Laser-arc hybrid welding of 12- and 15-mm thick structural steel

Abstract

High-power lasers are very effective in welding of plates thicker than 10 mm due to the keyhole mode. High-power intensity generates a vapor-filled cavity which provides substantial penetration depth. Due to the narrow and deep weld geometry, there is susceptibility to high hardness and weld defects. Imperfections occur due to keyhole instability. A 16-kW disk laser was used for single-pass welding of 12-to 15-mm thick plates in a butt joint configuration. Root humping was the main imperfection and persisted within a wide range of process parameters. Added arc source to the laser beam process may cause increased root humping and sagging due to accelerated melt flow. Humping was mitigated by balancing certain arc and other process parameters. It was also found that lower welding speeds (< 1.2 m/min) combined with lower laser beam power (< 13 kW) can be more positive for suppression of humping. Machined edges provided more consistent root quality and integrity compared with plasma cut welded specimens. Higher heat input (> 0.80 kJ/mm) welds provided hardness level below 325 HV. The welded joints had good Charpy toughness at − 50°C (> 50 J) and high tensile strength.

Root formation and metallurgical challenges in laser beam and laser-arc hybrid welding of thick structural steel

“…For 12 mm thick plates, high root quality was achieved with 0.45 kJ/mm laser heat input and > 15 mm laser-arc distance. The humping is decreasing with increase laser-arc distance which is related decrease of melt flows velocities [22] and lower negative interaction between the processes [30,31]. Autogenous LBW provided better keyhole stability compared to LAHW; thus, higher quality of the root may be achieved.…”

“…1.2). This is related to unfavorable effect on melt flows providing strong momentum in the root [22] with poor process control due to keyhole instability. The same parameters were repeated for another 0.5 m long plate with significant adjustments in WFR reaching 16 m/min to form larger weld reinforcement.…”

“…The present work is a part of the technology qualification for the longest fjord crossing bridge in Norway (called Bjørnafjorden which is 5 km long), the Ferry Free E39 road. First attempts have been made for butt welds without bevelling of plates in the previous work using 12 and 15 mm thick steel [22]. It has been shown that optimized parameters by repeating experiments did not provide the same quality over large lengths.…”

Advanced Welding Manufacturing: A Brief Analysis and Review of Challenges and Solutions

“…They concluded that focusing properties affected the weldability strongly during laser welding of the thick steel plate and that a long focus depth was particularly useful in producing sound welds. To overcome the fit-up issue, a common solution from process is to use a laser together with an arc to perform hybrid welding [33,34] that may be simply considered as arc melting the surface for the laser to initiate the interaction with the material.…”

Hybrid laser arc welding: State of the art in technology

“…In addition, during the welding process GMAW applies a high heat input to the welding material, resulting in large heat-affected zones HAZs and occurrence of the undesired microstructure [6]. On the other hand, LBW provides deep and narrow welds at high welding speeds, due to its high energy density, leading to a small HAZ and low distortion [7]. However, the LBW process like any other process has disadvantages, one of them is high cooling rate from the welding zone that leads to high weld metal hardness and low toughness, which sometimes cannot meet the minimum mechanical properties [8].…”