N. Siva Shanmugam

Influence of Beam Incidence Angle in Laser Welding of Austenitic Stainless Steel using Finite Element Analysis

This paper presents the influence of beam incidence angle on austenitic stainless steel sheet subjected to a high density laser beam having Gaussian power density distribution. Bead‐on trials are conducted on 3.15 mm thick commercial AISI 304 austenitic stainless steel sheet using a Nd:YAG laser source with a maximum output of 2kW in the continuous wave mode. The effects of beam incident angle on the weld bead geometry are studied using finite element analysis. Experiments are conducted with 600, 1000 and 1400W laser power and 800, 1400 and 2000mm/min welding speed. A three dimensional finite element model is developed for the simulation of non‐linear transient thermal analysis of the weld bead geometry for different beam incident angles using the finite element code ANSYS. The result reveals that by increasing the beam incident angle with constant beam power and welding speed, there is a considerable reduction in the depth of penetration‐to‐width ratio (d/w). Further, it is noticed that the process enters into conduction mode of welding from the keyhole mode of welding as the beam angle is increased beyond 10o. The comparison of the simulation results and the experimental data for weld bead geometry with different beam incident angles show good agreement.

Temperature Distribution Modeling of Friction Stir Spot Welding of AA 6061‐T6 Using Finite Element Technique

Friction stir welding (FSW), a process that involves joining of metals without fusion of filler materials. It is used already in routine, as well as critical application for the joining of structural components made of Aluminum and its alloys. Indeed it has been convincingly demonstrated that the process results in strong and ductile joints, some times in systems, which have proved difficult using conventional welding techniques. The process is most suitable for components that are flat & long (plates & sheets) but it can be adapted for pipes, hollow sections and positional welding. The welds are created by the combined action of frictional heating and mechanical deformation, due to a rotating tool. Recently, a new technology called friction stir spot welding (FSSW) has been developed that has a several advantages over the electric resistance welding process widely used in automotive industry in terms of weld quality and process efficiency. This welding technology involves a process similar to FSW, except that, instead of moving the tool along the weld seam, the tool only indents the parts, which are placed on top of each other. The conditions under which the deposition process in FSSW is successful are not fully understood. However, it is known that only under specific thermo‐mechanical conditions does a weld formation occur. The objective of the present work is to analyze the primary conditions under which the cavity behind the tool is filled. For this, a fully coupled thermo‐mechanical three‐dimensional FE model has been developed in ABAQUS/Explicit using the adaptive meshing scheme and the Johnson‐Cook material law. The contact forces are modeled by Coulomb’s law of friction, making the contact condition highly solution dependent. Temperature graph in the radial direction as well as stress, strain plots are presented.

Some studies on temperature field during plasma arc welding of thin titanium alloy sheets using parabolic Gaussian heat source model

In this paper, a new volumetric heat source model is developed for predicting the weld bead geometry during plasma arc welding of thin sheets of titanium alloy. Numerical simulations are carried out with the proposed parabolic Gaussian heat source (PGHS) model and already prevailing familiar heat source models namely, conical heat source and modified conical heat source, using finite element package COMSOL. The temperature-dependent material properties for Ti–6Al–4V alloy are considered for performing numerical calculations, which tend to influence the temperature fields while computing. Besides, the effect of trailing gas shielding, latent heat, and radiative and convective heat transfer are taken into account while performing the transient thermal analysis which significantly alters the sensitivity and accuracy of the model. Experimental trials on thin titanium alloy sheets are carried out to enable the validation of the proposed PGHS model. Subsequently, the outcome reveals that the PGHS model is capable and proved its high degree of efficiency in predicting the weld bead geometry more accurately than the existing heat source models. The distribution of heat intensity along the thickness of thin sheet is observed to be parabolic as predicted by the proposed model. The prediction appears to have a good correlation with the experimental result and it is clearly perceptible that the parabolic shape is more reliable and yields greater accuracy of the proposed heat source model.

Studies on Spring Back Effect of TIG Welded Ti-6Al-4V Sheets

The investigation presented streamlines its framework towards understanding the implications of spring back effect of Ti-6Al-4V alloy (Grade 5) sheet metals through experimental and numerical procedures. Base metal and automated TIG welded samples each of 2 mm thickness are subjected to three-point bend test on a Universal Testing Machine. Research reports are immense and provide an analytical insight into forecasting of the spring back effect in sheet metal. Yet, it raises several complexities while also excluding few critical contributories that have prominent repercussion posing disparity among literatures. These contradicting reports raise pointers thereby creating ambiguity and lack of understanding. Such shortcomings are addressed through this work undertaken with an aim to develop a finite element model on ABQUAS/CAE platform to estimate the spring back effect on base and welded samples, respectively. The results accomplished through the numerical model show good agreement with the experimentally recorded values. The outcome of the study demonstrates that punch stroke and thickness of the sheet metal are the key components dictating the degree of spring back effect in forming process. Sheet metal thickness shows disproportional variation with spring back effect, whereas contradictory observation is recorded for punch stroke variations.

Studies on the Parametric Effects of Plasma Arc Welding of 2205 Duplex Stainless Steel

This research study attempts to create an optimized parametric window by employing Taguchi algorithm for Plasma Arc Welding (PAW) of 2mm thick 2205 duplex stainless steel. The parameters considered for experimentation and optimization are the welding current, welding speed and pilot arc length respectively. The experimentation involves the parameters variation and subsequently recording the depth of penetration and bead width. Welding current of 60–70 A, welding speed of 250–300mm/min and pilot arc length of 1–2mm are the range between which the parameters are varied. Design of experiments is used for the experimental trials. Back propagation neural network, Genetic algorithm and Taguchi techniques are used for predicting the bead width, depth of penetration and validated with experimentally achieved results which were in good agreement. Additionally, micro-structural characterizations are carried out to examine the weld quality. The extrapolation of these optimized parametric values yield enhanced weld strength with cost and time reduction.

Experimental investigation and numerical simulation of weld bead geometry and temperature distribution during plasma arc welding of thin Ti-6Al-4V sheets

Numerical and experimental investigations of autogenous plasma arc welding of thin titanium alloy of 2 mm thick and modelling the temperature distribution for predicting the weld bead geometry are presented. The finite element code COMSOL Multiphysics is employed to perform non-linear unsteady heat transfer analysis using parabolic Gaussian heat source. Temperature-dependent material properties such as thermal conductivity, density and specific heat are used to enhance the efficiency of simulation process. A forced convective heat transfer coefficient was used to account for the effect of convection. The experimental trials were conducted by varying the welding speed and current using Fronius plasma arc welding equipment. The simulation results are in good agreement with the experimental results.