WO2018159764A1 - 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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- WO2018159764A1 WO2018159764A1 PCT/JP2018/007809 JP2018007809W WO2018159764A1 WO 2018159764 A1 WO2018159764 A1 WO 2018159764A1 JP 2018007809 W JP2018007809 W JP 2018007809W WO 2018159764 A1 WO2018159764 A1 WO 2018159764A1
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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
-
- 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
- B23K11/002—Resistance welding; Severing by resistance heating specially adapted for particular articles or work
- B23K11/0026—Welding of thin articles
-
- 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
- B23K11/16—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
- B23K11/16—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded
- B23K11/163—Welding of coated materials
-
- 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
- B23K11/163—Welding of coated materials
- B23K11/166—Welding of coated materials of galvanized or tinned materials
-
- 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
-
- 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
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
- B23K2103/04—Steel or steel alloys
Definitions
- the present invention relates to a resistance spot welding method.
- a resistance spot welding method which is a kind of a lap resistance welding method, is used for joining stacked steel plates.
- a high current welding current is applied between the upper and lower electrodes while pressing with a pair of electrodes 3 and 4 from above and below with two or more stacked steel plates 1 and 2 sandwiched between them.
- This is a method of joining by energizing for a short time.
- a spot-like welded portion 5 is obtained using resistance heat generated by flowing a high-current welding current.
- This spot-like welded portion 5 is called a nugget and is a portion where both steel plates 1 and 2 are melted and solidified at the contact points of the steel plates when an electric current is passed through the stacked steel plates. Are joined together.
- the surface-treated steel sheet is a zinc plating typified by electrogalvanizing or hot dip galvanizing (including galvannealed alloying), or a zinc alloy containing elements such as aluminum and magnesium in addition to zinc. It refers to a steel plate having a metal plating layer such as on the surface of a base material (underlying steel plate). Since the melting point of zinc plating or zinc alloy plating is lower than the melting point of the base material of the surface-treated steel sheet, there are the following problems.
- the cracks in the welded part melted when the low-melting point metal plating layer on the surface of the steel sheet was melted during welding, and when tensile stress due to electrode pressure, thermal expansion and contraction of the steel sheet was applied to the welded part.
- the low melting point metal is a crack caused by so-called liquid metal embrittlement that penetrates into the crystal grain boundary of the base material of the surface-treated steel sheet to lower the grain boundary strength and cause cracking.
- the occurrence position of the crack is various, such as the surface of the steel plates 1 and 2 on the side in contact with the electrodes 3 and 4 as shown in FIG.
- the composition of a steel sheet as a plate assembly is a specific range of composition, specifically, by weight percent, C: 0.003 to 0.01%, Mn: 0 .05-0.5%, P: 0.02% or less, sol. Al: 0.1% or less, Ti: 48 ⁇ (N / 14) to 48 ⁇ ⁇ (N / 14) + (S / 32) ⁇ %, Nb: 93 ⁇ (C / 12) to 0.1%, B: 0.0005 to 0.003%, N: 0.01% or less, Ni: 0.05% or less, the balance Fe and inevitable impurities are proposed.
- Patent Document 2 is characterized in that, in spot welding of a high-strength plated steel sheet, spot welding is performed by setting a welding energization time and a holding time after welding energization so as to satisfy the following conditions (1) and (2).
- a spot welding method of high strength plated steel sheet is proposed.
- welding is performed using a high-tensile galvanized steel sheet in which the energization time and the holding time of the electrode after energization are appropriately set according to the thickness of the steel sheet, and the amount of alloy elements in the steel sheet is below a certain level. It has also been proposed to do.
- the energization pattern is a multi-stage energization of three or more stages, and an appropriate current range ( ⁇ I: a current range in which a nugget having a desired nugget diameter or more and a molten residual thickness of 0.05 mm or more can be stably formed)
- ⁇ I a current range in which a nugget having a desired nugget diameter or more and a molten residual thickness of 0.05 mm or more can be stably formed
- the welding conditions such as energization time and welding current are adjusted so that the cooling time is provided between the stages so that the current becomes 1.0 kA or more, preferably 2.0 kA or more.
- joints obtained by resistance spot welding are required to have high joint strength such as cross tensile strength (strength when a tensile test is performed in the peeling direction of the joint).
- the energization pattern is a multi-stage energization of two or more stages, and after energization, post energization without increasing the nugget is performed at a higher current value than the main energization. It has been shown that doing so can improve the cross tensile strength.
- Patent Document 1 since it is necessary to limit the amount of alloy elements of the steel sheet, there is a problem that the use of the steel sheet that satisfies the required performance is restricted. In particular, the application of the steel sheet is extremely limited under the circumstances where high alloying is progressing with increasing strength.
- Patent Document 2 proposes only a crack suppressing method when an excessive welding current that causes scattering is set, and does not mention cracking in a state where no scattering occurs.
- Patent Document 3 there is a problem that many man-hours are required for optimizing the welding conditions, and the method cannot be applied to steel plates and plate assemblies in which it is difficult to ensure an appropriate current range.
- the present invention has been made in view of the circumstances as described above, and is capable of suppressing the occurrence of cracks in the welded portion according to the striking angle and sufficiently ensuring the joint strength regardless of the steel type.
- the purpose is to propose a spot welding method.
- the inventors have made extensive studies in order to achieve the above object. Cracks that occur during welding also occur in a range of welding conditions where no scattering occurs. The occurrence is affected by various factors, and in particular, the striking angle A (degree) during welding (the striking angle refers to the angle at which the axis of the electrode is inclined with respect to the vertical direction of the surface of the steel sheet, FIG. (See below). And in this order, the main energization for forming the nugget part, the non-energization for stopping energization for a predetermined time, and the post-energization for reheating without growing the nugget part, and depending on the size of the striking angle, etc. To energize under specific conditions. Thereby, the knowledge that a crack can be suppressed and joint strength is securable enough was acquired.
- the effect of the present invention on cracks that occur during welding cannot be simply explained because various factors affect it in a complicated manner, but the basic mechanism is considered as follows.
- the cause of cracks in the welded part is that the tensile stress described below occurs when the plated metal of the surface-treated steel sheet that has reached a high temperature is in contact with the base material of the surface-treated steel sheet (underlying steel sheet). Is mentioned. In this tensile stress, there is a region where the electrode is locally increased when the electrode is separated from the steel plate after the end of welding.
- a metal such as zinc on the surface of the steel sheet is alloyed with a metal plating layer or other elements of the steel sheet to increase the melting point, and the solidification upon cooling after reheating is promoted.
- CTS cross tensile strength
- the present invention is based on the above knowledge, and the gist is as follows.
- a resistance spot welding method in which a plate assembly in which a plurality of steel plates are overlapped is sandwiched between a pair of electrodes, and energized while being pressed and joined. At least one of the superposed steel plates is a surface-treated steel plate having a metal plating layer on the surface,
- a main energization process for energizing to form a nugget portion;
- a non-energization process in which the energization is suspended for the energization stop time Tc (cycle) after the main energization process;
- a post-energization step for conducting energization to reheat without growing the nugget part after the non-energization step,
- the striking angle of the electrode is A (degrees)
- the current value in the main energization process is Im (kA)
- the current value in the post-energization process is Ip (kA)
- 1 + 0.1 ⁇ Tc is a variable B, 1
- FIG. 1 is a diagram schematically illustrating an example of a resistance spot welding method.
- FIG. 2 is a diagram showing a striking angle in the resistance spot welding method.
- the present invention is a resistance spot welding method in which a plate set in which a plurality of steel plates are overlapped is sandwiched between a pair of electrodes and energized while being pressed and joined, and at least one of the plurality of stacked steel plates is: It is a surface-treated steel sheet having a metal plating layer on its surface, and energization is suspended during energization pause time Tc (cycle (cyc)) after energization and main energization process for energizing to form a nugget portion as energization.
- Tc cycle
- the electrode striking angle is A (degrees)
- the current value of the main energization process is Im ( kA)
- the current value in the post-energization process is Ip (kA)
- 1 + 0.1 ⁇ Tc is variable B
- 1 + 0.2 ⁇ Tc is variable C
- the energization satisfies the relationship of the following formula (I) It is.
- FIG. 1 schematically shows an example of a resistance spot welding method, and shows an example of resistance spot welding of two steel plates.
- FIG. 2 is a diagram showing a striking angle in the resistance spot welding method.
- the present invention is a resistance spot welding method in which a plate assembly in which a plurality of steel plates are overlapped is sandwiched between a pair of electrodes and is energized and joined while being pressed.
- a plurality of steel plates (steel plate 1, steel plate 2) are overlapped to form a plate set.
- At least one steel plate to be resistance spot welded is a surface-treated steel plate having a metal plating layer on the surface.
- the metal plating layer preferably has a melting point lower than the melting point of the base material of the surface-treated steel sheet. If it is a general metal plating layer, melting
- the melting point of the base material (underlying steel plate) is 1400 to 1570 ° C.
- the melting point of the metal plating layer is 300 to 1200 ° C.
- a metal plating layer is not specifically limited, For example, a Zn type plating layer and an Al type plating layer are mentioned.
- the Zn-based plating layer is superior to the Al-based plating layer. This is because the corrosion rate of the base steel sheet can be reduced by the sacrificial anticorrosive action of zinc (Zn).
- Zn-based plating layer general hot-dip galvanizing (GI), alloyed hot-dip galvanizing (GA), electrogalvanizing (EG), Zn-Ni-based plating (for example, containing 10 to 25% by mass of Ni) Examples thereof include Zn—Ni plating, Zn—Al plating, Zn—Mg plating, and Zn—Al—Mg plating.
- Al-based plating layer examples include Al—Si based plating (for example, Al—Si based plating containing 10 to 20% by mass of Si).
- the metal plating layer only needs to be provided on one side of the surface-treated steel sheet, but may be provided on both sides. Moreover, the metal plating layer may be provided on the surface of the side which becomes the joint surface (mating surface) between the steel plates, the metal plating layer may be provided on the surface in contact with the electrode, The metal plating layer may be provided on the surface on the side to be the bonding surface and the surface in contact with the electrode.
- the adhesion amount of a metal plating layer is also arbitrary, it is preferable that it is 120 g / m ⁇ 2 > or less per one surface from a viewpoint of weldability.
- the steel type (component composition) of the steel sheet to be resistance spot welded in the present invention is not particularly limited, and the steel sheet production method is arbitrary such as cold rolling and hot rolling, and the structure of the steel sheet is also arbitrary. Moreover, there is no problem even if a hot-pressed steel sheet is used. Further, the thickness of the steel plate is not particularly limited, but is preferably in a range (about 0.5 to 4.0 mm) that can be used for a general automobile body.
- At least one of the steel plates is a high strength steel plate having a tensile strength of 590 MPa or more, more preferably 780 MPa or more. Since cracks are likely to occur when the tensile strength is increased, the present invention is applied to a plate assembly in which at least one steel plate of the plate assembly has a tensile strength of 590 MPa or more. The effect of this is remarkably obtained. In particular, a greater effect can be obtained when at least one of the steel plates of the plate set has a tensile strength of 780 MPa or more.
- the plurality of steel plates to be stacked may be the same or different, and a plurality of the same type steel plates may be stacked or a plurality of different types of steel plates may be stacked. Further, there is no problem even if the thickness of each steel plate is different, and a surface-treated steel plate having a metal plating layer and a steel plate not having a metal plating layer may be overlapped. In addition, in FIG. 2, although the example which piled up two steel plates was shown, you may pile up three or more steel plates.
- a plate set in which a plurality of steel plates are overlapped is sandwiched between a pair of welding electrodes (electrode 3 and electrode 4), energized while being pressed, and then the electrodes are released from the steel plate.
- a welding apparatus that can be used in the resistance spot welding method of the present invention, a welding apparatus that includes a pair of upper and lower electrodes and can arbitrarily control the pressure and welding current during welding can be used.
- the pressure mechanism air cylinder, servo motor, etc.
- type stationary, robot gun, etc.
- electrode shape, etc. of the welding apparatus there are no particular limitations on the pressure mechanism (air cylinder, servo motor, etc.), type (stationary, robot gun, etc.), electrode shape, etc. of the welding apparatus.
- the present invention can be applied to both direct current and alternating current, and the type of power source (single-phase alternating current, alternating current inverter, direct current inverter) and the like are not particularly limited.
- current means “effective current”.
- the shape of the electrode is not particularly limited.
- the type of the electrode tip is, for example, DR type (dome radius type), R diameter (radius type), D type (dome type) described in JIS C 9304: 1999.
- the tip diameter of the electrode is, for example, 4 mm to 16 mm, and the radius of curvature of the tip of the electrode is, for example, 10 mm to 100 mm.
- resistance spot welding is performed in a state where the electrode is always water-cooled.
- a plate assembly in which a plurality of steel plates (steel plate 1 and steel plate 2) are overlapped is sandwiched between a pair of welding electrodes (electrode 3 and electrode 4), energized while being pressed, and a nugget is formed by resistance heat generation.
- a joint is obtained by joining the steel plates stacked together.
- this energization has a specific pattern, that is, a main energization process, a non-energization process after the main energization process, and a post-energization process after the de-energization process. Note that energization is stopped after the post-energization step.
- the main energization step is a step of forming a nugget portion that becomes the nugget 5 when solidified.
- the energizing conditions and pressurizing conditions for forming the nugget portion are not particularly limited, and conventionally used welding conditions can be employed.
- the “nugget” is a melt-solidified portion generated in a welded portion in lap resistance welding, and the “nugget portion” is a melted portion that becomes a nugget when solidified (that is, a melted portion before solidification).
- the non-energization process is a process that is performed subsequent to the main energization process and is de-energized during the energization stop time Tc (cycle). By stopping energization, the nugget portion is cooled.
- One cycle is 20 ms (50 Hz).
- the post-energization process is a process that is performed following the non-energization process and is reheated without growing the nugget portion.
- the striking angle of the electrode is A (degrees)
- the current value in the main energization process is Im (kA)
- the current value in the post-energization process is Ip (kA)
- 1 + 0.1 ⁇ Tc is the variable B
- 1 + 0.2 ⁇ Tc is a variable C
- the welding condition satisfies the relationship of the above formula (I).
- the striking angle A is an angle at which the axis of the electrode 3 is inclined with respect to the vertical direction of the surface of the steel plate 1 shown in FIG. 2, that is, “the electrode pressing direction and the steel plate thickness direction. "An angle formed by".
- the direction of electrode pressing force is indicated by an arrow in the spot welding diagram described in 4.2.1 of JIS Z 3001-6: 2013, and is also indicated by an arrow in FIG. .
- the main energization process for forming the nugget part, the non-energization process for stopping energization for a predetermined time, and the post-energization process for reheating without growing the nugget part in this order, and the striking angle A By conducting energization under specific conditions according to the size of the crack, even when the striking angle A is greater than 0 degrees, for example, when the striking angle A is 0.2 (degrees) or more, cracking can be suppressed, and The joint strength can be sufficiently secured.
- the striking angle A is preferably 15 degrees or less from the viewpoint of securing the welded portion. This is because the formation of the weld itself becomes difficult when the angle exceeds 15 degrees.
- the striking angle A exceeds 0 degrees and less than 3 degrees, the bending stress applied to the welded portion by the striking angle is relatively small, so the tensile stress generated in the welded portion after the electrode is released does not become so large. That is, the alloying of a metal such as molten zinc, which is a plating layer on the steel sheet surface, may be limited.
- the striking angle A is 3 degrees or more and less than 7 degrees
- the allowance (increase) in the tensile stress generated in the weld after the electrode is released becomes significant. For this reason, it is necessary to promote alloying by performing a post-energization process with a higher current.
- the striking angle A When the striking angle A is in the range of 7 degrees or more and less than 15 degrees, the tensile stress generated in the welded portion becomes very large. Therefore, it is necessary to promote alloying by performing a higher current post-energization process. .
- action of alloying by post-energization reheating
- the energization stop time cooling time
- welding itself becomes difficult. Therefore, in the above formula (I), when the striking angle A is 15 degrees or more, it is preferable to review the welding method.
- the post-energization current in the post-energization process is defined by the ratio with the main energization, and the upper limit is determined in relation to Tc.
- the relational expression shown in the above formula (I) was found. About the coefficient in a relational expression, the optimal coefficient was calculated
- the above formula (I) preferably satisfies the relationship shown below.
- the stability of the fracture form means whether or not the plug fracture during the cross tension test can be stably obtained.
- the total thickness of the superposed steel plates (total thickness of the superposed steel plates) is t (mm), and the tip of the electrode
- D the diameter of the electrode tip
- the striking angle A exceeds 0 degrees and less than 3 degrees, the bending stress applied to the welded portion by the striking angle is relatively small, so the tensile stress generated in the welded portion after the electrode is released does not become so large. . Therefore, the alloying of a metal such as molten zinc, which is a plating layer on the steel sheet surface, may be limited. Thereby, even if energization stop time Tc (cycle) in a non-energization process is lengthened, the effect of the crack suppression by a post-energization process can be acquired.
- the striking angle A is 3 degrees or more and less than 7 degrees
- the allowance (increase) in the tensile stress generated in the weld after the electrode is released becomes significant.
- the post-energization process with a higher current is performed, and the energization stop in the non-energization process before the post-energization process is further shortened compared to the case where the hitting angle A is in the range of 0 degrees and less than 3 degrees. It is preferable to promote alloying by limiting. Thereby, the action of alloying can be obtained effectively.
- the striking angle A is in the range of 7 degrees or more and less than 15 degrees
- the tensile stress generated in the welded portion is very large.
- the effect of alloying by post-energization (reheating) can be effectively obtained by limiting the length to be shorter than that in the range of 7 degrees or more and less than 15 degrees.
- the nugget may be rapidly cooled and hardened, and the toughness may be reduced.
- the above formula (II) quenching and hardening of the nugget is suppressed.
- the energization stop time Tc (cycle) in the non-energization process Preferably, it is 4 cycles (50 Hz) or more.
- Tc cycle
- the non-energization process is too long, the welded portion is excessively cooled, and the specific resistance is lowered, so that it is difficult to obtain the effect of the post-energization process.
- the non-energization process which is too long also has the effect of increasing the welding tact.
- the tip diameter D (mm) of the electrode is not particularly limited, and is preferably 6 mm to 8 mm, for example. If it is less than 6 mm, sufficient nugget may not be obtained. On the other hand, if it exceeds 8 mm, there is a risk of electrode wear during process welding.
- welding is performed so as to satisfy the above-described formula (I), or formula (I) and formula (II), for example, depending on the electrode striking angle A (degree).
- the energization stop process and the post-energization process described above may be repeated twice or more in this order.
- the energization stop process and the post-energization process described above may be repeated twice or more in this order.
- alloying on the steel sheet surface is promoted, and the effect of suppressing cracking can be further improved.
- the number of repetitions increases, the manufacturing cost increases. Therefore, it is preferably 1 to 9 times from the viewpoint of construction efficiency.
- the welding current value (current value when energized) in the present invention is not particularly limited, and the welding current is, for example, 4 to 18 kA. However, since it is necessary to obtain a predetermined nugget diameter in construction, an excessive current value causes scattering, so the current value Im (kA) in the main energization process is, for example, 4 to 11 kA, The current value Ip (kA) is, for example, 5 to 12 kA.
- the applied pressure is preferably, for example, 2000 N to 7000 N (2 kN to 7 kN).
- the time from the start of energization to the end of energization is not particularly limited, and is preferably 8 to 30 cycles (50 Hz) in the main energization process, and preferably 3 to 10 cycles (50 Hz) in the post-energization process. .
- a welded joint in which a plurality of steel plates including at least one surface-treated steel plate having a metal plating layer on its surface are welded.
- a step of superimposing a plurality of steel plates including at least one surface-treated steel plate having a metal plating layer on the surface to obtain a plate set, and a step of welding the obtained plate set by the resistance spot welding method A welded joint can be manufactured by the manufacturing method having the following.
- FIG. 1 shows the tensile strength TS, plate thickness, and plating type of the steel plate used.
- Table 1 shows the tensile strength TS, plate thickness, and plating type of the steel plate used.
- the welding conditions are shown in Table 2-1, Table 2-2, and Table 2-3.
- the welding machine was an inverter DC resistance spot welder, and the two electrodes 3 and 4 were of the same shape.
- the electrodes 3 and 4 used are DR type chromium copper electrodes having a tip diameter D (mm) and a curvature radius of 40 mm shown in Table 2. Resistance spot welding was performed at room temperature (20 ° C.), and the electrode was always water-cooled.
- the applied pressure (kN) was constant throughout the main energization process, the non-energization process, and the post-energization process.
- the holding time after the end of the post-energization process was set to 5 ms under all welding conditions.
- the melting point of the base material of each steel plate in this example and the comparative example is in the range of 1400 to 1570 ° C.
- the melting point of hot dip galvanizing (GI) and galvannealed alloy (GA) is 400 to 500 ° C., respectively.
- the range is 600 to 950 ° C.
- the tensile strength TS (MPa) shown in Table 1 is a tensile test in accordance with the provisions of JIS Z 2241: 2011 by preparing a JIS No. 5 tensile specimen from each steel plate in a direction parallel to the rolling direction. Is the tensile strength obtained by carrying out
- the rupture mode is the plug rupture
- the fracture to the base material progresses and the ratio represented by the rupture part diameter / melt part diameter is 110% or more, symbol ⁇ , rupture part diameter / melt part
- the case where the ratio represented by the diameter was 100% or more and less than 110% was a symbol ⁇
- the ratio represented by the fracture part diameter / melted part diameter was a partial plug fracture or an interface fracture at the nugget of less than 100%.
- the case was evaluated as a symbol x.
- (3) Evaluation of stability of rupture mode in CTS In the evaluation result of (2) above, rupture at the time of CTS was further performed for the case where the ratio represented by the rupture part diameter / melted part diameter was 110% or more. The stability of the form was evaluated.
- Evaluation A 10 out of 10 bodies represented by a fracture part diameter / melting part diameter is 115% or more
- Evaluation B 5 to 9 out of 10 bodies are represented by a fracture part diameter / melting part diameter
- Tables 2-1 and 2 -2 and Table 2-3 The results obtained when the ratio represented by the fracture part diameter / melting part diameter is 115% or more are shown in Tables 2-1 and 2 -2 and Table 2-3.
Abstract
Description
0.25・(10・t+2)/50≦WT≦0.50・(10・t+2)/50 ・・(1)
300-500・t+250・t2≦HT ・・(2)
ただし、t:板厚(mm)、WT:溶接通電時間(ms)、HT:溶接通電後の保持時間(ms)
重ね合わせた複数の鋼板のうち少なくとも1枚は、表面に金属めっき層を有する表面処理鋼板であり、
通電として、ナゲット部を形成する通電を行なう主通電工程と、
主通電工程の後に通電休止時間Tc(サイクル)の間通電を休止する無通電工程と、
無通電工程の後にナゲット部を成長させずに再加熱する通電を行なう後通電工程とを有し、
電極の打角をA(度)、主通電工程の電流値をIm(kA)、後通電工程の電流値をIp(kA)、1+0.1・Tcを変数B、1+0.2・Tcを変数Cとしたとき、前記通電は、下記式(I)の関係を満たす抵抗スポット溶接方法。
式(I)
0<A<3の場合は、(22+A)・B/100<Ip/Im<C
3≦A<7の場合は、(17+A)・B/80<Ip/Im<C
7≦A<15の場合は、(11+A)・B/60<Ip/Im<C
式(II)
0<A<3の場合は、0<Tc<(103-A)・t/D
3≦A<7の場合は、0<Tc<5・(23-A)・t/D
7≦A<15の場合は、0<Tc<8・(17-A)・t/D
式(I)
0<A<3の場合は、(22+A)・B/100<Ip/Im<C
3≦A<7の場合は、(17+A)・B/80<Ip/Im<C
7≦A<15の場合は、(11+A)・B/60<Ip/Im<C
打角Aは、溶接部確保の観点より、15度以下が好ましい。15度を超える場合には溶接部形成そのものが困難となるからである。
打角Aが15度以上の場合、溶接そのものが困難となる。そのため、上記式(I)において、打角Aが15度以上の場合には溶接方法の見直しが好ましい。
本発明では、上記式(I)の関係を満たす通電を行うことにより、鋼種に関わらず、溶接部の割れ発生を抑制し、高い継手強度を得られる。なお、破断形態の安定性を得る観点より、上記式(I)は下記に示す関係を満たすことが好ましい。ここで、破断形態の安定性とは、十字引張試験時のプラグ破断が安定して得られるかどうかを意味する。
0<A<3の場合は、(22+A)・B/80<Ip/Im<1+0.15・Tc
3≦A<7の場合は、(17+A)・B/64<Ip/Im<1+0.15・Tc
7≦A<15の場合は、(11+A)・B/48<Ip/Im<1+0.15・Tc
式(II)
0<A<3の場合は、0<Tc<(103-A)・t/D
3≦A<7の場合は、0<Tc<5・(23-A)・t/D
7≦A<15の場合は、0<Tc<8・(17-A)・t/D
ただし、無通電工程が長すぎる場合は、溶接部が過剰に冷却してしまい、固有抵抗が低下することにより、後通電工程の効果を得づらくなる。また、長すぎる無通電工程は溶接タクトを増加させるという影響もある。このため、無通電工程は長くとも20サイクル(50Hz)以下が好ましい。
電極の先端径D(mm)は、特に限定されず、例えば6mm~8mmが好ましい。6mm未満の場合には十分なナゲットが得られない恐れがある。一方、8mm超えの場合には工程溶接時に電極損耗しやすい恐れがある。
本発明の実施例を以下に示す。本発明は2枚以上の鋼板を重ね合わせて板組とすることができる。一部の実施例については、図1に示すように、2枚の鋼板1および鋼板2を重ね合わせて一対の電極3、4によって挟持し、所定の溶接条件で抵抗スポット溶接を行い、溶接継手を作成した。それ以外の実施例については、3枚の鋼板(鋼板1、鋼板2および鋼板3)を重ね合わせた板組を用い、同様に溶接継手を作製した。なお、この場合の板組は、例えば図1に示す鋼板2の下層に鋼板3を重ね合わせた。
用いた鋼板の引張強さTS、板厚、めっき種を表1に示す。また、溶接条件を表2-1、表2-2および表2-3に示す。
(1)溶接部の割れの有無の評価
得られた各溶接継手について、溶接部を切断して断面を鏡面研磨し、走査型電子顕微鏡(倍率2000倍)により溶接部周囲の鋼板表層全面の割れの有無を観察した。溶接部に割れが観察されなかった場合を記号○、割れが観察された場合を記号×と評価した。
(2)十字引張試験(CTS)における破断形態の評価
得られた各溶接継手について、JIS Z 3137に準拠し、十字引張試験を行い、その破断部径をノギスにて計測した。さらに断面を切断してピクリン酸エッチングを行い、断面から溶融部径を測定した。このとき破断形態が、プラグ破断のうち、母材への破断が進展し、破断部径/溶融部径で表される割合が110パーセント以上であった場合を記号◎、破断部径/溶融部径で表される割合が100パーセント以上110パーセント未満であった場合を記号○、破断部径/溶融部径で表される割合が100パーセント未満の部分プラグ破断あるいはナゲットでの界面破断であった場合を記号×と評価した。
(3)CTSにおける破断形態の安定性の評価
上記(2)の評価結果において、破断部径/溶融部径で表される割合が110パーセント以上であったものを対象に、さらにCTS時の破断形態の安定性について評価を行った。この評価に用いる溶接継手は、表1、表2-1、表2-2および表2-3に示した条件で、溶接継手を10体ずつ作製した。得られた各溶接継手について、上記(2)に示した方法と同じ方法で、破断部径および溶融部径をそれぞれ求めた。ここでは、以下に示した基準に照らし、各記号を付与して評価した。記号A、Bの場合を優れる、記号Cの場合を良いと評価する。
評価A:10体中10体が、破断部径/溶融部径で表される割合が115パーセント以上
評価B:10体中5体以上9体以下が、破断部径/溶融部径で表される割合が115パーセント以上
評価C:10体中1体以上4体以下が、破断部径/溶融部径で表される割合が115パーセント以上
以上により得られた結果を表2-1、表2-2および表2-3に示す。
3、4 電極
5 溶接部(ナゲット)
Claims (4)
- 複数の鋼板を重ね合わせた板組を、一対の電極によって挟み、加圧しながら通電して接合する抵抗スポット溶接方法において、
重ね合わせた複数の鋼板のうち少なくとも1枚は、表面に金属めっき層を有する表面処理鋼板であり、
通電として、ナゲット部を形成する通電を行なう主通電工程と、
主通電工程の後に通電休止時間Tc(サイクル)の間通電を休止する無通電工程と、
無通電工程の後にナゲット部を成長させずに再加熱する通電を行なう後通電工程とを有し、
電極の打角をA(度)、主通電工程の電流値をIm(kA)、後通電工程の電流値をIp(kA)、1+0.1・Tcを変数B、1+0.2・Tcを変数Cとしたとき、前記通電は、下記式(I)の関係を満たす抵抗スポット溶接方法。
式(I)
0<A<3の場合は、(22+A)・B/100<Ip/Im<C
3≦A<7の場合は、(17+A)・B/80<Ip/Im<C
7≦A<15の場合は、(11+A)・B/60<Ip/Im<C - 重ね合わせた複数の鋼板の総板厚をt(mm)、電極の先端径をD(mm)としたとき、前記無通電工程は、下記式(II)の関係を満たす請求項1に記載の抵抗スポット溶接方法。
式(II)
0<A<3の場合は、0<Tc<(103-A)・t/D
3≦A<7の場合は、0<Tc<5・(23-A)・t/D
7≦A<15の場合は、0<Tc<8・(17-A)・t/D - 前記主通電工程の後に、前記無通電工程および前記後通電工程をこの順で2回以上繰り返す請求項1または2に記載の抵抗スポット溶接方法。
- 重ね合わせた複数の鋼板のうち少なくとも1枚は、引張強さが590MPa以上であることを特徴とする請求項1~3のいずれか1項に記載の抵抗スポット溶接方法。
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