WO2018123350A1 - 抵抗スポット溶接方法 - Google Patents
抵抗スポット溶接方法 Download PDFInfo
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- WO2018123350A1 WO2018123350A1 PCT/JP2017/041734 JP2017041734W WO2018123350A1 WO 2018123350 A1 WO2018123350 A1 WO 2018123350A1 JP 2017041734 W JP2017041734 W JP 2017041734W WO 2018123350 A1 WO2018123350 A1 WO 2018123350A1
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- energization
- pressurizing
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- resistance spot
- spot welding
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/10—Spot welding; Stitch welding
- B23K11/11—Spot welding
- B23K11/115—Spot welding by means of two electrodes placed opposite one another on both sides of the welded parts
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/10—Spot welding; Stitch welding
- B23K11/11—Spot welding
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/16—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/24—Electric supply or control circuits therefor
Definitions
- the present invention relates to a resistance spot welding method.
- Resistance spot welding is widely used for the assembly of automobile bodies such as automobiles, and resistance spot welding with thousands of points is performed on one body.
- resistance spot welding two or more steel plates are overlapped, sandwiched between a pair of upper and lower welding electrodes and energized while applying pressure, thereby forming a nugget of a predetermined size at the joint of the steel plates and It joins and obtains a welded joint.
- high-strength steel sheets for the vehicle body to reduce the thickness reduces the vehicle body weight, that is, improves the fuel consumption.
- high-strength steel sheets are generally increased in strength by adding not only a large amount of C but also various alloying elements, and the hydrogen embrittlement sensitivity is increased.
- the rust preventive oil, moisture, plating layer, etc. on the steel sheet surface are entrained in the weld metal (molten part) during the melting and solidification process during welding, and as a hydrogen source that causes delayed fracture after cooling. Remains.
- Patent Document 1 discloses that the residual stress in the welded portion is controlled by increasing the applied pressure immediately after welding energization (main energization) and decreasing the current. A technique for preventing destruction is disclosed.
- Patent Document 2 discloses that the pressure and pressure are increased immediately after welding energization (main energization) and energized after a non-energized cooling time, thereby controlling the structure and hardness of the welded portion and preventing delayed fracture.
- Technology is disclosed. However, these technologies do not reduce the amount of hydrogen in the welded part, and also increase the pressure force in a state where the nugget immediately after welding energization is melted.
- Patent Document 1 also discloses a technique for increasing the pressure after a non-energized cooling time after welding energization.
- the weld is rapidly cooled by the non-energized cooling time, so that a large amount of hydrogen remains without diffusing from within the nugget and the amount of remaining hydrogen in the nugget increases, so delayed fracture is prevented. It is difficult to suppress.
- Patent Document 3 provides a pressurization holding time for holding the pressure during welding energization without energization after welding energization, and then increasing the pressure without energization to improve the strength of the welded joint.
- Technology is disclosed.
- the welded portion is rapidly cooled by the non-energized pressure holding time, so that the amount of residual hydrogen in the nugget increases and delay fracture is likely to occur.
- the problem is not limited to resistance spot welding of high-strength steel sheets for automobiles, but similarly exists in resistance spot welding of other steel sheets.
- the present invention has been made in view of such circumstances, and provides a resistance spot welding method capable of suppressing the occurrence of scattering during welding and the reduction of the thickness of the welded portion and suppressing delayed fracture of a welded joint. For the purpose.
- the present inventors diligently investigated suitable resistance spot welding conditions that can reduce the amount of residual hydrogen in the weld. The results will be described below.
- the present invention has been made on the basis of the above knowledge, and the gist is as follows.
- a resistance spot welding method in which two or more steel plates are overlapped, sandwiched between a pair of welding electrodes and energized while being pressed to form a nugget and join the steel plates, A main energizing step of forming a nugget portion by energizing the steel plate with a first current I 1 (kA) while pressurizing the steel plate with a first pressurizing force F 1 (kN); Following the main energization step, the nugget portion is cooled by energizing the second current I 2 (kA) represented by the following equation (1) for the energization time t a (ms) represented by the following equation (2).
- a post-energization process A first pressurizing step in which the post-energization step maintains the first pressurizing force F 1 (kN) for a pressurization delay time t b (ms) represented by the following formula (3) from the start of the post-energization step; , resistance spot welding process and a second pressing step of pressing the second pressing force F 2 which subsequently expressed by the following equation (4) to said first pressurizing step (kN).
- At least one of the steel plates is a high-strength steel plate having a carbon equivalent Ceq (%) represented by the following formula (5) of 0.2% or more and a tensile strength of 780 MPa or more [1].
- the second pressurization step are the following (8) gradually upslope pressure increase between pressure upslope pressing time t e from the first pressing force F 1 (kN) of the formula Process, and Subsequent to the upslope pressurizing step, it comprises a late pressurizing step for maintaining the applied pressure at the end of the upslope pressurizing step for the later pressurizing time t f (ms) represented by the following formula (9) [1]
- the resistance spot welding method according to any one of to [3]. 0 ⁇ t e ⁇ 200 (8 ) 0 ⁇ t f (9)
- FIG. 1 is a cross-sectional view schematically showing an example of a resistance spot welding method.
- FIG. 2 is a graph showing an example of an energization pattern and a pressurization pattern of the resistance spot welding method according to the present invention.
- FIG. 3 is a graph showing an example of an energization pattern and a pressurization pattern of the resistance spot welding method according to the present invention.
- FIG. 4 is a graph showing an example of an energization pattern and a pressurization pattern of the resistance spot welding method according to the present invention.
- FIG. 5 is a graph showing an example of an energization pattern and a pressurization pattern of the resistance spot welding method according to the present invention.
- FIG. 6 is a plan view and a side view showing a test piece for resistance spot welding.
- the resistance spot welding method of the present invention is a resistance spot welding method in which two or more steel plates are overlapped and sandwiched between a pair of welding electrodes and energized while being pressed to form a nugget and join the steel plates, A main energization step of forming a nugget portion by energizing the steel plate with a first current I 1 (kA) while pressurizing the steel plate with a first applied pressure F 1 (kN), and following the main energization step (1) A second current I 2 (kA) expressed by the following formula (2) and a post-energization step for cooling the nugget portion by energizing during the energization time t a (ms) expressed by the following formula (2): A first pressurizing step in which the energizing step maintains a first pressurizing force F 1 (kN) for a pressurization delay time t b (ms) represented by the following formula (3) from the start of the post-energizing step; second pressure
- FIG. 1 is a cross-sectional view schematically showing an example of a resistance spot welding method, and shows an example of performing resistance spot welding of two steel plates. The resistance spot welding method of the present invention will be described below with reference to FIG.
- a steel plate disposed on the lower side (hereinafter referred to as a lower steel plate 1) and a steel plate disposed on the upper side (hereinafter referred to as an upper steel plate 2) are overlapped.
- the steel type of the steel plate to be resistance spot welded in the present invention is not particularly limited, but at least one sheet has a carbon equivalent Ceq (%) represented by the following formula (5) of 0.2% or more and a tensile strength of 780 MPa or more.
- a high strength steel plate is preferred.
- the lower steel plate 1 and / or the upper steel plate 2 is a high-strength steel plate having a carbon equivalent represented by the following formula (5) of 0.2% or more and a tensile strength of 780 MPa or more. preferable. This is because in a steel plate having a Ceq (%) of 0.2% or more and a tensile strength of 780 MPa or more, delayed fracture of the resistance spot weld is likely to be a problem.
- the present invention can be applied to the resistance spot welding of the present invention to a steel plate having a Ceq (%) of less than 0.2% and a tensile strength of less than 780 MPa.
- Ceq C + Si / 30 + Mn / 20 + 2P + 4S (5) (The element symbol in the formula (5) indicates the content (% by mass) of each element.)
- the thickness of the steel plate to be resistance spot welded is not particularly limited, but is preferably in the range of, for example, 1.0 mm or more and 2.0 mm or less. A steel plate having a thickness within this range can be suitably used as an automobile member.
- the steel plate to be resistance spot welded may be plated and have a plating layer on the surface.
- the plating include Zn-based plating and Al-based plating.
- the Zn-based plating include hot dip galvanizing (GI), Zn—Ni based plating, and Zn—Al based plating.
- the Al plating include Al—Si plating (for example, Al—Si plating containing 10 to 20% by mass of Si).
- the galvanized layer may be an alloyed galvannealed layer.
- the alloyed hot dip plating layer include an alloyed hot dip galvanizing (GA) layer.
- the two or more steel plates to be resistance spot welded may be the same or different, may be the same type and the same shape, or may be different types or different shapes.
- a pair of welded electrodes that is, an electrode disposed on the lower side (hereinafter referred to as the lower electrode 4) and an electrode disposed on the upper side (hereinafter referred to as the upper electrode 5) are overlapped with the steel plate (lower steel plate 1 and The upper steel plate 2) is sandwiched and energized while being pressurized.
- the structure which pressurizes with the lower electrode 4 and the upper electrode 5 and controls the applied pressure is not particularly limited, and conventionally known devices such as an air cylinder and a servo motor can be used.
- There is no particular limitation on the configuration for supplying current and controlling the current value during energization and conventionally known devices can be used.
- the present invention can be applied to both direct current and alternating current.
- alternating current means “effective current”.
- the form of the tip of the lower electrode 4 or the upper electrode 5 is not particularly limited.
- DR type dome radius type
- R type radius type
- D type dome type
- the tip diameter of the electrode is, for example, 4 mm to 16 mm. Resistance spot welding is performed while the electrode is always water-cooled.
- a welded joint is obtained by energizing the steel plates stacked in this manner while being sandwiched between a pair of welding electrodes to form a nugget by resistance heating and joining the stacked steel plates.
- this pressurization and energization are performed in a specific pattern. Specifically, in the present invention, for example, as shown in FIG. 2, the stacked steel plates are energized with the first current I 1 (kA) while being pressed with the first applied pressure F 1 (kN).
- 2 to 5 are graphs showing examples of energization patterns and pressurization patterns of the resistance spot welding method according to the present invention. In the energization pattern and the pressurization pattern shown in FIGS. 2 to 5, the vertical axis represents the current value or the applied pressure, and both the current value and the applied pressure increase as they go upward in the axial direction on the graph.
- the main energization process is a process of forming a nugget part that becomes a nugget 3 when solidified, and the energization conditions and pressurization conditions for forming the nugget part are not particularly limited, and conventionally used welding conditions are adopted. can do.
- the first current I 1 is 1.0 kA or more and 15 kA or less
- the first pressure F 1 is 2.0 kN or more and 7.0 kN or less.
- the time for the main energization process is not particularly limited, and is, for example, 100 ms or more and 1000 ms or less.
- the “nugget” is a melted and solidified portion generated in a welded portion in lap resistance welding, and the “nugget portion” is a molten portion that becomes a nugget when solidified (that is, a molten portion before solidification).
- second current I 2 (kA) energizing time is represented by the above formula (2) t a of the formula (ms) Cool down. That is, the current value is decreased to the second current I 2 (kA) less than the first current I 1 (kA), and energization is performed for the energization time t a (ms) expressed by the above equation (2). Cool the nugget part. That is, by performing the post-energization step, the temperature range in which the solidification of the nugget portion is started and hydrogen diffusion can be promoted is maintained for a long time.
- the first current I 1 in the above formula (1) is a current value at the end of the main energization process.
- the nugget portion does not start to solidify and remains in the molten state even in the post-energization step. If the applied pressure is increased more than the process, problems such as the occurrence of scattering and the reduction of the thickness of the welded part (welded metal and heat-affected zone) may occur, resulting in a decrease in the strength of the welded joint obtained and the appearance of the welded part being damaged. A good welded joint cannot be obtained.
- the energization time t a of the rear energization process is less than 20 ms, can not be maintained for a long time high temperature state is a temperature range in which the hydrogen diffusion can be promoted, not to obtain the effect of discharging good hydrogen of the weld efficiency. Further, the energization time t a is equal to or larger than 400 ms, productivity total time is longer in the welding process itself is lowered.
- the post-energization step includes a first pressurization step for maintaining the first pressurizing force F 1 during the pressurization delay time t b (ms) represented by the above formula (3) from the start of the post-energization step, Following the first pressurization step and a second pressing step of pressing the second pressing force F 2 represented by the above equation (4). That is, the applied pressure in the post-energization process remains the first applied pressure F 1 that is the applied pressure in the main energization process during the pressurization delay time t b represented by the above formula (3) from the start of the post-energization process.
- Increase to. (4) first pressure F 1 of about the first pressure F 1 and first-pressing step in the equation is the pressure at the end the main power process.
- the second applied pressure F 2 may satisfy the formula (4), but when the applied pressure is constant in the second pressurizing step, it is preferable to satisfy 1.20F 1 ⁇ F 2.
- the time satisfying 1.20F 1 ⁇ F 2 in the second pressure step is 20% or more of the upslope pressure step.
- pressurized ⁇ is time t b is less than 10 ms, it becomes the nugget to impart a high pressure in the molten state without starting little coagulation, cause problems such thick plate reduction in expulsion generation and welds, A good weld joint cannot be obtained. Further, when the pressurized ⁇ is time t b is greater than the conduction time t a, the temperature of the nugget is too low, the effect of the compressive stress state is discharged efficiently weld hydrogen is not introduced can not be obtained.
- the second pressure F 2 of the first pressing force F 1 or less If the second pressure F 2 of the first pressing force F 1 or less, a large compressive stress can not be imparted to the nugget, it can not efficiently discharging hydrogen of the weld. If the second pressure F 2 is greater than 3F 1 is excessive depression is formed in the weld, problem impairing the decrease and appearance of the joint strength occurs.
- the present invention by using the above-described specific main energization process and post-energization process, it is possible to suppress the occurrence of scattering during welding and the reduction of the welded part plate thickness and to suppress delayed fracture of the welded joint. Even for high-strength steel sheets, if the resistance spot welding method of the present invention is applied, it is possible to suppress the occurrence of scattering during welding and the reduction of the welded plate thickness, and to suppress delayed fracture of welded joints.
- the spot welding method is suitable for welding high strength steel plates for automobiles.
- Second current I 2 the second pressing force F 2
- the energization time t a and pressurized ⁇ is time t b is not particularly limited if it meets the above conditions.
- the current value is gradually decreased from the first current I 1 during the down slope energization time t c (ms) expressed by the following equation (6) (for example, gradually decreased, or Down-slope energization step (multi-stage energization that decreases stepwise), and current at the end of the down-slope energization step for the later energization time t d (ms) expressed by the following equation (7) following the down-slope energization step You may make it consist of the late energization process which maintains a value.
- the current value at the end of the downslope energization may be maintained for the later energization time t d (ms) represented by the following equation (7).
- the second current I 2 in the late energization process satisfies 0.3I 1 ⁇ I 2 ⁇ 0.95I 1 (the first current I 1 in the formula is a current value at the end of the main energization process).
- the pressurization delay time t b preferably satisfies t b ⁇ 20.
- the second current I 2 in the down-slope energization process may satisfy the above formula (1) and gradually decrease from the first current I 1 .
- the second pressing step of the post-energizing step gradually between pressure from the first pressure F 1 below (8) represented by the upslope pressurizing time t e the formula (ms) Up-slope pressurizing step to increase (gradual increase or multi-stage pressurization to increase stepwise), and subsequent pressurization time t f (ms) expressed by the following equation (9) following the up-slope pressurization step )
- the pressurizing step at the end of the upslope pressurizing step may be maintained.
- upslope pressure is gradually increased between pressure upslope pressing time t e represented by the following equation (8) from the first pressing force F 1, it may be maintained the pressure between the upslope pressure at the end of the late pressing time t f continue represented by the following equation (9) to the up-slope pressure.
- t f 0, the latter pressurizing step is not performed, and the pressurizing force in the second pressurizing step consists only of the upslope pressurizing step.
- the upper limit value of t f is not particularly limited, but preferably t f ⁇ 400.
- the post-energization step gradually decreases the current value from the first current I 1 during the down-slope energization time t c (ms) expressed by the above equation (6).
- the second pressing step of the post-energizing step gradually increase between pressure upslope pressing time t e represented by the above equation (8) from the first pressure F 1 upslope pressurizing step of, and, late pressure to maintain the pressure at the end as during upslope pressurization step late pressing time t f continue represented by the equation (9) to the upslope pressurizing step
- pressure upslope pressing time t e represented by the above equation (8)
- F 1 upslope pressurizing step of and, late pressure to maintain the pressure at the end as during upslope pressurization step late pressing time t f continue represented by the equation (9) to the upslope pressurizing step
- the upslope pressurizing step As it consists of processes It may be.
- the pressing force may be applied simultaneously with the start of the main energization process, or may be applied before the main energization process as shown in FIGS.
- the applied pressure may be stopped simultaneously with the end of the post-energization process (the electrode is separated from the steel plate). Also, as shown in FIG. 2 to FIG. May be.
- the current value (first current I 1 ) in the main energization process may be constant as shown in FIGS. 2 to 5 and is gradually increased (gradual increase or increased in stages during the main energization process). Energization).
- the pressurizing force (first pressurizing force F 1 ) in the main energization process may be constant as shown in FIGS. 2 to 5, and gradually increases (increases gradually or increases stepwise) during the main energization process. (Multi-stage energization).
- the lower steel plate 1 and the upper steel plate 2 were overlapped and resistance spot welding was performed. Resistance spot welding was performed at room temperature, and the electrode was always water-cooled.
- Each of the lower electrode 4 and the upper electrode 5 had a tip diameter (tip diameter) of 6 mm and a curvature radius of 40 mm, and was a DR type electrode made of chromium copper.
- the pressurizing force was controlled by driving the lower electrode 4 and the upper electrode 5 with a servo motor, and a single-phase alternating current with a frequency of 50 Hz was supplied during energization.
- the steel type A tensile strength 1470 MPa, Ceq (%) expressed by the formula (5) is 0.4%, the long side 100 mm, the short side 30 mm, the plate With a thickness of 1.6 mm and no plating treatment, steel samples B (tensile strength 1470 MPa, Ceq (%) expressed by formula (5) is 0.4%, long side is 100 mm, short side is No. 29-56. 30 mm, plate thickness 1.6 mm, with plating treatment (hot dip galvanizing (GI), adhesion amount 50 g / m 2 per side)) was used.
- Tensile strength was determined by preparing JIS No. 5 tensile test pieces in parallel to the rolling direction from each steel sheet and conducting a tensile test in accordance with the provisions of JIS (Japanese Industrial Standards) Z 2241: 2011. Tensile strength.
- FIG. 6 is a plan view (FIG. 6 (a)) and a side view (FIG. 6 (b)) showing a test piece for resistance spot welding.
- reference numeral 7 is a welding point
- 8 is a temporary welding point. is there.
- the first current I 1 in the main energization process is a constant value.
- the downslope energization is not performed and the second current I 2 is set to a constant value.
- 38 to 40 and 52 to 54 down-slope energization is performed to linearly decrease the current value, and the second current I 2 after down-slope energization is set to a constant value.
- the test numbers 13 to 14, 27 to 28, 41 to 42, and 55 to 56 were set to have a constant current value after energization.
- the first pressure F 1 in the first pressurizing step of the main energizing step and the post-energizing step was set to a constant value.
- Test Nos. 2 to 8, 10, 11, 13, 16 to 22, 24, 25, 27, 30 to 36, 38 to 39, 41, 44 to 50, 52 to 53, 55 two pressure F 2 to a constant value increases linearly pressure in the second pressing step in Run No. 9,12,14,23,26,28,37,40,42,51,54,56 an up-slope pressure, the second pressure F 2 upslope after pressing was constant.
- trial numbers 1, 15, 29, and 43 are examples in which the post-energization process is not performed.
- Test numbers 3, 17, 31, and 45 are examples in which the current was increased in the post-energization process.
- Test numbers 7, 21, 35, and 49 are examples in which the pressing force was reduced in the second pressurizing step.
- Test numbers 8, 11, 25, 36, 39, and 53 are examples in which the applied pressure was increased immediately after the end of the main energization process.
- Trial numbers 13 to 14, 27 to 28, 41 to 42, and 55 to 56 are examples in which no energization is performed immediately after the main energization process.
- the obtained welded joint was allowed to stand in the atmosphere at room temperature (20 ° C.), and after 24 hours, the indentation depth of the weld and the presence or absence of delayed fracture were investigated.
- Welded joints were evaluated using three items: the depth of the indentation in the weld, the presence or absence of splatter during welding, and delayed fracture after welding. The results are shown in Table 1-1 and Table 1-2.
- the thickness after welding was 70% or more before welding, and the thickness less than 70% was rated as x.
- the scattering the case where no scattering occurred during welding was indicated as ⁇ , and the case where the scattering occurred was indicated as x.
- the case where delayed fracture did not occur after standing for 24 hours was indicated as ⁇ , and the case where it occurred was indicated as x.
- the case where peeling of the nugget (a phenomenon in which the nugget peels in two at the joining interface) was visually observed after welding was regarded as the occurrence of delayed fracture.
- all of the evaluation items with a result of ⁇ were marked as ⁇ in the judgment column as good weld joints.
- the nugget diameters of the obtained welded joints are also shown in Table 1-1 and Table 1-2.
- the nugget diameter is the maximum diameter of the mating surfaces of the two steel plates, and t is the thickness (mm) of the thinnest steel plate among the stacked steel plates.
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Abstract
Description
前記鋼板を第一加圧力F1(kN)で加圧しながら第一電流I1(kA)で通電をすることによりナゲット部を形成する主通電工程と、
該主通電工程に引き続き下記(1)式で表される第二電流I2(kA)で下記(2)式で表される通電時間ta(ms)の間通電してナゲット部を冷却する後通電工程とを有し、
該後通電工程が、該後通電工程開始から下記(3)式で表される加圧遅れ時間tb(ms)の間第一加圧力F1(kN)を維持する第一加圧工程と、該第一加圧工程に引き続き下記(4)式で表される第二加圧力F2(kN)で加圧する第二加圧工程とを有する抵抗スポット溶接方法。
0<I2<I1 (1)
20≦ta≦400 (2)
10≦tb≦ta (3)
F1<F2≦3F1 (4)
[2] 前記鋼板の少なくとも1枚が、下記(5)式で表される炭素当量Ceq(%)が0.2%以上であり、引張強さが780MPa以上の高強度鋼板である[1]に記載の抵抗スポット溶接方法。
Ceq=C+Si/30+Mn/20+2P+4S (5)
((5)式中の元素記号は各元素の含有量(質量%)を示す。)
[3] 前記後通電工程が、下記(6)式で表されるダウンスロープ通電時間tc(ms)の間電流値を第一電流I1(kA)から徐々に減少させるダウンスロープ通電工程、および、
該ダウンスロープ通電工程に引き続き下記(7)式で表される後期通電時間td(ms)の間ダウンスロープ通電工程終了時の電流値を維持する後期通電工程からなる[1]または[2]に記載の抵抗スポット溶接方法。
20≦tc≦ta (6)
td=ta-tc (7)
[4] 前記第二加圧工程が、下記(8)式で表されるアップスロープ加圧時間teの間加圧力を第一加圧力F1(kN)から徐々に増加させるアップスロープ加圧工程、および、
該アップスロープ加圧工程に引き続き下記(9)式で表される後期加圧時間tf(ms)の間アップスロープ加圧工程終了時の加圧力を維持する後期加圧工程からなる[1]~[3]のいずれか一つに記載の抵抗スポット溶接方法。
0<te≦200 (8)
0≦tf (9)
0<I2<I1 (1)
20≦ta≦400 (2)
10≦tb≦ta (3)
F1<F2≦3F1 (4)
本発明は、2枚以上の鋼板を抵抗スポット溶接によって接合するものである。図1は、抵抗スポット溶接方法の一例を模式的に示す断面図であり、2枚の鋼板の抵抗スポット溶接を行う例を示している。以下に図1を参照して、本発明の抵抗スポット溶接方法を説明する。
Ceq=C+Si/30+Mn/20+2P+4S (5)
((5)式中の元素記号は各元素の含有量(質量%)を示す。)
本発明において抵抗スポット溶接する鋼板の板厚は特に限定されないが、例えば1.0mm以上2.0mm以下の範囲内であることが好ましい。板厚がこの範囲内である鋼板は、自動車用部材として好適に使用することができる。
20≦tc≦ta (6)
td=ta-tc (7)
このように、後通電工程の開始部分に電流値の急激な変化を抑制できるダウンスロープ通電工程を行うことにより、水素拡散が促進できる温度域である高温状態をより長時間保持し効率よく水素を排出することができる。この場合、後期通電工程の第二電流I2が0.3I1≦I2<0.95I1(式中の第一電流I1は主通電工程終了時の電流値である。)を満足し、加圧遅れ時間tbがtb≧20を満足することが好ましい。ダウンスロープ通電工程での第二電流I2は、上記(1)式を満たし且つ第一電流I1から徐々に減少させればよい。
0<te≦200 (8)
0≦tf (9)
このように、第二加圧工程の開始部分に加圧力の急激な変化を抑制できるアップスロープ加圧工程を行うことにより、溶接部に過度な力を加えることなく水素拡散が促進できる温度域である高温状態で加圧を行って水素排出の効果をより顕著に発揮することができる。この場合、第二加圧力F2が後期加圧工程では1.20F1≦F2(式中の第一加圧力F1は、主通電工程終了時の加圧力である。)を満足することが好ましい。アップスロープ加圧工程での第二加圧力F2は、上記(4)式を満たし且つ第一加圧力F1から徐々に増加させればよい。
図1に示すように、下鋼板1と上鋼板2を重ね合わせて、抵抗スポット溶接を行った。抵抗スポット溶接は常温で行い、電極を常に水冷した状態で行った。下電極4と上電極5は、いずれも先端の直径(先端径)6mm、曲率半径40mmとし、クロム銅製のDR形電極とした。下電極4と上電極5をサーボモータで駆動することによって加圧力を制御し、通電の際には周波数50Hzの単相交流を供給した。下鋼板1と上鋼板2として、試番1~28では鋼種A(引張強さ1470MPa、(5)式で表されるCeq(%)が0.4%、長辺100mm、短辺30mm、板厚1.6mm、めっき処理無し)を用い、試番29~56では鋼種B(引張強さ1470MPa、(5)式で表されるCeq(%)が0.4%、長辺100mm、短辺30mm、板厚1.6mm、めっき処理有り(溶融亜鉛めっき(GI)、付着量は片面当たり50g/m2))を用いた。引張強さは、各鋼板から、圧延方向に対して平行方向にJIS5号引張試験片を作製し、JIS(日本工業規格) Z 2241:2011の規定に準拠して引張試験を実施して求めた引張強さである。
2 上鋼板
3 ナゲット
4 下電極
5 上電極
6 スペーサ
7 溶接点
8 仮溶接点
Claims (4)
- 2枚以上の鋼板を重ね合わせて1対の溶接電極で挟持し加圧しながら通電してナゲットを形成すると共に前記鋼板を接合する抵抗スポット溶接方法であって、
前記鋼板を第一加圧力F1(kN)で加圧しながら第一電流I1(kA)で通電をすることによりナゲット部を形成する主通電工程と、
該主通電工程に引き続き下記(1)式で表される第二電流I2(kA)で下記(2)式で表される通電時間ta(ms)の間通電してナゲット部を冷却する後通電工程とを有し、
該後通電工程が、該後通電工程開始から下記(3)式で表される加圧遅れ時間tb(ms)の間第一加圧力F1(kN)を維持する第一加圧工程と、該第一加圧工程に引き続き下記(4)式で表される第二加圧力F2(kN)で加圧する第二加圧工程とを有する抵抗スポット溶接方法。
0<I2<I1 (1)
20≦ta≦400 (2)
10≦tb≦ta (3)
F1<F2≦3F1 (4) - 前記鋼板の少なくとも1枚が、下記(5)式で表される炭素当量Ceq(%)が0.2%以上であり、引張強さが780MPa以上の高強度鋼板である請求項1に記載の抵抗スポット溶接方法。
Ceq=C+Si/30+Mn/20+2P+4S (5)
((5)式中の元素記号は各元素の含有量(質量%)を示す。) - 前記後通電工程が、下記(6)式で表されるダウンスロープ通電時間tc(ms)の間電流値を第一電流I1(kA)から徐々に減少させるダウンスロープ通電工程、および、
該ダウンスロープ通電工程に引き続き下記(7)式で表される後期通電時間td(ms)の間ダウンスロープ通電工程終了時の電流値を維持する後期通電工程からなる請求項1または2に記載の抵抗スポット溶接方法。
20≦tc≦ta (6)
td=ta-tc (7) - 前記第二加圧工程が、下記(8)式で表されるアップスロープ加圧時間teの間加圧力を第一加圧力F1(kN)から徐々に増加させるアップスロープ加圧工程、および、
該アップスロープ加圧工程に引き続き下記(9)式で表される後期加圧時間tf(ms)の間アップスロープ加圧工程終了時の加圧力を維持する後期加圧工程からなる請求項1~3のいずれか一項に記載の抵抗スポット溶接方法。
0<te≦200 (8)
0≦tf (9)
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