Research On Automatic Vertical Welding Technology Of Rotating-Arc Narrow-Gap GTAW For 9Ni Steel

A new process about rotating arc in narrow-gap TIG welding is put forward to solve the problem of fusion of the sidewalls in narrow gap welding process.The new method is that arc heat base metal on both sides of the narrow gap periodically when the motor control tungsten electrode that have been fashioned into asymmetric tip rotating.In order to realize the new welding technology,we design a new type of rotating arc narrow-gap TIG welding gun,with automatic wire feeding function that can realize wireless rotary conductive and dual gas protection method.The platform was set up to collect electrical parameters and image signal in the process of narrow gap welding.The change of electrical parameters was studied in the process of arc rotation by analyzing the welding electrical parameters and image signal acquired synchronously.The current and arc voltage changed periodically because of the distance between the tungsten tip and the liquid metal surface.The weld power ensured adequate heat input on sidewall.Exploring the arc shape in different welding parameters,the experimental results show that the area of arc heating is larger when the angle of non-axisymmetric tungsten tip is 45°,the rotating speed is moderate and the welding current is larger.It is benefit for sufficient fusion of sidewalls.Experiments were conducted including single pass narrow-gap welding and narrow-gap butt-welding experiments of 16 mm mild steel plates and 24mm 9%Ni steel plates.Results verified that the new technology could improve sidewall fusion and ensure a uniform and smooth weld appearance.The periodically rotating arc kept constantly stirring the molten pool throughout from its formation to solidification.The technology of novel rotating-arc narrow-gap GTAW perfectly realized the welding of 16mm and 24mm thick plates by the way of multi-layer and single-pass welding.Finally,the welding process at vertical position is studied.The welding equipment is optimized to realize the vertical position welding.Further,the wire feeding is analyzed in the welding process at the vertical position.The problem of the molten metal flowed by gravity is solved through the optimization of welding parameters.The sufficient fusion of sidewalls is ensured in the narrow gap welding at vertical position.