JP2017177112A - Manufacturing method for spot-welded product and manufacturing device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spot-welding technique for performing appropriate nugget formation.SOLUTION: A manufacturing method for a spot-welded product using a gun constituted of a pair of a first electrode and a second electrode, comprises: (i) a step for providing a laminate to be welded by laminating at least a part of two plates to be welded; (ii) a step for sandwiching the laminate to be welded between the first electrode and the second electrode; and (iii) a step for energizing between the first electrode and second electrode while pressing the laminate to be welded, with the first electrode and the second electrode. Since the laminate to be welded has at least two plates to be welded having respective plate thicknesses different from each other, the welding gun to be used comprises the first electrode and the second electrode having respective electric resistance different from each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to spot welding. More specifically, the present invention relates to a method of manufacturing a spot welded product by resistance spot welding in which welded plates such as stacked steel plates are melted and joined by electric resistance heat generation, and for manufacturing such a spot welded product. Also related to manufacturing equipment.

  An automobile body is generally configured by welding steel plates together. For such welding, spot welding has been used more frequently than before. Taking the production of one automobile as an example, it is said that 90% or more of the parts to be joined are joined by spot welding.

  In spot welding, resistance heat is generated by locally energizing the stacked steel plates between the electrodes. Since the steel plates are melted by the resistance heat generation, the steel plates are finally joined due to the melting. More specifically, in spot welding, a welding gun having a pair of electrodes is generally used. A current is passed between the electrodes while sandwiching the steel plates overlapped by the pair of electrodes and applying pressure. As a result, resistance heat is generated in the steel sheet, and the steel sheet is locally melted, so that the portion is finally cooled and solidified to form a dotted weld.

  A spot weld formed by spot welding is generally referred to as a “nugget”. Such a nugget corresponds to a portion where the melted portion of the steel plate due to resistance heat generation is cooled and solidified, and the presence of this nugget joins the steel plates as desired to obtain a spot welded product.

JP 2001-179464 A

  The inventors of the present application have noticed a problem associated with spot welding nugget formation, and have found it necessary to take countermeasures therefor.

  Specifically, the present inventors have found that there are the following problems. In spot welding, it is necessary to form the nugget so as to reach the mating surfaces of the steel plates. However, depending on the thickness of the steel plates, the nuggets may not be suitably formed on the mating surfaces. Although not bound by a specific theory, this is considered to be due to the fact that heat generation / melting is started from the center of the cross section of the steel plates stacked on each other at the spot welding spot. In other words, when spot welding is performed by superimposing “thick plate” and “thin plate” steel plates with different plate thicknesses, the plate is thinner than the melt diameter on the thick plate side due to the size of the molten part growing from the “cross-sectional center”. As a result, the nugget may not be suitably formed on the mating surface of the thick plate and the thin plate (see FIGS. 11A and 11B). Although it is possible to increase the heat generation amount by adjusting the pressure, current value or energization time so that the nugget reaches the mating surface, this will make it easier for spatter to occur, resulting in strength quality due to variations in the nugget. In addition to the above-mentioned effects, it is easy to cause deterioration in quality in terms of appearance, such as welding marks becoming deeper than necessary and the frequency of occurrence of pinholes increasing.

  The present invention has been made in view of such circumstances. That is, the main object of the present invention is to provide a spot welding technique that contributes to particularly suitable nugget formation.

  The inventor of the present application tried to achieve the above object by addressing in a new direction instead of responding on the extension of the prior art. As a result, the present invention has led to an invention of a method for manufacturing a spot welded article in which the above-mentioned main object has been achieved, and an invention of a manufacturing apparatus for carrying out the invention.

The invention of the manufacturing method of the present invention relates to a method of manufacturing a spot welded article using a welding gun composed of a pair of first electrode and second electrode,
(I) a step of obtaining a welded laminate by at least partially overlapping at least two welded plates;
(Ii) sandwiching the welded laminate with the first electrode and the second electrode, and (iii) between the first electrode and the second electrode while pressurizing the welded laminate with the first electrode and the second electrode Comprising a step of conducting electricity,
In the welded laminate, at least two welded plates have different plate thicknesses, and welding guns having different current resistances of the first electrode and the second electrode are used.

  Moreover, the invention of the manufacturing apparatus of the present invention relates to an apparatus for manufacturing a spot welded object composed of welded plates having different plate thicknesses. Such a manufacturing apparatus of the present invention has at least a welding gun composed of a first electrode and a second electrode forming a pair, and the conduction resistances of the first electrode and the second electrode are different from each other. .

  In the present invention, it is possible to favorably shift the melted part (particularly the “melting start point”) during spot welding. Accordingly, the nuggets can be suitably formed so as to extend to their mating surfaces even if the plates have different thicknesses. In particular, the nugget can be suitably formed so as to extend to the mating surfaces of different plate thicknesses while also taking into account the appearance of the weldment such as weld marks.

Sectional drawing showing the concept of the present invention (FIG. 1 (a): two welded plates, FIG. 1 (b): three welded plates) Sectional view and perspective view showing the concept of the present invention Sectional drawing which showed the aspect at the time of electricity supply of the manufacturing method of this invention typically (FIG.3 (a): Two to-be-welded plates, FIG.3 (b): Three to-be-welded plates) Sectional drawing schematically showing the melted part / nugget formed in the welded laminate Sectional drawing (FIG. 5 (a): process (i), FIG.5 (b): process (ii), FIG.5 (c): process (iii)) which showed the time-dependent aspect of the manufacturing method of this invention. )) Sectional drawing which showed the aspect of the electrode tip shape which is easy to sink into a to-be-welded laminated body Sectional drawing which showed the aspect of the electrode tip shape which is hard to dig into a to-be-welded laminated body Sectional drawing which showed the aspect of the manufacturing apparatus of this invention typically Graph showing the result of [Nugget Ratio Confirmation Test] Results of [Preferred electrode truncated surface diameter based on reduction of indentation] Sectional drawing which showed the concept of a prior art (FIG. 11 (a): Two to-be-welded plates, FIG.11 (b): Three to-be-welded plates)

  Hereinafter, a “spot welded article manufacturing method” and a “spot welded article manufacturing apparatus” according to an embodiment of the present invention will be described in more detail with reference to the drawings. Various elements in the drawings are merely schematically and exemplarily shown for understanding of the present invention, and the appearance, dimensional ratio, and the like may be different from the actual ones.

  In the present specification, the term “spot weld” refers to a weld obtained by so-called spot welding (resistance spot welding), that is, welded to each other using heat generated by electric resistance (ie, Joule heat). ing. Accordingly, in the present invention, the “spot welded product” means, in a broad sense, at least two plates to be welded that are spot-welded using a welding gun. It means “at least two plates to be welded having different plate thicknesses” spot-welded by a welding gun having one electrode and a second electrode.

  The “up and down” direction described directly or indirectly in the present specification is based on the superposition of the welded plates spot welded at the time of manufacture, and the direction in which at least two welded plates are superimposed ( That is, the lamination direction of the laminate to be welded obtained by polymerization corresponds to the vertical direction. In a typical aspect according to the present invention, the plates to be welded are often overlapped in a horizontal state as a whole. Therefore, typically, “vertical downward” corresponds to “downward”, and the opposite side is Corresponds to “upward”.

[Production method of the present invention]
The manufacturing method according to the present invention is a method for manufacturing a spot welded article using a welding gun including a first electrode and a second electrode forming a pair. Specifically, the method for producing a spot welded product of the present invention includes:
(I) a step of at least partially overlapping at least two plates to be welded to obtain a welded laminate,
(Ii) sandwiching the welded laminate with the first electrode and the second electrode, and (iii) between the first electrode and the second electrode while pressurizing the welded laminate with the first electrode and the second electrode Comprising a step of conducting electricity,
In the laminate to be welded, welding guns are used in which the plate thicknesses of at least two to-be-welded plates are different from each other and the energization resistances of the first electrode and the second electrode are different from each other.

  In the manufacturing method of the present invention, when a welded laminate comprising welded plates having different plate thicknesses is spot welded, the first electrode and the second electrode having different energization resistances in view of the difference in such plate thicknesses. Use a welding gun consisting of: Due to such characteristics, even a welded laminate comprising welded plates having different thicknesses can be suitably spot welded. More specifically, the nugget can be suitably formed up to the mating surfaces (interfaces) of the welded plates having different plate thicknesses.

  In order to suitably form the nugget, the production method of the present invention controls the formation position of the melted portion generated in the welded laminate. In particular, at the time of energization in the step (iii) of the present invention, the formation start position of the melted portion generated in the welded laminate is controlled. In other words, as shown in FIGS. 1 (a) and 1 (b), the first electrode 12 and the second electrode 16 melt on the electrode side having a relatively large conduction resistance due to different conduction resistances. The part 70 is shifted.

  As described with reference to FIGS. 11 (a) and 11 (b), in the conventional technique, when “thick plate” and “thin plate” and spot-welded steel plates having different thicknesses are overlapped and spot welded, “cross-sectional center” Therefore, the melt diameter on the thin plate side becomes smaller than the melt diameter on the thick plate side due to the melted portion growing from the thick plate side, and there is a possibility that the melt portion does not reach the thin plate side sufficiently. That is, the nugget may not be suitably formed on the mating surface of the thick plate and the thin plate. Although it may be possible to increase the heat generation by adjusting the applied pressure, current value, or energization time so that the nugget is suitably applied to the mating surfaces, this will make it easier for spatter to occur and improve the strength quality due to variations in the nugget. In addition to the above-mentioned effects, it is easy to cause deterioration in quality in terms of appearance, such as welding marks becoming deeper than necessary and the frequency of occurrence of pinholes increasing.

  In the present invention, a welding gun comprising a first electrode and a second electrode having different energization resistances is used, thereby shifting the melted portion to the electrode side having a relatively large energization resistance during energization in the step (iii). ing. Particularly preferably, by using the first electrode 12 and the second electrode 16 having such different energization resistances, the fusion zone 70 is provided so as to sufficiently reach the mating surface 55 of the welded plates having different plate thicknesses. Shift (see FIGS. 1A and 1B). Thereby, a nugget is suitably formed on the mating surface 55 of the thin plate 23 and the thick plate 27 (27A, 27B). In particular, the nugget is suitably formed on the mating surface 55 of the thick plate 23 and the thin plate 27 (27A, 27B) in a state where the indentation or the like is suppressed.

  As used herein, “different energization resistances” means that the energization resistances at the time of spot welding of the first electrode and the second electrode forming a pair of welding guns are different from each other. Therefore, “the energization resistances are different from each other” in the present invention broadly means that the difficulty of the energization current flow in the step (iii) is intentionally changed between the first electrode and the second electrode. In a narrow sense, it means that the electric resistance is different between the first electrode and the second electrode in the current path. This is because, in particular, the electrical resistance is different between the first electrode and the second electrode in the energization path when the spot welding conditions such as energization current, energization time, and electrode pressing force are substantially the same. It means that. Although it is only an example to the last, in this invention, the electrical resistance value (energization resistance value) in the electrode front end surface which contacts a to-be-welded laminated body at the time of spot welding, for example is mutually different by the 1st electrode and the 2nd electrode. (In the case of a “truncated” electrode described later, the electric resistance value (energization resistance value) on the truncated surface may be different between the first electrode and the second electrode).

  The materials for the first electrode and the second electrode of the welding gun are generally required to have good thermal conductivity and electrical conductivity, and more preferably high temperature deformation resistance and wear resistance. Therefore, the material of the first electrode and the second electrode can generally be copper and / or a copper alloy. Although it does not necessarily limit, hard copper, cadmium copper, zirconium copper, chromium copper, chromium zirconium copper, low beryllium copper, high beryllium copper, alumina dispersion copper (alumina dispersion strengthened copper), etc. are the first electrode and the second electrode. It can be specifically used as a material for the above.

  In the present invention, “different energization resistances” are preferably achieved by a difference in electrode material or by a difference in electrode tip shape. That is, it is preferable to change the material between the pair of first electrode and second electrode constituting the welding gun and / or change the electrode tip shape.

  When based on the difference in electrode material, the material is changed between one and the other of the first electrode and the second electrode. Specifically, “conductivity (or electrical resistivity) of one electrode material of the first electrode and the second electrode” and “conductivity (or electrical resistivity) of the other electrode material of the first electrode and the second electrode” Are preferably different from each other. For illustration purposes only, one electrode material of the first electrode and the second electrode includes “alumina-dispersed copper”, and the other electrode material of the first electrode and the second electrode is “chrome copper” or “Chromium zirconium copper” may be used.

  On the other hand, when based on the difference in electrode tip shape, the electrode tip shape is changed between one of the first electrode and the second electrode and the other. Specifically, “one electrode cutting edge portion / electrode cutting edge surface of one of the first electrode and second electrode” and “the other electrode cutting edge portion / electrode cutting edge surface of the first electrode and the second electrode” are It is preferable to make them different from each other.

In the welding gun, when each of the pair of first electrode 12 and second electrode 16 has a truncated shape, the truncated area of the first electrode 12 and the truncated area of the second electrode 16 are preferably different from each other (see FIG. 2). This means that one of the truncated areas of the first electrode and the second electrode is larger or smaller than the other. In other words, the truncated area of the first electrode 12 and S _{first electrode} and the truncated area of the second electrode 16 and S _{second electrode,} S _{the first electrode>} S _{second electrode} or S _{first electrode} <S _No. It is preferable that there are _{two electrodes} (that is, S _{first electrode} = S _{second electrode} or S _{first electrode≈S second electrode} is not satisfied).

For illustration purposes only, one of the truncated areas of the first electrode and the second electrode may be about 1.3 to 7.5 times the other. That is, in a preferable aspect, the ratio of the relatively large truncated area to the relatively small truncated area is 1.3 to 7 with respect to the truncated area ratio between the first electrode 12 and the second electrode 16. .5 or so. This is because when the truncated shape of each of the first electrode and the second electrode is a truncated cone shape (that is, when the tip of the electrode has a truncated cone shape), the first electrode and the second electrode are truncated. This corresponds to a diameter ratio of the head surface (that is, a circular truncated surface) of about 1.16 to about 2.67. In other words, the ratio of “relatively large diameter D _{large diameter} ” to “relatively small diameter D _{small diameter} ” with respect to the circular truncated surfaces of the first electrode 12 and the second electrode 16 as shown in FIG. That is, the value of D _{large diameter} / D _{small diameter} is preferably about 1.16 to about 2.67.

  In this way, when the truncated area (truncated surface diameter) is different, the “electrode with a small truncated area (truncated surface diameter)” has a higher conduction resistance than the “electrode with a large truncated area (truncated surface diameter)”. Can be bigger. In the manufacturing method of the present invention, the melting start point moves closer to the electrode side having a larger energization resistance among the two electrodes forming a pair, that is, the melting start point in a direction away from the electrode side having a smaller energization resistance. Will move (see FIGS. 1 (a) and 1 (b) and FIGS. 3 (a) and 3 (b)). Although not limited by a specific theory, this is because the peak temperature occurs in the temperature distribution during steady energization as shown in FIGS. 3 (a) and 3 (b) (hereinafter referred to as “peak temperature point”). This is because the peak temperature point shifts to the electrode side having a larger energization resistance, particularly from the intermediate point between the first electrode and the second electrode.

  Accordingly, as shown in FIGS. 1 (a) and 1 (b), when spot-welding a laminate 50 ′ to be welded, which is a welded plate different from “thin plate 23” and “thick plate 27 (27A, 27B)”, It is preferable that the electrode 12 having a larger energization resistance is positioned on the thin plate 23 side while the electrode 16 having a smaller energization resistance is positioned on the thick plate 27 side to perform energization. In this case, the melting start point moves to the thin plate 23 side, and as a result, the nugget can be suitably formed up to the mating surfaces 55 of the welded plates having different plate thicknesses from the “thin plate” and the “thick plate”. . In other words, among the first electrode and the second electrode, an electrode having a relatively large energization resistance is disposed in the vicinity of a welded plate having a relatively small plate thickness, while an electrode having a relatively small energization resistance is disposed on the plate. If it arrange | positions in the proximal of the to-be-welded board with comparatively large thickness, a nugget can be suitably formed even in the mutual mating surface of the to-be-welded board from which board thickness differs. By the way, if an electrode pair with the same energization resistance is used, the nugget formation can be made longer in order to form the nugget up to `` the mutual mating surfaces of the welded plates with different plate thicknesses ''. Is likely to occur, which may lead to deterioration of the quality of the welded material in terms of welding strength and appearance. In this regard, according to the present invention, the nugget can be formed up to “the mating surfaces of the plates to be welded having different plate thicknesses” under a constant energization current in a state in which the occurrence of such an undesirable spatter is further suppressed.

  The technical idea of the present invention is to use welding guns with different resistance values of opposing electrodes (for example, applying upper and lower atypical electrodes), and to-be-welded plates with different electrical thicknesses (or electrical conductivity) but different plate thicknesses. When spot-welding each other, the melting position in the thickness direction of the laminate to be welded is shifted to the electrode side having a large energization resistance value. Although not bound by a specific theory, the relationship between the volume and the resistance value in the current path is expressed by R = ρ × L / A (R: resistance value, ρ: electrical resistivity, L: current path length, A: If the section is set in the thickness direction in the cross section of the laminate to be welded, the amount of heat generated in each section may be larger on the side where the current path diameter is smaller and smaller on the side where the current path diameter is larger. Presumed to be related. The present invention can be particularly advantageous when welding a plurality of plates to be welded (for example, three or more plates to be welded). This is because the nugget can be suitably formed up to the mating surfaces of such a plurality of plates to be welded, and a desired weld can be obtained. For example, the number of welded plates constituting the welded laminate may be three, and at least two of them may have different thicknesses. Even in such a case, the nugget can be suitably formed up to the mating surfaces of the welded plates, and a desired weld can be obtained.

  This will be described based on a more specific aspect. According to the present invention, as shown in FIG. 4, the nuggets can be suitably formed on the mating surfaces of the welded plates even when the thicknesses of the three welded plates are different. it can. As shown in FIG. 4, in the case of a welded laminate 50 ′ composed of a thin plate 23 and two types of thick plates 27 </ b> A and 27 </ b> B, an energization resistance is relative to the thin plate 23 side as illustrated. It is preferable that the large electrode 12 is disposed on the thick plate 27A, 27B side, and the electrode 16 having a relatively small conduction resistance is disposed on the thick plate 27A, 27B side. Thereby, the melting start point can be moved to the thin plate 23 side when energized, and the nugget 70 can be suitably formed up to the mating surfaces of the welded plates.

“Nugget is suitably formed” as used in this specification indicates that the nugget diameter at the mating surface between the welded plates is within a predetermined range. This is only an example, but taking the case of three welded plates as an example means that the nugget diameters of the two mating surfaces are not significantly different from each other. This means that the ratio (L _{thin plate} / L _{thick plate} ) of the nugget diameter L _thin plate on the mating surface on the thin plate side to the nugget diameter L _thick plate on the surface is in the range of 0.8 to 1.1 (each electrode is (See FIG. 4 where a cross-sectional view cut in a half-divided plane is shown).

  Hereinafter, a manufacturing method according to an embodiment of the present invention will be described over time with reference to FIG.

  In carrying out the present invention, step (i) is first carried out. That is, at least two plates to be welded are at least partially overlapped to obtain a welded laminate. Specifically, as shown in FIG. 5A, for example, when spot welding a thin plate 23 and two kinds of thick plates 27A and 27B as three welded plates, they are overlapped so that they are stacked on each other. A welded laminate 50 ′ is obtained. In the illustrated embodiment, the thin plate 23 and the two types of thick plates 27A and 27B are overlapped with each other so that the thin plate 23 is positioned on the outer side to obtain a welded laminate 50 '.

  The “welded plate” in this specification refers to a plate-like member to be spot-welded, and particularly refers to plate-like members having different plate thicknesses. In spot welding, since it is necessary to secure a current path by contact between the plate to be welded and the electrode, it is preferable that the plate to be welded has electrical conductivity. Therefore, for example, a plate-like member comprising a metal material It is preferable that In one preferable embodiment, the welded plate is a metal plate. For example, when spot welding in automobile manufacture is taken as an example, the welded plate may correspond to a steel plate. The steel material itself of the steel plate is not particularly limited, and may be carbon steel, alloy steel, nickel chromium steel, nickel chromium molybdenum steel, chromium steel, chromium molybdenum steel, manganese steel, or the like. In terms of typical steel plate types, steel plates as welded plates include cold rolled steel plates (SPC materials), hot rolled steel plates, hot rolled mild steel plates (SPH materials), electrogalvanized steel plates (SEC materials). , SEH material), hot dip galvanized steel plate (SGC material, SGH material), hot dip galvanized steel plate, painted electroplated steel plate, stainless steel plate (SUS material), aluminum plate, copper plate and the like.

  In the present invention, at least two welded plates constituting the welded laminate have different plate thicknesses. For example, when two welded plates are subjected to spot welding, one welded plate is a “thin plate” and the other welded plate is a “thick plate”. In addition, when three welded plates are subjected to spot welding, one of them is a “thin plate” and the other two welded plates may be “thick plates” (the two thick plates are The thickness may be different from each other or the same. This is merely an example, but when the thickness of one welded plate is at least about 10% smaller than the thickness of the other welded plate (“about 10%” is the thickness of “one welded plate”). Such “one plate to be welded” may be regarded as “thin plate”, and “the other plate to be welded” may be regarded as “thick plate”. Moreover, although it is only one of the other judgment indexes, for example, a plate having a thickness less than 1.0 mm is regarded as a “thin plate” on the basis of a plate thickness of 1.0 mm, and a plate having a thickness greater than that is considered. May be regarded as a “thick plate”. For example, one case where three welded plates are subjected to spot welding is illustrated. For example, one of the three welded plates has a plate thickness of about 0.7 mm as a “thin plate”, and the other two The to-be-welded plate has a plate thickness of about 1.6 mm and a plate thickness of about 1.2 mm as a “thick plate”.

  Subsequent to step (i), step (ii) is performed. That is, the welded laminate 50 ′ is sandwiched between the first electrode 12 and the second electrode 16. As shown in FIG. 5B, it is preferable to sandwich the welded laminate with a welding gun so that the first electrode 12 and the second electrode 16 abut against the opposing outer surfaces of the welded laminate 50 '. If it does in this way, an energization way can be secured suitably. That is, a suitable energization path is formed in the next step (iii), and Joule heat can be generated in the welded laminate. As can be seen from the illustrated embodiment, in the step (ii), it is preferable that the first electrode 12 and the second electrode 16 have a positional relationship such that they face each other via the welded laminate 50 ′ ( That is, it is preferable that the axis of the first electrode and the axis of the second electrode are aligned with each other, more specifically, they are aligned.

  When spot-welding a laminate to be welded consisting of a plate to be welded different from “thin plate 23” and “thick plate 27”, an electrode having a higher current resistance is positioned on the thin plate side, while an electrode having a lower current resistance on the thick plate side. Is preferably located. As shown in FIG. 5B, in the case where the thin plate 23 and the two types of thick plates 27 (27A, 27B) are overlapped with each other so that the thin plate 23 is positioned outside, the thin plate 23 is formed. It is preferable to position an electrode having a smaller energization resistance so as to be in contact with the thick plate 27 (in the illustrated embodiment, so as to be in contact with the thick plate 27A).

  For example, in the welding gun, each of the first electrode and the second electrode has a truncated shape, and when the truncated area of the first electrode and the truncated area of the second electrode are different from each other, the first electrode and the second electrode Among them, an electrode having a relatively small truncated area is positioned on the thin plate side (positioned so as to be in contact with the thin plate 23 in the above three welded plates), and an electrode having a relatively large truncated area is positioned on the thick plate side ( The above three welded plates are preferably positioned so as to contact the thick plate 27). This is because, when the truncated shape of the first electrode and the second electrode is a truncated conical shape, an electrode having a relatively small truncated surface diameter is positioned on the thin plate side among the first electrode and the second electrode (see above). In the three to-be-welded plates, the first electrode 12 is positioned so as to be in contact with the thin plate 23), and the electrode having a relatively large truncated surface is positioned on the thick plate side (in the above three to-be-welded plates, the thick plate It is preferable that the second electrode 16 is positioned so as to be in contact with 27). The truncated shapes of the first electrode and the second electrode are not particularly limited to a truncated cone shape, and may be, for example, a truncated quadrangular pyramid shape or a truncated cylindrical shape. Further, such a welding gun electrode is not particularly limited to an “integrated type” in which the electrode tip and the electrode body are integrated, and may be a “cap type” in which the electrode tip can be replaced. . In the case of the “cap type”, it is possible to reduce the number of discarded parts when the electrode tip is consumed.

  Subsequent to step (ii), step (iii) is performed. That is, the first electrode 12 and the second electrode 16 are energized between the first electrode 12 and the second electrode 16 while pressurizing the welded laminate 50 ′. Thereby, Joule heat can be generated in the welded laminate 50 ′, and the melted portion 70 can be formed (see FIG. 5C).

  The current value, energization time, applied pressure, and the like during energization are not particularly limited as long as they contribute to suitable nugget formation, and may be employed, for example, in conventional spot welding. For example, the current value of energization may be in the range of 5 kA to 30 kA. Such an energizing current may be either an alternating current or a direct current. That is, the power source of the energizing current may be either an AC type (for example, a single-phase AC type or a three-phase low frequency type) or a DC type (for example, a single-phase rectification type, a three-phase rectification type, or an inverter type). . Similarly, although it is only an illustration, the pressure (pressing force) applied to the welded laminate by the electrode may be, for example, about 1 to 20 kN. Typically, the stronger the room temperature strength of the welded plate / welded laminate, and the greater the coefficient of thermal expansion, the greater the applied pressure. Furthermore, it is preferable to subject each of the first electrode and the second electrode to water cooling when energizing. More specifically, it is preferable to flow cooling water inside each of the first electrode 12 and the second electrode 16. This is because Joule heat can be generated in the welded laminate more preferably, and a melted portion is easily formed.

  At the time of energization in the step (iii), the peak temperature point is preferably deviated from an intermediate point between the first electrode and the second electrode in the temperature distribution at the time of steady energization, and can be shifted particularly to the electrode side having a larger energization resistance (FIG. 3). (See (a) and 3 (b)). This means that the formation start position of the melted portion generated in the laminate to be welded in step (iii) is controlled. More specifically, the first electrode and the second electrode are melted toward the electrode side having a relatively large energization resistance due to different energization resistances (to approach the first electrode 12 in the illustrated embodiment). The part 70 shifts (see FIG. 5C). Thus, the nugget is suitably formed even on the mating surfaces of the welded plates having different thicknesses from the “thin plate” and the “thick plate”. As described above, when the thin plate 23 and the two kinds of thick plates 27 (27A, 27B) are overlapped with each other so that the thin plate 23 is located outside, the welded laminate 50 ′ is formed on the thin plate 23 side. Therefore, the nugget can be suitably formed up to the mating surface of the welded plate located on the thin plate side (that is, the interface between the thin plate 23 and the thick plate 27). In addition, when energization is continued, the molten part grows, but excessive growth leads to spatter generation, so the molten part suitably reaches the mating surface of the welded plates located on the thin plate side. It is preferable to end the energization.

  As can be seen from the process described above, one preferred aspect of the present invention is to devise the shape of the electrode tip of the welding gun, thereby changing the starting point of Joule heat / melting according to the plate assembly to balance the melt diameter. They are optimized, and are preferably suppressed so as not to be particularly inconvenient in consideration of appearance problems such as welding marks.

  In the above, typical embodiments have been described for understanding the present invention. However, the manufacturing method of the present invention can be embodied in various forms.

(Suitable electrode truncated surface diameter based on indentation reduction viewpoint)
When the truncated shape of the first electrode and the second electrode of the welding gun is a truncated cone shape, the truncated surfaces of the first electrode and the second electrode can be circular (see FIG. 2). That is, the first electrode and the second electrode have a circular truncated surface. In such a case, it is preferable that the diameter dimension of the circular truncated surface be different between the first electrode and the second electrode, and it is preferable that one electrode has a larger or smaller diameter dimension than the other electrode.

  For example, when the first electrode has a relatively small diameter and the second electrode has a relatively large diameter, the diameter of the circular truncated surface of the first electrode is about 6 mm (φ6). In contrast, the diameter of the circular truncated surface of the second electrode is preferably about 7 mm (φ7) or more, more preferably about 7 mm to about 16 mm (φ7 to φ16), for example, about 8 mm to about 16 mm ( More preferably, it is φ8 to φ16). Specifically, the electrode body itself may be the same size for both the first electrode and the second electrode. For example, the diameter of the electrode body is 16 mm (φ16) to 20 mm (φ20) for both electrodes. In some cases, the diameter of the circular truncated surface of the first electrode is preferably about 6 mm (φ6), and the diameter of the circular truncated surface of the second electrode is preferably about 7 mm to about 16 mm (φ7 to φ16). ), For example, about 8 mm to about 16 mm (φ8 to φ16). In such an embodiment, not only can nuggets be suitably formed on the mating surfaces of the welded plates having different plate thicknesses, but also indentations (local surface of the plate formed due to the molten metal being pushed by the electrodes) Welds with effectively reduced dents) (see examples below). In particular, since an electrode having a large diameter size has a large effect of suppressing indentation, the electrode having a relatively large diameter size (second electrode 16 in FIG. 2) is positioned on the outer surface of the laminate to be welded. The appearance of things can be improved more effectively. That is, it is possible to perform spot welding more suitable not only in terms of bonding strength but also in terms of appearance.

  In the prior art, a copper flat plate (hereinafter also referred to as “copper plate”) may be used to reduce the indentation. Specifically, spot welding may be performed by sandwiching a copper plate between the electrode and the laminate to be welded. When this copper plate is used, there is a risk of welding and appearance quality deterioration due to the surface state of the copper plate (such as the wear state of the copper plate). Therefore, the copper plate surface is periodically polished or caused by the copper plate in the finishing process. It is necessary to confirm whether there is any deterioration in quality, and as a result, the line operation rate may be reduced. In addition, there may be a case where the copper plate can be used only at a specific location due to its shape (for example, it can be used only at a specific location within the body jig). In this regard, according to the present invention, when the diameter of the circular truncated surface of at least one of the electrodes is about 7 mm (φ7) or more, preferably about 8 mm (φ8) or more, a weld with reduced indentation can be obtained. Therefore, the need for a copper plate is reduced, and as a result, efficient spot welding can be performed.

(Preferred shape of electrode shoulder)
The aspect of “the preferred shape of the electrode shoulder” is based on the shape of the electrode tip that can suppress the welding trace particularly efficiently. In such an embodiment, the boundary between the electrode tip shoulder and the truncated surface is not angular for at least one of the first electrode and the second electrode.

  For example, in the electrode tip shape shown in FIG. 6, when the electrode is in an energized state in contact with the outer surface of the laminate to be welded “at an angle” (that is, the electrode shaft and the outer surface of the laminate to be welded) When the angle formed between the electrodes is not a right angle), the electrode is likely to be embedded in the welded laminate, and as a result, undesired welding marks may be generated. This is a matter that is preferably taken into consideration in a truncated electrode whose tip is “planar” (in other words, when a truncated electrode is used, the contact state between the electrode and the laminate to be welded varies. Can be said to be easily affected by

  In this regard, when the electrode tip shape shown in FIG. 7 is used according to the present invention, welding with reduced generation of the “undesired welding traces” becomes possible. Specifically, in the electrode tip shape shown in FIG. 7, the boundary between the electrode tip shoulder and the truncated surface is not square in at least one of the first electrode and the second electrode, that is, the electrode tip shoulder. And the truncated surface are continuous so as to form a smooth surface. Therefore, the electrode was brought into contact with the outer surface of the laminate to be welded “angled” (that is, the angle formed between the electrode axis and the outer surface of the laminate to be welded was not a right angle). However, it becomes difficult for the electrode to sink into the welded laminate, and as a result, undesired welding marks can be suppressed. This means that even in the case of a truncated electrode in the present invention, it is less likely to be affected by variations in the contact state between the electrode and the welded laminate. In addition, since welding marks can cause rust under special circumstances, the electrode tip shape shown in FIG. 7 can lead to rust reduction of the welded product.

  The electrode tip shape of FIG. 7 in the present invention will be described in detail. In the electrode of FIG. 7, the boundary between the electrode tip shoulder and the truncated surface is not angular, that is, the electrode tip shoulder and the truncated surface are continuous so as to form a smooth surface. This means that the electrode has a contour shape as shown in FIG. 7 when viewed in a cross section (electrode tip cross section) divided into two along the axial direction of the electrode. Specifically, it is preferable that the center of the arc that forms the shoulder contour of the electrode tip is located on the “line parallel to the electrode axis through the truncated surface edge (the outermost periphery of the truncated surface)”, Furthermore, it is preferable that the central angle of the circular arc that forms such a shoulder contour is 90 ° (see the upper diagram in FIG. 7). On the other hand, in the electrode tip shape of FIG. 6 (that is, the “easy shape”), the center of the arc that forms the shoulder contour of the electrode tip is located on the electrode axis. It is not located on the “line passing through and parallel to the electrode axis”, and the central angle of the arc forming the shoulder contour is not 90 ° (see the upper diagram in FIG. 6).

  Although it is only an example to the last, it explains in full detail by a specific dimension. In the present invention, for example, when the diameter of the electrode body is about 16 mm (φ16) and the truncated surface diameter is about 8 mm, the R of the electrode tip shoulder may be about 4 mm. Here, as shown in FIG. 7, the center of the arc that forms the contour of the electrode tip shoulder is located on the “line that is parallel to the electrode axis through the end of the truncated surface” and the center of the arc. The angle is about 90 °. In this example, the truncated surface diameter is about 8 mm. However, if the truncated surface diameter is larger than that, R (and the electrode body) of the shoulder portion of the electrode tip may be increased accordingly. Generally preferred. Therefore, considering such a large truncated face diameter, it can be said that R of the electrode shoulder is preferably 4 mm or more.

[Production apparatus of the present invention]
Next, the manufacturing apparatus of a spot weldment is demonstrated. The manufacturing apparatus of this invention is an apparatus suitable for manufacture of the above-mentioned spot weldment. That is, it is an apparatus for manufacturing a spot welded object composed of welded plates having different plate thicknesses. As shown in FIG. 8, the manufacturing apparatus includes at least a welding gun including a first electrode 12 and a second electrode 16 that form a pair, and the first electrode 12 and the second electrode 16 are energized. The resistances are different from each other.

  As used herein, “the energization resistances are different from each other” means, in a broad sense, that the difficulty of flowing the energization current is intentionally changed between the first electrode and the second electrode. In a narrow sense, it means that the electric resistance is different between the first electrode and the second electrode in the energization path. Here, in the manufacturing apparatus of the present invention, the material is changed between the first electrode and the second electrode of the welding gun and / or the electrode tip shape is changed (see “electrode tip in FIG. 8). "Aspects of different shapes" are specifically shown).

  In the manufacturing apparatus of the present invention, the opposing pair of electrodes of the welding gun have different energization resistance values, and when the welded plates having the same electrical resistivity but different plate thicknesses are spot-welded to each other, The position of the melted portion in the thickness direction of the welded laminate can be shifted to the electrode side having a large energization resistance value. Thereby, in the manufacturing apparatus of this invention, a nugget can be suitably formed even to the mutual mating surface of a several to-be-welded board, and a desired weldment can be obtained. For example, even when the number of plates to be welded constituting the welded laminate is three and at least two of the plates have different thicknesses, the nugget is suitably applied to the mating surfaces of the plates to be welded. The desired weldment can be obtained.

  The manufacturing apparatus of the present invention is used by being connected to a power source for energization between electrodes via a welded laminate. The power supply itself may be similar to that used in conventional spot welding equipment. That is, although not particularly limited, the power source of the manufacturing apparatus of the present invention may be either an AC type or a DC type. In the case of an AC type power supply, it may be a single phase AC type or a three phase low frequency type. The single-phase AC type uses a commercial frequency current. On the other hand, the three-phase low-frequency system is obtained by changing the commercial frequency current to a low-frequency current of, for example, about 10 to 20 Hz, thereby reducing the impedance of the circuit and facilitating the supply of a large current. In the case of a direct current type, it may be a single phase rectification type, a three phase rectification type, or an inverter type. The single-phase rectification type is a type in which a rectifier is inserted on the secondary side of a single-phase AC type welding machine, and can contribute to a reduction in input kVA. The three-phase rectification type is a three-phase full-wave rectification type that combines three single-phase rectification type power supplies or combines three individually, making large currents easier and reducing current pulsation. It can be effectively reduced. The inverter type converts the three-phase AC power source into DC, converts it into a medium frequency current of about 600 to 1000 Hz, for example, using a switching element, supplies it to a welding transformer, and rectifies it in a secondary circuit before welding. In this method, a direct current is supplied to the battery.

  The manufacturing apparatus of the present invention is particularly present in a gun electrode such that “the current-carrying resistances of the first electrode 12 and the second electrode 16 are different from each other”, and therefore the other parts are used in a conventional spot welding apparatus. (However, it should be noted that the manufacturing apparatus of the present invention is an apparatus for spot-welding plates to be welded with different plate thicknesses). In other words, the manufacturing apparatus of the present invention may be composed of a pressurizing / energizing unit, a power source unit, a power control unit, and cables for connection similar to those of a conventional spot welder, other than electrodes. In addition, the manufacturing apparatus of the present invention can be any one of “stationary spot welder”, “desktop spot welder”, “portable spot welder” or “multi-spot welder” for the device type as a whole. It may be a type.

  In the following, “electrodes having different energization resistances” which are features of the manufacturing apparatus of the present invention will be described in detail.

  The device of the present invention in which the difference in current resistance is achieved by “difference in electrode material” is, for example, “conductivity of one electrode material of the first electrode and the second electrode” and “first electrode and second electrode”. It preferably has welding guns that differ from each other in “conductivity of the other electrode material of the electrode”. Although it is only an example to the last, one of the first electrode and the second electrode is an electrode material including “alumina-dispersed copper”, and the other is an electrode material including “chromium copper” or “chromium zirconium copper”. It may consist of

  In addition, the apparatus of the present invention in which the difference between the energization resistances is achieved by the “difference in electrode tip shape” is such that one of the first electrode and the second electrode has a welding gun that is larger or smaller than the other. Preferably it has. In a preferred aspect, each of the first electrode and the second electrode has a truncated shape, and the truncated area of the first electrode and the truncated area of the second electrode are different from each other (that is, a flat electrode shape). In this case, the areas of the tip faces are different from each other).

For example, one of the truncated areas of the first electrode and the second electrode may be about 1.3 to 7.5 times the other. Here, in the manufacturing apparatus of the present invention, the truncated shape of the first electrode and the second electrode may be a truncated cone shape (see FIGS. 2 and 8). That is, the first electrode 12 and the second electrode 16 may have a shape obtained by cutting the most distal portion of the conical or columnar electrode along a plane parallel to the electrode radial direction. In such a case, it is preferable that the diameter ratio of the truncated surfaces (that is, circular truncated surfaces) of the first electrode 12 and the second electrode 16 is about 1.16 to about 2.67. More specifically, as shown in FIG. 2, the diameter of the first electrode 12 and the second electrode 16 on the side having a relatively large size relative to the _small diameter D on the side having a relatively small size among the circular truncated surfaces. It is preferable that the ratio of D _{large diameter} (that is, the value of D _{large diameter} / D _{small diameter} ) is about 1.16 to about 2.26. As a result, the peak temperature point is suitably shifted from the intermediate point between the first electrode and the second electrode in the temperature distribution at the time of steady energization, and the formation start position of the melted portion generated in the welded laminate is more preferably Can be controlled. That is, the nugget can be suitably formed up to the mating surfaces of the welded plates having different plate thicknesses.

  In the manufacturing apparatus of the present invention, the welding gun preferably has an electrode shape that can more effectively suppress welding marks. For example, it is preferable that at least one of the first electrode 12 and the second electrode 16 has an electrode tip shape as shown in FIG. That is, as explained in the above “preferred shape of the electrode shoulder”, the boundary between the electrode tip shoulder and the truncated surface is not angular, that is, the electrode tip shoulder and the truncated surface are smooth surfaces. It is preferable that the electrode is a continuous electrode. This results in an energized state where the electrode is in contact with the outer surface of the welded laminate so as to form an angle (ie, the angle formed by the electrode shaft and the outer surface of the welded laminate is not a right angle). Even so, it becomes difficult for the electrode to sink into the welded laminate, and as a result, the welding marks can be more effectively suppressed (see FIG. 7).

  Other details such as more detailed matters, further specific aspects, or aspects at the time of use of the electrodes in the production apparatus of the present invention have been described in the above [Production method of the present invention], so that duplication is avoided. Therefore, explanation is omitted.

  The embodiments of the present invention have been described above, but only typical examples within the scope of the present invention are shown. Therefore, it will be easily understood by those skilled in the art that the present invention is not limited to the above-described embodiment, and various modifications can be made.

  For example, in the above, description has been made centering on an aspect of obtaining a welded material by “resistance spot welding”, but the present invention is not limited to such an aspect. For example, “projection welding” where projections are provided on the welded portion of the surface of the welded plate, “seam welding” where the spot welding electrode is made into a roller shape, and brazing material is installed on the joint surface to generate resistance heat. A mode of “resistance brazing” in which brazing is performed may be used.

  Examples relating to the present invention will be described.

[Confirmation test of nugget ratio]
In order to confirm the effect when spot-welding plates to be welded having different plate thicknesses using electrodes having different energization resistances according to the present invention, the following demonstration test was conducted.

(Welding gun electrode)
・First electrode (small truncated diameter)
Overall shape: truncated cone shape, truncated diameter: 6 mm (φ6)
Material: Copper alloy (chromium copper)

・Second electrode (small to important head diameter)
Overall shape: truncated cone shape truncated diameter: (1) 6 mm (φ6), (2) 7 mm (φ7), (3) 8 mm (φ8), (4) 10 mm (φ10), (5) 12 mm (φ12) , (6) 16mm (φ16)
Material: Copper alloy (chromium copper)

(Conduction conditions)
・ Current values: 8.0 kA, 8.5 kA, 9.0 kA
・ Pressure: 3.43kN
・ Energization time: 20 cycles

(Welded plate)
・ Three steel plates (Material: All SGC materials)
・ Thickness: thin plate (0.7mm), first thick plate (1.6mm), second thick plate (1.2mm)

  Three welded plates were stacked with the first thick plate in the middle to obtain a welded laminate. Next, the laminate to be welded was sandwiched between the electrodes in such a manner that the first electrode (small truncated diameter) was positioned on the thin plate side and the second electrode (small to important head diameter) was positioned on the thick plate side. And a nugget was formed by performing pressurization and energization under the above-mentioned conditions, and a spot weld was obtained.

  Nugget formation was performed in the same manner by changing the truncated diameter of the second electrode having the important head diameter and the energization current value as parameters, and a spot weld was obtained.

  The size of the nugget formed at the interface of the plate to be welded with respect to the obtained spot welded product was visually confirmed. And, as an index for evaluating the shift of the melted part at the time of spot welding, that is, an index for evaluating suitable nugget formation, “nugget diameter at the thin plate side interface ÷ nugget diameter at the thick plate side interface” Calculated. FIG. 9 shows the result as a graph.

  As can be seen from the graph of FIG. 9, it was confirmed that the nugget can be suitably formed by spot welding according to the present invention. That is, as compared with the case of the electrodes having the same current resistance as before, the electrodes having different current resistances according to the present invention are sufficiently connected to their mating surfaces even if the plates have different plate thicknesses. It was confirmed that a nugget can be formed. More specifically, a welding gun using a second electrode having a truncated diameter of 7 mm to 16 mm with respect to a first electrode having a truncated diameter of 6 mm (that is, the second electrode corresponding to the circular truncated surface diameter of the first electrode). It has been found that particularly effective nugget formation can be achieved when the ratio of the circular truncated face diameter is about 1.16 to about 2.67).

[Preferred electrode truncated surface diameter based on reduction in indentation]
In order to confirm the influence of the indentation due to the increase in the diameter of the electrode truncated surface, the following demonstration test was conducted.

(Welding gun electrode)
・First electrode (small truncated diameter)
Overall shape: truncated cone shape, truncated diameter: 6 mm (φ6)
Material: Copper alloy (chromium copper)

・Second electrode (small to important head diameter)
Overall shape: truncated cone shape truncated diameter: 6 mm (φ6), 7 mm (φ7), 8 mm (φ8), 9 mm (φ9)
Material: Copper alloy (chromium copper)

(Conduction conditions)
・ Current value: 8.0 kA, 9.0 kA
・ Pressure: 2.45kN
・ Energization time: 15cycle

(Test plate)
・ Steel (Material: SGC material)
・ Thickness: 0.7mm and 0.9mm overlap

  A spot welding test was performed on the test plate by applying pressure and energization under the above conditions. The indentation size was determined by visually checking the test plate after the test. The results are shown in FIG.

  As can be seen from the results of FIG. 10, the circular truncated face diameter of the gun electrode is about 7 mm (φ7) or more, preferably about 8 mm (φ8) or more, and particularly about 8 mm to about 16 mm (from FIG. It was confirmed that a welded product having a reduced indentation can be obtained.

  The production method and production apparatus of the present invention can be used, for example, for the production of automobile bodies, and more specifically, can be used for welding steel plates. In particular, in the present invention, it can be particularly suitably applied to the welding of two or more steel plates having different thicknesses, so that the utility value can be said to be high.

  Further, the present invention is not limited to the field of automobile manufacture, and can be used in other manufacturing industries where welding is required. The present invention can be used in various fields of manufacturing such as motorcycles, trucks, tractors, shipbuilding, large-scale container manufacturing, high-rise building steel frames, various metal products / electrical appliances, and the like.

DESCRIPTION OF SYMBOLS 10 Electrode 12 1st electrode 16 2nd electrode 20 Plate to be welded 23 Plate to be welded (thin plate) with smaller plate thickness
27 Plate to be welded (thick plate) with larger plate thickness
27A 1st thick plate 27B 2nd thick plate 50 'welded laminated body 50 spot welded object 55 mating surface (interface) of welded plates
70 Melting Zone / Nugget

Claims (13)

A method of manufacturing a spot weld using a welding gun composed of a first electrode and a second electrode forming a pair,
(I) a step of at least partially overlapping at least two plates to be welded to obtain a welded laminate,
(Ii) sandwiching the welded laminate with the first electrode and the second electrode; and (iii) pressing the first laminate while pressing the welded laminate with the first electrode and the second electrode. Comprising a step of conducting electricity between the second electrode,
In the welded laminate, the at least two welded plates have different plate thicknesses, and the welding guns having different current resistances of the first electrode and the second electrode are used. Manufacturing method of weldments. In the step (iii), the formation position of the melted portion generated in the laminate to be welded is controlled, and the conduction resistance of the first electrode and the second electrode is caused by the different conduction resistances. 2. The method for manufacturing a spot welded product according to claim 1, wherein the melted portion is shifted to the electrode side having a relatively large diameter. 3. The spot welding method according to claim 1, wherein the melted portion is shifted so that the melted portion reaches the mating surfaces of the welded plates having different plate thicknesses. Each of the first electrode and the second electrode has a truncated shape, and the welding gun is used in which the truncated area of the first electrode and the truncated area of the second electrode are different from each other. The manufacturing method of the spot welded material in any one of Claims 1-3. The ratio of the truncated area between the first electrode and the second electrode, wherein the ratio of the relatively large truncated area to the relatively small truncated area is 1.3 to 7.5. The method for manufacturing a spot welded article according to claim 4, wherein a gun is used. 6. The method for manufacturing a spot welded product according to claim 4, wherein the truncated shape is a truncated cone shape. 7. The welding gun according to claim 4, wherein at least one of the first electrode and the second electrode uses the welding gun in which a boundary between an electrode tip shoulder and a truncated surface is not square. Manufacturing method for spot welds. The method of manufacturing a spot welded product according to any one of claims 1 to 7, wherein the number of plates to be welded is three, and at least two of the plates have different thicknesses. In the step (ii), an electrode having a relatively large conduction resistance among the first electrode and the second electrode is disposed in the vicinity of the plate to be welded having a relatively small plate thickness. The method for manufacturing a spot welded product according to any one of claims 1 to 8, wherein an electrode having a relatively small thickness is disposed in the vicinity of the welded plate having a relatively large plate thickness. An apparatus for manufacturing a spot welded article composed of welded plates having different plate thicknesses,
A spot welded product characterized in that it comprises at least a welding gun composed of a first electrode and a second electrode forming a pair, and the energization resistances of the first electrode and the second electrode are different from each other. apparatus. Each of the first electrode and the second electrode has a truncated shape, and the truncated area of the first electrode and the truncated area of the second electrode are different from each other, The spot welded product manufacturing apparatus according to claim 10. 12. The spot welded article manufacturing apparatus according to claim 11, wherein the truncated shape is a truncated cone shape. The spot welded article manufacturing apparatus according to claim 11 or 12, wherein a boundary between an electrode tip shoulder portion and a truncated surface is not square in at least one of the first electrode and the second electrode.