PUNCH LIFETIME IN FINE-BLANKING WITH OPTIMUM COMBINATION OF MECHANICAL PROPERTIES

摘要

The durability of the punches with complex shape are limited not only by the excessive wear or delamination of the hard thin PVD coating, but by chipping of the punch. Punch chipping often causes the premature tool failure in fine-blanking application, leading to short maintenance intervals of the punch and reduced quality of the stamped work piece. Increase of the thickness and strength of the blank sheet-metal in combination with strict requirements for edge finish and complex shape of the punch are factors leading to reduction of the punch lifetime during fine-blanking operations. This study is focusing on the selection criteria's of materials and heat treatment (HT) regimes with an attempt to find correlation between the mechanical properties and chipping failure mode of the fine-blanking punch. Same coating applied on punches made of PM tool steel (Bohler-Uddeholm S390) commonly used in fine-blanking applications are studied. The hardness of substrate material is varying in three ranges: 58 - 59 HRC, 62 - 63 HRC and 65 - 66 HRC. The failure patterns of the field-tested punches using four-row progressive tool are studied. Tool durability in fine-blanking of soft annealed C60E steel with thickness of 4,0 mm is studied. The optimum combination of the punch material mechanical properties such as compressive strength, impact strength and hardness and for prediction of the extended punch lifetime in fine-blanking is proposed.