Straightening is the finish operation for processing car body parts. Straightening is the last operation for processing car body parts. As it is finishing operation, it must be carried out carefully, which often takes a long time. Straightening is in eliminating surface irregularities to such an extent that its condition becomes almost the same as new. In the process of straightening, work hardening, which causes the sheet to harden.
Straightening have doing with hammer blows on the sheet, which is supported on the anvil. The anvil must have sufficient mass to absorb impact, and have a shape similar to the shape of the part to be straightened. It is important that working surface of the anvil must be smooth so as not to leave marks on the surface of the sheet.
When straightening, straightening hammers, also called trowels, and sledge hammers are used. Hammers are made of steel, and their strikers are hardened and polished. The thinning of the sheet caused by hammering occurs the faster the stronger the blows. The volume of the metal remains constant, its thinning is accompanied by elongation, which is prevented by the metal of the untreated areas. As a result of blocking this deformation, the surface of the sheet part bulges.
The best effect is achieved in the case of straightening with light frequent blows with low metal drawing, than when straightening with strong scattered blows that leave marks on the surface and strong metal drawing. If there is a fold on the part to be straightened, straightening begins with straightening this fold to the final shape, and then straightening the rest of the part.
Quality of the straightening
The quality of the straightening performed is assessed visually and by feeling the surface with the palm of the hand. Visually, convex or concave viewing surfaces are most easily controlled from an angle or from the side. Rulers are used to control flat surfaces.
When palpating, the slightest unevenness is felt with the palm of the hand. After straightening, the formation of two types of surface defects is possible:
- a depression forms on the convex section of a small sheet panel, which cannot be removed by extrusion;
- on a large area of the sheet panel, a bubble forms, which, when pressed on its convex side, moves laterally to one side of the sheet.
In this article you can familiarize yourself with the types of straightening.