RESISTANCE SPOT WELDING METHOD AND WELD MEMBER PRODUCTION METHOD
20210260684 · 2021-08-26
Assignee
Inventors
- Chikaumi SAWANISHI (Chiyoda-ku, Tokyo, JP)
- Hiroshi Matsuda (Chiyoda-ku, Tokyo, JP)
- Rinsei IKEDA (Chiyoda-ku, Tokyo, JP)
Cpc classification
B23K11/24
PERFORMING OPERATIONS; TRANSPORTING
B23K11/115
PERFORMING OPERATIONS; TRANSPORTING
B23K11/258
PERFORMING OPERATIONS; TRANSPORTING
B23K11/16
PERFORMING OPERATIONS; TRANSPORTING
International classification
Abstract
A resistance spot welding method comprises: performing test welding; and performing actual welding after the test welding, wherein in subsequent current passage in the test welding, current passage is performed by constant current control under a condition: 0.5≤Vtp/Vtm≤2.0 when tc<800 ms; 0.5−0.3×(tc−800)/800≤Vtp/Vtm≤2.0−0.5×(tc−800)/800 when 800 ms≤tc<1600 ms; and 0.2≤Vtp/Vtm≤1.5 when tc≥1600 ms, where Vtm is an average value of a voltage between the electrodes in main current passage in the test welding, and Vtp is an average value of a voltage between the electrodes in the subsequent current passage in the test welding, and wherein in main current passage in the actual welding, adaptive control welding is performed, and in subsequent current passage in the actual welding, current passage is performed by constant current control under a condition: 0.8×Itp≤Imp≤1.2×Itp, where Itp is a current in the subsequent current passage in the test welding, and Imp is a current in the subsequent current passage in the actual welding.
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 (a) in the test welding, main current passage for nugget formation and subsequent current passage for subsequent heat treatment are performed, in the main current passage in the test welding, 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 by performing current passage by constant current control are stored, and in the subsequent current passage in the test welding, current passage is performed by constant current control under a condition:
0.5≤Vtp/Vtm≤2.0 when tc<800 ms;
0.5−0.3×(tc−800)/800≤Vtp/Vtm≤2.0−0.5×(tc−800)/800 when 800 ms≤tc<1600 ms; and
0.2≤Vtp/Vtm≤1.5 when tc≥1600 ms, where Vtm is an average value of a voltage between the electrodes in the main current passage in the test welding, Vtp is an average value of a voltage between the electrodes in the subsequent current passage in the test welding, and tc is a cooling time between the main current passage and the subsequent current passage in the test welding, and (b) thereafter, in the actual welding, main current passage for nugget formation and subsequent current passage for subsequent heat treatment are performed, in the main current passage in the actual welding, the time variation curve of the instantaneous amount of heat generated per unit volume and the cumulative amount of heat generated per unit volume that are stored in the main current passage in the test welding are set as a target, and adaptive control welding is performed to control a current passage amount according to the target, and in the subsequent current passage in the actual welding, current passage is performed by constant current control under a condition:
0.8×Itp≤Imp≤1.2×Itp, where Itp is a current in the subsequent current passage in the test welding, and Imp is a current in the subsequent current passage in the actual welding.
2. The resistance spot welding method according to claim 1, wherein in the adaptive control welding in the main current passage in the actual welding, 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 of the instantaneous amount of heat generated per unit volume set as the target, the current passage amount is controlled in order to compensate for the difference from the time variation curve within a remaining welding time in the main current passage in the actual welding 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 a cooling time is set between the main current passage and the subsequent current passage in the actual welding, and the number of repetitions of a welding interval for the cooling time and the subsequent current passage after the main current passage in the actual welding is two or more times.
4. A weld member production method comprising joining a plurality of overlapping metal sheets by the resistance spot welding method according to claim 1.
5. The resistance spot welding method according to claim 2, wherein a cooling time is set between the main current passage and the subsequent current passage in the actual welding, and the number of repetitions of a welding interval for the cooling time and the subsequent current passage after the main current passage in the actual welding is two or more times.
6. A weld member production method comprising joining a plurality of overlapping metal sheets by the resistance spot welding method according to claim 2.
7. A weld member production method comprising joining a plurality of overlapping metal sheets by the resistance spot welding method according to claim 3.
8. A weld member production method comprising joining a plurality of overlapping metal sheets by the resistance spot welding method according to claim 5.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] In the accompanying drawings:
[0046]
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[0050]
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DETAILED DESCRIPTION
[0058] The presently disclosed techniques will be described below by way of embodiments.
[0059] 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 comprising: performing test welding; and performing actual welding after the test welding, wherein (a) in the test welding, main current passage for nugget formation and subsequent current passage for subsequent heat treatment are performed, in the main current passage in the test welding, 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 by performing current passage by constant current control are stored, and in the subsequent current passage in the test welding, current passage is performed by constant current control under a condition:
0.5≤Vtp/Vtm≤2.0 when tc<800 ms;
0.5−0.3×(tc−800)/800≤Vtp/Vtm≤2.0−0.5×(tc−800)/800 when 800 ms≤tc<1600 ms; and
0.2≤Vtp/Vtm≤1.5 when tc≥1600 ms,
[0060] where Vtm is an average value of a voltage between the electrodes in the main current passage in the test welding, Vtp is an average value of a voltage between the electrodes in the subsequent current passage in the test welding, and tc is a cooling time between the main current passage and the subsequent current passage in the test welding, and (b) thereafter, in the actual welding, main current passage for nugget formation and subsequent current passage for subsequent heat treatment are performed, in the main current passage in the actual welding, the time variation curve of the instantaneous amount of heat generated per unit volume and the cumulative amount of heat generated per unit volume that are stored in the main current passage in the test welding are set as a target, and adaptive control welding is performed to control a current passage amount according to the target, and in the subsequent current passage in the actual welding, current passage is performed by constant current control under a condition:
0.8×Itp≤Imp≤1.2×Itp,
[0061] where Itp is a current in the subsequent current passage in the test welding, and Imp is a current in the subsequent current passage in the actual welding.
[0062] 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. Herein, the “electrical property between the electrodes” means the interelectrode resistance or the voltage between the electrodes.
[0063] The test welding and the actual welding in the resistance spot welding method according to one of the disclosed embodiments will be described below.
[0064] Test Welding
[0065] In the test welding, main current passage for nugget formation and subsequent current passage for subsequent heat treatment are each performed by constant current control.
[0066] In the main current passage in the test welding, 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 by performing current passage by constant current control are stored.
[0067] The test welding may be performed in a state in which there is no disturbance, or performed in a state in which there is a disturbance such as current shunting or a sheet gap (i.e. a state assuming that there is a disturbance).
[0068] The current pattern in the main current passage in the test welding may be a current pattern of a constant current throughout the current passage. The current pattern may be a current pattern divided into two or more steps each of which has a constant current, as illustrated in
[0069] Herein, the term “constant current control” includes not only a current pattern of a constant current throughout the current passage, but also the current patterns illustrated in
[0070] In the subsequent current passage in the test welding, it is important to perform current passage by constant current control under the condition:
0.5≤Vtp/Vtm≤2.0 when tc<800 ms;
0.5−0.3×(tc−800)/800≤Vtp/Vtm≤2.0−0.5×(tc−800)/800 when 800 ms≤tc<1600 ms; and
0.2≤Vtp/Vtm≤1.5 when tc≥1600 ms,
[0071] where Vtm is the average value of the voltage between the electrodes in the main current passage, Vtp is the average value of the voltage between the electrodes in the subsequent current passage, and tc is the cooling time between the main current passage and the subsequent current passage.
[0072] As mentioned above, if the subsequent current passage in the below-described actual welding is performed by adaptive control in the presence of a disturbance, the current density distribution of the weld and thus the heat generation pattern change due to the disturbance in some cases, making it impossible to achieve the predetermined heat treatment effect.
[0073] In view of this, the subsequent current passage in the below-described actual welding is performed by constant current control with the current being set based on the current obtained in the subsequent current passage in the test welding when the foregoing relationship is satisfied. Thus, appropriate current passage can be performed with the effect of a disturbance such as current shunting being taken into consideration. That is, in the subsequent current passage in the actual welding, an appropriate amount of heat generated can be obtained and the desired heat treatment effect can be achieved. Moreover, since the current is kept from increasing excessively in the case where current shunting occurs, surface expulsion can be prevented. Consequently, while effectively preventing surface expulsion, at least a certain amount of heat generated can be ensured to achieve the predetermined heat treatment effect.
[0074] In the case where the cooling time tc between the main current passage and the subsequent current passage in the test welding is long, specifically in the case where tc≥800 ms, cooling of the weld progresses during the cooling time. This causes the temperature of the weld at the start of the subsequent current passage to decrease. Hence, the specific resistance tends to decrease, i.e. the voltage between the electrodes tends to decrease.
[0075] Thus, the range of Vtp/Vtm within which the desired heat treatment effect can be achieved changes depending on the value of tc. Therefore, in the test welding, it is important to control Vtp/Vtm depending on the value of tc so as to achieve the desired heat treatment effect. Specifically, it is important to perform current passage by constant current control under the condition:
0.5≤Vtp/Vtm≤2.0 when tc<800 ms;
0.5−0.3×(tc−800)/800≤Vtp/Vtm≤2.0−0.5×(tc−800)/800 when 800 ms≤tc<1600 ms; and
0.2≤Vtp/Vtm≤1.5 when tc≥1600 ms,
[0076] In particular, for example in the case where the effect of a disturbance is significant, it is preferable to satisfy:
0.7≤Vtp/Vtm≤2.0 when tc<800 ms;
0.7−0.3×(tc−800)/800≤Vtp/Vtm≤2.0−0.5×(tc−800)/800 when 800 ms≤tc<1600 ms; and
0.4≤Vtp/Vtm≤1.5 when tc≥1600 ms.
[0077] 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 subsequent current passage in the test welding may or may not be stored.
[0078] In each of the main current passage and the subsequent current passage, in the case where a cooling time is provided during the current passage, a time average value of the voltage between the electrodes during the current passage excluding the cooling time is taken to be the average value of the voltage between the electrodes.
[0079] In detail, in each of the main current passage and the subsequent current passage, a value obtained by dividing a time integration value of the voltage between the electrodes in the current passage by the total welding time in the current passage excluding the cooling time is taken to be the average value of the voltage between the electrodes in the current passage.
[0080] A preferable range of the current in the main current passage in the test welding varies depending on which sheet combination is used as the parts to be welded. For example, in the case of using a sheet combination of two overlapping steel sheets of 980 MPa-grade in tensile strength (TS) and 1.2 mm to 1.6 mm in sheet thickness, the current in the main current passage in the test welding is preferably in a range of 3.0 kA to 12.0 kA.
[0081] The total welding time in the main current passage in the test welding excluding the cooling time is preferably in a range of 60 ms to 1000 ms.
[0082] The welding time per one subsequent current passage in the test welding is preferably in a range of 20 ms to 3000 ms. The welding time per one subsequent current passage is more preferably in a range of 60 ms to 3000 ms.
[0083] Actual Welding
[0084] After the test welding, the actual welding is performed.
[0085] In the main current passage in the actual welding, the time variation curve of the instantaneous amount of heat generated per unit volume and the cumulative amount of heat generated per unit volume that are stored in the main current passage in the test welding are set as a target, and adaptive control welding is performed to control a current passage amount according to the target.
[0086] For example, in the adaptive control welding in the main current passage in the actual 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 per unit volume that are stored in the main current passage in the test welding being set as the target. 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 in the main current passage in the actual welding 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.
[0087] A 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.
[0088] 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 the 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).
[0089] The electrical resistance R of the columnar portion is given by the following Equation (2):
R=(r.Math.t)/S (2).
[0090] 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).
[0091] 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 V between the electrodes, 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 V between the electrodes 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.
[0092] 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.
[0093] In the subsequent current passage in the actual welding, welding is performed by constant current control. Here, it is important to satisfy the following formula:
0.8×Itp≤Imp≤1.2×Itp
[0094] where Itp is the current in the subsequent current passage in the test welding, and Imp is the current in the subsequent current passage in the actual welding.
[0095] As mentioned earlier, if the subsequent current passage in the actual welding is performed by adaptive control welding in the presence of a disturbance, the current density distribution of the weld and thus the heat generation pattern change due to the disturbance in some cases, making it impossible to achieve the predetermined heat treatment effect.
[0096] In view of this, the subsequent current passage in the actual welding is performed by constant current control with a predetermined current, based on the current Itp in the subsequent current passage in the test welding in the case of satisfying 0.5≤Vtp/Vtm≤2.0 when tc<800 ms and 0.2≤Vtp/Vtm≤1.5 when tc≥800 ms. Specifically, the subsequent current passage in the actual welding is performed by constant current control with the current Imp that is in a range of 0.8 times to 1.2 times the current Itp. Consequently, while effectively preventing surface expulsion, at least a certain amount of heat generated can be ensured to achieve the predetermined heat treatment effect.
[0097] It is therefore important to perform the subsequent current passage in the actual welding by constant current control under the condition:
0.8×Itp≤Imp≤1.2×Itp.
[0098] A preferable range is
0.9×Itp≤Imp≤1.1×Itp.
[0099] In each of the test welding and the actual welding, a cooling time may be set between the main current passage and the subsequent current passage. The cooling time is preferably in a range of 20 ms to 3000 ms.
[0100] In each of the test welding and the actual welding, the number of times a welding interval for the cooling time and the subsequent current passage are performed after the main current passage may be two or more times, as illustrated in
[0101] The current Itp in the subsequent current passage in the test welding and the current Imp in the subsequent current passage in the actual welding are each a value obtained by dividing a time integration value of the current in the subsequent current passage by the total welding time in the subsequent current passage excluding the cooling time.
[0102] The conditions in the actual welding other than those described above may be basically the same as the conditions in the test welding.
[0103] The parts to be welded or the sheet combination used is not limited. The resistance spot welding method may be used for steel sheets and coated steel sheets having various strengths from mild steel to ultra high tensile strength steel. The resistance spot welding method may also be used for a sheet combination of three or more overlapping steel sheets, and is particularly advantageous in the case where one or more steel sheets of the sheet combination has a tensile strength of 590 MPa or more.
[0104] In each of the test welding and the actual welding, the electrode force in the current passage may be constant, or be changed as appropriate. A preferable range of the electrode force varies depending on which sheet combination is used as the parts to be welded. For example, in the case of using a sheet combination of two overlapping steel sheets of 980 MPa-grade in tensile strength (TS) and 1.2 mm to 1.6 mm in sheet thickness, the electrode force is preferably in a range of 1.5 kN to 10.0 kN.
[0105] By joining a plurality of overlapping metal sheets by the resistance spot welding method described above, various high-strength 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
[0106] The presently disclosed techniques will be described below, by way of examples. The conditions in the examples are one example of conditions employed to determine the operability and effects of the presently disclosed techniques, and the present disclosure is not limited to such example of conditions. Various conditions can be used in the present disclosure as long as the object of the present disclosure is fulfilled, without departing from the scope of the present disclosure.
[0107] Test welding was performed under the conditions listed in Table 2 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 3 for the same sheet combination, to produce a weld joint (L-shaped tensile test piece).
[0108]
[0109] The test welding was performed in a state in which there was no disturbance, as illustrated in
[0110]
[0111]
[0112] The “welding time in subsequent current passage” in each of the test welding condition in Table 2 and the actual welding condition in Table 3 is the welding time per one subsequent current passage. The cooling time, the current in subsequent current passage, and the welding time in subsequent current passage in each of the test welding condition in Table 2 and the actual welding condition in Table 3 were the same for each subsequent current passage.
[0113] In the “control method of main current passage” in the actual welding condition in Table 3, “constant current control” indicates constant current control performed under the same condition as in the test welding.
[0114] In the case where actual welding was performed in a state in which there was an existing weld, the below-described tensile test was conducted after cutting off the part of the existing weld from the L-shaped tensile test piece.
[0115] 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.
[0116] Each obtained L-shaped tensile test piece was used to conduct a tensile test at a tension rate (in longitudinal direction) of 10 mm/min, and the joint strength (L-shape tensile strength (LTS)) was measured. Based on whether expulsion occurred in welding and the joint strength, evaluation was performed in the following three levels:
[0117] A: LTS was 2.0 kN or more regardless of welding spot spacing L, and no expulsion occurred.
[0118] B: LTS was 2.0 kN or more when there was no existing weld or when welding spot spacing L≥10 mm, LTS was less than 2.0 kN when welding spot spacing L<10 mm, and no expulsion occurred.
[0119] F: LTS was less than 2.0 kN when there was no existing weld or when welding spot spacing L≥10 mm, or expulsion occurred.
TABLE-US-00001 TABLE 1 Sheet combination ID Upper sheet Intermediate sheet Lower sheet A1 1180 Mpa-grade cold-rolled steel sheet 1180 Mpa-grade cold-rolled steel sheet (sheet thickness: 1.6 mm) (sheet thickness: 1.6 mm) A2 980 Mpa-grade cold-rolled steel sheet 980 Mpa-grade cold-rolled steel sheet (sheet thickness: 1.6 mm) (sheet thickness: 1.6 mm) A3 980 Mpa-grade cold-rolled steel sheet 1470 Mpa-grade cold-rolled steel sheet (sheet thickness: 1.2 mm) (sheet thickness: 1.4 mm) A4 980 Mpa-grade GA steel sheet 1470 Mpa-grade GA steel sheet (sheet thickness: 1.2 mm) (sheet thickness: 2.0 mm) A5 1470 Mpa-grade GA steel sheet 1470 Mpa-grade GA steel sheet (sheet thickness: 1.4 mm) (sheet thickness: 1.4 mm) A6 1800 Mpa-grade noncoated hot stamp steel sheet 980 Mpa-grade GA steel sheet (sheet thickness: 1.4 mm) (sheet thickness: 1.2 mm) A7 1800 Mpa-grade Zn-Ni-coated hot stamp steel 1180 Mpa-grade cold-rolled steel sheet sheet (sheet thickness: 1.6 mm) (sheet thickness: 1.4 mm) A8 1470 Mpa-grade cold-rolled steel sheet 1470 Mpa-grade cold-rolled steel sheet (sheet thickness: 1.4 mm) (sheet thickness: 1.4 mm) B1 270 Mpa-grade GA steel sheet 1470 Mpa-grade GA steel sheet 1470 Mpa-grade GA steel sheet (sheet thickness: 0.7 mm) (sheet thickness: 1.4 mm) (sheet thickness: 1.4 mm)
TABLE-US-00002 TABLE 2 Test welding condition Main current passage Average of voltage Welding Welding between Current 1 time 1 Current 2 time 2 electrodes in main in main in main in main in main current current current current current Sheet Electrode passage passage passage passage passage combination force F I.sub.tm1 t.sub.tm1 I.sub.tm2 t.sub.tm2 V.sub.tm No. ID (kN) (kA) (ms) (kA) (ms) (V) 1 1-1 A1 4.5 6.0 320 — — 1.2 1-2 A1 1-3 A1 2 2-1 A1 4.5 6.0 320 — — 1.2 2-2 A1 2-3 A1 4 4-1 A1 4.5 6.0 320 — — 1.2 4-2 A1 4-3 A1 5 5-1 A1 4.5 4.0 100 6.0 240 1.1 5-2 A1 5-3 A1 6 6-1 A1 4.5 7.0 320 — — 1.3 6-2 A1 6-3 A1 7 7-1 A1 4.5 6.0 320 — — 1.2 7-2 A1 7-3 A1 8 8-1 A1 4.5 6.0 320 — — 1.2 8-2 A1 8-3 A1 9 9-1 A2 3.5 5.5 300 — — 1 9-2 A2 9-3 A2 10 10-1 A3 5.0 5.5 280 — — 1.1 10-2 A3 10-3 A3 11 11-1 A4 5.5 5.0 120 6.0 300 1.2 11-2 A4 11-3 A4 12 12-1 A5 5.5 4.5 140 6.0 320 0.9 12-2 A5 12-3 A5 13 13-1 A6 5.5 4.5 140 8.0 320 1.1 13-2 A6 13-3 A6 14 14-1 B1 5.0 7.0 320 — — 1.2 14-2 B1 14-3 B1 15 15-1 B1 5.0 4.5 140 8.0 320 1.1 15-2 B1 15-3 B1 16 16-1 A1 5.5 7.0 400 — — 1.0 16-2 A1 16-3 A1 17 17-1 A1 6 7.5 480 — — 0.9 17-2 A1 17-3 A1 18 18-1 A1 4.5 6.0 320 — — 1.2 18-2 A1 18-3 A1 19 19-1 A7 5.5 5.0 240 7.0 280 1.0 19-2 A7 19-3 A7 20 20-1 A8 5.0 6.5 320 — — 0.9 20-2 A8 20-3 A8 21 21-1 A8 5.0 7.0 320 — — 1.0 21-2 A8 21-3 A8 Test welding condition Subsequent current passage Average of voltage Welding between Current in time in Number electrodes subsequent subsequent of in subsequent Cooling current current repe- current time passage passage titions passage t.sub.c I.sub.tp t.sub.tp N V.sub.tp V.sub.tp/ No. (ms) (kA) (ms) (times) (V) V.sub.tm Remarks 1 1-1 160 9.0 60 2 1.3 1.1 Ex. 1-2 1-3 2 2-1 120 5.4 100 1 0.8 0.7 Ex. 2-2 2-3 4 4-1 160 11.0 60 2 1.6 1.3 Ex. 4-2 4-3 5 5-1 160 9.0 60 2 1.2 1.1 Ex. 5-2 5-3 6 6-1 100 3.0 80 2 0.5 0.4 Comp. 6-2 Ex. 6-3 7 7-1 120 5.0 100 1 0.8 0.7 Comp. 7-2 Ex. 7-3 8 8-1 160 9.0 60 10 1.0 0.8 Ex. 8-2 8-3 9 9-1 160 8.0 60 2 1.0 1.0 Ex. 9-2 9-3 10 10-1 20 7.0 60 2 1.3 1.2 Ex. 10-2 10-3 11 11-1 80 7.0 60 3 1.1 0.9 Ex. 11-2 11-3 12 12-1 80 6.0 60 2 1.0 1.1 Ex. 12-2 12-3 13 13-1 80 9.0 60 2 1.0 0.9 Ex. 13-2 13-3 14 14-1 80 8.5 60 2 1.3 1.1 Ex. 14-2 14-3 15 15-1 20 8.5 60 2 1.3 1.2 Ex. 15-2 15-3 16 16-1 160 12.5 40 2 1.6 1.6 Comp. 16-2 Ex. 16-3 17 17-1 160 14.0 40 2 1.9 2.1 Comp. 17-2 Ex. 17-3 18 18-1 160 9.0 60 2 1.2 1.0 Comp. 18-2 Ex. 18-3 19 19-1 1500 5.0 2000 1 0.4 0.4 Ex. 19-2 19-3 20 20-1 850 4.5 1000 1 0.4 0.4 Ex. 20-2 20-3 21 21-1 1800 5.0 1000 1 0.3 0.3 Ex. 21-2 21-3
TABLE-US-00003 TABLE 3 Actual welding condition Main Subsequent current passage current Current in Welding passage Control subse- time in Number Sheet Elec- Control method of quent subse- of com- Welding trode method subse- Cool- current quent repe- bina- spot force of main quent ing passage current titions Evaluation result tion spacing F current current time I.sub.mp passage N Imp/ LTS Expul- Evalu- Re- No. ID L (kN) passage passage (ms) (kA) (ms) (times) Itp (kN) sion ation marks 1 1-1 A1 No existing 4.5 Adaptive Constant 160 9.0 60 2 1.0 3.4 None A Ex. weld control current 1-2 A1 10 mm control 3.3 None 1-3 A1 7 mm 3.5 None 2 2-1 A1 No existing 4.5 Adaptive Constant 120 5.4 100 1 1.0 2.9 None B Ex. weld control current 2-2 A1 10 mm control 2.6 None 2-3 A1 7 mm 1.4 None 4 4-1 A1 No existing 4.5 Adaptive Constant 160 11.0 60 2 1.0 2.9 None A Ex. weld control current 4-2 A1 10 mm control 2.9 None 4-3 A1 7 mm 2.8 None 5 5-1 A1 No existing 4.5 Adaptive Constant 160 9.0 60 2 1.0 3.3 None A Ex. weld control current 5-2 A1 10 mm control 3.5 None 5-3 A1 7 mm 3.2 None 6 6-1 A1 No existing 4.5 Adaptive Constant 100 3.0 80 2 1.0 2.5 None F Comp. weld control current Ex. 6-2 A1 10 mm control 1.7 None 6-3 A1 7 mm 1.6 None 7 7-1 A1 No existing 4.5 Constant Constant 120 5.0 100 1 1.0 2.9 None F Comp. weld current current Ex. 7-2 A1 10 mm control control 1.2 None 7-3 A1 7 mm 1.0 None 8 8-1 A1 No existing 4.5 Adaptive Constant 160 9.0 60 10 1.0 3.5 None A Ex. weld control current 8-2 A1 10 mm control 3.5 None 8-3 A1 7 mm 3.4 None 9 9-1 A2 No existing 3.5 Adaptive Constant 160 8.0 60 2 1.0 3.3 None A Ex. weld control current 9-2 A2 10 mm control 3.5 None 9-3 A2 7 mm 3.5 None 10 10-1 A3 No existing 5.0 Adaptive Constant 20 7.0 60 2 1.0 2.9 None A Ex. weld control current 10-2 A3 10 mm control 3.0 None 10-3 A3 7 mm 2.8 None 11 11-1 A4 No existing 5.5 Adaptive Constant 80 5.6 60 3 0.8 3.1 None A Ex. weld control current 11-2 A4 10 mm control 2.9 None 11-3 A4 7 mm 3.0 None 12 12-1 A5 No existing 5.5 Adaptive Constant 80 7.2 60 2 1.2 2.7 None A Ex. weld control current 12-2 A5 10 mm control 2.8 None 12-3 A5 7 mm 2.6 None 13 13-1 A6 No existing 5.5 Adaptive Constant 80 9.0 60 2 1.0 2.4 None A Ex. weld control current 13-2 A6 10 mm control 2.5 None 13-3 A6 7 mm 2.6 None 14 14-1 B1 No existing 5.0 Adaptive Constant 80 8.5 60 2 1.0 3.0 None A Ex. weld control current 14-2 B1 10 mm control 2.8 None 14-3 B1 7 mm 2.9 None 15 15-1 B1 No existing 5.0 Adaptive Constant 20 8.5 60 2 1.0 2.5 None A Ex. weld control current 15-2 B1 10 mm control 2.4 None 15-3 B1 7 mm 2.6 None 16 16-1 A1 No existing 5.5 Adaptive Adaptive 160 Successive 40 2 — 2.8 None F Comp. weld control control change Ex. 16-2 A1 10 mm due to 2.7 None 16-3 A1 7 mm adaptive 1.8 Occurred control 17 17-1 A1 No existing 6.0 Adaptive Constant 160 14.0 40 2 — 1.7 Occurred F Comp. weld control current Ex. 17-2 A1 10 mm control 1.8 Occurred 17-3 A1 7 mm 1.9 Occurred 18 18-1 A1 No existing 4.5 Adaptive Constant 160 13.0 60 2 1.4 1.9 Occurred F Comp. weld control current Ex. 18-2 A1 10 mm control 2.0 Occurred 18-3 A1 7 mm 1.7 Occurred 19 19-1 A7 No existing 5.5 Adaptive Constant 1500 5.0 2000 1 1.0 2.6 None A Ex. weld control current 19-2 A7 10 mm control 2.4 None 19-3 A7 7 mm 2.1 None 20 20-1 A8 No existing 5.0 Adaptive Constant 850 4.5 1000 1 1.0 2.4 None A Ex. weld control current 20-2 A8 10 mm control 2.5 None 20-3 A8 7 mm 2.1 None 21 21-1 A8 No existing 5.0 Adaptive Constant 1800 5.0 1000 1 1.0 2.6 None A Ex. weld control current 21-2 A8 10 mm control 2.6 None 21-3 A8 7 mm 2.3 None A: LTS was 2.0 kN or more regardless of welding spot spacing L, and no expulsion occurred. B: LTS was 2.0 kN or more when there was no existing weld or when welding spot spacing L ≥10 mm, LTS was less than 2.0 kN when welding spot spacing L <10 mm, and no expulsion occurred. F: LTS was less than 2.0 kN when there was no existing weld or when welding spot spacing L ≥10 mm, or expulsion occurred.
[0120] As can be seen in Table 3, all Examples (Ex.) were evaluated as A or B. In particular, all Examples in which the number of repetitions of the welding interval for the cooling time and the subsequent current passage after the main current passage was two or more times were evaluated as A.
[0121] All Comparative Examples (Comp. Ex.) not satisfying the appropriate conditions were evaluated as F, and could not obtain sufficient joint strength.