Sheet Metal Work and Body Panel Fabrication
Sheet Metal Work and Body Panel Fabrication
This domain covers metal properties, forming, cutting, flanging, patch fabrication and corrosion protection. Exam items often ask which process preserves strength or prevents future rust.
Core rules
- Low-carbon steel is formable; high-strength steel (HSS) and ultra-high-strength steel resist forming and need controlled heat or cold repair methods.
- Sheet gauge numbers work in reverse: a smaller gauge number is thicker metal.
- Stretching thins metal and creates a crown; shrinking thickens it and removes excess. Plan hammer blows so the panel returns to shape without overstretching.
- Cut clean edges, deburr, and fit patch butt joints with minimal gap. Flanged lap joints are faster but trap moisture unless sealed.
- Clean bare steel immediately and apply weld-through primer at welded joints. Protect the backside with cavity wax or seam sealer.
- Aluminium requires dedicated tools and isolation from steel to prevent galvanic corrosion.
Worked example
A lower quarter panel is perforated by rust. Reasoning: cut back to sound metal, make a patch from the same gauge and material, butt-fit it with a 1 mm gap, tack weld in sequence to control distortion, planish the weld, then apply epoxy primer, seam sealer and cavity wax. A lap patch over rust would trap moisture and fail again.
Traps
Welding rusty metal; overheating HSS; leaving weld scale under primer; mixing aluminium and steel tools; forgetting the backside of a repair.
Key points
Smaller gauge numbers mean thicker sheet. HSS needs controlled repair to preserve strength. Butt joints with minimal gap reduce distortion. Weld-through primer and cavity wax protect hidden surfaces. Aluminium needs separate tools to avoid galvanic corrosion.