What is Porosity in Laser Welding? Adverse Effects and Causes
Posted by： Hangao Time：6/16/2025 3:49:15 PM
I. Porosity in Laser Welding
Laser welding is a paragon of precision and efficiency in modern manufacturing, offering numerous advantages. However, even with this advanced technology, there are challenges, one of which is porosity. This article will delve into the meaning of porosity, its negative effects, its causes, its preventative measures, and why addressing this issue is crucial for anyone choosing laser welding.
II. What is Porosity?
During the laser welding process, if any air gaps exist, if zero gaps are not maintained, or if proper precautions are not taken during operation, air pockets or voids may remain in the weld metal. These air pockets or voids appear as spherical or elongated bubbles.
This is considered a laser welding defect because it not only causes defects but also fails to meet the fundamental requirements for a perfect laser weld: a continuous, smooth, and porosity-free workpiece.
To effectively avoid porosity during laser welding of stainless steel pipes, the following aspects can be controlled and optimized:
? I. Material Preparation (Very Critical)
1. Clean the weld surface
Remove oil, rust, moisture, and oxides. Use alcohol wipes or plasma cleaning to prevent moisture vaporization and the formation of pores.
2. Control the hydrogen content of the material.
Use dry base metal and welding wire and avoid storage in damp conditions.
It is recommended to keep the storage environment dry and, if necessary, dry it.
? II. Welding Parameter Optimization
1. Matching Laser Power and Speed
Excessive power can easily cause violent boiling, preventing the metal vapor from escaping quickly and forming pores.
It is recommended to use medium power and a reasonable scanning speed to ensure a stable weld pool and gas release.
2. Focus Position Control
Focus position that is too far up or too far down can affect weld pool stability. The focus should be precisely aligned with the weld interface.
? III. Shielding Gas Control
1. Gas Type Selection
Commonly used: Argon (Ar) offers excellent protection and stability.
Nitrogen (N?) can also be used for welding certain stainless steels, but it must be ensured that it does not cause embrittlement.
2. Gas Flow Rate and Nozzle Position
Too low a gas flow rate will result in insufficient protection, while too high a flow rate may disrupt the weld pool. The nozzle should be positioned appropriately away from the weld, at an angle of approximately 15-30°, to avoid turbulence.
? 4. Properly Design Welding Structure and Assembly Accuracy
Maintain consistent weld gaps and high positioning accuracy to avoid localized energy concentration or incomplete fusion.
The pipe ends should be machined smooth to avoid burrs or irregular gaps.
? 5. Select the Right Laser Equipment
Key Features Recommended:
Equipped with a closed-loop energy control system to ensure stable output.
Oscillating welding heads (scanning welding) can increase weld pool agitation, facilitate bubble escape, and reduce porosity.
? 6. Practical Case Tips (Based on Engineering Experience)
Dual gas shielding (top and bottom) can be used as appropriate, especially when achieving full penetration; the inner wall should also be protected.
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