3D Annular Spot Laser Welding System Based on Common Fiber Laser External Beam Shaping Technology

Professor Qin Yingxiong’s team from Huazhong University of Science and Technology published a research paper titled “A novel beam shaping method for adjustable focus Gaussian-ring mode laser in high-quality welding process” in the international journal Optics & Laser Technology, proposing an optical design solution to obtain a 3D Gaussian-ring laser beam by external optical shaping using a conventional fiber laser as the light source.

01 Paper Preview
The Gaussian-ring beam laser, as a novel laser mode with optimized energy distribution, can effectively suppress defects such as porosity and spatter in the welding process. It has been widely validated and applied to the welding of various materials such as steel, aluminum, and copper. However, existing Gaussian-ring beam lasers mostly rely on customized lasers with multi-cladding fibers, which have complex internal structures and high mode adjustment costs. Additionally, the focal lengths of the central Gaussian mode and the peripheral ring mode are the same, meaning this adjustment is limited to a 2D planar light field and cannot simultaneously optimize weld surface quality and depth. This paper proposes a novel shaping method to achieve freely designed focal lengths in a 3D Gaussian-ring beam laser based on 3D light field modulation. Without the need for a customized ring-mode laser, a standard single-mode Gaussian laser is used as the source. Through a single aspheric mirror, the shaping from 30-50 kW Gaussian laser to Gaussian-ring composite laser is realized. It is experimentally verified that the 3D Gaussian-ring beam improves weld depth and suppresses porosity in 304 stainless steel welding, providing an optimized solution for high-quality laser welding and other processing applications.

02 Full Paper Summary
Based on ray propagation theory and a self-designed ring-forming algorithm, an aspheric mirror with excellent surface quality is designed to achieve collimation, shaping, and focusing from a Gaussian single-mode laser to a 3D Gaussian-ring beam. We demonstrate 3D Gaussian-ring lasers with different spatial energy distributions through beam propagation simulations and measurements. Preliminary experiments were conducted to verify welding performance using 8-12 kW lasers for cladding on 16 mm thick 304 stainless steel plates, analyzing the weld seam’s 3D geometry and porosity under different parameters. Results show that with an appropriate power ratio and focal length difference, the peripheral ring focus expands and stabilizes the molten pool, aiding energy absorption and bubble escape, while the defocused central beam continuously acts on the keyhole bottom, deepening the molten pool and increasing weld depth.

03 Illustration and Interpretation
Figure 1 shows the design of the 3D Gaussian-ring beam. Based on a self-designed aspheric mirror, the collimation, shaping, and focusing from a standard Gaussian single-mode laser to a composite beam with adjustable energy distribution is realized.

Figure 1. Schematic of AFGRM laser propagation and aspheric mirror: (a) Collimation length of the aspheric mirror is Lc, with focal lengths Lf1 and Lf2. The divergence angle boundary is determined by the power ratio, where the center is shaped into a Gaussian beam and the outer region into a ring beam. (b) Actual surface division of the mirror. Red area has height z2(x,y), yellow area height z1(x,y) + z3(x,y) - Δz. Γ(r(θ),θ) denotes the shaping boundary.

Figure 2 shows four types of 3D Gaussian-ring beams with different power ratios, ring radii, and focal differences.

Figure 2. Power density distribution simulations of four AFGRM beams:
(a1)-(a3): 5:5 power ratio, Gaussian focal length 300 mm, ring 295 mm, radius 0.3 mm.
(b1)-(b3): 7:3 power ratio, same parameters.
(c1)-(c3): Same focal lengths (300 mm).
(d1)-(d3): Ring radius increased to 0.5 mm.

Figure 3 shows the simulated energy distribution of the AFGRM laser used in welding, with a ring focus at 297 mm (most concentrated), radius 0.3 mm; Gaussian focus at 300 mm with peak center intensity.

Figure 3. Simulated beam propagation of AFGRM:
(a) Propagation overview; center Gaussian beam focuses and then diverges, ring beam converges inward.
(b1)-(b2): 297 mm spot power density.
(c1)-(c2): 300 mm spot power density.

Figure 4 shows the measured power density distributions, matching the simulations in Figure 3, validating the reliability of the beam shaping method.

Figure 4. Measured laser propagation through AFGRM system:
(a) Overall beam form.
(b1)-(b2): 297 mm measured spot.
(c1)-(c2): 300 mm measured spot.

Figure 5 shows the welding experiment platform and laser head structure. The AFGRM head uses a single aspheric mirror and supports 30-50 kW lasers, stabilized via multi-channel water cooling and air curtain design.

Figure 5. AFGRM welding system:
(a) Real welding platform.
(b) Laser head schematic.

Figure 6 compares weld morphology from single-mode Gaussian vs 3D Gaussian-ring beams. Under the same total power, the 3D beam achieves deeper welds. With 10 kW total power and 8:2 power ratio, weld depth improves by 11.0%.

Figure 6. Weld results using Gaussian vs AFGRM beams:
(a1)-(a5): AFGRM welds (Gaussian 8 kW, ring 0–4 kW).
(b1)-(b4): Gaussian laser welds (9–12 kW). Yellow dashed lines show weld expansion from ring mode.

04 Conclusion

1. The proposed beam shaping method uses only one aspheric mirror and a standard Gaussian laser, simplifying structure and reducing cost.

2. The 3D Gaussian-ring beam (AFGRM) has adjustable power ratio, ring radius, and focal difference. The aspheric mirror maintains stable shaping under 30–50 kW laser exposure.

3. The mirror enables precise energy control. AFGRM energy distribution errors are 7% (simulation) and 6.5% (measurement).

4. The 3D Gaussian-ring beam offers superior weld depth. In experiments on 304 stainless steel, 10 kW AFGRM laser (8:2 ratio) increased depth by 37.0% and 11.0% over 8 kW and 10 kW Gaussian lasers, respectively.

**--Cite the article published by 高能束加工技术 on June 25, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."