HK1079655A - Method and device for thin plate article induction heating, and thin plate article - Google Patents

Description

Induction heating method and apparatus for thin plate article and thin plate article

Technical Field

The present invention relates to a method and apparatus for induction heating of an article made of a thin plate by a high-frequency current, which is applicable to heating of an article made of a thin plate constituting a vehicle body for quenching, for example.

Background

In order to impart necessary strength to a predetermined region defined in an article produced from a metal thin plate used as a material constituting a vehicle body, other equipment, or a component part of the equipment, the entire predetermined region is heated to a target temperature or higher and quenched. As an apparatus for performing such heating by an induction heating method by a high-frequency current, the following patent documents 1 and 2 are known.

In the apparatus of patent document 1, an inductor induction acting portion to which a high-frequency current is applied is configured to be movable with respect to a thin plate article, and by moving the induction acting portion with respect to the thin plate article, the induction acting portion heats a region of the moving thin plate article by an induced eddy current. Therefore, as opposed to the heating temperature being adjustable by setting the moving speed, a step of moving the induction action part by heating operation for each article is required, and therefore, it takes time to process 1 article, and a plurality of articles cannot be efficiently processed in a short time.

The induction action part of the inductor in the apparatus of patent document 2 corresponds to the entire region of the heated region of the thin plate-like article. Therefore, according to the apparatus of patent document 2, since the entire region of the heated region can be heated at the same time by only passing a high-frequency current through the inductor, it is possible to treat each article in a shorter time than the apparatus of patent document 1, and it is possible to improve the operation efficiency.

[ patent document 1] JP-A-10-17933 (paragraph number 0042, FIG. 4)

[ patent document 2] Japanese patent application laid-open No. 2000-256733 (paragraph No. 0045, FIG. 1)

Disclosure of Invention

In this way, the induction action part of the inductor has an advantage that the entire heated region of the article can be simultaneously inductively heated, and thus the entire heated region can be heated in batch, but when the article is made of a thin plate, unlike the case of a material having a sufficient thickness, eddy currents of eddy currents cannot be induced in the thickness direction, and the eddy currents are planar only in the heated region of the thin plate. Therefore, when eddy current is likely to occur in the thickness direction, it is difficult to adjust the intensity of induced eddy current for each portion on the plane of the heated region, and therefore, when temperature unevenness occurs in the heated region, it is difficult to deal with the temperature unevenness.

Further, since it is difficult to form a detour heat transfer path in the thickness direction as a thin plate, the temperature unevenness is difficult to be alleviated with time as compared with a thick plate.

However, from the above, it is considered that, when a sheet is produced as a material for heat-treating an article in a predetermined region, temperature unevenness is likely to occur as a result. Therefore, it is difficult to reduce the temperature rise unevenness of a predetermined region, in other words, to heat the region to a target temperature or higher by a small temperature difference, that is, to set a heating region as desired and to heat the region by a small temperature difference in the region.

As a countermeasure for solving this problem, it is conceivable to cool a portion where heat is generated by a heat radiation reinforcing method or a forced cooling method, and this method requires complicated equipment and increases the equipment cost. Further, it is also conceivable to adjust the input of heat to each part of the heated area by using a sensor which is divided into a plurality of systems and is arranged to control the systems, but this also causes a problem of increasing the cost of the apparatus.

On the other hand, the entire region including the heated region may be heated to a target temperature or higher while the temperature rise unevenness occurs as the input heat amount increases, and then the temperature difference may be reduced with the lapse of time. However, according to this, unlike the above-described method, there is obtained an advantage that no special equipment is required, however, resulting in loss of time and energy.

The present invention has been made in view of the above aspects. The invention provides an induction heating method and an induction heating apparatus for thin plate articles, which can reduce uneven temperature rise at the end of heating operation without requiring special equipment and ensure the shortened operation time which is the advantage of batch heating.

The present invention relates to heating a thin plate article by an induction heating method, and the present inventors have invented the following findings.

In the middle of raising the temperature of the heated region of the sheet-like article by induction heating, or in stopping the supply of the high-frequency current to the inductor, or in setting a period of reducing the supply current, the temperature difference in the heated region is reduced by stopping or suppressing the supply of heat to the heated region. However, if the temperature of the entire region is raised to the target temperature or higher by returning the high-frequency current to the inductor and raising the temperature of the region again, the temperature difference of the heated region is small at the end of the temperature raising and temperature unevenness can be reduced as compared with the case where an intermediate step of reducing the temperature difference during the temperature raising is not provided.

Fig. 10 to 13 are views for explaining theoretically considered heating operation in which an intermediate step for reducing the temperature difference is not provided during temperature rise and heating operation in which the intermediate step is provided. Fig. 10 is a temperature rise graph when the intermediate step is not provided, and fig. 13 is a temperature rise graph when the intermediate step is provided. Fig. 11 shows an equivalent circuit assumed in the heated region of the thin plate-like article when the temperature distribution is present in the heated region, and (1) to (5) of fig. 12 show changes in the equivalent circuit with an increase in temperature. In the equivalent circuit of fig. 11, the resistance R where joule heat is generated by the induced eddy current i and the inductance L where joule heat is not generated are shown in each of the regions a to D to be heated.

The temperature of each of the regions A to D does not reach the magnetic transition point T shown in FIG. 10 when the region to be heated is heated by induction heating_MWhen ω is an angular frequency of the high-frequency current, the impedance ω L of each of the portions a to D is very large compared to the resistance R because the specific permeability μ of each of the portions a to D is large. Therefore, i is shown in FIG. 11_RAnd induced eddy currents i are approximately equal, at ω L for negligible impedance. In fig. 12(1) showing the respective portions a to D having the temperature difference, the resistance R of the highest temperature portion a is the highest and the resistance R of the lowest temperature portion D is the lowest among the portions a to D based on the characteristic that the resistance R is larger as the high temperature is higher, so that the electric current substantially equal to the induced eddy current i flows in common in the resistances R of the respective portions a to D depending on the resistances R involved in the generation of joule heat, and the temperature difference between the portion a and the portion D is sequentially enlarged. This phenomenon is shown by temperature rise curves a 'to D' at the positions a to D in fig. 10.

Temperature rise of each part A to D is performed at time t 'in FIG. 10'_AThe temperature of the site A reaches the magnetic transition point T_MThe specific magnetic permeability of the portion A is drastically reduced. Therefore, the impedance ω L at this location A is smaller than the resistance R, i_RRatio of i to i_LLarge, i.e., negligible impedance ω L, reduces the occurrence of Joule heat at site A, and as a result, siteThe temperature rise of a is stagnant. Fig. 12 (2) shows an equivalent circuit at this time.

Then, the temperatures of the parts B to D are sequentially at time t 'in FIG. 10 in accordance with the temperature increase sequence'_B、t′_C、t′_DReaches the magnetic transition point T_MThe equivalent circuit at this time is shown in (3) to (5) of fig. 12. Even in this case, since the specific permeability of the portions B to D is sharply reduced and the joule heat generated in the portions B to D is reduced, the change in the joule heat is not concentrated on the local portion change, and therefore, the stagnation state of the temperature rise in the portions B to D is gradually alleviated as compared with the stagnation state of the temperature rise in the portion a.

Thereafter, the temperature of the regions A to D is raised by joule heat of the resistance R of the respective regions A to D, but the rate of expansion of the temperature difference decreases the resistance R of the respective regions A to D due to the impedance ω L of the respective regions A to D, for example, exceeds the magnetic transition point T_MThe temperature increase rate of the resistance R is decreased and the magnetic transition point T is reached_MThe former ratio becomes smaller.

When the temperatures of all the portions a to D exceed the target temperature Tz shown in fig. 10 and the induction heating is completed, the temperature difference Δ T' is generated in the portions a to D.

As described above, while an intermediate step intended to reduce the temperature difference between the respective portions a to D is not provided during the temperature rise, fig. 13 shows a case where this intermediate step is provided, and a to D in fig. 13 show temperature rise curves of the portions a to D.

If it is time t₁Front induction heating the heated area until time t₁The temperature difference of the first portions A to D is enlarged in the order as described above, but from time t₁To time t₂When the induction heating is stopped, the temperature difference between the respective portions a to D is reduced by natural uniform heating due to the heat conduction effect during this period. Then, induction heating is resumed, and the temperature difference of each part A-D is sequentially expanded, however, the time t₂Temperature difference ratio time t₁Has a small temperature difference, and each part A-D is at the time t_A～t_DExceed magnetismAfter the transition point TM, all the portions A-D have reached the target temperature T_ZAnd then the induction heating is finished, the temperature difference between the parts A to D becomes delta T. Since this temperature difference Δ T is smaller than the temperature difference Δ T' in fig. 10, the temperature rise unevenness at the end of the heating operation in fig. 13 is lower than that in fig. 10.

In other words, in the case of fig. 10, the temperature difference is large in the entire region of the heated region at the end of induction heating, and the average temperature of the heated region must be increased to be equal to or higher than the target temperature required for quenching, for example, so that the heat history is more than necessary for the high-temperature portion. In contrast, in the case of fig. 13, the temperature difference in the entire region of the heated region at the end of induction heating is small, and the entire region temperature can be set to the target temperature or higher while avoiding unnecessary thermal history. Therefore, in the case of fig. 13, unnecessary temperature rise related to temperature rise which adversely affects the quality of the material to be processed is avoided.

In the case of fig. 13, an intermediate step of stopping or reducing the high-frequency current to the inductor for only a short time is provided during the temperature rise, and the time of the intermediate step is sufficient in seconds, so that the heating operation of the article can be completed in a short time, and the advantage of the batch heating that improves the operation efficiency can be secured substantially as described above. Further, since the heating operation in fig. 13 can be performed without using a special facility such as a cooling method, the facility cost is not increased.

In the case of fig. 10, the maximum temperature of the heated region becomes higher than that in the case of fig. 13, and thus there is a fear that the surface coating material, which is a thin plate of the material of the article having the heated region, for example, a plate material having the surface coating material such as zinc plating, fails by heating, but the case of fig. 13 can eliminate such a problem

In the case of fig. 13, the temperature difference at the end of heating can be reduced to a small value, and the temperature of the entire heated region can be equalized, so that the temperature difference before quenching can be controlled to a satisfactory range even without causing unexpected structural changes in the material. As a result, distortion due to rapid cooling and residual stress after quenching can be suppressed.

The induction heating method and the apparatus according to the present invention are invented based on the heating operation principle of fig. 13 described above.

An induction heating method for a thin plate article according to the present invention for induction-heating a heated region to a target temperature higher than a magnetic transition point or higher by applying a high-frequency current to an inductor having an induction action section for simultaneously induction-heating the entire region of the heated region defined in the thin plate article, includes a temperature raising step for raising the temperature of the heated region by induction heating with the inductor; a temperature difference reduction step of reducing the temperature difference of the heated region by at least 1 time by temporarily stopping or temporarily reducing the high frequency current to energize the inductor after the temperature increase step; and a reheating step for reheating the temperature of the entire region of the heated region so that the temperature of the entire region of the heated region becomes equal to or higher than the target temperature by returning the high-frequency current to the inductor after the temperature difference reducing step.

In the induction heating method, the temperature difference reducing step is performed 1 time, even if performed a plurality of times. When the temperature is increased a plurality of times, the entire region of the heated region is heated after the previous step is completed, and the next step is started after the temperature is increased.

Further, the time period of the temperature difference reducing step is set, and the temperature of the heated region may be performed before the magnetic transition point is reached, or after the magnetic transition point is reached, or may be set so as to straddle the magnetic transition point.

In the induction heating method for a thin plate article according to the present invention, when the heated region is quenched, the next step of the reheating step is a quenching step of quenching and heating the entire heated region to the target temperature or higher. Therefore, the heated region can be quenched.

An induction heating apparatus for a thin plate article according to the present invention is an induction heating apparatus for a thin plate article, comprising an inductor having an induction action portion corresponding to an entire region of a region to be heated defined in the thin plate article, and a power supply device for supplying a high-frequency current to the inductor and causing the region to be heated to be a target temperature higher than a magnetic transition point or higher by induction heating, wherein the power supply device is provided with a current control device for temporarily stopping or temporarily reducing the supply of the high-frequency current to the inductor before the region to be heated reaches the target temperature.

In this apparatus, the above-mentioned induction heating method of a sheet-like article can be realized by temporarily stopping or reducing the supply of the high-frequency current to the inductor by the current control means before the heated region reaches the above-mentioned target temperature, and then restoring the supply of the high-frequency current to the inductor by the current control means.

In this device, a current control device that temporarily stops or temporarily reduces the high-frequency current from being supplied to the inductor may be an automatic device using a computer program, a relay circuit, or the like, or a manual device including a manually operated switch or the like.

The induction action part of the inductor may be linearly extended in the longitudinal direction of the heated region, and when the heated region has a large width, the induction action part may be bent in the width direction of the heated region and extended in the longitudinal direction of the heated region.

In the case where the current control device is an automatic type, the current control device may be configured in any form.

For example, in the case of the No. 1 example, the current control device is considered to be a timer type control device provided with a timer, and when the time measured by the timer reaches a predetermined time from the start of the energization of the inductor by the high-frequency current, the energization of the inductor is temporarily stopped or temporarily reduced.

In the example No. 2, the current control device is considered to be a temperature measurement type control device including a temperature measuring device for measuring the temperature of the region to be heated, and when the temperature of the region to be heated measured by the temperature measuring device reaches a predetermined temperature, the high-frequency current is temporarily stopped or temporarily reduced to be supplied to the inductor.

In the example No. 3, it is considered that the current control device includes an impedance-based control device of a frequency tracking device for tracking the frequency of the inductor high-frequency current corresponding to the impedance of the heated area, and when the resonant frequency of the high-frequency current tracked by the frequency tracking device reaches a predetermined frequency, the high-frequency current supply to the inductor is temporarily stopped or temporarily reduced.

These current control devices are configured to include a converter for supplying a high-frequency current to the inductor for the power supply device and a controller for controlling the converter, and the converter and the controller can be applied to the case where they are provided for separate devices, and the converter and the controller can be applied to the case where they are integrated into one device, not in various forms.

The structure of the inductor may be arbitrary. In one example, the inductor is configured such that a plurality of good conductors each having an induction action portion extending in an extending direction of the heated region are arranged in parallel in a direction perpendicular to the extending direction so as to cover the heated region, and the good conductors are connected in parallel.

Accordingly, when the temperature difference occurs due to the difference in resistance between the heated regions, the portion having a high temperature, that is, the good conductor disposed corresponding to the portion having an increased resistance, has a high impedance, and therefore the current flowing into the good conductor decreases, and the portion having a low temperature, that is, the good conductor disposed corresponding to the portion having a decreased resistance, has a low impedance, and therefore the current flowing into the good conductor increases. As a result, the induced eddy current at the high temperature portion is reduced, while the induced eddy current at the low temperature portion is increased. Therefore, the temperature difference of the heated region is equalized, and the temperature rise unevenness can be further reduced by the effect of the temperature difference reduction step.

In the present invention, when the heated region is quenched, the induction heating apparatus for a thin plate article according to the present invention includes a quenching device for quenching at least the heated region after the heated region reaches the target temperature or higher.

The quenching apparatus may discharge the cooling liquid to the heated region from one side surface of the thin plate article, or may discharge the cooling liquid to the heated region from both side surfaces of the thin plate article.

In the thin plate article according to the present invention, in the thin plate article in which the entire region to be heated is induction-heated to a target temperature higher than or equal to a magnetic transition point, the heating of the region to be heated to the target temperature or higher includes a temperature raising step of raising the temperature of the region to be heated by induction heating; a temperature difference reduction step of reducing the temperature difference of the heated region by at least 1 time by temporarily stopping or temporarily reducing the induction heating after the temperature increase step; and a reheating step of reheating the heated region by restoring the induction heating after the temperature difference reducing step so that the temperature of the entire heated region becomes equal to or higher than the target temperature.

In the thin plate-like article, the heated region to be quenched is heated to a target temperature or higher and then quenched.

The present invention described above can be applied to a heating area defined in advance for heating an article produced from a metal thin plate, but the heating area is not limited to a part of the article but is also applicable to the entire article.

The thin plate is a plate material having a thickness that is less likely to generate induced eddy currents in the thickness direction, and the thickness is 3.2mm or less, more narrowly 2.3mm or less. Depending on the material, various steel sheets (including high tensile steel sheets) having different carbon contents, ferrite stainless steel sheets, martensite stainless steel sheets, and the like are metal sheets in which magnetic transformation occurs in which the specific magnetic permeability is rapidly reduced. Further, the metal plate may be subjected to surface treatment such as zinc plating.

The time period and length of time for which the high-frequency current is temporarily stopped or temporarily reduced to be supplied to the inductor in the temperature difference reducing step described above can be determined according to various factors such as the material and thickness of the thin plate, the target temperature, and the voltage, current, and frequency of the high-frequency current. Further, the energization of the high-frequency current is temporarily stopped or temporarily reduced, which is also determined based on these elements.

In general, the present invention can be applied to heating an article formed into a predetermined shape by press molding a sheet, but can also be applied to heating a flat article. Further, the article whose sheet is flat may be heated and then press-molded, or the article whose sheet is flat may be heated and then quenched by rapid cooling and then press-molded.

The sheet-like article to which the present invention is applied can be used as a member of any machine, equipment, or equipment, and examples thereof include a reinforcing member for constituting a center pillar of a vehicle body of a four-wheeled vehicle, a collision beam of a door, a floor side member of the vehicle body, and a front side member.

According to the present invention, it is possible to obtain an effect of reducing temperature unevenness at the end of a heating operation by securing a shortened operation time which is an advantage of batch heating without requiring a special facility.

Drawings

Fig. 1 is a schematic view showing an operation of an induction heating apparatus according to an embodiment of the present invention for inductively heating a region to be heated of a thin plate-like article.

Fig. 2 is a cross-sectional view taken along line S2-S2 of fig. 1.

FIG. 3 is a graph showing the results of an experiment in which a temperature difference reducing step is provided during temperature rise and heating is performed.

Fig. 4 is a graph showing experimental results when the heating operation is performed without providing the temperature difference reduction step during the temperature rise.

FIG. 5 is a diagram showing an embodiment of a power supply apparatus in which a current control device is a timer type.

Fig. 6 is a diagram showing an embodiment of a power supply apparatus in which a current control device is a temperature measurement type.

Fig. 7 is a diagram showing an embodiment of a power supply device in which a current control device is of an impedance-based type.

Fig. 8 is the same as fig. 1 showing another embodiment of the inductor-inducing portion.

Fig. 9 is a cross-sectional view taken along line S9-S9 of fig. 8.

Fig. 10 is a graph showing temperature rise curves of respective portions of the region to be heated, which is theoretically considered, when the region to be heated is induction-heated without providing the temperature difference reduction step.

Fig. 11 is an equivalent circuit diagram showing the respective portions of the heated region in which the temperature distribution is generated.

Fig. 12 is a diagram showing changes in the equivalent circuit in the order of (1) to (5) as the temperature of each part of the region to be heated reaches the magnetic transition point.

Fig. 13 is a graph showing temperature rise curves of respective portions of a region to be heated, which is theoretically considered, when the region to be heated is inductively heated in the temperature difference reducing step.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The thin plate article 1 according to the embodiment thus described is disposed inside a center pillar constituting a vehicle body of a four-wheeled vehicle, and is used as a reinforcing member provided with the center pillar having sufficient strength against a side impact. The article 1 is produced by press molding a thin steel plate.

Fig. 1 is a schematic view showing a state where an article 1 is inductively heated by a high-frequency current, and fig. 2 is a sectional view taken along line S1-S2 in fig. 1. The article 1 is composed of edge portions 1A, 1B at both ends in the lateral direction; a protrusion 1C protruding from between these edge portions 1A and 1B; and left and right web portions 1D, 1E connecting the projection portion 1C and the edge portions 1A, 1B, and these edge portions 1A, 1B, the projection portion 1C and the web portions 1D, 1E are continuously extended in the longitudinal direction. Therefore, the article 1 has a hat-shaped cross section continuous in the longitudinal direction.

As shown in fig. 2, the joint between the protrusion 1C and the web portions 1D and 1E is the heated region 2 for induction heating, and these heated regions 2 extend in the longitudinal direction of the article 1.

As shown in fig. 1, the article 1 during the heating operation is mounted on a table 3, and the edge portions 1A and 1B are held on the table 3 by a holding device not shown in the drawing. As shown in fig. 2, each of the 2 induction action units 4A provided in the inductor 4 of the induction heating apparatus is disposed to face the heated region 2 with an appropriate gap from the heated region 2. The inductor 4 is connected to a power supply device 6 via a supply cable 5 shown in fig. 1. The cooling pipe 7 is inserted to heat the entire region of the region to be heated 2 to a target temperature or higher in the space between the article 1 and the table 3, and then to discharge the coolant to the region to be heated 2 from the back surface. These cooling pipes 7 quench at least the entire region of the heated region 2 heated to a target temperature or higher, and serve as a quenching device for quenching the entire region of the heated region 2.

The 2 induction action parts 4A connected by the continuous part 4B shown in fig. 1 have an air structure as shown in fig. 2. Then, in the air, the coolant flows from the inlet 8 shown in fig. 1 and flows out from the outlet 9. Therefore, heat generation of the induction acting portion 4A during induction heating of the heated region 2 can be suppressed.

The induction operation portion 4A has a size corresponding to the entire region of the heated region 2. Thus, the induction heating apparatus of the present embodiment is a heating apparatus for heating the entire region included in the heated region 2 at the same time.

When the switch of the power supply device 6 is turned on and the high-frequency current is started to flow to the inductor 4 by the power supply device 6, an induction eddy current is generated in the heated region 2 by the electromagnetic induction action of the induction action portion 4A, and the heated region 2 is heated by the joule heat generated thereby.

In the present embodiment, after the temperature raising step, the switch of the power supply 6 is turned off, so that the high-frequency current is temporarily stopped from being supplied to the inductor 4, and a step of reducing the temperature difference between the respective portions of the heated region 2 is provided during the temperature raising.

Then, when the temperature difference reducing step is completed, the switch of the power supply device 6 is turned on again, and the high-frequency current is turned on again to supply power to the inductor 4, thereby inductively heating the region 2 to be heated again, and thus the temperature re-increasing step is started. In the reheating step, after the entire heated region 2 is heated to a temperature equal to or higher than the target temperature, that is, after the entire heated region 2 is heated to a temperature equal to or higher than a temperature required to make the entire region have hardness of a predetermined strength for quenching, the operation of turning off the power supply device 6 is completed.

After the reheating step, a coolant is discharged from the cooling pipe 7 as a quenching means to quench the heated region 2 for quenching. Then, the article 1 is released from the clamping by the clamping device and sent to a subsequent step such as a painting step.

Fig. 3 and 4 are graphs showing temperature increases of heated regions obtained from experimental results. Fig. 3 shows a case where the temperature difference reducing step is provided 1 time during the temperature rise, and fig. 4 shows a case where the temperature difference reducing step is not provided.

This test article was press-molded from a steel plate having a carbon content of 0.16 and a thickness of 1.4mm, and was formed into a hat-shaped cross section as shown in fig. 1, and was also a reinforcing member disposed inside the center pillar of the four-wheeled vehicle. The article had a width dimension of 180mm, a height dimension of 70mm and a length dimension of 600 mm. The high-frequency current power supplied to the inductor is 50kW to 80kW, the voltage is about 240V, the current is 230A to 340A, and the frequency is 23kHz to 24.5 kHz. The temperature of the heated region 2 was measured for a total of 30 sites.

In fig. 3, X is a temperature rise curve for the highest temperature portion, Y is a temperature rise curve for the lowest temperature portion, and Z is a change curve for the difference between these highest and lowest temperatures. In fig. 4, X ' is a temperature increase curve for the highest temperature portion, Y ' is a temperature increase curve for the lowest temperature portion, and Z ' is a change curve for the difference between the highest and lowest temperatures.

Now, the case of the experiment of fig. 4 in which the high-frequency current was passed to the inductor 4 for 8.5 seconds continuously from the start of heating by operating the switch of the power-on device 6 and then the switch was operated to turn off will be described. The temperature of the highest temperature portion when the off switch is operated exceeds the necessary target temperature Tz due to the hardness of quenching the heated region 2 to a predetermined strength, but the temperature of the lowest temperature portion does not reach the target temperature Tz, and the temperature difference between the two temperature portions is a large difference of about 270 ℃.

In the case of the experiment of fig. 3, the temperature difference reducing step is provided by operating the off switch 3.9 seconds after the switch of the power-on device 6 is operated to start heating. Further, the switch was turned on by operating again after 6.0 seconds from the start of heating, and a re-temperature-raising step was provided in which the switch was continued until the operation was turned off after 11.8 seconds from the start of heating. At the end of this re-warming step, the respective temperatures of the highest temperature portion and the lowest temperature portion reach the target temperature Tz simultaneously, and these temperature differences are small differences of about 50 ℃.

In the case of the experiment of FIG. 3, the temperature difference at the beginning of the temperature difference reduction step was about 200 ℃, whereas the temperature difference at the end of the step was about 100 ℃, and thus, the temperature difference therebetween was improved by about 100 ℃. Moreover, the temperature of the heated region 2 reaches the magnetic transition point T_MThe temperature difference is improved later. This temperature differential improvementThe temperature difference at the last moment when the heating operation is finished is a small value of about 50 ℃.

As is clear from the above description, according to the present embodiment, since the high-frequency current is temporarily stopped from being supplied to the inductor 4 during the temperature rise, the step of reducing the temperature difference of the heated region 2 is provided, whereby the temperature difference of the heated region 2 at the end of the heating operation in which the temperature of the whole heated region 2 is raised to the target temperature or higher can be reduced, in other words, the temperature rise unevenness of the heated region 2 at the end of the heating operation can be reduced.

Further, the effect of reducing the temperature unevenness can be achieved without providing a special device for cooling the local region of the region to be heated 2 in the induction heating apparatus, and therefore, the apparatus is effective in terms of the cost and energy efficiency, and the operation time can be shortened by providing only a short time in seconds during the temperature rise without supplying the high-frequency current to the inductor 4, so that the heating advantage including the simultaneous heating of the entire region to be heated 2 in the induction action portion 4A of the inductor 4 can be substantially secured as it is.

Moreover, since the temperature difference of the heated area 2 at the time when the entire heated area 2 reaches the target temperature is small, the maximum temperature does not greatly exceed the temperature of the target temperature. Therefore, even if the sheet as the material of the article 1 is a plate material having a surface coating material such as zinc plating, for example, there is no fear that the surface coating material disappears by heating.

Further, since the temperature of the entire heated region 2 can be equalized at the end of heating, unexpected changes in material structure due to a high local temperature, distortion due to rapid quenching during quenching, and residual stress after quenching can be suppressed.

The power supply device 6 of the embodiment of fig. 1 has been described above, because the high-frequency current is temporarily stopped from being supplied to the inductor 4 by manually performing the switching operation, the switch in the embodiment of fig. 1 becomes a current control device for temporarily stopping the high-frequency current from being supplied to the inductor 4, but fig. 5 to 7 show a power supply device according to another embodiment which is different from that of fig. 1.

Fig. 5 shows an embodiment in which the current control device is a timer control device 25. The power supply device 16 of fig. 5 is composed of a power supply 17, a converter 18, a matching transformer 19, and a controller 20. The converter 18 is provided with a forward converter 21 for converting an alternating current of three phases or the like from the power supply 17 into a direct current or a pulsating current, a reverse converter 22 for converting a current from the converter 21 into a high-frequency current, and a conversion controller 23. The high-frequency current converted by the flyback converter 22 is supplied to a matching transformer arrangement 19, to which matching transformer arrangement 19 the inductor 4 is connected via the supply cable 5.

In the control device 20 for controlling the inverter device 18, a timer 24 is provided, and this timer 24 measures the heating operation time of the heated area 2 of the article 1 with respect to the start of energization of the inductor 4 by the high-frequency current. When the time after the heating operation of the article 1 is started is a predetermined time stored in the timer 24, the control device 20 instructs the inverter device 18 to stop transmitting the control signal for stopping the power supply from the inverter 22 to the matching transformer device 19 in accordance with the instruction from the timer 24, and therefore the aforementioned temperature difference reducing step for temporarily stopping the power supply to the inductor 4 by the high-frequency current is started. If the time after the heating operation for the article 1 is started is a predetermined additional time stored in the timer 24, the control device 20 sends a control signal for instructing the inverter 22 to supply power again to the matching transformer device 19 to the converter 18 in accordance with the instruction from the timer 24, and the temperature difference reducing step is ended.

In the power supply device 16, if the current control device is the timer control device 25 constituted by the timer 24, the temperature difference reduction step can be automatically started and ended according to the timer 24.

Fig. 6 shows an embodiment in which the current control device is a temperature measurement type control device 29. The power supply device 26 of fig. 6 includes a sensor 27 for measuring the temperature of a predetermined portion of the heated region 2 of the article 1, and the control device 20 is provided with a temperature comparator 28 for detecting measurement data from the sensor 27. The comparator 28 stores in advance the temperature at which the heating of the heated region 2 should be stopped and the temperature at which the heating of the heated region 2 should be resumed after the heating operation of the article 1 is started.

When the heating operation of the article 1 is started and the heating of the heated area 2 is to be temporarily stopped, the temperature difference reduction step of temporarily stopping the supply of the high-frequency current to the inductor 4 is started, because the control device 20 transmits a control signal for instructing the power supply from the inverter 22 to the matching transformer device 19 to be stopped to the inverter 18 in accordance with the instruction from the temperature comparator 28, when the heating of the heated area 2 is to be temporarily stopped. Then, when the temperature measured by the sensor 27 is lowered to a temperature at which heating of the heated region 2 should be resumed, the control device 20 sends a control signal for instructing resumption of power supply from the inverter 22 to the matching transformer device 19 to the converter 18 in accordance with an instruction from the temperature comparator 28, and the temperature difference reducing step is ended.

According to the embodiment in which the above-mentioned current control means in the power supply device 26 is the temperature measurement type control means 29 constituted by the sensor 27, the temperature comparator 28, and the like, the start and the end of the temperature difference reducing step can be accurately carried out in accordance with the actual temperature of the heated region 2.

In the temperature difference reducing step in each of the embodiments described above, although the high-frequency current is temporarily stopped from being supplied to the inductor 4, the high-frequency current supplied to the inductor 4 is temporarily reduced because the temperature difference of the region to be heated can be reduced, and the temperature difference reducing step may be performed to temporarily reduce the high-frequency current supplied to the inductor 4. Even if the current level is reduced by about 10%, the temperature rise of the heated region 2 can be made substantially zero.

Fig. 7 shows an embodiment in which the current control device is an impedance-based control device 41 provided with a frequency tracking device 40, and the frequency tracking device 40 is used for tracking the high-frequency current frequency of the inductor 4 corresponding to the impedance of the heated region 2. Further, the temperature difference reducing step of this embodiment is to temporarily reduce the energization of the inductor 4 by the high-frequency current.

In the inverter 18 of the power supply 36 shown in fig. 7, a current detector 37 is provided for detecting the behavior of supplying a high-frequency current from the flyback converter 22 to the inductor 4 via the matching transformer 19, and data on the frequency of the high-frequency current of the inductor 4 and the phase difference with the voltage obtained by the current detector 37 is transmitted to a resonant frequency detector 38. These current detection terminal 37 and resonance frequency detector 38, together with the inverter controller 23 of the converter 18, constitute a frequency tracking device 40. The frequency tracking device 40 is capable of performing a frequency tracking operation so that the frequency of the current supplied from the flyback converter 22 to the matching transformer device 19 and the resonant frequency of the high-frequency current of the inductor 4 always match each other by operating a circuit in which the voltage phase difference with the high-frequency current of the inductor 4 detected by the current detector 37 is zero.

The resonance frequency detector 38 detects the resonance frequency of the high-frequency current of the inductor 4 by the frequency tracking operation, and the detected resonance frequency is sent to the frequency comparator 39 of the control device 20 with a reference that the phase difference becomes zero. In the frequency comparator 39, predetermined 2 frequencies are stored. The 1 st frequency is a frequency at which the high-frequency current is to be temporarily reduced when the high-frequency current is supplied to the inductor 4, and the 2 nd frequency is a frequency at which the high-frequency current is to be restored by restoring the current supplied to the inductor 4 at the original current level, in other words, a frequency at the time of the current supply state immediately before the temporary reduction. The resonant frequency of the inductor 4 high frequency current, which is sent from the resonant frequency detector 38 to the frequency comparator 39, is compared with these 1 st and 2 nd frequencies.

The resonant frequency of the high-frequency current of the inductor 4 corresponds to the impedance of the heated region 2, and the impedance corresponds to the temperature of the heated region 2.

When the resonant frequency of the high-frequency current of the inductor 4 is transmitted from the resonant frequency detector 38 to the frequency comparator 39, the impedance of the heated region 2 is indirectly known to the frequency comparator 39 via the resonant frequency. Thus, the impedance-based control device 41 is configured by the frequency tracking device 40, the frequency comparator 39, and the like.

When the heating operation of the article 1 is started, the resonant frequency of the high-frequency current of the inductor 4 is transmitted from the resonant frequency detector 38 to the frequency comparator 39, and if the resonant frequency matches the 1 st frequency stored in the comparator 39, the control device 20 transmits a control signal for instructing the inverter 22 to reduce the power supply to the matching transformer device 19 to the inverter 18 in accordance with the instruction from the comparator 39, and therefore, the temperature difference reduction step for temporarily reducing the power supply of the high-frequency current to the inductor 4 is started. Then, if the resonant frequency of the inductor 4 high-frequency current transmitted from the resonant frequency detector 38 to the frequency comparator 39 matches the 2 nd frequency stored in the frequency comparator 39, the control device 20 transmits a control signal for returning the original current level to the matching transformer device 19 from the inverter 22 to the inverter 18 in accordance with the command from the frequency comparator 28, and thus the temperature difference reducing step is ended.

According to the embodiment shown in FIG. 7, since the change in the impedance of the heated region 2 corresponds to the change in the temperature of the entire region of the heated region 2, the temperature difference reducing step can be accurately set in accordance with the change in the temperature of the heated region 2, as compared with the embodiment of FIG. 6 in which the temperature of 1 part of the heated region 2 is measured by 1 sensor 27.

The temperature difference reducing step of the embodiment of fig. 7 described above is provided to temporarily reduce the energization of the inductor 4 by the high-frequency current, but may be provided to temporarily stop the energization of the inductor 4 by another timer for resuming the energization or by another resonance frequency detecting means for detecting the resonance frequency when the temperature of the heated region 2 is lowered before the energization temperature is resumed, in the embodiment of fig. 7.

Fig. 8 shows another embodiment of the induction-acting portion of the inductor, and fig. 9 is a sectional view taken along line S9-S9 of fig. 8. The inductors 44 through which a high-frequency current is passed by the power supply device 6 are provided in plural numbers for each of the heated areas 2 of the article 1, and 4 good conductors 44A are provided in the embodiment shown in the figure. These good conductors 44A form an induction action portion that generates an induced eddy current in the heated region 2. The good conductors 44A extending in the extending direction of the heated region 2 are provided in parallel in the width direction of the article 1 perpendicular to the extending direction of the heated region 2, and therefore the good conductors 44A cover the heated regions 2. In addition, 4 good conductors 44A are provided in each of the heated regions 2 at 2, and the 4 good conductors are connected in parallel with each other.

According to the present embodiment, temperature unevenness may occur in the heated region 2 of the size in the width direction of the article 1, and the current flowing through the good conductor 44A disposed corresponding to the high temperature portion having a large resistance becomes small, and the current flowing through the good conductor 44A disposed corresponding to the low temperature portion having a small resistance increases. Therefore, the input of heat to the high-temperature portion is suppressed, and the input of heat to the low-temperature portion is enhanced. Thus, the temperature difference of the heated region 2 can be corrected and equalized, and the temperature rise unevenness at the end of the heating operation can be combined with the effect of the temperature difference reducing step described above to further reduce the temperature difference.

The power supply device of the embodiment of fig. 8 and 9 may be the power supply devices 16, 26, and 36 shown in fig. 5 to 7, and may be the power supply device 6 of fig. 1 that is manually switched.

The present invention can be used, for example, for quenching a thin plate article or the like constituting a vehicle body, or for induction-heating the thin plate article with a high-frequency current.

Claims (12)

1. An induction heating method for a thin plate article, which induction-heats a whole region to be heated defined on the thin plate article while applying a high-frequency current to an inductor having an induction action part, and induction-heats the region to be heated to a target temperature higher than a magnetic transition point or higher, the method comprising:

a temperature raising step of raising the temperature of the heated region by induction heating by the inductor; a temperature difference reducing step of reducing the temperature difference of the heated region by at least 1 time by temporarily stopping or temporarily reducing the energization of the inductor by the high-frequency current after the temperature raising step; and a reheating step of reheating the heated region by returning a high-frequency current to the inductor after the temperature difference reducing step, so that the temperature of the entire heated region becomes equal to or higher than the target temperature.

2. The induction heating method of a thin plate-like article as recited in claim 1, wherein a next step of said reheating step is a quenching step of quenching at least the entire region of said heated region to be quenched heated to a temperature higher than said target temperature.

3. An induction heating apparatus for a sheet-like article, comprising: an inductor having an induction action part corresponding to the whole region of a heated region defined on a thin plate article, and a power supply device for supplying a high-frequency current to the inductor to raise the temperature of the heated region to a target temperature higher than a magnetic transition point by induction heating

The power supply device includes: and a current control device for temporarily stopping or temporarily reducing the high frequency current to energize the inductor before the heated region reaches the target temperature.

4. The induction heating apparatus for a sheet product according to claim 3, wherein said current control means is a timer type control means having a timer, and when a predetermined time period elapses from the start of the energization of said inductor by said high-frequency current after a time measured by said timer, the energization of said inductor by said high-frequency current is temporarily stopped or temporarily reduced.

5. The induction heating apparatus for a sheet product according to claim 3, wherein said current control means is a temperature measurement type control means provided with a temperature measuring means for measuring the temperature of said region to be heated, and when the temperature of said region to be heated measured by said temperature measuring means is a predetermined temperature, the energization of said inductor by said high-frequency current is temporarily stopped or temporarily reduced.

6. The induction heating apparatus for a sheet-like article according to claim 3, wherein said current control means is impedance-aware control means provided with frequency tracking means for tracking a frequency of said high-frequency current of said inductor corresponding to an impedance of said region to be heated, and wherein when a resonant frequency of said high-frequency current tracked by said frequency tracking means becomes a predetermined frequency, the energization of said inductor by said high-frequency current is temporarily stopped or temporarily reduced.

7. The induction heating apparatus for a sheet product according to claim 3, wherein said inductor is constituted by a plurality of good conductors, each of which has an induction action portion extending in an extending direction of said heated region, being arranged in parallel in a direction perpendicular to said extending direction so as to cover said heated region, and said good conductors being connected in parallel.

8. The induction heating apparatus for a sheet-like article according to claim 3, comprising: and a quenching device for quenching at least the heated region after the heated region reaches the target temperature or higher.

9. A thin plate article induction-heated over the entire region of a region to be heated to a target temperature higher than a magnetic transition point, characterized in that

The heating of the heated region to the target temperature or higher includes: a temperature raising step for raising the temperature of the heated region by induction heating; a temperature difference reduction step of reducing the temperature difference of the heated region by temporarily stopping or temporarily reducing the induction heating after the temperature increase step for at least 1 time; and a reheating step of reheating the heated region to a temperature equal to or higher than the target temperature by returning the induction heating to the heated region after the temperature difference reducing step.

10. The thin plate article as claimed in claim 9, wherein the entire region of the heated region heated to the temperature higher than the target temperature is quenched, and the quenched region is quenched by the quenching.

11. The thin plate-like article according to claim 9 is an article constituting a body of a four-wheeled vehicle.

12. The article constituting the body of the four-wheeled vehicle according to claim 11 is a reinforcing member for a center pillar.