Arc welding control method and arc welding apparatus

Abstract

In arc welding, the objective is to prevent welding adhesion between the welding wire and the molten pool at the end of welding, regardless of the welding conditions. [Solution] In an arc welding control method in which, when a welding termination command St is output at time t1, the process transitions from a steady welding period to an anti-stick period, during the anti-stick period the welding wire feeding speed Fw slows down over time due to inertia and stops, and welding is terminated by output control based on the anti-stick voltage setting value with positive electrode polarity, the output polarity is switched to negative electrode polarity during the negative electrode polarity period from time t1 to t11 during part of or the entire anti-stick period from time t1 to t2.

Description

Technical Field

[0001] The present invention relates to an arc welding control method and an arc welding apparatus for ending welding by anti-stick control.

Background Art

[0002] An arc welding method is used in which a welding wire is fed and welded using a robot or the like. The arc welding method performs welding through the following process. 1) When the robot moves and arrives at the welding start position, a welding start command is output, and welding is started and shifted to the steady welding period. 2) During the steady welding period, the robot moves along the welding line, and welding is performed while feeding the welding wire and output control is performed based on the steady welding voltage set value with the electrode positive polarity. 3) When the robot reaches and stops at the welding end position, a welding end command is output, and it shifts to the anti-stick period. 4) During the anti-stick period, the feeding speed decelerates and stops due to inertia, and welding is ended by output control based on the anti-stick voltage set value with the electrode positive polarity (see, for example, Patent Document 1). 5) When welding ends, the robot starts a retreat movement from the welding end position.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The anti-stick period described above prevents the welding wire, which is fed by inertia, from coming into contact with the molten pool and welding. However, conventional anti-stick period output control could not completely prevent welding under certain welding conditions. When welding occurs, welding must be interrupted and the welding must be undone, which reduces production efficiency.

[0005] Therefore, the present invention aims to prevent welding adhesion between the welding wire and the molten pool at the end of welding, regardless of the welding conditions. [Means for solving the problem]

[0006] An arc welding control method provided by a first aspect of the present invention transitions from a steady welding period to an anti-stick period when a welding termination command is output, and during the anti-stick period, the welding wire feeding speed is reduced over time by inertia and stops, and welding is terminated by output control based on an anti-stick voltage setting value with positive electrode polarity, wherein the output polarity is switched to negative electrode polarity during a period of negative electrode polarity for part of or the entire anti-stick period.

[0007] In a preferred embodiment of the present invention, the period of negative electrode polarity is set to a predetermined period shorter than the antistick period.

[0008] In a preferred embodiment of the present invention, the period of negative electrode polarity is set according to the antistick voltage setting value.

[0009] In a preferred embodiment of the present invention, the period of negative electrode polarity is defined as the period until the feeding speed is reduced to a reference value.

[0010] In a preferred embodiment of the present invention, the output control is performed based on the electrode negative polarity voltage set value during the period of negative electrode polarity.

[0011] An arc welding apparatus provided by a second aspect of the present invention transitions from a steady welding period to an anti-stick period when a welding termination command is output, and during the anti-stick period, the welding wire feeding speed is reduced over time by inertia and stops, and welding is terminated by output control based on an anti-stick voltage setting value with positive electrode polarity, wherein the output polarity is switched to negative electrode polarity during a period of negative electrode polarity for part of or all of the anti-stick period. [Effects of the Invention]

[0012] According to the present invention, welding adhesion between the welding wire and the molten pool at the end of welding can be prevented regardless of the welding conditions, thus suppressing a decrease in production efficiency. [Brief explanation of the drawing]

[0013] [Figure 1] This is a block diagram of an arc welding apparatus for implementing an arc welding control method according to an embodiment of the present invention. [Figure 2] Figure 1 shows a timing chart of each signal in an arc welding apparatus illustrating an arc welding control method according to an embodiment of the present invention. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described below with reference to the drawings.

[0015] Figure 1 is a block diagram of an arc welding apparatus for implementing an arc welding control method according to an embodiment of the present invention. Each block will be described below with reference to this figure.

[0016] The sequence circuit SC takes the anti-stick period setting signal Tar (described later), the welding start signal St (described later), and the reverse feed period setting signal Trr (described later) as inputs, performs the following processing, and outputs the sequence signal Sc. When the welding process is complete, the sequence signal Sc = 0. 1) During the steady welding period when the welding start signal St is at the High level (welding start command), output the sequence signal Sc = 1. 2) Output the sequence signal Sc = 2 during the period determined by the anti-sticking period setting signal Tar from the time when the welding start signal St changes to the Low level (welding end command). 3) Output the sequence signal Sc = 3 during the subsequent predetermined pause period (about 10 ms). 4) Output the sequence signal Sc = 4 during the backward feeding period determined by the subsequent backward feeding period setting signal Trr. 5) Output the sequence signal Sc = 5 during the subsequent predetermined retraction initial period (about 100 ms). 6) When the retraction initial period ends, output the sequence signal Sc = 0 (welding process end state).

[0017] The anti-sticking period setting circuit TAR outputs a predetermined anti-sticking period setting signal Tar.

[0018] The anti-sticking voltage setting circuit VAR outputs a predetermined anti-sticking voltage setting signal Var.

[0019] The electrode negative polarity voltage setting circuit VNR outputs a predetermined electrode negative polarity voltage setting signal Vnr.

[0020] The electrode negative polarity period circuit SN takes the above sequence signal Sc, the above anti-sticking voltage setting signal Var, and the feed speed detection signal Fd described later as inputs, performs any one of the following processes 1) to 4), and outputs the electrode negative polarity period signal Sn. 1) Output a High-level electrode negative polarity period signal Sn during a partial period or the entire period of the sequence signal Sc = 2 (anti-sticking period). 2) Output a High-level electrode negative polarity period signal Sn during a predetermined period from the time when the sequence signal Sc changes to 2 (anti-sticking period). The predetermined period is less than the value of the anti-sticking period setting signal Tar. 3) The predetermined period described above is set according to the value of the anti-stick voltage setting signal Var. The predetermined period becomes longer as the value of the anti-stick voltage setting signal Var increases. 4) From the moment the sequence signal Sc=2 (anti-stick period) until the value of the feed rate detection signal Fd slows down to the reference value, a high-level electrode negative polarity period signal Sn is output.

[0021] The wire feed path length setting circuit LFR is a touch panel or similar device located on the front panel of the arc welding equipment. When the welder inputs the length of the wire feed path from the feeder WF to the power supply tip in the welding torch AT, the circuit outputs this value as the wire feed path length setting signal Lfr. The wire feed path length setting signal Lfr is, for example, in the range of 10 cm to 300 cm. Since the welding wire 1 is fed through the conduit cable, the length of the feed path is also the length of the conduit cable.

[0022] The welding wire diameter setting circuit DR is a touch panel or similar device located on the front panel of the arc welding machine. When the welder selects the diameter of the welding wire 1 to be used, it outputs a welding wire diameter setting signal Dr corresponding to that selection. The diameter of the welding wire is, for example, in the range of 0.8 mm to 1.6 mm. Therefore, the value of the welding wire diameter setting signal Dr is 1 when the diameter is 1.6 mm, 2 when it is 1.2 mm, 3 when it is 1.0 mm, 4 when it is 0.9 mm, and 5 when it is 0.8 mm.

[0023] The power supply tip-base metal distance setting circuit ER is a touch panel or similar device located on the front panel of the arc welding machine. When the welder inputs the distance between the power supply tip and the base metal, the circuit outputs that value as the power supply tip-base metal distance setting signal Er. The power supply tip-base metal distance setting signal Er is, for example, in the range of 10 mm to 30 mm.

[0024] The retraction distance setting circuit LRR takes the above-mentioned feed path length setting signal Lfr, the above-mentioned welding wire diameter setting signal Dr, and the above-mentioned power supply tip-base material distance setting signal Er as inputs, performs the calculation in the following equation (1), and outputs the retraction distance setting signal Lrr. The standard value in the equation below is, for example, 2.5 mm. Lrr[mm] = Standard value + Lfr[cm] × 0.005 + Dr × 0.2 + Er[mm] × 0.04 (1) 1) Correction by transmission path length setting signal Lfr As the feed path length increases, the amount by which the welding wire 1 protrudes forward from the tip of the power supply chip increases due to the change in the shape of the conduit cable accompanying the robot's retraction movement. The value of Lfr is in the range of 10 cm to 300 cm. Therefore, a correction is made by adding (Lfr × 0.005) to the standard value. As a result, the added value increases as the value of Lfr increases, correcting the retraction distance setting signal Lrr to increase. 2) Correction by welding wire diameter setting signal Dr As the diameter of the welding wire decreases, the amount by which the welding wire 1 protrudes forward from the tip of the power supply chip increases due to the change in the shape of the conduit cable accompanying the robot's retraction movement. The value of Dr is 1 when the diameter is 1.6 mm, 2 when it is 1.2 mm, 3 when it is 1.0 mm, 4 when it is 0.9 mm, and 5 when it is 0.8 mm. Therefore, a correction is made by adding (Dr × 0.2) to the standard value. As a result, the added value increases as the diameter decreases and the value of Dr increases, correcting the retraction distance setting signal Lrr to increase. 3) Correction by the power supply chip-base material distance setting signal Er As the distance between the power supply tip and the base material increases, the amount by which the welding wire 1 protrudes forward from the tip of the power supply tip increases due to the change in the shape of the conduit cable accompanying the robot's retraction movement. The value of Er is in the range of 10 mm to 30 mm. Therefore, a correction is made by adding (Er × 0.04) to the standard value. As a result, the added value increases as the value of Er increases, and the retraction distance setting signal Lrr increases accordingly.

[0025] The retraction distance control setting circuit LCR takes the above-mentioned retraction distance setting signal Lrr and the welding discrimination signal Sd (described later) as inputs. When the welding discrimination signal Sd is at a high level, it adds a predetermined increment value to the value of the retraction distance setting signal Lrr and outputs the retraction distance control setting signal Lcr. The increment value is, for example, 2 mm.

[0026] The reverse feed period setting circuit TRR takes the reverse distance control setting signal Lcr as input, performs the calculation shown in the following equation, and outputs the reverse feed period setting signal Trr. In the following equation, the reverse feed speed is, for example, 12 m / min. If Lcr = 5 mm in this case, then Trr = 25 ms. Trr[ms]=(Lcr[mm] / (reverse feed speed [m / min]×1000 / 60))×1000

[0027] The start circuit ON takes the sequence signal Sc as input and outputs a start signal ON that is at a high level when the sequence signal Sc is 1 (steady welding period), 2 (anti-stick period), or 5 (initial retraction period).

[0028] The voltage setting circuit VR takes the above sequence signal Sc, the above electrode negative polarity period signal Sn, the above antistick voltage setting signal Var, and the above electrode negative polarity voltage setting signal Vnr as inputs, performs the following processing, and outputs the voltage setting signal Vr. 1) When the sequence signal Sc=1 (steady-state welding period), a voltage setting signal Vr is output, which is a predetermined steady-state voltage setting value. 2) When the sequence signal Sc = 2 (antistick period) and the electrode negative polarity period signal Sn = High level, a voltage setting signal Vr is output that is equal to the value of the electrode negative polarity voltage setting signal Vnr. 3) When the sequence signal Sc = 2 (antistick period) and the electrode negative polarity period signal Sn = Low level, a voltage setting signal Vr is output that is equal to the value of the antistick voltage setting signal Var. 4) When the sequence signal Sc=5 (initial retreat period), a voltage setting signal Vr is output, which is a predetermined welding discrimination voltage setting value.

[0029] The feed speed setting circuit FR takes the sequence signal Sc as input and outputs a feed speed setting signal Fr which is the steady feed speed setting value when the sequence signal Sc=1 (steady-state welding period), 0 when the sequence signal Sc=2 (anti-stick period) and 3 (pause period), the reverse feed speed setting value when the sequence signal Sc=4 (reverse feed period), and 0 when the sequence signal Sc=5 (initial retraction period).

[0030] The welding detection circuit SD takes the sequence signal Sc and the welding voltage Vw between the output terminals of the arc welding device as input. When the sequence signal Sc = 5 (initial retraction period), if the absolute value of the welding voltage Vw is less than or equal to the contact detection value (approximately 5V), it determines that welding has occurred between the welding wire 1 and the molten pool and outputs a welding detection signal Sd at a high level.

[0031] The main power supply circuit PS is connected to a commercial AC power supply such as 3-phase 200V (not shown in the diagram). It takes the above-mentioned start signal On, voltage setting signal Vr, and electrode negative polarity period signal Sn as inputs, and when the start signal On is at a high level, it performs constant voltage control such as inverter control based on the voltage setting signal Vr, and switches between electrode positive polarity EP and electrode negative polarity EN according to the electrode negative polarity period signal Sn, outputting an AC welding voltage Vw and welding current Iw suitable for welding, and generating an arc 3 between the welding wire 1 and the base material 2 (molten pool). This main power supply circuit PS, although not shown in the diagram, includes a primary rectifier circuit for rectifying AC commercial power, a capacitor for smoothing the rectified DC, a primary inverter circuit for converting the smoothed DC into high-frequency AC according to the start signal On, an inverter transformer for stepping down the high-frequency AC to a voltage suitable for welding, a secondary rectifier circuit for rectifying the stepped-down high-frequency AC, a reactor for smoothing the rectified DC, and a secondary inverter circuit for switching the smoothed DC between electrode positive polarity EP and electrode negative polarity EN according to the electrode negative polarity period signal Sn.

[0032] The feeder WF takes the above sequence signal Sc and the above feed speed setting signal Fr as inputs and feeds the welding wire 1 at the feed speed Fw set by the feed speed setting signal Fr when the sequence signal Sc is 1 to 5.

[0033] The feed speed detection circuit FD detects the feed speed Fw of the feeder WF and outputs a feed speed detection signal Fd.

[0034] The welding torch AT supplies the welding current Iw and welding voltage Vw mentioned above to the welding wire 1, and performs arc welding by spraying shielding gas onto the arc generation part 3.

[0035] The robot control device RC takes the sequence signal Sc as input and moves the robot RM from the welding start position along the weld line to the welding end position according to a pre-taught work program. When the sequence signal Sc changes to 5, it outputs an operation control signal Mc to move the robot RM away from the welding end position, and also outputs a welding start signal St, which is at a high level during the period of movement from the welding start position to the welding end position.

[0036] The robot RM is equipped with the feeder WF and the welding torch AT described above, and uses the operation control signal Mc described above as input to move the tip position of the welding torch AT along the welding line.

[0037] Figure 2 is a timing chart of each signal at the end of welding in the arc welding apparatus of Figure 1, which shows an arc welding control method according to an embodiment of the present invention. Figure (A) shows the time change of the welding start signal St, Figure (B) shows the time change of the start signal On, Figure (C) shows the time change of the average value Vav of the welding voltage Vw, Figure (D) shows the time change of the average value Iav of the welding current Iw, Figure (E) shows the time change of the feed rate Fw, Figure (F) shows the time change of the robot's movement speed vr, and Figure (G) shows the time change of the electrode negative polarity period signal Sn. The operation of each signal will be explained below with reference to the figure.

[0038] When the arc welding method is short-circuit transition arc welding, the system alternates between short-circuit periods and arc periods. The instantaneous value of the welding voltage Vw is approximately 0V during the short-circuit period and approximately 30V during the arc period. The instantaneous value of the welding current Iw gradually increases during the short-circuit period and gradually decreases during the arc period. When the arc welding method is pulsed arc welding, the system alternates between peak periods and base periods. The instantaneous value of the welding voltage Vw is approximately 30V during the peak period and approximately 25V during the base period. The instantaneous value of the welding current Iw is approximately 500A during the peak period and approximately 50A during the base period. The average welding voltage Vav shown in Figure (C) and the average welding current Iav shown in Figure (D) are for positive electrode polarity EP when above 0 and for negative electrode polarity EN when below 0. As shown in Figure (E), when the feed speed Fw is a positive value above 0, it is in a forward feed state, and when it is a negative value below 0, it is in a reverse feed state.

[0039] (1) Operation during steady-state welding period prior to time t1 The period prior to time t1 is the steady-state welding period, and the sequence signal Sc=1 in Figure 1. As shown in Figure (A), the welding start signal St from the robot control device RC in Figure 1 is at a high level (welding start command), and as shown in Figure (B), the start signal On is also at a high level. As shown in Figure (C), the average welding voltage Vav is controlled based on the steady-state voltage setting value of the voltage setting signal Vr in Figure 1, and has a waveform of approximately 20-40V, which is almost constant. As shown in Figure (D), the average welding current Iav is a value corresponding to the steady-state feed rate setting value of the feed rate setting signal Fr in Figure 1, and has a waveform of approximately 100-400A, which is almost constant. As shown in Figure (E), the feed rate Fw is a value set by the steady-state feed rate setting value of the feed rate setting signal Fr in Figure 1, and is approximately 3-10 m / min. As shown in Figure (F), the robot's movement speed vr is approximately 30-150 cn / min. As shown in Figure (G), the electrode negative polarity period signal Sn is at a low level, so the output polarity of the arc welding device is electrode positive polarity EP.

[0040] (2) Operation during the antistick period from time t1 to t2 At time t1, when the robot RM in Figure 1 reaches the welding end position and stops, as shown in Figure (A), the welding start signal St changes to a Low level (welding end command), and the sequence signal Sc in Figure 1 becomes 2. The period from time t1 to t2 is the antistick period set by the antistick period setting signal Tar (approximately 200ms) in Figure 1. As shown in Figure (B), the start signal On remains at a High level. As shown in Figure (G), during the period from time t1 to t11, the electrode negative polarity period signal Sn changes to a High level, so the output polarity of the arc welding device switches to electrode negative polarity EN. The electrode negative polarity period from time t1 to t11 is set as follows by the electrode negative polarity period circuit SN in Figure 1. 1) Set the anti-stick period to a portion or the entire period from time t1 to t11. 2) The predetermined period is set from the time t1 when the system transitions to the anti-stick period. The predetermined period is less than the value of the anti-stick period setting signal Tar in Figure 1. 3) The predetermined period described above is set according to the value of the anti-stick voltage setting signal Var in Figure 1. The predetermined period becomes longer as the value of the anti-stick voltage setting signal Var increases. 4) This period is set from the time t1 when the system transitions to the anti-stick period until the feed rate Fw (feed rate detection signal Fd in Figure 1), as shown in Figure (E), decelerates to a reference value.

[0041] At time t1, as shown in Figure (C), the average welding voltage Vav changes to a negative value and is controlled based on the value of the electrode negative polarity voltage setting signal Vnr in Figure 1, becoming a constant value with a smaller absolute value than during the steady-state welding period. As shown in Figure (E), as the feed rate Fw gradually decreases due to inertia, as shown in Figure (D), the average welding current Iav changes to a negative value and its absolute value decreases over time. As shown in Figure (F), the robot's movement speed vr stops and becomes 0 at time t1.

[0042] At time t11, as shown in Figure (G), when the electrode negative polarity period signal Sn changes to a low level, the output polarity of the arc welding apparatus is switched to the electrode positive polarity EP. In response, as shown in Figure (C), the average welding voltage Vav changes to a positive value and is controlled based on the value of the anti-stick voltage setting signal Var in Figure 1, becoming a constant value with a smaller absolute value than during the steady-state welding period. As shown in Figure (E), as the feed rate Fw slows down to almost 0 at time t2, as shown in Figure (D), the average welding current Iav changes to a positive value and decreases over time to 0A. As shown in Figure (F), the robot's movement speed vr is 0 because it is stopped. Then, at time t2, welding is completed.

[0043] In this embodiment, during the period of negative electrode polarity from time t1 to t11, the output polarity is negative electrode polarity EN, so the melting rate of the welding wire is greater than that of the positive electrode polarity EP. As a result, the melting of the welding wire is promoted, and the arc length is increased. During the remaining anti-stick period from time t11 to t2, the polarity returns to positive electrode polarity EP, the tip of the welding wire burns moderately, and at time t2, it is separated from the molten pool by about 3 mm. As a result, in this embodiment, welding between the welding wire and the molten pool at the end of welding can be reliably prevented regardless of the welding conditions.

[0044] (3) Operation during the pause period from time t2 to t3 When the anti-stick period ends at time t2, the sequence signal Sc=3 in Figure 1 becomes 3, and a predetermined pause period occurs from time t2 to t3. As shown in Figure (B), the start signal On changes to a Low level. In response, as shown in Figure (C), the average welding voltage Vav becomes 0V because the output control stops. As shown in Figure (D), the average welding current Iav also becomes 0A. As shown in Figure (E), the feed rate Fw also becomes 0.

[0045] (4) Operation during the reverse feed period from time t3 to t4 When the pause period ends at time t3, the sequence signal Sc=4 in Figure 1 becomes the reverse feed period from time t3 to t4. As shown in Figure (B), the start signal On remains at a low level. As shown in Figure (C), the average welding voltage Vav becomes 0V, and as shown in Figure (D), the average welding current Iav becomes 0A. As shown in Figure (E), the feed speed Fw becomes the reverse feed speed setting value of the feed speed setting signal Fr in Figure 1, resulting in a negative reverse feed speed. The welding wire is then fed backward by the reverse distance during the reverse feed period from time t3 to t4. The reverse distance is set by the reverse distance setting signal Lrr in Figure 1, and is set by inputting the feed path length setting signal Lfr, the welding wire diameter setting signal Dr, and the power tip-base material distance setting signal Er into the above-mentioned equation (1). That is, the reverse distance is corrected and set to the optimal value according to the feed path length, the welding wire diameter, and the power tip-base material distance. The reason for this correction is that the amount of welding wire protruding forward when the robot RM moves to a retracted position varies depending on these conditions. In this embodiment, the retraction distance is corrected using the three parameters described above, but it may also be corrected using at least one parameter.

[0046] (5) Operation during the initial escape period from time t4 to t5 At time t4, when the retraction feeding period ends, the sequence signal Sc=5 in Figure 1, and the predetermined initial retraction period from time t4 to t5 begins. As shown in Figure (B), the start signal On returns to a high level. As shown in Figure (C), the average welding voltage Vav is controlled based on the welding discrimination voltage setting value of the voltage setting signal Vr in Figure 1, and becomes the welding discrimination voltage value. As shown in Figure (D), the average welding current Iav is 0A because no arc is generated. As shown in Figure (E), the feeding speed Fw stops when the feeding speed setting signal Fr in Figure 1 becomes 0. As shown in Figure (F), the robot's movement speed vr becomes the predetermined retraction movement speed because the robot RM begins to retract. At time t4, as the robot RM begins to retract, the shape of the conduit cable changes, causing the welding wire to protrude forward. However, since the welding wire is fed back by the appropriate length during the retraction period, it is possible to suppress the occurrence of welding due to the tip of the welding wire coming into contact with the molten pool.

[0047] During the initial retreat period, the average welding voltage Vav is the welding detection voltage. This welding detection voltage is set to approximately 10V, a value at which arc generation does not occur. Therefore, in the very rare case where the welding wire protrudes too far forward and comes into contact with the molten pool, causing welding, the welding detection signal Sd in Figure 1 will reach a high level. When the welding detection signal Sd reaches a high level, the retreat distance is corrected to a value set by the retreat distance control setting signal Lcr in Figure 1, which is obtained by adding a predetermined increment to the value of the retreat distance setting signal Lrr in Figure 1. As a result, the retreat distance will increase from the next welding cycle onward, thus preventing welding from occurring.

[0048] (6) Operation of the welding process completion state after time t5 At time t5, when the initial retraction period ends, the sequence signal Sc=0 in Figure 1, and the welding process ends. As shown in Figure (B), the start signal On becomes Low level. As shown in Figure (C), the average welding voltage Vav becomes 0V, and as shown in Figure (D), the average welding current Iav becomes 0A. As shown in Figure (E), the feed rate Fw becomes 0, and the feed rate stops. As shown in Figure (F), the robot's movement speed vr remains at the retraction movement speed, so the retraction movement continues. This completes the welding process.

[0049] The effects of this embodiment will be described below. According to this embodiment, when a welding termination command is output, the system transitions from a steady-state welding period to an anti-stick period. During the anti-stick period, the welding wire feeding speed decreases over time due to inertia and stops. In this arc welding control method, the output is controlled based on the anti-stick voltage setting with positive electrode polarity to terminate welding. During a period of negative electrode polarity for part or all of the anti-stick period, the output polarity is switched to negative electrode polarity. With negative electrode polarity, the melting speed of the welding wire is greater than with positive electrode polarity. For this reason, setting the electrode polarity to negative for part or all of the anti-stick period promotes the melting of the welding wire and lengthens the arc, thereby suppressing short circuits between the welding wire and the molten pool. As a result, in this embodiment, welding between the welding wire and the molten pool at the end of the anti-stick period (end of welding) can be reliably prevented. Furthermore, in this embodiment, since the melting of the welding wire is promoted, the anti-stick period can be set to be about 50% shorter compared to conventional technology with positive electrode polarity, thereby increasing production efficiency.

[0050] More preferably, according to this embodiment, the electrode negative polarity period is set to a predetermined period shorter than the antistick period. In this way, melting of the welding wire is promoted during the electrode negative polarity period, the arc length is increased, and short circuits between the welding wire and the molten pool are suppressed. During the remaining antistick period that follows, the electrode returns to positive polarity, so the tip of the welding wire burns up appropriately, and the distance from the molten pool at the end of welding becomes the appropriate length. If the distance at the end of welding is longer than the appropriate length, the particle size of the welding wire tip becomes larger, and the ability to start the next arc deteriorates. Conversely, if the distance at the end of welding is shorter than the appropriate length, the particle size of the welding wire tip becomes smaller, and slag adheres to the tip. In this case, since slag is an insulator, there is a possibility that an arc will not be generated at the next arc start.

[0051] More preferably, according to this embodiment, the electrode negative polarity period is set according to the anti-stick voltage setting value. If the electrode negative polarity period is made longer as the anti-stick voltage setting value increases, the arc length at the end of the electrode negative polarity period will be at an appropriate value, so welding adhesion at the end of welding can be prevented more reliably.

[0052] More preferably, according to this embodiment, the electrode negative polarity period is defined as the period until the feed rate is reduced to a reference value. In this way, the arc length at the end of the electrode negative polarity period is at an appropriate value, so welding adhesion at the end of welding can be prevented more reliably.

[0053] More preferably, according to this embodiment, output control is performed based on the electrode negative polarity voltage setting value during the electrode negative polarity period. In this way, the arc length at the end of the electrode negative polarity period is set to an appropriate value, so welding adhesion at the end of welding can be prevented more reliably.

[0054] Furthermore, according to this embodiment, the arc welding apparatus switches the output polarity to the negative electrode polarity during the period of negative electrode polarity, which is part or all of the anti-stick period. The arc welding apparatus according to this embodiment provides the above-described effects.

[0055] More preferably, according to this embodiment, in an arc welding control method that uses a robot to feed a welding wire and perform welding, when welding is completed, the welding wire is fed backward by a backward distance, and the robot starts to move away from the welding completion position after the backward feeding is completed. In the conventional technology, when welding is completed and the robot starts to move away from the welding completion position, the welding wire may protrude forward and fuse to the molten pool due to a change in the shape of the conduit cable, which is the feeding path, accompanying this movement. When fusion occurs, it is necessary to interrupt welding and perform work to release the fusion, which reduces production efficiency. In contrast, in this embodiment, when welding is completed, the welding wire is fed backward by a backward distance, and the robot starts to move away from the welding completion position after the backward feeding is completed. In this way, even if the welding wire protrudes forward when the robot starts to move away, it will not fuse to the molten pool, thus suppressing a decrease in production efficiency.

[0056] More preferably, according to this embodiment, the retraction distance is set according to the length of the feed path. The longer the feed path, the greater the amount the welding wire protrudes forward due to the change in the shape of the conduit cable accompanying the robot's retraction movement. In this embodiment, the retraction distance is corrected to increase as the feed path lengthens. In this way, even if the feed path becomes longer and the amount of forward protrusion of the welding wire increases, the retraction distance is long, so the occurrence of welding can be suppressed.

[0057] More preferably, according to this embodiment, the retraction distance is set according to the diameter of the welding wire. As the diameter of the welding wire decreases, the amount by which the welding wire protrudes forward due to the change in the shape of the conduit cable accompanying the robot's retraction movement increases. In this embodiment, the retraction distance is corrected to increase as the diameter of the welding wire decreases. In this way, even if the diameter of the welding wire decreases and the amount of forward protrusion of the welding wire increases, the retraction distance is increased, so the occurrence of welding can be suppressed.

[0058] More preferably, according to this embodiment, the retraction distance is set according to the distance between the power supply tip and the base material. The longer the distance between the power supply tip and the base material, the greater the amount the welding wire protrudes forward due to the change in the shape of the conduit cable accompanying the robot's retraction movement. In this embodiment, the retraction distance is corrected to increase as the distance between the power supply tip and the base material increases. In this way, even if the distance between the power supply tip and the base material increases and the amount of forward protrusion of the welding wire increases, the retraction distance is long, so the occurrence of welding can be suppressed.

[0059] More preferably, according to this embodiment, if welding occurs between the welding wire and the molten pool after the robot has started to retract, the retraction distance is increased from the next welding. Even if the robot starts to retract after the welding wire has been fed backward, welding may rarely occur if the amount of forward protrusion of the welding wire is too large. In this embodiment, if welding occurs, the retraction distance is increased from the next welding. In this way, welding that rarely occurs can be reliably prevented. [Explanation of Symbols]

[0060] 1: Welding wire, 2: Base metal (molten pool), 3: Arc, AT: Welding torch, DR: Welding wire diameter setting circuit, Dr: Welding wire diameter setting signal, ER: Power supply tip-base metal distance setting circuit, Er: Power supply tip-base metal distance setting signal, FD: Feed speed detection circuit, Fd: Feed speed detection signal, FR: Feed speed setting circuit, Fr: Feed speed setting signal, Fw: Feed speed, Iav: Average welding current, Iw: Welding current, LCR: Reverse distance control setting circuit, Lcr: Reverse distance control setting signal, LFR: Feed path length setting circuit, Lfr: Feed path length setting signal, LRR: Reverse distance setting circuit, Lrr: Reverse distance setting signal, Mc: Operation control signal, ON: Start circuit, On: Start signal, PS: Power supply main circuit, RC: Robot RM: Robot, SC: Sequence circuit, Sc: Sequence signal, SD: Welding discrimination circuit, Sd: Welding discrimination signal, SN: Electrode negative polarity period circuit, Sn: Electrode negative polarity period signal, St: Welding start signal, TAR: Antistick period setting circuit, Tar: Antistick period setting signal, TRR: Reverse feed period setting circuit, Trr: Reverse feed period setting signal, VAR: Antistick voltage setting circuit, Var: Antistick voltage setting signal, Vav: Average welding voltage, VNR: Electrode negative polarity voltage setting circuit, Vnr: Electrode negative polarity voltage setting signal, VR: Voltage setting circuit, Vr: Voltage setting signal, vr: Robot movement speed, Vw: Welding voltage, WF: Wedge feeder

Claims

1. In an arc welding control method in which, upon outputting a welding termination command, the system transitions from a steady-state welding period to an anti-stick period, during the anti-stick period, the welding wire feeding speed is reduced over time by inertia and stops, and the welding is terminated by output control based on the anti-stick voltage set value with positive electrode polarity, During the period of negative electrode polarity for part or all of the aforementioned antistick period, the output polarity is switched to negative electrode polarity. An arc welding control method characterized by the following:

2. The period of negative electrode polarity is set to a predetermined period shorter than the antistick period. The arc welding control method according to feature 1.

3. The period of negative electrode polarity is set according to the anti-stick voltage setting value. The arc welding control method according to feature 1.

4. The period of negative electrode polarity is defined as the period until the feeding speed is reduced to a reference value. The arc welding control method according to feature 1.

5. During the period when the electrode is negatively polarized, the output control is performed based on the set value of the negative electrode voltage. The arc welding control method according to any one of claims 1 to 4.

6. In an arc welding apparatus where, upon outputting a welding termination command, the system transitions from a steady-state welding period to an anti-stick period, and during the anti-stick period, the welding wire feed speed is reduced over time by inertia and stops, and the welding is terminated by output control based on the anti-stick voltage setting value with positive electrode polarity, During the period of negative electrode polarity for part or all of the aforementioned antistick period, the output polarity is switched to negative electrode polarity. An arc welding apparatus characterized by the following features.

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