JP5640410B2 - Method of manufacturing resistance spot welded joint - Google Patents

Method of manufacturing resistance spot welded joint Download PDF

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JP5640410B2
JP5640410B2 JP2010059015A JP2010059015A JP5640410B2 JP 5640410 B2 JP5640410 B2 JP 5640410B2 JP 2010059015 A JP2010059015 A JP 2010059015A JP 2010059015 A JP2010059015 A JP 2010059015A JP 5640410 B2 JP5640410 B2 JP 5640410B2
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公一 谷口
公一 谷口
池田 倫正
倫正 池田
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Jfeスチール株式会社
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本発明は、重ね抵抗溶接法の一種である抵抗スポット溶接法に係り、とくに複数枚の薄肉の金属板(被溶接材)を重ね合わせた板組みを抵抗スポット溶接法により、散りの発生なく所望サイズのナゲットを形成して抵抗スポット溶接継手とする、抵抗スポット溶接継手の製造方法に関する。   The present invention relates to a resistance spot welding method which is a kind of lap resistance welding method, and in particular, a plate assembly in which a plurality of thin metal plates (materials to be welded) are overlapped is desired by a resistance spot welding method without causing any scattering. The present invention relates to a resistance spot welded joint manufacturing method in which a size nugget is formed to form a resistance spot welded joint.
一般に、重ね合わせられた金属板同士の接合には、重ね抵抗溶接法の一種である抵抗スポット溶接法が用いられている。例えば、自動車の製造にあたっては1台あたり数千点ものスポット溶接がなされている。この溶接法は、2枚以上の金属板を重ね合わせ、その表面を直接、上下の電極で挟み加圧力を加えながら、上下電極間に大電流の溶接電流を短時間通電して接合する方法である。大電流の溶接電流を流すことで発生する抵抗発熱を利用して、点状の溶接部が得られる。この点状の溶接部は、ナゲットと呼ばれ、両金属板に電流を流した際に両金属板の接触箇所で両金属板が溶融し、凝固した部分であり、これにより両金属板が点状に接合される。   In general, a resistance spot welding method, which is a kind of a lap resistance welding method, is used to join metal plates that are overlapped with each other. For example, in the manufacture of automobiles, several thousand spots are welded per vehicle. This welding method is a method in which two or more metal plates are overlapped, and the surface is directly sandwiched between the upper and lower electrodes and a large current is applied between the upper and lower electrodes for a short time to join them. is there. A spot-like weld is obtained by utilizing resistance heat generated by passing a large welding current. This spot-like weld is called a nugget and is a part where both metal plates melt and solidify at the contact points of both metal plates when current is passed through both metal plates. Are joined together.
抵抗スポット溶接部の接合強度は、ナゲット径により左右されるため、自動車部品等の高い接合強度を必要とする場合にはとくに、所定の径以上のナゲット径を確保することが重要となってくる。一般に、加圧力、通電時間を一定とした場合には、ナゲット径は、溶接電流の増加にしたがって徐々に増加するが、ある値以上になると金属板間に溶融金属が飛散する散りという現象が生じる。散りの発生は、危険である上に、溶接部周辺に散りが付着し外観を悪化させ、ナゲット径や継手引張強度にばらつきを生じさせ、継手部の品質が不安定になる。   Since the joint strength of resistance spot welds depends on the nugget diameter, it is important to ensure a nugget diameter of a predetermined diameter or greater, especially when high joint strength is required for automobile parts and the like. . In general, when the applied pressure and energization time are constant, the nugget diameter gradually increases as the welding current increases, but when the value exceeds a certain value, a phenomenon of scattering of molten metal between the metal plates occurs. . The occurrence of scatter is dangerous and scatters around the weld and deteriorates the appearance, causing variations in the nugget diameter and joint tensile strength, resulting in unstable joint quality.
また、近年、自動車車体の衝突安全性の向上という要求の高まりから、例えば、車両のフロア部を構成する、フロアパネルとメンバーとの間にリインフォースメントを挟み込んだ構造が採用されるようになっている。この構造では、従来の単純な二枚重ねの鋼板をスポット溶接する場合と異なり、3枚以上の鋼板を重ね合わせてスポット溶接することが要求される。   Also, in recent years, due to the increasing demand for improved collision safety of automobile bodies, for example, a structure in which reinforcement is sandwiched between a floor panel and a member constituting a floor portion of a vehicle has been adopted. Yes. In this structure, unlike the conventional simple two-ply steel plate spot-welded, it is required that three or more steel plates be superposed and spot-welded.
さらに、最近では、車体の衝突安全性の更なる向上要求にともない、リインフォースメントなどの高強度化、厚肉化が進み、外側に板厚の薄いフロアパネル(薄板)を配置し、内側に板厚の厚いメンバー、リインフォースメント(厚板)を組み合わせた板組みをスポット溶接することが必要となる場合が多い。なお、ここでは、薄板とは板組みされた金属板のうち、肉厚が相対的に小さいものを薄板と記載し、肉厚の相対的に大きいものを厚板と記載することとし、以下も同様の記載とする。   Furthermore, recently, with the demand for further improvement in the collision safety of the car body, reinforcement and other high-strength and thickening have progressed, and a thin floor panel (thin plate) has been placed on the outside, and the plate on the inside It is often necessary to spot weld a plate assembly that combines thick members and reinforcements (thick plates). In addition, suppose that a thin plate is described as a thin plate, and a relatively large thickness is described as a thick plate among metal plates assembled in a plate, and the following is also used. The same description is used.
このような板厚比(=総厚/一番薄い板の板厚)の大きな板組みにおいて、従来のような、加圧力、溶接電流を一定の値としたままにするスポット溶接を行った場合には一番外側(電極チップと接触する側)の薄板と厚板の間に必要なサイズのナゲットが形成されにくいことが知られている。とくに板厚比が5を超えるような板組みでは、この傾向が強い。   When spot welding is performed in such a plate assembly with a large thickness ratio (= total thickness / thickness of the thinnest plate) as in the past, with the pressure and welding current kept constant. Is known to be difficult to form a nugget of a necessary size between the thin plate and the thick plate on the outermost side (the side in contact with the electrode tip). This tendency is particularly strong when the plate thickness ratio exceeds 5.
これは、電極チップによる冷却によって一番外側の薄板と厚板の間では温度が上がりにくいことが原因である。ナゲットは、電極間の中央付近から鋼材の固有抵抗により体積抵抗発熱にて形成されるが、ナゲットが薄板にまで成長するまでに、電極間中央部に近い部分に位置する厚板と厚板間でのナゲットの成長が大きく、電極による加圧では抑えきれずに散りが発生するため、散り発生なく必要なサイズのナゲットを薄板−厚板間に得ることが困難となる。   This is because the temperature hardly rises between the outermost thin plate and the thick plate due to cooling by the electrode tip. Nugget is formed by volume resistance heat generation due to the specific resistance of steel material from the center between the electrodes, but before the nugget grows to a thin plate, between the thick plate and the thick plate located near the center between the electrodes The nugget grows at a large distance, and it is difficult to obtain a nugget of a necessary size between the thin plate and the thick plate without the occurrence of scattering, because the nugget grows greatly and cannot be suppressed by pressurization with an electrode.
また、一番外側に配置される薄板がフロアパネルの場合には、強度よりも成形性が重要となるため、使用される鋼板は軟鋼となることが多い。一方、板厚の厚い鋼板は強度補強部材であり高張力鋼板が使用される場合が多い。このような板組みでは、発熱する位置は、固有抵抗の高い高張力鋼板側に偏るため、厚板−薄板(軟鋼)間にはさらにナゲットが形成されにくくなる。また、使用される鋼板がめっき鋼板となると、低温で溶融しためっき層が鋼板間の通電経路を拡大するため電流密度が減少し、薄板側でのナゲットの形成がさらに困難となる。   Moreover, when the thin plate arrange | positioned on the outermost side is a floor panel, since a moldability becomes more important than intensity | strength, the steel plate used often becomes mild steel. On the other hand, a thick steel plate is a strength reinforcing member, and a high-tensile steel plate is often used. In such a plate assembly, the position where heat is generated is biased toward the high-tensile steel plate having a high specific resistance, so that nuggets are more difficult to be formed between the thick plate and the thin plate (mild steel). Moreover, when the steel plate used becomes a plated steel plate, the plating layer melted at a low temperature expands the current-carrying path between the steel plates, thereby reducing the current density and making it more difficult to form a nugget on the thin plate side.
このような問題に際し、例えば、特許文献1には、重ね合わされた2枚の厚板の少なくとも一方に薄板をさらに重ね合わせた板厚比の大きな板組みをスポット溶接する方法が提案されている。特許文献1に記載された技術は、薄板の溶接すべき部位に部分的に一般部より一段高い座面を形成するとともに、薄板に対抗する電極を、先端を球面に形成し、溶接初期は低加圧力で、薄板の座面を押しつぶすようにして、薄板とこれと隣り合う厚板とを溶接し、その後、高加圧力で2枚の厚板同士を溶接するスポット溶接方法である。この技術によれば、散りを発生することなく、薄板−厚板間にも必要サイズのナゲットを形成できるとしている。   In order to deal with such a problem, for example, Patent Document 1 proposes a method of spot welding a plate assembly having a large plate thickness ratio in which a thin plate is further overlapped with at least one of two stacked thick plates. The technique described in Patent Document 1 forms a seat surface that is one step higher than the general part at the portion to be welded of the thin plate, and forms an electrode that opposes the thin plate with a spherical tip, and is low in the initial stage of welding. This is a spot welding method in which a thin plate and an adjacent thick plate are welded so as to crush the seating surface of the thin plate with a pressing force, and then the two thick plates are welded with a high pressing force. According to this technique, a nugget of a necessary size can be formed between a thin plate and a thick plate without causing scattering.
しかし、特許文献1に記載された技術では、薄板−厚板間に必要サイズのナゲットを形成することができるが、薄板の溶接する部分に予め一般部より一段高い座面をプレスなどで形成する工程が必要となり、工程が複雑になり、生産性が低下するという問題がある。   However, in the technique described in Patent Document 1, a nugget of a necessary size can be formed between a thin plate and a thick plate, but a seat surface that is one step higher than a general portion is formed in advance on a portion to be welded by a press or the like. There is a problem that a process is required, the process becomes complicated, and productivity is lowered.
この問題に対して、特許文献2には、金属板の板組みを、重ね合わせた2枚以上の厚板の少なくとも一方に薄板を重ね合わせた、板厚比が5以上の板組みとし、抵抗スポット溶接を第一段および第二段の二段階からなる溶接とし、第二段の溶接が第一段の溶接に比べ、高加圧力、低電流又は同じ電流、長通電時間又は同じ通電時間の溶接とすることによって、板厚比の大きな板組みにおいても余計な工程を付加することなく、また散りを発生することなく、必要サイズのナゲットを形成できるようにしている。   In order to solve this problem, Patent Document 2 discloses that a plate assembly of metal plates is a plate assembly having a plate thickness ratio of 5 or more, in which a thin plate is superimposed on at least one of two or more thick plates that are overlapped, and resistance. Spot welding is a welding consisting of two stages, the first stage and the second stage. Compared to the first stage welding, the second stage welding has a higher pressure, lower current or the same current, longer energization time or the same energization time. By using welding, a nugget of a necessary size can be formed without adding an extra process and without generating a scatter even in a plate assembly having a large thickness ratio.
ただし、特許文献2に記載の技術によって得られた抵抗スポット溶接継手は、板組みに高強度鋼板(高張力鋼板)が含まれている場合、以下のような問題が生じる可能性がある。   However, the resistance spot welded joint obtained by the technique described in Patent Literature 2 may have the following problems when a high strength steel plate (high strength steel plate) is included in the plate assembly.
通常、得られた抵抗スポット溶接継手の品質の指標としてJISで定められるせん断引張強度(継手のせん断方向に引張試験をしたときの強さ)、十字引張強度(継手のはく離方向に引張試験をしたときの強さ)が重要である。   In general, the tensile strength of the resistance spot welded joint obtained is determined by JIS as a strength index (strength when the tensile test is performed in the shear direction of the joint) and cross tensile strength (the tensile test is performed in the direction of peeling of the joint). Strength when) is important.
高強度鋼板のスポット溶接部の引張せん断強さは、鋼板の引張強度の増加とともに増加する傾向にある一方で、十字引張強度は鋼板の引張強度の増加にかかわらずほとんど増加せず、逆に減少することもある。その原因として、高強度鋼板は、その強度を達成するために下記式で表される炭素当量Ceqが大きくならざるをえず、加えて溶接は急熱急冷現象であるために、溶接部及び熱影響部において硬度が上昇し、靭性が低下するからだと考えられる。   The tensile shear strength of spot welds in high-strength steel sheets tends to increase as the tensile strength of steel sheets increases, while the cross tensile strength hardly increases regardless of the increase in tensile strength of steel sheets, but decreases. Sometimes. The reason for this is that, in order to achieve the strength of the high-strength steel sheet, the carbon equivalent Ceq represented by the following formula must be large, and in addition, since welding is a rapid and rapid quenching phenomenon, This is probably because the hardness increases in the affected area and the toughness decreases.
Ceq=C+1/24×Si+1/6×Mn(%)
ここで、C、Si、Mnは、それぞれの質量%を示す。
Ceq = C + 1/24 × Si + 1/6 × Mn (%)
Here, C, Si, and Mn indicate mass% of each.
この問題を解決するために溶接法の観点からは、打点数の増加やナゲット径の拡大が考えられるが、打点数の増加はスペースが必要であり、かつ、打点数を増やしても強度が下がる傾向にある。さらに、ナゲット径を拡大するには電極を大きくしたり、加圧力を増加しなければいけないため、装置的な制約も受ける。   In order to solve this problem, from the viewpoint of the welding method, an increase in the number of hit points and an increase in the nugget diameter can be considered. However, an increase in the number of hit points requires a space, and the strength decreases even if the number of hit points is increased. There is a tendency. Furthermore, in order to enlarge the nugget diameter, the electrode must be enlarged or the applied pressure must be increased, which is also limited by the apparatus.
そこで、従来と同様のナゲット径で強度を確保するために、ナゲットを形成する本通電の後に通電(後熱通電)を行う様々な試みがなされてきた。   Accordingly, various attempts have been made to energize (post-heat energization) after the main energization for forming the nugget in order to ensure the strength with the same nugget diameter as in the prior art.
その一例として、特許文献3では、テンパー通電における通電時間To・通電電流Ioと本通電における通電時間Tt・通電電流Itを用いて、(It/To)の二乗と(Tt/To)の積が0.25/0.82の範囲に入っている事が望ましいとしている。
特許文献4では、引張強度が35kg/mm以上の高張力鋼板において、散り発生限界電流値以上の本通電に加えて、本通電より低い電流値にてテンパー通電を行うことでせん断強度と疲労強度の向上を達成出来るとしている。
As an example, in Patent Document 3, the product of the square of (It / To) and (Tt / To) is calculated using the energization time To and energization current Io in temper energization and the energization time Tt and energization current It in main energization. It is desirable to be in the range of 0.25 / 0.82.
In Patent Document 4, in a high-tensile steel sheet having a tensile strength of 35 kg / mm 2 or more, in addition to the main energization exceeding the scattering occurrence limit current value, the temper energization is performed at a current value lower than the main energization to thereby improve the shear strength and fatigue. It is said that the strength can be improved.
テンパー通電の代わりに、一定電流を何度かに分けて付加するパルセーション通電の提案もなされており、例えば特許文献5では、三枚重ねの鋼板に対して、本通電の後にパルセーション通電を行うことで十分なナゲット径が確保出来るとしている。   Instead of temper energization, pulsation energization has also been proposed in which a constant current is divided and added several times. For example, in Patent Document 5, pulsation energization is performed on a three-layer steel sheet after main energization. By doing so, it is said that a sufficient nugget diameter can be secured.
近年では、非特許文献に見られるように、一定の冷却の後、極短時間通電を行ってテンパー通電と同じ効果を得られるとしたSpike−Temperingという方法も提案されており、それによればテンパー通電に必要な時間は40サイクル(0.8秒)程度とされている。   In recent years, as seen in non-patent literature, a method called Spike-Tempering has been proposed in which energization is performed for an extremely short time after constant cooling to obtain the same effect as temper energization. The time required for energization is about 40 cycles (0.8 seconds).
さらに特許文献6では、本通電を行った後に、本通電より低い電流値にてテンパー通電を行うことにより、高張力鋼板の十字引張強度を改善することが出来るとしている。   Further, in Patent Document 6, it is stated that the cross tensile strength of the high-tensile steel sheet can be improved by performing temper energization with a current value lower than the main energization after performing the main energization.
しかしながら、前記特許文献3〜5に記載されているような通電方法は、本通電より低い電流値で、所定の抵抗発熱が可能な範囲を選ぶために、利用可能な電流範囲は狭く、僅かな通電電流・電流時間の変化で大きく影響を受けざるを得ず、様々な外乱要因の存在する製造の現場(例えば、本通電の50%を超える大きな電流低下が起きる)において実装するにあたっては、安定的な施工を行う上での余裕が小さいという問題点がある。   However, in the energization methods as described in Patent Documents 3 to 5, the current range that can be used is narrow and small in order to select a range in which a predetermined resistance heat generation is possible with a current value lower than the main energization. It must be greatly affected by changes in the energization current and current time, and is stable when mounted in production sites where various disturbance factors exist (for example, a large current drop exceeding 50% of the main energization occurs). There is a problem that there is a small margin for performing general construction.
また、一般的なマルテンサイトテンパー方式の通電方法は、前記非特許文献にて実施あるいは記載されているように、十分な冷却を置いた後に通電することで焼き戻しを行うテンパー通電であり、十分な冷却時間(非特許文献によれば40サイクル(0.8秒)程度)が必要であり、総溶接時間(最初の通電が開始してから、最後の通電が完了するまでと定義する)が長くなるという問題があった。   In addition, the general martensite temper type energization method is temper energization in which tempering is performed by energizing after sufficient cooling, as implemented or described in the non-patent document. Cooling time (according to non-patent literature, about 40 cycles (0.8 seconds)) is required, and the total welding time (defined from the start of the first energization to the completion of the last energization) There was a problem of becoming longer.
さらに、特許文献6は三枚以上重ねた板組に対して溶融部を確保する方法であり、すなわち、本通電で形成されたナゲットを後熱通電によって拡大することを目的としている。従来、ナゲット径と継手強度には密接な関係があるという観点から、後熱通電の有無に係わらず、最終的なナゲット径に対して継手強度を整理し、評価してきた。前述したように、特定のナゲット径で強度を向上させることが重要であることに加え、溶融状態から冷却したのではナゲットやHAZを急冷し、継手強度を向上させることは出来ない。   Further, Patent Document 6 is a method for securing a melted portion with respect to a set of three or more sheets, that is, an object of enlarging a nugget formed by main energization by post-heat energization. Conventionally, from the viewpoint that there is a close relationship between the nugget diameter and the joint strength, the joint strength has been arranged and evaluated with respect to the final nugget diameter regardless of the presence or absence of post-heat conduction. As described above, it is important to improve the strength with a specific nugget diameter. In addition, if the nugget or HAZ is cooled from the molten state, the joint strength cannot be improved.
特開2003−071569号公報JP 2003-071569 A 特許第3922263号公報Japanese Patent No. 3922263 特開昭58−003792号公報JP 58-003792 A 特開昭58−003793号公報JP 58-003793 A 特開2002−103048号公報JP 2002-103048 A 特開2008−093726号公報JP 2008-093726 A
本発明は、上記のような事情に鑑みてなされたものであり、高強度鋼板を含んだ板厚比の大きな板組みにおいても、余計な工程を付加することなく、また散りを発生することなく、必要サイズのナゲットが形成されているとともに、良好な引張強度を有する抵抗スポット溶接継手を安定して得ることができる、抵抗スポット溶接継手の製造方法を提案することを目的とする。   The present invention has been made in view of the circumstances as described above, and even in a plate assembly with a large plate thickness ratio including a high-strength steel plate, without adding an extra step and without generating scattering. An object of the present invention is to propose a method of manufacturing a resistance spot welded joint in which a nugget of a necessary size is formed and a resistance spot welded joint having a good tensile strength can be stably obtained.
本発明者らは、上記した課題を達成するため、前記特許文献2に記載の技術に基づいて第一段溶接および第二段溶接を行うことで、必要サイズのナゲットを形成した上で、後熱通電としての第三段溶接を行うことによって、必要な継手強度を確保することを考えた。   In order to achieve the above-described problems, the inventors have performed first-stage welding and second-stage welding based on the technique described in Patent Document 2, thereby forming a nugget of a necessary size, and We considered securing the required joint strength by performing third-stage welding as heat conduction.
そこで、本発明者らは、必要な継手強度を確保するための第三段溶接として、安定的な施工を行うことができる後熱通電について鋭意検討を行った。   Therefore, the present inventors have intensively studied post-heat energization capable of performing stable construction as third-stage welding for ensuring necessary joint strength.
従来、継手形成後に組織を焼き戻し、継手強度を向上させるため、後熱通電(テンパー通電)として低電流を付加する方法がとられてきたのに対し、逆に溶融部を形成する本通電電流よりも高電流を付加することで継手強度を向上させることが出来ないかを考えた。しかし、高電流の付加は散りや電極の溶着の原因となるほか、再溶融再急冷により継手強度の変化が無いか、逆に低下することもある。   Conventionally, in order to improve the strength of the joint by tempering the joint after forming the joint, a method of applying a low current as post-heat conduction (temper conduction) has been used, whereas the main conduction current that forms the melted part on the contrary. We thought whether joint strength could be improved by applying a higher current than that. However, the addition of a high current causes scattering and electrode welding, and there is no change in joint strength due to remelting and rapid cooling, or it may decrease.
そこで、その問題を解決するためにさらに検討を行った。   Therefore, further studies were conducted to solve the problem.
その際、図8、図9に示すように、重ね合わせた2枚の高強度鋼板(上側の高強度鋼板22、下側の高強度鋼板23)の板組を、上下一対の電極チップ(上側の電極チップ31、下側の電極チップ32)で挟み、加圧、通電することにより接合して抵抗スポット溶接継手を得る場合を例にした。   At that time, as shown in FIG. 8 and FIG. 9, a pair of two high strength steel plates (upper high strength steel plate 22 and lower high strength steel plate 23) that are superposed on each other is used as a pair of upper and lower electrode chips (upper side). The electrode tip 31 and the lower electrode tip 32) are joined together by pressurization and energization to obtain a resistance spot welded joint.
まず、抵抗スポット溶接継手の十字引張強度と破断形態には相関が有り、低強度溶接継手は鋼板に平行に破断するはく離破断を生じ、高強度になるにつれてボタン状に片方の鋼板が残ったまま抜けるように破断するプラグ破断へと変化する。同じナゲット径においての破断形態の変化を見るために、テンパー通電を施さない溶接継手とテンパー通電を施した溶接継手とを作成し、はく離破断したものとプラグ破断したものの継手を比較したところ、以下の事が分かった。   First, there is a correlation between the cross tensile strength and fracture mode of resistance spot welded joints, and low-strength welded joints cause peeling fracture that breaks parallel to the steel sheet, and one steel sheet remains in a button shape as the strength increases. It changes to plug rupture that breaks so as to come off. In order to see the change in fracture mode at the same nugget diameter, a welded joint that was not subjected to temper energization and a welded joint that was subjected to temper energization were created. I understood that.
すなわち、はく離破断したものでは破面がへき開面で脆性的な破断であり、プラグ破断したものでは破面が滑らかで延性的な破断であった。そして、図8に示すように、ナゲット16の周囲を取り巻く、加熱により組織が変化した部分を熱影響部17とすれば、はく離破断したものでは、熱影響部17にナゲット16内部よりも硬化した部分が見られたのに対して、プラグ破断したものでは、熱影響部17の軟化が見られた。この熱影響部17の軟化はテンパー通電によってマルテンサイト組織の焼き戻しが生じて起こったものであり、この軟化によってナゲット16外周での塑性変形が許容され、ナゲット16端部での応力集中が緩和されるために、破断形態がはく離破断からプラグ破断に変化したものだと考えられた。   That is, the fracture surface was a fracture surface with a cleavage plane and a brittle fracture, and the plug fracture surface was a smooth and ductile fracture. As shown in FIG. 8, if the portion surrounding the nugget 16 and the structure of which has been changed by heating is the heat-affected zone 17, the heat-affected zone 17 is hardened more than the inside of the nugget 16 in the case of peeling and breaking. Whereas the portion was seen, the heat-affected zone 17 was softened when the plug was broken. The softening of the heat-affected zone 17 is caused by tempering of the martensite structure caused by tempering. The softening allows plastic deformation at the outer periphery of the nugget 16 and alleviates stress concentration at the end of the nugget 16. Therefore, it was considered that the fracture mode was changed from the peeling fracture to the plug fracture.
そこで、発明者らは、後熱通電を高電流で行うに際して、上記と同様に効果を得るために、熱影響部17の全く新しい軟化手法を考えることにした。すなわち、図8に示したように、ナゲット16及び熱影響部17を一つの考え方で軟化させるのではなく、図9に示すように、熱影響部17を電極31、32側の熱影響部17aと軟化域18側の熱影響部17bとに分けて、別個に制御することができるのではないかと考えた。軟化域18側の熱影響部17bはナゲット16からの熱移動も有るために冷却速度は比較的遅いのに対して、電極31、32側の熱影響部17aは電極への放熱により冷却速度は速いからである。   Therefore, the inventors decided to consider a completely new softening method for the heat affected zone 17 in order to obtain the same effect as described above when the post-heat energization is performed at a high current. That is, as shown in FIG. 8, the nugget 16 and the heat-affected zone 17 are not softened by one idea, but the heat-affected zone 17 is replaced with the heat-affected zone 17a on the electrodes 31 and 32 side as shown in FIG. And the heat-affected zone 17b on the softened zone 18 side, it was thought that it could be controlled separately. The heat affected zone 17b on the softened region 18 side also has heat transfer from the nugget 16, so the cooling rate is relatively slow, whereas the heat affected zone 17a on the electrode 31 and 32 side has a cooling rate due to heat dissipation to the electrodes. Because it is fast.
テンパー通電を行わない時に熱影響部17がナゲット16より硬化するのは、抵抗スポット溶接ではナゲット16中央へ集中的な加熱が行われるために、温度が比較的低い電極31、32あるいは軟化域18と面している熱影響部17は、ナゲット16内部よりも冷却速度が速くなっていることが原因だと考えられる。   The heat-affected zone 17 is hardened from the nugget 16 when the temper energization is not performed because the resistance spot welding concentrates heating to the center of the nugget 16, so that the electrodes 31 and 32 having a relatively low temperature or the softened region 18 are heated. It is considered that the heat affected zone 17 facing is caused by the cooling rate being higher than that inside the nugget 16.
そこで、後熱通電において、熱影響部17の特に軟化域18側の熱影響部17bの冷却速度を遅くし、ナゲット16と同程度になるような適度な通電を与えればよいと考えた。一方、電極31、32側の熱影響部17aは温度が十分に下がるまでに要する時間が短く、その時間を待ってから加熱することによりテンパー処理と同じ効果を得られると考えた。   In view of this, in the post-heat energization, it was thought that the cooling rate of the heat affected zone 17b of the heat affected zone 17, particularly the softened zone 18 side, should be slowed down so as to give an appropriate energization that is comparable to the nugget 16. On the other hand, the heat affected zone 17a on the side of the electrodes 31 and 32 has a short time required for the temperature to sufficiently decrease, and it is considered that the same effect as the temper treatment can be obtained by heating after waiting for the time.
したがって、本発明は以下の原理により引張強度を向上させるものである。すなわち、本通電(前記特許文献2に記載の技術に基づく第一段溶接および第二段溶接)によるナゲット16の形成の後、後熱通電(第三段溶接)として、所定の冷却時間(休止時間)をおいて、高電流を付加することで、この入熱によりナゲット16および軟化域18側の熱影響部17bの急冷が抑制され硬化が抑制されると同時に、電極31、32側の熱影響部17aはテンパー効果により焼き戻しされ軟化するのである。テンパー通電やパルセーション通電のように、継手全体に焼き戻し効果などを付与するのではなく、継手の部分部分で効果が異なることが、従来技術と大きく異なる点である。   Therefore, the present invention improves the tensile strength according to the following principle. That is, after the formation of the nugget 16 by main energization (first-stage welding and second-stage welding based on the technique described in Patent Document 2), as a post-heat energization (third-stage welding), a predetermined cooling time (pause) By applying a high current after a certain period of time, this heat input suppresses rapid cooling of the heat affected zone 17b on the nugget 16 and softening region 18 side and suppresses hardening, and at the same time, heat on the electrodes 31 and 32 side. The affected part 17a is tempered and softened by the temper effect. Unlike the temper energization and pulsation energization, the tempering effect is not given to the entire joint, but the effect is different in the joint portion, which is a significant difference from the prior art.
上記原理を有効に成立させるためには、以下の点に着目する必要がある。すなわち、電極31、32側の熱影響部17aにおいては、十分に冷却された後に適切に加熱される必要がある。このためには、冷却時間(休止時間)を所定時間以上おく必要があるが、長くとも10サイクル程度で目的は達せられる。さらに、軟化域18側の熱影響部17bにおいては、後熱通電の通電時間が長すぎると、必要以上に加熱され、再急冷されることになってしまい、逆に硬化させてしまう要因となるし、散りの原因ともなる。したがって、通電時間は長くとも5サイクル程度とすべきである。また、電流値についても、同様の理由から設定されるべきであり、本通電における電流値の3倍程度までの電流値を溶接対象に応じて適切に選択すべきである。   In order to effectively establish the above principle, it is necessary to pay attention to the following points. In other words, the heat-affected zone 17a on the electrodes 31 and 32 side needs to be heated appropriately after being sufficiently cooled. For this purpose, the cooling time (resting time) needs to be longer than a predetermined time, but the purpose can be achieved in about 10 cycles at the longest. Furthermore, in the heat-affected zone 17b on the softened zone 18 side, if the energization time of the post-heat energization is too long, it will be heated more than necessary and will be re-quenched, causing conversely curing. However, it also causes scattering. Therefore, the energization time should be about 5 cycles at the longest. Also, the current value should be set for the same reason, and the current value up to about three times the current value in the main energization should be appropriately selected according to the object to be welded.
そして、これらは急冷による硬化が著しい引張強度590MPa以上の高張力鋼板に適用されることにより、著しい効果を発現する。   And when these are applied to a high-tensile steel plate having a tensile strength of 590 MPa or more, which is markedly hardened by rapid cooling, a significant effect is exhibited.
それに加えて、後熱通電における加圧力を本通電よりも増加させることで、後熱通電における電流値の余裕を増加させるばかりでなく、そのことによって散りを抑制することが出来る。   In addition, by increasing the applied pressure in the post-heat energization over the main energization, not only the current value margin in the post-heat energization is increased, but also scattering can be suppressed.
このようにして、第三段溶接での後熱通電において、上記のような高電流を短時間かつ好ましくは複数回通電するとともに加圧力を本通電よりも増加させることで、散りや電極の溶着なく、安定して継手強度を向上させることに成功したのである。   In this way, in the post-heat energization in the third stage welding, the above-described high current is energized in a short time, preferably a plurality of times, and the applied pressure is increased over the main energization, so that scattering and electrode welding are performed. It succeeded in improving the joint strength stably.
上記に基づいて、本発明は以下の特徴を有している。   Based on the above, the present invention has the following features.
[1]複数枚の金属板を重ね合わせた板組みを抵抗スポット溶接により溶接接合し抵抗スポット溶接継手を製造するにあたり、前記板組みを、重ね合わせた2枚以上の厚板の少なくとも一方に薄板を重ね合わせた、板厚比が5以上の板組みとし、前記抵抗スポット溶接を第一段・第二段・第三段の三段階からなる溶接とし、第二段の溶接は前記第一段の溶接に比べ、高加圧力、低電流又は同じ電流、長通電時間又は同じ通電時間の溶接とし、さらに第三段は第二段よりも高加圧力で、高電流の通電を繰り返すことを特徴とする抵抗スポット溶接継手の製造方法。   [1] In manufacturing a resistance spot welded joint by welding a plate assembly in which a plurality of metal plates are overlapped by resistance spot welding, the plate assembly is thinned on at least one of the two or more thick plates overlapped. And the resistance spot welding is a three-stage welding of the first stage, the second stage, and the third stage, and the second stage welding is the first stage. Compared to the welding of, welding with high pressure, low current or the same current, long energization time or the same energization time, and the third stage repeats high current energization with higher pressure than the second stage A method of manufacturing a resistance spot welded joint.
[2]前記第一段の溶接を、該溶接の加圧力P、溶接電流I、通電時間Tが、前記複数枚の金属板のうち最も薄肉の金属板の板厚tmとの関係で、下記(1)〜(3)式を満足する溶接とし、前記第二段の溶接を、該溶接の加圧力PII、溶接電流III、通電時間TIIが下記(4)〜(6)式を満足する溶接とすることを特徴とする前記[1]に記載の抵抗スポット溶接継手の製造方法。
0.8tm≦P≦5tm ………(1)
2≦T≦6 ………(2)
3tm+5≦I ………(3)
1.1P≦PII≦10P ………(4)
0.5I≦III≦I ………(5)
≦TII≦10T ………(6)
ここで、tm:複数枚の金属板のうち最も薄肉の金属板の板厚(mm)
、PII:加圧力(kN)
、III:溶接電流(kA)
、TII:通電時間(cycles/50Hz)
[2] In the first stage welding, the welding pressure P I , welding current I I , and energization time T I are related to the thickness tm of the thinnest metal plate among the plurality of metal plates. Thus, the welding satisfying the following formulas (1) to (3) is performed, and the welding of the second stage is performed with the welding pressure P II , welding current I II , and energization time T II being the following (4) to (6 The method of manufacturing a resistance spot welded joint according to [1], wherein the welding satisfies the formula (1).
0.8 tm ≦ P I ≦ 5 tm (1)
2 ≦ T I ≦ 6 (2)
3tm + 5 ≦ I I (3)
1.1 P I ≦ P II ≦ 10 P I (4)
0.5I I ≦ I II ≦ I I (5)
T I ≦ T II ≦ 10T I ......... (6)
Here, tm: plate thickness (mm) of the thinnest metal plate among the plurality of metal plates
P I , P II : Applied pressure (kN)
I I , I II : Welding current (kA)
T I , T II : energization time (cycles / 50 Hz)
[3]前記第三段の溶接における加圧力PIII、冷却時間Tc、溶接電流IIII、通電時間TIIIが、前記第二段の加圧力PII、溶接電流III、通電時間TIIとの関係において、下記(7)〜(10)式を満足することを特徴とする前記[1]または[2]に記載の抵抗スポット溶接継手の製造方法。
II<PIII ………(7)
1≦Tc≦20 ………(8)
1≦TIII≦5 ………(9)
II<IIII≦3III ………(10)
ここで、PII、PIII:加圧力(kN)
II、IIII:溶接電流(kA)
Tc:冷却時間(cycles/50Hz)
III:通電時間(cycles/50Hz)
[3] The pressure P III , the cooling time Tc, the welding current I III , and the energization time T III in the third stage welding are the second stage pressure P II , the welding current I II , and the energization time T II . In the above relationship, the following formulas (7) to (10) are satisfied. The method for producing a resistance spot welded joint according to the above [1] or [2].
P II <P III (7)
1 ≦ Tc ≦ 20 (8)
1 ≦ T III ≦ 5 (9)
I II <I III ≦ 3I II (10)
Here, P II and P III : Applied pressure (kN)
I II , I III : Welding current (kA)
Tc: Cooling time (cycles / 50 Hz)
T III : Energization time (cycles / 50 Hz)
[4]前記第三段の溶接における冷却時間Tcが、下記(8a)式を満足することを特徴とする前記[3]に記載の抵抗スポット溶接継手の製造方法。
1≦Tc≦10 ………(8a)
ここで、Tc:冷却時間(cycles/50Hz)
[4] The method of manufacturing a resistance spot welded joint according to [3], wherein a cooling time Tc in the third stage welding satisfies the following expression (8a).
1 ≦ Tc ≦ 10 (8a)
Here, Tc: Cooling time (cycles / 50 Hz)
[5]前記第三段の、冷却時間Tc及び通電時間TIIIと溶接電流IIIIで構成される通電を、1回以上5回以下で繰り返すことを特徴とする前記[1]〜[4]のいずれかに記載の抵抗スポット溶接継手の製造方法。 [5] the third stage, the the energization composed of cooling time Tc, and energization time T III and the welding current I III, and repeating the following five or more times [1] to [4] The manufacturing method of the resistance spot welding joint in any one of.
本発明においては、高強度鋼板を含んだ板厚比の大きな板組みであっても、余計な工程を付加することなく、また散りを発生することなく、必要サイズのナゲットが形成されているとともに、良好な引張強度を有する抵抗スポット溶接継手を安定して得ることができる。   In the present invention, a nugget of a necessary size is formed without adding an extra process and without generating scattering even in a large plate thickness ratio including a high-strength steel plate. Thus, a resistance spot welded joint having a good tensile strength can be obtained stably.
本発明の抵抗スポット溶接における第一段溶接時のナゲットの形成状況を模式的に示す説明図である。It is explanatory drawing which shows typically the formation condition of the nugget at the time of the 1st stage welding in the resistance spot welding of this invention. 本発明の抵抗スポット溶接における第二段溶接時のナゲットの形成状況を模式的に示す説明図である。It is explanatory drawing which shows typically the formation condition of the nugget at the time of the second stage welding in the resistance spot welding of this invention. 本発明の抵抗スポット溶接における第三段溶接時の状況を模式的に示す説明図である。It is explanatory drawing which shows typically the condition at the time of the 3rd stage welding in the resistance spot welding of this invention. 本発明の抵抗スポット溶接における加圧パターンを模式的に示す説明図である。It is explanatory drawing which shows typically the pressurization pattern in the resistance spot welding of this invention. 本発明の抵抗スポット溶接における通電パターンを模式的に示す説明図である。It is explanatory drawing which shows typically the electricity supply pattern in the resistance spot welding of this invention. 電極チップの形状を模式的に示す断面図である。It is sectional drawing which shows the shape of an electrode tip typically. 実施例で使用した板組みを模式的に示す断面図である。It is sectional drawing which shows typically the board assembly used in the Example. 抵抗スポット溶接における熱影響部と軟化域を示す説明図である。It is explanatory drawing which shows the heat affected zone and softening area | region in resistance spot welding. 本発明の原理を示す説明図である。It is explanatory drawing which shows the principle of this invention.
本発明では、複数枚の金属板を重ね合わせた板組みを、上下一対の電極チップで挟み、加圧、通電する抵抗スポット溶接により溶接接合して、必要サイズのナゲットを形成するとともに、必要な継手強度を得る。   In the present invention, a plate assembly in which a plurality of metal plates are overlapped is sandwiched between a pair of upper and lower electrode tips, welded by resistance spot welding to be pressurized and energized to form a nugget of a necessary size and necessary. Get joint strength.
本発明で好適に使用可能な溶接装置は、上下一対の電極チップを備え、溶接中に加圧力、溶接電流をそれぞれ任意に制御可能であれば、加圧機構(エアシリンダやサーボモータ等)、形式(定置式、ロボットガン等)、電極形状等はとくに限定されない。   A welding apparatus that can be suitably used in the present invention includes a pair of upper and lower electrode tips, and a pressurizing mechanism (such as an air cylinder or a servo motor), as long as the pressurizing force and welding current can be arbitrarily controlled during welding, The type (stationary, robot gun, etc.), electrode shape, etc. are not particularly limited.
本発明の一実施形態として、図1〜図3に示すような、重ね合わせた2枚以上の厚板12、13の外側に薄板11を重ね合わせた金属板の板組みをスポット溶接する場合を例に、以下、説明する。   As an embodiment of the present invention, as shown in FIGS. 1 to 3, a case where spot welding is performed on a plate set of metal plates in which thin plates 11 are stacked on the outside of two or more stacked thick plates 12 and 13. An example will be described below.
この実施形態では、抵抗スポット溶接を第一段、第二段、第三段の三段階からなる溶接とする。この実施形態の抵抗スポット溶接における加圧パターンを図4に、通電パターンを図5に模式的に示す。   In this embodiment, the resistance spot welding is a three-stage welding of a first stage, a second stage, and a third stage. A pressure pattern in resistance spot welding of this embodiment is schematically shown in FIG. 4, and an energization pattern is schematically shown in FIG.
まず、所望の溶接位置で板組みを上下一対の電極31、32で挟み、加圧を開始する。加圧力がかかり始めてから通電を開始する。第一段の溶接では、接触抵抗発熱が小さくならないように、加圧力、溶接電流を設定し、薄板11と厚板12間にナゲット16a(径N1)を形成する。第一段の溶接では、低加圧力で大溶接電流を短時間で加えることが好ましい。これにより、薄板11と厚板12間は通電経路が狭く電流密度が高くなり、めっきの溶融等による通電経路の拡大の影響も少なく、発生する接触抵抗発熱を有効にナゲットN1形成に作用させることができるようになる。   First, the plate assembly is sandwiched between a pair of upper and lower electrodes 31 and 32 at a desired welding position, and pressurization is started. Start energization after pressure is applied. In the first stage of welding, a pressing force and a welding current are set so that contact resistance heat generation does not become small, and a nugget 16a (diameter N1) is formed between the thin plate 11 and the thick plate 12. In the first stage welding, it is preferable to apply a large welding current in a short time with a low pressure. As a result, the current path between the thin plate 11 and the thick plate 12 is narrow and the current density is high, and there is little influence of expansion of the current path due to melting of plating, etc., and the generated contact resistance heat is effectively applied to the nugget N1 formation. Will be able to.
第一段の溶接では、加圧力P(kN)は、複数枚の金属板のうち最も薄肉の金属板の板厚tm(図1では金属板11の板厚:mm)との関係で、次の(1)式を満足するように設定することが好ましい。
0.8tm≦P≦5tm ………(1)
In the first stage welding, the pressure P I (kN) is related to the plate thickness tm of the thinnest metal plate among the plurality of metal plates (plate thickness of the metal plate 11 in FIG. 1). It is preferable to set so as to satisfy the following expression (1).
0.8 tm ≦ P I ≦ 5 tm (1)
第一段の溶接における加圧力Pが5tm(kN)超えでは、加圧力が高くなりすぎて、接触抵抗による発熱が小さくなり、薄板11と厚板12間にナゲットが形成されなくなる。一方、加圧力Pが0.8tm未満の場合には、電極チップ31と薄板11との間での接触抵抗が大きくなり、スパークが発生しやすくなるとともに、薄板11と厚板12間からも散りが発生しやすくなる。 The pressure P I in the welding of the first stage exceeds 5TM (kN), applied pressure becomes too high, heat generation due to contact resistance is reduced, the nugget is not formed between the thin sheet 11 and the thick sheet 12. On the other hand, if the pressure P I is less than 0.8tm, the contact resistance between the electrode tip 31 and the thin plate 11 is increased, along with the spark is likely to occur, from between sheet 11 and the thick 12 Scattering is likely to occur.
また、第一段の溶接では、通電時間T(cycles/50Hz)は、次の(2)式を満足するように設定することが好ましい。
2≦T≦6 ………(2)
In the first stage welding, it is preferable to set the energization time T I (cycles / 50 Hz) so as to satisfy the following expression (2).
2 ≦ T I ≦ 6 (2)
通電時間Tが2cycles未満では、通電時間が短かすぎるため、薄板11と厚板12間に所望サイズのナゲットが形成されなくなる。一方、通電時間Tが6cyclesを超えて長くなると、散りが発生する。 It is less than the energization time T I is 2 cycles, because the energization time is too short, the desired size of the nugget between the thin plate 11 and the thick 12 is not formed. On the other hand, the energization time T I is the longer beyond 6Cycles, expulsion occurs.
また、第一段の溶接では、溶接電流I(kA)は、複数枚の金属板のうち最も薄肉の金属板の板厚tm(図1では金属板11の板厚:mm)との関係で、次の(3)式を満足するように設定することが好ましい。
3tm+5≦I ………(3)
In the first-stage welding, the welding current I I (kA) is related to the thickness tm of the thinnest metal plate among the plurality of metal plates (the thickness of the metal plate 11 in FIG. 1 is mm). Therefore, it is preferable to set so as to satisfy the following expression (3).
3tm + 5 ≦ I I (3)
第一段の溶接における溶接電流Iが、(3tm+5)未満の小電流では、接触抵抗発熱を有効に利用できず、薄板11と厚板12間にナゲットが形成されなくなる。第一段の溶接では、初期の数サイクルの間、大電流を流すことが好ましい。 Welding current I I in the welding of the first stage, the (3tm + 5) less than a small current, can not be effectively utilized contact resistance heating, nugget is not formed between the thin sheet 11 and the thick sheet 12. In the first stage welding, it is preferable to pass a large current during the initial few cycles.
このようなことから、第一段の溶接では、前記した(1)、(2)、(3)式を満足するように加圧力P、溶接電流I、通電時間Tを設定することが、薄板11と厚板12間に所望サイズのナゲットを形成するために好ましい。 For this reason, in the welding of the first stage, the above-mentioned (1), (2), (3) the pressure P I to satisfy the equation, the welding current I I, setting the energization time T I Is preferable in order to form a nugget of a desired size between the thin plate 11 and the thick plate 12.
そして、この実施形態では、上記した第一段の溶接に続いて第二段の溶接を行なう。第二段の溶接は、第一段の溶接に比べ、高加圧力で低電流、長通電時間の溶接とする。この実施形態では、溶接途中で(第一段の溶接終了後)、第一段の溶接時に比べて、加圧力を増加させ、溶接電流を減少させ、通電時間を長くする。これにより、散りの発生が抑制されるとともに、体積抵抗発熱による発熱が主体となり、電極間中央部でナゲットが形成され、図2に示すように、薄板11と厚板12間にナゲット16b(径がN2)を形成することができる。   In this embodiment, the second stage welding is performed following the first stage welding described above. The second stage welding is a welding with a high pressure, a low current, and a long energization time as compared with the first stage welding. In this embodiment, during welding (after the completion of the first stage welding), the welding pressure is increased, the welding current is decreased, and the energization time is lengthened as compared with the first stage welding. As a result, the occurrence of scattering is suppressed, heat generation due to volume resistance heat generation is mainly performed, and a nugget is formed at the center between the electrodes, and as shown in FIG. 2, the nugget 16b (diameter) is formed between the thin plate 11 and the thick plate 12. Can form N2).
第二段の溶接では、加圧力PIIは、第一段溶接の加圧力Pとの関係で、次の(4)式を満足するように設定することが好ましい。
1.1P≦PII≦10P ………(4)
In the second stage welding, the pressure P II is preferably set so as to satisfy the following expression (4) in relation to the pressure P I in the first stage welding.
1.1 P I ≦ P II ≦ 10 P I (4)
また、溶接電流IIIは、第一段溶接の溶接電流Iとの関係で、次の(5)式を満足するように設定することが好ましい。
0.5I≦III≦I ………(5)
Further, the welding current I II is preferably set so as to satisfy the following expression (5) in relation to the welding current I I of the first stage welding.
0.5I I ≦ I II ≦ I I (5)
また、通電時間TIIは、第一段溶接の通電時間Tとの関係で、次の(6)式を満足するように設定することが好ましい。
≦TII≦10T ………(6)
Further, the energization time T II, in relation to the energization time T I of the first stage welding, it is preferable to set so as to satisfy the following equation (6).
T I ≦ T II ≦ 10T I ......... (6)
第二段の溶接の条件が上記した範囲から外れると、散りの発生防止や所定サイズのナゲット径を得ることが困難となり、また、加圧力を過大に増加するとヒートマークや浮き上がりが大きくなるという問題も生じる。   If the conditions of the second stage welding are out of the above range, it will be difficult to prevent the occurrence of scattering and obtain a nugget diameter of a predetermined size, and if the applied pressure is excessively increased, the heat mark and lift will increase. Also occurs.
そして、この実施形態では、上記した第二段の溶接に続いて第三段の溶接を行なう。この第三段の溶接は、上述したように、継手強度を確保するための後熱通電であり、第二段の溶接よりも加圧力を増加させて、高電流の通電を繰り返す。   In this embodiment, the third stage welding is performed subsequent to the second stage welding described above. As described above, the third-stage welding is a post-heat energization for securing the joint strength, and the energizing force is increased more than the second-stage welding, and the high-current energization is repeated.
このように高電流の通電を付加することで、図9に示したと同様に、図3に示すように、この入熱によりナゲット16および軟化域18側の熱影響部17bの急冷が抑制され硬化が抑制されると同時に、電極31、32側の熱影響部17aはテンパー効果により焼き戻しされ軟化し、継手の引張強度が向上する。   As shown in FIG. 9, by applying a high current in this way, as shown in FIG. 3, the heat input suppresses rapid cooling of the heat-affected zone 17b on the nugget 16 and the softened region 18 side, thereby hardening. At the same time, the heat-affected zone 17a on the electrodes 31 and 32 side is tempered and softened by the temper effect, and the tensile strength of the joint is improved.
第三段の溶接は、加圧力PIIIで加圧した状態で、溶接電流を通電しない冷却時間Tcと、溶接電流IIIIにて通電する通電時間TIIIとで構成されている。 Welding of the third stage, in a pressurized state under a pressure P III, the cooling time Tc is not energized the welding current, and a current time T III to be energized by the welding current I III.
その際に、前述したように、加圧力PIIIを第二段溶接の加圧力PIIより増加させる。すなわち、次の(7)式を満足するように設定する。
II<PIII ………(7)
At that time, as described above, the pressure P III increases from pressure P II of the second stage welding. That is, it is set so as to satisfy the following expression (7).
P II <P III (7)
この加圧力を増加させるタイミングとしては、加圧力の増加による効果が得られるように、第三段溶接(多段通電)の第一通電が付加されるまでに完了するのが望ましい。また、高すぎる加圧力は電極の劣化を引き起こす可能性があるため、より好ましくは、PII<PIII≦3PIIの範囲にとどめるのが望ましい。 It is desirable that the timing of increasing the applied pressure be completed before the first energization of the third stage welding (multi-stage energization) is applied so that the effect of the increase in the applied pressure can be obtained. Moreover, since an excessively high applied pressure may cause deterioration of the electrode, it is more preferable to keep the pressure in the range of P II <P III ≦ 3P II .
また、冷却時間Tcは、次の(8)式を満足するように設定することが好ましい。
6≦Tc≦20 ………(8)
The cooling time Tc is preferably set so as to satisfy the following equation (8).
6 ≦ Tc ≦ 20 (8)
さらには、冷却時間Tcは、次の(8a)式を満足するように設定することがより一層好ましい。
1≦Tc≦10 ………(8a)
Furthermore, the cooling time Tc is more preferably set so as to satisfy the following expression (8a).
1 ≦ Tc ≦ 10 (8a)
また、通電時間TIIIは、次の(9)式を満足するように設定することが好ましい。
1≦TIII≦5 ………(9)
Further, the energization time T III is preferably set so as to satisfy the following equation (9).
1 ≦ T III ≦ 5 (9)
また、溶接電流IIIIは、第二段溶接の溶接電流IIIとの関係で、次の(10)式を満足するように設定することが好ましい。
II<IIII≦3III ………(10)
Further, the welding current I III is preferably set so as to satisfy the following expression (10) in relation to the welding current I II of the second stage welding.
I II <I III ≦ 3I II (10)
そして、冷却時間Tc及び通電時間TIIIと溶接電流IIIIで構成される通電を、1回以上5回以下で繰り返すことが好ましい。 Then, the energization composed of cooling time Tc, and energization time T III and the welding current I III, it is preferable to repeat the following five or more times.
第三段溶接において、上記のような冷却時間Tc、通電時間TIII、溶接電流IIIIをとるのは、第二段溶接後の冷却が進むにつれて、抵抗値は低くなるため、溶接電流IIIIは第二段溶接の溶接電流IIIより高く取る必要があるが、冷却が進まない前に通電すると、ナゲット16が完全に再溶融してしまったり、あるいは高い温度に上がりすぎたりして、逆に強度を低下させる原因となりうる。また、長すぎる通電時間や、高すぎる電流値は散りの原因となるうえ、電極寿命を減少させる。また、長すぎる冷却時間はタクトタイムの増加につながり望ましくない。このため、通電時間TIIIは5サイクルまで、冷却時間Tcは20サイクルまで、溶接電流IIIIは第二段溶接の溶接電流IIIの3倍までとし、組み合わせによって適切に選択される。 In a third stage welding, cooling time Tc as described above, the energization time T III, taking the welding current I III, since as cooling after the second stage welding progresses, the resistance value is low, the welding current I III Must be higher than the welding current I II of the second stage welding. However, if the current is applied before the cooling proceeds, the nugget 16 may be completely remelted or excessively raised to a high temperature. It may cause a decrease in strength. In addition, an energization time that is too long or a current value that is too high causes scattering and decreases the electrode life. Also, an excessively long cooling time leads to an increase in takt time, which is undesirable. Therefore, energization time T III until five cycles, the cooling time Tc is up to 20 cycles, the welding current I III is up to three times the welding current I II of the second stage welding, is selected appropriately depending on the combination.
なお、施工面での安定性や散りの発生限界から鑑みて、長すぎない通電時間、短すぎない冷却時間、高すぎない通電電流を選択すべきであるから、通電時間TIIIは2〜4サイクル、冷却時間Tcは6〜10サイクル、溶接電流IIIIはIII<Ib≦2IIIの範囲に収まるようにするのが、最も好適であると考えられる。 Incidentally, in view of the stability and scattering occurrence limit of at the construction surface, the energization time not too long, the cooling time is not too short, because it should be selected energization current is not too high, the energization time T III 2-4 cycle, cooling time Tc is 6-10 cycles, the welding current I III is that falls in the range of I II <Ib ≦ 2I II, considered to be the most suitable.
ただし、温度や湿度などの施工雰囲気、また母材温度による影響で冷却が遅くなることが考えられる。この際、冷却時間Tcが20サイクルを超えていたとしても、第二段溶接の溶接電流IIIよりも高い電流を2回以上付加し、ナゲット全体を溶融させずに冷却速度を低下させたものであれば、本発明の範囲であるといえる。 However, it is conceivable that the cooling will be delayed due to the influence of the construction atmosphere such as temperature and humidity and the base material temperature. At this time, those cooling time Tc is even exceeded 20 cycles, the higher current than the welding current I II of the second stage welding by adding two or more times, reduced the cooling rate without melting the entire nugget If so, it can be said to be within the scope of the present invention.
また、引張強度590MPa未満の鋼板では、通常の溶接で十分な継手強度が達成されるという観点から、引張強度が590MPa以上1960MPa以下の高張力鋼板が含まれている板組に対して使用するのが好ましく、特に引張強度980MPa以上の高張力鋼板が含まれている板組で効果を得ることが出来る。   Moreover, in the case of a steel sheet having a tensile strength of less than 590 MPa, it is used for a plate assembly including a high-tensile steel sheet having a tensile strength of 590 MPa or more and 1960 MPa or less from the viewpoint that sufficient joint strength can be achieved by ordinary welding. In particular, the effect can be obtained with a plate set including a high-tensile steel plate having a tensile strength of 980 MPa or more.
さらに、前述した本発明の原理から、本発明の効果を達成するためには、必ずしも第三段溶接における冷却時間Tc、通電時間TIII、溶接電流IIIIは各パルスで一定でなくとも良い。例えば、1回目の冷却時間では十分に冷却が進まないが、2回目の冷却時間では冷却が進みすぎるということであれば、1回目の冷却時間を2回目の冷却時間よりも長くすることも考えられる。同様に、1回目の溶接電流値を小さくしたり、通電時間を短くしたりしてもよく、これらの理由から、第三段溶接における冷却時間Tc、通電時間TIII、溶接電流IIIIを個別に変更することは、本発明の意図を離れるものではない。 Furthermore, in order to achieve the effects of the present invention based on the principle of the present invention described above, the cooling time Tc, the energization time T III and the welding current I III in the third stage welding are not necessarily constant in each pulse. For example, if the cooling does not proceed sufficiently during the first cooling time, but the cooling proceeds too much during the second cooling time, the first cooling time may be longer than the second cooling time. It is done. Similarly, the first welding current value may be reduced or the energization time may be shortened. For these reasons, the cooling time Tc, the energization time T III and the welding current I III in the third stage welding are individually set. It does not depart from the intention of the present invention.
そして、本発明の抵抗スポット溶接継手の製造方法は、図1〜図3に例示した板組みに限定されることはない。また、被溶接材として本発明を適用する金属板には、鋼板が例示できる。鋼板としては、高張力鋼板が含まれている場合が好適であるが、強度レベル(軟鋼、高張力鋼板)や表面処理の有無(表面処理なし、めっき鋼板)に限定されることはない。本発明はいずれの種類の鋼板についても適用可能である。また、本発明は、板厚比(=総板厚mm/一番薄い板の板厚mm)が5以上の板組みの場合に適用する。   And the manufacturing method of the resistance spot welding joint of this invention is not limited to the board assembly illustrated to FIGS. 1-3. Moreover, a steel plate can be illustrated as a metal plate which applies this invention as a to-be-welded material. As the steel plate, a case where a high-tensile steel plate is included is suitable, but it is not limited to a strength level (soft steel, high-tensile steel plate) or presence / absence of surface treatment (no surface treatment, plated steel plate). The present invention is applicable to any type of steel sheet. Further, the present invention is applied to a plate assembly having a plate thickness ratio (= total plate thickness mm / plate thickness mm of the thinnest plate) of 5 or more.
図7(a)および表1(板組No.A)に示すような、板厚0.7mmの270MPa級軟鋼板1枚と、板厚1.6mmのGAめっき鋼板(原板750MPa級高張力鋼板、目付量45/45g/m)2枚の計3枚の薄鋼板を、270MPa級軟鋼板(薄板)11、GAめっき鋼板(厚板)12、GAめっき鋼板(厚板)13の順に重ね合せた板組について、表2に示す溶接条件で抵抗スポット溶接を行い、抵抗スポット溶接継手を作製した。 As shown in FIG. 7 (a) and Table 1 (plate assembly No. A), one sheet of a 270 MPa class mild steel plate having a thickness of 0.7 mm and a GA-plated steel plate having a thickness of 1.6 mm (original plate 750 MPa class high strength steel plate) , With a basis weight of 45/45 g / m 2 ), a total of three thin steel plates in the order of 270 MPa grade mild steel plate (thin plate) 11, GA plated steel plate (thick plate) 12, GA plated steel plate (thick plate) 13. The combined plate assembly was resistance spot welded under the welding conditions shown in Table 2 to produce a resistance spot welded joint.
ここで、本発明例は、上記の実施形態で示したような、第一段、第二段、第三段の三段階からなる抵抗スポット溶接を行ったものである。一方、比較例は、第一段、第二段の二段階からなる抵抗スポット溶接を行ったものである。   Here, the example of the present invention is one in which resistance spot welding including the first stage, the second stage, and the third stage as shown in the above embodiment is performed. On the other hand, the comparative example performs resistance spot welding consisting of two stages, a first stage and a second stage.
なお、抵抗スポット溶接は、定置式でサーボモータ加圧方式の単相交流抵抗スポット溶接機を用いて行った。使用した電極は、図6に示すDR(先端径6mm)の電極チップとした。   Resistance spot welding was performed using a stationary, servo-motor pressurization type single-phase AC resistance spot welding machine. The electrode used was an electrode tip of DR (tip diameter 6 mm) shown in FIG.
得られた各溶接継手について、薄板11と厚板12の間および厚板12と厚板13の間のそれぞれにおけるナゲット径を測定し、それぞれのナゲット径が4√t以上を満たす場合を良好(○)と評価し、そうでない場合を不良(×)と評価とした。なお、上記のtは隣り合う2枚の鋼板のうち薄い方の鋼板の板厚(mm)である。   About each obtained welded joint, the nugget diameter in each between the thin plate 11 and the thick plate 12 and between the thick plate 12 and the thick plate 13 is measured, and the case where each nugget diameter satisfy | fills 4√t or more is favorable ( (Circle)) and the case where it was not so was evaluated as bad (x). Note that t is the thickness (mm) of the thinner steel plate of the two adjacent steel plates.
また、得られた各溶接継手について、厚板12と厚板13の間の引張強度を測定した。   Moreover, about each obtained welded joint, the tensile strength between the thick plate 12 and the thick plate 13 was measured.
表3に、各溶接継手について、前記の(1)〜(10)式への適合(○)・不適合(×)を示すととともに、得られた評価結果(ナゲット、ナゲット径、厚板間の引張強度)を示す。   Table 3 shows the conformity (○) and nonconformity (×) to the above equations (1) to (10) for each welded joint, and the obtained evaluation results (nugget, nugget diameter, between thick plates) Tensile strength).
なお、表3において、ナゲットの良否は、薄板と厚板の間に良好なナゲットが形成されているかで判断することとし、比較例と比較して変化が無かった場合を○、再溶融や散り発生によって変化が著しかった場合を×とした。また、引張強度に関しては、比較例と比較して3kN以上上回った場合を◎、上回ったが3kN未満であったものを○、下回った場合を×とした。   In Table 3, the quality of the nugget is judged based on whether a good nugget is formed between the thin plate and the thick plate. If there is no change compared to the comparative example, ○, by remelting or scattering occurrence When the change was remarkable, it was set as x. Regarding the tensile strength, the case where it exceeded 3 kN or more compared with the comparative example was rated as ◎, the case where it exceeded but less than 3 kN was marked as ◯, and the case where it was lower than x.
表3に示すように、本発明例および比較例のいずれも良好なナゲットが形成されている。そして、本発明例においては、比較例に比べて、厚板間の引張強度が向上している。   As shown in Table 3, good nuggets are formed in both the inventive examples and the comparative examples. And in the example of this invention, the tensile strength between thick plates is improving compared with the comparative example.
図7(b)および表1(板組No.B)に示すような、板厚0.7mmの270MPa級軟鋼板2枚と、板厚2.3mmのGAめっき鋼板(原板270MPa級軟鋼板、目付量45/45g/m)2枚の計4枚の薄鋼板を、270MPa級軟鋼板(薄板)11、GAめっき鋼板(厚板)12、GAめっき鋼板(厚板)13、270MPa級軟鋼板(薄板)14の順に重ね合せた板組について、表4に示す溶接条件で抵抗スポット溶接を行い、抵抗スポット溶接継手を作製した。 As shown in FIG. 7 (b) and Table 1 (plate assembly No. B), two 270 MPa grade mild steel plates having a thickness of 0.7 mm and a GA plated steel plate having a thickness of 2.3 mm (original plate 270 MPa grade mild steel plate, the basis weight 45 / 45g / m 2) 2 sheets in total four thin steel, 270 MPa grade mild steel plate (thin plate) 11, GA-plated steel plate (thick plate) 12, GA-plated steel plate (thick plate) 13,270MPa grade mild steel Resistance spot welding was performed under the welding conditions shown in Table 4 on the plate assembly in which the plates (thin plates) 14 were superposed in order, and a resistance spot welded joint was produced.
ここで、本発明例は、上記の実施形態で示したような、第一段、第二段、第三段の三段階からなる抵抗スポット溶接を行ったものである。一方、比較例は、第一段、第二段の二段階からなる抵抗スポット溶接を行ったものである。   Here, the example of the present invention is one in which resistance spot welding including the first stage, the second stage, and the third stage as shown in the above embodiment is performed. On the other hand, the comparative example performs resistance spot welding consisting of two stages, a first stage and a second stage.
なお、抵抗スポット溶接は、定置式でサーボモータ加圧方式の単相交流抵抗スポット溶接機を用いて行った。使用した電極は、図6に示すDR(先端径6mm)の電極チップとした。   Resistance spot welding was performed using a stationary, servo-motor pressurization type single-phase AC resistance spot welding machine. The electrode used was an electrode tip of DR (tip diameter 6 mm) shown in FIG.
得られた各溶接継手について、薄板11と厚板12の間、厚板12と厚板13の間、厚板13と薄板14の間のそれぞれにおけるナゲット径を測定し、それぞれのナゲット径が4√t以上を満たす場合を良好(○)と評価し、そうでない場合を不良(×)と評価とした。なお、上記のtは隣り合う2枚の鋼板のうち薄い方の鋼板の板厚(mm)である。   About each obtained welded joint, the nugget diameter in each between the thin plate 11 and the thick plate 12, between the thick plate 12 and the thick plate 13, and between the thick plate 13 and the thin plate 14 is measured, and each nugget diameter is 4 A case satisfying √t or more was evaluated as good (◯), and a case other than that was evaluated as poor (×). Note that t is the thickness (mm) of the thinner steel plate of the two adjacent steel plates.
また、得られた各溶接継手について、厚板12と厚板13の間での引張強度を測定した。   Moreover, about each obtained welded joint, the tensile strength between the thick plate 12 and the thick plate 13 was measured.
表5に、各溶接継手について、前記の(1)〜(10)式への適合(○)・不適合(×)を示すととともに、得られた評価結果(ナゲット、ナゲット径、厚板間の引張強度)を示す。   Table 5 shows the conformity (◯) and nonconformity (×) to the above formulas (1) to (10) for each welded joint, and the obtained evaluation results (nugget, nugget diameter, between thick plates) Tensile strength).
なお、表5において、ナゲットの良否は、薄板と厚板の間に良好なナゲットが形成されているかで判断することとし、比較例と比較して変化が無かった場合を○、再溶融や散り発生によって変化が著しかった場合を×とした。また、引張強度に関しては、比較例と比較して3kN以上上回った場合を◎、上回ったが3kN未満であったものを○、下回った場合を×とした。   In Table 5, the quality of the nugget is judged based on whether a good nugget is formed between the thin plate and the thick plate. The case where there is no change compared to the comparative example is ○, due to the occurrence of remelting and scattering. When the change was remarkable, it was set as x. Regarding the tensile strength, the case where it exceeded 3 kN or more compared with the comparative example was rated as ◎, the case where it exceeded but less than 3 kN was marked as ◯, and the case where it was lower than x.
表5に示すように、本発明例および比較例のいずれも良好なナゲットが形成されている。そして、本発明例においては、比較例に比べて、厚板間の引張強度が向上している。   As shown in Table 5, good nuggets are formed in both the inventive examples and the comparative examples. And in the example of this invention, the tensile strength between thick plates is improving compared with the comparative example.
11 金属板(薄板)
12 金属板(厚板)
13 金属板(厚板)
14 金属板(薄板)
16 ナゲット
16a 薄板−厚板間のナゲット
16b 厚板−厚板間のナゲット
17 熱影響部
17a 電極側の熱影響部
17b 軟化域側の熱影響部
18 軟化域
22 高張力鋼板(上側)
23 高張力鋼板(下側)
31 電極チップ(上側)
32 電極チップ(下側)
11 Metal plate (thin plate)
12 Metal plate (thick plate)
13 Metal plate (thick plate)
14 Metal plate (thin plate)
16 Nugget 16a Nugget between thin plate and thick plate 16b Nugget between thick plate and thick plate 17 Heat-affected zone 17a Heat-affected zone on the electrode side 17b Heat-affected zone on the softened zone side 18 Softened zone 22 High tensile strength steel plate (upper side)
23 High-tensile steel sheet (lower side)
31 Electrode tip (upper side)
32 Electrode tip (lower side)

Claims (5)

  1. 複数枚の金属板を重ね合わせた板組みを抵抗スポット溶接により溶接接合し抵抗スポット溶接継手を製造するにあたり、前記板組みを、重ね合わせた2枚以上の厚板の少なくとも一方に薄板を重ね合わせた、板厚比が5以上の板組みとし、前記抵抗スポット溶接を第一段・第二段・第三段の三段階からなる溶接とし、第二段の溶接は前記第一段の溶接に比べ、高加圧力、低電流又は同じ電流、長通電時間又は同じ通電時間の溶接とし、さらに第三段は第二段よりも高加圧力で、高電流の通電を繰り返すことを特徴とする抵抗スポット溶接継手の製造方法。   In manufacturing a resistance spot welded joint by welding a plate assembly in which a plurality of metal plates are overlapped by resistance spot welding, the plate assembly is overlapped with at least one of two or more thick plates overlapped. In addition, the plate thickness ratio is 5 or more, and the resistance spot welding is a three-stage welding of the first stage, the second stage, and the third stage, and the second stage welding is the first stage welding. Compared to welding with high pressure, low current or the same current, long energization time or the same energization time, the third stage repeats high current energization with higher pressure than the second stage Manufacturing method of spot welded joint.
  2. 前記第一段の溶接を、該溶接の加圧力P、溶接電流I、通電時間Tが、前記複数枚の金属板のうち最も薄肉の金属板の板厚tmとの関係で、下記(1)〜(3)式を満足する溶接とし、前記第二段の溶接を、該溶接の加圧力PII、溶接電流III、通電時間TIIが下記(4)〜(6)式を満足する溶接とす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。
    0.8tm≦P≦5tm………(1)
    2≦T≦6 ………(2)
    3tm+5≦I ………(3)
    1.1P≦PII≦10P ………(4)
    0.5I≦III≦I ………(5)
    ≦TII≦10T ………(6)
    ここで、tm:複数枚の金属板のうち最も薄肉の金属板の板厚(mm)
    、PII:加圧力(kN)
    、III:溶接電流(kA)
    、TII:通電時間(cycles/50Hz)
    In the first stage welding, the welding pressure P I , welding current I I , and energization time T I are related to the thickness tm of the thinnest metal plate among the plurality of metal plates, (1) the welding satisfies - (3), the welding of the second stage, pressure P II of the welding, the welding current I II, the energization time T II is the following (4) to (6) The method of manufacturing a resistance spot welded joint according to claim 1, wherein the welding is satisfactory.
    0.8 tm ≦ P I ≦ 5 tm (1)
    2 ≦ T I ≦ 6 (2)
    3tm + 5 ≦ I I (3)
    1.1 P I ≦ P II ≦ 10 P I (4)
    0.5I I ≦ I II ≦ I I (5)
    T I ≦ T II ≦ 10T I ......... (6)
    Here, tm: plate thickness (mm) of the thinnest metal plate among the plurality of metal plates
    P I , P II : Applied pressure (kN)
    I I , I II : Welding current (kA)
    T I , T II : energization time (cycles / 50 Hz)
  3. 前記第三段の溶接における加圧力PIII、冷却時間Tc、溶接電流IIII、通電時間TIIIが、前記第二段の加圧力PII、溶接電流III、通電時間TIIとの関係において、下記(7)〜(10)式を満足することを特徴とする請求項1または2に記載の抵抗スポット溶接継手の製造方法。
    II<PIII ………(7)
    1≦Tc≦20 ………(8)
    1≦TIII≦5 ………(9)
    II<IIII≦3III ………(10)
    ここで、PII、PIII:加圧力(kN)
    II、IIII:溶接電流(kA)
    Tc:冷却時間(cycles/50Hz)
    III:通電時間(cycles/50Hz)
    The pressure P III , the cooling time Tc, the welding current I III , and the energization time T III in the third stage welding are related to the pressure P II , the welding current I II , and the energization time T II of the second stage. The method of manufacturing a resistance spot welded joint according to claim 1 or 2, wherein the following expressions (7) to (10) are satisfied.
    P II <P III (7)
    1 ≦ Tc ≦ 20 (8)
    1 ≦ T III ≦ 5 (9)
    I II <I III ≦ 3I II (10)
    Here, P II and P III : Applied pressure (kN)
    I II , I III : Welding current (kA)
    Tc: Cooling time (cycles / 50 Hz)
    T III : Energization time (cycles / 50 Hz)
  4. 前記第三段の溶接における冷却時間Tcが、下記(8a)式を満足することを特徴とする請求項3に記載の抵抗スポット溶接継手の製造方法。
    1≦Tc≦10 ………(8a)
    ここで、Tc:冷却時間(cycles/50Hz)
    The method of manufacturing a resistance spot welded joint according to claim 3, wherein a cooling time Tc in the third stage welding satisfies the following expression (8a).
    1 ≦ Tc ≦ 10 (8a)
    Here, Tc: Cooling time (cycles / 50 Hz)
  5. 前記第三段の、冷却時間Tc及び通電時間TIIIと溶接電流IIIIで構成される通電を、1回以上5回以下で繰り返すことを特徴とする請求項1〜4のいずれかに記載の抵抗スポット溶接継手の製造方法。 Of the third stage, the energization composed of cooling time Tc, and energization time T III and the welding current I III, according to any one of claims 1 to 4, characterized in that repeated below 5 times more than once A method of manufacturing a resistance spot welded joint.
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