WO2019124464A1 - Method for manufacturing resistance spot welded joint - Google Patents

Method for manufacturing resistance spot welded joint Download PDF

Info

Publication number
WO2019124464A1
WO2019124464A1 PCT/JP2018/046874 JP2018046874W WO2019124464A1 WO 2019124464 A1 WO2019124464 A1 WO 2019124464A1 JP 2018046874 W JP2018046874 W JP 2018046874W WO 2019124464 A1 WO2019124464 A1 WO 2019124464A1
Authority
WO
WIPO (PCT)
Prior art keywords
energization
current
steel plate
main
conduction
Prior art date
Application number
PCT/JP2018/046874
Other languages
French (fr)
Japanese (ja)
Inventor
古迫　誠司
泰山　正則
智伸 三浦
朋紀 柳川
Original Assignee
日本製鉄株式会社
豊田鉄工株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 日本製鉄株式会社, 豊田鉄工株式会社 filed Critical 日本製鉄株式会社
Priority to JP2019520159A priority Critical patent/JP6584728B1/en
Publication of WO2019124464A1 publication Critical patent/WO2019124464A1/en

Links

Images

Classifications

    • 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 method of manufacturing a resistance spot welded joint of a steel plate.
  • An automobile body is assembled by joining press-formed steel plates mainly by spot welding using resistance welding.
  • spot welding coexistence of securing of the nugget diameter according to plate thickness and generation
  • Patent Document 1 adopts spot welding of high-tensile steel plates by adopting a two-step energization method in which main energization is performed after improving the familiarity of contact surfaces of steel plates by preliminary energization.
  • a spot welding method is disclosed that suppresses the occurrence of dust.
  • Patent Document 2 after forming a nugget having a diameter of 3 t t to 5 t t by pre-energization, the current value is lowered, and then the current value is increased again to perform a constant current main energization or a pulsed main current
  • the spot welding method which suppresses generation
  • Patent Document 3 discloses a hot stamp steel plate covered with a film having high electrical resistance such as zinc oxide.
  • spot welding preliminary electrification is performed by pulsating electrification which repeats electrification and electrification stopping a plurality of times while pressurizing the steel plate with the electrode, and thereafter, the main electrification is continuously performed for a longer time than the maximum electrification time at the pulsation electrification
  • a spot welding method is disclosed that is adapted to do so.
  • Patent Document 4 when spot welding the same steel plate as in Patent Document 3, preliminary energization and main energization are performed by pulsation energization, and the maximum current of the main energization is conducted higher than the maximum current of the preliminary energization.
  • a spot welding method is disclosed.
  • vibration due to thermal expansion and contraction is given to the electrode contact surface of the steel sheet by repetition of energization and energization suspension at the time of pulsation energization of pre-energization, and high melting point
  • the oxide layer can be effectively eliminated to the outside of the welded portion, and the rapid cooling of the welded portion can be suppressed by sufficiently exerting the cooling effect of the electrode by stopping the energization of the pulsation electric current. For this reason, it is possible to obtain the effect of improving the familiarity of the contact surfaces of the steel plates in a short time while suppressing the generation of dust, and suppressing an increase in current density at the contact interface to suppress rapid nugget growth. Can. As a result, generation of dust in spot welding of a hot stamped steel sheet can be suppressed.
  • the nugget diameter is secured while suppressing the occurrence of indentation by setting the pressing force of the electrode in an appropriate range according to the plate thickness of the steel plate and further setting the energization pattern in an appropriate range.
  • a spot welding method is disclosed to prevent the occurrence of spattering.
  • steel plates used for hot stamping are often subjected to surface treatments such as zinc-based plating and aluminum-based plating.
  • surface treatments such as zinc-based plating and aluminum-based plating.
  • oxidation of the plating proceeds during heating to form an oxide layer such as zinc oxide or aluminum oxide.
  • oxide layers grow, the contact resistance of the steel plate after hot stamping (hot stamped steel plate) rises to 1 m ⁇ or more.
  • spot assembly welding of a vehicle body using such a hot stamped steel plate generation of dust is facilitated, and there is also a problem that it is difficult to ensure stable nugget diameter.
  • the high melting point oxide layer is formed of a welded portion by the action of pulsating current (current passing and current stopping repeated several times in a short time) using a welding power source of inverter direct current.
  • pulsating current current passing and current stopping repeated several times in a short time
  • inverter direct current current passing and current stopping repeated several times in a short time
  • the effect may not be sufficient, for example, when the oxide layer is thick, and even in such a case, it is desirable that generation of dust can be further suppressed.
  • the inverter direct current which has recently become mainstream because of advantages such as small current, has a narrower appropriate current range than alternating current as disclosed in Patent Document 4.
  • Patent Document 5 secures the nugget diameter and suppresses the generation of dust by changing the pressing force according to the plate thickness and setting the energization pattern in an appropriate range.
  • the layer is thick, the effect may not be sufficient. Even in such a case, it is desirable that the generation of dust can be further suppressed.
  • a manufacturing method of a resistance spot welded joint in which two or more steel plates are stacked, and the stacked portion is pressurized by an electrode and energized, and the stacked portion is pressed by the electrode at a pressure of 3.9 kN or more
  • the current in the preliminary electrification step and the main electrification step is all direct current, and in the preparatory electrification step, the electrification method of 80% or more of the electrification time ta is continuous electrification continuously, and the main A method of manufacturing a resistance spot welded joint, characterized in that the energization method of the energization step is pulsation energization which repeats energization and non-activation a
  • a welding method capable of suppressing dust and stably securing the nugget diameter against spot welding of a steel plate in which a substance having a high electrical resistance is present in the surface layer like a hot stamped steel plate.
  • “appropriate current range” refers to the first current at which the nugget diameter is 4 ⁇ t or more, where t is an average value of the plate thicknesses of the steel plates to be spot welded by gradually increasing the current.
  • it is a range from “4 t t current” to the current where dust is generated for the first time.
  • the surface-treated hot stamped steel plate an intermetallic compound and an iron-based solid solution are formed on the surface by an alloying reaction of a plated metal and a steel base, and a metal derived from plating (for example, It has an oxide film which has Zn as a main component. Therefore, compared with a cold pressed steel plate, the surface-treated hot stamped steel plate has a high resistance at the contact portion between the steel plates and a large amount of heat generation.
  • alloying between the plated metal and the steel proceeds in the hot stamping process, and the melting point in the vicinity of the surface also has a high value close to that of iron. Is hard to soften and expansion of the current-carrying path is suppressed.
  • the heat generation efficiency is higher in the inverter DC system energization than in the single-phase alternating current, the formation of the nugget at the initial stage of the energization becomes very rapid. For this reason, the growth of the pressure contact portion around the nugget can not catch up and the molten metal can not be confined, and it is presumed that internal dust is generated.
  • direct current does not have a current pause time like single-phase alternating current, it is difficult to obtain a cooling effect by the electrode. For this reason, it is presumed that the nugget easily grows in the thickness direction, the melted portion reaches the outermost layer of the steel plate, and surface dust is generated.
  • "direct current” does not include energization that reverses plus / minus like alternating current. For this reason, not only energization in which current is always flowing as in continuous energization, but also pulsation energization in which energization and energization suspension are repeated a plurality of times in a short time is determined as direct current unless plus / minus reversal occurs.
  • the present inventors divide the oxide layer regardless of the thickness of the oxide layer and the like during spot welding by two-step current conduction, and a part of the oxide layer is reliably excluded outside the weld, which is rapid.
  • We examined means to suppress the growth of molten metal.
  • the oxide dispersion / movement (exclusion) effect in the pre-energization is increased. It has been found that the passage of the pulsating current gradually increases the area in which the oxide is dispersed and moved, and also suppresses the rapid growth of molten metal, thereby enabling the suppression of dust.
  • the main energization is an energization pattern of constant current.
  • pre-energization with a current value Ia: 3.5 kA and an energization time ta: 0.4 sec is performed, and then, as shown in FIG.
  • the electrode is a DR (dome radius) type in which the curved surface at the tip is a DR (dome radius) type consisting of a tip curved surface (initial contact portion) and a corner curved surface as shown in FIG. Using.
  • the pressure applied during energization was 450 kgf (4.4 kN) and constant from the pre-energization to the main energization.
  • FIG. 1 shows the results of spot welding with a pattern of main current conduction only at a constant current, a pattern of main current conduction at a predetermined precurrent current + constant current, and a main current conduction pattern by precurrent current + pulsation current.
  • Point E in FIG. 1 indicates an experimental point at which dust is generated.
  • the upper limit current value generated by dust increases by welding by the two-step energization of the preliminary energization and the main energization, as compared with the case of welding with the energization pattern of only the main energization,
  • the upper limit current value generated by the dust greatly increases to 5 ⁇ t or more, and the appropriate welding current range is expanded, compared to the case where the main energization is performed with constant current. It was confirmed to do.
  • the present inventors further change the pressure of the electrode and the energization condition of the preliminary energization on the premise that the energization is performed in two stages of the preliminary energization and the main energization, and the dust is
  • the conditions that can suppress and obtain the necessary nugget diameter by setting it as the condition specified in at least the above (1) and (2), it is not appropriate to generate the required nugget diameter without generating dust Welding current range was found to be expanded.
  • the present invention heats a material steel plate (for example, an electroplated steel plate or a thin steel plate containing a hot-dip galvanized steel plate) made of high strength steel to a hardenable temperature and austenitizes it, and then simultaneously cools and bakes with a die and bakes.
  • a hot-stamped steel plate to be inserted hereinafter referred to as “hot-stamped steel plate”), the surface of which is subjected to surface treatment such as zinc-based plating or aluminum-based plating to prevent iron scale generation when heated to high temperatures.
  • Hot-stamped hot-stamped steel plates are mainly targeted for spot welding.
  • the present invention is also applicable to steel plates other than hot stamped steel plates, and is not particularly limited to hot stamped steel plates.
  • a hot stamped steel plate is not a flat plate but a formed body that has been formed and processed. However, since it is sufficient if the portion to be overlapped is a plate, in the present invention it is It is called "hot stamped steel plate” including.
  • a hot stamped steel plate obtained by hot stamping a zinc-based plated steel plate or an aluminum-based plated steel plate may be referred to as “surface-treated hot stamped steel plate” in the following description.
  • an intermetallic compound and an iron-based solid solution are formed on the surface by an alloying reaction between a zinc-based or aluminum-based plated film and the steel of the base material, and the outer surface is further derived from plating. It has an oxide layer containing a metal (for example, zinc in the case of zinc-based plating) as a main component. Therefore, the surface-treated hot stamped steel plate has a contact resistance as high as 1 m ⁇ or more as compared to a bare steel plate, and a large amount of heat is generated by energization.
  • the alloying of the plating and the steel proceeds in the hot stamping process, and the melting point in the vicinity of the surface also has a high value close to iron, so compared to the steel plate provided with the plated film before heating ,
  • the contact portion between the steel plates is difficult to soften.
  • the present invention is particularly effective when applied to spot welding of a steel plate having such contact resistance of 1 m ⁇ or more.
  • the measuring method of contact resistance is mentioned later.
  • the thickness of the steel plate there is no particular limitation on the thickness of the steel plate.
  • the thickness of a steel plate used in automobile parts or vehicle bodies is 0.6 to 3.2 mm, and the method of producing a resistance spot welded joint of the present invention has a sufficient effect in this range.
  • At least one of the steel plates on the side to which the electrode contacts includes a surface-treated hot stamped steel plate.
  • a steel plate combined with a surface treatment hot stamp steel plate a combination including a surface treatment hot stamp steel plate and a high tensile steel plate of 590 MPa grade or more is preferable.
  • resistance spot welding is performed on a plate assembly in which two or three steel plates are stacked.
  • the surface area of the tip surface of the electrode having a radius of curvature of 40 mm or more is the same as the electrode pressing direction (usually the electrode length method)
  • the area A of the region projected on a plane perpendicular to the above and the diameter of a circle equivalent to the area are defined as the electrode tip diameter d. That is, the electrode tip diameter d is calculated as 2 ⁇ (A / ⁇ ).
  • the surface area with a radius of curvature of 40 mm or more is projected onto a plane perpendicular to the pressing direction of the electrode (usually the same as the electrode length method). If the area is circular, the diameter of the circle is the electrode tip diameter d.
  • the diameter d and the radius of curvature (tip R) of the tip curved portion of the electrode are not particularly limited, but generally, the diameter is about 5 to 6 mm and the radius of curvature is about 40 to 60 mm.
  • an electrode for example, an electrode defined in JIS C9304: 1999 can be used.
  • an electrode having a curvature R of 40 to 60 mm for the DR-type tip curved portion is exemplified.
  • chromium copper or alumina-dispersed copper is preferable.
  • Alumina-dispersed copper is preferable in terms of preventing welding and surface dust.
  • a DC welding power source such as an inverter DC system
  • the inverter direct current method has a merit that it can be mounted on a robot with a small load and can be made small, and therefore it is used in particular in automation lines.
  • the inverter direct current method has high heat generation efficiency because it can continuously apply current without continuous on / off of the current as in the single-phase alternating current method conventionally used in continuous energization.
  • the pulse current waveform can be easily controlled.
  • the electrode pressurizing force and the energization condition of the preliminary energization are set as the specific conditions.
  • the pressing force is increased to break and disperse the oxide layer on the surface of the steel plate, and a part of the oxide layer is moved (excluded) outside the contact range of the electrode to make the surface contact resistance Reduce.
  • the current value is lowered to suppress the rapid growth of nuggets at the initial stage of contact and to prevent the generation of dust.
  • the pressure is set to 3.9 kN or more, and the maximum value of the current Ia (kA) in the pre-energization is set to satisfy Ia ⁇ 6 kA. By doing this, it is possible to reduce the contact resistance on the surface of the steel sheet without generating dust.
  • the applied pressure is preferably 4.4 kN or more. More preferably, it is 4.5 kN or more, 4.8 kN or more, 5.0 kN or more, or 5.4 kN or more.
  • the pressing force is preferably 10 kN or less, 9.5 kN or less, or 9.0 kN or less because the nugget formation during main conduction may be difficult due to a decrease.
  • the energization time in the pre-energization is equal to or longer than the time which can destroy the oxide layer of the portion of the steel plate surface in contact with the electrode and partially exclude it from the contact range. Specifically, electricity is applied for ta (sec) so as to satisfy the following equations (1) and (2).
  • Ia (t) (kA) in a formula (1) and a formula (2) is a current value of preliminary energization at the time of t (sec) progress from a preliminary energization start.
  • the current integral value S in the pre-energization defined by the following equation (3) is set to 0.5 kA ⁇ s or more as shown in the equation (2).
  • the lower limit of the current integral value S may be 0.6 kA ⁇ s, 0.8 kA ⁇ s, 1.0 kA ⁇ s or 1.2 kA ⁇ s.
  • the energization time of the pre-energization process it is often 0.05 to 1 s.
  • the lower limit of the current application time may be 0.1 s, 0.15 s, or 0.2 s.
  • the upper limit may be 0.9s, 0.8s, 0.7s or 0.8s.
  • the current in the preliminary energization (the maximum value of the current in the preliminary energization when the current fluctuates during the preliminary energization) is 6 kA or less.
  • the lower limit is 0 kA in consideration of the pulsation energization. If necessary, it may be 1 kA or 2 kA.
  • the main purpose is to destroy and separate the oxide layer of the part in contact with the electrodes on the surface of the steel plate and the part where steel plates are in contact with each other, and move a part out of the contact range. It is not necessary to form a nugget.
  • the energization time ta in the preliminary energization is equal to or longer than the time in which the oxide layer on the surface of the steel sheet can be separated, and more preferably, is energized to satisfy the above relationship in relation to the current value I (t).
  • Continuous energization means energizing so that the magnitude of the direct current does not reach 0 amps, and not only the current of a constant magnitude continues to flow but also the magnitude of the direct current increases with the passage of time.
  • the magnitude of the direct current may be increased or decreased over time so that the magnitude of the direct current does not become 0 amp.
  • continuous energization does not include energization for which there is a long-time energization suspension (for example, energization suspension for 1 s or more) which is not normal pulsation energization.
  • the time of the preliminary energization is continuous energization, and the current may be 100% continuous energization.
  • a short time (for example, about 0.01 to 0.1 s) of the energization stop time such as passage of electricity is included in the energization time, but the energization stop time of 1 second or more is excluded from the energization time.
  • pulsating energization is repeated, in which a cycle consisting of a period t1 of applying a pulse current and an energization stop period t0 is repeated twice or more.
  • a condition in which a nugget of a predetermined diameter is obtained without generating dust is adopted.
  • a nugget diameter of 4 ⁇ t or more is often used as a production control standard.
  • the current value Ib is a current value higher than the current value Ia of the pre-energization, that is, Ib> Ia.
  • the electricity supply system made into 0.02 s rest, for example after electing 0.06 s is illustrated.
  • the shape of the pulse current is not limited to the rectangular shape as shown in FIG. 2, but may be a shape in which rising and falling portions of the pulse are inclined with respect to time.
  • the first cycle of energization of pulsation although the pre-energization is conducted continuously in FIG. 2, the first cycle of energization can be started after the pause period as shown in FIG. .
  • the current value can be gradually increased.
  • the gradual increase of the current value may be continuous or stepwise.
  • FIG. 5 (a) shows an example in which the current is gradually increased at the initial stage of the start of the preliminary energization, that is, the up-slope energization is performed.
  • the solid line shows the example from the beginning, and the broken line shows an example in which up-slope conduction is performed from the current value in the middle.
  • FIG. 5 (b) an example in which up-slope energization is performed to gradually increase the peak current at the beginning of the start of the main energization is shown in FIG. 5 (c). An example is shown respectively.
  • the total of the energization time in the main energization by the pulsation energization can be within the normal condition range. For example, about 10 times the plate thickness per sheet (in the case of welding of steel plates having a plate thickness of 1 mm, about 0.2 s) is recommended as a measure of the energization time. Also in the present invention, the total conduction time in the main conduction is about 10 times the thickness of the plate. However, since the steel plate temperature rises due to the pre-energization and the interface of the steel plate melts depending on the conditions, it can be made shorter than this reference time. That is, depending on the conditions of the pre-energization, the total energization time at the time of main energization may be shortened to about 4 to 8 times the plate thickness in some cases.
  • the definition of the pre-energization and the main energization is as follows.
  • the measuring method of contact resistance is shown in FIG.
  • a steel plate (which may or may not be plated) is sandwiched between one spot welding electrode.
  • a current I of 1 A is supplied to the electrode.
  • the voltage V1 between the upper electrode 1a and the steel plate 2 and the voltage V2 between the lower electrode 1b and the steel plate 2 are measured.
  • the electric resistance between the upper electrode and the steel plate is R1
  • the electric resistance between the lower electrode and the steel plate is R3
  • the resistance due to the specific resistance of the steel plate bulk (base material) itself is R2.
  • R2 can be approximated to zero.
  • the resistance of the upper and lower electrodes can be approximated to zero. Therefore, the relationship between the measured voltages V1 and V2 and the electrical resistances R1 and R3 can be approximated as follows.
  • the larger one of R1 and R3 is used as the contact resistance in the present invention.
  • a steel plate having a contact resistance of 1 m ⁇ or more is mainly applied, but the present invention is applicable to a steel plate having a contact resistance of less than 1 m ⁇ , and it is not necessary to be limited to a steel plate having a contact resistance of 1 m ⁇ or more.
  • the lower limit of the contact resistance may be limited to 2 m ⁇ , 5 m ⁇ , 8 m ⁇ or 10 m ⁇ .
  • the upper limit of the contact resistance is not particularly limited, but may be 100 m ⁇ , 50 m ⁇ , 30 m ⁇ , or 20 m ⁇ .
  • the welding conditions are shown in Table 1.
  • the current value of the main conduction ranged from 4 kA to the current value at which dust is generated.
  • the pressing force in the two-stage energization was constant from the preliminary energization to the main energization.
  • the total energization time in the main energization was set to be about 0.4 s. All power supplies were inverter DC power supplies.
  • the current value of the main conduction step by setting the current value of the main conduction step to a value of 4 ⁇ t current or more and less than the dust generation current, dust is not generated even in welding of actual parts, and shunting and electrode wear and tear Even if there is a disturbance due to the above, it is possible to stably secure a spot welded portion in which the nugget diameter is 4tt or more.
  • the appropriate current range did not satisfy the target of 1.5 kA or more.

Abstract

Provided is a method for manufacturing a resistance spot welded joint in which generation of expulsion can be suppressed when spot welding is performed on a steel sheet including at least one hot stamping steel sheet. In the method, when two or more steel sheets are overlaid with each other and resistance spot welding is performed on the resultant overlaid part, the resistance spot welding is performed through two-step conduction comprising: a preliminary conduction step using an electrode pressing force of not less than 3.9 kN at a current Ia(t) (kA) for a time period ta (sec); and a main conduction step. All the currents for the preliminary conduction and the main conduction are direct currents, not less than 80% of the preliminary conduction time period is set to continuous conduction, Ia(t) and ta (sec) satisfy Ia(t) ≤ 6.0 (kA) and formula (AA), and the main conduction is set to pulsation conduction.

Description

抵抗スポット溶接継手の製造方法Method of manufacturing resistance spot welded joint
　本発明は、鋼板の抵抗スポット溶接継手の製造方法に関するものである。 The present invention relates to a method of manufacturing a resistance spot welded joint of a steel plate.
　自動車の車体はプレス成形された鋼板を、主に抵抗溶接によるスポット溶接にて接合することで組み立てられる。スポット溶接では、板厚に応じたナゲット径の確保とチリ（散り）の発生抑制の両立が求められる。 An automobile body is assembled by joining press-formed steel plates mainly by spot welding using resistance welding. In spot welding, coexistence of securing of the nugget diameter according to plate thickness and generation | occurrence | production suppression of a dust (dispersion) is calculated | required.
　近年、自動車の分野では、車体の軽量化と衝突安全性を確保するため、骨格部品に高強度鋼板の採用が拡大しつつある。中でも、高強度鋼板を用いて熱間成形したホットスタンプ鋼板は高い成形精度と低いプレス荷重を両立できるため、その採用が進んでいる。 In recent years, in the field of automobiles, in order to ensure weight reduction of a vehicle body and collision safety, adoption of high strength steel plates for frame parts is being expanded. Among them, a hot stamped steel plate which is hot-formed using a high-strength steel plate can be compatible with high forming accuracy and low press load, and therefore its adoption is in progress.
　しかし、高強度鋼板を１段通電方式でスポット溶接する場合ではチリが発生しやすく、適正電流範囲の確保が困難となる。また、ホットスタンプ用鋼板の表層に亜鉛めっきやアルミめっきがあると、加熱中にめっきの酸化が進んで酸化亜鉛や酸化アルミなどが形成される。これら酸化物が成長すると鋼板の接触抵抗が上昇する。その結果、車体のスポット組付溶接においてチリが発生しやすくなり、ナゲット径の安定確保が困難となるという問題もある。 However, in the case of spot welding a high strength steel plate in a one-step current application method, dust is easily generated, and it becomes difficult to secure an appropriate current range. In addition, if zinc plating or aluminum plating is present on the surface layer of the steel plate for hot stamping, oxidation of the plating proceeds during heating to form zinc oxide, aluminum oxide or the like. When these oxides grow, the contact resistance of the steel plate increases. As a result, in spot assembly welding of a vehicle body, dust is easily generated, and there is also a problem that it is difficult to ensure the stability of the nugget diameter.
　このような問題に対して、特許文献１には、予備通電により鋼板の接触面同士のなじみを向上させた後に本通電を行う２段通電方法を採用することによって、高張力鋼板のスポット溶接におけるチリの発生を抑制するスポット溶接方法が開示されている。 In order to solve such problems, Patent Document 1 adopts spot welding of high-tensile steel plates by adopting a two-step energization method in which main energization is performed after improving the familiarity of contact surfaces of steel plates by preliminary energization. A spot welding method is disclosed that suppresses the occurrence of dust.
　特許文献２には、予備通電により３√ｔ～５√ｔの径を有するナゲットを形成させた後に電流値を下げ、その後、再び電流値を上げて一定電流の本通電又はパルス状の本通電を行う通電方式を採用することによって、高張力鋼板のスポット溶接におけるチリの発生を抑制するスポット溶接方法が開示されている。 In Patent Document 2, after forming a nugget having a diameter of 3 t t to 5 t t by pre-energization, the current value is lowered, and then the current value is increased again to perform a constant current main energization or a pulsed main current The spot welding method which suppresses generation | occurrence | production of the dust in the spot welding of a high tension steel plate is disclosed by employ | adopting the electricity supply system which performs.
　また、そのような予備通電、本通電による２段通電方法をホットスタンプ鋼板のスポット溶接に適用した例として、特許文献３では、酸化亜鉛等の電気抵抗が高い皮膜で覆われたホットスタンプ鋼板をスポット溶接する際、予備通電を、電極で鋼板を加圧しながら通電と通電休止を複数回繰り返すパルセーション通電で行い、その後に、パルセーション通電時の最大通電時間よりも長時間連続的に本通電するようにしたスポット溶接方法が開示されている。 Further, as an example of applying such a preliminary electrification or a two-step electrification method by main electrification to spot welding of a hot stamp steel plate, Patent Document 3 discloses a hot stamp steel plate covered with a film having high electrical resistance such as zinc oxide. When spot welding, preliminary electrification is performed by pulsating electrification which repeats electrification and electrification stopping a plurality of times while pressurizing the steel plate with the electrode, and thereafter, the main electrification is continuously performed for a longer time than the maximum electrification time at the pulsation electrification A spot welding method is disclosed that is adapted to do so.
　さらに、特許文献４では、特許文献３と同様の鋼板をスポット溶接する際、予備通電と本通電を、パルセーション通電で行い、かつ、本通電の最大電流を予備通電の最大電流より高く通電するようにしたスポット溶接方法が開示されている。 Further, in Patent Document 4, when spot welding the same steel plate as in Patent Document 3, preliminary energization and main energization are performed by pulsation energization, and the maximum current of the main energization is conducted higher than the maximum current of the preliminary energization. A spot welding method is disclosed.
　この特許文献３、４に開示の方法では、予備通電のパルセーション通電時に、通電と通電休止とが繰り返されることにより、熱膨張、収縮による振動を鋼板の電極接触面に与えて、高融点の酸化物層を効果的に溶接部の外側に排除することができるとともに、パルセーション通電の通電休止により電極の冷却効果を十分に働かせて、溶接部の急激な温度上昇を抑制できる。このため、チリの発生を抑制しつつ、短時間で鋼板の接触面同士のなじみを向上させる効果を得ることができ、接触界面での電流密度の上昇を抑制し急激なナゲット成長を抑制することができる。その結果、ホットスタンプ鋼板のスポット溶接におけるチリの発生を抑制することができる。 According to the methods disclosed in Patent Documents 3 and 4, vibration due to thermal expansion and contraction is given to the electrode contact surface of the steel sheet by repetition of energization and energization suspension at the time of pulsation energization of pre-energization, and high melting point The oxide layer can be effectively eliminated to the outside of the welded portion, and the rapid cooling of the welded portion can be suppressed by sufficiently exerting the cooling effect of the electrode by stopping the energization of the pulsation electric current. For this reason, it is possible to obtain the effect of improving the familiarity of the contact surfaces of the steel plates in a short time while suppressing the generation of dust, and suppressing an increase in current density at the contact interface to suppress rapid nugget growth. Can. As a result, generation of dust in spot welding of a hot stamped steel sheet can be suppressed.
　特許文献５には、電極の加圧力を鋼板の板厚に応じた適正な範囲とし、さらに、通電パターンを適正範囲とすることで、インデンテーションの発生を抑制しつつナゲット径を確保し、かつ、散りの発生を防止するスポット溶接方法が開示されている。 In Patent Document 5, the nugget diameter is secured while suppressing the occurrence of indentation by setting the pressing force of the electrode in an appropriate range according to the plate thickness of the steel plate and further setting the energization pattern in an appropriate range. A spot welding method is disclosed to prevent the occurrence of spattering.
特開２０１０－１８８４０８号公報JP, 2010-188408, A 特開２０１０－２０７９０９号公報JP, 2010-207909, A 国際公開第２０１５／００５１３４号WO 2015/005134 国際公開第２０１５／０９３５６８号International Publication No. 2015/093568 国際公開第２０１４／０４５４３１号International Publication No. 2014/045431
　ホットスタンプに用いる鋼板は、高温に加熱した時に鉄スケールの発生を防止するため、亜鉛系めっき、アルミニウム系めっきなどの表面処理が施されたものが多い。そのような表面処理鋼板をホットスタンプすると、加熱中にめっきの酸化が進んで酸化亜鉛や酸化アルミなどの酸化物層が形成される。これら酸化物層が成長すると、ホットスタンプ後の鋼板（ホットスタンプ鋼板）では接触抵抗が１ｍΩ以上に上昇する。そのようなホットスタンプ鋼板を用いた車体のスポット組付溶接において、チリの発生が容易となり、ナゲット径の安定確保が困難となるという問題もある。 In order to prevent the generation of iron scale when heated to a high temperature, steel plates used for hot stamping are often subjected to surface treatments such as zinc-based plating and aluminum-based plating. When such a surface-treated steel sheet is hot-stamped, oxidation of the plating proceeds during heating to form an oxide layer such as zinc oxide or aluminum oxide. When these oxide layers grow, the contact resistance of the steel plate after hot stamping (hot stamped steel plate) rises to 1 mΩ or more. In spot assembly welding of a vehicle body using such a hot stamped steel plate, generation of dust is facilitated, and there is also a problem that it is difficult to ensure stable nugget diameter.
　特許文献３、４に開示の技術は、インバータ直流の溶接電源を用いたパルセーション通電（通電及び通電休止を短時間に複数回繰り返す通電）の作用によって、高融点の酸化物層を溶接部の外側に排除することにより、予備通電時における鋼板の接触面同士のなじみを向上させるものである。しかし、酸化物層が厚い場合など効果が十分でない場合があり、そのような場合でもさらにチリの発生を抑制できることが望まれる。また、電流が小さいなどの利点があるために最近は主流となりつつあるインバータ直流では、特許文献４の開示されているように、交流より適正電流範囲が狭くなるという問題がある。 In the techniques disclosed in Patent Documents 3 and 4, the high melting point oxide layer is formed of a welded portion by the action of pulsating current (current passing and current stopping repeated several times in a short time) using a welding power source of inverter direct current. Exclusion to the outside improves the familiarity of the contact surfaces of the steel plates at the time of pre-energization. However, the effect may not be sufficient, for example, when the oxide layer is thick, and even in such a case, it is desirable that generation of dust can be further suppressed. In addition, there is a problem that the inverter direct current, which has recently become mainstream because of advantages such as small current, has a narrower appropriate current range than alternating current as disclosed in Patent Document 4.
　特許文献５に開示の技術は、板厚に応じて加圧力を変え、さらに通電パターンを適正な範囲とすることにより、ナゲット径を確保し、チリの発生も抑制するものであるが、酸化物層が厚い場合など効果が十分でない場合があり、そのような場合でもさらにチリの発生を抑制できることが望まれる。 The technique disclosed in Patent Document 5 secures the nugget diameter and suppresses the generation of dust by changing the pressing force according to the plate thickness and setting the energization pattern in an appropriate range. When the layer is thick, the effect may not be sufficient. Even in such a case, it is desirable that the generation of dust can be further suppressed.
　本発明では、このような実情に鑑み、少なくとも一枚のホットスタンプ鋼板を含む鋼板のスポット溶接の際、チリの発生を抑制できるスポット溶接技術を提供することを課題とする。 In the present invention, in view of such circumstances, it is an object of the present invention to provide a spot welding technique capable of suppressing the generation of dust in spot welding of a steel plate including at least one hot stamped steel plate.
　表層に酸化亜鉛などの電気抵抗の高い物質が形成されている接触抵抗の高い鋼板同士を組合せてスポット溶接する場合において、表層の電気抵抗の高い物質を分散又は移動させてチリを抑制し、安定してナゲット径を確保する手段について検討した。 When spot welding is performed by combining steel plates with high contact resistance in which a substance with high electrical resistance such as zinc oxide is formed on the surface layer, the substance with high electrical resistance in the surface layer is dispersed or moved to suppress dust and stabilize We examined the means to secure the nugget diameter.
　その結果、特許文献１～５のように本通電の前に予備通電を実施する際に、電極の加圧力を高めた条件の下で予備通電を実施すると、表層の電気抵抗の高い物質を効果的に分散又は移動させることができ、さらに本通電をパルセーション通電とすることにより、酸化物が分散・移動する領域が徐々に拡大し、本通電でのチリの発生電流が上昇し、適正な溶接電流範囲を拡大することができることを見出した。 As a result, when performing pre-energization before main energization as in Patent Documents 1 to 5, if pre-energization is performed under conditions where the pressure of the electrode is increased, substances having high surface electric resistance can be effectively obtained. It is possible to disperse or move the main current, and further, by making the main current application a pulsation current, the region where the oxide is dispersed and moved is gradually expanded, and the current generated from dust during the main current is increased, which is appropriate. It has been found that the welding current range can be expanded.
　そして、電極加圧力、予備通電の通電条件についてさらに検討した結果、表層の電気抵抗の高い物質を分散又は移動させてチリを抑制し、安定してナゲット径を確保できる条件を見出した。 Then, as a result of further examination of the electrode pressing force and the energizing condition of the preliminary electrification, it was found that the substance having high electric resistance in the surface layer is dispersed or moved to suppress dust and stably maintain the nugget diameter.
　そのようにしてなされた本発明の要旨は、以下のとおりである。 The subject matter of the present invention thus made is as follows.
　［１］２枚以上の鋼板を重ね合わせ、その重ね合わせ部を電極により加圧して通電する抵抗スポット溶接継手の製造方法であって、３．９ｋＮ以上の加圧力で前記電極により前記重ね合わせ部を加圧しつつ電流Iａ（ｔ）(ｋＡ)を以下の式（１）、（２）を満たすように通電時間ｔａ（ｓｅｃ）の間通電する予備通電工程と、前記予備通電工程後に本通電工程を備え、前記予備通電工程及び前記本通電工程の電流はすべて直流であり、前記予備通電工程において、前記通電時間ｔａの８０％以上の通電方式が連続的に通電する連続通電であり、前記本通電工程の通電方式は通電と通電休止とを複数回繰り返すパルセーション通電であることを特徴とする抵抗スポット溶接継手の製造方法。 [1] A manufacturing method of a resistance spot welded joint in which two or more steel plates are stacked, and the stacked portion is pressurized by an electrode and energized, and the stacked portion is pressed by the electrode at a pressure of 3.9 kN or more Pre-energization step of energizing the current Ia (t) (kA) for the energizing time ta (sec) to satisfy the following equations (1) and (2) while pressurizing the current, and the main energization step after the pre-energization step The current in the preliminary electrification step and the main electrification step is all direct current, and in the preparatory electrification step, the electrification method of 80% or more of the electrification time ta is continuous electrification continuously, and the main A method of manufacturing a resistance spot welded joint, characterized in that the energization method of the energization step is pulsation energization which repeats energization and non-activation a plurality of times.
　　Iａ(t)≦６．０（ｋＡ）　　　　　　　　　　・・・式（１）
Figure JPOXMLDOC01-appb-M000002
 Ia (t) ≦ 6.0 (kA) formula (1)
Figure JPOXMLDOC01-appb-M000002
　［２］前記予備通電工程において電流を増大させることを特徴とする前記［１］の抵抗スポット溶接継手の製造方法。 [2] The method for producing a resistance spot welded joint according to the above [1], wherein the current is increased in the pre-energization step.
　［３］前記本通電工程において電流を増大させることを特徴とする前記［１］又は［２］の抵抗スポット溶接継手の製造方法。 [3] The method for producing a resistance spot welded joint according to the above [1] or [2], wherein the current is increased in the main conduction step.
　［４］前記鋼板の少なくとも1枚の鋼板の接触抵抗が１ｍΩ以上であることを特徴とする前記［１］～［３］のいずれかの抵抗スポット溶接継手の製造方法。 [4] The method for producing a resistance spot welded joint according to any one of the above [1] to [3], wherein the contact resistance of at least one steel plate of the steel plate is 1 mΩ or more.
　本発明によれば、ホットスタンプ鋼板のように、表層に電気抵抗の高い物質が存在している鋼板のスポット溶接に対し、チリを抑制し、安定してナゲット径を確保できる溶接方法を提供する。 According to the present invention, there is provided a welding method capable of suppressing dust and stably securing the nugget diameter against spot welding of a steel plate in which a substance having a high electrical resistance is present in the surface layer like a hot stamped steel plate. .
板厚１．４ｍｍの１８００ＭＰａ級ホットスタンプ材を、通電パターンを変化させてスポット溶接した場合におけるナゲット成長挙動を示すグラフである。It is a graph which shows the nugget growth behavior in the case of performing spot welding by changing an electricity supply pattern, and changing an electricity supply pattern, and a 1800 mm class hot stamp material of 1.4 mm of board thickness. スポット溶接の通電パターンの一例を示す図である。It is a figure which shows an example of the electricity supply pattern of spot welding. 電極先端部の直径を説明するための図である。It is a figure for demonstrating the diameter of an electrode front-end | tip part. スポット溶接の通電パターンの他の例を示す図である。It is a figure which shows the other example of the electricity supply pattern of spot welding. スポット溶接の通電パターンのさらに他の例を説明するための図である。It is a figure for demonstrating the further another example of the electricity supply pattern of spot welding. 接触抵抗の測定方法を説明するための図である。It is a figure for demonstrating the measuring method of contact resistance.
　以下、添付の図面を参照して本発明の実施の形態を説明する。 Hereinafter, embodiments of the present invention will be described with reference to the attached drawings.
　溶融めっきなどの表面処理がなされた鋼板をホットスタンプした後のホットスタンプ鋼板（表面処理ホットスタンプ鋼板）を抵抗スポット溶接すると、低い電流値でも中チリと共に表チリも出やすくなり、適正電流範囲が著しく狭くなり、チリの発生する電流が低くなる。このため適正電流範囲内（ただし、適正電流範囲の上限付近の電流を除く。）の電流値でチリを発生せずに溶接すると、得られるナゲット径も小さくなる。 When resistance stamp welding is performed on a hot stamped steel plate (surface treated hot stamped steel plate) after hot stamping a steel plate which has been surface-treated such as hot-dip plating, it becomes easy to come out with surface dust even at low current values. It becomes extremely narrow and the current generated by dust becomes low. For this reason, if welding is performed without generating dust at a current value within the appropriate current range (but excluding the current near the upper limit of the appropriate current range), the obtained nugget diameter also decreases.
　ここで、「適正電流範囲」とは、少しずつ電流を上げていき、スポット溶接される鋼板の板厚の平均値をｔとしたときに、ナゲット径が４√ｔ以上となる最初の電流（以下「４√ｔ電流」という）から、チリが初めて発生する電流までの範囲をいう。 Here, “appropriate current range” refers to the first current at which the nugget diameter is 4√t or more, where t is an average value of the plate thicknesses of the steel plates to be spot welded by gradually increasing the current. Hereinafter, it is a range from “4 t t current” to the current where dust is generated for the first time.
　表面処理ホットスタンプ鋼板を抵抗スポット溶接すると、チリが出やすくなり、適正電流範囲が狭くなる原因については次のように考えられる。 When resistance spot welding is performed on the surface-treated hot-stamped steel plate, dust is likely to be generated, and the reason why the appropriate current range is narrowed is considered as follows.
　表面処理ホットスタンプ鋼板は、めっき金属と基材の鋼との合金化反応によって、金属間化合物及び鉄基の固溶体がその表面に形成されており、さらにその外面にめっきに由来する金属（例えば、Ｚｎ）を主成分とする酸化皮膜を有している。そのため、表面処理ホットスタンプ鋼板は冷間でプレスした鋼板と比べて、鋼板同士の接触部での抵抗が高く発熱量が大きい。 In the surface-treated hot stamped steel plate, an intermetallic compound and an iron-based solid solution are formed on the surface by an alloying reaction of a plated metal and a steel base, and a metal derived from plating (for example, It has an oxide film which has Zn as a main component. Therefore, compared with a cold pressed steel plate, the surface-treated hot stamped steel plate has a high resistance at the contact portion between the steel plates and a large amount of heat generation.
　一方、ホットスタンプ工程でめっき金属と鋼との合金化が進行し、表面近傍の融点も鉄に近い高い値となっているので、ホットスタンプ前のめっき鋼板と比較して、鋼板同士の接触部が軟化しにくく通電パスの拡大が抑制される。特に、インバータ直流方式の通電では単相交流に比べ発熱効率が高いため、通電初期のナゲットの形成が非常に急激となる。このためナゲットの周囲における圧接部の成長が追い付かず溶融金属を閉じ込めることができなくなり、中チリが発生するものと推定される。 On the other hand, alloying between the plated metal and the steel proceeds in the hot stamping process, and the melting point in the vicinity of the surface also has a high value close to that of iron. Is hard to soften and expansion of the current-carrying path is suppressed. In particular, since the heat generation efficiency is higher in the inverter DC system energization than in the single-phase alternating current, the formation of the nugget at the initial stage of the energization becomes very rapid. For this reason, the growth of the pressure contact portion around the nugget can not catch up and the molten metal can not be confined, and it is presumed that internal dust is generated.
　また、直流は単相交流のような電流休止時間がないため、電極による冷却効果が得られにくい。このため、ナゲットが板厚方向に成長しやすく、鋼板の最表層まで溶融部が達して、表チリが発生するものと推定される。本発明において、「直流」とは、交流のようにプラス／マイナスが逆転するような通電は含まないこととする。このため、連続通電のように常に電流が流れている通電だけではなく、通電及び通電休止を短時間に複数回繰り返すパルセーション通電も、プラス／マイナスが逆転しない限り、直流と判定する。 Moreover, since direct current does not have a current pause time like single-phase alternating current, it is difficult to obtain a cooling effect by the electrode. For this reason, it is presumed that the nugget easily grows in the thickness direction, the melted portion reaches the outermost layer of the steel plate, and surface dust is generated. In the present invention, "direct current" does not include energization that reverses plus / minus like alternating current. For this reason, not only energization in which current is always flowing as in continuous energization, but also pulsation energization in which energization and energization suspension are repeated a plurality of times in a short time is determined as direct current unless plus / minus reversal occurs.
　本発明者らは、２段通電によるスポット溶接の際に、酸化物層の厚みなどによらず、酸化物層を分断し、その一部を溶接部の外側に確実に排除して、急激な溶融金属の成長を抑制する手段について検討した。 The present inventors divide the oxide layer regardless of the thickness of the oxide layer and the like during spot welding by two-step current conduction, and a part of the oxide layer is reliably excluded outside the weld, which is rapid. We examined means to suppress the growth of molten metal.
　その結果、予備通電において、高めの加圧力をホットスタンプ鋼板に作用させた状態で、適正な電流を流すことにより、予備通電における酸化物の分散・移動（排除）効果が増すとともに、本通電でのパルセーション通電により、酸化物が分散・移動する領域が徐々に拡大するとともに、急激な溶融金属の成長が抑制され、チリの抑制が可能となることを見出した。 As a result, in the pre-energization state, by applying an appropriate current to the hot stamp steel plate in a state where a high pressing force is applied to the hot stamp steel plate, the oxide dispersion / movement (exclusion) effect in the pre-energization is increased. It has been found that the passage of the pulsating current gradually increases the area in which the oxide is dispersed and moved, and also suppresses the rapid growth of molten metal, thereby enabling the suppression of dust.
　図１にそのような知見を得た試験結果の一例を示す。 An example of the test result which acquired such knowledge in FIG. 1 is shown.
　試験では、ホットスタンプされた板厚１．４ｍｍの亜鉛めっき鋼板（ホットスタンプ鋼板）を２枚重ね合わせ、本通電のみの１段通電でスポット溶接した場合と、予備通電及び本通電の２段通電でスポット溶接した場合において、本通電の電流値をチリが発生するまで増加させたときのナゲットの拡大挙動を調べた。 In the test, two hot-stamped galvanized steel sheets (hot stamped steel sheets) with a thickness of 1.4 mm are stacked and spot welded by one-step conduction only with main conduction, and two-step conduction with preliminary conduction and main conduction. In the case of spot welding, the expansion behavior of the nugget was investigated when the current value of the main current was increased until the generation of dust.
　１段通電では、本通電を電流一定の通電パターンとした。２段通電では、電流値Ｉａ：３．５ｋＡで、通電時間ｔａ：０．４ｓｅｃの予備通電を行い、続いて、図２に示すようなパルセーション通電による本通電を行う通電パターンと、電流一定の本通電を行う通電パターンを用いた。パルセーション通電は、予備通電後、休止時間なくただちに、０．０６ｓの通電を６回、０．０２ｓの休止を５回、交互に繰り返した。 In the one-stage energization, the main energization is an energization pattern of constant current. In the two-step energization, pre-energization with a current value Ia: 3.5 kA and an energization time ta: 0.4 sec is performed, and then, as shown in FIG. An energization pattern for performing the main energization of After the pre-energization, immediately after the pre-energization, the pulsation energization was alternately repeated six times for 0.06 s and five times for 0.02 s rest.
　電極には、先端部の曲面が、図３に示すような先端曲面部（初期接触部）とコーナー曲面部よりなるＤＲ（ドームラジアス）型で、後述の電極先端部直径ｄが６ｍｍのものを用いた。通電中の加圧力は４５０ｋｇｆ（４．４ｋＮ）とし、予備通電から本通電にいたるまで一定で行った。 The electrode is a DR (dome radius) type in which the curved surface at the tip is a DR (dome radius) type consisting of a tip curved surface (initial contact portion) and a corner curved surface as shown in FIG. Using. The pressure applied during energization was 450 kgf (4.4 kN) and constant from the pre-energization to the main energization.
　図１に、電流一定の本通電のみのパターン、予備通電＋電流一定の本通電のパターン、及び予備通電＋パルセーション通電による本通電のパターンで、それぞれスポット溶接した結果を示す。図１中のＥ点は、チリが発生した実験点を示す。 FIG. 1 shows the results of spot welding with a pattern of main current conduction only at a constant current, a pattern of main current conduction at a predetermined precurrent current + constant current, and a main current conduction pattern by precurrent current + pulsation current. Point E in FIG. 1 indicates an experimental point at which dust is generated.
　図１に示されるように、本通電のみの通電パターンで溶接した場合に対し、予備通電と本通電の２段通電によって溶接することによりチリの発生する上限電流値が上昇するが、２段通電で本通電をパルセーション通電により行う場合は、本通電を電流一定で行う場合に対して、さらにチリの発生する上限電流値が５√ｔ以上にまで大きく上昇し、適正な溶接電流範囲が拡大することが確認された。 As shown in FIG. 1, the upper limit current value generated by dust increases by welding by the two-step energization of the preliminary energization and the main energization, as compared with the case of welding with the energization pattern of only the main energization, In the case where the main energization is performed by pulsation energization, the upper limit current value generated by the dust greatly increases to 5√t or more, and the appropriate welding current range is expanded, compared to the case where the main energization is performed with constant current. It was confirmed to do.
　以上の知見をもとに、さらに本発明者らは、通電を予備通電と本通電の２段通電で行うことを前提として、電極の加圧力及び予備通電の通電条件を変化させて、チリを抑制して、必要なナゲット径を得られる条件を検討した結果、少なくとも前記（１）及び（２）で規定した条件とすることにより、チリを発生させないで、必要とするナゲット径が得られる適正な溶接電流範囲が拡大することを見出した。 Based on the above findings, the present inventors further change the pressure of the electrode and the energization condition of the preliminary energization on the premise that the energization is performed in two stages of the preliminary energization and the main energization, and the dust is As a result of examining the conditions that can suppress and obtain the necessary nugget diameter, by setting it as the condition specified in at least the above (1) and (2), it is not appropriate to generate the required nugget diameter without generating dust Welding current range was found to be expanded.
　本発明は、このような検討結果に基づいてなされたものであり、以下本発明に必要な要件や好ましい要件についてさらに説明する。 The present invention has been made based on the results of such studies, and the following further describes the requirements and preferable requirements of the present invention.
（スポット溶接の対象とする鋼板）
　本発明は、高強度鋼よりなる素材鋼板（たとえば、電気めっき鋼板又は溶融めっき鋼板を含む薄鋼板）を、焼入れ可能な温度まで加熱しオーステナイト化した後、金型でプレス成形と同時に冷却し焼き入れするホットスタンプされた鋼板（以下「ホットスタンプ鋼板」という）であって、表面に、高温に加熱した時に鉄スケールの発生を防止するための亜鉛系めっき、アルミニウム系めっきなどの表面処理が施された素材鋼板を用いてホットスタンプされたホットスタンプ鋼板をスポット溶接の主な対象とする。本発明はホットスタンプ鋼板以外の鋼板にも適用可能であり、特にホットスタンプ鋼板に限定される必要はない。 (Steel plate targeted for spot welding)
The present invention heats a material steel plate (for example, an electroplated steel plate or a thin steel plate containing a hot-dip galvanized steel plate) made of high strength steel to a hardenable temperature and austenitizes it, and then simultaneously cools and bakes with a die and bakes. A hot-stamped steel plate to be inserted (hereinafter referred to as “hot-stamped steel plate”), the surface of which is subjected to surface treatment such as zinc-based plating or aluminum-based plating to prevent iron scale generation when heated to high temperatures. Hot-stamped hot-stamped steel plates are mainly targeted for spot welding. The present invention is also applicable to steel plates other than hot stamped steel plates, and is not particularly limited to hot stamped steel plates.
　なお、ホットスタンプ鋼板は、多くの場合、平板ではなく成形加工された成形体であるが、要は、重ね合わされる部分が板状であればよいので、本発明では、成形体である場合も含めて「ホットスタンプ鋼板」という。また、亜鉛系めっき鋼板やアルミニウム系めっき鋼板をホットスタンプして得られるホットスタンプ鋼板を、以下の説明では「表面処理ホットスタンプ鋼板」という場合がある。 In many cases, a hot stamped steel plate is not a flat plate but a formed body that has been formed and processed. However, since it is sufficient if the portion to be overlapped is a plate, in the present invention it is It is called "hot stamped steel plate" including. In addition, a hot stamped steel plate obtained by hot stamping a zinc-based plated steel plate or an aluminum-based plated steel plate may be referred to as “surface-treated hot stamped steel plate” in the following description.
　ホットスタンプ鋼板は、亜鉛系又はアルミニウム系のめっき皮膜と基材の鋼との合金化反応によって、金属間化合物及び鉄基の固溶体がその表面に形成されており、さらにその外面にめっきに由来する金属（例えば、亜鉛系めっきであれば亜鉛を指す。）を主成分とする酸化物層を有している。そのため、表面処理ホットスタンプ鋼板は裸の鋼板と比べて、接触抵抗が１ｍΩ以上と高く、通電による発熱量が大きい。また、ホットスタンプ鋼板は、ホットスタンプ工程でめっきと鋼との合金化が進行し、表面近傍の融点も鉄に近い高い値となっているので、加熱前のめっき皮膜を備える鋼板と比較して、鋼板同士の接触部が軟化しにくくなっている。本発明は、そのような接触抵抗が１ｍΩ以上の鋼板のスポット溶接に適用することにより特に効果を発揮する。なお、接触抵抗の測定方法については後述する。 In a hot stamped steel sheet, an intermetallic compound and an iron-based solid solution are formed on the surface by an alloying reaction between a zinc-based or aluminum-based plated film and the steel of the base material, and the outer surface is further derived from plating. It has an oxide layer containing a metal (for example, zinc in the case of zinc-based plating) as a main component. Therefore, the surface-treated hot stamped steel plate has a contact resistance as high as 1 mΩ or more as compared to a bare steel plate, and a large amount of heat is generated by energization. Further, in the hot stamp steel plate, the alloying of the plating and the steel proceeds in the hot stamping process, and the melting point in the vicinity of the surface also has a high value close to iron, so compared to the steel plate provided with the plated film before heating , The contact portion between the steel plates is difficult to soften. The present invention is particularly effective when applied to spot welding of a steel plate having such contact resistance of 1 mΩ or more. In addition, the measuring method of contact resistance is mentioned later.
　鋼板の板厚について、特に制限はない。一般に、自動車用部品又は車体で使用される鋼板の板厚は０．６～３．２ｍｍであり、本発明の抵抗スポット溶接継手の製造方法は、この範囲において十分な効果を有する。 There is no particular limitation on the thickness of the steel plate. In general, the thickness of a steel plate used in automobile parts or vehicle bodies is 0.6 to 3.2 mm, and the method of producing a resistance spot welded joint of the present invention has a sufficient effect in this range.
（板組）
　２枚以上の鋼板を重ね合わせる際の板組みは、電極の当たる側の鋼板の少なくとも１枚が表面処理ホットスタンプ鋼板を含むことが好ましい。表面処理ホットスタンプ鋼板に組合わされる鋼板としては、表面処理ホットスタンプ鋼板や５９０ＭＰａ級以上の高張力鋼板を含む組み合わせが好ましい。通常の自動車車体の組立てでは、これらの鋼板を２枚又は３枚の鋼板を重ね合わせた板組みに対して抵抗スポット溶接が行われる。 (Plate set)
In the plate assembly when two or more steel plates are stacked, it is preferable that at least one of the steel plates on the side to which the electrode contacts includes a surface-treated hot stamped steel plate. As a steel plate combined with a surface treatment hot stamp steel plate, a combination including a surface treatment hot stamp steel plate and a high tensile steel plate of 590 MPa grade or more is preferable. In ordinary car body assembly, resistance spot welding is performed on a plate assembly in which two or three steel plates are stacked.
（電極）
　本発明では、電極の先端表面の曲率半径が４０ｍｍ以上の表面領域（ただし、電極の最先端部を含む表面領域とする。）が電極の加圧方向（通常は電極の長さ方法と同じになる。）に対して垂直な面へ投影された領域の面積Ａと、面積が等価な円の直径（いわゆる、等価円相当径）を、電極先端部直径ｄと定義する。つまり、電極先端部直径ｄは、２√（Ａ／π）として算出される。この定義によると、例えば、図３のように、曲率半径が４０ｍｍ以上の表面領域が、電極の加圧方向（通常は電極の長さ方法と同じになる。）に対して垂直な面へ投影された領域が、円形の場合、その円の直径が電極先端部直径ｄとなる。 (electrode)
In the present invention, the surface area of the tip surface of the electrode having a radius of curvature of 40 mm or more (however, the surface area including the tip of the electrode) is the same as the electrode pressing direction (usually the electrode length method) The area A of the region projected on a plane perpendicular to the above and the diameter of a circle equivalent to the area (so-called equivalent circle equivalent diameter) are defined as the electrode tip diameter d. That is, the electrode tip diameter d is calculated as 2√ (A / π). According to this definition, for example, as shown in FIG. 3, the surface area with a radius of curvature of 40 mm or more is projected onto a plane perpendicular to the pressing direction of the electrode (usually the same as the electrode length method). If the area is circular, the diameter of the circle is the electrode tip diameter d.
　電極の先端曲面部の直径ｄや曲率半径（先端Ｒ）は、特に限定されるものではないが、一般的には、直径は５～６ｍｍ程度、曲率半径は４０～６０ｍｍ程度が例示される。 The diameter d and the radius of curvature (tip R) of the tip curved portion of the electrode are not particularly limited, but generally, the diameter is about 5 to 6 mm and the radius of curvature is about 40 to 60 mm.
　電極としては、たとえば、ＪＩＳ　Ｃ９３０４：１９９９に規定されている電極を使用できる。たとえば、ＤＲ型先端曲面部の曲率Ｒが４０～６０ｍｍの電極が例示される。 As an electrode, for example, an electrode defined in JIS C9304: 1999 can be used. For example, an electrode having a curvature R of 40 to 60 mm for the DR-type tip curved portion is exemplified.
　電極材質としては、クロム銅又はアルミナ分散銅が好ましい。溶着及び表チリを防止する観点ではアルミナ分散銅の方が望ましい。 As an electrode material, chromium copper or alumina-dispersed copper is preferable. Alumina-dispersed copper is preferable in terms of preventing welding and surface dust.
（溶接電源）
　スポット溶接の通電には、インバータ直流方式などの直流の溶接電源を用いて通電する。インバータ直流方式はトランスを小さくでき、可搬重量の小さいロボットに搭載できるメリットがあるため、特に自動化ラインで多く用いられる。 (Welding power supply)
For spot welding, a DC welding power source such as an inverter DC system is used. The inverter direct current method has a merit that it can be mounted on a robot with a small load and can be made small, and therefore it is used in particular in automation lines.
　インバータ直流方式は、連続通電では、従来用いられてきた単相交流方式のような電流のオンオフがなく、連続的に電流を付与できるため、発熱効率が高い。また、パルセーション通電では、パルス電流波形を容易に制御できる。 The inverter direct current method has high heat generation efficiency because it can continuously apply current without continuous on / off of the current as in the single-phase alternating current method conventionally used in continuous energization. In addition, in the energization of pulsation, the pulse current waveform can be easily controlled.
（加圧・通電条件）
　図２に、スポット溶接における通電パターンの基本的な例をタイムチャートで示す。この通電パターンでは、まず、所定の加圧力を印加しながら電流値Ｉａで通電する予備通電を行い、次いで、電流値Ｉｂでパルセーション通電して、ナゲットが所定の径になるよう本通電を行う。そして、本通電の通電が終了した後、所定のホールド時間が経過した時点で電極を鋼板から離間し、加圧力を解放する。 (Pressure · energization condition)
The basic example of the electricity supply pattern in spot welding is shown by a time chart in FIG. In this energization pattern, first, pre-energization is performed by applying a predetermined pressing force, and then energization is performed with a current value Ia, and then pulsation current is applied with a current value Ib to perform main energization so that the nugget has a predetermined diameter. . Then, after completion of the main conduction, when the predetermined hold time has elapsed, the electrode is separated from the steel plate to release the pressure.
　その際、前記のように電極加圧力、予備通電の通電条件を特定の条件とする。 At that time, as described above, the electrode pressurizing force and the energization condition of the preliminary energization are set as the specific conditions.
　予備通電では、加圧力を増大させて、鋼板表面の酸化物層を破壊して分散させ、その一部を電極の接触範囲外の方向に移動（排除）させるようにして、表面の接触抵抗を低下させる。また、電流値を下げて、接触初期にナゲットの急速な成長を抑制し、チリが発生しないようにする。 In the pre-energization, the pressing force is increased to break and disperse the oxide layer on the surface of the steel plate, and a part of the oxide layer is moved (excluded) outside the contact range of the electrode to make the surface contact resistance Reduce. In addition, the current value is lowered to suppress the rapid growth of nuggets at the initial stage of contact and to prevent the generation of dust.
　そのために、加圧力を３．９ｋＮ以上とし、予備通電における電流Ｉａ（ｋＡ）の最大値が、Ｉａ≦６ｋＡ、を満足するようにする。このようにすることにより、チリを発生させないで、鋼板表面の接触抵抗を低下させることができる。 Therefore, the pressure is set to 3.9 kN or more, and the maximum value of the current Ia (kA) in the pre-energization is set to satisfy Ia ≦ 6 kA. By doing this, it is possible to reduce the contact resistance on the surface of the steel sheet without generating dust.
　加圧力は、好ましくは４．４ｋＮ以上である。さらに好ましくは４．５ｋＮ以上、４．８ｋＮ以上、５．０ｋＮ以上、又は５．４ｋＮ以上である。加圧力が適正な範囲を超えて大きくなると、たとえば電極加圧部の凹みが大きくなって(局所的に板厚の薄い部分が形成されて)継手強度が低下したり、又は電流密度が極端に低下して本通電時のナゲット形成が困難になったりする場合があるため、加圧力は１０ｋＮ以下、９．５ｋＮ以下、又は９．０ｋＮ以下とすることが好ましい。 The applied pressure is preferably 4.4 kN or more. More preferably, it is 4.5 kN or more, 4.8 kN or more, 5.0 kN or more, or 5.4 kN or more. When the pressure increases beyond the appropriate range, for example, the depression of the electrode pressing portion becomes large (locally formed thin portion is formed), the joint strength decreases, or the current density becomes extremely The pressing force is preferably 10 kN or less, 9.5 kN or less, or 9.0 kN or less because the nugget formation during main conduction may be difficult due to a decrease.
　予備通電での通電時間は、鋼板表面の電極と接触する部分の酸化層を破壊し、一部を接触範囲外に排除するできる時間以上とする。具体的には、以下の式（１）、（２）を満たすようにｔａ（ｓｅｃ）間通電する。 The energization time in the pre-energization is equal to or longer than the time which can destroy the oxide layer of the portion of the steel plate surface in contact with the electrode and partially exclude it from the contact range. Specifically, electricity is applied for ta (sec) so as to satisfy the following equations (1) and (2).
　　Ｉａ（ｔ）≦６．０（ｋＡ）　・・・式（１）
Figure JPOXMLDOC01-appb-M000003
 Ia (t) ≦ 6.0 (kA) formula (1)
Figure JPOXMLDOC01-appb-M000003
　ただし、式（１）及び式（２）中のＩａ（ｔ）（ｋＡ）は予備通電開始からｔ（ｓｅｃ）経過時における予備通電の電流値である。 However, Ia (t) (kA) in a formula (1) and a formula (2) is a current value of preliminary energization at the time of t (sec) progress from a preliminary energization start.
　予備通電の効果を発現させるため、以下の式（３）で定義される予備通電における電流積分値Ｓは、式（２）に示されるように、０．５ｋＡ・ｓ以上とする。必要に応じて、前記電流積分値Ｓの下限を０．６ｋＡ・ｓ、０．８ｋＡ・ｓ、１．０ｋＡ・ｓ又は１．２ｋＡ・ｓとしてもよい。予備通電工程の通電時間を特に定める必要はないが、０．０５～１ｓとなる場合が多い。必要に応じて、その通電時間の下限を０．１ｓ、０．１５ｓ又は０．２ｓとしてもよい。その上限を０．９ｓ、０．８ｓ、０．７ｓ又は０．８ｓとしてもよい。 In order to express the effect of the pre-energization, the current integral value S in the pre-energization defined by the following equation (3) is set to 0.5 kA · s or more as shown in the equation (2). If necessary, the lower limit of the current integral value S may be 0.6 kA · s, 0.8 kA · s, 1.0 kA · s or 1.2 kA · s. Although it is not necessary to set the energization time of the pre-energization process in particular, it is often 0.05 to 1 s. If necessary, the lower limit of the current application time may be 0.1 s, 0.15 s, or 0.2 s. The upper limit may be 0.9s, 0.8s, 0.7s or 0.8s.
Figure JPOXMLDOC01-appb-M000004
Figure JPOXMLDOC01-appb-M000004
　なお、上述のとおり、本発明の実施形態においては、予備通電における電流（予備通電時に電流が変動する場合は、予備通電時の電流の最大値）は６ｋＡ以下である。予備通電の電流の下限を特に定める必要はないが、パルセーション通電も考慮すると、その下限は０ｋＡである。必要に応じて、１ｋＡ又は２ｋＡとしてもよい。 As described above, in the embodiment of the present invention, the current in the preliminary energization (the maximum value of the current in the preliminary energization when the current fluctuates during the preliminary energization) is 6 kA or less. Although it is not necessary to set the lower limit of the pre-energization current in particular, the lower limit is 0 kA in consideration of the pulsation energization. If necessary, it may be 1 kA or 2 kA.
　予備通電では、鋼板表面の電極と接触する部分や鋼板同士が接触する部分の酸化層を破壊して分離し、一部を接触範囲外に移動させることを主な目的としているので、予備通電時にナゲットを形成しなくてもよい。 In pre-energization, the main purpose is to destroy and separate the oxide layer of the part in contact with the electrodes on the surface of the steel plate and the part where steel plates are in contact with each other, and move a part out of the contact range. It is not necessary to form a nugget.
　予備通電での通電時間ｔａは、鋼板表面の酸化物層の分離ができる時間以上、より好ましくは、電流値Ｉ（ｔ）との関係で上記関係を満たすように通電する。 The energization time ta in the preliminary energization is equal to or longer than the time in which the oxide layer on the surface of the steel sheet can be separated, and more preferably, is energized to satisfy the above relationship in relation to the current value I (t).
　予備通電での通電は、予備通電の時間のうち８０％以上を連続通電とする。連続通電とは、直流電流の大きさが０アンペアにならないように通電することであり、一定の大きさの電流を継続して流すだけでなく、直流電流の大きさを時間の経過とともに増加させてもよく、また、直流電流の大きさが０アンペアにならないように、直流電流の大きさを時間の経過とともに増減させてもよい。ただし、通常のパルセーション通電ではない長時間の通電休止（例えば、１ｓ以上の通電休止）がある通電は、連続通電に含まないこととする。また、予備通電での通電は、好ましくは、予備通電の時間のうち８５％以上が連続通電であり、１００％連続通電であってもよい。なお、パレセーション通電のような短時間(例えば、０．０１～０．１ｓ程度)の通電休止時間は、通電時間に含むが、１ｓ以上の通電休止時間は通電時間から除外する。 In the pre-energization, 80% or more of the pre-energization time is continuously applied. Continuous energization means energizing so that the magnitude of the direct current does not reach 0 amps, and not only the current of a constant magnitude continues to flow but also the magnitude of the direct current increases with the passage of time. The magnitude of the direct current may be increased or decreased over time so that the magnitude of the direct current does not become 0 amp. However, it is assumed that continuous energization does not include energization for which there is a long-time energization suspension (for example, energization suspension for 1 s or more) which is not normal pulsation energization. In addition, preferably, 85% or more of the time of the preliminary energization is continuous energization, and the current may be 100% continuous energization. A short time (for example, about 0.01 to 0.1 s) of the energization stop time such as passage of electricity is included in the energization time, but the energization stop time of 1 second or more is excluded from the energization time.
　予備通電に続く本通電では、図２に示すように、パルス電流を通電する期間ｔ１と通電休止期間ｔ０からなる周期を２回以上繰り返すパルセーション通電とする。 In the main energization following the preliminary energization, as shown in FIG. 2, pulsating energization is repeated, in which a cycle consisting of a period t1 of applying a pulse current and an energization stop period t0 is repeated twice or more.
　パルセーション通電では、通電と通電休止の繰り返しに伴う熱膨張、収縮による振動を電極接触面に与えることができるため、予備通電における酸化物の分散・移動（排除）をさらに促進することができるとともに、通電休止により、本通電中の溶接部の急激な温度上昇を抑制でき、連続通電に比べて表チリの発生が抑制できる。 In pulsation energization, since vibration due to thermal expansion and contraction accompanying repetition of energization and energization suspension can be applied to the electrode contact surface, dispersion and movement (exclusion) of oxide in preliminary energization can be further promoted. By stopping the energization, it is possible to suppress a rapid temperature rise of the weld during main energization, and to suppress generation of surface dust as compared to continuous energization.
　パルセーション通電における通電条件は、チリを発生させずに所定の径のナゲットが得られる条件が採用される。一般的には、４√ｔ以上のナゲット径が生産管理上の基準とされることが多い。本発明では、図１に示されるように、チリが発生することなくより大きいナゲット径（たとえば、４√ｔ以上）を有する溶接継手を得ることができる。 As the energization condition in the pulsation energization, a condition in which a nugget of a predetermined diameter is obtained without generating dust is adopted. In general, a nugget diameter of 4√t or more is often used as a production control standard. In the present invention, as shown in FIG. 1, it is possible to obtain a welded joint having a larger nugget diameter (for example, 4tt or more) without generating dust.
　なお、通電条件として、電流値Ｉｂは、予備通電の電流値Ｉａよりも高い電流値、すなわちＩｂ＞Ｉａで通電するのが好ましい。また、通電期間ｔ１と、休止期間ｔ０の各時間については、例えば、０．０６ｓ通電後、０．０２ｓ休止とする通電方式が例示される。また、パルス電流の形状は、図２のような矩形に限らず、パルスの立ち上り部分や立ち下り部分が時間に対し傾斜する形状でもよい。 It is preferable that the current value Ib is a current value higher than the current value Ia of the pre-energization, that is, Ib> Ia. Moreover, about each time of the electricity supply period t1 and rest period t0, the electricity supply system made into 0.02 s rest, for example after electing 0.06 s is illustrated. Further, the shape of the pulse current is not limited to the rectangular shape as shown in FIG. 2, but may be a shape in which rising and falling portions of the pulse are inclined with respect to time.
　パルセーション通電の第１周期目は、図２では、予備通電に連続して通電されているが、図４のように、休止期間をおいてから第１周期目の通電を開始することもできる。 In the first cycle of energization of pulsation, although the pre-energization is conducted continuously in FIG. 2, the first cycle of energization can be started after the pause period as shown in FIG. .
　以上では、通電パターンとして、図２、３に示されるような、予備通電を一定の電流値でまた本通電を一定高さのパルス電流で通電するパターンを例に説明したが、一定の電流値ではなく、電流値を徐々に増加させることができる。電流値を徐々に増加させるのは、連続的であっても、段階的であってもよい。 In the above, as the energization pattern, as shown in FIGS. 2 and 3, the pattern in which the preliminary energization is conducted at a constant current value and the main energization at a constant height pulse current has been described. Instead, the current value can be gradually increased. The gradual increase of the current value may be continuous or stepwise.
　図５（ａ）に、予備通電の開始初期に、電流を徐々に増大させる通電、すなわちアップスロープ通電を行う例を示す。実線は最初から、破線は途中の電流値からアップスロープ通電を行う例を示す。予備通電をアップスロープ通電で開始することにより、通電初期の接触抵抗が高い時期のナゲットの生成及び急成長を抑制することができる。 FIG. 5 (a) shows an example in which the current is gradually increased at the initial stage of the start of the preliminary energization, that is, the up-slope energization is performed. The solid line shows the example from the beginning, and the broken line shows an example in which up-slope conduction is performed from the current value in the middle. By starting pre-energization by up-slope energization, it is possible to suppress the formation and rapid growth of nuggets at a time when contact resistance at the initial stage of energization is high.
　また、図５（ｂ）に本通電の開始初期に、ピーク電流を徐々に増大させるアップスロープ通電を行う例を、図５（ｃ）に、本通電の途中でピーク電流を段階的に増加させる例をそれぞれ示す。 Also, in FIG. 5 (b), an example in which up-slope energization is performed to gradually increase the peak current at the beginning of the start of the main energization is shown in FIG. 5 (c). An example is shown respectively.
　本通電をアップスロープ通電で開始することにより、ナゲットの急成長を抑制することができる。また、途中で電流を増加させることにより通電時間を短縮することができる。 By starting the main energization by the up slope energization, it is possible to suppress the rapid growth of the nugget. In addition, by increasing the current midway, the conduction time can be shortened.
　パルセーション通電による本通電における通電時間の合計は、通常の条件範囲内とすることができる。たとえば、通電時間の目安として一枚当たりの板厚の１０倍（板厚１ｍｍの鋼板同士の溶接であれば０．２ｓ）程度が推奨される。本発明においても、本通電での通電時間の合計は板厚の１０倍程度が例示される。しかし、予備通電によって鋼板温度が上昇し、条件によっては鋼板の界面が溶融するため、この目安時間よりも短縮することができる。すなわち、予備通電の条件に応じて、本通電時の通電時間合計は板厚の４～８倍程度と短縮できる場合がある。 The total of the energization time in the main energization by the pulsation energization can be within the normal condition range. For example, about 10 times the plate thickness per sheet (in the case of welding of steel plates having a plate thickness of 1 mm, about 0.2 s) is recommended as a measure of the energization time. Also in the present invention, the total conduction time in the main conduction is about 10 times the thickness of the plate. However, since the steel plate temperature rises due to the pre-energization and the interface of the steel plate melts depending on the conditions, it can be made shorter than this reference time. That is, depending on the conditions of the pre-energization, the total energization time at the time of main energization may be shortened to about 4 to 8 times the plate thickness in some cases.
　本発明において、予備通電と本通電の定義は下記のとおりとする。 In the present invention, the definition of the pre-energization and the main energization is as follows.
　まず、一定電流の通電で１段階の通電の場合（連続通電又はパルセーション通電であろうとも、また通電休止時間の有無及び通電休止時間の長さにかかわらず）、予備通電はなく本通電のみとする。一定電流の通電後に異なる一定電流の通電の段階の通電の場合（連続通電又はパルセーション通電であろうとも、また通電休止時間の有無及び通電休止時間の長さにかかわらず）、１段階目を予備通電と、２段階目を本通電とする。前後の段階で電流が異なるものの各段階では一定電流の通電であり、かつ３段階以上の通電の場合（連続通電又はパルセーション通電であろうとも、また通電休止時間の有無及び通電休止時間の長さにかかわらず）、６ｋＡを初めて超えた段階以降の通電をすべて本通電とし、本通電以前の通電をすべて予備通電とする（ただし、各段階の電流がすべて６ｋＡ未満の場合、最後の段階の通電を本通電とし、本通電以前の通電を予備通電とする。）。 First, in the case of one-step energization with constant current conduction (whether continuous energization or pulsation energization or regardless of the presence or absence of the energization pause time and the length of the energization pause time), there is no preliminary energization, and only the main energization is performed. I assume. In the case of energization at different stages of constant current application after constant current application (whether continuous current or pulsation current or not, and the length of current interval), the first stage The pre-energization and the second step are the main energization. Although the current is different in the previous and subsequent stages, constant current is applied in each stage, and in the case of three or more stages of energization (whether continuous energization or pulsation energization is present or not and duration of energization rest time Regardless, all energization after the stage that first exceeds 6 kA is set to main energization, and all energization before main energization is set to pre-energization (however, if all the current at each stage is less than 6 kA, the final stage Energization is set to main energization, and energization before main energization is set to pre-energization.
　アップスロープ通電のように通電中の電流の増減がある場合（連続通電又はパルセーション通電であろうとも、また通電休止時間の有無及び通電休止時間の長さにかかわらず）、６ｋＡを初めて超えた時点以降の通電をすべて本通電とし、本通電以前の通電をすべて予備通電とする。したがって、このようなアップスロープ通電のように通電中の電流の増減がある場合であり、かつ、電流がすべて６ｋＡ未満の場合、本発明の実施形態と判断しない。 When there is an increase or decrease in current during energization (up or down, regardless of presence or absence of energization pause time and length of energization pause time), up to 6 kA is exceeded for the first time All energization after the point in time is set to main energization, and all energization before the main energization is set to preliminary energization. Therefore, if there is an increase or decrease in current during energization as in the case of such up-slope energization, and all currents are less than 6 kA, it is not determined as an embodiment of the present invention.
（接触抵抗）
　接触抵抗の測定方法を図６に示す。鋼板（めっきをしていてもしていなくてもよい）を１枚スポット溶接用電極で挟む。電極に１Ａの電流Ｉを通電する。上側電極１ａと鋼板２との間の電圧Ｖ１、下側電極１ｂと鋼板２との間の電圧Ｖ２を測定する。 (Contact resistance)
The measuring method of contact resistance is shown in FIG. A steel plate (which may or may not be plated) is sandwiched between one spot welding electrode. A current I of 1 A is supplied to the electrode. The voltage V1 between the upper electrode 1a and the steel plate 2 and the voltage V2 between the lower electrode 1b and the steel plate 2 are measured.
　上側電極と鋼板間の電気抵抗をＲ１、下側電極と鋼板間の電気抵抗をＲ３、鋼板バルク（母材）そのものの固有抵抗に起因する抵抗をＲ２とする。Ｒ２はゼロと近似できる。また、上下の電極の抵抗もゼロと近似できる。よって、測定された電圧Ｖ１、Ｖ２と電気抵抗Ｒ１、Ｒ３との間の関係は次のように近似できる。 The electric resistance between the upper electrode and the steel plate is R1, the electric resistance between the lower electrode and the steel plate is R3, and the resistance due to the specific resistance of the steel plate bulk (base material) itself is R2. R2 can be approximated to zero. Also, the resistance of the upper and lower electrodes can be approximated to zero. Therefore, the relationship between the measured voltages V1 and V2 and the electrical resistances R1 and R3 can be approximated as follows.
　V１= (R1+R2)×Ｉ ≒ R1×Ｉ = R1×1(A)= R１
　V２= (R2+R3)×Ｉ ≒ R3×Ｉ = R3×1(A)= R３ V1 = (R1 + R2) × I ≒ R1 × I = R1 × 1 (A) = R1
V2 = (R2 + R3) × I ≒ R3 × I = R3 × 1 (A) = R3
　Ｒ１、Ｒ３のいずれか大きいほうの抵抗値を本発明での接触抵抗とする。 The larger one of R1 and R3 is used as the contact resistance in the present invention.
　本発明では、接触抵抗が１ｍΩ以上の鋼板を主な適用対象とするが、接触抵抗が１ｍΩ未満の鋼板にも適用可能であり、接触抵抗が１ｍΩ以上の鋼板に限定される必要はない。必要に応じて、接触抵抗の下限を２ｍΩ、５ｍΩ、８ｍΩ又は１０ｍΩに限定してもよい。接触抵抗の上限を特に定める必要はないが、その上限を１００ｍΩ、５０ｍΩ、３０ｍΩ又は２０ｍΩとしてもよい。 In the present invention, a steel plate having a contact resistance of 1 mΩ or more is mainly applied, but the present invention is applicable to a steel plate having a contact resistance of less than 1 mΩ, and it is not necessary to be limited to a steel plate having a contact resistance of 1 mΩ or more. If necessary, the lower limit of the contact resistance may be limited to 2 mΩ, 5 mΩ, 8 mΩ or 10 mΩ. The upper limit of the contact resistance is not particularly limited, but may be 100 mΩ, 50 mΩ, 30 mΩ, or 20 mΩ.
　本発明は、以上説明したように構成されるものであるが、以下、実施例を用いて、本発明の実施可能性及び効果についてさらに説明する。 Although the present invention is configured as described above, the following will further explain the feasibility and effects of the present invention using examples.
　先端曲面部の直径６ｍｍ、曲面部曲率半径（先端Ｒ）４０ｍｍのＤＲ型電極（クロム銅）を備えた、サーボ加圧式インバータ直流スポット溶接機を用い、板厚２．０ｍｍの１５００ＭＰａ級のＧＡめっきホットスタンプ鋼板（ホットスタンプ前のめっき付着量：片側あたり５５ｇ／ｍ２、加熱条件：９００℃で４分炉加熱）から作成した試験片を２枚重ね合わせて、抵抗スポット溶接を実施した。試験片の形状は、巾３０ｍｍ、長さ５０ｍｍの短冊状とした。鋼板の接触抵抗を前記の方法で測定したところ、すべて１２ｍΩであった。 Using a servo-pressurized inverter DC spot welder equipped with a DR-type electrode (chrome copper) with a diameter of 6 mm at the tip curved portion and a radius of curvature of the curved portion (tip R) 40 mm, GA plating of 1500 MPa class with a plate thickness of 2.0 mm Two test pieces prepared from a hot stamped steel plate (plating adhesion amount before hot stamping: 55 g / m 2 per side, heating condition: furnace heating at 900 ° C. for 4 minutes) were overlapped to perform resistance spot welding. The shape of the test piece was a strip having a width of 30 mm and a length of 50 mm. When the contact resistance of the steel plate was measured by the above method, it was all 12 mΩ.
　溶接条件を表１に示す。本通電の電流値は、４ｋＡからちりが発生する電流値までふった。２段通電での加圧力は、予備通電から本通電にいたるまで一定で行った。いずれの条件においても、本通電での通電時間の合計が約０．４ｓとなるように設定した。すべての電源は、インバータ直流の電源とした。 The welding conditions are shown in Table 1. The current value of the main conduction ranged from 4 kA to the current value at which dust is generated. The pressing force in the two-stage energization was constant from the preliminary energization to the main energization. Under any of the conditions, the total energization time in the main energization was set to be about 0.4 s. All power supplies were inverter DC power supplies.
　溶接に当たっては、表１に示す電流値で本通電のみを行い、又は表１に示す電流値で予備通電工程を実施した後、本通電工程におけるパルセーション通電のパルス電流値などを変化させ、それぞれナゲット径及びチリ発生状況の調査を行った。各試験番号における供試鋼板の板厚、強度（引張強さ）、及び試験結果（本通電工程の適正電流範囲）を同じく表１に示す。 In welding, only the main energization is performed with the current values shown in Table 1, or after performing the pre-energization process with the current values shown in Table 1, the pulse current value of pulsation energization in the main energization process is changed, We investigated the nugget diameter and the occurrence of dust. The plate thickness, strength (tensile strength), and test results (appropriate current range of the main conduction step) of the test steel plate in each test number are also shown in Table 1.
　表１から分かるように、本発明例は、本通電工程での上限電流を上昇させることができるため、１段通電を行った比較例や、２段通電の本通電でパルセーション通電を行わなかった比較例よりも、幅広く１．５ｋＡ程度の適正電流範囲を試験片レベルで得ることができる。 As can be seen from Table 1, in the example of the present invention, since the upper limit current in the main energization process can be increased, the comparison example in which the first stage energization is performed or the pulsating energization in the main energization of the second stage energization is not performed. An appropriate current range of about 1.5 kA can be widely obtained at the specimen level than in the comparative example.
　これにより、本発明では４√ｔ電流以上、かつ、チリ発生電流以下の値に本通電工程の電流値を設定することで、実部品の溶接でもチリを発生させず、かつ、分流、電極損耗による外乱があってもナゲット径が４√ｔ以上となるスポット溶接部を安定して確保することができる。一方、比較例では適正電流範囲が目標の１．５ｋＡ以上を満たさなかった。 Thus, in the present invention, by setting the current value of the main conduction step to a value of 4√t current or more and less than the dust generation current, dust is not generated even in welding of actual parts, and shunting and electrode wear and tear Even if there is a disturbance due to the above, it is possible to stably secure a spot welded portion in which the nugget diameter is 4tt or more. On the other hand, in the comparative example, the appropriate current range did not satisfy the target of 1.5 kA or more.
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005
　以上、本発明の実施の形態を説明した。しかしながら、上述した実施の形態は本発明を実施するための例示にすぎない。したがって、本発明は上述した実施の形態に限定されることなく、その趣旨を逸脱しない範囲内で上述した実施の形態を適宜変更して実施することができる。 The embodiment of the present invention has been described above. However, the above-described embodiment is merely an example for implementing the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented without departing from the scope of the invention.
　１　　スポット溶接用電極
　１ａ　　上側電極
　１ｂ　　下側電極
　２　　鋼板
　３　　めっき層 1 spot welding electrode 1a upper electrode 1b lower electrode 2 steel plate 3 plated layer

Claims (4)

  1. 　２枚以上の鋼板を重ね合わせ、その重ね合わせ部を電極により加圧して通電する抵抗スポット溶接継手の製造方法であって、
    　３．９ｋＮ以上の加圧力で前記電極により前記重ね合わせ部を加圧しつつ電流Iａ（ｔ）(ｋＡ)を以下の式（１）、（２）を満たすように通電時間ｔａ（ｓｅｃ）の間通電する予備通電工程と、
    　前記予備通電工程後に本通電工程
    を備え、
    　前記予備通電工程及び前記本通電工程の電流はすべて直流であり、
    　前記予備通電工程において、前記通電時間ｔａの８０％以上の通電方式が連続的に通電する連続通電であり、
    　前記本通電工程の通電方式は通電と通電休止とを複数回繰り返すパルセーション通電である
    ことを特徴とする抵抗スポット溶接継手の製造方法。
    　　Iａ(t)≦６．０（ｋＡ）　　　　　　　　　　・・・式（１）
    Figure JPOXMLDOC01-appb-M000001
         It is a manufacturing method of a resistance spot welding joint which piles up two or more steel plates and pressurizes the piled part with an electrode and supplies electricity,
    The current Ia (t) (kA) is satisfied by the following equations (1) and (2) while pressing the overlapping portion by the electrode with a pressing force of 3.9 kN or more, for a period of current-flowing time ta (sec) A pre-energization step of energizing;
    The main energization step is provided after the preliminary energization step,
    The currents in the pre-energization step and the main energization step are all direct current,
    In the preliminary electrification step, the electrification method of 80% or more of the electrification time ta is continuous electrification to continuously energize,
    The method of manufacturing a resistance spot welded joint according to the present invention, wherein the current application method of the main current application step is pulse current application in which the current application and the current application stop are repeated a plurality of times.
    Ia (t) ≦ 6.0 (kA) formula (1)
    Figure JPOXMLDOC01-appb-M000001
  2. 　前記予備通電工程において電流を増大させることを特徴とする請求項１に記載の抵抗スポット溶接継手の製造方法。 The method for manufacturing a resistance spot welded joint according to claim 1, wherein the current is increased in the pre-energization step.
  3. 　前記本通電工程において電流を増大させることを特徴とする請求項１又は２に記載の抵抗スポット溶接継手の製造方法。 The method for manufacturing a resistance spot welded joint according to claim 1 or 2, wherein the current is increased in the main conduction step.
  4. 　前記鋼板の少なくとも1枚の鋼板の接触抵抗が１ｍΩ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継手の製造方法。 The method for producing a resistance spot welded joint according to any one of claims 1 to 3, wherein a contact resistance of at least one steel plate of the steel plate is 1 mΩ or more.
PCT/JP2018/046874 2017-12-19 2018-12-19 Method for manufacturing resistance spot welded joint WO2019124464A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2019520159A JP6584728B1 (en) 2017-12-19 2018-12-19 Method of manufacturing resistance spot welded joint

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2017-242981 2017-12-19
JP2017242981 2017-12-19

Publications (1)

Publication Number Publication Date
WO2019124464A1 true WO2019124464A1 (en) 2019-06-27

Family

ID=66992623

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2018/046874 WO2019124464A1 (en) 2017-12-19 2018-12-19 Method for manufacturing resistance spot welded joint

Country Status (2)

Country Link
JP (1) JP6584728B1 (en)
WO (1) WO2019124464A1 (en)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114850643A (en) * 2021-02-04 2022-08-05 杭州宝伟汽车零部件有限公司 Spot welding method for ultrahigh-strength hot-formed steel plate
WO2022219968A1 (en) * 2021-04-12 2022-10-20 Ｊｆｅスチール株式会社 Resistance spot welding method
WO2023008263A1 (en) * 2021-07-30 2023-02-02 Ｊｆｅスチール株式会社 Resistance spot welding method
DE102022104981A1 (en) 2022-03-03 2023-09-07 Thyssenkrupp Steel Europe Ag Process for resistance spot welding of hardened sheet steel components
JP7355281B1 (en) 2022-06-03 2023-10-03 Ｊｆｅスチール株式会社 Welded joints, welded parts and manufacturing methods thereof, and resistance spot welding methods
WO2023233704A1 (en) * 2022-06-03 2023-12-07 Ｊｆｅスチール株式会社 Welded joint, welding member, method for manufacturing same, and method of resistance spot welding
WO2024014146A1 (en) * 2022-07-14 2024-01-18 Ｊｆｅスチール株式会社 Resistance spot welding method
JP7476957B2 (en) 2021-04-12 2024-05-01 Ｊｆｅスチール株式会社 Resistance Spot Welding Method

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010207909A (en) * 2009-02-12 2010-09-24 Sumitomo Metal Ind Ltd Resistance welding method for high tensile strength steel sheet and method for producing resistance welded joint
JP2010247215A (en) * 2009-04-20 2010-11-04 Sumitomo Metal Ind Ltd Resistance welding method of high tensile steel sheet
WO2015170687A1 (en) * 2014-05-07 2015-11-12 新日鐵住金株式会社 Spot welding method
JP2016068142A (en) * 2014-09-30 2016-05-09 新日鐵住金株式会社 Spot welding method

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010207909A (en) * 2009-02-12 2010-09-24 Sumitomo Metal Ind Ltd Resistance welding method for high tensile strength steel sheet and method for producing resistance welded joint
JP2010247215A (en) * 2009-04-20 2010-11-04 Sumitomo Metal Ind Ltd Resistance welding method of high tensile steel sheet
WO2015170687A1 (en) * 2014-05-07 2015-11-12 新日鐵住金株式会社 Spot welding method
JP2016068142A (en) * 2014-09-30 2016-05-09 新日鐵住金株式会社 Spot welding method

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114850643A (en) * 2021-02-04 2022-08-05 杭州宝伟汽车零部件有限公司 Spot welding method for ultrahigh-strength hot-formed steel plate
WO2022219968A1 (en) * 2021-04-12 2022-10-20 Ｊｆｅスチール株式会社 Resistance spot welding method
JP7476957B2 (en) 2021-04-12 2024-05-01 Ｊｆｅスチール株式会社 Resistance Spot Welding Method
WO2023008263A1 (en) * 2021-07-30 2023-02-02 Ｊｆｅスチール株式会社 Resistance spot welding method
DE102022104981A1 (en) 2022-03-03 2023-09-07 Thyssenkrupp Steel Europe Ag Process for resistance spot welding of hardened sheet steel components
JP7355281B1 (en) 2022-06-03 2023-10-03 Ｊｆｅスチール株式会社 Welded joints, welded parts and manufacturing methods thereof, and resistance spot welding methods
WO2023233704A1 (en) * 2022-06-03 2023-12-07 Ｊｆｅスチール株式会社 Welded joint, welding member, method for manufacturing same, and method of resistance spot welding
WO2024014146A1 (en) * 2022-07-14 2024-01-18 Ｊｆｅスチール株式会社 Resistance spot welding method

Also Published As

Publication number Publication date
JP6584728B1 (en) 2019-10-02
JPWO2019124464A1 (en) 2019-12-19

Similar Documents

Publication Publication Date Title
WO2019124464A1 (en) Method for manufacturing resistance spot welded joint
KR101892828B1 (en) Resistive spot welding method
WO2019124467A1 (en) Method for manufacturing resistance spot welded joint
US10682723B2 (en) Resistance spot welding steel and aluminum workpieces with electrode having insert
RU2663659C2 (en) Method of resistance spot welding
KR101744427B1 (en) Spot welding method for high-strength steel sheet excellent in joint strength
JP6558443B2 (en) Resistance spot welding method
CN110461528B (en) Method for manufacturing resistance spot-welded joint
JP6278154B2 (en) Resistance spot welding method and manufacturing method of welded member
JP2007268604A (en) Resistance spot welding method
WO2016139951A1 (en) Resistance spot welding method and weld joint
JP6079934B2 (en) Resistance spot welding equipment
JP5392142B2 (en) Spot welding method for alloyed aluminized steel sheet or press part having aluminum alloy layer
WO2019124465A1 (en) Method for manufacturing resistance spot welded joint
WO2017033455A1 (en) Resistance spot welding method and method for manufacturing welded member
WO2018159764A1 (en) Resistance spot welding method
WO2020045678A1 (en) Resistance spot welding method
CN115335176A (en) Method for joining metallic materials
CN110475642B (en) Method for manufacturing resistance spot-welded joint
JP2007203319A (en) Resistance spot welding method

Legal Events

Date Code Title Description
ENP Entry into the national phase

Ref document number: 2019520159

Country of ref document: JP

Kind code of ref document: A

121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 18893257

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 18893257

Country of ref document: EP

Kind code of ref document: A1