The high speed rotating arc welding has great advantages in terms of improved efficiency of welding processes and more consistent quality. The advantages include an extensive improvement in precision and response when welding is controlled by an arc sensor for seam tracking and also a large increase in welding speed. Moreover the rotating arc welding can be applied to narrow gap welding and position welding, in which it is difficult to develop an automated process.
The arc rotation system was developed first in Japan and used for narrow gap welding and conventional seam weld seams such as fillet or V-welds in Japan and Germany. In these mechanisms an external motor rotates the electrode nozzle by a gear set. In this study, a new rotation mechanism was developed by using a hallow-shaft motor designed to be installed in the electrode nozzle. The electrode is deflected circularly by an eccentric tip which is rotated by the hollow shaft of the rotating motor and galvanized through carbon brushes. This mechanism can be connected to a conventional torch system and the weight and size of the nozzle can be reduced considerably by using a sufficiently small motor.
Self-regulation in GMAW occurs due to using a constant voltage power source. The arc length remains approximately constant for variations in the CTWD, because the time constant of the self-regulating process is shorter than the torch weaving rate in conventional GMA welding. However a dynamic wire melting phenomenon is found in rotating arc welding since self-regulation of the arc length is not fully performed. Consequently welding current and electrode extension vary rapidly in high speed rotating arc operation. This study presents the dynamic simulation of wire melting by using the variable space network method and by modeling the heat flux from the molten end of the wire into the electrode. The simulations are compared with simulations are compared with experimental results, which show a fairly good agreement. By using simulation analysis, it is clarified how the characteristics of the welding power source affect the sensitivity of the arc sensor.
The sensitivity of rotating arc sensors is greater than that of the conventional weaving arc sensor owing to insufficient self-regulation of the arc length, so the rotating arc sensor can be applied not only for steel welding, but also successfully for welding of aluminum alloy. Even though the low electrical resistance of aluminum can cause difficulties in conventional arc sensors. In this study, experiments and simulations are carried out in order to clarify the sensitivity and responsiveness of rotating arc sensors. In addition, the arc sensor is applied to automatic seam tracking for steel and aluminum alloy welding. From the results, the rotating arc sensor ensure more accurate seam tracking with increased sensitivity and responsiveness
The high-speed rotating arc process forms a float bead surface and decreased penetration depth because the molten droplets are deflected by centrifugal force. In order to analyze the weld bead characteristics of rotating arc welding, the numerical analysis for the temperature distribution of the base metal is carried out by solving the transient three-dimensional heat conduction equation considering the heat input from the welding arc, cathode heating and molten droplets. To estimate the heat flux distribution due to the molten droplet, the contact point where the droplet is transferred on the weld pool surface is calculated from the flight trajectory of the droplets under the arc plasma velocity field obtained from the arc plasma analysis. The numerical analysis shows a tendency of broadened bead width and shallow penetration depth with the increase of rotating frequency. The simulation results are in good agreement with those obtained by the experiments under various welding conditions.
Finally, the rotating arc welding is applied to horizontal fillet welding and position welding. The rotating arc welding for horizontal fillet welding increases the leg length with the increase of rotation frequency and prevents the deflection of weld bead and overlap. Moreover the sound weld beads showing no undercut, which is unavoidable for the conventional methods, are formed for horizontal fillet welding up to 4mm gap. The leg length may vary with gap size in horizontal fillet welding. Based on the Taguchi method, the effects of welding parameters on the bead consistency are investigated for selection of the adequate welding parameters to form consistent weld bead. As a result, the considerably consistent leg length is observed in test experiments by adopting the welding parameters insensitive to the gap size. For vertical-up welding, conventionally one of the dominant weld defects is be the bead inconsistency resulting from pool deflection by the gravity but it is remarkably decreased by the rotating arc.
