm, placing it 1 mm outside the lower tolerance limit.
Answer: No. 817 mm is 3 mm below the specification of 820 mm, which exceeds the ±2 mm tolerance. The repair does not pass dimensional inspection and must be corrected before the vehicle is returned to service.
3. You need to drill plug-weld holes through 1.2 mm steel. The procedure calls for holes spaced every 40 mm along a 200 mm lap joint. How many plug-weld holes are required, and what is the total span they cover?
  1. Determine the joint length: 200 mm.
  2. Determine the spacing: one hole every 40 mm.
  3. Number of intervals = 200 ÷ 40 = 5 intervals.
  4. Number of holes = 5 intervals + 1 hole at the start = 6 holes (placed at 0, 40, 80, 120, 160, and 200 mm).
  5. Total span covered: from the first hole at 0 mm to the last at 200 mm = 200 mm, matching the joint length.
Answer: 6 plug-weld holes are required, placed at 0, 40, 80, 120, 160, and 200 mm, covering the full 200 mm lap joint.
4. Your scoring rubric awards 10 points each for: correct cut location, weld-through primer applied, weld placement in OEM zone, weld profile acceptable, and alignment within ±2 mm. You earn 10, 10, 10, 8, and 6 respectively. Did you pass the 80% threshold?
  1. Calculate total points possible: 5 categories × 10 points = 50 points.
  2. Calculate your total score: 10 + 10 + 10 + 8 + 6 = 44 points.
  3. Calculate your percentage: (44 ÷ 50) × 100 = 88%.
  4. Compare to pass mark: 88% ≥ 80%.
Answer: Yes. 44 out of 50 points equals 88%, which meets the 80% pass mark. However, the low scores in weld profile (8/10) and alignment (6/10) indicate areas requiring additional practice before professional-level work.

The math in this lesson1

Learners measure cut-line distance from factory spot welds in millimeters and check it against the 25 mm minimum.
N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Using OEM or I-CAR sectioning guidelines, mark the correct cut location on a rail section mockup, avoiding factory welds and high-stress areas, then have the instructor verify before cutting. · Prepare the mating surfaces, fit the replacement section, and complete the required plug welds and butt welds in the specified sequence using the shop's MIG welder, applying weld-through primer to lap surfaces before assembly. · Inspect the completed section for weld penetration, profile, and alignment using a straight edge and measuring system; record results on a sectioning inspection form.
Materials: Rail section mockups or scrap vehicle sections, MIG welder (set to manufacturer-recommended settings for substrate gauge), weld-through primer, grinder, cut-off wheel, straight edge, sectioning inspection form, OEM/I-CAR sectioning guidelines
Check: Sectioning inspection form reviewed by instructor; weld placement within OEM-specified zones, weld-through primer applied to all lap surfaces, alignment within ±2 mm; pass mark 80% on scored rubric

Practice check8

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

Structural repair procedures — I-CAR ProLevel / ASE B5
1. Why does an OEM sectioning procedure specify a minimum distance between the cut location and an existing factory spot weld?
Corrosion protection and materials — I-CAR ProLevel / ASE B5
2. Weld-through primer must be applied to lap joint surfaces before assembly primarily because:
Welding and joining — I-CAR ProLevel / ASE B5
3. Which of the following best describes the purpose of placing tack welds at four equally spaced points before completing a rail butt joint?
Structural materials — I-CAR ProLevel / ASE B5
4. A technician completes all welds on a rail section without consulting the OEM procedure and applies maximum heat to ensure full penetration on the ultra-high-strength steel rails. What is the most likely structural consequence?
Quality control and inspection — I-CAR ProLevel / ASE B5
5. After welding a rail section, you measure alignment and find one point is 2.5 mm outside the OEM datum specification. What is the correct next action?
Welding and joining — I-CAR ProLevel / ASE B5
6. A plug weld is intended to replicate which type of factory joining method?
Safety and PPE — I-CAR ProLevel / ASE B5
7. Which personal protective equipment is specifically required when using a cut-off wheel to make the rail section cut?
Structural repair procedures — I-CAR ProLevel / ASE B5
8. The OEM sectioning guideline for a specific vehicle calls for an offset butt joint rather than a simple straight butt joint. What is the primary structural advantage of the offset design?
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