Residual stress-induced deformations are a major cause of tolerance loss in solid freeform fabrication process employing direct metal deposition. In this article, a three-dimensional finite-element (FE) thermo-mechanical model is presented to predict the residual stress-induced deformations with application to processes where material is added using a distributed moving heat source, e.g. gas metal arc welding (GMAW). A sequentially coupled thermo-mechanical analysis is performed simulating buildup of a single layer on a bolted rectangular substrate. The material used in the present study is mild steel, with temperature-dependent material properties and the material modelled as elastic perfectly plastic. The numerical results are compared with experimental data by manufacturing plate-shaped single-layered specimen, using an indigenously developed semi-automatic deposition system. The fusion zone and temperatures predicted by numerical model show good agreement with experimental data, and the deformations of the substrate in bolted and unbolted conditions are also in good agreement. It has been observed that the heat transfer conditions vary during deposition; therefore, any assumption of thermal symmetry is not valid. Thermal cycling during deposition is the main cause of deformations. The effect of bolting is also very important.

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Residual stress induced deformations are a major cause of loss in tolerances in solid freeform fabrication processes employing direct metal deposition. In this paper a 2D finite element thermo-mechanical model is being presented to predict the residual stress induced deformations with application to processes where material is added using a distributed, moving heat source. A sequentially coupled thermo-mechanical analysis is performed using a kinematic thermal model and a plane strain structural model. Temperature dependent material properties are used with the material modelled as elastic perfectly plastic. The material used is mild steel. The numerical results are checked against experimental data by manufacturing plate-shaped single layered specimens using an indigenously developed semi-automatic deposition system. The simulation results are compared with experimental data for successive sections along deposition and it is found that, with the exception of plate edges, the two are in very good agreement. The error at plate edges can be as high as 45% and the reason is that a 2D model cannot capture the effect of plate bolting accurately. The computational model is extended further to study the effects of various process parameters, like heat sink characteristics, rate of deposition and deposition sequence, on the buildup of residual stress and deformations. It has been observed that these parameters affect not only the magnitude of deformations but also its distribution. The residual stress distribution depends upon the sequence of deposition and the highest stresses are found at the last deposited row. In order to minimize distortions a proper combination of process parameters is essential.

This paper presents a finite element (FE)-based three-dimensional analysis to study the structural effects of deposition patterns in welding-based layered manufacturing (LM). A commercial finite element software ANSYS is used to simulate the deposition incorporating a double ellipsoidal heat source, material addition, and temperature-dependent material properties. Simulations carried out with various deposition sequences revealed that the thermal and structural effects on the workpiece are different for different patterns. The sequence starting from outside and ending at the centre is identified as the one which produces minimum warpage.

In this paper, a three dimensional numerical simulation is performed on a stationary arc to study the effect of torch angle in gas tungsten arc welding (GTAW) of SS304 stainless steel. A comparison has been made to investigate 90 o and 70 o torch angles and analyze the effect on arc and weld pool shape. Current density, heat flux and gas shear stress are calculated in the arc region and are used as input to the workpiece to determine the weld pool. Buoyancy and Marangoni shear also affect the weld pool shape and are taken into account. The computed and experimental results are observed symmetric for 90 o torch angle. For 70 o torch angle, current density and hence the heat flux due to electron contribution is found the maximum behind and heat flux due to conduction and convection is found the maximum ahead of the electrode tip in the welding direction. This makes the maximum of total heat flux symmetric along the arc center. Heat flux due to conduction and convection decreases as the torch angle decreases resulting in a shallow weld pool. The nonsymmetric "w" shaped weld pool is developed by the combined effect of the gas shear and Marangoni convection. It is found that for 70 o torch angle, the weld pool becomes non-symmetric, shallow and wide ahead of the electrode tip in the welding direction. The numerical weld pool shapes are verified through experiments.