Fine piercing of electromagnetic steel sheets by micro-punches under nearly zero clearance

Abstract

The fine piercing process under the nearly zero-clearance die-punch set-up was proposed as a non-traditional process with use of the plasma-nitrided SKD11 punch – die pair. With use of the high density plasma nitriding system, the SKD11 punch was nitrided to have the surface hardness up to 1600 HV. The annealed SKD11 die-substrate was shaved into a core die by accurately piercing the diamond-coated and the nitrided punches, respectively. After shaping and plasma-nitriding the shaved core die, both the punch and core-die was placed into the cassette die set for piercing experiments under the nearly-zero clearance. The electromagnetic steel sheets with the thickness of 0.5 mm were prepared to describe the shearing behavior in piercing. The piercing load and stroke histories were traced with increasing the number of shots. The engineering durability was also discussed with comments on the wear of punch and die. The brittle electromagnetic sheets were accurately blanked with the burr height ratio by 10% and the burnished surface area ratio by 70% when using the diamond-coated punch. Fine piercing process with less heights and fractured surface area ratio in dry was put into practice by using the plasma nitrided punch and die-core set with rational compliance under nearly zero clearance.