Rivet Fastening Process for CFRTP under Ultrasonic Vibration

CFRP can be classified as thermosetting or thermoplastic (CFRTP) depending on the properties of the matrix resin. In the case of using thermosetting resin, CFRP was made by using the Autoclave method where much time is necessary for the molding of the material. On the other hand, CFRTP which used heat workability resin to a matrix can use the die which is a conventional technique, so productivity and recyclability are high. Drilling is widely used as a secondary machining method for CFRTP. However, when secondary machining is performed on CFRTP, the carbon fibers in the continuous fiber composites get cut, which consequently leads to the degradation of mechanical properties. In this study, CFRTP is the material chosen for machining for which we propose a hole drilling method. A needle-shaped tool, to which ultrasonic vibrations are applied, is in contact with the CFRTP to soften the thermoplastic matrix resin, thereby avoiding the cutting of carbon fibers. In addition, the machining method serves as a fastening means without requiring a preliminary hole drilling process, similar to the self-piercing rivet process, by using the needle-shaped tool as a rivet for drilling holes. In this study, the machining characteristics of the hole machining by using various needle tools were investigated. In addition, a comparison of the material strength after the machining was carried out.