JPS6225068B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to welding where the welding speed fluctuates due to control problems or stability of the workpiece or the drive device of the welding machine. Regardless of fluctuations in
The present invention relates to an arc welding method that can always obtain uniform welding results, and an apparatus for carrying out the method.

On a continuous processing line, for example, a long metal tape is continuously run and formed into a circle, oval, or square shape with forming rolls, or wound into a spiral shape, and the abutting parts of the metal tape are welded. When manufacturing pipes continuously, or when welding narrow metal strips together at their edges to obtain wider strips,
The line drive device is extremely large and has large inertia.
Further, in order to prevent the metal tape from breaking due to the shock at the time of starting, a considerably long acceleration time and deceleration time are required to start and stop this.

If a stationary welding torch is placed opposite a moving object to be welded, the welding torch will move considerably relative to the object to be welded. Therefore, if an arc is generated between the welding torch and the workpiece, a continuous weld will be formed. At this time, the moving speed of the object to be welded becomes the welding speed. For this reason, not only when the workpiece starts and stops running, but also during steady running, speed fluctuations due to other factors in the drive device of the workpiece, such as other equipment at the end of the continuous processing line (such as winding There are constant decelerations of the entire running line due to problems with reels, cutting machines, etc., accelerations during failure recovery, and unexpected speed fluctuations due to fluctuations in power supply voltage. This variation in traveling speed immediately becomes a variation in welding speed.

[Conventional technology]

Conventionally, in welding where such fluctuations in welding speed are unavoidable, the moving speed of the welding object, that is, the welding speed, is detected with a detector, etc., and the welding current is increased or decreased in proportion to the detected value to increase or decrease the welding current to the welded object. The energy supplied per unit length was controlled to be approximately equal. (For example, JP-A No. 48-40183, JP-A No. 52-
114548) Therefore, when the welding speed is constant, the welding current is controlled to be a constant current, and when the welding speed changes, it changes accordingly.

[Problem that the invention seeks to solve]

However, when using this method, a sufficiently good result can be obtained even with slight welding speed fluctuations in a steady state, but the welding speed drops dramatically when the continuous processing line is started or stopped, so it is difficult to follow this. The welding current thus reduced is also extremely small, resulting in poor arc directionality and stability, making it impossible to obtain a good welding result. In order to prevent this, if the lowest value of welding current is kept at a current value that stabilizes the arc, when the speed is extremely slow, such as immediately after starting or stopping the line, excessive heat input may occur, causing dripping of the weld bead and holes. Opening occurs and the commercial value of the object to be welded is significantly reduced. For example, when TIG welding is performed using direct current, if the welding current is lower than about 30 to 40 A at a constant current, the directionality of the welding arc becomes poor and unstable, resulting in an uneven weld bead. For this reason, it is considered desirable to perform welding with a welding current of 30A to 40A or more. However, when the object to be welded is a thin plate, for example in a continuous production line for metal-coated cables where a metal tape is wrapped around the outside of the insulated cable and the tape is joined by welding, the plate thickness is 0.2. mm to 0.6 mm metal tape is often used. When welding such thin plate materials, it is necessary to weld at a welding speed of at least 2 to 3 m per minute in order to weld at a welding current of 30 to 40 A or more to stabilize the arc, and slower welding speeds are required. In this case, excessive heat input occurs, resulting in dripping of beads and perforations. For this reason, metal pipes for cable jackets that require high airtightness not only fail to meet this requirement, but if the metal tape melts off, this can cause damage to the internal cable, which can be fatal. This will result in a defective part. Therefore, the parts that are welded after starting the starting line until the driving speed, that is, the welding speed reaches 2 to 3 m/min, and during the deceleration period from this speed to the stop, cannot be used as products. There will be no. For this reason, when using the conventional method, when one welding is stopped, the length of one thread of the cable is determined. Therefore, in order to manufacture long cables, every precaution must be taken to prevent a significant drop in the speed of the welded object or to prevent welding from being interrupted until the required length of welding is completed. The need arose. However, in TIG welding, tungsten electrode wear is unavoidable, and the amount of wear is determined by the applied welding conditions. In addition, even in MIG welding using consumable electrode wire, the length of the welding electrode wire is finite, and there is always an opportunity to interrupt welding due to blockage of the shield gas nozzle due to spatter or fume generated during welding.
It is impossible to avoid this and continue welding continuously for any long period of time. Furthermore, an unexpected accident
For example, welding must be interrupted if the metal tape breaks due to a power outage or line abnormality, and in this case, if the welding length up to that point has not reached the required length, welding at the stopped point and restarting as described above. Due to the unavoidable occurrence of defects in the starting part, a perfect weld cannot be obtained subsequently, resulting in a product that is defective.

[Means for solving problems]

As a result of various experiments to solve the above-mentioned conventional drawbacks, the present inventor found that the instability of the welding arc and the occurrence of welding defects during periods when the welding speed is low can be partially solved by applying the pulse welding method. I found out what I can do. That is, when using the so-called pulse welding method in which high current and low current are periodically repeated, the arc has good directivity and stability even if the average welding power is extremely small. Therefore, by applying this to welding at low speeds, and by making the average value of the welding current correspond to an increase in welding speed, welding at extremely low speeds (such as when starting from zero speed) It was determined that sufficiently stable welding can be performed from to near steady welding speed.

On the other hand, during steady welding, high-speed welding is normally performed at a welding speed of 20 to 30 m/min, so even if the workpiece to be welded is a thin plate with a thickness of about 0.2 mm, the required welding current is 100 A or more. Therefore, the directivity of the arc is sufficiently good, and conversely, since the welding speed is high, even a very short welding current change appears as a long distance in the welding length, so the welding current is sufficiently stable. There is a need. It is also necessary to control the welding current in quick response to changes in welding speed. For this reason, even if the welding speed is high, if welding is performed with a current change such as a pulse welding method, the weld bead will become irregular and the weld will not meet the purpose. Therefore, in the present invention, while the welding speed is low, welding is performed using a pulse welding method in which the average value of the welding current corresponds to the welding speed, and when the welding speed becomes high, welding is performed using a pulse welding method using a voltage or current corresponding to the welding speed. By welding using the welding method,
This improves the various drawbacks mentioned above.

〔Example〕

FIG. 1 is a configuration diagram showing an example of a device for carrying out the welding method of the present invention, in which 1 is a welding torch, 2 is a cart on which the workpiece to be welded is placed, and 3 is a device for driving the cart 2. 4 is a welding speed setting device that determines the rotational speed of the electric motor 3; 5 is a motor control circuit that receives a setting signal from the welding speed setting device 4 and controls the power supplied to the electric motor 3; 6 is a commercial power source 7; This is a power supply circuit that receives electric power from an input terminal a, converts it into electric power suitable for welding, and supplies welding electric power between the torch 1 and the truck 2 via an output terminal b. 8
9 is a reference signal generator for setting a welding speed as a reference for switching the welding method, and 9 is an output signal of the reference signal generator 8 and an output signal of a welding speed detector 10 that detects the rotational speed of the electric motor 3. Compare and output a binary signal depending on the magnitude of both output signals, for example, if the output of the welding speed detector 10 is lower than the output signal of the reference signal generator 8, a zero signal or a low level signal is output, and in the opposite case, a binary signal is output. This is a welding speed discrimination circuit that outputs a finite voltage signal or a high level signal.

In the same figure, at the start of welding, a motor control circuit 5 controls the motor 3 according to a signal from a welding speed setting device 4.
begins to rotate, but the speed of this motor does not reach the set value immediately and the response speed of motor 3, trolley 2
The vehicle is accelerated to the set speed with a unique time constant determined by the inertia of the vehicle. During this time, the speed detector 10 feeds back a signal corresponding to the rotational speed of the motor, that is, the welding speed, to the motor control circuit 5, and outputs it to the welding speed determination circuit 9 and the power supply circuit 6. As described above, the welding speed determination circuit 9 compares the output signal of the speed detector 10 with the output signal of the reference signal generator 8, determines whether the welding speed is slower or faster than the reference value, and calculates the determination result. is output to the power supply circuit 6.

The power supply circuit 6 outputs welding power according to the output signal of the welding speed detector 10, but it outputs a high current and a low current while the welding speed is slower than the reference value according to the output signal from the welding speed discrimination circuit 9. Outputs a pulsed welding current whose average value corresponds to the welding speed, and outputs a normal welding current whose value corresponds to the welding speed when the welding speed increases and becomes faster than the standard value. do.

Such a power supply circuit 6 may be a single-phase or three-phase power supply circuit.
If it is a circuit that takes a phase commercial power supply as input, converts the input voltage to a voltage suitable for welding, then rectifies it and converts it to DC, or converts and controls AC to the desired output state, the method is particularly suitable. It is not limited. Typical configuration examples are shown in FIGS. 2 and 3. 2 and 3, a is an input terminal, b is an output terminal, and c and d are control signal input terminals, respectively, which are the same reference numerals of the power supply circuit 6 of the embodiment shown in FIG. Compatible with terminals. 601 is a transformer for converting the commercial power source obtained from input terminal a into a voltage suitable for arc welding, 602 is a rectifier circuit, and 603 is a current limiting element, which is connected in series to the output side of the rectifier circuit as shown in the same figure. When connecting, analog elements such as transistors are preferred; conversely, when connecting to the alternating current side, bidirectional thyristors, saturable reactors, anti-parallel connected transistors, thyristors, etc. can be used. 604
a control signal generator that receives a welding speed signal from the signal input terminal c and converts it into a signal suitable for determining the amount of conduction of the current limiting element 603 so that the welding current has a continuous value corresponding to the input signal; 605 is a pulse generator that receives a welding speed signal from terminal c and generates a pulse signal with an average value corresponding to the input signal;
606 is a signal selection circuit that selects a signal according to the discrimination signal of the welding speed discrimination circuit inputted from the input terminal d, and 607 is an OR circuit. In the circuit shown in FIG. 2, commercial power introduced from input terminal a passes through a transformer 601, is converted into direct current by a rectifier circuit 602, and is supplied to a current limiting element 603. The amount of conduction of the current limiting element 603 is controlled by the control signal selected by the signal selection circuit 606, and a predetermined output is obtained at the output terminal b. The signal selection circuit 606 supplies the output signal of the pulse generator 605 to the current limiting element 603 during a period in which the welding speed is slower than the reference value according to the binary signal from the welding speed discrimination circuit supplied from the input terminal d, and performs welding. When the speed becomes faster than the reference value, the output signal of the control signal generator 604 is supplied to the current limiting element 603. As a result, a current with a waveform whose average value corresponds to the welding speed is output to the output terminal b according to the output of the pulse generator 605 during a period when the welding speed is slow, and when the welding speed becomes faster, the output of the control signal generator 604 is output. The signal outputs a continuous current whose value corresponds to the welding speed.

In FIG. 3, the welding speed signal from the input terminal c is first selectively supplied to the control signal generator 604 or pulse generator 605 by the signal selection circuit 606 according to the output signal from the speed discrimination circuit, and the control signal is generated. The output signals of the generator 604 and the pulse generator 605 are passed through the OR circuit 607 to the current limiting element 603.
2, and the same results as in FIG. 2 can be obtained.

In FIGS. 2 and 3, when obtaining an AC output, it is necessary to omit the rectifier circuit 602 and to configure the current limiting element 603 to conduct current in both directions. In addition, the connection point of the current limiting element is not particularly limited, regardless of whether it is on the primary side or the secondary side of the welding transformer 601, as long as it is between input terminal a and output terminal b, and is not limited to the illustrated example. do not have. FIG. 4 schematically shows an example of the relationship between welding speed and welding current when welding is performed according to the present invention, where a shows the change in welding speed v with respect to time t, b shows how the welding current I _W changes. In the same figure, the welding speed v during acceleration
Until the welding speed reaches the reference speed v ₀ , welding is performed with a pulsed current of I _p at high current and I _b at low current, and the period occupied by high current increases approximately in proportion to the welding speed. When the welding speed exceeds the reference speed v ₀ , the welding current becomes a smooth direct current, and thereafter the welding current increases in proportion to the welding speed. During deceleration, the process reverses to that described above.

Pulse generators 605 having various functions can be used, but any pulse generator that can change the average value of the output signal depending on the magnitude of the input signal (welding speed signal) may be used. An example of the output waveform is shown in FIG. In the same figure, a shows a change in the input signal, that is, a change in welding speed, b shows the length of the high current period changing in response to the input signal level as it changes as shown in a, and c shows the period being constant. d is one in which the pulse peak value changes, d is one in which the length of the high current period and its pulse peak value both change, e is one in which the length of the low current period changes in inverse proportion to the welding speed, and f The length of the high current period, the current peak value of the high current period, and the length of the low current period all change. In b to f in the figure, the curves indicated by broken lines indicate the average value of the pulse signal output. Furthermore, in the pulse welding method, it is known that even if the peak value and pulse width are constant, the penetration depth and bead shape change in a specific frequency range simply by changing the frequency. When utilizing this, a welding speed signal generator having a speed frequency converter that generates a pulse with a frequency proportional to the welding speed can be used, and this can be replaced with a pulse generator.

In reality, it is desirable to use an appropriate combination of individual means for changing the length of each high and low current period and the peak value as the welding speed increases.

In the embodiment shown in FIG. 1, the welding speed signal is obtained from the welding speed detector 3, but the welding speed detector is omitted and the output signal of the welding speed setting device 4 is set to an appropriate value that matches the time constant of the drive system of the trolley 2. It may also be used as a welding speed signal after passing through a time delay element, such as an integrating circuit. In this case, if the welding speed setting device 4 is set to output an acceleration/deceleration command with a rate of change slower than the time constant of the bogie drive system, the output of the welding speed setting device 4 is used as a time delay element. It can be used as a welding speed signal without going through it or by just adjusting the level appropriately.

〔Effect of the invention〕

As described above, in the present invention, when the welding speed is slow, such as when starting or stopping welding, welding is performed using the pulse welding method, which has excellent arc directionality and stability, and when the welding speed is high, welding is performed using the pulse welding method. Since welding is performed using a predetermined continuous current that corresponds to the speed, there is no risk of arc instability or burn-through of the welded object even when the welding speed is slow.
Therefore, in continuous processing lines such as pipe manufacturing where relatively long acceleration and deceleration times are set during startup and shutdown, in the unlikely event that the speed of the workpiece to be welded significantly decreases or the line stops. Even when the welding process is carried out, there are no defects in the product and yields are dramatically improved.In addition, during normal line running, the continuous welding current is simply adjusted according to the welding speed, resulting in faster response speed. This allows a stable weld to be obtained at all times.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of an apparatus for carrying out the welding method of the present invention, and FIGS.
A configuration diagram showing an example of a power supply circuit in the embodiment shown in the figure,
Fig. 4 is a diagram schematically showing the relationship between welding speed and welding current when using the welding method of the present invention, and Fig. 5 is an input/output waveform of the pulse generator shown in the example of Figs. 2 and 3. FIG. DESCRIPTION OF SYMBOLS 1... Welding torch, 2... Cart, 3... Car drive motor, 4... Welding speed setting device, 6... Power supply circuit, 7... Commercial power supply, 8... Reference signal generator,
9... Welding speed discrimination circuit, 10... Welding speed detector, 601... Welding transformer, 603... Current limiting element, 604... Control signal generator, 605... Pulse generator, 606... Signal selection Circuit, 607...
...OR circuit.

Claims (1)

[Scope of Claims] 1. In an arc welding method performed while relatively moving a workpiece and a welding electrode, a signal regarding a welding speed is obtained, and the welding current is adjusted during a period in which the signal regarding the welding speed is smaller than a set value. Welding is performed by a pulse welding method that uses a pulsed current that periodically changes between high and low currents and increases or decreases the average value of the pulsed current in accordance with the welding speed, and the signal related to the welding speed is greater than the set value. An arc welding method in which welding is carried out using the normal welding method using a continuous current that corresponds to the welding speed. 2. A welding speed signal generator that outputs a signal approximately proportional to the welding speed, a reference signal generator, and comparing the output signal of the welding speed signal generator and the output signal of the reference signal generator to determine the magnitude of both output signals. a welding speed discrimination circuit that generates a binary signal according to the welding speed discrimination circuit; and a signal indicating a state in which the output signal of the welding speed signal generator is smaller than the output signal of the reference signal generator is input from the welding speed discrimination circuit. output a pulsed current whose average current corresponds to the output signal of the welding speed signal generator, and when the output signal of the welding speed signal generator exceeds the output signal of the reference signal generator. an arc welding device comprising: a power supply circuit that outputs a continuous current having a value corresponding to an output signal of a welding speed signal generator when a signal indicating a welding speed discriminating circuit is inputted from the welding speed discriminating circuit; 3. The power supply circuit includes a transformer that converts commercial power to a voltage suitable for welding, and a pulse generator that receives the output signal of the welding speed signal generator and generates a pulse signal having an average value corresponding to the input signal. , a control signal generator that receives the output signal of the welding speed signal generator and generates an output according to the input signal, or supplies the output signal of the welding speed signal generator as it is to the next stage; and the pulse generator. and an output signal of the control signal generator as input, and transmits either the output signal of the pulse generator or the output signal of the control signal generator to the next stage according to the output signal of the welding speed discrimination circuit. Claim 2, further comprising at least a signal selection circuit and a current limiting element connected in series to the primary side or secondary side of the transformer, the amount of conduction being determined by the output signal of the signal selection circuit. The described arc welding equipment. 4. The welding power source includes a transformer that converts a commercial power source to a voltage suitable for welding, a pulse generator that generates a pulse signal having an average value corresponding to the input signal, and a control signal or input having a value corresponding to the input signal. a control signal generator that supplies the signal as it is to the next stage; and a control signal generator that receives the output signal of the welding speed signal generator and transmits the input signal to the pulse generator or the control signal generator according to the output signal of the welding speed discrimination circuit. A signal selection circuit for transmitting the signal to one of the output terminals, an OR circuit that receives the output signal of the pulse generator and the output signal of the control signal generator, and is connected in series between the transformer and the output terminal. The arc welding apparatus according to claim 2, further comprising at least a current limiting element whose conduction amount is determined by the output signal of the OR circuit. 5. The arc welding apparatus according to any one of claims 2 to 4, wherein the welding speed signal generator is a welding speed detector that generates a voltage proportional to the welding speed. 6. The arc according to any one of claims 2 to 4, wherein the welding speed signal generator includes a speed/frequency converter that generates a pulse signal with a frequency proportional to the welding speed. Welding equipment. 7. The arc welding apparatus according to any one of claims 2 to 4, wherein the welding speed signal generator obtains a signal from a welding speed setting signal. 8. The pulse generator repeatedly generates a high level signal with a constant time width and a low level signal with a variable time width, or a high level signal with a variable time width and a low level signal with a constant time width, thereby increasing the input signal level. A pulse generator that causes the average value of the output signal level to correspond to changes in the input signal by decreasing the time width of the variable low level signal or increasing the time width of the variable high level signal in response to the increase. An arc welding apparatus according to any one of claims 3 to 7. 9. The arc welding according to any one of claims 3 to 7, wherein the pulse generator is a pulse generator in which the peak value of the output pulse signal increases in response to an increase in the input signal. Device.