Computational Modelling of Complex Physical Phenomena in TIG Weld Profile based on relationship between Coefficient of Thermal Expansion and Transient Temperature Variations in Mild Steel Plate

Abstract

To minimize welding experimental cost, time, and defects and prevent inaccurate results, finite element computational modelling and simulation were performed on AISI 1018 mild steel plate, which interacts seamlessly with Tungten Inert Gas (TIG) welding sequence due to its low carbon content. Goldak heat source distribution was employed to model the complex phenomena around the weld profile, considering convection and radiation heat losses in the thermal cycles to maintain a balance in the temperature gradients. The study focused on the heat input variation around the weld profile upper face and parallel plane situated 1.5 mm beneath the upper face to demystify the thermal behaviour of Coefficient of Thermal Expansion (CTE) and Transient Temperature Variations (TTVs) across the weld profile region. The heat input distributed across the parallel plane exhibited a different geometric profile compared to the upper face because heat input at this depth (1.5 mm parallel plane) is influenced by heat conducted via the base metal, the presence of any heat sinks or thermal barriers, and thermal conductivity of the base metal. The distribution of the heat input was observed to take after the geometric form of Gaussian distribution. Findings from the weld profiles revealed that maximum weld temperature of 1391, 1516, 1667, 2200, 2596 and 2834 oC yielded maximum CTE of 1.1e-014, 1.1e-012, 1.1e-011, 1.1e-009, 1.1e-007 and 1.1e-005 oC-1. From the trend of these values, it was observed that increasing weld temperatures obviously led to increasing CTE, which agrees with findings from existing research in this field of study. It was also noted that, at each of these CTE values, the corresponding thermal expansion lengths were 0.01, 0.03, 0.05, 0.07, 0.09, and 0.12 mm, indicating that increasing weld temperatures increased the corresponding CTE, which in turn led to an increase in the corresponding length of thermal expansion.