Welding, as a common metal connection method, plays a vital role in industrial production. However, deformation is inevitable during the welding process, which poses a great challenge to the quality and precision of the product. So, what exactly is welding deformation? How does it occur?
This article will explore the causes, types, effects and preventive measures of welding deformation to help everyone better understand and solve this problem.
What Is Welding Distortion
Welding distortion refers to a permanent deformation caused by uneven thermal expansion and contraction of materials due to local heating and cooling of materials caused by heat input during welding. This deformation will change the shape and size of the weldment, affecting the precision and appearance of the product.
What Are the Causes of Distortion in Welding
- Thermal stress: The high temperature generated by the welding heat source causes the local temperature of the material to rise, and the temperature gradient in different parts is large, thus generating thermal stress. When the thermal stress exceeds the elastic limit of the material, plastic deformation will occur.
- Constraint stress: The fixture of the weldment, the weld itself, and the adjacent unwelded parts constrain the shrinkage of the weld, resulting in stress concentration and deformation.
- Material properties: Factors such as the thermal expansion coefficient, thermal conductivity, and grain size of the material will affect the degree of welding deformation.
- Welding process parameters: Parameters such as welding current, voltage, and welding speed have a direct impact on the heat input, which in turn affects welding deformation.
What Are the Four Types of Distortion in Welding
Angular distortion: Common in T-joints and angle joints, the plates on both sides of the weld rotate relative to each other.
Bending distortion: Uneven weld distribution causes the weld to bend.
Twisting distortion: Asymmetric weld structure or unreasonable welding sequence causes weld distortion.
Shrinkage and cracks: Too fast cooling or excessive heat input causes shrinkage and cracks in the weld.
Distortion in Welding Affects Quality
Decrease in product dimensional accuracy: Welding deformation will cause product size to exceed tolerance, affecting its assembly performance.
Affect product appearance: Welding deformation will cause unevenness on the product surface, affecting product appearance.
Reduced product strength and rigidity: Welding deformation will cause stress concentration, reducing product strength and rigidity.
Shortened product service life: Residual stress generated by welding deformation will accelerate the generation of fatigue cracks and shorten product service life.
Increased processing costs: In order to eliminate welding deformation, additional processing is required, which increases production costs.
How to Reduce Distortion in Welding
Process parameter optimization: reduce heat input, use multi-layer and less-pass welding, reasonably select welding sequence, etc.
Structural design improvement: symmetrical design, increase rigidity, etc.
Preheating and post-heat treatment: reduce temperature gradient and slow down cooling rate.
Jig design: reduce constraints.
Welding auxiliary means: use vibration, magnetic field and other methods.
New welding technology: laser welding, electron beam welding, etc.
How to Avoid Distortion in Welding?
1.Optimize Welding Parameters:
Reduce Heat Input: Lowering the welding current, voltage, and welding speed can reduce the amount of heat input, minimizing thermal expansion and contraction.
Use Smaller Weld Beads: Smaller weld beads distribute heat more evenly, reducing the potential for distortion.
Balance Heat Input: Ensure consistent heat input across the weld joint to prevent uneven expansion and contraction.
2.Proper Joint Design:
Minimize Joint Restraint: Design joints with minimal restraint to allow for free thermal expansion and contraction.
Use Backing Bars: Backing bars can help to distribute heat and reduce distortion in butt welds.
Consider Joint Sequence: The sequence in which welds are made can influence distortion. Plan the welding sequence to minimize the buildup of residual stresses.
3.Effective Fixturing:
Rigid Fixtures: Use rigid fixtures to hold the workpiece securely and prevent distortion during welding.
Balanced Fixturing: Ensure that the fixture applies balanced forces to the workpiece to avoid uneven stress distribution.
Consider Thermal Expansion: Design fixtures to accommodate thermal expansion and contraction.
4.Post-Weld Heat Treatment:
Stress Relief Annealing: This process involves heating the welded component to a specific temperature and then slowly cooling it to relieve residual stresses.
Straightening: Mechanical straightening can be used to correct minor distortions.
How to Fixing Weld Distortion?
Mechanical Straightening:
Press Brakes: Use press brakes to bend the distorted component back into shape.
Hydraulic Presses: Hydraulic presses can apply significant force to straighten severe distortions.
Hand Tools: For minor distortions, hand tools like hammers and dollies can be used.
Thermal Stress Relieving:
Heat Treatment: Apply heat to the distorted area to relieve residual stresses and allow the metal to relax.
Flame Straightening: Use a flame to heat specific areas of the component, causing localized expansion and contraction to correct the distortion.
Machining:
Milling and Grinding: Remove excess material to correct dimensional inaccuracies caused by distortion.
Conclusion
Welding deformation is a common problem in the welding process, but by deeply understanding its causes and effects and taking corresponding preventive measures, we can effectively control welding deformation and improve welding quality.
If you want to learn more about welding, you can consult our Dowell laser welding machine manufacturer to learn more knowledge.
