JPH044074B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a consumable electrode type arc welding method in which short circuits and arc generation are repeated between a consumable electrode and a base material. Prior Art Figure 1 shows the process of droplet formation and transfer in the consumable electrode arc welding method, which alternately repeats short circuits and arc generation, where 1 shows the consumable electrode (hereinafter referred to as welding wire) and 2 shows the welding process. A droplet is formed at the tip of the wire 1, 3 is an arc, and 4 is a molten pool, that is, a base material. a is the initial short-circuit state where the droplet 2 is in contact with the molten pool 4, b is the intermediate short-circuit state where the contact between the droplet 2 and the molten pool 4 is ensured and the droplet 2 is moving to the molten pool 4, and c d is the late short circuit state where the droplet 2 moves to the molten pool 4 side and a constriction occurs in the droplet 2 between the welding wire 1 and the molten pool 4, and d is the moment when the short circuit is broken and the welding arc 3 is generated. e indicates the arc generation state where the tip of the welding wire 1 melts and the droplet 2 grows, and f and g indicate the arc generation state immediately before the droplet 2 short-circuits with the molten pool 4. It is done repeatedly. FIG. 2 shows the waveforms of welding current and welding voltage when using a conventional welding power source having constant voltage characteristics that also uses a reactor. In FIG. 2, symbols a to g indicating processes on the waveform correspond to processes a to g of droplet formation and transfer shown in FIG. 1, respectively. When this conventional welding power source is used, the following problems occur. In process a, the welding current begins to increase with a certain time constant immediately after the short circuit between the droplet 2 and the molten pool 4, and when the cross-sectional area of the contact area A between the droplet 2 and the molten pool 4 is small, That is, if the welding current increases before the transfer of the droplet 2 to the molten pool 4 progresses, the short circuit is broken, an arc is generated, and at this time spatter is generated. In steps c and d, a constriction occurs in the droplet 2, the short circuit is broken, and the arc is generated again.
When the arc is regenerated, the current value reaches its highest value, and the repulsion energy of the arc generates a large amount of spatter and causes the molten pool 4 to vibrate greatly. In processes e and f after arc generation, the welding current increases when the previous short-circuit period is long, and decreases when the previous short-circuit period is short. Therefore, the sizes of the droplets 2 formed in steps e and f vary, and sometimes, if the droplets are too small in step g, the unmelted part of the welding wire 1 will plunge into the molten pool 4. Welding may become extremely unstable. In addition, in processes f and g, droplet 2 and molten pool 4
The welding current needs to be small in order to bring the welding current closer to a short circuit and further short circuit the welding current. However, the welding current at this time is e ^{- (L/R)t} as shown in Fig. 2, depending on the inductance L and equivalent resistance R of the circuit.
decreases in proportion to the value of Therefore, when the welding wire feeding speed is high and the average value of the welding current is high, the current becomes high in processes f and g, and short circuits are less likely to occur. Furthermore, since the welding current has constant voltage characteristics, the current increases as the arc length becomes shorter. As a result, it becomes increasingly difficult for short circuits to occur, the droplets grow larger, and not only can a short circuit period on the outside cannot be expected, but also large spatters occur. Purpose of the Invention The present invention has been made in view of the above problems, and its purpose is to provide a consumable electrode type arc welding method that stabilizes the process of repeating short circuits and arc generation, and reduces the occurrence of spatter. It is to be. Summary of the Invention This is a consumable electrode type arc welding method in which a short circuit and arc generation are repeated between a consumable electrode and a base metal, and when the consumable electrode and the base metal are short-circuited, the welding current is a process of holding the welding current at a current value, then a process of holding the welding current at a relatively high level second current value, and a process of holding the welding current at the second current value between the consumable electrode and the base metal. When a constriction occurs in the welded part, the welding current is reduced to a third low-level current value, and then the welding current is increased at the timing when an arc is generated between the consumable electrode and the base metal. holding the welding current at a fourth current value at a relatively high level; and then holding the welding current at a fifth current value at a relatively low level until the consumable electrode and the base metal are short-circuited; The series of steps described above is repeated until the first current value is held at a relatively lower level than the fifth current value. Example An example of the present invention will be described below. In the present invention, the welding wire is fed to the base metal through a nozzle at a predetermined speed, while shielding gas is injected from the nozzle to surround the arc generated between the welding wire and the base metal. In addition, the welding current is controlled in the consumable electrode arc welding method in which welding is performed by repeatedly shorting and generating an arc between the welding wire and the base metal. The present inventors conducted various studies on the output waveform of the welding current in a consumable electrode type arc welding method in which short circuits and arc generation are alternately repeated, and as a result, it was found that the waveform shown in FIG. 3 is optimal. FIG. 3 shows the waveforms of welding current and welding voltage, and processes a to g on the waveforms correspond to processes a to g of droplet formation and transfer shown in FIG. 1 above, respectively. In steps a to b immediately after the short circuit between the welding wire 1 and the molten pool 4, the welding current is maintained at a low level of the current _ID to prevent the contact between the droplet 2 and the molten pool 4 from becoming stronger. The pinch force of the welding current is prevented from acting on the contact area A between the droplet 2 and the molten pool 4. The period T _D during which this low level current I _D is maintained is 1 to
4 msec, optimally 1.5 to 2.5 msec. The current _ID is preferably as small as possible in order to prevent current pinching force from acting on the contact area A between the droplet 2 and the molten pool 4, and is generally 100 A or less.
When the welding wire feeding speed is small, the current I _D
It was confirmed that even lower values are better. In process b, where the bond between the droplet 2 and the molten pool 4 becomes strong, an appropriate high current I _SP is applied to provide pulse energy and pinch force in order to promote the transition of the droplet 2 to the molten pool 4. do. This high current I _SP moves the droplet 2 to the molten pool 4 before the unmelted part of the welding wire 1 plunges into the molten pool 4, and
This high current is applied to create a constriction in the droplet 2 after the transfer, and if this high current I _SP is not applied, the welding process will be extremely unstable.
The period during which I _SP is applied is until the process c when the droplet 2 becomes constricted, but since this period usually varies between 1 and 5 msec, it is impossible to set it in advance. However, the constriction of the droplet is detected by changes in resistance, voltage, or current between the welding wire and the base metal, and the application of high current I _SP is terminated when constriction occurs, depending on the short circuit situation. , need to be automatically controlled. Specifically, the constriction of the droplet is detected when, for example, the time change (differential value dV/dt) of the voltage V between the welding wire and the base metal exceeds a certain value. In process c when the droplet 2 is constricted, the welding current is rapidly reduced to a low level current _IRA . Then, an arc occurs in process d following process c. The reason for rapidly reducing the current in step c is to prevent part of the droplet 2 from scattering when the constriction part B of the droplet 2 breaks and an arc occurs, and also to prevent the droplet 2 from melting at the moment the arc occurs. This is to reduce the pressure exerted on the pond by the arc. If this pressure is strong, the molten pool 4 is pushed against the outer periphery of the bead, which not only impairs the uniformity of the bead appearance, but also sometimes causes part of the molten pool to scatter, resulting in spatter. In process c, if the current is reduced,
There is a suspicion that the droplet will not break and the arc will not occur again, but if the droplet becomes constricted, the constriction will break due to surface tension. Therefore, in step b, the high current I _SP may be applied until the droplet 2 is constricted enough to break due to surface tension and gravity. Also, the low level current I _RA is
Although it depends on the welding wire feeding speed, etc., 20 to 200 A is desirable. When the current I _RA is less than 20 A, there is an increased possibility that an arc breakage occurs in which the arc disappears when the arc is regenerated, and when it is more than 200 A, the amount of spatter will increase. Ideally, this current _IRA should be as small as possible without causing arc breakage, and is not limited to 20A. At the timing when an arc occurs in step d, the welding current is increased to a high level current I _AP , and this high current I _AP is stored for a predetermined period until step e. Period from process d to process e
T _AP is a period during which droplets are formed at the tip of the welding wire to be transferred to the molten pool 4 in the next short circuit.
The period T _AP and the current value I _AP are determined so that the droplet has a desired size during this period T _AP . If a short circuit occurs between the welding wire and the molten pool during this period T _AP , the necessary droplets will not be formed and the short circuit will occur.
The unmelted portion of the welding wire enters the molten pool, which takes time to regenerate the arc and significantly impairs welding stability. Therefore, the current I _AP during the period T _AP uses a high level current that is sufficient to prevent the occurrence of a short circuit. The current I _AP sufficient to prevent a short circuit during this period T _AP varies depending on the welding wire feeding speed. For example, when the wire feeding speed is 5.2 m/min (average welding current 180 A), the current I AP is 260 A. It is about
Wire feeding speed is 8.4 m/min (average welding current
240A), it is about 340A. This current I _AP
must be at a level higher than the average welding current. Also, one way to prevent short circuits during this period T _AP is to make the current sufficiently high as described above, but as the arc length becomes shorter, the current increases and short circuits become less likely to occur. It is also effective to have constant voltage characteristics. in this case,
As the current increases, the arc force becomes stronger, and
Increases the amount of burnout of the welding wire and increases the gap between the droplet and the molten pool. Process e after droplet formation during period T _AP
~f, the welding current is kept at a low level of current I _AB in order to short-circuit the droplet 2 to the weld pool 4 as quickly as possible. In this case, with the constant voltage characteristic in which the current increases as the arc length becomes shorter, as the short circuit approaches, the current increases and the arc force increases, and this arc force presses the molten pool, so the droplets and molten This creates a situation where short circuits are less likely to occur by maintaining a gap with the pond. Therefore, in steps e to f, it is desirable to have substantially constant current characteristics in which the current value remains unchanged even if the arc length becomes short. Also, if the current I _AB is too high,
Short circuits are less likely to occur and the droplets become larger than necessary, and not only the period of short circuits is not constant, but also the generation of large spatters is promoted. This low level current I _AB at the time of arcing is maintained until the process g when a short circuit occurs. The above five-stage states are continuous, and this series of five-stage states is repeated. The respective stages have a correlation with each other, and even if any one stage is excluded, the three conditions of reduced spatter, good bead appearance, and good arc stability cannot be satisfied. Experimental Examples Experimental examples of the present invention will be described below. The three types of experimental examples 1, 2, and 3 are as described above.
When the welding wire 1 and the molten pool 4 are short-circuited, there is a first process in which the welding current is maintained at a relatively low first current value _ID , and following this first process, the welding current is maintained at a relatively high level. If a constriction occurs in the molten part between the welding wire 1 and the molten pool 4 during the second process of holding the current value I _SP at the second level, and while holding the second current value I _SP , A third process of reducing the welding current to a third low level current value I _RA , and following this third process, reducing the welding current at the timing when an arc is generated between the weld 1 and the molten pool 4. increase,
A fourth process in which the welding current is held at a fourth current value I _AP at a relatively high level, and a second process in which the welding current is maintained at a relatively low level until the molten wire 1 and the molten pool 4 are short-circuited. a fifth process of holding the first current value I _D at the fifth current value I _AB ;
I _AB was lowered and the series of steps 1 to 5 above were repeated. Furthermore, specifically, the welding conditions commonly used in each of Experimental Examples 1, 2, and 3 are as follows. Welding wire: YCW-2, 1.2φ Shielding gas: CO ₂ , 20/min Welding base material: SS41, plate thickness 12mm Welding method: The welding torch was held on a trolley, and bead-on-plate welding was performed for 10 minutes. Welding conditions other than those mentioned above, such as wire feeding speed, period T _D , T _AP , current I _D , I _SP , I _RA , and I _AP , were set in Experimental Example 1.
2 and 3 are shown in Table 1. Also, the first
The table shows the welding conditions, wire feeding speed and average current, for three conventional examples 1, 2, and 3.

[Table] The evaluation method is 10 for the amount of spatter.
The weight of spatter adhering to the nozzle per minute was measured, and the stability of the welding current waveform was observed using an oscilloscope to determine the stability of the arc. moreover,
The appearance of the bead was observed. The results of this evaluation are shown in Table 2. Table 2 also shows the results of evaluating Conventional Examples 1, 2, and 3 using the same method as the experimental example.

【table】

[Table] Figures 4 and 5 show the waveforms of welding current and welding voltage in Experimental Example 2 observed with an oscilloscope, and Figure 5 shows the waveforms when the time axis scale is made smaller than in Figure 4. show. In addition, Figures 6 and 7 show the waveforms of welding current and welding voltage in Conventional Example 2 observed with an oscilloscope, and Figure 7 shows the waveforms when the time axis scale is made smaller than in Figure 6. . As is clear from Table 2, in all of Experimental Examples 1, 2, and 3 of the welding method according to the present invention, the amount of spatter generated can be reduced to 1/5 to 1/6 compared to the conventional method. can. Furthermore, as shown in Fig. 4, the period and peak value of the welding current waveform by the method of the present invention are regular and almost constant, which means that short circuits and arc generation are regularly repeated, resulting in arc force and arc length. , droplet diameter,
This shows that both the short-circuit condition and the molten pool condition are stable. This proves that by using the method of the present invention, the amount of spatter generated can be reduced, a uniform and beautiful bead appearance can be obtained, and welding can be performed with good workability without the need for post-processing steps. be. On the other hand, the waveform of the welding current obtained by the conventional method shown in Figure 6 has irregular periods and peak values, which means that short circuits and arc generation are not performed regularly, and arc force, arc length, droplet diameter, etc. fluctuate. It shows that. That is,
In the conventional method, the arc becomes unstable and the molten pool becomes turbulent, resulting in a large amount of spatter, and sometimes a very large arc force acts, causing the molten pool to scatter, resulting in whiskers at the bead end. Protrusions occur, impairing the appearance of the bead and impairing workability. In fact, it was confirmed from visual observation of the welding state, arc sound, etc. that the arc is stable in the welding method of the present invention, and the welding current waveform corresponds to the state of the welding current waveform shown in FIG. Effects of the Invention As explained above, in the present invention, when the welding wire short-circuits with the base metal, the welding current is set to a relatively low level, and then the welding current is set to a relatively high level, so that the droplet is constricted. When arcing occurs, the welding current is reduced to a low level, and when an arc occurs, the welding current is increased to a relatively high level, and then the welding current is increased until the welding wire and the base metal short-circuit. Since the above-described series of processes using a relatively low level of current is repeated, it is possible to perform welding with a small amount of spatter, a stable arc, and a good bead appearance. As a result, the number of times welding is interrupted to remove spatter adhering to the nozzle is reduced, and continuous welding can be performed for a long time. This is effective for automatic welding by robots and the like. In addition, since the amount of spatter generated is small, it does not take much time to remove spatter from the product after the welding process is completed.
Furthermore, since there is no need to use a grinder to reshape defects in the appearance of the bead, there is not only a direct economic effect, but also an effect that contributes to the safety of welding workers.

[Brief explanation of drawings]

Figure 1 shows the process of droplet formation and migration in consumable electrode arc welding, Figure 2 shows the waveforms of welding current and welding voltage in conventional consumable electrode arc welding, and Figure 3 Figures 4 and 5 show the waveforms of the welding current and welding voltage in Experimental Example 2 observed with an oscilloscope. 6 and 7 are diagrams showing waveforms of welding current and welding voltage in Conventional Example 2 observed with an oscilloscope. 1... Welding wire, 2... Droplet, 3... Arc, 4...
melt pool.

Claims (1)

[Claims] 1. While feeding the consumable electrode to the base material at a predetermined speed, shielding gas is injected from the nozzle to surround the arc generated between the consumable electrode and the base material, This is a consumable electrode type arc welding method in which welding is performed by repeatedly shorting and generating an arc between the consumable electrode and the base metal.If the consumable electrode and the base metal are short-circuited, the welding current is reduced to a relatively low level. a first process of holding the welding current at a current value of , following this first process, holding the welding current at a second current value of a relatively high level; If a constriction occurs in the molten zone between the consumable electrode and the base metal during this process, a third process in which the welding current is reduced to a lower third current value, and this third process is followed by a consumable A fourth process in which the welding current is increased at the timing when an arc occurs between the electrode and the base metal and held at a relatively high fourth current value, and following this fourth process, the consumable electrode is and a fifth step of maintaining the welding current at a relatively low level fifth current value until the base metal and the welding current are short-circuited, and the first current value is lower than the fifth current value, A consumable electrode type arc welding method characterized by repeating the series of steps 1 to 5 above.