In order to apply aluminum alloys to structural components, they should be joined with sufficient strength and quality as high welding speed as possible. High-power laser welding is expected to achieve much higher productivity than conventional joining techniques. Welding of aluminum alloys was performed using 2-kW and 3-kW continuous wave Nd:YAG lasers. Two beams were delivered by optical cables 0.6 mm in diameter and focused on the surface of the specimens as dual spots. Overlap joints of 2-mm-thick sheets were made at various welding parameters, including beam distance, beam arrangement and welding speed. The quality of the bead, including its appearance and macrostructure, and the tensile strength of the joints were investigated. At a shorter beam distance of 0.36 mm, the weld bead surface was humped, making it unacceptable in terms of quality. Sound weld beads were obtained at beam distances of 0.6 mm and 1.0 mm. As the beam distance was increased, the weld depth became shallower. At a beam distance of 1.0 mm, the weld area was too small to provide sufficient strength.
Aluminum alloys were welded using dual focus beams formed with two Nd:YAG lasers with the aim ofobtaining a stable welding process. The relationship between the configuration of the spot beams and the quality of the weld beads was investigated using X-ray and high-speed camera observations. The number ofpores was clearly related to the ratio of the keyhole depth to the keyhole opening. A larger keyhole opening and/or a shallower keyhole depth resulted in a smaller number of pores caused by instability of the weld pool. Based on the investigation, a car body component was welded with a dual focus beam system. The results show that aluminum car body panels can be welded stably at high speed with little distortion under optimum conditions.
Laser beam welding of aluminum alloys is becoming of increasing interest with respect to light-weight structures. Compared to welding of steel, the process is rendered difficult by the specific material properties. On the basis of a fundamental understanding of the relevant physical mechanisms, guidelines for a successful conduction of the welding process and quality assurance are presented. Factors relevant for deep penetration threshold, process efficiency, process stability and for achieving high seam quality are discussed. In particular, by the combination of two individual focal spots along or normal to the welding direction a process-adapted distribution of the laser power yields substantial improvements. With respect to quality assurance a new method presented here uses the relationship between the geometry of the keyhole and the emitted laser light to control welding depth and to monitor seam defects.
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