JP2005161391A - Welding defect detecting apparatus for series spot welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding defect detecting apparatus capable of easily and surely detecting welding defects in series spot welding. <P>SOLUTION: On the basis of a voltage between respective electrode chips 26, 27 detected by a voltmeter 44 at the time of energization of a welding current to the respective electrode chips 26. 27 and on the basis of the welding current value, a control circuit 46 calculates an electric resistance between the respective electrode chips 26, 27 by the Ohm's law, discriminates that normal welding is carried out when the electric resistance is a prescribed value Vt or below, and discriminates that welding defects are caused when the electric resistance is greater than the prescribed value Vt. The prescribed value Vt is set to the electric resistance by carrying out an experiment in which welding strength of respective metallic plates Wa, Wb is examined by varying an electric resistance between the respective electrode chips 26, 27, and by finding the electric resistance at which a sufficient welding strength can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a welding failure detection apparatus for series spot welding.

  Conventionally, a direct spot welding method and a series spot welding method are known as welding methods for metal plates.

  In direct spot welding, spot welding is performed by using the resistance heating of the metal plate that is generated by applying pressure while sandwiching the two metal plates between the upper and lower electrodes and flowing the welding current in the plate thickness direction. Have gained a part. That is, when a welding current is passed, a melted portion of the metal plate (generally referred to as “weld nugget”) is generated at the contact point between the two metal plates, and the two metal plates are welded in a spot shape by the weld nugget.

In the series spot welding method, a point-like welded portion is obtained by flowing a welding current between two electrodes while applying pressure from one direction by a pair of electrodes that separate two stacked metal plates. This series spot welding method includes a type using a back electrode and a type not using it.
In the type using the back electrode, the back electrode is arranged on the back side of the metal plate located on the opposite side to the pressure side of the electrode, one electrode → superposed metal plate → back electrode → superposed metal plate → the other By constructing a current path called an electrode, and flowing a welding current through the current path, welding is performed in a dotted manner on the two metal plates that are overlapped.

  On the other hand, in the type that does not use the back electrode, a current path of one electrode → superimposed metal plate → the other electrode is configured, and a welding current is passed through the current path, so that both superposed metal plates Weld in a spot shape. Therefore, it is used when a separate member or the like assembled in the pre-welding process covers the back side of the metal plate to form a closed cross-section and the back electrode cannot be arranged on the back side of the metal plate.

However, the series spot welding method that does not use a back electrode has a drawback that it is difficult to form a sufficient nugget and a blow hole is formed, so that a sufficient welding strength cannot be obtained. It was.
Therefore, the applicant of the present invention presses and contacts a pair of spaced apart electrodes on one surface of two superimposed metal plates and causes a welding current to flow between the two electrodes, and welds the two metal plates. A series spot welding method, wherein the electrode of the one metal plate is press-contacted with a part of the seat surface that is partially higher than the general part, and the electrode has a spherical tip. A series spot welding method has been developed in which the electrode is welded to the seating surface under pressure contact so as to crush the seating surface (see Patent Document 1).
JP 2002-239742 A (pages 2 to 6, FIGS. 1 to 4)

  In direct spot welding, one of the two metal plates is used because a welding current flows in the plate thickness direction while pressing with a high pressure (about 300 kgf) while sandwiching the two metal plates between the upper and lower electrodes. Even when there is a gap between the metal plates due to deformation or the like, the two metal plates are brought into close contact with each other by a high pressure, and the gap is eliminated, so that reliable welding can be performed.

  Also, in the series spot welding method using a back electrode, when a current is passed between both electrodes while applying pressure from one direction by a pair of electrodes that separate two stacked metal plates, it is opposite to the pressure side of the electrode. A back electrode is disposed on the back side of the metal plate located on the side. Therefore, the applied pressure of the electrode in the series spot welding method using the back electrode is high as in the direct spot welding, and there is a gap between the metal plates because one of the two metal plates is deformed. Even in this case, both the metal plates are brought into close contact with each other by the applied pressure, and there is no gap, so that reliable welding can be performed.

  On the other hand, in the series spot welding method that does not use the back electrode including the technique of Patent Document 1, two superposed metal plates are applied with a relatively low pressure (about 50 kgf) from only one direction by a pair of electrodes. Therefore, when there is a gap between the metal plates because one of the two metal plates is deformed or the like, the larger the gap, the smaller the contact area of each metal plate. And since a welding nugget is formed only in the contact | adherence part of each metal plate and only the said contact | adherence part can be welded, when an adhesion | attachment area becomes small, welding strength will fall and a welding defect will generate | occur | produce.

  By the way, in the technique of Patent Document 1, the tip of the pressurized electrode crushes the seat surface, so that the seat surface is first deformed into a spherical shape, and then the seat surface deformed into a spherical shape is used as the other metal plate. Make point contact with. As a result, between the one metal plate and the other metal plate, an energization path narrowed in a dot shape by the spherically deformed bearing surface is formed, and the density of the welding current flowing through the energization path is increased. Therefore, a sufficient weld nugget can be generated at the contact portion between both metal plates, and a sufficient weld strength can be obtained without using a back electrode.

  Therefore, in the technique of Patent Document 1, there is an optimum value for the height of the seating surface formed on one metal plate. In other words, if the seating surface is too high, the electrode cannot sufficiently crush the seating surface when the electrode is brought into pressure contact with the seating surface, and the seat surface deformed into a spherical shape and the other metal plate As the point contact area (adhesion area) is reduced, and there is a gap between the two metal plates, the welding strength is reduced and welding failure occurs.

  And in the series spot welding method which does not use the back electrode including the technique of patent document 1, when a welding part is located in the closed cross-section part which the other member assembled | attached by the pre-process of welding covers the back side of a metal plate, etc. Since the gap between the two metal plates at the welding location is hidden and cannot be seen, the welding failure cannot be confirmed visually, and the welding failure can be confirmed only by performing a destructive test. However, 100% inspection cannot be performed in the destructive test. Therefore, there is a demand for a technique for easily and reliably detecting the above-described welding failure without performing a destructive test.

  The present invention has been made to satisfy the above-described requirements, and an object of the present invention is to provide a welding defect detection device for series spot welding that can easily and reliably detect welding defects.

  According to the first aspect of the present invention, a pair of spaced apart electrodes are brought into pressure contact with one surface of two superimposed metal plates, and a welding current is passed between the two electrodes. A welding failure detection device for series spot welding, wherein a seat surface that is partially higher than a general part is formed at a portion where the electrode of the one metal plate is in pressure contact, and the electrode The tip is formed into a spherical surface, and a welding current flows between the electrodes while the tip of the electrode is in pressure contact with the seat so as to crush the seat, and a welding current flows between the electrodes. Resistance detection for detecting the electrical resistance between the two electrodes based on the voltage detection means for detecting the voltage between the two electrodes, the voltage detected by the voltage detection means, and the welding current between the two electrodes Means and electric resistance detected by the resistance detecting means It is larger than a predetermined value, and technical features in that the two welding defects in the metal plate is a and determination means has occurred.

  According to the first aspect of the present invention, the electric resistance between the two electrodes when the welding current is applied to the pair of electrodes in order to weld the two metal plates is obtained from the predetermined value. If it is larger, it is possible to reliably detect the presence or absence of welding failure without performing a destructive inspection by determining that welding failure has occurred.

  Here, the electrical resistance between both electrodes can be easily calculated by Ohm's law based on the voltage between the electrodes and the welding current. And the electrical resistance between both electrodes is calculated at the time of energization of the welding current to the said electrode, and it is not necessary to provide the special work process for measuring electrical resistance. Therefore, according to the first aspect of the present invention, it is possible to easily detect defective welding.

  The predetermined value of the electrical resistance is obtained by conducting an experiment for examining the welding strength of the two metal plates by changing the electrical resistance between both electrodes, and finding an electrical resistance value at which a sufficient welding strength can be obtained. Set it to a value.

(Explanation of terms)
The correspondence between the constituent elements described in [Means for Solving the Problems] described above and the constituent members described in [Best Mode for Carrying Out the Invention] described below is as follows. .
The “welding failure detection device” corresponds to the welding device 20.
The “voltage detection means” corresponds to the voltage detector 44.
The “resistance detection unit” corresponds to the process of S102 executed by the microcomputer 56 of the control circuit 46.
The “determination means” corresponds to the processing of S103 and S106 executed by the microcomputer 56 of the control circuit 46.

[Configuration of the embodiment]
FIG. 1 is a perspective view showing a schematic configuration of a welding apparatus 20 for series spot welding according to an embodiment of the present invention.
The welding device 20 includes a six-axis robot arm 22, air cylinders 24 and 25, electrode tips 26 and 27, a control device 40, and the like.

  The electrode tip 26 is attached to the piston tip protruding from the air cylinder 24, and the electrode tip 27 is attached to the piston tip protruding from the air cylinder 25. The air cylinders 24 and 25 arranged in parallel are attached to the wrist portion 22 a of the 6-axis robot arm 22. The air cylinders 24 and 25 are supplied with compressed air from an air pump (not shown).

  The 6-axis robot arm 22 has the electrode chips 26 and 27 supported by the air cylinders 24 and 25 at predetermined positions on two metal plates Wa and Wb (for example, a steel plate and an aluminum alloy plate, for example). Move. Each of the air cylinders 24 and 25 expands and contracts the piston by the air pressure of the compressed air supplied from the air pump, thereby moving the electrode tips 26 and 27 attached to the tip of the piston forward and backward. The tip portions 26a and 27a of 26 and 27 are brought into pressure contact with the metal plate Wa.

  In the metal plate Wa, a convex portion 30 having a seating surface 30a that is partially higher than the general portion 35 is formed at a portion where the tip portions 26a, 27a of the electrode tips 26, 27 are in pressure contact.

  FIG. 2A is a side view of the tip portions 26a, 27a of the electrode tips 26, 27. FIG. FIG. 2B is a plan view of the convex portion 30 having a seating surface 30a formed on the metal plate Wa. FIG.2 (C) is a side view of the convex part 30 shown in FIG.2 (B).

The tip portions 26a and 27a of the electrode tips 26 and 27 are formed into spherical surfaces.
The convex part 30 is formed in the shape of a hollow truncated cone, and has a circular seating surface 30a on the top. That is, the convex portion 30 has a seat surface 30a formed on a circular flat surface at the top via a tapered portion 30b formed so as to rise while being reduced in diameter from the general portion 35 of the metal plate Wa. It is configured.

  As described above, the tip portions 26a, 27a of the electrode tips 26, 27 are formed in a spherical shape, and a circular flat surface is formed on the top portion of the seating surface 30a. The seating surface 30a can be easily deformed into a spherical shape by the tip portions 26a and 27b of 26 and 27. In addition, the convex part 30 is created by giving press work to the metal plate Wa.

  Here, the plate thickness of the metal plate Wa is set to 0.65 mm, and the plate thickness of the metal plate Wb is set to 0.8 mm or 2 mm. The tip diameters D0 of the tip portions 26a, 27b of the electrode tips 26, 27 are formed to 16 mm, and the separation distance between the tip portions 26a, 27b is set to about 35 mm. And when the seat surface diameter D1 which is the diameter of the seat surface 30a is set to 22 mm, the convex part diameter D2 which is the diameter of the convex part 30 is set to 28 mm, and is the height from the general part 35 to the seat surface 30a. The seat height H is set to 0.4 to 1 mm.

The seating surface diameter D1 of the seating surface 30a is set in the range of 1 to 3 times the tip diameter D0 of the tip portions 26a and 27a of the electrode tips 26 and 27, specifically 14 to 48 mm. The
Thus, by setting the seating surface diameter D1 to be one times the tip diameter D0 at least, even if the positions of the electrode tips 26, 27 and the seating surface 30a vary somewhat, the tip portions 26a, 27b of the electrode tips 26, 27 are arranged. The seating surface 30a can be deformed into a spherical shape by the spherical surface. Further, by setting the seat surface diameter D1 to be three times the tip diameter D0 at the maximum, the seat surface 30a can be partially deformed into a spherical shape without gently bending the entire seat surface 30a.

  FIG. 3 is a circuit diagram showing an electrical configuration of the control device 40 that controls the welding current supplied to the electrode tips 26 and 27 of the welding device 20 and detects a welding failure.

The control device 40 includes a welding transformer 42, a voltage detector 44, a control circuit 46, an AC power supply 48, thyristors SCR1 and SCR2, and the like. A device including the voltage detector 44, the control circuit 46, and the thyristors SCR1 and SCR2 is referred to as a “timer contactor”.
The electrode tips 26 and 27 are electrically connected to the secondary winding of the welding transformer 42. An AC power supply 48 is electrically connected to the primary winding of the welding transformer 42 via the thyristors SCR1 and SCR2.

  The voltage detector 44 detects the voltage between the electrode tips 26 and 27 (secondary voltage of the welding transformer 42) and outputs the voltage value (voltage data) to the control circuit 46. Then, as will be described later, the control circuit 46 detects the electrical resistance between the electrode tips 26 and 27 from the voltage between the electrode tips 26 and 27, and welds the metal plates Wa and Wb based on the electrical resistance. Detect defects.

  The gate terminals of the thyristors SCR 1 and SCR 2 that are connected in parallel in opposite directions are connected to the control circuit 46. The control circuit 46 outputs and controls a trigger signal to the gate terminals of the thyristors SCR1 and SCR2, thereby switching energization / interruption of the welding current supplied from the AC power supply 48 to the primary side of the welding transformer 42. Phase control is performed.

FIG. 4 is a circuit diagram showing the internal configuration of the control circuit 46.
The control circuit 46 includes a display device 52, a sound reproduction device 53, an operation device 54, and a microcomputer (hereinafter abbreviated as “microcomputer”) 56. In addition, you may comprise each apparatus 52-54 as an integrated teaching box integrated with the microcomputer 56. FIG.
The display device 52 is composed of a display, a display lamp, and the like, and displays a welding failure determination processing result by the microcomputer 56, as will be described later.
The operation device 54 includes a push button group and the like, and generates an operation signal corresponding to the operation result of the push button group by the operator of the welding device 20 and outputs the operation signal to the microcomputer 56.

The microcomputer 56 includes a central processing unit (CPU) 56a, a memory 56b, an external storage device (external recording device) 56c, and interfaces (I / O) 56d and 56e.
The memory 56b stores a program for performing a welding current control process, a program for performing a welding failure determination process, and the like. The interface 56d controls the exchange of data signals between the devices 52, 54, and 56c and the CPU 56a. The interface 56e controls the exchange of data signals between the voltage detector 44 and each thyristor SCR1, SCR2 and the CPU 56a.
The external storage device 56c includes a computer-readable recording medium, and a program similar to the memory 56b is stored in the recording medium. Incidentally, computer-readable recording media include semiconductor memory (smart media, memory stick, etc.), hard disk, FD (Floppy Disk), data card (IC card (IC: Integrated Circuit), magnetic card, etc.), optical disk ( CD-ROM, DVD, etc.), magneto-optical disk (MO, etc.), phase change disk, magnetic tape, etc. By the way, the names of specific examples of the recording medium include registered trademarks. The external storage device 56c may be omitted.

[Spot welding process]
FIG. 5 is a partial cross-sectional view for explaining a spot welding process of the metal plates Wa and Wb by the electrode tips 26 and 27 of the welding apparatus 20.

  First, as shown in FIG. 5A, the tip portions 26a, 27a of the electrode tips 26, 27 are positioned above the convex portion 30 of the steel plate Wa with respect to the two metal plates Wa, Wb that are superimposed. As described above, the electrode tips 26 and 27 are moved and positioned by the six-axis robot arm 22.

  Next, as shown in FIG. 5 (B), by extending the pistons of the air cylinders 24 and 25, the electrode tips 26 and 27 attached to the tips of the pistons are moved, and the electrode tips 26 are moved. , 27 are brought into pressure contact with the metal plate Wa.

  At this time, even after the tip portions 26a, 27a of the electrode tips 26, 27 are in contact with the seating surface 30a, the pistons of the air cylinders 24, 25 are extended and the pressurization by the electrode tips 26, 27 is continued. The seating surface 30a is crushed in the direction of the steel plate Wb. In other words, the presence of the convex portion 30 causes the electrode tips 26 and 27 to crush the seating surface 30a so as to narrow the space K formed between the metal plates Wa and Wb. As a result, a concave portion having a spherical recess is formed on the seat surface 30a, and a contact surface 30c that protrudes spherically toward the metal plate Wb is formed on the back side of the seat surface 30a.

  Subsequently, as shown in FIG. 5C, pressurization by the electrode tips 26 and 27 is further continued, and the top of the spherical contact surface 30c formed on the back side of the seating surface 30a is brought into contact with the metal plate Wb. Let That is, the most protruding portion of the contact surface 30c is brought into point contact with the metal plate Wb earlier than the other portions. As a result, the contact surface 30c is in point contact with the metal plate Wb through the point contact portion 30d.

In this state, the control circuit 46 controls the thyristors SCR1 and SCR2 to energize the welding current from the AC power supply 48 to the primary side of the welding transformer 42, so that the electrode tips 26 and 27 from the secondary side of the welding transformer 42 are supplied. Energize the welding current in between.
Then, an energization path (solid line with an arrow in the figure) having a large contact resistance narrowed in a dot shape by the point contact portion 30d is formed, and the welding current flowing through the energization path has a higher current density than the energization path by surface contact. It is done. The resistance heating value is increased by the welding current, and the metal plates Wa and Wb at the point contact portion 30d are melted to produce a weld nugget Na, and both the metal plates Wa and Wb are welded in a spot shape by the weld nugget Na. The

After that, by continuing the pressurization and energization by the electrode tips 26 and 27, the point contact portion 30d of the metal plate Wa sinks so as to sink into the metal plate Wb, and the surface direction along the spherical contact surface 30c. The welding nugget Na is sequentially formed so as to go to, and spot welding is completed.
Note that the pressure applied when the tip portions 26a, 27a of the electrode tips 26, 27 pressurize the metal plate Wa is set to a relatively low pressure (for example, about 50 kgf).

[Detection of welding defects]
FIG. 6 is a flowchart showing a flow of processing executed by the microcomputer 56 of the control circuit 46 in order to detect welding failure.
When the equipment of the welding apparatus 20 is started by an automatic work instruction on the automatic line where the welding apparatus 20 is installed, the microcomputer 56 first activates the CPU 56a and then records (stores) it in the memory 56b. The computer program is loaded on the CPU 56a, and then the following steps (hereinafter referred to as "S") are executed by various arithmetic processes executed by the CPU 56a according to the computer program. The computer program may be recorded (stored) in the external storage device 56c instead of the memory 56b, and the computer program may be loaded from the external storage device 56c to the CPU 56a and used as necessary.

First, the microcomputer 56 determines a welding current to flow between the electrode tips 26 and 27 from the secondary side of the welding transformer 42 based on a program for controlling the welding current read from the memory 56b and energizes the welding current. Therefore, a trigger signal to be output to the gate terminals of the thyristors SCR1 and SCR2 is generated and output (S101).
The welding current is energized continuously for a predetermined time (for example, 5/60 seconds), and the current value of the welding current is set to, for example, 10 kA.

At this time, the voltage detector 44 detects the voltage between the electrode tips 26 and 27 (secondary voltage of the welding transformer 42) and outputs the voltage value to the control circuit 46.
The microcomputer 56 determines the voltage value (electrode voltage) between the electrode tips 26 and 27 detected by the voltage detector 44 when the welding current is flowing between the electrode tips 26 and 27 and the processing of S101. Based on the welding current, the electrical resistance (interelectrode resistance) between the electrode tips 26 and 27 is calculated according to Ohm's law (S102).

Subsequently, the microcomputer 56 determines whether or not the electrical resistance between the electrode chips 26 and 27 is equal to or less than a predetermined value Vt described later (S103).
If the electrical resistance between the electrode tips 26 and 27 is equal to or less than the predetermined value Vt (S103: Yes), the microcomputer 56 determines that normal welding has been performed when energization is completed (S104). ) Complete the welding process.
Further, when the electrical resistance between the electrode tips 26 and 27 is larger than the predetermined value Vt (S103: No), the microcomputer 56 determines that the welding failure has occurred when the energization is completed, and the determination The result is displayed on the display device 52, an abnormal alarm is generated from the sound reproduction device 53 (S105), and the welding process is interrupted.

  When a welding failure is displayed on the display device 52 in the process of S105, the operator of the welding device 20 removes the metal plates Wa and Wb that have been welded from the production line as defective products and repairs them.

[Operations and effects of the embodiment]
FIG. 7A to FIG. 10A are explanatory diagrams for explaining the states of the electrode tips 26 and 27 and the metal plates Wa and Wb during welding, and the dotted lines in the figure indicate the current path of the welding current. It is. Moreover, (B) of FIGS. 7-10 is sectional drawing for demonstrating the state of one convex part 30 vicinity of the metal plate Wa in the same figure (A).

FIG. 7A shows that there is no gap between the metal plates Wa and Wb because one of the two metal plates is deformed or the like, and both metals are applied by the applied pressure from the electrode tips 26 and 27. A state where the plates Wa and Wb are brought into close contact with each other and the gap is eliminated is shown. In this state, a welding current flows through both the metal plates Wa and Wb to form an energization path.
At this time, as shown in FIG. 7B, the area M of the point contact portion 30d of each metal plate Wa, Wb is equal to or greater than a predetermined value Mt.
And the electrical resistance between each electrode tip 26 and 27 becomes below predetermined value Vt, and as shown in FIG. 5, each metal plate Wa and Wb is normally welded.

  In FIG. 8A, there is a gap between the metal plates Wa and Wb because one of the two metal plates is deformed or the like, and pressure is applied from the electrode tips 26 and 27. Also, a small gap remains between the metal plates Wa and Wb, and the metal plates Wa and Wb are in contact with each other only at the point contact portion 30d.

At this time, as shown in FIG. 8B, the area M of the point contact portion 30d of each metal plate Wa, Wb decreases as the gap between the metal plates Wa, Wb increases. And since a weld nugget is formed only at the point contact part 30d (contact part) and only the point contact part 30d can be welded, when the area M of the point contact part 30d becomes less than a predetermined value Mt, the welding strength is reduced, resulting in poor welding. Occur.
The predetermined value Mt is determined as a required value according to the spot welding standard.

And although a welding current flows into both metal plates Wa and Wb and an energization path is formed, a welding current becomes difficult to flow into metal plate Wb. Therefore, the electrical resistance between the electrode tips 26 and 27 increases as the gap between the metal plates Wa and Wb increases (that is, as the area M of the point contact portion 30d decreases), and the electrical resistance increases to a predetermined value Vt. If it is larger, the welding strength of each metal plate Wa, Wb is lowered, resulting in poor welding.
As will be described later, the predetermined value Vt is an electric resistance value at which a sufficient welding strength can be obtained by conducting an experiment for examining the welding strength of each of the metal plates Wa and Wb by changing the electric resistance between the electrode tips 26 and 27. Find and set the electrical resistance value.

In FIG. 9A, there is a gap between the metal plates Wa and Wb because one of the two metal plates is deformed or the like, and pressure is applied from the electrode tips 26 and 27. Also, a large gap remains between the metal plates Wa and Wb, and the metal plates Wa and Wb are not in contact at all.
In this state, a welding current flows only in the metal plate Wa and an energization path is formed. Therefore, the electrical resistance between the electrode tips 26 and 27 is greater than the predetermined value Vt, and the metal plates Wa and Wb are not weldable.

  FIG. 10 shows that the seating surface height H of the seating surface 30a is too high, and the electrode tips 26, 27 can sufficiently crush the seating surface 30a when the electrode tips 26, 27 are brought into pressure contact with the seating surface 30a. This shows a state in which the area M of the point contact portion 30d between the seat surface 30a deformed into a spherical shape and the metal plate Wb is small.

At this time, the area M of the point contact portion 30d becomes smaller as the seating surface height H becomes higher, and when the area M becomes less than the predetermined value Mt, the welding strength is lowered and poor welding occurs.
The electrical resistance between the electrode tips 26 and 27 increases as the seat height H increases (that is, as the area M of the point contact portion 30d decreases), and when the electrical resistance exceeds a predetermined value Vt, each metal is increased. The welding strength of the plates Wa and Wb is reduced, resulting in poor welding.

11 and 12, the gap between the metal plates Wa and Wb is changed from 0 to 3 mm at intervals of 1 mm, and the seating surface height H of the seating surface 30a is 0.2 mm, 0.4 mm, 0.7 mm, 1 It is a graph which shows the electrical resistance between each electrode tip 26,27 at the time of changing and welding to 0.0 mm and 1.2 mm.
As described above, the tip diameters D0 of the tip portions 26a and 27b of the electrode tips 26 and 27 are formed to 16 mm, the separation distance between the tip portions 26a and 27b is set to 35 mm, and the seat surface diameter of the seat surface 30a. D1 is set to 22 mm, the projection diameter D2 of the projection 30 is set to 28 mm, and the welding current flowing between the electrode tips 26 and 27 is set to 10 kA.

In FIG. 11, the thickness of the metal plate Wa is set to 0.65 mm, and the thickness of the metal plate Wb is set to 2 mm.
When the welding strength of each of the metal plates Wa and Wb at each measurement point in FIG. 11 was examined by a destructive test, it was found that a welding failure occurred when the electrical resistance between the electrode tips 26 and 27 was greater than 200 μΩ. Further, it was found that when the seat surface height H is 1.2 mm, poor welding occurs even when the gap between the metal plates Wa and Wb is zero.
That is, in FIG. 11, normal welding is performed when the seat surface height H is 0.4 mm or 0.7 mm, the gap between the metal plates Wa and Wb is 2 mm or less, and the seat surface height H is 1 mm. The case is when the gap is 1 mm or less.

In FIG. 12, the plate thickness of the metal plate Wa is set to 0.65 mm, and the plate thickness of the metal plate Wb is set to 0.8 mm.
When the welding strength of each metal plate Wa, Wb at each measurement point in FIG. 12 was examined by a destructive test, it was found that poor welding occurred when the electrical resistance between each electrode tip 26, 27 was 240 μΩ or more. Further, it was found that when the seat surface height H is 1.2 mm, poor welding occurs even when the gap between the metal plates Wa and Wb is zero.
That is, in FIG. 12, normal welding is performed when the seat height H is 0.4 to 1 mm and the gap between the metal plates Wa and Wb is 2 mm or less.

Thus, in the case of FIG. 11 (when the thickness of the metal plate Wa is 0.65 mm and the thickness of the metal plate Wb is 2 mm), the predetermined value Vt is set to 200 μΩ, and in the case of FIG. 12 (the metal plate Wa When the plate thickness of the metal plate Wb is 0.85 mm), the predetermined value Vt may be set to 240 μΩ.
The reason why the predetermined value Vt is higher in the case of FIG. 12 than in the case of FIG. 11 is that the welding current hardly flows to the metal plate Wb as much as the thickness of the metal plate Wb is reduced. .

  As described above in detail, according to the present embodiment, the electric current between the electrode tips 26 and 27 when the welding current is applied to the electrode tips 26 and 27 in order to weld the metal plates Wa and Wb. The resistance is obtained, and when the electrical resistance is larger than the predetermined value Vt, it is determined that a welding failure has occurred, so that the presence or absence of the welding failure can be reliably detected without performing a destructive inspection.

Here, the electrical resistance between the electrode tips 26 and 27 is based on the voltage value between the electrode tips 26 and 27 detected by the voltage detector 44 and the welding current applied to the electrode tips 26 and 27. It can be easily calculated by Ohm's law.
And the electrical resistance between each electrode tip 26 and 27 is calculated at the time of energization of the welding current to each electrode tip 26 and 27, and it is not necessary to provide the special work process for measuring electrical resistance.
Therefore, according to the present embodiment, a welding failure can be easily detected.

  In addition, the electrical resistance between the electrode tips 26 and 27 increases as the area M of the point contact portion 30d of the metal plates Wa and Wb decreases. Therefore, the operator of the welding apparatus 20 can know the area M of the point contact portion 30d of each metal plate Wa, Wb based on the electrical resistance between the electrode tips 26, 27.

The perspective view which shows schematic structure of the welding apparatus 20 of the series spot welding which concerns on one Embodiment which actualized this invention. 2A is a side view of the tip portions 26a and 27a of the electrode tips 26 and 27. FIG. FIG. 2B is a plan view of the convex portion 30 having a seating surface 30a formed on the metal plate Wa. FIG.2 (C) is a side view of the convex part 30 shown in FIG.2 (B). The circuit diagram which shows the electric constitution of the control apparatus 40 which detects the welding defect while controlling the welding current supplied to each electrode tip 26,27 of the welding apparatus 20. FIG. The circuit diagram which shows the internal structure of the control circuit 46 with which the welding apparatus 20 is provided. The partial cross section figure for demonstrating the spot welding process of the metal plates Wa and Wb by the electrode tips 26 and 27 of the welding apparatus 20. FIG. The flowchart which shows the flow of the process which the microcomputer 56 of the control circuit 46 performs in order to detect a welding defect. FIG. 7A is an explanatory diagram for explaining the states of the electrode tips 26 and 27 and the metal plates Wa and Wb during welding, and the dotted line in the figure indicates a current path for welding current. FIG. 7B is a cross-sectional view for explaining a state in the vicinity of one convex portion 30 of the metal plate Wa in FIG. FIG. 8A is an explanatory diagram for explaining the states of the electrode tips 26 and 27 and the metal plates Wa and Wb during welding, and the dotted lines in the figure indicate the energization paths of the welding current. FIG. 8B is a cross-sectional view for explaining a state in the vicinity of one convex portion 30 of the metal plate Wa in FIG. FIG. 9A is an explanatory diagram for explaining the states of the electrode tips 26 and 27 and the metal plates Wa and Wb during welding, and the dotted lines in the figure indicate the energization paths of the welding current. FIG. 9B is a cross-sectional view for explaining a state in the vicinity of one convex portion 30 of the metal plate Wa in FIG. FIG. 10A is an explanatory diagram for explaining the states of the electrode tips 26 and 27 and the metal plates Wa and Wb during welding, and the dotted lines in the figure indicate the energization paths of the welding current. FIG. 10B is a cross-sectional view for explaining a state in the vicinity of one convex portion 30 of the metal plate Wa in FIG. When the plate thickness of the metal plate Wa is 0.65 mm and the plate thickness of the metal plate Wb is 2 mm, the gap between the metal plates Wa and Wb is changed from 0 to 3 mm at intervals of 1 mm, and the seat surface of the seat surface 30a The graph which shows the electrical resistance between each electrode tips 26 and 27 at the time of welding by changing high H into 0.2 mm, 0.4 mm, 0.7 mm, 1.0 mm, and 1.2 mm. When the thickness of the metal plate Wa is 0.65 mm and the thickness of the metal plate Wb is 0.8 mm, the gap between the metal plates Wa and Wb is changed from 0 to 3 mm at intervals of 1 mm, and the seat surface 30a The graph which shows the electrical resistance between each electrode tip 26,27 at the time of welding by changing the seat surface height H to 0.2 mm, 0.4 mm, 0.7 mm, 1.0 mm, and 1.2 mm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Welding device 24, 25 ... Air cylinder 26, 27 ... Electrode tip 26a, 27a ... Tip part of electrode tip 30 ... Convex part 30a ... Seating surface 35 ... General part 40 ... Control device 42 ... Welding transformer 44 ... Voltage detector 46 ... Control circuit 48 ... AC power supply 56 ... Microcomputer SCR1, SCR2 ... Thyristor Wa, Wb metal plate

Claims (1)

Welding failure of series spot welding in which a pair of spaced electrodes are brought into pressure contact with one surface of two superimposed metal plates and a welding current flows between the two electrodes to weld these two metal plates A detection device,
A portion of the one metal plate that is in pressure contact with the electrode is partially formed with a seating surface that is one step higher than the general part, and the tip of the electrode is formed into a spherical surface so that the seating surface is crushed. A welding current is passed between both electrodes in a state where the tip of the electrode is in pressure contact with the seating surface,
Voltage detecting means for detecting a voltage between the electrodes when a welding current is passed between the electrodes;
Based on the voltage detected by the voltage detection means and the welding current between both electrodes, resistance detection means for detecting the electrical resistance between both electrodes,
Series spot welding welding, comprising: a judging means for judging that welding failure has occurred in the two metal plates when the electrical resistance detected by the resistance detecting means is larger than a predetermined value. Defect detection device.

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