JP3990182B2 - Arc start control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an arc start control method of consumable electrode arc welding in which a welding wire is fed forward and backward to a base material to start an arc by a wire feeding motor capable of forward and reverse rotation.
[0002]
[Prior art]
FIG. 1 is a block diagram of a conventional arc welding apparatus. Hereinafter, a description will be given with reference to FIG.
When a welding start signal St is input from a welding start circuit ST provided outside, the welding power supply device PS outputs a welding voltage Vw and a welding current Iw for generating an arc and feeds the welding wire 1. A feed control signal Fc for control is output to the wire feed motor WM. The welding wire 1 is fed through the welding torch 4 by the rotation of the feeding roll 5 directly connected to the wire feeding motor WM, and is fed through the feeding tip 4a to be connected to the base material 2. An arc 3 is generated between them. When the wire feed motor WM rotates in the forward direction, the welding wire 1 is fed forward to the base material 2, and when it rotates in the reverse direction, the welding wire 1 is fed backward in a direction away from the base material 2. When the welding wire 1 and the base material 2 are in a contact (short circuit) state or an arc generation state, the welding current Iw is energized. On the other hand, when the welding wire 1 and the base material 2 are separated from each other and the arc 3 is not generated, the welding voltage Vw becomes the maximum no-load voltage and the welding current Iw is not energized. Further, the distance between the tip of the welding wire 1 and the base material 2 is the wire tip / base material distance Lw [mm]. Therefore, the distance Lw between the wire tip and the base material during arc generation is substantially equal to the arc length.
[0003]
FIG. 2 is a timing chart of each signal of the above-described welding apparatus. FIG. 4A shows the time change of the welding start signal St, FIG. 4B shows the time change of the feed control signal Fc, FIG. 4C shows the time change of the welding voltage Vw, and FIG. (D) shows the time change of the welding current Iw, and FIG. (E) shows the time change of the wire tip / base material distance Lw. Hereinafter, a description will be given with reference to FIG.
[0004]
(1) Period from time t1 to t2 (forward feed)
At time t1, when the welding start signal St is input (High level) as shown in FIG. 9A, the feed control signal Fc is sent as a positive initial value as shown in FIG. The feed speed is set to Fsi [m / min], and the welding wire is fed forward to the base material at the initial feed speed. The initial feed speed setting value Fsi is set to a slow speed of about several m / min. When the feed control signal Fc is a positive value, forward feeding is performed, and when the feed control signal Fc is negative, backward feeding is performed. Further, the external characteristics of the welding power source apparatus during the period from the time t1 to the time t4 are output-controlled to a constant current characteristic or a drooping characteristic in order to pass an initial current Is described later. However, during this period from time t1 to time t2, since the welding wire and the base material are in an unloaded state, the welding voltage Vw becomes the no-load voltage Vnl as shown in FIG. As shown in (D), the welding current Iw is not energized. On the other hand, as shown in FIG. 5E, the wire tip / base material distance Lw gradually decreases with time due to forward feeding.
[0005]
(2) Period from time t2 to t3 (reverse feed)
At time t2, the welding wire comes into contact with the base metal by the above-described forward feeding, and the welding voltage Vw becomes a short-circuit voltage value equal to or lower than a predetermined reference voltage value Vth [V] as shown in FIG. When changed, the feed control signal Fc becomes a negative reverse feed speed setting value Fsr as shown in FIG. 5B, and the welding wire is fed backward from the base material at the reverse feed speed. At the same time, as shown in FIG. 4D, the initial current Is having a small current value determined by the constant current characteristic or the drooping characteristic of the welding power source described above is energized. The value of the initial current Is is set to a small current value of about several A to several tens of A. On the other hand, at time t2, the wire feed motor is switched from forward rotation (forward feed) to reverse rotation (reverse feed). During the delay time of the motor for this reverse rotation, the welding wire Forward feed is continued by inertia. However, since the welding wire is already in contact with the base material, the contact state is maintained.
[0006]
(3) Period from time t3 to t4 (reverse feed)
Immediately after time t3, when the welding wire and the base material are separated by the backward feeding, an initial arc in which the initial current Is is applied is generated. As shown in FIG. The arc voltage value exceeds the reference voltage value Vth. During the predetermined delay time Td from the time when the initial arc is generated, the feed control signal Fc remains at the reverse feed speed set value Fsr as shown in FIG. Will continue to be repatriated. For this reason, as shown in FIG. 4D, the initial arc in which the initial current Is is applied is generated, and the distance between the wire tip and the base material (arc length) Lw is as shown in FIG. It becomes longer with time. The arc length Lw becomes longer at a speed obtained by adding the upward wire feeding speed as well as the upward backward feeding speed. Accordingly, the change length of the arc length Lw during this period is determined by the backward feeding speed, the wire melting speed, the delay time Td, and the like.
[0007]
(4) Period after time t4 (re-forward feed)
When the delay time Td elapses at time t4, the feed control signal Fc becomes a positive steady feed speed set value Fs as shown in FIG. 5B, and the welding wire is at a steady feed speed. Re-forwarded. At the same time, the external characteristic of the welding power source device is switched to the constant voltage characteristic, and as shown in FIG. 4C, the welding voltage Vw becomes a voltage value corresponding to a predetermined voltage setting value Vs, and FIG. As shown, the welding current Iw is a steady welding current Ic determined by the steady feeding speed. Also, as shown in FIG. 5E, during the motor delay time for the wire feed motor after time t4 to reverse from reverse rotation (reverse feed) to normal rotation (re-forward feed). Since the backward feed continues, the arc length Lw further increases and reaches the longest arc length Lt, and then gradually decreases due to re-forward feed. At time t5, the arc length Lw converges to the steady arc length Lc. The period from time t4 to t5 is the convergence time Tc.
[0008]
[Problems to be solved by the invention]
FIG. 3 is a diagram showing a change waveform of the arc length Lw after time t3 in FIG. 2 described above. The horizontal axis of the figure shows the elapsed time from the initial arc occurrence time (time t3), and the vertical axis shows the change of the arc length Lw. The figure shows the case of MAG welding using a mild steel wire having a diameter of 0.9 mm. A waveform 1 indicated by a solid line is when a welding stop time Ts = 10 seconds, which will be described later, and a waveform 2 indicated by a dotted line is when the welding stop time Ts = 1 second. Hereinafter, a description will be given with reference to FIG.
[0009]
When a plurality of weldings are repeated, the elapsed time from the previous welding end time to the current welding start time is expressed as a welding stop time Ts [seconds]. When the welding stop time Ts is as short as several seconds or less, the tip of the welding wire is kept at a high temperature due to the residual heat from the previous welding, and the next arc start is performed. When the welding stop time Ts is as long as ten or more seconds, the next arc start is performed with the tip of the welding wire already cooled. As described above in the description of FIG. 2, the change in the arc length Lw after the initial arc generation after time t3 is determined by the backward feeding speed, the wire melting speed, and the delay time Td. Here, if the backward feed speed is set to 6 m / min and the delay time Td = 20 ms, the change in the arc length Lw is determined by the wire melting speed. The wire melting rate is determined mainly by the welding current value, the wire protrusion length, the material of the welding wire, the welding method, the preheating state of the wire tip, and the like. The welding current value is a constant value at the initial current Is, and when the wire protrusion length, the material of the welding wire, and the welding method are set in advance, the wire melting rate is determined by the remaining heat state of the wire tip. In particular, when using a welding wire having a large resistance value such as steel or stainless steel, the change in the arc length Lw is greatly affected by the residual heat state of the wire tip. As described above, the remaining heat state of the wire tip is determined by the welding stop time Ts. Therefore, the change in the arc length Lw is greatly influenced by the welding stop time Ts. This is shown in FIG.
[0010]
(1) Waveform 1 (Ts = 10 seconds)
As described above, the change in the arc length Lw is determined by the backward feeding speed, the delay time Td, and the wire melting speed (the remaining heat state of the wire tip). Here, since the welding stop time Ts = 10 seconds is sufficiently long, when the wire tip is in a cooled state, the reverse feed speed and the delay time Td are set to appropriate values so that the arc length overshoot is reduced. It is set. Therefore, as shown in the waveform 1, the arc length overshoot is small, the longest arc length Lt1 is substantially equal to the steady value, and the convergence time Tc1 is also shortened.
[0011]
(2) Waveform 2 (Ts = 1 second)
In the case of the waveform 2, since the welding stop time Ts is as short as 1 second, the residual heat at the tip of the wire is increased, and the wire melting rate is increased. For this reason, the arc length overshoot increases at the same reverse feed speed and delay time Td as described above. For this reason, the difference between the longest arc length Lt2 and the steady value increases, and the convergence time Tc2 also increases.
[0012]
As described above, since the remaining heat state of the wire tip changes depending on the welding stop time Ts, the overshoot of the arc length greatly changes. If the overshoot of the arc length is large, the melting, the bead appearance, etc. are deteriorated, resulting in a defective arc start.
[0013]
FIG. 4 is a diagram illustrating the relationship between the above-described welding stop time Ts and the longest arc length Lt. When the welding stop time Ts is 3 seconds or more, the tip of the wire is cooled and the difference from the peripheral temperature becomes small, so the overshoot becomes small and the longest arc length Lt becomes substantially equal to the steady value 3 mm. However, as the welding stop time Ts becomes shorter than 3 seconds, the overshoot increases and the longest arc length Lt also increases.
[0014]
Therefore, the present invention provides an arc start control method that can always reduce the overshoot of the arc length without being affected by the length of the welding stop time.
[0015]
[Means for Solving the Problems]
As shown in FIGS. 5 to 7, when a welding start signal St is input to the welding power source device, the first invention starts forward feeding of the welding wire to the base material and starts output of the welding power source device. When the welding wire comes into contact with the base material by this forward feeding, the welding wire starts to be fed backward from the base material at the backward feeding speed, and the initial current Is having a small current value is energized. After the delay time Td has elapsed from the time when the wire is separated from the base metal and the initial arc is generated, the welding wire is re-advanced and the steady welding current Ic is applied to the steady arc from the initial arc generation state. In the arc start control method of consumable electrode arc welding to shift to the generation state,
At least one of the delay time Td or the reverse feed speed is changed according to a predetermined function f (Ts) by inputting a welding stop time Ts that is an elapsed time from the previous welding end time to the current welding start time. An arc start control method characterized by:
[0016]
As shown in FIGS. 5 to 7, the second invention is characterized in that the function f (Ts) varies depending on at least one of the material of the welding wire or the welding method. Is the method.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
As described above in the description section of FIG. 3, the magnitude of the arc length overshoot is greatly influenced by the delay time Td, the reverse feed speed, and the wire melting speed (welding stop time Ts). Therefore, when the welding stop time Ts changes and the wire melting rate changes, the magnitude of the arc length overshoot also changes. In this case, in order to reduce the overshoot, the amount of change in the wire melting speed due to the welding stop time Ts may be compensated by correcting the delay time Td and / or the backward feed speed. That is, when the welding stop time Ts is shortened and the wire melting rate is increased, if the delay time Td is shortened or the backward feed rate is slowed to compensate for the amount of change in the wire melting rate, the arc length overshoot always occurs. Get smaller. Therefore, the embodiment of the present invention is an arc start control method in which at least one of the delay time Td or the reverse feed speed is changed according to a predetermined function f (Ts) with the welding stop time Ts as an input. An example of this function will be described below.
[0018]
FIG. 5 is a diagram illustrating a function that outputs the delay time Td with the welding stop time Ts as an input. In the figure, the broken line X1 is the case where the welding wire is made of steel and the welding method is MAG welding, the broken line X2 is the case where the welding wire is made of steel and the welding method is pulse MAG welding, and the broken line X3 is the welding wire. Is the case where the material is stainless steel and the welding method is MIG welding, and the broken line X4 is the case where the material of the welding wire is stainless steel and the welding method is pulsed MIG welding. A function can be defined based on this figure. For example, the function f (Ts) for the broken line X1 is represented by the following equation.
When 0 <Ts ≦ 3, Td = (10/3) Ts + 10 (1)
When 3 <Ts, Td = 20
[0019]
Therefore, at the time of MAG welding of a steel wire, the delay time Td may be changed according to the above function depending on the welding stop time Ts. As a result, the arc length overshoot can always be reduced.
[0020]
FIG. 6 is a diagram illustrating a function for outputting the reverse feed speed setting value Fsr with the welding stop time Ts as an input. In the figure, the broken line Y1 is the case where the welding wire material is steel and the welding method is MAG welding, the broken line Y2 is the welding wire material is steel and the welding method is pulse MAG welding, and the broken line Y3 is the welding wire. Is the case where the material is stainless steel and the welding method is MIG welding, and the broken line Y4 is the case where the material of the welding wire is stainless steel and the welding method is pulsed MIG welding. A function can be defined based on this figure. For example, the function f (Ts) for the broken line Y1 is as follows.
When 0 <Ts ≦ 3, Fsr = Ts + 3
When 3 <Ts, Fsr = 6
[0021]
Therefore, at the time of MAG welding of the steel wire, the reverse feed speed set value Fsr may be changed according to the above function according to the welding stop time Ts. As a result, the arc length overshoot can always be reduced.
[0022]
FIG. 7 is a block diagram of a welding power source device PS for carrying out the above-described present invention. Hereinafter, a description will be given with reference to FIG.
The output control circuit INV receives a commercial power supply (3-phase 200V, etc.) as input, performs output control such as inverter control and thyristor control according to a drive signal Dv described later, and outputs a welding voltage Vw and a welding current Iw suitable for welding. .
[0023]
The welding stop time measurement circuit TS receives the welding start signal St, measures the elapsed time from the previous welding end time to the current welding start time, and outputs a welding stop time measurement signal Ts. The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The short circuit determination circuit SD outputs the short circuit determination signal Sd which becomes High level when the voltage detection signal Vd is equal to or lower than the reference voltage value Vth as described above with reference to FIG. The delay time setting circuit TDS receives the welding stop time measurement signal Ts as an input and outputs the delay time setting signal Tds by a predetermined function as described above with reference to FIG. The delay circuit TD outputs a delay signal Td that becomes High level only during a delay time determined by the delay time setting signal Tds from the time when the short circuit determination signal Sd changes from High level to Low level (initial arc generation time). Output. The initial feed speed setting circuit FSI outputs a predetermined initial feed speed setting signal Fsi. The logic NOT circuit NOT logically inverts the short circuit determination signal Sd and outputs a switching signal Not. The initial feeding switching circuit SI is connected to the a side until the switching signal Not changes from the High level to the Low level (short circuit), and the initial feeding speed setting signal Fsi is used as the feeding speed control setting signal Fsc. After the output is changed from the High level to the Low level, the mode is switched to the b side, and a reverse feed switching circuit output signal Sr, which will be described later, is output as the feed speed control setting signal Fsc. The reverse feed speed setting circuit FSR receives the welding stop time measurement signal Ts as an input, and outputs the reverse feed speed setting signal Fsr according to a predetermined function as described above with reference to FIG. The steady feeding speed setting circuit FS outputs a predetermined steady feeding speed setting signal Fs. The reverse feed switching circuit SR is connected to the a side until the delay signal Td changes from High level to Low level, and outputs the reverse feed speed setting signal Fsr as the reverse feed switching circuit output signal Sr. Then, after changing from the High level to the Low level, it switches to the b side and outputs the above-mentioned steady feeding speed setting signal Fs as the backward feeding switching circuit output signal Sr. The feed control circuit FC outputs a feed control signal Fc for feeding a welding wire to the wire feed motor WM at a speed corresponding to the feed speed control setting signal Fsc.
[0024]
The voltage setting circuit VS outputs a predetermined voltage setting signal Vs. The initial current setting circuit ISI outputs a predetermined initial current setting signal Isi. The voltage error amplification circuit EV amplifies an error between the voltage setting signal Vs and the voltage detection signal Vd and outputs a voltage error amplification signal Ev. By the feedback control by this voltage error amplifier circuit EV, the external characteristic of the welding power source device becomes a constant voltage characteristic for supplying a steady welding current. The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The current error amplification circuit EI amplifies an error between the initial current setting signal Isi and the current detection signal Id and outputs a current error amplification signal Ei. By the feedback control by the current error amplifier circuit EI, the external characteristic of the welding power source device becomes a constant current characteristic or a drooping characteristic for supplying an initial current. The external characteristic switching circuit SP is connected to the a side until the delay signal Td changes from the High level to the Low level, and outputs the current error amplification signal Ei as the error amplification signal Ea, and from the High level to the Low level. Then, the voltage is switched to the b side, and the voltage error amplified signal Ev is output as the error amplified signal Ea. The drive circuit DV outputs a drive signal Dv in accordance with the error amplification signal Ea.
[0025]
[effect]
The effects of the present invention will be described below with reference to the drawings.
FIG. 8 is a diagram showing a change in the arc length Lw according to the present invention corresponding to FIG. 3 described above. Similar to FIG. 3, the horizontal axis of FIG. 3 indicates the elapsed time from the initial arc occurrence time, and the vertical axis indicates the change in the arc length Lw. As in FIG. 3, the welding conditions are for MAG welding using a mild steel wire having a diameter of 0.9 mm. Moreover, the waveform 2 of the figure is the same waveform as the waveform 2 of FIG. 3, and is a case of the prior art when the welding stop time Ts = 1 second. Waveform 3 is the case of the present invention when the welding stop time Ts = 1 second. Hereinafter, a description will be given with reference to FIG.
[0026]
In the prior art, even if the welding stop time Ts changes, the delay time is constant at Td1 = 20 ms. Therefore, as shown in the waveform 2, the arc length Lw greatly overshoots. On the other hand, in the present invention, the delay time Td varies depending on the welding stop time Ts. Since this figure is a case of MAG welding of a steel wire, the delay time Td changes according to the above-described equation (1). Substituting Ts = 1 into equation (1) yields the following equation.
Td = (10/3) ・ 1 + 10 = 13.3ms = Td2
Therefore, in the present invention, the delay time when the welding stop time Ts = 1 second changes to Td2 = 13.3 ms. As shown in the waveform 3, at the time t41 when the delay time Td2 = 13.3 ms has elapsed since the initial arc occurrence time, the reverse feed is switched to the re-forward feed, and the arc length overshoot becomes small.
[0027]
FIG. 9 is a relationship diagram between the welding stop time Ts and the longest arc length Lt in the present invention corresponding to FIG. 4 described above. In the figure, the dotted line is the case of the prior art of FIG. 4, and the solid line is the case of the present invention. As is apparent from the figure, in the present invention, the longest arc length Lt is a value near the steady value without being affected by the welding stop time Ts. This indicates that in the present invention, the arc length overshoot is small regardless of the welding stop time Ts.
[0028]
【The invention's effect】
According to the arc start control method of the present invention,
Even if the welding stop time changes and the residual heat state of the wire tip changes, the overshoot of the arc length can be reduced by correcting the delay time or the reverse feed speed or both to an appropriate value according to a predetermined function. Therefore, a good arc start can always be performed.
Furthermore, in the present invention, the function can be optimized under various welding conditions by changing the above function according to at least one of the material of the welding wire or the welding method. A good arc start can always be performed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a conventional welding apparatus.
FIG. 2 is a timing chart of each signal of a conventional welding apparatus.
FIG. 3 is a graph showing a change in arc length after the occurrence of an initial arc in the prior art.
FIG. 4 is a relationship diagram between a welding stop time Td and a longest arc length Lt in the prior art.
FIG. 5 is a change diagram of a delay time Td with respect to a welding stop time Ts in the present invention.
FIG. 6 is a change diagram of a reverse feed speed setting value Fsr with respect to a welding stop time Ts in the present invention.
FIG. 7 is a block diagram of a welding power supply device of the present invention.
FIG. 8 is a change diagram of the arc length in the present invention corresponding to FIG. 3;
9 is a relationship diagram between a welding stop time Ts and a longest arc length Lt in the present invention corresponding to FIG. 4;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Welding wire 2 Base material 3 Arc 4 Welding torch 4a Feed tip 5 Feed roll DV drive circuit Dv Drive signal Ea Error amplification signal EI Current error amplification circuit Ei Current error amplification signal EV Voltage error amplification circuit Ev Voltage Error amplification signal FC Feed control circuit Fc Feed control signal FS Steady feed speed setting circuit Fs Steady feed speed setting (value / signal)
FSI initial feed speed setting circuit Fsi initial feed speed setting (value / signal)
FSR Reverse feed speed setting circuit Fsr Reverse feed speed setting (value / signal)
Ic Steady welding current ID Current detection circuit Id Current detection signal Is Initial current ISI Initial current setting circuit Isi Initial current setting signal Iw Welding current Lc Steady arc length Lw Distance between wire tip and base material / arc length NOT Logic negation circuit Not switching Signal PS Welding power supply device SD Short circuit determination circuit Sd Short circuit determination signal SI Initial feed switching circuit SP External characteristic switching circuit SR Reverse feed switching circuit Sr Reverse feed switching circuit output signal ST Welding start circuit St Welding start signal Tc Convergence time TD Delay meeting and Td delay (time / signal)
TDS delay time setting circuit Tds delay time setting signal TS welding stop time measuring circuit Ts welding stop time (measurement signal)
VD voltage detection circuit Vd voltage detection signal Vnl no-load voltage VS voltage setting circuit Vs voltage setting (value / signal)
Vth Reference voltage value Vw Welding voltage WM Wire feed motor

Claims (2)

When a welding start signal is input to the welding power source device, the feed forward of the welding wire to the base material is started and the output of the welding power source device is started. When the welding wire comes into contact with the base material by the forward feed, the welding wire moves backward. Start the backward feeding of the welding wire from the base metal at the feeding speed and apply an initial current of a small current value. The delay time from the time when the welding wire is separated from the base metal by this backward feeding and the initial arc is generated. In the arc start control method of consumable electrode arc welding, which starts re-advancing feeding of the welding wire after the elapse of time and energizes a steady welding current to shift from the initial arc generation state to the steady arc generation state.
At least one of the delay time or the backward feed speed is changed according to a predetermined function with a welding stop time that is an elapsed time from the previous welding end time to the current welding start time as an input. Arc start control method. The arc start control method according to claim 1, wherein the function varies depending on at least one of a material of a welding wire or a welding method.

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