不同焊接位置下激光-CMT 复合焊成形特性分析

Objective Laser-arc hybrid welding (LAHW), particularly when employing cold metal transfer (CMT) as the arc source, has emerged as a promising technique for fabricating thick^-walled components with high precision, low heat input, and enhanced process controllability. It combines the advantages of laser welding—high energy density and deep penetration—with the low^-spatter, stable arc transfer characteristics of CMT. While previous research has demonstrated the benefits of LAHW in flat^-position welding, engineering practice frequently demands all^-position welding, including vertical welding and overhead welding, which introduce significant challenges due to gravity^-induced instabilities. The variation of gravitational direction across welding positions significantly affects molten pool behavior, solidification dynamics, and weld formation quality. Without effective control strategies, this often leads to reduced cladding efficiency, inconsistent bead geometry, and structural defects. To address this, the present study proposes a strategy for adjusting the energy distribution ratio based on welding position to dynamically regulate the balance between laser and arc input power. The objective is to elucidate the coupling mechanism of gravity and multi^-physics fields in laser^-arc hybrid welding in flat, vertical, and overhead positions and to establish optimized process windows, that ensure high-quality, stable, and efficient weld formation in all orientations. Methods Welding trials were carried out on 316L stainless steel using a laser^-CMT hybrid system. The effect of welding position on weld bead geometry, molten pool stability, microstructure, and cladding efficiency was investigated. High-speed imaging was employed to observe molten pool dynamics, while optical microscopy (OM), scanning electron microscopy (SEM), and quantitative image analysis (ImageJ) were used to assess weld profiles and internal features. Based on weld current, voltage, laser power, and travel speed, the energy distribution ratio between laser and arc was computed and adjusted for each welding position to suppress pool instability and optimize weld shape. Results and Discussions The results show that welding position significantly influences weld formation by altering the force balance and heat flow within the molten pool. Compared to flat welding, both vertical welding and overhead welding experience increased instability, manifested by distorted bead shapes, poor penetration uniformity, and spatter or hump formation. Specifically, the cladding efficiency declined to 89.0% and 82.2% for vertical and overhead positions, respectively, compared to flat welding (Figs. 3 and 4). High-speed camera images revealed that the molten pool surface was flat and stable in flat welding, while vertical welding caused downward metal flow due to the tangential component of gravity, and overhead welding displayed enlarged, unstable pools with a tendency to sag (Fig.5). Through detailed force analysis, it was found that gravity interacts with laser recoil pressure and arc force in a position-dependent manner (Fig. 6). In flat welding, gravity and recoil pressure combine to accelerate metal penetration. In vertical welding, gravity introduces shear flow, disrupting pool symmetry. In overhead welding, gravity acts in opposition to surface tension, increasing the risk of pool sagging and incomplete fusion. To compensate for these gravitational effects, the energy distribution ratio (laser∶arc) was optimized to 1.68∶1 (flat), 2.16∶1 (vertical), and 2.73∶1 (overhead), as calculated from the welding parameters (Table 2). These adjustments led to significant improvements in weld formation across all positions: the welds exhibited smoother surfaces, reduced reinforcement fluctuation, better fusion line symmetry, and consistent penetration (Figs. 7 and 8). The increase in laser contribution provided deeper keyhole penetration and greater pool stabilization force, especially critical in overhead welding where arc force alone was insufficient to resist gravity. Furthermore, position-specific thermal gradients induced distinct solidification patterns. The microstructural analysis revealed the formation of lathy δ ^-ferrite in vertical welding due to rapid cooling, coarse skeletal δ ^-ferrite in overhead welding due to slow solidification, and mixed features in flat welding (Fig.9). Importantly, by adjusting the energy distribution ratio, it was possible to manipulate molten pool convection and cooling rates, achieving position^-sensitive microstructure design. This establishes a processstructure linkage in laser^-CMT hybrid welding that has not been fully demonstrated before. Conclusions A novel strategy for regulating the energy distribution ratio was proposed to address the instability and defect issues encountered during vertical and overhead welding in laser^-CMT hybrid welding. Welding position was shown to significantly affect molten pool dynamics and solidification behavior, which in turn governed weld formation quality and cladding efficiency. Gravity-induced instabilities reduced cladding efficiency by up to 17.8 percentage points. Through targeted tuning of the laser^-to-arc energy input, optimized ratios of 1.68∶1, 2.16∶1, and 2.73∶1 for flat, vertical, and overhead positions respectively were found to effectively stabilize the molten pool and ensure uniform weld geometry. Additionally, the study revealed that position^-induced thermal gradients can be leveraged, together with energy regulation, to control microstructure evolution. The ability to tailor both macro^- and micro^-scale weld characteristics via adaptive energy control enhances the robustness and application scope of laser^-CMT hybrid welding. This work not only provides theoretical understanding of all^-position welding physics but also offers practical guidance for future industrial deployment of laser^-CMT hybrid welding systems for complex structural welding tasks.