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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This paper presents a comparative study of three- and two-dimensional axisymmetric finite element (FE) analyses of a welded pipe–flange joint for residual stresses and deformations in order to identify their merits or demerits. Sequentially coupled thermal stress analysis is performed to simulate single pass metal inert gas welding. Butt weld geometry with a single ‘V’ for a 100 mm nominal diameter pipe and same sized weld neck type ANSI class #300 flange is used. The heat input is modelled by using the Goldak double ellipsoidal heat source model. Temperature dependent material properties are used and deposition of filler metal is obtained by element birth and death feature. Both thermal and structural FE models are validated with experimental measurements. Residual stresses predicted by two-dimensional model are generally on the higher side and hence more conservative. However, we conclude that the three-dimensional FE model is preferable for the prediction of flange face distortion since it is a vital parameter for flange joint performance.

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 results of detailed three-dimensional finite element simulation of residual stress distribution in welded Pipe-Flange Joints with emphasis on the effect of welding parameters and geometrical size of the model. Single-pass Metal Inert Gas welding with single “V” Butt-weld geometry is used in the study. The effect of two basic welding parameters including welding current and speed and two geometrical parameters i.e. pipe diameter and wall-thickness are examined. For both welding current and welding speed, three sets of parameters comprising of low, medium and high values are used. To analyze the effect of each parameter explicitly only one parameter is changed at one time. In most of the cases 100 mm nominal pipe diameter is used. A FE Model for 200 mm nominal pipe diameter is also analyzed to determine the effect of pipe diameter.