3D Finite Element Modelling of Weld Bead Penetration in Tungsten Inert Gas (TIG) Welding of AISI 1020 Low Carbon Steel Plate

Abstract

Weld quality is adversely influenced by bead penetration depth, as deeper penetration can improve the strength and load bearing capacity of weldments in service condition. Based on Design of Experiment (DOE), an experimental design matrix having thirteen (13) center points, six (6) axial points and eight (8) factorial points resulting in twenty (20) experimental runs was generated for TIG welding current, voltage, gas flow rate L/min and temperature. Maximum bead penetration of 8.44 mm was obtained from the FEM simulation with corresponding input variables of 190 A, 19 V, 18 L/min and 298.44 oC compared to maximum bead penetration of 7.942 mm obtained from the welding experimentation with corresponding input variables of 155 A, 22 V, 15.50 L/min and 278.46 oC.  To clearly understand the rate of heat distribution across the as-welded plate, FEM bead penetration profiles were developed using Solid Works (2017 version) thermal transient analysis which revealed that the higher the temperature distribution the wider the Heat Affected Zones (HAZs) which are indications of phase transformations and alterations in mechanical properties of the welded metal which may lead to induced residual stresses if the welding parameters particularly the amperage is not controlled adequately. In addition, there was proximity in the trend of bead penetration from the regression plot where the FEM model had a coefficient of determination (R2) of 0.9799 while R2 of 0.9694 was obtained for the welding experimentation, indicating about 97.4% variance which in this context signifies that both bead penetration values can be adopted for real practical scenarios where deep weld bead penetrations are required.