Arc welding method

Abstract

This arc welding method is a short-circuit welding in which a welding wire (18) is repeatedly and alternately fed in the forward direction and in the reverse direction on a workpiece (17), and includes at least a first step to a third step. And the workpiece (17) and the welding wire (18) are respectively made of magnesium or magnesium alloy. In a first step, the welding current I is increased to a first value IA after the short circuit has been opened. In the second step, the welding current I is reduced after reaching the first value IA, and before the short circuit, the welding current I is set to a third value IC lower than the first value IA. In the third step, after the third value IC is reached, the welding current I is maintained at the third value IC until the short circuit starts.

Description

Technical Field

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

[0002] In recent years, magnesium or magnesium alloys (hereinafter, sometimes referred to as magnesium-based materials) are used as components of 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, sometimes referred to as aluminum-based materials), and thus, in order to obtain parts of various shapes, parts processing using welding is required.

[0004] For example, Patent Document 1 proposes a non-melting inert gas shielded arc welding method (TIG welding method) for magnesium-based materials using an AC power source as a welding power source. In this method, a shielding gas composed of an inert gas and an oxidizing gas is made to flow toward a workpiece as a welded object in a manner covering a tungsten electrode, thereby obtaining a deeper penetration depth.

[0005] Patent Document 1: Japanese Patent Publication No. 2016-036855 Summary of the invention

[0006] 1. Technical problem to be solved by the invention

[0007] However, the welding of magnesium-based materials is also required to improve productivity, in other words, to increase the welding speed. In order to increase the welding speed, welding using a consumable electrode such as a welding wire is more advantageous than TIG welding using an infusible electrode.

[0008] 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 excessive droplet growth and spatter are more likely to occur.

[0009] The present disclosure is completed to solve the above-mentioned technical problems, and its purpose is to provide an arc welding method for magnesium-based materials, which can improve the welding speed and suppress the generation of spatter and the like.

[0010] -Technical solutions for solving technical problems-

[0011] In order to achieve the above-mentioned purpose, the arc welding method involved in the present disclosure is an arc welding method for at least short-circuit welding. In the short-circuit welding, the forward feeding and reverse feeding of the welding wire to the workpiece are repeatedly and alternately performed, and it is characterized in that: the material of the workpiece and the material of the welding wire are magnesium or a magnesium alloy, and when the welding wire is fed forward, the welding wire is fed toward the workpiece in a manner that the welding wire and the workpiece are short-circuited, and when the welding wire is fed reversely, the welding wire is fed in a direction opposite to that when the welding wire is fed forward, in a manner that the short circuit between the welding wire and the workpiece is disconnected. The arc welding method The method comprises at least a first step, a second step and a third step, wherein in the first step, after the short circuit between the welding wire and the workpiece is broken, the welding current flowing to the welding wire is increased to a first value; in the second step, after the welding current reaches the first value, the welding current is reduced, and before the welding wire and the workpiece are short-circuited, the welding current is reduced to a third value lower than the first value; in the third step, from the time when the welding current reaches the third value until the welding wire and the workpiece are short-circuited, the welding current is controlled in such a manner as to maintain the welding current at the third value.

[0012] -Effects of the Invention-

[0013] According to the present disclosure, the welding speed is improved compared to TIG welding. In addition, since the excessive growth of the molten droplet can be suppressed, the occurrence of welding defects such as spatter can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic structural diagram of an arc welding device according to an embodiment;

[0015] Figure 2 is a diagram showing an output waveform of a welding current, an output waveform of a welding voltage, and changes in a wire feed speed during short-circuit welding;

[0016] Figure 3 is a diagram showing changes over time in the output waveform of the welding current and the output waveform of the welding voltage, and the distance between the tip of the welding wire and the workpiece during short-circuit welding;

[0017] Figure 4 This is an enlarged view of the waveform of the welding current during short-circuit welding;

[0018] Figure 5 is a diagram showing the relationship between the average current and the current immediately before short circuit according to the embodiment;

[0019] Figure 6 is a diagram showing the relationship between the average current and the forward feed speed involved in the embodiment;

[0020] Figure 7 is a diagram showing the relationship between the average current and the low current duration after short circuit disconnection according to the embodiment;

[0021] Figure 8 2 is a diagram showing the relationship between the average current and the power integration threshold value according to the embodiment. DETAILED DESCRIPTION

[0022] The following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its application targets, or its uses.

[0023] (Implementation Method)

[0024] [Structure of arc welding device]

[0025] Figure 1 1 is a schematic diagram of the structure of an arc welding device according to the present embodiment. The arc welding device 16 performs welding by repeating an arc state and a short circuit state between a welding wire 18 as a consumable electrode and a workpiece 17 as a welded object. It should be noted that the welding wire 18 is clamped by a welding torch (not shown), and the welding torch moves at a predetermined speed, so that the tip of the welding wire 18 also moves along a predetermined welding section at the same speed.

[0026] The arc welding device 16 includes a main transformer 2, a primary rectifier 3, a switch 4, a DCL (reactor) 5, a secondary rectifier 6, a welding current detector 7, a welding voltage detector 8, a control switch 9, an output controller 10, and a wire feed speed controller 13. In addition, the arc welding device 16 includes a robot controller (not shown) that controls the operation of a robot (not shown) that fixes a welding torch (not shown).

[0027] It should be noted that the control switching unit 9, the output control unit 10, and the wire feeding speed control unit 13 are all composed of one or more CPUs (Central Processing Units). Alternatively, the control switching unit 9, the output control unit 10, and the wire feeding speed control unit 13 are all composed of one or more MCUs (Micro Control Units). The control switching unit 9, the output control unit 10, and the wire feeding speed control unit 13 can also be composed of the same CPU or MCU.

[0028] The output control unit 10 includes a short-circuit welding control unit 11 and a pulse welding control unit 12. The wire feeding speed control unit 13 includes a wire feeding speed detection unit 14 and a calculation unit 15. The primary rectifier 3 rectifies the input voltage input from the input power supply (three-phase AC power supply) 1 located outside the arc welding device 16. The switch unit 4 controls the output of the primary rectifier 3 to an output suitable for welding. The main transformer 2 converts the output of the switch unit 4 into an output suitable for welding.

[0029] The secondary rectifier 6 rectifies the output of the main transformer 2. The DCL (reactor) 5 smoothes the output of the secondary rectifier 6 into a current suitable for welding. The welding current detector 7 detects the welding current I flowing to the welding wire 18. The welding voltage detector 8 detects the welding voltage V applied between the welding wire 18 and the workpiece 17.

[0030] The control switching unit 9 is a switching unit that outputs the time of switching from short-circuit welding control to pulse welding control to the output control unit 10. The control switching unit 9 has a timing function, counts the prescribed time set by the welding condition setting unit 22, and outputs the time of switching control to the output control unit 10 and the wire feeding speed control unit 13.

[0031] The output control unit 10 outputs a control signal to the switch unit 4 to control the welding output. The short-circuit welding control unit 11 controls short-circuit welding when the control switching unit 9 issues a short-circuit welding command. The pulse welding control unit 12 controls pulse welding when the control switching unit 9 issues a pulse welding command.

[0032] The output control unit 10 makes the welding current I become the average current I S The welding current I is controlled in this way. It should be noted that the average current I S It is a moving average value of welding current I within a predetermined period. In addition, output control unit 10 includes a calculation unit (not shown) that integrates the power supplied to welding wire 18 within a predetermined period to calculate a power integration value. The calculation unit calculates the power supplied to welding wire 18 based on the product of the welding current and the welding voltage.

[0033] The wire feeding speed control unit 13 controls the feeding speed S (hereinafter referred to as the wire feeding speed S) of the welding wire 18 by controlling the wire feeding unit 21. The wire feeding speed detection unit 14 detects the wire feeding speed S. The calculation unit 15 calculates the integrated amount of the feeding amount of the welding wire 18 based on the signal from the wire feeding speed detection unit 14, and controls the wire feeding speed S. Specifically, the command value of the wire feeding speed S is compared with the detection value, the difference between the two is obtained, and feedback control is performed based on the integrated amount of the difference so that the actual wire feeding speed S is consistent with the command value.

[0034] 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. In addition, the welding condition setting unit 22 includes 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 feeding speed control unit 13. It should be noted that a welding program, etc., which describes a welding output control sequence during short-circuit welding or pulse welding or a feeding sequence of the welding wire 18, etc., is stored in a storage unit (not shown).

[0035] When a welding torch SW (switch) not shown is turned on, welding output of arc welding device 16 is supplied to welding wire 18 via welding tip 20. Then, arc 19 is generated between welding wire 18 and workpiece 17 by the welding output of arc welding device 16, and welding is performed.

[0036] [Arc welding method]

[0037] Figure 2 The diagrams show the output waveform of the welding current, the output waveform of the welding voltage, and changes in the wire feed speed during short-circuit welding. Figure 3 The graphs show the output waveform of the welding current and the output waveform of the welding voltage during short-circuit welding, and the change over time in the distance between the tip of the welding wire and the workpiece. Figure 4 This is an enlarged view of the welding current waveform during short-circuit welding.

[0038] It should be noted that, in the present embodiment, the material of the welding wire 18 is a magnesium alloy (AZ61), the diameter of the welding wire is 1.2 mm, and the material of the workpiece 17 is a magnesium alloy (AZ31). It should be noted that both the welding wire 18 and the workpiece 17 can be magnesium alloys of other components, or magnesium itself. In addition, the shielding gas blown to the workpiece is Ar (argon) gas, and its flow rate is set to 20 L / min. However, the flow rate of the shielding gas is not particularly limited to this.

[0039] In addition, the average current I S It is adjusted according to the thickness of the workpiece 17. If the thickness is thin, the average current I S is set to a lower value; if the plate is thick, the average current I S For example, if the plate thickness is about 1 mm, the average current I S is set to about 40A. If the plate thickness is about 3mm, the average current I S is set to about 80A. If the plate thickness is about 6mm, the average current I s It is set to more than 140A.

[0040] As described above, welding output is supplied to the welding wire 18, and while the welding torch (not shown) moves, the tip of the welding wire 18 moves along a predetermined welding section, thereby short-circuiting the workpiece 17. Figure 2 , Figure 3 As shown, in the short-circuit welding shown in this embodiment, the arc period T ARC And then the arc period T ARC The short circuit period TS of the welding period T is taken as a basic unit, and the processing included in the welding period T is executed as many times as required. ARC , an arc 19 is generated between the workpiece 17 and the welding wire 18. During the short circuit period T SHORT , the workpiece 17 and the welding wire 18 are short-circuited.

[0041] In this embodiment, the welding period T is set to about 120 msec. ARC And the short circuit period T SHORT It is not necessarily constant, but can be changed according to the change of the short-circuit timing between welding wire 18 and workpiece 17.

[0042] like Figure 2 As shown, the wire feeding speed S changes periodically with the welding period T as a period. Figure 2 In the case of S = 0 (upper side of the line), the welding wire 18 is fed in a manner close to the workpiece 17, that is, a forward feeding action is performed. The wire feeding speed S in this case is sometimes referred to as the forward feeding speed S. F When the wire feeding speed S is negative ( Figure 2 In the case of S = 0, the welding wire 18 is fed away from the workpiece 17, that is, the reverse feeding action is performed. The wire feeding speed S in this case is sometimes referred to as the reverse feeding speed S. R It should be noted that the waveform of the wire feeding speed S, i.e., the shape of the amplitude or the inclination relative to time, is based on the above-mentioned average current I S Furthermore, the waveform of the wire feed speed S changes in conjunction with the output waveform of the welding current I.

[0043] like Figure 2 to Figure 4 As shown, the period from time tn1 to time tn3 is the arc period T ARC The period from time tn3 to time t(n+1)1 is the short-circuit period T SHORT It should be noted that n is an integer greater than or equal to 1, 1≤n≤m, and m is the number of repetitions of the welding period T during short-circuit welding.

[0044] The following describes 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 referred to as distance L) starting from time tn1.

[0045] First, during the arc period T ARC At the start time, i.e., time tn1, the wire feeding speed S is negative, and the welding wire 18 is in reverse feeding. After time tn1, the wire feeding speed control unit 13 controls the wire feeding speed S so that it approaches zero. That is, the movement of the welding wire 18 changes from reverse feeding to forward feeding. In addition, 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 be disconnected, and the distance L begins to change from zero to a positive value.

[0046] On the other hand, from time tn1 until the period T1 (see Figure 4 ), the output control unit 10 makes the current value of the welding current I become I D It should be noted that in the following description, the period T1 is sometimes referred to as the first period T1 or the low current continuation period T1 after the short circuit is disconnected, and the current value I D The fourth value I D .

[0047] At a time point after a period T1 has elapsed from time tn1, welding wire 18 enters the forward feeding operation. After a period T1 has elapsed, output control unit 10 greatly increases welding current I to current value I A . The fourth value I D is the current value I A It should be noted that in the following description, the current value I A The first value I A In addition, when the welding current I reaches the first value I A At the time tn2, the distance L reaches the maximum value, which is about 4 mm in this case. In addition, at the time tn2, a droplet of a predetermined size is formed at the tip of the welding wire 18, which is not shown.

[0048] After time tn2, the wire feeding speed control unit 13 reduces the wire feeding speed S. In addition, the output control unit 10 changes the welding current I to the current value I B (I B A ) is used to control the welding current I. It should be noted that the current value of the welding current I is set to I B This is to adjust the heat input to the weld bead (not shown) formed on the workpiece 17 by welding. B ​Or the time for maintaining the value can be appropriately changed according to the heat input amount to be adjusted.

[0049] When the welding current I reaches the current value I B After a period of time, before the welding wire 18 and the workpiece 17 are short-circuited, the output control unit 10 changes the welding current I to the current value I C In addition, the welding current I reaches the current value I C The output control unit 10 controls the welding current I to maintain the welding current I at the current value I until the welding wire 18 and the workpiece 17 are short-circuited. C Control welding current 1.

[0050] It should be noted that in the following description, the current value of the welding current I is sometimes maintained at I C During the period T2 (refer to Figure 4 ) is called the second period T2, and the current value I C The third value I C Or the current before short circuit I C The third value I C The first value I A In addition, in this embodiment, the third value I C is set to be greater than the fourth value I D However, it is not particularly limited to this, and the third value I C It is also possible to use the fourth value I D the following.

[0051] As the welding current I changes to I C The arc 19 generated between the welding wire 18 and the workpiece 17 becomes smaller rapidly, and the arc reaction force applied to the molten drop formed at the tip of the welding wire 18 also becomes smaller rapidly.

[0052] When the welding current I reaches I C After a period T2 has passed, at time tn3, welding wire 18 and workpiece 17 are short-circuited. SHORT start.

[0053] After the short circuit between welding wire 18 and workpiece 17 occurs, if the heat applied to welding wire 18 reaches a predetermined threshold, output control unit 10 sets welding current I to a fourth value I D At time t(n+1) which is the start time of the next welding period T, the welding current I becomes the fourth value I D , short-circuit welding is carried out in sequence.

[0054] It should be noted that the heat applied to the welding wire 18 corresponds to the above-mentioned power accumulation value. Therefore, in actual control, when the power accumulation value reaches a predetermined threshold value P TH When the output control unit 10 makes the welding current I become the fourth value I D The welding current I is controlled in this way. It should be noted that in the following description, the threshold value P is sometimes TH It is called the power accumulation threshold P TH .

[0055] After that, the output control unit 10 controls the welding current I and the wire feed speed control unit 13 controls the wire feed speed S during each welding period T, so that short-circuit welding is continued. When short-circuit welding of a predetermined length is performed along the welding line, a weld bead of a predetermined length is formed on the workpiece 17 after the short-circuit welding is completed.

[0056] [Effects, etc.]

[0057] As described above, the arc welding method according to this embodiment is short-circuit welding in which the forward feeding and reverse feeding of the welding wire 18 are repeated alternately to the workpiece 17. The material of the workpiece 17 and the material of the welding wire 18 are both magnesium-based materials, that is, magnesium or magnesium alloy.

[0058] When welding wire 18 is forwardly fed, welding wire 18 is fed toward workpiece 17 so that welding wire 18 and workpiece 17 are short-circuited.

[0059] When welding wire 18 is fed backward, welding wire 18 is fed in a direction opposite to that when welding wire 18 is fed forward so that the short circuit between welding wire 18 and workpiece 17 is disconnected.

[0060] Furthermore, the arc welding method according to the present embodiment includes at least the following first to third steps.

[0061] After the short circuit between the welding wire 18 and the workpiece 17 is broken, the welding current I flowing to the welding wire 18 is increased to a first value I A (First step).

[0062] When the welding current I reaches the first value I A After that, the welding current I is reduced to a value lower than the first value I before the welding wire 18 and the workpiece 17 are short-circuited. A Low third value I C (Second step).

[0063] From the welding current I reaches the third value I C Until the welding wire 18 and the workpiece 17 are short-circuited, the welding current I is maintained at the third value I C The welding current I is controlled in this way (third step).

[0064] According to the present embodiment, in particular, by providing the third step, the short circuit between the welding wire 18 and the workpiece 17 can be promoted. As a result, the excessive growth of the molten droplet formed at the tip of the welding wire 18 can be suppressed. As a result, the molten droplet can be suppressed from scattering and generating spatter during welding. This point will be further described.

[0065] Figure 5 is a diagram showing the relationship between the average current involved in the embodiment and the current immediately before the short circuit. Figures 5 to 8 For comparison, the average current I in short-circuit welding when the workpiece 17 is made of aluminum alloy is shown. S The relationship between various parameters.

[0066] like Figure 5 As shown, the current I before the short circuit C (Third value I C ), that is, the current value of the welding current I flowing to the welding wire 18 immediately before the short circuit is set to follow the average current I S This is the same when the material of the workpiece 17 is an aluminum-based material and when the material of the workpiece 17 is a magnesium-based material.

[0067] On the other hand, the current I before the short circuit C The absolute value of is set to be smaller when the material of the workpiece 17 is a magnesium-based material than when the material of the workpiece 17 is an aluminum-based material. Figure 5 In the example shown, the average current I S The range is 50A to 200A, that is, when it is above 50A and below 200A, the current I before short circuit C The range is 20A to 80A, that is, above 20A and below 80A.

[0068] As described above, since magnesium-based materials are lighter than aluminum-based materials, in the case of magnesium-based materials, the mass of the molten droplet formed at the tip of the welding wire 18 is also light. When the welding current I becomes higher in the state where the arc 19 is generated, the arc reaction force applied to the molten droplet also becomes larger, so it is less likely to short-circuit between the welding wire 18 and the workpiece 17. Therefore, there is a technical problem that the molten droplet grows excessively and spatter is easily generated.

[0069] On the other hand, when short-circuiting magnesium-based materials, as shown in this embodiment, the current I immediately before the short circuit is C By setting it low, the arc reaction force can be reduced, and the short circuit between welding wire 18 and workpiece 17 can be promoted. As a result, the excessive growth of the droplet can be suppressed, and the generation of spatter can be suppressed.

[0070] In addition, since the generation of spatter and the like can be suppressed, welding defects can be reduced, and a decrease in the yield of the welding process can be suppressed. In addition, the welding quality can be maintained at a high level.

[0071] In addition, according to the present embodiment, the welding speed can be increased compared to the TIG welding disclosed in Patent Document 1. Thus, the process time in the welding process of the magnesium-based material can be shortened, and productivity can be improved.

[0072] It should be noted that when the current before the short circuit I C If the setting is too low, other adverse conditions may occur. For example, if the current I C When the range is set too low, the temperature of the molten pool (not shown) formed on the workpiece 17 will also be lowered. As a result, pores are easily generated inside the workpiece 17. Or, the bulge of the weld bead will be higher than the desired level.

[0073] Therefore, as mentioned above, the average current I S When the range is 50A to 200A, the current I C The range of is preferably 20A to 80A.

[0074] In addition, by appropriately setting the forward feed speed S F , and can also promote the short circuit between the welding wire 18 and the workpiece 17.

[0075] Figure 6 : is a graph showing the relationship between the average current and the forward feed speed according to the embodiment.

[0076] like Figure 6 As shown, the forward feed speed S F It is also set to follow the average current I S This is the same when the material of the workpiece 17 is an aluminum-based material and when the material of the workpiece 17 is a magnesium-based material.

[0077] On the other hand, the forward feed speed S F When the material of the workpiece 17 is a magnesium-based material, it is set to be higher than when the material of the workpiece 17 is an aluminum-based material. Figure 6 In the example shown, the average current I S When the range is 50A to 200A, the forward feed speed S F The range is 30m / min to 70m / min, that is, above 30m / min and below 70m / min.

[0078] As shown in this embodiment, by adjusting the forward feed speed S FBy setting the welding wire 18 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 can suppress the excessive growth of the droplet and the generation of spatter.

[0079] It should be noted that when the forward feed speed S F If the setting is too high, the above-mentioned inconvenience may occur. That is, pores may be easily generated inside the workpiece 17. Or, the bulge of the weld bead may be higher than the desired level.

[0080] Therefore, as mentioned above, the average current I S When the range is 50A to 200A, the forward feed speed S F The range of speed is preferably 30 m / min to 70 m / min.

[0081] It should be noted that when the forward feed speed S F When the reverse feed speed S is set high as in the present embodiment, R It also needs to be improved. When only the forward feed speed S F Set it to a higher value, and set the reverse feed speed S R When the forward feed speed S is set to a lower value, there is a tendency for the weld bead to bulge excessively. Therefore, in the case of magnesium-based materials, the forward feed speed S is set to a lower value than that of aluminum-based materials. F The higher the setting, the higher the reverse feed speed S R Set higher.

[0082] Furthermore, by setting both the forward feed speed SF and the reverse feed speed SR to high values, the forward feed amount and the reverse feed amount of the welding wire 18 in the short-circuiting welding are increased in the case of the magnesium-based material in the present embodiment compared to the case of the aluminum-based material.

[0083] In addition, in the arc welding method according to the present embodiment, the welding current I is controlled so that it becomes a fourth value ID lower than the first value IA and is maintained at the fourth value ID during the first period T1 immediately after the short circuit between the welding wire 18 and the workpiece 17 is disconnected (fourth step). It should be noted that after the fourth step is completed, the process proceeds to the first step, and short-circuit welding is performed sequentially.

[0084] Furthermore, first period T1 (low current continuation period T1 after short circuit disconnection) is a period from when the short circuit between welding wire 18 and workpiece 17 is disconnected until distance L between welding wire 18 and workpiece 17 reaches a predetermined value.

[0085] In the present embodiment, the fourth step is provided and the low current continuation period T1 after the short circuit is disconnected is set to be long, thereby suppressing the scattering of droplets and suppressing the generation of spatter and the like. This point will be further described below.

[0086] Figure 7 1 is a diagram showing the relationship between the average current and the low current continuation period after the short circuit is disconnected according to the embodiment.

[0087] like Figure 7 As shown, the low current duration T1 after the short circuit is disconnected is set to follow the average current I S This is the same when the material of the workpiece 17 is an aluminum-based material and when the material of the workpiece 17 is a magnesium-based material.

[0088] It should be noted that in Figure 7 In the example shown, in both cases the average current I S In the region exceeding 150 A, the amount of decrease in the low current continuation period T1 after the short circuit is disconnected becomes smaller and eventually tends to converge to a certain value.

[0089] On the other hand, the low current continuation period T1 after the short circuit is disconnected is set to be longer when the material of the workpiece 17 is a magnesium-based material than when the material of the workpiece 17 is an aluminum-based material. Figure 7 In the example shown, the average current I S When the average current I is in the range of 50A to 200A, the low current continuation period T1 (first period T1) after the short circuit is disconnected is in the range of 4000μsec to 1000μsec. S When the average current I is 50A, the low current duration T1 after the short circuit is disconnected is 4000μsec. S The increase of the low current duration T1 after the short circuit is disconnected reduces the average current I S In the case of 200 A, the low current continuation period T1 after the short circuit is disconnected is 1000 μsec.

[0090] As described above, in the short-circuit welding of magnesium-based materials, the mass of the molten droplet formed at the tip of the welding wire 18 is lighter than that of the aluminum-based materials. In this case, when the welding current I is increased sharply immediately after the short circuit is disconnected, the arc reaction force received by the molten droplet also increases sharply, and the molten droplet may be blown away by the arc reaction force. When this happens, a large amount of spatter is generated, resulting in poor welding.

[0091] Therefore, as shown in the present embodiment, after the short circuit is disconnected, the output control unit 10 sets the current value of the welding current I to a lower value (the fourth value I D), and controls the welding current I in such a way that the lower value is maintained 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. In addition, in the middle or at the end of the first period T1, the action of the welding wire 18 is switched from reverse feeding to forward feeding, and the distance L between the welding wire 18 and the workpiece 17 becomes substantially the maximum value after the first period T1. When the distance L becomes sufficiently long, the process shifts to the first step, and the current value of the welding current I increases to the first value I A That is, since the welding current I is increased while the distance L is sufficiently ensured, a droplet of appropriate size can be formed at the tip of the welding wire 18. In addition, an increase in arc reaction force on the droplet and scattering of the droplet can be suppressed, thereby suppressing the generation of spatter and the like.

[0092] It should be noted that, in the present embodiment, the maximum value is about 4 mm, but it can be appropriately changed according to the wire diameter of the welding wire 18, the reverse feed speed SR, the inertia of the robot holding the welding torch, etc. In addition, after the first period T1, the distance L does not necessarily have to be the maximum value. As long as it can be ensured that even if the welding current I is increased to the first value I A The distance may be such that splashing of molten droplets does not occur.

[0093] In addition, the fourth value I D This is equivalent to the current value when the tip of the welding wire 18 becomes thinner just before the short circuit between the welding wire 18 and the workpiece 17 is about to be broken, that is, the current value when the part attached to the molten pool formed on the workpiece 17 becomes thinner, that is, the current value when the so-called necking phenomenon occurs.

[0094] In the arc welding method according to the present embodiment, after the short circuit between the welding wire 18 and the workpiece 17 occurs, if the heat applied to the welding wire 18 reaches a predetermined threshold value, the output control unit 10 controls the welding current I to be the fourth value I D The welding current I is controlled in this manner (fifth step).

[0095] The amount of heat applied to welding wire 18 corresponds to a power integrated value obtained by integrating the power supplied to welding wire 18 within a predetermined period after a short circuit occurs between welding wire 18 and workpiece 17 .

[0096] The power supplied to welding wire 18 is calculated based on the product of welding voltage V and welding current I applied between welding wire 18 and workpiece 17 .

[0097] In the fifth step, when the power accumulation value reaches the specified power accumulation threshold value P TH When the output control unit 10 makes the welding current I become the fourth value I D Control welding current 1.

[0098] In this embodiment, the fifth step is provided and the power integration threshold P is appropriately set. TH , it is possible to suppress the generation of splashes when the short circuit is disconnected. This point will be further explained below.

[0099] Figure 8 2 is a diagram showing the relationship between the average current and the power integration threshold value according to the embodiment.

[0100] like Figure 8 As shown, the power accumulation threshold P TH is set to follow the average current I S This is the same when the material of the workpiece 17 is an aluminum-based material and when the material of the workpiece 17 is a magnesium-based material.

[0101] On the other hand, the power accumulation threshold P TH When the material of the workpiece 17 is a magnesium-based material, it is set to be lower than when the material of the workpiece 17 is an aluminum-based material. Figure 8 In the example shown, the average current I S When the power accumulation threshold P is in the range of 50A to 200A, TH The range is 4kW~8kW. That is, when the average current I S When the power is above 50A and 200A, the power accumulation threshold P TH It is above 4kW and below 8kW.

[0102] Conventionally, in short-circuit welding of iron-based materials, the occurrence of the above-mentioned necking is detected based on the change in welding voltage V. When necking occurs between welding wire 18 and workpiece 17, the resistance value increases in the necking portion. In this case, in short-circuit control, the change in welding voltage becomes larger than the change in welding current I. Therefore, when the occurrence of necking is detected based on the voltage change, that is, when the imminent short circuit is detected, the welding current I is reduced just before the short circuit is disconnected, thereby suppressing the generation of spatter.

[0103] However, the resistivity of magnesium (about 4.3 μΩ·cm at room temperature) is lower 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).

[0104] When welding wire 18 made of a material with low resistivity such as magnesium or aluminum is used, even if necking occurs, the amount of change in welding voltage V due to necking is small and the variation is large, so whether necking occurs may be erroneously determined.

[0105] For example, when necking has occurred but it is erroneously determined that necking has not occurred, short-circuit welding is continued without reducing the welding current I. Therefore, the heat input amount when the short circuit is opened increases, and spatter may be generated.

[0106] Therefore, as shown in the present embodiment, when the heat applied to welding wire 18, specifically, the power integrated value corresponding to the heat, reaches the power integrated threshold value P TH When the welding current I reaches the fourth value I D The welding current I is controlled in such a manner. Thus, by reducing the welding current I before the short circuit is disconnected, the heat input amount provided to the welding wire 18 is reduced, and the generation of spatter when the short circuit is disconnected can be suppressed. In addition, since the occurrence of necking is not detected, but the welding current I is reduced before the short circuit is disconnected, it is possible to avoid the inconvenience caused by erroneous judgment of whether necking has occurred.

[0107] It should be noted that when calculating the power integrated value, it is preferred to start calculating the power integrated value after welding wire 18 and workpiece 17 are short-circuited, that is, after the short circuit is stabilized. This allows the power integrated value to be calculated excluding the period when the short circuit is unstable.

[0108] Alternatively, calculation of the power integrated value may be started after welding current I starts to rise after welding wire 18 is short-circuited. In this way, even when welding voltage V changes, appropriate heat can be supplied to welding wire 18.

[0109] (Other embodiments)

[0110] A pulse welding period may be provided at least one period before or after the short-circuit welding period (a period k times the welding period T (k is an integer greater than or equal to 1)). During the pulse welding period, the welding wire 18 is fed toward the workpiece 17 at a predetermined wire feed speed S, and a peak current and a base current are alternately passed through the welding wire 18, thereby generating an arc 19 between the workpiece 17 and the welding wire 18, thereby performing welding.

[0111] In addition, a cooling period may be provided between the pulse welding period and the short-circuit welding period to reduce the heat input to the workpiece 17 to zero. By providing a cooling period with zero heat input between the short-circuit welding period with low heat input and the pulse welding period with high heat input, the cooling effect of the welded part can be improved, the difference in heat input can be maximized, and a fish-scale weld with obvious wavy patterns can be achieved.

[0112] In addition, by adjusting short-circuit welding with low heat input, pulse welding with high heat input, and cooling period with zero heat input respectively, the heat input to the workpiece 17 can be controlled within a wide range, and the weld shape can be controlled more precisely.

[0113] -Industrial Practicality 1

[0114] The arc welding method of the present disclosure is useful because it can improve the welding speed in short-circuiting welding of magnesium-based materials and can suppress the generation of spatter and the like.

[0115] -Explanation of symbols-

[0116] 1 Input power

[0117] 2 Main transformer (transformer)

[0118] 3. Primary rectifier

[0119] 4 Switch

[0120] 5 DCL (reactor)

[0121] 6 Secondary rectifier

[0122] 7 Welding current detection unit

[0123] 8 Welding voltage detection unit

[0124] 9 Control switch unit

[0125] 10 Output control unit

[0126] 11 Short circuit welding control unit

[0127] 12 Pulse welding control unit

[0128] 13 Wire feeding speed control unit

[0129] 14 Wire feeding speed detection unit

[0130] 15. Operation unit

[0131] 16 Arc welding equipment

[0132] 17 Workpiece

[0133] 18 Welding wire

[0134] 19 Arc

[0135] 20 welding nozzle

[0136] 21 Wire feeding department

[0137] 22 Welding condition setting section

[0138] 23 Short circuit welding setting part

[0139] 24 Pulse welding setting section.

Claims

1. An arc welding method, which is an arc welding method for at least short-circuiting welding, in which forward feeding and reverse feeding of a welding wire to a workpiece are repeatedly and alternately performed, characterized in that: The material of the workpiece and the material of the welding wire are magnesium or magnesium alloy, During forward feeding of the welding wire, the welding wire is fed toward the workpiece in such a manner that the welding wire and the workpiece are short-circuited. During reverse feeding of the welding wire, the welding wire is fed in a direction opposite to that during forward feeding of the welding wire in such a manner that a short circuit between the welding wire and the workpiece is disconnected. The arc welding method comprises at least a first step, a second step and a third step. In the first step, after the short circuit between the welding wire and the workpiece is broken, the welding current flowing to the welding wire is increased to a first value; In the second step, after the welding current reaches the first value, the welding current is reduced, and before the welding wire and the workpiece are short-circuited, the welding current is reduced to a third value lower than the first value; In the third step, the welding current is controlled so as to be maintained at the third value from the time 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, characterized in that: The arc welding method further comprises a fourth step, In the fourth step, the welding current is controlled so that the welding current becomes a fourth value lower than the first value immediately after the short circuit between the welding wire and the workpiece is broken, and the welding current is maintained at the fourth value during a first period. After executing the fourth step, transfer to the first step. The first period is a period from when the short circuit between the welding wire and the workpiece is disconnected until the distance between the welding wire and the workpiece reaches a predetermined value.

3. The arc welding method according to claim 2, characterized in that: The arc welding method further comprises a fifth step, In the fifth step, if the amount of heat applied to the welding wire reaches a predetermined threshold value after the welding wire and the workpiece are short-circuited, the welding current is controlled so that the welding current becomes the fourth value.

4. The arc welding method according to claim 3, characterized in that: The amount of heat applied to the welding wire corresponds to a power integrated value obtained by integrating power supplied to the welding wire within a predetermined period. calculating the power supplied to the welding wire based on the product of the welding voltage applied between the welding wire and the workpiece and the welding current, In the fifth step, when the power integrated value reaches a predetermined power integrated threshold value, the welding current is controlled so that the welding current becomes the fourth value.

5. The arc welding method according to claim 1, characterized in that: When the moving average value of the welding current within a predetermined period is set as the average current, The third value increases monotonically as the average current increases. When the average current ranges from 50A to 200A, the third value ranges from 20A to 80A.

6. The arc welding method according to claim 1, characterized in that: The moving average value of the welding current within a predetermined period is defined as the average current. When the feed speed of the welding wire during forward feeding is set as the forward feeding speed, The forward feed speed increases monotonically with the increase of the average current. When the average current is in the range of 50A to 200A, the forward feed speed is in the range of 30m / min to 70m / min.

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

8. The arc welding method according to claim 4, characterized in that: When the moving average value of the welding current within a predetermined period is set as the average current, The power accumulation threshold increases monotonically with the increase of the average current. When the average current ranges from 50A to 200A, the power accumulation threshold ranges from 4kW to 8kW.

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