JPH0679776B2 - How to avoid burn-through - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for avoiding burn-through which may occur during consumable electrode arc welding.

[Conventional technology]

At the time of consumable electrode type arc welding, especially when the base material is a thin plate, a so-called burn-through phenomenon may occur in which the base material has holes. This occurs due to an increase in welding current, an increase in the number of gear gaps in the base metal groove, etc., but once this occurs, it will be in a fusing state after that, and normal welding cannot be restored. . Conventionally, there is no technique for predicting the occurrence of this burn-through phenomenon, and no technique for predicting and preventing or preventing the occurrence of the burn-through phenomenon.
Since the welding is stopped, the work efficiency is lowered, and in order to restart the welding, there is a problem that it is necessary to replace the work and repair the work, which is uneconomical. Further, in the case of robot welding, there is a problem that the efficiency is low because it is usual to set the welding conditions in consideration of safety, fearing the occurrence of the burn-through phenomenon.

[Object of the Invention]

The present invention has been made in order to solve the above-mentioned conventional problems, and it is an object of the present invention to obtain a burn-through avoiding method capable of preventing the occurrence of burn-through and realizing arc welding with higher efficiency than the conventional one. To aim.

[Structure of Invention]

In order to achieve the above-mentioned object, the present invention monitors a short-circuit cycle and predicts burn-through from an increase change of the short-circuit cycle exceeding a predetermined level, and at the same time as the prediction, an output current of a welding power source or a welding speed is preset. The non-step control is performed to the burn-through avoidance level, and the pre-prediction level is restored to the non-step level after a predetermined time.

Example of Invention

If so-called burn-through occurs, if welding is stopped when the burn-through occurs, the holes in the base metal will be naturally closed due to the surface tension of the molten metal, and repair welding can be performed. However, if you do not like the appearance of the weld bead and want to continue welding, you need to predict burn-through.If you can predict burn-through, change the welding conditions with a time margin before the burn-through. (Reduction of current or increase of welding speed)
By doing so, the occurrence of burn-through can be prevented in advance.

FIGS. 1 (a) to 1 (d) show typical waveform diagrams of the measurements performed by the inventors of the present invention repeatedly for a factor closely correlating with the burn-through phenomenon. Uses an optical sensor as shown in Fig. 8, and when arc welding a thin plate,
The optical sensor traces the welding point from the back surface side of the base material. FIG. 8 (A) is a plan view, and FIG. 8 (B) is a view seen from the direction aa. The arc voltage waveform in the arc welding is shown in FIG. The waveform of FIG. 1 (a) is an output waveform of the optical sensor, the Y-axis direction (time-axis direction) thereof indicates the magnitude of the short circuit period T at the arc voltage, and the A portion of the waveform is the burn-through portion. The output waveform in FIG. In a state where no burn-through has occurred, short-circuiting and re-arcing are repeated, and the change in the amount of light at this time is captured by the optical sensor through the gap in the groove of the unwelded portion.
When short-circuited, it is dark and the amount of light is small, and when re-arcing, it is bright and the amount of light is large. Therefore, the darkening cycle, that is, the cycle in which the output of the photosensor becomes small, indicates the short circuit cycle. FIG. 1 (b) is a waveform obtained by passing the above output waveform through a low-pass filter (LPF) (in this case, the cut-off frequency c = 5 Hz) and averaging the variations in the short circuit period T. c) is a waveform smoothed by the LPF of c = 1 Hz.

As is apparent from the waveforms of FIGS. 1 (b) and (c), the short-circuit period increases before the start of burn-through, and in the present invention, when the arc voltage is monitored and this increasing tendency appears. In addition, the burn-through is predicted by judging that it is a precursor of burn-through.

The increasing tendency of the short circuit period T can be electrically detected by setting a threshold level Vo (voltage) and comparing the output waveform of the LPF with the threshold level Vo by a comparator, According to the above measurement, the increasing tendency is, for example,
Since it starts 200 to 300 msec before the burn-through occurs, the output signal of the above-mentioned comparator ((d) in the figure) should be used as a predictive signal, and the welding conditions should be changed before the burn-through occurs using this signal. You can The faster the burn-through prediction, the easier it is to change the welding conditions, which is preferable for avoiding or preventing burn-through.However, if the threshold level Vo is set too low for that reason, variations in individual short-circuit cycles will occur. Therefore, the probability of false detection increases. As a method of coping with this, the threshold level can be set to a high threshold level VH (burn-through detection level) and a low threshold level VL (burn-through prediction level).
If the short circuit period T exceeds the low threshold level VL, the welding conditions are changed and the high threshold level is set.
The welding may be stopped when VH is exceeded.

By the way, the above-mentioned short circuit period T cannot be controlled by a welding power source, but the current, voltage, speed, wire protrusion length,
Since it varies depending on the plate thickness of the base metal, surface condition, etc., it is impossible to predict.The above-mentioned absolute value comparison method, which directly compares the measured short-circuit period with the threshold level, provides a general-purpose prediction or detection. Difficult to do. Moreover, since the individual short-circuit periods T vary, it is necessary to average the short-circuit periods by using the LPF as described above. However, when using the analog LPF, it is not necessary to select the optimum cutoff frequency c for each welding condition. There is a limit in terms of versatility.

The versatility of burn-through prediction and detection, which can cope with a wide range of welding conditions, can be realized as follows.
That is, the average value Td of a large number N of short circuit cycles and the average value Tc of a fractional number n of the measured short circuit period are obtained, and the ratio Tc / Td of both is compared with a certain threshold value A (prediction ratio). When the following equation is satisfied, that is, when the following equation is satisfied, a prediction signal is generated to predict burn-through.

Tc / Td> A (1) Here, (1) The average value Td is a value calculated from the data of the short-circuit cycle during normal welding captured during welding, and as shown in FIG. New data is taken in every cycle, old data is discarded, and operation is updated.

(2) The average value Tc is also updated by taking in new data and discarding old data for each short-circuit period, but since it is an average value of a small number of times n, while smoothing the variation of each short-circuit period,
In addition, the value can be set so as to sensitively follow the increase in the short circuit period.

(3) Since the threshold value A is for the average value ratio Tc / Td, it has a content as a relative value unlike Vo, VH, and VL, and it is not necessary to change it corresponding to each welding condition. A single value can correspond to a wide range of welding conditions.

Even in the case of this burn-through prediction method, the threshold value A is set to two levels, high and low, and when the low level ABL (burn-through prediction level) is exceeded, a predictive signal is generated to change the welding condition, and the high level is set. A burn-through detection signal for stopping welding may be generated when ABH (burn-through detection level) is exceeded. This burn-through prediction level ABL is a level at which burn-through can be prevented by changing welding conditions after prediction, and burn-through detection level ABH is a level at which burn-through occurs even if welding conditions are changed after detection. .

FIG. 4 is a block diagram showing a specific apparatus for carrying out the burn-through prediction method using the average value ratio of the short circuit period. In the figure, 1 is a short-circuit detector, 2 is a counter,
3 is a latch unit, 4 is a CPU, and 5 is an oscillating unit.

The short-circuit detection unit 1 receives the arc voltage, generates a short-circuit detection signal, sends a gate signal to the counter 2 during the arc generation period, supplies a latch signal to the latch unit 3 and an interrupt signal to the CPU 4. The counter 2 counts the clocks output by the oscillator 5 by being gated by the gate signal, and the counted value (short circuit period T) is stored in the latch 3. When the CPU 4 receives the interrupt signal, it reads the short-circuit period stored in the latch unit 3, calculates Td, Tc, Tc / Td, compares Tc / Td with ABL, ABH, and then Tc / Td> A burn-out prediction signal a is generated in the case of ABL, and a burn-through detection signal b is generated in the case of Tc / Td> ABH.

The present invention uses the prediction signal and the detection signal obtained as described above, and the flow of the burn-through avoidance method is shown in FIG. FIG. 7 is a block diagram showing the outline of a conventional welding apparatus. 10 is a welding power source (high frequency inverter), 11 is a transformer, 12 is a rectifier, 13 is a DC reactor, 14 is a power feeding chip, and 15 is welding. Reference numeral 16 is a wire, 16 is a welding base material, 17 is a voltage detector, 18 is a current detector, and 19 is a controller.

In the present invention, at the same time when the prediction signal a is generated,
The output current I supplied from the welding power source 10 in the figure to the wire 15 as an electrode is processed from a current level before prediction (this current is referred to as main current Is) to a predetermined low level (current at this level is processed). Current Ic), for example, 80 of this current Is
Limit to ~ 70%. This processing current Ic is of a current level (burn-through avoidance level) that maintains airtightness and can prevent burn-through without causing discontinuity of the weld bead. That is, if it is a step shape, the welding may be interrupted due to the inertia of the motor of the wire feeding device, etc. Therefore, the output current command value is reduced at a certain reduction rate ΔIdown, and as shown in FIG. , A predetermined time td (for example, 0.2
Welding power source 1 so that the processing current Ic will drop after ~ 0.5 sec)
To control. However, △ Idown = (Is-Ic) / td (2) After the output current of the welding power source has dropped to the processing current Ic, this current level is maintained for tf time (for example, 0 to 1 sec) and normal welding is performed. After returning to a possible state and the time has elapsed, the current
Raise to Is level. In this case, the conditions such as the work groove gear may change, and it is not preferable to raise in a step-like manner because there is a risk of burn-through, and it is raised at a certain increase rate ΔIup, and time tu, for example, 1
It should be restored to this current Is after ~ 3sec (> td). However, △ Iup = (Is-Ic) / tu (3) If burnout is predicted during the recovery to this main current Is, the output current of the welding power source 1 will decrease from that point. The processing current Ic is reduced to the level of the rate ΔIdown, the level is maintained for tf time, and then the main current Is is restored at the rate of increase / decrease ΔIup.

Such a current pattern can be realized by calculating a current pattern by the CPU 4 and giving the pattern output to the control device 19 of FIG. 7 as a current command.

As described above, in the present embodiment, when a burn-through transfer phenomenon occurs, the welding condition is predicted and the welding condition is adjusted to the burn-through avoidance level in a non-step manner, so that the discontinuity of the bead is reduced and the burn-through is avoided. When the welding condition is restored to the normal welding condition, it is restored to a non-step state. Therefore, if a burn-through transition phenomenon occurs during the restoration, it is predicted, but as a result, a burn-through occurs. Can be prevented, and the probability of occurrence of burn-through can be significantly reduced compared to the conventional case.

When burn-through occurs despite such changes in welding conditions at the time of burn-through prediction and a burn-through detection signal b is generated, the signal is used to suspend welding and to generate an alarm. To

In this embodiment, the case in which the output current of the welding power source is controlled to avoid burn-through has been described, but burn-through can be similarly avoided even if the welding speed is adjusted. In this case, burn-through can be avoided. With the prediction of, control to increase the speed level.

It goes without saying that the output current control and the welding speed control may be used together.

〔The invention's effect〕

As described above, the present invention controls the welding conditions to a burn-through avoidance level and stabilizes when there is a sign of burn-through, and returns to normal welding conditions while monitoring the possibility of burn-through. Since it is possible to eliminate the trouble of interrupting welding and replacing or reworking the work, it is possible to improve the efficiency of arc welding of thin plates. Especially when welding robots are used, welding on the safe side due to fear of burn through There is no need to set conditions, and the effect is particularly large.

[Brief description of drawings]

1 (a) to 1 (d) are waveform diagrams for explaining the principle of the welding prediction technique in the present invention, FIG. 2 is an arc voltage waveform diagram, and FIG. 3 is an embodiment of the welding prediction technique. FIG. 4 is a block diagram of a burn-through prediction device that implements the above-described burn-through prediction technology, FIG. 5 is a flow chart showing an embodiment of the present invention, and FIG. 6 is welding conditions in the above embodiment. A waveform time chart for explaining the change mode, FIG. 7 is a block diagram of the welding apparatus, and FIG. 8 is a diagram showing a measuring method for measuring the waveform of FIG. 1 (a).

Claims (2)

[Claims] 1. In consumable electrode type arc welding, a short circuit period, which is the time from the arc voltage to the short circuit between the wire and the base metal, is monitored, and burn-through is predicted from an increase change exceeding a predetermined level of the short circuit period. The present invention is characterized in that the output current of the welding power source or the welding speed is controlled non-stepwise to a preset burn-through avoidance level at the same time as the prediction, and non-stepwise recovers to the pre-prediction level after a predetermined time. How to avoid burn-through. 2. The burn-through prediction is performed by comparing the ratio of the average value of the number of short circuits to the average value of the number of short circuits for each short circuit period with a predetermined threshold level. Method for avoiding burn-through according to the section.