DE1963339A1 - Circuit for electrical welding - Google Patents

Description

FATE JiTANWALT

DIPL. ING. S. KOIiS

R9 AÜOS3ÜJIG

PHILIPPINB-AVELSEK-STItASSB IA ηωηκι »1STa

K. 313

Augsburg, the 16th December 1969

The British Oxygen Company Limited, Hammersmith House,

London, W.6, England

Electric welding circuit

The invention relates to circuits for electrical welding, in which periods of short-circuit contact between a consumable electrode and a workpiece alternate with periods of an arc between this electrode and this workpiece.

This type of welding is referred to below with

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. "Short-circuit welding". Be known In short-circuit welding, two power sources are used, which are electrically connected to the melting welding electrode are connected in parallel. One power source mainly supplies the short-circuit current and the other power source mainly the arc current.

A disadvantage of known, single-phase power source operated welders is that they cannot be used for satisfactory welding of thin metal sheets because the arc is too "hot", i.e. the arc releases too much energy and is therefore more prone to "drilling" or "cutting" than to welding. The arc energy in short-circuit processes depends on the frequency with which the arc and short-circuit periods take turns. In those cases where stable welding conditions are only possible with relatively high currents and stresses are achievable, the heat dissipation is too great for a satisfactory welding of thin sheets. One high arc voltage results in a low short-circuit frequency, the latter when using a wire from for example Q, 8 mm diameter only about 50 Hz or 60 Hz amounts to.

The invention aims to solve the problem

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to design a circuit for electric welding in such a way that it provides the necessary for short-circuit welding Has operating characteristics and moreover requires only a single-phase power source.

The circuit according to the invention should also be stable Create arcs at voltages so low that the frequency of short circuits is on the order of 100 Hz to 250 Hz, so that the heat emission is so low that thin mild steel sheets of, for example 0.56mm thick butt welded under the following conditions Can be: welding wire diameter: 0.6 mm, shielding gas: COp, 40 A, 16 V. This results in a short-circuit frequency of 210 Hz.

In order to achieve this object, the invention includes a circuit for electrical welding which periods of short-circuit contact between a consumable electrode and a workpiece with periods of an arc between this electrode and this workpiece alternate, which according to the invention by a source is characterized which rectifies a current supplied by a single-phase AC power source and is connected to a combined smoothing memory circuit, to the latter of which the welding electrode and

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the workpiece are connected, this smoothing memory circuit has a switch which connects the at least one storage element to the output terminal of a smoothing circuit as a function of the instantaneous characteristics or parameters controls the welding process.

The invention also includes the solution this object a method for electrical welding, in which periods of short-circuit contact between a consumable electrode and a workpiece with periods of an arc between that electrode and alternate this workpiece, which is characterized according to the invention that a during the short-circuit periods each current flowing directly from the single-phase power source to the welding electrode is increased by one current is, which from a depending on the respective operating state of the welding process by a Switch automatically controlled memory circuit is supplied.

The invention is described below with reference to the accompanying drawings, which show in detail:

Pig. 1 a circuit diagram of a

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circuit according to the invention,

Fig. 2 shows an embodiment of a

Energy storage circuit, which in the invention Circuit as shown in Fig. 1 is used,

FIGS. 3 to 7 show further embodiments of

Energy storage circuits used in the circuit shown in FIG circuit according to the invention are applicable,

Figure 8 is a block diagram of yet another

further embodiment of an energy storage circuit according to the invention,

Fig. 9 is a circuit diagram of an embodiment

form of a saturation energy storage circuit ,

10 and 11 B / H characteristics, which are used for explanation of the operating behavior a

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the circuit according to the invention to serve,

FIGS. 12 and 13 each show different embodiments of induction coils, which each have B / H characteristics of the desired course,

Yy'ig. 14 waveforms that can be found in

Short-circuit welding circuits result,

ij'ig. 15 waveforms that can be found in the

result in circuit according to the invention,

Big. 16 is a circuit diagram of another

Embodiment of a combined saturation energy storage device ehaltkreis, and

fig. 17 is a schematic circuit diagram of a

yet another embodiment of the invention, in which as an energy store an accumulator is used.

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In the basic circuit shown in Fig. 1 feeds a 50 Hz source E a single-phase mains transformer T, whose secondary terminals with the input terminals of a two-way Orleiehrichtersehaltkreises Z are connected, the latter being one shown in a dashed rectangle Combined smoothing and energy storage circuit 2 supplies a direct current. An output terminal of the Circuit 2 is electrically connected to a consumable electrode 4, the latter by feed rollers to a workpiece 8 connected to the other output terminal of the circuit. The clarity For the sake of this, a welding zone 10 is shown between the end of the electrode 4 and the workpiece 8, although in reality there is no gap between these two parts when the electrode is connected to the Workpiece has short-circuit contact.

The circuit 2 has a smoothing circuit S. on, the input of which is connected to a controller 12, the latter also having a connection point between a storage element 14 and a discharge switch 16 connected is. The storage element and the switch are connected in series and connected to the output of the ülättungsschalt circle S connected. When the holder 16 is open,

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the storage element 14 is effectively separated from the electrode 4, but it takes energy in the form a charging current supplied via the controller 12. Therefore only that current flows to electrode 4, which from the rectifier Z through the smoothing circuit flows. The voltage or the amplitude of this current are so large that between the electrode 4 and an arc is maintained on the workpiece 8, the amount of energy released by the arc is sufficient but only to melt the end of the electrode 4 without the molten tip of the electrode detaches from this. The speed of advance of the electrode is also dimensioned such that it moves towards the workpiece 8 at a speed which is greater is the speed at which the tip of the electrode melts, so that a point in time comes at which the molten tip of the electrode into the melt generated on the workpiece by the arc immersed and thus creates a short circuit.

When this short circuit occurs, the change in the voltage applied to switch 16 is so great that the switch is closed, causing the by the smoothing circuit S flowing current is increased by the current which is generated by the discharge of the storage element 14

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will. This increased short-circuit current releases energy so quickly that the electrode "freezes" to the workpiece is prevented. The electrode is consequently separated from the workpiece by the molten electrode tip is detached from the still solid part of the electrode. This interrupts the short-circuit current. The values of the Switching elements of the dlättungsschaltkreises are chosen so that a high overshoot when shorting the Arc is prevented.

Resetting the gap between the electrode and the workpiece results in a voltage change on the switch result, which thereby opens and effectively separates the storage element from the electrode. The storage element is then flowed through by the controller 12 Current is recharged while the arc current continues to flow through the smoothing circuit S. To this In this way, periods of an arc automatically alternate with periods of short-circuit contact and thus cause a welding company, which is also known as "short-circuit welding".

The energy storage circuit shown in flg. 2 has adjustable resistors R1 and R2 in the voltage divider circuit. The center of tension

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• tellers has a connection point between a storage capacitor Cl and a diode rectifier Dl connected. The flattening circuit S is only shown schematically.

In a typical circuit, the switching elements have the following values: R1 = 0.5 Ohm, R2 = 10 Ohm, capacitor C1 = 80 OOO ^ cF and rectifier Dl 100 A, 100 PIV.

In practice, the resistor R2 can have any value in the range from less than 1 ohm to infinity, the resistor Rl can have a value in the range from 0.1 ohm to 20 ohm and the capacitor Cl can have a value in the range from 1000 // F to 160,000 u & accept. The value of each of these switching elements is chosen so that the stored charge is sufficient to generate a discharge current, which, when added to the arc current, is so strong that the short circuit is quickly separated or that a sufficiently high voltage is generated * which in turn results in a relatively high frequency of the short-circuiter, for example about 100 Hz to 150 Hz. The short circuit does not break so quickly, however, that excessive splashing or spraying occurs. This creates an arc that is "cool" enough for welding thin metal sheets.

In the circuit shown in Fig. 3 is the

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Voltage divider replaced by a capacitor C2, which is connected in parallel with the capacitor Cl via a resistor R3 or is connected to the energy storage circuit. In this type of circuit, the capacitor C2 is used for Correction because the transformer T has a large time constant. The resistor R3 is used to control the den Capacitor Cl charging current required.

The circuit shown in Fig. 4 is essentially a modification of the circuit shown in Fig. 2 and has a capacitor C3, which is adjustable can be and is connected to the resistor Rl in the shunt. The capacitor C3 causes a change in speed, with which the capacitor Cl is charged. Accordingly, when the capacitance of the capacitor C3 is much larger than the capacitance of the capacitor C1, the rate at which the capacitor C1 is charged depends greatly on the speed with which the capacitor C3 discharges itself through the resistor Rl. Practically can the capacitor C3 have a fixed capacitance value which is 0.25 times to 20 times as large as the capacitance value of the capacitor Cl.

In the circuit shown in Fig. 5 is the

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/ Il

Capacitor C3 a resistor R 4 connected in parallel, so that the rate of charge of the capacitor Cl can also be controlled. Rectifiers D2 and D3 are also available and are used to decouple the Combination of the capacitor C3 with the resistor R4. One of these two rectifiers D2 or D3 can also can be omitted.

In the circuit shown in Fig. 6, the rectifier Dl is replaced by a thyristor THl, whose gate or control electrode is connected to an ignition circuit F. This ignition circuit F is conventional Way carried out and electrically connected to the electrode 4 in such a way that it is each dependent on of the respective operating mode is operated at any specific point in time. This ignition circuit can also be modified by the use of a delay element in such a way that the thyristor THl controlling Signal for a certain period of time after the welding operation has changed from the arc to the short-circuit condition or vice versa is delayed.

In Fig. 7 a further circuit is shown, by means of which the ratio of the increase in the arc current is changed by the short-circuit current. With reference

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the circuit shown in FIG. 2 is modified in such a way that the resistor R2 is replaced by series connected resistors R5, R6 and R7. The connection points between these resistors are as shown in FIG. 7, each with additional series connections between a rectifier D4 and a capacitor C4 and a rectifier D5 and a Capacitor C5 connected. The values of the storage capacitors Ci, C4 and C5 are each chosen such that their The voltages from capacitor C1 to capacitor C5 decrease each time they are fully charged. If accordingly the arc is initially short-circuited and thus the short-circuit current flows through the rectifier Dl the capacitor Cl is discharged until a value is reached at which the rectifier D4 becomes conductive and so that the capacitor C4 begins to discharge. The same process causes capacitor C5 to also is discharged. Because of the discharge times inherent in these capacitors, it is possible to use the waveform of the short-circuit discharge current3 to give a certain shape. Obviously, other combinations of resistances, Rectifiers and capacitors can be added as needed. The total capacitance of capacitors Cl, C4 and C5 is equal to the capacitance of the capacitor Cl as shown in Fig. 2.

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In the block circuit shown in FIG. 8, the controller 12 conducts the charging current for the storage element indirectly via the smoothing circuit S. Otherwise this circuit acts in the manner already described with reference to FIG.

The circuit shown in Fig. 9 shows the details of an inexpensive smoothing circuit according to the invention. This circuit has two induction coils Ll and L2 connected in series, their center point is connected to a smoothing capacitor C6. A current limiting resistor R8 is connected to the charging circuit of the Capacitor Cl connected.

This smoothing circuit inductor Ll and the capacitor ¹ 06 perform their normal functions, respectively. The induction coil L2, which is present in addition to the smoothing, also has a stabilizing effect on the arc in that it generates an increased reignition voltage. The illustration in FIGS. 10 and 11 relates to this, in which the applied field H is plotted over the flux B generated in the iron core of the induction coil. The curve in Figure represents a typical W / H curve one in a conventional manner

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induction coil used for smoothing, while in Jj'ig. the B / H curve of a special embodiment of an induction coil is shown, which is of particular advantage for the circuit according to the invention. The fundamental difference between these two curves is that the value of the induction increases in an initial region 18 of the curve shown in FIG. 11 is larger than in an adjoining area 20. The induction increase in area 18 is normally twice as large as in area 20.

In Fig. 12 is one embodiment of an induction coil which generates the B / H curve shown in FIG. This induction coil has an iron core 22 provided with a stepped air gap 24. When a current flows through an operating coil 26, it is concentrated the resulting flux at low field strength values of the applied field in the space between each other the closest stepped pole faces, whereby the part 18 of the B / H curve results. At higher field strength values H, however, these poles are saturated, so that the river then builds up over the stepped pole faces more distant from one another, whereby the normal part 20 of the B / H curve results. The relatively hot one

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transition between parts 18 and 20 of FIG. 11 The curve shown can be achieved by a tapering shape of the air gap as shown in FIG. 13 be smoothed, so that a curve results, which in the initial area still compared with the conventional B / H curve, has a steep slope.

The waveforms shown in FIG. 14 are drawn from oscillograms which are obtained in a conventional plunge-transition welding process in three-phase operation. In FIG. I ¹ Ja the current is shown over time and in FIG. 14b the voltage is shown over time. A single-phase plunge-transition welding operation exhibits essentially the same waveforms, but generally with a lower plunge frequency.

FIG. 15 shows the same waveforms with reference to FIG. 14, but for the immersion junction welding circuit according to the invention with a single-phase power supply. These curves show several significant differences, the rapid changes in the welding current when the arc is short- circuited in particular, see Fig. 15a. Another important feature is the amplitudes of the welding voltage immediately after a short circuit has been opened.

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Even when using conventional induction coils or choke coils, these are reignition voltages, respectively high and always result in stable arcs. When using choke coils as shown in the Figures 12 and 13, respectively, these reignition voltages are even higher.

The same effect that is achieved with the special induction coil L2 can also be achieved with the Use of two or more separate induction coils connected in series. In this case it often is favorable to those induction coils which produce the part 18 of the curve shown in FIG. 11, both with the output of the smoothing circuit S as well as the output of the energy storage circuit in series switch.

FIG. 16 shows a further modification of the circuit shown in FIG. The induction coil is L2 replaced by an induction coil L3 provided with a tap and the arc or short-circuit currents flow about this tap. In this circuit, the short-circuit current flows through a part on its way to the tap the winding of the induction coil L3 and generates

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Ίο

Ampere-turns corresponding to those ampere-turns generated by the arc current flowing through the smoothing circuit are generated, are oppositely directed. These opposing ampere-turns cause a temporary increase in the current supplied by the smoothing circuit and thus an increase in the short-circuit current. The number of turns ratio between the two named parts of the induction coil L3 is in a range between a low value (less than 1: 1) and a very large value (greater than 100: 1) and is depending on the costs or other factors.

The one in Pig. 17 has a household voltage source E, which supplies an alternating current and is connected to a power transformer T, which is in turn connected to a full-wave rectifier bridge Z. The positive terminal of the rectifier bridge Z is over a choke coil L3 with a positive output terminal 30 tied together. The negative terminal of the rectifier bridge Z is connected to a negative output terminal 32. With the Bridge Z and the output terminals are shunted to a rectifier D6, the latter with a Accumulator 34 is connected in series. The rectifier D6 a shunt resistor R9 is connected in parallel.

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The rectified alternating current supply circuit, which is provided with the choke coil L3, has a slightly decreasing voltage / current characteristic, whereby the short-circuit current is limited, although energy supply devices are also used whose characteristics are different. Before the welding arc is affected accordingly, the tensioned on the High voltage present at the output terminals feeds the rectifier D6 in the opposite direction, thus preventing the discharge of the accumulator 34. In addition, the resistor R9 enables the accumulator to be charged. As the With the welding current, the voltage at the output terminals drops until, when the welding electrode touches the workpiece Has short-circuit contact, this voltage has reached such a low value that the rectifier D6 becomes conductive and the welding current is supplied by the accumulator.

In the circuit shown in FIG. 17, the induction coil L3 acts, among other things, as a smoothing circuit. If necessary, this coil can be shunted with a capacitor, so that a (TT / 2) circuit is formed results. In addition, the charging resistor R9 can radio with the input of the induction coil L3 or with another be connected as needed.

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The accumulator works basically like a special capacitor, the differences between it however, and a true capacitor can be substantial in some applications.

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Claims (1)

Claims; 1.! Circuit for electrical welding, in which periods of short-circuit contact between a A consumable electrode and a workpiece with periods of an arc between this electrode and this Alternate workpieces, characterized by a source (Z), which is one of a single-phase alternating current source (E) rectified supplied current and connected to a combined smoothing memory circuit (2) is, to which the latter in turn the welding electrode (4) and the workpiece (8) are connected, this Smoothing memory circuit has a switch (16) which controls the at least one memory element (14) current flowing to the output terminal of a smoothing circuit (S) as a function of the instantaneous Characteristics or parameters of the welding process controls. 2. Circuit according to claim 1, characterized in that the switch (16) is a rectifier (Dl). - 21 - 009829/0985 J5. Circuit according to Claim 1, characterized in that that the switch (16) is a thyristor (THl) whose control electrode is connected to the welding electrode (4) is. 4. Circuit according to one of Claims 1 to J3 * characterized in that the storage element (14) is a capacitor (Cl) and that this capacitor and the switch (16) with respect to each other in series or with respect to the electrode (4) and the workpiece (8) are connected in parallel. 5. A circuit according to claim 4, characterized in that between the source (Z) and a connection point between the rectifier Dl and the capacitor (Cl-) there is a connection which see an ohm Has resistance (Rl, R2). 6. A circuit according to claim 5, characterized in that the ohmic resistance (Rl, R2) is adjustable. 7. Circuit according to one of claims 1 to 6, characterized in that the smoothing circuit (S) a circuit with at least one induction coil (Ll) - 22 - in the series connection between the source (Z) and the electrode (4) and a capacitor (C6) in the shunt arm having. 8. Circuit according to claim 7 * characterized in that that the smoothing circuit (S) has a T-circuit with two induction coils (Ll, L2) in series between the source (Z) and the welding electrode (4) and with a capacitor (C6) in the shunt arm. 9. A circuit according to claim 8, characterized in that each of the two induction coils (Ll, L2) one Choke coil with iron core (22), the air gaps (24) are each designed such that they are different Have impedances and saturation values. 10. Circuit according to claim 9 * characterized in that that at least one of the air gaps (24) is parallel to its associated pole faces along its extension has a non-uniform cross-section. 11. A circuit according to claim 10, characterized in that at least one of the pole faces is stepped is. - 23 009829/0985 12. A circuit according to claim 9, characterized in that the pole faces diverge with respect to one another along at least one axis. Ij5. Circuit according to one of Claims 7 to 12, characterized in that at least one (L ^) of the Induction coils tapped or otherwise adjustable. 14. Circuit according to one of claims 1 to 1J5, characterized in that the memory element (14) is formed by an accumulator (34). 15. Circuit according to one of claims 1 to 14, characterized by more than one combination (Dl, Cl or D4, C4 or D5, C5) one with a capacitor series-connected rectifier, these combinations each only with the capacitor of the each subsequent combination are connected in the shunt. 16. Circuit according to one of claims 1 to 15 * characterized in that the smoothing circuit (S) is formed by a T circuit which has two choke coils (Ll, L2) in the series connection as well as one - 24 009829/0985 Capacitor (C6) in the shunt or shunt branch has that further a charging resistor (r8) between the Input terminal of the T-circuit and a connection point connected between a storage capacitor (Cl) connected in series with a rectifier (Dl) is which latter is connected in shunt with the welding electrode (4) and the workpiece (8), the values of these circuit elements are each chosen such that the frequency of the short-circuit contact is considerably greater than the frequency of the single-phase AC power source (E), so that the Rectifier becomes conductive at times determined by the operation of the welding process. 17. A method for electrical welding, in which periods of short-circuit contact between a consumable electrode and a workpiece Periods of an arc between this electrode ( and alternate this workpiece, characterized in that a during the short-circuit periods the current flowing directly from the single-phase power source to the welding electrode is increased by one current, which from a switch depending on the respective operating state of the welding process - 25 - 00D829 / 0985 automatically controlled memory circuit supplied will. 18. According to the method of claim I7 welded Sheet metal workpiece. - 26 009829/0985