JPH0241776A - Gas shielded arc welding method - Google Patents

Abstract

PURPOSE:To improve an arc start characteristic and to ensure restarting by feedback- controlling the welding output to a constant current until the prescribed solidification control time elapses from the welding stop and controlling a solidification shape of the tip of an electrode to control the sticking position of slag. CONSTITUTION:When a switch 17 is turned off and the welding stop is commanded to control parts 7, 14 and 15, a motor 8 is rotated by inertia and the electrode 1 continues to be fed. In addition, even if an action of the control part 14 is stopped and a level of an output signal of the control part 14 is lowered, the welding voltage is decreased. A welding current is also decreased based on the feed speed decrease of the electrode 1 and the voltage decrease of the welding output. Meanwhile, with the control part 15, stop timing of an action is delayed by the prescribed solidification control time from off-timing of a contact point 18c by an inside delay means and the control part 15 is actuated. An output signal of the control part 15 is then increased by the decrease of the welding current and immediately after the welding stop is commanded, the output signal side of the control part 15 is increased to a higher level by the output signal of the control part 14 and the output signal of the control part 15 is supplied to an output part 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas-shielded arc welding method for gas-shielded arc welding a base material to be welded using a consumable electrode.

[Prior art] Conventionally, when gas-shielded arc welding is performed on base metals to be welded using a consumable single electrode, inexpensive carbon dioxide gas is used as the shielding gas instead of expensive inert gas such as argon or helium. It is hoped that

When performing gas-shielded arc welding using carbon dioxide, by driving the electrode feed motor.

A wire-shaped consumable electrode is fed in the direction (downward) of the base metal to be welded via a torch, and carbon dioxide gas as a shielding gas is supplied in the direction of the base metal from the nozzle at the tip of the 1-chi. .

Further, a feedback-controlled DC welding output is supplied to the welding load formed by the electrode and the base metal.

Then, when the tip of the electrode short-circuits to the base metal, a short-circuit arc is generated, and the arc is started, the welding output is controlled to a constant voltage by the feedback control, and the starting state shifts to a steady state. A short circuit and arc generation are alternately repeated between the electrode and the electrode, and at this time, the molten metal at the tip of the electrode is welded to the base metal, and the base metal is arc-welded.

Note that during welding, the l/-chi or the base metal is moved as welding progresses.

Furthermore, when the torch switch is turned off and a command is given to stop welding due to the completion or interruption of welding, the driving of the electrode feed motor is stopped, the feedback control is completely stopped, the welding output is cut off, and the parent phase welding is stopped.

[Problem to be solved by the invention]

When a gas with a large potential gradient, such as carbon dioxide gas, is used as a shielding gas in gas-shielded arc welding, based on the potential gradient, during arc generation, as shown in Figure 5,
The melted part (2) at the tip of the consumable electrode (1) grows into a spherical shape, and a part of the lower surface of the melted part (2) grows into a small point area (
An arc (A) occurs between 2 and lN14J (3).

Further, lj5 acid Ganu, which is inactive at room temperature, partially dissociates into carbon monoxide and oxygen in a high-temperature arc atmosphere.

Then, during arc generation, the oxygen combines with impurities such as silicon and manganese contained in the molten part (2),
Impurities are discharged from the fusion zone (2) as slag mainly composed of silicon oxide and manganese oxide, and based on this action, healthy molten metal is deposited on the base metal (3), resulting in good arc welding.

By the way, as shown in FIG. 5, the forces acting on the molten part (2) include gravity Fg1 surface tension Fs and arc force Fa.

One gravitational force Fg acts as a constant downward force, and the surface tension Fs acts as a downward force that changes depending on the temperature and the like.

However, the arc force Fa generated only during arc generation acts as an upward force in a carbon dioxide atmosphere where the diameter of the generation point region (2)' is smaller than the diameter of the electrode (1).

Then, during welding, based on the surface tension Fs and the arc force Fa, the sub-finish portion 1 (2) grows into a spherical shape as described above.

On the other hand, when the arc (A) is extinguished by stopping welding and the arc force Fa becomes zero, only the surface tension Fs acts on the molten part (2) as a force in two directions, and the melting occurs mainly due to the single surface tension Fs. The solidification shape of the portion (2) is determined, and when the solidification time is short, the molten portion (2) solidifies into a spherical shape.

However, the melting point of the slag is lower than that of the metal in the molten zone (2), and the specific gravity of the slag is higher than that of the metal in the molten zone (2), especially when the welding output current (welding current) is 1
When the current is medium to low, about 50A or less, the arc (A)
As shown in FIG. 5, the slag (4) solidified into a film is attached to the lowermost surface of the molten zone (2), which has solidified into a spherical shape due to the disappearance of the slag.

Then, the slag (4) becomes an electrical non-conductor at room temperature, and when welding is started again, the molten part (2) K slag (4)
If the slag (4) adheres to the arc (A)
The occurrence of the welding current is reduced, the rate of arc occurrence is reduced, and the generated arc is likely to disappear before reaching a steady state.
The arc start characteristics of restart will deteriorate, making restart extremely difficult.

By the way, the welding current and the feed speed of the electrode (1) have a proportional relationship, and even if the drive of the electrode feed motor is stopped due to stopping welding, the inertia of the motor causes the electrode ( 1) continues to be fed.

However, as the welding current increases, it takes more time for the welding output to decrease and be cut off by stopping the welding.

When the welding current becomes a large current of 20 OA or more, the electrode (1) remains in contact with the base metal (3
), and after the arc (A) is extinguished, the molten part (2) is pulled upward and the molten part (2)
It becomes possible to control the solidified shape of the slag (4) and the adhesion position of the slag (4).

In addition, when the welding power is large and the welding current is large, even if the solid shape of the molten part (2) and the adhesion position of the slag (4) are the same as when the welding current is medium or small, when restarting , it is relatively easy to create an arc (A
) occurs, and restarting is relatively easy.

However, when the welding output is small and the welding current is medium or small, the inertia of the motor is small, and the feeding of the electrode (1) is stopped in a short time after the welding stop command is issued, and the welding output Since the slag (4) is quickly cut off, the above-mentioned flare-up phenomenon cannot occur, and the slag (4) adheres to the lower surface of the molten part (2) which has solidified into a spherical shape as described above, and the welding Since the output energy is small, restarting is extremely difficult.

Therefore, especially when the welding current is low, such as about 150 A or less, the electrode (
1) It is necessary to cut the tip diagonally and process it into a sharp shape that exposes the metal surface so that arcing is easy to occur.

Even if pre-treatment is performed, it is not always possible to restart the machine reliably, so even when performing welding work in combination with a welding robot (X) and any automatic equipment, preparations must be made in case arc start fails. It is necessary to always have a staff member on hand, making it impossible to unattend welding work.

Even if the welding current is medium or small, the present invention can reliably restart the welding process without cutting the electrodes as pre-processing, and in combination with a welding robot etc., welding work can be automated. The purpose of the present invention is to provide a gas-shielded arc welding method that enables the following.

[Failure to solve the problem]

The means for achieving the above object will be explained below.

The present invention supplies a welding output feedback-controlled to a constant voltage to a welding load formed by a consumable electrode fed by driving an electrode feeding motor and a base material to be welded, and In a gas-shielded arc welding method in which short circuits and arc generation are alternately repeated between
When the driving of the motor and the constant voltage control of the welding output are stopped based on the welding stop, the welding output is feedback-controlled to a constant current until a predetermined solidification control time has elapsed from the welding stop; A technical measure is taken to control the position of slag adhesion by controlling the solidified shape of the tip of the electrode.

[Function] When the drive of the electrode feed motor and the constant voltage control of the welding output are stopped based on the welding stop, the electrode continues to be fed due to the inertia of the motor, and a predetermined coagulation control time has elapsed since the welding stop. Welding output is controlled at constant current until
Even if the welding current is medium or small, it is controlled so that energy is given to the molten part at the tip of the electrode and the solidification rate is slowed down. The shape of the part changes from a spherical shape, and the slag attachment position shifts from the bottom end of the electrode.

Therefore, at the time of restart, the slag does not stop the generation of an arc, and furthermore, the arc that has already occurred does not go out, so that the arc start characteristics are improved and the restart can be performed reliably.

〔Example〕

One embodiment will be described below with reference to FIGS. 1 to 4.

Figure 1 shows the case where carbon dioxide gas is used as the shielding gas.
In the same figure, (4) and (5) are welding equipment (6)
The first and second power supply terminals are connected to an AC power source such as a commercial AC power source, respectively. (7) is a wire feeding control unit connected to the power supply terminal (4), and the electrode feeding controller (
8), and the wire-shaped electrode (1) is connected to the torch (
9) in the direction (downward) of the base material (3).

00) is a control output unit connected to the power supply terminal (5), which supplies DC welding output generated by thyristor rectification or inverter drive to the welding load 0υ formed by the electrode (1) and base metal (3). do. 02. θ■ is a current detector and a voltage detector that detect the load current and load voltage, respectively.

Q4) is the detector α4. (This is a steady-state control unit to which the current and voltage detection signals in 1. The difference signal is output as a constant voltage control signal. 00 is a constant current control unit to which the current detection signal of the detector 02) is input.

αQ is the control unit (14), Q! It is a control switching unit into which the output signal of 9 is input, and the 1-car control unit α4) selects the larger output signal (the one with the larger control amount) of the 0-phrase output signal, and feeds back the selected output signal to the output unit αQ. Supplied as a signal.

α power is a torch switch that is turned on and off when welding starts and ends, and 08) is an operation control relay connected to the power supply terminal (5) via switch a. ), 05) are turned on, and the control units ('?), (143, (+5) are activated.

Note that an arc (A) is emitted from the nozzle at the tip of the torch (9).
) is injected in the direction of the base material (3).

Then, as shown in FIG. 2(a), a switch (171
is locked on at +1, and when the melt V start is commanded, relay α8) is energized and contacts (+8a) to (+SC
) is turned on, and the control units (7), Q4), and OF9 are activated.

By the way, the activated control unit (7) supplies a low-level startup feed control signal to the motor (8) during the initial arc startup period, and then supplies a high-level steady-state feed control signal to the motor (8). ).

And -Tl:-ta (8) is ('l:1) VC in Figure 2
As shown, low speed Ka is delayed by the operation delay time at +2 o'clock.
It starts to rotate.

The electrode (1) is slowly fed in the direction of the base material (3) until 13:00 when the arc starting period ends, and at 13:00, it is rotated at high speed Kb and the electrode (1) is fed at a steady speed toward the base material (3). ).

On the other hand, immediately after the command to start welding, the welding current changes.

When the voltage is zero, at this time, the level of the constant current control signal generated by the control unit 00 is higher than the constant voltage control signal generated by the control unit (14), and the output signal of the control unit a is supplied to the control unit Oυ via the switching unit O@.

Then, based on the output signal of the switching unit 00, at +2 o'clock, the output unit α0) supplies a larger welding output to the load 0υ than in the steady state, and at this time, the electrode (1) and the base material (3) Since the K arc (A) is not occurring and the load impedance is high, the welding voltage (load voltage) with the base material (3) positive and the electrode (1) negative, as shown in Figure 2 (C) ) is controlled to a high voltage Va.

That is, when a command is given to start welding, a constant current control signal from the control section 00 is sent to the output section 00 as a high voltage control signal for starting.
), and the load 0υ is supplied by the welding output of the output section 00.
A high voltage is applied to the

When the electrode (1) approaches the base metal (3) and a short-circuit arc (A) is generated, and the arc is activated by hot start at 1:00 p.m., the welding current increases and the welding voltage decreases, causing the control unit to The output signal of α0 becomes lower in level than the constant voltage control signal of the control section (14), and the output signal of the control section (A) is supplied to the output section 00 via the switching section 00.

However, at 13:00 when the starting state shifts to the steady state, the welding output is feedback-controlled to the steady voltage vb based on the output signal of the control section (14), as shown in FIG. 2(C).

Note that the constant current reference signal is set based on a current that is slightly lower than the steady state welding current, and during steady state welding,
The output signal of the control section 00 is never larger than the output signal of the control section Q4).

Then, based on the welding output that is feedback-controlled to the steady voltage vb, the base material (3) and the electrode (1
), short circuits and arcing occur alternately,
The molten metal at the tip of the electrode (1) is welded to the base metal (3), and the base metal (3) is arc welded.

Note that during welding, the torch (9) or the base material (3) is moved to move the welding location.

Also, if the welding current becomes excessive for some reason,
In order to protect the output section 00, the control section 04) supplies a current clamp signal for overcurrent protection to the output section θO instead of the constant voltage control signal through the switching section, so that the welding current is adjusted to the rated value, for example. Control to the maximum current Ia.

That is, the voltage and current characteristics of the welding output are as shown by the solid line in FIG. 3, and the voltage and current of the welding output during normal welding are the voltage ■b and current Ib at point α on the solid line.

Next, as shown in Fig. 2(a), the switch α force becomes t4.
When the relay 08) is de-energized, the contact (
18a) - (18c) are turned off, and the control unit (7),
(14), (l) When a command is given to stop welding, the operation of the control section (7) is stopped and the control signal from the control section (7) is cut off, but as shown in Fig. 2(b) As shown in , the motor (8) rotates due to inertia until after 3:00 pm, and the electrode (1) continues to be fed.

The operation of the control unit α4) is still stopped, and at this time, the level of the output signal of the control unit 04) decreases, and the welding voltage decreases as shown in FIG. 2(C).

Then, based on the decrease in the feeding speed of the electrode (1) and the decrease in the voltage of the welding output, the welding current also decreases as shown by the broken line in FIG. 3.

On the other hand, in the control unit 00, the timing of stopping the operation is delayed by a predetermined coagulation control time from the off timing of the contact (18C) by an internal delay means, as shown in FIG. 2(d).
The control unit α■ operates until 15:00.

Then, as the welding current decreases, the output signal of the control section 0e increases, and immediately after the welding stop command is issued, the output signal of the control section a becomes higher than the output signal of the control section 04). The output signal of the control unit αO is supplied to the output unit 00.

However, when a welding stop is commanded, the welding output is feedback-controlled to a constant current by the output signal of the control unit αυ until 15:00 when the solidification control time has elapsed, and a decrease in the welding current is prevented.

Therefore, even if a welding stop is commanded, energy for coagulation control continues to be supplied to the electrode (1), which is fed while being gradually decelerated for a certain period of time, and even if the welding current is 150 A or less, as shown in FIG. As shown in , rapid solidification of the melted part (2) at the tip of the electrode (1) is prevented, and at this time, the shape of the melted part (2) is controlled based on surface tension, and the melted part (2) is prevented from solidifying rapidly.
2) is deformed from its spherical shape, and the position of the slag (4) that solidifies and adheres to its surface is shifted from the lower end surface (1)' of the electrode (1).

Then, the slag (4) shifts from the lower end surface (1)' and adheres to it.

Since the metal surface is exposed on the lower end surface (1)', the next time the switch is turned on and restarted, the arc (A) occurs and will definitely restart.

Note that the solidification control time may be set based on the magnitude of the welding current, etc.

Further, when the feeding time of the electrode (1) due to inertia is extremely short, the output cutoff timing of the control signal of the control section (7) may be delayed and adjusted.

Of course, this method can also be applied when the shielding gas is other than carbon dioxide.

Next, the experimental results will be explained.

(A) Use a commercially available carbon dioxide welding wire of 1.2] @ for the electrode (1), and set the welding current to 10OA,
By restarting the coagulation control time T to either 0 or 200 m5ec, the success rate, failure rate,
The instantaneous arc failure rate was as shown in Table 1 below.

(B) Electrode (1), welding current under the same conditions as in (A), solidification delay time T +00m5ec, 200m5e
By restarting the engine at 300m5ec, the following results in Table 2 were obtained.

Table 1 Table 2 (C) By using a commercially available carbon dioxide welding wire with a convexity of 1.0 as the electrode (1) and repeatedly restarting the welding current under the conditions of +00 A and fixed control time T2O0m5ec. , the results shown in Table 3 below were obtained.

(2 lines, blank space) Table 3 [Effects of the Invention] Since the present invention is constructed as described above, it produces the effects described below.

When the drive of the electrode feeding motor and the constant voltage control of the welding output are stopped based on the welding stop, the electrode continues to be fed due to the inertia of the motor, and a predetermined solidification control time elapses from the welding stop. The welding output is constant current controlled until the welding current is medium.

Even with a small current, it is controlled so that energy is given to the molten part at the tip of the electrode, slowing down the solidification rate.

At this time, based on the feeding of the electrode and the effect of surface tension,
The shape of the molten zone changes from a spherical shape, and the slag adheres to the
The electrode can be moved from the bottom end, so when restarting, the generation of arc due to slag will not be detected, and the arc that has already occurred will not disappear, improving the arc starting characteristics and ensuring restart. Welding robot 1-
In combination with other devices, G-contact work can be automated.

[Brief explanation of the drawing]

1 to 4 show one embodiment of the gas shielded arc welding method of the present invention, FIG. 1 is a block diagram, and FIG. 2 (
a) to (d) are timing charts for explaining the operation;
The figure shows the relationship between welding current and welding voltage. FIG. 4 is an explanatory diagram of the solidified shape of the electrode tip, and FIG. 5 is an explanatory diagram of the shape of the electrode tip in a conventional gas-shielded arc welding method. (1)...Consumable electrode, (3)...Base material to be welded, (8)
... Electrode feeding motor. Agent Patent Attorney Fujita f'A-j Obe T5

Claims (1)

[Claims] (1) A welding output feedback-controlled to a constant voltage is supplied to the welding load formed by the consumable electrode fed by the drive of the electrode feeding motor and the base material to be welded, and In a gas-shielded arc welding method in which a short circuit with an electrode and arc generation are alternately repeated, and the generated arc is shielded with gas to weld the base metal, the motor is driven and the welding is performed based on a welding stop. When the constant voltage control of the output is stopped, the welding output is feedback-controlled to a constant current until a predetermined solidification control time has elapsed from the welding stop, and the solidification shape of the tip of the electrode is controlled to control the slag. A gas shielded arc welding method characterized in that the adhesion position is controlled.