The Study Of The Adaption Between Groove Width And Welding Parameters In Ultra-narrow Gap Welding

With the development of equipment manufacturing toward large-scale and heavy-duty, the welding of large-scale structural components becomes an important production process in the equipment manufacturing industry. Our research group develop a kind of ultra-narrow gap welding with flux strips constraining arc used for the weld of thick plates.In this method was applied to60kg rail jointing, in the process of welding, the actual groove width change between3.5-5.0mm.In this article, aimed at the change of the groove width, we designed a new welding gun which can work in the groove of3.5mm width,and research the influences of welding parameters and groove width on welding bead formation, hot crack and arc characteristics in the ultra-narrow gap welding of3.5～5.0mm width groove through arrange of ultra-narrow gap welding with flux strips constraining arc test.The design of welding gun are aimed at the changing welding gap whose narrowest width only is3.5mm.The new gun’s features of structure and function as follows:①The welding gun was designed to be clintheriform, the cross section width to3mm.②The welding gun apply clamping force on welding wire though the lever principle.③The surface of the welding gun is designed to be insulating.④The cuneal contact tube’s simple shape is in favour of replacing.The welding gun of the structure achieved the ultra-narrow gap welding whose minimum groove width is3.5mm.Using the designed welding gun for ultra-narrow gap welding with flux strips, whose groove width respectively are3.5mm,4.0mm,4.5mm.Realizing from the result:when groove width changes within lmm,the main factor influencing the welding surface morphology is the welding voltage;when the groove width increasing, the form factor increase and the groove root fusion depth decrease,and the region of parameters which can obtain the beads whose form factor is larger than0.8becomes larger, but the region which can obtain the beads whose groove root fusion is deeper than0.5mm becomes small.Analysis the form of hot crack in bead,we can realize that,in ultra-narrow gap welding,the hot crack mainly is crystallization crack,and it is influenced by heat input and bead form factor. The higher the heat input and the smaller the form factor, the higher the probability of hot cracking formation.When the groove width becomes smaller, the crack form easier.Analysis the ultra-narrow gap welding whose groove width respectively are3.5mm,4.0mm,4.0mm,5.0mm and a board surfacing welding, we can see that, welding current is proportional to the wire feed rate, and under the influence of groove width and the welding voltage, the smaller the groove width and the higher the welding voltage, welding current is larger. Under the same welding parameters, the frequency of droplet transfer in an ultra-narrow gap welding smaller than that in a board surfacing welding. In ultra-narrow gap welding, when the groove width becomes smaller or the welding voltage increase, the frequency of the droplet becomes smaller and the form of droplet transfer changes from short circuiting transfer to globular transfer. When the wire feed rate increase, the frequency of the droplet becomes larger first but then becomes smaller.