JPH0358828B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] 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 materials to be welded using a consumable electrode, inexpensive carbon dioxide gas has been used as the shielding gas instead of expensive inert gas such as argon or helium. is desired. When performing gas-shielded arc welding using carbon dioxide, the electrode feed motor is driven to
A wire-shaped consumable electrode is fed in the direction (downward) of the base material to be welded through the torch, and carbon dioxide gas as a shielding gas is supplied in the direction of the base material from a nozzle at the tip of the torch. Further, a feedback-controlled direct current welding output is supplied to the welding load formed by the electrode and the base metal. When the tip of the electrode is short-circuited 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 welding state shifts from the starting state to the steady state. Short circuits and arc generation are alternately repeated between the base metal 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 torch or the base metal is moved as the welding progresses. Furthermore, when the torch switch is turned off and a command is given to stop welding at the end of or during welding, the driving of the electrode feed motor is stopped, the feedback control is stopped, the welding output is cut off, and the welding output is cut off to welding is stopped. [Problems 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 FIG. The molten part 2 at the tip of the consumable electrode 1 grows into a spherical shape, and an arc A is generated between a part of the small point region 2' on the lower surface of the molten part 2 and the base material. Further, carbon dioxide gas, which is inert 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 zone 2, and the impurities are discharged from the molten zone 2 as slag mainly composed of silicon oxide and manganese oxide.
Based on this action, healthy molten metal is welded to the base metal 3, and good arc solubility is achieved. By the way, as shown in FIG. 5, the forces acting on the molten part 2 include gravity Fg and surface tension Fs force Fa. The gravity Fg acts as a constant downward force, and the surface tension Fs acts as an upward force that varies depending on temperature and other factors. Also, the arc force that occurs only during arc generation
Fa 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. During welding, the molten zone 2 grows into a spherical shape as described above based on the surface tension Fs and the arc force Fa. On the other hand, when the arc A disappears and the arc force Fa becomes zero by stopping welding, only the surface tension Fs acts on the molten part 2 as an upward force, and the surface tension Fs mainly causes the molten part 2 to The solidified shape of is determined,
When the solidification time is short, the molten portion 2 solidifies into a spherical shape. Furthermore, since 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, the welding output current (welding current) is particularly suitable for medium to small currents of 150 A or less. At this time, as shown in FIG. 5, a film-like solidified slag 4 adheres to the lowermost surface of the molten zone 2, which has solidified into a spherical shape due to the extinction of the arc A. Then, the slag 4 becomes an electrical non-conductor at room temperature, and when welding is started again, if the slag 4 is attached to the molten part 2, the arc A is caused by the slag 4.
The occurrence of arc is prevented, the arc occurrence rate is reduced, and the generated arc is likely to disappear before reaching a steady state.Especially when the welding current is medium to small as mentioned above, the arc start characteristics for restart are It gets worse and it becomes extremely difficult to restart. 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 will cause the welding current to continue for a period of time proportional to the welding current. Electrode 1 continues to be delivered. Furthermore, as the welding current increases, the welding output decreases when welding is stopped, and it takes more time until the welding is interrupted. When the welding current becomes a large current of 200A or more, based on the large inertia of the motor,
The electrode 1 continues to be fed in the direction of the base metal 3 for a relatively long time after the command to stop welding is given, and during that time, sufficient energy is given to the molten part 2 by the welding output, so that so-called flare-up occurs. After the arc A has disappeared, the molten part 2 is pulled upward to control the solidification shape of the molten part 2, thereby making it possible to control the adhesion position of the slag 4. In addition, when the welding power is high and the welding current is high, even if the solidified shape of the molten part 2 and the adhesion position of the slag 4 are the same as when the welding current is high, it is necessary to restart the welding power when the welding power is large. The arc A is generated relatively easily by the energy, and restarting can be performed relatively easily. 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 is quickly increased. As a result, 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 energy of the welding output is small. , restarting becomes extremely difficult. Therefore, when the welding current is lower than about 150A, especially when the welding current is small, the tip of the electrode 1 is cut diagonally as a pretreatment when restarting, and the tip of the electrode 1 is cut diagonally so that the metal surface is exposed so that an arc is easily generated. This requires complicated work to process it into a shape. Even if pretreatment is performed, restarting cannot always be guaranteed, and therefore, even when welding is performed in combination with automatic equipment such as welding robots, workers are required to prepare in case arc start fails. must be placed, making it impossible to unattended welding work. The present invention makes it possible to reliably restart the welding process even if the welding current is medium or small, without cutting the electrodes as pre-processing, and enables unmanned welding work by combining it with a welding robot. The purpose of the present invention is to provide a gas-shielded arc welding method that enables the following. [Means for solving the problem] The means for achieving the above object will be explained below. The present invention supplies a constant voltage feedback-controlled welding output to a welding load formed by a consumable electrode fed by driving an electrode feed motor and a base material to be welded, and A gas-shielded arc welding method in which a short circuit and an arc are alternately repeated with the electrode, and the generated arc is gas-shielded to weld the base metal. When the constant voltage control of the welding 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 reduce the slag. We have taken technical measures to control the adhesion position. [Operation] 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
The welding output is controlled at a constant current until a predetermined solidification control time elapses after welding stops, and even if the welding current is medium or small, energy is given to the molten part at the electrode tip and the solidification rate is controlled to slow down. At this time, due to the feeding of the electrode and the action of surface tension, the shape of the molten zone is deformed from a spherical shape, and the slag attachment position is shifted from the lowermost end of the electrode. Therefore, at the time of restart, the slag does not prevent the generation of an arc, and the generated arc does not disappear, improving the arc start characteristics and allowing reliable restart. [Example] One example 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, and in the figure, 4 and 5 are the first and second power terminals of the welding device 6, which are connected to an AC power source such as a commercial AC power source, respectively. . 7 is a wire feed control unit connected to the power supply terminal 4, which controls the drive of the electrode feed motor 8 and feeds the wire-shaped electrode 1 in the direction (downward) of the base material 3 via the torch 9. do. Reference numeral 10 denotes a control output section connected to the power supply terminal 5, which supplies DC welding output generated by thyristor rectification or inverter drive to the welding load 11 formed by the electrode 1 and the base material 3. Reference numerals 12 and 13 are a current detector and a voltage detector that detect load current and load voltage, respectively. Reference numeral 14 denotes a steady-state control unit to which the current and voltage detection signals of the detectors 12 and 13 are input, and in normal times when the current detection signal is below the overcurrent detection reference value, the voltage detection signal and the constant voltage in the steady state are input. The difference signal from the reference signal is output as a constant voltage control signal. A constant current control section 15 receives the current detection signal of the detector 12, and outputs a difference signal between the current detection signal and the constant current reference signal as a constant current control signal. Reference numeral 16 denotes a control switching unit to which the output signals of the control units 14 and 15 are input, and selects the larger output signal (the larger control amount) of both the control units 14 and 15.
The selected output signal is supplied as a feedback control signal to the output section 10. 17 is a torch switch that is turned on and off when welding starts and ends; 18 is an operation control relay connected to the power supply terminal 5 via the switch 17; The connected contacts 18a, 18b, and 18c are turned on, and the control units 7, 14, and 15 are activated. Incidentally, from a nozzle at the tip of the torch 9, carbon dioxide gas G that shields the arc A is injected in the direction of the base material 3. Then, as shown in FIG. 2a, the switch 17
is locked on at time _t1 and a command is given to start welding, relay 18 is energized and contacts 18a to 18 are
c is turned on, and the control units 7, 14, and 15 are activated. By the way, the activated control section 7 supplies a low level starting feed control signal to the motor 8 during the initial arc starting period, and then supplies a high level steady feed control signal to the motor 8. Then, as shown in FIG. 2b, the motor 8 starts rotating at a low speed Ka at t ₂ after an operation delay time, and rotates the electrode 1 in the direction of the base material 3 until t ₃ when the arc starting period ends. At time _t3 , the electrode 1 is rotated at a high speed Kb and fed in the direction of the base material 3 at a steady speed. On the other hand, immediately after the start of welding is commanded, the welding current and voltage are zero, and at this time, the constant current control signal generated by the control unit 15 is at a higher level than the constant voltage control signal generated by the control unit 14. becomes high, and the output signal of the control section 15 is supplied to the control section 10 via the switching section 16. Then, based on the output signal of the switching section 16, t ₂
When the time comes, the output section 10 supplies a larger welding output to the load 11 than in the steady state, and at this time,
Since arc A is not generated between electrode 1 and base metal 3 and the load impedance is high, the welding voltage (load voltage) with positive on the base metal and negative on electrode 1 is high, as shown in Figure 2c. Controlled by voltage Va. That is, when a command is given to start welding, the control section 1
A constant current control signal No. 5 is supplied to the output section 10 as a high voltage control section signal for starting, and a high voltage is applied to the load 11 by the welding output of the output section 10. 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 time _t3 , the welding current increases and the welding voltage decreases, causing the output signal of the control section 15 to change. Control part 1
4, the welding output of the control section 14 is transferred to the output section 10 via the switching section 16.
is supplied to Therefore, the transition from start-up state to steady state t ₃
When the time comes, as shown in FIG. 2c, the control unit 14
Based on the output signal of
controlled by feedback. Note that the constant current reference signal is set based on a current that is slightly lower than the welding current in the steady state, and the output signal of the control section 15 is set based on a current slightly lower than the welding current in the steady state.
It never becomes larger than the output signal of No. 4. Then, based on the welding output that is feedback-controlled to the steady voltage Vb, the base metal 3
A short circuit and arc generation are alternately repeated between the electrode 1 and the electrode 1, and the molten metal at the tip of the electrode 1 is welded to the base material 3, so that the base material 3 is arc-welded. Note that during welding, the torch 9 or the base material 3 is moved, and the welding location is moved. Furthermore, if the welding current becomes excessive for some reason, the control section 14 sends a current clamp signal for overcurrent protection via the switching section 16 instead of the constant voltage control signal in order to protect the output section 10. is supplied to the output section 10, and the welding current is controlled to, for example, the rated 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 Vb and current Ib at point α on the solid line. Next, the switch 17 is activated as shown in Figure 2a.
t ₄ o'clock, the relay 18 is de-energized, the contacts 18a to 18c are turned off, and the control units 7, 14,
15 is commanded to stop welding, at this time 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. 2b, the motor 8
rotates due to inertia until past t ₅ o'clock, and electrode 1
continues to be delivered. Further, the operation of the consumable electrode 14 also stops, and at this time, the level of the output signal of the control section 14 decreases, and the welding voltage decreases as shown in FIG. 2c. 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, the timing of stopping the operation of the control unit 15 is delayed by a predetermined coagulation control time from the off timing of the contact 18c by an internal delay means, and as shown in FIG. 2d, the control unit 15 operates until _t5 . do. Then, as the welding current decreases, the output signal of the control section 15 becomes larger, and almost immediately after the command to stop welding is given, the welding output of the control section 14 becomes larger than the output signal of the control section 15.
The output signal of the control section 15 has a higher level, and the output signal of the control section 15 is supplied to the output section 10. Therefore, when a command to stop welding is given, the welding output is feedback-controlled to a constant current by the output signal of the control section 15 until ₅ o'clock when the solidification control time has elapsed, and a decrease in the welding current is prevented. Ru. Therefore, even if a command is given to stop welding, the energy for coagulation control continues to be supplied to the electrode 1, which is gradually decelerated for a certain period of time, and even if the welding current is less than 150A, as shown in FIG. As shown in Figure 2, rapid solidification of the melted part 2 at the tip of the electrode 1 is prevented
At this time, the shape of the molten part 2 is controlled based on surface tension, the molten part 2 is deformed from a spherical shape, and the position of the slag 4 solidified and attached to the surface of the molten part 2 is shifted from the lower end surface 1' of the electrode 1. Then, the slag 4 deviates from the lower end surface 1' and adheres to it, exposing the metal surface to the lower end surface 1'.
The arc A is generated and reliably restarted without cutting the electrode 1 through conventional pre-treatment. Note that the stiffening 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 adjusted by delaying it. Of course, this invention can also be applied when the shielding gas is other than carbon dioxide. Next, the experimental results will be explained. (A) Successful restart by using a commercially available carbon dioxide welding wire with a diameter of 1.2 mm for electrode 1, setting the welding current to 100 A, and setting the solidification control time T to 0.200 msec. The rate, failure rate, and instantaneous arc failure rate were as shown in Table 1 below. (B) Electrode 1, welding current under the same conditions as in (A), and solidification delay time T of 100 msec, 200 msec, 300 msec.
By restarting the computer, the following results in Table 2 were obtained.

【table】

[Table] (C) By using a commercially available carbon dioxide welding wire with a diameter of 1.0 mm as electrode 1 and restarting it under the conditions of a welding current of 100 A and solidification control time T = 200 msec, the results shown in Table 3 below were obtained. The results were obtained.

〔Effect of the invention〕

Since the present invention is configured 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 coagulation control time elapses from the welding stop. The welding output is constant voltage controlled until the welding current is medium,
Even with a small current, energy is given to the molten part at the tip of the electrode and the solidification rate is controlled to slow down. At this time, the shape of the molten part becomes spherical based on the feeding of the electrode and the effect of surface tension. As a result, when restarting, the slag does not prevent the slag from generating an arc, and the generated arc does not disappear, resulting in poor arc start characteristics. This technology can be improved and restarted reliably, and can be combined with welding robots to make welding work unmanned.

[Brief explanation of drawings]

Figures 1 to 4 show one embodiment of the gas shielded arc welding method of the present invention, Figure 1 is a block diagram, Figures 2 a to d are timing charts for explaining the operation, and Figure 3 is a welding current. FIG. 4 is a diagram illustrating the solidified shape of the electrode tip, and FIG. 5 is a diagram illustrating the shape of the electrode tip in a conventional gas-shielded arc welding method. DESCRIPTION OF SYMBOLS 1...Consumable electrode, 3...Base material to be welded, 8...Electrode feeding motor.

Claims (1)

[Claims] 1. The welding load formed by the consumable electrode fed by the drive of the electrode feed motor and the base material to be welded,
A gas that supplies a constant voltage and feedback-controlled welding output, alternately repeats short circuit and arc generation between the base metal and the electrode, and shields the generated arc with gas to weld the base metal. In the shielded arc welding method, 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 controlled at a constant current until a predetermined solidification control time elapses from the welding stop. A gas-shielded arc welding method characterized in that the position of slag adhesion is controlled by controlling the solidification shape of the tip of the electrode through feedback control.