JP2935883B2 - Inspection method of spot weld and spot welding control system using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a spot welding inspection method for judging the quality of welding at a spot weld, and a spot welding for controlling spot welding conditions and the like using the inspection method. Related to control system.

(Prior art)

Spot welding is often used in production line systems for automobiles and the like because it can effectively weld a large amount of thin metal plate material (plate material to be welded). However, compared to gas welding or arc welding, it is more difficult for spot welding to easily judge the joint state from the appearance, and a destructive inspection method has not been established.

Accordingly, various researches and developments have been conducted to easily perform this nondestructive inspection method. As one of the methods, there is a method in which the distance between welding electrodes (thickness of a plate material to be welded) is measured to determine whether or not a welding state is good.

 Hereinafter, this method will be described with reference to the drawings.

FIG. 10 is a diagram showing how the distance between electrodes changes in each step of spot welding.

Spot welding is performed in four steps: initial pressurizing time (squeeze time), energizing time, holding time (hold time), and opening time (off time). The initial pressurization time refers to the time from when the pressure is applied to the electrodes until the current flows (energizes). During this time, the pressure between the electrodes is stabilized,
Improves the familiarity between the plates to be welded. The energization time is constituted by a time for actually flowing a welding current, a time for flowing a preheating current, and a time for flowing a tempering current for performing quenching after the welding current is applied. The holding time is the time from the end of energization until the electrode leaves the plate to be welded. The opening time is an interval time between weldings in the case where spot welding is repeated.

As is apparent from the figure, the distance between the electrodes gradually increases from the start of energization and saturates at the maximum displacement Hmax. Then, within the holding time after the end of the energization, the welded portion is cooled by the electrodes, and the distance between the electrodes rapidly decreases, and approaches the distance between the electrodes in the initial pressurization time as shown in the figure, or more. Become smaller. In addition, if the energization is continued even after reaching the maximum displacement amount Hmax, the melting of the plate material to be welded advances and the pressure between the electrodes causes the distance between the electrodes to gradually decrease, but as shown in FIG. It does not decrease sharply. Such a displacement characteristic of the distance between the electrodes indicates an ideal place, and in fact, this displacement characteristic changes every spot welding, and the joining state also changes accordingly.

JP-B-48-41422 discloses a method for judging the quality of the spot welding joint state based on the maximum displacement amount Hmax of the distance between the electrodes during the energization period obtained from the displacement characteristic curve.

Further, there is one described in U.S. Pat. No. 3,400,242 as a method for making a judgment based on a change rate (dh / dt) of the distance between electrodes at the beginning of energization.

Further, a method of judging the quality of the joining state based on both the maximum displacement Hmax and the change rate (dh / dt) is disclosed in
No. 53-4057.

[Problems to be solved by the invention]

Using the conventional spot welding inspection method, when inspecting the actual joint state of spot welding, the joint state,
It was found that there was no clear correlation between the maximum displacement Hmax of the distance between the electrodes during the current application period and the displacement rate (dh / dt) at the initial stage of the current application. In other words, in spite of the fact that the bonding state is actually good and the strength is sufficient, it is judged that the bonding state is poor when judged based on the maximum displacement Hmax or the displacement rate (dh / dt), or conversely, Despite poor condition and insufficient strength, the maximum displacement Hmax or displacement (dh / d
Judgment based on t) may result in "good joint condition".

Therefore, the reliability of such a spot welding inspection method is not very high, and the welding conditions cannot be controlled based on the inspection result.

The present invention has been made in view of the above points, and a first object of the present invention is to provide a method for inspecting a spot welded portion, which can accurately determine a joining state of the spot welded portion.

It is a second object of the present invention to provide a spot welding control system capable of automatically setting welding conditions while maintaining a good connection state of a spot weld.

[Means for solving the problem]

According to a first aspect of the present invention to solve the first object, at least two plates to be welded are overlapped, both surfaces thereof are sandwiched between two electrodes, and current is applied between the electrodes while applying pressure to the plate to be welded. This is an inspection method for judging the quality of a spot-welded portion in spot welding for welding a pre-welded plate material by detecting a contraction amount of a plate thickness of the spot-welded portion during a predetermined pressure holding time after the end of energization. Then, the inspection method of the spot welded portion is characterized in that the quality of the joining state of the spot welded portion is determined based on the shrinkage amount.

According to a second aspect of the present invention for solving the first object, at least two plates to be welded are overlapped, both surfaces thereof are sandwiched between two electrodes, and current is applied between the electrodes while applying pressure to the plate to be welded. In the spot welding for welding the plate material to be welded by the method, an inspection method for determining the quality of the spot welded portion, wherein the thickness of the spot welded portion that changes during a predetermined pressure holding time immediately after the end of energization is determined by the energization. Inspection of a spot welded portion, wherein a value obtained by integrating within the pressure holding time with reference to the plate thickness at the end point is determined, and based on the integrated value, the quality of the joining state of the spot welded portion is determined. Is the way.

According to a third aspect of the present invention for solving the second object, at least two plates to be welded are overlapped, both surfaces thereof are sandwiched between two electrodes, and current is applied between the electrodes while applying pressure to the plate to be welded. A spot welding control system for welding the plate material to be welded, comprising a control means for controlling welding conditions of the spot welding in accordance with an inspection result of the inspection method of the spot welding portion. It is.

[Action]

The distance between the electrodes in spot welding is represented by curve C0 in FIG.
And gradually increases as the energization time elapses as indicated by a curve C1 in FIG. In the case of FIG. 10, the energization is terminated when the distance between the electrodes reaches the maximum displacement Hmax, but as shown in FIG. 2, the energization is continued even after the maximum displacement Hmax has passed. On the other hand, it is known that the electrode distance decreases conversely.

Within the holding time after the end of the energization time, the distance between the electrodes sharply decreases as shown by the curve C0 in FIG. 10 and the curve C1 in FIG. In the figure, the case where the inter-electrode distance of the holding time is larger than the inter-electrode distance of the initial pressurization time is shown, but the reverse case may be applied.

A nugget is formed in the plate material to be melted by energization, and the nugget is formed so that the plate members to be welded are firmly connected. What most affects the state of formation of this nugget is the amount of energy (heat) applied to the weld during the energization time. However, it is very difficult to measure the amount of energy actually used to form the nugget in the weld. It is not simply determined from the energizing time and the energizing current. This is because the surface condition, contact resistance, and the like between the sheets to be welded are slightly different for each spot welding, so that even if the same current is applied for the same time, the joining state of the spot welded portion slightly changes.

Therefore, conventionally, the amount of energy applied to the welded portion is relatively detected by measuring a change in the plate material to be welded during the energization time, that is, the distance between the electrodes.

However, a nugget that ultimately determines the quality of the joined state is formed within a holding time after the end of energization, and during this holding time, the weld is cooled by the electrodes and the distance between the electrodes is reduced. If the nugget diameter is large, the amount of energy consumed for forming the nugget is large, and the amount of shrinkage due to cooling is large. Conversely, if the nugget diameter is small, energy escapes to the cold metal around the nugget, the amount of energy consumed to form the nugget is small, and the amount of shrinkage due to cooling is also small.

The inventors of the present invention perform spot welding many times under various conditions, and determine the shrinkage of the thickness of the spot welded portion and the nugget diameter at the time of spot welding at a predetermined pressure holding time immediately after the end of energization. It was found that there was a correlation between size and size.

Therefore, as in the first aspect of the present invention, the shrinkage amount of the thickness of the spot weld portion is detected during a predetermined pressurization holding time immediately after the end of energization, and the quality of the welded joint is inspected based on the shrinkage amount. I did it. Thereby, it becomes possible to obtain detection data correlated with the diameter of the nugget formed by spot welding from the amount of contraction of the plate thickness, and it is possible to determine the quality of the spot welding joint with high accuracy.

In addition, the value obtained by integrating the thickness of the spot weld at the predetermined pressure holding time immediately after the end of energization within the pressure holding time with respect to the thickness at the end of energization as in the above-described shrinkage amount, It was also found that there was a correlation with the size of the nugget diameter of the weld. Thus, by obtaining the integral value as in the second aspect of the present invention, it becomes possible to obtain detection data correlated with the nugget diameter formed by spot welding based on the integral value, and to determine whether the bonding state is good or bad. It is possible to determine with high accuracy.

Furthermore, in the third aspect of the present invention, since the welding conditions for spot welding are determined using the results of the determination of the welding conditions in the above-described spot welding inspection method, it is determined that the welding conditions are good if the welding conditions are poor. As described above, spot welding can be performed while changing and controlling the joining conditions, so that a spot welding control system that can always perform spot welding with a good joining state can be configured.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a view schematically showing an entire configuration of an inspection apparatus for realizing the spot welding inspection method of the present invention.

The two sheets 30 and 31 to be welded are joined by spot welding. The two plates 30 and 31 to be welded are sandwiched between two tip electrodes 32 and 33 on both sides of the overlapped portion. The tip electrodes 32 and 33 are provided on both sides of the plates 30 and 31 to be welded. The plates 30 and 31 to be welded are pressed by the pressure of.

The welding current control means 34 supplies a welding current to the tip electrodes 32 and 33 within the energizing time shown in FIG. 2, and also controls the pressing force of the tip electrodes 32 and 33.

The inter-electrode distance detection means 35 detects the absolute position of the inter-electrode distance between the chip electrodes 32 and 33, and outputs the detected position as an inter-electrode distance signal P to the pass / fail determination means 36. That is, although not shown in the chip electrodes 32 and 33, the chip electrodes 32 and
A position detecting device for detecting an absolute position between 33 is provided.

The pass / fail determination means 36 receives the inter-electrode distance signal P of the inter-electrode distance verification means 35 and the holding time signal HS of the welding current control means 34, detects the displacement of the inter-electrode distance signal P within the holding time, and detects the detected value. Is compared with a predetermined reference value to determine the quality of the joint state of the welded portion. If the joint state is defective, a failure signal NS1 is output to the display means 37. If the value of the inter-electrode distance signal P is extremely small, it is determined that some failure has occurred in the tip electrodes 32 and 33, and the tip exchange signal CS1 is output as the display signal 37. Furthermore, pass / fail judgment means 3
6 also inspects whether or not the thickness of the superposed plate materials 30 and 31 is within a predetermined range. That is, when welding, the number of sheets 30 and 31 to be welded must be two, but if the number is insufficient or too large for some reason, or if impurities are mixed between the sheets 30 and 31 to be welded, etc. Then, a thickness defect signal ES1 for notifying the defect information of the welding location is output. Since the tip portions of the tip electrodes 32 and 33 gradually wear due to repeated welding, the pass / fail determination means 36 detects the amount of wear and outputs a tip replacement signal ES.
Outputs 2.

When the display means 37 outputs the defect signal NS1, the sheet thickness defect signal ES1, and the chip exchange signals ES2 and CS1 of the pass / fail judgment means 36, the display means 37 generates a display or an alarm to inform the operator of the signals.

Next, the details of the pass / fail determination means 36 in FIG. 3 will be described with reference to FIGS. FIG. 1 is a diagram showing the configuration of the pass / fail judgment means 36, and FIG. 4 is a timing chart showing the operation thereof.

In the present embodiment, the quality of the bonding state is determined by the measurement circuit 10 and the comparison circuit 11.

The measurement circuit 10 receives the inter-electrode distance signal P of the inter-electrode distance detection means 35, resets the internal register in response to the rising of the holding signal HS, and outputs the inter-electrode distance signal P until the holding signal HS falls. Is measured and output to the comparison circuit 11 as a displacement amount (shrinkage amount) Hb within the holding time.

The comparison circuit 11 receives the contraction amount Hb and compares it with the contraction reference value Hrb and the chip replacement contraction reference value hrb.If the contraction amount Hb does not reach the contraction reference value Hrb, it outputs a failure signal NS1 and the contraction amount
When Hb does not reach the tip exchange contraction reference value hrb, the tip exchange signal CS1 is output. The tip replacement reference value hrb is sufficiently smaller than the contraction reference value Hrb, and the fact that the contraction amount Hb has not reached the tip replacement reference value hrb means that the tip electrodes 32 and 33 do not.
In this case, a chip replacement signal CS1 for prompting replacement of a chip electrode is output.

Next, the wear amount of the chip electrodes 32 and 33 is detected by the data shift circuit 12, the integrating circuit 13 and the wear amount detector 14, and the number of the plate materials 30 and 31 are detected by the plate thickness detector 15 and the timer 16. I do.

The data shift circuit 12 is for compensating the plate thickness detection data in accordance with the wear amount of the tip electrode. The data shift circuit 12 receives the inter-electrode distance signal P of the inter-electrode distance detection means 35 and receives the tip wear amount detection signal TS. The data is shifted so that the value of the inter-electrode distance signal P becomes "0" in response to the input of the input signal, and the shift amount is output to the integrating circuit 13, and the plate thickness signal indicating the true inter-electrode distance after the shift. hy is output to the thickness detector 15. That is, since the inter-electrode distance signal P output from the inter-electrode distance detection means 35 is a signal indicating the absolute position between the tip electrodes 32 and 33, the tip of the tip electrode is worn by performing spot welding several hundred times. Therefore, the distance between the electrodes becomes smaller than the actual distance between the electrodes, and the accurate distance between the electrodes cannot be detected. In order to prevent this, a chip wear amount detection instruction signal TS is generated according to a predetermined standard, and the tip electrodes 32 and 33 are brought into contact accordingly, and the data shift circuit 12 outputs an inter-electrode distance signal corresponding to the wear amount. The value of P is shifted.

For example, when the distance P between the electrodes when the tip electrodes 32 and 33 are in contact with each other is "0", and the distance P between the electrodes after performing the spot welding 200 times is "-3", the data shift circuit 10 Is shifted by “+3” to correct this “−3”, and the thickness signal hy of “0” is output from the data shift circuit 12.
Is output.

The integrating circuit 13 captures the shift amount of the data shift circuit 10 at the falling timing of the chip wear amount detection instruction signal TS, integrates the result, and outputs the wear amount signal Tm to the wear amount detector 14. Therefore, the total amount of wear of the tip electrode worn by spot welding is stored in the integrating circuit 13.

The wear amount detector 14 receives the wear amount signal Tm stored in the integrating circuit 13 and compares it with the wear reference value Tr.
Outputs the tip exchange signal ES2 when the value reaches the wear reference value Tr.

The thickness detector 15 receives the thickness signal hy of the data shift circuit 12 and compares it with the thickness reference value hr.
If it is less than ± 10% of hr, the thickness is normal and ± 10%
In the following cases, the thickness error signal ES1 is output. Since the thickness reference value hr is a value indicating the thickness when the welded plate materials 30 and 31 to be spot-welded are overlapped, the fact that the thickness defect signal ES1 is output means that only one plate material is welded. There are 3
This indicates that various obstacles have occurred, such as the number of sheets or the presence of impurities between the sheets to be welded. Therefore,
If the thickness defect signal ES1 is output, stop welding,
That obstacle must be eliminated.

The timer 16 generates a thickness detection instruction signal DS which is a timing signal for the detection operation of the thickness detector 15. The plate thickness detection operation by the plate thickness detector 15 is required to be performed within the initial pressurization time when energization starts after a pressure is applied to the electrode and after the pressure is stabilized. Therefore, the timer 16 measures a predetermined time in response to the input of the initial pressurizing signal YS, and detects the sheet thickness within the initial pressurizing time.
Is output to the thickness detector 15.

The operation of the pass / fail determination means of FIG. 1 will be described with reference to the timing chart of FIG.

As an example, the chip wear amount detection instruction signal TS is generated every 200 spot welding operations. The data shift circuit 12 shifts the value of the inter-electrode distance signal P to “0” according to the rise of the chip wear amount detection instruction signal TS. Then, in accordance with the falling edge of the chip wear amount detection instruction signal TS, the integrating circuit 13 integrates the shift amount of the data shift circuit 12,
The wear amount detector 14 compares the wear signal Tm of the integrating circuit 13 with the wear amount reference value Tr.

In response to the rise of the initial pressurization signal YS, the timer 16 starts measuring a predetermined time, and outputs a sheet thickness detection instruction signal DS to the sheet thickness detector 15 at the same time as the end of the counting. While the initial pressurizing signal YS is being output (initial pressurizing time), a predetermined pressing force is applied to the tip electrodes 32 and 33.

The sheet thickness detector 15 outputs the sheet thickness detection instruction signal DS from the timer 16 and the sheet thickness detector 15 simultaneously outputs the sheet thickness signal hy from the data shift circuit 12.
And the sheet thickness reference value hr.

Thickness defect signal ES1 and wear amount detector 1 from thickness detector 15
When the tip exchange signal ES2 is not output from 4, the welding current control means 34 supplies a predetermined welding current to the tip electrodes 32 and 33 according to the energization signal FS.

The measurement circuit 10 resets the value of the internal register in response to the rising of the holding signal HS, and ends the measurement in response to the falling of the holding signal HS. Accordingly, the measurement circuit 10 measures the contraction amount Hb of the plate materials 30 and 31 contracted within the holding time, that is, the displacement amount of the distance between the electrodes. For example, a measurement circuit
10 holds the value of the inter-electrode distance signal P at the rising time of the holding signal HS as P0, subtracts the value P1 of the inter-electrode distance signal P at the falling time of the holding signal HS from P0, and calculates P0− P1 is output as the contraction amount Hb.

The comparison circuit 11 compares the contraction amount Hb with the contraction reference value Hr. When the shrinkage amount Hb is equal to or greater than the shrinkage reference value Hr, the welding state is good, and when the shrinkage amount Hb does not reach the shrinkage reference value Hr, welding failure occurs, and a failure signal NS1 is output.

In response to the release signal OS, the tip electrodes 32 and 33 release the plates 30 and 31 to be welded.

The welding current control means 34 repeats the spot welding by a series of signals from the generation of the initial pressurization signal YS to the generation of the release signal OS. Further, the chip wear amount detection instruction signal TS is generated at intervals of 200 times of spot welding and at the interval time between spot welding and spot welding, and the wear amount of the tip electrodes 32 and 33 is detected.

In the embodiment shown in FIG. 1, the case where the pass / fail determination means 36 determines the pass / fail of the bonding state based on only the contraction amount Hb of the inter-electrode distance P within the holding time has been described. However, as shown in FIG. The distance Ha between the electrodes immediately after the termination (at the start of the holding time), the value Ia (area SA) obtained by integrating the change in the distance between the electrodes during the conduction time as shown in FIG. A value Ib (area SB) obtained by integrating the changed inter-electrode distance as a reference may be obtained, and these values may be subjected to a predetermined calculation to determine the quality of the bonding state.

Hereinafter, this will be described with reference to FIG. Fifth
In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

The measuring circuit 17 receives the inter-electrode distance signal P of the inter-electrode distance detecting means 35, resets an internal register according to the rise of the energization signal FS, and sets the inter-electrode distance signal P until the energization signal FS falls. Is measured and output to the comparison circuit 18 as the displacement Ha within the energization time.

The comparison circuit 18 inputs the displacement amount Ha within the energization time, compares it with the displacement reference value Hra and the tip replacement reference value hra, and outputs a failure signal NS3 when the displacement amount Ha within the energization time does not reach the displacement reference value Hra. If the displacement Ha within the energization time does not reach the chip replacement reference value hra, the chip replacement signal CS3 is output. The displacement reference value Hra is a value sufficiently larger than the tip replacement reference value hra, and the fact that the displacement amount Ha within the energization time did not reach the displacement reference value Hra causes scattering during welding, and the displacement of the distance between the electrodes is sharp. Signal NS3
Is output. In addition, since the displacement amount Ha within the energization time did not reach the tip replacement reference value hra, it means that some failure occurred in the tip electrodes 32 and 33, and therefore, a tip replacement signal for prompting replacement of the tip electrodes is provided. Output CS3.

The subtraction circuit 19 inputs the contraction amount Hb of the measurement circuit 10 and the displacement amount Ha within the energization time to the measurement circuit 17 and subtracts the contraction amount Hb from the displacement amount Ha within the energization time (Ha−Hb) as a subtraction signal Hab. Output to the comparison circuit 20. The subtraction signal Hab is the final thickness of the plate materials 30 and 31 deformed by spot welding, and may be negative or positive. When the subtraction signal Hab is negative, the absolute value of the contraction amount Hb is larger than the absolute value of the displacement amount Ha within the conduction time, and the plate materials 30 and 31 to be welded.
Means that the thickness of the sheet shrank by spot welding,
In the case of plus, the absolute value of the contraction amount Hb is the displacement amount within the energization time Ha
, Which means that the plate thicknesses of the plate materials 30 and 31 to be welded were expanded by spot welding.

If the subtraction signal Hab is a negative value, the joining state of the spot welding is good, and even if the subtracting signal Hab is a positive value, the joining state of the spot welding is better as the value is closer to zero. Therefore, the comparison circuit 20 determines whether the value of the subtraction signal Hab is smaller than a predetermined reference value.

The comparison circuit 20 receives the subtraction signal Hab and compares it with the displacement reference value Hab and the chip replacement reference value hrab.If the subtraction signal Hab is not smaller than the displacement reference value Hrab, it outputs a failure signal NS2, and the subtraction signal Hab If the value is not smaller than the chip exchange reference value Hrab, a chip exchange signal CS2 is output. The tip replacement reference value hrab is a value sufficiently larger than the displacement reference value Hrab, and the fact that the subtraction signal Hab did not become smaller than the displacement reference value Hrab means that appropriate melting was not performed at the time of spot welding and a nugget having a predetermined diameter or more. Is not formed, the failure signal NS2 is output. In addition, since the fact that the subtraction signal Hab has not become smaller than the tip replacement reference value hrab means that some failure has occurred in the tip electrodes 32 and 33, the tip replacement signal CS2 for prompting the replacement of the tip electrode is used. Is output.

The integration circuit 21 receives the inter-electrode distance signal P of the inter-electrode distance detection means 35 and determines the amount of displacement of the inter-electrode distance signal P between the rise and fall of the holding signal HS (within the holding time) immediately after the end of the energization time. Is integrated based on the distance between the electrodes of
The size of the area SB in the figure is output to the comparison circuit 22 as the integration value Ib within the holding time.

The comparison circuit 22 receives the integrated value Ib within the holding time, compares it with the integrated value of the holding time Irb and the reference value irb of the chip replacement, and if the integrated value Ib within the holding time does not reach the integrated value of the holding time Irb, a failure signal is output. NS4 is output, and if the integrated value Ib within the holding time does not reach the chip replacement reference value irb, a chip replacement signal CS4 is output. The tip replacement reference value irb is the holding time integration reference value I
It is sufficiently smaller than rb, and the fact that the integrated value Ib within the holding time has not reached the chip replacement reference value hrb means that some failure has occurred in the chip electrodes 32 and 33, so that the replacement of the chip electrodes is promoted. The chip exchange signal CS4 is output.

The integration circuit 23 receives the inter-electrode distance signal P of the inter-electrode distance detection means 35 and determines the amount of displacement of the inter-electrode distance signal P between the rise and fall of the energization signal FS (within the energization time) immediately after the start of energization. The integration is performed based on the distance between the electrodes, and the size of the area SA in FIG.
Output to

The comparison circuit 24 inputs the integrated value Ia within the energizing time, compares it with the standard value Ira for integrating the energizing time and the reference value ira for chip replacement.If the integrated value Ia within the energizing time does not reach the standard value Ira for the energizing time, a failure signal NS6 is output, and if the integrated value Ia within the energization time does not reach the chip replacement reference value ira, a chip replacement signal CS6 is output. The conduction time integration reference value Ira is the chip replacement reference value i.
It is a value that is sufficiently larger than ra, and the fact that the integral value Ia within the energizing time did not reach the energizing time integral reference value Ira means that scattering occurred during welding, and that the displacement of the distance between the electrodes sharply decreased. Therefore, the failure signal NS6 is output. Also,
Since the fact that the energization time inner product variance Ia did not reach the chip replacement reference value ira means that some failure has occurred in the chip electrodes 32 and 33, the chip replacement signal CS6 for prompting the replacement of the chip electrodes is output. I do.

The dividing circuit 25 receives the integral value Ib within the holding time and the integral value Ia within the energizing time from the integrating circuits 21 and 23, and divides the integral value Ib within the holding time by the integral value Ia within the energizing time (Ib / Ia). To the comparison circuit 26 as the division signal Iab.

The comparison circuit 26 receives the division signal Iab and outputs the division reference value Irab
And, when the division signal Iab is smaller than the division reference value Irab, the failure signal NS5 is output.When the division signal Iab is smaller than the chip exchange reference value irab, the chip exchange signal CS2 is output. I do. The chip replacement reference value irab is a value sufficiently smaller than the division reference value Irab, and that the division signal Iab did not become larger than the division reference value Irab does not perform appropriate melting during spot welding,
Since this means that a nugget having a diameter equal to or larger than a predetermined diameter has not been formed, a failure signal NS5 is output. Further, since the fact that the division signal Iab has not become larger than the chip replacement reference value irab means that some defect has occurred in the chip electrodes 32 and 33, the chip replacement signal CS5 for prompting the replacement of the chip electrode is used. Is output.

In the embodiment shown in FIG. 5, the defective signals NS1 to NS6 in the joined state are output as signals of the same level. However, the respective defective signals NS1 to NS6 are weighted, and the sum of the weights of these signals is joined. You may make it output as a signal which shows a state. For example, if the weight of the defective signal NS1 is "10",
Is "8", the weight of the defective signal NS2 is "6", the weight of the defective signals NS3 and NS6 is "4", the weight of the defective signal NS5 is "2", and the sum of the weights of these signals is "15". The joining state is determined based on whether it is greater than "." At this time, as for the chip exchange signals CS1 to CS6, the output of any one of the signals indicates that the necessity of chip exchange has occurred, so that the logical sum signal of each output is output.

As described above, in the embodiment of FIG. 5, the joining state of spot welding is detected based on various values obtained from the curves showing the displacement characteristics of the distance between the electrodes in FIGS. 2 and 6. The basic value remains the distance between the electrodes within the holding time.

Therefore, instead of the contraction amount Hb of the inter-electrode distance P within the holding time, the pass / fail determination means 36 integrates a value Ib obtained by integrating the inter-electrode distance changed based on the inter-electrode distance immediately after the end of the energization time as shown in FIG. The quality of the bonding state may be determined based on (area SB). That is, the measuring circuit 10 and the comparing circuit 11 shown in FIG.
22 may be substituted.

The pass / fail judgment means 36 is connected to the measuring circuit 10 of the embodiment shown in FIG.
And 17, the arithmetic circuit 19, and the comparison circuits 11, 18 and 20 alone, or the integration circuit 21 and 23, the division circuit 25, and the comparison circuits 22, 24 and 26 alone. Not even.

Next, an embodiment of a spot welding control system using the above-described spot welding inspection method will be described.

FIG. 7 is a diagram schematically showing an overall configuration of the spot welding control system. 7, the same components as those in FIG. 3 are denoted by the same reference numerals, and the description thereof will be omitted. In the present embodiment, the pass / fail determination means 39 determines whether or not the joining state is good or not, and supplies the welding current control means 38 with the power supply end signal EN1.
And outputs the failure signals NS1 and NS3, and the welding current control means 38 changes the welding conditions according to the energization end signal EN1 and the failure signals NS1 and NS3.

That is, the energization is terminated when the displacement amount Ha of the inter-electrode distance P reaches the displacement amount reference value Hra after the start of energization, or the maximum energization that allows the conduction even if the displacement amount Ha does not reach the displacement reference value Hra. When the time reaches Tmax, the energization ends. Then, the welding current control means 38 controls the magnitude of the welding current, the pressing force and the like according to whether or not the displacement amount Hb of the distance between the electrodes within the holding time has reached a predetermined displacement reference amount Hrb.

The details of the pass / fail determination means 39 will be described below with reference to FIGS.
This will be described with reference to the drawings. FIG. 8 is a diagram showing a schematic configuration of the pass / fail judgment means 39, and the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted. FIG. 9 is a timing chart showing the operation.

Timer 81 is the maximum energization time from the rise of energization signal FS
After the lapse of Tmax, an energization end signal EN1 is output to the measuring circuit 80 and the welding current control means 38. The welding current control means 38 forcibly terminates the energization by inputting the energization end signal EN1, and shifts to the processing of the holding time.

Since the measuring circuit 82 and the comparing circuit 83 have the same configuration as the measuring circuit 17 and the comparing circuit 18 in FIG. 5, their description will be omitted. However, the failure signal NS3 of the comparison circuit 83 is output not only to the welding current control means 38 but also to the measurement circuit 80.

The measurement circuit 80 receives the energization end signal EN1 of the timer 81 and the failure signal NS3 of the comparison circuit 83, and the energization end signal EN1 is output from the timer 81, or the failure signal NS3 of the comparison circuit 83 is inverted and the When the signal changes from a good signal to a good signal, the internal register is reset, and the displacement of the interelectrode distance P is started to be measured.

The operation of the pass / fail judgment means of FIG. 8 will be described with reference to the timing chart of FIG.

The chip wear amount detection instruction signal TS is output, for example, every 200 spot welding operations. The data shift circuit 12 shifts the value of the inter-electrode distance signal P to “0” according to the rise of the chip wear amount detection instruction signal TS. And
The integrating circuit 13 integrates the shift amount of the data shift circuit 12 in accordance with the falling of the chip wear amount detection instruction signal TS, and the wear amount detector 14 uses the wear signal Tm of the integrating circuit 13 and the wear amount reference value Tr.
Compare with

In response to the rise of the initial pressurization signal YS, the timer 16 starts measuring a predetermined time, and outputs a sheet thickness detection instruction signal DS to the sheet thickness detector 15 at the same time as the end of the counting. While the initial pressurizing signal YS is being output (initial pressurizing time), a predetermined pressing force is applied to the tip electrodes 32 and 33.

The sheet thickness detector 15 outputs the sheet thickness detection instruction signal DS from the timer 16 and the sheet thickness detector 15 simultaneously outputs the sheet thickness signal hy from the data shift circuit 12.
And the sheet thickness reference value hr.

Thickness defect signal ES1 and wear amount detector 1 from thickness detector 15
When the tip exchange signal ES2 is not output from 4, the welding current control means 34 outputs the conduction signal FS and supplies a predetermined welding current to the tip currents 32 and 33.

When the welding current control means 34 supplies a welding current to the tip electrodes 32 and 33, the displacement Ha of the distance P between the electrodes gradually increases, and reaches the displacement reference value Hra of the comparison circuit 83. The defective signal NS3 of 83 is inverted and changes to a good signal. The welding current control means 38 terminates the supply of the welding current in response to the reversal of the failure signal NS3, and immediately holds the holding signal HS
Is output.

The measurement circuit 80 resets the internal register by inverting the failure signal NS3 of the comparison circuit 83, and starts measuring the displacement Hb of the distance between the electrodes within the holding time.

The measurement circuit 10 resets the value of the internal register in response to the rise of the hold signal Hs, and ends the measurement in response to the fall of the hold signal HS. Accordingly, the measurement circuit 10 measures the contraction amount Hb of the plate materials 30 and 31 contracted within the holding time, that is, the displacement amount of the distance between the electrodes. The comparison circuit 11 compares the contraction amount Hb with the contraction reference value Hrb. When the contraction amount Hb is equal to or larger than the contraction reference value Hrb, the welding state is good, and when the contraction amount Hb does not reach the contraction reference value Hrb, welding failure occurs, and the failure signal NS1 is output.

On the other hand, the timer 81 starts timing in synchronization with the rise of the energization signal, and outputs the energization end signal EN1 when the maximum energization time Tmax is reached, but in this example, the energization is already performed by inverting the failure signal NS3 of the comparison circuit 83. Is completed, the energization end signal EN1 of the timer 81 is ignored.

Conversely, if the displacement Ha of the distance P between the electrodes does not reach the displacement reference value Hra of the comparison circuit 83 within the maximum energizing time Tmax, the energization is terminated by the energization end signal EN1 of the timer 81, and the holding signal When HS rises, the measurement circuit 80 resets the internal register and starts measuring the displacement Hb of the distance between the electrodes within the holding time.

Then, in response to the release signal OS, the tip electrodes 32 and 33 release the plate materials 30 and 31 to be welded.

The welding current control means 38 repeats spot welding by a series of signals from the generation of the initial pressurization signal YS to the generation of the release signal OS. Then, a tip wear amount detection instruction signal TS is generated every 200 spot welding operations, and the tip electrode 32 and
33 wear amount is detected.

The welding current control means 38 outputs the defect signal NS of the comparison circuits 11 and 83.
The welding conditions for spot welding are set as follows according to the input of 1 and NS3.

First, there is a case where both the failure signals NS1 and NS3 do not occur. In this case, since the joining state is determined to be good, the joining conditions are not changed.

Second, there is a case where the failure signal NS1 does not occur and only the failure signal NS3 occurs. In this case, the welding current is set to the maximum energizing time.
Despite flowing to Tmax, the displacement amount Ha is the displacement reference value
It means that Hra was not reached, so change the joining conditions. Specifically, the welding current value is increased or decreased, and the displacement amount Ha is set to the displacement reference value Hra within the maximum energizing time Tmax at the next welding.
Control to reach.

Third, there is a case where only the defective signal NS1 is generated and the defective signal NS3 is not generated. In this case, the displacement Ha is the displacement reference value.
Since it means that the shrinkage amount Hb has not reached the shrinkage reference value Hrb despite having reached Hra, the joining conditions are changed. Specifically, the pressure of the tip electrodes 32 and 33 is increased or decreased, and control is performed so that the contraction amount Hb reaches the contraction reference value Hrb at the next welding.

Fourth, both the failure signals NS1 and NS3 may occur. In this case, the displacement Ha does not reach the displacement reference value Hra,
Further, since it means that the shrinkage amount Hb has not reached the shrinkage reference value Hrb, the joining condition is changed. Specifically, the welding current value and the pressing force are increased or decreased so that this defective signal is not generated at the next welding.

In the second, third and fourth cases, if the same judgment result is obtained even at the next welding, a tip exchange signal is output to the display means, and the tip electrodes 32 and 33 are exchanged. .

In the embodiment of FIG. 8, the case where the welding conditions are set based on the displacement Ha and the shrinkage Hb has been described.
It goes without saying that the welding conditions may be set in accordance with the determination result of the pass / fail determination means in FIG. Also,
The maximum energizing time Tmax may be controlled in addition to the welding current and the pressing force.

Next, an example of a spot welding machine that can be used in the present invention will be described with reference to the drawings. This spot welding machine is configured so that the distance between the electrodes can be detected with high accuracy even during welding, and has a configuration different from the conventional one.

FIG. 11 is a view schematically showing an overall configuration of the spot welding machine of the present invention. The spot welding machine of the present embodiment is a portable type in which a C-type welding gun and a welding transformer 49 are integrally formed, and a sectional view of the pressurizing cylinder 1 and the position detector 2 is shown.

The welding gun includes a pressure cylinder 1, a position detector 2, an arm support member 3, an arm 4, a movable arm 5, electrode holders 6, 7,
It comprises chip electrodes 8, 9 and a secondary conductor 40.

Cylinder rod 41 of pressure cylinder 1 and position detector 2
Since the configuration of the other parts except for is the same as the conventional one, it will be briefly described.

The arm support member 3 includes a pressure cylinder 1, a position detector 2,
The arm 4 holds the welding transformer 49 and the like.

The arm 4 has an L-shape, and holds an electrode holder 6 at its tip. Since the arm 4 receives the pressing force from the pressurizing cylinder 1, it is made rigid so as not to bend.

The movable arm 5 is attached to the tip of the cylinder rod 41, and moves with the movement of the cylinder rod 41. The movable arm 5 holds the electrode holder 7 on the opposite side of the cylinder rod 41, and electrically connects the secondary conductor 40 and the electrode holder 7.

The electrode holders 6 and 7 insert and hold the tip electrodes 8 and 9.

The tip electrodes 8 and 9 come into contact with the plate material to be welded at a predetermined pressing force, apply a welding current between the plate materials to be welded, and perform spot welding.

The secondary conductor 40 supplies the welding current from the welding transformer 49 to the electrode holder 7 and the tip electrode 9. Supply of a welding current to the electrode holder 6 and the tip electrode 8 is performed by a secondary conductor (not shown) provided inside the arm support member 3 and the arm 4.

The welding transformer 49 is connected to an external control device via a connector 50.

A device for cooling the chip electrodes 8, 9 is omitted.

The position detector 2 is a phase shift type detector that detects the amount of movement of the cylinder rod 41 using the coil assembly 51 and the specially processed cylinder rod 41. That is, the position detector 2 detects the distance between the tip electrodes 8 and 9 by detecting the amount of movement of the cylinder rod 41 based on the position of the contact state between the tip electrodes 8 and 9. The details of this position detector are described in
No. 135917, Japanese Utility Model 58-136718 or Japanese Utility Model 59
-175105 and the like. On both sides of the coil assembly 51, packings 52 and 53 for sealing the air of the pressurizing cylinder 1 are provided. Various data for position detection are input / output to / from the coin assembly 51 via the connector 42.

The pressurizing cylinder 1 applies pressure to the piston 45 in the cylinder tube 48 by the air pressure flowing from the ports 43 and 44 to move the cylinder rod 41 and open and close the tip electrodes 8 and 9. The piston 45 is screwed and fixed to the cylinder rod 41 with a nut 46, and an O-ring 47 for sealing is provided around the piston 45. O-rings for sealing (not shown) are also provided on both sides of the cylinder tube 48. ) Is provided. The configuration of the pressurizing cylinder 1 is the same as the conventional one except for the cylinder rod 41.

The difference between the spot welding machine of the present embodiment and the conventional one is that the position detector 2 for absolutely detecting the moving amount of the cylinder rod 41 of the pressurizing cylinder 1 is provided, and the tip electrode 8 is detected from the output of the position detector 2. , 9 is detected. As described above, since the position detector 2 is provided integrally with the pressurizing cylinder 1 for applying a pressing force to the tip electrodes 5 and 6, there is no need to change the configuration of the welding gun, and the distance between the tip electrodes can be easily detected. can do.

FIG. 12 shows a detailed configuration of the pressurizing cylinder 1 and the position detector 2. FIG. 13 shows the connection relationship of the coil assembly 51 of the position detector 2 and the configuration of the position conversion means.

The details of the position detector 2 are known in Japanese Utility Model Laid-Open No. 57-135917, Japanese Utility Model Laid-Open No. 58-136718, Japanese Utility Model Laid-Open No. 59-175105, etc., and will be briefly described here. 12, the same components as those of the pressurizing cylinder 1 of FIG. 11 are denoted by the same reference numerals, and the description thereof will be omitted. The O-rings 57 and 58 are sealing O-rings omitted in FIG.

The position detector 2 detects a linear position by a phase shift method, and includes a coil assembly 51 and a cylinder rod 41.

The coil assembly 51 includes four primary coils 1A, 1C, which are arranged at predetermined intervals in the axial direction of the cylinder rod 41.
1B, 1D, and secondary coils 2A, 2C, 2 provided correspondingly
B, 2D. The coil assembly 51 is fixed to the casing 54 such that a cylindrical space formed therein is concentric with the cylinder rod 41.

The cylinder rod 41 has a magnetic body 55 around its circumference.
And a magnetic scale portion 41S including a ring-shaped non-magnetic material portion 56 having a predetermined width and provided alternately in the axial direction around the magnetic scale portion 41S. The magnetic member 55 and the non-magnetic member 56 may be made of any material as long as the magnetic circuit formed on the coil assembly 51 is configured to change the magnetic resistance. For example, the non-magnetic member 56 may be made of a non-magnetic material or air. Also an iron rod
The magnetic properties of the magnetic portions 55 differ from each other by changing the magnetic properties of the
And the non-magnetic portion 56 may be formed alternately.

As an example, if one coil length is “P / 2” (P is an arbitrary number), an interval of one pitch in the alternating arrangement of the magnetic portion 55 and the non-magnetic portion 56 is “P”. In that case, for example, the length of the magnetic material portion 55 and the length of the non-magnetic material portion 56 are equal and “P /
2 "and may not be necessarily equal.

In this embodiment, the coil assembly 51 is configured to operate in four phases. For convenience in these phases
A, C, B, and D codes are used for discrimination.

The positional relationship between the cylinder rod 41 and the coil assembly 51 is such that the reluctance generated in each of the phases A to D of the coil assembly 51 is shifted by 90 degrees according to the position of the magnetic body portion 55 of the cylinder rod 41. For example, if the A phase is a cosine (cos) phase, the C phase is a minus cosine (-cos) phase, the B phase is a sine (sin) phase, and the D phase is a minus sine (-sin) phase. I have.

In the embodiment of FIG. 12, primary coils 1A, 1C, 1B, 1D and secondary coils 2A, 2C, 2B, 2D are provided individually for each of the phases A to D. The secondary coils 2A, 2C, 2B, 2D of the respective phases A to D are wound around the corresponding primary coils 1A, 1C, 1B, 1D, respectively.

Each primary coil 1A, 1C, 1B, 1D and secondary coil 2A, 2C, 2B, 2D
Is "P / 2" as described above. In the example of FIG. 12, the A-phase coils 1A and 2A and the C-phase coils 1C and 2C are provided adjacent to each other, and the B-phase coils 1B and 2B and the D-phase coil
D and 2D are also provided adjacent to each other. The coil interval between the A phase and the B phase or between the C phase and the D phase is “P (n ± 1/4)” (n is an arbitrary natural number).

With this configuration, the reluctance of the magnetic circuit in each of the phases A to D periodically changes with the distance “P” as one cycle in accordance with the linear displacement of the cylinder rod 41, and the phase of the reluctance change is made in each of the phases A to D. It can be shifted by 90 degrees every time. Therefore, the phase A and the phase B are 180
The phase shift is 180 degrees between the B phase and the D phase.

The connection forms of the primary coils 1A, 1C, 1B, 1D and the secondary coils 2A, 2C, 2B, 2D are as shown in FIG. In FIG.
The A-phase and C-phase primary coils 1A and 1C are excited in the same phase by a sine signal sinωt, and the outputs of the secondary coils 2A and 2C are connected so as to be added in opposite phases. Similarly, the B-phase and D-phase primary coils 1B and 1D are excited in the same phase by a cosine signal cosωt, and the outputs of the secondary coils 2B and 2D are connected so as to be added in opposite phases. Secondary coil 2A, 2C, 2B, 2
The outputs of D are finally added and taken into the phase difference detection circuit 62 as the output signal Y.

This output signal Y is a reference AC signal (si) having a phase angle φ corresponding to the linear position of the magnetic body portion 55 in the cylinder rod 41.
nωt, cosωt) are phase-shifted. The reason is that the reluctance of each phase A to D is shifted by 90 degrees,
This is because the electrical phases of the excitation signals of one pair (A, C) and the other pair (B, D) are shifted by 90 degrees. Therefore, the output signal Y is Y = Ksin (ωt + φ). Here, K is a constant.

Since the phase φ of the reluctance change is proportional to the linear position of the magnetic body portion 55 according to a predetermined proportionality coefficient (or function), the reference signal sinωt (or cosω) of the output signal Y is obtained.
The straight line position can be detected by measuring the phase shift φ from t). However, the phase shift amount φ is 2π
In this case, the straight line position corresponds to the distance P described above. That is, according to the electric phase shift amount φ in the output signal Y,
An absolute straight line position within the range of the distance P can be detected. By measuring the electrical phase shift amount φ, it is possible to accurately determine the linear position within the range of the distance P with a considerably high resolution.

Note that the magnetic scale portion 41S of the rod 41 is
The material is not limited to 5 and the non-magnetic material portion 56, and other materials that can cause a change in magnetoresistance may be used. For example, a magnetic scale portion 41S is formed by a combination (a material having a different conductivity) of a material having a high conductivity such as copper and a material having a low conductivity (may be a non-conductive material) such as iron. A change in magnetoresistance according to the current loss may be caused. In that case, a pattern of a good conductor may be formed on the surface of the rod 41 of iron or the like by copper plating or the like. The shape of the pattern or the like may be any shape as long as the change in the magnetoresistance is efficiently generated.

Means for obtaining the phase shift amount φ between the output signal Y and the reference signal sinωt (or cosωt) can be appropriately configured. FIG. 13 is a diagram showing an example of a circuit in which the amount of phase shift φ is obtained as a digital amount.

In FIG. 13, the oscillation section 61 has a reference sine signal sinωt.
And a cosine signal cosωt. The phase difference detection circuit 62 is a circuit for measuring the phase shift amount φ.

The clock pulse CP oscillated from the clock oscillator 63 is counted by the counter 64. The counter 64 is, for example, a modulo M, and the count value is given to the register 75. From the 4 / M frequency-divided output of the counter 64, a pulse Pc obtained by frequency-dividing the clock pulse CP by 4 / M is extracted and supplied to the C input of the 1/2 frequency-dividing flip-flop 65.

Pulse Pb output from Q output of flip-flop 65
Is applied to the flip-flop 69, and the pulse Pa output from the * Q (* before the Q means an inverted output) is applied to the flip-flop 66, and the outputs of the flip-flops 66 and 69 are applied to the low-pass filters 67 and 70. The signal is supplied to the coil assembly 51 via the amplifiers 68 and 71 as a sine signal sinωt and a cosine signal cosωt.

The M count in the counter 64 corresponds to these reference signals sin
The phase angle corresponds to 2π radians of ωt and cosωt. That is, one count value of the counter 64 indicates a phase angle of 2π / M radian.

The output signal Y of the coil assembly 51 is applied to the comparator 73 via the amplifier 72, and a square wave signal corresponding to the positive / negative polarity of the output signal Y is output from the comparator 73. A pulse Ts is output from the rise detection circuit 74 in response to the rise of the output signal of the comparator 73, and the count value of the counter 64 corresponding to the pulse Ts is written in the register 75. As a result, the digital value D corresponding to the phase shift amount φ
φ is taken into the register 75. This makes it possible to detect the linear position of the cylinder rod 41 absolutely and with high accuracy.

In the above-described embodiment, a portable type welding gun has been described as an example of a spot welding machine, but any type of welding machine can be used as long as the type of spot welding machine generates a pressing force by a pressurizing cylinder. Even if there is, a similar configuration can be applied.

In practicing the present invention, the present invention is not limited to the welding machine shown in FIGS. 11 to 13, but may be implemented by using any other type of welding machine and a plate pressure detecting means or an inter-electrode distance detecting means. Of course, it is good.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, the joining state of a spot welding part can be determined accurately.

Further, since the inspection method of the present invention is a non-destructive inspection method, it is possible to automatically set welding conditions while monitoring a joining state using the inspection method, and perform spot welding while maintaining a good joining state.

[Brief description of the drawings]

FIG. 1 is a diagram showing a detailed configuration of a pass / fail determination means for realizing the spot welding portion inspection method of the present invention, and FIG. 2 is a spot welding for explaining the concept of the spot welding portion inspection method of the present invention. FIG. 3 is a diagram showing the displacement characteristics of the distance between the electrodes at the time, FIG. 3 is a diagram schematically showing the entire configuration of an inspection apparatus for realizing the spot welding inspection method of the present invention, and FIG. 5 is a timing chart for explaining the operation of FIG. 5, FIG. 5 is a diagram showing another embodiment of the pass / fail judgment means for realizing the spot welding inspection method of the present invention, and FIG. 6 is another embodiment of FIG. FIG. 7 is a view showing displacement characteristics of the distance between electrodes during spot welding for explaining the pass / fail determination means of the example; FIG. 7 is a view schematically showing the overall configuration of the spot welding control system; FIG. A diagram showing a detailed configuration of the determination means, FIG. 9 is a timing chart for explaining the operation of the pass / fail judgment means of FIG. 8, and FIG. 10 shows a change in the distance between the electrodes in each step of spot welding. FIG. 11 is a schematic diagram showing the overall configuration of an example of a spot welding machine that can be used in the present invention. FIG. 12 is a diagram showing the detailed configuration of the pressurizing cylinder and the position detector shown in FIG. FIG. 13 is a diagram showing a configuration of a position converting means for converting a detection signal from the position detector of FIG. 11 into a position signal. 30,31 …… Plate material to be welded, 32,33 …… Tip electrode, 34,38…
... Welding current control means, 35 ... Distance between electrodes detection means, 36,3
9 ... Pass / fail judgment means, 37 ... Display means

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaru Ohara 5-13-16, Bansyo, Suzuka-shi, Mie (72) Inventor Yasuyuki Mizutani 5- 15-17, Bansyo, Suzuka-shi, Mie (72) Inventor, Yuji Taya 2726-6 Takaoka-cho, Suzuka-shi, Mie (72) Inventor Toshiharu Nakajima 2-1-105, Akatsukidai, Yokkaichi-shi, Mie (72) Inventor Shinji Hoshino 1-5-6, Ino, Suzuka-shi, Mie (58) Field surveyed (58) Int.Cl. ⁶ , DB name) B23K 11/24 338 B23K 11/25 513

Claims (13)

(57) [Claims] 1. A spot for welding at least two plates to be welded by superposing at least two plates to be welded, sandwiching both surfaces between two electrodes, and applying a current between the electrodes while applying pressure to the plate to be welded. In welding, an inspection method for judging pass / fail of a spot-welded portion, comprising detecting a shrinkage amount of a plate thickness of the spot-welded portion at a predetermined pressure holding time immediately after the end of energization and detecting the spot based on the shrinkage amount. A method for inspecting a spot welded part, wherein the quality of a joint state of the welded part is determined. 2. A spot where at least two sheets to be welded are overlapped, both surfaces thereof are sandwiched between two electrodes, and a current is applied between the electrodes while applying pressure to the sheet to be welded, thereby welding the spot to be welded. In welding, an inspection method for judging pass / fail of a spot-welded portion, wherein a plate thickness of the spot-welded portion that changes during a predetermined pressure holding time immediately after the end of energization is determined based on the plate thickness at the end of energization. Find the value integrated within the pressure holding time,
A method for inspecting a spot welded portion, wherein the quality of the joint state of the spot welded portion is determined based on the integral value. 3. The spot welding inspection method according to claim 1, wherein the thickness of the plate to be welded is detected based on a distance between the two electrodes. 4. The spot welding according to claim 1, wherein the value of the plate thickness at the end of the holding pressurization time measured on the basis of the plate thickness immediately after the end of the energization is defined as the contraction amount. How to inspect the part. 5. A step of obtaining a value obtained by integrating a plate thickness of the spot welded portion, which changes during a predetermined pressure holding time immediately after the end of energization, within the pressure holding time with reference to the plate thickness at the end of the energization. The method according to claim 1, further comprising the step of determining whether the joining state of the spot weld is good or not based on the integrated value. 6. The method according to claim 1, further comprising a step of calculating a displacement amount of the sheet thickness at the end of energization with respect to the sheet thickness at the start of energization, and further determining whether or not the joining state of the spot welded portion is good based on the displacement amount. The spot weld inspection method according to any one of claims 1 to 5, wherein: 7. The method according to claim 1, further comprising the step of obtaining a displacement of the plate thickness at the end of the holding pressurizing time with respect to the plate thickness at the start of energization, and further determining whether or not the joining state of the spot weld is good based on the displacement. 7. The method according to claim 1, wherein:
The inspection method for spot welds according to any one of claims 1 to 4. 8. The method according to claim 1, further comprising the step of obtaining a value obtained by integrating the value of the sheet thickness that changes after the start of the energization within the energization time with reference to the thickness at the start of the energization, based on the integrated value. The inspection method of a spot welded part according to any one of claims 1 to 7, wherein the quality of the joining state of the spot welded part is further determined. 9. A value (SB) obtained by integrating the thickness of the spot welded portion, which changes during a predetermined press holding time immediately after the end of energization, within the press holding time with reference to the thickness at the end of the energization. Divided by the value (SA) integrated within the energization time based on the plate thickness at the start of energization (SB / S
The method according to any one of claims 1 to 8, further comprising a step of determining (A), and further determining whether or not the joining state of the spot welded portion is good based on the value (SB / SA). An inspection method of a spot welded part according to claim. 10. The method according to claim 1, further comprising the step of: detecting a thickness of the superimposed plate material before starting the energization to determine whether the number of the plate material to be welded is a predetermined number. The inspection method for spot welds according to any one of claims 1 to 9. 11. The method according to claim 1, further comprising a step of absolutely measuring a distance between said two electrodes and detecting a wear amount of an electrode tip caused by spot welding every time said spot welding is performed a predetermined number of times. The inspection method for spot welds according to any one of claims 1 to 10. 12. A spot where at least two sheets to be welded are overlapped, both surfaces thereof are sandwiched between two electrodes, and a current is applied between the electrodes while applying pressure to the sheets to be welded, thereby welding the spot to be welded. A welding control system, comprising: control means for controlling welding conditions of spot welding in accordance with an inspection result of the inspection method of a spot welded part according to any one of claims 1 to 11. Features a spot welding control system. 13. The spot welding control system according to claim 12, wherein at least one of a magnitude of a welding current of the spot welding, said energizing time and said pressure is controlled as said welding condition.