JPS5832037B2 - Welding defect detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for detecting defects in a welded area by resistance welding or the like.

BACKGROUND ART As devices for detecting weld defect sites, there have conventionally been ultrasonic flaw detectors that use ultrasonic waves, eddy current flaw detectors that flow eddy current and detect changes in leakage magnetic flux, and the like.

Non-destructive testing methods using these devices are for testing the presence or absence of flaws in joints.

Therefore, it has been extremely difficult to detect defective parts where the strength is weak, although the upper part appears to be pressed without any damage.

However, in actual welding operations, such as tube manufacturing, defects such as those described above are caused by scratches on the butt ends that occur during the forming process, etc., or by differences in the opposing ends called laps that occur at the butt part. and often occur.

At the moment such a welding defect occurs, especially a welding defect in low frequency resistance welding, the welding current usually decreases.

The present invention focuses on this point and aims to provide a device that monitors the welding current and detects an abnormal drop in the welding current to detect the occurrence of a defect.

What should be noted here is that if the purpose is simply to notify the occurrence of an abnormality when the welding current exceeds a predetermined lower limit or upper limit, a commercially available meter relay can also accomplish this function. However, the actual welding current has a certain degree of variation even when welding is performed normally due to the contact pressure of the butt part, the contact area, and other factors, and the average welding current Since the value also changes depending on the welding conditions, it is not possible to reliably detect the occurrence of welding defects using a meter relay or the like.

That is, when the average value of the welding current is high, even if a welding defect occurs and the welding current abnormally decreases, the value may not reach the lower limit set value and may not be detected by the meter relay.

In order to avoid such inconveniences, if this lower limit set value is set to a high value, it will always be determined that an abnormality has occurred even if normal welding is performed when the average welding current value is low.

The present invention solves the above-mentioned problems of the prior art, and an object of the present invention is to provide a highly reliable welding defect detection device that reliably detects welding defects when they truly occur. There is a particular thing.

The features of the present invention that achieve the above-mentioned objects include means for generating a first signal having a value corresponding to the absolute value of the welding primary current, and removing high frequency components from the first signal to change the value. means for generating a second signal reduced by a predetermined value;
The present invention further includes means for comparing the first and second signal values with each other and notifying the occurrence of a welding defect when the first signal value becomes equal to or less than the second signal value.

The present invention will be described in detail below using the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

This embodiment is a case of a low frequency resistance welding machine used in tube manufacturing.

In the figure, 10 is a tube which is a material to be welded,
This tube 10 is pressurized by a squeeze roll 11.

12 is a pair of disk electrodes arranged so that welding current flows across the abutting surfaces of the tubes 10, 14 is a welding transformer, and 16 is a primary side of the welding transformer 14 for adjusting the welding current. An autotransformer 18 adjusts the supply voltage, and 18 represents a welding current adjustment (heat control) by phase control and a sirisk contactor that opens and closes the welding current.

The low frequency resistance welding machine 20 having the above configuration has a wire R.
, S are supplied with a low frequency voltage, for example, 60 Hz, 400 V.

Next, the configuration of the welding defect detection device portion related to the present invention will be explained.

As shown in FIG. 1, the primary side of the welding transformer 14 is
A current transformer 22 for detecting the next current is provided, and the output terminal of this current transformer 22 is connected to the first amplifier 2 via a rectifier 24.
6.

The output terminal of the first amplifier 26 is connected to one input terminal of the first comparator 30 and the input terminal of the low-pass filter 32 via the second amplifier 28.
is connected to the other input terminal of the first comparator 30 via a voltage level converter 34.

The output terminal of the first amplifier 26 is connected to one input terminal of the second comparator 36.

The output terminal of a reference voltage generator 38 is connected to the other input terminal of the second comparator 36 .

The output terminals of the first and second comparators 30 and 36 are connected to the input terminal of a drive circuit 40 for driving the relay, and the output terminal of this drive circuit 40 is connected to the relay 42, and the output terminal of the relay 42 is connected to the input terminal of the drive circuit 40 for driving the relay. is the notification mechanism 4 that notifies the occurrence of a welding defect.
4' is connected.

Next, the operation of this embodiment will be explained using the waveform diagram shown in FIG.

In FIG. 2, the horizontal axis represents time, and the vertical axis represents voltage corresponding to the welding current.

The welding current is detected by the current transformer 22 as a welding primary current flowing through the primary side of the welding transformer 14, rectified by the rectifier 24, and sent to the first amplifier 26.

The output of this amplifier 26 becomes a voltage signal having a value corresponding to the absolute value of the welding current.

The output of this first amplifier 26 is level-adjusted and separated in a second amplifier 28 and sent to a first comparator 30 and a low-pass filter 32, respectively.

A in FIG. 2A represents the output signal waveform of this amplifier 28.

This signal of waveform a has its high frequency components removed by the low-pass filter 32, resulting in the waveform shown in FIG. 2B.

This waveform signal is reduced by a predetermined level or by a predetermined ratio in the voltage level converter 34 to become a waveform b/(FIG. 2C).

This type of voltage level converter 34 is comprised of, for example, a general bias circuit that adds a constant voltage of opposite polarity to the output of the low-pass filter 32, or a normal amplifier with an amplification factor of 1.0 or less.

The output of this voltage level converter 34 is used as a reference signal.
is applied to the comparator 30, and the level is compared with the signal of waveform a.

FIG. 2C represents the two input signals of this comparator 30.

As a result, the output waveform of the comparator 30 becomes like C shown in the second diagram, and only when this output C is at a low level, the drive circuit 40
is energized, thus activating the relay 42 to activate the notification mechanism 44.
will notify you that a welding defect has occurred.

Various drive circuits are possible for the drive circuit 40 that activates and energizes the relay 42 when the input signal is or becomes a low level. For example, a monostable drive circuit that is triggered at the falling edge of the input signal It can also be configured with a multivibrator or bistable multivibrator.

That is, in this embodiment, the envelope level of the welding primary current waveform is detected, and the reference voltage of the comparator 30 is controlled according to this envelope level, so even when the welding current fluctuates, welding may occur by mistake. It does not cause a malfunction due to the occurrence of a defect, and operates so as to notify the occurrence of a welding defect only when the welding current suddenly and abnormally decreases as shown by al in FIG. 2A.

In this embodiment, the output of the first amplifier 26 is further applied to a second comparator 36 and compared with a reference voltage corresponding to a lower limit of the welding current that cannot normally occur.

If the output level of the amplifier 26 is lower than this reference voltage, the drive circuit 40 is energized as in the case described above, and the notification mechanism 44 notifies the user of the occurrence of an abnormality.

Such an additional circuit including the second comparator 36 is useful when the welding current does not drop suddenly despite the occurrence of welding defects, for example, when welding defects occur continuously. Alternatively, it is provided to supplement the function of the welding defect detection device of the present invention by detecting a case where the welding current itself has decreased abnormally from the beginning and reporting the occurrence of the abnormality.

Note that the reference voltage generator 38 in this additional circuit is configured so that a desired reference voltage can be generated by the operator.

As explained in detail above, the welding defect detection device of the present invention is extremely reliable because it can reliably detect only when a welding defect actually occurs and the welding current suddenly drops abnormally. Furthermore, it has many advantages such as a simple circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is an operational waveform diagram in the above embodiment. 10...Tube, 11...Squeeze roll, 12
...Disk electrode, 14...Welding transformer, 16...Auto transformer, 18...Sirisk contactor, 20...
・Low frequency resistance welder, 22... Current transformer, 24... Rectifier, 26° 28... Amplifier, 30, 36... Comparator, 32... Low pass filter, 34... Voltage Level converter, 38... Reference voltage generator, 40... Drive circuit, 42... Relay, 44... Notification mechanism.

Claims (1)

[Claims] 1. Means for generating a first signal having a value corresponding to the absolute value of the welding primary current, and a second signal obtained by removing high frequency components from the first signal and reducing its value by a predetermined value. and means for comparing the first and second signal values with each other and notifying the occurrence of a welding defect when the first signal value becomes equal to or less than the second signal value. Features・
A welding defect detection device.