Patent Publication Number: US-2021162481-A1

Title: Expansion forming apparatus

Description:
RELATED APPLICATIONS 
     The contents of Japanese Patent Application No. 2018-186313, and of International Patent Application No. PCT/JP2019/037812, on the basis of each of which priority benefits are claimed in an accompanying application data sheet, are in their entirety incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     A certain embodiment of the present invention relates to an expansion forming apparatus. 
     Description of Related Art 
     An expansion forming apparatus that performs forming by mounting electrodes to both end portions in a longitudinal direction of a metal pipe material, increasing the temperature of the metal pipe material with Joule heating by energization, and supplying high-pressure air into the metal pipe material is known (refer to, for example, the related art). 
     SUMMARY 
     According to an embodiment of the present invention, there is provided an expansion forming apparatus that shapes a metal material with a die, including: 
     an electrode that comes into contact with the metal material and performs energization heating; and 
     an electrode mounting unit having an electrode movement actuator that moves the electrode along an extension direction of the metal material during heating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration diagram showing an expansion forming apparatus according to an embodiment of the present invention. 
         FIG. 2  is a front view of a pipe holding mechanism of the expansion forming apparatus of  FIG. 1 . 
         FIG. 3  is a left side view of the pipe holding mechanism. 
         FIG. 4  is a partially enlarged view of an electrode mounting unit provided in the pipe holding mechanism. 
         FIG. 5  is an operation explanatory diagram of the expansion forming apparatus. 
         FIG. 6  is an operation explanatory diagram of the expansion forming apparatus following  FIG. 5 . 
         FIG. 7  is an operation explanatory diagram of the expansion forming apparatus following  FIG. 6 . 
         FIG. 8  is an operation explanatory diagram of the expansion forming apparatus following  FIG. 7 . 
         FIG. 9  is an operation explanatory diagram of the expansion forming apparatus following  FIG. 8 . 
         FIG. 10  is an operation explanatory diagram of the expansion forming apparatus following  FIG. 9 . 
         FIG. 11  is an operation explanatory diagram of the expansion forming apparatus following  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     As described above, in a case where the temperature of the metal pipe material is increased due to the Joule heating by energization, the metal pipe material extends in the longitudinal direction thereof due to thermal expansion. In that case, in a case where both end portions of the metal pipe material are restrained by the electrodes, stress is generated in the longitudinal direction of the metal pipe material to cause deformation, and further, buckling occurs, so that there is a concern that forming failure may occur. 
     It is desirable to perform expansion forming of an appropriate metal material. 
     According to the present invention, even in a case where the metal material extends in the longitudinal direction thereof due to thermal expansion of the energization heating, the electrode can be moved along the extension direction of the metal material by the electrode movement actuator, and therefore, it becomes possible to effectively avoid deformation or buckling of the metal material and perform good expansion forming. 
     An embodiment of the present invention will be described based on the drawings. 
     This embodiment exemplifies an expansion forming apparatus  10  that shapes a metal pipe as a metal material by blow forming.  FIG. 1  is a schematic configuration diagram showing the expansion forming apparatus  10 . 
     Overview of Expansion Forming Apparatus 
     The expansion forming apparatus  10  is installed on a horizontal plane. Then, the vertical upper side with respect to the horizontal plane on which the expansion forming apparatus  10  is installed is referred to as “top”, the vertical lower side is referred to as “bottom”, one side in one direction parallel to the horizontal plane (the left side on the paper surface of  FIG. 1 ) is referred to as “left”, and the opposite side (the right side on the paper of  FIG. 1 ) is referred to as “right”. Further, the front side which is perpendicular to the paper surface of  FIG. 1  is referred to as “front” and the back side is referred to as “rear”. 
     The expansion forming apparatus  10  includes a blow-forming die  13  composed of a lower die  11  and an upper die  12  which are paired with each other, an upper die drive mechanism  80  that moves the upper die  12 , a pair of pipe holding mechanisms  20  that respectively hold a right end portion and a left end portion of a metal pipe material P on both the right and left sides with the lower die  11  and the upper die  12  interposed therebetween, a water circulation mechanism  14  that forcibly cools the blow-forming die  13  with water, a control device  100  that controls each of the above configurations, and a base stage  15  that supports almost the entire configuration of the apparatus on the upper surface. 
     The expansion forming apparatus  10  is installed such that the upper surface of the base stage  15  is horizontal. 
     The lower die  11  is configured with a steel block, has a recessed portion  111  provided on the upper surface thereof to correspond to a forming shape, and has a cooling water passage  112  formed in the interior. 
     The upper die  12  is configured with a steel block, has a recessed portion  121  provided on the lower surface thereof to correspond to the forming shape, and has a cooling water passage  122  formed in the interior. 
     The water circulation mechanism  14  is connected to the cooling water passages  112  and  122 , and cooling water is supplied thereto by a pump. 
     In a state where the lower die  11  and the upper die  12  are in close contact with each other, the recessed portion  111  and the recessed portion  121  form a space having a target shape into which the metal pipe material P is to be formed. 
     The target shape is a shape which is curved or bent in the middle with respect to a linear shape parallel to the right-left direction, so that both right and left end portions are inclined downward. The metal pipe material P is bent or curved in the same manner as the target shape. However, the metal pipe material P has an outer diameter smaller than that of the target shape over the entire length, and is formed into the target shape in the process of expansion forming. 
     Therefore, the metal pipe material P is held by the pair of pipe holding mechanisms  20  such that both end portions thereof are directed in the same direction as the target shapes by the lower die  11  and the upper die  12 . 
     Specifically, the right end portion of the metal pipe material P is held by the pipe holding mechanism  20  on the right side so as to be inclined slightly downward with respect to the right direction to be directed diagonally downward to the right. Further, the left end portion of the metal pipe material P is held by the pipe holding mechanism  20  on the left side so as to be inclined slightly downward with respect to the left direction to be directed diagonally downward to the left. 
     A lower die holder  97 , a lower die base plate  98 , and a slide  92 , which are stacked in order downward, are provided on the lower side of the lower die  11 . 
     The upper die drive mechanism  80  includes a first upper die holder  86 , a second upper die holder  87 , and an upper die base plate  88 , which are stacked in order upward from the upper side of the upper die  12 . 
     Further, the upper die drive mechanism  80  includes a slide  82  that moves the upper die  12  such that the upper die  12  and the lower die  11  are combined with each other, a pull-back cylinder  85  as an actuator that generates a force for pulling the slide  82  upward, a main cylinder  84  as a drive source for lowering and pressurizing the slide  82 , a hydraulic pump  81  that supplies pressure oil to the main cylinder  84 , a servomotor  83  that controls the amount of fluid with respect to the hydraulic pump  81 , a hydraulic pump (not shown) that supplies pressure oil to the pull-back cylinder  85 , and a motor (not shown) that serves as a drive source of the hydraulic pump. 
     The slide  82  is equipped with a position sensor such as a linear sensor for detecting a position in an up-down direction and a movement speed, and a load sensor such as a load cell for detecting the load of the upper die  12 . 
     The position sensor or the load sensor of the upper die drive mechanism  80  is not essential and can be omitted. 
     Further, in a case where hydraulic pressure is used in the upper die drive mechanism  80 , a measurement device that measures the hydraulic pressure can be used instead of the load sensor. 
     The control device  100  includes a CPU (Central Processing Unit), a storage device that stores a control program and control data, and a memory in which the CPU expands the data. In the control device  100 , the CPU executes the control program in the storage device to execute the forming operation control by the expansion forming apparatus  10 . 
     Further, the expansion forming apparatus  10  includes a radiation thermometer  102  for measuring the temperature of the metal pipe material P. However, the radiation thermometer is only an example of a temperature detection unit, and a contact type temperature sensor such as a thermocouple may be provided. 
     Pipe Holding Mechanism: Schematic Configuration 
     The pipe holding mechanism  20  is disposed one on each of the right and left sides of the blow-forming die  13  (hereinafter, simply referred to as a die  13 ) on the base stage  15 . 
     The pipe holding mechanism  20  on the right side holds one end portion directed diagonally downward to the right, of the metal pipe material P in which the direction thereof is determined by the die  13 , and the pipe holding mechanism  20  on the left side holds the other end portion directed diagonally downward to the left, of the metal pipe material P in which the direction thereof is determined by the die  13 . 
     The pipe holding mechanism  20  on the right side and the pipe holding mechanism  20  on the left side have the same structure except that the configuration of each of them is fixed on the base stage  15  at an angle adjusted according to the inclination of each of the end portions of the metal pipe material P to be held. Therefore, the following description is mainly performed on the pipe holding mechanism  20  on the right side. 
       FIG. 2  is a front view of the pipe holding mechanism  20  on the right side,  FIG. 3  is a left side view, and  FIG. 4  is a partially enlarged view of an electrode mounting unit  30  (described later). The pipe holding mechanism  20  on the right side is installed on the upper surface of the base stage  15  in a state where the entire configuration thereof is inclined according to the inclination angle of the right end portion of the metal pipe material P to be held, as described above. However, in  FIGS. 2 to 4 , for simplification and clarification of the description, the pipe holding mechanism  20  is shown in a state where the entire configuration thereof is not inclined, that is, in a direction in which the pipe holding mechanism  20  holds the right end portion of the metal pipe material P parallel to the right-left direction. 
     The pipe holding mechanism  20  includes a lower electrode  21  and an upper electrode  22  which are a pair of electrodes that grip the right end portion of the metal pipe material P, a nozzle  23  that supplies a compressed gas from the right end portion to the inside of the metal pipe material P, the electrode mounting unit  30  that supports the lower electrode  21  and the upper electrode  22 , a nozzle mounting unit  40  that supports the nozzle  23 , a lifting and lowering mechanism.  50  that lifts and lowers the lower electrode  21 , the upper electrode  22 , and the nozzle  23 , and a unit base  24  that supports all of these configurations. 
     Pipe Holding Mechanism: Unit Base 
     The unit base  24  is a rectangular plate-shaped block when viewed in a plan view, which supports the electrode mounting unit  30  and the nozzle mounting unit  40  on the upper surface through the lifting and lowering mechanism  50 . 
     The unit base  24  can be mounted on and dismounted from the upper surface of the base stage  15 , which is a horizontal plane, by fixing means such as a bolt. 
     The pipe holding mechanism  20  has a plurality of unit bases  24  in which the inclination angles of the upper surfaces are different from each other, and by exchanging these unit bases, it is possible to collectively change and regulate the inclination angles of the lower electrode  21 , the upper electrode  22 , the nozzle  23 , the electrode mounting unit  30 , the nozzle mounting unit  40 , and the lifting and lowering mechanism  50 . 
     Then, in this way, the unit base  24  performs adjustment such that the electrode mounting unit  30  can move the lower electrode  21  and the upper electrode  22  along the extension direction of each end portion of the metal pipe material P having a direction that is defined by the blow-forming die  13 . 
     The “extension direction of an end portion” refers to a direction in which the center line at the one-side end portion of the metal pipe material P linearly extends, or a vector direction along the direction in which the one-side end portion of the metal pipe material P is directed. 
     Further, similarly, the unit base  24  performs adjustment such that the nozzle mounting unit  40  can move the nozzle  23  along the extension direction of each end portion of the metal pipe material P having a direction that is defined by the blow-forming die  13 . 
     That is, the unit base  24  functions as an electrode adjustment unit and a nozzle adjustment unit. 
     As described above, in a case where the extension direction of the center line of the right end portion of the metal pipe material P which is defined by the blow-forming die  13  is a direction diagonally downward to the right (there is no inclination in the front-rear direction), the upper surface of the unit base  24  is an inclined surface inclined in the direction in which the right side is lowered with respect to the horizontal plane around an axis along the front-rear direction, and the inclination angle thereof coincides with the inclination angle of the extension direction of the right end portion of the metal pipe material P. 
     Pipe Holding Mechanism: Lifting and Lowering Mechanism 
     The lifting and lowering mechanism  50  includes a pair of front and rear lifting and lowering frame bases  51  and  52  which are mounted on the upper surface of the unit base  24 , and a lifting and lowering actuator  53  that imparts a lifting and lowering motion to a lifting and lowering frame  31  of the electrode mounting unit  30 , which is supported by the lifting and lowering frame bases  51  and  52  so as to be able to move up and down along the direction perpendicular to the upper surface of the unit base  24 . 
     The lifting and lowering frame bases  51  and  52  are detachably mounted on the upper surface of the unit base  24  by fastening means such as a bolt. 
     Then, the lifting and lowering frame base  51  on the front side and the lifting and lowering frame base  52  on the rear side have three-dimensional shapes which are plane-symmetrical with a plane parallel to the up-down direction and the right-left direction as a symmetrical plane, as shown in  FIG. 3 . The lifting and lowering frame bases  51  and  52  each have a frame shape and support the lifting and lowering frame  31  between them such that it can move up and down along the direction perpendicular to the upper surface of the unit base  24 . 
     Further, both the lifting and lowering frame bases  51  and  52  have plate-shaped liners  54  and  55  on the left side and the right side, and plate-shaped liners  56  on the front side and the rear side. The liners  54  and  55  stably guide a lifting and lowering motion along the direction perpendicular to the upper surface of the unit base  24  with respect to the front-side portion and the rear-side portion of the lifting and lowering frame  31 . Further, the liners  56  stably guide a motion in the right-left direction. 
     Further, the lifting and lowering actuator  53  is a direct acting type actuator that imparts a reciprocating motion along the direction perpendicular to upper surface of the unit base  24  to the lifting and lowering frame  31 , and for example, a hydraulic cylinder or the like can be used. 
     Pipe Holding Mechanism: Electrode 
     Each of the lower electrode  21  and the upper electrode  22  is a rectangular plate-shaped electrode in which a plate-shaped conductor is sandwiched between insulating plates. 
     A semicircular cutout is formed in each of the upper end portion at the center of the lower electrode  21  and the lower end portion at the center of the upper electrode  22  so as to perpendicularly penetrate the flat plate surface. Then, when the lower electrode  21  and the upper electrode  22  are disposed on the same plane and the upper end portion of the lower electrode  21  and the lower end portion of the upper electrode  22  are brought into close contact with each other, the semicircular cutouts are combined to form a circular through-hole. This circular through-hole substantially coincides with the outer diameter of the end portion of the metal pipe material P, and when the metal pipe material P is energized, the end portion thereof is gripped by the lower electrode  21  and the upper electrode  22  in a state of being fitted into the circular through-hole. 
     Further, the lower electrode  21  is electrically connected to a power source  101  that is controlled by the control device  100 . The upper electrode  22  energizes the metal pipe material P through the lower electrode  21 . The power source  101  is controlled by the control device  100  to energize the lower electrodes  21  of the right and left pipe holding mechanisms  20 , and can rapidly heat the metal pipe material P by Joule heating. 
     The outer shape of the end portion of the metal pipe material P is not limited to a circular shape. Therefore, the cutout of each of the lower electrode  21  and the upper electrode  22  has a shape obtained by halving the outer shape of the end portion of the metal pipe material P. 
     Pipe Holding Mechanism: Electrode Mounting Unit 
     The electrode mounting unit  30  supports the lower electrode  21  and the upper electrode  22  while maintaining the direction in which the flat plate surfaces of the lower electrode  21  and the upper electrode  22  are perpendicular to the extension direction of the right end portion of the metal pipe material P described above. For example, as shown in  FIG. 2 , in a case where the upper surface of the unit base  24  is horizontal, the electrode mounting unit  30  supports the lower electrode  21  and the upper electrode  22  in the direction in which the flat plate surfaces of the lower electrode  21  and the upper electrode  22  become parallel in the up-down direction and the front-rear direction. 
     As shown in  FIGS. 2 to 4 , the electrode mounting unit  30  includes the lifting and lowering frame  31  that is subjected to the lifting and lowering motion along the direction perpendicular to the upper surface of the unit base  24  by the lifting and lowering mechanism  50  described above, a lower electrode frame  32  that holds the lower electrode  21  at the left end portion of the lifting and lowering frame  31 , and an upper electrode frame  33  that is provided above the lower electrode frame  32  and holds the upper electrode  22 . 
     The lower electrode frame  32  is a frame body that holds the outer periphery excluding the upper end portion of the lower electrode  21 . The lower electrode frame  32  is supported by the left end portion of the lifting and lowering frame  31  so as to be movable along the direction parallel to the right-left direction when viewed in a plan view and parallel to the upper surface of the unit base  24  through two linear guides  321  provided at the front and the rear. 
     Further, the lower electrode frame  32  is provided with a lower electrode movement actuator  322 , which imparts a moving motion along the moving direction by each linear guide  321 . For the lower electrode movement actuator  322 , for example, a hydraulic cylinder or the like can be used. 
     The lower electrode frame  32  is provided with a position sensor such as a linear sensor that detects a position in the moving direction by each linear guide  321 . 
     With these configurations, the lower electrode  21  can reciprocate along the extension direction of the right end portion of the metal pipe material P. 
     Slide blocks  34  that are movable along the direction parallel to the right-left direction when viewed in a plan view and parallel to the upper surface of the unit base  24  are individually provided on the upper surfaces of the front end portion and the rear end portion of the lower electrode frame  32  through linear guides  341 . 
     Further, the slide block  34  is provided with an upper electrode movement actuator  342  as a one-side electrode movement actuator that imparts a moving motion along the moving direction by each linear guide  341 . For the upper electrode movement actuator  342 , for example, a hydraulic cylinder or the like can be used. 
     The slide block  34  is provided with a position sensor such as a linear sensor that detects a position in the moving direction by each linear guide  341 . 
     The upper electrode frame  33  is a frame body that holds the outer periphery excluding the lower end portion of the upper electrode  22 . The upper electrode frames  33  is supported by each slide block  34  so as to be movable along the direction perpendicular to the upper surface of the unit base  24  through linear guides  331  provided two by two at the front and the rear at the upper portion of each slide block  34 . 
     Further, an upper electrode levitation spring  332  is interposed between the upper electrode frame  33  and each slide block  34 , and thus the upper electrode frame  33  is always pressed upward with respect to each slide block  34 . 
     The upper electrode frame  33  is movable in the direction (the up-down direction) perpendicular to the upper surface of the unit base  24  with respect to each slide block  34 . Then, each slide block  34  is movable in the direction (the right-left direction) parallel to the right-left direction when viewed in a plan view and parallel to the upper surface of the unit base  24  with respect to the lower electrode frame  32 . 
     Therefore, the upper electrode frame  33  is movable up and down with respect to the lower electrode frame  32  and is movable along the extension direction (the right-left direction) of the end portion of the metal pipe material P. 
     Then, clamp actuators  333  for lifting and lowering the upper electrode frame  33  along the direction perpendicular to the upper surface of the unit base  24  are provided one by one at the front and the rear at the lower electrode frame  32 . For each clamp actuator  333 , for example, a hydraulic cylinder or the like can be used. 
     A tip portion of a plunger of each clamp actuator  333  is connected to the upper electrode frame  33  so as to movable along the extension direction (the right-left direction) of the end portion of the metal pipe material P. Therefore, the moving motion of the upper electrode frame  33  with respect to the lower electrode frame  32  along the extension direction (the right-left direction) of the end portion of the metal pipe material P is not hindered. 
     Pipe Holding Mechanism: Nozzle 
     The nozzle  23  is a cylinder into which the end portion of the metal pipe material P can be inserted. The center line of the nozzle  23  is supported by the nozzle mounting unit  40  so as to be parallel to the extension direction of the end portion of the metal pipe material P. 
     The inner diameter of the end portion of the nozzle  23  on the metal pipe material P side substantially coincides with the outer diameter of the metal pipe material P after expansion forming. 
     The nozzle  23  is provided with a pressing force sensor that detects the pressing force of the contact of the metal pipe material P. 
     Pipe Holding Mechanism: Nozzle Mounting Unit 
     The nozzle mounting unit  40  is mounted on the right end portion of the lifting and lowering frame  31  of the electrode mounting unit  30 . Therefore, in a case where the lifting and lowering motion by the lifting and lowering mechanism  50  is performed, the nozzle mounting unit  40  moves up and down integrally with the electrode mounting unit  30 . 
     The nozzle mounting unit  40  supports the nozzle  23  at a position where the end portion of the metal pipe material P and the nozzle  23  become concentric, in a state where the lower electrode  21  and the upper electrode  22  of the electrode mounting unit  30  grip the end portion of the metal pipe material P. 
     For example, as shown in  FIG. 2 , in a case where the upper surface of the unit base  24  is horizontal, the nozzle mounting unit  40  supports the nozzle  23  in the direction in which the center line of the nozzle  23  is parallel to the right-left direction. 
     As shown in  FIG. 2 , the nozzle mounting unit  40  has a hydraulic cylinder mechanism as a nozzle movement actuator that moves the nozzle  23  along the extension direction of the end portion of the metal pipe material P. This hydraulic cylinder mechanism is provided with a piston  41  that holds the nozzle  23 , and a cylinder  42  that imparts a advancing and retreating movement to the piston  41 . 
     The cylinder  42  is fixedly mounted on the right end portion of the lifting and lowering frame  31  in the direction in which the piston  41  advances and retreats in parallel with the extension direction of the end portion of the metal pipe material P. The cylinder  42  is connected to a hydraulic circuit  43  ( FIG. 1 ), and pressure oil, which is a working fluid, is supplied to and discharged from the inside thereof. 
     In the hydraulic circuit  43 , the supply and discharge of the pressure oil to and from the cylinder  42  is controlled by the control device  100 . 
     The hydraulic circuit  43  is also connected to the pipe holding mechanism  20  on the left side. However, a path showing the connection is not shown in  FIG. 1 . 
     The piston  41  is provided with a main body  411  stored in the cylinder  42 , a head portion  412  protruding from the left end portion (the electrodes  21  and  22  side) of the cylinder  42  to the outside, and a tubular portion  413  protruding from the right end portion of the cylinder  42  to the outside. 
     The main body  411 , the head portion  412 , and the tubular portion  413  each have a cylindrical shape and are concentrically and integrally formed. 
     The outer diameter of the main body  411  substantially coincides with the inner diameter of the cylinder  42 . Then, in the cylinder  42 , hydraulic pressure is supplied to both sides of the main body  411  to advance and retreat the piston  41 . 
     The head portion  412  has a smaller diameter than the main body  411 , and the nozzle  23  is concentrically and fixedly mounted to the tip portion on the left side (the electrodes  21  and  22  side) of the head portion  412 . 
     The tubular portion  413  is a circular tube having a smaller diameter than the main body  411  and the head portion  412 . The tubular portion  413  penetrates the right end portion of the cylinder  42  and protrudes to the outside of the cylinder  42 . 
     The piston  41  is formed with a compressed gas flow path  414  that penetrates the center over the entire length from the head portion  412  to the tip of the tubular portion  413  through the main body  411 . Then, the tip portion (right end portion) of the tubular portion  413  is connected to a pneumatic circuit  44  ( FIG. 1 ) that supplies and discharges a compressed gas to and from the nozzle  23 . 
     The pneumatic circuit  44  is also connected to the pipe holding mechanism  20  on the left side. However, a path showing the connection is not shown in  FIG. 1 . 
     Further, the nozzle  23  provided at the tip portion of the head portion  412  communicates with the compressed gas flow path  414 . 
     That is, the nozzle mounting unit  40  has a structure capable of supplying the compressed gas to the nozzle  23  through the piston  41  from the side opposite to the nozzle  23 . 
     The flow path  414  in the piston  41  does not need to be provided, and a configuration is also acceptable in which the compressed gas is directly supplied to the nozzle  23 . 
     Forming Operation of Expansion Forming Apparatus 
     The expansion forming operation of the expansion forming apparatus  10  having the above configuration will be described based on the operation explanatory diagrams of  FIGS. 5 to 11 . 
     The forming operation described below is performed based on the operation control of the control device  100 . Then, the control device  100  includes a storage unit that stores a processing program and various types of information related to the operation control, and a processing device that executes the operation control, based on the processing program. 
     First, the unit base  24  whose upper surface is inclined in the direction corresponding to the extension direction of the end portion of the metal pipe material P according to the target shape determined by the die  13  is selected and mounted to each pipe holding mechanism  20 . Then, each pipe holding mechanism  20  is fixed to the upper surface of the base stage  15 . 
     Then, as shown in  FIG. 5 , the control device  100  controls the lower electrode movement actuators  322  of the right and left pipe holding mechanisms  20  to advance the lower electrodes  21  to the positions where they come into contact with the lower die  11 . 
     Further, the control device  100  controls the upper electrode movement actuators  342  of the right and left pipe holding mechanisms  20  to retract the upper electrodes  22  with respect to the lower electrodes  21  to the positions separated from the end portions of the metal pipe material P. 
     The metal pipe material P is placed on the right and left lower electrodes  21  disposed in this way so as to be fitted into the semicircular cutout. Further, since the upper electrode  22  has been retracted, it does not interfere with the work of placing the metal pipe material P. 
     The metal pipe material P placed on the lower electrode  21  is located slightly above the lower die  11  and is not in contact with the lower die  11 . 
     Next, as shown in  FIG. 6 , the control device  100  controls the upper electrode movement actuator  342  to move the upper electrode  22  to a gripping position above the lower electrode  21 . The gripping position of the upper electrode  22  is the position where the upper electrode  22  is lowered toward the lower electrode  21  side, so that the end portion of the metal pipe material P can be gripped by them. 
     Next, as shown in  FIG. 7 , the control device  100  controls the clamp actuator  333  to lower the upper electrode  22  toward the lower electrode  21 . In this way, the end portion of the metal pipe material P is fitted into the semicircular cutout of the upper electrode  22 , and is gripped by the lower electrode  21  and the upper electrode  22 . 
     In a state where both end portions of the metal pipe material P are individually gripped by the lower electrodes  21  and the upper electrodes  22  of the right and left pipe holding mechanisms  20 , the control device  100  controls the power source  101  to energize the respective lower electrodes  21 . In this way, the metal pipe material P is Joule-heated. 
     At this time, the control device  100  monitors the temperature of the metal pipe material P with the radiation thermometer  102  and performs heating for a defined time within a defined target temperature range. 
     Due to the Joule heating, the metal pipe material P is subjected to thermal expansion, and the end portion thereof extends in the extension direction thereof. 
     The control device  100  stores the correlation between the temperature and the amount of thermal extension of the metal pipe material P as data, and acquires the amount of thermal extension of the metal pipe material P, based on the temperature of the metal pipe material P detected by the radiation thermometer  102 , with reference to this correlation data. 
     Further, the control device  100  controls the lower electrode movement actuator  322  from the acquired amount of thermal extension to moves the lower electrode  21  and the upper electrode  22  of each pipe holding mechanism  20  to the position where stress is not applied to the metal pipe material P or the position where stress is sufficiently reduced. 
     By performing this electrode position control, the control device  100  functions as an electrode position control unit. 
     This electrode position control is periodically and repeatedly executed while the lower electrodes  21  of the right and left pipe holding mechanisms  20  are being energized. 
     The electrode position control may perform control in which the lower electrode  21  and the upper electrode  22  move with respect to the end portion of the metal pipe material P while applying a weak tension that does not deform the metal pipe material P in the direction of extending in the extension direction, without using the correlation data between the temperature and the amount of thermal extension of the metal pipe material P. 
     In that case, in a case where the lower electrode movement actuator  322  is, for example, a hydraulic cylinder, the lower electrode  21  and the upper electrode  22  may be moved in the direction of extending in the extension direction with the hydraulic pressure set to the low pressure described above. 
     When the energization of the metal pipe material P ends, the lower electrode  21  is separated from the lower die  11  by the electrode position control, so that a gap S 1  is generated, as shown in  FIG. 8 . 
     Therefore, as shown in  FIG. 9 , the control device  100  controls the clamp actuator  333  to move the upper electrode  22  up, and further controls the lower electrode movement actuator  322  to bring the lower electrode  21  and the upper electrode  22  closer to the die  13  side and bring the lower electrode  21  into contact with the lower die  11 . Then, the upper electrode  22  is moved down to perform gripping again. 
     In this way, the control device  100  functions as a re-gripping operation control unit (re-contact operation control unit) that performs re-gripping operation control. 
     Next, as shown in  FIG. 10 , the control device  100  controls the lifting and lowering actuator  53  to move the metal pipe material P down to the position where it comes into contact with or approaches the recessed portion  111  of the lower die  11 . 
     At this time, in a case where the upper surface of the unit base  24  is inclined with respect to the horizontal plane to correspond to the extension direction of the metal pipe material P, when a lowering operation is performed by the lifting and lowering actuator  53 , all the configurations on the lifting and lowering frame  31  perform a change in position in the right-left direction. For example, the pipe holding mechanism  20  on the right side moves to the right, and the pipe holding mechanism  20  on the left side moves to the left. 
     As a result, the lower electrode  21  is separated from the lower die  11  to generate a gap S 2 . 
     Therefore, the control device  100  controls the clamp actuator  333  to move the upper electrode  22  up, and further controls the lower electrode movement actuator  322  to move the lower electrode  21  and the upper electrode  22  so as to come into contact with the die  13  side. Then, the upper electrode  22  is moved down to grip the end portion of the metal pipe material P again. 
     That is, the control device  100  performs the re-gripping operation control once more. 
     As described above, the case where the control device  100  performs the re-gripping operation control twice has been exemplified. However, the first re-gripping operation control at the time of the end of energization of the metal pipe material P shown in  FIG. 8  is not executed, and the re-gripping operation control may be performed only once after the lower electrode  21  and the upper electrode  22  are moved down under the control of the lifting and lowering actuator  53 . 
     Thereafter, the control device  100  controls the servomotor  83  of the upper die drive mechanism  80  to move the upper die  12  down to the position where it comes into contact with the lower die  11 . 
     Further, the control device  100  controls the hydraulic circuit  43  to control the nozzle mounting units  40  of the right and left pipe holding mechanisms  20 , and advances each nozzle  23  toward each end portion side of the metal pipe material P. 
     In this way, as shown in  FIG. 11 , the end portion of the metal pipe material P is inserted into the tip portion of the nozzle  23 . 
     Then, the control device  100  controls the pneumatic circuit  44  to supply the compressed gas from the nozzle  23  into the metal pipe material P. In this way, the metal pipe material P whose hardness has been lowered due to the Joule heating is formed into the target shape in the die  13  by internal pressure. 
     On the other hand, the metal pipe material P shrinks as the temperature gradually decreases during the forming, and thus the end portion thereof moves to the die  13  side. 
     The control device  100  stores the correlation between the temperature and the amount of thermal extension of the metal pipe material P as data, as described above, and therefore, the control device  100  acquires the amount of shrinkage of the metal pipe material P, based on the temperature of the metal pipe material P detected by the radiation thermometer  102 , with reference to this correlation data. 
     Further, the control device  100  controls the hydraulic circuit  43  from the acquired amount of shrinkage to operate the nozzle mounting unit  40  and move the nozzle  23  to the die  13  side. More specifically, the end portion of the metal pipe material P is moved to follow the amount of shrinkage of the metal pipe material P so as not to come off from the nozzle  23 . 
     By performing the nozzle position control, the control device  100  functions as a nozzle position control unit. 
     The nozzle position control is periodically and repeatedly executed while the compressed gas is being supplied from the nozzle  23  into the metal pipe material P. 
     The nozzle position control may perform control in which an upper limit value is determined in advance within the range where the nozzle  23  does not give the influence of buckling, deformation, or the like to the end portion of the metal pipe material P and the nozzle  23  moves while applying a pressing force so as not to exceed the upper limit value, without using the correlation data between the temperature and the amount of thermal extension of the metal pipe material P. 
     Then, after the expansion forming is performed on the metal pipe material P by supplying the compressed gas for a certain period of time, the control device  100  stops the supply of the compressed gas, releases the gripping state by the lower electrode  21  and the upper electrode  22 , and moves the upper die  12  up. 
     Further, the control device  100  controls the upper electrode movement actuator  342  of each pipe holding mechanism  20  to retract the upper electrode  22  in the direction away from the die  13 . In this way, the formed metal pipe material P can be easily taken out from the expansion forming apparatus  10 . 
     Technical Effects of Embodiment of Invention 
     In the expansion forming apparatus  10 , the electrode mounting units  30  of a pair of pipe holding mechanisms  20  have the lower electrode movement actuators  322  that move the paired lower electrodes  21  and upper electrodes  22  along the extension direction of the end portion of the metal pipe material P. 
     Therefore, even in a case where the metal pipe material P extends due to the thermal expansion of Joule heating, the lower electrode  21  and the upper electrode  22  can be moved in the extension direction of the end portion of the metal pipe material P by the lower electrode movement actuator  322 , and thus it becomes possible to effectively suppress the occurrence of deformation or buckling of the metal pipe material. 
     Further, the expansion forming apparatus  10  is provided with the unit base  24  that adjusts the moving directions of the lower electrode  21  and the upper electrode  22  by the lower electrode movement actuator  322  so as to follow the extension direction of the end portion of the metal pipe material P disposed in the die  13 . 
     Therefore, even in a case where the metal pipe material P does not have a linear shape but is curved or bent, so that the end portion thereof extends in a non-horizontal direction, or a case where both end portions of the metal pipe material P extend in different directions, it is possible to move the lower electrode  21  and the upper electrode  22  along the extension direction. 
     Therefore, in the expansion forming apparatus  10 , it becomes possible to perform good expansion forming on the curved or bent metal pipe material P by suppressing the occurrence of deformation or buckling. 
     Further, the expansion forming apparatus  10  is provided with the radiation thermometer  102  that detects the temperature of the metal pipe material P, and the control device  100  performs control as the electrode position control unit that performs the position control of the lower electrode  21  and the upper electrode  22  by the lower electrode movement actuator  322  according to the temperature detected by the radiation thermometer  102  during the energization heating. 
     Therefore, in a case where the metal pipe material P extends due to the thermal expansion of Joule heating, it is possible to move the lower electrode  21  and the upper electrode  22  to appropriate positions corresponding to the extension, and it becomes possible to more effectively suppress the occurrence of deformation or buckling of the metal pipe material. 
     Further, the control device  100  can also perform control as the electrode position control unit that performs the position control of the lower electrode  21  and the upper electrode  22  while applying a defined tension to the end portion of the metal pipe material P by the lower electrode movement actuator  322  during the energization heating of the metal pipe material P. 
     In this case, in a case where the metal pipe material P extends due to the thermal expansion of Joule heating, it is possible to eliminate stress that hinders the extension by the lower electrode  21  and the upper electrode  22 , and it becomes possible to more effectively suppress the occurrence of deformation or buckling of the metal pipe material. 
     Further, in the expansion forming apparatus  10 , the electrode mounting unit  30  is provided with the upper electrode movement actuator  342  that moves the upper electrode  22  with respect to the lower electrode  21  along the extension direction of the end portion of the metal pipe material P. 
     The upper electrode  22  can be disposed to be shifted in position with respect to the lower electrode  21 , and in a case where the metal pipe material P is installed in or taken out from the expansion forming apparatus  10 , it becomes possible to facilitate work without the upper electrode  22  getting in the way. 
     In particular, in a case where the installation work of the metal pipe material P in the expansion forming apparatus  10  is performed using a robot or the like, it is possible to easily perform the installation work by controlling the upper electrode movement actuator  342 , and it becomes possible to provide an expansion forming apparatus suitable for automation. 
     Further, in the expansion forming apparatus  10 , the nozzle mounting unit  40  has a hydraulic cylinder mechanism as the nozzle movement actuator that moves the nozzle  23  along the extension direction of the end portion of the metal pipe material P. 
     In a case where the metal pipe material P is expanded with high-pressure air after the Joule heating by the lower electrode  21  and the upper electrode  22 , the expanded metal pipe material P shrinks due to a decrease in temperature. Even in such a case, the hydraulic cylinder mechanism of the nozzle mounting unit  40  can move the nozzle  23  to follow the end portion of the metal pipe material P that shrinks, and therefore, it becomes possible to suppress the detachment of the nozzle  23  or the leakage of the high-pressure air and to perform good expansion forming. 
     Further, also in the case of the nozzle mounting unit  40 , the moving direction of the nozzle  23  can be adjusted by the unit base  24  so as to follow the extension direction of the end portion of the metal pipe material P disposed in the die  13 , and therefore, the expansion forming apparatus  10  can perform good expansion forming by stably supplying the high-pressure air to the curved or bent metal pipe material P. 
     Further, in the expansion forming apparatus  10 , the control device  100  performs control as the nozzle position control unit that performs the position control of the nozzle  23  by the hydraulic cylinder mechanism of the nozzle mounting unit  40  according to the temperature detected by the radiation thermometer  102 , at the time of the supply of the compressed gas from the nozzle  23 . 
     Therefore, in a case where the metal pipe material P shrinks due to a decrease in temperature after the Joule heating, it is possible to move the nozzle  23  to an appropriate position in response to the shrinkage, and it becomes possible to more effectively suppress the detachment of the nozzle  23  or the leakage of the high-pressure air and perform good expansion forming. 
     Further, the control device  100  can also perform control as the nozzle position control unit that performs the position control of the nozzle while applying a pressing force within a range not exceeding an upper limit value determined in advance to the end portion of the metal pipe material P by the hydraulic cylinder mechanism of the nozzle mounting unit  40 , at the time of the supply of the compressed gas from the nozzle  23 . 
     In this case, in a case where the metal pipe material P shrinks due to a decrease in temperature after the Joule heating, the nozzle  23  can be moved to follow the end portion of the metal pipe material P that shrinks, while applying a certain pressing force, and therefore, it becomes possible to more effectively suppress the detachment of the nozzle  23  or the leakage of the high-pressure air and perform good expansion forming. 
     Further, in the nozzle mounting unit  40 , the compressed gas flow path  414  of the nozzle  23  is formed to penetrate from the piston  41  to the end portion of the cylinder  42  on the side opposite to the end portion side of the metal pipe material P. 
     Many configurations related to the forming of the metal pipe material P, such as the lower electrode  21 , the upper electrode  22 , and the electrode mounting unit  30 , are densely disposed around the nozzle  23 , and thus it is difficult to secure a space for installing a hose or a pipe for supplying the compressed gas to the movable nozzle  23 . 
     Therefore, by making the compressed gas flow path  414  penetrate to the end portion of the cylinder  42  on the side opposite to the end portion side of the metal pipe material P, it becomes possible to dispose the hose or the pipe for supplying the compressed gas while avoiding a region where various configurations are densely disposed. Further, in this way, it is possible to reduce the hose or the pipe interfering with other configurations when the nozzle  23  advances and retreats, and it becomes possible to stably perform the expansion forming while avoiding damage to each part. 
     Further, in the expansion forming apparatus  10 , the lifting and lowering mechanism  50  is provided with the lifting and lowering actuator  53  which lifts and lowers the lower electrode  21  and the upper electrode  22 . The lifting and lowering actuator  53  also lifts and lowers the nozzle  23  together with the lower electrode  21  and the upper electrode  22 . 
     Therefore, it becomes possible to perform the installation work or the removal work of the metal pipe material P with respect to the die  13 , and it becomes possible to facilitate and speed up the work. 
     Further, the height of the metal pipe material P with respect to the die  13  can also be adjusted by the lifting and lowering actuator  53 , and the adjustment work can be facilitated. 
     Further, the control device  100  of the expansion forming apparatus  10  performs control as the re-gripping operation control unit that changes the gripping position of the metal pipe material P by the lower electrode  21  and the upper electrode  22  to the position closer to the die side than the position at the time of the start of the energization heating between the start of the energization heating by the lower electrode  21  and the upper electrode  22  and the start of the supply of the compressed gas by the nozzle  23 . 
     Therefore, even in a case where a gap is generated between the lower electrode  21  and the upper electrode  22 , and the die  13 , due to the thermal expansion of the metal pipe material P, the gripping position is changed to the position closer to the die side, and therefore, it becomes possible to suppress the occurrence of the gap. 
     In that case, when a gap is generated, it becomes possible to suppress the occurrence of the expansion deformation of the gap portion due to the supply of the compressed gas to the metal pipe material P, and it becomes possible to maintain high forming quality. 
     Other 
     Each embodiment of the present invention has been described above. However, the present invention is not limited to each embodiment described above. The details shown in each embodiment can be appropriately changed within a scope which does not depart from the gist of the invention. 
     For example, in the embodiment described above, the expansion forming apparatus  10  provided with the main cylinder  84  based on hydraulic pressure as the drive source for moving the slide  82  has been exemplified. However, the drive source is not limited thereto. 
     For example, a configuration may be made in which a servomotor is provided as the drive source for performs the lifting and lowering motion of the slide  82  and provides the lifting and lowering motion to the slide  82  through a crank mechanism. 
     Further, the metal pipe material has been exemplified as the metal material. However, the forming target does not need to have a pipe shape. 
     Further, in the expansion forming apparatus  10 , the case where the extension direction of the end portion of the metal pipe material P, which is defined by the die  13 , is the direction inclined downward with respect to the right-left direction (the horizontal direction) has been exemplified. However, there is no limitation thereto. For example, the extension direction of the end portion of the metal pipe material P, which is defined by the die  13 , may be the direction inclined downward with respect to the right-left direction (the horizontal direction), or may be an oblique direction in which the front-rear direction, the right-left direction, and the up-down direction are combined. In either case, by using the unit base  24  in which the upper surface of the unit base  24  is inclined at an angle corresponding to a corresponding direction and the direction of the pipe holding mechanism  20  is rotated and adjusted around an axis along the up-down direction and fixed to the base stage  15 , it is possible to correspond to the extension direction of the end portion of the metal pipe material P inclined in each direction. 
     Further, in a case where the extension direction of the end portion of the metal pipe material P, which is defined by the die  13  is held in the inclined direction in which the right-left direction and the front-rear direction that are the horizontal directions are combined, the position displacement in the right-left direction does not occur when the lifting and lowering frame  31  is moved down, as in the case shown in  FIG. 10  which is the operation explanatory diagram described above, and therefore, the re-gripping operation control when the lifting and lowering frame  31  is moved down is not required and the operation control can be simplified. 
     Further, as the lifting and lowering mechanism  50  of the pipe holding mechanism  20 , the configuration has been exemplified in which the electrode mounting unit  30  and the nozzle mounting unit  40  are integrally moved up and down. However, a configuration may be made in which the electrode lifting and lowering actuator that moves the electrode mounting unit  30  up and down and the nozzle lifting and lowering actuator that moves the nozzle mounting unit  40  up and down are individually provided and they can be individually lifted and lowered, making it possible for the electrode mounting unit  30  and the nozzle mounting unit  40  to individually moves up and down. 
     Further, the case where the electrode position control unit, the nozzle position control unit, and the re-gripping operation control unit described above function as the respective control units by the execution of a program by the control device  100  has been exemplified. However, there is no limitation thereto. 
     For example, the electrode position control unit, the nozzle position control unit, and the re-gripping operation control unit may be configured with individual processing devices or individual circuits. 
     The expansion forming apparatus according to the present invention has industrial applicability for an expansion forming apparatus that heats a metal material with an electrode. 
     It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.