JP2011189402A - Resistance heating method of metal sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resistance heating method of a metal sheet capable of adequately heating the metal sheet to be used for hot pressing. <P>SOLUTION: In the resistance heating method of the metal sheet, four or more electrodes 53 are mounted on the metal sheet 63 to be pressed, two electrodes (to-be-used electrodes A and B) out of the electrodes 53 are successively selected, and the current runs between the two electrodes (to-be-used electrodes A and B) to heat the metal sheet 63. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a resistance heating method for a metal plate, and is mainly used for hot press molding of structural parts of automobiles.

  In recent years, especially in the automobile industry, materials have been made thinner and higher in strength by reducing the weight of vehicle bodies due to environmental problems. In many cases, press molding is used for the production of such a component, but cracking of the material and poor dimensional accuracy are likely to occur in press molding using a highly strengthened material (metal plate).

  In order to solve such a problem, hot press molding (hot press molding) is known as a molding method capable of suppressing cracking of a material (metal plate) and poor dimensional accuracy. This technology is introduced in Non-Patent Document 1, and for example, a steel plate is heated to an austenite region of about 900 ° C., and is quenched (die quench) by press forming while cooling with a mold, thereby increasing the strength of the steel plate. This is a molding method.

  In this hot press molding, a heating furnace or direct energization is used for heating the metal plate (blank). At that time, the heating using the heating furnace has a problem that scale is generated on the surface during the heating or the conveyance from the heating furnace to the mold. On the other hand, in the case of heating using direct energization (resistance heating), since heating can be performed in an extremely short time, the generation of scale on the surface is extremely small.

  In this heating method by direct energization (resistance heating method), generally, a rectangular (square, rectangular) blank 61 is heated using a power source 51 and two wide electrodes 52, as shown in FIG. The reason for limiting to the rectangular blank 61 is that when the non-rectangular blank (for example, the trapezoidal blank 62) is heated using the two wide electrodes 52, the electric resistance (conduction resistance) is not uniform. Moreover, as shown in FIG. 11, the blank 62 cannot be heated uniformly.

  On the other hand, as a resistance heating method for non-rectangular blanks, in Patent Document 1, as shown in FIG. 12, five electrodes 53 (10 in total) are attached to opposite ends of a trapezoidal blank 62, respectively. An example is disclosed in which an electric current is passed between opposing electrodes 53 to uniformly heat the electrodes.

JP 2002-248525 A

Press Technology Vol.43 No.9 (August 2005)

  However, the resistance heating method disclosed in Patent Document 1 can be applied only to a blank having a shape formed by four straight lines such as a trapezoidal blank. That is, since the electrodes are installed at the opposite ends of the blank, a side where the electrodes cannot be installed is generated in the blank having no opposite ends, and a portion that is not heated is generated. In addition, since heating is performed by energizing only between the electrodes facing each other, if the temperature distribution of the blank becomes non-uniform, it is necessary to partially heat any part so that the non-uniform temperature distribution can be eliminated I can't. Moreover, the purpose is to uniformly heat the entire blank, and it is not in mind to have a desired temperature distribution (for example, half of the blank is 900 ° C. and the other half is 800 ° C.).

  This invention is made | formed in view of the above situations, and it aims at providing the resistance heating method of the metal plate which can heat the metal plate used for hot press molding appropriately. .

  In order to solve the above problems, the present invention has the following features.

  [1] At least four electrodes are attached to a press-molded metal plate, two of the electrodes are sequentially selected, and an electric current is passed between the two electrodes, whereby the metal A resistance heating method for a metal plate, comprising heating the plate.

  [2] The resistance heating method for a metal plate according to [1], wherein the metal plate is heated to have a desired temperature distribution having a temperature difference in the metal plate.

  [3] In the above [1], the shape of the metal plate is a shape excluding a rectangle and a trapezoid, and the metal plate is heated so as to have a uniform temperature distribution having no temperature difference in the metal plate. The resistance heating method of the metal plate as described.

  In this invention, the metal plate (blank) used for hot press molding can be heated appropriately.

It is a figure which shows the wiring state in one Embodiment of this invention. It is a figure which shows temperature measurement with the two-dimensional thermometer in one Embodiment of this invention. It is a figure which shows the electricity supply conditions of the example 1 of this invention. It is a figure which shows the temperature distribution after the electricity heating of the example 1 of this invention. It is a figure which shows the wiring state of the example 2 of this invention. It is a figure which shows the target heating temperature of the example 2 of this invention. It is a figure which shows the temperature distribution after the electricity heating of the example 2 of this invention. It is a figure which shows the target heating temperature of the example 3 of this invention. It is a figure which shows the temperature distribution after the electrical heating of the example 3 of this invention. It is explanatory drawing of a resistance heating method. It is a figure which shows the temperature distribution of the rectangular blank by the conventional resistance heating method. It is a figure which shows the resistance heating method of the rectangular blank in patent document 1. FIG.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a wiring state in an embodiment of the present invention. As shown in FIG. 1, in this embodiment, when hot-forming a deformed metal plate (blank) 63 that is not rectangular or trapezoidal, the deformed blank 63 is resistance-heated to a predetermined temperature. 36 electrodes 53 are attached to the peripheral edge of the blank 63, and the 36 electrodes 53 are connected to a switch box 54 connected to the power source 51. In addition, the numbers 1-36 attached | subjected to the electrode 53 in FIG. 1 have shown No (number) of the electrode. Then, an energization control device (not shown) sequentially switches the switches in the switch box 54 to select two of the 36 electrodes 53, and the two electrodes 53 (uses) The blank 63 is resistively heated by flowing a current at a predetermined current value between the electrode A and the used electrode B) for a predetermined time.

  Here, when the blank 63 is heated to a predetermined target temperature, the blank 63 may be heated so as to have a uniform temperature distribution without a temperature difference, or the blank 63 has a temperature difference. There are also cases where heating is performed to obtain a desired temperature distribution.

  As for the number of electrodes 53, it is preferable to arrange at least one electrode 53 on each peripheral edge (side or curved edge) of the blank 63. For example, when the shape of the blank 63 is a quadrangular shape, if at least one electrode 53 is disposed on each side, four or more electrodes 53 are used.

  Further, the interval between the adjacent electrodes 53 is preferably 100 mm or more, although it depends on the shape of the blank. This is because if the distance between the adjacent electrodes 53 is 100 mm or less, the number of the electrodes 53 becomes unnecessarily large, and it takes time to heat the current when a current is passed through the electrodes 53 in sequence.

  Moreover, about the energization time between the two electrodes 53 to be energized (the used electrode A and the used electrode B) is preferably 0.1 to 2.0 seconds. This is because when the energization time exceeds 2.0 seconds, not only because the total energization time is required, but also scale occurs when there is no antioxidant film on the surface of the blank. In addition, about the electric current value of electricity supply, it is set as the value which reaches target temperature within the electricity supply time of 0.1 to 2.0 second.

  The energization conditions such as the combination of the two energized electrodes 53 (used electrode A and used electrode B), energization order, energization time, and current value are determined in advance based on computer simulation and experiment / result data. As shown in FIG. 2, the temperature distribution of the blank 63 during and after heating is measured by a two-dimensional thermometer (thermo viewer) 55, and the feed forward of the energization condition of the blank is based on the measurement result. Control or feedback control to the energization condition of the next blank is performed. For example, if there is a part in the blank 63 that has not reached the target temperature, the part is additionally heated.

  The feed forward control and the feedback control based on the temperature distribution measurement of the thermo viewer 55 may be performed every time, but in the case of mass production or the like, after performing only the first time and confirming that there is no problem with the energization conditions, The rest may be performed under the same energization conditions.

  Incidentally, even if the resistance heating of the blank 63 is completed, the press molding may be performed with the electrode 53 attached as it is.

  As Example 1 of the present invention, resistance heating of the deformed blank 63 shown in FIG. 1 was performed. The plate blank 63 had a thickness of 1.6 mm, an approximate dimension (length × width) of 1000 mm × 300 mm, and a target heating temperature of 835 ° C. (uniform temperature distribution).

  And as this invention example 1, resistance heating was performed based on one Embodiment of the above-mentioned this invention. That is, as shown in FIG. 1, 36 electrodes 53 (No. 1 to No. 36) are attached to the periphery of the blank 63, and a current is sequentially passed between the two electrodes 53 (the used electrode A and the used electrode B). The blank 63 was heated by resistance. The energization conditions (the order of energization, the combination of the used electrode A and the used electrode B, and the energization time) at that time are shown in FIG. After flowing current between the electrodes (No. 2 and No. 33, No. 3 and No. 32,...) Facing in the width direction of the blank 63 in order 1 to 12, the temperature distribution measurement result of the thermo viewer 55 in order 13 to 20 In order to increase the temperature of the portion that has not reached the target temperature, current was passed between the electrodes (No 33 and No 36, No 36 and No 2,...) Facing the diagonal direction and the longitudinal direction of the blank 63. .

  As a result, in Example 1 of the present invention, as shown in FIG. 4 showing the temperature distribution after resistance heating, the blank 63 could be heated to a uniform temperature distribution of 825 to 850 ° C.

  As Example 2 of the present invention, resistance heating of the deformed blank 64 shown in FIG. 5 was performed. The thickness of the irregular blank 64 is 1.2 mm, the approximate dimensions (length × width) are 1200 mm × 400 mm, and the target heating temperature is 875 ° C. for a part as shown in FIG. A temperature distribution having a temperature difference in the blank 64 of 725 ° C. was obtained.

  Then, as Example 2 of the present invention, as shown in FIG. 5, 32 electrodes 53 (No1 to No32) are attached to the periphery of the blank 64, and two of the electrodes 53 (the used electrode A and the used electrode B) are sequentially installed. The blank 64 was resistance-heated by passing an electric current between them. The energization conditions (the order of energization, the combination of the used electrode A and the used electrode B, and the energization time) at that time were as shown in FIG. In order 1 to 9, the part to be heated to 875 ° C. and the high temperature is heated for a long time of 0.3 seconds, and in order 10 to 12, the part to be heated to 725 ° C. and the low temperature is heated to a short time of 0.1 seconds. did.

  As a result, in Example 2 of the present invention, the blank 64 could be heated to the target temperature distribution as shown in FIG. 7B after the resistance heating.

  As Example 3 of the present invention, similarly to Example 2, the deformed blank 64 shown in FIG. However, as shown in FIG. 8, the target heating temperature has a temperature distribution such that a part is 775 ° C., a part is 875 ° C., a part is 725 ° C., and a part is 825 ° C.

  Then, as Example 3 of the present invention, as shown in FIG. 5, 32 electrodes 53 (No1 to No32) are attached to the periphery of the blank 64, and two of the electrodes 53 (the used electrode A and the used electrode) are sequentially installed. A current was passed during B) to resistance-heat the blank 64. The energization conditions (the order of energization, the combination of the used electrode A and the used electrode B, and the energization time) at that time are as shown in FIG.

  As a result, in Example 3 of the present invention, as shown in FIG. 9B, the temperature distribution after resistance heating was able to heat the blank 64 to the target temperature distribution.

  In Example 2 and Example 3 above, a blank having an irregular shape was heated to a temperature distribution having a temperature difference in the blank, but in the present invention, a rectangular blank or a trapezoidal blank is used. In the same manner, it can be heated to a temperature distribution having a temperature difference in the blank.

51 Power Supply 52 Electrode 53 Electrode 54 Switch Box 55 Two-dimensional Thermometer (Thermo Viewer)
61 Rectangular blank 62 Trapezoidal blank 63 Deformed blank 64 Deformed blank

Claims (3)

  At least four electrodes are attached to a metal plate to be press-formed, and two of the electrodes are selected in sequence, and current is passed between the two electrodes to heat the metal plate. A resistance heating method for a metal plate.   2. The resistance heating method for a metal plate according to claim 1, wherein the metal plate is heated so as to have a desired temperature distribution having a temperature difference in the metal plate.   2. The metal plate according to claim 1, wherein the metal plate has a shape excluding a rectangle and a trapezoid, and the metal plate is heated so as to have a uniform temperature distribution without a temperature difference in the metal plate. Resistance heating method.

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