The Application Potential of Laser Welding in A Vacuum Environment

01 Introduction
Laser welding plays an important role in industrial manufacturing due to its high precision and efficiency. However, traditional high-power laser welding faces bottlenecks in pursuing higher welding efficiency and thicker material joining. Issues such as intense plasma plume, violent molten pool turbulence, and spatter limit further application expansion. Against this backdrop, researchers have turned their attention to a special process environment—vacuum. Vacuum laser welding technology combines high-power lasers with low-pressure environments to achieve greater weld depth. With the rapid development of high-power lasers in recent years, this technology has been revitalized, showing great research value and application potential.

02 Comparison Between Vacuum Laser Welding and Conventional Laser Welding
Compared to conventional laser welding in atmospheric conditions, laser welding under vacuum or low-pressure environments undergoes fundamental changes in physical processes and welding results. The most significant advantage is the drastic increase in weld depth. Numerous experiments show that as environmental pressure decreases, weld depth significantly increases, reaching two times or more than that in atmospheric conditions under certain conditions. This improvement exists within a “critical pressure” range, usually between 0.1 kPa and 10 kPa. Below this threshold, the increase in weld depth saturates or slightly decreases. Vacuum laser welding can achieve about 50 mm weld depth at 16 kW laser power, far exceeding atmospheric welding and reaching levels comparable to electron beam welding but requiring vacuum levels two orders of magnitude lower. Meanwhile, weld geometry is greatly optimized, becoming deeper and narrower, forming deep and parallel weld seams similar to electron beam welding. This deepening effect is particularly evident at low to medium welding speeds (approximately below 3.0 m/min), while at speeds above 4 m/min, environmental pressure influence becomes negligible.

Figure 1 Comparison of cross-sectional profiles using different welding processes (a) laser welding (laser power of 16 kW, welding speed of 0.3 m/min, ambient pressure of 1000 mbar), (b) laser welding under vacuum (laser power of 16 kW, welding speed of 0.3 m/min, ambient pressure of 10−1 mbar), (c) electron beam welding (electron beam power of 16 kW, welding speed of 0.3 m/min, ambient pressure of 10−3 mbar)

Figure 2 Effect of ambient pressure on penetration at different welding speeds

The vacuum environment fundamentally resolves plasma plume issues encountered in traditional high-power laser welding. In conventional welding, metal vapor generated by laser-material interaction forms a bright plasma plume, causing scattering, refraction, and absorption of the incident laser beam, creating a “shielding effect” that reduces effective energy reaching the workpiece, affecting weld depth and process stability. In vacuum conditions, as pressure drops from 101 kPa (atmospheric pressure), the size and brightness of the plasma plume dramatically decrease. At 10 kPa, intense luminescence and spatter largely disappear; at 0.1 kPa, the plasma plume is almost completely suppressed and invisible to the naked eye. The disappearance of plasma means laser energy can be delivered more stably and efficiently into the workpiece depth, making the entire welding process more stable.

This process stability improvement directly reflects in the optimization of molten pool and keyhole dynamics, resulting in a leap in weld quality. High-speed imaging shows the average keyhole entrance diameter decreases under vacuum, and the surface molten pool becomes narrower and more stable. Real-time X-ray observations further reveal significant increases in keyhole depth and larger keyhole front wall angles under vacuum. More stable keyhole and molten pool flows greatly reduce welding defects such as pores and spatter caused by keyhole collapse or violent molten pool fluctuations, enabling higher quality, dense, and pore-free welds.

Figure 3 Laser plasma of A5052 aluminum alloy observed under reduced pressure

03 Applications of Vacuum Laser Welding
Thanks to its process stability, spatter-free nature, and high weld quality, vacuum laser welding technology, although still in its infancy, has shown great potential in precision manufacturing fields with high demands, such as the automotive industry. It is particularly suitable for manufacturing automotive powertrain components. Some German research institutes and companies have successfully applied it to batch production of transmission parts like planetary gear carriers (as shown in Figure 4). Vacuum laser welding allows precise joining of gear parts with maximum weld depths up to 25 mm in a single pass without concerns about oxidation and spatter contamination, achieving defect-free high-quality joints.

Figure 4 Planetary wheel carrier welded by laser welding under vacuum

Moreover, the technology has made significant breakthroughs in thick plate welding, opening new paths for efficient, single-pass welding of thick plates, which traditionally was limited to thin sheet structures. Vacuum laser welding can handle thick plate welding of structural steels, stainless steels, nickel-based alloys, titanium alloys, and copper alloys. Studies show that using 16 kW laser power, full penetration welding of 50 mm thick S690QL steel plates and 38 mm thick nickel-based alloys can be achieved at low speeds with good weld formation. This powerful capability enables it to directly challenge electron beam welding in thick plate welding while offering additional advantages such as lower vacuum requirements and no X-ray radiation protection issues.

04 Conclusion
Vacuum laser welding technology, by placing laser welding in a low-pressure environment, effectively overcomes bottlenecks such as plasma interference and molten pool instability encountered in traditional high-power welding. Its most significant advantage is greatly increasing weld depth—typically more than twice that of atmospheric welding—and forming deep and parallel weld seams similar to electron beam welding, but with vacuum levels far lower than electron beam welding. This performance leap stems from the effective suppression of plasma plume in vacuum, enhancing energy utilization and process stability. Meanwhile, more stable keyhole and molten pool dynamics significantly reduce pores and spatter defects, yielding higher quality welds. Leveraging these advantages, vacuum laser welding has been successfully applied in precision manufacturing of automotive powertrain components and various thick plate single-pass welding fields, showing potential to challenge electron beam welding.

**--Cite the article published by 高能束加工技术 on July 3, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."