Method for polishing spot welding electrodes

Abstract

To accurately grasp a wear state of a tool used for polishing an electrode and thereby perform polishing of the electrode at low cost with productivity maintained.SOLUTION: A spot welding electrode polishing method includes: a polishing step S1 in which polishing is performed to an electrode 10 with a predetermined tool 21; an inspection step S2 in which a polishing state of the electrode 10 polished in the polishing step S1 is inspected; a re-polishing step S3 in which re-polishing is performed to the electrode 10 based on a detection result regarding the polishing state of the electrode 10 obtained in the inspection step S2; a re-polishing count step S5 in which the number of times of re-polishing performed is counted; and a prediction step 6 in which a wear state of the tool 21 is predicted based on the count number.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a method for polishing a spot welding electrode. [Background technology]

[0002] For example, in the assembly process of automobile bodies, spot welding is performed in which electrodes are placed in contact with multiple steel plates and electricity is passed through them, causing the contact points between the steel plates to melt due to resistance heating and form a nugget as a joint.

[0003] Here, since a large pressure is applied to the electrode used in spot welding at high temperatures and a large current flows through it during welding, it is assumed that the tip of the electrode will wear and change shape with continued use, or that metal components of the object to be welded will adhere to the electrode. If welding work is continued in this state, the current density will decrease and the welded area will not be heated sufficiently, which may cause poor welding. Therefore, at welding sites, the tip of the electrode is polished, for example, every time it is used a certain number of times, in order to return the tip of the electrode to the shape it had at the start of welding.

[0004] The above-mentioned electrodes are usually polished using a polishing device arranged near the welding robot. Here, the polishing device has a cutter holder with a cutter attached to a recessed portion into which the tip of the electrode can be introduced, as described in Patent Document 1, for example, and the tip of the electrode can be polished by pressing a pair of electrodes provided at the tip of the welding gun against the recessed portion to clamp the cutter holder and rotating the cutter holder in a fixed direction by the driving force of a motor.

[0005] Furthermore, when the electrode is polished as described above, a specified inspection device is used to inspect the state of the electrode tip after polishing, and the quality of the polished state of the electrode is judged (see, for example, Patent Document 2).

[0006] If the inspection determines that the electrode is in a good polished state, the polished electrode is used for the next spot welding, and if it determines that the electrode is not in a good polished state (is not polished enough), the electrode is re-polished using the above-mentioned polishing device (see, for example, Patent Document 3).

[0007] Meanwhile, Patent Document 4 describes a method for grinding an electrode using a grinding device equipped with a grinding number measuring means for counting the number of times the electrode has been ground, and a grinding number abnormality display means for displaying an abnormality when the number of times the electrode has been ground counted by the grinding number measuring means exceeds a preset maximum number of times the electrode has been ground. It also describes that when an operator visually recognizes the abnormality display, the operator recognizes that the number of times the electrode has been ground exceeds the maximum number of times the electrode has been ground, and replaces the grinding blade currently in use with a new grinding blade. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2018-167302 A [Patent Document 2] JP 2002-273535 A [Patent Document 3] JP 2017-87221 A [Patent Document 4] JP 2008-73715 A Summary of the Invention [Problem to be solved by the invention]

[0009] In this type of grinding process, attention must be paid not only to the electrodes for spot welding, but also to the wear state of the tool (usually a grinding blade) for grinding the electrodes. That is, the tool wears out with repeated use, and the grinding ability of the tool also decreases. Therefore, if it is determined that the grinding state is not good even in the inspection after re-grinding, a grinding abnormality is generated, and the line including the welding process is stopped, and the grinding abnormality is confirmed and dealt with (for example, the grinding time is extended or the grinding blade is replaced, assuming that the grinding ability of the tool has decreased as the cause of the abnormality). However, if the line is dealt with after some abnormality occurs as described above, it becomes necessary to stop the line at a time when it is not necessary to stop it, and there is a concern that productivity will decrease. In addition, it is not desirable in terms of human costs because an operator has to check the abnormality and consider how to deal with it every time an abnormality occurs.

[0010] Patent Document 4 describes replacing the grinding blade when the number of times the electrode is ground exceeds a predetermined number (maximum number of times). However, the degree of wear of the grinding blade depends on the type of plate assembly, the welding state, or the state of wear of the electrode. Therefore, even if the grinding blade is replaced at a predetermined replacement time (when the maximum number of times of grinding is exceeded), if the grinding blade is ground more frequently than initially expected and the grinding blade is more worn than initially expected, there is a high probability that grinding abnormalities will occur before the replacement.

[0011] In view of the above circumstances, the technical problem to be solved in this specification is to perform electrode polishing at low cost while maintaining productivity by accurately grasping the wear state of the tools used in electrode polishing. [Means for solving the problem]

[0012] The above-mentioned problems are solved by the present invention, which provides a method for grinding a spot welding electrode, comprising a grinding step of grinding a spot welding electrode with a predetermined tool, an inspection step of inspecting the grinding state of the electrode ground in the grinding step, and a re-grinding step of re-grinding the electrode based on the inspection result of the grinding state of the electrode obtained in the inspection step, and further comprises a prediction step of counting the number of times the re-grinding has been performed and predicting the wear state of the tool based on the counted number.

[0013] The inventors of the present invention have focused on the number of times that the electrode has been re-ground, and as a result of intensively studying the relationship between the number of times of re-grounding and the wear state of the tool used for grinding, they have found that there is a stronger correlation between the number of times of re-grounding and the wear state of the tool than the correlation between the number of times of grinding and the wear state of the tool. Therefore, as in the present invention, by counting the number of times that re-grounding has been performed and predicting the wear state of the tool based on the count number, it is possible to accurately predict the wear state reflecting the usage status of the individual tool. According to this, for example, the grinding conditions can be automatically changed according to the predicted degree of wear state of the tool, so that it is possible to maintain a good grinding state for the electrode in the grinding process without the worker having to actually check the state of the tool and change the grinding conditions. Therefore, excellent productivity can be maintained. In addition, since it is sufficient to only count the number of times of re-grounding, it is possible to easily and inexpensively predict the wear state of the tool and maintain a good grinding state of the electrode in the subsequent grinding process, compared to the case where the wear state of the tool is directly detected by a sensor, a camera, or the like.

[0014] In the method for grinding a spot welding electrode according to the present invention, the prediction step may include counting a cumulative number of times regrinding has occurred, and predicting the wear state of the tool based on the cumulative count number.

[0015] In this way, by counting the cumulative number of times regrinding has occurred and predicting the wear state of the tool based on the cumulative count, the wear state of the tool can be predicted easily and accurately, and various decisions based on the predicted wear state, such as whether or not the grinding conditions of the electrode need to be changed, can be made accurately.

[0016] In the method for grinding a spot welding electrode according to the present invention, the prediction step may count the number of consecutive occurrences of regrinding, and predict the wear state of the tool based on the number of consecutive counts.

[0017] In the inspection process after grinding, due to the limited inspection methods that can be used within the limited inspection time, a certain number of erroneous judgments (judging a grinding condition to be poor even though it is good) are inevitable. Therefore, by predicting the tool wear condition based on the number of consecutive occurrences of regrinding rather than the cumulative number of occurrences of regrinding, it is possible to more accurately predict the tool wear condition. Therefore, with this configuration, it becomes possible to make various judgments more accurately based on the prediction results of the tool wear condition.

[0018] In addition, the method for grinding a spot welding electrode according to the present invention may further include an extension determination step of determining whether or not it is necessary to extend the grinding time of the electrode in the grinding step, based on the prediction result regarding the wear state of the tool obtained in the prediction step.

[0019] As the tool wear progresses, the polishing ability of the tool decreases. Therefore, when it is determined (predicted) that the tool wear has progressed to a certain degree, the time for polishing the electrode with the tool is extended, thereby compensating for the decrease in the polishing ability of the tool itself. Therefore, according to this configuration, it is possible to easily maintain a good polished state of the electrode after the polishing process without changing other polishing conditions (such as the rotation speed of the tool or the pressure applied to the electrode).

[0020] In addition, the method for grinding a spot welding electrode according to the present invention may further include a replacement determination step of determining whether or not a notice to replace the tool is required based on the prediction result regarding the tool wear state obtained in the prediction step.

[0021] On the other hand, even if the decrease in the polishing ability of the tool is compensated for by extending the polishing time, etc., it is inevitable that the tool will reach the end of its useful life (the time when the tool substantially loses the minimum polishing ability required for a polishing tool). In consideration of this point, it is preferable to determine whether or not to give a notice that the tool should be replaced based on the prediction result regarding the wear state of the tool obtained in the prediction process, as in the present configuration. By predicting the wear state of the tool based on the number of re-grinding counts as in the present invention, the wear state reflecting the individual usage status of the tool can be accurately predicted. Therefore, the useful life of the tool can also be predicted with high accuracy according to the individual usage status, and by determining the need for a notice that the tool should be replaced as described above, it is possible to replace the tool at an appropriate time. Therefore, it is possible to reliably prevent the occurrence of electrode polishing defects after re-grinding and maintain high productivity. Effect of the Invention

[0022] As described above, according to the method for polishing a spot welding electrode of the present invention, by accurately grasping the wear state of the tool used to polish the electrode, it is possible to polish the electrode at low cost while maintaining productivity. [Brief description of the drawings]

[0023] [Figure 1] 2 is a flowchart showing a series of steps from a grinding step to a re-grinding step in a grinding method for a spot welding electrode according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a schematic diagram of the polishing step shown in FIG. [Diagram 3] FIG. 2 is a diagram showing a schematic diagram of the inspection process shown in FIG. 1. [Figure 4]4 is a flowchart showing a series of steps from a re-grind counting step to a replacement determination step in a grinding method according to one embodiment of the present invention. [Diagram 5] 5 is a flowchart showing the flow of the regrinding counting step shown in FIG. 4. [Figure 6] FIG. 1A is a graph showing the relationship between the cumulative number of polishings and the cumulative number of re-polishing counts, (b) is a graph showing the relationship between the cumulative number of polishings and the number of consecutive re-polishing counts, and (c) is a graph showing the relationship between the cumulative number of polishings and polishing time, when a polishing method according to one embodiment of the present invention is carried out. [Figure 7] 4 is a flowchart showing a flow of a prediction step and an extension determination step in a polishing method according to one embodiment of the present invention. [Figure 8] 1 is a graph showing the relationship between the cumulative number of polishing operations and polishing time when a polishing method according to one embodiment of the present invention is carried out. [Figure 9] 3 is a flowchart showing a series of steps from a prediction step to a replacement determination step in a polishing method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for polishing a spot welding electrode according to an embodiment of the present invention will be described with reference to the drawings.

[0025] 1 shows a flow chart illustrating a series of steps from the grinding step to the reinspection step in a method for grinding a spot welding electrode according to one embodiment of the present invention. As shown in this chart, the grinding method according to this embodiment includes an electrode grinding step S1, an inspection step S2, a re-grinding step S3, and a re-inspection step S4. Each of the steps S1 to S4 will be described in detail below.

[0026] (S1) Polishing process In this process, spot welding is performed a predetermined number of times (e.g., 1 to 5 × 10 2The tip of the electrode used once is polished. As an example of the electrode to be polished, an electrode 10 having a partially spherical tip is shown in FIG. 2. Of course, the shape of the tip of the electrode 10 is not limited to this, and may be an electrode having a tip shape consisting of one or more partially spherical surfaces, or an electrode having a known shape, such as an electrode having a flat surface at the tip and a tapered surface continuing from the outer periphery of the flat surface, although both are not shown.

[0027] The grinding device 20 used in this case has a grinding blade 21 that can be rotated by a motor (not shown). In this case, the grinding blade 21 corresponds to the grinding tool according to the present invention. In the grinding process using this grinding device 20, as shown in FIG. 2, for example, a pair of electrodes 10, 10 and the grinding blade 21 are arranged coaxially, and the pair of electrodes 10, 10 are pressed against the grinding blade 21 while the grinding blade 21 is rotated to grind the tip of each electrode 10. In this way, the tip of each electrode 10 is processed to the shape it will have when it is first used in welding work.

[0028] (S2) Inspection process In this step, the polished state of the electrodes 10 polished in the polishing step S1 is inspected. For example, in this embodiment, an inspection device 30 is disposed between a pair of electrodes 10, and based on the amount of reflected light of light irradiated from the inspection device 30 toward the tip of each electrode 10, it is determined whether or not an unpolished portion such as black skin remains at the tip of the electrode 10, thereby inspecting the polished state of each electrode 10.

[0029] If the inspection result shows that no unpolished portion remains, the electrodes 10 are in a good polished state (determined as "Yes" in FIG. 1), and the welding operation is resumed (step S21). That is, although not shown, when each electrode 10 is attached to the tip of the arm of a welding robot, the above-mentioned polishing step S1 and inspection step S2 are performed in the attached state, so that for the electrodes 10 determined to be in a good polished state, the arm of the welding robot is moved toward the welding step, and welding of the specified plate assembly is resumed.

[0030] Alternatively, if the inspection result shows that an unpolished portion remains, it is determined that the polishing state is not satisfactory (determined as "No" in FIG. 1), and the electrode 10 that has received the inspection result is polished again.

[0031] The above-mentioned inspection method in the inspection step S2 is merely an example. It goes without saying that any known inspection device capable of inspecting the polished state of the tip of the electrode 10 based on a criterion other than the amount of reflected light can be widely applied.

[0032] (S3)Re-polishing process In this step, only the electrodes 10 that are determined not to be in a good polished state in the inspection step S2 are re-polished. The polishing device used in this step can be the polishing device 20 used in the polishing step S1. For example, the arm of the welding robot is moved from the inspection device 30 toward the polishing device 20, and the electrode 10 is polished by the polishing device 20. The polishing conditions (the number of rotations of the polishing blade 21, the pressure applied to the electrode 10, the polishing time, etc.) are set to be the same as the polishing conditions performed in the immediately preceding polishing step S1, for example. In addition, as described later, when the polishing conditions (here, the polishing time) of the electrode 10 in the polishing step S1 are changed, the polishing conditions in the re-polishing step S3 may be set to be the same as the changed polishing conditions in the polishing step S1. Of course, the polishing conditions in the re-polishing step S3 may be different from the polishing conditions in the polishing step S1.

[0033] (S4) Re-inspection process In this step, inspection of the polished state is performed only on the electrode 10 that has been reground in the reground step S3. The inspection device used in this step can be the inspection device 30 used in the inspection step S2, and for example, the arm of the welding robot is moved from the polishing device 20 toward the inspection device 30, and the electrode 10 is inspected by the inspection device 30. That is, based on the amount of reflected light, it is determined whether or not an unpolished portion remains at the tip of the electrode 10 after reground.

[0034] If the reinspection reveals that no unground portions remain, it is determined that the electrodes 10 have been ground in a good condition (determined as "Yes" in FIG. 1), and the welding operation is resumed (step S21). That is, as described above, if the electrodes 10 are attached to the tip of the arm of the welding robot, the arm of the welding robot is moved toward the welding process, and welding of the specified plate combination is resumed.

[0035] Alternatively, if the reinspection reveals that an unground portion remains, it is determined that the regrinding state of the electrode 10 is not good (determined as "No" in FIG. 1), in other words, it is determined that there is a grinding abnormality, and the line including the welding process is stopped (step S41). In this case, the operator checks, for example, the state of the grinding device 20 including the grinding blade 21, which is a grinding tool, and the state of the inspection device 30, and considers the reason why a good grinding state cannot be obtained even after regrinding and how to deal with it.

[0036] As described above, each time the electrode 10 is used for spot welding a certain number of times, a series of steps from the grinding step S1 to the reinspection step S4 are performed as necessary. That is, in this embodiment, re-grinding (regrinding step S3) is performed once for each grinding (grinding step S1), and based on the inspection result of the inspection after one regrinding (reinspection step S4), it is determined whether the electrode should be returned to welding work or whether there is a welding abnormality. In this way, spot welding is repeatedly performed using the electrode 10 whose grinding ability has been restored.

[0037] Next, a method for managing the polishing tool (here, the polishing blade 21) will be described in detail mainly with reference to FIGS.

[0038] The grinding method for spot welding electrodes according to this embodiment includes, in addition to the grinding step S1, the inspection step S2, the re-grinding step S3, and the re-inspection step S4 described above, a re-grinding counting step S5, a prediction step S6, an extension determination step S7, and a replacement determination step S8, as shown in Fig. 4. In this case, the re-grinding counting step S5 and the prediction step S6 according to this embodiment correspond to the prediction step according to the present invention. Details of each step will be described in order below.

[0039] (S5) Regrinding and counting process In this step, each time the grinding step S1 is performed, it is determined whether or not regrind has been performed (step S51). If it is determined that regrind has been performed (regrinding step S3), the cumulative number of occurrences of regrind is counted (step S52). This increases the cumulative number of regrinds by one.

[0040] When the cumulative number of times regrinding has occurred is counted in this way, it is then determined whether or not regrinding has been performed in the immediately preceding grinding step S1. In other words, it is determined whether or not the above-mentioned regrinding has occurred consecutively (step S53). Then, if regrinding (regrinding step S3) has occurred consecutively, the number of consecutive occurrences of regrinding is counted (step S54). This increases the number of consecutive counts of regrinding by one.

[0041] On the other hand, if it is determined in step S51 that regrinding has not been performed, then the process S5 is terminated without counting either the cumulative number of occurrences of regrinding or the number of consecutive occurrences. If it is determined in step S53 that regrinding has not been performed in the immediately preceding polishing process S1, then the process S5 is terminated without counting the number of consecutive occurrences of regrinding. In this way, each time the polishing process S1 is performed once, it is determined whether or not there has been an increase in the cumulative number of counts and the consecutive number of counts of regrinding. Of these, the consecutive number of counts is reset (returns to zero) if not counted.

[0042] (S6) Prediction process (S7) Extension determination process As described above, when at least one of the cumulative number of occurrences of regrinding and the number of consecutive occurrences is counted in the regrinding count step S5, the wear state of the grinding blade 21 as a tool is predicted. In this embodiment, as shown in Fig. 7, first, each time the consecutive count number of regrinding increases, it is determined whether or not the consecutive count number is equal to or greater than a preset threshold value (first threshold value) (step S71).

[0043] Then, when it is determined that the continuous count number of regrinding is equal to or greater than the first threshold value, it is predicted (determined) that the grinding blade 21 has worn down to the extent that it does not have sufficient grinding ability for the electrode 10, and the grinding conditions are changed. Here, the grinding time is extended (step S72).

[0044] Alternatively, if it is determined that the continuous count number of regrinding is less than the first threshold, the process proceeds to a next step of determining whether or not an extension is necessary based on the cumulative count number. Then, it is determined whether or not the cumulative count number of regrinding is equal to or greater than a preset threshold number (second threshold number) (step S73).

[0045] Here, if it is determined that the cumulative count number of regrinds is equal to or greater than the second threshold value, it is predicted (determined) that the grinding blade 21 has worn down to the point where it no longer has sufficient grinding ability for the electrode 10, and the grinding conditions are extended (step S72).

[0046] Alternatively, if it is determined that the cumulative count number of repolishing is less than the second threshold value, i.e., if it is determined that both the continuous count number and the cumulative count number are less than the corresponding threshold values ​​(first threshold value, second threshold value), steps S6 and S7 are terminated without extending the polishing time.

[0047] Fig. 6(a) is an example of a graph showing the relationship between the cumulative number of times the electrode 10 has been sharpened (the total number of times the sharpening step S1 has been performed since the start of use of the sharpening blade 21) and the number of times re-sharpening has been performed for each sharpening step S1, and the relationship between the cumulative number of times sharpening has occurred (the cumulative count number). Fig. 6(b) is an example of a graph showing the relationship between the cumulative number of times the electrode 10 has been sharpened and the number of times re-sharpening has been performed for each sharpening step S1, and the relationship between the cumulative number of times sharpening has occurred consecutively (the consecutive count number). Fig. 6(c) is an example of a graph showing the relationship between the cumulative number of times the electrode 10 has been sharpened and the number of times re-sharpening has been performed for each sharpening step S1, and the relationship between the cumulative number of times sharpening has occurred consecutively (the consecutive count number).

[0048] Here, in this illustrated example, if the threshold value of the continuous count number (first threshold value) is, for example, 5 times, and the threshold value of the cumulative count number (second threshold value) is, for example, 10 times, as shown in Fig. 6(a) to (c), when the cumulative number of polishing times is, for example, 10 times, the continuous count number of repolishing is 3 times and the cumulative count number is 4 times, both of which are less than the threshold value, so the polishing time is not extended (maintained). When the cumulative number of polishing times is, for example, 16 times, the continuous count number of repolishing is 4 times and the cumulative count number is 8 times, both of which are less than the threshold value, so the polishing time is not extended yet. On the other hand, when the cumulative number of polishing times is, for example, 17 times, the continuous count number of repolishing is 5 times and reaches the threshold value (first threshold value), so the polishing time is extended from Ta to Tb. Note that the extension amount (Tb-Ta) at this time is basically arbitrary, and is appropriately set within a range of, for example, 10 to 20% of the polishing time Ta before the extension.

[0049] When the sharpening time is extended in this manner, the continuous and cumulative counts of regrinding in the wear state prediction step S6 and the extension determination step S7 are both reset, and the above-mentioned steps S5 to S7 are repeated. Then, after one or more extensions of the sharpening time, a determination is made as to whether or not the sharpening blade 21 needs to be replaced based on the extended sharpening time (replacement determination step S8). Details of the replacement determination step S8 will be described below.

[0050] (S6) Prediction process (S8) Replacement judgment process In this step, when the sharpening time is extended as described above, it is determined whether or not replacement of the sharpening blade 21 as a tool is required. In this embodiment, each time the sharpening time in the sharpening step S1 is extended in the extension determination step S7, it is determined whether or not the sharpening time is equal to or greater than a preset threshold value (third threshold value) as shown in Fig. 9 (step S81).

[0051] If it is determined that the extended sharpening time is equal to or greater than the third threshold value, it is predicted (determined) that the sharpening blade 21 has worn down to the point where it no longer has the minimum sharpening ability required for continued use on the electrode 10, and a warning is given that the sharpening blade 21 should be replaced (step S82).

[0052] Alternatively, if it is determined that the extended sharpening time is less than the third threshold, the process proceeds to a next step of determining whether or not the tool needs to be replaced based on the cumulative number of sharpening times. Then, it is determined whether or not the cumulative number of sharpening times since the start of use of the tool (the sharpening blade 21) is equal to or greater than a preset threshold (a fourth threshold) (step S83).

[0053] Here, if it is determined that the cumulative number of sharpening times is equal to or greater than the fourth threshold value, it is predicted (determined) that the sharpening blade 21 has worn down to the point where it no longer has the minimum sharpening ability required for continued use on the electrode 10, and a notice is given to the effect that the sharpening blade 21 should be replaced (step S82).

[0054] Here, if a notice is given to the effect that the grinding blade 21 should be replaced, the grinding blade 21 is replaced, for example, at the next equipment operation shutdown (usually at the scheduled time of equipment operation shutdown, such as for regular line maintenance).

[0055] The notice of replacement can be given in a manner that allows the worker to visually recognize it, such as by displaying the notice on a specified monitor or by turning on a lamp indicating that replacement is required. Alternatively, the notice of replacement can be given by voice, allowing the worker to audibly recognize it.

[0056] Furthermore, in step S82, if it is determined that the cumulative number of sharpening times is less than the fourth threshold value, i.e., if it is determined that both the extended sharpening time and the cumulative number of sharpening times are less than the corresponding threshold values ​​(third threshold value, fourth threshold value), this process S8 is terminated without giving a notice that the sharpening blade 21 should be replaced (step S84).

[0057] Fig. 8 is an example of a graph showing the relationship between the cumulative number of times the electrode 10 has been sharpened and the number of times re-sharpening has been performed for each sharpening step S1, and the relationship between the cumulative number of times sharpening has been performed and sharpening time, before and after replacement of the sharpening blade 21. Note that the vertical dashed dotted line in Fig. 8 indicates the point in time at which the sharpening blade 21 as a tool was replaced, from the viewpoint of the cumulative number of times sharpening has been performed. Therefore, at that point in time, the cumulative number of times sharpening has been reset (returned to zero).

[0058] Here, when the grinding time is extended according to the same criteria as in the case shown in FIG. 6, the maximum number of times the grinding time is extended is, for example, four times, and the threshold value (third threshold value) of the extended grinding time is Td (the grinding time immediately before the grinding time is extended to the maximum grinding time Tm), for example, at the time point after the first grinding time extension (at the time point after the grinding time is extended from Ta to Tb), the grinding time Tb after the extension is less than the third threshold value (Td), so no notice is given to the effect that the grinding blade 21 should be replaced. Similarly, at the time point after the second grinding time extension (at the time point after the grinding time is extended from Tb to Tc), the grinding time Tc after the extension is less than the third threshold value (Td), so no notice is given to the effect that the grinding blade 21 should be replaced. On the other hand, at the time point after the third grinding time extension (at the time point after the grinding time is extended from Tc to Td), the grinding time Td after the extension reaches the third threshold value (Td), so a notice is given to the effect that the grinding blade 21 should be replaced at this point. Therefore, when the equipment operation is stopped after the fourth extension of the grinding time (indicated by the vertically extending dashed line in FIG. 8), the grinding blade 21 is replaced with a new grinding blade. At this point, the cumulative number of grinding operations is reset (to zero), and the above-mentioned steps S1 to S8 are repeated. In this way, the grinding state of the electrode 10 is managed, and the wear state of the grinding blade 21 can be appropriately managed.

[0059] As described above, according to the method for grinding the spot welding electrode of the present embodiment, the number of times the electrode 10 has been re-ground is counted, and the wear state of the grinding blade 21 as a tool is predicted based on the count number, so that the wear state reflecting the usage status of the grinding blade 21 can be accurately predicted. According to this, for example, the grinding conditions can be automatically changed according to the predicted degree of wear state of the grinding blade 21, so that it is possible to maintain a good grinding state for the electrode 10 in the grinding process S1 without the worker having to stop the line, etc., to check the state of the grinding blade 21 and change the grinding conditions. Therefore, excellent productivity can be maintained. In addition, since it is sufficient to only count the number of re-grounds, it is possible to easily and inexpensively predict the wear state of the tool and maintain a good grinding state of the electrode 10 in the subsequent grinding process S1, compared to the case where the wear state of the grinding blade 21 is directly detected by a sensor, a camera, etc.

[0060] In addition, as in this embodiment, the re-sharpening step S3 is performed once for each grinding step S1, and the wear state of the grinding blade 21 is predicted based on the count number of each re-sharpening, so that the wear state can be predicted more accurately. That is, if the grinding conditions during re-sharpening are set relatively gentle (shorter in the case of grinding time), over-grinding can be suppressed, but the number of re-sharpenings may vary greatly (for example, 0 to 3 times) depending on the state of the electrode 10. In such a case, since the amount of grinding may vary for each re-sharpening, if the number of re-sharpenings is counted uniformly, the correlation between the count number and the wear state of the grinding blade 21 is likely to be relatively low. In contrast, if the re-sharpening step S3 is performed once for each grinding step S1, the grinding conditions during re-sharpening are set relatively strict (longer in the case of grinding time). In this case, the amount of grinding for each re-sharpening is stable, so that a high correlation can be obtained between the various count numbers of re-sharpenings and the wear state of the grinding blade 21. Therefore, by determining whether or not the sharpening conditions need to be changed (here, extending the sharpening time) or whether or not the sharpening blade 21 needs to be replaced based on preset threshold values ​​(first to fourth threshold values) for various resharpening count numbers, it is possible to accurately determine whether or not these needs are necessary.

[0061] In this embodiment, in the extension judgment step S7, the necessity of extending the grinding time is judged first based on the continuous count number of regrind (step S71), and if it is judged in step S71 that the extension is not necessary, the necessity of extending the grinding time is judged based on the cumulative count number of regrind. In this way, by first judging the necessity of extending the grinding time based on the continuous count number, it is possible to more accurately predict the wear state of the grinding blade 21 while removing noise such as erroneous detection in the inspection step S2. Also, if it is judged that the grinding time is not necessary in the necessity judgment based on the continuous count number, it is possible to detect the state where the grinding blade 21 is significantly worn out without fail, and to reliably improve the grinding conditions.

[0062] Although one embodiment of the present invention has been described above, the method for polishing a spot welding electrode according to the present invention can have configurations other than those described above without departing from the spirit of the method.

[0063] For example, in the above embodiment, the case where the necessity of extending the polishing time is determined based on both the cumulative count number and the continuous count number of regrinding has been described (see FIG. 7), but of course this is not limited to this. For example, the necessity of extending the polishing time may be determined based on either the cumulative count number or the continuous count number of regrinding. Alternatively, the necessity of extending the polishing time may be determined based on a count number related to regrinding of a type different from both the cumulative count number and the continuous count number.

[0064] In the above embodiment, when the polishing time is extended, the above-mentioned steps S5 to S7 are repeated in a state where both the continuous and cumulative counts of regrinds in the wear state prediction step S6 and the extension determination step S7 are reset, but the present invention is not limited to this. For example, a plurality of thresholds (second thresholds) for extending the polishing time based on the cumulative counts of regrinds may be set, and the polishing time may be extended each time the cumulative count reaches each threshold.

[0065] In the above embodiment, the case where the necessity of extending the grinding time is judged based on the count number for regrinding has been described, but of course other conditions may be changed. That is, for example, the rotation speed of the grinding blade 21 may be increased or the pressure of the electrode 10 against the grinding blade 21 may be increased based on the count number for regrinding.

[0066] In the above embodiment, the case has been described in which the necessity of replacing the grinding blade 21 is determined based on the extended sharpening time, and the necessity of giving a notice to the effect that the grinding blade 21 should be replaced is determined based on the accumulated number of sharpenings (see FIG. 9), but of course the present invention is not limited to this. For example, step S83 for determining the necessity of replacing the grinding blade 21 based on the accumulated number of sharpenings may be omitted. Alternatively, the necessity of replacing the grinding blade 21 may be determined based on a count number relating to a type of re-sharpening different from both the extended sharpening time and the accumulated sharpening time, or a numerical value resulting from the count number, for example, the accumulated number of occurrences of re-sharpening. [Explanation of symbols]

[0067] 10 electrodes 20 Polishing equipment 21 Polishing blade 30 Inspection Equipment S1 Polishing process S2 inspection process S3 Re-polishing process S4 Re-inspection process S5 Regrinding count process S6 Prediction process S7 Extension determination process S8 Replacement judgment process Ta,Tb,Tc,Td polishing time Tm Maximum polishing time

Claims

1. a polishing step of polishing the electrode for spot welding with a predetermined tool; an inspection step of inspecting the polished state of the electrode polished in the polishing step; and a re-polishing step of re-polishing the electrode based on an inspection result regarding a polished state of the electrode obtained in the inspection step, a prediction step of counting a cumulative number of times that the regrinding has been performed with respect to a plurality of the electrodes using the same tool, and predicting a wear state of the tool based on the count number.

2. 2. The method for grinding a spot welding electrode according to claim 1, wherein the prediction step includes counting a cumulative number of times the tool has been regrind since the tool was first used, and predicting the wear state of the tool based on the cumulative count number.

3. A polishing process for polishing a spot welding electrode with a predetermined tool; an inspection step of inspecting the polished state of the electrode polished in the polishing step; and a re-polishing step of re-polishing the electrode based on an inspection result regarding a polished state of the electrode obtained in the inspection step, A prediction step of counting the number of times the regrinding has been performed and predicting a wear state of the tool based on the counted number, a step of counting the number of times that the regrinding has occurred consecutively in the prediction step, and predicting the wear state of the tool based on the number of consecutive counts.

4. A polishing step of polishing an electrode for spot welding with a predetermined tool; an inspection step of inspecting the polished state of the electrode polished in the polishing step; and a re-polishing step of re-polishing the electrode based on an inspection result regarding a polished state of the electrode obtained in the inspection step, A prediction step of counting the number of times the regrinding has been performed and predicting the wear state of the tool based on the count number; and a grinding time for the electrode in the grinding step, based on the prediction result regarding the wear state of the tool obtained in the prediction step, for determining whether or not it is necessary to extend the grinding time of the electrode in the grinding step.

5. 5. The method for polishing a spot welding electrode according to claim 1, further comprising a replacement determination step of determining whether or not a notice to replace the tool is required based on a prediction result regarding a wear state of the tool obtained in the prediction step.

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