Scratching-induced surface characteristics and material removal mechanisms in rotary ultrasonic surface machining of CFRP.

Rotary ultrasonic machining has been successfully explored in surface machining of carbon fiber reinforced plastic (CFRP) composites. It has been proven to be an effective and efficient CFRP machining method. Both theoretical and experimental investigations have been conducted with the assumption that the CFRP is removed by brittle fracture removal mode. However, in brittle material machining, ductile flow phenomenon still exists. Ductile scratching marks are also observed on the machined CFRP surfaces. It is still unknown that what actual material removal modes are under different machining variables. To investigate the material removal mechanisms in rotary ultrasonic surface machining (RUSM) of CFRP, single abrasive scratching tests were conducted. The scratching induced characteristics and scratching forces were analyzed. Both the ductile removal mode and the brittle fracture removal mode were observed and identified in both carbon fiber layers and epoxy resin layers on the machined marks by using scanning electron microscopy (SEM) imaging. With the increase of scratching depth, the material removal mode of CFRP was changed from the ductile removal mode to the brittle fracture mode. From the analysis of kinematic trajectory of diamond grain, the scratching cutting forces were decreased in the tests with the assistance of ultrasonic vibration under the same machining variables. The generation mechanisms of the delamination were analyzed and discussed.