Papers by Keyword: Multipass Welding

Abstract: Weld distortion and residual stresses are two major issues in the fabrication process. Numerical techniques are being tried out to accurately predict the structural integrity of the welding. Interpass time in the multipass welding is an important parameter which influences the weld distortion and residual stresses. In this study two pass tungsten inert gas (TIG) welding of 6 mm mild steel plates has been analyzed using Finite element analysis (FEA) software Sysweld and parametric study is conducted with different interpass time. The temperature distribution, distortion and residual stresses are calculated using three dimensional finite element model (FEM) considering phase transformations in the material. The transient thermo-metallurgical analysis followed by elasto-plastic analysis is carried out using temperature dependent and phase dependent material properties. The material deposition in the multipass welding is numerically simulated using chewing gum method, where dummy phase and dummy material are assigned for the element activation. The phase proportions are calculated by assigning suitable phase kinetics parameter extracted from continuous cooling transformation (CCT) diagram of a given material. Experiments are conducted for validation after given edge preparation and using same material as filler wire. The FEM analysis is carried out for eight cases with different time interval between passes, starting from 30 s to 240 s in the steps of 30 s. FEM results are verified with experimentally measured values. It is found that the time interval between passes has less influence on the residual stresses but significantly affects the distortion and phase proportion due to the first pass preheating effect on second pass and second pass postheating effect on first pass.

Abstract: In this project, the residual stress due to multipassed welding process at the fillet weld will be studied using 2D Finite Element Analysis (FEA) simulation method and experimental investigation. Due to the extensive capabilities and dedicated tools for the simulation of welding, including material deposit via element activation or deactivation and predefined or customized moving heat sources, SYSWELD 2010 was chosen as the FEA software. The material with a thickness of 9 mm was structural steel S355J2G3 for simulation and low carbon steel for the experiment. The clamping condition was selected to obtain the best relationship between simulation and experiment by using Strain Gage. The model was dedicated to multipassed welding using the robotic welding system

Abstract: This paper investigates the simulation technique for analyzing the distortion behavior induced by welding process on welded plate which was clamped on one side. This clamping method is intended to enable the investigation of the maximum distortion on the other side. FEA software SYSWELD was employed to predict multipassed butt weld distortion of low carbon steel with thicknesses of 6 mm and 9 mm. The simulation begins with the development of model geometry and meshing type followed by suitable selection of heat source model represented by the Goldak’s double ellipsoid model. Other parameters such as travel speed, heat input, clamping method etc. were determined. The model is dedicated for multipass welding techniques using Gas Metal Arc Welding (GMAW). The experimental works were conducted by using Robotic welding process.

Abstract: Finite element simulation is an efficient method for studying factors affecting weld-induced residual stress distributions. In this paper, a validated three-dimensional finite element model consisting of sequentially coupled thermal and structural analyses was developed. Three possible symmetrical welding sequences, i.e. one-welder, two-welder and four-welder sequence, which were perceived to generate the least distortion in actual welding circumstances, were proposed and their influences on the residual stress fields in a thick-walled tee joint were investigated. Appropriate conclusions and recommendations regarding welding sequences are presented.

Abstract: This paper investigates the microstructural induced hardness variation in multirun welded plain carbon steel at different interpass time. Beveled 16mm thick mild steel samples were welded in 2 and 4 passes at interpass time of 90, 120 and 240s respectively via manual metal arc. The result showed that the differences in hardness values of the fusion zone and heat affected zone reduce as interpass time increases for both 2 and 4 runs. The effect was however quite distinct in the 4 runs welding cycle. In the 2 run cycle, the fusion zone and heat affected zone merge at 100 seconds; while in the 4 runs cycle, the merging occurred at 25 seconds; indicating that the higher the multipass, the shorter the time required to produce uniformity in hardness and structural homogeneity. Thereby increasing the resistance of the weld to crack susceptibility and failure. At these instances, the microstructure revealed fine grained pearlite interpassed in martensite.

Abstract: The occurrence of microcracks, especially ductility-dip crack in multipass weld metal during GTAW and laser overlay welding processes of Ni-base alloy 690 was predicted by the mechanical approach. The stress/strain analysis in multipass welds was conducted using the thermo elasto-plastic finite element method. The brittle temperature range for ductility-dip cracking (DTR) of the reheated weld metal was determined by the Varestraint test. Plastic strain in the weld metal accumulated with applying the weld thermal cycle in multipass welding. The plastic strain-temperature curve in the La free weld metal did not cross the DTR in the cooling stage of GTAW process, however, it crossed the DTR in the cooling stage of reheating process by subsequent welding. On the other hand, the plastic strain-temperature curves of any weld passes in the La added weld metal did not cross the DTR. Ductility-dip cracks occurred in the La free weld metal except for the final layer, however, any ductility-dip cracks did not occur in the La added weld metal during multipass welding. It could be understood that ductility-dip crack would occur during not only single-pass welding but also multipass welding when plastic strain intersected the DTR.