Power and welding speed influence on bead quality for overlapped joint laser welding

Laser welding has gained more and more industry acceptance due to narrow Heat Affected Zone (HAZ), low distortion levels, possibility of remote processing and outstanding welding speeds when compared to traditional electric arc processes. Automotive industry requires a significant amount of overlapped joint welding, which usually is applied to the chassis assembling. Thus, as a mean to support laser users to optimize the welding process, this paper presents an approach through an experimental methodology followed by a phenomenological discussion about the quality of overlapped welded joints. Arguments are based on power and welding speed parameters variation and their related outcomes. This approach allows mapping of main defects such as porosity, undercut and insufficient penetration, as well as identifying eventual preventive actions. A 10 kW IPG Photonics YLS 10000 fiber laser was used to weld 3 mm SAE 1008 steel sheets. The power ranged from 5 kW to 7 kW, while the welding speed ranged from 2 to 5 m/min. High power levels at low welding speeds led to high temperature, resulting into an undercut issue, and low power levels at high welding speed led to insufficient penetration. Porosity was the most common defect. The best results, which did not show any type of discontinuity, were obtained at a laser power of 5 kW and a welding speed of 3m/min and 4m/min.