Visualisation of alternating shielding gas flow in GTAW

Abstract

The alternating shielding gas technique is a method of achieving transient arc characteristics during arc welding; however the complex flow that occurs through its use has not been investigated previously. A schlieren system was used to image density gradients that arise when alternating argon and helium shield gases, under varying flow parameters, with gas tungsten arc welding (GTAW). A theoretical analysis was carried out to determine the conditions under which the technique facilitates arc pulsing, in particular to avoid mixing the shield gases in the delivery pipe prior to the welding nozzle. At appropriate pulsing frequency and flow rates, a stable horizontal region of helium was obseved in the weld region, maintained in position by the denser argon from the preceding pulse. This higher than average mass fraction of helium when applying the shielding gases alternately, compare to a premixed gas with the same volume of argon and helium, increased the weld penetration by 13% on average, suggesting a modest improvement in heat transfer

Laser powder bed fusion in high-pressure atmospheres

“…A portable z-type schlieren system [11] used a 300-W tungsten lamp to introduce collimated white light illumination across the powder bed through the two end viewports [4]. Images were recorded with the high-speed camera using a variable focus telephoto lens (focal length 200-500 mm) at 80,000 fps and 384 × 512 pixels resolution.…”

Comparison of empirical and predicted substrate temperature during surface melting of microalloyed steel using TIG technique and considering three shielding gases

“…The current (I), the voltage (V), the speed (s), were changed as shown in Table 1 in order to guarantee a constant energy input (E) of ~ 840 J/mm along the melt track when using three different shielding gases, argon (Ar), nitrogen (N) and helium (He) at a constant flow rate of 10 L/min. The energy input was chosen from previous results [10,15]. Table 2 gives the thermal properties of the microalloyed steel and the shielding gases used in this research.…”

“…Following [11][12][13][14][15][16][17], the boundary condition on the TIG affected boundary is proposed to be ( , 10, ) = 0 + (P/kd) −( ( − ) 2 ) + (Pβ/kd)(1/(x-vt)) 2 (Eq.4)…”

“…Both techniques require a gaseous shielding atmosphere, usually 2, Ar, He, CO2 or mixture of these gases. The shielding gas protects the metal transfer stream and the molten weld pool from contamination resulting from dissolution from the atmosphere of nitrogen, oxygen and water vapour , which often have a deleterious effect on the mechanical properties of the modified surface ] [13][14][15][16][17]. Shielding gases also provide a medium for the electrical current to flow in the plasma jet between workpiece and electrode.…”

A probabilistic model of weld penetration depth based on process parameters

“…Beside these, various predictive tools have been developed, such as mathematical models based on experimental results [1], artificial neural network (ANN) models [8], and numerical simulations [9]. Furthermore, many efforts have been carried out to highlight variables that affect weld penetration depth, such as shielding gas type [10,11], arc type [12], arc stability [13], gun angle [1], initial gap [14], welding current [15][16][17], arc voltage [15,18], and welding speed [15]. However, the limitation of having uncertainties in those welding parameters is not addressed.…”