The present invention relates to a direct resistance heating apparatus, a direct resistance heating method, a heating apparatus, a heating method, and a hot-press molding method.
Heat treatment is applied to, for example, vehicle structures, such as a center pillar and a reinforcement, to improve strength. Heat treatment can be classified into two types, indirect heating and direct heating. An example of indirect heating is a furnace heating in which a workpiece is placed inside a furnace and the temperature of the furnace is controlled to heat the workpiece. Examples of direct heating include an induction heating in which eddy current is applied to a workpiece to heat the workpiece, and a direct resistance heating in which current is applied directly to a workpiece to heat the workpiece.
According to a first related art (see, e.g., JPH06-79389A), a metal blank is passed through heating means and heated by induction heating or direct resistance heating so as to improve workability of the metal blank prior to being subjected to plastic working. For example, the heating means including an induction coil or electrode rollers is arranged upstream of a cutter machine, and in the case of the electrode rollers, the metal blank is subjected to direct resistance heating by the electrode rollers while at the same time being continuously conveyed by the electrode rollers.
In order to heat a flat steel plate having a substantially equal width along the longitudinal direction by direct resistance heating, voltage may be applied between electrodes arranged at longitudinal ends of the steel plate respectively. In this case, because current flows uniformly through the steel plate, amount of heat generated is uniform over the entire steel plate.
According to a second related art (see, e.g., JP3587501B2), a steel plate having a varying width along a longitudinal direction of the steel plate is heated by arranging a plurality of pairs of electrodes side by side along the longitudinal direction, each pair of electrodes having one electrode disposed on one side of the steel plate and another electrode disposed on the opposite side of the steel plate in the widthwise direction of the steel plate, and applying equal current between each pair of electrodes, so that the steel plate is heated to a uniform temperature.
According to a third related art (see, e.g., JPS53-07517A), one electrode is fixed to one end of a steel rod, and a clamping-type second electrode is provided at a boundary between a heating target portion of the steel rod and a non-heating portion of the steel rod, so that the steel rod is partially heated.
When heating a steel workpiece having a varying width along its longitudinal direction, it is generally desirable to make the amount of heat applied per unit volume of the steel workpiece to be uniform over the entire steel workpiece, like in furnace heating. However, furnace heating requires large-scale equipment, and temperature control of the furnace is difficult.
Accordingly, direct resistance heating is preferable in terms of production cost. However, when a plurality of pairs of electrodes is provided as in the first related art, amount of current applied is controlled for each pair of electrodes, which increases equipment cost. Further, arranging a plurality of pairs of electrodes with respect to one workpiece results in low productivity.
Illustrative aspect of the present invention provide a direct resistance heating apparatus, a direct resistance heating method, a heating apparatus, and a heating method capable of uniformly heating a workpiece or heating a workpiece to have a desired temperature distribution, reducing cost, and improving productivity, and also provide a hot-press molding method in which the direct resistance heating method and the heating method can be used.
According to an illustrative aspect of the present invention, a direct resistance heating apparatus includes a first electrode and a second electrode arranged to oppose to each other with a space provided between the first electrod and the second electrode, a power supply electrically connected to the first electrode and the second electrode, an electrode moving mechanism configured to move, in a state in which the first electrode and the second electrode are in contact with a workpiece and in a state in which current is applied from the power supply to the workpiece through the first electrode and the second electrode, at least one of the first electrode and the second electrode along an opposing direction in which the first electrode and the second electrode are opposed to each other, a first holder and a second holder configured to hold the workpiece such that, in a state in which the at least one of the first electrode and the second electrode is moved, a heating target region of the workpiece located between the first electrode and the second electrode is held between the first holder and the second holder in the opposing direction, and a holder moving mechanism configured to move at least one of the first holder and the second holder to pull the workpiece along the opposing direction.
According to another illustrative aspect of the present invention, a heating apparatus is configured to heat a plate workpiece having a first heating target region and a second heating target region is provided. A sectional area of the first heating target region is substantially constant along a longitudinal direction of the first heating target region or monotonically increases or decreases along the longitudinal direction. The second heating target region is adjoining a portion of the first heating target region in a width direction of the first heating target region in a monolithic manner. The heating apparatus includes a first heating section configured to heat the first heating target region, and a second heating section configured to heat the second heating target region. The first heating section includes the direct resistance heating apparatus described above. At least one of the first electrode and the second electrode of the direct resistance heating apparatus is moved on the first heating target region in the longitudinal direction.
According to another illustrative aspect of the present invention, another heating apparatus configured to heat a plate workpiece having a first heating target region and a second heating target region is provided. A sectional area of the first heating target region is substantially constant along a longitudinal direction of the first target heating region or monotonically increases or decreases along the longitudinal direction. The second heating target region is adjoining the first heating target region in the longitudinal direction in a monolithic manner. The second heating target region is wider than the first heating target region. The heating apparatus includes a partial heating section configured to heat the second heating target region, and an overall heating section configured to heat the first heating target region and the second heating target region. The overall heating section includes the direct resistance heating apparatus described above. At least one of the first electrode and the second electrode of the direct resistance heating apparatus is moved in the longitudinal direction of the plate workpiece.
According to another illustrative aspect of the present invention, a direct resistance heating method includes heating a workpiece by direct resistance heating, and flattening the workpiece that has been expanded due to the direct resistance heating by pulling the workpiece. The direct resistance heating includes moving at least one of a first electrode and a second electrode arranged to oppose to each other with a space provided between the first electrod and the second electrode, along an opposing direction in which the first electrode and the second electrode are opposed to each other, in a state in which the first electrode and the second electrode are in contact with the workpiece and in a state in which current is applied to the workpiece through the first electrode and the second electrode. The pulling of the workpiece includes holding the workpiece by a first holder and a second holder such that, in a state in which the at least one of the first electrode and the second electrode is moved, a heating target region of the workpiece located between the first electrode and the second electrode is held between the first holder and the second holder in the opposing direction, and moving at least one of the first holder and the second holder along the opposing direction.
According to another illustrative aspect of the present invention, a heating method for heating a plate workpiece having a first heating target region and a second heating target region is provided. A sectional area of the first heating target region is substantially constant along a longitudinal direction of the first heating target region or monotonically increases or decreases along the longitudinal direction. The second heating target region is adjoining a portion of the first heating target region in a width direction of the first heating target region. The heating method includes heating the second heating target region, and after the heating of the second heating target region, heating the first heating target region by the direct resistance heating method described above to heat the first heating target region and the second heating target region to be within a predetermined temperature range. The at least one of the first electrode and the second electrode is moved in the longitudinal direction.
According to another illustrative aspect of the present invention, a heating method for heating a plate workpiece having a first heating target region and a second heating target region is provided. A width of the first heating target region is substantially constant along a longitudinal direction of the first heating target region or monotonically increases or decreases along the longitudinal direction. The second heating target region is adjoining the first heating target region in the longitudinal direction in a monolithic manner. The second heating target region is wider than the first heating target region. The heating method includes heating the second heating target region, and after the heating of the second heating target region, heating the first heating target region and the second heating target region by the direct resistance heating method described above to heat the first heating target region and the second heating target region to be within a predetermined temperature range. The at least one of the first electrode and the second electrode is moved in the longitudinal direction.
According to another illustrative aspect of the present invention, a hot-press molding method includes heating the heating target region of the workpiece by the direct resistance heating method described above, and pressing the workpiece by a press mold.
According to another illustrative aspect of the present invention, a hot-press molding method includes heating the first heating target region and the second heating target region of the plate workpiece by the heating method described above, and pressing the workpiece by a press mold.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A workpiece W1 illustrated in
A direct resistance heating apparatus 1 for heating the workpiece W1 by direct resistance heating includes a first holder 10 and a second holder 11 each of which configured to hold the workpiece W1, a pair of electrodes 14 including a first electrode 12 and a second electrode 13, a power supply 15 electrically connected to the pair of electrodes 14, an electrode moving mechanism 16, a holder moving mechanism 17, and a controller 18. The controller 18 may include at least one processor and at least one memory.
The first holder 10 is arranged on one end portion L of the workpiece W1 in the longitudinal direction, and the second holder 11 is arranged on the other end portion R of the workpiece W1 in the longitudinal direction to hold a heating target region of the workpiece W1 between the first holder 10 and the second holder.
The first electrode 12 and the second electrode 13 are arranged between the first holder 10 and the second holder 11 to be spaced apart from each other in the longitudinal direction of the workpiece W1, the first electrode 12 is arranged on the first holder 10 side, and the second electrode 13 is arranged on the second holder 11 side.
The power supply 15 is electrically connected to the first electrode 12 and the second electrode 13 and supplies current to the pair of electrodes 14 including the first electrode 12 and the second electrode 13. The power supply 15 may be a DC power supply or an AC power supply. The current supplied from the power supply 15 to the pair of electrodes 14 is controlled by the controller 18.
The electrode moving mechanism 16 has a first moving unit 20 which moves the first electrode 12, and a second moving unit 21 which moves the second electrode 13. The first moving unit 20 can move the first electrode 12 in the longitudinal direction of the workpiece W1 while being in contact with the first electrode 12 and the workpiece W1. In the same manner, the second moving unit 21 can move the second electrode 13 in the longitudinal direction of the workpiece W1 while being in contact with second electrode 13 and the workpiece W1. The movement of the first electrode 12 by the first moving unit 20 and the movement of the second electrode 13 by the second moving unit 21 are controlled by the controller 18.
The holder moving mechanism 17 moves the second holder 11 in the longitudinal direction of the workpiece W1 in the example. The movement of the second holder 11 by the holder moving mechanism 17 is controlled by the controller 18.
In the example illustrated in
First, as illustrated in
As illustrated in
During a period from the start of the current application to the workpiece W1 to the termination of the current application, at least one of the moving speed of the first electrode 12 and the amount of current passing through the workpiece W1 are controlled by the controller 18. Accordingly, when the heating target region of the workpiece W1 is divided into a plurality of strip-shaped segment regions (w1, w2, . . . wn) arranged side by side in the longitudinal direction, the amount of heat generated in each segment region can be controlled.
wherein, ρe represents resistivity (Ω·m), ρ presents density (kg/m3), c represents specific heat (J/kg·° C.), and Ai represents a sectional area (m2) of the i-th divided area.
In the workpiece W1 in which the thickness and width are constant along the longitudinal direction, that is, the sectional area is constant along the longitudinal direction, basically, as illustrated in
Although thermal expansion occurs in the heated workpiece W1, the second holder 11 is moved in the longitudinal direction of the workpiece W1 and the workpiece W1 is pulled in the longitudinal direction to flatten the workpiece W1. Preferably, as illustrated in
The workpiece W1 may be flattened by moving the first holder 10 or moving both the first holder 10 and the second holder 11. In a case where the first holder 10 is moved, preferably, in a state in which the first electrode 12 is separated from the workpiece W1, the first holder 10 is moved in the longitudinal direction of the workpiece W1.
In the example illustrated in
First, as illustrated in
As illustrated in
In the example, basically, as illustrated in
As illustrated in
In this manner, in a state in which the current is applied from the power supply 15 to the workpiece W1 through the first electrode 12 and the second electrode 13, at least one of the first electrode 12 and the second electrode 13 is moved in the longitudinal direction of the workpiece W1 and at least one of the moving speed of the moved electrode and the amount of current passing through the workpiece W1 are controlled, so that the heating target region of the workpiece W1 divided into a plurality of strip-shaped segment regions (w1, w2, . . . wn) arranged side by side in the longitudinal direction can be heated to have a predetermined temperature distribution only with a pair of electrodes 14 by controlling the amount of heat generated in each segment region. Accordingly, there is no need to arrange a plurality of pairs of electrodes in the workpiece W1 in the width direction to oppose each other and to control the amount of current for each of the pairs of electrodes in accordance with a temperature distribution as in the related art, and the configuration of the direct resistance heating apparatus 1 can be simplified.
By holding the workpiece W1 by the first holder 10 and the second holder 11 which are arranged to hold the heating target region of the workpiece W1 therebetween, even in a case where both the first electrode 12 and the second electrode 13 are moved between the first holder 10 and the second holder 11 as illustrated in
Preferably, each of the first electrode 12 and the second electrode 13 has a size that extends across the heating target region of the workpiece W1 in the width direction of the workpiece W1, for example, in a direction intersecting the moving direction of the electrode. Accordingly, the temperature distribution in the width direction of the workpiece W1 is suppressed.
The direct resistance heating apparatus 1 can also be applied to a workpiece having a varying sectional area in the longitudinal direction due to a variation in the width and thickness of the heating target region in the longitudinal direction and a workpiece having a varying sectional area in the longitudinal direction due to an opening or a cut-out region present in the heating target region.
A workpiece W2 in the example illustrated in
The sectional area in the width direction monotonically increases or decreases along the longitudinal direction means that a variation in the sectional area along the longitudinal direction, that is, a sectional area at respective points along the longitudinal direction increases or decreases along one direction without an inflection point. The sectional area can be considered as monotonically increasing or monotonically decreasing, if a partially low-temperature portion or a partially high-temperature portion, which may be practically problematic, is not generated at the time of direct resistance heating due to current density being excessively non-uniform in the width direction as a result of a sharp variation in the sectional area in the longitudinal direction.
In the example illustrated in
First, as illustrated in
As illustrated in
As illustrated in
During a period from the start of the current application to the workpiece W2 to the termination of the current application, at least one of the moving speed of the first electrode 12 and the amount of current passing through the workpiece W2 are controlled by the controller 18. Accordingly, when the heating target region of the workpiece W2 is divided into a plurality of strip-shaped segment regions (w1, w2, . . . wn) arranged side by side in the longitudinal direction, the amount of heat generated in each segment region can be controlled. Particularly, by moving the first electrode 12 in the longitudinal direction of the workpiece W2, it is possible to heat the workpiece W2 to be within a predetermined temperature range considered as a uniform temperature in the workpiece W2 in which the sectional area monotonically decreases along the moving direction of the first electrode 12.
In a case where the heating target region of the workpiece W2 is divided into n segment regions by a unit length ΔI, the amount of temperature rise of an i-th segment region is obtained from the foregoing equation, and to make the amount of temperature rise of each of the segment regions constant such as θ1=θ2= . . . =θn, the amount of current Ii and the time ti (electrode moving speed Vi) may be controlled so as to satisfy the following equation.
In a case where the second electrode 13 is fixed to the end portion R of the workpiece W2 and the first electrode 12 is moved from the end portion R to the end portion L of the workpiece W2, the current application time of each segment region is different and the segment region closer to the end portion R side has longer current application time. In a case where an equal current is applied to the segment region on the end portion R side and the segment region on the end portion L side for the same period of time, the resistance per unit length is relatively small and the amount of heat generated in the segment regions decreases toward the end portion R.
When the amount of heat generated in each segment region is adjusted by controlling at least one of the moving speed of the first electrode 12 and the amount of current passing through the workpiece W2 based on a variation in the resistance per unit length, the workpiece W2 can be uniformly heated.
In the example illustrated in
In the example illustrated in
A workpiece W3 in the example illustrated in
Accordingly, when the amount of heat generated in each segment region is adjusted by fixing the second electrode 13 to the end portion R of the workpiece W3, moving the first electrode 12 from the end portion R to the end portion L of the workpiece W3, and controlling at least one of the moving speed of the first electrode 12 and the amount of current passing through the workpiece W3 based on a variation in the resistance per unit length of the workpiece W3, the workpiece W3 can be uniformly heated.
A workpiece W4 in the example illustrated in
Accordingly, when the amount of heat generated in each segment region is adjusted by arranging the first electrode 12 and the second electrode 13 at the center portion of the workpiece W4 in the longitudinal direction, moving the first electrode 12 to the end portion L of the workpiece W4 and also moving the second electrode 13 to the end portion R of the workpiece W4 in combination, controlling at least one of the moving speed of each of the first electrode 12 and the second electrode 13 and the amount of current passing through the workpiece W4 based on a variation in the resistance per unit length of the workpiece W4, the workpiece W4 can be uniformly heated.
In this manner, at least one of the moving speed of each of the first electrode 12 and the second electrode 13 and the amount of current passing through the workpiece are controlled based on variations in the resistance of each segment region obtained from the shape and size of the heating target region of the workpiece, so that the heating target region of the workpiece can be heated to be within a predetermined temperature range considered as a substantially uniform temperature.
A part of the workpiece can be formed into a heating target region. In the example illustrated in
The sectional area of the heating target region W2a monotonically decreases from the boundary with the non-heating region W2b to the end portion L, and in other words, the resistance per unit length in the longitudinal direction monotonically increases from the boundary with the non-heating region W2b to the end portion L.
Accordingly, when the amount of heat generated in each segment region is adjusted by providing the first electrode 12 and the second electrode 13 in the heating target region W2a to be adjacent to the boundary between the heating target region W2a and the non-heating region W2b, fixing the second electrode 13 and moving the first electrode 12 to the end portion L, and controlling at least one of the moving speed of the first electrode 12 and the mount of current passing through the workpiece W2 based on a variation in the resistance per unit length of the heating target region W2a, the heating target region W2a can be uniformly heated.
The direct resistance heating apparatus 1 includes a slide rail 31 arranged on a mounting base 30. The slide rail 31 extends in one direction and the first holder 10, the second holder 11, the first electrode 12, and the second electrode 13 are arranged on the slide rail 31 and supported on the slide rail 31 to be movable along the slide rail 31.
The holder moving mechanism 17 for moving the second holder 11 is configured to include a thread shaft 32 which extends parallel to the slide rail 31, and a motor 33 which rotationally drives the thread shaft 32. The second holder 11 is screwed to the thread shaft 32 and the second holder 11 is moved along the thread shaft 32 according to rotation of the thread shaft 32. The rotation of the motor 33 is controlled by the controller 18 (refer to
The first holder 10 can be moved in a movement range from the center portion of the slide rail 31 in the longitudinal direction to the other end portion of the slide rail 31 and is fixed at an appropriate location corresponding to the length of a workpiece in this movement range. The first holder 10 may also be moved by the holder moving mechanism 17 and in this case, the thread shaft and the motor corresponding to the first holder 10 are provided in the holder moving mechanism 17.
The first electrode 12 and the second electrode 13 are arranged between the first holder 10 and the second holder 11 on the slide rail 31.
The first moving unit 20 which moves the first electrode 12 is configured to include a thread shaft 34 which extends parallel to the slide rail 31 and a motor 35 which rotationally drives the thread shaft 34. The first electrode 12 is screwed to the thread shaft 34 and the first electrode 12 is moved along the thread shaft 34 according to rotation of the thread shaft 34. The rotation of the motor 35 is controlled by the controller 18 and based on the control of the motor 35 by the controller 18, the first electrode 12 is moved by the first moving unit 20 in a movement range from the center portion of the slide rail 31 in the longitudinal direction to the first holder 10.
The second moving unit 21 which moves the second electrode 13 is configured to include the thread shaft 34 and the motor 35 similar to the first moving unit 20, and based on the control of the motor 35 by the controller 18, the second electrode 13 is moved by the second moving unit 21 in a movement range from the center portion of the slide rail 31 in the longitudinal direction to the second holder 11.
The holder moving mechanism 17, the first moving unit 20, and the second moving unit 21 may be configured by another linear motion mechanism such as a fluid pressure cylinder.
The direct resistance heating apparatus 1 further includes a first bus bar 36 arranged on the mounting base 30 along the workpiece held by the first holder 10 and the second holder 11, and a second bus bar 37. The first bus bar 36 extends over a substantially entire length of the movement range of the first holder 10 including in the movement range of the first electrode 12 and the second bus bar 37 extends over the substantially entire length of the movement range of the second holder 11 including in the movement range of the second electrode 13.
The first bus bar 36 and the second bus bar 37 are formed of a highly conductive material, such as copper, and for example, a hard plate material having a sectional area sufficient for supplying the current required at the time of direct resistance heating of the workpiece may be used. The first bus bar 36 and the second bus bar 37 are insulated from each other, the first bus bar 36 is electrically connected to one electrode of the power supply 15 (refer to
The second holder 11 moved by the holder moving mechanism 17 has a chuck 40 which holds a workpiece, a driving unit 41 which drives the chuck 40 to be opened or closed, and a movement frame 42 which supports the chuck 40 and the driving unit 41.
The movement frame 42 is supported on the slide rail 31 to be movable, is screwed to the thread shaft 32 (refer to
In the example, as the first holder 10, a clamp which is manually opened or closed is used. However, the first holder may have a chuck, a driving unit which drives the chuck to be opened or closed, and a movement frame which is supported on the slide rail 31 to be movable similar to the second holder 11.
The first electrode 12 includes a movable electrode 50 arranged to come into contact a heating target region of a workpiece W, a power feeding mechanism 51 for feeding power from the first bus bar 36 to the movable electrode 50, a pressing member 52 arranged to oppose to the movable electrode 50, a press mechanism 53 for driving the pressing member 52, and a movement frame 54 on which these parts are integrally supported. The movement frame 54 is supported on the slide rail 31 to be movable and is screwed to the thread shaft 34 of the first moving unit 20. Here, in a state in which the movable electrode 50 and the power feeding mechanism 51 are arranged between the first bus bar 36 and the workpiece W, the movable electrode and the power feeding mechanism can be moved integrally with the movement frame 54 by the first moving unit 20.
The movable electrode 50 is formed by current-applying roller 55 which rolls in contact with a surface of the workpiece W. The entire peripheral surface of the current-applying roller 55 is formed of a conductive material and is rotatably supported on a bearing portion 55b which is fixed to the movement frame 54 in a state in which a shaft portion 55a of the current-applying roller is insulated from a peripheral surface thereof. The peripheral surface of the current-applying roller 55 is formed of a highly conductive material such as copper, cast iron, and carbon and is formed to have a smooth surface having a circular section. The peripheral surface of the current-applying roller 55 is electrically connected to the first bus bar 36 through the power feeding mechanism 51 and comes in contact with the heating target region of the workpiece W in a direction perpendicular to a moving direction of the current-applying roller. The line of contact between the peripheral surface of the current-applying roller 55 and the heating target region of the workpiece W extends across the entire width of the heating target region.
The power feeding mechanism 51 includes a power feeding roller 56 which rolls in contact with the surface of the first bus bar 36. The entire peripheral surface of the power feeding roller 56 is made of a conductive material. The power feeding roller 56 is rotatably supported on a bearing portion 56b which is fixed to the movement frame 54 in a state in which a shaft portion 56a of the power feeding roller is insulated from a peripheral surface thereof. The peripheral surface of the power feeding roller 56 is formed of a highly conductive material such as copper, cast iron, and carbon and is formed to have a smooth surface having a circular section. The peripheral surface of the power feeding roller 56 comes into contact with the surface of the first bus bar 36 on the workpiece W side in a direction perpendicular to the moving direction of the power feeding roller 56, and the line of contact between the peripheral surface of the power feeding roller 56 and the surface of the first bus bar 36 extends substantially across the entire width of the bus bar.
Although other rollers or the like may be interposed between the power feeding roller 56 and the current-applying roller 55, in the embodiment, the current-applying roller 55 comes into direct contact with the power feeding roller 56 over the substantially entire axial length. Here, since the current-applying roller 55 and the power feeding roller 56 are rotated in opposite directions, the current-applying roller and the power feeding roller are always in contact with each other without sliding. During direct resistance heating, large current can be supplied to the current-applying roller 55 from the first bus bar 36 through the peripheral surface of the power feeding roller 56.
The pressing member 52 includes a pressing roller 58 which is arranged at a location facing the current-applying roller 55 through the workpiece W. Although material of the pressing roller 58 is not particularly limited as long as the pressing roller can come into contact the workpiece W to pressurize the workpiece, it is preferable that the pressing roller is formed of a material having a thermal conductivity lower than the current-applying roller 55. For example, the pressing roller may be formed of cast iron, ceramics, and the like. The shaft portion 58a is rotatably supported on a bearing portion 58b which is supported on the movement frame 54 to be movable. In this embodiment, the bearing portion 58b is supported on a movable bracket 57 provided in the press mechanism 53 and thus can be moved in a contact or separation direction with respect to the current-applying roller 55. Further, the pressing roller 58 is supported on the movement frame 54 and thus can be moved together with the current-applying roller 55 and the power feeding roller 56.
The press mechanism 53 includes a pressing cylinder 59 mounted on the movement frame 54, and a movable bracket 57 which is connected to the pressing cylinder 59 to be movable. Here, the movable bracket 57 is pressed against the current-applying roller 55 by being pressed by the pressing cylinder 59 and the pressing roller 58 presses the workpiece W toward the current-applying roller 55. The pressing operation by the pressing cylinder 59 is released and then the pressing roller 58 and the current-applying roller 55 are separated from the workpiece W, that is, the first electrode 12 is separated from the workpiece W.
The second electrode 13 includes a movable electrode 70 arranged to come into contact the heating target region of the workpiece W, a power feeding mechanism 71 for feeding power from the second bus bar 37 to the movable electrode 70, a pressing member 72 arranged to oppose to the movable electrode 70, a press mechanism 73 for driving the pressing member 72, and a movement frame 74 on which these parts are integrally supported. The movement frame 74 is supported on the slide rail 31 to be movable and is screwed to the thread shaft 34 of the second moving unit 21. Here, in a state in which the movable electrode 70 and the power feeding mechanism 71 are arranged between the second bus bar 37 and the workpiece W, the movable electrode and the power feeding mechanism can be moved integrally with the movement frame 74 by the second moving unit 21.
The movable electrode 70 includes current-applying roller 75 which rolls in contact with the surface of the workpiece W similar to the movable electrode 50 of the first electrode 12. The power feeding mechanism 71 includes a power feeding roller 76 which rolls in contact with a surface of the second bus bar 37 similar to the power feeding mechanism 51 of the first electrode 12. The pressing member 72 includes a pressing roller 78 which is arranged at a location facing the current-applying roller 75 through the workpiece W similar to the pressing member 52 of the first electrode 12, the press mechanism 73 includes a pressing cylinder 79 and a movable bracket 77 similar to the press mechanism 53 of the first electrode 12, and the pressing roller 78 presses the workpiece W toward the current-applying roller 75. The pressurization by the pressing cylinder 79 is released and then the pressing roller 78 and the current-applying roller 75 are separated from the workpiece W, that is, the second electrode 13 is separated from the workpiece W.
According to the direct resistance heating apparatus 1, since the first bus bar 36 and the second bus bar 37 are arranged along the workpiece W, a loop is not formed by the first bus bar 36 and the second bus bar 37 so that it is possible to reduce inductance component. As a result, the power factor is not degraded and therefore it is possible to apply a predetermined current to the workpiece W. The movable electrode 50 of the first electrode 12 can be moved relative to the first bus bar 36 and the workpiece W in a contact state and in current-applying state, and the movable electrode 70 of the second electrode 13 can be moved relative to the second bus bar 37 and the workpiece W in a contact state and in current-applying state. Therefore, it is possible to change the region of the workpiece W to which large current is supplied or to change the current-applying time.
Therefore, the relative position between the workpiece W and the first bus bar 36 and the second bus bar 37 is not changed and the constant of a circuit configured by including the workpiece W as a load is not changed.
The current-applying region or the current-applying time can be changed just by moving at least one of the movable electrode 50 of the first electrode 12 and the movable electrode 70 of the second electrode 13. Thus, it is not necessary to make a complicated structure by providing a large number of electrodes or power feeding structures or providing a structure for moving the workpiece W, the first bus bar 36, or the second bus bar 37 as in the related art. The direct resistance heating apparatus 1 can be formed into a simple and compact manner. Accordingly, it is possible to realize a configuration in which a predetermined large current can be easily and simply supplied to the current-applying region of the workpiece W by changing the current-applying region or the current-applying time.
In the direct resistance heating apparatus 1, the movable electrode 50 of the first electrode 12 is arranged between the first bus bar 36 and the workpiece W, and the movable electrode 70 of the second electrode 13 is arranged between the second bus bar 37 and the workpiece W. Thus, it is possible to shorten a power feeding path from the first bus bar 36 to the workpiece W and a power feeding path from the second bus bar 37 to the workpiece W and to reduce the loss.
Since the movable electrode 50 of the first electrode 12 is the current-applying roller 55 and the movable electrode 70 of the second electrode 13 is the current-applying roller 75, the mechanical resistance when the movable electrodes 50 and 70 are moved can be reduced and the movable electrodes can be easily moved even in a state in which the movable electrodes are brought into contact with the workpiece W over a long range. Accordingly, it is possible to efficiently heat the heating target region of the workpiece W by increasing the contact length with the workpiece W. Further, when the movable electrode 50 is the current-applying roller 55 and the movable electrode 70 is the current-applying roller 75, the movable electrodes can be stably moved in a state in which the movable electrodes are in contact with the surface of the workpiece W. For example, the movable electrodes can be prevented from being floated from the surface of the workpiece W due to vibration or the like, thereby preventing occurrence of spark. Further, even when the movable electrodes 50 and 70 are moved in current-applying state, it is possible to stably supply large current to the workpiece W.
In the direct resistance heating apparatus 1, since the first bus bar 36 extends over the substantially entire length of the movement range of the first holder 10 including the movement range of the movable electrode 50 of the first electrode 12 and the movable electrode 50 and the first bus bar 36 can be always connected in a proximity location when the movable electrode 50 is moved and the power feeding path can be shortened. Further, since the power feeding path from the first bus bar 36 to the workpiece W is not changed when the movable electrode 50 is moved, it is possible to maintain a stable current-applying state. Similarly, the second bus bar 37 extends over the substantially entire length of the movement range of the second holder 11 including the movement range of the movable electrode 70 of the second electrode 13, the movable electrode 70 and the second bus bar 37 can be always connected in a proximity location when the movable electrode 70 is moved and the power feeding path can be shortened. Further, since the power feeding path from the second bus bar 37 to the workpiece W is not changed when the movable electrode 70 is moved, it is possible to maintain a stable current-applying state.
In the direct resistance heating apparatus 1, since the workpiece W is pressed against the movable electrode 50 by the pressing member 52 of the first electrode 12 and the workpiece W is pressed against the movable electrode 70 by the pressing member 72 of the second electrode 13, the movable electrodes 50 and 70 can be prevented from being floated from the surface of the workpiece W when the movable electrodes 50 and 70 are moved and current can stably be applied to workpiece W. Since the current is applied by bringing the movable electrodes 50 and 70 into contact with the workpiece W across the entire length of the heating target region in the width direction, the current can be applied to the entire heating target region when the movable electrodes are moved in one direction intersecting the width direction of the workpiece W. Thus, it is possible to shorten the current-applying time by efficiently heating the workpiece with a simple configuration.
Particularly, since the direct resistance heating apparatus 1 includes the power feeding roller 56 of the first electrode 12 which rolls in contact with the first bus bar 36, it is possible to reduce the moving resistance when the power feeding roller is moved in contact with the surface of the first bus bar 36. Thus, the power feeding roller can be easily moved in a state in which the power feeding roller is brought into contact with the first bus bar 36 over a long range thereof. Similarly, since the direct resistance heating apparatus includes the power feeding roller 76 of the second electrode 13 which rolls in contact with the second bus bar 37, it is possible to reduce the moving resistance when the power feeding roller is moved in a contact with the surface of the second bus bar 37. Thus, the power feeding roller can be easily moved in a state in which the power feeding roller is brought into contact with the second bus bar 37 over a long range thereof. Therefore, a long contact length of the first bus bar 36 and the power feeding roller 56 and a long contact length of the second bus bar 37 and the power feeding roller 76 can be secured and large current can be easily supplied from the first bus bar 36 and the second bus bar 37.
In the direct resistance heating apparatus 1, since the power feeding roller 56 of the first electrode 12 is moved together with the current-applying roller 55, the power feeding path from the first bus bar 36 to the movable electrode 50 can be kept substantially constant when the movable electrode 50 is moved. Similarly, since the power feeding roller 76 of the second electrode 13 is moved together with the current-applying roller 75, the power feeding path from the second bus bar 37 to the movable electrode 70 can be kept substantially constant when the movable electrode 70 is moved. Therefore, it is possible to reduce or eliminate variations in the electrical conditions when the movable electrodes 50 and 70 are moved and thus it is possible to stably supply large current to the workpiece W.
In the direct resistance heating apparatus 1, since the current-applying roller 55 and the power feeding roller 56 of the first electrode 12 come into direct contact with each other while rolling in opposite directions, the peripheral surface of the power feeding roller 56 and the peripheral surface of the current-applying roller 55 do not slide at their mutually contacting portions and the power feeding roller 56 and the current-applying roller 55 can be moved in a state in which the rollers are brought into contact with each other over a wide range with low contact resistance. For this reason, a wide contact width between the surface of the power feeding roller 56 and the surface of the current-applying roller 55 can be secured, so that large current can be easily supplied from the current-applying roller 56 to the current-applying roller 55. Further, since the power feeding path from the first bus bar 36 to the workpiece W is provided by the surface of the power feeding roller 56 and the surface of the current-applying roller 55, the power feeding path can be significantly simplified. Similarly, since the current-applying roller 75 and the power feeding roller 76 of the second electrode 13 come into direct contact with each other while rolling in opposite directions, the peripheral surface of the power feeding roller 76 and the peripheral surface of the current-applying roller 75 do not slide at their mutually contacting portions and the power feeding roller 76 and the current-applying roller 75 can be moved in a state in which the rollers are brought into contact with each other over a wide range with low contact resistance. For this reason, a wide contact width between the wide contact width between the surface of the power feeding roller 76 and the surface of the current-applying roller 75 can be secured, so that large current can be easily supplied from the power feeding roller 76 to the current-applying roller 75. Further, since the power feeding path from the second bus bar 37 to the workpiece W is provided by the surface of the power feeding roller 76 and the surface of the current-applying roller 75, the power feeding path can be significantly simplified. Thus, it is possible to more easily supply large current.
In the example illustrated in
When the power feeding roller 56 is arranged at a location shifted with respect to the current-applying rollers 55 in this manner, the workpiece W and the first bus bar 36 can be arranged at adjacent locations. The current-applying roller 75 and the power feeding roller 76 of the second electrode 13 can also be configured similarly and thus the workpiece W and the second bus bar 37 can be arranged adjacent to each other. As a result, it is possible to make inductance smaller and also it is possible to achieve compactness of the direct resistance heating apparatus 1.
The power feeding mechanism 51 illustrated in
The electrically-conductive brush 62 is configured to have sufficient electrical conductivity to supply sufficient power from the first bus bar 36 to the movable electrode 50 during direct resistance heating. For example, the electrically-conductive brush 62 and the first bus bar 36 are in close contact with each other to provide good electrical conductivity therebetween, the electrically-conductive brush 62 has sufficient electrical conductivity up to its distal end portion that contacts the movable electrode 50, the electrically-conductive brush 62 has heat resistance to prevent occurrence of melting or thermal deformation when current is applied, and deterioration hardly occurs even when the electrically-conductive brush 62 is deformed due to the repetitive contact of the movable electrode.
The electrically-conductive brush 62 can be made in a suitable form, such as one obtained by arranging and bundling linear conductive fibers in the substantially same direction, one obtained by collecting conductive fibers into woven or non-woven fabric shape, one obtained by fixing conductive fibers by other material to allow a portion thereof to protrude, one obtained by molding conductive fibers together with flexible material, and the like. Further, the electrically-conductive brush 62 may be formed integrally with the first bus bar 36 by embedding a portion thereof into a material layer forming the surface of the first bus bar 36. As a material forming conductive fibers, carbon fiber or the like can be exemplified.
In the first electrode 12, when the current-applying roller 55 is moved by the movement frame 54, the current-applying roller 55 rolls in contact with the surface of the workpiece W. At this time, since the current-applying roller 55 moves in sliding contact with the electrically-conductive brush 62 arranged on the surface of the first bus bar 36 and the current from the first bus bar 36 is supplied to the entire peripheral surface of the current-applying roller 55 through the electrically-conductive brush 62, the current-applying roller 55 can be moved in a state in which current is applied to the workpiece W.
In the first electrode 12, since the movable electrode 50 is in sliding contact with the electrically-conductive brush 62 of the first bus bar 36, the contact resistance of the movable electrode 50 can be reduced and the first bus bar 36 and the movable electrode 50 can move in contact with each other over a long range. Therefore, a long contact length between the movable electrode 50 and the first bus bar 36 can be secured and large current can be supplied more easily from the first bus bar 36 to the movable electrode 50. Further, since the power feeding path from the first bus bar 36 to the workpiece W is configured by the electrically-conductive brush 62 and the movable electrode 50, the configuration can be significantly simplified.
In the first electrode 12, since the electrically-conductive brush 62 is arranged to oppose to the substantially entire region of the heating target region of the workpiece W, power can be fed to each portion of the heating target region from each facing portion of the electrically-conductive brush 62. Therefore, the power feeding path from the electrically-conductive brush 62 to the workpiece W can be shortened and substantially fixed and current can be applied to the entire heating target region in a uniform manner.
The power feeding mechanism 71 of the second electrode 13 can also be configured similarly and may include an electrically-conductive brush which is integrally or separately provided on the surface of the second bus bar 37 on the workpiece W side so as to allow the current-applying roller 75 to come into contact therewith and arranged on the substantially entire surface of the second bus bar facing toward the workpiece W.
The power feeding mechanism 51 of the first electrode 12 illustrated in
In the first electrode 12, when the current-applying roller 55 and the power feeding roller 63 are moved, in a state in which the current-applying roller 55 is in contact with the workpiece W, the power feeding roller 63 can moves in contact with the first bus bar 36.
As the pressing member 52 is pressed, the workpiece W is pressed against the current-applying roller 55. Since the power feeding roller 63 has a diameter larger than the diameter of the current-applying roller 55, in a state in which the current-applying roller 55 is separated from the surface of the first bus bar 36, the current-applying roller is pressed against the workpiece W. Since the power feeding roller 63 is arranged on the outside of both sides of the workpiece W, the power feeding roller is pressed against both edge sides of the first bus bar 36 without contact with the workpiece W.
In the first electrode 12, since the power feeding rollers 63 are provided at respective ends of the movable electrode 50 and are moved in contact with the first bus bar 36, a space between the first bus bar 36 and the workpiece W can be reduced. Further, it is possible to reduce the moving resistance to the first bus bar 36 or the moving resistance to the workpiece W regardless of the size of the movable electrode 50. Therefore, large current can be supplied more easily.
Although the current-applying roller 55 and the power feeding roller 63 are mounted on the same shaft, the current-applying roller and the power feeding roller may be mounted on different shafts such that the current-applying roller 55 and the power feeding roller 63 are electrically connected.
The power feeding mechanism 71 of the second electrode 13 can also be configured in a similar manner. The power feeding mechanism may include power feeding rollers configured to contact and roll on the surface of the second bus bar 37. Each of the power feeding rollers may have a diameter larger than a diameter of the current-applying roller 75 and may be mounted on the shaft portion 75a at each end of the current-applying roller 75 or on a shaft different from the shaft portion 75a.
In the first electrode 12 having the movable electrode 50 which comes into contact with the workpiece W and the pressing member 52 which is arranged to oppose to the movable electrode 50, the workpiece W is held by the movable electrode 50 and the pressing member 52 so as to hold the workpiece W. In the same manner, in the second electrode 13 having the movable electrode 70 which comes into contact with the workpiece W and the pressing member 72 which is arranged to oppose to the movable electrode 70, the workpiece W is held by the movable electrode 70 and the pressing member 72 so as to hold the workpiece W. The first holder 10 may be configured to include the first electrode 12 so as to hold the workpiece W by the first electrode 12 and the second holder 11 may be configured to include the second electrode 13 so as to hold the workpiece W by the second electrode 13. Accordingly, compared to a configuration in which the first holder 10 and the second holder 11 are provided separately from the first electrode 12 and the second electrode 13, the apparatus configuration can be simplified.
In a case where the first holder 10 is configured to include the first electrode 12 so as to hold the workpiece W by the first electrode 12 and the second holder 11 configured to include the second electrode 13 so as to hold the workpiece W by the second electrode 13, as illustrated in
The examples in which the entire region or a part of the workpiece is set as one heating target region and the heating target region is heated by direct resistance heating to be within a predetermined temperature range have been described above. However, in examples described below, a heating target region of a workpiece is divided into a plurality of heating target regions and the plurality of heating target regions is heated by direct resistance heating in different temperature ranges from each other by the direct resistance heating apparatus I.
A workpiece W5 in the example illustrated in
First, as illustrated in
Thereafter, while current is being applied between the first electrode 12 and the second electrode 13, in a state in which the second electrode 13 is fixed without moving, the first electrode 12 is moved by the first moving unit 20 in a direction opposite to the moving direction of the second electrode 13, and the space between the first electrode 12 and the second electrode 13 is widened.
Then, as illustrated in
The current application to the workpiece W5 is terminated, in a state in which the second electrode 13 is separated from the workpiece W5, the second holder 11 is moved in the longitudinal direction of the workpiece W5 and the workpiece W5 is pulled in the longitudinal direction to make the workpiece W5 flat.
Through the above process, for example, as illustrated in
Here, in a case where the first electrode 12 is moved to heat the first heating target region W5a so that a state illustrated in
Further, in a case where the amount of heat generated in each segment region of the first heating target region W5a is adjusted by controlling at least one of the moving speed of the first electrode 12 and the amount of current passing through the workpiece W5, the first heating target region W5a can be heated to have a temperature distribution, for example, as indicated by a dotted line in
In both cases, since the sectional area of the second heating target region W5b of the workpiece W5 is increased in the moving direction of the second electrode 13, the temperature rise in the second heating target region W5b including the location of the weld bead portion W5c is decreased as it becomes farther from the weld bead portion W5c as illustrated in
Thus, the first heating target region W5a is heated to the hot working temperature by direct resistance heating and the second heating target region W5b is heated to the warm working temperature by direct resistance heating. In this manner, each of the first heating target region W5a and the second heating target region W5b can be heated to different temperatures by using the pair of electrodes 14 and individually moving the first electrode 12 and the second electrode 13 in the opposite directions on the workpiece W5 which is fixed.
The example illustrated in
As in the example illustrated in
As in the example illustrated in
Meanwhile, as in the example illustrated in
A workpiece W6 in the example illustrated in
The workpiece W6 is different from the workpiece W5 in the example illustrated in
First, as illustrated in
Thereafter, in a state in which the second electrode 13 is fixed with current being applied between the first electrode 12 and the second electrode 13, the first electrode 12 is moved by the first moving unit 20 in a direction opposite to the moving direction of the second electrode 13, and the space between the first electrode 12 and the second electrode 13 is widened. As illustrated in
Then, as illustrated in
Thereafter, in a state in which the second electrode 13 is fixed with current being applied between the first electrode 12 and the second electrode 13, the first electrode 12 is moved by the first moving unit 20 in a direction opposite to the moving direction of the second electrode 13 and the space between the first electrode 12 and the second electrode 13 is widened. As illustrated in
Through the above process, for example, as illustrated in
As illustrated in
The direct resistance heating method described above can be used in, for example, quenching performed by rapid cooling after heating and can also be used in hot-press press molding in which the workpiece in a high temperature state after heating is molded by pressing using a press mold. According to the above-described direct resistance heating method, it is sufficient to configure the heating equipment only with a simple construction, and thus the heating equipment can be provided adjacent to or integrally with the press machine. Therefore, the workpiece can be press-molded in a short period of time after being heated and temperature drop of the heated workpiece is suppressed to reduce energy loss. In addition, it is possible to prevent surface oxidation of the workpiece, thereby preparing a high quality press-molded article.
The examples in which the workpiece having relatively simple shapes such as a substantially rectangular shape and a substantially trapezoidal shape is heated by direct resistance heating have been described above. However, the direct resistance heating apparatus 1 can also be used in heating a workpiece formed by combining a plurality of shapes.
In the following description, an example in which a plate workpiece is heated and quenched by cooling will be described. In the example illustrated in
As illustrated in
The sectional area in the width direction monotonically increases or monotonically decreases in one direction in the longitudinal direction means that a variation in the sectional area in the longitudinal direction, that is, the sectional area at each location in longitudinal direction increases or decreases in one direction without an inflection point. The sectional area can be considered as monotonically increasing or monotonically decreasing, if a partial low-temperature portion or a partial high-temperature portion, which may be practically problematic, is not generated due to current density at the time of direct resistance heating being excessively non-uniform in the width direction as a result of a sharp variation in the sectional area in the longitudinal direction. The sectional area in the width direction may be substantially continuously uniform in the longitudinal direction.
The plate workpiece W7 includes a narrow portion 80 extending along a long axis X and wide portions 81 integrally provided at both ends of the narrow portion 80. The first heating target region W7a is formed by the narrow portion 80, extended portions 81x defined in the wide portions 81 by boundary lines 80x obtained by respectively extending both side edges of the narrow portion 80 along the long axis X. The long axis X can be appropriately set to a line extending in the longitudinal direction.
A heating apparatus for heating the plate workpiece W7 includes the direct resistance heating apparatus 1, an example of a first heating section configured to heat the first heating target region W7a as illustrated in
It is preferable that the second heating section 101 is designed to restrict heating of the first heating target region W7a when heating the second heating target region W7b as illustrated in
The plate workpiece W7 is heated in the following manner using such a heating apparatus. First, as illustrated in
Next, as illustrated in
When heating of the second heating target region W7b is terminated, it is preferable that the second heating target region W7b is heated to a temperature higher than a target heating temperature. Consequently, it is possible to heat the second heating target region W7b to be within a predetermined temperature range even when the temperature of the second heating target region is lowered by heat dissipation until the first heating target region W7a is subsequently heated by direct resistance heating.
Next, after the second heating target region W7b is heated, as illustrated in
Since the second heating target region W7b is heated to a high temperature at this time, the resistance of the second heating target region W7b is increased. This allows the current to flow a lot through the first heating target region W7a maintained at low temperature, thereby heating the first heating target region W7a. Thus, the first heating target region W7a is heated to be within a predetermined temperature range around a target temperature.
The first heating target region W7a and the second heating target region W7b are heated to be within a predetermined temperature range by adjusting the heating temperature of the second heating target region W7b and the heating timing of the first heating target region W7a. Meanwhile, according to the amount of time or heat transfer between the heating of the second heating target region W7b and the direct resistance heating of the first heating target region W7a, the temperature of the second heating target region W7b may often be lowered due to heat dissipation. When the second heating target region W7b is excessively heated at the time of heating, the temperature of the heated first heating target region W7a and the temperature of the heat-dissipated second heating target region W7b are equal to each other and the first heating target region W7a and the second heating target region W7b can be heated to be within a predetermined temperature range. Thereafter, the current application to the workpiece W7 is terminated, in a state in which the second electrode 13 is separated from the workpiece W7, the second holder 11 is moved in the longitudinal direction of the workpiece W7 and the workpiece W7 is pulled in the longitudinal direction to make the workpiece flat. Then, quenching by rapid cooling is performed.
In a case of heating the plate workpiece W7 as described above, the plate workpiece W7 is divided into the first heating target region W7a and the second heating target region W7b and then heated, and thus each region can be formed into simplified shapes to facilitate heating. The first heating target region W7a of the two regions has the shape of which the width in the width direction slightly monotonically increases or decreases along the longitudinal direction. Thus, when the current flows in the longitudinal direction, the first heating target region has no constricted portion or expanded portion where the current does not smoothly flow along current-flowing path.
Accordingly, when the current is applied to the first heating target region W7a longitudinal direction so as to resistance heat the first heating target region, there is no site where current density distribution in the width direction varies excessively. Thus, when the first heating target region W7a is heated by direct resistance heating in accordance with a variation in the sectional area of the first heating target region W7a in the longitudinal direction, q wide range of the first heating target region W7a can be easily and uniformly heated, and the plate workpiece W7 can be efficiently heated in the longitudinal direction.
Further, when the first heating target region W7a is heated after the second heating target region W7b becomes an appropriate heated state, a wide combined area of the first heating target region W7a and second heating target region W7b can be heated to be within a predetermined temperature range. Furthermore, since respective regions are not required to be heated at the same time, the first heating target region W7a can be heated by direct resistance heating in the longitudinal direction, and the second heating target region W7b can be heated by a method that is suitable for the second heating target region W7b, it is possible to heat a wide combined area of the first heating target region W7a and the second heating target region W7b with a simple configuration.
Further, the plate workpiece W7 is formed such that the second heating target region W7b is adjoining a portion of the first heating target region W7a in the width direction and is provided integrally with the first heating target region. Thus, when the second heating target region W7b is first heated, the current-flowing path corresponding to the first heating target region W7a is formed in the plate workpiece W7. Accordingly, a wide area of the first heating target region W7a and the second heating target region W7b can be easily heated to be within a predetermined temperature range by uniformly heating the first heating target region W7a over the wide area by direct resistance heating in the longitudinal direction after heating the second heating target region W7b to an appropriate heated state.
The example has been described in which the boundary lines 80x are set by extending both side edges of the narrow portion 80, thereby setting the first heating target region W7a. However, the boundary lines 80x may be set such that the width of each longitudinal end of the first heating target region W7a is the same. In this case, when the first heating target region is heated by bringing the first electrode 12 and the second electrode 13 into contact with the first heating target region W7a, the electrodes are moved in a short period of time over the extended portions 81x more rapidly than other regions, thereby uniformly heating the entire region of the first heating target region. Further, even in a case where a region in which the sectional area in the width direction is constant along the longitudinal direction exists in another portion of the first heating target region W7a, for example, the first electrode 12 and the second electrode 13 are also moved in a short period of time over that portion more rapidly than over other portion, thereby uniformly heating the first heating target region W7a.
In the example illustrated in
The heating apparatus used in this example has the same as the heating apparatus used in the example illustrated in
To heat the plate workpiece W7 using this heating apparatus, as already illustrated in
Next, as indicated by a solid line illustrated in
At this time, the moving order, moving speed or the like when the first electrode 12 and the second electrode 13 are moved may be controlled according to various heating conditions such as a shape, a target temperature range, or the like of the first heating target region W7a. For the moving order, for example, the first electrode 12 and the second electrode 13 may be moved at the same time, or the first electrode 12a which requires a long period of time may be first moved and then the second electrode 13 may be moved. For the moving speed, for example, the first electrode 12 and the second electrode 13 may be moved at different speeds, and the second electrode 13 may be moved at a variable speed according to a variation in the sectional area in the width direction of the first heating target region W7a in the longitudinal direction.
The current-applying time at each location in the longitudinal direction is adjusted by controlling the moving order, moving speed, or the like of the first electrode 12 and the second electrode 13 such that the current-applying time of a portion having a large sectional area is increased and the current-applying time of a portion having a small sectional area is decreased to heat each location of the first heating target region W7a in a target heating temperature range. Here, the first heating target region W7a of the wide portion 81b is heated in a first temperature range and the first heating target region W7a of the remaining portion is heated to a second temperature range.
As described above, since the second heating target regions W7b1 and W7b2 are heated in advance when each location of the first heating target region W7a is heated, the heating temperature of the second heating target regions W7b1 and W7b2, the heating timing of the first heating target region W7a, and the like are appropriately controlled so that as indicated by a broken line in
In the example, as the plate workpiece W7, a plate workpiece of which thickness is generally constant is used. However, a tailored blank in which a region having different thicknesses is provided can also be used. For example, a plate workpiece W7 in which the wide portion 81b and the remaining portion have different thicknesses may be heated in the same manner. In this case, it is easy to heat the wide portion 81b and the remaining portion in the same temperature range. Even when the workpiece has a uniform thickness, the entire workpiece may be heated in the same temperature range in the same manner.
In the example illustrated in
As illustrated in
As illustrated in
The plate workpiece W8 is heated using such a heating apparatus in the following manner. First, as illustrated in
Next, as illustrated in
After the second heating target region W8b is heated, as illustrated in
According to the heating method and the heating apparatus as described above, since the plate workpiece W8 is heated separately for a plurality of regions, i.e., the first heating target region W8a and the second heating target region W8b adjoining a portion of the first heating target region W8a, each region can be formed into simplified shapes to facilitate heating. Since the workpiece W8 has a shape in which the sectional area in the width direction of the first heating target region W8a and the second heating target region W8b in the width direction monotonically increases or monotonically decreases along the longitudinal direction, when the current flows in the longitudinal direction, the workpiece has no constricted portion or expanded portion where the current does not smoothly flow in the current-flowing path. Therefore, when the first heating target region W8a is heated by direct resistance heating in accordance with a variation in the sectional area in the longitudinal direction, a wide area of the first heating target region W8a can be easily and uniformly heated. Thereby, the plate workpiece W8 can be efficiently heated in the longitudinal direction.
Further, the second heating target region W8b that is wider than the first heating target region W8a is adjoining the first heating target region W8a in the longitudinal direction of the plate workpiece W8 in a monolithic manner. Thus, when the second heating target region W8b is first preheated by heating and the entire regions along the entire length is heated by direct resistance heating, the entire plate workpiece W8 does not need to be preheated and it is easy to perform direct resistance heating in the longitudinal direction. As a result, the second heating section 102 can be miniaturized, and the entire apparatus can be made compact.
Although the plate workpiece W8 which has a substantially trapezoidal shape in which the sectional area of the first heating target region W8a and the second heating target region W8b in the width direction monotonically increases or monotonically decreases in one direction of the longitudinal direction has been described, the present invention is not limited thereto. For example, the present invention can of course be adapted to the workpiece in which the first heating target region W8a and the second heating target region respectively have sectional areas that are different in the width direction, but are substantially uniform in the longitudinal direction.
The above-described heating method can be used in hot-press press molding in which the workpiece in a high temperature state after heating is molded by pressing using a press mold. According to the above-described heating method, it is sufficient to configure the heating equipment only with a simple construction, and thus the heating equipment can be provided adjacent to or integrally with the press machine. Therefore, the workpiece can be press-molded in a short period of time after being heated and temperature drop of the heated workpiece is suppressed to reduce energy loss. In addition, it is possible to prevent surface oxidation of the workpiece, thereby preparing a high quality press-molded article.
This application claims priority to Japanese Patent Application No. 2017-174053 filed on Sep. 11, 2017, the entire content of which is incorporated herein by reference.
Number | Date | Country | Kind |
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2017-174053 | Sep 2017 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2018/033300 | 9/7/2018 | WO | 00 |