The Generation Process And Suppression Of Humping Bead In High-speed GMAW

The fast development of modern manufacturing industry demands for much higher welding production efficiency. One important approach to increase welding production efficiency is to increase the welding speed. However, with increasing welding speed some weld bead defects such as undercut or humping bead will occur in conventional welding processes. The occurrence of these weld bead defects affect welding quality seriously and restricts the further increasing of welding speed. Though good weld bead formation can be achieved under high speed laser beam welding (LBW) or electron beam welding (EBW), their high equipment investment, high operating cost and high requirement for assembly precision before welding limit their wider applications. If the generation mechanism of weld bead defects is understood and some suppression measures are proposed, then some improvements can be made for conventional arc welding process so that low-cost and widely used high speed welding process is obtained. In this way, the welding production efficiency can be increased in a wide range. Thus it is of great theoretical significance and important engineering value.The experimental system of high speed GMAW was developed and the clamping fixture to hold the welding torches was designed. Then high speed GMAW experiments were conducted, the forming procedure and the characteristics of humping bead under different process conditions were investigated, and the effect of welding current and welding speed on humping bead was analyzed. Through real-time vision-based sensing of the forming process of humping bead by the industrial CCD camera with light filters, some images of weld pools in high-speed GMAW were achieved. Based on the experimental results the generation mechanism of humping bead was explained, and was verified by up-hill and down-hill welding experiments. The effect of compositions of shielding gases on the humping bead formation tendency was compared and analyzed. Then the morphology characteristics of humping bead were further determined by analyzing the transverse cross-sections of "hump" and "valley". The effects of welding current, welding voltage and metal transfer mode on the critical welding speed were also analyzed according to the experimental results.A novel welding process, i.e., double-electrode gas metal arc welding (DE-GMAW) which can implement high speed welding, was developed using available equipment in the lab. The geometric parameters for assembling two welding torches were optimized through DE-GMAW experiments. Several groups of values of wire current I, base metal current I_bm and bypass current I_bP were measured. Through comparing the experimental results of conventional GMAW and DE-GMAW under the same welding condition, the by-passing action of the GTAW torch in DE-GMAW was validated. The relationship between I_bP and the DE-GMAW process as well as the experimental results were determined. For DE-GMAW process, when the welding speed was increased to a certain value, the weld bead formation was good without occurring any bead defects. Finally, the critical welding speed of DE-GMAW and conventional GMAW under the same welding condition were compared, and the reason why the critical welding speed of DE-GMAW was much higher than that of conventional GMAW was analyzed.