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.

Resistance spot welding (RSW) includes many variables that can influence the weld properties. The purpose of this study is to develop an analytical model for prediction of thermal history and weld microstructure in RSW and to find the most important process parameters that influence the weld microstructure. A one dimensional model is proposed for prediction about thermal history during cooling step of RSW process. The reliability of analytical model is evaluated by experiments and numerical simulations. The calculations reveal that the current analytical model is reliable particularly at the temperatures lower than Tm/2. Sheet surface temperature at electrode-sheet interface and sheet thickness are recognized as the most important factors affecting the cooling rate at T

In this study, the effect of welding parameters on the residual stresses of Resistance spot welding of AZ31 magnesium alloy was investigated. Resistance spot welding is a complicated multi-regime phenomenon which simulated by a developed electro-thermo-mechanical coupled finite element model. Interactions of parameters were determined using DOE method. The FE model was used to predict temperature changes, nugget growth, and the residual stresses distribution. The results of the simulation were validated with experimental data, based on the nugget diameter. The results showed that by increasing current and welding time the residual stresses are reduced. Increasing electrode force causes to increase residual stress but increasing holding time creates a peak in the amount of residual stresses. Also, evaluation of current sources revealed, in the same conditions, using direct current creates less residual stress than alternating current.

In this research, the mechanical and microstructural properties of AISI 316L sheets welded by RSW method using copper interlayer were investigated. In this regard, two types of connections were made, one without the use of an interlayer and the other with the use of a copper interlayer in different currents. In order to choose the optimal current for both types of connections, tensile tests were first performed, and microstructural, microhardness, elemental evaluation and failure mode tests were conducted on the selected samples. According to the obtained results, by increasing the electric current, the heat input in the welding pool is sufficiently high and the microstructural and mechanical properties of the welding zone were improved(Conversion of coarse grain to fine grain). Also, due to the optimality of the electric current in both samples with and without the interface layer, both samples had environmental failure, which indicates the high strength of the interface and their welding point. Changes in the chemical composition in different welding zones were insignificant and the distribution of elements was uniform in all zones. Also, the hardness changes from the base metal to the center of the welding zone were in the order of welding zone > base metal > heat-affected zone, which was consistent with the results obtained from the microstructural investigations. According to the results obtained for both cases with and without the use of an interface layer, the Resistance spot welding method showed a successful connection for both types of cases.

Resistance Spot welding (RSW) is a powerful tool for overlap joint of thin sheets. The welding procedure contributes to affecting the electrical, thermal and mechanical properties of the sheets. In this article, Resistance spot welding of ultrathin IF steel sheets (0. 67 mm thickness) have been studied. The IF steel sheets were welded by different welding currents (65, 70, 80, 90 and 100 A). The microstructure of the samples was observed using an optical microscope and the tensile test has been carried out to determine the joint strength and fracture mode. The microstructural observations showed that the grain size increase in the fusion zone by increasing the welding current and the heat-affected zone experienced recrystallization and small equiaxed grains were formed in the heat-affected zone. The base metal keeps its high hardness value from the work-hardening induced by the previous rolling process. Best joint strength was obtained at 80 A welding current (2600 N). The fracture mode changes from partial interfacial failure (at lower welding current) to the pullout with tearing of the sheets (at higher welding current).

Resistance spot welding is an important manufacturing process in the automotive industry for assembling bodies. The quality and strength of the welds and, by extension, the body is mainly defined by the quality of the weld nuggets. The most effective parameters in this process are sheet material, geometry of electrodes, electrode force, current intensity, welding time and sheet thickness. The present research examined the effect of process parameters on nugget formation. A mechanical/ electrical/ thermal coupled model was created in a finite element analysis environment. The effect of welding time and current, electrode force, contact resistivity and sheet thickness was simulated to investigate the effect of these parameters on temperature of the faying surface. The physical properties of the material were defined as nonlinear and temperature dependent. The shape and size of the weld nuggets were computed and compared with experimental results from published articles. The proposed methodology allows prediction of the quality and shape of the weld nuggets as process parameters are varied. It can assist in adjusting welding parameters that eliminates the need for costly experimentation. This process can be economically optimized to manufacture quality automotive bodies.

Many parameters affect the quality of welding in the Resistance upset welding (UW) process. These parameters are material and geometry of parts, welding force, thermal cycle at the weld zone, current density and welding time. The controllable parameters in this process are current density, welding time, and welding force, where current density and welding time are more significant. In this paper, the effect of welding time and current density on the temperature distribution of the welding zone is presented. For this purpose, a thermal-electrical finite element model is developed to analyze the thermal behavior of the joint produced. A transient temperature field obtained from thermal-electrical simulation of UW process is applied as nodal load on the model. The results of thermal-electrical analysis are used to predict the status of the weldment. Specifically, the quality of the weld at the seam can be evaluated. The simulation results are evaluated by performing tensile test on the welded joints. The experimental results show that by increasing in the length of the joint, the maximum tensile load applied to the joint increases.

The purpose of this study is to investigate the effect of Resistance spot welding (RSW) parameters on nugget size and ultimate strength of Magnesium alloy sheets AZ61 under tensile-shear test. In this study microstructural examination and hardness measurements were carried out on the welded samples. The results show that the weld nugget zone is divided into two separate parts: the equiaxed dendritic zone (EDZ) perched at the center of the weld nugget and the columnar dendritic zone (CDZ) situated around the fine-grained zone having it surrounded. The effect of the following three parameters: electric current, welding time and electrode force on the dimensions of the weld nugget and the welded ultimate strength is investigated. The response surface method (RSM) is employed to examine the effects of welding parameters and to attain optimum parameters. The analysis of variance (ANOVA) results of RSM model shows that however the tensile-shear strength and nugget size are improved with increasing the welding current and welding time, the welding current is the most influential parameter. In addition, the optimal values for the welding parameters are calculated to achieve the maximum nugget size and the ultimate strength of welded joint. Finally, a regression model is proposed in order to predict the peak load and the nugget size as function of the mentioned welding parameters.