Material Flow Behavior on Weld Pool Surface in Plasma Arc Welding Process Considering Dominant Driving Forces

Abstract

In this study, the effect of oxygen in the shielding gas on the material flow behavior of the weld pool surface was discussed to clarify the dominant driving weld pool force in keyhole plasma arc welding (KPAW). To address this issue, the convection flow on the top surface of weld pool was observed using a high-speed video camera. The temperature distribution on the surface along keyhole wall was measured using the two-color pyrometry method to confirm the Marangoni force activity on the weld pool. The results show that the inclination angle of the keyhole wall (keyhole shape) increased especially near the top surface due to the decrease in the surface tension of weld pool through surface oxidation when a shielding gas of Ar + 0.5% O2 was used. Due to the change in the keyhole shape, the upward and backward shear force compositions created a large inclination angle at the top surface of the keyhole. From the temperature measurement results, the Marangoni force was found to alter the direction when 0.5% O2 was mixed with the shielding gas. The shear force was found to be the strongest force among the four driving forces. The buoyant force and Lorentz force were very weak. The Marangoni force was stronger than the Lorentz force but was weaker than shear force. The interaction of shear force and Marangoni force controlled the behavior and speed of material flow on the weld pool surface. A strong upward and backward flow was observed in the case of mixture shielding gas, whereas a weak upward flow was observed for pure Ar. The heat transportation due to the weld pool convection significantly changed when only a small amount of oxygen was admixed in the shielding gas. The results can be applied to control the penetration ratio in KPAW.

Reduction of Spatter Generation Using Atmospheric Gas in Laser Powder Bed Fusion of Ti–6Al–4V

“…9(b). 32,33) Thus, the molten metal maintained a high temperature with active flow, which was a suitable condition for spatter generation.…”

Relationship among Welding Defects with Convection and Material Flow Dynamic Considering Principal Forces in Plasma Arc Welding

“…In this case, because the intensity of the arc plasma is too high, the movement of particles around the keyhole is difficult to visualize clearly. In order to overcome this problem, a diode laser apparatus with the power of 30 W and the wavelength of 940 nm was utilized [19]. The laser head was adapted to cut mostly the brightness of the arc plasma.…”

“…In this case, a Phantom V4 thermal camera (Phantom Co., Ltd., Tokyo, Japan) was utilized. The measurement mechanism is based on two-color pyrometry [19]. The frame rate was 2000 pfs.…”

“…Then, this change could be ignored, and the result could be utilized to explain the visualization data in this paper. More details of this measurement can be read in ref [19]. To discuss the influence of driving forces on the convection and the heat transport, a temperature measurement on the melted domain surface was performed.…”

“…The results showed that the velocity was much lower in the case of aluminum due to its low mass density. In a recent paper, Manh et al [19] verified by experiment that the fluid dynamics of the weld pool in PAW was controlled mainly by shear force. This is totally different to the Tungsten inert gas (TIG) welding process in which the molten flow is mainly controlled by Marangoni force.…”