Method for extrusion-molding different-thickness pipe, and device for extrusion-molding different-thickness pipe

Abstract

In the present invention, a raw pipe is set on a container (dice) that includes, on a tip end side and a base end side, respectively, a small inner diameter region having an inner diameter smaller than an outer diameter of the raw pipe and a large inner diameter region having an inner diameter larger than the outer diameter of the raw pipe. A mandrel (core metal) includes, on a tip end side and a base end side, respectively, a small outer diameter region having an outer diameter corresponding to an inner diameter of the raw pipe and a large outer diameter region having an outer diameter larger than the inner diameter of the raw pipe. After the mandrel is pressed into the raw pipe and the end of the base end side of the raw pipe is expanded, the end of the base end side of the raw pipe is pressed using a sleeve, and the raw pipe into which the mandrel is inserted is pressed into the small inner diameter region of the container and contracted. Due to this configuration, a method for extrusion-molding a different-thickness pipe and a device for extrusion-molding same are provided, which make it possible to set the diameter difference between the large diameter part (ear part) and the small diameter part (contracted different-thickness part) to a large value without excessively increasing the machining load, and which also make it possible to set the length in the axial direction as desired.

Description

[Technical field]

[0001] The present invention relates to a method for extruding a pipe having a different thickness and an apparatus for extruding a pipe having a different thickness. [Background technology]

[0002] In the technical field, there is known a differential thickness pipe (also called a "butted pipe" or "butted tube") in which a thick-walled portion is formed in a portion of the axial direction of the pipe for the purpose of achieving a desired mechanical strength in the thick-walled portion while reducing weight in the thin-walled portion (portion other than the thick-walled portion).

[0003] As an extrusion molding method for obtaining the above-mentioned differential thickness pipe, for example, the method described in Japanese Patent No. 6933762 (Patent Document 1) by the present applicant is known. According to this method, a mother tube having a constant outer diameter and wall thickness is integrally formed into a large diameter portion (ear portion) that maintains the outer diameter of the mother tube and a small diameter portion that is reduced in diameter and extends in the axial direction (extrusion direction), and two portions (differential thickness portions) having different wall thicknesses are formed in the small diameter portion.

[0004] In the above method, in order to obtain a pipe with a large diameter portion having a larger outer diameter, it is necessary to increase the outer diameter of the blank pipe accordingly. In this case, if the outer diameter of the small diameter portion of the blank pipe is maintained unchanged, the diameter reduction ratio (diameter reduction amount) in the extrusion molding of the pipe with a large thickness will increase as a result, and the processing load will increase. Therefore, depending on the processing limit of the extrusion molding device, which is determined by, for example, the material constituting the blank pipe, the material of the member constituting the extrusion molding device, and the extrusion performance of the extrusion molding device, it may be difficult or impossible to achieve the desired diameter reduction ratio. In addition, even if the diameter reduction processing (extrusion processing) is performed within the processing limit, the extrusion resistance increases as the diameter reduction amount increases, so the extrusion amount must be reduced, and it may be difficult or impossible to form a small diameter portion having a desired shape (for example, the length in the axial direction, etc.).

[0005] Meanwhile, Japanese Patent No. 6256668 (Patent Document 2) proposes a forming method in which a plug is pushed into a mother tube from its base end while the end portion of the mother tube on the tip side in the plug pushing direction is blocked so as not to proceed further toward the tip and the position of the mother tube in the longitudinal direction relative to the die is fixed (see, for example, paragraph

[0022] , etc.). According to this method, the end portion on the base end side of the mother tube is made into an enlarged diameter portion with an enlarged outer diameter, and an ironing process is performed on the part of the mother tube on the tip side of the enlarged diameter portion (non-enlarged diameter portion) to enlarge the inner diameter of a region adjacent to the tip side of the enlarged diameter portion while maintaining the outer diameter, thereby making it possible to change the wall thickness of the non-enlarged diameter portion (to make the thickness different).

[0006] However, in the above method, because the end portion on the tip side of the mother tube is blocked, the material constituting the non-expanded diameter portion, whose inside diameter expands as the plug advances, flows toward the base end, which is the opposite direction to the direction of advancement of the plug, causing the non-expanded diameter portion to extend toward the base end and increasing the contact area with the plug. As a result, the processing load increases as the plug advances due to an increase in the frictional force between the non-expanded diameter portion and the plug, and the above method is not suitable for forming a long product (an axially long pipe with different thicknesses). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6933762 [Patent Document 2] Patent No. 6256668 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, in the art, there is a need for an extrusion molding method for differential thickness pipes that allows the diameter difference between the large diameter portion (ear portion) and the small diameter portion (reduced diameter differential thickness portion) to be set large without excessively increasing the processing load, and that also allows the axial length to be set arbitrarily. [Means for solving the problem]

[0009] In view of the above-mentioned problems, the present inventors conducted intensive research and found that the above-mentioned problems can be solved by forcing a mandrel (core metal) having a small outer diameter region having an outer diameter corresponding to the inner diameter of the mother tube and a large inner diameter region having an outer diameter larger than the inner diameter of the mother tube, at its tip and base ends, respectively, into a mother tube set in a container (die) having a small inner diameter region having an inner diameter smaller than the outer diameter of the mother tube, and a large inner diameter region having an inner diameter larger than the outer diameter of the mother tube, thereby expanding the diameter of the base end of the mother tube, and then pressing the base end of the mother tube with a sleeve, thereby forcing the mother tube with the mandrel inserted inside into the small inner diameter region of the container to reduce its diameter.

[0010] Specifically, the method for extrusion molding a differential thickness pipe according to the present invention (hereinafter, may be referred to as the "method of the present invention") includes first to third steps carried out in an extrusion molding apparatus. The extrusion molding apparatus includes a mandrel which is a core metal having a predetermined shape, a sleeve which is a cylindrical member arranged coaxially around the outside of the mandrel, a container which is a die in which a container hole which is a through hole having a predetermined shape is formed, and a drive mechanism configured to push the mandrel and the sleeve into the container hole.

[0011] The first step is to set a blank tube having a predetermined shape at a predetermined position inside the container hole. The second step is to push a mandrel into the blank tube using a drive mechanism to expand the diameter of the base end side, which is the upstream side in the extrusion direction of the blank tube. The third step is to press the base end side of the blank tube with a sleeve after the first time point, which is the time point when the second step is started, to push the blank tube into the tip side, which is the downstream side in the extrusion direction of the container hole, thereby performing an extrusion process and reducing the diameter of the tip end side of the blank tube.

[0012] The blank pipe is a cylindrical member having a first outer diameter, a first inner diameter, and a first thickness. The differential thickness pipe formed by the method of the present invention includes, in order from the tip side to the base side, a first small diameter region, a second small diameter region, and a large diameter region. The first small diameter region is a region having a second outer diameter, which is a predetermined outer diameter smaller than the first outer diameter, a second inner diameter, which is an inner diameter equal to the first inner diameter, and a second thickness, which is a predetermined thickness smaller than the first thickness. The second small diameter region is a region having a third outer diameter, which is an outer diameter equal to the second outer diameter, and a third thickness, which is a predetermined thickness smaller than the second thickness. The large diameter region is a region having a fourth outer diameter, which is a predetermined outer diameter larger than the first outer diameter, and a fourth thickness, which is a predetermined thickness.

[0013] The mandrel includes a small cross-sectional region, a large cross-sectional region, and an expanding cross-sectional region. The small cross-sectional region is a cylindrical region formed at the distal end and having a first cross-sectional area that is a circular cross-sectional area having a fifth outer diameter that is an outer diameter corresponding to the first inner diameter and the second inner diameter. The large cross-sectional region is a cylindrical region formed at the proximal end and having a second cross-sectional area that is a cross-sectional area that corresponds to a cross-sectional area of ​​the internal space of the second small diameter region and the large diameter region. The expanding cross-sectional region is a region formed between the small cross-sectional region and the large cross-sectional region and has a cross-sectional area that expands from the first cross-sectional area to the second cross-sectional area as the small cross-sectional area approaches the large cross-sectional area.

[0014] The sleeve includes a pressing region that is a cylindrical region formed on the tip side and has a columnar internal space having a seventh outer diameter that is an outer diameter equal to the fourth outer diameter and a third cross-section that is a cross-section corresponding to the second cross-section.

[0015] The cross-sectional shapes of the internal spaces of the second small diameter region and the large diameter region of the differential thickness pipe are not particularly limited, and can be a wide variety of shapes, such as polygonal, elliptical, circular, etc. In other words, the shapes of the internal spaces of the second small diameter region and the large diameter region are not particularly limited, and can be a wide variety of shapes, such as polygonal, elliptical, cylindrical, etc.

[0016] For example, the internal space of the second small diameter region may have a cylindrical shape with a third inner diameter that is a predetermined inner diameter larger than the first inner diameter, and the internal space of the large diameter region may have a cylindrical shape with a fourth inner diameter that is an inner diameter equal to the third inner diameter. In this case, the large cross-sectional region of the mandrel has a cylindrical shape with a sixth outer diameter that is an outer diameter corresponding to the fourth inner diameter, and the enlarged cross-sectional region of the mandrel has a truncated cone shape whose outer diameter increases from a fifth outer diameter that is the outer diameter of the small cross-sectional region to a sixth outer diameter that is the outer diameter of the large cross-sectional region as it approaches the small cross-sectional region. Also, the pressing region of the sleeve has a cylindrical shape with a seventh outer diameter and a seventh inner diameter that is an inner diameter equal to the third inner diameter and the fourth inner diameter.

[0017] The container bore includes a large inner diameter region, a small inner diameter region, and an inner diameter decreasing region. The large inner diameter region is a region formed on the base end side and has a sixth inner diameter that is an inner diameter corresponding to the fourth outer diameter. The small inner diameter region is a region formed on the tip end side and has a seventh inner diameter that is an inner diameter corresponding to the second outer diameter and the third outer diameter. The inner diameter decreasing region is a region formed between the large inner diameter region and the small inner diameter region and has an inner diameter that decreases from the sixth inner diameter to the seventh inner diameter as it approaches the small inner diameter region.

[0018] Furthermore, in the method of the present invention, at a second point in time when the third step is started, the tip end of the mandrel in the extrusion direction has reached the tip end of the mother tube or is further tip than the tip end of the mother tube, and the base end of the small cross-sectional area of ​​the mandrel is located further base than the base end of the small inner diameter area of ​​the container hole.

[0019] Another embodiment of the present invention relates to a method for extrusion molding a differential thickness pipe, in which a blank tube having a predetermined shape is forced into a container hole by a sleeve in an extrusion molding apparatus to form a differential thickness pipe having a predetermined shape. The extrusion molding apparatus used in the method of the present invention according to this embodiment includes a mandrel which is a core metal having a predetermined shape, a sleeve which is a tubular member arranged coaxially outside the mandrel, a container which is a die in which a container hole which is a through hole having a predetermined shape is formed, and a drive mechanism configured to force at least the sleeve into the container hole.

[0020] The blank tube is a cylindrical member having an 11th outer diameter, an 11th inner diameter, and an 11th wall thickness. The differential thickness pipe includes an 11th small outer diameter region, an 11th large outer diameter region, and an 11th increasing outer diameter region. The 11th small outer diameter region is formed at the tip end, which is the downstream side in the pressing direction, which is the direction in which the blank tube is pressed into the container hole, and has a 12th outer diameter, which is a predetermined outer diameter smaller than the 11th outer diameter, a 12th inner diameter, which is an inner diameter equal to the 11th inner diameter, and a 12th wall thickness, which is a predetermined wall thickness smaller than the 11th wall thickness. The 11th large outer diameter region is formed at the base end, which is the upstream side in the pressing direction, and has a 13th outer diameter, which is a predetermined outer diameter larger than the 11th outer diameter, a 13th inner diameter, which is an inner diameter equal to the 11th inner diameter, and a 13th wall thickness, which is a predetermined wall thickness larger than the 11th wall thickness. The 11th increasing outer diameter region is formed between the 11th small outer diameter region and the 11th large outer diameter region, and as it approaches from the 11th small outer diameter region to the 11th large outer diameter region, the outer diameter increases from the 12th outer diameter to the 13th outer diameter, the wall thickness increases from the 12th wall thickness to the 13th wall thickness, and the inner diameter is constant at a 14th inner diameter that is equal to the 11th inner diameter.

[0021] The mandrel includes a base outer diameter region that is a cylindrical region formed on the tip side and has a 14th outer diameter that is an outer diameter corresponding to the 11th inner diameter. The sleeve includes an 11th pressing region that is a tubular region formed on the tip side and has a cylindrical internal space with a 15th outer diameter that is an outer diameter equal to the 13th outer diameter and a 15th inner diameter that is an inner diameter corresponding to the 14th outer diameter. The container hole includes an 11th large inner diameter region, an 11th small inner diameter region, and an 11th inner diameter decreasing region. The 11th large inner diameter region is a region formed on the base end side and has a 16th inner diameter that is an inner diameter corresponding to the 13th outer diameter. The 11th small inner diameter region is a region formed on the tip side and has a 17th inner diameter that is an inner diameter corresponding to the 12th outer diameter. The eleventh inner diameter decreasing region is formed between the eleventh large inner diameter region and the eleventh small inner diameter region, and the inner diameter decreases from the sixteenth inner diameter to the seventeenth inner diameter as it approaches the eleventh small inner diameter region from the eleventh large inner diameter region.

[0022] The method of the present invention according to this embodiment includes steps 11 to 13 listed below. The eleventh step is a step of setting the blank tube at a predetermined position inside the container hole by abutting the tip end of the blank tube against the eleventh inner diameter reduced region of the container hole. The 12th step is a step in which, with the mandrel inserted into the mother tube, the base end of the mother tube is pressed with a sleeve to cause the material constituting the mother tube to plastically flow and fill the space between the container and the mandrel in the 11th large inner diameter region and the 11th reduced inner diameter region of the container hole, thereby expanding the outer diameter of the mother tube to a 13th outer diameter while maintaining the inner diameter of the mother tube at the 11th inner diameter. The 13th step is a step in which, with the mandrel inserted into the mother tube, the base end of the mother tube is further pressed with the sleeve to perform an extrusion process in which the material constituting the mother tube is pushed into the 11th smaller inner diameter region of the container hole through the gap between the base end of the 11th smaller inner diameter region of the container hole and the mandrel, thereby reducing the diameter of the tip end of the mother tube.

[0023] Furthermore, at time 11, when step 12 is started, the tip end of the mandrel has reached position 11, which is the same position in the pushing direction as the position of the base end of the 11 small inner diameter region of the container hole, or further tip than position 11. In addition, at time 12, when step 13 is started, the tip end of the mandrel has reached position 12, which is a position a predetermined distance further tip than the base end of the 11 small inner diameter region of the container hole, or further tip than position 12.

[0024] The present invention also relates to an extrusion molding apparatus for a differential thickness pipe (hereinafter, sometimes referred to as the "apparatus of the present invention") that molds a differential thickness pipe by carrying out the above-mentioned method of the present invention. Effect of the Invention

[0025] In the method of the present invention, as described above, in the first step, a mother tube is set in a container having a container hole having a small inner diameter region having an inner diameter smaller than the outer diameter of the mother tube and a large inner diameter region having an inner diameter larger than the outer diameter of the mother tube, at its tip and base ends, respectively. Then, in the second step, a mandrel having a small outer diameter region having an outer diameter corresponding to the inner diameter of the mother tube and a large outer diameter region having an outer diameter larger than the inner diameter of the mother tube, at its tip and base ends, respectively, is forced into the mother tube to expand the diameter of the base end of the mother tube. Furthermore, in the third step, the base end of the mother tube is pressed with a sleeve, and the mother tube with the mandrel inserted therein is forced into the small inner diameter region of the container to reduce its diameter.

[0026] Therefore, according to the present invention, it is possible to reduce the increase in processing load compared to the case where the outer diameter of the mother tube is increased to increase the diameter difference between the large diameter portion and the small diameter portion of the differential thickness pipe. Also, as will be described in detail later, it is possible to reduce the increase in processing load that accompanies the elongation of the differential thickness pipe to be formed. In other words, according to the present invention, it is possible to provide a method and an apparatus for extrusion molding of a differential thickness pipe, which makes it possible to set the diameter difference between the large diameter portion (ear portion) and the small diameter portion (reduced diameter differential thickness portion) large without excessively increasing the processing load, and also to arbitrarily set the length in the axial direction.

[0027] In a differential thickness pipe formed by the method of the present invention according to another embodiment, the 11 large outer diameter region is formed by increasing the thickness of the mother tube, and the 11 small outer diameter region is formed by decreasing the thickness of the mother tube. Therefore, a larger diameter difference can be achieved with a smaller processing load than when the large outer diameter region is formed while maintaining the outer diameter of the mother tube and the small outer diameter region is formed by significantly reducing the outer diameter of the mother tube. Furthermore, since the wall thickness of the large outer diameter region can be increased, a differential thickness pipe suitable for applications requiring high mechanical strength in the large diameter portion can be formed.

[0028] In addition, the axial lengths of the 11th large outer diameter region and the 11th small outer diameter region vary depending on the axial length of the mother tube, the amount of diameter expansion in step 12, the amount of diameter reduction in step 13, and the amount of pushing the mother tube into place by the sleeve. That is, the axial lengths of the 11th large outer diameter region and the 11th small outer diameter region of the differential thickness pipe can be set as desired.

[0029] Other objects, features and attendant advantages of the present invention will become readily apparent from the following description of the embodiments of the present invention which are given with reference to the accompanying drawings. [Brief description of the drawings]

[0030] [Figure 1] 1 is a flowchart showing the flow of each step included in a method for extrusion molding a differential thickness pipe according to a first embodiment of the present invention (first method). [Diagram 2] FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a mother tube used in a first method and a differential thickness pipe formed from the mother tube. [Diagram 3] FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a mandrel, a sleeve, and a container used in a first method. [Figure 4] FIG. 2 is a schematic cross-sectional view showing an example of a change in the shape of a blank tube resulting from the execution of a first method. [Diagram 5] 4 is a photograph showing the smoothing of the inner peripheral surface of a blank tube accompanying the execution of the second step included in the first method. [Figure 6] FIG. 11 is a schematic cross-sectional view showing an example of change in the shape of a blank tube when a differential thickness pipe having a second small diameter region including two portions with different shapes is formed by a first method according to a modified example. [Figure 7] FIG. 11 is a schematic cross-sectional view of a container used in the first method according to another modified example and a differential thickness pipe formed using the container.

[0031] [Figure 8] FIG. 13 is a schematic cross-sectional view showing an example of the configuration of a mother tube used in a method for extrusion molding a differential thickness pipe according to a fifth embodiment of the present invention (fifth method) and a differential thickness pipe molded from the mother tube. [Figure 9] FIG. 13 is a schematic cross-sectional view showing an example of the configuration of a mandrel, a sleeve, and a container used in a fifth method. [Figure 10] 13 is a flowchart showing the flow of each step included in the fifth method. [Figure 11] 11 is a schematic cross-sectional view showing an example of changes in the positional relationships and shapes of a mother tube, a mandrel, a sleeve, a container and a differential thickness pipe as the fifth method progresses. FIG. [Figure 12] 11 is a schematic cross-sectional view showing another example of changes in the positional relationship and shape of the mother tube, mandrel, sleeve, container and differential thickness pipe as the fifth method progresses. FIG. [Figure 13]FIG. 13 is a schematic cross-sectional view showing an example of the configuration of a base tube used in one aspect of the extrusion molding method (sixth method) for a differential thickness pipe according to the sixth embodiment of the present invention, and a differential thickness pipe molded from the base tube. [Figure 14] FIG. 13 is a schematic cross-sectional view showing one example of the configuration of a mandrel, a sleeve, and a container used in a sixth method according to the first embodiment. [Figure 15] FIG. 13 is a schematic cross-sectional view showing one example of changes in the positional relationships and shapes of a mother tube, a mandrel, a sleeve, a container, and a differential thickness pipe as the sixth method according to the first embodiment progresses. [Figure 16] FIG. 13 is a schematic cross-sectional view showing one example of changes in the positional relationships and shapes of a mother tube, a mandrel, a sleeve, a container, and a differential thickness pipe as the modified sixth method of the first embodiment progresses. [Figure 17] FIG. 13 is a schematic cross-sectional view showing one example of the configuration of a mother tube used in a sixth method according to the second embodiment and a differential thickness pipe formed from the mother tube. [Figure 18] FIG. 13 is a schematic cross-sectional view showing one example of the configuration of a mandrel, a sleeve, and a container used in a sixth method according to the second embodiment. [Figure 19] FIG. 13 is a schematic cross-sectional view showing one example of changes in the positional relationships and shapes of a mother tube, a mandrel, a sleeve, a container and a differential thickness pipe as the sixth method according to the second embodiment progresses.

[0032] [Figure 20] FIG. 13 is a schematic cross-sectional view showing an example of the configuration of a mother tube used in a method for extrusion molding a differential thickness pipe according to a seventh embodiment of the present invention (seventh method) and a differential thickness pipe molded from the mother tube. [Figure 21] FIG. 23 is a schematic cross-sectional view showing an example of the configuration of a mandrel, a sleeve, and a container used in the seventh method. [Figure 22] 13 is a schematic cross-sectional view showing an example of changes in the positional relationships and shapes of a mother tube, a mandrel, a sleeve, a container and a differential thickness pipe as the seventh method progresses. FIG. [Figure 23]FIG. 11 is a schematic cross-sectional view showing an example of changes in the positional relationships and shapes of a mother tube, a mandrel, a sleeve, a container, and a differential thickness pipe as the process progresses when the seventh method is applied to the sixth method according to the second embodiment. [Figure 24] FIG. 24 is a schematic front view showing the appearance of a blank pipe 111' and a variable thickness pipe 121' illustrated in FIG. 23. [Diagram 25] 25 is a cross-sectional view of a portion surrounded by a thick dashed line in FIG. 24. [Figure 26] FIG. 13 is a schematic cross-sectional view showing an example of the configuration of a mother tube used in an extrusion molding method (eighth method) for a differential thickness pipe according to an eighth embodiment of the present invention and a differential thickness pipe molded from the mother tube. [Figure 27] 13 is a schematic cross-sectional view showing an example of changes in the positional relationships and shapes of a mother tube, a mandrel, a sleeve, a container and a differential thickness pipe as the eighth method progresses. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] First Embodiment Hereinafter, a method for extrusion molding a differential thickness pipe according to a first embodiment of the present invention (hereinafter, may be referred to as a "first method") will be described with reference to the drawings.

[0034] <composition> The first method includes first to third steps performed in an extrusion molding apparatus. The extrusion molding apparatus includes a mandrel which is a core metal having a predetermined shape, a sleeve which is a cylindrical member arranged coaxially around the mandrel, a container which is a die having a container hole which is a through hole having a predetermined shape, and a drive mechanism configured to push the mandrel and the sleeve into the container hole.

[0035] The basic configuration of an extrusion molding apparatus is well known to those skilled in the art and will not be described in detail here, but the components including the mandrel, sleeve, and container are made of materials having properties (e.g., mechanical strength and durability) that can withstand processing conditions such as the load acting on the components in the extrusion process described below. The drive mechanism for pushing the mandrel and sleeve into the container hole can be appropriately selected from various drive mechanisms well known in the art depending on the properties (e.g., mechanical strength and hardness) of the material constituting the blank tube to be subjected to the extrusion process. Typically, a press such as a hydraulic press is used as the drive mechanism.

[0036] 1 is a flowchart showing the flow of each step included in the first method. The first step, which is carried out in step S01, is a step of setting a blank tube having a predetermined shape at a predetermined position inside a container hole. Specifically, in the first step, the blank tube is set at a predetermined position inside a container hole by abutting a tip end of the blank tube against an inner diameter reduced region (each of these regions will be described later) formed between a large inner diameter region and a small inner diameter region of a container hole formed in a container.

[0037] In order to form a differential thickness pipe having a predetermined shape by the first method, it is necessary to set the blank tube coaxially with the mandrel, sleeve, and container. The method for setting the blank tube in this manner is not particularly limited, but for example, the blank tube can be set coaxially with the mandrel, sleeve, and container by providing a tapered portion at the end portion on the tip side of the mandrel and inserting the tapered portion into the blank tube when the diameter expansion of the blank tube is about to start in the second step.

[0038] The second step performed in step S02 is a step in which the mandrel is pushed into the blank tube by the driving mechanism to expand the diameter of the base end side, which is the upstream side in the extrusion direction of the blank tube. The third step performed in step S03 is a step in which the base end side end of the blank tube is pressed by the sleeve after the first time point at which the second step is started, to push the blank tube into the tip side, which is the downstream side in the extrusion direction of the container hole, thereby performing an extrusion process to reduce the diameter of the tip side of the blank tube. Although details will be described later, by performing these first to third steps included in the first method, a differential thickness pipe having a predetermined shape can be formed.

[0039] The mother tube, mandrel, sleeve and container used in the first method, as well as the differential thickness pipe formed by carrying out the first method, will be described in detail below with reference to the drawings.

[0040] Fig. 2 is a schematic cross-sectional view showing an example of the configuration of a mother tube used in the first method and a differential thickness pipe formed from the mother tube. As shown in Fig. 2(a), the mother tube 11 is a cylindrical member having a first outer diameter DO1 which is a predetermined outer diameter, a first inner diameter DI1 which is a predetermined inner diameter, and a first thickness T1 which is a predetermined wall thickness.

[0041] The shape of the mother tube is not necessarily limited to a simple cylindrical shape as exemplified in Fig. 2, and for example, a portion having a different structure may be provided at the end portion near the tip side of the mother tube, so long as it does not interfere with carrying out the first method. Specifically, for example, a cylindrical portion having a predetermined outer diameter smaller than the outer diameter of the small inner diameter region of the container hole, a predetermined inner diameter equal to or smaller than a first inner diameter DI1 which is the inner diameter of the mother tube, and a predetermined wall thickness smaller than a first wall thickness T1 which is the wall thickness of the mother tube may be provided at the end portion near the tip side of the mother tube.

[0042] Moreover, the material constituting the plain tube 11 is not particularly limited as long as it can be formed into a desired shape by plastic deformation in extrusion processing. Typically, the material constituting the plain tube 11 is a metal such as, for example, lead, tin, aluminum, copper, zirconium, titanium, molybdenum, vanadium, niobium, and steel.

[0043] Next, as shown in FIG. 2(b), the differential thickness pipe 21 formed by the first method includes, in order from the tip side (lower side in the drawing) to the base end side (upper side in the drawing), a first small diameter region RSD1, a second small diameter region RSD2, and a large diameter region RLD. The first small diameter region RSD1 is a region having a second outer diameter DO2 (DO2 < DO1) that is a predetermined outer diameter smaller than the first outer diameter DO1, a second inner diameter DI2 (DI2 = DI1) that is equal to the first inner diameter DI1, and a second wall thickness T2 (T2 < T1) that is a predetermined wall thickness smaller than the first wall thickness T1. The second small diameter region RSD2 is a region having a third outer diameter DO3 (DO3 = DO2) that is equal to the second outer diameter DO2 and a third wall thickness T3 (T3 < T2) that is a predetermined wall thickness smaller than the second wall thickness T2. The large diameter region RLD is a region having a fourth outer diameter DO4 (DO4 > DO1) that is a predetermined outer diameter larger than the first outer diameter DO1 and a fourth wall thickness T4 that is a predetermined wall thickness. Note that since the internal spaces of the second small diameter region RSD2 and the large diameter region RLD are both formed by expanding the internal space of the plain tube 11 by the large cross-sectional region of the mandrel described later, the cross-sectional shapes of the internal spaces of the second small diameter region RSD2 and the large diameter region RLD are the same.

[0044] Between the first small diameter region RSD1 and the second small diameter region RSD2, a first taper region RtDI1 is formed, in which the thickness decreases from the second thickness T2 to the third thickness T3 and the cross section of the internal space expands (however, the outer diameter does not change) as it approaches from the first small diameter region RSD1 to the second small diameter region RSD2. Furthermore, between the second small diameter region RSD2 and the large diameter region RLD, a second taper region RtDI2 is formed, in which the thickness increases from the third thickness T3 to the fourth thickness T4 and the outer diameter increases (however, the cross section of the internal space does not change) as it approaches from the second small diameter region RSD2 to the large diameter region RLD. Details of these first taper region RtDI1 and second taper region RtDI2 will be described later.

[0045] As described above, the cross-sectional shapes of the internal spaces of the second small diameter region RSD2 and the large diameter region RLD are not particularly limited, and can be a wide variety of shapes, such as polygonal, elliptical, and circular. In other words, the cross-sectional shapes of the internal spaces of the second small diameter region RSD2 and the large diameter region RLD are not particularly limited, and can be a wide variety of shapes, such as polygonal, elliptical, and cylindrical. Therefore, the shape of the internal space of the first taper region RtDI1 is also not particularly limited, as long as the cross-sectional shape of the internal space of the first small diameter region RSD1 approaches the cross-sectional shape of the internal space of the second small diameter region RSD2 from the cross-sectional shape (circular) of the internal space of the first small diameter region RSD1 as it approaches the cross-sectional shape of the internal space of the second small diameter region RSD2 as it approaches the cross-sectional shape of the internal space of the first small diameter region RSD1. As described above, the cross-sectional shapes of the internal spaces of the second small diameter region RSD2 and the large diameter region RLD are the same. Therefore, the cross-sectional shape of the internal space of the second taper region RtDI2 formed between the second small diameter region RSD2 and the large diameter region RLD is also identical over the entire area to the cross-sectional shape of the internal space of the second small diameter region RSD2 and the large diameter region RLD.

[0046] The mandrel includes a small cross-sectional region, a large cross-sectional region, and an expanding cross-sectional region. The small cross-sectional region is a cylindrical region formed at the distal end and having a first cross-sectional area that is a circular cross-section having a fifth outer diameter that is an outer diameter corresponding to the second inner diameter. The large cross-sectional region is a cylindrical region formed at the proximal end and having a second cross-sectional area that is a cross-section corresponding to a cross-section of the internal space of the second small diameter region and the large diameter region. The expanding cross-sectional region is a region formed between the small cross-sectional region and the large cross-sectional region and has a cross-sectional area that expands from the first cross-sectional area to the second cross-sectional area as the small cross-sectional area approaches the large cross-sectional area.

[0047] The sleeve includes a pressing region that is a cylindrical region formed on the tip side and has a columnar internal space having a seventh outer diameter that is an outer diameter equal to the fourth outer diameter and a third cross-section that is a cross-section corresponding to the second cross-section.

[0048] The container bore includes a large inner diameter region, a small inner diameter region, and an inner diameter decreasing region. The large inner diameter region is a region formed on the base end side and has a sixth inner diameter that is an inner diameter corresponding to the fourth outer diameter. The small inner diameter region is a region formed on the tip end side and has a seventh inner diameter that is an inner diameter corresponding to the second outer diameter and the third outer diameter. The inner diameter decreasing region is a region formed between the large inner diameter region and the small inner diameter region and has an inner diameter that decreases from the sixth inner diameter to the seventh inner diameter as it approaches the small inner diameter region.

[0049] As described above, the shapes of the internal spaces of the second small diameter region RSD2 and the large diameter region RLD of the differential thickness pipe 21 are not particularly limited, and can be various shapes such as polygonal columnar, elliptical columnar, and cylindrical. However, in the following description, in order to facilitate understanding of the present invention, a case will be described in which the internal spaces of the second small diameter region RSD2 and the large diameter region RLD of the differential thickness pipe 21 each have a cylindrical shape. Specifically, as shown in parentheses in (b) of FIG. 2, a case will be described in which the internal space of the second small diameter region RSD2 of the differential thickness pipe 21 has a cylindrical shape with a third inner diameter DI3 (DI3>DI1) that is a predetermined inner diameter larger than the first inner diameter DI1, and the internal space of the large diameter region RLD of the differential thickness pipe 21 has a cylindrical shape with a fourth inner diameter DI4 (DI4=DI3) that is an inner diameter equal to the third inner diameter DI3. In this case, as will be described below with reference to FIG. 3(a), the shapes of the large cross-sectional area of ​​the mandrel and the internal space of the sleeve also each have a cylindrical shape.

[0050] FIG. 3 is a schematic cross-sectional view showing an example of the configuration of the mandrel, sleeve, and container used in the first method. FIG. 3(a) is a schematic cross-sectional view showing an example of the configuration of the mandrel and sleeve used in the first method. As shown in FIG. 3(a), the mandrel 31 includes a small cross-sectional area RSC, a large cross-sectional area RLC, and an enlarged cross-sectional area ReC. The small cross-sectional area RSC is a cylindrical area formed on the tip side and having a first cross-sectional area that is a circular cross-sectional area having a fifth outer diameter DO5 that is an outer diameter corresponding to the second inner diameter DI2. The large cross-sectional area RLC is a cylindrical area formed on the base side and having a second cross-sectional area that is a circular cross-sectional area having a sixth outer diameter DO6 that is an outer diameter corresponding to the third inner diameter DI3 and the fourth inner diameter DI4 (i.e., a cross-sectional area corresponding to the cross-sectional area of ​​the internal space of the second small diameter area RSD2 and the large diameter area RLD). The enlarged cross-sectional region ReC is a region formed between the small cross-sectional region RSC and the large cross-sectional region RLC, and has a truncated cone shape whose outer diameter increases from a fifth outer diameter DO5 to a sixth outer diameter DO6 as it approaches the small cross-sectional region RSC to the large cross-sectional region RLC (i.e., a region whose cross section expands from the first cross section to the second cross section). In the second step, the small cross-sectional region RSC of the mandrel 31 having such a shape is inserted into the internal space of the mother tube 11 from the base end side (upper side in the drawing) and the enlarged cross-sectional region ReC and the large cross-sectional region RLC are pushed toward the tip side (lower side in the drawing), thereby expanding the diameter of the base end side of the mother tube 11 and forming the large diameter region RLD of the differential thickness pipe 21.

[0051] The sleeve 41 includes a pressing region RP formed on the tip side and having a cylindrical shape with a seventh outer diameter DO7 that is an outer diameter equal to the fourth outer diameter DO4 and a fifth inner diameter DI5 that is an inner diameter corresponding to the sixth outer diameter DO6 (i.e., a tubular region having a columnar internal space with a third cross section that is a cross section corresponding to the second cross section). In the third step, the tip side (lower side in the drawing) end of the pressing region RP having such a shape is used to press the base side (upper side in the drawing) end of the blank tube 11 to force the blank tube 11 into the tip side of the container hole, thereby performing the extrusion process.

[0052] Next, FIG. 3(b) is a schematic cross-sectional view showing an example of the configuration of a container used in the first method. As shown in FIG. 3(b), a container hole 51a formed in a container 51 includes a large inner diameter region RLDI, a small inner diameter region RSDI, and an inner diameter decreasing region RsDI. The large inner diameter region RLDI is a region formed on the base end side and has a sixth inner diameter DI6 that is an inner diameter corresponding to the fourth outer diameter DO4. The small inner diameter region RSDI is a region formed on the tip side and has a seventh inner diameter DI7 that is an inner diameter corresponding to the second outer diameter DO2 and the third outer diameter DO3. The inner diameter decreasing region RsDI is a region formed between the large inner diameter region RLDI and the small inner diameter region RSDI and the inner diameter decreases from the sixth inner diameter DI6 to the seventh inner diameter DI7 as it approaches from the large inner diameter region RLDI to the small inner diameter region RSDI. In the third process, the first small diameter region RSD1, the first tapered region RtDI1, the second small diameter region RSD2 and the second tapered region RtDI2 of the differential thickness pipe 21 can be formed by pushing the blank tube 11 into the container hole 51a having such a shape using the sleeve 41.

[0053] During the period in which the first small diameter region RSD1 of the differential thickness pipe 21 is formed, it is necessary to perform the extrusion through a gap corresponding to the second thickness T2, which is the thickness of the first small diameter region RSD1. Therefore, in the first method, at the second time point when the third step is started, the tip end of the mandrel 31 in the extrusion direction reaches the tip end of the mother tube 11 or is closer to the tip end than the tip end of the mother tube 11. In other words, when the tip end of the sleeve 41 abuts against the base end of the mother tube 11, the tip end of the mandrel 31 has reached the tip end of the mother tube 11 or has already passed the tip end of the mother tube 11. In addition, at the second time point, the base end end of the small cross-sectional region RSC of the mandrel 31 is located closer to the base end than the base end of the small inner diameter region RSDI of the container hole 51a. This allows the material to be formed into the first small diameter region RSD1 of the differential thickness pipe 21 to be extruded toward the tip side through the gap between the small cross-sectional area RSC of the mandrel 31 and the small inner diameter area RSDI of the container hole 51a, which is a gap corresponding to the second thickness T2 of the first small diameter area RSD1. That is, the extrusion process of the first small diameter area RSD1 of the differential thickness pipe 21 can be performed. The distance between the base end side end of the small cross-sectional area RSC of the mandrel 31 and the base end side end of the small inner diameter area RSDI of the container hole 51a can be appropriately determined based on, for example, the length in the extrusion direction of the first small diameter area RSD1 of the differential thickness pipe 21 to be formed and the second thickness T2, which is the wall thickness.

[0054] The length of the small cross-sectional area RSC of the mandrel 31 can also be appropriately determined based on, for example, the length in the extrusion direction of the first small diameter area RSD1 of the differential thickness pipe 21 to be formed. Specifically, for example, when the length of the small cross-sectional area RSC of the mandrel 31 is excessively short, when the material for forming the first small diameter area RSD1 of the differential thickness pipe 21 reaches the base end of the small inner diameter area RSDI of the container hole 51a, and the tip end of the small cross-sectional area RSC of the mandrel 31 has not reached the base end of the small inner diameter area RSDI of the container hole 51a, the material may wrap around further to the tip side than the small cross-sectional area RSC of the mandrel 31, and the wall thickness of the tip side of the first small diameter area RSD1 of the differential thickness pipe 21 may become thicker than the second wall thickness T2. In order to avoid such problems, it is preferable that, at the latest, when the material to form the first small diameter region RSD1 of the differential thickness pipe 21 reaches the base end of the small inner diameter region RSDI of the container hole 51a, the tip end of the small cross-sectional region RSC of the mandrel 31 has reached the base end of the small inner diameter region RSDI of the container hole 51a or is closer to the tip than the base end of the small inner diameter region RSDI of the container hole 51a.

[0055] Fig. 4 is a schematic cross-sectional view showing an example of a change in the shape of a blank tube accompanying the execution of the first method. In Fig. 4, the reference symbols attached to the respective parts shown in Fig. 2 and Fig. 3 are omitted in order to simplify the drawing. However, in the following explanation of Fig. 4, the reference symbols shown in Fig. 2 and Fig. 3 are used for the sake of accuracy, so please refer to Fig. 2 and Fig. 3 as necessary.

[0056] Fig. 4(a) shows a state in which the first step of the first method is completed, in which the mother tube 11 is inserted into the large inner diameter region RLDI of a container hole 51a formed in a container 51, and the tip end of the mother tube 11 abuts against the reduced inner diameter region RsDI. That is, the mother tube 11 is set at a predetermined position inside the container hole 51a. In the example shown in Fig. 4(a), the small cross-sectional region RSC of the mandrel 31 is inserted into the mother tube 11, so that the mother tube 11 is set coaxially with the mandrel 31, sleeve 41, and container 51.

[0057] Next, in Fig. 4(b), in the second step included in the first method, the mandrel 31 is pushed into the mother tube 11 by a driving mechanism (not shown), the base end side of the mother tube 11 is expanded in diameter by the large cross-sectional area RLC of the mandrel 31, and the tip end of the sleeve 41 abuts against the base end side of the mother tube 11. That is, Fig. 4(b) shows a state at a second time point when the third step is about to be started. In the example shown in Fig. 4(b), the tip end of the mandrel 31 reaches the tip side of the mother tube 11. Therefore, during the period in which the first small diameter region RSD1 of the differential thickness pipe 21 is formed in the third step executed thereafter, the first small diameter region RSD1 of the differential thickness pipe 21 is extruded through the gap between the small cross-sectional area RSC of the mandrel 31 and the small inner diameter area RSDI of the container hole 51a, which is the gap corresponding to the second thickness T2, which is the thickness of the first small diameter region RSD1. Therefore, as described above, the problem that the material to form the first small diameter region RSD1 of the differential thickness pipe 21 wraps around further to the tip side than the small cross-sectional area RSC of the mandrel 31, for example, the wall thickness of the tip side of the first small diameter region RSD1 of the differential thickness pipe 21 becomes thicker than the second wall thickness T2 can be avoided. In addition, the base end of the small cross-sectional area RSC of the mandrel 31 is located on the base end side than the base end of the small inner diameter area RSDI of the container hole 51a. Therefore, the material to form the first small diameter region RSD1 of the differential thickness pipe 21 can be pushed out to the tip side through the gap between the small cross-sectional area RSC of the mandrel 31 and the small inner diameter area RSDI of the container hole 51a to form the first small diameter region RSD1 of the differential thickness pipe 21.

[0058] In the second step, as the mandrel 31 and sleeve 41 are pushed further toward the tip side and the extrusion process progresses further, the material constituting the blank tube 11 is pushed toward the tip side through the gap between the enlarged cross-sectional region ReC of the mandrel 31 and the small inner diameter region RSDI of the container hole 51a to form the first taper region RtDI1 of the differential thickness pipe 21, and then the material constituting the blank tube 11 is pushed toward the tip side through the gap between the large cross-sectional region RLC of the mandrel 31 and the small inner diameter region RSDI of the container hole 51a to form the second small diameter region RSD2 of the differential thickness pipe 21.

[0059] 4(c) shows a state in which the extrusion processing of the first small diameter region RSD1 and the second small diameter region RSD2 of the differential thickness pipe 21 in the third step is completed as described above, and the molding of the differential thickness pipe 21 is completed. As shown in the part surrounded by the thick dashed line in FIG. 4(c), the inclination of the inner peripheral surface of the first taper region RtDI1 of the differential thickness pipe 21 is gentler than the inclination of the outer peripheral surface of the cross-sectional enlarged region ReC of the mandrel 31. This is because the flow rate of the material extruded toward the tip side increases as the gap between the base end of the small inner diameter region RSDI and the mandrel 31 gradually narrows as the cross-sectional enlarged region ReC of the mandrel 31 passes through a position facing the base end of the small inner diameter region RSDI of the container hole 51a, so that the inclination of the inner peripheral surface of the first taper region RtDI1 becomes longer and more gentle in the extrusion direction than the inclination of the outer peripheral surface of the cross-sectional enlarged region ReC.

[0060] Also, a gap is generated between the portion of the differential thickness pipe 21 adjacent to the base end side of the first taper region RtDI1 and the mandrel 31. This is because, as the enlarged cross-sectional region ReC of the mandrel 31 passes a position facing the base end side of the small inner diameter region RSDI of the container hole 51a, the gap between the base end side end of the small inner diameter region RSDI and the mandrel 31 gradually narrows and the cross-sectional area of ​​the gap between the large cross-sectional region RLC of the mandrel 31 and the small inner diameter region RSDI of the container hole 51a becomes smaller than the cross-sectional area of ​​the blank tube 11 (expanded in diameter as the large diameter region RLD of the differential thickness pipe 21) pushed into the gap, so the flow rate of the material extruded toward the tip side increases and the first taper region RtDI1 and the second small diameter region RSD2 of the differential thickness pipe 21 become longer in the extrusion direction.

[0061] The gap becomes longer as the extrusion processing of the second small diameter region RSD2 of the differential thickness pipe 21 in the third step progresses, and the contact area between the differential thickness pipe 21 and the mandrel 31 decreases. As a result, according to the first method, the processing load decreases as the extrusion processing of the second small diameter region RSD2 of the differential thickness pipe 21 in the third step progresses, so that the first method is suitable for forming a long object (a differential thickness pipe that is long in the axial direction).

[0062] <effect> As described above, in the first method, in a first step, a mother tube is set in a container having a container hole having a small inner diameter region having an inner diameter smaller than the outer diameter of the mother tube and a large inner diameter region having an inner diameter larger than the outer diameter of the mother tube, at the tip and base ends, respectively. Then, in a second step, a mandrel having a small outer diameter region having an outer diameter corresponding to the inner diameter of the mother tube and a large outer diameter region having an outer diameter larger than the inner diameter of the mother tube, at the tip and base ends, respectively, is forced into the mother tube to expand the base end of the mother tube. Furthermore, in a third step, the base end of the mother tube is pressed with a sleeve, and the mother tube with the mandrel inserted therein is forced into the small inner diameter region of the container to reduce its diameter.

[0063] Therefore, according to the first method, it is possible to reduce the increase in processing load compared to when the outer diameter of the mother tube is increased to increase the diameter difference between the large diameter portion and the small diameter portion of the differential thickness pipe. Also, it is possible to reduce the increase in processing load that accompanies the elongation of the differential thickness pipe to be formed. In other words, according to the first method, it is possible to set the diameter difference between the large diameter portion (ear portion) and the small diameter portion (reduced diameter differential thickness portion) large without an excessive increase in processing load, and the axial length can also be set arbitrarily.

[0064] In addition to the above, in the second step included in the first method, as described above, the mandrel is pressed into the blank tube, and the base end side of the blank tube is expanded in diameter by the large cross-sectional area of ​​the mandrel. In this process, the inner peripheral surface of the blank tube is treated by the mandrel, so that machining marks (tool marks) and the like generated, for example, when drilling a hole (internal space) in the blank tube are crushed, and the inner peripheral surface of the blank tube is smoothed. FIG. 5 is a photograph showing the smoothing of the inner peripheral surface of the blank tube accompanying the execution of the second step included in the first method. FIG. 5(a) is a photograph of the inner peripheral surface of the blank tube before the execution of the second step or in a method in which the base end side of the blank tube is not expanded in diameter by the large cross-sectional area of ​​the mandrel, and machining marks generated when drilling a hole in the blank tube can be seen. Such machining marks may become the starting point for defects such as cracks when the blank tube is subjected to stress such as tensile stress during use after the extrusion processing and / or forming of a differential thickness pipe, which is executed in the subsequent third step. On the other hand, Fig. 5(b) is a photograph of the inner circumferential surface of the first small diameter region of the differential thickness pipe formed by the first method, and it can be seen that no processing marks as shown in Fig. 5(a) are found and the surface is smoothed. In other words, according to the first method, it is possible to reduce the risk of defects such as cracks occurring when the pipe is subjected to stress such as tensile stress during the extrusion process performed in the third step and / or during use after the formation of the differential thickness pipe.

[0065] <Modification> As described with reference to FIG. 2B, the differential thickness pipe 21 formed by the above-mentioned first method includes, in order from the tip side to the base side, a first small diameter region RSD1, a second small diameter region RSD2, and a large diameter region RLD. The second small diameter region RSD2 of this differential thickness pipe 21 is composed of one part having a third outer diameter DO3, which is an outer diameter equal to a second outer diameter DO2 smaller than a first outer diameter DO1, which is an outer diameter of the mother tube 11, an internal space having a cross section corresponding to the cross section of the large cross-sectional region RLC of the mandrel 31, and a third wall thickness T3, which is a wall thickness smaller than the second wall thickness T2, which is a wall thickness of the first small diameter region RSD1. However, the second small diameter region of the differential thickness pipe 21 does not necessarily have to be composed of one part, and may include a plurality of parts having different shapes of cross sections of the internal space.

[0066] FIG. 6 is a schematic cross-sectional view showing an example of a change in the shape of a blank pipe when a differential thickness pipe having a second small diameter region including two parts with different shapes is formed by the first method according to the modified example. (a) to (c) of FIG. 6 show the states corresponding to (a) to (c) of FIG. 4 referred to in the description of the first method. In FIG. 6, as in FIG. 4, the reference numerals attached to the parts shown in FIG. 2 and FIG. 3 are omitted in order to simplify the drawing. However, in the following description of FIG. 6, the reference numerals shown in FIG. 2 and FIG. 3 are used for accuracy, so please refer to FIG. 2 and FIG. 3 as necessary. (d) of FIG. 6 is a schematic cross-sectional view of a differential thickness pipe 21' formed by the first method according to the modified example.

[0067] In the example shown in Fig. 6, the large cross-sectional area RLC of the mandrel 31' includes a portion formed on the base end side having a cross section corresponding to the cross section of the internal space of the large diameter area RLD of the differential thickness pipe 21' to be formed, and a portion formed on the tip end side having a cross section corresponding to the cross section of the internal space of the second small diameter area RSD2 of the differential thickness pipe 21' to be formed. Therefore, as illustrated in Fig. 6(b), in the region on the base end side of the blank tube 11 expanded in diameter by the large cross-sectional area RLC of the mandrel 31' in the second step included in the first method, two portions having internal spaces with cross sections of different sizes (and a portion formed between these two portions in which the cross section of the internal space expands as it approaches from the tip side to the base side) are formed. Thereafter, the first small diameter area RSD1 and the second small diameter area RSD2 of the differential thickness pipe 21' are formed by performing the extrusion process in the third step, and the forming of the differential thickness pipe 21' is completed as illustrated in Fig. 6(c).

[0068] In the second small diameter region RSD2 of the differential thickness pipe 21' formed as described above, as illustrated in (d) of Fig. 6, a portion PSD2 having a columnar internal space (a cylindrical internal space having a fourth inner diameter DI4 when the cross section is circular) having the same cross section as the internal space of the large diameter region RLD is formed on the base end side, and a portion PSD1 having a columnar internal space (a cylindrical internal space when each cross section is circular) having an intermediate cross section between the cross section of the internal space of the large diameter region RLD and the cross section of the internal space of the first small diameter region RSD1 is formed on the tip end side. In addition, between these two portions PSD1 and PSD2, a tapered portion PtDI is formed in which the cross section of the internal space expands from the cross section of the internal space of the portion PSD1 to the cross section of the internal space of the portion PSD2 as it approaches from the tip end side to the base end side. That is, the second small diameter region RSD2 of the differential thickness pipe 21' illustrated in FIG. 6(d) is multi-staged by these two portions PSD1 and PSD2 and the tapered portion PtDI.

[0069] As described above, according to the first method of the modified example, it is possible to form a pipe having a second small diameter region including a plurality of portions having different cross-sectional shapes of the internal space. When forming a plurality of portions having different cross sections in the large cross-sectional region RLC of the mandrel 31' as described above, it is of course necessary to form the large cross-sectional region RLC so that the cross section of the tip side portion is smaller than the cross section of the base side portion.

[0070] In the above modified example, the second small diameter region of the differential thickness pipe is multi-staged to include a plurality of portions having different cross-sectional shapes of the internal space. However, the multi-staged differential thickness pipe is not limited to the above, and depending on, for example, the mechanical strength, degree of work hardening, and / or ease of plastic flow of the material constituting the mother tube, and / or the mechanical strength of the members constituting the extrusion molding device and / or the processing capacity of the extrusion molding device, it is also possible to form a multi-staged outer peripheral surface of the first small diameter region, the second small diameter region, and / or the large diameter region of the formed differential thickness pipe by providing a plurality of portions having different inner diameters in the large inner diameter region and / or the small inner diameter region of the container.

[0071] 7 is a schematic cross-sectional view of a container used in the first method according to another modified example as described above and a differential thickness pipe formed using the container. In a container hole 51a' formed in a container 51' illustrated in (a) of FIG. 7, a large inner diameter region RLDI is multi-staged (two-staged) into a portion having a sixth inner diameter DI6 formed on the tip side and a portion having an inner diameter DI6' larger than the sixth inner diameter DI6 formed on the base side. By carrying out the first method using a container 51' having such a configuration and a sleeve (not shown) corresponding to the container 51', it is possible to form a differential thickness pipe 21" having a multi-stage (two-stage) large diameter region RLD with a portion having the fourth outer diameter DO4 formed on the tip side and a portion having an outer diameter DO4' larger than the fourth outer diameter DO4 formed on the base end side, as illustrated in (b) of Figure 7. Although not shown, by making the small inner diameter region RSDI of the container multi-stage, in the same manner as described above, it is also possible to form a differential thickness pipe 21" having a multi-stage first small diameter region RSD1 and / or second small diameter region RSD2.

[0072] Second Embodiment Hereinafter, a method for extrusion molding a differential thickness pipe according to a second embodiment of the present invention (hereinafter, sometimes referred to as the "second method") will be described with reference to the drawings.

[0073] As described above in the description of the first method, in the third step, the gap between the base end of the small inner diameter region and the mandrel gradually narrows as the enlarged cross-sectional region of the mandrel passes a position facing the base end of the small inner diameter region of the container hole. Also, the cross-sectional area of ​​the gap between the large cross-sectional region of the mandrel and the small inner diameter region of the container hole is smaller than the cross-sectional area of ​​the blank tube (expanded as the large diameter region of the differential thickness pipe) to be pushed into the gap. As a result, the flow rate of the material extruded from the gap between the large cross-sectional region of the mandrel and the small inner diameter region of the container hole to the tip side increases, and the first tapered region and the second small diameter region of the differential thickness pipe become longer in the extrusion direction. For this reason, a gap is generated between the mandrel and the part of the differential thickness pipe adjacent to the base end side of the first tapered region.

[0074] In the above process, the first tapered region and the second small diameter region of the differential thickness pipe extend toward the tip side faster than the mandrel, so that the mandrel is pulled toward the tip side by the first small diameter region of the differential thickness pipe. Therefore, if the mandrel is fixed to the sleeve so that the mandrel does not advance toward the tip side faster than the sleeve, the sleeve is pulled toward the tip side by the first tapered region and the second small diameter region of the differential thickness pipe via the mandrel. In other words, part of the processing load required to perform extrusion by pressing the blank tube with the sleeve in the third step can be covered by the tensile stress due to the first tapered region and the second small diameter region of the differential thickness pipe, which extend toward the tip side faster.

[0075] <composition> Therefore, the second method is the above-mentioned first method, which is an extrusion molding method for differential thickness pipes, in which the mandrel and the sleeve are fixed so that the distance between the tip end of the mandrel and the tip end of the sleeve in the extrusion direction is not greater than the distance between the tip end of the mandrel and the tip end of the sleeve at the second point in time.

[0076] Here, reference is made again to FIG. 3(a) referred to in the description of the first method. The mandrel 31 illustrated in FIG. 3(a) is inserted into a columnar internal space formed in the sleeve 41. That is, the sleeve 41 is coaxially disposed on the outside of the mandrel 31. A portion having a cross section (outer diameter larger than the fifth inner diameter DI5) larger than the cross section of the internal space of the sleeve 41 is formed at the base end of the mandrel 31, and this portion abuts against the sleeve 41 at the base end of the internal space of the sleeve 41. Therefore, the mandrel 31 cannot advance to the tip side of the sleeve 41 beyond the position illustrated in FIG. 3(a). That is, the mandrel 31 and the sleeve 41 are fixed so that the distance between the tip end of the mandrel 31 and the tip end of the sleeve 41 does not become further large.

[0077] <effect> As a result, when the first tapered region and the second small diameter region of the differential thickness pipe are extruded in the third step, the mandrel is pulled toward the tip by the first small diameter region of the differential thickness pipe as described above, so that the mandrel 31 drives the sleeve 41 toward the tip. As a result, part of the processing load required to perform the extrusion process by pressing the blank tube with the sleeve 41 in the third step can be covered by the tensile stress of the first tapered region and the second small diameter region of the differential thickness pipe which extend toward the tip more quickly, so that the processing load in the third step can be reduced. This effect is extremely effective when attempting to form a long differential thickness pipe.

[0078] In order to achieve the above effect, it is sufficient that the mandrel and the sleeve are fixed so that the distance between the tip end of the mandrel and the tip end of the sleeve in the extrusion direction is not greater than the distance between the tip end of the mandrel and the tip end of the sleeve at the second point in time. However, the positional relationship between the mandrel and the sleeve may be fixed throughout from the viewpoint of reducing manufacturing costs by simplifying the configuration of the extrusion molding device, for example.

[0079] Third Embodiment As described at the beginning of this specification, the present invention relates not only to the extrusion molding method for a pipe with different thicknesses, including the above-mentioned first and second methods, but also to an extrusion molding device for a pipe with different thicknesses. Therefore, the extrusion molding device for a pipe with different thicknesses according to various embodiments of the present invention will be described below.

[0080] First, an extrusion molding apparatus for a differential thickness pipe according to a third embodiment of the present invention (hereinafter, sometimes referred to as a "third apparatus") will be described.

[0081] <composition> The third device is an extrusion molding device for a differential thickness pipe, comprising a mandrel which is a core metal having a predetermined shape, a sleeve which is a cylindrical member arranged coaxially around the outside of the mandrel, a container which is a die in which a container hole which is a through hole having a predetermined shape is formed, and a drive mechanism configured to push the mandrel and the sleeve into the container hole. The third device is configured to mold a differential thickness pipe having a predetermined shape by executing the first to third steps.

[0082] The first to third steps and the details of the mandrel, sleeve and container have already been described with reference to Figs. 1 to 4 in the description of the first method, and therefore will not be described here in detail.

[0083] As described above, the cross-sectional shapes of the internal spaces of the second small diameter region RSD2 and the large diameter region RLD of the differential thickness pipe 21 are not particularly limited, and can be various shapes such as polygonal, elliptical, and circular. Typically, as described with reference to Figs. 2 and 3 in the explanation of the first method, the internal space of the second small diameter region RSD2 of the differential thickness pipe 21 has a cylindrical shape with a third inner diameter DI3 (DI3>DI1) that is a predetermined inner diameter larger than the first inner diameter DI1, and the internal space of the large diameter region RLD of the differential thickness pipe 21 has a cylindrical shape with a fourth inner diameter DI4 (DI4=DI3) that is an inner diameter equal to the third inner diameter DI3. In this case, the large cross-sectional region RLC of the mandrel 31 and the internal space of the sleeve 41 also have cylindrical shapes.

[0084] <effect> By carrying out the first to third steps in the third apparatus having the above-mentioned configuration, it is possible to reduce the increase in processing load compared to the case where the outer diameter of the mother tube is increased to increase the diameter difference between the large diameter portion and the small diameter portion of the differential thickness pipe. Also, it is possible to reduce the increase in processing load that accompanies the elongation of the differential thickness pipe to be formed. In other words, with the third apparatus, it is possible to set the diameter difference between the large diameter portion (ear portion) and the small diameter portion (reduced diameter differential thickness portion) to a large value without an excessive increase in processing load, and the axial length can also be set arbitrarily.

[0085] Fourth Embodiment Next, an extrusion molding apparatus for a differential thickness pipe according to a fourth embodiment of the present invention (hereinafter, sometimes referred to as a "fourth apparatus") will be described.

[0086] <composition> The fourth apparatus is the third apparatus described above, which is an extrusion molding apparatus for differential thickness pipes, in which the mandrel and the sleeve are fixed so that the distance between the tip end of the mandrel and the tip end of the sleeve in the extrusion direction is not greater than the distance between the tip end of the mandrel and the tip end of the sleeve at the second point in time.

[0087] <effect> According to the fourth device, when the first tapered region and the second small diameter region of the differential thickness pipe are extruded in the third step, the mandrel is pulled toward the tip by the first small diameter region of the differential thickness pipe as described above, so that the mandrel 31 drives the sleeve 41 toward the tip. As a result, part of the processing load required to perform the extrusion process by pressing the blank tube with the sleeve 41 in the third step can be covered by the tensile stress of the first tapered region and the second small diameter region of the differential thickness pipe which extend toward the tip more quickly, so that the processing load in the third step can be reduced. This effect is extremely effective when attempting to form a long differential thickness pipe.

[0088] In order to achieve the above effect, it is sufficient that the mandrel and the sleeve are fixed so that the distance between the tip end of the mandrel and the tip end of the sleeve in the extrusion direction is not greater than the distance between the tip end of the mandrel and the tip end of the sleeve at the second point in time. However, the positional relationship between the mandrel and the sleeve may be fixed throughout from the viewpoint of reducing manufacturing costs by simplifying the configuration of the extrusion molding device, for example.

[0089] Fifth Embodiment Next, a method for extrusion molding a pipe with different thicknesses according to a fifth embodiment of the present invention (hereinafter, sometimes referred to as the "fifth method") will be described. Please note that the drawings referred to in the following description are merely schematic diagrams for the purpose of explaining the present invention, and that the dimensions, size relationships, positional relationships, etc. of the individual components depicted in each drawing do not strictly and accurately represent the constituent elements of the present invention. The above also applies to other embodiments of the present invention described later.

[0090] In the extrusion molding methods for a differential thickness pipe according to the first and second embodiments of the present invention (first and second methods), a mandrel including a region having an outer diameter larger than the inner diameter of the mother tube is forced into the mother tube to expand the diameter of the base end of the mother tube, and then the base end of the mother tube is pressed by a sleeve to force the mother tube into the small inner diameter region of the container to reduce its diameter. This makes it possible to set the diameter difference between the large diameter portion and the small diameter portion (reduced diameter differential thickness portion) large and to set the axial length as desired without excessively increasing the processing load, compared to when the outer diameter of the mother tube is increased to increase the diameter difference between the large diameter portion and the small diameter portion of the differential thickness pipe.

[0091] In the above method, however, not only the outer diameter but also the inner diameter of the large diameter portion is expanded by the mandrel, and therefore the wall thickness of the large diameter portion naturally decreases. However, in applications where high mechanical strength is required in the large diameter portion, it is preferable to maintain the wall thickness of the large diameter portion as that of the mother tube or to make it thicker than that of the mother tube.

[0092] <composition> Therefore, the fifth method is a method for extrusion molding a differential thickness pipe having a predetermined shape, in which a blank tube having a predetermined shape is forced into a container hole by a sleeve in an extrusion molding apparatus, to form a differential thickness pipe having a predetermined shape. The extrusion molding apparatus used in the fifth method includes a mandrel which is a core metal having a predetermined shape, a sleeve which is a tubular member arranged coaxially on the outside of the mandrel, a container which is a die in which a container hole which is a through hole having a predetermined shape is formed, and a drive mechanism configured to force at least the sleeve into the container hole.

[0093] As described in the explanation of the first method, the basic configuration of the extrusion molding apparatus is well known to those skilled in the art and will not be described in detail here, but the components including the mandrel, sleeve and container are made of materials having properties (e.g., mechanical strength and durability) that can withstand processing conditions such as the load acting on the components in each step described below. In addition, the drive mechanism for pushing the mandrel and sleeve into the container hole can be appropriately selected from various drive mechanisms well known in the art depending on the properties (e.g., mechanical strength and hardness) of the material constituting the blank tube to be subjected to extrusion. Typically, a press machine such as a hydraulic press machine is used as the drive mechanism.

[0094] The mother tube, mandrel, sleeve and container used in the fifth method, as well as the differential thickness pipe formed by carrying out the fifth method, will be described in detail below with reference to the drawings.

[0095] 8A and 8B are schematic cross-sectional views showing an example of the configuration of a mother tube used in the fifth method and a differential thickness pipe formed from the mother tube. As shown in (a) of Fig. 8, the mother tube 111 is a cylindrical member having an eleventh outer diameter DO11 which is a predetermined outer diameter, an eleventh inner diameter DI11 which is a predetermined inner diameter, and an eleventh wall thickness T11 which is a predetermined wall thickness.

[0096] Furthermore, the shape of the base pipe is not necessarily limited to the simple cylindrical shape exemplified in FIG. 8. For example, as long as it does not interfere with the execution of the fifth method, portions having different structures may be provided at the tip side and / or the base end side of the base pipe. A method of forming a differential thickness pipe having a predetermined shape from such a base pipe will be described in detail later in the description of other embodiments of the extrusion molding method of the differential thickness pipe according to the present invention (the method of the present invention).

[0097] The material constituting the base pipe 111 is not particularly limited as long as it can be formed into a desired shape by plastic deformation in extrusion, similar to the base pipe 11 used in the first method. Typically, the material constituting the base pipe 111 is a metal such as, for example, lead, tin, aluminum, copper, zirconium, titanium, molybdenum, vanadium, niobium, and steel.

[0098] Next, as shown in FIG. 8(b), the differential thickness pipe 121 formed by the fifth method includes an eleventh small outer diameter region RSDO11, an eleventh large outer diameter region RLDO11, and an eleventh outer diameter increasing region ReDO11. The eleventh small outer diameter region RSDO11 is formed on the tip side, which is the downstream side in the pressing direction, which is the direction in which the base pipe 111 is pushed into the container hole, and has a twelfth outer diameter DO12 (DO12 <DO11) that is a predetermined outer diameter smaller than the eleventh outer diameter DO11, a twelfth inner diameter DI12 (DI12 = DI11) that is equal to the eleventh inner diameter DI11, and a twelfth wall thickness T12 (T12 <T11) that is a predetermined wall thickness smaller than the eleventh wall thickness T11. The eleventh large outer diameter region RLDO11 is formed on the base end side, which is the upstream side in the pressing direction, and has a thirteenth outer diameter DO13 (DO13> DO11) that is a predetermined outer diameter larger than the eleventh outer diameter DO11, a thirteenth inner diameter DI13 (DI13 = DI11) that is equal to the eleventh inner diameter DI11, and a thirteenth wall thickness T13 (T13> T11) that is a predetermined wall thickness larger than the eleventh wall thickness T11.

[0099] The eleventh increasing outer diameter region ReDO11 is a region formed between the eleventh small outer diameter region RSDO11 and the eleventh large outer diameter region RLDO11, and has an outer diameter increasing from the twelfth outer diameter DO12 to the thirteenth outer diameter DO13 as it approaches the eleventh small outer diameter region RSDO11 to the eleventh large outer diameter region RLDO11, a wall thickness increasing from the twelfth wall thickness T12 to the thirteenth wall thickness T13, and an inner diameter that is constant at a fourteenth inner diameter DI14 (DI14=DI11) equal to the eleventh inner diameter DI11. That is, the cross section of the internal space of the differential thickness pipe 121 is constant and identical to the cross section of the internal space of the mother tube 111 throughout the entirety of the eleventh small outer diameter region RSDO11, the eleventh increasing outer diameter region ReDO11, and the eleventh large outer diameter region RLDO11.

[0100] Therefore, the region where the wall thickness of the mother tube 111 is reduced from the eleventh wall thickness T11 to the twelfth wall thickness T12 by performing the fifth method, and the outer diameter of the mother tube 111 is reduced from the eleventh outer diameter DO11 to the twelfth outer diameter DO12, is the eleventh small outer diameter region RSDO11 of the differential thickness pipe 121. Also, the region where the wall thickness of the mother tube 111 is increased from the eleventh wall thickness T11 to the thirteenth wall thickness T13 by performing the fifth method, and the outer diameter of the mother tube 111 is expanded from the eleventh outer diameter DO11 to the thirteenth outer diameter DO13, is the eleventh large outer diameter region RLDO11 of the differential thickness pipe 121. Thus, according to the fifth method, it is possible to increase the outer diameter by increasing the wall thickness in the eleventh large outer diameter region RLDO11 of the differential thickness pipe 121, while maintaining the inner diameter of the mother tube 111. Therefore, the fifth method is suitable for forming a pipe with a different thickness used in applications where high mechanical strength is required in the large diameter portion, for example.

[0101] Fig. 9 is a schematic cross-sectional view showing an example of the configuration of a mandrel, a sleeve, and a container used in the fifth method. Fig. 9(a) is a schematic cross-sectional view showing an example of the configuration of a mandrel and a sleeve used in the fifth method. As shown in Fig. 9(a), the mandrel 131 includes a basic outer diameter region RBDO which is a cylindrical region formed on the tip side and has a 14th outer diameter DO14 which is an outer diameter corresponding to an 11th inner diameter DI11 which is the inner diameter of the mother tube 111.

[0102] The sleeve 141 includes an 11th pressing region RP11 which is a cylindrical region having a cylindrical internal space and a 15th outer diameter DO15 which is an outer diameter equal to the 13th outer diameter DO13 which is the outer diameter of the 11th large outer diameter region RLD11 of the differential thickness pipe 121, and a 15th inner diameter DI15 which is an inner diameter corresponding to the 14th outer diameter DO14 which is the outer diameter of the basic outer diameter region RBDO of the mandrel 131.

[0103] Next, Fig. 9(b) is a schematic cross-sectional view showing an example of the configuration of a container used in the fifth method. As shown in Fig. 9(b), a container hole 151a formed in a container 151 includes an eleventh large inner diameter region RLDI11, an eleventh small inner diameter region RSDI11, and an eleventh inner diameter decreasing region RsDI11. The eleventh large inner diameter region RLDI11 is a region formed on the base end side and has a sixteenth inner diameter DI16 that is an inner diameter corresponding to the thirteenth outer diameter DO13. The eleventh small inner diameter region RSDI11 is a region formed on the tip end side and has a seventeenth inner diameter DI17 that is an inner diameter corresponding to the twelfth outer diameter DO12. The eleventh inner diameter decreasing region RsDI11 is formed between the eleventh large inner diameter region RLDI11 and the eleventh small inner diameter region RSDI11, and is a region whose inner diameter decreases from a sixteenth inner diameter DI16 to a seventeenth inner diameter DI17 as it approaches from the eleventh large inner diameter region RLDI11 to the eleventh small inner diameter region RSDI11.

[0104] In the fifth method, by carrying out steps 11 to 13 described below, with the mandrel 131 inserted into the internal space of the blank tube 111 from the base end side (top side in the drawing), the base end side end of the blank tube 111 is pressed by the 11th pressing region RP11 of the sleeve 141 to force the blank tube 111 into the container hole 151a, thereby forming the above-mentioned differential thickness pipe 121.

[0105] 10 is a flowchart showing the flow of each step included in the fifth method. The eleventh step, which is performed in step S11, is a step of setting a blank tube having a predetermined shape at a predetermined position inside a container hole. Specifically, in the eleventh step, the blank tube 111 is set at a predetermined position inside the container hole 151a by abutting an end portion on the tip side of the blank tube 111 against a first inner diameter reduced region RsDI11 formed between an eleventh large inner diameter region RLDI11 and an eleventh small inner diameter region RSDI11 of a container hole 151a formed in the container 151.

[0106] Next, in step S12, a twelfth step is performed in which the base end of the mother tube 111 is pressed by a sleeve while the mandrel is inserted into the mother tube, thereby expanding the diameter of the mother tube. Specifically, in the twelfth step, while the mandrel 131 is inserted into the mother tube 111, the base end of the mother tube 111 is pressed by the sleeve 141. This causes the material constituting the mother tube 111 to plastically flow and fill the space between the container 151 and the mandrel 131 in the eleventh large inner diameter region RLDI11 and the eleventh inner diameter reduced region RsDI11 of the container hole 151a. As a result, the outer diameter of the mother tube 111 can be expanded to a thirteenth outer diameter DO13 while maintaining the inner diameter of the mother tube 111 at the eleventh inner diameter DI11.

[0107] Next, the thirteenth step performed in step S13 is a step of further pressing the base end side of the blank tube with the sleeve to force the tip side of the blank tube into the eleventh small inner diameter region of the container hole to reduce the diameter. Specifically, the base end side of the blank tube 111 is further pressed by the sleeve 141 while the mandrel 131 is inserted into the blank tube 111. This executes an extrusion process in which the material constituting the blank tube 111 is extruded into the eleventh small inner diameter region RSDI11 of the container hole 151a through the gap between the base end side end of the eleventh small inner diameter region RSDI11 of the container hole 151a and the mandrel 131. As a result, the tip side of the blank tube 111 can be reduced in diameter. By performing the eleventh to thirteenth steps included in the fifth method in this manner, a differential thickness pipe having a predetermined shape can be formed.

[0108] As described above, both the 12th step and the 13th step are performed with the mandrel 131 inserted into the mother tube 111. The insertion of the mandrel 131 into the mother tube 111 only needs to be completed by the time the 12th step is started at the latest. Therefore, the mandrel 131 may be inserted into the mother tube 111 after the mother tube 111 is set inside the container hole 151a in the 11th step, or the mother tube 111 with the mandrel 131 inserted therein may be set inside the container hole 151a in the 11th step.

[0109] As described above, in order to press the base end of the blank tube 111 with the sleeve 141 in the 12th step and fill the space between the container 151 and the mandrel 131 with the material that constitutes the blank tube 111 to expand the diameter of the blank tube 111, the tip of the mandrel needs to reach the base end of the 11th small inner diameter region of the container hole in the pressing direction. Therefore, in the fifth method, at an 11th time point when the 12th step is started, the tip end of the mandrel has reached an 11th position, which is the same position in the pressing direction as the position of the base end of the 11th small inner diameter region of the container hole, or a position further forward than the 11th position.

[0110] Furthermore, in the 13th step, as described above, the base end side of the mother tube 111 is further pressed by the sleeve 141, and the tip end of the mother tube 111 is forced into the 11th small inner diameter region RSDI11 of the container bore 151a through the gap between the base end side end of the 11th small inner diameter region RSDI11 of the container bore 151a and the mandrel 131, thereby reducing the diameter. At this time, if the amount by which the mandrel 131 protrudes from the base end side end of the 11th small inner diameter region RSDI11 in the pressing direction is too small, the material of the mother tube 111 forced into the 11th small inner diameter region RSDI11 may turn inward in the radial direction, and the 11th small outer diameter region RSDO11 of the differential thickness pipe 121 may not be formed into the desired shape.

[0111] Therefore, in the fifth method, at a twelfth time point when the thirteenth step is started, the tip end of the mandrel reaches a twelfth position, which is a position a predetermined distance forward of the base end of the eleventh small inner diameter region of the container hole in the pressing direction, or reaches a position forward of the twelfth position. The "predetermined distance" here refers to a distance that prevents the material of the blank tube 111 pressed into the eleventh small inner diameter region RSDI11 from flowing inward in the radial direction, thereby enabling the eleventh small outer diameter region RSDO11 of the differential thickness pipe 121 to be formed into a desired shape. The specific size of such a distance can be determined as appropriate based on, for example, the results of preliminary experiments and / or simulation analysis using a finite element method, in which the distance by which the tip end of the mandrel protrudes forward from the base end of the eleventh small inner diameter region of the container hole in the pressing direction is changed in various ways.

[0112] The arrangement of the mandrel in steps 12 and 13 of the fifth method is not particularly limited as long as the above conditions are satisfied. For example, the mandrel and the sleeve may be integrally formed and driven integrally by the drive mechanism. Conversely, when the mandrel and the sleeve are formed separately, they may be integrally driven by the drive mechanism or driven individually, or the mandrel may be fixed at a position that satisfies the above conditions and only the sleeve may be driven by the drive mechanism.

[0113] Fig. 11 is a schematic cross-sectional view showing an example of changes in the positional relationship and shape of the blank tube, mandrel, sleeve, container, and differential thickness pipe as the fifth method progresses. In Fig. 11, the reference symbols attached to the respective parts shown in Fig. 8 and Fig. 9 are omitted for the sake of simplicity. However, in the following explanation of Fig. 11, the reference symbols shown in Fig. 8 and Fig. 9 are used for the sake of accuracy, so please refer to Fig. 8 and Fig. 9 as necessary.

[0114] Fig. 11(a) shows a state in which, as a result of the 11th step, the blank tube 111 has been set at a predetermined position inside the container hole 151a and the mandrel 131 has been inserted into the blank tube 111. Fig. 11(b) shows a state in which, as a result of the 12th step, the base end of the blank tube 111 has been pressed by the sleeve 141, and the material constituting the blank tube 111 has been filled into the space between the container 151 and the mandrel 131, thereby expanding the diameter of the blank tube 111. Fig. 11(c) shows a state in which, as a result of the 13th step, the base end of the blank tube 111 has been further pressed by the sleeve 141, and the tip end of the blank tube 111 has been forced into the 11th small inner diameter region RSDI11 of the container hole 151a through the gap between the base end of the 11th small inner diameter region RSDI11 of the container hole 151a and the mandrel 131, thereby reducing the diameter.

[0115] 11, in the fifth method, the thickness of the mother tube 111 is increased from the eleventh thickness T11 to the thirteenth thickness T13, and the region in which the outer diameter of the mother tube 111 is expanded from the eleventh outer diameter DO11 to the thirteenth outer diameter DO13 becomes the eleventh large outer diameter region RLDO11 of the differential thickness pipe 121. In addition, the thickness of the mother tube 111 is decreased from the eleventh outer diameter DO11 to the twelfth outer diameter DO12, and the region in which the outer diameter of the mother tube 111 is reduced from the eleventh outer diameter DO11 to the twelfth outer diameter DO12 becomes the eleventh small outer diameter region RSDO11 of the differential thickness pipe 121. In this way, in the fifth method, the outer diameter can be increased by increasing the thickness in the eleventh large outer diameter region RLDO11 of the differential thickness pipe 121 while maintaining the inner diameter of the mother tube 111. Therefore, according to the fifth method, it is possible to form a differential thickness pipe having a diameter difference (between the eleventh large outer diameter region RLDO11 and the eleventh small outer diameter region RSDO11) that is suitable for applications requiring high mechanical strength in the large diameter portion, for example, without excessively increasing the processing load, compared to when the diameter difference between the large diameter portion and the small diameter portion of the differential thickness pipe is increased by increasing the outer diameter of the base tube.

[0116] The axial lengths of the eleventh large outer diameter region RLDO11 and the eleventh small outer diameter region RSDO11 vary depending on the axial length of the mother tube 111, the amount of diameter expansion in the twelfth step (the difference between the eleventh outer diameter DO11, which is the outer diameter of the mother tube 111, and the sixteenth inner diameter DI16, which is the inner diameter of the eleventh large inner diameter region RLDI11 of the container hole 151a), the amount of diameter reduction in the thirteenth step (the difference between the eleventh outer diameter DO11, which is the outer diameter of the mother tube 111, and the seventeenth inner diameter DI17, which is the inner diameter of the eleventh small inner diameter region RSDI11 of the container hole 151a), and the amount of pressing of the mother tube 111 by the sleeve 141. That is, according to the fifth method, the axial lengths of the eleventh large outer diameter region RLDO11 and the eleventh small outer diameter region RSDO11 of the differential thickness pipe 121 can be set arbitrarily.

[0117] 11(b), the material constituting the blank tube 111 has not yet started to flow into the eleventh small inner diameter region RSDI11 of the container bore 151a. However, depending on, for example, the ease of plastic flow of the material constituting the blank tube 111, the configurations of the mandrel, sleeve, and container provided in the extrusion molding apparatus used in the fifth method, and the pressing speed of the sleeve by the drive mechanism, the material constituting the blank tube 111 may start to flow into the eleventh small inner diameter region RSDI11 of the container bore 151a before the blank tube 111 is completely expanded. In other words, the 13th step may start before the 12th step is completed.

[0118] 11, in the fifth method illustrated in Fig. 11, the mandrel 131 is fixed at a position (the 12th position described above) that is a predetermined distance d1 toward the tip side in the pressing direction from the end portion on the base end side of the 11th small inner diameter region RSDI11 of the container hole 151a, and only the sleeve 141 is driven by a driving mechanism (not shown). However, as described above, the mandrel 131 and the sleeve 141 may be driven integrally by the driving mechanism.

[0119] Figure 12 is a schematic cross-sectional view showing another example of changes in the positional relationship and shape of the blank tube, mandrel, sleeve, container, and differential thickness pipe as the fifth method progresses. In Figure 12, the reference symbols attached to the respective parts shown in Figures 8 and 9 are also omitted in order to simplify the drawing. However, in the following explanation of Figure 12, the reference symbols shown in Figures 8 and 9 will be used for accuracy, so please refer to Figures 8 and 9 as necessary.

[0120] The left side of the central axis AX in Fig. 12(a) shows the state of each component at time point 11, when the blank tube 111 is set at a predetermined position inside the container hole 151a by performing the 11th step, the mandrel 131 is inserted into the blank tube 111, and the 12th step is started. The right side of the central axis AX in Fig. 12(a) shows the state in which the base end of the blank tube 111 is pressed by the sleeve 141, the material constituting the blank tube 111 is filled into the space between the container 151 and the mandrel 131, the blank tube 111 is expanded in diameter, and the front end of the blank tube 111 is forced into the 11th small inner diameter region RSDI11 of the container hole 151a through the gap between the base end of the 11th small inner diameter region RSDI11 of the container hole 151a and the mandrel 131, thereby reducing the diameter, and the desired differential thickness pipe 121 is formed.

[0121] In the example shown in Fig. 12, the amount by which the sleeve 141 presses the blank tube 111 is greater than in the example shown in Fig. 11. As a result, the axial length of the eleventh large outer diameter region RLDO11 of the differential thickness pipe 121 is shorter than in the example shown in Fig. 11, and a flange-shaped eleventh large outer diameter region RLDO11 is formed. In the example shown in Fig. 12, the mandrel 131 and the sleeve 141, which are formed as separate bodies, are driven together by a drive mechanism (not shown).

[0122] Fig. 12(b) is an enlarged view of the part surrounded by the thick dashed line in Fig. 12(a). However, in Fig. 12(b), the mandrel 131 and the sleeve 141 are omitted in order to clearly show the change in shape from the mother tube 111 to the differential thickness pipe 121. As illustrated in Fig. 12(b), by carrying out the fifth method, the eleventh large outer diameter region RLDO11 of the differential thickness pipe 121 is expanded from the eleventh outer diameter DO11, which is the outer diameter of the mother tube 111 depicted by the thin dashed line, to the thirteenth outer diameter DO13 (amount of expansion = ΔDe). On the other hand, the eleventh small outer diameter region RSDO11 of the differential thickness pipe 121 is reduced from the eleventh outer diameter DO11, which is the outer diameter of the mother tube 111 depicted by the thin dashed line, to the twelfth outer diameter DO12 (amount of reduction = ΔDs).

[0123] Fig. 12(c) is an enlarged view of the part surrounded by the thick dashed line in Fig. 12(b). However, in Fig. 12(c), not only the mandrel 131 and the sleeve 141 but also the container 151 are omitted in order to clearly show the change in shape from the mother tube 111 to the differential thickness pipe 121. As illustrated in Fig. 12(c), by performing the fifth method, in the eleventh large outer diameter region RLDO11 of the differential thickness pipe 121, the wall thickness is increased from the eleventh wall thickness T11, which is the wall thickness of the mother tube 111 depicted by the thin dashed line, to the thirteenth wall thickness T13 (wall thickness increase amount = ΔTe). On the other hand, in the eleventh small outer diameter region RSDO11 of the differential thickness pipe 121, the wall thickness is decreased from the eleventh wall thickness T11, which is the wall thickness of the mother tube 111 depicted by the thin dashed line, to the twelfth wall thickness T12 (wall thickness reduction amount = ΔTs).

[0124] <effect> As described above, in a differential thickness pipe formed by the fifth method, the 11 large outer diameter region is formed by increasing the thickness of the mother tube, and the 11 small outer diameter region is formed by decreasing the thickness of the mother tube. Therefore, a larger diameter difference can be achieved with a smaller processing load than when the large outer diameter region is formed while maintaining the outer diameter of the mother tube and the small outer diameter region is formed by significantly reducing the outer diameter of the mother tube. Furthermore, according to the fifth method, the wall thickness of the large outer diameter region can be increased, so that a differential thickness pipe suitable for applications requiring high mechanical strength in the large diameter portion can be formed.

[0125] In addition, as described above, the axial lengths of the 11th large outer diameter region and the 11th small outer diameter region vary depending on the axial length of the mother tube, the amount of diameter expansion in the 12th step, the amount of diameter reduction in the 13th step, and the amount of pushing the mother tube by the sleeve. That is, according to the fifth method, the axial lengths of the 11th large outer diameter region and the 11th small outer diameter region of the differential thickness pipe can be set as desired.

[0126] Sixth Embodiment Next, a method for extrusion molding a differential thickness pipe according to a sixth embodiment of the present invention (hereinafter, sometimes referred to as the "sixth method") will be described.

[0127] The 11th small outer diameter region of the differential thickness pipe formed by the above-mentioned fifth method is a region having a straight pipe shape with a 12th outer diameter, a 12th inner diameter, and a 12th wall thickness. However, depending on the application of the differential thickness pipe, it may be necessary to form two parts (differential thickness parts) having different wall thicknesses in the small diameter part (small outer diameter region) as in the differential thickness pipe formed by the above-mentioned first method.

[0128] <composition> Therefore, the sixth method is the fifth method described above, which is a method for extrusion molding a pipe with different thicknesses, in which a 12th small outer diameter region is formed at the end of the pipe on the tip side, and the mandrel further includes a 13th small outer diameter region and a 12th increasing outer diameter region. The 12th small outer diameter region is a region having a 16th outer diameter that is an outer diameter equal to the 12th outer diameter, an 18th inner diameter that is a predetermined inner diameter smaller than the 12th inner diameter, and a 14th wall thickness that is a predetermined wall thickness larger than the 12th wall thickness. The 13th small outer diameter region is a cylindrical region formed on the tip side of the basic outer diameter region of the mandrel and has an 18th outer diameter that is an outer diameter corresponding to the 18th inner diameter that is the inner diameter of the 12th small outer diameter region of the pipe with different thicknesses. The 12th increasing outer diameter region is a region formed between the 13th small outer diameter region and the basic outer diameter region of the mandrel, and the outer diameter increases from the 18th outer diameter to the 14th outer diameter as it approaches the basic outer diameter region from the 13th small outer diameter region.

[0129] Furthermore, in the sixth method, at a twelfth time point when the thirteenth step is started, the base end of the thirteenth small outer diameter region of the mandrel is located closer to the base end than the eleventh position, which is the position of the base end of the eleventh small inner diameter region of the container hole in the pressing direction. As described above, the thirteenth small outer diameter region is formed on the tip side of the mandrel. That is, at the twelfth time point, the base end of the eleventh small inner diameter region of the container hole faces the thirteenth small outer diameter region of the mandrel. Therefore, at the twelfth time point, the material constituting the blank tube 111 starts to flow into the eleventh small inner diameter region RSDI11 of the container hole 151a through the gap between the base end of the eleventh small inner diameter region of the container hole and the thirteenth small outer diameter region of the mandrel. This results in the formation of a 12 small outer diameter region at the tip end of the differential thickness pipe, which has a 16th outer diameter which is an outer diameter equal to the 12th outer diameter, an 18th inner diameter which is a predetermined inner diameter smaller than the 12th inner diameter, and a 14th thickness which is a predetermined thickness larger than the 12th thickness.

[0130] <Sixth method according to the first aspect> The shape of the differential thickness pipe formed by the sixth method varies depending on the position of the mandrel at time 13, which is the time when the thirteenth step is completed. For example, in the sixth method according to the first aspect, at time 13, the tip end of the basic outer diameter region of the mandrel is located more tip-side than the eleventh position, which is the position of the base end of the eleventh small inner diameter region of the container hole. The resulting differential thickness pipe includes an eleventh large outer diameter region, an eleventh increasing outer diameter region, an eleventh small outer diameter region, a twelfth small outer diameter region formed more tip-side than the eleventh small outer diameter region, and an eleventh increasing inner diameter region. The 11th increasing inner diameter region is formed between the 12th smaller outer diameter region and the 11th smaller outer diameter region of the differential thickness pipe, and as it approaches the 12th smaller outer diameter region, the inner diameter increases from the 18th inner diameter to the 12th inner diameter, the wall thickness decreases from the 14th wall thickness to the 12th wall thickness, and the outer diameter is constant at the 17th outer diameter which is equal to the 12th outer diameter.

[0131] Fig. 13 is a schematic cross-sectional view showing one example of the configuration of a mother tube used in the sixth method according to the first aspect and a differential thickness pipe formed from the mother tube. The mother tube 111 shown in Fig. 13(a) is a cylindrical member having an eleventh outer diameter DO11 which is a predetermined outer diameter, an eleventh inner diameter DI11 which is a predetermined inner diameter, and an eleventh wall thickness T11 which is a predetermined wall thickness, similar to the mother tube 111 shown in Fig. 8(a) referred to in the explanation of the fifth method.

[0132] Next, as shown in FIG. 13(b), the thickness-varying pipe 121 formed by the sixth method according to the first aspect has the same configuration as the thickness-varying pipe 121 illustrated in FIG. 8(b) referred to in the description of the fifth method, except that it further includes a 12th small outer diameter region RSDO12 and an 11th inner diameter increasing region ReDI11 on the tip side of the 11th small outer diameter region RSDO11. As described above, the 12th small outer diameter region RSDO12 is formed on the tip side of the 11th small outer diameter region RSDO11 of the thickness-varying pipe 121 and has a 16th outer diameter DO16 (DO16 = DO12) equal to the 12th outer diameter DO12, an 18th inner diameter DI18 (DI18 < DI12) smaller than the 12th inner diameter DI12, and a 14th wall thickness T14 (T14 > T12) larger than the 12th wall thickness T12.

[0133] The 11th inner diameter increasing region ReDI11 is formed between the 12th small outer diameter region RSDO12 and the 11th small outer diameter region RSDO11 of the thickness-varying pipe 121, and the inner diameter increases from the 18th inner diameter DI18 to the 12th inner diameter DI12 as it approaches from the 12th small outer diameter region RSDO12 to the 11th small outer diameter region RSDO11, the wall thickness decreases from the 14th wall thickness T14 to the 12th wall thickness T12, and the outer diameter is constant at the 17th outer diameter DO17 (DO17 = DO12) equal to the 12th outer diameter DO12.

[0134] FIG. 14 is a schematic cross-sectional view showing an example of the configuration of the mandrel, sleeve, and container used in the sixth method according to the first embodiment. FIG. 14(a) is a schematic cross-sectional view showing an example of the configuration of the mandrel and sleeve used in the sixth method according to the first embodiment. As shown in FIG. 14(a), the mandrel 131 used in the sixth method according to the first embodiment has a configuration similar to that of the mandrel 131 illustrated in FIG. 9(a) referred to in the description of the fifth method, except that it further includes a thirteenth small outer diameter region RSDO13 and a twelfth increasing outer diameter region ReDO12. As described above, the thirteenth small outer diameter region RSDO13 is a cylindrical region formed on the tip side of the basic outer diameter region RBDO of the mandrel 131 and having an 18th outer diameter DO18 that is an outer diameter corresponding to the 18th inner diameter DI18 that is the inner diameter of the twelfth small outer diameter region RSDO12 of the differential thickness pipe 121. The 12th outer diameter increasing region ReDO12 is formed between the 13th smaller outer diameter region RSDO13 and the basic outer diameter region RBDO of the mandrel 131, and is a region in which the outer diameter increases from the 18th outer diameter to the 14th outer diameter as it approaches from the 13th smaller outer diameter region RSDO13 to the basic outer diameter region RBDO.

[0135] The sleeve 141 used in the sixth method of the first embodiment, like the mandrel 131 illustrated in (a) of Figure 9 referenced in the explanation of the fifth method, includes an 11th pressing region RP11 which is a cylindrical region having a cylindrical internal space formed on the tip side and having a 15th outer diameter DO15 which is an outer diameter equal to the 13th outer diameter DO13 which is the outer diameter of the 11th large outer diameter region RLD11 of the differential thickness pipe 121, and a 15th inner diameter DI15 which is an inner diameter corresponding to the 14th outer diameter DO14 which is the outer diameter of the basic outer diameter region RBDO of the mandrel 131.

[0136] Next, Fig. 14(b) is a schematic cross-sectional view showing an example of the configuration of a container used in the sixth method according to the first aspect. The container hole 151a formed in the container 151 shown in Fig. 14(b) includes an eleventh large inner diameter region RLDI11, an eleventh small inner diameter region RSDI11, and an eleventh inner diameter decreasing region RsDI11, similar to the container hole 151a formed in the container 151 shown in Fig. 9(b) referred to in the description of the fifth method. The details of each region of the container hole 151a have already been described in the description of the fifth method, so a description thereof will be omitted here.

[0137] In the sixth method of the first aspect, too, by carrying out steps 11 to 13 similar to those of the fifth method, with the mandrel 131 inserted into the internal space of the blank tube 111 from the base end side (top side in the drawing), the base end side end of the blank tube 111 is pressed by the eleventh pressing region RP11 of the sleeve 141 to force the blank tube 111 into the container hole 151a, thereby forming the above-mentioned differential thickness pipe 121.

[0138] Fig. 15 is a schematic cross-sectional view showing an example of changes in the positional relationship and shape of the blank tube, mandrel, sleeve, container, and differential thickness pipe as the sixth method according to the first embodiment progresses. In Fig. 15, the reference symbols given to the respective parts shown in Fig. 13 and Fig. 14 are omitted for the sake of simplicity. However, in the following explanation of Fig. 15, the reference symbols shown in Fig. 13 and Fig. 14 are used for the sake of accuracy, so please refer to Fig. 13 and Fig. 14 as necessary.

[0139] Fig. 15(a) shows the state in which, by performing the 11th step, the mandrel 131 is about to be inserted into the mother tube 111 that has been set at a predetermined position inside the container hole 151a. The outer diameter DO18 of the 13th small outer diameter region RSDO13 formed at the tip of the mandrel 131 is smaller than the 11th inner diameter DI11 of the mother tube 111, and the inner diameter DI18 of the 11th large inner diameter region RLDI11 of the container hole 151a is larger than the 11th outer diameter DO11 of the mother tube 111. Therefore, in the state shown in Fig. 15(a), there are voids on both the outside of the outer circumferential surface and the inside of the inner circumferential surface of the mother tube 111.

[0140] Fig. 15(b) shows a state where the 12th step is started, and the base end of the mother tube 111 is pressed by the sleeve 141, filling the space between the container 151 and the mandrel 131 with the material for the mother tube 111, thereby expanding the diameter of the mother tube 111. In the state shown in Fig. 15(b), the material for the mother tube 111 has not yet been filled into the gap between the 13th small outer diameter region RSDO13 formed at the tip of the mandrel 131 and the inner circumferential surface of the mother tube 111, and the gap between the vicinity of the tip end of the 11th large inner diameter region RLDI11 of the container hole 151a and the outer circumferential surface of the mother tube 111. However, as the base end of the mother tube 111 is further pressed by the sleeve 141, the material for the mother tube 111 is also filled into these gaps, completing the diameter expansion of the mother tube 111 and completing the 12th step.

[0141] (c) of Figure 15 shows a state in which, as a result of performing the 13th step, the base end side of the blank tube 111 is further pressed by the sleeve 141, and the tip side of the blank tube 111 is forced into the 11th small inner diameter region RSDI11 of the container hole 151a through the gap between the base end side end of the 11th small inner diameter region RSDI11 of the container hole 151a and the mandrel 131, thereby reducing the diameter. As illustrated in (c) of Figure 15, the material constituting the blank tube 111 flows into the 11th small inner diameter region RSDI11 of the container hole 151a through the gap between the base end side end of the 11th small inner diameter region RSDI11 of the container hole 151a and the 13th small outer diameter region RSDO13 and the 12th outer diameter increasing region ReDO12 formed at the tip of the mandrel 131, and forms a 12th small outer diameter region RSDO12 and an 11th inner diameter increasing region ReDI11 that are thicker than the 11th small outer diameter region RSDO11 on the tip side of the 11th small outer diameter region RSDO11 of the differential thickness pipe 121. In other words, in the differential thickness pipe 121 formed by the sixth method relating to the first embodiment, the large diameter portion (large outer diameter region) has an outer diameter enlarged as a whole due to an increase in thickness toward the outside while the inner diameter remains unchanged, the outer diameter of the base end side of the small diameter portion (small outer diameter region) is reduced by a decrease in thickness while the inner diameter remains unchanged, and the outer diameter of the portion from the middle of the small diameter portion to the tip side is reduced by a decrease in thickness while the inner diameter is reduced by an increase in thickness.

[0142] As described above, the mandrel used in the sixth method further includes a thirteenth small outer diameter region, which is a cylindrical region thinner than the basic outer diameter region and formed distally of the basic outer diameter region, and a twelfth increasing outer diameter region, which is a region formed between the thirteenth small outer diameter region and the basic outer diameter region and whose outer diameter increases as it approaches the basic outer diameter region from the thirteenth small outer diameter region. Furthermore, in the sixth method, at a twelfth time point when the thirteenth step is started, the base end of the thirteenth small outer diameter region of the mandrel is proximal to an eleventh position, which is the position of the base end of the eleventh small inner diameter region of the container hole in the pressing direction. In addition, in the sixth method according to the first embodiment, at a thirteenth time point, the tip end of the basic outer diameter region of the mandrel is tip-side to an eleventh position, which is the position of the base end of the eleventh small inner diameter region of the container hole. As a result, according to the sixth method of the first aspect, it is possible to mold a differential thickness pipe having a 12th small outer diameter region thicker than the 11th small outer diameter region and an 11th increased inner diameter region formed at the tip.

[0143] <Modification of the sixth method according to the first aspect> As described with reference to Fig. 13 to Fig. 15, the mandrel used in the sixth method according to the first embodiment further includes a thirteenth small outer diameter region, which is a cylindrical region thinner than the basic outer diameter region and formed on the tip side of the basic outer diameter region, and a twelfth increasing outer diameter region, which is a region in which the outer diameter increases as it approaches the basic outer diameter region from the thirteenth small outer diameter region and is formed between the thirteenth small outer diameter region and the basic outer diameter region. As a result, the small diameter portion (small outer diameter region) of the differential thickness pipe 121 illustrated in Fig. 13 and Fig. 15 has two types of small outer diameter regions with different inner diameters and wall thicknesses. However, the small diameter portion (small outer diameter region) of the differential thickness pipe formed by the sixth method according to the first embodiment may have three or more types of small outer diameter regions, as in the differential thickness pipe formed by the modified sixth method according to the first embodiment illustrated in Fig. 16.

[0144] Fig. 16 is a schematic cross-sectional view showing an example of changes in the positional relationship and shape of the blank tube, mandrel, sleeve, container, and differential thickness pipe as the modified sixth method according to the first embodiment progresses. In Fig. 16 as well, the reference symbols attached to the respective parts shown in Fig. 13, Fig. 14, etc. are omitted in order to simplify the drawing. However, in the following explanation of Fig. 16, the reference symbols shown in Fig. 13, Fig. 14, etc. will be used for accuracy, so please refer to Fig. 13, Fig. 14, etc. as necessary.

[0145] 16(a), the mandrel 131 used in the above-described sixth method according to the modified embodiment has a thirteenth small outer diameter region divided into the above-described RSDO13 and an RSDO13' that is formed further forward than RSDO13 and is narrower than the above-described RSDO13. When the thirteenth step is performed using the mandrel 131 having such a configuration, the portion of the mandrel 131 facing the base end of the eleventh small inner diameter region RSDI11 changes from the thirteenth small outer diameter region RSDO13' through RSDO13 to the basic outer diameter region RBDO during the process in which the material constituting the blank tube 111 flows into the eleventh small inner diameter region RSDI11 of the container hole 151a. As a result, the size of the gap between the base end of the 11th small inner diameter region RSDI11 and the mandrel 131 gradually decreases, and as shown to the right of the central axis AX in Figure 16(a), the thickness of the small diameter portion (reduced diameter difference thickness portion) of the differential thickness pipe 121 also gradually decreases as it progresses from the tip side to the base side.

[0146] Fig. 16(b) is an enlarged view of the portion surrounded by the thick dashed line in Fig. 16(a). As illustrated in Fig. 16(b), the small diameter portion (diameter-reduced small diameter portion) of the differential thickness pipe 121 formed by the above-mentioned embodiment of the sixth method according to the modified example includes, in order from the tip side to the base side, a small diameter region RSDO12' having the largest wall thickness T14', a twelfth small diameter region RSDO12 having an intermediate wall thickness T14, and an eleventh small diameter region RSDO11 having the smallest wall thickness T12.

[0147] As described above, according to the modified example of the sixth method according to the first aspect, a "multi-stage" differential thickness pipe having a small diameter portion (diameter-reduced differential thickness portion) divided into a plurality of small diameter regions having different wall thicknesses and inner diameters can be formed. Note that the multi-stage of the differential thickness pipe is not limited to the above, and depending on, for example, the mechanical strength of the material constituting the blank tube, the degree of work hardening and / or the ease of plastic flow, and / or the mechanical strength of the members constituting the extrusion molding device and / or the processing capacity of the extrusion molding device, it is also possible to form a multi-stage outer surface of the 11th small outer diameter region, the 12th small outer diameter region and / or the 11th large outer diameter region of the formed differential thickness pipe by providing a plurality of portions having different inner diameters in the 11th large inner diameter region and / or the 11th small inner diameter region of the container, as exemplified in FIG. 7 referred to in the explanation of the first method according to another modified example.

[0148] <Sixth method according to the second aspect> As described above, the shape of the differential thickness pipe formed by the sixth method varies depending on the position of the mandrel at the thirteenth time point when the thirteenth step is completed. For example, in the sixth method according to the second embodiment, at the thirteenth time point, the base end of the thirteenth small outer diameter region of the mandrel is closer to the base end than the eleventh position, which is the position of the base end of the eleventh small inner diameter region of the container hole. The resulting differential thickness pipe includes a twelfth small outer diameter region, an eleventh large outer diameter region, a twelfth large outer diameter region, a thirteenth increasing outer diameter region, and a twelfth increasing inner diameter region.

[0149] The 12th large outer diameter region is a region formed between the 12th small outer diameter region and the 11th large outer diameter region, and has a 19th outer diameter that is an outer diameter equal to the 13th outer diameter, a 19th inner diameter that is an inner diameter equal to the 18th inner diameter, and a 15th thickness that is a predetermined thickness greater than the 13th thickness. The 13th increasing outer diameter region is formed between the 12th small outer diameter region and the 12th large outer diameter region, and has an outer diameter that increases from a 16th outer diameter to a 19th outer diameter and a thickness that increases from a 14th thickness to a 15th thickness as it approaches the 12th small outer diameter region and the 12th large outer diameter region, and an inner diameter that is constant at a 20th inner diameter that is equal to the 18th inner diameter. The 12th increasing inner diameter region is formed between the 12th larger outer diameter region and the 11th larger outer diameter region, and as it approaches the 11th larger outer diameter region from the 12th larger outer diameter region, the inner diameter increases from the 19th inner diameter to the 13th inner diameter, the thickness decreases from the 15th thickness to the 13th thickness, and the outer diameter is constant at a 20th outer diameter which is equal to the 13th outer diameter.

[0150] Fig. 17 is a schematic cross-sectional view showing one example of the configuration of a mother tube used in the sixth method according to the second aspect and a differential thickness pipe formed from the mother tube. The mother tube 111 shown in Fig. 17(a) is a cylindrical member having an eleventh outer diameter DO11 which is a predetermined outer diameter, an eleventh inner diameter DI11 which is a predetermined inner diameter, and an eleventh wall thickness T11 which is a predetermined wall thickness, similar to the mother tube 111 shown in Fig. 8(a) and Fig. 13(a) referred to in the explanation of the fifth and sixth methods.

[0151] Next, as shown in (b) of Figure 17, a differential thickness pipe 121 formed by the sixth method relating to the second embodiment includes a 12th small outer diameter region RSDO12, an 11th large outer diameter region RLDO11, a 12th large outer diameter region RLDO12, a 13th increasing outer diameter region ReDO13, and a 12th increasing inner diameter region ReDI12.

[0152] The 12th large outer diameter region RLDO12 is a region formed between the 12th small outer diameter region RSDO12 and the 11th large outer diameter region RLDO11 and has a 19th outer diameter DO19 (DO19 = DO13) which is an outer diameter equal to the 13th outer diameter DO13, a 19th inner diameter DI19 (DI19 = DI18) which is an inner diameter equal to the 18th inner diameter DI18, and a 15th wall thickness T15 (T15 > T13) which is a predetermined thickness greater than the 13th wall thickness T13. The 13th outer diameter increasing region ReDO13 is formed between the 12th small outer diameter region RSDO12 and the 12th large outer diameter region RLDO12, and as it approaches from the 12th small outer diameter region RSDO12 to the 12th large outer diameter region RLDO12, the outer diameter increases from the 16th outer diameter DO16 to the 19th outer diameter DO19, the thickness increases from the 14th wall thickness T14 to the 15th wall thickness T15, and the inner diameter is constant at a 20th inner diameter DI20 (DI20 = DI18) that is equal to the 18th inner diameter DI18. The 12th inner diameter increasing region ReDI12 is formed between the 12th large outer diameter region RLDO12 and the 11th large outer diameter region RLDO11, and as it approaches from the 12th large outer diameter region RLDO12 to the 11th large outer diameter region RLDO11, the inner diameter increases from the 19th inner diameter DIO19 to the 13th inner diameter DI13, the thickness decreases from the 15th thickness T15 to the 13th thickness T13, and the outer diameter is constant at a 20th outer diameter DO20 (DO20 = DO13) that is equal to the 13th outer diameter DO13.

[0153] Fig. 18 is a schematic cross-sectional view showing an example of the configuration of the mandrel, sleeve, and container used in the sixth method according to the second embodiment. Fig. 18(a) is a schematic cross-sectional view showing an example of the configuration of the mandrel and sleeve used in the sixth method according to the second embodiment. As shown in Fig. 18(a), the mandrel 131 used in the sixth method according to the second embodiment has a similar configuration to the mandrel 131 illustrated in Fig. 14(a) referred to in the explanation of the sixth method according to the first embodiment, except that the proportion of the thirteenth small outer diameter region RSDO13 in the total length in the axial direction is high (long) and the proportion of the basic outer diameter region RBDO is low (short).

[0154] The sleeve 141 used in the sixth method of the second embodiment, like the sleeve 141 illustrated in (a) of Figure 9 and (a) of Figure 14, respectively, referenced in the explanations of the fifth method and the sixth method of the first embodiment, includes an eleventh pressing region RP11 which is a cylindrical region having a cylindrical internal space formed on the tip side and having a 15th outer diameter DO15 which is an outer diameter equal to the 13th outer diameter DO13 which is the outer diameter of the 11th large outer diameter region RLD11 of the differential thickness pipe 121, and a 15th inner diameter DI15 which is an inner diameter corresponding to the 14th outer diameter DO14 which is the outer diameter of the basic outer diameter region RBDO of the mandrel 131.

[0155] Next, Fig. 18(b) is a schematic cross-sectional view showing an example of the configuration of a container used in the sixth method according to the second embodiment. The container hole 151a formed in the container 151 shown in Fig. 18(b) includes an eleventh large inner diameter region RLDI11, an eleventh small inner diameter region RSDI11, and an eleventh inner diameter decreasing region RsDI11, similar to the container hole 151a formed in the container 151 shown in Fig. 9(b) and Fig. 14(b) respectively, which are referred to in the description of the fifth method and the sixth method according to the first embodiment. The details of each region of the container hole 151a have already been described in the description of the fifth method, so a description thereof will be omitted here.

[0156] In the sixth method relating to the second aspect, too, by carrying out steps 11 to 13 similar to those of the fifth method, with the mandrel 131 inserted into the internal space of the blank tube 111 from the base end side (top side in the drawing), the base end side end of the blank tube 111 is pressed by the eleventh pressing region RP11 of the sleeve 141 to force the blank tube 111 into the container hole 151a, thereby forming the above-mentioned differential thickness pipe 121.

[0157] Fig. 19 is a schematic cross-sectional view showing one example of changes in the positional relationship and shape of the blank tube, mandrel, sleeve, container, and differential thickness pipe as the sixth method according to the second embodiment progresses. In Fig. 19, the reference symbols attached to the respective parts shown in Fig. 17 and Fig. 18 are omitted for the sake of simplicity. However, in the following explanation of Fig. 19, the reference symbols shown in Fig. 17 and Fig. 18 are used for the sake of accuracy, so please refer to Fig. 17 and Fig. 18 as necessary.

[0158] Fig. 19(a) shows the state in which the mandrel 131 has been inserted into the mother tube 111, which has been set at a predetermined position inside the container hole 151a, by performing the 11th step. The outer diameter DO18 of the 13th small outer diameter region RSDO13 formed at the tip of the mandrel 131 is smaller than the 11th inner diameter DI11 of the mother tube 111, and the inner diameter DI18 of the 11th large inner diameter region RLDI11 of the container hole 151a is larger than the 11th outer diameter DO11 of the mother tube 111. Therefore, in the state shown in Fig. 19(a), there are voids on both the outside of the outer circumferential surface and the inside of the inner circumferential surface of the mother tube 111.

[0159] Fig. 19(b) shows a state where the 12th step has started, and the base end of the mother tube 111 is being pressed by the sleeve 141, filling the space between the container 151 and the mandrel 131 with the material for the mother tube 111, thereby expanding the diameter of the mother tube 111. In the state shown in Fig. 19(b), the material for the mother tube 111 has not yet been filled into the gap between the 13th small outer diameter region RSDO13 formed at the tip of the mandrel 131 and the inner circumferential surface of the mother tube 111, and the gap between the vicinity of the tip end of the 11th large inner diameter region RLDI11 of the container hole 151a and the outer circumferential surface of the mother tube 111. However, as the base end of the mother tube 111 is further pressed by the sleeve 141, the material for the mother tube 111 is also filled into these gaps, completing the diameter expansion of the mother tube 111 and completing the 12th step.

[0160] 19(c) shows a state after the 13th step is completed, in which the base end of the mother tube 111 is further pressed by the sleeve 141 and the tip end of the mother tube 111 is forced into the 11th small inner diameter region RSDI11 of the container hole 151a through the gap between the base end of the 11th small inner diameter region RSDI11 of the container hole 151a and the mandrel 131, thereby reducing the diameter. As described above, in the sixth method according to the second aspect, at a 13th point in time when the 13th step is completed, the base end of the 13th small outer diameter region RSDO13 of the mandrel 131 is located closer to the base than the 11th position, which is the position of the base end of the 11th small inner diameter region RSDI11 of the container hole 151a.

[0161] Therefore, in the sixth method according to the second aspect, throughout the entire period of the thirteenth step, the material constituting the mother tube 111 flows into the eleventh small inner diameter region RSDI11 of the container bore 151a through the gap between the base end of the eleventh small inner diameter region RSDI11 of the container bore 151a and the thirteenth small outer diameter region RSDO13 formed at the tip of the mandrel 131. Thus, the small diameter portion (small outer diameter region) of the differential thickness pipe 121 is constituted only by the twelfth small outer diameter region RSDO12 which is a region having the sixteenth outer diameter DO16 which is an outer diameter smaller than the eleventh outer diameter DO11 which is the outer diameter of the mother tube 111, the eighteenth inner diameter DI18 which is an inner diameter smaller than the eleventh inner diameter DI11 which is the inner diameter of the mother tube 111, and the predetermined fourteenth wall thickness T14.

[0162] Furthermore, since the base end of the thirteenth small outer diameter region RSDO13 of the mandrel 131 is still closer to the base end than the eleventh position, which is the position of the base end of the eleventh small inner diameter region RSDI11 of the container hole 151a, the tip end portion of the large diameter portion (large outer diameter region) of the differential thickness pipe 121 is also thickened toward the inside to form the twelfth large outer diameter region RLDO12. In other words, in the differential thickness pipe 121 formed by the sixth method according to the second embodiment, the base end portion of the large diameter portion (large outer diameter region) has an outer diameter enlarged by thickening toward the outside and an inner diameter unchanged, the portion from the middle of the large diameter portion to the tip end side has an outer diameter enlarged by thickening toward the outside and an inner diameter reduced by thickening toward the inside, and the small diameter portion (small outer diameter region) has an outer diameter reduced by thinning and an inner diameter reduced by thickening as a whole.

[0163] As described above, the mandrel used in the sixth method further includes a thirteenth small outer diameter region, which is a cylindrical region thinner than the basic outer diameter region and formed on the tip side of the basic outer diameter region, and a twelfth increasing outer diameter region, which is a region formed between the thirteenth small outer diameter region and the basic outer diameter region and whose outer diameter increases as it approaches the basic outer diameter region from the thirteenth small outer diameter region. Furthermore, in the sixth method, at a twelfth time point when the thirteenth step is started, the base end of the thirteenth small outer diameter region of the mandrel is more base-side than an eleventh position, which is the position of the base end of the eleventh small inner diameter region of the container hole in the pressing direction. In addition, in the sixth method according to the second embodiment, at a thirteenth time point, the base end of the thirteenth small outer diameter region of the mandrel is more base-side than an eleventh position, which is the position of the base end of the eleventh small inner diameter region RSDI11 of the container hole 151a. As a result, according to the sixth method of the second aspect, the inner diameter of the range extending from the middle of the large diameter portion (large outer diameter region) whose outer diameter has been expanded by outward thickening to the tip end of the small diameter portion (small outer diameter region) can be reduced by thickening.

[0164] <effect> As described above, according to the sixth method, the range in which the inner diameter is reduced by wall thickness increase in a differential thickness pipe formed by the sixth method can be changed by appropriately adjusting the size and / or length of the twelfth smaller outer diameter region, which is a portion formed on the tip side of the mandrel and which is narrower than the inner diameter of the mother tube, and the position of the mandrel at the time when the thirteenth step is completed. Therefore, for example, the structure of the differential thickness pipe, such as its shape and wall thickness distribution, can be designed with a high degree of freedom according to the application.

[0165] Seventh Embodiment Next, a method for extrusion molding a differential thickness pipe according to a seventh embodiment of the present invention (hereinafter, sometimes referred to as the "seventh method") will be described.

[0166] As described above, the shape of the mother tube used in the extrusion molding methods for differential thickness pipes according to the fifth and sixth embodiments of the present invention (Fifth Method and Sixth Method) is not necessarily limited to a simple cylindrical shape as exemplified in Figures 8, 13, 17, etc., and for example, a portion having a different structure may be provided at the tip and / or base end of the mother tube, as long as it does not interfere with the execution of the fifth and sixth methods. By molding a differential thickness pipe from such a mother tube, the structure provided at the tip and / or base end of the mother tube can be incorporated into the differential thickness pipe.

[0167] <composition> Therefore, the seventh method is a method for forming a differential thickness pipe by the fifth method or the sixth method using a mother tube having, at its base end portion, a portion having an outer diameter smaller than the outer diameter of the mother tube and an inner diameter equal to or larger than the inner diameter of the mother tube. Specifically, the seventh method is a method for extrusion molding a differential thickness pipe by the fifth method or the sixth method described above, in which the eleventh to thirteenth steps are performed using a mother tube further having, at its base end portion, an eleventh thin-wall portion which is a portion having a 21st outer diameter which is a predetermined outer diameter smaller than the 11th outer diameter which is the outer diameter of the mother tube, a 21st inner diameter which is a predetermined inner diameter equal to or larger than the 11th inner diameter which is the inner diameter of the mother tube, and a 16th thickness which is a predetermined thickness smaller than the 11th thickness which is the wall thickness of the mother tube.

[0168] The sleeve used in the seventh method includes a housing portion which is a space that opens at the end face on the tip side and has a shape corresponding to the eleventh thin-walled portion. In the seventh method, in a state where the eleventh thin-walled portion of the base pipe is housed in the housing portion of the sleeve, the twelfth step and the thirteenth step are executed, whereby the eleventh thin-walled portion is left at the end portion on the base end side of the base pipe. As a result, the differential thickness pipe formed by the seventh method further includes the eleventh thin-walled portion at the end portion on the base end side.

[0169] FIG. 20 is a schematic cross-sectional view showing an example of the configuration of the base pipe used in the seventh method and the differential thickness pipe formed from the base pipe. The base pipe 111' illustrated in FIG. 20(a) has the same configuration as the base pipes 111 illustrated in FIGS. 8(a), 13(a), and 17(a) referred to in the description regarding the fifth method and the sixth method, except that it further includes the eleventh thin-walled portion PST11 at the end portion on the base end side. The eleventh thin-walled portion PST11 has a twenty-first outer diameter DO21 (DO21 < DO11) which is smaller than the eleventh outer diameter DO11 which is the outer diameter of the base pipe 111', a twenty-first inner diameter DI21 (DI21 ≧ DI11. However, in FIG. 20, DI21 = DI11) which is an inner diameter equal to or greater than the eleventh inner diameter DI11 which is the inner diameter of the base pipe 111', and a sixteenth wall thickness T16 (T16 < T11) which is a predetermined wall thickness smaller than the eleventh wall thickness T11 which is the wall thickness of the base pipe 111'. Further, as shown in FIG. 20(b), the differential thickness pipe 121' formed by the seventh method has the same configuration as the differential thickness pipe 121 illustrated in FIG. 8(b) referred to in the description regarding the fifth method, except that it further includes the eleventh thin-walled portion PST11 at the end portion on the base end side.

[0170] Fig. 21 is a schematic cross-sectional view showing an example of the configuration of a mandrel, a sleeve, and a container used in the seventh method. Fig. 21(a) is a schematic cross-sectional view showing an example of the configuration of a mandrel and a sleeve used in the seventh method. As shown in Fig. 21(a), the mandrel 131 used in the seventh method includes a basic outer diameter region RBDO which is a cylindrical region formed on the tip side and has a 14th outer diameter DO14 which is an outer diameter corresponding to an 11th inner diameter DI11 which is the inner diameter of the mother tube 111', similar to the mandrel 131 illustrated in Fig. 9(a) referred to in the description of the first method.

[0171] The sleeve 141' used in the seventh method has a configuration similar to that of the sleeve 141 illustrated in Figures 9(a), 14(a), and 18(a) respectively referenced in the explanations of the fifth and sixth methods, except that it has a storage portion PC which is a space that opens to the end face on the tip side and has a shape corresponding to the eleventh thin-walled portion PST11.

[0172] Next, Fig. 21(b) is a schematic cross-sectional view showing an example of the configuration of a container used in the seventh method. The container hole 151a formed in the container 151 shown in Fig. 21(b) includes an eleventh large inner diameter region RLDI11, an eleventh small inner diameter region RSDI11, and an eleventh inner diameter decreasing region RsDI11, similar to the container hole 151a formed in the container 151 shown in Fig. 9(b), Fig. 14(b), and Fig. 18(b) respectively, which are referred to in the description of the fifth and sixth methods. The details of each region of the container hole 151a have already been described in the description of the fifth method, so a description thereof will be omitted here.

[0173] In the seventh method, the above-mentioned blank tube 111', mandrel 131, sleeve 141', and container 151 are used to carry out the 11th to 13th steps similar to those of the fifth method. In a state where the mandrel 131 is inserted into the internal space of the blank tube 111' from the base end side (upper side in the drawing), the base end side end of the blank tube 111' is pressed by the 11th pressing region RP11 of the sleeve 141' to push the blank tube 111' into the container hole 151a, thereby forming the above-mentioned differential thickness pipe 121'. As described above, in the seventh method, the 12th and 13th steps are carried out in a state where the 11th thin-walled portion PST11 of the blank tube 111' is accommodated in the accommodation portion PC of the sleeve 141'. As a result, the 11th thin-walled portion PST11 is left at the base end side end of the blank tube 111'. As a result, the differential thickness pipe 121' formed by the seventh method further includes an eleventh thin-wall portion PST11 at the end on the base end side.

[0174] Fig. 22 is a schematic cross-sectional view showing an example of changes in the positional relationship and shape of the blank tube, mandrel, sleeve, container, and differential thickness pipe as the seventh method progresses. In Fig. 22, the reference symbols attached to the respective parts shown in Fig. 20 and Fig. 21 are omitted in order to simplify the drawing. However, in the following explanation of Fig. 22, the reference symbols shown in Fig. 20 and Fig. 21 are used for accuracy, so please refer to Fig. 20 and Fig. 21 as necessary.

[0175] 22 shows a state in which, as a result of execution of the 11th step, the blank tube 111' having the 11th thin-walled portion PST11 at its base end is set at a predetermined position inside the container hole 151a, the mandrel 131 is inserted into the blank tube 111', and the 11th thin-walled portion PST11 is received in the receiving portion PC of the sleeve 141'. In this state, the 12th step is started, and the base end of the blank tube 111' is pressed by the sleeve 141'. As a result, the material constituting the blank tube 111' plastically flows and fills the space between the container 151 and the mandrel 131 in the 11th large inner diameter region RLDI11 and the 11th inner diameter reduced region RsDI11 of the container hole 151a, thereby maintaining the inner diameter of the blank tube 111' at the 11th inner diameter DI11 while expanding the outer diameter of the blank tube 111' from the 11th outer diameter DO11 to the 13th outer diameter DO13.

[0176] In the 13th step, the base end side of the blank tube 111' is further pressed by the sleeve 141', and the tip end side of the blank tube 111' is forced into the 11th small inner diameter area RSDI11 of the container hole 151a to reduce the diameter. As a result, the outer diameter of the tip end portion of the blank tube 111' is reduced from the 11th outer diameter DO11 to the 12th outer diameter DO12. The right side of the central axis AX in FIG. 22 shows a state in which the 13th step is completed and a desired differential thickness pipe 121' is formed. As illustrated in FIG. 22, according to the seventh method, a differential thickness pipe 121' having the 11th thin-walled portion PST11 at its base end can be easily and reliably formed from a blank tube 111' having the 11th thin-walled portion PST11 at its base end.

[0177] In the differential thickness pipe 121' illustrated in Fig. 22, the thickness (16th thickness T16) of the eleventh thin portion PST11 formed at the end on the base end side and the thickness (12th thickness T12) of the eleventh small outer diameter region RSDO11 formed at the end on the tip end side appear to be substantially equal, but the 16th thickness T16 and the 12th thickness T12 may be the same or different, and both can be appropriately designed depending on the application of the differential thickness pipe 121'. Also, the inner diameter of the differential thickness pipe 121' illustrated in Fig. 22 is constant throughout the eleventh small outer diameter region RSDO11, the eleventh increased outer diameter region ReDO11, the eleventh large outer diameter region RLDO11, and the eleventh thin portion PST11, which is the same as the eleventh inner diameter DI11, which is the inner diameter of the blank tube 111'. However, for example, the seventh method may be applied to the sixth method described above to form a plurality of regions with different inner diameters in the differential thickness pipe 121'. Alternatively, as described with reference to Fig. 7 in relation to the first method according to another modified example, the large inner diameter region and / or the small inner diameter region of the container hole may be multi-staged to form a plurality of regions with different outer diameters in the differential thickness pipe 121'.

[0178] Fig. 23 is a schematic cross-sectional view showing an example of the change in the positional relationship and shape of the blank pipe, mandrel, sleeve, container, and differential thickness pipe with the progress of the process when the seventh method is applied to the sixth method according to the second embodiment described above. The states shown on the left and right sides of the central axis AX in Fig. 23 are similar to the states shown on the left and right sides of the central axis AX in Fig. 22, respectively, and therefore will not be described here. In the differential thickness pipe 121' shown in Fig. 23, by applying the seventh method to the sixth method according to the second embodiment, the inner diameter of the range from the eleventh large outer diameter region RLDO11 of the differential thickness pipe 121' to the end on the tip side is reduced by thickening.

[0179] Fig. 24 is a schematic front view showing the appearance of the blank tube 111' and the differential thickness pipe 121' illustrated in Fig. 23. By the seventh method illustrated in Fig. 23, it is possible to form a differential thickness pipe 121' having an eleventh thin-wall portion PST11 at the end on the base end side as illustrated in Fig. 24(b) from an eleventh blank tube 111' having an eleventh thin-wall portion PST11 at the end on the base end side as illustrated in Fig. 24(a). In the differential thickness pipe 121' illustrated in Figs. 23 and 24, the eleventh large outer diameter region RLDO11 has a short axial length and has a flange-like shape.

[0180] Fig. 25 is a cross-sectional view of a portion surrounded by a thick dashed line in Fig. 24. Fig. 25(a) is a cross-sectional view of the blank tube 111' illustrated in Fig. 24(a), and Fig. 25(b) is a cross-sectional view of the variable thickness pipe 121' illustrated in Fig. 24(b). As described above, in the seventh method, the twelfth and thirteenth steps are performed in a state in which the eleventh thin-walled portion PST11 of the blank tube 111' is accommodated in the accommodation portion PC of the sleeve 141'. As a result, the eleventh thin-walled portion PST11 is maintained at the end on the base end side in the variable thickness pipe 121' as well.

[0181] As described above, in the example shown in FIG. 23, by applying the seventh method to the sixth method according to the second embodiment, the inner diameter of the range from the eleventh large outer diameter region RLDO11 of the differential thickness pipe 121' to the tip end is reduced by thickening. Therefore, as illustrated in FIG. 25(b), in the eleventh large outer diameter region RLDO11 of the differential thickness pipe 121', the outer diameter is enlarged by thickening outward, and the inner diameter is reduced by thickening inward, so that the wall thickness is significantly increased. In addition, in the eleventh small outer diameter region RSDO11 located on the tip side of the eleventh large outer diameter region RLDO11 of the differential thickness pipe 121', the outer diameter is reduced by the extrusion process performed in the third step, and the inner diameter is reduced by thickening inward, so that the wall thickness is thicker than that of the blank tube 111'. In this way, according to the forming method of the differential thickness pipe according to the present invention, including the fifth to seventh methods, it is possible to form a differential thickness pipe having a wide variety of configurations.

[0182] <effect> As described above, in the seventh method, the eleventh to thirteenth steps are performed using a mother tube further including an eleventh thin-walled portion at its base end, the eleventh outer diameter being a predetermined outer diameter smaller than the eleventh outer diameter, the 21st inner diameter being a predetermined inner diameter equal to or larger than the eleventh inner diameter, the inner diameter of the mother tube, and the sixteenth thickness being a predetermined thickness smaller than the eleventh thickness, the thickness of the mother tube. The sleeve used in the seventh method includes a receiving portion which is a space that opens at the end face at the tip end and has a shape corresponding to the eleventh thin-walled portion. Therefore, in the seventh method, the twelfth and thirteenth steps are performed in a state in which the eleventh thin-walled portion of the mother tube is received in the receiving portion of the sleeve, so that the eleventh thin-walled portion remains at the base end of the mother tube. As a result, the seventh method makes it possible to easily and reliably form a differential thickness pipe further including an eleventh thin-walled portion at its base end.

[0183] Eighth Embodiment Next, a method for extrusion molding a differential thickness pipe according to an eighth embodiment of the present invention (hereinafter, sometimes referred to as the "eighth method") will be described.

[0184] As mentioned above, the shape of the base tube used in the extrusion molding methods for differential thickness pipes according to the fifth and sixth embodiments of the present invention (Fifth Method and Sixth Method) is not necessarily limited to a simple cylindrical shape as illustrated in Figures 8, 13, 17, etc., and for example, a portion having a different structure may be provided at the tip and / or base end of the base tube, as long as it does not interfere with the execution of the fifth and sixth methods.

[0185] Furthermore, as described above, the shape of the mother tube used in the extrusion molding method for a differential thickness pipe according to the first embodiment of the present invention (first method) is also not necessarily limited to the simple cylindrical shape as exemplified in Fig. 2, and for example, a portion having a different structure may be provided at the end on the tip side of the mother tube, as long as it does not interfere with the execution of the first method. By molding a differential thickness pipe from such a mother tube, the structure provided at the end on the tip side and / or base side of the mother tube can be incorporated into the differential thickness pipe.

[0186] <composition> Therefore, the eighth method is a method of forming a differential thickness pipe by any one of the first, second, and fifth to seventh methods using a blank tube having a portion at its tip end that has an outer diameter smaller than the smallest inner diameter of the container hole and an inner diameter equal to or larger than the inner diameter of the blank tube. Or the second method The 22nd outer diameter is a predetermined outer diameter equal to or smaller than the outer diameter corresponding to the smallest inner diameter of the container hole, and the 23rd outer diameter is an inner diameter of the blank tube. No. 1 The second inner diameter is equal to or larger than the inner diameter of the raw pipe, and the second inner diameter is equal to or larger than the inner diameter of the raw pipe. No. 1 A blank tube is further provided at the end on the tip side with a 12th thin-walled portion having a 17th wall thickness smaller than the wall thickness of the blank tube. No. 1 From the process Third This is a method for extrusion molding a pipe with different thicknesses, in which steps are carried out. Alternatively, the eighth method is any of the fifth to seventh methods described above, in which the eleventh to thirteenth steps are carried out using a mother tube which further has, at its tip end, a 12th thin-walled portion which has a 22nd outer diameter which is a predetermined outer diameter equal to or smaller than an outer diameter corresponding to the smallest inner diameter of a container hole, a 22nd inner diameter which is a predetermined inner diameter equal to or larger than the 11th inner diameter which is the inner diameter of the mother tube, and a 17th thickness which is a predetermined thickness smaller than the 11th thickness which is the wall thickness of the mother tube.

[0187] In the eighth method, when the twelfth thin-walled portion of the blank tube at the tip end satisfies the above-mentioned requirements, the mandrel, sleeve, and container can be used to manufacture the blank tube without requiring any particular configuration change. Step 1 to Step 3 or By carrying out the 11th to 13th steps, a differential thickness pipe further including a 12th thin-walled portion at the end on the tip side can be formed.

[0188] Figure 26 shows According to the fifth method described aboveFIG. 0 is a schematic cross-sectional view showing an example of the configuration of a raw pipe used in the eighth method and a differential thickness pipe formed from the raw pipe. The raw pipe 111” illustrated in FIG. 26(a) has the same configuration as the raw pipes 111 illustrated in FIGS. 8(a), 13(a), and 17(a) referred to in the descriptions regarding the fifth and sixth methods, except that it further includes a twelfth thin-walled portion PST12 at the end on the tip side. The twelfth thin-walled portion PST12 has a twenty-second outer diameter DO22 (DO22 ≦ DI17), which is a predetermined outer diameter equal to or less than the outer diameter corresponding to the minimum inner diameter (e.g., the seventeenth inner diameter DI17) in the container hole 151a, a twenty-second inner diameter DI22 (DI22 ≧ DI11. However, in FIG. 26, DI22 = DI11), which is an inner diameter equal to or greater than the eleventh inner diameter DI11, which is the inner diameter of the raw pipe 111”, and a seventeenth wall thickness T17 (T17 < T11), which is a predetermined wall thickness smaller than the eleventh wall thickness T11, which is the wall thickness of the raw pipe 111”. Further, as shown in FIG. 26(b), the differential thickness pipe 121” formed by the eighth method has the same configuration as the differential thickness pipe 121 illustrated in FIG. 8(b) referred to in the description regarding the fifth method, except that it further includes the twelfth thin-walled portion PST12 at the end on the tip side.

[0189] On the other hand, regarding the mandrel, sleeve, and container used in the eighth method, as described above, they can be used in the eighth method using the raw pipe 111” having the above-described configuration without any particular configuration change. Therefore, in the eighth method, for example, a mandrel 131, a sleeve 141, and a container 151 as illustrated in FIG. 9 referred to in the description regarding the fifth method can be used. Therefore, the descriptions of the mandrel, sleeve, and container used in the eighth method are omitted here.

[0190] In the eighth method, the above-mentioned blank tube 111", mandrel 131, sleeve 141 and container 151 are used to carry out the 11th to 13th steps similar to the fifth method, whereby, with the mandrel 131 inserted into the internal space of the blank tube 111" from the base end side (top side in the drawing), the base end side end of the blank tube 111" is pressed by the 11th pressing region RP11 of the sleeve 141 to force the blank tube 111" into the container hole 151a, thereby forming the above-mentioned differential thickness pipe 121". In other words, the differential thickness pipe 121" formed by the eighth method further includes a 12th thin-walled portion PST12 at the tip side end.

[0191] Fig. 27 is a schematic cross-sectional view showing an example of changes in the positional relationship and shape of the blank tube, mandrel, sleeve, container, and differential thickness pipe as the eighth method progresses. In Fig. 27, the reference symbols attached to the respective parts shown in Fig. 26, Fig. 9, etc. are omitted in order to simplify the drawing. However, in the following explanation of Fig. 27, the reference symbols shown in Fig. 26, Fig. 9, etc. are used for accuracy, so please refer to Fig. 26, Fig. 9, etc. as necessary.

[0192] The left side of the central axis AX in Figure 27 shows a state in which, as a result of performing the 11th step, a blank tube 111″ having a 12th thin-wall portion PST12 at its tip end is set at a predetermined position inside the container bore 151a, and the mandrel 131 is inserted into the blank tube 111′. In this state, the 12th step is started, and the base end of the blank tube 111″ is pressed by the sleeve 141. As a result, the material constituting the blank tube 111″ plastically flows and fills the space between the container 151 and the mandrel 131 in the 11th large inner diameter region RLDO11 and the 11th inner diameter reduced region RsDI11 of the container bore 151a. As a result, the inner diameter of the blank tube 111″ is maintained at the 11th inner diameter DI11, while the outer diameter of the blank tube 111″ is expanded from the 11th outer diameter DO11 to the 13th outer diameter DO13.

[0193] Then, in the 13th step, the base end side of the mother tube 111" is further pressed by the sleeve 141, and the tip side of the mother tube 111" is forced into the 11th small inner diameter region RSDI11 of the container hole 151a to reduce its diameter. As a result, the outer diameter of the tip side portion of the mother tube 111" is reduced from the 11th outer diameter DO11 to the 12th outer diameter DO12. The right side of the central axis AX in Figure 27 shows the state after the 13th step is completed and the desired differential thickness pipe 121" is formed. As illustrated in Figure 27, according to the eighth method, a differential thickness pipe 121" having the 12th thin-wall portion PST12 at its tip side end can be easily and reliably formed from a mother tube 111" having the 12th thin-wall portion PST12 at its tip side end.

[0194] The inner diameter of the differential thickness pipe 121" illustrated in Figure 27 is constant throughout the 12th thin-wall portion PST12, the 11th small outer diameter region RSDO11, the 11th increased outer diameter region ReDO11 and the 11th large outer diameter region RLDO11, and is the same as the 11th inner diameter DI11, which is the inner diameter of the blank tube 111". However, for example, the 8th method may be applied to the 6th method described above to form multiple regions with different inner diameters in the differential thickness pipe 121". Alternatively, as explained with reference to Figure 7 in relation to the 1st method related to another modified example, the large inner diameter region and / or the small inner diameter region of the container hole may be made multi-staged to form multiple regions with different outer diameters in the differential thickness pipe 121".

[0195] <effect> As described above, in the eighth method, the 22nd outer diameter, which is a predetermined outer diameter equal to or smaller than the outer diameter corresponding to the minimum inner diameter of the container hole, More than the inner diameter The specified inner diameter is the 22nd inner diameter and the blank tube More than thick A blank tube is used, which further includes a 12th thin-walled portion at the end on the tip side, the 17th thin-walled portion being a portion having a small predetermined wall thickness. Step 1 to Step 3 or In the eighth method, when the 12th thin-walled portion provided at the tip end of the blank tube satisfies the above-mentioned requirements, the blank tube can be used to manufacture a sintered product without requiring any particular configuration change for the mandrel, sleeve, and container. Step 1 to Step 3 orThe 12th thin-wall portion remains at the end portion near the tip of the mother pipe even when steps 11 to 13 are performed. As a result, according to the eighth method, a differential thickness pipe further including the 12th thin-wall portion at the end portion near the tip can be easily and reliably formed.

[0196] Ninth Embodiment As described at the beginning of this specification, the present invention relates not only to the method for extruding a pipe having different thicknesses, including the fifth method to the eighth method described above, but also to an extrusion molding device for a pipe having different thicknesses. Therefore, the extrusion molding device for a pipe having different thicknesses according to various embodiments of the present invention will be described below.

[0197] First, an extrusion molding apparatus for a differential thickness pipe according to a ninth embodiment of the present invention (hereinafter, sometimes referred to as a "ninth apparatus") will be described.

[0198] <composition> The ninth apparatus is an extrusion molding apparatus for a differential thickness pipe, the extrusion molding apparatus comprising a mandrel which is a core metal having a predetermined shape, a sleeve which is a cylindrical member arranged coaxially around the outside of the mandrel, a container which is a die in which a container hole which is a through hole having a predetermined shape is formed, and a drive mechanism configured to push at least the sleeve into the container hole. The ninth apparatus is configured to mold a differential thickness pipe having a predetermined shape by pushing a blank tube having a predetermined shape into the container hole with the sleeve.

[0199] The configurations of the mother tube, mandrel, sleeve and container have already been described in detail with reference to Figs. 8 to 12 in the explanation of the fifth method, so a detailed explanation will be omitted here.

[0200] Furthermore, the ninth device is configured to mold a differential thickness pipe by executing steps 11, 12, and 13. Steps 11 to 13 have already been described in detail in the explanation of the fifth method, so the explanation will be omitted here.

[0201] The ninth device is further configured so that, at an eleventh time point when the twelfth step is started, the distal end of the mandrel reaches an eleventh position which is the same position in the pushing direction as the base end of the eleventh small inner diameter region of the container hole, or reaches a position further distal than the eleventh position. In addition, the ninth device is further configured so that, at a twelfth time point when the thirteenth step is started, the distal end of the mandrel reaches a twelfth position which is a predetermined distance further distal than the base end of the eleventh small inner diameter region of the container hole, or reaches a position further distal than the twelfth position.

[0202] <effect> By carrying out the 11th to 13th steps in the 9th apparatus having the above-mentioned configuration, the 11th large outer diameter region is formed by increasing the thickness of the mother tube, and the 11th small outer diameter region is formed by decreasing the thickness of the mother tube. Therefore, a larger diameter difference can be achieved with a smaller processing load than when the large outer diameter region is formed while maintaining the outer diameter of the mother tube and the small outer diameter region is formed by significantly reducing the outer diameter of the mother tube. Furthermore, according to the 9th apparatus, since the wall thickness of the large outer diameter region can be increased, it is possible to form a differential thickness pipe suitable for applications requiring high mechanical strength in the large diameter portion, for example.

[0203] In addition, the axial lengths of the 11th large outer diameter region and the 11th small outer diameter region vary depending on the axial length of the mother tube, the amount of diameter expansion in the 12th step, the amount of diameter reduction in the 13th step, and the amount of pushing the mother tube by the sleeve. That is, according to the 9th apparatus, the axial lengths of the 11th large outer diameter region and the 11th small outer diameter region of the differential thickness pipe can be set as desired.

[0204] Tenth Embodiment Next, an extrusion molding apparatus for a differential thickness pipe according to a tenth embodiment of the present invention (hereinafter, may be referred to as "tenth apparatus") will be described.

[0205] <composition> The tenth apparatus is the ninth apparatus described above, and is configured to form a differential thickness pipe having a twelfth small outer diameter region on the tip side of the eleventh small outer diameter region by carrying out the sixth method described above. The tip end of the differential thickness pipe formed by the tenth apparatus is formed with a twelfth small outer diameter region having a 16th outer diameter equal to the 12th outer diameter, an 18th inner diameter which is a predetermined inner diameter smaller than the 12th inner diameter, and a 14th thickness which is a predetermined thickness larger than the 12th thickness.

[0206] In order to form the 12th smaller outer diameter region as described above, the mandrel provided in the 10th apparatus further includes a 13th smaller outer diameter region and a 12th increasing outer diameter region. The 13th smaller outer diameter region is a cylindrical region formed on the tip side of the basic outer diameter region and having an 18th outer diameter that is an outer diameter corresponding to the 18th inner diameter. The 12th increasing outer diameter region is formed between the 13th smaller outer diameter region and the basic outer diameter region and has an outer diameter that increases from the 18th outer diameter to the 14th outer diameter as it approaches the basic outer diameter region from the 13th smaller outer diameter region.

[0207] Furthermore, the tenth device is configured such that, at a twelfth point in time, the base end side end of the thirteenth smaller outer diameter region is located closer to the base end side than the eleventh position.

[0208] The tenth device may be configured to carry out the sixth method according to the first aspect described above. In this case, the tenth device is configured so that the tip end of the basic outer diameter region is located further tip-side than the eleventh position at a thirteenth time point, which is the time point when the thirteenth step is completed.

[0209] The differential thickness pipe formed by carrying out the sixth method according to the first aspect in the tenth device includes an eleventh large outer diameter region, an eleventh increasing outer diameter region, an eleventh small outer diameter region, a twelfth small outer diameter region formed on the tip side of the eleventh small outer diameter region, and an eleventh increasing inner diameter region. The eleventh increasing inner diameter region is formed between the eleventh small outer diameter region and the eleventh small outer diameter region, and is a region in which the inner diameter increases from the 18th inner diameter to the 12th inner diameter as it approaches the eleventh small outer diameter region, the wall thickness decreases from the 14th thickness to the 12th thickness, and the outer diameter is constant at a 17th outer diameter equal to the 12th outer diameter.

[0210] The tenth apparatus may be configured to carry out the sixth method according to the second aspect described above, in which the tenth apparatus is configured such that the base end of the thirteenth small outer diameter region is located more base end than the eleventh position at a thirteenth time point, which is the time point when the thirteenth step is completed.

[0211] The differential thickness pipe formed by carrying out the sixth method according to the second embodiment in the tenth device includes a twelfth small outer diameter region, an eleventh large outer diameter region, a twelfth large outer diameter region, a thirteenth increasing outer diameter region, and a twelfth increasing inner diameter region. The twelfth large outer diameter region is a region formed between the twelfth small outer diameter region and the eleventh large outer diameter region, and has a 19th outer diameter that is an outer diameter equal to the 13th outer diameter, a 19th inner diameter that is an inner diameter equal to the 18th inner diameter, and a 15th wall thickness that is a predetermined thickness greater than the 13th wall thickness. The 13th increasing outer diameter region is formed between the 12th smaller outer diameter region and the 12th larger outer diameter region, and has an outer diameter increasing from the 16th outer diameter to the 19th outer diameter as it approaches the 12th larger outer diameter region, and a wall thickness increasing from the 14th wall thickness to the 15th wall thickness, and an inner diameter constant at a 20th inner diameter equal to the 18th inner diameter. The 12th increasing inner diameter region is formed between the 12th larger outer diameter region and the 11th larger outer diameter region, and has an inner diameter increasing from the 19th inner diameter to the 13th inner diameter as it approaches the 12th larger outer diameter region, and a wall thickness decreasing from the 15th wall thickness to the 13th wall thickness, and an outer diameter constant at a 20th outer diameter equal to the 13th outer diameter.

[0212] Details of the sixth method performed in the tenth apparatus and the differential thickness pipe formed by performing the sixth method in the tenth apparatus have already been described in detail with reference to Figures 13 to 19 in the explanation of the sixth method, so further explanation will be omitted here.

[0213] <effect> As described above, according to the tenth apparatus, by appropriately adjusting the size and / or length of the twelfth smaller outer diameter region, which is a portion formed on the tip side of the mandrel that is narrower than the inner diameter of the mother tube, and the position of the mandrel at the time when the thirteenth step is completed, it is possible to change the range in which the inner diameter is reduced by wall thickness increase in the differential thickness pipe formed by carrying out the sixth method in the tenth apparatus. Therefore, for example, the structure of the differential thickness pipe, such as its shape and wall thickness distribution, can be designed with a high degree of freedom according to the application.

[0214] Eleventh Embodiment Next, an extrusion molding apparatus for a differential thickness pipe according to an eleventh embodiment of the present invention (hereinafter, sometimes referred to as "eleventh apparatus") will be described.

[0215] <composition> The 11th apparatus is the 9th or 10th apparatus described above, and is configured to mold a differential thickness pipe having an 11th thin-walled portion at its base end from a blank tube having an 11th thin-walled portion having a predetermined shape at its base end by executing the 7th method described above.

[0216] The 11th apparatus is the 9th or 10th apparatus described above, and is configured to perform the 11th to 13th steps using a blank tube further including an 11th thin-walled portion at an end portion on the base end side. The 11th thin-walled portion is a portion having a 21st outer diameter which is a predetermined outer diameter smaller than the 11th outer diameter, a 21st inner diameter which is a predetermined inner diameter equal to or larger than the 11th inner diameter, and a 16th thickness which is a predetermined thickness smaller than the 11th thickness.

[0217] The sleeve provided in the 11th device has a receiving portion that is a space that opens to an end face on the tip side and has a shape corresponding to the 11th thin-walled portion. Furthermore, the 11th device is configured to perform the 12th and 13th steps in a state in which the 11th thin-walled portion is received in the receiving portion of the sleeve. This leaves the 11th thin-walled portion at the end on the base end side of the blank tube. As a result, the differential thickness pipe formed by the 11th device further includes the 11th thin-walled portion at the end on the base end side.

[0218] Details of the seventh method performed in the 11th apparatus and the differential thickness pipe formed by performing the seventh method in the 11th apparatus have already been described in detail with reference to Figures 20 to 25 in the explanation of the seventh method, so they will not be explained here.

[0219] <effect> As described above, in the 11th device, the 11th to 13th steps are performed using a blank tube further including an 11th thin-walled portion at its base end, the 21st outer diameter being a predetermined outer diameter smaller than the 11th outer diameter being the outer diameter of the blank tube, the 21st inner diameter being a predetermined inner diameter equal to or larger than the 11th inner diameter being the inner diameter of the blank tube, and the 16th thickness being a predetermined thickness smaller than the 11th thickness being the wall thickness of the blank tube. The sleeve included in the 11th device has a receiving portion which is a space that opens at the end face at the tip end and has a shape corresponding to the 11th thin-walled portion. Therefore, in the 11th device, the 12th and 13th steps are performed in a state in which the 11th thin-walled portion of the blank tube is received in the receiving portion of the sleeve, so that the 11th thin-walled portion remains at the base end of the blank tube. As a result, the 11th device can easily and reliably form a differential thickness pipe further including an 11th thin-walled portion at its base end.

[0220] Twelfth Embodiment Next, an extrusion molding apparatus for a differential thickness pipe according to a twelfth embodiment of the present invention (hereinafter, may be referred to as a "twelfth apparatus") will be described.

[0221] <composition> The 12th apparatus is any of the above-mentioned third apparatus, fourth apparatus, ninth apparatus and tenth apparatus, and is configured to form a differential thickness pipe having a 12th thin-walled portion at its tip end from a blank tube having a 12th thin-walled portion having a predetermined shape at its tip end by executing the above-mentioned eighth method.

[0222] In the 12th apparatus related to the above-mentioned 3rd apparatus or 4th apparatus, the 12th thin-walled portion is a portion having a 22nd outer diameter which is a predetermined outer diameter equal to or smaller than an outer diameter corresponding to the smallest inner diameter of the container hole, a 22nd inner diameter which is a predetermined inner diameter equal to or larger than the first inner diameter, and a 17th thickness which is a predetermined thickness smaller than the first thickness. The 12th apparatus is configured to carry out the 1st to 3rd steps by using a blank tube further comprising a 12th thin-walled portion at an end portion on the tip side. Meanwhile, in the 12th apparatus related to the above-mentioned 9th apparatus or 10th apparatus, The 12th thin-walled portion is a portion having a 22nd outer diameter, which is a predetermined outer diameter equal to or smaller than the outer diameter corresponding to the smallest inner diameter of the container hole, a 22nd inner diameter, which is a predetermined inner diameter equal to or larger than the 11th inner diameter, and a 17th thickness, which is a predetermined thickness smaller than the 11th thickness. The The 12th device is , No. The apparatus is configured to execute steps 11 to 13 using a blank tube further having a thin-walled portion at its tip end. As a result, the differential thickness pipe formed by the apparatus 12 further includes a thin-walled portion at its tip end.

[0223] Details of the 8th method performed in the 12th apparatus and the differential thickness pipe formed by performing the 8th method in the 12th apparatus have already been described in detail in the explanation of the 8th method with reference to Figures 26 and 27, so they will not be explained here.

[0224] <effect> As described above, in the 12th device, the 22nd outer diameter is a predetermined outer diameter equal to or smaller than the outer diameter corresponding to the minimum inner diameter of the container hole, and the 23rd outer diameter is a predetermined outer diameter equal to or smaller than the outer diameter corresponding to the minimum inner diameter of the container hole. More than the inner diameter The specified inner diameter is the 22nd inner diameter and the blank tube More than thick A blank tube is used, which further includes a 12th thin-walled portion at the end on the tip side, the 17th thin-walled portion being a portion having a small predetermined wall thickness. Step 1 to Step 3 or Steps 11 to 13 are carried out. In the case where the 12th thin-walled portion of the blank tube at the tip side of the blank tube satisfies the above-mentioned requirements, the blank tube can be used for the manufacturing process without requiring any particular configuration change for the mandrel, sleeve, and container. Step 1 to Step 3 orThe 12th thin-walled portion remains at the tip end of the mother pipe even when steps 11 to 13 are performed, and as a result, the 12th device makes it possible to easily and reliably form a differential thickness pipe that further includes the 12th thin-walled portion at the tip end.

[0225] For the purpose of explaining the present invention, several embodiments and modifications having specific configurations have been described above, sometimes with reference to the attached drawings. However, the scope of the present invention should not be construed as being limited to these exemplary embodiments and modifications, and it goes without saying that appropriate modifications can be made within the scope of the claims and the matters described in the specification. [Explanation of symbols]

[0226] 11…Plain tube DO1…1st outer diameter DI1…First inner diameter T1…First thickness 21, 21', 21"…Different thickness pipes RSD1…1st small diameter area DO2…2nd outer diameter DI2…Second inner diameter T2…Second wall thickness RSD2…Second small diameter area DO3…3rd outer diameter DI3…Third inner diameter T3…Third wall thickness PSD1, PSD2... parts (multi-stage second small diameter area RSD2) PtDI...Tapered section (multi-stage second small diameter region RSD2) RLD…Large diameter area DO4…4th outer diameter DI4…4th inner diameter T4…4th wall thickness RtDI1…First taper region RtDI2: Second taper region 31,31'...Mandrel RSC…Small cross-sectional area DO5…5th outer diameter RLC…Large cross-sectional area DO6…6th outer diameter ReC: Cross-sectional expansion area 41...Sleeve RP: Pressing area DO7…7th outer diameter DI5…5th inner diameter 51,51'...Container 51a, 51a'...container hole RLDI: Large inner diameter area DI6…6th inner diameter RSDI…Small inner diameter area DI7…7th inner diameter RsDI…Inner diameter reduction area 111, 111', 111"...Plain tube DO11…11th outer diameter DI11…11th inner diameter T11…11th thickness PST11...11th thin section DO21…21st outer diameter DI21…21st inner diameter T16…16th wall thickness PST12…12th thin section DO22…22nd outer diameter DI22…22nd inner diameter T17…17th thickness 121, 121', 121"...Different thickness pipes RSDO11...11th small outer diameter area DO12…12th outer diameter DI12…12th inner diameter T12…12th thickness RSDO12,RSDO12'...12th small outer diameter area DO16…16th outer diameter DI18…18th inner diameter T14, T14'...14th thickness RLDO11…11th large outer diameter area DO13…13th outer diameter DI13…13th inner diameter T13…13th wall thickness RLDO12…12th large outer diameter area DO19…19th outer diameter DI19…19th inner diameter T15…15th wall thickness ReDO11: 11th outer diameter increase region DI14…14th inner diameter ReDO13: 13th outer diameter increase region DI20…20th inner diameter ReDi11: 11th inner diameter increase region DO17…17th outer diameter ReDi12: 12th inner diameter increase region DO20…20th outer diameter 131…Mandrel RBDO…Basic outer diameter area DO14…14th outer diameter RSDO13,RSDO13'...13th small outer diameter area DO18…18th outer diameter ReDO12: 12th outer diameter increase region 141,141'...Sleeve RP11: 11th pressing area DO15…15th outer diameter DI15…15th inner diameter PC…Containment section 151…Container 151a…Container hole RLDI11: 11th large inner diameter area DI16…16th inner diameter RSDI11…11th small inner diameter area DI17…17th inner diameter RsDI11…11th inner diameter reduction area

Claims

1. An extrusion molding apparatus comprising: a mandrel which is a core metal having a predetermined shape; a sleeve which is a cylindrical member arranged coaxially around the outside of the mandrel; a container which is a die having a container hole which is a through hole having a predetermined shape; and a drive mechanism configured to push the mandrel and the sleeve into the container hole, a first step of setting a blank tube having a predetermined shape at a predetermined position inside the container hole; a second step of pushing the mandrel into the mother tube by the driving mechanism to expand a diameter of a base end side of the mother tube, the base end side being an upstream side in an extrusion direction of the mother tube; a third step of pressing the base end side end of the mother tube with the sleeve after a first time point at which the second step is started, thereby forcing the mother tube into a tip side, which is downstream in the extrusion direction of the container hole, thereby reducing the diameter of the tip side of the mother tube; A method for extruding a pipe having a different thickness, comprising: the blank tube is a cylindrical member having a first outer diameter that is a predetermined outer diameter, a first inner diameter that is a predetermined inner diameter, and a first wall thickness that is a predetermined wall thickness, The differential thickness pipe includes, in order from the tip side to the base end side, a first small diameter region having a second outer diameter that is a predetermined outer diameter smaller than the first outer diameter, a second inner diameter that is an inner diameter equal to the first inner diameter, and a second thickness that is a predetermined thickness smaller than the first thickness, a second small diameter region having a third outer diameter that is an outer diameter equal to the second outer diameter and a third thickness that is a predetermined thickness smaller than the second thickness, and a large diameter region having a fourth outer diameter that is a predetermined outer diameter larger than the first outer diameter and a fourth thickness that is a predetermined thickness, the mandrel includes: a small cross-sectional region formed on the tip end side, the first cross-sectional region being a cylindrical region having a circular cross-section with a fifth outer diameter that is an outer diameter corresponding to the second inner diameter; a large cross-sectional region formed on the base end side, the second cross-sectional region being a cylindrical region having a second cross-sectional region corresponding to a cross-section of an internal space of the second small diameter region and the large diameter region; and a cross-sectional enlarged region formed between the small cross-sectional region and the large cross-sectional region, the cross-sectional region enlarging from the first cross-sectional region to the second cross-sectional region as the small cross-sectional region approaches the large cross-sectional region; the sleeve includes a pressing region that is a cylindrical region having a columnar internal space formed on the tip side and having a seventh outer diameter that is an outer diameter equal to the fourth outer diameter and a third transverse cross section that is a transverse cross section corresponding to the second transverse cross section, the container hole includes: a large inner diameter region formed on the base end side and having a sixth inner diameter which is an inner diameter corresponding to the fourth outer diameter; a small inner diameter region formed on the tip end side and having a seventh inner diameter which is an inner diameter corresponding to the second outer diameter and the third outer diameter; and an inner diameter decreasing region formed between the large inner diameter region and the small inner diameter region and whose inner diameter decreases from the sixth inner diameter to the seventh inner diameter as the large inner diameter region approaches the small inner diameter region, at a second time point when the third step is started, the tip end of the mandrel in the extrusion direction reaches the tip end of the mother tube or reaches a tip side of the tip end of the mother tube, and the base end of the small cross-sectional area is located base side of the base end of the small inner diameter area. A method for extrusion molding of pipes with different thicknesses.

2. The method for extrusion molding a pipe having a different thickness according to claim 1, The internal space of the second small diameter region of the differential thickness pipe has a cylindrical shape having a third inner diameter that is a predetermined inner diameter larger than the first inner diameter, The internal space of the large diameter region of the differential thickness pipe has a cylindrical shape having a fourth inner diameter that is equal to the third inner diameter, the mandrel large cross-sectional region has a cylindrical shape having a sixth outer diameter corresponding to the fourth inner diameter; the enlarged cross-sectional region of the mandrel has a frusto-conical shape with an outer diameter increasing from the fifth outer diameter to the sixth outer diameter as the enlarged cross-sectional region approaches the smaller cross-sectional region; The pressing region of the sleeve has a cylindrical shape having a fifth inner diameter that is an inner diameter corresponding to the seventh outer diameter and the sixth outer diameter. A method for extrusion molding of pipes with different thicknesses.

3. The method for extrusion molding a pipe having a different thickness according to claim 1 or 2, the mandrel and the sleeve are fixed such that a distance between the tip end of the mandrel and the tip end of the sleeve in the extrusion direction is not greater than a distance between the tip end of the mandrel and the tip end of the sleeve at the second point in time. A method for extrusion molding of pipes with different thicknesses.

4. the mandrel being a core metal having a predetermined shape, the sleeve being a cylindrical member arranged coaxially around the mandrel, the container being a die having a container hole being a through hole having a predetermined shape, and a drive mechanism configured to push the mandrel and the sleeve into the container hole, a first step of setting a blank tube having a predetermined shape at a predetermined position inside the container hole; a second step of pushing the mandrel into the mother tube by the driving mechanism to expand a diameter of a base end side of the mother tube, the base end side being an upstream side in an extrusion direction of the mother tube; a third step of pressing the base end side end of the mother tube with the sleeve after a first time point at which the second step is started, thereby forcing the mother tube into a tip side, which is downstream in the extrusion direction of the container hole, thereby reducing the diameter of the tip side of the mother tube; The method is configured to form a differential thickness pipe having a predetermined shape by executing the steps. An extrusion molding device for a pipe with different thicknesses, the blank tube is a cylindrical member having a first outer diameter that is a predetermined outer diameter, a first inner diameter that is a predetermined inner diameter, and a first wall thickness that is a predetermined wall thickness, The differential thickness pipe includes, in order from the tip side to the base end side, a first small diameter region having a second outer diameter that is a predetermined outer diameter smaller than the first outer diameter, a second inner diameter that is an inner diameter equal to the first inner diameter, and a second thickness that is a predetermined thickness smaller than the first thickness, a second small diameter region having a third outer diameter that is an outer diameter equal to the second outer diameter and a third thickness that is a predetermined thickness smaller than the second thickness, and a large diameter region having a fourth outer diameter that is a predetermined outer diameter larger than the first outer diameter and a fourth thickness that is a predetermined thickness, the mandrel includes: a small cross-sectional region formed on the tip end side, the first cross-sectional region being a cylindrical region having a circular cross-section with a fifth outer diameter that is an outer diameter corresponding to the second inner diameter; a large cross-sectional region formed on the base end side, the second cross-sectional region being a cylindrical region having a second cross-sectional region corresponding to a cross-section of an internal space of the second small diameter region and the large diameter region; and a cross-sectional enlarged region formed between the small cross-sectional region and the large cross-sectional region, the cross-sectional region enlarging from the first cross-sectional region to the second cross-sectional region as the small cross-sectional region approaches the large cross-sectional region; the sleeve includes a pressing region that is a cylindrical region having a columnar internal space formed on the tip side and having a seventh outer diameter that is an outer diameter equal to the fourth outer diameter and a third transverse cross section that is a transverse cross section corresponding to the second transverse cross section, the container hole includes: a large inner diameter region formed on the base end side and having a sixth inner diameter which is an inner diameter corresponding to the fourth outer diameter; a small inner diameter region formed on the tip end side and having a seventh inner diameter which is an inner diameter corresponding to the second outer diameter and the third outer diameter; and an inner diameter decreasing region formed between the large inner diameter region and the small inner diameter region and whose inner diameter decreases from the sixth inner diameter to the seventh inner diameter as the large inner diameter region approaches the small inner diameter region, at a second time point when the third step is started, a first position, which is a position of the end of the mandrel on the tip side in the extrusion direction, is equal to a second position, which is a position of the end of the blank tube on the tip side, or is at a third position, which is a position located a predetermined distance toward the tip side from the second position. Extrusion molding equipment for pipes with different thicknesses.

5. The extrusion molding apparatus for a pipe having different thicknesses according to claim 4, The internal space of the second small diameter region of the differential thickness pipe has a cylindrical shape having a third inner diameter that is a predetermined inner diameter larger than the first inner diameter, The internal space of the large diameter region of the differential thickness pipe has a cylindrical shape having a fourth inner diameter that is equal to the third inner diameter, the mandrel large cross-sectional region has a cylindrical shape having a sixth outer diameter corresponding to the fourth inner diameter; the enlarged cross-sectional region of the mandrel has a frusto-conical shape with an outer diameter increasing from the fifth outer diameter to the sixth outer diameter as the enlarged cross-sectional region approaches the smaller cross-sectional region; the pressing region of the sleeve has a cylindrical shape having a fifth inner diameter equal to the seventh outer diameter and the third inner diameter and the fourth inner diameter; Extrusion molding equipment for pipes with different thicknesses.

6. The extrusion molding apparatus for a differential thickness pipe according to claim 4 or 5, the mandrel and the sleeve are fixed such that a distance between the tip end of the mandrel and the tip end of the sleeve in the extrusion direction is not greater than a distance between the tip end of the mandrel and the tip end of the sleeve at the second point in time. Extrusion molding equipment for pipes with different thicknesses.

7. A method for extrusion molding a differential thickness pipe having a predetermined shape, comprising: an extrusion molding apparatus including a mandrel which is a core metal having a predetermined shape; a sleeve which is a tubular member arranged coaxially around the mandrel; a container which is a die having a container hole which is a through hole having a predetermined shape; and a drive mechanism configured to press at least the sleeve into the container hole, the method comprising the steps of: forcing a blank tube having a predetermined shape into the container hole by the sleeve, the method comprising the steps of: the blank tube is a cylindrical member having an eleventh outer diameter that is a predetermined outer diameter, an eleventh inner diameter that is a predetermined inner diameter, and an eleventh wall thickness that is a predetermined wall thickness, The differential thickness pipe has an eleventh small outer diameter region formed on a tip end side, which is a downstream side in a pressing direction, which is a direction in which the blank tube is pressed into the container hole, and having a twelfth outer diameter that is a predetermined outer diameter smaller than the eleventh outer diameter, a twelfth inner diameter that is an inner diameter equal to the eleventh inner diameter, and a twelfth wall thickness that is a predetermined wall thickness smaller than the eleventh wall thickness; and a thirteenth small outer diameter region formed on a base end side, which is an upstream side in the pressing direction, and having a thirteenth outer diameter that is a predetermined outer diameter larger than the eleventh outer diameter, a twelfth inner diameter that is an inner diameter equal to the eleventh inner diameter, and a twelfth wall thickness that is a predetermined wall thickness smaller than the eleventh wall thickness. an eleventh large outer diameter region which is a region having a thirteenth inner diameter which is a small inner diameter and a thirteenth thickness which is a predetermined thickness larger than the eleventh thickness; and an eleventh increasing outer diameter region which is formed between the eleventh small outer diameter region and the eleventh large outer diameter region, and which is a region in which the outer diameter increases from the 12th outer diameter to the 13th outer diameter and the thickness increases from the 12th thickness to the 13th thickness as it approaches the eleventh small outer diameter region, and the inner diameter is constant at a fourteenth inner diameter which is equal to the eleventh inner diameter, the mandrel includes a basic outer diameter region that is a cylindrical region formed on the tip side and has a 14th outer diameter that is an outer diameter corresponding to the 11th inner diameter, the sleeve includes an eleventh pressing region that is a cylindrical region having a cylindrical internal space formed on the tip side and having a fifteenth outer diameter that is an outer diameter equal to the thirteenth outer diameter and a fifteenth inner diameter that is an inner diameter corresponding to the fourteenth outer diameter, the container hole includes: an eleventh large inner diameter region formed on the base end side and having a sixteenth inner diameter which is an inner diameter corresponding to the thirteenth outer diameter; an eleventh small inner diameter region formed on the tip end side and having a seventeenth inner diameter which is an inner diameter corresponding to the twelfth outer diameter; and an eleventh inner diameter decreasing region formed between the eleventh large inner diameter region and the eleventh small inner diameter region and having an inner diameter which decreases from the sixteenth inner diameter to the seventeenth inner diameter as the eleventh large inner diameter region approaches the eleventh small inner diameter region, The method for extrusion molding the differential thickness pipe comprises: an eleventh step of abutting the tip end of the blank tube against the eleventh inner diameter reduced region of the container hole to set the blank tube at a predetermined position inside the container hole; a twelfth step of pressing the base end side end of the mother tube with the sleeve while the mandrel is inserted into the mother tube, thereby causing a material constituting the mother tube to plastically flow and fill a space between the container and the mandrel in the eleventh large inner diameter region and the eleventh reduced inner diameter region of the container hole, thereby expanding the outer diameter of the mother tube to the thirteenth outer diameter while maintaining the inner diameter of the mother tube at the eleventh inner diameter; a thirteenth step of further pressing the base end of the mother tube with the sleeve while the mandrel is inserted into the mother tube, thereby performing an extrusion process in which a material constituting the mother tube is extruded into the eleventh small inner diameter region of the container hole through a gap between the base end of the eleventh small inner diameter region of the container hole and the mandrel, thereby reducing the diameter of the front end of the mother tube; Including, At an eleventh time point when the twelfth step is started, the tip end of the mandrel has reached an eleventh position that is the same position in the pressing direction as the position of the base end end of the eleventh small inner diameter region of the container hole, or has reached a position further towards the tip side than the eleventh position, At a 12th time point when the 13th step is started, the tip end of the mandrel has reached a 12th position, which is a position that is a predetermined distance toward the tip side in the pressing direction from an end of the base end side of the 11th small inner diameter region of the container hole, or has reached a position further toward the tip side than the 12th position. A method for extrusion molding of pipes with different thicknesses.

8. The method for extrusion molding a pipe having a different thickness according to claim 7, The tip end of the differential thickness pipe is formed with a 12th small outer diameter region having a 16th outer diameter equal to the 12th outer diameter, an 18th inner diameter smaller than the 12th inner diameter, and a 14th thickness larger than the 12th thickness; the mandrel further includes a thirteenth smaller outer diameter region that is formed on the tip side of the base outer diameter region and is a cylindrical region having an eighteenth outer diameter that is an outer diameter corresponding to the eighteenth inner diameter; and a twelfth increasing outer diameter region that is formed between the thirteenth smaller outer diameter region and the base outer diameter region and has an outer diameter that increases from the eighteenth outer diameter to the fourteenth outer diameter as it approaches the base outer diameter region from the thirteenth smaller outer diameter region, At the 12th time point, the end portion on the base end side of the 13th small outer diameter region is located on the base end side of the 11th position. A method for extrusion molding of pipes with different thicknesses.

9. The method for extrusion molding a pipe having a different thickness according to claim 8, At a thirteenth time point when the thirteenth step is completed, an end portion of the basic outer diameter region on the tip side is located on the tip side of the eleventh position, The differential thickness pipe includes the 11th large outer diameter region, the 11th increasing outer diameter region, the 11th small outer diameter region, the 12th small outer diameter region formed on the tip side of the 11th small outer diameter region, and an 11th increasing inner diameter region formed between the 12th small outer diameter region and the 11th small outer diameter region, the inner diameter increasing from the 18th inner diameter to the 12th inner diameter as it approaches the 12th small outer diameter region and the 11th small outer diameter region, the wall thickness decreasing from the 14th wall thickness to the 12th wall thickness, and the outer diameter being constant at a 17th outer diameter equal to the 12th outer diameter. A method for extrusion molding of pipes with different thicknesses.

10. The method for extruding a pipe having a different thickness according to claim 8, At a thirteenth time point when the thirteenth step is ended, an end portion on the base end side of the thirteenth small outer diameter region is located on the base end side of the eleventh position, The differential thickness pipe includes the 12th small outer diameter region, the 11th large outer diameter region, a 12th large outer diameter region formed between the 12th small outer diameter region and the 11th large outer diameter region and having a 19th outer diameter that is an outer diameter equal to the 13th outer diameter, a 19th inner diameter that is an inner diameter equal to the 18th inner diameter, and a 15th thickness that is a predetermined thickness larger than the 13th thickness, and a 16th small outer diameter region formed between the 12th small outer diameter region and the 12th large outer diameter region and changing from the 16th outer diameter to the 19th outer diameter as it approaches the 12th large outer diameter region. a thirteenth outer diameter increasing region, which is a region in which the outer diameter increases from the fourteenth thickness to the fifteenth thickness, and the inner diameter is constant at a twentieth inner diameter equal to the eighteenth inner diameter; and a twelfth inner diameter increasing region, which is formed between the twelfth larger outer diameter region and the eleventh larger outer diameter region, and which is a region in which the inner diameter increases from the nineteenth inner diameter to the thirteenth inner diameter as it approaches the eleventh larger outer diameter region, and which has a wall thickness decreasing from the fifteenth thickness to the thirteenth thickness, and the outer diameter is constant at a twentieth outer diameter equal to the thirteenth outer diameter. A method for extrusion molding of pipes with different thicknesses.

11. The method for extrusion molding a differential thickness pipe according to any one of claims 7 to 10, the 11th step to the 13th step are performed using the mother tube which further includes, at an end portion on the base end side, an 11th thin-wall portion which has a 21st outer diameter which is a predetermined outer diameter smaller than the 11th outer diameter, a 21st inner diameter which is a predetermined inner diameter equal to or larger than the 11th inner diameter, and a 16th thickness which is a predetermined thickness smaller than the 11th thickness, the sleeve includes a receiving portion that is a space that opens to an end surface on the tip side and has a shape corresponding to the eleventh thin-walled portion, by performing the twelfth step and the thirteenth step in a state in which the eleventh thin-wall portion is accommodated in the accommodation portion, the eleventh thin-wall portion is left at the end portion on the tip side of the mother tube, The differential thickness pipe further includes the eleventh thin-walled portion at the end portion on the base end side. A method for extrusion molding of pipes with different thicknesses.

12. The method for extrusion molding a pipe having a different thickness according to claim 1 or 2, the first step to the third step are performed using the blank tube, which further includes, at an end portion of the tip side, a 12th thin-wall portion having a 22nd outer diameter which is a predetermined outer diameter equal to or smaller than an outer diameter corresponding to a minimum inner diameter of the container hole, a 22nd inner diameter which is a predetermined inner diameter equal to or larger than the first inner diameter, and a 17th thickness which is a predetermined thickness smaller than the first thickness, The differential thickness pipe further includes the twelfth thin-walled portion at the end portion on the tip side. A method for extrusion molding of pipes with different thicknesses.

13. A method for extrusion molding a differential thickness pipe according to any one of claims 7 to 10, comprising: the 11th step to the 13th step are performed using the blank tube which further includes, at an end portion of the tip side, a 12th thin-wall portion which has a 22nd outer diameter which is a predetermined outer diameter equal to or smaller than an outer diameter corresponding to a smallest inner diameter of the container hole, a 22nd inner diameter which is a predetermined inner diameter equal to or larger than the 11th inner diameter, and a 17th thickness which is a predetermined thickness smaller than the 11th wall thickness; The differential thickness pipe further includes the twelfth thin-walled portion at the end portion on the tip side. A method for extrusion molding of pipes with different thicknesses.

14. 1. An extrusion molding device for a differential thickness pipe, comprising: a mandrel which is a core metal having a predetermined shape; a sleeve which is a cylindrical member arranged coaxially around the outside of the mandrel; a container which is a die having a container hole which is a through hole having a predetermined shape; and a drive mechanism configured to press at least the sleeve into the container hole, the extrusion molding device being configured to mold a differential thickness pipe having a predetermined shape by pressing a blank tube having a predetermined shape into the container hole with the sleeve, the blank tube is a cylindrical member having an eleventh outer diameter that is a predetermined outer diameter, an eleventh inner diameter that is a predetermined inner diameter, and an eleventh wall thickness that is a predetermined wall thickness, The differential thickness pipe has an eleventh small outer diameter region formed on a tip end side, which is a downstream side in a pressing direction, which is a direction in which the blank tube is pressed into the container hole, and having a twelfth outer diameter that is a predetermined outer diameter smaller than the eleventh outer diameter, a twelfth inner diameter that is an inner diameter equal to the eleventh inner diameter, and a twelfth wall thickness that is a predetermined wall thickness smaller than the eleventh wall thickness; and a thirteenth small outer diameter region formed on a base end side, which is an upstream side in the pressing direction, and having a thirteenth outer diameter that is a predetermined outer diameter larger than the eleventh outer diameter, a twelfth inner diameter that is an inner diameter equal to the eleventh inner diameter, and a twelfth wall thickness that is a predetermined wall thickness smaller than the eleventh wall thickness. an eleventh large outer diameter region which is a region having a thirteenth inner diameter which is a small inner diameter and a thirteenth thickness which is a predetermined thickness larger than the eleventh thickness; and an eleventh increasing outer diameter region which is formed between the eleventh small outer diameter region and the eleventh large outer diameter region, and which is a region in which the outer diameter increases from the 12th outer diameter to the 13th outer diameter and the thickness increases from the 12th thickness to the 13th thickness as it approaches the eleventh small outer diameter region, and the inner diameter is constant at a fourteenth inner diameter which is equal to the eleventh inner diameter, the mandrel includes a basic outer diameter region that is a cylindrical region formed on the tip side and has a 14th outer diameter that is an outer diameter corresponding to the 11th inner diameter, the sleeve includes an eleventh pressing region that is a cylindrical region having a cylindrical internal space formed on the tip side and having a fifteenth outer diameter that is an outer diameter equal to the thirteenth outer diameter and a fifteenth inner diameter that is an inner diameter corresponding to the fourteenth outer diameter, the container hole includes: an eleventh large inner diameter region formed on the base end side and having a sixteenth inner diameter which is an inner diameter corresponding to the thirteenth outer diameter; an eleventh small inner diameter region formed on the tip end side and having a seventeenth inner diameter which is an inner diameter corresponding to the twelfth outer diameter; and an eleventh inner diameter decreasing region formed between the eleventh large inner diameter region and the eleventh small inner diameter region and having an inner diameter which decreases from the sixteenth inner diameter to the seventeenth inner diameter as the eleventh large inner diameter region approaches the eleventh small inner diameter region, The extrusion molding device for the differential thickness pipe includes: an eleventh step of abutting the tip end of the blank tube against the eleventh inner diameter reduced region of the container hole to set the blank tube at a predetermined position inside the container hole; a twelfth step of pressing the base end side end of the mother tube with the sleeve while the mandrel is inserted into the mother tube, thereby causing a material constituting the mother tube to plastically flow and fill a space between the container and the mandrel in the eleventh large inner diameter region and the eleventh reduced inner diameter region of the container hole, thereby expanding the outer diameter of the mother tube to the thirteenth outer diameter while maintaining the inner diameter of the mother tube at the eleventh inner diameter; a thirteenth step of further pressing the base end of the mother tube with the sleeve while the mandrel is inserted into the mother tube, thereby performing an extrusion process in which a material constituting the mother tube is extruded into the eleventh small inner diameter region of the container hole through a gap between the base end of the eleventh small inner diameter region of the container hole and the mandrel, thereby reducing the diameter of the front end of the mother tube; The method is configured to form the differential thickness pipe by executing At an eleventh time point when the twelfth step is started, the tip end of the mandrel has reached an eleventh position that is the same position in the pressing direction as the position of the base end end of the eleventh small inner diameter region of the container hole, or has reached a position further towards the tip side than the eleventh position, At a 12th time point when the 13th step is started, the tip end of the mandrel has reached a 12th position, which is a position that is a predetermined distance toward the tip side in the pressing direction from an end of the base end side of the 11th small inner diameter region of the container hole, or has reached a position further toward the tip side than the 12th position. Extrusion molding equipment for pipes with different thicknesses.

15. The extrusion molding apparatus for a pipe having a different thickness according to claim 14, The tip end of the differential thickness pipe is formed with a 12th small outer diameter region having a 16th outer diameter equal to the 12th outer diameter, an 18th inner diameter smaller than the 12th inner diameter, and a 14th thickness larger than the 12th thickness; the mandrel further includes a thirteenth smaller outer diameter region that is formed on the tip side of the base outer diameter region and is a cylindrical region having an eighteenth outer diameter that is an outer diameter corresponding to the eighteenth inner diameter; and a twelfth increasing outer diameter region that is formed between the thirteenth smaller outer diameter region and the base outer diameter region and has an outer diameter that increases from the eighteenth outer diameter to the fourteenth outer diameter as it approaches the base outer diameter region from the thirteenth smaller outer diameter region, At the 12th time point, the end portion on the base end side of the 13th small outer diameter region is located on the base end side of the 11th position. Extrusion molding equipment for pipes with different thicknesses.

16. The extrusion molding apparatus for a pipe having a different thickness according to claim 15, At a thirteenth time point when the thirteenth step is completed, an end portion of the basic outer diameter region on the tip side is located on the tip side of the eleventh position, The differential thickness pipe includes the 11th large outer diameter region, the 11th increasing outer diameter region, the 11th small outer diameter region, the 12th small outer diameter region formed on the tip side of the 11th small outer diameter region, and an 11th increasing inner diameter region formed between the 12th small outer diameter region and the 11th small outer diameter region, the inner diameter increasing from the 18th inner diameter to the 12th inner diameter as it approaches the 12th small outer diameter region and the 11th small outer diameter region, the wall thickness decreasing from the 14th wall thickness to the 12th wall thickness, and the outer diameter being constant at a 17th outer diameter equal to the 12th outer diameter. Extrusion molding equipment for pipes with different thicknesses.

17. The extrusion molding apparatus for a pipe having a different thickness according to claim 15, At a thirteenth time point when the thirteenth step is ended, an end portion on the base end side of the thirteenth small outer diameter region is located on the base end side of the eleventh position, The differential thickness pipe includes the 12th small outer diameter region, the 11th large outer diameter region, a 12th large outer diameter region formed between the 12th small outer diameter region and the 11th large outer diameter region and having a 19th outer diameter that is an outer diameter equal to the 13th outer diameter, a 19th inner diameter that is an inner diameter equal to the 18th inner diameter, and a 15th thickness that is a predetermined thickness larger than the 13th thickness, and a 16th small outer diameter region formed between the 12th small outer diameter region and the 12th large outer diameter region and changing from the 16th outer diameter to the 19th outer diameter as it approaches the 12th large outer diameter region. a thirteenth outer diameter increasing region, which is a region in which the outer diameter increases from the fourteenth thickness to the fifteenth thickness, and the inner diameter is constant at a twentieth inner diameter equal to the eighteenth inner diameter; and a twelfth inner diameter increasing region, which is formed between the twelfth larger outer diameter region and the eleventh larger outer diameter region, and which is a region in which the inner diameter increases from the nineteenth inner diameter to the thirteenth inner diameter as it approaches the eleventh larger outer diameter region, and which has a wall thickness decreasing from the fifteenth thickness to the thirteenth thickness, and the outer diameter is constant at a twentieth outer diameter equal to the thirteenth outer diameter. Extrusion molding equipment for pipes with different thicknesses.

18. The extrusion molding apparatus for a differential thickness pipe according to any one of claims 14 to 17, the 11th step to the 13th step are performed using the blank tube which further includes, at an end portion on the base end side, an 11th thin-wall portion which has a 21st outer diameter which is a predetermined outer diameter smaller than the 11th outer diameter, a 21st inner diameter which is a predetermined inner diameter equal to or larger than the 11th inner diameter, and a 16th thickness which is a predetermined thickness smaller than the 11th thickness, the sleeve includes a receiving portion that is a space that opens to an end surface on the tip side and has a shape corresponding to the eleventh thin-walled portion, By performing the twelfth step and the thirteenth step in a state in which the eleventh thin-walled portion is accommodated in the accommodation portion, the eleventh thin-walled portion remains at the end portion on the tip side of the mother tube, The differential thickness pipe further includes the eleventh thin-walled portion at the end portion on the base end side. Extrusion molding equipment for pipes with different thicknesses.

19. The extrusion molding apparatus for a differential thickness pipe according to claim 4 or 5, the first step to the third step are performed using the blank tube which further includes, at an end portion of the tip side, a 12th thin-wall portion which has a 22nd outer diameter which is a predetermined outer diameter equal to or smaller than an outer diameter corresponding to a smallest inner diameter of the container hole, a 22nd inner diameter which is a predetermined inner diameter equal to or larger than the first inner diameter, and a 17th thickness which is a predetermined thickness smaller than the first thickness, The differential thickness pipe further includes the twelfth thin-walled portion at the end portion on the tip side. Extrusion molding equipment for pipes with different thicknesses.

20. An extrusion molding apparatus for a differential thickness pipe according to any one of claims 14 to 17, the 11th to 13th steps are performed using the blank tube which further includes, at an end portion of the tip side, a 12th thin-wall portion which has a 22nd outer diameter which is a predetermined outer diameter equal to or smaller than an outer diameter corresponding to a smallest inner diameter of the container hole, a 22nd inner diameter which is a predetermined inner diameter equal to or larger than the 11th inner diameter, and a 17th thickness which is a predetermined thickness smaller than the 11th wall thickness, The differential thickness pipe further includes the twelfth thin-walled portion at the end portion on the tip side. Extrusion molding equipment for pipes with different thicknesses.