A hydroforming processing method, mold, mold module, and hydroforming processing apparatus.

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 processing method by hydroforming, a mold, a mold module, and a hydroforming processing apparatus.

Background Art

[0002] Hydroforming is a processing method in which internal pressure is applied to a steel pipe or the like to cause it to bulge and then shaped along the shape of a mold to form a desired shape. Since hydroforming can impart work hardening or perform integral molding, it is expected to contribute to weight reduction of vehicle bodies such as automobiles. On the other hand, in hydroforming, due to the friction between the mold and the steel pipe (workpiece), changes in wall thickness after processing may become a problem.

[0003] Regarding such a problem, for example, Patent Document 1 discloses a technique for controlling the friction between a mold and a workpiece by providing a large number of holes on the inner surface of the mold and supplying a lubricating fluid through such holes.

Prior Art Documents

Patent Documents

[0004] [[ID=二十七]]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technique disclosed in Patent Document 1, since the lubricating fluid also flows to portions where there is no contact or weak contact between the workpiece and the mold, sufficient contact pressure by the lubricating fluid cannot be obtained, it is difficult to obtain the effect of fluid lubrication, and it is difficult to control the wall thickness of the workpiece.

[0006] Therefore, this disclosure has been made in view 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 greater precision. [Means for solving the problem]

[0007] The present disclosure provides a hydroforming method comprising: 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 lubrication fluid supply step of supplying lubricant to the central region of a planar portion sandwiched between the corner portions of the cross-section of the mold in the width direction perpendicular to the first direction of the workpiece on the inner surface of the mold; and a forming step of supplying a liquid from a source different from the lubricant to the inside of the workpiece while supplying the lubricant, thereby applying pressure from the inside of the workpiece and deforming the workpiece along the inner surface of the mold.

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

[0009] Furthermore, according to this disclosure, a mold module is provided which is detachably provided on the inside of a mold for forming a tubular workpiece, on a flat surface sandwiched between corner portions in the cross-section of the mold, wherein a supply port for supplying lubricating fluid is provided on the inner surface of the mold module in the central region in the width direction of the mold module.

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

[0011] According to this disclosure, the thickness of the workpiece can be controlled with greater precision. [Brief explanation of the drawing]

[0012] [Figure 1] This figure illustrates the outline of the hydroforming processing method according to this embodiment. [Figure 2] This figure illustrates the outline of the hydroforming processing method according to the same embodiment. [Figure 3] This figure shows an example of the configuration of a hydroforming processing apparatus according to the same embodiment. [Figure 4] This is a perspective view showing an example of the configuration of the mold 1 according to the same embodiment. [Figure 5] This is a cross-sectional view of the mold 1 according to the same embodiment, taken in a cross section perpendicular to the longitudinal direction at the location where the inlet 1F and supply port 11 are provided in the longitudinal direction. [Figure 6] This figure shows an example of the internal structure of the upper mold 1A according to the same embodiment. [Figure 7] This figure shows a first example of a mold module according to the same embodiment. [Figure 8] This figure shows a second example of a mold module according to the same embodiment. [Figure 9]It is a diagram showing a third example of the mold module according to the same embodiment. [Figure 10] It is a diagram showing a fourth example of the mold module according to the same embodiment. [Figure 11] It is a diagram showing an example of the positional relationship between the mold module according to the same embodiment and the upper mold 1A of mold 1, and an enlarged view thereof. [Figure 12] It is a diagram showing an example of the positional relationship between the mold module according to the same embodiment and the upper mold 1A of mold 1, and an enlarged view thereof. [Figure 13] It is a graph showing an example of the supply control of the lubricating fluid and the internal pressure fluid according to the same embodiment. [Figure 14] It is a graph showing an example of another supply control of the lubricating fluid and the internal pressure fluid according to the same embodiment. [Figure 15] It shows a graph of the pressure control of the internal pressure fluid and the lubricating fluid according to this example. [Figure 16] It shows a graph of the pressure control of the internal pressure fluid according to the comparative example. [Figure 17] It is a diagram showing the properties of the steel pipe after processing in this example. [Figure 18] It is a diagram showing the properties of the steel pipe after processing in the comparative example [Figure 19] It is a graph showing the wall thickness distribution of the steel pipe after processing in this example and the comparative example. [Figure 20] It is a graph showing the wall thickness distribution of the steel pipe after processing in this example.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, preferred embodiments of the present disclosure will be described in detail while referring to the attached drawings. In this specification and the drawings, for components having substantially the same functional configuration, the same reference numerals are given to omit redundant explanations.

[0014] <Summary> First, an overview of a hydroforming processing method according to one embodiment of this disclosure will be described. Figures 1 and 2 are diagrams illustrating an overview of the hydroforming processing method according to this embodiment. Figures 1 and 2 show cross-sections perpendicular to the longitudinal direction (elongation direction) of the mold 1 and the workpiece (steel pipe) 2.

[0015] The mold 1 is a mold used for hydroforming and is composed of, for example, an upper mold and a lower mold. The mold 1 has at least one wall portion extending in the longitudinal direction. The workpiece 2 is placed between the upper mold and the lower mold, and a liquid such as high-pressure water is supplied into the workpiece 2 from the longitudinal end of the mold 1. As a result, the workpiece 2 expands and is pushed out onto the inner surface of the mold 1. In this embodiment, the workpiece 2 is assumed to be a steel pipe, but 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, and in addition to being tubular or cylindrical, the workpiece 2 may be formed by joining parts of two plate-shaped members and expanding each plate-shaped member to form an annular member. These members are also defined as "tubular workpieces" in this embodiment.

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

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

[0018] In this manner, a lubricating fluid supply port is provided in the mold 1 at a position relative to the central region of the workpiece 2. During hydroforming, lubricating fluid is supplied to the mold 1 from this supply port, and sufficient pressure is applied to the lubricating fluid to form a fluid lubrication layer. This reduces friction between the mold 1 and the workpiece 2, improving the fluidity of the workpiece 2. This makes it possible to control the thickness of the workpiece 2 after hydroforming more uniformly. A specific example of the configuration according to this embodiment will be described below.

[0019] <Example Configuration> Figure 3 shows an example of the configuration of a hydroforming processing apparatus according to this embodiment. The processing apparatus according to this embodiment includes a mold 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 mold 1 is composed of an upper mold 1A, a lower mold 1B, a nozzle-equipped lid mold 1C, and a lid mold 1D. Although the processing apparatus according to this embodiment is a type of apparatus that does not have a axial-press punch type that axially presses the end of the workpiece 2 along the longitudinal direction, this technology is not limited to this example. That is, such a processing apparatus may have a axial-press punch type.

[0020] The workpiece 2, set inside the mold 1, expands due to the pressure applied by the internal pressure fluid P1 supplied from the internal pressure fluid pump 6 through the nozzle-equipped lid mold 1C. At the same time, the lubricating fluid L1 supplied from the lubrication fluid pump 3 through the supply port of the upper mold 1A forms a fluid lubrication layer between the lubricating fluid L1 and the surface of the workpiece 2 inside the mold 1.

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

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

[0023] Furthermore, 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 relationship. In addition, it is preferable that the lubricating fluid L1 flowing out from the one inlet 1F through the supply port 11 is supplied only from one supply source (e.g., a lubricating fluid pump 3). This allows the lubricating fluid L1, which is supplied at a high pressure, to be introduced into the mold 1. If multiple supply ports 11 are provided, for example, each of the multiple supply ports 11 may be provided with a corresponding lubricating fluid 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 lubricating fluid is supplied to only one supply port 11. This allows the pressure of the lubricating fluid to be maintained at a high level. The positions where the multiple supply ports 11 are provided are not particularly limited, but it is preferable that they be provided in close proximity to each other.

[0024] Furthermore, the mold 1 may be provided with an outlet 12 for discharging the lubricating fluid L1 and an outlet 1H for allowing the fluid 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] The supply port 11 may be provided directly on the upper mold 1A, or it may be provided on a mold module that is detachable from the upper mold 1A. The mold module may have a nested structure relative to the mold 1. By using a mold module, it is possible to control the flow of lubricating fluid between the mold and the steel pipe. Furthermore, by making the mold module detachable from the mold, the shape of the mold surface can be easily changed. Note that the shape on the mold module described below may be set on the mold module or formed directly on the mold.

[0026] Figure 7 shows a first example of a mold module according to this embodiment. As shown in Figure 7, the mold module 21 is detachably provided in the central part 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 surface on the inner surface of the mold. Even if the mold shape is curved rather than straight, it is preferable that the groove 13 passes through the central region of the flat surface and follows the change in the curved shape of the mold.

[0027] Figure 8 shows a second example of a mold module according to this embodiment. As shown in Figure 8, the mold module 22 is provided with a plurality of grooves 14 around the supply port 11. The plurality of grooves 14 consist of a groove extending longitudinally from the supply port 11 and a plurality of annular grooves surrounding this groove. This makes it easier for lubricating fluid to flow to the area slightly outside the center of the workpiece 2, where friction between the mold 1 and the workpiece 2 tends to be high. In particular, since the contact position between the mold module 22 and the workpiece 2 gradually moves from the center outward, the lubricating fluid flows appropriately along that position. This effectively reduces friction. The shape and position of the plurality of grooves 14 are not particularly limited. It is preferable that these plurality of grooves do not intersect with each other. By not intersecting the plurality of grooves, as the contact position between the workpiece 2 and the mold 1 moves from the center outward, the lubricating fluid can be supplied to the contact position in an appropriate amount and pressure along with the transition.

[0028] Figure 9 shows a third example of a mold module according to this embodiment. As shown in Figure 9, the mold module 23 has a supply port 11 and a groove 13 extending longitudinally from the supply port 11. Furthermore, an inclined portion 15 is provided that slopes outward from the groove 13 so as to approach the opposing inner surface. That is, the supply port 11 and the groove 13 are located at the bottom of the inclined portion 15. As a result, during hydroforming, a space is created between the workpiece 2 and the supply port 11 provided in the upper mold 1A where lubricating fluid can accumulate. As the workpiece 2 expands, the workpiece 2 and the inner surface of the mold 1 attempt to come into contact, starting from the part of the inclined portion 15 closest to the supply port 11. However, the part closest to the supply port 11 is pushed back by the pressure of the lubricating fluid, preventing the workpiece 2 from directly contacting the mold 1. That is, a complete fluid lubrication state can be created in this area. As the workpiece 2 expands, the inclined portion 15 is tilted, so the position of direct contact between the workpiece 2 and the inner surface of the mold 1 moves outward, allowing the molding process to proceed while expanding the area of ​​complete fluid lubrication.

[0029] Figure 10 shows a fourth example of the mold module according to this embodiment. As shown in Figure 9, the mold module 24 has a plurality of grooves 16 along the longitudinal direction at the widthwise end of the mold module 23 shown in Figure 9. These grooves 16 have the function of discharging the lubricating fluid flowing out from the supply port 11. This makes it possible to create a state where there is less lubricating fluid in the small surface 17 between the grooves 16. This makes it possible to increase the friction with the workpiece 2 during hydroforming in the areas where many of these grooves 16 are arranged. Since the workpiece 2 comes into contact with the grooves 16 in the later stages of forming, it is possible to control the flow of the material in the later stages of forming and suppress deformation of already deformed areas (material near the grooves 13), thereby preventing cracking of the material. These grooves 16 can be provided in the other examples of mold modules described above, or they can be provided directly on the upper mold 1A. Furthermore, these grooves 16 may be provided along the entire longitudinal direction as shown in Figure 10, or they may be provided only in parts. For example, the position where the groove 16 is provided can be appropriately adjusted according to the circumference of the workpiece 2 (before or after processing).

[0030] By using a mold module that can be attached to and detached from such a mold 1, it can be applied, for example, to existing hydroforming processing equipment. Specifically, in the processing equipment shown in Figure 3, by simply adding the lubrication fluid pump 3 and its associated line, as well as the mold module, to an existing hydroforming processing equipment, hydroforming according to this embodiment becomes possible.

[0031] Figure 11 is a diagram showing an example of the positional relationship between the mold module and the upper mold 1A of the mold 1 according to this embodiment, and an enlarged view thereof. As shown in Figure 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 more than the surface of the upper mold 1A. The amount of protrusion D1 is preferably, for example, 0.01 mm or more. This makes it possible to suppress the material from getting stuck at the boundary between the mold module 20 and the upper mold 1A during material flow in processing.

[0032] Furthermore, the distance D2 between the boundary between the mold module 20 and the upper die 1A and the boundary 18A of the corner portion 18 of the upper die 1A is preferably within 10 mm. Alternatively, the boundary between the mold module 20 and the upper die 1A may be on the inside of the corner portion 18. This reduces the possibility of the workpiece 2 coming into contact with the boundary between the mold module 20 and the upper die 1A before the processing of the workpiece 2 is completed, thereby suppressing material snagging.

[0033] Furthermore, as described above, the supply port 11 is preferably located in the central part of the mold 1 in the longitudinal direction. The supply port 11 is preferably located in a region where, in the longitudinal direction L of the mold 1, the perimeter of the cross section perpendicular to the longitudinal direction L of the mold 1 is 1.03 times or more the perimeter of the end of the mold 1. Figure 12 is a diagram illustrating the internal shape of the mold 1 according to this embodiment and the preferred installation position of the supply port 11. As shown in Figure 12, with respect to the perimeter C1 of the end 19A of the mold 1, the supply port 11 is preferably located in a region where the perimeter C2 of the cross section 19B perpendicular to the longitudinal direction L of the mold 1 is 1.03 times or more the perimeter C1. Since the region where the perimeter C2 is 1.03 times or more the perimeter C1 is the region where the workpiece 2 expands, the effect of supplying lubricating fluid from the supply port 11 becomes greater.

[0034] <Control of lubricant supply> Next, an example of controlling the supply of lubricating fluid will be described. In this embodiment, during molding, it is preferable that the pressure applied to the workpiece 2 by the lubricating fluid during molding is higher than the processing pressure applied by the internal pressure fluid supplied to the inside of the workpiece 2. Figure 13 is a graph showing an example of the supply control of lubricating fluid and internal pressure fluid according to this embodiment. The graph shown in Figure 13 shows an example of the time-series changes of the measured and set values ​​of the internal pressure applied by the internal pressure fluid and the pressure applied by the lubricating fluid (lubrication pressure). The timing at which the lubrication pressure (measured value) rises in Figure 13 corresponds to the timing at which the workpiece 2 comes into contact with the surface of the mold 1 and molding begins. Furthermore, before the completion of molding, when the lubrication pressure (measured value) falls, the supply of lubricating fluid is stopped to reduce the lubrication pressure.

[0035] As shown in the graph in Figure 13, the lubrication pressure (measured value) is controlled to be higher than the internal pressure due to the internal pressure fluid from the time the deformation of the workpiece 2 begins until the supply of lubricating fluid is stopped. This makes it possible to maintain the lubricated state between the mold 1 and the workpiece 2 while performing hydroforming, thereby reducing friction.

[0036] Figure 14 is a graph showing other examples of supply control for lubricating fluid and internal pressure fluid according to this embodiment. In the example shown in Figure 14, the lubricating fluid is controlled to be supplied intermittently. By deliberately fluctuating the lubrication pressure in this way, the friction between the mold 1 and the workpiece 2 can be deliberately increased during periods when the lubricating fluid pressure is low, thereby gripping the workpiece 2 and promoting deformation of the uncontacted parts. In addition, in such supply control, the lubrication pressure may be repeatedly fluctuated up and down, or it may be reduced during molding. In this case, the deformation after the lubrication pressure is reduced can preferentially deform the parts that are not in contact with the mold 1, similar to normal hydroforming. [Examples]

[0037] Next, embodiments relating to this disclosure will be described. It should be noted that the technology shown in these embodiments is merely an example, and this technology is not limited to the examples described below.

[0038] (Example 1) This embodiment demonstrates the effectiveness of a hydroforming processing method using the lubricant supply method and control method described in the above embodiment.

[0039] The hydroforming processing apparatus used in this embodiment is the processing apparatus and mold 1 shown in Figures 3 to 6. The workpiece 2 is a steel pipe 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 mold 1. Both the internal pressure fluid and the lubricating fluid were hydraulic oil (viscosity 32). The processing conditions were calculated using the following formula (1). Hereinafter, P is the processing pressure, t is the wall thickness of the workpiece 2, and σ θ r is the maximum tensile stress of the workpiece 2, and r is the curvature of the corner after processing. In this embodiment and comparative example, the central part of a cylindrical steel pipe in the longitudinal direction is deformed into a square pipe with a corner of R5. Although a pressure of 72 MPa would normally be required to process the steel pipe, the processing was carried out at the maximum pressure of 70 MPa because the maximum pressure of the internal pressure fluid pump 6 is 70 MPa.

[0040] P = t × σ θ / r ···(1)

[0041] In the embodiment, lubricating fluid was supplied during the hydroforming process using internal pressure fluid. In contrast, in the comparative example, only hydroforming with internal pressure fluid was performed, and no lubricating fluid was supplied. Figure 15 shows a graph of the pressure control of the internal pressure fluid and lubricating fluid in this embodiment. Figure 16 shows a graph of the pressure control of the internal pressure fluid in the comparative example. In both cases, the output of each pump was manually adjusted.

[0042] Figures 17 and 18 show the properties of the steel pipes after processing in this embodiment and comparative example. The steel pipe according to this embodiment shown in Figure 17 shows no particular abnormalities, but the surface of the steel pipe according to the comparative example shown in Figure 18 is fractured. Therefore, this suggests that the wall thickness of the steel pipe can be controlled during processing by supplying the lubricating fluid as described above.

[0043] Figure 19 is a graph showing the distribution of wall thickness of the processed steel pipe in this embodiment and comparative example. The circumference L shown on the horizontal axis indicates the position in the circumferential direction when the center of the opposing vertical walls of the processed steel pipe is taken as the endpoint. In the comparative example (Conventional), the wall thickness does not decrease particularly in the center of the wall, but the wall thickness decreases (fractures) on the outside of the wall. On the other hand, in this embodiment (proposed), the wall thickness decreases almost uniformly along the circumferential direction, suggesting that the wall thickness is controlled almost uniformly.

[0044] (Example 2) This embodiment shows an example where the mold module 21 shown in Figure 7 is applied to the mold 1. The processing conditions, etc., are the same as in Example 1, so they are omitted here.

[0045] Figure 20 is a graph showing the distribution of wall thickness of the steel pipe after processing in this embodiment. Line 106 represents the wall thickness before processing (1.2 mm), and lines 107 to 109 represent the circumference of the central part of the workpiece 2 in the longitudinal direction (the part opposite the supply port 11) and the part located 27 mm away from the central part along the longitudinal direction (0 mm is the central part of the vertical wall, and 50 mm is the central part of the bottom wall), respectively. As shown in Figure 20, since the lubricating fluid is supplied in the longitudinal direction of the mold 1 by the groove 13 provided along the longitudinal direction, there is no difference in the distribution of wall thickness between the central part and the position 27 mm away in the longitudinal direction. This suggests that hydroforming can be used to process the workpiece 2 to achieve a uniform wall thickness along the longitudinal direction.

[0046] While preferred embodiments of the present disclosure have been described in detail above with reference to the attached drawings, the technical scope of the present disclosure is not limited to such examples. It is clear to any person with ordinary skill in the art of the present disclosure that various modifications or alterations may be conceived within the scope of the technical idea set forth in the claims, and these will naturally also fall within the technical scope of the present disclosure.

[0047] Furthermore, the effects described herein are merely descriptive or illustrative and not limiting. In other words, the technology relating to this disclosure may produce other effects that are obvious to those skilled in the art from the description herein, in addition to or in lieu of the effects described herein.

[0048] Furthermore, the following configurations also fall within the technical scope of this disclosure. (Item 1) The process involves placing a tubular workpiece into a mold formed according to a first direction corresponding to the extension direction of the workpiece, A lubrication fluid supply step of supplying lubricating fluid to the central region of the planar portion sandwiched between the corner portions of the cross-section of the mold, in the width direction perpendicular to the first direction of the workpiece on the inner surface of the mold, A molding step in which, while supplying the lubricating liquid, a liquid is supplied to the inside of the workpiece from a source different from the lubricating liquid to apply pressure from the inside of the workpiece, thereby deforming the workpiece along the inner surface of the mold, A hydroforming process, including the following: (Item 2) The hydroforming method according to item 1, wherein a supply port for supplying the lubricating fluid is provided on the inner surface of the mold in the central region in the width direction perpendicular to the direction corresponding to the first direction of the mold. (Item 3) The hydroforming method described in item 2, wherein the lubricating fluid discharged from the supply port of 1 is supplied only from the supply source of 1. (Item 4) The hydroforming method according to item 2 or 3, wherein the flow path connecting one or more of the supply ports and one supply source for supplying the lubricating fluid is controlled by a valve so that the lubricating fluid is supplied to only one of the supply ports. (Item 5) A hydroforming method according to any one of items 2 to 4, wherein a first groove is provided on the inner surface of the mold, extending from the supply port in the direction of extension of the mold. (Item 6) On the inner surface of the mold, a second groove is provided around the first groove, along the first groove. The hydroforming method described in item 5, wherein the second groove does not intersect with the first groove. (Item 7) The hydroforming method described in item 6, wherein the second groove is formed so as to surround the first groove. (Item 8) A 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 outward in the width direction of the first groove of the mold. (Item 9) The hydroforming method according to item 8, wherein at least a plurality of the third grooves are provided along the elongation direction of the mold. (Item 10) The hydroforming method according to any one of items 2 to 9, wherein the inner surface of the mold is inclined outward from the supply port so as to approach the opposing inner surface. (Item 11) A hydroforming method according to any one of items 1 to 10, wherein the pressure applied to the workpiece by the lubricating liquid during molding in the molding step is higher than the processing pressure applied by the liquid supplied to the inside of the workpiece. (Item 12) A hydroforming method according to any one of items 1 to 11, wherein in the molding step, control is performed to reduce the pressure applied to the workpiece by the lubricating liquid after the start of molding but before the completion of molding. (Item 13) A 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) The hydroforming method according to any one of items 1 to 13, wherein the inner surface of the mold is provided with a supply port for supplying the lubricating fluid and is the surface of a mold module that is detachably provided with the mold. (Item 15) The hydroforming method according to item 14, wherein the mold module is provided so as to protrude from the inner surface of the mold and from the surface on which the mold module is not provided. (Item 16) A mold for forming a tubular workpiece, The mold has at least one wall portion extending in the longitudinal direction, A mold in which a supply port for supplying lubricating fluid is provided on the inner surface of the wall portion, in the central region of the flat portion sandwiched between the corner portions of the mold in the width direction perpendicular to the longitudinal direction of the wall portion. (Item 17) The mold according to item 16, wherein the supply port of 1 is connected only to a supply source of 1 via a flow path. (Item 18) The mold according to item 16 or 17, wherein the flow path connecting one or more of the supply ports to one supply source for supplying the lubricating fluid is controlled by a valve so that the lubricating fluid is supplied to only one of the supply ports. (Item 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, extending from the supply port in the longitudinal direction. (Item 20) On the inner surface of the wall portion, a second groove is provided around the first groove, along the first groove. The mold described in item 19, wherein the second groove does not intersect with the first groove. (Item 21) The mold according to item 20, wherein the second groove is formed to surround the first groove. (Item 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 outward in the width direction of the first groove. (Item 23) The mold according to item 22, wherein the third groove is provided in at least a plurality along the longitudinal direction of the wall portion. (Item 24) The mold according to any one of items 16 to 23, wherein the inner surface of the wall portion is inclined outward from the supply port so as to approach the inner surface of the opposing wall portion. (Item 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 perimeter of the cross section perpendicular to the longitudinal direction of the mold is 1.03 times or more the perimeter of the end of the mold. (Item 26) The mold according to any one of items 16 to 25, wherein the inner surface of the mold is the surface of a mold module that has a supply port and is detachably provided with respect to the mold. (Item 27) The mold according to item 26, wherein the mold module is provided on the inner surface of the mold and protrudes from the surface on which the mold module is not provided. (Item 28) A mold module that is detachably provided on the inside of a mold for forming a tubular workpiece, and is sandwiched between the corner portions of the cross-section of the mold, A mold module having a supply port for supplying lubricating fluid located in the central region in the width direction of the mold module on its inner surface. (Item 29) A mold having at least one longitudinally extending wall, wherein a supply port for supplying lubricating fluid is provided on the inner surface of the wall in the central region in the width direction perpendicular to the longitudinal direction of the wall, A lubricant supply source for supplying lubricant from the supply port on the inner surface of the mold to a position in the central region of the flat portion sandwiched between the corner portions of the cross-section of the mold, in the width direction perpendicular to the longitudinal direction of the workpiece, An internal pressure fluid supply source for supplying the aforementioned lubricating fluid to the inside of the workpiece from a different source than the aforementioned lubricating fluid, thereby applying pressure from the inside of the workpiece and causing deformation, A hydroforming processing apparatus equipped with [a specific feature]. [Explanation of Symbols]

[0049] 1. Mold 2 Work material 3. Lubrication fluid pump (lubrication fluid supply source) 6. Internal pressure fluid pump (internal pressure fluid supply source) 11 supply ports 13, 14, 16 grooves

Claims

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

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

3. The mold according to claim 1 or 2, wherein the flow path connecting one or more supply ports and one supply source for supplying the lubricating fluid is controlled by a valve so that the lubricating fluid 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 the inner surface of the wall portion, extending from the supply port in the longitudinal direction.

5. On the inner surface of the wall portion, a second groove is provided around the first groove, along the first groove. The mold according to 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 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 outward in the width direction of the first groove.

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 surface of the wall portion is inclined outward from the supply port so as to approach the inner surface of the opposing wall portion.

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 the cross section perpendicular to the longitudinal direction of the mold is 1.03 times or more the perimeter of the end of the mold.

11. The mold according to any one of claims 1 to 10, wherein the inner surface of the mold is the 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 on the inner surface of the mold and protrudes more than the surface on which the mold module is not provided.

13. A mold module that is detachably provided on the inside of a mold for forming a tubular workpiece, and is sandwiched between the corner portions of the cross-section of the mold, A mold module having a supply port for supplying lubricating fluid located in the central region in the width direction of the mold module on its inner surface.

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