Arc welding method

Abstract

The arc welding method of the present disclosure is a short circuit welding method in which the forward feeding and the reverse feeding of a welding wire (18) are alternately repeated with respect to a workpiece (17), and includes at least a first step to a third step. The material of the workpiece (17) and the material of the welding wire (18) are each magnesium or a magnesium alloy. In the first step, after short circuiting is released, the welding current I is increased to a first value I A . In the second step, after the welding current I reaches the first value I A , the welding current I is decreased, and before short circuiting, the welding current I is set to a third value I A lower than the first value I C . In the third step, after the welding current I reaches the third value I C , the welding current I is maintained at the third value I C until short circuiting begins.

Description

Technical Field

[0001] This disclosure relates to an arc welding method, and more particularly to an arc welding method for magnesium-based materials. Background Technology

[0002] In recent years, magnesium or magnesium alloys (hereinafter sometimes referred to as magnesium-based materials) have been used as components in vehicles and other applications because they are lighter than aluminum.

[0003] On the other hand, compared to aluminum or aluminum alloys (hereinafter sometimes referred to as aluminum-based materials), magnesium-based materials are not easily deformed at room temperature, and welding is required for component processing in order to obtain parts of various shapes.

[0004] For example, Patent Document 1 proposes a non-consumable electrode inert gas shielded arc welding method (TIG welding method) for magnesium-based materials using an AC power source as the welding power source. In this method, a deeper penetration depth is achieved by allowing a shielding gas composed of inert and oxidizing gases to flow toward the workpiece as the weldment in a manner that covers the tungsten electrode.

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

[0006] The technical problem that the invention aims to solve is...

[0007] However, increased productivity is also required in the welding of magnesium-based materials; in other words, increased welding speed is also required. To increase welding speed, welding using consumable electrodes such as welding wire is more advantageous than TIG welding using non-consumable electrodes.

[0008] However, magnesium-based materials are lighter than aluminum-based materials, so when the arc reaction force is high, there are technical problems such as short circuits, excessive droplet growth, and easy spattering.

[0009] This disclosure was made 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, etc.

[0010] -Technical solutions for solving technical problems-

[0011] To achieve the above objectives, the arc welding method disclosed herein is an arc welding method that at least performs short-circuit welding. In this short-circuit welding, the workpiece is repeatedly and alternately fed forward and backward with a welding wire. The method is characterized in that: the material of the workpiece and the material of the welding wire are magnesium or magnesium alloy; during the forward feeding of the welding wire, the welding wire is fed towards the workpiece to short-circuit it; during the reverse feeding of the welding wire, the welding wire is fed in the opposite direction to the forward feeding to break the short circuit between the welding wire and the workpiece. The method includes at least three steps: 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, from the time the welding current reaches the third value until the welding wire and the workpiece are short-circuited, the welding current is controlled to maintain the welding current at the third value.

[0012] -The Effects of the Invention-

[0013] According to this disclosure, compared with TIG welding, the welding speed is increased. Furthermore, since excessive droplet growth can be suppressed, welding defects such as spatter can be suppressed. Attached Figure Description

[0014] Figure 1 This is a simplified structural diagram of the arc welding apparatus involved in the implementation method;

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

[0016] Figure 3 It is a graph showing the output waveform of welding current, the output waveform of welding voltage, and the change of distance between the tip of welding wire and the workpiece over time 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 It is a graph showing the relationship between the average current involved in the implementation method and the current before the short circuit;

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

[0020] Figure 7 It is a graph showing the relationship between the average current involved in the embodiment and the duration of low current after the short circuit is broken;

[0021] Figure 8 This is a graph illustrating the relationship between the average current and the cumulative power threshold involved in the implementation method. Detailed Implementation

[0022] The present embodiment will now be described in detail with reference to the accompanying drawings. The following description of preferred embodiments is merely illustrative in nature and is not intended to limit the invention, its application, or its uses.

[0023] (Implementation Method)

[0024] [Structure of the arc welding apparatus]

[0025] Figure 1 This is a simplified structural diagram of the arc welding apparatus according to this embodiment. The arc welding apparatus 16 performs welding by repeatedly switching between an arc state and a short-circuit state between the welding wire 18, which serves as a fusion electrode, and the workpiece 17, which is the object to be welded. It should be noted that the welding wire 18 is held by a welding torch (not shown), which moves at a predetermined speed, thereby causing the tip of the welding wire 18 to move along a predetermined welding zone at the same speed.

[0026] The arc welding apparatus 16 includes a main transformer 2, a primary rectifier 3, a switch 4, a DCL (reactor) 5, a secondary rectifier 6, a welding current detection unit 7, a welding voltage detection unit 8, a control switching unit 9, an output control unit 10, and a wire feed speed control unit 13. Additionally, the arc welding apparatus 16 includes a robot control unit (not shown) that controls the movements of a robot (not shown) that holds the 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 can all be 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 feed speed control unit 13 includes a wire feed speed detection unit 14 and an arithmetic unit 15. The first-stage rectifier unit 3 rectifies the input voltage from the input power supply (three-phase AC power supply) 1 located outside the arc welding apparatus 16. The switching unit 4 controls the output of the first-stage rectifier unit 3 to an output suitable for welding. The main transformer 2 converts the output of the switching unit 4 to an output suitable for welding.

[0029] The secondary rectifier unit 6 rectifies the output of the main transformer 2. The DCL (reactor) 5 smooths the output of the secondary rectifier unit 6 into a current suitable for welding. The welding current detection unit 7 detects the welding current I flowing to the welding wire 18. The welding voltage detection unit 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 timing 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, which times the predetermined time set by the welding condition setting unit 22, and outputs the timing of the switching control to the output control unit 10 and the wire feed 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 This is the moving average of the welding current I over a specified period. Additionally, the output control unit 10 includes a calculation unit (not shown) that calculates a cumulative power value by accumulating the power supplied to the welding wire 18 over the specified 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.

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

[0034] A wire feeder 21 and a welding condition setting unit 22 are connected to the arc welding apparatus 16. The welding condition setting unit 22 is used to set the welding conditions for the arc welding apparatus 16. In addition, the welding condition setting unit 22 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. It should be noted that welding programs, such as the welding output control sequence for short-circuit welding or pulse welding, or the feeding sequence of the welding wire 18, are stored in a storage unit (not shown).

[0035] When the welding torch SW (switch) (not shown) is turned on, the welding output of the arc welding device 16 is supplied to the welding wire 18 via the welding nozzle 20. Furthermore, the welding output of the arc welding device 16 generates an arc 19 between the welding wire 18 and the workpiece 17 for welding.

[0036] [Arc Welding Methods]

[0037] Figure 2 It is a graph showing the output waveforms of the welding current, welding voltage, and wire feed speed during short-circuit welding. Figure 3 It is a graph showing the output waveform of the welding current, the output waveform of the welding voltage, and the change of the distance between the tip of the welding wire and the workpiece over time during short-circuit welding. Figure 4 This is an enlarged view of the waveform of the welding current during short-circuit welding.

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

[0039] In addition, the average current I S It is adjusted separately based on the thickness of workpiece 17. If the plate thickness is thin, the average current I... S It is set to a lower value; if the plate is thick, the average current I is... S This is then set to a higher value. For example, if the board thickness is around 1mm, the average current I... S It is set to around 40A. If the board thickness is around 3mm, then the average current I... S It is set to around 80A. If the board thickness is around 6mm, then the average current I... s It was then set to 140A or higher.

[0040] As described above, welding output is supplied to welding wire 18, and while the welding torch (not shown) moves, the tip of welding wire 18 moves along a predetermined welding zone, thereby performing short-circuit welding on workpiece 17. Figure 2 , Figure 3 As shown, in the short-circuit welding illustrated in this embodiment, the arc period T is included. ARC And then during the arc period T ARC The welding period T during the short-circuit period TS is the basic unit, and the processing included in the welding period T is performed according to the required number of times. During the arc period T ARC An electric arc 19 is generated between the workpiece 17 and the welding wire 18. During the short circuit, T... SHORT Workpiece 17 and welding wire 18 short-circuited.

[0041] In this embodiment, the welding period T is set to approximately 120 msec. However, the welding period T and the arc period T... ARC and during the short circuit T SHORT It is not necessarily constant, but can vary depending on the timing of the short circuit between the welding wire 18 and the workpiece 17.

[0042] like Figure 2 As shown, the wire feed speed S varies periodically with a period of T during welding. When the wire feed speed S is positive (in... Figure 2 In the case where S=0 (above the line), the welding wire 18 is fed close to the workpiece 17, i.e., a forward feed action is performed. Sometimes, the wire feed speed S in this case is called the forward feed speed S0. F When the wire feeding speed S is negative (in Figure 2 In the case where S=0 (below the line), the welding wire 18 is fed away from the workpiece 17, i.e., a reverse feed action is performed. Sometimes, the wire feed speed S in this case is called the reverse feed speed S0. R It should be noted that the waveform of the wire feeding speed S, i.e., the shape of the amplitude or the tilt relative to time, is based on the average current I mentioned above. S And it is predetermined. Furthermore, the waveform of the wire feed speed S changes in tandem with the output waveform of the welding current I.

[0043] like Figures 2-4 As shown, the period from time tn1 to time tn3 is the arc duration 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] Starting from time tn1, the following explanation is given regarding the changes in welding current I, welding voltage V, wire feed speed S, and distance L (hereinafter referred to as distance L) between welding wire 18 and workpiece 17 over time.

[0045] First, during the arc T ARC At the beginning of time tn1, the wire feed speed S is negative, and the welding wire 18 is in reverse feed. After time tn1, the wire feed speed control unit 13 controls the wire feed speed S to approach zero. That is, the movement of the welding wire 18 changes from reverse feed to forward feed. 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 break, and the distance L begins to change from zero to a positive value.

[0046] On the other hand, from time tn1 until the elapsed period T1 (refer to...) Figure 4 Until then, the output control unit 10 makes the current value of the welding current I become I. D Control is performed in this manner. It should be noted that in the following description, period T1 is sometimes referred to as the first period T1 or the low current duration period T1 after the short circuit is broken, and the current value I is... D Called the fourth value I D .

[0047] After a period T1 has elapsed from time tn1, the welding wire 18 begins forward feed. After period T1, the output control unit 10 significantly increases the welding current I to the current value I. A The fourth value I D For the current value I A Approximately 25% to 40%. It should be noted that in the following explanation, the current value I may sometimes be... A Called the first value I A Additionally, when the welding current I reaches the first value I... A At time tn2, the distance L reaches its maximum value, which is approximately 4 mm in this case. Additionally, at time tn2, a molten droplet of a specified size forms at the tip of the welding wire 18, not shown in the diagram.

[0048] After time tn2, the wire feed speed control unit 13 reduces the wire feed speed S. Additionally, the output control unit 10 changes the welding current I to the current value I. B (I B A The welding current I is controlled in a manner that... It should be noted that the value of the welding current I is set to I... B This is to regulate the heat input to the weld bead (not shown) formed on workpiece 17 by welding. Current value I B ​The duration for which this value is maintained can be appropriately changed depending on the amount of heat input 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 The welding current is controlled by a method called I. Additionally, the welding current I reaches the current value I... C Until the welding wire 18 is short-circuited with the workpiece 17, the output control unit 10 maintains the welding current I at the current value I. C The welding current is controlled in the following way: 1.

[0050] It should be noted that in the following description, the welding current I is sometimes maintained at I. C During period T2 (refer to) Figure 4 This is called the second period T2, where the current value I is... C Called the third value I C Or the current I before a short circuit C The third value I C The first value I A Approximately 30% to 40%. Additionally, in this embodiment, the third value I... C Set to be greater than the fourth value I D High. However, it is not specifically limited to this; the third value I C It can also be in the fourth value I D the following.

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

[0052] When the current value from the welding current I reaches I C After time T2, at time tn3, welding wire 18 and workpiece 17 short-circuit, during the short-circuit period T. SHORT start.

[0053] After a short circuit occurs between the welding wire 18 and the workpiece 17, if the heat applied to the welding wire 18 reaches a predetermined threshold, the output control unit 10 will set the welding current I to the fourth value I. D The welding current I is controlled in a specific manner. At time t(n+1), which is the start time of the next welding period T, the welding current I changes to its fourth value I. D Short-circuit welding is performed sequentially.

[0054] It should be noted that the heat applied to the welding wire 18 corresponds to the aforementioned cumulative power value. Therefore, in actual control, when the cumulative power value reaches the specified threshold P... TH At that time, 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 explanation, the threshold P is sometimes referred to as... TH This is called the power accumulation threshold P. TH .

[0055] Subsequently, during each welding period T, the output control unit 10 controls the welding current I, and the wire feed speed control unit 13 controls the wire feed speed S to allow the short-circuit welding to continue. When short-circuit welding of a specified length is performed along the welding line, a weld bead of a specified 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 involved in this embodiment involves short-circuit welding of the workpiece 17 by repeatedly alternating forward and reverse feeds of the welding wire 18. The material of the workpiece 17 and the material of the welding wire 18 are both magnesium-based materials, i.e., magnesium or magnesium alloy.

[0058] During the forward feed of the welding wire 18, the welding wire 18 is fed toward the workpiece 17 in a manner that short-circuits the welding wire 18 with the workpiece 17.

[0059] During the reverse feed of the welding wire 18, the welding wire 18 is fed in the opposite direction to the forward feed of the welding wire 18 in such a way that the short circuit between the welding wire 18 and the workpiece 17 is broken.

[0060] In addition, the arc welding method involved in this 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 the first value I. A (First step)

[0062] When the welding current I reaches the first value I A Then, 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 a value lower than the first value I. A Low third value I C (Second step)

[0063] From the welding current I reaching the third value I C The welding current I is maintained at the third value I until the welding wire 18 is short-circuited with the workpiece 17. C The welding current I is controlled in the following way (third step).

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

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

[0066] like Figure 5 As shown, the current I before the short circuit is about to occur. C (Third value I) C That is, the welding current I flowing to the welding wire 18 before the short circuit is set to be equal to the average current I. S The value increases monotonically with the increase of the material. This is the same whether the material of workpiece 17 is aluminum-based or magnesium-based.

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

[0068] As mentioned above, magnesium-based materials are lighter than aluminum-based materials, resulting in a lighter mass of the molten droplet formed at the tip of the welding wire 18. When the welding current I increases while the arc 19 is generated, the arc reaction force applied to the molten droplet also increases, making it less likely for a short circuit to occur between the welding wire 18 and the workpiece 17. Therefore, there are technical problems such as excessive droplet growth and easy spattering.

[0069] On the other hand, when performing short-circuit welding of magnesium-based materials, as shown in this embodiment, the current I before the short circuit is reached is... C Setting the arc to a lower value reduces the arc reaction force, thereby promoting a short circuit between the welding wire 18 and the workpiece 17. This suppresses excessive droplet growth and spatter.

[0070] Furthermore, by suppressing spatter and other defects, welding defects can be reduced, thereby preventing a decrease in the yield of the welding process. Additionally, welding quality can be maintained at a high level.

[0071] Furthermore, compared to the TIG welding shown in Patent Document 1, the welding speed can be increased according to this embodiment. This shortens the process time in the welding of magnesium-based materials, thereby improving productivity.

[0072] It should be noted that when the current I before the short circuit is... C Setting it too low may lead to other adverse effects. For example, when the current I before a short circuit is reached... C When the temperature range is set too low, the temperature of the molten pool (not shown) formed on the workpiece 17 will also be low. As a result, porosity is more likely to occur inside the workpiece 17. Alternatively, the weld bead bulge may be higher than desired.

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

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

[0075] Figure 6 This is a graph showing the relationship between the average current and the forward feed rate involved in the embodiment.

[0076] like Figure 6 As shown, the forward feed rate S F It is also set to follow the average current I S The value increases monotonically with the increase of the material. This is the same whether the material of workpiece 17 is aluminum-based or magnesium-based.

[0077] On the other hand, the forward feed rate S F It is set to be higher when the material of workpiece 17 is magnesium-based than when the material of workpiece 17 is aluminum-based. Figure 6 In the example shown, in the average current I S When the range is 50A to 200A, the forward feed rate 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 increasing the forward feed rate S FA higher setting forces the welding wire 18 closer to the workpiece 17, thereby promoting a short circuit between them. This suppresses excessive droplet growth and spatter.

[0079] It should be noted that when the forward feed rate S is... F Setting the value too high may result in the aforementioned problems. Specifically, porosity may easily form inside the workpiece 17. Alternatively, the weld bead bulge may be higher than desired.

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

[0081] It should be noted that when the forward feed rate S is... F When the reverse feed rate S is set high as shown in this embodiment, the reverse feed rate S R It also needs to be improved. When only the forward feed rate S is increased... F Set it to a higher value, and set the reverse feed rate S R When set to a lower value, there is a tendency for excessive weld bead bulging. Therefore, compared to the case of aluminum-based materials, in the case of magnesium-based materials, the forward feed rate S... F Setting it to a higher value will correspondingly increase the reverse feed rate S. R It's set too high.

[0082] Furthermore, by setting both the forward feed rate SF and the reverse feed rate SR to higher values, the forward and reverse feed amounts of the welding wire 18 in the short-circuit welding are increased in the case of magnesium-based materials in this embodiment, compared to the case of aluminum-based materials.

[0083] Furthermore, regarding the arc welding method according to this embodiment, from the moment the short circuit between the welding wire 18 and the workpiece 17 is broken, the welding current I is controlled to become a fourth value ID, which is lower than the first value IA, and the welding current I is maintained at the fourth value ID during the first period T1 (fourth step). It should be noted that after the fourth step is completed, the process returns to the first step described above, and short-circuit welding is performed sequentially.

[0084] In addition, the first period T1 (the low current duration T1 after the short circuit is broken) is the period from the breaking of the short circuit between the welding wire 18 and the workpiece 17 until the distance L between the welding wire 18 and the workpiece 17 reaches the specified value.

[0085] In this embodiment, by setting a fourth step and setting a longer low current duration T1 after the short circuit is broken, droplet scattering is suppressed, thereby suppressing the generation of splashes and the like. This point will be explained further below.

[0086] Figure 7 This is a graph showing the relationship between the average current involved in the embodiment and the duration of low current after the short circuit is broken.

[0087] like Figure 7 As shown, the low current duration T1 after the short circuit is broken is set to increase with the average current I. S Increases and decreases. This is the same whether the material of workpiece 17 is aluminum-based or magnesium-based.

[0088] It should be noted that, in Figure 7 In the example shown, in both cases, the average current I S In regions exceeding 150A, the reduction in T1 during the low current duration after short-circuit disconnection becomes smaller, eventually tending to converge to a certain value.

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

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

[0091] Therefore, as shown in this embodiment, after the short circuit is broken, the output control unit 10 sets the current value of the welding current I to a lower value (fourth value I). DThe welding current I is controlled by maintaining this lower value for a certain period (the first period T1). By doing so, firstly, the arc reaction force generated between the welding wire 18 and the workpiece 17 can be reduced. Secondly, at the midpoint or end of the first period T1, the action of the welding wire 18 switches from reverse feed to forward feed, and the distance L between the welding wire 18 and the workpiece 17 approximately reaches its maximum value after the first period T1. When the distance L becomes sufficiently long, the process moves to the first step, and the current value of the welding current I increases to the first value I. A That is, by increasing the welding current I while ensuring sufficient distance L, a molten droplet of appropriate size can be formed at the tip of the welding wire 18. Moreover, the increase in the arc reaction force on the molten droplet and the scattering of the molten droplet can be suppressed, thereby suppressing the generation of spatter and the like.

[0092] It should be noted that in this embodiment, the maximum value is approximately 4 mm, but it can be appropriately changed based on factors such as the diameter of the welding wire 18, the reverse feed speed SR, and the inertia of the robot holding the welding torch. Furthermore, the distance L may not necessarily reach its maximum value after the first period T1. This is as long as it ensures that even if the welding current I is increased to the first value I... A The distance should be such that it does not produce splashing of molten droplets.

[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 of the molten pool attached to the workpiece 17 becomes thinner, that is, the current value when the so-called necking phenomenon occurs.

[0094] Furthermore, in the arc welding method according to this embodiment, if the heat applied to the welding wire 18 reaches a predetermined threshold after a short circuit between the welding wire 18 and the workpiece 17, the output control unit 10 will make the welding current I become the fourth value I. D The welding current I is controlled in the following way (step 5).

[0095] The heat applied to the welding wire 18 corresponds to the cumulative power value obtained by accumulating the power supplied to the welding wire 18 during a specified period after a short circuit between the welding wire 18 and the workpiece 17.

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

[0097] In the fifth step, when the cumulative power value reaches the specified cumulative power threshold P... TH At that time, the output control unit 10 makes the welding current I become the fourth value I. D The welding current is controlled in the following way: 1.

[0098] In this embodiment, a fifth step is set, and the power accumulation threshold P is appropriately set. TH This can suppress the splashing that occurs when a short circuit is broken. This will be explained further below.

[0099] Figure 8 This is a graph illustrating the relationship between the average current and the cumulative power threshold involved in the implementation method.

[0100] like Figure 8 As shown, the power accumulation threshold P TH Set to follow the average current I S The value increases monotonically with the increase of the material. This is the same whether the material of workpiece 17 is aluminum-based or magnesium-based.

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

[0102] In the prior art, in short-circuit welding of ferrous materials, the occurrence of necking is detected based on changes in the welding voltage V. When necking occurs between the welding wire 18 and the workpiece 17, the resistance value increases at the necked portion. In this case, during short-circuit control, the change in welding voltage becomes larger relative to the change in welding current I. Therefore, when necking is detected based on the voltage change, i.e., when the short circuit is about to be broken, the welding current I is reduced before the short circuit is broken, thereby suppressing spatter.

[0103] However, the resistivity of magnesium (around 4.3 μΩ·cm at room temperature) is smaller than that of iron (around 10.4 μΩ·cm at room temperature in the case of pure iron) and close to that of aluminum (around 2.8 μΩ·cm at room temperature).

[0104] When welding wire 18 is made of a material with low resistivity, such as magnesium or aluminum, even if necking occurs, the change in welding voltage V caused by necking is small and the deviation is large, so it is possible to misjudge whether necking has occurred.

[0105] For example, if necking occurs but is mistakenly identified as not occurring, short-circuit welding continues without reducing the welding current I. As a result, the heat input when the short circuit is broken increases, which may cause spatter.

[0106] Therefore, as shown in this embodiment, when the heat applied to the welding wire 18, specifically the cumulative power value corresponding to that heat, reaches the cumulative power threshold P, TH At that time, so that the welding current I becomes the fourth value I D The welding current I is controlled in this way. By reducing the welding current I before the short circuit is broken, the amount of heat input to the welding wire 18 is reduced, thus suppressing spatter during short circuit breaking. Furthermore, since the welding current I is reduced before the short circuit is broken without detecting necking, adverse situations caused by incorrect judgments about whether necking has occurred can be avoided.

[0107] It should be noted that when calculating the cumulative power value, it is preferable to start the calculation after the welding wire 18 and the workpiece 17 are short-circuited, that is, after the short circuit has stabilized. By doing so, the period of short-circuit instability can be excluded from the calculation of the cumulative power value.

[0108] Alternatively, the calculation of the cumulative power value can begin after the welding current I starts to rise following the short circuit of welding wire 18. By doing so, appropriate heat can be provided to welding wire 18 even when the welding voltage V changes.

[0109] (Other implementation methods)

[0110] Alternatively, a pulse welding period can be set at least one period before and after the short-circuit welding period (a period that is k times the welding period T, where k is an integer greater than or equal to 1). During the pulse welding period, welding is performed by feeding the welding wire 18 toward the workpiece 17 at a specified wire feed speed S and by alternately flowing peak current and base current through the welding wire 18, thereby generating an arc 19 between the workpiece 17 and the welding wire 18.

[0111] Alternatively, a cooling period with zero heat input to the workpiece 17 can be set between the pulse welding period and the short-circuit welding period. By setting 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 distinct wavy, fish-scale pattern weld bead can be achieved.

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

[0113] -Industrial Practicality

[0114] The electric arc welding method disclosed herein is useful because it can increase the welding speed in short-circuit welding of magnesium-based materials and suppress the generation of spatter, etc.

[0115] -Symbol Explanation-

[0116] 1. Input power

[0117] 2. Main Transformer (Transformer)

[0118] 3. First-stage rectifier section

[0119] 4 Switch section

[0120] 5. DCL (Reactor)

[0121] 6 Second-stage rectifier section

[0122] 7 Welding Current Detection Department

[0123] 8 Welding Voltage Detection Department

[0124] 9. Control Switching 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 Department

[0130] 15. Arithmetic Unit

[0131] 16. Arc welding equipment

[0132] 17 workpieces

[0133] 18 Welding wire

[0134] 19 Electric Arc

[0135] 20 Welding nozzles

[0136] 21. Wire feeding section

[0137] 22 Welding Condition Setting Section

[0138] 23 Short-circuit welding setting section

[0139] 24. Pulse welding setting unit.

Claims

1. An arc welding method which is an arc welding method of at least performing short circuit welding in which forward feeding and reverse feeding of a welding wire are alternately repeated with respect to a workpiece, characterized by: the material of the workpiece and the material of the welding wire being magnesium or a magnesium alloy, the welding wire being fed toward the workpiece in a manner that the welding wire is short-circuited to the workpiece at the time of forward feeding of the welding wire, the welding wire being fed in a direction opposite to the direction of the forward feeding of the welding wire in a manner that the short circuit between the welding wire and the workpiece is broken at the time of reverse feeding of the welding wire, the arc welding method including at least a first step, a second step, and a third step, in the first step, the welding current flowing to the welding wire is increased to a first value after the short circuit between the welding wire and the workpiece is broken, in the second step, the welding current is decreased after the welding current reaches the first value, and the welding current is decreased to a third value lower than the first value before the welding wire is short-circuited to the workpiece, in the third step, the welding current is controlled in a manner that the welding current is maintained at the third value from when the welding current reaches the third value until the welding wire is short-circuited to the workpiece, the arc welding method further including a fourth step, in the fourth step, the welding current is controlled in a manner that the welding current becomes a fourth value lower than the first value and the welding current is maintained at the fourth value for a first period from when the short circuit between the welding wire and the workpiece is broken, after the fourth step is executed, the first step is shifted to, the first period is a period from when the short circuit between the welding wire and the workpiece is broken until a distance between the welding wire and the workpiece reaches a prescribed value.

2. The arc welding method according to claim 1, characterized by: the arc welding method further including a fifth step, in the fifth step, if heat applied to the welding wire reaches a prescribed threshold value after the short circuit between the welding wire and the workpiece, the welding current is controlled in a manner that the welding current becomes the fourth value.

3. The arc welding method according to claim 2, characterized by: the heat applied to the welding wire corresponds to a power accumulation value obtained by accumulating power supplied to the welding wire for a prescribed period, 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, in the fifth step, when the power accumulation value reaches a prescribed power accumulation threshold value, the welding current is controlled in a manner that the welding current becomes the fourth value.

4. The arc welding method according to claim 1, characterized by: when a moving average value of the welding current for a prescribed period is set as an average current, the third value monotonously increases with an increase in the average current, in a case where the average current ranges from 50 A to 200 A, the third value ranges from 20 A to 80 A. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 5. The arc welding method according to claim 1, characterized in that: when a moving average value of the welding current over a prescribed period is set as an average current, the feed rate of the welding wire at the time of forward feed is set as a forward feed rate, the forward feed rate monotonously increases with an increase in the average current, in a case where the average current ranges from 50 A to 200 A, the forward feed rate ranges from 30 m / min to 70 m / min.

6. The arc welding method according to claim 1, characterized in that: when a moving average value of the welding current over a prescribed period is set as an average current, the first period decreases with an increase in the average current, in a case where the average current ranges from 50 A to 200 A, the first period ranges from 4000 μsec to 1000 μsec.

7. The arc welding method according to claim 3, characterized in that: when a moving average value of the welding current over a prescribed period is set as an average current, the power accumulation threshold monotonously increases with an increase in the average current, in a case where the average current ranges from 50 A to 200 A, the power accumulation threshold ranges from 4 kW to 8 kW. ​ ​ ​

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