JP2001321839A - Steel plate heating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel plate heating apparatus arranged in a transfer press and capable of heating a work prior to bending. SOLUTION: A high frequency induction coil 50 of a coiled shape of an outer peripheral shape roughly same as a part to be worked of a work 26 is arranged at a more upstream side in a feed direction A of the work than a bending part 22, the high frequency induction coil 50 is controlled by a S control board (heating controller) 28, the work 26 is heated by the high frequency induction coil 50 in synchronism with a press period Tp periodically repeating. By this method, in the transfer press 12, the work 26 is uniformly heated at a high temperature prior to bending, thus, the formability in bending is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet heating apparatus provided in a transfer press and for heating a steel sheet to be processed.

[0002]

2. Description of the Related Art A transfer press is capable of performing multiple steps such as punching, punching, and bending with a single press, and is excellent in productivity and labor saving. Widely used in the production of parts. For example, a transfer press according to the invention described in Japanese Utility Model Laid-Open No. 5-44394 and a transfer press described as a conventional device in the publication are applicable.

[0003]

On the other hand, in order to increase the rigidity of pressed parts for vehicles, high-strength steel sheets having high tensile strength and a high yield point (tensile strength) are used as materials for pressed parts for vehicles. However, the necessity of using 350MPa or more is increasing. However, a high-tensile steel sheet is inferior in press formability to a mild steel sheet due to a high yield point, and is likely to cause poor forming. In particular, in the transfer press,
The time taken for one step reduces the overall efficiency, so that the pressing time is limited. For this reason, in the transfer press, cracking occurred in deep drawing of a high-tensile steel sheet having a tensile strength exceeding 800 MPa, and press forming was not possible.

The inventor of the present invention has conducted various studies to solve the above-mentioned problems, and it has been difficult to press a high-tensile steel sheet at room temperature in a conventional transfer press because the steel sheet was pressed at room temperature. Accordingly, it has been concluded that press formability such as stretch flangeability is improved, and that even a high-tensile steel sheet can be easily pressed. That is,
It is an object of the present invention to provide a steel sheet heating apparatus provided in a transfer press and heating a steel sheet to be processed prior to press working.

[0005]

The gist of the present invention to achieve the above object is to provide a transfer press having a press section for performing press working on a steel sheet to be worked in one direction. A steel sheet heating device, which is provided on the upstream side in the feed direction of the steel plate to be processed with respect to the press unit, and is a high-frequency induction coil that locally heats the steel plate to be processed, and is synchronized with a periodically repeated press period of the transfer press. And a heating control device for causing the high-frequency induction coil to heat the steel plate to be processed.

[0006]

With this arrangement, the high-frequency induction coil provided on the upstream side in the feed direction of the steel sheet to be processed with respect to the press section is controlled by the heating control device, and the high-frequency induction coil is used to periodically repeat the high-frequency induction coil. The steel plate to be processed is heated in synchronization with the pressing period. Therefore, in the transfer press, the steel plate to be processed is heated prior to the press working, and the formability in the press working is improved.

[0007]

In another preferred embodiment of the present invention, the high-frequency induction coil preferably has a winding shape in which a conductor is wound in a size equal to or greater than an area shape of a pressed portion of the steel plate to be processed. The winding region surrounded by the conductor has a curved shape as a whole, and the winding region is opposed to the pressed portion of the steel plate to be processed. With this configuration, since the high-frequency induction coil has portions where the magnetic flux density is increased on both sides of the interwinding region, the steel plate to be processed has a high temperature on both sides of the portion opposed to the interwinding region. Become. Further, the portion of the steel sheet to be processed, which is opposed to the inter-winding region, is weakly heated directly by the high-frequency induction coil, but has a high temperature on both sides, and is heated by heat transfer from both sides. Therefore, the heated portion of the steel plate to be processed has a high temperature and uniform temperature as a whole, so that the formability in the press working is further improved.

[0008] Preferably, the heating control device sets the maximum heating point of the steel plate to be processed to a value lower than a target temperature at the time of press working before the elapse of 2/5 of the press period. First heating control means for rapidly increasing the temperature of the steel plate to be processed by the high-frequency induction coil so that the first temperature is set, and following the first heating control means,
And a second heating control means for raising the temperature of the steel sheet to be processed at a lower speed than the heating rate by the first heating control means. With this configuration, the first heating control means rapidly raises the temperature of the steel sheet to be processed until the maximum heating point of the steel sheet to be processed reaches the first temperature set to a value lower than the target temperature during the press working. Therefore, the temperature of the portion opposed to the high-frequency induction coil quickly increases. Subsequently, since the temperature of the steel plate to be processed is raised by the second heating control unit at a lower temperature raising rate than that of the first heating control unit, the steel plate to be processed is formed in a portion opposed to the inter-winding region. However, since the temperature of the steel sheet becomes higher due to heat transfer from the surroundings, the rate of temperature rise in the portion opposed to the high-frequency induction coil is lower than before, so that the heated portion of the steel plate to be processed has a more uniform temperature as a whole. Therefore, the formability in the press working is further improved.

[0009]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a plan view schematically showing an apparatus 10 for manufacturing a vehicle component. In FIG. 1, the transfer press 12 includes a punching portion 14 (first stage) for performing punching (first step), and a contour punching portion 16 (second stage) for performing contour punching (second step). Stage), an idle unit 18 (third stage) for performing the third step, a heating unit 20 (fourth stage) for heating the work 26, and a bending unit 22 (fifth stage) for performing bending. ,
And six stages of a punch-out portion 24 (sixth stage) for performing a punching process. The punch-out portion 14, the outer shape punching portion 16, the bending portion 22, and the punch-out portion 24 are respectively provided with predetermined upper and lower portions. Press die is attached. Further, the transfer press 12 is provided with a work transfer device (not shown) provided with fingers and the like (not shown) reciprocating in the direction shown by arrow A and the opposite direction. The workpiece 26 (steel plate to be processed) is intermittently moved to the next stage at a predetermined transfer time T _T. Then, after the workpiece 26 has been moved by the workpiece transport device at a predetermined pressing time T _P, the work 26 in each stage 14 to 24 is processed into a predetermined shape.

The transfer press 12 processes the workpiece 26 continuously by repeating the cycle of transporting the workpiece 26 by the workpiece transport device and subsequent press forming as one cycle. Here, the transport time T _T is set to, for example, 1.5 seconds. Further, the above-mentioned pressing time T _P, the period in which the workpiece 26 is then positioned on the stage 14 to 24, i.e., the next stage by the workpiece transfer device from the work 26 is provided is positioned to each stage 14-24 Is set to 1.5 seconds, for example. Thus, the transport time T _T and press duration T _P is, if the set both 1.5 seconds, one cycle of 3
Seconds.

The vehicle component manufacturing apparatus 10 further includes a control panel 28, a transformer (transformer) 30, and a high-frequency oscillator 3
2 and a cooling water tank (not shown). The high-frequency oscillation device 32 supplies a high-frequency current to the steel sheet heating device 34 shown in FIGS. 2 to 4 through the transformer 30, and the control panel 28 has a function of controlling the high-frequency oscillation device 32.

FIG. 2 is a diagram conceptually showing the first stage 14 to the fifth stage 22 of the transfer press 12. In the first stage, that is, the punching section 14, a punching process for forming a reference hole in the work 26 in a subsequent process is performed. In the second stage, that is, the outer shape punching section 16, an outer shape punching process for forming the outer shape of the work 26 is performed. In the fourth stage, that is, the heating section 20, the work 26 is locally heated to a predetermined temperature.
The heating unit 20 is provided with a steel plate heating device 34, and the work 26 is heated in-line. In the fifth stage, that is, in the bending section 22, the work 26 is subjected to a predetermined bending process. In the third stage, i.e., in the idle section 18, the workpiece 26 is not subjected to any processing.

FIG. 3 is an enlarged plan view showing the steel sheet heating device 34, and FIG. 4 is a side view of the steel sheet heating device 34 viewed from a direction opposite to the feeding direction A. 3 and 4
As shown in FIG. 7, in the steel sheet heating device 34, a first conductive body 38 and a second conductive body 40 which are made of a conductive material such as copper, aluminum, or an alloy thereof and are electrically insulated from each other are mounted on a base. 36. Between the first conductive body 38 and the second conductive body 40, there is provided a gap having a substantially longitudinal shape and one end bent at right angles to the longitudinal shape, and an insulator 41 is provided in the gap. By being filled, the first conductor 38 and the second conductor 40 are prevented from contacting each other. Also, the first conductor 3
8 and the insulator 41 between the second conductor 40 and the base 36.
Insulated by Furthermore, a pair of coil leads (copper plates) 42, which are strip-shaped conductors, are connected to the first conductor 38 and the second conductor 40, respectively, from one end of the gap in the longitudinal direction to a predetermined length. The other end of the coil lead 42 is connected to the transformer 30. An insulator 44 is provided between the pair of coil leads 42.
Insulated by

Further, the first conductor 38 and the second conductor 4
0, a pair of cooling water hoses 46 are connected to the ends connected to the coil leads 42, respectively, and the first conductive water is supplied to the pair of cooling water hoses 46 and circulated. The body 38 and the second conductive body 40 and the high-frequency induction coil 50 connected to them can be cooled. A pair of conductive columns 48 is vertically fixed to the end opposite to the side to which the cooling water hose 46 is connected, and a flat high-frequency induction coil 50 is provided at the tip of the column 48. Fixed. Since the high-frequency induction coil 50 is electrically connected to the high-frequency oscillator 32 via the first conductor 38, the second conductor 40, the coil lead 42, the support 48, and the transformer 30, the high-frequency induction coil 50 A predetermined high-frequency current is supplied to 50. When a high-frequency current is supplied to the high-frequency induction coil 50, an eddy current is generated in the work 26 placed on the steel plate heating device 34, so that the work 26 is positioned right above the high-frequency induction coil 50 in the work 26. The located part is locally heated.

The base 36 has a pair of columns 52, 54 at positions where the high-frequency induction coil 50 is sandwiched in the longitudinal direction of the base 36 (ie, a direction orthogonal to the feed direction A).
Is fixed, and the width direction of the base 36 (that is, the feeding direction A)
In the position parallel to the high-frequency induction coil 50
The work 26 is mounted on the upper surface, that is, the receiving surfaces 58, 60, 62 located in the same horizontal plane, with the work 26 being separated from the high-frequency induction coil 50 by a very small gap. In FIG. 4, the support 56 is omitted.

FIG. 5 is an enlarged plan view of the high-frequency induction coil 50. The high-frequency induction coil 50 is formed of a single flat tubular conductive band member, and one end face 64 and the other end face 66 are spaced apart from each other and face each other. A pair of quadrants 68, 70 forming a quadrant on the same circumference with 66 as one end
And a semicircular portion 72 centered about the same point as the two quadrants 68 and 70 and having a diameter larger than the quadrants 68 and 70.
And a pair of connecting portions 74 and 76 for connecting both ends of the semicircular portion 72 and the quarter circular portions 68 and 70. That is, the high-frequency induction coil 50 has a winding shape in which one belt-shaped member is turned in a horizontal plane.
Note that the winding shape means that the coil is wound one or more times like the high-frequency induction coil 50. The outer peripheral shape of the high-frequency induction coil 50 is a shape that substantially matches a curved shape of a bent portion (processed portion) of the molded body 82 described later. Further, a region surrounded by the inner peripheral edge of the semicircular portion 72, the outer peripheral circles of the quadrant circular portions 68 and 70, and the inner peripheral edges of the connecting portions 74 and 76, and having a semicircular arc shape (that is, a curved shape) as a whole, This is the area 78.

The control panel 28 is a component of the steel plate heating device 34 and functions as a heating control device. The control panel 28 is supplied to the high frequency induction coil 50 by controlling the high frequency oscillation device 32. Controls high frequency current. That is, the control panel 28, in synchronization with the press period T _P which is periodically repeated, the high-frequency oscillator current control signal SI ₀ in order to generate a constant high frequency current 3
Output to 2. Here, synchronized to the press duration T _P which is periodically repeated, a sense that every preset period of time in each press time T _P, the current control signal SI
Period for outputting a ₀ is not limited to the period from the start to the end of the press time T _P, it may be shorter than that. FIG. 6 shows that the current control signal SI
₀ shows a time chart illustrating the relationship between the heating control and the molding cycle when the output from the start to the end of each press time T _P.

The high-frequency oscillator 32 has a current control signal SI
_{When 0} is supplied, a high-frequency current is generated within a period based on the current control signal SI ₀ , and the high-frequency current is supplied to the high-frequency induction coil 50 via the transformer 30 or the like. The high-frequency induction coil 50 supplied with the high-frequency current locally heats the work 26 located directly above the high-frequency induction coil 50. In the control by the control panel 28, the strength of the high-frequency current generated by the high-frequency oscillation device 32 is determined by a predetermined target temperature T ₀ (500 to 800) suitable for bending the work 26 in bending after heating. (About ° C) is determined in advance based on experiments.

According to the above, the control panel 28
Bending frequency induction coil 50 provided in the heating portion 20 located on the upstream side is controlled in the feed direction A than the processing unit 22, by the high frequency induction coil 50 in synchronization with the pressing period T _P repeated periodically Thus, the work 26 is heated. Therefore, in the transfer press 12, the work 26 is heated prior to the bending, and the formability in the bending is improved.

Next, an experiment of heating a work (steel plate to be processed) 82 by the steel sheet heating apparatus 34 of this embodiment, and a steel sheet heating apparatus of another embodiment of the present invention provided with a semicircular high-frequency induction coil 84 Will be described in comparison with a heating experiment of the workpiece 82 according to the first embodiment.

FIG. 7 shows a work 8 on a high-frequency induction coil 84 provided in a steel sheet heating apparatus according to another embodiment of the present invention.
FIG. 4 is a plan view showing a state where 2 is arranged. In addition, in the steel plate heating device provided with the high-frequency induction coil 84, other portions have the same configuration as the above-described steel plate heating device 34. As shown in FIG. 7, the high-frequency induction coil 84
The relatively wide band-shaped member has a shape bent into a semicircle, and its width dimension is the same as that of the wound high-frequency induction coil 50.
Of the semi-circular portion 72 to the outer edge of the semi-circular portion 72. Also, the work 82 to be heated
Is a substantially rectangular shape made of SPH590 (plate thickness of 2.3 mm), and a concave portion 86 cut out in a semicircular shape toward the center at substantially the center of one side is formed in advance. This work 82
Are arranged on the high-frequency induction coil 84 such that the cut-out shape of the concave portion 86 and the semicircular shape of the inner surface of the high-frequency induction coil 84 match in plan view. The overlapping range is the bent portion to be bent. In FIG. 7, A to E
The point is a temperature measurement point at which the temperature of the work 82 is measured.

FIG. 8 is a plan view showing a state in which the work 82 is arranged on the high-frequency induction coil 50 provided in the steel plate heating device 34 described above. As shown in FIG. 8, the high-frequency induction coil 50 has an outer peripheral shape that is substantially the same as the bent portion of the work 82, and the winding region 78 of the high-frequency induction coil 50 Part. Points A to E are shown in FIG.
Are the same positions as points A to E of FIG.

FIG. 7 shows a case where the work 82 is placed at the position shown in FIG. 7 and the work 82 is heated by the high-frequency induction coil 84 with a constant power output for 1.5 seconds as shown in FIG. FIG. 10 shows a temperature change at points A to E. FIG. 10 shows a case where the work 82 is arranged at the position shown in FIG. 8 and the work 82 is heated by the high-frequency induction coil 50 under the conditions shown in FIG. A to E shown in 8
FIG. 11 shows a temperature change at a point.

In the transfer press 12, after heating in the heating unit 20, there is a transfer time (air cooling time) T _{T of} 1.5 seconds, and thereafter, bending is performed in the bending unit 22. That is, the temperature of the work 82 when the bending is started is the temperature at the time when three seconds have elapsed from the start of the heating in FIGS.
Comparing the temperatures at 3 seconds after the start of heating in FIGS. 10 and 11, the temperature in FIG. 11 is higher overall and the temperature distributions at points A to E are also uniform. The higher the temperature and the more uniform the temperature, the more uniformly the work 82 extends in the bending process, and the less the cracks occur. Therefore, when the work 82 is heated using the wound high-frequency induction coil 50, the formability in the bending process is more improved than when the work 82 is heated using the semicircular high-frequency induction coil 84. I do.

As described above, the wound high-frequency induction coil 5
The reason why 0 can heat the workpiece 82 at a higher temperature and more uniformly than the semicircular high-frequency induction coil 84 is as follows. In the case of a circular or curved coil, the magnetic flux density at the inner edge is the highest, and the magnetic flux density decreases outward, so that the portion of the work 82 facing the inner edge of the coil has the highest temperature. That is, in the heating by the semicircular high-frequency induction coil 84, the point A has the highest temperature (highest heating point) and the point E has the lowest temperature. On the other hand, in the wound high-frequency induction coil 50, the point A opposed to the quadrants 68 and 70 is the highest heating point. In addition, the point D is also opposed to the inner edge of the semicircular part 72. Therefore, the point D also becomes relatively high temperature. Further, in the portion opposed to the inter-winding region 78 (point C indicates the temperature of this portion), direct heating is weakened, but both sides, that is, the points A and D become high temperature, and the points A and D become high. Heated by heat conduction from Further, the point E becomes relatively high due to the heat conduction from the point D when the point D becomes a high temperature. Therefore, the work 82 is uniformly heated at a high temperature.

As described above, when the work 82 is heated by using the wound high-frequency induction coil 50, the high-frequency induction coil 50 has portions where the magnetic flux density is increased on both sides of the inter-turn region 78. , The work 82 is located between the winding areas 7.
Both sides (points A and D) of the portion opposed to 8 become hot. Further, the portion (point C) of the work 82 which is opposed to the inter-winding region 78 is weakly heated directly by the high-frequency induction coil 50, but has a high temperature on both sides (points A and D). Is heated by the heat transfer from Accordingly, when the wound high-frequency induction coil 50 is used, the points A to E are generally high and uniform in temperature as compared with the case where the semicircular high-frequency induction coil 84 is used. Formability is further improved.

Next, a control function of a control panel (heating control device) 28 for controlling a high-frequency current supplied to the high-frequency induction coil 50, which is different from that of the above-described embodiment, will be described. FIG. 12 is a functional block diagram for explaining a main part of the control function.

The first heating control means 90 controls the press period
T_PThe maximum load of the work 82 by the time when 2/5
The hot spot (point A) is the target temperature T₀Preset to a value close to
First temperature T₁To generate a predetermined high-frequency current.
Current control signal SI ₁To the high-frequency oscillator 32
Output, and the workpiece 82 is rapidly raised to the high-frequency induction coil 50.
Let warm. The preset first temperature T₁Works
82 at the beginning of bending
Target temperature T₀(600 ° C in this example)
The target temperature T₀Subtract a predetermined value a that is sufficiently smaller than
The predetermined value a is, for example, 200 to 50.
Set to about ° C. Press period T_P2/5
By the time the time elapses, the maximum heating point is the first temperature T₁become
To heat the work 82, is the point C the point A or the point D?
Are heated by the heat transfer,
In order to extend the heating period and raise the temperature of point C
is there. It should be noted that the first heating control means 90
The output of the high-frequency oscillator 32 is determined in advance based on experiments.
And the constant output shown in FIG.
The range is about 1.2 to 2 times. Also, the current control signal
SI₁Is output, a temperature sensor is provided and
By directly measuring the temperature of the
May be fixed or fixed based on experiments in advance.
It can be time.

Following the heating by the first heating control means 90, the second heating control means 92
The temperature of the work 82 is increased at a lower speed than the temperature of the work 82 at the time of. That is, the current control signal SI for causing the first heating control means 90 to generate a high-frequency current smaller than the high-frequency current generated by the high-frequency oscillator 32
₂ is output to the high-frequency oscillator 32. The output of the high-frequency oscillator 32 controlled by the second heating control means 92 may be constant, or may be reduced stepwise or continuously.

FIG. 13 is a diagram showing an example of the output of the high-frequency oscillator 32 by the first heating control means 90 and the second heating control means 92. In FIG. 13, the heating period of the work 82 by the first heating control unit 90 is 0.5 seconds, and the heating period of the work 82 by the second heating control unit 92 is 1.0 second. Further, when the output of FIG. 9 is set to 1, the output of the first heating control means 90 is about 1.3, and the output of the second heating control means 92 is about 0.9. It is.

FIG. 14 is a diagram showing the temperature change at points A to E shown in FIG. 8 in an experiment in which the heating control is the control shown in FIG. 13 and other conditions are the same as the experiment in FIG. It is. In this experiment, the first temperature T ₁ was set to 500 ° C. When FIG. 14 is compared with FIG. 11, in FIG. 11, point C has a slower rate of temperature rise than points B, D, and E. Even after 3 seconds, point C is 500 ° C. or less, and points A to The temperature distribution at point E is not uniform. On the other hand, in FIG. 14, the temperature of the point C also rises at a rate close to the rate of temperature rise of the points B, D, and E. After 3 seconds, the point C is about 30 ° C. higher than in FIG. The temperature distribution at points A to E is also more uniform than in FIG.

As described above, the maximum heating point (point A) of the work 82 is set to the first temperature T ₁ set to a value lower than the target temperature T ₀ at the time of bending by the first heating control means 90. When the temperature of the workpiece 82 is rapidly increased, the portions opposed to the high-frequency induction coil 50 (points A and B)
The temperatures at points (D, D, E) increase quickly. Then, the second
When the temperature of the work 82 is increased by the heating control unit 92 at a heating rate lower than that by the first heating control unit 90, the work 82 has a portion (point C) opposed to the inter-winding region 78. While the temperature becomes higher due to the heat transfer from the surroundings, the rate of temperature rise of the portions (points A, B, D, and E) opposed to the high-frequency induction coil 50 is lower than before, so that points A to Point E has a more uniform temperature throughout. Therefore, the formability in the press working is further improved.

While the embodiment of the present invention has been described with reference to the drawings, the present invention can be applied to other embodiments.

For example, in the high-frequency induction coil 50 of the above-described embodiment, a pair of quadrants 68 and 70 and a semicircular portion 72 are connected by a pair of connecting portions 74 and 76.
Although the outer peripheral shape is a wound shape having a semicircular shape, when the shape of the bent portion is different, the outer shape of the high-frequency induction coil may be changed so as to conform to the shape of the bent portion.

The above-described high-frequency induction coil 50 has an outer peripheral shape substantially matching the shape of the bent portion of the work 82 so that only the bent portion of the work 82 can be locally heated. Was configured as
The outer peripheral shape of the high frequency induction coil may be larger than the bent portion.

The above-described high-frequency induction coil 50 includes
Although the coil is wound around the circumference, it may be wound twice as in the high-frequency induction coil 94 shown in FIG. 16 or may have more turns.

In the above embodiment, the work 82 is S
Although it was made of PH590, a steel plate having a higher tensile strength (for example, SPH780) may be used.

Although nothing is inserted in the inter-turn region 78 of the high-frequency induction coil 50, an insulating material may be inserted.

In the transfer press 12 described above, the fourth stage, that is, the fifth stage following the heating section 20 is the bending section 22 for bending the work 26, but the drawing section for drawing the work 26. For example, a processed portion to be subjected to another press working may be used.

Although the embodiment of the present invention has been described in detail with reference to the drawings, this is merely an embodiment,
The present invention can be implemented in various modified and improved aspects based on the knowledge of those skilled in the art.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing an apparatus for manufacturing a vehicle component.

FIG. 2 is a diagram conceptually showing a first stage to a fifth stage of the transfer press of FIG.

FIG. 3 is an enlarged plan view showing a steel sheet heating device provided in the transfer press of FIG. 2;

FIG. 4 is a side view of the steel sheet heating device of FIG.

FIG. 5 is an enlarged plan view of a high-frequency induction coil provided in the steel sheet heating device of FIG. 3;

[6] the current control signal SI ₀ in the control panel is a time chart illustrating the relationship between the heating control and the molding cycle when the output from the start to the end of each press time T _P.

FIG. 7 is a plan view showing a state in which a work is arranged on a high-frequency induction coil provided in a steel sheet heating device according to another embodiment of the present invention.

FIG. 8 is a plan view showing a state in which a work is arranged on a high-frequency induction coil provided in the steel sheet heating device of FIG. 2;

FIG. 9 is a diagram showing a relationship between time and an output of a high-frequency oscillator controlled by a control panel.

10 is a diagram showing temperature changes at points A to E shown in FIG. 7 when the work 82 is heated by the high-frequency induction coil 84 under the conditions shown in FIG. 9;

11 is a diagram showing temperature changes at points A to E shown in FIG. 8 when the work 82 is heated by the high-frequency induction coil 50 under the conditions shown in FIG. 9;

FIG. 12 is a functional block diagram illustrating a control function for controlling a high-frequency current supplied to the high-frequency induction coil of FIG. 3, which is different from the above-described embodiment.

FIG. 13 is a diagram illustrating an example of an output of the high-frequency oscillator by the first heating control unit and the second heating control unit in FIG. 12;

FIG. 14 is a diagram showing temperature changes at points A to E shown in FIG. 8 in an experiment in which heating control is the control shown in FIG. 13 and other conditions are the same as the experiment in FIG. 11;

FIG. 15 is a plan view showing a high-frequency induction coil provided in the steel sheet heating device of the present invention, which is different from FIGS. 3 and 7;

[Explanation of symbols]

 12: Transfer press 22: Bending part 26: Work (steel plate to be processed) 28: Control panel (heating control device) 34: Steel plate heating device 50: High frequency induction coil 78: Inter-winding area 82: Work (steel plate to be processed) 84 : High frequency induction coil 88: heating control means 90: first heating control means 92: second heating control means

Claims (3)

[Claims] 1. A steel sheet heating apparatus provided in a transfer press having a press section for performing press working on a steel sheet to be processed which is progressively fed in one direction, wherein the apparatus is provided at a position upstream of the press section in the feed direction of the steel sheet to be processed. A high-frequency induction coil for locally heating the steel sheet to be processed, and a heating control device for heating the steel sheet to be processed to the high-frequency induction coil in synchronization with a periodically repeated press period of the transfer press, A steel sheet heating device characterized by including: 2. The high-frequency induction coil has a winding shape in which a conductor is wound to a size equal to or greater than an area shape of a pressed portion of the steel plate to be processed, and a winding region surrounded by the conductor is The steel plate heating device according to claim 1, wherein the heating device has a curved shape as a whole, and the inter-winding region is opposed to the pressed portion of the steel plate to be processed. 3. The heating control device according to claim 1, wherein a maximum heating point of said steel plate to be processed is set to a value lower than a target temperature at the time of press working before 2/5 of said press period elapses. A first heating control means for rapidly increasing the temperature of the steel plate to be processed by the high-frequency induction coil so as to reach a temperature of 1; and a rate of temperature increase by the first heating control means following the first heating control means. 3. The steel sheet heating apparatus according to claim 2, further comprising: a second heating control unit configured to raise the temperature of the steel sheet to be processed at a low speed.