JP5937323B2 - Plasma keyhole welding method and plasma keyhole welding system - Google Patents

Description

  The present invention relates to a plasma keyhole welding method and a plasma keyhole welding system.

  In the plasma keyhole welding method, for example, when welding a butt joint having an I-shaped groove as a base material, an arc generated when a tungsten electrode is generally used as a cathode, a water-cooled nozzle, a plasma gas gas flow, Restrained by. The high temperature plasma flow having good concentration is generated, and this high temperature plasma flow moves on the welding line while forming a keyhole penetrating the base material at the tip of the molten pool. This welding is directly applied until the arc heat reaches the back surface, and the back surface can be appropriately melted. The plasma keyhole welding method is described in Patent Document 1, for example. In the method described in Patent Document 1, a keyhole is formed in a state where the torch is stopped, and the movement of the torch is started after the keyhole has penetrated. This method is intended to form a beautiful bead immediately after the start of welding.

  If the time required for the keyhole to penetrate in the plasma keyhole welding method is long, the start of steady welding is delayed, and the work efficiency of the welding work is reduced. For this reason, when performing such a plasma keyhole welding method, it is desired to penetrate the keyhole earlier so as to start the welding operation early.

Japanese Patent Publication No. 02-18893

  The present invention has been conceived under the circumstances described above, and its main object is to provide a plasma keyhole welding method and a plasma keyhole welding system that can penetrate the keyhole more quickly. To do.

According to the first aspect of the present invention, an arc is ignited between the plasma electrode and the base material, and the key hole is penetrated by the arc, and after the key hole has penetrated, the plasma electrode is moved to the mother electrode. A step of performing steady welding while moving the material, and the step of penetrating is a keyhole formation period that is a period from the start of formation of the keyhole to the time of penetration of the keyhole Including a step of flowing a welding current flowing between the plasma electrode and the base material as a pulse current whose frequency is an initial frequency, and the step of performing the steady welding includes the welding current at a frequency of the steady frequency. includes a step of flowing a pulse current is, the initial frequency is the steady-state frequency is less than the plasma keyhole welding method is provided.

Preferably, the time average value of the absolute value of the welding current in the penetrating step and the time average value of the absolute value of the welding current in the step of performing steady welding are the same.

  Preferably, the step of penetrating includes a step of ejecting a plasma gas ejected toward the base material at an initial gas flow rate during the keyhole formation period, and the step of performing the steady welding includes the plasma gas Is ejected at a steady gas flow rate, and the initial gas flow rate is larger than the steady gas flow rate.

  Preferably, the method further includes the step of calculating the value of the initial frequency by decreasing the value of the stationary frequency by an initial frequency calculation circuit.

  Preferably, the step of penetrating includes a step of setting a moving speed, which is a speed of the plasma electrode with respect to the base material, in an welding progress direction along the base material to an initial speed, and performing the steady welding. The performing step includes a step of setting the moving speed to a steady speed, and the initial speed is smaller than the steady speed.

According to the second aspect of the present invention, an output circuit that allows a pulse current to flow between the plasma electrode and the base material, an initial frequency storage unit that stores a value of the initial frequency, and a steady frequency memory that stores a value of the steady frequency And a keyhole penetration detection circuit that generates a keyhole penetration detection signal when detecting that the keyhole has penetrated through the base material, and the output circuit generates the keyhole penetration detection signal. the before, it passed the pulse current frequency as the initial frequency, and, after the keyhole through detection signal is generated, and the flow of the pulsed current frequency as the stationary frequency, the initial frequency, A plasma keyhole welding system is provided that is less than the stationary frequency .

  Preferably, a set current value storage unit for storing a set current value is further provided, and the output circuit is generated before the keyhole penetration detection signal is generated and after the keyhole penetration detection signal is generated. Then, the pulse current is passed with the time average value of the absolute value as the set current value.

Preferably, a gas flow rate control circuit that controls a gas flow rate that is a flow rate of plasma gas ejected toward the base material, an initial gas flow rate storage unit that stores a value of the initial gas flow rate, and a steady gas flow rate value are stored. A stationary gas flow rate storage unit, wherein the gas flow rate control circuit sets the gas flow rate to the initial gas flow rate and generates the keyhole before the keyhole penetration detection signal is generated. After the penetration detection signal is generated, the gas flow rate is set to the steady gas flow rate, and the initial gas flow rate is larger than the steady gas flow rate .

  Preferably, an initial frequency calculation circuit is further provided that stores a value obtained by reducing the value of the steady frequency stored in the steady frequency storage unit in the initial frequency storage unit as the initial frequency.

Preferably, an operation control circuit that controls a moving speed that is a speed of the plasma electrode with respect to the base material in a welding progress direction along the base material, and an initial speed storage unit that stores a value of the initial speed And a steady speed storage unit that stores a value of the steady speed, and the operation control circuit sets the moving speed to the initial speed before the keyhole penetration detection signal is generated. After the keyhole penetration detection signal is generated, the moving speed is set to the steady speed, and the initial speed is smaller than the steady speed .

  According to such a configuration, the keyhole can be penetrated more quickly.

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

It is a figure which shows the structure of the plasma keyhole welding system concerning 1st Embodiment of this invention. It is a partial expanded sectional view which shows the welding torch shown in FIG. It is a block diagram which shows the internal structure of the steady welding start judgment circuit of FIG. It is a timing chart which shows an example of the plasma keyhole welding method concerning 1st Embodiment of this invention. It is a figure which shows an example of the waveform of a welding current in detail. It is a figure which shows an example of the waveform of a welding current in detail. It is a figure which shows an example of the waveform of a welding current in detail. It is sectional drawing which shows the state of the base material in the plasma keyhole welding method of 1st Embodiment of this invention. It is a figure which shows the welding state desired when performing plasma keyhole welding. It is a figure which shows the example of a malfunction which may arise when performing plasma keyhole welding. It is a figure which shows the example of a malfunction which may arise when performing plasma keyhole welding. It is sectional drawing which shows the surface of the molten pool during a keyhole formation period. It is a figure which shows the structure of the plasma keyhole welding system concerning the 1st modification of 1st Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

<First Embodiment>
1st Embodiment of this invention is described using FIGS.

  FIG. 1 is a diagram showing a configuration of a plasma keyhole welding system according to a first embodiment of the present invention.

  A plasma keyhole welding system A1 shown in FIG. 1 includes a welding robot 1, a robot control device 2, a welding power supply device 3, and a gas supply device 4.

  The welding robot 1 includes a welding torch 11 and a manipulator 12.

  As shown in FIG. 2, the welding torch 11 has a nozzle 111 and a plasma electrode 112. The nozzle 111 is a cylindrical member made of a metal such as copper. The nozzle 111 has a water cooling structure as appropriate. The plasma electrode 112 is a non-consumable electrode. The plasma electrode 112 is a metal rod made of tungsten, for example. The plasma electrode 112 is an electrode for applying a welding voltage Vw to the base material W. The plasma gas PG is ejected from the nozzle 111 so as to surround the plasma electrode 112. The plasma gas PG is, for example, Ar. When a welding voltage Vw is applied between the plasma electrode 112 and the base material W, an arc a1 is generated using the plasma gas PG as a medium. When the arc a <b> 1 is generated, a welding current Iw flows between the plasma electrode 112 and the base material W. The manipulator 12 holds the welding torch 11. The manipulator 12 is, for example, an articulated robot. The base material W is made of, for example, aluminum, an aluminum alloy, or stainless steel.

  The gas supply device 4 is for supplying a plasma gas PG to be ejected toward the base material W. The amount of plasma gas PG supplied by the gas supply device 4 (that is, the amount of plasma gas PG ejected from the nozzle 111) is determined by a gas flow rate setting signal Pgs described later.

  The robot control device 2 includes an operation control circuit 21, a teach pendant 23, an initial speed storage unit 251, and a steady speed storage unit 252. The robot control device 2 is for controlling the operation of the welding robot 1.

  The teach pendant 23 is connected to the operation control circuit 21. The teach pendant 23 is for the user of the plasma keyhole welding system A1 to set various operations. When the teach pendant 23 receives an instruction to start welding from the user of the plasma keyhole welding system A1, it sends a welding start signal St.

  The initial speed storage unit 251 stores the value of the initial speed vr1. The initial speed vr1 is input from the teach pendant 23, for example, and stored in the initial speed storage unit 251 via the operation control circuit 21. The steady speed storage unit 252 stores the value of the steady speed vr2. The value of the steady speed vr2 is input from the teach pendant 23, for example, and stored in the steady speed storage unit 252 via the operation control circuit 21.

  The operation control circuit 21 has a microcomputer and a memory (not shown). The memory stores a work program in which various operations of the welding robot 1 are set. Further, the operation control circuit 21 controls the moving speed VR of the plasma electrode 112. The moving speed VR is the speed of the plasma electrode 112 with respect to the base material W in the welding progress direction Dr along the base material W. The operation control circuit 21 sends an operation control signal Ms to the welding robot 1 based on the work program, the coordinate information from the encoder, the moving speed VR, and the like. The welding robot 1 receives the operation control signal Ms and rotates a motor (not shown). As a result, the welding torch 11 moves to a predetermined welding start position on the base material W or moves along the in-plane direction of the base material W.

  The operation control circuit 21 sets the moving speed VR to the initial speed vr1 before a keyhole penetration detection signal Cm2 (see FIG. 4E) described later is generated. On the other hand, after the keyhole penetration detection signal Cm2 is generated, the operation control circuit 21 sets the moving speed VR to the steady speed vr2. In the present embodiment, the operation control circuit 21 receives the welding start signal St from the teach pendant 23 and sends it to the welding power source device 3.

  The welding power supply device 3 is a device for applying a welding voltage Vw and causing a welding current Iw to flow between the plasma electrode 112 and the base material W. The welding power source device 3 includes an output circuit 31, a voltage detection circuit 32, a steady welding start determination circuit 33, a gas flow rate control circuit 35, an initial frequency storage unit 361, a steady frequency storage unit 362, and a set current value storage. A unit 364, an initial gas flow rate storage unit 365, and a steady gas flow rate storage unit 366.

  The initial frequency storage unit 361 stores the value of the initial frequency ff1. The stationary frequency storage unit 362 stores the value of the stationary frequency ff2. The set current value storage unit 364 stores the set current value ir1. The initial gas flow rate storage unit 365 stores the value of the initial gas flow rate pg1. The steady gas flow rate storage unit 366 stores the steady gas flow rate pg2. The values of the initial frequency ff1, the steady frequency ff2, the set current value ir1, the initial gas flow rate pg1, and the steady gas flow rate pg2 are input from the teach pendant 23, for example, and stored in each storage unit via the operation control circuit 21. .

  The output circuit 31 is for causing the welding current Iw to flow at a value instructed between the plasma electrode 112 and the base material W. In the present embodiment, the welding current Iw is a pulse current. The output circuit 31 includes a power supply circuit 311, a frequency control circuit 312, a current control circuit 313, a current detection circuit 314, and a current error calculation circuit 315.

  The power supply circuit 311 receives, for example, a commercial power supply such as three-phase 200 V, performs output control such as inverter control and thyristor phase control according to a current error signal Ei described later, and outputs a welding voltage Vw and a welding current Iw. The power supply circuit 311 receives the welding start signal St from the operation control circuit 21.

  The frequency control circuit 312 controls the frequency Ff of the welding current Iw that is a pulse current. The frequency control circuit 312 is connected to the initial frequency storage unit 361 and the steady frequency storage unit 362. The frequency control circuit 312 sends a frequency setting signal Ffs for controlling the frequency Ff to the power supply circuit 311. Specifically, before a keyhole penetration detection signal Cm2 (see FIG. 4E), which will be described later, is generated, the frequency control circuit 312 causes the welding current Iw whose frequency Ff is the initial frequency ff1 to flow. The frequency setting signal Ffs is sent to the power supply circuit 311. As a result, the power supply circuit 311 (that is, the output circuit 31) causes the pulse current having the frequency Ff to be the initial frequency ff1 to flow as the welding current Iw before the keyhole penetration detection signal Cm2 is generated. On the other hand, after the keyhole penetration detection signal Cm2 is generated, the frequency control circuit 312 sends to the power supply circuit 311 a frequency setting signal Ffs for flowing the welding current Iw whose frequency Ff is the steady frequency ff2. As a result, after the keyhole penetration detection signal Cm2 is generated, the power supply circuit 311 (that is, the output circuit 31) causes a pulse current having the frequency Ff to be the steady frequency ff2 to flow as the welding current Iw. The frequency control circuit 312 receives the welding start signal St from the operation control circuit 21.

  The current detection circuit 314 is for detecting the value of the welding current Iw flowing between the plasma electrode 112 and the base material W. The current detection circuit 314 sends a current detection signal Id corresponding to the welding current Iw. The current error calculation circuit 315 is for calculating a difference ΔIw between the value of the welding current Iw that is actually flowing and the value of the set welding current. Specifically, the current error calculation circuit 315 receives a current detection signal Id and a current setting signal Ir described later corresponding to the set welding current value, and sends a current error signal Ei corresponding to the difference ΔIw. The current error calculation circuit 315 may send a current error signal Ei corresponding to a value obtained by amplifying the difference ΔIw.

  The current control circuit 313 is for setting the time average value Ia of the absolute value of the welding current Iw flowing between the plasma electrode 112 and the base material W. Based on the set current value ir1 stored in the set current value storage unit 364, the current control circuit 313 generates a current setting signal Ir for indicating the time average value Ia of the absolute value of the welding current Iw. Then, the current control circuit 313 sends the generated current setting signal Ir to the current error calculation circuit 315. In this embodiment, the current control circuit 313 is absolute before and after the keyhole penetration detection signal Cm2 (see FIG. 4E), which will be described later, is generated and after the keyhole penetration detection signal Cm2 is generated. A current setting signal Ir for sending the welding current Iw having the time average value Ia of the value being the set current value ir1 is sent. As a result, the power supply circuit 311 (that is, the output circuit 31) sets the absolute time average value Ia before the keyhole penetration detection signal Cm2 is generated and after the keyhole penetration detection signal Cm2 is generated. The welding current Iw is passed as the set current value ir1.

  The voltage detection circuit 32 is for detecting the value of the welding voltage Vw between the plasma electrode 112 and the base material W. The voltage detection circuit 32 sends a voltage detection signal Vd corresponding to the value of the welding voltage Vw.

  The steady welding start determination circuit 33 receives the voltage detection signal Vd from the voltage detection circuit 32. The steady welding start determination circuit 33 determines whether to start steady welding based on the voltage detection signal Vd. When the steady welding start determination circuit 33 determines that steady welding should be started, the steady welding start instruction signal Cm3 is sent to the frequency control circuit 312 (that is, the output circuit 31), the gas flow rate control circuit 35, and the operation control circuit 21. .

  As shown in FIG. 3, in the present embodiment, the steady welding start determination circuit 33 includes a keyhole penetration detection circuit 331 and a comparison circuit 332. When the keyhole penetration detection circuit 331 detects that the keyhole 889 has penetrated the base material W, the keyhole penetration detection circuit 331 generates a keyhole penetration detection signal Cm2 and sends it to the comparison circuit 332.

  Specifically, the keyhole penetration detection circuit 331 includes an absolute value calculation circuit 341, a low-pass filter 342, and a voltage fluctuation detection circuit 343.

  The absolute value calculation circuit 341 receives the voltage detection signal Vd. The absolute value calculation circuit 341 calculates the absolute value of the input voltage detection signal Vd. Then, the absolute value calculation circuit 341 outputs the result of the calculation as a voltage absolute value signal Va. The low-pass filter 342 receives the voltage absolute value signal Va. The low-pass filter 342 performs an operation for removing the high frequency component of the input voltage absolute value signal Va and passing only the low frequency component. The low-pass filter 342 outputs the result of the calculation as a shaped voltage signal Vf. The absolute value calculation circuit 341 is not necessary when the voltage absolute value signal Va is a direct current instead of an alternating current.

  The voltage fluctuation detection circuit 343 is a circuit for detecting fluctuations in the shaped voltage signal Vf. The voltage fluctuation detection circuit 343 is provided for detecting the fluctuation of the shaping voltage signal Vf and detecting the time when the keyhole 889 penetrates. The voltage fluctuation detection circuit 343 includes a differentiation circuit BV, a comparison circuit CM1, a keyhole formation start reference voltage setting circuit VS, and a comparison circuit CM2.

  A shaping voltage signal Vf is input to the differentiation circuit BV. The differentiating circuit BV calculates a time differential value of the input shaped voltage signal Vf and outputs a voltage differential signal Bv. The voltage differentiation signal Bv is input to the comparison circuit CM1. The comparison circuit CM1 determines that the formation of the keyhole 889 has started when the voltage differential signal Bv becomes equal to or less than a predetermined reference value Bth1. At this time, the comparison circuit CM1 outputs a keyhole formation start signal Cm1 that becomes High level for a short time.

  The keyhole formation start reference voltage setting circuit VS receives a keyhole formation start signal Cm1 and a shaping voltage signal Vf. The keyhole formation start reference voltage setting circuit VS sets the shaping voltage signal Vf when the keyhole formation start signal Cm1 is input as the keyhole formation start reference voltage signal Vs. The keyhole formation start reference voltage setting circuit VS outputs a keyhole formation start reference voltage signal Vs.

  The comparison circuit CM2 receives the keyhole formation start reference voltage signal Vs and the shaping voltage signal Vf. When the difference between the keyhole formation start reference voltage signal Vs and the shaping voltage signal Vf is equal to or greater than a reference value Bth2 determined in advance by the type of the plasma gas PG, the comparison circuit CM2 penetrates the keyhole 889. Judge. At this time, the comparison circuit CM2 outputs a keyhole penetration detection signal Cm2 that becomes High level for a short time.

  Comparison circuit 332 receives keyhole penetration detection signal Cm2 and voltage differential signal Bv. When the voltage differential signal Bv reaches a predetermined reference value Bth3 or less after receiving the keyhole penetration detection signal Cm2, the comparison circuit 332 appropriately forms the weld back bead and the keyhole 889 has an appropriate size. Judging that it has come. At this time, the comparison circuit 332 determines that steady welding should be started, and sends a steady welding start instruction signal Cm3 that is at a high level for a short time. The steady welding start instruction signal Cm3 is sent to the frequency control circuit 312 (that is, the output circuit 31), the gas flow rate control circuit 35, and the operation control circuit 21.

  The gas flow rate control circuit 35 is for controlling the gas flow rate that is the flow rate of the plasma gas PG ejected toward the base material W. The gas flow rate control circuit 35 is connected to the initial gas flow rate storage unit 365 and the steady gas flow rate storage unit 366. The gas flow rate control circuit 35 sends a gas flow rate setting signal Pgs for controlling the gas flow rate of the plasma gas PG to the gas supply device 4. The gas flow rate control circuit 35 sets the gas flow rate setting signal Pgs for setting the gas flow rate of the plasma gas PG to the initial gas flow rate pg1 before the keyhole penetration detection signal Cm2 (see FIG. 4E) is generated. Is sent to the gas supply device 4. Thus, the gas supply device 4 ejects the plasma gas PG so that the gas flow rate is the initial gas flow rate pg1 before the keyhole penetration detection signal Cm2 is generated. On the other hand, after the keyhole penetration detection signal Cm2 is generated, the gas flow rate control circuit 35 sends a gas flow rate setting signal Pgs for setting the gas flow rate of the plasma gas PG to the steady gas flow rate pg2 to the gas supply device 4. send. Thereby, after the keyhole penetration detection signal Cm2 is generated, the gas supply device 4 ejects the plasma gas PG so that the gas flow rate is the steady gas flow rate pg2. Note that a welding start signal St is sent from the operation control circuit 21 to the gas flow rate control circuit 35.

  Next, an example of a plasma keyhole welding method using the plasma keyhole welding system A1 will be described with further reference to FIGS.

  (A) shows the time change of the voltage detection signal Vd, (b) shows the time change of the voltage absolute value signal Va, (c) shows the time change of the shaped voltage signal Vf, and (d) the keyhole. The time change of the formation start signal Cm1 is shown, (e) shows the time change of the keyhole penetration detection signal Cm2, (f) shows the time change of the steady welding start instruction signal Cm3, and (g) shows the plasma electrode 112. (H) shows the time change of the welding start signal St, (i) shows the time change of the time average value Ia of the absolute value of the welding current Iw, (j) The time change of the frequency Ff of the pulse of the welding current Iw is shown, and (k) shows the time change of the gas flow rate of the plasma gas PG.

  8 (s-1), (s-2), and (s-3) are the states of the arc a1 and the base material W in FIGS. 4 (s-1), (s-2), and (s-3), respectively. Corresponding to

  A voltage detection signal Vd shown in FIG. 4A represents an AC pulse waveform voltage signal having a peak value and a base value.

<Time t1 to Time t2>
When the welding start signal St from the outside is input to the operation control circuit 21 via the teach pendant 23 at time t1, the operation control circuit 21 outputs the welding start signal St to the output circuit 31 (specifically, To the power supply circuit 311 and the frequency control circuit 312). Then, the power supply circuit 311 applies the welding voltage Vw between the plasma electrode 112 and the base material W, and the arc a1 is ignited. Then, energization of the welding current Iw is started.

  As shown in FIG. 4 (i), when the output circuit 31 receives the welding start signal St at time t1, the output circuit 31 starts to energize the welding current Iw whose absolute value time average value Ia is the set current value ir1. The set current value ir1 is about 240 A, for example.

  When receiving the welding start signal St at time t1, the frequency control circuit 312 sends a frequency setting signal Ffs for flowing the welding current Iw to the power supply circuit 311 as a pulse current having the frequency Ff of the initial frequency ff1. As a result, as shown in FIG. 4J, the power supply circuit 311 (that is, the output circuit 31) starts to energize the welding current Iw as a pulse current whose frequency Ff is the initial frequency ff1. The initial frequency ff1 is, for example, 2 to 10 Hz, and preferably 5 to 6 Hz. The value of the initial frequency ff1 may vary depending on the type of the base material W and the thickness of the base material W.

  Here, the waveform of the welding current Iw will be described with reference to FIG. FIG. 5 is a graph showing approximately two pulse periods of the welding current Iw. Note that the time scale in FIG. 5 is extremely smaller than the time scale in FIG. The time average value Ia of the absolute value of the welding current Iw shown in FIG. 5 coincides with the time average value Ia shown in FIG.

  In FIG. 5, the vertical axis indicating the welding current Iw is positive for the current that flows when the plasma electrode 112 becomes the anode. As can be understood from this figure, the welding current Iw is an alternating current that takes the electrode positive polarity current Iep and the electrode negative polarity current Ien once in the period Te. The electrode positive polarity current Iep is a current that flows when the plasma electrode 112 is an anode and the base material W is a cathode. The electrode negative polarity current Ien is a current that flows when the plasma electrode 112 is a cathode and the base material W is an anode.

  The electrode negative polarity current Ien is a pulse current having a period Te2. The period Te2 is shorter than the electrode negative polarity period Ten. During this period Te2, the electrode negative polarity current Ien takes the electrode negative polarity peak current Inp and the electrode negative polarity base current Inb once.

  In FIG. 5, the absolute value of the electrode negative polarity current Ien is indicated by a broken line. Furthermore, the figure shows the time average value Ia of the welding current Iw. As described above, the time average value Ia in FIG. 5 matches the time average value Ia in FIG.

The relationship between the frequency Ff and the period Te is as follows.
Ff = 1 / Te

Further, the EN ratio is defined by the following equation using the period Te, the electrode negative polarity period Ten, or the electrode positive polarity period Tep.
EN ratio (%) = Ten / Te × 100
= Ten / (Ten + Tep) × 100

  In order to change the frequency Ff, for example, both the electrode negative polarity period Ten and the electrode positive polarity period Tep are changed without changing the EN ratio and the time average value Ia. However, changing the frequency Ff is not limited to this, and the frequency Ff may be adjusted while changing the EN ratio. In order to change the time average value Ia, for example, the maximum absolute value Iepp or the maximum absolute value Ienp is changed without changing the EN ratio.

  The waveform of the welding current Iw is not limited to that shown in FIG. 5, and may be that shown in FIG. 6 or FIG.

  When receiving the welding start signal St at time t1, the gas flow rate control circuit 35 sends a gas flow rate setting signal Pgs for setting the gas flow rate of the plasma gas PG to the initial gas flow rate pg1 to the gas supply device 4. Accordingly, as shown in FIG. 4 (k), the gas supply device 4 starts to eject the plasma gas PG such that the gas flow rate is the initial gas flow rate pg1. The initial gas flow rate pg1 is, for example, 2.3 to 2.5 L / min.

  At time t1, when the operation control circuit 21 receives the welding start signal St, the operation control signal Ms for setting the moving speed VR to the initial speed vr1 as shown in FIG. Send to. As a result, the moving speed VR of the plasma electrode 112 becomes the initial speed vr1. In the present embodiment, the initial speed vr1 is 0, and the plasma electrode 112 is stopped with respect to the base material W in the welding progress direction Dr between time t1 and time t4. Unlike the present embodiment, the moving speed VR may not be zero. For example, the plasma electrode 112 may be slightly moved with respect to the base material W in the welding progress direction Dr between time t1 and time t4.

  3 calculates the absolute value of the voltage detection signal Vd corresponding to the welding voltage Vw, and sends the voltage absolute value signal Va shown in FIG. 4B. The low-pass filter 342 removes the high frequency component of the voltage absolute value signal Va and outputs a shaped voltage signal Vf shown in FIG. As shown in FIG. 8 (s-1), after time t 1, the arc a 1 forms a molten pool 881 on the surface of the base material W. When the molten pool 881 starts to be formed, the arc a1 is unstable. Therefore, the shaping voltage signal Vf is likely to fluctuate.

<Time t2 to Time t3 (Keyhole formation period)>
As shown in FIG. 4C, when the forming voltage signal Vf rises and reaches time t2, the arc a1 is stabilized. Therefore, after time t2, the rate of increase of the shaped voltage signal Vf becomes small. The comparison circuit CM1 in FIG. 3 starts to dig the keyhole 889 in the base material W when the voltage differential signal Bv obtained by time-differentiating the shaped voltage signal Vf becomes equal to or less than a predetermined reference value Bth1, It is determined that the formation of 889 has started. When it is determined that the formation of the keyhole 889 is started, the comparison circuit CM1 outputs a keyhole formation start signal Cm1 that becomes High level for a short time as shown in FIG. When the keyhole formation start reference voltage setting circuit VS receives the keyhole formation start signal Cm1, the keyhole formation start reference voltage signal Vs (see FIG. c) See). As shown in FIG. 8 (s-2), after the time t2, the formation of the keyhole 889 is continued, and the surface 882 of the molten pool 881 gradually decreases. Note that the period from the time when the formation of the keyhole 889 is started (time t2) to the time when the keyhole 889 penetrates (time t3 described later) is a keyhole formation period.

  As shown in FIG. 4G, during the keyhole formation period (time t2 to time t3), the moving speed VR of the plasma electrode 112 is the initial speed vr1. In this embodiment, as described above, the initial speed vr1 is 0, and the plasma electrode 112 is stopped with respect to the base material W. As shown in FIG. 4 (i), during the keyhole formation period (time t2 to time t3), the time average value Ia of the absolute value of the welding current Iw is the set current value ir1. As shown in FIG. 4 (j), during the keyhole formation period (time t2 to time t3), the welding current Iw flows as a pulse current whose frequency Ff is the initial frequency ff1. As shown in FIG. 4 (k), the plasma gas PG is ejected at the initial gas flow rate pg1 during the keyhole formation period (time t2 to time t3).

<Time t3 to Time t4>
At time t3, the keyhole 889 penetrates through the base material W as shown in FIG. When the keyhole 889 penetrates, at time t3, as shown in FIG. 4C, the difference between the shaping voltage signal Vf and the keyhole formation start reference voltage signal Vs becomes larger than a predetermined reference value Bth2. In this case, the comparison circuit CM2 determines that the keyhole 889 has penetrated. Then, the comparison circuit CM2 sends a keyhole penetration detection signal Cm2 to the comparison circuit 332 as shown in FIG. Immediately after the keyhole 889 penetrates, the molding voltage signal Vf is unstable due to the penetration of the keyhole 889. After a while from the time t3 when the keyhole 889 penetrates, the welding voltage Vw becomes stable after the forming voltage signal Vf decreases, and the reduction rate of the forming voltage signal Vf becomes small.

<After time t4>
At time t4, when the voltage differential signal Bv reaches a predetermined reference value Bth3 or less, the comparison circuit 332 in FIG. 3 determines that the weld back bead is properly formed and the keyhole 889 has an appropriate size. . At this time, as shown in FIG. 4 (f), the comparison circuit 332 determines that the steady welding should be started, and sends a steady welding start instruction signal Cm3 that becomes a high level for only a short time.

  When the frequency control circuit 312 receives the steady welding start instruction signal Cm3 at time t4, the frequency control circuit 312 sends a frequency setting signal Ffs for flowing the welding current Iw to the power supply circuit 311 as a pulse current whose frequency Ff is the steady frequency ff2. Thereby, as shown in FIG.4 (j), from the time t4, the power supply circuit 311 (namely, output circuit 31) begins to supply the welding current Iw as a pulse current whose frequency Ff is the steady frequency ff2. The initial frequency ff1 is smaller than the steady frequency ff2. The stationary frequency ff2 is, for example, 10 to 20 Hz.

  At time t4, when receiving the steady welding start instruction signal Cm3, the gas flow rate control circuit 35 sends a gas flow rate setting signal Pgs for setting the gas flow rate of the plasma gas PG to the steady gas flow rate pg2 to the gas supply device 4. . Accordingly, as shown in FIG. 4 (k), from time t4, the gas supply device 4 starts to eject the plasma gas PG so that the gas flow rate is the steady gas flow rate pg2. The initial gas flow rate pg1 is larger than the steady gas flow rate pg2. The steady gas flow rate pg2 is, for example, 2.0 L / min.

  At time t4, when receiving the steady welding start instruction signal Cm3, the motion control circuit 21 welds a motion control signal Ms for setting the moving speed VR to the steady speed vr2, as shown in FIG. 4 (g). Send to robot 1. As a result, the moving speed VR of the plasma electrode 112 becomes the steady speed vr2. The initial speed vr1 is smaller than the steady speed vr2. In the present embodiment, the movement of the plasma electrode 112 relative to the base material W in the welding progress direction Dr is started from time t4.

  Even after time t4, as shown in FIG. 5I, the time average value Ia of the absolute value remains the set current value ir1. That is, the time average value Ia of the absolute value of the welding current Iw during the time t2 to the time t3 (keyhole formation period), and the time average value Ia of the absolute value of the welding current Iw in the process of performing steady welding after the time t4 Are identical to each other.

  As described above, the process of performing steady welding is started from time t4, and welding to the base material W is performed. As a result, as shown in FIG. 9, a weld surface bead is formed on the surface of the base material W along the welding progress direction Dr, and a weld back bead is formed on the back surface of the base material W along the welding progress direction Dr. Each length from time t1 to time t2 and from time t3 to time t4 is very short compared to the length from time t2 to time t3. The length of time t2 to time t3 is, for example, about 10 seconds.

  Next, the effect of this embodiment is demonstrated.

  According to this embodiment, the keyhole 889 can be penetrated more quickly. The reason is as follows.

  First, a reduction in time required for welding has been demanded. If the steady speed vr2 is slowed, the time required for welding increases, and the time required for welding cannot be reduced. Therefore, at least in the process of performing steady welding after time t4, the steady speed vr2 cannot be made very slow.

  In the present embodiment, the welding current Iw is a pulse current. Therefore, the period during which heat is easily input to the base material W and the period during which heat is difficult to input to the base material W are periodically repeated. For example, the period during which the electrode positive polarity current Iep and the electrode negative polarity peak current Inp flow in FIG. On the other hand, the period during which the electrode negative polarity base current Inb flows is a period during which it is difficult for heat to enter the base material W. Further, for example, the electrode negative polarity period Ten in which the electrode negative polarity current Ien flows in FIGS. 6 and 7 is a period during which heat is easily input to the base material W. On the other hand, the electrode plus polarity period Tep in which the electrode plus polarity current Iep flows is a period during which it is difficult to input heat to the base material W. Therefore, when welding is performed without slowing down the steady-state speed vr2, if the steady-state frequency ff2 is too small, a portion where the arc a1 is irradiated only during a period during which heat input is difficult may occur in the base material W. As a result, there is a possibility that a part of the base material W that hardly receives heat is generated. If there is a portion where heat is not input to the base material W, there may be inconveniences such as the width of the weld front bead and the weld back bead becoming narrow, or the keyhole 889 not being generated as shown in FIG. From the above, the steady frequency ff2 cannot be made too small and needs to be larger than a certain level.

  FIG. 12 shows the state of the molten pool 881 during the period from time t2 to time t3 (keyhole formation period). As shown in the figure, the surface 882 of the molten pool 881 vibrates up and down during at least the period from time t2 to time t3 (keyhole formation period). As shown on the left side of the figure, when the surface 882 is lowered, the distance between the tip of the arc a1 and the portion 886 to be melted next in the base material W is small, so the heat from the arc a1 is the portion 886. Easy to get to. On the other hand, as shown on the right side of the figure, when the surface 882 is raised, the distance between the tip of the arc a1 and the part 886 is large, so that the heat from the arc a1 is not easily transmitted to the part 886. And the inventor acquired knowledge that the frequency of the surface 882 of the molten pool 881 is smaller than the stationary frequency ff2. In the present embodiment, during the period from time t2 to time t3 (keyhole formation period), the welding current Iw is supplied as a pulse current having an initial frequency ff1 smaller than the steady frequency ff2. Therefore, the repetition cycle of the period in which heat input is easy and the period in which heat input is difficult, which is derived from the fact that the welding current Iw is a pulse current, can be brought close to the vibration period of the surface 882. Therefore, the welding current Iw is a pulse current, and the repetition period of the period during which heat is easily input and the period during which it is difficult to input heat, the state in which heat from the arc a1 is easily transmitted to the portion 886 (left side in FIG. 12), It is possible to approach the repetition period of the state where the heat from the arc a1 is difficult to be transmitted to the part 886 (right side in FIG. 12). Therefore, according to the present embodiment, the portion 886 to be melted next in the base material W can be efficiently melted during the period from the time t2 to the time t3 (keyhole formation period). Thereby, the keyhole 889 can be penetrated more quickly.

  In order to determine the value of the initial frequency ff1, for example, plasma keyhole welding for determining the initial frequency ff1 is performed at several frequencies Ff lower than the steady frequency ff2 before starting welding. A value that minimizes the time for forming the keyhole 889 may be used as the initial frequency ff1.

  In the present embodiment, the welding current Iw is expressed as the absolute time average value Ia during the period from time t2 to time t3 (keyhole formation period) and during the period during which steady welding is performed after time t4. It flows as a set current value ir1. That is, the time average value Ia is the same set current value ir1 during the period from time t2 to time t3 and during the period in which steady welding is performed after time t4, and is the same. According to such a configuration, it is possible to prevent excessive heat input to the base material W during the period from time t2 to time t3. If it is possible to prevent the heat input to the base material W from being excessive, it is possible to suppress the melt-off (see FIG. 11).

  In the present embodiment, the plasma gas PG is ejected at the initial gas flow rate pg1 during the period from time t2 to time t3 (keyhole formation period). During the period in which steady welding is performed after time t4, the plasma gas PG is ejected at a steady gas flow rate pg2. The initial gas flow rate pg1 is larger than the steady gas flow rate pg2. Such a configuration is suitable for increasing the pressure of the arc a1 during the period from the time t2 to the time t3 (keyhole formation period). Therefore, the keyhole 889 can be penetrated faster. When the initial gas flow rate pg1 is larger than the steady gas flow rate pg2, the heat affected zone in the base material W is reduced by narrowing the arc a1 during the period from time t2 to time t3 (keyhole formation period). can do. Therefore, it can suppress that the hole diameter of the keyhole 889 formed in the time t2-time t3 becomes large. As a result, the occurrence of burn-out can be suppressed.

<First Modification of First Embodiment>
A first modification of the first embodiment of the present invention will be described with reference to FIG.

  In the following description, the same or similar components as those described above will be denoted by the same reference numerals as those described above, and description thereof will be omitted as appropriate.

  The plasma keyhole welding system A11 shown in the figure is different from the above-described plasma keyhole welding system A1 in that it further includes an initial frequency calculation circuit 37. In the present modification, the initial frequency calculation circuit 37 has the configuration of the welding power supply device 3, but is not limited thereto, and may be the configuration of the robot control device 2, for example.

  The initial frequency calculation circuit 37 calculates the value of the initial frequency ff1 based on the value of the steady frequency ff2. Specifically, the initial frequency calculation circuit 37 calculates a value obtained by reducing the value of the steady frequency ff2 stored in the steady frequency storage unit 362. For example, the initial frequency calculation circuit 37 calculates a value of 30% or 50% of the value of the stationary frequency ff2, or calculates a value obtained by subtracting 5 to 8 Hz from the value of the stationary frequency ff2. Then, the initial frequency calculation circuit 37 stores the calculated value in the initial frequency storage unit 361 as the initial frequency ff1.

  Since the plasma keyhole welding method using the plasma keyhole welding system A11 is the same as that described with respect to the plasma keyhole welding system A1, description thereof will be omitted.

  According to this modification, the same advantages as those described with respect to the plasma keyhole welding system A1 can be obtained.

  According to this modification, the user of the plasma keyhole welding system A11 can set the steady frequency ff2, and can use the welding method of this embodiment without setting the initial frequency ff1. Such a plasma keyhole welding system A11 is easy to use for the user.

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

  The steady welding start determination circuit 33 in FIG. 3 does not necessarily include the comparison circuit 332. The steady welding start determination circuit 33 may determine that steady welding should be started when a predetermined time has elapsed since the keyhole penetration detection signal Cm2 was generated. Alternatively, the steady welding start determination circuit 33 may determine that steady welding should be started when a predetermined time has elapsed since the output by the output circuit 31 started.

  Unlike the above embodiment, the comparison circuit CM2 determines that the keyhole 889 has penetrated when the amount of change in the formed voltage signal Vf exceeds a certain value after time t2, and outputs the keyhole penetration detection signal Cm2. May be.

  In the above embodiment, the frequency Ff is changed from the initial frequency ff1 to the steady frequency ff2 at time t4, but the present invention is not limited to this. For example, the frequency Ff may be changed from the initial frequency ff1 to the steady frequency ff2 when a predetermined time has elapsed since the time when the keyhole 889 penetrated. Further, it is not necessary to change the frequency Ff from the initial frequency ff1 to the steady frequency ff2 after the time t3. That is, the frequency Ff may be changed from the initial frequency ff1 to the steady frequency ff2 before the time t3 when the keyhole 889 penetrates.

  The frequency Ff is the initial frequency ff1 from the time t1 to the time t3, but the frequency Ff may be the initial frequency ff1 during a certain period between the time t2 and the time t3. For example, the frequency Ff is from the time t1 to the time t2. Ff may be different from the initial frequency ff1.

  In the above embodiment, the frequency Ff is suddenly changed from the initial frequency ff1 to the steady frequency ff2 at time t4. However, the frequency Ff may be gradually changed from time t3 to time t4.

  In the above embodiment, the gas flow rate of the plasma gas PG is changed from the initial gas flow rate pg1 to the steady gas flow rate pg2 at time t4, but the present invention is not limited to this. For example, the gas flow rate of the plasma gas PG may be changed from the initial gas flow rate pg1 to the steady gas flow rate pg2 when a predetermined time has elapsed since the time when the keyhole 889 penetrated. Further, it is not necessary to change the gas flow rate of the plasma gas PG from the initial gas flow rate pg1 to the steady gas flow rate pg2 after the time t3. That is, the gas flow rate of the plasma gas PG may be changed from the initial gas flow rate pg1 to the steady gas flow rate pg2 before the time t3 when the keyhole 889 penetrates. Further, the gas flow rate of the plasma gas PG may always be constant from time t1.

  From the time t1 to the time t3, the gas flow rate of the plasma gas PG is the initial gas flow rate pg1, but the plasma gas PG gas flow rate may be the initial gas flow rate pg1 during a certain period between the time t2 and the time t3. Between time t1 and time t2, the gas flow rate of the plasma gas PG may be different from the initial gas flow rate pg1.

  In the above embodiment, the gas flow rate of the plasma gas PG is suddenly changed from the initial gas flow rate pg1 to the steady gas flow rate pg2 at time t4, but the gas flow rate of the plasma gas PG is gradually increased from time t3 to time t4. It may be changed to.

A1 Plasma keyhole welding system A11 Plasma keyhole welding system 1 Welding robot 11 Welding torch 111 Nozzle 112 Plasma electrode 12 Manipulator 2 Robot controller 21 Operation control circuit 23 Teach pendant 251 Initial speed storage unit 252 Steady speed storage unit 3 Welding Power supply device 31 Output circuit 311 Power supply circuit 312 Frequency control circuit 313 Current control circuit 314 Current detection circuit 315 Current error calculation circuit 32 Voltage detection circuit 33 Steady welding start determination circuit 331 Keyhole penetration detection circuit 341 Absolute value calculation circuit 342 Low-pass filter 343 Voltage fluctuation detection circuit 332 Comparison circuit 35 Gas flow rate control circuit 361 Initial frequency storage unit 362 Steady frequency storage unit 364 Set current value storage unit 365 Initial gas flow rate storage unit 366 Steady gas flow rate storage unit 37 Phase frequency calculation circuit 4 Gas supply device 881 Molten pool 882 Surface 886 Part 889 Keyhole a1 Arc Bth1 Reference value Bth2 Reference value Bth3 Reference value BV Differentiation circuit Bv Voltage differentiation signal CM1 Comparison circuit Cm1 Keyhole formation start signal CM2 Comparison circuit Cm2 Key Hole penetration detection signal Cm3 Steady welding start instruction signal Dr Welding direction Ei Current error signal Ff Frequency Ffs Frequency setting signal ff1 Initial frequency ff2 Steady frequency Ia Time average value Id Current detection signal Iep Electrode plus polarity current Ien Electrode minus polarity current Iepp Maximum Absolute value Ienp Maximum absolute value Inp Electrode minus polarity peak current Inb Electrode minus polarity base current Ir Current setting signal ir1 Setting current value Iw Welding current Ms Operation control signal PG Plasma gas Pgs Gas flow rate setting signal w Welding voltage VR Movement speed St Welding start signal pg1 Initial gas flow rate pg2 Steady gas flow rate Te2 Period Te cycle Ten Electrode negative polarity period Tep Electrode positive polarity period t1 Time t2 Time t3 Time t4 Time Va Voltage absolute value signal Vd Voltage detection signal Vf Molding voltage signal Vs Keyhole formation start reference voltage signal VS Keyhole formation start reference voltage setting circuit vr1 Initial speed vr2 Steady speed W Base material

Claims (10)

Igniting an arc between the plasma electrode and the base material and penetrating the keyhole by the arc;
A step of performing steady welding while moving the plasma electrode relative to the base material after the keyhole has penetrated,
The step of penetrating includes a welding current flowing between the plasma electrode and the base material during a keyhole formation period, which is a period from the start of the formation of the keyhole to the time of the penetration of the keyhole. , Including a step of flowing as a pulse current whose frequency is an initial frequency,
The step of performing the steady welding includes a step of flowing the welding current as a pulse current whose frequency is a steady frequency,
The initial frequency, the stationary frequency is less than the plasma keyhole welding process.   2. The plasma keyhole welding according to claim 1, wherein a time average value of the absolute value of the welding current in the penetrating step and a time average value of the absolute value of the welding current in the penetrating step are the same. Method. The step of penetrating includes the step of jetting plasma gas to be jetted toward the base material at an initial gas flow rate during the keyhole formation period,
The step of performing the steady welding includes a step of ejecting the plasma gas at a steady gas flow rate,
The plasma keyhole welding method according to claim 1 or 2, wherein the initial gas flow rate is larger than the steady gas flow rate.   The plasma keyhole welding method according to any one of claims 1 to 3, further comprising a step of calculating the value of the initial frequency by decreasing the value of the stationary frequency by an initial frequency calculation circuit. The step of penetrating includes the step of setting the moving speed, which is the speed of the plasma electrode with respect to the base material, in the welding progress direction along the base material to an initial speed,
The step of performing the steady welding includes a step of setting the moving speed to a steady speed,
The plasma keyhole welding method according to any one of claims 1 to 4, wherein the initial speed is smaller than the steady-state speed. An output circuit for passing a pulse current between the plasma electrode and the base material;
An initial frequency storage unit for storing an initial frequency value;
A stationary frequency storage unit that stores a value of the stationary frequency;
A keyhole penetration detection circuit that generates a keyhole penetration detection signal when detecting that the keyhole has penetrated the base material;
The output circuit causes the pulse current to flow with the frequency as the initial frequency before the keyhole penetration detection signal is generated, and the frequency is set to the steady state after the keyhole penetration detection signal is generated. to flow the pulse current as the frequency,
The plasma keyhole welding system, wherein the initial frequency is lower than the steady frequency . A set current value storage unit for storing the set current value;
The output circuit allows the pulse current to flow with the time average value of the absolute value as the set current value before the keyhole penetration detection signal is generated and after the keyhole penetration detection signal is generated. The plasma keyhole welding system according to claim 6. A gas flow rate control circuit that controls a gas flow rate that is a flow rate of plasma gas ejected toward the base material;
An initial gas flow rate storage unit for storing an initial gas flow rate value;
A stationary gas flow rate storage unit for storing a value of the steady gas flow rate,
The gas flow rate control circuit sets the gas flow rate to the initial gas flow rate before the keyhole penetration detection signal is generated, and after the keyhole penetration detection signal is generated, the gas flow rate control circuit sets the gas flow rate to the initial gas flow rate. While setting the flow rate to the above steady gas flow rate ,
The plasma keyhole welding system according to claim 6 or 7, wherein the initial gas flow rate is larger than the steady gas flow rate .   9. The initial frequency calculation circuit for storing in the initial frequency storage unit a value obtained by reducing the value of the steady frequency stored in the steady frequency storage unit as the initial frequency. The plasma keyhole welding system described in 1. An operation control circuit for controlling a moving speed, which is a speed of the plasma electrode with respect to the base material, in a welding progress direction along the base material;
An initial speed storage unit for storing an initial speed value;
A steady speed storage unit that stores a value of the steady speed;
The operation control circuit sets the moving speed to the initial speed before the keyhole penetration detection signal is generated, and the movement control circuit sets the movement speed after the keyhole penetration detection signal is generated. While setting the speed to the above steady speed ,
The plasma keyhole welding system according to any one of claims 6 to 9, wherein the initial speed is smaller than the steady speed .

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