JP5803116B2 - Indirect spot welding method - Google Patents

Description

  The present invention presses a welding electrode while pressing a welding electrode against a metal plate from one surface side against a member in which at least two metal plates are overlapped, and feed terminal at a position away from the metal plate on the other surface side The indirect spot welding method in which welding is performed by energizing between the welding electrode and the power supply terminal is intended to enable the formation of a stable melt nugget by a particularly simple pre-welding process. .

  Conventionally, resistance spot welding, mainly direct spot welding, has been used for welding automobile bodies and parts, but recently, series spot welding and indirect spot welding methods have been used. .

The characteristics of the above three types of spot welding will be described with reference to FIG.
In any spot welding, there is no change in that at least two superposed metal plates are joined by welding.
FIG. 1A shows the direct spot welding method. In this welding, as shown in the figure, a current is applied while pressing a pair of electrodes 3 and 4 from above and below between the two stacked metal plates 1 and 2, and the resistance heating of the metal plates is used. This is a method for obtaining a spot-like welded portion 5. Each of the electrodes 3 and 4 includes pressurization control devices 6 and 7 and a current control device 8, so that the pressurizing force and the current value to be energized can be controlled by these.

  In the series spot welding method shown in FIG. 1 (b), a pair of electrodes 13 and 14 are pressed from the same surface side (in the same direction) at a position apart from two superimposed metal plates 11 and 12. In this method, a current is passed to obtain the spot welds 15-1 and 15-2.

  In the indirect spot welding method shown in FIG. 1 (c), the electrode 23 is pressed against one metal plate 21 while pressing the two metal plates 21, 22, and the other metal plate 22 is pressed against the other metal plate 22. Is a method of forming a spot-like welded portion 25 on the metal plates 21 and 22 by attaching the power supply terminal 24 at a distant position and energizing between them.

Of the three types of welding methods described above, direct spot welding is used when there is sufficient space and an opening that sandwiches the metal plate from above and below is obtained.
However, in actual welding, there are many cases where there is not enough space and the metal plate cannot be sandwiched from above and below with a closed cross-sectional structure. In such cases, the series spot welding method or indirect spot welding method is used. It is done.

  However, when the series spot welding method or the indirect spot welding method is used for the above-mentioned applications, the stacked metal plates are pressed by the electrode only from one direction, and the opposite side is a hollow with no support. It is in a state. Therefore, it is not possible to apply a high applied pressure directly under the electrodes as in the direct spot welding method in which the electrodes are sandwiched from both sides. Further, since the electrode sinks into the metal plate during energization, the contact state between the electrode-metal plate and the metal plate-metal plate changes. For these reasons, there is a problem in that the current energization path is not stable between the stacked metal plates, and it is difficult to form a fusion weld.

  In order to solve the above problems, Patent Documents 1 to 3 disclose a series spot welding method or an indirect spot welding method in which a current during welding or an electrode pressing force is changed.

  Patent Document 1 describes a series spot welding in which “a nugget is formed at a contact point where metal plates are overlapped, so that a large current is passed at the beginning of welding to form an electrode nugget and then a steady current is passed”. Has been.

  Patent Document 2 discloses a welding method consisting of “repeating alternately a time zone in which a current value is kept high and a time zone in which a current value is kept low during energization of series spot welding or indirect spot welding”; Discloses a welding method that consists of “gradually increasing the current value in the time period in which the current value is kept high as the time period in which the current value is kept high and the time period in which the current value is kept low are alternately repeated”. ing.

Further, Patent Document 3 states that “a member in which at least two metal plates are overlapped is pressed against a metal plate while pressing a welding electrode from one surface side, and the metal plate on the other surface side is In the indirect spot welding method in which a power supply terminal is attached at a position separated from the welding electrode, and welding is performed by energizing between the welding electrode and the power supply terminal, the current value to be energized is constant from the start to the end of the energization. On the other hand, the pressure applied to the electrode is divided into two time zones t ₁ and t ₂ from the start of energization. In the first time zone t ₁ , after pressurizing with the pressure F ₁ , in the next time zone t ₂ , An indirect spot welding method characterized by pressurizing at a pressure F ₂ lower than F ₁ is disclosed.

  In order to solve the above problem, a series spot welding method and an indirect spot welding method that define the contact state between the metal plates around the welded portion are disclosed in Patent Document 4 and the prior application (Japanese Patent Application 2009). -200946).

  Patent Document 4 states that “a seat surface that is one step higher than other portions is formed at a position where the electrode is brought into contact, and that the seat surface is pressed and contacted so as to crush, thereby providing sufficient welding strength without a back electrode. Series spot welding is disclosed.

  In addition, Japanese Patent Application No. 2009-200946 states that “a member in which at least two metal plates are overlapped is pressed against a metal plate while pressing a welding electrode from one surface side to the metal plate on the other surface side. In indirect spot welding in which a power supply terminal is attached at a position separated from the welding electrode and welding is performed by energizing between the welding electrode and the power supply terminal, the overlapping surface between the metal plates excluding the welded portion is electrically An indirect spot welding method is described in which the dispersion of current during welding is effectively suppressed by insulating, so that a molten nugget can be stably formed. In this indirect spot welding method, the insulator for electrically insulating the overlapping surface between the metal plates excluding the welded part has a sufficiently large specific resistance and is heated by heat conducted to the periphery of the welded part during welding. It is composed of materials that do not deteriorate due to melting, oxidation, etc., specifically, organic materials and inorganic materials such as acrylic resins, melamine resins, silicone resins and fluororesins, or paints and coating materials based on these materials, or Examples include organic materials such as aramid and quartz glass, inorganic materials, and fiber materials based on these materials.

  On the other hand, in recent years, with respect to the assembly of automobiles and the like, a weld bond method using a combination of adhesion and direct spot welding has been attracting attention, and its application range has been gradually expanded. The conventional direct spot welding method is point bonding, but since the weld bond method is surface bonding, the bonding strength and rigidity are improved. Therefore, it is effective for reducing the weight of the vehicle body, and further has excellent advantages such as excellent vibration and impact characteristics, noise reduction, and sealing performance. Direct spot welding methods using an adhesive are disclosed in Patent Documents 5 to 10.

Japanese Patent Laid-Open No. 11-333569 JP 2006-198676 JP 2010-194609 Japanese Patent No. 3753005 Japanese Unexamined Patent Publication No. 4-123879 Japanese Patent No. 3184260 JP-A-6-55277 Japanese Unexamined Patent Publication No. 2-211986 Japanese Patent No. 3169902 JP 2008-80394 A

  However, in Patent Documents 1 to 3, there is a restriction that it is necessary to use welding equipment capable of changing the current and the electrode pressing force during welding.

  Further, in Patent Document 4, it is considered effective for series spot welding, but it is not always effective for indirect spot welding, and it is one step higher than the other parts at the position where the electrode contacts. There is a problem that a process for forming the seating surface with a press or the like is required, resulting in high cost.

  In addition, in Japanese Patent Application No. 2009-200946, in order to “electrically insulate the overlapping surfaces between the metal plates excluding the welded portion”, a complicated process of selectively interposing an insulator in the region excluding the welded portion is used. Not only is it necessary, it also leaves some problems where it is difficult to weld uninsulated positions with sufficient accuracy.

  On the other hand, the weld bond method disclosed in Patent Documents 5 to 10 is only a resistance spot welding method in which joint strength and rigidity are improved by using an adhesive in combination as described above to achieve surface bonding. Does not disclose an indirect spot welding method using an adhesive. Further, there is no disclosure about using an adhesive to electrically insulate the overlapping surface between the metal plates excluding the welded portion.

  The present invention has been developed in view of the above-mentioned present situation. In the indirect spot welding in which the stacked metal plates are pressurized with electrodes only from one direction and the opposite side is welded in a hollow state without support, welding is performed. An object of the present invention is to propose an indirect spot welding method capable of stably obtaining a nugget formed in a molten state by a simple pre-welding process without being restricted by the function of the equipment.

As a result of intensive studies to solve the above problems, the inventors have obtained the following knowledge.
a) When indirect spot welding is performed in a hollow state where the electrodes are contacted and pressed only in one direction and the opposite side is unsupported on the opposite side, as in the direct spot welding method in which the electrodes are sandwiched from both sides Since a high pressurizing force cannot be applied locally directly under the electrode, a high current density cannot be obtained on the contact surface generated when the metal plate is pressed directly under the electrode, and the energization path is dispersed in the vicinity thereof. Therefore, in indirect spot welding, it is difficult to obtain sufficient heat to reach melting at the contact surface, and a molten nugget is difficult to form. In addition, even when a molten nugget is formed, the position at which the molten nugget is formed is biased toward the metal plate in contact with the electrode with respect to the thickness direction of the metal plate, and sufficient melting on the adhesion surface is obtained. There may not be.
b) In order to solve the problem of a), welding is performed in a state where the overlapping surfaces between the metal plates excluding the region to be welded are insulated, and the energization path is limited to the welded portion. It is effective to form a molten nugget stably.
However, a complicated process is required to interpose the insulator only in the region other than the welded portion.
c) The solution of b) can be easily achieved by interposing an insulating viscous substance over the entire polymerization surface between the metal plates. In other words, by interposing an insulating viscous material between the overlapping surfaces of the metal plates, it is possible to electrically insulate the metal plates in areas other than the welded portion, while adding electrodes to the welded portion. By pressing, the viscous material is pushed away, so that energization between the metal plates is ensured. Thereby, the problem that the energization path is dispersed around the welded portion can be solved, and the nugget formed in a molten state can be stably obtained.
d) Moreover, as the above-mentioned insulating viscous substance, for example, an organic resin such as a thermosetting or room temperature curable epoxy resin may be used. If the viscous material is a thermosetting organic resin-based adhesive, the adhesive is welded by interposing it in a polymerized surface between metal plates in an unsolidified state, and then, for example, in an automobile baking coating process. In addition to the effect of forming a stable molten nugget as described above, the bonding strength and rigidity can be improved. Further, the same effect can be obtained even when the viscous substance is used as a room temperature curable organic resin adhesive.

e) On the other hand, when welding is performed as in c) above, depending on the type and thickness of the metal plate, the position where the molten nugget is formed is opposite to the tendency described in a) above. There may be a tendency to be biased toward the metal plate on the side where the electrode is not in contact with the thickness direction.

f) In order to correct the tendency of d) and form a molten nugget at a more suitable position, an insulating viscous substance is interposed on the polymerization surface between the metal plates as in c). In addition, it is advantageous to control the ratio of the current flowing in the welded portion relative to the total current supplied by adjusting the current flowing in the current-carrying route at the place other than the welded portion and adjusting the current flowing in the energized route during welding. The position of the molten nugget formed immediately below the electrode in the thickness direction can be adjusted. That is, when the ratio of the current flowing through the welded portion to the total current fed from the current control device is reduced, resistance heat generation at the adhesion surface of the welded portion can be suppressed, while the metal around which the electrodes around the electrode are in contact In the plate, since the total of the currents applied at the portions other than the welded portion and the welded portion is concentrated, resistance heat generation becomes significant. Therefore, the molten nugget tends to be formed on the side of the metal plate that contacts the electrode. By the method shown above, the position of the molten nugget in the plate thickness direction can be adjusted to a position that sufficiently crosses between the metal plates, and a sufficient diameter of the molten nugget can be obtained at the close contact surface of the welded portion.

The present invention is based on the above findings.
That is, the gist configuration of the present invention is as follows.
1. Pressing the welding electrode against the metal plate from one side while pressing the welding electrode against a member on which at least two metal plates are overlapped, and feeding the terminal on the other side of the metal plate at a position separated from the welding electrode In indirect spot welding in which welding is performed by energizing between the welding electrode and the power supply terminal,
The entire overlapping surface between the metal plates is in a state where a viscous material having a thickness of 0.5 mm to 2.0 mm and an insulating property of 0.7 Pa · s to 20 Pa · s is interposed , and the welding electrode is added in this state. An indirect spot welding method characterized in that welding is performed by starting energization after pressing and pressing the viscous material into contact with the metal plate .
2. In the above 1, the viscous substance having insulating properties is an adhesive, and welding is performed by interposing the adhesive on the entire overlapping surface between metal plates in an unsolidified state, and then solidifying the adhesive. And an indirect spot welding method.
3. In 1 or 2 above, an energization path is provided in a portion other than the welded portions of the overlapped metal plates, and the current flowing in the energization path is adjusted to control the ratio of the current flowing in the welded portion to the total current supplied. The indirect spot welding method characterized by adjusting the position of the molten nugget formed in this welding part in the plate | board thickness direction.

According to the present invention, welding is performed in a state where an insulating viscous material is interposed between the overlapping surfaces of the metal plates, so that there is no restriction on the function of the welding equipment, and by a simple pre-welding process, It is possible to effectively suppress the dispersion of current in and to stably form a nugget formed in a molten state.
Further, according to the present invention, a viscous substance having insulating properties is used as an adhesive, and the adhesive is solidified after being welded by interposing the adhesive on the entire overlapping surface between the metal plates in an unsolidified state. Thereby, joint strength and rigidity can be improved effectively.
Further, according to the present invention, welding is performed by adjusting the current flowing in the energization path provided in a place other than the welded portion of the overlapped metal plates and controlling the ratio of the current flowing in the welded portion to the total current supplied. The position of the molten nugget formed in the portion in the plate thickness direction can be adjusted. As a result, a molten nugget having a sufficient diameter can be obtained at the contact surface between the metal plates of the welded portion.

It is explanatory drawing of the welding point of the direct spot welding method (a), the series spot welding method (b), and the indirect spot welding method (c). It is the figure which showed the welding procedure of indirect spot welding according to this invention, Comprising: (a) is a step which interposes an insulating viscous substance in the superposition | polymerization surface between metal plates, (b) is a metal plate. Step (c) of pressing the welding electrode while pressing the welding electrode from one surface side shows a step of energizing between the welding electrode and the power supply terminal. In indirect spot welding according to this invention shown in FIG. 2, it is a figure which shows the welding point in the case of providing an electricity supply path | route in places other than the welding part of the piled metal plate. When (a) attaches a contact terminal to the overlapped metal plate and connects the current-carrying terminal via a resistor, (b) applies current by providing a welded portion in advance on the overlapping surface between the overlapped metal plates. In the case of the path, (c) shows a case where a part of the polymerized surface between the stacked metal plates is pressed to push away the viscous substance and the metal plates are brought into close contact to form an energization path. It is a figure which shows another example of the welding procedure of indirect spot welding according to this invention. When (a) does not provide a current-carrying path in a place other than the welded portion of the overlapped metal plate, (b) attaches a contact terminal to the overlapped metal plate and connects the current-carrying terminal via a resistor. (C) shows the case where a welding part is previously provided in the superposition | polymerization surface between the piled metal plates, and it is set as an electricity supply path | route.

Hereinafter, the present invention will be specifically described with reference to the drawings.
In FIG. 2, in accordance with the present invention, an insulating viscous material is interposed between the overlapping surfaces of the metal plates, that is, the overlapping surfaces between the metal plates excluding the welded portion are electrically connected by the viscous material. The welding procedure of indirect spot welding in which welding is performed in an electrically insulated state is shown. Since the structure is the same as that of the conventional indirect spot welding shown in FIG. 1C, the same reference numeral is given, and reference numeral 26 in the figure is an insulating viscous substance.

The viscous material 26 has a sufficiently large specific resistance, and is composed of a material having an insulation property that cuts off the electric current between the metal plates at the time of welding when disposed between the metal plates. Viscosity and coating thickness, that is, when the metal plate is pressurized by the electrode, the welded portion has a viscosity and coating thickness that will allow the viscous material to be pushed away and ensure electrical conduction between the metal plates. ing.
Here, the viscosity is preferably in the range of 0.1 Pa · s to 1000 Pa · s. If the viscosity is smaller than this range, when the metal plate is pressurized by the electrode, the viscous material is excessively displaced, and the effect of limiting the current conduction to the welded portion cannot be sufficiently obtained. On the other hand, if the viscosity is larger than this range, when the metal plate is pressurized by the electrode, the viscous material is not sufficiently pushed away from the welded portion, and there is a risk that the welded portion may not be energized. Because. A more preferable viscosity range is 0.7 Pa · s to 20 Pa · s.
The coating thickness is preferably in the range of 0.1 mm to 3 mm. If the coating thickness is smaller than this range, when the metal plate is pressed by the electrode, the viscous material is excessively pushed away, and the effect of limiting the energization to the welded portion cannot be sufficiently obtained. On the other hand, if the coating thickness is larger than this range, when the metal plate is pressurized by the electrode, the viscous material is not sufficiently pushed away from the welded portion, and the welded portion is energized. This is because there is a risk of not being broken. A more preferable coating thickness is 0.5 mm to 2.0 mm.
Note that the pressure applied by the electrode does not completely displace the viscous material in the weld zone around it, but if the metal plates are in contact with each other locally, they will be energized, enabling welding. .
Examples of the viscous substance of the present invention include liquid heat curable epoxy organic resins and the above organic resin adhesives.

The welding procedure according to the present invention performed using such a viscous material 26 is as follows.
That is,
a) First, as shown in FIG. 2 (a), an insulating viscous material 26 is interposed between the overlapping surfaces of the stacked metal plates. Thereby, between metal plates can be electrically insulated.
b) Further, as shown in FIG. 2B, the welding electrode 23 is pressed from one side of these metal plates while being pressed. By this electrode pressurization, the viscous material 26 is pushed away in the welded portion, and a close contact surface between the metal plates is secured.
c) With this electrode pressure applied, welding is performed by energizing between the welding electrode 23 and the power supply terminal 24 as shown in FIG. 2 (c).
By performing the welding in the above-described manner, the current conduction between the metal plates is limited to the welded portion, and a high current density can be obtained. Therefore, the molten nugget 25 can be stably formed in the welded portion.
In addition, by using an adhesive as the insulating viscous material 26, not only the above-described molten nugget 25 can be stably formed, but also a weld bond method using a combination of conventional bonding and direct spot welding methods. Similarly, it goes without saying that advantages such as improved bonding strength and rigidity, excellent vibration / impact characteristics, noise reduction, and sealing performance can be obtained.
In addition, when using a thermosetting adhesive such as an epoxy-based organic resin as the insulating viscous substance 26, it can be solidified by heating at the time of baking coating of the steel sheet, which is usually performed after welding. It is not necessary to provide a special process for solidifying the unsolidified adhesive 26.

By the way, as described above, when welding is performed in a state where the overlapping surfaces between the metal plates excluding the region to be welded are insulated, the position where the molten nugget is formed depends on the type and thickness of the metal plate. It shows a tendency to be biased toward the metal plate on the side where the electrode is not in contact with the plate thickness direction of the plate.
Therefore, in such a case, it is advantageous to adjust the current flowing through the path during welding by providing an energization path in a place other than the welded portion in the overlapped metal plate and operating the electrical resistance of the path. It is. As a result, the ratio of the current flowing through the weld to the total current fed from the current controller can be controlled, and the position of the molten nugget formed immediately below the electrode in the thickness direction can be changed. A sufficient diameter of the melted nugget can be obtained at the close contact surfaces.

  Specifically, when the ratio of the current flowing through the welded portion relative to the total current supplied from the current control device is reduced, resistance heat generation at the adhesion surface of the welded portion is suppressed, while the metal around which the electrodes around the electrode are in contact In the plate, since the total of the currents applied at the portions other than the welded portion and the welded portion is concentrated, resistance heat generation becomes significant. Therefore, the molten nugget tends to be formed on the side of the metal plate in contact with the electrode, and the bias of the molten nugget to the metal plate on the side where the electrode is not in contact with the plate thickness direction can be adjusted. Suitable for adjusting the position of the molten nugget in the sheet thickness direction to a position that sufficiently spans between the metal sheets, the range of the ratio of the current flowing through the weld to the total current depends on the type and thickness of the stacked metal sheets Since they are different, it is preferable to control the resistance value of the energization path provided at a place other than the welded portion so that the ratio of the current is within a suitable range. Moreover, the electricity supply path | route provided in locations other than this welding part can be made into multiple.

FIG. 3 (a) shows a case where indirect spot welding is performed in addition to a welded portion in addition to interposing an insulating viscous substance between the overlapping surfaces between metal plates according to the present invention. Shows the welding procedure. Since the structure is the same as that shown in FIG. 2, the same reference numerals are used. In the figure, reference numeral 27 denotes an energizing terminal and 28 denotes a resistor.
As shown in FIG. 3A, by attaching a contact terminal 27 that can be energized to the overlapped metal plates, and connecting the energization terminal 27 via a conductor having a predetermined electric resistance value such as a resistor. The energization path can be provided at a location different from the overlapped portion of the stacked metal plates.
Further, as shown in FIGS. 3B and 3C, a method is conceivable in which an energized portion is provided on the overlapping surface between the stacked metal plates in addition to the region where welding is performed. FIG. 3B shows a case where a welding portion 29 is provided in advance on the overlapping surface between the overlapped metal plates to form an energization path, and FIG. 3C shows one of the overlapping surfaces between the overlapped metal plates. This is a case where the portion is pressurized, the viscous material 26 is pushed away from the pressurization location, the metal plate is brought into close contact, and the close contact location 30 is used as an energization path.

  In controlling the current flowing through the energization path obtained in this way, the resistance value of the energization path is relatively adjusted by adjusting the positions of the power supply terminals, electrodes, and the energization points connected to the current control device. Thus, as described above, the position of the molten nugget formed immediately below the electrode is changed in the thickness direction, and the position of the molten nugget in the thickness direction is sufficiently crossed between the metal plates. By adjusting, it is possible to obtain a sufficient melt nugget diameter at the contact surface of the metal plate. In addition, the electricity supply path | route provided in places other than this welding part is not necessarily restricted to one place, It can also be made into multiple places.

Moreover, when performing the indirect spot welding of this invention, you may use the method as shown in FIG. 4 other than the method shown in FIG.2, 3. FIG.
In the method shown in FIG. 4 (a), a concave metal jig 31 is provided to support the steel plates stacked from below the welded portion, and the welded portions are excluded from the stacked steel plates. This is a method of performing indirect spot welding in a state where the superposed surface between steel plates is electrically insulated by a viscous material 26, and can be carried out through the same steps as in FIGS. 2 (a) to 2 (c). .
Moreover, FIG. 4B shows that the superposed surface between the steel plates excluding the welded portion is electrically insulated by the viscous material 26, and the energization path other than the welded portion is different from the superposed surface between the steel plates. This is a method of providing indirect spot welding at a location.
Further, FIG. 4 (c) shows that the overlapping surface between the steel plates excluding the welded portion is electrically insulated by the viscous material 26, and the welded portion 29 provided in advance on the overlapping surface between the stacked steel plates is energized. This is a method of performing indirect spot welding as a route.

The indirect spot welding method according to the present invention was performed on two superposed steel plates. The steel sheet has a thickness of 0.65mm and the chemical composition shown in Table 1. Tensile strength: 270 N / mm ² or more cold-rolled steel sheet (SPC270) and the thickness of 1.2mm and the chemical composition shown in Table 1 A tensile strength of 270 N / mm ² or more SPC270 steel plate was used. As the viscous substance, a liquid heat curable epoxy organic resin was used.

  On the concave metal jig as shown in Fig. 4 (a), two superposed steel plates are placed, the support interval is set to 30 mm, the power supply terminal is attached to the lower part of the jig, and the electrode is viewed from above. Welding was performed using a chrome-copper alloy electrode having a curved surface of R40 mm at the tip and a DC inverter type power source.

  Also, welding was performed in the manner shown in FIGS. 4 (b) and 4 (c). In FIG. 4C, the center of the region to be welded is the midpoint of the line segment connecting the centers of the two existing welds. In addition, the distance from the center of the welding area to the center of any existing weld was set to 40 mm, 80 mm, and 120 mm.

  Table 2 shows the thicknesses of the upper and lower steel plates made of SPC270 steel plates, the pressure applied to the electrodes, the current value, and the presence or absence of a viscous substance on the superposed surface of the steel plates. As shown in FIG. 4 (a), when there is no energization path other than the welded portion as shown in FIG. 4 (a), “None”, and as shown in FIG. Yes, if it is a conductor installed at a place other than the overlapped surface of the superposed steel plates, “conductor”, as shown in FIG. When the distance from the center of the area where the welding is performed to the center of any existing welded portion is 40 mm, the “existing welded portion: 40 mm” In the case of 80 mm, “existing welded part: 80 mm”, and in the case of 120 mm, “existing welded part: 120 mm”. In all conditions, the time from the start to the end of energization was set to 0.30 seconds.

In Table 2, Invention Examples 1 to 3 were welded by using an upper steel plate and a lower steel plate as an SPC270 steel plate having a thickness of 1.2 mm and interposing a viscous substance in the overlapped portion.
In Invention Examples 4 to 6, the upper steel plate was an SPC270 steel plate having a thickness of 0.65 mm, the lower steel plate was an SPC270 steel plate having a thickness of 1.2 mm, and welding was performed with a viscous substance interposed in the overlapped portion.
Inventive Examples 7 to 9 are such that the upper steel plate is an SPC270 steel plate having a thickness of 0.65 mm and the lower steel plate is an SPC270 steel plate having a thickness of 1.2 mm, and a viscous substance is interposed in the overlapping portion, and the upper and lower steel plates are superposed. Conductors were installed at other locations to provide an energization path other than the welded portion, and welding was performed.
Invention Examples 10 to 14 are such that the upper steel plate is a SPC270 steel plate having a thickness of 0.65 mm, the lower steel plate is a plate thickness: 1.2 mm SPC270 steel plate, a viscous substance is interposed in the superposition part, and the upper and lower steel plates are superposed. Welding was performed using the already-welded part as an energizing path other than the welded part.
On the other hand, in Comparative Examples 1 to 3, the upper steel plate and the lower steel plate are SPC270 steel plates having a plate thickness of 1.2 mm, and in Comparative Examples 4 to 6, the upper steel plate is a plate thickness: 0.65 mm SPC270 steel plates and the lower steel plate are plate thicknesses: A 1.2 mm SPC270 steel plate was used, and welding was carried out without interposing a viscous substance in the overlapped portion.

Table 3 shows the results of investigating the nugget diameter, nugget thickness, nugget thickness / diameter, 1.5T value described below, and appearance defects when welding was performed under the conditions shown in Table 2.
In Table 3, the nugget diameter is the length on the overlapping surface between the upper steel plate and the lower steel plate in the cross section cut around the weld. The nugget thickness was the maximum thickness of the melted portion formed between the upper steel plate and the lower steel plate in the cross section cut at the welded portion. The thickness from the superposed surface to the upper steel plate side was described as “upper plate”, the thickness from the superposed surface to the lower steel plate side as “lower plate”, and the total thickness from the upper steel plate to the lower steel plate as “total”. The nugget thickness / diameter is obtained by dividing the above-described nugget thickness by the nugget diameter.
Here, if the nugget diameter ND satisfies the following formula (1), the nugget thickness / diameter is 0.22 or more, and the thickness on the upper and lower steel plate side from the superposition surface is 0.2 mm or more, it is melted. It can be judged that the meteorite-shaped suitable nugget formed in the state is formed at a position sufficiently straddling the upper and lower steel plates.
ND ≧ 1.5 T (1)
However, ND: Nugget diameter (mm)
T: Total thickness of superposed metal plates (mm)

As shown in Table 3, all of Inventive Examples 1 to 14 that were subjected to indirect spot welding according to the present invention can obtain a molten nugget having a sufficient nugget diameter and a sufficient thickness with respect to this diameter. In addition, the molten nugget was formed at a position sufficiently straddling between the upper and lower steel plates. In addition, no appearance defects were observed.
In contrast, in Comparative Example 5, the nugget diameter was 2.1 mm, but a sufficient nugget thickness was not obtained, and the nugget thickness / diameter was smaller than 0.22. In other Comparative Examples 1 to 4 and 6, nugget formation was not observed.

  According to the present invention, in indirect spot welding in which the stacked metal plates are pressed with an electrode only from one direction and the opposite side is in an unsupported hollow state, the entire overlapping surface between the metal plates is insulated. By performing welding with a viscous substance interposed, a sufficient nugget diameter and a molten nugget having a sufficient thickness with respect to this diameter can be stably formed by a simple pre-welding process.

DESCRIPTION OF SYMBOLS 1, 2 Metal plate 3, 4 Electrode 5 Point-like welding part 6, 7 Pressurization control apparatus 8 Current control apparatus
11, 12 Metal plate
13, 14 electrodes
15-1, 15-2 Spot welds
21,22 Metal plate
23 electrodes
24 Power supply terminal
25 welds
26 viscous material
27 Power terminal
28 resistance
29 welds
30 Removal points
31 Recessed metal jig

Claims (3)

Pressing the welding electrode against the metal plate from one side while pressing the welding electrode against a member on which at least two metal plates are overlapped, and feeding the terminal on the other side of the metal plate at a position separated from the welding electrode In indirect spot welding in which welding is performed by energizing between the welding electrode and the power supply terminal,
The entire overlapping surface between the metal plates is in a state where a viscous material having a thickness of 0.5 mm to 2.0 mm and an insulating property of 0.7 Pa · s to 20 Pa · s is interposed , and the welding electrode is added in this state. An indirect spot welding method characterized in that welding is performed by starting energization after pressing and pressing the viscous material into contact with the metal plate .   The adhesive viscous material according to claim 1, wherein the insulating viscous material is an adhesive, and welding is performed by interposing the adhesive on the entire overlapping surface between the metal plates in an unsolidified state. An indirect spot welding method characterized by solidifying.   In Claim 1 or 2, an energization path is provided in places other than the welding part of the metal plate which overlap | superposed, the electric current which flows into this energization path is adjusted, and the ratio of the electric current which flows into a welding part with respect to the total electric current supplied is controlled. By adjusting the position of the molten nugget formed in the welded portion in the plate thickness direction, an indirect spot welding method is characterized.

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