| Twin deposition electrode arc welding (TDEAW) is an advanced welding technology that work-piece is not linked to power source, arc is ignited and burns between mutual parallel insulating welding rods. This technology changes welding thermal cycle of work-piece and has advantages of high deposition efficiency, high usage of electric energy, having no active spot areas on work-piece and large regulating range of fusion ratio. In order to increase penetration of the weld and reduce content of diffusible hydrogen for ensuring the welding quality, pulse power source is applied to twin deposition electrode arc welding. The research is of important realistic significance to the application of pulsed twin deposition electrode arc welding (PTDEAW).In this study, pulsed parameters for welding were initially determined for good weld bead formation. Effects of pulsed parameters on weld penetration were analyzed by orthogonal experiment combined with analytic hierarchy process. And optimal combination of pulse parameters of obtaining greater penetration was determined. In this paper, effects of other welding parameters on weld bead shaping and weld penetration were also researched, which include welding speed, distance between burning arc end of twin electrode with work-piece, swing way of electrode, angle of electrode and relative position of two core wires in welding process. Microstructure of weld in PTDEAW was carried out for comparing that in TDEAW without pulse power source. Diffusible hydrogen contents of weld with different kinds of electrodes under different welding conditions were determined by the draining away liquid method. Those gave technical reference for application of PTDEAW.The results of orthogonal experiment indicate the change of pulsed parameters would result in the corresponding change of weld penetration, and the descending order of pulsed parameters influencing weld penetration is as follows:peak current (Ip) > frequency (f)> duty ratio (D)> base current (Ⅰb). The weights of the factors (Ⅰp,Ib and D) on different numerical level are correspondingly:(0.1202 0.0865 0.1057, 0.1413 0.1110 0.1850,0.0207 0.0216 0.0202,0.0577 0.0591 0.0707). Greater penetration could be obtained with these pulsed parameters:peak current of 230A-240A, frequency of 3.3Hz-3.7Hz, duty ratio of 48%-52% and base current of 160A-175A. Optimal combination of pulse parameters of obtaining greater penetration is determined, which is frequency of 3.5Hz, peak current of 230A, base current of 160A and duty ratio of 50%.Effects of other welding parameters on weld penetration were investigated. Results show that weld penetration begins to increase and then decrease with increasing the welding speed in a certain range. Greater penetration can be obtained with these welding parameters:lower height of arc (distance between burning arc end with work-piece with 4mm is better), welding speed of 4.5mm/s-6.3mm/s, electrode walking in a straight line, electrode's angle of 50°-70°and two core wires running lengthwise (one at the front and one at the back). In the condition of the nearly same heat input, the weld of PTDEAW has smaller crystal grain and narrower overheated zone, and the weak planes in widmanstatten structure are fewer than that in TDEAW without pulse power source.The experimental results of diffusible hydrogen testing indicate diffusible hydrogen content changes little after application of pulse power source for E4303 shielded metal arc welding (SMAW). Diffusible hydrogen content in deposited metal of TDEAW is decreased against that in deposited metal of SMAW. And there has been some decrease in diffusible hydrogen content in deposited metal of PTDEAW against that in deposited metal of TDEAW. Results also indicate that less content of diffusible hydrogen is obtained when the coating has the increased content of marble and the decreased content of organic matter. |
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