# Laser Welding under Vacuum: A Review
## 5 Applications of Laser Welding under Vacuum  
As an emerging welding technology, laser welding under vacuum has received much attention in recent years. The reports of laser welding under vacuum mainly focused on the effect of ambient pressure on laser welding phenomena. Laser welding under vacuum is still at the beginning stages of application. Based on the advantages of laser welding under vacuum, the applications of this competitive technology are expected. The main application attempt was on the mass production of drive section components with radial and/or axial weld seams [47; 59; 60]. Within the framework of a cooperation of PTR Company and RWTH Aachen University, a cycle machine for welding with laser beam under vacuum was implemented. The planet wheel carrier and gear wheel were fabricated by the cycle machine for laser welding under vacuum. As shown in Figure 11, the plate wheel carriers consist of a planet wheel carrier with axle arm and a coronoid bole carrier. The welding zone is triangular and the maximally required penetration depth is 25 mm. A sound welded joint without oxides and spatters was fabricated using a laser power of 7.5 kW, a welding speed of 0.42 m/min, a focus position of \(-\)5 mm and an ambient pressure of 2 kPa. At the same time, Pro-beam, TRUMPF and the its at TU Braunschweig are also adapting the process for the low-pressure, spatter-free laser welding of powertrain components into industrial application [61; 62]. The powertrain components requiring weld penetration depths of between three and six millimeters and a high feed rate were manufactured. Because of stable process without spatter, high weld quality and proper penetration depth, laser welding under vacuum is very suitable for the fabrication of powertrain components.  
Figure 11: The planet wheel carrier welded by laser welding under vacuum ((laser power is 7.5 kW, welding speed is 0.42 m/min, defocus distance is \(-\)5 mm, ambient pressure is 20 mbar-1). Reproduced with permission from [59], John Willey and Sons, 2015. (**a**) The schematic of planet wheel carrier, (**b**) Cross-section in stud center, (**c**) Longitudinal section through the weld.  
Laser welding has been widely used in various productions. However, laser welding is mainly used in the sheet structure with small thickness. With the advent of new high power solid lasers, the use of solid-state laser in deep penetration welding has been constantly explored. The exceeding expected phenomena of laser welding under vacuum make it very suitable for thick plate applications where low welding speeds can be applied to achieve very high penetration depth and for welding tasks with the highest demands on the weld quality. Some various materials, such us copper alloys, structural steels, duplex stainless steels, nickel-based alloys, titanium alloys and so on, have been welded by ISF at RWTH Aachen University [30; 31; 32; 46]. As shown in Figure 12, the plate thickness of 50 mm for unalloyed steel S690 QL was achieved by single pass laser welding under vacuum at a laser power of 16 kW, a welding speed of 0.5 m/min, a focus position of \(-\)5 mm and an ambient pressure of 10 Pa. The full penetration weld joint of 38 mm nickel-base alloy without was fabricated at a laser power of 16 kW, a welding speed of 0.4 m/min, a focus position of 0 mm and an ambient pressure of 10 Pa. As shown in Figure 12, both the weld joints presented a sound weld with super deep penetration depth. It is clear that laser welding under vacuum has the developing prospect of welding heavy section components under low vacuum. As we know, electron beam welding is thought to be suitable for single pass weld of thick plate [29; 63]. In this regard, laser welding under vacuum is able to challenge the electron beam welding in terms of the weld quality and penetration depth. In addition, laser welding under vacuum has the following advantages: relatively low vacuum level, lack of X-ray radiation protection and possible arising of nonmetallic [29; 64].