Laser Oscillation Welding - Defect Control

01 Introduction

Laser, as an advanced processing tool, is playing an increasingly important role in the field of industrial welding. Although traditional laser welding technology can control certain defects to some extent, its effectiveness is often limited by fixed welding parameters and processes. In recent years, the emergence of laser oscillation welding technology has provided a new solution for controlling welding defects. By introducing laser beam oscillation during the welding process, this technology can significantly improve the dynamic characteristics of the molten pool, thereby optimizing welding quality. Laser oscillation welding technology mainly relies on precise control of the laser beam and oscillation techniques to achieve efficient and high-quality welding.

02 Laser Oscillation Welding

Appearance improvement: During welding, the laser beam is rapidly and precisely oscillated to cover the entire welding area. While moving along the welding direction, the beam simultaneously performs circular, figure-eight, spiral, and other forms of oscillation. Chen et al. used oscillating laser welding for dissimilar aluminum alloys and found that the weld appearance on both the front and back sides was significantly improved compared with non-oscillating welding. In addition, transverse oscillation was applied to increase gap adaptability in groove welding. For conductive connection parts, it is sometimes necessary to enlarge the current-carrying area or metallurgical bonding area, which also requires oscillating laser welding to transform the metallurgical bonding surface into a "U" shape.

Figure 1. (a) and (b) Cross-sectional morphology and weld size statistics of welds under different oscillation modes; (c) Upper surface formation of welds under different oscillation modes.

Improving sidewall fusion defects: In traditional narrow-gap laser welding of medium-thickness plates, sidewall lack of fusion is a common defect due to the uneven energy distribution in the groove—central areas receive high heat input while sidewalls receive little, resulting in poor bonding. The key measure to solve sidewall fusion defects is to increase the heat input to the sidewalls. Laser beam oscillation adjusts the spatial energy distribution. During welding, oscillation enables a more reasonable energy distribution across the surface. When groove width changes, adjusting the oscillation amplitude to match the groove width allows effective heat input to the sidewalls.

Figure 2. Macroscopic images of welds from the first layer (L1) to the seventh layer (L7) for welding with and without oscillating laser welding.

Reducing porosity defects: The mechanism by which laser oscillation suppresses porosity is attributed to improved keyhole stability and enhanced molten metal flow. Figure 3 shows molten pool flow behavior tracked by tracer particles during welding. Beam oscillation causes the keyhole to perform high-frequency, high-speed rotational stirring, which promotes bubble escape and has a “capture” effect on already solidified pores. Meanwhile, the oscillation increases the keyhole area and reduces its instability and collapse probability, thus decreasing bubble formation.

Figure 3. (a) and (b) Trajectory of tracer particles during welding; Keyhole opening area: (c) without oscillating laser welding (d) with oscillating laser welding.

Reducing crack defects: Hot cracks are defects formed due to internal stresses and metallurgical factors during welding, typically in the heat-affected zone (HAZ). These cracks result from the material’s vulnerability at high temperatures, welding stress, and chemical composition. Traditional laser welding may cause hot cracks due to the following reasons: First, high energy input leads to rapid heating and cooling, creating steep thermal gradients and high stress; second, metallurgical reactions during welding may cause segregation of low-melting-point impurity elements, forming brittle phases and increasing crack sensitivity; finally, rapid solidification may lead to microstructural inhomogeneity, with columnar grains growing from the molten pool edges toward the center, as shown in Figure 4. This significantly increases crack sensitivity.

Figure 4. Laser welding solidification modes: (a) conventional laser welding (b) oscillating laser welding.

Laser oscillation welding effectively alleviates or eliminates hot cracks by introducing laser beam oscillation. The periodic oscillation of the beam promotes metal flow in the molten pool, thereby improving microstructural uniformity. Grains grow coaxially from the center of the molten pool, as shown in Figure 5. These coaxial grains serve as protective barriers preventing crack propagation and act as thermal insulation layers. At the same time, laser oscillation helps reduce brittle phase formation caused by element segregation, thus lowering the risk of hot cracking.

Figure 5. (A) Solidification microstructure characteristics of conventional laser welding welds (B) solidification microstructure characteristics of laser oscillating (CCW) welds.

03 Conclusion

Compared with autogenous laser welding, oscillating laser welding technology is recognized for effectively reducing porosity formation and improving defects such as sidewall lack of fusion. Due to the stirring effect of the beam on the molten pool, it has significant advantages in enhancing gap adaptability, improving microstructure uniformity, and refining grains. The application of laser oscillation welding expands the usability of laser welding, enabling high-efficiency precision welding for larger or wider weld seam components, and relaxing requirements on base process and assembly precision.

**--Cite the article published by 高能束加工技术 on January 24, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."