Papers by Keyword: Resistance Spot Welding (RSW)

Abstract: In this paper, with the ANSYS, a 2D axisymmetric coupled thermo-electro-mechanical model was developed to analyze the spot welding process（RSW） of zinc coated steels with copper strips as an insert material between electrode and workpiece. A transient temperature field obtained from a prior performed thermal–electrical simulation of RSW process is applied as nodal load on the model to simulate the stress distribution. The temperature and stress distributions in such a welding process were obtained and compared with a conventional resistance spot welding process. The results show that using the same welding process parameters, the maximum transient temperature at the electrode surface is lower than the conventional RSW process due to the use of copper strips, which helps to extend electrode lifetime. In addition, the presence of inserted copper strip increased the resistance of welding system, thus generated much more heat to form larger nugget.

Abstract: Resistance spot welding (RSW) has been extensively used as a sheet metal joining process, and the welding process identification is the essential issue for the design of high performance control strategy and set-up of a new welding schedule. However the RSW is a nonlinear time-varying uncertain process which couples the thermal, electrical, mechanical and metallurgical dynamics. To understand this complicated physical phenomenon an M-series pseudo-random electrical pattern is adopted to excite the RSW electrical-thermal dynamics and the thermal response is recorded according to the welding power outputs. Based on the experimental information the transfer function of an RSW electrical-thermal mechanism is identified, and the optimum model order and parameters are determined. Subsequently a control-oriented RSW model is established to explore the welding power control algorithm. The simulated results from the control model show their agreement with the experimental data, which validates its feasibility for corresponding welding control.

Abstract: Resistance spot welded magnesium alloy joints contain the nugget and heat affected zone (HAZ), and the weld nugget of magnesium alloy generally contains two different microstructures, the cellular dendritic crystals at the edge of the nugget and the equiaxed dendritic crystals in the center of the nugget. Characteristics of cellular dendritic crystals make the cellular dendritic crystals zone to be the weak area, and the more unfortunate thing is that it is located in the high-stress zone, which further degrades the mechanical properties of the joints. Based on this conditions, inoculation would be tried to refine the cellular dendritic crystals in order to improve the mechanical properties of resistance spot welded magnesium alloy joints. Al-10Sr was chosen as the inoculant in this experiment. As the addition of Al-10Sr increases from zero to 1.4mg, the average width of cellular dendritic crystal zone decreases from 332μm to 58μm while the microstructure tends to be refined, accordingly, tensile shear load of the joints increases by 24.3% from 2.379 KN to 2.959 KN. It is favorable to select a relative higher content of Al-10Sr addition to improve the mechanical properties of the spot welded magnesium alloy joints.

Abstract: The objective of this work is to investigate the relationship between nugget development and electrode displacement curves during micro RSW of stainless steel sheets. A DC transistor type micro RSW machine equipped with a real-time monitoring system was employed for this study. A laser displacement sensor was used to detect the displacement signals in the movement of upper electrode. This research can provide references for monitoring and control micro RSW quality using maximum electrode displacement. The results showed that electrode displacement increased rapidly at the initial heating stage of welding, and then at a reducing rate under normal cooling stage. The maximum electrode displacement is proportional to the weld current and is inversely proportional to the electrode force. An electrode displacement curve is an ideal monitoring signal can reflect the formation and growth of a nugget during micro RSW.

Abstract: Resistance spot welding (RSW) is one of the most commonly used form of manufacturing process. To efficiently search for the optimal RSW parameters in a new welding power control scheme to obtain the maximum tensile strength of welded joints, a design of experiments (DoE) using orthogonal arrays has been conducted. However the lack of success of conventional DoE is attributed to two facts that the weld quality is quantitatively measured and level-based evaluated, and the welding expulsion compromises the continuity of response surface, which is an underlying hypothesis of normal DoE analysis. Hereby a fuzzy analysis methodology for the experimentation design, referred as fuzzy orthogonal experiments (FOE) in this paper, has been proposed. With the fuzzification of factor levels and experimental objectives, the proposed method is able to explore the results of arbitrarily given factors without additional experiments, and identifies the varying tendency under condition of discontinuity experimental responses. The FOE application for a specifically planned RSW process presents a detailed FOE analyzing procedures, and yields the optimal parameter settings. The case study shows that FOE outperforms the traditional orthogonal DoE for its minimized experiment numbers and robust response tendency analysis.

Abstract: On-line quality assessment becomes one of the most critical requirements for improving the efficiency of automatic resistance spot welding (RSW) processes. Accurate and efficient model to perform non-destructive quality estimation is an essential part of the assessment. Besides the usual welding parameters, various measured variables have been considered for quality estimation in RSW. Among these variables, dynamic resistance (DR) gives a relative clear picture of the welding nugget formation and presents a significant correlation with the RSW quality indicators (QI). This paper presents a structured approach developed to design an effective DR-based model for on-line quality assessment in RSW. The proposed approach examines welding parameters and conditions known to have an influence on weld quality, and builds a quality assessment model step by step. The modeling procedure begins by examining, through a structured experimental design, the relationships between welding parameters, typical characteristics of the RD curves and multiple welding QI. Using these results and various statistical tools, different integrated quality assessment models combining an assortment of DR attributes are developed and evaluated. The results demonstrate that the proposed approach can lead to a general model able to accurately and reliably provide an appropriate assessment of the weld quality under variable welding conditions.

Abstract: Nowadays online quality estimation for the resistance spot welding (RSW) has benefited a lot from monitoring the electrode displacement caused by nugget thermal expansion. Based on these emerging monitoring techniques a new approach is proposed to classify the weld quality and assure the quality for mass-produced weld group, which enables the continuous quality improvement concept during the welding process. A causal models are built with the offline trained Bayesian Belief Networks (BBN). It is a weld quality assessment net reveals the dependency of the weld quality on the features displayed by the displacement curve, which can be used for overdesigning the safety welds or as the probabilistic forecasting model for online weld quality assessment. The experimental results show that the proposed approach is valid and feasible to predict the weld quality and assure the overall quality for weld group in real applications.

Abstract: A series of spot welding technology, joint mechanical properties and microhardness test analysis of TRIP800 high strength steel were researched. Based on these experiments and analysis, effect of spot welding parameters such as welding current, welding time and electrode pressure on joint mechanical properties were explored. The relevant spot welding parameters of TRIP800 high strength steel of spot welding were recommended, such as welding current is7.5~8.0KA, electrode pressure is 450 kgf and welding time is 20cyc. Welding electrode should be to ensure that as much as possible and clean the surface,to avoid welding current and welding time is too high or too long, as well as forging lack of power, to prevent the occurrence of welding defects.

Abstract: In this study, the effect of welding parameter on the microstructure and properties of resistance spot welding joint for 400MPa ultra fine-grained steel is investigated. The results indicated that the microstructure of HAZ of ultra fine-grained steel joint consists of hardening organization: bainite, martensite, M-A constituent, i.e. while the fusion zone mainly consists of the coarse martensite. By applied forge-delay force during resistance spot welding will increase the nugget diameter, eliminate the shrinkage defect in nugget zone and improve the shearing strength of joints.

Abstract: Dual-phase steel is a type of sheet material newly developed to adapt to the lightweight and safety needs of vehicle. In this paper, 1.7 mm thick dual-phase steel DP600 was taken as the object of study, its resistance spot welding performance characteristics and welding mechanism was studied in detail. The thermoelectricity transient process of welding was simulated with the finite element software and the experiment under corresponding welding parameters. It’s found that, under proper current circumstances, the simulated nugget size and the experimental result is in good agreement except the large current, the simulated deformation morphology and experimental result can be consistent, which indicates the good accuracy of analysis on resistance spot welding mechanism of dual-phase steel DP600. According to the results, the specific method and theoretical basis about nugget size and welding deformation predictive control was discussed, created the mutual relations between the resistance spot welding performance characteristics and welding mechanism of dual-phase steel DP600. The study effort has practical significance in comprehensively understanding the resistances spot welding mechanism of dual-phase steel, as well as in application and quality control of duplex steel in automotive body welding.