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.
^ 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

^ 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.
^ 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.
^ 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.

^ 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.

Safety measures

^ The electronic control modules (ECM) fitted to vehicles make it advisable to follow suitable precautions prior to carrying out welding repair operations. Harsh conditions of heat and vibration may be generated during these operations which could cause damage to the modules. In particular, it is essential to follow the appropriate precautions when disconnecting or removing the airbag RCM.
^ Do not allow electronic modules or lines to come into contact with the ground connection or the welding electrode.
^ Seat belt anchorages are a safety critical. When making repairs in these areas, it is essential to follow design specifications. Note that extra strength low alloy steel may be used for seat belt anchorages. Where possible, the original production assembly should be used, complete with its seat belt anchorages, or the cut line should be so arranged that the original seat belt anchorage is not disturbed.
^ All welds within 250mm (9.842) of seat belt anchorages must be carefully checked for weld quality, including spacing of spot welds.
^ Remove the battery before carrying out welding work in its vicinity.
^ Utmost care must be taken when welding near the fuel tank or other components that contain fuel. If the tank filler neck or a fuel line must be detached to allow access for welding work, then the fuel tank must be drained and removed.
^ Never weld, on components of a filled air conditioning system. The same applies if there is a risk of the air conditioning system heating up.
^ Connect the ground connection of the electrical welder directly to the part that is to be welded. Ensure that there are no electrically insulating parts between the ground connection and the welding point.
^ Adjacent vehicle parts and adjacent vehicles must be shielded against flying sparks and heat.