METHOD AND APPARATUS FOR FORMING RECESS OF HOLLOW PIPE

摘要

A roll support block (10) has roll-forming rolls (6-9) arranged in four stages, and the roll support block (10) moves while being guided by a guide hole (13) of a pipe holder (5). The rolls (6-9) sequentially come, through a forming window (35) formed in the pipe holder (5), in press-contact with a hollow pipe (2) fixed by the pipe holder (5). First, while rolling, a first-stage roll (6) comes in press-contact with the hollow pipe (2), preliminarily forming a recess. Then, second- and third-stage rolls (7, 8), whose diameters are larger in that order, perform preliminary forming to enlarge the recess. Finally, a fourth roll (9) forms a final shape of a first or a second lock groove (3, 4).