Pankaj Biswas

Numerical and experimental study on prediction of thermal history and residual deformation of double-sided fillet welding

Abstract Distortions occur in almost every arc welded joint. The nature of the created distortion depends on several parameters including the welding speed, plate thickness, welding current, voltage, and restraints applied to the job. The distortions and thermal history of a joint can be measured experimentally but the measurement procedure may be costly and time-consuming. In the present work a numerical elasto-plastic thermomechanical model has been developed for predicting the thermal history and resulting angular distortions of submerged arc welded double-sided fillet joints. A moving distributed heat source was used in the finite element modelling of the double-sided fillet welding to create a realistic simulation of the process. The effect of filler metal deposition was taken into account by implementing a birth-and-death process for the elements. The transient temperature distributions were predicted using temperature-dependent material properties. The angular distortion profiles were predicted based on the transient temperature distributions of the fillet welds. The model yielded results that match the experimental values (with a variation of 5–10 per cent for the maximum values of the distortions and a variation of 8 per cent for peak temperatures).

Friction stir welding of aluminum alloy with varying tool geometry and process parameters

The present investigation had two objectives: first, to study the effect of the geometry of the tool pin, and second, the effect of tool rotation and welding speeds on the mechanical properties of friction stir welded joints made for samples of commercial grade aluminium alloys. The results obtained from the performed experiments showed that tools with tapered pins created superior mechanical properties for the friction stir welded joints. It was also found that overall mechanical response depended on the ratio of the tool rotation speed to the tool traverse speed. Suitable values for this ratio were isolated that lead to high quality mechanical properties for the created joints.

Thermomechanical finite element analysis and experimental investigation of single-pass single-sided submerged arc welding of C—Mn steel plates

Abstract Determination of distortions are important while designing the arc-welded joints. These distortions occur in a varied way in almost every type of welded joint, depending on several parameters, i.e. welding speed, plate thickness, welding current and voltage, restraints applied to the job while welding, thermal history, etc. In the present work a numerical model based on the finite element package ANSYS was developed for single-pass single-sided submerged arc welding of square butt joints. Suitable macros were developed to simulate the situation of a moving distributed heat source, metal deposition to account for top and bottom reinforcements, a time step, and a meshing scheme. In this model the effect of bead geometry was incorporated. The effect of filler metal deposition was taken into account by implementing the element birth and death technique. Submerged arc welding (SAW) can be conveniently used to weld a range of plate thicknesses in a single run using a suitable backing strip achieving adequate top and bottom reinforcements. The welding methodology established in the present work resulted in minimizing angular distortions in butt welds. The numerical model yielded results comparing well with those of the experimental ones.

Three-dimensional finite element prediction of transient thermal history and residual deformation due to line heating

The parameters of the line heating process have significant effect on thermal history and the resulting residual deformation of the heated plate. The thermal transients are dependent on torch speed, torch height, gas pressure, and nozzle size, which in turn controls the residual deformation of the plate. In the present work, three-dimensional transient finite element thermomechanical analysis of line heating using oxyacetylene gas flame is presented. The analysis is carried out using temperature-dependent material properties, Newtons convection, and Gaussian distribution of heat. To reduce the computation time, a fine mesh was used along and near the heating line that was coarsened at the edges and away from the heating line. Numerical thermal transients and residual deformation were presented for various torch speeds, heat inputs, and different thicknesses of plate (6 mm, 8 mm, 10 mm, and 12 mm thick plates). The results compared fairly well with experimental and previously published results. The reduction in peak temperature, for similar heating conditions, and the increase in structural stiffness of thicker plates resulted in a reduction in out-of-plane deformation. In this work, the computational model for correlation of deformation pattern with heat input for a single heating line has been achieved. This model will further be extended to predict deformation patterns due to multiple parallel and oblique heating lines.

Prediction of welding deformations of large stiffened panels using average plastic strain method

Abstract Curved or flat stiffened steel panels used in ships and offshore structures are fabricated mainly by fusion welding. It leads to heat induced plastic strains, distortions and residual stresses. These distortions may adversely affect the subsequent fit-up and alignment of the adjacent panels. A solution methodology named average plastic strain method was developed and adopted based on evaluation of average plastic strains of butt and fillet joints of small scale specimens. These were obtained using the conventional thermomechanical analysis. These plastic strains were then used to determine the overall distortions of large stiffened plate panels. The results obtained were compared with those of established inherent strain method for prediction of distortion of large stiffened plate panels. Computational efficiency of the average plastic strain method was found to be comparable with the inherent strain method. However, the accuracy in the plastic strain method was found to be better than that in the inherent strain method.

A Comparative Study of Material Flow Behavior in Friction Stir Welding Using Laminar and Turbulent Models

Friction stir welding has been quite successful in joining aluminum alloy which has gained importance in almost all industrial sectors over the past two decades. It is a newer technique and therefore needs more attention in many sectors, flow of material being one among them. The material flow pattern actually helps in deciding the parameters required for particular tool geometry. The knowledge of material flow is very significant in removing defects from the weldment. In the work presented in this paper, the flow behavior of AA6061 under a threaded tool has been studied. The convective heat loss has been considered from all the surfaces, and a comparative study has been made with and without the use of temperature-dependent properties and their significance in the finite volume method model. The two types of models that have been implemented are turbulent and laminar models. Their thermal histories have been studied for all the cases. The material flow velocity has been analyzed to predict the flow of material. A swirl inside the weld material has been observed in all the simulations.

Modelling and optimizing the effects of process parameters on galvanized steel sheet resistance spot welds

This paper investigates the choice of input process variables that create acceptable welds in the resistance spot welding of galvanized steel sheets. The effects created by the interactions between the process variables in terms of the size of the weld nugget, tensile-shear strength, and peel strength are also investigated. Regression equations are obtained and their ability to predict the size of the weld nugget, tensile-shear strength, and peel strength is tested in a series of test cases. The obtained data is then used in response optimization studies. The predicted optimized input process variables were experimentally verified by comparing measured and predicted optimized target responses. The methodology adopted in the present investigation is shown to be able to model, predict, and response optimize the input process variables for resistance spot welding of galvanized steel sheets.

Study on the effect of tool profiles on temperature distribution and material flow characteristics in friction stir welding

The present investigation describes a computational fluid dynamics approach to study the effects of friction stir welding tool profiles on the thermal conditions and material flow in welds. The aim is to observe the temperatures of the weld and material flow with respect to different probe profiles. For the modeling purpose, temperature dependent material properties and stick–slip conditions between the tool and work material were incorporated. The results from the model exhibited most of the process characteristics of friction stir welding, such as the difference in temperatures of advancing and retreating sides of the weld, temperature contours ahead and behind the tools along the weld, and flow fields. The thermal condition exhibited temperatures that were close to experimental values and below the melting point of the aluminum alloy.

Optimization and Prediction of Angular Distortion and Weldment Characteristics of TIG Square Butt Joints

Abstract Autogenous arc welds with minimum upper weld bead depression and lower weld bead bulging are desired as such welds do not require a second welding pass for filling up the upper bead depressions (UBDs) and characterized with minimum angular distortion. The present paper describes optimization and prediction of angular distortion and weldment characteristics such as upper weld bead depression and lower weld bead bulging of TIG-welded structural steel square butt joints. Full factorial design of experiment was utilized for selecting the combinations of welding process parameter to produce the square butts. A mathematical model was developed to establish the relationship between TIG welding process parameters and responses such as upper bead width, lower bead width, UBD, lower bead height (bulging), weld cross-sectional area, and angular distortions. The optimal welding condition to minimize UBD and lower bead bulging of the TIG butt joints was identified.

Prediction of welding sequence induced thermal history and residual stresses and their effect on welding distortion

Stiffened plate panel is the major structural part of a fabrication industry where fillet welding joint is one of the most important fabrication techniques. Large stiffened structures are generally joined by several welding passes which generates thermal stresses and angular deformation. Tensile residual stresses which are generated due to welding in the weld region may lead to early failure of the structure when subjected to cyclic loading. The weld-induced residual distortion causes dimensional inaccuracy and needs rework to achieve the desired shape. Use of multiple welding passes without any optimized welding sequences typically leads to an increased degree of nonuniform heating and cooling, i.e., creating complex welding residual stress and angular deformation in the structure. In this present study, the effect of four different welding sequences on submerged arc welded fillet joint has been studied. A finite element-based numerical model has been developed to predict the thermal profile, welding residual stress, and angular deformation. The developed model considers temperature-dependent material property and material deposition by using element death and birth technique. The results have been compared with experimental one. In the effect of welding sequence on residual stress, angular deformation has been studied. Thus, the developed model presents the effect of welding sequence on the weld induced residual stresses and distortions which provide one of the most optimal welding sequence for enhanced fabrication process.