Method for molding cylindrical body with tapered part

Abstract

To provide a technology to reliably mold a cylindrical body with a tapered part by plastic working and to impart compressive residual stress to the cylindrical body even in a high-hardness and difficult-to-process material.SOLUTION: A closed end part of a bottomed cylindrical material is pressed by a punch and stretched while reducing the diameter to form a small diameter cylindrical part, and an opening end is left as it is without reducing the diameter to form a tapered part, thereby generating an intermediate material. Then, the closed end part of the intermediate material is pressed by another punch, and the small diameter cylindrical part is further reduced in diameter and stretched without reducing the diameter of the tapered part. Then, the inner peripheral surface of the tapered part is pressed by still another punch, and the small diameter cylindrical part is further reduced in diameter and stretched without reducing the diameter of the tapered part. Finally, the tapered part is clamped between the punch and a die.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for forming a cylindrical body having a tapered portion. [Background technology]

[0002] A known method for forming a cylindrical body having a tapered portion (flared portion), where the diameter increases from the straight portion toward the end, is described in Patent Document 1 (WO 2023 / 105883). As illustrated in Fig. 9, this method involves placing a bottomed, cylindrical blank 101 inside a die hole 310 formed in a die 301, inserting a substantially truncated cone-shaped mandrel 401 into the open end of blank 101 to expand the diameter and form a tapered portion, and then pressing the end face of the tapered portion with a step formed on the side of mandrel 401 to force the cylindrical portion of blank 101 into the small-diameter portion of die hole 310, thereby performing a drawing process, thereby stretching and reducing the diameter of the cylindrical portion to obtain the desired shape.

[0003] The above-described method is a useful processing method for forming a "cylinder having a tapered portion" as an intermediate material for products such as nozzles. However, in the case of high-hardness, difficult-to-process materials (such as austenitic stainless steel materials with a thick plate thickness of several millimeters), pressing the end face of the flared portion, which has a small area, places an excessive load on the end face and the step portion of the punch that contacts the end face, resulting in problems such as deformation of the end face of the flared portion, inability to press, and / or damage to the step portion of the punch, making it impossible to perform drawing.

[0004] Meanwhile, Patent Document 2 (Japanese Patent No. 4388187) proposes a method for forming a cylindrical body having a tapered portion by repeatedly stretching and reducing the diameter of the cylindrical portion of a cup-shaped semifinished product. In this method, as illustrated in Figs. 10(a) to 10(c), a cup-shaped semifinished product 20 having a cylindrical wall with one open end and the other closed is drawn from the bottom wall 22 toward the open end of the cylindrical wall 21 using several pairs of plastic dies (not shown), each consisting of a punch and a die. This results in a semifinished product 50 having a stepped flange 55 consisting of several steps at the open end of the cylindrical wall 51, as illustrated in Fig. 10(d). Then, as illustrated in Fig. 11, the flange 55 of the semifinished product is clamped between dies 71 and 72 to form a flared portion 15.

[0005] In the above-mentioned method, since the end face of the tapered portion (flared portion) is not pressed, theoretically no problems occur as with the method described in the above-mentioned Patent Document 1. However, in order to obtain a cylindrical portion having a desired shape, multiple sets of punches and dies must be prepared and processing must be repeated sequentially, which raises concerns about work hardening with each process and is not practical in terms of the number of steps and cost involved in the processing process.

[0006] Furthermore, while the above-mentioned method can be applied to ordinary materials, for high-hardness, difficult-to-process materials, the processing load increases significantly due to work hardening caused by repeated sequential processing, making heat treatment such as "annealing" necessary, further increasing the number of steps and costs involved in the processing. The same problems as those mentioned above also exist in forming a stepped flange portion and forming a flared portion by clamping the flange portion. Therefore, it is difficult or impossible to apply the above-mentioned method to high-hardness, difficult-to-process materials to form a cylindrical body with a tapered portion (flared portion).

[0007] Furthermore, when the cylindrical portion is stretched and reduced in diameter only by drawing, as in the above-mentioned method, tensile stress remains in the final molded product, which may lead to so-called "delayed fracture" depending on the material. In particular, residual tensile stress in molded products used as products that are internally subjected to pressure (e.g., nozzles) is undesirable because it weakens the fatigue limit and reduces the margin for internal pressure. From this perspective, residual compressive stress is preferable in molded products that are used as products that are internally subjected to pressure. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2023 / 105883 [Patent Document 2] Patent No. 4388187 Summary of the Invention [Problem to be solved by the invention]

[0009] As mentioned above, there is a need in this technical field for a technology that can reliably form a cylindrical body having a tapered portion by plastic processing even in a high-hardness, difficult-to-process material, and that can impart compressive residual stress to the cylindrical body. [Means for solving the problem]

[0010] In view of the above problems, the present inventors conducted extensive research and found that the above problems can be solved by: pressing the closed end of a bottomed cylindrical material with a punch to reduce its diameter and stretch it to form a small-diameter cylindrical portion, while leaving the open end unreduced to form a tapered portion, thereby obtaining an intermediate material; then pressing the closed end of the intermediate material with another punch to further reduce the diameter of the small-diameter cylindrical portion while stretching it, without reducing the diameter of the tapered portion; next pressing the inner surface of the tapered portion with yet another punch to further reduce the diameter of the small-diameter cylindrical portion while stretching it, without reducing the diameter of the tapered portion; and finally clamping the tapered portion between the punch and die.

[0011] Specifically, the method for forming a cylindrical body having a tapered portion according to the present invention (hereinafter sometimes referred to as the "method of the present invention") is a method for forming a cylindrical body having a tapered portion by using a die hole and a punch to form a tapered portion and a cylindrical portion from a bottomed cylindrical material. The first method includes the first to third steps listed below.

[0012] The first step is to insert a first punch into the open end of the blank and press the bottom of the blank with the tip of the first punch to force the blank into a first die hole formed in the first die. This causes the closed end of the blank, which includes the closed end, to be reduced in diameter and elongated to form a first small-diameter cylindrical portion. Meanwhile, the open end is left unreduced to form a first tapered portion, which is located between the open end and the first small-diameter cylindrical portion and connects them. As a result, a first intermediate blank having a first small-diameter cylindrical portion and a first tapered portion can be obtained.

[0013] The second step involves inserting a second punch through the open end of the first intermediate material and pressing the bottom of the first intermediate material with the tip of the second punch to force the first intermediate material into a second die hole formed in the second die. This reduces and stretches the first closed end of the first intermediate material, which includes the closed end of the first small-diameter cylindrical portion, to form a second small-diameter cylindrical portion. Meanwhile, the first tapered portion of the first intermediate material is left unreduced to form a second tapered portion that is interposed between the first tapered portion and the second small-diameter cylindrical portion and connects them. As a result, a second intermediate material having a second small-diameter cylindrical portion, a second tapered portion, and a first tapered portion can be obtained.

[0014] The third step involves inserting a third punch through the open end of the second intermediate material and pressing the inner circumferential surfaces of the first and second tapered portions of the second intermediate material into a third die hole formed in the third die. This reduces and stretches the second closed end of the second intermediate material, which includes the closed end of the second small-diameter cylindrical portion, to form a third small-diameter cylindrical portion. Meanwhile, the first and second tapered portions of the second intermediate material are left unreduced, and the portion between the open end and the third small-diameter cylindrical portion is clamped and pressed between the third punch and the third die, forming a third tapered portion that connects the open end and the third small-diameter cylindrical portion. As a result, a molded product having a third small-diameter cylindrical portion and a third tapered portion can be obtained. That is, a cylindrical body having a tapered portion can be molded. [Effects of the Invention]

[0015] As described above, in the method of the present invention, the closed end of a bottomed cylindrical material is pressed with a punch to reduce its diameter and elongate it to form a small-diameter cylindrical portion, while the open end is left unreduced to form a tapered portion, thereby obtaining an intermediate material; then, the closed end of the intermediate material is pressed with another punch to further reduce the diameter of the small-diameter cylindrical portion while elongating it without reducing the diameter of the tapered portion; next, the inner circumferential surface of the tapered portion is pressed with yet another punch to further reduce the diameter of the small-diameter cylindrical portion while elongating it without reducing the diameter of the tapered portion; and finally, the tapered portion is clamped between the punch and the die. Therefore, according to the method of the present invention, even in high-hardness, difficult-to-work materials, it is possible to reliably form a cylindrical body having a tapered portion by plastic working and impart compressive residual stress to the cylindrical body.

[0016] Other objects, other features and attendant advantages of the present invention will be readily apparent from the following description of the embodiments of the present invention which will be given with reference to the drawings. [Brief explanation of the drawings]

[0017] [Figure 1]1 is a flowchart showing the flow of each step included in a method (first method) for molding a cylindrical body having a tapered portion according to a first embodiment of the present invention. [Figure 2] 3A to 3C are schematic cross-sectional views illustrating changes in the position and shape of a material as the first and second steps performed in the first method progress. [Figure 3] 5 is a schematic cross-sectional view illustrating the correspondence between the amount of a first intermediate material pressed into a second die hole by a second punch and the shape of the resulting second intermediate material. FIG. [Figure 4] 5A to 5C are schematic cross-sectional views illustrating changes in the position and shape of the material as the third step performed in the first method progresses. [Figure 5] 1 is a schematic diagram illustrating an example of overlapping cross sections of a plane including the central axis of a material, a first intermediate material, a second intermediate material, and a molded product (a cylindrical body having a tapered portion). [Figure 6] 1 is a graph illustrating the distribution of plate thickness in the axial direction of a cylindrical body having a tapered portion and a small-diameter cylindrical portion. [Figure 7] 10A and 10B are schematic cross-sectional views illustrating forces acting on a second intermediate material in a third step. [Figure 8] 10A to 10C are schematic cross-sectional views illustrating changes in the position and shape of the material as the second step performed in the method for molding a cylindrical body having a tapered portion (third method) according to the third embodiment of the present invention progresses. [Figure 9] 1 is a schematic diagram illustrating how a cylindrical body having a tapered portion is formed by the method described in Patent Document 1. FIG. [Figure 10] FIG. 1 is a schematic diagram illustrating a process for forming a cylindrical portion of a semi-finished product that will become the stem of a cylindrical body having a tapered portion and a flange portion of the semi-finished product that will become the flared portion in the method described in Patent Document 2. [Figure 11] FIG. 10 is a schematic diagram illustrating a process in which a flange portion of a semi-finished product is clamped and pressed by a mold to form a flared portion of a cylindrical body having a tapered portion in the method described in Patent Document 2. DETAILED DESCRIPTION OF THE INVENTION

[0018] First Embodiment A method for molding a cylindrical body having a tapered portion according to a first embodiment of the present invention (hereinafter, sometimes referred to as "first method") will be described below with reference to the drawings.

[0019] <composition> The first method is a method for forming a cylindrical body having a tapered portion by forming a tapered portion and a cylindrical portion from a bottomed cylindrical material using a die hole and a punch.

[0020] The basic configuration of an apparatus for carrying out the first method is well known to those skilled in the art, and therefore a detailed description thereof will be omitted. However, the components, including the die and punch, are made of materials having properties (e.g., mechanical strength and durability) that can withstand the processing conditions, such as the load acting on the components, during the process of carrying out the first method. Furthermore, for example, the drive mechanism for forcing the punch into the die hole in steps 1 to 3 described below can be appropriately selected from various drive mechanisms well known in the art, depending on the properties (e.g., mechanical strength and hardness) of the material that constitutes the blank. Typically, a press, such as a hydraulic press, is used as the drive mechanism.

[0021] The material for forming the cylindrical body having a tapered portion is a bottomed cylindrical member made of a material that can be formed by cold forging. The material constituting such a material is not particularly limited as long as it can be formed into a desired shape by plastic deformation in drawing. Typically, the material constituting the material is a metal such as lead, tin, aluminum, copper, zirconium, titanium, molybdenum, vanadium, niobium, iron, etc., or an alloy containing two or more of these metals.

[0022] Furthermore, the method for manufacturing the above-described cylindrical blank with a bottom is not particularly limited and can be appropriately selected from various methods known to those skilled in the art. For example, the cylindrical blank with a bottom can be manufactured by drawing a flat plate-like member made of the above-described material.

[0023] Fig. 1 is a flowchart showing the flow of each step included in the first method. Fig. 2 is a schematic cross-sectional view illustrating changes in the position and shape of a material as the first step and second step performed in the first method progress. Fig. 3 is a schematic cross-sectional view illustrating changes in the position and shape of a material as the third step performed in the first method progresses. As illustrated in Fig. 1, the first method includes the first step (step S10), second step (step S20), and third step (step S30) listed below.

[0024] 2(a) and 2(b), the first process executed in step S10 is a process in which a first punch 121 is inserted from the open end of the blank 110 and the tip of the first punch 121 presses the bottom of the blank 110 to force the blank 110 into a first die hole 131a formed in a first die 131. The outer diameter of the first punch 121 is smaller than the inner diameter of the blank 110, and the inner diameter of the first die hole 131a is smaller than the outer diameter of the blank 110.

[0025] As a result of the above, the closed end portion of the material 110, which is a portion including the closed end, is drawn while being reduced in diameter to form the first small diameter cylindrical portion 111s. Meanwhile, the open end is left unreduced in diameter to form the first tapered portion 111t, which is a portion interposed between the open end and the first small diameter cylindrical portion 111s and connecting the open end and the first small diameter cylindrical portion 111s. As a result, a first intermediate material 111 having the first small diameter cylindrical portion 111s and the first tapered portion 111t can be obtained, as shown in FIG. 2(b).

[0026] 2(c) and 2(d), the second process executed in step S20 is a process in which a second punch 122 is inserted from the open end of the first intermediate material 111 and the tip of the second punch 122 is pressed against the bottom of the first intermediate material 111 to force the first intermediate material 111 into a second die hole 132a formed in a second die 132. The outer diameter of the second punch 122 is smaller than the inner diameter of the first small diameter cylindrical portion 111s of the first intermediate material 111, and the inner diameter of the second die hole 132a is smaller than the outer diameter of the first small diameter cylindrical portion 111s of the first intermediate material 111.

[0027] As a result of the above, the first closed end portion, which is a portion including the closed end of the first small diameter cylindrical portion 111s of the first intermediate material 111, is drawn while being reduced in diameter to form the second small diameter cylindrical portion 112s. Meanwhile, the first tapered portion 111t of the first intermediate material 111 is left unreduced in diameter to form the second tapered portion 112t, which is a portion interposed between the first tapered portion 111t and the second small diameter cylindrical portion 112s and connecting the first tapered portion 111t and the second small diameter cylindrical portion 112s. As a result, as illustrated in FIG. 2(d), a second intermediate material 112 having the second small diameter cylindrical portion 112s, the second tapered portion 112t, and the first tapered portion 111t can be obtained.

[0028] In the second step, to obtain the second intermediate material 112 having the initial shape, it is necessary to press an appropriate amount of the first intermediate material 111 into the second die hole 132a by the second punch 122. Figure 3 is a schematic cross-sectional view illustrating the correspondence between the amount by which the first intermediate material 111 is pressed into the second die hole 132a by the second punch 122 and the shape of the second intermediate material 112 obtained as a result.

[0029] 3(a), the amount of pressing by the second punch 122 is insufficient, so the second small diameter cylindrical portion 112s of the second intermediate material 112 is not sufficiently formed, and the region adjacent to the first tapered portion 111t of the first small diameter cylindrical portion 111s of the first intermediate material 111 remains unreduced in diameter. As a result, a step is created in the region that should be a smoothly tapered portion consisting of the second tapered portion 112t and the first tapered portion 111t (see the portion surrounded by the thick dashed line).

[0030] 3(c), although a smoothly tapered portion consisting of the second tapered portion 112t and the first tapered portion 111t is formed, the first small diameter cylindrical portion 111s of the first intermediate material 111 is excessively elongated due to an excessive pressing amount by the second punch 122. As a result, thinning and / or fracture occurs near the bottom of the second small diameter cylindrical portion 112s of the second intermediate material 112 (see the portion surrounded by the thick solid line).

[0031] In contrast to the above, in the example shown in Figure 3(b), the amount of pressing by the second punch 122 is appropriate, so the second intermediate material 112 is well formed, having a smooth tapered portion without steps consisting of the second tapered portion 112t and the first tapered portion 111t, and a second small diameter cylindrical portion 112s without thinning or fracture.

[0032] Next, the third process executed in step S30 is a process of inserting a third punch 123 from the open end of the second intermediate material 112 and pressing the inner circumferential surfaces of the first tapered portion 111t and the second tapered portion 112t of the second intermediate material 112 with the third punch 123 to force the second intermediate material 112 into a third die hole 122a formed in a third die 133, as illustrated in Figures 4(a) to 4(c). The outer circumferential surface of the third punch 123 has a tapered shape whose outer diameter decreases toward the tip so as to conform to the inner circumferential surfaces of the first tapered portion 111t and the second tapered portion 112t of the second intermediate material 112. The inner diameter of the third die hole 133a is smaller than the outer diameter of the second small-diameter cylindrical portion 112s of the second intermediate material 112.

[0033] As a result of the above, the second closed end portion of the second intermediate material 112, which includes the closed end of the second small-diameter cylindrical portion 112s, is stretched while being reduced in diameter to form the third small-diameter cylindrical portion 113s. Meanwhile, the first tapered portion 111t and the second tapered portion 112t of the second intermediate material 112 are left unreduced, and the portion between the open end and the third small-diameter cylindrical portion 113s is clamped and pressed by the third punch 123 and the third die 133 to form the third tapered portion 113t, which is located between the open end and the third small-diameter cylindrical portion 113s and connects the open end and the third small-diameter cylindrical portion 113s. As a result, a molded product 113 having the third small-diameter cylindrical portion 113s and the third tapered portion 113t can be obtained, as illustrated in FIG. 4(c). That is, a cylindrical body having a tapered portion can be molded.

[0034] <effect> As described above, in the first method, the closed end of a bottomed cylindrical material is pressed with a punch to reduce its diameter and stretch it to form a small-diameter cylindrical portion, while the open end is left unreduced to form a tapered portion, thereby obtaining an intermediate material; then, the closed end of the intermediate material is pressed with another punch to extend the small-diameter cylindrical portion while further reducing its diameter without reducing the diameter of the tapered portion; next, the inner surface of the tapered portion is pressed with yet another punch to extend the small-diameter cylindrical portion while further reducing its diameter without reducing the diameter of the tapered portion; and finally, the tapered portion is clamped between a punch and a die.

[0035] That is, the first method does not include a step of pressing the end face of the small-area flared portion (tapered portion) with the step portion of the punch, as in the method described in Patent Document 1. Therefore, even when a high-hardness, difficult-to-process material is used, the first method does not encounter problems such as deformation of the end face of the flared portion, inability to press, and / or damage to the step portion of the punch due to excessive load being applied between the end face of the flared portion and the step portion of the punch, as in the method described in Patent Document 1. As a result, a cylindrical body having a tapered portion (flared portion) and a small-diameter cylindrical portion with a desired shape (a molded product having a third small-diameter cylindrical portion and a third tapered portion) can be reliably formed.

[0036] Furthermore, the end surface of the open end of a bottomed cylindrical material produced by drawing a flat plate-like member is generally not flat but has a wavy shape. Therefore, when the end surface of the flared portion (tapered portion) is pressed by the step portion of the punch, as in the method described in Patent Document 1, it is necessary to flatten the end surface of the flared portion by secondary processing such as cutting in order to bring the end surface of the flared portion into surface contact with the step portion of the punch. However, in the first method, the end surface of the flared portion is not pressed, so such secondary processing is not necessary, thereby reducing the number of steps and the increase in cost of the processing process.

[0037] Furthermore, in the second and third steps included in the first method, as described above, the opening end is left unreduced in the first step, thereby forming a first tapered portion 111t between the opening end and the first small-diameter cylindrical portion 111s, and the first tapered portion 111t is left unreduced in the second step, thereby forming a second tapered portion 112t between the first tapered portion 111t and the second small-diameter cylindrical portion 112s. That is, the first tapered portion and the second tapered portion formed in the first method are not formed by expanding the opening end as in the method described in Patent Document 1, nor are they formed in a stepped shape by being sandwiched between a punch and a die as in the method described in Patent Document 2, but are formed by the remaining portion without being reduced in diameter. As a result, the first method can reduce the deviation in plate thickness (wall thickness) of the first tapered portion and the second tapered portion.

[0038] FIG. 5 is a schematic diagram illustrating overlapping cross sections of the blank 110, the first intermediate blank 111, the second intermediate blank 112, and the formed product (a cylindrical body having a tapered portion) 113, taken along a plane including the central axis AX. As is apparent from FIG. 5, as the processing associated with the first method progresses from the blank 110 to the first intermediate blank 111, the second intermediate blank 112, and the formed product (a cylindrical body having a tapered portion) 113, the blank 110 undergoes diameter reduction and elongation from its open end to the first small-diameter cylindrical portion 111s, the second small-diameter cylindrical portion 112s, and the third small-diameter cylindrical portion 113s. Meanwhile, there is little difference in the outer diameters of the open ends of the blank 110, the first intermediate blank 111, the second intermediate blank 112, and the formed product 113. Therefore, work hardening in the tapered portion formed by the first method is smaller (less severe) than work hardening in the tapered portion formed by the methods described in Patent Documents 1 and 2. As a result, even when a high-hardness, difficult-to-process material is used, the first method can reduce the increase in processing load caused by work hardening compared to the methods described in the above-mentioned Patent Documents 1 and 2. As will be described later in the description of the method for forming a cylindrical body having a tapered portion according to the third embodiment of the present invention, the second small-diameter cylindrical portion and the second tapered portion may be formed gradually by repeating the second step multiple times.

[0039] Additionally, in the third step included in the first method, as described above, the inner circumferential surfaces of the first tapered portion and the second tapered portion of the second intermediate material are pressed by the third punch to force the second closed end portion of the second intermediate material into the third die hole formed in the third die, and the portion between the open end and the third small-diameter cylindrical portion is clamped between the third punch and the third die. Therefore, the third small-diameter cylindrical portion and the third tapered portion can be formed while applying a compressive load, which allows compressive stress to remain in the third small-diameter cylindrical portion and the third tapered portion. As a result, problems such as a decrease in fatigue limit and / or margin for internal pressure due to residual tensile stress can be reduced.

[0040] Furthermore, in the third step as described above, the end face of the opening end is not constrained (pressed) when the portion between the opening end and the third small diameter cylindrical portion is clamped by the third punch and the third die, unlike the method described in Patent Document 1. Therefore, the plastic flow of the material constituting the clamped portion is easier, and the flatness of the tapered portion of the finally obtained cylindrical body having a tapered portion (flared portion) and a small diameter cylindrical portion (molded product having a third small diameter cylindrical portion and a third tapered portion) can be further improved.

[0041] FIG. 6 is a graph illustrating the distribution of thickness in the axial direction of a cylindrical body having a tapered portion and a small-diameter cylindrical portion. Below the graph is a cross-sectional view of the tapered portion and the small-diameter cylindrical portion of the cylindrical body taken along a plane including the axis of the cylindrical body. As illustrated in FIG. 6(a), in a cylindrical body formed by the method described in Patent Document 1, the thickness of the small-diameter cylindrical portion (the portion on the left side of the drawing) is almost constant. In contrast, the thickness of the tapered portion (the portion on the right side of the drawing) is smaller (thinner) than that of the small-diameter cylindrical portion at the open end (right end), increases as it approaches the small-diameter cylindrical portion, and is larger (thicker) than that of the small-diameter cylindrical portion near the boundary between the small-diameter cylindrical portion and the tapered portion. As a result, the thickness deviation in the tapered portion and the small-diameter cylindrical portion was approximately 1.0 mm.

[0042] As mentioned above with reference to Figure 9, this is thought to be because, in the method described in Patent Document 1, the approximately truncated cone-shaped core 401 is inserted into the open end of the material 101 and expanded in diameter to form a tapered portion, resulting in a reduction in the plate thickness near the open end of the tapered portion, and because the step portion formed on the side of the core 401 presses (restrains) the end face of the tapered portion, forcing the cylindrical portion of the material 101 into the small diameter portion of the die hole 310 and performing drawing, thereby stretching and reducing the diameter of the cylindrical portion, resulting in an increase in plate thickness near the boundary with the small diameter cylindrical portion of the tapered portion.

[0043] On the other hand, as shown in Figure 6(b), even in the cylindrical body formed by the first method, the thickness of the small-diameter cylindrical portion (the portion on the left side of the drawing) is almost constant. Furthermore, the thickness of the tapered portion (the portion on the right side of the drawing) is slightly larger (thicker) than that of the small-diameter cylindrical portion near the boundary between the small-diameter cylindrical portion and the tapered portion, but is constant at a thickness almost equal to that of the small-diameter cylindrical portion in the range from that portion to the open end (right end). As a result, the deviation in thickness between the tapered portion and the small-diameter cylindrical portion was approximately 0.2 mm.

[0044] As described above, in the first method, unlike the method described in Patent Document 1 in which a tapered portion is formed by expanding the diameter of the open end and the cylindrical portion is stretched and reduced in diameter while the end face of the tapered portion is pressed (restrained) to form a small-diameter cylindrical portion, the tapered portion is formed by the cylindrical portion that remains unreduced in diameter and the cylindrical portion is stretched and reduced in diameter while the end face of the tapered portion is not pressed (restrained), and this is thought to be due to the fact that deviation in plate thickness (wall thickness) at the tapered portion is reduced and flatness is improved.

[0045] As described above, according to the first method, even when a hard-to-process material has high hardness, it is possible to reliably form a cylindrical body having a tapered portion by plastic processing, and to impart compressive residual stress to the cylindrical body.

[0046] Incidentally, for example, in order to improve the dimensional accuracy of the inner diameter and / or the smoothness of the inner surface of the third small diameter cylindrical portion 113s of a molded product 113 (a cylindrical body having a tapered portion) having a third small diameter cylindrical portion 113s and a third tapered portion 113t formed by the first method, a finishing process may be carried out after the first method, in which a scraping process is performed on the inner surface of the third small diameter cylindrical portion 113s.

[0047] Furthermore, depending on the required specifications for the intended use of a molded product 113 (a cylindrical body having a tapered portion) having a third small diameter cylindrical portion 113s and a third tapered portion 113t formed by, for example, the first method, the closed end of the third small diameter cylindrical portion 113s may be cut off with, for example, a cutting tool to form the molded product 113 into a bottomless cylindrical body. Alternatively, for the purpose of adjusting the molded product 113 to the dimensions (correct dimensions) required for the intended use, the closed end of the third small diameter cylindrical portion 113s and / or the open end of the third tapered portion 113t may be cut off (trimmed) with, for example, a cutting tool.

[0048] Second Embodiment Next, a method for molding a cylindrical body having a tapered portion according to a second embodiment of the present invention (hereinafter, sometimes referred to as the "second method") will be described below with reference to the drawings.

[0049] As described above, in the third step included in the first method, the third punch presses the inner circumferential surfaces of the first and second tapered portions of the second intermediate material to force the second intermediate material into the third die hole, thereby reducing and elongating the second closed end portion of the second intermediate material to form a third small-diameter cylindrical portion. FIG. 7 is a schematic cross-sectional view illustrating the forces acting on the second intermediate material in the third step. Note that in FIG. 7, the reference numerals assigned to the various components of the second intermediate material have been omitted for the sake of simplicity. However, in the following description, the reference numerals shown in FIGS. 2 to 4 will be used for accuracy, so please refer to FIGS. 2 to 4 as necessary.

[0050] As illustrated in FIG. 7 , in the third step, the inner peripheral surfaces of the first tapered portion 111t and the second tapered portion 112t of the second intermediate material 112 are pressed by the third punch 123 (see the open arrows). Accordingly, the first tapered portion 111t and the second tapered portion 112t of the second intermediate material 112 are subjected to stresses resulting from the drawing resistance associated with the drawing of the second closed end portion of the second intermediate material 112 (see the filled arrows), and stresses resulting from the frictional resistance between the outer peripheral surface of the second closed end portion of the second intermediate material 112 and the inner peripheral surface of the third die hole (see the arrows hatched with a diagonal grid). Hereinafter, the former stresses may be referred to as "drawing stresses," and the latter stresses may be referred to as "frictional stresses."

[0051] Therefore, in order to form the third small-diameter cylindrical portion 113s by drawing while reducing the diameter of the second closed end portion of the second intermediate material 112 in the third step, it is necessary to press the second closed end portion of the second intermediate material 112 into the third die hole while the first tapered portion 111t and the second tapered portion 112t of the second intermediate material 112 maintain their shapes without causing unintended deformation against the above-mentioned stress. In other words, the maximum stress (hereinafter, sometimes referred to as "load capacity") at which the first tapered portion 111t and the second tapered portion 112t of the second intermediate material 112 can maintain their shapes without causing unintended deformation against the stress acting in the axial direction must be greater than the sum of the drawing stress and the frictional stress described above.

[0052] <composition> Therefore, the second method is the above-mentioned first method, which is a method for molding a cylindrical body having a tapered portion, characterized in that in the third step, the load capacity, which is the maximum stress at which the first tapered portion and the second tapered portion of the second intermediate material can maintain their shape against stress acting in the axial direction, is greater than the sum of the drawing stress, which is the stress caused by the drawing resistance of the second small diameter cylindrical portion of the second intermediate material, and the friction stress, which is the stress caused by the frictional resistance with the third die (load capacity > drawing stress + frictional stress).

[0053] That is, in the second method, the load capacity Lmax, which is the maximum stress at which the first tapered portion 111t and the second tapered portion 112t of the second intermediate material 112 can maintain their shape without unintended deformation against the stress acting in the axial direction, is greater than the sum of the drawing stress Sd, which is the stress caused by the drawing resistance of the second small diameter cylindrical portion 112s of the second intermediate material 112 in the third step, and the frictional stress Sf, which is the stress caused by the frictional resistance between the second intermediate material 112 and the third die hole 133a (Lmax > Sd + Sf).

[0054] The load capacity Lmax, which is the maximum stress at which the first tapered portion 111t and the second tapered portion 112t of the second intermediate material 112 can maintain their shape without causing unintended deformation against stress acting in the axial direction, varies depending on, for example, the size and thickness of the first tapered portion 111t and the second tapered portion 112t of the second intermediate material 112 and the ease of plastic flow of the material constituting the material. Furthermore, the drawing stress Sd, which is the stress caused by the drawing resistance of the second small diameter cylindrical portion 112s of the second intermediate material 112 in the third step, varies depending on, for example, the diameter reduction rate from the second small diameter cylindrical portion 112s of the second intermediate material 112 to the third small diameter cylindrical portion 113s of the formed product 113 and the drawing radius (also referred to as "die radius") of the inner peripheral surface of the third die hole 113a. Furthermore, the frictional stress Sf, which is the stress caused by the frictional resistance between the second intermediate material 112 and the third die hole 133a in the third step, changes depending on, for example, the lubrication treatment on the outer surface of the second small diameter cylindrical portion 112s of the second intermediate material 112 and / or the inner surface of the third die hole 113a (for example, a bonder treatment on the outer surface of the second small diameter cylindrical portion 112s and application of a lubricant to the inner surface of the third die hole 113a).

[0055] <effect> As described above, in the second method, the above parameters are appropriately adjusted so that the load capacity, which is the maximum stress at which the first tapered portion and the second tapered portion of the second intermediate material can maintain their shape without unintended deformation against the stress acting in the axial direction, is greater than the sum of the drawing stress, which is the stress caused by the drawing resistance of the second small diameter cylindrical portion of the second intermediate material, and the friction stress, which is the stress caused by the frictional resistance with the third die (Lmax>Sd+Sf).

[0056] Therefore, in the second method, in the third step, the first tapered portion and the second tapered portion of the second intermediate material can be pressed and forced into the third die hole while maintaining their shapes without unintended deformation against the stress. As a result, according to the second method, the second closed end portion of the second intermediate material can be stretched while reducing its diameter in the third step, thereby reliably forming the third small diameter cylindrical portion.

[0057] Third Embodiment Next, a method for molding a cylindrical body having a tapered portion according to a third embodiment of the present invention (hereinafter, sometimes referred to as the "third method") will be described below with reference to the drawings.

[0058] As described above, the second step included in the first and second methods is a step of inserting a second punch into the open end of the first intermediate material and pressing the bottom of the first intermediate material with the tip of the second punch to force the first intermediate material into a second die hole formed in the second die. This reduces and stretches the first closed end of the first intermediate material, which includes the closed end of the first small-diameter cylindrical portion, to form a second small-diameter cylindrical portion. Meanwhile, the first tapered portion of the first intermediate material is left unreduced to form a second tapered portion that is interposed between the first tapered portion and the second small-diameter cylindrical portion and connects the first tapered portion and the second small-diameter cylindrical portion. As a result, a second intermediate material having a second small-diameter cylindrical portion, a second tapered portion, and a first tapered portion can be obtained.

[0059] However, when the second step is performed once to obtain the second intermediate material from the first intermediate material obtained by performing the first step, there is a risk of work hardening and / or an excessive increase in the processing load. For example, in order to suppress the work hardening and the excessive increase in the processing load, it is necessary to repeatedly perform the second step multiple times and to reduce the diameter reduction rate in each second step.

[0060] <composition> Therefore, the third method is a method for molding a cylindrical body having a tapered portion, which is the above-mentioned first or second method, characterized in that the second step is repeated multiple times to gradually form the second small diameter cylindrical portion and the second tapered portion.

[0061] 8 is a schematic cross-sectional view illustrating changes in the position and shape of the material as the second step performed in the third method progresses. In the example shown in FIG. 8, the second step is repeated twice to gradually form the second small-diameter cylindrical portion and the second tapered portion. First, the first second step is performed in (a) and (b) of FIG. 8. The second step illustrated in (a) and (b) of FIG. 8 is basically the same as the second step illustrated in (c) and (d) of FIG. 2, which was referred to in the description of the first method.

[0062] In the third method, a second second step is then performed as shown in FIGS. 8(c) and 8(d). As illustrated in FIGS. 8(c) and 8(d), in the second second step, the second intermediate material 112 obtained by the first second step is treated the same as the first intermediate material. That is, a second punch 122' is inserted from the open end of the second intermediate material 112, and the tip of the second punch 122' presses the bottom of the second intermediate material 112 (the first intermediate material 111) into a second die hole 132a' formed in a second die 132'. The outer diameter of the second punch 122' is smaller than the inner diameter of the second small-diameter cylindrical portion 112s of the second intermediate material 112, and the inner diameter of the second die hole 132a' is smaller than the outer diameter of the second small-diameter cylindrical portion 112s of the second intermediate material 112.

[0063] As a result of the above, the second closed end portion, which is a portion including the closed end of the second small diameter cylindrical portion 112s of the second intermediate material 112, is drawn while being reduced in diameter to form a second small diameter cylindrical portion 112s'. Meanwhile, the first tapered portion 111t and the second tapered portion 112t of the second intermediate material 112 are left unreduced in diameter to form a second tapered portion 112t', which is a portion interposed between the second tapered portion 112t and the second small diameter cylindrical portion 112s' and connects the second tapered portion 112t and the second small diameter cylindrical portion 112s'. As a result, as illustrated in FIG. 8(d), a second intermediate material 112' having the second small diameter cylindrical portion 112s', the second tapered portion 112t', the second tapered portion 112t, and the second tapered portion 111t' can be obtained.

[0064] 8, the second small diameter cylindrical portion and the second tapered portion are gradually formed by repeating the second step twice as described above. However, in the third method, the number of times the second step is repeated is not limited to two, and the second step may be repeated three or more times depending on, for example, the shape of the cylindrical body having a tapered portion to be finally formed and the material constituting the raw material.

[0065] <effect> As described above, in the third method, the second small diameter cylindrical portion and the second tapered portion are gradually formed by repeating the second step multiple times, and as a result, the third method can suppress, for example, work hardening and an excessive increase in the working load.

[0066] For the purpose of explaining the present invention, several embodiments having specific configurations have been described above, sometimes with reference to the accompanying drawings. However, the scope of the present invention should not be construed as being limited to these exemplary embodiments, and it goes without saying that appropriate modifications can be made within the scope of the claims and the matters described in the specification. [Explanation of symbols]

[0067] 110...Material 111...First intermediate material 111t...First tapered section 111s...First small diameter cylindrical section 112...Second intermediate material 112t...Second tapered section 112s...Second small diameter cylindrical section 112'...Second intermediate material 112t'...Second taper section 112s'...Second small diameter cylindrical section 113...Molded object (cylinder with tapered portion) 113t...Third taper section 113s...Third small diameter cylindrical section 121...First punch 122...Second punch 122'...2nd punch 123...Third punch 131...First die 131a...First die hole 132...Second die 132a...Second die hole 132'...2nd roll of the second die 132a'...Second die hole of the second run 133...3rd die 133a...Third die hole

Claims

1. A method for forming a cylindrical body having a tapered portion, in which a tapered portion and a cylindrical portion are formed from a bottomed cylindrical material using a die hole and a punch, comprising the steps of: a first step of inserting a first punch into the open end of the material and pressing the bottom of the material with the tip of the first punch to force the material into a first die hole formed in a first die, thereby reducing and extending the closed end, which is a portion including the closed end of the material, to form a first small-diameter cylindrical portion, while leaving the open end unreduced to form a first tapered portion, which is a portion interposed between the open end and the first small-diameter cylindrical portion and connecting the open end and the first small-diameter cylindrical portion, thereby obtaining a first intermediate material having the first small-diameter cylindrical portion and the first tapered portion; a second step of inserting a second punch from the open end of the first intermediate material and pressing the bottom of the first intermediate material with the tip of the second punch to force the first intermediate material into a second die hole formed in a second die, thereby reducing and extending a first closed end portion of the first intermediate material, which is a portion including the closed end of the first small diameter cylindrical portion, to form a second small diameter cylindrical portion, while leaving the first tapered portion of the first intermediate material without reducing its diameter, to form a second tapered portion that is interposed between the first tapered portion and the second small diameter cylindrical portion and connects the first tapered portion and the second small diameter cylindrical portion, thereby obtaining a second intermediate material having the second small diameter cylindrical portion, the second tapered portion, and the first tapered portion; a third step of inserting a third punch from the open end of the second intermediate material and pressing inner peripheral surfaces of the first tapered portion and the second tapered portion of the second intermediate material with the third punch to force the second intermediate material into a third die hole formed in a third die, thereby reducing and extending a second closed end portion of the second intermediate material, which is a portion including the closed end of the second small diameter cylindrical portion, to form a third small diameter cylindrical portion, while leaving the first tapered portion and the second tapered portion of the second intermediate material unreduced in diameter and sandwiching and pressing a portion between the open end and the third small diameter cylindrical portion between the third punch and the third die to form a third tapered portion that is interposed between the open end and the third small diameter cylindrical portion and connects the open end and the third small diameter cylindrical portion, thereby obtaining a molded product having the third small diameter cylindrical portion and the third tapered portion; At least including 1. A method for forming a cylindrical body having a tapered portion, comprising:

2. 2. A method for forming a cylindrical body having a tapered portion according to claim 1, comprising: In the third step, a load capacity, which is a maximum stress at which the first tapered portion and the second tapered portion of the second intermediate material can maintain their shapes against a stress acting in the axial direction, is greater than a sum of a drawing stress, which is a stress caused by a drawing resistance of the second small diameter cylindrical portion of the second intermediate material, and a friction stress, which is a stress caused by a friction resistance between the second small diameter cylindrical portion and the third die.

1. A method for forming a cylindrical body having a tapered portion, comprising:

3. 3. A method for forming a cylindrical body having a tapered portion according to claim 1 or 2, comprising: The second step is repeated a plurality of times to gradually form the second small-diameter cylindrical portion and the second tapered portion.

1. A method for forming a cylindrical body having a tapered portion, comprising:

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