Ultrasonic Vibration Machining of Copper Graphite Electrode Sheet

Abstract Copper graphite electrode sheet (CGES) has been widely utilized as an electrode material due to its excellent electrical conductivity and heat dissipation capabilities. However, it bears challenge to achieve the qualitied surface finish of machined CGES by conventional machining methods due to the mechanical property of copper layer different from that of graphite layer, and also due to the scale effect of CGES with the thickness of 0.2mm or smaller. The typical defects including lamination, cracks, and uneven cross-sections are therefore associated with the machining process of CGES. Additionally, the internal material distortion of copper layer accompanies these defects to deteriorate the machined surface integrity. Ultrasonic Vibration Machining (UVM) is thus selected to acquire much superior surface finish of machined CGES by addressing the scale effect and interlayer deformation mechanisms of brittle and ductile materials. This study aims to provide practical optimization parameters in succeeding the ultrasonic vibration machining of CGES. In this research, Finite Element Method (FEM) is implemented to investigate the plastic deformation and fracture mechanism in the ultrasonic vibration machining of CGES, and experiments were conducted to calibrate the FE-based simulation model within 13% predicted error. It shows that ultrasonic vibration machining is beneficial for reducing cutting forces and improving surface integrity by coordinating the fracture evolution behavior of brittle graphite layer and the internal plastic deformation of ductile copper layers. The stress distribution becomes more uniform under ultrasonic vibration to relieve stress concentration along machining direction. Therefore, UVM is beneficial to the formation of favorable surface finish in the machined CGES. Based on the analysis, the optimal vibration frequency is determined as 80kHz with an amplitude of 20μm. The die clearance should be sufficiently small since increased clearances decrease die’s supporting stiffness, alter ductile-brittle transition behavior and eventually deteriorate machined surface integrity.