What Welding Defects Can Occur in Laser Welding? How to solve it?

Laser welding is widely used in various industries due to its advantages of high efficiency, high precision, good effect, and easy automation integration. It plays an important role in industrial production and manufacturing, including military, medical, aerospace, new energy, and other industries. However, any processing method, if its principles and processes are not properly understood, may produce defects or defective products, and laser welding is no exception. To maximize the value of laser welding and produce a quality product with a flawless appearance, it is important to understand these pitfalls and learn how to avoid them.

Principles of Laser Welding

Laser welding is one of the important applications of laser material processing technology. Laser welding operates in two fundamentally different modes: conduction-limited welding and deep-hole welding. Heat conduction is carried out during the welding process, that is, laser radiation heats the surface, and the surface heat diffuses to the interior through heat conduction. By controlling the laser pulse width, energy, peak power and repetition frequency, element melting, and other parameters, a specific molten pool is formed on the metal surface. The heat melts the material to create a weld bead between the two surfaces, completing the weld.
Laser welding has high welding precision and welding quality. Since the laser itself generates very little heat, the weld seam produced after laser welding is also relatively small, which makes laser welding especially suitable for thinner materials, such as electronics or glass/metal seals. Whereas when welding thicker materials, narrow and deep welds are produced between square-edged parts. Additionally, the laser can reach incredibly high temperatures (thousands of degrees Celsius), so it can produce very strong and durable welds that can withstand extreme temperatures and harsh environments.

Common welding defects in laser welding and how to solve them

Laser welding has the advantages of high efficiency, high precision, good effect, easy automation, integration, etc., but improper operation can also lead to serious quality defects in products. Only by understanding these defects well can the value of laser welding be brought into full play, and products with beautiful appearance and high quality can be processed. The following are 8 welding defects that often occur in laser welding.

Porosity

Pores are one of the defects that are prone to occur in laser welding. Porosity in laser welding can be caused by the board or surface contamination or insufficient pre-cleaning, such as grease, oil, oxides, absorbed water vapor, cutting fluid residues, etc. The laser welding pool is deep and narrow, and the cooling speed is fast. The gas generated in the liquid molten pool has no time to escape due to surface pollution, and it is easy to form pores. However, laser welding cools quickly, and the pores produced are generally smaller than in traditional fusion welding.
To avoid porosity in laser welding:

ensure proper shielding gas: Use a high-quality shielding gas (usually a mixture of argon or helium) to provide adequate protection from atmospheric gases.
optimize gas flow: set the appropriate shielding gas flow and direction, to effectively protect the welding area to the greatest extent.
Clean the surface of the workpiece: Thoroughly clean the surface to be welded to remove any contaminants such as oil, grease, rust, or dirt to prevent gas entrapment. Use appropriate cleaning methods such as solvent cleaning, mechanical cleaning, or chemical cleaning as required.
Proper joint preparation: Ensure proper joint fit and alignment to avoid creating gaps where gas may be trapped. If applicable, use back purging techniques to prevent gas entrapment.

Undercut

An undercut is a groove or depression formed at the edge of a weld. Usually caused by excessive heat input or welding speed. When the welding speed is too fast, the liquid metal behind the small hole in the center of the weld has no time to redistribute, and it will solidify on both sides of the weld to form an undercut.
To avoid undercuts in laser welding:

Optimizing Laser Parameters: Adjust laser power, pulse duration, and focus position to achieve proper heat input. Avoid using too high a power or welding too fast, as this can cause overheating and undercutting.
Maintain a consistent welding speed: Control the movement of the laser beam or workpiece to maintain a constant speed of travel. Rapid speed changes can cause uneven heat distribution and undercut formation.
Proper joint design and fit: Ensure proper joint preparation, including accurate fit, proper bevel angle, and proper gap tolerance. Maintaining a tight fit helps prevent excessive melting of the edges and reduces undercutting.

Weld cracks

Welding hot cracks refer to the cracks generated in the high-temperature area when the metal in the weld and heat-affected zone cools to near the solidus line during the welding process. Generally can be divided into high-temperature cracks and low-temperature cracks. During the laser welding process, due to the small heat input of the laser, the deformation after welding is small, and the stress generated by welding is also small, so high-temperature cracks generally do not occur. However, due to different materials and improper selection of process parameters, high-temperature cracks will appear in the form of defects.
To avoid weld cracks:

control heat input: Optimize laser parameters to control heat input and reduce thermal stress. Avoid excessive heat buildup and rapid cooling rates, which may result in cracking. This can be achieved by adjusting laser power, and pulse duration or using pulse shaping techniques.
Preheating and post-weld heat treatment: Preheating the workpiece before welding helps to reduce thermal gradients and stresses and improve weldability. Post-weld heat treatment techniques such as annealing or stress relieving can also be used to relieve residual stresses, enhance mechanical properties, and reduce the risk of cracking.
Selection of Filling Material: Use a filling material with the proper composition and ductility to match the base material to minimize the risk of cracking.

Incomplete fusion or lack of penetration

Incomplete fusion, or incomplete penetration, occurs when the weld metal does not fully fuse with the wood or penetrate the full thickness of the joint.
To avoid incomplete or non-penetrated fusion:

optimize laser parameters: Adjust laser power, pulse duration, and focus position to achieve proper material fusion and penetration. A higher power setting or adjusting the focus position can help achieve deeper penetration.
Joint preparation and assembly: Ensure proper joint design and assembly. Groove angles, gap tolerances, and joint preparation techniques should be selected to promote proper fusion and penetration.
Adjust welding speed: Adjust the welding speed to allow sufficient heat input and penetration into the joint. Optimizing the welding speed ensures that the laser energy fully interacts with the material.

Splash

The spatter produced by laser welding can seriously affect the surface quality of the weld seam. After welding, many metal particles may appear on the surface of the workpiece or material, which not only affects the appearance but also affects the use. When the splash is serious, it will also pollute and damage the lens.
To avoid spatter in laser welding:

optimize laser beam focus and position: Properly adjust the laser beam focus position and shape to achieve stable and precise welding. Avoid misalignment or unstable focus of the laser beam, which may cause spattering.
Use proper shielding gas and flow rate: Choose the proper shielding gas composition and flow rate to provide adequate protection. Shielding gas helps prevent oxidation and contamination of the weld pool and reduces spatter. The gas flow needs to be adjusted according to welding requirements.
Clean the surface of the workpiece: Thoroughly clean the surface of the workpiece and remove any contamination that may cause spatter formation.

Deformation

Deformation refers to the deformation or bending of a welded structure or workpiece due to the welding process.
To avoid laser welding deformation:

Use the correct fixation and clamping technique: Fix the workpiece or structure to minimize movement or deformation during welding. Adequate support and alignment of the workpiece help maintain dimensional stability.
preheating the workpiece: Consider preheating the workpiece to reduce thermal gradients and minimize distortion.
controlled Cooling: Implement controlled cooling techniques, such as the use of heat sinks or fixtures, to regulate cooling rates and minimize thermal gradients.

Heat Affected Zone (HAZ) Issues

Laser welding creates a highly concentrated heat-affected zone around the weld. The heat-affected zone undergoes thermal cycling and microstructural changes that can result in reduced strength and changes in the hardness of the material.
To avoid HAZ problems:

Optimizing Laser Parameters: Adjust laser parameters to minimize the size and depth of the heat-affected zone. This includes controlling laser power, pulse duration, and beam focus.
Using sweeping or oscillating techniques: Using sweeping or oscillating techniques enables more even distribution of heat and reduces heat concentration in specific areas, thereby minimizing problems associated with heat-affected zones.
perform post-weld heat treatment: Apply appropriate post-weld heat treatment processes, such as annealing or stress relieving, to refine the microstructure and reduce problems associated with the heat-affected zone. Heat treatment helps restore material properties in the heat-affected zone.

Weld Collapse

Laser welding collapse refers to the inward deformation or sinking of the weld seam during the welding process. This can happen for a variety of reasons, such as too high laser power, insufficient melt pool control, insufficient material support, improper joint assembly, poor thermal management, material selection issues, and lack of process monitoring and control.
To avoid weld collapse:

optimize laser parameters: reduce laser power or energy density to prevent excessive melting of surrounding materials. Adjust laser power, pulse duration, and beam shape to achieve a balance between penetration and avoiding excessive melting that could lead to collapse.
Proper Material Support: Provide proper material support during welding using fixtures, jigs, or clamps to hold the workpiece in place and provide stability. Consider using support rods or heat sinks to dissipate heat and provide additional support for the joints.
ensure proper joint assembly: Proper joint assembly helps prevent collapse. Make sure the mating surfaces are properly prepared and aligned before welding. Enhance joint strength and stability by implementing proper joint design and edge preparation techniques.
Manage Heat Input: Control heat input and properly manage thermal cycles. Optimize scanning or movement strategies to evenly distribute heat and avoid localized overheating. Implement preheating or controlled cooling techniques to minimize thermal gradients and reduce the risk of collapse.
Material Selection and Compatibility: Select appropriate materials and mutually compatible welding parameters. Consider material properties such as thermal conductivity and melting point to ensure proper heat transfer and prevent excessive localized melting.
Monitoring and Controlling the Process: Implement a real-time process monitoring and control system to detect signs of collapse or deviations from desired welding parameters. Use feedback mechanisms during welding to adjust laser parameters, scanning speed, or material support. Adopt advanced technologies such as adaptive control systems or closed-loop feedback control to achieve consistent and stable welding conditions.
Ensure proper melt pool control: Control the size and shape of the melt pool by adjusting laser parameters and scanning speed. Use proper welding techniques, such as keyhole welding or conduction mode welding, to ensure a stable and controlled weld pool formation.

Summarize

Of course, other flaws can be associated with laser welding. In addition to technical operational problems, some defects can lead to changes in the properties of the material. Only by correctly understanding the defects that may occur in the laser welding process and the causes of different defects can we solve the abnormal welding problem in a more targeted manner.
AccTek Laser has a wide range of laser welding machines, including portable, cleaning, and welding 3-in-1 laser welding machines, suitable for welding your metal sheets and pipes. If you are looking for a machine for a special application, AccTek Laser can also be equipped with suitable components to realize a customized solution according to the customer’s requirements.

Laser Equipment

Contact information

Get Laser Solutions