 | 2004 |
Abstract:
This paper renders the welding of extruded aluminium profiles by a hybrid bifocal laser system. The aluminium alloy considered within the research project TR10 is EN AW-6060 (AlMgSi0,5) temper T66 without and with filler wire Al4047 A (SG-AlSi12) to avoid hot cracks. The hybrid laser system is realized by combining an Nd:YAG laser with a high power diode laser (HPDL), both of 3 kW maximum power. The beam parameter product (BPP) of the employed Nd:YAG of 25 mm*mrad translates with an optical system of focal length f = 150 mm into a circular focus of diameter 0.45 mm whereas the BBP of the HPDL of 85 x 200 mm*mrad can achieve a rectangular focus of 0.9 x 3.7 mm. The optical system allows the respective focal plane and relative position of the foci to be independently positioned. This paper presents research into the fundamentals governing the melt pool dynamics for each separate laser source and how successfully they dissolve the surface oxygen layer. The process parameters for extruded AW-6060 were determined by butt joints of 2 mm plate specimens. The influence of different inert shielding gas mixtures with or without active components is considered. The parameters are validated by weld tests according to DIN EN 895 and 970. First results promising for application in production industry are that the hybrid system increases the maximum feed speed from 2.0 m min-1 of the Nd:YAG to 3.75 m min-1 of the hybrid system and analogously reduces the roughness of the weld surface from 60 micro m to about 10 micro m. Moreover, the effects of the hybrid system on a welded structure are shown by simulation. Approaches are developed by means of the Finite Element Method (FEM) to consider multiple heat sources to model and calculate the distortional influence of different beams focussed on a given structure. The results of the simulation are validated by congruence with measurements of distortions of the real structure.
Keywords: Laser beam welding, hybrid, EN AW-6060