Ball screw device, manufacturing method of machine part, manufacturing method of machine device, manufacturing method of vehicle, machine part, machine device, vehicle, hydroforming method, and hydroforming mold

Abstract

To provide a method for manufacturing a ball screw device and a machine part, which is advantageous for cost reduction. [Solution] The ball screw device includes a nut (3), a screw shaft, and a plurality of balls arranged between the nut (3) and the screw shaft. The nut (3) has a first member (11) arranged around the screw shaft, a second member (10) arranged between the screw shaft and the first member (11), and a third member (12) arranged between the first member (11) and the second member (10). The third member (12) has a laminated body (12A) in which a plurality of plates (22a, 22b) are stacked in the axial direction. The laminated body (12A) has an inner surface facing the outer surface of the second member (10). The inner surface of the laminated body (12A) has a shape corresponding to the shape of the outer surface of the second member (10).

Description

[Technical Field]

[0001] The present invention relates to a ball screw device, a method for manufacturing a machine part, a method for manufacturing a machine device, a method for manufacturing a vehicle, a machine part, a machine device, a vehicle, a hydroforming method, and a hydroforming mold. This application claims priority based on Japanese Patent Application No. 2020-138722, filed on August 19, 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, hydroforming methods have been applied to the manufacture of various mechanical parts for automobiles and the like. In one example of a hydroforming method, a metallic tubular material is placed radially inside a forming peripheral surface provided on the inner peripheral surface of a forming mold, and hydrostatic pressure is applied to the inner peripheral surface of the tubular material, thereby plastically deforming the tubular material radially outward until it assumes a shape that conforms to the forming peripheral surface (see, for example, Japanese Patent No. 3843222 (Patent Document 1)). This hydroforming method makes it relatively easy to form metallic tubular members having complex shapes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3843222 Summary of the Invention [Problem to be solved by the invention]

[0004] A specific example of a method for manufacturing a mechanical component using a hydroforming method will be described with reference to Figures 12 to 21. In this example, the mechanical component to be manufactured is a nut 100 that constitutes a ball screw device. Note that this example (including the structure of the nut 100) is an example for comparison with a non-public example.

[0005] As shown in FIGS. 12 to 14, the nut 100 is configured in a tubular shape (for example, a cylindrical shape or a square cylindrical shape). The nut 100 has a spiral nut-side ball screw groove 101 and a circulation groove 102 on its inner peripheral surface. The nut-side ball screw groove 101 has a length of less than one revolution (for example, 0.6 to 0.8 revolutions) in the spiral direction, which is the direction in which the nut-side ball screw groove 101 is formed. The circulation groove 102 is a groove connecting both ends of the nut-side ball screw groove 101, and has a substantially S-shape when viewed in the radial direction. The circulation groove 102 has a groove depth that allows balls (not shown) moving in the circulation groove 102 to ride over the threads of the shaft-side ball screw groove provided on the outer peripheral surface of the screw shaft when the ball screw device is in use.

[0006] Such a nut 100 is configured to have an overall cylindrical shape by combining a cylindrical member 103, a holder 104, and a reinforcing member 105.

[0007] In one example, the cylindrical member 103 is a thin-walled member having a substantially cylindrical shape formed by a hydroforming method described later. The cylindrical member 103 has a nut-side ball screw groove 101 and a circulation groove 102 on its inner circumferential surface. The outer circumferential surface of the cylindrical member 103 has a shape such that the inner circumferential surface of the cylindrical member 103 is offset radially outward by the wall thickness (plate thickness) of the cylindrical member 103. That is, the cylindrical member 103 has a spiral protruding portion 106a on the outer circumferential surface located radially outward from the nut-side ball screw groove 101, which protrudes radially outward compared to the surrounding portion, and a protruding portion 106b on the outer circumferential surface located radially outward from the surrounding portion, which protrudes radially outward compared to the surrounding portion and has a substantially S-shape when viewed in the radial direction, which is formed in the radial direction.

[0008] The holder 104 is configured to have a cylindrical shape as a whole by combining a pair of semi-cylindrical holder elements 107. The holder 104 holds the cylindrical member 103 via a reinforcing member 105 on the radially inner side.

[0009] The reinforcing member 105 is a member for preventing deformation of the tubular member 103 when the ball screw device is in use. That is, when the ball screw device is in use, radial loads and thrust loads act on the nut-side ball screw groove 101 of the tubular member 103 from multiple balls. Therefore, it is necessary to prevent deformation of the tubular member 103, which is a thin-walled member having a substantially cylindrical shape, due to these loads. For this reason, the reinforcing member 105 is arranged so as to fill the gap between the outer circumferential surface of the tubular member 103 and the inner circumferential surface of the holder 104 as tightly as possible. This allows the reinforcing member 105 to support the radial load and thrust load acting on the nut-side ball screw groove 101, thereby reinforcing the tubular member 103. The inner circumferential surface of the reinforcing member 105 has a shape that matches the portion of the outer circumferential surface of the tubular member 103 that is not located at the protruding portion 106b. In the illustrated example, the reinforcing material 105 has a through-hole 115 that penetrates in the radial direction in a portion corresponding to the protruding portion 106b.

[0010] When assembling a ball screw device using the nut 100 described above, a screw shaft is inserted into and positioned radially inside the nut 100. Then, a nut-side ball screw groove 101 of the nut 100 and a spiral-shaped shaft-side ball screw groove provided on the outer circumferential surface of the screw shaft are radially opposed to each other to form a spiral load path. Both ends (start point and end point) of the load path are connected by a circulation groove (circulation path, unloaded path) 102 of the nut 100. A plurality of balls are rotatably disposed in the load path and circulation groove 102. When the ball screw device assembled in this manner is used, as the nut 100 and the screw shaft rotate relative to each other, the balls that have traveled from the start point to the end point of the load path are returned to the start point of the load path through the circulation groove 102. The start point and end point of the load path are interchanged depending on the direction of relative displacement (relative rotation direction) between the screw shaft and the nut 100 in the axial direction.

[0011] When manufacturing the tubular member 103 of the nut 100 using the hydroforming method, first, a thin-walled cylindrical metallic tubular material 108 is prepared as shown in Fig. 15. Then, this tubular material 108 is formed into the tubular member 103 as shown in Fig. 16 by the hydroforming method. In the illustrated example, a hydroforming device 109 as shown in Figs. 17 to 21 is used for this purpose.

[0012] The hydroforming device 109 includes a forming die 110 and a pair of lids 111a and 111b.

[0013] The molding die 110 is cylindrical and has a molding surface 113 on its inner circumferential surface. The molding surface 113 has a shape that matches the outer circumferential surface of the completed tubular member 103. In other words, the molding surface 113 has a shape that is substantially the same as the inner circumferential surface of the completed tubular member 103, offset radially outward by the wall thickness of the tubular member 103. In particular, in the illustrated example, the molding die 110 is configured cylindrically as a whole by combining a pair of semi-cylindrical molding die elements 112a, 112b. The molding surface 113 is formed by combining the radially inner surfaces of the pair of molding die elements 112a, 112b.

[0014] Each of the pair of lids 111a, 111b is formed in a disk shape. Of the pair of lids 111a, 111b, one lid 111a has a through-hole 114 that passes through the radial center in the axial direction. The pair of lids 111a, 111b are arranged on both axial sides of the forming die 110.

[0015] When the tubular blank 108 is molded into the tubular member 103 using the hydroforming device 109, first, as shown in FIGS. 17 and 18 , the tubular blank 108 is placed radially inside the molding circumferential surface 113 of the forming die 110, and both axial end openings of the tubular blank 108 are closed with a pair of lids 111 a and 111 b. Then, in this state, a liquid is filled into the radially inside of the tubular blank 108 through the through-hole 114 of one of the lids 111 a. Then, by applying the pressure of the liquid (hydraulic pressure) to the inner circumferential surface of the tubular blank 108, the tubular blank 108 is plastically deformed radially outward until it forms a shape that conforms to the molding circumferential surface 113, thereby molding the tubular member 103.

[0016] 19, the pair of molding die elements 112a, 112b and the pair of lids 111a, 111b are disassembled to remove the cylindrical member 103 from the hydroforming device 109. Then, the holder 104 and the reinforcing member 105 are arranged around the cylindrical member 103 to complete the nut 100.

[0017] The shape of the molding peripheral surface 113 of the mold 110 used in the hydroforming method described above is transferred directly to the cylindrical member, so the precision of the cylindrical member can be improved by increasing the processing precision according to the precision required for the cylindrical member. However, if the shape is complex, the cost of molding the molding peripheral surface 113 (the radially inner surfaces of each of the pair of mold elements 112a, 112b) increases, and the manufacturing cost of the mold 110 also increases.

[0018] An object of aspects of the present invention is to provide a ball screw device, a method for manufacturing a mechanical component, a method for manufacturing a mechanical device, a method for manufacturing a vehicle, a mechanical component, a mechanical device, a vehicle, a hydroforming method, and a hydroforming mold that are advantageous in terms of reducing costs. [Means for solving the problem]

[0019] A ball screw device according to one aspect of the present invention includes a nut, a screw shaft, and a plurality of balls arranged between the nut and the screw shaft. The nut has a first member arranged to surround the screw shaft, a second member arranged between the screw shaft and the first member, and a third member arranged between the first member and the second member. The third member has a laminated body in which a plurality of plates are stacked in the axial direction. The laminated body has an inner surface facing the outer surface of the second member. The inner surface of the laminated body has a shape corresponding to the shape of the outer surface of the second member.

[0020] In one example, the outer surface of the second member has a convex shape and the inner surface of the laminate has a concave shape that substantially matches the convex shape of the second member.

[0021] In one example, the plurality of plates in the stack include a plurality of annular plates, and the plurality of annular plates have inner peripheral surfaces with substantially the same circumferential shape and / or different circumferential shapes.

[0022] In one example, the plurality of plates in the stack have phase matching portions provided at specific positions in the circumferential direction.

[0023] In one example, the material of the third member is different from the material of the second member.

[0024] In one example, the inner surface of the stack has a plurality of steps, each step being based on the difference in inner surface height between two adjacent plates.

[0025] In one example, the plurality of plates of the third member include a first plate and a second plate having a thickness different from that of the first plate.

[0026] A mechanical device according to one aspect of the present invention includes the above-described ball screw device.

[0027] A vehicle according to one aspect of the present invention includes the above-described ball screw device.

[0028] A method for manufacturing a mechanical part according to one aspect of the present invention comprises the steps of: preparing a mold having a laminate in which a plurality of plates are stacked in the axial direction, the laminate having an inner surface for molding; placing a workpiece inside the mold; applying hydraulic pressure to the inner surface of the workpiece to plastically deform the workpiece toward the inner surface of the mold; and assembling a part using a plurality of elements including the plastically deformed workpiece and the laminate.

[0029] A machine component according to one aspect of the present invention is manufactured by the above manufacturing method.

[0030] A mechanical device according to one aspect of the present invention includes the mechanical component described above.

[0031] A vehicle according to one aspect of the present invention includes the above mechanical component.

[0032] A method for manufacturing a mechanical device according to one aspect of the present invention includes a step of manufacturing a mechanical component using the above-described manufacturing method.

[0033] A vehicle manufacturing method according to one aspect of the present invention includes a step of manufacturing a mechanical component using the manufacturing method described above.

[0034] A hydroforming method according to one aspect of the present invention comprises the steps of preparing a cylindrical forming mold having a laminate in which a plurality of plates are stacked in the axial direction, the laminate having an inner peripheral surface for forming; placing a workpiece inside the cylindrical forming mold; and applying hydrostatic pressure to the inner surface of the workpiece, thereby plastically deforming the workpiece toward the inner peripheral surface of the cylindrical forming mold.

[0035] A hydroforming die according to one aspect of the present invention includes a cylindrical laminate in which a plurality of plates are stacked in an axial direction, and the laminate has an inner peripheral surface for forming. [Effects of the Invention]

[0036] According to aspects of the present invention, it is possible to provide a ball screw device, a method for manufacturing a mechanical component, a method for manufacturing a mechanical device, a method for manufacturing a vehicle, a mechanical component, a mechanical device, a vehicle, a hydroforming method, and a hydroforming mold, which are advantageous in reducing costs. [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 1 is a plan view showing a ball screw device. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 3 is a perspective view showing the nut with one of a pair of holder elements omitted. [Figure 4] FIG. 4 is a view of the nut as seen from the right side of FIG. [Figure 5] FIG. 5 is a cross-sectional view taken along line BB in FIG. [Figure 6] FIG. 6 is an enlarged view of part C in FIG. [Figure 7] FIG. 7 is a perspective view of a tubular material. [Figure 8] FIG. 8 is a perspective view of the cylindrical member. [Figure 9] FIG. 9 is an exploded perspective view of the hydraulic molding device and the cylindrical material. [Figure 10] FIG. 10 is a perspective view of a hydroforming device and a cylindrical material. [Figure 11] FIG. 11 is a perspective view showing the state in which the holder is attached to the combined body of the cylindrical member, key, and molding die removed from the hydroforming device. [Figure 12] FIG. 12 is a view of a comparative nut as seen from the axial direction, with one of a pair of holder elements shown in phantom lines. [Figure 13] FIG. 13 is a cross-sectional view taken along line DD in FIG. [Figure 14] FIG. 14 is a perspective view showing a nut according to a comparative example, in which one of a pair of holder elements and a reinforcing member are omitted. [Figure 15] FIG. 15 is a perspective view of a tubular material for comparison. [Figure 16]FIG. 16 is a perspective view of a cylindrical member for comparison. [Figure 17] FIG. 17 is an exploded perspective view of a hydraulic forming device and a cylindrical material, relating to a comparative example. [Figure 18] FIG. 18 is a perspective view of a hydroforming device and a cylindrical material, relating to a comparative example. [Figure 19] FIG. 19 is a perspective view showing the inside of the hydroforming device in an open state after hydroforming of a cylindrical member, as a comparative example. [Figure 20] FIG. 20 is a perspective view showing one of a pair of mold elements constituting a hydroforming apparatus, in relation to a comparative example. [Figure 21] FIG. 21 is a perspective view showing the other of a pair of mold elements constituting a hydroforming apparatus, in relation to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0038] An embodiment of the present invention will be described with reference to the drawings. In one example, a nut of a ball screw device is applied as a mechanical component. In another example, the present invention can be applied to various mechanical components having a molded element (a molded element).

[0039] The ball screw device 1 of this example is incorporated into various mechanical devices, such as electric brake devices for vehicles, automatic manual transmissions (AMTs), and positioning devices for machine tools, and is used to convert the rotational motion of a drive source such as an electric motor into linear motion to operate a driven part.

[0040] The ball screw device 1 includes a screw shaft 2, a nut 3 that corresponds to a mechanical component, and a plurality of balls 4 arranged between the nut 3 and the screw shaft 2. The ball screw device 1 is not limited to the example described below, and various forms are applicable.

[0041] In the following description of the ball screw device 1, unless otherwise specified, the axial direction, radial direction, and circumferential direction refer to the axial direction, radial direction, and circumferential direction of the screw shaft 2 and the nut 3. With respect to the ball screw device 1, one axial side is the right side in Figures 1, 2, 3, and 5, and the other axial side is the left side in Figures 1, 2, 3, and 5.

[0042] The screw shaft 2 is inserted into the radially inner side of the cylindrical nut 3 and is arranged coaxially with the nut 3. A spiral load path 5 (see Figure 2) exists between the outer peripheral surface of the screw shaft 2 and the inner peripheral surface of the nut 3. Both ends (starting point and ending point) of the load path 5 are connected by a circulation groove (circulation path, unloaded path) 9 formed on the inner peripheral surface of the nut 3. A plurality of balls 4 are arranged in a rollable manner in the load path 5 and the circulation groove 9. As the screw shaft 2 and the nut 3 rotate relative to each other, the balls 4 that have traveled from the starting point to the ending point of the load path 5 are returned to the starting point of the load path 5 through the circulation groove 9. The starting point and ending point of the load path are interchanged depending on the direction of relative displacement between the screw shaft 2 and the nut 3 in the axial direction (relative rotation direction). The ball screw device 1 is used in a mode in which the nut 3 is rotated relative to the screw shaft 2 to cause the screw shaft 2 to move linearly relative to the nut 3, or in a mode in which the screw shaft 2 is rotated relative to the nut 3 to cause the nut 3 to move linearly relative to the screw shaft 2. The structure of each component of the ball screw device 1 will be described below.

[0043] As shown in Figs. 1 and 2, the screw shaft 2 is made of metal and has a spiral shaft-side ball screw groove 7 on its outer circumferential surface. The shaft-side ball screw groove 7 is formed by grinding (cutting) or rolling on the outer circumferential surface of the screw shaft 2. In this example, the shaft-side ball screw groove 7 has one thread. The cross-sectional groove shape (groove bottom shape) of the shaft-side ball screw groove 7 is a Gothic arch groove or a circular arc groove.

[0044] The nut 3 includes a first member (holder 11) surrounding the screw shaft, a second member (workpiece 10) disposed between the screw shaft 2 and the holder 11, and a third member (reinforcement member 12) disposed between the holder 11 and the workpiece 10. In one example, as shown in FIGS. 1 to 6 , the nut 3 is cylindrical and has a spiral nut-side ball screw groove 8 and a circulation groove 9 on its inner circumferential surface. The nut-side ball screw groove 8 has the same lead as the shaft-side ball screw groove 7. Therefore, when the screw shaft 2 is inserted radially inside the nut 3, the shaft-side ball screw groove 7 and the nut-side ball screw groove 8 are disposed so as to face each other in the radial direction, thereby forming a spiral load path 5. The nut-side ball screw groove 8 has a single thread, similar to the shaft-side ball screw groove 7. The cross-sectional groove shape of the nut-side ball screw groove 8 is a gothic arch groove or a circular arc groove, similar to the shaft-side ball screw groove 7. For example, the nut-side ball screw groove 8 has a length of less than one revolution (for example, 0.6 to 0.8 revolutions) in the helical direction in which the nut-side ball screw groove 8 is formed. The circulation groove 9 is a groove connecting both ends of the nut-side ball screw groove 8, and has a substantially S-shape when viewed in the radial direction. As shown in FIG. 2, the circulation groove 9 has a groove depth that allows the balls 4 moving in the circulation groove 9 to climb over the threads of the shaft-side ball screw groove 7. In other examples, nuts of various shapes different from the above examples can be applied.

[0045] In this example, the nut 3 is configured to have a tubular (for example, cylindrical) shape as a whole by combining a workpiece 10, a holder 11, a reinforcing member 12, and a key 13.

[0046] The formed member 10 is a member formed by a hydroforming method described below. In one example, the formed member 10 is a thin-walled member made of metal (e.g., bearing steel (SUJ2)) and has a substantially cylindrical shape. Alternatively, the formed member 10 is made of another material. Also, alternatively, the formed member 10 has a shape other than a cylindrical shape. In one example, the formed member (cylindrical member) 10 has a nut-side ball screw groove 8 and a circulation groove 9 on its inner circumferential surface. The outer circumferential surface of the cylindrical member 10 has a shape such that the inner circumferential surface of the cylindrical member 10 is offset radially outward by the wall thickness of the cylindrical member 10. 8, the cylindrical member 10 has a spiral protruding portion 14a that protrudes radially outward compared to the surrounding portion on a portion of its outer peripheral surface located radially outside the nut-side ball screw groove 8, and also has a protruding portion 14b that protrudes radially outward compared to the surrounding portion and has a substantially S-shape when viewed in the radial direction on a portion located radially outside the circulation groove 9. Furthermore, the portion of the inner peripheral surface of the cylindrical member 10 that is outside the nut-side ball screw groove 8 and the circulation groove 9, and the portion of the outer peripheral surface of the cylindrical member 10 that is outside the protruding portions 14a, 14b are configured by cylindrical surfaces that are coaxially arranged with each other.

[0047] In the structure of this example, the cylindrical member 10 has a cylindrical portion 15 at the other axial end, which is a portion where the nut-side ball screw groove 8, the circulation groove 9, and the protruding portions 14a, 14b are not formed (see FIGS. 5 and 8). Note that such a cylindrical portion is not limited to the other axial end of the cylindrical member, but can also be provided at one axial end of the cylindrical member, or it may be possible not to provide a cylindrical portion at either of the axial ends of the cylindrical member.

[0048] The nut-side ball screw groove 8 is a portion where the plurality of balls 4 roll while receiving a compressive load. For this reason, in this example, the metallic material constituting the cylindrical member 10 is a metallic material, such as bearing steel, that has excellent durability against rolling fatigue and rolling friction.

[0049] 3, the holder 11 is configured in a cylindrical shape and holds the tubular member 10 on its radially inner side via a reinforcing member 12 and a key 13. The holder 11 includes a cylindrical tubular portion 17, inward flange portions 18a and 18b that protrude radially inward from both axial ends of the tubular portion 17, and an outward flange portion 19 that protrudes radially outward from one axial end of the tubular portion 17.

[0050] As shown in Figure 4 in particular, the cylindrical portion 17 has an outer key groove 20 that extends in the axial direction at one location on its inner peripheral surface. The outer key groove 20 is provided over the entire axial length of the inner peripheral surface of the cylindrical portion 17 and has a rectangular cross-sectional shape. The radially outer half of a metal key 13 that is shaped like a square pillar is tightly engaged with the outer key groove 20. In other words, in this state, the radially inner half of the key 13 protrudes radially inward beyond the portion of the inner peripheral surface of the cylindrical portion 17 that is not engaged with the outer key groove 20.

[0051] The outward flange 19 has mounting holes 21 that penetrate the holder 11 in the axial direction at multiple locations around the circumference. When using the ball screw device 1 of this example, the holder 11 is connected and fixed to a member that rotates or moves linearly together with the nut 3 using bolts that are inserted into or screwed into the mounting holes 21.

[0052] In this example, the holder 11 is formed cylindrically by combining a pair of semi-cylindrical metal holder elements 16. The pair of holder elements 16 are joined and fixed to each other by an appropriate method such as adhesive bonding, welding, or crimping. The outer keyway 20 is formed to bridge the inner circumferential surfaces of the pair of holder elements 16. When implementing the present invention, the type of material constituting the holder elements 16 is not particularly limited as long as the strength level required for the holder 11 is satisfied and the formability of the holder elements 16 is ensured. By using a member made of a material (such as cast steel, die-cast aluminum alloy, ceramics, or an injection-molded polymer member) that is cheaper than metal materials such as bearing steel for the holder element 16, the material cost of the holder element 16 can be reduced.

[0053] The reinforcing member 12 is a metal member that prevents deformation of the tubular member 10 when the ball screw device 1 is in use. That is, when the ball screw device 1 is in use, radial loads and thrust loads act on the nut-side ball screw groove 8 provided on the inner peripheral surface of the tubular member 10 from the plurality of balls 4. Therefore, it is necessary to prevent deformation of the tubular member 10, which is a thin-walled member having a substantially cylindrical shape, due to these loads. For this reason, in this example, the reinforcing member 12 is arranged so as to fill as tightly as possible the gap that exists between the outer peripheral surface of the tubular member 10 and the inner peripheral surface of the tubular portion 17 of the holder 11. This allows the reinforcing member 12 to support the radial load and thrust load acting on the nut-side ball screw groove 8, thereby reinforcing the tubular member 10.

[0054] In this example, the reinforcing material 12 is used as a molding die 30 when the cylindrical member 10 is formed by a hydroforming method, as will be described later. In other words, in this example, the molding die 30 when the cylindrical member 10 is formed by a hydroforming method is used as the reinforcing material 12.

[0055] In one example, the reinforcing member 12 is cylindrical. In another example, the reinforcing member 12 has a shape other than a cylinder. In one example, the reinforcing member 12 is provided so as to extend over the entire circumferential direction. In another example, the reinforcing member 12 is provided so as to extend over a portion of the circumferential direction. In another example, the reinforcing member 12 has a plurality of elements arranged side by side in the circumferential direction. The reinforcing member 12 is arranged so as to fill the gap between the outer circumferential surface of the tubular member 10 and the inner circumferential surface of the tubular portion 17 of the holder 11 as tightly as possible, and is sandwiched from both axial sides by a pair of inward flanges 18a, 18b of the holder 11.

[0056] At least a portion of the inner surface (inner circumferential surface) of such a reinforcing member 12 has an inner surface (forming circumferential surface) 23 facing the outer surface of the tubular member 10. The forming circumferential surface 23 is a circumferential surface for forming the outer circumferential surface of the tubular member 10 when the tubular member 10 is formed by a hydroforming method. Such a forming circumferential surface 23 has a shape that substantially matches the outer circumferential surface of the tubular member 10. In one example, the outer surface of the tubular member 10 has a convex shape 41, and the inner surface 23 of the reinforcing member 12 has a concave shape 42 that substantially matches the convex shape of the tubular member 10. At least a portion of the inner surface 23 of the reinforcing member 12 has a contour that substantially follows the contour of the outer surface of the tubular member 10. In an axial cross section, the contour of the outer surface of the tubular member 10 and the contour of the inner surface 23 of the reinforcing member 12 have curved shapes that substantially match each other. In a cross section intersecting the axial direction, the contour of the outer surface of the tubular member 10 and the contour of the inner surface 23 of the reinforcing member 12 have curved shapes that substantially match each other. For example, the inner surface (forming peripheral surface) 23 has a shape that is substantially the same as the inner peripheral surface of the cylindrical member 10, offset radially outward by the wall thickness of the cylindrical member 10.

[0057] The reinforcing member 12 also has an inner key groove 24 (see FIG. 9) extending in the axial direction at one location on its outer circumferential surface. The inner key groove 24 is provided over the entire axial length of the outer circumferential surface of the reinforcing member 12 and has a rectangular cross-sectional shape. The radially inner half of the key 13 is engaged with the inner key groove 24 without any rattle. This regulates the circumferential position of the reinforcing member 12 relative to the holder 11. The portion of the outer circumferential surface of the reinforcing member 12 that is separated from the inner key groove 24 has a shape (cylindrical surface shape) that matches the portion of the inner circumferential surface of the tubular portion 17 of the holder 11 that is separated from the outer key groove 20.

[0058] The reinforcing member (third member) 12 has a laminated structure (laminate) in which multiple plates (plates 22a, 22b) are stacked in the axial direction. In one example, the laminate 12A has an inner surface 23 facing the outer surface of the cylindrical member (second member) 10, and the inner surface 23 of the laminate 12A has a shape (42) corresponding to the shape (41) of the outer surface of the cylindrical member 10. In this example, the reinforcing member 12 is configured into a cylindrical shape by stacking multiple (N plates (N: a natural number)) flat plate-like plates 22a, 22b each having an inner circumferential surface 35 ( FIG. 9 ). That is, each of the plates 22a, 22b has a shape (inner circumferential surface shape and outer circumferential surface shape) that resembles a cross-section of the cylindrical reinforcing member 12 taken along an imaginary plane perpendicular to the central axis of the reinforcing member 12. The multiple plates (22a, 22b) in the reinforcing member 12 (laminate 12A) include multiple annular plates. The inner peripheral surfaces 35 of the multiple annular plates have substantially the same circumferential shape and / or different circumferential shapes (FIG. 9). The forming peripheral surface 23 is formed by combining the inner peripheral surfaces 35 of multiple plate materials 22a, 22b. Each of the plate materials 22a, 22b has a rectangular notch 25 corresponding to a phase alignment engagement portion at one circumferential position on the outer peripheral surface. The multiple plates (plate materials 22a, 22b) in the reinforcing material 12 have phase alignment portions (e.g., flat portions, grooves, curved portions, holes, notches) 25 provided at specific circumferential positions. The inner keyway 24 is formed by combining the notches 25 of the multiple plate materials 22a, 22b. When implementing the present invention, the phase alignment engagement portion may be, for example, an insertion hole for inserting a pin or the like.

[0059] In this example, each of the plates 22a and 22b is fabricated by press-punching or laser cutting a metal plate. Therefore, the cross-sectional shape of the inner peripheral surface of each of the plates 22a and 22b is a linear shape extending in the axial direction, as shown in FIG. 6 . When implementing the present invention, the type of material constituting the plates 22a and 22b is not particularly limited as long as the required reinforcement level of the reinforcing member 12 is met and the formability of the plates 22a and 22b is ensured. However, to reduce the material cost of the reinforcing member 12, it is preferable to use plates 22a and 22b made from a material (such as steel, light metal, ceramics, or polymeric material) that is less expensive than the metal material, such as bearing steel, constituting the tubular member 10. In other words, it is preferable to adopt a configuration in which the tubular member 10 and the plates 22a and 22b are made from different materials. The material of the reinforcing member 12 (laminated body 12A) is different from the material of the tubular member 10.

[0060] In this example, the axial cross-section of the inner peripheral surface of each of the plate members 22a and 22b has a linear shape. For example, the linear shape extends in the axial direction. Alternatively, the linear shape extends in a direction inclined relative to the axial direction. In another example, the axial cross-section of the inner surface of each of the plate members 22a and 22b has a shape different from a linear shape (e.g., an uneven shape or a curved shape). In one example, the inner surface of the reinforcing member 12 (laminated body 12A) has multiple steps (multiple corners, multiple fine protrusions) 45, each of which is based on the difference in inner surface height between two adjacent plates. At least some of the multiple steps 45 extend in the circumferential direction. The protruding portions (corners, peaks) 46 of the multiple steps 45 correspond to the edges of the multiple plates. In the axial cross-section, a line connecting the protruding portions (corners, peaks) 46 of the multiple steps 45 has a curved shape that substantially matches the curved shape of the contour of the outer surface of the tubular member 10. In one example, the reinforcing material 12 employs the following configuration to ensure the shape accuracy of the forming peripheral surface 23. That is, the multiple plate materials (22a, 22b) of the reinforcing material 12 include multiple plate materials with different thicknesses. The multiple plate materials (22a, 22b) of the reinforcing material 12 have a first plate and a second plate with a thickness different from that of the first plate. In this example, the multiple plate materials (22a, 22b) have multiple thicknesses that are different from each other and set according to the axial positions of the plate materials 22a, 22b. The number of different plate thicknesses can be 2, 3, 4, 5, 6, 7, 8, 9, 10, or more.

[0061] Specifically, of the multiple (N) plate materials 22a, 22b constituting the reinforcing member 12, at least the plate materials arranged around the protruding portions 14a, 14b of the tubular member 10, specifically the first to (N-1)th plate materials 22a counting from one axial side, have a sufficiently small thickness Ta (see FIGS. 5 and 6). This reduces the radial step between the inner peripheral surfaces of axially adjacent plate materials 22a, thereby ensuring the shape accuracy of the portion of the forming peripheral surface 23 that mates with the protruding portions 14a, 14b. In other words, the portion of the forming peripheral surface 23 that mates with the protruding portions 14a, 14b approximates a smooth curved surface. The (N-1)th plate material 22a counting from one axial side is, in other words, the second plate material 22a counting from the other axial side. Furthermore, each of the first to (N-1)th plate materials 22a counting from one side of the axial direction has an inner peripheral surface shape corresponding to the axial position at which it is located, but in this example, for convenience, the common symbol "22a" is used to refer to these plate materials.

[0062] The smaller the thickness Ta of the plate material 22a, the better the shape accuracy of the portions of the forming circumferential surface 23 that align with the protruding portions 14a, 14b of the tubular member 10. Therefore, the thickness Ta of the plate material 22a can be appropriately set in accordance with the shape accuracy required of the portions of the forming circumferential surface 23 that align with the protruding portions 14a, 14b of the tubular member 10.

[0063] Furthermore, in this example, of the multiple (N) plate materials 22a, 22b constituting the reinforcing member 12, only one plate material 22b is arranged around the cylindrical portion 15 of the tubular member 10, namely, the Nth plate material 22b counting from one axial side, i.e., the plate material 22b located closest to the other axial side. The thickness Tb (see FIG. 5 ) of this plate material 22b is sufficiently larger than the thickness Ta of the plate material 22a (Tb>>Ta) and, in the illustrated example, is slightly larger than the axial dimension of the cylindrical portion 15. The outer peripheral surface of the cylindrical portion 15 is formed by a cylindrical surface whose cross-sectional shape does not change in the axial direction. Therefore, even if only one plate material 22b is arranged around the cylindrical portion 15, the shape accuracy of the portion of the forming peripheral surface 23 that matches the outer peripheral surface of the cylindrical portion 15 can be improved. Thus, in this example, by only one plate material 22b being arranged around the cylindrical portion 15, the number of plate materials constituting the reinforcing member 12 is reduced. However, when implementing the present invention, a plurality of plate materials may be arranged around the cylindrical portion 15. In this case, for example, the thickness of each of these plate materials may be the same as or greater than Ta.

[0064] The plurality of balls 4 are each made of steel or ceramics and are arranged so as to be able to roll in the load path 5 and the circulation groove 9. The balls 4 arranged in the load path 5 roll while being subjected to a compressive load, whereas the balls 4 arranged in the circulation groove 9 roll by being pushed by the following balls 4 without being subjected to a compressive load.

[0065] As can be seen from the above explanation, in this example, the thickness Ta of the plate material 22a arranged at the axial position corresponding to the portion where the balls 4 of the nut 3 are arranged is made thinner than the thickness Tb of the plate material 22b arranged at the axial position corresponding to the portion where the balls 4 of the nut 3 are not arranged (Ta< <Tb)。

[0066] In this example, when manufacturing the nut 3 to produce the ball screw device 1, first, a metallic, thin-walled, cylindrical tubular material 26 as shown in FIG. 7 is prepared. Then, this tubular material 26 is formed into a tubular member 10 as shown in FIG. 8 by a hydroforming method. In this example, a hydroforming device 27 as shown in FIGS. 9 and 10 is used for this process. The manufacturing method includes the steps of preparing a forming die (cylindrical forming die) 30 having a laminate 12A in which multiple plates are axially stacked, placing a workpiece (the tubular material 26) inside the forming die 30, applying hydrostatic pressure to the inner surface of the workpiece 26 to plastically deform the workpiece 26 toward the inner surface of the forming die 30, and assembling a part using multiple elements including the plastically deformed workpiece 26 and the forming die (laminate) 30.

[0067] The hydroforming device 27 includes an outer cylindrical member 28, a pair of lids 29a, 29b, and a forming die 30 corresponding to a hydroforming die.

[0068] The outer cylindrical member 28 is cylindrical and has a key retaining groove 31 extending in the axial direction at one location on the inner peripheral surface. The key retaining groove 31 is provided over the entire axial length of the inner peripheral surface of the outer cylindrical member 28 and has a rectangular cross-sectional shape.

[0069] Each of the pair of lid bodies 29a, 29b is configured in a disk shape and has a through-hole 32 that passes through the radial center in the axial direction. The pair of lid bodies 29a, 29b are arranged on both axial sides of the outer cylindrical member 28.

[0070] The forming die 30 is made up of the reinforcing material 12 (laminate 12A) which is a component of the nut 3 to be manufactured. The forming die (laminate) 30 has an inner surface (inner peripheral surface) for forming.

[0071] When the tubular blank 26 is molded into the tubular member 10 using the hydraulic molding device 27, first, a cylindrical molding die 30 (reinforcement member 12) is formed by stacking a plurality of plate materials 22a, 22b, and this molding die 30 (reinforcement member 12) is then positioned radially inside the outer tubular member 28 without any radial play. In this state, the radially outer portion of the key 13 is engaged with the key retaining groove 31, and the radially inner portion of the key 13 is engaged with the inner key groove 24 of the molding die 30 (reinforcement member 12). This regulates the circumferential position of the molding die 30 (reinforcement member 12) relative to the outer tubular member 28. Furthermore, when stacking multiple plate materials 22a, 22b to form a cylindrical molding die 30 (reinforcement material 12), if the notches 25 of each of the plate materials 22a, 22b are engaged with the radially inner portion of the key 13, the circumferential phase alignment of the plate materials 22a, 22b can be easily performed.

[0072] Next, the cylindrical material 26 is placed radially inside the molding peripheral surface 23 provided on the inner peripheral surface of the molding die 30 (reinforcement material 12).

[0073] Next, as shown in FIG. 10 , the openings at both axial ends of the tubular blank 26 are closed with a pair of lids 29 a, 29 b. In this state, a liquid is filled into the radially inside of the tubular blank 26 through the through-holes 32 of the lids 29 a, 29 b. The pressure of the liquid (liquid pressure) is then applied to the inner circumferential surface of the tubular blank 26, thereby plastically deforming the tubular blank 26 radially outward until it forms a shape that conforms to the forming circumferential surface 23, thereby forming the tubular member 10. Note that when practicing the present invention, a through-hole for supplying a liquid to the radially inside of the tubular blank 26 may be provided in only one of the pair of lids.

[0074] 11, the assembled tubular member 10, forming die 30 (reinforcement material 12), and key 13 are then extracted in the axial direction from the radially inner side of the outer cylindrical member 28. Then, a pair of holder elements 16 are assembled to form a holder 11, and at the same time, the assembled tubular member 10, forming die 30 (reinforcement material 12), and key 13 are held radially inside the holder 11 to form the nut 3.

[0075] 2, the screw shaft 2 is inserted radially inside the nut 3 manufactured in this way, thereby forming a spiral load path 5 between the outer peripheral surface of the screw shaft 2 and the inner peripheral surface of the nut 3. At the same time, a plurality of balls 4 are rollably arranged in the load path 5 and the circulation groove 9, thereby forming the ball screw device 1.

[0076] According to the hydroforming method of this example as described above, the manufacturing cost of the forming die 30 (reinforcement material 12) can be reduced. That is, in this example, the forming die 30 (reinforcement material 12) is formed by stacking a plurality of flat plate-shaped plate materials 22a, 22b each having an inner peripheral surface, and the forming peripheral surface 23 is formed by combining the inner peripheral surfaces of these plate materials 22a, 22b. Meanwhile, each of the plate materials 22a, 22b can be manufactured at a relatively low cost by subjecting a metal plate to a press punching process or a laser cutting process. Therefore, in this example, the cost of forming the forming peripheral surface 23 can be reduced, and as a result, the manufacturing cost of the forming die 30 (reinforcement material 12) can be reduced.

[0077] Furthermore, in this example, the manufacturing cost of the nut 3 can be reduced. That is, the nut-side ball screw groove 8 provided on the inner peripheral surface of the nut 3 is the portion where the plurality of balls 4 roll while receiving a compressive load. For this reason, the nut-side ball screw groove 8 needs to be formed using a metal material, such as bearing steel, that has excellent durability against rolling contact fatigue and rolling friction. However, if the entire nut were formed using such a metal material, the material cost of the nut would increase. In contrast, in this example, the nut-side ball screw groove 8 is provided on the inner peripheral surface of the tubular member 10, which is a thin-walled member having a substantially cylindrical shape. For this reason, a material, such as bearing steel, that has excellent durability against rolling contact fatigue and rolling friction need only be used for the tubular member 10. Therefore, the material cost of the nut 3 can be reduced, and from this perspective, the manufacturing cost of the nut 3 can also be reduced.

[0078] Furthermore, in this example, as described above, the manufacturing cost of the reinforcing member 12 (forming die 30) can be reduced. That is, in order to firmly support the radial load and thrust load acting on the nut-side ball screw groove 8, the reinforcing member must be arranged so as to densely fill the complex-shaped gap that exists between the outer peripheral surface of the cylindrical member 10 and the inner peripheral surface of the cylindrical portion 17 of the holder 11. Constructing such a reinforcing member as a single component and ensuring sufficient durability increases the material and molding costs of the reinforcing member. In contrast, in this example, the reinforcing member 12 (forming die 30) is formed by stacking multiple plate materials 22a and 22b. Each of the plate materials 22a and 22b can be manufactured at relatively low cost by subjecting a metal plate to press-punching or laser cutting. This reduces the manufacturing cost of the reinforcing member 12 (forming die 30). Therefore, this also reduces the manufacturing cost of the nut 3.

[0079] Furthermore, in this example, the molding die 30 used when forming the cylindrical member 10 by the hydroforming method is used as the reinforcing member 12 that constitutes the nut 3. This makes it possible to easily assemble the nut 3, which also reduces the manufacturing cost of the nut 3.

[0080] In the above-described embodiment, the mechanical part manufactured using the hydroforming method of the present invention is a nut that constitutes a ball screw device. However, the mechanical part can be various other mechanical parts, such as an outer ring that constitutes a radial rolling bearing or a steering column that constitutes a steering device. When the mechanical part is an outer ring that constitutes a radial rolling bearing, the formed member (cylindrical member) has an outer ring raceway on its inner peripheral surface.

[0081] Furthermore, when carrying out the manufacturing method of the mechanical component of the present invention, after the final product, the molded member, is formed by the hydroforming method, the mold may be removed from around the molded member; in other words, the mold does not need to be used as a reinforcing material.

[0082] In one embodiment, the hydroforming method includes the steps of stacking a plurality of flat plate-shaped sheet materials each having an inner peripheral surface to obtain a forming mold having a forming peripheral surface on the inner peripheral surface, placing a material radially inward of the forming peripheral surface of the forming mold, and applying hydrostatic pressure to the inner peripheral surface of the material to plastically deform the material radially outward until it assumes a shape that conforms to the forming peripheral surface.

[0083] In one embodiment, a method for manufacturing a mechanical component is a method for manufacturing a mechanical component including a formed member, and is manufactured using the above-described hydroforming method.

[0084] In one aspect of the method for manufacturing a mechanical part, the mechanical part further includes a holder that holds the molded member radially inward, and a reinforcing material arranged between the outer peripheral surface of the molded member and the inner peripheral surface of the holder.

[0085] In one aspect of the method for manufacturing a mechanical component, the mechanical component is a nut that constitutes a ball screw device, and the workpiece has a nut-side ball screw groove on its inner circumferential surface.

[0086] In one aspect of the method for manufacturing a mechanical component, the mechanical component is an outer ring constituting a radial rolling bearing, and the workpiece has an outer ring raceway on its inner peripheral surface.

[0087] In one aspect of the method for manufacturing a mechanical component, the mechanical component is a steering column that constitutes a steering device.

[0088] In one embodiment, the method for manufacturing a mechanical device targets the manufacture of a mechanical device having a mechanical component. In one embodiment, a method for manufacturing a mechanical device includes manufacturing the mechanical component by the method for manufacturing a mechanical component of the present invention.

[0089] In one embodiment, the method for manufacturing a vehicle is directed to manufacturing a vehicle having a mechanical component. In one embodiment, a method for manufacturing a vehicle includes manufacturing the mechanical component by the method for manufacturing a mechanical component of the present invention.

[0090] In one embodiment, the ball screw device includes a nut having a nut-side ball screw groove on its inner peripheral surface, a screw shaft having a shaft-side ball screw groove on its outer peripheral surface, and a plurality of balls arranged between the nut-side ball screw groove and the shaft-side ball screw groove. The nut comprises a metal formed member having the nut-side ball screw groove on its inner surface, a holder that holds the tubular member radially inward, and a reinforcing material arranged between the outer surface of the tubular member and the inner surface of the holder. The reinforcing member is formed by stacking a plurality of flat plate-shaped plates each having an inner peripheral surface. The inner peripheral surface of the reinforcing member has a shape that matches the outer peripheral surface of the workpiece.

[0091] In one aspect of the ball screw device, the workpiece and each of the plurality of plate materials are made of different materials.

[0092] In one aspect of the ball screw device, the inner peripheral surface of the reinforcing member has a shape such that the inner peripheral surface of the formed member is offset radially outward by an amount equivalent to the thickness of the formed member.

[0093] In one aspect of the ball screw device, the thickness of the plate material varies depending on the axial position of the plate material.

[0094] In this case, for example, the thickness of the plate material arranged at an axial position corresponding to the portion of the nut where the balls are arranged is thinner than the thickness of the plate material arranged at an axial position corresponding to the portion of the nut where the balls are not arranged.

[0095] In one embodiment, the mechanical device includes a ball screw device, which is the ball screw device of the present invention.

[0096] In one embodiment, a vehicle is provided with a ball screw device, which is the ball screw device of the present invention.

[0097] In one embodiment, the hydroforming mold is configured by stacking a plurality of flat plate-shaped plates each having an inner peripheral surface, and the inner peripheral surface has a forming peripheral surface.

[0098] In one aspect of the hydroforming die, each of the plurality of plate materials includes a phase-aligning engaging portion for aligning the phases of the plurality of plate materials relative to one another in the circumferential direction.

[0099] The technical scope of the present invention is not limited to the scope of the embodiments. Various modifications or improvements can be made to the embodiments. Forms incorporating such modifications or improvements can also be included in the technical scope of the present invention. Furthermore, the present invention is not limited to the described embodiments, and any combination of these configurations may be used.

[0100] The mechanical part can be applied to machines with rotating parts, various manufacturing equipment, and rotation support parts of linear motion devices such as actuators (combinations of linear guide bearings and ball screws, XY tables, etc.). The mechanical part can also be applied to steering devices such as wipers, power windows, electric doors, electric seats, steering columns (e.g., electric tilt-telescopic steering columns), universal joints, intermediate gears, rack-and-pinions, electric power steering devices, and worm reducers. Furthermore, the mechanical part can be applied to various vehicles such as automobiles, motorcycles, and trains. This configuration can be suitably applied to any mechanical part that has molded elements, leading to cost reduction. [Explanation of symbols]

[0101] 1. Ball screw device 2 screw shaft 3 nuts 4 balls 5 Load path 7. Ball screw groove on shaft side 8 Nut side ball screw groove 9 Circulation groove 10 Molded member (second member, cylindrical member) 11 Holder (first member) 12 Reinforcement material (third member) 12A laminate 13 keys 14a, 14b Overhang 15 Cylindrical part 16 Holder element 17 Cylindrical part 18a, 18b Inward flange 19 Outward flange 20 Outer keyway 21 Mounting hole 22a, 22b Plate material (board) 23 Inner surface (molding surface) 24 Inner keyway 25 Notch (phase matching engagement part) 26 Material (Cylindrical Material) 27 Hydroforming Equipment 28 Outer cylinder member 29a, 29b lid body 30 mold 31 Key retaining groove 32 Through hole 100 nuts 101 Nut side ball screw groove 102 Circulation groove 103 Cylindrical member 104 Holder 105 Reinforcement 106a, 106b Overhang 107 Holder element 108 Cylindrical material 109 Hydroforming Equipment 110 Molding mold 111a, 111b Lid body 112a, 112b molded element 113 Surrounding surface for molding 114 Through hole 115 Through hole

Claims

1. Nut and A screw shaft, a plurality of balls disposed between the nut and the screw shaft; Equipped with The nut is A first member disposed around the screw shaft; a second member disposed between the screw shaft and the first member; a third member disposed between the first member and the second member; and the third member has a stack of plates stacked in the axial direction, the laminate has an inner surface facing the outer surface of the second member; The inner surface of the laminate has a plurality of steps, each step being based on the difference in inner surface height between two adjacent plates. Ball screw device.

2. the outer surface of the second member has a convex shape; the inner surface of the laminate has a concave shape that substantially matches the convex shape of the second member; The ball screw device according to claim 1 .

3. The plurality of plates in the stack includes a plurality of annular plates. The ball screw device according to claim 1 or 2.

4. The plurality of plates in the laminate have phase matching portions provided at specific positions in the circumferential direction. The ball screw device according to any one of claims 1 to 3.

5. The material of the third member is different from the material of the second member.

5. The ball screw device according to claim 1.

6. The inner surface of the laminate has a plurality of steps, each step being based on the difference in inner surface height between two adjacent plates. The ball screw device according to any one of claims 1 to 5.

7. The plurality of plates of the third member include a first plate and a second plate having a thickness different from that of the first plate. The ball screw device according to any one of claims 1 to 6.

8. A mechanical device comprising the ball screw device according to any one of claims 1 to 7.

9. A vehicle comprising the ball screw device according to any one of claims 1 to 7.

10. a step of preparing a mold having a laminate in which a plurality of plates are stacked in an axial direction, the laminate having an inner surface for molding; placing a workpiece inside the mold; applying a hydraulic pressure to an inner surface of the workpiece to plastically deform the workpiece toward the inner surface of the forming die; A process of assembling a part using a plurality of elements including the plastically deformed workpiece and the laminate, wherein the inner surface of the laminate has a plurality of steps each based on the difference in inner surface height between two adjacent plates; A method for manufacturing a machine component, comprising:

11. A machine component manufactured by the manufacturing method according to claim 10, The mechanical component includes the plastically deformed workpiece and the laminate used as the forming die during the plastic deformation of the workpiece.

12. A mechanical device comprising the mechanical component according to claim 11.

13. A vehicle comprising the mechanical component according to claim 11.

14. a step of manufacturing a machine part using the manufacturing method according to claim 10; mounting the mechanical component on a mechanical device; Equipped with Manufacturing methods for machinery and equipment.

15. a step of manufacturing a machine part using the manufacturing method according to claim 10; mounting the mechanical component on a vehicle; Equipped with Vehicle manufacturing method.

16. a step of preparing a cylindrical molding die having a laminate in which a plurality of plates are stacked in an axial direction, the laminate having an inner peripheral surface for molding; placing a workpiece inside the cylindrical forming die; a step of applying a hydraulic pressure to an inner surface of the workpiece to plastically deform the workpiece toward the inner peripheral surface of the cylindrical forming die; Equipped with the plurality of plates include (a) a first plate and a second plate having a thickness different from that of the first plate, and / or (b) a plurality of annular plates having inner circumferential surfaces with circumferential shapes different from each other; The inner peripheral surface of the laminated body has a plurality of steps, each of which is based on a difference in inner surface height between two adjacent plates, the contour of the outer surface of the plastically deformed workpiece has a curved shape; a line connecting the corners of the steps has a shape that substantially corresponds to the curved shape; Hydroforming method.

17. A cylindrical laminated body is provided in which a plurality of plates are laminated in the axial direction, the plurality of plates include (a) a first plate and a second plate having a thickness different from that of the first plate, and / or (b) a plurality of annular plates having inner circumferential surfaces with circumferential shapes different from each other; the laminate has an inner peripheral surface for molding; The inner peripheral surface of the laminated body has a plurality of steps, each of which is based on a difference in inner surface height between two adjacent plates, The plurality of steps are set so that a line connecting the plurality of corners of the plurality of steps substantially corresponds to a contour of an outer surface of the workpiece after forming. Mould for hydroforming.

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