Patent ID: 6223576
Filing Date: 2001-05-01
Classification: B21H

Abstract:
A method of forming a peripheral portion of a blank in the form of a circular plate, so as to thicken said peripheral portion, comprising the steps of:providing a roller die supported rotatably about an axis thereof and having an outer circumferential surface and an annular forming groove which is open in said outer circumferential surface, said forming groove having a first side surface, a second side surface spaced from said first side surface in an axial direction of said roller die, and a bottom surface which has rounded end portions smoothly connecting said first and second side surfaces;providing a blank holder jig which has an axis of rotation and an outer circumferential surface and which holds said blank;holding said blank on said blank holder jig such that said blank is coaxial with said blank holder jig and said peripheral portion extends radially outwardly from said outer circumferential surface over a predetermined radial distance;rotating said blank about said axis of said blank holder jig such that said blank is held in pressing contact at an outer circumferential surface thereof with said bottom surface of said annular forming groove of said roller die, so that said outer peripheral portion of said blank is thickened following a shape of said forming groove in cross section taken in a plane including said axis of said roller die;forming said first side surface and positioning said roller die relative to said blank holder jig such that said first side surface is inclined at an angle .alpha.1 larger than 0.degree. with respect to a radial direction of said blank holder jig such that an axial distance between said first and second side surfaces in an axial direction of said blank holder jig increases in a radially outward direction of said roller die; andcontrolling a force acting between said outer circumferential surface of said blank and said bottom surface of said forming groove, during rotation of said blank in pressing contact with said bottom surface, so that said outer peripheral portion of said blank is held flexed in a convex shape following said first side surface and so that a radially outermost part of said outer peripheral portion is thickened in opposite directions toward said first and second side surfaces while said outer peripheral portion is spaced apart from said first and second side surfaces, and is prevented from buckling within said forming groove.