Heat-Treatment of Panels

Heat-treatment of panels

- It is usually inevitable that some parts of the body panels show excess material as a result of mechanical strain. If there are any areas of excess material this will cause localised instabilities due to differences in tension. These localised instabilities can be stabilised by applying heat-treatment techniques.

- NOTE: This does not apply to high-strength low alloy steel, ultra high strength steel and aluminium.

Rule: Flattening panels by heat-treatment reduces the amount of excess material by more than they were originally stretched.

Different heat-treatment techniques.

NOTE: Different heat-treatment techniques are used depending on the amount of excess material.

- Flattening using a flame.
- A welding torch is used if the material excess extends over a larger area (torch size 0.5 - 1.0 mm). Use a soft flame.
- The surface of the metal is briefly spot-heated and then immediately cooled with a wet sponge.
- Requirement: Ability to handle a welding torch safely and knowledge of annealing colours of steel.
- Advantage: No damage to the surface of the metal.
- Flattening using a flame, supported by hammer and counterhold.

- NOTE: The flattening effect is increased by speeding up the heating and cooling stages.

If the material excess is concentrated, then the flattening effect can be increased after heating by carefully using an aluminium or wooden hammer.

- Requirement: Ability to recognise material tension by feeling the surface that is to be flattened.
- Flattening using a carbon electrode.
- If panel areas are only accessible from one side, or the panel is only slightly destabilised, then the preferred method is flattening using a carbon electrode.
- Requirement: Bare metal surface.
- Disadvantage: Scarring and hardening of the surface.
- Flattening using a copper electrode.
- Small, sharp dents that face outwards can be worked on with a copper electrode.
- Flattening using a flame and body files.

- NOTE: When applied correctly, this method can be used with all the attached parts still in place (roof headlining, wiring harnesses etc.).

Small, soft dents (only slight stretching): Working at the edges of the dent in an inward spiral pattern, the dent is heated with an oxyacetylene torch (torch size 1 - 2 mm, excess gas flame) to approx. 250° C.

- Working rapidly with a body file extracts heat from the edge area until the dent is flattened. Preferably alternate between two files. This increases the amount of heat that can be extracted.