| 摘要 |
PROBLEM TO BE SOLVED: To efficiently manufacture a collar of high accuracy by constantly applying the compressive stress to the inside and the outside of the bending before the bending is applied to a work, and applying the rotation and the compressive stress in the case of implementing the return bending. SOLUTION: In a work fitting condition, straight metal shafts or metal tubes which are works, are held by a pair of rotary holding bodies with appropriate intervals D, the rotary holding bodies are brought close to each other to apply the compression force. In a collar forming initial condition, the rotary holding bodies are off-centered to generate projecting portions on the works on the inner side of the bending. In the collar growing condition, the projecting portions are accumulated on the whole circumference to form a desired collar. In a straightened condition, the return bending is implemented to straighten the works while applying the rotation and the compressive stress. In the collar forming initial condition, the low pressure is preferably applied under the condition where the compressive stress is constantly exerted in the inside and the outside of the bending, and the high pressure is preferably applied as the collar is formed.
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