The Research On The Process Stability And Molten Pool Forming In Ultra-narrow-gap Welding

In order to improve stability of constricted arc,a redesign of welding torch is presented based on the previous studies of ultra-narrow gap welding with constricted arc by successive feeding flux strips.under the condition of a certain welding parameters and a wide range of feeding speed of flux strips,welding experiments were carried out with the new torch,and analysis of the position of flux strips in the welding arc were made on the base of welding voltage and flux strips voltage waveforms.It was found that uncertainty of flux strips position in arc leads to the low stabilization of constraints degree of welding arc during ultra-narrow gap welding with constricted arc by successive feeding flux strips.Furthermore,flux strips deviate from the axis of welding wire because of welding spatter and friction,this may lead to the arc climb up along the sidewall from the bottom.All above these problems can be come down to the lack of stiffness of successive feeding flux strips.For understanding characteristics of base metal melting and mechanism of pool formation in ultra-narrow gap with constricted arc by flux strip,a new type of flux strip was developede,and metal arc welding tests were carried out on I groove deposited with the flux strips.By using of method for interrupting arc quickly,the melting forms of flux strips, groove's bottom and sidewalls in the welding process were hold and observed.Results show that,the arc is thermally constricted due to melting flux strips,in addition,the arc is obtained a wall constriction as it contacts with the non-molten flux strips.These constrictions can control the heating area of the arc in narrow gap.While the height of lower sidewalls uncovered by flux strips is proper,heating area of the arc is constricted within groove's bottom and the roots of sidewalls,filler metal droplet impingement and arc pressure were concentrated on the front portion of molten pool.As a result,these factors cause the backward flow of molten weld metal,which facilitate expelling the gas and the slag in the molten metal, and welds without the defect can be obtained.When the height of lower sidewalls uncovered by flux strips increases to a certain value,the heating area of the arc extend to higher position of groove's sidewalls,and filler metal droplet impingement is scattered on the groove's bottom and sidewalls.In this case,the backward flow of molten weld metal can not be formed, so that the gas and the slag can not be expelled in the molten pool,which make welds contain a lot of pores.