JPH07116865A - Spot welding method - Google Patents

Abstract

PURPOSE:To suppress the generation of expulsion resulting from the contact resistance between electrode and object to be welded without cleaning the surface of object to be welded in particular. CONSTITUTION:In the spot welding method to execute automatic welding work of an object to be welded so that a welding gun 21 to perform spot welding with pressurizing an object to be welded 90 by a pair of electrode tip 24, 33 is moved by a robot 61, after both electrodes 24, 33 are brought in contact with the object to be welded 90 and before energizing, the electrodes 24, 33 are rotated around the axis center with controlling movement of the robot 61.

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 capable of suppressing the occurrence of scattering during welding.

[0002]

2. Description of the Related Art In spot welding, a phenomenon called "scattering" occurs in which molten metal is scattered during welding of an object to be welded, if welding conditions are inappropriate. In spot welding work in which a large amount of dust is generated, the scattered molten metal solidifies and accumulates in the surroundings, so the working environment deteriorates and periodic cleaning is required. Further, when the spatter occurs, the molten metal scatters toward the surrounding workers, which is not preferable for safety. Further, when the scattering phenomenon is remarkable, there is a problem that the joint strength of the objects to be welded is adversely affected. Therefore, in spot welding, it is desirable to suppress the occurrence of dust as much as possible.

A technique for suppressing the generation of dust caused by the welding current is disclosed in, for example, Japanese Patent Publication No. 57-37430. In this control method, displacement of the electrode tip, displacement acceleration of the electrode tip, by measuring any of the inter-electrode voltage, to detect the change in the thickness of the workpiece,
The welding current is controlled based on this change in wall thickness.

[0004]

However, in some cases, even if the welding current is controlled, the occurrence of dust cannot be completely suppressed. The cause of the scattering other than the welding current is that the contact resistance between the electrode tip and the workpiece is too large. The reason why the contact resistance between the electrode tip and the object to be welded becomes large is that oil, minute dust, or the like adheres to the surface of the object to be welded. Therefore, in order to suppress the occurrence of scattering due to the contact resistance between the electrode tip and the workpiece, it is necessary to clean the surface of the workpiece in advance, which requires a device and labor. .

The present invention provides a spot welding method capable of preventing the occurrence of scattering due to the contact resistance between the electrode tip and the object to be welded without particularly cleaning the surface of the object to be welded. With the goal.

[0006]

In order to achieve this object, a spot welding method according to the present invention comprises a welding gun for spot welding by pressurizing an object to be welded with a pair of electrode tips by a robot to move the welding gun. In a spot welding method for performing an automatic welding operation of a welded object, after the both electrode tips come into contact with the object to be welded and before the current is applied to the object to be welded, the movement of the robot is controlled to rotate the electrode tip around the axis. It consists of a method of rotating.

[0007]

In the spot welding method thus constructed, the electrode tips move toward the object to be welded by the pressing operation of the welding gun, and both electrode tips come into contact with the object to be welded. When both electrode tips are in contact with the object to be welded, the movement of the robot is controlled and the electrode tips of the welding gun are rotated around the axis. Therefore, the electrode tip and the object to be welded are in sliding contact with each other, and the electrode tip and the object to be welded are brought into a sufficiently close contact. Therefore, the contact resistance between the electrode tip and the object to be welded at the start of energization is reduced, and the occurrence of scattering due to the contact resistance is suppressed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the spot welding method according to the present invention will be described below with reference to the drawings. 1 to 7 show an embodiment of the present invention, particularly an example applied to spot welding of an automobile body. First, a spot welding apparatus to which the spot welding method of the present invention is applied will be described.

FIG. 6 shows the overall structure of the spot welding apparatus. As shown in FIG. 6, the spot welding device 20
Is composed of a welding gun 21, a robot 61, a control means 71 and the like. The welding gun 21 is attached to the wrist portion 65 of the robot 61. The opening of the welding gun 21, the pressurizing operation, and the movement of the robot 61 are controlled by the control means 71.

As shown in FIG. 6, the welding gun 21 is constructed as follows. The welding gun 21 has a C-shaped frame 22, and an electrode tip 24 is attached to a lower portion of the C-shaped frame 22 via a holder 23. A servo motor 26 is attached to the upper portion of the C-shaped frame 22. The output shaft of the servo motor 26 has a shaft coupling 27.
The ball screw 28 is connected via. The ball screw 28 is mounted on the C-shaped frame 2 via the bearings 29a and 29b.
It is rotatably held at 2. The ball screw 28 has
The nut 30 is screwed. The nut 30 moves in the axial direction of the ball screw 28 as the ball screw 28 rotates.

A connecting member 31 is attached to the outer peripheral portion of the nut 30. The holder 3 is attached to one end of the connecting member 31.
The electrode tip 33 is attached via 2. The electrode tip 33 is adapted to move in the axial direction by the rotation of the servo motor 26. The position of the electrode tip 33 can be detected by an encoder 34 provided at the rear portion of the servo motor 26. In the present embodiment, the position of the electrode tip 33 is indirectly detected by the amount of rotation of the servo motor 26, but the configuration may also be such that the advance / retreat distance of the electrode tip 33 is directly detected.

The C-shaped frame 22 is provided with an equalizer (positional deviation correction mechanism) 41 for absorbing positional deviation of the object to be welded (vehicle body) 90 made of a thin steel plate. The equalizer 41 is connected to the wrist of a robot 61 described later. The C-shaped frame 22 is held in a floating state on a wrist portion 65 of a welding robot 61 described later via an equalizer 41.

The electrode tip 33 is electrically connected to one of the kickless cables 55 via a cable (not shown). The electrode tip 24 is electrically connected to one of the kickless cables 55 via the C-shaped frame 22. The other side of the kickless cable 55 is the robot 6
It is connected to the welding transformer 56 fixed to 1. The welding transformer 56 is a controller 5 having a timer function.
It is connected to a welding power source (not shown) via 7. The controller 57 is connected to the control means 71 described later.

As shown in FIG. 2, the robot 61 has six control axes, and is driven by a servo motor 62 provided for each of the control axes M _{1 to} M ₆ . Since the robot 61 is a well-known technique, detailed description thereof will be omitted.

The movement of the robot 61 is controlled by the control means 71. The control means 71 includes
A plurality of welding positions are taught and the robot 61 positions the welding gun 21 at the taught welding positions. The position information of each control axis of the robot 61 is input to the control means 71, and the position information of the welding gun 21 moved by the robot 61 is grasped based on this. Further, positional information of the electrode tip 33 is input to the control means 71 from the encoder 34.

FIG. 7 shows a schematic structure of the control means 71. The control means 71 includes a main CPU 72 and a servo CP.
It is composed of a U73, an interface 74, and a servo amplifier 75. First trajectory calculator 7 of main CPU 72
2a has a function of calculating a trajectory of the robot 61 itself, and the second trajectory calculating unit 72b has a function of calculating a trajectory of the electrode tip 33 of the welding gun 21 in consideration of the trajectory of the robot 61. ing. Further, the pressing force setting unit 72c of the main CPU 72 has a function of commanding a load current corresponding to the pressing force set for each welding point.

The servo CPU 73 has a first trajectory calculation section 7
It has a command function of calculating the difference between the calculated value from 2a and the value of the speed and position fed back, and moving the robot 61 to the welding position taught in advance at a predetermined speed. The robot 61 has a tacho generator 63 that detects the speed of the servo motor 62 for each control axis, and a sensor 64 for position detection.

The servo CPU 73 has a second trajectory calculating section 7
It has a command function of calculating the difference between the calculated value from 2b and the value of the speed and position fed back, and moving the electrode tip 33 to a predetermined position at a predetermined speed. Welding gun 21
Has a tacho-generator 35 for detecting the moving speed of the electrode tip 33 by the servo motor 26, and an encoder 34 for position detection. Further, the servo CPU 73 is
The main CPU 72 has a function of obtaining the load current corresponding to the pressing force from the difference between the command information from the pressing force setting unit 72c and the fed back load current value.

The interface 74 is a servo CPU 73.
It has a function of converting a digital signal from the device into an analog signal. The servo amplifier 75 detects the current flowing through the servo motor 62 of each control axis of the robot 61, and controls the load current of the servo motor 62 based on the difference between the fed back current value and the command value. . Similarly, the servo amplifier 75 is used for the electrode tip 3 of the welding gun 21.
3 functions as a motor current detecting means for detecting a motor current flowing in the servo motor 26 for moving the servo motor 3, and controls the motor current of the servo motor 26 based on the difference between the fed back current value and the command value. ing.

As shown in FIG. 5, the main CPU 72 of the control means 71 is provided with a contact detection means 76 and a scattering suppression operation command means 77. The contact detection means 76 and the scattering suppression operation command means 77 are composed of programs stored in the main CPU 72. Contact detection means 76
Is connected to a servo amplifier 75 as a motor current detecting means for detecting the motor current of the servo motor 26. The contact detection means 76 has a function of determining that the electrode tips 24 and 33 have come into contact with the workpiece 90 at the time when the motor current of the servo motor 26 rapidly increases.

The scattering suppression operation command means 77 has a function of controlling the movement of the robot 61 based on a signal from the contact detection means 76 and rotating the electrode tips 24 and 33 around the axis (pressurizing axis). is doing. Scattering suppression operation command means 7
Reference numeral 7 controls the servo motors 62 of the respective axes of the robot 61 to rotate the electrode tips 24 and 33 of the welding gun 21 around the shaft center (pressurizing shaft center). The axes M _{1 to} M ₆ of the robot are changed. Here, the axial center of the electrode tip is an axial center (pressure axis) that passes through a portion where the electrode tips 24 and 33 come into contact with the workpiece 90, and the axial center of the electrode tip and the axial center of the ball screw are It is applied even when eccentric.

Next, the spot welding method and operation will be described. In an automobile assembly line, a vehicle body is intermittently moved by a conveyor, and spot welding work is performed when the vehicle body is stopped. When the vehicle body is positioned at a predetermined position, the robot 6 in the waiting state
1, the welding gun 21 is moved toward the welding position.

As shown in step 101 of FIG. 1, when the robot 61 reaches the teaching point, the process proceeds to step 102, where the electrode tip 33 is moved by the rotation of the servo motor 26 of the welding gun 21, and the workpiece 90 is pressed. The operation is started. In step 103, it is determined whether or not both electrode tips 24 and 33 have come into contact with the object 90 to be welded by the pressurizing operation. Both of the electrode tips 24 and 33 are welded objects 90.
When the object to be welded 90 is pressed and the motor current of the servo motor 26 rises sharply, the contact detection means 76 causes the electrode tips 24 and 33 to move in response to a signal from the motor current detection means 75. It is possible to detect that the workpiece 90 is touched.

In step 103, both electrode chips 2
If it is determined that Nos. 4 and 33 have come into contact with the workpiece 90, the process proceeds to step 104. In step 104, the electrode tips 24 and 33 are rotated about the taught position (three-dimensional position X, Y, Z and postures α, β, γ) about the axis (pressure axis) by 2 to 3 °. Then, the servo motors 62 of the axes M _{1 to} M ₆ of the robot 61 are controlled. When the electrode tips 24, 33 rotate about the axis (pressure axis), the electrode tips 24, 33 and the workpiece 90 slide,
The electrode tips 24 and 33 and the object to be welded 90 are brought into a sufficiently close contact state.

The electrode tips 24, 33 by the robot 61
When the rotating operation of No. 1 is completed and a predetermined pressure is applied, the process proceeds to step 105, where a welding current is applied to the object to be welded 90 through the electrode tip 24 and the electrode tip 33, and the object to be welded 90
Spot welding is performed. Immediately before the start of energization of the workpiece 90, as shown in the characteristics of FIG.
Since the contact resistance between the electrode tips 24, 33 and the object to be welded 90 is small due to the rotation operation of 33, the occurrence of scattering due to the contact resistance during step welding is suppressed.

In this embodiment, the spot welding using the welding gun 21 which moves the electrode tip 33 by the rotation of the servo motor 26 and pressurizes the workpiece 90 has been described. It is of course applicable to a welding gun for moving the object to press the object to be welded.

[0027]

According to the present invention, after the electrode tip of the welding gun contacts the object to be welded and before the current is applied to the object to be welded,
Since the movement of the robot is controlled to rotate the electrode tip around the axis, the electrode tip and the object to be welded can be sufficiently brought into close contact with each other. Therefore, the contact resistance between the electrode tip and the object to be welded at the start of energization can be reduced, and the occurrence of scattering due to the contact resistance can be suppressed.

[Brief description of drawings]

FIG. 1 is a flowchart showing a procedure of a spot welding method according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a rotating operation of an electrode tip in the spot welding method of FIG.

FIG. 3 is a partially enlarged sectional view of FIG.

4 is a characteristic diagram showing the relationship between the pressing operation of the welding gun of FIG. 2 and the rotating operation of the electrode tip.

5 is a control block diagram of the spot welding method of FIG. 1. FIG.

6 is an overall configuration diagram of a spot welding apparatus to which the spot welding method of FIG. 1 is applied.

FIG. 7 is a control system diagram of the control means in FIG.

[Explanation of symbols]

 20 Spot Welding Equipment 21 Welding Gun 24 Electrode Tip 33 Electrode Tip 61 Robot 90 Workpiece

Claims (1)

[Claims] 1. A spot welding method in which a welding gun, which pressurizes an object to be welded by a pair of electrode tips to perform spot welding, is moved by a robot to perform an automatic welding operation on the object to be welded. A spot welding method comprising: controlling the movement of the robot and rotating the electrode tip around the axis after contacting the object and before energizing the object to be welded.