JP7152895B2 - Evaluation method of joint point of spot welding - Google Patents

Evaluation method of joint point of spot welding Download PDF

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JP7152895B2
JP7152895B2 JP2018142672A JP2018142672A JP7152895B2 JP 7152895 B2 JP7152895 B2 JP 7152895B2 JP 2018142672 A JP2018142672 A JP 2018142672A JP 2018142672 A JP2018142672 A JP 2018142672A JP 7152895 B2 JP7152895 B2 JP 7152895B2
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圭一郎 木許
知嗣 加藤
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Daihatsu Motor Co Ltd
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Description

本発明は、スポット溶接により形成された接合点の品質を評価するための方法に関する。 The present invention relates to a method for evaluating the quality of joints produced by spot welding.

スポット溶接により形成された接合点（ナゲット）の品質を評価する方法として、たがね試験が知られている（例えば、特許文献１参照）。 A chisel test is known as a method for evaluating the quality of joints (nuggets) formed by spot welding (see, for example, Patent Document 1).

例えば、断面ハット形状の金属板で覆われた袋構造（図１参照）に溶接を施す場合、たがねを挿入することが不可能な場所にナゲットが形成されることがある。このような場所に形成されたナゲットには、たがね試験を適用することができないため、他の評価方法として、例えば超音波検査が適用される（例えば、特許文献２参照）。超音波検査は、ナゲットに向けて超音波を発振し、その反射波を受信することにより、ナゲットの大きさを測定するものである。 For example, when welding a bag structure covered with a hat-shaped metal plate (see FIG. 1), a nugget may be formed in a place where a chisel cannot be inserted. Since a chisel test cannot be applied to a nugget formed in such a place, another evaluation method such as ultrasonic inspection is applied (see, for example, Patent Document 2). Ultrasonic inspection measures the size of a nugget by oscillating ultrasonic waves toward the nugget and receiving the reflected waves.

特開２０１１－０４７７３８号公報JP 2011-047738 A 特開２００８－２０３０８２号公報Japanese Unexamined Patent Application Publication No. 2008-203082

スポット溶接では、金属板が電極で加圧されるため、金属板に凹状の打痕が形成される。特に、インダイレクトスポット溶接では、電極で加圧する金属板が反対側から支持されていないため、打痕が深くなる。このような深い凹状の打痕に超音波を発振すると、超音波が打痕の表面を通過する際に分散してしまい、反射した超音波を正常に受信することができず、ナゲットの大きさの正確な測定ができない恐れがある。 In spot welding, since the metal plate is pressed by the electrode, a concave dent is formed in the metal plate. In particular, in indirect spot welding, the metal plate pressed by the electrode is not supported from the opposite side, resulting in deep dents. When an ultrasonic wave is oscillated in such a deep concave dent, the ultrasonic wave scatters when passing through the surface of the dent, and the reflected ultrasonic wave cannot be received normally. may not be able to measure accurately.

本発明者らは、スポット溶接を行いながら、接合点の品質に寄与するパラメータを取得し、このパラメータに基づいて接合点の品質を評価することを試みた。具体的に、このようなパラメータとして、一対の電極間を流れる電流値をＩ、両電極間の電圧をＶ、接合する複数の金属板同士の接触面積をＳとしたとき、Ｄ＝Ｉ・Ｖ／Ｓで表される発熱密度Ｄを用いた。そして、多数のサンプルに対し、発熱密度Ｄを取得しながらインダイレクトスポット溶接を施し、形成された接合点（ナゲット）の状態を確認し、良好なナゲットが形成される発熱密度Ｄの範囲を設定した。これを用いて、実際の製品のインダイレクトスポット溶接の接合点の品質を評価したが、評価の精度はそれほど高くなかった。 The inventors of the present invention acquired parameters that contribute to the quality of joints while performing spot welding, and attempted to evaluate the quality of joints based on these parameters. Specifically, as such parameters, when the current value flowing between a pair of electrodes is I, the voltage between both electrodes is V, and the contact area between a plurality of metal plates to be joined is S, D=IV. A heat generation density D expressed as /S was used. Then, indirect spot welding is performed on a large number of samples while obtaining the heat density D, the state of the formed joint (nugget) is confirmed, and the range of heat density D that allows good nuggets to be formed is set. did. This was used to evaluate the quality of joints of indirect spot welding of actual products, but the accuracy of the evaluation was not so high.

そこで、本発明は、スポット溶接の接合点の評価の精度を高めることを目的とする。 SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the accuracy of evaluation of joint points of spot welding.

前記課題を解決するために、本発明は、重ね合わせた複数の金属板に一対の電極を当接させた状態で、前記一対の電極間に通電することにより前記複数の金属板を接合するスポット溶接において、接合点の品質を評価するための方法であって、前記一対の電極間に通電しながら、接合点の品質に寄与するパラメータを取得する工程と、前記一対の電極間に通電する期間を複数の区間に分け、各区間の前記パラメータの接合点の品質への寄与度を考慮して、各区間の前記パラメータを用いた評価式を作成する工程と、前記評価式を用いて接合点の品質を評価する工程とを有するスポット溶接の接合点の評価方法を提供する。 In order to solve the above-mentioned problems, the present invention provides a spot for joining a plurality of metal plates by energizing between the pair of electrodes in a state in which a pair of electrodes are in contact with the plurality of superimposed metal plates. A method for evaluating the quality of a joint in welding, comprising the steps of obtaining a parameter contributing to the quality of the joint while passing an electric current between the pair of electrodes, and a period during which the pair of electrodes is energized. is divided into a plurality of sections, and considering the contribution of the parameters of each section to the quality of the junction point, creating an evaluation formula using the parameters of each section; and a step of evaluating the quality of spot welded joints.

上記のように、一対の電極間に通電しながら、接合点の品質に寄与するパラメータを取得した場合、通電期間の全体では、接合点が良好な場合と不良の場合とでパラメータの値に明確な差が見られない場合でも、通電期間の一部では、接合点が良好な場合と不良の場合とでパラメータの値に明確な差が現れることがある。そこで、本発明では、上記のように、一対の電極間に通電する期間を複数の区間に分け、各区間の前記パラメータの接合点の品質への寄与度を考慮して、各区間の前記パラメータを用いた評価式を作成した。この評価式を用いることで、接合点の品質を正確に評価することができる。 As described above, when the parameters that contribute to the quality of the junction are obtained while energizing between the pair of electrodes, the values of the parameters are clearly defined depending on whether the junction is good or bad during the entire energization period. Even if no significant difference is observed, there may be a clear difference in parameter values between good and bad junctions during part of the energization period. Therefore, in the present invention, as described above, the period in which the pair of electrodes is energized is divided into a plurality of sections, and the contribution of the parameter of each section to the quality of the junction point is considered. We created an evaluation formula using By using this evaluation formula, the quality of the junction can be accurately evaluated.

以上のように、本発明によれば、スポット溶接の接合点を正確に評価することができる。 As described above, according to the present invention, the joint points of spot welding can be accurately evaluated.

ワークに対してインダイレクトスポット溶接を施す様子を示す断面図である。FIG. 4 is a cross-sectional view showing how indirect spot welding is applied to a work; 上記インダイレクトスポット溶接の溶接中の電流値、加圧力、及び発熱密度を示すグラフである。4 is a graph showing the current value, applied pressure, and heat density during welding in the indirect spot welding. （Ａ）～（Ｅ）は、図２の各ステップＳ１～Ｓ５終了時におけるワークの接合予定部周辺の断面図である。(A) to (E) are cross-sectional views of the parts to be joined of the work at the end of steps S1 to S5 in FIG. 2, respectively. 溶接電極の変位量と金属板同士の接触面積との関係を示すグラフである。4 is a graph showing the relationship between the amount of displacement of a welding electrode and the contact area between metal plates.

以下、本発明の実施の形態を図面に基づいて説明する。 BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

本実施形態では、自動車の車体の組立工程において行われるインダイレクトスポット溶接方法を示し、具体的には、図１に示すようなワーク１００（車体の骨格部品）を溶接する場合を示す。ワーク１００は、紙面直交方向に延びるフレーム状の部品であり、略平板状を成した第１の金属板１と、断面ハット形状を成した第２の金属板２と、第１の金属板１と第２の金属板２とで構成される中空部に配された断面ハット形状を成した第３の金属板３とで構成される。金属板１～３としては、例えば鋼板が使用され、具体的には軟鋼板、高張力鋼板（引張強度４９０ＭＰａ以上）、超高張力鋼板（引張強度９８０ＭＰａ以上）等が使用される。 In this embodiment, an indirect spot welding method performed in the assembly process of an automobile body is shown, and more specifically, a case of welding a workpiece 100 (body frame part) as shown in FIG. 1 is shown. The workpiece 100 is a frame-shaped part extending in the direction perpendicular to the plane of the paper, and includes a first metal plate 1 having a substantially flat plate shape, a second metal plate 2 having a hat-shaped cross section, and the first metal plate 1. and a third metal plate 3 having a hat-shaped cross section disposed in a hollow portion composed of the second metal plate 2 and the second metal plate 2 . As the metal plates 1 to 3, for example, steel plates are used. Specifically, mild steel plates, high-tensile steel plates (tensile strength of 490 MPa or more), ultra-high-tensile steel plates (tensile strength of 980 MPa or more), etc. are used.

第１の金属板１と第２の金属板２のフランジ部２ａとは、ダイレクトスポット溶接により予め溶接された既接合点Ｑ１を介して接合されている。第２の金属板２の底部２ｂと第３の金属板３のフランジ部３ａとは、ダイレクトスポット溶接により予め溶接された既接合点Ｑ２を介して接合されている。 The first metal plate 1 and the flange portion 2a of the second metal plate 2 are joined via a pre-welded joint Q1 by direct spot welding. The bottom portion 2b of the second metal plate 2 and the flange portion 3a of the third metal plate 3 are joined via a pre-welded point Q2 by direct spot welding.

そして、第１の金属板１と第３の金属板３の天板部３ｂとの接合予定部Ｐを、インダイレクトスポット溶接により接合する。インダイレクトスポット溶接装置は、溶接電極１０及びアース電極２０と、溶接電極１０を軸線方向に駆動して金属板を加圧する加圧手段（エアシリンダや電動シリンダ等）と、加圧手段による溶接電極１０の加圧力及び両電極１０，２０間の電流値を制御する制御部（図示省略）とを備える。 Then, the portion to be joined P between the first metal plate 1 and the top plate portion 3b of the third metal plate 3 is joined by indirect spot welding. The indirect spot welding apparatus includes a welding electrode 10 and a ground electrode 20, a pressurizing means (such as an air cylinder or an electric cylinder) for driving the welding electrode 10 in the axial direction to pressurize a metal plate, and a welding electrode by the pressurizing means. 10 and a control unit (not shown) that controls the current value between the two electrodes 10 and 20 .

接合予定部Ｐに対するインダイレクトスポット溶接は、以下の手順で行われる。まず、ワーク１００のうち、接合予定部Ｐと異なる部位にアース電極２０を当接させる。図示例では、第２の金属板２の底部２ｂ、特に、第２の金属板２の底部２ｂと第３の金属板３のフランジ部３ａとの既接合点Ｑ２に、アース電極２０を下方から当接させている。この状態で、第１の金属板１と第３の金属板３の天板部３ｂとの接合予定部Ｐを厚さ方向一方側（図中上側）から溶接電極１０で加圧しながら、両電極１０，２０間に通電することにより、接合予定部Ｐを溶接する。 Indirect spot welding to the part to be joined P is performed in the following procedure. First, the ground electrode 20 is brought into contact with a portion of the workpiece 100 that is different from the portion P to be joined. In the illustrated example, the ground electrode 20 is connected from below to the bottom portion 2b of the second metal plate 2, particularly to the already joined point Q2 between the bottom portion 2b of the second metal plate 2 and the flange portion 3a of the third metal plate 3. abutting. In this state, both electrodes are pressurized by the welding electrode 10 from one side in the thickness direction (upper side in the figure) to the joint portion P between the first metal plate 1 and the top plate portion 3b of the third metal plate 3. By energizing between 10 and 20, the part to be joined P is welded.

本実施形態では、溶接電極１０による加圧力及び両電極１０，２０間の電流値の一方又は双方を変化させながら、溶接が行われる。具体的には、図２に示す加圧通電パターンに従って溶接が行われる。以下、この加圧通電パターンを詳しく説明する。 In this embodiment, welding is performed while changing one or both of the pressure applied by the welding electrode 10 and the current value between the two electrodes 10 and 20 . Specifically, welding is performed according to the pressurization current pattern shown in FIG. This pressurizing energization pattern will be described in detail below.

［第１のステップＳ１］
第１のステップＳ１では、溶接電極１０で接合予定部Ｐを、相対的に高い第１の加圧力Ｆ１で加圧する。これにより、金属板１，３間の隙間を詰めて両金属板１，３を確実に接触させると共に、溶接電極１０と第１の金属板１との接触面積、及び、第１の金属板１と第３の金属板３との接触面積を確保することができる。この状態で、電極１０，２０間に、相対的に低い第１の電流値Ｉ１を通電することにより、電流密度を抑えて金属板１，３表面の溶融飛散を防止しながら、金属板１を軟化させて、溶接電極１０と第１の金属板１との接触面積、及び、第１の金属板１と第３の金属板３との接触面積を拡大することができる｛図３（Ａ）参照｝。尚、図３に散点で示す領域は、熱影響部である。 [First step S1]
In the first step S1, the welding electrode 10 applies pressure to the part to be welded P with a relatively high first pressure F1. As a result, the gap between the metal plates 1 and 3 is closed and the two metal plates 1 and 3 are reliably brought into contact with each other. and the third metal plate 3 can be secured. In this state, by applying a relatively low first current value I1 between the electrodes 10 and 20, the current density is suppressed to prevent the surfaces of the metal plates 1 and 3 from being melted and scattered, and the metal plate 1 is removed. By softening, the contact area between the welding electrode 10 and the first metal plate 1 and the contact area between the first metal plate 1 and the third metal plate 3 can be enlarged {Fig. 3(A) reference}. Note that the area indicated by dotted dots in FIG. 3 is the heat affected zone.

［第２のステップＳ２］
第２のステップＳ２では、始めに、溶接電極１０に加圧力を付与する加圧手段に対して加圧力低下の指令を出す（図２参照）。このとき、加圧手段の構造上、指令を受けると同時に実際の加圧力がＦ１からＦ２まで瞬時に降下するのではなく、Ｆ１からＦ２まで徐々に低下する移行期間が必然的に設けられる。こうして加圧力をＦ１からＦ２まで徐々に降下させながら、第１のステップの電流値Ｉ１よりも低い電流値Ｉ２で通電する。このように、加圧力が不安定な状態での投入熱量を抑えることで、溶接電極１０及び金属板１，３を適度に冷却あるいは保温してヒートバランスを調整することができる。この第２のステップＳ２では、金属板１，３の接合予定部Ｐ周辺の状態はほとんど変化しない｛図３（Ｂ）参照｝。 [Second step S2]
In the second step S2, first, a command to decrease the pressure is issued to the pressure means that applies pressure to the welding electrode 10 (see FIG. 2). At this time, due to the structure of the pressurizing means, a transition period is inevitably provided in which the actual pressurizing force does not drop instantaneously from F1 to F2 upon receipt of the command, but gradually drops from F1 to F2. In this way, while the pressing force is gradually decreased from F1 to F2, the current value I2 lower than the current value I1 of the first step is applied. In this way, by suppressing the amount of heat input when the pressure is unstable, the welding electrode 10 and the metal plates 1 and 3 can be appropriately cooled or kept warm to adjust the heat balance. In this second step S2, the state of the vicinity of the portion to be joined P of the metal plates 1 and 3 hardly changes {see FIG. 3(B)}.

［第３のステップＳ３］
その後、加圧手段の加圧力を検知する加圧力検知部（図示省略）が、加圧力がＦ２まで降下したことを検知したら、電流値を上昇させる。本実施形態では、加圧力がＦ２まで降下すると同時に、電流値を上昇させる（図２参照）。このとき、第２のステップＳ２の低電流値Ｉ２から、ナゲットを形成する本通電の電流値（次の第４のステップＳ４の電流値Ｉ４）まで一気に高めると、スパッタが発生する恐れがある。そこで、第３のステップＳ３において、低加圧力Ｆ２で加圧しながら、まずは本通電の電流値Ｉ４よりも低い電流値Ｉ３で通電することにより、金属板１，３を軟化させてこれらの接触面積を拡大することができる｛図３（Ｃ）参照｝。 [Third step S3]
After that, when the pressure detection unit (not shown) that detects the pressure of the pressure means detects that the pressure has fallen to F2, the current value is increased. In this embodiment, the current value is increased at the same time as the applied force drops to F2 (see FIG. 2). At this time, if the current value for main energization for forming a nugget (the current value I4 in the next fourth step S4) is suddenly increased from the low current value I2 in the second step S2, spatter may occur. Therefore, in the third step S3, while applying pressure with a low pressure F2, the metal plates 1 and 3 are first energized with a current value I3 lower than the current value I4 of the main energization, thereby softening the metal plates 1 and 3 and increasing the contact area between them. can be enlarged {see FIG. 3(C)}.

［第４のステップＳ４］
こうして金属板１，３同士の接触面積を確保した状態で、続く第４のステップＳ４で本通電の電流値Ｉ４まで上昇させて通電する（図２参照）。これにより、スパッタを発生させることなくナゲットの種（所望の大きさには至らないナゲット）を確実に形成することができる｛図３（Ｄ）参照｝。図示例では、第４のステップＳ４で、両金属板１，３の接合予定部Ｐに環状のナゲットＮが形成される。 [Fourth step S4]
With the contact area between the metal plates 1 and 3 secured in this manner, the current is increased to the current value I4 of the main energization in the subsequent fourth step S4 (see FIG. 2). As a result, nugget seeds (nuggets not reaching the desired size) can be reliably formed without generating spatter (see FIG. 3D). In the illustrated example, in the fourth step S4, an annular nugget N is formed at the part to be joined P of both metal plates 1 and 3. As shown in FIG.

［第５のステップＳ５］
上記のステップＳ４でナゲットの種を形成した後、第５のステップＳ５で、溶接電極１０により第２の加圧力Ｆ２で加圧しながら、両電極１０，２０間に、第４の電流値Ｉ４よりも低い第５の電流値Ｉ５を通電する（図２参照）。これにより、金属板１，３への投入熱量を抑えながら、第４のステップＳ４で加熱した金属板１，３の予熱を利用して、ナゲットの状態を安定化させることができる｛図３（Ｅ）参照｝。図示例では、第４のステップＳ４で形成された環状のナゲットＮが第５のステップＳ５で内径側に成長し、中空部が埋められて略円盤状となる。 [Fifth step S5]
After the nugget seeds are formed in the above step S4, in the fifth step S5, while applying the second pressure force F2 from the welding electrode 10, between the electrodes 10 and 20, a current value higher than the fourth current value I4 is applied. A fifth current value I5, which is the lowest, is applied (see FIG. 2). As a result, the state of the nugget can be stabilized by utilizing the preheating of the metal plates 1 and 3 heated in the fourth step S4 while suppressing the amount of heat input to the metal plates 1 and 3 {Fig. 3 ( E) See}. In the illustrated example, the annular nugget N formed in the fourth step S4 grows to the inner diameter side in the fifth step S5, and the hollow portion is filled to form a substantially disk shape.

以上により、金属板１と金属板３の天板部３ｂとの接合予定部Ｐに、所望の大きさ及び形状を有する接合点としてのナゲットＮが形成され、このナゲットＮを介して両金属板１，３が接合される。 As described above, a nugget N as a joint point having a desired size and shape is formed at the joint planned portion P between the metal plate 1 and the top plate portion 3b of the metal plate 3. 1 and 3 are joined.

上記のインダイレクトスポット溶接により形成された接合点の品質を、溶接中の発熱密度Ｄを用いて評価する。具体的には、両電極１０，２０間に通電を開始してから終了するまでの間、両電極１０，２０間を流れる電流値Ｉと、両電極１０，２０間の電圧Ｖと、金属板１，３同士の接触面積Ｓとを測定する。 The quality of the joint formed by the above indirect spot welding is evaluated using the heat generation density D during welding. Specifically, the current value I flowing between the electrodes 10 and 20, the voltage V between the electrodes 10 and 20, and the metal plate A contact area S between 1 and 3 is measured.

このとき、金属板１，３同士の接触面積Ｓを直接測定することは困難であるため、溶接電極１０の変位量ｘで代替する。本実施形態では、通電開始時における溶接電極１０の位置を基準とし、ここからの溶接電極１０の軸方向（加圧方向）移動量を変位量ｘとする。溶接中の接触面積Ｓの具体的な取得方法は以下の通りである。まず、予め、溶接電極１０の変位量ｘと金属板１，３の接触面積Ｓとの相関関係を取得する。例えば、上記のワーク１００と同様のサンプルの接合予定部にインダイレクトスポット溶接を施し、通電を途中の複数段階で止めた複数のサンプルを作製する。そして、各サンプルの切断面から金属板１，３の接触面積Ｓを測定すると共に、そのときの溶接電極１０の変位量ｘを記録し、グラフ上に（ｘ，Ｓ）をプロットする（図４参照）。このグラフから、変位量ｘと接触面積Ｓとの相関関係を算出する。図示例では、接触面積Ｓと変位量ｘとがおおよそ比例関係にあり、Ｓ＝ａ・ｘ＋ｂで表される（ａ，ｂは定数）。この関係式を用いることにより、実際の製品にインダイレクトスポット溶接を施す際に、測定が容易な溶接電極１０の変位量ｘから、直接測定することが困難な金属板１，３同士の接触面積Ｓを取得することができる。 At this time, since it is difficult to directly measure the contact area S between the metal plates 1 and 3, the displacement amount x of the welding electrode 10 is substituted. In the present embodiment, the position of the welding electrode 10 at the start of energization is used as a reference, and the amount of movement of the welding electrode 10 in the axial direction (pressing direction) from this point is defined as the displacement amount x. A specific method of obtaining the contact area S during welding is as follows. First, the correlation between the displacement amount x of the welding electrode 10 and the contact area S of the metal plates 1 and 3 is obtained in advance. For example, indirect spot welding is applied to the portions to be joined of samples similar to the workpiece 100 described above, and a plurality of samples are produced by stopping the current supply at a plurality of stages along the way. Then, the contact area S between the metal plates 1 and 3 is measured from the cut surface of each sample, the displacement amount x of the welding electrode 10 at that time is recorded, and (x, S) is plotted on a graph (Fig. 4 reference). From this graph, the correlation between the displacement amount x and the contact area S is calculated. In the illustrated example, the contact area S and the amount of displacement x are approximately in a proportional relationship, represented by S=a·x+b (a and b are constants). By using this relational expression, when indirect spot welding is applied to an actual product, the contact area between the metal plates 1 and 3, which is difficult to measure directly, can be calculated from the displacement amount x of the welding electrode 10, which is easy to measure. S can be obtained.

これらの電流値Ｉ、電圧Ｖ、及び接触面積Ｓ（溶接電極１０の変位量ｘ）から、Ｄ＝Ｖ・Ｉ／Ｓ＝Ｖ・Ｉ／（ａ・ｘ＋ｂ）で表される発熱密度Ｄを算出する（図２の鎖線参照）。この発熱密度Ｄを用いて、ナゲットＮの品質を評価する。以下、発熱密度Ｄを用いたナゲットＮの評価方法の具体的手順の一例を説明する。 From these current value I, voltage V, and contact area S (displacement amount x of welding electrode 10), heat generation density D expressed by D=VI/S=VI/(ax+b) is calculated. (see dashed line in FIG. 2). Using this heat generation density D, the quality of the nugget N is evaluated. An example of a specific procedure for evaluating the nugget N using the heat generation density D will be described below.

まず、通電開始から終了までの期間を複数の区間に分ける。本実施形態では、電流値が一定の各ステップＳ１～Ｓ５の少なくとも一つを複数の区間に分け、具体的には、図２に示すように、第１～第５のステップＳ５をそれぞれ２つの区間に等分して区間Ｃ１～Ｃ１０を形成する。そして、予め、様々な条件でインダイレクトスポット溶接を行った多数のサンプルを作成し、このときの各区間Ｃ１～Ｃ１０の発熱密度の値（例えば、各区間の発熱密度の平均値や積分値等）を取得すると共に、各サンプルの切断面から接合点の不良の有無を確認する。そして、発熱密度と接合点の品質との相関が高い区間、すなわち、接合点が良好である場合と不良である場合とで発熱密度の値に明確な差が生じている一又は複数の区間を選択し、選択した区間において発熱密度の値の許容範囲を設定する。 First, the period from the start to end of energization is divided into a plurality of sections. In this embodiment, at least one of steps S1 to S5 with a constant current value is divided into a plurality of sections. Specifically, as shown in FIG. It is equally divided into sections to form sections C1 to C10. Then, a large number of samples were prepared in advance by performing indirect spot welding under various conditions, and the values of the heat generation density of each section C1 to C10 at this time (for example, the average value and integral value of the heat generation density of each section) ) is obtained, and the presence or absence of defective joint points is checked from the cut surface of each sample. Then, the section where the heat generation density and the quality of the joint point are highly correlated, that is, one or more sections where there is a clear difference in the heat generation density value between the case where the joint point is good and the case where the joint point is defective is selected. Select to set the allowable range of heat generation density values in the selected interval.

そして、実際の製品において、インダイレクトスポット溶接を施した接合点の品質を評価する。すなわち、選択した区間の発熱密度の値が許容範囲内であれば、金属板１，３の接合予定部Ｐに良好なナゲットＮが形成されていると判定し、選択した区間の発熱密度の値が許容範囲外であれば、ナゲットＮに何らかの不良（ナゲット径不足、金属板の割れ、ブローホール等）が生じていると判定する。 Then, in an actual product, the quality of joints subjected to indirect spot welding is evaluated. That is, if the value of the heat generation density of the selected section is within the allowable range, it is determined that a good nugget N is formed in the joint planned portion P of the metal plates 1 and 3, and the value of the heat generation density of the selected section is out of the permissible range, it is determined that the nugget N has some defect (nugget diameter shortage, metal plate cracks, blowholes, etc.).

尚、接合点を評価するにあたり、上記で選択した区間の発熱密度の値（平均値、積分値等）をそのまま用いるのではなく、これらの区間の発熱密度から統計的手法（例えば判別分析法）により作成した評価式を用いてもよい。例えば、各区間Ｃ１～Ｃ１０の発熱密度の値をｃ１～ｃ１０としたとき、Ｆ＝ｋ１・ｃ１＋ｋ２・ｃ２＋・・・＋ｋ１０・ｃ１０で表される評価式Ｆを用いてもよい。ｋ１～ｋ１０は、各項の寄与率を踏まえた係数である。このような評価式を用いることで、接合点の品質をより正確に評価することが可能となる。この評価式には、上記のような各区間の発熱密度の値の項の他、何れかの区間の発熱密度の値の累乗（例えばｃ１２等）の項や、複数の区間の発熱密度の値の積（例えばｃ１・ｃ２等）や比（例えばｃ１／ｃ２等）の項を加えてもよい。 In evaluating the junction point, instead of using the heat generation density values (average value, integral value, etc.) of the sections selected above as they are, statistical methods (e.g., discriminant analysis method) are used from the heat generation densities of these sections. You may use the evaluation formula created by. For example, an evaluation formula F expressed by F=k1·c1+k2·c2+ . k1 to k10 are coefficients based on the contribution rate of each term. By using such an evaluation formula, it becomes possible to more accurately evaluate the quality of the junction. In this evaluation formula, in addition to the term of the value of the heat generation density of each section as described above, the term of the power of the value of the heat generation density of any section (for example, c1 2 etc.) and the term of the heat generation density of a plurality of sections A product of values (eg, c1·c2, etc.) or a ratio (eg, c1/c2, etc.) terms may be added.

上記のように、溶接中の電流値Ｉ、電圧Ｖ、及び金属板１，３同士の接触面積Ｓ（溶接電極１０の変位量ｘ）の関係を表す発熱密度Ｄを用いてナゲットＮの品質を評価することで、たがね試験や超音波検査を適用できないナゲットＮの品質であっても評価できる。 As described above, the quality of the nugget N is determined using the current value I during welding, the voltage V, and the heat density D that represents the relationship between the contact area S between the metal plates 1 and 3 (the amount of displacement x of the welding electrode 10). By evaluating, even the quality of the nugget N to which the chisel test and ultrasonic inspection cannot be applied can be evaluated.

また、発熱密度Ｄ（＝Ｉ・Ｖ／Ｓ＝Ｉ２・Ｒ／Ｓ）は、電流密度（＝Ｉ／Ｓ）だけでなく、金属板１，３の温度や接触面積Ｓに伴って時々刻々と変化する抵抗値Ｒを考慮したパラメータである。この発熱密度Ｄを用いることで、金属板１，３の接触部における抵抗発熱による発熱状態をモニタリングできるため、ナゲットＮの品質を正確に評価することができる。 In addition, the heat generation density D (=I·V/S=I 2 ·R/S) varies not only with the current density (=I/S) but also with the temperatures of the metal plates 1 and 3 and the contact area S. It is a parameter considering the resistance value R that changes with . By using this heat generation density D, it is possible to monitor the heat generation state due to resistance heat generation at the contact portion of the metal plates 1 and 3, so that the quality of the nugget N can be evaluated accurately.

尚、上記のようなナゲットＮの品質評価は、インダイレクトスポット溶接工程とは別に設けた検査工程で行ってもよいし、インダイレクトスポット溶接工程内で行ってもよい。後者の場合、例えば、インダイレクトスポット溶接の完了と同時に、発熱密度Ｄの算出及びナゲットＮの良否判定を自動で行うことができる。この場合、サイクルタイムの短縮が図られ、製造コストを低減できる。 The quality evaluation of the nugget N as described above may be performed in an inspection process provided separately from the indirect spot welding process, or may be performed in the indirect spot welding process. In the latter case, for example, calculation of the heat generation density D and determination of the quality of the nugget N can be automatically performed simultaneously with the completion of the indirect spot welding. In this case, the cycle time can be shortened, and the manufacturing cost can be reduced.

本発明は、上記の実施形態に限られない。例えば、上記の実施形態では、接合点の品質に寄与するパラメータが発熱密度Ｄである場合を示したが、これに限られない。例えば、このようなパラメータとして、金属板同士の接触面積Ｓ、両電極１０，２０間の電圧Ｖ、両電極１０，２０間の通電経路の抵抗値Ｒ、あるいは金属板同士の接触部における電流密度（＝Ｉ／Ｓ）等を使用することができる。 The invention is not limited to the above embodiments. For example, in the above embodiment, the parameter that contributes to the quality of the junction is the heat density D, but the present invention is not limited to this. For example, such parameters include the contact area S between the metal plates, the voltage V between the electrodes 10 and 20, the resistance value R of the current path between the electrodes 10 and 20, or the current density at the contact portion between the metal plates. (=I/S) etc. can be used.

また、本発明に係る評価方法は、インダイレクトスポット溶接の接合点に限らず、ダイレクトスポット溶接やシリーズ溶接等の他のスポット溶接の接合点の評価に適用することができる。 In addition, the evaluation method according to the present invention can be applied not only to the joint points of indirect spot welding, but also to the evaluation of joint points of other spot welding such as direct spot welding and series welding.

１-３ 金属板
１０ 溶接電極
２０ アース電極
１００ ワーク
Ｎ ナゲット（接合点）
Ｐ 接合予定部
Ｑ１，Ｑ２ 既接合点 1-3 Metal plate 10 Welding electrode 20 Earth electrode 100 Workpiece N Nugget (joint point)
P Parts to be welded Q1, Q2 Already welded points

Claims (1)

重ね合わせた複数の金属板に一対の電極を当接させた状態で、前記一対の電極間に通電することにより前記複数の金属板を接合するスポット溶接において、接合点の品質を評価するための方法であって、
前記一対の電極間に通電しながら、両電極間の電流値Ｉ、電圧Ｖ、及び金属板同士の接触面積Ｓを測定し、これらから発熱密度Ｄ＝Ｖ・Ｉ／Ｓを算出する工程と、
前記一対の電極間に通電する期間を複数の区間に分け、各区間の前記発熱密度Ｄと接合点の品質との相関を調べる工程と、
各区間の前記発熱密度Ｄと接合点の品質との相関を考慮して、各区間の前記発熱密度Ｄを用いた評価式を作成する工程と、
前記評価式を用いて接合点の品質を評価する工程とを有するスポット溶接の接合点の評価方法。 In spot welding that joins the plurality of metal plates by energizing between the pair of electrodes with a pair of electrodes in contact with the plurality of overlapping metal plates, to evaluate the quality of the joint point. a method,
A step of measuring the current value I between the electrodes, the voltage V, and the contact area S between the metal plates while passing current between the pair of electrodes, and calculating the heat generation density D = V I / S from these ;
a step of dividing the period in which the pair of electrodes is energized into a plurality of sections and examining the correlation between the heat generation density D and the quality of the junction in each section;
A step of creating an evaluation formula using the heat generation density D of each section in consideration of the correlation between the heat generation density D of each section and the quality of the junction ;
and evaluating the quality of the joint using the evaluation formula.
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JP2010214380A (en) 2009-03-13 2010-09-30 Osaka Univ Real-time welding quality determination apparatus and determination method
JP2012076146A (en) 2010-09-07 2012-04-19 Sumitomo Metal Ind Ltd Device and method for determining quality of welding in real time

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JP2010214380A (en) 2009-03-13 2010-09-30 Osaka Univ Real-time welding quality determination apparatus and determination method
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