The utility model discloses a heat -stewed bend scratch start department ovality is school device in advance relates to big radius -thickness ratio return bend and makes technical field. Including the nut, go up pinch -off blades, pinch -off blades, connecting rod, gusset, slips down, the connecting rod is connected and is gone up pinch -off blades and pinch -off blades down, pinch -off blades and pinch -off blades are down gone up in nut locking, the slips is fixed at last pinch -off blades under and on the pinch -off blades. The body ovality problem of exceeding standard of scratch start department when big radius -thickness ratio return bend shaping can be solved to this device, how much size precision of outward appearance after the shaping of improvement return bend.