جستجوی مقالات مرتبط با کلیدواژه « resistance spot welding » در نشریات گروه « مکانیک »

The shunting effect in resistance spot welding (RSW) occurs due to the side electrical current created through the previous spot welds. In creation of alternating welding points, the quality of subsequent welding points is affected by a side electric current due to electro-thermal changes. This shows that the analysis of the effect of the side current is important for achieving cognition of how different parameters affect this process. Therefore, the dimensions of the welding nuggets, the metallurgical structures and the mechanical strength of the welding points are affected by the changes in the electric current and the temperature distribution caused by this current. The amount of this current depends mostly on factors such as distance, number and size of previous spot welds. In this study, experimental research was performed to investigate the shunting effect on the tensile-shear strength of RSW spot welds in aluminum alloy 2219 sheets. The most important factor in shunting (welding distance) together with welding current and time was investigated by three design of experiment factor (DOE) within the welding range to achieve a statistical model based on tensile-shear strength results. An experimental regression model was derived. Results show that increasing the welding current or distance increases the tensile-shear strength of the joints.

Resistance spot welding is one of the most common methods of joining especially in sheet metal assemblies. The number of spot welds and their pattern, strongly affects the joint strength, time and costs. So, a hybrid method of finite element and particle swarm optimization was introduced for determining the pattern of spot welds in this paper. At first, one spot weld joint was created on a sheet specimen, and mechanical properties of this joint were determined. The spot welding process of three cases was simulated and verified by three different experimental data. Particle swarm optimization and finite element method were linked to determine an optimum pattern of spot weld joint. This method was utilized for two, three and four spot welds. According to this research, fracture force of two, three, and four spot welds were 1.9, 2.13 and 2.76 times of one spot with the optimal pattern. The results indicate that the best pattern has four spots distributed on a circle with a radius of 18mm and the angle between loading axis and symmetric axis was 66 degrees.

The main purpose of this study is investigation the effects of mechanical and thermal properties on accuracy of finite element model in resistance spot welding of AZ61 Mg alloy. In this study temperature dependent thermo-mechanical properties of AZ61 Magnesium alloy sheets and also thermal and electrical contact conductance (TCC and ECC) have been experimentally determined to use in a coupled electrical-thermal-mechanical finite element (FE) model in order to predict distribution of residual stresses and nugget size in resistance spot welding (RSW) process. The thermo-mechanical properties, TCC and ECC have been employed in FE model as: constant, linear and temperature dependent to investigate the effects of these parameters on accuracy of the FE model. In addition, different welding parameters such as welding current, welding time and electrode force have been used in FE model to achieve different nugget size. The results showed that thermal conductivity, electrical resistivity and ECC have significant effect on nugget size and also yield stress and elastic modulus have important influence on distribution of residual stresses. Therefore, the thermal conductivity, electrical resistivity and ECC for prediction of nugget size and also the yield stress and young modulus for prediction of distribution of residual stresses should be assumed to be temperature dependent and linear, respectively. Moreover, remaining thermo-mechanical properties can be taken as constant.

Shunting effect occurs in RSW when the electrical current passes through previous spot welds. Value of this current depends mostly on distance, number, and size of previous spot welds. This will cause some dimensional and metallurgical changes in welding nugget as well as heat affected zone (HAZ). In this study, shunting effect of RSW is considered in a finite element analysis (FEA) model and the results are compared to experiments performed on aluminum alloy 2219. Weld spacing together with welding current and time are considered to discover the effect of shunting current in the final quality of nugget. A three factor experiment design has been performed to find the significance of factors and interactive effects, as well as FEA model verification. Electrothermal and mechanical interactions are considered in the FEA model. Experimental and numerical solutions have yielded comparable similar results in terms of welding nugget properties. Asymmetry in electrical potential, temperature, and stress distribution and geometry of shunted nugget are predicted and verified directly or indirectly. Intense effect of shunting current on nugget height, asymmetric growth of heat affected zone (HAZ) toward previous welding nugget, as well as concentration of alloying elements along grain boundaries are also discovered.

This paper aims at investigating the effect of heat input in resistance spot welding on microstructure and mechanical behavior of 2304 duplex stainless steel, as a promising candidate for automotive application. The results showed that due to rapid cooling rate inherent to resistance spot welding, the ferrite-austenite phase balance is destroyed and nitride-type precipitates are formed within the ferrite grains. The amount of austenite in the weld nugget was a function of welding current, as the most important factor affecting welding heat input. Increasing welding current increased the austenite volume fraction from 4 to 18%. Moreover, the nitride precipitation was reduced upon using higher welding currents. Investigation of weld mechanical performance during the tensile-shear loading showed that increasing welding current enhances both load bearing capacity and energy absorption capability. The maximum achievable peak load and energy absorption of 2304 duplex stainless steel resistance spot welds were 25 kN and 40 J indicating a superior weldability.

In the present research، the effects of the shape and size nugget variations in the AISI 1008 resistance spot weldment were showed by the parametric study using the finite element method. The verification of some of the finite element results was done by comparison with the experimental study results and other was compared with the published researchs. The results show that the electrical current is the most important parameter in the formation of the nugget. The heat affected zone was grown by increasing the electrode diameter and the sheet thickness; as a result the time and the electrical current should be increased for welding. In addition، the nugget size was reduced and the temperature gradiant in the heat affected zone was raised by decreasing the electrical current and the welding time، as a result the tension residual stresses in the heat affected zone were increased.

Disjoining of spot welds in steel sheets because of fatigue failure is one of the main reasons for noise in used cars. Fatigue life of spot welding connections of ST12 steel sheets, used in car industry, with 6mm nugget diameter and subjected to uniaxial dynamic shear load is studied and determined in this research. Sheet thickness and other spot welding parameters including weld pitch are considered and compared according to C-G006 standard utilizing the test sample selected according to DIN50165 standard. ABAQUS and FE-SAFE soft wares are used for static and fatigue life analysis respectively. To generate Stress-Number of life cycle (S-N) diagram, the equivalent fully reversed load is determined using Goodman and Gerber theories since the applied load is unidirectional. The resultant finite element results were verified experimentally by a fatigue test machine designed and manufactured during this study by the authors. The finite element results showed a good agreement with Gerber criterion and it was concluded that with increase in sheet thickness, both static strength and fatigue life would be increased. The results also depicts that the weld pitch has no effect on fatigue life. Stress – life graph for 6mm nugget diameter spot weld on ST12 sheet is the most important outputs of this research that can be used in automobile industry.