Papers by Keyword: Resistance Spot Welding (RSW)

Abstract: Due to its high productivity, low cost, and increased work efficiency, resistance spot welding (RSW) can instantly join two or more steel sheets and it is widely used in the automotive industry and lately in the manufacturing of thin-walled cold-formed steel constructions. However, the RSW of zinc-coated mild steel sheets presents metallurgical challenges, especially when different thickness combinations are used. Therefore, in the present paper a resistance welding machine was used which uses direct current (MFDC) inverter technology combined with SMART AUTOSET technology to weld S250 GD and S350 GD galvanised mild steel sheets with different thicknesses. It is well known that, due to the elevated temperature that occurs during the welding process, followed by rapid cooling, defects such as cracking, porosity, lack of fusion, and an increased amount of brittle phases affect the welding quality. Therefore, the influence of the RSW process parameters established by an automatic sequence on the nugget geometry, microstructure, and mechanical properties was investigated. The phase transformations that took place during the heating-cooling cycle were analysed in detail through metallographic studies. The results showed that the microstructure of the weld nuggets was similar, characterised by columnar grains elongated in the direction of heat evacuation. Nevertheless, there were differences in terms of phase dispersion, defects and mechanical properties that have been linked to the RSW process parameters.

Abstract: Resistance spot welding (RSW) is still the ideal joining method in the automotive industry. Mostly steel sheets are used in the car body, so overlap and layering are required for welding or riveting, as spot welding provides simultaneous clamping force with interfacial welding to ensure the required strength and quality. A fundamental understanding of heating and cooling rates in thermal distributions is essential for predicting microstructure formation in the weld and the heat-affected zones (HAZ) of RSW joints. The ability to measure the heat cycle in the RSW process can be valuable in weld control and welding parameter optimization. RSW parameters can be optimized through tensile shear tests and microscopic investigations. Heat cycle measurement (HCM) demonstrates the welding consequences in terms of the change in mechanical properties and microstructural formations. The accuracy of cooling rate measurements including t_8/5 cooling time is very important to predict the microstructural evolution in the HAZ, however, the thermocouple measurement raises numerous challenges due to the high temperature gradient and small weld and HAZ size. During our investigations heat cycle measurement has been conducted experimentally by a K-type thermocouple. The data logger is connected to the output of the thermocouple for recording the voltage to measure the temperature distributions as a function of both time and position during the welding process. Measurement results of 1 mm thick martensitic MS1400 steel overlapped RSW joints are discussed, and the HCM curve of heating and cooling rates of the spot-welding process is presented. The heat cycle during RSW was measured with two different welding parameter combinations. In addition to welding current, welding time, and electrode force, pulsation has shown disparate curves. Numerous experiments have been attempted to measure the heat cycle in HAZ sub-zones due to the difficulty of positioning the thermocouple accurately, uppercritical HAZ, intercritical HAZ, and subcritical HAZ were investigated and measured in both welding parameter combinations. Difficulties were encountered in the experimental work as a result of the instantaneous welding time and the vibration resulting from the passage of alternating electrical current between the two electrodes. A magnetic field is generated that affects the thermocouple measurement and appears as a noisy curve that is filtered out and smoothed. Joule heat, interfacial heat generation, and cooling effects of electrodes are also considered in the experiment.

Abstract: This research is a finite element simulation on resistance spot welding (RSW) process between dissimilar sheet metals consist of Titanium alloy, Ti-6Al-4V and Austenitic Stainless Steel (ASS) 316L. The problem statement was inability to visualize the stress concentration profile over weld nugget joint when Titanium alloy and steel welded with variable electrode geometry of circle, triangle, square and hexagon. To determine the best geometry for best weld with lowest maximum stress concentration. The methodology of simulation was tensile-shear test using SOLIDWORKS software. The tensile-stress load of 664.09 N was applied across all 4 different weld geometries. The result for the lowest magnitude of maximum stress 180.6 MPa was on circle weld geometry. Triangle geometry registered highest stress concentration of 219.6 MPa. This proves that most common weld geometry used in industry was circle. Even for dissimilar material joint the result supports that circle weld geometry as the best geometry. Keywords: Resistance spot welding (RSW), stress concentration, weld nugget, weld geometry.

Abstract: Resistance spot welding (RSW) is one of the most common welding methods for steel sheets, as it is mainly used to join the automotive body structure parts. Different types of ultra-high strength steels (UHSS) have become widely used in the automotive body to obtain the required demands such as lower car weight, improving crashworthiness behavior, and enhancing strength–ductility combination. Martensitic UHSS belong to the highest grades width their tensile strength above 1000 MPa. During the lifetime of the vehicle cyclic loading generally occurs, therefore the optimization of welding technology should be performed considering the fatigue resistance of the welded joints. In our research 1 mm thick standardized lap shear sheets of martensitic MS1400 steel were welded by a TECNA 8007 RSW equipment with two different welding parameter combinations. The idea was to analyze the effect of welding and pulsation parameters on joint properties under static and cyclic loading. The welding parameters have been calibrated to produce the same weld nugget size for both technological combinations. Macroscopic, hardness, and tensile-shear tests were carried out to determine the fundamental mechanical characteristics of the RSW joints. The relation between the weld nugget microstructure and mechanical properties was explored. The high cycle fatigue (HCF) tests were performed on an MTS 810.23 universal electro-hydraulic materials testing system. A statistical approach was applied during the preparation and evaluation of the investigations, which increased their reliability. Measured and analyzed data of the lap shear welded joints, prepared by different technological parameters, were compared and discussed. The parameters of the HCF experiments were calculated considering the Japanese testing method (JSME S 002-1981). In most of the samples it was observed from both welding parameter combinations that the fatigue cracks initiate and grow in curvature shape in the softened part of the heat-affected zone towards the base metals in both directions symmetrically. A slight difference was observed in the HCF resistance of the welded joints prepared by different welding parameters.

Abstract: Hybrid joints between aluminium and steel are used sometimes in case of thin sheets for example for a car body. Resistance welding for this joining challenge is not frequently used, but the resistance welded joints basically have good mechanical properties. During resistance spot joining of these hybrid joints, fusion between the two materials cannot occur, but with the right technological parameters an intermetallic compound (IMC) appears in the joint line. The properties of the IMC have significant effect to the joint properties, because the researchers basically investigate this. The original static mechanical tests can show good, comparable results for the joint properties. If we see the dynamic tests basically really difficult to find results in case of spot welding of steels and joining of hybrid aluminium – steel joints. The aim of this paper to show the dynamic properties of these hybrid joints. During our investigation DP600 dual-phase steel was used as the steel part because this grade is frequently used in a car chassis. For the aluminium part, two types of aluminium were applied: non-heat treatable 5754-H22 alloy, and heat-treatable 6082-T6 alloy. The different aluminium alloys have different properties, so different technological parameter combinations were used. To test the resistance of hybrid joints against dynamic loading, instrumented impact tests were performed. This special impact test is considered as an impact-bending test, because the load is perpendicular to the welded point joint. Force – time diagrams of impact tests were shown too in this paper. The intermetallic compound is necessary for joint, but it is very brittle with very big hardness, but in case of dynamic testing this hardness has no significant effect, so these specimens show good result in case of dynamic loading. The two different aluminium – steel joints show different resistance against dynamic loading, and the fracture modes were different too.

Abstract: Resistance spot welding has significant role in the joining technologies of automotive industry. In the recent period there were some rival technologies, but resistance spot welding remains important. This has numerous reasons however mass production is one of the main motivations. The applied base materials both steel and aluminium develop rapidly. The dual-phase (DP) steels with different strength are typical in the automotive chassis, and the high strength aluminium alloys also continuously spread. These special material combinations mean new challenges for joining technologies, sometimes hybrid aluminium - steel joints should be prepared. In this paper hybrid joints between DP800 steel and 5754-H22/6082-T6 sheets were prepared. The microstructural and strength properties of the joints were investigated and compared. An intermetallic compound was formed between the dissimilar sheets during welding which is basically determine the joint properties.

Abstract: This study focused on investigation of the effect of process parameter to the tensile strength of a spot welded S235 low carbon steel through simulation and experiment. Resistance spot welding (RSW) is commonly used in joining metal sheets due to its key capabilities, which is time and cost effective as well as high adaptability for automation. However, strength and reliability of a spot welded joint especially in an auto vehicle can be unpredictable. Premature failure of a spot welded joint can be difficult to be predicted but common factors that had been discussed in many research is related with fatigue and residual stress. Process parameter is recognized as one of critical factors affecting the reliability and quality of a spot welded joint. Different type of material and thickness may require different set of parameter to achieve an optimum result. Experimental procedure alone to demonstrate and investigate the effect could be too costly and time inefficient. Therefore, design of experiment and non-linear FEM simulation analysis were used to analyze and validate the result. This study shows the significance of process parameters such as weld current and electrode pressure to the strength of a spot welded joint and accurate setting is needed prior to the welding process to achieve an optimum result.

Abstract: Resistance spot welding (RSW), generally which is one of the most often used to joint metal plate in the automotive and aviation industries. RSW welding process involves electrical, thermal mechanical, metallurgy, and complex surface phenomenon. Unlike the other welding processes, weld joint formation in RSW process occurs very quick (in milli-seconds) and took place between the workpieces overlap each other. Welding simulation allows visual examination of the weld joint without having to perform an expensive experiment. Weld nugget size is the most important parameter in determining the mechanical behavior of welded joints in RSW process. The quality and strength of the weld joint in RSW process is predominantly determined by the shape and size of the weld nugget. Simulation modeling of RSW process performed using ANSYS Parametric Design Language (APDL) module based on the finite element method (FEM), embedded in ANSYS Workbench. Electrical and transient-thermal interaction was developed to study the weld nugget growth on resistance spot welding of aluminum A1100 metal plate with a thickness of 0.4 mm respectively. Weld nugget diameter can be well predicted by using this simulation model from the temperature distribution during the welding process. Welding is performed by varying the weld current (1 kA and 2 kA) and the welding time for each electric current, which are start from 0.5, 1.0, and 1.5 cycle time. Nugget diameter for each of the welding parameters from the simulation modelling were 4,276 mm, 4,372 mm, 4,668 mm, 5,616 mm and 5,896 mm. Weld expulsion occurred for the specimen with welding current 2 kA and welding time 1.5 cycle time, characterized by the decreasing of the tensile-shear strength of the specimen.

Abstract: The paper presents an analysis of load capacity for welded specimens made of titanium Grade 5 of 0.8 mm thickness. The lap joins were made by Resistance Spot Welding (RSW). The load capacity for joints with a single spot were assessed. The joints were welded with 5 variants of welding parameters. On the basis of the capacity of the joints, the best performance were selected. The best welding parameters were used to make three types of joints with different spacing of the welds: with a single weld, the two welds arranged parallel to the shearing direction and two welds arranged perpendicular to the shearing direction. The load capacity, a plastic strains distribution and a method of cracking were assessed. An example of the feasibility of a beam construction made of titanium grade 5 sheets welded by resistance spot welding were shown.

Abstract: This paper presents the effects of spot welding parameters on multi-response weld quality and optimizes the governing parameters of Resistance Spot Welding (RSW) towards the tensile shear strength and nugget size using Taguchi method. The main affecting welding parameters such as electrode force, weld time and weld current were determined as the basis for quality evaluation. The selected quality features were classified into shear strength and nugget size which were required for application with highly dynamic loading. The optimum welding parameter was obtained using multi signal-to-noise ratio (MSNR) and the significant level of welding parameters was further analysed using analysis of variance (ANOVA). Based on the results, electrode force was found to be most effective parameter affecting shear strength and nugget size. The experiment was conducted at optimum welding parameter and validated the used of multi-objective Taguchi method for enhancing performance and optimizing the welding parameters in RSW process.