Spot welding

About: Spot welding is a research topic. Over the lifetime, 12491 publications have been published within this topic receiving 89845 citations. The topic is also known as: Spot_welding.

Mechanical properties and microstructures of magnesium alloy AZ31B joint fabricated by resistance spot welding with cover plates

Abstract: The authors welded magnesium alloy AZ31B sheets using the technique of resistance spot welding with cover plates, and investigated the effects of welding parameters on the tensile shear strength of joints and shape characteristic of nugget. The joints with high tensile shear strength were obtained under relatively low welding current. The equiaxed grains with the many intragranularly precipitated particles Mg17Al12 in the nugget were observed.

Thermal process and material flow during dissimilar double-sided friction stir spot welding of AZ31/ZK60 magnesium alloys

Abstract: A computational fluid dynamics (CFD) model for double-sided friction stir spot welding (FSSW) between AZ31 and ZK60 magnesium alloys using adjustable pins is proposed in this paper. Multiple phase flow theories are combined to track the metal interface and phase distribution using FLUENT software. The heat transfer and material flow for the 5 stages of the friction stir welding process, including the pre-heating, plunging, welding, rising and post-heating stages, are presented. For further evaluation, the calculated flow and thermal responses are compared with experimental data, which overall showed good agreement. The material between the upper and lower pins is softened after the pre-heating process and is then driven by the plunging pin to form a keyhole below the upper tool and a bulge region in the bottom of the plates. The welding interface between the pins is bowl-shaped after plunging, and grows uneven during the welding stage due to the extensive plastic material flow. The keyhole is then fully eliminated after the rising of the pins. After welding, the region between the tools is heated to a maximum temperature of 670 K and the welding interface slightly fluctuates and a phase mixing phenomenon occurs, suggesting that AZ31 and ZK60 plates are well joined by using the adjustable pins.

Numerical Thermal Model of Resistance Spot Welding in Aluminum

Abstract: A three-dimensional thermal model for resistance spot welding in aluminum is presented. The numerical model, validated with experimental findings, considered phase change and the associated weld pool convection. A parametric study was performed to determine the influence of welding features such as welding current, faying surface (workpiece contact surface) electrical contact resistance, and electrode-workpiece (E/W) thermal contact conductance. These parameters have significant effects on the nugget and heat-affected-zone geometry. The phase change morphology, including melting and solidification rates and weld pool dynamics, was also significantly influenced by the parameters studied. The strongest convection was observed at the center of the molten pool in a vertical plane, aligned with gravity. Although two prominent convection cells developed, the phase change morphology was not significantly affected by convection due to the short welding time (less than 0.1 s) and low fluid velocity (smaller than 0.01 mm/s). The nugget grew nonlinearly with increasing current and faying surface electrical contact resistance, whereas it diminished with increasing E/W thermal contact conductance. The influence of electrical contact resistance at the faying surface on nugget size was less pronounced than that of the other parameters. The length of time that the weld pool existed was directly proportional to current and indirectly proportional to E/W thermal contact conductance.

Development of Appropriate Resistance Spot Welding Practice for Transformation-Hardened Steels A repeatable and effective methodology for producing a temper diagram for different steels is demonstrated

Abstract: High-strength steels (HSS) are one of the most popular alternative materials for weight reduction in next- generation vehicles. One of the known concerns with using HSS is an issue called "hold-time sensitivity." Previous work has shown susceptibility to hold-time- related failures can be remedied through in-process quench and tempering of the weld. In this study, dual-phase, transforma- tion-hardened steels of 690- and 960- MPa (100- and 140-ksi) tensile strengths and nominally 0.9-mm (0.035-in.) gauge were examined. Each steel was welded and in-process quenched and tempered. A matrix of temper times and currents were used to define the range of effective tempering. Effectiveness of tempering was related to hardness of the weld nugget and corresponding temper dia- grams were developed for each sample. The resulting temper diagrams showed a characteristic C-curve shape for the main part of the diagram with a tran- sient region that extended asymptotically to higher currents and shorter times. The C-shape supported the existence of steady-state thermal conditions for longer heating times during tempering. The transient region was associated with

Automatic Inspection of Spot Welds by Thermography

Abstract: The interest for thermography as a method for spot weld inspection has increased during the last years since it is a full-field method suitable for automatic inspection. Thermography systems can be developed in different ways, with different physical setups, excitation sources, and image analysis algorithms. In this paper we suggest a single-sided setup of a thermography system using a flash lamp as excitation source. The analysis algorithm aims to find the spatial region in the acquired images corresponding to the successfully welded area, i.e., the nugget size. Experiments show that the system is able to detect spot welds, measure the nugget diameter, and based on the information also separate a spot weld from a stick weld. The system is capable to inspect more than four spot welds per minute, and has potential for an automatic non-destructive system for spot weld inspection. The development opportunities are significant, since the algorithm used in the initial analysis is rather simplified. Moreover, further evaluation of alternative excitation sources can potentially improve the performance.