Experimental sensing of molten flow velocity, weld pool and keyhole geometries in ultrasonic-assisted plasma arc welding

Abstract

• Comparative experiments were performed to investigate the ultrasonic effect in plasma arc welding. • The molten flow velocity on the weld pool surface was measured by tracer particle approach. • With ultrasonic vibration, the front wall and the back wall of the keyhole became steeper. • With ultrasonic vibration, the backward flow velocity of the molten metal decreased obviously. • Ultrasonic vibration causes small sizes of weld pool and keyhole but enhanced keyholing/penetrating capability. Comparative experiments were performed to investigate how the ultrasonic vibration exerted on the tungsten electrode affect the molten metal flow on weld pool surface and the sizes of weld pool and keyhole in plasma arc welding (PAW). The fluid flow velocity on the molten pool surface was measured by tracer particle approach. The images of front molten pool and keyhole entrance were captured synchronously from different directions with two CCD cameras. Special algorithms were developed to calibrate and integrate the weld pool and keyhole images into a single picture in one coordinate system. It was found that when ultrasonic vibration was applied, the keyhole shape was changed, the front wall and the back wall of the keyhole became steeper, and the backward flow velocity of the molten metal decreased obviously. The size of the molten pool and the keyhole entrance in ultrasonic-assisted PAW was smaller than that in PAW, and the keyholing/penetrating capability was enhanced.