Analysis and Countermeasures of Common Problems in Laser Welding of BIW (1)

During the process of laser fusion welding, various factors such as laser beam agitation of the weld pool, evaporation of alloying elements in the base material, temperature gradient of the weld pool, and metal vapor will all impact the quality of the welding. The following is a detailed analysis of defects in laser fusion welding.

1.Incomplete Penetration and Lack of Fusion

Incomplete penetration and lack of fusion are serious defects in laser fusion welding. The root cause is low laser energy at the weld seam.

(1) Factors contributing to low laser energy at the weld seam include:

  • Low laser power;
  • Contaminated or damaged protective lenses in the welding mirror assembly, affecting laser transmittance;
  • Off-center laser focus on the weld seam or skewed angle of laser beam incidence.

(2) Long-term solutions for this defect involve:

  • Configuring appropriate laser power parameters;
  • Regularly inspecting and replacing protective lenses in the welding mirror assembly;
  • Calibrating the laser focus and ensuring a laser beam incidence angle of 90 degrees;
  • Temporary rework measures for this defect include spot welding from the front or CO2 plug welding and grinding after backside seam grinding.

2. Burn-Through

If only the first-layer plate experiences burn-through, the defect’s cause could be an excessive gap between the plates. If the entire weld seam is burned through, it indicates improper welding parameter settings. A long-term control measure for this defect is to ensure that the gap between plates is less than 0.2 mm and to configure appropriate laser power and welding speed. In the case of burn-through in the first-layer plate, MIG welding and grinding can be applied for rework. If the entire weld seam is burned through, the welded component should be considered scrap and be disposed of accordingly.

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