Process and strength analysis of joining CF/PA6 composite plates without energy director by a servo-driven ultrasonic welder

Abstract

A servo-driven ultrasonic welding (USW) offers a good control for joining carbon fiber reinforced thermoplastic composites (CFRTP) with a constant plunging speed, a dynamic applied force and adjusting power in real time. This study focuses on the process and strength analysis during servo-driven USW of CF/PA6 composites without energy director (ED) to obtain the correlation between the operation parameters and joint strength. The results show that a servo-driven welder benefits in USW without ED due to the initial intimate contact between workpieces without horn retraction. It is also found that a typical vibration process can be divided into four stages following the heat evolution and characteristic temperature of CFRTP, i.e., “initial stage”, “soften stage”, “melting stage” and “steady stage”. High energy and amplitude bring enough total energy and high power to melt materials; while a low trigger force and a slow plunging speed can mitigate the excessive squeeze-out with a result of the increase in weld strength. Thus, as the melted material remained in the weld region decides the bonding efficiency, the desired joints can be obtained under the enough welding energy (≥400 J) and amplitude (≥80%), not too high welding force (≤800 N) and plunging speed (≤0.8 mm/s). Meanwhile, weld quality can be online inspected and judged based on welding force evolution, and the measured displacement relative to the set value. This work contributes to the optimal parametric selection for USW of CFRTP plates without ED applying a servo-driven welder.

Keywords

• Ultrasonic welding
• Carbon fiber reinforced thermoplastic composites
• Joining mechanisms
• Weld quality