JPS583787A - Controller for preventing melt sticking of tungsten electrode - Google Patents

Abstract

PURPOSE:To prevent melt sticking of a W electrode and deposited metal or the groove surfaces of base materials that takes place during welding in an automatic TIG welding device by so controlling the device as to stop the welding when the arc voltage value during welding attains a correct value or below. CONSTITUTION:When a switch 7 is turned on, a relay 9 is energized, and A contacts 9a close. Since B contacts 10a are held closed, the relay 9 latches itself and welding is started. On energizing of the relay 9, a timer 10 starts operating and the contacts 10a open in a constant time after arc generation. When the arc is generated between an electrode 2 and base materials 3, the output relay 6 of a comparator 4 goes off, and the B contacts 6a thereof close, thereby keeping the relay 9 latched on. The arc voltage Va and the correct arc voltage VRef of a lower limit voltage setter 5 are compared by the comparator 4, and when Va>VRef, the relay 6 turns off and the relay 9 turns on, thus the welding is continued. When Va<VRef on account of certain disturbance, a signal is outputted from the comparator 4, and the relay 6 turns on, the contacts 6a open and the relay 9 turns off, whereby the welding is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tungsten electrode welding prevention control device for preventing welding between a tungsten electrode and a weld metal or a groove surface of a base material that occurs during welding.

Among arc welding methods, TIG welding does not cause spatter, has a good bead appearance, and allows the welding current, voltage, speed, and amount of filler wire to be set independently.
Furthermore, in recent years, combinations with arc length control (AVC control), which detects the arc voltage and keeps the arc length constant, have become popular, and it has excellent characteristics as an automatic welding method.

During TIC automatic welding, if welding occurs between the tungsten electrode and the weld metal or the groove surface of the base metal, the welding is interrupted, the groove surface b) of the welded tungsten electrode is removed, and the tungsten is welded. Removal of metal and complicated work such as bead shaping to restart welding are required. These operations require grinding and gouging, but if the weld is too narrow to use these tools, or if the weld requires careful handling of the dust generated during the operation, it may be necessary to use a grinder or gouge. In order to completely eliminate rework, it is necessary to prevent welding.

The present invention has been made in view of the above circumstances, and its purpose is to detect the arc voltage during welding in a TIG automatic welding device, and to stop welding when the arc voltage value falls below the appropriate voltage value. This prevents TIG automatic welding equipment from malfunctioning or from welding between the tungsten electrode and the weld metal or the groove surface of the base material, which would otherwise occur due to some kind of disturbance. It is an object of the present invention to provide a tungsten electrode welding prevention control device that can take a step forward.

The welding condition parameters for TIG automatic welding are:
There are arc current, voltage, filler wire amount, etc., but as a result of the inventor's study, the parameter related to welding of the tungsten electrode was the arc voltage value.

That is, when tested using a TIG automatic welding system combined with AVC control, in the low welding current range of 50 to 100 amperes, the arc voltage was reduced to about 8.5 volts for a proper arc voltage value of about 9 volts. If the voltage is lowered below volts, the AVC
Due to the effect of the control, the welding torch begins to hunt above the AVC control slider, and as the hunting continues, the tungsten electrode welds to the molten crater. In the high current range of 100 to 400 amps, which reduces the arc voltage to about 10 volts or less for a suitable voltage value of 11 to 13 volts, hunting of the welding torch also occurs, and the hunting or continuous (and tungsten electrode) Welding occurs with the molten crater.Furthermore, when the welding torch began to weld, the arc voltage value fluctuated even more.

After further consideration, we conducted a welding reproduction test by generating a welding stop signal when the voltage reached 9 volts, which is about 1 volt lower than the appropriate arc voltage of 10 volts, and found that the tungsten electrode melted. If the welding torch comes abnormally close to metal or the groove surface, or if the welding torch causes hunting, a welding stop operation is executed instantly, preventing welding between the tungsten electrode and the weld metal or base metal groove surface. It has been confirmed that this can be prevented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a tungsten electrode welding prevention control device according to the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a welding power source 1 is connected to a tungsten electrode 2.
and is connected to the base metal 3 which is the material to be welded.

Further, the tungsten electrode 2 and the base material 3 are connected to a comparator 4, and a lower limit voltage setter 5 is connected to the comparator 4. Comparator 4 is also connected to output relay '-6.

In the sequence control circuit shown in FIG. 2, a normally closed welding stop pushbutton switch 8 is connected in series with the normally open welding start pushbutton switch 7, and a relay 9 is connected in series with the welding stop pushbutton switch 8. A timer 10 is connected in parallel with this relay 9. Further, a series circuit of the A contact 9a of the relay 9 and the B contact 6a of the output relay 6 is connected in parallel with the welding start push button switch 7, and the on-delay B of the timer 10 is connected in parallel with the B contact 6a.
Contact 10a is connected.

Now, when the welding start push button switch 7 is pressed, the relay 9 is energized and the A contact 9a of the relay 9 is closed, and since the B contact 10a is closed at this time, the relay 9 is self-held, and welding starts here. be done.

Also, at the same time as the relay 9 is energized, the timer 10 starts operating, and the on-delay B contact 10a of the timer 10
opens a certain time after the arc occurs.

When welding starts, an arc is generated between the tungsten electrode 2 and the base metal 3-, but once the arc occurs, the comparator 4
The output relay 6 is turned off, its B contact 6a is closed, and the relay 9 continues to maintain itself through this contact. In addition, in the timer 10, due to transient fluctuations in the arc voltage at the start of welding, the comparator 4 is activated and the output relay 6 is energized, its B contact 6a is opened and the relay 9 is turned off, and welding is stopped. This is provided to prevent this for a certain period of time from the start of welding.

In the comparator 4, the arc voltage Va between the tungsten electrode 2 and the base metal -3 is compared with the appropriate arc voltage ■Ref set in the lower limit voltage setting device 5, and under normal conditions when ■3>■Ref. Since the output relay 6 of the comparator 4 remains off, the relay 9 remains on and welding continues. Now, due to some disturbance, the arc voltage V
When a decreases to ■3<■Ref, a signal is output from the comparator 4, the output relay 6 is turned on, and the B contact 6a of the output relay 6 is opened, so the self-holding of the relay 9 is released, and the relay 9 is turned off and welding is stopped.

Generally, the appropriate arc voltage varies depending on the current used. This is because even if the arc length is the same, as the current increases, the arc voltage increases. FIG. 3 shows the relationship between arc voltage and arc current using the distance between the tungsten electrode and the base metal, that is, the arc length, as a parameter, where the arc length 0LIII11 was determined by calculation.

The curve corresponding to this arc length OW is V=0.0031111+8.827, where arc voltage is ■ and arc current is I.
...(1) can be approximated to a straight line.

Using the above relationship, it is possible to automatically set the appropriate voltage by detecting the arc current.

To explain one embodiment of a control device for doing this, as shown in FIG. 4, a welding power source 1 and a tungsten electrode 2 are connected, and a current detector 7 connected via. A comparator 4 is connected between the tungsten electrode 2 and the base material 3, a current detector 7 is connected to a function generator 8, and the function generator 8 is connected to the comparator 4.
Further, an output relay 6 is connected to the comparator 4.

Now, when an arc occurs between the tungsten electrode 2 and the base metal 3, this arc current is detected by the current detector 7, this current value is input to the function generator 8, and the calculation of equation (1) is performed. The appropriate arc voltage setting value ■Ref is outputted and inputted to the comparator 4. In the comparator 4, the arc voltage between the tungsten electrode 2 and the base metal 3 is
1 and the arc voltage setting value ■Ref are compared, and Va
) VRe (then the output relay 6 remains off and the second
Welding continues according to the circuit shown in the figure, and Va (■Re
When the time reaches f, the output relay 6 is turned on and welding is stopped.

For example, when the arc current I is 20OA, the arc voltage setting value ■Ref from equation (1) is VRe[-=0.03111X200+8.827=9
．． 449 (V) That is, the arc voltage Va is about 9.
When the voltage falls below 5V, the comparator 4 is activated, the output relay 6 is turned on, and welding is stopped.

As explained above, in the tungsten electrode welding prevention control device according to the present invention, the arc voltage is detected, and when the arc voltage drops below a certain value due to some reason, welding is stopped, so the AVC control In automatic TIG welding equipment that is combined with AVC control, it is possible to prevent welding between the tungsten electrode and the groove surface caused by hunting due to arc voltage drop, and in automatic TIG welding equipment that is not combined with AVC control. Also, by using the present invention, it is possible to detect abnormal proximity between the tungsten electrode and the welding part and execute a welding stop operation, thereby preventing welding between the electrode and the groove. In addition, the arc current is detected, a function generator is used to calculate the appropriate arc voltage for this arc current, this is used as a set value, and compared with the actual arc voltage, the actual arc voltage is smaller than the set voltage. If this occurs, by stopping welding, even if welding conditions are changed, an appropriate voltage value can be automatically set, and welding can be reliably prevented.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing an embodiment of the invention, and Fig. 3 is a graph showing the relationship between arc voltage and arc current. FIG. 2 is a block diagram showing another embodiment of the present invention. 2... Tungsten electrode, 3... Base material, 4... Comparator, 5... Lower limit voltage setter, 8... Function generator. Patent applicant Kobe Steel, Ltd.

Claims (1)

[Claims] (1) In a TIG automatic welding device that generates an arc between a tungsten electrode and a workpiece to weld the workpiece, an arc voltage detection section that detects the arc voltage between the tungsten electrode and the workpiece; , a voltage setting part that sets a set voltage, and a comparison part that compares the detected arc voltage and the set voltage and outputs a signal to stop welding when the arc voltage is lower than the set voltage. A tungsten electrode welding prevention device characterized by comprising: