Bead penetration depth plays a significant role on the quality and integrity of welds, 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 o C 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 o C. 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 (R 2) of 0.9799 while R 2 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.

The mechanical properties (Ultimate Tensile Strength (UTS), modulus of elasticity (E), elongation and strain (e)) for twenty samples of AISI 4130 Low carbon steel plate were studied in this paper. Statistical design of experiment (DOE) using the central composite design method (CCD) was employed in Design Expert 7.01 software to generate DOE for twenty (20) experimental runs as input variables (current, voltage and gas flowrate) which were used in predicting and optimizing the output parameters (maximum UTS and maximum modulus of elasticity with corresponding elongation and strain). One out of the 20 welding runs was found to be optimum using the Artificial Neural Network (ANN) optimization approach. The same twenty (20) predicted variables were subjected to TIG welding experimentation which showed close proximity between the predicted and experimental values. Optimized ANN predicted output parameters were UTS of 421 MPa, modulus of elasticity of 793 MPa, strain of 0.61 and elongation of 61% while experimental values using the optimized input variables produced output parameters of 427 MPa for UTS of 421 MPa, 806 MPa for modulus of elasticity, strain of 0.62 and 62% elongation. Visuals of the weldment obtained from Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS) revealed a uniformly distributed grain sizes in the weldment primarily composing of iron (Fe), chromium (Cr), molybdenum (Mo), and nickel (Ni). To save time, energy and resources required for welding experimentation processes, conventional software such as ANN can be used to obtain accurate results.

Variations of welding parameters and their effects on weld bead width of gas Tungsten Arc Weldment of 10 mm (thickness) AISI 1020 low carbon steel plate was investigated in this paper. Welding experimentation was carried out for Twenty seven (27) runs with three (3) ranges of current (120A, 150A and 190A), three (3) ranges of voltage (19V, 21V and 25V) and three (3) ranges of gas flow rate (13, 15 and 18 L/min) respectively. Applying the same range of parameters as inputs in Solid Works 2017 version, Finite Element Method (FEM) was employed to predict the weld bead width variations. To avoid wider weld bead width which can contribute to poor weld quality, a condition was established, in which the bead width values from both experimental and FEM prediction must not exceed 1.25 mm. Thermal transient flow simulation was also carried out with Solid Works 2017 version to determine the melting behavior of the material which revealed 1694 K as the solidus temperature and 1738 K as the liquidus temperature. It was observed that varying the welding current, arc voltage and the gas flow rate for the welding experimentation and finite element simulation, alternating weld bead widths of close proximity were produced. However, certain sets of parameters used for the welding experimentation met the aforementioned condition (≤1.25 mm) with the following values 1.02 mm, 1.05 mm, 1.10 mm, 1.07 mm, 1.15 mm and 1.19 mm while the same combination of parameters in the FEM met the condition with the following FEM predicted values 1.0 mm, 1.03 mm, 1.08 mm, 1.05 mm, 1.13 mm and 1.15 mm respectively. These findings are only applicable to AISI 1020 low carbon steel, therefore, melting point of materials should be adequately understood with proper knowledge of welding parameters prior to commencement of welding operation to avoid excessive increase in weld bead width.

Induced residual stresses on AISI 1020 low carbon steel plate during Tungsten Inert Gas (TIG) welding process was evaluated in this study using experimental and Finite Element Method (FEM). The temperature range measured from the welding experimentation was 251°C-423°C, while the temperature range measured from the FEM was 230°C-563°C; whereas, the residual stress range measured from the welding experimentation was 144MPa-402Mpa, while the residual range measured from the FEM was 233-477MPa respectively. Comparing the temperature and stress results obtained from both methods, it was observed that the range of temperature and residual stresses measured were not exactly the same due to the principles at which both methods operate but disparities between the methods were not outrageous. However, these values can be fed back to optimization tools to obtain optimal parameters for best practices.  Results of the induced stress distribution was created from a static study where the thermal results were used as loading conditions and it was observed that the temperature increased as the von-Mises stress increased, indicating that induced stresses in welded component may hamper the longevity of such component in service condition. Hence, post-weld heat treatment is imperative in order to stress relieve metals after welding operation and improve their service life.

In this study, temperature and time dependence analysis was carried out on Tungsten Inert Gas (TIG) Welding of AISI 1020 Low Carbon Steel Plate of 10 mm thickness. The TIG welding parameters deduced from design of experiment for current ranging from 96-213 A, voltage ranging from 16-25 V and gas flow rate ranging from 11-19 L/min was used as input variables for the welding experimentation and simulation using Finite Element Method (FEM) based on Goldak model heat source. There was proximity in the regression plot of temperature outputs for both the experimental and FEM predicted values. The temperature and time dependence transient thermal analysis was simulated for 20 seconds at welding speed of 1.5 mm/s in steps of 2.5 seconds for each heat source and the result revealed that at each increasing step, the heat distribution characterized by intense heat, phase transformation and alteration in mechanical properties gradually formed a spiral transient patterns from the weldment known as Heat Affected Zone (HAZ). Hence the longer the arc heat at a given weldment the wider the HAZ which result in high residual stress build-ups, undercut and other welding defects that hampers the welded component in service condition.