PURPOSE: To improve the concentricity and roundness, by preheating the blank so as to generate a temperature difference between the outer surface and central part, before heating up to a specified temperature, and by pushing three roller dies into the outer surface of the blank, letting the blank automatically align to th center of the dies correspondingly to the quantity of unbalance among dies.
CONSTITUTION: The blank 11, mounted on the rotary shaft 22 separate from the thread rolling bench, is preheated by the high frequency coil 23 surrounding the blank 11, so as to generate a temperature difference between the outer surface and central part; thus preheated blank 11 is inserted to the small diameter part 10 of the retaining shaft 1; then, the cylinder brings the arbor 8 down so as to press and retain the blank 11 which is then rotated; and next, the electricity is supplied to the heating coil 19 for the final heating. Then, each tool stand 3 of rotating three roller dies 6 is proceeded so as to push dies 6 into the outer surface of the blank 11; hereupon, even if the quantity of indentation or thread rolling load of each dies 6 is unbalanced, the retaining mechanism 25 lets the blank 11 automatically align to the center of dies 6 by the spring 31; as a result, the concentricity and roundness are improved.
TANAKA TOSHIAKI
KANAMARU TOSHIMASA
TOYOTA MOTOR CO LTD