WO2023105883A1

WO2023105883A1 - Method for molding cylindrical body having tapered part

Info

Publication number: WO2023105883A1
Application number: PCT/JP2022/034792
Authority: WO
Inventors: 隆太高井; 大貴川端; 司角田
Original assignee: 株式会社三五
Priority date: 2021-12-06
Filing date: 2022-09-16
Publication date: 2023-06-15
Also published as: JPWO2023105883A1

Abstract

In this method for molding a cylindrical body having a tapered part by pushing a cylindrical element tube into a die hole formed in a die by a metal core, an outer diameter increasing part formed on a distal end of the metal core presses the inner side of an end of the element tube to expand the diameter on the proximal end side of the element tube, and also presses an end of the element tube with a step part formed on the proximal end side of the outer diameter increasing part of the core metal to push the end into a small inner diameter part through an inner diameter decreasing part of the die hole, thereby shrinking the distal end side of the tube. By forming a small diameter part by decreasing the diameter of the element tube while compressing the element tube by pressing in the axial direction, it is possible to solve the aforementioned problem. The foregoing provides a method for molding a cylindrical body having a tapered part, which can be carried out via plastic processing, regardless of the size of the wall thickness of the element tube, while mitigating an increase in the set number of dies and an increase in work steps.

Description

Forming method for cylindrical body with tapered portion

The present invention relates to a method for forming a cylindrical body having a tapered portion. More specifically, the present invention provides a cylindrical body having a tapered portion that can be processed by plastic working regardless of the wall thickness of the blank pipe, while reducing the number of mold sets and work processes. It relates to a molding method.

It is known in the art to use a cylindrical body having a tapered portion, for example, as illustrated in FIG. 2, as an intermediate material for molding a funnel-shaped member such as a nozzle or tank liner.

For example, as a method of forming a bottomed cylindrical body having a tapered portion as illustrated in FIG. A common method is to obtain a desired shape by reducing the diameter of the cylindrical portion while reducing the diameter.

In Patent Document 1 (Japanese Patent No. 4681143), a side wall of an intermediate material is passed between a mandrel and a die having a coaxial double structure, and the mandrel presses the bottom of the intermediate material, and the outer mandrel and the die A forming method is disclosed in which the side wall of the intermediate material is handled between and the reduced diameter portion is extended. Further, Patent Document 2 (Japanese Patent No. 5741771) discloses a molding method in which, in the molding method described above, counter punches are arranged so as to face the mandrel with the bottom portion of the intermediate material interposed therebetween.

Further, in Patent Document 3 (Japanese Patent No. 5244529), a flange portion of a hat-shaped intermediate material having a flange portion on the peripheral edge of the open end is sandwiched between the outer die and a wrinkle pressing plate and restrained, and the inner side of the outer die is held. A molding method is disclosed in which an inner die provided in the inner die is pushed down to cover the intermediate material with a center punch provided inside the outer punch and the side wall of the intermediate material is pressed inward to form a small diameter portion.

The methods described in Patent Literature 1 and Patent Literature 2 are rolling of thin plates, and when applied to thick plates having a thickness of 2 mm or more, for example, damage to the mold and / or the raw tube during forming There is a possibility that problems such as the occurrence of cracks in the In addition, since the method described in Patent Document 3 is an upsetting process into a simple shape, in order to obtain a member having the shape illustrated in FIG. It is necessary to reduce the diameter of the cylindrical portion while enlarging the diameter of the cylinder, which causes, for example, an increase in the number of mold sets and work processes, which is not economical. In addition, the method described in Patent Document 3 also has a limit of about 2 mm for the thickness of the blank tube that can be applied, and a member having a shape as illustrated in FIG. It is difficult to obtain.

As described above, in the technical field, in order to obtain a thick member having the shape illustrated in FIG. are common, but these molding methods are also not economical.

Japanese Patent No. 4681143 Japanese Patent No. 5741711 Japanese Patent No. 5244529

As described above, in the technical field, it is possible to reduce the number of mold sets and increase the number of work processes, and to have a tapered portion that can be performed by plastic working regardless of the thickness of the blank pipe. A method of forming a cylinder is needed.

Therefore, as a result of extensive research, the present inventors have found a method of forming a cylindrical body having a tapered portion and a small diameter portion by pushing a cylindrical blank pipe into a die hole having a predetermined shape with a metal core having a predetermined shape. In the above, it was found that the above problem can be solved by reducing the diameter of the blank tube while compressing it by pressing it in the axial direction to form the small-diameter portion.

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 through hole having a predetermined shape formed in a die. A taper is formed by pushing a base tube, which is a bottomed or bottomless cylindrical member, into a certain die hole in the axial direction of the base tube and the die hole using a first core bar having a predetermined shape. A method for forming a cylindrical body having a part.

The cylindrical body has a tapered portion, which is a portion whose diameter increases as it approaches one open end, and a small-diameter portion, which is a cylindrical portion formed between the other end and the tapered portion. The maximum outer diameter of the tapered portion is larger than the outer diameter of the blank tube, and the outer diameter of the small-diameter portion is smaller than the outer diameter of the blank tube.

The die hole has a large inner diameter portion, a small inner diameter portion, and a reduced inner diameter portion. The large inner diameter portion is a portion having a first inner diameter corresponding to the maximum outer diameter of the tapered portion of the cylindrical body. The small inner diameter portion is a portion having a second inner diameter that is smaller than the inner diameter corresponding to the outer diameter of the small diameter portion of the cylindrical body. The reduced inner diameter portion is formed between the large inner diameter portion and the small inner diameter portion, and is a portion in which the inner diameter decreases from the first inner diameter to the second inner diameter as it approaches the small inner diameter portion from the large inner diameter portion.

The first cored bar has an increased outer diameter portion and a first stepped portion. The increased outer diameter portion is a portion whose outer diameter increases from the outer diameter corresponding to the minimum inner diameter of the tapered portion of the cylindrical body to the outer diameter corresponding to the maximum inner diameter of the tapered portion of the cylindrical body as the distance from the tip increases. The first stepped portion is an annular step formed so as to expand radially outward at a position adjacent to the base end side of the increased outer diameter portion, and has an outer diameter equal to the maximum outer diameter of the tapered portion of the cylindrical body. It is a portion having an inner diameter equal to the maximum inner diameter of the tapered portion of the cylinder.

The method of the present invention includes the following first and second steps.
1st step: inserting the blank pipe from the large inner diameter side of the die hole so that the first end, which is the open end of the blank pipe, faces the upstream side in the first direction, which is the direction in which the blank pipe is pushed into the die hole. By bringing the second end opposite to the first end of the blank pipe into contact with the reduced inner diameter portion of the die hole, the blank pipe is placed at a predetermined position inside the die hole.
Second step: inserting the first cored bar into the first end of the blank pipe and pressing the blank pipe in the first direction by the first cored bar, thereby forming a tapered portion in the region facing the reduced inner diameter portion of the die hole. is formed and a small diameter portion is formed in a region facing the small inner diameter portion of the die hole.

In the second step, the diameter expansion process, the diameter reduction process and the completion process shown below are executed.
Diameter expansion process: The inside of the first end of the blank pipe is pressed by the increased outer diameter portion of the first core bar to expand the diameter of the first end of the blank pipe.
Diameter reduction process: After a first time point at which the first stepped portion of the first cored bar abuts on the first end portion of the blank tube at the latest, the blank tube is pressed in the first direction by the first cored bar to form the blank tube. is pushed toward the small inner diameter portion of the die hole to reduce the diameter of the second end side of the blank tube.
Completion process: The first end side region of the blank tube is sandwiched between the reduced inner diameter portion of the die hole and the increased outer diameter portion of the first cored bar to complete the forming of the tapered portion and the small diameter portion.

Preferably, the diameter reduction process is started after the diameter expansion process is started. Specific measures for this will be described later. Alternatively, a blank pipe may be used in which the thickness of the region corresponding to the tapered portion of the cylindrical body is greater than the thickness of the region corresponding to the small-diameter portion of the cylindrical body. Furthermore, the material forming the mother tube may be austenitic stainless steel.

As described above, in the method of the present invention, in the diameter reduction process executed in the second step, the first core bar presses the blank pipe in the first direction after the first time point at the latest, and the second end of the blank pipe is is pushed toward the small inner diameter portion of the die hole to reduce the diameter of the second end side of the blank tube. That is, the diameter of the tube is reduced while compressing it by pressing it in the axial direction to form the small-diameter portion of the cylindrical body. Therefore, according to the method of the present invention, the tapered portion and the small diameter portion can be formed at the same time while reducing problems such as buckling and/or breakage even when using a thick blank pipe. can be smoothly molded.

Preferably, the diameter reduction process is started after the diameter expansion process is started. As a result, the tapered portion and the small diameter portion can be formed more smoothly with good balance. In addition, by using a blank pipe in which the thickness of the region corresponding to the tapered portion of the cylindrical body is greater than the thickness of the region corresponding to the small diameter portion of the cylindrical body, the material in the diameter expansion process executed in the second step is The reduction in wall thickness (thickness) associated with the expansion of the first end of the tube can be at least partially offset to make the wall thickness of the cylinder more uniform. Furthermore, by selecting austenitic stainless steel as the material for the blank pipe, the mechanical strength of the cylindrical body can be increased by work hardening that accompanies execution of the second step.

Other objects, features and attendant advantages of the present invention will be easily understood from the description of each embodiment of the present invention described with reference to the following drawings.

FIG. 2 is a schematic cross-sectional view illustrating the configuration of a cylindrical body having a tapered portion formed by a method (first method) for forming a cylindrical body having a tapered portion according to the first embodiment of the present invention; FIG. 4 is a schematic cross-sectional view illustrating the configuration of a blank pipe used in the first method; FIG. 4A is a schematic cross-sectional view illustrating the configuration of a die used in the first method; FIG. 4 is a schematic cross-sectional view illustrating the configuration of a first cored bar used in the first method; It is a flowchart which shows the flow of each process and each process included in a 1st method. FIG. 5 is a schematic cross-sectional view illustrating changes in the position of the first cored bar and the shape of the first mother pipe as the second step performed in the first method progresses; FIG. 10 is a schematic cross-sectional view showing Modified Example 1-1 of the first method; FIG. 4 is a schematic cross-sectional view showing an example of a method of forming a blank pipe used in Modification 1-1 of the first method. The first core bar and the second core bar along with the progress of the second step executed in Modified Example 2-1 of the method for forming a cylindrical body having a tapered portion (second method) according to the second embodiment of the present invention FIG. 5 is a schematic cross-sectional view illustrating changes in position and shape of the first mother pipe; 8 is a flow chart showing each process and the flow of each process included in a method for forming a cylindrical body having a tapered portion (third method) according to a third embodiment of the present invention;

FIG. 11 is a schematic cross-sectional view showing an example of the configuration of a first cored bar used in the method of forming a cylindrical body having a tapered portion (fourth method) according to the fourth embodiment of the present invention; It is a flow chart which shows each process included in the 4th method, and the flow of each process. FIG. 11 is a schematic cross-sectional view illustrating changes in the positions of the central member and the peripheral member that constitute the first cored bar and the shape of the first blank pipe as the second step performed in the fourth method progresses; A method for forming a cylindrical body having a tapered portion according to the fifth and sixth embodiments of the present invention, in which the punching process is performed after the treatment process performed in the third step included in the third method (the fifth method and the sixth method) is a flow chart showing each step and the flow of each process. 10 is a flow chart showing each step and the flow of each step included in the fifth method and the sixth method, in which the removal process is performed after the treatment process is performed in the second process included in the fourth method. FIG. 11 is a schematic cross-sectional view showing an example of the extraction process performed in the fifth method; FIG. 11 is a schematic cross-sectional view showing an example of the extraction process performed in the sixth method; FIG. 20 is a schematic cross-sectional view showing a state immediately before the second step is started in modification 7-1 of the method for forming a cylindrical body having a tapered portion (seventh method) according to the seventh embodiment of the present invention; FIG. 20 is a schematic cross-sectional view showing a state immediately before the second step is started in modification 7-2 of the seventh method;

<<1st Embodiment>>
A method of forming a cylindrical body having a tapered portion according to the first embodiment of the present invention (hereinafter sometimes referred to as "first method") will be described below with reference to the drawings. The term "cored bar" used in this specification is a general term for a male mold for pressurizing, deforming and/or drilling a member to be processed in plastic working, and is a technical field. It includes synonyms such as "mandrel", "punch" and "punch" that are widely used in .

In the first method, a bottomed or bottomless cylindrical member is formed by inserting a first cored bar having a predetermined shape into a die hole, which is a through hole having a predetermined shape formed in a die. In this method, a cylindrical body having a tapered portion is formed by pushing a blank pipe in the axial direction of the blank pipe and the die hole. That is, the first method is a method of forming a cylindrical body having a tapered portion by cold forging.

Since the basic configuration of the apparatus for executing the first method is well known to those skilled in the art, detailed description is omitted. It is composed of a material having properties (eg, mechanical strength, durability, etc.) that can withstand processing conditions such as loads acting on components in the process. In addition, the drive mechanism for pushing the first cored bar into the die hole can be any one of various drive mechanisms known in the art, depending on the properties of the material forming the blank tube (for example, mechanical strength and hardness). It can be appropriately selected from among them. Typically, a press, such as a hydraulic press, is employed as the drive mechanism.

A blank tube, which is a material for forming a cylindrical body with a tapered portion, is a cylindrical member made of a material that can be formed by cold forging. The base pipe may be, for example, a base pipe 101 made of a bottomed cylindrical member as illustrated in FIG. , the base pipe 102 may be a cylindrical member of . Such a blank tube is not particularly limited as long as it can be formed into a cylindrical body having a tapered portion by the first method. For example, the blank pipe may be a plate-wrapped pipe or a seamless pipe, and may be manufactured by forging or cutting. Alternatively, a base pipe with a bottom may be manufactured by drawing from a plate-like member.

The cylindrical body has a tapered portion, which is a portion whose diameter increases as it approaches one open end, and a small-diameter portion, which is a cylindrical portion formed between the other end and the tapered portion. As explained at the beginning of the description, such cylinders can be used as intermediate blanks for forming funnel-shaped parts, such as nozzles or tank liners. A specific example of such a cylindrical body is a cylindrical body having a tapered portion as illustrated in FIG.

The

cylindrical bodies

201 and 202 illustrated in FIGS. 2(a) and 2(b) have a tapered portion 220 and a tapered portion 212, which are portions whose diameters increase as they approach one open end portion 211 and the other end portion 212. It has a small diameter portion 230 which is a cylindrical portion formed between the portion 220 and the portion 220 . However, the cylindrical body 201 is a bottomed cylindrical body with a closed second end 212 , whereas the cylindrical body 202 is a bottomless cylindrical body with an open second end 212 . Thus, depending on the product to be molded, a bottomed or bottomless cylinder can be used as an intermediate material.

Specifically, when forming a bottomless member such as a nozzle or a tank liner from a bottomed cylindrical body such as the cylindrical body 201 described above, the bottom is naturally cut off or cut, for example. You have to drill holes in the bottom. On the other hand, when forming a bottomed member from a bottomed cylindrical body, it is not always necessary to cut off the bottom or drill a hole in the bottom. Conversely, when molding a bottomless member such as a nozzle or tank liner from a bottomless cylinder such as the cylinder 202 described above, it is not necessary to cut off or drill a hole in the bottom, for example. None. On the other hand, when forming a bottomed member from a bottomless cylindrical body, it is, of course, necessary to form the bottom portion by, for example, further plastic working or bonding of members constituting the bottom portion.

In the cylindrical body, the maximum outer diameter of the tapered portion is larger than the outer diameter of the blank pipe, and the outer diameter of the small diameter portion is smaller than the outer diameter of the blank pipe. This is because the tapered portion of the cylindrical body is formed by expanding the diameter of the blank tube, and the small-diameter portion of the cylindrical body is formed by reducing the diameter of the blank tube, as will be described later in detail. The maximum outer diameter of the tapered portion refers to the outer diameter at the end of the tapered portion of the cylindrical body on the upstream side in the first direction in which the blank pipe is pushed into the die hole in the first method.

The die hole has, in order from the upstream side in the first direction, a large inner diameter portion, a reduced inner diameter portion, and a small inner diameter portion. The large inner diameter portion is a portion having a first inner diameter corresponding to the maximum outer diameter of the tapered portion of the cylindrical body. The small inner diameter portion is a portion having a second inner diameter that is smaller than the inner diameter corresponding to the outer diameter of the small diameter portion of the cylindrical body. The reduced inner diameter portion is formed between the large inner diameter portion and the small inner diameter portion, and the inner diameter decreases from the first inner diameter to the second inner diameter as it approaches the small inner diameter portion from the large inner diameter portion.

FIG. 3 is a schematic cross-sectional view illustrating the configuration of the dice used in the first method. A die hole 310 formed in a die 301 illustrated in FIG. 3 includes a large inner diameter portion 311, a reduced inner diameter portion 312, and a small inner diameter portion 313 in order from the upstream side in the first direction. The large inner diameter portion 311 is a portion having a first inner diameter DI<b>1 that corresponds to the maximum outer diameter of the tapered portion 220 of the cylindrical body 201 . The small inner diameter portion 313 is a portion having a second inner diameter DI<b>2 that is smaller than the inner diameter corresponding to the outer diameter of the small diameter portion 230 of the cylindrical body 201 . The reduced inner diameter portion 312 is formed between the large inner diameter portion 311 and the small inner diameter portion 313, and the inner diameter decreases from the first inner diameter DI1 to the second inner diameter DI2 as it approaches the small inner diameter portion 313 from the large inner diameter portion 311. part.

The first cored bar includes, in order from the downstream side in the first direction, an outer diameter increasing portion and a first stepped portion. The increased outer diameter portion is a portion whose outer diameter increases from the outer diameter corresponding to the minimum inner diameter of the tapered portion of the cylindrical body to the outer diameter corresponding to the maximum inner diameter of the tapered portion of the cylindrical body as the distance from the tip increases. The first stepped portion is an annular step formed so as to expand radially outward at a position adjacent to the base end side of the increased outer diameter portion, and has an outer diameter equal to the maximum outer diameter of the tapered portion of the cylindrical body. It is a portion having an inner diameter equal to the maximum inner diameter of the tapered portion of the cylinder. A small-diameter guide portion, which is a substantially cylindrical portion having an outer diameter corresponding to the inner diameter of the small-diameter portion of the cylindrical body, may be provided adjacent to the distal end side of the increased outer diameter portion.

FIG. 4 is a schematic cross-sectional view illustrating the configuration of the first cored bar used in the first method. The first cored bar 401 illustrated in FIG. 4 includes a small diameter guide portion 411, an outer diameter increasing portion 412, and a first stepped portion 413 in order from the downstream side in the first direction. The small-diameter guide portion 411 is a substantially cylindrical portion having an outer diameter corresponding to the inner diameter of the small-diameter portion of the cylindrical body. The increased outer diameter portion 412 is a portion whose outer diameter increases from the outer diameter corresponding to the minimum inner diameter of the tapered portion of the cylindrical body to the outer diameter corresponding to the maximum inner diameter of the tapered portion of the cylindrical body as the distance from the distal end increases. The first stepped portion 413 is an annular stepped portion formed so as to expand radially outward at a position adjacent to the base end side of the increased outer diameter portion 412 and has an outer diameter equal to the maximum outer diameter of the tapered portion of the cylindrical body. A portion having an inner diameter equal to the diameter and the maximum inner diameter of the tapered portion of the cylinder. A dashed-dotted line AX drawn in FIG. 4 represents a common central axis of the first cored bar, the blank tube and the die hole. That is, in the first method, the first cored bar, the blank tube and the die hole are coaxially arranged with the axis AX as a common axis.

From the viewpoint of effectively reducing the diameter of the tip side (second end portion side) of the blank tube 101 by pushing the blank tube 101 into the die hole 310, the first stepped portion 413 of the first cored bar 401 is the blank tube. It is desirable that the first stepped portion 413 and the end face of the blank tube 101 make surface contact when the base end side (first end portion side) of the tube 101 is brought into contact. Therefore, in the first stepped portion 413 of the first cored bar 401 illustrated in FIG. inclined to

FIG. 5 is a flow chart showing each process included in the first method and the flow of each process. As illustrated in FIG. 5, the first method includes the following first step (step S10) and second step (step S20).

First step (Step S10): The raw pipe is pushed from the large inner diameter side of the die hole so that the first end, which is the open end of the raw pipe, faces the upstream side in the first direction, which is the direction in which the raw pipe is pushed into the die hole. By inserting the pipe and bringing the second end opposite to the first end of the pipe into contact with the reduced inner diameter portion of the die hole, the pipe is placed at a predetermined position inside the die hole. Install.

As described above, in the cylindrical body, the maximum outer diameter of the tapered portion is larger than the outer diameter of the blank tube, and the outer diameter of the small-diameter portion is smaller than the outer diameter of the blank tube. In the die hole, the inner diameter of the large inner diameter portion is the inner diameter (first inner diameter) corresponding to the maximum outer diameter of the tapered portion of the cylindrical body, and the inner diameter of the small inner diameter portion corresponds to the outer diameter of the small diameter portion of the cylindrical body. It has an inner diameter (second inner diameter) smaller than the inner diameter, and the inner diameter of the reduced inner diameter portion decreases from the first inner diameter to the second inner diameter as it approaches the small inner diameter portion from the large inner diameter portion. Therefore, the tip (second end) of the blank pipe inserted into the die hole in the first step abuts the reduced inner diameter portion of the die hole, and the inner peripheral surface of the large inner diameter portion of the die hole and the outer circumference of the blank pipe It is held in a state in which a gap exists between it and the surface.

Second step (Step S20): A first mandrel is inserted into the first end of the blank pipe, and the blank pipe is pressed in the first direction by the first core bar, thereby facing the reduced inner diameter portion of the die hole. A cylindrical body having a tapered portion formed in a region and a small diameter portion formed in a region facing the small inner diameter portion of the die hole is molded.

As described above, the tip of the first cored bar has an outer diameter that increases from the outer diameter corresponding to the minimum inner diameter of the tapered portion of the cylindrical body to the outer diameter corresponding to the maximum inner diameter of the tapered portion of the cylindrical body. An increasing outer diameter is provided. Therefore, when the first cored bar is inserted into the first end of the base pipe, the first end of the base pipe abuts on the middle of the increased outer diameter portion of the first cored bar. After that, by pressing the first cored bar in the first direction by the drive mechanism described above, a tapered portion is formed in a region facing the reduced inner diameter portion of the die hole and a small diameter portion is formed in a region facing the small inner diameter portion of the die hole. A section is formed to form the desired "tapered cylinder".

As illustrated in FIG. 5, in the second step (step S20), the diameter expansion process (step S21), the diameter reduction process (step S22), and the completion process (step S23) shown below are executed.
Diameter expansion process (step S21): The diameter of the first end side of the mother pipe is expanded by pressing the inside of the first end of the mother pipe with the increased outer diameter portion of the first cored bar. That is, the first end side of the blank pipe is expanded by the increased outer diameter portion of the first cored bar to be expanded in diameter.
Diameter reduction process (step S22): After a first time point at which the first stepped portion of the first core bar contacts the first end of the blank tube at the latest, the blank tube is pressed in the first direction by the first core bar. Then, the second end portion of the blank tube is pushed toward the small inner diameter portion of the die hole to reduce the diameter of the second end side of the blank tube. That is, the second end side of the blank pipe is pushed into the small inner diameter portion of the die hole to reduce the diameter.
Completion process (step S23): The region of the first end side of the blank pipe is sandwiched between the reduced inner diameter portion of the die hole and the increased outer diameter portion of the first cored bar to complete the forming of the tapered portion and the small diameter portion. .

As described above, in the first method, in the diameter reduction process (step S21) executed in the second step (step S20), the first core bar presses the base pipe in the first direction at the latest after the first point of time. Then, the second end portion of the blank tube is pushed toward the small inner diameter portion of the die hole to reduce the diameter of the second end side of the blank tube. That is, the diameter of the tube is reduced while compressing it by pressing it in the axial direction to form the small-diameter portion of the cylindrical body. Therefore, according to the first method, the tapered portion and the small-diameter portion can be simultaneously formed while reducing problems such as buckling and/or breakage even when using a thick blank pipe. can be smoothly molded.

The order of starting the diameter-expanding process (step S21) and the diameter-reducing process (step S22) in the second step (step S20) is not particularly limited as long as problems such as buckling of the blank tube do not occur. For example, when the diameter increasing process (step S21) starts simultaneously with the start of the second step (step S20), the diameter decreasing process (step S22) may start simultaneously with the starting of the diameter increasing process (step S21). Alternatively, the diameter reduction process (step S22) may be started after the diameter expansion process (step S21) is started. However, as described above, at a position adjacent to the base end side of the increased outer diameter portion of the first cored bar, there is an annular step formed so as to spread outward in the radial direction, which is the tapered portion of the cylindrical body. A first stepped portion is provided which is a portion having an outer diameter equal to the maximum outer diameter and an inner diameter equal to the maximum inner diameter of the tapered portion of the cylinder. Therefore, even if the diameter-reducing process (step S22) is started after the diameter-expanding process (step S21) is started, the first stepped portion of the first cored bar is positioned at the first end of the tube. After the point of contact (first time point), the first cored bar presses the blank tube in the first direction, the second end of the blank tube is pushed toward the small inner diameter portion of the die hole, and the second end of the blank tube is pushed toward the small inner diameter portion of the die hole. The diameter of the two end portions is reduced. Conversely, the diameter reduction process (step S22) may be started simultaneously with the start of the second step (step S20). In this case, the diameter expansion process (step S21) may be started at the same time as the diameter reduction process (step S22) is started, or the diameter expansion process (step S21) may be started after the diameter reduction process (step S22) is started. may be started.

Preferably, the diameter reduction process is started after the diameter expansion process is started. More preferably, the diameter reduction process is started after the first stepped portion of the first core bar contacts the first end portion of the blank tube (first time point). As a result, the tapered portion and the small diameter portion can be formed more smoothly with good balance.

The timing at which the diameter-expanding process is started and the timing at which the diameter-reducing process is started in the second step are determined, for example, by the shape (diameter, length, thickness, etc.) and material of the blank tube, and the portion to be the tapered portion of the cylindrical body. and the diameter reduction ratio of the portion to be the small diameter portion of the cylindrical body, and the change rate (taper angle) of the inner diameter of the die hole at the inner diameter reduction portion.

As a specific measure for starting the diameter-reducing process after the diameter-expanding process has started, for example, The difference between the outer diameter of the second end of the blank tube and the outer diameter of the small diameter portion of the cylindrical body is greater than the diameter expansion ratio, which is the ratio to the outer diameter of the first end of the blank tube. For example, the base tube, the die hole, and the first cored bar are configured so that the diameter reduction rate, which is the ratio of the portion to the outer diameter, becomes greater. As a result, the tapered portion and the small diameter portion can be formed more smoothly with good balance. However, as will be described later, measures for starting the diameter-reducing process after the diameter-expanding process is started are not limited to the above.

<Details of the second step>
The change in shape of the blank tube in the second step performed in the first method will now be described in more detail with reference to further drawings. FIG. 6 is a schematic cross-sectional view illustrating changes in the position of the first mandrel and the shape of the first mother pipe as the second step progresses. In FIG. 6, only the right side of the common axis AX (see FIG. 4) of the first mandrel, tube and die hole is shown, but the left side of the axis AX is shown. The same is true for Also, in order to simplify the drawings, only some of the reference numerals attached to the parts shown in FIGS. 1 to 4 are shown. However, in the following description of FIG. 6, the reference numerals shown in FIGS. 1-4 are used for the sake of accuracy, and reference should be made to FIGS. 1-4 as necessary.

First, in (a) of FIG. 6, the tip of the first cored bar 401 (specifically, Specifically, it shows a state in which the small-diameter core portion 411 and a portion of the increased outer diameter portion 412) are inserted. In this state, as described above, the tip (second end 112) of the blank tube 101 is in contact with the reduced inner diameter portion 312 of the die hole 310, and the inner peripheral surface of the large inner diameter portion 311 of the die hole 310 is in contact with the inner peripheral surface of the die hole 310. A gap exists between the outer peripheral surface of the blank tube 101 .

Next, in FIG. 6B, in the second step (step S20), the first cored bar 401 begins to press the blank tube 101 in the first direction, and the side surface of the outer diameter increased portion 412 of the first cored bar 401 shows a state in which the first end portion 111 side of the base tube 101 is pushed out and a flare is formed. That is, at this time point, the diameter expansion process (step S21) is started and the diameter expansion of the first end portion 111 side of the raw pipe 101 has started, but the diameter reduction of the second end portion 112 side of the raw pipe 101 is It hasn't started yet.

Next, in (c) of FIG. 6, the first cored bar 401 moves further in the first direction, and the expansion of the diameter of the base tube 101 on the first end portion 111 side progresses further, and the first cored bar 401 413 is in contact with the first end 111 of the blank pipe 101 and the second end 112 of the blank pipe 101 has begun to be pushed toward the small inner diameter portion 313 of the die hole 310. FIG. That is, at this time point, the diameter reduction process (step S22) is started, and the diameter reduction of the second end side of the blank tube 101 has started.

Next, in (d) of FIG. 6, the first cored bar 401 moves further in the first direction, and the expansion of the diameter of the first end portion 111 side of the base pipe 101 further progresses. The second end portion 112 is shown to have begun to enter the small inner diameter portion 313 of the die hole 310 . That is, at this time point, the small-diameter portion 230 of the cylindrical body 201 begins to be formed by the diameter-reducing process (step S22).

Next, in (e) of FIG. 6, the first cored bar 401 moves further in the first direction, and the expansion of the diameter of the first end side of the base pipe 101 further progresses, and the base pipe 101 moves toward the second end. The end portion 112 further enters the small inner diameter portion of the die hole 310, and the formation of the small diameter portion 230 of the cylindrical body 201 is further advanced by the diameter reduction process (step S22).

Finally, in (f) of FIG. 6 , the first cored bar 401 moves further in the first direction, and the gap between the reduced inner diameter portion 312 of the die hole 310 and the increased outer diameter portion 412 of the first cored bar 401 is shown. A state is shown in which the region on the first end portion 111 side of the blank pipe 101 is sandwiched and the forming of the tapered portion 220 and the small diameter portion 230 of the cylindrical body 201 is completed.

As described above, in the example shown in FIG. 6, the diameter reduction process starts from the point in time when the first stepped portion 413 of the first cored bar 401 contacts the first end portion 111 of the blank tube 101 (first point in time). has started. However, as described above, the timing at which the diameter-expanding process is started and the timing at which the diameter-reducing process is started in the second step depend, for example, on the shape (diameter, length, thickness, etc.) and material of the blank pipe, the cylinder Various factors such as the size relationship between the diameter expansion rate of the tapered part of the body and the diameter reduction rate of the small diameter part of the cylindrical body, and the change rate (taper angle) of the inner diameter at the inner diameter reduction part of the die hole change depending on

However, in the first method, as described above, the first core bar presses the blank pipe in the first direction at the latest after the first time point in the diameter reduction process executed in the second step, thereby reducing the blank pipe. By pushing the second end toward the small inner diameter portion of the die hole, the diameter of the second end of the blank tube can be reduced. That is, the small-diameter portion of the cylindrical body can be formed by pressing and compressing the blank pipe in the axial direction to reduce the diameter. Therefore, according to the first method, the tapered portion and the small-diameter portion can be simultaneously formed while reducing problems such as buckling and/or breakage even when using a thick blank pipe. can be smoothly molded.

<Modification 1-1>
By the way, in the diameter expansion process executed in the second step, the diameter of the first end side of the blank pipe is expanded to form the tapered portion of the cylindrical body. thinning). On the other hand, depending on the application of the tapered cylindrical body molded by the first method, it may be desirable to make the thickness uniform throughout the cylindrical body. In such a case, the wall thickness of the region of the blank pipe that will be the tapered portion of the cylindrical body may be increased in advance. That is, in the first method, a blank tube may be used in which the thickness of the region corresponding to the tapered portion of the cylindrical body is greater than the thickness of the region corresponding to the small diameter portion of the cylindrical body.

FIG. 7 schematically shows a modification 1-1 of the first method in which the thickness of the region corresponding to the tapered portion of the cylindrical body is greater than the thickness of the region corresponding to the small diameter portion of the cylindrical body. It is a cross-sectional view. In the blank tube 101a illustrated in FIG. 7A, the thickness of the region corresponding to the tapered portion of the cylindrical body (see the portion surrounded by the thick dashed line) corresponds to the small diameter portion of the cylindrical body. It has the same configuration as the base pipe 101 illustrated in FIG. In this way, by increasing the thickness of the region of the blank pipe that will be the tapered portion of the cylindrical body in advance, as illustrated in FIG. It is possible to at least partially offset the reduction in thickness (thickness reduction) accompanying the expansion of the diameter of the cylindrical body 201a, thereby making the thickness of the cylindrical body 201a more uniform.

In addition, the method for manufacturing a blank pipe as described above makes it possible to obtain a blank pipe in which the thickness of the region corresponding to the tapered portion of the cylindrical body is greater than the thickness of the region corresponding to the small-diameter portion of the cylindrical body. As long as it is not particularly limited. For example, the base tube as described above may be manufactured by forging or cutting. Further, the blank tube as described above may be manufactured by drawing from a plate-like member.

FIG. 8 is a schematic cross-sectional view showing an example of a method of forming the blank tube 101a used in Modification 1-1 of the first method. (a) on the left side of the axis AX in the drawing shows the situation during machining of the tube 101a, and (b) on the right side of the axis AX in the drawing shows the situation after machining the tube 101a. each depicted. As exemplified in FIG. 8A, the die hole formed in the die for forming the blank tube 101a by drawing is tapered so as to become wider as it approaches the opening on the side where the core metal is inserted. part is provided (see thick solid line). As a result, as illustrated in FIG. 8B, the thickness of the region corresponding to the tapered portion of the cylinder in the blank tube 101a after processing can be made larger than the thickness of other regions (thick see the part enclosed by the dashed line).

In addition, in the blank tube 101a illustrated in FIGS. 7 and 8, the thickness of the region corresponding to the tapered portion of the cylindrical body increases linearly as it approaches the first end. However, the blank tube 101a shown in FIGS. 7 and 8 is merely an example, and the shape of the region of the blank tube used in Modification 1-1 of the first method is different from that of the blank tube in the diameter expansion process. There is no particular limitation as long as it is possible to at least partially offset the decrease in thickness (thickness) associated with the diameter expansion on the one end side.

<Modification 1-2>
By the way, when cold forging a material made of a material that easily causes work hardening, such as austenitic stainless steel, there may be problems such as an increase in the working load or cracking of the material during working. . Therefore, such materials tend to be avoided in cold forging. However, in the first method, as described above, the first metal core presses the blank pipe in the first direction at the latest after the first point in the diameter reduction process executed in the second step, and the blank pipe is pushed in the second direction. The end portion is pushed toward the small inner diameter portion of the die hole to reduce the diameter of the second end side of the blank tube. That is, since the tube is pressed in the axial direction (first direction) to reduce its diameter while compressing it to form the small-diameter portion of the cylindrical body, cracking, etc. less likely to cause problems. Further, according to the first method, a thick blank pipe can be used, so that a large load can be applied to the first end of the blank pipe in the diameter reduction process executed in the second step.

Therefore, in the first method, the material forming the mother tube may be austenitic stainless steel. In this case, since work hardening occurs as described above, the hardness of the cylindrical body having the tapered portion formed by the first method increases, and the mechanical strength also increases. Therefore, the cylindrical body formed by the first method from the tube made of austenitic stainless steel is suitable for applications that require high mechanical strength, such as applications that receive high pressure from the fluid that exists inside the cylindrical body. is suitable for

In addition, while tensile residual stress is generated in products formed by the processing method of stretching the raw material, products formed by the first method of pressing and compressing the blank tube in the axial direction (first direction) is a compressive residual stress. Cylinders formed by the first method are suitable for applications subject to high tensile stress, such as applications subject to high pressure due to the fluid present inside the cylinder.

<<Second embodiment>>
Hereinafter, a method of forming a cylindrical body having a tapered portion according to a second embodiment of the present invention (hereinafter sometimes referred to as "second method") will be described with reference to the drawings.

The second method is any of the first methods described above,
The blank tube is a bottomed cylindrical member closed at the second end,
A method for forming a cylindrical body having a tapered portion, characterized by:

As specific examples of the bottomed base pipe whose second end is closed as described above, for example, the base pipe 101 illustrated in FIG. 1(a) and the base pipe 101a illustrated in FIG. can be mentioned. By using such a bottomed base pipe, it is possible to reduce the problem of unintended deformation of the second end side of the base pipe during the diameter reduction process.

<Modification 2-1>
By the way, as described above, preferably, the diameter-reducing process is started after the diameter-expanding process is started. More preferably, the diameter reduction process is started after the first stepped portion of the first core bar contacts the first end portion of the blank tube (first time point). As a result, the tapered portion and the small diameter portion can be formed more smoothly with good balance.

As an example of a specific measure for starting the diameter reduction process after the diameter expansion process is started, as described above, the diameter reduction rate is larger than the diameter expansion rate. Constructing a tube, a die hole and a first mandrel can be mentioned. However, in the second method, in which a bottomed cylindrical member with a closed second end is used as the base pipe, a so-called "counter punch" is inserted from the small inner diameter side of the die hole to punch the base pipe. The counterpunch is kept in contact with the two ends (bottom), and the counterpunch is also moved in the first direction in accordance with the movement of the second end of the blank tube in the first direction after the time when the diameter reduction process should be started. Thereby, the diameter reduction process can be started at the desired timing after the diameter expansion process is started.

Therefore, the modification 2-1 of the second method is
Before the second step is started, a second metal core, which is a metal core having a predetermined shape, is inserted from the small inner diameter side of the die hole and fixed at a position where it abuts on the second end of the blank tube. cage,
The second core bar starts moving in the first direction at a predetermined speed at a predetermined point in time during which the second step is performed;
A method for forming a cylindrical body having a tapered portion, characterized by:

The specific means for fixing the second cored bar at the position where it contacts the second end of the blank tube is not particularly limited, and may be, for example, a releasable mechanical means, or the first cored bar. The second core bar may be urged in the direction opposite to the first direction by a force that resists the force that pushes the blank tube in the first direction. In addition, the time at which the movement of the second cored bar in the first direction is started depends on, for example, the progress of the diameter expansion process at that time, the buckling strength of the blank tube, and the magnitude of the compressive residual stress to be generated in the blank tube. It can be determined as appropriate according to various requirements. However, the period from the first point in time when the first step portion of the first cored bar abuts against the first end of the blank tube to the point in time when the second cored bar starts to move in the first direction is excessive. Care must be taken because if the length is increased, problems such as an increase in processing load and/or unintended deformation of the mother pipe may occur.

In addition, the speed at which the second core bar is moved in the first direction also includes, for example, the progress of the diameter expansion process at that time, the buckling strength of the blank pipe, and the magnitude of the compressive residual stress to be generated in the blank pipe. etc., can be determined as appropriate according to various requirements. However, if the speed of movement of the second mandrel in the first direction is excessively slow relative to the speed of movement of the first mandrel in the first direction, for example, an increase in processing load and/or unintended deformation of the blank tube may occur. It is necessary to be careful because there is a possibility that it will lead to problems.

9 is the same as FIG. 6 except that the second core bar 501 is inserted from the small inner diameter portion 313 side of the die hole 310 and is in contact with the second end portion 112 (bottom portion) of the blank tube 101. . In FIG. 9 as well, only the portion on the right side of the axis AX as viewed in the drawing is drawn, but the same applies to the portion on the left side of the axis AX. Also, in order to simplify the drawings, only some of the reference numerals attached to the parts shown in FIGS. 1 to 4 are shown. However, in the following description of FIG. 9, the reference numbers shown in FIGS. 1-4 are used for the sake of accuracy, and reference should be made to FIGS. 1-4 as necessary.

In the example shown in FIG. 9, the second cored bar 501 is fixed at a position where it abuts against the second end portion 112 (bottom portion) of the base pipe 101 until the first time point (FIGS. 9A and 9B). b)), and starts moving in the first direction at a predetermined speed at a predetermined timing after the first time point (see (c) and the white arrows in FIG. 9). ing.

According to modification 2-1 of the second method, for example, the shape (diameter, length, wall thickness, etc.) and material of the blank pipe, the diameter expansion ratio of the tapered portion of the cylindrical body, and the small diameter portion of the cylindrical body Depending on various factors such as the size relationship with the diameter reduction rate of the portion where the diameter is reduced, and the rate of change (taper angle) of the inner diameter at the inner diameter reduction portion of the die hole, for example, an increase in the processing load and / or an unintended The diameter reduction process can be started at a suitable timing that does not cause problems such as deformation. Also, the moving speed of the second cored bar in the first direction can also be appropriately set according to various factors. For example, if the moving speed of the second cored bar in the first direction is set lower than the moving speed of the tip of the small-diameter portion that accompanies the pressing by the first cored bar, the compressive residual stress in the axial direction of the cylindrical body increases. It is possible to promote the thickening of the small diameter portion. Conversely, when the moving speed of the second cored bar in the first direction is set higher than the moving speed of the tip of the small-diameter portion accompanying the pushing by the first cored bar, the compressive residual stress in the axial direction of the cylindrical body is reduced. It is possible to suppress the increase in thickness of the small diameter portion. As described above, according to Modified Example 2-1 of the second method, the tapered portion and the small diameter portion of the cylindrical body can be formed in a better balance and more smoothly.

<<Third Embodiment>>
Hereinafter, a method for forming a cylindrical body having a tapered portion according to a third embodiment of the present invention (hereinafter sometimes referred to as "third method") will be described with reference to the drawings.

As described above, in the method of forming a cylindrical body having a tapered portion according to the present invention (method of the present invention) including the first method and the second method, in the diameter reduction process performed in the second step, at the latest After time point 1, the first core bar presses the blank tube in the first direction to push the second end of the blank tube toward the small inner diameter portion of the die hole, thereby reducing the diameter of the second end side of the blank tube. . That is, the diameter of the tube is reduced while compressing it by pressing it in the axial direction to form the small-diameter portion of the cylindrical body.

Therefore, the thickness of the small-diameter portion of the cylindrical body becomes larger (increases) than the thickness of the region of the blank corresponding to the small-diameter portion of the cylindrical body. In addition, as the thickness of the small-diameter portion increases, variations in the thickness of the small-diameter portion tend to increase.

Therefore, the third method is a method for forming a cylindrical body having a tapered portion, which is any of the second methods described above, and further includes a third step described below.
Third step: After the second step, the first cored bar is extracted from the cylindrical body, and the third cored bar, which is a cylindrical cored bar having an outer diameter corresponding to the inner diameter of the small diameter portion of the cylindrical body, is inserted into the cylindrical body. By inserting from the tapered portion side of the body and moving in the first direction, a squeezing process of shaving the inner surface of the small diameter portion of the cylindrical body is performed.

FIG. 10 is a flowchart showing each process included in the third method and the flow of each process. The flowchart illustrated in FIG. 10 is similar to the flowchart for the first method illustrated in FIG. 5 except that the third step (step S30) is included after the second step (step S20). The details of the treatment process (treatment process) for treating the inner surface of the cylindrical member are well known to those skilled in the art, and therefore the description thereof is omitted here.

As described above, in the third method, after performing the above-described second method (i.e., after performing the second step), the shaving process of shaving the inner surface of the small-diameter portion of the cylindrical body is performed. be. Therefore, according to the third method, it is possible to provide a cylindrical body with high dimensional accuracy that can be used in applications requiring high dimensional accuracy for the inner diameter and/or wall thickness of the small-diameter portion.

<<Fourth Embodiment>>
Hereinafter, a method for forming a cylindrical body having a tapered portion according to a fourth embodiment of the present invention (hereinafter sometimes referred to as "fourth method") will be described with reference to the drawings.

In the above-described third method, after performing the above-described second method (that is, after performing the second step), a rubbing process is performed for the inner surface of the small-diameter portion of the cylindrical body. As a result, it is possible to provide a cylindrical body with high dimensional accuracy that can be used in applications requiring high dimensional accuracy, for example, for the inner diameter and/or thickness of the small-diameter portion.

However, performing the third step of extracting the first cored bar from the cylindrical body and inserting the third cored bar into the cylindrical body to treat the inner surface of the small diameter portion of the cylindrical body after the second step is difficult to produce the cylindrical body. This can lead to decreased efficiency and increased manufacturing costs. Further, even if a portion for performing the scraping process is provided at the tip of the first cored bar, the diameter of the small diameter portion is smaller than the diameter of the tapered portion. Therefore, the flow of the material forming the small diameter portion is faster than the speed of movement of the portion, so the material forming the small diameter portion increases the thickness of the small diameter portion ahead of the portion. (Increase in thickness) is a concern.

Therefore, in the fourth method, the first core bar is a central member which is a cylindrical portion having an outer diameter corresponding to the inner diameter of the small diameter portion of the cylindrical body, and is provided around the central member coaxially with the central member. and a peripheral member, which is the portion that is cut. Furthermore, the central member is configured to be slidable in the first direction with respect to the peripheral member.

FIG. 11 is a schematic cross-sectional view showing an example of the configuration of the first cored bar used in the fourth method. The first cored bar 402 illustrated in FIG. 11 includes a central member 402a, which is a cylindrical portion having an outer diameter corresponding to the inner diameter of the small-diameter portion of the cylindrical body, and a central member 402a provided coaxially around the central member. It is divided into a peripheral edge member 402b which is a flat portion. Furthermore, the central member 402a is configured to be slidable in the first direction with respect to the peripheral member 402b (see the white double-headed arrow).

In addition, the fourth method is any one of the second methods described above, wherein in the second step, the central member is moved in the first direction at a higher speed than the peripheral member to move the inner surface of the bottom of the mother tube. A method for forming a cylindrical body having a tapered portion, characterized in that, by pressing, the inner surface of the small-diameter portion of the cylindrical body is treated in parallel with at least part of the diameter-reducing process.

FIG. 12 is a flow chart showing each process included in the fourth method and the flow of each process. In the third method described above, after the second step (step S20), the third step (step S30) is performed as a separate step of replacing the first cored bar with the third cored bar and performing the handling process. On the other hand, in the fourth method, the handling process (step S24) is executed in the second process (step S20). Except for this point, the flowchart for the fourth method illustrated in FIG. 12 is the same as the flowchart for the first method illustrated in FIG.

As illustrated in FIG. 12, in the second step (step S20) executed in the fourth method, in addition to the diameter expansion process (step S21), the diameter reduction process (step S22) and the completion process (step S23) , a handling process (step S24) is also performed. In this way, in the fourth method, the drawing (diameter reduction process) by pressing and the rolling process (rolling process) for adjusting the inner shape and thickness of the small-diameter portion are performed in parallel in one process. Therefore, it is possible to reduce the decrease in the production efficiency of the cylindrical body and the increase in the manufacturing cost due to the execution of the rolling process.

FIG. 13 schematically illustrates changes in the positions of the central member 402a and the peripheral member 402b, which constitute the first cored bar 402, and the shape of the first blank tube 101 as the second step executed in the fourth method progresses. It is a cross-sectional view. In FIG. 13 as well, only the portion on the right side of the axis AX as viewed in the drawing is drawn, but the same applies to the portion on the left side of the axis AX. Also, in order to simplify the drawings, only some of the reference numerals assigned to the parts shown in FIGS. 1 to 4 and 11 are shown. However, in the following description of FIG. 13, the reference numerals shown in FIGS. 1-4 and 11 are used for the sake of accuracy, and reference should be made to FIGS. 1-4 and 11 as necessary.

As the second step progresses from the state shown in (a) of FIG. 13 to the state shown in (b) of FIG. (see arrow). As a result, the diameter of the first end portion 111 side of the base pipe 101 is increased, and the tapered portion 220 of the cylindrical body 201 is formed. At the same time, the first end portion 111 of the blank pipe 101 is pressed in the first direction by the first stepped portion 413 of the first cored bar 402 , and the second end portion 112 of the blank pipe 101 is pushed into the small inner diameter portion 313 of the die hole 310 . , the diameter of the second end portion 112 side of the blank tube 101 is reduced, and the small diameter portion 230 of the cylindrical body 201 is formed. In parallel with this, the central member 402a of the first cored bar 402 moves faster (larger) than the peripheral member 402b in the first direction (see the white arrow). As a result, the inner peripheral surface of the small-diameter portion 230 of the cylindrical body 201 formed by reducing the diameter of the second end portion 112 side of the blank pipe 101 is handled by the central member 402a, and the inner diameter and/or wall thickness of the small-diameter portion 230 are increased. Accuracy is achieved. At the same time, the central member 402a presses the inner surface of the bottom of the tip of the small diameter portion 230 in the first direction. As a result, the tensile stress in the axial direction acts on the small diameter portion 230, so the compressive stress caused by the pressing of the first end portion 111 by the first stepped portion 413 is reduced. Therefore, for example, it is possible to reduce the buckling of the small-diameter portion even in a blank tube having a small wall thickness, and to reduce the residual stress due to thickening and compression in the small-diameter portion.

In order to move the central member 402a and the peripheral member 402b in the first direction at different speeds as described above, a drive mechanism capable of individually controlling the movement of the central member 402a and the peripheral member 402b is required. is necessary. A specific example of such a driving mechanism is a driving device such as a double-acting press.

<<Fifth Embodiment and Sixth Embodiment>>
Hereinafter, methods for forming a cylindrical body having a tapered portion according to the fifth embodiment and the sixth embodiment of the present invention (hereinafter referred to as "fifth method" and "sixth method", respectively) There are cases.) will be explained.

As described above, when forming a bottomless member such as a nozzle or a tank liner from a bottomed cylindrical body such as the cylindrical body 201 illustrated in FIG. You have to drill holes. Performing secondary processing in such a separate process may lead to problems such as a decrease in production efficiency and an increase in manufacturing costs for products molded using a cylindrical body as an intermediate material. From the viewpoint of reducing such problems, it is desirable to open the bottom portion of the cylindrical body while the cylindrical body is set in the die provided in the apparatus for carrying out the method of the present invention.

Therefore, the fifth method is the above-described third method or fourth method,
A protrusion for punching is formed at the tip of the third core bar or the central member,
After performing the squeezing process, the third core bar or the central member is further moved in the first direction to perform the punching process of punching the bottom portion at the tip of the small diameter portion of the cylindrical body with the projection.
A method for forming a cylindrical body having a tapered portion, characterized by:

Further, the sixth method is the above-described third method or fourth method,
A fourth mandrel, which is a mandrel for punching, is configured to move in a second direction opposite to the first direction from the end of the die hole on the side of the small inner diameter portion,
After performing the squeezing process, the cylindrical body is fixed so as not to move in the second direction by a predetermined member or peripheral member, and after moving the third core bar or the central member in the second direction, the fourth core bar is moved to the second direction. By moving in two directions, a punching process is performed in which the bottom portion at the tip of the small diameter portion of the cylindrical body is punched out by the fourth core bar.
A method for forming a cylindrical body having a tapered portion, characterized by:

As described above, in both the fifth method and the sixth method, the treatment process executed in the third step included in the third method or the second step included in the fourth method is executed. Afterwards, a punching process is performed to open the bottom portion of the cylinder while the cylinder is set in the die. The fifth method and the sixth method have the same configuration except that the mechanism for executing the extraction process is different.

FIG. 14 is a flow chart showing each process and the flow of each process included in the fifth and sixth methods in which the removal process is performed after the treatment process performed in the third process included in the third method. In the third method described above, after the second step (step S20), the third step (step S30) of replacing the first cored bar with the third cored bar and performing the handling process is performed. On the other hand, in the fifth method and sixth method illustrated in FIG. 14, in the third step (step S30), the removal step (step S32) is continuously performed after the treatment step (step S31). Except for this point, the flowcharts for the fifth and sixth methods illustrated in FIG. 14 are similar to the flowchart for the third method illustrated in FIG.

On the other hand, FIG. 15 is a flow chart showing each process and the flow of each process included in the fifth method and the sixth method, in which the removal process is performed after the handling process is performed in the second process included in the fourth method. be. In the fourth method described above, the second step (step S20) is executed to execute the diameter expansion process (step S21), the diameter reduction process (step S22), the completion process (step S23), and the handling process (step S24). be done. On the other hand, in the fifth method and the sixth method illustrated in FIG. 15, the execution of the second step (step S20) includes the diameter expansion process (step S21), the diameter reduction process (step S22), the completion process (step After S23) and the handling step (step S24), the extraction step (step S25) is performed continuously. Except for this point, the flowcharts for the fifth and sixth methods illustrated in FIG. 15 are the same as the flowcharts for the fourth method illustrated in FIG.

As described above, the fifth method and the sixth method differ in the mechanism for executing the extraction process. FIG. 16 is a schematic cross-sectional view showing an example of the extraction process (step S32 or step S25) performed in the fifth method. (a) on the left side of the axis AX as viewed in the drawing shows the situation at the time of completion of the handling process (step S31 or step S24), and (b) on the right side of the axis AX as viewed in the drawing shows the situation at the time of completion of the drawing process (step The situation at the time of execution of S32 or step S25) is depicted respectively.

As illustrated in (a) of FIG. 16, at the time of completion of the handling process (step S31 or step S24), the punching projection 601a formed at the tip of the third cored bar 601 or the central member 402a is cylindrical. Although it abuts against the inner surface of the bottom of body 201, the bottom is not yet open. Next, the third cored bar 601 or the central member 402a is further moved in the first direction (see the white arrow). As a result, the bottom of the cylindrical body 201 is punched out by the protrusion 601a, as illustrated in FIG. 16(b).

On the other hand, FIG. 17 is a schematic cross-sectional view showing an example of the extraction process (step S32 or step S25) performed in the sixth method. (a) on the left side of the axis AX as viewed in the drawing shows the situation at the time of completion of the handling process (step S31 or step S24), and (b) on the right side of the axis AX as viewed in the drawing shows the situation at the time of completion of the drawing process (step The situation at the time of execution of S32 or step S25) is depicted respectively.

As illustrated in (a) of FIG. 17, at the completion of the handling process (step S31 or step S24), the tip of the third cored bar 601 or the central member 402a is in contact with the inner surface of the bottom of the cylindrical body 201. Although there is, the bottom has not yet opened. Next, the cylindrical body 201 is fixed so as not to move in the second direction by the predetermined fixing member 701 or the peripheral member 402b, and the third cored bar 601 or the central member 402a is moved in the direction opposite to the first direction (the second direction). ). Then, by moving the fourth cored bar 801, which is a cored bar for punching, in the second direction (see the black arrow), the bottom portion of the cylindrical body 201 is moved as illustrated in FIG. 17(b). is punched out by the fourth mandrel 801 .

As described above, in the fifth method and the sixth method, the bottom portion of the cylindrical body that has been subjected to the rolling process performed in the third step or the second step is set in the die. can be opened. That is, in the fifth method and the sixth method, the bottom portion of the cylindrical body can be opened while the cylindrical body is set in the die without performing secondary processing in a separate step. Therefore, according to the fifth method and the sixth method, even in the case of forming a bottomless member such as a nozzle or a tank liner from a bottomed cylindrical body, problems such as a decrease in production efficiency and an increase in manufacturing cost can be avoided. can be reduced.

<<Seventh embodiment>>
Hereinafter, a method for forming a cylindrical body having a tapered portion according to a seventh embodiment of the present invention (hereinafter sometimes referred to as "seventh method") will be described with reference to the drawings.

A seventh method is any of the first methods described above,
The blank tube is a bottomless cylindrical member with an open second end,
A method for forming a cylindrical body having a tapered portion, characterized by:

As a specific example of the bottomless base pipe with the second end open as described above, for example, the base pipe 102 illustrated in FIG. 1(b) can be cited. By using such a bottomless blank tube, a bottomless member such as a nozzle or a tank liner can be easily formed.

<Modification 7-1>
By the way, when the method of forming a cylindrical body having a tapered portion according to the present invention (method of the present invention) is carried out using a bottomless blank pipe having an open second end as described above, the blank pipe Compared to the case of using a bottomed base pipe with the second end closed, unintended deformation may occur on the second end side of the base pipe during the diameter reduction process.

Therefore, the modification 7-1 of the seventh method is
Before the second step is started, the fifth core is a cylindrical core bar having a first outer diameter equal to or smaller than the inner diameter of the small-diameter portion of the cylindrical body. Gold is inserted from the small inner diameter side of the die hole,
In the diameter reduction process performed in the second step, the opening on the second end side of the diameter-reduced mother pipe is fitted onto the fifth core bar.
A method for forming a cylindrical body having a tapered portion, characterized by:

FIG. 18 is a schematic cross-sectional view showing a state immediately before the second step is started in modification 7-1 of the seventh method. It should be noted that the drawings attached to this specification, not limited to FIG. 18, are merely schematic drawings for the purpose of illustration. is not necessarily accurate.

As exemplified in FIG. 18, in the modification 7-1 of the seventh method, before the second step is started, the outer diameter is equal to or less than the outer diameter corresponding to the inner diameter of the small diameter portion 230 of the cylindrical body 202. A fifth metal core 901, which is a cylindrical metal core having a first outer diameter DO1, is inserted into the die hole 310 from the small inner diameter portion 313 side. Thus, in the diameter reduction process executed in the second step, the opening portion of the diameter-reduced tube 102 on the side of the second end portion 112 is aligned with the inner peripheral surface of the small inner diameter portion 313 and the outer peripheral surface of the fifth cored bar 901 . It enters the gap between the surface and the fifth cored bar 901 and fits over it.

As described above, the shape of the opening of the tube 102 on the side of the second end 112 is regulated by the gap between the inner peripheral surface of the small inner diameter portion 313 and the outer peripheral surface of the fifth cored bar 901 during the diameter reduction process. . As a result, as described above, it is possible to reduce the possibility of unintended deformation occurring on the second end portion 112 side of the blank pipe 102 during the diameter reduction process.

<Modification 7-2>
By the way, as described above, preferably, the diameter-reducing process is started after the diameter-expanding process is started. More preferably, the diameter reduction process is started after the first stepped portion of the first core bar contacts the first end portion of the blank tube (first time point). As a result, the tapered portion and the small diameter portion can be formed more smoothly with good balance.

As an example of a specific measure for starting the diameter reduction process after the diameter expansion process is started, as described above, the diameter reduction rate is larger than the diameter expansion rate. Constructing a tube, a die hole and a first mandrel can be mentioned. In the second method of using a bottomed cylindrical member with a closed second end as the base pipe, a so-called "counter punch" is inserted from the small inner diameter side of the die hole to punch the base pipe. The counterpunch is kept in contact with the two ends (bottom), and the counterpunch is also moved in the first direction in accordance with the movement of the second end of the blank tube in the first direction after the time when the diameter reduction process should be started. Thereby, the diameter reduction process can be started at the desired timing after the diameter expansion process is started.

On the other hand, even in the case of using a bottomless tube having an open second end as in the seventh method, the second end can be closed by devising the structure of the above-described fifth cored bar. As in the second method in which a bottomed cylindrical member is used as a blank pipe, the diameter reduction process can be started at a desired timing after the diameter expansion process is started.

That is, the modification 7-2 of the seventh method is
Modification 7-1 of the seventh method described above,
At a predetermined position on the outer peripheral surface of the fifth cored bar, there is an annular step extending outward in the radial direction, the step being larger than the first outer diameter and less than or equal to the outer diameter of the small diameter portion of the cylindrical body. A second stepped portion, which is a portion having an outer diameter, is formed,
The second stepped portion of the fifth core bar is formed at a position facing the upstream end in the first direction of the small inner diameter portion of the die hole or at a predetermined position downstream of the end,
In the second step, the fifth core bar moves at a predetermined speed in the first direction at a predetermined time point after the second time point at which the second end portion of the base pipe comes into contact with the second stepped portion of the fifth core bar. start moving to
A method for forming a cylindrical body having a tapered portion, characterized by:

FIG. 19 is a schematic cross-sectional view showing a state immediately before the second step is started in modification 7-2 of the seventh method. As illustrated in FIG. 19, in the modification 7-2 of the seventh method, at a predetermined position on the outer peripheral surface of the fifth cored bar 901, an annular step is formed so as to spread outward in the radial direction. A second stepped portion 901a is formed as a portion having an outer diameter larger than the first outer diameter DO1 and equal to or smaller than the outer diameter of the small-diameter portion 230 of the cylindrical body 202 . The second stepped portion 901a of the fifth cored bar 901 is formed at a position facing the upstream end in the first direction of the small inner diameter portion 313 of the die hole 310 or a predetermined position downstream of the end. It is

In the second step, at a predetermined time point after the second end portion 112 of the tube 102 contacts the second step portion 901a of the fifth core bar 901 (second time point), the fifth core is moved at a predetermined speed. The gold 901 is started to move in the first direction. The time at which the fifth cored bar 901 starts to move in the first direction is, for example, the progress of the diameter reduction process at that time, the buckling strength of the blank tube, and the magnitude of the compressive residual stress to be generated in the blank tube. etc., can be determined as appropriate according to various requirements. However, if the period from the second time point to the time point of starting the movement of the fifth cored bar 901 in the first direction is excessively long, problems such as an increase in processing load and/or unintended deformation of the mother tube may occur. Caution is required as the risk increases.

Further, the speed at which the fifth cored bar 901 is moved in the first direction is also determined, for example, by the progress of the diameter reduction process at that time, the buckling strength of the blank pipe, and the magnitude of the compressive residual stress to be generated in the blank pipe. It can be determined as appropriate according to various requirements. However, if the moving speed of the fifth cored bar 901 in the first direction becomes excessively slow with respect to the moving speed of the second end portion 112 of the reduced-diameter tube 102 in the first direction, for example, the processing load increases. And/or there is an increased risk of problems such as unintended deformation of the blank pipe, so caution is required.

According to the modification 7-2 of the seventh method, for example, the shape (diameter, length, wall thickness, etc.) and material of the blank pipe, the diameter expansion ratio of the tapered portion of the cylindrical body, and the small diameter portion of the cylindrical body Depending on various factors such as the size relationship with the diameter reduction rate of the portion where the diameter is reduced, and the rate of change (taper angle) of the inner diameter at the inner diameter reduction portion of the die hole, for example, an increase in the processing load and / or an unintended The diameter reduction process can be advanced at a suitable timing that does not cause problems such as deformation. In addition, the moving speed of the fifth cored bar 901 in the first direction can also be appropriately set according to various factors. For example, when the moving speed of the fifth cored bar 901 in the first direction is set lower than the moving speed of the tip of the small-diameter portion 230 of the cylindrical body 202 accompanying the pushing by the first cored bar 401, the axial direction of the cylindrical body 202 It is possible to increase the compressive residual stress in and promote the thickening of the small-diameter portion 230 . Conversely, when the moving speed of the fifth cored bar 901 in the first direction is set higher than the moving speed of the tip of the small-diameter portion 230 accompanying the pushing by the first cored bar, residual compression in the axial direction of the cylindrical body 202 It is possible to reduce the stress and suppress the thickening of the small diameter portion 230 . Thus, according to the modification 7-2 of the seventh method, the tapered portion 220 and the small-diameter portion 230 of the cylindrical body 202 can be formed more smoothly with good balance.

<<Eighth Embodiment>>
Hereinafter, a method of forming a cylindrical body having a tapered portion according to the eighth embodiment of the present invention (hereinafter sometimes referred to as "eighth method") will be described with reference to the drawings.

As described in the explanation of the third method using the bottomed tube with the second end closed, in the method of the present invention, the tube is axially pressed and compressed while being reduced in diameter to form a cylindrical body. Therefore, the thickness of the small-diameter portion of the cylindrical body becomes larger (increases) than the thickness of the region of the blank corresponding to the small-diameter portion of the cylindrical body. In addition, as the thickness of the small-diameter portion increases, variations in the thickness of the small-diameter portion tend to increase. This point also applies to the seventh method using a bottomless blank pipe with an open second end.

Therefore, the eighth method is a method for forming a cylindrical body having a tapered portion, which is any of the seventh methods described above and further includes a third step described below.
Third step: After the second step, the first cored bar is extracted from the cylindrical body, and the third cored bar, which is a cylindrical cored bar having an outer diameter corresponding to the inner diameter of the small diameter portion of the cylindrical body, is inserted into the cylindrical body. By inserting from the tapered portion side of the body and moving in the first direction, a squeezing process of shaving the inner surface of the small diameter portion of the cylindrical body is performed.

The steps and the flow of each process included in the eighth method are the same as those of the third method described with reference to FIG. 10, so description thereof will be omitted here as well. Further, the details of the treatment process (treatment process) for treating the inner surface of the tubular member are well known to those skilled in the art, so the description thereof will be omitted here.

As described above, in the eighth method, after performing the above-described seventh method (i.e., after performing the second step), the shaving step of shaving the inner surface of the small-diameter portion of the cylindrical body is performed. be. Therefore, according to the eighth method, it is possible to provide a cylindrical body with high dimensional accuracy that can be used in applications requiring high dimensional accuracy for the inner diameter and/or wall thickness of the small diameter portion, for example.

Although several embodiments and variations having specific configurations have been described above for the purpose of illustrating the present invention, sometimes with reference to the accompanying drawings, the scope of the present invention is not limited to these exemplary embodiments. It should not be construed as being limited to the embodiments and modifications, and it goes without saying that modifications can be made as appropriate within the scope of the claims and the matters described in the specification.

DESCRIPTION OF

SYMBOLS

101, 101a, 102... Base tube 111... First end 112...

Second end

201, 201a, 202... Cylindrical body having a tapered portion 211... One open end 212... The other end 220... Tapered portion 230 Small diameter portion 301 Die 310 Die hole 311 Large inner diameter portion 312 Reduced inner diameter portion 313 Small

inner diameter portion

401, 402 First core metal 402a Central member 402b Peripheral member 411 Small diameter core portion 412 ... Outside diameter increasing part 413... First stepped part 501... Second core metal 601... Third core metal 601a... Projection for punching 701... Fixing member 801... Fourth core metal 901... Fifth core metal 901a... Second core metal step

Claims

A base tube, which is a bottomed or bottomless cylindrical member, is inserted into a die hole, which is a through hole having a predetermined shape and formed in a die, by a first metal core, which is a metal core having a predetermined shape. A method of forming a cylindrical body having a tapered portion by pushing in the axial direction of the blank tube and the die hole,
The cylindrical body has a tapered portion, which is a portion whose diameter increases as it approaches one open end, and a small-diameter portion, which is a cylindrical portion formed between the other end and the tapered portion. , the maximum outer diameter of the tapered portion is larger than the outer diameter of the blank tube, the outer diameter of the small diameter portion is smaller than the outer diameter of the blank tube,
The die hole has a large inner diameter portion which is a portion having a first inner diameter corresponding to the maximum outer diameter of the tapered portion of the cylindrical body, and an inner diameter corresponding to the outer diameter of the small diameter portion of the cylindrical body. a small inner diameter portion, which is a portion having a second inner diameter that is smaller than the inner diameter; an inner diameter decreasing portion, which is a portion where the inner diameter decreases from the inner diameter to the second inner diameter,
The outer diameter of the first cored bar is a portion whose outer diameter increases from the outer diameter corresponding to the minimum inner diameter of the tapered portion of the cylindrical body to the outer diameter corresponding to the maximum inner diameter of the tapered portion of the cylindrical body as it moves away from the tip. an enlarged portion and an annular step formed so as to widen outward in a radial direction at a position adjacent to the base end side of the increased outer diameter portion and having an outer diameter equal to the maximum outer diameter of the tapered portion of the cylindrical body. and a first stepped portion that is a portion having an inner diameter equal to the maximum inner diameter of the tapered portion of the cylindrical body,
The raw pipe is pushed from the large inner diameter side of the die hole so that the first end, which is the opening end of the raw pipe, faces the upstream side in the first direction, which is the direction in which the raw pipe is pushed into the die hole. By inserting and bringing the second end opposite to the first end of the blank pipe into contact with the reduced inner diameter portion of the die hole, the die hole is held at a predetermined position inside the die hole. a first step of installing the base pipe; a second step of forming the cylindrical body in which the tapered portion is formed in a region facing the reduced inner diameter portion of the die hole and the small diameter portion is formed in a region facing the small inner diameter portion of the die hole;
including
In the second step,
A diameter-enlarging process in which the inner diameter of the first end portion of the raw pipe is pressed by the increased outer diameter portion of the first core bar to expand the diameter of the first end side of the raw pipe;
After a first time point at which the first stepped portion of the first cored bar comes into contact with the first end of the raw pipe at the latest, the raw pipe is pressed in the first direction by the first cored bar. a diameter reducing process in which the second end portion of the blank pipe is pushed toward the small inner diameter portion of the die hole to reduce the diameter of the second end portion side of the blank pipe, and the inner diameter reduction of the die hole a completion process of completing molding of the tapered portion and the small diameter portion by sandwiching the region on the first end side of the base pipe between the portion and the increased outer diameter portion of the first cored bar;
run the
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to claim 1,
The diameter reduction process is started after the diameter expansion process is started,
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to claim 2,
the diameter reduction process is started after the first time point;
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to any one of claims 1 to 3,
Than the diameter expansion rate, which is the ratio of the difference between the maximum outer diameter of the tapered portion of the cylindrical body and the outer diameter of the first end of the base pipe to the outer diameter of the first end of the base pipe, A diameter reduction ratio, which is a ratio of the difference between the outer diameter of the second end of the blank pipe and the outer diameter of the small diameter portion of the cylindrical body to the outer diameter of the second end of the blank pipe, is larger. ,
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to any one of claims 1 to 4,
The thickness of the region corresponding to the tapered portion of the cylindrical body on the first end side of the blank tube is the thickness of the region corresponding to the small diameter portion of the cylindrical body on the second end side of the blank tube. greater than the wall thickness,
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to any one of claims 1 to 5,
A material constituting the base pipe is austenitic stainless steel,
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to any one of claims 1 to 6,
The base pipe is a bottomed cylindrical member closed at the second end,
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to claim 7,
Before the second step is started, a second metal core, which is a metal core having a predetermined shape, is inserted from the small inner diameter portion side of the die hole and comes into contact with the second end of the blank tube. fixed in position,
the second core bar starts moving in the first direction at a predetermined speed at a predetermined point in time during which the second step is performed;
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to claim 7 or claim 8,
After the second step, the first cored bar is extracted from the cylindrical body, and a third cored bar having a cylindrical shape with an outer diameter corresponding to the inner diameter of the small diameter portion of the cylindrical body is obtained. a third step of performing a shaving step of shaving the inner surface of the small diameter portion of the cylindrical body by inserting the cylindrical body from the tapered portion side and moving it in the first direction;
further comprising
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to claim 7 or claim 8,
The first core bar is a central member that is a cylindrical portion having an outer diameter corresponding to the inner diameter of the small diameter portion of the cylindrical body, and a portion that is provided around the central member and coaxially with the central member. is divided into a peripheral member that is
The central member is configured to be slidable in the first direction with respect to the peripheral member,
In the second step, the central member is moved in the first direction at a speed higher than that of the peripheral member to press the inner surface of the bottom portion of the blank tube, thereby at least partly paralleling the diameter-reducing process. to perform a treatment process for treating the inner surface of the small diameter portion of the cylindrical body;
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to claim 9 or 10,
A projection for punching is formed at the tip of the third core bar or the central member,
After the rolling step is performed, the third core bar or the central member is further moved in the first direction to perform a punching step of punching the bottom portion at the tip of the small-diameter portion of the cylindrical body by the projection. ,
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to claim 9 or 10,
A fourth mandrel, which is a mandrel for punching, is provided so as to move from the end of the die hole on the side of the small inner diameter portion in a second direction opposite to the first direction. and
After the handling process is performed, the cylindrical body is fixed so as not to move in the second direction by a predetermined member or the peripheral member, and the third core bar or the central member is moved in the second direction. , by moving the fourth cored bar in the second direction, performing a punching process of punching the bottom portion at the tip of the small diameter portion of the cylindrical body with the fourth cored bar;
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to any one of claims 1 to 6,
The base pipe is a bottomless cylindrical member with the second end open,
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to claim 13,
Before the second step is started, a core bar having a cylindrical shape with a first outer diameter equal to or smaller than the outer diameter corresponding to the inner diameter of the small-diameter portion of the cylindrical body. A fifth core bar is inserted from the small inner diameter portion side of the die hole,
In the diameter-reducing process performed in the second step, the diameter-reduced opening on the second end side of the base pipe is fitted onto the fifth core bar.
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to claim 14,
At a predetermined position on the outer peripheral surface of the fifth cored bar, an annular step formed so as to spread outward in the radial direction is larger than the first outer diameter and outside the small diameter portion of the cylindrical body. A second stepped portion, which is a portion having an outer diameter equal to or smaller than the diameter, is formed,
The second stepped portion of the fifth core bar is located at a position facing an upstream end portion in the first direction of the small inner diameter portion of the die hole or a predetermined position downstream of the end portion. is formed and
In the second step, at a predetermined time point after a second time point at which the second end portion of the base pipe comes into contact with the second stepped portion of the fifth core bar, the fifth core bar reaches a predetermined level. initiate movement in the first direction at a velocity;
A method for forming a cylindrical body having a tapered portion, characterized by:
A method for forming a cylindrical body having a tapered portion according to any one of claims 13 to 15,
After the second step, the first cored bar is extracted from the cylindrical body, and a third cored bar having a cylindrical shape with an outer diameter corresponding to the inner diameter of the small diameter portion of the cylindrical body is obtained. a third step of performing a shaving step of shaving the inner surface of the small diameter portion of the cylindrical body by inserting the cylindrical body from the tapered portion side and moving it in the first direction;
further comprising
A method for forming a cylindrical body having a tapered portion, characterized by: