Twist springback and microstructure analysis of PEEK sheets in ultrasonic-assisted thermal incremental forming

Abstract

With a view to reducing the springback and twist of PEEK during the incremental forming process, the ultrasonic vibration is introduced into polymer thermal single-point incremental forming process (SPIF). In this study, the effects of temperature and ultrasonic vibration on twist and springback of formed parts are investigated. Several modified tool trajectories are developed, and the influence of tool trajectory on twist and springback are also studied. Finally, the microstructures of PEEK parts are analyzed by XRD. The results show that the increase of temperature is helpful to reduce the twist and springback. The ultrasonic vibration is beneficial to the improvement of geometric accuracy, while the side wall bulge aggravates at 140 ℃ after the ultrasonic vibration is applied. The optimized tool trajectory can effectively eliminate twist and reduce the springback of PEEK parts. The XRD result shows that the ultrasonic vibration is helpful to increase the molecular chain orientation, improve crystallinity, and refine crystallite at 60 ℃ and 100 ℃. However, the opposite trend occurs at 140 ℃ due to the disorientation effect of molecular chain.