The effect of laser impingement angle on the optimization of melt pool geometry to improve process stability during high-speed laser welding of thin-gauge automotive steels

Automated laser welding is a popular fusion joining method used for numerous applications involving the joining of similar and dissimilar materials of varying thicknesses. Laser welding offers several advantages over other fusion joining methods such as: high reliability and consistency in the quality of the welds, high production rates, ease of process optimization, higher power density and lower heat input, significantly reduced heat affected zone due to the ability to effectively deliver energy to a highly localized area, and most importantly, improved joint efficiency. However, without proper optimization, the laser welded joints can have significant external and internal defects such as porosity, humping, concavity, and undercut which are widely known to adversely affect the mechanical performance of the joint. The laser welding process is most commonly optimized by adjusting the laser power and the welding speed, but this usually increases the processing time which can be costly in an industrial setting. This work explores the optimization of high-speed laser welding of thin-gauge automotive steels by changing the laser impingement angle during open-keyhole mode welding. The numerical simulations and the experimental results presented in this study clearly show that by optimizing the laser impingement angle, the melt pool geometry can be effectively controlled which eliminates surface defects such as weld concavity and undercut when welding thin-gauge steels at high-speeds without the need for expensive consumables and tighter setups needed for wire-feeding capabilities. The findings presented in this paper hold a major relevance to industries that employ fiber laser systems in welding and additive manufacturing applications which can benefit from improved process efficiencies while minimizing defects.