Fluid pressure cylinder, method for manufacturing a fluid pressure cylinder

Abstract

To provide an inexpensive fluid pressure cylinder having a structure for enclosing burrs on the inner peripheral side of a tube generated by friction welding. 【Solution means】The tube 10 has a large-diameter portion 11 with a larger inner diameter than other portions formed in a predetermined range at the end. The predetermined range where the large-diameter portion 11 is formed is such that when the joining by friction welding is completed, the flange portion 23 contacts the edge 11a. The cylinder end 20 has a slightly smaller diameter than the tube 10, and a cylinder-end side large-diameter portion 21 having the same diameter as the tube 10 is formed at the friction welding portion. A protruding portion 22 having a smaller diameter than the inner diameter of the tube 10 is formed from the end face of the large-diameter portion. A flange portion 23 having an outer diameter substantially equal to the inner diameter of the large-diameter portion 11 is formed at the tip of the protruding portion 22. The flange portion 23 is formed in a thin plate shape that spreads in the radial direction, and a depression is formed in the range surrounded by the cylinder-end side large-diameter portion 21, the protruding portion 22, and the flange portion 23.

Description

Technical Field

[0001] The present invention relates to the structure of a hydraulic cylinder manufactured by friction pressure welding.

Background Art

[0002] Conventionally, when manufacturing a cylinder tube of a hydraulic cylinder, a disk-shaped member is aligned and held at one end of a cylindrical member, and the boundary portion is welded while rotating each member. However, when welding is performed in this way, the welded portion is only on the outside of the cylinder tube and the cylindrical member, and there is a limit to the range to be welded with respect to the thickness of the member. In particular, as the cylinder becomes larger and the cylindrical member becomes thicker, the ratio of the joint portion to the cross section decreases.

[0003] In addition, when joining members by welding, if the management of welding defects is not thorough, it may cause the working fluid to leak from the welded portion. However, if a precise inspection of the welded portion is performed for this purpose, there is a problem that the manufacturing cost increases.

[0004] Therefore, friction pressure welding is used as a joining method that can join the entire cross section of a cylindrical member and can suppress the occurrence of welding defects. Friction pressure welding is a method of joining by bringing two members into contact, generating frictional heat by rotating one member at high speed while keeping the other member stationary, heating the members to a high temperature by this frictional heat, and then pressing the members against each other at high pressure (upset pressurization) after stopping the rotation.

[0005] When joining a cylindrical member by friction pressure welding, burrs extruded by high pressure are generated on both the outer peripheral side and the inner peripheral side. Since the inner peripheral surface of the hydraulic cylinder separates the working fluid chambers on the extending side and the shortening side by sliding while the packing fitted to the piston is in close contact, the burrs may damage the packing. In addition, when the burrs are peeled off from the inner peripheral surface during the operation of the cylinder, there is also a risk of damaging the entire flow path of the working fluid. Therefore, in the manufacturing process of the cylinder, it is desirable to remove burrs. However, in the case of a cylinder tube, the location where burrs are generated is away from the opening, and moreover, burrs are generated over the entire circumference. Therefore, it is difficult to remove the burrs on the inner circumferential side of the cylinder.

[0006] Therefore, the hydraulic cylinder disclosed in Patent Document 1 forms a space in a disc-shaped member in order to contain the burrs generated on the inner circumferential side of the cylinder, and further includes a flange portion (reference numeral 101 in FIG. 2 of Patent Document 1) for covering this space. The flange portion is sized such that a gap is formed between it and the inner circumferential surface of the cylindrical member. Since the gap is as narrow as 0.5 mm to 1 mm, burrs larger than the gap are prevented from entering the inside of the working fluid chamber. Note that if no gap is formed, frictional heat is also generated in the flange portion due to high-speed rotation during joining, leading to the occurrence of defective products such as the formation of an unexpected gap through which burrs can pass.

[0007] In addition, Patent Document 2 discloses a hydraulic cylinder having a structure in which tapered surfaces are brought into contact with each other to seal the burr-containing space. Briefly explained, during rotation, the tapered surfaces are separated from each other, but during upset pressing, the tapered portions approach each other by the amount of the approach allowance, so the tapered surfaces also approach and finally come into close contact. Therefore, the burr-containing space is sealed.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] Since the flange disclosed in Patent Document 1 has a gap formed between it and the inner peripheral surface of the cylinder, there is a possibility that burrs smaller than the gap may enter the working oil chamber. On the other hand, since the cylinder disclosed in Patent Document 2 confines burrs by bringing the tapered surfaces formed on the tube and the lid portion into close contact with each other, the possibility of burrs entering the working fluid chamber is extremely low. However, in the case of such a structure, in order to ensure sealing, the tapered surface must be machined with high dimensional accuracy, and furthermore, the entire circumference must be evenly pressurized during upset pressing, requiring high-precision machining, resulting in a problem of high machining costs.

[0010] In view of such circumstances, an object of the present invention is to inexpensively provide a fluid pressure cylinder having a structure for enclosing burrs on the inner peripheral side of a tube generated by friction pressure welding.

Means for Solving the Problems

[0011] A first invention is a fluid pressure cylinder in which a tube and a cylinder end are joined by friction pressure welding, wherein a surface of the cylinder end facing the inside of the tube has a cylindrical protruding portion protruding into the tube coaxially with the tube, and between a position on the inner peripheral surface of the tube that overlaps with the tip portion of the protruding portion in the radial direction and the joint portion with the cylinder end, it is a large-diameter portion having a larger inner diameter than other portions of the inner peripheral surface, and a space for accommodating internal burrs generated by friction pressure welding is formed between the inner peripheral surface of the large-diameter portion and the peripheral surface of the protruding portion, and a flange portion having an outer diameter smaller than the inner diameter of the large-diameter portion and larger than the inner diameter of the other portions is formed over the entire circumference at the tip portion of the protruding portion, and the fluid pressure cylinder is characterized in that the flange portion is in close contact with an edge that is a boundary between the large-diameter portion and the other portion of the tube over the entire circumference.

[0012] A second invention is a fluid pressure cylinder, wherein the flange portion according to the first invention is bent toward the joint portion.

[0013] The third invention is a fluid pressure cylinder characterized in that the edge described in the first invention is located closer to the center in the longitudinal direction of the tube than the end face of the protruding portion, and the flange portion is bent toward the center in the longitudinal direction of the tube over the entire circumference and is in close contact with the edge.

[0014] The fourth invention is a fluid pressure cylinder characterized in that the inner burr described in the first to third inventions does not contact the flange portion.

[0015] The fifth invention is a fluid pressure cylinder characterized in that the inner burr described in any one of the first to third inventions contacts the flange portion.

[0016] The sixth invention is a fluid pressure cylinder in which a tube and a cylinder end are joined by friction pressure welding. On the surface of the cylinder end facing the inside of the tube, a cylindrical protruding portion protruding into the tube is provided coaxially with the tube. From the position where the tip portion of the protruding portion overlaps in the radial direction on the inner peripheral surface of the tube to the joint portion with the cylinder end, it is a taper with an increasing inner diameter toward the side of the joint portion. A space for accommodating the inner burr generated by friction pressure welding is formed between the inner peripheral surface of the taper and the peripheral surface of the protruding portion. A flange portion having an outer diameter smaller than the inner diameter of the end portion on the joint portion side of the tube and larger than the inner diameter of the portion where the taper is not formed is formed over the entire circumference at the tip portion of the protruding portion. The fluid pressure cylinder is characterized in that the flange portion is in close contact with the taper over the entire circumference.

[0017] The seventh invention is a fluid pressure cylinder characterized in that the taper described in the sixth invention is formed by flaring the tube.

[0018] The eighth invention is a hydraulic cylinder in which a tube and a cylinder end are joined by friction pressure welding, wherein on the surface of the cylinder end facing the inside of the tube, a cylindrical protrusion protruding into the inside of the tube is provided coaxially with the tube, and a space for accommodating an internal burr generated by friction pressure welding is formed between the inner peripheral surface of the tube and the peripheral surface of the protrusion, and on the tip portion of the protrusion, a flange portion is formed over the entire circumference such that the outer peripheral portion is in close contact with the inner peripheral surface of the tube and the axial position of the outer peripheral portion is inclined to be on the side of the joining portion of the tube and the cylinder end rather than the end surface of the protrusion, and the hydraulic cylinder is characterized in that the internal burr is in contact with the flange portion.

Advantages of the Invention

[0019] According to the present invention, it is possible to inexpensively provide a hydraulic cylinder having a structure for enclosing a burr on the inner peripheral side of the tube generated by friction pressure welding.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Modes for Carrying Out the Invention

[0021] <First Embodiment> Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals, and duplicate descriptions are omitted. Note that the drawings are schematic. Therefore, it should be noted that the relationship between the thickness and the planar dimensions, the ratio, etc. may be different from the actual ones, and there are parts where the dimensional relationships and ratios are different between the drawings. Further, the embodiments shown below are examples of devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention does not specify the materials, shapes, structures, displays, etc. of the components in the following embodiments. Note that, in the following embodiments, a hydraulic cylinder, which is an example of a fluid pressure cylinder to be described, is fixed in a direction in which the axial direction is along the left - right direction, and it is described that the cylinder end is located on the left side and the tube is located on the right side.

[0022] (Overall Structure of Hydraulic Cylinder) First, the overall structure of the hydraulic cylinder will be described with reference to FIG. 1. The hydraulic cylinder 1 friction - press - contacts a cylinder end 20 serving as a lid at one axial end of a cylindrical tube 10. Although not shown, after inserting a cylinder rod provided with a piston, a cylinder head through which the cylinder rod penetrates is bolted to the other end of the tube 10. In the following description, the description of parts other than the periphery of the joint portion between the tube 10 and the cylinder end 20 according to the present invention will be omitted.

[0023] (Structure of the tube) With reference to FIG. 2, the structure of the tube 10 will be described. The tube 10 has a large-diameter portion 11 with a larger inner diameter than other portions of the inner peripheral surface in a predetermined range on the inner peripheral surface of the end portion on the side where the cylinder end 20 is joined. The predetermined range in which the large-diameter portion 11 is formed is such that when the joining by friction pressure welding is completed, the flange portion 23 described below contacts the edge 11a which is the boundary between the large-diameter portion and the other portion of the tube. That is, it is the length obtained by adding the length of the flange portion 23 up to the length reduced by the formation of burrs during friction pressure welding (extrusion allowance).

[0024] (Structure of the cylinder end) Next, with reference to FIG. 2, the structure of the cylinder end 20 will be described. Most of the cylinder end 20 has a slightly smaller diameter than the inner diameter of the tube 10, but a cylinder end side large-diameter portion 21 having the same diameter as the outer diameter of the tube 10 is formed at one end portion which is the friction pressure welding portion. Further, a cylindrical protrusion 22 having a smaller diameter than the inner diameter of the tube 10 is formed at a position coaxial with the other portions from the surface facing the inside of the tube 10 of the cylinder end side large-diameter portion 21. When the cylinder end 20 is joined to the tube 10, since the tube 10 and the cylinder end 20 are coaxial, the protrusion 22 and the tube 10 are also coaxial.

[0025] A flange portion 23 having an outer diameter substantially equal to the inner diameter of the large-diameter portion 11 is formed over the entire circumference at the tip portion on the circumferential surface of the protrusion 22. The flange portion 23 is formed in a thin plate shape that spreads in the radial direction, and a depression is formed in the range surrounded by the cylinder end side large-diameter portion 21, the protrusion 22, and the flange portion 23. The region surrounded by this depression and the inner peripheral surface of the tube 10 becomes a space 30 for accommodating the internal burr IB in the friction pressure welding process described below.

[0026] (Enclosure of burrs by friction pressure welding) Next, with reference to FIGS. 2 to 7, the generation of burrs when the tube 10 and the cylinder end 20 are friction pressure welded and the enclosure of these burrs will be described. First, as shown in FIG. 2, the cylinder end 20 is rotated at high speed at a position separated from the tube 10. Then, as shown in FIG. 3, by pressing the rotating cylinder end 20 against the tube 10, frictional heat is generated at the joint portion TP. At this time, as shown in FIG. 4, since the flange portion 23 is formed to have a slightly smaller diameter than the inner diameter of the large-diameter portion 11, it rotates without contacting anywhere on the tube 10.

[0027] When the joint portion TP reaches a temperature suitable for joining due to frictional heat, as shown in FIG. 5, the rotation of the cylinder end 20 is stopped, and upset pressure is applied to strongly press it against the tube 10. At this time, the tube 10 and the large-diameter portion 21 on the cylinder end side of the cylinder end 20 are joined by being strongly pressed against each other. At the same time, as shown in FIG. 6, a part of the tube 10 and the cylinder end 20 is extruded, and burrs containing impurities are formed. Hereinafter, the burr formed on the outer peripheral side of the tube 10 is called the outer burr OB, and the burr formed on the inner peripheral side is called the inner burr IB.

[0028] Furthermore, upset pressure is applied, and the upset pressure is stopped when, as shown in FIG. 7, the flange portion 23 contacts the edge 11a of the large-diameter portion 11 and bends toward the joint portion TP. As a result, the flange portion 23 is deformed, and a spring-back force that tries to press itself against the edge 11a of the large-diameter portion 11 is generated. Therefore, the flange portion 23 and the edge 11a of the large-diameter portion 11 are in close contact, and the inner burr IB is confined by the space 30 being sealed. After that, by removing the outer burr OB, the friction pressure welding is completed.

[0029] After removing the outer burr OB, a cylinder head is bolted to the end of the tube 10 on the side opposite to the cylinder end 20, and piping is performed to complete the hydraulic cylinder 1. Furthermore, after that, the hydraulic cylinder 1 is attached to industrial machinery or the like, and the inside is filled with hydraulic oil. The hydraulic oil gradually flows into the space 30 as the hydraulic cylinder 1 operates. This is a phenomenon caused by the flange portion 23 being elastically deformed slightly when receiving the hydraulic pressure, and the sealed state being temporarily released. However, even in such a case, due to the narrow gap between the flange portion 23 and the large-diameter portion 11 and the flow of the hydraulic oil in the direction flowing into the space 30, the entry of small pieces or metal particles that have fallen off into the hydraulic oil is avoided.

[0030] After the inside of the space 30 is filled with the hydraulic oil, the flange portion 23 does not deform even when hydraulic pressure is applied. This is because the hydraulic oil is an incompressible fluid. In reality, however, the space 30 is rarely completely filled with the hydraulic oil, and there are often slightly remaining air bubbles. However, when the flange portion 23 deforms by the volume of the slightly remaining air bubbles being compressed, the deformation remains slight enough to maintain the sealed state, or only a narrower flow path is formed than when it was filled with air, so the entry of metal particles and the like into the hydraulic oil is avoided.

[0031] (Effect of the First Embodiment) With the hydraulic cylinder 1 having the configuration shown in this embodiment, it is possible to prevent small pieces and metal particles from entering the hydraulic oil without removing the internal burr IB. Also, since the containment of the internal burr IB is automatically performed in the friction pressure welding process without requiring special work, the manufacturing cost of the fluid pressure cylinder by friction pressure welding can be reduced.

[0032] Furthermore, since the internal burr IB is contained in the space 30, a removal process using a dedicated cutting tool becomes unnecessary. Therefore, it can be diverted without significantly changing the equipment and process for joining the bars.

[0033] <Second Embodiment> Next, the second embodiment will be described with reference to FIG. 8. The description of the parts having the same structure as those in the first embodiment will be omitted, and only the characteristic parts will be described.

[0034] (Structure of the Tube and the Cylinder End) The tube 10 of this embodiment has a large-diameter portion 12 that is shorter than that of the first embodiment. Also, in accordance with the length of the large-diameter portion 12, the protruding portion 24 of the cylinder end 20 is also shorter than that of the first embodiment.

[0035] (Enclosure of Burrs by Friction Pressure Welding) When joining the tube 10 and the cylinder end 20 by friction pressure welding, since the space 31 formed by the large-diameter portion 12 and the protruding portion 24 becomes narrower than that of the first embodiment due to the above-described structure, the inner burr IB comes into contact with the bent flange portion 25. Therefore, when the inner burr IB grows, the flange portion 25 is pressed by the inner burr IB. As a result, the flange portion 25 is sandwiched between the edge 12a and the inner burr IB, and in addition to the spring-back force generated by its own deformation, it is also pressed against the edge 12a by the pressing force of the inner burr IB.

[0036] (Effects of the Second Embodiment) The hydraulic cylinder according to this embodiment can strongly seal the space 31, so the ability to enclose the inner burr IB is improved. Therefore, it is applicable to hydraulic cylinders that operate at high pressure more than the first embodiment.

[0037] <Third Embodiment> Next, the third embodiment will be described with reference to FIG. 9. The description of the parts having the same structure as those of the first embodiment will be omitted, and only the characteristic parts will be described.

[0038] (Structure of Tube and Cylinder End) The cylinder end 20 of this embodiment has a protruding portion 26 that is shorter than that of the first embodiment. Also, for the tube 10, the length of the large-diameter portion 13 excluding the extrusion allowance is a length that is separated from the length of the protruding portion 26 by a distance equal to or less than the thickness of the flange portion 27.

[0039] (Enclosure of Burrs by Friction Pressure Welding) When joining the tube 10 and the cylinder end 20 by friction welding, since the protruding portion 26 is shorter than the large-diameter portion 13, the flange portion 27 and the edge 13a of the large-diameter portion 13 do not contact each other when the flange portion 27 is not deformed. However, when the internal burr IB is formed, the flange portion 27 is pressed, and the flange portion 27 deforms toward the edge 13a of the large-diameter portion 13, is sandwiched between the internal burr IB and the edge 13a, and the space 32 is sealed. As a result, the internal burr IB is enclosed inside the space 32.

[0040] (Effect of the third embodiment) The fluid pressure cylinder according to the present embodiment can enclose the internal burr IB while shortening the protruding portion 26. Therefore, it is easier to increase the volume of the working fluid chamber than in the first embodiment. That is, when securing a predetermined cylinder stroke, the tube 10 can be shortened, which is advantageous for miniaturization and weight reduction.

[0041] Note that the flange portion 27 may be formed by being inclined in advance toward the central side in the length direction of the tube 10. In that case, even when the internal burr IB does not contact, the flange portion 27 contacts the edge 13a, so that the space 32 is easily sealed.

[0042] <Fourth Embodiment> Next, a fourth embodiment will be described with reference to FIG. 10. Description of parts having the same structure as those in the first embodiment will be omitted, and only characteristic parts will be described.

[0043] (Structure of tube and cylinder end) The tube 40 according to the present embodiment does not have a large-diameter portion, and the inner peripheral surface is smooth. Further, the flange portion 29 of the cylinder end 20 has a diameter larger than the inner diameter of the tube 10 when taking a posture parallel to the end surface of the cylinder end 20. However, the flange portion 29 is inclined toward the joining portion TP so as to have a diameter equal to or smaller than the inner diameter of the tube 40 in advance before performing friction welding.

[0044] (Enclosure of burr by friction welding) When joining the tube 40 and the cylinder end 20 by friction pressure welding, the flange portion 29 does not contact the tube 40 until the initial stage of upset pressure application, and maintains a bent state. Thereafter, when upset pressure is applied, an internal burr IB is formed, and the tip portion contacts the flange portion 29. Then, as the internal burr IB grows, the flange portion 29 is pressed toward the tip side of the protruding portion, and the outer peripheral portion deforms into a posture in which it is in close contact with the inner peripheral surface of the tube 40. Note that even after deformation, the axial position of the outer peripheral portion of the flange portion 29 is located on the side of the joint portion TP with respect to the end surface of the protruding portion 22. In the process of this deformation, the flange portion 29 contacts the inner peripheral surface of the tube 10, and as the internal burr IB grows and is further strongly pressed, the space 33 is sealed and the internal burr IB is confined.

[0045] (Effect of the Fourth Embodiment) The fluid pressure cylinder according to the present embodiment can enclose the internal burr IB in the space 33 even when joining a tube 10 that has not been subjected to processing for forming a large-diameter portion. As a result, it is not necessary to process the inner peripheral surface of the tube 40, and only the cylinder end 20 needs to be processed, so that the manufacturing cost can be reduced. Further, when performing friction pressure welding using a tube manufactured without assuming friction pressure welding, it is possible to enclose the internal burr IB by adjusting the dimensions of the flange portion 29.

[0046] <Fifth Embodiment> Next, referring to FIG. 11, the fourth embodiment will be described. However, the description of the portions having the same structure as those in the first embodiment will be omitted, and only the characteristic portions will be described.

[0047] (Structure of Tube and Cylinder End) The tube 50 according to the present embodiment is thinner in wall thickness than the first embodiment. Instead of the large-diameter portion 11, a taper 51 is formed such that the wall thickness becomes thinner toward the end. Further, the cylinder end 60 has the same diameter as the outer diameter of the tube 50, and the portions other than the protruding portion 62 have the same diameter.

[0048] (Enclosure of Burr by Friction Pressure Welding) When joining the tube 50 and the cylinder end 60 by friction welding, while the cylinder end 60 is rotating, the flange portion 63 is located inside the tube 50, but before upset pressing, the taper 51 and the flange portion 63 do not contact each other. Thereafter, during upset pressing, as the cylinder end 60 moves toward the axial center side of the tube 50, the flange portion 63 comes into contact with the taper 51. Then, the flange portion 63 gradually deforms along the taper 51 and stops at an angle capable of exerting sufficient springback force. As a result, the flange portion 61 is pressed against the taper 71 by the springback force, the space 34 is sealed, and the internal burr IB is contained. Further, since the flange portion 63 is also pressed against the taper 51 by the grown internal burr IB, the space 34 is sealed more powerfully than the springback force.

[0049] (Effect of the Fifth Embodiment) The taper 51 can be set to an angle close to the angle when the flange portion 63 deforms. Therefore, it is possible to widen the contact surface compared to the case of contacting the large-diameter portion 11, and the ability to contain the internal burr IB is high. Also, since the flange portion 63 is deformed to achieve surface contact instead of contacting pre-processed surfaces, the required machining accuracy of the taper surface can be low, and the cost of machining can be reduced.

[0050] <Sixth Embodiment> Next, referring to FIG. 12, the fifth embodiment will be described. For parts having the same structure as the first embodiment, the description will be omitted, and only the characteristic parts will be described. (Structure of the Tube) The tube 70 according to this embodiment is subjected to a flaring process at the end on the cylinder end 80 side, and a taper 71 is formed between the large-diameter portion and the other portion. Also, the tube 70 has a thinner wall thickness than the tubes shown in other embodiments.

[0051] (Structure of the Cylinder End) The cylinder end 80 according to this embodiment has the same configuration as that of the first embodiment. However, since the tube 70 is small as described above, the cylinder end 80 is also smaller than those of other embodiments.

[0052] (Enclosure of Burrs by Friction Welding) When joining the tube 70 and the cylinder end 80 by friction welding, while the cylinder end 80 is rotating, the flange portion 83 is located inside the tube 70, but before upset pressing, the taper 71 and the flange portion 83 do not contact each other. After that, during upset pressing, as the cylinder end 80 moves toward the central side in the axial direction of the tube 70, the flange portion 83 contacts the taper 71 and deforms. As a result, since the flange portion 83 is pressed against the taper 71 by its own spring-back force, the space 35 is sealed and the internal burr IB is contained.

[0053] (Effect of the Sixth Embodiment) The fluid pressure cylinder according to this embodiment forms a taper shape by flaring the end of the tube 10. That is, this embodiment is different from the embodiments described so far in that it is assumed that cutting is performed to form a large-diameter portion or a taper. By forming a taper by flaring, the present invention can be applied even to a tube 70 with a wall thickness that is difficult to machine by cutting.

[0054] Tubes 70 with a wall thickness not suitable for cutting are particularly used in small air dampers and the like. When using such a tube 70, the inner diameter is often small, and the process of removing internal burrs is particularly difficult. However, by applying the present invention, the process of removing the internal burr IB can be omitted, so that joining by friction welding can be easily performed.

[0055] <Modification Example> In Embodiments 1 to 6, the hydraulic cylinder 1 in which the flange portion is deformed during upset pressing has been described. However, these embodiments show an example of a manufacturing method of the hydraulic cylinder 1 according to the present invention, and the flange portion does not necessarily have to be deformed in the implementation of the present invention. Further, the amount of bending, size, and thickness of the flange portion shown in Embodiments 1 to 6 can be changed according to the size of the hydraulic cylinder 1.

[0056] For example, the flange portion 23 described in Embodiment 1 may be processed into a shape as shown in FIG. 7 in advance, and only the large-diameter portion 11 may come into contact during upset pressing. Further, in the implementation of the present invention, the flange portion does not necessarily have to be bent. Even in such a case, the stepped portion bites into the flange portion and adheres thereto, so that the space can be sealed and the internal burr IB can be contained.

Explanation of Reference Numerals

[0057] 1... Hydraulic cylinder 10, 50, 70... Tubes 11, 12, 13... Large-diameter portions 21... Cylinder end-side large-diameter portion 11a, 12a, 13a... Edges 51, 71... Tapers 20, 60, 80... Cylinder ends 22, 62, 82... Protrusions 23, 25, 27, 63, 83... Flange portions 30, 31, 32, 33, 34, 35... Spaces OB... Outer burr IB... Inner burr Joint portion... TP

Claims

1. A fluid pressure cylinder in which a tube and a cylinder end are joined by friction welding, a cylindrical protrusion protruding into the tube and coaxially with the tube is provided on a surface of the cylinder end facing the inside of the tube, a portion of an inner circumferential surface of the tube, between a position where the tip end of the protrusion overlaps with the inner circumferential surface of the tube in a radial direction and a joint portion with the cylinder end, is a large-diameter portion having an inner diameter larger than that of other portions of the inner circumferential surface of the tube; a space for accommodating internal burrs generated by friction welding is formed between an inner peripheral surface of the large diameter portion and a peripheral surface of the protruding portion; a flange portion having an outer diameter smaller than the inner diameter of the large diameter portion and larger than the inner diameter of the other portion is formed around the entire periphery of the tip portion of the protruding portion, A fluid pressure cylinder characterized in that, in a state in which the flange is bent and deformed toward the joint portion, a springback force is generated that tries to press the flange itself against the edge of the large diameter portion, and the flange is in close contact with the edge that is the boundary between the large diameter portion and the other portion of the tube around its entire circumference.

2. 2. The fluid pressure cylinder according to claim 1, wherein the inner burr is not in contact with the flange portion.

3. 2. The fluid pressure cylinder according to claim 1, wherein the inner burr is in contact with the flange portion.

4. A fluid pressure cylinder in which a tube and a cylinder end are joined by friction welding, a cylindrical protrusion protruding into the tube and coaxially with the tube is provided on a surface of the cylinder end facing the inside of the tube, an inner circumferential surface of the tube has a taper that increases in inner diameter toward the joint portion from a position where the inner circumferential surface overlaps with the tip portion of the protruding portion in a radial direction to a joint portion with the cylinder end; a space for accommodating internal burrs generated by friction welding is formed between an inner peripheral surface of the taper and a peripheral surface of the protruding portion; a flange is formed around the entire periphery of a tip portion of the protruding portion, the flange having an outer diameter smaller than an inner diameter of the end portion of the tube on the joint portion side and larger than an inner diameter of a portion where the taper is not formed, A fluid pressure cylinder characterized in that the flange comes into contact with the taper and deforms as a result of the cylinder end moving toward the axial center of the tube, and the flange is pressed against the taper by its own springback force, with the flange being in close contact with the taper around its entire circumference.

5. 5. The fluid pressure cylinder according to claim 4, wherein the taper is formed by flaring the tube.

6. A method for manufacturing a fluid pressure cylinder, comprising a friction welding process for joining a tube and a cylinder end by friction welding, a cylinder end having a cylindrical protrusion protruding into the inside of the tube at a position coaxial with the tube after the joining on a surface of the cylinder end that faces the inside of the tube after the joining, the protrusion having a flange formed around the entire circumference of a tip end portion; and a tube having a large diameter portion whose inner diameter is larger than the outer diameter of the flange on an inner circumferential surface of the tube between a position that will overlap with the tip end portion of the protrusion when viewed from the radial direction after the joining to the cylinder end and a joining portion with the cylinder end, and an inner diameter smaller than the outer diameter of the flange on the other portion of the inner circumferential surface other than the large diameter portion, a cylinder end that is rotated at a position away from the tube and is pressed against the tube to generate frictional heat at the joint; after the frictional heat causes the joint to reach a temperature suitable for joining, the rotation of the cylinder end is stopped and an upset pressure is applied to press the cylinder end against the tube to join the tube and then the tube and the cylinder end are joined together, and when the flange comes into contact with the edge of the large diameter portion and bends toward the joint, the upset pressure is stopped to generate a springback force that presses the flange itself against the edge of the large diameter portion, bringing the flange and the edge of the large diameter portion into close contact with each other, thereby sealing a space that is formed between the inner peripheral surface of the large diameter portion and the peripheral surface of the protruding portion and that accommodates internal burrs generated by the friction welding.

7. A method for manufacturing a fluid pressure cylinder, comprising a friction welding process for joining a tube and a cylinder end by friction welding, the cylinder end is provided with a cylindrical protrusion protruding into the inside of the tube at a position coaxial with the tube after joining on a surface of the cylinder end that faces the inside of the tube after joining, the protrusion having a flange formed around the entire circumference of a tip end portion; and the tube has an inner diameter that increases toward the joint from a position on the inner circumferential surface of the tube that will overlap with the tip end portion of the protrusion when viewed from the radial direction after joining with the cylinder end to a joint with the cylinder end, the inner diameter of the taper being smaller than the outer diameter of the flange at the overlapping position and larger than the outer diameter of the flange at the joint, a cylinder end that is rotated at a position away from the tube and is pressed against the tube to generate frictional heat at the joint; after the frictional heat causes the joint to reach a temperature suitable for joining, the rotation of the cylinder end is stopped and an upset pressure is applied to press the cylinder end against the tube to join the tube and the cylinder end. After that, the cylinder end is moved toward the center of the axial direction of the tube to bring the flange into contact with the taper and gradually deform the flange along the taper; the movement is stopped at an angle at which a sufficient springback force can be exerted, so as to seal a space formed between the inner peripheral surface of the taper and the peripheral surface of the protruding portion to accommodate an internal burr generated by the friction welding, and the flange is pressed against the taper by the springback force and the internal burr.

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