WELDING RESEARCH Fig. 5 — Electron temperature for three welding processes. JULY 2016 / WELDING JOURNAL 241-s A B A B C C shown in Fig. 1. The welding gun was fixed, and the workpiece moved at a constant speed. The angle between the axis of the welding gun and the workpiece was 90 deg. It consisted of two parts, the welding system and ultrasonic radiation system.The ultrasonic radiation system included the ultrasonic power and ultrasonic transducer. Synchronous mechanical vibration generated by the ultrasonic transducer was radiated to surrounding space in the form of ultrasonic waves by the ultrasonic radiator after being amplified by the amplitude transformer and subsequently ultrasonic energy acted on the arc. With reasonable structure design, the vibration reached maximum amplitude when the transducer was resonant (Ref. 23). Different resonance modes could be obtained by adjusting the distance between the radiator and workpiece. The periodic cycle of pulsed ultrasound consists of three parts: the establishment, stability, and disappearance of the ultrasonic field. The ultrasonic, with the same excitation frequency of 19.5 kHz, including continuous ultrasonic and pulsed ultrasonic, was generated by the ultrasonic transducer using a concave spherical surface ultrasonic radiator with a height of 14 mm. The height of the ultrasonic radiator was determined by the experiment; the specific method can be found in Ref. 24. These geometric parameters of the ultrasonic radiator were designed to be optimal by the boundary element method (Ref. 25). For pulsed ultrasonic, the pulsed current frequency (pulsed frequency) was 5 Hz. The input power of the ultrasonic power source was regulated to 2000 W for both the U-GMAW and the PU-GMAW. The welding parameters are listed as follows: the constant voltage power supply was used during the experiments, and the welding process was performed under direct current electrode positive conditions. The nozzle height was 11 mm. Argon with a purity of 99.99% was utilized as the shielding gas and the flow rate Fig. 4 — Arc shape and droplets under different welding conditions: A — GMAW; B — UGMAW; C — PUGMAW. Fig. 6 — Macroscopic appearances of the weld and EBSD maps of the weld joint center: A — GMAW; B — UGMAW; C — PUGMAW.
Welding Journal | July 2016
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