Search Results (14)

Friction stir spot welding (FSSW) is a solid-state joining technique increasingly favored in industries requiring high-quality, defect-free welds in lightweight and durable structures, such as the automotive, aerospace, and marine industries. This review examines the current advancements in FSSW, focusing on the relationships between microstructure, properties, and performance under load. FSSW offers numerous benefits over traditional welding, particularly for joining both similar and dissimilar materials. Key process parameters, including tool design, rotational speed, axial force, and dwell time, are discussed for their impact on weld quality. Innovations in robotics are enhancing FSSW’s accuracy and efficiency, while numerical simulations aid in optimizing process parameters and predicting material behavior. The addition of nano/microparticles, such as carbon nanotubes and graphene, has further improved weld strength and thermal stability. This review identifies areas for future research, including refining robotic programming, using artificial intelligence for autonomous welding, and exploring nano/microparticle reinforcement in FSSW composites. FSSW continues to advance solid-state joining technologies, providing critical insights for optimizing weld quality in sheet material applications. Full article

This study proposes an improved stiffness ellipsoid method to enhance the stiffness and precision of robotic arms in friction stir welding (FSW) operations. The method involves establishing a joint stiffness model through static identification experiments and developing a novel stiffness index derived from the improved stiffness ellipsoid method. This index provides a refined metric for evaluating the robot’s performance under variable loads during FSW. Simulation experiments demonstrate significant improvements in welding trajectory precision and computational efficiency. The findings highlight the potential of this method to elevate FW quality and consistency. Full article

In aerospace and new-energy vehicle manufacturing, there is an increasing demand for the high-quality joining of large, curved aluminum alloy structures. This study presents a robotic friction stir welding (RFSW) system employing a force/position hybrid control. An eight-axis linkage platform integrates an electric spindle, multidimensional force sensors, and a laser displacement sensor, ensuring trajectory coordination between the robot and the positioner. By combining long-range constant displacement with small-range constant pressure—supplemented by an adaptive transition algorithm—the system regulates the axial stirring depth and downward force. The experimental results confirm that this approach effectively compensates for robotic flexibility, keeping weld depth and pressure deviations within 5%, significantly improving seam quality. Further welding verification was performed on typical curved panels for aerospace applications, and the results demonstrated strong adaptability under high-load, multi-DOF conditions, without crack formation. This research could advance the field toward more robust, automated, and adaptive RFSW solutions for aerospace, automotive, and other high-end manufacturing applications. Full article

Robotic Friction Stir Welding (RFSW) technology integrates the advantages of friction stir welding and industrial robots, finding extensive applications and research in aerospace, shipbuilding, and new energy vehicles. However, the high-speed rotational process of friction stir welding combined with the low stiffness characteristics of serial industrial robots inevitably introduces vibrations during the welding process. This paper investigates the vibration patterns and impacts during the RFSW process and proposes an active vibration avoidance control method for variable speed welding based on constant heat input. This method utilizes a vibration feedback strategy that adjusts the spindle speed actively if the end-effector’s vibration exceeds a threshold, thereby avoiding the modal frequencies of the robot at its current pose. Concurrently, it calculates and adjusts the welding speed of the robot according to the thermal equilibrium equation to maintain constant heat input. A simplified dynamic model of the RFSW robot was established, and the feasibility of this method was validated through simulation experiments. This study fills the gap in vibration analysis of RFSW and provides new insights into control strategies and process optimization for robotic friction stir welding. Full article

Robotic friction stir welding (RFSW), with its wide application range, ample working space, and task flexibility, has emerged as a vital development in friction stir welding (FSW) technology. However, the low stiffness of serial industrial robots can lead to end-effector deviations and vibrations during FSW tasks, adversely affecting the weld quality. This paper proposes a dynamic dual particle swarm optimization (DDPSO) algorithm through a new comprehensive stability index that considers both the stiffness and vibration stability of the robot to optimize the installation position of complex space curve weldments, thereby enhancing the robot’s stability during the FSW process. The algorithm employs two independent particle swarms for exploration and exploitation tasks and dynamically adjusts task allocation and particle numbers based on current results to fully utilize computational resources and enhance search efficiency. Compared to the standard particle swarm optimization (PSO) algorithm, the DDPSO approach demonstrated superior search capabilities and stability of optimization results. The maximum fitness value improved by 4.2%, the average value increased by 12.74%, and the concentration level of optimization results rose by 72.91% on average. The new optimization method pioneers fresh perspectives for optimizing the stability of RFSW, providing significant grounds for the process optimization and offline programming of complex spatial curve weldments. Full article

Robotic friction stir welding has become an important research direction in friction stir welding technology. However, the low stiffness of serial industrial robots leads to substantial, difficult-to-measure end-effector deviations under the welding forces during the friction stir welding process, impacting the welding quality. To more effectively measure the deviations in the end-effector, this study introduces a digital twin model based on the five-dimensional digital twin theory. The model obtains the current data of the robot and six-axis force sensor and calculates the real-time end deviations using the robot model. Based on this, a virtual welding model was realized by integrating the FEA model with the digital twin model using a co-simulation approach. This model achieves pre-process simulation by iteratively cycling through the simulated force from the FEA model and the end displacement from the robot model. The virtual welding model effectively predicts the welding outcomes with a mere 6.9% error in lateral deviation compared to actual welding, demonstrating its potential in optimizing welding parameters and enhancing accuracy and quality. Employing digital twin models to monitor, simulate, and optimize the welding process can reduce risks, save costs, and improve efficiency, providing new perspectives for optimizing robotic friction stir welding processes. Full article

Refill friction stir spot welding (RFSSW) is an emerging solid-state welding technology that demonstrates an outstanding ability to join aerospace aluminum alloys. The thermomechanical processing of RFSSW may cause variations in the workpiece in the form of distortion. This study aims to establish a metrology method for sheet metal distortion with the intent to investigate the effects of RFSSW sequences on sheet metal distortion. The approach employs a robotic metrology system and the least squares method to measure and estimate the flatness of sheet metal before RFSSW and after RFSSW. The RFSSW experimentation produces five 10-spot-weld panels with five different RFSSW sequences, whereas the RFSSW sequences are based on the common practice of making sheet metal assemblies. A panel consists of two lap-welded sheets where the top sheet, a 6013-T6 aluminum alloy, is refill friction stir spot welded onto the bottom sheet, a 2029-T8 aluminum alloy. The results suggest that RFSSW sequences do have effects on sheet metal distortion. The panel with the worst distortion has a root-mean-square error of 0.8 mm as an average deviation from the ideal flatness. Full article

2198 aluminum–lithium alloy was friction stir-welded with a KUKA Robot integrated with a compact friction stir-welding head with a rotation speed of 800 rpm at different welding speeds. The real-time tool force in the three directions of Fx, Fy and Fz was measured with a load sensor. Mechanical properties and microstructure evolution were investigated systematically. The results showed that Fz force increased from 3.2 kN to 8.5 kN as welding speed increased from 50 mm/min to 500 mm/min. Ultimate tensile strength of 383 MPa, 88% of base metal, was obtained when the welding speed was 100 mm/min. The nugget zone consisted of refined grains with an average size of 4 μm. TEM investigation demonstrates that T1 precipitation predominated in the base metal and disappeared in the nugget zone, as a small amount of δ’ was retained. The W-shape hardness profile in all weldments and higher welding speed lead to a higher hardness value. Full article

Refill friction stir spot welding (RFSSW) is an innovative solid-state welding technology for aluminum structures. The presented study aimed to evaluate the mechanical properties of refill spot welds and their failure mechanisms with the use of industrial test standards. The mechanical properties of refill spot welds were compared with those of rivet joints with comparable joint sizes. Static load tests indicated that RFSSW coupons demonstrate higher ultimate shear strengths but slightly lower ultimate tension strengths than those of rivet coupons. Fatigue test results indicated that both RFSSW coupons and rivet coupons demonstrate comparable performances during low-load-level fatigue lap shear tests but RFSSW coupons outperform rivet coupons during high-load-level fatigue lap shear tests. The failure mechanisms of refill spot welds were characterized in terms of external loading, parent metal properties, and weld properties. Refill spot weld failures included parent metal tensile failures, nugget pullouts, and interfacial failures. A refill spot weld may demonstrate one or a combination of these mechanical failures. Although the mechanical tests of refill spot welds demonstrated promising results with predictable failure mechanisms, the metallurgical evolution involved in RFSSW remains a subject to study. Full article

In this study, fatigue behavior of surface finished and precorroded friction stir welded (FSW) specimens using various tool configurations were comparatively investigated by the load increase method. The FSW using conventional, stationary shoulder and dual-rotational configurations was carried out by a robotized tool setup on 2 mm EN AW-5754 aluminum sheets in butt joint formation. After extraction of the specimens, their weld seam and root surfaces were milled to two different depths of 200 µm and 400 µm to remove the surface and the FSW tool shoulder effects. This surface finishing process was performed to investigate the effect of the surface defects on the fatigue behavior of the FSW EN AW-5754 aluminum alloy sheets. It was found that material removal from the weld and root surfaces of the specimens, increased the fracture stresses of conventional and dual-rotational FSW from 204 to 229 MPa and 196 to 226 MPa, respectively. However, this increase could not be detected in stationary shoulder FSW. Specimens with finished surfaces, which showed superior properties, were used in salt spray and cyclic climate change test to investigate the effect of corrosion on the fatigue behavior of FSW specimens. It was shown that cyclic climate change test reduced the fatigue properties of the base material, conventional, stationary shoulder and dual-rotational FSW approximately 1%–7%. This decrease in the fatigue properties was greater in the case of the salt spray test, which was 7% to 21%. Full article

Friction stir welding (FSW) is an innovative solid-state welding technology that produces high quality joints and is widely used in the aerospace industry. Previous studies have revealed welding temperature to be a decisive factor for joint quality. Consequently, several temperature control systems for FSW have been developed. These output feedback control systems usually require delicate and expensive temperature measuring equipment, which reduces their suitability for industrial practice. This paper presents a novel state feedback system of the welding temperature to remedy this shortcoming. The system uses a physical model of the FSW process (digital twin) for the determination of the welding temperature signal from the process torque signal. The digital twin is based on a multi-input nonlinear time invariant model, which is fed with the torque signal from the spindle motor. A model-based ℒ₁ adaptive controller was employed for its robustness with respect to model inaccuracies and fast adaption to fluctuations in the controlled system. The experimental validation of the feedback control system showed improved weld quality compared to welded joints produced without temperature control. The achieved control accuracies depended on the results of the temperature calculation. Control deviations of less than 10 K could be achieved for certain welding parameters, and even for a work piece geometry, which deliberately caused heat accumulation. Full article

Friction stir welding (FSW) has become an up-and-coming joining method with a wide range of industrial applications. Besides the unique weld seam properties, recent investigations have focused on the process-related tool wear of shoulder and probe, which can have detrimental economic and technological effects. This paper presents a systematic quantitative characterization of FSW tool wear using stripe light projection as a novel method to detect weight and form deviations of shoulder and probe. The investigations were carried out with a robotic welding setup in which AA-6060 T66 sheets, with a thickness of 8 mm, were joined by weld seams up to a total length of 80 m. During the experimental tests, geometrical deviations of the tool induced by wear were detected for varying weld seam lengths and different measuring points on the probe and shoulder. It was shown that wear depended on welding length which in turn caused significant deviations and weight losses on shoulder and probe. Furthermore, it was demonstrated that the wear on shoulder and probe can be considered separately. It was found that there is a progressive wear rate on the shoulder and a degressive wear rate on the probe depending on the weld seam length. To demonstrate the negative impact of tool wear on shoulder and probe after 80 m weld seam length, visual and metallographic inspections and tensile tests were carried out to detect resultant irregularities in the weld seam. Full article

Refill friction stir spot welding (RFSSW) is an emerging technology for joining aerospace aluminum alloys. The aim of the study is to investigate the effects of the refill friction stir spot weld spacing and the edge margin on the mechanical properties of multi-spot-welded AA7075-T6 panels. AA7075-T6 is a baseline aerospace aluminum alloy used in aircraft structures. The study employs an innovative robotic RFSSW system that is designed and developed by Kawasaki Heavy Industries (KHI). The experimental strategy uses Design of Experiments (DoE) to characterize the failure loads of multi-spot-welded panels in terms of the spot weld spacing, edge margin, and heat-affected zone (HAZ) of the spot weld. The RFSSW process leaves behind a thermal “imprint” as HAZ in heat-treatable aluminum alloys. According to the DoE results, larger spot weld spacings with no HAZ overlap produce higher failure loads of multi-spot-welded panels. On the other hand, edge margins that are equal to or less than the spot weld diameter demonstrate abnormal plastic deformations, such as workpiece edge swelling and weld crown dents, during the RFSSW process. The larger edge margins do not demonstrate such abnormal deformations during the welding process. Full article

In the grinding process of friction stir weld seams, excessive grinding will cause damage to the base metal and bring significant economic losses. In this paper, the authors design a robotic system for grinding the weld seam and present a monitoring method of excessive grinding. The designed system consists of an industrial robot, a line scanner for measuring the weld seam and a force-controlled grinding tool. Since the result of the measurement of the weld seam is a point cloud, the extraction method of the weld seam point cloud based on graph-cut is proposed in this paper. The extracted features are used as prior knowledge of the monitoring algorithm. On the other hand, by combining the features from the point cloud and force-position information during the processing, a monitoring method for excessive grinding based on PSO-SVM is proposed and verified by experiments. The experiments demonstrate that the proposed method can identify excessive grinding, and the accuracy of recognition is 91.5%. Full article