Ultrasonic Welding of Carbon Fiber Reinforced Nylon 66 Composite Without Energy Director

In this study, weldability of ultrasonic welding of 4-mm-thick fiber carbon/nylon 66 composite in lap configuration was investigated. Ultrasonic welding tests were performed, and the weld appearance, microstructure, and fractography of the welded joints were examined using optical and scanning electron microscope. The transient temperatures near the faying surfaces and horn-workpiece interfaces were recorded to understand the weld growth mechanism. It was found that it is feasible to join 4-mm-thick lapped carbon fiber reinforced nylon 66 composite with ultrasonic welding. Under the ultrasonic vibration, the weld initiated and grew at the faying surfaces, while the weld indentation developed at the horn-workpiece interface. The pores observed in the regions between the heat-affected-zone (HAZ) and the fusion zone (FZ), and the severe weld indentation on the surface of upper workpieces decreased the loading capacity of the ultrasonic welded (UW) joints and caused the welded carbon/nylon 66 composite fractured prematurely. The strengths of the ultrasonic welds were determined by the balance of positive effect of the weld area and negative effects of the weld indentation and porosity near the FZ. To ensure the joint strength, it is necessary to apply the proper weld schedules (i.e., welding time and horn pressure) in ultrasonic welding of 4-mm-thick carbon fiber reinforced nylon 66 composite, which were developed based on the joint strength criterion.