Patent Description:
In the related art, a forming apparatus in which a metal pipe is closed by a forming die and blow-formed is known. For example, a forming apparatus disclosed in PTL <NUM> includes a forming die, and a gas supply unit which supplies gas into a metal pipe material. In this forming apparatus, the metal pipe material is formed into a shape corresponding to the shape of the forming die by disposing a heated metal pipe material in the forming die and expanding the metal pipe material by supplying gas from the gas supply unit to the metal pipe material in a state where the forming die is closed.

A further apparatus for manufacturing pipe products is disclosed in PTL <NUM> and forms the basis for the preamble of claim <NUM>.

In the forming apparatus of the related art, the metal pipe material is heated by holding both end portions of the metal pipe material with electrodes and energizing each electrode. Here, the electrodes on both sides hold the metal pipe material with substantially the same engagement force and frictional force. In a case where the metal pipe material has expanded with heating, the metal pipe material does not extend evenly from the electrodes on both sides, and in some cases, the amount of expansion of the metal pipe material on either electrode side increases according to a slight difference in engagement force and frictional force. Therefore, the form of expansion changes for each metal pipe material to be formed. In this manner, there is a case where the change in the form of expansion of the metal pipe material affects an error of a process after the heating.

Therefore, the present invention has an object to provide a forming apparatus in which it is possible to control the form of expansion of a metal pipe material with respect to electrodes on both sides.

The above object is achieved by the invention as set out in the appended set of claims.

According to an aspect of the present invention, there is provided a forming apparatus which forms a metal pipe by expanding a metal pipe material, including: a forming die for forming the metal pipe; a first electrode and a second electrode which clamp the metal pipe material at both end sides and heat the metal pipe material by causing an electric current to flow through the metal pipe material; and a first fluid supply unit and a second fluid supply unit which supply a fluid into the metal pipe material heated by the first electrode and the second electrode to expand the metal pipe material, in which at least one of the first electrode and the second electrode is provided with a movement restriction mechanism which restricts a movement of the metal pipe material in an axial direction of the metal pipe material.

According to this forming apparatus, the first electrode and the second electrode clamp the metal pipe material disposed in the forming die at both end sides. The movement restriction mechanism provided in at least one of the first electrode and the second electrode restricts the movement of the metal pipe material in the axial direction of the metal pipe material. Therefore, in a case where the first electrode and the second electrode heat the metal pipe material by causing an electric current to flow through the metal pipe material, the movement of the expanded metal pipe material is restricted at least on the electrode side where the movement restriction mechanism is provided. By the above, it is possible to control the form of expansion of the metal pipe material with respect to the electrodes on both sides.

In the forming apparatus, the movement restriction mechanism may include a protrusion portion which is formed on a contact surface of one of the first electrode and the second electrode and protrudes with respect to the metal pipe material. The movement restriction mechanism is provided in one of the first electrode and the second electrode. Therefore, the expanded metal pipe material is held on the electrode side where the movement restriction mechanism is provided, and extends toward the other electrode side. In this way, it is possible to control the expansion direction of the metal pipe material with respect to the electrodes on both sides. Further, the protrusion portion formed on the contact surface of one of the first electrode and the second electrode bites into and engages with the metal pipe material, so that the movement of the metal pipe can be restricted with a simple configuration.

In the forming apparatus, the movement restriction mechanism may make a pressing force of a contact surface of one of the first electrode and the second electrode with respect to the metal pipe material larger than a pressing force of a contact surface of the other of the first electrode and the second electrode with respect to the metal pipe material. The movement restriction mechanism is provided in one of the first electrode and the second electrode. Therefore, the expanded metal pipe material is held on the electrode side where the movement restriction mechanism is provided, and extends toward the other electrode side. In this way, it is possible to control the expansion direction of the metal pipe material with respect to the electrodes on both sides. Further, in this way, it is possible to restrict the movement of the metal pipe material <NUM> by increasing the frictional force between the contact surface of one electrode of the first electrode and the second electrode and the metal pipe material with simple setting of adjusting only the pressing force.

In the forming apparatus, the movement restriction mechanism may include a first restriction member which restricts a movement of the metal pipe material by coming into contact with a first end portion of the metal pipe material on the first electrode side in the axial direction, and a second restriction member which restricts a movement of the metal pipe material by coming into contact with a second end portion of the metal pipe material on the second electrode side in the axial direction. In this way, the movement due to expansion of the first end portion of the metal pipe material is restricted by the first restriction member, and the movement due to expansion of the second end portion of the metal pipe material is restricted by the second restriction member. In this way, the movement restriction mechanism can control the amount of movement of the end portion of the metal pipe material on both sides of the first electrode and the second electrode. By the above, it is possible to control the form of expansion of the metal pipe material with respect to the electrodes on both sides.

The forming apparatus may further include a control unit which controls heating by the first electrode and the second electrode, in which the control unit may consider that the metal pipe material has reached a target temperature, based on the contact of the first end portion with the first restriction member and the contact of the second end portion with the second restriction member. In this way, the control unit can control the amount of movement of both end portions of the metal pipe material by the first restriction member and the second restriction member, and can also control a timing of stop of the heating.

The forming apparatus may further include a control unit which controls movements of the first restriction member and the second restriction member in the axial direction, in which in a case where the control unit has detected that an amount of movement of one end portion of the first end portion and the second end portion of the metal pipe material is larger than an amount of movement of the other end portion, the control unit may move the first restriction member and the second restriction member from the other end portion side to the one end portion side. In this case, in a case where the amount of movement of one end portion of the first end portion and the second end portion of the metal pipe material becomes larger than the amount of movement of the other end portion, it is possible to suppress a load which occurs between the metal pipe material which tries to expand and the restriction member from becoming too large.

In the forming apparatus, the control unit may perform alignment of the metal pipe material in the axial direction by pushing the metal pipe material in the axial direction with at least one of the first restriction member and the second restriction member after stop of the heating by the first electrode and the second electrode. In this case, in a case where the amount of movement of one end portion of the first end portion and the second end portion of the metal pipe material becomes larger than the amount of movement of the other end portion, it is possible to align the metal pipe material at a position suitable for forming after stop of the heating while suppressing a load acting on the metal pipe material from becoming too large during the heating.

The forming apparatus may further include a detection unit which detects the amount of movement of an end portion of the metal pipe material in the axial direction. In this way, it is possible to control the metal pipe material to an appropriate expansion amount.

The forming apparatus may further include a non-contact type detection unit which detects positions of the first end portion and the second end portion in a non-contact manner to detect contact of the first end portion with the first restriction member and contact of the second end portion with the second restriction member. In this case, even if a complicated detection mechanism or the like is not provided at each of the first restriction member and the second restriction member, it is possible to detect the contact between the metal pipe material and the restriction member.

According to the forming apparatus of the present invention, it is possible to control the form of expansion of the metal pipe material with respect to the electrodes on both sides.

Hereinafter, a preferred embodiment of a forming apparatus according to the present invention will be described with reference to the drawings. Those embodiments in which no movement restriction mechanism is provided on at least one of the electrodes are not according to the invention and are present for illustration purposes only. In each drawing, identical or corresponding portions are denoted by the same reference numerals, and overlapping description will be omitted.

<FIG> is a schematic configuration diagram of a forming apparatus according to this embodiment. As shown in <FIG>, a forming apparatus <NUM> for forming a metal pipe is configured to include a forming die <NUM> which includes an upper die <NUM> and a lower die <NUM>, a drive mechanism <NUM> for moving at least one of the upper die <NUM> and the lower die <NUM>, a pipe holding mechanism <NUM> for holding a metal pipe material <NUM> which is disposed between the upper die <NUM> and the lower die <NUM>, a heating mechanism <NUM> for energizing and heating the metal pipe material <NUM> held by the pipe holding mechanism <NUM>, a gas supply unit <NUM> for supplying high-pressure gas (gas) into the metal pipe material <NUM> held between the upper die <NUM> and the lower die <NUM> and heated, a pair of gas supply mechanisms (first fluid supply unit and second fluid supply unit) <NUM> for supplying the gas from the gas supply unit <NUM> into the metal pipe material <NUM> held by the pipe holding mechanism <NUM>, a water circulation mechanism <NUM> for forcibly water-cooling the forming die <NUM>, and a control unit <NUM> that controls the drive of the drive mechanism <NUM>, the drive of the pipe holding mechanism <NUM>, the drive of the heating mechanism <NUM>, and the gas supply of the gas supply unit <NUM>.

The lower die <NUM> which is one side of the forming die <NUM> is fixed to a base <NUM>. The lower die <NUM> is formed of a large steel block and has, for example, a rectangular cavity (recessed portion) <NUM> on the upper surface thereof. A cooling water passage <NUM> is formed in the lower die <NUM>, and the lower die <NUM> is provided with a thermocouple <NUM> inserted from below at substantially the center. The thermocouple <NUM> is supported by a spring <NUM> so as to be movable up and down.

Further, a space 11a is provided in the vicinity of each of the right and left ends (right and left ends in <FIG>) of the lower die <NUM>, and electrodes <NUM> and <NUM> (lower electrodes) (described later), which are movable parts of the pipe holding mechanism <NUM>, and the like are disposed in the spaces 11a so as to be able to move up and down. Then, the metal pipe material <NUM> is placed on the lower electrodes <NUM> and <NUM>, whereby the lower electrodes <NUM> and <NUM> come into contact with the metal pipe material <NUM> which is disposed between the upper die <NUM> and the lower die <NUM>. In this way, the lower electrodes <NUM> and <NUM> are electrically connected to the metal pipe material <NUM>.

Insulating materials <NUM> for preventing electric conduction are respectively provided between the lower die <NUM> and the lower electrode <NUM>, below the lower electrode <NUM>, between the lower die <NUM> and the lower electrode <NUM>, and below the lower electrode <NUM>. Each of the insulating materials <NUM> is fixed to an advancing and retreating rod <NUM> which is a movable portion of an actuator (not shown) configuring the pipe holding mechanism <NUM>. The actuator is for moving the lower electrodes <NUM> and <NUM> and the like up and down, and a fixed portion of the actuator is held on the base <NUM> side together with the lower die <NUM>.

The upper die <NUM> which is the other side of the forming die <NUM> is fixed to a slide <NUM> (described later) configuring the drive mechanism <NUM>. The upper die <NUM> is formed of a large steel block and has a cooling water passage <NUM> formed in the interior thereof and, for example, a rectangular cavity (recessed portion) <NUM> provided on the lower surface thereof. The cavity <NUM> is provided at a position facing the cavity <NUM> of the lower die <NUM>.

Similar to the lower die <NUM>, a space 12a is provided in the vicinity of each of the right and left ends (right and left ends in <FIG>) of the upper die <NUM>, and electrodes <NUM> and <NUM> (upper electrodes) (described later), which are movable parts of the pipe holding mechanism <NUM>, and the like are disposed in the spaces 12a so as to be movable up and down. Then, the upper electrodes <NUM> and <NUM> move downward in a state where the metal pipe material <NUM> is placed on the lower electrodes <NUM> and <NUM>, whereby the upper electrodes <NUM> and <NUM> come into contact with the metal pipe material <NUM> disposed between the upper die <NUM> and the lower die <NUM>. In this way, the upper electrodes <NUM> and <NUM> are electrically connected to the metal pipe material <NUM>.

Insulating materials <NUM> for preventing electric conduction are provided between the upper die <NUM> and the upper electrode <NUM>, above the upper electrode <NUM>, between the upper die <NUM> and the upper electrode <NUM>, and above the upper electrode <NUM>. Each of the insulating materials <NUM> is fixed to an advancing and retreating rod <NUM> which is a movable portion of the actuator configuring the pipe holding mechanism <NUM>. The actuator is for moving the upper electrodes <NUM> and <NUM> and the like up and down, and a fixed portion of the actuator is held on the slide <NUM> side of the drive mechanism <NUM> together with the upper die <NUM>.

A semicircular arc-shaped concave groove 18a corresponding to the outer peripheral surface of the metal pipe material <NUM> is formed in each of the surfaces of the electrodes <NUM> and <NUM>, which face each other, in the right side portion of the pipe holding mechanism <NUM> (refer to <FIG>), and the metal pipe material <NUM> can be placed so as to exactly fit to the portion of the concave groove 18a. Similar to the concave groove 18a, a semicircular arc-shaped concave groove corresponding to the outer peripheral surface of the metal pipe material <NUM> is formed in each of exposed surfaces of the insulating materials <NUM> and <NUM>, which face each other, in the right side portion of the pipe holding mechanism <NUM>. Further, a tapered concave surface 18b in which the periphery is recessed to be inclined in a tapered shape toward the concave groove 18a is formed on the front surface of the electrode <NUM> (the surface in an outer direction of the die). Accordingly, a configuration is made such that, if the metal pipe material <NUM> is clamped from an up-down direction at the right side portion of the pipe holding mechanism <NUM>, the outer periphery of the right end portion of the metal pipe material <NUM> can be exactly surrounded so as to be in close contact over the entire circumference.

A semicircular arc-shaped concave groove 17a corresponding to the outer peripheral surface of the metal pipe material <NUM> is formed in each of the surfaces of the electrodes <NUM> and <NUM>, which face each other, in the left side portion of the pipe holding mechanism <NUM> (refer to <FIG>), and the metal pipe material <NUM> can be placed so as to exactly fit to the portion of the concave groove 17a. Similar to the concave groove 17a, a semicircular arc-shaped concave groove corresponding to the outer peripheral surface of the metal pipe material <NUM> is formed in each of exposed surfaces of the insulating materials <NUM> and <NUM>, which face each other, in the left side portion of the pipe holding mechanism <NUM>. Further, a tapered concave surface 17b in which the periphery is recessed to be inclined in a tapered shape toward the concave groove 17a is formed on the front surface of the electrode <NUM> (the surface in the outer direction of the die). Accordingly, a configuration is made such that, if the metal pipe material <NUM> is clamped from the up-down direction at the left side portion of the pipe holding mechanism <NUM>, the outer periphery of the left end portion of the metal pipe material <NUM> can be exactly surrounded so as to be in close contact over the entire circumference.

As shown in <FIG>, the drive mechanism <NUM> includes the slide <NUM> for moving the upper die <NUM> such that the upper die <NUM> and the lower die <NUM> are combined with each other, a shaft <NUM> for generating a driving force for moving the slide <NUM>, and a connecting rod <NUM> for transmitting the driving force generated by the shaft <NUM> to the slide <NUM>. The shaft <NUM> extends in a right-left direction above the slide <NUM>, is rotatably supported, and has an eccentric crank 82a which protrudes from the right and left ends and extends in the right-left direction at a position separated from the shaft center thereof. The eccentric crank 82a and a rotary shaft 81a provided above the slide <NUM> and extending in the right-left direction are connected to each other by the connecting rod <NUM>. In the drive mechanism <NUM>, the height in the up-down direction of the eccentric crank 82a is changed by controlling the rotation of the shaft <NUM> by the control unit <NUM>, and the up-and-down movement of the slide <NUM> can be controlled by transmitting the positional change of the eccentric crank 82a to the slide <NUM> through the connecting rod <NUM>. Here, the oscillation (rotary motion) of the connecting rod <NUM>, which occurs when the positional change of the eccentric crank 82a is transmitted to the slide <NUM>, is absorbed by the rotary shaft 81a. The shaft <NUM> rotates or stops in response to the drive of a motor or the like, which is controlled by the control unit <NUM>, for example.

The heating mechanism <NUM> includes a power supply unit <NUM>, and a bus bar <NUM> which electrically connects the power supply unit <NUM> and the electrodes <NUM> and <NUM>. The power supply unit <NUM> includes a direct-current power supply and a switch, and can energize the metal pipe material <NUM> through the bus bar <NUM> and the electrodes <NUM> and <NUM> in a state where the electrodes <NUM> and <NUM> are electrically connected to the metal pipe material <NUM>. Here, the bus bar <NUM> is connected to the lower electrodes <NUM> and <NUM>.

In the heating mechanism <NUM>, the direct-current current output from the power supply unit <NUM> is transmitted by the bus bar <NUM> and input to the electrode <NUM>. Then, the direct-current current passes through the metal pipe material <NUM> and is input to the electrode <NUM>. Then, a direct-current current is transmitted by the bus bar <NUM> to be input to the power supply unit <NUM>.

Returning to <FIG>, each of the pair of gas supply mechanisms <NUM> includes a cylinder unit <NUM>, a cylinder rod <NUM> which advances and retreats in accordance with the operation of the cylinder unit <NUM>, and a seal member <NUM> connected to the tip of the cylinder rod <NUM> on the pipe holding mechanism <NUM> side. The cylinder unit <NUM> is placed on and fixed to a block <NUM>. A tapered surface <NUM> which is tapered is formed on the tip of the seal member <NUM>, and is configured in a shape which is fitted to the tapered concave surfaces 17b and 18b of the electrodes <NUM> and <NUM> (refer to <FIG>). A gas passage <NUM> which extends from the cylinder unit <NUM> side toward the tip and through which the high-pressure gas supplied from the gas supply unit <NUM> flows, as specifically shown in <FIG>, is provided in the seal member <NUM>.

The gas supply unit <NUM> includes a gas source <NUM>, an accumulator <NUM> for storing the gas supplied by the gas source <NUM>, a first tube <NUM> extending from the accumulator <NUM> to the cylinder unit <NUM> of the gas supply mechanism <NUM>, a pressure control valve <NUM> and a switching valve <NUM> provided in the first tube <NUM>, a second tube <NUM> extending from the accumulator <NUM> to the gas passage <NUM> formed in the seal member <NUM>, and a pressure control valve <NUM> and a check valve <NUM> provided in the second tube <NUM>. The pressure control valve <NUM> plays a role of supplying a gas having an operating pressure adapted to a pressing force of the seal member <NUM> with respect to the metal pipe material <NUM> to the cylinder unit <NUM>. The check valve <NUM> plays a role of preventing the high-pressure gas from flowing backward in the second tube <NUM>. The pressure control valve <NUM> provided in the second tube <NUM> plays a role of supplying a gas having an operating pressure for expanding the metal pipe material <NUM> to the gas passage <NUM> of the seal member <NUM> by the control of the control unit <NUM>.

The control unit <NUM> controls the pressure control valve <NUM> of the gas supply unit <NUM> to be able to supply a gas having a desired operating pressure into the metal pipe material <NUM>. Further, the control unit <NUM> acquires temperature information from the thermocouple <NUM> from information which is transmitted from (A) shown in <FIG>, and controls the drive mechanism <NUM>, the power supply unit <NUM>, and the like.

The water circulation mechanism <NUM> includes a water tank <NUM> for storing water, a water pump <NUM> for pumping up the water stored in the water tank <NUM>, pressurizing it, and sending it to the cooling water passage <NUM> of the lower die <NUM> and the cooling water passage <NUM> of the upper die <NUM>, and a pipe <NUM>. Although omitted, a cooling tower for lowering a water temperature or a filter for purifying water may be provided in the pipe <NUM>.

Next, a method of forming a metal pipe using the forming apparatus <NUM> will be described. First, a quenchable steel grade cylindrical metal pipe material <NUM> is prepared. The metal pipe material <NUM> is placed (loaded) on the electrodes <NUM> and <NUM> provided on the lower die <NUM> side by using, for example, a robot arm or the like. Since the concave grooves 17a and 18a are formed in the electrodes <NUM> and <NUM>, the metal pipe material <NUM> is positioned by the concave grooves 17a and 18a.

Next, the control unit <NUM> controls the drive mechanism <NUM> and the pipe holding mechanism <NUM>, thereby causing the pipe holding mechanism <NUM> to hold the metal pipe material <NUM>. Specifically, the upper die <NUM>, the upper electrodes <NUM> and <NUM>, and the like held on the slide <NUM> side move to the lower die <NUM> side by the drive of the drive mechanism <NUM>, and both end portions of the metal pipe material <NUM> are clamped from above and below by the pipe holding mechanism <NUM> by operating the actuator which allows the upper electrodes <NUM> and <NUM> and the like and the lower electrodes <NUM> and <NUM> and the like, which are included in the pipe holding mechanism <NUM>, to advance and retreat. The clamping is performed in such an aspect as to be in close contact over the entire circumference in the vicinity of both end portions of the metal pipe material <NUM> due to the presence of the concave grooves 17a and 18a formed in the electrodes <NUM> and <NUM> and the concave grooves formed in the insulating materials <NUM> and <NUM>.

At this time, as shown in <FIG>, the end portion of the metal pipe material <NUM> on the electrode <NUM> side protrudes further toward the seal member <NUM> side than the boundary between the concave groove 18a and the tapered concave surface 18b of the electrode <NUM> in an extending direction of the metal pipe material <NUM>. Similarly, the end portion of the metal pipe material <NUM> on the electrode <NUM> side protrudes further toward the seal member <NUM> side than the boundary between the concave groove 17a and the tapered concave surface 17b of the electrode <NUM> in the extending direction of the metal pipe material <NUM>. Further, the lower surfaces of the upper electrodes <NUM> and <NUM> and the upper surfaces of the lower electrodes <NUM> and <NUM> are in contact with each other. However, there is no limitation to the configuration of being in close contact over the entire circumference of each of both end portions of the metal pipe material <NUM>, and a configuration may be made such that the electrodes <NUM> and <NUM> are in contact with a part in the circumferential direction of the metal pipe material <NUM>.

Subsequently, the control unit <NUM> controls the heating mechanism <NUM> to heat the metal pipe material <NUM>. Specifically, the control unit <NUM> controls the power supply unit <NUM> of the heating mechanism <NUM> to supply electric power. Then, the electric power which is transmitted to the lower electrodes <NUM> and <NUM> through the bus bar <NUM> is supplied to the upper electrodes <NUM> and <NUM> clamping the metal pipe material <NUM> and the metal pipe material <NUM>, and due to resistance which exists in the metal pipe material <NUM>, the metal pipe material <NUM> itself generates heat by Joule heat. That is, the metal pipe material <NUM> is in the energized and heated state.

Subsequently, the forming die <NUM> is closed to the heated metal pipe material <NUM> by the control of the drive mechanism <NUM> by the control unit <NUM>. In this way, the cavity <NUM> of the lower die <NUM> and the cavity <NUM> of the upper die <NUM> are combined, and the metal pipe material <NUM> is disposed and sealed in the cavity portion between the lower die <NUM> and the upper die <NUM>.

Thereafter, each of both ends of the metal pipe material <NUM> is sealed by advancing the seal member <NUM> by operating the cylinder unit <NUM> of the gas supply mechanism <NUM>. At this time, as shown in <FIG>, the seal member <NUM> is pressed against the end portion of the metal pipe material <NUM> on the electrode <NUM> side, whereby the portion protruding further toward the seal member <NUM> than the boundary between the concave groove 18a and the tapered concave surface 18b of the electrode <NUM> is deformed in a funnel shape so as to follow the tapered concave surface 18b. Similarly, the seal member <NUM> is pressed against the end portion of the metal pipe material <NUM> on the electrode <NUM> side, whereby the portion protruding further toward the seal member <NUM> than the boundary between the concave groove 17a and the tapered concave surface 17b of the electrode <NUM> is deformed in a funnel shape so as to follow the tapered concave surface 17b. After the completion of the sealing, a high-pressure gas is blown into the metal pipe material <NUM> to form the metal pipe material <NUM> softened by heating so as to follow the shape of the cavity portion.

The metal pipe material <NUM> is softened by being heated to a high temperature (about <NUM>), and therefore, the gas supplied into the metal pipe material <NUM> thermally expands. For this reason, for example, the gas to be supplied is set to be compressed air, and thus the metal pipe material <NUM> having a temperature of <NUM> can be easily expanded by the thermally expanded compressed air.

The outer peripheral surface of the blow-formed and expanded metal pipe material <NUM> is rapidly cooled in contact with the cavity <NUM> of the lower die <NUM> and at the same time, is rapidly cooled in contact with the cavity <NUM> of the upper die <NUM> (since the upper die <NUM> and the lower die <NUM> have large heat capacity and are controlled to a low temperature, if the metal pipe material <NUM> comes into contact with the upper die <NUM> and the lower die <NUM>, the heat of the pipe surface is removed to the die side at once), and thus quenching is performed. Such a cooling method is called die contact cooling or die cooling. Immediately after the rapid cooling, austenite is transformed into martensite (hereinafter, the transformation of austenite to martensite is referred to as martensitic transformation). Since a cooling rate is reduced in the second half of the cooling, the martensite is transformed into another structure (troostite, sorbite, or the like) due to reheating. Therefore, it is not necessary to separately perform tempering treatment. Further, in this embodiment, instead of the die cooling or in addition to the die cooling, cooling may be performed by supplying a cooling medium into, for example, the cavity <NUM>. For example, the martensitic transformation may be generated by performing cooling by bringing the metal pipe material <NUM> into contact with the dies (the upper die <NUM> and the lower die <NUM>) before a temperature at which the martensitic transformation begins, and then performing the die opening and blowing a cooling medium (cooling gas) to the metal pipe material <NUM>.

As described above, the metal pipe material <NUM> is blow-formed and then cooled, and then the die opening is performed, thereby obtaining a metal pipe having, for example, a substantially rectangular tubular main body portion.

Next, characteristic parts of the forming apparatus <NUM> according to this embodiment will be described with reference to <FIG> and <FIG>. <FIG> are enlarged diagrams showing a movement restriction mechanism for restricting the movement of the metal pipe material <NUM> with respect to a contact surface of the electrode. <FIG> are schematic diagrams for explaining an expansion direction of the metal pipe material with respect to the electrodes on both sides.

In the forming apparatus <NUM> according to this embodiment, one of the electrode <NUM> and the electrode <NUM> is provided with a movement restriction mechanism <NUM> which restricts the movement of the metal pipe in the axial direction of the metal pipe material <NUM>. The movement restriction mechanism <NUM> may restrict the movement by the engagement force between the electrode on one side and the metal pipe (the metal pipe material). Alternatively, the movement restriction mechanism <NUM> may have a structure that increases the frictional force of the contact surface of the electrode on one side. The expression "increasing the frictional force of the contact surface of the electrode on one side" also includes relatively increasing the frictional force of the electrode on one side by reducing the frictional force of the contact surface of the electrode on the other side. The restriction of the movement of the metal pipe by the movement restriction mechanism <NUM> shall also include the restriction of the movement of the metal pipe material <NUM> in a state before the completion of the metal pipe. In this embodiment, the movement restriction mechanism <NUM> performs the movement restriction by the engagement of the contact surface of the electrode with the metal pipe material <NUM>.

In this embodiment, as shown in <FIG>, the movement restriction mechanism <NUM> is configured to make the engagement force of a contact surface <NUM> of the electrode <NUM> with the metal pipe material <NUM> larger than the engagement force of a contact surface <NUM> of the electrode <NUM> with the metal pipe material <NUM>. In this case, the electrode <NUM> corresponds to "one of the first electrode and the second electrode" in the claims, and the electrode <NUM> corresponds to "the other of the first electrode and the second electrode" in the claims. In this embodiment, the contact surface <NUM> of the electrode <NUM> corresponds to the inner peripheral surface of the concave groove 18a in each of the upper and lower electrodes <NUM>. The contact surface <NUM> of the electrode <NUM> corresponds to the inner peripheral surface of the concave groove 17a in each of the upper and lower electrodes <NUM>. A configuration may be made such that the engagement force of the contact surface <NUM> of the electrode <NUM> with the metal pipe material <NUM> becomes larger than the engagement force of the contact surface <NUM> of the electrode <NUM> with the metal pipe material <NUM>. In this case, the electrode <NUM> corresponds to "one of the first electrode and the second electrode" in the claims, and the electrode <NUM> corresponds to "the other of the first electrode and the second electrode" in the claims.

Specifically, a protrusion portion <NUM> which protrudes with respect to the metal pipe material <NUM> is formed on the contact surface <NUM> of the electrode <NUM>. The movement restriction mechanism <NUM> is configured with the protrusion portion <NUM>. In particular, as shown in <FIG>, the contact surface <NUM> strongly presses the metal pipe material <NUM> at the portion of the protrusion portion <NUM>, thereby improving the engagement force with respect to the metal pipe material <NUM>. As shown in <FIG>, a plurality of (here, two) protrusion portions <NUM> are formed at each of the upper and lower electrodes <NUM>. The protrusion portions <NUM> are formed equally at a constant angle (here, <NUM>°) on the contact surface <NUM>. However, the number of the protrusion portions <NUM> is not limited, and the protrusion portions <NUM> may not be equally formed on the contact surface <NUM>. Further, the protrusion portion <NUM> may be formed at only one of the upper electrode <NUM> and the lower electrode <NUM>. Further, although the protrusion portion <NUM> protrudes in a spherical shape, the shape is not particularly limited. For example, the protrusion portion <NUM> may have a shape that extends in the axial direction or the circumferential direction of the metal pipe material <NUM>. In the drawings, the amount of protrusion of the protrusion portion <NUM> is emphasized for easy understanding. On the other hand, the protrusion portion <NUM> is not formed on the contact surface <NUM> of the electrode <NUM>.

The operation and effects of the forming apparatus <NUM> according to this embodiment will be described.

First, a forming apparatus according to a comparative example will be described with reference to <FIG>. In the forming apparatus according to the comparative example, both the electrodes <NUM> and <NUM> hold the metal pipe material with substantially the same engagement force and frictional force. In a case where the metal pipe material <NUM> expands with heating, the metal pipe material <NUM> does not extend equally from the electrodes <NUM> and <NUM> on both sides, and the metal pipe material extends from either of the electrode <NUM> side or the electrode <NUM> side according to a slight difference in engagement force and frictional force. For example, in a certain metal pipe material <NUM>, as shown in <FIG>, the metal pipe material <NUM> extends from the electrode <NUM> side. On the other hand, in the other metal pipe material <NUM>, as shown in <FIG>, the metal pipe material <NUM> extends from the electrode <NUM> side. That is, the expansion direction changes for each metal pipe material <NUM> to be formed. In this manner, there is a case where the change in the expansion direction of the metal pipe material <NUM> affects an error of the process after heating. For example, the pushing amount of the seal members <NUM> of the gas supply mechanisms <NUM> varies depending on the expansion direction of the metal pipe material <NUM>, and therefore, there is a case where it affects an error during forming.

In contrast, according to the forming apparatus <NUM> of this embodiment, the electrodes <NUM> and <NUM> clamp the metal pipe material <NUM> disposed in the forming die <NUM> at both end sides. The contact surface <NUM> of the electrode <NUM> is provided with the movement restriction mechanism <NUM> which restricts the movement of the metal pipe in the axial direction of the metal pipe material <NUM>. Therefore, in a case where the electrode <NUM> and the electrode <NUM> cause an electric current to flow through the metal pipe material <NUM> to heat the metal pipe material <NUM>, as shown in <FIG>, the expanded metal pipe material <NUM> is held on the electrode <NUM> side where the movement restriction mechanism <NUM> is provided, and extends toward the electrode <NUM> side. By the above, it is possible to control the expansion direction of the metal pipe material <NUM> with respect to the electrodes <NUM> and <NUM> on both sides.

Further, in the forming apparatus <NUM>, the movement restriction mechanism <NUM> is configured with the protrusion portion <NUM> which is formed on the contact surface <NUM> of the electrode <NUM> and protrudes with respect to the metal pipe material <NUM>. The protrusion portion <NUM> formed on the contact surface <NUM> of the electrode <NUM> bites into and engages with the metal pipe material <NUM>, so that the movement of the metal pipe can be restricted with a simple configuration.

The present invention is not limited to the embodiment described above. It may encompass further embodiments also falling within the scope of the invention as defined by the claims.

For example, instead of the configuration of restricting the movement by using the protrusion portion as shown in <FIG>, the movement may be restricted by using a difference in frictional force between the electrodes. In the following configuration, the frictional force is increased by increasing the pressing force of the electrode on one side with respect to the metal pipe material <NUM>.

That is, one of the electrode <NUM> and the electrode <NUM> is provided with the movement restriction mechanism <NUM> which makes the frictional force between the contact surface of the electrode on one side and the metal pipe material <NUM> larger than the frictional force between the contact surface of the electrode on the other side and the metal pipe material <NUM>. The "frictional force" is a force acting in the direction opposite to a movement direction in a case where the outer peripheral surface of the metal pipe material <NUM> tries to move relative to the contact surface in the axial direction (for example, due to thermal expansion or the like).

In this embodiment, a configuration is made such that the frictional force between the contact surface <NUM> of the electrode <NUM> and the metal pipe material <NUM> becomes larger than the frictional force between the contact surface <NUM> of the electrode <NUM> and the metal pipe material <NUM>. That is, the movement restriction mechanism <NUM> makes the frictional force between the contact surface <NUM> of the electrode <NUM> and the metal pipe material <NUM> larger than the frictional force between the contact surface <NUM> of the electrode <NUM> and the metal pipe material <NUM>. In this case, the electrode <NUM> corresponds to "one of the first electrode and the second electrode" in the claims, and the electrode <NUM> corresponds to "the other of the first electrode and the second electrode" in the claims. A configuration may be made such that the frictional force between the contact surface <NUM> of the electrode <NUM> and the metal pipe material <NUM> becomes larger than the frictional force between the contact surface <NUM> of the electrode <NUM> and the metal pipe material <NUM>. In this case, the electrode <NUM> corresponds to "one of the first electrode and the second electrode" in the claims, and the electrode <NUM> corresponds to "the other of the first electrode and the second electrode" in the claims.

More specifically, as shown in <FIG>, a pressing force F1 of the contact surface <NUM> of the electrode <NUM> with respect to the metal pipe material <NUM> is larger than a pressing force F2 of the contact surface <NUM> of the electrode <NUM> with respect to the metal pipe material <NUM>. Therefore, in a case where the electrode <NUM> and the electrode <NUM> cause an electric current to flow through the metal pipe material <NUM> to heat the metal pipe material <NUM>, as shown in <FIG>, the expanded metal pipe material <NUM> is held on the electrode <NUM> side where the frictional force is larger, and extends toward the electrode <NUM> side where the frictional force is smaller. In this way, it is possible to increase the frictional force between the contact surface <NUM> of the electrode <NUM> and the metal pipe material <NUM> with simple setting of adjusting only the pressing force. The adjustment of the pressing force can be realized by setting different values as the setting value of an actuator <NUM> that drives the electrode <NUM> and the setting value of an actuator <NUM> that drives the electrode <NUM>. In this form, the movement restriction mechanism <NUM> is configured with the actuator <NUM> in which a larger pressing force is set.

In addition, the configuration of the movement restriction adjustment mechanism which adjusts the frictional force between the contact surface of the electrode and the metal pipe material is not particularly limited. For example, the frictional force may be adjusted by adjusting the roughness of the contact surface. In this case, the contact surface having a higher roughness than the contact surface of the electrode on the other side corresponds to the movement restriction mechanism.

In the embodiment described above, the gas supply mechanism is adopted as the fluid supply unit. However, the fluid is not limited to gas, and liquid may be supplied.

Further, as shown in <FIG>, <FIG>, and <FIG>, the forming apparatus may further include a detection unit which detects the amount of movement of the end portion of the metal pipe material <NUM> in the axial direction. In this way, it is possible to control the metal pipe material <NUM> to an appropriate expansion amount.

Specifically, as shown in <FIG>, the forming apparatus may include a proximity switch <NUM> which detects the proximity of an end portion 14a of the metal pipe material <NUM> in a non-contact manner. The end portion 14a is an end portion on the electrode <NUM> side where the movement restriction mechanism is not provided, and the movement of the metal pipe material <NUM> is restricted by the movement restriction mechanism on the other electrode <NUM> side. The proximity switch <NUM> detects the proximity of the end portion 14a in a case where the end portion 14a has approached a predetermined range. The proximity switch <NUM> is a high magnetic field resistant switch. Therefore, even if the surroundings is in a high magnetic field due to energization heating, the proximity switch <NUM> can normally perform the detection. Further, the forming apparatus includes the control unit <NUM>. The control unit <NUM> is electrically connected to the proximity switch <NUM> and can receive a detection result detected by the proximity switch <NUM>. Further, the control unit <NUM> is electrically connected to the electrodes <NUM> and <NUM> and can control the energization heating of the electrodes <NUM> and <NUM>.

Here, the amount of expansion when the metal pipe material <NUM> has reached a target temperature (or the full length of the metal pipe material <NUM> at the time of the completion of heating) can be grasped in advance by experiments, calculations, or the like. Therefore, the proximity switch <NUM> can grasp in advance an expected arrival position where the end portion 14a reaches when the metal pipe material <NUM> has reached the target temperature. Therefore, the proximity switch <NUM> is disposed at the expected arrival position of the end portion 14a. Further, the control unit <NUM> stops the energization heating at a timing when the proximity switch <NUM> has detected the proximity of the end portion 14a. In this way, the control unit <NUM> can appropriately stop the energization heating at a timing when the metal pipe material <NUM> has reached the target temperature, based on the detection result of the proximity switch <NUM>.

As shown in <FIG>, the forming apparatus may include a limit switch <NUM> which detects the contact with the end portion 14a of the metal pipe material <NUM>. Also in this case, the end portion 14a is an end portion on the electrode <NUM> side where the movement restriction mechanism is not provided, and the movement of the metal pipe material <NUM> is restricted by the movement restriction mechanism on the other electrode <NUM> side. The limit switch <NUM> detects the arrival of the end portion 14a by coming into contact with the end portion 14a when the end portion 14a has reached the expected arrival position described above. A kicker portion (a contact portion with the end portion 14a) of the limit switch <NUM> is formed of a heat-resistant insulating material, for example, alumina ceramics. The control unit <NUM> stops the energization heating at a timing when the limit switch <NUM> has detected the contact with the end portion 14a. In this way, the control unit <NUM> can appropriately stop the energization heating at a timing when the metal pipe material <NUM> has reached the target temperature, based on the detection result of the limit switch <NUM>.

As shown in <FIG>, the forming apparatus may include an imaging unit <NUM> that is a camera-type sensor which detects the amount of movement of the end portion 14a of the metal pipe material <NUM> in a non-contact manner. In this case, the end portion 14a is an end portion on the electrode <NUM> side where the movement restriction mechanism is not provided, and the movement of the metal pipe material <NUM> may be restricted by the movement restriction mechanism on the other electrode <NUM> side. However, in a case where the imaging unit <NUM> is used, the movement of the metal pipe material <NUM> due to expansion may be allowed in both the electrodes <NUM> and <NUM> (a specific example will be described later). The imaging unit <NUM> can detect the position of the end portion 14a, that is, the amount of movement of the end portion 14a, by acquiring the image of the end portion 14a. Therefore, the imaging unit <NUM> detects the arrival of the end portion 14a at the expected arrival position described above, based on the acquired image. The disposition of the imaging unit <NUM> is not particularly limited as long as the image of the end portion 14a can be acquired, and may be disposed at a position away from an energization heating portion. Therefore, the imaging unit <NUM> may not be a high magnetic field resistant sensor, like the proximity switch <NUM>. The control unit <NUM> stops the energization heating at a timing when the imaging unit <NUM> has detected the arrival of the end portion 14a at the expected arrival position. In this way, the control unit <NUM> can appropriately stop the energization heating at a timing when the metal pipe material <NUM> has reached the target temperature, based on the detection result of the imaging unit <NUM>.

Further, the configuration shown in <FIG> may be adopted as a forming apparatus according to a modification example. A movement restriction mechanism shown in <FIG> includes a restriction member (a first restriction member) <NUM> which restricts the movement of the metal pipe material <NUM> by coming into contact with the end portion (a first end portion) 14a on the electrode <NUM> side in the axial direction of the metal pipe material <NUM>, and a restriction member (a second restriction member) <NUM> which restricts the movement of the metal pipe material <NUM> by coming into contact with an end portion (a second end portion) 14b on the electrode <NUM> side in the axial direction of the metal pipe material <NUM>. Further, the forming apparatus includes an imaging unit <NUM> which detects the amount of movement of the end portion 14a, and an imaging unit <NUM> which detects the amount of movement of the end portion 14b.

The control unit <NUM> is electrically connected to the imaging units <NUM> and <NUM> and can receive the amount of movement of each of the end portions 14a and 14b detected by each of the imaging units <NUM> and <NUM>. Further, the control unit <NUM> is electrically connected to the electrodes <NUM> and <NUM> and can control the energization heating of the electrodes <NUM> and <NUM> and the opening and closing of a clamp.

The restriction member <NUM> has a contact surface 210a which extends substantially perpendicular to the axial direction so as to face the end portion 14a. The restriction member <NUM> has a contact surface 211a which extends substantially perpendicular to the axial direction so as to face the end portion 14b. The restriction members <NUM> and <NUM> can be moved in the axial direction by a drive unit (not shown). The control unit <NUM> is electrically connected to the restriction members <NUM> and <NUM> and can control the movements of the restriction members <NUM> and <NUM> in the axial direction.

In the state before the energization heating, the restriction members <NUM> and <NUM> are disposed at positions separated from the respective end portions 14a and 14b in the axial direction. At this time, a separation distance L1 in the axial direction between the contact surface 210a and the contact surface 211a is set to be substantially the same as the full length of the metal pipe material <NUM> when the metal pipe material <NUM> has reached the target temperature (the full length of the metal pipe material <NUM> in the state of <FIG>) In <FIG>, the protrusion amount of the end portion 14a from the electrode <NUM> and the protrusion amount of the end portion 14b from the electrode <NUM> are the same, and therefore, the separation distance of the restriction member <NUM> from the end portion 14a and the separation distance of the restriction member <NUM> from the end portion 14b are set to be the same. However, depending on the relationship between the protrusion amount of the end portion 14a from the electrode <NUM> and the protrusion amount of the end portion 14b from the electrode <NUM>, the separation distance of the restriction member <NUM> from the end portion 14a and the separation distance of the restriction member <NUM> from the end portion 14b may not be the same.

The electrodes <NUM> and <NUM> according to this modification example do not have the movement restriction mechanisms as shown in <FIG> and <FIG>. Therefore, if the energization heating is started from the state before the energization heating in <FIG>, the metal pipe material <NUM> expands toward both sides in the axial direction. Both the end portion 14a and the end portion 14b move outward in the axial direction. As shown in <FIG>, in a case where the end portion 14a has come into contact with the restriction member <NUM>, the end portion 14a stops at the position, and the amount of movement of the end portion 14a does not increase any more. Further, in a case where the end portion 14b has come into contact with the restriction member <NUM>, the end portion 14b stops at the position, and the amount of movement of the end portion 14b does not increase any more.

For example, in a case where a timing when the end portion 14a comes into contact with the restriction member <NUM> and a timing when the end portion 14b comes into contact with the restriction member <NUM> are substantially the same, the restriction members <NUM> and <NUM> can control the amount of expansion such that the metal pipe material <NUM> does not extend any more due to expansion.

Further, for example, in a case where the end portion 14a first comes into contact with the restriction member <NUM>, the movement of the end portion 14a is restricted by the restriction member <NUM>. Thereafter, the metal pipe material <NUM> expands from the electrode <NUM> side toward the electrode <NUM> side with the position of the end portion 14a in which the movement has been restricted as the reference. Thereafter, the end portion 14b comes into contact with the restriction member <NUM>. In this way, the restriction members <NUM> and <NUM> can control the amount of expansion such that the metal pipe material <NUM> does not extend any more due to expansion. In this manner, in a case where a difference occurs in the timing of the contact with the restriction member between the end portion 14a and the end portion 14b, it is preferable that the difference in the timing is within the range of a predetermined allowable value such that buckling does not occur in the metal pipe material <NUM>. The operation in a case where it does not fall within the range of the allowable value will be described later with reference to <FIG>, <FIG>, and <FIG>. Alternatively, in a case where a difference occurs in the timing of the contact with the restriction member between the end portion 14a and the end portion 14b, it is preferable that the electrodes <NUM> and <NUM> have a configuration in which the metal pipe material <NUM> can easily slide in the axial direction (a configuration in which a clamping force is loosened, or a configuration in which a frictional force is reduced).

As described above, the separation distance L1 between the restriction members <NUM> and <NUM> is set to the full length of the metal pipe material <NUM> when the metal pipe material <NUM> has reached the target temperature. Therefore, when the end portion 14a has come into contact with the restriction member <NUM> and the end portion 14b has come into contact with the restriction member <NUM>, the control unit <NUM> recognizes that the metal pipe material <NUM> has reached the target temperature, based on the contact of the end portion 14a with the restriction member <NUM> and the contact of the end portion 14b with the restriction member <NUM>. The control unit <NUM> grasps that the end portion 14a has come into contact with the restriction member <NUM> and that the end portion 14b has come into contact with the restriction member <NUM>, based on the detection results of the imaging units <NUM>. At this time, the control unit <NUM> stops the energization heating by the electrodes <NUM> and <NUM>. In the example shown in <FIG>, the separation distance of the restriction member <NUM> from the electrode <NUM> and the separation distance of the restriction member <NUM> from the electrode <NUM> are set to be the same. Therefore, the amount of movement of the end portion 14a of the metal pipe material <NUM>, that is, the amount of elongation due to expansion on the end portion 14a side, and the amount of movement of the end portion 14b of the metal pipe material <NUM>, that is, the amount of elongation due to expansion on the end portion 14b side, become uniform.

As described above, in the forming apparatus according to the modification example, the movement restriction mechanism includes the restriction member <NUM> which restricts the movement of the metal pipe material <NUM> by coming into contact with the end portion 14a on the electrode <NUM> side in the axial direction of the metal pipe material <NUM>, and the restriction member <NUM> which restricts the movement of the metal pipe material <NUM> by coming into contact with the end portion 14b on the electrode <NUM> side in the axial direction of the metal pipe material <NUM>. In this way, the movement of the end portion 14a of the metal pipe material <NUM> due to expansion is restricted by the restriction member <NUM>, and the movement of the end portion 14b of the metal pipe material <NUM> due to expansion is restricted by the restriction member <NUM>. The movement restriction mechanism can control the amount of movement of each of the end portions 14a and 14b of the metal pipe material <NUM> on both sides of the electrode <NUM> and the electrode <NUM>. By the above, it is possible to control the form of expansion of the metal pipe material <NUM> with respect to the electrodes <NUM> and <NUM> on both sides.

In the embodiment described above, the metal pipe material <NUM> has a shape extending straight. However, it may have a shape curved as a whole. In this case, a temperature difference easily occurs in the metal pipe material <NUM>, so that the form of expansion becomes further complicated. Even in such a case, the form of expansion of the curved metal pipe material can also be appropriately controlled by using the forming apparatus according to the modification example.

The forming apparatus further includes the control unit <NUM> which controls the heating by the electrode <NUM> and the electrode <NUM>, and the control unit <NUM> recognizes that the metal pipe material <NUM> has reached the target temperature, based on the contact of the end portion 14a with the restriction member <NUM> and the contact of the end portion 14b with the restriction member <NUM>. In this way, the control unit <NUM> can control the amount of movement of both end portions of the metal pipe material <NUM> by the restriction member <NUM> and the restriction member <NUM> and can also control a timing of the stop of the heating.

The forming apparatus further includes the imaging units <NUM> that are non-contact type detection units which detect the positions of the end portion 14a and the end portion 14b in a non-contact manner, thereby detecting the contact of the end portion 14a with the restriction member <NUM> and the contact of the end portion 14b with the restriction member <NUM>. In this case, even if a complicated detection mechanism (a mechanism for detecting a load acting on each of the restriction members <NUM> and <NUM>) or the like is not provided in each of the restriction member <NUM> and the restriction member <NUM>, it is possible to detect the contact of the metal pipe material <NUM> with the restriction members <NUM> and <NUM>. However, the forming apparatus may detect the contact with the end portions 14a and 14b by a mechanism for detecting a load acting on each of the restriction members <NUM> and <NUM>, instead of the imaging unit <NUM>.

Here, in a case where the amount of movement of one end portion of the end portion 14a and the end portion 14b of the metal pipe material <NUM> is excessively larger than the amount of movement of the other end portion, depending on the frictional force between the electrodes <NUM> and <NUM> and the metal pipe material <NUM>, a load between the end portion which tries to move due to expansion and the restriction member becomes large. In this case, there is also a possibility that buckling may occur in the metal pipe material <NUM>. Therefore, the control unit <NUM> may perform control as shown in <FIG>, <FIG>, and <FIG>, in order to suppress such buckling.

The control unit <NUM> can detects that the amount of movement of one end portion of the end portion 14a and the end portion 14b of the metal pipe material <NUM> is larger than the amount of movement of the other end portion. In a case where the control unit <NUM> has detected that the amount of movement of one end portion is larger than the amount of movement of the other end portion, the control unit <NUM> moves the restriction member <NUM> and the restriction member <NUM> from the other end portion side to the one end portion side.

For example, as shown in <FIG>, in a case where the amount of movement of the end portion 14a is excessively larger than the amount of movement of the end portion 14b, the end portion 14a comes into contact with the restriction member <NUM> in an early stage in spite of a state where the separation distance between the end portion 14b and the restriction member <NUM> is large. In such a case, the control unit <NUM> detects that the amount of movement of the end portion 14a is excessively larger than the amount of movement of the end portion 14b. A detection method in which the control unit <NUM> detects the above matter is not particularly limited. However, the following methods may be adopted. For example, the control unit <NUM> may determine whether or not the separation distance between the end portion 14b and the restriction member <NUM> at the time of the contact of the end portion 14a exceeds a threshold. Or, the control unit <NUM> may count a contact time from the point in time of the contact of the end portion 14a and determine whether or not the count exceeds a threshold. Alternatively, in a case where a load acting on the restriction member <NUM> can be detected, the control unit <NUM> may detect a load that the restriction member <NUM> receives from the end portion 14a due to the expansion of the metal pipe material <NUM> and determine whether or not the load has exceeded a threshold.

As shown in <FIG>, in a case where the control unit <NUM> has detected that the amount of movement of the end portion 14a is larger than the amount of movement of the end portion 14b, the control unit <NUM> moves the restriction member <NUM> and the restriction member <NUM> from the end portion 14b side to the end portion 14a side. At this time, a moving method when the control unit <NUM> moves the restriction members <NUM> and <NUM> is not particularly limited, and various methods may be adopted. For example, the control unit <NUM> may estimate an expected arrival position of the end portion 14a and an expected arrival position of the end portion 14b when the metal pipe material <NUM> has reached a target temperature, and move the restriction members <NUM> and <NUM> to the expected arrival positions. In the example shown in <FIG>, the restriction members <NUM> and <NUM> have moved to the expected arrival positions of the end portions 14a and 14b. The estimation method is not particularly limited. However, the control unit <NUM> may perform the estimation, based on the separation distance between the end portion 14b and the restriction member <NUM> at the time of the contact of the end portion 14a, a time from the start of the energization heating until the end portion 14a comes into contact with the restriction member <NUM>, or the like. The control unit <NUM> may not perform a direct change from the state shown in <FIG> to the state shown in <FIG>. For example, the control unit <NUM> may greatly separate the restriction members <NUM> and <NUM> from the end portions 14a and 14b. once after the end portion 14a comes into contact with the restriction member <NUM>. Thereafter, the control unit <NUM> may move the restriction members <NUM> and <NUM> to the expected arrival positions after the calculation is completed.

Thereafter, the end portions 14a and 14b further move to the outside in the axial direction and come into contact with the restriction members <NUM> and <NUM> when the metal pipe material <NUM> has reached the target temperature, as shown in <FIG>. In this way, the restriction members <NUM> and <NUM> can control the amount of expansion such that the metal pipe material <NUM> does not extend any more due to expansion. Further, the control unit <NUM> stops the energization heating by the electrodes <NUM> and <NUM> at the timing.

The control unit <NUM> may not move the restriction members <NUM> and <NUM> to the expected arrival positions of the end portions 14a and 14b, as shown in <FIG>. For example, when the end portion 14a has come into contact with the restriction member <NUM>, the control unit <NUM> may move the restriction member <NUM> so as to be separated from the end portion 14a by a certain distance. At the same time, the control unit <NUM> moves the restriction member <NUM> so as to approach the end portion 14b by the same distance. The control unit <NUM> may repeat the movement of the restriction members <NUM> and <NUM> by such a constant distance until the end portions 14a and 14b come into contact with the restriction members <NUM> and <NUM> substantially at the same time. Alternatively, the control unit <NUM> may cause the drive unit of the restriction member <NUM> to be in a free state, and move the restriction member <NUM> by the amount pushed to the end portion 14a. On the other hand, the control unit <NUM> moves the restriction member <NUM> so as to approach the end portion 14b by the same distance as the distance by which the restriction member <NUM> is pushed to the end portion 14a. The control unit <NUM> locks the positions of the restriction members <NUM> and <NUM> at the point in time when the end portion 14b has come into contact with the restriction member <NUM>.

As shown in <FIG>, after the metal pipe material <NUM> reaches the target temperature, the control unit <NUM> stops the energization heating. Therefore, the metal pipe material <NUM> is cooled, whereby the metal pipe material <NUM> contracts from a state where the amount of expansion is the largest (the state of <FIG>), as shown in <FIG>. Therefore, the end portions 14a and 14b move inward in the axial direction and move so as to be separated from the restriction members <NUM> and <NUM>. In this state, since the energization heating has been ended, the electrodes <NUM> and <NUM> may not completely clamp the metal pipe material <NUM>. Therefore, as shown in <FIG>, the clamping forces of the electrodes <NUM> and <NUM> with respect to the metal pipe material <NUM> are relaxed. The control unit <NUM> moves the restriction members <NUM> and <NUM> inward in the axial direction so as to come into contact with the end portions 14a and 14b. Then, as shown in <FIG>, the control unit <NUM> performs alignment of the metal pipe material <NUM> by moving the entire metal pipe material <NUM> in the axial direction by pushing the end portion 14a toward the end portion 14b side with the restriction member <NUM>. The control unit <NUM> performs the alignment of the metal pipe material <NUM> such that the protrusion amount of the end portion 14a from the electrode <NUM> and the protrusion amount of the end portion 14b from the electrode <NUM> become uniform. In this way, when the metal pipe material <NUM> is formed in the forming die <NUM>, the metal pipe material <NUM> can be formed at an optimal position.

As describe above, the forming apparatus according to the modification example further includes the control unit <NUM> that controls the movements of the restriction member <NUM> and the restriction member <NUM> in the axial direction, and in a case where the control unit <NUM> has detected that the amount of movement of one end portion of the end portion 14a and the end portion 14b of the metal pipe material <NUM> is larger than the amount of movement of the other end portion, the control unit <NUM> moves the restriction member <NUM> and the restriction member <NUM> from the other end portion side to the one end portion side. In this case, in a case where the amount of movement of one end portion of the end portion 14a and the end portion 14b of the metal pipe material <NUM> becomes too larger than the amount of movement of the other end portion, it is possible to suppress a load which occurs between the metal pipe material <NUM> which tries to expand and the restriction member from becoming too large.

Further, in the forming apparatus, the control unit <NUM> may perform the alignment of the metal pipe material <NUM> in the axial direction by pushing the metal pipe material <NUM> in the axial direction with at least one of the restriction member <NUM> and the restriction member <NUM> after the stop of the heating by the electrode <NUM> and the electrode <NUM>. In this case, in a case where the amount of movement of one end portion of the end portion 14a and the end portion 14b of the metal pipe material <NUM> becomes too larger than the amount of movement of the other end portion, it is possible to align the metal pipe material <NUM> at a position suitable for forming after the stop of the heating, while suppressing the load acting on the metal pipe material <NUM> from becoming too large during the heating.

Claim 1:
A forming apparatus (<NUM>) which forms a metal pipe by expanding a metal pipe material (<NUM>), comprising:
a forming die (<NUM>) for forming the metal pipe;
a first electrode (<NUM>) and a second electrode (<NUM>) which clamp an outer peripheral surface of the metal pipe material (<NUM>) at both end sides and heat the metal pipe material (<NUM>) by causing an electric current to flow through the metal pipe material (<NUM>); and,
a first fluid supply unit (<NUM>) and a second fluid supply unit (<NUM>) which supply a fluid into the metal pipe material (<NUM>) heated by the first electrode (<NUM>) and the second electrode (<NUM>) to expand the metal pipe material (<NUM>),
characterized in that
at least one of the first electrode (<NUM>) and the second electrode (<NUM>) is provided with a movement restriction mechanism (<NUM>, <NUM>, <NUM>) which restricts a movement of the metal pipe material (<NUM>) in an axial direction of the metal pipe material (<NUM>) and controls a form of expansion of the metal pipe material (<NUM>) during heating of the metal pipe material (<NUM>), wherein the electrodes (<NUM>) and (<NUM>) are in contact with a part in the circumferential direction of the metal pipe material (<NUM>).