JP2019034341A - Resistance spot welding method and manufacturing method for welding member - Google Patents

Abstract

To provide a resistance spot welding method by which a nugget with an appropriate diameter can be obtained without occurrence of scatter and an increase of energization time, while reducing man days for work even in a case where the leading end of an electrode wears and/or disturbance is present.SOLUTION: Preliminary energization and main energization are carried out in both main welding and test welding. In the test welding, a disturbed state is simulated, and the preliminary energization and the main energization are carried out under constant-current control. A time change curve of a quantity of instantaneous heat generation per unit volume and a cumulative quantity of heat generation per unit volume, which are calculated from an electrical characteristic between electrodes when an appropriate nugget is formed, are stored for each of the preliminary energization and the main energization. In the main welding, welding is carried out using, as a reference, the time change curve of the quantity of instantaneous heat generation per unit volume and the cumulative quantity of heat generation, stored for each of the preliminary energization and the main energization for the test welding.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a resistance spot welding method, and in particular, it is intended 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. It is.

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

  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 applied pressure. Therefore, in order to form an appropriate nugget diameter, it is necessary to appropriately set the above-described welding conditions in accordance with the welded material conditions such as the material of the welded material, the plate thickness, and the number of stacked sheets.

  For example, in the manufacture of automobiles, thousands of spot welding is performed per vehicle, and it is necessary to weld workpieces (workpieces) that flow one after another. At this time, if the condition of the material to be welded, such as the material of the material to be welded at each welding location, the plate thickness, and the number of stacked sheets, is the same, the welding conditions such as welding current, energization time, and pressure are the same under the same conditions. The nugget diameter can be obtained. However, in continuous welding, the contact surface of the electrode to be welded material gradually wears, and the contact area gradually becomes wider than the initial state. When a welding current having the same value as that in the initial state is applied in a state where the contact area is increased in this way, the current density in the material to be welded is lowered and the temperature rise of the welded portion is lowered, so the nugget diameter is reduced. . For this reason, the electrode is ground or exchanged every several hundred to several thousand points of welding so that the tip diameter of the electrode does not become too large.

  In addition, a resistance welding apparatus having a function (stepper function) that increases a welding current value when a predetermined number of times of welding is performed and compensates 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 appropriately set the above-described welding current change pattern in advance. However, for this purpose, much time and cost are required to derive a welding current change pattern corresponding to a large number of welding conditions and workpiece conditions by testing or the like. Moreover, in actual construction, since the progress of electrode wear varies, a predetermined welding current change pattern is not always appropriate.

  Furthermore, when there is a disturbance during welding, for example, when there is a point that has already been welded (an already welded point) near the point to be welded, If a contact point exists, current is shunted to the already-welded point or the contact point during welding. In such a state, even if welding is performed under a predetermined condition, the current density at the position to be welded directly under the electrode is lowered, so that a nugget having a necessary diameter cannot be obtained. In order to compensate for this shortage of heat generation and obtain a nugget with a required diameter, it is necessary to set a high welding current in advance.

  Also, if the periphery of the welding point is strongly constrained due to surface irregularities or the shape of the member, or if foreign matter is sandwiched between the steel plates around the welding point, the gap between the steel plates will increase. In this case, the contact diameter between the steel plates is narrowed, and scattering is likely to occur.

In order to solve the above problems, the following techniques have been proposed.
For example, Patent Document 1 discloses a first step in which nugget generation is performed by gradually increasing an energization current to a high-tensile steel plate, a second step in which current is decreased after the first step, and the second step. After the step, the current is increased and main welding is performed, and spot welding is performed by a process including a third step for gradually decreasing the energization current, thereby attempting to suppress scattering due to the familiarity failure at the initial energization. A method for spot welding high strength steel sheets is described.

  In Patent Document 2, the current value is maintained at a current value that can suppress the occurrence of spatter at the beginning of the energization time for a predetermined time to soften the surface of the workpiece, and then the current value is maintained high for a predetermined time to generate spatter. An energization control method for spot welding in which nuggets are grown while suppressing the above is described.

  Patent Document 3 describes a resistance welding machine control device that obtains a set nugget diameter by comparing the estimated temperature distribution of a welded portion with a target nugget to control the output of the welding machine. .

  In Patent Document 4, welding current and chip-to-chip voltage are detected, a weld is simulated by heat conduction calculation, and the formation state of the nugget of the weld during welding is estimated to perform good welding. A welding condition control method for a resistance welder is described.

  In Patent Document 5, a cumulative heat generation amount per unit volume capable of satisfactorily welding the workpiece is calculated from the thickness of the workpiece and energization time, and the calculated unit volume / unit time is calculated. Describes a resistance welding system that performs good welding regardless of the type of workpiece and the wear state of the electrodes by using a welding system that adjusts the welding current or voltage to generate a heat generation amount of Yes.

JP 2003-236684 A JP 2006-43731 A Japanese Patent Laid-Open No. 9-216071 JP-A-10-94883 JP 11-33743 A 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 the disturbance and the magnitude of the disturbance. There was a problem that a 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 necessary, and the configuration of the welding control device is complicated. In addition, there is a problem that the welding control device itself is expensive.

Furthermore, with the technique described in Patent Document 5, it is considered that good welding can be performed by controlling the accumulated heat generation amount to a target value even if the electrode is worn by a certain amount. However, if the set welding material conditions and the actual welding material conditions are significantly different, for example, when there is a disturbance such as the already-welded point nearby, or the temporal change pattern of the heat generation amount changes greatly in a short time. For example, in the case of welding of hot dip galvanized steel sheet with a large amount of fabric, adaptive control cannot follow, and even if the final accumulated heat generation can be adjusted 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 from which the desired good weld is obtained, and the required nugget diameter cannot be obtained or scattering occurs.
For example, when the cumulative heat generation amount is to be adjusted when the influence of the diversion is large, heat is generated not only between the steel plates but in the vicinity of the electrode-steel plate, and scattering from the steel plate surface tends to occur.

  In addition, all of the techniques of Patent Documents 3 to 5 are effective to some extent when the electrode tip is worn, but when the influence of the diversion is large, such as when the distance from the welded point is short. Has not been studied at all, and in some cases, adaptive control did not actually work.

Therefore, the inventors firstly solved the above problem as follows:
“In a resistance spot welding method in which a material to be welded on which a plurality of metal plates are superimposed is sandwiched between a pair of electrodes and energized while being pressed and joined.
We shall divide the energization pattern into two or more multi-steps and perform welding.
First, prior to the main welding, for each step, the temporal change in instantaneous calorific value per unit volume and unit volume calculated from the electrical characteristics between the electrodes when energizing with constant current control to form an appropriate nugget at each step Test welding to memorize the cumulative calorific value per hit as a target value,
Next, as the main welding, welding is started on the basis of the time variation curve of the instantaneous calorific value per unit volume obtained by the test welding, and at any step, the time at which the temporal variation of the instantaneous calorific value is the reference is started. In order to compensate for the difference within the remaining energization time of the step when it deviates from the change curve, the energization amount is controlled so that the cumulative heat generation amount of the main welding matches the cumulative heat generation amount obtained in advance by test welding. A resistance spot welding method characterized by performing adaptive control welding. Was developed and disclosed in US Pat.

  With the technique of Patent Document 6, a nugget with a good diameter can be obtained even when the electrode tip is worn or a disturbance exists.

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

The present invention relates to the improved invention of Patent Document 6 listed above, and even when the electrode tip is worn or there is a disturbance, the occurrence of scattering is reduced while reducing the work man-hours. 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 energization time.
Moreover, this invention aims at providing the manufacturing method of the welding member which joins the several metal plate piled up by said resistance spot welding method.

Now, the inventors have made extensive studies to achieve the above object.
First, the inventors performed test welding without dividing the energization pattern in the technique of Patent Document 6, and based on the time variation curve of the instantaneous heat generation amount per unit volume and the cumulative heat generation amount obtained by this test welding. As an attempt to perform adaptive control welding.
However, when the influence of the disturbance is large, adaptive control cannot be followed, and the form of heat generation in the main welding, that is, the temporal change in the temperature distribution of the welded portion, is determined from the heat quantity pattern that provides the desired good welded portion. There arises a problem that the required nugget diameter cannot be obtained or scattering occurs.

Therefore, when the inventors further studied,
・ Review the test welding conditions. Specifically,
While 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,
In the pre-energization and main energization of the main welding, adaptive control welding is performed based on the temporal change curve of the instantaneous calorific value and the cumulative calorific value memorized at the time of 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 It becomes possible to reduce the man-hour related to the preliminary test for determining,
・ In particular, in actual work such as automobile manufacturing, the materials to be processed that are flowing one after another are continuously welded. However, depending on the construction conditions and dimensional errors of the materials to be processed, etc. The state of disturbance varies from material to material.
-In this respect, according to the welding method described above, adaptive control is effective for a wider range of disturbance conditions than when the time change curve obtained by test welding in the absence of disturbance is used as a reference. Therefore, it is possible to stably secure a desired nugget diameter in response to fluctuations in the state of disturbance, which is advantageous from the viewpoint of improving work efficiency and yield in actual work.
And gained knowledge.

Here, test welding is performed after simulating the state of disturbance expected in actual welding, and pre-energization is performed before main energization in test welding and main welding, respectively. In energization, adaptive control welding based on the time variation curve of the instantaneous calorific value memorized at the time of pre-energization of test welding and main energization and the cumulative calorific value is performed. The inventors consider the reason why the heat quantity pattern of the welded part at the time of adaptive control welding can be made to conform to the heat quantity pattern in test welding as follows.
That is,
(A) When test welding is performed without disturbance as in Patent Document 6 listed above, the test welding conditions are set very strictly in order to make adaptive control work effectively in a state where the influence of disturbance is particularly large. In order to derive this test welding condition, it is necessary to perform many preliminary tests.
(B) In this respect, in the test welding, if a state with a disturbance assumed in actual welding is simulated, even when the influence of the disturbance is large, the adaptive control can be effectively operated.
(C) However, if the effect of the actual disturbance in the main welding is small, if the adaptive control welding is performed along the heat quantity pattern of test welding obtained by simulating a severe disturbance, the welding current tends to be excessive at the beginning of energization. , The risk of scattering increases.
In addition, 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 point, in test welding and main welding, pre-energization is performed before main energization, and in the pre-energization and main energization in main welding, the instantaneous heating value stored at the time of pre-energization and main energization of test welding is stored. By performing adaptive control welding based on the time-varying curve and cumulative heat generation, there is a difference between the actual disturbance state in main welding and the disturbance state assumed in test welding at the start of pre-energization. Even if there is, the state of the energization path between the metal plates that are the welded materials is close at the start of the main energization, and the difference is greatly reduced.
(E) Therefore, test welding is performed after simulating the state of disturbance expected in actual welding, and pre-energization is performed before main energization in test welding and main welding, respectively. In the main energization, the pre-energization of the test welding and the time-dependent curve of the instantaneous calorific value memorized during the main energization and the adaptive control welding based on the cumulative calorific value are applied to a wider range of disturbance conditions. , It becomes possible to match the heat quantity pattern of the welded part during adaptive control welding with the heat quantity pattern in test welding.
The inventors think.
The present invention has been completed based on the above findings and further studies.

That is, the gist configuration of the present invention is as follows.
1. It is a resistance spot welding method in which a material to be welded in which a plurality of metal plates are overlapped is sandwiched between a pair of electrodes, and energized while being pressed and joined.
The main welding and the test welding prior to the main welding are performed, and in the main welding and the test welding, pre-energization and main energization are performed,
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 variation curve of instantaneous calorific value per unit volume and the cumulative calorific value per unit volume, which are calculated from the electrical characteristics between the electrodes when an appropriate nugget is formed in the pre-energization and the main energization, respectively. Remember,
In the main welding,
Pre-energization and main energization are performed on the basis of the time variation curve of the instantaneous calorific value per unit volume and the cumulative calorific value memorized 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 determined as the remaining pre-energization or main energization time. So that the accumulated heat generation amount per unit volume in the pre-energization or the main energization matches the cumulative heat generation amount per unit volume determined in advance in the pre-energization or the main energization of the test welding. Control the energization amount,
Resistance spot welding method.

2. 2. The resistance spot welding method according to 1, wherein a relationship of I1 <I2 is satisfied, where I1 is a pre-energization welding current for the test welding and I2 is a main energization current for the test welding.

3. 3. The resistance spot welding method according to 1 or 2, wherein the test welding is performed in a state where there is an already-welded point at a position 6 to 30 mm apart from the welding position.

4). 3. The resistance spot welding method according to 1 or 2, wherein the test welding is performed in a state where there is a gap of 0.2 to 3.0 mm on a mating surface between metal plates to be welded.

5. The manufacturing method of the welding member which joins the several metal plate piled up by the resistance spot welding method in any one of said 1-4.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to obtain the nugget of a suitable diameter, without generation | occurrence | production of scattering and increase in energization time, reducing work man-hours.
In addition, according to the present invention, the materials to be processed flowing one after another in actual work such as automobile manufacturing are continuously welded (the state of disturbance varies for each welding position and materials to be processed). However, since a nugget with an appropriate diameter can be stably obtained without occurrence of scattering, it is advantageous in terms of improving work efficiency and yield in actual work.

It is a figure which shows typically an example in the case of performing test welding with respect to the board assembly with an already-welded point. It is a figure which shows typically another example in the case of performing test welding with respect to the board assembly with an already-welded point. It is a figure which shows typically an example in the case of performing test welding with respect to the board assembly with a board gap. It is a figure which shows typically another example in the case of performing test welding with respect to the board assembly with a clearance gap. It is a figure which shows typically an example in the case of performing test welding in a state without a disturbance. It is a figure which shows typically another example in the case of performing test welding in a state without a disturbance. It is a figure which shows typically an example of the electricity supply pattern by constant current control. It is a figure which shows typically another example of the electricity supply pattern by constant current control.

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 overlapped is sandwiched between a pair of electrodes and energized and joined while being pressurized,
The main welding and the test welding prior to the main welding are performed, and in the main welding and the test welding, pre-energization and main energization are performed,
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 variation curve of instantaneous calorific value per unit volume and the cumulative calorific value per unit volume, which are calculated from the electrical characteristics between the electrodes when an appropriate nugget is formed in the pre-energization and the main energization, respectively. Remember,
In the main welding,
Pre-energization and main energization are performed on the basis of the time variation curve of the instantaneous calorific value per unit volume and the cumulative calorific value memorized 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 determined as the remaining pre-energization or main energization time. So that the accumulated heat generation amount per unit volume in the pre-energization or the main energization matches the cumulative heat generation amount per unit volume determined in advance in the pre-energization or the main energization of the test welding. It controls the energization amount.

  Note that a welding apparatus that can be used in the resistance spot welding method according to an embodiment of the present invention is only required to have a pair of upper and lower electrodes and to arbitrarily control the pressing force and the welding current during welding. The pressure mechanism (air cylinder, servo motor, etc.), type (stationary, robot gun, etc.), electrode shape, etc. are not particularly limited. Moreover, the electrical property between electrodes means the resistance between electrodes or the voltage between electrodes.

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

・ Test welding In test welding, a state with a disturbance, specifically, a state with a disturbance assumed in main welding is simulated, and then pre-energization and main energization are performed by constant current control, respectively. In the main energization, the temporal change curve of the instantaneous heat generation amount per unit volume and the cumulative heat generation amount per unit volume, which are calculated from the electrical characteristics between the electrodes when an appropriate nugget is formed, are stored.

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

For example, when it is assumed that there is an already-welded point within 40 mm from the welding position, it is preferable that the test welding is performed in a state where the already-welded point is located at a position 6 to 30 mm away from the welding position. More preferably, it is preferable to carry out in a state where there is an already-welded point at a position 6 to 20 mm apart from the welding position. Moreover, the lower limit of the distance from the welding position to the already-welded point is normally about 6 mm as expected. Further, the number of already welded points simulated by test welding may be one point or two or more points. In addition, the upper limit of the number of already welded points simulated by test welding is not particularly limited, and it is preferable to set the highest number among the assumed number of already welded points. Furthermore, the size of the already welded point simulated by the test welding may be the same size as the assumed size of the already welded point.
In addition, the distance of the welding position here and an already-welded point is distance between each center.

In addition, when it is assumed that there is a gap of 0.2 mm or more at the mating surface between the metal plates to be welded, the test welding is performed at 0.2 to 0.2 at the mating surface between the metal plates to be welded. It is preferable to carry out with a gap of 3.0 mm. More preferably, it is performed 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. In addition, the upper limit of the gap between the joining surfaces of the metal plates that are assumed to be welded is practically about 3.0 mm.
Note that the gap between the mating surfaces of the metal plates is the gap (distance between the mating surfaces) between the metal plates at the welding position before being pressed by the electrodes.

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

Further, it is important to perform pre-energization before main energization in test welding and further in main welding described later.
This is because test welding is performed after simulating the state of disturbance expected in actual welding, and pre-energization is performed before main energization in test welding and main welding, respectively. In the main energization, pre-energization of test welding and adaptive control welding based on the time variation curve of the instantaneous calorific value memorized during the main energization and the cumulative calorific value, respectively,
Even if there is a difference between the actual state of disturbance in main welding and the state of disturbance assumed in test welding at the start of pre-energization in main welding, The state of the current-carrying path between the metal plates that are the welding materials becomes closer, and the difference is greatly reduced.
As a result, the heat quantity pattern of the welded part during adaptive control welding can be made to conform to the heat quantity pattern in test welding for a wider range of disturbance conditions.

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

Further, the main energization conditions are not particularly limited, but satisfy the relationship of I1 <I2 with respect to the welding current I1 by constant current control during pre-energization and the welding current I2 by constant current control during main energization. Is preferred.
The energization time is preferably 20 to 1000 ms.

In addition, an energization stop time may be provided between pre-energization and main energization. In that case, the energization stop time is preferably 20 to 400 ms.
In the constant current control referred to in the present application, not only the welding current is made constant as shown in FIG. 7, but also the welding current is linearly (continuously) in pre-energization and / or main energization as shown in FIG. This includes cases where the number is increased or decreased. In addition, when increasing / decreasing a welding current linearly (continuously), it is preferable that the welding current in each energization satisfies the relationship of I1 <I2 on the basis of the average value.

・ Main welding After the above test welding, main welding is performed. In the main welding, the pre-energization and the main energization are performed based on the time variation curve of the instantaneous calorific value per unit volume and the cumulative calorific value memorized in the pre-energization and main energization of the test welding, respectively. If the instantaneous change in the amount of instantaneous heat is along the reference time change curve, welding is performed as it is, and the welding is terminated.
However, in the pre-energization or the main energization, when the temporal change in the instantaneous calorific value per unit volume deviates from the reference time change curve, the deviation is determined as the remaining pre-energization or the main energization. In order to compensate within the energization time, the accumulated heat generation amount per unit volume in the pre-energization or the main energization matches the cumulative heat generation amount per unit volume determined in advance in the pre-energization or main energization of the test welding, respectively. The energization amount is controlled as follows.
(That is, when pre-energization, when the temporal change in instantaneous calorific value per unit volume deviates from the standard time change curve, to compensate for the deviation within the remaining pre-energization time, The energization amount is controlled so that the accumulated heat generation amount per unit volume in the pre-energization coincides with the cumulative heat generation amount per unit volume obtained in advance in the pre-energization of the test welding.
Further, when the time variation of instantaneous calorific value per unit volume deviates from the reference time variation curve during main energization, the deviation is compensated within the remaining energization time of the main energization. The energization amount is controlled so that the accumulated heat generation amount per unit volume in the main energization matches the accumulated heat generation amount per unit volume obtained in advance in the main energization of the test welding. )
As a result, even when the tip of the electrode is worn or the influence of disturbance such as diversion or plate gap is large, a necessary accumulated heat generation amount can be secured and an appropriate nugget diameter can be obtained.

Note that there is no particular limitation on the method of calculating the calorific value, but an example thereof is disclosed in Patent Document 5, and this method can also be adopted in the present invention. The calculation procedure of the calorific value q per unit volume and unit time and the cumulative calorific value Q per unit volume by this method is as follows.
The total thickness of the material to be welded is t, the electrical resistivity of the material to be welded is r, the voltage between the electrodes is V, the welding current is I, and the area where the electrode and the material to be welded are in contact is S. In this case, the welding current has a cross-sectional area 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 the columnar part is obtained by the following equation (1).
q = (V · I) / (S · t) --- (1)
Moreover, the electrical resistance R of this columnar part is calculated | required by following Formula (2).
R = (r · t) / S --- (2)
When the equation (2) is solved for S and is substituted into the equation (1), the calorific value q is expressed by the following equation (3)
q = (V · I · R) / (r · t ² )
= (V ² ) / (r · t ² ) --- (3)
It becomes.

As is apparent from the above equation (3), the calorific value q per unit volume / unit time can be calculated from the voltage V between electrodes, the total thickness t of the workpiece, and the electrical resistivity r of the workpiece, And the area S where the workpiece is in contact is not affected. In addition, although the calorific value is calculated from the interelectrode voltage V in the expression (3), the calorific value q can also be calculated from the interelectrode current I, and at this time, the area S where the electrode and the workpiece are in contact with each other Need not be used. And if the calorific value q per unit volume and unit time is accumulated over the energization period, the cumulative calorific value Q per unit volume applied to welding is 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 workpiece are in contact.
The case where the cumulative heat generation amount 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.

  The conditions other than the welding current in the main welding (the energization time and the set pressure in the pre-energization and the main energization) may be the same as the conditions in the test welding.

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

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

Examples according to embodiments of the present invention will be described below.
The conditions of the examples are employed to confirm the feasibility and effects of the present invention, and the present invention is not limited to the conditions of these examples. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
Resistance spot welding was performed on the two-layer or three-layer metal plate assembly shown in Table 1 under the conditions shown in Table 2 to produce a welded joint.
Here, the test welding was performed in a state simulating disturbance as shown in FIGS. 1 to 4 or in a state without disturbance as shown in FIGS. In the figure, reference numerals 11 to 13 are metal plates, 14 are electrodes, 15 is a spacer, and 16 is a welded point. As shown in FIGS. 1 and 2, the number of welded points 16 is two, and the welding position (center between the electrodes) is intermediate between the already welded points (the distance L to the already welded point is the same). Adjusted. It should be noted that the nugget diameter between the metal plates at the weld point (in the case of a three-layer plate assembly, between the thinnest metal plate of the plate assemblies and the metal plate in contact therewith (for example, plate assembly No. In this case, the nugget diameter) between the metal plates 11 and 12) is 4√t ′ (t ′: the thickness (mm) of the thin metal plate of the two adjacent metal plates. In the case of this plate assembly, the thickness (mm) of the thinnest metal plate in the plate assembly was used.
Moreover, in FIG.3 and FIG.4, the spacer 15 was inserted between each metal plates 11-13, and it clamped from the upper and lower sides (not shown), and provided the clearance gap which becomes various clearance gap thickness tg ( In the case of a three-layer plate assembly, the gap thickness tg between the metal plates 11 and 12 and the gap thickness tg between the metal plates 12 and 13 are the same value). The plate gap distance was 60 mm.
Furthermore, in the test welding, the main energization only, or the pre-energization and the main energization are performed by constant current control under the conditions shown in Table 2, and the time variation curve of the instantaneous calorific value per unit volume and the cumulative calorific value are obtained. I remembered it. In some conditions, an energization stop time between pre-energization and main energization was provided.

In addition, in this welding, welding was performed based on the time change curve of the instantaneous calorific value per unit volume memorized in the test welding and the cumulative calorific value. Here, conditions such as energization time, applied pressure, energization stop time between pre-energization and main energization are the same in test welding and main welding.
An inverter DC resistance spot welder was used as the welding machine, and a chromium copper electrode having a DR tip diameter of 6 mm was used as the electrode.

For each of the obtained joints, the welded portion was cut and the cross section was etched, then observed with an optical microscope, and the nugget diameter between the metal plates (however, in the three-layer plate assembly, the thinnest metal plate and the The target diameter is 5√t 'or more (t': the thickness of the thin metal plate of the two adjacent metal plates (mm)), but the three layers overlap. In the case of this plate assembly, the case of the thinnest metal plate thickness (mm) of the plate assembly and no occurrence of scattering was evaluated as ◎.
A case where the nugget diameter was 4.5√t ′ or more and less than 5√t ′ and no scattering occurred was evaluated as “good”. On the other hand, the case where the nugget diameter was less than 4.5√t ′ or scattering occurred was evaluated as x.

In each of the invention examples, a nugget having a diameter of 4.5√t ′ or more is obtained without occurrence of scattering for a wide range of disturbance states, and adaptive control of the main welding is performed for a wide range of disturbance states. It was possible to match the heat quantity pattern of the welded part at the time of welding with the heat quantity pattern in the test welding.
On the other hand, in the comparative example, depending on the state of disturbance, the occurrence of scattering or a nugget with a sufficient diameter cannot be obtained. It was not possible to match the heat quantity pattern of the heat quantity pattern in the test welding.

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

Claims (5)

It is a resistance spot welding method in which a material to be welded in which a plurality of metal plates are overlapped is sandwiched between a pair of electrodes, and energized while being pressed and joined.
The main welding and the test welding prior to the main welding are performed, and in the main welding and the test welding, pre-energization and main energization are performed,
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 variation curve of instantaneous calorific value per unit volume and the cumulative calorific value per unit volume, which are calculated from the electrical characteristics between the electrodes when an appropriate nugget is formed in the pre-energization and the main energization, respectively. Remember,
In the main welding,
Pre-energization and main energization are performed on the basis of the time variation curve of the instantaneous calorific value per unit volume and the cumulative calorific value memorized 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 determined as the remaining pre-energization or main energization time. So that the accumulated heat generation amount per unit volume in the pre-energization or the main energization matches the cumulative heat generation amount per unit volume determined in advance in the pre-energization or the main energization of the test welding. Control the energization amount,
Resistance spot welding method.   2. The resistance spot welding method according to claim 1, wherein a relation of I1 <I2 is satisfied, where I1 is a pre-energization welding current for the test welding and I2 is a main current for the test welding.   The resistance spot welding method according to claim 1 or 2, wherein the test welding is performed in a state where there is an already-welded point at a position 6 to 30 mm away from a welding position.   The resistance spot welding method according to claim 1 or 2, wherein the test welding is performed in a state where there is a gap of 0.2 to 3.0 mm on a mating surface between the metal plates to be welded.   The manufacturing method of the welding member which joins the several metal plate piled up by the resistance spot welding method in any one of Claims 1-4.

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