JP3883499B2

JP3883499B2 - Resistance spot welding method

Info

Publication number: JP3883499B2
Application number: JP2002356328A
Authority: JP
Inventors: 博司阿部
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-06-05
Filing date: 2002-12-09
Publication date: 2007-02-21
Anticipated expiration: 2022-12-09
Also published as: JP2004058153A

Description

【０００１】
【発明に属する利用分野】
本発明は金属板の溶接物を一対の電極チップで挟みつけて，これに加圧力をかけながら通電して溶接する抵抗スポット溶接方法において，自動的に溶接電流または加圧力を調節して散りを予防しながら適正なナゲットを得る抵抗スポット溶接方法に関する。
【０００２】
【従来の技術および課題】
従来の抵抗スポット溶接は一般に，溶接電流を一定に制御する定電流機能によって行われていた。しかしながら定電流機能だけでは電極チップが磨耗して起きる通電路面積の拡大による溶接部の電流密度の低下などを補償できないため，これに所定の打点数ごとに溶接電流を上昇させていくステップアップ制御を組み合わせたり，電極チップ間電圧を検出して溶接部の電力を算出して電流を調整して溶接部の発熱密度を維持したりしようとしていた。しかしながらこれらはいずれもステップアップ電流の上昇率やそれを切り替える打点数，あるいは溶接部の電力を算出するための電極チップ間電圧と電極先端径との相関定数など，特有のパラメータの適正な設定が不可欠で，しかもそれらのパラメータは実験を行って求める必要があり，実際の生産ラインに適用するには手間を要して実用化が困難な面があった。
【０００３】
【課題を解決するための手段】
本発明では抵抗スポット溶接方法において，通電中の溶接電流と電極チップ間電圧とを時々刻々に検出し，縦軸に溶接電流と電極チップ間電圧の積である電力（Ｐ），横軸に溶接電流（Ｉ）または溶接電流の２乗値（Ｉ^２）を取るところのＰ−ＩまたはＰ−Ｉ^２曲線を演算して求め，その曲線形状の推移によってナゲットの形成状態を判定して，それ以降のサイクルの溶接電流または加圧力を調節するか，またはその時点で溶接電流を打ち切って散りの発生を予防するか，溶接電流が過小または過大または散りの発生を判定して警報を出力するようにして作業者が溶接条件の妥当性を判断することができるようにするか，またはその次の溶接打点の溶接電流または加圧力を自動的に調節して散りを予防しながら適正なナゲットを得るようにした。
【０００４】
Ｐ−ＩまたはＰ−Ｉ^２曲線は縦軸に溶接電流（Ｉ）と電極チップ間電圧（Ｖ）の積である電力（Ｐ），横軸に溶接電流（Ｉ）または溶接電流の２乗値（Ｉ^２）を取る。電力ＰはＰ＝Ｖ・Ｉであり，言い換えれば電極チップ間抵抗をＲとすれば，Ｐ＝Ｉ^２Ｒであるから，Ｐの値は電極チップ間抵抗に比例している。図１に示すように，電極チップ間抵抗１は溶接部である溶接物の板間接触抵抗２と，溶接物自体の固有抵抗３と，電極チップ６と溶接物７との接触抵抗４と，電極チップ自体の固有抵抗５の合成値である。電極チップ間抵抗は溶接物が通電により軟化して溶接物の板間接触抵抗と電極チップと溶接物との接触抵抗の接触状態が良好になり通電路面積が広がれば低下し，溶接部の温度が変化すれば溶接物の材質の固有抵抗の温度係数の特性により変化する。
【０００５】
【発明の実施の態様】
図２は本発明による実施例で，通電開始の第０．５サイクル以降の溶接電流波形（Ｉ）と電力波形（Ｐ）を模式的に示したものである。これから縦軸に溶接電流と電極チップ間電圧の積である電力（Ｐ），横軸に溶接電流（Ｉ）または溶接電流の２乗値（Ｉ^２）を取るところのＰ−ＩまたはＰ−Ｉ^２曲線を演算して求める。それらの曲線の増加過程と減少過程は溶接電流波形の増加過程と減少過程の区間と一致している。Ｐ−ＩまたはＰ−Ｉ^２曲線の増加過程の曲線の方が減少過程より上側に来るのはＰの値が大きいということで，図２における第０．５サイクルのように電力波形の方が電流波形より急峻に立ち上がっていることを示している。また増加過程と減少過程の曲線が一致して重なるというのは，第７．０サイクルのように電力波形と電流波形の立ち上がりと立ち下りが揃って相似の傾斜になることを示す。
【０００６】
図３は散りも出ずに所定のナゲットが形成される適正な溶接条件（１），すなわち板厚０．８ｍｍの２枚重ねのＳＰＣＣ材を電極加圧力３１５ｄａＮ，溶接電流１０．５ｋＡで溶接した場合の第０．５サイクルのＰ−Ｉ^２曲線の例である。通電開始の第０．５サイクルの先頭においてはまだ溶接物が軟化しておらず，溶接物の板間接触や電極チップとの接触状態がよくないために電極チップ間抵抗は高く，その後通電が開始されると溶接物が軟化し，接触面積が拡大して抵抗値は急激に低下する。前述したようにＰの値は抵抗値に比例するので，図３に示すように第０．５サイクル前半の増加過程のＰ−ＩまたはＰ−Ｉ^２曲線の方が後半の減少過程の曲線より上側に来る。この傾向は本溶接条件（１）の場合は図４のように，第１．０サイクルまで継続する。なお，この電極チップ間抵抗の変化傾向は，たとえば第０．５サイクルの後半の減少過程と第１．０サイクルの前半の増加過程の間についても同様のことがいえるが，本実施例では同一半サイクル内のＰ−ＩまたはＰ−Ｉ^２曲線の増加過程と減少過程を比較するようにしている。
【０００７】
本実施例の溶接条件（１）においては図５に示すように，第１．５サイクルになるとＰ−ＩまたはＰ−Ｉ^２曲線の上下関係が逆転して，減少過程の方が増加過程の曲線より上側に来る。これは増加過程の期間では抵抗発熱により溶接物の固有抵抗が高くなるが，同時に通電路面積も広がって相殺しあうのに対し，減少過程では溶接電流，すなわちエネルギー供給を下降させていくとその相殺バランスが増加過程におけるより通電路面積の拡大による抵抗低下の率が小さく，全体としては抵抗が高くなるためである。
【０００８】
本実施例の溶接条件（１）においては第２．０から第６．５サイクルの期間では第１．５サイクルにおけるＰ−ＩまたはＰ−Ｉ^２曲線の上下関係が維持され，減少過程の方が増加過程の曲線より上側に来る状態が続く。この期間はナゲットの成長過程にあたる。ただし第５．０サイクル近辺から増加過程と減少過程の曲線が徐々に接近して，第７．０サイクルになると図６のようにほぼ一致して重なってくる。これ以降は同一の溶接電流で通電を継続しても増加過程と減少過程の曲線はほぼ一致したままとなる。これは本溶接条件（１）においては第７．０サイクル付近で溶接部に所定のナゲットが形成され，熱的平衡に達したことを示している。
【０００９】
【発明の効果】
本発明の請求項１による実施例は，適正な溶接条件（１）においてＰ−ＩまたはＰ−Ｉ^２曲線の増加過程と減少過程の曲線の上下関係が前記のような経過を経て，第７．０サイクルで増加過程と減少過程の曲線がほぼ一致して重なり，それらの曲線間の面積があらかじめ定めた所定値以下になったことを検出して，以降の溶接電流を所定値だけ下げるか，または加圧力を所定値だけ高くするか，またはその時点で通電を打ち切り，所定のナゲットを得ながら散りの発生を予防する抵抗スポット溶接方法である。
【００１０】
溶接電流が適切値より過小の場合でも，適正な溶接条件（１）の場合と同様に，通電開始の第０．５サイクルに対する第１．５から第２．０サイクル近辺におけるＰ−ＩまたはＰ−Ｉ^２曲線の増加過程と減少過程の曲線の上下関係の逆転現象は溶接条件により発生時点は異なるが同様に発生する。もちろん溶接条件が半分以下など極端であればこの限りではないが，それは一般に公開されている溶接条件表から経験的に分かる範囲であり，そのような非常識な設定は行われないものとして除外して考える。溶接電流がある程度過小であると，上記の第１．５から第２．０サイクル近辺での増加過程と減少過程の曲線の逆転現象の後，両曲線が接近して両曲線間の面積が所定値以下になるのが，溶接条件が適切である場合に比べて溶接条件にもよるが数サイクル程度遅れる。これは溶接部に与えるエネルギーが小さすぎるので，ナゲットの成長プロセスが遅くなるためである。
【００１１】
本発明の請求項２による実施例は，溶接電流が過小の場合に増加過程と減少過程のＰ−ＩまたはＰ−Ｉ^２曲線が接近して両曲線間の面積が所定値以下になるのが，溶接条件が適正である場合に比べて所定サイクル以上遅れたことを検出して，溶接電流過小警報を出力することを特徴とした抵抗スポット溶接方法である。作業者はこの警報を受けて現在の溶接電流が過小であることを知り，次の溶接打点の溶接条件の設定を大きくするように変更する。
【００１２】
本発明の請求項３による実施例は，溶接電流が過小の場合に増加過程と減少過程のＰ−ＩまたはＰ−Ｉ^２曲線が接近して両曲線間の面積が所定値以下になるのが，溶接条件が適正である場合に比べて所定サイクル以上遅れたことを検出して，自動的にその次の溶接打点の溶接条件の設定を上げる，すなわち溶接電流を所定値だけ上げるか，または加圧力を所定値だけ低くして適正なナゲットを得るようにする。
【００１３】
溶接電流が適正値より過大の場合でも，適正な溶接条件（１）の場合と同様に，通電開始の第０．５サイクルに対する第１．５から第２．０サイクル近辺におけるＰ−ＩまたはＰ−Ｉ^２曲線の増加過程と減少過程の曲線の上下関係の逆転現象は溶接条件により発生時点は異なるが同様に発生する。もちろん溶接条件が２倍以上など極端であればこの限りではないが，それは一般に公開されている溶接条件表から経験的に分かる範囲であり，そのような非常識な設定は行われないものとして除外して考える。溶接電流がある程度過大であると，上記の第１．５から第２．０サイクル近辺での増加過程と減少過程の曲線の逆転現象の後，両曲線の上下関係が再度逆転するか，ある半サイクル内で増加過程と減少過程の曲線が交差するなど過大電流の程度によってランダムな挙動を示す。これは過大電流により散りが発生すると溶融した溶接物の一部が外部に飛散してしまうので溶接部が冷却され，溶接物の固有抵抗が変化するためである。
【００１４】
図７は過大な溶接条件（２），すなわち板厚０．８ｍｍの２枚重ねのＳＰＣＣ材を電極加圧力２５８ｄａＮ，溶接電流１１．０ｋＡで溶接した場合の第４．０サイクルにおけるＩ^２−Ｐ曲線の例である。この溶接条件（２）ではＰ−ＩまたはＰ−Ｉ^２曲線は，第０．５および第１サイクルにおいては増加過程の曲線の方が減少過程の曲線より上側に来て，第１．５サイクルではこれが逆転して第３．５サイクルまでその状態が継続しており，ここまでは適正な溶接条件（１）のパターンと同様であったが，第４．０サイクルに至って増加過程と減少過程の曲線の上下関係が逆転するとともに交差現象も発生し，このときに散りも観測されている。そして続く２半サイクル，すなわち第４．５および第５．０サイクルでは増加過程の曲線の方が減少過程より上側に来て，第５．５サイクル以降は両曲線は接近してほぼ一致している。これは散りが発生したことによって溶接部が冷却され，以降は２半サイクルの加熱期間があって，その後熱平衡の状態に達したことを示している。この場合，所定のナゲットは得られていたのだが，散りが発生したこと自体が溶接品質および作業環境に対して悪影響を与えていると解釈される。
【００１５】
本発明の請求項４による実施例は過大な溶接条件（２）の場合に，前記の第４．５サイクルのように増加過程と減少過程の曲線の上下関係が再度逆転するか，両曲線が交差したことを検出して，それ以降の溶接電流を下げるか，または加圧力を高くするか，またはその時点で通電を打ち切って散りの発生を軽減させることを特徴とした抵抗スポット溶接方法である。この場合第４．０サイクルですでに散りは発生してしまっているのだが，それに引き続く通電時間のうち，特に第４．５および第５．０サイクルの加熱期間の溶接電流を下げるか，または加圧力を高くするか，またはその時点で通電を打ち切ることにより，この期間での散りの発生を抑制することができる。
【００１６】
本発明の請求項５による実施例は過大な溶接条件（２）の場合に，前記の第４．５サイクルのように増加過程と減少過程の曲線の上下関係が再度逆転するか，両曲線が交差したことを検出して，溶接電流過大もしくは散り発生の警報を出力することを特徴とした抵抗スポット溶接方法である。作業者はこの警報を受けて現在の溶接電流が過大であることを知り，次の溶接打点の溶接条件の設定を下げるように変更する。
【００１７】
本発明の請求項６による実施例は過大な溶接条件（２）の場合に，前記の第４．５サイクルのように増加過程と減少過程の曲線の上下関係が再度逆転するか，両曲線が交差したことを検出して，自動的にその次の溶接打点の溶接条件の設定を下げる，すなわち溶接電流を下げるか，または加圧力を高くするか，またはその時点で通電を打ち切って散りの発生を軽減させる。
【００１８】
本発明の請求項７による実施例である，図８は半サイクルにおける溶接電流と電極チップ間電圧および電極チップ間電力を示したものである。
時々刻々に変化する溶接電流の半サイクルの増加過程と減少過程のそれぞれに対応した電極チップ間電圧を所定の同一電流値（I）のもとで，それぞれを検出して，その時の電極チップ間電圧（EupおよびEdown）と所定の同一電流値（I）との積であるところの電極チップ間電力（Pup=Eup×I および Pdown＝Edown×I）の差（Pdown−Pup）または比（Pdown／Pup）あるいは電極チップ間電圧の比（Edown／Eup）をPsとして求めると，このPsはP−I曲線上で同一電流における増加過程と減少過程における前記電極チップ間電力の差あるいは比もしくは電極チップ間電圧の比に等しく従って，適正な溶接条件（１）におけるＰ−Ｉ曲線の増加過程と減少過程の曲線の上下関係が前記のような経過を経て，第７．０サイクルで増加過程と減少過程の曲線がほぼ一致して重なる時，Psの値を縦軸にサイクル数を横軸に取ったところのPs−Cycle線図は，電極チップ間電力差を例にとると図９のようになり，同一電流値における電極チップ間電力差または電極チップ間電力比もしくは電極チップ間電圧比があらかじめ定めた所定値以下になったことを検出して，以降の溶接電流を所定値だけ下げるか，または加圧力を所定値だけ高くするか，あるいはその時点で通電を打ち切り，所定のナゲットを得ながら散りの発生を予防することができる。
【００１９】
本発明の請求項８による実施例では，時々刻々に変化する溶接電流の半サイクルの増加過程と減少過程のそれぞれに対応した電極チップ間電圧を所定の同一電流値（I）のもとで，それぞれを検出して，その時の電極チップ間電圧（EupおよびEdown）と所定の同一電流値（I）との積であるところの電極チップ間電力（Pup=Eup×I および Pdown＝Edown×I）の差（Pdown−Pup）または比（Pdown／Pup）あるいは電極チップ間電圧の比（Edown／Eup）をPsとして求めるが，このPsがあらかじめ定めた半サイクル毎の所定値より大きく（または小さく）なったことを検出して，次半サイクル毎の溶接電流を所定値だけ下げる（または上げる）か，または加圧力を所定値だけ高く（または低く）するか，あるいはその時点で通電を打ち切り，所定のナゲットを得ながら散りの発生を予防することができる。
【００２０】
本発明の請求項９の実施例において，図1０は半サイクルにおける溶接電流と電極チップ間電圧を示したものである。時々刻々変化する溶接電流の通電中の溶接電流と電極チップ間電圧とを時々刻々に検出して，各半サイクルにおける溶接電流の最大値に到達した時点（Ti-peak）と電極チップ間電圧が最大値に到達する時点（Te-peak）までの時間差(Ts)は，所定の同一電流値（I）のもとで，電流増加過程及び電流減少過程それぞれのその時の電極チップ間電圧（EupおよびEdown）と所定の同一電流値（I）との積であるところの電極チップ間電力（Pup=Eup×I および Pdown＝Edown×I）の差（Pdown−Pup）または比（Pdown／Pup）あるいは電極チップ間電圧の比（Edown／Eup）が大きい(または小さい)場合は，時間差が大きく(または小さく)なる。従って，適正な溶接条件（１）におけるＰ−Ｉ曲線の増加過程と減少過程の曲線の上下関係が前記のような経過を経て，第７．０サイクルで増加過程と減少過程の曲線がほぼ一致して重なる時，時間差(Ts)の値を縦軸にサイクル数を横軸に取ったところのTs−Cycle線図は図１１のようになり，各半サイクルの溶接電流の最大値に到達した時点（Ti-peak）と電極チップ間電圧が最大値に到達する時点（Te-peak）までの時間差（Ts）が，あらかじめ定めた所定値以下になったことを検出して，以降の溶接電流を所定値だけ下げるか，または加圧力を所定値だけ高くするか，またはその時点で通電を打ち切り，所定のナゲットを得ながら散りの発生を予防することができる。
【図面の簡単な説明】
【図１】本発明の実施例である電極チップ間電圧の構成要素を示す図である。
【図２】本発明の実施例において通電開始の第０．５サイクル以降の溶接電流波形（Ｉ）と電力波形（Ｐ）を模式的に示したものである。
【図３】本発明の実施例において適正な溶接条件（１）の第０．５サイクルのＰ−Ｉ^２曲線を示したものである。
【図４】本発明の実施例において適正な溶接条件（１）の第１．０サイクルのＰ−Ｉ^２曲線を示したものである。
【図５】本発明の実施例において適正な溶接条件（１）の第１．５サイクルのＰ−Ｉ^２曲線を示したものである。
【図６】本発明の実施例において適正な溶接条件（１）の第７．０サイクルのＰ−Ｉ^２曲線を示したものである。
【図７】本発明の実施例において過大な溶接条件（２）の第４．０サイクルのＰ−Ｉ^２曲線を示したものである。
【図８】本発明の実施例において同一電流値における電極チップ間電力の差を示したものである。
【図９】本発明の実施例において同一電流値における電極チップ間電力の差（Ps）の推移を示したものである。
【図１０】本発明の実施例において，半サイクルにおける溶接電流の最大値と電極チップ間電圧の最大値の時間差(Ts)を示したものである。
【図１１】本発明の実施例において溶接電流の最大値と電極チップ間電圧の最大値の時間差(Ts)の推移を示したものである。
【符号の説明】
１電極チップ間抵抗２溶接物の板間接触抵抗
３溶接物自体の固有抵抗４電極チップと溶接物との接触抵抗
５電極チップ自体の固有抵抗６一対の電極チップ
７溶接物[0001]
[Field of use belonging to the invention]
The present invention is a resistance spot welding method in which a welded metal plate is sandwiched between a pair of electrode tips and energized while applying pressure to the weld, and the welding current or pressure is automatically adjusted to reduce scattering. The present invention relates to a resistance spot welding method for obtaining an appropriate nugget while preventing.
[0002]
[Prior art and problems]
Conventional resistance spot welding is generally performed by a constant current function for controlling the welding current to be constant. However, the constant current function alone cannot compensate for the decrease in the current density of the weld due to the enlargement of the current path area caused by the wear of the electrode tip. Therefore, the step-up control increases the welding current for each predetermined number of striking points. Or by detecting the voltage between the electrode tips and calculating the power of the weld and adjusting the current to maintain the heat density of the weld. However, each of these has an appropriate setting of specific parameters such as the rate of increase of the step-up current, the number of dots for switching, or the correlation constant between the electrode tip voltage and the electrode tip diameter for calculating the power of the weld. These parameters are indispensable, and it is necessary to determine these parameters through experiments, and it was difficult to put them into practical use because they were troublesome to apply to actual production lines.
[0003]
[Means for Solving the Problems]
In the present invention, in the resistance spot welding method , the welding current and the voltage between the electrode tips are detected momentarily, the power (P) which is the product of the welding current and the voltage between the electrode tips is plotted on the vertical axis, and the welding is plotted on the horizontal axis. The PI or PI ² curve where the current (I) or the square value of the welding current (I ² ) is taken is calculated, and the nugget formation state is determined by the transition of the curve shape. Adjust the welding current or pressure in the subsequent cycles, or stop the welding current at that point to prevent the occurrence of scattering, or output a warning by judging whether the welding current is too small, too large, or scattering So that the operator can judge the appropriateness of the welding conditions or automatically adjust the welding current or pressure at the next welding point to obtain the proper nugget while preventing scattering like It was.
[0004]
The PI or PI ² curve shows the power (P), which is the product of the welding current (I) and the voltage between the electrode tips (V) on the vertical axis, and the square value of the welding current (I) or welding current on the horizontal axis. Take (I ² ). The power P is P = V · I. In other words, if the resistance between the electrode chips is R, P = I ² R, and therefore the value of P is proportional to the resistance between the electrode chips. As shown in FIG. 1, the resistance 1 between the electrode tips is the inter-plate contact resistance 2 of the weld, which is a weld, the specific resistance 3 of the weld itself, the contact resistance 4 between the electrode tip 6 and the weld 7, This is a composite value of the specific resistance 5 of the electrode tip itself. The resistance between the electrode tips decreases when the weld is softened by energization, and the contact state between the contact between the plates of the weld and the contact resistance between the electrode tip and the weld becomes good and the current path area increases and the temperature of the welded part decreases. Will change depending on the temperature coefficient characteristic of the specific resistance of the material of the weld.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 2 is an embodiment according to the present invention, and schematically shows a welding current waveform (I) and a power waveform (P) after the 0.5th cycle of starting energization. From now on, P-I or PI where the vertical axis takes the power (P) which is the product of the welding current and the voltage between the electrode tips, and the horizontal axis takes the welding current (I) or the square value of the welding current (I ² ). Calculate ^two curves. The increasing and decreasing processes of these curves are consistent with the increasing and decreasing intervals of the welding current waveform. The increase process curve of the PI or PI- ² curve comes above the decrease process because the value of P is larger, and the power waveform is more like the 0.5th cycle in FIG. It shows that it rises more steeply than the current waveform. In addition, the fact that the curves of the increasing process and the decreasing process coincide and overlap indicates that the rising and falling edges of the power waveform and current waveform are aligned and have similar slopes as in the 7.0th cycle.
[0006]
FIG. 3 shows an appropriate welding condition (1) in which a predetermined nugget is formed without scattering, that is, a two-layer SPCC material having a plate thickness of 0.8 mm is welded at an electrode pressure of 315 daN and a welding current of 10.5 kA. If it is an example of a ^{P-I 2} curve of a 0.5 cycle. At the beginning of the 0.5th cycle of the start of energization, the welded material has not yet softened, and the contact between the plates of the weldment and the contact state with the electrode tip is not good, so the resistance between the electrode tips is high. When started, the weldment softens, the contact area expands, and the resistance value decreases rapidly. As described above, since the value of P is proportional to the resistance value, as shown in FIG. 3, the PI or PI ² curve in the first half of the 0.5th cycle is better than the curve in the second half of the decrease process. Coming up. This tendency continues until the 1.0th cycle as shown in FIG. 4 in the case of the main welding condition (1). The same tendency can be said for the change in resistance between the electrode tips, for example, between the decrease process in the second half of the 0.5th cycle and the increase process in the first half of the 1.0th cycle. and so as to compare the increase process and reduction process of P-I or P-I ² curve in one half cycle.
[0007]
In the welding condition (1) of this embodiment, as shown in FIG. 5, when the 1.5th cycle is reached, the vertical relationship of the PI or PI- ² curve is reversed, and the decreasing process is the increasing process. Come above the curve. This is because the specific resistance of the weldment increases due to resistance heat generation during the increase process, but at the same time, the area of the current path widens and offsets, whereas in the decrease process, the welding current, that is, when the energy supply is decreased This is because the rate of resistance decrease due to expansion of the current path area is smaller than in the process of increasing the offset balance, and the resistance as a whole increases.
[0008]
In the welding condition (1) of this example, the vertical relationship of the PI or PI- ² curve in the 1.5th cycle is maintained during the period from the 2.0th to 6.5th cycle, and the decreasing process Continues to be above the increasing curve. This period is the nugget growth process. However, the curve of the increasing process and the decreasing process gradually approach from the vicinity of the 5.0th cycle, and when the 7.0th cycle is reached, they almost overlap as shown in FIG. After this, even if energization is continued with the same welding current, the curves of the increasing process and the decreasing process remain almost the same. This indicates that, under the main welding condition (1), a predetermined nugget was formed in the welded portion near the 7.0th cycle, and thermal equilibrium was reached.
[0009]
【The invention's effect】
In the embodiment according to claim 1 of the present invention, the upper and lower relations between the increase process and the decrease process curve of the PI or PI- ² curve under the appropriate welding condition (1) are as follows. Whether the increase and decrease curves are almost coincident and overlap in 0 cycle, and the area between these curves is detected to be below a predetermined value, and then the welding current is reduced by a predetermined value. Alternatively, it is a resistance spot welding method in which the applied pressure is increased by a predetermined value, or the energization is interrupted at that time to prevent the occurrence of scattering while obtaining a predetermined nugget.
[0010]
Even when the welding current is less than the appropriate value, as in the case of the appropriate welding condition (1), PI or P in the vicinity of the 1.5th to 2.0th cycles with respect to the 0.5th cycle of the energization start. The reverse phenomenon of the vertical relationship between the increasing and decreasing processes of the −I ² curve occurs in the same manner, although the generation time differs depending on the welding conditions. Of course, this is not necessary if the welding conditions are extreme, such as less than half, but this is an empirical range from the publicly available welding conditions table, and such insane settings are excluded as not being performed. Think. If the welding current is too small, after the reversal phenomenon of the increasing and decreasing curves in the vicinity of cycle 1.5 to 2.0 described above, the two curves approach each other and the area between the two curves is predetermined. When the welding condition is appropriate, the value is less than the value, but it is delayed by several cycles depending on the welding condition. This is because the energy applied to the weld is too small, which slows the nugget growth process.
[0011]
Example according to claim 2 of the present invention, that by P-I or P-I ² curve increase process and reduction process when the welding current is too small approaches the area between the two curves becomes less than a predetermined value This is a resistance spot welding method characterized by detecting a delay of a predetermined cycle or more compared to the case where the welding conditions are appropriate and outputting a welding current under alarm. Upon receiving this warning, the operator learns that the current welding current is too low, and changes the setting to increase the welding condition for the next welding spot.
[0012]
Example according to claim 3 of the present invention, that by P-I or P-I ² curve increase process and reduction process when the welding current is too small approaches the area between the two curves becomes less than a predetermined value Detecting a delay of more than a predetermined cycle compared to when the welding conditions are appropriate, automatically increasing the setting of the welding conditions for the next welding point, that is, increasing the welding current by a predetermined value or adding The pressure is lowered by a predetermined value to obtain an appropriate nugget.
[0013]
Even when the welding current is larger than the appropriate value, as in the case of the appropriate welding condition (1), PI or P in the vicinity of the 1.5th to 2.0th cycles with respect to the 0.5th cycle of the energization start. The reverse phenomenon of the vertical relationship between the increasing and decreasing processes of the −I ² curve occurs in the same manner, although the generation time differs depending on the welding conditions. Of course, this is not necessary if the welding conditions are extreme, such as twice or more, but this is an empirical range from the publicly available welding conditions table, and it is excluded that such insane settings are not made. Think about it. If the welding current is excessive to some extent, the up-and-down relationship between the two curves is reversed again after the reverse phenomenon of the increase and decrease curves in the vicinity of cycle 1.5 to 2.0 above. Random behavior is exhibited depending on the degree of overcurrent, such as the curves of increasing and decreasing processes intersect in a cycle. This is because, when scattering occurs due to excessive current, a part of the molten welded material is scattered to the outside, so that the weld is cooled and the specific resistance of the welded material changes.
[0014]
FIG. 7 shows I ² -P in the 4.0th cycle in the case of welding with an excessive welding condition (2), that is, a double-layer SPCC material having a plate thickness of 0.8 mm at an electrode pressure of 258 daN and a welding current of 11.0 kA. It is an example of a curve. Under this welding condition (2), the PI or PI ² curve shows that the increasing curve is higher than the decreasing curve in the 0.5th and 1st cycles, and the 1.5th cycle. In this case, the state was reversed and the state continued until the 3.5th cycle. The pattern was the same as the pattern of the appropriate welding conditions (1) up to this point, but the increase and decrease processes reached the 4.0th cycle. The vertical relationship of the curve is reversed and a crossing phenomenon occurs, and scattering is also observed at this time. Then, in the following two half cycles, that is, in the 4.5th and 5.0th cycles, the curve of the increasing process comes to the upper side of the decreasing process, and after the 5.5th cycle, both curves are close and almost in agreement. Yes. This indicates that the weld has cooled due to the occurrence of splashing, and after that, there has been a half-cycle heating period, after which a thermal equilibrium state has been reached. In this case, the predetermined nugget was obtained, but it is interpreted that the occurrence of scattering itself has an adverse effect on the welding quality and the working environment.
[0015]
In the embodiment according to claim 4 of the present invention, in the case of excessive welding conditions (2), the upper and lower relations of the curves of the increasing process and the decreasing process are reversed again as in the aforementioned 4.5th cycle, or both curves are It is a resistance spot welding method characterized by detecting the crossing and lowering the welding current thereafter, increasing the pressure, or cutting off the current at that time to reduce the occurrence of scattering. . In this case, the scattering has already occurred in the 4.0th cycle, but during the energization time that follows, the welding current is lowered particularly in the heating period of the 4.5th and 5.0th cycles, or By increasing the applied pressure or stopping the energization at that time, the occurrence of scattering during this period can be suppressed.
[0016]
In the embodiment according to claim 5 of the present invention, in the case of excessive welding conditions (2), the upper and lower relations of the curves of the increasing process and the decreasing process are reversed again as in the aforementioned 4.5th cycle, or both curves are It is a resistance spot welding method characterized by detecting the crossing and outputting an alarm of excessive welding current or occurrence of scattering. Upon receiving this warning, the operator learns that the current welding current is excessive, and changes the setting so that the welding conditions for the next welding point are lowered.
[0017]
In the embodiment according to claim 6 of the present invention, in the case of excessive welding conditions (2), the upper and lower relations of the curves of the increasing process and the decreasing process are reversed again as in the above-mentioned 4.5th cycle, or both curves are Detects crossing and automatically lowers the welding condition setting for the next welding spot, that is, lowers the welding current, increases the applied pressure, or interrupts the energization at that time to generate scattering. Reduce.
[0018]
An embodiment according to claim 7 of the present invention, FIG. 8 shows the power between the welding current and the electrode tip voltage and the electrode tip in a half-cycle.
The voltage between the electrode tips corresponding to each of the increasing and decreasing processes of the half cycle of the welding current that changes from moment to moment is detected under the same current value (I), and the current between the electrode tips is detected. voltage (Eup and Edown) the difference (Pdown-Pup) or ratio of the same predetermined current value electrode tip between the power where a product of (I) (Pup = Eup × I and Pdown = Edown × I) (Pdown / Pup) or the ratio of the voltage between the electrode tips (Edown / Eup) as Ps, this Ps is the difference or ratio of the power between the electrode tips in the increase process and the decrease process in the same current on the PI curve or the electrode According to the ratio of the voltage between the chips, the vertical relationship between the PI curve increasing process and the decreasing process curve under the appropriate welding condition (1) is as follows. The decreasing process curves are almost identical and overlapped When, Ps-Cycle diagram where taken on the horizontal axis the number of cycles on the vertical axis the value of Ps can take between electrode tip power difference Examples is shown in Figure 9, between the electrode tip at the same current value Detect that the power difference or the power ratio between the electrode tips or the voltage ratio between the electrode tips is below a predetermined value, and then lower the welding current thereafter by a predetermined value or increase the applied pressure by a predetermined value Alternatively , the energization can be stopped at that time, and the occurrence of scattering can be prevented while obtaining a predetermined nugget.
[0019]
In the embodiment according to claim 8 of the present invention, the voltage between the electrode tips corresponding to each of the increase process and the decrease process of the half cycle of the welding current which changes from moment to moment is obtained under a predetermined same current value (I). by detecting the respective electrode tip voltage at that time (Eup and Edown) and the same predetermined current value (I) the electrode tip between the power where a product of (Pup = Eup × I and Pdown = Edown × I) The difference (Pdown-Pup) or ratio (Pdown / Pup) or the voltage ratio between electrode tips (Edown / Eup) is obtained as Ps, but this Ps is larger (or smaller) than a predetermined value for each predetermined half cycle. The welding current for each next half cycle is decreased (or increased) by a predetermined value, or the pressurizing force is increased (or decreased) by a predetermined value, or the energization is stopped at that time Scatter while getting nuggets It is possible to prevent the occurrence.
[0020]
In an embodiment of claim 9 of the present invention, FIG. 10 shows the welding current and the voltage between the electrode tips in a half cycle. The welding current and the voltage between the electrode tips are detected every moment, and the voltage between the electrode tips and the point when the maximum value of the welding current in each half cycle (Ti-peak) is reached. The time difference (Ts) until the point of reaching the maximum value (Te-peak) is the voltage between the electrode tips (Eup and Eup) at each of the current increasing process and current decreasing process under the same current value (I). Edown) is the product of the same current value (I) and the difference (Pdown-Pup) or ratio (Pdown / Pup) between the power between the electrode tips (Pup = Eup × I and Pdown = Edown × I) or When the voltage ratio between electrode tips (Edown / Eup) is large (or small), the time difference becomes large (or small). Accordingly, the vertical relationship between the PI curve increasing process and the decreasing process curve under the appropriate welding condition (1) passes through the above-described process, and in the 7.0th cycle, the increasing process and the decreasing process curve are almost identical. When overlapped, the time difference (Ts) value is plotted on the vertical axis and the cycle number is plotted on the horizontal axis, and the Ts-Cycle diagram is as shown in Fig. 11, reaching the maximum welding current for each half cycle. It is detected that the time difference (Ts) from the time (Ti-peak) to the time when the voltage between the electrode tips reaches the maximum value (Te-peak) is less than a predetermined value, and the subsequent welding current Can be reduced by a predetermined value, or the applied pressure can be increased by a predetermined value, or the energization can be stopped at that point to prevent the occurrence of scattering while obtaining a predetermined nugget.
[Brief description of the drawings]
FIG. 1 is a diagram showing components of voltage between electrode chips according to an embodiment of the present invention.
FIG. 2 schematically shows a welding current waveform (I) and a power waveform (P) after the 0.5th cycle of energization start in an embodiment of the present invention.
FIG. 3 is a diagram showing a PI- ² curve of the 0.5th cycle under proper welding conditions (1) in an example of the present invention.
FIG. 4 shows a PI ² curve of the 1.0th cycle under proper welding conditions (1) in an example of the present invention.
FIG. 5 shows a PI- ² curve of the 1.5th cycle under proper welding conditions (1) in an example of the present invention.
FIG. 6 shows a P-I ² curve of 7.0th cycle under proper welding conditions (1) in an example of the present invention.
FIG. 7 shows a PI- ² curve of 4.0th cycle under excessive welding conditions (2) in an example of the present invention.
FIG. 8 shows the difference in power between electrode tips at the same current value in an example of the present invention.
FIG. 9 shows the transition of the difference (Ps) in power between electrode tips at the same current value in the example of the present invention.
FIG. 10 shows the time difference (Ts) between the maximum value of the welding current and the maximum value of the voltage between the electrode tips in a half cycle in the example of the present invention.
FIG. 11 shows the transition of the time difference (Ts) between the maximum value of the welding current and the maximum value of the voltage between the electrode tips in the example of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Resistance between electrode tips 2 Contact resistance between plates of welded material 3 Specific resistance of welded material 4 Contact resistance between electrode tip and welded product 5 Specific resistance of electrode tip itself 6 Pair of electrode tips 7 Welded product

Claims

In the resistance spot welding method , in which a welded metal plate is sandwiched between a pair of electrode tips and energized while applying pressure to this, the welding current and the voltage between the electrode tips are detected momentarily. P-I or P- where the vertical axis represents the product of the welding current and the voltage between the electrode tips (P), and the horizontal axis represents the welding current (I) or the square value of the welding current (I ² ). An I ² curve is obtained by calculation, and the curve starts from the zero point of I = P = 0 where the welding current starts flowing in each half cycle, and increases to the right, and I reaches a peak. In the decreasing process curve that turns to decrease and then returns to the zero point again after energization, while excluding data in the vicinity of the zero point of I, the vertical relationship between these increasing process and decreasing process curves is 0.5. Start from cycle, cycle 1.0 and cycle Compared with each half-cycle in each other continues .5 cycles, in the first of the 0.5 cycle coming curves increase process in the upper, curve of the reduction process becomes upward then reversed, after which the two curves When it approaches and detects that the area between the two curves is less than the predetermined value, the welding current after that is decreased by a predetermined value, or the applied pressure is increased by a predetermined value, or energization is performed at that time. A resistance spot welding method characterized by cutting off and preventing the occurrence of scattering.

In the resistance spot welding method , in which a welded metal plate is sandwiched between a pair of electrode tips and energized while applying pressure to this, the welding current and the voltage between the electrode tips are detected momentarily. P-I or P- where the vertical axis represents the product of the welding current and the voltage between the electrode tips (P), and the horizontal axis represents the welding current (I) or the square value of the welding current (I ² ). determined by calculating the I ² curve, by comparing the vertical relationship of the curves of the process of reduction and the increase process, the curve of the increase process in the first of the 0.5 cycle came upward, the then reversed to decrease process It is characterized by detecting that the curve is on the upper side, then the two curves approach each other and the area between the two curves is less than the predetermined value is longer than the predetermined cycle length, and an undercurrent alarm is output. Resistance spot welding method.

In the resistance spot welding method according to claim 2, it took longer than a predetermined cycle length for the PI or PI ² curves of the increasing process and the decreasing process to approach and the area between the two curves to be equal to or less than a predetermined value. A resistance spot welding method characterized in that an appropriate nugget is obtained by detecting this and automatically increasing the welding current at the next welding point by a predetermined value or decreasing the pressure by a predetermined value.

In the resistance spot welding method , in which a welded metal plate is sandwiched between a pair of electrode tips and energized while applying pressure to this, the welding current and the voltage between the electrode tips are detected momentarily. P-I or P- where the vertical axis represents the product of the welding current and the voltage between the electrode tips (P), and the horizontal axis represents the welding current (I) or the square value of the welding current (I ² ). determined by calculating the I ² curve, by comparing the vertical relationship of the curves of the process of reduction and curve of the increase process, in the first of the 0.5 cycle coming curves increase process in the upper, reduced then reversed The process curve is on the upper side, but after that, it is detected again that the upper and lower relations are reversed, or the curve of the increasing process and the decreasing process intersects within a half cycle, and the welding current after that is set to the predetermined value. Decrease or apply pressure to the specified value Kusuru either, or discontinued the energization at that time, scattered resistance spot welding method, characterized in that to reduce the occurrence of.

In such resistance spot welding method in claim 4, the vertical relationship between the P-I or P-I ² curve increase process and reduction process, in the first of the 0.5 cycle coming curve of increasing process upward, then The curve of the decrease process goes up and reverses, but then the vertical relationship is reversed again, or it is detected that the increase process and the decrease process have crossed within a half cycle. A resistance spot welding method characterized by outputting an alarm.

In such resistance spot welding method in claim 4, the vertical relationship between the P-I or P-I ² curve increase process and reduction process, in the first of the 0.5 cycle coming curve of increasing process upward, then The curve of the decreasing process goes upside down, but after that it detects that the relationship between the top and bottom is reversed again, or the curve of the increasing process and the decreasing process crosses within a half cycle, and then automatically A resistance spot welding method characterized in that an appropriate nugget is obtained while reducing the occurrence of scattering by lowering the welding current at the welding point of the electrode by a predetermined value or increasing the applied pressure by a predetermined value.

In a resistance spot welding method in which a welded metal sheet is sandwiched between a pair of electrode tips and energized while applying pressure to the weld, a welding current and a voltage between the electrode tips that vary from moment to moment. detecting bets every moment, to detect the electrode tip between the voltage corresponding to the same predetermined current value of the increase process and reduction process each of the welding current (I) in each half cycle, the same current value (I) the ratio of the difference between the product of a is at the electrode tip between the power of the electrode tip voltage (Pup = Eup × I and Pdown = Edown × I) (Pdown -Pup) or ratio (Pdown / Pup) or the electrode tip voltage (Edown / Eup) is obtained as Ps, and it is detected that the transition value of Ps every half cycle is less than a predetermined value, and the welding current after that cycle is decreased by a predetermined value or the pressure is reduced. or higher by a predetermined value, if The resistance spot welding method characterized in that it aborted the energization at that time, to prevent the occurrence of expulsion.

In a resistance spot welding method in which a welded metal sheet is sandwiched between a pair of electrode tips and energized while applying pressure to the weld, a welding current and a voltage between the electrode tips that vary from moment to moment. detecting bets every moment, to detect the electrode tip between the voltage corresponding to the same predetermined current value of the increase process and reduction process each of the welding current (I) in each half cycle, the same current value (I) the ratio of the difference between the product of a is at the electrode tip between the power of the electrode tip voltage (Pup = Eup × I and Pdown = Edown × I) (Pdown -Pup) or ratio (Pdown / Pup) or the electrode tip voltage (Edown / Eup) is obtained as Ps, and the value that changes every half cycle of Ps is compared with the value that changes every half cycle stored in advance, and the value that changes every half cycle of Ps is stored in advance. In addition, every half cycle of Ps A resistance spot welding method, wherein the welding current is controlled every half cycle so as to obtain a value to be transferred.

In a resistance spot welding method in which a welded metal sheet is sandwiched between a pair of electrode tips and energized while applying pressure to the weld, a welding current and a voltage between the electrode tips that vary from moment to moment. Are detected from time to time, and the time difference (Ts) from when the maximum value of the welding current in each half cycle is reached to the time when the voltage waveform between the electrode tips reaches the maximum value is obtained. Detecting that the value has fallen below the specified value and reducing the welding current after that half cycle by a specified value, or increasing the applied pressure by a specified value, or cutting off the current at that point to prevent the occurrence of scattering Resistance spot welding method characterized by