Metal fabrication projects using welding processes inevitably experience at least some degree of welding distortion, which results from the expansion and contraction of the weld metal and base metal during the welding process. Prevention of excessive distortion is recommended. Welding distortions can threaten the structural integrity or aesthetic of your project. Depending on the type and size of the distortion and materials, different corrective techniques are available to fix weld distortion.
Types of Welding Distortion
The amount of residual stress and the degree of restraint used during the welding process impacts the amount and type of distortion. The root cause of welding distortion is high heat application. Several types of welding distortion are possible, and your project can experience more than one type simultaneously.
- Transverse shrinkage: Shrinkage results from contractions that run perpendicular to the weld. This type of distortion travels vertically through the cross-section of the weld and occurs parallel to the weld.
- Longitudinal shrinkage: This distortion results from forces parallel to the weld, and the shrinkage occurs perpendicular to the weld.
- Angular distortion: This deformation, a form of transverse shrinkage, tends to be the most frequently occurring. This occurs when stronger contractive forces on one side of the neutral axis causes bending of the material in that direction.
- Bowing and dishing: When the weld is not balanced along the neutral axis of the cross section, longitudinal shrinkage in the welds bends the section into a curved shape.
- Buckling: Frequently occurring in thin metal structures, buckling is time-consuming and difficult to correct.
Mechanical Corrective Techniques
Hammering and pressing are the primary mechanical corrections for weld distortion. Mechanical straightening involves using force, with a hammer, wedge, pneumatic ram, machine press or similar instrument, to push the distorted area flat.
Thermal Corrective Techniques
With thermal correction, heat creates local stress that is sufficiently high enough that the component is pulled back into shape upon cooling. This technique, also known as flame straightening, is applied with the following methods:
- Spot heating: This technique removes buckling in thin sheet structures. Distortion is corrected by applying heat to spots on the convex side. Many small spots are substantially more effective than only a few large ones.
- Line heating: Heating the component in a straight line along the welded joint on the opposite side to the weld often corrects angular distortion.
- Wedge-shaped heating: Wedge shapes are heated to correct distortion in larger complex fabrications.