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

Abstract

As part of an ongoing process to fully evaluate the effects of an alternating shielding gas supply on the gas tungsten arc and gas metal arc welding processes, a comparison between arc pressures produced using argon, helium, alternating gases and GTAW-P has been conducted. The alternating shielding gas process is reported to create a dynamic stirring action within the liquid weld metal as a result of three independent phenomena: a) variation in weld pool fluidity, b) arc pressure variation, and c) arc pressure peaking. These effects have been the basis of previous advantages associated with the process, however these phenomena have not previously been verified and are based solely on theoretical assumptions. Arc pressure measurements are presented which allowed for the numerical derivation of various forces acting on the liquid weld metal in order to estimate the flow vectors present when each shielding gas is present. List of SymbolsArc pressure (stagnation pressure at anode) (N/m 2 ), Density of the shielding gas (kg/m 3 ) Velocity (m/s) Plasma shear stress (N/m 2 ) Dynamic viscosity of the arc plasma (kg/(m.s)) Distance in the radial direction (m) Arc force (N) Radius of arc (m) Lorentz force (N/m 3 ) Current density (A/m 2 ) Self-induced azimuthal magnetic field (N/(A.m)) Current (A) Permeability of free space (N/A 2 ) Buoyancy force Density of the weld metal (kg/m 3 ) Gravity acceleration in the negative z direction (m/s 2 ) Thermal expansion coefficient of the weld metal (1/K) Local reference temperature (K) Arbitrary reference temperature (melting temperature) (K) Marangoni number (dimensionless)

Microstructure characterization of SS308LSi components manufactured by GTAW-based additive manufacturing: shaped metal deposition using pulsed current arc

“…When this arc pressure impinges on the surface of a liquid, it may induce flow motion in the liquid, and so, it influences the penetration shape of the liquid-solid boundary [34]. Campbell et al [35] emphasized that there is a relation between the P arc and the welding current and the arc radius. Lin and Eagar [33] reported the relationship between the arc pressure and the square of welding current and square of arc radius for the TIG arc as expressed in Eq.…”