METHOD FOR MANUFACTURING A TUBE-SHAPED COMPONENT

Abstract

Method for manufacturing a tubular component (10, 10A, 10B) comprising the following steps: Bending an axial end section of a tubular material (4) having a constant thickness in a direction transverse to an axial direction of the tubular material (4) in order to form a bent section (8) in the tubular material (4), Drawing the tubular material (4) to form a tubular component (10, 10A, 10B) having a non-constant thickness by drawing at least one section of the tubular material (4) except for the bent section (8) using a drawing device (20) having a punch (26) and a die (22) having a side surface (24) with a convex section (24a) and a concave section (24b) opposite the punch (26).

Description

[0001] The present invention relates to a method for producing a tubular component and in particular to a method for producing a tubular component having a non-constant thickness from a tubular material. Background of the invention

[0002] JP 2004-512963 A discloses a tubular component for use in a vehicle wheel rim having a non-constant thickness, as an example of a tubular component having a non-constant thickness made from a sheet material having a constant thickness. In the manufacturing process of the vehicle rim having a non-constant thickness according to JP 2004-512963 A, a cylindrical, hollow material having a constant thickness is produced from a flat sheet material having a constant thickness, and then the cylindrical material is formed into a cylindrical hollow component having a non-constant thickness by flow forming, such as flow forming, pressing, etc. The cylindrical component is roll-formed into a rim configuration, thus producing the vehicle rim having a non-constant thickness.

[0003] However, the following problems arise in the manufacturing process of the tubular component, which has a non-constant thickness, using flow forming: i) The equipment used in flow forming is expensive.

[0004] In flow forming, because a roller must be moved in two directions to press the tubular material against a mandrel – namely in an axial direction of the material and a thickness direction of the material – the flow forming system is expensive compared to a drawing machine, where a punch is only moved in one direction.

[0005] It was previously considered impossible to transform a tubular material into a component with a non-constant thickness using a drawing device for the following reasons: a) Since the punch does not move in a direction perpendicular to the axial direction of the tubular material, the thickness of the tubular material cannot be varied. Even if the punch were designed to move in a direction perpendicular to the axial direction of the tubular material, a large pressing force would be required to create a tubular material with a variable thickness. As a result, the mechanism would become complicated and expensive. b) Furthermore, if the tubular material is mounted on a drawing device which has a die and a punch, and it is drawn so that the thickness of the tubular material is changed to a non-constant thickness, the tubular material cannot be removed from the die because a section of the material enters a concave section of the die. c) Furthermore, in forming processes where the material is mounted in the drawing device, which has a die and a punch, and is then drawn so that the material thickness is changed to a non-constant thickness, in an example using a cylindrical, hollow material that does not have a flange engaging with the die, the material is drawn into the die by the punch and moved relative to the die. As a result, it is difficult to provide forming with high accuracy. The productivity of flow forming is low.

[0006] The productivity of flow forming is approximately one-third that of forming using a drawing machine. If a rim production line were branched into three auxiliary lines, each equipped with a flow forming machine, the productivity problem could be solved. However, since three groups of flow forming machines would be required, the equipment costs and the space required to arrange them would be three times greater than those of a single flow forming machine group. Therefore, the three-auxiliary-line system cannot be implemented.

[0007] iii) Drawing defects (cracks) caused by the flow forming roller remain on the surface of the material and reduce the quality of the design.

[0008] Further methods for manufacturing a tubular component according to the prior art are known from US 3 438 111 A, US 5 119 662 A, DE 199 10 474 A1, US 4 346 581 A and DE 31 10 756 A1. Summary

[0009] The object of the invention is to provide a method for manufacturing a tubular component which can achieve at least the advantage of (i) reducing plant costs, (ii) improving productivity and (iii) improving the quality of the design.

[0010] The object of the present invention is achieved by a method for manufacturing a tubular component with the features of claim 1.

[0011] Advantageous further developments according to the present invention are defined in the dependent claims. (1) According to the invention, a method for producing a tubular component with the features of claim 1 is provided. (2) Preferably the drawing step comprises the following steps: Fixing (setting) the tubular material to (in) the die; Operating the drawing device by moving one element of the punch and die relative to the other element of the punch and die; and Drawing the tubular material to form the tubular component, which is accompanied by a change in the diameter and thickness of the tubular material caused by the surface with a convex section and a concave section of the die and punch. (3) Preferably, the surface with a convex section and a concave section is formed by providing at least one convex section, which makes the space between the die and the punch narrower than the thickness of the tubular material, on the die in an axial direction of the die along the side surface of the die opposite the punch. (4) Preferably, in the drawing step after the production of the tubular component, which has a non-constant thickness, the tubular component is removed from the die by applying an axial force to the tubular component, so that the tubular component is deformed in a radial direction. (5) Preferably, the surface with a convex section and a concave section is formed by providing at least one section which makes the space between the die and the punch narrower than the thickness of the tubular material on the die in a circumferential direction of the die along the side surface of the die opposite the punch. (6) Preferably, the step of bending an axial end section of the tubular material in a direction transverse to an axial direction of the tubular material is provided in order to form the bent section in the tubular material before the drawing step, and wherein in the drawing step the bent section of the tubular material is brought into axial contact with the die and then the drawing is carried out. (7) Preferably, in the drawing step, the bent section of the tubular material is axially engaged with the die and clamped between the die and a pressing component, and then at least one section of the tubular material is drawn, with the exception of the bent section. (8) Preferably the method further comprises a step for producing the tubular material from a flat material which has a constant thickness before the drawing step. (9) Preferably the method further comprises a step for roll forming the tubular material which has a non-constant thickness in order to form a vehicle wheel rim design after the drawing step.

[0012] According to the inventive method, since the tubular material is formed into the tubular component, which has a non-constant thickness, by drawing, the setup and the step of conventional flow forming are not required. As a result, the aforementioned problems (i), (ii) and (iii) that exist in flow forming are solved in the following ways (i), (ii) and (iii): (i) Since the conventional flow molding plant is replaced by the die and punch for drawing and the drawing device according to the present invention, and the combined cost of the die and punch for drawing and the drawing device is lower than that of the flow molding plant, the plant costs can be reduced. (ii) Since, in the step for producing the non-constant thickness of the material, the flow forming step is replaced by a drawing step performed by the drawing device according to the present invention, the time required for producing the non-constant thickness of the material can be reduced to approximately one-third of the time required for flow forming, thus improving productivity. If a step for producing the non-constant thickness of a cylindrical, hollow material is provided in a rim production line, three groups of flow forming units are required, which must be provided in the conventional line. However, since the three groups of flow forming units can be replaced by a single drawing device according to the present invention, the problems arising with regard to cost and the space required for arranging the equipment can be solved. (iii) Since flow forming is replaced by drawing using the punch and die, drawing defects (cracks) due to the flow forming roller do not occur on the surface of the material, thus improving the quality of the design.

[0013] According to the method described in the preceding subject matter (2), since the punch is moved axially relative to the die, thereby drawing the tubular material to be formed into a tubular component with a non-constant thickness, the movement of the punch relative to the die is only axial and is not accompanied by radial movement. Therefore, the drawing device can be used for the one-dimensional movement of the punch relative to the die. As a result, the forming time can be reduced and the plant costs can be lowered.

[0014] According to the method described in the preceding subject matter (3), since the surface with convex section and with concave section is formed on the die in the axial direction of the die along the side surface of the die opposite the punch by providing at least one convex section which makes a distance (space) between the die and the punch narrower than a thickness of the tubular material, a tubular component which has a thickness which changes in the axial direction can be produced.

[0015] According to the method described in the preceding subject matter (4), since, after the production of the tubular component which has a non-constant thickness, the tubular component is removed from the die by applying an axial force to the tubular component, so that the tubular component is deformed in a radial direction, it is not necessary for the die to be divided in a circumferential direction and an integral (one-piece) die can be used. As a result, the plant costs can be kept low compared to a case in which a circumferentially divided die is used, since a mechanism for moving the divided die elements in a radial direction is not required.Furthermore, no burr is created on the section of the drawn tubular component that corresponds to a section of the circumferentially subdivided die elements, and no machining is required to remove the burrs.

[0016] According to the method described in the preceding subject matter (5), since the surface with convex section and with concave section is formed on the die in the circumferential direction of the die along the side surface of the die opposite the punch, a tubular component having a thickness that changes in the circumferential direction can be produced by providing at least one convex section which makes a distance (space) between the die and the punch narrower than a thickness of the tubular material.

[0017] According to the method described in the preceding article (6), since the drawing step causes the bent section of the tubular material to engage axially with the die before the drawing is carried out, the material is prevented from being drawn into the die by the punch and from being moved relative to the die during the drawing, thus enabling forming with high accuracy.

[0018] According to the method of the preceding item (7), since the curved section is clamped between the die and the press part during drawing, it prevents the tubular material from being moved in the axial direction in which the punch pushes the tubular material.

[0019] According to the method of the foregoing subject matter (8), since the method includes a step for producing the tubular material from a flat material having a constant thickness prior to the drawing step, it is possible to produce a tubular material having a constant thickness.

[0020] According to the method described in the preceding subject matter (9), since the method includes a step for rolling the tubular material which has a non-constant thickness in order to form a vehicle wheel rim design after the drawing step, it is possible to produce a vehicle wheel rim which has a non-constant thickness and is lightweight. Brief description of the drawings Fig. Figure 1 is a process diagram illustrating a forming step for a bent section and a drawing step of a method for producing a tubular component according to a first embodiment of the present invention, wherein a step (a) represents a tubular material, a step (b) represents the tubular material after a curved section has been formed, wherein a left half of (b) is a sectional view of the material and a right half of (b) is a front view of the material, a step (c) represents a drawing step, wherein a left half of (c) represents the material before a drawing and a right half of (c) represents the material after the drawing, and a step (d) represents a tubular component after drawing, wherein a left half (d) is a sectional view of the component and a right half of (d) is a front view of the component, Fig. 1 is applicable in a second embodiment of the present invention if the relationship between the die and the punch is reversed; Fig. Figure 2 is a process diagram illustrating a manufacturing step for a tubular material of the method for manufacturing a tubular component according to the first embodiment of the present invention, wherein a step (a) represents a step to round off a sheet material having a constant thickness to form a rounded material, and then represents welding opposite ends of the rounded material together to produce a tubular material, and a step (b) represents a step to cut the tubular material to a predetermined length in order to produce the tubular material, Fig. 2 is applicable in the second embodiment of the present invention; Fig. Figure 3 is a process diagram illustrating a rolling forming step of the method for producing a tubular component according to the first embodiment of the present invention, wherein (a) a side view of an upper roll and a lower roll, between which a wall of the tubular component, having a non-constant thickness, is arranged and is roll-formed, (b) a front view of the upper roll and the lower roll, between which the wall of the tubular component, which has a non-constant thickness, is arranged and is roll-formed, and (c) represents the tubular component which has a rim design after roll forming, Fig. 3 is applicable in the second embodiment of the present invention; Fig. Figure 4 is a sectional view of a drawing device used in the method for producing a tubular component according to the first embodiment of the present invention, wherein a left half of Fig. 4 represents a state prior to drawing, in which the tubular material is inserted into the die, and a right half of Fig. 4 represents a state after the pulling, where Fig. 4 is applicable in the second embodiment of the present invention if the relationship between the die and the punch is reversed; Fig. Figure 5 is a partial sectional view of the punch, die, and tubular material of the method for producing a tubular component according to the first embodiment of the present invention, wherein a left half of Fig. 5 represents a state before the draw and a right half of Fig. 5 represents a state after pulling; Fig. Figure 6 is a sectional view of the die (outer die) from the perspective of an axial direction of the die of the method for producing a tubular component according to the first embodiment of the present invention; Fig. Figure 7 is a partial sectional view of a punch, a die, and a tubular material of a method for producing a tubular component according to a second embodiment of the present invention, wherein a left half of Fig. 7 represents a state before the draw and a right half of Fig. 7 represents a state after the draw; and Fig. Figure 8 is a sectional view of the die (inner die) from the perspective of an axial direction of the die of the method for producing a tubular component according to the second embodiment of the present invention. Detailed description

[0021] A method for manufacturing a tubular component according to the present invention is explained below with reference to the drawings.

[0022] Fig. 1 to 6 are applicable in a first embodiment of the present invention and Fig. 7 and Fig. 8 are applicable in a second embodiment of the present invention. Fig. 1 and Fig. 4 are applicable in the second embodiment of the present invention when a relationship between a die, a punch and a pressing component is changed, and Fig. 2 and Fig. 3 are also applicable to the second embodiment of the present invention.

[0023] Sections that are the same or similar in all embodiments of the present invention are designated by the same reference numerals in all embodiments of the present invention.

[0024] First, sections that are the same or similar in all embodiments of the present invention are described with regard to the Fig. 1 to 8 explained.

[0025] As in Fig. Figure 1 shows a method for producing a tubular component 10 according to the present invention. The tubular component 10 (10A, 10B), which has a non-constant thickness, is made from a tubular material 4. The tubular material 4 is made of metal, and the metal is, for example, steel, non-ferrous metal (including aluminum, magnesium, titanium, and alloys thereof), etc.The tubular component 10, which has a non-constant thickness, can be a first tubular component 10A with a wall having an inner surface and an outer surface, one of which has a convex section and a concave section and the other of which is a flat surface extending parallel to an axis of the tubular component, or can be a second tubular component 10B with a wall designed to curve in a direction perpendicular to an axis of the tubular component 10B by further rolling of the tubular component 10A.The tubular component 10A, which has a non-constant thickness, is, for example, a tubular component having an inner or outer surface section extending parallel to the axis of the tubular component, except for a bent section 8 after drawing. The tubular component 10B is, for example, a wheel rim used in a car, truck, bus, or industrial vehicle. The tubular component 10B is not limited to wheel rims. Furthermore, the tubular component 10 (10A, 10B) is not limited to a component having a circular cross-section; it can be a tubular component having a polygonal or elliptical cross-section.

[0026] As in Fig. As shown in Figure 1, the method for manufacturing a tubular component 10 has the following features: (a) a forming step for a bent section for bending an axial end section of the tubular material 4 in a direction transverse to an axial direction of the tubular material 4 in order to form a bent section 8 in the tubular material 4; and (b) a drawing step for producing the tubular material 10 (10A) having a non-constant thickness, using a drawing device 20 comprising a punch 26, a die 22 having a side surface 24 with a convex section and a concave section opposite the punch 26, and a pressing component 23.

[0027] The preceding step (b) comprises the following steps: causing the tubular material 4 to engage axially with the die 22 through the bent section 8; then moving the press component 23 relative to the die 22 in order to clamp the bent section 8 of the tubular material 4 between the press component 23 and the die 22; and then moving the punch 26 relative to the die 22 in order to draw out at least one section of the tubular material 4 except for the bent section 8 and to produce the tubular component 10 (10A).

[0028] In the drawing step (c) of Fig. 1 represents a left half of step (c) a step in which the bent section 8 of the tubular component 4 is clamped between the press component 23 and the die 22, and represents the right half of step (c) a step in which, by moving the punch 26 relative to the die 22 and by drawing the tubular material 4, the tubular material 4 was formed as the tubular component 10 (10a) which has a non-constant thickness.

[0029] If the tubular material 4 has a shape that corresponds to the bent section 8 and can engage with the die 22, for example if the tubular material is a cast component, it is not necessary to provide the forming step for the bent section.

[0030] Before the forming step for the curved section 8, as shown in Fig. Figure 2 shows that the method for manufacturing a tubular component includes a manufacturing step for a tubular material 4, which has a constant thickness, from a flat sheet material 2, which has a constant thickness. In the manufacturing step for a tubular material, as in step (a) of Fig. As shown in Figure 2, the flat sheet material (a rectangular material) is produced by drawing a straight sheet of constant thickness from a coil of sheet material and cutting the drawn-out straight sheet at predetermined intervals to produce a large number of sheets in succession. The flat material 2 is then rounded, and opposite ends of the rounded material are welded together by flash butt welding, butt welding, arc welding, etc. Finally, a burr from the welded section 6 is machined (butted), producing a tubular material 4 of constant thickness.

[0031] In the manufacturing step for a tubular material, as in step (b) of Fig. Figure 2 shows that the tubular material 4, which has a constant thickness, is produced by cutting a tubular material 2' at a predetermined length interval.

[0032] In the example where the curved section 8 is formed as in (b) of Fig. As shown in Figure 1, the forming step for a bent section is used before the drawing step. During the drawing step, the bent section 8 engages axially (in the axial direction) with the die 22 to axially position the tubular material 4, which has a constant thickness, relative to the die 22 and to prevent the tubular material 4 from moving axially relative to the die 22 during drawing. The angle of the bent section 8 can be between 0 degrees and 180 degrees inwards or outwards with respect to the axial direction of the tubular material 4. The larger the angle, the more effectively axial movement of the tubular material 4 relative to the die 22 can be prevented. The tubular material 4 can be fed to the drawing step without the bent section 8 being formed in the tubular material.

[0033] In the drawing step, the tubular material 4, which has a constant thickness (with the bent section 8), is inserted into the die 22 such that the tubular material 4 engages axially with the die 22 through the bent section 8. Then the drawing device 20 is operated, whereby the pressing component 23 and the punch 26 move relative to the die 22 only in the axial direction of the tubular material 4 (to approach the die). When the press component 23 and the punch 26 are moved relative to the die 22, the press component 23 first touches the bent section 8 of the tubular material 4 which is inserted in the die 22, clamping the bent section 8 between the press component 23 and the die 22 (that is, the bent section 8 of the tubular material 4 is pressed or pushed against the die 22 by the press component 23), and then the press component 23 stops.The punch 26 continues to move relative to the die 22 (approaching the die) only in the axial direction of the tubular material 4, whereby the section of the tubular material 4, with the exception of the curved section 8, is drawn through the surface with convex section and with concave section 24 of the die 22 and the punch 26, resulting in a change in the diameter and thickness of the tubular material 4.

[0034] While the tubular material 4 is being pulled, the tubular material 4 is elongated (stretched) in the axial direction of the tubular material 4.

[0035] In an example where the force required to pull is small, the press component 23 can be removed.

[0036] The drawing device 20 is installed in a press machine 30, as shown in Fig. Figure 4 shows that the press machine 30 comprises a frame 32, a piston drive unit 34 coupled to the frame 32, a piston 36 movable in a vertical direction by the piston drive unit 34, a base plate 38, a material support and ejection plate 40, and a plate drive unit 42 connected to the material support and ejection plate 40 and transmitting a material ejection force to the material support and ejection plate 40. The die 22 is attached to the base plate 38 or to a component attached to the base plate 38, and the punch 26 is attached to the piston 36 or to a component attached to the piston 36. When the piston drive device 34 is operated (that is, the press machine 30 is operated) to lower the piston 36, the punch 26 moves only in the axial direction of the tubular material 4 relative to the die 22 (that is, it moves closer to the die).

[0037] The piston drive unit 34 of the press machine 30 can be a hydraulic press unit using a hydraulic cylinder, a mechanical press unit using a motor and crankshaft, or a servo-driven press unit using a servo motor and threaded spindle. The plate drive unit 42 can be a hydraulic cylinder, a pneumatic cylinder, or a lifting mechanism using an electric motor.

[0038] The die 22 is fixed and the punch 26 is movable. As in (c) of Fig. As shown in Figure 1, the side surface of the die 22 opposite a projection 28 of the punch 26 is the surface 24 with a convex and a concave section. The surface 24 with a convex and a concave section is a surface whose space is not constant with respect to the projection 28 of the punch 26 (a space in one thickness direction of the tubular material 4, which has a constant thickness). To provide the space between the projection 28 of the punch 26 and the side surface of the die 22 opposite the projection 28 of the punch 26, the surface 24 with a convex and a concave section of the die 22 can be configured as follows: (a) by providing at least one convex section 24a which is convex to the projection 28 of the punch 26 relative to an adjacent section (that is, a concave section 24b) in an axial direction of the die along the side face of the die 22, as shown in Fig. 5 is shown; (b) by providing at least one convex section 24a which is convex to the projection 28 of the punch 26 relative to an adjacent section (that is, a concave section 24b) in a circumferential direction of the die along the side face of the die 22, as shown in Fig. 6 is shown; or (c) by combining points (a) and (b) above.

[0039] The projection of the convex section 24a is determined by the objective thickness of a corresponding section of the tubular component 10 and can be constant or variable within a region of each convex section 24a. Furthermore, in an example where a plurality of convex sections 24a are provided, the projections of the respective convex sections 24a are determined by the objective thicknesses of corresponding sections of the tubular component 10, and the projections of the respective convex sections 24a can be equal or unequal to each other. The convex section 24a is required to extend along at least one section of the side face of the die 22 opposite the projection 28 of the punch 26.

[0040] As in Fig. As shown in Figure 5, a convex section 24a and a concave section 24b are arranged in the axial direction of the die 22 along the side surface of the die. The concave section 24b is positioned in front of the punch 26 with respect to the direction of movement of the punch 26 during drawing and is adjacent to the convex section 24a. They are connected by a first inclined surface 24c1, which is not perpendicular to the axis of the die 22 and forms a section of the side surface of the die. Due to the inclined surface, which is not perpendicular to the axis of the die, the tubular component 10A is not adversely affected by the convex section 24a and can be removed uniformly from the die 22 when an ejection force is applied to the tubular component 10A by the material support and ejection plate 40.

[0041] Furthermore, in the axial direction of the die 22 along the side surface of the die, a convex section 24a and a concave section 24b, which is arranged in front of the material support and ejection plate 40 in a direction of movement of the material support and ejection plate 40 during the ejection of the tubular component 10 (10A) from the die 22 and which is adjacent to the one convex section 24a, are connected via a second inclined surface 24c2, which is not perpendicular to the axis of the die 22 and forms a section of the side surface of the die. Due to the inclined surface, which is not perpendicular to the axis of the die, the tubular component 10A is not adversely affected by the convex section 24a and can be removed uniformly from the die 22 when an ejection force is applied to the tubular component 10A by the material support and ejection plate 40.

[0042] The angles of the first inclined surface 24c1 and the second inclined surface 24c2, which are inclined with respect to the axial direction of the die 22 along the side surface of the die 22, are set at an angle equal to or less than preferably 60 degrees, and more preferably 45 degrees. The angle of inclination of each first inclined surface 24c1 may be constant or may change gradually. The angle of inclination of each second inclined surface 24c2 may be constant or may change gradually.

[0043] The punch 26 has the projection 28, which protrudes towards the die 22 at a front end section of the punch 26, which is moved towards the die 22, and the tubular material 4 is drawn through the projection 28.

[0044] The material support and ejection plate 40 receives (supports) the tubular material 4 (in the axial direction of the tubular material 4) from a direction opposite to the direction in which the punch 26 moves during drawing (the direction in which the punch 26 pushes the tubular material 4), so that the axial end section of the tubular material 4, opposite the bent section 8, extends axially more than an expected extension during drawing and is displaced from an expected position relative to the die 22. The axial length of the tubular material 4 is gradually extended as the tubular material 4 is drawn. The position of the material support and ejection plate 40 is controlled by the plate drive device 42. The material support and ejection plate 40 retracts in accordance with a change in the axial length of the tubular material 4.The material support and ejection plate 40 pushes the tubular material 4 in the axial direction with a constant force or with a substantially constant force during the pulling process. The load acting on the material support and ejection plate 40 can be controlled, or the extent of the displacement of the material support and ejection plate 40 can be controlled.

[0045] As in (c) of Fig. As shown in Figure 1, in the drawing step, after the punch 26 has been lowered and the tubular component 10 (10A) has been produced, the punch 26 is removed from the die 22. After the punch 26 has been removed from the die 22, or when the punch 26 is removed from the die 22, an axial force is applied by the material support and ejection plate 40 to the tubular component 10 (10A) in order to remove the tubular component 10 (10A) from the die 22. In a case where the tubular component 10 (10A) is a component for a vehicle wheel rim, the rate of change of the diameter of the tubular component 10 (10A) required to remove the tubular component 10 (10A) from the die 22 is at most approximately 1.2%, which is in the range of elastic deformation.Therefore, the tubular component 10 (10A) can be removed from the die 22 by elastic deformation of the tubular component 10 (10A) in a radial direction (i.e., in a thickness direction) by the axial force from the material support and ejection plate 40. The tubular component 10 (10A) can also be removed from the die 22 by plastic deformation of the tubular component 10 (10A) in the radial direction, even if the tubular component 10 (10A) is a component for a vehicle wheel rim.

[0046] The material support and ejection plate 40 pushes the tubular component 10 (10A) in the opposite direction to the direction in which the punch 26 moves during the drawing process (the direction in which the punch 26 pushes the tubular material 4). The axial force exerted by the material support and ejection plate 40 on the tubular component 10 (10A) when the tubular component 10 (10A) is removed is equal to or greater than the force required to deform the tubular component 10 (10A) in the radial direction, thereby removing the tubular component 10 (10A) when the material support and ejection plate 40 pushes the tubular component 10 (10A) in the axial direction. The force is much smaller than the pulling force with which the punch 26 pushes the tubular material 4 in the axial direction.Since it is not necessary to subdivide the die 22 in the circumferential direction of the die in order to remove the tubular component 10 (10A), the die 22 is not subdivided and is designed as an integral (one-piece) die.

[0047] The tubular component 10, which has a non-constant thickness, features a thick section (a section where the thickness is constant) and a thin section (a section where the thickness is reduced). The thick section of the tubular component 10 corresponds to a section where a large force (in the case of a vehicle rim, a curved section and a flange section of the rim) is applied during use of the final product. The thin section corresponds to a section where a small force (in the case of the vehicle rim, a section other than the curved section and the flange section of the rim) is applied during use of the final product. This design results in weight reduction, material savings, and cost reduction while maintaining the required strength and stiffness of the final product.

[0048] As in Fig. As shown in Figure 3, the method for manufacturing the tubular component 10 according to the present invention can include a roll forming step of the tubular component 10 (10A), which has a non-constant thickness, in order to form a vehicle wheel rim after the drawing step. A vehicle wheel rim having a non-constant thickness is an example of a tubular component 10 (10B) having a non-constant thickness.

[0049] The roll forming step is performed after axially opposite ends of the tubular component 10A, which has a non-constant thickness, have been flared (not shown). In the roll forming step, one wall of the tubular component 10A is clamped between a lower roll 31 and an upper roll 32, and then the rolls are rotated to transform the tubular component 10A into the tubular component 10B, which has a rim shape (design). The tubular component 10B is then formed into a rim end shape (design) using a stretching device and / or a shrinking device (to achieve a precise circular shape and rim profile).

[0050] The rim formed by the tubular component 10 (10B) has a flange section 10a, a seat section 10b, a side wall section 10c, a recess section 10d, a side wall section 10e, a seat section 10f, and a flange section 10g in that order from one axial end to the other axial end of the rim. A disc (not shown) is fitted into the rim and then welded to it, thus producing a wheel of welded construction. Curved sections are located between the aforementioned sections of the rim shown. Greater stresses are generated at the curved sections and the flange sections 10a and 10g, which are greater than the stresses generated at the other sections. Preferably, the thickness of the curved sections and the thickness of the flange sections 10a and 10g are greater than the thicknesses of the other sections.

[0051] When a tubular material 4 having a constant thickness has been formed as a wheel rim, the constant thickness of the tubular material was not usually transformed into a non-constant thickness by drawing. The tubular material having a constant thickness is usually fed, as is, to a rim forming forming step that uses roll forming. When it is necessary to transform the tubular material having a constant thickness into a tubular material having a non-constant thickness, other processes other than pressing have usually been used, and their use has not been considered as explained in the prior art, so that they have not actually been used.According to the present invention, the drawing step is inserted between the step to produce the tubular material 4 and the step to roll forming the tubular component 10 (10A), whereby the thickness of the tubular material 4 cannot be made constant without using a pressing process.

[0052] The following are explanations of the operational and technical advantages of the sections that are the same or similar in all embodiments of the present invention.

[0053] According to the present invention, since the tubular material 4, which has a constant thickness, is formed into the tubular component 10 (10A), which has a non-constant thickness, by drawing, it is not necessary to provide the equipment and flow forming step as in the usual flow forming process. As a result, the aforementioned problems (i), (ii), and (iii) that arise in flow forming are solved in the following ways (i), (ii), and (iii): (i) Since the conventional flow forming plant has been replaced by the die 22 and the punch 26 for drawing and by the drawing device 20 (the pressing device 30) in the present invention, and the combined cost of the die 22 and the punch 26 for drawing and the drawing device 20 (the pressing device 30) is lower than that of the flow forming plant, the plant costs can be reduced. (ii) Since, in the step for producing the thickness of the tubular material 4 in a non-constant manner, the usual flow forming step is replaced by a drawing step using the drawing device 20 (the press 30) according to the present invention, the time required for producing the thickness of the tubular material 4 in a non-constant manner can be reduced to approximately one-third of the time required for flow forming, thus increasing productivity. If a step for producing the thickness of a cylindrical, hollow material in a non-constant manner is provided in a rim production line, three groups of flow forming units must be provided in the usual rim production line. However, since the three groups of flow forming units are replaced by a single drawing device 20 according to the present invention, the problems arising from the cost and space required for arranging the units in flow forming can be solved. (iii) Since flow forming is replaced by drawing using the punch 26 and die 22, any drawing defects (cracks) due to the flow forming roller do not occur on the surface of the material and the quality of the design is improved.

[0054] Since the piston 26 is moved axially relative to the die 22, drawing the tubular material 4 to form the tubular component 10 (10A), which has a non-constant thickness, the movement of the ram 26 relative to the die 22 is only axial and not accompanied by radial movement. Therefore, the press 30 can be used for the one-dimensional movement of the piston 26 relative to the die 22. As a result, the forming time can be reduced and the plant costs can be lowered.

[0055] Since, after the production of the tubular material 10 (10A), which has a non-constant thickness, the tubular component 10 (10A) is removed from the die 22 by applying an axial force to it, causing the tubular component 10 (10A) to deform in the radial direction, an integral (one-piece) die that is not subdivided in a circumferential direction can be used as the die 22. As a result, the setup costs can be kept low compared to a case where a circumferentially subdivided die is used, since a mechanism for moving the subdivided die elements in a radial direction is not required. Furthermore, no burr is generated on a section of the drawn tubular component corresponding to a section of the circumferentially subdivided die elements, and no machining is required to remove burrs.

[0056] Since the drawing step causes the bent section 8 to engage axially with the die 22 and then the drawing is carried out, the tubular material 4 is prevented from moving in the direction in which it is forced by the punch 26, thus enabling forming with high accuracy.

[0057] Since the bent section 8 is clamped between the die 22 and the press component 23 during drawing, and then at least one section of the tubular material 4, which is different from the bent section 4, is drawn, the tubular material 4 is prevented from moving in the axial direction in which the tubular material 4 is forced by the punch 26, so that forming with high accuracy is possible.

[0058] Since the tubular material 4 is supported and drawn at the end section by the material support and ejection plate 40, it is further prevented that the tubular material is moved in the axial direction in which it is forced by the punch 26. Furthermore, controlling the extension of the tubular material 4 during drawing is straightforward.

[0059] Since the surface 24 with convex section and with concave section is formed by providing at least one convex section 24a, which makes a space between the die 22 and the punch 26 smaller than the thickness of the tubular material 4, on the die in the axial direction of the die 22 along the side surface of the die 22, the tubular component 10A, which has a thickness that changes in the axial direction of the tubular component, can be produced.

[0060] Since the surface 24 with convex section and with concave section is formed by providing at least one convex section 24a, which makes a space between the die 22 and the punch 26 smaller than the thickness of the tubular material 4, on the die in the circumferential direction of the die 22 along the side surface of the die 22, the tubular component 10A, which has a thickness that changes in the circumferential direction of the tubular component, can be produced.

[0061] Since the process for manufacturing the tubular component includes the step of roll forming the tubular component 10 (10A), which has a non-constant thickness, to form a vehicle wheel rim design after the drawing step, it is possible to produce a vehicle wheel rim that has a non-constant thickness and is lightweight.

[0062] The structures that are unique to each embodiment of the present invention are explained below. [First embodiment]

[0063] In the method for manufacturing the tubular component 10 according to the first embodiment of the present invention, as shown in Fig. 1 and Fig. As shown in Figure 5, the die 22 is formed from an outer die having a cylindrical bore 22a and an inner surface 22b. The inner surface 22b of the outer die is configured as surface 24 with a convex and a concave section. The punch 26 is configured as an inner punch that moves into or out of the cylindrical bore 22a of the outer die 22. The projection 28 is formed on an outer surface 26a of the inner punch.

[0064] As in Fig. As shown in Figure 5, a flange receiving section 22c, which can engage with the bent section 8 of the tubular material 4, is formed on an upper end section of the inner surface 22b of the outer die 22. The tubular material 4 is fixed (inserted) on (in) the outer die 22 such that the bent section 8 contacts and engages with the flange receiving section 22c.

[0065] The inner diameter of a section of the outer die 22, where the convex section 24a is provided, is larger before drawing than the outer diameter of a section of the tubular material 4, which differs from the bent section 8. Therefore, the tubular material 4 can be fixed (inserted) onto (into) the outer die 22 before drawing.

[0066] Before drawing, the outer diameter of the projection 28 of the inner punch 26 is larger than the inner diameter of the tubular material 4, which differs from the bent section 8. Therefore, a convex and a concave design of the surface 24 with a convex cut and a concave section of the die 22 can be transferred to the tubular material 4 by drawing it into the die 22.

[0067] The difference between the outer radius of the projection 28 of the inner punch 26 and the inner radius of the section of the outer die 22, where the convex section 24a is provided, is smaller than the thickness of the tubular material 4 before drawing. Therefore, the thickness of the tubular material 4 can be reduced by drawing on the convex section 24a.

[0068] When the punch 26 is moved into the cylindrical bore 22a of the outer die 22 by the drawing device 20 (the press 30), the projection 28 of the punch 26 draws the tubular material 4, thereby increasing the diameter of the tubular material 4, and the section of the outer die 22 where the convex section 24a is provided reduces the thickness of the tubular material 4.

[0069] In a case where the difference between the inner radius of the section of the outer die 22, where the convex section 24a is not provided, and the outer radius of the projection 28 of the inner punch 26 is equal to or greater than the thickness of the tubular material 4 before drawing, the thickness of the tubular material 4 is not reduced during drawing. The thickness of the tubular material 4 can be increased relative to an initial thickness of the tubular material 4, and the thickness of the tubular material 4 can be further increased by controlling the material support and ejection plate 40 to receive the tubular material 4.

[0070] When the tubular material 4 is drawn, it tends to move as a whole in the axial direction in which the inner punch 26 pushes it. This axial movement is prevented because the bent section 8 of the tubular material 4 engages with the flange receiving section 22c of the outer die 22, because the bent section 8 of the tubular material 4 is clamped between the pressing component 23 and the die 22, and because the material support and ejection plate 40 receives the tubular material 4 in a direction opposite to the direction in which the inner punch 26 pushes it.As a result, the axial positions of a thick section and a thin section formed in the tubular component 10 are prevented from being offset relative to the axial positions of the convex and concave surfaces 24 of the outer die 22. In a wheel rim 10 (10B) produced by roll forming the tubular component 10 (10A), a section requiring a relatively large thickness is thick, and a section not requiring a relatively large thickness is thin, making the wheel rim 10 (10B) lightweight.

[0071] In the method for manufacturing the tubular component 10 according to the first embodiment of the present invention, the die 22 is formed from the outer die, which has the cylindrical bore 22a and the inner surface 22b, which is the surface 24 with a convex and a concave section, and the punch 26 is formed from the inner punch, which is moved into and out of the cylindrical bore 22a of the outer die 22. The outer die 22 is attached to the base plate 38, which is arranged on a lower section of the drawing device 20 (the press 30), and the inner punch 26 is attached to the piston 36, which is arranged on the upper section of the drawing device 20 (the press 30). The inner punch 26 is moved up and down in the perpendicular direction relative to the outer die 22.This structure allows the drawing device 20 (the press machine 30) to be used to produce the tubular component 10 (10A). [Second embodiment]

[0072] In the method for manufacturing the tubular component 10 according to the second embodiment of the present invention, as shown in Fig. 7 and Fig. As shown in Figure 8, the die 22 is formed from an inner die having an outer surface 22e. The outer surface 22e of the inner die 22 is configured as surface 24 with a convex and a concave section. The punch 26 is configured as an outer punch having a cylindrical bore 26a and an inner surface 26b. The projection 28 is formed on the inner surface 26b of the outer punch.

[0073] A flange receiving section 22d, which can engage with the bent section 8 of the tubular material 4, is formed on an upper end section of the outer surface 22e of the inner die 22. The tubular material 4 is fixed (placed) on the inner die 22 because the bent section 8 contacts and engages with the flange receiving section 22d.

[0074] The outer diameter of a section of the inner die 22, where the convex section 24a is provided, is smaller before drawing than the inner diameter of a section of the tubular material 4, which differs from the bent section 8. Therefore, the tubular material 4 can be fixed (set) on the inner die 22 before drawing.

[0075] The inner diameter of the projection 28 of the outer punch 26 is smaller before drawing than the outer diameter of the tubular material 4, which differs from the bent section 8. Therefore, a concave and a convex shape can be transferred to the tubular material 4 by pressing it along the die 22 during drawing.

[0076] The difference between the inner radius of the projection 28 of the outer punch 26 and the outer radius of the section of the inner die 22, where the convex section 24a is provided, is smaller than the thickness of the tubular material 4 before drawing. Therefore, the thickness of the tubular material 4 can be reduced by drawing.

[0077] When the outer punch 26 is moved towards the inner die 22 and the inner die 22 enters the cylindrical bore 26a of the outer punch 26, the projection 28 of the outer punch 26 pulls the tubular material 4 in order to reduce (shrink) the diameter of the tubular material 4, and the section of the inner die 22 where the convex section 24a is provided reduces the thickness of the tubular material 4.

[0078] In a case where the difference between the outer radius of the section of the inner die 22, where the convex section 24a is not provided, and the inner radius of the projection 28 of the outer punch 26 is equal to or greater than the thickness of the tubular material 4 before drawing, the thickness of the tubular material 4 is not reduced during drawing. The thickness of the tubular material 4 can be increased relative to an initial thickness of the tubular material.

[0079] When the tubular material 4 is drawn, it tends to move as a whole in the axial direction in which the outer punch 26 pushes it. This axial movement is prevented because the bent section 8 of the tubular material 4 engages with the flanged receiving section 22d of the inner die 22, as the bent section 8 of the tubular material 4 is positioned between the die assembly 23 (not shown in [reference missing]). Fig.7) and the die 22 is clamped, and since the material support and ejection plate 40 receives the tubular material 4 in a direction opposite to the direction in which the outer punch 26 pushes the tubular material 4. As a result, the axial positions of a thick section and a thin section formed in the tubular component 10 are prevented from being offset relative to the axial positions of the convex and concave sections of the inner die 22. In a vehicle rim produced by roll forming the tubular component 10 (10A), a section where a relatively large thickness is required is thick, and a section where a relatively large thickness is not required is thin, so that the wheel rim 10 (10B) is lightweight.

[0080] In the method for manufacturing the tubular component 10 according to the second embodiment of the present invention, the die 22 is formed from the inner die, which has the outer surface being surface 24 with a convex and a concave section, and the punch 26 is formed from the outer punch, which has the cylindrical bore 26a and the inner surface. The inner die 22 is attached to the lower base plate 38 of the drawing device 20 (the press 30), and the outer punch 26 is attached to the upper piston 36 of the drawing device 20 (the press 30). The outer punch 26 is moved back and forth in the perpendicular direction relative to the inner die 22. This structure allows the drawing device 20 (the press 30) to be used for manufacturing the tubular component 10 (10A). Explanation of reference symbols 2 flat sheet material that has a constant thickness 4 tubular material that has a constant thickness 6 welded section 8 curved section 10 (10A, 10B) tubular component having a non-constant thickness 20 drawing device 22 Matrix (outer matrix, inner matrix) 22a cylindrical bore of the outer die 22b Inner surface of the outer die 22c Flange mounting section of the outer die 22d Flange mounting section of the inner die 22e Outer surface of the inner die 23 Pressed component 24 Surface with a convex section and a concave section 24a convex section 24b concave section 26 stamps (inner stamp, outer stamp) 26a cylindrical bore of the outer punch 26b Inner surface of the outer stamp 26e Outer surface of the inner stamp 28 lead 30 press machines 32 frames 34 hydraulic cylinders 36 pistons 38 Base plate 40 Material support and ejection plate 42 hydraulic cylinders

Claims

[1] Method for producing a tubular component (10, 10A, 10B) comprising the following steps: Bending an axial end section of a tubular material (4) having a constant thickness in a direction transverse to an axial direction of the tubular material (4) in order to form a bent section (8) in the tubular material (4), Drawing the tubular material (4) to form a tubular component (10, 10A, 10B) having a non-constant thickness by drawing at least one section of the tubular material (4) except for the bent section (8) using a drawing device (20) having a punch (26) and a die (22) having a side surface (24) with a convex section (24a) and a concave section (24b) opposite the punch (26). [2] Method for producing a tubular component (10, 10A, 10B) according to claim 1, wherein the drawing step comprises the following steps: Causing the curved section (8) to engage with the die (22) in an axial direction; Operating the drawing device (20) by moving one element of the punch (26) and the die (22) relative to the other element of the punch (26) and the die (22); and Drawing of the tubular material (4) to form the tubular component (10, 10A, 10B) is accompanied by a change in the diameter and thickness of the tubular material (4) caused by the surface (24) with a convex section (24a) and a concave section (24b) of the die (22) and the punch (26). [3] Method for producing a tubular component (10, 10A, 10B) according to claim 1, wherein the surface (24) is formed with a convex section (24a) and a concave section (24b) by providing at least one convex section (24a) which makes a space between the die (22) and the punch (26) narrower than a thickness of the tubular material (4), on the die (22) in an axial direction of the die (22) along the side surface (24) of the die (22) which is opposite the punch (26). [4] Method for producing a tubular component (10, 10A, 10B) according to claim 1, wherein in the drawing step after producing the tubular component (10, 10A, 10B), which has a non-constant thickness, the tubular component (10, 10A, 10B) is removed from the die (22) by applying an axial force to the tubular component (10, 10A, 10B), so that the tubular component (10, 10A, 10B) is deformed in a radial direction of the tubular component (10, 10A, 10B). [5] Method for producing a tubular component (10, 10A, 10B) according to claim 1, wherein the surface (24) is formed with a convex section (24a) and a concave section (24b) by providing at least one section which makes a space between the die (22) and the punch (26) narrower than a thickness of the tubular material (4) on the die (22) in a circumferential direction of the die (22) along the side surface (24) of the die (22) opposite the punch (26). [6] Method for producing a tubular component (10, 10A, 10B) according to claim 1, wherein in the drawing step the bent section (8) of the tubular material (4) is axially engaged with the die (22) and clamped between the die (22) and a press component (23) and then the drawing is carried out. [7] Method for producing a tubular component (10, 10A, 10B) according to claim 1, further comprising a step for producing the tubular material (4) from a flat material (2) having a constant thickness before the drawing step. [8] Method for producing a tubular component (10, 10A, 10B) according to claim 1, which further comprises a step for roll forming the tubular material (4) which has a non-constant thickness in order to form a vehicle wheel rim design after the drawing step.

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