Welding, Brazing and Panel Bonding
Processes
MIG/MAG welding is the main process for steel body panels; TIG for aluminium and thin steel; resistance spot welding for factory-style joints; oxy-acetylene for brazing and heat. Brazing filler melts above 450 °C but below the parent metal; soldering melts below 450 °C. Structural adhesives bond and seal, often combined with rivets or spot welds.
Rules
- Follow OEM weld locations, count and type. Plug welds replace factory spot welds; stitch welds control distortion.
- Apply weld-through primer to mating flanges before closing them.
- Clean galvanised and coated steel in the weld zone and use fume extraction.
- Clamp and cool; backstep to reduce heat input, and planish welds before grinding.
- Restore corrosion protection: primer, seam sealer, cavity wax.
- Keep a fire watch and an extinguisher; screens protect glass and trim.
Worked example
Replacing a rear quarter panel: prepare the flanges, apply weld-through primer, bond with structural adhesive and add plug welds at OEM positions, then seam seal and wax the cavity. Reasoning: the adhesive spreads load and seals, while the welds provide the specified structural connection. Skipping the primer creates a rust line within months.
Traps
- Brazing a structural joint that the OEM specifies as welded.
- Welding galvanised steel without cleaning and extraction, causing metal fume fever.
- Grinding structural welds flush and thinning them.
- Leaving bare steel inside a closed flange.