Electric heating device, molding device, and electric heating method

Abstract

An electric heating device according to the present invention is used in a molding device for expansion-molding a metal material and includes a heating unit for heating the metal material by allowing a current to pass through the metal material, and a detection unit for detecting an electrical property value in the heating by the heating unit. The heating unit controls the temperature of the metal material on the basis of the electrical property value detected by the detection unit.

Description

[Technical Field]

[0001] The present disclosure relates to an electrical heating apparatus, a forming apparatus, and an electrical heating method. [Background Art]

[0002] Conventionally, forming apparatuses for forming heated metal materials are known. For example, the following Patent Document 1 discloses a forming apparatus including a die having a pair of lower die and upper die, a gas supply unit that supplies gas into a metal pipe material held between the dies, and a heating unit that heats the metal pipe material by electrical heating. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Patent Laid-Open No. 2009-220141 [Summary of Invention] [Problem to be Solved by the Invention]

[0004] Here, the electrical heating apparatus performs temperature control for electrical heating. As a method of electrical heating, there can be mentioned a method of performing energization for a preset fixed period of time. However, in these methods, since there are always variations in the shape, power supply state, and the like among individual members, highly accurate temperature control results cannot be obtained. The influence of variations among individual metal materials becomes extremely large particularly when the metal material is large and a large current is required. If the influence of variations among individual metal materials is large, the energization time becomes shorter than necessary, which may cause problems such as failure of the metal material to obtain a desired shape. Alternatively, when the energization time becomes longer than necessary, there may be problems such as increased power consumption accompanying the increase in the electrical heating time of the forming apparatus and early wear of electrodes.

[0005] Therefore, the purpose of this disclosure is to provide an electrically heated device, a molding device, and an electrically heated method that can accurately control the temperature regardless of the power supply state and variations in the metal material. [Means for solving the problem]

[0006] An electrically heated device according to one aspect of the present disclosure is an electrically heated device used in a molding apparatus for expanding and molding a metal material, comprising a heating unit that heats the metal material by passing an electric current through it, and a detection unit that detects electrical characteristic values ​​during heating by the heating unit, wherein the heating unit controls the temperature of the metal material based on the electrical characteristic values ​​detected by the detection unit.

[0007] This electrically heated device includes a detection unit that detects electrical characteristic values ​​during heating by the heating unit. Electrical characteristic values ​​exhibit similar behavior in relation to temperature, regardless of the power supply state or variations in the metal material. Therefore, the heating unit controls the temperature of the metal material based on the electrical characteristic values ​​detected by the detection unit. This allows the heating unit to perform accurate temperature control based on electrical characteristic values, regardless of the power supply state or variations in the metal material. This ability to perform accurate temperature control regardless of variations in the metal material suppresses problems related to the molding device that occur when the energizing time is unnecessarily short or long (such as the metal material not forming the desired shape, increased power consumption, or electrode wear).

[0008] The detection unit detects a change point indicating a change in the pattern of change of the electrical properties, and the heating unit may control the temperature of the metal material based on the detection result of the change point by the detection unit. The pattern of change of the electrical properties changes significantly at the austenite transformation temperature. Therefore, a change point indicating a change in the pattern of change of the electrical properties indicates that the metal material is at or near the austenite transformation temperature, regardless of the power supply state or variations in the metal material. Thus, the heating unit can perform highly accurate temperature control based on the detection result of the change point.

[0009] The heating unit may stop supplying power to the metal material after a change point is detected and the electrical characteristic value has changed by a predetermined amount. The electrical characteristic value increases steadily after the austenite transformation temperature, regardless of the power supply conditions or variations in the metal material. Therefore, the heating unit can stop supplying power at the desired target temperature once the electrical characteristic value has changed by a predetermined amount after a change point is detected.

[0010] The heating unit may stop supplying power to the metal material after a predetermined time has elapsed since the detection of the change point. The electrical properties after the austenite transformation temperature increase steadily regardless of the power supply conditions or variations in the metal material. Therefore, the heating unit can stop supplying power at the desired target temperature after a predetermined time has elapsed since the detection of the change point.

[0011] The molding apparatus according to this disclosure includes the above-described electrically heated device and molds the heated metal material.

[0012] This molding apparatus can achieve the same effects and functions as the electrically heated apparatus described above.

[0013] The electric heating method according to this disclosure comprises a heating step of heating a metal material by passing an electric current through it, and a detection step of detecting electrical characteristic values ​​during heating in the heating step, wherein the heating step controls the temperature of the metal material based on the electrical characteristic values ​​detected in the detection step.

[0014] This electric heating method allows for the same effects and functions as the electric heating device described above to be obtained. [Effects of the Invention]

[0015] According to this disclosure, it is possible to provide an electrically heated device, a molding device, and an electrically heated method that can accurately control the temperature regardless of the power supply state and variations in the metal material. [Brief explanation of the drawing]

[0016] [Figure 1]It is a schematic configuration diagram showing a forming apparatus according to an embodiment of the present disclosure. [Figure 2] Fig. 2(a) is a schematic side view showing a heating expansion unit. Fig. 2(b) is a cross-sectional view showing a state when a nozzle seals a metal pipe material. [Figure 3] It is a schematic diagram showing an electric heating apparatus according to the present embodiment. [Figure 4] It is a graph showing an example of electrical characteristic values. [Figure 5] It is a graph plotting the relationship between electrical characteristic values and time. [Figure 6] It is a graph showing measurement results. [Figure 7] It is a graph showing a change in resistance value after a change point. [Figure 8] It is a graph showing an example of a method for a detection unit to detect a change point. [Figure 9] It is a graph showing an example of a method for a detection unit to detect a change point. [Figure 10] It is a flowchart showing an electric heating method according to an embodiment of the present disclosure.

Mode for Carrying Out the Invention

[0017] Hereinafter, preferred embodiments of the forming apparatus according to the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and overlapping descriptions are omitted.

[0018] FIG. 1 is a schematic configuration diagram of a forming apparatus including an electric heating apparatus according to the present embodiment. As shown in FIG. 1, the forming apparatus is an apparatus for forming a hollow metal pipe by blow molding. In the present embodiment, the forming apparatus is installed on a horizontal surface. The forming apparatus includes a forming die, a drive mechanism, a holding portion, a heating portion, a fluid supply portion, a cooling portion, and a control portion. In this specification, the metal pipe material (metal material) refers to a hollow article before forming is completed in the forming apparatus. The metal pipe material is a pipe material of a quenchable steel grade. In addition, among the horizontal directions, the direction in which the metal pipe material extends during forming may be referred to as the "longitudinal direction", and the direction orthogonal to the longitudinal direction may be referred to as the "width direction".

[0019] The forming die is a die for forming a metal pipe from the metal pipe material, and includes a lower die and an upper die that face each other in the vertical direction. The lower die and the upper die are formed of steel blocks. Each of the lower die and the upper die is provided with a recess for accommodating the metal pipe material. When the lower die and the upper die are in close contact with each other (die closed state), the respective recesses form a space of a target shape for forming the metal pipe material. Therefore, the surface of each recess serves as the forming surface of the forming die. The lower die is fixed to a base via a die holder or the like. The upper die is fixed to a slide of the drive mechanism via a die holder or the like.

[0020] The drive mechanism is a mechanism that moves at least one of the lower die and the upper die. In FIG. 1, the drive mechanism is configured to move only the upper die. The drive mechanism includes a slide that moves the upper die such that the lower die and the upper die are aligned with each other, a pull-back cylinder as an actuator that generates a force for pulling the slide upward, a main cylinder as a drive source that presses the slide downward, and a drive source that applies a driving force to the main cylinder.

[0021] The holding part 4 is a mechanism for holding a metal pipe material 40 positioned between the lower mold 11 and the upper mold 12. The holding part 4 comprises a lower electrode 26 and an upper electrode 27 that hold the metal pipe material 40 at one end in the longitudinal direction of the molding die 2, and a lower electrode 26 and an upper electrode 27 that hold the metal pipe material 40 at the other end in the longitudinal direction of the molding die 2. The lower electrode 26 and the upper electrode 27 on both sides in the longitudinal direction hold the metal pipe material 40 by clamping the vicinity of the end of the metal pipe material 40 from above and below. Grooves having a shape corresponding to the outer circumferential surface of the metal pipe material 40 are formed on the upper surface of the lower electrode 26 and the lower surface of the upper electrode 27. The lower electrode 26 and the upper electrode 27 are provided with a drive mechanism (not shown) that allows them to move independently in the vertical direction.

[0022] The heating unit 5 heats the metal pipe material 40. The heating unit 5 is a mechanism that heats the metal pipe material 40 by passing an electric current to the metal pipe material 40. The heating unit 5 heats the metal pipe material 40 while it is separated from the lower mold 11 and the upper mold 12, between the lower mold 11 and the upper mold 12. The heating unit 5 comprises the lower electrodes 26 and upper electrodes 27 on both sides in the longitudinal direction as described above, a power supply 28 that supplies current to the metal pipe material 40 via these electrodes 26 and 27, and a control unit 8 that controls the power supply 28. The heating unit 5 may be placed in the pre-processing stage of the molding apparatus 1 and heated externally.

[0023] The fluid supply unit 6 is a mechanism for supplying high-pressure fluid into a metal pipe material 40 held between the lower mold 11 and the upper mold 12. The fluid supply unit 6 supplies high-pressure fluid to the metal pipe material 40, which has become hot due to heating in the heating unit 5, thereby expanding the metal pipe material 40. The fluid supply unit 6 is provided on both ends in the longitudinal direction of the molding die 2. The fluid supply unit 6 comprises a nozzle 31 that supplies fluid into the metal pipe material 40 from an opening at the end of the metal pipe material 40, a drive mechanism 32 that moves the nozzle 31 back and forth relative to the opening of the metal pipe material 40, and a supply source 33 that supplies high-pressure fluid into the metal pipe material 40 via the nozzle 31. The drive mechanism 32 ensures a tight seal when supplying and exhausting fluid by making the nozzle 31 tightly attached to the end of the metal pipe material 40, and separates the nozzle 31 from the end of the metal pipe material 40 at other times. The fluid supply unit 6 may supply gases such as high-pressure air or inert gas as the fluid. Furthermore, the fluid supply unit 6 may be the same device as the heating unit 5, together with the holding unit 4 which has a mechanism for moving the metal pipe material 40 in the vertical direction.

[0024] The components of the holding section 4, the heating section 5, and the fluid supply section 6 may be configured as a unitized heating and expansion unit 150. Figure 2(a) is a schematic side view showing the heating and expansion unit 150. Figure 2(b) is a cross-sectional view showing the nozzle 31 sealing the metal pipe material 40.

[0025] As shown in Figure 2(a), the heating expansion unit 150 comprises the lower electrode 26 and upper electrode 27 described above, an electrode mounting unit 151 on which the electrodes 26 and 27 are mounted, the nozzle 31 and drive mechanism 32 described above, a lifting unit 152, and a unit base 153. The electrode mounting unit 151 comprises a lifting frame 154 and electrode frames 156 and 157. The electrode frames 156 and 157 function as part of the drive mechanism 60 that supports and moves the electrodes 26 and 27. The drive mechanism 32 drives the nozzle 31 and moves it up and down together with the electrode mounting unit 151. The drive mechanism 32 comprises a piston 61 that holds the nozzle 31 and a cylinder 62 that drives the piston. The lifting unit 152 includes a lifting frame base 64 attached to the upper surface of the unit base 153, and a lifting actuator 66 that uses these lifting frame bases 64 to provide lifting motion to the lifting frame 154 of the electrode mounting unit 151. The lifting frame base 64 has guide portions 64a and 64b that guide the lifting motion of the lifting frame 154 relative to the unit base 153. The lifting unit 152 functions as part of the drive mechanism 60 of the holding unit 4. The heating expansion unit 150 has multiple unit bases 153 with different inclination angles on their upper surfaces, and by exchanging these, it is possible to change and adjust the inclination angles of the lower electrode 26 and upper electrode 27, nozzle 31, electrode mounting unit 151, drive mechanism 32, and lifting unit 152 all at once.

[0026] The nozzle 31 is a cylindrical member into which the end of the metal pipe material 40 can be inserted. The nozzle 31 is supported by the drive mechanism 32 such that its centerline coincides with the reference line SL1. The inner diameter of the supply port 31a at the end of the nozzle 31 on the metal pipe material 40 side is approximately the same as the outer diameter of the metal pipe material 40 after expansion molding. In this state, the nozzle 31 supplies high-pressure fluid to the metal pipe material 40 from the internal flow path 63. An example of high-pressure fluid is gas.

[0027] Returning to Figure 1, the cooling unit 7 is a mechanism for cooling the molding die 2. By cooling the molding die 2, the cooling unit 7 can rapidly cool the expanded metal pipe material 40 when it comes into contact with the molding surface of the molding die 2. The cooling unit 7 includes a flow path 36 formed inside the lower mold 11 and the upper mold 12, and a water circulation mechanism 37 that supplies and circulates cooling water to the flow path 36.

[0028] The control unit 8 is a device that controls the entire molding apparatus 1. The control unit 8 controls the drive mechanism 3, the holding unit 4, the heating unit 5, the fluid supply unit 6, and the cooling unit 7. The control unit 8 repeatedly performs the operation of molding the metal pipe material 40 in the molding die 2.

[0029] Specifically, the control unit 8 controls the timing of transport from a transport device such as a robot arm to position the metal pipe material 40 between the open lower mold 11 and the upper mold 12. Alternatively, the control unit 8 allows an operator to manually position the metal pipe material 40 between the lower mold 11 and the upper mold 12. The control unit 8 also controls the actuators of the holding unit 4 to support the metal pipe material 40 with the lower electrodes 26 on both sides in the longitudinal direction, and then lower the upper electrodes 27 to sandwich the metal pipe material 40. The control unit 8 also controls the heating unit 5 to energize and heat the metal pipe material 40. As a result, an axial current flows through the metal pipe material 40, and the metal pipe material 40 itself generates heat through Joule heating due to its own electrical resistance.

[0030] The control unit 8 controls the drive mechanism 3 to lower the upper mold 12 and bring it close to the lower mold 11, thereby closing the molding die 2. Meanwhile, the control unit 8 controls the fluid supply unit 6 to seal the openings at both ends of the metal pipe material 40 with the nozzle 31 and supply fluid. As a result, the metal pipe material 40, which has been softened by heating, expands and comes into contact with the molding surface of the molding die 2. The metal pipe material 40 is then molded to conform to the shape of the molding surface of the molding die 2. When forming a metal pipe with a flange, a portion of the metal pipe material 40 is inserted into the gap between the lower mold 11 and the upper mold 12, and then the mold is closed again to crush the inserted portion and form the flange. When the metal pipe material 40 comes into contact with the molding surface, it is rapidly cooled by the molding die 2, which has been cooled by the cooling unit 7, thereby quenching the metal pipe material 40.

[0031] Next, with reference to Figure 3, the electrically heated device 100 according to this embodiment will be described in detail. The electrically heated device 100 is a device used in a molding apparatus 1 for expanding and molding a metal material. As shown in Figure 3, the electrically heated device 100 comprises the aforementioned heating unit 5 and the detection unit 70. As described above, the heating unit 5 comprises two sets of electrodes 26 and 27, a power supply 28, and a control unit 8.

[0032] The detection unit 70 detects electrical characteristic values ​​during heating by the heating unit 5. The detection unit 70 includes an information acquisition unit 71 that acquires information for detecting electrical characteristic values, and a control unit 8 that calculates electrical characteristic values ​​based on the information acquired by the information acquisition unit 71. The electrical characteristic values ​​detected by the detection unit 70 can be any values ​​that change between the start and stop of energization, such as resistance, current, voltage, and power. For example, when the control unit 8 performs constant voltage control, as shown in Figure 4(a), the resistance increases over time, and the current (power) decreases over time. Therefore, when performing constant voltage control, the detection unit 70 only needs to detect resistance, current, or power as the electrical characteristic value. When the control unit 8 performs constant current control, as shown in Figure 4(b), the resistance increases over time, and the voltage (power) increases over time. Therefore, when performing constant current control, the detection unit 70 only needs to detect resistance, voltage, or power as the electrical characteristic value.

[0033] If the power supply 28 is a device capable of outputting voltage and current values ​​during energized heating, the power supply 28 functions as an information acquisition unit 71. In this case, the power supply 28 outputs voltage and current values ​​to the control unit 8. The information acquisition unit 71 may also have a measuring instrument 72. The measuring instrument 72 is provided on both electrodes 26 and 27 and can measure the voltage value applied to the metal pipe material 40 or the current value flowing through the metal pipe material 40. The control unit 8 may detect the information acquired from the information acquisition unit 71 directly as electrical characteristic values, or it may detect the electrical characteristic values ​​by performing calculations using the information acquired from the information acquisition unit 71.

[0034] When resistance is detected as an electrical characteristic value, Figure 5 shows graph G1 plotting the relationship between resistance and time. In graph G1, the vertical axis represents resistance, and the horizontal axis represents time. Note that graph G1 shown in Figure 5 is a simplified representation for ease of understanding. From the start of heating until time t1, the resistance increases at a certain rate of change (slope of graph G1). At change point P1, the resistance increases at a smaller rate of change (slope of graph G1) than time t1. Change point P1 indicates a change in the manner in which the electrical characteristic value (resistance in this case) of the metal pipe material changes. The displacement increases from change point P1 until the output of power supply 28 is stopped.

[0035] Here, Figure 6(a) is a graph showing the relationship between electrical resistivity and temperature. In Figure 6(a), the electrical resistivity during heating is plotted for metal pipe materials 40 made of different materials. As shown in Figure 6(a), the behavior of the resistance value (electrical characteristic value) changes significantly around the austenite transformation temperature. The austenite transformation temperature CT shown in Figure 6(a) is approximately 720°C. Since the austenite transformation temperature CT is a physical characteristic, it remains constant regardless of the size of the object being heated or the power supply state. Therefore, in Figure 6(a), the point where the change in the manner of change occurs, such as from a state where the resistance value changes at a predetermined rate of change to a state where it changes at a smaller rate of change, indicates that it is either the austenite transformation temperature or a temperature near the austenite transformation temperature, regardless of the power supply state or variations in the metal material. The temperature near the change point P1 in Figure 5 is close to the austenite transformation temperature regardless of the shape of the metal pipe material 40 or the power supply state. Therefore, the temperature can be estimated by the detection unit 70 detecting the change point P1.

[0036] The change point P1 in graph G1 can be set at any position as long as it indicates a change in the manner of change of the electrical characteristic value of the metal pipe material 40. For example, when a graph of displacement (graph G2 in Figure 8) is created by differentiating the resistance graph G1, the point where the change in value switches from an increasing state to a decreasing state (maximum point) can be set as the change point P1. Alternatively, when an acceleration graph (graph G3 in Figure 8) is created by differentiating graph G1 twice, the point where the acceleration switches from positive to negative can be set as the change point P1. Note that the actual change in resistance value contains noise as shown in Figure 6(b), so the vertical fluctuations due to noise can be ignored, and the change point P1 can be detected after converting it to an approximation line or similar.

[0037] Furthermore, as shown in Figure 7, the slope of the temperature rise after the change point remains constant regardless of the shape of the metal material or the power supply state. Note that ΔR in Figure 7 represents the variation in resistance value caused by the shape of the metal material and the power supply state. In this embodiment, control is performed by detecting the change point P1 rather than the absolute value of the resistance value, so it is possible to avoid being affected by the variation in the resistance value. As shown in Figure 5, if heating is performed for a predetermined time Δt after the detection unit 70 detects the change point P1, the metal pipe material 40 can be heated to the desired target temperature. Alternatively, if heating is performed until the resistance value changes by a predetermined amount Δω after the detection unit 70 detects the change point P1, the metal pipe material 40 can be heated to the desired target temperature.

[0038] Based on the above, the detection unit 70 detects a change point P1 indicating a change in the pattern of change of the electrical characteristic value. The heating unit 5 controls the temperature of the metal pipe material 40 based on the electrical characteristic value detected by the detection unit 70. Specifically, the heating unit 5 stops supplying power to the metal pipe material 40 after a predetermined time Δt has elapsed since detecting the change point P1. The predetermined time Δt is set in advance, taking into consideration the time required to reach the target temperature from the austenite transformation temperature. Alternatively, the heating unit 5 stops supplying power to the metal pipe material 40 after the resistance value has reached a predetermined predetermined change amount Δω since detecting the change point P1. The predetermined change amount Δω is set in advance, taking into consideration the change amount required to reach the target temperature from the austenite transformation temperature.

[0039] Refer to Figure 8 to explain the specific temperature control details. Figure 8 shows an example in which the detection unit 70 detects a change point P1 in the resistance value. Figure 8 shows two methods for detecting the change point P1: one using a graph G2 that shows the displacement of the resistance value, and another using a graph G3 that shows the acceleration of the resistance value.

[0040] First, we will explain an example in which the detection unit 70 detects the change point P1 using the displacement of the resistance value. As shown in Figure 8, we will explain assuming that the time at which the maximum point P2 of the displacement graph G2 occurs coincides with the time at which the change point P1 occurs. As shown in Figure 8, the control unit 8 of the detection unit 70 calculates the displacement by differentiating the resistance value at a constant time interval tx. Up until the time at which the maximum point P2 occurs, the control unit 8 detects a monotonically increasing displacement at the time interval tx. For example, at time ta just before reaching the maximum point P2, the control unit 8 detects a high displacement. On the other hand, after the time at which the maximum point P2 occurs, the displacement decreases rapidly. Therefore, at time tb following time ta, the control unit 8 detects a value lower than the displacement value at time ta.

[0041] The control unit 8 detects the change point P1 by detecting the maximum point P2 if the detected displacement is lower than the previous value and is below the threshold TH. At time tb, the control unit 8 detects the detection point P4 between the maximum point P2 and the minimum point P3. However, by detecting the detection point P4, it is possible to detect that the maximum point P2 (i.e., the change point P1) has just been passed. Thus, detecting that the change point P1 has just been passed is also included in the detection of the change point P1 by the detection unit 70. Next, the control unit 8 stops the power supply after a predetermined time Δt has elapsed from time tb when the maximum point P2 was detected. Alternatively, the control unit 8 stops the power supply after the resistance value has changed by a predetermined amount Δω from the value at the time the change point P1 was detected.

[0042] The time interval tx is not particularly limited, but a smaller interval improves the detection accuracy of the maximum point P2. Furthermore, it is preferable that the time interval tx is smaller than the time interval between the maximum point P2 and the minimum point P3 on graph G2. Also, the amount of displacement does not decrease from immediately after the start of heating until approaching the maximum point P2. Therefore, a predetermined time from the start of heating may be set as a negligible period t3. During the negligible period t3, the control unit 8 does not need to perform calculations of the displacement amount or comparisons with previous values.

[0043] Next, we will explain an example in which the detection unit 70 detects the change point P1 using the acceleration of the resistance value. As shown in Figure 8, we will explain assuming that the time when the acceleration graph G3 switches from positive to negative coincides with the time when the change point P1 occurs. As before, the control unit 8 of the detection unit 70 calculates the acceleration at a constant time interval tx. The acceleration is the acceleration of the change in resistance value. The control unit 8 calculates the acceleration by differentiating the displacement. Until the time of the change point P1, the control unit 8 detects a constant acceleration at the time interval tx. At the change point P1, the acceleration drops sharply from positive to negative. For example, at time ta just before reaching the change point P1, the control unit 8 detects a positive acceleration. On the other hand, at the timing immediately after the change point P1, the acceleration is negative. Therefore, the control unit 8 detects a negative acceleration at time tb following time ta.

[0044] The control unit 8 detects a change point P1 if the detected acceleration is negative. Next, the control unit 8 stops the power supply after a predetermined time Δt has elapsed from the time tb at which the change point P1 was detected. Alternatively, the control unit 8 stops the power supply after the resistance value has changed by a predetermined amount Δω from the resistance value at the time the change point P1 was detected.

[0045] Figure 9 shows an example where the detection unit 70 detects the change point P1 as an electrical characteristic value when performing constant voltage control. Figure 9 shows graph G4 showing the change in current value, graph G5 showing the displacement of the current value, and graph G6 showing the acceleration of the current value. In this case, since the current value decreases over time, the detection unit 70 and the control unit 8 perform the same processing as in Figure 8, except that the positive and negative signs in graph G5 of the displacement and graph G6 of the acceleration are reversed compared to graphs G2 and G3 shown in Figure 8.

[0046] Next, with reference to Figure 10, the electric heating method according to this embodiment will be described.

[0047] First, the heating unit 5 heats the metal pipe material 40 by passing an electric current through it (step S10: heating process). Next, the detection unit 70 detects the electrical characteristic values ​​during heating by the heating unit 5 (step S20: detection process). Then, the detection unit 70 determines whether or not a change point P1 has been detected (step S30: detection process). If it is determined in step S30 that a change point P1 has not been detected, the detection unit 70 returns to step S20 and detects the electrical characteristics again at a predetermined timing.

[0048] If it is determined in step S30 that a change point P1 has been detected, the heating unit 5 waits for a predetermined time Δt (step S40: heating process). During this time, the heating unit 5 continues to apply power for heating. Next, after the predetermined time Δt has elapsed, the heating unit 5 stops applying power for heating (step S50: heating process). In this way, during the heating process, the temperature of the metal pipe material 40 is controlled based on the electrical characteristic values ​​detected in the detection process.

[0049] Next, the operation and effects of the electrically heated device 100 and the electrically heated method according to this embodiment will be described.

[0050] The energized heating device 100 includes a detection unit 70 that detects electrical characteristic values ​​during heating by the heating unit 5. The electrical characteristic values ​​exhibit similar behavior in relation to temperature, regardless of the power supply state or variations in the metal material. Therefore, the heating unit 5 controls the temperature of the metal material based on the electrical characteristic values ​​detected by the detection unit 70. This allows the heating unit 5 to perform accurate temperature control based on the electrical characteristic values, regardless of the power supply state or variations in the metal material. This enables accurate temperature control regardless of variations in the metal material, thereby suppressing problems related to the molding apparatus that occur when the energizing time is unnecessarily short or long (such as the metal material not forming the desired shape, worsening power consumption, or electrode wear).

[0051] The detection unit 70 detects a change point indicating a change in the pattern of change of the electrical characteristic value, and the heating unit 5 may control the temperature of the metal material based on the detection result of the change point by the detection unit 70. The pattern of change of the electrical characteristic value changes significantly at the austenite transformation temperature. Therefore, the change point P1, which indicates a change in the pattern of change of the electrical characteristic, indicates that the metal material is at or near the austenite transformation temperature, regardless of the power supply state or variations in the metal material. Thus, the heating unit 5 can perform highly accurate temperature control based on the detection result of the change point P1.

[0052] The heating unit 5 may stop supplying power to the metal material after the change point P1 is detected and the electrical characteristic value has changed by a predetermined amount. The electrical characteristic value increases steadily after the austenite transformation temperature, regardless of the power supply state or variations in the metal material. Therefore, the heating unit 5 can stop supplying power at the desired target temperature once the electrical characteristic value has changed by a predetermined amount after the change point P1 is detected.

[0053] The heating unit 5 may stop supplying power to the metal material after a predetermined time has elapsed since the detection of the change point P1. The electrical characteristics after the austenite transformation temperature increase steadily regardless of the power supply conditions or variations in the metal material. Therefore, the heating unit 5 can stop supplying power at the desired target temperature after a predetermined time has elapsed since the detection of the change point P1.

[0054] The molding apparatus 1 according to this embodiment includes the above-described electrically heated device 100 and molds the heated metal material.

[0055] This molding apparatus 1 can achieve the same effects and functions as the electrically heated apparatus 100 described above.

[0056] The electric heating method according to this embodiment is an electric heating method used in a molding apparatus 1 for expanding and molding a metal material, and comprises a heating step of heating the metal material by passing an electric current through it, and a detection step of detecting the electrical characteristic value of the heating by the heating step, wherein the heating step controls the temperature of the metal material based on the electrical characteristic value detected in the detection step.

[0057] This electric heating method allows for the same effects and functions as the electric heating device 100 described above to be obtained.

[0058] This disclosure is not limited to the embodiments described above.

[0059] The molding apparatus can be any apparatus that heats the metal material, and a hot stamping molding apparatus may be used. In this case, the metal material will be a sheet material. [Explanation of Symbols]

[0060] 1... Molding device, 5... Heating unit, 40... Metal pipe material (metal material), 70... Detection unit, 100... Electrical heating device.

Claims

1. An electrically heated device used in a molding apparatus for expanding and molding a metal material, A heating unit that heats a metal material by passing an electric current through it, The system includes a detection unit for detecting electrical characteristic values ​​during heating by the heating unit, The detection unit detects a change point that indicates a change in the pattern of change of the electrical characteristic value, The heating section is Based on the detection result of the change point by the detection unit, the temperature of the metal material is controlled. An electric heating device that stops supplying current to the metal material after the change point has been detected and the electrical characteristic value has changed by a predetermined amount.

2. An electrically heated device used in a molding apparatus for expanding and molding a metal material, A heating unit that heats a metal material by passing an electric current through it, The system includes a detection unit for detecting electrical characteristic values ​​during heating by the heating unit, The detection unit detects a change point that indicates a change in the pattern of change of the electrical characteristic value, The heating section is Based on the detection result of the change point by the detection unit, the temperature of the metal material is controlled. An electric heating device that stops supplying power to the metal material after a predetermined time has elapsed since the detection of the aforementioned change point.

3. A molding apparatus comprising an electrically heated device according to claim 1 or 2, for molding the heated metal material.

4. An electric heating method used in a molding apparatus for expanding and shaping metal materials, A heating process in which an electric current is passed through a metal material to heat it, The system includes a detection step for detecting the electrical characteristic values ​​during heating by the aforementioned heating step, In the detection step, a change point indicating a change in the manner of change of the electrical characteristic value is detected, In the aforementioned heating step, Based on the detection results of the change point in the aforementioned detection step, the temperature of the metal material is controlled. An electric heating method comprising stopping the supply of current to the metal material after the change point has been detected and the electrical characteristic value has changed by a predetermined amount.

5. An electric heating method used in a molding apparatus for expanding and shaping metal materials, A heating process in which an electric current is passed through a metal material to heat it, The system includes a detection step for detecting the electrical characteristic values ​​during heating by the aforementioned heating step, In the detection step, a change point indicating a change in the manner of change of the electrical characteristic value is detected, In the aforementioned heating step, Based on the detection results of the change point in the aforementioned detection step, the temperature of the metal material is controlled. An electric heating method comprising stopping the supply of current to the metal material after a predetermined time has elapsed since the detection of the change point.

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