JP3209139B2 - Welding condition adaptive control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adaptively controlling welding conditions in arc welding, and more particularly, to accurately detecting a change in a root gap immediately below an arc by using an arc sensor technology of a high-speed rotating arc welding method. In addition, the present invention relates to a welding condition adaptive control method for applying an appropriate welding condition in response to a change in the root gap.

[0002]

2. Description of the Related Art Conventionally, in an adaptive control technique relating to welding conditions, a skilled worker constructs a welding condition database, and determines appropriate welding conditions before welding by using welding information such as geometrical shape information of members and leg length. Has been decided. Therefore, the welding conditions during welding are open-loop control.
This is because the technology for sensing the root gap and the leg length of the groove in the in-process has not been established. However, as a conventional technology, there is a technology that controls the welding conditions by measuring the gap and detecting the bead width by combining an image processing device and a laser sensor.However, sensing the gap immediately below the arc during welding and feedback to the controller are performed. There is no technology to control welding conditions.

[0003] In the case of welding work by automatic equipment using a welding robot or the like, an operation program is created by an off-line program method before welding work. This operation program calculates operation path points such as welding start and end points, which are operation path points of the robot, and a posture change point due to interference avoidance processing based on CAD data, and sets welding conditions for the points. It is configured to assign parameters such as welding current, welding voltage, welding speed, and torch angle.

However, at the time of welding, there is a difference between the actual member and the CAD data. Therefore, the welding start point is detected by the wire touch sensor, and the welding operation is performed while controlling the groove during welding by the arc sensor. Welding is performed by sequentially interpolating path points. However, there is a problem that the method cannot cope with the change of the welding condition parameter accompanying the interpolation of the operation path point. That is, a feedback routine using an arc sensor or the like is performed for an operation path point, whereas open loop control is performed without feedback for welding conditions. Therefore, despite the existence of a gap in the actual member,
If welding is performed under the welding conditions selected in the CAD database before welding, the leg length may be insufficient and it may be difficult to maintain proper welding quality. In addition, such gaps are inevitably generated due to processing accuracy of the work, mounting accuracy, dynamic thermal deformation during welding, and the like.

[0005]

Generally, in adaptive control, a controlled object is represented by a mathematical model, a dynamic behavior of the controlled object is estimated based on the mathematical model, and an optimum value is held. However, in the welding condition adaptive control, there is a problem that it is very difficult to express a welding phenomenon by a mathematical model because of many parameters and complicated intertwining. The present inventors have conducted intensive studies on this problem, and as a result, by using the well-known principle of a high-speed rotating arc sensor, there is a certain correlation between the change in the surface shape of the molten pool immediately below the arc and the change in the root gap. And succeeded in expressing the welding phenomenon with a mathematical model.

The present invention has been made based on such knowledge, and enables accurate detection of a root gap based on information of a welding phenomenon obtained by a high-speed rotating arc sensor. It is an object of the present invention to provide a method for adaptively controlling welding conditions in order to obtain a stable welding quality in response to welding.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method for adaptively controlling welding conditions according to the present invention, wherein a welding is performed while controlling the height of a welding line and the height of a welding torch by an arc sensor method by a high-speed rotating arc welding method. In addition, a change in the surface shape of the molten pool immediately below the arc, which is changed by a change in the root gap G of the groove, is recognized based on the waveform of the welding voltage or welding current of the high-speed rotating arc, and an appropriate value corresponding to the current root gap G is recognized. In the welding condition adaptive control method for controlling to apply the welding condition, the welding voltage or the welding current waveform for one rotation of the arc is calculated based on the integral value of the phase section θ1 to θ2 behind the arc rotation position, The area difference SG of the waveform is obtained by subtracting the integral value of the section θ2 to (2π + θ1), while the gap Gre serving as a reference is obtained.
For the reference waveform of the welding voltage or the welding current under the appropriate welding conditions for f, the area difference obtained by subtracting the integral value of the same phase section as above is stored as SGref, and the SG from the SG in the current waveform is stored as SGref. By subtraction, the waveform difference ΔSG is obtained, the relationship between the value of ΔSG and the root gap G is obtained in advance by experiments, the current root gap G is recognized from the current value of ΔSG, and the appropriate welding conditions for G = Gref are obtained. At, from the weld bead shape, bead height, leg length, or penetration obtained when welding a joint in which the root gap G changes,
The allowable ranges + Δg1 and −Δg2 of the root gap G are determined, and the allowable ranges + ΔS1 and −ΔS2 of the waveform difference ΔSG are determined from the ΔSG-G characteristic curve obtained by the above method. When the ΔSG reaches the allowable range, the welding conditions are determined. Is changed to an appropriate welding condition in which the gap is previously determined for G = Gref + Δg1 or G = Gref−Δg2.

First, the root gap detecting method according to the present invention is based on an arc sensor based on a high-speed rotating arc welding method in a fillet welding, a V-shaped butt welding, or the like. Is recognized by the waveform of the welding voltage VT or welding current I of the high-speed rotating arc. In this case, if the welding torch is displaced from the center of the groove, the detected waveform has an effect other than the fluctuation of the gap. Therefore, the VT waveform or I waveform is used, that is, the groove width direction is controlled by the groove profile control by the arc sensor. And the position in the height direction of the welding torch is controlled. The difference (area deviation) ΔSG of the welding voltage waveform VT when welding is performed at the gap G with respect to the reference welding voltage waveform VTref under appropriate welding conditions for the reference gap Gref has a certain correlation with the gap G. It turns out that there is. Therefore, if the ΔSG-G characteristic curve is obtained in advance by an experiment, the current root gap G can be recognized from the current detected value of ΔSG.

Next, in the welding condition adaptive control method of the present invention, the allowable range of the gap G + Δg 1, based on the weld bead shape, bead height, leg length, or penetration when welding is performed under appropriate welding conditions for G = Gref, −Δg 2 is determined, and ΔSG detected by the above method is compared with the allowable range of ΔSG + ΔS 1 from the ΔSG-G characteristic curve.
When ΔSG is within the allowable range, the welding conditions are unchanged, and when ΔSG reaches the allowable range, the welding conditions are set to G = Gref + Δg1 or G = Gre.
This is to change the welding conditions to f-Δg2 which are determined in advance as appropriate.

Hereinafter, the principle of the present invention will be described.

(1) Fluctuation of Welding Voltage Waveform due to Fluctuation of Root Gap of Groove FIG. 1 is a diagram showing an example of the waveform of the welding voltage VT that changes with the change of the gap G in fillet welding. In the drawing, Cf, R, Cr, and L indicate the rotational positions of the arc (see FIG. 2), and θ on the horizontal axis is the phase of the welding voltage waveform. FIG.
The VTref waveform (waveform indicated by the solid line) in FIG.
Is a reference welding voltage waveform when welding is performed under appropriate welding conditions when the value of the reference value is the reference value Gref, and VTAV is an average voltage of the VTref waveform. The positions of Cf, R, Cr and L are
As shown in FIG. 2, in one rotation of the rotating arc, the front center position of θ = 0 ° is Cf,
The right 90 ° position is R, the rear center position (180 °) is C
r, L is the position at 270 ° on the left side. These position signals are determined by pulse signals output from the encoder of the rotary motor of the welding torch.

The welding voltage waveform is highest at the positions of Cf and Cr and lowest at the positions of R and L under the influence of the arc length which changes according to the surface shape of the molten pool. Under these welding conditions, the welding voltage waveform when the gap G becomes larger than Gref is defined as a VT waveform (broken line) in FIG.
Is shown in That is, when the gap G becomes larger than Gref, VT> VTref in the range of the phase .theta.1 to .theta.2 in the Cr portion, and VT <VTref in other portions. This is because, as shown in FIG. 3, when the gap becomes large, the leg length (bead height) decreases, and the molten pool 4 immediately below the arc 3 recedes, so that the arc voltage of the Cr portion increases. Since the average voltage becomes constant by controlling the torch height of the welding torch 1, the arc voltage in other portions decreases.
Conversely, when the gap G becomes smaller than Gref, FIG.
As shown in FIG. 7, VT <VTref in the Cr portion, and VT> VTref in the other portions. 2 and 3, 1 is a welding torch, 2 is a welding wire, 3 is a rotating arc, 4 is a molten pool, 5 is a welding bead, 6 is a standing plate, and 7 is a lower plate.

(2) Method of Detecting Waveform Difference ΔSG From the results shown in FIG. 1, by detecting the welding voltage waveform without using any other detector during welding, that is, by using the arc sensor method, the arc immediately below the arc can be obtained. It can be seen that the change in the root gap can be detected. The sum of the area of the deviation portion (the hatched portion 8 in FIG. 1) of the current waveform VT with respect to the reference welding voltage waveform VTref for one rotation of the rotating arc can be recognized as the absolute value of the gap change amount with respect to the reference gap Gref. When the sign of the integral of the deviation of the voltage waveform in the phase θ1 to θ2 (Cr portion) is positive, G>
When Gref is negative, it can be determined that G <Gref.
The reason why the integral value is used instead of the instantaneous value of the voltage waveform is to prevent harmonic noise caused by the welding arc phenomenon from being superimposed on the voltage waveform, thereby preventing the influence. Although a voltage waveform is used here, a current waveform can be naturally used according to a well-known principle of an arc sensor, and a description thereof is omitted here.

(3) How to Calculate Waveform Difference ΔSG The area of the hatched portion 8 in FIG.
When expressed as the sum of the parts (θ2 to 2π + θ1),

(Equation 1) If the first term on the right side of the equation (2) is SG and the second term is SGref,

(Equation 2) Becomes

From the equation (3), the value of the waveform difference ΔSG can be obtained. However, in an actual voltage waveform, the phases θ1 and θ2 vary considerably with each rotation of the rotating arc, or depending on welding conditions and gap values, so that it is not easy to detect them in-process. Therefore, it is given as an approximate value from the experimental results. According to the method for calculating ΔSG, the detection device can be inexpensive because the reference waveform can be one data of the integral value for one rotation of the arc.

(4) Method of Recognizing Root Gap The value of ΔSG obtained from the equation (3) corresponds to the amount of change in the gap, and has a substantially linear relationship with the root gap G as shown in FIG. Has been confirmed by experiment. The ΔSG-G characteristic line obtained here is obtained when welding is performed under an appropriate condition of G = Gref. Therefore, Δ
The current route gap can be recognized from the value of SG.

(5) Method of controlling welding conditions by recognizing the root gap The allowable range of the gap in which the weld bead shape, weld bead penetration, bead height, leg length, and the like obtained by proper welding conditions of G = Gref can be obtained properly. Is + g1 and -g2 as shown in FIG. 4, the permissible range of the waveform difference output .DELTA.SG is also obtained as + .DELTA.S1 and -.DELTA.S2 as shown in FIG.
Therefore, when ΔSG reaches this range, G = (Gref + Δ
g1) or (Gref-Δg2). FIG. 5 shows a change in the .DELTA.SG output waveform when the welding is started at G = Gn and thereafter the gap G increases or decreases by a thick solid line. Therefore, it is possible to apply the change of the appropriate welding conditions immediately during the welding to the change of the gap G, so that a stable and high quality welded joint can be always obtained regardless of the existence of the gap.

[0018]

FIG. 6 is a block diagram showing an example of a control circuit used in the welding condition adaptive control method according to the present invention. 6, reference numeral 11 denotes a differential amplifier for amplifying a deviation between the current welding voltage VT0 detected by the arc sensor and the average voltage VTAV under welding line tracing control and torch height control. The Cr integrator 13 integrates the area of the hatched portion 8 with respect to the Cr portion (.theta.1 to .theta.2), and the R and L portions (.theta.2 to 2.pi. +. Theta.1) represent the area of the hatched portion 8 in FIG.
The R / L integrator 14 calculates the difference between the integrated value of the Cr integrator 12 and the integrated value of the R / L integrator 13, that is, the deviation of the first term on the right side of the above equation (2). The differential amplifier 15 is an integral value memory in which the integral value of the second term on the right side of the expression (2) is stored, and 16 is S in accordance with the expression (3).
This is a differential amplifier for obtaining a deviation between G and SGref. The above differential amplifier 11, Cr section integrator 12, and R / L section integrator 1
3, the differential amplifier 14, the integral value memory 15, and the differential amplifier 16 constitute a ΔSG detecting section 10 of the control circuit.

Reference numeral 21 denotes an output ΔSG of the ΔSG detecting unit 10;
Allowable range ΔS1, which is set in advance for ΔSG,-
A comparator 22 for comparing ΔS2 with the allowable range ΔS1
, -ΔS2, 23 is a gap determiner for determining whether the gap G is appropriate or not based on the output of the comparator 21; 24 is a CAD / CAM system 25.
Or a database of proper welding conditions provided by this system.
Appropriate welding conditions are:
Welding conditions such as welding current, welding voltage, welding speed, wire feed speed, etc. determined from the penetration of the weld bead, the bead height, and the leg length, and the above ΔSG-G characteristic curve, ΔS
The allowable range of G (+ ΔS1, −ΔS2) is stored.

In the ΔSG detecting section 10, the current welding voltage VT0 detected by the arc sensor and the reference value are compared with the current welding voltage VT0 detected by the arc sensor during the welding while performing the groove contouring control and the torch height control by the arc sensor of the high-speed rotating arc welding. The average voltage VTAV under the proper welding conditions for the gap Gref is input to the differential amplifier 11, and the differential amplifier 11 outputs the deviation VT. When the current gap G has changed from the reference gap Gref, the differential amplifier 11 inputs the output VT to the Cr part integrator 12 and the R / L part integrator 13, and the Cr part integrator 12 The area of the hatched portion 8 is integrated for the Cr portion (θ1 to θ2), while the area of the hatched portion 8 in FIG. 1 is integrated for the R and L portions (θ2 to 2π + θ1) by the RL integrator 13. These integrated values are input to the differential amplifier 14, which calculates SG of the first term on the right side of the above equation (3), and is provided as an output SG to the integrated value memory 15 and the differential amplifier 16. . The integrated value memory 15 stores a value obtained by integrating the area of the hatched portion 8 in FIG. 1 for the Cr portion (θ1 to θ2) and the R and L portions (θ2 to 2π + θ1) of the reference welding voltage waveform VTref corresponding to the reference gap Gref. Then, the stored SGref is taken out, and this data is input to the differential amplifier 16. Then, the differential amplifier 16 calculates a deviation between the first term and the second term on the right side of the equation (3),
ΔSG is output by the differential amplifier 16.

Further, the output ΔSG of the ΔSG detecting section 10
Is input to the comparator 21, where the allowable range of ΔSG is +
Are compared with ΔS1 and −ΔS2, and the comparison result is input to the gap determination unit 23. When ΔSG is within the allowable range, the gap determination unit 23 outputs a signal as an appropriate gap, and outputs the upper limit value of the allowable range + ΔS1 or the lower limit value −
When ΔS2 has been reached, a signal indicating an improper gap is input to the welding condition database 24.
When the allowable range of SG reaches + ΔS1 and −ΔS2, the high-speed rotating arc welding is performed while the welding conditions are feedback-controlled by the welding condition database 24 so as to change to the appropriate welding conditions to be applied to the next gap. Will be constructed.

As described above, the route gap G and ΔS
By determining the relationship of G experimentally, the current Δ
From the value of SG, the current gap G can be recognized, whereby the current gap G becomes the reference gap Gref.
It can be recognized in-process whether it has become larger, smaller, or remains at the reference gap Gref. Further, since the welding result can be changed to an appropriate welding condition corresponding to the current gap G from the calculation result of ΔSG, welding condition adaptive control corresponding to a change in the root gap can be performed.

[0023]

As described above, according to the present invention,
Without using any detector near the welding torch, only the information of welding voltage or welding current by the arc sensor of the high-speed rotating arc welding method can recognize the change of the root gap just below the arc during welding, and the change of the root gap Accordingly, there is an effect that appropriate welding conditions can be changed and applied immediately during welding. In addition, since the welding phenomenon is represented by a mathematical model based on the correlation between the change in the surface shape of the molten pool immediately below the arc and the change in the root gap, feedback control of appropriate welding conditions has been enabled, The control system is stable, therefore, if the control method of the present invention is used,
There is an effect that a stable and high-quality welded joint can be obtained immediately corresponding to the actual work.

[Brief description of the drawings]

FIG. 1 is a waveform diagram showing a change in welding voltage of a rotating arc when a root gap changes with respect to a reference gap.

FIG. 2 is a definition diagram of an arc rotation position.

FIG. 3 is an explanatory diagram showing a situation in which a molten pool retreats when an arc length changes in a rear part of a rotating arc.

FIG. 4 is a ΔSG-G characteristic diagram showing a relationship between a waveform difference ΔSG and a root gap G.

FIG. 5 is a waveform difference ΔS due to increase and decrease of the root gap.
FIG. 9 is a waveform chart showing a change in G.

FIG. 6 is a block diagram of a control circuit used in the welding condition adaptive control method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Welding torch 2 Welding wire 3 Rotating arc 4 Weld pool 5 Weld bead 6 Standing plate 7 Lower plate 8 Hatched part (deviation part of VT waveform and VTref waveform) 11 Differential amplifier 12 Cr part integrator 13 R ・ L part integrator Reference Signs List 14 differential amplifier 15 integrated value memory 16 differential amplifier 21 comparator 22 threshold value setting device 23 gap judgment device 24 welding condition database 25 CAD / CAM system

Continuation of the front page (72) Inventor Yoshihiro Hashi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Masatomo Murayama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) reference Patent Sho 63-80971 (JP, a) JP Akira 62-24862 (JP, a) JP Akira 62-248571 (JP, a) (58 ) investigated the field (Int.Cl. ⁷ , DB name) B23K 9/095 B23K 9/127

Claims (1)

(57) [Claims] 1. An arc which changes due to a change in a root gap G of a groove when welding is performed by controlling a welding torch height and a welding line by an arc sensor by a high-speed rotating arc welding method. In a welding condition adaptive control method of recognizing a change in the surface shape of a molten pool immediately below by a welding voltage or a welding current waveform of a high-speed rotating arc and controlling to apply an appropriate welding condition corresponding to the current root gap G, With respect to the waveform of the welding voltage or the welding current for one rotation of the arc, the phase section θ1 behind the arc rotation position.
From the integrated value of .theta.2, the other sections .theta.2 to (2.pi. +. Theta.1
) Is subtracted to obtain an area difference SG of the waveform,
On the other hand, with respect to the reference waveform of the welding voltage or the welding current under the proper welding conditions for the reference gap Gref, the area difference obtained by subtracting the integral value of the same phase section as above is stored as SGref, and The waveform difference ΔSG is obtained by subtracting the SGref from the SG, the relationship between the value of the ΔSG and the root gap G is previously obtained by an experiment, and the current root gap G is recognized from the current ΔSG value. = Appropriate range of root gap G + Δg 1, −Δg 2 is determined from the weld bead shape, bead height, leg length, or penetration obtained when welding a joint having a variable root gap G under appropriate welding conditions for Gref. From the ΔSG-G characteristic curve obtained by the above method, the waveform difference ΔS
The allowable ranges of G + ΔS1 and −ΔS2 are obtained. When the ΔSG reaches the allowable range, the welding conditions are changed to G = Gre.
A welding condition adaptive control method characterized in that f + .DELTA.g1 or G = Gref-.DELTA.g2 is changed to an appropriate welding condition previously determined.