JP2017100179A - Arc welding control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement good arc starting even in a case that slag is deposited on a welding wire tip and a preform surface in a forward and reverse feeding arc welding.SOLUTION: In an arc welding control method in which, upon starting welding, a forward and reverse feeding control of exchanging a feeding speed Fw for a forward feeding period and a reverse feeding period alternatively is implemented during the initial period Ti from the welding wire feeding start point t1 until the welding current conduction start point t7, a welding torch Lt is vibrated in the direction of the plane of the preform surface during the initial period Ti. After finishing the initial period Ti, the feeding speed Fw is exchanged to the reverse feeding period, and the reverse feeding period is continued until the time 10 when the welding torch reaches the welding starting point. As the welding wire tip is vibrated by vibration of the welding torch so as to stroke the preform surface, the slag can be removed to implement good arc starting.SELECTED DRAWING: Figure 2

Description

  In the present invention, when welding is started, during the initial period from the welding wire feed start time to the welding current energization start time, the feed speed is alternately switched between the forward feed period and the reverse feed period. The present invention relates to an arc welding control method for performing feed control.

  In general consumable electrode arc welding, a welding wire that is a consumable electrode is fed at a constant speed, and an arc is generated between the welding wire and a base material to perform welding. In the consumable electrode type arc welding, the welding wire and the base material are often in a welding state in which a short circuit period and an arc period are alternately repeated.

  In order to further improve the welding quality, arc welding that performs welding by generating a short-circuit period and an arc period by performing forward / reverse feed control that alternately switches the feed speed of the welding wire between the forward feed period and the reverse feed period. A control method is used. Here, forward feeding is to feed the welding wire in a direction approaching the base material, and reverse feeding is to feed the welding wire in a direction opposite to the normal feeding and in a direction in which the welding wire moves away from the base material. .

  In forward / reverse feed control arc welding, the forward feed period and the reverse feed period of the feed speed are switched at a high speed with a frequency of about 100 Hz. In order to switch the direction of the feeding speed at high speed, it is necessary to use a feeding motor having a good transient characteristic. In general, a motor with good transient characteristics has a relatively small maximum torque.

  By the way, in consumable electrode arc welding, an insulator called slag may be attached to the tip of the welding wire at the end of welding. Slag is produced by a chemical reaction of components contained in the welding wire. The adhesion state of the slag varies depending on welding conditions such as the type of welding wire, the average welding current value, and the welding posture. When the next arc start is performed with the slag adhering to the tip of the welding wire, even if the welding wire comes into contact with the base material, the slag is an insulator, so that no arc is generated, resulting in poor arc start. It becomes. The same applies to arc welding by forward / reverse feed control.

  Patent Document 1 discloses a method for improving arc start failure due to slag in forward / reverse feed control arc welding. In the invention of Patent Document 1, forward / reverse feed control is performed even during an initial period from the start of welding wire feed at the start of welding until the welding current is energized. Thus, when the welding current does not flow even if the welding wire tip contacts the base material because the slag is adhered to the tip of the welding wire, the collision between the tip of the welding wire and the base material is repeated. In the invention of Patent Document 1, an arc is generated by removing the slag at the tip of the welding wire by repeating this collision.

Japanese Patent No. 52012266

  The method of Patent Document 1 can prevent arc start failure when slag is adhered to the tip of the welding wire. However, the slag may adhere not only to the tip of the welding wire but also to the base material side. This is the case where the current welding is started from the top of the previously welded bead. In such a case, it is because the slag has adhered to the surface of the weld bead. In the method of Patent Document 1, it is difficult to remove the slag adhering to the base material side, which causes a problem of arc start failure.

  Therefore, the present invention provides an arc welding control method that can always perform a good arc start even in the case of slag adhering to the tip of the welding wire and the surface of the base metal in forward and reverse feed arc welding. With the goal.

In order to solve the above-described problems, the invention of claim 1
When starting welding, during the initial period from the welding wire feed start time to the welding current energization start time, forward / reverse feed control is performed to alternately switch the feed speed between the forward feed period and the reverse feed period. In the arc welding control method to be performed,
During the initial period, the welding torch is vibrated in the plane direction of the base material surface,
An arc welding control method characterized by the above.

The invention of claim 2 moves the welding torch to the taught welding start position after the end of the initial period.
The arc welding control method according to claim 1, wherein:

The invention of claim 3 switches the feed speed to the reverse feed period after the end of the initial period, and continues the reverse feed period until the welding torch reaches the welding start position.
The arc welding control method according to claim 2, wherein:

According to a fourth aspect of the present invention, the welding current is an average value of the welding current during the steady welding period during the period from when the arc is generated after the initial period ends until the welding torch reaches the welding start position. Less than
The arc welding control method according to claim 3.

  According to the present invention, during the initial period, by performing forward / reverse feed control of the feed speed and vibration control of the welding torch, the slag at the tip of the welding wire is removed, and the tip of the welding wire is placed on the surface of the base material. It can be moved to a place where no slag is attached. For this reason, in this invention, in forward / reverse feed arc welding, even if the slag adheres to the tip of the welding wire and the surface of the base material, a good arc start can always be performed.

It is a block diagram of the welding power supply for implementing the arc welding control method which concerns on Embodiment 1 of this invention. It is a timing chart of each signal at the time of the welding start in the welding power supply of FIG. 1 which shows the arc welding control method which concerns on Embodiment 1 of this invention.

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

[Embodiment 1]
FIG. 1 is a block diagram of a welding power source for carrying out an arc welding control method according to Embodiment 1 of the present invention. Hereinafter, each block will be described with reference to FIG.

  The power supply main circuit PM receives a commercial power supply (not shown) such as a three-phase 200V, performs output control by inverter control or the like according to a drive signal Dv described later, and outputs an output voltage E. Although not shown, the power supply main circuit PM is driven by a primary rectifier that rectifies commercial power, a smoothing capacitor that smoothes the rectified direct current, and the drive signal Dv that converts the smoothed direct current to high-frequency alternating current. An inverter circuit, a high-frequency transformer that steps down the high-frequency alternating current to a voltage value suitable for welding, and a secondary rectifier that rectifies the stepped-down high-frequency alternating current into direct current.

  The reactor WL smoothes the output voltage E. The inductance value of the reactor WL is, for example, 200 μH.

  The feed motor WM receives a feed control signal Fc, which will be described later, and alternately switches between a forward feed period and a reverse feed period and feeds the welding wire 1 at a feed speed Fw. A motor with good transient characteristics is used as the feed motor WM. In order to increase the rate of change of the feeding speed Fw of the welding wire 1 and the reversal of the feeding direction, the feeding motor WM may be installed near the tip of the welding torch 4. In some cases, two feed motors WM are used to form a push-pull feed system. The feed motor WM is mounted on the robot.

  The welding wire 1 is fed through the welding torch 4 by the rotation of the feeding roll 5 coupled to the feeding motor WM, and an arc 3 is generated between the welding wire 1 and the base material 2. A welding voltage Vw is applied between the power feed tip (not shown) in the welding torch 4 and the base material 2, and a welding current Iw is conducted. The welding torch 4 is held by a robot.

  The welding start circuit ST outputs a welding start signal St that becomes High level when starting welding. The welding start circuit ST is a switch that is turned on when welding is started, a programmable logic controller (PLC) that controls the welding process, and the like.

The robot controller RC receives the welding start signal St and the initial period timer signal Sti, which will be described later, as an input, performs the following processing, and sends an operation control signal Mc for moving the robot RM to a plurality of servo motors ( The welding start position coincidence signal Wp which becomes a High level when the start signal On for starting the welding power source and the position of the welding torch 4 coincide with the taught welding start position is outputted.
1) When the welding start signal St changes to a high level (welding start), an operation control signal Mc is output. Thereby, the robot RM is moved and the welding torch 4 is moved to the welding start position.
2) When the welding torch 4 reaches the welding start position, the activation signal On is set to High level (activation) and output. At the same time, the robot RM is vibrated around the welding start position, and the welding torch 4 is vibrated toward the surface of the base material 2.
3) When the initial period timer signal Sti changes from High level to Low level, the vibration of the welding torch 4 is stopped. At the same time, the welding torch 4 is moved to the welding start position.
4) When the welding torch 4 reaches the welding start position, the welding start position coincidence signal Wp is set to High level (coincidence) for a short time and output.
5) Thereafter, the welding torch 4 is moved along the taught weld line.

  The robot RM is equipped with a feed motor WM and a welding torch 4 and moves the welding torch 4 in accordance with the operation control signal Mc.

  The output voltage setting circuit ER outputs a predetermined output voltage setting signal Er. The output voltage detection circuit ED detects and smoothes the output voltage E and outputs an output voltage detection signal Ed.

  The voltage error amplification circuit EV receives the output voltage setting signal Er and the output voltage detection signal Ed, and amplifies an error between the output voltage setting signal Er (+) and the output voltage detection signal Ed (−). The voltage error amplification signal Ev is output. By this circuit, the welding power source is controlled at a constant voltage.

  The initial current setting circuit IIR outputs a predetermined initial current setting signal Iir. The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id.

  The current error amplifier circuit EI receives the initial current setting signal Iir and the current detection signal Id as input and amplifies an error between the initial current setting signal Iir (+) and the current detection signal Id (−) to obtain a current. An error amplification signal Ei is output. This circuit controls the constant current of the welding power source.

  The current energization determination circuit CD receives the current detection signal Id as described above, and determines that the welding current Iw is energized when this value is equal to or greater than a threshold value (about 10 A), and the current energization determination becomes a high level. The signal Cd is output.

  The power supply characteristic switching circuit SW receives the current error amplification signal Ei, the voltage error amplification signal Ev, the activation signal On and the welding start position coincidence signal Wp, and the activation signal On is at a high level (activation). The current error amplification signal Ei is output as the error amplification signal Ea during the period from when the welding start position coincidence signal Wp changes to the high level (coincidence) until it changes to the voltage error amplification signal Ev during the other periods. Is output as an error amplification signal Ea.

  The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The short circuit determination circuit SD receives the voltage detection signal Vd as described above, and when this value is less than the short circuit determination value (about 10 V), it determines that it is a short circuit period and becomes a high level, and when it is above, it is an arc period. And a short circuit determination signal Sd that is at a low level is output.

  The drive circuit DV receives the error amplification signal Ea and the activation signal On, and performs PWM modulation control based on the error amplification signal Ea when the activation signal On is at a high level (activation). A drive signal Dv for driving the inverter circuit in the circuit PM is output.

  The initial period timer circuit STI receives the activation signal On and the current energization determination signal Cd as described above, and at the time when the activation signal On changes to the high level (activation), the current energization determination signal Cd becomes the high level. The timer signal Sti is output for the initial period that becomes Low level at the time of changing to (energization).

  The steady normal transmission peak value setting circuit FSCR outputs a predetermined steady normal transmission peak value setting signal Fscr. The steady reverse feed peak value setting circuit FRCR outputs a predetermined steady reverse feed peak value setting signal Fcrr.

  The steady welding period feed speed setting circuit FCR receives the short circuit determination signal Sd, the normal forward peak value setting signal Fscr and the steady reverse peak value setting signal Frcr as input, and is based on the short circuit determination signal Sd. The trapezoid formed from the steady forward feed peak value Fsc determined by the steady forward feed peak value setting signal Frcr and the steady forward feed peak value Frc determined by the steady forward feed peak value setting signal Fscr is switched between the forward feed period and the reverse feed period. A wave steady welding period feed speed setting signal Fcr is output. The steady welding period feed speed setting signal Fcr will be described in detail with reference to FIG.

  The initial forward feed peak value setting circuit FSIR outputs a predetermined initial forward feed peak value setting signal Fsir. The initial reverse feed peak value setting circuit FRIR outputs a predetermined initial reverse feed peak value setting signal Frir.

  The initial frequency setting circuit SIR outputs a predetermined initial frequency setting signal Sir for setting a frequency for switching between the forward transmission period and the reverse transmission period in the initial period. The initial time ratio setting circuit DIR outputs an initial time ratio setting signal Dir for setting the time ratio between the forward transmission period and the reverse transmission period in the initial period. Time ratio = (time length of forward feed period) / (forward feed period + time length of reverse feed period). That is, it is the time ratio of the normal transmission period occupying one cycle determined by the reciprocal 1 / Sir of the initial frequency setting signal Sir. Therefore, the time length of the forward transmission period = Dir / Sir, and the time length of the reverse transmission period = (1−Dir) / Sir.

  The initial period feed speed setting circuit FIR receives the initial forward peak value setting signal Fsir, the initial reverse peak value setting signal Fir, the initial frequency setting signal Sir, and the initial time ratio setting signal Dir. Based on the initial frequency setting signal Sir and the initial time ratio setting signal Dir, the forward feed period and the reverse feed period are determined, the initial forward feed peak value setting signal Fsir determines the initial forward feed peak value Fsi, and the initial reverse feed peak value. A trapezoidal wave initial period feed speed setting signal Fir whose initial reverse feed peak value Fri is determined by the setting signal Fir is output. The initial period feeding speed setting signal Fir will be described in detail with reference to FIG.

  The feed speed setting circuit FR receives the above-described steady welding period feed speed setting signal Fcr, the above-described initial period feed speed setting signal Fir, and the above-described initial period timer signal Sti, and the initial period timer signal Sti is at a high level. The initial period feed speed setting signal Fir is output as the feed speed setting signal Fr during the initial period, and the steady welding period feed speed setting signal Fcr is output during the steady welding period when the initial period timer signal Sti is at the low level. It is output as a feed speed setting signal Fr. The feed speed setting signal Fr will be described in detail with reference to FIG.

  The feed control circuit FC receives the start signal On and the feed speed setting signal Fr as an input, and when the start signal On is at a high level (start), the feed control circuit FC corresponds to the feed speed setting signal Fr. A feed control signal Fc for feeding the welding wire 1 at the speed Fw is output to the feed motor WM.

  FIG. 2 is a timing chart of each signal at the start of welding in the welding power source of FIG. 1, showing the arc welding control method according to the first embodiment of the present invention. (A) shows the time change of the start signal On, (B) shows the time change of the feeding speed Fw, (C) shows the time change of the welding current Iw, (D) ) Shows the time change of the welding voltage Vw, FIG. 5E shows the time change of the current application determination signal Cd, FIG. 8F shows the time change of the short circuit determination signal Sd, and FIG. The time change of the initial period timer signal Sti is shown, and FIG. 9H shows the time change of the welding torch locus Lt which is the distance between the position of the welding torch representing the vibration of the welding torch and the welding start position. Hereinafter, the operation of each signal at the start of welding will be described with reference to FIG.

  First, an operation before time t1 (not shown) will be described. When the operator turns on a switch for starting welding, the welding start signal St changes to a high level (welding start). In response to this, the robot RM starts moving, and the welding torch 4 moves to the welding start position taught. When the welding torch 4 reaches the welding start position at time t1, the movement of the welding torch 4 stops. At the same time, the activation signal On changes to a high level (activation) as shown in FIG.

  As shown in FIG. 5B, the feed speed Fw is a forward feed period above 0 and a reverse feed period below. The feed speed Fw is controlled by the initial period feed speed setting signal Fir during the initial period Ti, and the forward feed period and the reverse feed period are switched at a predetermined frequency. On the other hand, the feeding speed Fw is controlled by the steady welding period feeding speed setting signal Fcr during the steady welding period Tc, and the normal feeding period and the reverse feeding period are switched in synchronization with the short circuit period and the arc period. The feeding speed Fw changes in a trapezoidal wave shape. The average value of the feeding speed Fw is a positive value, and the welding wire 1 is normally fed on average.

  At time t1, the tip of the welding wire 1 and the surface of the base material 2 are separated by about 2 to 15 mm. The period from time t1 when the activation signal On shown in FIG. 5A becomes High level (activation) to time t7 when the current energization determination signal Cd shown in FIG. 5E becomes High level (energization) is the initial period Ti. It becomes. A period from time t7 to time t10 when the welding torch 4 returns to the welding start position is a transition period. The period after time t10 is the steady welding period Tc.

[Operation in Initial Period Ti at Times t1 to t7]
At time t1, when the activation signal On changes to the high level (activation) as shown in FIG. 5A, the initial period timer signal Sti changes to the high level as shown in FIG. Period Ti starts. At the same time, since the welding power source is activated, the welding voltage Vw becomes the no-load voltage value of the maximum output voltage value as shown in FIG. Since the tip of the welding wire 1 and the surface of the base material 2 are separated from each other, the welding current Iw is not applied as shown in FIG. At the same time, feeding of the welding wire 1 is started as shown in FIG.

  As shown in FIG. 5B, for the feed speed Fw during the initial period Ti, forward / reverse feed control that alternately repeats the forward feed period and the reverse feed period at a predetermined initial frequency Si [Hz]. Is done. The initial frequency Si is set by an initial frequency setting signal Sir. The normal transmission period and the reverse transmission period in the initial period are set by the initial frequency setting signal Sir and the initial time ratio setting signal Dir. The feeding speed Fw during the normal feeding period from time t1 to t2 is accelerated from 0 at a predetermined rate of change and is maintained when a predetermined initial forward peak value Fsi is reached. Decrease to 0 at the rate of change. The initial forward feed peak value Fsi is set by the initial forward feed peak value setting signal Fsir. The feed speed Fw during the reverse feed period from the time t2 to the time t3 is accelerated at a predetermined change rate from 0, and when the initial reverse feed peak value Fri, which is a predetermined negative value, is reached, the value is maintained. When the period elapses, it decelerates to 0 at a predetermined rate of change. The initial reverse peak value Fri is set by the initial reverse peak value setting signal Frir. The period from time t1 to t3 is one cycle, which is the reciprocal 1 / Si of the initial frequency Si.

  The distance between the tip of the welding wire and the base metal gradually decreases during the forward feed period from time t1 to t2, and gradually increases during the reverse feed period from time t2 to t3. However, the distance at time t3 is shorter than the distance at time t1. This is because the waveform parameter of the feeding speed is adjusted so that the average value of the feeding speed Fw per cycle becomes a positive value. The average value of the feeding speed Fw during the initial period Ti will be referred to as an average initial feeding speed Fi. The period from time t3 to t4 is the same as the period from time t1 to t3.

  Further, during the initial period Ti, the welding torch 4 vibrates at a predetermined frequency and a predetermined amplitude with the welding start position as the center. For this reason, as shown in FIG. 5H, the welding torch trajectory Lt, which is the distance between the position of the welding torch 4 and the welding start position, changes in a positive and negative sine wave shape. This figure shows the case where the welding torch 4 is vibrating in a linear reciprocating motion centered on the welding start position. In addition, it may vibrate so as to rotate on a circumference centered on the welding start position. The vibration direction is the surface direction of the base material 2. That is, it is the direction of movement so as to stroke the surface of the base material in a state where the tip of the welding wire is in contact with the surface of the base material. The absolute value of the welding torch trajectory Lt indicates the distance from the welding start position, and the positive and negative signs indicate directions such as left and right. The vibration frequency of the welding torch 4 is set lower than the frequency of the forward / reverse feed control of the welding wire 1.

  As shown in FIG. 4B, when the tip of the welding wire 1 comes into contact (collision) with the surface of the base material 2 at time 41 during the forward feed period from time t4 to time t5, the distance between the tip of the welding wire and the base material. = 0. However, since slag adheres to the tip of the welding wire 1 and the surface of the base material 2, a non-conductive contact state is established. For this reason, the welding current Iw is not applied as shown in FIG. 5C, and the welding voltage Vw remains at the no-load voltage value as shown in FIG. The distance between the tip of the welding wire and the base material during the normal feeding period from time t41 to t5 remains zero. During the subsequent reverse feed period from time t5 to t6, the distance between the welding wire tip and the base material gradually increases from zero.

  As shown in FIG. 5B, when the tip of the welding wire 1 comes into contact (collision) with the surface of the base material 2 again at time t7 during the normal feed period from time t6, as shown in FIG. In addition, the distance between the welding wire tip and the base material becomes zero. The slag adhering to the tip of the welding wire 1 is scraped off by the first contact (collision) at times t41 to t5 and the movement of the welding wire tip while contacting the surface of the base material in accordance with the vibration of the welding torch 4. Has been removed. At the time t7 at the time of the second contact (collision), as shown in FIG. 5H, the welding torch locus Lt has a positive value, so that the welding wire tip is separated from the welding start position. It is in the position where slag does not adhere to the material surface. This is because locations where slag is adhered and locations where slag is not adhered are mixed on the surface of the base material. As a result, the current contact is in a conductive contact state (short circuit state). For this reason, as shown in FIG. 5C, the welding current Iw starts energization, and as shown in FIG. 4D, the welding voltage Vw decreases from the no-load voltage value and shorts several V. It becomes a voltage value. In response to this, at time t7, as shown in FIG. 5E, the current energization determination signal Cd becomes High level (energization), so as shown in FIG. Changes to Low level, and the initial period Ti ends. At time t7, as shown in FIG. 5F, the short circuit determination signal Sd becomes High level (short circuit). Since the initial period Ti ends, the vibration of the welding torch 4 stops and the welding torch 4 starts moving to the welding start position.

  In the figure, the period from the start of feeding at time t1 to the occurrence of the first contact (collision) at time t41 is drawn as the middle of the third cycle. A period will be included. The vibration of the welding torch 4 also includes dozens of cycles. Further, in the figure, the slag is scraped off by the second contact (collision) and becomes conductive, but when the slag adhesion state is severe, the contact may be repeated ten times or more. When there is almost no slag adhering to the tip of the welding wire 1 and the surface of the base material 2, there may be a conduction state at the first contact. In other words, in the present embodiment, it is possible to always lead to a conducting state regardless of whether the slag adhesion state on the welding wire tip and the base material surface is severe or small.

[Operation during transition period from time t7 to t10]
When a short-circuit state occurs at time t7, a predetermined initial current is applied as shown in FIG. The initial current is set by the initial current setting signal Iir. The value is about 20-50A. The initial current is controlled at a constant current and is energized until time t10 when the welding torch 4 returns to the welding start position. The value of the initial current is preferably set to be less than the average value of the welding current Iw during the steady welding period Tc. This is because the occurrence of sputtering is reduced if the current value when a short circuit occurs at time t7 is small. Furthermore, when an arc is generated during the transition period, if the initial current is a small value, melting of the welding wire 1 is suppressed and the arc length is maintained in an appropriate range.

  At time t8 when a predetermined delay period has elapsed since the current energization determination signal Cd changed to high level at time t7, the feed speed Fw is switched from forward feed to reverse feed as shown in FIG. Then, it accelerates rapidly to a predetermined steady reverse feed peak value Frc and maintains that value. The delay period is set to about 1 to 10 ms. The delay period may be set to 0 so as not to be delayed. This delay is provided in order to generate an initial arc smoothly when the welding wire 1 contacts the base material 2.

  When the initial period Ti ends at time t7, the welding torch 4 stops vibrating and moves to the welding start position. For this reason, as shown in FIG. 5H, the welding torch locus Lt is a positive value at time t7 and becomes 0 at time t10. The welding torch 4 moves along the weld line from time t10. The welding torch trajectory Lt after time t10 is drawn as zero. At time t10, since the position of the welding torch 4 and the welding start position coincide with each other, the welding start position coincidence signal Wp (not shown) becomes a high level (coincidence) for a short time. By moving the welding torch 4 along the weld line after returning the welding torch 4 to the welding start position after the initial period Ti is completed, the bead formation from the welding start position can be reliably performed, and the welding quality is improved. Can do.

  When the arc 3 is generated by the above reverse feed at time t9, the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts as shown in FIG. ), The short circuit determination signal Sd changes to the low level (arc). When the short circuit determination signal Sd changes to a low level (arc) during the reverse peak period, the feed speed Fw is decelerated to a predetermined reverse transition value as shown in FIG. Maintain until t10. The reverse transition value is about 10 m / min. By continuing the reverse feed period during the transition period, it is possible to prevent a short circuit from occurring again after the arc has once occurred, and to stabilize the welding state.

[Operation during steady welding period Tc after time t10]
When the welding start position coincidence signal Wp changes to High level (coincidence) at time t10, the steady welding period Tc is entered. In response to this, the characteristic of the welding power source is switched to the constant voltage characteristic, so that the welding current Iw increases to a value determined by the arc load, as shown in FIG. At the same time, as shown in FIG. 5B, the feed speed Fw is switched to the forward feed period, accelerated from 0 at a predetermined rate of change, and maintained at a predetermined steady forward feed peak value Fsc. To do. If a short circuit occurs at time t11 during the forward feed peak period, the welding voltage Vw rapidly decreases to a short circuit voltage value of several volts as shown in FIG. 4D, and the short circuit occurs as shown in FIG. The determination signal Sd changes to a high level (short circuit). In response to this, as shown in FIG. 5B, the feeding speed Fw starts to shift to the reverse feeding period. The feeding speed Fw is decelerated at a predetermined change rate during the period from time t11 to t12 and becomes zero. As shown in FIG. 5C, the welding current Iw gradually increases during the short-circuit period at times t11 to t13.

  A reverse feed period starts at time t12, and is accelerated from 0 at a predetermined rate of change. When a predetermined steady reverse feed peak value Frc is reached, the value is maintained. When an arc is generated by reverse feed at time t13, the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts as shown in FIG. 4D, and as shown in FIG. Sd changes to a low level (arc). In response to this, as shown in FIG. 5B, the feeding speed Fw starts shifting to the normal feeding period. The feeding speed Fw is reduced to 0 at a predetermined rate of change during the period from time t13 to t14. As shown in FIG. 5C, the welding current Iw gradually decreases during the arc period.

  Thereafter, the operation from time t10 to t14 is repeated.

An example of each numerical value in the present embodiment is shown below.
(Initial period TI parameter)
The initial frequency Si is usually 50 to 150 Hz, and is about 100 Hz in the present embodiment, for example. The initial time ratio is usually 0.5017 to 0.505, and is about 0.5033 in the present embodiment, for example. The initial forward peak value Fsi is 30 to 50 m / min, and is about 30 to 40 m / min in the present embodiment, for example. The initial reverse peak value Fri is normally 30 to 50 m / min, and is about 30 to 40 m / min in the present embodiment, for example. The average initial feed speed Fi is 1 to 3 m / min. In the present embodiment, it is about 2 m / min, for example.
(Transition period parameters)
The vibration frequency of the welding torch is usually 1 to 50 Hz, and in this embodiment, for example, 10 Hz. The vibration amplitude of the welding torch is usually about 3 to 10 mm, and is 5 mm, for example, in the present embodiment. The reverse transfer value is normally 5 to 15 m / min, and is about 10 m / min in the present embodiment, for example. The initial current is usually 20 to 50 A, and is about 30 A, for example, in the present embodiment. The transition period is normally 5 to 200 ms, and is about 50 ms in the present embodiment, for example.
(Parameters for steady welding period Tc)
One cycle of the feeding speed is normally 8 to 20 ms, and is about 10 ms in the present embodiment, for example. The short-circuit period is normally 2 to 10 ms, and is about 4 ms in the present embodiment, for example. The arc period is usually 3 to 15 ms, and is about 6 ms in the present embodiment, for example. The steady forward peak value Fsc is usually 30 to 100 m / min, and is about 80 m / min in the present embodiment, for example. The steady reverse feed peak value Frc is usually −30 to −100 m / min, and is about −70 m / min, for example, in the present embodiment. The average feeding speed is usually 3 to 15 m / min. In the present embodiment, for example, it is about 10 m / min. The change rate at the time of switching between the forward feed period and the reverse feed period is usually a change of 30 to 200 m / min per 1 ms, and in this embodiment, for example, a change of about 100 m / min per ms. The average welding current is usually 70 to 350 A, and is about 250 A in the present embodiment, for example.

  Hereinafter, the function and effect of the present embodiment will be described. In the present embodiment, during the initial period from the welding wire feed start time to the welding current energization start time, forward / reverse feed control is performed to alternately switch the feed speed between the forward feed period and the reverse feed period. At the same time, the welding torch is vibrated in the plane direction of the base material surface. In the present embodiment, the contact (collision) between the welding wire tip and the base material is repeated by forward / reverse feed control until the welding current is applied, so that the slag adhering to the welding wire tip can be removed. Further, in the present embodiment, the position where the tip of the welding wire comes into contact with the base material can be moved by vibrating the welding torch toward the base material surface. For this reason, even if slag adheres to the surface of the base material, it can be moved to a location where the tip of the welding wire is not attached, so that the welding wire and the base material can be brought into conduction. As a result, in this embodiment, the slag at the tip of the welding wire is removed, and the tip of the welding wire can be moved to a location where the slag is not attached to the surface of the base material. be able to.

  Further, in the present embodiment, the welding torch is moved to the taught welding start position after the end of the initial period. Thereby, since a weld bead can be formed from the taught welding start position, good welding quality can be obtained.

  Further, in the present embodiment, after the initial period ends, the feed speed is switched to the reverse feed period, and the reverse feed period is continued until the welding torch reaches the welding start position. Thus, in the present embodiment, a short circuit occurs again after the arc is generated once during the transition period from when the welding current is applied and the initial period ends to when the welding torch reaches the welding start position. Can be prevented. For this reason, in this Embodiment, the welding state during a transition period can be stabilized.

  Furthermore, in the present embodiment, the welding current is smaller than the average value of the welding current during the steady welding period during the period from the occurrence of the arc after the end of the initial period until the welding torch reaches the welding start position. Value. Thus, in the present embodiment, during the period from when the arc is generated after the end of the initial period until the welding torch reaches the welding start position, the welding current becomes a smaller value than during the steady welding period. For this reason, in this Embodiment, since melting of a welding wire can be suppressed and an arc length can be maintained in an appropriate range, a welding state can be stabilized more.

  In the above-described embodiment, the case where the waveform of the feeding speed of the forward / reverse feeding control is a trapezoidal wave has been described.

DESCRIPTION OF SYMBOLS 1 Welding wire 2 Base material 3 Arc 4 Welding torch 5 Feed roll CD Current energization discrimination circuit Cd Current energization discrimination signal DIR Initial time ratio setting circuit Dir Initial time ratio setting signal DV Drive circuit Dv Drive signal E Output voltage Ea Error amplification signal ED Output voltage detection circuit Ed Output voltage detection signal EI Current error amplification circuit Ei Current error amplification signal ER Output voltage setting circuit Er Output voltage setting signal EV Voltage error amplification circuit Ev Voltage error amplification signal FC Feed control circuit Fc Feed control signal FCR steady welding period feed speed setting circuit Fcr steady welding period feed speed setting signal Fi average initial feed speed FIR initial period feed speed setting circuit Fir initial period feed speed setting signal FR feed speed setting circuit Fr feed speed Setting signal Frc Steady reverse feed peak value FRCR Steady reverse feed peak value setting circuit Frcr Steady reverse feed peak value setting signal ri initial reverse feed peak value FRIR initial reverse feed peak value setting circuit Frir initial reverse feed peak value setting signal Fsc steady forward feed peak value FSCR steady forward feed peak value setting circuit Fscr steady forward feed peak value setting signal Fsi initial forward feed peak value FSIR initial forward feed peak value setting circuit Fsir initial forward feed peak value setting signal Fw feed speed ID current detection circuit Id current detection signal IIR initial current setting circuit Iir initial current setting signal Iw welding current Lt welding torch locus Mc operation control signal On Start signal PM Power supply main circuit RC Robot controller RM Robot SD Short circuit determination circuit Sd Short circuit determination signal Si Initial frequency SIR Initial frequency setting circuit Sir Initial frequency setting signal ST Welding start circuit St Welding start signal STI Initial period timer circuit Sti Initial period timer Signal SW Power supply characteristic switching circuit Ti Initial period VD Voltage detection circuit V d Voltage detection signal Vw Welding voltage WL Reactor WM Feeding motor Wp Welding start position coincidence signal

Claims (4)

When starting welding, during the initial period from the welding wire feed start time to the welding current energization start time, forward / reverse feed control is performed to alternately switch the feed speed between the forward feed period and the reverse feed period. In the arc welding control method to be performed,
During the initial period, the welding torch is vibrated in the plane direction of the base material surface,
An arc welding control method characterized by the above. Moving the welding torch to the taught welding start position after the end of the initial period;
The arc welding control method according to claim 1, wherein: The feed speed is switched to the reverse feed period after the end of the initial period, and the reverse feed period is continued until the welding torch reaches the welding start position.
The arc welding control method according to claim 2, wherein: During the period from when the arc is generated after the end of the initial period until the welding torch reaches the welding start position, the welding current is set to a value smaller than the average value of the welding current during the steady welding period.
The arc welding control method according to claim 3.

Images