JPS6139147B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a narrow gap automatic welding method for welding multiple layers of I-shaped or I-shaped butt grooves of thick plates by swinging an arc in a shielding gas atmosphere.

Narrow gap welding has recently become widely used due to its improved welding efficiency, saving on welding materials, low welding heat input, resulting in high-quality joints, and low welding distortion, and many methods have been developed. There is.

FIG. 1 shows an example of an apparatus for performing such narrow gap welding. In this drawing, two planks 1 are arranged with their end faces facing each other to form an I-shaped groove 2.
Welding torch 12 attached to welding head 11 inside
is inserted. On the other hand, a welding wire 7 having a small diameter of, for example, 1.2 mm is sent from a wire reel 13 by a feeding device 14 through a conduit tube 15 to a bending straightening mechanism 16, and is warped into an arc shape with a constant curvature. The welding wire 7 is wound around the rotating wheel 18 on the wire swing plate 17 and goes around the rotating wheel 18 once, and then is fed to the welding torch 12 through the guide tube 19. The wire swing plate 17 swings in the direction of arrow R by rotating the swing motor 21 connected thereto via a worm gear mechanism 20 in the forward and reverse directions, and accordingly, the wire protrusion 8 also moves in the direction of the welding torch 12. It swings in the direction of arrow S about the axis. Welding is performed while swinging the wire protrusion 8, and the welding pool is formed by the welding torch 1.
It is shielded by the shield gas from the second shield gas hole 22 and the side nozzle 22. Note that the welding torch 12 is cooled by cooling water flowing through the water cooling hole 23.

By the way, when forming an I-shaped groove by making the end faces of thick plates face each other, the end faces of the thick plate are usually processed by gas cutting, and therefore the groove width is along the weld line. . If the groove width fluctuates,
When welding is carried out at a constant welding speed and wire feed speed, the weld bead height becomes low at wide groove widths and high at narrow groove widths, resulting in irregularities in weld bead height along the weld line. Further, since the arc length is kept constant, the wire protrusion length becomes longer at the concave portions of the weld bead, and conversely becomes shorter at the convex portions.

As mentioned above, if the groove width fluctuates and unevenness occurs in the weld bead height, welding defects will occur due to excessive or insufficient wire amplitude. That is, suppose that the groove width _B1 has expanded to a groove width _B2 as shown in FIG. At this time, the wire extension is r ₁
However, if the swing angle θ is kept constant, the tip of the arc will not reach by δ when the groove _{width is B 2 .} Therefore, insufficient penetration occurs at the corner portion 6 where the groove side surface 2a and the weld bead surface 5a contact. On the other hand, when the groove width becomes narrow, too much melting occurs, causing slag entrainment or insufficient melting. For this reason, conventionally, an operator has to monitor the arc and, when the groove width changes, manually change the swing angle of the wire or the height of the welding torch 12 to adjust the swing amplitude of the wire. However, this method requires continuous monitoring of the arc, which poses problems in terms of labor and work efficiency.

Therefore, this invention solves the above-mentioned problems in narrow gap welding, and aims to provide an automatic narrow gap welding method that can prevent welding defects due to insufficient penetration, reduce labor, and improve work efficiency. It is.

This invention will be explained in detail below.

This invention maintains the welding torch at a constant height from the surface of the welding base material, and changes the wire swing amplitude and swing according to changes in welding current caused by changes in wire protrusion length based on irregularities in bead height. Automatically control speed.

As shown in Fig. 3, the motor 26 is driven by a signal from the surface scanning mechanism 25 that detects irregularities on the surface 3 of the base material corresponding to the welding location, and the welding head 11 is raised and lowered to be constantly attached to the welding head 11 during welding. The welding torch 12 is held at a constant height from the base metal surface 3. Welding torch 1 as above
The reason why the height position of 2 is kept constant is to determine the standard wire protrusion length of the weld bead 3 with respect to the reference plane A, that is, the standard of the welding current, which will be described later.

Further, in this invention, a DC power source with constant voltage characteristics is used and the welding wire is fed at a constant speed, so that the amount of metal at part a of the welding bead 5 is insufficient and the bead height becomes a recessed part. In some places (as mentioned above, the groove width is widened in this place), the wire protrusion length increases, the electrical resistance in this part increases, and the welding current decreases. On the other hand, in a part where the bead height is convex like part b, the wire protrusion length is reduced and the welding current increases. Therefore, irregularities in the height of the weld bead 5 can be detected by increasing and decreasing the welding current. That is, the welding current corresponding to the reference wire protrusion length is set as the reference welding current,
By comparing this with the actual welding current, it is possible to know the unevenness of the height of the weld bead 5 with respect to the reference plane A. Therefore, by adjusting the wire swing angle θ, that is, the swing amplitude, in accordance with changes in the welding current, it is possible to perform welding with just enough amplitude.

Furthermore, in this welding method, the oscillation speed and wire feeding speed are kept constant, so the oscillation speed must also change as the oscillation amplitude changes. In other words, unless the rocking speed is adjusted according to the rocking amplitude,
The rocking pitch becomes rough, resulting in insufficient penetration.
Experiments have shown that the oscillation density (=number of oscillations per unit time/welding speed) is preferably 1 (times/cm) or more in order to prevent insufficient penetration.

Here, the narrow gap automatic welding method of the present invention will be explained using a specific example. First, the welding conditions are as follows.

Welding power source DC constant voltage characteristics (DC500A) Welding wire (solid) 1.2φ Loop diameter 180φmm Shielding gas Ar＋CO ₂ 10% Flow rate 40/min Bevel shape I-type narrow gap Standard gear 11mm Standard welding current 300A Standard welding voltage 27V Oscillation Speed 25cm/min Wire feeding speed 10m/min Standard overhang length 26mm Standard bead height 4mm/Pass standard swing amplitude 9mm The reason why the standard swing amplitude is 2mm narrower than the standard groove width is because the tip of the arc is at its maximum. This is because good welding can be achieved by positioning the weld 1 mm inside the corner when the weld swings out.

FIG. 4 is a graph showing the relationship between the change in bead height ΔH and the change in groove width ΔB. This example shows that the bead height decreases by 1 mm because the groove width increases by 3.7 mm.

Figure 5 is a graph showing the relationship between the change in welding current △A and the change in bead height △H.
This shows a decrease of 2.5A.

FIG. 6 is a graph showing the relationship between the change Δα in the oscillation amplitude with respect to the change ΔA in the welding current and the ratio N/No between the reference oscillation speed No and the adjusted oscillation speed N. As is clear from this figure, in response to an increase in groove width of 3.7 mm, or a decrease in welding current of 2.5 A, the wire swing amplitude must be increased by 3.7 mm and the swing speed must be doubled (80 times/min). .

The swing amplitude is changed by changing the swing angle as shown in FIG. In this example, to change the swing amplitude from 9 mm to 12.7 mm, the swing angle must be increased from 90° to 180°.

Next, an example of the control means used to implement the method of the present invention will be explained.

FIG. 8 is a block diagram of a control system that maintains the welding torch 12 at a predetermined height. In the figure, the height position of the welding torch 12 is set in the welding torch 12 height setting part 31 so that the tip of the welding wire is separated from the reference surface of the welding bead by a predetermined distance, that is, the reference wire protrusion length. do. On the other hand, the base material surface 3 is
The comparison section 32 compares the signal with the signal from the welding torch height setting section 31. The motor drive circuit 33 drives the welding head drive motor 26 based on the signal from the comparator 32 to raise and lower the welding head 11 and position the welding torch 12 at a predetermined height. Note that the signal from the welding torch movement amount detector 34 is input to the comparison section 32, and the welding torch 12 is always maintained at a constant height position with respect to the base metal surface 3 by feedback control.

FIG. 9 is a block diagram of the wire swing amplitude and swing speed control system. The anode and cathode of the welding power source 41 are connected to the welding wire 8 and the base metal 1, respectively, and a shunt 42 for detecting welding current is provided between the anode and the welding wire 8. shant 42
The signal from is sent to comparators 44 and 45 via an amplifier 43. The comparator 44 includes the amplifier 43
, a signal from the amplitude setting section 46 and a feedback signal from the swing angle detector 47 are input, and the signal from the comparison section 44 determines the switching point of the swing direction so that the swing angle is a predetermined swing angle. The signal is sent to the swing direction discrimination circuit 48 for judgment. Then, the signal from the swing direction discrimination circuit 48 is sent to the swing direction switching section 49. The comparison section 45 also includes the amplifier 43
A signal from the swing speed setting section 50 is input, and a required swing speed is calculated based on the signal from the swing motor drive circuit 45. A speed signal from the swing motor drive circuit 51 is input to the swing motor 21 via the swing direction switching section 49, and the welding wire 8
is driven to swing at the required amplitude and speed based on this signal.

As described above in detail, the narrow gap welding method of the present invention allows the welding work to be performed automatically instead of manually, thereby significantly reducing labor and improving work efficiency. In addition, the automatic operation method detects the welding current and controls the swing amplitude and swing speed of the wire based on the difference between the detection signal and the reference welding current, so there is no need to over or under the weld bead width. , and narrow gap welding can be performed with a small unevenness difference. Therefore, welding defects due to insufficient or excessive penetration rarely occur.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an example of a narrow gap welding device to which the present invention is applied, Fig. 2 is an explanatory diagram of changes in oscillation amplitude due to changes in groove width, and Fig. 3 is a welding head and surface. A schematic diagram showing the copying mechanism and a cross section of the weld bead; FIG. 4 is a graph showing the relationship between the change in groove width ΔB and the change in weld bead height ΔH;
The figure is a graph showing the relationship between the change △H in welding bead height and the change △A in welding current, and Figure 6 shows the relationship between the change △A in welding current, the change in oscillation amplitude △α, and the oscillation speed ratio.
Graph showing the relationship with M/No, Figure 7 is an explanatory diagram of swing amplitude and swing angle, Figure 8 is a block diagram of the welding torch height position control system, and Figure 9 is wire swing amplitude and speed. FIG. 2 is a block diagram of the control system of DESCRIPTION OF SYMBOLS 1... Base metal, 2... Bevel, 5... Welding bead, 6... Corner part, 7, 8... Welding wire, 11... Welding head, 12... Welding torch, 14... Wire feeding device,
16... Wire bending habit imparting mechanism, 17... Rocking plate,
21... Swing motor, 22... Shield gas hole, 25
...Surface copying mechanism, 26...Welding head lifting motor,
41... Welding power source, 42... Shunt.

Claims (1)

[Claims] 1. The welding wire is fed to the welding torch by passing through a rocking plate that has a constant curvature and deforms it in an arc shape, and by rocking the rocking plate around the axis of the welding torch, the wire protrusion is rocked. In this method, a constant voltage power source is used, the welding speed and wire feeding speed are kept constant, and the welding torch is aligned in a plane. The wire is oscillated according to the difference between the standard welding current and the actual welding current to keep the wire at a constant height from the surface of the welding base material using a mechanism, and to prevent welding defects from occurring due to excessive or insufficient wire oscillation amplitude. A narrow gap automatic welding method characterized in that welding is performed while changing the swinging angle of a moving plate to change the amplitude of wire swinging and controlling the vibration speed of the swinging plate.