• Proceedings of the KWS Conference
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• 1999.05a
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• pp.215-218
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• 1999

With increasing demand of energy saving, -many efforts were made to employ aluminium alloys in the automobile industry. Especially, resistance spot welding has been widely used in the steel metal joining process because of its high productively and convenience. In this paper, spot weldability of 7075-T6 aluminium thin sheets for various welding conditions were examined by series of experiments. The tensile shear strength and microstructure of welded specimens was observed, and The optimal welding conditions were found for each welding conditions.

• Journal of Welding and Joining
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• v.24 no.6
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• pp.13-20
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• 2006

Resistance spot welding is widely used for joining sheet metals in the automotive manufacturing process. Recently, servo-gun is used to increase the productivity and precise control the acting force. However, force control mechanisms have not been investigated with servo-guns until now. In this paper, it is proved that servo-motor current is proportional to torque and by experiment, experimental equation between servo-motor current and electrode force was derived. Algorithm for feedback control of electrode force was suggested using current measurement. In addition, applying soft touch method to this system the impact between electrode and specimen, which is the problem of air gun, could be reduced. Indentation made the force decrease in holding time of resistance spot welding. In order to overcome this problem, force compensation using the servo gun was used and it improved weld strength in good welding current range.

• Journal of Korean Society for Quality Management
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• v.48 no.1
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• pp.69-86
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• 2020

Purpose: This study aims to determine the optimal conditions for the spot welding process that mechanically connects the case of a cylindrical secondary battery and the negative tab. Methods: We use 33 factorial design to derive the optimal conditions for the spot welding process. The pulling strength, the cross-sectional area of nugget, and the shock test life are selected as response variables, which can represent the resistance welding quality. The input variables are selected as the welding time, welding voltage, and pressure, which are the controllable factors in the spot welding process. Results: The main effects of welding time and welding voltage and the interaction effect of welding time and welding voltage are significant. Conclusion: The optimal conditions for the spot welding process to mechanically join the negative electrode tab of the cylindrical secondary battery and the battery case are developed. The result shows that the pulling strength is increased by 44% compared to before improvement under optimal conditions.

• Journal of Welding and Joining
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• v.33 no.2
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• pp.56-61
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• 2015

IRW(Inverter Resistance Welding) process and DSW(Delta-spot welding) process for dissimilar materials of DP590 and Al5052 were performed to evaluate the welding quality and mechanical properties. IRW experiment was carried out with changing the welding current. The other welding parameters such as pressure force, weld time, squeezing time and holding time were fixed. On the anther hand, DSW experiment was performed using the process tape at welding current of 11.5kA. The other conditions were same as IRW conditions. The various testes such as shear tensile strength, nugget diameters, EDS, SEM and cross-sectional observation for weld zone was performed. As a result, IMC(Inter Metallic Compound) thickness at 11.5kA was thinner than those of 9.5kA and 10.5kA conditions. In addition, thined IMC layer was observed when high electric current apply to the materials(DP590 and Al5052) in a short time throught dissimilar resistance spot welding controling welding conditions. The relationship between the thickeness of IMC and current intensity was after discussed.

• Proceedings of the KWS Conference
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• 2008.05a
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• pp.24-24
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• 2008

• Journal of Welding and Joining
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• v.28 no.2
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• pp.66-73
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• 2010

Conventional fracture test of resistance spot weld had been performed without consideration of paint baking process in automobile manufacturing line. This study was aim to investigate the effect of paint baking on fracture mode and load carrying capacity in fracture test for resistance spot welded 780TRIP steels. With paint baking cycle after resistance spot welds, peel tests and microhardness were conducted on the as-welded and baked samples. Resistance spot welds in AHSS (Advanced High Strength Steels) are prone to display partial interfacial fractures during fracture test or vehicle crash. Baking cycle increased the load-carrying capacity of the resistance spot welded samples and improved the fracture appearance from partial to full button fracture for the L-type peel tests. Specially, the differences in fracture appearance are apparent when the nugget size of spot welds is small enough to produce the partial interfacial fracture. The comparison of macrohardness and microstructure between as-welded and baked samples showed that there are no large difference in change the fracture mode. However, the results of the instrumented indentation test suggested that fusion zone and HAZ of baked sample have less tensile and yield strength and proves that the tempering effects are applied and enhanced the resistance to fracture on welds with application of baking cycle.

• Journal of Welding and Joining
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• v.33 no.2
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• pp.47-55
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• 2015

With using adaptive control of the resistance spot welding machine, the advantage on electrode life time for galvanized steels has been addressed. This study was aimed to evaluate the electrode life time of galvanized steels with applying the constant current control and the adaptive control resistance spot welding process for a comparison purpose. The growth in diameter of electrode face was similar for both the constant current and the adaptive control up to 2000 welds. The button diameter was decreased with weld numbers, however, sudden increase in button diameter with use of the adaptive control after 1500 welds was observed. The peak load was continuously decreased with increasing number of welds for both the constant current and the adaptive control. The current compensation during a weld was observed with using the adaptive control after 1800 welds since the ${\beta}$-peak on dynamic resistance curve was detected at later weld time. The current compensation with adaptive control during resistance spot welding enhanced the nugget diameter at the faying interface of steel sheets and improved the penetration to thinner steel sheet.

• Journal of Welding and Joining
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• v.33 no.2
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• pp.69-77
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• 2015

High strength steels have been continually being developed to improve in fuel economy in automotive and ensure safety of passengers. New bonding and welding methods have been required for improving weldability on high strength steels. In this study, resistance spot welding and Weld-bond with nugget diameters of 4.0mm, 5.0mm, 6.0mm and 7.0mm were produced and tested, respectively. In order to confirm the effect of nugget diameters on tensile shear characteristic of the Weld-bond, tensile shear characteristics of Weld-bond were compared with those of resistance spot welding and adhesive bonding. Peak load of Weld-bond were increased as the nugget diameter increases. After appearing maximum peak load continuous fracture followed with second peak owing to load being carried by resistance spot weldment. Fracture modes of the adhesive layer in Weld-bond fractures were represented by mixed fracture mode, which are cohesive failure on adhesive part and button failure at resistance spot welds. The results showed that the tensile shear properties can be improved by applying Weld-bond on TRIP steel, and more apparent with nugget diameter higher than 5${\surd}$t.

• Journal of Welding and Joining
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• v.20 no.2
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• pp.102-108
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• 2002

Resistance spot welding of aluminum alloys is based upon Joule heating of the components by passing a large current in a short duration. Since aluminum alloys have the potential to replace steels fur automobile body assemblies, it is important to study the process robustness of aluminum spot welding process. In order to evaluate the effects of process parameters on the weld quality, major process variables and abnormal process conditions were selected and analyzed. A newly developed two-stage, sliding-level experiment was adopted fur effective parameter design and analysis. Suitable ranges of welding current and button diameters were obtained through the experiment. The effects of the factors and their levels on the variation of acceptable welding current were considered in terms of main effects. From the results, it is concluded that any abnormal process condition decreases the suitable current range in the weld lobe curve. Pareto analysis of variance was also introduced to estimate the significant factors on the signal-to-noise (S/N) ratio. Among the six factors studied, fit-up condition is found to be the most significant factor influencing the SM ratio. Using a Pareto diagram, the optimal condition is determined and the SM ratio is significantly improved using the optimal condition.

• 제어로봇시스템학회:학술대회논문집
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• 1988.10a
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• pp.370-373
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• 1988

Althouah there have been many attempts to control weld quality in resistance spot welding processes, design method for an on-line feedback controller based upon process dynamics has not been suggested. This is due to the fact that the resistance spot welding is a highly complicated process, whice involves the interaction of electrical, thermal, mechanical and metallurgical phenomena. In this paper, an optimal control method based on FDM model with shunt effect is presented, which can regulate the nugget size, at the same time minimizing the control heat input. Optimal PI gain of the controller were determined by numerical optimization. Simulation results show that, as a result of the proposed optimal control, the weld nugget can be made to approach a desired nugget size with less control heat input than that required for the conventional spot welding process in the face of the shunt effect.