JP6913062B2 - Resistance spot welding method and welding member manufacturing method - Google Patents

Description

The present invention relates to a resistance spot welding method, and aims to make it possible to stably secure a nugget diameter without causing scattering even when the influence of disturbance such as diversion or plate gap is large. Is.

Generally, a resistance spot welding method, which is a kind of lap resistance welding method, is used for joining the stacked steel plates.
This welding method is a method in which two or more stacked steel plates are sandwiched and pressed by a pair of electrodes from above and below, and a high current welding current is applied between the upper and lower electrodes for a short time to join them. A point-shaped welded portion can be obtained by utilizing the resistance heat generated by passing the welding current of. This point-shaped welded portion is called a nugget, and is a portion where both steel plates are melted and solidified at a contact point between the steel plates when an electric current is passed through the stacked steel plates. With this nugget, the steel plates are joined in dots.

In order to obtain good weld quality, it is important that the nugget diameter is formed in an appropriate range. The nugget diameter is determined by welding conditions such as welding current, energization time, electrode shape and pressing force. Therefore, in order to form an appropriate nugget diameter, it is necessary to appropriately set the above welding conditions according to the conditions of the material to be welded, such as the material of the material to be welded, the plate thickness, and the number of stacked sheets.

For example, in the manufacture of automobiles, thousands of spot welds are performed on each vehicle, and it is necessary to weld the materials (workpieces) to be treated that flow one after another. At this time, if the state of the material to be welded such as the material, plate thickness and the number of layers of the material to be welded at each welding location is the same, the welding conditions such as the welding current, energization time and pressing force are also the same under the same conditions. You can get the nugget diameter. However, in continuous welding, the contact surface of the electrode to be welded is gradually worn and the contact area is gradually wider than in the initial state. If a welding current of the same value as the initial state is applied in a state where the contact area is widened in this way, the current density in the material to be welded decreases and the temperature rise of the welded portion decreases, so that the nugget diameter becomes smaller. .. Therefore, the electrode is polished or replaced every several hundred to several thousand points of welding so that the tip diameter of the electrode does not expand too much.

In addition, a resistance welding device having a function (stepper function) of increasing the welding current value when welding is performed a predetermined number of times to compensate for a decrease in current density due to electrode wear has been conventionally used. .. In order to use this stepper function, it is necessary to properly set the above-mentioned welding current change pattern in advance. However, for this reason, it takes a lot of time and cost to derive a welding current change pattern corresponding to a large number of welding conditions and welding material conditions by a test or the like. Further, in actual construction, since the progress state of electrode wear varies, it cannot be said that the predetermined welding current change pattern is always appropriate.

Further, when there is a disturbance during welding, for example, when there is an already welded point (already welded point) near the welding point, or when the surface unevenness of the material to be welded is large, the material to be welded is near the point where it is welded. If there is a contact point, a current is diverted to the existing weld point or contact point during welding. In such a state, even if welding is performed under predetermined conditions, the current density at the position to be welded immediately below the electrode decreases, so that a nugget having a required diameter cannot be obtained. In order to compensate for this insufficient calorific value and obtain a nugget with a required diameter, it is necessary to set a high welding current in advance.

In addition, when the circumference of the welding point is strongly restrained by the surface unevenness or the shape of the member, or when foreign matter is caught between the steel plates around the welding point, the plate gap between the steel plates becomes large. In some cases, the contact diameter between the steel sheets is narrowed, and scattering is likely to occur.

The following techniques have been proposed to solve the above problems.
For example, Patent Document 1 describes a first step of generating a nugget by gradually increasing the energizing current of a high-strength steel plate, a second step of lowering the current after the first step, and the second step. After the step, the current is increased for main welding, and spot welding is performed by a step including a third step of gradually decreasing the energizing current in an attempt to suppress scattering due to poor familiarity at the initial stage of energization. A method of spot welding a high-strength steel plate is described.

In Patent Document 2, the surface of the workpiece is softened by maintaining a current value that can suppress the occurrence of spatter at the initial stage of the energization time for a predetermined time, and then the current value is maintained high for a predetermined time to generate spatter. The energization control method of spot welding that grows the nugget while suppressing the pressure is described.

Patent Document 3 describes a control device for a resistance welder that attempts to obtain a set nugget diameter by controlling the output of the welder by comparing the estimated temperature distribution of the welded portion with the target nugget. ..

Patent Document 4 attempts to perform good welding by detecting the welding current and the inter-chip voltage, simulating the welded portion by heat conduction calculation, and estimating the nugget formation state of the welded portion during welding. The welding condition control method of the resistance welding machine is described.

In Patent Document 5, the cumulative calorific value per unit volume at which the object to be welded can be welded satisfactorily is calculated from the plate thickness of the object to be welded and the energization time, and the calculated unit volume and per unit time. A resistance welding system that attempts to perform good welding regardless of the type of object to be welded or the wear state of the electrodes is described by using a welding system that adjusts to the welding current or voltage that generates the calorific value of the above. There is.

Japanese Unexamined Patent Publication No. 2003-236674 Japanese Unexamined Patent Publication No. 2006-43731 Japanese Unexamined Patent Publication No. 9-216071 Japanese Unexamined Patent Publication No. 10-94883 Japanese Unexamined Patent Publication No. 11-33743 International Publication No. 2014/136507

However, in the techniques described in Patent Documents 1 and 2, it is considered that the appropriate welding conditions change depending on the presence or absence of disturbance and the magnitude of the disturbance. There was a problem that the desired nugget diameter could not be secured.

Further, in the techniques described in Patent Documents 3 and 4, since the temperature of the nugget is estimated based on a heat conduction model (heat conduction simulation) or the like, complicated calculation processing is required, and the configuration of the welding control device becomes complicated. Not only that, there is a problem that the welding control device itself becomes expensive.

Further, in the technique described in Patent Document 5, it is considered that by controlling the cumulative calorific value to a target value, good welding can be performed even if the electrodes are worn by a certain amount. However, when the set conditions for the material to be welded and the actual conditions for the material to be welded are significantly different, for example, when there is a disturbance such as the already welded point described above nearby, or when the time change pattern of the calorific value changes significantly in a short time. In this case, for example, in the case of welding a hot-dip galvanized steel sheet with a large amount of grain, adaptive control cannot follow and even if the final cumulative calorific value can be matched to the target value, the form of heat generation, that is, welding. The time variation of the temperature distribution of the part deviates from the calorific value pattern that can obtain the target good welded part, and the required nugget diameter cannot be obtained or scattering occurs.
For example, if the cumulative heat generation amount is adjusted when the influence of the diversion is large, the heat generation becomes remarkable not between the steel plates but near the electrode and the steel plate, and there is a problem that the heat is easily scattered from the surface of the steel plate.

In addition, all the techniques of Patent Documents 3 to 5 are effective to some extent against the change when the electrode tip is worn, but when the influence of the diversion is large such as when the distance to the existing welding point is short. Has not been examined at all, and there were cases where adaptive control did not actually work.

Therefore, the inventors first, as a solution to the above problem,
"In a resistance spot welding method in which a material to be welded, which is a stack of multiple metal plates, is sandwiched between a pair of electrodes and energized while being pressurized.
Welding shall be carried out by dividing the energization pattern into two or more multi-step steps.
First, prior to the main welding, the time change and unit volume of the instantaneous calorific value per unit volume calculated from the electrical characteristics between the electrodes when energized by constant current control to form an appropriate nugget for each step. Perform test welding to memorize the cumulative calorific value per hit as a target value.
Then, as the main welding, welding is started based on the time change curve of the instantaneous calorific value per unit volume obtained in the test welding, and in any step, the time when the time change amount of the instantaneous calorific value is the reference. When the change curve is deviated, the energization amount is controlled so that the cumulative calorific value of the main welding matches the cumulative calorific value obtained in advance in the test welding in order to compensate for the difference within the remaining energization time of the step. A resistance spot welding method characterized by performing adaptive control welding. Was developed and disclosed in Patent Document 6.

According to the technique of Patent Document 6, a nugget having a good diameter can be obtained even when the tip of the electrode is worn or a disturbance is present.

However, in the technique of Patent Document 6, when the influence of disturbance is particularly large, it is necessary to strictly set the timing for dividing the energization pattern into two or more stages, and many preliminary tests are performed to determine this timing. It was necessary to do this, leaving a problem in terms of work man-hours.

The present invention relates to the improved invention of Patent Document 6 described above, and even when the tip of the electrode is worn or a disturbance is present, the work man-hours are reduced and scattering is generated. It is an object of the present invention to provide a resistance spot welding method capable of obtaining a nugget having an appropriate diameter without increasing the energization time.
Another object of the present invention is to provide a method for manufacturing a welded member, which joins a plurality of overlapping metal plates by the above-mentioned resistance spot welding method.

Now, the inventors have made extensive studies to achieve the above-mentioned purpose.
First, in the technique of Patent Document 6, the inventors perform test welding without dividing the energization pattern, and based on the time change curve of the instantaneous calorific value per unit volume and the cumulative calorific value obtained by this test welding. We tried to perform adaptive control welding.
However, when the influence of disturbance is large, adaptive control cannot follow, and the form of heat generation in the main weld, that is, the time change of the temperature distribution of the weld, is based on the calorific value pattern that can obtain the target good weld. There was a problem that it came off, the required nugget diameter could not be obtained, and scattering occurred.

Therefore, when the inventors further examined it,
・ Review the test welding conditions, specifically
In addition to performing test welding after simulating the state of disturbance expected in actual welding,
In test welding and main welding, pre-energization is performed before main energization, respectively.
In the pre-energization and main energization of the main welding, adaptive control welding is performed based on the time change curve and the cumulative calorific value of the instantaneous calorific value stored during the pre-energization and main energization of the test welding.
Is effective,
-This makes it possible to match the heat quantity pattern of the welded part during adaptive control welding to the heat quantity pattern in test welding for a wider range of disturbance conditions, and as a result, the timing of dividing the energization pattern can be determined. It is possible to reduce the man-hours required for the preliminary test for determination.
-In particular, in actual work such as automobile manufacturing, the materials to be treated that flow one after another are continuously welded, but due to construction conditions and dimensional errors of the materials to be treated, the welding position and the material to be treated are usually welded. The state of disturbance varies from material to material,
-In this respect, according to the above welding method, adaptive control is effective for a wider range of disturbance conditions than when the time change curve obtained by test welding without disturbance is used as a reference. It is possible to stably secure the desired nugget diameter in response to fluctuations in the state of disturbance, which is advantageous in terms of improving work efficiency and yield in actual work.
I got the knowledge.

Here, the test welding is performed after simulating the state of disturbance assumed in the actual welding, and in the test welding and the main welding, the pre-energization is performed before the main welding, respectively, and the pre-energization and the main welding of the main welding are performed. In energization, adaptive control welding is performed based on the time change curve of the instantaneous calorific value memorized during the pre-energization of the test welding and the cumulative calorific value, and by performing adaptive control welding based on the cumulative calorific value, it is possible to deal with a wider range of disturbance conditions. The inventors consider the reason why the calorific value pattern of the welded portion at the time of adaptive control welding can be made to follow the calorific value pattern at the test welding as follows.
That is,
(A) When the test welding is performed in a state without disturbance as in Patent Document 6 described above, the test welding conditions are set very strictly in order for the adaptive control to work effectively in a state where the influence of the disturbance is particularly large. And many preliminary tests need to be done to derive this test welding condition.
(B) In this respect, in the test welding, if a state with a disturbance assumed in actual welding is simulated, the adaptive control can be effectively operated even when the influence of the disturbance is large.
(C) However, when the influence of the actual disturbance in the main welding is small, if the adaptive control welding is performed according to the calorific value pattern of the test welding obtained by simulating the severe disturbance, the welding current tends to become excessive at the initial stage of energization. , The risk of scattering increases.
Further, when the influence of the actual disturbance in the main welding is significantly larger than the influence of the disturbance assumed in the test welding, the welding current may still be insufficient and a sufficient nugget diameter may not be obtained. ..
(D) In this regard, in the test welding and the main welding, pre-energization is performed before the main energization, respectively, and in the pre-energization and the main energization of the main welding, the instantaneous calorific value stored during the pre-energization and the main energization of the test welding is performed. By performing adaptive control welding based on the time change curve and cumulative calorific value, there is a difference between the actual disturbance state in the main welding and the disturbance state assumed in the test welding at the start of pre-energization. Even if there is, at the start of the main energization, the state of the energization path between the metal plates to be welded becomes close, and the difference is greatly alleviated.
(E) Therefore, the test welding is performed after simulating the state of disturbance expected in the actual welding, and the test welding and the main welding are pre-energized before the main welding, respectively, and the pre-energization of the main welding is performed. In the main energization, by pre-energizing the test welding and performing adaptive control welding based on the time change curve of the instantaneous calorific value stored during the main energization and the cumulative calorific value, a wider range of disturbance conditions can be obtained. , It becomes possible to make the calorific value pattern of the welded part in adaptive control welding follow the calorific value pattern in test welding.
The inventors think.
The present invention has been completed with further studies based on the above findings.

That is, the gist structure of the present invention is as follows.
1. 1. This is a resistance spot welding method in which a material to be welded, which is a stack of multiple metal plates, is sandwiched between a pair of electrodes and energized while being pressurized.
Main welding and test welding prior to the main welding shall be performed, and pre-energization and main energization shall be performed in the main welding and the test welding, respectively.
In the test welding,
After simulating a state with disturbance, pre-energization and main energization are performed by constant current control.
In addition, the time change curve of the instantaneous calorific value per unit volume and the cumulative calorific value per unit volume calculated from the electrical characteristics between the electrodes when forming an appropriate nugget in the pre-energization and the main energization, respectively. Remember,
In the main welding,
Pre-energization and main energization are performed by welding based on the time change curve and cumulative calorific value of the instantaneous calorific value per unit volume stored in the pre-energization and main energization of the test welding, respectively.
In the pre-energization or the main energization, when the time change amount of the instantaneous calorific value per unit volume deviates from the reference time change curve, the deviation amount is used as the remaining pre-energization or the main energization time. In order to compensate within, the cumulative calorific value per unit volume in the pre-energization or the main energization matches the cumulative calorific value per unit volume obtained in advance in the pre-energization or the main energization of the test welding, respectively. Control the amount of electricity,
Resistance spot welding method.

2. The resistance spot welding method according to 1 above, which satisfies the relationship of I1 <I2 when the pre-energized welding current of the test welding is I1 and the main current welding current of the test welding is I2.

3. 3. The resistance spot welding method according to 1 or 2 above, wherein the test welding is performed with a welded point at a position 6 to 30 mm away from the welding position.

4. The resistance spot welding method according to 1 or 2, wherein the test welding is performed with a gap of 0.2 to 3.0 mm on the mating surfaces of the metal plates to be welded.

5. A method for manufacturing a welded member, wherein a plurality of overlapping metal plates are joined by the resistance spot welding method according to any one of 1 to 4.

According to the present invention, it is possible to obtain a nugget having an appropriate diameter without causing scattering or increasing the energizing time while reducing the work man-hours.
Further, according to the present invention, it is a case where the materials to be treated that flow one after another in actual work such as manufacturing of an automobile are continuously welded (the state of disturbance varies depending on the welding position and the material to be treated). However, since a nugget having an appropriate diameter can be stably obtained without the occurrence of scattering, it is also advantageous in terms of improving work efficiency and yield in actual work.

It is a figure which shows typically an example of the case where the test welding is performed on the plate assembly which has already welded points. It is a figure which shows typically another example in the case of performing test welding on the plate assembly which has the existing welding points. It is a figure which shows typically an example of the case where the test welding is performed on the plate assembly with a plate gap. It is a figure which shows typically another example in the case of performing test welding on a plate assembly with a plate gap. It is a figure which shows typically an example of the case where the test welding is performed in the state of no disturbance. It is a figure which shows another example typically in the case of performing test welding in a state without disturbance. It is a figure which shows typically an example of the energization pattern by constant current control. It is a figure which shows another example of the energization pattern by a constant current control schematically.

The present invention will be described based on the following embodiments.
One embodiment of the present invention is a resistance spot welding method in which a material to be welded in which a plurality of metal plates are superposed is sandwiched between a pair of electrodes and energized while being pressurized.
Main welding and test welding prior to the main welding shall be performed, and pre-energization and main energization shall be performed in the main welding and the test welding, respectively.
In the test welding,
After simulating a state with disturbance, pre-energization and main energization are performed by constant current control.
In addition, the time change curve of the instantaneous calorific value per unit volume and the cumulative calorific value per unit volume calculated from the electrical characteristics between the electrodes when forming an appropriate nugget in the pre-energization and the main energization, respectively. Remember,
In the main welding,
Pre-energization and main energization are performed by welding based on the time change curve and cumulative calorific value of the instantaneous calorific value per unit volume stored in the pre-energization and main energization of the test welding, respectively.
In the pre-energization or the main energization, when the time change amount of the instantaneous calorific value per unit volume deviates from the reference time change curve, the deviation amount is used as the remaining pre-energization or the main energization time. In order to compensate within, the cumulative calorific value per unit volume in the pre-energization or the main energization matches the cumulative calorific value per unit volume obtained in advance in the pre-energization or the main energization of the test welding, respectively. It controls the amount of energization.

The welding device that can be used in the resistance spot welding method according to the embodiment of the present invention may be provided with a pair of upper and lower electrodes and can arbitrarily control the pressing force and the welding current during welding. The pressure mechanism (air cylinder, servo motor, etc.), type (stationary type, robot gun, etc.), electrode shape, etc. are not particularly limited. The electrical characteristics between the electrodes mean the resistance between the electrodes or the voltage between the electrodes.

Hereinafter, the test welding and the main welding of the resistance spot welding method according to the embodiment of the present invention will be described.

-Test welding In test welding, after simulating a state with disturbance, specifically, a state with disturbance assumed in main welding, pre-energization and main energization are performed by constant current control, respectively, and the pre-energization and main energization are performed. In each of the main currents, the time change curve of the instantaneous calorific value per unit volume and the cumulative calorific value per unit volume calculated from the electrical characteristics between the electrodes when forming an appropriate nugget are stored.

Here, the disturbance assumed in the main welding is a disturbance such as a diversion or a plate gap, specifically, an already welded point within 40 mm from the welding position (electrode center position), or a metal plate to be welded. Examples thereof include a gap of 0.2 mm or more on the mating surfaces of each other.

For example, when it is assumed that there is a pre-welded point within 40 mm from the welding position, it is preferable to perform test welding with the pre-welded point at a position 6 to 30 mm away from the welding position. More preferably, it is performed in a state where there is a welded point at a position 6 to 20 mm away from the welding position. Further, as is usually assumed, the lower limit of the distance from the welding position to the existing welding point is about 6 mm. Further, the number of existing welding points simulated in the test welding may be one point or two or more points. Further, the upper limit of the number of existing weld points simulated in the test welding is not particularly limited, and it is preferable to set the maximum number of existing weld points among the assumed existing weld points. Further, the size of the existing welding point simulated by the test welding may be set to be about the same as the size of the assumed existing welding point.
The distance between the welding position and the existing welding point referred to here is the distance between the centers.

In addition, if it is assumed that there is a gap of 0.2 mm or more on the mating surfaces of the metal plates to be welded, the test welding will be performed from 0.2 to 0.2 on the mating surfaces of the metal plates to be welded. It is preferable to carry out with a gap of 3.0 mm. More preferably, it is carried out in a state where there is a gap of 0.5 to 2.0 mm on the mating surfaces of the metal plates to be welded. Further, the upper limit of the gap between the mating surfaces of the metal plates to be welded is practically about 3.0 mm.
The gap between the mating surfaces of the metal plates is the gap between the mating surfaces of the metal plates (distance between the mating surfaces) at the welding position before being pressurized by the electrodes.

The test welding conditions other than the above are appropriately set by performing a preliminary welding test of the same steel type and thickness as the material to be welded under various conditions under constant current control under the assumption of the above disturbance. do it.

Further, in test welding and further in main welding described later, it is important to perform pre-energization before main current energization.
This is because the test welding is performed after simulating the state of disturbance expected in the actual welding, and in the test welding and the main welding, pre-energization is performed before the main energization, respectively, and the pre-energization of the main welding is performed. And in the main energization, the pre-energization of the test welding and the adaptive control welding based on the time change curve of the instantaneous calorific value stored during the main energization and the cumulative calorific value are performed, respectively.
Even if there is a difference between the actual disturbance state in the main welding and the disturbance state assumed in the test welding at the start of the pre-energization of the main welding, it is covered at the start of the main energization of the main welding. The state of the energization path between the metal plates, which are the welding materials, becomes closer, and the difference is greatly reduced.
As a result, it becomes possible to make the calorific value pattern of the welded portion at the time of adaptive control welding follow the calorific value pattern at the test welding for a wider range of disturbance states.

The pre-energization is energization for softening the metal plate to be welded before expanding the nugget to secure an energization path between the metal plates. In the pre-energization, the nugget does not have to be formed, and the nugget is small enough not to generate scattering (for example, the nugget diameter is about 4√t'or less (t': the thinner of the two adjacent metal plates). The plate thickness (mm) of the metal plate may be formed.
The pre-energization conditions are not particularly limited, but it is preferable that the welding current I1 by constant current control during pre-energization is 2 to 13 kA and the energization time is 20 to 400 ms.

Further, the main energization condition is not particularly limited, but the relationship of I1 <I2 is satisfied with respect to the welding current I1 by the constant current control at the time of pre-energization and the welding current I2 by the constant current control at the time of the main energization. Is preferable.
The energizing time is preferably 20 to 1000 ms.

In addition, an energization pause time may be provided between the pre-energization and the main energization. In that case, the energization suspension time is preferably 20 to 400 ms.
In the constant current control referred to in the present application, not only when the welding current is constant as shown in FIG. 7, but also when the welding current is linearly (continuously) in pre-energization and / or main energization as shown in FIG. It shall include the case of increasing / decreasing. When the welding current is linearly (continuously) increased or decreased, it is preferable that the welding current at each energization satisfies the relationship of I1 <I2 with reference to the average value.

-Main welding After the above test welding, perform main welding. In the main welding, the pre-energization and the main energization are performed based on the time change curve of the instantaneous calorific value per unit volume and the cumulative calorific value stored in the pre-energization and the main energization of the test welding, respectively, and the welding is performed per unit volume. If the amount of time change of the instantaneous calorific value of is along the time change curve which is the reference, welding is performed as it is and welding is completed.
However, in the pre-energization or the main energization, if the time change amount of the instantaneous calorific value per unit volume deviates from the reference time change curve, the deviation amount is used for the remaining pre-energization or the main energization. In order to compensate within the energization time, the cumulative calorific value per unit volume in the pre-energization or the main energization coincides with the cumulative calorific value per unit volume obtained in advance in the pre-energization or the main energization of the test welding, respectively. The amount of energization is controlled so as to.
(That is, when the time change amount of the instantaneous calorific value per unit volume deviates from the reference time change curve at the time of pre-energization, the deviation amount is compensated within the remaining energization time of the pre-energization. The energization amount is controlled so that the cumulative calorific value per unit volume in the pre-energization matches the cumulative calorific value per unit volume obtained in advance in the pre-energization of the test welding.
In addition, when the time change amount of the instantaneous calorific value per unit volume deviates from the reference time change curve at the time of main energization, the deviation amount is compensated within the remaining energization time of the main energization. The amount of energization is controlled so that the cumulative calorific value per unit volume in the main energization matches the cumulative calorific value per unit volume obtained in advance in the main energization of the test welding. )
As a result, even if the tip of the electrode is worn or the influence of disturbance such as diversion or plate gap is large, the required cumulative calorific value can be secured and an appropriate nugget diameter can be obtained.

The method for calculating the calorific value is not particularly limited, but an example thereof is disclosed in Patent Document 5, and this method can also be adopted in the present invention. The procedure for calculating the calorific value q per unit volume / unit time and the cumulative calorific value Q per unit volume by this method is as follows.
Let t be the total thickness of the material to be welded, r be the electrical resistivity of the material to be welded, V be the voltage between the electrodes, I be the welding current, and S be the area where the electrodes and the material to be welded come into contact. In this case, the welding current has a cross-sectional area of S and passes through a columnar portion having a thickness t to generate resistance heat. The calorific value q per unit volume and unit time in this columnar portion is calculated by the following equation (1).
q = (VI) / (ST) --- (1)
Further, the electric resistance R of this columnar portion is obtained by the following equation (2).
R = (rt) / S --- (2)
When equation (2) is solved for S and this is substituted into equation (1), the calorific value q is calculated by the following equation (3).
q = (V ・ I ・ R) / (r ・ t ² )
= (V ² ) / (r · t ² ) --- (3)
Will be.

As is clear from the above equation (3), the calorific value q per unit volume / unit time can be calculated from the voltage V between the electrodes, the total thickness t of the work piece, and the electrical resistivity r of the work piece. It is not affected by the area S in which the object to be welded and the object to be welded come into contact with each other. In Eq. (3), the calorific value is calculated from the voltage V between the electrodes, but the calorific value q can also be calculated from the current I between the electrodes. There is no need to use. Then, by accumulating the calorific value q per unit volume and unit time over the energization period, the cumulative calorific value Q per unit volume applied to welding can be obtained. As is clear from the equation (3), the cumulative calorific value Q per unit volume can also be calculated without using the area S where the electrode and the material to be welded contact.
The case where the cumulative calorific value Q is calculated by the method described in Patent Document 5 has been described above, but it goes without saying that other calculation formulas may be used.

In addition, the conditions other than the welding current in the main welding (pre-energization, energization time in the main energization, and set pressing force) may be the same as those in the test welding.

The material to be welded is not particularly limited, and can be applied to welding of steel plates having various strengths from mild steel to ultra-high-strength steel plates and light metal plates such as plated steel plates and aluminum alloys, and three or more metal plates can be used. It can also be applied to stacked boards.

Further, after the energization for forming the nugget, the post-energization for heat treatment of the welded portion may be applied. In this case, the energization condition is not particularly limited, and the magnitude relationship with the welding current of the previous step is not particularly limited. Further, the pressing force during energization may be constant or may be changed as appropriate.

Hereinafter, examples according to the embodiment of the present invention will be described.
The conditions of the examples are adopted to confirm the feasibility and effect of the present invention, and the present invention is not limited to the conditions of these examples. Further, the present invention can adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.
A welded joint was produced by performing resistance spot welding under the conditions shown in Table 2 for the two-layer or three-layer metal plate assembly shown in Table 1.
Here, the test welding was performed in a state simulating the disturbance as shown in FIGS. 1 to 4 or in a state without disturbance as shown in FIGS. 5 and 6. In the figure, reference numerals 11 to 13 are metal plates, 14 is an electrode, 15 is a spacer, and 16 is a welded point. As shown in FIGS. 1 and 2, the existing welding points 16 are set to two points, and the welding positions (centers between electrodes) are intermediate between the existing welding points (the distance L from the existing welding points is the same). Adjusted to. It should be noted that the nugget diameter between the metal plates at the welded point (however, in the case of a three-ply plate assembly, between the thinnest metal plate of the plate assembly and the metal plate in contact with the metal plate (for example, the plate assembly No. F in Table 1). In the case of, the nugget diameter) in (between 11 and 12 of the metal plates) is 4√t'(t': the thickness (mm) of the thinner metal plate of the two adjacent metal plates. In the case of the plate assembly, the thickness (mm) of the thinnest metal plate among the plate assembly was used.
Further, in FIGS. 3 and 4, by inserting the spacer 15 between the metal plates 11 to 13 and clamping from above and below (not shown), plate gaps having various plate gap thicknesses tg are provided (not shown). In the case of a three-ply plate assembly, the plate gap thickness tg between the metal plates 11 and 12 and the plate gap thickness tg between the metal plates 12 and 13 are the same value). The plate gap distance was set to 60 mm.
Further, in the test welding, under the conditions shown in Table 2, only the main energization or the pre-energization and the main energization are performed by constant current control, and the time change curve and the cumulative calorific value of the instantaneous calorific value per unit volume at that time are obtained. I remembered it. Further, under some conditions, an energization suspension time was provided between the pre-energization and the main energization.

In addition, in the main welding, welding was performed based on the time change curve of the instantaneous calorific value per unit volume and the cumulative calorific value stored in the test welding. Here, conditions such as energization time, pressing force, energization suspension time between pre-energization and main energization are the same for test welding and main welding.
An inverter DC resistance spot welder was used as the welder, and a DR type chrome copper electrode having a tip diameter of 6 mm was used as the electrode.

For each of the obtained joints, the welded part is cut, the cross section is etched, and then observed with an optical microscope. The target diameter (nugget diameter between the metal plates in contact) is 5√t'or more (t': the thickness of the thinner metal plate of the two adjacent metal plates (mm), but three layers are stacked. In the case of the plate assembly of, the case where the thickness of the thinnest metal plate among the plate assembly (mm) and no scattering occurred was evaluated as ⊚.
In addition, the case where the nugget diameter was 4.5√t'or more and less than 5√t' and no scattering occurred was evaluated as ◯. On the other hand, when the nugget diameter was less than 4.5√t'or when scattering occurred, it was evaluated as x.

In each of the examples of the invention, a nugget having a diameter of 4.5√t'or more can be obtained without occurrence of scattering in a wide range of disturbance states, and adaptive control of this welding is performed in a wide range of disturbance states. It was possible to make the calorific value pattern of the welded portion at the time of welding follow the calorific value pattern in the test welding.
On the other hand, in the comparative example, depending on the state of disturbance, scattering may occur or a nugget having a sufficient diameter cannot be obtained. The calorific value pattern of was not able to follow the calorific value pattern in the test welding.

11, 12, 13: Metal plate 14: Electrode 15: Spacer 16: Already welded point

Claims (2)

This is a resistance spot welding method in which a material to be welded, which is a stack of multiple metal plates, is sandwiched between a pair of electrodes and energized while being pressurized.
Main welding and test welding prior to the main welding shall be performed, and pre-energization and main energization shall be performed in the main welding and the test welding, respectively.
In the test welding,
A gap of 0.2 to 2.0 mm is provided on the mating surfaces of the metal plates to be welded, and then pre-energization and main energization are performed by constant current control.
In addition, the time change curve of the instantaneous calorific value per unit volume and the cumulative calorific value per unit volume calculated from the electrical characteristics between the electrodes when forming an appropriate nugget in the pre-energization and the main energization, respectively. Remember,
In the main welding,
Pre-energization and main energization are performed by welding based on the time change curve and cumulative calorific value of the instantaneous calorific value per unit volume stored in the pre-energization and main energization of the test welding, respectively.
In the pre-energization or the main energization, when the time change amount of the instantaneous calorific value per unit volume deviates from the reference time change curve, the deviation amount is used as the remaining pre-energization or the main energization time. In order to compensate within, the cumulative calorific value per unit volume in the pre-energization or the main energization matches the cumulative calorific value per unit volume obtained in advance in the pre-energization or the main energization of the test welding, respectively. Control the amount of electricity ,
When the welding current of the pre-energization of the test welding is I1 and the welding current of the main current of the test welding is I2, the relationship of I1 <I2 is satisfied .
Resistance spot welding method. A method for manufacturing a welded member, in which a plurality of overlapping metal plates are joined by the resistance spot welding method according to claim 1.

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