Numerical analysis of ultrasonic waves in the gas tungsten arc welding (GTAW) with ultrasonic excitation of current

Abstract

A fully coupled plasma-acoustic 3D mathematical model is first proposed to analyze the generation, propagation and attenuation of ultrasonic waves in weakly ionized arc plasma, based on experiments of a typical man-made arc plasma-acoustic emitting system-Gas tungsten arc welding with ultrasonic excitation of current. Comprehensive analyses of background incompressible arc flow, the acoustic characteristics of arc plasma and ultrasound enhanced fluid flow responded to ultrasonic frequencies are performed to study the arc plasma-acoustic coupling mechanism, aiming at extending nonlinear acoustics theory with acoustic streaming from thermal-viscous fluids to electromagnetic fluids-weakly ionized arc plasma and providing a basic understanding of acoustic generation, attenuation and acoustic streaming for similar research of acoustic analysis in arc welding with pulsed current, The U-GTAW system was also designed to validate the predictions of the model. Our work reveals that the ultrasonic waves is actuated by a combination of thermal pressure and Lorentz force from harmonic perturbation of exciting current, generating near the electrode tip in the arc plasma region with high acoustic power, then attenuating significantly and propagating in the argon gas area. Most of acoustic energy is absorbed and converting into acoustic streaming momentum of arc plasma in the vicinity of tungsten electrode tip. The ultrasonic frequency has great influence on the acoustic power, the acoustic absorption and acoustic streaming, and the ultrasound could promote concentration and acceleration of arc plasma significantly at 20kHz and 30kHz.