Research On Physical Mechanism Of Pulsed Laser Induced Arc And Technique Of Hybrid Welding Based On Low Energy Consumption And High Efficiency Purpose

With the development of manufacturing industry and engineering construction in world wide, the modern welding technology is developing in the direction of high efficiency, energy saving and high quality. It is one of the important problems to be solved urgently in the welding field to improve efficiency, and save energy. In this background, the laser-arc hybrid welding, which characterized by low energy consumption and high efficiency, was proposed. In this thesis, the influence of process parameters on induced efficiency (the ratios between penetration depth in different welding process with fixed laser power and arc current) in hybrid welding process is analyzed, and the physical essence of low energy consumption and high efficiency is analyzed. The energy consumption and efficiency in different welding process are compared. And low energy consumption laser-arc hybrid welding on special structural and materials work piece are carried out to widen the application scope of hybrid welding. The main contents and conclusions of this paper are as follows:(1) Phenomenal analysis in laser induced arc hybrid welding process. The effects of relative position between laser and arc and laser pulse parameters on the induced efficiency of the heat source without changing laser power and arc current are investigated. The results show that the induced efficiency increases with the decrease of Dla in L-T (laser leads arc) hybrid welding process. The induced effect of laser on arc is to stabilize arc, which is suitable for high speed welding. In T-L (arc leads laser) welding process, the induced efficiency increases and then decreased with the increase of Dla. While the induced efficiency gets maximum, the Dla increases with the increase of arc current. The induced effect of laser on arc is to compresses arc, which is suitable for full penetration welding on middle and thick plate. In hybrid welding process, the decrease of laser pulse width and pulse frequency and the increase of laser pulse current appropriately can improve induced efficiency. The change of the plasma shape can reflect the change of induced efficiency of laser on arc.(2) Mechanism analysis of laser induced arc. The additional pressure, electron kinetic energy and plasma relaxation time were calculated by theoretical calculation while the induced efficiency gets maximun. The results show that the additional pressure of arc column increases 5.2 times, and the kinetic energy of the electron is increased by 27.5%, and the energy density is improved during laser pulse action period. The combination of the three effects mentioned above benefit the decrease of energy consumption and the increase of welding efficiency. After laser pulse action period, plasma relaxation enhance the laser induce effect on arc. In this experimental, the calculated relaxation time is about 7.5 ms and the actual relaxation time is about 8.0 ms, the calculated result is consistent with the experimental data. The recoil pressure is the main force that maintain the open state of laser keyhole. The open state of laser keyhole lasts a long time when laser acts on AC arc current wave peak. In this process, the electrons in plasma move from keyhole to the liquid metal and promots the evaporation, vaporization and ionization of base metal. The open state of laser keyhole and the formation of plasma are mutually improved. The changes of plasma go together with keyhole behaviors.(3) Analysis of the effect of laser induced arc. Different welding methods including laser welding, arc welding and laser induced arc hybrid welding were adopted on the same size materials to achieve full penetrated joints, and energy consumption and welding efficiency were calculated and compared between the different welding methods. The results showed that the induced effect of laser on arc significantly improves the welding efficiency and decreases the energy consumption. The efficiency of hybrid welding is 7.14 times of laser welding and 4.29 times of arc welding. And the energy consumption of hybrid welding is 22.23% of laser welding and 63.85% of t arc welding.(4) Application of laser induced arc and new technology development. Under the guidance of the theoretical analysis, low energy consumption laser induced arc hybrid welding of T shaped structure and butt welding processes are developed. Results show that hybrid welding realizes quality connection of T-type structure of 1.4 mm magnesium alloy sheet. And connection angle at both sides of the wall panel and strengthening rib are smooth and beautiful. Weld reinforcement is controlled in a suitable range, and the shear strength of the joint reaches 89% of that of base metal. Low energy consumption laser induced arc hybrid welding has a great applicability on T-type structure of 1.4 mm titanium alloy sheet. The hybrid heat source has achieved one-side welding with back formation of 2.5 mm titanium alloy sheet. Uniform and continuous ripples form on the top surface of the weld seam and no welding defects included macro porosity, undercut are found. Weld penetration is moderate, uniform, continuous, and the joint performance can reach or exceed base matal.