Eccentric tube-expanding plug for tube-expanding drawing, tube-expanding drawing method using eccentric tube-expanding plug, and tube with uneven thickness.

Abstract

This invention provides an eccentric tube expansion plug for tube expansion drawing, which enables the creation of tubes with uneven thickness using tube expansion drawing. [Solution] An eccentric tube-expanding plug for tube-expanding drawing is constructed, comprising a tip portion provided at the end of the tube material in the insertion direction, an enlarged diameter portion with a larger outer diameter than the tip portion, and a tapered surface arranged across the entire outer circumference between the tip portion and the enlarged diameter portion. In the cross-section of the eccentric tube-expanding plug in a direction perpendicular to the insertion direction into the tube material, the center position of the tip portion and the center position of the enlarged diameter portion are offset with respect to the insertion direction into the tube material.

Description

[Technical Field]

[0001] The present invention relates to an eccentric tube-expanding plug for tube-expanding drawing, a tube-expanding drawing method using an eccentric tube-expanding plug, and a tube with an uneven thickness. [Background technology]

[0002] In recent years, improving the formability of pipe materials has become crucial for achieving the lightweighting of vehicle bodies to improve fuel efficiency and for enhancing collision safety, as well as for expanding the application of high-strength steel pipes and realizing the integration of parts through large deformation processing. As a method for forming pipe materials, an expansion-type drawing process is known, in which an expansion plug is pressed into a cylindrical pipe material to expand it. For example, expansion-type drawing devices and pipe expansion methods using these devices have been proposed (see, for example, Patent Documents 1 and 2). In addition, expansion plugs for expansion-type drawing processes used in expansion-type drawing devices have been proposed (see, for example, Patent Document 3). Thus, because expansion-type drawing is a simple and highly productive method, it has been widely used for a long time.

[0003] Furthermore, as a tubing material, there is a type of pipe with varying wall thickness in the circumferential direction, i.e., a pipe with uneven wall thickness. By setting the thicker section on the bending tension side during bending, it is possible to suppress insufficient strength and cracking due to wall thinning on the bending tension side, and to reduce flattening deformation. In addition, by adjusting the eccentricity of the pipe with uneven wall thickness, the wall thickness after processing can be made close to a set target value. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-82326 [Patent Document 2] Japanese Patent Publication No. 2023-28687 [Patent Document 3] Japanese Patent Publication No. 2021-192919 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, a manufacturing method for tubes with varying wall thickness has not yet been established. For example, one method of manufacturing tubes with varying wall thickness is machining, but this process is time-consuming, making mass production difficult. Furthermore, manufacturing tubes with varying wall thickness by machining results in a low yield and low productivity. Therefore, there is a need to produce tubes with varying wall thickness using a simple and highly productive method called tube expansion drawing.

[0006] To solve the above-mentioned problems, the present invention provides an eccentric tube-expanding plug for tube-expanding drawing, a tube-expanding drawing method using the eccentric tube-expanding plug, and a tube with an uneven thickness produced by tube-expanding drawing, all of which are capable of producing tubes with uneven thickness using tube-expanding drawing. [Means for solving the problem]

[0007] The eccentric tube-expanding plug for tube-expanding drawing of the present invention is used in the tube-expanding drawing process of pipe materials. The eccentric tube-expanding plug comprises a tip portion provided at the end of the pipe material in the direction of insertion, an enlarged diameter portion with a larger outer diameter than the tip portion, and a tapered surface arranged on the entire outer circumference between the tip portion and the enlarged diameter portion. In a cross-section perpendicular to the direction of insertion into the pipe material, the center position of the tip portion and the center position of the enlarged diameter portion are offset with respect to the direction of insertion into the pipe material.

[0008] Furthermore, the pipe-expanding type drawing method using the eccentric pipe-expanding plug of the present invention is a method of expanding a pipe material by drawing using a pipe-expanding plug. The pipe-expanding type drawing method uses an eccentric pipe-expanding plug as the pipe-expanding plug, which has a tip portion provided at the tip in the insertion direction of the pipe material, an enlarged diameter portion with a larger outer diameter than the tip portion, and a tapered surface arranged on the entire outer circumference between the tip portion and the enlarged diameter portion, wherein in a cross section perpendicular to the insertion direction into the pipe material, the center position of the tip portion and the center position of the enlarged diameter portion are offset with respect to the insertion direction into the pipe material.The pipe-expanding type drawing method then performs a mouth-widening process by inserting the eccentric pipe-expanding plug from the tip portion to the rear end of the enlarged diameter portion into one opening of the pipe material.

[0009] In addition, the uneven wall tube of the present invention is manufactured by an expanding and drawing method using an expanding plug. The expanding and drawing method uses, as the expanding plug, a tip portion provided at the tip in the insertion direction with respect to the pipe material, an enlarged diameter portion having an outer diameter larger than that of the tip portion, and a taper surface disposed on the entire outer periphery between the tip portion and the enlarged diameter portion. In a cross section in a direction orthogonal to the insertion direction into the pipe material, the center position of the tip portion and the center position of the enlarged diameter portion are offset with respect to the insertion direction into the pipe material, and an eccentric expanding plug is used. Further, the uneven wall tube is manufactured by a mouth widening process in which the eccentric expanding plug is inserted from the tip portion to the rear end portion of the enlarged diameter portion into one opening of the pipe material, and a drawing process in which the eccentric expanding plug is pulled out from the other opening of the pipe material after the mouth widening process.

Effects of the Invention

[0010] According to the present invention, it is possible to provide an eccentric expanding plug for expanding and drawing, an expanding and drawing method using the eccentric expanding plug, and an uneven wall tube manufactured by expanding and drawing, which can produce an uneven wall tube using expanding and drawing.

Brief Description of the Drawings

[0011] [Figure 1] It is a three-view drawing showing the configuration of an eccentric expanding plug for expanding and drawing. [Figure 2] It is a three-view drawing showing the configuration of another form of an eccentric expanding plug for expanding and drawing. [Figure 3] It is a diagram showing the configuration of a pipe material and an eccentric expanding plug used in an expanding and drawing method. [Figure 4] It is a diagram showing the state of the mouth widening process of the expanding and drawing method. [Figure 5] It is a diagram showing the state of the drawing process of the expanding and drawing method. [Figure 6] It is a diagram showing the configuration of an uneven wall tube manufactured by expanding and drawing using an eccentric expanding plug. [Figure 7] It is a diagram showing the conditions of the FEM analysis of the expanding and drawing using an eccentric expanding plug. [Figure 8] This diagram illustrates the measurement location for the wall thickness of a pipe with uneven wall thickness in FEM analysis. [Figure 9] This graph shows the relationship between the eccentricity e and the circumferential wall thickness t of an eccentric expanded tube plug in FEM analysis. [Figure 10] This graph shows the effect of the outer diameter Dmax of the enlarged diameter section of an eccentric pipe-expanding plug and the eccentricity e on the wall thickness variation ratio te in FEM analysis. [Figure 11] This is a diagram of the FEM analysis model showing an eccentric pipe-expanding plug passing through a pipe. [Figure 12] This graph shows the relationship between the position of the eccentric expansion plug and the wall thickness ratio te in FEM analysis. [Figure 13] This figure shows the experimental conditions for the tube expansion drawing process. [Figure 14] This diagram illustrates the measurement position of the variable-walled tube in the experiment. [Figure 15] This graph shows the relationship between the eccentricity e of the eccentric expanded tube plug obtained through experimentation and the circumferential wall thickness t of the eccentric tube. [Modes for carrying out the invention]

[0012] The following describes examples of embodiments for carrying out the present invention, but the present invention is not limited to these examples. The explanation will be given in the following order. 1. Eccentric tube expansion plug for tube expansion drawing process. 2. Expansion-type drawing process using an eccentric tube expansion plug (method for manufacturing tubes with varying thickness) 3.Uneven wall thickness tube

[0013] <1. Eccentric tube expansion plug for tube expansion drawing process> This document describes an eccentric tube expansion plug for tube expansion drawing, which enables the creation of tubes with uneven thickness using the tube expansion drawing process. [Eccentric expanding tube plug (1)] Figure 1 shows three views of an eccentric tube-expanding plug for tube-expanding drawing processes. The eccentric pipe expansion plug 10 shown in Figure 1 has a tip portion 13 provided on the leading end side in the direction of insertion into the pipe material to be processed, an enlarged diameter portion 11 provided on the rear end side, and a tapered surface 12 formed between the tip portion 13 and the enlarged diameter portion 11.

[0014] The eccentric tube expansion plug 10 has a circular cross-section in the direction perpendicular to the insertion direction into the pipe, from the tip portion 13 to the enlarged diameter portion 11. The eccentric tube expansion plug 10 also has a circular cross-section in the direction perpendicular to the insertion direction into the pipe, even in the region where the tapered surface 12 is formed.

[0015] The tip portion 13 has a rotational diameter corresponding to the inner diameter of the pipe material to be subjected to the pipe-expanding drawing process. Specifically, the tip portion 13 has a rotational diameter less than the inner diameter of the pipe material. The tip portion 13 does not have to be flat. The tip portion 13 is not particularly limited as long as it has a shape that can be inserted into the pipe material to be processed. In Figure 1, the outer diameter of the tip portion 13 of the eccentric pipe-expanding plug 10 is D min It is stipulated as follows.

[0016] The tapered surface 12 is formed over the entire outer circumference of the eccentric expansion plug 10 in the region between the tip portion 13 and the enlarged diameter portion 11. Therefore, the eccentric expansion plug 10 has a tapered surface 12 around its entire circumference between the tip portion 13 and the enlarged diameter portion 11. In the region where the tapered surface 12 is formed, the eccentric expansion plug 10 has a shape in which the relative distance between two opposing sides in a direction perpendicular to the insertion direction widens in any cross-section along the insertion direction into the pipe. However, this excludes shapes in the region where the tapered surface 12 is formed, where the cross-section along the insertion direction into the pipe is a vertical trapezoid in any cross-section along the insertion direction into the pipe. Furthermore, the tapered surface 12 has straight surfaces on two opposing sides perpendicular to the insertion direction in any cross-section along the insertion direction of the pipe. Moreover, these two sides of the tapered surface 12 have a constant angle with respect to the insertion direction of the pipe from the tip portion 13 to the enlarged diameter portion 11.

[0017] The expanding diameter portion 11 has a rotational diameter corresponding to the inner diameter of the target pipe material in the pipe-expanding type drawing process using the eccentric pipe-expanding plug 10. The expanding diameter portion 11 is formed in a cylindrical or columnar shape. The eccentric pipe-expanding plug 10 has an outer diameter of the expanding diameter portion 11 that corresponds to the inner diameter of the pipe material after processing. In Figure 1, the outer diameter of the expanding diameter portion 11 of the eccentric pipe-expanding plug 10 is D max It is stipulated that the enlarged diameter portion 11 has a circular cross-section in a direction perpendicular to the insertion direction.

[0018] In the eccentric pipe-expanding plug 10, the center position of the tip portion 13 and the center position of the expanded diameter portion 11 are offset relative to the insertion direction in a cross-section perpendicular to the insertion direction into the pipe. That is, the center position of the expanded diameter portion 11 is not located on the extension line in the insertion direction from the center position of the tip portion 13. Therefore, in the cross-section perpendicular to the insertion direction into the pipe, the center position of the tip portion 13 and the center position of the expanded diameter portion 11 do not coincide in the insertion direction. Furthermore, in the eccentric pipe-expanding plug 10, the circular center position of the cross-section in a direction perpendicular to the insertion direction into the pipe material is shifted in one direction perpendicular to the insertion direction into the pipe material. Hereinafter, the shift between the center position of the tip portion 13 and the center position of the expanded diameter portion 11 with respect to the insertion direction will be referred to as eccentricity.

[0019] In Figure 1, the directions in which the center position of the circular cross-section of the eccentric expansion plug 10 is eccentric, perpendicular to the direction of insertion into the pipe, are defined as 0° and 180°, and the center line in this eccentric direction is shown as the eccentricity direction center line 15. Furthermore, in a direction perpendicular to the eccentricity direction center line 15, the line extending in the insertion direction from the center position of the circular cross-section of the tip portion 13 perpendicular to the direction of insertion into the pipe is shown as the tip portion center line 16. In addition, in a direction perpendicular to the eccentricity direction center line 15, the line extending in the insertion direction from the center position of the circular cross-section of the expanded diameter portion 11 perpendicular to the direction of insertion into the pipe is shown as the expanded diameter portion center line 17.

[0020] As shown in Figure 1, the center line 16 of the tip section and the center line 17 of the enlarged diameter section are offset in the direction in which the center line 16 of the tip section and the center line 17 of the enlarged diameter section are perpendicular to each other, that is, in the direction along the eccentricity center line 15. The amount of this offset between the center line 16 of the tip section and the center line 17 of the enlarged diameter section is denoted as the eccentricity amount e. In the region where the tapered surface 12 is formed, the position of the circular center of the cross-section in a direction perpendicular to the insertion direction into the pipe material changes continuously in displacement from the tip 13 side to the enlarged diameter 11 with respect to the tip centerline 16 or the enlarged diameter centerline 17. Therefore, in the region where the tapered surface 12 is formed, the position of the circular center of the cross-section in a direction perpendicular to the insertion direction into the pipe material approaches the tip centerline 16 on the tip 13 side and approaches the enlarged diameter centerline 17 on the enlarged diameter 11 side. As the distance from the tip 13 to the enlarged diameter 11 approaches, the position of the circular center of the cross-section in a direction perpendicular to the insertion direction into the pipe material moves from the tip centerline 16 towards the enlarged diameter centerline 17 side. In this way, in the region where the tapered surface 12 is formed, the position of the circular center of the cross-section in a direction perpendicular to the insertion direction into the pipe material moves along the eccentricity centerline 15 within the range of eccentricity amount e.

[0021] Furthermore, since the eccentricity e of the eccentric expansion plug 10 is a value along the eccentricity direction centerline 15, the tip centerline 16 and the expansion diameter centerline 17 coincide on the eccentricity direction centerline 15. For this reason, even in the region where the tapered surface 12 is formed, the circular center position of the cross-section in the direction perpendicular to the insertion direction into the pipe material coincides on the eccentricity direction centerline 15 from the tip 13 to the expansion diameter 11.

[0022] In a plan view taken from the 0° direction (180° direction) relative to the eccentric centerline 15, the angles α of the two opposing sides of the tapered surface 12 are the same with respect to the insertion direction. On the other hand, in a plan view taken from the 90° direction relative to the eccentric centerline 15, the angles α of the two opposing sides of the tapered surface 12 are different with respect to the insertion direction. Similarly, in a plan view taken from a direction other than the 0° direction (180° direction) relative to the eccentric centerline 15, the angles α of the two opposing sides of the tapered surface 12 are different with respect to the insertion direction. In the eccentric expanding plug 10, the angle α of the tapered surface 12 in the 0° direction is greater than the angle α of the tapered surface 12 in the 90° direction. Also, the angle α of the tapered surface 12 in the 180° direction is smaller than the angle α of the tapered surface 12 in the 90° direction. Therefore, the eccentric expanding plug 10 has a tapered surface 12 where the angle α is in the relationship [0° direction > 90° direction > 180° direction].

[0023] [Eccentric expanding tube plug (2)] Next, Figure 2 shows another form of the eccentric tube expansion plug for tube expansion drawing. Figure 2 is a three-view drawing of the other form of the eccentric tube expansion plug for tube expansion drawing. The eccentric tube expansion plug 20 shown in Figure 2 has a tip portion 23 provided on the leading end side in the insertion direction into the pipe material to be processed, an enlarged diameter portion 21 provided on the rear end side, and a tapered surface 22 formed between the tip portion 23 and the enlarged diameter portion 21. Furthermore, the eccentric tube expansion plug 20 is provided with a guide portion 28 between the tapered surface 22 and the tip portion 23. Note that the eccentric tube expansion plug 20 shown in Figure 2 has the same configuration as the eccentric tube expansion plug 10 shown in Figure 1, except for the presence of the guide portion 28. For this reason, a detailed explanation of the configuration similar to the eccentric tube expansion plug 10 shown in Figure 1 will be omitted.

[0024] The guide portion 28 can be inserted into the pipe material before processing and has an outer diameter (rotation diameter) approximately the same as the inner diameter of the pipe material. The guide portion 28 serves as a guide when inserting the eccentric expansion plug 20 into the pipe material. The guide portion 28 stabilizes the position of the eccentric expansion plug 20 inside the pipe material when the tip portion 23 is inserted into the pipe material.

[0025] In the eccentric expansion plug 20, the center position of the tip portion 23 and the center position of the expanded diameter portion 21 are offset in a cross-section perpendicular to the insertion direction into the pipe. That is, in the eccentric expansion plug 20, the center line 26 of the tip portion and the center line 27 of the expanded diameter portion are offset in a direction along the eccentricity center line 25. Furthermore, the amount of offset of the circular center position in the cross-section perpendicular to the insertion direction into the pipe in the region where the tapered surface 22 is formed changes continuously from the tip portion 23 side to the expanded diameter portion 21 with respect to the center line 26 of the tip portion or the center line 27 of the expanded diameter portion. The center of the circular cross-section of the guide portion 28, in a direction perpendicular to the insertion direction into the pipe, is at the same position as the center of the tip portion 23.

[0026] <2. Expansion-type drawing process using an eccentric tube expansion plug (method for manufacturing tubes with varying thickness)> Next, we will describe the tube-expanding drawing method using the eccentric tube-expanding plug described above, and the method for manufacturing a tube with uneven thickness by tube-expanding drawing using the eccentric tube-expanding plug. In the following description, we will describe an example using the eccentric tube-expanding plug 10 shown in Figure 1. Note that even when using the eccentric tube-expanding plug 20 shown in Figure 2, or other shapes of eccentric tube-expanding plugs, it is possible to manufacture a tube with uneven thickness by tube-expanding drawing using the same method. In the following description, we will use the reference numerals for the eccentric tube-expanding plugs shown in Figures 1 and 2 above as needed.

[0027] [Mouth widening process] First, as shown in Figure 3, prepare the pipe material 30 to be processed and the eccentric pipe expansion plug 10 having a tip portion 13 with an outer diameter that matches the inner diameter of the opening of the pipe material 30. Next, as shown in Figure 4, the opening of the pipe 30 is widened. First, the shaft 42 is passed through the eccentric pipe expansion plug 10. The shaft 42 is long enough to pass through the pipe 30 and be exposed from the openings at both ends. Next, the eccentric pipe expansion plug 10 is fixed to one end of the shaft 42. For example, the shaft 42 is inserted from the tip 13 side of the eccentric pipe expansion plug 10 toward the enlarged diameter portion 11.

[0028] Furthermore, a stopper 45, a nut 44, and a dummy block 43 are positioned on the rear end side of the enlarged diameter portion 11 to fix the eccentric tube expansion plug 10 to the shaft 42. The stopper 45 is positioned in contact with the rear end of the eccentric tube expansion plug 10 and the outer circumference of the shaft 42 to prevent the eccentric tube expansion plug 10 from shifting position on the shaft 42. The dummy block 43 fills the step on the outer circumference between the stopper 45 and the enlarged diameter portion 11 of the eccentric tube expansion plug 10, and the area between the stopper 45 and the nut 44. The nut 44 then fixes the eccentric tube expansion plug 10, the stopper 45, and the dummy block 43 to the shaft 42.

[0029] Next, the center position of the cross-section of the tip 13 of the eccentric expansion plug 10 in a direction perpendicular to the insertion direction into the pipe material is aligned with the center position of the cross-section of the pipe material 30 in a direction perpendicular to the longitudinal direction (insertion direction of the eccentric expansion plug 10). That is, as shown in Figure 3, the pipe material centerline 35, which represents the center position of the cross-section perpendicular to the longitudinal direction of the pipe material 30, is aligned with the tip centerline 16 of the eccentric expansion plug 10. This positions the eccentric expansion plug 10 relative to the pipe material 30 so that the tip 13 faces the opening of the pipe material 30. Furthermore, the pipe material 30 is fixed to the chuck 40. The chuck 40 fixes the outer circumference of the pipe material 30. The chuck 40 secures the pipe material 30 at least from the end of the pipe material 30 into which the eccentric expansion plug 10 is inserted, to the center in the longitudinal direction, beyond the tip 13 when the entire eccentric expansion plug 10 is inserted. After passing the shaft 42 through the pipe 30, the other end of the shaft 42 is fixed to the hydraulic cylinder 41.

[0030] Next, the eccentric expansion plug 10 is inserted into the pipe 30. The eccentric expansion plug 10 is inserted into the pipe 30 until the dummy block 43 is inserted into the pipe 30 to a sufficient length. As a result, the opening at one end of the pipe 30 is stretched outward by the eccentric expansion plug 10. This increases the diameter of the opening of the pipe 30.

[0031] [Drawing] Next, as shown in Figure 5, the pipe material 30 is drawn. First, remove the nut 44 from the shaft 42. Then, open the chuck 40 and remove the chuck 40 from the pipe 30. Next, as shown in Figure 5, change the fixing position of the chuck 40 and fix the pipe 30 with the chuck 40 at the position of the dummy block 43. Then, by pulling out the shaft with the hydraulic cylinder 41, the eccentric expansion plug 10 inside the pipe 30 is pulled out towards the hydraulic cylinder 41. As a result, the pipe 30 at the position where the eccentric expansion plug 10 passes is stretched outward, and the pipe diameter is expanded. By withdrawing the eccentric pipe expansion plug 10 to the end of the pipe material 30 (towards the hydraulic cylinder 41), the diameter of the pipe material 30 can be increased along its entire length. The withdrawal of the eccentric pipe expansion plug 10 may be stopped at a desired position. In this case, only a portion of the pipe material 30 from the end (insertion side) is expanded by the drawing process.

[0032] 〈3. Uneven thickness tube〉 Next, we will describe the eccentric tube-expanding type drawing process using the eccentric tube-expanding plug described above. In the following description, the symbols shown in Figure 1-5 above will be used as needed.

[0033] Figure 6 shows a schematic diagram of a tube with a variable thickness produced by the tube-expanding drawing process using the eccentric tube-expanding plug described above. Figure 6 shows a plan view of the tube with a variable thickness 50 as seen from the longitudinal direction, and a cross-sectional view along the 0°-180° lines of the plan view. Furthermore, the plan view of the tube with a variable thickness 50 as seen from the longitudinal direction shown in Figure 6 is a drawing rotated by 180° compared to the eccentric tube-expanding plug 10 shown in Figure 1 and the eccentric tube-expanding plug 20 shown in Figure 2.

[0034] As shown in Figure 6, the wall thickness of the variable-thickness pipe 50 is smallest in the 0° direction and largest in the 180° direction. Furthermore, the wall thickness of the variable-thickness pipe 50 gradually increases from the 0° direction to the 180° direction. Thus, the wall thickness of the pipe material of the variable-thickness pipe 50 is variable. Hereafter, the part of the variable-thickness pipe 50 with the smallest wall thickness in the 0° direction will be referred to as the thin-walled section 52, and the part with the largest wall thickness in the 180° direction will be referred to as the thick-walled section 51. Furthermore, in the variable-walled pipe 50, the center position of the inner diameter and the center position of the outer diameter are offset. That is, in the width direction (direction perpendicular to the longitudinal direction), the inner diameter and outer diameter of the variable-walled pipe 50 are eccentric. As a result, in the variable-walled pipe 50, the inner diameter center line 54, which is the extension of the inner diameter center position in the longitudinal direction, and the outer diameter center line 53, which is the extension of the outer diameter center position in the longitudinal direction, are offset in the 0°-180° direction in the plan view.

[0035] Furthermore, the eccentric tube 50 shown in Figure 6 has a smaller wall thickness in the 0° direction when machined in contact with the side where the angle α of the tapered surface 12 of the eccentric expanding plug 10 (Figure 1) is larger (0° direction). Conversely, the wall thickness in the 180° direction is larger when machined in contact with the side where the angle α of the tapered surface 12 of the eccentric expanding plug 10 (Figure 1) is smaller (180° direction). This trend is similar when machined using the eccentric expanding plug 20 (Figure 2). Thus, the wall thickness and eccentricity ratio of the eccentric tube 50 are controlled by the angle α of the tapered surfaces 12 and 22 of the eccentric expanding plug 10 (Figure 1) and the eccentric expanding plug 20 (Figure 2), the difference in angle α between two opposing sides (Figures 1 and 2), and the eccentricity amount e.

[0036] The inventor speculates the following regarding the difference between the thickness-adjustable tube 50 manufactured by the aforementioned expansion-type drawing process and the thickness-adjustable tubes manufactured by conventional cutting or the expanded tubes manufactured by the reduction-type drawing process: In the thickness-adjustable tube 50 manufactured by the aforementioned expansion-type drawing process, plastic deformation is thought to occur in the tube. Therefore, it is presumed that the microstructure of the metal atoms constituting the tube material, including the state of crystal grains and grain boundaries, has changed from before the processing. In other words, it is presumed that the thickness-adjustable tube 50 after expansion-type drawing has a different microstructure in its constituent metal structure compared to the tube material before processing or the thickness-adjustable tube manufactured by cutting. In particular, the variable-walled pipe 50 undergoes deformation that expands outward due to the expansion process, so it is presumed that a circumferentially stretched and deformed microstructure is generated. Furthermore, the variable-walled pipe 50 produced by the aforementioned expansion-type drawing process is less prone to stretching deformation in the longitudinal direction of the stretched pipe material, so it is presumed that a circumferentially stretched and deformed microstructure is less likely to be generated. On the other hand, in the case of expanded pipes manufactured by the shrinking-type drawing process, it is thought that compression deformation occurs in the circumferential direction, and stretch deformation occurs in the longitudinal direction of the stretched pipe material. Furthermore, it is presumed that pipes with uneven thickness produced by cutting do not have a circumferentially stretched structural structure like the pipe with uneven thickness produced by the expansion-type drawing process described above (50). [Examples]

[0037] The present invention will be described more specifically below based on examples, but the present invention is not limited to the following examples. In the following description, the reference numerals shown in Figures 1-6 above will be used as necessary.

[0038] [FEM analysis] To investigate the shape of the eccentric tube-expanding plug used in tube-expanding drawing, a Finite Element Method (FEM) analysis was performed. The conditions for the FEM analysis are shown in Figure 7. Figure 7 also shows the conditions used for the experiment (Exp.) described later, along with the conditions used for the FEM analysis. The conditions for the eccentric tube-expanding plug used in the FEM analysis are the same shape as the eccentric tube-expanding plug 20 shown in Figure 2 above, with an eccentricity amount e of 0.2 to 1.8 mm, an angle α of the tapered surface 12 in the 90° direction of 11°, an outer diameter Dmax of the expanded diameter section 11 of 28, 30, 32 mm, and an outer diameter Dmin of the guide section 28 of 26 mm. Furthermore, the conditions for pipe material 30 used in the FEM analysis are as follows: material is aluminum (A1070), wall thickness t0 is 2 mm, outer diameter D0 is 30 mm, length L0 is 180 mm, Young's modulus E is 66 GPa, Poisson's ratio ν is 0.34, and yield stress σ Y With a pressure of 88 MPa, a friction coefficient μ of 0.2, and using Swift's formula [σ=F(ε+ε0)], the stress-strain diagram for aluminum is given by 88 MPa. n When approximated using [ ], the parameters F is 121.26 MPa, ε0 is 0.0013, and n is 0.048. Some of the conditions for the pipe material 30 used in the FEM analysis are shown in Figure 3 above. In addition, in the FEM analysis, to stabilize the analysis, an elastic body 36 with a low Young's modulus (10 MPa) was installed on the free end side of the pipe material 30, as shown in Figure 3.

[0039] In addition, the FEM analysis was performed by the static condensation method using the general-purpose finite element code ELFEN manufactured by Rockfield Software. The model was three-dimensional, and the eccentric expansion plug 20 was set as a rigid body and the pipe material 30 was set as an elastoplastic body. In the FEM analysis, the elements of the pipe material 30 were divided at intervals of 0.5 mm in the radial direction, 5° in the circumferential direction, and 2 mm in the axial direction.

[0040] [Evaluation] Based on the above FEM analysis, the formed product (eccentric wall thickness pipe) obtained by tube expansion drawing using an eccentric expansion plug was evaluated from the perspective of the wall thickness eccentricity ratio t e . The t e of the eccentric wall thickness pipe was defined by the following formula (1). t e = [(t max - t min ) / t ave × 100 (%) ···(1)

[0041] In formula (1), t0 is the initial wall thickness, t is the wall thickness after processing, t max is the maximum wall thickness of the eccentric wall thickness pipe, t min is the minimum wall thickness of the eccentric wall thickness pipe, and t ave is the average wall thickness of the eccentric wall thickness pipe.

[0042] The measurement positions of the eccentric wall thickness pipe in the analysis are shown in Fig. 8. For the eccentric wall thickness pipe, in the region from 60 to 80 mm from the mouth widening part, four positions in the axial direction were set as the measurement positions, and the wall thicknesses at five positions every 45° in the circumferential direction within the range of 0 to 180° at each measurement position were measured. By this measurement, the influence of the eccentricity e of the eccentric expansion plug on the wall thickness eccentricity ratio t e and the wall thickness t was investigated.

[0043] Fig. 9 shows the relationship between the eccentricity e of the eccentric expansion plug and the circumferential wall thickness t. In Fig. 9, the vertical axis represents the wall thickness (mm) of the eccentric wall thickness pipe, the horizontal axis represents the angle (θ) of the measurement position, and graphs of the eccentricity e of the eccentric expansion plug being 0.2, 0.6, 1.0, 1.4, and 1.8 are shown respectively. As shown in Figure 9, as the eccentricity e increases, the wall thickness t at the 0° position decreases, and the wall thickness t at the 180° position increases. From this, it was found that as the eccentricity e increases, the wall thickness difference in the circumferential direction increases. Therefore, by having an eccentricity e in the eccentric expansion plug, a wall thickness variation occurs in the circumferential direction of the pipe material, and a pipe with a wall thickness variation can be formed. In particular, as the eccentricity e of the eccentric expansion plug increases, the wall thickness variation ratio t increases. e This increases the amount of eccentricity e in the circumferential direction of the pipe material, thus increasing the amount of wall thickness variation. Therefore, by adjusting the eccentricity e of the eccentric expansion plug, it is possible to form a pipe with the desired wall thickness variation.

[0044] Figure 10 shows the outer diameter D of the enlarged diameter portion of the eccentric tube-expanding plug. max And, the eccentricity e and the thickness variation ratio t e This shows the effect on the pipe thickness. Figure 10 shows the thickness variation ratio t on the vertical axis. e (%), the horizontal axis is the eccentricity e (mm) of the eccentric expanding plug, and the outer diameter D of the expanded diameter portion of the eccentric expanding plug. max The graphs for 28, 30, and 32 are shown below. As shown in Figure 10, the thickness variation ratio t increases as the eccentricity e increases. e This increases. On the other hand, the outer diameter D of the enlarged diameter portion of the eccentric tube-expanding plug increases. max Even if the thickness variation rate t changes, e There is no significant difference in the way the changes occur. Figures 11 and 12 show the outer diameter D of the enlarged diameter portion of the eccentric expansion plug. max Under the condition of =30mm, the axial thickness variation t of the pipe material during drawing is e This shows the changes. Figure 11 is a diagram of the FEM analysis model in which the eccentric expansion plug 10 is passing through the pipe. Behind the eccentric expansion plug 10 has passed through the pipe, an eccentric pipe 50 is formed with a thick-walled section 51 and a thin-walled section 52. Also, in Figure 11, the boundary between the tapered surface 12 and the expanded diameter section 11 of the eccentric expansion plug 10 is set to z=0, and the longitudinal position of the pipe is defined with respect to this z=0. For example, the position of the tip 13 is defined as z=-12mm. Figure 12 shows the position of the eccentric expansion plug 10 and the thickness variation ratio t. e This graph shows the relationship, with the vertical axis representing the thickness variation rate t. eThe graphs show the position z (mm) of the eccentric expansion plug 10 on the horizontal axis (%), with eccentricity amounts e of 0.6, 1.0, and 1.4, respectively. As shown in Figure 12, the thickness variation t gradually increases from the position where the tip 13 of the eccentric expansion plug 10 has passed. e The thickness ratio t begins to increase. Then, within the region in contact with the tapered surface 12, e The thickness ratio t increases significantly. Furthermore, after passing through the tapered surface 12 and after passing a certain distance, the thickness ratio t increases. e The ratio remained constant. As shown in Figure 12, after passing through the tapered surface 12, the thickness variation ratio t was at the position z = +8 mm. e It became constant. [Examples]

[0045] Next, based on the analysis results described above, two types of eccentric expansion plugs with different eccentricity amounts e were actually fabricated, and experiments were conducted on the expansion-type drawing process of the pipe material. In this experiment, the elastic body that was placed at the free end of the pipe material during the FEM analysis described above was not used.

[0046] Figure 13 shows the experimental conditions (Exp.) for the tube-expanding drawing process. The conditions for the eccentric tube-expanding plug used in the experiment are the same as those for the eccentric tube-expanding plug 20 shown in Figure 2 above, with eccentricity amounts e of 1.0 and 1.4 mm, and the outer diameter D of the expanded diameter section 21. max The diameter is 30 mm, the angle α of the tapered surface 22 in the 90° direction is 11°, and the outer diameter D of the guide section 28 is 30 mm. min The diameter is 26 mm. The specifications of the pipe 30 used in the experiment are as follows: material is aluminum (A1070), wall thickness t0 is 2 mm, outer diameter D0 is 30 mm, and length L0 is 360 mm. Castor S-846M manufactured by Taiyu was used as the lubricant.

[0047] Under the above conditions, an experiment was conducted on the tube expansion type drawing process using an eccentric tube expansion plug, and the wall thickness t of the manufactured tube with uneven thickness was measured. The measurement locations of the tube with uneven thickness in the experiment are shown in Figure 14. As shown in Figure 14, in the experiment, measurements were taken at four locations in the axial direction (longitudinal direction), excluding both ends, and the wall thickness was measured at eight locations at 45° intervals within the circumferential range of 0 to 360° at each measurement location.

[0048] Figure 15 shows the relationship between the eccentricity e of the eccentric expanded tube plug obtained experimentally and the circumferential wall thickness t of the eccentric tube. In Figure 15, the vertical axis is the wall thickness t (mm) of the eccentric tube, and the horizontal axis is the angle (θ) of the measurement point, and the graphs for eccentricity e of the eccentric expanded tube plug of 1.0 and 1.4 are shown, respectively.

[0049] As shown in Figure 15, the wall thickness of the eccentric tubes formed in the experiment was maximum at the 180° position for all eccentric expansion plugs with an eccentricity e, and decreased from the 180° position to the 0° position. Furthermore, the wall thickness t of the eccentric tubes processed with an eccentric expansion plug with an eccentricity e = 1.4 mm was generally lower than the wall thickness t of the eccentric tubes processed with an eccentric expansion plug with an eccentricity e = 1.0 mm. Also, the wall thickness ratio t at eccentricity e = 1.0 mm and 1.4 mm was... e The percentages were 13% in all cases. From these results, it became clear that it is possible to form tubes with uneven thickness by expanding and drawing using an eccentric tube expansion plug.

[0050] It should be noted that the present invention is not limited to the configuration described in the above-described embodiments, and various modifications and changes are possible without departing from the configuration of the present invention. [Explanation of Symbols]

[0051] 10,20 Eccentric expanding pipe plug, 11,21 Expanded diameter section, 12,22 Tapered surface, 13,23 Tip section, 15,25 Centerline in eccentric direction, 16,26 Centerline of tip section, 17,27 Centerline of expanded diameter section, 28 Guide section, 30 Pipe material, 35 Centerline of pipe material, 40 Chuck, 41 Hydraulic cylinder, 42 Shaft, 43 Dummy block, 44 Nut, 45 Stopper, 50 Uneven wall diameter pipe, 51 Thick-walled section, 52 Thin-walled section, 53 Centerline of outer diameter, 54 Centerline of inner diameter

Claims

1. An eccentric tube expansion plug used in the tube expansion drawing process of pipe materials, A tip portion provided at the end of the pipe material in the insertion direction, An enlarged diameter portion having a larger outer diameter than the aforementioned tip portion, It comprises a tapered surface disposed over the entire outer circumference between the tip portion and the enlarged diameter portion, In a cross-section perpendicular to the insertion direction into the pipe, the center position of the tip portion and the center position of the enlarged diameter portion are offset with respect to the insertion direction into the pipe. Eccentric tube expansion plug for tube expansion drawing processes.

2. The center position of the tip portion and the center position of the enlarged diameter portion are offset in one direction perpendicular to the insertion direction. An eccentric tube expansion plug for tube expansion type drawing process according to claim 1.

3. In a cross-section perpendicular to the insertion direction into the pipe, the center position of the region where the tapered surface is formed changes continuously between the center position of the tip and the center position of the enlarged diameter portion. An eccentric tube expansion plug for tube expansion type drawing process according to claim 1.

4. The tip portion, the enlarged diameter portion, and the region where the tapered surface is formed have a circular cross-section in a direction perpendicular to the insertion direction into the pipe material. An eccentric tube expansion plug for tube expansion type drawing process according to claim 1.

5. A method for expanding a pipe material by drawing using an expansion plug, As the tube expansion plug, an eccentric tube expansion plug is used, which comprises a tip portion provided at the end in the insertion direction into the tube material, an enlarged diameter portion having a larger outer diameter than the tip portion, and a tapered surface arranged on the entire outer circumference between the tip portion and the enlarged diameter portion, wherein in a cross section perpendicular to the insertion direction into the tube material, the center position of the tip portion and the center position of the enlarged diameter portion are offset with respect to the insertion direction into the tube material. The opening of one of the pipe materials is widened by inserting the eccentric expanding plug from the tip to the rear end of the enlarged diameter portion. A tube-expanding drawing method using an eccentric tube-expanding plug.

6. After the widening process, an extraction process is performed to pull out the eccentric expanding plug from the other opening of the pipe material. A pipe-expanding type drawing process using the eccentric pipe-expanding plug described in claim 5.

7. A tube with a variable thickness manufactured by an expansion-type drawing process using an expansion plug, The tube expansion plug comprises a tip portion provided at the end of the tube material in the insertion direction, an enlarged diameter portion having a larger outer diameter than the tip portion, and a tapered surface arranged on the entire outer circumference between the tip portion and the enlarged diameter portion, wherein in a cross section perpendicular to the insertion direction into the tube material, the center position of the tip portion and the center position of the enlarged diameter portion are offset with respect to the insertion direction into the tube material, and the widening process involves inserting the eccentric tube expansion plug into one opening of the tube material from the tip portion to the rear end of the enlarged diameter portion. After the mouth widening process, the eccentric expanding plug is drawn out from the other opening of the pipe material, and manufactured by this process. Uneven-walled tube.

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