Optimization of Installation Position for Complex Space Curve Weldments in Robotic Friction Stir Welding Based on Dynamic Dual Particle Swarm Optimization

Abstract

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.

Active Vibration Avoidance Method for Variable Speed Welding in Robotic Friction Stir Welding Based on Constant Heat Input

“…The vibration intensity signific increases, while the tensile strength decreases compared to when the eccentric err smaller. The end-effector vibration signals at 1200 rpm, before and after changin welding position, were subjected to a low-pass filter with a cutoff frequency of 200 H shown in Figure 12c [32]. After changing the welding position, with a larger eccentric Comparing Figure 12a with Figures 7 and 12b with Figure 8b, it is evident that when the eccentric error of the stirring tool is small, both the vibration intensity at the robot's end-effector and the longitudinal tensile strength of the weld are similar to those before the welding position was changed.…”

“…The vibration intensity significantly increases, while the tensile strength decreases compared to when the eccentric error is smaller. The end-effector vibration signals at 1200 rpm, before and after changing the welding position, were subjected to a low-pass filter with a cutoff frequency of 200 Hz as shown in Figure 12 c [ 32 ]. After changing the welding position, with a larger eccentric error, the amplitude of the robot end-effector vibration signal significantly increased, with peak acceleration values exceeding 2 g. Comparing the weld surface morphology as shown in Figure 12 d, it is apparent that with a larger eccentric error, the surface quality of the weld decreases under intense vibrations.…”

“…During the RFSW process, the frequency of the vibration signals generated by welding is solely dependent on the spindle speed [ 32 ]. When the spindle rotational frequency approaches a natural frequency of the robot at its current pose, the vibration intensity significantly increases.…”