CS196438B2 - Electric connection for automatic regulation of the d.c.arc welding of the thin sheets - Google Patents

Abstract

1,267,108. Arc welding control systems. KABEL-UND METALLWERKE GUTEHOFFNUNGSHUTTE A.G. Dec.8, 1969 [Jan.9, 1969], No.59743/69. Heading G3R. Apparatus for the automatic control of D.C. arc welding of thin sheets which are fed past a stationary welding head comprises electrodes 4 which are fed from an A.C. source 1 by way of a transformer 2, an adjusting element 3 - shown as a transductor but which may be a thyrlstor - rectifiers and a D.C. current transformer 5, the current transformer 5 producing a signal representing the actual welding current, which signal is compared in a controller 7 with a signal from a tachogenerator 6 which produces a signal representing the welding current required according to the speed of the sheet being welded past the welding head, the error signal effecting a control on the adjusting element 3 thereby to maintain the welding current at the value required for the speed of the sheet. The apparatus also compensates for current variations causes by temperature fluctuations .

Description

The invention relates to an electrical circuit for automatic regulation of direct current. arc welding of thin sheets,. protahovaných pod. a stationary welding head, for example for welding into a coiled sheet metal tube by a longitudinal weld seam under a protective atmosphere by means of welding electrodes supplied from a welding transformer via a welding current regulating member and rectifier elements, the speed-dependent tachogenerator acting on the regulating member.

From German Pat. No. 1146,992, a circuit of this kind is known, wherein the regulating element is a choke pre-magnetized by direct current, with an adjustable circuit in the excitation circuit of the generator. Voltage divider to set the basic value of the welding current depending on the material to be welded. A variable resistor is connected in the tachogenerator armature circuit ·. to set the proportionality factor 'determining the slope. welding current characteristics depending on the object to be welded. The adjustment of the control element, i.e. the change of the DC biasing of the choke, is thus carried out by the tachogenerator,. which is coupled with or directly with the device for withdrawing the welded sheet. Thus, the welding current is controlled as a function of the rate of passage of the sheet under the welding head. Supply voltage fluctuations and welding electrode gap fluctuations are not monitored in this circuit, so that welding is sometimes produced. seams that are not sufficiently welded and burst with greater mechanical stress.

The invention relates, as well as the known connection, to shielded welding by a tungsten electrode, where a solid, non-molten electrode is used and the counter electrode forms a workpiece. From. In this method, welding in a shielded atmosphere with a melting electrode requires a welding rectifier with a constant voltage characteristic. The distance of the electrode tip from the welded spot is a measure of the arc voltage which constitutes the control variable for the electrode displacement. The welding current is completely unattractive, since at a fluctuating current intensity, the electrode draws off more quickly or more slowly by a self-alignment, which results in a smaller or greater thickness of the weld bead.

This known voltage regulator of the welding rectifier can be applied to tungsten electrode welding but for welding. The metering of sheets and especially thin sheets is absolutely inappropriate. Characteristics · welding198438. - ·. . because the melting electrode is parallel to the line and the arc characteristics are slightly ascending; Thus, the characteristics are almost parallel, which results in a large change in the welding current at a slight voltage deviation; if the current is too high. then the sheets burn through and do not weld if the current is too low

The purpose of the invention is to overcome these disadvantages and to provide a control circuit in such a way that:. ensure constant weld quality.

In electric. wiring for automatic regulation of DC arc. welding thin sheets drawn under a stationary welding head, for example. for welding into a coiled sheet metal by longitudinal - welding seam under protection - atmosphere by welding electrodes, fed from the welding transformer via a welding current - regulating member, and - through the rectifier elements, wherein:. according to the invention, a DC converter is connected between the rectifiers and the electrodes, the secondary winding of which flows through the current corresponding to the actual welding current value and is connected to the controller together with the output of the tachogenerator whose output current corresponds to the and - controller. it is connected to the input of a control element connected between the welding transformer and the electrodes.

Thus, in the circuit according to the invention, the actual value of the welding current is continuously determined and compared with the desired value, so that in the case of deviation from the desired value, the regulator adjusts the regulating element in terms of alignment. - The regulation is very sensitive - and fast - so - fluctuations - in the supply voltage, electrode distance and - temperature - changes do not affect the welding current, which is constantly - maintained - at the value needed to check the weld.

The invention is explained in the description with reference to the accompanying drawing, in which Figures 1 and 2 show two examples of connection according to the invention, with a differently formed control member.

Wiring according to FIG. 1 is supplied from a power supply 1, which may be, for example, an AC voltage with a frequency of 50 Hz. The power supply -1 is connected to the primary winding of the welding-transformer 2, the secondary winding of which is connected to the transducer 3. Between the welding-head-4 whose welding electrodes are indicated by + and -, and the transducer - 3 a DC - converter - 5 is connected, of which - the secondary winding - draws current corresponding to the actual welding current value. The tachogenerator 6 produces a current that corresponds to the set welding current value. - The setpoint value and the actual value of the welding current are compared to each other by superimposing and the resulting differential signal is applied to the -7 input. The output signal of the regulator 7 changes the pre-magnetization of the cores of the transducer 3. If there is a control deviation, i.e. a difference between the actual and the set welding current value, the regulator 7 changes the pre-magnetization of these cores. The required energy is - supplied to the controller 7 by an auxiliary transformer 8. The potentiometer 9 is used to make - the desired setpoint changes - the welding current. .. ···

The circuit described in FIG.

After switching on the welding aggregate, a certain pre-magnetization of the transducer core 3 is determined, determined by the regulator 7, depending on the setting of the potentiometer 9 which is carried out before the beginning of the welding - depending on the properties of the material to be welded, e.g. If - due to any unexpected circumstances - the electrode gap increases, the voltage must be increased. The welding current is reduced for a short time and thus also - the current in the secondary winding of the DC inverter - 5, which is - the actual value signal - the welding current. Therefore, the input of the controller 7 reaches the signal of the difference between the actual and the set welding current value. In this case, the output signal of the regulator 7 reduces the pre-magnetization of the cores of the transducer 3, thereby increasing the current flowing through the welding electrodes of the head 4. In the same way the voltage fluctuation of the power supply 1 is equalized. Also, changes that occur in the described circuit due to temperature fluctuations, which also have an influence on the welding current value, are immediately compensated by the regulator 7. It is therefore ensured by the connection according to the invention that the welding current flowing through the electrodes of the welding head 4 still has a value which is necessary to produce a fully tested welding seam. .

Connection according to fig. 2 differs from the circuit according to FIG. 1 by a different design of the control member. In the circuit of FIG. 1, the control member is a transducer. 2, the thyristor 10 is the regulating member. In the wiring diagram of FIG. 2, one thyristor is shown for simplicity, but in practice several thyristors may be used. The operation of the circuit according to FIG. 2 is essentially the same as the operation of the circuit according to FIG. 1. The difference is that the use of an electronic element as a thyristor control element 10 reduces the time of the control process. because '- thyristor -10. It is known that the thyristor-10 goes into a 'non-conductive' state 'each time the control voltage hulou is passed and must be re-ignited. This ignition is carried out by the regulator 7, which sets the moment of ignition of the thyristor 10 to an earlier or a later time, depending on whether it appears that a greater or lesser current should flow into the electrodes of the welding head 4.

196

The circuit according to the invention has the additional advantage over the prior art circuitry that no auxiliary circuits are required for starting the welding unit. By gradually increasing the set current value at start-up, a precisely defined start of welding and a sudden increase in welding current can be ensured.

According to a further feature of the invention, the welding transformer 2 can be designed as a leakage transformer which has the advantage that it reacts softly to rapid changes in current in the secondary winding, thus preventing the

Claims (5)

1. Electrical connection for the automatic regulation of direct arc welding of thin sheets drawn under a stationary welding head, for example for welding into a coiled sheet metal tube by a longitudinal welding seam under a protective atmosphere using welding electrodes supplied from a welding transformer via a welding current regulating member. and via rectifier elements, wherein a speed-dependent tachogenerator acts on the regulating element, characterized in that a DC converter (5) is connected between the rectifier elements and the electrodes (4), the secondary winding of which flows through current corresponding to the actual welding current value is connected to the regulator (7) ) together with tachogene439 output • damage to the control circuit. Especially when the thyristor 10 is used as a regulating element, the welding current surge changes, so that the use of the dispersion welding transformer 2 is very advantageous. The regulator 7, which is essentially a regulating amplifier, can be designed as a transistor amplifier of known type with high amplification. It is advantageous to design the controller 7 so that it has the characteristics of a proportional integration controller. CLAIMS-laboratory (6) whose output current corresponds to the value _of the welding current, and a controller (7) is connected to the input control member connected between the welding transformer (2) and electrodes (4). 2. The electrical connection according to claim 1, characterized in that the control element is a transducer (3). . < Electrical connection according to Claim 1, characterized in that the control element is a thyristor (10). Electrical connection according to Claims 1 to 3, characterized in that the welding transformer (2) is a leakage transformer. Electrical connection according to Claims 1 to 4, characterized in that the regulator (7) consists of a transistor amplifier with a proportional-integral character.