JP2013193084A - Electric heating method and hot press forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily suppress unevenness of heating temperature of a member to be heated, particularly, a member to be heated formed in a non-rectangular shape while avoiding a problem of fusing of mutual members to be heated, which is possibly be caused when the members to be heated are electrically heated.SOLUTION: A method for electrically heating a platy member to be heated includes: a step of preparing a plurality of members to be heated; a step of overlapping the members to be heated; a step of attaching a pair of electrodes 11 in a state where the members to be heated are overlapped; and a step of supplying a current between both of the electrodes 11. The total of products S/ρ of a cross sectional area S of a predetermined cross section of each member to be heated in the direction orthogonal to the direction of current supply and an inverse number of electric resistivity ρ is substantially constant in the direction of the current supply, and a pair of platy fusing preventing members 14 having electric resistivity smaller than that of the members to be heated is interposed to both end portions and between each of the members to be heated so that the end portions of the members 14 opposing with each other are in substantially the same positions as the opposing end portions of the pair of electrodes.

Description

  The present invention relates to an energization heating method for heating a conductive member to be heated having a predetermined electric resistance by energization heating, and a hot press molding method for press-molding a member to be heated heated by the energization heating method.

  For example, a plate-like material (plate-like workpiece) such as a steel plate used for a car body such as an automobile is generally used after being formed into a predetermined shape by press molding. In addition, when using a plate-like workpiece such as a high-tensile steel plate in order to reduce the weight or increase the strength of the vehicle body, it is possible to perform hot press molding in which the workpiece is heated and press-molded after improving the formability. Molding is done.

  Thus, when press-molding by heating a plate-shaped workpiece, it is required to heat the plate-shaped workpiece 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 plate-shaped workpiece and the electrodes are energized to quickly heat the workpiece by Joule heat generated in the plate-shaped workpiece.

  However, when electrodes are attached to both ends of a plate-shaped workpiece and heated by energization heating, the plate-shaped workpiece formed in a rectangular shape can be heated substantially uniformly, but is formed in a non-rectangular shape. In a plate-shaped workpiece, since the cross-sectional areas differ in the energization direction between the electrodes, the heating temperature of the workpiece varies, and the workpiece elongation and the strength of the molded product may vary in press molding. Even when the plate-like workpiece is formed in a rectangular shape, the same problem occurs when the thickness of the workpiece differs in the energization direction between the electrodes.

  On the other hand, as an example of suppressing variation in the heating temperature of a non-rectangular plate workpiece, for example, Patent Document 1 discloses that the sides of the plate workpiece facing each other in the longitudinal direction are orthogonal to the direction. A plurality of pairs of electrodes opposed to each other in the direction to be attached and the energization amount is adjusted for each electrode pair is disclosed.

  Further, for example, in Patent Document 2, four or more electrodes are attached to the peripheral portion of a plate-shaped workpiece, two of the electrodes are sequentially selected, and a current is passed between the two electrodes. In addition, there is disclosed a technique in which a plate-like workpiece is heated to have a desired temperature distribution.

  Further, for example, in Patent Document 3, a pair of bar electrodes are arranged in parallel on opposite sides of each part in the longitudinal direction of the plate-like workpiece to form a rectangular shape between the pair of bar electrodes. A device that appropriately controls energization between a pair of electrodes is disclosed.

JP 2002-248525 A JP 2011-189402 A JP 2011-183418 A

  However, when the plate-like workpiece is heated by energization heating as described in Patent Literature 1 to Patent Literature 3, variation in the heating temperature of the plate-like workpiece formed in a non-rectangular shape can be suppressed. Since it is necessary to prepare a very large number of electrodes according to the shape of the workpiece or to perform complicated energization control between the electrodes, the apparatus used for energization heating becomes complicated and the cost increases. Therefore, when heating a plate-shaped workpiece formed in a non-rectangular shape by energization heating, it is desired to relatively easily suppress variations in the heating temperature of the plate-shaped workpiece.

  For this, when energizing between both electrodes by preparing and stacking a plurality of plate-like workpieces so that the sum of the cross-sectional areas in the cross section orthogonal to the energizing direction is substantially constant in the energizing direction. Joule heat generated from a plurality of plate-like workpieces can be made substantially equal in the energizing direction, and variations in the heating temperature of the plate-like workpieces formed in a non-rectangular shape can be suppressed relatively easily.

  In addition, even when a plate-like workpiece and a plate-like heating auxiliary member corresponding to this are overlapped with each other, a plurality of plate-like workpieces can be formed by considering the electrical resistivity of the plate-like workpiece and the plate-like heating auxiliary member. The same effect as when they are superimposed on each other can be obtained.

  However, when a plurality of heated members are energized in this way, depending on the material of the member, the energization amount, the pressing force at the time of overlapping, etc., the superimposed heated members are welded by heating by energization. The occurrence of the problem is expected. When welding occurs, it is necessary to carefully convey the plate-like workpiece. In addition, traces may remain in the portion where the welding has occurred, and the portion cannot be used as a product, resulting in a reduction in production efficiency.

  Therefore, the present invention avoids the problem of welding of heated members that may occur when the heated members are energized and heated, while the heated member, particularly the heated member formed in a non-rectangular shape. It is an object to easily suppress variations in heating temperature.

  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 a plurality of plate-like heated members each having a predetermined electrical resistivity, each of the plurality of heated members formed in a predetermined shape. A step of preparing a member, a step of superimposing the plurality of heated members, a step of attaching a pair of electrodes to the heated members in a state where the plurality of heated members are stacked, and a space between the electrodes The step of preparing the plurality of heated members and the step of superposing the heated members in each of the heated portions in a predetermined cross section orthogonal to the energizing direction of the heated members. The plurality of heated members are prepared and overlapped so that the sum of the product of the cross-sectional area of the member and the product of the reciprocal of the electrical resistivity is substantially constant in the energization direction, In the step of superimposing the heated members, the pair of plate-like welding prevention members having an electrical resistivity smaller than those of the heated members are substantially the same as the opposed ends of the pair of electrodes. It is characterized by interposing between the heated members at both ends of the heated members so as to be in the same position.

  According to a second aspect of the present invention, in the first aspect of the invention, in the step of superimposing the plurality of heated members, the welding prevention member has a thickness of the plurality of coated members when the electrodes are energized. A welding prevention member having a thickness at which at least the central portions of the heating members are in contact with each other is used.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein a gap is generated between the electrode and the welding prevention member or between the welding prevention members due to different shapes of the heated members. In the state where the plurality of heated members are stacked, an electrode having a thick portion that fills the gap is used as the electrodes in the step of attaching a pair of electrodes to the heated members, or the plurality of heated members A welding prevention member having a thick portion that fills the gap is used as the welding prevention member in the step of overlapping the members, or a plate-like welding prevention auxiliary member having an electrical resistivity smaller than these heated members is used as the gap. There is provided a step of interposing in.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the heated member is made of iron and the welding prevention member is made of copper. To do.

  Moreover, the invention which concerns on Claim 5 is a hot press molding method, Comprising: The said to-be-heated member is heated with the electric heating method of any one of Claims 1-4, The said mold is used, 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 first aspect of the present invention, the sum of the products of the cross-sectional area of each heated member and the reciprocal of the electrical resistivity in a predetermined cross section orthogonal to the energization direction is substantially constant in the energization direction. Thus, since a plurality of heated members are prepared and stacked, the Joule heat generated from the heated member when energizing between both electrodes can be made substantially equal in the energizing direction, so that it is relatively easy. Variations in the heating temperature of the member to be heated can be suppressed.

  Even when a non-rectangular heated member is heated, the sum of the products of the cross-sectional area of each heated member and the reciprocal of the electrical resistivity of each heated member in a predetermined cross section orthogonal to the energizing direction is In this case, the heating auxiliary member is prepared and superposed so as to be substantially constant, so that variation in the heating temperature of the member to be heated formed in a non-rectangular shape can be suppressed.

  Without interfering with suppression of variation in the heating temperature of the heated member by interposing a plate-like welding prevention member having an electrical resistivity smaller than the heated member at a predetermined position between the heated members, Welding between the heated members can be prevented.

  Further, according to the invention of claim 2, by using the welding prevention member having such a thickness that at least the center portions of the plurality of heated members are in contact with each other when energizing between the two electrodes, the heating temperature is further reduced. Variations can be suppressed.

  Moreover, according to the invention which concerns on Claim 3, it forms so that the clearance gap between an electrode and the welding prevention member produced by using a non-rectangular to-be-heated member or the gap between welding prevention members may be filled. Current can be made to flow uniformly to the heated member by interposing a plate-like welding preventing auxiliary member having an electrical resistivity smaller than that of the heated member in the gap, Furthermore, variation in heating temperature can be suppressed.

  According to the fifth aspect of the present invention, the sum of the products of the cross-sectional area of each heated member and the reciprocal of the electrical resistivity in a predetermined cross section orthogonal to the energization direction is substantially constant in the energization direction. Are heated by energizing and heating the members to be heated between each member to be heated, and press-molding the heated member using a mold. Welding between members can be prevented, heated member can be heated quickly while suppressing variation in heating temperature, variation in material characteristics of heated member can be prevented, and heating member It is possible to shorten the press molding cycle time.

It is a schematic plan view of the electric heating apparatus which concerns on 1st Embodiment of this invention. FIG. 2 is a side view of the energization heating device viewed from the YA direction, the YB direction, and the YC direction in FIG. 1. It is explanatory drawing for demonstrating the plate-shaped workpiece | work heated by electricity. It is explanatory drawing for demonstrating the cross-sectional area in the cross section orthogonal to the electricity supply direction of the plate-shaped workpiece | work heated by electricity. It is explanatory drawing for demonstrating the temperature measurement conditions of the plate-shaped workpiece | work heated by electricity. It is a conceptual diagram which shows the plate-shaped workpiece before and behind electric heating. It is the schematic which shows an example of the press molding apparatus provided with the electric heating apparatus. It is explanatory drawing for demonstrating the product of the cross-sectional area in the cross section orthogonal to the electricity supply direction of the plate-shaped workpiece | work heated by electricity, and a heating auxiliary member, and the inverse number of an electrical resistivity. It is the schematic of the electricity heating apparatus which concerns on 2nd Embodiment of this invention. It is the schematic of the electricity heating apparatus which concerns on 3rd Embodiment of this invention. The modification of the plate-shaped workpiece | work heated by electricity is shown.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic plan view of an electric heating device according to the first embodiment of the present invention. 2 is a side view of the energization heating device viewed from the YA direction, YB direction, and YC direction in FIG. 1, and FIGS. 2 (a) to 2 (c) are YA direction, YB direction, and YC, respectively. It is a side view of the electric heating apparatus seen from the direction. In each of FIGS. 2A to 2C, a part of a positioning member to be described later is indicated by a two-dot chain line, which is shown in a transmissive state. As shown in FIGS. 1 and 2, the x direction is the energization direction, and the y direction is the direction in which an electrode 11 and a welding prevention member 14 described later extend.

  The energization heating apparatus 1 heats a work by Joule heat generated in the work by attaching electrodes that are separated from each other to a work (blank) formed in a substantially flat plate shape, and in this embodiment, Although it is not limited, it shows about what heats two piled works.

  As shown in FIGS. 1 and 2, the energization heating device 1 includes an energization means 10 for electrically heating two conductive workpieces W1 and W2 having a predetermined electric resistance. The energization means 10 includes a pair of electrodes 11 that are spaced apart from each other in parallel, a power source 12 that supplies DC or AC power to the electrode 11, and a cable 13 that connects the power source 12 and the electrode 11. The workpieces W1 and W2 are heated by bringing the pair of electrodes 11 into contact with both ends of the superimposed workpieces W1 and W2 and energizing them. The pair of electrodes 11 are bar electrodes formed in a substantially rectangular parallelepiped shape using a material such as copper, for example, and one electrode 11a is used as a positive electrode and the other electrode 11b is used as a negative electrode.

  The electric heating device 1 also includes a pair of welding prevention members 14a and 14b between the workpieces W1 and W2. The welding prevention member 14 is formed in a plate shape using a material such as copper, for example, similarly to the electrode 11, but is not limited thereto, and is made of a material having a lower electrical resistivity than the workpieces W <b> 1 and W <b> 2. Can do. Moreover, the welding prevention member 14 can be formed in a substantially rectangular parallelepiped shape like the electrode.

  As will be described later, the workpieces W1 and W2 are subjected to pressure by the clamp member 15 at their ends. Therefore, when the work is heated by energization, welding is likely to occur at a portion that receives pressure from the clamp member 15. Even if a current of the same magnitude flows through the workpiece and the welding prevention member by interposing the welding prevention member 14 made of a material having a lower electrical resistivity than the workpiece between the workpieces W1 and W2, it is more than that between irons. Since iron and copper have lower contact resistance and less heat generation, the temperature of the welding prevention member 14 does not rise to the temperature at which welding occurs, and therefore welding can be prevented.

  In FIGS. 1 and 2, the welding preventing member 14 has the same length (x direction) and width (y direction) as the electrode 11. The welding prevention member 14 should just have the width | variety which covers work W1, W2 in ay direction, for example, may have a width | variety larger than an electrode.

  On the other hand, it is preferable that the welding prevention member 14 does not enter the energization range inside the electrode 11 in the x direction. First, this is because the welding prevention member 14 is made of a material having a low electrical resistivity. That is, when the welding prevention member 14 enters the energization range inside the electrode, the current flows preferentially through the welding prevention member 14, so that the workpieces W1 and W2 cannot be uniformly heated in the x direction. Second, when the welding prevention member 14 enters the energization range inside the electrode 11, the sum of the products of the cross-sectional area of each workpiece and the reciprocal of the electrical resistivity in a predetermined cross section orthogonal to the energization direction is constant. Because it disappears, it cannot be heated uniformly. Third, contact between the workpieces W1 and W2 during energization is hindered. The third reason will be described later.

  Furthermore, when the welding prevention member 14 is outside the electrode 11 in the x direction, the workpieces W1 and W2 may come into contact with each other when receiving pressure by the clamp member 15. In this case, there is a possibility that welding cannot be sufficiently prevented by a part of the workpieces W1, W2.

  As described above, the + x side end of the welding prevention member 14a and the + x side end of the electrode 11a, and the −x side end of the welding prevention member 14b and the −x side end of the electrode 11b are formed. By arranging the welding prevention members 14 so as to be in substantially the same position, welding can be suitably prevented.

  As shown in FIG. 2, the electric heating device 1 also includes clamp members 15 that are respectively disposed above the pair of electrodes 11. The clamp member 15 is coupled to the clamp base portion 16 having a substantially rectangular parallelepiped shape extending substantially parallel to the extending direction of the electrode 11, the pin portion 17 having a tip portion contacting the workpieces W 1 and W 2, and the clamp base portion 15 and the pin portion 17. The clamp base 16 is connected to clamp base moving means (not shown) and is movable in the vertical direction (z direction) as indicated by an arrow Z1.

  The clamp member 15 is disposed on the opposite side of the electrode 11 across the workpieces W1 and W2, and is moved downward when the clamp base 16 is moved downward by the clamp base moving means. When the electrode 11 is attached to the workpieces W1 and W2, the clamp member 15 is moved downward, and the workpieces W1 and W2 can be sandwiched and attached by the electrode 11 and the clamp member 15. Thereby, the electrode 11 can be reliably attached to the workpieces W1 and W2 by a relatively simple method.

  In addition, the electric heating device 1 includes positioning members 21 and 22 for holding the workpieces W1 and W2 at predetermined positions. The positioning member 21 is formed in a substantially rectangular parallelepiped shape, and is disposed outside the pair of electrodes 11. As shown in FIG. 2A, the pair of electrodes 11 has a side on which the other electrode 11 is disposed. The other surface is coupled to extend upward from the electrode 11.

  Thereby, the positioning member 21 extends a part of the peripheral edge of the workpieces W1 and W2, specifically, the parallel opposite sides W1a and W2a of the workpieces W1 and W2 with the positioning member 21 so that the electrode 11 extends. The workpieces W1, W2 can be held at predetermined positions in a direction substantially orthogonal to the direction.

  On the other hand, the positioning member 22 is formed in a substantially rectangular parallelepiped shape and is disposed inside the pair of electrodes 11. As shown in FIG. 1, the positioning member 22 extends in a direction substantially orthogonal to the direction in which the electrodes 11 extend between the opposing ends of the pair of electrodes 11, and as indicated by a two-dot chain line in FIG. , Extending upward from the electrode 11.

  Thereby, the positioning member 22 engages the positioning member 22 with a part of the peripheral edge of the workpieces W1, W2, specifically, the sides W1b, W2b perpendicular to the parallel opposite sides W1a, W2a of the workpieces W1, W2. Thus, the workpieces W1 and W2 can be held at predetermined positions in the extending direction of the electrode 11.

  The electric heating apparatus 1 is also provided with a control unit (not shown) that comprehensively controls the configuration related to the electric heating apparatus 1, and the control unit operates the energizing means 10, the clamp base moving means, and the like. It can be controlled. The control unit is preferably configured with a microcomputer as a main part.

  In the electric heating apparatus 1 configured as described above, two workpieces W1 and W2 each having a predetermined shape are prepared in a state where the clamp member 15 is moved upward, and predetermined positions are determined by the positioning members 21 and 22, respectively. The two workpieces W1 and W2 are superposed on the electrode 11 while being positioned, and the clamp member 15 is moved downward with respect to the two superposed workpieces W1 and W2, whereby the electrode 11 and the clamp member 15 are moved. The workpieces W1 and W2 are held in close contact with each other, the pair of electrodes 11 is attached to the workpieces W1 and W2, and then the two workpieces W1 and W2 are heated by energizing both the electrodes 11. Is called.

  Here, the workpiece | work W1, W2 heated in the electricity heating apparatus 1 which concerns on this embodiment is demonstrated. FIG. 3 is an explanatory diagram for explaining a plate-like workpiece heated in the energization heating device. FIG. 3A and FIG. 3B show the workpieces before and after being formed into a predetermined shape, respectively.

  In the electric heating device 1, conductive works W1 and W2 having a predetermined electrical resistance such as a high-tensile steel plate are energized and heated, but the heated works W1 and W2 are as shown in FIG. It is formed by cutting a rectangular plate-shaped workpiece having a predetermined thickness by a point-symmetrical straight line L1 (indicated by a two-dot chain line) passing through a diagonal intersection C1. In FIG. 3 (b), the workpiece W1 is shown upside down. However, as shown in this drawing, the workpieces W1 and W2 have the same electrical resistivity and the same shape, and a pair of opposite sides. Are formed in a right trapezoidal shape parallel to each other.

  In the case of using a rectangular plate-like workpiece, for example, 1) cut by a point-symmetrical straight line passing through the diagonal intersection C1 to form the same right triangle 2) point symmetry passing through the diagonal intersection C1 It is possible to cut by a step-like line and 3) cut by a point-symmetric curved line passing through the diagonal intersection C1.

  Similarly, in the case of using a plate-like workpiece formed in a parallelogram, 1) the same isosceles trapezoid is formed by cutting along a point-symmetric linear line passing through the intersection of diagonal lines. It is possible to form a trapezoidal shape in which the length of another opposite side between parallel opposite sides having the same shape is cut by a point-symmetric linear line passing through the intersection.

  FIG. 4 is an explanatory diagram for explaining a cross-sectional area of a plate-shaped workpiece to be energized and heated. FIG. 4 (a) shows a state in which two plate-shaped workpieces are superimposed on an electrode, and FIG. b) shows the relationship between the distance from the positive electrode in the energization direction between the electrodes and the cross-sectional area of the plate-like workpiece. In FIG. 4B, the cross-sectional areas in the cross section orthogonal to the energizing direction of the workpieces W1 and W2 are indicated by lines L2 and L3, respectively, and the sum of the cross-sectional areas in the cross section orthogonal to the energizing direction of the workpieces W1 and W2 is shown. This is indicated by line L4.

  In the electric heating device 1, the workpieces W <b> 1 and W <b> 2 are superposed on the electrode 11 and arranged at a predetermined position. The workpiece W1 and the workpiece W2 are overlapped so that the right-angle portions thereof coincide with each other, and are arranged so that the electrodes 11 are respectively attached to both ends of the workpieces W1, W2.

  As shown in FIG. 4A, at the distance x1 from the positive electrode 11a in the energization direction between the electrodes 11, the widths perpendicular to the energization direction of the workpieces W1 and W2 are y1 and y2, and the thicknesses of the workpieces W1 and W2 Where t is the cross-sectional area S1, S2 in the cross section perpendicular to the energizing direction of the workpieces W1, W2, respectively, the product of the widths y1, y2 of the workpieces W1, W2 and the thickness t of the workpieces W1, W2 (y1 · t ), (Y2 · t), and the total cross-sectional area (S1 + S2) in the cross section perpendicular to the energizing direction of the workpieces W1 and W2 is represented by (y1 · t + y2 · t).

  As shown in FIG. 4B, the workpiece W1 has a cross-sectional area in a cross section perpendicular to the energizing direction of the workpiece W1 as the distance from the positive electrode 11a in the energizing direction increases (see the line L2). As for W2, the cross-sectional area in the cross section orthogonal to the energization direction of the workpiece W2 decreases as the distance from the positive electrode 11a in the energization direction increases (see the line L3). The workpieces W1 and W2 are prepared and overlaid so that the sum of the cross-sectional areas in the cross section perpendicular to the energization direction of W2 is substantially constant regardless of the distance from the positive electrode 11a in the energization direction (see line L4).

  In the present embodiment, the workpieces W1 and W2 are formed and overlaid so that the sum of the cross-sectional areas in the cross section orthogonal to the energization direction is substantially constant in the energization direction. As described above, the sum of the cross-sectional areas in the cross section orthogonal to the energization direction of the workpiece may be substantially constant in the energization direction.

  Thus, in the present embodiment, in the energization heating in which the workpieces W1 and W2 are heated by attaching and energizing the pair of electrodes 11 separated from each other to the plurality of conductive workpieces W1 and W2 having a predetermined electric resistance, Prepare workpieces W1 and W2 each formed in a predetermined shape, superimpose workpieces W1 and W2, and attach a pair of electrodes 11 to a plurality of workpieces W1 and W2 in a state where workpieces W1 and W2 are superimposed, A current is passed between both electrodes 11. In this case, the workpieces W1 and W2 are prepared and overlapped so that the sum of the cross-sectional areas in the cross section orthogonal to the energization direction is substantially constant in the energization direction.

  As a result, when the electrodes 11 are energized, the resistance values of the workpieces W1 and W2 stacked in the energization direction are made substantially constant, and the Joule heat generated from the workpieces W1 and W2 can be made substantially equal in the energization direction. Therefore, variations in the heating temperature of the workpieces W1, W2 can be suppressed relatively easily. Work pieces W1 and W2 are prepared so that the sum of the cross-sectional areas in the cross section perpendicular to the energizing direction is substantially constant in the energizing direction even when heating the workpieces W1 and W2 formed in a non-rectangular shape such as a right trapezoid shape. By superimposing them, it is possible to suppress variations in the heating temperature of the workpieces W1, W2 formed in a non-rectangular shape.

  Further, positioning members 21 and 22 are provided for engaging at least a part W1a, W1b, W2a, and W2b of the peripheral portions of the plurality of stacked workpieces W1 and W2 to position the workpieces W1 and W2 at predetermined positions. As a result, the positions of the workpieces W1, W2 can be prevented from shifting and the workpieces W1, W2 can be accurately held at predetermined positions, and the above-described effects can be effectively achieved.

  In the energization heating apparatus 1, the positioning member 21 is coupled to each of the pair of electrodes 11, and the electrode 11 and the positioning member 21 are formed separately. However, the positioning member is formed of an electrode, and the electrode and the positioning member May be formed integrally.

  Next, in the state in which the plate-like workpieces W1 and W2 formed as shown in FIG. 3B are provided with the welding prevention member 14 therebetween, the sum of the cross-sectional areas in the cross section perpendicular to the energizing direction is A description will be given of the result of conducting heating by applying electricity so as to be substantially constant.

  FIG. 5 is an explanatory diagram for explaining temperature measurement conditions for a workpiece that is electrically heated. In FIG. 5, only the workpieces W1 and W2 and the electrode 11 are shown. As the workpieces W1 and W2, a cold-rolled high-tensile steel plate SPFC440 having a thickness of 1.6 mm is used, and as shown in FIG. 3, a plate-like workpiece having a length of 280 mm and a width of 110 mm is formed. What was formed in the right trapezoid shape which has the same shape by cut | disconnecting by the point-symmetrical linear line L1 passing through the intersection C1 of a diagonal line was prepared. Specifically, as shown in FIG. 5A, the plate-like workpieces W1 and W2 were formed in a right trapezoidal shape having an upper side of 22 mm, a lower side of 88 mm, and a length of 280 mm. The distance between the electrodes was set to 230 mm.

  A DC power source was used for energization, and the current value was set to 4.2 kA for 10 seconds. The energized results are shown in Table 1 below. The determination of “heating state” is the result of examining the temperature difference between the hottest portion and the coldest portion of the workpieces W1 and W2 immediately after energization using thermography. If the temperature difference is less than 200 ° C., press forming after heating can be performed very well, and therefore the result was set to ○ (uniform). The determination of “contact between heated members during energization heating” was confirmed by visual observation during energization. The determination of “welding” was made based on whether or not a force greater than the weight of the workpiece was necessary when separating the workpieces W1 and W2. Further, when welding has occurred, traces of welding may be visually recognized on the workpieces W1 and W2.

  As shown in Table 1, it is understood that no welding occurs when the welding preventing member 14 is interposed between the workpieces W1 and W2. However, when the thickness of the welding prevention member is too large, the workpieces do not come into contact with each other, and therefore the heating state is not uniform as compared with the case where the workpieces do not come into contact with each other. Therefore, it can be seen that by making the thickness of the welding prevention member 14 equal to or less than a predetermined value, it is possible to prevent the welding temperature from being varied while preventing the welding.

Next, the reason why the workpieces come into contact with each other when the thickness of the welding prevention member 14 interposed between the workpieces W1 and W2 is set to the predetermined value or less will be described.
FIG. 6 is a conceptual diagram showing a plate-like work before and after energization heating. FIG. 6A shows the workpiece when not energized, and FIGS. 6B and 6C show the workpiece when energized. As shown in FIG. 6A, since the welding preventing member 14 is interposed between the workpieces W1 and W2, the workpieces W1 and W2 are not in contact when not energized. On the other hand, as shown in FIG. 6B, when energized, the workpieces W1 and W2 are thermally expanded by the generated Joule heat. Furthermore, since currents flow through the workpieces W1 and W2 in the same direction (+ x direction), a force attracting the workpieces W1 and W2 is generated by the magnetic field generated by the current flowing through one workpiece at the position of the other workpiece.

  The amount of deformation of the workpiece depends on the magnitude of the current flowing through the workpiece and the physical property values of the material constituting the workpiece, such as the elastic modulus and the coefficient of thermal expansion. The workpieces W1 and W2 are in contact with the electrode 11 at both ends, and receive pressure from the upper side by the clamp member 15. Therefore, as shown in FIG. 6B, the workpieces W1 and W2 come into contact with each other so as to bend from the central portion indicated by the alternate long and short dash line. That is, the workpieces W1 and W2 have the largest deformation amount at the center. Therefore, the said predetermined value of the welding prevention member 14 can be set to the thickness which the center parts contact at least at the time of electricity supply. Thereby, the workpieces W1 and W2 can be brought into contact with each other during energization, and variations in heating temperature can be suppressed.

  Here, as described above, it is preferable that the welding prevention member 14 does not enter the energization range inside the electrode in the x direction. As a third reason, it was described that the contact of the workpieces W1, W2 during energization is hindered. FIG. 6B and FIG. 6C illustrate the case where the welding preventing member does not enter inside the position of the electrode indicated by the dotted line, and the case where it enters. The workpieces W1 and W2 are fixed by receiving pressure from the upper side at the end portion in contact with the welding prevention member 14 by the clamp member 15. Therefore, when the welding prevention member 14 enters larger inside than the electrode 11, as shown in FIG. 6C, the deformation amount of the workpieces W1 and W2 becomes small, and the contact may be hindered.

  In this way, the plurality of workpieces W1, W2 are prepared and overlapped so that the sum of the cross-sectional areas in the cross section orthogonal to the energization direction between the electrodes 11 is substantially constant in the energization direction, and the welding prevention member 14 is provided. By interposing between the workpieces W1 and W2, when the plate-like workpiece formed in a non-rectangular shape is heated by energization heating, it is possible to suppress variations in the heating temperature of the workpiece while preventing welding. Further, by disposing the welding prevention member 14 at a predetermined position, suppression of variation in the heating temperature of the workpiece is not hindered, and further, by setting the thickness of the welding prevention member 14 to a predetermined value or less. During the energization, the workpieces W1, W2 can be reliably brought into contact with each other, and variations in the heating temperature can be suppressed.

  After heating the workpieces W1 and W2 using the electric heating device 1 in this way, the heated workpieces W1 and W2 are press-molded with a molding die using a conveyance means such as a conveyance robot or a conveyance belt. The workpieces W1 and W2 can be hot press-molded by being transported to the apparatus and press-molded, but the work heated by the energization heating is press-molded by incorporating the current heating apparatus 1 into the press molding apparatus. It may be.

  FIG. 7 is a schematic view showing an example of a press forming apparatus provided with an electric heating apparatus. The press molding apparatus 31 provided with the electric heating apparatus 1 shown in FIG. 7 includes a punch 40 provided with a projecting part 41 projecting downward, and a die provided with a recessed part 51 formed in a concave shape corresponding to the projecting part 41. 50 is provided, and the workpiece can be formed in a predetermined shape by combining the projecting portion 41 and the recessed portion 51.

  The punch 40 is attached to a punch plate 44 via a spring 42 and a spring guide 43, and the punch plate 44 is attached to a punch holder 45. The punch holder 45 is connected to a punch moving mechanism (not shown), and the punch 40 is moved in the vertical direction (z direction) by the punch moving mechanism, so that the punch 40 can be moved in the vertical direction. ing. On the other hand, the die 50 is fixed to the die holder 52.

  The press molding apparatus 31 is also provided with the energization heating apparatus 1 having the above-described energization means 10, and the die 50 is provided with a pair of electrodes 11 on both sides of the recess 51 with the recess 51 of the die 50 interposed therebetween. . The pair of electrodes 11 is provided so as to protrude from the upper surface of the die 50, and is connected to the power source 12 by the cable 13. A clamp member 15 is attached above each of the pair of electrodes 11.

  The press forming apparatus 31 is prepared so that the sum of the cross-sectional areas in the cross section perpendicular to the energizing direction of the workpieces W1 and W2 is substantially constant in the energizing direction in a state where the punch 40 is moved upward. Next, after attaching the pair of electrodes 11 to the workpieces W1 and W2 by sandwiching the workpieces W1 and W2 superposed with the welding prevention member 14 interposed therebetween by the electrode 11 and the clamp member 15, both electrodes The workpieces W1 and W2 are energized and heated by energizing 11.

  Subsequently, after the workpieces W1 and W2 are heated, the clamp member 15 is moved upward, and the workpiece W1 is removed from the press forming apparatus 31 by using a conveying unit (not shown). Next, the punch 40 is moved downward, the heated workpiece W2 is press-molded using the molding die 30, and hot press-molding of the workpiece W2 is performed.

  As described above, the press forming apparatus 31 incorporating the energization heating apparatus 1 is used to heat the workpieces W1 and W2 by the energization heating apparatus 1, and then the heated work W2 is press molded using the mold 30. Alternatively, hot press molding may be performed. The hot press molding is not limited to press molding by heating the workpiece to a temperature higher than the quenching temperature, but also includes press molding by heating the workpiece to a temperature lower than the quenching temperature.

  In this manner, with the welding prevention member 14 interposed therebetween, the workpieces W1 and W2 that are overlapped so that the sum of the cross-sectional areas in the cross section orthogonal to the energization direction is substantially constant in the energization direction are energized and heated. Subsequently, the workpieces W1 and W2 heated by using the mold are press-molded, so that the workpieces can be prevented from being welded, and the workpieces can be rapidly heated while suppressing the variation in the heating temperature of the workpieces. As a result, it is possible to prevent variations in the material properties of the workpiece, and it is possible to shorten the press molding cycle time of the workpiece.

  In the present embodiment, the case where a plurality of workpieces W1, W2 are stacked has been described. On the other hand, it will be described below that the same effect can be obtained even when the heating auxiliary member W2 made of a material different from that of the workpiece W1 is stacked. This also applies to the following embodiments.

(When overlapping heated members with different electrical resistivity)
FIG. 8 shows the relationship between the distance from the positive electrode in the energization direction between the electrodes and the product of the cross-sectional area in the cross section orthogonal to the energization direction of the plate workpiece and the heating auxiliary member and the reciprocal of the electrical resistivity. In addition, in FIG. 8, the product of the cross-sectional area in the cross section orthogonal to an energizing direction and the reciprocal of an electrical resistivity is shown by the line L2 and the line L3, respectively about the plate-shaped workpiece W1 and the heating auxiliary member W2, and the cross section orthogonal to the energizing direction. The sum of the product of the cross-sectional area of the plate-like workpiece and the reciprocal of the electrical resistivity of the plate-like workpiece and the product of the cross-sectional area of the heating auxiliary member and the reciprocal of the electrical resistivity of the heating auxiliary member in the cross-section is shown by line L4. Show.

  In the electric heating apparatus 1, the workpiece W <b> 1 and the heating auxiliary member W <b> 2 are overlapped on the electrode 11 and arranged at a predetermined position. The workpiece W1 and the heating auxiliary member W2 are overlapped so that their right-angle portions coincide with each other, and are arranged so that the electrodes 11 are attached to both ends of the workpiece W1 and the heating auxiliary member W2, respectively.

  As shown in FIG. 8, at a distance x1 from the positive electrode 11a in the energization direction between the electrodes 11, the widths orthogonal to the energization direction of the workpiece W1 and the heating auxiliary member W2 are y1 and y2, and the workpiece W1 and the heating auxiliary member W2 Both have a predetermined thickness t. Cross-sectional areas S1 and S2 in a cross section perpendicular to the energizing direction of the workpiece W1 and the heating auxiliary member W2 are represented by (y1 · t) and (y2 · t), respectively.

  Further, it is assumed that the workpiece W1 has a predetermined electric resistivity ρ1 and the heating auxiliary member W2 has a predetermined electric resistivity ρ2. At a distance x1 from the positive electrode 11a in the energization direction, the product of the cross-sectional area S1 of the work W1 and the reciprocal of the electrical resistivity ρ1 of the work W1 is represented by (S1 / ρ1), and the cross-sectional area S2 of the heating auxiliary member W2 And the inverse of the electrical resistivity ρ2 of the heating auxiliary member W2 is represented by (S2 / ρ2).

  In the overlapped work W1 and heating auxiliary member W2, at a distance x1 from the positive electrode 11a in the energization direction, the cross-sectional area S1 of the work W1 in the cross section orthogonal to the energization direction and the reciprocal of the electrical resistivity ρ1 of the work W1. The sum (S1 / ρ1 + S2 / S2) of the product (S1 / ρ1) and the product (S2 / ρ2) of the cross-sectional area S2 of the heating auxiliary member W2 and the reciprocal of the electrical resistivity ρ2 of the heating auxiliary member W2 in the cross section orthogonal to the energization direction ρ2) is expressed by (y1 · t / ρ1 + y2 · t / ρ2).

  In the workpiece W1 and the heating auxiliary member W2 shown in FIG. 8, as the distance from the positive electrode 11a in the energization direction increases, the reciprocal of the cross-sectional area S1 in the cross section orthogonal to the energization direction of the workpiece W1 and the electrical resistivity ρ1 of the workpiece W1. Product (S1 / ρ1) increases (see line L2). On the other hand, as the distance from the positive electrode 11a in the energization direction increases, the product of the cross-sectional area S2 in the cross section orthogonal to the energization direction of the heating auxiliary member W2 and the reciprocal of the electrical resistivity ρ2 of the heating auxiliary member W2 (S2 / ρ2). ) Becomes smaller (see line L3).

  However, in this embodiment, the product of the cross-sectional area S1 of the workpiece W1 in the cross section orthogonal to the energization direction and the reciprocal of the electrical resistivity ρ1 of the work W1 and the cross-sectional area S2 of the heating auxiliary member W2 in the cross section orthogonal to the energization direction. And the product of the inverse of the electrical resistivity ρ2 of the heating auxiliary member W2 (S1 / ρ1 + S2 / ρ2) so as to be substantially constant regardless of the distance from the positive electrode 11a in the energization direction (see line L4). A workpiece W1 and a heating auxiliary member W2 are prepared and overlaid.

  The product of the cross-sectional area S1 of the workpiece W1 in the cross section orthogonal to the energization direction and the reciprocal of the electrical resistivity ρ1 of the work W1, and the cross-sectional area S2 of the heating auxiliary member W2 and the electricity of the heating auxiliary member W2 in the cross-section orthogonal to the energization direction. The sum of the product of the resistivity ρ2 and the reciprocal (S1 / ρ1 + S2 / ρ2) is substantially constant in the energizing direction because the resistance per unit length of the workpiece W1 in the energizing direction (ΔR1 = ρ1 · ΔL / S1) and the resistance per unit length of the heating auxiliary member W2 (ΔR2 = ρ2 · ΔL / S2) are regarded as a parallel circuit, and the combined resistance per unit length of the workpiece W1 and the heating auxiliary member W2 in the energizing direction. This is to make the value substantially constant. ΔL represents a unit length in the energization direction, and ΔR1 and ΔR2 represent resistances per unit length of the workpiece W1 and the heating auxiliary member W2 in the energization direction, respectively.

  As described above, the case where the heating auxiliary member W2 is overlaid on one workpiece W1 has been described, but the heating auxiliary member is overlaid on two or more workpieces, and the cross-sectional area of each plate-like workpiece in a predetermined cross section orthogonal to the energization direction. The sum of the product of the reciprocal of the electrical resistivity for each plate-like workpiece and the product of the cross-sectional area of the heating auxiliary member and the reciprocal of the electrical resistivity of the heating auxiliary member in the predetermined cross section becomes substantially constant in the energization direction. You may do it.

  As a workpiece used in the present embodiment, for example, aluminum, stainless steel, magnesium, cast iron, titanium, or CFRP (carbon fiber reinforced plastic) is assumed. Further, as the heating auxiliary member, a member made of high-tensile steel plate, resin, or other materials such as stainless steel or cast iron which is difficult to oxidize can be used.

(Second Embodiment)
Fig.9 (a)-FIG.9 (c) are side views of the electric heating apparatus which concerns on 2nd Embodiment of this invention. 9 (a) to 9 (c) are side views of the energization heating device as seen from the YB direction, corresponding to FIG. 2 (c). The same configurations as those of the energization heating device 1 of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the current heating device 61 of the present embodiment, an electrode having a thick portion 71d is used to fill a gap generated between the negative electrode 71b and the welding prevention member 74b when the non-rectangular plate-like workpieces W1 and W2 are stacked. 71 (FIG. 9A), or a welding prevention member 74 having a thick portion 74d (FIG. 9B), or a welding prevention auxiliary member 19 is provided in the gap (FIG. 9C). .

  As shown in FIG. 2B, there is no gap between the electrode 71a and the welding prevention member 74a on the positive electrode 71a side. Therefore, the positive electrode 71a and the welding prevention member 74a (not shown) are formed in the same manner as the positive electrode 11a and the welding prevention member 14a of the energization heating device 1, respectively.

  On the other hand, as illustrated in FIG. 9A, when the shape of the negative electrode 71 b is changed to fill a gap generated between the electrode 71 b and the welding prevention member 74 b, the negative electrode 71 b is the negative electrode of the current heating device 1. Similarly to 11b, a main body 71c formed in a substantially rectangular parallelepiped shape and a thick part 71d protruding from the main body 71c are provided, and the main body 71c and the thick part 71d are integrally formed.

  The thick portion 71d has the same length as the main body portion 71c in the energization direction (x direction) and the same thickness as the thickness of the workpiece W2 (z direction), and the main body portion 71c and the welding prevention member 74b It is formed so as to fill the space formed between the two.

  Further, as shown in FIG. 9B, when the shape of the welding prevention member 74b is changed and the gap is filled, the welding prevention member 74b is substantially a rectangular parallelepiped like the welding prevention member 14b of the energization heating device 1. The main body portion 74c is formed in a shape, and a thick portion 71d protruding from the main body portion 74c. The main body portion 74c and the thick portion 74d are integrally formed.

  The thick wall portion 74d has the same length as the main body portion 74c in the energization direction (x direction) and the same thickness as the thickness of the workpiece W2 (z direction). The main body portion 71c and the welding prevention member 74b It is formed so as to fill the space formed between the two.

  Furthermore, as shown in FIG. 9C, when the welding prevention auxiliary member 19 is provided to fill the gap, the welding prevention auxiliary member 19 has the same length as the electrode 71 in the energization direction (x direction), It has the same thickness as the workpiece W2 (y direction), and is formed so as to fill a space formed between the main body 71c and the welding prevention member 74b. The welding prevention auxiliary member 19 can be made of a material whose electrical resistivity is smaller than the workpieces W1 and W2, for example, copper. Thereby, also about the welding prevention auxiliary member 19, it is provided so that it may contact the whole y direction orthogonal to the electricity supply direction of a workpiece | work.

  In the present embodiment, the structure for filling the gap between the electrode and the welding prevention member has been described. However, when three or more non-rectangular plate-like workpieces are stacked, the welding prevention member interposed between the workpieces. There is a gap between them. In this case, it is possible to fill the gap between the welding prevention members by using a welding prevention member having a thick portion or by interposing a further welding prevention auxiliary member in the gap.

  Also in the energization heating device 61 configured as described above, the workpieces W1 and W2 are prepared and overlapped so that the sum of the cross-sectional areas in the cross section orthogonal to the energization direction of the workpieces W1 and W2 is substantially constant in the energization direction. Thus, since the Joule heat generated from the workpieces W1 and W2 when energizing between the electrodes 71 can be made substantially equal in the energizing direction, variations in the heating temperature of the workpiece can be suppressed relatively easily.

  In addition, when the non-rectangular workpieces W1 and W2 are overlapped, the electrode 71b or the welding prevention member 74b having a thick portion that fills the gap generated between the negative electrode 71b and the welding prevention member 74b is used, or the gap By interposing the welding prevention auxiliary member 19, the current from the positive electrode 71a can be made to flow uniformly over the entire workpiece W1, that is, heat generation due to the current flowing in a specific portion can be suppressed. Variation in the heating temperature of the workpiece can be further suppressed.

(Third embodiment)
FIG. 10 is a schematic view of an electric heating device according to a third embodiment of the present invention, FIG. 10 (a) is a schematic plan view of the electric heating device, and FIG. 10 (b) is FIG. 10 (a). It is a side view of the said electricity heating apparatus seen from the YB direction. In FIG. 10B, the positioning member 22 is indicated by a two-dot chain line, which is shown in a transmissive state. The electric heating device 81 according to the third embodiment of the present invention is the electric heating device 1 according to the first embodiment, further provided with clamping means for clamping the workpieces W1, W2 between the electrodes 11. The same components as those of the heating device 1 are denoted by the same reference numerals and description thereof is omitted.

  In the energization heating device 81, a clamping means 85 for clamping the workpieces W1 and W2 is provided at a substantially central portion between the electrodes 11, and the clamping means 85 includes an upper clamping member 91 for clamping the workpieces W1 and W2 from above, The lower clamp member 95 clamps W1 and W2 from below.

  The upper clamp 91 is configured in the same manner as the clamp member 15 and has a substantially rectangular parallelepiped clamp base 92 extending substantially parallel to the direction in which the electrode 11 extends, and a pin portion 93 having a tip portion that contacts the workpieces W1 and W2. A clamp base 92 and a spring 94 coupled to the pin portion 93 are provided, and the clamp base 92 is connected to an upper clamp moving means (not shown) and is movable in the vertical direction (z direction) as indicated by an arrow Z2. It is configured.

  On the other hand, the lower clamp 95 is a vertically inverted version of the upper clamp 91 and includes a substantially rectangular parallelepiped clamp base 96 extending substantially parallel to the extending direction of the electrode 11 and a tip portion contacting the workpieces W1 and W2. A pin portion 97 and a spring 98 coupled to the clamp base portion 96 and the pin portion 97 are provided. The clamp base 96 is connected to a lower clamp moving means (not shown) and is configured to be movable in the vertical direction (z direction) as indicated by an arrow Z3.

  In the clamp means 85, the clamp base 91 is moved downward by the upper clamp moving means to move the upper clamp member 91 downward, and the clamp base 96 is moved upward by the lower clamp moving means. The lower clamp member 95 is moved upward. As a result, the clamping means 85 can clamp the workpieces W1 and W2 disposed on the electrode 11 at the substantially central portion between the electrodes 11 by the upper clamp member 91 and the lower clamp member 95. .

  The energization heating device 81 is provided with one clamping means 85 for clamping the workpieces W1 and W2 between the electrodes 11, and is configured to clamp the workpieces W1 and W2 at one location between the electrodes 11. A plurality of clamping means may be provided to clamp the workpieces W1, W2 at a plurality of locations between the electrodes 11.

  Also in the energization heating device 81 configured in this way, the clamp member 15 and the upper clamp member 91 are respectively moved upward and the lower clamp member 95 is moved downward. Two workpieces W1 and W2 are prepared. Next, the two workpieces W1 and W2 are overlapped on the electrode 11, and the clamp member 15 is moved downward with respect to the two overlapped workpieces. Accordingly, the workpieces W1 and W2 are sandwiched between the electrode 11 and the clamp member 15, and the pair of electrodes 11 are attached to the workpieces W1 and W2.

  In the energization heating device 81, after the workpieces W1 and W2 are overlapped, before the two electrodes 11 are energized, the upper clamp member 91 is moved downward with respect to the overlapped workpieces W1 and W2. Further, the workpieces W1 and W2 are clamped between the electrodes 11 by the upper clamp member 91 and the lower clamp member 95 by moving the lower clamp member 95 upward. Thereafter, the workpieces W1 and W2 are heated by energizing between the electrodes 11.

  As described above, even when the energization heating device 81 is used, the workpieces W1 and W2 are prepared and overlapped so that the sum of the cross-sectional areas in the cross section perpendicular to the energization direction is substantially constant in the energization direction. When energizing between the electrodes 11, Joule heat generated from the workpieces W1 and W2 can be made substantially equal in the energizing direction. Therefore, variations in the heating temperature of the workpieces W1, W2 can be suppressed relatively easily. Further, even when the workpieces W1 and W2 formed in a non-rectangular shape are heated, variations in the heating temperature of the workpieces W1 and W2 can be suppressed.

  Further, in the energization heating device 81, the workpieces W <b> 1 and W <b> 2 are clamped at least at one or more locations between the electrodes 11 using the clamping means 85, so that there is a gap between the superimposed workpieces W <b> 1 and W <b> 2 between the electrodes 11. Can be prevented. Therefore, even when the welding prevention member 14 is interposed between the workpieces W1 and W2, the workpieces W1 and W2 can be surely brought into contact with each other, and hence variation in heating temperature can be further suppressed.

(Modification)
In the above embodiment, in the electric heating devices 1, 61, 81, the workpieces W1, W2 are formed in a non-rectangular shape having a certain thickness. On the other hand, it is also possible to use the plate-like workpieces W1, W2 whose thickness changes in the longitudinal direction (x direction).

  FIG. 11 is a view showing a modification of the plate-like workpiece heated in the energization heating apparatus according to the embodiment of the present invention. In FIG. 15, the plate-shaped workpiece is shown in a state of being attached to the electric heating device 1 according to the first embodiment of the present invention. FIG. 11A is a schematic plan view of the electric heating apparatus to which the workpiece is attached, and FIGS. 11B, 11C, and 11D are respectively YB directions in FIG. 11A. It is a side view of the said electricity heating apparatus seen from the YC direction and the YD direction.

  As shown in FIG. 11B, in this modification, the welding prevention member 14 is formed in a substantially parallelepiped shape corresponding to the thickness changing in the longitudinal direction. Further, the + x side end of the welding prevention member 14a and the + x side end of the electrode 11a, and the −x side end of the welding prevention member 14b and the −x side end of the electrode 11b, respectively. The welding prevention member 14 is disposed so as to be in substantially the same position.

  When the workpieces W1 and W2 are formed and overlapped so that the sum of the cross-sectional areas in the cross section orthogonal to the energization direction in the energization heating device 1 is substantially constant in the energization direction, the workpieces W1 and W2 are formed in a rectangular shape and have a thickness. It is also possible to use the workpieces W1 and W2 whose length changes in the longitudinal direction.

  Even in such a case, since the Joule heat generated from the workpieces W1 and W2 can be made substantially equal in the energization direction when the electrodes 11 are energized, the comparison is made while preventing welding between the workpieces W1 and W2. The variation in the heating temperature of the workpieces W1, W2 can be suppressed easily.

  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 a plate-shaped workpiece formed in a non-rectangular shape is heated when the plate-shaped workpiece is heated by energization heating, the plate-shaped workpiece is substantially uniformly made relatively easily. Therefore, it may be suitably used for heating at the time of press forming of a high-strength steel plate used for a body constituting member such as a pillar or an impact bar.

1, 61, 81 Current heating device, 11, 71 electrode, 15, 91, 95 Clamp member, 21, 22 Positioning member, 30 Mold, 31 Press molding device, 85 Clamp means, W1, W2 Workpiece

Claims (5)

An energization heating method for heating a plurality of plate-shaped heated members each having a predetermined electrical resistivity,
Preparing the plurality of heated members each formed in a predetermined shape;
Superposing the plurality of heated members;
Attaching the pair of electrodes to the heated members in a state where the heated members are stacked;
Energizing between the electrodes, and
In the step of preparing the plurality of members to be heated and the step of superimposing these members to be heated, the reciprocal number of the cross-sectional area and electric resistivity of each member to be heated in a predetermined cross section orthogonal to the energizing direction of these members to be heated. The plurality of heated members are prepared and overlapped so that the sum of the product and the product is substantially constant in the energization direction, and
In the step of superimposing the plurality of heated members, a pair of plate-like welding prevention members having an electrical resistivity smaller than those of the heated members are used, and the ends facing each other are the ends facing the pair of electrodes. And interposing between the heated members at both ends and the heated members so as to be substantially the same position as
An electric heating method characterized by that. In the step of superimposing the plurality of heated members, a welding preventing member having a thickness such that at least the center portions of the plurality of heated members are in contact with each other when the electrodes are energized is used as the welding preventing member. ,
The energization heating method according to claim 1. When a gap is generated between the electrode and the anti-adhesion member or between the anti-adhesion members due to different shapes of each heated member,
In the state where the plurality of heated members are stacked, an electrode having a thick portion that fills the gap as the electrodes in the step of attaching a pair of electrodes to the heated members, or the plurality of heated members Using a welding prevention member having a thick part that fills the gap as the welding prevention member in the step of overlapping, or
Providing a step of interposing a plate-like welding prevention auxiliary member having an electrical resistivity smaller than these heated members in the gap;
The energization heating method according to claim 1 or 2. The heated member is made of iron, and the welding prevention member is made of copper,
The energization heating method according to any one of claims 1 to 3.   The hot press molding method which heats the said to-be-heated member by the electric heating method of any one of Claims 1-4, and press-molds the said to-be-heated member using the shaping | molding die.

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