JP7469541B2 - Metal pipe and method for forming metal pipe - Google Patents

Description

This disclosure relates to a metal pipe and a method for forming a metal pipe.

Conventionally, there is known an apparatus for forming a metal pipe having a pipe section and an outer flange section extending outward from the pipe section by expanding a metal pipe material in a forming die. For example, Patent Document 1 discloses a forming apparatus equipped with a forming die that forms a main cavity section for forming the pipe section and a pair of sub-cavity sections that communicate with the main cavity section and are used to form a pair of outer flange sections. This forming apparatus closes the forming die and blows gas into the heated metal pipe material, thereby expanding the metal pipe material in the main cavity section and the pair of sub-cavity sections, thereby forming a metal pipe having a pipe section and a pair of outer flange sections.

International Publication No. 2017/150110

In the device described in Patent Document 1, a pair of outer flanges are formed on the metal pipe to increase the rigidity of the metal pipe. However, a metal pipe with outer flanges has a larger outer dimension in the width direction of the metal pipe by the amount of the outer flanges compared to a metal pipe without outer flanges, and this may cause interference with other components, making it impossible to place the metal pipe within a specified space.

Therefore, the present invention aims to provide a metal pipe that has high rigidity while suppressing an increase in external dimensions, and a molding method thereof.

In one embodiment, a steel metal pipe is provided that is an integrally molded product. The metal pipe has a cylindrical main body and an inner flange that protrudes from the main body to the inside of the main body.

In this embodiment, the inner flange portion can increase the rigidity of the metal pipe. Because the inner flange portion protrudes inwardly from the main body portion, an increase in the outer dimensions of the metal pipe can be prevented.

In one embodiment, the flange portion may be made of steel material folded inward. By making the inner flange portion out of steel material folded inward, the main body portion and the inner flange portion can be integrally constructed, and as a result, the rigidity of the metal pipe can be increased.

In one embodiment, the metal pipe may further include another inner flange portion that protrudes from the main body portion toward the inside of the main body portion, and the inner flange portion and the other inner flange portion may protrude from the main body portion in a direction toward each other. By providing the inner flange portion and the other inner flange portion that protrude in a direction toward each other, the rigidity of the metal pipe can be further increased.

In one embodiment, the metal pipe may further include an outer flange portion that protrudes from the main body portion to the outside of the main body portion. By including such an outer flange portion, the rigidity of the metal pipe can be further increased.

In one aspect, a method for forming a steel metal pipe having a cylindrical main body and an inner flange protruding from the main body to the inside of the main body is provided using a forming device. The forming device includes a forming die having an upper die and a lower die, and forming a main cavity between the upper die and the lower die for forming a metal pipe material, a double-acting die capable of moving forward and backward in the main cavity along the opposing direction of the upper die and the lower die, a heating mechanism for heating the metal pipe material arranged in the main cavity, and a gas supply unit for supplying gas into the heated metal pipe material. The upper die includes an upper die base and a pair of upper sliding parts arranged at a distance from each other via the main cavity part, the pair of upper sliding parts being slidable relative to the upper die base so that the distance between them changes, and the lower die includes a lower die base and a pair of lower sliding parts arranged at a distance from each other via the main cavity part, the pair of lower sliding parts being slidable relative to the lower die base so that the distance between them changes. The above molding method includes the steps of: inserting the double-action die into the main cavity portion to crush the first portion of the metal pipe material arranged in the main cavity portion from the opposing direction; sliding the pair of upper sliding portions and the pair of lower sliding portions against the upper die base and the lower die base, respectively, so as to reduce the separation distance between the pair of upper sliding portions and the pair of lower sliding portions; and, while supplying gas from the gas supply portion into the heated metal pipe material, retracting the double-action die from the main cavity portion to mold the first portion of the metal pipe into the inner flange portion and the second portion of the metal pipe into the main body portion.

The method according to the above aspect can form a metal pipe having a main body portion and an inner flange portion. Therefore, it is possible to increase the rigidity of the metal pipe while preventing an increase in the external dimensions of the metal pipe.

In one embodiment of the molding method, the molding die further forms a sub-cavity portion between the pair of upper sliding portions and the pair of lower sliding portions, which is connected to the main cavity portion and is used to mold an outer flange portion that protrudes from the main body portion to the outside of the main body portion, and a gas supply portion supplies gas into the heated metal pipe material, thereby expanding a third portion of the metal pipe material in the sub-cavity to mold it into the outer flange portion. In this embodiment, a metal pipe further including an outer flange portion can be molded, thereby further increasing the rigidity of the metal pipe.

According to one aspect and various embodiments of the present invention, it is possible to provide a metal pipe that has high rigidity while suppressing an increase in external dimensions.

FIG. 1 is a schematic configuration diagram showing a molding device according to an embodiment. 1A is an enlarged view of the periphery of the electrode, in which (a) shows a state in which the electrode holds a metal pipe material, (b) shows a state in which a gas supply nozzle is pressed against the electrode, and (c) is a front view of the electrode. FIG. 2A to 2C are diagrams illustrating a method for forming a metal pipe according to the first embodiment. FIG. 2 is a cross-sectional view showing a metal pipe according to one embodiment. 11A to 11C are diagrams illustrating a method for forming a metal pipe according to a second embodiment. FIG. 2 is a cross-sectional view showing metal pipes according to Examples 1 to 3 and Comparative Examples 1 and 2. FIG. 2 is a diagram showing the second moment of area and the section modulus of metal pipes according to Examples 1 to 3 and Comparative Examples 1 and 2.

The molding device used in one embodiment of the metal pipe molding method will be described below with reference to the drawings. Note that the same or corresponding parts in each drawing will be given the same reference numerals, and duplicated explanations will be omitted. In the following description, one horizontal direction will be defined as the X-axis direction, the horizontal direction perpendicular to the X-axis direction will be defined as the Y-axis direction, and the vertical direction will be defined as the Z-axis direction.

<Configuration of molding device>
FIG. 1 is a schematic diagram of a molding device according to the present embodiment. As shown in FIG. 1, a molding device 10 for molding a metal pipe includes a molding die 13 consisting of an upper die 12 and a lower die 11, a drive mechanism 80 for moving at least one of the upper die 12 and the lower die 11, a pipe holding mechanism 30 for holding a metal pipe material 14 arranged between the upper die 12 and the lower die 11, a heating mechanism 50 for applying electricity to the metal pipe material 14 held by the pipe holding mechanism 30 to heat it, a gas supply unit 60 for supplying high-pressure gas (gas) into the metal pipe material 14 held between the upper die 12 and the lower die 11 and heated, a pair of gas supply mechanisms 40, 40 for supplying gas from the gas supply unit 60 into the metal pipe material 14 held by the pipe holding mechanism 30, and a water circulation mechanism 72 for forcibly water-cooling the molding die 13. The molding device 10 is also configured to include a control unit 70 for controlling the driving of the drive mechanism 80, the driving of the pipe holding mechanism 30, the driving of the heating mechanism 50, and the gas supply of the gas supply unit 60.

The lower die 11, which is one of the molding dies 13, is fixed to a base 15. The lower die 11 is made of a large steel block, and has, for example, a rectangular cavity (recess) 16 on its upper surface. The lower die 11 has a cooling water passage 19 formed therein, and is equipped with a thermocouple 21 inserted from below in approximately the center. This thermocouple 21 is supported by a spring 22 so that it can move freely up and down.

Furthermore, a space 11a is provided near the left and right ends of the lower mold 11 (the left and right ends in FIG. 1), and electrodes 17, 18 (lower electrodes) described below, which are movable parts of the pipe holding mechanism 30, are arranged in the space 11a so that they can move up and down. Then, by placing the metal pipe material 14 on the lower electrodes 17, 18, the lower electrodes 17, 18 come into contact with the metal pipe material 14 arranged between the upper mold 12 and the lower mold 11. As a result, the lower electrodes 17, 18 are electrically connected to the metal pipe material 14.

Between the lower die 11 and the lower electrode 17 and below the lower electrode 17, and between the lower die 11 and the lower electrode 18 and below the lower electrode 18, insulating materials 91 are provided to prevent electrical current from passing through. Each insulating material 91 is fixed to a reciprocating rod 95, which is the movable part of an actuator (not shown) that constitutes the pipe holding mechanism 30. This actuator is used to move the lower electrodes 17, 18, etc. up and down, and the fixed part of the actuator is held on the base 15 side together with the lower die 11.

The other part of the molding die 13, the upper die 12, is fixed to a slide 81 (described below) that constitutes the drive mechanism 80. The upper die 12 is made of a large steel block, has a cooling water passage 25 formed inside, and has a cavity (recess) 24, for example, of a rectangular shape, on its underside. This cavity 24 is provided in a position opposite the cavity 16 of the lower die 11.

Similar to the lower die 11, a space 12a is provided near the left and right ends of the upper die 12 (left and right ends in FIG. 1), and within this space 12a, electrodes 17, 18 (upper electrodes) described below, which are movable parts of the pipe holding mechanism 30, are arranged so that they can move up and down. Then, with the metal pipe material 14 placed on the lower electrodes 17, 18, the upper electrodes 17, 18 move downward to come into contact with the metal pipe material 14 arranged between the upper die 12 and the lower die 11. As a result, the upper electrodes 17, 18 are electrically connected to the metal pipe material 14.

Between the upper die 12 and the upper electrode 17 and above the upper electrode 17, and between the upper die 12 and the upper electrode 18 and above the upper electrode 18, insulating materials 101 are provided to prevent electrical current from passing through. Each insulating material 101 is fixed to a reciprocating rod 96, which is the movable part of an actuator constituting the pipe holding mechanism 30. This actuator is for moving the upper electrodes 17, 18, etc. up and down, and the fixed part of the actuator is held on the slide 81 side of the drive mechanism 80 together with the upper die 12.

In the right part of the pipe holding mechanism 30, a semicircular groove 18a corresponding to the outer peripheral surface of the metal pipe material 14 is formed on each of the surfaces where the electrodes 18, 18 face each other (see FIG. 2(c)), and the metal pipe material 14 can be placed so that it fits exactly into the groove 18a. In the right part of the pipe holding mechanism 30, a semicircular groove corresponding to the outer peripheral surface of the metal pipe material 14 is formed on the exposed surface where the insulating materials 91, 101 face each other, similar to the groove 18a. In addition, a tapered concave surface 18b is formed on the front surface of the electrode 18 (the surface facing the outside of the mold), with the periphery tapered toward the groove 18a. Therefore, when the metal pipe material 14 is clamped from above and below by the right part of the pipe holding mechanism 30, it is configured so that it can surround the outer periphery of the right end of the metal pipe material 14 in a tight contact manner all around.

In the left part of the pipe holding mechanism 30, a semicircular groove 17a corresponding to the outer peripheral surface of the metal pipe material 14 is formed on each of the surfaces where the electrodes 17, 17 face each other (see FIG. 2(c)), and the metal pipe material 14 can be placed so that it fits exactly into the groove 17a. In the left part of the pipe holding mechanism 30, a semicircular groove corresponding to the outer peripheral surface of the metal pipe material 14 is formed on the exposed surface where the insulating materials 91, 101 face each other, similar to the groove 18a. In addition, a tapered concave surface 17b is formed on the front surface of the electrode 17 (the surface facing the outside of the mold), with the periphery tapered toward the groove 17a. Therefore, when the metal pipe material 14 is clamped from above and below by the left part of the pipe holding mechanism 30, it is configured so that it can just surround the outer periphery of the left end of the metal pipe material 14 in a tight contact manner all around.

1, the drive mechanism 80 includes a slide 81 that moves the upper mold 12 so that the upper mold 12 and the lower mold 11 are aligned with each other, a shaft 82 that generates a drive force for moving the slide 81, and a connecting rod 83 for transmitting the drive force generated by the shaft 82 to the slide 81. The shaft 82 extends in the left-right direction above the slide 81 and is supported rotatably, and has an eccentric crank 82a that protrudes from the left and right ends at a position spaced apart from the axis and extends in the left-right direction. The eccentric crank 82a and the rotating shaft 81a that is provided on the upper part of the slide 81 and extends in the left-right direction are connected by a connecting rod 83. In the drive mechanism 80, the control unit 70 controls the rotation of the shaft 82 to change the vertical height of the eccentric crank 82a, and the vertical movement of the slide 81 can be controlled by transmitting the position change of the eccentric crank 82a to the slide 81 via the connecting rod 83. Here, the oscillation (rotational movement) of the connecting rod 83 that occurs when the position change of the eccentric crank 82a is transmitted to the slide 81 is absorbed by the rotating shaft 81a. The shaft 82 rotates or stops in response to the drive of a motor or the like controlled by the control unit 70, for example.

Figure 3 is a cross-sectional view of the molding die 13 shown in Figure 1. As shown in Figure 3 (a), the lower die 11 has a lower die base 110, a first lower sliding part 112a, and a second lower sliding part 112b. The upper die 12 has an upper die base 120, a first upper sliding part 122a, and a second upper sliding part 122b. Hereinafter, unless there is a need to distinguish between them, the first lower sliding part 112a and the second lower sliding part 112b will be referred to as a pair of lower sliding parts 112, and the first upper sliding part 122a and the second upper sliding part 122b will be referred to as a pair of upper sliding parts 122.

On the upper surface of the lower mold 11, a step is formed by a pair of lower sliding parts 112, with the bottom surface of the cavity 16 in the center of the lower mold 11 being the reference line LV1. A first lower sliding part 112a is formed on the right side of the cavity 16 (the right side in FIG. 3, the back side of the paper in FIG. 1), and a second lower sliding part 112b is formed on the left side of the cavity 16 (the left side in FIG. 3, the front side of the paper in FIG. 1). The first lower sliding part 112a and the second lower sliding part 112b have a substantially rectangular cross-sectional shape and extend parallel to each other along the X-axis direction (the paper direction in FIG. 3). The first lower sliding part 112a and the second lower sliding part 112b protrude from the reference line LV1 toward the upper mold 12. The amount by which the first lower sliding part 112a protrudes from the reference line LV1 is approximately the same as the amount by which the second lower sliding part 112b protrudes from the reference line LV1.

On the other hand, if the bottom surface of the cavity 24 in the center of the upper mold 12 is taken as the reference line LV2, a step is formed by a pair of upper sliding parts 122 on the lower surface of the upper mold 12. A first upper sliding part 122a is formed on the right side of the cavity 24 (right side in FIG. 3, rear side of the paper in FIG. 1), and a second upper sliding part 122b is formed on the left side of the cavity 24 (left side in FIG. 3, front side of the paper in FIG. 1). The first upper sliding part 122a and the second upper sliding part 122b have a substantially rectangular cross-sectional shape and extend parallel to each other along the X-axis direction (paper direction in FIG. 3). The first upper sliding part 122a and the second upper sliding part 122b protrude from the reference line LV2 toward the lower mold 11. The amount by which the first upper sliding part 122a protrudes from the reference line LV2 is approximately the same as the amount by which the second upper sliding part 122b protrudes from the reference line LV2.

In addition, the first lower sliding part 112a faces the first upper sliding part 122a, and the second lower sliding part 112b faces the second upper sliding part 122b. As a result, when the upper mold 12 and the lower mold 11 are fitted together, the upper surface 112a1 of the first lower sliding part 112a abuts against the lower surface 122a1 of the first upper sliding part 122a, and the upper surface 112b1 of the second lower sliding part 112b abuts against the lower surface 122b1 of the second upper sliding part 122b. At this time, a main cavity part MC is formed between the cavity 24 of the upper mold 12 and the cavity 16 of the lower mold 11 (see FIG. 3(b)). This main cavity portion MC is a space defined by the cavity 24 of the upper mold 12, the cavity 16 of the lower mold 11, a pair of opposing side surfaces 112a2, 112b2 of the pair of lower sliding parts 112, and a pair of opposing side surfaces 122a2, 122b2 of the pair of upper sliding parts 122 when the upper mold 12 and the lower mold 11 are fitted together.

A pair of lower drive mechanisms 113 for driving the pair of lower sliding parts 112 are provided on the upper surface of the lower mold base 110. Each of the pair of lower drive mechanisms 113 has a frame body 114. The frame body 114 has a U-shaped cross section and is provided on the lower mold base 110 so as to be positioned adjacent to the pair of lower sliding parts 112. The frame body 114, together with the upper surface of the lower mold base 110, defines a fluid chamber 115.

A partition plate 116 is housed in the fluid chamber 115. The partition plate 116 divides the interior of the fluid chamber 115 into a first fluid chamber 115a and a second fluid chamber 115b located closer to the pair of lower sliding parts 112 than the first fluid chamber 115a. The partition plate 116 is configured to be able to slide along the Y-axis direction within the fluid chamber 115. The volumes of the first fluid chamber 115a and the second fluid chamber 115b change as the partition plate 116 slides in the Y-axis direction. One end of a connecting member 117 is connected to one main surface of the partition plate 116, and the other end of the connecting member 117 is connected to the pair of lower sliding parts 112.

The lower die base 110 is also formed with a pair of first flow paths 118a and a pair of second flow paths 118b, which are flow paths for the working fluid. One end of each of the pair of first flow paths 118a is connected to the first fluid chambers 115a of the pair of lower drive mechanisms 113. The other ends of each of the pair of first flow paths 118a are connected to the pair of fluid supply devices 105 via piping 119a. Similarly, one end of each of the pair of second flow paths 118b is connected to the second fluid chambers 115b of the pair of lower drive mechanisms 113. The other ends of each of the pair of second flow paths 118b are connected to the pair of fluid supply devices 105 via piping 119b.

Each fluid supply device 105 is a device that supplies working fluid to the first fluid chamber 115a and the second fluid chamber 115b via the pipe 119a and the pipe 119b. The fluid supply device 105 is also capable of recovering the working fluid in the first fluid chamber 115a and the second fluid chamber 115b.

The pair of lower sliding parts 112 are attached to the lower mold base 110 so as to be movable in the Y-axis direction (left-right direction in FIG. 3). In one embodiment, a groove extending in the left-right direction is formed on the upper surface of the lower mold base 110. On the other hand, a rail that engages with the groove is formed on the lower surface of the pair of lower sliding parts 112. Therefore, for example, when a working fluid is supplied from the fluid supply device 105 to the first fluid chamber 115a, the pressure in the first fluid chamber 115a increases, and the partition plate 116 moves in the Y-axis direction in the fluid chamber 115 so that the volume of the first fluid chamber 115a increases and the volume of the second fluid chamber 115b decreases. Conversely, when the working fluid is supplied from the fluid supply device 105 into the second fluid chamber 115b, the pressure in the second fluid chamber 115b increases, causing the volume of the first fluid chamber 115a in the Y-axis direction to decrease, and the volume of the second fluid chamber 115b to increase. In this way, the partition plate 116 moves in the fluid chamber 115 in the Y-axis direction, causing the pair of lower sliding parts 112 connected to the partition plate 116 to move toward each other or away from each other while the rails formed on the pair of lower sliding parts 112 and the grooves formed on the lower mold base 110 are engaged. By individually changing the positions of the pair of lower sliding parts 112 in the Y-axis direction, the separation distance D1 in the Y-axis direction of the pair of lower sliding parts 112 is adjusted.

A pair of upper drive mechanisms 123 for driving the pair of upper sliding parts 122 are provided on the lower surface of the upper mold base 120. Each of the pair of upper drive mechanisms 123 has a frame 124. The frame 124 has a U-shaped cross section and is attached to the lower surface of the upper mold base 120 so as to be positioned adjacent to the pair of upper sliding parts 122. The frame 124, together with the lower surface of the upper mold base 120, defines a fluid chamber 125.

A partition plate 126 is housed in the fluid chamber 125. The partition plate 126 divides the interior of the fluid chamber 125 into a first fluid chamber 125a and a second fluid chamber 125b located closer to the pair of upper sliding parts 122 than the first fluid chamber 125a. The partition plate 126 is configured to be able to slide along the Y-axis direction within the fluid chamber 125. The volumes of the first fluid chamber 115a and the second fluid chamber 115b change as the partition plate 126 slides in the Y-axis direction. One end of a connecting member 127 is connected to one main surface of the partition plate 126, and the other end of the connecting member 127 is connected to the pair of upper sliding parts 122.

The upper mold base 120 also has a pair of third flow paths 128a and a pair of fourth flow paths 128b formed therein, which are flow paths for the working fluid. One end of each of the pair of third flow paths 128a is connected to the first fluid chambers 125a of the pair of upper drive mechanisms 123. The other ends of each of the pair of third flow paths 128a are connected to the pair of fluid supply devices 105 via piping 129a. Similarly, one end of each of the pair of fourth flow paths 128b is connected to the second fluid chambers 125b of the pair of upper drive mechanisms 123. The other ends of each of the pair of fourth flow paths 128b are connected to the pair of fluid supply devices 105 via piping 129b.

The fluid supply device 105 can supply working fluid to the first fluid chamber 125a and the second fluid chamber 125b via the pipes 129a and 129b, or can recover working fluid from the first fluid chamber 125a and the second fluid chamber 125b.

The pair of upper sliding parts 122 are attached to the upper mold base 120 so as to be movable in the Y-axis direction (left-right direction in FIG. 3). In one embodiment, a groove extending in the left-right direction is formed on the lower surface of the upper mold base 120. On the other hand, a rail that engages with the groove is formed on the upper surface of the pair of upper sliding parts 122. Therefore, for example, when a working fluid is supplied from the fluid supply device 105 to the first fluid chamber 125a, the pressure in the first fluid chamber 125a increases, and the partition plate 126 moves in the Y-axis direction in the fluid chamber 125 so that the volume of the first fluid chamber 125a increases and the volume of the second fluid chamber 125b decreases. Conversely, when the working fluid is supplied from the fluid supply device 105 into the second fluid chamber 125b, the pressure in the second fluid chamber 125b increases, causing the volume of the first fluid chamber 125a to decrease and the volume of the second fluid chamber 125b to increase, causing the partition plate 126 to move in the fluid chamber 125. In this way, the partition plate 126 moves in the fluid chamber 125, causing the pair of upper sliding parts 122 connected to the partition plate 126 to move toward each other or away from each other while the rails formed in the pair of upper sliding parts 122 and the grooves formed in the upper mold base 120 are engaged. By individually changing the positions of the pair of upper sliding parts 122 in the Y-axis direction, the separation distance D2 in the Y-axis direction of the pair of upper sliding parts 122 is adjusted.

The pair of fluid supply devices 105 are connected to a control unit 70, which will be described later. The control unit 70 controls the left-right separation distance D1 between the pair of lower sliding parts 112 and the left-right separation distance D2 between the pair of upper sliding parts 122 by sending control signals to the pair of fluid supply devices 105. By adjusting the separation distances D1 and D2 in this manner, the width of the main cavity portion MC in the Y-axis direction is adjusted.

As shown in Figs. 3(a) and (b), the molding device 10 further includes a first double-action mold 130a and a second double-action mold 130b. The first double-action mold 130a and the second double-action mold 130b are plate-shaped and are arranged along the XZ plane. The first double-action mold 130a and the second double-action mold 130b extend through the lower mold base 110 and the upper mold base 120, respectively, so as to pass through the center lines of the lower mold 11 and the upper mold 12 in the Y-axis direction. Hereinafter, unless there is a need to distinguish between them, the first double-action mold 130a and the second double-action mold 130b will be referred to as a pair of double-action molds 130.

The pair of double-acting dies 130 are configured to be movable along the Z-axis direction (the opposing direction of the lower die 11 and the upper die 12). An actuator 134 is connected to the first double-acting die 130a (see FIG. 1), and the first double-acting die 130a moves in the Z-axis direction when the actuator 134 is activated. An actuator 132 is connected to the second double-acting die 130b (see FIG. 1), and the second double-acting die 130b moves in the Z-axis direction when the actuator 132 is activated. As shown in FIG. 3(b), the pair of double-acting dies 130 move in the Z-axis direction, so that the pair of double-acting dies 130 advance and retreat in the Z-axis direction within the main cavity portion MC.

Refer back to FIG. 1. As shown in FIG. 1, the heating mechanism 50 includes a power supply unit 55 and a bus bar 52 that electrically connects the power supply unit 55 to the electrodes 17, 18. The power supply unit 55 includes a DC power source and a switch, and when the electrodes 17, 18 are electrically connected to the metal pipe material 14, electricity can be passed through the bus bar 52 and the electrodes 17, 18 to the metal pipe material 14. Here, the bus bar 52 is connected to the lower electrodes 17, 18.

In this heating mechanism 50, the DC current output from the power supply unit 55 is transmitted by the bus bar 52 and input to the electrode 17. The DC current then passes through the metal pipe material 14 and is input to the electrode 18. The DC current then is transmitted by the bus bar 52 and input to the power supply unit 55.

Each of the pair of gas supply mechanisms 40 has a cylinder unit 42, a cylinder rod 43 that moves forward and backward in accordance with the operation of the cylinder unit 42, and a seal member 44 connected to the tip of the cylinder rod 43 on the pipe holding mechanism 30 side. The cylinder unit 42 is mounted and fixed on the block 41. A tapered surface 45 is formed at the tip of the seal member 44 so as to taper, and is configured in a shape that fits the tapered concave surfaces 17b and 18b of the electrodes 17 and 18 (see Figures 2(a) and (b)). The seal member 44 has a gas passage 46 that extends from the cylinder unit 42 side toward the tip, and through which high-pressure gas supplied from the gas supply unit 60 flows, as shown in Figures 2(a) and (b) in detail.

The gas supply unit 60 comprises a gas source 61, an accumulator 62 for storing gas supplied by the gas source 61, a first tube 63 extending from the accumulator 62 to the cylinder unit 42 of the gas supply mechanism 40, a pressure control valve 64 and a switching valve 65 interposed in the first tube 63, a second tube 67 extending from the accumulator 62 to the gas passage 46 formed in the seal member 44, and a pressure control valve 68 and a check valve 69 interposed in the second tube 67. The pressure control valve 64 serves to supply gas to the cylinder unit 42 at an operating pressure appropriate to the pressing force of the seal member 44 against the metal pipe material 14. The check valve 69 serves to prevent high-pressure gas from flowing back in the second tube 67. The pressure control valve 68 interposed in the second tube 67 serves to supply gas having an operating pressure for expanding the metal pipe material 14 to the gas passage 46 of the seal member 44 under the control of the control unit 70.

The control unit 70 can supply gas at a desired operating pressure into the metal pipe material 14 by controlling the pressure control valve 68 of the gas supply unit 60. In addition, the control unit 70 acquires temperature information from the thermocouple 21 by receiving information from (A) shown in FIG. 1, and controls the drive mechanism 80 and the power supply unit 55, etc.

The water circulation mechanism 72 consists of a water tank 73 for storing water, a water pump 74 for pumping up the water stored in the water tank 73, pressurizing it, and sending it to the cooling water passage 19 of the lower mold 11 and the cooling water passage 25 of the upper mold 12, and piping 75. Although omitted, it is acceptable to insert a cooling tower for lowering the water temperature and a filter for purifying the water in the piping 75.

<Method of forming metal pipe using a forming device>
Next, a method for forming a metal pipe according to the first embodiment will be described. This method is performed using a forming device 10 shown in FIG. 1. First, a cylindrical metal pipe material 14 made of a hardenable steel is prepared. The metal pipe material 14 is placed (thrown) on the electrodes 17, 18 provided on the lower die 11 side, for example, using a robot arm or the like. Grooves 17a, 18a are formed in the electrodes 17, 18, and the metal pipe material 14 is positioned by the grooves 17a, 18a. As a result, the metal pipe material 14 is placed between the lower die 11 and the upper die 12, as shown in FIG. 4(a).

Next, the control unit 70 controls the drive mechanism 80 and the pipe holding mechanism 30 to hold the metal pipe material 14. Specifically, the drive mechanism 80 drives the upper die 12 and the upper electrodes 17, 18, etc. held on the slide 81 side to move toward the lower die 11 side, and the actuator that allows the upper electrodes 17, 18, etc. and the lower electrodes 17, 18, etc. included in the pipe holding mechanism 30 to move forward and backward is operated, so that the metal pipe material 14 is clamped near both ends from above and below by the pipe holding mechanism 30. At this time, the metal pipe material 14 is clamped in such a manner that it is in close contact with the entire circumference near both ends of the metal pipe material 14 due to the presence of the grooves 17a, 18a formed in the electrodes 17, 18 and the grooves formed in the insulating materials 91, 101.

Then, the control unit 70 heats the metal pipe material 14 by controlling the heating mechanism 50. Specifically, the control unit 70 controls the power supply unit 55 of the heating mechanism 50 to supply power. Then, the power transmitted to the lower electrodes 17, 18 via the bus bar 52 is supplied to the upper electrodes 17, 18 and the metal pipe material 14 that are sandwiching the metal pipe material 14, and the metal pipe material 14 itself generates heat due to Joule heat due to the resistance present in the metal pipe material 14. In other words, the metal pipe material 14 is in a state of being heated by electrical current.

4(b), the control unit 70 controls the drive mechanism 80 to close the molding die 13 on the heated metal pipe material 14. As a result, the cavity 16 of the lower die 11 and the cavity 24 of the upper die 12 are combined, and the metal pipe material 14 is placed and sealed in the main cavity portion MC between the lower die 11 and the upper die 12. At the same time as the molding die 13 is closed, the actuators 132 and 134 are actuated to move the pair of double-acting dies 130 along the Z-axis direction and enter the main cavity portion MC. As the pair of double-acting dies 130 enter the main cavity portion MC, parts (first parts) 14a and 14b of the metal pipe material 14 placed in the main cavity portion MC are crushed from both sides in the Z-axis direction (process of crushing the first part of the metal pipe material from opposite directions). As a result, parts 14a and 14b of the metal pipe material 14 protrude inward from another part (second part) 14c of the metal pipe material 14, and are bent radially inward of the metal pipe material 14.

Next, the working fluid is supplied from the fluid supply device 105 to the first fluid chambers 115a, 125a, so that the pair of lower sliding parts 112 and the pair of upper sliding parts 122 move so that the side surfaces 112a2, 112b2 of the pair of lower sliding parts 112 and the side surfaces 122a2, 122b2 of the pair of upper sliding parts 122 come into contact with the outer peripheral surface of the metal pipe material 14, as shown in FIG. 4(b). That is, the pair of lower sliding parts 112 and the pair of upper sliding parts 122 slide against the lower mold base 110 and the upper mold base 120, respectively, so that the width of the main cavity part MC in the Y-axis direction becomes narrower (a process of sliding the pair of upper sliding parts and the pair of lower sliding parts against the upper mold base and the lower mold base, respectively). This reduces the separation distance D1 between the pair of lower sliding parts 112 and the separation distance D2 between the pair of upper sliding parts 122 in the Y-axis direction (see FIG. 3(a)).

Then, the cylinder unit 42 of the gas supply mechanism 40 is operated to advance the sealing member 44 and seal both ends of the metal pipe material 14 (see FIG. 2(b)). After sealing is completed, high-pressure gas is blown into the metal pipe material 14. Next, as shown in FIG. 4(c), while blowing high-pressure gas into the metal pipe material 14, the actuators 132, 134 are operated to move the pair of double-acting dies 130 out of the main cavity portion MC.

Since the metal pipe material 14 is heated to a high temperature (around 950°C) and softened, the gas supplied into the metal pipe material 14 expands due to heat. For this reason, for example, the gas supplied can be compressed air, and the metal pipe material 14 at 950°C can be easily expanded by the thermally expanded compressed air. Due to the pressure of the thermally expanded gas, a portion 14c of the metal pipe material 14 softened by heating is molded along the shape of the main cavity portion MC (process of molding the second portion into the main body portion). At this time, the portions 14a and 14b of the metal pipe material 14 that are crushed by the pair of double-acting dies 130 and bent inwardly of the metal pipe material 14 are crimped in the folded state and molded into the inner flange portion 104 extending inwardly of the metal pipe material 14 (process of molding the first portion into the inner flange portion).

The outer peripheral surface of the blow-molded and expanded metal pipe material 14 comes into contact with the cavity 16 of the lower mold 11 and is quenched, and at the same time, comes into contact with the cavity 24 of the upper mold 12 and is quenched (because the upper mold 12 and the lower mold 11 have a large heat capacity and are controlled at a low temperature, when the metal pipe material 14 comes into contact, the heat of the pipe surface is taken away by the mold side at once.) and quenching is performed. This type of cooling method is called mold contact cooling or mold cooling. Immediately after quenching, austenite transforms into martensite (hereinafter, the transformation of austenite into martensite is referred to as martensitic transformation). In the latter half of the cooling, the cooling rate becomes slow, so that martensite transforms into another structure (troostite, sorbite, etc.) due to reheating. Therefore, there is no need to perform a separate tempering process. In addition, in this embodiment, instead of or in addition to mold cooling, cooling may be performed by supplying a cooling medium, for example, into the cavity 24. For example, the metal pipe material 14 may be cooled by contacting it with the molds (upper mold 12 and lower mold 11) until the temperature at which martensitic transformation begins, and then the molds may be opened and a cooling medium (cooling gas) may be sprayed onto the metal pipe material 14 to cause martensitic transformation.

As described above, the metal pipe material 14 is blow molded and then cooled to obtain the metal pipe 100.

Figure 5 is a cross-sectional view of a metal pipe 100 formed by the forming method according to the embodiment described above. As shown in Figure 5, the metal pipe 100 is a steel metal pipe that is an integrally molded product, and has a main body 102 and a pair of inner flanges 104. The main body 102 is cylindrical and defines a space S therein. The main body 102 is formed into a cylindrical shape by injecting high-pressure gas into the metal pipe material 14, and a portion 14c of the metal pipe material 14 expands along the shape of the wall surface that defines the main cavity portion MC.

A pair of inner flanges 104 protrude from the main body 102 toward the inside of the metal pipe 100. That is, the pair of inner flanges 104 extend from the main body 102 and are disposed in the space S. The pair of inner flanges 104 are formed by compressing the ends of parts 14a, 14b of the metal pipe material 14 (steel material) that are bent toward the inside of the metal pipe material 14 by a pair of double-acting dies 130 and crimping them with the pressure of high-pressure gas. In the embodiment shown in FIG. 5, the pair of inner flanges 104 protrude (extend) from the main body 102 in a direction approaching each other.

The provision of the pair of inner flange portions 104 increases the rigidity of the metal pipe 100. On the other hand, because the pair of inner flange portions 104 protrude inward from the main body portion 102, an increase in the external dimensions of the metal pipe 100 is suppressed.

Next, a method for forming a metal pipe according to the second embodiment will be described. The method according to this embodiment is performed using a forming device having a configuration substantially identical to that of the forming device 10 shown in FIG. 1. However, this forming device has a forming die 13A instead of the forming die 13. The forming die 13A differs from the forming die 13 in that it does not have the first double-acting die 130a. Below, the differences from the method for forming a metal pipe according to the first embodiment described above will be mainly described, and overlapping explanations will be omitted.

In the method according to this embodiment, first, a cylindrical metal pipe material 14 made of a hardenable steel is prepared. This metal pipe material 14 is placed (thrown) onto the electrodes 17, 18 provided on the lower die 11 side, for example, using a robot arm or the like. As a result, the metal pipe material 14 is placed between the lower die 11 and the upper die 12, as shown in FIG. 6(a).

Next, the control unit 70 controls the drive mechanism 80 and the pipe holding mechanism 30 to hold the metal pipe material 14 in the pipe holding mechanism 30. Specifically, the drive mechanism 80 drives the upper die 12 and the upper electrodes 17, 18, etc. held on the slide 81 side to move toward the lower die 11 side, and the actuator that allows the upper electrodes 17, 18, etc. and the lower electrodes 17, 18, etc. included in the pipe holding mechanism 30 to move forward and backward is operated, so that the vicinity of both ends of the metal pipe material 14 is clamped from above and below by the pipe holding mechanism 30.

Then, the control unit 70 heats the metal pipe material 14 by controlling the heating mechanism 50. Specifically, the control unit 70 controls the power supply unit 55 of the heating mechanism 50 to supply power. Then, the power transmitted to the lower electrodes 17, 18 via the bus bar 52 is supplied to the upper electrodes 17, 18 and the metal pipe material 14 that are sandwiching the metal pipe material 14, and the metal pipe material 14 itself generates heat due to Joule heat due to the resistance present in the metal pipe material 14. In other words, the metal pipe material 14 is in a state of being heated by electrical current.

Next, as shown in FIG. 6(b), the control unit 70 controls the drive mechanism 80 to close the molding die 13 on the heated metal pipe material 14. At this time, the molding die 13 is not completely closed, and the upper die 12 moves toward the lower die 11 so that gaps are formed between the upper surface 112a1 of the first lower sliding part 112a and the lower surface 122a1 of the first upper sliding part 122a, and between the upper surface 112b1 of the second lower sliding part 112b and the lower surface 122b1 of the second upper sliding part 122b.

In this way, by moving the upper mold 12, a main cavity portion MC is formed between the bottom surface (surface that is the reference line LV1) of the cavity 24 of the upper mold 12 and the bottom surface (surface that is the reference line LV2) of the cavity 16 of the lower mold 11. In addition, a sub-cavity portion SC1 that is connected to the main cavity portion MC and has a smaller volume than the main cavity portion MC is formed between the upper surface 112a1 of the first lower sliding portion 112a and the lower surface 122a1 of the first upper sliding portion 122a. Similarly, a sub-cavity portion SC2 that is connected to the main cavity portion MC and has a smaller volume than the main cavity portion MC is formed between the upper surface 112b1 of the second lower sliding portion 112b and the lower surface 122b1 of the second upper sliding portion 122b. The sub-cavity portions SC1 and SC2 are spaces for forming a pair of outer flange portions 106 in the metal pipe.

As shown in FIG. 6(b), at the same time as the molding die 13 is closed, the actuator 132 is actuated, and the second double-acting die 130b moves along the Z-axis direction and enters the main cavity portion MC. As the second double-acting die 130b enters the main cavity portion MC, a portion (first portion) 14a of the metal pipe material 14 arranged in the main cavity portion MC is crushed from above (Z-axis direction). As a result, the portion 14a of the metal pipe material 14 protrudes inward from the other portion (second portion) 14c of the metal pipe material 14, and is bent radially inward of the metal pipe material 14.

6(b), the pair of lower sliding parts 112 and the pair of upper sliding parts 122 move so that the side surfaces 112a2, 112b2 of the pair of lower sliding parts 112 and the side surfaces 122a2, 122b2 of the pair of upper sliding parts 122 come into contact with a portion 14c of the metal pipe material 14. That is, the pair of lower sliding parts 112 and the pair of upper sliding parts 122 slide against the lower mold base 110 and the upper mold base 120 so that the width of the main cavity part MC in the Y-axis direction becomes narrower. As a result, the separation distance D1 between the pair of lower sliding parts 112 and the separation distance D2 between the upper sliding parts 122 in the Y-axis direction become smaller.

Then, the cylinder unit 42 of the gas supply mechanism 40 is operated to advance the sealing member 44 and seal both ends of the metal pipe material 14 (see FIG. 2(b)). After sealing is completed, low-pressure gas is injected into the metal pipe material 14. Since the metal pipe material 14 is heated to a high temperature (around 950°C) and softened, the gas supplied into the metal pipe material 14 thermally expands. As a result, a portion 14c of the metal pipe material 14 expands to follow the recesses 16, 24 in the main cavity portion MC, and other portions (third portions) 14d, 14e of the metal pipe material 14 expand to enter the sub-cavity portions SC1, SC2, respectively.

Next, as shown in FIG. 6(c), the actuator 132 is operated while blowing low pressure gas into the metal pipe material 14, thereby retracting the second double-acting die 130b from the main cavity portion MC. At this time, the part 14a of the metal pipe material 14 that has been crushed by the second double-acting die 130b and bent inwardly of the metal pipe material 14 is crimped in the folded state, and the inner flange portion 104 extending inwardly of the metal pipe material 14 is formed.

Next, the molding die 13 is further closed, and as shown in FIG. 6(d), the main cavity portion MC and the sub-cavity portions SC1 and SC2 are further narrowed between the lower die 11 and the upper die 12. Also, a high-pressure gas higher than the low-pressure gas described above is blown into the metal pipe material 14. As a result, as shown in FIG. 6(d), the metal pipe material 14 is molded to conform to the shape of the main cavity portion MC, and parts 14d and 14e of the metal pipe material 14 are each crimped in a folded outward state, forming a pair of outer flange portions 106.

The outer surface of the blow-molded and expanded metal pipe material 14 comes into contact with the cavity 16 of the lower die 11 and is rapidly cooled, and at the same time, comes into contact with the cavity 24 of the upper die 12 and is rapidly cooled (because the upper die 12 and the lower die 11 have a large heat capacity and are controlled at low temperatures, when the metal pipe material 14 comes into contact, the heat on the pipe surface is instantly taken away by the die side), and quenching is performed. As described above, the metal pipe material 14 is blow-molded and then cooled to obtain the metal pipe 100A.

The metal pipe 100A formed by the method according to the second embodiment has a main body 102, an inner flange 104, and a pair of outer flanges 106 (see FIG. 6(d)). The main body 102 is cylindrical and defines a space S therein. The main body 102 is formed into a cylindrical shape by injecting high-pressure gas into the metal pipe material 14, which expands along the shape of the wall surface that defines the main cavity MC.

The inner flange portion 104 protrudes from the main body portion 102 to the inside of the metal pipe 100A. That is, the inner flange portion 104 extends from the main body portion 102 and is disposed within the space S. This inner flange portion 104 is formed by compressing the end of the metal pipe material 14 that is bent inwardly of the metal pipe material 14 by the second double-action die 130b and crimping it.

The pair of outer flanges 106 protrude from the main body 102 to the outside of the metal pipe 100. The pair of outer flanges 106 are formed by crimping portions 14d and 14e of the metal pipe material 14 in a folded state within the sub-cavity portions SC1 and SC2. In the embodiment shown in FIG. 6(d), the pair of outer flanges 106 protrude from the main body 102 in directions away from each other.

Next, the function and effect of the metal pipes 100 and 100A according to the above embodiment will be described with reference to FIG. 7.

Figure 7 is a cross-sectional view showing metal pipes according to Examples 1 to 3 and Comparative Examples 1 and 2. The metal pipe SA1 shown in Figure 7 is a metal pipe according to Comparative Example 1, and has a cylindrical main body 102 and a pair of outer flanges 106 extending outward from the main body 102. The main body 102 has a width of 46 mm in the y direction and a height of 28 mm in the x direction. The pair of outer flanges 106 protrude from the main body 102 in the y direction by 17 mm. The metal pipe SA4 shown in Figure 7 is a metal pipe according to Comparative Example 2, and is composed only of a cylindrical main body 102. The main body 102 has a width of 46 mm in the y direction and a height of 28 mm in the x direction.

Metal pipes SA2 and SA3 shown in FIG. 7 are metal pipes according to Examples 1 and 2, respectively. Metal pipes SA2 and SA3 have a cylindrical main body 102 and a pair of inner flanges 104 protruding inward from the main body 102. These main bodies 102 have the same dimensions as the main bodies 102 of metal pipes SA1 and SA4. In addition, the pair of inner flanges 104 of metal pipe SA2 are longer than the pair of inner flanges 104 of metal pipe SA3.

The metal pipe SA5 shown in FIG. 7 is a metal pipe according to Example 3, and has a cylindrical main body 102, an inner flange 104 protruding inward from the main body 102, and a pair of outer flanges 106 protruding outward from the main body 102. The main body 102 of the metal pipe SA5 has the same dimensions as the main body 102 of the metal pipe SA1 and the metal pipe SA4. The outer flanges 106 of the metal pipe SA5 have the same dimensions as the outer flanges 106 of the metal pipe SA1.

Figure 8 shows the area moment of inertia and section modulus of metal pipes SA1 to SA5. Note that Ix in Figure 8 shows the area moment of inertia for bending along the x direction shown in Figure 7, and Iy shows the area moment of inertia for bending along the y direction. Similarly, Zx in Figure 8 shows the area moment of inertia for bending along the x direction, and the area moment of inertia for bending along the y direction.

From the results shown in Figure 8, it was confirmed that the metal pipes SA2 and SA3 (metal pipes with a pair of inner flanges) according to Examples 1 and 2 have a higher geometric moment of inertia Iy and section modulus Zy than the metal pipe SA4 (metal pipe having only a main body) according to Comparative Example 2, and thus have high rigidity. In addition, when comparing the metal pipes SA2 and SA3, it was confirmed that the metal pipe SA2, which has a longer inner flange portion 104, has a higher geometric moment of inertia Iy and section modulus Zy than the metal pipe SA3.

On the other hand, it was confirmed that the area moment of inertia Iy and area modulus Zy of the metal pipes SA2 and SA3 were lower than the area moment of inertia Iy and area modulus Zy of the metal pipe SA1 of Comparative Example 1. However, the external dimensions in the y direction of the metal pipes SA2 and SA3 were smaller than the external dimensions in the y direction of the metal pipe SA1. From these results, it was confirmed that the metal pipes SA2 and SA3 of Examples 1 and 2 can ensure high rigidity without increasing the external dimensions.

In addition, it was confirmed that the metal pipe SA5 of Example 3 (metal pipe with an inner flange portion and a pair of outer flange portions) has a higher area second moment Iy and section modulus Zy than the metal pipes SA2 and SA3, and has higher rigidity.

The above describes various embodiments of metal pipes and methods for forming the same, but the invention is not limited to the above-mentioned embodiments and can be modified in various ways without departing from the spirit of the invention.

For example, while the metal pipe 100 shown in FIG. 5 has a pair of inner flange portions 104, the metal pipe 100 can have any number of inner flange portions. For example, three or more inner flange portions may be disposed within the space S of the metal pipe 100. Similarly, the metal pipe 100A may have only one outer flange portion 106, or may have three or more outer flange portions 106.

The shape of the inner flange portion is not limited to that of the above-described embodiment, and various shapes can be adopted. For example, the inner flange portion may extend continuously along the longitudinal direction of the metal pipe 100, or multiple inner flanges may be arranged along the longitudinal direction of the metal pipe 100.

Furthermore, although the metal pipe 100 shown in FIG. 5 has a main body 102 with a rectangular cross section, the main body 102 may have a different cross section, such as a circular cross section. In addition, although a pair of fluid supply devices 105 are provided in the embodiment shown in FIG. 3, in one embodiment, one fluid supply device 105 may supply the working fluid to a pair of fluid chambers 115 and a pair of fluid chambers 125.

10...molding device, 11...lower mold, 12...upper mold, 13, 13A...molding mold, 14...metal pipe material, 14a, 14b...part of metal pipe (first part), 14c...part of metal pipe (second part), 14d, 14e...part of metal pipe (third part), 17, 18...electrodes, 40...gas supply mechanism, 50...heating mechanism, 55...power supply unit, 60...gas supply unit, 100, 100A...metal pipe, 102...main body, 104...inner flange, 106...outer flange, 110...lower mold base, 112...lower sliding part, 113...lower drive mechanism, 120...upper mold base, 122...upper sliding part, 123...upper drive mechanism, 130...double-acting mold, D1, D2...separation distance, MC...main cavity part, SC1, SC2...sub-cavity part.

Claims (3)

A method for manufacturing a metal pipe by forming a metal pipe material, comprising the steps of:
Heating the metal pipe material,
A double action die is inserted into the metal pipe material while the metal pipe material is heated.
Supplying a fluid into the interior of the metal pipe material;
a metal pipe manufacturing method comprising: forming a protrusion inside the metal pipe material by retracting the double-action die while the inside of the metal pipe material is pressurized after the fluid is supplied. The method for manufacturing a metal pipe according to claim 1 , wherein the pair of double action dies are inserted into the metal pipe material from directions opposite to each other, thereby forming the pair of protrusions inside the metal pipe material. The method for manufacturing a metal pipe according to claim 1 , further comprising the step of forming an outer flange portion protruding outward from the metal pipe material by supplying the fluid into the inside of the metal pipe material.

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