JP2003285193A - Welding device and welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding device in which the structures of welding and thermally affected parts are improved. <P>SOLUTION: This welding machine comprises a storage means 21 for storing a target cooling curve based on a target continuous cooling transformation curve of a member 1 to be welded and control means 20, 22 for controlling a temperature lowering rate in a way that the temperature lowering rate of the welded part of the member 1 to be welded and the stored target cooling curve correspond to each other. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a welding apparatus and a welding method.

[0002]

2. Description of the Related Art For example, a high-strength steel sheet has a large amount of carbon equivalent as a base material component, and therefore, when joined by welding, it tends to cause hardening of a welded portion and a heat-affected zone as compared with a mild steel sheet. is doing.

Therefore, when the welded portion and the heat-affected zone are hardened, for example, "Welding Complete Book 8 Resistance Welding" published by Kobo Publishing Co., Ltd.
Attempts have been made to improve the hardened structure by tempering, as described in US Pat.

[0004]

However, in the tempering process, after the welding is completed and the weld is sufficiently cooled, the hardness of the weld is improved by applying an appropriate amount of heat to the weld and reheating it. It lowers. Therefore, the time required for cooling and reheating becomes, for example, several times as long as the welding time, and there is a problem in productivity.

The present invention has been made in order to solve the problems associated with the prior art described above, and an object of the present invention is to provide a welding apparatus and welding method capable of improving the structures of the welded portion and the heat affected zone. To do.

[0006]

In order to achieve the above object, the invention according to claim 1 is a storage means for storing a target cooling curve set based on a continuous cooling transformation curve of a material to be welded. A welding device, comprising: a control unit for controlling the temperature decrease rate so that the temperature decrease rate of the welded portion of the material to be welded matches the stored target cooling curve.

The invention according to claim 2 is characterized by comprising welding means having a pair of welding electrodes for generating resistance heat for welding the material to be welded.

According to a third aspect of the present invention, the control means adjusts the amount of current supplied to the welding electrode and / or the flow rate of cooling water for cooling the welding electrode, whereby the material to be welded is adjusted. It is characterized in that the rate of temperature decrease of the welded part is controlled.

According to a fourth aspect of the present invention, there is provided a measuring means for measuring an electrode-to-electrode displacement speed of the welding electrode, and the control means is based on the measured electrode-to-electrode displacement speed, and the workpiece is welded. It is characterized in that the temperature decrease rate of the welded part is estimated.

The invention according to claim 5 is characterized in that it has an irradiation means for irradiating a laser beam for welding the material to be welded.

According to a sixth aspect of the present invention, there is provided reheating means for following the operation of the irradiation means to reheat the welded portion of the material to be welded, and the control means is configured to operate by the reheating means. It is characterized in that the rate of temperature decrease of the welded part of the material to be welded is controlled by adjusting the amount of heat applied.

According to a seventh aspect of the present invention, there is provided measuring means for measuring the temperature between the laser beam irradiation area by the irradiation means and the reheating area by the reheating means, and the control means comprises: Based on the measured temperature, the temperature decrease rate of the welded part of the material to be welded is detected, and the amount of heat added by the reheating means is adjusted.

The invention according to claim 8 is characterized in that the material to be welded is a high-tensile steel plate.

The invention according to claim 9 is characterized in that the high-strength steel sheet passes through a process of transforming to bainite or pearlite before transforming from austenite to martensite.

The invention according to claim 10 is characterized in that the material to be welded is made of a light alloy.

According to the invention of claim 11, a storage step for storing a target cooling curve set based on a continuous cooling transformation curve of the material to be welded, a temperature decrease rate and a memory of a welding portion of the material to be welded are stored. And a control step for controlling the temperature decrease rate so that the target cooling curve is matched with the target cooling curve.

According to a twelfth aspect of the present invention, there is provided a welding step for welding the material to be welded by a welding means having a pair of welding electrodes for generating resistance heating.

According to a thirteenth aspect of the present invention, in the control step, the amount of current supplied to the welding electrode and / or the flow rate of cooling water for cooling the welding electrode is adjusted to adjust the welding target. It is characterized in that the temperature decrease rate of the welded part of the material is controlled.

According to a fourteenth aspect of the present invention, there is provided a measuring step for measuring an electrode-to-electrode displacement speed of the welding electrode, and in the control step, a welding target is welded based on the measured electrode-to-electrode displacement speed. It is characterized in that the temperature decrease rate of the welded part of the material is estimated.

The invention as set forth in claim 15 is characterized in that it has a welding step for welding the material to be welded by an irradiation means for irradiating a laser beam.

According to a sixteenth aspect of the present invention, there is provided a reheating step for reheating the welded portion of the material to be welded by the reheating means that follows the operation of the irradiation means, and in the control step, By adjusting the amount of heat added by the reheating means, the temperature decrease rate of the welded portion of the material to be welded is controlled.

According to a seventeenth aspect of the present invention, there is provided a measuring step for measuring a temperature between the laser beam irradiation area by the irradiation means and the reheating area by the reheating means, and in the control step, The temperature decrease rate of the welded portion of the material to be welded is detected based on the measured temperature, and the amount of heat added by the reheating means is adjusted.

The invention according to claim 18 is characterized in that the material to be welded is a high-tensile steel plate.

The invention described in claim 19 is characterized in that the high-strength steel sheet passes through a process of transforming into bainite or pearlite before transforming from austenite to martensite.

The invention according to claim 20 is characterized in that the material to be welded is made of a light alloy.

[0026]

The present invention configured as described above has the following effects.

According to the first aspect of the invention, the temperature decrease rate of the welded portion of the material to be welded matches the ideal target cooling curve set on the basis of the continuous cooling transformation curve. Therefore, rapid hardening of the structure that causes cracking and deterioration of formability (toughness) is suppressed, so that the structures of the welded portion and the heat-affected zone are improved.

According to the second aspect of the present invention, since resistance heat generation can be used as the welding heat source, the welding means can be made relatively inexpensive.

According to the third aspect of the invention, the temperature is lowered by the amount of current supplied to the electrode and / or the flow rate of the cooling water for cooling the electrode, which has a fast response to the rate of temperature decrease. The speed is controlled. Therefore, it is easy to control.

According to the fourth aspect of the invention, the temperature decrease rate is estimated based on the inter-electrode displacement rate corresponding to the contraction rate of the nugget diameter having a high correlation with the temperature decrease rate. . Therefore, the estimated temperature decrease rate has good accuracy.

According to the fifth aspect of the invention, since the laser beam can be used as the welding heat source, various materials can be applied as the material to be welded.

According to the sixth aspect of the invention, even if the heat-affected zone of the material to be welded is small and the rate of temperature decrease is extremely high, the temperature decrease rate can be easily controlled by the reheating means. You can

According to the seventh aspect of the invention, the temperature decrease rate of the welded portion of the workpiece is detected based on the temperature measured between the laser beam irradiation region and the reheating region. Therefore, the reheating means can be controlled with high accuracy.

According to the invention described in claim 8, it is possible to suppress the hardening of the welded portion and the heat-affected zone of the high-strength steel sheet, and to suppress the solidification crack, the embrittlement crack, the quench crack, and the liquid metal embrittlement crack due to molten Zn. be able to. Therefore, the improvement of moldability,
It is possible to suppress the occurrence of shrinkage cavities inside the nugget in resistance welding such as spot welding, and to suppress the occurrence of defects in the bead portion and its vicinity in laser welding and the like. That is, it is possible to improve the structures of the welded portion and the heat-affected zone of the high-strength steel sheet in which the carbon equivalent of the base material component is large.

According to the ninth aspect of the invention, since bainite or pearlite is mixed with the solidified structure of the high-strength steel sheet, the hardness is lower and the cracking susceptibility is lower than the structure of martensite alone. To do.

According to the tenth aspect of the present invention, for example, the structures of the welded portion and the heat affected zone of a light alloy such as aluminum can be improved.

According to the eleventh aspect of the present invention, the temperature decrease rate of the welded portion of the material to be welded matches the ideal target cooling curve set on the basis of the continuous cooling transformation curve. Therefore, rapid hardening of the structure that causes cracking and deterioration of formability (toughness) is suppressed, so that the structures of the welded portion and the heat-affected zone are improved.

According to the twelfth aspect of the invention, since resistance heat generation can be used as the welding heat source, a relatively inexpensive welding means can be applied.

According to the thirteenth aspect of the present invention, the temperature is lowered by the amount of current supplied to the electrode and / or the flow rate of the cooling water for cooling the electrode, which has a fast response to the temperature lowering rate. The speed is controlled. Therefore,
Easy to control.

According to the fourteenth aspect of the invention, the temperature decrease rate is estimated based on the inter-electrode displacement rate corresponding to the contraction rate of the nugget diameter having a high correlation with the temperature decrease rate. . Therefore, the estimated temperature decrease rate has good accuracy.

According to the fifteenth aspect of the invention, since the laser beam can be used as the welding heat source, various materials can be applied as the material to be welded.

According to the sixteenth aspect of the present invention, even if the heat-affected zone of the material to be welded is small and the rate of temperature decrease is very high, the rate of temperature decrease can be easily controlled by the reheating means. You can

According to the seventeenth aspect of the invention, the temperature decrease rate of the welded portion of the material to be welded is detected based on the temperature measured between the laser beam irradiation region and the reheating region. Therefore, the reheating means can be controlled with high accuracy.

According to the eighteenth aspect of the present invention, the hardening of the welded portion and the heat-affected zone of the high-strength steel sheet is suppressed, solidification cracking,
Embrittlement cracking, quenching cracking, and liquid metal embrittlement cracking due to molten Zn can be suppressed. Therefore, it is possible to improve the formability, suppress the occurrence of shrinkage cavities inside the nugget in resistance welding such as spot welding, and suppress the occurrence of defects in the bead portion and its vicinity in laser welding and the like. . That is, it is possible to improve the structures of the welded portion and the heat-affected zone of the high-strength steel sheet in which the carbon equivalent of the base material component is large.

According to the invention of claim 19, bainite or pearlite is mixed with the solidified structure of the high-strength steel plate, so that compared with the structure of martensite alone,
The hardness is low and the crack sensitivity is low.

According to the twentieth aspect of the invention, for example, the structures of the welded portion and the heat affected zone of a light alloy such as aluminum can be improved.

[0047]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

The welding apparatus according to the first embodiment is, for example,
A resistance welding apparatus such as a spot welding machine, which is relatively inexpensive, and has a welding system 10 and a control system 20 as shown in FIG.
Have and.

The welding system 10 includes an electrode (welding means) 13 composed of a pair of electrode tips 11 and a holder 12 for generating resistance heat generation as a welding heat source, and the electrode tips 11.
For example, and a pressurizing cylinder (pressurizing means) 14 for pressing the superposed materials 1 to be welded.

The control system 20 includes a storage device 21 for storing a database in which a target cooling curve set on the basis of the continuous cooling transformation curve of the workpiece 1 is stored, and the temperature of the welded portion of the workpiece 1. A controller 22 for controlling the temperature decrease rate so that the decrease rate and the target cooling curve match.
Have and. The target cooling curve is obtained by an experiment for each material of the material to be welded 1, for example. FIG. 2 is a continuous cooling transformation diagram in the case where the material to be welded 1 is a high-tensile steel plate, and shows an example of a target cooling curve.

The storage device 21 is composed of, for example, a high speed random access memory such as a RAM. The control device 22 is a control circuit including a microprocessor and the like, and controls the entire control system 20.

The control system 20 further includes a current adjusting device 23 and a flow rate adjusting device 24. The current adjusting device 23 is used to adjust the amount of current supplied to the electrode tip 11. The flow rate adjusting device 24 adjusts the flow rate of the cooling water for cooling the electrode tip 11 by opening and closing the valve (opening / closing means) 15 provided in the circulation line of the cooling water (refrigerant) supplied to the electrode tip 11. Used to

The amount of current and the flow rate of cooling water are the
It has a high-speed response to the temperature decrease rate of the welded part. Therefore, the control system 20 can easily control the temperature decrease rate by adjusting the current amount and / or the cooling water flow rate.

The control system 20 further has a displacement velocity measuring device 25 for measuring the displacement velocity between the electrodes. The displacement speed between electrodes corresponds to the contraction speed of the nugget diameter, which has a high correlation with the temperature decrease speed. Therefore, the temperature decrease rate can be estimated with high accuracy based on the inter-electrode displacement rate, and thus the estimated temperature decrease rate has good accuracy.

Next, with reference to FIG. 3, the relationship between the displacement velocity between electrodes and the nugget diameter will be described.

The nugget formed by resistance heating is
After the saturation point of the nugget diameter, solidification shrinks due to the influence of the cooling water supplied to the electrode tip 11. The shrinkage speed of the nugget diameter corresponds to the temperature decrease speed of the welded portion of the workpiece 1.

On the other hand, at the saturation point of the nugget diameter, the thermal expansion amount (interelectrode displacement amount) of the welded portion is saturated, and therefore the interelectrode displacement speed (gradient (d of the interelectrode displacement amount H with respect to time t) (d
H / dt)) becomes “0”.

Therefore, by measuring the displacement velocity between the electrodes, the saturation point of the nugget diameter and the temperature decrease rate after the saturation point of the nugget diameter can be estimated with high accuracy.

Next, with reference to FIG. 4, a method of controlling the temperature decrease rate will be described.

First, a current is supplied to the electrode tips 11 and 11 to start welding the superposed materials 1 to be welded (step S01). Then, the position measurement of the electrode chips 11 and 11 is started at the same time when the energization starts, and the inter-electrode displacement speed is calculated from the obtained inter-electrode displacement amount (step S0).
2). The measurement frequency is, for example, an interval of several milliseconds.

Next, it is judged whether or not the nugget diameter has reached the saturation point based on the calculated inter-electrode displacement speed (step S03). If the nugget diameter has not reached the saturation point, the process returns to step S02.

When the nugget diameter reaches the saturation point, the current inter-electrode displacement speed is calculated and converted into the temperature decrease speed (steps S04, S05). The obtained temperature decrease rate is compared with the target cooling curve corresponding to the material of the workpiece 1 (step S06).

When the temperature decrease rate is larger than the target cooling curve (step S07: YES), the supply of cooling water to the electrode tip 11 is stopped and the electrode chip 11 is cooled until the temperature decrease rate matches the target cooling curve. Increase the amount of current supplied to (step S08). The supply of the cooling water can be configured to be reduced stepwise, if necessary.

When the temperature decrease rate is smaller than the target cooling curve (step S07: NO), the amount of current supplied to the electrode tip 11 is reduced until the temperature decrease rate matches the target cooling curve (step S09).

Next, it is judged whether or not the temperature of the welded portion is a boundary temperature at which the transformation of the welded portion structure becomes stable, for example, 400 ° C. or less (step S10).

If the temperature of the welded portion has not reached the boundary temperature, the process returns to step S04, and if it is below the boundary temperature, the process is completed. Note that it is also possible to complete the treatment at a temperature higher than the boundary temperature in consideration of the rate of temperature decrease due to air cooling. In this case, the time from the start of welding to the end of control can be shortened, which is industrially advantageous.

As a result of the above, the temperature decrease rate of the welded part of the material to be welded matches the ideal target cooling curve set based on the continuous cooling transformation curve. Therefore, rapid hardening of the structure that causes cracking and deterioration of formability (toughness) is suppressed, so that the structures of the welded portion and the heat-affected zone are improved.

For example, when a high-strength steel sheet having a large amount of carbon equivalent as a base material is applied as the material to be welded, hardening of the welded portion and heat-affected zone is suppressed, solidification cracking, embrittlement cracking, quenching crack, and molten Zn. It is possible to suppress liquid metal embrittlement cracking due to. Therefore, it is possible to improve the formability and suppress the occurrence of shrinkage cavities inside the nugget in resistance welding such as spot welding.

Further, it is preferable to control the temperature decrease rate of the welded portion of the high-strength steel plate so as to match the target cooling curve shown in FIG. 2, for example.

In this case, before the transformation from austenite to martensite, the process of transformation into bainite or pearlite is passed, whereby bainite or pearlite is mixed with the structures of the welded portion and the heat affected zone after solidification. Therefore, for example, as compared with the structure of only martensite formed by controlling in the quench hardening region A shown in FIG.

Next, a welding apparatus according to the second embodiment of the present invention will be described.

The welding apparatus according to the second embodiment is a laser welding machine and is different from the welding apparatus according to the first embodiment with respect to the welding heat source. Since the laser welding machine welds with a laser beam, it is preferable in that various materials can be applied as the material to be welded.

The welding system of the welding apparatus according to the second embodiment is
As shown in FIG. 5, a laser beam 3 that is a welding heat source.
1 for irradiating 1 and 1st irradiation part 32
And a second irradiation unit 34 that irradiates the laser beam 33 in accordance with the above operation. The 2nd irradiation part 34 is a reheating means for reheating the welded part of the to-be-welded material 1.

The control system of the welding apparatus according to the second embodiment is
Storage device 41 for storing the database in which the target cooling curve is accumulated, and control for controlling the temperature lowering rate so that the temperature lowering rate of the welded portion of the workpiece 1 and the target cooling curve match. A device 42.

Therefore, similar to the welding device according to the first embodiment, the structures of the welded portion and the heat affected zone of the material to be welded can be improved.

The controller 42 controls the rate of temperature decrease by adjusting the amount of heat added by the second irradiator 34. Although a laser welder generally has a small welded portion and a heat-affected zone of a material to be welded and has a high temperature decrease rate, the control device 42 according to the second embodiment can easily control the temperature decrease rate. .

The control system also includes a temperature measuring device 43 having a non-contact temperature sensor 35 such as an infrared temperature sensor. The temperature sensor 35 is used to measure temperatures T1 and T2 at two positions P1 and P2 (see FIG. 6) located between the irradiation area and the reheating area.

The temperature decrease rate of the welded portion of the material to be welded 1 is detected based on the temperatures T1 and T2 at the positions P1 and P2 and the temperature gradient between the positions P1 and P2. It can be controlled with high precision. The first
Since the temperature gradient is large in the vicinity of the molten pool (welding keyhole 2) formed by the laser beam 31 of the irradiation unit 32, it is preferable as a place for measuring the temperature by the temperature sensor 35.

Next, with reference to FIG. 7, a method of controlling the temperature decrease rate will be described.

First, the laser beam 3 is emitted from the first irradiation section 32.
1 is irradiated to start welding of the materials 1 to be welded to each other (step S21).

Next, the temperatures T1 and T2 at the positions P1 and P2 located between the irradiation area and the reheating area are measured by the temperature sensor 35 (step S22). Then, the temperature decrease rate is calculated based on the temperature T1 and T2 at the positions P1 and P2 and the temperature gradient change between the positions P1 and P2 (step S23).

The obtained temperature decrease rate is compared with the target cooling curve corresponding to the material of the material to be welded 1 (step S2).
4).

When the temperature decrease rate is larger than the target cooling curve (step S25: YES), the reheating laser beam 33 emitted from the second irradiation section 34 following the operation of the first irradiation section 32 is irradiated. The output is increased (step S26).

When the rate of temperature decrease is smaller than the target cooling curve (step S25: NO), the output of the reheating laser beam 33 emitted from the second irradiation section 34 is reduced (step S27).

Next, it is judged whether or not the temperature of the welded portion is below the boundary temperature at which the transformation of the welded portion structure becomes stable (step S28). If the temperature of the welded portion has not reached the boundary temperature, the process returns to step S02, and if it is below the boundary temperature, the control ends.

FIG. 8 shows the hardness distribution near the weld obtained by the method of controlling the temperature decrease rate according to the second embodiment,
The hardness distribution in the vicinity of the welded portion when the temperature decrease rate is not controlled is shown. In the second embodiment, the hardness in the vicinity of the welded portion is reduced.

As described above, also in the laser welding machine according to the second embodiment, similarly to the resistance welding apparatus according to the first embodiment, the rapid quench hardening of the structure that causes cracking and deterioration of formability (toughness). It is possible to suppress the occurrence of defects in the bead portion and its vicinity in laser welding or the like. Therefore, the structures of the weld and the heat affected zone are improved.

The present invention is not limited to the above-mentioned embodiments, but can be variously modified within the scope of the claims.

For example, the material to be welded is not limited to a high-strength steel plate, and, for example, a light alloy such as aluminum can be applied.

In the first embodiment, the interelectrode resistance value can be used instead of the interelectrode displacement speed. In this case, constant current control is applied to the welding current control timer, and the changing speed of the interelectrode resistance value during energization is "0".
When it becomes, it is judged as the saturation point of the nugget diameter. Then, the temperature decrease rate is estimated based on the resistance change rate after the saturation point.

Further, the temperature decrease rate is, for example, the surface temperature directly detected by a non-contact type temperature sensor such as an infrared temperature sensor or the heat around the heat affected zone detected by a contact type temperature sensor such as a thermocouple. It can be detected based on the temperature estimated from the strain.

Further, in the second embodiment, reheating means (second irradiation section) for reheating the welded portion of the material to be welded.
The heat source is not limited to the laser beam, and a plasma beam can be used.

Further, as shown in FIG. 9, an irradiation unit 3 capable of irradiating a twin spot laser beam.
When 2A is applied, one laser beam 31A of the twin spot can be used as a welding heat source, and the other laser beam 33A of the twin spot can be used as a heat source for reheating. That is, it is possible to integrate the first irradiation unit (irradiation means) and the second irradiation unit (reheating means).

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a resistance welding device according to a first embodiment.

FIG. 2 is a diagram showing an example of a target cooling curve accumulated in a database included in the resistance welding apparatus according to the first embodiment.

FIG. 3 is a diagram for explaining a relationship between a displacement speed between electrodes and a nugget diameter.

FIG. 4 is a flowchart for explaining a method of controlling the temperature decrease rate in the resistance welding device according to the first embodiment.

FIG. 5 is a conceptual diagram of a laser welding device according to a second embodiment of the present invention.

FIG. 6 is an enlarged view of a main part for explaining a position where a temperature is measured by a temperature measuring device of a laser welding device according to a second embodiment of the present invention.

FIG. 7 is a schematic diagram for explaining a method of controlling the temperature decrease rate by the laser welding device according to the second embodiment of the present invention.

FIG. 8 is a diagram for explaining a hardness distribution in the vicinity of a welded portion.

FIG. 9 is a schematic diagram for explaining a modified example according to the second embodiment of the present invention.

[Explanation of symbols]

1 ... Material to be welded, 2 ... Welding keyhole, 10 ... Welding system, 11 ... Electrode tip, 12 ... Holder, 13 ... Electrode, 14 ... Pressurizing cylinder, 15 ... Valve, 20 ... Control system, 21 ... storage device, 22 ... Control device, 23 ... Current regulator, 24 ... Flow rate adjusting device, 25 ... Displacement velocity measuring device, 31, 31A, 33, 33A ... Laser beam, 32 ... 1st irradiation part, 32A ... Irradiation part, 34 ... 2nd irradiation part, 35 ... Non-contact type temperature sensor, 41 ... Storage device, 42 ... Control device 43 ... Temperature measuring device, A ... Quench hardening area, P1, P2 ... Position, T1, T2 ... Temperature.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B23K 26/00 B23K 26/00 MF term (reference) 4E065 EA06 4E068 BA00 CA08 CB02 CB03 CC03 DB01

Claims (20)

[Claims] 1. A storage means for storing a target cooling curve set based on a continuous cooling transformation curve of a material to be welded, a temperature decrease rate of a welded portion of the material to be welded, and a stored target cooling curve. And a control means for controlling the rate of temperature decrease so that 2. The welding device according to claim 1, further comprising welding means having a pair of welding electrodes for generating resistance heat for welding the material to be welded. 3. The control means adjusts the amount of current supplied to the welding electrode and / or the flow rate of cooling water for cooling the welding electrode to reduce the temperature of the welded portion of the material to be welded. The welding device according to claim 2, wherein the welding device is controlled. 4. The measuring means for measuring the inter-electrode displacement speed of the welding electrode, wherein the control means is based on the measured inter-electrode displacement speed, and the temperature decrease speed of the welded portion of the material to be welded. The welding apparatus according to claim 2 or 3, wherein 5. An irradiation means for irradiating a laser beam for welding a material to be welded is provided.
The welding device according to. 6. A reheating unit for reheating a welded portion of a material to be welded, following the operation of the irradiation unit, wherein the control unit adjusts the amount of heat added by the reheating unit. The welding apparatus according to claim 5, wherein the temperature decrease rate of the welded portion of the material to be welded is controlled thereby. 7. The measuring means for measuring the temperature between the laser beam irradiation area by the irradiation means and the reheating area by the reheating means, the control means comprising:
The welding apparatus according to claim 6, wherein the temperature decrease rate of the welded portion of the material to be welded is detected based on the measured temperature, and the amount of heat added by the reheating means is adjusted. 8. The welding device according to claim 1, wherein the material to be welded is a high-strength steel plate. 9. The welding apparatus according to claim 8, wherein the high-strength steel sheet passes through a process of transforming into bainite or pearlite before transforming from austenite to martensite. 10. The welding apparatus according to claim 1, wherein the material to be welded is made of a light alloy. 11. A storage step for storing a target cooling curve set on the basis of a continuous cooling transformation curve of a material to be welded, a temperature decrease rate of a weld portion of the material to be welded and a stored target cooling curve. And a control step for controlling the temperature decrease rate so that the two values are matched with each other. 12. The welding method according to claim 11, further comprising a welding step for welding the material to be welded by a welding means having a pair of welding electrodes that generate resistance heat. 13. In the control step, by adjusting the amount of current supplied to the welding electrode and / or the flow rate of cooling water for cooling the welding electrode, the temperature of the welded portion of the workpiece is lowered. 13. Welding method according to claim 12, characterized in that the speed is controlled. 14. A measuring step for measuring an inter-electrode displacement speed of the welding electrode, wherein in the control step, a temperature drop of a welded portion of a material to be welded is performed based on the measured inter-electrode displacement speed. The welding method according to claim 12, wherein the speed is estimated. 15. The welding method according to claim 11, further comprising a welding step for welding the material to be welded by an irradiation unit that emits a laser beam. 16. A reheating step for reheating a welded part of a material to be welded by a reheating means that follows the operation of the irradiation means, wherein the reheating means adds in the control step. The welding method according to claim 15, wherein the rate of temperature decrease of the welded portion of the material to be welded is controlled by adjusting the amount of heat that is applied. 17. A measuring step for measuring a temperature between a laser beam irradiation area by said irradiation means and a reheating area by said reheating means, wherein said control step is based on the measured temperature. The welding method according to claim 16, wherein the rate of decrease in temperature of the welded portion of the material to be welded is detected, and the amount of heat added by the reheating means is adjusted. 18. The welding method according to claim 11, wherein the material to be welded is a high-strength steel plate. 19. The welding method according to claim 18, wherein the high-strength steel sheet passes through a process of transforming into bainite or pearlite before transforming from austenite to martensite. 20. The welding method according to claim 11, wherein the material to be welded is made of a light alloy.