The Influence of Varying Welding Positions on Laser Welding Seam Quality.

01 Introduction

Laser welding, as a key technology in modern manufacturing, is affected by various factors, among which the welding position is a critical variable. Different welding positions can lead to significant variations in molten pool flow, heat conduction, and solidification behavior, thereby influencing weld formation, porosity defects, and mechanical properties. According to different welding positions, welding methods can be classified into flat welding, horizontal welding, vertical-up welding, and vertical-down welding. Figure 1 shows schematic diagrams of various welding positions.

Figure 1. Schematic diagram of welding under different welding positions.

02 Influence of Welding Position on Weld Quality

Welding stress conditions vary under different positions, resulting in differences in weld morphology. In flat welding, the molten pool exhibits good symmetry, and the weld is uniformly shaped and aesthetically pleasing. Due to evenly distributed gravity, penetration depth remains stable, offering optimal mechanical properties and welding stability. In horizontal welding, gravity causes partial molten pool displacement, leading to less stable welding than in flat welding. In vertical-up welding, the welding direction opposes gravity; molten metal behind the keyhole tends to flow downward, and excessive heat input may cause burn-through, resulting in significant molten pool fluctuation and lower welding stability. In vertical-down welding, molten metal also flows downward due to gravity. However, in this case, the gravity direction aligns with the molten metal flow, avoiding metal separation and leading to smoother molten pool flow and better welding stability.

Figure 2. X-ray images of weld seams in different welding positions.

Figure 2 presents X-ray images of welds at different positions, showing that porosity is lower in flat and vertical-up welding, while higher in horizontal and vertical-down welding.

Figure 3. Schematic illustration of pore migration in welds under different welding positions.

Figure 3 illustrates the gas behavior in different welding positions. In flat welding, gas bubbles formed in the molten pool float upward under melt flow and buoyancy, and most escape before solidification, resulting in low porosity. In horizontal welding, the molten pool surface contacts unmelted base metal, blocking bubble escape and leading to higher porosity. In vertical-up welding, voids or bubbles rise under buoyancy, and some escape through the molten pool and keyhole before solidification, leading to relatively low porosity. In vertical-down welding, the upper edge of the molten metal is constrained by recently solidified metal instead of a free keyhole area as in vertical-up welding, making gas escape difficult and resulting in higher porosity.

Figure 4. Comparative analysis of tensile properties of welds in different welding positions.

Figure 4 compares the tensile properties of welds at different positions. Significant differences are observed among the four positions: flat and vertical-up welding show higher tensile strength than horizontal and vertical-down welding. Flat welding also exhibits the highest elongation, while horizontal welding shows the lowest.

Figure 5. Fracture morphology of tensile specimens after testing in different welding positions.

Figure 5 shows fracture morphologies of tensile specimens welded at different positions. No pores are observed on the fracture surfaces of flat and vertical-up specimens, while numerous pores are seen on the fractures of horizontal and vertical-down specimens. Porosity reduces the mechanical properties of laser welds by decreasing bearing area and concentrating stress, hence weld quality in horizontal and vertical-down welding is inferior.
Each welding position is suited for different applications. Flat welding is widely used in car body parts, 3C electronics precision components, aerospace thin-wall structures, and household appliance shells. Horizontal welding is commonly applied in circumferential welds of oil and gas pipelines and large pressure vessels. Vertical-up welding is mostly used in pipe riser butt joints and high-rise structural welding in construction and heavy machinery. Vertical-down welding is mainly applied in ship bottom structures and underground pipeline installation.

05 Conclusion

Welding position significantly impacts laser welding quality. Flat welding offers the best weld quality, while horizontal welding yields the most unstable results. In practical applications, flat welding should be prioritized. When vertical welding is necessary, vertical-up welding is preferred, with process parameters adjusted to minimize gravity effects and improve weld quality. With the advancement of intelligent welding technologies, the processes for different welding positions will be effectively optimized, significantly improving weld stability and narrowing quality differences between positions.

**--Cite the article published by 高能束加工技术 on March 19, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."