JP2013212520A - Electrical heating method and hot press forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a desired temperature distribution in a to-be-heated member formed into a non-rectangular shape and in a to-be-heated member different in energizing direction between electrodes in thickness when heating the to-be-heated member by electrical heating.SOLUTION: An electrical heating method for heating a to-be-heated member by installing and energizing a pair of electrodes spaced mutually includes a step for preparing a plate-like to-be-heated member formed into a prescribed shape, a step for deciding the pre-heating condition of the to-be-heated member, a step for installing a pair of electrodes on the to-be-heated member by preheating the to-be-heated member in accordance with the preheating condition, and a step for energizing the interelectrode in a state in which the temperature state of the preheated to-be-heated member is maintained, wherein the preheating condition is decided so that a target temperature distribution can be made in the to-be-heated member by energization in the step for deciding the preheating condition of the to-be-heated member.

Description

  The present invention relates to an electric heating method for heating a member to be heated by electric heating and a hot press molding method for press-molding a heated member heated by the electric heating method.

  For example, a plate-like material (heated member) such as a steel plate used for a vehicle body such as an automobile is generally used after being formed into a predetermined shape by press molding. In addition, when a heated member such as a high-strength steel plate is used to reduce the weight or strength of the vehicle body, hot press forming is performed in which the member is heated and press forming is performed after improving the formability. ing.

  Thus, when press-molding by heating a member to be heated, it is required to heat the member to be heated quickly in order to shorten the molding cycle time. In response to such demands, there is known an energization heating method in which electrodes are attached to both ends of a member to be heated and the members are energized to quickly heat the member by Joule heat generated in the member to be heated.

  However, when a heated member formed in a non-rectangular shape or a heated member having a different thickness in the energization direction between the electrodes is used in the energization heating, the cross-sectional area differs in the energization direction. Therefore, there is a variation in the heating temperature of the member to be heated, and there may be a variation in the elongation of the member, the strength of the molded product, etc. during press molding.

  In some cases, it is desired to create a desired temperature distribution on the member to be heated from the viewpoint of mechanical properties required for the final product, efficiency of post-processing, and the like.

  On the other hand, in order to provide a desired temperature distribution in the heated member formed in a non-rectangular shape, for example, Patent Document 1 discloses that the sides of the heated member opposite to each other are orthogonal to the direction. A method is disclosed in which a plurality of pairs of electrodes facing each other in a direction are attached and the energization amount is adjusted for each electrode pair.

  Further, for example, in Patent Document 2, a temperature distribution is controlled by setting a current density changing portion whose width direction end portion is inclined at an angle of 15 degrees or more and 90 degrees or less between the both ends and the center portion of the heated member. A method is disclosed.

JP 2002-248525 A JP 2009-274122 A

  However, in the method described in Patent Document 1, it is necessary to prepare an extremely large number of electrodes according to the shape of the member, which is very expensive. Further, in the method described in Patent Document 2, since the temperature distribution depends on the shape of the heated member, a desired temperature distribution cannot be provided on the heated member depending on the shape of the heated member.

  Therefore, the present invention creates a desired temperature distribution on a heated member formed in a non-rectangular shape or a heated member whose thickness differs in the energizing direction between the electrodes when the heated member is heated by energization heating. The task is to do.

  In order to solve the above problems, the present invention is configured as follows.

  First, the invention according to claim 1 of the present application is an energization heating method for heating the member to be heated by attaching a pair of spaced electrodes to the member to be heated and energizing the member to be heated, which is formed in a predetermined shape. Preparing a plate-like member to be heated, determining a preheating condition for the member to be heated, preheating the member to be heated according to the determined preheating condition, and attaching a pair of electrodes to the member to be heated And a step of energizing between the electrodes while maintaining a temperature state of the preheated member to be heated. In the step of determining the preheating condition, a target is applied to the member to be heated by energization. The preheating conditions are determined so that the temperature distribution of the above is created.

  According to a second aspect of the present invention, in the first aspect of the invention, in the step of determining the preheating condition of the heated member, the heated member has a predetermined target temperature in a cross section perpendicular to the energizing direction. It divides | segments into the several area | region which has, and preheating conditions are determined for every area | region.

  According to a third aspect of the present invention, in the second aspect of the present invention, in the step of determining the preheating condition of the member to be heated, the cross-sectional area of the cross section perpendicular to the energizing direction of each region and the temperature are determined. The preheating condition is determined based on the electrical resistivity of the member to be heated, which varies depending on the condition.

  According to a fourth aspect of the present invention, in the invention according to the second or third aspect, in the step of determining the preheating condition of the heated member, the cross-sectional area of the cross section perpendicular to the energizing direction of the heated member is energized. When the direction changes, the size of the region in the energization direction is smaller on the side where the cross-sectional area is smaller than on the larger side.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the member to be heated is preheated according to the determined preheating condition, and a pair of electrodes is provided on the member to be heated. In the step of attaching the preheated device to the heated member, the heated member is preheated, a pair of electrodes is attached to the heated member, and the preheated device is arranged side by side in the energization direction, respectively. A preheating device provided with a bar heater capable of controlling the heating temperature is used.

  Moreover, in the invention which concerns on Claim 6 in the invention of any one of Claims 1-4, in the step which preheats the said to-be-heated member, let the inner side of the energized hollow high frequency coil pass, and the said When the heated member is induction-heated and the heated member passes through the center of the high-frequency coil, the cross-sectional center of the cross-section of the heated member orthogonal to the passing direction of the heated member and the hollow portion of the high-frequency coil It is characterized by substantially matching the center.

  Moreover, the invention which concerns on Claim 7 is a hot press molding method which heats the said to-be-heated member with the electric heating method of any one of Claims 1-6, Comprising: Said heating using a shaping | molding die The heated member to be heated is press-molded.

  With the above configuration, according to the invention of each claim of the present application, the following effects can be obtained.

  First, according to the invention according to claim 1 of the present application, preheating is performed so that a target temperature distribution is created in the heated member by energization heating, and the temperature state of the preheated heated member is maintained. By energizing between the electrodes, a desired temperature distribution can be created in the heated member after energization heating.

  Moreover, according to the invention which concerns on Claim 2 or 3, since the preheating conditions of a to-be-heated member can be determined for every divided | segmented area | region, temperature distribution with higher precision can be created.

  Further, according to the invention of claim 4, fine control can be performed in a region where the temperature change is larger by reducing the size of the region in the energizing direction on the side where the cross-sectional area is small compared to the large side. Therefore, a temperature distribution with higher accuracy can be created.

  Moreover, according to the invention which concerns on Claim 5, it can heat easily according to to-be-heated conditions by using the preheating apparatus provided with the rod-shaped heater which can respectively control heating temperature as a preheating apparatus. it can.

  According to the invention of claim 6, the inside of the high-frequency coil is passed so that the cross-sectional center of the cross section perpendicular to the passing direction of the heated member and the center of the hollow portion of the high-frequency coil substantially coincide. By induction heating, heating according to the heating condition can be easily performed.

  According to the seventh aspect of the present invention, the heated member is preheated and energized so that a target temperature distribution is created, and the heated heated member is press-molded using a mold. Thus, the member to be heated can be quickly heated in a state where a desired temperature distribution is created. Therefore, the member to be heated can be press-molded in a temperature distribution state required according to the final product, and the cycle time of press molding can be shortened.

It is a figure explaining the flow of the press molding method including the electric heating method by Embodiment 1 of this invention. It is the side view (FIG.2 (a)) and top view (FIG.2 (b)) of the preheating apparatus used with the electric heating method by Embodiment 1 of this invention. It is a front view of the electric heating apparatus used with the electric heating method by embodiment of this invention. It is a flowchart which shows the determination method of preheating conditions. It is a graph which shows the temperature dependence of the electrical resistivity of the material which can be used as a to-be-heated member. It is a figure explaining the division | segmentation into each area of a to-be-heated member. It is a figure explaining the relationship between preheating temperature distribution and electricity supply time. It is a figure corresponding to FIG. 2 which shows the pre-heating apparatus in pre-heating. It is a perspective view of the preheating apparatus used with the electric heating method by Embodiment 2 of this invention. It is a block diagram of the preheating apparatus used with the electric heating method by Embodiment 2 of this invention. It is a figure for demonstrating the effect of the electric heating method by Embodiment 2 of this invention. It is a perspective view which shows another Example of the preheating apparatus used with the electricity heating method by Embodiment 2 of this invention.

Hereinafter, a hot press forming method including an electric heating method according to an embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a diagram illustrating a flow of a press molding method including an electric heating method according to Embodiment 1 of the present invention. The high-strength material P supplied from the supply means 1 is blanked by the blanking device 2. The blanked plate-like high-strength material P (hereinafter referred to as a plate-like heated member W) is conveyed to the preheating device 20 through the first conveying means 3. In the preheating device 20, preheating is performed according to preheating conditions controlled by the preheating control device 40. The preheated member W to be heated is transported to the energization heating device 30 by the arm 4a of the second transport means 4 as indicated by an arrow (A) in FIG. The energization heating device 30 is energized and heated according to the energization time controlled by the energization control device 50. The heated member W that is heated by conduction is transported to the press molding device 6 by the third transport means 5 and is press-molded into a desired shape by the press molding device 6. Preheating conditions and energization time will be described later.

  The conveyance from the preheating device 20 to the energization heating device 30 is performed as quickly as possible so as to be energized and heated while the temperature distribution state of the heated member W preheated according to the preheating conditions is maintained. . Alternatively, the preheating device 20 can be integrated with the electric heating device 30 so that the electric heating is performed while the preheated temperature distribution state is maintained. Further, the conveyance from the electric heating device 30 to the press molding device 6 is performed as quickly as possible so that the press molding is performed in a state where the temperature distribution state created by the electric heating is maintained.

  Next, the preheating device 20 will be described with reference to FIGS. 2A and 2B showing a side view and a top view of the preheating device used in the electric heating method according to Embodiment 1 of the present invention. The preheating member 20 according to the present embodiment heats the heated member W, a main body 21 on which the plate-shaped heated member W is installed, positioning members 22a to 22c for positioning the heated member W at predetermined positions. And a plurality of rod-shaped heaters 23.

  The rod heater 23 is inserted into a mounting hole provided in the main body 21. Further, since each bar heater 23 is independently connected to the preheating control device 40 via each lead wire 24, the current value flowing through each bar heater 23 can be controlled. Therefore, the heating temperature of each bar heater 23 can also be controlled.

  The main body 21 is made of a material having a high thermal conductivity, for example, a metal, in order to efficiently conduct the heat generated by the rod-shaped heater 23 to the heated member W. The positioning members 22a to 22c can be made of a porous inorganic material such as ceramic that does not let the heat of the rod-shaped heater 23 escape to the outside and can withstand the preheating temperature.

Next, with reference to FIG. 3, the energization heating apparatus 30 used in the energization heating method according to the embodiment of the present invention will be described.
The energization heating device 30 includes bar electrodes 31a and 31b for energizing the plate-shaped heated member W, and a power supply 32 that is connected to the energization control device 50 and applies a DC voltage or an AC voltage between the electrodes 31a and 31b. And a cable 33 connecting the power source 32 and the electrodes 31a and 31b. Further, positioning members 34a and 34b are provided outside the electrodes 31a and 31b, and a positioning member 34c is provided between the electrodes 31a and 31b, and the heated member W is positioned at a predetermined position. In FIG. 3, the direction from the small cross-sectional area S to the large side is defined as the energization direction, but the reverse direction may be the energization direction.

  Here, the cross section refers to a cross section perpendicular to the energizing direction corresponding to the longitudinal direction of the member to be heated W indicated by an arrow in FIG. 3, and the cross sectional area S is the area of the cross section. The same applies to the following description.

Next, preheating conditions (hereinafter referred to as preheating conditions) performed by the energization heating method according to the embodiment of the present invention will be described with reference to FIGS.
FIG. 4 is a flowchart showing a method for determining preheating conditions. In the present invention, the “preheating condition” refers to information on preheating applied to the preheating control device 40, including a preheating temperature distribution created on the plate-shaped heated member W by preheating. As shown in FIG. 4, the preheating condition determining method includes step S1 for functionalizing the temperature dependence of the electrical resistivity of the member to be heated by regression analysis, step S2 for determining the shape of the member to be heated, and the final target. Step S3 for determining the heating temperature distribution, Step S4 for temporarily setting the preheating temperature distribution, Step S5 for calculating the temperature distribution after a predetermined time for each area, Step S6 for determining the preheating temperature distribution, and Target temperature distribution Step S7 for correcting the setting of the preheating temperature distribution of each area from the deviation from the above is included.

  FIG. 5 is a graph showing the temperature dependence of the electrical resistivity of a material that can be used as a member to be heated. FIG. 5 shows the electrical resistivity of mild steel (SPCC) having a carbon content of 0.06% and a manganese content of 0.38%. The material of the member to be heated is not limited to mild steel, and for example, aluminum, stainless steel, magnesium, cast iron, titanium, or CFRP (carbon fiber reinforced plastic) can be used.

  In step S1, the values of the electrical resistivity ρ of the material measured at various temperatures in advance are input to a computer, and a regression curve indicating the temperature dependence of the electrical resistivity ρ is determined. In general, the temperature dependence of the electrical resistivity ρ depends on the material used. In FIG. 5, the regression analysis is performed with a cubic function, but it may be functionalized with other polynomials or other functions.

Next, in step S2, the shape of the plate-shaped heated member W is determined based on the shape of the final product. Subsequently, in step S3, a desired temperature distribution to be created in the heated member W after the heating by heating is determined in consideration of mechanical characteristics required for the final product after press molding, efficiency of post-processing, and the like. Desired temperature distribution, the resistance heating apparatus 30 in consideration of the temperature drop in the transport time to the press-forming device 6, may be set higher by overall [Delta] T _A. Further, as described below, to account for the temperature change in the cross-sectional area S is smaller side of the heating member W is greater, [Delta] T _A is the side cross-sectional area S is small, compared to the side cross-sectional area S is larger You can make it bigger.

  FIG. 6 is a diagram illustrating the division of the member to be heated into each area. In step S4, as shown in FIG. 6, first, the member to be heated W is divided into a plurality of areas in a cross section orthogonal to the longitudinal direction (x direction) that is the energization direction during energization heating. Next, a preheating temperature is temporarily set for each area.

  In general, the magnitude R of the electrical resistance is proportional to the electrical resistivity ρ of the resistance and inversely proportional to the cross-sectional area S of the resistance. In the case of a non-rectangular member to be heated, the cross-sectional area differs in the energization direction. Further, Joule heat generated by energizing and heating the member to be heated increases on the side where the resistance R is large, that is, on the side where the cross-sectional area S is small. Therefore, when the member to be heated is energized, the temperature increases on the side where the cross-sectional area S is small.

  When a non-rectangular heated member having a large cross-sectional area on the + x side as shown in FIG. 6 is used, when energization heating is performed without preheating, the temperature increases on the −x side. Therefore, for example, when it is desired to make the entire heated member W uniform temperature, the preheating temperature on the + x side can be set high as shown in FIG.

  In FIG. 6A, the widths of the divided areas in the x direction are made equal. On the other hand, as shown in FIG. 6 (b), the cross-sectional area of the heated member is small, and the width on the -x side may be set smaller. As can be seen from FIG. 7A described below, the temperature change due to the current heating becomes larger on the side where the cross-sectional area S of the heated member W is smaller. This is because the heat capacity is smaller on the side where the cross-sectional area S is smaller than on the side where the cross-sectional area S is large. Therefore, by setting the width of the area on the side where the cross-sectional area S is small, a finer temperature setting is possible.

FIG. 7 is a diagram illustrating the relationship between the preheating temperature distribution and the energization time. FIG. 7A shows the temperature distribution in the x direction of the heated member before energization heating and after energization heating for a predetermined time. T _{1 to} T ₃ are initial temperatures of the heated members at positions x _{1 to} x ₃ shown in FIG. Further, FIG. 7 (b), the time variation of temperature when energized heating the heating member, respectively show the position x ₁ ~x _3.

Here, in consideration of the temperature drop in the conveyance time from preheat unit 20 to the conduction heating apparatus 30 may be set higher by overall [Delta] T _P a desired temperature distribution. Moreover, taking into account the thermal capacity of the cross-sectional area S is smaller side is small, [Delta] T _P is the side cross-sectional area S is small, it may be larger than the cross-sectional area S is larger side.

In step S5, first, a representative cross section is determined for each area. For example, the central cross section of the width in the x direction of the area can be used as the representative cross section. Next, for each area, 1) the cross-sectional area of the representative cross section of each area, 2) the width in the x direction of each area, 3) the temperature dependence of the electrical resistance value functioned in step S1, 4) the specific heat, 5 ) Using the current value flowing between the electrodes during energization heating, the temperature distribution after a lapse of a certain time is calculated, and the graphs shown in FIGS. 7A and 7B are created. The temperature distribution in the x direction of the heated member W before the electric heating is converted into a function by a quadratic function by regression analysis, for example. Note that the positions x _{1 to} x ₃ in FIG. 7A are positions in the x direction of the representative cross sections of the areas 1 to 3, respectively.

  Next, in step S6, the desired temperature distribution created in the heated member W determined in step S3 is compared with the graphs shown in FIGS. 7A and 7B to determine the preheating temperature distribution. . If a desired temperature distribution can be created by subsequent energization heating based on the set preheating temperature distribution, it is determined as “good”, and the preheating condition is determined based on the preheating temperature distribution. At the same time, the energization time in the subsequent energization heating is determined so that the target temperature distribution is obtained. When there are a plurality of energization times with the target temperature distribution, the shortest time is set as the energization time.

  For example, when the entire heated member W is desired to have a completely uniform temperature, there is no energization time in which the temperatures of the areas 1 to 3 are equal in the graph shown in FIG. A completely uniform temperature cannot be achieved. However, in press molding, for example, ± 100 ° C. is an acceptable temperature difference. Therefore, for example, the preheating condition may be determined in a state where the temperature of each area can be ± 100 ° C.

  Here, in general, the specific heat also depends on the material and temperature of the heated member W, similarly to the electrical resistivity. Therefore, the method for determining the preheating condition may include the step of performing regression analysis and functionalizing the temperature dependence of specific heat in the same manner as step S1 of performing regression analysis and functionalizing the temperature dependence of electrical resistivity. . The temperature dependence of the functionalized specific heat can be used in step S5.

  If it is determined in step S6 that a desired temperature distribution cannot be created on the heated member W after energization heating depending on the set preheating temperature distribution, it is determined as x and the process proceeds to step S7. In step S7, the preheating temperature distribution is corrected. In step S5, the current value flowing between the electrodes during energization heating is fixed and the temperature distribution after a lapse of a fixed time is calculated. However, in step S7, the current value may be changed simultaneously with the preheating temperature distribution. Based on the preheating temperature distribution corrected in step S7, the graphs of FIGS. 7A and 7B are created again in step S5, and the preheating temperature distribution is determined again in step S6. By repeating steps S5 to S7, the optimum preheating conditions can be determined.

Hereinafter, effects of the energization heating method according to Embodiment 1 of the present invention will be described.
FIG. 8 is a view corresponding to FIG. 2, showing the preheating device during preheating. In FIG. 8, it shows in the state which the to-be-heated member W installed. In the preheating device 20, the preheating control device 40 operates according to the preheating conditions determined in step S <b> 6 of FIG. 4, and a current of a predetermined magnitude flows through each rod heater 23 by the control of the preheating control device 40. . Thereby, each area of the to-be-heated member W conveyed to the preheating apparatus 20 is heated by desired preheating temperature distribution according to preheating conditions. In the energization heating device 30, the energization control device 50 controls the power supply 32, and a current flows through the heated member W during the energization time determined in step S <b> 6 in FIG. 4.

  According to the preheating conditions and the energization time determined in step S6 of FIG. 4, the temperature of the entire heated member W can be made uniform by preheating the plate-like heated member W, and further the desired temperature. Distribution can be created. Further, by using the preheating device 20 provided with the rod heaters 23 each capable of controlling current, preheating according to preheating conditions can be easily performed.

  In addition, the preheating conditions are determined for each area, and further, the preheating conditions are determined in consideration of the electrical resistivity of the heated member W that varies depending on the temperature. Can be created.

  Further, the heated member W preheated and heated in this way is press-molded in a state where a desired temperature distribution is created. Therefore, the member to be heated can be press-molded in a temperature distribution state required according to the final product. Furthermore, the member to be heated can be quickly heated by preheating and current heating, and the cycle time of press molding can be shortened.

  Next, the preheating device 70 used for the energization heating method according to the second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the configuration of the preheating device is different from that of the first embodiment. Other than that, it is the same as the first embodiment, and the description is omitted.

  FIG. 9 is a perspective view of a preheating device used in the energization heating method according to Embodiment 2 of the present invention. As shown in FIG. 9, the preheating device 70 according to the present embodiment includes a high-frequency coil 71 having a hollow rectangular parallelepiped shape, and a conveyor 72 that conveys a plate-shaped heated member W and passes the inside of the coil 71. . The high frequency coil 71 is connected to the preheating control device 90.

  FIG. 10 is a block diagram of a preheating device used in the energization heating method according to Embodiment 2 of the present invention. As shown in FIG. 10, the preheating control device 90 includes an AC power supply 73 that applies an AC voltage to the coil 71 and a power supply control device 75 that controls the AC power supply 73. In accordance with the preheating condition determined in step S6 of FIG. A predetermined high frequency alternating current flows through the coil 71 by the alternating current power source 73 to generate an alternating magnetic field. As a result, an induced current flows through the heated member W passing through the inside of the coil 71, and the heated member W is heated by the generated Joule heat.

  Hereinafter, the case where the heated member W first passes the side where the cross-sectional area S of the cross section orthogonal to the direction passing through the coil 71 is large will be described. The passing direction may coincide with the energizing direction described above.

  In FIG. 9, the x direction coincides with the direction indicated by the arrow (A) in which the heated member W passes on the conveyor 72. Further, the y direction and the z direction are directions perpendicular to the x direction, respectively. The high frequency coil 71 is disposed so that the z-direction position of the center of the hollow portion of the coil 71 coincides with the z-direction position of the cross-sectional center orthogonal to the passing direction (x direction) of the heated member W.

  The high frequency coil 71 is connected to a coil driving device 74 and is configured to be movable in a direction (y direction) indicated by an arrow (A) in FIG. The high frequency coil 71 is moved by the coil driving device 74 so that the position in the y direction at the center of the hollow portion of the coil 71 coincides with the position in the y direction at the center of the cross section perpendicular to the passing direction of the heated member W. Have

FIG. 11 is a diagram for explaining the effect of the energization heating method according to the second embodiment of the present invention. FIG. 11A shows a cross-sectional view of the cross section orthogonal to the x direction of the coil 71. When viewed from the + x direction, the first surface to the fourth surface of the coil 71 are defined as shown in FIG. 11A. To do. FIGS. 11B and 11C are cross-sectional views of the coil 71 and the heated member W when an area having a large cross-sectional area S and a small area pass through the high-frequency coil 71, respectively. Moreover, FIG.11 (d) shows sectional drawing corresponding to FIG.11 (c) about the case where the coil 71 has a structure which does not move to ay direction. 11B to 11D, y ₁ represents the distance from the −y end of the heated member W to the first surface of the coil 71. Similarly, y ₂ , z ₁ and z ₂ are respectively the distance from the + y end of the heated member W to the second surface of the coil 71, the distance from the + z end of the heated member W to the third surface of the coil 71, This represents the distance from the −z end of the heated member W to the fourth surface of the coil 71.

When z ₁ is smaller than z ₂ , the magnitude of the magnetic field received by the + z side principal surface of the heated member W from the coil is greater than the magnitude of the magnetic field received by the −z side principal surface. As a result, the generated Joule heat is larger on the + z side main surface than on the −z side main surface, and thus the member to be heated W cannot be preheated uniformly in the z direction.

On the other hand, in this embodiment, the z-direction position of the center of the hollow portion of the high-frequency coil 71 is configured to coincide with the z-direction position of the center of the cross section orthogonal to the x direction. Therefore, as shown in FIGS. 11B to 11D, z ₁ and z ₂ are equal, and the member to be heated W can be preheated uniformly in the z direction.

When using a thickness in the current direction (x-direction) are different from heated member W, by movable in also in the z direction by a member to be heated W coil driving unit 74, it becomes equal to the z ₁ and z ₂ The member to be heated W can be preheated uniformly in the z direction.

As shown in FIG. 11B, when an area having a large cross-sectional area S passes through the coil 71, that is, when the heated member W starts to pass through the coil 71, y ₁ and y ₂ are made equal. It is assumed that the heated member W is arranged. Here, when the coil 71 does not have a configuration to move in the y direction, as shown in FIG. 11D, as the heated member W passes, y ₁ becomes smaller than y ₂ , so The heating member W cannot be preheated uniformly in the y direction.

  On the other hand, in the present embodiment, the high-frequency coil 71 moves in the y direction, and the y-direction position of the center of the hollow portion of the coil 71 coincides with the y-direction position of the cross-sectional center orthogonal to the x direction. The heated member W can be preheated evenly in the y direction.

Further, when a non-rectangular heated member W as shown in FIG. 9 is used, y ₁ + y ₂ increases as the heated member W passes. Therefore, when the member to be heated W is passed at a constant speed, preheating is further performed on the + x side, which is larger than the −x side where the cross-sectional area S is small.

  This is very convenient when it is desired to make the entire heated member W uniform temperature after the electric heating. This is because, in the preheating device 70, the temperature rises more on the + x side where the cross-sectional area S is smaller than on the -x side, whereas in the current heating device 30, the temperature rises more on the -x side than on the + x side. To do. Therefore, the temperature gradient in the energization direction (x direction) caused by the preheating is offset by the energization heating, and the entire heated member W can be made to have a uniform temperature.

  In this case, even if the -x side having a small cross-sectional area S is kept at a normal temperature, the energization of the coil 71 is stopped in the middle of passage when the entire heated member W can be brought to a uniform temperature by subsequent energization heating. May be.

  The coil 71 is connected to the power supply control device 75. A desired preheating temperature distribution can be created in the member to be heated W by controlling the value of the current flowing through the AC power supply 73 by the power supply control device 75 as the coil 71 passes.

  Further, the conveyor 72 may be connected to a speed control device (not shown) that controls the speed of the conveyor 72. In that case, a desired preheating temperature distribution can be created in the heated member W also by controlling the passing speed of the conveyor 72 and the heated member W moving on the conveyor 72 by the speed control device.

  In this embodiment, the member to be heated W is preheated uniformly in the y direction and the z direction by moving the coil 71 in the y direction and the z direction by the coil driving device 74. Similarly, it is also possible to create a desired temperature distribution in the y direction and the z direction by moving in the y direction and the z direction.

  FIG. 12 is a perspective view showing another example of the preheating device according to the second embodiment of the present invention. In FIG. 9, the coil 71 is arranged in a direction perpendicular to the passing direction (x direction) of the heated member W. On the other hand, as shown in FIG. 12, the member to be heated W can be preheated uniformly in the y direction also by arranging the coil 71 in a direction crossing the x direction.

  In the present embodiment, the case where the coil 71 is first passed through the side having the larger cross-sectional area S of the member to be heated W has been described. Conversely, the coil 71 may be passed through the side having the smaller cross-sectional area S first.

  While the embodiments of the present invention have been described with reference to the accompanying drawings, the present invention is not limited to the illustrated embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. Needless to say, design changes are possible.

  As described above, according to the present invention, when heating a member to be heated formed in a non-rectangular shape when heating the member to be heated by energization heating, the member to be heated is relatively easy. In addition, since a desired temperature distribution can be created, it may be suitably used for heating during press forming of high-strength steel plates used for vehicle body components such as pillars and impact bars.

  6 Press forming device, 20, 70 Preheating device, 23 Bar heater, 30 Current heating device, 32 Power source, 31a, 31b Electrode, 40, 90 Preheating control device 50 Current control device, 71 High frequency coil, W Heated member

Claims (7)

An energization heating method for heating the heated member by attaching and energizing a pair of electrodes that are spaced apart from the heated member,
Preparing a plate-like member to be heated formed in a predetermined shape;
Determining preheating conditions for the member to be heated;
Preheating the member to be heated in accordance with the determined preheating condition, and attaching a pair of electrodes to the member to be heated;
Energizing between the electrodes in a state where the temperature state of the preheated member to be heated is maintained,
In the step of determining the preheating condition of the member to be heated, the preheating condition is determined so that a target temperature distribution is created in the member to be heated by energization.   In the step of determining preheating conditions for the member to be heated, the member to be heated is divided into a plurality of regions each having a predetermined target temperature in a cross section orthogonal to the energizing direction, and the preheating conditions are determined for each region. The energization heating method according to claim 1.   In the step of determining the preheating condition of the member to be heated, the preheating condition is determined based on the cross-sectional area of the cross section orthogonal to the energizing direction of each region and the electrical resistivity of the member to be heated that changes according to the temperature. The energization heating method according to claim 2, wherein:   In the step of determining the preheating condition of the heated member, when the cross-sectional area of the cross section orthogonal to the energizing direction of the heated member changes to the energizing direction, the size of the region in the energizing direction is set to be small. 4. A method according to claim 2 or 3, characterized in that the side is smaller than the larger side. In the step of preheating the member to be heated according to the determined preheating condition and attaching the pair of electrodes to the member to be heated, the member to be heated is preheated by bringing the preheating device into contact with the member to be heated. Attach a pair of electrodes to the heated member,
5. The energization heating according to claim 1, wherein the preheating apparatus is a preheating apparatus provided with a bar heater arranged in the energization direction and capable of controlling the heating temperature. Method. In the step of preheating the member to be heated according to the determined preheating condition and attaching a pair of electrodes to the member to be heated, the heated member is induction heated by passing through the inside of an energized hollow high-frequency coil,
When the heated member passes through the center of the high frequency coil, the center of the cross section of the heated member perpendicular to the passing direction of the heated member and the center of the hollow portion of the high frequency coil are substantially matched. The electric heating method according to any one of claims 1 to 4, wherein the method is an electric heating method.   The hot press molding method which heats the said to-be-heated member with the electric heating method of any one of Claims 1-6, and press-molds the said to-be-heated member using the shaping | molding die.

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