Welded tubular joints are widely used in various industry structures for high efficiency subjected to pressure, bending and twisting. Welded structures are the main parts of structures, buildings, bridges, gas pipes, pressure vessels and power transmission equipment in the ship building, construction, oil, gas, petrochemical industries and power plants. A sample of pipe-welded joints is a X-tubular joint that has been investigated in this study. The main objective of the present work is to investigate the heat transfer and residual stress caused by the three-stage WELDING process in Xtubular joint made of St52 using Simufact WELDING software. The WELDING process involves three WELDING steps using arc WELDING. The finite element model contains the thermal and mechanical properties of base metal and WELDING metal as a function of temperature. Also, advanced modeling tools such as mesh adaptation during the process and meshing compatible with the WELDING site, the birth and death technique of the element and the source of heat transfer have been used. WELDING simulation showed that significant residual stresses were created in the joint after WELDING. Comparison of the results shows that the numerical results and empirical measurements are in good agreement with each other and the existing model can provide a good prediction of temperature distribution and stress control in this WELDING process.

In WELDING process, stresses after cooling, which remain in body, are called residual stresses. Sometimes, the magnitude of stresses is high and reduces the strength of welded pieces, moreover, they cause crack in the weld. To predict WELDING residual stresses, it is necessary to do thermal and mechanical analysis.In this paper, some parameters which influence the WELDING using ANSYS software are investigated. Results show that even by decreasing the travel speed of torch, it makes no differences in the amount of residual stresses, but preheating causes decreasing the produced stresses about 22 percentages. Suitable WELDING sequences also, decreases residual stresses up to 25 percentages.

The main purpose of this study is optimization of resistance spot WELDING of AZ61 Mg alloy to achieve maximum nugget size and minimum tensile residual stresses in WELDING area. Since the stability and strength of a welded structure is strongly dependent on the nugget size and the residual stresses, an integrated artificial neural networks and genetic algorithm is utilized to optimize the WELDING parameters. In this study, the resistance spot WELDING process is simulated by a 2D fully coupled structural-electrical-thermal finite element model. The finite element model is developed to predict of the nugget size and the residual stresses in the WELDING area. In order to validate the FE model, the results are compared with the obtained results from the experimental tests. The results show that the FE model has a good agreement with the experimental tests. The input parameters for optimization are: electrical current, WELDING time and electrode force. The results show that the integrated optimization algorithm is successful in determining the optimized WELDING parameters. Based on the optimization results, the maximum nugget size 6. 33 mm and the minimum tensile residual stress 228 MPa are achievable by using 16kA, 16 Cycles and 848 N as current, WELDING time and electrode force respectively.

Friction stir WELDING (FSW) can be defined as a green technology, because the consumption of energy during this process is less than other WELDING methods. In addition, during the process there is no gas, filler material or other consumables. It should be noted that, complex curved shapes are now commonly used in different industries in a bid to have lightweight structures. According to the above-mentioned descriptions, several investigations into the potential benefits of adopting Friction Stir WELDING (FSW) in the production and joining different materials are being undertaken. The work presented in this paper is focused on thermal behavior of the curved FSW and its benefits for the green technology. Due to the robust nature of FSW process aluminum 6061-T6 alloy has been selected as the WELDING material. The results of the study showed that, the total peak temperature value of 300° C happened at time, t = 3 s at the plunge stage (outside of the WELDING seam). Meanwhile, at the dwell stage (between t = 3 s to t = 5 s), there is a stable situation in the amount of the generated heat from the plastic deformation as well as the contact shear stress at the tool-workpiece contact interfaces, thus the interfacial temperature is found to be stable. By the end of the dwelling step, the total generated heat is stable to the maximum value of 300° C. At the step time of t = 12. 8 s, the temperature is distributed asymmetrically across the workpiece until the time step of 19. 6 s which at this point the asymmetric contour expanded in the stir zone.

Some Micro structural Aspects of Explosive WELDING Interface between Aluminum and Steel which welded in Different Conditions have been studied. Wavelength, amplitude and Interlayer Phase Dimensions Formed in the WELDING Interface have been measured by means of an Optical Microscope. By Comparing Welded Samples, it is Determined that the Greater Stand off Distance, the Larger Interface Dimensions, But Interface Wavelength and Amplitude have not been Changed with Stand off Distance Variations. It has been concluded which an Increase in Explosive Mass and a Decrease in Flyer Tube Thickness, Will Result in Increase in Wavelength and Amplitude and Interlayer Phase Dimensions.

A-TIG WELDING is a WELDING method in which TIG WELDING is conducted by covering a thin layer of activating flux on the weld bead beforehand. The most benefit of this process is the gain in weld penetration depth. A-TIG welds were produced on mild steel plates with TiO2 flux. The emphasis of this paper lies in introducing the effects of various process parameters (WELDING current, WELDING speed, powder/acetone ratio of the flux, arc length and electrode angle) in mild steel A-TIG WELDING. The weld penetration depth was the measured metallographically. An optimum value was determined for each WELDING parameter.