Introduction
The small hole mode swing laser welding has gained increasing recognition due to its ability to bridge gaps, refine microstructures, and enhance the mechanical properties of welds. However, the effects of amplitude, frequency, welding speed, laser beam power, and beam radius on heat flux distribution, melting mode, and three-dimensional temperature field have not been well understood. To meet this demand, we report a combined experimental and computational study to investigate the effects of key swing welding parameters on the energy distribution, pinhole formation, three-dimensional fluid flow, and heat transfer of the impact welding trajectory during Inconel 740H swing laser welding. Strictly test the modeling results using experiments that vary welding speed, laser power, swing amplitude, and frequency. When the swing amplitude significantly exceeds the diameter of the laser beam, a bimodal power density distribution appears, with power density near the edge higher than in the middle of the orbit. The high swing amplitude results in a wide and shallow pool, while the swing frequency used in this study does not significantly affect the geometric shape of the fusion zone. A set of process diagrams was constructed to understand the role of oscillating laser parameters in achieving the desired fusion zone geometry during small hole mode oscillating laser welding. Finally, it was found that high amplitude swing laser welding is beneficial for rapid solidification and the formation of finer solidified structures.
main chart
Figure 1. Schematic diagram of swing laser welding process. The circular oscillation path is displayed in blue. The width of a circular oscillation path is called the amplitude. The width of the welding trajectory is approximately equal to the sum of the amplitude and twice the radius of the laser beam. The number of rotations of a laser beam along a circular path per unit time is called frequency.
Figure 2. The spatiotemporal variation of laser power density at three different positions along the laser beam axis (shown by black dots on the oscillation path). (d) The power density at point "B" shown in Figure (a). (e) Time integrated power density along path ABC. The result is for a laser power of 5 kW, a welding speed of 12.7 mm/s, a swing amplitude of 1.6 mm, and a frequency of 300 Hz.
Figure 3. Three dimensional temperature and velocity distribution of Inconel 740H keyhole mode swing laser welding. (a) Two different 3D isometric views are shown in (b). The result is for a laser power of 5 kW, a welding speed of 12.7 mm/s, a swing amplitude of 0.4 mm, and a frequency of 300 Hz.
Figure 4. (a) 3D melt pool geometry, displaying a cross-sectional view of the longitudinal plane at the middle width of the weld seam. (B) Transverse views of the molten pool at section A, (c) section B, and (d) section c. The cross-section is shown in Figure (A). (e) Horizontal view of the fusion zone. The result is for a laser power of 5 kW, a welding speed of 12.7 mm/s, a swing amplitude of 0.4 mm, and a frequency of 300 Hz.
Figure 5. The changes in power density at amplitudes of (a) 0 mm, (b) 0.4 mm, and (c) 1.6 mm. The changes in the geometry of the molten pool with amplitudes of (d) 0 mm, (e) 0.4 mm, and (f) 1.6 mm. The result is for a 5 kW laser power, a welding speed of 12.7 mm/s, and a frequency of 150 Hz.
Figure 6. (a) Comparison between calculated and experimentally measured fusion zones for linear welding and swing welding with amplitudes of (b) 0.4 mm and (c) 1.6 mm. The result is for a 5 kW laser power, a welding speed of 12.7 mm/s, and a frequency of 150 Hz.
Figure 7. The variation of power density and melt geometry with frequency. (a) The power density and (b) melt pool display are 150 Hz. Because frequency has no significant effect on power density and melt geometry, the results for 300 Hz and 411 Hz frequencies are not displayed. Comparison between calculated and experimentally measured fusion zones at frequencies of (c) 150 Hz, (d) 300 Hz, and (e) 411 Hz. The result is for a laser power of 7.5 kW, a welding speed of 12.7 mm/s, and a swing amplitude of 0.4 mm.
Figure 8. The power density varies with (a) 5 kW, (b) 7.5 kW, and (c) 10 kW laser power. The changes in the geometry of the molten pool when the laser power is (d) 5 kW, (e) 7.5 kW, and (f) 10 kW. The result is a welding speed of 12.7 millimeters per second, a swing amplitude of 1.6 millimeters, and a frequency of 411 hertz.
Figure 9. Comparison between calculated and experimentally measured fusion zones at laser powers of (a) 5 kW, (b) 7.5 kW, and (c) 10 kW. The result is a welding speed of 12.7 millimeters per second, a swing amplitude of 1.6 millimeters, and a frequency of 411 hertz.
Figure 10. The change in power density at welding speeds of (a) 12.7 mm/s and (b) 25.4 mm/s. The changes in the geometry of the molten pool at welding speeds of (c) 12.7 mm/s and (d) 25.4 mm/s. Comparison between calculated and experimentally measured fusion zones at welding speeds of (e) 12.7 mm/s and (f) 25.4 mm/s. The result is for a 5 kW laser power, 1.6 mm swing amplitude, and 300 Hz frequency.
Figure 11. (a) Comparison of calculated and experimentally measured melt pool depths for linear welding with (b) swing amplitude of 0.4 mm and (c) swing amplitude of 1.6 mm at different laser powers and welding speeds. Comparison between calculated and experimentally measured melt pool widths at different laser powers and welding speeds for (d) linear welding, (e) swing amplitude of 0.4 mm, and (f) swing amplitude of 1.6 mm. The result is for a frequency of 300 Hz.
Figure 12. The process diagram of the fusion zone width relative to (a) laser power and welding speed, (b) laser power and swing amplitude, and (c) welding speed and swing amplitude. Process diagram of fusion zone depth relative to (d) laser power and welding speed, (e) laser power and swing amplitude, and (f) welding speed and swing amplitude. The contour values in the map represent the width and depth of the fusion zone in millimeters. For figures (a) and (d), the amplitude remains constant at 1.0 mm. For figures (b) and (e), the scanning speed remains constant at 18 mm/s. For figures (c) and (f), the laser power remains constant at 7 kW. For all numbers, the frequency remains constant at 300 hertz.
Figure 13. (a) The variation of cooling rate during the solidification process along the depth of the workpiece under different swing amplitudes. The result is for a laser power of 5 kW, a welding speed of 12.7 mm/s, and a frequency of 300 Hz. (b) The linear correlation between the logarithm of secondary dendrite arm spacing (SDAS) and the logarithm of cooling rate during solidification under different oscillation amplitudes. The data points are targeted at different laser powers and welding speeds. The frequency remains constant at 300 hertz. Other welding parameters are shown in Table 1. The SEM images (c-d) show the microstructure of dendritic solidification under the two conditions shown in Figure (b).
main conclusion
In this study, we revealed the effects of oscillation welding parameters, laser power, welding speed, amplitude, and frequency on laser energy distribution, pinhole formation, and fusion zone geometry during the oscillation laser welding process in Inconel 740H pinhole mode. We developed, tested, and utilized a three-dimensional heat transfer and fluid flow model for keyhole mode swing laser welding. Conduct experiments under different processing conditions to rigorously verify the model results.
The specific findings are as follows:
(1) For a laser beam with a given power and welding speed, the geometric shape of the fusion zone can be effectively controlled by adjusting the swing amplitude. On the contrary, oscillation frequencies above 150 Hz do not significantly affect the geometry of the fusion zone, as they have minimal impact on the power density distribution.
As expected, the low power density under high swing amplitude results in a wide and shallow pool.
(2) When the swing amplitude is significantly greater than the diameter of the laser beam, the impact power density distribution on the welding trajectory shows a bimodal distribution, with the peak power density near the edge of the trajectory and the lower power density in the middle of the trajectory. Within the range of oscillation amplitude and frequency studied, high laser power and low welding speed result in a fusion zone with linear welding characteristics of pinhole mode.
(3) The cooling rate (GR) during the solidification process, where G is the temperature gradient and R is the solidification growth rate, increases with amplitude. Therefore, it was found that oscillating laser welding is beneficial for rapid solidification and the formation of finer solidification microstructures.
(4) The process diagram of the fusion zone width and depth constructed in this article proves that the fusion zone width can be increased at higher laser power and swing amplitude, as well as lower welding speed.
Therefore, the data indicates that high amplitude swing laser welding can fill the gaps in the mating surfaces of large workpieces. On the contrary, it was found that high laser power, low oscillation amplitude, and welding speed increased the depth of the fusion zone.
The flowchart generated by this work can be used to select the appropriate set of process parameters in the workshop without the need for repeated experimentation.
Source: Yangtze River Delta Laser Alliance
