METHOD AND DEVICE FOR MONITORING BACK SPRING PHENOMENON AT TIME OF BENDING OF SLENDER BLANK SUCH AS PIPE

摘要

PURPOSE: To improve the accuracy of bending by determining backspring value by releasing the rear part of a bended base stock and also putting the reference mark and, next, determining the position of a rotational angle by detecting the instance when the rear part reaches a predetermined position. CONSTITUTION: An annular groove 3 is provided in a part of a forming roller 3 and rotatable around the axial line 2 together with a bending arm 5. Moreover, the groove 10 is formed on a bar material 9 which is extended parallel to the axial line 8 of a tube 7 in the length direction. The tube 7 is clamped between a movable clamp jaw 5 and the part 6 of the forming roller 1, the bar material 9 is brought into contact and the arm 4 is rotated to a rotational angle A. Next, the arm 4 is rotated to an angle B in the inverse direction and, moreover, a clamp is detached. At this time, by utilizing the instance when the rear part 7b of the tube 7 crosses the light beam of a sensor 13, the position of the rotational angle is determined and bending work is executed by rotating the arm 4. Because the amount of backspring is exact, the accuracy of bending is improved.