JP5330677B2 - Resistance welding monitoring method and resistance welding control method - Google Patents

Description

  The present invention relates to a resistance welding monitoring method for monitoring welding quality by resistance welding such as spot welding and a resistance welding control method.

  As a conventional technique, the welding current and the voltage between the electrode tips are detected, the temperature distribution of the welded material is calculated based on the heat conduction model using these detection results, and the nugget dimension characteristic value is estimated from the temperature distribution. A resistance welding monitoring device is known that discriminates welding quality from the estimation result (see, for example, Patent Document 1).

  In addition, the welding current and the voltage between the electrode tips are detected, the temperature distribution of the welded material is calculated based on the heat conduction model using the detection results, the nugget dimension characteristic value is estimated from the temperature distribution, There has been proposed a resistance welding control apparatus that performs welding control so as to obtain the welding quality of (see, for example, Patent Document 2).

  Further, the welding current and the voltage between the electrode tips are detected, and the temperature distribution of the welded material is calculated based on the heat conduction model using the detection results, and the nugget dimension characteristic value is estimated from the temperature distribution, and the predetermined value is obtained. A resistance welding control device has been proposed in which welding control is performed so as to obtain the welding quality of the above, while the influence of the eddy current by the jig is corrected (for example, see Patent Document 3).

  In the resistance welding monitoring device or the resistance welding control device as described above, it is important to accurately grasp the voltage applied to the workpiece (or the resistance value of the workpiece). In general, the voltage between electrode tips in an unloaded short-circuit state is measured in advance, and the welding voltage applied to the member to be welded is calculated by subtracting from the voltage between electrode tips measured during welding.

  When actually measuring, the voltage measurement wiring between the electrode tips attached near the tip holder is affected by the eddy current generated in the magnetic material around the weld, such as the welded member, peripheral member, and welding jig. In response, an electromotive force is induced, and the voltage between the electrode tips is measured in a form in which the electromotive forces are added.

For example, in the past, assuming that the effective value is fixed by fixing the arrangement of the voltage measurement lines and canceling out at the time of the following calculation, (voltage between electrode tips used for calculation) = (no load short circuit) The inter-electrode voltage in the state)-(the inter-electrode voltage measured at the time of welding) has been constructed (Summary of the National Conference of the Japan Welding Society, Vol. 56 ('95 -4) "Inductance between Chips in Resistance Welding" Measurement and its application ”).
Japanese Patent No. 3396602 Japanese translation of PCT publication No. 2004-510583 Japanese Patent Laid-Open No. 2004-230425

  However, even if the arrangement of the electrode measurement lines is fixed, if the member to be welded, peripheral members, welding jigs, etc. change, especially in a C-type spot welding gun with a large pocket size, it is caused by the influence of this eddy current. Electric power cannot be ignored. In this case, since the calculated value of the welding voltage applied to the material to be welded does not become a correct value, a calculation error occurs, and the functions of welding control and quality discrimination cannot be performed.

  Here, a welding monitoring apparatus that determines the welding quality using the peak value of the average temperature estimated value based on the energy balance model described in Patent Document 2 will be described as an example. Using a C-type spot welding gun (H = 300 mm, D = 200 mm) as shown in FIG. 1, two flat plates (plate thickness t = 4.5 mm, 4.0 mm) are overlapped as shown in FIG. In the case of welding (welding condition is 120 cyc / 18 kA), if the relationship between the peak value of the average temperature estimated value of the welded portion and the welding area is shown in a graph, it is as shown in FIG.

  In FIG. 3, it is possible to monitor the welding quality based on the estimated temperature peak value. However, for example, when a building construction material as shown in FIG. 4 is welded to a welding spot position as shown in FIG. 5 (FIG. 5 is a view when FIG. 4 is viewed from the direction A), As shown in FIG. 6, the correlation between the peak value of the average temperature estimated value and the welded area varies depending on the position of the welding spot, depending on the type of material (plate thickness, presence / absence of additional members), and the like. Further, the correlation is also shifted when the stop position of the welding gun varies mechanically. As a result, it becomes difficult to properly determine the welding quality.

  Further, in Patent Document 3, when a jig for holding a workpiece is inserted into the pocket of the arm of the welding gun, the calculation value error of the weld resistance value is corrected by an eddy current due to the influence of the jig. However, in this method, calculation correction is performed by registering a short-circuit resistance value for each predetermined welding spot position based on a jig configuration with a limited pattern. In this method, when the influence of eddy currents due to the jig and workpiece is infinite, the influence of the eddy current due to the influence of the equipment structure such as the stop position accuracy of the welding gun is not stable even at the same welding point position. Changes, and the calculated value cannot be accurately corrected.

  An object of the present invention is to provide a resistance welding monitoring method and a resistance welding control method capable of accurately correcting the influence of eddy currents and appropriately determining welding quality.

In order to solve the above problem, the invention according to claim 1 measures the current applied between the electrode tips and the voltage between the electrode tips, and uses the measurement result to determine the resistance value of the material to be welded. A resistance welding monitoring method for calculating and estimating the welding quality for the workpiece based on the calculation result, measuring voltage V, measuring current i, resistance between electrode tips in short-circuit state R, measuring When the mutual inductance of the welder circuit is M and the self-inductance of the welder circuit is L, the following equation (3) is used during energization:
V = i * R + (L + M) * di / dt (3)
A relational expression between (L + M) and R in a state where the electrode tip is short-circuited is set, and at the time of welding, the measurement voltage due to the influence of eddy current at the time of welding is corrected using the relational expression, and based on the correction result Calculating the welding voltage to be applied to the workpiece and correcting the measurement voltage due to the influence of eddy current during welding, calculating the welding quality index value from the corrected voltage, and using the index value, the welding quality It is characterized by monitoring.
The invention according to claim 2 measures the current applied between the electrode tips and the voltage between the electrode tips, calculates the resistance value of the welded material using the measurement result, and calculates the calculation A resistance welding monitoring method for inferring the welding quality of the material to be welded based on the result, wherein the measurement voltage is V, the measurement current is i, the resistance between the electrode tips in a short-circuit state is R, and the circuit between the measurement and the welding machine When the inductance is M and the self-inductance of the welder circuit is L, the following equation (3 ′) is used during energization:
V = i * R + (L + M) * di / dt (3 ')
When setting the relational expression between (L + M) and R with the electrode tip short-circuited, the electrode is short-circuited at the position where the hole is drilled , and the effect of eddy current during welding using the relational expression is used during welding. The measurement voltage is corrected, and the welding voltage applied to the workpiece is calculated based on the correction result.

According to a third aspect of the present invention, in the first or second aspect , the relational expression between M and R is set by energizing with an up slope / down slope in a state where the electrode tip is short-circuited. It is characterized by that.

The invention according to claim 4 measures the current applied between the electrode tips and the voltage between the electrode tips, calculates the resistance value of the material to be welded using the measurement result, and A resistance welding control method for estimating a welding quality of the workpiece to be welded and controlling a welding current so that the estimation result approaches a welding quality target value, wherein the measurement voltage is V, the measurement current is i, and the short-circuit state When the resistance between the electrode tips is R, the mutual inductance of the circuit between the measurement and the welding machine is M, and the self-inductance of the welding machine circuit is L, the following equation (4) is used during energization:
V = i * R + (L + M) * di / dt (4)
A relational expression between (L + M) and R in a state where the electrode tip is short-circuited is set, and at the time of welding, the measurement voltage due to the influence of the eddy current at the time of welding is corrected using the relational expression, and based on the corrected voltage The welding voltage to be applied to the workpiece is calculated, while (L + M) is obtained every 0.5 to 1 cycle and the welding quality index value is calculated using the correction voltage.

The invention according to claim 5 calculates the welding quality index value in claim 4 by dividing the energization time at the time of welding into the first section, the second section, and the third section which are continuous as follows. It is a feature.
First section: section in which constant current control is performed to obtain an average value of (L + M) Second section: constant current control is performed, the average value of (L + M) obtained in the first section is used, and the above equation (2) is Section used to correct the measured voltage from the first section and calculate the welding quality index value Third section: Average of (L + M) obtained in the first section following calculation of the welding quality index value in the second section Section in which the welding quality index value is calculated using the correction voltage

According to a sixth aspect of the present invention, in the fourth aspect of the present invention, the welding quality index value is calculated by dividing the energization time during welding into the first section, the second section, and the third section that are continuous as follows. It is a feature.
First section: section in which constant current control is performed to obtain an average value of (L + M) Second section: energization is stopped, the average value of (L + M) obtained in the first section is used, and the above formula (2) is used Section for correcting the measured voltage from the first section and calculating the welding quality index value Third section: Average value of (L + M) obtained in the first section following calculation of the welding quality index value in the second section And using the correction voltage to calculate the weld quality index value

  According to the present invention, it is possible to accurately correct the influence of eddy currents and appropriately determine the welding quality.

  Moreover, the man-hour which sets a short circuit resistance value etc. for every welding spot position, and the man-hour which measures a short circuit resistance value etc. for every member variation can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 and 2 show a schematic configuration of the C-type spot welding gun 1. The C-type spot welding gun 1 includes a spot welding gun main body 2 that is substantially C-shaped, an upper tip holder 3 attached to the tip of an arm 2A at the top of the spot welding gun main body 2, and a leg portion at the bottom of the spot welding gun main body 2. And a lower chip holder 4 attached to the tip of 2B. Electrode chips 5 and 6 are attached to the upper and lower chip holders 3 and 4, respectively.

  The spot welding gun body 2 is electrically connected to a voltage detection circuit 7 that detects a voltage applied between the electrode tips 5 and 6. Furthermore, the spot welding gun main body 2 is provided with a toroidal coil 8, and a current detection circuit 9 for detecting a current flowing through the toroidal coil 8 is electrically connected.

  The voltage detection circuit 7 and the current detection circuit 9 are connected to an A / D converter 10, and the A / D converter 10 is connected to a welding control device (or quality monitoring device) 12 via an arithmetic device 11.

In the present embodiment, in the C-type spot welding gun 1 configured as described above, the following control is performed when welding is performed on the workpiece.

  The welding current and the voltage between the electrode tips are measured, and using the measurement results, the temperature distribution of the member to be welded is calculated based on the heat conduction model, and the nugget dimension characteristic value is estimated from the temperature distribution. In a system that discriminates welding quality and controls welding conditions, the electrode tips are placed in a short-circuit state without load, the voltage between the electrode tips is measured in advance, and the electrode tips measured during welding are measured. By subtracting from the voltage, the welding current applied to the member to be welded is calculated.

  When the measured value when the electrode tip is energized in a short-circuit state with no load is expressed by an equation, the following equation (5) is obtained.

V = i × Ro + (L + M) × di / dt (5)
Where V: measurement voltage
i: Measurement current Ro: Resistance between electrode tips in no-load short-circuit state
M: Circuit and mutual inductance of measurement and welding machine
L: Self-inductance of the welder circuit.

  Assuming that resistance and inductance do not change in a very short time, apply multiple sets of current-voltage data obtained by sampling within a half cycle of energization to the above formula (5), and convert the multiple sets of formulas using the least squares method. By analyzing, Ro and (L + M) can be obtained (for example, refer to the National Welding Society Conference Summary Vol. 56 ('95 -4) "Measurement of Inductance between Chips in Resistance Welding and Its Application").

  However, when actually measuring, the wiring for measuring the voltage between the electrode tips attached in the vicinity of the tip holder is wired to follow the arm of the spot welding gun body, or the member to be welded, peripheral member, welding jig, etc. When wiring is made within the range affected by the eddy current generated in the magnetic material around the weld, the electromotive force generated by the influence is induced, and the voltage between the electrode tips is calculated by adding this electromotive force. Will be calculated. The voltage Vm generated by the influence of this eddy current is considered to be strongly influenced by the self-inductance in the spot welding gun body and the value of the flowing current.

  Actually, when both electrode tips are short-circuited and energized in a no-load state and in an eddy current load state, as shown in FIG. 7, a characteristic (L + M) depending on the shape of the spot welding gun main body and the wiring state of the voltage detection line. ) And R are required. From this result, it can be predicted that an electromotive force Vm (≈i × (R−Ro)) of eddy current related to (L + M) is generated.

  In the present embodiment, using the relationship between (L + M) and R, the following correction is performed on the voltage during welding.

  When the current voltage measured at the time of welding is expressed by an equation, the following equation (6) is obtained.

V = i × (Ro + Rt) + (L + M) × di / dt (6)
Where V: measurement voltage
i: Measurement current Ro: Resistance between electrode tips in a short-circuit state without load Rt: Resistance of a steel plate to be welded
M: Circuit and mutual inductance of measurement and welding machine
L: Self-inductance of the welder circuit.

Normally, i and V are measured, and (Ro + Rt) and (L + M) are obtained from a plurality of sets of current and voltage data obtained in a short time by the least square method, and Ro (no load) measured in advance. The resistance Rt of the steel sheet can be obtained by subtracting the resistance between the electrode tips in the short-circuit state.
Heat transfer calculation should be possible using this Rt.

  However, when the eddy current load is large and the electromotive force component of the influence is included, the following equation (7) is actually obtained. In the above calculation, the value is far from the true Rt value. End up.

V = i × (Ro + Rt) + (L + M) × di / dt + Vm (7)
Here, Vm is an electromotive force due to the influence of eddy current.

  Therefore, in this embodiment, the value of (L + M) is used to calculate the R value from the relationship shown in FIG. Replacing R with Ro cancels the influence of eddy currents. That is, the following equations (8) and (9) are obtained.

Vm = i × Ro≈i × R (8)
V = i × (R + Rt) + (L + M) × di / dt (9)
Where V: measurement voltage
i: Measurement current
R: Value obtained from (L + M) obtained by equation (6) based on FIG. 7 Rt: Resistance of the steel sheet to be welded
M: Circuit and mutual inductance of measurement and welding machine
L: Self-inductance of the welder circuit.

  And Rt is calculated | required by subtracting R from (R + Rt) calculated | required by said (9) Formula. By using this Rt, it is possible to perform accurate heat conduction calculation in which the influence of eddy current is corrected.

  Depending on the shape of the welding gun and the wiring state of the voltage detection line, the following (a) to (c) may be mentioned as a method of taking the R relationship with (L + M) in short circuit energization.

  (a) A relational expression of (L + M) and R that can be calculated every half cycle is used.

  (b) The relational expression between the average value of (L + M) and the minimum value of R calculated for each cycle in all energization cycles is used.

  (c) A relational expression between the average value of (L + M) and the average value of R calculated for each cycle in all energization cycles is used.

  Of the above (a) to (c), (a) is considered preferable.

  The following methods (d) and (e) are mentioned as actual data collection methods.

(d) A method using a test work that makes it possible to short-circuit the electrode at the welding spot position by drilling holes at the spot position of the actual workpiece (see Fig. 8)
(e) Method of arranging a magnetic material such as an iron member around the welding gun In the case of (a) above, instead of changing the eddy current load, (L + M) is also changed by changing the welding current. (Refer to Fig. 9) Using points, create an eddy current load jig that is easy to attach to the welding gun, and by using functions such as up-slope and down-slope during energization, A wider range of relationship between (L + M) and R can be obtained.

  As a method for correcting Ro at the time of welding, the following methods may be mentioned.

  (f) Using the value of (L + M) calculated every half cycle, R is calculated from the relational expression.

  (g) R is calculated from the relational expression using an average value of (L + M) calculated for each cycle in all energization cycles.

Next, FIGS. 10 and 11, welds estimated temperature when performing the spot welding against the building structure shown in FIG. 4 - shows the evaluation results of the welding area. FIG. 10 shows a case where the measurement voltage is not corrected due to the influence of the eddy current during welding, and FIG. 11 shows a case where the measurement voltage is corrected due to the influence of the eddy current during welding.

10 and 11, R ² indicates a correlation coefficient, and when the correction is made (FIG. 11) compared to the case where the correction is not made (FIG. 10), the estimated weld temperature and the welding area are increased. It can be seen that the correlation with is large.

  Next, the flow of welding quality monitoring in this embodiment will be described with reference to FIG.

  In FIG. 12, first, no-load short-circuit energization and load short-circuit energization are performed, and L (self-inductance of the welder circuit), M (measurement and circuit mutual inductance of the welder), and R (resistance between the electrode tips in the short-circuit state). And the relational expression (L + M) −R in a state where the electrode tip is short-circuited is set using the above-described formula (7) (step S1).

  Next, current voltage is measured during welding (step S2), an average value of (L + M) is calculated every 0.5 cyc (cycle), and Rt (which is the object to be welded) from a relational expression of (L + M) -R. The resistance of the steel plate is calculated (step S3).

  Further, the heat conduction calculation is performed with the short-circuit resistance value as Rt, and the average weld temperature estimated value is calculated (step S4). At this time, the calculated weld zone average temperature estimated value is stored in the storage unit (step S5). And the process of step S2-step S4 is repeated in multiple times at the time of welding.

  After the welding is completed, the estimated average temperature of the weld is read from the storage unit, the peak value of the estimated average temperature of the weld is obtained, and the peak value is output as a quality index value (step S6).

  FIG. 13 shows a flow according to another example of welding quality monitoring. In FIG. 13, first, no-load short-circuit energization and load short-circuit energization are performed, L, M, and R are measured, and (L + M) −R in a state where the electrode tip is short-circuited using the above-described equation (7). Is set (step S11).

  Next, current voltage is measured during welding (step S12), and the measurement result is stored in the storage unit (step S13). Further, an average value of (L + M) is calculated every 0.5 cyc (step S14), and the calculation result is stored in the storage unit (step S15).

  Then, after the energization is completed, the average value of (L + M) is read from the storage unit, and Rt is calculated from the relational expression of (L + M) −R (step S16). Further, the current voltage data is read from the storage unit, and the heat conduction calculation is performed with the short-circuit resistance value as Rt (step S17).

  Further, the peak value of the weld zone average temperature estimated value is obtained, and the peak value is output as a quality index value (step S18).

  Next, a resistance welding control method will be described. FIG. 14 shows the transition of the average temperature of the weld when welding is performed at a constant current. As shown in the figure, the average temperature of the weld zone rises in the initial stage, but then falls with the passage of time.

  FIG. 15 is a flowchart illustrating an example of a resistance welding control method. In FIG. 15, first, no-load short-circuit energization and load short-circuit energization are performed, L, M, and R are measured using the above-described equation (7), and (L + M) −R in a state where the electrode tips are short-circuited. Is set (step S21).

  Next, the set current is applied (step S22), and the current voltage is measured (step S23). Then, an average value of (L + M) is calculated every 0.5 cyc, and Rt is calculated from a relational expression of (L + M) −R (step S24).

  Moreover, heat conduction calculation is implemented by making short circuit resistance value into Rt, and a welding part average temperature estimated value is calculated (step S25). At this time, the calculated weld zone average temperature estimated value is stored in the storage unit (step S26). Further, the set current is adjusted so as to approach the set temperature level (step S27). Further, after the processing in step S27, the flow returns to step S22.

  After the end of welding, the welding portion average temperature estimated value is read from the storage portion, the peak value of the welding portion average temperature estimated value is obtained, and the peak value is output as the quality index value (step S28).

  FIG. 16 shows the transition of the welding current and the average weld temperature in the resistance welding control method shown in FIG.

  FIG. 17 is a flowchart illustrating another example of the resistance welding control method. In FIG. 17, first, no-load short-circuit energization and load short-circuit energization are performed, and L, M, and R are measured using the above-described equation (7), and (L + M) −R with the electrode tip short-circuited. Is set (step S31).

  Next, the set current is energized with a constant current (step S32), and the current voltage is measured (step S33). At this time, the measured value is stored in the storage unit (step S34).

  After the process in step 33, the average value of (L + M) at the time of energization in step S32 is calculated, and further Rt is calculated from the relational expression of (L + M) -R (step S35). Thereafter, the set current is supplied again with a constant current (step S36), and the current voltage is measured (step S37), and the measured value at this time is stored in the storage unit (step S38).

  Moreover, after the process in step S35, the heat conduction calculation at the time of energization in steps S32 and S36 is performed by setting the short-circuit resistance value to Rt (step S39). Furthermore, the heat conduction calculation at the time of energization is implemented and a welding part average temperature estimated value is calculated (step S40). At this time, a memory | storage part memorize | stores the calculated welding part average temperature estimated value (step S41).

  Further, after the process in step S37, the calculation result of the heat conduction in step S40 is taken in and the set current is adjusted so as to approach the set temperature level (step S42). Then, the set current is applied (step S43), and the current voltage is measured (step S44).

  After the end of welding, a peak value of the weld zone average temperature estimated value is obtained, and the peak value is output as a quality index value (step S45).

  FIG. 18 shows transition of the welding current and the average weld temperature in the resistance welding control method shown in FIG.

  FIG. 19 is a flowchart showing still another example of the resistance welding control method. In FIG. 19, first, no-load short-circuit energization and load short-circuit energization are performed, L, M, and R are measured using the above-described equation (7), and (L + M) −R in a state where the electrode tips are short-circuited. Is set (step S51).

  Next, the set current is energized with a constant current (step S52), and the current voltage is measured (step S53). At this time, the measured value is stored in the storage unit (step S54).

  After the process in step 53, the average value of (L + M) at the time of energization in step S52 is calculated, and further Rt is calculated from the relational expression of (L + M) -R (step S55). Thereafter, the calculation time is waited (step S56).

  Further, after the process in step S55, the short circuit resistance value is set to Rt, and the heat conduction calculation during energization in steps S52 and S56 is performed (step S57). Furthermore, the heat conduction calculation at the time of energization is implemented and a welding part average temperature estimated value is calculated (step S58). At this time, a memory | storage part memorize | stores the calculated welding part average temperature estimated value (step S59).

  Further, after the process in step S58, the calculation result of heat conduction is taken in and the set current is adjusted so as to approach the set temperature level (step S60).

  On the other hand, after the process in step S56, the adjustment result in step S60 is taken in, the set current is applied (step S61), and the current voltage is measured (step S62).

  After the end of welding, the peak value of the weld zone average temperature estimated value is obtained, and the peak value is output as a quality index value (step S63).

  FIG. 20 shows the transition of the welding current and the average weld temperature in the resistance welding control method shown in FIG.

It is a basic system block diagram of a C type spot welding gun. It is a figure which shows a mode that flat plate welding is performed using a C-type spot welding gun. It is the figure which showed the relationship between the peak value of the average temperature estimated value of a welding part, and the welding area in welding of a flat plate overlap. It is a figure which shows a mode that the building construction material is welded using a C-type spot welding gun. It is the figure which looked at the building structural material of FIG. 4 from A direction, and is a figure which shows the spot welding hit point position. It is the figure explaining that the relationship of the peak value of the average temperature estimated value of a welding part and a welding area produces a shift | offset | difference in a correlation according to a welding spot position. It is the figure which showed the relationship of (L + M) -Ro. It is a figure which shows a mode that the hole processing was given to the spot position of a building structure material in order to short-circuit an electrode at the welding spot position. It is the figure which showed the relationship between electric current, (L + M), and R. It is a figure which shows the evaluation result of welding part estimated temperature-welding area at the time of not correcting the measurement voltage by the influence of the eddy current at the time of welding. It is a figure which shows the evaluation result of welding part estimated temperature-welding area at the time of performing correction of the measurement voltage by the influence of the eddy current at the time of welding. It is a figure which shows the flow of welding quality monitoring. It is a figure which shows the flow by the other example of welding quality monitoring. It is a figure which shows transition of the welding part average temperature at the time of welding with a constant current. It is a flowchart which shows an example of the resistance welding control method. It is a figure which shows transition of the welding current and welding part average temperature in the resistance welding control method shown in FIG. It is a flowchart which shows the other example of a resistance welding control method. It is a figure which shows transition of the welding current and welding part average temperature in the resistance welding control method shown in FIG. It is a flowchart which shows the other example of the resistance welding control method. It is a figure which shows transition of the welding current and welding part average temperature in the resistance welding control method shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 C type spot welding gun 2 Spot welding gun main body 5,6 Electrode tip 7 Voltage detection circuit 9 Current detection circuit 11 Arithmetic device 12 Welding control device (control means) or quality monitoring device

Claims (6)

The current applied between the electrode tips and the voltage between the electrode tips are measured, and the resistance value of the welded material is calculated using the measurement result, and the welding quality for the welded material based on the calculated result A resistance welding monitoring method for estimating
When the measurement voltage is V, the measurement current is i, the resistance between the electrode tips in a short-circuit state is R, the mutual inductance of the measurement and the welding machine is M, and the self-inductance of the welding machine is L, the following (1 )
V = i * R + (L + M) * di / dt (1)
A relational expression between (L + M) and R in a state where the electrode tip is short-circuited is set, and at the time of welding, the measurement voltage due to the influence of eddy current at the time of welding is corrected using the relational expression, and based on the correction result To calculate the welding voltage applied to the workpiece,
A resistance welding monitoring method comprising: calculating a welding quality index value from the corrected voltage when the measurement voltage due to the influence of eddy current during welding is corrected, and monitoring the welding quality using the index value. The current applied between the electrode tips and the voltage between the electrode tips are measured, and the resistance value of the welded material is calculated using the measurement result, and the welding quality for the welded material based on the calculated result A resistance welding monitoring method for estimating
When the measurement voltage is V, the measurement current is i, the resistance between the electrode tips in a short-circuit state is R, the mutual inductance of the measurement and the welding machine is M, and the self-inductance of the welding machine is L, the following (1 ') Using the formula,
V = i * R + (L + M) * di / dt (1 ')
When setting the relational expression between (L + M) and R with the electrode tip short-circuited, the electrode is short-circuited at the position where the hole is drilled , and the effect of eddy current during welding using the relational expression is used during welding. A resistance welding monitoring method, comprising: correcting a measurement voltage according to claim 1 and calculating a welding voltage to be applied to the material to be welded based on the correction result. 3. The resistance welding monitor according to claim 1 , wherein the relational expression between M and R is set by energizing with an up slope / down slope in a state where the electrode tip is short-circuited. Method. The current applied between the electrode tips and the voltage between the electrode tips are measured, and the resistance value of the workpiece is calculated using the measurement result, and the welding quality of the workpiece is calculated based on the calculation result. Is a resistance welding control method for controlling the welding current so that the estimation result approaches the welding quality target value,
When the measurement voltage is V, the measurement current is i, the resistance between the electrode tips in a short-circuit state is R, the mutual inductance of the measurement and the welding machine is M, and the self-inductance of the welding machine is L, the following (2 )
V = i * R + (L + M) * di / dt (2)
A relational expression between (L + M) and R in a state where the electrode tip is short-circuited is set, and at the time of welding, the measurement voltage due to the influence of the eddy current at the time of welding is corrected using the relational expression, and based on the corrected voltage While calculating the welding voltage applied to the workpiece to be welded,
A resistance welding control method characterized by obtaining (L + M) every 0.5 to 1 cycle and calculating a welding quality index value using the correction voltage . 5. The resistance welding control method according to claim 4, wherein the welding quality index value is calculated by dividing the energization time during welding into a first section, a second section, and a third section that are continuous as described below.
First section: A section where constant current control is performed and an average value of (L + M) is obtained.
Second section: Constant current control is performed, the average value of (L + M) obtained in the first section is used, the measured voltage from the first section is corrected using the above equation (2), and the welding quality index value Interval to calculate
Third section: A section in which the average value of (L + M) obtained in the first section is used subsequent to the calculation of the welding quality index value in the second section, and the welding quality index value is calculated using the correction voltage. 5. The resistance welding control method according to claim 4 , wherein the welding quality index value is calculated by dividing the energization time during welding into a first section, a second section, and a third section that are continuous as described below.
First section: section in which constant current control is performed to obtain an average value of (L + M) Second section: energization is stopped, the average value of (L + M) obtained in the first section is used, and the above formula (2) is used Section for correcting the measured voltage from the first section and calculating the welding quality index value Third section: Average value of (L + M) obtained in the first section following calculation of the welding quality index value in the second section And using the correction voltage to calculate the weld quality index value

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