JP3289508B2 - Welding tip management device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for managing a welding tip mounted on a welding gun.

[0002]

2. Description of the Related Art In an automobile body assembly line or the like, automatic spot welding is performed by a welding robot, and a welding portion of a workpiece is welded from both sides by a pair of welding tips (electrodes) mounted on a welding gun. It is spot-welded by pressing and holding. When spot welding is performed continuously, tip dressing (shaping of the tip of the welding tip) is performed by a tip dresser at a certain number of spots and at the time of welding.

[0003] As the number of hit points increases, the tip diameter of the welding tip increases, the contact area increases, the electrical resistance decreases, and heat is less likely to be generated. This is because it is necessary to shape the tip by cutting the tip.

[0004]

FIG. 14 shows the relationship between the number of hit points and the tip diameter when continuous welding is performed. At normal time, if the tip diameter changes like curve 1 and tip dressing is performed with the number of hit points A,
The tip diameter is kept below B. However, when for some reason wear of the welding tip becomes severe and the tip diameter changes as shown by curve 2 in FIG. 14, the tip diameter is determined by the number of hits A ′ (<A).
Is already the same as the tip diameter at the normal tip dress time (number of hit points A), but until the number of hit points reaches A, and thus the tip diameter becomes B '(> B), the tip dress is not formed. Therefore, there is a possibility that the tip diameter exceeds B between the numbers of hit points A 'to A and welding defects occur.

Therefore, instead of judging the tip dressing time based on the number of hit points, as shown in Japanese Patent Application Laid-Open No. 1-215467, the length of the welding tip is repeatedly measured, and the amount of change or the amount of change for each measurement is measured. In some cases, when the accumulated change amount exceeds a certain reference value, it is determined to be abnormal and tip dressing is performed. However, it is not the length of the welding tip, but the tip diameter that is directly related to poor welding.Therefore, detecting the degree of wear from a change in the length does not always make it possible to accurately determine the tip dress time. Can not.

Further, simply determining the tip dress time,
Simply performing tip dressing does not extend the life of the welding tip by removing the factor when the welding tip is severely worn due to various factors. In view of such conventional problems, the present invention seeks to optimize the tip dressing time, finds out abnormalities or failures due to various factors at an early stage from the relationship between the number of hit points and the tip end diameter, and welds the welding tip. The purpose is to be able to extend the life.

[0007]

Therefore, according to the present invention, as shown in FIG. 1A, a number-of-points counting means a for counting the number of points of a welding tip, and a tip for measuring a tip diameter of the welding tip. Tip diameter measuring means b, change characteristic extracting means c for extracting a change characteristic of the tip diameter with respect to the number of hitting points of the welding tip, and comparing the tip diameter measured by the tip tip diameter measuring means b with an upper limit value, The tip dress command means d for shaping the tip of the welding tip by the tip dresser when it exceeds, and the change characteristics extracted by the change characteristic extraction means c are compared with the reference characteristics. Alarm means e for analyzing and alarming
Construct a welding tip management device.

Here, the change characteristic extracting means c may detect the number of hit points when the tip diameter of the welding tip reaches the upper limit value as the change characteristic of the tip diameter with respect to the number of hit points of the welding tip. Alternatively, a change characteristic curve may be detected. In addition to the configuration of FIG. 1A, as shown in FIG. 1B, an initial tip diameter measuring means f for measuring the tip diameter of the welding tip after tip dressing, and a tip diameter of the welding tip after tip dressing. The initial tip diameter determining means g to determine by comparing with the upper limit and the lower limit, the result of the determination, tip dress re-instruction means h to perform the tip dress again when it is out of the range from the upper limit to the lower limit, It is preferable to provide a tip dresser abnormality determining means i for determining that the tip dresser is abnormal when the tip dress is out of the range even if it is repeated a predetermined number of times.

Further, in addition to the configuration of FIG.
As shown in (C), a tip length measuring means j for measuring the length of the welding tip, and a tip replacement for comparing the welding tip length with a lower limit value and exchanging the welding tip when the length exceeds the lower limit value. Command means k may be provided. FIG. 1 (B)
As shown by the dotted line, the tip length measuring means j for measuring the length of the welding tip, and the upper and lower limits for comparison in the initial tip diameter determining means g are varied according to the length of the welding tip. -It is preferable to provide a lower limit variable means m.

[0010]

In the above arrangement, the tip diameter of the welding tip is measured, the measured tip diameter is compared with an upper limit value, and when the measured tip diameter exceeds the upper limit value, tip dressing is performed. Thus, the tip diameter of the welding tip can always be controlled to be equal to or less than the upper limit value, and the possibility of poor welding can be reduced.

[0011] Then, a change characteristic of the tip diameter with respect to the number of hit points of the welding tip is extracted, and the extracted change characteristic is compared with a reference characteristic (the relationship between the number of hit points at normal time and the tip diameter of the tip) and deviates therefrom. Sometimes the cause is analyzed and a warning is issued. This makes it possible to find out abnormalities and failures due to various factors at an early stage from the relationship between the number of hit points and the tip end diameter, thereby extending the life of the welding tip.

Here, when extracting the change characteristic of the tip diameter with respect to the number of hit points of the welding tip, the method of detecting the number of hit points when the tip diameter of the welding tip reaches the upper limit value is easily implemented. In addition, by adopting a method of detecting the curve itself of the change characteristic, it is possible to more accurately grasp the change characteristic. Also, after the tip dress, the tip diameter of the welding tip is measured and determined by comparing with the upper limit and the lower limit.Based on the determination result, when the tip dress is out of the range from the upper limit to the lower limit, the tip dress is again performed. By performing this, the initial tip diameter after the tip dressing can be appropriately managed, and even if the tip dressing is repeated a predetermined number of times, it is determined that the tip dresser is abnormal when the tip dresser is out of the range, so that the tip dresser can be properly controlled. Can manage.

[0013] In addition, by measuring the length of the welding tip and, when exceeding the lower limit value, exchanging the welding tip, it is possible to appropriately manage the timing of replacing the welding tip. Furthermore,
When the average value of the measured values of the initial tip diameter after tip dressing when the welding and tip dressing are repeatedly performed after the replacement of the welding tip is averaged, the measured value of the initial tip diameter is:
It is small at the time of new article (immediately after replacement), but gradually increases with each repetition of tip dressing, and tends to reach its maximum immediately before replacement. This is because the shape of a new chip is slightly different from that of a chip after chip dressing.For example, when measuring using a laser beam, the laser beam has a thickness, so even if the tip diameter itself is the same, the top and bottom of the tip It is considered that the measurement value is different between a new chip and a chip that has been repeatedly dressed.

Therefore, when determining the tip diameter of the welding tip after tip dressing by comparing it with the upper limit value and the lower limit value, the length of the welding tip is measured, and the length of the welding tip is determined according to the length of the welding tip. By changing the upper limit and the lower limit, the accuracy of the chip dresser abnormality determination and the like becomes more appropriate.

[0015]

Embodiments of the present invention will be described below. FIG. 2 shows an overall configuration of an embodiment of the present invention. A welding robot 2 is arranged near a robot welding process line 1 and is controlled by a robot control panel 3. 4 is a personal computer and 5 is a controller.

A tip dresser 6 is arranged near the welding robot 2, and is controlled by a control interlock board 8 together with a brush 7 for removing shavings. Here, a laser type line sensor 9 is arranged near the tip dresser 6 so that the tip diameter of the welding tip mounted on the tip of the welding gun of the welding robot 2 can be measured. Therefore, the laser type line sensor 9 corresponds to a tip end diameter measuring means.

FIG. 3 shows a configuration of a welding gun portion operated by the welding robot 2. The welding tip 11 is mounted on the lower part of the welding gun 10 upward, and the gun pressurizing air cylinder 12 is mounted on the upper part of the welding gun 10. And a welding tip 13 which is mounted downward through the intermediary of the workpiece, and presses and clamps the workpiece 14 to perform spot welding. 15 is a spring balancer, 16 is a gun hanger, and 17 is a manual grip switch. Reference numeral 18 denotes a primary cable for power supply, 19 denotes a transformer, 20 denotes a secondary cable, and 21 denotes an auxiliary cable. Reference numeral 22 denotes an air inlet for gun pressurizing air, 23 denotes an air regulator, 24 denotes an electromagnetic valve, 25 denotes a pressurizing air hose, and 26 denotes an opening air hose. Also, 27
Is a cooling water inlet for gun cooling, 28 is a water stop valve, 29
Is a cooling water supply hose, and 30 is a cooling water outlet.

Here, an air pressure sensor 31 is arranged in the air regulator 23 so that the applied pressure can be measured. Also, a cooling water flow sensor near the cooling water outlet 30
32 is arranged so that the flow rate of the cooling water can be measured. FIG. 4 shows the configuration of the tip dresser 6, in which a sprocket 43 is attached to the tip of a rotating shaft of a motor 42 fixed to the base side of a bracket 41 attached to a base 40, and the belt (or chain) 44 is rotated by the rotation of the sprocket 43. The sprocket 45 rotatably supported on the distal end side of the bracket 41 is rotatably driven through the intermediary of the sprocket 45. The sprocket 45 has a cylindrical shape and is provided with a blade (cutting blade) 46 for shaping a chip on an inner peripheral portion thereof. The tips of the welding tips 11 and 13 mounted on the welding gun are advanced and pressed against the blade 46. Thereby, the tips of the welding tips 11 and 13 are cut and shaped.

FIG. 5 is a flowchart of the welding tip management. In step 1 (indicated as S1 in the figure, the same applies hereinafter), the number C of hit points is counted and integrated during welding. In Step 2, after welding (after production of one unit),
The tip diameter D of the welding tip by the laser type line sensor 9
Is measured.

In step 3, the measured tip diameter D of the welding tip is compared with a predetermined upper limit value Dmax, and D ≦ Dm
If ax, the next welding is continued as it is. If D> Dmax, it is determined that tip dressing is necessary, and step 4 is performed.
Proceed to. In step 4, as the parameter of the change characteristic of the tip diameter D with respect to the number C of welding tips of the welding tip, the number of hits when the tip diameter D reaches the upper limit value Dmax (current number of hitting points)
C and is stored as the upper limit value reaches bats point C _0.

[0021] In the present embodiment, as the parameters of the change characteristics of the tip diameter to the RBI number of welding tip, but to detect the upper limit arrival bats point C _0, that for each measurement of the tip diameter of the welding tip By storing the tip diameter in relation to the number of hit points at that time, the curve itself of the change characteristic may be detected. In step 5, it is checked whether the life of the welding tip has been reached. Specifically, the length of the welding tip is measured, and when the length becomes less than the predetermined length, the life is reached, or the number of times of tip dress after the welding tip is replaced is stored and this is stored as a predetermined value. When the value exceeds the value, it is assumed that the life has expired.

If the life has not been reached, the routine proceeds to step 6, where the tip dresser 6 performs tip dressing to shape the tip of the welding tip. After the tip dress,
In step 7, the tip diameter D of the welding tip is measured by the laser type line sensor 9. Then, it is determined whether or not the tip diameter D measured in step 8 is abnormal as the initial tip diameter.

If it is determined in step 8 that the initial tip diameter is abnormal after tip dressing, the process proceeds to step 9 and the initial tip diameter abnormality after tip dressing frequently occurs (for example, 2).
It is determined whether or not it is a continuation), and if it does not occur frequently, it is regarded as a sudden abnormality, and the tip dress (step 6) is performed again in that state. If it occurs frequently, it is estimated that as a cause of the initial tip diameter abnormality after tip dressing, the blade 46 in the tip dresser 6 cannot be cut due to wear or chipping.
After instructing the replacement of 46, the tip dress (step 6) is performed again after the replacement.

If the result of the determination of the tip diameter after tip dressing in step 8 is normal (appropriate value) as the initial tip diameter, the process proceeds to step 12. If the life of the chip has been reached as a result of the chip life determination in step 5, the step
After proceeding to step 11 to instruct the replacement of the welding tip, proceed to step 12 after the replacement. In step 12, the change characteristic of the tip diameter D with respect to the number C of the welding tips is checked for conformity with the reference characteristic. This is performed according to the flowchart of FIG.

After the check, the number of strokes C is returned to 0 in step 13, and welding is resumed. Next, the processing contents of the characteristic check (step 12) will be described with reference to the flowchart of FIG. In step 21, the number C of welding tips
This is a parameter change characteristics of the tip diameter D for comparison with an upper limit predetermined value determined in advance of the arrival bats point C _0, if below a predetermined value, it is determined that the tip径早life limit reached abnormal, step Proceed to 22.

In step 22, it is determined whether or not such an abnormality in reaching the tip diameter early upper limit value occurs frequently (for example, two consecutive times). If not, the process is terminated as a sudden abnormality, and the process ends. If so, it is determined that it is a chronic abnormality, and the process proceeds to step 23. In step 23, the presence or absence of a decrease in the pressing force is determined based on a signal from the air pressure sensor 31, and if the pressing force is reduced, the primary air pressure of the primary side air pressure is determined as a cause of the tip diameter early upper limit reaching abnormality. Drop, air leak,
Since it can be estimated that the air regulator has failed, step 24
Proceed to to warn of a decrease in pressure, and instruct air leak and check the air regulator.

In step 25, it is determined whether or not the flow rate of the cooling water has decreased based on the signal from the cooling water flow rate sensor 32. Since it can be estimated that the flow rate is decreased due to an increase in the load of the cooling water circuit, or the flow rate is decreased due to the clogging of the cooling water circuit, the process proceeds to step 26 to warn of a shortage of the cooling water flow rate, and instructs to check the cooling water circuit.

In step 27, it is determined whether or not the production ratio of the special vehicle type (specifically, the vehicle type used for export) has increased. The vehicles used for export use rust-prevention treated steel sheets and Dura steel (galvanized steel sheets), etc. If the number of these increases, the electrical resistance of the plating increases, and the chip wear rate increases. Instruct to review dress conditions and welding conditions. Specifically, it is preferable to increase the upper limit value Dmax of the tip end diameter for dress timing determination and increase the welding current value.

If none of the above applies, step 29
Proceed to and warn that there is an abnormality of unknown cause. In this embodiment, step 1 in FIG. 5 corresponds to the number of hit points counting means, and step 2 in FIG. 5 corresponds to the tip diameter measuring means together with the laser line sensor 9.
Step 4 corresponds to the change characteristic extracting means.
Steps 3 and 6 correspond to tip dress command means, and step 12 (FIG. 6) in FIG. 5 corresponds to alarm means.

The step 7 in FIG. 5 corresponds to the initial tip diameter measuring means, and the step 8 in FIG. 5 corresponds to the initial tip diameter judging means. The part returning to 6 corresponds to the tip dress re-instruction means, and the part of steps 9 and 10 in FIG. 5 corresponds to the abnormality determination means. Next, another embodiment of the present invention will be described.

In this embodiment, the processing is performed according to the flow charts of the welding tip management shown in FIGS. Steps
At 51, the number of dots C is counted and integrated during welding.
In step 52, the tip diameter D of the welding tip is measured by the laser line sensor 9 each time after welding (after production of one unit).

In step 53, for each measurement of the tip diameter D of the welding tip, the tip diameter D is stored in relation to the number of hit points C at that time, whereby the change characteristic of the tip diameter D with respect to the number C of welding points of the welding tip is stored. Is stored. In step 54, the curve of the change characteristic of the tip diameter D with respect to the number C of the welding tips is compared with a reference curve.

Here, when the actual curve substantially corresponds to the reference curve illustrated in FIG.
Proceed directly to step 56. If the actual curve does not correspond to the reference curve, the type shown in FIG.
Is determined, and processing is performed according to the determination result. In the case of type: It is caused by dust adhesion, etc., and when several points are welded, it automatically returns to the base. Therefore, the process directly proceeds to step 56.

In the case of the type: If this occurs once, it is considered the same as the type, but if it occurs sporadically, it is considered that there is some cause of abnormal wear of the welding tip. Therefore, the process proceeds to step 55 to output an alarm, and thereafter proceeds to step 56. In the case of type: It is considered that the welding tip is abnormally worn due to explosion or the like. Therefore, the process proceeds to step 57 in order to perform chip dress.

In step 56, the measured tip diameter D of the welding tip is compared with a predetermined upper limit value Dmax, and D ≦ Dm
If ax, the next welding is continued, and if D> Dmax, it is determined that a tip dress is necessary, and the routine proceeds to step 57. In step 57, tip dressing is performed by the tip dresser 6, and the tip of the welding tip is shaped.

In step 58, the number of chip dress times CD is counted up. After the tip dressing, the tip diameter (initial tip diameter) D of the welding tip is measured by the laser line sensor 9 in step 59. Then, the initial tip diameter D measured in step 60 is compared with the upper limit value DOmax and the lower limit value D0min.
, It is determined whether or not it is within these ranges (D0min ≦ D ≦ Domax).

That is, when the measured value of the initial tip diameter after the tip dressing is smaller than the lower limit value D0min, a state as shown in FIG. Fig. 10 due to damage
(C), and when the measured value of the initial tip diameter is larger than the upper limit value D0max, the state shown in FIG.
The state as shown in FIG.

Therefore, the measured value of the initial tip diameter is equal to the upper limit value D0m.
If it is out of the range from ax to the lower limit value D0min, the process proceeds to step 61, where the number of chip dresses CD is compared with the predetermined value CD1, and if it is less than the predetermined value CD1, the process returns to step 57 to perform the chip dress again. . However, if the tip dress is repeated a predetermined number of times and is out of the above range, the blade 46 is at the limit of breakage or settling. Then, an error is output, the line is stopped, and the blade 46 is replaced.

In addition, if the predetermined number of times (CD1) is not reached, but the chip dressing does not fall within the above range unless chip dressing is performed several times, or if this state occurs sporadically, the blade 46 has begun to sag. Can be considered. For this reason, if the result of the determination in step 60 is within the range, the flow advances to step 63 to compare the number of chip dress times CD with a predetermined value CD2 (<CD1). An alarm for instructing replacement of the blade 46 is output.

After the end of the tip dress and the measurement, the process proceeds to step 65. In step 65, the length (tip length) L of the welding tip is measured using the laser type line sensor 9. In step 66, the measured tip length L is compared with a predetermined lower limit value Lmin, and if L <Lmin, the flow advances to step 67 to output an alarm for instructing replacement of the welding tip.

In step 67, the upper limit value D0m for determining the initial tip diameter is determined by referring to the map based on the measured chip length L (if replaced, the initial chip length after replacement) L.
ax and the lower limit D0min are set. The reason will be described later. Finally, in step 68, the number of strokes C and the number of tip dresses CD are returned to 0, and welding is restarted (return to step 51).

The reason why the upper limit value D0max and the lower limit value D0min for determining the initial tip diameter are made variable according to the chip length L will be described. When the average value of the measured values of the initial tip diameter after tip dressing when the welding and tip dressing are repeatedly performed after the replacement of the welding tip is averaged, the measured value of the initial tip diameter is as shown in FIG. As shown in (1), it is small at the time of new article (immediately after replacement), but gradually increases each time the tip dress is repeated, and reaches the maximum immediately before replacement. This is because the shape of the new tip and the tip after tip dressing are slightly different as shown in Fig. 12, but the laser beam used for measurement has a thickness, so even if the tip diameter itself is the same, It is considered that the measurement value is different between a new chip and a chip that has been repeatedly dressed since the measurement is performed inclusively.

Therefore, when determining the tip diameter of the welding tip after tip dressing by comparing it with the upper limit value and the lower limit value, it is necessary to consider the above-mentioned change in the measured value of the tip diameter. Therefore, the tip length data and the initial tip diameter data after tip dressing immediately after the exchange of the welding tip to immediately before the lap exchange are statistically processed, and the relationship between the tip length and the initial tip diameter as shown by a dotted line in FIG. 13 is obtained. Figure out this relationship
As shown by the solid line in FIG. 13, the upper limit value D0max for the initial tip diameter determination
And the lower limit D0min.

Therefore, when determining the tip diameter of the welding tip after tip dressing by comparing it with D0max and the lower limit value D0min, the tip length L is measured in advance, and according to this tip length L, the map shown in FIG. Therefore, by setting the upper limit value D0max and the lower limit value D0min for the initial tip diameter determination, the accuracy of the tip dresser abnormality determination and the like becomes more appropriate.

In this embodiment, the steps shown in FIG.
The portion 51 corresponds to the number of hit points counting means, and corresponds to step 52 in FIG.
7 corresponds to the tip diameter measuring means together with the laser type line sensor 9, step 53 in FIG. 7 corresponds to the change characteristic extracting means, and steps 56 and 57 in FIG. 7 correspond to the tip dress commanding means. Steps 54 and 55 in FIG. 7 correspond to the alarm means.

The step 59 in FIG. 8 corresponds to the initial tip diameter measuring means, and the step 60 in FIG. 8 corresponds to the initial tip diameter determining means.
The portion returning to step 57 via 61 corresponds to the tip dress re-instruction means, and the portions of steps 61 and 62 in FIG. 8 correspond to the abnormality determination means. 8 corresponds to the chip length measuring means, and the step 67 in FIG. 8 corresponds to the chip replacement instructing means. Further, the step 68 in FIG. 8 corresponds to upper / lower limit value changing means.

[0047]

As described above, according to the present invention, the tip dressing time of the welding tip is determined by measuring the tip tip diameter, so that the tip tip diameter is always controlled to be equal to or less than the upper limit value and the welding failure is determined. The effect that the possibility of occurrence can be reduced is obtained. The relationship between the number of hit points at normal time and the tip diameter is used as a reference characteristic, and by monitoring deviations from the reference characteristic, abnormalities and failures due to various factors can be found at an early stage to extend the life of the welding tip. The effect that it can be obtained is obtained.

Further, when the change characteristic of the tip diameter with respect to the number of hit points of the welding tip is extracted, a method of detecting the number of hit points reaching the upper limit value can be easily implemented, and the change characteristic curve itself is detected. By adopting the method,
The change characteristics can be more accurately grasped. Further, after tip dressing, the tip diameter of the welding tip is compared with the upper limit value and the lower limit value to determine, based on the determination result, when the tip dress is out of the range from the upper limit value to the lower limit value, the tip dressing is performed again. In addition, the initial tip diameter after the tip dressing can be appropriately managed, and the tip dresser can be appropriately managed by determining that the tip dresser is abnormal when the tip dress is out of the range even if the tip dress is repeated a predetermined number of times.

Further, by measuring the length of the welding tip and, when the length of the welding tip exceeds the lower limit, exchanging the welding tip, it is possible to appropriately manage the timing of replacing the welding tip. Furthermore,
When comparing the tip diameter of the welding tip after tip dressing with the upper limit value and the lower limit value to determine, according to the length of the welding tip, by changing the upper limit value and the lower limit value for comparison,
The accuracy of the chip dresser abnormality determination and the like is further improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the present invention.

FIG. 2 is a diagram showing the overall configuration of an embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a welding gun portion;

FIG. 4 is a diagram showing a configuration of a chip dresser.

FIG. 5 is a flowchart of welding tip management.

FIG. 6 is a flowchart of a characteristic check.

FIG. 7 is a flowchart (part 1) of welding tip management of another embodiment.

FIG. 8 is a flowchart (part 2) of welding tip management of another embodiment.

FIG. 9 is a diagram showing an aspect of characteristic discrimination.

FIG. 10 is a diagram showing an example of an abnormal initial tip diameter.

FIG. 11 is a diagram showing a change characteristic of an initial tip diameter.

FIG. 12 is a diagram comparing a new chip with that immediately before replacement.

FIG. 13 is a diagram showing a relationship between a chip length and an upper limit value and a lower limit value.

FIG. 14 is a characteristic diagram of the number of hits versus the tip diameter.

[Explanation of symbols]

 2 Welding robot 6 Tip dresser 9 Laser line sensor 10 Welding gun 11 Welding tip 12 Air cylinder 13 Welding tip 14 Workpiece 31 Air pressure sensor 32 Cooling water flow sensor 46 Blade

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-80659 (JP, A) JP-A-3-297584 (JP, A) JP-A-54-107845 (JP, A) 134281 (JP, U) JP-A 1-172484 (JP, U) JP-A 61-107481 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B23K 11/24 B23K 11 / 30

Claims (6)

(57) [Claims] 1. A welding tip management device mounted on a welding gun in a pair to perform spot welding while pressing and holding an object to be welded, a spot number counting means for counting the number of spots of the welding tip, Tip tip diameter measuring means for measuring the tip diameter of the tip, change characteristic extracting means for extracting a change characteristic of the tip diameter with respect to the number of hitting points of the welding tip, and the upper limit of the tip diameter measured by the tip tip diameter measuring means And a tip dress command means for shaping the tip of the welding tip by a tip dresser when exceeding this, and comparing the change characteristic extracted by the change characteristic extraction means with a reference characteristic and deviating therefrom. And a warning means for analyzing the cause when the condition is present, and providing a warning. 2. The method according to claim 1, wherein the change characteristic extracting means detects a number of hit points when the tip diameter of the welding tip reaches an upper limit value as a change characteristic of the tip diameter with respect to the number of hit points of the welding tip. The welding tip management device according to claim 1, wherein: 3. The welding tip management apparatus according to claim 1, wherein said variation characteristic extracting means detects a curve as a variation characteristic of a tip diameter with respect to the number of hit points of said welding tip. 4. An initial tip diameter measuring means for measuring the tip diameter of the welding tip after tip dressing, and an initial tip diameter determining means for determining by comparing the tip diameter of the welding tip after tip dressing with an upper limit value and a lower limit value. A result of the determination, a tip dress re-instruction means for performing a tip dress again when the tip dress is out of the range from the upper limit to the lower limit, and determining that the tip dresser is abnormal when the tip dress is out of the range even if the tip dress is repeated a predetermined number of times. 4. The welding tip management device according to claim 1, further comprising: 5. A tip length measuring means for measuring the length of a welding tip, and a tip replacement command means for comparing the length of the welding tip with a lower limit value and exchanging the welding tip when the length exceeds the lower limit value. The welding tip management device according to any one of claims 1 to 4, further comprising: 6. A tip length measuring means for measuring the length of a welding tip, and upper and lower limits for varying upper and lower limits for comparison in said initial tip diameter determining means according to the length of said welding tip. The welding tip management device according to claim 4, further comprising: a variable unit.