Fluid pressure cylinder and manufacturing method of fluid pressure cylinder

Abstract

To provide a fluid pressure cylinder with a structure for encapsulating burrs on a tube inner peripheral side generated by friction welding, at a reduced price.SOLUTION: In a tube 10, a large diameter part 11 whose inner diameter is larger than that of other parts is formed in a predetermined range of an end part. The predetermined range in which the large diameter part 11 is formed is a range where a collar part 23 comes in contact with an edge 11a when joining by friction welding is completed. A cylinder end 20 is of a diameter slightly smaller than that of the tube 10 but is formed with a cylinder end side large diameter part 21 in the friction welding part, whose diameter is the same as that of the tube 10. A protrusion 22 whose diameter is smaller than the inner diameter of the tube 10 is formed from the end surface of the large diameter part. A tip part of the protrusion 22 is formed with a collar part 23 of an outer diameter roughly the same as the inner diameter of the large diameter part 11. The collar part 23 is formed in a thin plate shape expanding in a radial direction, and a recess is formed in a range surrounded by the cylinder end side large diameter part 21, the protrusion 22, and the collar part 23.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a structure of a fluid pressure cylinder manufactured by friction welding. [Background technology]

[0002] Conventionally, when manufacturing a cylinder tube for a fluid pressure cylinder, a disk-shaped member is placed on one end of a cylindrical member, and the members are rotated while welding the boundary. However, when welding is performed in this manner, the welding points are limited to the outside of the cylinder tube and the cylindrical member, and there is a limit to the area that can be welded relative to the thickness of the members. In particular, as the cylinder becomes larger and the cylindrical member becomes thicker, the ratio of the joint area to the cross section decreases.

[0003] Furthermore, when joining components by welding, thorough management of welding defects is required, as this can cause leakage of working fluid from the welded parts. However, if detailed inspections of the welded parts are carried out for this purpose, there is a problem that manufacturing costs increase.

[0004] Therefore, friction welding is used as a joining method that can join the entire cross section of a cylindrical member and can prevent the occurrence of welding defects. Friction welding is a method of joining two parts by bringing one part into contact with the other and rotating it at high speed while keeping the other stationary, generating frictional heat. This frictional heat heats up the parts, and then the rotation is stopped and the parts are pressed together with high pressure (upset pressure).

[0005] When joining cylindrical members by friction welding, burrs are generated on both the inner and outer peripheries due to the high pressure. The inner periphery of a fluid pressure cylinder is divided into an extension side and a contraction side working fluid chamber by a packing fitted to the piston that slides in close contact with the inner periphery. Therefore, burrs can damage the packing. Furthermore, if burrs peel off from the inner periphery during operation of the cylinder, they can damage the entire flow path of the working fluid. Therefore, it is desirable to remove burrs during the manufacturing process of the cylinder. However, in the case of cylinder tubes, the burrs are generated in positions away from the opening and are generated all around the circumference, making it difficult to remove burrs on the inner circumference of the cylinder.

[0006] Therefore, the fluid pressure cylinder disclosed in Patent Document 1 forms a space in the disk-shaped member to contain burrs generated on the inner periphery of the cylinder, and further includes a flange portion (reference numeral 101 in Patent Document 1, Figure 2) to cover this space. The flange portion is sized to form a gap between it and the inner surface of the cylindrical member, but because the gap is narrow at 0.5 mm to 1 mm, burrs larger than the gap are prevented from entering the working fluid chamber. Furthermore, if no gap is formed, frictional heat is generated in the flange due to the high speed rotation during joining, which can unexpectedly form gaps through which burrs can pass, leading to defective products.

[0007] Additionally, Patent Document 2 discloses a hydraulic cylinder having a structure in which tapered surfaces come into contact with each other to seal the space containing the burrs. To put it simply, the tapered surfaces are separated during rotation, but when upset pressure is applied, the tapered sections move closer to each other by an allowance, so the tapered surfaces also move closer to each other and finally come into close contact, thus sealing the space containing the burrs. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Utility Model Application Publication No. 4-87064 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-72160 Summary of the Invention [Problem to be solved by the invention]

[0009] The flange disclosed in Patent Document 1 has a gap between it and the inner peripheral surface of the cylinder, which means that burrs smaller than the gap may enter the hydraulic oil chamber. On the other hand, the cylinder disclosed in Patent Document 2 seals in burrs by tightly contacting the tapered surfaces formed on the tube and the lid, making it extremely unlikely that burrs will enter the hydraulic fluid chamber. However, to ensure a tight seal with this structure, the tapered surface must be machined with high dimensional accuracy, and the entire circumference must be pressurized evenly during upset pressure application, which requires high-precision machining, resulting in high machining costs.

[0010] In view of the above circumstances, an object of the present invention is to provide an inexpensive fluid pressure cylinder having a structure for sealing in burrs on the inner peripheral side of a tube that are generated by friction welding. [Means for solving the problem]

[0011] A first invention is a fluid pressure cylinder in which a tube and a cylinder end are joined by friction welding, wherein a cylindrical protrusion is provided on a surface of the cylinder end facing the interior of the tube, protruding into the interior of the tube coaxially with the tube, and a large diameter portion of the inner circumferential surface of the tube, between a position where the tip of the protrusion overlaps radially with the joint with the cylinder end, has an inner diameter larger than that of the rest of the inner circumferential surface, and a space is formed between the inner circumferential surface of the large diameter portion and the circumferential surface of the protrusion to accommodate internal burrs produced by friction welding, and a flange is formed around the entire circumference of the tip of the protrusion, the outer diameter of which is smaller than the inner diameter of the large diameter portion and larger than the inner diameter of the rest of the tube, and the flange is in close contact with an edge that is the boundary between the large diameter portion and the rest of the tube, all around the circumference.

[0012] A second invention is the fluid pressure cylinder according to the first invention, characterized in that the flange portion 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 of the tube in the longitudinal direction than the end face of the protrusion, and the flange portion is bent toward the center of the tube in the longitudinal direction around the entire circumference, thereby being in close contact with the edge.

[0014] A fourth invention is a fluid pressure cylinder according to any one of the first to third inventions, characterized in that the inner burr does not contact the flange portion.

[0015] A fifth invention is a fluid pressure cylinder according to any one of the first to third inventions, characterized in that the inner burr is in contact with the flange portion.

[0016] A sixth invention is a fluid pressure cylinder in which a tube and a cylinder end are joined by friction welding, wherein a cylindrical protrusion that protrudes into the tube coaxially with the tube is provided on a surface of the cylinder end facing the inside of the tube, and the inner circumferential surface of the tube is tapered from a position that overlaps with the tip end of the protrusion in the radial direction to a joint with the cylinder end, with the inner diameter increasing toward the joint, and a space that accommodates internal flash generated by friction welding is formed between the inner circumferential surface of the taper and the circumferential surface of the protrusion, The fluid pressure cylinder is characterized in that a flange is formed around the entire circumference at the tip of the protrusion, the flange having an outer diameter smaller than the inner diameter of the end of the tube on the joint side and larger than the inner diameter of the portion where the taper is not formed, and the flange is in close contact with the taper around the entire circumference.

[0017] A seventh invention is the fluid pressure cylinder according to the sixth invention, characterized in that the taper is formed by flaring the tube.

[0018] An eighth invention is a fluid pressure cylinder in which a tube and a cylinder end are joined by friction welding, wherein a cylindrical protrusion is provided on a surface of the cylinder end facing the inside of the tube, protruding into the tube coaxially with the tube, a space is formed between the inner circumferential surface of the tube and the circumferential surface of the protrusion for accommodating internal burrs generated by friction welding, a flange is formed around the entire tip of the protrusion, whose outer circumferential portion is in close contact with the inner circumferential surface of the tube, and whose outer circumferential portion is inclined so that its axial position is closer to the joint between the tube and the cylinder end than the end face of the protrusion, and the internal burr is in contact with the flange. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide at low cost a fluid pressure cylinder having a structure for sealing in burrs on the inner peripheral side of the tube that are generated by friction welding. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a vertical cross-sectional view of a hydraulic cylinder according to a first embodiment. [Figure 2] 5A to 5C are vertical cross-sectional views showing a procedure for friction welding of the hydraulic cylinder according to the first embodiment. [Figure 3] 5A to 5C are vertical cross-sectional views showing a procedure for friction welding of the hydraulic cylinder according to the first embodiment. [Figure 4] FIG. 4 is an enlarged view of part A shown in FIG. [Figure 5] 5A to 5C are vertical cross-sectional views showing a procedure for friction welding of the hydraulic cylinder according to the first embodiment. [Figure 6] FIG. 6 is an enlarged view of part B shown in FIG. 5. [Figure 7] FIG. 6 is an enlarged view of part B shown in FIG. 5 at the time when friction welding is completed. [Figure 8] FIG. 10 is an enlarged view showing a joint portion of a hydraulic cylinder according to a second embodiment. [Figure 9] FIG. 10 is an enlarged view showing a joint portion of a hydraulic cylinder according to a third embodiment. [Figure 10] FIG. 10 is an enlarged view showing a joint portion of a hydraulic cylinder according to a fourth embodiment. [Figure 11] FIG. 13 is an enlarged view showing a joint portion of a hydraulic cylinder according to a fifth embodiment. [Figure 12] FIG. 13 is an enlarged view showing a joint portion of a hydraulic cylinder according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] First Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, identical or similar parts are denoted by identical or similar reference numerals, and redundant explanations are omitted. It should be noted that the drawings are schematic. Therefore, it should be noted that the relationship between thickness and planar dimensions, ratios, etc. may differ from the actual ones, and the drawings also include parts where the relationship between dimensions and ratios differ. Furthermore, the embodiments shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the materials, shapes, structures, markings, etc. of component parts to the following embodiments. In the following embodiments, the hydraulic cylinder, which is an example of a fluid pressure cylinder, is described as having an axial direction fixed along the left-right direction, with the cylinder end located on the left side and the tube 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. The hydraulic cylinder 1 has a cylindrical tube 10 at one axial end of which a cylinder end 20, which serves as a lid, is friction-welded. Although not shown in the figure, a cylinder rod equipped with a piston is inserted, and then a cylinder head through which the cylinder rod passes is bolted to the other end of the tube 10. In the following description, explanations of parts other than the periphery of the joint between the tube 10 and the cylinder end 20 according to the present invention will be omitted.

[0023] (Tube structure) The structure of the tube 10 will be described with reference to FIG. The tube 10 has a large diameter portion 11 formed in a predetermined range on the inner circumferential surface of the end portion to which the cylinder end 20 is joined, the large diameter portion 11 having a larger inner diameter than the rest of the inner circumferential surface. The predetermined range in which the large diameter portion 11 is formed is a range in which, when joining by friction welding is completed, a flange 23, which will be described next, comes into contact with an edge 11a that is the boundary between the large diameter portion and the rest of the tube. In other words, this length is the sum of the length up to the flange 23 and the length (extrusion allowance) that is reduced due to the formation of burrs during friction welding.

[0024] (Cylinder end structure) Next, the structure of the cylinder end 20 will be described with reference to FIG. Most of the cylinder end 20 has a diameter slightly smaller than the inner diameter of the tube 10, but one end, which is the friction-welded portion, is formed with a cylinder-end-side large-diameter portion 21 whose diameter is the same as the outer diameter of the tube 10. In addition, a cylindrical protrusion 22 with a diameter smaller than the inner diameter of the tube 10 is formed on the surface of the cylinder-end-side large-diameter portion 21 facing the inside of the tube 10, in a position coaxial with the other portions. Note that when the cylinder end 20 is joined to the tube 10, the tube 10 and the cylinder end 20 are coaxial, and therefore the protrusion 22 and the tube 10 are also coaxial.

[0025] A flange 23 having an outer diameter substantially equal to the inner diameter of the large diameter portion 11 is formed around the entire periphery at the tip of the peripheral surface of the protruding portion 22. The flange 23 is formed as a thin plate that expands in the radial direction, and a recess is formed in the area surrounded by the cylinder end-side large diameter portion 21, the protruding portion 22, and the flange 23. The area surrounded by this recess and the inner peripheral surface of the tube 10 becomes a space 30 that accommodates the inner burr IB in the friction welding process described next.

[0026] (burr encapsulation by friction welding) Next, with reference to FIGS. 2 to 7, the generation of burrs when the tube 10 and the cylinder end 20 are friction-welded and the inclusion of these burrs will be described. First, as shown in Figure 2, the cylinder end 20 is rotated at high speed at a position separated from the tube 10. Then, as shown in Figure 3, the cylinder end 20, which is rotating at high speed, is pressed against the tube 10, generating frictional heat at the joint TP. At this time, as shown in FIG. 4, flange portion 23 is formed to have a diameter slightly smaller than the inner diameter of large diameter portion 11, and therefore rotates without coming into contact with any part of tube 10.

[0027] When the temperature of the joint TP reaches a temperature suitable for joining due to frictional heat, the rotation of the cylinder end 20 is stopped as shown in FIG. 5, and an upset pressure is applied by strongly pressing it against the tube 10. At this time, the tube 10 and the cylinder end-side large diameter portion 21 of the cylinder end 20 are strongly pressed together to join them. At the same time, as shown in Figure 6, parts of the tube 10 and cylinder end 20 are pushed out, forming burrs containing impurities. Hereinafter, the burr formed on the outer periphery of the tube 10 will be referred to as outer burr OB, and the burr formed on the inner periphery will be referred to as inner burr IB.

[0028] Further upset pressure is applied, and the upset pressure is stopped when flange 23 comes into contact with edge 11a of large diameter portion 11 and bends toward joint TP, as shown in Figure 7. This causes flange 23 to deform, generating a springback force that tries to press flange 23 against edge 11a of large diameter portion 11. As a result, flange 23 and edge 11a of large diameter portion 11 come into close contact, sealing space 30 and containing inner flash IB. After that, the outer flash OB is removed and the friction welding is completed.

[0029] After removing external flash OB, a cylinder head is bolted to the end of the tube 10 opposite the cylinder end 20, and piping is installed to complete the hydraulic cylinder 1. After that, the hydraulic cylinder 1 is attached to industrial machinery or the like, and the interior is filled with hydraulic oil. As the hydraulic cylinder 1 operates, hydraulic oil gradually flows into the space 30. This is because the flange 23 is subjected to hydraulic oil pressure and undergoes slight elastic deformation, temporarily releasing the sealed state. However, even in this case, the narrow gap between the flange 23 and the large diameter portion 11 and the hydraulic oil flowing in the direction of entering the space 30 prevent shed chips and metal particles from getting mixed into the hydraulic oil.

[0030] Once the space 30 is filled with hydraulic oil, the flange 23 will not deform even when hydraulic pressure is applied. This is because hydraulic oil is an incompressible fluid. In reality, however, the space 30 is rarely completely filled with hydraulic oil, and a small amount of air bubbles often remains. However, when the flange 23 deforms due to the volume of the compressed air bubbles, the deformation is only small enough to maintain a sealed state, or only a narrower flow path is formed than when the space is filled with air, preventing metal particles and the like from becoming mixed into the hydraulic oil.

[0031] (Effects of the first embodiment) The hydraulic cylinder 1 has the configuration shown in this embodiment, so it is possible to prevent small pieces and metal particles from getting into the hydraulic oil without removing the internal burrs IB. Furthermore, since the containment of the internal burrs IB does not require any special work and is performed automatically in the friction welding process, it is possible to reduce the manufacturing costs of fluid pressure cylinders by friction welding.

[0032] Furthermore, since the inner burrs IB are contained within the space 30, there is no need for a removal process using a dedicated cutting tool. Therefore, the equipment and process for joining the rods can be used without major changes.

[0033] Second Embodiment Next, a second embodiment will be described with reference to FIG. 8. However, explanations of parts having the same structure as the first embodiment will be omitted and only the characteristic parts will be described.

[0034] (Tube and cylinder end structure) The tube 10 of this embodiment has a shorter large diameter portion 12 than that of the first embodiment. In addition, 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] (burr encapsulation by friction welding) When the tube 10 and the cylinder end 20 are joined by friction welding, the space 31 formed by the large diameter portion 12 and the protruding portion 24 due to the above-described structure is narrower than in the first embodiment, so the inner burr IB comes into contact with the bent flange portion 25. Therefore, as 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 is pressed against the edge 12a by the springback force generated by its own deformation as well as 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, thereby improving the ability to seal in the inner burrs IB. Therefore, this embodiment is applicable to hydraulic cylinders that operate at higher pressures than the first embodiment.

[0037] Third Embodiment Next, a third embodiment will be described with reference to FIG. 9. However, explanations of parts having the same structure as the first embodiment will be omitted and only the characteristic parts will be described.

[0038] (Tube and cylinder end structure) In the cylinder end 20 of this embodiment, the protruding portion 26 is shorter than that of the first embodiment. Also, in the tube 10, the length of the large diameter portion 13 excluding the extrusion allowance is set to be a distance equal to or less than the thickness of the flange portion 27 beyond the length of the protruding portion 26.

[0039] (burr encapsulation by friction welding) When the tube 10 and the cylinder end 20 are joined by friction welding, the protruding portion 26 is short compared to the large diameter portion 13, so when the flange 27 is not deformed, the edge 13a of the large diameter portion 13 and the flange 27 do not come into contact. However, when the inner burr IB is formed, the flange 27 is pressed, and the flange 27 deforms toward the edge 13a of the large diameter portion 13, becoming sandwiched between the inner burr IB and the edge 13a, sealing the space 32. As a result, the inner burr IB is enclosed within the space 32.

[0040] (Effects of the third embodiment) The fluid pressure cylinder according to this embodiment can contain the internal burr IB while shortening the protrusion 26. Therefore, it is easier to increase the volume of the working fluid chamber compared to the first embodiment. In other words, when ensuring a predetermined cylinder stroke, it is possible to shorten the tube 10, which is advantageous for reducing the size and weight.

[0041] The flange 27 may be formed in advance so as to be inclined toward the center in the longitudinal direction of the tube 10. In this case, even if the inner burr IB does not come into contact, the flange 27 comes into contact with the edge 13a, making it easier to seal the space 32.

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

[0043] (Tube and cylinder end structure) The tube 40 according to this embodiment does not have a large diameter portion formed therein, and the inner peripheral surface is smooth. Furthermore, the flange 29 of the cylinder end 20 has a diameter larger than the inner diameter of the tube 10 when it is positioned parallel to the end face of the cylinder end 20. However, before friction welding, the flange 29 is inclined toward the joint TP so that its diameter is equal to or smaller than the inner diameter of the tube 40.

[0044] (burr encapsulation by friction welding) When the tube 40 and the cylinder end 20 are joined by friction welding, the flange 29 does not come into contact with the tube 40 and remains bent until the initial stage of upset pressure application. Thereafter, when upset pressure is applied, an internal burr IB is formed, and its tip comes into contact with flange portion 29. As the internal burr IB grows, flange portion 29 is pressed toward the tip of the protruding portion, and the outer periphery is deformed into a position where it is in close contact with the inner circumferential surface of tube 40. Even after deformation, the axial position of the outer periphery of flange portion 29 remains closer to joint portion TP than the end face of protruding portion 22. During this deformation process, flange portion 29 comes into contact with the inner circumferential surface of tube 10, and as the internal burr IB grows, it is pressed even more strongly, sealing space 33 and trapping the internal burr IB.

[0045] (Effects of the fourth embodiment) The fluid pressure cylinder according to this embodiment is capable of sealing the internal burr IB within the space 33 even when joining a tube 10 that has not been processed to form a large diameter portion. This eliminates the need to process the inner peripheral surface of the tube 40, and only the cylinder end 20 needs to be processed, thereby reducing manufacturing costs. Furthermore, when friction welding is performed using a tube that was manufactured without considering friction welding, it is possible to seal the internal burr IB by adjusting the dimensions of the flange 29.

[0046] Fifth Embodiment Next, a fourth embodiment will be described with reference to FIG. 11. However, the description of the parts having the same structure as the first embodiment will be omitted, and only the characteristic parts will be described.

[0047] (Tube and cylinder end structure) The tube 50 according to this embodiment has a thinner wall thickness than that of the first embodiment, and instead of the large diameter portion 11, a taper 51 is formed so that the wall thickness becomes thinner toward the end. The cylinder end 60 has the same outer diameter as the tube 50, and the diameters of the portions other than the protruding portion 62 are the same.

[0048] (burr encapsulation by friction welding) When the tube 50 and the cylinder end 60 are joined by friction welding, the flange 63 is located inside the tube 50 while the cylinder end 60 is rotating, but the taper 51 and the flange 63 do not come into contact with each other before upset pressure is applied. Thereafter, during upset pressure application, the cylinder end 60 moves toward the center of the axial direction of the tube 50, causing the flange 63 to come into contact with the taper 51. The flange 63 then gradually deforms along the taper 51 and stops at an angle where it can exert a sufficient springback force. As a result, the flange 61 is pressed against the taper 51 by the springback force, sealing the space 34 and containing the internal burr IB. Furthermore, the flange 63 is also pressed against the taper 51 by the grown internal burr IB, so the space 34 is sealed more tightly than the springback force.

[0049] (Effects of the fifth embodiment) The taper 51 can be set to an angle close to the angle when the flange 63 is deformed. Therefore, it is possible to make the contact surface wider than when it is in contact with the large diameter portion 11, and the ability to contain internal burrs IB is high. Furthermore, since the flange 63 is deformed to make surface contact rather than bringing pre-machined surfaces into contact, the required machining precision of the tapered surface can be low, which allows for reduction in machining costs.

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

[0051] (Cylinder end structure) 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 the other embodiments.

[0052] (burr encapsulation by friction welding) When the tube 70 and the cylinder end 80 are joined by friction welding, the flange 83 is located inside the tube 70 while the cylinder end 80 is rotating, but before upset pressure is applied, the taper 71 and the flange 83 do not come into contact with each other. Thereafter, when upset pressure is applied, the cylinder end 80 moves toward the center of the axial direction of the tube 70, causing the flange 83 to come into contact with and deform the taper 71. As a result, the flange 83 is pressed against the taper 71 by its own springback force, sealing the space 35 and containing the internal flash IB.

[0053] (Effects of the sixth embodiment) The fluid pressure cylinder according to this embodiment has a tapered shape formed by flaring the end of the tube 10. That is, each of the embodiments described so far differs from this embodiment in that it is assumed that cutting is performed to form the large diameter portion or the taper. By forming a taper by flaring, the present invention can be applied even to a thick-walled tube 70 that is difficult to cut.

[0054] Thick-walled tubes 70 that are not suitable for cutting are used particularly for small air dampers, etc. When using such tubes 70, the inner diameter is often small, making the process of removing the inner burrs particularly difficult. However, by applying the present invention, the process of removing the inner burrs IB can be omitted, making it possible to easily perform joining by friction welding.

[0055] <Modification> In the first to sixth embodiments, the hydraulic cylinder 1 in which the flange deforms when upset pressure is applied has been described, but these embodiments show examples of the manufacturing method of the hydraulic cylinder 1 according to the present invention, and the flange does not necessarily have to deform in carrying out the present invention. In addition, the bending amount, size, and thickness of the flange shown in the first to sixth embodiments can be changed depending on the size of the hydraulic cylinder 1.

[0056] For example, the flange portion 23 described in the first embodiment may be machined in advance into a shape as shown in FIG. 7, so that the large diameter portion 11 only comes into contact with it when upset pressure is applied. Furthermore, in the practice of the present invention, the flange does not necessarily have to have a bent shape. Even in such a case, the step bites into the flange and makes close contact, thereby sealing the space and confining the internal burr IB. [Explanation of symbols]

[0057] 1...Hydraulic cylinder 10, 50, 70...Tube 11, 12, 13...Large diameter section 21...Large diameter part on cylinder end 11a, 12a, 13a...Edge 51,71...Taper 20, 60, 80...Cylinder end 22,62,82…Protrusion 23, 25, 27, 63, 83... Tsuba section 30,31,32,33,34,35…space OB…Outer burr IB…Inner burr Joint…TP

Claims

1. A fluid pressure cylinder in which a tube and a cylinder end are joined by friction welding, a cylindrical protrusion that protrudes into the tube and is coaxial with the tube is provided on a surface of the cylinder end that faces the inside of the tube, a large-diameter portion of the inner circumferential surface of the tube, from a position where the position overlaps with the tip end portion of the protrusion in a radial direction to a joint portion with the cylinder end, the large-diameter portion having an inner diameter larger than that of other portions of the inner circumferential surface; a space for accommodating internal burrs generated by friction welding is formed between the inner peripheral surface of the large diameter portion and the 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 at the tip portion of the protruding portion, A fluid pressure cylinder characterized in that the flange portion is in close contact with the edge that is the boundary between the large diameter portion and the other portion of the tube over the entire circumference.

2. 2. The fluid pressure cylinder according to claim 1, wherein the flange is bent toward the connecting portion.

3. the edge is located closer to the center of the tube in the longitudinal direction than the end face of the protrusion, 2. The fluid pressure cylinder according to claim 1, wherein the flange is bent toward the center in the length direction of the tube over the entire circumference, thereby being in close contact with the edge.

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

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

6. A fluid pressure cylinder in which a tube and a cylinder end are joined by friction welding, a cylindrical protrusion that protrudes into the tube and is coaxial with the tube is provided on a surface of the cylinder end that faces the inside of the tube, an inner circumferential surface of the tube has a tapered shape from a position where the tube overlaps with the tip end of the protrusion in a radial direction to a joint with the cylinder end, the inner diameter of the tube increasing toward the joint; a space for accommodating internal burrs generated by friction welding is formed between the inner peripheral surface of the tapered portion and the peripheral surface of the protruding portion; a flange is formed around the entire periphery of the tip of the protrusion, the flange having an outer diameter smaller than the inner diameter of the end of the tube on the joining portion side and larger than the inner diameter of the portion where the taper is not formed; A fluid pressure cylinder characterized in that the flange portion is in close contact with the taper over the entire circumference.

7. 7. The fluid pressure cylinder according to claim 6, wherein the taper is formed by flaring the tube.

8. A fluid pressure cylinder in which a tube and a cylinder end are joined by friction welding, a cylindrical protrusion that protrudes into the tube and is coaxial with the tube is provided on a surface of the cylinder end that faces the inside of the tube, a space for accommodating internal burrs formed by friction welding is formed between the inner peripheral surface of the tube and the peripheral surface of the protruding portion; a flange is formed around the entire periphery of the tip end of the protrusion, the outer periphery of which is in intimate contact with the inner periphery of the tube, and the axial position of the outer periphery of the flange is closer to the joint between the tube and the cylinder end than the end face of the protrusion; A fluid pressure cylinder, characterized in that the inner burr is in contact with the flange portion.

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