JP3598683B2 - Optimal position control method of spot welding electrode - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for controlling an optimum position of a spot welding electrode.
[0002]
[Prior art]
Conventionally, in pneumatic spot welding, the pressing force P of the electrode gun is kept constant during the energizing time and a certain time before and after the energizing time. Therefore, the behavior of the electrode during welding is as follows.
[0003]
First, a very small amount of the base material during welding is elastically compressed by the squeeze of the welding gun. Then, when the energization is started, the electrode position recedes due to thermal expansion due to heat generation. Thereafter, a nugget (melted portion) is formed at the contact portion of the material to be welded, and when it grows, the base material contracts in the opposite direction, whereby the pressure for pressing decreases, so that the electrode position moves forward.
[0004]
As a technique for preventing the occurrence of scattering due to insufficient electrode pressure, there is a technique disclosed in Japanese Patent Application Laid-Open No. 7-96376.
[0005]
By the way, excessive pressurization, welding current and energizing time promote excessive growth of the nugget, and the weld breaks the surface and scatters, that is, causes spatter.
[0006]
[Problems to be solved by the invention]
However, when the pressing force P is kept constant as in the related art, "push-in" of the welding gun to the material to be welded inevitably occurs during the growth of the nugget. This causes spatter.
[0007]
In order to avoid the occurrence of the spatter, the technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 7-96376 solves the decrease in the welding pressure during welding by changing the value of the current flowing through the servomotor. .
[0008]
In the control for adjusting the pressing force as described above, the responsiveness of the control becomes a problem. That is, since welding is completed in a very short time, it is considered that it is extremely difficult to control the pressing force of the electrode during that time.
[0009]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for controlling an optimum position of a spot welding electrode which can prevent generation of spatter by controlling an electrode position which is relatively easy to control in spot welding.
[0010]
[Means for Solving the Problems]
The present invention has the following configuration in order to solve the above problems.
In the invention of claim 1, when spot welding a workpiece to be welded by a welding gun, at least during energization, the position of the welding gun in the pressure contact direction of the welding electrode is controlled to a fixed position at which welding of desired quality can be obtained. This is a method for controlling the optimum position of a spot welding electrode.
[0012]
The invention according to claim 2 is that, when spot welding a workpiece to be welded by a welding gun, a pressing force of the welding electrode of the welding gun against the workpiece is detected, and based on the pressing force, the welding electrode is provided at least during energization. And controlling the position in the pressure contact direction to a fixed position at which welding of desired quality can be obtained.
[0013]
The invention according to claim 3 is characterized in that the position of the welding electrode in the pressure contact direction is detected, and the position of the welding electrode in the pressure contact direction is controlled to the target position by using a servomotor based on the detected position and the target position. An optimum position control method for a spot welding electrode according to claim 1 or 2 .
[0015]
According to the first aspect of the present invention, at least during energization, the position of the welding electrode is controlled to be constant. Therefore, when the nugget is formed after expansion and contracts when the welding portion is energized, the welding electrode is pressed in ”Can be reliably prevented from being generated.
[0016]
According to the second aspect of the present invention, the pressing force of the welding electrode of the welding gun on the workpiece is detected, and based on the pressing force, the position of the welding electrode is set to a predetermined position at which welding of desired quality can be obtained at least during energization. To control. That is, depending on the material of the material to be welded and the welding conditions, it may be better to reduce the amount of pressure reduction during contraction of the base material. In this case, the generation of spatter can be further suppressed by controlling according to the pressing force as in the second aspect of the present invention.
[0017]
According to the invention of claim 3 , since the position of the welding electrode is detected and the position is controlled by the servomotor from the detected position and the target position, accurate position control becomes possible, and generation of spatter can be reliably prevented.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a control block diagram of a spot welding apparatus that performs the spot welding method according to the first embodiment, FIG. 2 is a control flowchart of spot welding, FIG. FIG. 5 is an explanatory diagram of an example of a pressing force and an expansion amount for position control, FIG. 5 is an explanatory diagram of a nugget growth process, and FIG. 6 is an explanatory diagram of an example of a pressing force and an expansion amount for position control in the second embodiment.
[0019]
In the spot welding apparatus, as shown in FIG. 1, a welding gun 12 provided with opposing welding electrodes 10 (upper electrode 10U, lower electrode 10L), lower welding electrode 10L are fixed, and upper welding electrode 10 is fixed. A servo motor 14 that drives 10U in the vertical direction is a target of welding electrode position control of a servo gun provided at the distal end of the robot arm 16.
[0020]
That is, the servomotor 14 is provided with an encoder, which monitors the current position signal of the upper electrode 10U, inputs the current position signal to the control unit (controller) 18, and uses the current of the servomotor 14 to perform welding by the electrodes 10U, 10L. The pressure applied to the material 20 is monitored and input to the control unit 18. The control unit outputs a position command to the servo motor 14, and controls the electrode 10U position X to be the command position.
[0021]
Therefore, the electrode position X can be controlled by the servomotor 14, the pressing force can be monitored by the motor current, and the electrode position X can be monitored by the encoder, whereby the position between the electrodes 10U and 10L can be controlled.
[0022]
The control of the welding device will be described based on the flowchart of FIG.
As shown in FIG. 3, first, squeezing (advancing) of the electrode 10U is started by sandwiching the workpiece 20 between the electrodes 10U and 10L, and the electrode 10U is brought closer to the workpiece 20 (S1). Next, it waits until the pressing force P of the electrodes 10U and 10L exceeds a certain value P1 (S2), and if it exceeds (S2: Y), a command is input to the servomotor 14 to move the electrode position X to the position. Start positioning control. Thereafter, control is performed so that the position X of the electrode is not changed (S3).
[0023]
Then, after the squeeze is completed (S4: Y), welding energization is started (S5). When the energization for a certain period of time is completed (S6: Y) and the completion of the holding is also completed (S7: Y), the positioning control of the electrode 10U is ended, and the electrode is retracted to the original position (S8). After confirming that the welding is completed, the welding control is ended (S9).
[0024]
As shown in FIG. 3, when the welding electrode 10 is squeezed, the tip tip comes into contact with the workpiece 20 and is elastically compressed. When it is detected that the applied pressure P has reached a constant value, the servo motor 14 positions the welding electrode 10 on the spot. Thereafter, the position X of the upper electrode 10U is positioned in a state where the workpiece 20 is sandwiched by energization, but the expansion amount E of the workpiece 20 changes due to thermal expansion of heat generated by energization.
However, the position X of the electrode is controlled to be always at a constant position regardless of the increase or decrease of the expansion amount.
[0025]
FIG. 4 shows a graph of the pressing force P, the base material expansion amount E, and the electrode position X. For the positioned electrodes 10U and 10L, the reaction force changes due to the change in the expansion amount E, but the control unit 18 continues to issue a position command to the servomotor 14 so that the electrode position X becomes constant. After the energization is completed, the electrode position X is held for a certain time, and after the end of the holding time, the control unit 18 evacuates the electrode tip.
[0026]
As shown in FIG. 5A, the nugget grows at the welded portion of the workpiece 20 by applying a welding current from the upper and lower electrodes 10U and 10L to the welded portion 20a of the workpiece 20 abutted by squeezing. When flowing, the heat-affected zone 22 is generated as shown in FIG. The heat affected zone 22 increases the expansion amount E. Further, as time elapses, as shown in (c), a corona bond and a nugget 22a are generated in the heat-affected zone 22 and melted, and the expansion amount E stops increasing and starts to decrease. Furthermore, as shown in (d), when the nugget 22a grows, the contraction of the weld 20a proceeds.
[0027]
When spot welding the work piece 20 with the welding gun 12, the positions of the welding electrodes 10U and 10L of the welding gun 12 are controlled to be fixed positions at which welding of desired quality can be obtained. The pressure can be reduced when the weld changes from thermal expansion to contraction due to the nugget 22a. Therefore, "push-in" of the electrode due to excessive pressure at the time of growing the nugget 22a can be eliminated, and generation of spatter can be suppressed, so that appropriate welding quality can be obtained.
[0028]
Next, a second embodiment will be described. Since the configuration is the same as that of the first embodiment, the configuration is not shown.
[0029]
In the spot welding method according to the second embodiment, as shown in FIG. 6, when spot welding the work piece 20 by the welding gun 12, positioning is performed when the pressing force becomes P1 due to squeezing of the electrodes. After the energization is started, the pressing force P of the welding electrodes 10U and 10L of the welding gun 12 to the workpiece 20 is detected and monitored. This pressing force can be detected by the current of the servomotor 14. When the detected pressing force P falls below the predetermined pressure reference P2, the control unit 18 moves the electrode in a positive direction (a direction in which the electrode is slightly pressed) by a fixed amount to change the position X of the welding electrode to a desired quality. Correct to the obtained predetermined position. That is, the electrode position X is controlled in accordance with the pressing force P so as to obtain an appropriate welding quality.
[0030]
That is, depending on the material of the material to be welded 20, depending on the welding conditions, it may be better to reduce the amount of decrease in the pressing force when the base material contracts. At this time, the generation of spatter can be more reliably suppressed by correcting the electrode position X in the positive direction as described above.
[0031]
If the position of the electrode is detected in this way and the position is controlled by the servomotor based on the detected position and the target position, accurate position control can be performed and generation of spatter can be reliably prevented.
[0032]
【The invention's effect】
As described above, according to the first aspect of the invention, it is possible to reduce the pressing force when the weld changes from thermal expansion to shrinkage due to generation of a nugget during energization. Therefore, "push-in" of the electrode due to excessive pressure during nugget growth and after expansion can be eliminated, and generation of spatter can be suppressed, so that appropriate welding quality can be obtained.
[0034]
According to the second aspect of the present invention, it may be better to reduce the amount of decrease in pressure during contraction of the base material depending on the material of the material to be welded and welding conditions. In this case, the generation of spatter is controlled by the pressing force. Can be further suppressed .
[0035]
According to the third aspect of the present invention, accurate position control is enabled, so that generation of spatter can be reliably prevented.
[Brief description of the drawings]
FIG. 1 is a control block diagram of a spot welding apparatus that performs a spot welding method according to a first embodiment.
FIG. 2 is a control flowchart of spot welding.
FIG. 3 is an explanatory diagram of a contact state of an electrode against a material to be welded.
FIG. 4 is an explanatory diagram of an example of a pressing force and an expansion amount with respect to electrode position control.
FIGS. 5A to 5D are explanatory views of a nugget growth process during spot welding.
FIG. 6 is a diagram illustrating an example of a pressing force and an expansion amount with respect to an example of position control according to the second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Welding electrode 10U, 10L Upper and lower welding electrodes 12 Welding gun 14 Servo motor 18 Control unit 20 Material to be welded

Claims (3)

In spot welding a workpiece to be welded with a welding gun, at least during energization, the position of the welding gun in the pressure contact direction of the welding electrode is controlled to a fixed position where welding of desired quality is obtained. Optimal position control method. When spot welding a workpiece to be welded by a welding gun, a pressing force of the welding electrode on the workpiece to be welded is detected, and based on the pressing force, a position of the welding electrode in a pressure contact direction is desired at least during energization. An optimal position control method for a spot welding electrode, characterized in that the position is controlled to a fixed position at which quality welding is obtained. The position of the welding electrode in the pressure contact direction is detected, and the position of the welding electrode in the pressure contact direction is controlled to the target position by using a servomotor based on the detected position and the target position. Optimal position control method for spot welding electrodes.

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