JPS6376762A - automatic welding method - Google Patents

Abstract

PURPOSE:To prevent interruption or burn through of the welding by detecting an arc sound at the time of welding and judging a welding state to control the operation of the welding based on the judgement. CONSTITUTION:A sound collecting device 13 is provided to a torch 11 in opposition to a work 10 and a frequency analyzing device 14 and a welding condition changing device 15 are provided to the sound collecting device 13. The arc sound generating at the time of welding is collected by the sound collecting device 13 provided to the torch 11 and frequency is analyzed by the frequency analyzing device 14. At this time, the abnormality of the welding state is detected via the comparison between the an integration value and a threshold of the arc sound in a prescribed time or the comparison of a characteristic value for every frequency. Next, a welding current of the torch 11 is lowered by the welding condition changing device and held for a prescribed period of time and afterward, returned to the current at the time of the normal welding. Since the welding state can be maintained normally, the interruption or the burn through of the welding can be prevented by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic welding method in which a welding portion of a workpiece is automatically welded with a torch.

As an example of a conventional automatic welding method, as shown in FIG.
is arranged as a constant, the welding part 2 is detected by some means and the torch 3 is moved along the entire welding part 2,
A method is known in which the current supplied to the torch 3 is kept constant.

Further, as shown in FIG. 11, the torch 3 is opposed to the welding part 2 of the workpiece 1 at a predetermined angle θ, and the position where the extension line 3a of the torch 3 touches is a predetermined distance from the back part 2a of the welding part 2. There is a known method for controlling welding reliability in real time using an arc sensor.

In the welding method for the former type of inter-assembly point that the invention seeks to solve, if the shape of the welded part 2 differs due to machining errors or incorrect setting of the workpiece 1, the weld bead protrudes from the back part 2a of the welded part 2, resulting in so-called punch-through. When this occurs, the torch 3 moves forward around the workpiece 1 in order to keep the current constant, so the torch 3 moves forward when the 12th
As shown in the figure, the robot system that moves the torch 3 is turned off due to the shock when it comes into contact with the workpiece 1, or because a minute force b1ε flows from the torch to the workpiece 1. The robot system that moves the torch 3 is turned off, and the torch 3 stops and the welding operation is interrupted. It will be temporarily interrupted.

In addition, in the case of the latter welding method, if a penetration occurs, welding continues with the penetration, resulting in a welding defect.When positioning the torch 3 using a contact sensor, The position of the torch 3 has shifted due to the shift of the workpiece, etc., and the torch 3 cannot be placed in the correct position and is brought into contact with the torch.
This will lead to poor fusion.

Measures and functions to solve the problem Detect the arc noise generated during welding, determine whether it is a steady welding state or an abnormal welding state based on this arc sound, and then operate to achieve a steady welding state. This prevents the welding work from being temporarily interrupted or from continuing welding with the butt in place.

In the torch II arranged opposite to the example workpiece 10, there is a welded part υ.
12 supplies current, and a concentrator 13 is provided to detect the arc sound during welding, send the arc sound to the frequency analyzer 14 to detect changes in the welding state, and based on that, determine the welding conditions. The change device 15 outputs a welding current change signal to the welding power source 12 to change the welding current sent to the torch 11.

Specifically, the frequency of the collected arc sound is analyzed by the frequency analyzer 15, and the integrated value of the arc sound over a certain period of time is compared with the magnitude of a threshold value to detect a difference and detect an abnormality.
Alternatively, an abnormality is detected by comparing characteristic values for each frequency and finding the difference.

If the difference becomes large and an abnormal welding condition is determined,
As shown in FIG. 2, based on the difference, the current to the torch 11 is increased from 1 to 1 in the steady welding state. Δt1 is maintained for a predetermined time, and then the slightly high current II C,I
＞I! > 11) for a predetermined time Δt, and then the current is returned to 1 in the steady welding state.

Figure 3 (a), (b) and Figure 4 ('l, (b)
are the arc sound detection waveform and frequency analysis result waveform during steady welding conditions, and the arc sound detection waveform and frequency analysis result waveform during abnormal welding conditions.The arc sound detection waveform is displayed by converting sound pressure into voltage. In addition, the frequency analysis result waveform is an arc sound pressure integral value from 0 to 500 Hz, and indicates the magnitude of the frequency contributing to the sound pressure.

To summarize the above, it detects changes in the arc sound that occur during welding, detects abnormal welding conditions such as butt welding, reduces the current for a certain period of time, increases it slightly, and continues welding for a certain period of time. The current is controlled so as to return to the current in the steady welding state, thereby preventing continuous butt contact and allowing continuous welding.

In addition, as another example, arc sound is detected in the same manner as described above, and if the arc sound is large and the low frequency level is large with respect to the reference value (threshold value), as shown in FIG. 5 (a). As shown in Fig. 6 CQ), the torch 11 is moved away from the welding part 16, and if the arc volume is small, the pigeon wave is low, and the bell is small (Fig. 6 CQ). Figure 8 σ, b)
In this case, as shown in FIG. 5Cb), it is determined that there is poor penetration, and the torch 11 is brought closer to the welding part 16 as shown in FIG. 6H.

In this way, as shown in FIG. 5(C), the welding bead 17 always protrudes slightly from the back 16σ of the welded portion 16, and welding can be performed in a steady welding state in which a correct back wave is obtained. In addition, at this time, the waveform of the arc sound is intermediate between FIG. 7 and FIG. 8.

Alternatively, the magnitude of the current in the torch 11 may be detected based on the arc volume, and as shown in FIG. 9, the torch may be moved away when the current is larger than a reference value, and may be moved closer when the current is smaller than the reference value.

Effects of the Invention Since the operation is controlled to always maintain a steady welding state based on the arc sound generated during welding, it is possible to prevent welding work from being temporarily interrupted or to continue welding with the butt welding state unchanged.

[Brief explanation of the drawing]

Figures 1 to 4 show one embodiment of the present invention, with Figure 1 being an explanatory diagram of the overall configuration, Figure 2 being a chart showing the current control state, and Figure 3 ('+ + (b) and Figure 4 <a) and (b> are charts showing the arc sound waveform and the frequency analysis result waveform.
Figures to Figures 8 show the second embodiment, and Figures 5 (Q), (,
6+, (C) is an explanatory diagram of the welded state, FIG. 6(a). (h) Vi operation control explanatory diagram, Fig. 7'Tb% Fig. 8a. A chart showing the arc volume waveform and the frequency analysis result waveform,
FIG. 9 is an explanatory diagram of the operation of the third embodiment, and FIGS. 10, 11, and 12 are explanatory diagrams of the conventional example.

Claims (1)

[Claims] It is characterized by detecting the arc sound generated during welding, determining whether it is a steady welding state or an abnormal welding state based on this arc sound, and controlling the operation accordingly to maintain a steady welding state. Automatic welding method.