Friction stir welding tool trajectory error on the load capacity of EN AW-2024-T3 aluminum alloy joints

This study investigates the influence of tool trajectory deviations on the load capacity and material flow of friction stir welded (FSW) overlap joints made of EN AW-2024-T3 aluminum alloy. Given that robotic movement is inherently burdened with deviation errors from a theoretically linear trajectory, this study aimed to assess the impact of these deviations on weld quality. Since the FSW-capable robot has low stiffness, a HAAS TM1P milling machine was used to simulate the robot's motion, incorporating recorded deviation errors. The welding process of 1 mm thick sheets was first conducted under ideal rectilinear conditions, establishing optimal parameters: feed rate of 200 mm/min, tool rotational speed of 1517 rpm, and plunge depth of 1.46 mm. Subsequently, controlled trajectory errors with standard deviations ranging from 0.05 mm to 0.2 mm were introduced into the milling machine's movement to replicate robotic deviation. The results indicate that trajectory deviations with a standard deviation of up to 0.1 mm do not significantly affect the load capacity (increase from 1.01% to 1.95%) but increase dispersion in mechanical performance (2.22% - 2.5%). SEM analysis revealed that when trajectory errors exceeded 0.15 mm, material folding and microcracks appeared, compromising weld integrity. Furthermore, multi-criteria optimization demonstrated that compensating for trajectory deviations is possible by adjusting welding parameters specifically, reducing the feed rate to increase heat accumulation. This approach enables the production of welds with a minimal decrease in load capacity (1.55% lower than an ideal trajectory weld), mitigating the negative effects of robotic trajectory errors. The use of a feed rate of x2 = 296 mm/min and a rotational speed of x3 = 800 rpm allows for achieving a load capacity of the joints with an average value of 5.36 kN with a standard deviation of sF = 0.07 kN.