The Research On Net Forming Process With Dual Laser-TIG Hybrid Butt Welding For Thin Sheets Of GH3128

The complex internal flow passage component is a thin-walled sandwich structure with complex dense channels.As the three-dimensional structure and thin-walled feature of the outer skin of component,it is challenging to manufacture it integrated,so the laser butt welding process to weld multiple skin-parts together is necessary.Limited by the machining precision,the butt gap is difficult to completely eliminate.Therefore,it is easy to cause welding defects(e.g.top weld undercut,bottom weld convexity and spatters,etc.)with pure laser butt welding.The defects decrease mechanical properties of the weld and block the internal channels.Therefore,in order to meet the technical requirements of butt welding for the outer skin of complex internal flow passage component,it is necessary to develop a new butt welding process to achieve the good welding effect and obtain the net forming weld joint.A new technology of dual beam laser-TIG hybrid welding for thin sheets butt welding is proposed in this paper.The influence of welding parameters(e.g.laser power,arc current,welding speed,heat sources distance,focal distance,etc.)on weld formation,especially on the bottom weld formation and spatters,is systematically studied with the butt welding process experiment in a butt gap condition(the gap is not more than 0.2 times of the sheet thickness).The net forming welding mechanism is analysed with relevant experiment.The results show that the change of top weld width is positively correlated with arc current,and negatively correlated with welding speed;the change of bottom weld width,bottom convexity and spatters are positively correlated with laser power,and negatively correlated with welding speed and focal distance.With the increase of the arc current,the bottom weld width and convexity remain unchanged first and then begin to increase.Meanwhile,the bottom spatters decrease first and then increase.With the increase of the heat sources distance,the bottom weld width,convexity and spatters show a tendency of decreasing first and then remaining unchanged.The result in this paper shows that the welding parameters(e.g.laser power,arc current,welding speed,heat sources distance,focal distance,etc.)have important influence on weld formation.The weld joints with good welding effect of double-side forming and net forming is obtained under the optimized process parameters.In the meantime,the mechanical properties of the joints are studied.The results show that the microhardness of the welds is slightly lower than the base metal,and the tensile strength of the joints is 90% of the base metal.The above test results show that the welding joint under the optimized process parameters can meet the forming requirements of butt welding for the outer skin of complex internal flow passage component.The interaction of the laser and arc,and the weld pool behavior are observed with high speed camera in this paper.And then,the net forming welding mechanism of thin sheets butt welding is analysed.It is found that the dual-beam laser plays the key role of bridging welding seam in the butt gap condition at the front position,and the arc plays the key role of regulating molten pool and shaping welding seam at the rear position in the welding direction.The optimized combination of the two heat sources ensures the good forming of the weld.The main reason leading to bottom spatters is the excessive laser energy.The dual laser energy is too high to penetrate the welding seam,leading to the spare energy jet from the bottom surface of the welding seam.To achieve the net forming effect and eliminate the bottom spatters,it is necessary to control the laser power and make the laser heat source can't penetrate the welding seam.Finally,the 2 mm thin sheets butt welding experiment(in the gap condition)is carried out.The results show that the dual beam laser-TIG hybrid welding process can realize the net forming butt welding.This experiment further illustrates that the mechanism – increasing the molten volume,the welding quality will be improved for thin sheets butt welding in the gap condition – is effective.