Causes and solutions for air bubbles during laser welding
Welding bubble generation principle
We can understand that laser welding works by using a high energy laser beam to heat and melt the material being joined. The molten material then solidifies to form a strong and lasting bond. However, if the welding conditions are not ideal, or if there are impurities or contaminants in the material being welded, pores or voids can be created in the weld. Porosity is a pocket of gas trapped in the weld which can weaken the weld and make it more likely to crack or fracture under pressure.
The hazards of porosity in welding
The danger of porosity in laser welding is that they can compromise the integrity of the weld, reducing its mechanical strength and durability. Pores can also act as stress concentration points, which can lead to premature failure of the weld under load. In addition, porosity can create channels for liquids, gases or other contaminants to penetrate the weld, leading to corrosion or other forms of degradation. The consequences of poor welds require rework or replacement at the cost of time and money.
Common causes and solutions
Weld material contamination.
Any contaminants on the surface of the material being welded can create pores that are trapped as the material is heated and fused together. This can lead to porosity or voids in the weld seam.
solution
Before starting the welding process, it is important to ensure that the surface to be welded is clean and free of any contaminants. Any dirt, oil, grease or other debris on the surface should be removed using a suitable solvent or cleaning solution. This can be done using methods such as ultrasonic cleaning, steam degreasing or chemical cleaning. Alternatively, a laser cleaner can be used to pre-treat the surface prior to welding. Also, the use of a suitable shielding gas can help to protect the weld pool from contamination.
Improper use of protective gases
In most laser welding processes, the nozzle of the laser welding machine needs to be fed with a shielding gas to prevent oxidation of the weld seam and to avoid contamination of the focal lens with metal gas. Most of the gas holes are caused by the improper use of shielding gas during the laser welding process, but the reasons for this vary slightly from one shielding gas to another.
1, nitrogen produces the cause of porosity
In the laser welding process, nitrogen from the outside into the molten pool, nitrogen in the liquid iron solubility and nitrogen in the solid iron solubility is very different, and thus in the cooling solidification process of the metal, as the solubility of nitrogen with the drop in temperature, when the molten pool of metal cooling to the start of crystallization, solubility will occur a substantial and sudden drop, at this time, a large number of gas precipitation to form bubbles, if the bubble floating speed is less than metal crystallization speed, then generate pores.
2, argon gas generated by the causes of porosity
Laser welding, the small hole inside the metal steam outward eruption caused by the small hole at the opening of the steam vortex, the argon gas into the bottom of the small hole, with the small hole to move forward, these argon gas will enter the molten pool in the form of bubbles. Due to the extremely low solubility of argon, coupled with the rapid cooling rate of laser welding, the bubbles do not have time to escape and are left in the weld, forming a porosity.
solution
1. The use of metallurgical principles and the use of reactive gases allows the gas to dissolve in the weld or react with the molten pool metal to produce a compound.
2. The use of pulsed laser welding changes the behaviour of the pores and reduces the amount of shielding gas being drawn into the pores. This method is not yet able to completely eliminate porosity.
3, The use of beam oscillation to reduce or eliminate porosity in laser deep fusion welding. Due to the addition of swing in welding, the reciprocal swing of the beam to the weld on the one hand, part of the weld occurs repeatedly remelting, extending the time of the weld pool liquid metal stay, at the same time, the beam deflection also increases the unit area input heat, reducing the depth to width ratio of the weld, which is conducive to the bubble floating out, thus playing a role in eliminating porosity. On the other hand, the oscillation of the beam causes the small holes to oscillate, which in turn provides a stirring force to the weld pool, increasing the convection and stirring of the weld pool, which is beneficial to the elimination of porosity.
More notes on the use of gases can be found in this article：The use of gases in laser welding
Welding speed too fast
The laser beam may not provide enough energy to completely melt and fuse the materials together, resulting in incomplete fusion between the materials, which can create voids. At the same time the rapid cooling of the weld can cause thermal stresses and create cracks or fissures in the weld.
solution
Reduce the travel speed: If the welding process is moving too fast, the welding speed can be reduced to allow more time for the material to melt and fuse. This can be achieved by adjusting the welding parameters, such as the laser power or the travel speed of the weld head.
Increase the laser power: Increasing the laser power can help compensate for faster welding speeds as it provides more energy to the weld area, allowing the material to melt and fuse together more quickly.
Use a different laser beam shape. The shape of the laser beam can also influence the welding speed. For example, a wider beam can cover a larger area and make the weld faster. Conversely, a narrower beam can provide more precise control and may require slower welding speeds.
Adjusting the laser’s focus. The focal point of the laser beam can also affect the welding speed. If the focus is too high, the laser will not have enough energy to melt the material, while a focus that is too low will result in excessive melting and distortion. Adjusting the focal point to the optimum position can help to achieve a better balance between speed and weld quality.
Check for any mechanical problems. Finally, it is also important to check for any mechanical problems that may affect the welding speed. This could include problems with the welding equipment, such as worn or damaged parts, or problems with the material being welded, such as uneven thickness or inconsistent properties.
By taking these steps it is possible to adjust the laser welding speed and optimise the process to achieve the best possible results.
The following are common laser welding materials welding speeds：
SS – stainless steel, AL – aluminium
Incorrect laser parameters
Laser welding requires precise control of laser parameters such as power, pulse duration, and beam focus. If any of these parameters are set incorrectly, then bubbles may form in the weld.
solution
Review the operating manual: The first step in correcting the laser welding parameters is to review the operating manual for the welding equipment. The manual will provide information on the recommended parameters for different materials and thicknesses, and can help identify any potential issues with the current settings.
Consult with a technician: If you are not familiar with the equipment or the welding process, it is recommended to consult with a technician who has experience with laser welding. They can provide guidance on the correct parameters to use for the specific material and application, and can also help identify any issues with the equipment that may be affecting the welding process.
Adjust the parameters: Based on the recommendations from the manual and the technician, adjust the welding parameters to the correct settings. This may involve adjusting the laser power, pulse duration, spot size, and other parameters depending on the material being welded and the desired weld quality.
Test the weld: Once the parameters have been adjusted, perform a test weld to ensure that the settings are correct and the weld quality meets the required standards. If the weld quality is not satisfactory, continue to adjust the parameters until the desired results are achieved.
Poor fit-up
If the materials being welded are not properly aligned or have gaps between them, then the laser beam may not be able to fully penetrate the joint, leading to the formation of bubbles.
To avoid bubbles in laser welding, it is important to carefully prepare the materials being welded, ensure proper shielding gas flow, and use the correct laser parameters for the job. Additionally, it is important to monitor the welding process closely and make adjustments as needed to prevent the formation of bubbles.
In addition, the use of an oscillating laser head and a 976nm laser pump source has a good effect on the elimination of porosity during laser welding
