JP2006326656A - Resistance welding machine, and method for deciding normal/defective condition of resistance welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of accurately deciding normal/defective condition of resistance welding during or immediately after the implementation without being least affected by external disturbance or the like. <P>SOLUTION: The resistance welding machine comprises: a first welding electrode; a second welding electrode; an energizing means for making a welding current flow between the first and second welding electrodes through a workpiece; a ultrasonic transmitter installed on the first welding electrode side; a ultrasonic receiver installed on the second welding electrode side; and an inter-electrode timer that measures time from the point of time at which the ultrasonic transmitter transmits a ultrasonic wave until the point of time at which the ultrasonic receiver receives it. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for determining the quality of resistance welding. In particular, the present invention relates to a technique for determining whether or not resistance welding is currently being performed or has just been performed using ultrasonic waves.

In resistance welding, a welding current is applied to a plurality of workpieces (materials to be welded) arranged in a superimposed manner, the workpieces are melted by resistance heat generated between the workpieces, and the workpieces are joined to each other. The joint strength of resistance welding corresponds to the size of the melted portion (so-called nugget) formed between the workpieces. In general, the quality of resistance welding can be determined based on the size of the nugget.
Techniques have been developed for determining the quality of resistance welding currently being performed using ultrasonic waves. For example, Patent Document 1 discloses a technique for transmitting an ultrasonic wave from one welding electrode, receiving the transmitted ultrasonic wave at the other welding electrode, and estimating the size of the melted portion formed from the intensity change of the received wave. Is disclosed.
Japanese Patent Laid-Open No. 52-150760

In the technique of Patent Document 1, the size of the melted portion is estimated by utilizing the fact that the intensity of ultrasonic waves that pass through the melted portion changes as the melted portion grows. However, since the intensity of the received ultrasonic wave is easily affected by disturbances and the like, the size of the melted part may be erroneously estimated.
The present invention solves the above problems. The present invention provides a technique capable of correctly determining whether or not resistance welding is being performed or is being performed immediately without being affected by disturbance or the like as much as possible.

  The technique of the present invention can be embodied in a resistance welder. The resistance welding machine is provided on the first welding electrode side, a first welding electrode, a second welding electrode, an energizing means for energizing a welding current through the material to be welded between the first welding electrode and the second welding electrode, and the first welding electrode side. The ultrasonic wave receiving means, the ultrasonic wave receiving means provided on the second welding electrode side, and the ultrasonic wave receiving means receive the ultrasonic waves from the time when the ultrasonic wave transmitting means transmits the ultrasonic waves. Inter-electrode time measuring means for measuring the time until the time is provided. The term “interelectrode timing means” is used to mean a means for measuring the time required for the ultrasonic wave to propagate between the electrodes.

The propagation speed of the ultrasonic wave propagating in the substance changes depending on the temperature of the substance. FIG. 10 shows an example of this, and shows the relationship between the temperature of the workpiece (workpiece) and the ultrasonic wave propagation speed in the workpiece. As shown in FIG. 10, the higher the temperature of the material to be welded, the slower the propagation speed of the ultrasonic wave. Therefore, the temperature of the welded material can be estimated based on the propagation speed of the ultrasonic wave in the welded material.
The size (so-called nugget diameter) of the melted portion formed in the workpiece is changed depending on the temperature of the workpiece (particularly the temperature at the joint surface). FIG. 11 shows an example of this, and shows the relationship between the temperature of the material to be welded and the nugget diameter formed in the material to be welded. As shown in FIG. 11, the higher the temperature of the material to be welded, the larger the nugget diameter formed in the material to be welded. Therefore, the nugget diameter formed in the material to be welded can be estimated based on the temperature of the material to be welded.
From the above, if the propagation speed of the ultrasonic wave in the welded material can be known, the diameter of the nugget formed in the welded material can be estimated. The quality of resistance welding can be determined based on the estimated nugget diameter.

In this resistance welding machine, an ultrasonic wave is transmitted from the first welding electrode side, the ultrasonic wave is received at the second welding electrode side, and the ultrasonic wave passes through the material to be welded from the first welding electrode side to perform the second welding. The transmission time to reach the electrode side can be measured. Since the measured transmission time corresponds to the propagation speed at which the ultrasonic wave propagates through the workpiece, the measured transmission time corresponds to the temperature of the workpiece. Therefore, based on the measured transmission time, the nugget diameter formed in the material to be welded can be estimated, and the quality of resistance welding can be determined. Whether the resistance welding is good or bad can be determined during energization or immediately after energization.
In this resistance welding machine, when receiving the ultrasonic wave on the second welding electrode side, it is not necessary to identify the intensity of the ultrasonic wave, and it is sufficient to detect the reception of the ultrasonic wave. Even if the reception intensity of the ultrasonic wave fluctuates due to disturbance or the like, the pass / fail judgment does not fluctuate following it.
According to this resistance welder, it is possible to correctly determine whether or not resistance welding is being performed or is being performed immediately without being affected by disturbance or the like as much as possible.

In the above resistance welding machine, it is preferable that a time measuring unit for determining whether or not the time measured by the inter-electrode time measuring unit is within a reference range is added.
The measured transmission time and the nugget diameter formed in the material to be welded substantially correspond. Therefore, the reference range of the transmission time to be timed can be determined based on the nugget diameter or the like that provides the required bonding strength. By determining whether or not the measured transmission time is within the reference range, it can be determined whether or not resistance welding has been performed normally.

The determination means preferably corrects the reference range based on the time measured by the inter-electrode time measuring means before energization of the welding current.
The transmission time measured by the time measuring means also varies depending on the thickness of the material to be welded and the length of the welding electrode. Therefore, when a manufacturing error occurs in the thickness of the material to be welded or when the welding electrode is worn, it is necessary to correct the reference range regarding the transmission time.
In this resistance welding machine, the transmission time before the temperature of the workpiece is increased is grasped by measuring the transmission time before energization of the welding current. The transmission time before the temperature rise varies mainly depending on the thickness of the material to be welded and the length of the welding electrode. By correcting the reference range related to the transmission time based on the transmission time before the temperature rise, even if there is a manufacturing error in the thickness of the material to be welded or if the welding electrode is worn, The quality of resistance welding can be correctly determined.

The energizing means preferably adjusts the welding current to increase or decrease based on the determination result of the determining means. Alternatively, it is preferable to adjust the energizing time of the welding current to be longer or shorter based on the determination result of the determining means.
Thereby, it is possible to prevent the resistance welding from being ended with a defect.

  In the above resistance welding machine, the ultrasonic wave receiving means provided on the first welding electrode side, the ultrasonic wave transmission means provided on the second welding electrode side, and the ultrasonic wave transmission on the first welding electrode side A first electrode-side time measuring means for measuring a time from when the means transmits ultrasonic waves until the ultrasonic receiving means on the first welding electrode side receives ultrasonic waves; and an ultrasonic transmission means on the second welding electrode side. It is preferable that a second electrode-side time measuring unit for measuring a time from when the ultrasonic wave is transmitted until the ultrasonic receiving unit on the second welding electrode side receives the ultrasonic wave is preferably added.

The transmission time measured by the interelectrode timing means includes the time required for the ultrasonic wave to propagate between the ultrasonic transmission means on the first welding electrode side and the tip of the first welding electrode, and the ultrasonic wave It includes the time required to penetrate the workpiece and the time required for the ultrasonic wave to propagate between the tip of the second welding electrode and the ultrasonic receiving means on the second welding electrode side. If the actual transmission time required for the ultrasonic wave to pass through the material to be welded can be extracted, the quality of resistance welding can be more correctly determined without being affected by the temperature or wear of the welding electrode.
In this resistance welding machine, the ultrasonic wave transmitted by the ultrasonic transmission means on the first welding electrode side is transmitted through the material to be welded and propagates to the second welding electrode side, and is reflected at the tip of the first welding electrode. Is also received by the ultrasonic wave receiving means on the first welding electrode side. Therefore, the time measured by the first electrode side time measuring means corresponds to the time required for the ultrasonic wave to propagate between the ultrasonic transmitting means on the first welding electrode side and the tip of the first welding electrode. To do. Similarly, the time measured by the second electrode side time measuring means corresponds to the time required for ultrasonic waves to propagate between the tip of the second welding electrode and the ultrasonic receiving means on the second welding electrode side. .
Based on the transmission time measured by the interelectrode time measuring means, the time measured by the first electrode side time measuring means, and the time time measured by the second electrode side time measuring means, the ultrasonic wave passes through the workpiece. It is possible to calculate the time required for.
According to this resistance welder, it is possible to accurately grasp the time required for the ultrasonic wave to penetrate the workpiece, so that the resistance welding can be properly performed without being affected by the temperature or wear of the welding electrode. Can be determined.

In the resistance welding machine, the ultrasonic wave calculated from the time measured by the inter-electrode time measuring means, the time measured by the first electrode-side time measuring means, and the time measured by the second electrode-side time measuring means is It is preferable that a transmission time determination means for determining whether or not the actual transmission time required for passing through the workpiece is within a predetermined reference range is added.
By determining whether or not the calculated actual transmission time is within the reference range, it is possible to more correctly determine whether or not resistance welding has been performed normally.

The determining means may correct the calculated actual transmission time and / or the reference range based on the time measured by the first electrode side time measuring means and the time measured by the second electrode side time measuring means. preferable.
If the temperature distribution in the plate thickness direction (energization direction) of the material to be welded is biased, the obtained bonding strength may be lower than the ultimate temperature of the material to be welded. The temperature distribution in the plate thickness direction (energization direction) of the material to be welded can be estimated by the balance between the temperature of the first welding electrode and the temperature of the second welding electrode. When the balance between the temperature of the first welding electrode and the temperature of the second welding electrode is inappropriate, sufficient bonding strength may not be obtained. Necessary.
The time measured by the first electrode side time measuring means varies depending on the temperature of the first electrode. Therefore, the time measured by the first electrode side time measuring means substantially corresponds to the temperature of the first electrode. Similarly, the time measured by the second electrode side time measuring means substantially corresponds to the temperature of the second electrode.
In this resistance welding machine, it was necessary for the calculated ultrasonic wave to pass through the workpiece based on the time measured by the first electrode side time measuring means and the time measured by the second electrode side time measuring means. The actual transmission time can be corrected. Alternatively, the reference range for the actual transmission time can be corrected. Accordingly, when it is estimated that the temperature distribution in the plate thickness direction of the welded member is deviated based on the time measured by the first electrode side time measuring means and the time measured by the second electrode side time measuring means, It is possible to determine whether the resistance welding is good or not after increasing the temperature to be reached.

The technique of the present invention can also be embodied in a method for determining the quality of resistance welding during or immediately after implementation. This determination method includes a transmission step of transmitting ultrasonic waves from one welding electrode side, a reception step of receiving ultrasonic waves on the other welding electrode side, and an ultrasonic wave in the reception step from the time when ultrasonic waves are transmitted in the transmission step. And a determination step of determining whether or not the time measured in the time measurement step is within a predetermined range.
According to this determination method, the quality of resistance welding during or immediately after the execution can be correctly determined without being affected by disturbances or the like as much as possible.

  According to the present invention, it is possible to accurately determine the quality of resistance welding in the process, and it is possible to improve manufacturing quality and reduce manufacturing cost.

First, the main features of the embodiments described below are listed.
(Mode 1) The resistance welder includes a first ultrasonic transducer provided on the first welding electrode and a second ultrasonic transducer provided on the second welding electrode.
(Mode 2) The resistance welder uses a reference value for the transmission time required for the ultrasonic wave to pass through the workpiece from the first ultrasonic transducer and propagate to the second ultrasonic transducer as a function of the energization time of the welding current. Remember by.
(Mode 3) The resistance welding machine determines that the resistance welding is correctly completed with respect to the transmission time required for the ultrasonic wave to pass through the workpiece from the first ultrasonic transducer and propagate to the second ultrasonic transducer. The completion reference value is stored.
(Mode 4) The resistance welding machine is a normal value with respect to the transmission time required for the ultrasonic wave to propagate from the first ultrasonic transducer to the second ultrasonic transducer and to the second ultrasonic transducer before the start of energization of the welding current. A certain starting reference value is stored.

Example 1
Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows the configuration of a resistance welder according to a first embodiment in which the technique of the present invention is implemented. As shown in FIG. 1, the resistance welding machine 2 of the present embodiment generates a welding current between the first electrode 10, the second electrode 20 facing the first electrode 10, and the pair of welding electrodes 10 and 20. A power supply circuit 42 for energizing is provided. Although not shown, the welding electrodes 10 and 20 are provided in a moving device such as a robot arm. The moving device moves the pair of welding electrodes 10 and 20 to a welding location, or moves the pair of welding electrodes 10 and 20 closer to or away from each other. Although the moving device is not an essential component in the resistance welder 2, since it is necessary to operate in synchronization with the resistance welder 2, the resistance welder 2 may include a moving device.
Like the conventional resistance welding machine, the resistance welding machine 2 makes a pair of welding electrodes 10 and 20 contact from both sides of the workpiece W1 and the workpiece W2 that are arranged in a superimposed manner, and welds between the pair of welding electrodes 10 and 20. Energize current. When a welding current is applied between the workpieces W1 and W2, heat generation due to electric resistance occurs in the workpieces W1 and W2 (particularly the contact surfaces of the workpieces W1 and W2). As a result, a melted portion (so-called nugget) N is generated over the workpieces W1 and W2, and the workpieces W1 and W2 are welded. The joint strength when the workpieces W1 and W2 are welded varies depending on the size of the generated nugget N. It is known that the size of the generated nugget N depends on the temperature reached by the workpieces W1 and W2 when a welding current is passed through the workpieces W1 and W2. The ultimate temperature of the workpieces W1 and W2 varies depending on, for example, the welding current, the energization time, the contact force that causes the welding electrodes 10 and 20 to contact the workpieces W1 and W2, and the like. These parameters are set based on the dimensions (plate thickness) of the workpieces W1 and W2, the material of the workpieces W1 and W2, the required bonding strength, and the like.

As shown in FIG. 1, in the resistance welding machine 2 of the present embodiment, the first ultrasonic transducer 12 is provided on the first electrode 10 side, and the second ultrasonic transducer 22 is provided on the second electrode 22 side. Is provided. The ultrasonic transducers 12 and 22 are configured using piezoelectric elements, and can vibrate by an input electric signal (vibration voltage) and transmit ultrasonic waves. Further, the ultrasonic transducers 12 and 22 can vibrate by receiving ultrasonic waves and can output an electric signal (vibration voltage). The first ultrasonic transducer 12 is disposed toward the second ultrasonic transducer 22, and the second ultrasonic transducer 22 is disposed toward the first ultrasonic transducer 12. Thereby, the first ultrasonic transducer 12 can transmit ultrasonic waves toward the welding position of the workpieces W <b> 1 and W <b> 2 (the position where the nugget N is formed) and the second ultrasonic transducer 22. Further, the first ultrasonic transducer 12 can receive with high sensitivity the ultrasonic wave transmitted from the second ultrasonic transducer 22 and passed through the welding positions of the workpieces W1 and W2 (nugget N formation position). it can. Similarly, the second ultrasonic transducer 22 can transmit ultrasonic waves toward the welding position of the workpieces W <b> 1 and W <b> 2 (position where the nugget N is formed) and the first ultrasonic transducer 12. Further, the second ultrasonic transducer 22 can receive the ultrasonic wave transmitted from the first ultrasonic transducer 12 and passed through the welding positions of the workpieces W1 and W2 (the nugget N formation position) with high sensitivity. it can.
The attachment positions of the first ultrasonic transducer 12 and the first ultrasonic transducer 22 shown in FIG. 1 are merely examples, and are not limited to this. For example, it can be attached to an electrode tip provided in each electrode 10, 20 or a shank for fixing the electrode tip.

The resistance welder 2 includes a transmission circuit 14, a reception circuit 26, a transmission time measuring circuit 32, a determination circuit 38, a display device 34, a controller 50, and the like.
The transmission circuit 14 is connected to the first ultrasonic transducer 12. The transmission circuit 14 is a circuit that transmits ultrasonic waves from the first ultrasonic transducer 12 by outputting an electrical signal to the first ultrasonic transducer 12. On the other hand, the transmission circuit 14 is also connected to a transmission time measuring circuit 32. The transmission circuit 14 outputs a transmission timing signal to the transmission time measuring circuit 32 simultaneously with the timing of outputting the ultrasonic transmission electrical signal to the first ultrasonic transducer 12.
The receiving circuit 26 is connected to the second ultrasonic transducer 22. The reception circuit 26 is a circuit that detects that the second ultrasonic transducer 22 has received an ultrasonic wave by inputting an electrical signal output from the second ultrasonic transducer 22. The receiving circuit 26 only needs to detect that the second ultrasonic transducer 22 has received the ultrasonic wave, and does not necessarily need to identify the intensity of the received ultrasonic wave. On the other hand, the receiving circuit 26 is also connected to a transmission time measuring circuit 32. The reception circuit 26 outputs a reception timing signal to the transmission time measuring circuit 32 at the same time as the electric signal is input from the second ultrasonic transducer 22.
In the resistance welder 2, the first ultrasonic transducer 12 functions as an ultrasonic transmission transducer, and the second ultrasonic transducer 22 functions as an ultrasonic reception transducer. As is apparent from FIG. 1, the ultrasonic wave transmitted from the first ultrasonic transducer 12 propagates in order through the first electrode 10, the workpiece W <b> 1, the workpiece W <b> 2, and the second electrode 20, and the second ultrasonic transducer 22. Received by.

The transmission time measuring circuit 32 is a circuit that measures the time from when the ultrasonic wave is transmitted from the first ultrasonic transducer 12 to when the ultrasonic wave is received by the second ultrasonic transducer 22. That is, the time required for the ultrasonic wave to reach the second ultrasonic transducer 22 from the first ultrasonic transducer 12 through the first electrode 10 and the workpieces W1 and W2 and the second electrode 20 is measured. Circuit. The transmission time measuring circuit 32 measures the transmission time of this ultrasonic wave by measuring from the time when the transmission timing signal is input from the transmission circuit 14 to the time when the reception timing signal is input from the reception circuit 26.
The determination circuit 38 is connected to the transmission time timer circuit 32 and inputs the transmission time measured by the transmission time timer circuit 32. The determination circuit 38 determines the quality of the welding applied to the workpieces W1 and W2 based on the transmission time measured by the transmission time measuring circuit 32.

Here, the principle of determining the quality of the welding applied to the workpieces W1 and W2 based on the measured transmission time will be described with reference to FIGS. FIG. 10 is a graph showing the relationship between the temperature of the workpieces W1 and W2 and the ultrasonic wave propagation speed in the workpieces W1 and W2. FIG. 11 shows the relationship between the temperature of the workpieces W1 and W2 during welding and the size of the nugget formed (so-called nugget diameter). Here, each of the workpieces W1 and W2 is a cold-rolled steel plate (SPC material), and the plate thickness thereof is 1.2 mm.
As shown in FIG. 10, the propagation speed of the ultrasonic waves in the workpieces W1 and W2 varies depending on the temperatures of the workpieces W1 and W2. Specifically, the higher the temperature of the workpieces W1 and W2, the slower the propagation speed of the ultrasonic waves in the workpieces W1 and W2. Therefore, if the workpieces W1 and W2 have the same thickness, the longer the measured transmission time is, the slower the propagation speed of the ultrasonic waves in the workpieces W1 and W2 is. Means high. From this, it becomes possible to estimate the temperatures of the workpieces W1 and W2 based on the measured transmission time.
On the other hand, as shown in FIG. 11, the nugget diameter formed during welding varies depending on the temperatures of the workpieces W1 and W2. Specifically, nugget generation starts when the temperature of the workpieces W1 and W2 exceeds a predetermined temperature (melting point), and the higher the temperature of the workpieces W1 and W2, the larger the nugget diameter formed. From this, the diameter of the nugget formed can be estimated based on the temperatures of the workpieces W1 and W2. Since the temperature of the workpieces W1 and W2 can be estimated based on the measured transmission time as described above, the formed nugget diameter is estimated based on the measured transmission time. Can do. Specifically, it can be estimated that the longer the measured transmission time, the larger the nugget diameter.

The determination circuit 38 in FIG. 1 stores a reference value related to the transmission time in order to determine the quality of welding based on the measured transmission time. FIG. 2 shows an example of a reference value related to the transmission time stored in the determination circuit 38. As shown in FIG. 2, the determination circuit 38 stores a reference value related to the transmission time as a function (curve A) of the energization time t. The curve A shown in FIG. 2 is referred to as a reference transition curve A related to the transmission time. In FIG. 2, the energization time 0 indicates the time when the welding current is started to be applied to the workpieces W1 and W2, and the energization time t4 indicates the time when the energization is finished. That is, the energization time of the planned welding current is t4. As the energization time elapses, the temperature of the workpieces W1 and W2 increases, so that the reference value for the transmission time also increases. For example, if the measured transmission time exceeds the reference transmission time P6 at the end of energization t4, the workpieces W1 and W2 have reached a predetermined temperature, and as a result, a nugget of a predetermined size is formed. Can be determined. Hereinafter, the reference value P1 of the transmission time for the welding current energization start time t = 0 may be referred to as a start reference value P1, and the reference value P6 of the transmission time for the welding completion time t = t4 may be referred to as a completion reference value P6.
The reference transition curve relating to the transmission time varies depending on the workpiece size, workpiece material, required bonding strength, and the like. The reference transition curve relating to the transmission time can be prepared in advance based on experiments and calculations. The reference transition curve takes into account changes in the propagation speed of ultrasonic waves accompanying changes in temperature of the workpieces W1 and W2, changes in volume of the workpieces W1 and W2 accompanying changes in temperature of the workpieces W1 and W2, and the like. The determination circuit 38 stores a plurality of types of reference transition curves.

The display device 34 is a device for displaying a determination result by the determination circuit 38 and is a device for notifying an operator or the like of the determination result by the determination circuit 38. The display device 34 can display, for example, “welding normal”, “temperature not reached”, “welding abnormality”, and the like.
The controller 50 is a control device that controls the operation of the resistance welding machine 2. The controller 50 stores parameters such as a welding current, an energization time, and an abutting force for bringing the welding electrodes 10 and 20 into contact with the workpieces W1 and W2 for each welding portion to be applied to the workpieces W1 and W2. The controller 50 controls the operation of each part of the resistance welding machine 2 based on the stored welding parameters or the like, or gives an operation command to a moving device provided with the pair of welding electrodes 10 and 20. . Further, the controller 50 is input with the determination result by the determination circuit 38. Although described in detail later, the controller 50 controls the operation of the power supply circuit 42 based on the determination result by the determination circuit 38.

FIG. 3 is a flowchart showing a flow of operations performed by the resistance welder 2. The flow of operation when the resistance welding machine 2 performs resistance welding on the workpieces W1 and W2 will be described along the operation flow shown in FIG.
In step S <b> 2, the work W <b> 1 and the work W <b> 2 that are arranged to overlap are pressed and clamped by the first welding electrode 10 and the second welding electrode 20. As described above, the positions of the first welding electrode 10 and the second welding electrode 20 can be adjusted by a moving device such as a robot arm. The moving device receives an operation command from the controller 50 and pressurizes the workpieces W1 and W2 with the pair of welding electrodes 10 and 20.

In step S4, prior to energizing the welding current, the ultrasonic transmission time before energization is measured. The transmission circuit 14 receives an operation command from the controller 50 and transmits ultrasonic waves from the first ultrasonic transducer 12. At the same time, the transmission circuit 14 outputs a transmission timing signal to the transmission time measuring circuit 32. As shown in FIG. 4A, the ultrasonic wave transmitted from the first ultrasonic transducer 12 passes through the workpieces W 1 and W 2 and is received by the second ultrasonic transducer 22. When the second ultrasonic transducer 22 receives the ultrasonic wave, the reception circuit 26 outputs a reception timing signal to the transmission time measuring circuit 32. The transmission time measuring circuit 32 measures the transmission time of ultrasonic waves from the first ultrasonic transducer 12 to the second ultrasonic transducer 22 based on the transmission timing signal and the reception timing signal. The transmission time measured by the transmission time measuring circuit 32 is output to the determination circuit 38.
Since the ultrasonic transmission time before energization is before the workpieces W1 and W2 are heated, the ultrasonic transmission time varies mainly depending on the distance between the ultrasonic transducers 12 and 22. Therefore, if a manufacturing error occurs in the plate thickness of the workpieces W1 and W2 or the welding electrodes 10 and 20 are worn, the transmission time of the ultrasonic wave before energization varies.
Hereinafter, the subsequent operation flow will be described on the assumption that the measured time value of the transmission time in step S4 is, for example, P2 (see FIG. 2). As shown in FIG. 2, it is assumed that the transmission time P2 is longer than the start reference value P1.

  In step S6, the determination circuit 38 corrects the stored reference transition curve (curve A in FIG. 2) regarding the transmission time based on the transmission time P2 before energization measured in step S4. As shown in FIG. 2, the determination circuit 38 corrects the reference transition curve A based on the difference between the transmission time P2 measured in step S4 and the stored start reference value P1. Specifically, the difference P2-P1 is added to the reference value of the transmission time described by the reference transition curve A to create a new reference transition curve B. Thereby, the completion reference value P6 is corrected to a new completion reference value P7. Here, P7 = P6 + (P2-P1). By the process of step S6, it becomes possible to make an accurate determination without being affected by manufacturing errors occurring in the plate thicknesses of the workpieces W1 and W2, wear due to the welding electrodes 10 and 20, and the like. .

In step S8 of FIG. 3, energization of the welding current is started. The power supply circuit 42 supplies a welding current between the pair of electrodes 10 and 20 in accordance with a command from the controller 50. The workpieces W1 and W2 are rapidly heated by applying a welding current.
In step S10, as shown in FIG. 4B, the ultrasonic transmission time is measured while the welding current is applied. The ultrasonic transmission time is measured in the same manner as step S6 described above. As will be described later, the ultrasonic wave transmission time during energization is repeated over the energization period. FIG. 5 illustrates a change with time in the transmission time during energization (curve C in the figure). A curve B in FIG. 5 shows the corrected reference transition curve B shown in FIG.
Hereinafter, assuming that the current energization time is t3 and the measured value of the transmission time is, for example, Pm3 (FIG. 5), the subsequent operation flow will be described.

  In step S12, the determination circuit 38 determines the transmission time of the ultrasonic wave during energization measured in step S10 based on the corrected reference transition curve B. Specifically, the measured transmission time (here, P3) based on the reference value (here, P3) described by the corrected reference transition curve B with respect to the energization time (here, t3) at the time of measuring the transmission time. Then, Pm3) is determined. If the measured transmission time Pm3 is substantially equal to the reference value P3, it can be determined that the temperatures of the workpieces W1 and W2 are rising as planned, and welding is proceeding normally. If the measured transmission time Pm3 is less than the reference value P3, it can be determined that the temperature rise of the workpieces W1 and W2 is insufficient and the progress of welding is delayed. If the measured transmission time Pm3 exceeds the reference value P3, it can be determined that the temperature rise of the workpiece W1W2 is excessive and the progress of welding is excessively advanced. The determination circuit 38 of this embodiment sets an allowable width ΔP with respect to the reference value P3. Then, if the measured transmission time Pm3 is within the allowable range P3 ± ΔP, it is determined that the temperature is normal, and if the measured transmission time Pm3 is equal to or less than the allowable range P3-ΔP, it is determined that the temperature is insufficient. If the measured transmission time Pm3 is less than or equal to the allowable range P3 + ΔP, it is determined that the temperature is excessive.

In step S14, it is determined whether or not the scheduled energization time has elapsed. If the scheduled energization time t4 has elapsed, the process proceeds to step S16, and if the scheduled energization time has not elapsed, the process proceeds to step S22.
If the scheduled energization time has not elapsed and the process proceeds to step S22, the welding current is increased or decreased based on the determination result of step S12. Specifically, if it is determined that the temperature is insufficient, the welding current is increased, if it is determined that the temperature is excessive, the welding current is decreased, and if it is determined that the temperature is normal, the welding current is adjusted. Not performed. For example, as shown in FIG. 5, when the welding current is increased during the energization time t3, the temperature increase rate of the workpieces W1 and W2 is increased, so that the increase rate of the transmission time measured thereafter is also increased.
After adjusting the welding current, the process returns to step S10 again. Thereafter, the processes in steps S10, S12, S14, and S22 are sequentially repeated until the scheduled energization time elapses and the answer is YES in step S14.
When the scheduled energization time t4 has elapsed and the process proceeds to step S16, the energization of the welding current is stopped. That is, resistance welding is completed.

  In step S18, the determination result in step S12 is displayed on the display device 34 or the like. As shown in FIG. 5, the determination result displayed in step S18 is a determination result obtained by determining the transmission time Pm4 counted at the welding completion time point t4 based on the completion reference value P7. That is, it is possible to know whether or not the applied welding has been normally performed by the determination result displayed on the display device 34 or the like. For example, when “insufficient temperature” is displayed, it can be determined that a sufficiently large nugget N is not formed and the required bonding strength is not obtained.

In the resistance welding machine 2 of the present embodiment, it is possible to determine normality / abnormality of the welded portion simultaneously with the resistance welding. Thereby, it is not necessary to inspect the welded part in the subsequent process. Moreover, it can also prevent that the workpiece | work W1, W2 in which resistance welding was performed abnormally progresses to a post process.
In the resistance welding machine 2 of the present embodiment, ultrasonic waves are transmitted from the first ultrasonic transducer 12 of the first welding electrode 10, and ultrasonic waves are received by the second ultrasonic transducer 22 of the second welding electrode 12. The quality of welding is determined based on the time difference between the transmission and reception. Thereby, the second ultrasonic transducer 22 does not need to identify the intensity of the received ultrasonic wave, and it is sufficient to identify whether or not the ultrasonic wave is received. When determining the quality of welding, since the intensity of ultrasonic waves that are easily affected by disturbance is not used, accurate determination can be performed without being affected by disturbance.

(Example 2)
FIG. 6 schematically shows the configuration of the resistance welder 102 according to the second embodiment in which the technology of the present invention is implemented. The same configuration as that of the resistance welding machine 2 of the first embodiment is adopted for a part of the resistance welding machine 102 of the second embodiment. Therefore, about the same structure as the resistance welding machine 2 of Example 1, it attaches | subjects the same code | symbol and strives to avoid overlapping description.
The resistance welder 102 according to the present embodiment can perform resistance welding on, for example, the workpiece W1, the workpiece W2, and the workpiece W3 that are arranged in a superimposed manner. The work W3 is a plated steel plate, and the plating layer Y is formed on the surface thereof.

The resistance welder 102 of this embodiment includes a first electrode 10, a second electrode 20, and a power supply circuit 42. A first ultrasonic transducer 12 is provided on the first electrode 10 side, and a second ultrasonic transducer 22 is provided on the second electrode 22 side.
The resistance welder 102 includes a first transmission circuit (corresponding to the transmission circuit of the first embodiment) 14, a first reception circuit 116, a second transmission circuit 124, and a second reception circuit (in the reception circuit of the first embodiment). (Corresponding) 26 is provided. The first transmission circuit 14 and the second transmission circuit 124 can be configured by the same circuit. The first receiving circuit 116 and the second receiving circuit 26 can be configured by the same circuit. The first transmission circuit 14 and the first reception circuit 116 are connected to the first ultrasonic transducer 12. The second transmission circuit 124 and the second reception circuit 26 are connected to the second ultrasonic transducer 22. Therefore, in the resistance welding machine 102 of the present embodiment, each of the first ultrasonic transducer 12 of the first welding electrode 10 and the second ultrasonic transducer 22 of the second welding electrode 20 is an ultrasonic transmission transducer. As well as a transducer for receiving ultrasonic waves. For example, the ultrasonic wave transmitted from the first ultrasonic transducer 12 is received by the second ultrasonic transducer 22 and also received by the first ultrasonic transducer 12 itself. The ultrasonic wave transmitted from the second ultrasonic transducer 22 is received by the first ultrasonic transducer 12 and also received by the second ultrasonic transducer 22 itself.

As shown in FIG. 6, the first transmission circuit 14 is connected to each of the first time measuring circuit 118 and the transmission time measuring circuit 32. The transmission timing signal output from the first transmission circuit 14 is input to each of the first time measuring circuit 118 and the transmission time measuring circuit 32. The first receiving circuit 116 is connected to the first time measuring circuit 118. The reception timing signal output from the first reception circuit 116 is input to the first timer circuit 118.
The first timing circuit 118 is a circuit that counts from the time when the transmission timing signal is input from the first transmission circuit 14 to the time when the reception timing signal is input from the first reception circuit 116. That is, the first time measuring circuit 118 can measure the time from the time when the first ultrasonic transducer 12 transmits the ultrasonic wave to the time when the first ultrasonic transducer 12 receives the ultrasonic wave. As shown in FIG. 8A, the time counted by the first time measuring circuit 118 is that the ultrasonic wave transmitted from the first ultrasonic transducer 12 is reflected by the tip 10a of the first welding electrode 10, and the first time This is the time Pa until reception by the ultrasonic transducer 12. A time Pa in which the ultrasonic wave propagates in the first electrode 10 is defined as a first propagation time Pa.

The second transmission circuit 124 is connected to the second timing circuit 128. The transmission timing signal output from the second transmission circuit 124 is input to the second timing circuit 128. The second receiving circuit 26 is connected to each of the second time measuring circuit 128 and the transmission time measuring circuit 32. The reception timing signal output from the second receiving circuit 26 is input to each of the second time measuring circuit 128 and the transmission time measuring circuit 32.
The second timing circuit 128 is a circuit that counts from the time when the transmission timing signal is input from the second transmission circuit 124 to the time when the reception timing signal is input from the second reception circuit 26. In other words, the second timing circuit 128 can measure the time from the time when the second ultrasonic transducer 22 transmits the ultrasonic wave to the time when the second ultrasonic transducer 22 receives the ultrasonic wave. As shown in FIG. 8A, the time counted by the second timing circuit 128 is that the ultrasonic wave transmitted from the second ultrasonic transducer 22 is reflected by the tip 20a of the second welding electrode 20, 2 is a time Pb until reception by the ultrasonic transducer 22. A time Pb in which the ultrasonic wave propagates through the second welding electrode 20 is defined as a second propagation time Pb.

The determination circuit 138 is connected to each of the first clock circuit 118, the second clock circuit 128, and the transmission time clock circuit 32. The determination circuit 138 inputs the first propagation time Pa timed by the first timekeeping circuit 118, the second propagation time Pb timed by the second timekeeping circuit 128, and the transmission time timed by the transmission timekeeping circuit 32. The quality of welding that is being constructed is judged based on the measured time.
As shown in FIGS. 8A and 8B, the first propagation time Pa timed by the first timekeeping circuit 118, the second propagation time Pb timed by the second timekeeping circuit 128, and the transmission timekeeping circuit 32 timed. The following relationship is established between the transmitted transmission time Pc and the actual transmission time Pd required for the ultrasonic waves to pass through the workpieces W1, W2, and W3.
Pd = Pc-{(Pa / 2) + (Pb / 2)}
The determination circuit 138 calculates the actual transmission time Pd using the above relational expression, and determines the quality of welding based on the actual transmission time Pd. The propagation speed of the ultrasonic waves in the welding electrodes 10 and 20 varies depending on the temperature of the welding electrodes 10 and 20. By using the actual transmission time Pd, it is possible to correctly determine the quality of welding without being affected by changes in the propagation speed of ultrasonic waves in the welding electrodes 10 and 20.
The determination circuit 138 stores a reference transition curve regarding the actual transmission time Pd instead of the reference transition curve A regarding the transmission time described in the first embodiment. Similar to the reference transition curve A of the first embodiment, the reference transition curve related to the actual transmission time Pd can be prepared in advance by experiments and calculations.

FIG. 7 is a flowchart showing a flow of operations performed by the resistance welder 102. The operation flow when the resistance welding machine 102 performs resistance welding on the workpieces W1, W2, and W3 will be described along the operation flow shown in FIG.
In step S102, as shown in FIG. 8A, prior to pressurizing the workpieces W1, W2, and W3 by the pair of welding electrodes 10 and 20, the first propagation time Pa and the second propagation before the welding current is supplied. Time Pb is measured. The first propagation time Pa and the second propagation time Pb change due to wear occurring in the first welding electrode 10 and the second welding electrode 20, respectively. By measuring the first propagation time Pa and the second propagation time Pb before energization of the welding current, wear or the like occurring in the first welding electrode 10 or the second welding electrode 20 can be grasped. At this time, for example, when the first propagation time Pa is less than a predetermined value and it is estimated that wear exceeding an allowable level occurs in the first welding electrode 10, the welding operation may be stopped. .
In step S104, the workpieces W1, W2, and W3 are pressed and clamped by the pair of welding electrodes 10 and 20.
In step S106, as shown in FIG. 8B, prior to applying the welding current, the ultrasonic transmission time Pc before the energization is measured. An ultrasonic wave is transmitted from the first ultrasonic transducer 12 by the first transmission circuit 14, and it is detected by the second reception circuit 26 that the second ultrasonic transducer 22 has received the ultrasonic wave. The transmission time measuring circuit 32 measures the ultrasonic transmission time Pc based on the transmission timing signal input from the first transmission circuit 14 and the reception timing signal input from the second reception circuit 26.

In step S108, the determination circuit 138 calculates the actual transmission time Pd before energization from the first propagation time Pa and the second propagation time Pb measured in step S2 and the transmission speed Pc measured in step S106.
In step S110, the determination circuit 138 corrects the reference transition curve related to the actual transmission time based on the actual transmission time Pd before energization calculated in step S108. This correction process is executed in the same manner as the correction process in step S6 of FIG. 3 described in the first embodiment.
In step S112, energization of the welding current is started.
In step S114, as shown in FIG. 8C, the first propagation time Pa and the second propagation time Pb during energization are measured. During the energization of the welding current, the temperature of the welding electrodes 10 and 20 rises. As the temperature of the welding electrodes 10 and 20 rises, the speed at which ultrasonic waves propagate through the welding electrodes 10 and 20 decreases. As a result, the first propagation time Pa and the second propagation time Pb during energization increase as the temperature of the welding electrodes 10 and 20 increases. Therefore, for example, the temperature of the first welding electrode 10 can be estimated based on the first propagation time Pa during energization. When estimating strictly, it is good to estimate the temperature of the 1st welding electrode 10 based on ratio of the 1st propagation time Pa before electricity supply (normal temperature) and the 1st propagation time Pa in electricity supply. Similarly, the temperature of the second welding electrode 20 can be estimated based on the second propagation time Pb during energization.

In step S116, as shown in FIG. 8D, the transmission time Pc during energization is counted. The ultrasonic wave transmitted from the first ultrasonic transducer 12 passes through the melted portion (nugget) N formed in the workpieces W1, W2, and W3, and is received by the second ultrasonic transducer 22. The transmission time Pc timed in step S116 changes according to the temperatures of the workpieces W1, W2, and W3.
In step S118, the determination circuit 138 calculates an actual transmission time Pd during energization from the first propagation time Pa and the second propagation time Pb measured in step S114 and the transmission speed Pc measured in step S116.

In step S120, the determination circuit 138 determines the actual transmission time Pd based on the first propagation time Pa and the second propagation time Pb during energization measured in step S114 prior to the determination process of the calculated actual transmission time Pd. The reference transition curve for is corrected again.
FIG. 9 is a diagram for explaining the temperature distribution in the plate thickness direction of the workpieces W1, W2, and W3. FIG. 9A shows the formation position of the nugget N when the temperature distribution in the plate thickness direction is appropriate, and FIG. 9B shows the temperature distribution in the plate thickness direction at that time. FIG. 9C shows the formation position of the nugget N when the temperature distribution in the plate thickness direction is biased, and FIG. 9D shows the temperature distribution in the plate thickness direction at that time. As shown in FIG. 9, for example, even if the ultimate temperatures in the workpieces W1, W2, and W3 are the same Tc, the nuggets N formed by the temperature distribution in the plate thickness direction are different. As shown in FIG. 9C, when the temperature distribution is biased toward the workpiece W1, the nugget N is biased toward the workpiece W1, and a bonding failure occurs between the workpiece W2 and the workpiece W3. Such a phenomenon is likely to occur when a large number of workpieces are welded simultaneously as in this embodiment.

  In the resistance welding machine 102 of the present embodiment, the temperature Ta (corresponding to the surface temperature of the workpiece W1) Ta of the first welding electrode 10 is estimated based on the first propagation time Pa, and the second propagation time Pb. Based on this, the temperature Tb (corresponding to the surface temperature of the workpiece W3) Tb of the tip 20a of the second welding electrode 20 is estimated. As shown in FIG. 9B, if the estimated temperature Ta and the estimated temperature Tb are substantially equal, it can be determined that the temperature distribution in the thickness direction is appropriate. In this case, the determination circuit 138 does not correct the reference transition curve. On the other hand, as shown in FIG. 9D, if there is a significant difference between the estimated temperature Ta and the estimated temperature Tb, it can be determined that the temperature distribution in the thickness direction is biased. In this case, the determination circuit 138 executes a process for correcting the reference transition curve. The determination circuit 138 increases the actual transmission time Pd described by the reference transition curve, and creates a corrected reference transition curve. As a result, the target temperature of the workpieces W1, W2, and W3 is increased, and the nugget N is formed larger. Even if the nugget N is unevenly distributed as shown in FIG. 9C, the workpieces W1, W2, and W3 can be welded together, and a necessary joint strength can be obtained.

In step S122 of FIG. 7, the actual transmission time Pd calculated in step S118 is determined based on the reference transition curve corrected in step S120. This determination process is executed in the same manner as the determination process in step S12 of FIG. 3 described in the first embodiment. In step S124, the actual transmission time Pd calculated in step S118 is the completion reference value for the actual transmission time Pd. Determine if it has exceeded. If the calculated actual transmission time Pd exceeds the completion reference value, it can be determined that the temperatures of the workpieces W1, W2, and W3 are sufficiently increased, and the nugget N that can obtain the necessary bonding strength is formed. In this case, the process proceeds to step S126, and energization of the welding current is terminated. On the other hand, if the calculated actual transmission time Pd does not exceed the completion reference value, it is necessary to continue energization of the welding current. In this case, it progresses to step S132 and the increase / decrease adjustment of a welding current is performed based on the determination result of S122. Next, the process returns to step S114 again, and step S114 and subsequent steps are repeatedly executed until the calculated actual transmission time Pd exceeds the completion reference value.

The resistance welder 102 can sequentially estimate the welding state in the workpieces W1, W2, and W3 during welding based on the time during which ultrasonic waves pass through the workpieces W1, W2, and W3. The resistance welder 102 continues energizing the welding current until a sufficient nugget N is formed on the workpieces W1, W2, and W3. The resistance welder 102 can more reliably perform welding that provides the necessary joint strength by adjusting the energization period of the welding current based on the determination result of the determination circuit 138.
According to the resistance welding machine 102, even if there is a dimensional error in the plate thickness of each workpiece, the welding electrode is worn, or the temperature distribution in the plate thickness direction of the workpiece is uneven, It can be welded with sufficient joint strength.

As mentioned above, although embodiment of this invention was described in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. The technology illustrated in this specification or the drawings achieves a plurality of objects at the same time, and achieving one of the objects itself has technical utility.

FIG. 3 is a schematic diagram illustrating a configuration of a resistance welder according to the first embodiment. The figure which illustrates the reference | standard transition curve regarding transmission time, and its correction. 3 is a flowchart showing a flow of operations of the resistance welder of the first embodiment. The figure which shows a mode that the transmission time of an ultrasonic wave is timed. The figure which illustrates the time-dependent change of the transmission time measured. FIG. 5 is a schematic diagram illustrating a configuration of a resistance welder according to a second embodiment. 10 is a flowchart showing a flow of operations of the resistance welder according to the second embodiment. The figure which shows a mode that the propagation time and transmission time of an ultrasonic wave are timed. The figure explaining the suitable temperature distribution in a workpiece | work, and the biased temperature distribution. The figure which shows the relationship between the temperature of a workpiece | work, and the propagation speed of the ultrasonic wave in a workpiece | work. The figure which shows the relationship between the temperature of a workpiece | work, and the magnitude | size of the nugget formed.

Explanation of symbols

2. Resistance welding machine 10 of the first embodiment. First welding electrode 12. First ultrasonic transducer 14. Transmission circuit (first transmission circuit)
20 .... second welding electrode 22 .... second ultrasonic transducer 26 ... receiving circuit (second receiving circuit)
32..Transmission time measuring circuit 34..Display device 38..Determination circuit 42 of the first embodiment..Power supply circuit 50..Controller 102..Resistance welder 116 of the second embodiment..First receiving circuit 118 .. First timing circuit 124... Second transmission circuit 128... Second timing circuit 138...

Claims (9)

A first welding electrode;
A second welding electrode;
An energizing means for energizing a welding current through the material to be welded between the first welding electrode and the second welding electrode;
Ultrasonic transmission means provided on the first welding electrode side;
Ultrasonic receiving means provided on the second welding electrode side;
An inter-electrode time measuring means for measuring the time from the time when the ultrasonic transmitting means transmits ultrasonic waves to the time when the ultrasonic receiving means receives ultrasonic waves;
Resistance welding machine with   2. The resistance welding machine according to claim 1, further comprising time measuring time determining means for determining whether or not the time measured by the inter-electrode time measuring means is within a predetermined reference range.   3. The resistance welding machine according to claim 1, wherein the time measuring unit corrects the reference range based on a time measured by the time measuring unit before energization of the welding current. 4.   The resistance welding machine according to any one of claims 1 to 3, wherein the energizing unit adjusts the welding current to increase or decrease based on a determination result of the determining unit.   The resistance welding machine according to any one of claims 1 to 4, wherein the energizing means adjusts the energizing time of the welding current for a long or short period based on a determination result of the determining means. Ultrasonic receiving means provided on the first welding electrode side;
Ultrasonic transmission means provided on the second welding electrode side;
First electrode-side time measuring means for measuring the time from when the ultrasonic transmitting means on the first welding electrode side transmits ultrasonic waves until the ultrasonic receiving means on the first welding electrode side receives ultrasonic waves; ,
Second electrode side timing means for timing the time from when the ultrasonic transmitting means on the second welding electrode side transmits ultrasonic waves until the ultrasonic receiving means on the second welding electrode side receives ultrasonic waves; ,
The resistance welding machine according to claim 1, further comprising:   The ultrasonic wave calculated from the time measured by the inter-electrode time measuring means, the time measured by the first electrode-side time measuring means, and the time measured by the second electrode-side time measuring means is applied to the workpiece. The resistance welding machine according to claim 6, further comprising transmission time determining means for determining whether or not the actual transmission time required for transmission is within a predetermined reference range.   The determination unit corrects the calculated actual transmission time and / or the reference range based on the time measured by the first electrode side time measuring unit and the time measured by the second electrode side time measuring unit. The resistance welding machine according to claim 7, wherein A method for judging the quality of resistance welding,
A transmission step of transmitting ultrasonic waves from one welding electrode side;
A receiving step of receiving ultrasonic waves on the other welding electrode side;
A time measuring process for measuring the time from when the ultrasonic wave is transmitted in the transmitting process to the time when the ultrasonic wave is received in the receiving process;
A determination step of determining whether or not the time measured in the time measurement step is within a predetermined reference range;
A determination method comprising:

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