Resistance spot welding method and weld member production method
11623298 · 2023-04-11
Assignee
Inventors
Cpc classification
B23K11/24
PERFORMING OPERATIONS; TRANSPORTING
B23K11/257
PERFORMING OPERATIONS; TRANSPORTING
B23K11/115
PERFORMING OPERATIONS; TRANSPORTING
B23K11/255
PERFORMING OPERATIONS; TRANSPORTING
International classification
Abstract
A resistance spot welding method comprises: performing test welding; and performing actual welding after the test welding. The test welding is performed under each of two or more welding conditions. In the actual welding, preliminary current passage is performed by constant current control in the same current pattern as in the preliminary current passage of the test welding, an electrical property between the electrodes in the preliminary current passage in the actual welding and an electrical property between the electrodes stored in the preliminary current passage in the test welding are compared for each welding condition to set a target in main current passage in the actual welding, and thereafter adaptive control welding is performed to control a current passage amount as the main current passage.
Claims
1. A resistance spot welding method of squeezing, by a pair of electrodes, parts to be welded which are a plurality of overlapping metal sheets, and passing a current while applying an electrode force to join the parts to be welded, the resistance spot welding method comprising: performing test welding; and performing actual welding after the test welding, wherein the test welding is performed under each of two or more welding conditions, at least one welding condition is that welding is performed in a simulated state of disturbance, and another welding condition is that welding is performed in a state of no current shunting or a sheet gap, in the test welding, for each of the welding conditions: preliminary current passage is performed by constant current control in a same current pattern, and an electrical property between the electrodes in the preliminary current passage is stored; and thereafter main current passage is performed by constant current control, and a time variation curve of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume that are calculated from an electrical property between the electrodes in forming an appropriate nugget are stored, and in the actual welding: preliminary current passage is performed by constant current control in the same current pattern as in the preliminary current passage of the test welding, an electrical property between the electrodes in the preliminary current passage in the actual welding and an electrical property between the electrodes stored in the preliminary current passage in the test welding are compared to determine a difference therebetween for each of the welding conditions of the test welding, and a time variation curve of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume in the main current passage in the test welding that are stored for a welding condition corresponding to a smallest difference are set as a target in main current passage in the actual welding; and thereafter adaptive control welding is performed to control a current passage amount according to the target, as the main current passage in the actual welding.
2. The resistance spot welding method according to claim 1, wherein in the adaptive control welding, welding is performed with the time variation curve of the instantaneous amount of heat generated per unit volume and the cumulative amount of heat generated being set as the target, and in the case where an amount of time variation of an instantaneous amount of heat generated per unit volume differs from the time variation curve, the current passage amount is controlled in order to compensate for the difference from the time variation curve within a remaining welding time so that a cumulative amount of heat generated per unit volume in the main current passage in the actual welding matches the cumulative amount of heat generated per unit volume set as the target.
3. The resistance spot welding method according to claim 1, wherein the test welding is performed under each of three or more welding conditions.
4. The resistance spot welding method according to claim 1, wherein a relationship
Fp<Fm is satisfied, where Fp is a set electrode force in the preliminary current passage in the test welding and Fm is a set electrode force in the main current passage in the test welding.
5. A weld member production method comprising joining a plurality of overlapping metal sheets by the resistance spot welding method according to claim 1.
6. The resistance spot welding method according to claim 2, wherein the test welding is performed under each of three or more welding conditions.
7. The resistance spot welding method according to claim 2, wherein a relationship
Fp<Fm is satisfied, where Fp is a set electrode force in the preliminary current passage in the test welding and Fm is a set electrode force in the main current passage in the test welding.
8. The resistance spot welding method according to claim 3, wherein a relationship
Fp<Fm is satisfied, where Fp is a set electrode force in the preliminary current passage in the test welding and Fm is a set electrode force in the main current passage in the test welding.
9. The resistance spot welding method according to claim 6, wherein a relationship
Fp<Fm is satisfied, where Fp is a set electrode force in the preliminary current passage in the test welding and Fm is a set electrode force in the main current passage in the test welding.
10. A weld member production method comprising joining a plurality of overlapping metal sheets by the resistance spot welding method according to claim 2.
11. A weld member production method comprising joining a plurality of overlapping metal sheets by the resistance spot welding method according to claim 3.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) In the accompanying drawings:
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DETAILED DESCRIPTION
(12) The presently disclosed techniques will be described below by way of embodiments.
(13) One of the disclosed embodiments relates to a resistance spot welding method of squeezing, by a pair of electrodes, parts to be welded which are a plurality of overlapping metal sheets, and passing a current while applying an electrode force to join the parts to be welded. The resistance spot welding method comprises: performing test welding; and performing actual welding after the test welding. The test welding is performed under each of two or more welding conditions. In the test welding, for each of the welding conditions: preliminary current passage is performed by constant current control in a same current pattern, and an electrical property between the electrodes in the preliminary current passage is stored; and thereafter main current passage is performed by constant current control, and a time variation curve of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume that are calculated from an electrical property between the electrodes in forming an appropriate nugget are stored. In the actual welding: preliminary current passage is performed by constant current control in the same current pattern as in the preliminary current passage of the test welding, an electrical property between the electrodes in the preliminary current passage in the actual welding and an electrical property between the electrodes stored in the preliminary current passage in the test welding are compared to determine a difference therebetween for each of the welding conditions of the test welding, and a time variation curve of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume in the main current passage in the test welding that are stored for a welding condition corresponding to a smallest difference are set as a target in main current passage in the actual welding; and thereafter adaptive control welding is performed to control a current passage amount according to the target, as the main current passage in the actual welding.
(14) Any welding device that includes a pair of upper and lower electrodes and is capable of freely controlling each of the electrode force and the welding current during welding may be used in the resistance spot welding method according to one of the disclosed embodiments. The force mechanism (air cylinder, servomotor, etc.), the type (stationary, robot gun, etc.), the electrode shape, and the like are not limited.
(15) Herein, the “electrical property between the electrodes” means the resistance between electrodes or the voltage between electrodes.
(16) The test welding and the actual welding in the resistance spot welding method according to one of the disclosed embodiments will be described below.
(17) Test Welding
(18) The test welding is performed under each of two or more welding conditions and preferably under each of three or more welding conditions. For each welding condition, preliminary current passage and main current passage are performed.
(19) The preliminary current passage is performed by constant current control, and the electrical property between the electrodes in the preliminary current passage is stored.
(20) Thereafter, the main current passage is performed by constant current control, and a time variation curve of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume that are calculated from the electrical property between the electrodes in forming an appropriate nugget are stored.
(21) The combination of the welding conditions in the test welding where data are stored is preferably made up of at least one welding condition of performing welding in a simulated state of a disturbance expected in the actual welding and a welding condition of performing welding in a state of no disturbance.
(22) Examples of the disturbance expected in the actual welding include the above-mentioned disturbances such as current shunting and a sheet gap, e.g. an existing weld within 40 mm from the welding position (electrode center position) and a gap of 0.2 mm or more between the mating surfaces of the steel sheets as the parts to be welded.
(23) For example, in the case where it is expected that there is an existing weld within 40 mm from the welding position and the distance therebetween varies for each welding position, preferably one welding condition in the test welding is that welding is performed in a state in which an existing weld is present at a position of 6 mm to 30 mm (preferably 6 mm to 20 mm) away from the welding position, and another welding condition is that welding is performed in a state of no disturbance. Typically, the lower limit of the distance from the welding position to the existing weld expected is about 6 mm. The number of existing welds simulated in the test welding may be 1, or 2 or more. No upper limit is placed on the number of existing welds simulated in the test welding, and the number is preferably the largest number of existing welds expected (specifically, about 3). The size of the existing weld simulated in the test welding may be approximately the same as the size of the existing weld expected.
(24) Herein, the distance between the welding position and the existing weld is the distance between the respective centers of the welding position and the existing weld.
(25) In the case where it is expected that there is a gap of 0.2 mm or more between the mating surfaces of the metal sheets as the parts to be welded and the gap varies for each welding position, preferably one welding condition in the test welding is that welding is performed in a state in which there is a gap of 0.2 mm to 3.0 mm (preferably 0.5 mm to 3.0 mm) between the mating surfaces of the metal sheets as the parts to be welded, and another welding condition is that welding is performed in a state of no disturbance. The upper limit of the gap between the mating surfaces of the metal sheets as the parts to be welded as expected is practically about 3.0 mm.
(26) Herein, the gap between the mating surfaces of the metal sheets is the gap between the mating surfaces of the metal sheets (the distance between the mating surfaces) at the welding position before the electrode force is applied.
(27) Depending on variations of expected disturbances and the like, preferably one welding condition in the test welding is that welding is performed in a state in which an existing weld is present as mentioned above, another welding condition is that welding is performed in a state in which there is a gap between the mating surfaces of the metal sheets as the parts to be welded as mentioned above, and yet another welding condition is that welding is performed in a state of no disturbance. Thus, an appropriate time variation curve can be selected by effectively responding to various disturbance states.
(28) The current pattern in the preliminary current passage is not limited as long as constant current control is used. The target in the main current passage in the actual welding is set depending on the electrical property between the electrodes, etc. in this preliminary current passage. Accordingly, the current pattern (welding current, welding time, and set electrode force) in the preliminary current passage in the test welding is the same for all welding conditions. An error of about 5% is, however, allowable for each of the welding current, the welding time, and the set electrode force.
(29) To prevent an increase in welding time and excessive heat generation during the preliminary current passage, the welding time Tp in the preliminary current passage is preferably 400 ms or less. The welding time Tp is more preferably 200 ms or less. No lower limit is placed on the welding time Tp in the preliminary current passage, but the lower limit is preferably 10 ms. In the case where a nugget is formed in the preliminary current passage, the nugget diameter (mm) is preferably 4√t or less (t: the sheet thickness (mm) of the thinnest steel sheet). Moreover, a welding interval time Tc of 20 ms or more and 1000 ms or less is preferably provided between the preliminary current passage and the subsequent main current passage.
(30) The current pattern in the main current passage is not limited. The current pattern may be divided into two or more steps, and the cumulative amount of heat generated per unit volume may be stored for each step. The current pattern in the main current passage is typically divided into five steps or less.
(31) The set electrode force in the preliminary current passage in the test welding may be the same as the set electrode force in the main current passage, but the relationship
Fp<Fm is preferably satisfied where Fp is the set electrode force in the preliminary current passage in the test welding and Fm is the set electrode force in the main current passage in the test welding.
(32) As mentioned earlier, particularly in the case where the sheet gap between the steel sheets is large, nugget growth in the sheet thickness direction is hindered, and a thin nugget tends to form. Further, with a decrease in the volume of a fusion zone, the specific resistance of the weld tends to decrease, causing a decrease in voltage between electrodes. If the voltage between electrodes decreases, in the case of performing adaptive control welding using, as the target, the time variation of the instantaneous amount of heat generated per unit volume and the cumulative amount of heat generated per unit volume, the welding control unit recognizes such a decrease in voltage between electrodes as a decrease in the amount of heat generated. Consequently, the welding control unit rapidly increases the welding current even when actually an appropriate nugget diameter has been obtained. This can cause expulsion.
(33) In view of this, it is important in the present disclosure that the preliminary current passage is performed before the main current passage, and the time variation curve, etc. as the target in the main current passage in the actual welding is selected from the electrical property between the electrodes in the preliminary current passage that takes into account the effect of a disturbance such as the foregoing sheet gap between the steel sheets.
(34) However, if the set electrode force Fp in the preliminary current passage in the test welding is large, particularly if the set electrode force Fp in the preliminary current passage is more than the set electrode force Fm in the main current passage, the current passage state (specifically, the contact diameter between the steel sheets) in the preliminary current passage in the case where there is a sheet gap is close to the current passage state in the preliminary current passage in the case where there is no sheet gap, and the effect of a disturbance is not sufficiently reflected in the electrical property between the electrodes in the preliminary current passage. This may make it difficult to appropriately select the time variation curve, etc. as the target in the main current passage in the actual welding.
(35) If the set electrode force Fp in the preliminary current passage is less than the set electrode force Fm in the main current passage in the test welding, on the other hand, the effect of a disturbance is appropriately reflected in the electrical property between the electrodes in the preliminary current passage, so that the time variation curve, etc. as the target in the main current passage in the actual welding can be selected more appropriately.
(36) Therefore, it is preferable to satisfy the relationship Fp<Fm. It is more preferable to satisfy the relationship Fp<0.9×Fm. No lower limit is placed on Fp, but the lower limit is preferably 0.1×Fm.
(37) The set electrode force Fm in the main current passage is preferably 1.0 kN or more. The set electrode force Fm in the main current passage is preferably 10.0 kN or less.
(38) To prevent expulsion in the preliminary current passage in the test welding, it is preferable to satisfy the relationship
Ip<Im where Ip is the welding current in the preliminary current passage and Im is the welding current in the main current passage in the test welding.
(39) Particularly when welding high tensile strength steel sheets or the like for which the appropriate current range is narrow, it is more preferable to satisfy the relationship
Ip<0.8×Im.
(40) In the case where the current pattern in the main current passage is divided into two or more steps, Im is an average value of the welding currents in all current passage steps. For example, in the case where the current pattern in the main current passage is divided into two steps, Im=(I1+I2)/2, where I1 and I2 are the respective welding currents in the first and second current passage steps. No lower limit is placed on Ip, but the lower limit is preferably 0.2×Im.
(41) The welding current Im in the main current passage is preferably 4.0 kA or more. The welding current Im in the main current passage is preferably 12.0 kA or less.
(42) The test welding conditions other than the above are not limited, and may be set as appropriate by performing a preliminary welding test for the same steel type and thickness as the parts to be welded, under various conditions by constant current control in each of a state of no disturbance and the foregoing simulated state of a disturbance.
(43) Actual Welding
(44) After the test welding, the actual welding is performed.
(45) In the actual welding, first, preliminary current passage is performed by constant current control in the same current pattern as in the preliminary current passage of the test welding. The electrical property between the electrodes in the preliminary current passage in the actual welding and the electrical property between the electrodes stored in the preliminary current passage in the test welding are compared to determine the difference therebetween for each of the welding conditions of the test welding, and a time variation curve of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume in the main current passage in the test welding that are stored for a welding condition corresponding to the smallest difference are set as the target in the main current passage in the actual welding.
(46) In the case where current shunting to an existing weld occurs, typically the voltage between electrodes decreases as compared with the case where no current shunting occurs. Accordingly, for example, an average value of the voltage between electrodes for a predetermined time (100 ms) from the start of the preliminary current passage stored in the preliminary current passage in the test welding and an average value of the voltage between electrodes for 100 ms from the start of the preliminary current passage in the actual welding are compared to determine the difference therebetween for each welding condition, and a time variation curve of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume in the main current passage in the test welding that are stored for a welding condition corresponding to the smallest difference are set as the target in the main current passage in the actual welding.
(47) A maximum value or amount of time variation of the voltage between electrodes, an average value, maximum value, or amount of time variation of the resistance between electrodes, a cumulative amount of heat generated in the preliminary current passage, or the like may be used as an index for setting the target in the main current passage.
(48) Herein, “preliminary current passage is performed by constant current control in the same current pattern as in the preliminary current passage of the test welding” means that the preliminary current passage in the actual welding is performed by constant current control using the same welding current, welding time, and set electrode force as those in the preliminary current passage in the test welding. An error of about 5% is, however, allowable for each of the welding current, the welding time, and the set electrode force.
(49) Thereafter, adaptive control welding is performed to control the current passage amount according to the target set as a result of the preliminary current passage, as the main current passage.
(50) For example, in the adaptive control welding in the main current passage, welding is performed with the time variation curve of the instantaneous amount of heat generated per unit volume and the cumulative amount of heat generated being set as the target as a result of the preliminary current passage. If the amount of time variation of the instantaneous amount of heat generated per unit volume follows the time variation curve, the welding is continued without change and completed. If the amount of time variation of the instantaneous amount of heat generated per unit volume differs from the time variation curve, the current passage amount is controlled in order to compensate for the difference within a remaining welding time so that the cumulative amount of heat generated per unit volume in the main current passage in the actual welding matches the cumulative amount of heat generated per unit volume set as the target.
(51) The method of calculating the amount of heat generated is not limited. PTL 5 describes an example of the method, which may be used herein. The following is the procedure of calculating the amount q of heat generated per unit volume and per unit time and the cumulative amount Q of heat generated per unit volume according to this method.
(52) Let t be the total thickness of the parts to be welded, r be the electrical resistivity of the parts to be welded, V be the voltage between electrodes, I be the welding current, and S be the contact area of the electrodes and the parts to be welded. In this case, the welding current passes through a columnar portion whose cross-sectional area is S and thickness is t, to generate heat by resistance. The amount q of heat generated per unit volume and per unit time in the columnar portion is given by the following Equation (1):
q=(V.Math.I)/(S.Math.t) (1).
(53) The electrical resistance R of the columnar portion is given by the following Equation (2):
R=(r.Math.t)/S (2).
(54) Solving Equation (2) for S and substituting the solution into Equation (1) yields the amount q of heat generated as indicated by the following Equation (3):
q=(V.Math.I.Math.R)/(r.Math.t.sup.2)=(V.sup.2)/(r.Math.t.sup.2) (3).
(55) As is clear from Equation (3), the amount q of heat generated per unit volume and per unit time can be calculated from the voltage between electrodes V, the total thickness t of the parts to be welded, and the electrical resistivity r of the parts to be welded, and is not affected by the contact area S of the electrodes and the parts to be welded. Although the amount of heat generated is calculated from the voltage between electrodes V in Equation (3), the amount q of heat generated may be calculated from the interelectrode current I. The contact area S of the electrodes and the parts to be welded need not be used in this case, either. By cumulating the amount q of heat generated per unit volume and per unit time for the welding time, the cumulative amount Q of heat generated per unit volume for the welding is obtained. As is clear from Equation (3), the cumulative amount Q of heat generated per unit volume can also be calculated without using the contact area S of the electrodes and the parts to be welded.
(56) Although the above describes the case of calculating the cumulative amount Q of heat generated by the method described in PTL 5, the cumulative amount Q may be calculated by any other method.
(57) In the case where the current pattern in the main current passage in the test welding is divided into two or more steps and the target of adaptive control welding is set based on the data stored in the test welding with a welding condition divided into the two or more steps as mentioned above, the current pattern in the main current passage in the actual welding is preferably divided into two or more steps as with the current pattern in the main current passage in the test welding and the adaptive control welding is preferably performed for each step in the main current passage in the actual welding.
(58) In the adaptive control welding for each step, if the amount of time variation of the instantaneous amount of heat generated per unit volume in the step differs from the time variation curve, the current passage amount is controlled in order to compensate for the difference within a remaining welding time in the step so that the cumulative amount of heat generated per unit volume in the step matches the cumulative amount of heat generated per unit volume in the step in the test welding.
(59) The set electrode force Fm′ in the main current passage may be basically the same as the test welding condition set as the target in the main current passage in the actual welding, but may be different from the test welding condition according to need. It is preferable to satisfy the relationship
Fp′<Fm′
(60) where Fp′ is the set electrode force in the preliminary current passage in the actual welding and Fm′ is the set electrode force in the main current passage in the actual welding. It is more preferable to satisfy the relationship Fp′<0.9×Fm′. No lower limit is placed on Fp′, but the lower limit is preferably 0.1×Fm′.
(61) The set electrode force Fm′ in the main current passage is preferably 1.0 kN or more. The set electrode force Fm′ in the main current passage is preferably 10.0 kN or less.
(62) The parts to be welded that are used are not limited. The resistance spot welding method may be used for welding of steel sheets and coated steel sheets having various strengths from mild steel to ultra high tensile strength steel and light metal sheets of aluminum alloys and the like. The resistance spot welding method may also be used for a sheet combination of three or more overlapping steel sheets.
(63) Moreover, a subsequent current may be applied to heat-treat the weld after the current for nugget formation. The current passage condition in this case is not limited, and the magnitude relationships with the welding currents in the preceding steps are not limited. A current pattern of an upslope or a downslope may be used. The electrode force in the current passage may be constant, or be changed as appropriate.
(64) By joining a plurality of overlapping metal sheets by the resistance spot welding method described above, various weld members, in particular weld members of automotive parts and the like, are produced while stably ensuring a desired nugget diameter by effectively responding to variations in the disturbance state.
EXAMPLES
(65) Test welding was performed under the conditions listed in Table 1 for each sheet combination of two or three overlapping metal sheets listed in Table 1, and then actual welding was performed under the conditions listed in Table 2 for each sheet combination of two or three overlapping metal sheets listed in Table 2, to produce a weld joint.
(66) The test welding and the actual welding were performed in a state of no disturbance as illustrated in each of
(67) In the test welding, preliminary current passage and main current passage were performed by constant current control for each welding condition, in each of the patterns of current and electrode force illustrated in
(68) In the actual welding, first, preliminary current passage was performed by constant current control in the same current pattern as in the preliminary current passage of the test welding. For the voltage between electrodes (average value) as an index to set the target in the main current passage, the value in the preliminary current passage in the actual welding and the value stored in the preliminary current passage in the test welding were compared to determine the difference therebetween for each welding condition (compared test welding No. in Table 2), and the time variation curve of the instantaneous amount of heat generated per unit volume and the cumulative amount of heat generated per unit volume stored for the welding condition corresponding to the smallest difference were set as the target in the main current passage in the actual welding. Thereafter, adaptive control welding was performed to control the current passage amount according to the target, as the main current passage in the actual welding. In No. 3 in Table 2, preliminary current passage was not performed. The conditions such as the welding time and the electrode force in the main current passage and the welding interval time between the preliminary current passage and the main current passage were the same in the test welding and the actual welding. In the case of setting the target of adaptive control welding based on a test welding condition divided into two or more steps, adaptive control welding for each step was performed in the main current passage in the actual welding.
(69) An inverter DC resistance spot welder was used as the welder, and chromium copper electrodes with 6 mm face diameter DR-shaped tips were used as the electrodes.
(70) For each obtained joint, the weld was cut and etched in section, and then observed with an optical microscope. Each sample in which the nugget diameter between the metal sheets was not less than 4.5√t′ as a target diameter (t′: the sheet thickness (mm) of the thinner metal sheet of adjacent two metal sheets) and no expulsion occurred was evaluated as good. Each sample in which any nugget diameter was less than 4.5√t′ or expulsion occurred was evaluated as poor. For a sheet combination of three overlapping sheets, evaluation was conducted based on the nugget diameter between the thinnest outer metal sheet and the metal sheet adjacent to it.
(71) TABLE-US-00001 TABLE 1 Test welding condition Preliminary current passage Average Sheet combination value of Steel sheet Steel sheet Steel sheet Set voltage Welding Test of reference of reference of reference electrode Welding Welding between interval welding sign 11 in sign 12 in sign 13 in force Fp current time Tp electrodes time Tc No. the drawings the drawings the drawings (kN) Ip (kA) (ms) (V) (ms) A 980 MPa-grade 980 MPa-grade 5.0 4.0 100 1.2 100 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) B 980 MPa-grade 980 MPa-grade 5.0 4.0 100 1.4 100 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) C 980 MPa-grade 980 MPa-grade 5.0 4.0 100 0.9 100 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) D 980 MPa-grade 980 MPa-grade cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) E 1180 MPa-grade 1180 MPa-grade 5.0 2.0 100 1.9 140 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) F 1180 MPa-grade 1180 MPa-grade 5.0 2.0 100 1.4 140 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) G 1180 MPa-grade 1180 MPa-grade 5.0 2.0 100 2.0 140 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) H 1180 MPa-grade 1180 MPa-grade 3.0 2.0 120 1.7 160 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) I 1180 MPa-grade 1180 MPa-grade 3.0 2.0 120 1.4 160 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) J 1180 MPa-grade 1180 MPa-grade 3.0 2.0 120 2.5 160 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) K 1470 MPa-grade 1470 MPa-grade 3.0 2.0 100 0.5 160 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) L 1470 MPa-grade 1470 MPa-grade 3.0 2.0 100 0.3 160 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) M 1470 MPa-grade 1470 MPa-grade 3.0 2.0 100 0.9 160 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) N 270 MPa-grade 980 MPa-grade 980 MPa-grade 2.5 2.5 80 1.2 160 GA steel sheet GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: (sheet thickness: 0.7 mm) 1.4 mm) 1.2 mm) O 270 MPa-grade 980 MPa-grade 980 MPa-grade 2.5 2.5 80 0.9 160 GA steel sheet GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: (sheet thickness: 0.7 mm) 1.4 mm) 1.2 mm) P 270 MPa-grade 980 MPa-grade 980 MPa-grade 2.5 2.5 80 1.6 160 GA steel sheet GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: (sheet thickness: 0.7 mm) 1.4 mm) 1.2 mm) Q 1470 MPa-grade 1470 MPa-grade 3.0 3.0 200 0.4 200 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.0 mm) 1.0 mm) R 1470 MPa-grade 1470 MPa-grade 3.0 3.0 200 0.3 200 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.0 mm) 1.0 mm) S 1470 MPa-grade 1470 MPa-grade 3.0 3.0 200 0.5 200 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.0 mm) 1.0 mm) T 1800 MPa-grade 1800 MPa-grade 3.0 3.0 60 1.4 100 Zn—Ni-coated hot Zn—Ni-coated hot stamp steel sheet stamp steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) U 1800 MPa-grade 1800 MPa-grade 3.0 3.0 60 1.1 100 Zn—Ni-coated hot Zn—Ni-coated hot stamp steel sheet stamp steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) V 1800 MPa-grade 1800 MPa-grade 3.0 3.0 60 1.9 100 Zn—Ni-coated hot Zn—Ni-coated hot stamp steel sheet stamp steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) W 270 MPa-grade 2000 MPa-grade 1180 MPa-grade 3.0 3.0 100 1.6 240 GA steel sheet Zn—Ni-coated hot GA steel sheet (sheet thickness: stamp steel sheet (sheet thickness: 0.7 mm) (sheet thickness: 1.6 mm) 1.4 mm) X 270 MPa-grade 2000 MPa-grade 1180 MPa-grade 3.0 3.0 100 1.2 240 GA steel sheet Zn—Ni-coated hot GA steel sheet (sheet thickness: stamp steel sheet (sheet thickness: 0.7 mm) (sheet thickness: 1.6 mm) 1.4 mm) Y 270 MPa-grade 2000 MPa-grade 1180 MPa-grade 3.0 3.0 100 2.0 240 GA steel sheet Zn—Ni-coated hot GA steel sheet (sheet thickness: stamp steel sheet (sheet thickness: 0.7 mm) (sheet thickness: 1.6 mm) 1.4 mm) Test welding condition Main current passage Set Test electrode Welding Welding Welding Welding welding force Fm current time T1 current time T2 Disturbance No. (kN) I1 (kA) (ms) I2 (kA) (ms) state A 5.0 7.5 320 None B 5.0 9.0 320 Existing weld L = 10 mm C 5.0 7.0 320 Sheet gap tg = 1.0 mm D 5.0 7.5 320 None E 5.0 5.0 140 8.0 260 None F 5.0 7.0 140 9.0 260 Existing weld L = 10 mm G 5.0 4.0 160 7.5 260 Sheet gap tg = 1.0 mm H 5.5 8.5 320 None I 5.5 9.5 320 Existing weld L = 10 mm J 5.5 8.0 320 Sheet gap tg = 2.0 mm K 5.0 8.0 320 None L 5.0 9.5 320 Existing weld L = 10 mm M 5.0 5.0 100 8.0 260 Sheet gap tg = 2.0 mm N 5.0 8.2 340 None O 5.0 9.7 340 Existing weld L = 10 mm P 5.0 5.0 120 8.0 260 Sheet gap tg = 1.6 mm Q 4.0 8.0 240 None R 4.0 9.0 240 Existing weld L = 10 mm S 4.0 7.5 240 Sheet gap tg = 1.6 mm T 5.0 4.0 120 6.0 260 None U 5.0 6.0 120 7.5 260 Existing weld L = 10 mm V 5.0 3.5 200 5.7 260 Sheet gap tg = 2.0 mm W 6.0 4.5 180 6.5 280 None X 6.0 6.0 180 8.0 280 Existing weld L = 10 mm Y 6.0 4.0 240 6.0 280 Sheet gap tg = 1.6 mm
(72) TABLE-US-00002 TABLE 2 Actual welding condition Sheet combination Compared Steel sheet Steel sheet Steel sheet Set test of reference of reference of reference electrode Joint welding sign 11 in sign 12 in sign 13 in force No. No. No. the drawings the drawings the drawings Fm′ (kN) 1 1-1 A, B, C 980 MPa-grade 980 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 1-2 980 MPa-grade 980 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 1-3 980 MPa-grade 980 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 1-4 980 MPa-grade 980 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 1-5 980 MPa-grade 980 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 2 2-1 A, B 980 MPa-grade 980 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 2-2 980 MPa-grade 980 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 2-3 980 MPa-grade 980 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 3 3-1 D 980 MPa-grade 980 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 3-2 980 MPa-grade 980 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 3-3 980 MPa-grade 980 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 4 4-1 E, F, G 1180 MPa-grade 1180 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 4-2 1180 MPa-grade 1180 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 4-3 1180 MPa-grade 1180 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 4-4 1180 MPa-grade 1180 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 4-5 1180 MPa-grade 1180 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 5 5-1 H, I, J 1180 MPa-grade 1180 MPa-grade 5.5 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 5-2 1180 MPa-grade 1180 MPa-grade 5.5 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 5-3 1180 MPa-grade 1180 MPa-grade 5.5 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 5-4 1180 MPa-grade 1180 MPa-grade 5.5 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 5-5 1180 MPa-grade 1180 MPa-grade 5.5 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 6 6-1 K, L, M 1470 MPa-grade 1470 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 6-2 1470 MPa-grade 1470 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 6-3 1470 MPa-grade 1470 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 6-4 1470 MPa-grade 1470 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 6-5 1470 MPa-grade 1470 MPa-grade 5.0 cold-rolled cold-rolled steel sheet steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 7 7-1 N, O, P 270 MPa-grade 980 MPa-grade 980 MPa-grade 5.0 GA steel sheet GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: (sheet thickness: 0.7 mm) 1.4 mm) 1.2 mm) 7-2 270 MPa-grade 980 MPa-grade 980 MPa-grade 5.0 GA steel sheet GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: (sheet thickness: 0.7 mm) 1.4 mm) 1.2 mm) 7-3 270 MPa-grade 980 MPa-grade 980 MPa-grade 5.0 GA steel sheet GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: (sheet thickness: 0.7 mm) 1.4 mm) 1.2 mm) 7-4 270 MPa-grade 980 MPa-grade 980 MPa-grade 5.0 GA steel sheet GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: (sheet thickness: 0.7 mm) 1.4 mm) 1.2 mm) 7-5 270 MPa-grade 980 MPa-grade 980 MPa-grade 5.0 GA steel sheet GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: (sheet thickness: 0.7 mm) 1.4 mm) 1.2 mm) 8 8-1 Q, R, S 1470 MPa-grade 1470 MPa-grade 4.0 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.0 mm) 1.0 mm) 8-2 1470 MPa-grade 1470 MPa-grade 4.0 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.0 mm) 1.0 mm) 8-3 1470 MPa-grade 1470 MPa-grade 4.0 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.0 mm) 1.0 mm) 8-4 1470 MPa-grade 1470 MPa-grade 4.0 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.0 mm) 1.0 mm) 8-5 1470 MPa-grade 1470 MPa-grade 4.0 GA steel sheet GA steel sheet (sheet thickness: (sheet thickness: 1.0 mm) 1.0 mm) 9 9-1 T, U, V 1800 MPa-grade 1800 MPa-grade 5.0 Zn—Ni-coated hot Zn—Ni-coated hot stamp steel sheet stamp steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 9-2 1800 MPa-grade 1800 MPa-grade 5.0 Zn—Ni-coated hot Zn—Ni-coated hot stamp steel sheet stamp steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 9-3 1800 MPa-grade 1800 MPa-grade 5.0 Zn—Ni-coated hot Zn—Ni-coated hot stamp steel sheet stamp steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 9-4 1800 MPa-grade 1800 MPa-grade 5.0 Zn—Ni-coated hot Zn—Ni-coated hot stamp steel sheet stamp steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 9-5 1800 MPa-grade 1800 MPa-grade 5.0 Zn—Ni-coated hot Zn—Ni-coated hot stamp steel sheet stamp steel sheet (sheet thickness: (sheet thickness: 1.6 mm) 1.6 mm) 10 10-1 W, X, Y 270 MPa-grade 2000 MPa-grade 1180 MPa-grade 6.0 GA steel sheet Zn—Ni-coated hot GA steel sheet (sheet thickness: stamp steel sheet (sheet thickness: 0.7 mm) (sheet thickness: 1.6 mm) 1.4 mm) 10-2 270 MPa-grade 2000 MPa-grade 1180 MPa-grade 6.0 GA steel sheet Zn—Ni-coated hot GA steel sheet (sheet thickness: stamp steel sheet (sheet thickness: 0.7 mm) (sheet thickness: 1.6 mm) 1.4 mm) 10-3 270 MPa-grade 2000 MPa-grade 1180 MPa-grade 6.0 GA steel sheet Zn—Ni-coated hot GA steel sheet (sheet thickness: stamp steel sheet (sheet thickness: 0.7 mm) (sheet thickness: 1.6 mm) 1.4 mm) 10-4 270 MPa-grade 2000 MPa-grade 1180 MPa-grade 6.0 GA steel sheet Zn—Ni-coated hot GA steel sheet (sheet thickness: stamp steel sheet (sheet thickness: 0.7 mm) (sheet thickness: 1.6 mm) 1.4 mm) 10-5 270 MPa-grade 2000 MPa-grade 1180 MPa-grade 6.0 GA steel sheet Zn—Ni-coated hot GA steel sheet (sheet thickness: stamp steel sheet (sheet thickness: 0.7 mm) (sheet thickness: 1.6 mm) 1.4 mm) Actual welding condition Test welding No. followed in main Nugget Joint Disturbance current diameter No. No. state passage (mm) Expulsion Evaluation Remarks 1 1-1 Existing weld A 5.9 None Good Ex. L = 40 mm 1-2 Existing weld B 6.0 None Good L = 7.5 mm 1-3 Sheet gap A 6.1 None Good tg = 0.5 mm 1-4 Sheet gap C 5.9 None Good tg = 1.0 mm 1-5 None A 6.2 None Good 2 2-1 Existing weld A 5.9 None Good Ex. L = 40 mm 2-2 Existing weld B 6.0 None Good L = 7.5 mm 2-3 None A 6.2 None Good 3 3-1 Existing weld D 4.7 None Poor Comp. L = 7.5 mm Ex. 3-2 None D 5.8 None Good 3-3 Sheet gap D 6.7 Occurred Poor tg = 1.0 mm 4 4-1 Existing weld E 6.2 None Good Ex. L = 40 mm 4-2 Existing weld F 6.1 None Good L = 7.5 mm 4-3 Sheet gap E 6.5 None Good tg = 0.5 mm 4-4 Sheet gap G 6.2 None Good tg = 1.0 mm 4-5 None E 6.4 None Good 5 5-1 Existing weld H 6.3 None Good Ex. L = 40 mm 5-2 Existing weld I 6.2 None Good L = 7.5 mm 5-3 Sheet gap J 6.1 None Good tg = 1.8 mm 5-4 Sheet gap J 5.8 None Good tg = 2.0 mm 5-5 None H 6.4 None Good 6 6-1 Existing weld K 6.0 None Good Ex. L = 40 mm 6-2 Existing weld L 6.4 None Good L = 7.5 mm 6-3 Sheet gap M 5.9 None Good tg = 2.0 mm 6-4 Sheet gap M 6.1 None Good tg = 1.8 mm 6-5 None K 6.2 None Good 7 7-1 Existing weld N 4.4 None Good Ex. L = 40 mm 7-2 Existing weld O 4.1 None Good L = 7.5 mm 7-3 Sheet gap N 4.4 None Good tg = 0.5 mm 7-4 Sheet gap P 3.9 None Good tg = 2.0 mm 7-5 None N 4.2 None Good 8 8-1 Existing weld Q 4.8 None Good Ex. L = 40 mm 8-2 Existing weld R 5.0 None Good L = 7.5 mm 8-3 Sheet gap Q 4.9 None Good tg = 0.5 mm 8-4 Sheet gap S 4.7 None Good tg = 2.0 mm 8-5 None Q 5.0 None Good 9 9-1 Existing weld T 6.0 None Good Ex. L = 40 mm 9-2 Existing weld U 5.9 None Good L = 7.5 mm 9-3 Sheet gap T 6.2 None Good tg = 0.5 mm 9-4 Sheet gap V 6.1 None Good tg = 2.0 mm 9-5 None T 6.0 None Good 10 10-1 Existing weld W 4.2 None Good Ex. L = 40 mm 10-2 Existing weld X 4.3 None Good L = 7.5 mm 10-3 Sheet gap W 4.1 None Good tg = 0.5 mm 10-4 Sheet gap Y 4.5 None Good tg = 2.0 mm 10-5 None W 4.1 None Good
(73) In all Examples (Ex.), no expulsion occurred, and a nugget with a diameter of 4.5√t′ or more was obtained, regardless of the disturbance state. In Comparative Examples (Comp. Ex.), a nugget with a diameter of 4.5√t′ or more was obtained without expulsion in a state of no disturbance, but expulsion occurred or a nugget with a sufficient diameter was not formed in the case where the effect of a disturbance was significant.
(74) The same results as above were obtained in the case where an average value of resistance between electrodes was stored in the preliminary current passage in the test welding, and an average value of resistance between electrodes in the preliminary current passage in the actual welding and an average value of resistance between electrodes stored in the preliminary current passage in the test welding were compared for each welding condition to set the target of the time variation curve of the instantaneous amount of heat generated and the cumulative amount of heat generated when performing adaptive control welding in the main current passage in the actual welding.
REFERENCE SIGNS LIST
(75) 11, 12, 13 metal sheet
(76) 14 electrode
(77) 15 spacer
(78) 16 existing weld