JP2011240368A - Method and system for determining weld quality - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method that accurately and easily determines whether weld quality is acceptable or not without the need to set a threshold to determine the weld quality according to a welding condition for each welded spot, nor being influenced by diverse disturbances, and to provide a system thereof.SOLUTION: The method for determining whether weld quality is acceptable or not, determines right and failure states of the quality of a lap resistance welding. The method includes: a resistance value waveform generation step (S3) of generating a resistance value waveform representing a variation of a resistance value with respect to an energization time by measuring (S2) a resistance value between electrodes during welding; a resistance value waveform classification step (S4) of identifying the generated resistance value waveform with one of the resistance value waveform patterns caused by the predetermined diverse disturbances; and a first weld quality determination step (S5) for determining whether the weld quality is right or failure state based on the determination standard predetermined for each resistance value waveform pattern.

Description

  The present invention relates to a welding quality determination method and a welding quality determination system, and more specifically, superimposes joint portions of workpieces to be welded to each other, and press-clamps the joint portions with a pair of electrodes. The present invention relates to a method for judging the quality of lap resistance welding and a system for judging the quality of lap resistance welding.

  In spot welding, which is lap resistance welding, generally, welds of a plurality of plate-shaped workpieces (hereinafter referred to as workpieces) are overlapped, and the workpiece welds are sandwiched between a pair of electrodes and pressed, and current is applied. Is flowing. The portion sandwiched between the electrodes of the welded portion is melted by Joule heat generated by current resistance and then solidified to form a nugget. If the nugget is not properly formed, the welded portion is weakly joined or not joined, so-called Hanare phenomenon occurs, and it is necessary to perform welding again so as to improve the welding quality.

  As a conventional general technique for determining the quality of such welding quality, an operator extracts a workpiece to be welded for each predetermined number from a plurality of spot-welded workpieces, and inspects it. In accordance with the list, a predetermined spot of the welded portion was hit with a hammer and struck with a hammer, and the determination was made based on the feel and sound of the struck (hereinafter, this welding quality determination method is referred to as “sag check”).

  Further, as a conventional technique, for example, as disclosed in Patent Document 1, whether or not welding quality is good is determined based on a resistance value of a current flowing through an electrode. In Patent Document 1, when determining the quality of spot welding quality welded by a constant current type spot welding machine, a resistance value between electrodes in a predetermined period at the beginning of energization of spot welding is detected (monitored), and the resistance It is disclosed whether the value is lower or higher than a preset threshold value, and when the comparison result is low, the energization is continued, while when it is high, the energization is immediately stopped and the welding apparatus is stopped. . Further, Patent Document 1 further detects a change in resistance value between electrodes during energization of spot welding, and the difference between the maximum resistance value during the energization period and the final resistance value at the end of energization is a preset threshold value. If the comparison result is small, immediately re-energize under the condition that the welding current is increased at a predetermined rate, and also detect the change in resistance between the electrodes during spot welding. The average or integrated resistance value during energization is calculated from this resistance value, and whether the average resistance value is within a predetermined range set in advance, the comparison result is outside the predetermined range, It is also disclosed that when no spatter is generated, re-energization is immediately performed under a condition in which the welding current or the welding voltage is increased at a predetermined rate.

JP 2006-058593 A

  However, in the conventional technique for monitoring the resistance value as in Patent Document 1, the threshold value for determining the welding quality according to the welding conditions such as the thickness and type of the workpiece, the current or voltage applied to the electrode, and the like. Therefore, there is a problem in that a complicated operation for presetting each welding location (spotting point) is required, so that the cost and time are required, and the configuration for determining the welding quality is complicated.

Also, in lap resistance welding, due to the following disturbances, even under the same welding conditions, the resistance value waveform is different, the nugget is not formed properly, and a hanare phenomenon may occur. is there. Examples of the disturbance include the following.
A) Wear due to use of tip at electrode tip (FIG. 20)
B) Straightness between electrode and workpiece (Fig. 21)
C) Chamfer (Fig. 23)
D) Board ski (Fig. 25)
E) Sliding during welding (Fig. 28)

  In the above disturbance, as shown in FIG. 20, regarding the wear of the electrodes 10 and 11 of A), when the workpieces Wa, Wb... Are thin plates or plated materials, It has been found that the resistance value rises once after the start of welding and then decreases, but as the tip wears, the resistance value rises less and the change becomes smaller. It was. On the other hand, when the workpieces Wa, Wb,... Are thick plates or bare materials, the resistance value of a new chip once increases and then decreases, but as the chip wears (see FIG. 20) After 50 points, after 200 points, after 500 points, it is only an example) It was found that the timing of reaching the maximum resistance value is delayed and the change is also small. .

  Also, among the above disturbances, as shown in FIG. 22, the surface straightness of B) (FIG. 21) is correct when the workpiece is two thick plates Wa and Wb and one thin plate Wc. Compared with the straightness state (FIG. 21A), in the state where the surface straightness is inclined (FIG. 21B), the resistance value increases from the start of welding as shown in FIG. It has been found that the resistance gradually decreases (the resistance waveform decreases to the right), the nugget is not properly formed, and the joint portion is broken.

  On the other hand, among the above disturbances, as shown in FIG. 23, for the edge of C), the joints of the workpieces Wa, Wb, Wc are displaced (the workpiece Wa in FIG. 23), etc. 11 is out of the joint or very close to the edge of the joint, and as shown in FIG. 25, for the plate ski of D), the workpieces Wa, Wb, Wc are joined. This is a case in which the polymerization of the portions is not sufficiently in close contact but there is a gap (in FIG. 25, the workpiece Wb is bent and separated from the workpiece Wa). As shown in FIG. 26, the larger the gap (plate gap) at the joint portion of the workpiece, the higher the current to a certain extent, and even when spatter occurs, the welding quality becomes poor. Both the edge punching of C) (FIG. 23) and the plate gap of FIG. D) (FIG. 25) are both thick plates Wa having two workpieces as in the case of the straightness between the electrode of B) and the workpiece. In the case of Wb and one thin plate Wc, as shown in FIG. 24 and FIG. 27, the resistance value once rises and then falls, so that the welding quality with the new tip in the electrode wear of A) Was found to be similar to a good resistance waveform (see the general waveform of a new chip in FIG. 20). For this reason, it is difficult to accurately determine the quality of the welding quality from the resistance waveform for the end edge of C) (FIG. 23) and the plate gap of D) (FIG. 25).

  Further, in the above disturbance, as shown in FIG. 28, the slippage during welding of E) is caused by at least one of the electrodes 10 and 11 slipping due to expansion due to heat generation of the workpieces Wa and Wb. As shown in FIG. 29, it is found that the resistance value once increases from the start of welding, then decreases, then increases again in the middle (see the arrow in FIG. 29), and then decreases again. It was. In addition, when the electrodes 10 and 11 slip, the dent becomes an ellipse or an ellipse, and the appearance is not good.

  Therefore, under the conditions of these disturbances A) to E), as disclosed in Patent Document 1, even if the measured resistance value is simply compared with a preset threshold value, the quality of the welding quality is good. It was difficult to determine accurately.

  The present invention has been made in view of the above-described problems, and it is not necessary to set a threshold value for determining welding quality in accordance with welding conditions for each welding location (spot), and it is affected by various disturbances. It is an object of the present invention to provide a method and system capable of easily and accurately determining the quality of welding quality without any problems.

In order to achieve the above object, the welding quality judgment method according to claim 1 superimposes the joints of the workpieces to be welded together, and press-clamps the joints with a pair of electrodes, between the pair of electrodes. This is a method for determining the quality of lap resistance welding by passing a current through the resistance, measuring the resistance value between the electrodes during welding, and generating a resistance value waveform representing the change in resistance value with respect to the energization time. A resistance value waveform generation step, a resistance value waveform classification step of classifying the generated resistance value waveform into one of a plurality of resistance value waveform patterns due to various disturbances set in advance, and for each resistance value waveform pattern in advance A first welding quality pass / fail judgment step for judging whether or not the weld quality is good based on a set judgment criterion is characterized.
In order to achieve the above object, the invention according to the welding quality determination method of claim 2 is the invention according to claim 1, wherein it is determined that the welding quality is not good in the first welding quality determination step. A sputter presence / absence determination step for determining the presence / absence of spatter from the resistance value waveform, a change amount of the resistance value in the generated resistance value waveform, and the resistance value waveform pattern when it is determined that spatter has occurred. And a second welding quality pass / fail judgment step for judging whether or not the weld quality is good based on a comparison with a preset change amount threshold value of the resistance value at the time of occurrence of sputtering. .
In order to achieve the above object, the welding quality determination system according to claim 3 superimposes the joints of the workpieces to be welded together, and press-clamps the joints with a pair of electrodes. A system that determines the quality of lap resistance welding by passing current between electrodes, and measures the resistance value between electrodes during welding to generate a resistance value waveform that shows the change in resistance value with respect to energization time. And classifying the generated resistance value waveform into one of a plurality of resistance value waveform patterns due to various disturbances set in advance, and welding quality based on a criterion set in advance for each of the resistance value waveform patterns It is characterized by comprising a determination means for determining whether the first welding quality is good or not.
In order to achieve the above object, the invention relating to the welding quality judgment system according to claim 4 determines that the welding quality is not good in the first welding quality judgment in the invention according to claim 3. In this case, the presence or absence of spatter is determined based on the resistance value waveform, and when it is determined that spatter is generated, the amount of change in the resistance value in the generated resistance value waveform and the resistance value waveform pattern are determined in advance. It is characterized in that a second weld quality pass / fail judgment is made as to whether or not the weld quality is good based on a comparison with a set threshold value of change in resistance value at the time of occurrence of spattering.

According to the first aspect of the present invention, the joint portions of the workpieces are superposed on each other, the joint portions are pressed and clamped by a pair of electrodes, and a current is passed between the pair of electrodes to perform lap resistance welding. In addition, a resistance value waveform generating step for measuring a resistance value between electrodes during welding and generating a resistance value waveform representing a change in the resistance value with respect to the energization time, and the generated resistance value waveform are set in advance. Determines whether welding quality is good based on a resistance value waveform classification step for classifying into one of a plurality of resistance value waveform patterns due to various disturbances and a criterion set in advance for each of the resistance value waveform patterns By performing the first welding quality pass / fail determination step, the resistance value waveform generated in the first weld quality pass / fail determination step is similar to the resistance value waveform of the non-defective product in the classified resistance value waveform pattern. For products, the welding quality is judged to be good. Therefore, it is not necessary to set a threshold for determining the welding quality according to the welding conditions for each welding location (spot), and the quality of the welding quality can be accurately determined without being affected by various disturbances. It is possible to provide a welding quality determination method that can be easily determined.
According to the invention of claim 2, in the invention of claim 1, when it is determined that the welding quality is not good in the first welding quality good / bad determination step, it is determined whether or not spatter is generated from the resistance value waveform. When determining whether or not spatter is generated, and the amount of change in the resistance value in the generated resistance value waveform and the resistance value at the time of spattering preset for each of the resistance value waveform patterns. It is determined that the welding quality is not good in the first welding quality pass / fail judgment step by performing a second weld quality pass / fail judgment step for judging whether the weld quality is good based on the comparison with the change amount threshold. Even in the welded portion, the amount of change in the resistance value in the resistance value waveform generated in the second welding quality pass / fail judgment step is changed in the resistance value at the time of occurrence of sputtering, which is preset for each resistance value waveform pattern. Just by comparing with the amount threshold, it can be determined whether the nugget is properly formed, that is, whether the welding quality is good. Therefore, the threshold for determining the welding quality according to the welding conditions is set to the welding location ( It is not necessary to set for each spot), and it is possible to provide a welding quality judgment method capable of accurately and easily judging the quality of welding quality without being affected by various disturbances.
According to the invention of claim 3, the resistance value between the electrodes at the time of welding is measured, a resistance value waveform indicating a change in the resistance value with respect to the energization time is generated, and the generated resistance value waveform is The first welding quality is classified into one of a plurality of resistance value waveform patterns due to various set disturbances, and whether or not the welding quality is good based on a criterion set in advance for each of the resistance value waveform patterns. By providing judgment means for judging pass / fail judgment, the joint parts of the workpieces are superposed on each other, the joint parts are pressed and clamped by a pair of electrodes, and an electric current is passed between the pair of electrodes to perform lap resistance welding. In performing the first welding quality pass / fail judgment, the determination means can determine that the generated resistance value waveform is similar to the resistance value waveform of the non-defective product because the weld quality is good. Threshold for judging welding quality according to conditions Can be provided for each welding location (spot), and it is possible to provide a welding quality judgment system capable of accurately and easily judging the quality of welding quality without being affected by various disturbances. .
According to the invention of claim 4, in the invention of claim 3, when the determination means determines that the welding quality is not good in the first welding quality determination, spatter is generated by the resistance value waveform. When the presence / absence is determined and it is determined that spatter is generated, the amount of change in the resistance value in the generated resistance value waveform and the amount of change in the resistance value at the time of spattering preset for each resistance value waveform pattern The second weld quality quality determination for whether or not the weld quality is good based on the comparison with the threshold value is further performed, so that the weld quality determined by the first weld quality quality determination is not good. Even if the resistance value change amount in the generated resistance value waveform exceeds the resistance value change amount threshold value at the time of occurrence of sputtering in the resistance value waveform pattern in the second welding quality pass / fail judgment, a nugget is generated. Suitable Therefore, it is not necessary to set a threshold value for determining the welding quality according to the welding conditions for each welding point (spot), and various disturbances are caused. It is possible to provide a welding quality determination system capable of easily and accurately determining the quality of welding quality without being affected.

(Aspect of the Invention)
In the following, the invention that is claimed to be claimable in the present application (hereinafter referred to as “claimable invention”. The claimable invention is at least the “present invention” to the invention described in the claims. Some aspects of the present invention, including subordinate concept inventions of the present invention, superordinate concepts of the present invention, or inventions of different concepts) will be illustrated and described. As with the claims, each aspect is divided into sections, each section is numbered, and is described in a form that cites the numbers of other sections as necessary. This is for the purpose of facilitating the understanding of the claimable invention, and is not intended to limit the combinations of the constituent elements constituting the claimable invention to those described in the following sections. In other words, the claimable invention should be construed in consideration of the description accompanying each section, the description of examples, etc., and as long as the interpretation is followed, a mode in which other components are added to the mode of each section. In addition, an aspect in which constituent elements are deleted from the aspect of each item can be an aspect of the claimable invention. In each of the following terms, (1) corresponds to claim 1, (2) corresponds to claim 2, (3) corresponds to claim 3, and (4) claims. This corresponds to item 4.

(1) A method of judging quality of lap resistance welding by superimposing joints of workpieces on each other, press-clamping the joints with a pair of electrodes, and passing a current between the pair of electrodes. And
A resistance value waveform generation step for measuring a resistance value between electrodes during welding and generating a resistance value waveform representing a change in the resistance value with respect to the energization time;
A resistance value waveform classification step for classifying the generated resistance value waveform into one of a plurality of resistance value waveform patterns due to various disturbances set in advance;
A welding quality determination method comprising: performing a first welding quality pass / fail determination step for determining whether or not weld quality is good based on a predetermined determination criterion for each resistance value waveform pattern.

  In the invention of (1), when joining portions of the workpieces are superposed on each other, the joint portions are pressed and sandwiched between a pair of electrodes, and a current is passed between the pair of electrodes to perform lap resistance welding. A resistance value waveform generating step for measuring a resistance value between the electrodes during welding and generating a resistance value waveform representing a change in the resistance value with respect to the energization time; It is determined whether or not the welding quality is good based on a resistance value waveform classification step for classifying the resistance value waveform patterns into one of a plurality of resistance value waveform patterns due to disturbance and a criterion set in advance for each of the resistance value waveform patterns. A 1st welding quality quality determination process is performed. In the first welding quality pass / fail judgment step, if the generated resistance value waveform is similar to the good resistance value waveform in the resistance value waveform pattern, it is judged that the weld quality is good. Therefore, it is not necessary to set a threshold for determining the welding quality according to the welding conditions for each welding location (spot), and the quality of the welding quality is easily and accurately determined without being affected by various disturbances. be able to.

(2) In the case where it is determined that the welding quality is not good in the first welding quality quality determination step,
Sputter presence / absence determination step for determining the presence / absence of spatter from the resistance value waveform;
When it is determined that spatter has occurred, the resistance value change amount in the generated resistance value waveform is compared with a resistance value change amount threshold value at the time of spattering preset for each resistance value waveform pattern. A welding quality determination method according to item (1), characterized in that a second welding quality determination step for determining whether or not the welding quality is good is performed.

  In the invention of the item (2), in the invention described in the item (1), a predetermined time is determined in the sputter presence / absence determination step for the welded portion determined to have poor welding quality in the first welding quality determination step. When the resistance value falls below a predetermined value within the range, it is determined that spatter has occurred. Here, when the nugget is properly formed and the welding quality is good, spatter occurs. Therefore, in the second welding quality pass / fail judgment step, the resistance value change amount in the generated resistance value waveform is compared with a resistance value change amount threshold value at the time of occurrence of sputtering, which is preset for each resistance value waveform pattern, If the change amount of the resistance value in the generated resistance value waveform exceeds the resistance value change amount threshold value during sputtering, it is determined that the nugget is appropriately formed and the welding quality is good. Therefore, it is not necessary to set a threshold for determining the welding quality according to the welding conditions for each welding location (spot), and the quality of the welding quality is easily and accurately determined without being affected by various disturbances. be able to.

(3) This is a system for judging the quality of lap resistance welding, in which the joints of the workpieces are superposed on each other, the joints are pressed and sandwiched between a pair of electrodes, and a current flows between the pair of electrodes. And
The resistance value between the electrodes at the time of welding is measured, a resistance value waveform indicating a change in the resistance value with respect to the energization time is generated, and the generated resistance value waveform is a plurality of resistance value waveforms caused by various preset disturbances. Classification means is provided for determining whether the first welding quality is good or not based on a judgment criterion preset for each resistance value waveform pattern. A characteristic welding quality judgment system.

  In the invention of the item (3), when joining parts to be welded are superposed on each other, the joint parts are pressed and clamped by a pair of electrodes, and a current is passed between the pair of electrodes to perform lap resistance welding. The resistance value between the electrodes at the time of welding is measured, and a resistance value waveform indicating a change in the resistance value with respect to the energization time is generated by the determination unit, and the generated resistance value waveform is generated by a plurality of preset disturbances. The resistance value waveform patterns are classified into one of the resistance value waveform patterns, and whether or not the welding quality is good is determined based on a criterion set in advance for each resistance value waveform pattern. In the first welding quality determination, the determination unit determines that the welding quality is good when the generated resistance value waveform is similar to the good resistance value waveform. Therefore, it is not necessary to set a threshold for determining the welding quality according to the welding conditions for each welding location (spot), and the quality of the welding quality is easily and accurately determined without being affected by various disturbances. be able to.

  (4) When the determination means determines that the welding quality is not good in the first welding quality determination, the presence / absence of spatter is determined from the resistance waveform, and the determination is that there is spatter. Whether or not the welding quality is good based on a comparison between a resistance value change amount in the generated resistance value waveform and a resistance value change threshold value at the time of occurrence of sputtering, which is set in advance for each resistance value waveform pattern. The welding quality determination system according to item (3), wherein the second welding quality quality determination is further performed.

  In the invention according to item (4), in the invention according to item (3), the determination means provides resistance within a predetermined time range for a welded portion that is determined to have poor welding quality in the first welding quality determination. When the value decreases by a predetermined value or more, it is determined that spatter is generated. Here, when the nugget is properly formed and the welding quality is good, spatter occurs. Therefore, when the determination means further determines that there is spatter generation, the change amount of the resistance value in the generated resistance value waveform is preset for each resistance value waveform pattern in the second welding quality determination. If the resistance value change amount threshold value at the time of occurrence of sputtering is exceeded, it is determined that the nugget is properly formed and the welding quality is good. Therefore, it is not necessary to set a threshold for determining the welding quality according to the welding conditions for each welding location (spot), and the quality of the welding quality is easily and accurately determined without being affected by various disturbances. be able to.

It is the flowchart shown in order to demonstrate one Embodiment of the welding quality determination method of this invention. It is the conceptual diagram shown in order to demonstrate one Embodiment of the system of this invention. 6 is a graph of “general resistance value waveform pattern” shown to explain one embodiment of a plurality of resistance value waveform patterns due to various disturbances set in advance in the first welding quality pass / fail judgment step of the present invention. FIG. 5 is a graph of a “downward-pointing resistance value waveform pattern” shown in order to explain one embodiment of a plurality of resistance value waveform patterns due to various preset disturbances in the first welding quality pass / fail judgment step of the present invention. . FIG. 5 is a “root resistance value waveform pattern” graph for explaining one embodiment of a plurality of resistance value waveform patterns due to various disturbances set in advance in the first welding quality pass / fail determination step of the present invention. 6 is a graph of “horizontal resistance value waveform pattern” shown to explain one embodiment of a plurality of resistance value waveform patterns due to various disturbances set in advance in the first welding quality pass / fail judgment step of the present invention. 6 is a graph showing an example in which the welding quality is determined to be good in the “general resistance value waveform pattern” in the first welding quality quality determination step. 7 is a graph showing an example in which the welding quality is determined to be poor in the “general resistance value waveform pattern” in the first welding quality pass / fail determination step. 7 is another graph showing an example in which the welding quality is determined to be good in the “general resistance value waveform pattern” in the first welding quality quality determination step. 7 is a graph showing another example when the welding quality is determined to be poor in the “general resistance value waveform pattern” in the first welding quality pass / fail determination step. 6 is a graph showing an example in which the welding quality is determined to be good in the “downward-pointing resistance value waveform pattern” in the first welding quality quality determination step. 5 is a graph showing an example in which the welding quality is determined to be poor in the “downward-decreasing resistance value waveform pattern” in the first welding quality quality determination step. 6 is a graph showing an example in which the welding quality is determined to be good in the “root type resistance value waveform pattern” in the first welding quality quality determination step. 6 is a graph showing an example in which the welding quality is determined to be poor in the “root type resistance value waveform pattern” in the first welding quality pass / fail determination step. 7 is a graph showing another example when the welding quality is determined to be good in the “root type resistance value waveform pattern” in the first welding quality quality determination step. 7 is a graph showing another example when the welding quality is determined to be poor in the “root resistance value waveform pattern” in the first welding quality pass / fail determination step. 7 is a graph showing another example when the welding quality is determined to be good in the “horizontal resistance value waveform pattern” in the first welding quality quality determination step. 6 is a graph showing another example when the welding quality is determined to be poor in the “horizontal resistance value waveform pattern” in the first welding quality pass / fail determination step. In order to perform the 2nd welding quality quality determination process of this invention, it is explanatory drawing containing the graph shown in order to demonstrate determination of sputter | spatter generation | occurrence | production from a resistance value waveform. It is explanatory drawing shown in order to demonstrate the relationship between abrasion by use of the tip of the tip of an electrode, and a resistance value waveform among disturbances. It is the enlarged view shown in order to demonstrate B) the surface straightness of an electrode and a workpiece | work among disturbances. It is a graph which shows an example of the resistance value waveform in the state shown in FIG. It is the enlarged view shown in order to demonstrate C) edge-cutting among disturbances. It is a graph which shows an example of the resistance value waveform in the state shown in FIG. It is the enlarged view shown in order to demonstrate D) board skiing among disturbances. It is the graph shown in order to demonstrate the quality of the welding by a plate | board ski and the change of an electric current. It is a graph which shows an example of the resistance value waveform in the state shown in FIG. It is the enlarged view shown in order to demonstrate the sliding during welding E) among disturbances. It is a graph which shows an example of the resistance value waveform in the state shown in FIG.

First, an embodiment of a welding quality determination system of the present invention and a welding machine to which the welding quality determination system is applied will be described in detail mainly with reference to FIG. In addition, about the structure similar or equivalent to the prior art mentioned above, the same or corresponding code | symbol is attached | subjected and the description is abbreviate | omitted.
The system of the present invention superimposes the joints of the workpieces Wa, Wb,... To each other and press-clamps them with a pair of electrodes 10, 11, and a current flows between the pair of electrodes 10, 11. The quality of resistance welding is determined. The resistance value between the electrodes 10 and 11 at the time of welding is measured, and a resistance value waveform indicating a change in the resistance value with respect to the energization time is generated. The resistance value waveform is classified into one of a plurality of resistance value waveform patterns due to various disturbances set in advance, and whether the welding quality is good based on a criterion set in advance for each resistance value waveform pattern Determination means 4 for determining whether the first welding quality is good or bad.
Then, when the determination means 4 further determines that the welding quality is not good in the first welding quality determination, the presence / absence of spatter is determined from the resistance value waveform, and when it is determined that spatter is generated. The resistance value change amount in the generated resistance value waveform is compared with a resistance value change amount threshold value at the time of occurrence of sputtering that is preset for each resistance value waveform pattern. 2 Welding quality determination is further performed.

  For example, a panel material constituting a body of an automobile is conveyed to the welding line L as workpieces Wa, Wb. One or a plurality of robots 2 supporting the welding gun 1 are arranged at predetermined positions so as to face the welding line L. Further, a monitor 6 capable of displaying the contents as described later is disposed downstream of the welding line L.

  In the case of this embodiment, the welding gun 1 is a so-called C-type welding gun, and is arranged so that the electrode tips at the tips of the electrodes 10 and 11 are opposed to the arm, and at least one of the electrodes 10 or 11 is disposed. It is held by the actuator so as to approach and move away from the other electrode 11 or 10 and to hold the joined portion of the superposed workpieces Wa, Wb,... With a predetermined force. Both electrodes 10 and 11 are connected to an AC power source that supplies an AC current in a controllable manner. And in the system of this invention, the ammeter which measures the electric current value supplied to both electrodes 10 and 11, and the voltmeter which measures the voltage of 10 and 11 between both electrodes are provided, and the determination means 4 is provided. The resistance value between the electrodes during welding is measured by calculating from the current value and voltage value output from the ammeter and voltmeter, respectively.

  The robot 2 is connected to a controller 3 that controls its operation. The controller 3 includes a determination unit 4 that determines the welding quality as described later, and predetermined information obtained from the controller 3 and the determination unit 4. To the monitor 6 is connected.

Next, an embodiment of the welding quality determination method of the present invention will be described based on FIGS. 1 to 19 together with the operation of the welding quality determination system configured as described above.
In the method of the present invention, the joint portions of the workpieces Wa, Wb... Are superposed on each other, the joint portions are pressed and sandwiched between the pair of electrodes 10 and 11, and an electric current is applied between the pair of electrodes 10 and 11. The resistance value between the electrodes 10 and 11 at the time of welding is measured (S2), and a resistance value waveform representing a change in the resistance value with respect to the energization time is determined. A resistance value waveform generation step (S3) to be generated, and a resistance value waveform classification step (S4) for classifying the generated resistance value waveform into one of a plurality of resistance value waveform patterns due to various disturbances set in advance; The first welding quality pass / fail judgment step (S5) for judging whether or not the weld quality is good based on a judgment criterion set in advance for each resistance value waveform pattern is performed.
And in the case where it is determined that the welding quality is not good in the first welding quality pass / fail judgment step (S5) (in the case of NO), a sputter presence / absence judgment step (S6) for judging the presence / absence of spatter from the resistance value waveform, When it is determined that there is spatter generation (in the case of YES), a resistance value change amount in the generated resistance value waveform, and a resistance value change amount threshold value at the time of spatter generation preset for each resistance value waveform pattern, The second welding quality pass / fail judgment step (S7) for judging whether or not the weld quality is good based on the comparison.

  The workpieces Wa, Wb,... Are conveyed on the welding line L before the joints are spot-welded, and the joints are preliminarily polymerized with each other and are pressed and clamped by the electrodes 10 and 11. The number of workpieces to be spot welded is 2 (Wa, Wb) or 3 (Wa, Wb, Wc). The thickness is also the same. And may be different.

  When starting welding (S1), an alternating current is passed from the alternating current power source to the electrodes 10 and 11, and the current value flowing through the electrodes 10 and 11 every half cycle of the alternating current and the voltage between the electrodes 10 and 11 at that time. The value is measured and the result is output to the determination means 4. The determination means 4 measures by calculating a resistance value from the obtained current value and voltage value (S2). And the determination means 4 produces | generates the change of the measured resistance value which changes with progress of energization time as a resistance value waveform, and from the produced | generated resistance value waveform, 1st welding quality quality determination is mentioned so that it may mention later. A basic variable used for a criterion including a process is calculated (S3). The basic variables calculated by the determination means 4 are as follows: initial resistance value Rs, final resistance value Re, average resistance value μ, maximum resistance value Rmax, minimum resistance value Rmin, resistance value In the waveform, the area S surrounded by the straight line connecting the initial resistance value Rs and the final resistance value Re and the resistance value waveform generated in the resistance value waveform generation process, from the start of energization to the maximum resistance value Rmax And the time Tmin required from the start of energization to the minimum resistance value Rmin.

  Here, the resistance value waveform pattern stored in advance in the determination means 4 will be described with reference to FIGS. The resistance value waveform pattern shown in FIG. 3 temporarily increases from the initial resistance value Rs at the start of energization, and after reaching the maximum resistance value Rmax, the resistance value greatly decreases to the minimum resistance value Rmin, and then the final resistance value. Since it is a general one that changes little to slightly up to Re and is relatively large when normal welding is performed without being affected by disturbance, it will be referred to as a general type.

  The resistance value waveform pattern shown in FIG. 4 is a typical example in which the initial resistance value Rs at the start of energization is high and then the resistance value decreases (ΔRs) as the energization time elapses. Since the value waveform falls to the right, it is referred to as a right-falling type.

  In the resistance value waveform pattern shown in FIG. 5, the initial resistance value Rs at the start of energization becomes the minimum resistance value Rmin, the resistance value increases once from the minimum resistance value Rmin, and after reaching the maximum resistance value Rmax, the resistance value increases. Although it descends (ΔR), the resistance value changes little after that, and is referred to as a root type because of its waveform shape.

  The resistance value waveform pattern shown in FIG. 6 is a representative one in which the difference (Rmax−Rmin) between the maximum resistance value Rmax and the minimum resistance value Rmin from the start of energization to the end of energization is relatively small (small). The horizontal shape is referred to from the waveform shape.

  The determination means 4 determines which resistance value waveform pattern is classified among the resistance value waveform patterns as shown in FIGS. 3 to 6 (S4). Subsequently, the determination means 4 performs a first welding quality pass / fail determination step according to the determination criteria set for each classified resistance value waveform pattern, and determines whether or not the weld quality is good (S5).

Here, one embodiment of the determination criterion set for each resistance value waveform pattern in the first welding quality pass / fail determination step (S5) will be described with reference to FIGS.
FIG. 7 shows that the resistance value waveform classified into the general type waveform is judged to have good welding quality (also referred to as “OK”), and FIG. 8 shows the resistance value waveform classified into the general type waveform. It is determined that the welding quality is poor (also referred to as NG). In FIG. 7, the difference between the maximum resistance value Rmax and the minimum resistance value Rmin, that is, the amount of change in the resistance value (see the arrow) is larger than the threshold set from experience, and the resistance value waveform and the average resistance value μ Since the area S of the region formed by (see the portion indicated by the stripes) is larger than the threshold value set from experience, it is determined that the nugget is properly formed and thus the welding quality is good. The On the other hand, in FIG. 8, the difference between the maximum resistance value Rmax and the minimum resistance value Rmin, that is, the change amount of the resistance value (see the arrow) is smaller than the threshold set from experience, and the resistance value waveform Since the area S of the region formed by the average resistance value μ and the average resistance value μ (see the portion indicated by the stripes) is smaller than the threshold value set based on experience, the nugget is not formed properly, and thus welding is performed. It is determined that the quality is poor. That is, in the case of the general type waveform, the criterion is that the change amount of the resistance value that is the difference between the maximum resistance value Rmax and the minimum resistance value Rmin, and the area S of the region formed by the resistance value waveform and the average resistance value μ. And are included.

  9 shows that the resistance value waveform classified into the general type waveform is determined to have good welding quality (also referred to as OK) as in FIG. 7, and FIG. 10 shows the same as FIG. In the resistance value waveform classified into the general type waveform, it is determined that the welding quality is poor (also referred to as NG). In FIG. 9, the time (timing) Tmax when the maximum resistance value Rmax is reached is earlier than the threshold value set from experience, and the slope dRe indicating the change in resistance value at the end is greater than the threshold value set from experience. Is large (the arrow is pointing upward), it is determined that the nugget is properly formed and therefore the welding quality is good. On the other hand, in FIG. 10, the time (timing) Tmax when the maximum resistance value Rmax is reached from the start of energization is later than the threshold set from experience, and the slope dRe indicating the change in resistance value at the end. Is smaller than the threshold set from experience (the arrow is pointing downward), it is determined that the nugget is not properly formed and therefore the welding quality is poor. That is, the determination criterion in the case of the general waveform includes a time Tmax from the start of energization to the maximum resistance value Rmax and a slope dRe indicating a change in resistance value at the end. These criteria can be combined as appropriate.

  FIG. 11 shows that the resistance value waveform classified into the right-down waveform is judged to have good welding quality (also referred to as OK), and FIG. 12 shows the resistance value classified into the right-down waveform. In the waveform, it is determined that the welding quality is poor (also referred to as NG). In FIG. 11, the rate of change dR of the resistance value from the maximum resistance value Rmax to the minimum resistance value Rmin is greater than a threshold set from experience, and the slope indicating the change in resistance value from the minimum resistance value Rmin to the end stage. Since dRe is greater than a threshold set from experience (the arrow is pointing upward), it is determined that the nugget is properly formed and thus the welding quality is good. On the other hand, in FIG. 12, the rate of change dR of the resistance value from the maximum resistance value Rmax to the minimum resistance value Rmin is smaller than the threshold value set from experience, and the resistance value from the minimum resistance value Rmin to the end stage. Since the slope dRe indicating the change in the distance is smaller than the threshold set based on experience (in FIG. 12, the arrow as shown in FIG. 11 cannot be represented), the nugget is not formed properly, so the welding quality is low. It is determined to be defective. In other words, the criterion for the downward-sloping waveform includes the rate of change dR of the resistance value from the maximum resistance value Rmax to the minimum resistance value Rmin, and the slope dRe indicating the change in resistance value from the minimum resistance value Rmin at the end. included.

  FIG. 13 shows that the resistance value waveform classified into the root type waveform is judged to have good welding quality (also referred to as “OK”), and FIG. 14 shows the resistance value waveform classified into the root type waveform. It is determined that the welding quality is poor (also referred to as NG). In FIG. 13, the amount of increase in the resistance value from the initial resistance value (in this case, the minimum resistance value Rmin) to the maximum resistance value Rmax is larger than a threshold set from experience, and the minimum resistance Since the time from the value Rmin to the maximum resistance value Rmax is shorter than the threshold set from experience, that is, the slope dRs is larger than the threshold set from experience, the nugget is appropriately formed, and therefore the welding quality is improved. It is determined to be good. On the other hand, in FIG. 14, the amount of increase in the resistance value from the minimum resistance value Rmin, which is the initial resistance value, to the maximum resistance value Rmax is smaller than the threshold set from experience, and the minimum resistance value Since the time from Rmin to the maximum resistance value Rmax is longer than the threshold set from experience, that is, the slope dRs is smaller than the threshold set from experience, the nugget is not formed properly, and therefore welding is performed. It is determined that the quality is poor. That is, the criterion for the root type waveform includes the amount of increase in resistance value from the start of energization to the maximum resistance value Rmax and the time from the start of energization to the maximum resistance value Rmax.

  FIG. 15 shows that the resistance value waveform classified into the root type waveform is determined to have good welding quality (also referred to as “OK”), as in FIG. 13, and FIG. 16 is similar to FIG. 14. In the resistance value waveform classified into the root type waveform, it is determined that the welding quality is poor (also referred to as NG). In FIG. 15, the slope of the straight line drawn between the initial resistance value Rs and the final resistance value Re is larger than the threshold value set from experience, and the area of the region formed by this straight line and the resistance value waveform Since S (see the part indicated by the stripes) is greater than a threshold set from experience, it is determined that the nugget is properly formed and therefore the weld quality is good. On the other hand, in FIG. 16, the slope of the straight line drawn between the initial resistance value Rs and the final resistance value Re is larger than the threshold set from experience as in FIG. Since the area S of the region formed by the waveform (refer to the portion indicated by the stripes) is smaller than the threshold set from experience, the nugget is not formed properly, so the welding quality is poor. It is determined that there is. That is, the criterion for the root type waveform includes the slope of the straight line drawn between the initial resistance value Rs and the final resistance value Re, and the area S of the region formed by this straight line and the resistance value waveform. It is. These criteria can be combined as appropriate.

  FIG. 17 shows that the resistance value waveform classified into the horizontal waveform is judged to have good welding quality (also referred to as “OK”), and FIG. 18 shows the resistance value waveform classified into the horizontal waveform. It is determined that the welding quality is poor (also referred to as NG). In FIG. 17, the resistance value once rises with a predetermined slope (dR1), then gradually decreases with a predetermined slope (dR2), and then rises again with a predetermined slope (dR3). As described above, when the resistance value changes, it is determined that the nugget is appropriately formed and thus the welding quality is good. On the other hand, in FIG. 18, the resistance value once decreases with a predetermined inclination (dR1), then further decreases with a predetermined inclination (dR2), and slightly increases with a predetermined inclination (dR3) at the end. Thus, when the resistance value changes, it is determined that the nugget is not properly formed and therefore the welding quality is poor. As described above, the criterion for the horizontal waveform is based on the transition of the resistance value.

  As described above, in the present invention, the generated resistance value waveform is classified into one of a plurality of resistance value waveform patterns set in advance according to characteristics caused by various disturbances, and the classified resistance Since it is determined whether or not the welding quality is good based on the criterion set in advance in the value waveform pattern, it is not necessary to set a threshold for determining the welding quality according to the welding conditions for each hit point. Moreover, it is possible to easily and accurately determine the quality of the welding quality without being affected by various disturbances.

  When the determination of the welding quality in the first welding quality pass / fail determination step is OK (YES in S5), the determination means 4 gives a welding quality OK determination signal via the controller 3 for the welding location of the workpiece. And output to the server 5 (S9). On the other hand, when the determination of the welding quality in the first welding quality pass / fail determination step is NG (NO in S5), the determination means 4 determines whether or not spatter has occurred from the resistance value waveform determined to be NG. Is determined (S6 in FIG. 1). As shown in FIG. 19, the determination of the occurrence of spatter increases from the initial resistance value due to heat generation, and the resistance value gradually decreases from when the maximum resistance value Rmax is reached until sputtering occurs. When a rapid and large drop in resistance value is recognized, it is determined that sputtering has occurred (in the case of YES at S6). Further, when such a rapid and large decrease in the resistance value is not recognized, it is determined that sputtering has not occurred (NO in S6). Until the large resistance value, which is recognized as the occurrence of spatter (the first half of the energization time), the minute decrease in resistance value is attributed to dust or the like adhering to the surface of the workpiece and should not be determined as spatter. And

  When the determination means 4 determines that spatter has occurred (YES in S6), the determination means 4 compares the resistance value change amount in the resistance value waveform with the resistance value change amount threshold value when sputtering occurs. A second welding quality pass / fail determination step is performed to determine whether the weld quality is good or not. The specific content of the second welding quality pass / fail determination step is to determine whether or not the change amount of the resistance value due to the occurrence of spatter has exceeded the change amount threshold value set for each resistance value waveform pattern (S7). In each of the resistance value waveform patterns described above, a threshold value of a sudden drop (inclination) of the resistance value recognized as the occurrence of spatter is individually set, and when there is a drop in resistance value exceeding the threshold value (in S7). In the case of YES), it is determined that the nugget is properly formed and therefore the welding quality is good (OK), and the determination means 4 determines the welding quality OK determination signal via the controller 3 for the welding location of the workpiece. Is output to the server 5 (S9). On the other hand, when the resistance value does not decrease beyond the threshold value (NO in S7), it is determined that the nugget is not properly formed, and therefore the welding quality is poor, and the determination means 4 Outputs a warning signal of welding quality NG determination to the server 5 via the controller 3 for the welding location of the workpiece (S10).

  That is, the determination criterion in the second welding quality pass / fail determination step is the amount of decrease in the resistance value when sputtering occurs. Accordingly, in the present invention, based on the amount of decrease in the resistance value in the case where spatter occurs in the second welding quality pass / fail determination step, the weld location where the weld quality is not determined good in the first weld quality pass / fail determination step. Since the quality of the welding quality is determined, the welding quality can be accurately determined.

When it is determined in the above-described sputter generation determination (S6) that no sputter has occurred (NO in S6), it is further determined whether the determination by the discriminant analysis is OK (S8). The specific contents of the determination by the discriminant analysis are, for example, a multiple regression analysis and discriminant analysis by the following secondary discriminant analysis determination formula.
Determination formula = F (Xa) ² + F (Xb) ² + F (Xc) ² ... F (Xa) + F (Xb) + F (Xc) + C (constant)
The basic variable calculated in step S3 in FIG. 1 described above can be used as the variable of the determination formula.

  When it is determined by the calculation of the determination formula that the welding quality is good (YES in S8), it is determined that the nugget is properly formed, and therefore the welding quality is good (OK), and the determination means 4 Outputs a welding quality OK determination signal to the server 5 via the controller 3 for the welding location of the workpiece (S9). On the other hand, when it is determined by the calculation of the determination formula that the welding quality is poor (in the case of NO in S8), the nugget is not properly formed, and therefore the welding quality is poor (NG). The determination means 4 outputs a warning signal for determining the welding quality NG to the server 5 via the controller 3 for the welding location of the workpiece (S10).

  When it is determined NO in Steps S7 and S8 shown in FIG. 1 and a signal for determining the welding quality NG is output via the controller 3 for the welding location of the workpiece by the determination means 4 in Step S10, the server 5 Information on the welding quality NG determination is transmitted to the monitor 6 provided in the inspection process downstream of the welding line L. In the inspection process, the type of workpiece (for example, vehicle type) and the quality of the welding quality for each welding location are collectively displayed on the monitor 6, and only the welding location determined to be defective is inspected by the inspection operator (S12).

  The welding quality judgment method and welding quality judgment system of the present invention are not limited to the number of workpieces to be superposed, and are not limited to spot welding, but are to be welded with a roller-shaped or disk-shaped electrode. The present invention can also be applied to the case where seam welding is continuously performed on a joint portion of an object. Further, the welding gun used for spot welding is not limited to the so-called C-type, and other types such as the so-called X-type can be adopted, and without being supported by the arm of the robot 2, A stationary type or portable manual type can also be adopted. In the present invention, the current supplied to the electrode is not particularly limited, such as a single phase or a three phase.

  1: welding gun, 2: robot, 3: controller, 4: determination means, 5: server, 6: monitor, L: welding line, S2: resistance value measurement process, S3: resistance value waveform generation process, S4: Resistance value waveform classification step, S5: Weld quality determination step (first welding quality pass / fail determination step) in the resistance value waveform pattern, S6: Sputter generation presence / absence determination step, S7: Resistance value change determination step due to spatter generation ( Second welding quality pass / fail judgment process)

Claims (4)

A method for determining quality of lap resistance welding by superimposing joint portions of workpieces to each other, press-clamping the joint portions with a pair of electrodes, and passing a current between the pair of electrodes,
A resistance value waveform generation step for measuring a resistance value between electrodes during welding and generating a resistance value waveform representing a change in the resistance value with respect to the energization time;
A resistance value waveform classification step for classifying the generated resistance value waveform into one of a plurality of resistance value waveform patterns due to various disturbances set in advance;
A welding quality determination method comprising: performing a first welding quality pass / fail determination step for determining whether or not weld quality is good based on a predetermined determination criterion for each resistance value waveform pattern. In the case where it is determined that the welding quality is not good in the first welding quality quality determination step,
Sputter presence / absence determination step for determining the presence / absence of spatter from the resistance value waveform;
When it is determined that spatter has occurred, the resistance value change amount in the generated resistance value waveform is compared with a resistance value change amount threshold value at the time of spattering preset for each resistance value waveform pattern. The welding quality determination method according to claim 1, wherein a second welding quality determination step for determining whether or not the welding quality is good is performed. It is a system for judging the quality of lap resistance welding by superposing the joints of the workpieces to each other, pressing and sandwiching the joints with a pair of electrodes, and passing a current between the pair of electrodes,
The resistance value between the electrodes at the time of welding is measured, a resistance value waveform indicating a change in the resistance value with respect to the energization time is generated, and the generated resistance value waveform is a plurality of resistance value waveforms caused by various preset disturbances. Classification means is provided for determining whether the first welding quality is good or not based on a judgment criterion preset for each resistance value waveform pattern. A characteristic welding quality judgment system.   When the determination means determines that the welding quality is not good in the first welding quality determination, the generation of spatter is determined based on the resistance waveform, and the generation is performed when it is determined that spatter is generated. The second of whether or not the welding quality is good based on a comparison between the resistance value change amount in the resistance value waveform and a resistance value change threshold value at the time of occurrence of sputtering preset for each resistance value waveform pattern. 4. The welding quality judgment system according to claim 3, wherein the quality judgment is further performed.

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