Extrusion molding method and extrusion molding device for unequal-thickness pipe with solid part

Abstract

A first step in which a cylindrical blank having a hollow base end side and a solid tip end side is inserted into a large inner diameter portion of a container hole, and an end portion of the tip end side of the blank is brought into contact with a reduced inner diameter portion of the container hole, and a second step in which the base end side of the blank is inserted into the large inner diameter portion of the container hole, and the tip end side of the blank is brought into contact with the reduced inner diameter portion of the container hole. In the first step, a sleeve is brought into contact with the base-end-side end of the blank, a mandrel is inserted into the hollow hole of the blank, and the distance between the tips, which is the distance between the tip of the sleeve and the tip of the mandrel, is fixed to a predetermined distance, and in the second step, the inner diameter of the sleeve is reduced while the tip of the mandrel reaches the reduced-diameter portion of the extrusion container hole. In the first step, the sleeve and the mandrel are advanced in the extrusion direction while the distance between the front ends is maintained, and the blank is pressed into the small-inner-diameter portion through the inner-diameter-reduced portion of the container hole, and in the third step, the advancing of the sleeve and the mandrel is further continued while the distance between the front ends is maintained. As a result, it is possible to reduce the occurrence of defects such as cracks and / or material deposits without requiring a blank having a complicated shape.

Description

Technical Field

[0001] The present invention relates to an extrusion molding method and an extrusion molding apparatus for an unequal-thickness pipe having a solid portion. Background Art

[0002] In this technical field, an unequal-thickness pipe (also referred to as a "butted pipe" and a "butted tube", etc.) having a thick-walled portion formed in a part in the axial direction of the pipe is known, for example, for the purpose of achieving a desired mechanical strength in the thick-walled portion and realizing weight reduction in the thin-walled portion (a portion other than the thick-walled portion). As disclosed in, for example, Patent Document 1 (Japanese Patent No. 6933762), such an unequal-thickness pipe that is hollow throughout its length can be integrally formed by extrusion molding from a cylindrical pipe material.

[0003] In addition, for example, in the field of shafts and the like, there is also a need to apply an unequal-thickness pipe, but sometimes it is required to have a solid portion having a predetermined length in the axial direction on one end side instead of being hollow throughout its length. For example, from the viewpoint of reducing manufacturing costs and the like, it is preferable that such an unequal-thickness pipe having a solid portion is also integrally formed by extrusion molding. However, it is impossible to mold such an unequal-thickness pipe having a solid portion by the above processing method.

[0004] On the other hand, in this technical field, a processing method for manufacturing an unequal-thickness pipe having a short length in the axial direction but having a solid portion at one end, that is, a hollow metal product with a bottom, by extrusion molding is known. For example, Patent Document 2 (Japanese Patent Publication No. 49-035497) discloses the following processing method: a piercing compression process of forming a hollow hole by inserting a punch into a substantially cylindrical and solid blank, and a process of forming a hollow portion (unequal-thickness portion) and a solid portion (bottom) by extruding the whole while pressing the bottom of the hollow hole with another punch in the next process, to manufacture a hollow metal product with a bottom.

[0005] In addition, Patent Document 3 (Japanese Patent Publication No. 58-048264) discloses the following processing method: a blank having a flange portion and a hollow hole (and a bottom) in a predetermined positional relationship is preformed by a forging process, and in the next process, a cornered intermediate blank is formed by pressing the bottom of the hollow hole with the tip of a center punch, and in the next process, a hollow portion (unequal-thickness portion) and a solid portion (bottom) are formed by pressing the end portion of the intermediate blank on the side opposite to the bottom with a sleeve punch.

[0006] However, in any of the above processing methods, it is necessary to prepare a blank having a relatively complex shape that satisfies specific requirements. In addition, the bottomed hollow metal product manufactured by the above processing method is a so-called "bottomed cylindrical member", which does not conform to the above-mentioned unequal-thickness tube having a solid portion with a specified length in the axial direction. Further, in the latter processing method, in the process of forming an angle by pressing the bottom of the hollow hole with the front end of the center punch, cracks are likely to occur at the boundary between the bottom and the side wall portion of the blank, so there is a problem that the pressing force of the center punch cannot be set strong.

[0007] Patent Document 1: Japanese Patent No. 6933762 Gazette

[0008] Patent Document 2: Japanese Patent Publication No. 49-035497 Gazette

[0009] Patent Document 3: Japanese Patent Publication No. 58-048264 Gazette. Summary of the Invention

[0010] Therefore, the present inventor considered the problems in the prior art as described above and conducted the following experiment: Based on the technology described in Patent Document 1, with a mandrel (metal core) inserted through the hollow hole of a blank having a hollow portion and a solid portion, the blank was pressed into an extrusion cylinder (die) having a small inner diameter portion on the front end side to reduce the diameter, thereby extruding and forming an unequal-thickness tube having a solid portion. However, it was confirmed that: If the bottom of the hollow hole of the blank (the uppermost portion of the solid portion) is pressed in the extrusion direction by the front end of the mandrel, then as illustrated by the thick solid line example in Figure 6 , cracks are likely to occur throughout the circumference at the boundary between the bottom of the hollow hole and the side wall portion.

[0011] On the other hand, it was confirmed that: In order to prevent the occurrence of cracks as described above, while maintaining a space between the front end of the mandrel and the bottom of the hollow hole and performing extrusion molding, then as illustrated by the black semi-circular example in Figure 6 , as the blank is compressed toward the inner side in the radial direction, the material (forming material) of the blank plastically flows toward the space, resulting in the formation of material accumulation throughout the circumference within the space, and the desired hollow shape cannot be achieved.

[0012] That is, in this technical field, there is a need for a manufacturing method and a manufacturing apparatus for an unequal-thickness tube having a solid portion that can reduce the occurrence of defects such as cracks and / or material accumulation as described above without requiring a blank having a complex shape.

[0013] Based on the above insights, as a result of further in-depth research by the present inventor, it was found that the above problems can be solved by appropriately controlling the positional relationship between the front end of the mandrel and the bottom of the hollow hole of the blank and the movement of the sleeve and the mandrel.

[0014] Specifically, the extrusion molding method of the non-uniform wall thickness tube with a hollow portion involved in the present invention (hereinafter sometimes referred to as "the method of the present invention") is an extrusion molding method for forming a non-uniform wall thickness tube with a hollow portion from a blank having a specified shape by extrusion processing in an extrusion molding apparatus. The extrusion molding apparatus includes: a mandrel having a specified shape; a sleeve having a specified shape; an extrusion cylinder formed with a through hole having a specified shape, that is, an extrusion cylinder hole; and a drive mechanism configured to press the mandrel into the extrusion cylinder hole.

[0015] The blank is a member composed of a first hollow portion and a first solid portion, and as a whole has a cylindrical outer shape with a first outer diameter having a specified outer diameter. The first hollow portion is open at the end face on the upstream side in the extrusion direction, that is, the base end side, and forms a first hollow hole which is a cylindrical space with a first inner diameter having a specified inner diameter, and is a cylindrical portion with a first wall thickness having a specified wall thickness. The first solid portion is a cylindrical portion located between the end face on the downstream side in the extrusion direction, that is, the front end side, and the first hollow portion.

[0016] The non-uniform wall thickness tube is a member composed of a second hollow portion, a third hollow portion, a fourth hollow portion, and a second solid portion. The second hollow portion is a cylindrical portion having the first outer diameter and the first wall thickness. The third hollow portion is adjacent to the front end side of the second hollow portion, and the outer diameter changes from the first outer diameter to a second outer diameter which is smaller than the first outer diameter and has a specified outer diameter from the base end side toward the front end side, and the wall thickness changes from the first wall thickness to a second wall thickness which is smaller than the first wall thickness from the base end side toward the front end side. The fourth hollow portion is adjacent to the front end side of the third hollow portion and is a cylindrical portion having the second outer diameter and the second wall thickness. The second solid portion is a cylindrical portion located between the end portion on the front end side and the fourth hollow portion and having the second outer diameter. And a second hollow hole is continuously formed from the second hollow portion to the fourth hollow portion, and the second hollow hole is open at the end face on the base end side and is a cylindrical space having the first inner diameter.

[0017] The mandrel is coaxially and slidably embedded in the sleeve in the axial direction, and is a member having a cylindrical shape with a third outer diameter corresponding to the first inner diameter. The sleeve is coaxially and slidably externally embedded in the mandrel in the axial direction, and is a member having a cylindrical shape with a second inner diameter corresponding to the third outer diameter and the first outer diameter.

[0018] The extrusion cylinder hole is composed of a large inner diameter part, a small inner diameter part, and an inner diameter reduction part. The large inner diameter part is formed on the base end side and has a third inner diameter corresponding to the first outer diameter. The small inner diameter part is formed on the front end side and has a fourth inner diameter corresponding to the second outer diameter. The inner diameter reduction part is formed between the large inner diameter part and the small inner diameter part, and the inner diameter decreases from the third inner diameter to the fourth inner diameter as it approaches the small inner diameter part from the large inner diameter part.

[0019] The method of the present invention includes the first to third processes listed below.

[0020] The first process is as follows: Insert the blank into the large inner diameter part of the extrusion cylinder hole, make the end on the front end side of the blank abut against the inner diameter reduction part of the extrusion cylinder hole, make the sleeve abut against the end on the base end side of the blank, insert the mandrel into the first hollow hole of the blank, and fix the front end distance to a first distance which is a specified distance. The above front end distance is the relative distance in the extrusion direction between the end on the front end side of the sleeve and the end on the front end side of the mandrel.

[0021] The second process is as follows: Maintain the front end distance at the first distance and move the sleeve and the mandrel forward in the extrusion direction, thereby pressing the blank into the small inner diameter part through the inner diameter reduction part of the extrusion cylinder hole for extrusion processing, and continue to move the sleeve and the mandrel forward until the first moment. The above first moment is the moment when the end on the front end side of the mandrel reaches the end on the base end side of the inner diameter reduction part of the extrusion cylinder hole.

[0022] The third process is as follows: After the first moment, also maintain the front end distance at the first distance and move the sleeve and the mandrel forward in the extrusion direction.

[0023] In addition, the present invention also relates to an extrusion molding device for an unequal-thickness tube with a hollow part (hereinafter referred to as "the device of the present invention" in some cases) that forms an unequal-thickness tube with a hollow part by performing the method of the present invention described above.

[0024] By performing the method of the present invention including the above first to third processes in the device of the present invention having the above structure, it is possible to accurately and easily form an unequal-thickness tube with a hollow part from a blank having a simple structure. That is, according to the present invention, it is possible to provide a manufacturing method and a manufacturing device for an unequal-thickness tube with a solid part that can reduce the occurrence of defects such as cracks and / or material accumulation without requiring a blank with a complex shape.

[0025] Based on the description of the embodiments of the present invention described with reference to the following drawings, other objects, other features, and attendant advantages of the present invention can be easily understood. Description of the Drawings

[0026] Figure 1 It is a schematic cross-sectional view showing an example of the structure of the original blank, the blank, and the unequal-thickness tube with a solid part formed from the blank, which is the source of the blank used in the extrusion molding method (the first method) of the unequal-thickness tube having a solid part according to the first embodiment of the present invention.

[0027] Figure 2 It is a schematic cross-sectional view showing an example of the structure of the mandrel, the sleeve, and the extrusion cylinder used in the first method.

[0028] Figure 3 It is a flowchart illustrating the process flow of the first to third processes performed in the first method.

[0029] Figure 4 It is a schematic cross-sectional view showing an example of the shape of the blank and the unequal-thickness tube at the end of the first process, at the start and end of the third process, and the positional relationship between the mandrel, the sleeve, and the extrusion cylinder and the blank and the unequal-thickness tube in the first method.

[0030] Figure 5 It is a schematic cross-sectional view showing an example of the positional relationship between the bottom of the first hollow hole near the bottom of the first hollow hole of the blank and the mandrel at the start of the second process included in the extrusion molding method (the second method) of the unequal-thickness tube having a solid part according to the second embodiment of the present invention.

[0031] Figure 6 It is a schematic cross-sectional view illustrating the problems recognized during the experiment of attempting to extrude and mold an unequal-thickness tube with a solid part based on the prior art. Detailed Embodiment

[0032] 《First Embodiment》

[0033] Hereinafter, the extrusion molding method of the unequal-thickness tube having a solid part according to the first embodiment of the present invention (hereinafter sometimes referred to as the "first method") will be described with reference to the drawings.

[0034] 〈Structure〉

[0035] The first method is an extrusion molding method in an extrusion molding apparatus for molding a non-uniform wall thickness tube having a hollow portion from a blank having a specified shape by extrusion processing. The extrusion molding apparatus includes: a mandrel having a specified shape; a sleeve having a specified shape; an extrusion cylinder formed with a through hole having a specified shape, that is, an extrusion cylinder hole; and a drive mechanism configured to press the mandrel into the extrusion cylinder hole. Regarding the basic structure of such an extrusion molding apparatus, it is well-known to those skilled in the art, and thus detailed description is omitted. Constituent elements represented by the mandrel, the sleeve, and the extrusion cylinder are made of a material having properties (such as mechanical strength and durability) that can withstand processing conditions such as loads acting on the constituent elements during the subsequent extrusion processing. In addition, the drive mechanism for pressing the mandrel into the extrusion cylinder hole can be appropriately selected from various drive mechanisms well-known in the technical field according to the properties (such as mechanical strength and hardness) of the material constituting the blank to be subjected to extrusion processing. Typically, for example, a press such as a hydraulic press can be used as the drive mechanism.

[0036] Figure 1 (a), (b), and (c) thereof are respectively schematic cross-sectional views showing an example of the structure of the original blank 11, the blank 21, and the non-uniform wall thickness tube 31 having a solid portion formed from the blank 21, which are the sources of the blanks used in the first method. As Figure 1 Illustrated in (b) thereof, the blank 21 is a member having a cylindrical outer shape with a first outer diameter DO1 having a specified outer diameter, and is composed of a first hollow portion PH1 and a first solid portion PS1. The first hollow portion PH1 is open at the end face on the upstream side, that is, the base end side in the extrusion direction, and has a first hollow hole HH1, which is a cylindrical space having a first inner diameter DI1 with a specified inner diameter, and is a cylindrical portion having a first wall thickness T1 with a specified wall thickness. The first solid portion PS1 is a cylindrical portion located between the end face on the downstream side, that is, the front end side in the extrusion direction, and the first hollow portion PH1.

[0037] As described above, since the blank 21 has a relatively simple structure, it can be easily manufactured by forming the first hollow hole HH1 in the original blank 11, which is a cylindrical member having the first outer diameter DO1 as illustrated in (a) of Figure 1 thereof. The specific method for forming the first hollow hole HH1 in the original blank 11 is not particularly limited. For example, the first hollow hole HH1 can be easily formed in the original blank 11 by methods such as machining.

[0038] In addition, the material constituting the original blank 11 is not particularly limited as long as it can be formed into a desired shape by plastic deformation during extrusion processing. Typically, the material constituting the original blank 11 is, for example, a metal represented by lead, tin, aluminum, copper, zirconium, titanium, molybdenum, vanadium, niobium, and steel.

[0039] As Figure 1 illustrated in (c) of [reference], the non-uniform wall thickness tube 31 is a component composed of a second hollow portion PH2, a third hollow portion PH3, a fourth hollow portion PH4, and a second solid portion PS2. The second hollow portion PH2 is a cylindrical portion having a first outer diameter DO1 and a first wall thickness T1. The third hollow portion PH3 is adjacent to the front end side of the second hollow portion PH2, and the outer diameter changes from the first outer diameter DO1 at the base end side to a second outer diameter DO2 smaller than the first outer diameter DO1 toward the front end side, and the wall thickness changes from the first wall thickness T1 at the base end side to a second wall thickness T2 smaller than the first wall thickness T1 toward the front end side. The fourth hollow portion PH4 is adjacent to the front end side of the third hollow portion PH3 and is a cylindrical portion having the second outer diameter DO2 and the second wall thickness T2. The second solid portion PS2 is a cylindrical portion located between the end portion on the front end side and the fourth hollow portion PH4 and having the second outer diameter DO2. And a second hollow hole HH2 is continuously formed from the second hollow portion PH2 to the fourth hollow portion PH4. The second hollow hole HH2 is a cylindrical space that is open at the end face on the base end side and has a first inner diameter DI1.

[0040] In addition, in Figure 1 the non-uniform wall thickness tube 31 illustrated in (c) of [reference], the rate of change of the outer diameter of the third hollow portion PH3 is greater from the base end side toward the front end side, and the contour of the outer diameter of the third hollow portion PH3 becomes a convex curve on the outer side in the radial direction. However, the pattern of the change of the outer diameter of the third hollow portion PH3 from the first outer diameter DO1 to the second outer diameter DO2 is not limited to this. For example, the contour of the outer diameter of the third hollow portion PH3 may also be a concave curve on the outer side in the radial direction, or the rate of change of the outer diameter of the third hollow portion PH3 may be constant from the end portion on the base end side to the end portion on the front end side, and the contour of the outer diameter of the third hollow portion PH3 is a straight line.

[0041] In addition, in Figure 1 the non-uniform wall thickness tube 31 illustrated in (c) of [reference], the bottom (end portion on the front end side) of the second hollow hole HH2 has a conical shape. However, the shape of the bottom of the second hollow hole HH2 is not limited to this. For example, it can be set to various shapes according to the use of the non-uniform wall thickness tube 31 and the like. For example, the shape of the bottom of the second hollow hole HH2 may also be a plane perpendicular to the axial direction of the non-uniform wall thickness tube 31, or may be a convex curved surface (such as a spherical surface, etc.) on the front end side. Such a shape of the bottom of the second hollow hole HH2 can be realized, for example, by setting the shape of the end portion on the front end side of the mandrel to a shape corresponding to the shape of the bottom of the second hollow hole HH2.

[0042] Figure 2Figs. (a) and (b) are schematic cross-sectional views showing an example of the structures of the mandrel 41, the sleeve 51, and the extrusion cylinder 61 used in the first method. As Figure 2 Illustrated in Fig. (a), the mandrel 41 is coaxially and axially slidably fitted inside the sleeve 51, and is a cylindrical member having a third outer diameter DO3 with a specified outer diameter corresponding to the inner diameter, i.e., the first inner diameter DI1, of the first hollow portion PH1 of the blank 21. The sleeve 51 is coaxially and axially slidably fitted outside the mandrel 41, and is a cylindrical member having a second inner diameter DI2 with a specified inner diameter corresponding to the outer diameter, i.e., the third outer diameter DO3, of the mandrel 41 and the outer diameter, i.e., the first outer diameter DO1, of the blank 21.

[0043] In addition, Figure 2 Although not depicted, the proximal end side portions of the mandrel 41 and the sleeve 51 can have structures and / or mechanisms suitable for driving by a drive mechanism provided in the extrusion molding apparatus and / or loading and unloading from the drive device.

[0044] As Figure 2 Illustrated in Fig. (b), the extrusion cylinder hole HC1 formed in the extrusion cylinder 61 is composed of a large inner diameter portion PDIL, a small inner diameter portion PDIS, and an inner diameter reducing portion PDIT. The large inner diameter portion PDIL is formed on the proximal end side and has a third inner diameter DI3 with an inner diameter corresponding to the outer diameter, i.e., the first outer diameter DO1, of the blank 21. The small inner diameter portion PDIS is formed on the distal end side and has a fourth inner diameter DI4 with an inner diameter corresponding to the outer diameter, i.e., the second outer diameter DO2, of the fourth hollow portion PH2 and the second solid portion PS2 of the unequal thickness tube 31. The inner diameter reducing portion PDIT is formed between the large inner diameter portion PDIL and the small inner diameter portion PDIS, and the inner diameter decreases from the third inner diameter DI3 to the fourth inner diameter DI4 as it approaches the small inner diameter portion PDIS from the large inner diameter portion PDIL.

[0045] In addition, in the Figure 2 extrusion cylinder 61 illustrated in Fig. (b), the large inner diameter portion PDIL is composed of two members, the inner diameter reducing portion PDIT and the most proximal end side portion of the small inner diameter portion PDIS are integrally formed by one member, and the remaining portion of the small inner diameter portion PDIS is composed of two members. That is, Figure 2 the entire extrusion cylinder 61 illustrated in Fig. (b) is composed of five members. However, the structure of the extrusion cylinder 61 is not limited to this. For example, it can be composed of one member as a whole, or the large inner diameter portion PDIL, the small inner diameter portion PDIS, and the inner diameter reducing portion PDIT can each be composed of one member, and it can be composed of three members as a whole.

[0046] As shown by Figure 3As illustrated in the flowchart example, the first method includes the first to third processes listed below.

[0047] The first process executed in step S01 is as follows: Insert the blank into the large inner diameter portion of the extrusion cylinder hole, make the end portion on the front end side of the blank abut against the inner diameter reducing portion of the extrusion cylinder hole, make the sleeve abut against the end portion on the base end side of the blank, insert the mandrel into the first hollow hole of the blank, and fix the front end distance to a first distance that is a specified distance. The above front end distance is the relative distance in the extrusion direction between the end portion on the front end side of the sleeve and the end portion on the front end side of the mandrel. That is, in the first process, the blank, the mandrel, the sleeve, and the extrusion cylinder are set in specified positions.

[0048] The second process executed in step S02 is as follows: Maintain the front end distance at the first distance and move the sleeve and the mandrel forward in the extrusion direction. As a result, the blank is pressed into the small inner diameter portion through the inner diameter reducing portion of the extrusion cylinder hole to perform extrusion processing, and continue to move the sleeve and the mandrel forward until the first moment. The above first moment is the moment when the end portion on the front end side of the mandrel reaches the base end side of the inner diameter reducing portion of the extrusion cylinder hole. That is, in the second process, through the coordinated driving of the mandrel and the sleeve, the front end distance is maintained at the first distance, and the sleeve and the mandrel are moved forward in the extrusion direction until the end portion on the front end side of the mandrel reaches the base end side of the inner diameter reducing portion of the extrusion cylinder hole. Thereby, extrusion processing is performed from the first solid portion of the blank to the second solid portion of the unequal-thickness tube.

[0049] The third process executed in step S03 is as follows: After the first moment, also maintain the front end distance at the first distance and move the sleeve and the mandrel forward in the extrusion direction. That is, in the process executed after the first moment, which is the third process, also through the coordinated driving of the mandrel and the sleeve, the front end distance is maintained at the first distance, and the sleeve and the mandrel are moved forward in the extrusion direction, thereby performing extrusion processing from a part of the front end side of the first hollow portion of the blank to the third hollow portion and the fourth hollow portion of the unequal-thickness tube. In addition, the portion of the first hollow portion of the blank that is not given extrusion processing in the third process becomes the second hollow portion of the unequal-thickness tube.

[0050] Figure 4 (a) is a schematic cross-sectional view showing an example of the shape of the blank 21 at the end of the first process, and the positional relationship between the mandrel 41, the sleeve 51, and the extrusion cylinder 61 and the blank 21. In addition, in Figure 4 In order to simplify the drawings, only Figure 1 and Figure 2 A part of the reference numerals marked on each part shown in Figure 4 is shown. However, in the following description related to Figure 1 andFigure 2 the reference numerals shown in Figure 1 and Figure 2 .

[0051] As Figure 4 illustrated in (a) of [], the blank 21 is inserted into the large inner diameter portion PDIL of the extrusion cylinder hole HC1, and the end portion on the front end side of the blank 21 abuts against the inner diameter reducing portion PDIT of the extrusion cylinder hole HC1. Thereby, the blank 21 is held at a specified position inside the extrusion cylinder hole HC1. Further, the sleeve 51 abuts against the end portion on the base end side of the blank 21, and the mandrel 41 is inserted into the first hollow hole HH1 formed in the blank 21. Then, the sleeve 51 and the mandrel 41 are arranged such that the front end interval DT becomes the first distance D1 which is a specified distance (i.e., DT = D1), and the above-mentioned front end interval DT is the relative distance in the extrusion direction between the end portion on the front end side of the sleeve 51 and the end portion on the front end side of the mandrel 41.

[0052] Thereafter, although not shown, in the second process following the first process, by the coordinated drive of the mandrel 51 and the sleeve 41, the front end interval DT is maintained as the first distance D1, and the sleeve 51 and the mandrel 41 are advanced in the extrusion direction ( Figure 4 the downward direction in []). Thereby, the first solid portion PS1 of the blank 21 is pressed into the small inner diameter portion PDIS from the front end side via the inner diameter reducing portion PDIT of the extrusion cylinder hole HC1, and the extrusion process from the first solid portion PS1 of the blank 21 to the second solid portion PS2 of the unequal thickness tube 31 is performed.

[0053] In addition, the outer diameter of the second solid portion PS2 of the unequal thickness tube 31, that is, the second outer diameter DO2, is smaller than the outer diameter of the first solid portion PS1 of the blank 21, that is, the first outer diameter DO1 (DO2 < DO1). That is, the cross-sectional area of the second solid portion PS2 of the unequal thickness tube 31 is smaller than the cross-sectional area of the first solid portion PS1 of the blank 21. Therefore, the length of the second solid portion PS2 of the unequal thickness tube 31 extruded from the first solid portion PS1 of the blank 21 in the extrusion direction is larger than the length of the first solid portion PS1 of the blank 21 in the extrusion direction (details will be described later).

[0054] In addition, from the viewpoint of avoiding, for example, Figure 6From the viewpoint of problems such as the occurrence of cracks as exemplified in (a) above, it is preferable that at least at the start time of the above-mentioned extrusion direction in the second process, that is, the second time, the end portion on the proximal end side of the blank 21 is pressed by the sleeve 51 in the extrusion direction, but the bottom of the first hollow hole HH1 is not pressed by the mandrel 41. Such a state can be achieved, for example, by preventing the bottom of the first hollow hole HH1 of the blank 21 from coming into contact with the mandrel 41 at the second time, or by providing a gap of a specified size between the bottom of the first hollow hole HH1 of the blank 21 and the end portion on the front end side of the mandrel 41 at the second time (details will be described later).

[0055] Although not shown, depending on, for example, the materials constituting the blank, the mandrel, the sleeve, and / or the extrusion cylinder, and the conditions of the extrusion process such as the extrusion load and / or the extrusion speed, there is a case where a so-called "upsetting phenomenon" occurs during the above-mentioned extrusion process. In this case, due to the plastic flow of the material constituting the blank and / or the elastic deformation of the extrusion cylinder, etc., the blank expands outward in the radial direction and contracts in the axial direction, and the bottom of the first hollow hole formed in the blank is slightly displaced toward the proximal end side. Therefore, even if there is a gap between the bottom of the first hollow hole of the blank and the end portion on the front end side of the mandrel at the second time, there is a case where this gap disappears or shrinks due to the above-mentioned upsetting phenomenon.

[0056] As the above-mentioned extrusion process proceeds, finally, the end portion on the front end side of the mandrel 41 reaches the end portion on the proximal end side of the inner diameter reducing portion PDIT of the extrusion cylinder hole HC1. Thus, the period up to the first time corresponds to the second process, the period after the first time corresponds to the third process, and the above-mentioned first time is the time when the end portion on the front end side of the mandrel 41 reaches the end portion on the proximal end side of the inner diameter reducing portion PDIT of the extrusion cylinder hole HC1.

[0057] Figure 4 Figure (b) is a schematic cross-sectional view showing an example of the shape of the blank 21 immediately after the end of the second process, that is, immediately before the start of the third process, and the positional relationship between the mandrel 41, the sleeve 51, the extrusion cylinder 61, and the blank 21. In the third process, after the first time, the front-end distance DT is maintained at the first distance D1 and the advancement of the sleeve 51 and the mandrel 41 in the extrusion direction is continued. As a result, the first hollow portion PH1 of the blank 21 is pressed into the small inner diameter portion PDIS from the front end side via the inner diameter reducing portion PDIT of the extrusion cylinder hole HC1, and the extrusion process is performed from a part of the front end side of the first hollow portion PH1 of the blank 21 to the fourth hollow portion PH4 and the third hollow portion PH3 of the unequal thickness tube 31. In addition, as described above, the portion of the first hollow portion PH1 of the blank 21 that is not subjected to the extrusion process in the third process becomes the second hollow portion PH2 of the unequal thickness tube 31.

[0058] In addition, the outer diameter of the fourth hollow portion PH4 of the non-uniform wall thickness tube 31, which is also the second outer diameter DO2, is smaller than the outer diameter of the first hollow portion PH1 of the blank 21, which is also the first outer diameter DO1 (DO2 < DO1). Further, the inner diameter of the second hollow hole HH2 of the non-uniform wall thickness tube 31 is maintained by the mandrel 41 to be the same as the inner diameter of the first hollow portion PH1 of the blank 21, which is also the first inner diameter DI1. That is, the cross-sectional area of the fourth hollow portion PH4 of the non-uniform wall thickness tube 31 is smaller than the cross-sectional area of the first hollow portion PH1 of the blank 21. On the other hand, the outer diameter of the third hollow portion PH3 of the non-uniform wall thickness tube 31 changes from the first outer diameter DO1 to a second outer diameter DO2 smaller than the first outer diameter DO1 from the base end side toward the front end side as described above, but the inner diameter of the third hollow portion PH3 of the non-uniform wall thickness tube 31 is also maintained by the mandrel 41 to be the first inner diameter DI1 without change. That is, the cross-sectional area of the third hollow portion PH3 of the non-uniform wall thickness tube 31 is also smaller than the cross-sectional area of the first hollow portion PH1 of the blank 21. Therefore, the lengths in the extrusion direction of the fourth hollow portion PH4 and the third hollow portion PH3 of the non-uniform wall thickness tube 31, which is extruded from the first hollow portion PH1 of the blank 21, are larger than the length in the extrusion direction of the portion of the first hollow portion PH1 of the blank 21 that has been subjected to the extrusion process (details will be described later).

[0059] Therefore, as shown by the area enclosed by the thick dashed line in Figure 4 (b), when the extrusion process from the first hollow portion PH1 of the blank 21 to the fourth hollow portion PH4 and the third hollow portion PH3 of the non-uniform wall thickness tube 31 starts in the third process, the bottom of the first hollow hole of the blank and the end portion on the front end side of the mandrel start to separate from each other.

[0060] Figure 4 (c) is a schematic cross-sectional view showing an example of the shape of the non-uniform wall thickness tube 31 at the end of the third process, and the positional relationship between the mandrel 41, the sleeve 51, and the extrusion cylinder 61 and the non-uniform wall thickness tube 31. As illustrated in Figure 4 (c), by performing the above-described first to third processes, it is possible to easily form the non-uniform wall thickness tube 31 composed of the second hollow portion PH2, the third hollow portion PH3, the fourth hollow portion PH4, and the second solid portion PS2 having a desired shape from the blank 21 having a simple shape.

[0061] In addition, in the second process included in the first method, as described above, the relative distance in the extrusion direction, i.e., the front-end distance DT, between the end portion on the front-end side of the sleeve and the end portion on the front-end side of the mandrel is maintained at a first distance D1 which is a specified distance, and the sleeve 51 and the mandrel 41 are advanced in the extrusion direction. Thereby, the first solid portion PS1 of the blank 21 is pressed into the small inner-diameter portion PDIS through the inner-diameter reducing portion PDIT of the extrusion cylinder hole HC1, and the extrusion process from the first solid portion PS1 of the blank 21 to the second solid portion PS2 of the unequal-thickness tube 31 is performed.

[0062] On the other hand, in the third process, as described above, the bottom of the first hollow hole of the blank and the end portion on the front-end side of the mandrel are separated from each other. That is, in the third process, the mandrel 41 does not contribute to the extrusion process, but has the following function: during the process in which a part on the front-end side of the first hollow portion PH1 of the blank 21 changes into the fourth hollow portion PH4 and the third hollow portion PH3 of the unequal-thickness tube 31, the cross-sectional shape of the second hollow hole HH2 formed in the unequal-thickness tube 31 is maintained to be the same as that of the first hollow hole HH1 formed in the blank 21.

[0063] Here, the lengths in the extrusion direction (the same as the axial direction of the blank 21) of the respective parts of the blank 21 and the unequal-thickness tube 31 mentioned above are described in detail below. Among them, in the following description, for the purpose of easy understanding, it is assumed that the shapes of the bottoms of the first hollow hole HH1 formed in the blank 21 and the second hollow hole HH2 formed in the unequal-thickness tube 31 are both planes perpendicular to the axial direction. Therefore, when the shapes of their bottoms are not planes perpendicular to the axial direction, corrections corresponding to the shapes are of course required.

[0064] The second hollow portion PH2, the third hollow portion PH3, and the fourth hollow portion PH4 of the unequal-thickness tube 31 are formed from the first hollow portion PH1 of the blank 21, and the second solid portion PS2 of the unequal-thickness tube 31 is formed from the first solid portion PS1 of the blank 21. Therefore, the following relationships hold between the lengths in the axial direction (hereinafter sometimes simply referred to as "lengths") of the respective parts of the blank 21 and the lengths in the axial direction of the respective parts of the unequal-thickness tube 31.

[0065] First, the length (LPH2) of the second hollow portion PH2 of the unequal-thickness tube 31 is the length of the portion that remains in the state of the blank 21 without being given extrusion processing at the moment when the third process is completed. Therefore, as long as it is smaller than the length (LPH1) of the first hollow portion PH1 of the blank 21, LPH2 can be determined to be any size by the timing of completing the third process.

[0066] Next, the length (LPH3) of the third hollow portion PH3 of the non-uniform wall thickness tube 31 is naturally determined by the length (LPDIT) of the inner diameter reduction portion PDIT of the extrusion cylinder hole HC1 formed in the extrusion cylinder 61. Therefore, by adjusting the LPDIT of the extrusion cylinder hole HC1 formed in the extrusion cylinder 61, LPH3 can be determined to be any size.

[0067] Next, the length (LPH4) of the fourth hollow portion PH4 of the non-uniform wall thickness tube 31 can be calculated by dividing the remaining volume obtained by subtracting the volumes (VPH2 + VPH3) of the materials of the second hollow portion PH2 and the third hollow portion PH3 constituting the non-uniform wall thickness tube 31 from the volume (VPH1) of the material of the first hollow portion PH1 constituting the blank 21 by the area (APH4) of the annular cross-section of the fourth hollow portion PH4. Therefore, in order to obtain the desired LPH4, the blank 21, the non-uniform wall thickness tube 31, and the extrusion cylinder hole HC1 formed in the third extrusion cylinder 61 need to be formed in such a manner that the following equation (1) holds. In addition, VPH1, VPH2, and APH4 can be expressed by the following equations (2) to (4). In addition, VPH3 varies according to the pattern of the change in the outer diameter of the third hollow portion PH3 (i.e., the shape of the contour), and therefore, it needs to be calculated according to the shape of the third hollow portion PH3.

[0068] [Equation 1]

[0069] LPH4 = {VPH1 - (VPH2 + VPH3)} / APH4 (1)

[0070] VPH1 = π{(DO1 / 2) 2 - (DI1 / 2) 2} × LPH1 (2)

[0071] VPH2 = π{(DO1 / 2) 2 - (DI1 / 2) 2} × LPH2 (3)

[0072] APH4 = π{(DO2 / 2) 2 - (DI1 / 2) 2} (4)

[0073] The relationship between the length (LPS1) of the first solid portion PS1 of the blank 21 and the length (LPS2) of the solid portion PS2 of the non-uniform wall thickness tube 31 can be expressed by the following equation (5).

[0074] [Equation 2]

[0075] LPS1 : LPS2 = (DO2 / 2) 2 : (DO1 / 2) 2 (5)

[0076] Therefore, in order to obtain the desired LPS2, the length (LPS1) of the first solid portion of the blank 21 needs to be determined based on the first outer diameter DO1 of the blank 21 and the second outer diameter DO2 of the non-uniform wall thickness tube 31 in such a manner that the following formula (6) holds.

[0077] [Equation 3]

[0078] LPS2 = LPS1 × (DO1 / DO2) 2 (6)

[0079] <Effect>

[0080] As described above, in the extrusion molding apparatus including the mandrel, the sleeve, the extrusion cylinder, and the drive mechanism having the above-described structure, by performing the first method including the above-described first to third processes, it is possible to highly accurately and easily mold a non-uniform wall thickness tube having a hollow portion from a blank having a simple structure. That is, the first method is a manufacturing method of a non-uniform wall thickness tube having a solid portion that can reduce the occurrence of defects such as cracks and / or material accumulation without requiring a blank having a complex shape.

[0081] Such a non-uniform wall thickness tube having a solid portion is useful as a component that is required to achieve a desired mechanical strength in the thick wall portion and to achieve weight reduction in the thin wall portion (portion other than the thick wall portion). Further, for example, if a non-uniform wall thickness tube having a solid portion as described above is used as a component that requires a oil seal device among the components of the shaft system, a bolt for the oil seal device is not required, and the degree of freedom in design can be increased and the manufacturing cost can be reduced.

[0082] <<Second Embodiment>>

[0083] Hereinafter, an extrusion molding method of a non-uniform wall thickness tube having a solid portion according to the second embodiment of the present invention (hereinafter sometimes referred to as the "second method") will be described with reference to the drawings.

[0084] As described above, in the first method, the relative distance in the extrusion direction, i.e., the front-end distance, between the end of the front-end side of the sleeve and the end of the front-end side of the mandrel is maintained at a first distance that is a specified distance, and the sleeve and the mandrel are advanced in the extrusion direction. As a result, the blank is pressed into the small-inner-diameter portion through the inner-diameter reducing portion of the extrusion cylinder hole, and extrusion processing is performed. As a result, in the third process in which a part of the front-end side of the first hollow portion PH1 of the blank 21 is extruded into the fourth hollow portion PH4 and the third hollow portion PH3 of the unequal-thickness tube 31, the bottom of the first hollow hole of the blank and the end of the front-end side of the mandrel are separated from each other. That is, in the third process, the mandrel does not contribute to the extrusion processing but has the following function: maintaining the cross-sectional shape of the hollow hole during the change from the first hollow hole formed in the blank to the second hollow hole formed in the unequal-thickness tube 31.

[0085] As a result, an unequal-thickness tube having a hollow portion can be formed from a blank having a simple structure with high precision and easily. That is, according to the first method, the occurrence of defects such as cracks and / or material accumulation can be reduced, and an unequal-thickness tube having a solid portion can be easily manufactured without a blank having a complex shape.

[0086] However, as described above, depending on, for example, the materials constituting the blank, the mandrel, the sleeve, and / or the extrusion cylinder, and the conditions of the extrusion processing such as the extrusion load and / or the extrusion speed, there is a case where a so-called "upsetting phenomenon" occurs at the moment of starting to press the blank into the small-inner-diameter portion through the inner-diameter reducing portion of the extrusion cylinder hole formed in the extrusion cylinder (i.e., the start moment of the extrusion processing). In this case, due to the plastic flow of the material constituting the blank and / or the elastic deformation of the extrusion cylinder, the blank expands outward in the radial direction and contracts in the axial direction, and the bottom of the first hollow hole formed in the blank is slightly displaced toward the base end side. As a result, the end of the front-end side of the mandrel is pressed toward the base end side by the bottom of the first hollow hole, and due to the reaction, stress acts on the bottom of the first hollow hole, and there is a case where cracks are generated at the boundary between the bottom of the first hollow hole and the side wall portion.

[0087] <Structure>

[0088] Therefore, the second method is an extrusion molding method of an unequal-thickness tube having a hollow portion, which is characterized in that at least at the start moment of the extrusion processing in the second process, i.e., the second moment, the bottom of the first hollow hole of the blank and the mandrel are not in contact.

[0089] Figure 5 is a schematic cross-sectional view showing an example of the positional relationship between the bottom of the first hollow hole and the mandrel near the bottom of the first hollow hole of the blank at the start moment of the second process included in the second method, and is in Figure 4An enlarged view of the area enclosed by the thick dashed line in (a) of. As Figure 5 As exemplified in, in the second method, at least at the moment (the second moment) when the sleeve 51 (not shown) and the mandrel 41 start to move forward in the extrusion direction, the bottom of the first hollow hole HH1 of the blank 21 does not contact the mandrel 41. Specifically, in Figure 5 In the example shown, a gap G is provided between the bottom of the first hollow hole HH1 of the blank 21 and the mandrel 41.

[0090] In summary, even in the case where upsetting occurs at the start of the extrusion process in the second process as described above and the bottom of the first hollow hole formed in the blank is displaced toward the base end side, the possibility of the bottom of the hollow hole squeezing the front end of the mandrel can be reduced. As a result, the concern about cracking at the boundary between the bottom and the side wall of the first hollow hole due to the reaction of the bottom of the first hollow hole squeezing the front end of the mandrel can be reduced.

[0091] In addition, in Figure 5 In the blank 21 exemplified in, the bottom (the end on the front end side) of the first hollow hole HH1 has a conical shape. Therefore, in Figure 5 In the example shown, the distance between the average position in the axial direction of the bottom surface of the first hollow hole HH1 of the blank 21 and the front end surface of the mandrel 41 is used as the gap G between the bottom of the first hollow hole HH1 of the blank 21 and the mandrel 41. However, the shape of the bottom of the first hollow hole HH1 is not limited to this. For example, it can be set to various shapes according to the use of the non-uniform wall thickness tube 31 and / or the shape of the end on the front end side of the mandrel. For example, the shape of the bottom of the first hollow hole HH1 can be a plane perpendicular to the axial direction of the blank 21, or a curved surface convex on the front end side (such as a spherical surface, etc.).

[0092] <Effect>

[0093] As described above, according to the second method, even in the case where upsetting occurs at the start of the extrusion process in the second process and the bottom of the first hollow hole formed in the blank is displaced toward the base end side, the possibility of the bottom of the hollow hole squeezing the front end of the mandrel can be reduced. As a result, the concern about cracking at the boundary between the bottom and the side wall of the first hollow hole due to the reaction of the bottom of the first hollow hole squeezing the front end of the mandrel can be reduced.

[0094] <Third Embodiment>

[0095] Hereinafter, an extrusion molding method of a non-uniform wall thickness tube having a solid part according to the third embodiment of the present invention (hereinafter, there is a case called "the third method") will be described with reference to the drawings.

[0096] As described above, in the second method, at least at the moment when the sleeve and the mandrel start to advance toward the extrusion direction (the second moment), the bottom of the first hollow hole of the blank does not contact the mandrel. Therefore, according to the second method, even when upsetting occurs at the start of the extrusion process in the second step and the bottom of the first hollow hole formed in the blank is displaced toward the proximal end side, the possibility of the bottom of the hollow hole squeezing the front end of the mandrel can be reduced. As a result, the concern about cracking occurring at the boundary between the bottom of the first hollow hole and the side wall portion due to the reaction of the bottom of the first hollow hole squeezing the front end of the mandrel can be reduced.

[0097] However, if the gap G (initial gap) between the bottom of the first hollow hole of the blank and the mandrel at the second moment is too small, there is a concern that cracking at the boundary between the bottom of the first hollow hole and the side wall portion cannot be sufficiently reduced. Therefore, it is considered preferable to set the initial gap to be sufficiently large in order to sufficiently reduce the concern about cracking at the boundary between the bottom of the first hollow hole and the side wall portion. However, as a result of further research by the present inventors, it has been found that there are cases where, depending on, for example, the materials constituting the blank, the mandrel, the sleeve, and / or the extrusion cylinder, and the extrusion processing conditions such as the extrusion load and / or the extrusion speed, even if the initial gap is too large, the concern about cracking at the boundary between the bottom of the first hollow hole and the side wall portion cannot be sufficiently reduced. That is, for the initial gap, there is an appropriate range in order to sufficiently reduce the concern about cracking at the boundary between the bottom of the first hollow hole and the side wall portion.

[0098] <Structure>

[0099] Therefore, the third method is an extrusion molding method of an unequal-thickness tube having a hollow portion, which is based on the above-described second method and is characterized in that the length of the initial gap in the extrusion direction, that is, the initial length, is equal to or greater than a specified first length and less than a specified second length that is longer than the first length. The initial gap is the gap between the bottom of the first hollow hole of the blank and the end portion on the front end side of the mandrel at the second moment.

[0100] In addition, the first length can be determined based on the magnitude of the dimensional change of the blank during the period from the second moment to the third moment, and the third moment is the moment when the end portion on the front end side of the blank starts to enter the inner diameter reducing portion of the extrusion cylinder hole. Preferably, the first length can be determined based on the magnitude of the displacement of the bottom of the first hollow hole toward the proximal end side during the period from the second moment to the third moment. The magnitude of the dimensional change of the blank such as the displacement of the bottom of the first hollow hole toward the proximal end side can be determined, for example, through verification of a preliminary experiment in advance and / or computer simulation such as flow analysis.

[0101] On the other hand, the second length can be determined to be a specified length that is equal to or less than the maximum length such that the material forming the blank does not flow into the first gap during the period from the second moment to the first moment (the specified moment after the end portion on the front end side of the mandrel passes through the inner diameter reduction portion of the extrusion cylinder hole). The second length can also be determined by, for example, verification through preliminary experiments in advance and / or computer simulations such as flow analysis.

[0102] <Effect>

[0103] As described above, in the third method, in order to sufficiently reduce the concern about cracking occurring at the boundary between the bottom and the side wall portion of the first hollow hole at the moment (the second moment) when the sleeve and the mandrel start to advance in the extrusion direction, the initial gap is set within an appropriate range. As a result, according to the third method, the concern about cracking occurring at the boundary between the bottom and the side wall portion of the first hollow hole of the blank can be more reliably reduced.

[0104] <<Fourth Embodiment>>

[0105] In addition, as described at the beginning of this specification, the present invention relates not only to an extrusion molding method for an unequal-thickness tube having a solid portion represented by the above-described first to third methods, but also to an extrusion molding apparatus for an unequal-thickness tube having a solid portion. Therefore, an extrusion molding apparatus for an unequal-thickness tube having a solid portion according to various embodiments of the present invention will be described below.

[0106] First, an extrusion molding apparatus for an unequal-thickness tube according to the fourth embodiment of the present invention (hereinafter sometimes referred to as the "fourth apparatus") will be described.

[0107] <Structure>

[0108] The fourth apparatus is an extrusion molding apparatus for an unequal-thickness tube having a solid portion, and includes: a mandrel having a specified shape, a sleeve having a specified shape, an extrusion cylinder formed with a through hole having a specified shape, that is, an extrusion cylinder hole, and a drive mechanism configured to press the mandrel into the extrusion cylinder hole. As described above, the basic structure of such an extrusion molding apparatus is well known to those skilled in the art, and constituent elements represented by the mandrel, the sleeve, and the extrusion cylinder are made of a material having properties (such as mechanical strength and durability) that can withstand processing conditions such as loads acting on the constituent elements during the above-described extrusion process.

[0109] The fourth apparatus is configured to form an unequal-thickness tube having a hollow portion from a blank having a specified shape by extrusion processing by performing the first to third processes listed below.

[0110] The first step is as follows: Insert the blank into the large inner diameter portion of the extrusion cylinder hole, make the end portion on the front end side of the blank abut against the inner diameter reducing portion of the extrusion cylinder hole, make the sleeve abut against the end portion on the base end side of the blank, insert the mandrel into the first hollow hole of the blank, and fix the front end distance to a first distance which is a specified distance. The above-mentioned front end distance is the relative distance in the extrusion direction between the end portion on the front end side of the sleeve and the end portion on the front end side of the mandrel.

[0111] The second step is as follows: Maintain the front end distance at the first distance and move the sleeve and the mandrel forward in the extrusion direction. Thereby, press the blank into the small inner diameter portion through the inner diameter reducing portion of the extrusion cylinder hole to perform extrusion processing, and continue to move the sleeve and the mandrel forward until the first moment. The above-mentioned first moment is the moment when the end portion on the front end side of the mandrel reaches the end portion on the base end side of the inner diameter reducing portion of the extrusion cylinder hole.

[0112] The third step is as follows: After the first moment, also maintain the front end distance at the first distance and move the sleeve and the mandrel forward in the extrusion direction.

[0113] Details regarding the first step to the third step have been described in the above description related to the first method, and thus the description here is omitted.

[0114] As already referred to Figure 1 As described above, the blank 21 is composed of a first hollow portion PH1 and a first solid portion PS1, and is a member having a cylindrical outer shape with a first outer diameter DO1 having a specified outer diameter as a whole. The first hollow portion PH1 is open at the end face on the upstream side in the extrusion direction, that is, the base end side, and has a first hollow hole HH1 which is a cylindrical space having a first inner diameter DI1 with a specified inner diameter, and is a cylindrical portion having a first wall thickness T1 with a specified wall thickness. The first solid portion PS1 is a cylindrical portion located between the end face on the downstream side in the extrusion direction, that is, the front end side, and the first hollow portion PH1.

[0115] In addition, the unequal-thickness tube 31 is a component composed of a second hollow portion PH2, a third hollow portion PH3, a fourth hollow portion PH4, and a second solid portion PS2. The second hollow portion PH2 is a cylindrical portion having a first outer diameter DO1 and a first wall thickness T1. The third hollow portion PH3 is adjacent to the front-end side of the second hollow portion PH2, and the outer diameter changes from the first outer diameter DO1 at the base-end side toward the front-end side to a second outer diameter DO2 that is smaller than the first outer diameter DO1, and the wall thickness changes from the first wall thickness T1 at the base-end side toward the front-end side to a second wall thickness T2 that is smaller than the first wall thickness T1. The fourth hollow portion PH4 is adjacent to the front-end side of the third hollow portion PH3 and is a cylindrical portion having the second outer diameter DO2 and the second wall thickness T2. The second solid portion PS2 is a cylindrical portion located between the end portion on the front-end side and the fourth hollow portion PH4 and having the second outer diameter DO2. Further, a second hollow hole HH2 is continuously formed from the second hollow portion PH2 to the fourth hollow portion PH4. The second hollow hole HH2 is a cylindrical space that opens at the end face on the base-end side and has a first inner diameter DI1.

[0116] As already referred to Figure 2 As described above, the mandrel 41 is coaxially and axially slidably inserted into the sleeve 51 and is a component having a cylindrical shape with a third outer diameter DO3 corresponding to the inner diameter of the first hollow portion PH1 of the blank 21, that is, the first inner diameter DI1. The sleeve 51 is coaxially and axially slidably externally inserted into the mandrel 41 and is a component having a cylindrical shape with a second inner diameter DI2 corresponding to the outer diameter of the mandrel 41, that is, the third outer diameter DO3, and the outer diameter of the blank 21, that is, the first outer diameter DO1.

[0117] In addition, the extrusion cylinder hole HC1 formed in the extrusion cylinder 61 is composed of a large-inner-diameter portion PDIL, a small-inner-diameter portion PDIS, and an inner-diameter reduction portion PDIT. The large-inner-diameter portion PDIL is a portion formed at the base-end side and having a third inner diameter DI3 corresponding to the outer diameter of the blank 21, that is, the first outer diameter DO1. The small-inner-diameter portion PDIS is a portion formed at the front-end side and having a fourth inner diameter DI4 corresponding to the outer diameter of the fourth hollow portion PH2 and the second solid portion PS2 of the unequal-thickness tube 31, that is, the second outer diameter DO2. The inner-diameter reduction portion PDIT is a portion formed between the large-inner-diameter portion PDIL and the small-inner-diameter portion PDIS, and the inner diameter decreases from the third inner diameter DI3 to the fourth inner diameter DI4 as it approaches the small-inner-diameter portion PDIS from the large-inner-diameter portion PDIL.

[0118] As described above, the fourth device is an extrusion molding device for an unequal-thickness tube with a solid part corresponding to the first method described above. Therefore, regarding the unequal-thickness tube formed by the fourth device, the blank that is the source of the formed unequal-thickness tube, the original blank that is the source of the blank, and the mandrel, sleeve, and extrusion cylinder that make up the fourth device, it can be clearly understood from the above description related to the first method, so the description here is omitted.

[0119] <Effect>

[0120] By performing the first to third processes in the fourth device having the structure described above, it is possible to accurately and easily form an unequal-thickness tube with a hollow part from a blank having a simple structure. That is, the fourth device is a manufacturing device for an unequal-thickness tube with a solid part that can reduce the occurrence of defects such as cracks and / or material accumulation without requiring a blank with a complex shape.

[0121] <<Fifth Embodiment>>

[0122] Next, an extrusion molding device for an unequal-thickness tube with a solid part according to the fifth embodiment of the present invention (hereinafter sometimes referred to as the "fifth device") will be described.

[0123] <Structure>

[0124] The fifth device is an extrusion molding device for an unequal-thickness tube with a hollow part, which is characterized in that at least at the start time of the extrusion process in the second process, that is, the second time, the bottom of the first hollow hole of the blank does not contact the mandrel, based on the above fourth device.

[0125] As described above, the fifth device is an extrusion molding device for an unequal-thickness tube with a solid part corresponding to the second method described above. Therefore, regarding the structure and working details of the fifth device, it can be clearly understood from the description related to the second method, so the description here is omitted.

[0126] <Effect>

[0127] According to the fifth device, even when a upsetting phenomenon occurs at the start time of the extrusion process in the second process and the bottom of the first hollow hole formed in the blank is displaced toward the base end side, the possibility of the bottom of the hollow hole squeezing the front end of the mandrel can be reduced. As a result, the concern about cracks occurring at the boundary between the bottom and the side wall part of the first hollow hole due to the reaction of the bottom of the first hollow hole squeezing the front end of the mandrel can be reduced.

[0128] <<Sixth Embodiment>>

[0129] Next, an extrusion molding device for an unequal-thickness tube with a solid part according to the sixth embodiment of the present invention (hereinafter sometimes referred to as the "sixth device") will be described.

[0130] <Structure>

[0131] The sixth device is an extrusion molding method of an unequal-thickness tube with a hollow part, which is based on the above-mentioned fifth device and is characterized in that the length of the initial gap in the extrusion direction, that is, the initial length, is equal to or greater than a specified first length and less than a specified second length that is longer than the first length. The initial gap is the gap between the bottom of the first hollow hole of the blank at the second moment and the end portion on the front end side of the mandrel. The first length can be determined based on the magnitude of the dimensional change of the blank during the period from the second moment to the third moment, and the third moment is the moment when the end portion on the front end side of the blank starts to enter the inner diameter reduction portion of the extrusion cylinder hole. The second length can be determined as a specified length that is equal to or less than the maximum length during which the material constituting the blank does not flow into the first gap during the period from the second moment to the first moment (a specified moment after the moment when the end portion on the front end side of the mandrel passes through the inner diameter reduction portion of the extrusion cylinder hole).

[0132] As described above, the sixth device is an extrusion molding device for an unequal-thickness tube with a solid part corresponding to the above-mentioned third method. Therefore, regarding the structure and working details of the sixth device, they can be clearly understood according to the description related to the third method, and thus the description here is omitted.

[0133] <Effect>

[0134] In the sixth device, in order to sufficiently reduce the concern about cracking at the boundary between the bottom of the first hollow hole and the side wall portion at the moment (the second moment) when the sleeve and the mandrel start to advance in the extrusion direction, the initial gap is set within an appropriate range. As a result, according to the sixth device, the concern about cracking at the boundary between the bottom of the first hollow hole of the blank and the side wall portion can be more reliably reduced.

[0135] As described above, in order to explain the present invention, several embodiments with specific structures have been sometimes described with reference to the drawings. Of course, the scope of the present invention should not be construed as being limited by the above-mentioned exemplary embodiments, but can be appropriately modified within the scope of the matters described in the claims and the specification.

[0136] Description of Reference Numerals

[0137] 11…Original blank; 21…Blank; 31…Uneven-wall tube; 41…Mandrel; 51…Casing; 61…Extrusion cylinder; DO1…First outer diameter; DO2…Second outer diameter; DO3…Third outer diameter; DI1…First inner diameter; DI2…Second inner diameter; DI3…Third inner diameter; DI4…Fourth inner diameter; HH1…First hollow hole; HH2…Second hollow hole; T1…First wall thickness; T2…Second wall thickness; PH1…First hollow part; PH2…Second hollow part; PH3…Third hollow part; PH4…Fourth hollow part; PS1…First solid part; PS2…Second solid part; HC1…Extrusion cylinder hole; PDIL…Large inner diameter part; PDIS…Small inner diameter part; PDIT…Inner diameter reduction part; G…Gap.

Claims

1. An extrusion molding method for an unequal-thickness tube with a hollow part, which is an extrusion molding method for forming an unequal-thickness tube with a hollow part from a blank having a specified shape through extrusion processing in an extrusion molding device. The extrusion molding device includes: a mandrel having a specified shape; a sleeve having a specified shape; an extrusion cylinder formed with a through hole having a specified shape, that is, an extrusion cylinder hole; and a drive mechanism configured to press the mandrel into the extrusion cylinder hole. The extrusion molding method for the unequal-thickness tube with a hollow part is characterized in that the blank is a component composed of a first hollow part and a first solid part, and has a cylindrical outer shape with a first outer diameter having a specified outer diameter as a whole. The first hollow part is open at the end face on the upstream side, that is, the base end side in the extrusion direction, and forms a first hollow hole with a cylindrical space having a first inner diameter with a specified inner diameter, and a cylindrical part with a first wall thickness having a specified wall thickness. The first solid part is a cylindrical part located between the end face on the downstream side, that is, the front end side in the extrusion direction and the first hollow part. the unequal-thickness tube is a component composed of a second hollow part, a third hollow part, a fourth hollow part, and a second solid part, and a component in which a second hollow hole is continuously formed from the second hollow part to the fourth hollow part. The second hollow part is a cylindrical part having the first outer diameter and the first wall thickness. The third hollow part is adjacent to the front end side of the second hollow part, and the outer diameter changes from the first outer diameter to a second outer diameter smaller than the first outer diameter from the base end side to the front end side, and the wall thickness changes from the first wall thickness to a second wall thickness smaller than the first wall thickness from the base end side to the front end side. The fourth hollow part is adjacent to the front end side of the third hollow part and is a cylindrical part having the second outer diameter and the second wall thickness. The second solid part is a cylindrical part located between the end portion on the front end side and the fourth hollow part and having the second outer diameter. The second hollow hole is open at the end face on the base end side and has a cylindrical space having the first inner diameter. The mandrel is coaxially and slidably embedded in the sleeve in the axial direction, and is a component having a cylindrical shape with a third outer diameter corresponding to the first inner diameter. The sleeve is coaxially and slidably externally embedded in the mandrel in the axial direction, and is a component having a cylindrical shape with a second inner diameter corresponding to the third outer diameter and the first outer diameter. The extrusion cylinder hole is composed of a large inner diameter part, a small inner diameter part, and an inner diameter reduction part. The large inner diameter part is formed on the base end side and has a third inner diameter corresponding to the first outer diameter. The small inner diameter part is formed on the front end side and has a fourth inner diameter corresponding to the second outer diameter. The inner diameter reduction part is formed between the large inner diameter part and the small inner diameter part, and the inner diameter decreases from the third inner diameter to the fourth inner diameter as it approaches the small inner diameter part from the large inner diameter part. The extrusion molding method of the unequal-thickness tube with a hollow part includes: The first step, in this first step, insert the blank into the large inner diameter part of the extrusion cylinder hole, make the end of the front end side of the blank abut against the inner diameter reduction part of the extrusion cylinder hole, make the sleeve abut against the end of the base end side of the blank, insert the mandrel into the first hollow hole of the blank, and fix the front end distance to a first distance which is a specified distance. The front end distance is the relative distance in the extrusion direction between the end of the front end side of the sleeve and the end of the front end side of the mandrel. The second step, in this second step, maintain the front end distance as the first distance and move the sleeve and the mandrel forward in the extrusion direction, thereby pressing the blank through the inner diameter reduction part of the extrusion cylinder hole into the small inner diameter part for extrusion processing, and continue to move the sleeve and the mandrel forward until the first moment. The first moment is the moment when the end of the front end side of the mandrel reaches the end of the base end side of the inner diameter reduction part of the extrusion cylinder hole. And The third step, in this third step, also maintain the front end distance as the first distance and move the sleeve and the mandrel forward in the extrusion direction after the first moment.

2. The extrusion molding method of the unequal-thickness tube with a hollow part according to claim 1, wherein At least at the start moment of the extrusion processing in the second step, that is, the second moment, the bottom of the first hollow hole of the blank is not extruded by the mandrel.

3. The extrusion molding method of the unequal-thickness tube with a hollow part according to claim 2, wherein At the second moment, the bottom of the first hollow hole of the blank and the mandrel are not in contact.

4. The extrusion molding method of the unequal-thickness tube with a hollow part according to claim 3, wherein The initial length is equal to or greater than a specified first length and less than a specified second length which is longer than the first length. The initial length is the length in the extrusion direction of the initial gap. The initial gap is the gap between the bottom of the first hollow hole of the blank at the second moment and the end of the front end side of the mandrel. The first length is determined based on the magnitude of the dimensional change of the blank during the period from the second moment to the third moment, where the third moment is the moment when the end on the front end side of the blank starts to enter the inner diameter reducing portion of the extrusion cylinder hole. The second length is determined as a specified length that is equal to or less than the maximum length such that the material constituting the blank does not flow into the first gap during the period from the second moment to the first moment.

5. An extrusion molding apparatus for an unequal-thickness tube having a hollow portion, comprising: a mandrel having a specified shape; a sleeve having a specified shape; an extrusion cylinder formed with a through hole having a specified shape, namely an extrusion cylinder hole; and a drive mechanism configured to press the mandrel into the extrusion cylinder hole. It is configured to form an unequal-thickness tube having a hollow portion by extrusion processing from a blank having a specified shape. The extrusion molding apparatus for the unequal-thickness tube having a hollow portion is characterized in that the blank is a member having a cylindrical outer shape with a first outer diameter having a specified outer diameter, and is composed of a first hollow portion and a first solid portion. The first hollow portion is a first hollow hole having a cylindrical space with a first inner diameter having a specified inner diameter and opening at the end face on the upstream side, i.e., the base end side, in the extrusion direction, and is a cylindrical portion having a first wall thickness having a specified wall thickness. The first solid portion is a cylindrical portion located between the end face on the downstream side, i.e., the front end side, in the extrusion direction and the first hollow portion. The unequal-thickness tube is a member composed of a second hollow portion, a third hollow portion, a fourth hollow portion, and a second solid portion, and is formed with a second hollow hole continuously from the second hollow portion to the fourth hollow portion. The second hollow portion is a cylindrical portion having the first outer diameter and the first wall thickness. The third hollow portion is adjacent to the front end side of the second hollow portion, and the outer diameter changes from the first outer diameter to a second outer diameter smaller than the first outer diameter from the base end side toward the front end side, and the wall thickness changes from the first wall thickness to a second wall thickness smaller than the first wall thickness from the base end side toward the front end side. The fourth hollow portion is adjacent to the front end side of the third hollow portion and is a cylindrical portion having the second outer diameter and the second wall thickness. The second solid portion is a cylindrical portion located between the end on the front end side and the fourth hollow portion and having the second outer diameter. The second hollow hole opens at the end face on the base end side and has a cylindrical space with the first inner diameter. The mandrel is coaxially and slidably embedded in the sleeve in the axial direction, and is a member having a cylindrical shape with a third outer diameter corresponding to the first inner diameter. The sleeve is coaxially and slidably externally embedded in the mandrel in the axial direction, and is a member having a cylindrical shape with a second inner diameter corresponding to the third outer diameter and the first outer diameter. The extrusion cylinder hole is composed of a large inner diameter portion, a small inner diameter portion, and an inner diameter reduction portion. The large inner diameter portion is formed on the base end side and has a third inner diameter corresponding to the first outer diameter. The small inner diameter portion is formed on the front end side and has a fourth inner diameter corresponding to the second outer diameter. The inner diameter reduction portion is formed between the large inner diameter portion and the small inner diameter portion, and the inner diameter decreases from the third inner diameter to the fourth inner diameter as it approaches the small inner diameter portion from the large inner diameter portion. The extrusion molding apparatus for an unequal-thickness tube having a hollow portion is configured to mold the unequal-thickness tube by performing the following steps: A first step, in this first step, the blank is inserted into the large inner diameter portion of the extrusion cylinder hole, the end portion on the front end side of the blank is brought into contact with the inner diameter reduction portion of the extrusion cylinder hole, the sleeve is brought into contact with the end portion on the base end side of the blank, the mandrel is inserted into the first hollow hole of the blank, and the front end-to-front end distance is fixed to a first distance that is a specified distance. The front end-to-front end distance is the relative distance in the extrusion direction between the end portion on the front end side of the sleeve and the end portion on the front end side of the mandrel. A second step, in this second step, the front end-to-front end distance is maintained at the first distance and the sleeve and the mandrel are advanced in the extrusion direction, thereby pressing the blank through the inner diameter reduction portion of the extrusion cylinder hole into the small inner diameter portion for extrusion processing, and continuing the advancement of the sleeve and the mandrel until a first moment, which is the moment when the end portion on the front end side of the mandrel reaches the end portion on the base end side of the inner diameter reduction portion of the extrusion cylinder hole. And A third step, in this third step, after the first moment, the front end-to-front end distance is also maintained at the first distance and the sleeve and the mandrel are advanced in the extrusion direction.

6. The extrusion molding apparatus for an unequal-thickness tube having a hollow portion according to claim 5, wherein: At least at the start moment of the extrusion processing in the second step, that is, the second moment, the bottom of the first hollow hole of the blank is not pressed by the mandrel.

7. The extrusion molding apparatus for an unequal-thickness tube having a hollow portion according to claim 6, wherein: At the second moment, the bottom of the first hollow hole of the blank and the mandrel are not in contact.

8. The extrusion molding apparatus for an unequal-thickness tube having a hollow portion according to claim 7, wherein: The initial length is equal to or greater than a specified first length and less than a specified second length that is longer than the first length. The initial length is the length in the extrusion direction of the initial gap, and the initial gap is the gap between the bottom of the first hollow hole of the blank at the second moment and the end portion on the front end side of the mandrel. The first length is determined based on the magnitude of the dimensional change of the blank during the period from the second moment to the third moment, where the third moment is the moment when the end portion on the front end side of the blank starts to enter the inner diameter reducing portion of the extrusion cylinder hole. The second length is determined as a specified length that is equal to or less than the maximum length at which the material constituting the blank does not flow into the first gap during the period from the second moment to the first moment.

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