Laser welding is widely used in numerous industries due to its advantages of concentrated energy, high precision and excellent results.
However, the use of laser welding machines also brings potential uncertainties.
Improper operation or imperfect processes during laser welding can often result in porosity in the weld.
To solve this problem, it is important to first identify the causes of porosity and then provide appropriate solutions based on root cause analysis.
Why do pores occur during welding?
Porosity in laser welding is caused by gas entrapment during the solidification process of the weld metal. The cooling rate of the weld metal in laser welding is significantly faster compared to conventional welding, making it difficult for gas to escape and leading to the formation of pores.
There are two main causes of porosity in laser welding:
- Limitations on sintering and pressing conditions for powder metallurgy materials, which result in lower compaction compared to foundry materials.
- Porosity is also a common defect in laser welding processes. During the plasma control process, the dynamic pressure of the auxiliary gas affects the flow of the molten pool and the escape of gas from small holes, which directly affects deep penetration welding.
Weld porosity
Weld Formation Process
There is a correlation between the number of pores in a weld and the size of the laser power used. An increase in laser power is associated with an increase in the number of pores.
It is believed that the high heat generated by increased laser power causes the molten metal to reach extremely high temperatures, resulting in the production of metallic vapor, making the liquid metal in the molten pool unstable and causing turbulence.
To reduce pore formation, it is recommended to decrease the laser power and increase the welding speed. This will reduce metallic vapor production and minimize pore formation.
Method to prevent laser welding from producing air holes
The principle of metallurgy is used to minimize pore formation by introducing an active gas that dissolves in the weld or reacts with the molten metal to form compounds. Pulsed laser welding is also used to change the behavior of small holes and reduce the influx of shielding gas.
Although these methods can help reduce the number of pores, they cannot eliminate them completely. The beam oscillation method is used to minimize or eliminate pores in deep penetration laser welding.
The reciprocating movement of the beam over the weld prolongs the residence time of the liquid metal in the welding pool and increases the heat input per unit area, reducing the depth-to-width ratio of the weld. This promotes bubble formation and helps eliminate pores. Additionally, the oscillation of the beam flux agitates the welding puddle, increasing convection and helping to eliminate pores.
Using a surface cleanliness meter and an RFU unit, the cleanliness of parts can be assessed quickly and accurately. This data helps to avoid the impact of human subjectivity on the cleaning process and optimize it for greater efficiency, reducing rework and production costs.
