Arc welding method

Abstract

In the present invention, an arc period includes a first period, a second period after the first period, and a third period after the second period. During the first period, the welding current is changed into a straight line connecting a first change point P1 and a second change point P2. During the second period, the welding current is changed such that the welding current becomes larger than an imaginary straight line connecting the second change point P2 and a third change point P3. During the third period, the welding current is changed into a straight line connecting the third change point P3 and a fourth change point P4.

Description

Arc welding method

[0001] The present invention relates to an arc welding method.

[0002] Patent Document 1 discloses an arc welding machine that, after a predetermined time has elapsed since the short circuit was released, performs constant current control for a predetermined period at a current value higher than the current value output by conventional constant voltage control, thereby suppressing the occurrence of a short circuit immediately after the short circuit is released and suppressing the occurrence of spatter.

[0003] Japanese Patent Application Publication No. 10-109163

[0004] In arc welding, in order to ensure a sufficient bead width and penetration, it is necessary to increase the amount of molten metal.

[0005] However, if the welding current is increased at a steep rate until it reaches a peak current in order to increase the amount of molten metal, there is a problem in that spatter is more likely to occur.

[0006] The aspects of the present disclosure have been made in consideration of the above points, and have an object to suppress the generation of spatter by appropriately changing the welding current during the arc period.

[0007] A first aspect is an arc welding method for welding by cyclically repeating forward and reverse feed of a welding wire, which is a consumable electrode, and alternately repeating short circuit periods in a short circuit state and arc periods in an arc state, wherein the arc periods include a first period, a second period after the first period, and a third period after the second period, and a point in time during the first period when the welding current reaches a predetermined initial holding current that is greater than a base current is referred to as a first change point, a point in time during the second period when the change in the welding current begins is referred to as a second change point, a point in time during the third period when the change in the welding current begins is referred to as a third change point, and a point in time during the third period when the change in the welding current begins is referred to as a second change point. a first step of changing the welding current in the first time period along a straight line connecting the first change point and the second change point, a time point at which the welding current reaches a peak current during the first time period being a fourth change point; a second step of changing the welding current in the second time period so that the welding current becomes larger than a virtual line connecting the second change point and the third change point; and a third step of changing the welding current in the third time period so that the welding current becomes larger than a virtual line connecting the third change point and the fourth change point or a virtual line connecting the third change point and the fourth change point.

[0008] In the first aspect, the welding current is changed linearly between the first and second change points during the first period, and the initial holding current is, for example, 20 to 100 A.

[0009] This allows the tip of the welding wire to begin to melt with a minute welding current, thereby ensuring wettability of the molten region at the tip of the welding wire, and as a result, it is possible to more stably form a molten droplet at the tip of the welding wire in the initial state of the arc period.

[0010] In addition, in the second period, the welding current is changed so that it is greater than the imaginary line connecting the second change point and the third change point, thereby ensuring the heat input to the welding wire. This allows stable formation of a droplet at the tip of the welding wire in the initial state of the arc period.

[0011] In addition, in the third period, the welding current is changed along a straight line connecting the third change point and the fourth change point, thereby ensuring a constant rate of increase in the heat input to the welding wire. Alternatively, the welding current is changed so that the welding current is larger than the imaginary line connecting the third change point and the fourth change point, thereby ensuring a constant rate of increase in the heat input to the welding wire.

[0012] This allows droplets to be constantly held at the tip of the welding wire from the initial stage of droplet formation through to the growth stage. Furthermore, droplet growth is stably carried out until the peak current is reached, allowing droplets of a desired size to be formed.

[0013] Furthermore, the molten metal droplet held at the tip of the welding wire can be stably transferred toward the molten pool, which makes it easier to form a wide bead and suppresses the generation of spatter due to micro-short circuits.

[0014] In a second aspect, in the arc welding method of the first aspect, in the second step, the welding current is changed along an arc-shaped curve in which the welding current is greater than the virtual straight line.

[0015] In the second aspect, the welding current is changed along an arc-shaped curve in the second period to ensure the heat input to the welding wire, thereby enabling stable formation of a droplet at the tip of the welding wire in the initial state of the arc period.

[0016] In a third aspect, in the arc welding method of the first aspect, a predetermined point between the second change point and the third change point is set as a fifth change point, and in the second step, the welding current is changed in a linear manner connecting the second change point and the fifth change point, and then the welding current is changed in a linear manner connecting the fifth change point and the third change point.

[0017] In the third aspect, in the second period, the welding current is changed in a linear fashion connecting the second change point and the fifth change point, and then the welding current is changed in a linear fashion connecting the fifth change point and the third change point, thereby ensuring the heat input to the welding wire. This allows stable formation of a droplet at the tip of the welding wire in the initial state of the arc period.

[0018] A fourth aspect is the arc welding method according to any one of the first to third aspects, wherein the period from the first change point to the second change point is not less than 0.1 msec and not more than 1.0 msec.

[0019] In the fourth aspect, by starting to melt the tip of the welding wire with a minute welding current, it is possible to ensure that the tip of the welding wire is wettable by the molten region.

[0020] A fifth aspect is the arc welding method of any one of the first to third aspects, wherein a gradient of a line connecting the first change point and the second change point is 50 A / msec or more and 2000 A / msec or less.

[0021] In the fifth aspect, by appropriately setting the gradient of the line connecting the first change point and the second change point, it is possible to ensure wettability of the tip of the welding wire by the molten region.

[0022] In a sixth aspect, in the arc welding method of the first aspect, in the third step, the welding current is changed along an arc-shaped curve in which the welding current is greater than the virtual straight line.

[0023] In the sixth aspect, by changing the welding current along an arc-shaped curve in the third period, it is possible to ensure the amount of heat input to the welding wire.

[0024] According to an aspect of the present disclosure, the occurrence of spatter can be suppressed by appropriately changing the welding current during the arc period.

[0025] Fig. 1 is a diagram showing a schematic configuration of an arc welding apparatus according to the first embodiment. Fig. 2 is a graph showing the time waveforms of a welding wire feed speed and a welding current. Fig. 3 is a graph showing the time waveforms of a welding wire feed speed and a welding current of a comparative example. Fig. 4 is a graph showing the time waveforms of a welding wire feed speed and a welding current of the second embodiment. Fig. 5 is a graph showing the time waveforms of a welding wire feed speed and a welding current of the third embodiment. Fig. 6 is a graph showing the time waveforms of a welding wire feed speed and a welding current of the fourth embodiment.

[0026] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses.

[0027] First Embodiment As shown in FIG. 1 , an arc welding device 1 periodically repeats forward and reverse feeding of a welding wire 15, and alternates between a short-circuit period in a short-circuit state and an arc period in an arc state between the welding wire 15 and a workpiece W to generate an arc 16, thereby welding the workpiece W.

[0028] Arc welding apparatus 1 includes welding unit 10 and control unit 30. Welding unit 10 includes welding torch 11, feed motor 12, and power conversion unit 20. Feed motor 12 feeds welding wire 15 to welding torch 11 at a predetermined feed speed.

[0029] The power conversion unit 20 includes a primary side rectifier 21 , a switching unit 22 , a main transformer 23 , a secondary side rectifier 24 , a reactor 25 , a voltage detection unit 26 , and a current detection unit 27 .

[0030] Primary side rectifier 21 rectifies and outputs the output of input power source 5. Switching unit 22 converts the DC output from primary side rectifier 21 into AC. Switching unit 22 controls the welding output, which is made up of a welding current and a welding voltage.

[0031] The main transformer 23 converts the AC voltage output by the switching unit 22. The output of the main transformer 23 is output as a welding output via the secondary side rectifier 24 and the reactor 25. The secondary side rectifier 24 rectifies the secondary side output of the main transformer 23. The voltage detector 26 detects the welding voltage. The current detector 27 detects the welding current.

[0032] The control unit 30 has a drive unit 31, a state detection unit 32, a short circuit control unit 33, an arc control unit 34, a set current setting unit 35, a basic frequency setting unit 36, a basic speed amplitude setting unit 37, and an average feed speed setting unit 38. The drive unit 31 controls the switching unit 22.

[0033] The state detection unit 32 detects whether the state is a short circuit state or an arc state based on the detection result from the voltage detection unit 26. Specifically, the state detection unit 32 determines whether the welding output voltage is equal to or greater than a certain value or less than a certain value based on the signal from the voltage detection unit 26. Based on this determination result, the state detection unit 32 determines whether the state is a short circuit state in which the welding wire 15 is in contact with the workpiece W and short-circuited, or an arc state in which a welding arc is generated in a non-contact state. A determination signal indicating the determination result from the state detection unit 32 is output to the short circuit control unit 33 and the arc control unit 34.

[0034] The short circuit control unit 33 controls the short circuit current during the short circuit period in response to a short circuit signal from the state detection unit 32. The short circuit control unit 33 outputs a command to the drive unit 31 based on the set current so that the short circuit current has a predetermined waveform.

[0035] The arc control unit 34 receives the arc signal from the state detection unit 32 and controls the arc voltage during the arc period in the arc state.

[0036] The arc control unit 34 outputs a command to the drive unit 31 to output the peak current IP and the base current IB for a predetermined time during the arc period. In this embodiment, the transition period from the peak current IP to the base current IB during the arc period is controlled by current control.

[0037] The set current setting unit 35 sets a set current. A signal indicating the set current is output to the short circuit control unit 33 and the arc control unit 34.

[0038] The basic frequency setting unit 36 ​​determines a wire feeding frequency appropriate for each set current based on the set current. Specifically, the basic frequency setting unit 36 ​​has a table or a relational expression that correlates the set current with the frequency, and the frequency is determined from this table based on the set current. A signal indicating the frequency is output to the feed motor 12.

[0039] The speed amplitude basic setting unit 37 determines a wire feeding speed amplitude appropriate for each set current based on the set current. Specifically, the speed amplitude basic setting unit 37 has a table or a relational expression that associates the set current with the speed amplitude, and determines the speed amplitude from this table based on the set current. A signal indicating the speed amplitude is output to the feed motor 12.

[0040] The average feed rate setting unit 38 determines a welding wire feed rate, which is an average wire feed rate appropriate for each set current, based on the set current. Specifically, the average feed rate setting unit 38 has a table or a relational expression that associates the set current with the average feed rate, and determines the average feed rate from this table or the like based on the set current. A signal indicating the welding wire feed rate is output to the feed motor 12.

[0041] The feed motor 12 controls the feeding of the welding wire 15 in a cyclically repeated forward and reverse directions based on the frequency, speed amplitude, and welding wire feed speed. The wire feed speed command is a command to repeat the forward and reverse feed in a sinusoidal manner using the frequency and speed amplitude in accordance with the average wire feed speed appropriate for the current value of the set current.

[0042] <Regarding the Time Waveform of the Welding Current> In Fig. 2, time t1 indicates the time when the short circuit starts. During the short circuit period from time t1 to time t2, an initial short circuit current is output for a predetermined time from time t1, and then the welding current is gradually increased.

[0043] Between time t1 and time t2, a constriction of the droplet is detected between the molten pool and the tip of the welding wire 15. When the constriction of the droplet is detected, the welding current is instantly shifted to a low current, and the short-circuit state is terminated.

[0044] Time t2 indicates the time when the short circuit state ends and an arc state occurs. The period from time t2 to time t3 is an arc period during which an arc 16 is generated between the welding wire 15 and the workpiece W. During this arc period, the arc 16 is generated between the welding wire 15 and the workpiece W, and the heat of the arc 16 forms a molten droplet at the tip of the welding wire 15 and melts a portion of the workpiece W.

[0045] During the arc period from time t2 to time t3, the welding current is increased from base current IB to peak current IP. If the welding current is increased at a steep slope from base current IB to peak current IP, spatter is more likely to occur.

[0046] Therefore, in this embodiment, the welding current is appropriately changed during the arc period to suppress the occurrence of spatter.

[0047] Specifically, the arc period includes a first period, a second period that follows the first period, and a third period that follows the second period.

[0048] The point in time when the welding current reaches a predetermined initial holding current IS that is greater than the base current IB in the first period is designated as a first change point P1, the point in time when the welding current starts to change in the second period is designated as a second change point P2, the point in time when the welding current starts to change in the third period is designated as a third change point P3, and the point in time when the welding current reaches a peak current IP in the third period is designated as a fourth change point P4. Here, the initial holding current IS is, for example, 20 to 100 A.

[0049] During the first period, the welding current is changed linearly between the first change point P1 and the second change point P2. As a result, the welding current changes from the base current IB to the initial holding current IS. The period from the first change point P1 to the second change point P2 is preferably set to 0.1 msec or more and 1.0 msec or less.

[0050] As a result, the tip of the welding wire 15 begins to melt with a minute welding current, and the tip of the welding wire 15 can be ensured to be wettable by the molten region.

[0051] The gradient of the line connecting the first change point P1 and the second change point P2 may be set to 50 A / msec or more and 2000 A / msec or less.

[0052] In the second period, the welding current is changed so that it is greater than the imaginary line connecting the second change point P2 and the third change point P3. In the example shown in Fig. 2, the welding current is changed along an arc-shaped curve where the welding current is greater than the imaginary line.

[0053] This ensures a sufficient amount of heat input to the welding wire 15, and allows droplets to be stably formed at the tip of the welding wire 15 in the initial state of the arc period.

[0054] Next, in the third period, the welding current is changed in a linear fashion connecting the third change point P3 and the fourth change point P4.

[0055] This ensures that the heat input to the welding wire 15 increases at a constant rate, and droplet growth is stably carried out until the peak current IP is reached, thereby making it possible to form droplets of a desired size.

[0056] Furthermore, the molten metal droplet held at the tip of the welding wire 15 can be stably transferred toward the molten pool. As a result, a wide bead can be easily formed, and the generation of spatter due to micro-short circuits can be suppressed.

[0057] Here, if the gradient of the line connecting the third change point P3 and the fourth change point P4 is smaller than 200 A / msec, the heat input to the welding wire 15 is small, and droplet growth becomes unstable at the tip of the welding wire 15. As a result, the periodicity between the short-circuit period and the arc period is disrupted, which may result in unstable welding.

[0058] On the other hand, if the gradient of the line connecting the third change point P3 and the fourth change point P4 is greater than 1500 A / msec, the heat input to the welding wire 15 becomes excessive, increasing the arc pressure applied to the molten pool. The increased arc pressure may then vibrate the molten pool, potentially causing spatter.

[0059] Furthermore, if the heat input to the welding wire 15 is excessive, the tip of the welding wire 15 will rise significantly from the droplet, which may cause unstable droplet transfer to the molten pool and unstable bead formation.

[0060] Therefore, in this embodiment, the slope of the line connecting the third change point P3 and the fourth change point P4 is set to 200 A / msec or more and 1500 A / msec or less. Preferably, the slope of the line connecting the third change point P3 and the fourth change point P4 is set to 1200 A / msec.

[0061] In this way, by appropriately setting the gradient of the line connecting the third change point P3 and the fourth change point P4, it is possible to ensure the heat input to the welding wire 15 while suppressing the generation of spatter.

[0062] During the arc period from time t2 to time t3, the distance between the tip of the welding wire 15 and the molten pool of the workpiece W transitions from T1 (first arc growth), to T2 (second arc growth), to T3 (third arc growth), to T4 (securing arc length), where T1<T2<T3<T4.

[0063] This allows the droplets, from the initial state of droplet formation to the process of growth, to be constantly held at the tip of the welding wire 15. Furthermore, by stably growing the droplets until the peak current IP is reached, it is possible to form droplets of a desired size.

[0064] Time t3 indicates the time when the next short circuit occurs, and is in the same state as time t1. When the welding wire 15 and the workpiece W come into contact and short-circuit, the molten metal droplet formed at the tip of the welding wire 15 during the arcing period is transferred to the workpiece W by short-circuiting, forming a molten pool and performing short-circuit welding.

[0065] 2, welding wire feed control is performed by periodically repeating forward and reverse feed alternately multiple times in a sinusoidal waveform with a predetermined frequency and a predetermined speed amplitude. At the peak of the forward feed, a short circuit occurs around time t1, and at the peak of the reverse feed, an arc 16 occurs around time t2. At the peak of the forward feed after time t2, a next short circuit occurs around time t3.

[0066] As described above, the period from time t1 to time t3 is defined as one control cycle, and welding is performed by repeating this cycle.

[0067] Comparative Example Below, a description will be given of a time waveform when the welding current is changed during the arc period by a method different from that of the arc welding method according to the present embodiment. In the drawings illustrating the comparative example below, the change in the welding current according to the present embodiment is shown by a virtual line to make it easier to compare with the change in the welding current according to the comparative example.

[0068] In the comparative example shown in Figure 3, from the first period to the third period, the welding current is changed along an arc-shaped curve in which the welding current is larger than the virtual line connecting the first change point P1' and the fourth change point P4'.

[0069] Here, the first change point P1' is later than the first change point P1 and the second change point P2 in the previous embodiment. The transition to the first change point P1' is performed at the base current IB. The wire feed speed is slower than that in the previous embodiment, and the peak current IP' at the fourth change point P4' is smaller than the peak current IP at the fourth change point P4 in the previous embodiment.

[0070] In this case, in the period from the first change point P1′ to the fourth change point P4′, the welding current applied to the welding wire 15 is small, resulting in insufficient heat input, and therefore the growth of the droplet at the tip of the welding wire 15 becomes relatively small, which may result in a narrower bead width.

[0071] In addition, the change in welding current becomes steeper overall, and the welding current also increases when rising, which increases the arc pressure on the molten pool, causing it to vibrate and potentially scattering as spatter.

[0072] -Effects of First Embodiment- As described above, according to the arc welding method of the first embodiment, by changing the welding current in a linear manner connecting the first change point P1 and the second change point P2 in the first period, it is possible to ensure wettability of the tip of the welding wire 15 by the molten region.

[0073] In addition, during the second period, the welding current is changed so that it is greater than the imaginary line connecting the second change point P2 and the third change point P3, thereby ensuring the heat input to the welding wire 15.

[0074] Furthermore, by changing the welding current in a linear manner connecting the third change point P3 and the fourth change point P4 in the third period, the heat input to the welding wire 15 can be ensured at a constant rate of increase.

[0075] This allows the droplet held at the tip of the welding wire 15 to be stably transferred toward the molten pool, making it easier to form a wide bead and suppressing the generation of spatter due to micro-short circuits.

[0076] Furthermore, even if the feeding speed of the welding wire 15 is increased, the welding can be stabilized, and therefore the tact time can be reduced.

[0077] For example, when welding two overlapping plate materials with a thickness of 1.6 to 6.0 mm as the workpieces W, the welding speed can be set in the range of 0.6 to 1.5 m / min. Also, productivity can be improved by improving the gap tolerance.

[0078] Second Embodiment Hereinafter, the same parts as those in the first embodiment will be denoted by the same reference numerals, and only the differences will be described.

[0079] As shown in FIG. 4, the arc period includes a first period, a second period after the first period, and a third period after the second period.

[0080] The point in time during the first period when the welding current reaches a predetermined initial holding current IS that is greater than the base current IB is designated as the first change point P1, the point in time during the second period when the welding current begins to change is designated as the second change point P2, the point in time during the third period when the welding current begins to change is designated as the third change point P3, the point in time during the third period when the welding current reaches the peak current IP is designated as the fourth change point P4, and a predetermined point between the second change point P2 and the third change point P3 is designated as the fifth change point P5.

[0081] During the first period, the welding current is changed along a straight line connecting the first change point P1 and the second change point P2, so that the welding current reaches the initial holding current IS from the base current IB.

[0082] In the second period, the welding current is changed so that it is greater than the imaginary line connecting the second change point P1 and the third change point P3. In the example shown in Figure 4, the welding current is changed along a line connecting the second change point P2 and the fifth change point P5, and then along a line connecting the fifth change point P5 and the third change point P3. Thereafter, the welding current is changed along a line connecting the third change point P3 and the fourth change point P4.

[0083] As described above, according to the arc welding method of the second embodiment, by changing the welding current in a linear manner connecting the first change point P1 and the second change point P2, it is possible to ensure wettability of the tip of the welding wire 15 by the molten region.

[0084] Third Embodiment As shown in FIG. 5, the arc period includes a first period, a second period that follows the first period, and a third period that follows the second period.

[0085] The point in time during the first period when the welding current reaches a predetermined initial holding current IS that is greater than the base current IB is designated as the first change point P1, the point in time during the second period when the welding current begins to change is designated as the second change point P2, the point in time during the third period when the welding current begins to change is designated as the third change point P3, the point in time during the third period when the welding current reaches the peak current IP is designated as the fourth change point P4, and a predetermined point between the second change point P2 and the third change point P3 is designated as the fifth change point P5.

[0086] During the first period, the welding current is changed along a straight line connecting the first change point P1 and the second change point P2, so that the welding current reaches the initial holding current IS from the base current IB.

[0087] During the second period, the welding current is changed so that it is greater than the imaginary line connecting the second change point P1 and the third change point P3. In the example shown in Figure 5, the welding current is changed along a line connecting the second change point P2 and the fifth change point P5, and then along a line connecting the fifth change point P5 and the third change point P3. Thereafter, the welding current is changed along a line connecting the third change point P3 and the fourth change point P4. Here, the line connecting the fifth change point P5 and the third change point P3 extends so that the welding current remains constant.

[0088] As described above, according to the arc welding method of the third embodiment, by changing the welding current in a linear manner connecting the first change point P1 and the second change point P2 in the first period, it is possible to ensure wettability of the tip of the welding wire 15 by the molten region.

[0089] Fourth Embodiment As shown in FIG. 6, the arc period includes a first period, a second period that follows the first period, and a third period that follows the second period.

[0090] The point in time when the welding current reaches a predetermined initial holding current IS that is greater than the base current IB during the first period is designated as the first change point P1, the point in time when the welding current begins to change during the second period is designated as the second change point P2, the point in time when the welding current begins to change during the third period is designated as the third change point P3, and the point in time when the welding current reaches the peak current IP during the third period is designated as the fourth change point P4.

[0091] In the first period, the welding current is changed from the base current IB until it reaches the initial holding current IS.

[0092] In the second period, the welding current is changed along an arc-shaped curve where the welding current is greater than the imaginary line connecting the second change point P1 and the third change point P3. Thereafter, the welding current is changed along an arc-shaped curve where the welding current is greater than the imaginary line connecting the third change point P3 and the fourth change point P4.

[0093] As described above, according to the arc welding method of the fourth embodiment, by changing the welding current in a linear manner connecting the first change point P1 and the second change point P2 in the first period, it is possible to ensure wettability of the tip of the welding wire 15 by the molten region.

[0094] As described above, the present invention has a highly practical effect of suppressing the generation of spatter by appropriately changing the welding current during the arc period, and is therefore extremely useful and has high industrial applicability.

[0095] 1 Arc welding device 15 Welding wire IB Base current IP Peak current IS Initial holding current P1 First change point P2 Second change point P3 Third change point P4 Fourth change point P5 Fifth change point

Claims

1. An arc welding method for welding by periodically repeating forward and reverse feed of a welding wire, which is a consumable electrode, and alternately repeating short circuit periods in a short circuit state and arc periods in an arc state, wherein the arc periods include a first period, a second period after the first period, and a third period after the second period, wherein a first change point is a point in time in the first period when the welding current reaches a predetermined initial holding current that is greater than a base current, a second change point is a point in time in the second period when the welding current starts to change, a third change point is a point in time in the third period when the welding current starts to change, and a fourth change point is a point in time in the third period when the welding current reaches a peak current, and wherein a first step in the first period is changing the welding current along a straight line connecting the first change point and the second change point, and a second step in the second period is changing the welding current so that the welding current becomes greater than a virtual straight line connecting the second change point and the third change point. and a third step of changing the welding current during the third period so that the welding current is greater than a line connecting the third change point and the fourth change point or a virtual line connecting the third change point and the fourth change point.

2. The arc welding method according to claim 1, wherein in the second step, the welding current is changed along an arc-shaped curve in which the welding current is greater than that on the virtual straight line.

3. The arc welding method of claim 1, wherein a predetermined point between the second change point and the third change point is defined as a fifth change point, and in the second step, the welding current is changed in a linear manner connecting the second change point and the fifth change point, and then the welding current is changed in a linear manner connecting the fifth change point and the third change point.

4. An arc welding method according to any one of claims 1 to 3, wherein the period from the first change point to the second change point is 0.1 msec or more and 1.0 msec or less.

5. An arc welding method according to any one of claims 1 to 3, wherein the gradient of the line connecting the first change point and the second change point is not less than 50 A / msec and not more than 2000 A / msec.

6. The arc welding method according to claim 1, wherein in the third step, the welding current is changed along an arc-shaped curve in which the welding current is greater than that on the virtual straight line.

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