JPH0454547B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a single-sided automatic arc welding method using a backing material, and in particular, performs stable single-sided welding, maintains a good back bead shape, and improves the front bead shape. The present invention relates to a single-sided welding control method that controls the height to be kept constant.

[Prior art]

In welded joints, variations in shape such as groove width and angle cannot be avoided, so it is necessary to detect these variations and automatically control welding conditions. It can be said that there are currently no useful detection sensors for this purpose.
There are only a few methods that use ITV or laser light to detect the groove width in front of the arc.

[Problem that the invention seeks to solve]

However, even in the above method, there is a limit to the detection accuracy due to the deviation between the arc position and the detection position, and furthermore, since a unique device called a sensor separate from the welding torch is installed near the torch, it is difficult to measure due to the size. There are restrictions on its application. Therefore, in single-sided welding under such circumstances, no effective sensor or control method has yet been proposed that accurately reflects the state of the molten metal at the arc position with respect to fluctuations in the groove shape.

The present invention utilizes the characteristics of the welding arc to automatically control welding conditions by detecting the state of molten metal at the arc position without using a separate sensor, even if there are fluctuations in the groove state. We developed a single-sided welding control method that always maintains the thickness of the molten metal directly under the arc and performs stable single-sided welding, thereby forming a good back bead shape and a front bead of a constant height at the same time. This is what we are trying to provide.

[Means for solving problems]

In order to achieve the above object, the present invention provides a single-sided automatic arc welding method using a backing material, in which the axial direction (Y axis) of the welding electrode is maintained so as to maintain a preset welding current or arc voltage. In an arc welding method that uses a moving mechanism to change the distance between the electrode tip and the surface of the base material, thereby performing a control operation that keeps the arc length constant, detection is performed based on the bottom of the groove or the surface of the base material. The axial height distance of the welding electrode is used to detect changes in the thickness of the molten metal directly under the arc, and to obtain a good back bead shape and a front bead of constant height over the entire length of the welded joint. Automatically control welding speed.

[Effect]

In single-sided welding, where the molten metal is directly below the arc, the penetration and back bead are formed by heat transfer by conduction and convection. Maintaining a constant value is a condition for stable welding.

FIG. 7 shows a cross section of a weld bead including a welding torch during single-sided welding.

The molten metal behind just below the arc is pushed up by the arc pressure and is balanced at a molten metal head h at a certain height. Since the arc pressure depends on the welding current value, if the welding current is constant, the height h of the molten metal head is constant.

On the other hand, the thickness hm of the molten steel directly under the arc is the value obtained by subtracting the molten metal head h from the total thickness H of the bead.If the welding speed is constant, for example, if the groove width tends to increase, hm will be As the arc decreases, the backing bead protrudes too much and the arc penetrates into the backing material. Furthermore, if the groove width tends to decrease, hm increases, leading to insufficient protrusion of the back bead.

Therefore, by keeping the welding current constant and controlling the welding speed so as to keep the thickness hm of the molten metal directly under the arc constant, stable one-sided welding is possible, and a good back bead shape can be obtained. The height of the surface bead can also be kept constant.

[Embodiments of the invention]

FIG. 1 is a configuration diagram of a welding apparatus showing an embodiment of the present invention, in which 1 is a base material to be welded, 2 is a groove, 3 is a welding cart, 4 is a mechanism for moving the welding electrode in the height direction, and 5 is a consumable or non-consumable welding electrode, 6 is a displacement meter, 7 is a
8 is a welding power source, 8 is an arc voltage detector, 9 is an arc current detector, 10 is a motor, and 11 is a position detector.

In the figure, the welding cart 3 is movable in the direction of the groove line, and the welding electrode 5 is supported by the welding cart 3 via the moving mechanism 4. It is movable in both forward direction. Further, the displacement of the electrode 5 in the Y-axis direction is detected by a displacement meter 6 such as a potentiometer, and the displacement in the groove line direction is detected by a detector 1 such as a contact roller.
1, the position of the electrode 5 on the surface of the base material is always determined.

A power source 7 is connected between the electrode 5 and the base material 1, and a constant current power source or a constant voltage power source can be used as the power source 7 depending on the welding purpose.

The basic control in this welding device is constant arc length control welding, which is performed by moving the electrode 5 in the height direction (Y-axis) so that the arc length is always constant. This is performed by a moving mechanism 4 driven by a motor 10.

Figure 2 shows the basic circuit block for constant arc length control by the motor 10, and shows the arc voltage from the welding voltage detector 8 when the power supply 7 is a constant current power supply, and the arc voltage from the welding voltage detector 8 when the power supply 7 is a constant voltage power supply. inputs the welding current from the welding current detector 9 to the differential amplifier 14, causes the amplifier 14 to output the difference from the reference value set in advance in the setting device 12, and operates the motor 10 at a speed according to this differential output. A drive controller 13 for driving is provided. This circuit keeps the arc voltage (or welding current) constant and the arc length constant.

Fig. 3 shows the movement of the electrode and the states of the molten metal and weld bead during single-sided welding using the apparatus of Fig. 1 having the control system shown in Fig. 2, where a indicates stable welding under appropriate conditions. b is the case where the groove width becomes wider.

In the figure, 15 is a backing material, 16 is a front bead, and 17 is a back bead.

In Figure 3a, an appropriate thickness is placed directly under the arc.
There is molten metal hm ₁ , the electrode is kept at a height such that the welding current is constant, and the height of the molten metal head is h.

In addition, if the groove width increases while the welding conditions shown in b remain constant, the total height of molten metal within the groove will be
On the other _hand , since the welding current is constant, the height h of the head of the molten metal is constant, so the thickness of the molten metal directly under the arc decreases to hm _{2 ,} and the welding current decreases. The electrode height, whose movement is controlled to be constant, is △ey compared to the case of a.
only becomes lower.

Figure 4 is an example of experimental results showing the electrode height ey and the front and back bead heights h _F and h _B with respect to changes in the root cap when welding under constant welding conditions.
If the welding conditions are constant and the root gap increases, the back bead height h _B will hardly change, but the front bead height h _F will decrease. Also, the electrode height at this time
ey decreases as the root gap increases. Furthermore, in this case, at a position where the root gap exceeds 9 mm, there is no molten metal directly under the arc, resulting in extremely unstable welding, which eventually becomes impossible.

According to the present invention, the change in the electrode height at this time is detected, the welding speed is controlled to keep the electrode height constant, and stable one-sided welding is performed to achieve a good back bead shape and at the same time. This is to obtain a surface bead of a certain height.

FIG. 5 is a circuit block diagram for detecting the height distance in the axial direction of the welding electrode with respect to the base metal surface and controlling the speed of the welding cart 3 so that the height distance is always maintained at a predetermined value. . Using the output of the detector 11 for detecting the position of the base metal surface, the output of the displacement meter 6 for detecting the electrode height position is always corrected based on the base metal surface, and the difference is compared with the reference value 18 of the electrode height. The running speed of the welding cart 3 is controlled by the cart driving machine 20 by changing the speed command value from the cart running speed setter 19 so that the value becomes zero.

In the above description, the height distance in the axial direction of the welding electrode is based on the surface of the base material, but it may be based on the bottom of the groove instead of the surface of the base material. That is, the contact roller of the detector 11 is caused to run on the bottom of the groove, and the output of the displacement meter 6 for detecting the electrode height position is always corrected based on the bottom of the groove. When using the bottom of the groove as a reference, instead of using the roller described above, the depth of the groove may be determined and calculated relative to the surface of the base material.

Although this embodiment is an example in which the electrode is not oscillated, even when welding is performed while the electrode is oscillated in the width direction within the groove, the height of the electrode near the center of the groove can be detected, for example. Accordingly, the present invention can be applied in the same way as the above method.

〔Effect of the invention〕

As described above, in single-sided arc welding, the present invention detects changes in the height distance of the welding electrode with respect to the base metal surface, and controls the welding speed to keep the electrode height constant. Stable single-sided welding became possible, and a good back bead shape as well as a front bead of a constant height were obtained.

FIG. 6 shows the results of the control method according to the present invention. As shown in the figure, as the root gap G increases, the welding speed is controlled and decreased, and the electrode height is kept almost constant. An unstable state was not caused, and a good back bead and a front bead with a constant height h _F were obtained over the entire weld length.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a welding device showing one embodiment of the present invention, Fig. 2 is a configuration diagram of constant arc length control, and Fig. 3 is a configuration diagram of a welding device showing an embodiment of the present invention.
The figure is an explanatory diagram of the welding situation, where a shows the situation when stable welding is performed under proper conditions, and b shows the situation when the groove width becomes wide. Fig. 4 is a diagram showing the relationship between the electrode height and the height of the front and back beads when welding under constant welding conditions, Fig. 5 is a configuration diagram of the control according to the present invention, and Fig. 6 is the effect of the present invention. FIG. 7 is an explanatory diagram of welding. In the figure, 1 is the base material to be welded, 2 is the groove, 3 is the welding cart, 4 is the electrode height movement mechanism, 5 is the welding electrode, 6 is the electrode height displacement meter, 7 is the power source, 8 9 is a welding voltage detector, 9 is a welding current detector, 10 is a motor, 11 is an electrode position detector, 12 is a setting device,
13 is a drive controller, 14 is a differential amplifier, 15 is a backing material, 16 is a front bead, 17 is a back bead, 18
19 is a reference value for the electrode height, 19 is a truck running speed setting device, and 20 is a truck driving machine.

Claims (1)

[Claims] 1. A single-sided arc welding method using a backing material on the back side of the groove, in which a welding electrode axially moving mechanism is used to maintain a preset welding current or arc voltage. Therefore, in a single-sided welding method using arc welding, in which the distance between the electrode tip and the surface of the base metal is changed, thereby performing a control operation in which the arc length is always constant; By detecting the bottom of the tip or the surface of the base metal as a reference and controlling the welding speed to keep the height and distance constant, the thickness of the molten metal directly under the arc can be kept constant and stable single-sided welding can be performed. Therefore, the method for controlling single-sided welding is characterized in that a good back bead shape can be obtained and the height of the front bead can be kept constant.