The dimensions of the tools used in slight clearance punching with a moving die are given in Fig. 1(c). A TiCNcoated
punch having a small round edge and a SKD 11 moving die were used for punching ultra-high strength steel
sheets. The clearance between the punch and moving die was 0.008 mm (a ratio of clearance to thickness of
0.57%). The moving die was set within an eccentricity of 0.14 mm measured from a KEYENCE AT-V 500
displacement sensor, and therefore a gap of 0.14 mm between the moving die and holder was chosen. The
JSC980Y and JSC1180Y steel sheets were used in this study. The mechanical properties of ultra-high strength
steel sheets are given in Table 1.