The Influence of Laser Beam Intensity Distribution on Lock Hole Geometry and Process Stability under Green Laser Radiation

Researchers from the University of Aveiro in Portugal and the School of Engineering at Porto Institute of Technology (ISEP) in Portugal reported a study on the influence of laser beam intensity distribution on the geometric shape and process stability of lock holes under green laser radiation. The relevant paper titled "Influence of Laser Beam Intensity Distribution on Keyhole Geometry and Process Stability Using Green Laser Radiation" was published in the conference "Flexible Automation and Intelligent Manufacturing: Establishing Bridges for More Sustainable Manufacturing Systems".

Laser beam welding is increasingly being used for connecting copper materials. Compared with near-infrared radiation, green laser radiation has a significantly higher absorption rate advantage for these metals. Therefore, it is expected that there will be changes in process stability and the occurrence of defects. In addition, the influence of changing the strength distribution on the formation of weld defects and the geometric characteristics of welds in deep penetration welding mode has not been fully studied to a large extent. Therefore, the purpose of this work is to characterize the process dynamics and defect formation related to focal position and intensity distribution through high-speed imaging and metallographic analysis. Compared with the flat top intensity distribution, the weld defects observed under the Gaussian beam profile are significantly reduced. The favorable shape of the weld seam and the earlier start of deep welding process are the advantageous reasons for adopting this strength distribution, and the medium to high processing speed further improves the processing quality.

Keywords: laser beam welding; Green laser radiation; Intensity distribution; Electric vehicles; Process observation; quality improvement

Figure 1 Weld Defects in Copper Welding - Typical Top and Cross Sectional Views - a) Pores, b) Splashing Formation, c) Melt Spray, d) Collapse at the Root of the Weld.

Figure 2: Schematic diagram of the experimental setup used in this study (left), derivation of the composition of the weld cross-section (yellow), and defect evaluation of pores marked in green (right).

Figure 3 shows the measured intensity distribution of the flat top (left) and Gaussian (right) beam profiles.

Figure 4: The relationship between the deep penetration welding threshold and feed rate of oxygen free copper (Cu ETP) under different intensity distributions.

Figure 5: Overlapping weld profiles under different intensity distributions (laser power PL=2/3 kW, speed v=4m/min).

Figure 6 shows the relationship between the amount of spatter per unit weld length and feed rate under different intensity distributions and laser power settings.

Figure 7 shows the process instability observed in copper laser beam welding (LBW) through high-speed imaging (HSI), λ=515nm, PL=3kW, v=10 m/min， Flat top (top) and Gaussian (bottom) intensity distributions.

Figure 8 The relationship between quality loss (left) and defect area (right) under different intensity distributions and feed rate, λ=515nm, PL=1.5-3kW, dWorkpiece=340 µ m.

The purpose of this work is to characterize the process dynamics and defect formation directly related to the focal position and intensity distribution in copper welding under green laser radiation through high-speed imaging and metallographic analysis. In summary, the following conclusions can be drawn:

Compared with a flat top contour, the process under Gaussian intensity distribution is more stable, which has been consistently confirmed by splash analysis and quality loss measurement.

The favorable shape of the weld seam and the earlier start of deep penetration welding process are the advantageous reasons for adopting this strength distribution.

For Gaussian contours, selecting the appropriate focal position in the workpiece can minimize the number of weld defects, while from the perspective of melt pool area, reverse seems to be more effective.

In summary, choosing medium to high processing speeds (v>8 m/min) can improve process stability, and appropriate process parameters should be set considering application requirements (joint type, weld shape, etc.).

Source: Yangtze River Delta Laser Alliance