Sheet metal work and straightening of bodywork

The bodywork is the car's skeleton and its shell at the same time. It carries load, protects passengers in a collision and gives the car its shape. When you straighten a damaged bodywork, you are therefore not only working with how the car looks, but also with how it behaves in the next crash.

Where older cars were built from ordinary steel plate, modern cars combine multiple materials: soft steel qualities for energy-absorbing zones, high-strength steel for the safety cabin and aluminium or plastic in selected parts. The choice of material determines how you may repair: some high-strength steels must not be heated or straightened but must be replaced according to the manufacturer's instructions.

With straightening the plate is brought back to its original shape. On accessible surfaces hammer and dolly are used where you strike from one side against the dolly on the other. On inaccessible dents pulling techniques are used where pins or discs are welded to the plate which are then pulled out. The goal is to restore the shape without stretching or weakening the plate more than necessary.

Important principles for direction

• 01Work from outside and in on a dent — from the edge toward the deepest point.
• 02Take a little at a time; it's easier to go further than to go back too much.
• 03Feel with your hand — the eye deceives, but fingertips find unevenness.
• 04Avoid unnecessary heat on high-strength steel that can lose its strength.
• 05Always follow the manufacturer's repair method for the specific material.

Damaged panels are often replaced by separating the factory's welds and installing new parts. MIG/MAG welding, resistance spot welding and bonding are used depending on material and placement. Correct joining is critical: a too weak joint in a load-bearing part weakens the entire structure while too much heat can deform the surrounding plates.

After straightening and replacement the form is checked against the unbroken side or against the manufacturer's dimensions. The fit of doors, bumpers, and lights shows whether the geometry is correct. Only when the metal is clean, flat, and in shape is it ready for primer preparation.