JP5410126B2 - Power supply for plasma welding and plasma welding equipment - Google Patents

Description

  The present invention relates to a plasma welding power source capable of determining penetration of a keyhole in plasma keyhole welding.

  In plasma keyhole welding, when welding a welded butt joint with an I-shaped groove, a plasma arc is discharged when a tungsten electrode is generally used as the cathode. And restrained by. The high temperature plasma flow with good concentration is generated, and this high temperature plasma flow moves on the welding line while forming a circular hole penetrating the work piece at the tip of the weld pool. This welding is directly applied until the arc heat reaches the back surface, and the back surface can be appropriately melted.

  When plasma keyhole welding is started, the high temperature plasma flow penetrates the work piece, but when the keyhole penetrates, the plasma arc voltage rises. Conventionally, a starting method for detecting the increased voltage and starting the movement of the plasma torch has been proposed. This prior art will be described below.

  FIG. 5 is a diagram showing a configuration of a conventional plasma welding apparatus. In the figure, a plasma nozzle 2 for constraining a plasma arc 3 is provided concentrically with the plasma electrode 1. Electric power is supplied from the plasma welding power source 5 between the plasma electrode 1 and the workpiece 4, and a plasma gas 13 is supplied from the plasma gas supply source 6 into the plasma nozzle 2, thereby generating a plasma arc 3. A high-temperature plasma flow moves on the welding line while penetrating the work piece 4 at the tip of the molten pool while forming the keyhole 7, and also melts the back surface.

  The voltage fluctuation detection device 8 detects the fluctuation (for example, 1 to 2 V) of the plasma arc voltage when the keyhole 7 penetrates, and forms it into a signal suitable for the welding control sequencer 10 by the waveform shaper 9. The welding control sequencer 10 inputs the formed signal, inputs a signal for starting the travel of the plasma torch 12 to the torch travel device 11, and the torch travel device 11 starts the travel of the plasma torch 12. (For example, refer to Patent Document 1).

Japanese Patent Publication No. 2-18953

  The above-described plasma welding power source 5 detects the voltage change when the keyhole 7 penetrates and starts the travel of the plasma torch 12 when a DC voltage is applied from the plasma welding power source 5. It is. In addition to the DC voltage, the plasma welding power source may use the DC pulse voltage shown in FIG. 6A, the AC voltage shown in FIG. 6B, or the AC pulse voltage shown in FIG. In these cases, when the above-described conventional technique is applied, it is impossible to determine that the keyhole of plasma keyhole welding has penetrated because the steady waveform fluctuates.

  An object of the present invention is to provide a plasma welding power source and a plasma welding apparatus that can determine that a keyhole of plasma keyhole welding has penetrated.

The first invention is
A voltage detection circuit for detecting a plasma arc voltage between the plasma electrode and the work piece at the start of plasma keyhole welding;
A voltage absolute value circuit that inputs a voltage detection signal output from the voltage detection circuit and calculates an absolute value;
A low-pass filter that has a cutoff frequency set in a range of 0.8 Hz to 1.6 Hz, removes a high-frequency component by inputting a voltage absolute value signal output from the voltage absolute value circuit;
A voltage differentiating circuit for differentiating the low-pass signal output from the low-pass filter;
When the voltage differential signal output from the voltage differentiating circuit is input and the voltage differential signal reaches a predetermined reference value or less, it is determined that the formation of the keyhole is started, and only a short time is High. A comparison circuit that outputs a keyhole formation start signal that becomes a level,
A keyhole start reference voltage signal setting circuit that inputs the keyhole formation start signal and the low pass signal, and sets the low pass signal when the keyhole formation start signal is input as a keyhole start reference voltage signal;
When the low-pass signal and the keyhole start reference voltage signal are input and the difference between the low-pass signal and the keyhole start reference voltage signal is equal to or greater than a predetermined reference value, the keyhole penetrates. And another comparison circuit that outputs a keyhole penetration signal that becomes High level for a short time;
A power supply for plasma welding, comprising:

The second invention is
A power source for plasma welding according to claim 1,
A plasma torch for generating a plasma arc power is supplied from the plasma welding power source,
A plasma torch moving means for initiating movement of the torch by the keyhole through signal output from the pre-Symbol plasma welding power source,
A plasma welding apparatus comprising:

  The power source for plasma welding and the plasma welding apparatus of the present invention can determine the penetration of the keyhole of the plasma keyhole welding even when outputting the DC pulse voltage, the AC voltage and the AC pulse voltage in addition to the DC voltage, A weld bead in which the back bead is appropriately formed can be obtained.

It is a figure which shows the structure of the plasma welding apparatus of this invention. It is a figure which shows the time passage of the voltage detection signal Vd of the power supply PS for plasma welding of this invention, the voltage absolute value signal Va, and the low-pass signal Vf. It is a figure which shows the relationship between the cutoff frequency (horizontal axis) of the low-pass filter VF of the power supply PS for plasma welding of this invention, and the determination state (vertical axis) of a keyhole penetration. It is a figure which shows the time passage of the low-pass signal Vf of the power supply PS for plasma welding of this invention, the keyhole formation start signal Cm1, and the keyhole penetration signal Cm2. It is a figure which shows the structure of the plasma welding apparatus of a prior art. It is a figure which shows the waveform of DC pulse voltage, AC voltage, and AC pulse voltage.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on examples with reference to the drawings. FIG. 1 is a diagram showing the configuration of the plasma welding apparatus of the present invention. In the figure, a power supply main circuit PM in the plasma welding power source PS inputs an AC commercial power supply (three-phase 200 V, etc.), performs inverter control power control according to an error amplification signal Ei described later, and plasma keyhole welding. A plasma arc current Ip and a plasma arc voltage Vp suitable for the above are output. The plasma torch 22 is supplied with power from the plasma welding power source PS, and is supplied with plasma gas from a plasma gas supply source (not shown), and plasma is generated between the electrode in the plasma torch 22 and the workpiece 4. Arc 3 is generated. The current detector ID detects the plasma arc current Ip and outputs a current detection signal Id. The current absolute value circuit IA calculates the absolute value of the current detection signal Id and outputs a current absolute value signal Ia. The current setting unit IS sets a plasma arc current and outputs a current setting signal Is. The error amplification circuit EI amplifies an error between the current setting signal Is and the current absolute value signal Ia, and outputs an error amplification signal Ei. Accordingly, the plasma arc current Ip corresponding to the current setting signal Is is energized.

  The voltage detection circuit VD detects a plasma arc voltage Vp between the plasma electrode in the plasma torch 22 and the workpiece 4 and outputs a voltage detection signal Vd. The voltage absolute value circuit VA is a bridge-type full-wave rectifier circuit in which, for example, four diodes are connected in a bridge shape, and calculates the absolute value of the voltage detection signal Vd and outputs the voltage absolute value signal Va. The low pass filter VF receives the voltage absolute value signal Va, removes a high frequency component, and outputs a low pass signal Vf. The low-pass filter VF is a low-pass filter composed of, for example, a resistor R (Ω) and a capacitor C (F), and based on a time constant τ = R × C (seconds), a cutoff frequency Fc = 1 / 2πτ (Hz). Determined by This cutoff frequency will be described later. The voltage differentiation circuit BV differentiates the low-pass signal Vf and outputs a voltage differentiation signal Bv. The comparison circuit CM1 inputs the voltage differential signal Bv, and when the voltage differential signal Bv reaches a predetermined reference value Bth1 or less, it determines that the formation of the keyhole has started, and is high only for a short time. The keyhole formation start signal Cm1 that becomes level is output.

  The keyhole start reference voltage signal setting circuit VS inputs the keyhole formation start signal Cm1 and the low pass signal Vf, and uses the low pass signal Vf when the keyhole formation start signal Cm1 is input as the keyhole start reference voltage signal Vs. Set and output.

  The comparison circuit CM2 inputs the low pass signal Vf and the keyhole start reference voltage signal Vs, and the difference between the low pass signal Vf and the keyhole start reference voltage signal Vs is the output waveform of the plasma welding power source and the type of plasma gas. When the threshold value exceeds a predetermined reference value Bth2 due to the above, it is determined that the keyhole has penetrated, and a keyhole penetration signal Cm2 that is at a high level for a short time is output. The robot control circuit RC inputs the keyhole penetration signal Cm2, outputs a plasma torch movement start signal St to the manipulator 21, and the movement of the plasma torch 22 is started.

  Next, the cutoff frequency of the low-pass filter VF will be described with reference to FIGS. FIG. 2 is a diagram showing the passage of time of the voltage detection signal Vd, the voltage absolute value signal Va, and the low-pass signal Vf of the plasma welding power source PS of the present invention. FIG. 3 is a diagram showing the relationship between the cutoff frequency (horizontal axis) of the low-pass filter VF of the plasma welding power source PS of the present invention and the state of determination of keyhole penetration (vertical axis).

  A voltage detection signal Vd shown in FIG. 2A represents a voltage signal having an AC pulse waveform having a peak value and a base value. The voltage absolute value signal Va shown in FIG. 2B is a voltage signal obtained by calculating the absolute value of the voltage detection signal Vd shown in FIG. In FIG. 2C, the low-pass signal Vfa has a cut-off frequency of less than 0.8 Hz in the range A shown in FIG. Cannot be read. The low-pass signal Vfc has a cut-off frequency in the range of C shown in FIG. 3 that exceeds 1.6 Hz, and is greatly affected by welding noise and the like. Therefore, a slight change cannot be accurately determined. An erroneous determination may be made. The low-pass signal Vfb has a cut-off frequency in the range B shown in FIG. 3 in the range of 0.8 Hz to 1.6 Hz, is less affected by welding noise, and has a slight voltage change before and after the time when the keyhole penetrates. The keyhole penetration can be accurately determined. Therefore, the cut-off frequency of the low-pass filter VF is appropriately in the range of 0.8 Hz to 1.6 Hz.

  The operation will be described below with reference to FIG. FIG. 4A is a diagram showing the passage of time of the low-pass signal Vf of the plasma welding power source PS of the present invention, and FIG. 4B is a diagram showing the passage of time of the keyhole formation start signal Cm1. FIG. 6C is a diagram showing the time passage of the keyhole penetration signal Cm2.

  When energization of the plasma arc current Ip is started at time t1 shown in FIG. 4A, the voltage absolute value circuit VA calculates the absolute value of the voltage detection signal Vd and outputs the voltage absolute value signal Va. This voltage absolute value signal Va is freed from high frequency components by a low pass filter VF, and a low pass signal Vf is output. Then, the plasma arc 3 forms a molten pool on the surface of the workpiece 4, and when the plasma arc 3 starts to be formed, the plasma arc 3 is also unstable and easily fluctuates in voltage.

  When the low-pass signal Vf rises and time t2 is reached, the plasma arc 3 is stabilized, and then the voltage fluctuation range of the plasma arc 3 becomes smaller and the rate of increase becomes smaller. At this time, the comparison circuit CM1 determines that the plasma arc 3 starts to dig a keyhole in the work piece 4 when the voltage differential signal Bv reaches a predetermined reference value Bth1 or less, and the formation of the keyhole is started. Then, as shown in FIG. 4B, a keyhole formation start signal Cm1 that becomes High level only for a short time is output. The keyhole start reference voltage signal setting circuit VS sets the low pass signal Vf when the keyhole formation start signal Cm1 is input as the keyhole start reference voltage signal Vs.

  Then, when the formation of the keyhole is continued and at time t3, it is determined that the keyhole has penetrated when the difference between the low-pass signal Vf and the keyhole start reference voltage signal Vs is equal to or greater than a predetermined reference value Bth2. Then, as shown in FIG. 4C, the keyhole penetration signal Cm2 is output from the comparison circuit CM2. The robot control circuit RC receives the keyhole penetration signal Cm2 and outputs a plasma torch movement start signal St to the manipulator 21 so that the movement of the plasma torch 22 is started.

  As a result, the power source for plasma welding and the plasma welding apparatus of the present invention can discriminate penetration of a keyhole in plasma keyhole welding even when outputting DC pulse voltage, AC voltage, and AC pulse voltage in addition to DC voltage. Therefore, it is possible to obtain a weld bead in which the back bead is appropriately formed.

  The inventors of the present invention use the plasma welding power source of the present invention, and the work piece is aluminum magnesium alloy A5052, the base current of the reverse polarity plasma arc current of AC pulse is IB, the period is TB, the pulse current is IP, the pulse width Is TP, positive plasma arc current is IEN, period is EN, EN ratio = (IEN x TEN) / (IP x TP + IEN x TEN) is 75%, average voltage of plasma arc is 30V, A plasma keyhole with an average current of 250 A, a mixed gas of plasma 70% argon and 30% helium, a reference value Bth2 when it is determined that the keyhole has penetrated, 5V, and a low-pass filter cutoff frequency of 1.28 Hz. Welding was performed. As a result, it was possible to obtain a weld bead in which the back bead was appropriately formed.

  Since the reference values Bth1 to 2 vary depending on the output waveform of the plasma welding power source, the type of plasma gas, and the like, the reference values Bth1 to 2 corresponding to the welding conditions and the like are stored in the database in advance and used. The reference values Bth1 to Bth2 may be set corresponding to the welding conditions.

  In the plasma welding power source of the present invention described above, the case where the output is an AC pulse voltage has been described. However, the present invention can be applied to a DC voltage, a DC pulse voltage, and an AC voltage in addition to the AC pulse voltage. it can. In the case of a DC voltage, the voltage absolute value circuit VA described above is not necessary.

DESCRIPTION OF SYMBOLS 1 Plasma electrode 2 Plasma nozzle 3 Plasma arc 4 To-be-welded object 5 Plasma welding power supply 6 Plasma gas supply source 7 Keyhole 8 Voltage fluctuation detection apparatus 9 Waveform shaper 10 Welding control sequencer 11 Torch travel apparatus 12 Plasma torch 13 Plasma gas 21 Manipulator 22 Plasma torch Bth1 Reference value Bth2 Reference value BV Voltage differentiation circuit Bv Voltage differentiation signal C Capacitor Cm1 Keyhole formation start signal CM1 Comparison circuit Cm2 Keyhole penetration signal CM2 Comparison circuit EI Error amplification circuit Ei Error amplification signal IA Current absolute value circuit Ia Current absolute value signal ID Current detector Id Current detection signal Ip Plasma arc current IS Current setter Is Current set signal PM Power supply main circuit PS Power supply for plasma welding R Resistance RC Robot control circuit St Plasma torch movement start signal t1 Time t2 Time t3 Time VA Voltage absolute value circuit Va Voltage absolute value signal VD Voltage detection circuit Vd Voltage detection signal VF Low pass filter Vf Low pass signal Vfa Low pass signal Vfb Low pass signal Vfc Low pass signal Vp Plasma arc voltage Vs Keyhole start reference voltage signal VS Keyhole Start reference voltage signal setting circuit τ Time constant

Claims (2)

A voltage detection circuit for detecting a plasma arc voltage between the plasma electrode and the work piece at the start of plasma keyhole welding;
A voltage absolute value circuit that inputs a voltage detection signal output from the voltage detection circuit and calculates an absolute value;
A low-pass filter that has a cutoff frequency set in a range of 0.8 Hz to 1.6 Hz, removes a high-frequency component by inputting a voltage absolute value signal output from the voltage absolute value circuit;
A voltage differentiating circuit for differentiating the low-pass signal output from the low-pass filter;
When the voltage differential signal output from the voltage differentiating circuit is input and the voltage differential signal reaches a predetermined reference value or less, it is determined that the formation of the keyhole is started, and only a short time is High. A comparison circuit that outputs a keyhole formation start signal that becomes a level,
A keyhole start reference voltage signal setting circuit that inputs the keyhole formation start signal and the low pass signal, and sets the low pass signal when the keyhole formation start signal is input as a keyhole start reference voltage signal;
When the low-pass signal and the keyhole start reference voltage signal are input and the difference between the low-pass signal and the keyhole start reference voltage signal is equal to or greater than a predetermined reference value, the keyhole penetrates. And another comparison circuit that outputs a keyhole penetration signal that becomes High level for a short time;
A power source for plasma welding, comprising: A power source for plasma welding according to claim 1,
A plasma torch for generating a plasma arc power is supplied from the plasma welding power source,
A plasma torch moving means for initiating movement of the torch by the keyhole through signal output from the pre-Symbol plasma welding power source,
A plasma welding apparatus comprising:

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