A novel electrode-arc-weld pool model for studying the keyhole formation in the keyhole plasma arc welding process

Abstract

A novel electrode-arc-weld pool model considering the influence of the backside keyhole deviation on the heat source distribution, the influence of the keyhole constraint on the arc pressure and the keyhole geometry dependent plasma shear stress, is developed to study the keyhole formation in the KPAW process. The numerical and experimental results show that: the keyhole depth increases very quickly at first, then smoothly, and then quickly again. In the blind keyhole stage, the arc pressure deepens the keyhole. The plasma shear stress facilitates the fluid flow along the rear keyhole wall and decreases the curvature of the keyhole. The process between the weld pool penetration and the keyhole penetration is defined as the blasting penetration stage, in which the molten bridge under the arc is quickly broken. The pressure balance and mass conservation mechanisms are proposed to be responsible for the blasting penetration. The low melting temperature, low surface tension and bottom surface deformation promote the blasting penetration, while the high thermal conductivity suppresses the blasting penetration. In the penetrated keyhole stage, two contrary convective eddies are found inside the weld pool. At the top surface of the weld pool, the molten metal flows upward and backward near the keyhole, but obviously flows forward at the rear part of the weld pool. At the bottom surface of the weld pool, the molten metal flows downward and backward.

Numerical Analysis of Keyhole and Weld Pool Behaviors in Ultrasonic-Assisted Plasma Arc Welding Process

“…Under the conditions listed in Table 1 , the calculated gas shear stress on the anode surface are shown in Figure 3 . It can be seen that after the ultrasound application, the plasma arc velocity increases, and then the peak value of the gas shear stress on the workpiece surface increases, and the peak value of the gas shear stress is 2 mm away from the torch axis, which is different from the result in the literature [ 18 , 19 ]. In this paper, the nozzle exit radius is 3.2 mm, so the arc pressure and gas shear stress are small.…”

“…As shown in Figure 8f Figures 9 and 10 show the fluid flow and heat transfer in the weld pool during the dynamic keyhole evolution in PAW and U-PAW, respectively. The main driving forces of the molten metal flow include the Marangoni shear force caused by the surface tension gradient, gas shear stress, arc pressure, electromagnetic force, and buoyancy [18,19]. Figure 9 shows the temperature and fluid flow fields at the longitudinal cross-section in PAW.…”

“…The total ultrasound reflection occurs at the interface between the plasma arc and weld pool. The difference of the acoustic radiation force at the end of the tungsten electrode and the anode surface, F , is written as follows [24]: Recently, many researchers have conducted a numerical analysis of weld pool and keyhole behaviors in PAW [13][14][15][16][17][18][19]. However, there is little such work on the newly developed U-PAW.…”

“…Recently, many researchers have conducted a numerical analysis of weld pool and keyhole behaviors in PAW [ 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. However, there is little such work on the newly developed U-PAW.…”

Prediction of the Weld Pool Stability by Material Flow Behavior of the Perforated Weld Pool

“…Using stainless steel as the welding material, Wu et al [9][10][11][12][13][14] developed a thermo-mechanical model to gain a better understanding of energy propagation and calculate the dynamic keyhole evolution and the fluid flow in the weld pool. Wu, Shinichi Tashino et al [15,16] investigated the weld pool convection and keyhole formation mechanism in the keyhole plasma arc welding (PAW). The experimental methods of the above numerical studies were PAW.…”