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.

Microstructure and mechanical behaviour of pinless friction stir spot welded AA2198 joints

Abstract: In this study, pinless friction stir spot welding of 1.8 mm thick 2198-T8 aluminium–lithium alloy plates was carried out. The change of the angle between the nugget edge and the surface, and the relationship between this angle and joint mechanical property were analysed. The results show that the angle increases rapidly initially and then approaches 45°, which is due to the extrusion of nugget material and its flow along the surrounding ‘cold’ metal during welding. The tensile strength is determined by the nugget edge angle and hook defect. Tensile loads reach a higher value when the nugget edge angle approaches 45° but have a slight decrease with the hook angle changing from obtuse to acute. The maximum tensile/shear strength could be 8.57 kN at the rotation speed of 1500 rev min− 1 and the dwell time of 12 s.

Failure loads of spot weld specimens under impact opening and shear loading conditions

Abstract: Failure loads of spot weld specimens are investigated under impact combined loading conditions. A set of test fixtures was designed and used to obtain failure loads of mild steel spot weld specimens under combined opening and shear loading conditions. Three different impact speeds were applied to examine the effects of separation speed on failure loads. Micrographs of the cross-sections of failed spot welds were obtained to understand the failure processes in mild steel specimens under different impact combined loads. The experimental results indicate that the failure mechanisms of spot welds are very similar for mild steel specimens at various impact speeds. These micrographs show that the sheet thickness can affect the failure mechanisms. For 1.0 mm specimens, the failure occurs near the base metal in a necking/shear failure mode. For 1.5 mm specimens, the failure occurs near the heat-affected zone in a shear failure mode. Based on the experimental results, the effects of the inertia force, the separation speed, and the loading angle on the failure loads of spot welds are investigated. Failure criteria are proposed to characterize the failure loads of spot welds under impact combined opening and shear loads for engineering applications. The failure load can be expressed as a function of the tensile strength of the base metal, the nugget size, the sheet thickness, the maximum separation speed, the loading angle, and empirical coefficients for a given welding schedule.

Real Time Monitoring Weld Quality of Resistance Spot Welding for Stainless Steel

Abstract: Resistance spot welding (RSW) is one of the most widely used processes in sheet metal fabrication. Although used in mass production for several decades, RSW has a major problem of inconsistent quality from weld to weld, which results from both the complexity of basic process as well as from various process conditions, noise and errors. There have been a number of investigations on monitoring and controlling the resistance spot welding of low carbon steel by using dynamic resistance, but those for stainless steel are limited because the dynamic resistance has descent property. Dynamic resistance curve in spot welding for low carbon steel has a typical shape: the resistance drops sharply at the beginning, and then rises; before the current is terminated, the resistance starts to drop, which results in a peak. Unlike low carbon steel, dynamic resistance for stainless steel decreases rapidly at the beginning and then decreases at a reducing rate.The objective of this research is to explore the effects of various process conditions in spot welded stainless steel on quality by using dynamic resistance. The process conditions studied in this research are chosen to be the most often observed in production, such as variations of welding parameters, edge weld, small weld spacing, poor fitup and axial misalignment. A series of experiments will be conducted to research how process conditions affect the dynamic resistance. The results show that dynamic resistance responds well to the variations of process conditions and can serve as an important indicator of weld quality.

Resistance spot welding of martensitic stainless steel: Effect of initial base metal microstructure on weld microstructure and mechanical performance

Abstract: This paper addresses the microstructure-properties relationship during resistance spot welding of martensitic stainless steel (MSS). The effect of the initial base metal microstructure (ferritic microstructure in annealed condition vs. partially tempered martensitic in quench and tempered condition) on the weld microstructure evolution is highlighted. Regardless of the initial base metal microstructure, the fusion zone exhibited a predominantly martensitic structure plus some δ-ferrite. The heat affected zone (HAZ) in the quenched and partially tempered (Q-PT) sheet was featured by formation of martensite and carbide in upper-critical zone and tempering of martensite in sub-critical zone. The latter caused pronounced softening in the HAZ compared to the base metal. However, the HAZ in the annealed sheet exhibited hardening compared to the base metal due to the formation of a dual phase microstructure composed of martensite plus carbide. Nor high strength mismatch between fusion zone and base metal (when welding in the annealed condition), neither severe HAZ softening (when welding in the Q-PT condition) did not promote pullout failure mode. The consistently predominant interfacial failure of the MSS welds was governed by the low fracture toughness of the fusion zone.