Arc welding method

Abstract

An arc welding method according to the present disclosure is short-circuit welding in which a workpiece 17 is subjected to an alternating repetition of forward feeding and reverse feeding of a welding wire 18, and the arc welding method comprises at least first to third steps. The materials of the workpiece 17 and the welding wire 18 are each magnesium or a magnesium alloy. In the first step, after a short circuit has been released, a welding current I is increased to a first value IA. In the second step, after the welding current I has reached the first value IA, the welding current I is reduced and is set to a third value IC that is lower than the first value IA before a short circuit occurs. In the third step, after the welding current I has reached the third value IC, the welding current I is maintained at the third value IC until a short circuit is started.

Description

Arc welding method

[0001] The present disclosure relates to arc welding methods, and in particular to methods for arc welding magnesium-based materials.

[0002] BACKGROUND ART In recent years, magnesium and magnesium alloys (hereinafter sometimes referred to as magnesium-based materials) have come to be used as components for vehicles and the like because they are lighter than aluminum.

[0003] On the other hand, magnesium-based materials are less likely to deform at room temperature than aluminum or aluminum alloys (hereinafter referred to as aluminum-based materials), and thus, in order to obtain components of various shapes, component processing using welding becomes necessary.

[0004] For example, Patent Document 1 proposes a TIG welding method for magnesium-based materials using an AC power source as the welding power source. In this method, a shielding gas consisting of an inert gas and an oxidizing gas is flowed toward the workpiece to be welded so as to cover the tungsten electrode, thereby achieving a deep penetration depth.

[0005] JP 2016-036855 A

[0006] However, in the welding of magnesium-based materials, there is a demand for improved productivity, in other words, improved welding speed. To improve the welding speed, welding using a consumable electrode such as a welding wire is more advantageous than TIG welding using a non-consumable electrode.

[0007] However, magnesium-based materials are lighter than aluminum-based materials, so when the arc reaction force is high, short circuits are less likely to occur, and droplets grow excessively, making spattering and other problems more likely to occur.

[0008] The present disclosure has been made in view of the above points, and an object of the present disclosure is to provide a method for arc welding of magnesium-based materials that can improve the welding speed and suppress the generation of spatter and the like.

[0009] In order to achieve the above object, an arc welding method according to the present disclosure is an arc welding method that at least performs short-circuit welding by alternately repeating forward and reverse feed of a welding wire relative to a workpiece, wherein the workpiece and the welding wire are made of magnesium or a magnesium alloy, and the method includes at least the following steps: during forward feed of the welding wire, the welding wire is fed toward the workpiece so as to short-circuit the welding wire and the workpiece; and during reverse feed of the welding wire, the welding wire is fed in a direction opposite to that of forward feed of the welding wire so as to release the short-circuit between the welding wire and the workpiece; after the short-circuit between the welding wire and the workpiece is released, increasing a welding current flowing through the welding wire to a first value; after the welding current reaches the first value, reducing the welding current and further reducing the welding current flowing through the welding wire to a third value lower than the first value before the welding wire and the workpiece are short-circuited; and a third step of controlling the welding current so as to maintain the third value from when the welding current reaches the third value until the welding wire and the workpiece are short-circuited.

[0010] According to the present disclosure, the welding speed can be improved compared to TIG welding. In addition, excessive growth of droplets can be suppressed, thereby suppressing the occurrence of welding defects such as spatter.

[0011] FIG. 1 is a schematic diagram of an arc welding device according to an embodiment. FIG. 2 is a diagram showing output waveforms of welding current and welding voltage and changes in wire feed speed during short-circuit welding. FIG. 3 is a diagram showing output waveforms of welding current and welding voltage and changes over time in the distance between the tip of the welding wire and the workpiece during short-circuit welding. FIG. 4 is an enlarged view of the waveform of the welding current during short-circuit welding. FIG. 5 is a diagram showing the relationship between the average current and the current just before a short circuit according to an embodiment. FIG. 6 is a diagram showing the relationship between the average current and the forward feed speed according to an embodiment. FIG. 7 is a diagram showing the relationship between the average current and the low current duration after opening the short circuit according to an embodiment. FIG. 8 is a diagram showing the relationship between the average current and the power integration threshold according to an embodiment.

[0012] The present embodiment will be described in detail below with reference to the drawings. The following description of the preferred embodiment is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses.

[0013] 1 is a schematic diagram of an arc welding device according to the present embodiment. Arc welding device 16 performs welding by repeatedly switching between an arc state and a short-circuit state between welding wire 18, which is a consumable electrode, and workpiece 17, which is a workpiece to be welded. Welding wire 18 is held by a torch (not shown), and as the torch moves at a predetermined speed, the tip of welding wire 18 also moves at the same speed along a predetermined welding section.

[0014] Arc welding device 16 has a main transformer 2, a primary side rectifier 3, a switching unit 4, a DCL (reactor) 5, a secondary side rectifier 6, a welding current detector 7, a welding voltage detector 8, a control switching unit 9, an output controller 10, and a wire feed speed controller 13. Arc welding device 16 also has a robot controller (not shown) that controls the operation of a robot (not shown) that holds a torch (not shown).

[0015] The control switching unit 9, the output control unit 10, and the wire feed speed control unit 13 are each configured with one or more central processing units (CPUs). Alternatively, the control switching unit 9, the output control unit 10, and the wire feed speed control unit 13 are each configured with one or more micro control units (MCUs). The control switching unit 9, the output control unit 10, and the wire feed speed control unit 13 may be configured with the same CPU or MCU.

[0016] Output control unit 10 has a short-circuit welding control unit 11 and a pulse welding control unit 12. Wire feed speed control unit 13 has a wire feed speed detection unit 14 and a calculation unit 15. Primary side rectification unit 3 rectifies an input voltage input from an input power source (three-phase AC power source) 1 external to arc welding device 16. Switching unit 4 controls the output of primary side rectification unit 3 to an output suitable for welding. Main transformer 2 converts the output of switching unit 4 into an output suitable for welding.

[0017] A secondary side rectifier 6 rectifies the output of the main transformer 2. A DCL (reactor) 5 smoothes the output of the secondary side rectifier 6 to a current suitable for welding. A welding current detector 7 detects a welding current I flowing through a welding wire 18. A welding voltage detector 8 detects a welding voltage V applied between the welding wire 18 and a workpiece 17.

[0018] Control switching unit 9 is a switching unit that outputs the timing for switching from short circuit welding control to pulse welding control to output control unit 10. Control switching unit 9 has a timing function, and measures a predetermined time set by welding condition setting unit 22, and outputs the timing for switching control to output control unit 10 and wire feed speed control unit 13.

[0019] The output control unit 10 controls the welding output by outputting a control signal to the switching unit 4. The short circuit welding control unit 11 controls short circuit welding when the control switching unit 9 commands short circuit welding. The pulse welding control unit 12 controls pulse welding when the control switching unit 9 commands pulse welding.

[0020] The output control unit 10 calculates the average current I Ｓ The welding current I is controlled so that the average current I Ｓ is a moving average value of the welding current I over a predetermined period. The output control unit 10 also has a calculation unit (not shown) that calculates an integrated power value by integrating the power supplied to the welding wire 18 within a predetermined period. The calculation unit calculates the power supplied to the welding wire 18 based on the product of the welding current and the welding voltage.

[0021] Wire feed speed control unit 13 controls wire feed unit 21 to control the feed speed S of welding wire 18 (hereinafter referred to as wire feed speed S). Wire feed speed detection unit 14 detects wire feed speed S. Based on a signal from wire feed speed detection unit 14, calculation unit 15 calculates an integrated amount of the feed amount of welding wire 18 and controls wire feed speed S. Specifically, calculation unit 15 compares a command value and a detected value of wire feed speed S to determine a difference, and performs feedback control based on the integrated amount of the difference so as to match the actual wire feed speed S with the command value.

[0022] A wire feeder 21 and a welding condition setting unit 22 are connected to the arc welding device 16. The welding condition setting unit 22 is used to set welding conditions for the arc welding device 16. The welding condition setting unit 22 also has a short-circuit welding setting unit 23 and a pulse welding setting unit 24. The wire feeder 21 controls the feeding of the welding wire 18 based on a signal from the wire feed speed control unit 13. A welding program, which describes the welding output control procedure and the feeding procedure of the welding wire 18 during short-circuit welding and pulse welding, is stored in a storage unit (not shown).

[0023] When a torch switch (SW) (not shown) is turned on, the welding output of the arc welding device 16 is supplied to the welding wire 18 via the welding tip 20. Then, the welding output of the arc welding device 16 generates an arc 19 between the welding wire 18 and the workpiece 17, thereby performing welding.

[0024] [Arc welding method] Fig. 2 is a diagram showing output waveforms of welding current and welding voltage and changes in wire feed speed during short-circuit welding. Fig. 3 is a diagram showing output waveforms of welding current and welding voltage and changes in the distance between the tip of the welding wire and the workpiece over time during short-circuit welding. Fig. 4 is an enlarged view of the welding current waveform during short-circuit welding.

[0025] In this embodiment, the welding wire 18 is made of a magnesium alloy (AZ61) with a wire diameter of 1.2 mm, and the workpiece 17 is made of a magnesium alloy (AZ31). Both the welding wire 18 and the workpiece 17 may be made of magnesium alloys of other compositions, or magnesium itself. The shielding gas sprayed onto the workpiece is argon (Ar) gas, and the flow rate of the shielding gas is set to 20 L / min. However, the flow rate of the shielding gas is not particularly limited to this.

[0026] In addition, depending on the thickness of the workpiece 17, the average current I Ｓ is adjusted separately. If the plate thickness is thin, the average current I Ｓ is set to a low value, and if the plate thickness is large, the average current I Ｓ is set to a high value. For example, if the plate thickness is about 1 mm, the average current I Ｓis set to about 40A, and if it is about 3mm, the average current I Ｓ is set to about 80 A. If the plate thickness is about 6 mm, the average current I Ｓ is set to be 140 A or more.

[0027] As described above, welding power is supplied to the welding wire 18, and the tip of the welding wire 18 moves along a predetermined welding section as the torch (not shown) moves, thereby performing short-circuit welding on the workpiece 17. As shown in FIGS. 2 and 3 , in the short-circuit welding shown in this embodiment, the arc period T ＡＲＣ and the following short-circuit period T Ｓ The welding period T including the above is used as a basic unit, and the processing included in the welding period T is executed as many times as necessary. ＡＲＣ During the short-circuit period T ＳＨＯＲＴ In this case, the workpiece 17 and the welding wire 18 are short-circuited.

[0028] In this embodiment, the welding period T is set to about 120 msec. However, the welding period T and the arc period T ＡＲＣ and short-circuit period T ＳＨＯＲＴ are not necessarily constant, and may vary depending on the timing at which welding wire 18 and workpiece 17 are short-circuited.

[0029] As shown in Fig. 2, the wire feed speed S changes periodically with the welding period T as the period. When the wire feed speed S is positive (above the line S = 0 in Fig. 2), the welding wire 18 is fed so as to approach the workpiece 17, that is, a forward feed operation is performed. The wire feed speed S in this case is called the forward feed speed S Ｆ When the wire feed speed S is negative (below the line of S=0 in FIG. 2), the welding wire 18 is fed away from the workpiece 17, that is, a reverse feed operation is performed. The wire feed speed S in this case is called the reverse feed speed S Ｒ The waveform of the wire feed speed S, i.e., the shape of the amplitude and the slope with respect to time, is calculated by the above-mentioned average current I ＳFurthermore, the waveform of the wire feed speed S also changes in conjunction with the output waveform of the welding current I.

[0030] As shown in FIGS. 2 to 4, the period from time tn1 to time tn3 is the arc period T ＡＲＣ The period from time tn3 to t(n+1)1 is the short-circuit period T ＳＨＯＲＴ Here, n is an integer of 1 or more, 1≦n≦m, and m is the number of times the welding period T is repeated during short-circuit welding.

[0031] Starting from time tn1, the changes over time of welding current I, welding voltage V, wire feed speed S, and distance L between welding wire 18 and workpiece 17 (hereinafter simply referred to as distance L) will be described below.

[0032] First, the arc period T ＡＲＣ At time tn1, which is the start point of the welding wire 18, the wire feed speed S is negative and the welding wire 18 is being fed in the reverse direction. After time tn1, the wire feed speed control unit 13 controls the wire feed speed S so that it approaches zero. That is, the movement of the welding wire 18 changes from reverse feeding to forward feeding. Also, after time tn1, the welding voltage V changes from zero to a positive value. That is, the short circuit between the welding wire 18 and the workpiece 17 begins to open, and the distance L begins to change from zero to a positive value.

[0033] On the other hand, the output control unit 10 controls the current value of the welding current I to I from time tn1 until the time period T1 (see FIG. 4) has elapsed. Ｄ In the following description, the period T1 is referred to as the first period T1 or the low current duration period T1 after the short circuit is opened, and the current value I Ｄ the fourth value I Ｄ It is sometimes called.

[0034] When the period T1 has elapsed since time tn1, the welding wire 18 is in the forward feed operation. After the period T1 has elapsed, the output control unit 10 adjusts the welding current I to a current value I Ａ The fourth value I Ｄ is the current value I Ａ In the following explanation, the current value I Ａ the first value IＡ Also, when the welding current I is the first value I Ａ At time tn2, that is, at time tn3, the distance L reaches its maximum value, which is about 4 mm in this case. Although not shown, at time tn3, a droplet of a predetermined size is formed at the tip of the welding wire 18.

[0035] After time tn2 has elapsed, wire feed speed control unit 13 reduces wire feed speed S. Also, output control unit 10 reduces welding current I to current value I Ｂ (I Ｂ <I Ａ The welding current I is controlled to be I Ｂ The current value I is set to 0.5 V in order to adjust the heat input to the weld bead (not shown) formed on the workpiece 17 by welding. Ｂ The time for which this value is maintained can be changed as appropriate.

[0036] The welding current I is the current value I Ｂ After a further time has elapsed, before the welding wire 18 and the workpiece 17 are short-circuited, the output control unit 10 reduces the welding current I to a current value I Ｃ The welding current I is controlled to be equal to the current value I Ｃ From the time when the current value I Ｃ The welding current I is controlled so as to maintain

[0037] In the following description, the current value of the welding current I is I Ｃ The period T2 (see FIG. 4) during which the current value I Ｃ the third value I Ｃ , or the current just before the short circuit I Ｃ The third value I Ｃ is the first value I Ａ In this embodiment, the third value I Ｃ is the fourth value I Ｄ However, the third value I is not particularly limited to this. Ｃ is the fourth value I Ｄ It may be the following:

[0038] The current value of the welding current I is I Ｃ As a result, the arc 19 generated between the welding wire 18 and the workpiece 17 becomes suddenly smaller, and the arc reaction force acting on the droplet formed at the tip of the welding wire 18 also becomes suddenly smaller.

[0039] The current value of the welding current I is I Ｃ When the period T2 has elapsed since the time tn1 is reached, the welding wire 18 and the workpiece 17 are short-circuited at time tn3, and the short-circuit period T ＳＨＯＲＴ will begin.

[0040] After the welding wire 18 and the workpiece 17 are short-circuited, when the amount of heat applied to the welding wire 18 reaches a predetermined threshold, the output control unit 10 sets the fourth value I Ｄ At time t(n+1), which is the start point of the next welding period T, the welding current I is controlled to a fourth value I Ｄ The short circuit welding proceeds sequentially.

[0041] The amount of heat applied to the welding wire 18 corresponds to the integrated power value described above. Therefore, in actual control, when the integrated power value exceeds a predetermined threshold value P ＴＨ When the fourth value I Ｄ In the following description, the welding current I is controlled so that the threshold value P ＴＨ power integration threshold P ＴＨ It is sometimes called.

[0042] Thereafter, the output control unit 10 and the wire feed speed control unit 13 respectively control the welding current I and the wire feed speed S for each welding period T, and short-circuit welding progresses. When short-circuit welding is performed for a predetermined length along the weld line, the short-circuit welding is completed, and a weld bead of a predetermined length is formed on the workpiece 17.

[0043] [Effects, etc.] As described above, the arc welding method according to this embodiment is short-circuit welding in which welding wire 18 is alternately fed forward and backward relative to workpiece 17. Workpiece 17 and welding wire 18 are each made of a magnesium-based material, that is, magnesium or a magnesium alloy.

[0044] When the welding wire 18 is fed forward, the welding wire 18 is fed toward the workpiece 17 so that the welding wire 18 and the workpiece 17 are short-circuited.

[0045] When the welding wire 18 is fed backward, the welding wire 18 is fed in the opposite direction to when the welding wire 18 is fed forward so that the short circuit between the welding wire 18 and the workpiece 17 is released.

[0046] The arc welding method according to this embodiment includes at least the following first to third steps.

[0047] After the short circuit between the welding wire 18 and the workpiece 17 is released, the welding current I flowing through the welding wire 18 is set to a first value I Ａ (first step).

[0048] The welding current I is a first value I Ａ After the welding current I reaches the first value I, the welding current I is reduced, and before the welding wire 18 and the workpiece 17 are short-circuited, the welding current I is reduced to the first value I Ａ a third value I that is lower than Ｃ (second step).

[0049] The welding current I is a third value I Ｃ The third value I Ｃ The welding current I is controlled so as to maintain the above (third step).

[0050] According to this embodiment, by providing the third step in particular, it is possible to promote short-circuiting between the welding wire 18 and the workpiece 17. This makes it possible to suppress excessive growth of droplets formed at the tip of the welding wire 18. As a result, it is possible to suppress the scattering of droplets during welding, thereby suppressing the generation of spatter. This will be further described.

[0051] 5 is a diagram showing the relationship between the average current and the current immediately before short-circuit welding according to the embodiment. For comparison, in FIGS. 5 to 8, the average current I Ｓ and various parameters.

[0052] As shown in FIG. 5, the current just before the short circuit I Ｃ (The third value IＣ ), that is, the current value of the welding current I flowing through the welding wire 18 immediately before the short circuit is the average current I Ｓ This is the same whether the material of the workpiece 17 is an aluminum-based material or a magnesium-based material.

[0053] On the other hand, the current just before the short circuit I Ｃ The absolute value of the average current I is set to be smaller when the workpiece 17 is made of a magnesium-based material than when it is made of an aluminum-based material. Ｓ is in the range of 50 A to 200 A, that is, 50 A or more and 200 A or less, the current just before the short circuit I Ｃ is in the range of 20A to 80A, that is, 20A or more and 80A or less.

[0054] As described above, magnesium-based materials are lighter than aluminum-based materials, and therefore the mass of the droplets formed at the tip of the welding wire 18 is also lighter when the magnesium-based material is used. When the welding current I increases while the arc 19 is generated, the arc reaction force acting on the droplets also increases, making it less likely that a short circuit will occur between the welding wire 18 and the workpiece 17. This has led to a problem in that the droplets grow excessively, making it more likely that spatter and the like will occur.

[0055] On the other hand, when performing short-circuit welding of magnesium-based materials, as shown in this embodiment, the current just before short circuit I Ｃ By setting the value of the arc pressure to a low value, it is possible to reduce the arc reaction force and promote short-circuiting between the welding wire 18 and the workpiece 17. This makes it possible to prevent excessive growth of droplets and further to suppress the occurrence of spatter.

[0056] Furthermore, since the occurrence of spatters and the like can be suppressed, welding defects can be reduced, and a decrease in the yield of the welding process can be suppressed. Also, high welding quality can be maintained.

[0057] Furthermore, according to this embodiment, the welding speed can be improved compared to TIG welding as disclosed in Patent Document 1. This allows the process time in the welding process of magnesium-based materials to be shortened, and productivity to be improved.

[0058] The current just before the short circuit I Ｃ If the current just before the short circuit I is set too low, other problems may occur. Ｃ If the setting range of is set too low below the above-mentioned range, the temperature of the molten pool (not shown) formed in the workpiece 17 will be low, which will result in blowholes being more likely to occur inside the workpiece 17. Alternatively, the weld bead will rise higher than desired.

[0059] Therefore, as mentioned above, the average current I Ｓ is in the range of 50 A to 200 A, the current just before the short circuit I Ｃ is preferably in the range of 20A to 80A.

[0060] In addition, the normal feed speed S Ｆ By appropriately setting the value of the welding wire 18, it is possible to promote a short circuit between the welding wire 18 and the workpiece 17.

[0061] FIG. 6 is a diagram showing the relationship between the average current and the forward feed rate according to the embodiment.

[0062] As shown in FIG. 6, the forward feed rate S Ｆ Also, the average current I Ｓ This is the same whether the material of the workpiece 17 is an aluminum-based material or a magnesium-based material.

[0063] On the other hand, the forward feed speed S Ｆ is set to be higher when the workpiece 17 is made of a magnesium-based material than when it is made of an aluminum-based material. Ｓ When the range of 50A to 200A is 50A to 200A, the normal feed rate S Ｆ is in the range of 30 m / min to 70 m / min, that is, 30 m / min or more and 70 m / min or less.

[0064] As shown in this embodiment, the forward feed rate S Ｆ By setting the temperature to a high value, the welding wire 18 can be forced to approach the workpiece 17, thereby promoting a short circuit between the two. This makes it possible to prevent the droplets from growing excessively, and further to prevent the occurrence of spatter.

[0065] The normal feed speed S Ｆ If the value is set too high, the above-mentioned problems may occur, i.e., blowholes may be more likely to occur inside the workpiece 17. Alternatively, the weld bead may rise higher than desired.

[0066] Therefore, as mentioned above, the average current I Ｓ When the range of 50A to 200A is 50A to 200A, the normal feed rate S Ｆ is preferably in the range of 30 m / min to 70 m / min.

[0067] The normal feed speed S Ｆ When the reverse feed speed S is set high as in this embodiment, Ｒ The forward feed speed S Ｆ Only the reverse feed speed S Ｒ If the value is set to a low value, the weld bead tends to bulge excessively. Therefore, the forward feed speed S is set to a higher value for magnesium-based materials than for aluminum-based materials. Ｆ In response to the high setting of Ｒ Also set it high.

[0068] In addition, the normal feed speed S Ｆ and reverse feed speed S Ｒ By setting both of these to high values, both the forward feed amount and the reverse feed amount of the welding wire 18 during short-circuit welding become larger in this embodiment, that is, in the case of a magnesium-based material, than in the case of an aluminum-based material.

[0069] In the arc welding method according to the present embodiment, the welding current I is increased to the first value I immediately after the short circuit between the welding wire 18 and the workpiece 17 is released. Ａ a fourth value I that is lower than Ｄ and the first period T1, the fourth value I Ｄ The welding current I is controlled so as to maintain the value of I (fourth step). After the fourth step is executed, the process moves to the first step, and short-circuit welding proceeds in sequence.

[0070] In addition, the first period T1 (low current duration T1 after the short circuit is released) is the period from when the short circuit between the welding wire 18 and the workpiece 17 is released until the distance L between the welding wire 18 and the workpiece 17 reaches a predetermined value.

[0071] In this embodiment, by providing the fourth step and setting the low current duration T1 after the short circuit is opened to be long, it is possible to suppress the scattering of droplets and the occurrence of spatter, etc. This will be described in further detail below.

[0072] FIG. 7 is a diagram showing the relationship between the average current and the low current duration after the short circuit is opened according to the embodiment.

[0073] As shown in FIG. 7, the low current duration T1 after the short circuit is opened is Ｓ This is the same whether the material of the workpiece 17 is an aluminum-based material or a magnesium-based material.

[0074] In the example shown in FIG. 7, the average current I Ｓ In the region where the current exceeds 150 A, the decrease in the low current duration T1 after the short circuit is released becomes smaller, and there is a tendency for the period to eventually converge to a constant value.

[0075] On the other hand, the low current duration T1 after the short circuit is released is set to be longer when the workpiece 17 is made of a magnesium-based material than when it is made of an aluminum-based material. Ｓ is in the range of 50 A to 200 A, the low current duration T1 (first period T1) after the short circuit is opened is in the range of 4000 μsec to 1000 μsec. Ｓ When the current is 50 A, the low current duration T1 after the short circuit is opened is 4000 μsec, and the average current I Ｓ As the value of T1 increases, the low current duration T1 after the short circuit is opened decreases, and the average current I Ｓ When the current is 200 A, the low current duration T1 after the short circuit is opened is 1000 μsec.

[0076] As described above, in short-circuit welding of magnesium-based materials, the mass of the droplets formed at the tip of the welding wire 18 is lighter than in the case of aluminum-based materials. In this case, if the welding current I is suddenly increased immediately after the short circuit is released, the arc reaction force acting on the droplets also increases suddenly, and there is a risk that the droplets will be blown away by the arc reaction force. If this happens, a large amount of spatter will be generated, resulting in a poor weld.

[0077] Therefore, as shown in this embodiment, after the short circuit is opened, the current value of the welding current I is set to a low value (fourth value I Ｄ ), and the output control unit 10 controls the welding current I so that the welding current I is maintained at this low value for a certain period (first period T1). By doing so, first, the arc reaction force generated between the welding wire 18 and the workpiece 17 can be reduced. Also, during or at the end of the first period T1, the operation of the welding wire 18 switches from reverse feeding to forward feeding, and the distance L between the welding wire 18 and the workpiece 17 reaches approximately its maximum value after the first period T1 has elapsed. When the distance L has become sufficiently long, the process moves to the first step, and the current value of the welding current I reaches the first value I. Ａ In other words, since the welding current I is increased while the distance L is sufficiently secured, droplets of an appropriate size can be formed at the tip of the welding wire 18. Furthermore, an increase in the arc reaction force that the droplets receive is suppressed, and scattering of the droplets, and consequently the occurrence of spatter, etc. can be suppressed.

[0078] In this embodiment, the maximum value is about 4 mm, but it may vary depending on the wire diameter of the welding wire 18 and the reverse feed speed S Ｒ The distance L may be changed as appropriate depending on the inertia of the robot holding the torch, the welding current I, and the like. Also, after the first period T1 has elapsed, the distance L does not necessarily have to be at its maximum value. Ａ Even if the temperature is increased to 1000 K, it is sufficient to ensure a distance that does not cause scattering of droplets.

[0079] Also, the fourth value I Ｄ corresponds to the current value at which the tip of the welding wire 18, which is attached to the molten pool formed on the workpiece 17, becomes thinner just before the short circuit between the welding wire 18 and the workpiece 17 is released, i.e., the so-called necking phenomenon occurs.

[0080] In the arc welding method according to the present embodiment, when the amount of heat applied to the welding wire 18 reaches a predetermined threshold after the welding wire 18 and the workpiece 17 are short-circuited, the output control unit 10 sets a fourth value I Ｄ The welding current I is controlled so that:

[0081] The amount of heat applied to welding wire 18 corresponds to an integrated power value obtained by integrating the power supplied to welding wire 18 within a predetermined period after welding wire 18 and workpiece 17 are short-circuited.

[0082] The power supplied to the welding wire 18 is calculated based on the product of the welding voltage V and the welding current I applied between the welding wire 18 and the workpiece 17 .

[0083] In the fifth step, the power integration value is set to a predetermined power integration threshold P ＴＨ When the fourth value I Ｄ The welding current I is controlled so that

[0084] In this embodiment, a fifth step is provided, and the power accumulation threshold P ＴＨ By appropriately setting the value of the resistance, it is possible to suppress the occurrence of spatter when a short circuit is opened. This will be explained in more detail below.

[0085] FIG. 8 is a diagram illustrating the relationship between the average current and the power integration threshold value according to the embodiment.

[0086] As shown in FIG. 8, the power accumulation threshold P ＴＨ is the average current I Ｓ This is the same whether the material of the workpiece 17 is an aluminum-based material or a magnesium-based material.

[0087] On the other hand, the power integration threshold P ＴＨ is set to be lower when the workpiece 17 is made of a magnesium-based material than when it is made of an aluminum-based material. Ｓ is in the range of 50 A to 200 A, the power integration threshold P ＴＨ is in the range of 4kW to 8kW. That is, the average current I ＳWhen the power integration threshold P ＴＨ is 4 kW or more and 8 kW or less.

[0088] Conventionally, in short-circuit welding of ferrous materials, the occurrence of the aforementioned necking has been detected based on changes in welding voltage V. When a necking occurs between welding wire 18 and workpiece 17, the resistance value increases at the necked portion. In this case, the amount of change in welding voltage increases relative to the amount of change in welding current I under short-circuit control. Therefore, when the occurrence of a necking, that is, the time when the short circuit is about to be released, is detected based on the amount of voltage change, the welding current I is reduced just before the short circuit is released to suppress the generation of spatter.

[0089] However, the electrical resistivity of magnesium (about 4.3 μΩ·cm at room temperature) is smaller than that of iron (about 10.4 μΩ·cm at room temperature in the case of pure iron) and is close to that of aluminum (about 2.8 μΩ·cm at room temperature).

[0090] When a welding wire 18 made of a material with low electrical resistivity, such as magnesium or aluminum, is used, even if a constriction occurs, the amount of change in the welding voltage V caused by the constriction is small and there is also a large variation, so there is a risk of incorrectly determining whether or not a constriction has occurred.

[0091] For example, if it is erroneously determined that there is no constriction when there is actually one, short-circuit welding will continue without reducing the welding current I, which could increase the amount of heat input when the short circuit is released and cause spatter.

[0092] Therefore, as shown in this embodiment, the amount of heat applied to the welding wire 18, specifically, the power integration value corresponding to the amount of heat, is set to the power integration threshold value P ＴＨ When the welding current I reaches the fourth value I Ｄ In this way, by reducing the welding current I before opening the short circuit and reducing the amount of heat input to the welding wire 18, it is possible to suppress the generation of spatter when the short circuit is opened. Furthermore, because the welding current I is reduced before opening the short circuit without detecting the occurrence of a constriction, it is possible to avoid problems caused by erroneous determination of the presence or absence of a constriction.

[0093] It is preferable to start calculating the integrated power value after the welding wire 18 and the workpiece 17 are short-circuited, that is, after the short circuit has stabilized, so that the integrated power value can be calculated excluding the period during which the short circuit is not stable.

[0094] Alternatively, calculation of the integrated power value may be started after the welding current I starts to increase after the welding wire 18 is short-circuited. In this way, even if there is a change in the welding voltage V, an appropriate amount of heat can be applied to the welding wire 18.

[0095] (Other Embodiments) A pulse welding period may be provided at least either before or after the short-circuit welding period (a period that is k times the welding period T (k is an integer of 1 or more)). During the pulse welding period, welding wire 18 is fed toward workpiece 17 at a predetermined wire feed speed S, and a peak current and a base current are alternately passed through welding wire 18 to generate arc 19 between workpiece 17 and welding wire 18, thereby performing welding.

[0096] Furthermore, a cooling period in which the heat input to the workpiece 17 is reduced to zero may be provided between the pulse welding period and the short-circuit welding period. By providing a cooling period in which the heat input is reduced to zero between the low-heat-input short-circuit welding period and the high-heat-input pulse welding period, the cooling effect at the welding point can be enhanced, the difference in heat input can be maximized, and a clearly wavy, scale-like weld bead can be achieved.

[0097] In addition, by adjusting the low heat input short circuit welding, the high heat input pulse welding, and the cooling period during which the heat input is zero, the amount of heat input to the workpiece 17 can be controlled over a wide range, allowing for more precise control of the weld bead shape.

[0098] The arc welding method of the present disclosure is useful in short-circuit welding of magnesium-based materials because it can improve the welding speed and suppress the generation of spatter and the like.

[0099] REFERENCE SIGNS LIST 1 Input power supply 2 Main transformer (transformer) 3 Primary side rectifier 4 Switching unit 5 DCL (reactor) 6 Secondary side rectifier 7 Welding current detector 8 Welding voltage detector 9 Control switching unit 10 Output controller 11 Short circuit welding controller 12 Pulse welding controller 13 Wire feed speed controller 14 Wire feed speed detector 15 Calculation unit 16 Arc welding device 17 Workpiece 18 Welding wire 19 Arc 20 Welding tip 21 Wire feeder 22 Welding condition setting unit 23 Short circuit welding setting unit 24 Pulse welding setting unit

Claims

1. 1. An arc welding method for at least performing short-circuit welding by alternately repeating forward and reverse feed of a welding wire to a workpiece, comprising: The material of the workpiece and the welding wire is magnesium or a magnesium alloy, During forward feeding of the welding wire, the welding wire is fed toward the workpiece so as to short-circuit the welding wire and the workpiece, During the reverse feeding of the welding wire, the welding wire is fed in a direction opposite to that during the forward feeding of the welding wire so as to open a short circuit between the welding wire and the workpiece; a first step of increasing a welding current flowing through the welding wire to a first value after a short circuit between the welding wire and the workpiece is released; a second step of reducing the welding current after the welding current reaches the first value, and further reducing the welding current to a third value lower than the first value before the welding wire and the workpiece are short-circuited; and a third step of controlling the welding current so as to maintain the third value from when the welding current reaches the third value until the welding wire and the workpiece are short-circuited.

2. The arc welding method according to claim 1, a fourth step of controlling the welding current so that the welding current becomes a fourth value lower than the first value and is maintained at the fourth value for a first period immediately after the short circuit between the welding wire and the workpiece is released, After the fourth step is executed, the first step is executed; The arc welding method according to claim 1, wherein the first period is a period from when a short circuit between the welding wire and the workpiece is released until a distance between the welding wire and the workpiece reaches a predetermined value.

3. The arc welding method according to claim 2, a fifth step of controlling the welding current so that the welding current becomes the fourth value when an amount of heat applied to the welding wire reaches a predetermined threshold value after a short circuit between the welding wire and the workpiece is formed.

4. The arc welding method according to claim 3, the amount of heat applied to the welding wire corresponds to an integrated power value obtained by integrating power supplied to the welding wire within a predetermined period of time, The power supplied to the welding wire is calculated based on a product of a welding voltage applied between the welding wire and the workpiece and the welding current, The arc welding method according to claim 5, wherein, when the power integration value reaches a predetermined power integration threshold, the welding current is controlled so as to become the fourth value.

5. The arc welding method according to claim 1, When the moving average value of the welding current in a predetermined period is defined as an average current, the third value increases monotonically as the average current increases; The arc welding method according to claim 1, wherein when the average current is in the range of 50 A to 200 A, the third value is in the range of 20 A to 80 A.

6. The arc welding method according to claim 1, A moving average value of the welding current in a predetermined period is set as an average current, When the feed speed of the welding wire during forward feed is defined as a forward feed speed, the positive feed rate increases monotonically with increasing average current; The arc welding method according to claim 1, wherein when the average current is in the range of 50 A to 200 A, the forward feed speed is in the range of 30 m / min to 70 m / min.

7. The arc welding method according to claim 2, When the moving average value of the welding current in a predetermined period is defined as an average current, the first period of time decreases as the average current increases; An arc welding method, characterized in that when the average current is in the range of 50 A to 200 A, the first period is in the range of 4000 μsec to 1000 μsec.

8. The arc welding method according to claim 4, When the moving average value of the welding current in a predetermined period is defined as an average current, the power accumulation threshold increases monotonically as the average current increases; The arc welding method according to claim 1, wherein when the average current is in a range of 50 A to 200 A, the power integration threshold is in a range of 4 kW to 8 kW.