[1] Dept. of Mech. Eng., Northern Jiaotong Univ., Beijing 100044, China
[2] Dept. of Mech. Eng., Tsinghua Univ., Beijing 100084, China
[3] Metal Forming Dept., Northeastern Univ., Shenyang 110004, China
[4] Anshan Automobile Fittings Factory, Anshan 114014, China