What is welding distortion?
Welding distortion is defined as the change in shape of metal that occurs due to non uniform expansion and contraction of the weld due to the heating and cooling cycle of the welding process.
When metal is heated, it expands. And similarly when the metal is cooled, it contracts.
If the expansion of metal is resisted, then its deformation takes place. And if the contraction is resisted, then stress is developed.
Hence in simple words, welding distortion is nothing but the change in shape of the metal piece due to resistance in thermal expansion or contraction of the metal.
Types of welding distortion
There are basically 3 types of welding distortions observed in the welded joints.
- Longitudinal distortion
- Transverse distortion
- Angular distortion
Let’s discuss these welding distortions one by one in detail.
#1) Longitudinal distortion
The longitudinal distortion is a type of welding distortion that occurs parallel to the weld line.
When the weld is deposited on a flat metal strip which is not clamped, the metal strip will tend to bend slightly upward (see image).
The bend of the metal strip occurs in the direction of the weld bead.
On what factors does longitudinal distortion depend?
Longitudinal distortion depends on the following factors.
- Contraction forces
- Distance between centroids of weld and section
- Stiffness of section being welded
#2) Transverse distortion
The transverse weld distortion is a distortion which occurs in the direction perpendicular to the weld line.
When the two metal plates are butt welded, the contraction of weld takes place which moves the metal plates towards each other (see above image).
This type of contraction is also called transverse contraction.
How to prevent transverse distortion?
The transverse welding distortion can be prevented by following ways.
- Metal pieces should be fitted properly in vice or other work holding devices.
- Placing wedge between the two plates.
- By increasing the arc travel speed.
#3) Angular distortion
In welding, the angular distortion generally occurs in butt welding.
When the two bevelled metal plates are welded, the plates tend to move outward from the original position.
In order to avoid the angular distortion, the double groove weldings are preferred.
How to control welding distortion (10 methods)
There are various methods to control the welding distortion.
Here I have listed 10 things that you can do to control the welding distortion.
- Use only the recommended amount of weld deposition that can reduce the contraction force.
- Use less number of weld passes to get the desired weld.
- Place the weld near the neutral axis.
- Balance the weld near the neutral axis.
- Use the back step welding method.
- Balance the shrinkage force with the opposing force.
- Follow the recommended welding sequence.
- Removal of shrinkage force during or after the welding operation.
- Reduce the welding time (or increases the arc travel speed).
- Use jigs and fixtures to hold the metal pieces.