Preventing Laser Welding Pores: Causes and Methods

Laser welding is widely utilized in numerous industries for its advantages of concentrated energy, high precision, and excellent results.

However, the use of laser welding machines also brings about potential uncertainties.

Improper operation or imperfect processes during laser welding can often result in porosity in the weld.

To address this issue, it is important to first identify the causes of porosity and then provide appropriate solutions based on the root cause analysis.

Why do pores occur during welding?

Porosity in laser welding is caused by the entrapment of gas 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 in sintering and pressing conditions for powder metallurgy materials, which result in lower compactness compared to smelting materials.
  • Porosity is also a common defect in laser welding processes. During the process of plasma control, 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 porosity

Weld formation process

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 metal vapor production, making the liquid metal in the molten pool unstable, and causing turbulence.

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To reduce the formation of pores, it is recommended to lower the laser power and increase the welding speed. This will reduce the production of metal vapor and minimize the formation of pores.

Method for preventing laser welding from producing air hole

The principle of metallurgy is utilized to minimize the formation of pores by introducing an active gas that dissolves in the weld or reacts with the molten metal to form compounds. Pulse laser welding is also employed to alter the behavior of small holes and reduce the influx of shielding gas.

While these methods can help reduce the number of pores, they cannot completely eliminate them. The beam swing 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 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 flow stirs the welding pool, increasing convection and helping to eliminate pores.

By using a surface cleanliness meter and an RFU unit, the cleanliness of parts can be quickly and accurately assessed. This data helps to avoid the impact of human subjectivity in the cleaning process and optimize it for greater efficiency, reducing rework and production costs.

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