Microstructure and Mechanical Properties of Narrow Gap Laser-Arc Hybrid Welded 40 mm Thick Mild Steel
Both laser-arc hybrid welding and narrow gap welding have potential for the fabrication of thick sections, but their combination has been seldom studied. In this research, 40 mm thick mild steel was welded by narrow gap laser-arc hybrid welding. A weld with smooth layer transition, free of visible defects, was obtained by nine passes at a 6 mm width narrow gap. The lower part of the weld has the lowest mechanical properties because of the lowest amount of acicular ferrite, but its ultimate tensile strength and impact absorbing energy is still 49% and 60% higher than those of base metal, respectively. The microhardness deviation of all filler layers along weld thickness direction is no more than 15 HV0.2, indicating that no temper softening appeared during multiple heat cycles. The results provide an alternative technique for improving the efficiency and quality of welding thick sections.
Metal transfer characteristics of rotating arc narrow gap horizontal GMAW
Abstract The metal transfer process in rotating arc narrow gap horizontal welding is successfully observed by the high speed photography system. Because of the difference of the arc length induced by the molten pool surface shape in the rotating arc horizontal welding, the metal transfer has certain change regularity. In the weld width direction, the transfer frequency in the area of near both sidewalls is larger than that in the centre of the groove. In a rotating period, the transfer frequency in the downward motion process is larger than that in the upward motion process. The rotating arc process can improve the metal transfer. The results indicated that the centrifugal force induced by the arc rotating has great effect on the globular transfer mode which has lower transfer frequency and larger droplet size. Regarding the spray transfer mode, it has limited effect.
Analysis of the hybrid pulsed MAG-YAG laser plasma with synchronization of multiple signals
In this paper, a synchronization system is developed for collecting multiple signals of arc plasma which is generated by the hybrid pulsed metal active gas (MAG)-YAG laser welding process. The synchronization system can collect spectra of the plasma, arc voltage, welding current, and high speed video simultaneously. Because the hybrid arc plasma fluctuates with the variation of pulsed welding parameters, acquiring the transient signals is very important for analysis of the coupling effect. With the application of synchronization signals, the transient state of the hybrid plasma can be detected and analyzed. The results show that the interaction between laser beam and welding arc is quite different for different stage of the welding parameter. In the background level of welding current, the laser beam acts directly on the front edge of welding pool, which obviously decreases the effect of diffraction by the solid weld plate. The arc plasma is attracted by the laser and shifts to the laser beam. In the puls...