Welding distortion happens when welded metal shrinks, contracts, or warps during the welding process. The distortion in welding usually occurs due to uneven heating and cooling. As a result, compressive or tensile stress impacts the weld’s strength and integrity and causes an inferior weld.
Minimizing distortion in welding is key to producing a clean, strong weld and avoid creating a distorted plate. Some ways of preventing welding distortion include intermittent welding, avoiding over-welding, clamping parts, and planning the weld process to allow for some shrinkage.
Here you will learn what causes distortion in welding, what six common types of distortion in welding are, and how to prevent welding distortion.
What is Welding Distortion?
Welding distortion is an undesirable change in the base metal shape after the welding process. Metal expands when it’s heated and contracts when it cools. Resistance in the heating and cooling process causes resistance. The result is that deformation in the metal plates occurs, causing bending, twisting, dishing, or buckling.
Causes of Distortion in Welding?
Heating metals to high temperatures is the primary cause of welding distortion. Metal expands and contracts in all directions, causing residual stresses in the weld joint. In addition, the fact that only part of the metal plate is heated causes non-uniform expansion and contraction around the welding pool, resulting in welding distortion.
Various individual factors in the weld process cause distortion in welding.
- Metal properties: Different types of metal expand and contract at different rates. Therefore, the coefficient of thermal expansion of the material plays a significant role in determining the stresses during welding, which affects distortion. For example, stainless steel is more likely to suffer distortion than carbon steel because it has a higher expansion coefficient.
- Restraint: A lack of sufficient restraint during a weld causes the metal to move and can result in distortion.
- Welding procedure: A higher weld volume can result in distortion.
- Joint design: Fillet joints and butt joints are prone to welding distortion. In some cases, choosing a double-sided weld is better for reducing distortion than a single-sided weld.
Six Types of Welding Distortion
Welding distortion is categorized by the way the metal changes shape. For example, some welds result in warping, where the metal plate bends up or down at an angle. In addition, transverse distortion affects the welded metal width. However, longitudinal distortion and shrinkage affect the length of the weld plate.
1. Longitudinal Shrinkage in Welding
Longitudinal shrinkage occurs when a molten metal in the weld cools and contracts, and the surrounding material shrinks with it. The result is that the length of the weld shortens, causing the end of the metal to be distorted.
TIP #1: You can prevent or minimize longitudinal distortion by properly securing weld items before welding.
2. Longitudinal Distortion
Longitudinal bending (also called camber distortion) can also occur. For example, when the weld center is not in line with the neutral axis of the welded plate. This can result in a distorted weld where the plate bends into a curved shape.
3. Angular Distortion
Welding distortion can happen when the angles between the welded parts contract unevenly during the cooling process. Also called angular distortion, this typical weld issue occurs when a weld is hotter at the top than at the bottom. The result is that the edges of the welded plates move outward from their original position, distorting the weld.
TIP #2: You can prevent angular distortion by using a double groove welding process.
4. Transverse Distortion
Transverse shrinkage can happen when two metal plates are butt welded, and a higher rate of contraction occurs during cooling. This pulls the edges together, causing transverse contraction or distortion.
TIP #3: The best way to prevent transverse distortion is by clamping weld items and increasing the arc speed.
5. Buckling Distortion
Weld distortion and defects can occur when welding thin plates. Thin metal is especially prone to buckling, which can cause the welded materials to have a rippling, bowing, or dishing appearance. Buckled plates are also likely to snap if you try to flatten them.
TIP #4: Reducing the tensile stresses around the weld joint should help to prevent buckling, bowing, twisting, and dishing.
6. Rotational Distortion
Rotational distortion is common in butt welds where an irregular, uneven welding arc speed causes issues with the weld. Typically, a slower welding speed causes the weld end to split and open. On the other hand, welding butt joints too fast can cause the plates to cross over each other or close. Adjusting the travel speed should eliminate problems with rotational distortion.
How to Prevent Welding Distortion
Various steps can help to prevent or minimize weld distortion. Of course, some distortion will inevitably occur due to the movement of the metal. However, you can reduce distortion by using intermittent welding, making fewer weld passes, and welding near the neutral axis help to prevent warping.
Let’s look in more detail at the best ways to reduce welding distortion significantly.
Avoid Over-Welding to Prevent Weld Distortion
Larger welds are more prone to shrinkage and more significant distortion. Therefore, it’s essential to size the weld correctly before starting. A weld gauge is an excellent tool for welders to ensure the weld size is correct. Not only does this prevent distortion, but it also saves weld metal and welding time.
Welding Sequence to Control Welding Distortion
It’s vital to weld toward the joint’s free end; therefore, welding direction is crucial for reducing distortion. For example, short runs or intermittent welding rather than continuous welds are effective in distortion control on long welds.
Make fewer Weld Passes to Control Residual Distortion
Each weld pass has a cumulative effect on shrinkage. So, the more passes you make, the greater the risk of shrinkage in the weld seam. To reduce distortion, try to make larger weld passes rather than several small ones.
Weld Close to the Neutral Axis
It is crucial to weld as near the neutral axis as is possible to prevent welding distortion. This welding technique helps offset one shrinkage force with another to minimize distortion. Similarly, it is vital to balance welds around the neutral axis.
Distortion control is also possible by using balanced welding around the neutral axis. Again, the goal should be to minimize the number of runs.
Back step Welding Techniques to Control Distortion
Back-step welding is typically accomplished by working the electrode from left to right while depositing each weld bead segment right to left. This technique creates a weld bead that causes plate panels to expand less.
Presetting Parts to offset Weld Distortion
The prediction of welding distortion can also help to create welded items free from shrinkage. For example, if you predict welding deformation, it is possible to pre-bend parts to make shrinkage work for you. Then, natural shrinkage bends the parts into the correct shape as you weld.
Plan Weld Sequence to Counteract Distortion in Welding
Since shrinkage and distortion are natural in welding, planning how to weld several parts together can help minimize distortion. For example, shrinkage in one place can be counteracted by shrinkage in another place.
Other Methods to Prevent Welding Distortion
Depending on the type of assembly, other welding techniques can be helpful to ensure shrinkage doesn’t cause distortion.
- Clamping: Use clamps to secure parts in their required position. This significantly reduces distortion during welding. However, some slight distortion may occur when removing the clamps.
- Thermal stress relief: This is a controlled method to heat the weldment to an elevated temperature and then cooling of the welded structure. This method is an excellent way to reduce the impact of stresses pulling on the plate.
- Peening: In some cases, hitting the flat plate with the back of a hammer stretches the weld bead and relieves welding residual stress. However, this is not recommended for the final pass because it could hide possible cracks.
- Reduce welding time to a minimum: Using mechanized welding equipment can help to minimize distortion and weld time.
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Welding Distortion — In Conclusion
Distortion in welding is an occurrence that all welders must deal with. Stresses on metal plates during the heating and cooling process can cause buckling, warping, bending, twisting, and other forms of distortion. However, planning for distortion and using appropriate weld techniques can reduce or eliminate distortion from a weld.