The pressure level needs to be finely optimized based on parameters such as the welding material, laser power, welding speed, nozzle type and distance. Its influence mainly manifests in the following aspects:
The influence on the protection effect of the weld seam
Low air pressure
Insufficient protection: The gas flow and pressure are insufficient to effectively expel the air beneath the nozzle, resulting in the entrainment of air, oxidation and nitriding of the weld metal. The weld surface will appear dark yellow, blue or even black. In severe cases, defects such as pores and slag inclusions will occur, and the toughness and strength of the weld will significantly decrease.
Shielding failure: Unable to effectively suppress the plasma cloud, the plasma expands excessively, absorbs and scatters laser energy, resulting in a decrease in the welding penetration depth or even the inability to continue the welding process (the weld does not penetrate).
Excessive air pressure
Formation of turbulence: Excessive airflow will change from laminar flow to turbulent flow, thereby drawing in the surrounding air into the protected area, disrupting the protective effect of the gas and also causing the weld to oxidize.
Interference with the molten pool: High-speed airflow will exert a strong impact on the surface of the molten pool, which may cause the molten pool to vibrate and splash, resulting in irregular weld formation, rough surface, and even pooling or weld penetration (especially in thin plate welding).
2. Effects on weld formation and penetration depth
Moderate pressure: It can effectively suppress the plasma and ensure that the laser energy is efficiently input into the workpiece, thereby achieving the maximum and stable penetration depth. At the same time, the stable airflow helps to form a smooth, continuous and aesthetically pleasing weld surface.
Low air pressure: Due to the plasma shielding effect, the effective laser energy decreases and the penetration depth becomes shallower.
Excessive pressure: Although it can more effectively disperse the plasma, it may slightly increase the weld penetration depth. However, the more significant effect is that the blowing force of the airflow on the molten liquid will change the geometry of the weld, making it wider, reducing the weld height, and even forming "finger-like" weld penetration, which is not conducive to mechanical properties.
3. Impact on welding defects
Porosity: Porosity is one of the most common defects in laser welding. Appropriate pressure helps to smoothly discharge the metal vapor and small bubbles generated during the welding process from the molten pool, thereby reducing the formation of porosity.
The air pressure is too low, and the scavenging ability of the protective gas is weak, making it difficult for the gases in the molten pool to be discharged.
Excessive pressure causes turbulence and disturbance in the molten pool, which may instead cause the gas to be drawn into the molten pool or disrupt the normal exhaust process, thereby increasing the tendency for gas pores.
Spatter: Excessive pressure is one of the main causes of spatter. The high-speed airflow impacts the molten pool, blowing the molten metal particles away from the pool and spraying them onto the workpiece surface. This not only contaminates the workpiece and affects its appearance, but also leads to loss of the base material of the weld seam, resulting in defects such as undercut and pits, and reducing the effective bearing area of the weld seam.
III. How to Select and Optimize Air Pressure
Gas type: Helium (He) has a high ionization energy and provides the best suppression effect for plasma; the required pressure can be relatively lower. Argon (Ar) is heavier and offers good protection but has a weaker ability to suppress plasma; sometimes a slightly higher pressure is needed to compensate. Nitrogen (N₂) is suitable for certain specific steels, but is generally not used for aluminum alloys, high alloy steels, etc.
Nozzle Design: The diameter, height and angle of the nozzle determine the gas flow field and coverage area. Nozzles with larger diameters usually require higher pressure and flow rate to maintain an adequate protective gas curtain.
Welding parameters: High laser power and high welding speed will generate more metal vapor and plasma, and usually a higher pressure is required to effectively control it.
Practical debugging: The optimal pressure is usually determined through process experiments (DoE). After fixing all other parameters, by changing the pressure value, observe the formation, color of the weld seam, test its porosity rate and mechanical properties, and thereby find the optimal range.
In conclusion, the pressure of the protective gas is a crucial parameter that needs to be finely controlled in the laser welding process. Insufficient pressure will lead to inadequate protection, plasma shielding failure, and a shallower weld depth; excessively high pressure will cause turbulence, interference in the molten pool, and increased spatter. Only by fully understanding its mechanism of action, combining specific materials, equipment, and process parameters, and through systematic experiments to find an appropriate and stable pressure range, can the positive effects of the protective gas be maximized, and high-quality laser weld seams with beautiful formation, excellent performance, and no defects be obtained. Therefore, precise control of the pressure size is a necessary skill for achieving high-quality laser welding production.