Manufacturing method of tubular part and press device

Abstract

To provide a tubular component manufacturing method in which a constraint in shape of tubular component is limited and wrinkles or cracks are difficult to occur, and a press device.SOLUTION: A method for manufacturing a tubular component 4 comprises: a preparation step of preparing a metal plate 1; and a molding step of molding the metal plate 1 into the tubular component 4 through hole-expanding drawing. The molding step includes a first molding step of providing a first intermediate product 2 having an inclined wall 2k by pressing the metal plate to execute hole-expanding drawing, a second molding step of providing a second intermediate product 3 having an inclined front wall 3f and a rear wall 3r parallel to an axial direction or inclined in a direction opposite to inclining of the front wall 3f in the axial direction through push-in drawing executed for the first intermediate product 2 by using an intermediate drawing punch 20P and intermediate drawing die 20D, and a third molding step of pushing the rear wall of the second intermediate product 3 disposed in a push-in die 30D by a push-in punch 30P to execute push-in drawing, thereby providing the tubular component 4.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a tubular part and a press device used in the manufacturing method. [Background technology]

[0002] For example, metal tubular parts (cylindrical parts) are used for bearing races, gears, wheels, oil pump parts, etc. As a manufacturing method for such tubular parts, a method is known in which a tubular part is formed by drawing a donut-shaped steel disk with a hole in the center (see, for example, JP-A-7-155877 (Patent Document 1) and JP-A-2009-226422 (Patent Document 2)).

[0003] Japanese Patent No. 6616027 (Patent Document 3) describes a method for manufacturing a cylindrical rotating part that suppresses the occurrence of wrinkles and cracks due to drawing. This manufacturing method includes a step of obtaining a truncated cone-shaped intermediate product by pressing the entire surfaces of a doughnut-shaped metal disk with the tapered surfaces of a tapered punch and die to perform hole expansion drawing, and a step of obtaining a cylindrical rotating part by pressing the intermediate product with a punch and die with a small taper angle to further perform hole expansion drawing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-155877 [Patent Document 2] JP 2009-226422 A [Patent Document 3] Patent No. 6616027 Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors found that the manufacturing method described in the above-mentioned Japanese Patent No. 6616027 may not be able to manufacture the desired tubular part depending on the wall thickness and diameter conditions. In the above-mentioned method, a truncated cone-shaped intermediate product is formed from a metal disk. Furthermore, in the final forming process, a hole expansion and drawing process is performed by inserting a punch from the large diameter side of the intermediate product with the small diameter side of the intermediate product placed in the die. At this stage, for example, if the wall thickness of the intermediate product is thin and the inner diameter of the large diameter side of the intermediate product is larger than the diameter of the die, the intermediate product cannot be pushed into the die with a punch of a size that can be inserted into the die. Therefore, the above-mentioned manufacturing method has restrictions on the shape of the tubular part that can be manufactured.

[0006] Therefore, the present application discloses a manufacturing method and pressing device for a tubular part that places fewer restrictions on the shape of the tubular part and is less susceptible to wrinkles and cracks. [Means for solving the problem]

[0007] A method for manufacturing a tubular part according to an embodiment of the present invention includes a preparation step of preparing a metal plate having a hole penetrating from an upper surface to a lower surface, and a forming step of forming the metal plate into a tubular part by hole expansion drawing. The forming step includes a first forming step of performing hole expansion drawing by pressing the metal plate with a tapered surface of a tilt drawing punch and a tapered surface of a tilt drawing die to obtain a first intermediate product having an inclined wall inclined with respect to the axial direction, a second forming step of performing press drawing on the first intermediate product using an intermediate drawing punch and an intermediate drawing die to obtain a second intermediate product having a front wall inclined with respect to the axial direction at a front portion in the pressing direction and a rear wall inclined with respect to the axial direction in a rear portion in the pressing direction relative to the front wall, the rear wall being parallel to the axial direction or inclined in a direction opposite to the inclination of the front wall, and a third forming step of performing press drawing by pressing the rear wall of the second intermediate product arranged in the press die with a press punch to obtain a tubular part. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a manufacturing method and a pressing apparatus for a tubular part that have few restrictions on the shape of the tubular part and are less likely to cause wrinkles or cracks. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram for explaining a method for manufacturing a tubular part in this embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of a case where indentation drawing is not possible. [Diagram 3] FIG. 3 is a diagram showing a modification of the first molding step in FIG. [Figure 4] FIG. 4 is a diagram showing a modified example of the second molding step in FIG. [Diagram 5] FIG. 5 is a diagram showing another modified example of the second molding step in FIG. [Figure 6] FIG. 6 is a diagram showing a modification of the metal plate 1 and the tubular part shown in FIG. [Figure 7] FIG. 7 is a diagram showing the steps in the test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A method for manufacturing a tubular part according to an embodiment of the present invention includes a preparation step of preparing a metal plate having a hole penetrating from an upper surface to a lower surface, and a forming step of forming the metal plate into a tubular part by hole expansion drawing. The forming step includes a first forming step of performing hole expansion drawing by pressing the metal plate with a tapered surface of a tilt drawing punch and a tapered surface of a tilt drawing die to obtain a first intermediate product having an inclined wall inclined with respect to the axial direction, a second forming step of performing press drawing on the first intermediate product using an intermediate drawing punch and an intermediate drawing die to obtain a second intermediate product having a front wall inclined with respect to the axial direction at a front portion in the pressing direction and a rear wall inclined with respect to the axial direction in a rear portion in the pressing direction relative to the front wall, the rear wall being parallel to the axial direction or inclined in a direction opposite to the inclination of the front wall, and a third forming step of performing press drawing by pressing the rear wall of the second intermediate product arranged in the press die with a press punch to obtain a tubular part.

[0011] In the above manufacturing method, in the first forming step, the metal plate is formed into a first intermediate product having an inclined wall, and in the second forming step, the first intermediate product is formed into a second intermediate product having a front wall at the front of the pushing direction and a rear wall at the rear. The rear wall is parallel to the axial direction or inclined in the opposite direction to the front wall. In the third forming step, the second intermediate product is pushed into the pushing die by the pushing punch to form a tubular part. The pushing punch pushes the rear wall of the second intermediate product. In this manufacturing method, the rear wall can be formed in the second forming step so as to fit the pushing punch in the third forming step. Therefore, tubular parts of various shapes can be formed without being restricted by the size of the pushing punch. Therefore, the restrictions on the shape of the tubular part are reduced. In addition, the metal plate is successively formed into the first intermediate product and the second intermediate product having inclined walls, and then the tubular part is formed by the pushing drawing process, so that the occurrence of wrinkles and cracks due to the drawing process is suppressed. As a result, there are fewer restrictions on the shape of the tubular part, and the occurrence of wrinkles and cracks can be suppressed.

[0012] In the second forming step, the second intermediate product may be obtained by performing the press-drawing process multiple times using multiple sets of the intermediate drawing punch and the intermediate drawing die, which makes it easier to prevent wrinkles and cracks from occurring due to the press-drawing process.

[0013] In the nth (n is a natural number of 2 or more) press-drawing in the second forming step, an intermediate drawing die having a smaller diameter than the intermediate drawing die used in the (n-1)th press-drawing may be used. This allows the diameter of the intermediate product to be reduced stepwise in the second forming step. As a result, the occurrence of wrinkles and cracks due to the press-drawing can be more effectively suppressed.

[0014] The diameter of the die refers to the inner diameter of the die. The diameter of the die refers to the dimension in the direction perpendicular to the pushing direction of the internal space into which the material to be processed (e.g., the first intermediate product, the second intermediate product, etc.) is pushed, at the widest point. If the internal space of the die is cylindrical, i.e., the cross section is circular, the diameter of the cross section is the diameter of the die. If the inner surface of the die includes a tapered surface, the diameter of the die refers to the diameter at the position where the cross section area is the smallest in the internal space into which the material to be processed is pushed.

[0015] In the first forming step, a first intermediate product may be obtained by performing the hole expansion drawing process multiple times using multiple sets of the oblique drawing punch and the oblique drawing die. In this case, for example, in the second or subsequent hole expansion drawing process, the hole expansion drawing process may be performed using an oblique drawing punch having a taper angle smaller than that of the previous oblique drawing punch and an oblique drawing die having a taper angle smaller than that of the previous oblique drawing die.

[0016] In the second forming step, the intermediate drawing punch and the intermediate drawing die may each have a tapered surface. In this case, in the second forming step, the first intermediate product can be supported and drawn by at least a corner of the tapered surface of the intermediate drawing punch and a corner of the tapered surface of the intermediate drawing die.

[0017] In the second forming step, the intermediate drawing die may have a vertical wall portion having an inner circumferential surface parallel to the pushing direction, and a tapered portion having a tapered surface that widens from the vertical wall portion toward the rear in the pushing direction. The intermediate drawing punch may have a base portion having an outer circumferential surface parallel to the pushing direction, and a leading portion having a tapered surface that narrows from the base portion toward the front in the pushing direction. The first intermediate product may be supported between the boundary between the vertical wall portion and the tapered portion of the intermediate drawing die and the boundary between the base portion and the front end portion of the intermediate drawing punch, and the pressure drawing process may be performed. By using the intermediate drawing punch and intermediate drawing die having the above configurations, a second intermediate product having a front wall and a rear wall can be efficiently formed. The diameter of the base of the intermediate drawing punch may be smaller than the diameter of the intermediate drawing die (the diameter of the inner surface of the vertical wall portion).

[0018] In the second forming step, the second intermediate product may be obtained having the rear wall with an inclination angle of 15 to 45° with respect to the axial direction, thereby making it possible to efficiently form the second intermediate product in which the diameter of the rear end of the rear wall is smaller than the maximum diameter.

[0019] In the second forming step, the intermediate drawing die in each of the second and subsequent press-drawing processes among the multiple processes may satisfy the condition represented by the following formula, which makes it possible to more effectively prevent wrinkles and cracks from occurring due to the press-drawing process. 1<(Dd_n-1 / Dd_n)≦1.35 Dd_n: Diameter of the intermediate drawing die used in the nth (n is a natural number of 2 or more) pressing process Dd_n-1: Diameter of the intermediate drawing die used in the n-1th pressing

[0020] The tensile strength of the metal plate is not particularly limited, but may be, for example, 780 MPa or less, and is preferably 590 MPa. By processing a material with this level of strength under the above-mentioned drawing ratio conditions, the above-mentioned effects become more pronounced.

[0021] In the first forming step, the first intermediate product may have the inclined wall with an inclination angle of 30 to 45° with respect to the axial direction, which makes it possible to more effectively prevent wrinkles and cracks from occurring due to the pressing and drawing process.

[0022] In the third forming step, the pressing drawing may be performed on the second intermediate product using the pressing punch and the pressing die that satisfy the relationship of the following formula: rd3-rp3 <t rp3-rcp>0 t: wall thickness of the second intermediate product rd3: Radius of the pressing die rp3: Radius of the pressing punch rcp: Radius from the central axis to the inner periphery of the rear end of the second intermediate part in the pushing direction

[0023] A press machine according to an embodiment of the present invention forms a metal plate having a hole penetrating from an upper surface to a lower surface into a tubular part by hole expansion and drawing. The press machine includes an inclined drawing die and an inclined drawing punch used to obtain a first intermediate product having an inclined wall inclined with respect to an axial direction by hole expansion and drawing the metal plate, an intermediate drawing punch and an intermediate drawing die used to obtain a second intermediate product by performing a forcing drawing process on the first intermediate product, the second intermediate product having a front wall inclined with respect to the axial direction at a front portion in the forcing direction and a rear wall parallel to the axial direction or inclined in a direction opposite to the forcing direction of the front wall at a rear portion in the forcing direction relative to the front wall, a forcing die for arranging the second intermediate product, and a forcing punch for forcing the rear wall of the arranged second intermediate product to obtain a tubular part by forcing drawing. The oblique drawing die and the oblique drawing punch each have a tapered surface and are configured to press the metal plate with the tapered surface of the oblique drawing die and the tapered surface of the oblique drawing punch to form the oblique wall of the first intermediate product. The intermediate drawing die has a vertical wall portion having an inner peripheral surface parallel to the pushing direction, and a tapered portion having a tapered surface that widens from the vertical wall portion toward the rear in the pushing direction. The intermediate drawing punch has a base portion having an outer circumferential surface parallel to the pushing direction, and a front portion having a tapered surface which narrows from the base portion toward the front in the pushing direction. The pressing die has a recess having an inner surface corresponding to the shape of the tubular part, and the pressing punch has a protrusion insertable into the recess.

[0024] In the above press device, a first intermediate product having an inclined wall is formed by hole expansion drawing using an inclined drawing die and an inclined drawing punch. The first intermediate product is formed into a second intermediate product having a front wall at the front of the pushing direction and a rear wall at the rear of the first intermediate product by push drawing using an intermediate drawing punch and an intermediate drawing die. The rear wall is parallel to the axial direction or inclined in the opposite direction to the front wall. The second intermediate product is pushed into the push die by a push punch to form a tubular part. The push punch pushes the rear wall of the second intermediate product. In this press device, the rear wall of the second intermediate product can be formed using an intermediate drawing die and an intermediate drawing punch so as to fit the push punch. Therefore, tubular parts of various shapes can be formed without being restricted by the size of the push punch. Therefore, there are fewer restrictions on the shape of the tubular part. In addition, the metal plate is successively formed into a first intermediate product and a second intermediate product having an inclined wall, and then formed into a tubular part by indentation, so that the occurrence of wrinkles and cracks due to drawing is suppressed. As a result, there are fewer restrictions on the shape of the tubular part, and the occurrence of wrinkles and cracks can be suppressed. The above manufacturing method can be carried out using the above press device.

[0025] The press device may include a plurality of sets of the intermediate drawing punch and intermediate drawing die. In this case, the press device can obtain the second intermediate product by performing the forcing drawing process a plurality of times using the plurality of sets of the intermediate drawing punch and intermediate drawing die. In this case, the diameters of the plurality of intermediate drawing dies may be different. Also, the diameters of the plurality of intermediate drawing punches may be different. For example, in the forcing drawing process performed a plurality of times, an intermediate drawing die having a smaller diameter than the intermediate drawing die used in the forcing drawing process (n-1) may be used in the n-th time (n is a natural number of 2 or more).

[0026] In a modified example, the intermediate drawing die may have a vertical wall portion having an inner peripheral surface parallel to the pushing direction, and a tapered portion having a tapered surface that spreads from the vertical wall portion toward the rear in the pushing direction, and the intermediate drawing punch may have a leading portion having a tapered surface that spreads toward the front in the axial direction at a position axially opposite to the tapered portion of the intermediate drawing die. This makes it possible to obtain a second intermediate product having a front wall that is inclined with respect to the axial direction at the front portion in the pushing direction, and a rear wall that is inclined with respect to the axial direction in the opposite direction to the inclination of the front wall at the rear portion in the pushing direction relative to the front wall. In this case, the taper angle of the tapered surface of the tapered portion of the intermediate drawing die with respect to the axial direction and the taper angle of the tapered surface of the leading portion of the intermediate drawing punch with respect to the axial direction may be the same. This can improve the symmetry of the axial shape of the tubular part. Note that the form in which the taper angle of the intermediate drawing punch and the taper angle of the intermediate drawing die are the same includes cases in which these taper angles are strictly the same, as well as cases in which they are slightly different to an extent that is permissible from the viewpoint of the symmetry of the shape of the tubular part.

[0027] Hereinafter, a method for manufacturing a tubular part according to an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are given the same reference numerals, and the description of those parts will not be repeated. Furthermore, the dimensions of the components in each drawing do not faithfully represent the actual dimensions of the components and the dimensional ratios of each component.

[0028] (Embodiment) FIG. 1 is a diagram for explaining a manufacturing method of a tubular part in this embodiment. The manufacturing method in this embodiment includes a preparation step of preparing a metal plate 1 and a forming step of processing the metal plate 1. The forming step includes a first forming step, a second forming step, and a third forming step. In the first forming step, the metal plate 1 is processed into a first intermediate product 2 having an inclined wall 2k. In the first forming step, the metal plate 1 is subjected to hole expansion and drawing using an inclined drawing punch 10P and an inclined drawing die 10D. In the second forming step, the first intermediate product 2 is processed into a second intermediate product 3. The second intermediate product 3 has a front wall 3f in the forward direction in the pushing direction and a rear wall 3r in the rear. The front wall 3f is inclined so as to become thinner toward the front in the pushing direction. The rear wall 3r is inclined parallel to the pushing direction or inclined in the opposite direction to the inclination of the front wall 3f. In the second forming step, the first intermediate product 2 is subjected to a force drawing process using an intermediate drawing punch 20P and an intermediate drawing die 20D. In the third forming step, the second intermediate product 3 is processed into a tubular part 4. In the third forming step, the second intermediate product 3 is subjected to a force drawing process using a force punch 30P and a force drawing die 30D.

[0029] As shown in Fig. 1, a metal plate 1 is processed into a tubular part 4 through a first intermediate product 2 and a second intermediate product 3. This prevents wrinkles and cracks from occurring during processing. In addition, the second intermediate product 3, which has a front wall 3f and a rear wall 3r, is pressed and drawn to obtain a tubular part, which provides a wider range of options for the diameter, wall thickness, and other properties of the desired tubular part. This makes it possible to manufacture tubular parts of various shapes. Each process will be described in detail below.

[0030] (preparation process) The prepared metal plate 1 is in the form of a plate having a hole 1h penetrating from the upper surface 1a to the lower surface 1b. In the example shown in FIG. 1, the metal plate 1 is a disk having a hole 1h in the center. The shape of the metal plate 1 is not limited to this. For example, the thickness of the metal plate 1 may not be uniform, and at least one of the upper surface 1a and the lower surface 1b may have irregularities. The metal plate 1 is obtained, for example, by punching a metal plate (blank). By punching, for example, a metal disk having a predetermined inner diameter and outer diameter and a hole formed in the center is obtained. The punched metal plate may also be processed into a desired shape by coining.

[0031] (1st molding process) In the first forming step, the metal sheet 1 is subjected to hole expansion drawing using an oblique drawing punch 10P and an oblique drawing die 10D to form a first intermediate product 2. The first intermediate product 2 has an inclined wall 2k. The inclined wall 2k becomes thinner toward the front in the pushing direction (press direction). As an example, the first intermediate product 2 has a truncated cone shape. In the first forming step, the metal sheet 1 is processed so that an upper surface 1a of the metal sheet 1 becomes the inner surface of the first intermediate product 2, and a lower surface 1b of the metal sheet 1 becomes the outer surface of the first intermediate product 2.

[0032] The hole expansion drawing process in the first forming step includes a step of placing the metal sheet 1 between the tilt drawing punch 10P and the tilt drawing die 10D, and pressing them relatively close to each other. The tilt drawing punch 10P has a convex portion with a diameter larger than the diameter of the hole 1h in the metal sheet 1. The tilt drawing die 10D has a concave portion with a diameter smaller than the outer diameter of the metal sheet 1. The convex portion of the tilt drawing punch 10P presses the upper surface 1a of the metal sheet 1, and the concave portion of the tilt drawing die 10D presses the lower surface 1b of the metal sheet 1. The metal sheet 1 is deformed as the hole 1h is expanded.

[0033] Both the oblique drawing punch 10P and the oblique drawing die 10D have tapered surfaces. The tapered surfaces of the oblique drawing punch 10P and the oblique drawing die 10D press the entire upper surface 1a and the lower surface 1b of the metal sheet 1 to perform hole expansion and drawing. The taper angles of these tapered surfaces are set to angles according to the angle of inclination of the inclined wall 2k of the first intermediate product 2 to be targeted. In the example of FIG. 1, the taper angle θp10 of the oblique drawing punch 10P and the taper angle θd10 of the oblique drawing die 10D are the same (θp10=θd10). In this case, the wall thickness of the inclined wall 2k is uniform. By setting θp10≠θd10, a first intermediate product 2 having an inclined wall 2k with a non-uniform wall thickness is obtained. From the viewpoint of suppressing the occurrence of wrinkles or cracks due to processing, θp10 and θd10 are not limited to these, but are preferably, for example, 30 to 50°, and more preferably 30 to 45°.

[0034] In this embodiment, the pushing direction (press direction) is the same as the direction in which the punch moves relative to the die during processing. The axial direction C of the first intermediate product 2, the second intermediate product 3, and the tubular part 4 is the same as the pushing direction. The taper angle of the tapered surface is the angle of the tapered surface with respect to the pushing direction, i.e., the axial direction.

[0035] (Second molding process) In the second forming step, the first intermediate product 2 is subjected to a pressing process using an intermediate pressing punch 20P and an intermediate pressing die 20D to form a second intermediate product 3. The front wall 3f of the second intermediate product 3 is a wall inclined in the axial direction and has a shape that tapers toward the front in the pressing direction (the tip in the axial direction). As an example, the front wall 3f is in a truncated cone shape. The rear wall 3r extends along the axial direction behind the front wall 3f in the pressing direction. In the example of FIG. 1, the rear wall 3r is parallel to the axial direction, but the shape of the rear wall 3r is not limited to this. For example, as described later, the rear wall 3r may be inclined in the opposite direction to the front wall 3f.

[0036] The press-drawing process in the second forming step includes a step of placing the first intermediate product 2 between an intermediate drawing punch 20P and an intermediate drawing die 20D, and pressing them together while bringing them relatively close to each other. The intermediate drawing punch 20P has a base 20P1 that is smaller in diameter than the first intermediate product 2. The intermediate drawing die 20D has a vertical wall 20D2 that includes a recess with a diameter larger than the diameter of the front end of the first intermediate product 2 in the pressing direction.

[0037] Both the intermediate drawing punch 20P and the intermediate drawing die 20D have tapered surfaces. Specifically, the intermediate drawing die 20D has a vertical wall portion 20D2 and a tapered portion 20D1. The vertical wall portion 20D2 has an inner surface parallel to the pushing direction. The tapered portion 20D1 has a tapered surface and becomes wider from the vertical wall portion 20D2 toward the rear in the pushing direction. The intermediate drawing punch 20P has a base portion 20P1 and a leading portion 20P2. The base portion 20P1 has an outer peripheral surface parallel to the pushing direction. The leading portion 20P2 has a tapered surface and becomes thinner from the base portion 20P1 toward the front in the pushing direction. The diameter of the base portion 20P1 of the intermediate drawing punch 20P is smaller than the diameter of the intermediate drawing die 20D, i.e., the inner diameter (diameter of the inner surface) of the vertical wall portion 20D2. A diameter Sp20 of the front end of the leading portion 20P2 of the intermediate drawing punch 20P in the pushing direction is smaller than both the inner diameter of the vertical wall portion 20D2 and the inner diameter of the front end of the first intermediate product 2 in the pushing direction.

[0038] In the second forming step, the first intermediate product 2 is supported at least between the boundary (corner of the tapered surface) between the vertical wall portion 20D2 and the tapered portion 20D1 of the intermediate drawing die 20D and the boundary (corner of the tapered surface) between the base portion 20P1 and the front portion 20P2 of the intermediate drawing punch 20P, and a press-drawing process is performed. The first intermediate product 2 is pressed by the intermediate drawing punch 20P into the intermediate drawing die 20D. The portion pressed by the base portion 20P1 of the intermediate drawing punch 20P and the vertical wall portion 20D2 of the intermediate drawing die 20D becomes the rear wall 3r. That is, the rear wall 3r is formed by pressing the rear portion of the first intermediate product 2 with the base portion 20P1 and the vertical wall portion 20D2.

[0039] (Third molding process) In the third forming step, the rear wall 3r of the second intermediate product 3 placed in the pressing die 30D is pressed by the pressing punch 30P to perform pressing and drawing, thereby obtaining a tubular part 4. The pressing and drawing process in the third forming step includes a step of placing the second intermediate product 3 between the pressing punch 30P and the pressing die 30D and pressing them relatively close to each other. The pressing die 30D includes a recess having a diameter smaller than that of the second intermediate product 3. The pressing punch 30P has a protrusion having a diameter smaller than that of the pressing die 30D. The diameter of the tip of the pressing die 30D in the pressing direction is larger than the inner diameter of the rear end of the second intermediate product 3 in the pressing direction. The pressing punch 30P is inserted into the recess of the pressing die 30D while pressing the second intermediate product 3 placed in the pressing die 30D. The second intermediate product 3 is pressed by a pressing punch 30P and a pressing die 30D to be formed into a tubular part.

[0040] In the example of Fig. 1, the pressing die 30D and the pressing punch 30P have surfaces parallel to the pressing direction. By pressing the second intermediate product with the pressing die 30 and the pressing punch 30P, a tubular part having vertical walls parallel to the axial direction is formed. The diameter (inner diameter, i.e., diameter of the recess) of the pressing die 30D is smaller than the diameter (inner diameter, i.e., diameter of the recess) of the intermediate drawing die 20D in the second forming step.

[0041] 1, in the third forming step, the wall thickness t of the second intermediate product, the radius rd3 of the pressing die 30D, the radius of the pressing punch 30P, and the radius rcp of the inner circumference at the rear end of the second intermediate product in the pressing direction satisfy the following relationship: Note that the radius rcp is the dimension from the central axis C to the inner circumference at the rear end of the second intermediate product in the pressing direction. rd3-rp3 <t rp3-rcp>0

[0042] In the example shown in FIG. 1, the tubular part 4 is a cylindrical part having vertical walls parallel to the axial direction. That is, the diameter of the tubular part 4 is uniform in the axial direction. The tubular part 4 may have a shape having an inclined wall inclined in the axial direction. In this case, the taper angle of the inclined wall with respect to the axial direction may be smaller than the taper angle of the first intermediate product 2 with respect to the axial direction. That is, the taper angle of the pressing die 30D may be smaller than that of the inclined drawing die 10D.

[0043] In the example shown in Fig. 1, a second intermediate product 3 having a rear wall 3r is obtained in the second forming step, and then the press-drawing process is performed in the third forming step. Therefore, the second forming step can form a second intermediate product that can be easily pressed in the third forming step. For example, when attempting to press-draw the first intermediate product 2 into a tubular part, press-drawing may not be possible depending on the shape of the tubular part.

[0044] FIG. 2 is a diagram showing an example in which push-molding is not possible. In the example shown in FIG. 2, the plate thickness of the workpiece is thin compared to the diameter (hole diameter) Dd80 of the die. Therefore, the inner diameter Dcp of the workpiece (intermediate product having an inclined wall) at the rear end in the push-in direction is larger than the diameter Dd80 of the die 80D. To push this workpiece, a punch 80P having a diameter Dp80 larger than the diameter Dd80 of the die 80D is required. However, if Dp80>Dd80, the punch 80P cannot pass through the hole of the die 80D. Therefore, push-in is not possible.

[0045] In this embodiment, as shown in Fig. 1, a first intermediate product 2 having an inclined wall is subjected to a press-drawing process in a second forming step to form a second intermediate product 3 having a smaller inner diameter at the pressed end. This makes it possible to perform the press-drawing process in a third forming step.

[0046] (Modification of the first molding process) Fig. 3 is a diagram showing a modified example of the second forming step. In the example shown in Fig. 3, a first intermediate product 2 is produced by multiple hole expansion drawing processes Op11 and Op12 using multiple sets of oblique drawing punches 11P and 12P and oblique drawing dies 11D and 12D.

[0047] In the example of Fig. 3, the taper angle θp12 of the inclined drawing punch 12P used in the second or subsequent hole expansion drawing Op12 with respect to the axial direction is smaller than the taper angle θp11 of the inclined drawing punch 11P used in the previous hole expansion drawing Op11 (θp12>θp11). Similarly, the taper angle θd12 of the inclined drawing die 12D used in the second or subsequent hole expansion drawing Op2 with respect to the axial direction is smaller than the taper angle θd12 of the inclined drawing die 11D used in the previous hole expansion drawing Op1 (θd12>θd11). In this way, by changing the inclination of the vertical wall stepwise during processing, it is possible to more effectively suppress the occurrence of wrinkles or cracks due to processing.

[0048] (Modification of the second molding process) Fig. 4 is a diagram showing a modified example of the second forming step. In the example shown in Fig. 4, a second intermediate product 3 is produced by multiple push drawing processes Op21 to Op23 using multiple sets of intermediate drawing punches 21P to 23P and intermediate drawing dies 21D to 23D.

[0049] In the example of Fig. 4, the diameters (inner diameters of the vertical walls) of the intermediate drawing dies 22D, 23D used in the second and subsequent drawing Op22, Op23 are smaller than the diameters of the intermediate drawing dies 21D, 22D used in the previous drawing Op21, Op22 (Dd21>Dd22, Dd22>Dd23). Similarly, the diameters (outer diameters of the bases) of the intermediate drawing punches 22P, 23P used in the second and subsequent drawing Op22, Op23 are smaller than the diameters of the intermediate drawing punches 21P, 22P used in the previous drawing Op21, Op22 (Dp21>Dp22, Dp22>Dp23).

[0050] In the second forming step, the first intermediate product 2 is drawn while the inclined wall 2k is supported by the corner of the tapered surface of the intermediate drawing punch and the inner surface of the intermediate drawing die. In the second and subsequent drawing steps, the first intermediate product 2 is drawn using a die having a smaller die hole diameter and punch diameter than those in the previous drawing step, and the second intermediate product 3 having the desired front wall 3f and rear wall 3r is produced. In this way, by changing the drawing ratio stepwise during processing, the occurrence of wrinkles or cracks due to processing can be more effectively suppressed.

[0051] In the second forming step, Dd_n is the diameter of the intermediate drawing die used in the nth drawing, and Dd_n-1 is the diameter of the intermediate drawing die used in the n-1th drawing. The drawing ratio is Dd_n-1 / Dd_n. In this case, the drawing ratio in each of the second and subsequent drawing steps in the second forming step can be set to satisfy, for example, the condition shown in the following formula. This makes it possible to more effectively suppress the occurrence of wrinkles or cracks due to processing. 1<(Dd_n-1 / Dd_n)≦1.35

[0052] In the example in Figure 4, 1 <Dd21 / Dd22≦1.35、1<Dd22 / D23≦1.35とすることができる。

[0053] (Another modified example of the second molding step) Fig. 5 is a diagram showing another modified example of the second forming step. In the example shown in Fig. 5, a second intermediate product 3 is produced by multiple push drawing processes Op21 and Op24 using multiple sets of intermediate drawing punches 21P and 24P and intermediate drawing dies 21D and 24D. The second intermediate product 3 is formed so that the inclination of the rear wall 3r is opposite to the inclination of the front wall 3f. Op21 in Fig. 5 can be performed in the same manner as Op21 in Fig. 4. Op30 in Fig. 5 can be performed in the same manner as the third forming step shown in Fig. 1.

[0054] In the forced drawing process Op24 of FIG. 5, the leading portion 24P2 of the intermediate drawing punch 24P has a recess with an inner surface being a tapered surface. The tapered surface of the intermediate drawing punch 24P is inclined in the opposite direction to the tapered surface of the intermediate drawing die 24D. The tapered surface of the leading portion 24P2 of the intermediate drawing punch 24P is inclined with respect to the axial direction so as to widen in the pushing direction. The tapered surface of the tapered portion 24D1 of the intermediate drawing die 24D is inclined with respect to the axial direction so as to narrow in the pushing direction. The diameter of the rear end of the tapered portion 24D1 of the intermediate drawing die 24D in the pushing direction is larger than the diameter of the front end of the first intermediate product 2, which is the material to be processed, in the pushing direction. The diameter of the inner surface of the front end of the leading portion 24P1 of the intermediate drawing punch 24P in the pushing direction is larger than the diameter of the inner surface of the rear end of the first intermediate product 2 in the pushing direction.

[0055] In the pressing and drawing process Op24, the second intermediate product 3 placed in the intermediate drawing die 24D is pressed by the intermediate drawing punch 24P to bend and draw the second intermediate product 3. The tapered surface of the intermediate drawing die 24D presses the outer peripheral surface of the front part in the pressing direction of the first intermediate product, and the tapered surface of the intermediate drawing punch 24P presses the outer peripheral surface of the rear part in the pressing direction of the outer peripheral surface of the first intermediate product. This forms the second intermediate product 3 in which the rear wall 3r and the front wall 3f are inclined in opposite directions. The wall of the second intermediate product 3 is bent so that the central part in the axial direction protrudes radially outward. The cross section of the surface parallel to the axis of the wall of the second intermediate product 3 is shaped like the Japanese hiragana character "K". This allows the inner diameter of the rear end in the pressing direction of the second intermediate product 3 to be reduced. Therefore, for example, even if the wall thickness of the second intermediate product 3 is smaller than the outer diameter, in the pressing and drawing process Op30, it is possible to press the rear end of the second intermediate product 3 with the pressing punch 30P and press it into the pressing die 30D.

[0056] 5, the rear wall 3r of the second intermediate product 3 is inclined radially inward by the forced drawing Op24. Therefore, the amount of drawing of the inner diameter of the rear end of the second intermediate product 3 by one forced drawing can be made larger than when the rear wall 3r is parallel to the axial direction. Also, the inclination of the rear wall 3r can be adjusted by adjusting the taper angle θp24 of the tapered surface of the intermediate drawing punch 24P.

[0057] In the example shown in FIG. 5, the taper angle θd24 of the intermediate drawing die 24D of Op24 and the taper angle θp24 of the intermediate drawing punch 24P are the same (θp24=θd24). This may improve the symmetry of the shape of the tubular part 4. For example, when the tubular part 4 is formed in the process of FIG. 5, springback may result in a shape (a constricted shape) in which the diameter of the axial center of the formed tubular part 4 is slightly smaller than that of both ends. In this case, by setting θp24=θd24, the tubular part 4 is likely to have a constricted shape that is symmetric in the axial direction. Note that these taper angles θp24 and θd24 may be different (θp24≠θd24).

[0058] (Modification of metal plate) FIG. 6 is a diagram showing modified examples of the metal sheet 1 in the preparation step and the tubular part 4 obtained by forming this metal sheet 1. The metal sheet 1 prepared in the preparation step has a shape in which the thickness varies in the radial direction. For example, the radial thickness distribution of the metal sheet 1 can be adjusted by coining. As an example, as shown in FIG. 6, the metal sheet 1 can be shaped so that the thickness increases toward the inner periphery in the radial direction. This makes it possible to make the wall thickness at both axial ends of the tubular part 4 obtained in the forming step closer to uniform.

[0059] The outer side of the metal plate 1 is the outer diameter surface 1d, and the inner side of the metal plate 1, i.e., the inner surface of the hole 1h, is the inner diameter surface 1c. In the example of Fig. 6, the axial dimension of the outer diameter surface 1d (outer diameter plate thickness) is smaller than the axial dimension of the inner diameter surface 1c (inner diameter plate thickness). The upper surface 1a is inclined with respect to the plate thickness direction. The lower surface 1b is perpendicular to the plate thickness direction.

[0060] The sheet thickness t0_out of the outer diameter portion of the metal sheet 1 is smaller (thinner) than the sheet thickness t0_in of the inner diameter portion. In the metal sheet 1, the outer diameter thickness t0_out at the outer diameter surface 1d may be set based on a first correlation with a target value of the wall thickness a_up of one end portion including one end face 4d of the tubular part 4. The inner diameter thickness t0_in at the inner diameter surface 1c of the metal sheet 1 may be set based on a second correlation with a target value of the wall thickness a_down of the other end portion including the other end face 4c of the tubular part 4.

[0061] The first correlation and the second correlation may be different from each other. The first correlation may be, for example, a relationship in which the wall thickness a_up at one end of the tubular part is expressed by a linear function of the plate thickness t0_out of the outer diameter part. The second correlation may be, for example, a relationship in which the wall thickness a_down at the other end of the tubular part is expressed by a linear function of the plate thickness t0_in of the outer diameter part. In this case, for example, the slope K1 of the linear function showing the first correlation may be larger than the slope K2 of the linear function showing the second correlation. These correlations have been found by the inventor. As an example, the slope K1 may be 1.19≦K1≦1.55, and the slope K2 may be 0.63≦K2≦0.83.

[0062] In the example shown in FIG. 6, a depression 1ah is formed on the upper surface 1a of the metal plate 1. The depression 1ah is a groove that surrounds the entire periphery of the hole 1h. The depression 1ah is a groove with a curved cross section. The cross-sectional shape of the depression 1ah may or may not be a circular arc. When viewed from above, the depression 1ah is formed concentrically with the hole 1h. For example, a metal plate 1 having a depression can be manufactured by coining processing using a die having a shape corresponding to the desired depression 1ah.

[0063] The metal plate 1 is subjected to hole expansion and drawing to obtain a tubular part 4 as shown in Fig. 6. The depression 1ah on the upper surface 1a of the metal plate 1 becomes a recess 4ah on the inner circumferential surface 4a of the tubular part. The recess 4ah on the inner circumferential surface 4a of the tubular part 4 is formed over the entire circumference of the inner circumferential surface 4a, at a portion of the axial direction. The shape of the recess 4ah can be adjusted by adjusting the shape of the depression 1ah on the upper surface 1a of the metal plate 1.

[0064] The distance a0_out from the deepest point C0 of the recess 1ah on the upper surface 1a of the metal sheet 1 to the outer diameter surface 1d before the hole expansion and drawing process is smaller than the distance a0_in from the deepest point C0 of the recess 1ah to the inner diameter surface 1c. The position of the recess 1ah is set to have a third correlation with the target position of the recess 4ah of the tubular part 4. Specifically, the ratio a0_out / a0_in between the distance a0_in from the deepest point C0 of the recess 1ah of the metal sheet 1 to the inner diameter surface 1c and the distance a0_out from the deepest point C0 of the recess 1ah to the outer diameter surface 1d is set to have a third correlation with the target value of the ratio h_up / h_down between the distance h_up from the deepest point C1 of the recess 4ah on the inner peripheral surface 4a of the tubular part to one end surface 4d and the distance h_down from the deepest point C1 of the recess to the other end surface 4c. The third correlation can be, for example, a relationship in which the ratio h_up / h_down of the recess after machining is expressed by a linear function of the ratio a0_out / a0_in of the dent before the hole expansion and drawing.

[0065] The shape of the prepared metal plate 1 is not limited to the above example. For example, the metal plate may have no recess on the upper surface, or may have a recess and have a uniform thickness. The material of the metal plate 1 may be, for example, steel, aluminum, copper, nickel, titanium, an alloy containing at least one of these, or other metals. The tensile strength of the material of the metal plate 1 is not particularly limited, but may be, for example, 780 MPa or less, and is preferably 590 MPa.

[0066] This embodiment is suitably applicable to, for example, the manufacture of annular or tubular parts such as bearing races, but is not limited thereto. For example, the manufacturing method and press apparatus of this embodiment can be applied to the manufacture of tubular (cylindrical) molded products such as the outer races of rolling bearings and bushes of plain bearings. Alternatively, this embodiment can be applied to the manufacture of tubular molded products with irregular cross-sectional shapes (depressions, protrusions, tapers, etc.) used in automobile bushes, oil pump parts, etc.

[0067] <Test Results> FIG. 7 is a diagram showing the molding steps in the test. In FIG. 7, in Example 1, a second intermediate product was produced in the second molding step in which the rear wall 3r was parallel to the axial direction. In Example 2, a second intermediate product was produced in the second molding step in which the rear wall 3r was inclined inward with respect to the axial direction. Steps (1) to (5) and (8) shown in FIG. 7 are the same in Examples 1 and 2. Step (1) is a blank punching process. Step (2) is a coining process. Step (3) is the same as Op11 in FIG. 3, and step (4) is the same as Op12 in FIG. 3. Step (5) is the same as Op21 in FIG. 4 and FIG. 5. Step (6) in Example 1 is the same as Op22 in FIG. 4, and step (7) is the same as Op23. Step (6a) in Example 2 is the same as Op24 in FIG. 5. In Example 1, a test was also performed in the case where one of steps (6) to (7) was omitted.

[0068] The taper angles of the punch and die in step (3) were θp11 = 45° and θd11 = 45°. The taper angles in step (4) were θp12 = θd12 = 30°. The taper angles in steps (5) to (8) were as follows: θp21 = θd21 = 30°, θp22 = θd22 = 30°, θp23 = θd23 = 30°, θd30 = 30°.

[0069] A plated steel sheet was used as the metal sheet 1. Table 1 below shows the chemical composition (mass%) and coating weight of the material (base material) of the metal sheet 1. Table 2 below shows the mechanical properties of the base material of the metal sheet 1. The sheet thickness of the metal sheet 1 was 6 mm. [Table 1]

[0070] [Table 2]

[0071] Table 3 below shows the test results. In the evaluation of each process in the table below, a mark of ○ was given if the molded product had no cracks or wrinkles in each process, and a mark of △ was given if the molded product had wrinkles that did not affect the quality but no cracks. The condition was evaluated as Pass if the metal plate was able to be processed into a good tubular part throughout the entire process.

[0072] [Table 3]

[0073] The test results showed that in both Examples 1 and 2, by producing a second intermediate product in the second forming process and then performing the indentation drawing process in the second forming process, it was possible to process a thin metal plate into a good tubular part while suppressing the occurrence of wrinkles and cracks.

[0074] In Example 1, when step (6) or step (7) is omitted, the drawing ratio becomes large. It was found that the larger the drawing ratio, the more likely wrinkles are to occur. It is presumed that when the drawing ratio is large, the difference in peripheral length between the dies in the rear process and the front process becomes large, making it difficult for in-plane deformation to occur and making it easier for out-of-plane plastic buckling, that is, wrinkles, to occur. Within the range of the above test results, it can be determined that the wrinkles that occur do not have a significant effect on the quality. However, as the drawing ratio becomes large and the incidence of wrinkles increases, the possibility of cracking also increases. From the above test results, it was found that the drawing ratio is preferably greater than 1 and not more than 1.35.

[0075] In Example 2, a tubular part without wrinkles on the outside could be manufactured with fewer steps than in Example 1. This is presumably because in Example 2, the cross-sectional shape of the intermediate product is curved (L-shaped) so that the center part protrudes radially outward, and the perimeter of the intermediate product is reduced by the pressing and drawing process compared to Example 1. [Explanation of symbols]

[0076] 1 metal plate 2. First intermediate product 3. Second intermediate product 4 Tubular parts 10P, 11P, 12P Oblique drawing punch 10D, 11P, 12P Oblique drawing dies 20P, 21P, 22P, 23P, 24P Intermediate drawing punch 20D, 21D, 22D, 23D, 24D Intermediate drawing dies 30P Push-in punch 30D Pressing Die

Claims

1. A preparation step of preparing a metal plate having a hole penetrating from an upper surface to a lower surface; and a forming step of forming the metal plate into a tubular part by hole expansion and drawing. The molding step includes: A first forming step in which the metal plate is pressed with a tapered surface of a tilt drawing punch and a tapered surface of a tilt drawing die to perform hole expansion and drawing to obtain a first intermediate product having an inclined wall inclined with respect to the axial direction; a second forming step in which the first intermediate product is subjected to a pressing-drawing process using an intermediate pressing punch and an intermediate pressing die to obtain a second intermediate product having a front wall inclined with respect to the axial direction at a front portion in the pressing direction, and a rear wall inclined with respect to the axial direction or inclined with respect to the axial direction in a direction opposite to the inclination of the front wall at a rear portion in the pressing direction relative to the front wall; and a third forming step of pressing the rear wall of the second intermediate product placed in a pressing die with a pressing punch to perform pressing and drawing to obtain a tubular part.

2. 2. A method for producing a tubular part according to claim 1, comprising the steps of: In the second forming step, a plurality of sets of the intermediate drawing punch and the intermediate drawing die are used to perform a plurality of press-drawing processes to obtain the second intermediate product.

3. 3. A method for producing a tubular part according to claim 2, comprising the steps of: In the nth (n is a natural number of 2 or more) press-drawing process in the second forming step, an intermediate drawing die having a smaller diameter than the intermediate drawing die used in the (n-1)th press-drawing process is used.

4. The method according to any one of claims 1 to 3, In the second molding step, The intermediate drawing die has a vertical wall portion having an inner surface parallel to the pushing direction, and a tapered portion having a tapered surface that becomes wider from the vertical wall portion toward the rear in the pushing direction, The intermediate drawing punch has a base portion having an outer circumferential surface parallel to the pushing direction, and a leading portion having a tapered surface that narrows from the base portion toward the front in the pushing direction, A method for manufacturing a tubular part, in which the first intermediate product is supported between the boundary between the vertical wall portion and the tapered portion of the intermediate drawing die, and the boundary between the base portion and the front end portion of the intermediate drawing punch, and the push-drawing process is performed.

5. A method for producing a tubular part according to any one of claims 1 to 4, comprising the steps of: In the second forming step, a second intermediate product is obtained, the second intermediate product having a rear wall with an inclination angle of 15 to 45 degrees relative to an axial direction.

6. 3. A method for producing a tubular part according to claim 2, comprising the steps of: A method for manufacturing a tubular part, wherein in the second forming step, the intermediate drawing die in each of the second and subsequent press-drawing processes among the multiple press-drawing processes satisfies the condition represented by the following formula. 1<(Dd_n-1 / Dd_n)≦1.35 Dd_n: Diameter of the intermediate drawing die used in the nth (n is a natural number of 2 or more) pressing Dd_n-1: Diameter of the intermediate drawing die used in the n-1th pressing

7. A method for producing a tubular part according to any one of claims 1 to 6, comprising the steps of: In the first forming step, a first intermediate product is obtained, the first intermediate product having an inclined wall with an inclination angle of 30 to 50 degrees relative to an axial direction.

8. A method for producing a tubular part according to any one of claims 1 to 7, comprising the steps of: In the third forming step, the second intermediate product is subjected to the pressing drawing process using the pressing punch and the pressing die that satisfy the following formula: rd3-rp3<t rp3-rcp>0 t: wall thickness of the second intermediate product rd3: radius of the pressing die rp3: radius of the pressing punch rcp: Radius from the central axis to the inner circumferential edge of the rear end of the second intermediate product in the pushing direction

9. A press apparatus for forming a metal plate having a hole penetrating from an upper surface to a lower surface into a tubular part by hole expansion and drawing, A diagonal drawing die and a diagonal drawing punch used to obtain a first intermediate product having an inclined wall inclined with respect to the axial direction by performing hole expansion and drawing on the metal plate; an intermediate drawing punch and an intermediate drawing die used to obtain a second intermediate product by performing a drawing process on the first intermediate product, the second intermediate product having a front wall inclined with respect to the axial direction at a front portion in the drawing direction, and a rear wall parallel to the axial direction or inclined with respect to the axial direction in a direction opposite to the inclination of the front wall at a rear portion in the drawing direction relative to the front wall; a pressing die for placing the second intermediate product therein, and a pressing punch for pressing the rear wall of the placed second intermediate product to perform pressing and drawing to obtain a tubular part, The oblique drawing die and the oblique drawing punch each have a tapered surface, and are configured to press the metal plate with the tapered surface of the oblique drawing die and the tapered surface of the oblique drawing punch to form the oblique wall of the first intermediate product, The intermediate drawing die has a vertical wall portion having an inner surface parallel to the pushing direction, and a tapered portion having a tapered surface that widens from the vertical wall portion toward the rear in the pushing direction, The intermediate drawing punch has a base portion having an outer circumferential surface parallel to the pushing direction, and a leading portion having a tapered surface that narrows from the base portion toward the front in the pushing direction, The pressing die has a recess having an inner surface corresponding to a shape of the tubular part, and the pressing punch has a protrusion insertable into the recess.

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