Materials
Materials
This domain tests knowledge of the steels, aluminium, plastics and consumables used in light vehicle bodies and how each material changes repair method, welding and finishing.
Core rules
- Mild steel is formable and weldable; high-strength low-alloy (HSLA) and boron steels are used in safety cells and must not be heated or straightened outside the manufacturer's procedure because heat destroys their strength.
- Aluminium panels need separate tools, separate abrasives and dedicated MIG wire (5356 or 4043) to prevent galvanic corrosion when steel dust contaminates the surface.
- Galvanised and zinc-coated steel must be stripped back at weld zones; zinc fumes are toxic.
- Plastics are identified by ISO codes: PP, ABS, PA and PUR need different adhesives, and some need plastic welding.
- Laminated glass is used in windscreens; tempered glass in side and rear windows.
- Body filler, epoxy primer, etch primer and seam sealer are matched to the substrate.
Worked example
A boron-steel B-pillar is creased in a side impact. Reasoning: the panel is structural and heat-sensitive; it must be replaced at the factory seams using the OEM sectioning procedure, not heated and pulled. The repair plan changes from "panel beat" to "replace and weld", and the weld type and seam sealer are specified by the vehicle maker.
Traps
Heating AHSS to shrink a dent, using the same grinding disc on aluminium and steel, and applying etch primer where an epoxy primer is specified. Also, treating plastic bumpers as if they were steel.