Arc characteristics and metal transfer behavior of CMT + P welding process

Profile Map of Weld Beads and Its Formation Mechanism in Gas Metal Arc Welding

“…The samples were ground and polished with colloidal silica and were subsequently etched for metallographic analysis using the standard Keller's agent for 20 s. Then, the profiles of the cross section were observed using the LIOO SZ850T microscope (Beijing-Jinghao Co. Ltd., Beijing, China) and the dimensions were measured using the included software. Pang et al [7] pointed out that the formation of a weld bead in the GMAW process is closely associated with the heat input and the weld pool behavior, which was studied by many researchers. Wang et al [4] demonstrated that during the welding process, the surface of a weld pool is significantly depressed under the combined effects of droplet impingement and the arc pressure, which leaves a thin liquid pool area between the arc and the base metal.…”

“…The smaller the welding current, the greater the volume deviation of the melted wire over the melted base metal, and thus the greater volume of the overflowing melted wire, which leads to a greater width deviation between the reinforcement and the weld pool. An example for this viewpoint is the bead welded by cold metal transfer (CMT) + pulse process [7], which is characterized by a significant width deviation: The maximum width of reinforcement is 219% of that of the weld pool and the contact angle is only 26.8 degrees, as can be seen from Figure 2h. Another example is the bead welded by tungsten inert gas welding (TIG) + CMT hybrid welding [12] in which the maximum width of reinforcement is also double that of the weld pool and the contact angle is nearly 90 • .…”

“…The decreased volume difference makes most of the melted filler wire held by the growing weld pool, thus leaving less melted filler wire overflowing the weld pool. Hence, less melted filler wire spreads and [7], with permission of Elsevier, 2016); and (i) bead of TIG-CMT (reproduced from [12], with permission of Elsevier, 2017).…”

“…If the average current continues to grow, reinforcement then will become flat or even sunken due to the greater heat input and the combined effect of all kinds of driving forces exerted on the weld pool [7]. With the base metal fully penetrated, the bottom wall of a weld pool is no longer in its solid state and it is in delicate balance between the surface tension of liquid bottom and the driving forces acted on weld pool.…”

“…Pang et al [7] pointed out that the formation of a weld bead in the GMAW process is closely associated with the heat input and the weld pool behavior, which was studied by many researchers. Wang et al [4] demonstrated that during the welding process, the surface of a weld pool is significantly depressed under the combined effects of droplet impingement and the arc pressure, which leaves a thin liquid pool area between the arc and the base metal.…”