JP5139587B2 - Arc welding method - Google Patents

Description

  The present invention relates to an arc welding method.

  2. Description of the Related Art Conventionally, an arc welding method is known in which welding is performed by generating an arc between a consumable electrode and a base material while feeding the consumable electrode (see, for example, Patent Document 1). In such a welding method, the consumable electrode is fed forward toward the base material by rotating the feeding motor of the wire feeding device in the normal direction. Then, the short circuit period starts when the consumable electrode and the base material are short-circuited. When the consumable electrode and the base material are short-circuited, the consumable electrode is moved backward by reversing the feeding motor. Then, the consumable electrode and the base material are separated from each other, and an arc generation period in which an arc is generated between the consumable electrode and the base material starts. When the arc is generated, the feeding motor is rotated forward again. Thus, welding is performed by repeating normal rotation and reverse rotation of the feeding motor of the wire feeding device.

  In the welding method, the short circuit period and the arc generation period are repeated at a relatively high speed. When the repetition of the short-circuit period and the arc generation period becomes high speed, the forward rotation and reverse rotation of the feeding motor must be repeated at high speed. For this reason, a feed motor that can respond at high speed is required. However, a feed motor that can respond at high speed is not widely used. Furthermore, when the device for feeding the consumable electrode is a single pull torch, the feedability of the consumable electrode is affected by disturbances during operation of the welding robot, feeding resistance in the conduit cable through which the consumable electrode is inserted, etc. Therefore, stable welding cannot be performed.

JP 2006-247710 A

  The present invention has been conceived under the circumstances described above, and an object thereof is to provide an arc welding method capable of performing stable welding.

  The arc welding method provided by the present invention includes a forward feed period in which the speed from the welding torch to the base material is a positive value at a portion surrounded by the welding torch among the consumable electrodes, and the speed is negative. An arc welding method that repeats a unit period consisting of a reverse feed period that is a value, the step of feeding the consumable electrode with the speed as a periodic function whose one period is the unit period, and each forward A step of short-circuiting the consumable electrode to the base material at a certain point in the feeding period, and a step of opening a short circuit between the consumable electrode and the base material at a certain point in each of the backward feeding periods. .

  Preferably, based on the first short-circuit opening time information regarding the first short-circuit opening time when the short-circuit opening occurred, the second short-circuiting regarding the second short-circuit opening time when the short-circuit opening occurs after the first short-circuit opening time. The value of the welding current flowing from the consumable electrode to the base material is reduced at a time before the first short-circuit opening time by a first set time based on the step of obtaining the opening-time information and the second short-circuit opening time information. And a short-circuit pre-opening preparation step.

  Preferably, when the consumable electrode and the base material are short-circuited, short-circuit opening is performed to reduce the value of the welding current flowing from the consumable electrode to the base material before the transition from the forward feeding period to the backward feeding period. A preparation process is further provided.

  Preferably, based on the first short-circuit occurrence time information related to the first short-circuit occurrence time when the short-circuit between the consumable electrode and the base material occurs, the consumable electrode and the base material after the first short-circuit occurrence time The consumable electrode is obtained at a time that is a second set time before the second short-circuit occurrence time based on the second short-circuit occurrence time information related to the second short-circuit occurrence time and the second short-circuit occurrence time information. Reducing the value of the welding current flowing from the base material to the base material, and a step of increasing the value of the welding current after the second short-circuit occurrence time and before the short-circuit opening preparation step. In addition.

  Preferably, based on the first short-circuit occurrence time information related to the first short-circuit occurrence time when the short-circuit between the consumable electrode and the base material occurs, the consumable electrode and the base material after the first short-circuit occurrence time Based on the second short-circuit occurrence time information about the second short-circuit occurrence time information regarding the second short-circuit occurrence time when the short-circuit occurs, and from the consumable electrode at a time that is a set time before the second short-circuit occurrence time. And a step of reducing the value of the welding current flowing to the base material.

  According to such a configuration, the consumable electrode is fed so that the speed becomes a periodic function of a constant period regardless of changes in the values of the welding current and the welding voltage. And a short circuit period and an arc generation period can be repeated so as to follow the speed. Then, since the speed is not changed based on a change in the welding current or the welding voltage, there is an advantage that a problem such as a response delay in the supply of the consumable electrode does not occur in the first place. Therefore, stable welding can be performed.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

It is a figure which shows the structure of the arc welding system concerning 1st Embodiment of this invention. It is a principal part enlarged view (partially see-through | perspective view) of the vicinity of the feed path length change apparatus in the arc welding system shown in FIG. FIG. 3 is an enlarged view showing only the feeding path length changing device of FIG. 2. It is a figure which shows the change state of the cam mechanism of the feed path length change apparatus of FIG. It is a principal part expanded sectional view which shows typically the state by which the feed path | route length change apparatus was fixed to the welding torch and the conduit cable. It is a figure which shows typically the supply path | route length of a consumable electrode. It is a block diagram which shows the detail of the robot control apparatus and power supply device in the arc welding system of FIG. It is a timing chart which shows each signal etc. in the welding steady state of the arc welding method of a 1st embodiment of the present invention. It is a block diagram which shows the detail of the robot control apparatus and power supply device in the arc welding system concerning 2nd Embodiment of this invention. It is a timing chart which shows each signal etc. in the welding steady state of the arc welding method of a 2nd embodiment of the present invention.

  1st Embodiment of this invention is described using FIGS.

[About arc welding system A1]
An arc welding system A1 shown in FIG. 1 includes an arc welding device 1, a robot control device 2, and a power supply device 3.

  The arc welding apparatus 1 is a welding robot and automatically performs, for example, arc welding on the base material W. The arc welding apparatus 1 includes a base member 11, a plurality of arms 12, a plurality of motors 13, a welding torch 14, a wire feeding device 16, a feeding path length changing device 17, and a conduit cable 19. Including.

  The base member 11 is fixed to an appropriate location such as a floor. Each arm 12 is connected to the base member 11 via a shaft.

  The welding torch 14 is provided at the distal end portion of the arm 12 a provided on the most distal end side of the arc welding apparatus 1. The welding torch 14 guides the consumable electrode 15 to a predetermined position in the vicinity of the base material W. As schematically shown in FIG. 5, the welding torch 14 has a contact tip 141 and a nozzle 142. The contact chip 141 is made of, for example, Cu or Cu alloy. The contact chip 141 is provided with a through hole for inserting the consumable electrode 15. The through hole has a size such that the inner surface rubs against the consumable electrode 15. The nozzle 142 is made of, for example, Cu or a Cu alloy. The nozzle 142 has a water cooling structure as appropriate. An opening 143 is formed in the nozzle 142. A shield gas SG such as Ar is supplied between the nozzle 142 and the contact chip 141. The supplied shield gas SG is ejected from the opening 143. The consumable electrode 15 is fed into the shield gas SG.

  The motor 13 is provided at both ends or one end of the arm 12 (partially omitted from illustration). The motor 13 is rotationally driven by the robot control device 2. By this rotational drive, the movement of the plurality of arms 12 is controlled, and the welding torch 14 can move freely up and down, front and rear, and left and right. The motor 13 is provided with an encoder (not shown). The output of this encoder is given to the robot controller 2. Based on this output value, the robot controller 2 recognizes the current position of the welding torch 14.

  The wire feeding device 16 is provided in the upper part of the arc welding device 1. The wire feeding device 16 is for feeding the consumable electrode 15 to the welding torch 14. The wire feeding device 16 includes a feeding motor 161 (see FIG. 1) and a wire push device 162 (see FIG. 6). The wire pusher 162 feeds the consumable electrode 15 wound around the wire reel WL (see FIG. 6) to the welding torch 14 using the feeding motor 161 as a drive source.

  The conduit cable 19 is used to insert the consumable electrode 15 and lead the consumable electrode 15 from the wire feeder 16 to the welding torch 14. As clearly shown in FIG. 1, the conduit cable 19 has a curved portion in the middle portion from the wire feeding device 16 to the welding torch 14. As schematically shown in FIG. 5, the conduit cable 19 includes a coil liner 191 and a covering tube 192.

The coil liner 191 is formed, for example, by forming a metal wire into a coil shape. The consumable electrode 15 is inserted through the coil liner 191. As described above, the conduit cable 19 has a curved portion. Therefore, the consumable electrode 15 is fed while being rubbed against the inner wall of the coil liner 191 at the curved portion. The covering tube 192 has a tube shape. The coated tube 192 is made of, for example, chlorinated polyethylene (CPE: chlorinated).
polyethylene). The covering tube 192 surrounds the coil liner 191. Since the conduit cable 19 has a curved portion as described above, the covering tube 192 rubs against the coil liner 191 at the curved portion.

  The feeding path length changing device 17 shown in FIGS. 1 to 3 changes the feeding path length La (see FIG. 6). The feeding path length La refers to the length of the consumable electrode 15 from the wire push device 162 to the welding torch 14 in the axial direction of the consumable electrode 15. In the present embodiment, the feed path length changing device 17 includes a motor 171, an eccentric shaft 172, a cam mechanism 173, bearings 174 a and 174 b, a mount 175, a bush 176, and a shaft 177.

  As shown in FIG. 2, the motor 171 is fixed to the welding torch 14. That is, the motor 171 does not move relative to the welding torch 14. The motor 171 uses a shaft extending in the left-right direction in FIG. An encoder (not shown) is attached to the motor 171. The eccentric shaft 172 is fixed to the rotating shaft of the motor 171. The eccentric shaft 172 is provided with a bolt at a position eccentric with respect to the rotation axis of the motor 171. The cam mechanism 173 is a drive cam, and two holes are formed in the cam mechanism 173 (see FIG. 4). The cam mechanism 173 is connected to the bolt of the eccentric shaft 172 via a bearing 174a provided in one of these two holes. The mount 175 is connected to the cam mechanism 173 via a bearing 174b provided in the other of the two holes. The mount 175 is connected to the shaft 177 via the bush 176. The shaft 177 is fixed to the main body of the motor 171. The mount 175 can move in the vertical direction of FIG. 2 along the shaft 177. As shown in FIG. 5, the mount 175 is fixed to the coil liner 191 of the conduit cable 19.

  When the motor 171 rotates, the bolt of the eccentric shaft 172 rotates eccentrically. Then, according to the eccentric rotation, as shown in FIG. 4, the cam mechanism 173 performs a series of operations from (K1) to (K4). As shown in FIG. 3, the mount 175 reciprocates along the shaft 177. As a result, the conduit cable 19 (in this embodiment, the coil liner 191) reciprocates slightly up and down in FIG. As the coil liner 191 reciprocates, the consumable electrode 15 that rubs against the coil liner 191 reciprocates. The reciprocating motion of the coil liner 191 changes the feeding path length La. A rotation angle signal Sθ related to the rotation angle θ (t) of the motor 171 is sent from the feed path length changing device 17 to a current control circuit 32 described later. When the cam mechanism 173 is in the state shown in FIG. 4 (K1), the rotation angle θ (t) = 0 (rad). When the cam mechanism 173 is in the state shown in FIG. 10K2, the rotation angle θ (t) = π / 2 (rad). When the cam mechanism 173 is in the state shown in the figure (K3), the rotation angle θ (t) = π (rad). When the cam mechanism 173 is in the state shown in FIG. 4K4, the rotation angle θ (t) = 3π / 2 (rad).

  FIG. 7 is a block diagram showing details of the robot control device 2 and the power supply device 3 in the arc welding system A1 of FIG.

  The robot control device 2 includes an operation control circuit 21 and a teach pendant 23. The robot control device 2 is for controlling the operation of the arc welding device 1.

  The operation control circuit 21 has a microcomputer and a memory (not shown). In this memory, a work program in which various operations of the arc welding apparatus 1 are set is stored. Further, the operation control circuit 21 sets a robot moving speed VR described later. The operation control circuit 21 sends an operation control signal Ms to the arc welding apparatus 1 based on the work program, the coordinate information from the encoder, the robot moving speed VR, and the like. The arc welding apparatus 1 receives the operation control signal Ms, and each motor 13 is driven to rotate. As a result, the welding torch 14 moves to a predetermined welding start position in the base material W or moves along the in-plane direction of the base material W.

  The teach pendant 23 is connected to the operation control circuit 21. The teach pendant 23 is for the user of the arc welding system A1 to set various operations.

  The power supply device 3 includes a power supply circuit 31, a current control circuit 32, an arc generation current value storage circuit 33, a set time storage circuit 34, a voltage control circuit 35, an arc state detection circuit 36, and a feed path length control. A circuit 37 and a feed control circuit 38 are included. The power supply device 3 is a device for applying the welding voltage Vw between the consumable electrode 15 and the base material W and causing the welding current Iw to flow, and for supplying the consumable electrode 15.

  The power supply circuit 31 includes a power generation circuit MC, a power supply characteristic switching circuit SW, a current error calculation circuit EI, a voltage error calculation circuit EV, a current detection circuit ID, and a voltage detection circuit VD. The power supply circuit 31 applies a welding voltage Vw with a value instructed between the consumable electrode 15 and the base material W, or allows a welding current Iw to flow at a value instructed from the consumable electrode 15 to the base material W. Is.

  The power generation circuit MC receives, for example, a commercial power supply such as a three-phase 200V as input, performs output control such as inverter control and thyristor phase control according to an error signal Ea described later, and outputs a welding voltage Vw and a welding current Iw.

  The current detection circuit ID is for detecting the value of the welding current Iw flowing between the consumable electrode 15 and the base material W. The current detection circuit ID sends a current detection signal Id corresponding to the welding current Iw. The current error calculation circuit EI is for calculating a difference ΔIw between the value of the welding current Iw that is actually flowing and the set value of the welding current. Specifically, the current error calculation circuit EI receives a current detection signal Id and a current setting signal Ir described later corresponding to the set welding current value, and sends a current error signal Ei corresponding to the difference ΔIw. The current error calculation circuit EI may send a current error signal Ei corresponding to a value obtained by amplifying the difference ΔIw.

  The voltage detection circuit VD is for detecting the value of the welding voltage Vw applied between the consumable electrode 15 and the base material W. The voltage detection circuit VD sends a voltage detection signal Vd corresponding to the welding voltage Vw. The voltage error calculation circuit EV is for calculating a difference ΔVw between the value of the welding voltage Vw actually applied and the value of the set welding voltage. Specifically, the voltage error calculation circuit EV receives a voltage detection signal Vd and a voltage setting signal Vr described later corresponding to the set welding voltage value, and sends a voltage error signal Ev corresponding to the difference ΔVw. The voltage error calculation circuit EV may send a voltage error signal Ev corresponding to a value obtained by amplifying the difference ΔVw.

  The power supply characteristic switching circuit SW switches the power supply characteristic (constant current characteristic or constant voltage characteristic) of the power supply circuit 31. When the power supply characteristic of the power supply circuit 31 is a constant current characteristic, the output is controlled in the power supply circuit 31 so that the value of the welding current Iw becomes a set value. On the other hand, when the power supply characteristic of the power supply circuit 31 is a constant voltage characteristic, the output of the power supply circuit 31 is controlled so that the value of the welding voltage Vw becomes a set value. More specifically, the power supply characteristic switching circuit SW receives a power supply characteristic switching signal Sw described later, a current error signal Ei, and a voltage error signal Ev. When the power supply characteristic switching signal Sw received by the power supply characteristic switching circuit SW is at a high level, the switch in the power supply characteristic switching circuit SW is connected to the a side in FIG. In this case, the power supply characteristic of the power supply circuit 31 is a constant voltage characteristic, and the power supply characteristic switching circuit SW sends the voltage error signal Ev to the power generation circuit MC as the error signal Ea. At this time, the power generation circuit MC performs control such that the value of the welding voltage Vw becomes a set value (that is, the above difference ΔVw becomes zero). On the other hand, when the power supply characteristic switching signal Sw received by the power supply characteristic switching circuit SW is at the low level, the switch in the power supply characteristic switching circuit SW is connected to the b side in FIG. In this case, the power supply characteristic of the power supply circuit 31 is a constant current characteristic, and the power supply characteristic switching circuit SW sends the current error signal Ei to the power generation circuit MC as the error signal Ea. At this time, the power generation circuit MC performs control such that the value of the welding current Iw becomes a set value (that is, the above-described difference ΔIw becomes zero).

  The arc generation current value storage circuit 33 stores the arc generation current value ir1. The set time storage circuit 34 stores the value of the set time Td as the first set time. Each value of the arc generation current value ir1 and the set time Td is input from the teach pendant 23, for example, and stored in each storage circuit via the operation control circuit 21.

  The current control circuit 32 is for setting the value of the welding current Iw flowing between the consumable electrode 15 and the base material W. The current control circuit 32 generates a current setting signal Ir for indicating the value of the welding current Iw based on at least one of the arc generation current value ir1 and the set time Td stored in each storage circuit. Then, the current control circuit 32 sends the generated current setting signal Ir to the power supply circuit 31. Current control circuit 32 receives arc state signal Asd and rotation angle signal Sθ. The current control circuit 32 sends a power supply characteristic switching signal Sw to the power supply characteristic switching circuit SW.

  The voltage control circuit 35 is for setting the value of the welding voltage Vw applied between the consumable electrode 15 and the base material W. The voltage control circuit 35 sends a voltage setting signal Vr for instructing the value of the welding voltage Vw to the power supply circuit 31 based on the set voltage value stored in a storage unit (not shown).

  The arc state detection circuit 36 detects whether the arc a1 between the consumable electrode 15 and the base material W is generated or disappears. In the present embodiment, the arc state detection circuit 36 receives the voltage detection signal Vd. The arc state detection circuit 36 determines whether or not the arc a1 is generated based on the value of the welding voltage Vw. The arc state detection circuit 36 determines that the arc a1 has disappeared when the welding voltage Vw is below a certain threshold value. The arc state detection circuit 36 determines that the arc a1 is generated when the welding voltage Vw exceeds the threshold value. The arc state detection circuit 36 sends an arc state signal Asd regarding whether or not the arc a1 is generated to the current control circuit 32.

  The feed path length control circuit 37 is for controlling the value of the feed path length La described above. In the present embodiment, the feed path length control circuit 37 sends the rotation speed signal Wc to the feed path length changing device 17. The rotation speed signal Wc indicates the rotation speed dθ (t) / dt of the motor 171 in the feed path length changing device 17.

  The feed control circuit 38 is for controlling the speed (feed speed Vf) at which the wire feeding device 16 feeds the consumable electrode 15. The feed control circuit 38 sends a feed speed control signal Fc for instructing the feed speed Vf to the wire feeder 16.

[Arc welding method using arc welding system A1]
Next, an arc welding method using the arc welding system A1 will be described with reference to FIG. FIG. 8 is a timing chart showing signals and the like in a steady welding state of the arc welding method of the present embodiment.

  8A shows the rotation angle θ (t) of the motor 171, FIG. 8B shows the amount of change V1 (t) of the feed path length La, and FIG. 8C shows the part surrounded by the welding torch 14 (Ra in FIG. 5). ) Of the consumable electrode 15 from the welding torch 14 toward the base material W, (d) is the welding voltage Vw, (e) is the current setting signal Ir, (f) is the welding current Iw, (g) is The change state of the current characteristic switching signal Sw is shown. Note that the amount of change V1 (t), speed V2 (t), feed speed Vf, and the like is positive in the direction from the welding torch 14 toward the base material W. The speed V2 (t) is the same as the speed of the portion of the consumable electrode 15 at the tip of the welding torch 14.

In the welding steady state of the present embodiment, the feed path length control circuit 37 sends a rotation speed signal Wc for instructing the rotation speed dθ (t) / dt of the motor 171 to a constant value 2π / T _W. Send to change device 17 (T _W is, for example, 10-20 ms). Thus, the motor 171
Rotates at a rotational speed dθ (t) / dt value 2π / T _W. The rotation angle θ (t) of the motor 171 shown in FIG. 8A is represented by the following equation (1).

θ (t) = (2π / T _w ) · (t− (n−1) T _w )
((N−1) T _w ≦ t <nT _w ) (n is an integer) (1)

As shown in FIG. 8A, when the motor 171 rotates, the change amount V1 (t) of the feed path length La changes as shown in FIG. 8B. The change amount V1 (t) is expressed by the following equation (2).

V1 (t) = Va · cos (θ (t)) (2)

In the equation (2), Va is an amplitude and is a constant value. Thus, the change amount V1 (t) changes periodically.

On the other hand, in the steady welding state of this embodiment, the feed control circuit 38 sends a feed speed control signal Fc for instructing the feed speed Vf to the wire feeder 16. Therefore, the consumable electrode 15 is fed from the wire feeding device 16 toward the welding torch 14 at a feeding speed Vf. Therefore, as shown in FIG. 8C, the speed V2 (t) of the portion surrounded by the welding torch 14 (Ra in FIG. 5) is obtained by adding the above-described V1 (t) and the feeding speed Vf. It becomes. That is, the speed V2 (t) is expressed by the following equation (3).

V2 (t) = Vf + Va · cos (θ (t)) (3)

As shown in FIG. 8 (c), the welding steady state of the present embodiment, the consumable electrode 15, so that the speed V2 (t) is a periodic function of the one period of the unit period T _W, fed . In fact, (1)
According to the equations (3) and (3), the relationship V2 (t + T _w ) = V2 (t) is satisfied. The unit period _Tw is composed of a forward feed period T _{W1 in} which the speed V2 (t) is a positive value and a reverse feed period T _{W2 in} which the speed V2 (t) is a negative value. In the forward feeding period T _W 1, the speed V2 (t) is a positive value, so the consumable electrode 15 is in a state of being fed from the welding torch 14 (a state of being fed forward). On the other hand, in the reverse feed period T _W 2, the speed V2 (t) is a negative value, so the consumable electrode 15 is in a state of being pulled up from the welding torch 14 (in a reverse feed state).

As described above, in the steady welding state of the present embodiment, the consumable electrode 15 is fed so that the speed V2 (t) becomes a periodic function of a constant period regardless of changes in the values of the welding current Iw and the welding voltage Vw. Be paid. Then, in a state where the consumable electrode 15 is fed in this way, an arc a1 is generated between the consumable electrode 15 and the base material W and a short circuit period Ts in which the consumable electrode 15 and the base material W are short-circuited. The arc generation period Ta is repeated. In each forward feed period T _W 1, the consumable electrode 15 is attached to the base material W.
Short circuit to Thereby, the short circuit period Ts starts. Further, in each backward feeding period T _W 2, the consumable electrode 15 is separated from the base material W, and the short-circuit state between the consumable electrode 15 and the base material W is released. Thereby, the arc generation period Ta starts. Hereinafter, the process from the start of welding will be specifically described.

  First, at the start of welding, a welding start signal St for starting welding is input to the teach pendant 23 with the welding torch 14 and the base material W separated to some extent. The input welding start signal St is sent from the teach pendant 23 to the feed path length control circuit 37, the feed control circuit 38, and the current control circuit 32 via the operation control circuit 21. Then, the feeding control circuit 38 sends a feeding control signal Fc to the wire feeding device 16, and the feeding path length control circuit 37 sends a rotation speed signal Wc to the feeding path length changing device 17, so that the consumable electrode 15 Is fed at a speed V2 (t) shown in FIG. Next, the welding torch 14 is moved closer to the base material W to shift to a steady welding state in which the short-circuit period Ts and the arc generation period Ta are repeatedly generated. In the welding steady state, the welding torch 14 moves at the robot moving speed VR along the welding progress direction in the in-plane direction of the base material W while keeping the distance from the base material W constant.

(1) Arc generation period Ta (time t0 to time t3)
The arc generation period Ta is a period for generating the arc a1 and heating the base material W. As shown in FIG. 8G, the power supply characteristic switching signal Sw is at a high level in almost the entire arc generation period Ta (time t1 to time t3). Therefore, from time t1 to time t3, the power supply characteristic of the power supply circuit 31 is a constant voltage characteristic. Further, as shown in FIG. 5C, at time t2, the state where the consumable electrode 15 is fed backward is changed from the state where it is fed forward.

(2) Short-circuit period Ts (time t3 to time t6)
<Time t3 to Time t4>
The short-circuit period Ts is a period for bringing the tip of the consumable electrode 15 into contact with the base material W and transferring a part of the consumable electrode 15 to the base material W. When the consumable electrode 15 is fed forward, the consumable electrode 15 and the base material W come into contact with each other and the consumable electrode 15 and the base material W are short-circuited at time t3. Thereby, as shown in FIG.8 (d), the value of the welding voltage Vw falls rapidly at the time t3. Based on the decrease in the value of the welding voltage Vw, the arc state detection circuit 36 determines that the arc a1 has disappeared. Then, the arc state detection circuit 36 sends an arc state signal Asd indicating that the arc a1 is extinguished to the current control circuit 32. On the other hand, from time t3 to time t4, the consumable electrode 15 is melted by Joule heat, and the contact area between the consumable electrode 15 and the base material W gradually increases. Thereby, the resistance value of the welding current Iw flowing from the consumable electrode 15 to the base material W decreases, and the value of the welding current Iw gradually increases. As shown in FIG. 8C, the consumable electrode 15 is fed forward from time t3 to time 4. However, from time t3 to time t4, the consumable electrode 15 is difficult to buckle because it is melted and softened as described above.

<Time t4 to Time t6>
As shown in FIG. 8G, the current control circuit 32 changes the power supply characteristic switching signal Sw from High level to Low level at time t4. Thereby, the power supply characteristic of the power supply circuit 31 changes to a constant current characteristic. On the other hand, as shown in FIG. 5E, the current control circuit 32 generates a current control signal Ir for energizing the welding current Iw with a relatively small arc generation current value ir1 in the power supply circuit 31 (in this embodiment, Current error calculation circuit EI). Therefore, as shown in FIG. 5F, the welding current Iw flows at the arc generation current value ir1 from time t4. Arc generation current value ir1 is, for example, 30 to 60 A and is relatively small. The method for determining time t4 will be described later. Then, as shown in FIG. 5C, at time t5, the consumable electrode 15 changes from the forward feed state to the reverse feed state.

(3) Arc generation period Ta (from time t6)
At time t6, the consumable electrode 15 and the base material W are separated from each other, and an arc a1 is generated. Since welding current Iw flows at a relatively small arc generation current value ir1 at time t6, it is possible to suppress the occurrence of spatter that may occur when arc a1 occurs. As shown in FIG. 8D, at time t6, the value of the welding voltage Vw increases rapidly due to the generation of the arc a1. Based on the increase in the welding voltage Vw, the arc state detection circuit 36 determines that the arc a1 has occurred. Then, the arc state detection circuit 36 sends an arc state signal Asd indicating that the arc a1 is generated to the current control circuit 32. The current control circuit 32 changes the power supply characteristic switching signal Sw from the Low level to the High level at a time t7 when a certain time has elapsed from the time when the arc state signal Asd indicating that the arc a1 is generated is received. Thereby, the power supply characteristic of the power supply circuit 31 changes to a constant voltage characteristic. Then, as shown in FIG. 5F, the welding current Iw rises to a value sufficient to heat the base material W, and the same process as described above is performed again.

  In the above steps, the time t4 is determined by the current control circuit 32. An example of a method for determining time t4 is as follows.

  First, the current control circuit 32 generates the second short circuit opening after the time t0 based on the first short circuit opening time information regarding the first short circuit opening time (time t0 in this embodiment) when the short circuit is opened. The second short-circuit opening time information related to the short-circuit opening time (time t6 in this embodiment) is obtained. The first short circuit opening time information includes, for example, the time t0 when the short circuit is opened, the rotation angle θ (t) at the time t0, the change amount V1 (t) at the time t0, and the speed V2 (t) at the time t0. The value of. In the present embodiment, the first short circuit opening time information is the rotation angle θ (t) at time t0. Similarly, the second short-circuit opening time information includes, for example, the time t6 when the short-circuit opening occurs, the rotation angle θ (t) at the time t6, the change amount V1 (t) at the time t6, and the speed V2 ( The value of t). In the present embodiment, the second short-circuit opening time information is the rotation angle θ (t) at time t6. That is, when the short circuit is eliminated and the arc a1 is generated at time t0, the current control circuit 32 receives the arc state signal Asd indicating that the arc a1 is generated from the arc state detection circuit 36. Then, the current control circuit 32 recognizes that the rotation angle θ (t) at time t0, which is information at the time of opening the first short circuit, is θ3 based on the rotation angle signal Sθ sent from the feeding path length changing device 17. To do. In the present embodiment, the speed V2 (t) changes periodically. Therefore, the current control circuit 32 predicts that the rotation angle θ (t) (second short-circuit open time information) at the time when the short circuit is opened again and the arc a1 is generated is θ3.

  Next, the current control circuit 32 predicts that the rotation angle θ (t), which is the second short-circuit opening time information, is θ3, and then the time when the short circuit is opened and the arc a1 is generated after time t0. Is predicted to be time t6. Then, the current control circuit 32 determines the time before the set time Td from the time t6 as the time t4. The set time Td is, for example, 100 to 500 μs.

  Next, the effect of this embodiment is demonstrated.

  In the arc welding apparatus 1, the feed path length La shown in FIG. 6 is changed. The change amount V1 (t) of the feed path length La is changed by the feed path length changing device 17 having the cam mechanism 173. Therefore, the change amount V1 (t) can be changed only by rotating the motor 171 forward. As a result, the forward feeding and the backward feeding of the consumable electrode 15 are periodically repeated as shown in FIG. 8C while keeping the feeding speed Fw of the consumable electrode 15 by the wire feeding device 16 constant. Can do. Therefore, it is possible to feed the consumable electrode 15 with more responsiveness than when the consumable electrode 15 is fed forward and backward by rotating the feed motor 161 of the wire feeder 16 forward and backward. it can. Therefore, even when the forward feeding and the backward feeding of the consumable electrode 15 are switched at high speed, the consumable electrode 15 can be fed with good responsiveness. As a result, stable welding can be performed.

  Further, in the arc welding apparatus 1, the feeding path length changing device 17 reciprocates the conduit cable 19 with respect to the welding torch 14. Therefore, in the arc welding apparatus 1, the consumable electrode 15 can be fed forward and backward while keeping the distance between the welding torch 14 and the base material W constant in a steady welding state. If the distance between the welding torch 14 and the base material W can be kept constant, the distance between the opening 143 and the base material W in the nozzle 142 is also constant, so that the supply state of the shield gas SG changes in the steady welding state. Hard to do. This is advantageous for stable welding.

  In the present embodiment, as shown in FIG. 8C, in the steady welding state of the present embodiment, the speed V2 (t) is a constant cycle regardless of changes in the values of the welding current Iw and the welding voltage Vw. The consumable electrode 15 is fed so as to have a periodic function of And the short circuit period Ts and the arc generation period Ta are repeated so as to follow the speed V2 (t). In such a configuration, since the speed V2 (t) is not changed based on the change in the welding current Iw or the welding voltage Vw, there is a merit that the problem of the response delay of the supply of the consumable electrode 15 does not occur in the first place. is there. Further, when the speed V2 (t) is a periodic function having a constant period, the short-circuit period Ts and the arc generation period Ta can be repeated at a substantially constant period. Therefore, stable welding can be performed.

  In the present embodiment, by utilizing the fact that the speed V2 (t) is a periodic function having a constant period, it is predicted that the time at which the short circuit is opened and the arc a1 occurs after the time t0 is the time t6. doing. Then, the welding current Iw is decreased at time t4 before the set time Td from time t6. By determining the time at which the welding current Iw is reduced in this way, the value of the welding current Iw can be reliably reduced before the short circuit is opened at time t6. This is suitable for suppressing the occurrence of spatter when the arc a1 is generated.

  Note that it is not necessary to determine the time t4 as described above and decrease the value of the welding current Iw. The welding current Iw may be decreased after the consumable electrode 15 and the base material W are short-circuited and before time t5 (time when the consumable electrode 15 changes from the forward feeding state to the backward feeding state). . The opening of the short circuit is considered to occur after a certain period of time has elapsed after the consumable electrode 15 starts to be retracted. Then, also by reducing the welding current Iw before time t5, the value of the welding current Iw can be reliably reduced before the short circuit is opened.

  The mount 175 of the feeding path length changing device 17 may be fixed to the covering tube 192 instead of the coil liner 191.

  Next, a second embodiment of the present invention will be described with reference to FIGS. In these drawings, the same or similar elements as those in the above embodiment are denoted by the same reference numerals as those in the above embodiment.

  FIG. 9 is a block diagram showing details of the robot control device and the power supply device in the arc welding system according to the present embodiment.

  The arc welding system A2 according to the present embodiment includes an arc welding apparatus 1, a robot control apparatus 2, and a power supply apparatus 3. Since the arc welding apparatus 1 and the robot control apparatus 2 are the same as those in the above-described embodiment, description thereof is omitted. The arc welding system A2 is different from the above-described arc welding system A1 in that the power supply device 3 further includes a set time storage circuit 391, 392 and a short-circuit period current value storage circuit 393, and the other points are the same. is there.

  The set time storage circuit 391 stores the value of the set time Tc1, which is the second set time, and the set time storage circuit 392 stores the set time Tc2. The short-circuit period current value storage circuit 393 stores the short-circuit period current value ir2. The values of the set times Tc1 and Tc2 and the short-circuit period current value ir2 are input from the teach pendant 23 and stored in the storage circuits via the operation control circuit 21, for example.

  Next, with respect to the arc welding method using the arc welding system A2, differences from the above embodiment will be described with reference to FIG.

(1) Arc generation period Ta (time t0 to time t3)
<Time t0 to Time ts1>
The arc generation period Ta is a period for generating the arc a1 and heating the base material W. In the present embodiment, as shown in FIG. 10G, the power supply characteristic switching signal Sw is at a high level from time t1 to time ts1 in the arc generation period Ta. Therefore, from time t1 to time ts1, the power supply characteristic of the power supply circuit 31 is a constant voltage characteristic. Further, as shown in FIG. 10C, at time t2, the state is changed from the state where the consumable electrode 15 is fed backward to the state where it is fed forward.

<Time ts1 to time t3>
As shown in FIG. 10G, the current control circuit 32 changes the power supply characteristic switching signal Sw from the high level to the low level at time ts1. Thereby, the power supply characteristic of the power supply circuit 31 changes to a constant current characteristic. On the other hand, as shown in FIG. 5E, the current control circuit 32 generates a current setting signal Ir for energizing the welding current Iw with a relatively small arc generation current value ir1 in the power supply circuit 31 (in this embodiment, Current error calculation circuit EI). Therefore, as shown in FIG. 5F, the welding current Iw flows at the arc generation current value ir1 from time ts1. Arc generation current value ir1 is, for example, 30 to 60 A and is relatively small. A method for determining time ts1 will be described later.

(2) Short-circuit period Ts (time t3 to time t6)
<Time t3 to Time t4>
When the consumable electrode 15 is fed forward, the consumable electrode 15 and the base material W come into contact with each other and the consumable electrode 15 and the base material W are short-circuited at time t3. Since the welding current Iw flows at a relatively small arc generation current value ir1 at time t3, it is possible to suppress the occurrence of spatter that may occur when the consumable electrode 15 and the base material W are short-circuited. As shown in FIG. 10 (d), at time t3, the consumable electrode 15 and the base material W are short-circuited, so that the value of the welding voltage Vw rapidly decreases. Based on the decrease in the value of the welding voltage Vw, the arc state detection circuit 36 determines that the arc a1 has disappeared. Then, the arc state detection circuit 36 sends an arc state signal Asd indicating that the arc a1 is extinguished to the current control circuit 32. As shown in FIG. 5E, the current control circuit 32 short-circuits the welding current Iw at the time ts2 when the set time Tc2 has elapsed from the time when the arc state signal Asd indicating that the arc a1 is extinguished. A current setting signal Ir for flowing at the period current value ir2 is sent to the power supply circuit 31. As a result, the welding current Iw increases and flows at the short-circuit current value ir2 as shown in FIG. The short-circuit period current value ir2 is larger than the arc generation current value ir1, and is, for example, 325 to 375A. From time ts2 to time t4, the consumable electrode 15 is melted by Joule heat, and the contact area between the consumable electrode 15 and the base material W gradually increases. Thereby, the resistance value of the welding current Iw flowing from the consumable electrode 15 to the base material W decreases, and the value of the welding current Iw gradually increases. As shown in FIG. 10C, the consumable electrode 15 is fed forward from time t3 to time 4. However, from time t3 to time t4, the consumable electrode 15 is difficult to buckle because it is melted and softened as described above.

  After time t4, a process similar to the process described in the above embodiment, such as reducing the value of the welding current Iw again, is performed.

  In the above steps, the time ts1 is determined by the current control circuit 32. An example of a method for determining the time ts1 is as follows.

  First, the current control circuit 32 generates a second short-circuit after the time t0 ′ based on the first short-circuit occurrence information related to the first short-circuit occurrence time (in this embodiment, time t0 ′) when the short-circuit occurs. The second short-circuit occurrence time information regarding the time (time t3 in this embodiment) is obtained. The first short-circuit occurrence information includes, for example, the time t0 ′ when the short-circuit occurs, the rotation angle θ (t) at the time t0 ′, the change amount V1 (t) at the time t0 ′, and the speed V2 ( The value of t). In the present embodiment, the first short-circuit occurrence time information is the rotation angle θ (t) at time t0 ′. Similarly, the second short-circuit occurrence time information includes, for example, time t3 when the short-circuit occurs, rotation angle θ (t) at time t3, change amount V1 (t) at time t3, and speed V2 (t) at time t3. The value of. In the present embodiment, the second short-circuit occurrence time information is the rotation angle θ (t) at time t3. That is, when a short circuit occurs at time t0 ', current control circuit 32 receives arc state signal Asd indicating that arc a1 has disappeared from arc state detection circuit 36. Then, based on the rotation angle signal Sθ sent from the feed path length changing device 17, the current control circuit 32 determines that the rotation angle θ (t) at time t0 ′, which is information when the first short circuit occurs, is θ4. recognize. In the present embodiment, the speed V2 (t) changes periodically. Therefore, the current control circuit 32 predicts that the rotation angle θ (t) (second short circuit occurrence information) at the time when the short circuit occurs again is θ4.

  Next, the current control circuit 32 predicts that the rotation angle θ (t), which is the second short-circuit occurrence information, is θ4, and the time when the short-circuit occurs after the time t0 ′ is the time t3. Predict. Then, the current control circuit 32 determines the time before the set time Tc1 from the time t3 as the time ts1. The set time Tc1 is, for example, 50 to 200 μs.

  Next, the effect of this embodiment is demonstrated.

  In the present embodiment, using the fact that the speed V2 (t) is a periodic function having a constant period, the time when the short circuit occurs after the time t0 'is predicted to be the time t3. The welding current Iw is decreased at time ts1 before the set time Tc1 from time t3. By determining the time for reducing the welding current Iw in this manner, the value of the welding current Iw can be reliably reduced before a short circuit occurs at the time t3. This is suitable for suppressing the occurrence of spatter when a short circuit occurs.

  Also in this embodiment, there are advantages similar to those described in the first embodiment. In this embodiment, the welding current Iw is decreased to the current value iw1 at both the time ts1 and the time t4. However, even if the welding current Iw is decreased to a different value at the time ts1 and t4. Good. At time ts1, the welding current Iw is reduced based on the prediction that the rotation angle θ (t), which is the second short-circuit occurrence information, is θ4, and thereafter, the rotation angle θ, which is the first second short-circuit elimination information. The welding current Iw may be decreased again before time t5 when the supply of the consumable electrode 15 changes from forward feed to backward feed without being based on (t). As described above, it is preferable to increase the welding current Iw after decreasing the welding current Iw at the time ts1, and then decrease the welding current Iw again at the time t4. However, it is possible to employ a configuration in which the welding current Iw is decreased only at the time ts1. good.

  The scope of the present invention is not limited to the embodiment described above. The specific configuration of each part of the present invention can be changed in various ways.

A1, A2 Arc welding system 1 Arc welding device 11 Base member 12 Arm 13 Motor 14 Welding torch 141 Contact tip 142 Nozzle 15 Consumable electrode 16 Wire feeding device 161 Feeding motor 17 Feeding path length changing device 171 Motor 172 Eccentric shaft 173 Cam mechanism 174a, 174b Bearing 175 Mount 176 Bush 177 Shaft 19 Conduit cable 191 Coil liner 192 Covered tube 2 Robot control device 21 Operation control circuit 23 Teach pendant 3 Power supply device 31 Power supply circuit 32 Current control circuit 33 Arc generation current value storage circuit 34 set time storage circuit 35 voltage control circuit 36 arc state detection circuit 37 feed path length control circuit 38 feed control circuits 391, 392 set time storage circuit 393 short circuit period current value storage circuit sd Arc state signal Ea Error signal EI Current error calculation circuit Ei Current error signal EV Voltage error calculation circuit Ev Voltage error signal Fc Feed speed control signal Fw Feed speed ID Current detection circuit Id Current detection signal Ir Current setting signal Iw Welding current La Feeding path length MC Power generation circuit Ms Operation control signal Sw Power supply characteristic switching signal Sθ Rotation angle signal St Welding start signal V1 (t) Change amount V2 (t) Speed VD Voltage detection circuit Vd Voltage detection signal Vr Voltage setting signal VR Robot moving speed Vw Welding voltage W Base material Wc Rotational speed signal θ (t) Rotation angle

Claims (1)

The portion of the consumable electrode surrounded by the welding torch is composed of a forward feeding period in which the speed from the welding torch to the base material is a positive value and a backward feeding period in which the speed is a negative value. An arc welding method that repeats a unit period,
Feeding the consumable electrode as a function of the speed as a periodic function in which one period is the unit period;
A step of short-circuiting the consumable electrode to the base material at a certain point in each of the forward feeding periods;
Opening a short circuit between the consumable electrode and the base material at a certain point in each of the backward feeding periods,
As a function of time t represented the speed V2 (t), when the above unit period a constant value Tw, meets the relationship of V2 (t) = V2 (t + Tw),
A short circuit between the consumable electrode and the base material occurs after the first short-circuit occurrence time based on the first short-circuit occurrence time information on the first short-circuit occurrence time when the short-circuit between the consumable electrode and the base material occurs. Obtaining second short-circuit occurrence information related to the second short-circuit occurrence time;
A step of reducing a value of a welding current flowing from the consumable electrode to the base material at a time that is a set time before the second short-circuit occurrence time based on the second short-circuit occurrence time information. Method.

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