Papers by Keyword: Resistance Spot Welding (RSW)

Abstract: Resistance spot welding process is strongly related to interfacial contact behaviors. The effects of thermal contact is rarely investigated so far and generally ignored in numerical models. In this work, a parametric FE model, which considers the variation of the surface roughness of the electrodes and workpieces, has been developed to investigate the effects of thermal contact on weld nugget formation. With the parametric model, four cases, e.g. ideal smooth surface, minimal roughness surface and maximum roughness surface for steel sheets and electrodes of as-received condition, and highly rough electrode surface, are investigated. Researches show that when the surface roughness of the electrodes exceeds some limit, the thermal contact conductance will substantially affect the weld nugget formation, therefore, must be considered in numerical models to precisely predict welding process.

Abstract: Resistance spot welding is the dominant process for joining sheet metals in automotive industry. Even-thickness combinations are rarely used in practice; therefore, there is clearly a practical need for failure behaviour investigation of uneven-thickness resistance spot welds. The aim of this paper is to investigate and analyze the failure mode and failure mechanism of dissimilar thickness low carbon steel resistance spot welds during tensile-shear overload test. Microstructural investigations, microhardness tests and tensile-shear tests were conducted. Mechanical properties of the joint were described in terms of peak load, energy absorption and failure mode. It was concluded that weld nugget size and the strength of the thinner base metal are the controlling factors of the peak load and energy absorption of dissimilar thickness spot welds.

Abstract: In order to reduce vehicle weight and improve crash performance, dual-phase (DP) steels are increasingly used for lightweight auto-body. the high cooling rates in Resistance spot welding (RSW) process will make the nugget very brittle and result in interfacial fracture modes. In this study, a servo resistance welding system is firstly introduced to control process parameters during the welding process. The influences of different process parameters (weld current, weld time and electrode force) on the weld strength, nugget diameter, facture modes and weld indentation are analyzed. Finally, an on-line weld failure mode inspection method is proposed based on servo gun’s feedback characteristics.

Abstract: The increased application of lightweight materials, such as aluminium has triggered many investigations into new joining techniques for aluminium alloys. The Resistance Spot Welding concept for aluminium has always attracted many researchers from different organizations. Self-piercing riveting is the major production process used to join aluminium sheet body structures for the automotive industry. Mean while, interest in laser welding and application as a candidate for joining aluminium is also growing. These key technologies for aluminium assembly are therefore being investigated by the research team at the University Of Warwick. The paper reported here looks at the feasibility of each process for joining thin gauge aluminium and compares the mechanical behavior for each joint type. The results suggested that all three joining technologies are feasible for joining aluminum and their mechanical behaviour is strongly dependent on the selection of process parameters

Abstract: While resistance spot welding (RSW) has been the most successful sheet metal joining process in automotive industry, there are still certain quality and reliability issues due to the control system and its application process. Some weld spots have hard-to-reach areas and new materials make the process more complicated resulting in new challenges for quality welds. Recently, a new welding machine called one-sided RSW was introduced to make a weld of hard-to-reach areas in automotive application. Intelligent current regulation algorithm of welding machine timer helps to control welding current and time with more stablility than conventional constant current regulation. Newly developed RSW simulation tool is another advanced technology to improve weld quality and production stability. In this research, advanced RSW technologies, including one-sided RSW, intelligent adaptive control, and simulation of RSW process, are discussed with various automotive applications.

Abstract: A finite element analysis was conducted to study the roles of temperature and pressure in the formation of electrode pitting in resistance spot welding of an aluminum alloy. The distributions of pressure and temperature were computed at the electrode tip surface. Results showed that the highest temperature is always located at the center of electrode tip surface, while electrode pressure is concentrated mainly at the edge of contact region. The location of the concentrated electrode pressure coincides with that of electrode pitting, which indicates that the pressure concentration plays a more significant role than the temperature in the formation of pitting.

Abstract: Resistance microwelding is an important joining process used in the fabrication of miniature instruments. The small-scale resistance spot weldability of Zr based glassy thin sheet alloys was investigated. Metallic glass sheets were successfully welded and amorphous structure was maintained in both weld nugget and heat affected zone. Joint strength that is evaluated by shear breaking force increased as the welding current increased, resulting from nugget growth. Fractured surface showed typical vein pattern.

Abstract: Dual-phase steel is a mixture of ferrite matrix and martensitic islands distributed at grain boundaries with the possible addition of bainite. Its formability, capacity to absorb crash energy, and ability to resist fatigue make it a desirable material for use in the automotive industry to enhance automobile’s strength and reduce its weight. However, the resistance spot weldability of dual-phase steel is sometimes limited by a propensity for weld metal failure due to the welding process. To improve its weldability, a servo gun spot welding system is introduced to control electrode force during the welding process. The paper take 1.5mm DP600 steels as an example, experimental data shows that by optimizing electrode force during welding process, the width of weld lobe can be enlarged from 0.9kA to 2.1kA and the weldability of dual phase steel is improved greatly.

Abstract: Expulsion is undesirable during the resistance spot welding due to the weld quality decrease. The expulsion happening during the resistance spot welding of AZ31B magnesium alloy was studied related to the distribution of maximum temperature in the interface due to the existing of contact resistance, and connected with the increased pressure in the nugget due to melting and expansion of liquid metal. The influence of welding parameters on expulsion is presented and discussed in this investigation.

Abstract: We tried to join steel to Al-Mg alloy using a resistance spot welding method. The effect of Mg in Al-Mg alloy on the strength and the interfacial microstructure of the joint was investigated. Additionally, the effect of insert metal of commercially pure aluminum, which was put into the bonding interface, on the joint strength was examined. The obtained results were as follows. The cross-tensile strength of a joint between SS400 steel and commercially pure aluminum (SS400/Al) was high and fracture occurred in the aluminum base metal. However, the strength of a joint between SS400 and Al-Mg alloy was remarkably low and less than 30% of that of the SS400/Al joint. An intermetallic compound layer developed so thickly at the bonded interface of the SS400/Al-Mg alloy joint that the joint strength decreased. The intermetallic compound layer developed more thickly as Mg content in the Al-Mg alloy increased. Using insert metal of commercially pure aluminum containing little Mg successfully improved the strength of the SS400/Al-Mg alloy joint and the strength was equivalent to that of the base metal.