JP2502642B2 - Automatic welding method with arc sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial field In order to automate the arc welding process, it is necessary to automatically correct the temporary welding error of the arc welding work, the error when fixing it on the workbench, the error due to thermal strain during welding, etc. Must be corrected to. For this purpose, a position sensor that detects the actual displacement of the joint position with respect to the welding line, which has been taught to an automatic welding machine in advance, is required.

Various types of position sensors have been devised,
One of them is an arc sensor that uses the welding phenomenon itself as a sensor. The present invention relates to an automatic welding method using this type of arc sensor.

2. Description of the Related Art As an arc welding power source, a power source having a constant voltage characteristic is the most common. Regarding the arc characteristics of this type of power source, the arc current and voltage change as the arc length changes. On the other hand, since the joint to be welded has some shape change, the arc length changes due to this shape change, and thus the current or voltage changes. Therefore, by observing the welding current or the welding voltage, the change in the work shape can be known.

The above is the principle of the arc sensor. However, in reality, there are various noise components, and the above-mentioned changes in current and voltage may not be clearly obtained. Particularly, a work whose shape change is small, for example, a stacked work of thin plates, corresponds to that. Further, there are cases where the welding arc phenomenon itself is not stable, for example, welding may be necessary in a current region where there are many short circuit transitions. FIG. 4 shows a record of welding current and voltage in a relatively low current region by the mixed gas. A point where the voltage drops to 0V indicates that a short circuit has occurred. It can be seen that the current changes greatly when a short circuit occurs.

On the other hand, conventionally, it has been dealt with by removing noise by devising software of a circuit or a high-speed microcomputer, or by making a welding power source suitable for a sensor.

Problems to be Solved by the Invention As described above, removal of noise components is essential, but there are drawbacks in that the software of the high-speed microcomputer is complicated and a welding power source suitable for sensors is required. The present invention is to obtain a welding current or voltage which originally has less noise by devising a weaving method.

Means for Solving the Problems In order to solve the above problems, the present invention oscillates a welding torch by a motion that is a combination of a motion along a joint of a workpiece and a circular motion or a polygonal motion. The circular motion or polygonal motion is divided into several phases, and welding is performed under different welding conditions such as different current, voltage or peripheral speed.

Action With the above means, the preceding portion in the welding bead forming direction is sensed in a current state where the arc phenomenon is stable, and then welding is performed under the required welding conditions.

Since the sensing is in a stable current range, it is possible to detect a change in current due to a shape change in a state where there are few fluctuation components.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, 1 is the work, 2 is the welding line of the lap joint, and 3 is the trajectory of the torch tip. FIG. 2 shows the locus of the torch tip when movement in the welding line direction is removed, and 4 is the welding line direction and 5 is the locus of the torch tip. In FIG. 2, I and II represent each of the two circular motions. FIG. 3 schematically shows the variation ratio of the welding current. (A) is a low current region, and (b) and (c), the welding current increases toward the right. If the current becomes small, a short circuit will occur during welding. Therefore, the fluctuation of the welding current is generally small when the current is large to some extent. These will be described in detail using actual measurement data.

4 to 6 show welding currents and voltages that actually flow when welding is performed with a mixed gas of 80% Ar and 20% CO ₂ . The condition instruction to the welding power source is 170A, 18.5V in Fig. 4 and 225A, 21.5 in Fig. 5.
V, Fig. 6 is 280A, 25.5V. A voltage drop to 0V indicates a short circuit between the wire and the base metal. Obviously Figure 4 is the most numerous Figure 6
Is the least. The range of current change is 50 to 300 A in Fig. 4, and Fig. 5
110-430A, 170-450A in FIG. When the change width / indicating current value is obtained as an index of the magnitude of change, it is 1.5 in FIG. 4, 1.4 in FIG. 5 and 1.0 in FIG. 6, and it can be said that the case of FIG.

It is shown in FIG. These figures are experimental data of arc sensor output. The horizontal axis shows the amount of deviation from the welding line. The vertical axis represents the difference between the welding current value on the right side and the welding current value on the left side of the welding line output by the arc sensor. In this experiment, the center of the joint and the center of displacement of the horizontal axis do not exactly coincide with each other because of the device. In the figure, the abscissa indicates the section with an arrow in the range where good results are obtained as welding. By comparing the ranges of FIGS. 7 to 9, it is apparent that FIG. 9 is better as a sensor than FIGS. 7 and 8.

Next, the peripheral speed will be described. As the speed across the weld line is increased, the difference between the actual currents on the right and left sides of the weld line generally increases. This is shown in FIG. The horizontal axis represents the weaving frequency, and the vertical axis represents the difference current for each time. If the weaving frequency is increased, in addition to this, the number of detections per unit time is increased, so that the detection capability of the sensor is further improved.

In Fig. 2, when the torch tip is moving in the circular region II, that is, the region preceding the welding bead forming direction is sensed by a stable current state of the arc phenomenon or by moving the torch quickly. Then, the region I is welded under the required welding conditions. This state is repeated in the weaving cycle.

Since it is a stable current region, it is possible to capture the change in current due to the shape change in a state where there are few fluctuation components. The bead generated at this time is immediately replaced with the bead generated under appropriate welding conditions, so there is no problem. As a result, stable sensing can be performed even when the desired welding conditions are large variations in current and voltage.

The welding conditions in the region I should be appropriate considering the welding conditions in the region II. Generally, the welding conditions in the phase section where the sensing is performed are different from the welding conditions for obtaining the necessary weld beads. Therefore, the phase widths of the regions I and II in FIG. 2 are not the same and generally differ depending on the required welding condition values. Since an ordinary weaving pattern is realized by a combination of short linear movements, it is preferable to teach a polygonal pattern if the difference in the two phase widths is realized by teaching the weaving pattern.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to distinguish between a phase section in which no sensing is performed and a phase section in which no sensing is performed, and it is possible to perform sensing under favorable welding conditions for the sensor. It can be obtained as sensing information.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part showing a locus of a torch tip in an automatic welding method using an arc sensor showing an embodiment of the present invention, and FIG. 2 is a plan view of a main part showing a locus of circular motion of the torch tip. FIG. 3 is a characteristic diagram showing the variation ratio with respect to the welding current, and FIGS. 4 to 10 are diagrams showing experimental data. 1 ... Work, 2 ... Weld line, 3 ... Torch tip locus.

Claims (1)

(57) [Claims] 1. An automatic welding method using an arc sensor, wherein a welding torch is oscillated in a direction traversing a welding line, a change in arc current or arc voltage is detected, and a relation between a joint of a work and an arc generation position is obtained. When the welding torch is not rocked, the welding torch is rocked by a motion that is a combination of the motion in the direction along the joint and the motion of the tip of the welding torch in the circle or polygon direction. Alternatively, an automatic welding method using an arc sensor, characterized in that the movement in the polygonal direction is divided into several phases and welding is performed under different welding conditions such as different current, voltage or peripheral speed.