1. College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing 100124, China e-mail:
2. College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing 100124, China;
3. Beijing Municipal Key Laboratory of Electrical Discharge Machining Technology Beijing 100191, China e-mail:
4. China National Machine Tool, Quality Supervision Testing Center, Beijing 100102, China e-mail: