JP5789483B2 - Resistance welding method and apparatus - Google Patents

Description

  In the present invention, a plurality of workpieces are sandwiched between a first electrode tip and a second electrode tip, and the workpieces are joined together by energization between the first electrode tip and the second electrode tip. The present invention relates to a welding method and an apparatus therefor.

  As is well known, resistance welding (also referred to as “spot welding”), which is a welding method, sandwiches a plurality of workpieces that are in contact with each other with a set of electrode tips, and between these electrode tips. By energizing, the workpieces are welded in a dot shape.

  Resistance welding is performed by, for example, a welding gun disposed at the tip of a robot arm capable of teaching. That is, the robot that has been taught in advance operates so that a workpiece is inserted between the electrode tips provided in the openable / closable clamp part of the welding gun, and then the clamp part is closed. The workpiece is held between the electrode tips. In this state, electricity is applied between the electrode tips, and a melted part is generated in the workpiece. Eventually, as the melted portion solidifies into a solid phase called a nugget, a dotted weld is formed on the workpiece.

  In resistance welding performed in this way, it may be investigated to what extent the melted portion generated in the workpiece has grown. As this type of investigation technique, for example, as described in Patent Document 1, it is possible to estimate the diameter of the melted portion based on the resistance value between the electrode tips. Patent Document 2 describes a technique for performing numerical analysis using a heat conduction model and obtaining contact resistance between workpieces based on this analysis.

  Furthermore, the present applicant has found that the detection accuracy of the interface position of the melted portion, and hence the calculation accuracy of the growth rate of the melted portion, is reduced due to the electrode tip gradually being worn and the contact area between the electrode tip and the workpiece being changed. In view of this, a technique has been proposed in which the growth rate of the melted portion can be evaluated with high accuracy even if the above change occurs (see Patent Document 3).

JP 2005-334935 A JP-A-9-196881 JP 2010-60412 A

  The present invention has been made in connection with the technique described in Patent Document 3, and an object thereof is to provide a resistance welding method and apparatus capable of evaluating the degree of growth of a melted portion with higher accuracy.

In order to achieve the above object, the present invention is a resistance welding method in which a current is passed between a first electrode tip and a second electrode tip sandwiching a plurality of workpieces, and the workpieces are welded together.
During the resistance welding, a step of obtaining an inter-chip resistance value from the first electrode tip to the second electrode tip in a state of sandwiching the plurality of workpieces;
Obtaining each resistance value of the first electrode chip and the second electrode chip based on the temperature dependence of the resistance of the first electrode chip and the second electrode chip;
A first contact resistance value between the first electrode tip and the workpiece in contact with the first electrode tip is obtained based on a contact area of both, and the workpiece in contact with the second electrode tip and the second electrode tip A step of obtaining a second contact resistance value based on both contact areas;
Obtaining a resistance value of each of the plurality of workpieces based on the temperature dependence of the resistance of the workpieces;
Subtracting each resistance value of the first electrode chip and the second electrode chip, the first contact resistance value and the second contact resistance value, and each resistance value of the plurality of workpieces from the inter-chip resistance value, Obtaining a contact resistance value between the workpieces;
It is characterized by having.

  Note that the “inter-chip resistance value” in this specification includes the resistance value of the first electrode chip and the resistance value of the second electrode chip. That is, the inter-chip resistance value is a value that takes into account both resistance values of the first electrode chip and the second electrode chip.

  In the present invention, the temperature of the first electrode tip, the second electrode tip and the plurality of workpieces rises during resistance welding, and the resistance rises along with this, or the resistance increases as the molten part is generated. In consideration of the decrease, the resistance values of the first electrode tip, the second electrode tip and the plurality of workpieces during resistance welding are obtained based on the temperature. In other words, these resistance values are obtained in real time.

  Furthermore, the contact area between the first electrode tip and the workpiece that contacts the first electrode tip, and the contact area between the second electrode tip and the workpiece that contacts the first electrode tip also change with the progress of resistance welding. This is because the work is softened so that the first electrode chip and the second electrode chip are easily embedded in the work.

  Therefore, in the present invention, the contact resistance value between the first electrode tip and the workpiece in contact with the first electrode tip, and the contact resistance value between the second electrode tip and the workpiece in contact with the second electrode tip are changed in each contact area. Based on the request. That is, these contact resistance values are also obtained in real time. This technique is described in detail in Patent Document 3.

  By subtracting the resistance value obtained as described above from the inter-chip resistance value, the contact resistance value between the workpieces can be obtained accurately and in real time. Based on this contact resistance value, the degree of growth of the melted portion can be evaluated. Since the contact resistance value between the workpieces can be obtained with high accuracy, the evaluation becomes highly accurate.

  In addition, in order to evaluate the degree of growth of the melted portion based on the contact resistance value between the workpieces, for example, the correlation between the contact resistance value between the workpieces and the diameter of the melted portion formed between the workpieces. Is obtained in advance. Then, the diameter of the melted portion may be obtained based on this correlation and the actual contact resistance value between the workpieces.

Further, the present invention is a resistance welding apparatus for energizing between a first electrode tip and a second electrode tip sandwiching a plurality of workpieces, and welding the workpieces,
A controller for controlling energization between the first electrode chip and the second electrode chip;
The control unit, during the resistance welding, the inter-chip resistance value from the first electrode tip in a state of sandwiching the plurality of workpieces to the second electrode tip,
Each resistance value based on the temperature dependence of the resistance of the first electrode chip and the second electrode chip;
A first contact resistance value between the first electrode tip and the workpiece based on a contact area between the first electrode tip and the workpiece; and a first contact resistance value between the second electrode tip and the workpiece. A second contact resistance value between the two-electrode tip and the workpiece;
Each resistance value based on the temperature dependence of the resistance of the plurality of workpieces,
Seeking
Further, from the inter-chip resistance value, the resistance values of the first electrode chip and the second electrode chip, the first contact resistance value and the second contact resistance value, and the resistance values of the plurality of workpieces are obtained. The contact resistance value between the workpieces is obtained by subtraction.

  By setting it as such a structure, the above-mentioned resistance welding method can be implemented automatically and easily.

  According to the present invention, when resistance welding is performed, both the resistance value changes as the temperature of the electrode tip and the workpiece changes, and the contact area between the electrode tip and the workpiece changes. The contact resistance value between workpieces is obtained in consideration of the above. For this reason, it becomes possible to obtain | require the contact resistance value of workpiece | work more accurately and in real time.

  Based on this contact resistance value, for example, the diameter of the melted part, and thus the degree of growth of the melted part can be obtained. As described above, since the contact resistance value between the workpieces is obtained with high accuracy, the degree of growth of the melted portion can be evaluated with higher accuracy.

It is a principal part schematic block diagram of the resistance welding apparatus which concerns on embodiment of this invention. (A) is a graph simply showing the time-dependent change in the contact resistance value between the workpieces and the diameter of the melted part, and (b) shows the contact resistance value between the works and the size of the diameter of the melted part. It is a graph which shows a correlation simply.

  Hereinafter, the preferred embodiment of the resistance welding method according to the present invention will be described in detail in relation to the resistance welding method for carrying out the same, with reference to the accompanying drawings.

  First, the resistance welding apparatus according to the present embodiment will be described with reference to FIG. This resistance welding apparatus 10 has a welding gun (not shown) that is openable and closable that is disposed at the tip of an arm portion of a robot (not shown). A first electrode tip 12 and a second electrode tip 14 are provided at the tips of the welding gun. Are provided so as to face each other. As shown in FIG. 1, the first electrode chip 12 and the second electrode chip 14 sandwich two workpieces W1 and W2 stacked on each other. Accordingly, the tip of the first electrode tip 12 contacts the upper workpiece W1, and the tip of the second electrode tip 14 contacts the lower workpiece W2.

  The first electrode chip 12 includes a first transmitter / receiver 16 capable of transmitting and receiving ultrasonic waves. Similarly, the second transmitter / receiver 18 capable of transmitting and receiving ultrasonic waves is also incorporated in the second electrode chip 14.

  The correlation between the contact area of the first electrode chip 12 and the second electrode chip 14 with respect to the workpieces W1 and W2 and the incident wave rate of the ultrasonic waves to the workpieces W1 and W2 is known as described in Patent Document 3. Pre-required by technology.

  The first transmitter / receiver 16 and the second transmitter / receiver 18 are connected to an echo measuring device 20. The echo measuring device 20 can measure the intensity of the ultrasonic wave (reflected wave) that has returned to the first transmitter / receiver 16 and the intensity of the ultrasonic wave (transmitted wave) that has reached the second transmitter / receiver 18.

  Furthermore, the welding gun is provided with an encoder 22 for measuring the distance between the tip of the first electrode tip 12 and the tip of the second electrode tip 14, in other words, the inter-chip distance D. The inter-chip distance D is constantly measured by the encoder 22.

  In the above configuration, the echo measuring instrument 20 and the encoder 22 are electrically connected to the control circuit 24 (control unit).

  Next, a resistance welding method according to the present embodiment using the resistance welding apparatus 10 basically configured as described above will be described.

In resistance welding, the inter-chip resistance R from the first electrode tip 12 to the second electrode tip 14 is the resistance r1 of the first electrode tip 12, the contact resistance r2 between the first electrode tip 12 and the workpiece W1, and the workpiece W1. Of the workpiece W1, the contact resistance r4 of the workpiece W2, the resistance r5 of the workpiece W2, the contact resistance r6 of the workpiece W2 and the second electrode chip 14, and the resistance r7 of the second electrode chip 14. That is, the following formula (1) is established.
R = r1 + r2 + r3 + r4 + r5 + r6 + r7 (1)

  Needless to say, the melting part 30 (nugget) is generated at the contact interface between the workpieces W1 and W2. As shown in FIGS. 2A and 2B, the contact resistance r <b> 4 and the diameter of the melting part 30 have a correlation, and the contact resistance r <b> 4 decreases as the diameter of the melting part 30 increases. This is because if the diameter of the melted part 30 is large, the current density flowing through the melted part 30 becomes small.

  Of course, the correlation shown as (a) and (b) in FIG. 2 is measured by preliminary resistance welding and is input to the control circuit 24 (see FIG. 1). Based on the correlation and the actual value of the contact resistance r4, the control circuit 24 determines the diameter of the fusion zone 30 during which resistance welding proceeds. Therefore, if the actual value of the contact resistance r4 between the workpieces W1 and W2 can be obtained with high accuracy, the diameter of the molten part 30 during resistance welding, that is, the degree of growth of the molten part 30 is evaluated with high accuracy. It becomes possible to do.

  For this reason, the actual values of the resistances r1 to r3 and r5 to r7 during the progress of resistance welding are individually obtained and subtracted from the actual value of the inter-chip resistance R. As a result, the actual value of the contact resistance r4 can be obtained.

  Here, the first electrode tip 12, the workpieces W1 and W2, and the second electrode tip 14 rise in temperature during resistance welding (energization). Along with this, the resistances r1, r3, r5, r7 increase. Therefore, in order to obtain the contact resistance r4 with high accuracy, it is necessary to obtain the values of the resistors r1, r3, r5, r7 during the resistance welding with high accuracy.

  Therefore, prior to performing welding resistance, the temperature dependence of the resistance r1 of the first electrode tip 12 is obtained. Specifically, the resistance value of the first electrode chip 12 may be measured while changing the temperature. Similarly, the temperature dependence of the resistances r3 and r5 of the workpieces W1 and W2 and the resistance r7 of the second electrode chip 14 is obtained.

  On the other hand, the contact resistance r2 between the first electrode tip 12 and the workpiece W1 and the contact resistance r6 between the workpiece W2 and the second electrode tip 14 are the first electrode tip 12 with respect to the workpieces W1 and W2 softened by the start of resistance welding. The second electrode tip 14 is changed by being embedded (in other words, the contact area is increased). Therefore, as described above, in accordance with the description in Patent Document 3, the contact areas of the first electrode chip 12 and the second electrode chip 14 with respect to the workpieces W1 and W2 and the incident waves of the ultrasonic waves to the workpieces W1 and W2 The correlation with the rate is obtained in advance. In the following description, the incident wave rate at the first electrode chip 12 is referred to as a first incident wave rate, and the incident wave rate at the second electrode chip 14 is referred to as a second incident wave rate.

  Furthermore, ultrasonic waves are respectively transmitted from the first transmitter / receiver 16 and the second transmitter / receiver 18 in the first electrode chip 12 and the second electrode chip 14. At this time, each of the first electrode chip 12 and the second transceiver 18 is not in contact with the workpiece W1 or the workpiece W2. Accordingly, all of the ultrasonic waves reaching the tips of the first electrode chip 12 and the second transmitter / receiver 18 are reflected by a medium such as air or vacuum having a large difference in acoustic impedance, and the first reflected wave and the second reflected wave, respectively. Return to the first transceiver 16 and the second transceiver 18 as waves. The intensities of the first reflected wave and the second reflected wave are measured by the echo measuring device 20 and transmitted to the control circuit 24 as information. The control circuit 24 stores the intensity of the first reflected wave and the second reflected wave at this time as the first intensity and the second intensity.

  Next, when the robot operates, the workpieces W1 and W2 stacked on each other are inserted between the first electrode tip 12 and the second electrode tip 14 of the welding gun. Of course, the welding gun is open at this point, and therefore the first electrode tip 12 and the second electrode tip 14 are separated from the workpieces W1 and W2.

  Next, the welding gun is closed, the tip of the first electrode tip 12 comes into contact with the upper workpiece W1, and the tip of the second electrode tip 14 comes into contact with the lower workpiece W2. That is, the workpieces W1 and W2 are sandwiched between the first electrode chip 12 and the second electrode chip 14.

  At this time, an ultrasonic wave is transmitted from the first transmitter / receiver 16 toward the second transmitter / receiver 18. The control circuit 24 stores the propagation time from transmission to reception of the transmitted wave that has been transmitted through the workpieces W1 and W2 and received by the second transmitter / receiver 18. The control circuit 24 further calculates the velocity (sound velocity) of the transmitted wave from the propagation time and the total thickness of the workpieces W1 and W2. The total thickness of the workpieces W1 and W2 is equal to the inter-chip distance D between the first electrode chip 12 and the second electrode chip 14 obtained by the encoder 22.

  Next, a voltage is applied to the first electrode chip 12 and the second electrode chip 14, and energization is performed between the first electrode chip 12 and the second electrode chip 14. Of course, along with this, current passes through the workpieces W1 and W2, and as a result, the interface between the workpieces W1 and W2 is melted. That is, the melting part 30 is generated.

  Simultaneously with the energization, ultrasonic waves are retransmitted from the first transceiver 16. At this time, a part of the ultrasonic waves is incident on the inside of the work W1 from a portion in contact with the work W1 at the tip of the first electrode chip 12. On the other hand, even if it is a site where the ultrasonic wave can be incident on the workpiece W1 in the first electrode chip 12 (hereinafter also referred to as an ultrasonic wave incident-possible site), it is super in a region that is not in contact with the workpiece W1. Sound waves are reflected. Further, even an ultrasonic wave that has reached a portion in contact with the workpiece W1 is partially reflected without being incident on the workpiece W1. A third reflected wave is generated by such reflection and returns to the first transceiver 16.

  The third reflected wave is received by the first transceiver 16. The echo measuring instrument 20 measures the intensity of the third reflected wave at this time. The control circuit 24 stores the intensity of the third reflected wave at this time as the third intensity.

  Similarly to the above, ultrasonic waves are retransmitted from the second transceiver 18. A part of the ultrasonic waves is incident on the inside of the work W2 from a portion in contact with the work W2 at the tip of the second electrode chip 14. On the other hand, even if it is a site where the ultrasonic wave can be incident on the second electrode chip 14, the ultrasonic wave is reflected at a site that is not in contact with the workpiece W2. Further, even an ultrasonic wave that has reached a portion in contact with the workpiece W2 is partially reflected without being incident on the workpiece W2. A fourth reflected wave is generated by such reflection and returns to the second transceiver 18.

The control circuit 24 determines the first intensity of the first reflected wave and the third intensity of the third reflected wave, the second intensity of the second reflected wave, and the fourth intensity of the fourth reflected wave, measured as described above. Then, the first intensity ratio (first reflected wave rate) and the second intensity ratio (second reflected wave rate) are calculated. For this calculation, the following formulas (2) and (3) are used.
First intensity ratio = third intensity / first intensity (2)
Second intensity ratio = fourth intensity / second intensity (3)

  For example, even if the welding gun is closed, if the first electrode tip 12 is not in contact with the workpiece W1 due to malfunction of the welding gun, all ultrasonic waves are reflected at the tip of the first electrode tip 12. Therefore, the third intensity becomes equal to the first intensity, and the first intensity ratio obtained by the above equation (2), in other words, the first reflected wave rate is 1.

  On the other hand, when the first electrode tip 12 is in contact with the workpiece W1, ultrasonic waves are incident on the workpiece W1. If the intensity of the third reflected wave is zero, the first intensity ratio (first reflected wave rate) is zero, so that all of the ultrasonic waves are incident on the workpiece W1. In this case, it is evaluated that the ultrasonic incident portion of the first electrode chip 12 is in contact with the workpiece W1 over the entire area, and the total area of the ultrasonic incident portion is equal to the contact area.

  Of course, the second electrode chip 14 is evaluated in the same manner based on the numerical value of the second intensity ratio (second reflected wave rate).

  Actually, immediately after the first electrode tip 12 and the second electrode tip 14 are brought into contact with the workpieces W1 and W2 and energization is started, the temperatures of the workpieces W1 and W2 do not increase so much. For this reason, the workpieces W1 and W2 are not softened at this time, and therefore, the first electrode tip 12 and the second electrode tip 14 only have their pole tips in contact with the workpieces W1 and W2.

  That is, the entire area of the ultrasonic wave incident possible portion of the first electrode chip 12 and the second electrode chip 14 is not necessarily in contact with the workpieces W1 and W2. As can be understood from this, in particular, immediately after the start of resistance welding, the total area and the contact area of the ultrasonic incident portion are not always equal.

Therefore, the control circuit 24 uses the following formulas (4) and (5) based on the first and second intensity ratios (first and second reflected wave ratios) to generate the first incident wave rate and the second incident wave wave. Calculate the rate.
First incident wave rate = 1-first intensity ratio
= 1-third strength / first strength (4)
Second incident wave rate = 1-second intensity ratio
= 1−4th strength / second strength (5)

  For example, when the intensity of the first reflected wave and the third reflected wave is 100 and 20, respectively, the intensity ratio calculated according to the above equation (3) is 0.2. This means that 20% of the ultrasonic wave transmitted by the first transmitter / receiver 16 during resistance welding is reflected as the third reflected wave.

  Then, when the first incident wave rate is obtained according to the equation (4), it is 0.8. That is, in this case, 80% of the ultrasonic wave transmitted from the first transmitter / receiver 16 is incident on the workpiece W1. The control circuit 24 obtains the contact area of the first electrode chip 12 with respect to the workpiece W1 when the first incident wave rate is 80% from the correlation obtained in advance.

  The control circuit 24 further obtains the contact resistance r2 between the first electrode chip 12 and the workpiece W1 based on the contact area obtained as described above. Of course, the contact area of the second electrode tip 14 with respect to the workpiece W2 and the contact resistance r6 between the second electrode tip 14 and the workpiece W2 are obtained by the control circuit 24 in the same manner.

  The control circuit 24 further obtains respective values of the resistance r1 of the first electrode tip 12, the resistances r3 and r5 of the workpieces W1 and W2, and the resistance r7 of the second electrode tip 14 during resistance welding.

  Here, if the temperature of the 1st electrode tip 12 and the 2nd electrode tip 14 rises with progress of resistance welding, these 1st transmitter-receiver 16 and the 2nd transmitter-receiver 18 will transmit these ultrasonic waves after transmitting. The time until the third reflected wave and the fourth reflected wave return to the transceiver 16 and the second transceiver 18 changes. This is because, as is well known, the higher the temperature, the slower the sound speed.

  The correlation between temperature and the speed of sound of ultrasonic waves is known. Accordingly, after the first transmitter / receiver 16 and the second transmitter / receiver 18 transmit ultrasonic waves, the third reflected wave and the fourth reflected wave return to the first transmitter / receiver 16 and the second transmitter / receiver 18. The speed of sound can be calculated based on this time, and the temperatures of the first electrode chip 12 and the second electrode chip 14 can be determined from the correlation between the calculated speed of sound and temperature.

  Then, the temperature dependence of the temperatures of the first electrode chip 12 and the second electrode chip 14 obtained in this way and the resistance values of the first electrode chip 12 and the second electrode chip 14 obtained in advance as described above. Based on the above, it is possible to accurately determine the actual value of the resistance r1 of the first electrode chip 12 and the actual value of the resistance r7 of the second electrode chip 14 at the temperature.

  On the other hand, when the temperature of the workpieces W1 and W2 increases as the resistance welding progresses, the total thickness of the workpieces W1 and W2 changes as the workpieces W1 and W2 undergo thermal expansion. Correspondingly, the inter-chip distance D between the first electrode chip 12 and the second electrode chip 14 also changes. The inter-chip distance D changing in this way is measured one by one by the encoder 22 and sent to the control circuit 24 as information.

  The control circuit 24 further determines the first electrode chip 12, the first electrode chip 12 from the time from when the first transmitter / receiver 16 starts transmitting ultrasonic waves until the second transmitter / receiver 18 receives the first transmitted wave after energization is started. The propagation time of the first transmitted wave in the two-electrode chip 14 is subtracted to determine the propagation time for the transmitted wave to pass through the workpieces W1 and W2. Based on the propagation time in the workpieces W1 and W2 and the inter-chip distance D after the change, the sound speed in the workpieces W1 and W2 is calculated.

  The propagation time of the first transmitted wave in the first electrode chip 12 is first obtained as the time from when the first transmitter / receiver 16 transmits an ultrasonic wave until the first transmitter / receiver 16 receives the third reflected wave. Then, this time can be calculated by multiplying by 1/2. Similarly, the propagation time of the first transmitted wave in the second electrode chip 14 is also the distance from the second transmitter / receiver 18 to the interface of the work W2, and the second transmitter / receiver 18 after the second transmitter / receiver 18 transmits ultrasonic waves. The time until 18 receives the fourth reflected wave is obtained, and this time is calculated by multiplying by 1/2.

  The sound speed obtained as described above is slower than the sound speed before starting energization. This is because, as described above, the sound speed becomes slower as the temperature becomes higher.

  Therefore, the control circuit 24 can obtain the temperatures of the workpieces W1 and W2 at this time based on the correlation (known) between the temperature and the sound speed in the workpieces W1 and W2. Then, the control circuit 24 determines the work W1, W2 when the ultrasonic wave is transmitted based on the obtained temperature and the temperature dependence of the resistances r3, r5 of the work W1, W2 stored in advance by the control circuit 24. The actual values of the resistors r3 and r5 are obtained.

  As described above, the contact resistance r2 between the first electrode tip 12 and the workpiece W1 when the ultrasonic wave is transmitted, the contact resistance r6 between the workpiece W2 and the second electrode tip 14, the first electrode tip 12, the workpiece W1, The actual values of W2 and the respective resistances r1, r3, r5, r7 of the second electrode chip 14 are obtained.

  On the other hand, the actual value of the inter-chip resistance R is actually measured. For this reason, the actual value of the inter-chip resistance R and the actual values of the resistors r1 to r3 and r5 to r7 are known. Therefore, the actual value of the contact resistance r4 between the workpieces W1 and W2 can be obtained with high accuracy by substituting the actual value into the above equation (1).

  As described above, the correlation (see FIG. 2) between the contact resistance r4 and the diameter of the melted part 30 is input to the control circuit 24 in advance. Therefore, the control circuit 24 (see FIG. 1) can determine the diameter of the melted part 30 in real time from the actual value of the contact resistance r4 obtained as described above.

  In the technique described in Patent Document 3, the contact areas of the first electrode tip 12 and the second electrode tip 14 with respect to the workpieces W1 and W2 change with the progress of resistance welding, and thereby the contact resistances r2 and r6 change. The degree of growth of the melted part 30 is evaluated in consideration of the above. On the other hand, in the present embodiment, not only the contact resistances r2 and r6 but also the resistances r1, r3, r5, and r7 change as the temperature of the first electrode tip 12, the workpieces W1, W2, and the second electrode tip 14 rises. In addition, the resistances r1 to r3, r5 to r7, and eventually the contact resistance r4 are obtained in real time, and then the degree of growth of the melted portion 30 is evaluated.

  Therefore, the actual value of the contact resistance r4 between the workpieces W1 and W2 can be obtained with high accuracy. For this reason, the diameter of the fusion | melting part 30 can be calculated | required with still higher precision, and the degree of growth of the fusion | melting part 30 can be evaluated with higher precision after all.

  For example, temperature measuring means such as a radiation thermometer may be provided. In this case, whether the resistances r3 and r5 of the workpieces W1 and W2 have decreased due to the pressure contact by determining that the melted portion 30 has been generated when the temperatures of the workpieces W1 and W2 exceed a predetermined threshold, or There exists an advantage that it becomes easy to distinguish whether it fell with the production | generation of the fusion | melting part 30. FIG.

  In the above-described embodiment, the case where two workpieces W1 and W2 are resistance-welded is described as an example. However, the number of workpieces is not particularly limited to this. For example, the number of workpieces is three. Also good. In this case, it is possible to recognize the degree of growth of the melted part from the propagation time of the reflected wave that is reflected back to the melted part.

DESCRIPTION OF SYMBOLS 10 ... Resistance welding apparatus 12, 14 ... Electrode tip 16, 18 ... Transmitter / receiver 20 ... Echo measuring device 22 ... Encoder 24 ... Control circuit 30 ... Melting part W1, W2 ... Workpiece

Claims (3)

It is a resistance welding method of energizing between a first electrode tip and a second electrode tip sandwiching a plurality of workpieces and welding the workpieces,
During the resistance welding, a step of obtaining an inter-chip resistance value from the first electrode tip to the second electrode tip in a state of sandwiching the plurality of workpieces;
Obtaining each resistance value of the first electrode chip and the second electrode chip based on the temperature dependence of the resistance of the first electrode chip and the second electrode chip;
A first contact resistance value between the first electrode tip and the workpiece in contact with the first electrode tip is obtained based on a contact area of both, and the workpiece in contact with the second electrode tip and the second electrode tip A step of obtaining a second contact resistance value based on both contact areas;
Obtaining a resistance value of each of the plurality of workpieces based on the temperature dependence of the resistance of the workpieces;
Subtracting each resistance value of the first electrode chip and the second electrode chip, the first contact resistance value and the second contact resistance value, and each resistance value of the plurality of workpieces from the inter-chip resistance value, Obtaining a contact resistance value between the workpieces;
The resistance welding method characterized by having.   The resistance welding method according to claim 1, wherein a correlation between a contact resistance value between the workpieces and a diameter of a melted portion formed between the workpieces is obtained in advance, and from an actual contact resistance value between the workpieces. The resistance welding method is characterized in that the diameter of the molten part is obtained. A resistance welding device for energizing between a first electrode tip and a second electrode tip sandwiching a plurality of workpieces and welding the workpieces,
A controller for controlling energization between the first electrode chip and the second electrode chip;
The control unit, during the resistance welding, the inter-chip resistance value from the first electrode tip in a state of sandwiching the plurality of workpieces to the second electrode tip,
Each resistance value based on the temperature dependence of the resistance of the first electrode chip and the second electrode chip;
A first contact resistance value between the first electrode tip and the workpiece based on a contact area between the first electrode tip and the workpiece; and a first contact resistance value between the second electrode tip and the workpiece. A second contact resistance value between the two-electrode tip and the workpiece;
Each resistance value based on the temperature dependence of the resistance of the plurality of workpieces,
Seeking
Further, from the inter-chip resistance value, the resistance values of the first electrode chip and the second electrode chip, the first contact resistance value and the second contact resistance value, and the resistance values of the plurality of workpieces are obtained. A resistance welding apparatus characterized by subtracting and obtaining a contact resistance value between the workpieces.

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