Formed material manufacturing method
A formed material 1 having a cylindrical trunk portion 10 and a flange portion 11 formed at an end section of the trunk portion is manufactured by performing multi-stage drawing of a material metal sheet. Multi-stage drawing includes: preliminary drawing that forms, from a material metal sheet 2 , a preform 20 having a trunk element 20 a ; compression drawing that is performed at least once after the preliminary drawing and that forms the trunk portion 10 by drawing the trunk element 20 a while applying a pressure-adjustable compressive force to the trunk element 20 a ; and finish-ironing that is performed for securing dimensional precision at least once following the compression drawing.
1. A formed material manufacturing method, comprising manufacturing a formed material having a cylindrical trunk portion and a flange portion formed at an end section of the trunk portion by performing multi-stage drawing of a material metal sheet,
wherein the multi-stage drawing includes:
preliminary drawing that forms, from the material metal sheet, a preform having a trunk element, wherein the trunk element comprises a top wall and a peripheral wall;
compression drawing that is performed at least once after the preliminary drawing and that forms the trunk portion by drawing the trunk element while applying, to the trunk element, a compressive force along a depth direction of the trunk element, by using a forming die including a die having a push-in hole, a punch that is inserted into the trunk element and that pushes the trunk element into the push-in hole, and pressing means for applying the compressive force to the peripheral wall of the trunk element extending along the depth direction of the trunk element, wherein the trunk portion that is formed by the compression drawing comprises a top wall and a peripheral wall; and
finish-ironing that is performed at least once after the compression drawing is performed at least once,
the pressing means is a lifter pad having a pad portion which is disposed at an outer peripheral position of the punch so as to oppose the die and on which a lower end of the peripheral wall of the trunk element is placed, and a support portion configured to support the pad portion from below and to be capable of adjusting a support force with which the pad portion is supported,
the compression drawing performed at least once is performed so as to be complete by the time at which the pad portion reaches a bottom dead center, and
the support force acts on the trunk element, as the compressive force, during compression drawing of the trunk element,
wherein, the compression drawing performed at least once comprises adjusting an average thickness of the peripheral wall of the trunk element by adjusting the support force with which the pad portion is supported, in accordance with a thickness of the material metal sheet,
wherein the flange portion is formed during the compression drawing.
2. The formed material manufacturing method according to claim 1 ,
wherein, in the finish-ironing performed at least once, a clearance c re of a forming die is established so as to satisfy the relationship given by Expression (1) below, where X denotes a ratio of a radius of curvature r of a die shoulder of the forming die used in the finish-ironing to an average thickness tre of the peripheral wall of the trunk portion before the finish-ironing, and Y denotes an ironing rate represented by {(t re −c re )/t re }×100:
0< Y≤ 11.7 X− 3.1 Expression (1).
3. The formed material manufacturing method according to claim 1 , wherein the material metal sheet is a Zn-based plated steel sheet obtained by performing Zn-based plating on a surface of a steel sheet prior to the multi-stage drawing.