ELECTRICAL HEATING DEVICE, FORMING DEVICE, AND ELECTRICAL HEATING METHOD

An electrical heating device includes a heating unit that causes a current to flow through a metal material to heat the metal material, and a measurement unit that measures a displacement amount of the metal material, in which the heating unit performs temperature control of the metal material based on the displacement amount of the metal material measured by the measurement unit.

BACKGROUND

Technical Field

A certain embodiment of the present disclosure relates to an electrical heating device, a forming device, and an electrical heating method.

Description of Related Art

In the related art, a forming device that forms a heated metal material has been known. For example, the related art discloses a forming device including a die including a pair of a lower die and an upper die, a gas supply unit that supplies a gas into a metal pipe material held between the dies, and a heating unit that heats the metal pipe material by electrical heating.

SUMMARY

According to an aspect of the present disclosure, there is provided an electrical heating device including a heating unit that causes a current to flow through a metal material to heat the metal material, and a measurement unit that measures a displacement amount of the metal material, in which the heating unit performs temperature control of the metal material based on the displacement amount of the metal material measured by the measurement unit.

According to another aspect of the present disclosure, there is provided a forming device including the electrical heating device described above, in which the forming device forms the heated metal material.

According to still another aspect of the present disclosure, there is provided an electrical heating method including: a heating process of causing a current to flow through a metal material to heat the metal material, and a measurement process of measuring a displacement amount of the metal material, in which in the heating process, temperature control of the metal material is performed based on the displacement amount of the metal material measured in the measurement process.

DETAILED DESCRIPTION

Here, the electrical heating device performs temperature control of electrical heating. Examples of an electrical heating method include a method of performing energization for a certain time set in advance and a method of plotting a relationship between a resistance value and a temperature for each member in advance to estimate a temperature from a correlation relationship thereof. However, since there are always variations in a shape or a power supply state for each member, a high-accuracy temperature control result cannot be obtained in these methods. In particular, in a case where the metal material is large and a large current is required, the influence of the variations for each metal material is very large. Additionally, there is a method of performing the temperature control by measuring a change point of resistance accompanying austenite transformation, but it is necessary to measure the current and the voltage in order to measure the resistance. However, the measurement of the current and the voltage is likely to be affected by noise due to the energization, and high-accuracy measurement may not be performed.

Therefore, it is desirable to provide an electrical heating device, a forming device, and an electrical heating method that can accurately perform temperature control regardless of a power supply state and variations in a metal material.

The electrical heating device includes the measurement unit that measures the displacement amount of the metal material. The displacement amount of the metal material has a portion indicating the same behavior in a relationship with the temperature regardless of the power supply state or the variations in the metal material. Therefore, the heating unit performs the temperature control of the metal material based on the displacement amount of the metal material measured by the measurement unit. Therefore, the heating unit can perform the temperature control with high accuracy regardless of the power supply state or the variations in the metal material, based on the displacement amount of the metal material.

The measurement unit may measure a change point indicating a change from a state where the displacement amount of the metal material increases to a state where the displacement amount of the metal material decreases, and the heating unit may perform the temperature control of the metal material based on a measurement result of the change point via the measurement unit. The displacement amount greatly decreases with an austenite transformation temperature as a boundary. Therefore, the change point indicating the change from a state where the displacement amount of the metal material increases to a state where the displacement amount of the metal material decreases indicates that the metal material is at the austenite transformation temperature or a temperature in the vicinity of the austenite transformation temperature regardless of the power supply state or the variations in the metal material. Therefore, the heating unit can perform the temperature control with high accuracy based on the measurement result of the change point.

The heating unit may stop energizing the metal material after a predetermined time has elapsed from the measurement of the change point. The displacement amount after the austenite transformation temperature increases at a constant rate regardless of the power supply state or the variations in the metal material. Therefore, the heating unit can stop the energization at a desired target temperature after the predetermined time has elapsed from the measurement of the change point.

The measurement unit may measure the displacement amount of the metal material in a non-contact manner. In this case, the measurement unit can measure the displacement amount from a position spaced apart from a high-temperature metal material.

With the forming device, it is possible to obtain the actions and effects having the same meaning as those of the above-described electrical heating device.

With the electrical heating method, it is possible to obtain the actions and effects having the same meaning as those of the above-described electrical heating device.

Hereinafter, a preferred embodiment of a forming device according to the present disclosure will be described with reference to the drawings. In the drawings, the same reference numerals will be given to the same portions or equivalent portions, and the redundant description thereof will be omitted.

FIG.1is a schematic configuration view of a forming device1including an electrical heating device100according to the present embodiment. As illustrated inFIG.1, the forming device1is a device that forms a metal pipe having a hollow shape by blow forming. In the present embodiment, the forming device1is installed on a horizontal plane. The forming device1includes a forming die2, a drive mechanism3, a holding unit4, a heating unit5, a fluid supply unit6, a cooling unit7, and a control unit8. In the present specification, a metal pipe material40(metal material) refers to a hollow article before the completion of forming via the forming device1. The metal pipe material40is a steel-type pipe material that can be quenched. In addition, in a horizontal direction, a direction in which the metal pipe material40extends during the forming may be referred to as a “longitudinal direction”, and a direction perpendicular to the longitudinal direction may be referred to as a “width direction”.

The forming die2is a die that forms a metal pipe from the metal pipe material40, and includes a lower die11and an upper die12that face each other in an up-down direction. The lower die11and the upper die12are configured by blocks made of steel. Each of the lower die11and the upper die12is provided with a recessed part in which the metal pipe material40is accommodated. In a state where the lower die11and the upper die12are in close contact with each other (die closed state), the respective recessed parts form a space having a target shape in which the metal pipe material is to be formed. Therefore, surfaces of the respective recessed parts are forming surfaces of the forming die2. The lower die11is fixed to a base stage13via a die holder or the like. The upper die12is fixed to a slide of the drive mechanism3via a die holder or the like.

The drive mechanism3is a mechanism that moves at least one of the lower die11and the upper die12. InFIG.1, the drive mechanism3has a configuration of moving only the upper die12. The drive mechanism3includes a slide21that moves the upper die12such that the lower die11and the upper die12are joined together, a pull-back cylinder22as an actuator that generates a force for pulling the slide21upward, a main cylinder23as a drive source that downward-pressurizes the slide21, and a drive source24that applies a driving force to the main cylinder23.

The holding unit4is a mechanism that holds the metal pipe material40disposed between the lower die11and the upper die12. The holding unit4includes a lower electrode26and an upper electrode27that hold the metal pipe material40on one end side in the longitudinal direction of the forming die2, and a lower electrode26and an upper electrode27that hold the metal pipe material40on the other end side in the longitudinal direction of the forming die2. The lower electrodes26and the upper electrodes27on both sides in the longitudinal direction hold the metal pipe material40by interposing vicinities of end portions of the metal pipe material40from the up-down direction. Upper surfaces of the lower electrodes26and lower surfaces of the upper electrodes27are formed with groove portions having a shape corresponding to an outer peripheral surface of the metal pipe material40. Drive mechanisms (not illustrated) are provided in the lower electrodes26and the upper electrodes27and are movable independently of each other in the up-down direction.

The heating unit5heats the metal pipe material40. The heating unit5is a mechanism that heats the metal pipe material40by energizing the metal pipe material40. The heating unit5heats the metal pipe material40in a state where the metal pipe material40is spaced apart from the lower die11and the upper die12, between the lower die11and the upper die12. The heating unit5includes the lower electrodes26and the upper electrodes27on both sides in the longitudinal direction, a power supply28that causes a current to flow through the metal pipe material40via the electrodes26and27, and the control unit8that controls the power supply28. The heating unit5may be disposed in a preceding process of the forming device1to perform heating externally.

The fluid supply unit6is a mechanism that supplies a high-pressure fluid into the metal pipe material40held between the lower die11and the upper die12. The fluid supply unit6supplies the high-pressure fluid into the metal pipe material40that has been brought into a high-temperature state by being heated by the heating unit5, to expand the metal pipe material40. The fluid supply units6are provided on both end sides of the forming die2in the longitudinal direction. The fluid supply unit6includes a nozzle31that supplies the fluid from an opening portion of an end portion of the metal pipe material40to an inside of the metal pipe material40, a drive mechanism32that moves the nozzle31forward and backward with respect to the opening portion of the metal pipe material40, and a supply source33that supplies the high-pressure fluid into the metal pipe material40via the nozzle31. The drive mechanism32brings the nozzle31into close contact with the end portion of the metal pipe material40in a state in which sealing performance is secured during the fluid supply and exhaust, and causes the nozzle31to be spaced apart from the end portion of the metal pipe material40in other cases. The fluid supply unit6may supply a gas such as high-pressure air and an inert gas, as the fluid. Additionally, the fluid supply unit6may include the heating unit5together with the holding unit4including a mechanism that moves the metal pipe material40in the up-down direction as the same device.

Components of the holding unit4, the heating unit5, and the fluid supply unit6may be configured as a unitized heating and expanding unit150.FIG.2Ais a schematic side view illustrating the heating and expanding unit150.FIG.2Bis a sectional view illustrating a state where the nozzle31has sealed the metal pipe material40.

As illustrated inFIG.2A, the heating and expanding unit150includes the lower electrode26, the upper electrode27, an electrode mounting unit151in which the electrodes26and27are mounted, the nozzle31, the drive mechanism32, an elevating unit152, and a unit base153. The electrode mounting unit151includes an elevating frame154and electrode frames156and157. The electrode frames156and157function as a part of a drive mechanism60that supports and moves each of the electrodes26and27. The drive mechanism32drives the nozzle31and moves up and down together with the electrode mounting unit151. The drive mechanism32includes a piston61that holds the nozzle31, and a cylinder62that drives the piston. The elevating unit152includes an elevating frame base64attached to an upper surface of the unit base153, and an elevating actuator66that applies an elevating operation to the elevating frame154of the electrode mounting unit151by using the elevating frame base64. The elevating frame base64includes guide portions64aand64bthat guide the elevating operation of the elevating frame154with respect to the unit base153. The elevating unit152functions as a part of the drive mechanism60of the holding unit4. The heating and expanding unit150includes a plurality of the unit bases153of which the upper surfaces have different inclination angles, and is allowed to collectively change and adjust inclination angles of the lower electrode26, the upper electrode27, the nozzle31, the electrode mounting unit151, the drive mechanism32, and the elevating unit152by replacing the unit bases153.

The nozzle31is a cylindrical member into which the end portion of the metal pipe material40can be inserted. The nozzle31is supported by the drive mechanism32such that a center line of the nozzle31coincides with a reference line SL1. An inner diameter of a feed port31aat an end portion of the nozzle31on the metal pipe material40side substantially coincides with an outer diameter of the metal pipe material40after expansion forming. In this state, the nozzle31supplies the high-pressure fluid from an internal flow path63to the metal pipe material40. Examples of the high-pressure fluid include a gas.

Returning toFIG.1, the cooling unit7is a mechanism that cools the forming die2. The cooling unit7can rapidly cool the metal pipe material40when the expanded metal pipe material40comes into contact with the forming surface of the forming die2, by cooling the forming die2. The cooling unit7includes flow paths36formed inside the lower die11and the upper die12and a water circulation mechanism37that supplies a cooling water and causes the cooling water to circulate through the flow paths36.

The control unit8is a device that controls the entire forming device1. The control unit8controls the drive mechanism3, the holding unit4, the heating unit5, the fluid supply unit6, and the cooling unit7. The control unit8repeatedly performs the operation of forming the metal pipe material40using the forming die2.

Specifically, the control unit8controls, for example, a transport timing from a transport device, such as a robot arm, to dispose the metal pipe material40between the lower die11and the upper die12in an open state. Alternatively, a worker may manually dispose the metal pipe material40between the lower die11and the upper die12. Additionally, the control unit8controls an actuator of the holding unit4and the like such that the metal pipe material40is supported by the lower electrodes26on both sides in the longitudinal direction, and then the upper electrodes27are lowered to interpose the metal pipe material40. In addition, the control unit8controls the heating unit5to electrically heat the metal pipe material40. Therefore, an axial current flows through the metal pipe material40, and an electric resistance of the metal pipe material40itself causes the metal pipe material40itself to generate heat due to Joule heat.

The control unit8controls the drive mechanism3to lower the upper die12and bring the upper die12close to the lower die11, thereby closing the forming die2. Meanwhile, the control unit8controls the fluid supply unit6to seal the opening portions of both ends of the metal pipe material40with the nozzle31and supply the fluid. Therefore, the metal pipe material40softened by the heating expands and comes into contact with the forming surface of the forming die2. Then, the metal pipe material40is formed to follow a shape of the forming surface of the forming die2. In addition, in a case where a metal pipe with a flange is formed, a part of the metal pipe material40is made to enter a gap between the lower die11and the upper die12, and then die closing is further performed to crush the entering part to form a flange portion. When the metal pipe material40comes into contact with the forming surface, the metal pipe material40is quenched by being rapidly cooled by using the forming die2cooled by the cooling unit7.

Hereinafter, the electrical heating device100according to the present embodiment will be described in detail with reference toFIG.3. As illustrated inFIG.3, the electrical heating device100includes the heating unit5and a measurement unit70. As described above, the heating unit5includes two sets of the electrodes26and27, the power supply28, and the control unit8.

The measurement unit70measures a displacement amount of the metal pipe material40. The measurement unit70includes a detector71that acquires information for measuring the displacement amount, and the control unit8that calculates the displacement amount based on the information acquired by the detector71. The measurement unit70measures the displacement amount of the metal pipe material40in a non-contact manner. In the present embodiment, the measurement unit70adopts a camera that acquires an image of the metal pipe material40, as the detector71. The detector71captures the image of the metal pipe material40from a position spaced apart from the metal pipe material40. The detector71acquires an image of an end portion40ain which the displacement due to thermal expansion of the metal pipe material40is easily confirmed on the image (seeFIG.4). The disposition of the detector71is not particularly limited as long as the detector71does not interfere with other members, such as the forming die2, and is disposed at a position at which the image of the end portion40acan be easily acquired. The control unit8calculates the displacement amount of the metal pipe material40based on the image acquired by the detector71.

FIG.4is a view illustrating an example of an image110acquired by the detector71. As illustrated inFIG.4, a position of the end portion40aof the metal pipe material40at the start of the heating is defined as a reference position SP. When the heating is started, the metal pipe material40is thermally expanded, so that a length of the metal pipe material40increases. A position of the end portion40aat a time when a time t has elapsed from the start of the heating is defined as a displacement position CP. The control unit8measures a dimension between the displacement position CP and the reference position SP from the image110. The control unit8acquires the dimension as a displacement ΔL. Then, the control unit8acquires the displacement amount of the metal pipe material40by calculating “displacement ΔL/time t”. The displacement amount corresponds to a speed at which the end portion40aextends due to the thermal expansion.

FIG.5illustrates a graph G1in which a relationship between the displacement amount and the time is plotted. In the graph G1, a vertical axis indicates the displacement amount and a horizontal axis indicates the time. In addition, a graph G2illustrates a relationship between the current and the time. The displacement amount increases from the start of the heating with a constant current to a time t1. The displacement amount is curved to protrude upward and draws a maximum point P1. The maximum point P1is a change point indicating a change from a state where the displacement amount of the metal pipe material40increases to a state where the displacement amount of the metal pipe material40decreases. The displacement amount decreases from the maximum point P1to a time t2. The displacement amount is curved to protrude downward and draws a minimum point P2. The displacement amount increases until the output of the power supply28is stopped after the minimum point P2.

Here,FIG.6illustrates a relationship between a change in a length due to the heating of a steel material and the temperature. As illustrated inFIG.6, the behavior of the dimensional change greatly changes with an austenite transformation temperature CT as a boundary. The austenite transformation temperature CT illustrated inFIG.6is approximately 720° C. Since the austenite transformation temperature CT is a physical property, the austenite transformation temperature CT is always constant regardless of a size or a power supply state of a heating target. The dimensional change after the transformation is constant. Therefore, inFIG.6, the change point indicating the change from a state where the displacement amount of the metal material increases to a state where the displacement amount of the metal material decreases indicates that the metal material is at the austenite transformation temperature or a temperature in the vicinity of the austenite transformation temperature regardless of the power supply state or the variations in the metal material. The temperature in the vicinity of the maximum point P1inFIG.5is a temperature close to the austenite transformation temperature CT regardless of the size or the power supply state of the metal pipe material40. Therefore, the temperature can be estimated by measuring the maximum point P1via the measurement unit70. The dimensional change after the transformation is constant. Therefore, when the measurement unit70measures the maximum point P1and the heating is performed for a predetermined time Δt that has been determined in advance, the metal pipe material can be heated to a desired target temperature. In the present embodiment, the maximum point P1is adopted as the change point indicating a change from a state where the displacement amount of the metal pipe material40increases to a state where the displacement amount of the metal pipe material40decreases. It should be noted that any change point may be adopted as long as the change point indicates a change from a state where the displacement amount increases to a state where the displacement amount decreases. The maximum point P1is a change point at which a state where the displacement amount increases is switched to a state where the displacement amount decreases, and is a maximum value in a range in the vicinity of the maximum point P1, but is not always a maximum value in the entire graph G1. That is, the displacement amount at the output stop may be larger than that of the maximum point P1.

From the above, the measurement unit70measures the maximum point P1at which a state where the displacement amount of the metal pipe material40increases is changed to a state where the displacement amount of the metal pipe material40decreases. In addition, the heating unit5performs the temperature control of the metal pipe material40based on the displacement amount of the metal pipe material40measured by the measurement unit70. The heating unit5performs the temperature control of the metal pipe material40based on the measurement result of the maximum point P1via the measurement unit70. Specifically, the heating unit5stops energizing the metal pipe material40after the predetermined time Δt that has been determined in advance has elapsed from the measurement of the maximum point P1. The predetermined time Δt is set in consideration of a time required to reach the target temperature from the austenite transformation temperature CT.

A specific temperature control content will be described with reference toFIGS.7and8.FIG.7illustrates an example in a case where the measurement unit70measures the maximum point P1by using the displacement amount. As illustrated inFIG.7, the control unit8of the measurement unit70calculates the displacement amount at a constant time interval tx. Before the time when reaching the maximum point P1, the control unit8measures the displacement amount that monotonically increases at the time interval tx. For example, at a time ta immediately before reaching the maximum point P1, the control unit8measures a large displacement amount. On the other hand, the displacement amount sharply decreases after the time when reaching the maximum point P1. Therefore, at a time tb following the time ta, the control unit8measures a value lower than a value of the displacement amount at the time ta.

The control unit8measures the maximum point P1in a case where the measured displacement amount is a value lower than that of the previous time and is a value equal to or lower than a threshold value TH. A measurement point P3between the maximum point P1and the minimum point P2is measured by the control unit8at the time tb. However, in a case where the measurement point P3is measured, it can be detected that the measurement point P3is immediately after passing through the maximum point P1. In this way, the detection of the fact that the measurement point P3is immediately after passing through the maximum point P1is also included in the measurement of the maximum point P1via the measurement unit70. Next, the control unit8stops the energization when the predetermined time Δt has elapsed from the time tb at which the maximum point P1has been measured. The time interval tx is not particularly limited, but the measurement accuracy of the maximum point P1is higher as the time interval tx is smaller. The time interval tx is preferably smaller than the time interval between the maximum point P1and the minimum point P2. The displacement amount does not decrease from immediately after the start of the heating to when the displacement amount reaches the maximum point P1. Therefore, a predetermined time from the start of the heating may be set as an ignoring period t3. In the ignoring period t3, the control unit8need not perform the calculation of the displacement amount or the comparison with the previous value.

FIG.8illustrates an example in a case where the measurement unit70measures the maximum point P1by using acceleration. A graph G3illustrates a relationship between the acceleration and the time. As illustrated inFIG.8, the control unit8of the measurement unit70calculates the acceleration at the constant time interval tx. The acceleration is acceleration of the extension of the metal pipe material40. The control unit8calculates the acceleration by differentiating the displacement amount. Before the time when reaching the maximum point P1, the control unit8measures constant acceleration at the time interval tx. At the maximum point P1, the acceleration sharply decreases from positive to negative. For example, the control unit8measures positive acceleration at the time ta immediately before reaching the maximum point P1. On the other hand, at the timing immediately after the maximum point P1, the acceleration is negative. Therefore, the control unit8measures the negative acceleration at the time tb after the time ta.

In a case where the measured acceleration is negative, the control unit8measures the maximum point P1. Next, the control unit8stops the energization when the predetermined time Δt has elapsed from the time tb at which the maximum point P1has been measured.

Hereinafter, an electrical heating method according to the present embodiment will be described with reference toFIG.9.

First, the heating unit5causes the current to flow through the metal pipe material40to heat the metal pipe material40(step S10: heating process), and then the measurement unit70measures the displacement amount of the metal pipe material40(step S20: measurement process). Next, the measurement unit70determines whether or not the maximum point P1is measured (S30: measurement process). In a case where it is determined in step S30that the maximum point P1is not measured, the measurement unit70returns to step S20and measures the displacement amount again at a predetermined timing.

In a case where it is determined in step S30that the maximum point P1is measured, the heating unit5waits for a predetermined time Δt that has been determined in advance (step S40: heating process). During this time, the heating unit5continues the electrical heating. Next, the heating unit5stops the electrical heating after the predetermined time Δt has elapsed (step S50: heating process). In this way, in the heating process, the temperature control of the metal pipe material40is performed based on the displacement amount of the metal pipe material40measured in the measurement process.

Hereinafter, the actions and effects of the electrical heating device100, the forming device1, and the electrical heating method according to the present embodiment will be described.

The electrical heating device100includes the measurement unit70that measures the displacement amount of the metal pipe material40. The displacement amount of the metal pipe material40has a portion indicating the same behavior in a relationship with the temperature regardless of the power supply state or the variations in the metal pipe material40. Therefore, the heating unit5performs the temperature control of the metal pipe material40based on the displacement amount of the metal pipe material40measured by the measurement unit70. Therefore, the heating unit5can perform the temperature control with high accuracy regardless of the power supply state or the variations in the metal pipe material40, based on the displacement amount of the metal pipe material40.

The measurement unit70may measure the change point (maximum point P1) indicating a change from a state where the displacement amount of the metal pipe material40increases to a state where the displacement amount of the metal pipe material40decreases, and the heating unit5may perform the temperature control of the metal pipe material40based on the measurement result of the change point (maximum point P1) via the measurement unit70. The displacement amount greatly decreases with an austenite transformation temperature as a boundary. Therefore, the change point indicating the change from a state where the displacement amount of the metal pipe material40increases to a state where the displacement amount of the metal pipe material40decreases indicates that the metal pipe material40is at the austenite transformation temperature or a temperature in the vicinity of the austenite transformation temperature regardless of the power supply state or the variations in the metal pipe material40. Therefore, the heating unit5can perform the temperature control with high accuracy based on the measurement result of the maximum point P1.

The heating unit5may stop energizing the metal pipe material40after the predetermined time has elapsed from the measurement of the maximum point P1. The displacement amount after the austenite transformation temperature increases at a constant rate regardless of the power supply state or the variations in the metal material. Therefore, the heating unit5can stop the energization at a desired target temperature after the predetermined time has elapsed from the measurement of the maximum point P1.

The measurement unit70may measure the displacement amount of the metal pipe material40in a non-contact manner. In this case, the measurement unit70can measure the displacement amount from a position spaced apart from the high-temperature metal pipe material40.

The forming device1according to the present embodiment includes the electrical heating device100, and forms the heated metal pipe material40.

With the forming device1, it is possible to obtain the actions and effects having the same meaning as those of the electrical heating device100.

The electrical heating method according to the present embodiment includes the heating process of causing the current to flow through the metal pipe material40to heat the metal pipe material40, and the measurement process of measuring the displacement amount of the metal pipe material40, in which in the heating process, the temperature control of the metal pipe material40is performed based on the displacement amount of the metal pipe material40measured in the measurement process.

With the electrical heating method, it is possible to obtain the actions and effects having the same meaning as those of the electrical heating device100.

The present disclosure is not limited to the above-described embodiment described above.

In the above-described embodiment, the camera is adopted as the detector, but another non-contact type sensor, such as a laser measuring instrument, may be used. A contact type measuring instrument may also be used as the detector.

The forming device need only be any forming device that heats the metal material, and a forming device using a hot stamping method may be adopted. In this case, the metal material is a plate material.

An electrical heating device including: a heating unit that causes a current to flow through a metal material to heat the metal material; and a measurement unit that measures a displacement amount of the metal material, in which the heating unit performs temperature control of the metal material based on the displacement amount of the metal material measured by the measurement unit.

The electrical heating device according to aspect 1, in which the measurement unit measures a change point indicating a change from a state where the displacement amount of the metal material increases to a state where the displacement amount of the metal material decreases, and the heating unit performs the temperature control of the metal material based on a measurement result of the change point via the measurement unit.

The electrical heating device according to aspect 2, in which the heating unit stops energizing the metal material after a predetermined time has elapsed from the measurement of the change point.

The electrical heating device according to any one of aspects 1 to 3, in which the measurement unit measures the displacement amount of the metal material in a non-contact manner.

A forming device including: the electrical heating device according to any one of aspects 1 to 4, in which the forming device forms the heated metal material.

An electrical heating method including: a heating process of causing a current to flow through a metal material to heat the metal material; and a measurement process of measuring a displacement amount of the metal material, in which in the heating process, temperature control of the metal material is performed based on the displacement amount of the metal material measured in the measurement process.