JP2022033399A - Weld power supply, weld system, control method of weld power supply and program - Google Patents

Abstract

To provide a weld power supply for making a spatter hardly scattered more than the case of a wire feeding speed which is changed by a sine wave.SOLUTION: A weld power supply for supplying a weld current to a consumable electrode wire, and desorbing a droplet in an open arc state without short-circuiting a wire to a molten pond comprises: feed control means for controlling the feed of the wire while being accompanied by the periodical switching of a forward feed period and a reverse feed period; and current control means for changing the weld current according to a tip position of the wire in which a distance from a surface of a mother material is periodically varied. The feed control means performs control so as to shorten a time in which a tip of the wire reaches the farthest point being a position which is most apart from the mother material from the nearest point being a position which is most approximate to the mother material shorter than a time in which the tip of the wire reaches the nearest point from the farthest point, and the current control means performs control for setting a low-current period for lowering the weld current lower than a preset current value within a period in which the tip of the wire is reversely fed.SELECTED DRAWING: Figure 2

Description

The present invention relates to a welding power source, a welding system, a method and a program for controlling a welding power source.

In a welding power source that supplies a welding current to a wire as a consumable electrode, the tip of the wire is fed toward the base metal with periodic switching between the period of normal feeding and the period of reverse feeding. In some cases, the control means has a control means for changing the welding current according to the position of the tip of the wire whose distance from the surface of the base metal varies periodically, and the control means is used within the period when the tip of the wire is back-fed. , A welding power source that controls a welding current so as to provide a low current period lower than a predetermined current value is known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2020-49506

Low current within the period when the tip of the wire is fed back to the base metal with periodic switching between the period when the tip of the wire is fed forward and the period when it is fed backward. There is a technique for reducing the scattering of spatter due to droplet detachment by setting a period. In such a technique, if a configuration is adopted in which the wire is fed according to the feeding speed of the wire changing in a sinusoidal shape, the droplets are separated during the period when the tip of the wire is reverse-fed, that is, during the low current period. There is a limit to increasing the likelihood of doing so. That is, there is a limit to making it difficult for spatter to scatter.

It is an object of the present invention that the tip of the wire is reverse-fed when it is fed toward the base metal with periodic switching between the period in which the tip of the wire is forward-fed and the period in which the wire is reverse-fed. In the technique of providing a low current period within a certain period, it is intended to make it difficult for spatter to scatter as compared with the case of adopting a configuration in which the wire is fed according to the feeding speed of the wire changing in a sinusoidal shape.

For this purpose, the present invention is a welding power source that supplies a welding current to a wire as a consumable electrode to release droplets in an open arc state without short-circuiting the wire to a molten pool, and the tip of the wire is , A feed control means that controls the feed of the wire so that it is fed toward the base material with periodic switching between the period of normal feed and the period of reverse feed, and the surface of the base material. It is equipped with a current control means that changes the welding current according to the position of the tip of the wire whose distance from the wire changes periodically, and the feed control means is from the latest point where the tip of the wire is closest to the base metal. The time to reach the farthest point, which is the farthest position from the base metal, is controlled to be shorter than the time from the tip of the wire to the latest point, and the current control means is the tip of the wire. Provided is a welding power source that controls so as to provide a low current period in which the welding current is lowered below a predetermined current value within the period in which the wire is fed back.

The feed control means is such that the maximum feed rate of the wire during the period when the tip of the wire is reverse fed is higher than the maximum feed rate of the wire during the period when the tip of the wire is positively fed. It may be something to control.

The current control means initiates a low current period when the periodically fluctuating wire tip position is closer to the base metal than half the wave height defined by the perigee and apogee. It may be something that is controlled as such. In that case, the current control means feeds the wire from the position of the tip of the wire at the time when the low current period switches from the period in which the tip of the wire is forward-fed to the period in which the tip of the wire is fed in reverse. It may be controlled so as to start within the range up to the tip position of the wire at the time when the command value of the speed is maximized. Further, the current control means starts from the wire tip position at the time when the command value of the wire feeding speed switched to the reverse feeding becomes maximum during the low current period, and from the period when the wire tip is reverse feeding. It may be controlled so as to end within the range up to the tip position of the wire at the time of switching to the period of normal feeding.

Further, the present invention is a welding system in which a welding current is supplied to a wire as a consumable electrode for arc welding, and the droplets are released in an open arc state without short-circuiting the wire to a molten pool, and the tip of the wire is , A feed control means that controls the feed of the wire so that it is fed toward the base metal with periodic switching between the normal feed period and the reverse feed period, and the surface of the base metal. It is equipped with a current control means that changes the welding current according to the position of the tip of the wire whose distance from the wire changes periodically, and the feed control means is from the latest point where the tip of the wire is closest to the base metal. The time to reach the farthest point, which is the farthest position from the base metal, is controlled to be shorter than the time from the tip of the wire to the latest point, and the current control means is the tip of the wire. Also provided is a welding system that controls to provide a low current period in which the welding current is lower than a predetermined current value within the period in which the welding current is back-fed.

Further, the present invention is a method for controlling a welding power source in which a welding current is supplied to a wire as a consumable electrode to separate the droplets in an open arc state without short-circuiting the wire to the molten pool, and the tip of the wire has a welding current. The distance between the step of controlling the wire feed so that it is fed toward the base metal and the surface of the base metal with periodic switching between the normal feed period and the reverse feed period. In the step of controlling the feeding, including the step of changing the welding current according to the position of the tip of the wire which fluctuates periodically, the step of controlling the feeding is the position where the tip of the wire is the closest to the base material. In the step of changing the welding current by controlling the time to reach the farthest point, which is the farthest position, so that the time from the tip of the wire to the latest point is shorter than the time from the tip of the wire to the latest point, the tip of the wire Also provided is a method of controlling a welding power source that controls to provide a low current period in which the welding current is lower than a predetermined current value within the period of back feeding.

Furthermore, the present invention applies a welding current to a wire as a consumable electrode for arc welding, and the tip of the wire is applied to a computer of a welding system in which droplets are released in an open arc state without short-circuiting the wire to a molten pool. However, the function to control the feeding of the wire so that it is fed toward the base metal with the periodic switching between the period of normal feeding and the period of reverse feeding, and the surface of the base metal. The function to change the welding current according to the position of the tip of the wire whose distance fluctuates periodically is realized, and the function to control the feeding is the mother from the latest point where the tip of the wire is the position closest to the base metal. The function to change the welding current by controlling the time to reach the farthest point, which is the farthest position from the material, so that the tip of the wire is shorter than the time from the farthest point to the latest point is the wire. We also provide a program that controls to provide a low current period in which the welding current is lower than a predetermined current value within the period in which the tip of the wire is fed back.

According to the present invention, the tip of the wire is reverse-fed when the tip of the wire is fed toward the base metal with periodic switching between the period of normal feeding and the period of reverse feeding. In the technique of providing the low current period within the period, the spatter is less likely to be scattered as compared with the case where the wire is fed according to the feeding speed of the wire changing in a sinusoidal shape.

It is a figure which shows the structural example of the arc welding system which concerns on this embodiment. It is a figure explaining the structural example of the control system part of a welding power source. It is a waveform diagram explaining the time change of a wire feeding speed. It is a waveform diagram explaining the time change of the tip position of a welding wire. It is a flowchart explaining the control example of the welding current in this embodiment. It is a figure which shows the control example of the current setting signal which specifies the current value of a welding current. It is a graph which showed the wire feed rate, the waveform of the welding current and the welding voltage, and the droplet detachment timing according to Patent Document 1. It is a graph which showed the wire feed rate, the waveform of the welding current and the welding voltage, and the droplet detachment timing by this embodiment. It is a graph which showed the measurement result of the droplet detachment timing by Patent Document 1. It is a graph which showed the measurement result of the droplet detachment timing by this embodiment. It is a graph which showed the result of having measured the time from the start of the current suppression period to the withdrawal in Patent Document 1. It is a graph which showed the result of having measured the time from the start of the current suppression period to the withdrawal in this embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Problems to be solved by this embodiment>
There are two problems to be solved by this embodiment.

The first problem is that spatter is likely to scatter.
The technique of Patent Document 1 appropriately controls the wire feeding speed and the welding current in carbon dioxide gas welding (open arc welding) without short circuit, and welds by separating the droplets (molten metal) in a low current period. It is to be transferred to the base material.
What is important here is to positively detach the droplets by pulling back the welding wire in a state where the droplets are easily detached. The ease of detachment of a droplet is affected by the size (weight) of the droplet, surface tension, arc reaction force, and the like. For example, the larger the droplet size, the easier it is to detach, and the smaller the droplet size, the more difficult it is to detach.
An automatic welding machine using a robot uses an "arc length self-holding function" that keeps the arc length constant in order to obtain stable welding results. The "self-holding function of the arc length" is to give the welding power supply "constant voltage characteristics", and when the arc length becomes long, the welding current is slightly lowered (delaying the melting of the welding wire) to shorten the arc length. It is a function to operate and operate in the direction of increasing the arc length by increasing the welding current (accelerating the melting of the welding wire) when the arc length becomes shorter. In Patent Document 1, when the arc length becomes long and the welding current decreases due to some external factor during welding, the droplet growth in the droplet growth period is delayed and the droplet size becomes smaller, and the droplets are desired to be detached. It may not come off during the current suppression period. There is a problem that spatter is likely to scatter when the droplets are separated during the current non-suppression period.

The second problem is that the contact tip is easily worn.
In arc welding, a welding current is supplied to the welding wire by a copper alloy feeding component called a "contact tip" attached to the tip of the welding torch. Joule heat is generated at the contact portion between the contact tip and the welding wire due to the passage of a large current, and the contact tip tends to soften. When the welded wire moves while contacting the surface of the softened contact tip, it is gradually scraped off by the welded wire and worn. When the wire feeding portion of the contact tip is worn, the feeding to the welding wire becomes unstable, a predetermined welding current cannot flow, the amount of welding changes, and problems such as welding of the contact tip and the welding wire occur. The larger the welding current, the more easily the contact tip wears, and the larger the wire feeding speed, the more easily the contact tip wears.
In Patent Document 1, the peak period of the welding current and the peak period of the wire feeding rate overlap, and the welding wire is passed through the contact tip softened by a large current at high speed, so that the contact tip is easily worn. There's a problem.

Therefore, in the present embodiment, when the droplets are separated in the open arc state without short-circuiting the wire to the molten pool, the spatter is less likely to be scattered and the contact tip is less likely to be worn. Hereinafter, such an embodiment will be described in detail.

<Overall system configuration>
FIG. 1 is a diagram showing a configuration example of an arc welding system 10 according to the present embodiment.
The arc welding system 10 includes a welding robot 120, a robot controller 160, a welding power supply 150, a feeding device 130, and a shield gas supply device 140.
The welding power supply 150 is connected to the weld electrode via a positive power cable, and is connected to an object to be welded (hereinafter, also referred to as “base material” or “work”) 200 via a negative power cable. This connection is for welding with opposite polarity, and when welding is performed with positive polarity, the welding power supply 150 is connected to the base metal 200 via a positive power cable, and the welding electrode is connected via a negative power cable. Connected to.
Further, the welding power supply 150 and the feeding device 130 of the consumable electrode (hereinafter, also referred to as “welding wire”) 100 are also connected by a signal line, and the feeding speed of the welding wire can be controlled.

The welding robot 120 includes a welding torch 110 as an end effector. The welding torch 110 has an energizing mechanism (contact tip) for energizing the welding wire 100. The welding wire 100 generates an arc from the tip by energization from the contact tip, and the heat thereof welds the base metal 200 to be welded.
Further, the welding torch 110 includes a shield gas nozzle (a mechanism for ejecting the shield gas). The shield gas may be either carbon dioxide gas or a mixed gas such as argon + carbon dioxide gas (CO2). Carbon dioxide gas is more preferable, and in the case of a mixed gas, a system in which Ar is mixed with 10 to 30% carbon dioxide gas is preferable. The shield gas is supplied from the shield gas supply device 140.
The welding wire 100 used in the present embodiment may be either a solid wire containing no flux or a flux-cored wire containing flux. The material of the welding wire 100 does not matter. For example, the material may be mild steel, stainless steel, aluminum, or titanium. Further, the diameter of the welding wire 100 is not particularly limited. In the case of this embodiment, the upper limit of the diameter is preferably 1.6 mm and the lower limit is 0.8 mm.

The robot controller 160 controls the operation of the welding robot 120. The robot controller 160 holds teaching data in which the operation pattern, welding start position, welding end position, welding conditions, weaving operation, etc. of the welding robot 120 are determined in advance, and instructs the welding robot 120 to perform these, and the welding robot 120. Controls the operation of. Further, the robot controller 160 gives a command to the welding power supply 150 to control the power supply during the welding operation according to the teaching data.
The arc welding system 10 here is an example of a welding system. The welding power supply 150 is also an example of a control means for changing the welding current.

<Structure of welding power supply>
FIG. 2 is a diagram illustrating a configuration example of a control system portion of the welding power supply 150.
The control system portion of the welding power supply 150 is executed, for example, through the execution of a program by a computer.
The control system portion of the welding power supply 150 includes a current setting unit 36. The current setting unit 36 in the present embodiment has a function of setting various current values that define the welding current flowing through the welding wire 100, and a time at which the period in which the current value of the welding current is suppressed starts and ends. (Current suppression period setting unit 36A) and a wire tip position conversion unit 36B for obtaining information on the tip position of the welding wire 100.
In the case of this embodiment, it is a pulse current, and the current setting unit 36 sets a peak current Ip, a base current Ib, and a steady current Ia for droplet detachment. In the case of this embodiment, the welding current is basically controlled by two values of the peak current Ip and the base current Ib. Therefore, the time t1 at which the period in which the current value is suppressed starts represents the time at which the base current Ib starts (base current start time), and the time t2 at which the period in which the current value is suppressed ends represents the base current Ib. Represents the time when is finished (base current end time).

The power supply main circuit of the welding power supply 150 includes an AC power supply (here, a three-phase AC power supply) 1, a primary side rectifier 2, a smoothing capacitor 3, a switching element 4, a transformer 5, and a secondary side rectifier 6. It is composed of a reactor 7.
The AC power input from the AC power supply 1 is full-wave rectified by the primary side rectifier 2, further smoothed by the smoothing capacitor 3, and converted into DC power. Next, the DC power is converted into high-frequency AC power by inverter control by the switching element 4, and then converted into secondary power via the transformer 5. The AC output of the transformer 5 is full-wave rectified by the secondary side rectifier 6 and further smoothed by the reactor 7. The output current of the reactor 7 is applied to the welding tip 8 as an output from the power supply main circuit, and is energized to the welding wire 100 as a consumable electrode.

The welding wire 100 is fed by the feed motor 24 to generate an arc 9 with the base metal 200. In the case of the present embodiment, the feed motor 24 feeds the tip of the welding wire 100 to the base metal 200 at a speed faster than the average speed, and the tip of the welding wire 100 at a speed slower than the average speed. The weld wire 100 is fed so that the reverse feed period for feeding to the base material 200 is periodically switched. The tip of the welding wire 100 during the reverse feeding period moves away from the base metal 200.
The feeding of the welding wire 100 by the feeding motor 24 is controlled by the control signal Fc from the feeding drive unit 23. The average value of the feeding rate is almost the same as the melting rate. In the case of this embodiment, the feeding of the welding wire 100 by the feeding motor 24 is also controlled by the welding power supply 150.

A target value (voltage setting signal Vr) of the voltage applied between the welding tip 8 and the base metal 200 is given to the current setting unit 36 from the voltage setting unit 34.
The voltage setting signal Vr here is also given to the voltage comparison unit 35 and is compared with the voltage detection signal Vo detected by the voltage detection unit 32. The voltage detection signal Vo is an actually measured value.
The voltage comparison unit 35 amplifies the difference between the voltage setting signal Vr and the voltage detection signal Vo, and outputs the voltage error amplification signal Va to the current setting unit 36.
The current setting unit 36 controls the welding current so that the length of the arc 9 (that is, the arc length) becomes constant. In other words, the current setting unit 36 executes constant voltage control through the control of the welding current.

The current setting unit 36 has a peak current Ip value, a base current Ib value, a period for giving the peak current Ip, or a peak current Ip value, and a base current based on the voltage setting signal Vr and the voltage error amplification signal Va. The magnitude of the value of Ib is reset, and the current setting signal Ir corresponding to the reset period or the magnitude of the value is output to the current error amplification unit 37.
In the case of the present embodiment, the period in which the peak current Ip is given is a period other than the period in which the base current Ib is given. In other words, the period in which the peak current Ip is applied is the period in which the current is not suppressed (current non-suppression period). The period for giving this peak current Ip is an example of the first period.
On the other hand, the period in which the base current Ib is applied is also referred to as a current suppression period. The current suppression period is an example of a low current period and also an example of a second period.
The current error amplification unit 37 amplifies the difference between the current setting signal Ir given as the target value and the current detection signal Io detected by the current detection unit 31, and outputs the difference as the current error amplification signal Ed to the inverter drive unit 30. ..
The inverter drive unit 30 corrects the drive signal Ec of the switching element 4 by the current error amplification signal Ed.

The current setting unit 36 is also given an average feed rate Fab of the weld wire 100 to be fed. The average feed rate Fave is output by the average feed rate setting unit 20 based on the teaching data stored in a storage unit (not shown).
The current setting unit 36 sets the values of the peak current Ip, the base current Ib, the steady current Ia, the time t1 at which the base current Ib starts, and the time t2 at which the base current Ib ends, based on the given average feed rate Fab. decide.
In the present embodiment, as shown in FIG. 2, the average feed rate Fave is input to the current setting unit 36, but the signal input to the current setting unit 36 is set to a value related to the average feed rate Fave. As a result, it may be used in place of the average feed rate Fave. For example, when a database of an average feeding rate and an average current value that enables optimum welding for the average feeding rate is stored in a storage unit (not shown), the average current value is set as a set value and averaged. It may be used in place of the feed rate Fave.
The average feed rate Fave is also given to the amplitude feed rate setting unit 21 and the feed rate command setting unit 22.
Here, the amplitude feeding speed setting unit 21 determines the values of the amplitude Wf and the period Tf as the basic feeding conditions based on the input average feeding speed Fab. The amplitude Wf is the change width with respect to the average feed rate Fave, and the period Tf is the time of the amplitude change which is a repeating unit.

The wire feeding in Patent Document 1 has a period in which the feeding speed is faster than the average feeding speed Fave (normal feeding period) and a period in which the feeding speed is slower than the average feeding speed Fave (reverse feeding period). It appeared alternately, and the time width of the normal feeding period and the time width of the reverse feeding period were the same feeding method.
On the other hand, in the present embodiment, the forward / reverse speed ratio setting unit 38 sets PFR (%), which is the ratio of the reverse feed period to the period Tf, and gives it to the amplitude feed rate setting unit 21.
Here, in the amplitude feed rate setting unit 21, the amplitude feed rate Ff in the normal feed period and the amplitude feed rate Ff in the reverse feed period are based on the amplitude Wf, the period Tf, and the forward / reverse feed ratio PFR. And are calculated.
The amplitude feed rate Ff of the reverse feed period is given by the following equation. Here, t represents the time.

Further, the amplitude feed rate Ff of the normal feed period is given by the following equation.

As described above, the amplitude feeding speed setting unit 21 generates and outputs different amplitude feeding speeds Ff for the normal feeding period and the reverse feeding period.

The feed rate command setting unit 22 outputs a feed rate command signal Fw based on the amplitude feed rate Ff and the average feed rate Fave.
In the case of this embodiment, the feed rate command signal Fw is expressed by the following equation.
Fw = Ff + Fave ... Equation 3

The feed rate command signal Fw is output to the phase shift detection unit 26, the feed error amplification unit 28, and the current setting unit 36.
The feeding error amplification unit 28 amplifies the difference between the feeding speed command signal Fw, which is the target speed, and the feeding speed detection signal Fo, which is the actual measurement of the feeding speed of the welded wire 100 by the feeding motor 24, and calculates the error amount. The corrected speed error amplification signal Fd is output to the feed drive unit 23.
The feed drive unit 23 generates a control signal Fc based on the speed error amplification signal Fd and feeds it to the feed motor 24.
Here, the feeding speed conversion unit 25 converts the rotation amount of the feeding motor 24 and the like into the feeding speed detection signal Fo of the welding wire 100.
The phase shift detection unit 26 in the present embodiment compares the feed rate command signal Fw with the feed rate detection signal Fo which is a measured value, and outputs the phase shift time Tθd. The phase shift detection unit 26 measures the feeding operation of the feeding motor 24 when the parameters (period Tf, amplitude Wf, average feeding speed Fave) that define the amplitude feeding are changed, and the phase shift time Tθd. You may ask for.

The phase shift time Tθd is given to the wire tip position conversion unit 36B of the current setting unit 36. The wire tip position conversion unit 36B calculates the tip position of the welding wire 100 with the base material 200 as a reference plane based on the feed rate command signal Fw and the phase shift time Tθd, and obtains the calculated tip position information. It is given to the current suppression period setting unit 36A.
Here, the current suppression period setting unit 36A suppresses the welding current based on the information on the tip position of the welding wire 100 or based on the information on the tip position of the welding wire 100 and the feed rate command signal Fw. (That is, the period for controlling the current setting signal Ir to the base current Ib) is set.
The current setting unit 36 here is an example of a feed control means for controlling the feed of the welding wire 100 and a current control means for changing the welding current according to the position of the tip of the welding wire 100.

<Welding current control example>
Hereinafter, an example of controlling the welding current by the welding power source 150 will be described.
The control of the welding current is realized by the current setting unit 36 constituting the welding power supply 150. As described above, the current setting unit 36 in the present embodiment realizes control through the execution of the program.
The current setting unit 36 in the present embodiment controls switching of the current value of the welding current based on the feed rate command signal Fw of the welding wire 100 and the information of the tip position of the welding wire 100. Therefore, prior to the explanation of the control of the welding current, the time change of the feed rate command signal Fw and the time change of the tip position of the welding wire 100 will be described.

FIG. 3 is a waveform diagram illustrating a time change of the feed rate command signal Fw. The horizontal axis is time (phase), and the vertical axis is velocity. The unit of the vertical axis is meters per minute or rotation speed. However, the numerical value is an example. For example, when the diameter of the welding wire 100 (see FIG. 1) is 1.2 mm, the average feed rate Fave is 12 to 25 meters per minute. However, in order to maintain the globule transition or the spray transition described later, it is desirable that the feeding speed be 8 meters per minute or more, although it depends on the protrusion length of the welding wire 100. For example, when the protrusion length of the welding wire 100 is 25 mm, the welding current is about 225 A. The critical region for short-circuit and globule transitions is approximately 250A.

In FIG. 3, a speed faster than the average feeding speed Fave is represented by a positive value, and a speed slower than the average feeding speed Fave is represented by a negative value. The period in which the feeding speed is faster than the average feeding speed Fave is called the normal feeding period, and conversely, the period in which the feeding speed is slower than the average feeding speed Fave is called the reverse feeding period. The welding wire 100 (see FIG. 1) is sent so as to approach the base metal 200 (see FIG. 1).
In Patent Document 1, since the time width of the normal feed period and the time width of the reverse feed period are equal to each other, and the velocity amplitude of the forward feed period and the velocity amplitude of the reverse feed period are equal to each other, the velocity waveform has a period Tf. , It was a sine wave with an amplitude Wf.
In the case of the present embodiment, the feed rate command signal Fw has a difference between the time width of the normal feed period and the time width of the reverse feed period, and the speed amplitude Wf_f of the normal feed period and the speed of the reverse feed period. The amplitude is different from Wf_r.
That is, if the ratio of the reverse feed time in one feed cycle is defined as PFR (%), the cycle and speed amplitude of the normal feed period and the cycle and speed amplitude of the reverse feed period are defined as follows. can.
Positive feeding period: A half wave of a sine wave having a period of ((100-PFR) × Tf_f) / 50 and a velocity amplitude Wf_f of PFR × Wf / 50.
Reverse feeding period: A half wave of a sine wave having a period of PFR × Tf / 50 and a velocity amplitude Wf_r of ((100-PFR) × Wf / 50.
Here, Wf is the velocity amplitude when the PFR is 50, that is, when the velocity waveform is a sine wave as in Patent Document 1.
Further, in the present embodiment, it is assumed that PFR <50. As a result, the velocity amplitude Wf_f becomes smaller than the velocity amplitude Wf, and the velocity amplitude Wf_r becomes larger than the velocity amplitude Wf.
The average feed rate Fave can be regarded as the wire melting rate Fm.

FIG. 4 is a waveform diagram illustrating a time change of the tip position (wire tip position) of the welding wire 100 (see FIG. 1). The horizontal axis represents time (phase), and the vertical axis represents the distance (height) from the surface of the base material 200 (base material surface) upward in the normal direction.
However, in FIG. 4, the distance (height) when the welding wire 100 is fed at the average feeding speed Fave is set as the reference distance, the distance larger than the reference distance is a positive value, and the distance smaller than the reference distance is negative. It is represented by a value.
As shown in FIG. 4, the period in which the tip position of the welding wire 100 approaches the surface of the base metal with the passage of time is the normal feeding period, and the period in which the tip position of the welding wire 100 moves away from the surface of the base metal with the passage of time is. It is a reverse delivery period.
In FIG. 4, the time points corresponding to the positions where the tip position of the welding wire 100 is closest to the surface of the base metal (the lowest point) are represented by T0 and T4, and the position where the tip position of the welding wire 100 is the farthest from the surface of the base metal. The time point corresponding to (highest point) is represented by T2. The lowest point here is an example of the latest point, and the highest point is an example of the farthest point.

Further, the time points corresponding to the reference distance are T1 and T3. T1 is an intermediate time point in which the tip position of the welding wire 100 goes from the position closest to the surface of the base metal (lowest point) to the position farthest from the position (highest point). T3 is an intermediate time point in which the tip position of the welding wire 100 moves from the position farthest to the surface of the base metal to the position closest to the surface of the base metal. As shown in FIG. 4, the difference between the tip position of the welding wire 100 and the positions at the reference points T1 and T3 is the amplitude.

FIG. 5 is a flowchart illustrating a welding current control example according to the present embodiment. The control shown in FIG. 5 is executed by the current setting unit 36 (see FIG. 2). The symbol S in the figure is a step.
The control shown in FIG. 5 corresponds to a change (1 cycle) in the tip position of the welding wire 100. Therefore, in FIG. 5, the state where the time T is the time point T0 is set as step 1.
The current setting unit 36 in the present embodiment calculates the tip position of the welding wire 100 for controlling the current setting signal Ir.
The average feed rate Fave is equivalent to the wire melting rate Fm. Therefore, the tip position of the welded wire 100 can be obtained by integrating the difference between the feed rate command signal Fw and the wire melting rate Fm (≈Fave).
Therefore, the current setting unit 36 sets the tip position of the welding wire 100 based on the following equation.
Wire tip position = ∫ (Fw-Fave) ・ dt… Equation 4
The change in tip position calculated by Equation 4 corresponds to FIG.

However, when the feeding motor 24 (see FIG. 2) is used for feeding the welding wire 100, a phase shift may occur between the command and the actual feeding speed (that is, the feeding speed detection signal Fo). Therefore, the current setting unit 36 is calculated according to the tip position of the welding wire 100 calculated from the average feed rate Fab and the feed rate command signal Fw by the phase shift time Tθd given by the phase shift detection unit 26. The base current start time t1 is corrected. Specifically, as shown in the following equation, the value of the base current start time t1 is reset.
t1 = t1 + Tθd ... Equation 5
Similarly, the current setting unit 36 corrects the base current end time t2 calculated from the average feed rate Fave and the feed rate command signal Fw by the phase shift time Tθd.
t2 = t2 + Tθd ... Equation 6
Here, the case where the base current start time t1 and the base current end time t2 are controlled from the viewpoint of the feeding speed is described, but the same applies from the viewpoint of the position control.

FIG. 6 is a diagram showing a control example of the current setting signal Ir that specifies the current value of the welding current. The horizontal axis is time, and the vertical axis is the current detection signal Io. Time points T0, T1, T2, T3, and T4 in the figure correspond to time points T0, T1, T2, T3, and T4 in FIG. 4, respectively. Here, the time points T0, T1, T2, T3, and T4 are determined from the tip position of the welding wire 100 calculated from the average feed rate Fabe and the feed rate command signal Fw.
As shown in FIG. 6, the base current start time t1 represents a phase delayed from the time point T0 at which the tip of the welding wire 100 is located at the lowest point (that is, the time point at which the normal feeding period is switched to the reverse feeding period). .. In FIG. 6, the maximum value of the base current start time t1 is represented by t1'.
Returning to the description of FIG.
When the tip position of the welding wire 100 reaches the lowest point (that is, the time point T0), the current setting unit 36 determines whether or not the time T at which the measurement is started from the time point T0 is equal to or longer than the base current start time t1 (step). 2).
While the determination result in step 2 is negative (False), the current setting unit 36 outputs the peak current Ip as the current setting signal Ir (step 3).
This period corresponds to the current non-suppression period in FIG.

By the way, the supply period of the peak current Ip immediately before switching to the base current Ib is a period in which the welding wire 100 is melted by the peak current Ip and the droplets formed at the tip thereof are greatly grown. Further, the position of the tip of the welding wire 100 is also a period of approaching the surface of the base metal. This period is also a period in which a short circuit is likely to occur and spatter due to the short circuit is likely to occur.
Therefore, in the present embodiment, the peak current Ip is applied until the time t1 elapses to prevent or suppress the occurrence of a short circuit. In other words, the supply of welding current is controlled so that a short circuit does not occur.
In the case of this embodiment, the preferred range of the peak current Ip is 300A to 650A. The preferred range of the base current Ib is 10A to 250A.

While there is a possibility of a short circuit, it is desirable to supply the peak current Ip even after the reverse feeding period has started. This period is approximately between time points T0 and T1. Therefore, it is desirable that the end of the period in which the peak current Ip is supplied (current non-suppression period) is executed between the time points T0 and T1. That is, the time point T0 and its vicinity are in a so-called "buried arc" state in which the droplets at the tip of the wire are located so as to be surrounded in the molten pool pushed away by the force of the arc, and a short circuit is likely to occur. Therefore, by executing the end of the period in which the peak current Ip is supplied between the time points T0 and T1, the effect of pushing down the surface of the molten pool and the effect of lifting the droplets by the arc can be maintained, and the “buried arc” can be maintained. It is possible to prevent the occurrence of a short circuit at the time.
Therefore, it is desirable that a little after the time point T0 where the tip of the welding wire 100 is located at the lowest point (for example, one-ninth to two-thirds time point from the time point T0 to the time point T1). It is desirable to set the time t1 so that switching to the base current Ib is performed.

Returning to the description of FIG.
When the determination result in step 2 becomes affirmative (True), the current setting unit 36 starts outputting the base current Ib as the current setting signal Ir (step 4). As described above, when the switching to the base current Ib starts, the feed of the weld wire 100 has already been switched to the reverse feed period, and the tip of the weld wire 100 moves away from the surface of the base metal. I'm starting to move.
When the peak current Ip is large, the droplets detached from the tip of the welding wire 100 differ depending on the shield gas applied and the transition mode that changes depending on the current range. It becomes a large grain shape, and in the case of spray transfer, it becomes a small grain shape.
When carbon dioxide gas is used as the shield gas, the arc contracts and the arc reaction force concentrates on the bottom of the droplet (the part facing the surface of the molten pool), so the force to lift the droplet increases. , It will be a global shift. Further, when the shield gas is argon gas or a gas having a high mixing ratio of argon, the spray shifts.

Since the droplet near the time point T0 where the tip of the welding wire 100 is located at the lowest point is located near the molten pool, the arc length is shortened. Further, after the time point T0, the period is switched to the reverse feed period. That is, the tip of the welding wire 100 moves so as to be pulled up. Inertial force acts on the entire grown droplets in the normal feeding direction (direction approaching the base material 200 (see FIG. 1)), whereas the welding wire 100 is in the opposite direction (from the base material 200). As it moves away), the droplets change to a more suspended shape, further facilitating detachment.
Moreover, by switching the current value of the welding current to the base current Ib during the period in which the detachment is predicted, the arc reaction force can be reduced as compared with the period in which the peak current Ip is supplied. As a result, the force for lifting the droplet becomes weaker, and the droplet becomes more likely to have a suspended shape.
During the period from T0 to T1, as described above, the droplets at the tip of the wire are in a “buried arc” state in which they are buried in the molten pool, so that the shearing force due to the pinch force or the like is large with respect to the droplets. Work and withdrawal are more promoted.
In this way, reduction of spatter can be expected by separating the droplets from the tip of the welding wire 100 during the period in which the welding current is suppressed (current suppression period).

Returning to the description of FIG.
The current setting unit 36 (see FIG. 2) in which the current setting signal Ir is switched to the base current Ib determines whether or not the time T is equal to or longer than the base current end time t2 (step 5). In FIG. 5, the maximum value of the base current end time t2 is indicated by t2'.
While the determination result in step 5 is negative (False), the current setting unit 36 outputs the base current Ib as the current setting signal Ir (step 4).
After the supply of the base current Ib is started, the tip of the welding wire 100 is moved so as to be pulled up to the highest point (the position where the tip is farthest from the base material 200) with the detachment of droplets.
After the droplets are separated, the supply period of the base current Ib (current suppression period) is terminated and the peak current Ip is supplied (current non-suppression period) in order to melt the welding wire 100 to form the droplets. Need to switch to.

Therefore, it is desirable that the supply of the base current Ib ends between the time points T1 and T2.
On the other hand, if the switching from the base current Ib to the peak current Ip is performed too quickly, the droplets grow excessively, and a short circuit is likely to occur when the welding wire 100 is located at the lowest point. Problems such as the droplets being lifted too much and the enlarged droplets being difficult to come off occur.
Therefore, more preferably, the end of the supply period of the base current Ib (base current end time t2) is set between, for example, one-third from the time point T1 to the time point T2 to the time point T2.
When the determination result in step 5 becomes affirmative (True), the current setting unit 36 starts outputting the peak current Ip as the current setting signal Ir (step 6).
Subsequently, the current setting unit 36 determines whether or not the time T at which the measurement is started from the time point T0 has reached the time point T4 (step 7).
While the determination result in step 7 is negative (False), the current setting unit 36 outputs the peak current Ip as the current setting signal Ir (step 6).
On the other hand, when the determination result in step 7 becomes affirmative (True), the current setting unit 36 returns to step 1.
By the above control, the current setting signal Ir becomes a pulse waveform that periodically repeats the peak current Ip and the base current Ib.

<Effect of this embodiment>
Hereinafter, the effects of this embodiment will be described in comparison with Patent Document 1.
The following effects are based on lab experiment results.
Welding conditions are that the forward / reverse feeding frequency is 100 Hz, the forward / reverse amplitude is 4.8 mm, and a solid wire of Φ1.2 mm (MG-50R manufactured by Kobe Steel) is used as the welding wire 100, and the welding wire 100 is fed. The average speed (wire feeding speed) was 16 m / min, and a bead-on plate was used as the welding method.

FIG. 7 is a graph showing the wire feeding speed, the waveforms of the welding current and the welding voltage, and the droplet detachment timing according to Patent Document 1. The wire feed rate is given as a sine wave centered on the average wire feed rate (thin dashed line), as shown by the thin solid line. Here, the wire feeding speed is a command value, and the average wire feeding speed is a detected value. The thick solid line indicates the welding current, and the thick broken line indicates the welding voltage. Here, the welding current is a command value and the welding voltage is a detected value. Furthermore, the timing of droplet withdrawal is indicated by ↓.
FIG. 8 is a graph showing the wire feeding speed, the waveforms of the welding current and the welding voltage, and the droplet detachment timing according to the present embodiment. As shown by the thin solid line, the wire feeding speed is centered on the average wire feeding speed (thin broken line), the speed amplitude is smaller on the upper side (normal feeding side), and the speed amplitude is smaller on the lower side (reverse feeding side). The velocity amplitude is large. In addition, the time width for regular feeding is longer than the time width for reverse feeding. Similarly, here, the wire feeding speed is a command value, and the average wire feeding speed is a detected value. The thick solid line indicates the welding current, and the thick broken line indicates the welding voltage. Similarly, here, the welding current is a command value and the welding voltage is a detected value. Furthermore, the timing of droplet withdrawal is indicated by ↓.

In FIGS. 7 and 8, from the time point T0 when the wire feeding speed is switched from the normal feeding to the reverse feeding (that is, the timing at which the wire feeding speed intersects the average wire feeding speed) to the droplet withdrawal timing. I measured the time. The measurement target period is 5 seconds from 3 seconds after the start of welding out of 10 seconds of welding.
FIG. 9 is a graph showing the measurement results of the droplet detachment timing according to Patent Document 1. That is, it is a graph in the case of PFR = 50. In this graph, the distribution of withdrawal timing spreads almost uniformly from 3.2 msec to 4.8 msec.
FIG. 10 is a graph showing the measurement results of the droplet detachment timing according to the present embodiment. Here, the graph when PFR = 45 is shown. In this graph, the distribution of withdrawal timing is generally biased from 3.0 msec to 4.0 msec, and those withdrawal after 4.0 msec are less than those of Patent Document 1.

Next, FIGS. 11 and 12 are graphs showing the results of measuring the time from the start of the current suppression period to the withdrawal. FIG. 11 is a graph in Patent Document 1, and FIG. 12 is a graph in the present embodiment.
From FIG. 11, it can be seen that in Patent Document 1, there are many cases in which the withdrawal is delayed from the current suppression period and the withdrawal occurs during the current non-suppression period.
On the other hand, from FIG. 12, it can be seen that in the present embodiment, most of the droplets are withdrawn during the current suppression period, and the rate of withdrawal during the current non-suppression period is decreasing.

As described above, in the present embodiment, since the wire feeding speed at the time of pulling back is higher than that of the technique of Patent Document 1, the probability of droplet detachment during the current suppression period is higher than that of the technique of Patent Document 1. I was able to prove it. Regarding the spatter reduction effect, since it has been confirmed by observation with a high-speed camera that the spatter scatters when the droplets are separated during the current non-suppression period, it is presumed that the spatter is reduced by this embodiment.

Further, in the present embodiment, the maximum wire feeding speed at the time of feeding is smaller than that of the technique of Patent Document 1. Generally, it is known that the wear of the contact tip increases as the wire feeding speed increases, so that the effect of reducing the wear of the contact tip can be expected.

Further, in the present embodiment, according to FIG. 12, the release timing of the droplets is earlier than that of the technique of Patent Document 1, and the distribution is also concentrated. From this, it can be seen that it is not necessary to secure the current suppression period unnecessarily long, and it is sufficient to set it by observing the distribution of the withdrawal timing. Therefore, the current suppression period can be set shorter than that of the technique of Patent Document 1.
Here, since the wire feeding cycle Tf is constant, it is possible to lengthen the current non-suppression period. The current non-suppressing period is a period for droplet growth, but the fact that this can be taken for a long time means that the targeted droplet growth is possible even if the current value in the current non-suppressing period is lowered. Since it is generally known that the larger the welding current, the more the wear of the contact tip progresses, it can be expected that the reduction of the current during the current non-suppression period leads to the reduction of the wear of the contact tip.

<Other embodiments>
Although the embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the scope described in the above-described embodiments. It is clear from the description of the claims that the above-described embodiment with various modifications or improvements is also included in the technical scope of the present invention.
For example, in the description of the above-described embodiment, the amplitude feed rate setting unit 21 (see FIG. 2), the feed rate command setting unit 22 (see FIG. 2), the current setting unit 36 (see FIG. 2), and the forward / reverse speed ratio. Although the case where the setting unit 38 (see FIG. 2) and the like are built in the welding power supply 150 (see FIG. 2) has been described, these may be built in the robot controller 160. In that case, in the robot controller 160, for example, a CPU (Central Processing Unit) (not shown) reads a program stored in a ROM (Read Only Memory) (not shown) into a RAM (Random Access Memory) (not shown) and executes it. , These functional parts are realized.

10 ... Arc welding system, 23 ... Feed drive unit, 36 ... Current setting unit, 36A ... Current suppression period setting unit, 36B ... Wire tip position conversion unit, 100 ... Consumable electrode (welding wire), 110 ... Welding torch, 120 ... Welding robot, 130 ... Feeding device, 140 ... Shielded gas supply device, 150 ... Welding power supply, 160 ... Robot controller, 200 ... Base material

Claims (8)

It is a welding power supply that supplies a welding current to a wire as a consumable electrode and releases the droplets in an open arc state without short-circuiting the wire to the molten pool.
Feeding control means for controlling the feeding of the wire so that the tip of the wire is fed toward the base metal with periodic switching between the period of normal feeding and the period of reverse feeding. When,
A current control means for changing the welding current according to the position of the tip of the wire whose distance from the surface of the base material fluctuates periodically is provided.
In the feeding control means, the time from the nearest point where the tip of the wire is closest to the base material to the farthest point where the tip of the wire is farthest from the base material is set by the tip of the wire. Controlled to be shorter than the time from the farthest point to the latest point.
The current control means is a welding power source that controls so as to provide a low current period in which the tip of the wire is fed back to a lower current value than a predetermined current value. The feed control means sets the maximum feed rate of the wire during the period when the tip of the wire is reversely fed to the maximum feed rate of the wire during the period when the tip of the wire is positively fed. The welding power source according to claim 1, wherein the wire is also controlled to be increased. The current control means said when the position of the tip of the wire, which fluctuates periodically, is located closer to the base metal than the position of 1/2 of the wave height defined by the latest point and the farthest point. The welding power source according to claim 1, wherein the welding power source is controlled so as to start a low current period. The current control means of the wire is switched from the position of the tip of the wire at the time when the low current period is switched from the period in which the tip of the wire is positively fed to the period in which the tip of the wire is fed in reverse. The welding power source according to claim 3, wherein the welding power supply is controlled so as to be started within the range up to the tip position of the wire at the time when the command value of the feeding speed is maximized. In the current control means, the tip of the wire is reverse-fed from the position of the tip of the wire at the time when the command value of the feeding speed of the wire switched to the reverse feeding is maximized during the low current period. The welding power source according to claim 3, wherein the welding power supply is controlled so as to be terminated within the range up to the tip position of the wire at the time of switching from the period to the normal feeding period. It is a welding system that supplies welding current to a wire as a consumable electrode to perform arc welding, and releases the droplets in an open arc state without short-circuiting the wire to the molten pool.
Feeding control means for controlling the feeding of the wire so that the tip of the wire is fed toward the base metal with periodic switching between the period of normal feeding and the period of reverse feeding. When,
A current control means for changing the welding current according to the position of the tip of the wire whose distance from the surface of the base material fluctuates periodically is provided.
In the feeding control means, the time from the nearest point where the tip of the wire is closest to the base material to the farthest point where the tip of the wire is farthest from the base material is set by the tip of the wire. Controlled to be shorter than the time from the farthest point to the latest point.
The current control means is a welding system characterized in that a low current period in which the welding current is lower than a predetermined current value is provided within a period in which the tip of the wire is back-fed. It is a method of controlling a welding power source in which a welding current is supplied to a wire as a consumable electrode and the droplets are separated in an open arc state without short-circuiting the wire to a molten pool.
A step of controlling the feeding of the wire so that the tip of the wire is fed toward the base metal with periodic switching between the period of normal feeding and the period of reverse feeding.
The step includes a step of changing the welding current according to the position of the tip of the wire whose distance from the surface of the base metal varies periodically.
In the step of controlling the feeding, the time from the nearest point where the tip of the wire is closest to the base material to the farthest point which is the position farthest from the base material is set. Is controlled to be shorter than the time from the farthest point to the latest point.
The step of changing the welding current is characterized in that, within the period in which the tip of the wire is fed back, a low current period in which the welding current is lowered from a predetermined current value is provided. Welding power supply control method. To the computer of the welding system that supplies welding current to the wire as a consumable electrode for arc welding and releases the droplets in an open arc state without short-circuiting the wire to the molten pool.
A function to control the feeding of the wire so that the tip of the wire is fed toward the base metal while periodically switching between the period of normal feeding and the period of reverse feeding.
The function of changing the welding current according to the position of the tip of the wire whose distance from the surface of the base metal fluctuates periodically is realized.
The function of controlling the feeding is to set the time from the latest point where the tip of the wire is closest to the base material to the farthest point which is the farthest position from the base material. Is controlled to be shorter than the time from the farthest point to the latest point.
The function of changing the welding current is characterized by controlling so as to provide a low current period in which the tip of the wire is fed back to a lower current value than a predetermined current value. program.

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