METHOD FOR WORKING BOLT BASE-STOCK, BOLT BASE-STOCK AND DIE FOR WORKING BOLT BASE-STOCK

PROBLEM TO BE SOLVED: To improve measuring accuracy when bolt axial force is measured by using ultrasonic wave. SOLUTION: A round bar workpiece WO is inserted into a through-hole 12b in a die 12, and the projected part WA of the round bar workpiece held so as to partly project from the upper end surface 12a of the die 12 with a knock pin 14, is bent with a bending punch 16. Successively, the bending part WB is upset on the upper end surface 12a of the die 12 with an upsetting punch 18. Further, the flatness and the surface roughness of the end surface of the round bar workpiece can be improved by blanking the upset part WC with a blanking punch 20 into the through-hole 12a in the die 12. In the bolt which is obtained by cold-forging the round bar workpiece as a bolt base-stock, the flatness and the surface roughness at the end surface can be improved. The measured accuracy of the axial force can be improved by performing the measurement of the bolt axial force using the ultrasonic wave to the bolt. COPYRIGHT: (C)2006,JPO&NCIPI