A first piece (13) includes a first ring portion (13b) and a second ring portion (13c) which are arranged side by side in an axial direction and an inner diameter and an outer diameter of the first ring portion (13b) are respectively larger than an inner diameter and an outer diameter of the second ring portion (13c). A second piece (16) is obtained by pressing the first piece (13) while the first piece (13) is disposed between a first set and a second set.

A first piece (13) includes a first ring portion (13b) and a second ring portion (13c) which are arranged side by side in an axial direction and an inner diameter and an outer diameter of the first ring portion (13b) are respectively larger than an inner diameter and an outer diameter of the second ring portion (13c). A second piece (16) is obtained by pressing the first piece (13) while the first piece (13) is disposed between a first set and a second set.

A process for producing bearing ring blanks, or gearwheel ring blanks or tubular connection-member blanks, comprises the steps of: •a) providing a steel tube; •b) dividing the tube into a plurality of slugs (30, 30′) each having an axial through cavity; •c) supplying the slugs (30, 30′) to a die assembly (20) of a cold-forming station, the forming station including a punch assembly (10); and •d) subjecting the slugs (30, 30′) to contained forward extrusion through the die assembly (20), wherein the thrust imparted by a pushing member (11) of the punch assembly (10) on a subsequent slug (30′) causes passage of a preceding slug (30) through the die assembly (20), with deformation thereof into a blank (40), while a restraining member (12) of the punch assembly (10) occupies the axial cavity of the subsequent slug (30′) and at least part of the axial cavity of the preceding slug (30).

A process for producing bearing ring blanks, or gearwheel ring blanks or tubular connection-member blanks, comprises the steps of: •a) providing a steel tube; •b) dividing the tube into a plurality of slugs (30, 30′) each having an axial through cavity; •c) supplying the slugs (30, 30′) to a die assembly (20) of a cold-forming station, the forming station including a punch assembly (10); and •d) subjecting the slugs (30, 30′) to contained forward extrusion through the die assembly (20), wherein the thrust imparted by a pushing member (11) of the punch assembly (10) on a subsequent slug (30′) causes passage of a preceding slug (30) through the die assembly (20), with deformation thereof into a blank (40), while a restraining member (12) of the punch assembly (10) occupies the axial cavity of the subsequent slug (30′) and at least part of the axial cavity of the preceding slug (30).

In a preparation step, a frame (10), a concave spherical seat (15), a convex spherical seat (13), a rotation body (16), a rotating shaft (12), and a work holder (17) are assembled, a laser head (33) is attached to the convex spherical seat (13), and a light receiving unit (38) is attached to the work holder (17). In a rotation body centering step, an irradiation position of a laser beam (LB) with respect to a laser irradiation surface (41) is changed by rotating the rotation body (16) while allowing the laser irradiation surface (41) to be irradiated with the laser beam (LB) emitted from the laser head (33) and a trajectory of the irradiation position is checked.

A ball screw is provided in which an outer circumferential formation is formed at a portion facing a ball circulating passage out of outer circumferential surface of a nut. The ball screw includes: a screw shaft having on its outer circumferential surface a screw groove; a nut having on its inner circumferential surface a screw groove facing the screw groove; a plurality of balls rollably loaded in a spiral ball rolling passage formed by both screw grooves; and a ball circulating passage to return the balls from a start point to an end point of the ball rolling passage for recirculation. The ball circulating passage is a concaved groove formed by concaving a groove on a part of the cylindrical inner circumferential surface of the nut by plastic working. Then, a flange is integrally provided at a portion facing the ball circulating passage and the screw groove.

A ball screw is provided in which an outer circumferential formation is formed at a portion facing a ball circulating passage out of outer circumferential surface of a nut. The ball screw includes: a screw shaft having on its outer circumferential surface a screw groove; a nut having on its inner circumferential surface a screw groove facing the screw groove; a plurality of balls rollably loaded in a spiral ball rolling passage formed by both screw grooves; and a ball circulating passage to return the balls from a start point to an end point of the ball rolling passage for recirculation. The ball circulating passage is a concaved groove formed by concaving a groove on a part of the cylindrical inner circumferential surface of the nut by plastic working. Then, a flange is integrally provided at a portion facing the ball circulating passage and the screw groove.

A method of manufacturing a rotating bearing unit includes to cause one end surface in the axial direction of the forming punch (46), formed by combining a plurality of punch elements (46, 46) divided in the circumferential direction, which are displaceable in the axial direction and which are not displaceable in the circumferential direction, and having a processing teeth (44, 44) at one end surface in the axial direction, to face the other end surface of the caulking section (20) in the axial direction. In this state, rolls (30a) are rotated about the central axis (α) of the hub main body (8) while pressing the other end surface of the forming punch (46) in the axial direction with a pressing surface (43) of the roll (30a) having a central axis (β) that is inclined with respect to the central axis (α) of the hub main body (8).

A method of manufacturing a rotating bearing unit includes to cause one end surface in the axial direction of the forming punch (46), formed by combining a plurality of punch elements (46, 46) divided in the circumferential direction, which are displaceable in the axial direction and which are not displaceable in the circumferential direction, and having a processing teeth (44, 44) at one end surface in the axial direction, to face the other end surface of the caulking section (20) in the axial direction. In this state, rolls (30a) are rotated about the central axis (α) of the hub main body (8) while pressing the other end surface of the forming punch (46) in the axial direction with a pressing surface (43) of the roll (30a) having a central axis (β) that is inclined with respect to the central axis (α) of the hub main body (8).

Provided is a method for manufacturing a tubular rotary component from a donut-shaped metal disc, wherein the generation of wrinkles or cracks due to a drawing process can be suppressed. This method for manufacturing a tubular rotary component 100B includes: an intermediate molding step in which the entirety of both surfaces of a donut-shaped metal disc 100 having a prescribed inner diameter D.sub.1 and outer diameter D.sub.2 are pressed by the respective tapered surfaces of a punch 10A and a die 20A provided with a prescribed taper to carry out bore-expansion drawing, thereby obtaining a frustoconical intermediate molded article 100A; and a final molding step in which the intermediate molded article 100A is pressed by a punch 10B and a die 20B having a desired shape to carry out bore-expansion drawing again, thereby obtaining a tubular rotary component 100B.