Characteristics of alternate supply of shielding gases in aluminum GMA welding

Derivation of Forces Acting on the Liquid Weld Metal Based on Arc Pressure Measurements Produced Using Alternating Shielding Gases in the Gtaw Process

“…The Marangoni number for argon is in line with those presented elsewhere [26]. Considering the forces evaluated, it can be inferred that the flow vectors are opposite in direction to that of argon as stated by Kang et al [2]. It was calculated that helium produced a greater plasma shear stress, buoyancy force and Marangoni convection, whereas argon produced a greater arc force and Lorentz force.…”

“…This can be attributed to the fact that during the alternating shielding gas process the arc is continually being re-established when each gas is present, whereas when using GTAW-P the power source is simply changing the magnitude of the current supply. As can be seen, the alternating shielding gas transient pressure measurements are considerably different to Figure 2(a) produced by Kang et al [2]. Firstly, the alternating frequency of 2 Hz meant each gas was only supplied for 0.25 seconds before changing to the other gas, thus the entire time either gas is supplied is within the arc initiation pressure impulse and did not have sufficient time to reach steady-state.…”

“…Alternating shielding gases is a relatively new method of delivering the shielding gas to the weld region and involves the discrete delivery of two gases to the welding region in order to take advantage of the beneficial properties of each gas [1][2][3][4][5][6], with the added advantage of complex flow patters within the liquid weld metal. To date, this has involved alternating between argon/argon based mixture and helium, and has been found to produce various benefits from both a technical and economic viewpoint.…”

“…The mechanical properties of the weld have been shown to be a function of the shielding gas delivery method [3,4]; improvements in the transverse and all-weld yield and tensile strength, Charpy impact toughness and ductility have been achieved, whilst a more uniform hardness through the weld, heat affected zone and parent plate was also found. Several studies have reported [1][2][3][4] that the alternating shielding gas process has resulted in a lower percentage of porosity in the solidified weld than conventional shielding gas mixtures. The benefits of using alternating shielding gases are linked to three independent phenomenon [1]: a) variation in arc pressure, b) arc pressure peaking and c) variation in weld pool fluidity, and are said to result in flow vectors opposite in direction for argon and helium [2].…”

“…Several studies have reported [1][2][3][4] that the alternating shielding gas process has resulted in a lower percentage of porosity in the solidified weld than conventional shielding gas mixtures. The benefits of using alternating shielding gases are linked to three independent phenomenon [1]: a) variation in arc pressure, b) arc pressure peaking and c) variation in weld pool fluidity, and are said to result in flow vectors opposite in direction for argon and helium [2]. Arc pressure measurements conducted when using argon have been published whilst investigating the effects of a variety of welding parameters including welding current [7][8][9][10][11], tungsten electrode geometry [10][11][12], arc length [10], nozzle outlet diameter [13] and shielding gas pressure [13].…”