| 摘要 |
<p>A bent member having excellent dimensional accuracy is manufactured by stably forming a high temperature portion uniformly in the circumferential direction of a steel tube and in a narrow region in the axial direction of the steel tube using a manufacturing apparatus of Patent Document 1. A bent member is manufactured by supporting a steel tube 1 at a first position while feeding it, performing induction heating of the steel tube at a second position B with an induction heating coil 14, cooling the steel tube 1 at a third position C to form a high temperature portion la which moves in the axial direction of the steel tube 1, and three-dimensionally varying the position of a gripping mechanism 15 for the steel tube 1 in a region D to apply a bending moment to the high temperature portion 1a. When the wall thickness of the steel tube 1 is at most 2.0 mm, the feed speed V of the steel tube 1 is made 5 - 150 mm/sec, and an alternating current at 5 - 100 kHz is supplied to an induction heating coil 14 having 1 winding. When the wall thickness of the steel tube 1 is greater than 2.0 mm and at most 3.0 mm, an induction heating coil 14 having 2 windings is used, and the current frequency f (kHz) of the alternating current supplied to the induction heating coil 14 and the feed speed V (mm/sec) of the steel tube 1 are adjusted so as to satisfy f < 3000/V and f >= 0,08 V, wherein 5 kHz <= f <= 100 kHz, and 5 mm/sec <= V <= 150 mm/sec.</p> |
