High Surface Quality Welding of Aluminum Using a Tunable Ring-Shaped Fiber Laser

Researchers from Okayama University in Japan published "High surface quality welding of aluminum using adjustable ring-mode fiber laser" in the Journal of Materials Processing Technology.

01 Paper Introduction

Laser welding technology, due to its high efficiency, high precision, and applicability to a wide range of materials, has been widely applied in industrial production. However, the high reflectivity and high thermal conductivity of aluminum present challenges to welding quality, especially in deep penetration welding where surface quality issues and molten pool instability easily occur. In recent years, Adjustable Ring Mode (ARM) fiber lasers, with their ability to dynamically adjust beam distribution, have provided new possibilities for solving these problems. This study investigates the performance optimization of ARM fiber lasers in aluminum welding through experiments and numerical simulations.

02 Overview

This paper presents experimental and simulation studies on aluminum welding using ARM fiber lasers, aiming to optimize welding quality by adjusting the power distribution between the center and ring, as well as the direction and flow rate of shielding gas. The key focuses of the study include:

1. Experimental design: Testing different power combinations and gas parameters in aluminum plate welding.

2. Result analysis: Evaluating welding quality through cross-sections, surface roughness, and penetration depth data.

3. Numerical simulation: Using Finite Element Method (FEM) modeling to verify experimental results and analyze the influence of temperature distribution.

The study demonstrates that ARM fiber lasers, through dynamic power distribution adjustment combined with optimized shielding gas parameters, can achieve efficient and high-quality aluminum welding, providing technical guidance for industrial applications.

03 Figures and Analysis

Figure 1 shows the surface and cross-sectional morphology of welds under 2.0 kW center power and 4.0 kW ring power with different shielding gas flow rates and directions.

Figure 1. Surface and cross-sectional appearances at different shielding gas flow rates and directions

Figure 2 illustrates the variations of reinforcement, penetration depth, and surface roughness. Reducing gas flow rate (from 50 L/min to 15 L/min) increases penetration by about 9%, decreases reinforcement by about 40%, and reduces surface roughness by about 28%. Changing the shielding gas direction from back to side further increases penetration by about 18%, decreases reinforcement by about 37%, and reduces surface roughness by about 29%. Overall, low-flow back shielding gas achieves high-quality welding with deep penetration, low reinforcement, and low surface roughness.

Figure 2. Changes in reinforcement, penetration, and surface roughness at different shielding gas flow rates and directions

Figure 3 shows weld surface and cross-sectional appearance under different power densities, with nitrogen shielding gas supplied from the back at 15 L/min. The total laser power increases gradually from 5.0 kW to 6.0 kW.

Figure 3. Surface and cross-sectional appearances at different power densities

Figure 4 presents the variations of reinforcement, penetration depth, and surface roughness with power density. As power density increases, penetration, reinforcement, and surface roughness all increase. For each additional 1.0 kW in total power, weld roughness increases by about 12%. The increase in laser power enhances energy density, achieving deeper penetration, but excessive power may cause spatter, leading to higher weld surface roughness.

Figure 4. Changes in reinforcement, penetration, and surface roughness at different power densities

Figure 5 shows the temperature distribution along the welding direction on the top surface under dual-mode welding with 1.5 kW center power and 3.5 kW ring power. The laser beam is located at the sample center. Sixteen milliseconds after laser irradiation, the surface temperature gradually rises and rapidly decreases with distance from the weld center. Under laser irradiation, the weld center temperature exceeds the evaporation point, while adjacent points are around 1000 K and 700 K. When only center power is used, due to the smaller spot size, the high-temperature region concentrates in a smaller area, resulting in a narrower weld.

Figure 5. Top surface temperature distribution along the welding direction

Figure 6 compares temperature history between dual-mode welding and pure ring-mode welding at t = 16 ms, transverse to the welding direction. Both cases have a total power of 5.0 kW. Temperature fluctuations occur due to the gap between the ring mode and fiber center. In both cases, the peak temperature appears at the laser beam center, with similar temperature histories, but the peak temperature in dual-mode welding is higher. Variations in peak temperature greatly influence weld appearance, as they affect keyhole formation and molten metal behavior.

Figure 6. Top surface temperature history for dual-die and pure ring die welding

04 Conclusion

1. Advantages of dual-mode power distribution: By reasonably allocating center and ring power, ARM fiber lasers achieve deep penetration welding with high penetration capability and low surface roughness.

2. Optimization of shielding gas parameters: Low-flow back shielding gas significantly improves welding quality and reduces surface irregularities.

3. Temperature distribution and welding stability: Dual-mode power distribution optimizes molten pool temperature fields, enhances stability, and reduces spatter and surface defects.

4. Industrial application prospects: ARM fiber lasers provide efficient and high-quality welding, supporting aluminum applications in aerospace and automotive manufacturing.

**--Cite the article published by 高能束加工技术 on December 18, 2024, in the WeChat public account "High-Energy Beam Processing Technology and Applications."