JP2022023127A - Electrification heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrification heating device capable of suppressing influences caused by arc discharge upon an electrode between a metal body and the electrode.

SOLUTION: Before heating a metal pipe material to a target temperature at a second current value C2, for a first predetermined time T1, power is supplied to an electrode at a first current value C1 that is smaller than the second current value C2. Therefore, if an electrical connection between the metal pipe material and the electrode is insufficient (e.g., if a gap is generated), weak arc discharge EA1 occurs and a surface of the electrode is molten without being damaged considerably, thereby short-circuiting the electrode and the metal pipe material. When the heating of the metal pipe material to the target temperature is started thereafter by supplying power to the electrode at the second current value C2, the electrode and the metal pipe material have been already short-circuited, such that arc discharge strong enough to considerably damage the surface of the electrode is prevented from occurring.

SELECTED DRAWING: Figure 3

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to an energizing heating device.

Conventionally, a molding apparatus for heating a metal pipe material, which is a metal body, and supplying a gas into the metal pipe material to form a metal pipe is known. As such a molding apparatus, for example, in Patent Document 1, a pair of molds, an electrode that is in contact with a metal pipe material arranged between the pair of molds and can be electrically connected, and an electrode are used as a metal pipe material. Described is a molding apparatus comprising a power supply unit capable of energizing a metal pipe material via electrodes in an electrically connected state. This molding device is an energization heating device that heats a metal pipe material by Joule heat generated by energizing the metal pipe material and molds the metal pipe material.

Japanese Patent Application Laid-Open No. 2015-112608

By the way, in the above-mentioned energization heating device, since a high current is passed to energize and heat the metal pipe material, there is no electrical connection between the metal pipe material and the electrode in contact with the metal pipe material. If it is sufficient (for example, if there is a gap), there is a high possibility that spark (arcing; hereinafter referred to as arc discharge) will occur. When a particularly strong arc discharge is generated, the surface of the electrode is damaged and becomes a resistance at the time of energization, which causes problems such as heat generation of the electrode itself and hindering the temperature rise of the metal pipe material.

Therefore, an object of the present invention is to provide an energization heating device capable of suppressing the influence of an arc discharge on an electrode between a metal body such as a metal pipe material and an electrode.

The electric current heating device according to the present invention is an electric current heating device that supplies electric power to a metal body and energizes and heats the metal body, and includes at least two electrodes that come into contact with the metal body and a power supply unit that supplies electric power to the electrodes. A control unit that controls the power supply unit is provided, and the control unit supplies power to the electrode at the first current value for the first predetermined time after starting the supply of power to the electrode. The power supply unit is controlled, and after the lapse of the first predetermined time, the power supply unit is controlled so as to supply power to the electrodes with a second current value larger than the first current value.

According to such an energization heating device, the first predetermined time after starting the supply of electric power to the electrodes before the electric power is supplied to the electrodes at the second current value to start heating the metal body to the target temperature. During that time, power is supplied to the electrodes at a first current value smaller than the second current value. This causes a weak arc discharge if the electrical connection between the metal body and the electrodes is inadequate (eg, if there is a gap). When a weak arc discharge occurs, the electrode surface melts but is not significantly damaged because the current value is small. Then, when the electrode surface melts, the electrode and the metal body are short-circuited, and the arc discharge disappears. After that, when power is supplied to the electrode at a second current value larger than the first current value and the metal body is started to be heated to the target temperature, the electrode and the metal body are already short-circuited, so that the electrode surface is touched. It is suppressed that a strong arc discharge that causes great damage is generated. Therefore, it is possible to suppress the influence of the arc discharge on the electrode between the metal body such as the metal pipe material and the electrode.

Here, the energization heating device includes a voltage measuring unit that measures the voltage between the electrodes, and the control unit controls the power supply unit so as to supply power to the electrodes by the second current value. When the occurrence of arc discharge between the electrode and the metal body is detected based on the voltage value between the electrodes measured by the voltage measuring unit, the third current smaller than the second current value for the second predetermined time. The power supply unit may be controlled so as to supply power to the electrode by the value, and the power supply unit may be controlled so as to supply power to the electrode by the second current value after the lapse of the second predetermined time. According to this, if power is supplied to the electrode at the first current value and a weak arc discharge is generated, it is sufficient to generate a strong arc discharge due to power being supplied to the electrode at the second current value. When the electrode and the metal body are not short-circuited to the extent that they can be suppressed and a strong arc discharge occurs, power is supplied to the electrode at a third current value smaller than the second current value for the second predetermined time. However, it suppresses the large damage to the electrode surface. Even if an arc discharge occurs in a state where power is supplied to the electrodes at this third current value, the arc discharge becomes a weak arc discharge. When a weak arc discharge occurs, the electrode surface melts again, but the current value is small, so that the electrode surface is not significantly damaged. Then, when the electrode surface melts, the electrode and the metal body are sufficiently short-circuited, and the arc discharge disappears. After that, when the electric power is supplied to the electrode again at the second current value, the electrode and the metal body are sufficiently short-circuited, so that the generation of a strong arc discharge is suppressed.

According to the present invention as described above, it is possible to provide an energization heating device capable of suppressing the influence of arc discharge on the electrode between the metal body and the electrode.

It is a schematic block diagram which shows the energization heating apparatus which concerns on one Embodiment of this invention. An enlarged view of the periphery of the electrode, (a) is a view showing a state in which the electrode holds a metal pipe material, (b) is a view showing a state in which a sealing member is pressed against the electrode, and (c) is a front view of the electrode. Is. It is a timing chart which shows the current and voltage at the time of energization heating, (a) is the figure which shows the supply current, (b) is the figure which shows the time-dependent change of voltage with respect to the supply current of (a).

Hereinafter, a preferred embodiment of the energization heating device according to the present invention will be described with reference to the drawings. In each figure, the same parts or corresponding parts are designated by the same reference numerals, and duplicate description will be omitted.

<Structure of molding equipment>
FIG. 1 is a schematic configuration diagram of a molding device as an energization heating device. As shown in FIG. 1, the molding apparatus 10 for molding a metal pipe moves at least one of a blow molding mold (mold) 13 including an upper mold 12 and a lower mold 11 and an upper mold 12 and a lower mold 11. Energize the drive mechanism 80 to cause the gas, the pipe holding mechanism 30 for holding the metal pipe material 14 arranged between the upper mold 12 and the lower mold 11, and the metal pipe material 14 held by the pipe holding mechanism 30. The heating mechanism 50 for heating, the gas supply unit 60 for supplying high-pressure gas (gas) into the heated metal pipe material 14 held between the upper mold 12 and the lower mold 11, and the pipe holding mechanism 30 hold the gas. A pair of gas supply mechanisms 40, 40 for supplying gas from the gas supply unit 60 into the metal pipe material 14, a water circulation mechanism 72 for forcibly cooling the blow molding mold 13, and an arc discharge are generated. In addition to being provided with a warning device 71 that issues a warning in the event of a problem, the drive mechanism 80 is driven, the pipe holding mechanism 30 is driven, the heating mechanism 50 is driven, the gas supply unit 60 is supplied with gas, and the warning device 71 is operated. A control unit 70 for controlling each of the above is provided.

The lower mold 11 which is one of the blow molding dies 13 is fixed to the base 15. The lower mold 11 is composed of a large steel block, and has, for example, a rectangular cavity (recess) 16 on the upper surface thereof. A cooling water passage 19 is formed in the lower mold 11, and a thermocouple 21 inserted from below is provided substantially in the center. The thermocouple 21 is supported by a spring 22 so as to be vertically movable.

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

An insulating material 91 for preventing energization is provided between the lower mold 11 and the lower electrode 17 and the lower portion of the lower electrode 17, and between the lower mold 11 and the lower electrode 18 and the lower portion of the lower electrode 18. Each is provided. Each of the insulating materials 91 is fixed to an advancing / retreating rod 95 which is a movable portion of an actuator (not shown) constituting the pipe holding mechanism 30. This actuator is for moving the lower electrodes 17, 18 and the like up and down, and the fixed portion of the actuator is held on the base 15 side together with the lower mold 11.

The upper mold 12, which is the other side of the blow molding mold 13, is fixed to a slide 81, which will be described later, which constitutes the drive mechanism 80. The upper mold 12 is composed of a large steel block, has a cooling water passage 25 formed therein, and has, for example, a rectangular cavity (recess) 24 on the lower surface thereof. The cavity 24 is provided at a position facing the cavity 16 of the lower mold 11.

Similar to the lower mold 11, a space 12a is provided in the vicinity of the left and right ends (left and right ends in FIG. 1) of the upper mold 12, and the space 12a is described later as a movable portion of the pipe holding mechanism 30. Electrodes 17, 18 (upper electrode) and the like are arranged so as to be able to move up and down. Then, in a state where the metal pipe material 14 is placed on the lower electrodes 17 and 18, the upper electrodes 17 and 18 are arranged between the upper mold 12 and the lower mold 11 by moving downward. Contact the metal pipe material 14. As a result, the upper electrodes 17 and 18 are electrically connected to the metal pipe material 14.

Insulating material 101 for preventing energization is provided between the upper mold 12 and the upper electrode 17 and the upper part of the upper electrode 17, and between the upper mold 12 and the upper electrode 18 and the upper part of the upper electrode 18, respectively. There is. Each insulating material 101 is fixed to an advancing / retreating rod 96 which is a movable portion of an actuator constituting the pipe holding mechanism 30. This actuator is for moving the upper electrodes 17, 18 and the like up and down, and the fixed portion of the actuator is held on the slide 81 side of the drive mechanism 80 together with the upper mold 12.

In the right side portion of the pipe holding mechanism 30, a semicircular concave groove 18a corresponding to the outer peripheral surface of the metal pipe material 14 is formed on each of the surfaces of the electrodes 18 and 18 facing each other (see FIG. 2). The metal pipe material 14 can be placed so as to fit into the portion of the concave groove 18a. In the right side portion of the pipe holding mechanism 30, a semicircular concave groove corresponding to the outer peripheral surface of the metal pipe material 14 is formed on the exposed surface where the insulating materials 91 and 101 face each other, similarly to the concave groove 18a. ing. Further, on the front surface of the electrode 18 (the surface in the outer direction of the mold), a tapered concave surface 18b having a tapered peripheral edge toward the concave groove 18a is formed. Therefore, when the metal pipe material 14 is sandwiched from the vertical direction by the right side portion of the pipe holding mechanism 30, it is configured so that the outer periphery of the right end portion of the metal pipe material 14 can be surrounded so as to be in close contact with the entire circumference. ing.

In the left side portion of the pipe holding mechanism 30, a semicircular concave groove 17a corresponding to the outer peripheral surface of the metal pipe material 14 is formed on each of the surfaces of the electrodes 17 and 17 facing each other (see FIG. 2). The metal pipe material 14 can be placed so as to fit into the portion of the concave groove 17a. In the left side portion of the pipe holding mechanism 30, a semicircular concave groove corresponding to the outer peripheral surface of the metal pipe material 14 is formed on the exposed surface where the insulating materials 91 and 101 face each other, similarly to the concave groove 18a. ing. Further, on the front surface of the electrode 17 (the surface in the outer direction of the mold), a tapered concave surface 17b having a tapered peripheral edge toward the concave groove 17a is formed. Therefore, when the metal pipe material 14 is sandwiched from the vertical direction by the left side portion of the pipe holding mechanism 30, it is configured so that the outer periphery of the left end portion of the metal pipe material 14 can be surrounded so as to be in close contact with the entire circumference. ing.

As shown in FIG. 1, the drive mechanism 80 includes a slide 81 for moving the upper die 12 so that the upper die 12 and the lower die 11 are aligned with each other, and a shaft 82 for generating a driving force for moving the slide 81. And a connecting rod 83 for transmitting the driving force generated by the shaft 82 to the slide 81. The shaft 82 extends in the left-right direction above the slide 81 and is rotatably supported, and the eccentric crank 82a that protrudes from the left-right end and extends in the left-right direction at a position separated from the axis thereof. Have. The eccentric crank 82a and the rotating shaft 81a provided on the upper part of the slide 81 and extending in the left-right direction are connected by a connecting rod 83. In the drive mechanism 80, the rotation of the shaft 82 is controlled by the control unit 70 to change the height of the eccentric crank 82a in the vertical direction, and the position change of the eccentric crank 82a is transmitted to the slide 81 via the connecting rod 83. Thereby, the vertical movement of the slide 81 can be controlled. Here, the swing (rotational motion) of the connecting rod 83 generated when the position change of the eccentric crank 82a is transmitted to the slide 81 is absorbed by the rotating shaft 81a. The shaft 82 rotates or stops according to the drive of a motor or the like controlled by, for example, the control unit 70.

The heating mechanism 50 includes a power supply unit 55, a bus bar 52 that electrically connects the power supply unit 55 and the electrodes 17 and 18, and a voltmeter 53 as a voltage measurement unit that measures the voltage between the electrodes 17 and 18. , Equipped with. The power supply unit 55 includes a DC power supply and a switch, and can energize the metal pipe material 14 via the bus bar 52 and the electrodes 17 and 18 in a state where the electrodes 17 and 18 are electrically connected to the metal pipe material 14. Has been done. Here, the bus bar 52 is connected to the lower electrodes 17 and 18, and the voltmeter 53 is connected to a position closer to the lower electrode 17 of the bus bar 52 and a position closer to the lower electrode 18 of the bus bar 52. It is connected to the. The power supply unit 55 is adapted to supply power of about 10,000 A20 V or more.

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

The voltage value measured by the voltmeter 53 (information from (B) shown in FIG. 1) is input to the arc discharge detection unit 70a of the control unit 70. The arc discharge detection unit 70a detects the occurrence of an arc discharge between the electrodes 17 and 18 and the metal pipe material 14 based on the voltage value measured by the voltmeter 53. When the arc discharge detection unit 70a detects the occurrence of an arc discharge, the control unit 70 sends a power adjustment command for adjusting the power to be output to the power supply unit 55 of the heating mechanism 50, and also sends a power adjustment command to the warning device 71. Send a warning command. The warning device 71 issues a warning with, for example, a lamp, a sound, a screen display, or the like.

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

The gas supply unit 60 includes a gas source 61, an accumulator 62 for storing the gas supplied by the gas source 61, a first tube 63 extending from the accumulator 62 to the cylinder unit 42 of the gas supply mechanism 40, and a first tube 63 thereof. The pressure control valve 64 and the switching valve 65 interposed in the 1 tube 63, the second tube 67 extending from the accumulator 62 to the gas passage 46 formed in the seal member 44, and the second tube 67. It is composed of a pressure control valve 68 and a check valve 69 provided. The pressure control valve 64 serves to supply the cylinder unit 42 with a gas having an operating pressure adapted to the pushing force of the sealing member 44 against the metal pipe material 14. The check valve 69 serves to prevent the high pressure gas from flowing back in the second tube 67. The pressure control valve 68 interposed in the second tube 67 serves to supply a gas having an operating pressure for expanding the metal pipe material 14 to the gas passage 46 of the seal member 44 under the control of the control unit 70. Fulfill.

The control unit 70 can supply gas having a desired operating pressure into the metal pipe material 14 by controlling the pressure control valve 68 of the gas supply unit 60. Further, the control unit 70 acquires temperature information from the thermocouple 21 and controls the drive mechanism 80 and the like by transmitting information from (A) shown in FIG.

The water circulation mechanism 72 includes a water tank 73 for storing water, a water pump 74 that pumps up the water stored in the water tank 73, pressurizes it, and sends it to the cooling water passage 19 of the lower mold 11 and the cooling water passage 25 of the upper mold 12. It consists of a pipe 75. Although omitted, it is permissible to interpose a cooling tower that lowers the water temperature or a filter that purifies the water in the pipe 75.

<Molding method of metal pipe using molding equipment>
Next, a method of forming a metal pipe using the forming apparatus 10 will be described. First, a hardenable steel grade cylindrical metal pipe material 14 is prepared. The metal pipe material 14 is placed (loaded) on the electrodes 17 and 18 provided on the lower mold 11 side by using, for example, a robot arm or the like. Since the concave grooves 17a and 18a are formed in the electrodes 17 and 18, the metal pipe material 14 is positioned by the concave grooves 17a and 18a.

Next, the control unit 70 controls the drive mechanism 80 and the pipe holding mechanism 30 to cause the pipe holding mechanism 30 to hold the metal pipe material 14. Specifically, the upper mold 12 and the upper electrodes 17, 18 and the like held on the slide 81 side are moved to the lower mold 11 side by the drive of the drive mechanism 80, and the upper electrode 17 and the like included in the pipe holding mechanism 30 are included. By operating an actuator that allows the metal pipe material 14 and the lower electrodes 17, 18 and the like to move forward and backward, the vicinity of both ends of the metal pipe material 14 is sandwiched by the pipe holding mechanism 30 from above and below. Due to the presence of the concave grooves 17a and 18a formed in the electrodes 17 and 18 and the concave grooves formed in the insulating materials 91 and 101, this pinching is brought into close contact with the metal pipe material 14 over the entire circumference near both ends. It will be sandwiched in various manners.

At this time, as shown in FIG. 2A, the end portion of the metal pipe material 14 on the electrode 18 side has a concave groove 18a and a tapered concave surface 18b of the electrode 18 in the extending direction of the metal pipe material 14. It protrudes toward the seal member 44 side from the boundary of the above. Similarly, the end portion of the metal pipe material 14 on the electrode 17 side protrudes toward the seal member 44 from the boundary between the concave groove 17a and the tapered concave surface 17b of the electrode 17 in the extending direction of the metal pipe material 14. Further, the lower surfaces of the upper electrodes 17 and 18 and the upper surfaces of the lower electrodes 17 and 18 are in contact with each other, respectively. However, the configuration is not limited to the structure in which the metal pipe material 14 is in close contact with the entire circumference of both ends, and the electrodes 17 and 18 may be in contact with a part of the metal pipe material 14 in the circumferential direction.

Subsequently, the control unit 70 heats the metal pipe material 14 by controlling the heating mechanism 50. Specifically, the control unit 70 controls the power supply unit 55 of the heating mechanism 50 to supply electric power, and performs current control as shown in FIG. 3A. More specifically, the control unit 70 supplies electric power to the electrodes 17 and 18 at the first current value C1 during the first predetermined time T1 after starting the electric power supply to the electrodes 17 and 18. , The power supply unit 55 is controlled (constant current control). The "first predetermined time T1" is a preset time. For example, the first predetermined time T1 may be a time of less than 1 second. Further, the "first current value C1" is a current value smaller than the second current value C2. For example, the first current value C1 may be a current value of 10 A or more and 100 A or less. The “second current value C2” is a current value supplied to the electrodes 17 and 18 when the metal pipe material 14 is energized and heated to a target temperature. For example, the second current value C2 may be a current value of 10,000 A or more.

Assuming that the control unit 70 controls the power supply unit 55 and sets the current value to the first current value C1, the electric power transmitted to the lower electrodes 17 and 18 via the bus bar 52 sandwiches the metal pipe material 14. It is supplied to the upper electrodes 17 and 18 and the metal pipe material 14.

At this time, if the electrical connection between the metal pipe material 14 and the electrodes 17 and 18 is insufficient (for example, if a gap is formed), the electrodes 17 and 18 are shown in FIG. 3 (b). An arc discharge EA1 is generated between the metal pipe material 14 and the metal pipe material 14.

When the arc discharge EA1 is generated, the power supply unit 55 supplies power to the electrodes 17 and 18 at the first current value C1 which is a current value smaller than the second current value C2. Therefore, the arc discharge EA1 is weaker than the arc discharge generated when the power supply unit 55 supplies power to the electrodes 17 and 18 at the second current value C2 (that is, low output and low power). ) Arc discharge. When the arc discharge EA1 is generated, the surfaces of the electrodes 17 and 18 are melted but not significantly damaged. Then, when the surfaces of the electrodes 17 and 18 are melted, the electrodes 17 and 18 and the metal pipe material 14 are short-circuited, and the arc discharge EA1 disappears.

When the arc discharge EA1 is generated, the arc discharge detection unit 70a of the control unit 70 detects the generation of the arc discharge EA1 between the electrodes 17 and 18 and the metal pipe material 14 based on the voltage value measured by the voltmeter 53. .. For example, the arc discharge detection unit 70a detects the occurrence of the arc discharge EA1 based on the amount of change in voltage (dv / dt; derivative) per unit time. Specifically, the arc discharge detection unit 70a determines that the arc discharge EA1 has occurred when the amount of change in voltage per unit time is equal to or greater than a predetermined value. This predetermined value is a predetermined value, and is a value at which it can be determined that the arc discharge EA1 has occurred.

When the control unit 70 detects the occurrence of the arc discharge EA1, it sends a command to the warning device 71 to generate a warning by, for example, a lamp, a sound, or a screen display.

Subsequently, the control unit 70 supplies electric power to the electrodes 17 and 18 at the second current value C2 after the first predetermined time T1 has elapsed from the start of supplying electric power to the electrodes 17 and 18. The power supply unit 55 is controlled (constant current control). As a result, the resistance present in the metal pipe material 14 causes the metal pipe material 14 itself to generate heat due to Joule heat.

At this time, if the electrical connection between the metal pipe material 14 and the electrodes 17 and 18 is insufficient (for example, the short circuit between the electrodes 17 and 18 and the metal pipe material 14 due to the arc discharge EA1 is insufficient). , As shown in FIG. 3B, an arc discharge EA2 is generated between the electrodes 17 and 18 and the metal pipe material 14.

When the arc discharge EA2 is generated, the power supply unit 55 supplies power to the electrodes 17 and 18 at the second current value C2, which is a current value larger than the first current value C1. Therefore, the arc discharge EA2 is a slightly stronger (that is, high output / high power) arc discharge than the arc discharge EA1. However, since the weak arc discharge EA1 has already been generated and the electrodes 17 and 18 and the metal pipe material 14 are short-circuited, the arc discharge EA2 has the electrode 17 at the second current value C2 before the arc discharge EA1 is generated. , 18 is a weak arc discharge compared to the very strong arc discharge that can occur when power is supplied to 18.

When the arc discharge EA2 is generated, the arc discharge detection unit 70a of the control unit 70 together with the electrodes 17 and 18 and the metal pipe material 14 based on the voltage value measured by the voltmeter 53, as in the case where the arc discharge EA1 is generated. The generation of arc discharge EA2 during the period is detected.

When the control unit 70 detects the occurrence of the arc discharge EA2, it sends a command to the warning device 71 to generate a warning by, for example, a lamp, a sound, or a screen display. The control unit 70 may generate a warning prompting maintenance of the electrodes 17 and 18 or replacement of the electrodes 17 and 18 when the arc discharge detection unit 70a detects a plurality of predetermined times.

Then, when the control unit 70 detects the occurrence of the arc discharge EA2, the control unit 70 sends a power adjustment command for adjusting the power to be output to the power supply unit 55 of the heating mechanism 50. As a result, the control unit 70 controls the power supply unit 55 so as to supply power to the electrodes 17 and 18 with a third current value C3 smaller than the second current value C2 during the second predetermined time T2. Here, the "second predetermined time T2" is a preset time. For example, the second predetermined time T2 may be a time of less than 1 second. Further, the "third current value C3" is a current value smaller than the second current value C2. The third current value C3 shown in FIG. 3A is a current value larger than the first current value C1 and smaller than the second current value C2. The third current value C3 may be a current value having the same magnitude as the first current value C1.

When the arc discharge EA2 is generated, the surfaces of the electrodes 17 and 18 are further melted. Here, as described above, when the control unit 70 detects the occurrence of the arc discharge EA2, the control unit 70 supplies power so as to supply power to the electrodes 17 and 18 with a third current value C3 smaller than the second current value C2. Since the portion 55 is controlled, the state in which the strong arc discharge EA2 is generated is not continued and short-circuited, and the surfaces of the electrodes 17 and 18 are suppressed from being significantly damaged.

In a state where power is supplied to the electrodes 17 and 18 at the third current value C3, even if an arc discharge occurs, the arc discharge becomes a weak arc discharge. When a weak arc discharge occurs, the surfaces of the electrodes 17 and 18 are melted again, but the current value of the third current value C3 is smaller than the second current value C2, so that the surface is not significantly damaged. When the surfaces of the electrodes 17 and 18 are melted, the electrodes 17 and 18 and the metal pipe material 14 are sufficiently short-circuited, and the arc discharge is extinguished.

Subsequently, the control unit 70 supplies electric power to the electrodes 17 and 18 at the second current value C2 after the second predetermined time T2 has elapsed from the start of supplying electric power to the electrodes 17 and 18. The power supply unit 55 is controlled (constant current control). As a result, the resistance present in the metal pipe material 14 causes the metal pipe material 14 itself to generate heat due to Joule heat. Then, the voltage value measured by the voltmeter 53 gradually increases, and when it reaches a predetermined value, the energization is terminated.

Subsequently, the blow molding die 13 is closed with respect to the heated metal pipe material 14 under the control of the drive mechanism 80 by the control unit 70. As a result, the cavity 16 of the lower mold 11 and the cavity 24 of the upper mold 12 are combined, and the metal pipe material 14 is arranged and sealed in the cavity portion between the lower mold 11 and the upper mold 12.

After that, by operating the cylinder unit 42 of the gas supply mechanism 40, the sealing member 44 is advanced to seal both ends of the metal pipe material 14. At this time, as shown in FIG. 2B, the sealing member 44 is pressed against the end portion of the metal pipe material 14 on the electrode 18 side, so that the groove 18a of the electrode 18 and the tapered concave surface 18b are more than the boundary. The portion protruding toward the seal member 44 is deformed into a funnel shape along the tapered concave surface 18b. Similarly, when the seal member 44 is pressed against the end portion of the metal pipe material 14 on the electrode 17 side, a portion of the metal pipe material 14 protruding toward the seal member 44 side from the boundary between the concave groove 17a and the tapered concave surface 17b of the electrode 17 is formed. It is deformed into a funnel shape along the tapered concave surface 17b. After the sealing is completed, high-pressure gas is blown into the metal pipe material 14 to form the metal pipe material 14 softened by heating so as to follow the shape of the cavity portion.

Since the metal pipe material 14 is heated to a high temperature (around 950 ° C.) and softened, the gas supplied into the metal pipe material 14 thermally expands. Therefore, for example, the gas to be supplied is compressed air, and the metal pipe material 14 at 950 ° C. can be easily expanded by the thermally expanded compressed air.

The outer peripheral surface of the blow-molded and swollen metal pipe material 14 contacts the cavity 16 of the lower mold 11 and is rapidly cooled, and at the same time, it contacts the cavity 24 of the upper mold 12 and is rapidly cooled (the upper mold 12 and the lower mold 11 are quenched). Since the heat capacity is large and the temperature is controlled to a low temperature, if the metal pipe material 14 comes into contact with the metal pipe material 14, the heat on the surface of the pipe is taken away to the mold side at once) and quenching is performed. Such a cooling method is called mold contact cooling or mold cooling. Immediately after being quenched, austenite transforms into martensite (hereinafter, the transformation of austenite into martensite is referred to as martensitic transformation). Since the cooling rate decreased in the latter half of cooling, martensite transforms into another structure (troostite, sorbite, etc.) by reheating. Therefore, it is not necessary to perform a separate tempering process. Further, in the present embodiment, cooling may be performed by supplying a cooling medium, for example, into the cavity 24, instead of cooling the mold or in addition to cooling the mold. For example, until the temperature at which martensitic transformation begins, the metal pipe material 14 is brought into contact with the mold (upper mold 12 and lower mold 11) for cooling, and then the mold is opened and the cooling medium (cooling gas) is used as the metal pipe material. Martensitic transformation may be generated by spraying on 14.

As described above, the metal pipe material 14 is blow-molded, then cooled, and the mold is opened to obtain, for example, a metal pipe having a substantially rectangular tubular body portion.

As described above, according to the present embodiment, the electric power to the electrodes 17 and 18 is supplied before the metal pipe material 14 is started to be heated to the target temperature by supplying electric power to the electrodes 17 and 18 at the second current value C2. During the first predetermined time T1 after the start of supply, power is supplied to the electrodes 17 and 18 at the first current value C1 smaller than the second current value C2. Therefore, if the electrical connection between the metal pipe material 14 and the electrodes 17 and 18 is insufficient (for example, if there is a gap), a weak arc discharge EA1 is generated, and the weak arc discharge EA1 is generated. When it occurs, the surfaces of the electrodes 17 and 18 melt, but the current value is small, so that the surface is not significantly damaged. Then, when the surfaces of the electrodes 17 and 18 are melted, the electrodes 17 and 18 and the metal pipe material 14 are short-circuited, and the arc discharge EA1 disappears. After that, when the metal pipe material 14 starts to be heated to the target temperature by supplying power to the electrodes 17 and 18 at the second current value C2 larger than the first current value C1, the electrodes 17 and 18 and the metal pipe material have already been heated. Since the 14 is short-circuited, it is possible to suppress the generation of a strong arc discharge that greatly damages the surfaces of the electrodes 17 and 18. Therefore, it is possible to suppress the influence of the arc discharge on the electrodes 17 and 18 between the metal pipe material 14 and the electrodes 17 and 18.

Further, the molding apparatus 10 includes a voltmeter 53 that measures the voltage between the electrodes 17 and 18, and the control unit 70 has a power supply unit 55 so as to supply power to the electrodes 17 and 18 at the second current value C2. When the occurrence of arc discharge EA2 between the electrodes 17 and 18 and the metal pipe material 14 is detected based on the voltage value between the electrodes 17 and 18 measured by the voltmeter 53, During the second predetermined time T2, the power supply unit 55 is controlled so as to supply power to the electrodes 17 and 18 with a third current value C3 smaller than the second current value C2, and after the lapse of the second predetermined time T2. The power supply unit 55 is controlled so as to supply power to the electrodes 17 and 18 with the second current value C2. Therefore, if power is supplied to the electrodes 17 and 18 at the first current value C1 and a weak arc discharge EA1 is generated, the power is supplied to the electrodes 17 and 18 at the second current value C2, which is strong. When the electrodes 17 and 18 and the metal pipe material 14 are not short-circuited to the extent that the generation of the arc discharge EA2 can be sufficiently suppressed and a strong arc discharge EA2 is generated, the second current is generated during the second predetermined time T2. Power is supplied to the electrodes 17 and 18 at a third current value C3 smaller than the value C2, and it is suppressed that the surfaces of the electrodes 17 and 18 are significantly damaged. Even if an arc discharge occurs in a state where power is supplied to the electrodes 17 and 18 at the third current value C3, the arc discharge becomes a weak arc discharge. When a weak arc discharge occurs, the surfaces of the electrodes 17 and 18 are melted again, but the current value of the third current value C3 is smaller than the second current value C2, so that the surface is not significantly damaged. Then, when the surfaces of the electrodes 17 and 18 are melted, the electrodes 17 and 18 and the metal pipe material 14 are sufficiently short-circuited, and the arc discharge is extinguished. After that, when power is supplied to the electrodes 17 and 18 again at the second current value C2, the electrodes 17 and 18 and the metal pipe material 14 are sufficiently short-circuited, so that strong arc discharge is suppressed. To.

Although the present invention has been specifically described above based on the embodiment, the present invention is not limited to the above embodiment. For example, in the above embodiment, the two electrodes 17 and 18 are used, but the electrodes are the same. Electrodes may be added inward in the axial direction from 17 and 18, and the number of electrodes may be three or more.

Further, if the arc discharge detection unit 70a can detect the occurrence of an arc discharge between the electrodes 17 and 18 and the metal pipe material 14 based on the voltage value measured by the voltmeter 53, a specific determination thereof is made. The method is not particularly limited. For example, the arc discharge detection unit 70a may detect the occurrence of arc discharge based on the difference between the voltage value measured by the voltmeter 53 and the predetermined set value. The set value referred to here is a predetermined voltage value, and is a voltage value at which it can be determined that an arc discharge has occurred. Then, the arc discharge detection unit 70a determines whether or not an arc discharge has occurred based on the difference between the measured voltage value and the set value. For example, it is determined that an arc discharge has occurred when the voltage value measured by the voltmeter 53 exceeds the set value.

Further, the control unit 70 provides a period in which the current value temporarily different from the third current value C3 is provided when the power supplied to the electrodes 17 and 18 is switched from the second current value C2 to the third current value C3. You may. For example, the control unit 70 may switch to the third current value C3 after passing through the state of the second current value C2 to the current value of 0A.

Further, the control unit 70 controls the power supply unit 55 so as to supply power to the electrodes 17 and 18 at the second current value C2, and supplies power to the electrodes 17 and 18 at the third current value C3. The state of controlling the power supply unit 55 so as to be performed may be repeated a plurality of times until the arc discharge does not occur. In this case, the third current value C3 at each time may be a different current value from each other.

Further, in the above embodiment, the molding target is the metal pipe material 14, but the molding target is not limited to the metal pipe material 14, and can be applied to a metal rod-shaped body, a metal plate-shaped body, or the like. Applicable to metal bodies that extend to some extent. Further, the molding apparatus can also be a forging apparatus or the like that performs energization heating without supplying gas.

10 ... Molding device (electric current heating device), 14 ... Metal pipe material (metal body), 17, 18 ... Electrode, 53 ... Voltmeter (voltage measuring unit), 55 ... Power supply unit, 70 ... Control unit, C1 ... 1 current value, C2 ... second current value, C3 ... third current value, EA1, EA2 ... arc discharge, T1 ... first predetermined time, T2 ... second predetermined time.

Claims (2)

An energizing heating device that supplies electric power to a metal body and energizes and heats the metal body.
With at least two electrodes in contact with the metal body,
A power supply unit that supplies power to the electrodes and
A control unit that controls the power supply unit is provided.
The control unit
During the first predetermined time after starting the supply of electric power to the electrode, the electric power supply unit is controlled so as to supply electric power to the electrode at the first current value.
An energization heating device that controls the power supply unit so as to supply power to the electrodes with a second current value larger than the first current value after the lapse of the first predetermined time. A voltage measuring unit for measuring the voltage between the electrodes is provided.
The control unit
When the power supply unit is controlled so as to supply power to the electrode with the second current value, the electrode and the metal are based on the voltage value between the electrodes measured by the voltage measurement unit. When the occurrence of an arc discharge with the body is detected, the power supply unit is set so as to supply power to the electrode with a third current value smaller than the second current value for a second predetermined time. Control and
The energization heating device according to claim 1, wherein after the lapse of the second predetermined time, the power supply unit is controlled so as to supply power to the electrode at the second current value.

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