JP2013099762A - One side spot welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a one side spot welding method by which the increase of machining man-hour of a work piece can be suppressed, and furthermore the strength and the rigidity of the work piece can be secured.SOLUTION: The one side spot welding method which is used to weld by applying a welding electrode 15 only from the one side in the work piece 13 to the part of a plate-like work piece 13 on which a plurality of plates are folded includes, as shown in (B) and (C), forming the work piece 13, specifically, a notch 26b in the upper plate 26, in the periphery of the welding electrode 15 by generating a scatter as shown by the arrow marks Q and Q in the vicinity directly under the welding electrode 15 in the work piece 13 by making a welding electric current flow in the upper plate 26 by carrying out the first electrification to earth electrodes 17 and 17 through the work piece 13 from the welding electrode 15 by applying the welding electrode 15 and the earth electrodes 17 and 17 to the one side of the work piece 13 with pressure, and then, as shown in (D), forming a nugget 31 between the upper plate 26 and the lower plate 27 directly under the welding electrode 15 by making the welding electric current flow in the lower plate 27 by carrying out the second electrification which electrifies a prescribed electric current value.

Description

  The present invention relates to a one-side spot welding method in which a welding electrode and a ground electrode are applied to a welding portion of a workpiece only from one side of the workpiece for welding.

In the case where a plurality of plate-like workpieces are overlapped and joined, spot welding is generally performed in which a welding current is applied while pressurizing the workpiece, and the workpiece is joined by melting the metal with resistance heat generated thereby.
Depending on the welding current application method, this spot welding is a double-side spot welding in which current is applied while pressing the workpiece from both sides, and one-side spot welding (indirect spot welding, series in which current is applied while applying pressure from only one side of the workpiece) (Spot welding).
For example, in a bag-like workpiece having a complicated shape or having an internal space, it is physically difficult to apply the welding electrode (welding gun) to the workpiece from both sides, and inevitably one-side spot welding is used.

As such a one-side spot welding method, among a plurality of metal plates arranged to be overlapped in the plate thickness direction, a plurality of welding electrodes are applied to one of the outermost two metal plates to resist the plurality of metal plates. A method of welding is known (see, for example, Patent Document 1).
The one metal plate is formed with a slit so as to divide at least one of a plurality of regions connecting portions where each welding electrode hits, and the slit causes an ineffective current flowing through the one metal plate. Lost.

JP 2009-279597 A

In patent document 1, it is necessary to form a slit in a metal plate beforehand, and a processing man-hour increases. Further, depending on the part where the slit is formed, the strength and rigidity of the metal plate may decrease.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a one-side spot welding method capable of suppressing an increase in the number of processing steps of a workpiece and further ensuring the strength and rigidity of the workpiece. Yes.

In order to solve the above-described problem, the present invention is a one-side spot welding method in which a welding electrode is applied to a welding portion of a plurality of stacked plate-like workpieces from only one side of the workpiece, and welding is performed. A ground electrode is applied to one side of the workpiece while being pressed, and a first energization is performed from the welding electrode to the ground electrode through the workpiece, thereby generating a scatter in the vicinity of the welding electrode immediately below the welding electrode. A notch is formed in the workpiece, and then a second energization is performed with a predetermined current value to form a nugget between the workpieces immediately below the welding electrode.
According to this configuration, by forming a notch around the welding electrode of the workpiece on the welding electrode side, the electrical resistance of the workpiece on the welding electrode side where the notch is formed increases, and an ineffective current that is not used for welding flows. Since it becomes difficult, the welding current flowing through the workpiece in contact with the workpiece on the welding electrode side increases, so that a good nugget can be formed between the workpieces immediately below the welding electrode.

  In the above-described configuration, after forming the nugget, the notch is filled by performing third energization for energizing the work with a current value lower than the second energization while pressurizing the work from one side by the welding electrode. You may make it return. According to this configuration, it is possible to ensure the strength and rigidity of the work by melting the periphery of the work notch and backfilling the notch by the third energization.

In the present invention, the welding electrode and the ground electrode are applied to one side of the work while being pressed, and the first current is applied from the welding electrode to the ground electrode through the work, thereby generating scattering in the vicinity of the work electrode immediately below the weld electrode. A notch is formed in the workpiece around the welding electrode, and then a second energization is performed with a predetermined current value to form a nugget between the workpieces immediately below the welding electrode. Since the electrical resistance of the workpiece on the electrode side increases and the ineffective current that is not used for welding becomes difficult to flow, the welding current flowing to the workpiece in contact with the workpiece on the welding electrode side increases. A nugget can be formed.
In addition, after the nugget is formed, the notch is backfilled by performing third energization to energize the work with a current value lower than the second energization while pressurizing the work from one side with the welding electrode. Rigidity can be ensured.

It is explanatory drawing which shows the one side spot welding apparatus of 1st Embodiment in this invention. FIG. 2A is an operation diagram for explaining a one-side spot welding method, FIG. 2A is an operation diagram showing a state in which a welding gun is disposed above a workpiece before welding, and FIG. 2B is a diagram in which scattering occurs during the first energization. FIG. 2C is an operation diagram showing a state in which a notch is formed, FIG. 2D is an operation diagram showing a state in which a nugget is formed by the second energization, and FIG. ) Is an operation diagram showing a state in which the periphery of the notch is heated by the third energization, and FIG. 2F is an operation diagram showing a state in which the notch after the end of welding is backfilled. It is a graph which shows the temporal change of the applied pressure at the time of welding in a one-side spot welding apparatus, and an energization current value. It is a graph which shows the relationship between a scattering current value and the thickness of a workpiece | work. It is a flowchart explaining the flow of the one-side spot welding method. It is a side view which shows the welding electrode of 2nd Embodiment in this invention. It is a side view which shows the welding electrode of 3rd Embodiment in this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
<First Embodiment>
FIG. 1 is an explanatory view showing a one-side spot welding apparatus of the present invention.
The one-side spot welding device 10 is attached to the base 11 via an insulating material 12 and is applied to a work 13 made of a steel plate from above, and a lower portion of the base 11 so as to be positioned on both sides of the welding electrode 15. The ground electrodes 17 and 17 that are mounted so as to be movable up and down via compression coil springs 16 and are applied to the work 13 from above, and the base 11, the welding electrode 15, and the ground electrodes 17 and 17 are lowered collectively. The pressing mechanism 21 that presses the welding electrode 15 and the ground electrodes 17 and 17 against the upper surface of the work 13, the power supply 22 that supplies a welding current to the welding electrode 15 and the ground electrodes 17, 17, and the welding electrode 15 and the ground electrode 17. , 17 for setting the current value of the welding current supplied to the predetermined value, and the operation and current setting of the pressurizing mechanism 21. And a control unit 24 which controls the current value setting parts 23.

The base 11, the insulating material 12, the welding electrode 15, the compression coil springs 16 and 16, and the ground electrodes 17 and 17 constitute, for example, a welding gun 25 attached to the arm tip of an arm type robot.
The base 11 supports the welding electrode 15 via the insulating material 12 and supports the ground electrodes 17 and 17 via the compression coil spring 16.
The insulating material 12 is a member that electrically insulates between the base 11 and the welding electrode 15.
The work 13 includes an upper plate 26 and a lower plate 27, and is overlapped and joined.
The welding electrode 15 is formed in a hemispherical shape with a tip portion 15a projecting downward, and an upper plate 26 and a lower plate are formed by applying a welding current to the workpiece 13 while pressing the upper surface of the upper plate 26 of the workpiece 13 with a predetermined pressure. It is an electrode for forming a nugget described later between the plates 27, and is electrically connected to the positive electrode of the power source 22 via the current setting unit 23.

The compression coil spring 16 is compressed by the amount of lowering of the welding gun 25 from when the ground electrode 17 hits the work 13 until the welding electrode 15 hits the work 13 when the welding gun 25 is lowered. The work 13 is pressed downward by the elastic force generated in the spring 16.
The ground electrode 17 is an electrode whose tip 17a is formed in a flat surface and grounds the workpiece 13 by pressing the upper surface of the upper plate 26 of the workpiece 13 with a predetermined pressing force.
The ground electrode 17 is integrally provided with a slide bar (not shown) extending in the vertical direction on the upper portion, and the slide electrode is supported by the base 11 so as to be vertically slidable. It is made slidable.
The welding electrode 15, the ground electrodes 17, 17, the power source 22, the current setting unit 23, and the conductors connecting the ground electrodes 17, 17, the welding electrode 15, the power source 22, and the current setting unit 23 are welded. An energization circuit 28 is formed.

The pressurizing mechanism 21 is a mechanism that raises and lowers the welding gun 25 and presses the welding electrode 15 against the work 13 with a predetermined pressurizing force. For example, a mechanism that pressurizes with a servo motor, a cylinder, and a movement within the cylinder A pneumatic type cylinder device composed of a freely inserted rod is suitable, and other pressurizing means may be used.
The power source 22 has a positive electrode connected to the welding electrode 15 via the current setting unit 23, a negative electrode connected to the ground electrode 17 via the base 11 and the compression coil spring 16, and supplies a direct current to the welding electrode 15.
The control unit 24 includes a storage unit (not shown), and pressurizes based on a program stored in the storage unit (describes the vertical position of the welding gun, the applied pressure, and the energization current value at each time). The mechanism 21 controls the raising and lowering of the welding gun 25 and the pressing force of the welding electrode 15 that pressurizes the work 13, and the current value of the welding current supplied to the welding electrode 15 from the current setting unit 23 connected to the power source 22. To control.

Next, the welding procedure by the one-side spot welding apparatus 10 described above will be described.
FIG. 2 is an operation diagram for explaining the one-side spot welding method.
FIG. 2A shows a state in which the welding gun 25 is disposed above the workpiece 13 before welding. At this time, each tip portion 17 a of the ground electrodes 17, 17 is positioned below the tip portion 15 a of the welding electrode 15.
FIG. 2B shows a state where scattering occurs during initial energization (first energization). The welding gun 25 is lowered so that the welding electrode 15 and the ground electrodes 17, 17 are brought into contact with the upper surface 26 a of the upper plate 26 of the work 13, and the work 13 is pressed with a predetermined pressing force by the ground electrodes 17, 17. The work 13 is energized (first energization) from the welding electrode 15 while pressurizing the work 13 with a predetermined pressure.
At this time, as indicated by arrows P and P, the welding current flows from the welding electrode 15 to the ground electrodes 17 and 17 through the upper plate 26 of the work 13. At this time, since the energization current value to the work 13 is high, scattering occurs as indicated by arrows Q and Q around the vicinity of the welding electrode 15 in the upper plate 26.
Here, the term “scattering” refers to a phenomenon in which the base material is locally heated and melted and scattered, but may also refer to the scattered metal. The above-mentioned scattering is surface scattering generated on the surface of the base material.

FIG. 2C shows a state in which the notch 26b is formed. That is, when scattering occurs, the base material is scattered as molten metal, so that a cutout 26 b is formed on the upper plate 26 around the welding electrode 15. As a result, in the upper plate 26, the energization path is reduced due to the formation of the notches 26b, the electric resistance of the upper plate 26 is increased, and the welding current is less likely to flow.
The notches 26b described above may be continuously formed in an annular shape around the periphery of the welding electrode 15, or may be formed in a plurality of locations around the periphery of the welding electrode 15.
FIG. 2D shows a state in which the nugget 31 is formed by the second energization. Main energization (second energization) is performed at a predetermined welding current value in which the current value of the welding current is lower than in the case of the first energization.
Since the notch 26b is formed in the upper plate 26 of the work 13, a current (invalid current) that does not contribute to welding flowing from the welding electrode 15 through the upper plate 26 to the ground electrodes 17 and 17 becomes difficult to flow. As indicated by arrows R and R, the welding current flows from the welding electrode 15 mainly through the lower plate 27 of the work 13 to the ground electrodes 17 and 17. As a result, the welding current is concentrated at the contact portion between the upper plate 26 and the lower plate 27 immediately below the welding electrode 15, and a good nugget 31 is generated.

FIG. 2E shows a gradual cooling process in which the periphery of the notch 26b is heated by the third energization, and the temperature of the workpiece 13 is lowered as compared with the second energization. FIG. 2 (F) shows a state in which the welding gun 25 is moved above the workpiece 13 to complete the one-side spot welding and the notch 26b (see FIG. 2 (E)) is backfilled. Yes.
In FIG. 2 (E), the welding current value is lowered with respect to the second energization described in FIG. 2 (D), and the work 13 is energized as indicated by arrows S and S. As a result, the range including the notch 26b (range T where the temperature is equal to or higher than a certain temperature) is heated, and particularly the portion with the notch 26b close to the welding electrode 15 is melted at a high temperature. As shown, a portion of the notch 26b (FIG. 2E) is backfilled, and the notch 26b disappears. In addition, the code | symbol 26c is the dent made in the trace of the notch 26b filled back.

FIG. 3 is a graph showing temporal changes in the applied pressure and energization current during welding in the one-side spot welding apparatus. The vertical axis of the graph represents the pressure of the welding electrode that pressurizes the workpiece, the current value of the energization current supplied from the welding electrode to the workpiece during welding (energization current value), and the horizontal axis represents time.
At time t1, pressurization of the workpiece is started with the welding electrode. The applied pressure is F, and this applied pressure F is constant during welding.
Initial energization (first energization) is started at time t2. The energization current value at this time is A1.
In the initial energization, a high energization current value A1 is required in order to generate scattering on the workpiece. The energization current value at this time varies depending on the thickness of the upper plate of the workpiece. The relationship between the energization current value and the thickness of the upper plate will be described with reference to FIG.

At time t3, the energization current value is changed to A2 lower than A1, and the main energization (second energization) is performed until time t4. In the main energization, an energization current value A2 suitable for generating a nugget on the workpiece while suppressing the occurrence of scattering is set.
At time t4, the energization current value is changed to A3, which is lower than A2, and energization for backfilling and slow cooling of the notch formed in the workpiece (third energization (slow cooling process)) is performed until time t5. . In the slow cooling process, the current value is set to A3 lower than A2, thereby lowering the temperature of the workpiece and melting the notched portion formed on the upper plate of the workpiece to refill the notch.
At time t6, the pressurization of the workpiece by the welding electrode is finished.
The pressurizing force and energization current value at each time described above are stored in the storage unit of the control unit 24 shown in FIG.

FIG. 4 is a graph showing the scattered current value depending on the thickness of the workpiece. The vertical axis of the graph represents the current value (scattering current value) that causes scattering in the current value (energization current value) of the energizing current supplied from the welding electrode to the workpiece during welding, and the horizontal axis represents the thickness of the workpiece (top plate). ing.
The scattering current value increases almost linearly as the thickness of the upper plate increases. For example, when the thickness of the upper plate is T1 = 2 mm, the scattered current value is A4 = 9 kA.
Thus, by grasping the relationship between the scattering current value and the thickness of the workpiece, it is possible to generate an appropriate scattering according to the workpiece and form a notch. As a result, energization of the lower plate of the work can be promoted, and a good nugget can be formed between the upper plate and the lower plate.

The flow of the one-side spot welding method described above will be described with reference to a flowchart.
FIG. 5 is a flowchart for explaining the flow of the one-side spot welding method.
In step S1, a notch is formed in the upper plate of the workpiece by generating scattering by the first energization (initial energization). The notch formed in the upper plate makes it difficult for reactive current to flow through the upper plate.
In step S2, the second energization (main energization) causes a welding current to flow mainly to the lower plate of the workpiece, and promotes the generation of nuggets between the upper plate and the lower plate of the workpiece.
In step S3, the third energization (slow cooling process) melts the notched portion near the welding electrode on the upper plate, and fills the notch back. In this way, it is possible to suppress a decrease in strength and rigidity of the welded workpiece by filling the notch back.

  As described above with reference to FIGS. 2 (A) to 2 (F), a one-side spot welding method in which the welding electrode 15 is applied only to one side of the work 13 to the welded portion of the stacked plate-like work 13 for welding. Then, the welding electrode 15 and the ground electrodes 17 and 17 are applied to one side of the work 13 while being pressed, and a first energization is performed from the welding electrode 15 to the work 13, specifically, the ground electrode 17 through the upper plate 26. Scattering is generated in the vicinity of the welding electrode 15 in the plate 26 to form a notch 26b in the upper plate 26 around the welding electrode 15, and then welding is performed by applying a second energization with a predetermined current value. Since the nugget 31 is formed at the contact portion between the upper plate 26 and the lower plate 27 directly below the electrode 15, the electric resistance of the upper plate 26 on the side of the welding electrode 15 in which the notch 26b is formed increases, Used for welding Ineffective current does not flow easily, so that the welding current flowing through the lower plate 27 in contact with the upper plate 26 on the welding electrode 15 side increases, so that the contact portion between the upper plate 26 and the lower plate 27 directly below the welding electrode 15 is good. Nuggets 31 can be formed.

  Further, after the nugget 31 is formed, the notch 26b is refilled by performing the third energization for energizing the work 13 with a current value lower than the second energization while pressurizing the work 13 from one side by the welding electrode 15. The strength and rigidity of the workpiece 13 can be ensured. Moreover, the notch 26b is eliminated on the outer surface of the work 13, and the appearance of the work 13 can be improved.

Second Embodiment
FIG. 6 is a side view showing a welding electrode according to the second embodiment of the present invention.
The welding electrode 41 is an electrode in which the front end portion 41a is composed of a spherical portion 41b having a part of a hemispherical shape and a flat portion 41c formed on the lower end side of the spherical portion 41b.
Thus, by constituting the tip portion 41a with the spherical surface portion 41b and the flat surface portion 41c, the amount of increase in the area of the flat surface portion 41c when the flat surface portion 41c is worn in the vertical direction can be increased. Since the surface pressure acting on 41c can be reduced, the amount of wear in the vertical direction can be reduced. Therefore, it is possible to lengthen the replacement cycle when the welding electrode 41 reaches a predetermined wear amount and is replaced.

<Third Embodiment>
FIG. 7 is a side view showing a welding electrode according to a third embodiment of the present invention.
The welding electrode 45 is an electrode having a tapered portion 45b with a tapered tip 45a and a flat portion 45c formed on the leading end side of the tapered portion 45b.
In this way, by configuring the tip portion 45a with the tapered portion 45b and the flat portion 45c, the tip portion 45a can be easily formed, and the cost can be reduced.

The first to third embodiments described above merely show one aspect of the present invention, and can be arbitrarily modified and applied without departing from the gist of the present invention.
For example, in the above embodiment, as shown in FIG. 1, the welding current is supplied to the welding electrode 15 from the DC power supply 22, but the present invention is not limited thereto, and the welding current is supplied to the welding electrode from the AC power supply. You may do it.
In addition, as shown in FIG. 3, the energization current value for the second energization is changed to A2 lower than the energization current value A1 for the first energization. The current value is not necessarily lower than the energization current value A1 of the first energization because the optimal current value for forming the nugget of the plate assembly is obtained.

10 One-side spot welding equipment 13 Workpiece 15 Welding electrode 17 Ground electrode 26b Notch 31 Nugget

Claims (2)

It is a one-side spot welding method in which welding is performed by applying a welding electrode only from one side of the workpiece to a welding portion of a plurality of stacked plate-like workpieces,
The welding electrode and the ground electrode are applied to one side of the workpiece while being pressed, and a first energization is performed from the welding electrode to the ground electrode through the workpiece, thereby generating a scatter in a portion immediately below the welding electrode in the workpiece. A one-side spot characterized in that a notch is formed in a work around a welding electrode, and then a nugget is formed between the works immediately below the welding electrode by performing a second energization to energize at a predetermined current value. Welding method.   After the nugget is formed, the notch is refilled by performing third energization to energize the work with a current value lower than the second energization while pressurizing the work from one side with the welding electrode. The one-side spot welding method according to claim 1.

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