JPS6117590B2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an automatic arc welding method using a consumable electrode that moves along the weld line direction of a weld joint, and in particular, the arc welding method uses a consumable electrode that moves along the weld line direction of a weld joint, and in particular, the arc welding method uses the arc itself to control the movement of the weld joint without using a groove position detector. This article relates to an arc welding method for imitating parts.

To achieve unmanned automatic welding, a detection sensor and a torch position adjustment mechanism are needed to automatically detect and control the torch position in response to two-dimensional deviations in the groove line that change momentarily during welding. is necessary.

Conventionally, there have been various types of detection sensors of this kind, such as contact type differential transformer type, potentiometer type or limit switch type, and non-contact type electromagnetic or optical position detection type. It is used. However, in any case, in addition to the torch, a unique device called a sensor is installed near the torch, so a certain distance is required between the detection position and the control target position due to dimensional restrictions. Despite the complexity of controlling the torch position by giving a time difference corresponding to the above-mentioned interval size to the output of the sensor, only a control method with limited precision could be realized.

In contrast to the method using such a sensor, there is a method in which the arc itself has a sensor function, such as the one disclosed in Japanese Patent Application Laid-open No. 130660/1983, but the method described in this publication The number of short circuits at the groove edge due to the swing of the groove is compared between the left and right sides of the groove, and the swing center of the arc is controlled to move so that the number of times is equal on both sides. Accurate tracing is not possible, and if the electrical properties of the inner surface of the groove are not uniform on the left and right sides, unexpected malfunctions may occur.

As another method, for example, Japanese Patent Laid-Open No. 7845/1983 discloses a method in which the welding current value at the reference torch position is monitored and the arc itself functions as a sensor. In this method, when a change occurs with respect to the welding current under the standard state, the torch is first shifted in the width direction by a small amount on a trial basis, and the change in welding current due to this shift is determined to be positive or negative, and then the amount of change is zero. Because the torch is controlled to move in the direction of No countermeasures have been disclosed for this, so if the wire protrusion length from the torch tip is constant, the number of short circuits will naturally vary, and even if the number of short circuits is symmetrical with respect to the welding line, the number of short circuits will vary. There is a drawback that the welding conditions cannot be accurately matched. Yet another method is the arc tracing method in weaving welding, in which arc current measurement values are integrated for a certain period of time at both ends of the weaving, and tracing is performed by comparing the integral values at both ends, as disclosed in Japanese Patent Laid-Open No. 52-9657. As indicated in the official gazette, in actual welding, the arc current detection result contains many large noise components, and in addition to the noise components, the arc current itself fluctuates greatly due to unique ripples. As shown in the publication, it is not possible to average the arc current values for each weaving period with the integrated value over a range of at most several tens of milliseconds, and the fluctuation of the detected arc current value at the time of integration is large, making it impossible to achieve the desired result. Tracing control is not possible, but if you increase the integration time using this method, since the weaving end is the starting point, as the integration time approaches half a period of weaving, the transition from one weaving end to the other will increase. As a result, the comparison results for each half period of each weaving period will approach zero, and the control itself will no longer be effective.

In other words, in the method disclosed in Japanese Patent Application Laid-Open No. 52-9657, the arc current detection value is integrated for a certain period of time up to several tens of milliseconds starting from this turning point at each turning point of weaving, and By accumulating the same number of integration results for the instantaneous value of
The aim is to detect how much the weaving torch has deviated from the groove route in the width direction from the difference between the two accumulated results, and to trace the width in such a way as to set this to zero. The reality is that a practical machine using this method has not yet been developed.

This invention has been made to solve all the drawbacks of the above-mentioned conventional methods and to achieve accurate and stable tracing control using the arc characteristics of the arc itself.
The present invention provides an arc welding method using an arc self-tracing method that is particularly suitable for weaving welding. That is, in the arc welding method of the present invention, both groove surfaces on both sides of the root of the joint are inclined with respect to the width direction of the welding direction with respect to the wire directed toward the weld joint, and In arc welding using a consumable electrode, in which a torch supporting a wire is relatively moved in the direction of welding progress, the wire is fed at a constant speed and the welding current or welding voltage of the wire flows from the welding power source to the wire. While detecting the arc, a. While moving the wire in the welding direction, the arc is oscillated by reciprocating the torch at a constant amplitude in the width direction of the welding direction, and b. , a half cycle in which the torch swings from the swing center to one side in the width direction, and then returns to the swing center again after reversing, and then the torch swings from the swing center to the other width direction. The center of oscillation of the torch is set such that the time integral values of the welding current or welding voltage of the wire over each half period are equal to each other for the half period from the time when the torch returns to the oscillation center after reversing. It is characterized by controlling the movement in the width direction of the welding progress direction.

In the arc welding method of the present invention, as described in b above, when taking the time integral value of the welding current or welding voltage of the wire, instead of setting the integral time, the position range to be integrated is set to the center of the oscillation of the torch. A half period of swinging in one direction and a half period of swinging in the other direction are determined based on the reference point, and the time integral values over each half period are compared with each other to control the widthwise position of the center of swing of the torch. As a result, stable tracing control can be achieved without being significantly affected by the noise and ripple waveforms characteristic of consumable electrode arc welding, and as described in a above, the torch oscillation is made into a parallel reciprocating motion. When time integration is performed over a wide range of oscillation periods, the correlation with the cross-sectional area of the groove traced by the actual torch tip can be accurately determined, and control accuracy is therefore improved.

To explain this invention in detail with reference to the drawings, FIG. 1 is a principle explanatory diagram showing a general arc generation part of automatic arc welding, in which the feeding speed V _f of the wire 2 with respect to the base material 1 is constant, Assuming that the distance between the lower end surface of the electrode torch tip 3 and the upper surface of the base metal is l, there is a second difference between the welding current I and the welding voltage E when l is changed.
As shown in the figure, when l is sequentially decreased as l ₀ > l ₁ > l ₂ > l ₃ , the current I increases sequentially as I ₀ < I ₁ < I ₂ < I ₃ , and the voltage E There is a relationship in which E ₀ > E ₁ > E ₂ > E ₃ decreases sequentially. In this case, if the external characteristic curve of the power source 4 is close to a constant voltage type as shown in Fig. 2, a large change in current I will appear, and as a matter of course, if the power source 4 is a constant current type, then the voltage E Since a large change appears, either one is used as the measured quantity of l depending on the characteristics of the power supply.

In this invention, the value of l is measured from the welding current or welding voltage using the geometric relationship between the cross-sectional shape of the weld joint and the wire orientation, and the center position of the electrode is always aligned with the width center of the joint. It controls the movement of the torch to match the

In other words, Fig. 3 is a diagram showing the fluctuation state of the relative position between the welding torch 3 and the base metal groove in a butt welded joint, and Fig. 3a shows the reference state, and the distance between the lower end surface of the torch tip and the upper surface of the base material is shown in Fig. 3. When the torch 3 is swung horizontally (weaving) equally in the width direction at a constant width like A-B-A-C-A at a distance H, with the center in the groove width direction as the base point, the The protruding length of the wire changes accordingly, and the welding current I of the wire in this case changes equally every half period of the oscillation, as shown in FIG. 4a.

Now, while the above distance H remains constant, the center of oscillation A
If it shifts to the left in the drawing as shown in Fig. 3b, the change in the welding current of the wire will be as shown in Fig. 4b, and conversely, if it shifts to the right as shown in Fig. 3c, the welding current of the wire will change as shown in Fig. 4b. changes as shown in FIG. 4c. Furthermore, when the above-mentioned interval distance H changes, the state in which H increases to H + △H is shown in Figures 3d and 4d, and the state in which H decreases to H - △H is shown in Figures 3e and 4e. Each is shown, each △H
A variation ΔI in the welding current average value corresponding to ΔI appears.

The relationship between the wire protrusion length and the welding current is determined by experiment, and if the speed of the swing in the width direction is constant, the temporal change in the welding current according to the relative position relationship between the torch and the groove is shown in Figure 4a. - As shown in Fig. 4c, it can be extracted as a triangular wave with respect to the period T of the oscillation.

5 and 6 show the torch drive mechanism and drive control block in this case, and the swing mechanism is omitted in FIG. 5 for convenience of explanation.

In Fig. 5, 8 is a motor that moves the torch 3 in the width direction of the welding progress direction, and 9 is the same as the torch 3.
This is a motor that moves toward and away from the base material. The drive control system of this motor is as shown in Figure 6.
In FIG. 6, 10 is a current detector that detects the welding current of the wire 2, 11 is a noise removal circuit that removes high frequency noise from the output of the detector 10, and 12 is a time integral of the detected welding current according to the oscillation period. It is an integrator that The output of this integrator 12 is compared with a reference signal from a reference signal source 13 by a comparator 14, and the motor 9 is activated via a driver 15 so that the integrator output 1/ ^T∫T0Idt becomes a predetermined value _. controlled. 16 provides a periodic signal of oscillation to the integrator 12 and a switch 17
This is a trigger circuit that gives a switching signal every half period of the oscillation, and the switch 17 sends the welding current detection output from the noise removal circuit 11 to two integrators 18 and 19 every half period with the oscillation center as the starting point. Divide and give alternately. One integrator 18 integrates and holds the detection output for a half period of oscillation from 0 to T/2 with the oscillation center as the reference point, and the other integrator 19 integrates and holds the detection output for the half period of oscillation from 0 to T/2 using the oscillation center as the reference point. The detection output is integrated over the half period from T/2 to T, and both integrator outputs 2/T∫ ^T/2 ₀ Idt and 2/T∫ ^T _T/2 Idt are compared by the differential amplifier 20. As a result, the motor 8 is drive-controlled via the drive circuit 21 so that the output of the differential amplifier 20 becomes zero.

By controlling the motors 8 and 9 in this manner, the swing center of the torch is held at the center in the groove width direction, and the distance H from the base material is also held at the value set in the reference signal source 13. be.

As described above, according to the present invention, the widthwise position of the swinging center of the torch is controlled by reciprocating for half a period in one direction and reciprocating for half a period in the other direction from the swinging center. Since this is performed by comparing the time-integrated values of welding current or welding voltage over half a period, it is possible to prevent ripple components and noise components of the waveform that are characteristic of consumable electrode arc welding from adversely affecting tracing control. Not only welding but also automatic tracing in short arc welding, which is indispensable for all-position welding, is now possible.Also, since the torch oscillates in a parallel reciprocating motion instead of rotating in a circular arc as in the past, the oscillation period can be reduced. When performing the time integration over a wide range of , it is possible to obtain a result that accurately correlates with the cross-sectional area of the groove traced by the actual torch tip, thereby improving control accuracy. In addition, in the present invention, since the tracing control is performed by the arc itself without using a special tracing sensor, the control target position is the detection position, the control system does not include delay time, and the area around the torch can be made compact. This makes it possible to perform automatic copy welding in narrow spaces, and enables stable control without being affected by disturbances such as spatter.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of arc welding, Fig. 2 is a diagram showing examples of welding current-voltage characteristics when the torch-base metal distance is changed, and Figs. 3a to 3e are graphs of the present invention. A front view of a welded part for explaining a welding method according to an embodiment, FIGS. 4a to 4
Figure e is a diagram showing periodic changes in welding current corresponding to Figures 3a to 3e, respectively, Figure 5 is a front view showing an example of a torch drive mechanism, and Figure 6 is a control example according to the present invention. FIG. 2 is a block diagram showing the system. 1: Base material, 2: Wire, 3: Torch, 8, 9:
Motor, 10: Current detector, 12, 18, 19:
Integrator, 14: Comparator, 17: Switch, 20: Differential amplifier.

Claims (1)

[Claims] 1 The groove surfaces on both sides of the root of the joint are inclined with respect to the width direction of the welding direction with respect to the wire directed toward the welding joint, and the torch supporting the wire is directed in the welding direction with respect to the welding joint. In the arc welding method using a consumable electrode that is performed while moving relative to each other, the wire is fed at a constant speed, and the welding current flowing from the welding power source to the wire or the welding voltage of the wire is detected, and The wire is moved in the welding progress direction while swinging the arc by reciprocating the torch in parallel with a constant amplitude, and the torch moves from the swing center to one side in the width direction, with the center of the swing being the reference point. Half a cycle until the torch oscillates and returns to the oscillating center after reversing, and then until the torch oscillates from the oscillating center to the other side in the width direction and returns to the oscillating center after reversing. The swing center of the torch is controlled to move in the width direction in the welding progress direction so that the time integral values of the welding current or welding voltage of the wire over each half period are equal to each other. Characteristic arc welding method.