抄録
In a previous paper by the authours chipping phenomenon was described as fracture having initiated from fatigue cracks occurring from the stress concentration at the bottom of wear pits on the side surface of the blanking punches which are subjected to tensile stress by friction when pulled upwards. On the basis of this finding a laboratory test was designed where simulated chipping could be reproduced and tool steels could be assessed as to their resistance to chipping.
When the test piece is repeatedly moved up and down while applying side-wise stress by pressing a “side-pressure piece” against its side surface, chipping phenomenon appear on the side surface of test piece. The process of this phenomenon are as follows.
(1) Numerous wear pits appeared on the side surface. Fatigue cracks are initiated at their bottom and grow as fracture. The phenomenon is thought as being essentially identical to that observed on the punches in actual operation.
(2) A test was conducted on SKD-1 steel and a quantitative relation between the side-wise stress and the tool life was obtained.
(3) The proposed method was found satisfactory as a test of tool steels for blanking punches with respect to their chipping resistance.
