JP2000317651A - Method and device for detecting defective welding by ultrasonic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for detecting defective welding by a ultrasonic wave, by which the presence or the absence of the generation of a weld crack can be detected. SOLUTION: By a monitoring device 14 provided on a ultrasonic welding device 1, the maximum value of a horn current is measured in a maximum value measurement area where a horn displacement quantity L reaches a prescribed value ΔL from the start of welding, the minimum value of the horn current is measured in a minimum value measurement area from a time when the horn displacement quantity L has reached the prescribed value ΔL to the completion of the welding. When a difference between the maximum value and the minimum value of the horn current is larger than Δi, a weld crack is detected. Consequently, the visual detection check of the weld crack becomes unnecessary, and a cost required for the welding can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method and an apparatus for detecting a defect in ultrasonic welding.

[0002]

2. Description of the Related Art As a means for detecting a defect in ultrasonic welding, a technique disclosed in Japanese Patent Application Laid-Open No. 6-344159 is known. This technique monitors a horn current during welding and detects a welding defect when the current value exceeds a predetermined range. In addition to the above, as a means for detecting a defect in ultrasonic welding, there is known a technique of measuring a pressing force of an object to be welded, a welding time, comparing the measured value with a preset upper limit and a lower limit, and determining the quality of welding. I have.

[0003]

The detection means described above is effective for monitoring welding strength. However, in the case of ultrasonic welding, since welding is performed by applying ultrasonic waves to the workpiece, the welding conditions may vary due to deterioration of the tip of the horn, the state of the welding jig, and the surface roughness of the workpiece. Even when constant, welding cracks may occur. FIG. 2B shows an example of a specific welded object in which a weld crack has occurred, and the portion where the weld crack has occurred is indicated by an arrow A. This welding crack is difficult to be detected by the detecting means described above, and at present, after welding, an operator visually checks all the workpieces for occurrence of welding cracks.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ultrasonic welding defect detecting method and apparatus capable of detecting whether or not welding cracks have occurred.

[0005]

[Means for Solving the Problems] [Means for Claims 1 and 2]
In normal welding, the vibration given by the horn
Since the workpiece vibrates uniformly, the horn current waveform gradually rises and then becomes flat. On the other hand, when welding cracks occur, a part of the work is fixed, so the vibration energy concentrates only on the other part, the other part of the welding progresses at a stretch, and the horn current waveform changes. Get up sharply. Then, after the other part is welded, the horn slips on the other part for a while, so that the horn does not require a driving force, and as a result, the horn current largely drops.

[0006] As described above, when welding cracks occur, the horn current waveform once rises sharply, and then has a characteristic that the horn current largely drops. For this reason, the maximum value of the horn current due to the rise of the horn current waveform is measured in the maximum value measurement region, and the minimum value of the horn current due to the decrease in the horn current is measured in the minimum value measurement region. When the difference is larger than a predetermined determination value, occurrence of a weld crack can be determined.

[Means of Claim 3] When welding is performed so that the welded object has a constant penetration amount, the welding time varies. For this reason, when measuring the maximum and minimum values over time,
The possibility of malfunction will increase. Therefore, the maximum value and minimum value are accurately measured even if the welding time varies by dividing the maximum value measurement region and the minimum value measurement region before and after the knurling bite allowance reaches the predetermined value. can do.

[0008]

Embodiments of the present invention will be described with reference to the drawings. The ultrasonic welding apparatus 1 will be described with reference to FIG. The ultrasonic welding device 1 includes an ultrasonic vibrator 2 using a piezoelectric element or the like, a controller 3 for applying an ultrasonic driving current (horn current) to the ultrasonic vibrator 2, and a horn ultrasonically vibrated by the ultrasonic vibrator 2. 4 and an anvil 7 for sandwiching the workpiece 6 between the knurled portion 5 at the tip of the horn and a root portion of the horn 4 held by a holding portion 8 so as to be capable of ultrasonic vibration. In addition, the ultrasonic welding apparatus 1 in this embodiment performs welding so that the workpiece 6 has a constant penetration amount, and includes a displacement sensor 9 for measuring the penetration amount. The displacement sensor 9 measures the amount of penetration of the workpiece 6 by measuring the displacement L of the horn 4.

The welding by the ultrasonic welding apparatus 1 is performed as follows. The superposed workpiece 6 is placed between the horn 4 and the anvil 7, the horn 4 is pressed against the workpiece 6, and the joint of the workpiece 6 is pressurized. When a horn current for driving ultrasonic vibration is supplied from the controller 3 to the ultrasonic vibrator 2, the ultrasonic vibrator 2 and the horn 4 are ultrasonically vibrated and transmitted to the workpiece 6. As a result, micro-vibration plastic sliding occurs on the contact surface of the workpiece 6 and the sliding action generates frictional heat on the contact surface, and cold welding and welding using this frictional heat is performed. When the displacement amount L of the horn 4 measured by the displacement sensor 9 reaches a predetermined value, the controller 3 determines that the penetration amount has reached the predetermined value, and ends the welding.

As shown in FIG. 2A, a specific example of the workpiece 6 to be welded by the ultrasonic welding apparatus 1 in this embodiment is a copper plate 10, an aluminum fin 11, and a B bolt made of carbon steel. Twelve three-layer simultaneous ultrasonic welding is performed, and the workpiece 6 is used for a rectifier of an alternator. Then, the workpiece 6 is
Deterioration of tip of horn 4, condition of welding jig, workpiece 6
2B, a welding crack may occur in the B bolt 12 as shown by an arrow A in FIG.

The ultrasonic welding apparatus 1 determines whether or not a welding crack has occurred in the workpiece 6 being welded, and generates an alarm sound when it is determined that welding failure has occurred due to the welding crack. A sonic welding failure detection device is provided. This device includes a current sensor 13 that measures a horn current value i applied to the ultrasonic transducer 2 and a monitoring device 14 (monitoring device) that detects welding cracks based on the horn current value i measured by the current sensor 13. Equivalent to means)
It is composed of

As shown in FIG. 3, the monitoring device 14 has a maximum value Maxi of the horn current in the maximum value measurement region within a predetermined period after the welding is started, and the maximum value measurement region has passed. If the difference between the horn current and the minimum value Min i in the minimum value measurement region within a predetermined period from is larger than a predetermined determination value Δi (eg, 600 mA) (Max i−Min i> Δi), This is for judging poor welding.

The maximum value measurement area in this embodiment is:
Horn 4 that presses workpiece 6 after welding is started
Is a predetermined value ΔL (for example,
The minimum value measurement region is a period from when the maximum value measurement region elapses to when the welding is completed. The bite allowance of the knurl portion 5 is calculated by the displacement amount L of the horn 4 by the displacement sensor 9.
Measured from

The monitoring device 14 has a horn current value i
A horn current measurement circuit 15 for measuring the horn displacement amount, a horn displacement amount measurement circuit 16 for measuring the horn displacement amount L, a setting circuit 17 for storing the judgment value Δi and the predetermined value ΔL, an arithmetic circuit 18, a comparison circuit 19, and an alarm circuit 20 Is done. Arithmetic circuit 1
8, the comparison circuit 19 and the alarm circuit 20 perform the above-described measurement and determination, and their operations will be described based on the flowchart of FIG.

When the welding is started (start), the maximum value Max i of the horn current is measured from the horn current value i read by the horn current measuring circuit 15 (step S1). Next, it is determined whether or not the horn displacement L read by the horn displacement measuring circuit 16 has reached a predetermined value ΔL (step S2). If the result of this determination is NO, it is determined that the region is the maximum value measurement region, and the process returns to step S1.

If the decision result in the step S2 is YES,
It is determined that the maximum value measurement area has ended and the minimum value measurement area has been entered, and the minimum value of the horn current Min i is measured from the horn current value i read by the horn current measurement circuit 15 (step S3). Next, it is determined whether the penetration amount has reached a predetermined value and welding has been completed (step S4). If the result of this determination is NO, it is determined that the area is the minimum value measurement area, and the flow returns to step S3.

If the decision result in the step S4 is YES,
It is determined that the minimum value measurement area has also ended, and the maximum value Max i measured in step S1 and the minimum value Mi measured in step S3
It is determined whether or not the difference from n i is greater than the determination value Δi (step S5). If the result of this determination is NO, it is determined that welding cracks have not occurred, and the process ends (END).
However, if the result of the determination in step S5 is YES, it is determined that a weld crack has occurred, and the alarm circuit 20 is operated to notify the worker of the occurrence of a defective product or to automatically select the defective product (step S5). S6).

The change in the horn current depending on the presence or absence of the welding crack will be described with reference to FIG. In normal welding, the workpiece 6 vibrates uniformly due to the vibration applied from the horn 4, so that the horn current waveform gradually rises and then becomes flat as shown by the solid line B in FIG.

On the other hand, if a welding crack occurs, a part of the workpiece 6 is fixed, so that vibration energy is concentrated only on the other part, and the other part of the welding proceeds at a stretch.
As shown by the broken line C in FIG. 5, the waveform of the horn current sharply rises. Then, after the other part is welded, the horn 4 slips over the other part for a while, so that the horn 4 does not require a driving force, and as a result, the horn current largely drops.

As described above, when welding cracks occur, the horn current waveform suddenly rises once, and then has a characteristic that the horn current largely drops. For this reason, the maximum value Max i of the horn current due to the rise of the horn current waveform is measured in the maximum value measurement region, and the minimum value of the horn current due to the drop of the horn current is measured in the minimum value measurement region.
Min i is measured, and when a difference between the maximum value Max i and the minimum value Min i is larger than a predetermined judgment value Δi, occurrence of a weld crack can be judged.

As described in the above embodiment, the difference between the maximum value Max i in the maximum value measurement area and the minimum value Min i in the minimum value measurement area is obtained, and the difference is compared with the judgment value Δi to obtain the welding value. Since it is possible to determine the occurrence of cracks, it is possible to eliminate the work of checking the presence or absence of weld cracks by visually checking all the workpieces 6 by the operator. In other words, there is no need for a visual operator,
As a result, costs required for welding the workpiece 6 can be reduced.

[Modification] In the above-described embodiment, an example is adopted in which welding is performed so that the workpiece 6 has a constant penetration amount. Therefore, the maximum value measurement area and the minimum value measurement area are measured by the displacement sensor 9. Although the example in which the distinction is made based on the penetration amount is shown, for example, in a case where the welding is time-controlled, the maximum value measurement region and the minimum value measurement region may be distinguished by the time width.
The workpieces 6 and the numerical values shown in the above embodiment are merely examples for explanation, and other workpieces 6 and numerical values may be used.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an ultrasonic welding defect detection device.

FIG. 2 is a perspective view of a workpiece.

FIG. 3 is a graph showing a relationship between a horn displacement amount and a horn current value.

FIG. 4 is a flowchart showing the operation of the monitoring device.

FIG. 5 is a graph showing a change in a horn current value depending on the presence or absence of a weld crack.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultrasonic welding apparatus 2 Ultrasonic transducer 4 Horn 5 Knurl part 6 Workpiece 7 Anvil 13 Current sensor 14 Monitoring device (monitoring means)

Claims (3)

[Claims] An ultrasonic vibration generated by an ultrasonic vibrator is transmitted to a horn, and the ultrasonic vibrator is used in an ultrasonic welding apparatus for joining an object to be welded sandwiched between the horn and an anvil. The horn current for driving is monitored, and the maximum value of the horn current in the maximum value measurement region within a predetermined period from the start of welding and the minimum value within a predetermined period after the maximum value measurement region elapses. An ultrasonic welding failure detection method for determining a welding failure when a difference from a minimum value of the horn current in a value measurement region is larger than a predetermined determination value. 2. An ultrasonic welding device for transmitting ultrasonic vibrations generated by an ultrasonic vibrator to a horn, and joining an object to be welded sandwiched between the horn and an anvil; A current sensor for monitoring a horn current for driving the ultrasonic vibrator; (c) a maximum value of the horn current in a maximum value measurement area within a predetermined period after starting welding; Monitoring means for judging a welding defect when a difference from the minimum value of the horn current in the minimum value measurement region within a predetermined period after elapse is larger than a predetermined judgment value. Ultrasonic welding failure detection device. 3. The maximum value measurement area is a period from the start of welding to a time when the knurling portion of the horn of the horn pressing the work piece reaches a predetermined value, and the minimum value measurement area is 3. The ultrasonic welding defect detection method according to claim 1, wherein the ultrasonic welding defect detection method or the ultrasonic welding defect detection device is a period from when the maximum value measurement area elapses to when the welding is completed.