JPH0375267B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an arc welding machine that performs welding while automatically feeding a consumable electrode. The present invention relates to an arc welding method and a welding machine in which a spherical lump is not formed at the tip of a consumable electrode.

In general, in arc welding machines that feed consumable electrodes by a feeding mechanism using an electric motor or the like, consideration is given to stopping the feeding mechanism suddenly at the end of welding to minimize the elliptical movement of the consumable electrodes. ing. However, in reality, it is impossible to completely reduce the coasting amount to zero, and the feed mechanism decelerates and stops along a curve that decays with a unique time constant. Therefore, a small amount of the consumable electrode is fed between when the welding end command signal is issued and when the welding completely stops. For this reason, when welding ends, when the welding end signal is simultaneously applied, the consumable electrode feeding mechanism is braked, and the output of the welding power source is also cut off at the same time. Due to this coasting, the consumable electrode sticks up to the workpiece and welds as it is. You end up doing it. Therefore, in order to melt this coasting amount, as shown in Figure 1, which shows the relationship between the temporal change in the feeding speed S of the consumable electrode and the temporal change in the output voltage E, the welding power source is A method is known in which the output is not cut off, but after a certain period of time is delayed from the welding end signal. However, when using such a method, after the welding end signal is issued, the feed rate of the consumable electrode gradually decreases along the deceleration curve and finally reaches zero. On the other hand, in arc welding, there is a substantially proportional relationship between the feeding speed S of the consumable electrode and the welding current Iw, as shown in FIG. Therefore, as the feeding speed of the consumable electrode gradually decreases, the welding current also decreases, and it becomes difficult for the molten metal to separate from the tip of the consumable electrode, forming a large spherical shape at the tip as shown in Figure 3. After the current is cut off, this spherical molten metal solidifies to form a spherical mass. Since such a spherical lump has a large cross-sectional area, even if the tip of the electrode contacts the workpiece when welding is restarted, it is not rapidly overheated, and therefore cannot be fused and quickly transferred to an arc. In order to reduce the size of such spherical lumps, a device has been proposed that changes the output voltage over time as shown in FIGS. 4 to 6. That is, in the case shown in FIG. 4, the output voltage of the welding power source is switched to a constant voltage E' lower than the voltage E during welding simultaneously with the welding end signal.
Further, in FIG. 5, the voltage change shown in FIG. 4 is performed, and at the end, the high output voltage Ep is applied again to complete the process. Furthermore, FIG. 6 shows that the output of the welding power source is gradually decreased in a pattern similar to the attenuation of the electrode feed rate.

In the devices shown in Figures 4 and 5, the voltage value that should be set as the output voltage after the welding end signal is issued is the optimum value depending on the magnitude of the output voltage during welding or the magnitude of the feeding speed of the consumable electrode. If this selection is incomplete, there will be a disadvantage that the consumable electrode will be welded or the ball formed at the tip of the electrode will become large. In other words, there is generally a seventh difference between welding voltage Ea and welding current Iw that can sustain stable arc welding.
As shown by the shaded area in the figure, there is a substantially direct proportional relationship. Therefore, considering that the output voltage E' after the welding end signal is issued is set to the optimum value for a certain output voltage E, when welding is performed at a higher output voltage, the From FIG. 7, the welding current is naturally selected to have a high value. At this time, as can be seen from Figure 2, in order to obtain this high welding current, the electrode feeding speed is also selected to a high value, so at the end of welding, the amount of coasting of the electrode becomes large, and it rushes into the welding part and welds. On the other hand, when welding with a low output voltage, the electrode feeding speed is slow, and the amount of coasting at the end of welding is small, so the electrode tends to burn up, which causes burnout to occur at the tip of the electrode. The ball becomes too large to achieve its purpose. The system shown in Figure 6 has been proposed to completely solve these problems, but although this is theoretically close to ideal, it is not possible to exactly match the deceleration characteristics of the electrode and the attenuation characteristics of the power output. This was difficult, and the circuit configuration was therefore complicated, making it impractical.

In the present invention, after the welding end signal is issued, the output voltage is switched to a low voltage, and most of the coasting of the consumable electrode supplied by inertia is maintained at this low output voltage value. By supplying a pulsed output at a relatively early stage during the period, the electrode melts and is prevented from entering the weld zone, while the low output voltage is maintained until after the pulsed output. This prevents the formation of molten balls at the tip of the electrode.

FIG. 8 is a configuration diagram showing an embodiment of the arc welding machine of the present invention. In the figure, a welding power source 1 receives power from a commercial AC power source 2 and supplies a voltage to a welding torch 3 and a workpiece 4 according to a setting signal from the outside. 5 is a consumable electrode supplied to the welding part by a feed roll 6. 7 is a first reference voltage setting device for setting the output voltage during welding;
8 is a second reference voltage setter set to a value lower than the setting value of the first reference voltage setter; 9 is a first reference voltage setter 7 and a second reference voltage setter 8
a first output signal that selectively outputs one of the two outputs in response to an external command signal;
10 is a third reference voltage setting device for determining the peak value of the pulsed output; 11 is a switching circuit that receives the outputs of the first switching circuit 9 and the third reference voltage setting device 10 and receives commands from the outside; A second switching circuit 12 selectively outputs either of the two outputs according to a signal, and a switch 12 transmits the output of the second switching circuit 11 to the control section of the welding power source 1. Reference numeral 13 denotes a starting circuit that commands the start and stop of welding, and is, for example, a relay circuit or flip-flop circuit that outputs a continuous signal from the start of welding to the end of welding in accordance with the operation of a torch switch provided on the welding torch 3. configured. 14 and 15 are the first and second
This is a time limit circuit, which operates according to the welding start signal of the starting circuit 13, and starts the time limit after the welding end signal, that is, the output signal indicating that welding is in progress from the starting circuit 13 disappears,
An instantaneous operation time-limit return type timer that returns after a set time limit or a mono-multivibrator that generates an output for a certain period of time in response to the fall of the output signal of the starting circuit 13 is used. Reference numeral 16 denotes a third time limit circuit which generates an output for a fixed period of time from the end of the time limit of the second time limit circuit 15. 17 is a feed speed setting device for the consumable electrode 5, and 18 is a setting value of the feed speed setting device 17 which receives power from the power source 19 and continuously operates the electric motor 20 while the starting circuit 13 is emitting a welding signal. This is a motor rotation speed control circuit for driving at a speed corresponding to the motor speed.

The operation of the embodiment shown in FIG. 8 will be explained with reference to the explanatory diagram shown in FIG. In FIG. 9, (1) is the starting circuit 13
(2) is the rotational speed of the electric motor 20, that is, the feeding speed S of the consumable electrode 5, (3) is the output of the first timer circuit 14, (4) is the output of the second timer circuit 15, ( 5) shows the output of the third time limit circuit 16, and (6) shows the change in the output of the switch 12, that is, the output voltage of the welding power source 1. As shown in the figure, when the start switch is operated at time a, a welding signal is output from the start circuit 13, and this output signal is transmitted to the first switching circuit 9,
It is supplied to first and second timer circuits 14 and 15, and a motor control circuit 18, respectively. In the first switching circuit 9, the output signal of the first reference voltage setter 7 is selected by this welding signal, and the reference voltage is applied to the second switching circuit 11.
to communicate. Further, the first time limit circuit 14 receives a signal indicating that welding is in progress and instantaneously operates to close the switch 12. As a result, the output of the first reference voltage setting device 7 is supplied to the welding power source 1, and the welding power source 1 supplies the welding output voltage E ₁ according to the setting value of the first reference voltage setting device 7 to the welding torch 3. and applied to the workpiece 4. On the other hand, the motor control circuit 18 rotates at the speed set by the motor speed setting device 17 based on the output from the starting circuit 13, and drives the feed roll 6 linked thereto to apply the consumable electrode 5 at the speed S. It is fed toward the workpiece 4 to be welded. When the consumable electrode 5 comes into contact with the workpiece 4, an arc is generated and welding is started. Then time b
Consider when welding is finished at . When the welding end signal, that is, the welding signal from the startup circuit 13 disappears at time b, the motor rotation speed control circuit 18 immediately cuts off the output, so that the motor 20
is rapidly decelerated and stops after a time of Δt. When the output of the starting circuit 13 disappears, the first switching circuit 9 switches to transmit the output of the second reference voltage setter 8 instead of the output of the first reference voltage setter 7. With the disappearance of the output of the starting circuit 13, the first and second timer circuits 14 and 15 start timing, and the second timer circuit 15 starts counting again after time _t2 .
The timer circuit 14 ends its timer after a longer time _t1 . When the second time limit circuit 15 ends its time limit, the third time limit circuit 16 starts its time limit. During _t2 from the end of welding until the second time limit circuit 15 ends its time limit, the low set value of the second reference voltage setting device 8 is supplied to the welding power source 1, and the welding torch 3 and workpiece 4 are supplied with the low setting value. A lower voltage E ₂ is supplied than during welding. When the second time limit circuit 15 ends its time limit, the third time limit circuit 16 starts its time limit and supplies the output signal to the second switching circuit 11 only for the set time _t3 . As a result, the second switching circuit 11 supplies the output of the third reference voltage setter 10 to the switch 12 instead of the output of the second reference voltage setter. Therefore, the welding power source 1 has a third time limit circuit 16.
The voltage Ep corresponding to the set value of the third reference voltage setter 10 is output only during the set time period. When the time limit of the third time limit circuit 16 ends, the second switching circuit 11 again transmits the output of the second reference voltage setting device 8 to the switch 12, so that the output voltage of the welding power source 1 returns to the low value of _E2 again. Return to This low output voltage
_E2 continues until the first timer circuit 14 finishes its timer, and the output of the timer circuit 14 disappears at the time when the welding signal of the starting circuit 13 disappears, that is, after the time _t1 from the welding end command time b. At this point, the switch 12 opens, and as a result, the output of the welding power source 1 is cut off.

When the feeding motor of the consumable electrode 5 is braked at the end of welding and simultaneously switched to a low voltage determined by the second reference voltage setting device 8, the feeding speed of the consumable electrode is still high; Since the output from the supplied welding power source is too low, the amount of melting at the tip of the consumable electrode becomes too small, and the arc length gradually becomes shorter. When the output of the welding power source 1 is returned to a high value once the arc length has become sufficiently short, a larger welding current than during normal welding flows due to the extremely short arc length, resulting in a short period of time. The consumable electrode fed by coasting is melted and the molten metal is separated from the tip of the electrode by a large pinch force generated by a large current. The arc length increases rapidly in conjunction with the deceleration of the consumable electrode, thereby preventing the consumable electrode from entering the weld zone. Furthermore, after supplying this high voltage, the voltage is kept low again, and by that time, the melting of the consumable electrode has been sufficiently slowed down, and the arc is maintained while suppressing the melting of the consumable electrode. Disappears the molten ball.

Generally speaking, in arc welding that uses a consumable electrode, when welding is complete, both the voltage and current are switched to lower values to fill the crater that is created on the workpiece due to the arc pressure during welding, and gradual welding is performed. Set a processing period. Even in this case, the output voltage according to the present invention may be changed after the crater treatment period ends based on the welding voltage during the crater treatment.

Since the arc welding machine of the present invention operates as described above, the time from the welding end signal to when the high voltage is applied again, that is, the time for the second time limit circuit 15, may be relatively short, and in some cases It is not necessary to provide most of the edges. Further, the value of the high voltage supplied at time t ₃ may be the same as the voltage during welding, but the value needs to be larger as the time of application is later, that is, the time t ₂ is longer. Further, the waveform at that time is not limited to the rectangular waveform pulse voltage as shown in FIG. 9, but may be any other waveform. FIG. 10 shows these various deformations, with only the change in voltage taken out at the end of welding. (1) in the figure shows the case where a triangular waveform pulse voltage is supplied instead of a rectangular waveform voltage, and this is done by discharging a capacitor charged to a constant voltage as a third reference voltage setter at this point You can easily get it. In addition, (2) and (3) are for supplying a pulsed voltage following the completion of welding, and the peak value of the pulsed voltage applied subsequent to welding voltage E is larger than the average value of the welding voltage. be. (4) shows an example when multiple pulsed voltages are supplied.

Here, the duration of the pulsed voltage supplied during the period in which the low voltage is supplied at the end of welding can be made substantially constant if the peak value of the pulsed voltage is determined in accordance with the welding voltage.

The reason for this will be explained next. As can be seen from FIGS. 2 and 7, in order to perform stable arc welding, the feeding speed of the consumable electrode and the welding voltage, that is, the output voltage of the welding power source, are in a substantially directly proportional relationship. Therefore, when the welding current used is large, that is, when welding is performed while supplying the consumable electrode at high speed, a high welding voltage is set. Therefore, the amount of coasting of the consumable electrode at the end of welding increases, but in this case, if the peak value is determined according to the high voltage during welding, it will coast at high speed while the pulsed voltage is supplied. Since a large amount of the consumable electrode that continues to run is melted, it is possible to effectively prevent the object to be welded from entering the welding area.
Conversely, if the welding current used is low and the feeding speed of the consumable electrode is slow, the coasting amount will also be small, but in this case the welding voltage should also have been selected to a low value, so the welding voltage should be selected to correspond to this. If the peak value of the pulsed voltage is determined based on the pulsed voltage, the amount of the consumable electrode melted during the period when the pulsed voltage is supplied will be reduced, and no flare-up will occur. Therefore, the duration of the pulsed voltage can be selected to be approximately constant.

In the embodiment shown in Fig. 8, the outputs of the first, second, and third reference voltage setters are switched and used, respectively, but these output voltage control circuits are configured as shown in (6) or in Fig. 9. (1) to (4) in Figure 10
Any circuit can be used as long as it is programmed to change the waveform as shown in each of the following.For example, during welding, the sum of the output of the first reference setter and the output of the second reference setter is used, At the end of welding, the output of the first reference voltage setting device is disconnected and the output of the second reference voltage setting device is disconnected.
Only the output of the reference voltage setting device is used as the output setting signal of the welding power source 1, and when pulsed output is supplied, the output of the third reference voltage setting device is added to the output of the second reference voltage setting device to output the welding power source 1. It may also be a setting signal. Furthermore, an output voltage setting signal may be stored in advance using a semiconductor memory element or the like, and this may be read out as appropriate to determine the output voltage of the welding power source. Further, the starting circuit 13 may output a welding start signal and a welding end signal as independent signals. The position of the switch 12 is between the first and second reference voltage setters 7 and 8 and the welding power source 1, between the commercial AC power source and the welding power source, or in the output control circuit inside the welding power source. It can be opened or closed.

In the embodiment shown in Fig. 8, a welding power source that outputs a voltage according to an output voltage setting signal from the outside is used, and an output voltage control circuit that changes the output voltage setting signal to a desired form. Although described above, the present invention is not limited to this. For example, a welding power source includes a main power circuit that outputs a relatively high voltage for welding, and a relatively high voltage that outputs a relatively high voltage for welding at the end of welding in place of the output of the main power circuit. A power supply equipped with an auxiliary power supply that outputs a low voltage and a pulse voltage generation power supply that outputs a pulsed voltage during the output period of this auxiliary power supply is used, and the output voltage control circuit uses the outputs of these power supplies as described above. It is also possible to use a sequence control circuit that sequentially switches the output voltage state so that the output voltage state is the same.

As described above, in the present invention, when welding is completed, the output voltage of the welding power source is lowered to a value lower than that during welding and continued for a predetermined time, and during the period of this low output voltage, especially in the initial stage, a predetermined Since the structure changes the time width and voltage value into a pulse-like output, the consumable electrode does not rush into the welding part at the end of welding due to the inertia of the consumable electrode feeding mechanism, and the tip of the electrode This can effectively prevent the formation of spherical lumps. Furthermore, when setting the peak value of the pulsed voltage to a value corresponding to the welding voltage, the duration of the pulsed voltage can be set almost constant regardless of changes in the welding current, so adjustment is not necessary, and an external regulator is provided. There will be no need.

[Brief explanation of drawings]

Figure 1 is a diagram showing how the output voltage changes over time to prevent inrush, Figure 2 is a diagram showing the relationship between welding current and feeding speed of the consumable electrode, and Figure 3 is a graph showing the relationship between welding current and feeding speed of the consumable electrode. Figure 1 shows how a spherical lump occurs at the tip of a consumable electrode when the voltage is changed, and Figures 4 to 6 show known methods for preventing spherical lumps. 7 is a diagram showing the relationship between voltage and current when the arc is stably maintained, FIG. 8 is a configuration diagram showing an embodiment of the present invention, and FIG. FIG. 8 is an explanatory diagram for explaining the operation of the embodiment, and FIG. 10 is a diagram showing another example of a pulsed voltage waveform. DESCRIPTION OF SYMBOLS 1... Welding power source, 5... Consumable electrode, 7... First reference voltage setter, 8... Second reference voltage setter, 9... First switching circuit, 10... Third Reference voltage setting device, 11... Second switching circuit, 12... Switch, 13... Starting circuit, 1
4...first timer circuit, 15...second timer circuit, 16...third timer circuit.

Claims (1)

[Scope of Claims] 1. In an arc welding method in which power from a welding power source is supplied to a consumable electrode and a workpiece, the output voltage of the welding power source is maintained at a lower value than during welding for a predetermined period of time at the end of welding. An arc welding method in which the output of the welding power source is changed to a pulsed output having a predetermined time width and peak value at the beginning or in the middle of a period of low output voltage. 2. In an arc welding machine that supplies electric power from a welding power source to a consumable electrode and a workpiece to be welded, which are supplied by an electric motor, a starting circuit that issues a welding start command and a welding stop command; a first reference voltage setter that sets an output voltage during welding, and a value lower than the set value of the first reference voltage setter. a second reference voltage setter that sets a pulse voltage having a higher peak value than the setting signal of the second reference voltage setter; a first switching circuit that outputs a setting signal for the first reference voltage setter after receiving the welding stop command, and outputs a setting signal for the second reference voltage setter after receiving the welding stop command; after receiving the first signal for a predetermined number of times for a first predetermined period of time before cutting off the power.
a second switching circuit that switches and outputs the output of the switching circuit to the output of the third reference voltage setter; and a second switching circuit that switches the output of the first reference voltage setter from the second switching circuit in response to the welding start command. is transmitted to the welding power source, and upon receiving the welding completion command, the first
and a switch that stops the output of the second switching circuit after a second predetermined time period that is longer than the product of the predetermined time period and the predetermined number of times.