JPH11291041A - Method for controlling pulse arc welding and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling pulsed arc welding and a device therefor capable of executing the stable welding without being affected with external disturbance factors by searching a welding voltage under the condition suitable for a weld joint and less in the number of times of short-circuits during welding. SOLUTION: In a control device of pulsed arc welding to execute welding by energizing a welding current made into a pulse between a welding wire and a base material and executing the droplet transfer of the welding wire to the base material with the generated arc, a short-circuit detecting means 27 detects a short-circuit in an initial period of start of welding and a voltage search means 32 searches a voltage to maintain the number of times of short- circuits in a less state. This searched voltage maintains the welding less in the generation of a spatter or the like and a voltage arithmetic circuit 24 fixes the searched voltage as a target voltage for constant voltage control and executes feed back control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a consumable electrode type pulse arc welding control method and apparatus using a shielding gas.

[0002]

2. Description of the Related Art It has been found that in pulse arc welding, a set current range is extremely wide, and when welding is performed at an ideal voltage, welding with an excellent bead appearance with very little spatter or the like can be performed on an arbitrary welded joint. ing. As shown in FIG. 8, when the number of short circuits is extremely small, the amount of spatters generated and the number of short-circuiting phenomena in which the droplets coming off from the welding wire also come into contact with the base metal are as follows. Type) The amount of generation is small. This is because when a short circuit occurs, the current increases, and the detachment of the droplet is disturbed by the influence of electromagnetic force or the like. Furthermore, the number of blow holes is reduced when the number of short circuits is small.

Accordingly, the inventors of the present application disclosed in Japanese Patent Application No. 241406 in 1995 that the welding voltage is controlled by detecting the number of short-circuit phenomena so that the number of short-circuit phenomena becomes a preset value during pulse welding. A welding device has been disclosed. The above welding equipment sets the optimal voltage value and current value for on-site welding based on experience and experiments, and instructs these set values, and at the same time, detects the short circuit phenomenon by detecting the welding voltage that sharply decreases. . This detection is performed, for example, when the number of occurrences of the short-circuit phenomenon during a unit time such as 1 sec is suppressed between a predetermined upper limit number and a lower limit number, and the optimum state is set. When the number of short circuits becomes smaller than the lower limit number, the control is performed to decrease the voltage.

[0004]

However, in the pulse arc welding, the voltage range of the region where the short circuit is small is extremely narrow, and if the voltage is too high to eliminate the short circuit, the arc spreads and a welding defect called undercut easily occurs. . On the other hand, the conventional welding apparatus always controls the voltage from the start of welding to the end of welding under the condition that the number of short circuits is small, but the target value of the control is a set value obtained by experience or experiment. Therefore, if the preset value does not match the voltage in the region where the short circuit suitable for the joint is small, it is difficult to say that welding with less generation of spatter is performed even if control is performed. Will increase.

The relationship between the current and the voltage under the condition that the short circuit is small varies depending on disturbance factors such as the distance between the tip of the welding torch and the base material, the wiring condition of the welding wire, the tip wear, and the positioning accuracy of the jig. Even if the optimum voltage and current are set based on experience and experiments, it is impossible to cope with actual field welding unless correction is made for each joint. In particular, in the case of robot welding, even if the parameters of current and voltage commanded from the robot side to the welding machine side and their relations are obtained in advance, differences occur due to the fluctuation of the disturbance factor, and it is difficult to set optimal conditions. Extremely.

According to the present invention, a welding voltage is searched under a condition where the number of short circuits suitable for the welded joint is small during welding, and stable welding is performed without being affected by disturbance factors (minimum spatter, constant penetration depth, etc.). It is an object of the present invention to provide a method and an apparatus for controlling pulse arc welding, which enable the control.

[0007]

According to the pulse arc welding control method of the present invention, which solves the above-mentioned problems, a pulsed welding current is applied between a welding wire and a base metal, and the welding wire is generated by the generated arc. In the control method of pulse arc welding in which welding is performed by transferring droplets to the base material, a short circuit phenomenon of the welding wire is detected based on the detected welding voltage, and the welding voltage is controlled such that the number of detected short circuits is maintained at a predetermined number. The target voltage is searched based on the width of the upper peak value and the lower peak value and the upper peak value or the lower peak value, and the searched target voltage is used as a reference voltage for welding voltage control. It is a feature.

[0008] The control device for pulse arc welding of the present invention comprises:
A pulsed welding current is passed between the welding wire and the base metal by a pulsed welding current, and the generated arc causes the welding wire to transfer to the base material in a droplet form, thereby performing welding by a pulse arc welding control device. Short-circuit detecting means for detecting a short-circuit phenomenon of the welding wire, and raising and lowering the welding voltage so as to maintain the number of detected short-circuits at a predetermined number, the width of the upper peak value and the lower peak value and the upper peak value or the lower peak value. Voltage search means for searching for a target voltage based on the peak value, and using the searched target voltage as a reference voltage for welding voltage control.

[0009]

In the control method and apparatus for pulse arc welding according to the present invention, the number of short circuits is controlled to be small in the initial period of the start of welding, that is, welding in which generation of spatter and the like is small is maintained, and the welding voltage at that time is searched. doing. And
The voltage at which the searched welding voltage is stabilized is fixed to the target value of the constant voltage feedback control as the optimum target voltage for the welded joint. With this, the ideal welding voltage that exists for each welded joint is tested by experience and experiments based on disturbance factors such as the distance between the tip of the welding torch and the base metal, the wiring state of the welding wire, chip wear, and the positioning accuracy of the jig. It is possible to search during actual welding without finding it by mistake, and preparation work can be greatly simplified.

According to the pulse arc welding control method and apparatus of the present invention, the search is terminated after the width of the upper peak value and the lower peak value converge to a predetermined value, and feedback control is performed based on the obtained target voltage. The welding voltage can be made to follow the target voltage. In addition, it is possible to perform a constant current feedback control of the welding current to a preset current from the start of welding.

[0011] Thus, since a constant voltage feedback control is not performed at a set voltage based on experience or the like set in advance, a high voltage of a small amount, a small amount of spatter, a constant amount of penetration and the like are obtained. It is possible to perform welding. The pulse arc welding control method and apparatus of the present invention are suitable for robot welding. In this case, it is preferable that the robot controller that controls the robot based on the teaching data and the welding power supply controller that controls the welding power supply according to the present invention be communicably linked.

The microcomputer for the welding power supply controller includes a short-circuit detecting means for detecting a short-circuit phenomenon of the welding wire based on the detected welding voltage according to the present invention, and the welding voltage for maintaining the number of detected short circuits at a predetermined number. Voltage search means for searching for a target voltage based on the width of the upper and lower peak values and the upper and lower peak values, and a target current preset from the start of welding to a reference for welding current control. Current control means for controlling a welding current as a current, and the search is terminated after the width of the upper peak value and the lower peak value converge to a predetermined value, and the welding voltage is controlled by feedback control based on the obtained target voltage. Functions of the voltage control means.

In the method and apparatus for controlling pulse arc welding according to the present invention, the output terminal of the welding power supply connects a power supply line between the wire holding cable and the jig for fixing the base material. It is preferable that the welding voltage is detected by connecting the detection line to a wire holding cable and a jig at a position as close as possible to the tip of the wire where the arc is generated.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a specific embodiment of a method and apparatus for controlling pulse arc welding according to the present invention will be described with reference to the drawings. FIG. 1 schematically shows a welding system to which the pulse arc welding control method and apparatus of the present invention can be applied.
This welding system comprises a robot 2 holding a welding torch (hereinafter referred to as a torch) 1 and a welding current and a welding voltage of output terminals 3a (positive electrode) and 3b (negative electrode) between a tip 16 of the torch tip and a base material. And a robot that controls the robot 2 based on the teaching data TD and transmits a preset target current command value PIt and initial voltage command value Pv ₀ to the welding machine 3. The controller 5 includes a jig 9 on which a base material is placed, and a wire feeding device 8 for feeding a welding wire 7 as a consumable electrode filled in the drum 6 to the torch 1.

The wire feeder 8 mounted on the robot 2 includes a bending straightener 11, a pair of feed rollers 13 a and 13 b sandwiching the welding wire 7, a motor 14 for driving the rollers 13 a and 13 b, and a welding wire 7. With a torch cape 1a for guiding the welding wire 7 to the torch 1.
Are projected from the chip 16 in the nozzle portion 15 at the point. Then, the motor 14 is controlled by a motor control circuit of the welding machine 3 with a drive signal having a feed rate proportional to the current command value PI, and feeds out the welding wire 7.

As shown in FIG. 2, the welding machine 3 comprises a welding power source 21 and a welding power source controller 22 mainly composed of a microcomputer. The welding power supply 21 includes, for example, an inverter circuit unit including a rectifier circuit, an inverter, an output transformer, a rectifier, and the like, and a voltage command value (average value) P.
and a PWM circuit unit that controls the switching of the inverter by its output by controlling the pulse control circuit with v, and the output of the rectifier is led to the output terminals 3a and 3b.

The welding power supply controller 22 has an output terminal 3
The voltage command value P is set so as to reduce an error between the voltage Vd (detected welding voltage) appearing at the detection terminals 4a and 4b connected to the terminals a and 3b and the voltage set value written in the set value memory 23.
The voltage calculation circuit 24 calculates v and feeds back the command value to the pulse control circuit of the welding power source 21; the current Vd (detection welding current) flowing to the one detection terminal 4a; A current calculation circuit that feeds back a current command value PI to a motor control circuit of the welding power source 21 so as to reduce an error with the current set value. The voltage calculation circuit 24 performs voltage control by instructing the pulse frequency output by the pulse control circuit with the voltage command value Pv. The current calculation circuit 26 controls the current by changing the rotation speed of the motor 14 by the motor control circuit with the current command value PI.

The welding power supply controller 22 inputs the detected welding voltage Vd between the detection terminals 4a and 4b,
A short-circuit detecting means 27 for detecting a short-circuit phenomenon between the wire base metals by detecting a state in which the detected welding voltage Vd drops sharply; a timer 28 for starting counting with an output 27a of the short-circuit detecting means 27; 28 counts up the output to voltage command value Pv of the output 28a voltage calculation circuit 24 of the sampling, as shown by a plurality of sampling values in FIG. 4, the upper peak value Pv _U1, Pv _U2, P
v _U3, ... and the lower peak value Pv _D1, Pv _D2, Pv _D3, a sampling circuit 29 for outputting a ..., receives the output 29a of the sampling circuit 29, on the adjacent peak value Pv
By using the width W of one and two values of _U and the lower peak value Pv _D calculated command value of the target voltage Vt (target voltage value) Pvt (search) and the target value calculation circuit 30 which outputs, the target value A comparison circuit 31 that compares a calculated value 30b of the width W obtained by the calculation circuit 30 with a predetermined convergence width Wd, and outputs a switching signal 31a when the calculation output 30b is equal to or smaller than the convergence width Wd; Is provided.

The switching signal 31a output from the comparison circuit 31 controls a switch 32 for selecting the voltage command value Pv. The switch 32 is connected to the initial voltage command value Pv ₀ and the voltage command value P
v and the target voltage value Pvt from the target value calculation circuit 30 are selectively derived to the welding power source 21. The control device for pulse arc welding of the present invention is configured as described above, and the control method for pulse arc welding of the present invention using this control device will be described.

[0020] The control device as shown in step S1 of FIG. 3, the command value PIt target current It from the robot controller 5, a command value Pv ₀ of the initial voltage V ₀ is input.
With these inputs, the welding power supply controller 22 recognizes the command value PIt and the command value Pv ₀ (S2), and
It is output to the welding power source 21 (S3), and the command value Pv ₀ is selected by the switch 32 and output to the welding power source 21 (S3) to start welding (S4).

The initial voltage V _{0 at the} start of welding can be arbitrarily determined, but the relationship between the number of short circuits and the arc length has the characteristics shown in FIG. 9 and the arc length is almost directly proportional to the voltage. Therefore, the voltage value is set to be close to the voltage value of the arc length region set as the optimum region where the penetration shape defect, non-short-circuit type spatter and short-circuit type spatter, undercut, blowhole, etc. hardly occur. The target current It is an ideal current value determined in advance according to the welding joint.

At the start of welding, the number of short circuits St is detected (S
The voltage control based on 5) and the current constant control (S6) are performed in parallel so that the welding current I becomes the target current It. Step S6 is the control shown in FIGS. 5 and 7 for the welding current I. First, the control from step S5 onward for the welding voltage V is performed as follows. In the detection of the number Sd of short circuits, FIG.
For example, the moment when the detected welding voltage Vd between the detection terminals 4a and 4b suddenly drops is detected, and the sampling circuit 29 is triggered by the output 27a indicating the first short circuit. When the short circuit is detected, the welding power supply controller 22 performs step S8 “increase voltage” or step S9 “decrease voltage” following the next step S7 “St <Sd”.

In steps S7 → S8 or S7 → S9, a short circuit is detected during welding with the initial voltage V ₀ , and when the voltage sampled at that time is the first lower peak value PV _D1 in FIG. The target value calculation circuit 30 outputs a voltage value larger than PV _D1 as the command value PVt of the target voltage Vt (S
8). At this time, the switch 32 has selected the output 30 a from the target value calculation circuit 30, and the command value PVt is sent to the welding power source 21 as the voltage command value Pv. As a result, the number of short circuits is reduced by the increased voltage. When the number of short circuits is reduced and no short circuit occurs during one cycle of the timer 28, the sampling circuit 29 samples the voltage command value Pv from the voltage calculation circuit 24 at the output 28a of the timer 28. The voltage at this time is the first upper peak value PV _U1
When it is, the target value calculation circuit 30 is the target voltage Vt ₁ between the width W1 of the determined, first lower peak value PV _D1 and the upper peak value PV _U1 of the first lower peak value PV _D1 and the upper peak value PV _U1 Command value PVt ₁ = PV _D1 + αW1 (α = 1/4 to 4/3,
Usually, it is calculated from the operation formula of １ ／). Then, it sent to the welding power source 21 a command value PVt ₁ of the target voltage Vt ₁ as the voltage command value Pv (S9). An externally operable volume for determining α may be provided.

The width W1 is compared with the convergence width Wd by the comparison circuit 31. If W1> Wd, the comparison circuit 31
Maintains the current state of the switch 32 (the state in which the output 30a of the target value calculation circuit 30 is set to the voltage command value Pv). The operation of the comparison circuit 31 is the same as that of Step S10 “St =
Sd? ". Since the target voltage Vt ₁ lowers the welding voltage, a short circuit is likely to occur. Therefore, when the short circuit is detected and the second lower peak value PV _D2 is sampled, the first upper peak value is calculated from the same arithmetic expression. command value PV target voltage Vt ₂ between the value PV _U1 and the lower peak value PV _U2
t ₂ is calculated.

This operation is further repeated, and for example, the second upper pin
Work value PV_U2And the third lower peak value PV _D3Width W4
If the convergence width is equal to or smaller than the set convergence width Wd
(W4 ≦ Wd), PV_U2And PV_D3Eye calculated during
Standard voltage Vt_{i (i = 1,2,3}…₎Outputs the optimal target voltage Vt.
The operation of the voltage search circuit 32 is terminated.
You. A period for obtaining the target voltage Vt is referred to as a search period,
The target voltage Vt finally output in the search period is detected.
A voltage for maintaining the number of short circuits Sd at the target number of short circuits St.
Then, the welding power supply controller 22 proceeds to the next step S11.
move on.

In step S11, the switch 32 is switched by the output 31a from the comparison circuit 31 so as to select the voltage command value Pv of the voltage calculation circuit 24, and the finally obtained command value PVt is calculated by the voltage calculation. An operation of fixing the value in the set value memory 23 of the circuit 24 is performed. As a result, the welding power supply controller 24 fixes the searched command value PVt in the set value memory 23 and enters the voltage constant control mode performed by the voltage calculation circuit 24 (S12).

The voltage constant control is performed as shown in FIG.
The arc length a obtained from the tip base metal distance EXT, welding voltage V (detection voltage), peak current of pulse arc current, base current and average current Iav is the maximum allowable arc length a.
_The voltage calculation circuit 24 controls the welding voltage V using the searched target voltage Vt as a reference voltage while suppressing the welding voltage V to ₀ or less. By limiting the arc length a to the maximum allowable arc length a ₀ or less, undercuts and blow holes are eliminated.

[0028] After the calculation of the arc length a of the step S14 in FIG. 6, in step S15, compares the calculation arc length a and the maximum allowable arc length a _0, in the case of a> a _0, step S
16 “Pv = PVt−K1” (K1 is a unit change amount), and Pv is D / A converted in the next step S17.
The voltage command value Pv of the converted analog signal is used as the welding power source 2
1 (S18).

Further, in the comparison step S15 of the arc length, if a is a ₀ less than the step S19 "〓V =
Vt−Vd ”is used to calculate the difference between the target voltage Vt and the detected welding voltage Vd. Next, it is determined in step S20 "Vt>Vd" whether the welding voltage V is higher or lower than the target voltage Vt. If Vt> Vd, the difference .DELTA.V is subtracted from the target voltage Vt. Value is voltage command value P
v (S21), and when Vt <Vd, the difference ΔV is set to Vt.
, And the added voltage value is set as a voltage command value Pv (S22). As a result, the welding voltage V is controlled with the target voltage Vt as the reference voltage, and the welding voltage V is controlled to the target voltage Vt more stably without control swell, as shown in the constant voltage control period in FIG. You.

As shown in FIG. 10, the constant current control which is continuously executed from the start of welding to the end of welding is performed when the distance EXT between the chip base materials fluctuates due to variation in teaching accuracy, as shown in FIG. This suppresses the fluctuation and the fluctuation of the current caused by changing the target voltage value in the initial stage of welding. This control is performed by the current calculation circuit 2
The current calculation circuit 26 performs feedback control (proportional integration control) of the welding current I using the target current value It written in the set value memory 25 as a reference current. As shown in FIG. 7, this proportional-integral control uses the target current value It.
〓I (proportional constant term) between the detected welding current Id during the peak current period and the welding current Id during the peak current period are obtained in step S23, and then the time Ti required for the current change until the difference 〓I becomes substantially zero is obtained by integration (S24). ) And step S25 "PI '= PI
+ K2〓 {I + K3 ・ Ti ”to obtain a corrected current command value PI '. K2 is a proportional constant term, and K3 is an integral constant term. The current command value PI 'thus calculated is converted into a signal form in step S26 "PI' → D / A conversion", and the current command value is supplied to the motor control circuit of the welding power source 21 in step S27 "PI 'analog signal output". Sent as value PI.

In step S13, when the end of welding is sent from the robot controller 5, this is recognized and the welding is ended. As shown in FIG. 5, the welding current I subjected to the proportional-integral control is controlled to be constant with the target current It as the reference current, irrespective of the variation in the distance between the chip base materials, thereby achieving a constant control of the penetration amount.

Thus, according to the pulse arc welding control method and apparatus of the present embodiment, a rough voltage in an area where the number of short circuits is small is reduced to an initial target voltage without strictly obtaining a predetermined voltage command value. By simply determining, even an inexperienced operator can easily perform the operation. At the beginning of the welding start, a search is made for a target voltage at which the number of short circuits is minimized, and after the search, the welding voltage is controlled only by controlling the welding voltage to this target voltage so that a short circuit occurs more stably. The welding can be performed in a state where the spatter is controlled and in a minimum area.

Further, by the constant current control performed from the start of welding, it is possible to suppress the fluctuation of the current caused by raising and lowering the target voltage and the fluctuation of the current caused by the variation of the teaching accuracy, thereby securing a good appearance and welding strength. Welding can be performed. In the method and apparatus for controlling pulse arc welding according to the present invention, the method and apparatus disclosed in Japanese Patent Application Laid-Open No. 9-108837 can be used for searching for the target voltage at the beginning of the welding start. The method and the apparatus include: an absolute value of an integral value of a voltage error between a detected welding voltage Vd and a target voltage Vt during a peak current energizing period; and an integral of a voltage error between the detected welding voltage Vd and the target voltage Vt during a base current energizing period. So that the target voltage V
It raises and lowers t.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of pulse arc welding of the present invention.

FIG. 2 is a block diagram illustrating a control device for pulse arc welding according to the present invention.

FIG. 3 is a flowchart showing an operation of the welding power supply controller according to the present invention.

FIG. 4 is an explanatory diagram showing a welding voltage controlled by the present invention.

FIG. 5 is an explanatory diagram showing a welding current controlled by the present invention.

FIG. 6 is a flowchart showing an operation of constant voltage control according to the present invention.

FIG. 7 is a flowchart showing an operation of constant current control according to the present invention.

FIG. 8 is a characteristic diagram obtained by an experiment of a spatter generation amount and the number of short circuits.

FIG. 9 is a graph showing the effect of the number of short circuits on welding quality, wherein the vertical axis represents the arc length and the horizontal axis represents the number of short circuits.

FIG. 10 is a characteristic diagram of a welding current that changes due to a change in the distance between tip base materials.

[Explanation of symbols]

I: welding current, V: welding voltage, 27: short-circuit detecting means, P
VU: Upper peak value, PVD: Peak value, W: Width, 32:
Voltage search means, Vt: target voltage, It: target current value,
26 ... current calculation circuit (current control means), 24 ... voltage calculation circuit (voltage control means).

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masanori Chikuma 2-7-1 Muroya, Nishi-ku, Kobe City, Hyogo Prefecture Inside the Kobe Plant of Osaka Electric Co., Ltd.

Claims (4)

[Claims] 1. A method for controlling a pulse arc welding in which a pulsed welding current is applied between a welding wire and a base material, and the generated arc causes the welding wire to transfer to the base material by droplets to perform welding. A short circuit phenomenon of the welding wire is detected based on the detected welding voltage, and the welding voltage is increased or decreased so as to maintain the number of detected short circuits at a predetermined number, and the width of the upper peak value and the lower peak value and the upper peak value or A method for controlling pulse arc welding, wherein a target voltage is searched based on a lower peak value, and the searched target voltage is used as a reference voltage for welding voltage control. 2. An average value of the welding current is feedback-controlled to a constant value using a target current value set in advance from the start of welding as a reference current for the welding current control, and the width of the upper peak value and the lower peak value converges to a predetermined value. 2. The pulse arc welding control method according to claim 1, wherein after the search, the search is terminated, and the average value of the welding voltage is controlled to be constant by feedback control based on the obtained target voltage. 3. A pulse arc welding control device for applying a pulsed welding current between a welding wire and a base material and transferring the welding wire to the base material by a generated arc to perform welding. A short-circuit detecting means for detecting a short-circuit phenomenon of the welding wire based on the detected welding voltage; and raising and lowering the welding voltage so as to maintain the number of detected short-circuits at a predetermined number. A voltage search means for searching for a target voltage based on an upper peak value or a lower peak value, wherein the searched target voltage is used as a reference voltage for welding voltage control. . 4. A current control means for controlling the feedback so that the average value of the welding current is constant using a target current value preset from the start of welding as a reference current for the welding current control, and the width of the upper peak value and the lower peak value is 4. The pulse arc welding control apparatus according to claim 3, further comprising voltage control means for terminating the search after the convergence to a predetermined value and controlling the average value of the welding voltage to be constant by feedback control based on the obtained target voltage. .