JPH1110353A - Spot welding method and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of expulsion and welding defects by actually applying a proper pressurizing force between members in a weld zone, in a spot welding method in which the weld zone of a liquid tank is held between a pair of electrode tips, pressurized and energized for welding. SOLUTION: In the servo gun electrode tips oppositely vertically arranged with a weld zone of a liquid tank in between, the upper electrode tip is advanced by a servo motor, pressurizing a weld zone (S4). With the inter- electrode distance detected based on the output signal of the servo motor (S5), and with the distance equalized to the total thicknesses of a work in the weld zone (S6), the pressurizing force to the weld zone by the electrode is detected and stored (S8). The weld zone is pressurized with the value in which the detected pressurizing force is added to the preset proper pressurizing force required for welding (S9, 10, 11).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding method and apparatus suitable for joining plate materials and the like, and particularly to the technical field of setting a pressing force in spot welding.

[0002]

2. Description of the Related Art Conventionally, as a spot welding method and apparatus of this kind, for example, as disclosed in Japanese Patent Application Laid-Open No. Hei 8-90251, by monitoring a pressurized state, defects such as poor welding can be detected beforehand. Some are known to prevent this. In this apparatus, a spot welding apparatus is used in which two plate-shaped works, which are vertically overlapped, are sandwiched between a pair of electrodes and pressurized, and current is applied between the electrodes to perform welding. A U-shaped spring member disposed laterally so as to be displaced in accordance with the pressing force applied to the upper electrode; and a linear displacement sensor for detecting a displacement amount of the spring member. Based on the detected value, it is determined whether the pressing force applied to the electrode is within a predetermined proper range, and if it is determined that the pressing force is out of the proper range, the welding operation is stopped. It is designed to prevent the occurrence of dispersion due to overheating when the amount is too small, and to prevent poor welding due to insufficient melting when the pressing force is excessive.

[0003]

Generally, there is a slight gap between the overlapped workpieces in the welded portion. Therefore, when the workpieces are pressurized, the pressing force actually acting between the workpieces is as follows. The value obtained by subtracting the force for elastically deforming the work and bringing it into close contact with each other is subtracted from the pressing force applied from the electrode. However, in the above-mentioned conventional spot welding method, since the pressing force applied to the electrode, that is, the pressing force for pressing the work by the electrode is set to a constant value within an appropriate range, it actually acts between the works in the non-welded portion. The applied pressure may change due to dimensional errors of individual workpieces, misalignment at non-welded portions, and the like, and may deviate from an appropriate range. As a result, there is a problem that scattering and poor welding cannot be sufficiently prevented. is there.

[0004] The present invention has been made in view of such a point, and an object of the present invention is to make it so that the pressing force actually acting between the overlapped works in the welded portion becomes an appropriate pressing force. The purpose of the present invention is to sufficiently prevent the occurrence of scattering and poor welding.

[0005]

In order to achieve the above-mentioned object, according to the solution of the present invention, the state in which the workpieces are in close contact with each other at the portion to be welded is used as a reference. By applying pressure, an appropriate pressing force is actually applied between the overlapped workpieces in the welded portion.

More specifically, the first aspect of the present invention is directed to a spot welding method in which a welded portion of a superposed work is sandwiched between a pair of electrodes and pressurized, and current is applied between the electrodes to perform welding. . Then, pressure is applied until the welded portions of the work are brought into close contact with each other, and the pressure applied to the welded portion by the pair of electrodes at this time is detected, and the pressure is adjusted to a predetermined appropriate pressure required for welding. The workpiece is pressurized and welded by the pair of electrodes with the pressure applied to the detection value.

[0007] In this method, the workpieces are actually brought into close contact with each other at the welded portion, and from this state, the workpiece is further pressurized with an appropriate pressure required for welding. Even if the pressing force for bringing the work into close contact varies due to displacement or the like, an appropriate pressing force for welding can be actually applied between the works in the non-welded portion. As a result, the contact resistance at the welded portion can be set to a constant appropriate value irrespective of the dimensional error and displacement of the work, and therefore, the overheating and insufficient melting of the welded portion can be avoided to generate the scattering. And poor welding can be sufficiently prevented.

According to a second aspect of the present invention, in the first aspect of the invention, an increase in the pressure applied to the workpiece by the pair of electrodes is detected, and when the degree of the detected increase suddenly changes to a predetermined value or more, It is determined that the welded portions of the work are in close contact with each other, and the pressure applied to the work by the pair of electrodes is detected.

That is, while the electrode presses and elastically deforms the welded portion of the work, the pressing force increases relatively slowly due to the reaction force from the work as the electrode advances. When the welds are in close contact with each other, the electrode can hardly move forward, and the pressure increases rapidly.
Thus, when the degree of increase in the pressing force changes abruptly beyond a predetermined value, it can be determined that the workpiece is in close contact. This makes it possible to easily detect the actual contact state of the work.

A third aspect of the present invention is directed to a spot welding method in which a welded portion of a superposed workpiece is sandwiched between a pair of electrodes and pressurized, and current is applied between the electrodes to perform welding. When the distance between the pair of electrodes that presses the welded portion of the work becomes equal to the total thickness of the work in the welded portion, the pressure applied to the welded portion by the pair of electrodes is detected. Then, the work is pressurized by the pair of electrodes and welded by a pressure obtained by adding the above detected value to a predetermined appropriate pressure required for welding.

According to this method, when the distance between the pair of electrodes for pressing the welded portion of the work becomes equal to the total thickness of the work at the welded portion, the welded portions of the work are brought into close contact with each other. Pretend to be in a state. Then, from this state, pressure is further applied with an appropriate pressing force necessary for welding. As a result, an appropriate pressing force for welding can be actually applied between the workpieces in the non-welded portion without actually detecting the close contact state of the workpieces, similarly to the first aspect of the invention. Irrespective of the dimensional error of the work or the positional deviation at the non-welded portion, the occurrence of scattering and poor welding can be sufficiently prevented.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the feed motor uses a spot welding machine for driving at least one of a pair of electrodes arranged to face each other forward by a feed motor. The distance between the electrodes is detected based on the signal of the amount, and when the detected distance between the electrodes becomes equal to the total thickness of the work in the welded portion, the pressing force to the welded portion is detected. I made it.

That is, the forward drive amount of the electrode by the feed motor is calculated based on the signal of the feed amount output from the feed motor, and the distance between the pair of electrodes can be easily detected from the calculation result.

According to a fifth aspect of the present invention, there is provided a pair of electrodes arranged so as to face each other with a welded portion of the overlapped workpiece interposed therebetween, and at least one of the two electrodes is driven forward by a feed motor. The present invention is directed to a spot welding apparatus in which a portion to be welded is pressurized and a current is applied between the electrodes to perform welding. Then, an inter-electrode distance detecting means for detecting a distance between the electrodes based on a signal of a feed amount of the feed motor, and an inter-electrode distance detected by the inter-electrode distance detecting means is a total of a work in a welded portion. When the thickness becomes equal to the thickness, the pressing force detecting means for detecting the pressing force of the pair of electrodes on the welded portion, and the pressing force on the workpiece by the pair of electrodes are set to an appropriate value necessary for welding set in advance. And a pressure setting means for setting the pressure to a value obtained by adding the value detected by the pressure detection means to the pressure.

According to this configuration, when the inter-electrode distance detected by the inter-electrode distance detecting means becomes equal to the total thickness of the work in the welded portion, the pressure applied to the welded portion by the pair of electrodes is increased. The pressure detected by the pressure detection means and a value obtained by adding a predetermined appropriate pressure to the detected value are set as the pressure applied to the welded portion of the workpiece by the pair of electrodes by the pressure setting means. For this reason, similarly to the third aspect of the invention, it is possible to sufficiently prevent the occurrence of scattering and poor welding regardless of the dimensional error of each work or the displacement of the non-welded portion.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

(Structure of Spot Welding Apparatus) FIG. 1 shows an embodiment in which the present invention is applied to a welding robot, 1 is a liquid tank as a work assembled by spot welding, and 2 is a servo gun as a spot welding machine. The servo gun 2 is supported by a welding robot 4 controlled by a controller 3.
The liquid tank 1 is spot-welded in response to an operation command from the controller.

The liquid tank 1 has a pair of members 1 formed in a cylindrical shape with a bottom and overlapped with each other at the opening end side.
The pair of members 10, 10 are spot-welded at a flange-shaped welded portion 1a protruding outward from the opening end side and are integrally connected.

As shown in FIG. 2, the servo gun 2 is provided on a casing 21 having a U-shape in plan view and an opening side (right side in FIG. 2) of the casing 21 and substantially moves up and down in the vertical direction. A cylindrical main body 22 and the casing 21
A servo motor 23 as a feed motor disposed in parallel with the main body 22 therein, and a power supply 24 for supplying power to the servo motor 23 and an electrode chip described later are provided.
A J-shaped arm 25 extending downward is provided at the lower end of the casing 21, and a distal end 25 a of the arm 25 is positioned on the axis of a rod 26 extending downward from the lower end of the main body 22. A pair of vertically opposed electrode tips 27, 27 are externally fitted and fixed to the tip 26a of the rod 26 and the tip 25a of the arm 25, respectively.

The main body 22 is attached to the casing 21 via a pair of left and right sliders (not shown) disposed on the peripheral surface so as to be able to move up and down in a vertical direction, and includes a feed mechanism comprising a nut 22a and a feed screw 22b. To drive forward and backward. That is, a nut 22a is non-rotatably mounted on the upper end side of the main body 22, and a feed screw 22b screwed with the nut 22a is disposed coaxially through the upper end surface of the main body 22. A pulley 22c is externally fitted and fixed to the upper end side of the feed screw 22b, and the transmission belt 2 is rotated so that the pulley 22c rotates in conjunction with a pulley 22d externally fitted to the shaft of the servomotor 23.
2e. And the servo motor 23
The feed screw 22b is rotationally driven by the rotation operation of the above, and the main body portion 22 is driven forward and backward in the vertical direction. The servomotor 23 is provided with an encoder 23a for detecting the rotation angle of the shaft. An output signal from the encoder 23a is input to the controller 3 as a signal of the feed amount of the servomotor 23. That is, the servo gun 2 is rotated by the servo motor 23 to rotate the main body 22.
Is moved downward, and a predetermined amount of current is applied between the electrodes for a predetermined time in a state where the welded portion 1a of the liquid tank 1 is pressed from above and below by the pair of upper and lower electrode tips 27, 27 to perform spot welding. It has become.

The controller 3 receives an operation input by an operator via an operation panel (not shown), and controls the servo gun 2 and the welding robot 4 based on the input. That is, the controller 3 moves the servo gun 2 by the operation of the welding robot 4 and positions the servo gun 2 at the point where the spot welding is performed, and then spot welds the welded portion 1a by the operation of the servo gun 2. At this time, as a characteristic part of the present invention, the controller 3 detects the distance between the pair of electrode tips 27, 27 based on an input signal from the encoder 23a of the servomotor 23, and the detected value is used as the welding target 1a. The pressure applied to the welded portion 1a by the electrode tips 27, 27 when the thickness becomes equal to the thickness of the welded portion 1a is detected. Then, the output torque of the servomotor 23 is changed and adjusted so that the pressure applied by the pair of electrode tips 27, 27 becomes a value obtained by adding the detected value to the appropriate pressure required for welding. .

It should be noted that the welding robot 4 includes first to sixth welding robots.
Is an articulated robot having six rotation axes A to F,
The motors provided on the respective axes A, B,... Are operated by the operation control of the controller 3 to move the servo gun 2 connected and fixed to the hand unit 31 by the connecting bolts in three-dimensional directions, and the posture of the servo gun 2. Is changed.

(Spot Welding Method) Next, a specific operation procedure and a control procedure for performing spot welding using the spot welding apparatus according to the above embodiment will be described with reference to FIGS.

The operator performing the spot welding inputs and sets the total plate thickness and the proper pressing force (Pn) in the welded portion 1a of the liquid tank 1 in the controller 3 and stores them in the memory in advance. Then, when actually performing spot welding, in step S1 of FIG. 3, first, the servo gun 2 is operated in a state where there is nothing between the pair of electrode tips 27, 27. In step S2, the distance between the electrodes detected based on the input signal from the encoder 23a is reset to zero. That is, calibration is performed so that the distance between the electrodes can be accurately detected. Subsequently, in step S3, the thickness of the welded portion 1a is read from the memory.

In step S4, the operator moves the servo gun 2 by the operation of the welding robot 4 so that the pair of electrodes 27, 27 sandwich the welded portion 1a.
Then, the servo gun 2 is operated at the opposite hitting point at a position substantially orthogonal to the position. And servo motor 2
3, the upper electrode tip 27 is driven forward, and the upper and lower electrode tips 27, 27 are used to move the welded portion 1
a is pressurized and the members 10, 1 in the welded portion 1a are
The gap between zeros gradually decreases (see FIG. 4).

In step S5, the forward drive amount of the upper electrode tip 27 is calculated based on the input signal from the encoder 23a of the servo gun 2, and the distance between the electrodes of the pair of electrode tips 27 is detected from the calculated value. You. In the following step S6, the inter-electrode distance detected in step S5 is compared with the total plate thickness of the welded portion 1a. If the inter-electrode distance is not equal to the plate thickness, the welded portion 1a must be in a close contact state. The process proceeds to step S7, and the process returns to step S5 while continuing the pressurization. During this time, the pressing force increases as the reaction force from the welded portion 1a increases.

On the other hand, if the distance between the electrodes becomes equal to the plate thickness in step S6, ie,
Assuming that a is in close contact (see FIG. 5), the process proceeds to step S8, where the current electrode pressure (P0) calculated based on the current output torque of the servo motor 23 is stored in the memory. Is stored. That is, the pressure is gradually increased while monitoring the distance between the electrodes, and the pressure (P0) when the welded portion 1a is considered to be in a close contact state is stored.

In step S9, the appropriate pressure (Pn) required for welding is read from the memory, and the value obtained by adding the electrode pressure (P0) stored in step S8 to the appropriate pressure (Pn) is given by In step S10, the pressure is set as the pressure applied to the welded portion 1a by the electrode tips 27,27. Finally, in step S11, the output of the servomotor 23 is adjusted, and the pressure applied to the portion to be welded 1a by the pair of electrode tips 27, 27 is set as described above (P = P
0 + Pn). As a result, an appropriate pressing force (indicated by a thick arrow in FIG. 6) acts between the superposed members 10 in the welded portion 1a. Thereafter, a predetermined amount of current is applied between the pair of electrodes 27 for a predetermined time to perform spot welding.

In the above flowchart, step S
5 corresponds to the inter-electrode distance detecting means 31 for detecting the inter-electrode distance between the pair of electrodes 27, 27. Steps S6 and S8 correspond to the inter-electrode distance detecting means 31.
Corresponds to the pressing force detecting means 32 for detecting the pressing force by the pair of electrodes 27 when the distance between the electrodes detected by the above becomes equal to the plate thickness of the welded portion 1a. Further, steps S9 and S10 correspond to the pressing force detecting means 32.
The value obtained by adding the appropriate pressure to the value detected by
7 and 27 correspond to the pressing force setting means 33 which sets the pressing force to the welded portion 1a.

Therefore, according to the spot welding method of this embodiment, the pair of electrode tips 27,
27, the welded portion 1a of the liquid tank 1 is pressurized until it can be considered to be in close contact (S4 to S7), and the pressure applied to the welded portion 1a by the electrode tips 27, 27 at this time is detected. (S8), and a pressure obtained by adding a predetermined appropriate pressure to the detected value (S9, S1).
0), the welded portion 1a is pressurized (S
11).

For this reason, even if the pressure required to bring the welded portion 1a into close contact varies due to dimensional errors of the individual liquid tanks 1 or misalignment in the non-welded portion 1a, the above-described welding The pressurizing force actually acting between the members 10 in the portion 1a can be the above-described appropriate pressurizing force set in advance. This allows the contact resistance at the welded portion 1a to be a constant appropriate value irrespective of the dimensional error and the displacement of the liquid tank 1 and the like. Generation and poor welding can be sufficiently prevented.

In this embodiment, when the distance between the pair of electrode tips 27 of the servo gun 2 becomes equal to the total thickness of the welded portion 1a, the welded portion 1a comes into close contact. Since the simulation is performed, it is not necessary to actually detect the close contact state of the welded portion 1a.
In addition, the distance between the pair of electrode tips 27 can be easily detected based on the input signal from the encoder 23a of the servo gun 2.

(Other Embodiments) The present invention is not limited to the above embodiments, but includes various other embodiments. That is, in the above embodiment, the present invention is applied to a case where spot welding is performed using the welding robot 4. However, the present invention is not limited to this, and can be applied to a case where a welding robot is not used as long as spot welding is performed. It is.

For example, when an air gun is used, a dedicated distance measuring sensor may be used for detecting the distance between the electrodes. At this time, the detection of the pressure applied to the welded portion by the electrode tip may be calculated based on, for example, air pressure supplied to an air cylinder for driving the electrode tip forward, or A load cell may be arranged between the air cylinder and the air cylinder to directly detect the pressing force.

In the above embodiment, the distance between the pair of electrode tips 27 in the servo gun 2 is
When the thickness of the welded portion 1a becomes equal to the thickness of the welded portion 1a, the welded portion 1a is considered to be in a close contact state.
It is not limited to this. That is, for example, an increase in the pressure applied to the welded portion 1a by the pair of electrode tips 27, 27 is detected in a time series, and as shown in FIG. When it becomes larger, the actual state of close contact of the welded portion a may be detected. In this case, the contact state can be easily detected without inputting and setting the thickness of the welded portion 1a in advance.

In FIG. 7, the abscissa represents the amount of advance of the electrode, while the ordinate represents the pressing force. For example, in the graph A of FIG.
When the electrode tip 27 advances, the welded portion 1a is elastically deformed and the pressing force increases. When the advance amount of the electrode tip 27 reaches x2 (pressure P0), the welded portion 1a comes into close contact with
Only the pressing force rapidly increases while the amount of advance of the electrode tip 27 hardly increases. Therefore, the electrode tip 2
If the pressing force is detected in chronological order while advancing 7 at a constant rate, it is possible to detect the actual close contact state of the welded portion 1a based on the rapid increase in the pressing force.

[0037]

As described above, in the spot welding method according to the first aspect of the present invention, the workpieces are actually brought into close contact with each other at the portion to be welded, and from this state, the workpiece is further pressed with an appropriate pressing force. As a result, the contact resistance at the welded portion can be set to a constant appropriate value regardless of the dimensional error of each work or the displacement of the non-welded portion, thereby avoiding overheating and insufficient melting of the welded portion. As a result, it is possible to sufficiently prevent the occurrence of scattering and poor welding.

According to the second aspect of the present invention, when the degree of increase in the pressure applied to the work by the pair of electrodes suddenly changes, the state of close contact of the work is determined, so that the thickness of the work is set in advance. Without this, it is possible to easily detect the actual close contact state of the work.

According to the third aspect of the present invention, when the distance between the pair of electrodes is equal to the total thickness of the work in the welded portion, it is assumed that the welded portion is in close contact. Thus, the same effect as that of the first aspect can be obtained without actually detecting the close contact state of the welded portion.

According to the fourth aspect of the present invention, the distance between the electrodes can be easily detected based on the signal from the feed motor for driving the electrodes forward.

According to the spot welding apparatus of the fifth aspect, the same effect as the third aspect of the invention can be obtained.

[Brief description of the drawings]

FIG. 1 is an all-pair configuration diagram showing an embodiment of the present invention.

FIG. 2 is an enlarged view showing a configuration of the servo gun of FIG.

FIG. 3 is a flowchart illustrating a procedure for setting a pressing force in a servo gun.

FIG. 4 is a schematic diagram showing an initial state in which a pair of electrode tips come into contact with a welded portion of a work and pressurize the work.

FIG. 5 is a schematic diagram showing a state where a welded portion of a pressurized work is brought into a close contact state.

FIG. 6 is a schematic diagram showing a state in which a proper pressing force is further applied to a work in a close contact state.

FIG. 7 is a diagram showing a forward operation amount of an upper electrode and an increase in a pressing force accompanying the forward operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid tank (work) 1a Welded part 2 Servo gun (spot welding machine) 23 Servo motor (feed motor) 27, 27 Electrode tip (electrode) 31 Inter-electrode distance detection means 32 Pressure detection means 33 Pressure setting means

Claims (5)

[Claims] 1. A spot welding method in which a welded portion of a superposed work is sandwiched between a pair of electrodes and pressurized, and a current is applied between the electrodes to perform welding, until the welded portions of the work are brought into close contact with each other. Pressurized, the pressure applied to the welded portion by the pair of electrodes at this time is detected, and the pressure is obtained by adding the detection value to the appropriate pressure required for welding set in advance. A spot welding method characterized in that a workpiece is pressurized and welded. 2. The method according to claim 1, wherein an increase in the pressure applied to the work by the pair of electrodes is detected, and when the degree of the detected increase suddenly changes to a predetermined value or more, the welded portions of the work are mutually connected. A spot welding method comprising: judging that the electrodes are in close contact with each other, and detecting a pressure applied to the workpiece by the pair of electrodes. 3. A spot welding method in which a welded portion of a superposed work is sandwiched between a pair of electrodes and pressurized, and a current is applied between the electrodes to perform welding. Is equal to the total thickness of the work in the welded portion, the pressure applied to the welded portion by the pair of electrodes is detected, and the appropriate pressure required for welding set in advance is set to the appropriate value. A spot welding method characterized in that a workpiece is pressurized and welded by the pair of electrodes with a pressing force to which a detection value is added. 4. The method according to claim 3, wherein a spot welding machine is used in which at least one of a pair of electrodes disposed to face each other is driven forward by a feed motor. A spot welding method, wherein when the detected inter-electrode distance becomes equal to the total thickness of the work in the welded portion, the pressure applied to the welded portion is detected. 5. A pair of electrodes arranged so as to face each other across a welded portion of a superposed work, and at least one of the two electrodes is driven forward by a feed motor to pressurize the welded portion. A spot welding apparatus configured to conduct welding between the electrodes so as to perform welding between the electrodes; an inter-electrode distance detecting means for detecting a distance between the electrodes based on a signal of a feed amount of the feed motor; When the distance between the electrodes detected by the above becomes equal to the total thickness of the work in the welded portion, the pressure detection means for detecting the pressure applied by the pair of electrodes to the welded portion, A pressure setting means for setting a pressure applied to the workpiece to a value obtained by adding a value detected by the pressure detection means to an appropriate pressure required for welding set in advance. Welding equipment.