JP6816334B2 - Polishing method for spot welding electrodes - Google Patents

Description

The present invention relates to a method for polishing an electrode for spot welding.

Electrodes used for spot welding are subject to pressure at high temperatures during welding work and a large current flows, so the tips wear and flat parts are formed during use, and metal components of the welding object adhere to them. Or If the welding operation is continued in this state, the current density decreases and a predetermined Joule heat cannot be obtained, causing welding failure. In order to prevent welding defects due to such deterioration of the electrode, the tip of the electrode is cut and polished at regular intervals in order to return the tip of the electrode to a predetermined curved surface shape.

Polishing of the electrode tip is performed using a polishing device located near the welding robot. The polishing device has, for example, a cutter holder in which a cutter is mounted in a recess into which an electrode tip can be fitted. When polishing the electrodes, the cutter holder is pressed and sandwiched by a pair of electrodes provided at the tip of the welding gun, and the cutter holder is rotated in a certain direction by the driving force of the motor.

During the electrode polishing work, the tip of the electrode is scraped to generate cutting chips. Here, most of the cutting chips are discharged from the cutter holder while being appropriately divided. On the other hand, cutting chips may be continuously connected or welded to the cutter. In such a case, cutting chips are retained in the recessed portion of the cutter holder, the discharge of the cutting chips is hindered, the cutting chips are clogged, and the electrodes are not properly polished. In order to prevent such a situation, a technique for rotating the cutter holder in the forward and reverse directions, which is the electrode cutting direction, and the reverse direction opposite to the electrode cutting direction during the electrode polishing operation is disclosed (for example, Patent Document 1). See). In the same document, the cutter holder repeats forward and reverse rotations a plurality of times during electrode polishing. As a result, it can be expected that clogging of cutting chips in the recessed portion of the cutter holder will be suppressed.

In Patent Document 1, the cutter holder at the time of electrode polishing is rotated and controlled so as to repeat forward and reverse rotation according to a predetermined time chart. In such forward / reverse control under fixed conditions during electrode polishing, the clogging of cutting chips in the cutter holder is not always cleared, and polishing is continued in a state where the clogging of cutting chips is not cleared. However, the tip of the electrode may not be finished in an appropriate shape. On the other hand, if the forward / reverse operation is repeated a plurality of times even though the cutting chips are not clogged, the electrode polishing work becomes wasteful, which may lead to a decrease in the work efficiency of the entire welding work.

Japanese Unexamined Patent Publication No. 2001-287046

The present invention has been conceived under the above circumstances, and is suitable for spot welding to prevent inconvenience (clogging of cutting chips) during electrode polishing work and to avoid deterioration of work efficiency. The main subject is to provide a method for polishing the electrode for use.

In order to solve the above problems, the following technical means are adopted in the present invention.

The method for polishing the electrodes for spot welding provided by the present invention is performed by rotating the cutter holder while pressing and sandwiching the cutter holder on which the cutter is mounted by a pair of electrodes provided at the tip of the welding gun. This is a method for polishing the electrode for use, in which the cutter holder is rotated in the forward rotation direction to cut the tip of the electrode, and the presence or absence of clogging of cutting chips in the cutter holder is determined based on the driving state of the motor. When it is determined that there is cutting chips in the step of determining the presence or absence of clogging of the cutting chips, the motor is rotated in the reverse direction opposite to the forward rotation direction, and the pair of electrodes are separated from the cutter. It is characterized by performing a cutting debris removal process.

Preferably, after the cutting debris removing step, the step of determining the presence or absence of clogging of the cutting debris is performed again.

Other features and advantages of the present invention will become more apparent with the detailed description given below with reference to the accompanying drawings.

It is a schematic perspective view which shows an example of the polishing apparatus for carrying out the polishing method of the electrode for spot welding which concerns on this invention. It is a partially enlarged perspective view of a cutter holder. It is an enlarged vertical sectional view of a cutter holder. It is a schematic diagram which shows an example of the welding robot equipped with the electrode for spot welding. It is a processing flow diagram which shows an example of the polishing method of the electrode for spot welding which concerns on this invention.

Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1 shows an example of a polishing apparatus for carrying out the method for polishing a spot welding electrode according to the present invention. The polishing apparatus A1 shown in FIG. 1 includes a cutter holder 2 provided at the tip end portion of the gear case 1 and a motor 3 attached to the base end portion of the gear case 1. The cutter holder 2 is supported by the gear case 1 in a state where it can rotate around the rotation axis Ox along the vertical direction. The motor 3 can be rotationally driven in the forward rotation direction and the reverse rotation direction, and is, for example, a servo motor. When the motor 3 rotates, the rotational driving force of the motor 3 is transmitted to the cutter holder 2 via a power transmission mechanism (not shown) in the gear case 1.

As shown in FIGS. 2 and 3, the cutter holder 2 is sandwiched between the pair of electrodes 6 and 6 during the polishing operation of the pair of electrodes 6 and 6 as spot welding electrodes. The main portion of the pair of electrodes 6 and 6 is substantially columnar, and the tip portion has a tapered curved surface shape. The cutter holder 2 has a pair of recessed portions 21 into which the tips of the pair of electrodes 6 and 6 can be fitted. One of the pair of recessed portions 21 faces upward and the other faces downward, and each has a concave curved surface shape corresponding to the tip end portion of the electrode 6, and functions as a guide during polishing.

A cutter 22 for cutting and polishing the tip of the electrode 6 is mounted on the cutter holder 2. In this embodiment, two cutters 22 are fixed. The cutter 22 has a blade portion 22a having a substantially arc shape corresponding to the tip shape of the electrode 6. The blade portion 22a slightly protrudes from the surface of the recessed portion 21.

Further, in the present embodiment, the cutter holder 2 is formed with a notch groove 23. The notch groove 23 is for discharging cutting chips outward in the radial direction, and has a shape in which a part of the recessed portion 21 is dug down. The notch groove 23 is provided so as to be adjacent to each cutter 22. The notch groove 23 is in front of the cutter 22 in the direction of rotation of the cutter holder 2 when cutting the electrode 6 (the direction in which the arrow N1 in FIG. 2 faces, hereinafter appropriately referred to as the "forward rotation direction"). It is located adjacent to.

The spot welding electrodes (a pair of electrodes 6 and 6) are mounted on a welding robot, for example. FIG. 4 is a schematic view showing an example of a welding robot equipped with a spot welding electrode. The welding robot B1 has a movable arm 4 in which a plurality of arm portions 41 are rotatably connected to each other around a predetermined rotation axis, and a welding gun 5 is supported at the tip of the movable arm 4. The spot welding electrodes (pair of electrodes 6 and 6) are arranged so as to face the tip of the welding gun 5.

Regarding the pair of electrodes 6 and 6, the one located below is a fixed electrode fixed to the tip of the welding gun 5, and the one located above is relative to the fixed electrode by the servomotor 7 so as to approach or separate from the fixed electrode. It is a movable electrode that can be moved.

During welding work, a predetermined value of welding current flows between the pair of electrodes 6 and 6 while sandwiching the object to be welded (work) between the pair of electrodes 6 and 6 with a predetermined pressing force. A flow path for cooling water (not shown) for preventing overheating of the electrodes 6 is formed inside the pair of electrodes 6 and 6, and the cooling water flows through the flow path during welding work. Is done.

The drive control of the welding robot B1 is performed by a robot control panel (not shown). The robot control panel also controls the drive of the polishing device A1. For example, during welding work, while a control signal is output from the robot control panel to the welding robot B1, detection signals from various sensors and the like are input to the robot control panel. Further, during the polishing operation, various detection signals are input to the robot control panel while the control signal is output from the robot control panel to the welding robot B1 and the polishing device A1.

When polishing a pair of electrodes 6 and 6 using the polishing device A1, the number of rotations of the motor 3, the distance between the pair of electrodes 6 and 6, the pressure applied to the cutter holder 2 by the pair of electrodes 6 and 6 and the like are determined. The polishing conditions are variably controlled and executed according to a predetermined time chart. Further, during the polishing operation, the driving state of the motor 3 (for example, torque, current, etc.) is detected, and the detected value information is input to the robot control panel. When polishing the pair of electrodes 6, cooling water is flowed through each of the electrodes 6.

The spot welding electrode polishing operation performed by using the polishing device A1 is executed every time a predetermined number of hit points is reached, for example, during the welding operation. FIG. 5 is a processing flow chart showing an example of a method for polishing a spot welding electrode according to the present invention. As shown in the figure, in the present embodiment, the number of hit points is determined (S1) during the welding operation. When it is determined in the determination of the number of dots that the predetermined number of dots has been reached, the welding operation of the predetermined cycle is completed, and the polishing operation is started after the end of the cycle (S2). Here, the cutter holder 2 is sandwiched between the pair of electrodes 6 and 6, and the motor 3 is rotated in the forward rotation direction. As a result, the tip of each electrode 6 is cut and polished. During the polishing operation, it is determined whether or not the cutting chips are clogged (S3). The presence or absence of clogging of cutting chips is determined based on the detected value of the driving state of the motor 3. The detected value here is, for example, a torque value or a current value of the motor 3. If cutting chips are clogged in the notch groove 23 or the like during polishing work, the cutting resistance changes as compared with normal cutting and polishing. As a result, the torque value and the current value of the motor 3 change, such as decreasing or increasing as compared with the case of normal cutting and polishing. Then, when the torque value or the current value deviates from the range of the predetermined threshold value, it is determined that the cutting chips are clogged (NG) (S3: YES). In the present embodiment, the case of shifting from the welding work to the polishing work based on the number of hit points at the time of the welding work has been described, but the criteria for shifting to the polishing work is not limited to this. For example, the welding work may be shifted to the polishing work based on the quantity of the object to be welded (workpiece such as an automobile) or the instruction of the operator.

When it is determined that the cutting chips are clogged (S3: YES), the polishing apparatus A1 removes the cutting chips (S4). When removing cutting chips, the motor 3 is rotated in the reverse direction opposite to the forward rotation direction, and the pair of electrodes 6 and 6 are separated from the cutter 22. Here, when the motor 3 is rotated in the reverse direction, the cutter holder 2 rotates in the reverse direction opposite to the forward rotation direction (the direction in which the arrow N1 points) shown in FIG. The clogging of the cutting chips is caused by the cutting chips being collected and welded to the cutter 22 without being separated into individual pieces, and the cutting chips are lumpy in the notch groove 23 or the recessed portion 21. Therefore, when the cutter holder 2 is reversed while the cutter holder 2 is pressurized by the pair of electrodes 6 and 6, a lump of cutting chips is pulled away from the cutter 22. Next, the pair of electrodes 6 and 6 are separated from the cutter 22 while the cutter holder 2 is reversed. Then, the lump of cutting chips is removed from the notch groove 23 or the recessed portion 21.

When removing cutting chips, the time for reversing the cutter holder 2 is short (for example, about 0.2 sec), and the rotation speed of the cutter holder 2 at reversal is about 60% of the rotation speed at normal rotation. Will be done.

The process of determining the presence or absence of clogging of cutting chips (S3) is always executed from the start to the end of, for example, the polishing operation. Further, it may be executed after a predetermined time has elapsed from the start of polishing within the preset polishing time T (for example, about 1.2 sec).

In the present embodiment, it is determined that the cutting chips are clogged (S3: YES), and after the cutting chips are removed (S4), the polishing operation is restarted and the presence or absence of the cutting chips is determined again. (S3). Assuming that the polishing time until it is determined that the cutting chips are clogged is T1 (T1 <T) with respect to the preset polishing time T, the polishing time T2 from the restart of the polishing work to the end is, for example, T2. = T-T1. In this way, even if the cutting chips are removed during the polishing work, the total polishing time does not change. Therefore, the polishing amount of the electrode 6 is appropriately adjusted while avoiding the lengthening of the polishing work. Can be secured. The polishing time T2 from the restart of the polishing work to the end may be T2> T-T1 or T2 <T-T1 unlike the above.

Next, the operation of this embodiment will be described.

In the method of polishing the electrode for spot welding of the present embodiment, the cutter holder 2 is rotated in the forward rotation direction to cut the tip of the electrode 6, and the cutter holder 2 is clogged with cutting chips based on the driving state of the motor 3. The presence or absence is determined (S3). Then, when it is determined that there is cutting chips in the step of determining the presence or absence of clogging of cutting chips (S3: YES), the motor 3 is rotated in the reverse direction opposite to the forward rotation direction, and the pair of electrodes 6, 6 is separated from the cutter 22 to remove cutting chips (S4). According to such a configuration, the motor 3 is reversed to remove the cutting chips only when it is determined that there is cutting chips (NG) in the determination of the presence or absence of clogging of the cutting chips. As a result, an unnecessary reverse operation of the cutter holder is omitted as compared with the case where the motor (cutter holder) is rotated forward and reverse under fixed conditions, for example, when polishing the electrodes. Therefore, the polishing work time can be substantially shortened while polishing the tip of the electrode 6 necessary for maintaining the welding quality.

In the present embodiment, it is determined that the cutting chips are clogged (S3: YES), and after the cutting chips are removed (S4), the polishing operation is restarted and the presence or absence of the cutting chips is checked again. Judgment (S3). According to such a configuration, even if the cutting chips are not properly removed, the presence or absence of the cutting chips is determined again, so that the inconvenience of continuing the polishing work with the cutting chips clogged is avoided. can do.

As can be understood from these facts, according to the method of polishing the spot welding electrode of the present embodiment, the polishing work can be efficiently performed by shortening the polishing work time, and the polishing amount of the electrode 6 is reduced. It will not be excessive. Therefore, the life of the electrode 6 can be extended and the electrode replacement cycle can be extended, so that the work efficiency of the entire welding work including the electrode replacement work can be improved.

Although the embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the above-described embodiments. The specific configuration of each part of the present invention can be changed in various ways.

A1 Polishing device B1 Welding robot Ox Rotating axis 1 Gear case 2 Cutter holder 21 Recessed part 22 Cutter 22a Blade part 23 Notch groove 3 Motor 4 Movable arm 41 Arm part 5 Welding gun 6 Electrode 7 Servo motor

Claims (2)

A method for polishing electrodes for spot welding, in which a cutter holder equipped with a cutter is pressed by a pair of electrodes provided at the tip of a welding gun and the cutter holder is rotated while sandwiching the cutter holder.
While rotating the cutter holder in the forward rotation direction and cutting the tip of the electrode, a step of determining whether or not the cutter holder is clogged with cutting chips is performed based on the driving state of the motor.
When it is determined that there is cutting chips in the process of determining the presence or absence of clogging of cutting chips, the motor is rotated in the reverse direction opposite to the forward rotation direction, and the pair of electrodes are separated from the cutter. A method of polishing electrodes for spot welding that performs a cutting debris removal process. The method for polishing a spot welding electrode according to claim 1, wherein the step of determining the presence or absence of clogging of the cutting chips is performed again after the cutting chips removing step.

Images