Processing method by hydroforming, mold, mold module, and processing device of hydroforming

Abstract

To control a thickness of a workpiece with high accuracy.SOLUTION: A mold is used to mold a pipe-like workpiece and has at least one wall part extending in a longitudinal direction. On an inner surface of the wall part, a supply port for supplying a lubricating liquid is provided in a center area as seen in a width direction orthogonal to the longitudinal direction of the wall part of a plane part sandwiched by corner parts of the mold.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a hydroforming processing method, a die, a die module, and a hydroforming processing apparatus. [Background technology]

[0002] Hydroforming is a processing method in which steel pipes and other materials are swelled by applying internal pressure to them, forcing them to conform to the shape of a die, thereby forming them into the desired shape. Hydroforming can impart work hardening and produce one-piece molding, so it is expected to contribute to reducing the weight of automobiles and other vehicles. However, with hydroforming, friction between the die and the steel pipe (workpiece) can cause problems with changes in wall thickness after processing.

[0003] To address this problem, for example, Patent Document 1 discloses a technology for controlling friction between a die and a workpiece by providing a large number of holes on the inner surface of the die and supplying a lubricating liquid through these holes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-150049 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the technology disclosed in Patent Document 1, the lubricating liquid flows into areas where there is no contact or where the contact between the workpiece and the die is weak, so the contact pressure from the lubricating liquid is not sufficient, the effect of fluid lubrication is not easily obtained, and it is difficult to control the thickness of the workpiece.

[0006] Therefore, the present disclosure has been made in consideration of the above-mentioned problems, and its purpose is to provide a hydroforming processing method, a mold, a mold module, and a hydroforming processing apparatus that can control the thickness of the workpiece with higher precision. [Means for solving the problem]

[0007] According to the present disclosure, there is provided a hydroforming processing method including: an arrangement step of placing a tubular workpiece in a mold formed according to a first direction corresponding to the elongation direction of the workpiece; a lubricating liquid supply step of supplying lubricating liquid to a central region of a flat portion of the inner surface of the mold, in a width direction of the workpiece perpendicular to the first direction, which is sandwiched between corner portions of the cross section of the mold; and a forming step of supplying liquid from a supply source different from the lubricating liquid to the inside of the workpiece while supplying the lubricating liquid, thereby applying pressure from the inside of the workpiece and deforming the workpiece along the inner surface of the mold.

[0008] Furthermore, according to the present disclosure, there is provided a mold for forming a tubular workpiece, the mold having at least one wall portion extending in the longitudinal direction, and a supply port for supplying lubricating liquid provided on the inner surface of the wall portion in a central region of a flat portion sandwiched between corner portions of the mold in a width direction perpendicular to the longitudinal direction of the wall portion.

[0009] Furthermore, according to the present disclosure, there is provided a mold module that is detachably mounted inside a mold for molding a tubular workpiece, on a flat surface sandwiched between corner portions in the cross section of the mold, and a supply port for supplying lubricating liquid is provided on the inner surface of the mold module in a central region in the width direction of the mold module.

[0010] Furthermore, according to the present disclosure, there is provided a hydroforming processing device comprising: a mold having at least one wall portion extending in the longitudinal direction, and a supply port for supplying lubricating liquid on the inner surface of the wall portion, the supply port being provided in a central region in a width direction perpendicular to the longitudinal direction of the wall portion; a lubricating liquid supply source for supplying lubricating liquid from the supply port on the inner surface of the mold to a position in a central region of a flat portion sandwiched between corner portions in a cross section of the mold, in a width direction perpendicular to the longitudinal direction of the workpiece; and an internal pressure liquid supply source for supplying liquid from a supply source different from the lubricating liquid to the inside of the workpiece while supplying the lubricating liquid, thereby applying pressure from the inside of the workpiece to deform it. [Effects of the Invention]

[0011] According to the present disclosure, the thickness of the workpiece can be controlled with higher precision. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram for explaining an outline of a processing method by hydroforming according to an embodiment of the present invention. FIG. [Figure 2] 3A to 3C are diagrams for explaining an outline of a processing method by hydroforming according to the embodiment. [Figure 3] FIG. 2 is a diagram showing a configuration example of a processing device using hydroforming according to the embodiment. [Figure 4] FIG. 2 is a perspective view showing a configuration example of a mold 1 according to the embodiment. [Figure 5] 1 is a cross-sectional view of a mold 1 according to the embodiment, taken along a cross section perpendicular to the longitudinal direction at a position where an inlet 1F and a supply port 11 are provided in the longitudinal direction. [Figure 6] 10 is a diagram showing an example of the internal structure of an upper mold 1A according to the embodiment. FIG. [Figure 7] FIG. 2 is a diagram showing a first example of a mold module according to the embodiment. [Figure 8] FIG. 10 is a diagram showing a second example of the mold module according to the embodiment. [Figure 9]FIG. 10 is a diagram showing a third example of the mold module according to the same embodiment. [Figure 10] FIG. 10 is a diagram showing a fourth example of the mold module according to the same embodiment. [Figure 11] 2A and 2B are diagrams showing an example of the positional relationship between the mold module and an upper mold 1A of the mold 1 according to the embodiment, and an enlarged view thereof. [Figure 12] 2A and 2B are diagrams showing an example of the positional relationship between the mold module and an upper mold 1A of the mold 1 according to the embodiment, and an enlarged view thereof. [Figure 13] 6 is a graph showing an example of supply control of lubricating liquid and internal pressure liquid according to the embodiment. [Figure 14] 10 is a graph showing another example of supply control of lubricating liquid and internal pressure liquid according to the embodiment. [Figure 15] 4 shows graphs of pressure control of the internal pressure fluid and the lubricating fluid according to the present embodiment. [Figure 16] 10 is a graph showing pressure control of internal pressure fluid according to a comparative example. [Figure 17] FIG. 2 is a diagram showing the properties of the steel pipe after processing in this example. [Figure 18] 1 is a diagram showing the properties of a steel pipe after processing in a comparative example. [Figure 19] 1 is a graph showing the distribution of wall thickness of steel pipes after processing in the present example and the comparative example. [Figure 20] 1 is a graph showing the distribution of wall thickness of a steel pipe after processing in this example. DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0014] <Summary> First, an outline of a hydroforming method according to an embodiment of the present disclosure will be described. Figures 1 and 2 are diagrams for explaining an outline of a hydroforming method according to this embodiment. Figures 1 and 2 show cross sections perpendicular to the longitudinal direction (extension direction) of a die 1 and a workpiece (steel pipe) 2.

[0015] The die 1 is a die used for hydroforming and is composed of, for example, an upper die and a lower die. The die 1 has at least one wall extending in the longitudinal direction. The workpiece 2 is placed between the upper die and the lower die, and high-pressure liquid, such as water, is supplied into the workpiece 2 from the longitudinal end of the die 1. This causes the workpiece 2 to expand and be extruded onto the inner surface of the die 1. Note that, although the workpiece 2 in this embodiment is assumed to be a steel pipe, the workpiece 2 is not limited to this example. For example, the workpiece 2 may be made of a different material, such as another metal. The workpiece 2 may be tubular, cylindrical, or may be formed by joining two plate-shaped members and expanding each of the plate-shaped members to form an annular member. These members are also defined as "tubular workpieces" in this embodiment.

[0016] In this embodiment, as shown in Fig. 1, a lubricating liquid is introduced from the outside to the inside of the die 1 as the workpiece 2 expands due to hydroforming. The lubricating liquid may be any liquid, such as water or oil, and may also contain additives such as molybdenum disulfide or graphite. The lubricating liquid is supplied to a central region in the width direction of the workpiece 2, as will be described in detail later. A lubricating liquid supply port is preferably provided in one location in the die 1.

[0017] As a result, as shown in Figure 2, the workpiece 2 expanded by hydroforming conforms to the inner surface of the die 1, and at this time, a fluid lubrication layer of lubricating liquid is formed between the die 1 and the workpiece 2. At this time, the lubricating liquid is supplied to the central region of the workpiece 2, so the lubricating liquid flows into the small gap between the die 1 and the workpiece 2. As a result, sufficient pressure is applied to the lubricating liquid, and a fluid lubrication layer can be formed along the die 1. The lubricating liquid can be discharged, for example, from a hole other than the supply port of the die 1.

[0018] In this way, a lubricating liquid supply port is provided in the die 1 at a position corresponding to the central region of the workpiece 2, and the lubricating liquid is supplied to the die 1 from this supply port during hydroforming. Sufficient pressure is applied to the lubricating liquid to form a fluid lubrication layer, thereby reducing friction between the die 1 and the workpiece 2 and improving the fluidity of the material of the workpiece 2. This makes it possible to more uniformly control the thickness of the workpiece 2 after hydroforming. Specific configuration examples according to this embodiment will be described below.

[0019] <Configuration example> FIG. 3 is a diagram showing an example of the configuration of a processing apparatus using hydroforming according to this embodiment. The processing apparatus according to this embodiment includes a die 1, a lubricating fluid pump 3 (lubricating fluid supply source), a Bourdon tube pressure gauge 4, a pressure sensor 5, an internal pressure fluid pump 6 (internal pressure fluid supply source), a Bourdon tube pressure gauge 7, and a pressure sensor 8. The die 1 is composed of an upper die 1A, a lower die 1B, a nozzle-equipped lid die 1C, and a lid die 1D. Note that the processing apparatus according to this embodiment is a type of apparatus that does not have a so-called axial punch die that axially presses the end of the workpiece 2 along the longitudinal direction, but the present technology is not limited to this example. In other words, such a processing apparatus may also have an axial punch die.

[0020] The workpiece 2 set inside the die 1 is expanded by the pressure applied by the internal pressure liquid P1 supplied from the internal pressure liquid pump 6 through the nozzle-equipped cover die 1C. At this time, the lubricating liquid L1 supplied from the lubricating liquid pump 3 through the supply port of the upper die 1A forms a fluid lubrication layer between the surface of the workpiece 2 inside the die 1.

[0021] Next, a configuration example of the mold 1 will be described. Fig. 4 is a perspective view showing a configuration example of the mold 1 according to this embodiment. Fig. 5 is a cross-sectional view of the mold 1 according to this embodiment in a cross section perpendicular to the longitudinal direction at a position where the introduction port 1F and the supply port 11 are provided in the longitudinal direction. Fig. 6 is a view showing an example of the internal structure of the upper mold 1A according to this embodiment.

[0022] As shown in FIG. 4, the mold 1 is composed of an upper mold 1A and a lower mold 1B assembled vertically. A space 1G for processing a workpiece 2 is provided between the upper mold 1A and the lower mold 1B, and internal pressure liquid P1 is supplied from a nozzle of a nozzle-equipped lid mold 1C through a hole 1E. A supply port 11 is provided on the inner surface of the mold 1. The upper mold 1A also has a supply port 11. The inlet port 1F is a hole for supplying lubricating liquid L1 to the space 1G inside the mold 1. The inlet port 1F is provided in a central region in a width direction W perpendicular to the longitudinal direction L (an example of a first direction) of the mold 1. The central region refers to a central region in the width direction of a flat portion 111 sandwiched between corner portions 110 in the cross-sectional shape of the inner surface of the mold where the supply port 11 is provided in the longitudinal direction. The inlet port 1F and the supply port 11 may also be provided in the lower mold 1B.

[0023] The inlet 1F and the supply port 11 are connected by a single flow path, and it is preferable that the inlet 1F and the supply port 11 are provided in a one-to-one correspondence. Furthermore, it is preferable that the lubricating liquid L1 flowing out from one inlet 1F through the supply port 11 is supplied only from one supply source (e.g., lubricating liquid pump 3). This allows the lubricating liquid L1 to be introduced into the mold 1 at high pressure. When multiple supply ports 11 are provided, for example, each of the multiple supply ports 11 may be provided with a corresponding lubricating liquid supply source, or a valve may be provided in the flow path connecting the multiple supply ports 11 and the inlet 1F, and the valve may be controlled so that the lubricating liquid is supplied to only one supply port 11. This allows the pressure of the lubricating liquid to be maintained high. The locations at which the multiple supply ports 11 are provided are not particularly limited, but it is preferable that they are provided in close proximity to each other.

[0024] The mold 1 may also be provided with an outlet 12 for discharging the lubricating liquid L1 and an outlet 1H for allowing the lubricating liquid L1 to flow out of the mold 1 from the outlet 12. The number of such outlets 12 and outlets 1H is not particularly limited.

[0025] Such a supply port 11 may be provided directly on the upper die 1A, or on a die module that is detachable from the upper die 1A. Such a die module may have a nested structure with respect to the die 1. By using a die module, it is possible to control the flow of the lubricating liquid between the die and the steel pipe. Furthermore, by making the die module detachable from the die, the shape of the die surface can be easily changed. Note that the shape on the die module described below may be set on the die module, or may be formed directly on the die.

[0026] FIG. 7 is a diagram showing a first example of a mold module according to this embodiment. As shown in FIG. 7, the mold module 21 is detachably provided in the central portion of the upper mold 1A. The mold module 21 has a supply port 11 and a groove 13 extending longitudinally from the supply port 11. The length of the groove 13 is not particularly limited. However, it is preferable that the groove 13 passes through the central region of the flat portion of the inner surface of the mold. Even if the mold shape is curved rather than linear, it is preferable that the groove 13 pass through the central region of the flat portion and follow the change in the curved shape of the mold.

[0027] FIG. 8 is a diagram showing a second example of a die module according to this embodiment. As shown in FIG. 8, the die module 22 has multiple grooves 14 formed around the supply port 11. The multiple grooves 14 are composed of a groove extending longitudinally from the supply port 11 and multiple annular grooves surrounding the groove. This facilitates the flow of lubricant to a region slightly outside the center of the workpiece 2, where friction between the die 1 and the workpiece 2 tends to be high. In particular, the contact position between the die module 22 and the workpiece 2 gradually shifts from the center to the outside, allowing the lubricant to flow appropriately along that position. This effectively reduces friction. The shape and location of the multiple grooves 14 are not particularly limited. It is preferable that these multiple grooves do not intersect with each other. By not intersecting the multiple grooves, the lubricant can be supplied to the contact position with an appropriate amount and pressure as the contact position between the workpiece 2 and the die 1 shifts from the center to the outside.

[0028] FIG. 9 illustrates a third example of a die module according to this embodiment. As shown in FIG. 9, the die module 23 includes a supply port 11 and a groove 13 extending longitudinally from the supply port 11. Furthermore, a sloped portion 15 is provided, sloping outward from the groove 13 toward the opposing inner surface. That is, the supply port 11 and the groove 13 are provided at the bottom of the sloped portion 15. This creates a space for lubricant accumulation between the workpiece 2 and the supply port 11 provided in the upper die 1A during hydroforming. As the workpiece 2 expands, the workpiece 2 and the inner surface of the die 1 attempt to come into contact with each other, starting from the portion of the sloped portion 15 closest to the supply port 11. However, the portion closest to the supply port 11 is pushed back by the pressure of the lubricant, preventing direct contact between the workpiece 2 and the die 1. In other words, a complete fluid lubrication state can be achieved in this region. As the workpiece 2 expands, the inclined portion 15 becomes inclined, and the position of direct contact between the workpiece 2 and the inner surface of the mold 1 moves outward, allowing molding to proceed while expanding the complete fluid lubrication area.

[0029] FIG. 10 is a diagram showing a fourth example of a die module according to this embodiment. As shown in FIG. 9, a die module 24 has a plurality of grooves 16 formed along the longitudinal direction at the widthwise end of the die module 23 shown in FIG. 9. These grooves 16 function to drain the lubricant flowing out from the supply port 11. This allows for a state in which the amount of lubricant is small on the small surfaces 17 between the grooves 16. This increases friction with the workpiece 2 during hydroforming in the areas where many of these grooves 16 are arranged. Because the workpiece 2 comes into contact with the grooves 16 in the later stages of forming, the flow of material in the later stages of forming can be controlled to suppress deformation of already deformed areas (material near the grooves 13), thereby preventing cracking of the material. The grooves 16 can be formed in the die modules of the other examples described above, or directly on the upper die 1A. The grooves 16 may be formed entirely along the longitudinal direction, as shown in FIG. 10, or may be formed partially. For example, the position where the groove 16 is provided can be adjusted appropriately depending on the circumferential length of the workpiece 2 (before or after processing).

[0030] This type of die 1 can be applied to, for example, existing hydroforming processing equipment by using a detachable die module. Specifically, in the processing equipment shown in Fig. 3, simply adding the lubricating liquid pump 3 and its associated line, as well as the die module, to the existing hydroforming processing equipment enables processing by hydroforming according to this embodiment.

[0031] FIG. 11 is a diagram and an enlarged view showing an example of the positional relationship between the mold module 20 and the upper mold 1A of the mold 1 according to this embodiment. As shown in FIG. 11, the positions of the surface of the mold module 20 and the surface of the upper mold 1A may be different. Specifically, it is preferable that the surface of the mold module 20 protrudes from the surface of the upper mold 1A. The protrusion amount D1 is preferably, for example, 0.01 mm or more. This makes it possible to prevent the material from getting caught at the boundary between the mold module 20 and the upper mold 1A during material flow during processing.

[0032] Furthermore, it is preferable that the distance D2 between the boundary between the die module 20 and the upper die 1A and the boundary 18A of the corner portion 18 of the upper die 1A is within 10 mm. Furthermore, the boundary between the die module 20 and the upper die 1A may be on the inside of the corner portion 18. This reduces the possibility that the workpiece 2 will come into contact with the boundary between the die module 20 and the upper die 1A before processing of the workpiece 2 is completed, thereby preventing the material from getting caught.

[0033] As described above, the supply port 11 is preferably located in the longitudinal center of the die 1. The supply port 11 is preferably located in a region in the longitudinal direction L of the die 1 where the perimeter of a cross section perpendicular to the longitudinal direction L of the die 1 is 1.03 times or more the perimeter of an end of the die 1. FIG. 12 is a diagram illustrating the inner shape of the die 1 according to this embodiment and a preferred installation position of the supply port 11. As shown in FIG. 12, when the perimeter C1 of the end 19A of the die 1 is used as a reference, the supply port 11 is preferably located in a region where the perimeter C2 of a cross section 19B perpendicular to the longitudinal direction L of the die 1 is 1.03 times or more the perimeter C1. The region where the perimeter C2 is 1.03 times or more the perimeter C1 is the region where the workpiece 2 expands, and therefore the effect of supplying the lubricant from the supply port 11 is greater.

[0034] <Lubricant supply control> Next, an example of control of the supply of lubricating liquid will be described. In this embodiment, during forming, the pressure applied to the workpiece 2 by the lubricating liquid during forming is preferably higher than the processing pressure applied by the internal pressure liquid supplied to the inside of the workpiece 2. FIG. 13 is a graph showing an example of control of the supply of lubricating liquid and internal pressure liquid according to this embodiment. The graph shown in FIG. 13 shows an example of time-series changes in the internal pressure applied by the internal pressure liquid and the pressure applied by the lubricating liquid (lubrication pressure), both measured and set. The timing at which the lubricating pressure (measured value) shown in FIG. 13 rises corresponds to the timing at which the workpiece 2 comes into contact with the surface of the die 1 and forming begins. Furthermore, before forming is completed, when the lubricating pressure (measured value) drops, the supply of lubricating liquid is stopped and the lubricating pressure is reduced.

[0035] As shown in the graph in Figure 13, from the start of deformation of the workpiece 2 until the supply of lubricating liquid is stopped, the lubricating pressure (actual measured value) is controlled to be higher than the internal pressure due to the internal pressure liquid. This makes it possible to maintain a lubricated state between the die 1 and the workpiece 2 and reduce friction while performing processing by hydroforming.

[0036] FIG. 14 is a graph showing another example of supply control of lubricating fluid and internal pressure fluid according to this embodiment. In the example shown in FIG. 14, the lubricating fluid is controlled to be supplied intermittently. By intentionally varying the lubricating pressure in this manner, the friction between the die 1 and the workpiece 2 can be increased during the period when the lubricating fluid pressure is decreasing, thereby gripping the workpiece 2 and promoting deformation of the non-contacting portions. Note that in this supply control, the lubricating pressure may not only be repeatedly increased and decreased, but may also be decreased during forming. In this case, the deformation after the lubricating pressure is decreased can prioritize the non-contacting portions with the die 1, as in normal hydroforming. [Example]

[0037] Next, an example according to the present disclosure will be described. Note that the technology described in the example is merely an example, and the present technology is not limited to the example described below.

[0038] Example 1 This example demonstrates the effectiveness of the hydroforming processing method using the lubricating liquid supply method and control method shown in the above embodiment.

[0039] The hydroforming processing equipment used in this example is the processing equipment and die 1 shown in Figures 3 to 6. The workpiece 2 is a steel pipe made of STKM11A, with an outer diameter Φ of 50.8 mm and a thickness t of 1.2 mm. The workpiece 2 is placed in the die 1. Hydraulic oil (viscosity 32) is used for both the internal pressure fluid and the lubricating fluid. The processing conditions were calculated using the following formula (1). Note that P is the processing pressure, t is the thickness of the workpiece 2, and σ θ is the maximum tensile stress of the workpiece 2, and r is the curvature of the corner after processing. In this example and comparative example, the central portion of a cylindrical steel pipe in the longitudinal direction is deformed into a square pipe with a corner portion of R5. A pressure of 72 MPa was originally required to process the steel pipe, but since the maximum pressure of the internal pressure fluid pump 6 is 70 MPa, processing was carried out at the maximum pressure of 70 MPa.

[0040] P=t×σ θ / r ···(1)

[0041] In the example, lubricating fluid was supplied during hydroforming using internal pressure fluid. On the other hand, in the comparative example, only hydroforming using internal pressure fluid was performed, and lubricating fluid was not supplied. Figure 15 shows a graph of pressure control of internal pressure fluid and lubricating fluid in this example. Figure 16 shows a graph of pressure control of internal pressure fluid in the comparative example. Both pressures were manually adjusted by adjusting the output of the respective pumps.

[0042] 17 and 18 are diagrams showing the properties of steel pipes after processing in this example and a comparative example. The steel pipe according to this example shown in Fig. 17 has no particular abnormalities, but the steel pipe according to the comparative example shown in Fig. 18 has fractures on the surface. This suggests that the supply of the lubricating liquid as described above makes it possible to control the wall thickness during processing of the steel pipe.

[0043] Figure 19 is a graph showing the distribution of wall thickness of steel pipes after processing in this example and a comparative example. The circumferential length L shown on the horizontal axis indicates the position in the circumferential direction when the centers of the opposing vertical walls of the processed steel pipe are set as the end points. In the comparative example (Conventional), the wall thickness does not particularly decrease at the center of the wall, but decreases (fractures) on the outer side of the wall. On the other hand, in this example (Proposed), the wall thickness decreases almost uniformly along the circumferential direction, suggesting that the wall thickness is controlled almost uniformly.

[0044] Example 2 In this embodiment, an example is shown in which the mold module 21 shown in Fig. 7 is applied to the mold 1. The processing conditions and the like are the same as those in the first embodiment, and therefore will not be described.

[0045] FIG. 20 is a graph showing the distribution of wall thickness of the steel pipe after processing in this example. Line 106 represents the wall thickness (1.2 mm) before processing, and lines 107-109 represent the longitudinal center of the workpiece 2 (the portion facing the supply port 11) and the circumferential length of the portion 27 mm away from the center along the longitudinal direction (0 mm represents the center of the vertical wall, and 50 mm represents the center of the bottom wall). As shown in FIG. 20, because the lubricating liquid is supplied longitudinally through the grooves 13 provided along the longitudinal direction of the die 1, there is no difference in the distribution of wall thickness between the longitudinal center and the position 27 mm away. This suggests that hydroforming can be used to obtain a uniform wall thickness along the longitudinal direction of the workpiece 2.

[0046] Although the preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the technical scope of the present disclosure is not limited to such examples. It is clear that a person skilled in the art of the present disclosure can conceive of various modified or altered examples within the scope of the technical idea described in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0047] Furthermore, the effects described herein are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present disclosure may achieve other effects that will be apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0048] The following configurations also fall within the technical scope of the present disclosure. (Item 1) a positioning step of positioning a tubular workpiece in a mold formed according to a first direction corresponding to an elongation direction of the workpiece; a lubricating liquid supplying step of supplying a lubricating liquid to a central region of a flat portion of an inner surface of the mold, the flat portion being sandwiched between corner portions of a cross section of the mold in a width direction of the workpiece perpendicular to the first direction; a forming step in which, while supplying the lubricating liquid, a liquid is supplied from a supply source different from the lubricating liquid to the inside of the workpiece to apply pressure from the inside of the workpiece, thereby deforming the workpiece along the inner surface of the die; A hydroforming method including: (Item 2) Item 2. The hydroforming method according to item 1, wherein a supply port for supplying the lubricating liquid is provided on the inner surface of the die in a central region in a width direction of the die that is perpendicular to a direction corresponding to the first direction. (Item 3) 3. The hydroforming method according to item 2, wherein the lubricating liquid flowing out from the supply port (1) is supplied only from the supply source (1). (Item 4) 4. The hydroforming method according to item 2 or 3, wherein a flow path connecting one or more of the supply ports and one supply source for supplying the lubricating liquid is controlled by a valve so that the lubricating liquid is supplied to only one of the supply ports. (Item 5) 5. The hydroforming method according to any one of items 2 to 4, wherein a first groove is provided on the inner surface of the die from the supply port along the extension direction of the die. (Item 6) A second groove is provided on the inner surface of the mold along the periphery of the first groove, 6. The hydroforming method according to item 5, wherein the second groove does not intersect with the first groove. (Item 7) Item 7. The hydroforming method according to item 6, wherein the second groove is formed so as to surround the first groove. (Item 8) 8. The hydroforming method according to any one of items 5 to 7, wherein at least one third groove is provided on the inner surface of the mold, extending from the first groove toward the outside in the width direction of the mold. (Item 9) Item 9. The hydroforming method according to item 8, wherein at least a plurality of the third grooves are provided along the extension direction of the die. (Item 10) 10. The hydroforming method according to any one of items 2 to 9, wherein the inner surface of the die is inclined outward from the supply port so as to approach the opposing inner surface. (Item 11) 11. The hydroforming method according to any one of items 1 to 10, wherein the pressure applied to the workpiece by the lubricating liquid during forming in the forming step is higher than the processing pressure by the liquid supplied to the inside of the workpiece. (Item 12) 12. The hydroforming method according to any one of items 1 to 11, wherein in the forming step, control is performed to reduce the pressure applied to the workpiece by the lubricating liquid after starting forming and before completing forming. (Item 13) 13. The hydroforming method according to any one of items 1 to 12, wherein in the forming step, the pressure applied to the workpiece by the lubricating liquid is controlled to fluctuate up and down. (Item 14) 14. The hydroforming method according to any one of items 1 to 13, wherein the inner surface of the die is a surface of a die module that is provided with a supply port for supplying the lubricating liquid and is detachably attached to the die. (Item 15) Item 15. The hydroforming method according to item 14, wherein the die module is provided so as to protrude from an inner surface of the die on which the die module is not provided. (Item 16) A mold for forming a tubular workpiece, the mold has at least one longitudinally extending wall; A mold wherein a supply port for supplying lubricating liquid is provided on the inner surface of the wall portion in a central region of a flat portion sandwiched between corner portions of the mold in a width direction perpendicular to the longitudinal direction of the wall portion. (Item 17) Item 17. The mold according to item 16, wherein one of the supply ports is connected only to one supply source via a flow path. (Item 18) Item 18. The mold according to item 16 or 17, wherein a flow path connecting one or more of the supply ports and one supply source for supplying the lubricating liquid is controlled by a valve so that the lubricating liquid is supplied to only one of the supply ports. (Item 19) 19. The mold according to any one of items 16 to 18, wherein a first groove is provided on the inner surface of the wall portion along the longitudinal direction from the supply port. (Item 20) a second groove is provided on the inner surface of the wall portion around and along the first groove; 20. The mold of claim 19, wherein the second groove does not intersect with the first groove. (Item 21) Item 21. The mold according to item 20, wherein the second groove is formed to surround the first groove. (Item 22) 22. The mold according to any one of items 19 to 21, wherein at least one third groove is provided on the inner surface of the wall portion, extending from the first groove toward the outer side in the width direction of the wall portion. (Item 23) Item 23. The mold according to item 22, wherein at least a plurality of the third grooves are provided along the longitudinal direction of the wall portion. (Item 24) 24. The mold according to any one of items 16 to 23, wherein the inner surfaces of the wall portions are inclined outward from the supply port so as to approach the inner surfaces of the opposing wall portions. (Item 25) 25. The mold according to any one of items 16 to 24, wherein the supply port is provided in a region in the longitudinal direction of the mold where the circumferential length of a cross section of the mold perpendicular to the longitudinal direction is 1.03 times or more the circumferential length of an end portion of the mold. (Item 26) 26. The mold according to any one of items 16 to 25, wherein the inner surface of the mold is a surface of a mold module that is provided with the supply port and is detachably attached to the mold. (Item 27) Item 27. The mold according to item 26, wherein the mold module is provided so as to protrude beyond an inner surface of the mold on which the mold module is not provided. (Item 28) A mold module is provided inside a mold for forming a tubular workpiece, and is detachably provided on a flat surface portion sandwiched between corner portions in a cross section of the mold, A mold module, wherein a supply port for supplying lubricating liquid is provided on an inner surface of the mold module in a central region in the width direction of the mold module. (Item 29) a mold having at least one wall extending in a longitudinal direction, the wall having an inner surface provided with a supply port for supplying a lubricating liquid in a central region in a width direction perpendicular to the longitudinal direction of the wall; a lubricating liquid supply source for supplying lubricating liquid from the supply port on the inner surface of the die to a central region of a flat surface portion sandwiched between corner portions in a cross section of the die in a width direction perpendicular to the longitudinal direction of the workpiece; an internal pressure fluid supply source for supplying fluid from a supply source different from the lubricating fluid to the inside of the workpiece while supplying the lubricating fluid, thereby applying pressure from the inside of the workpiece to deform it; A hydroforming processing device comprising: [Explanation of symbols]

[0049] 1. Mold 2 Work material 3 Lubricating fluid pump (lubricating fluid supply source) 6. Internal pressure fluid pump (internal pressure fluid supply source) 11 Supply port 13, 14, 16 grooves

Claims

1. A mold for forming a tubular workpiece, the mold has at least one longitudinally extending wall; A mold wherein a supply port for supplying lubricating liquid is provided on the inner surface of the wall portion in a central region of a flat portion sandwiched between corner portions of the mold in a width direction perpendicular to the longitudinal direction of the wall portion.

2. The mold according to claim 1 , wherein one of the supply ports is connected to only one supply source via a flow path.

3. 3. The mold according to claim 1, wherein a flow path connecting one or more of the supply ports to one supply source for supplying the lubricating liquid is controlled by a valve so that the lubricating liquid is supplied to only one of the supply ports.

4. The mold according to any one of claims 1 to 3, wherein a first groove is provided on an inner surface of the wall portion, extending from the supply port along the longitudinal direction.

5. a second groove is provided on the inner surface of the wall portion around and along the first groove; The mold of claim 4 , wherein the second groove does not intersect with the first groove.

6. The mold according to claim 5 , wherein the second groove is formed so as to surround the first groove.

7. The mold according to any one of claims 4 to 6, wherein at least one third groove is provided on the inner surface of the wall portion, extending from the first groove toward the outside in the width direction of the wall portion.

8. The mold according to claim 7 , wherein at least a plurality of the third grooves are provided along the longitudinal direction of the wall portion.

9. The mold according to any one of claims 1 to 8, wherein the inner surfaces of the wall portions are inclined outward from the supply port so as to approach the inner surfaces of the opposing wall portions.

10. The mold according to any one of claims 1 to 9, wherein the supply port is provided in a region in the longitudinal direction of the mold where the perimeter of a cross section of the mold perpendicular to the longitudinal direction is 1.03 times or more the perimeter of an end of the mold.

11. The mold according to any one of claims 1 to 10, wherein an inner surface of the mold is a surface of a mold module that is provided with the supply port and is detachably attached to the mold.

12. The mold according to claim 11 , wherein the mold module is provided so as to protrude beyond an inner surface of the mold on which the mold module is not provided.

13. A mold module is provided inside a mold for forming a tubular workpiece, and is detachably provided on a flat surface portion sandwiched between corner portions in a cross section of the mold, A mold module, wherein a supply port for supplying lubricating liquid is provided on an inner surface of the mold module in a central region in the width direction of the mold module.

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