Abstract
A method for synchronizing welding currents of at least two welding current sources prior to performing a simultaneous welding process on at least one workpiece, in particular a welding process with non-consumable electrodes, wherein the method includes the following steps: a first welding current source outputting a reference signal, wherein the reference signal contains synchronization information; a second welding current source measuring or receiving the reference signal and evaluating the synchronization information contained in the reference signal; synchronizing a second welding current of the second welding current source with a first welding current of the first welding current source on the basis of the synchronization information. The invention furthermore relates to a welding current source and to a system having at least two welding current sources.
Claims
1. A method for synchronizing welding currents (I.sub.1, I.sub.2) of at least two welding current sources (1, 2) prior to performing a simultaneous welding process on at least one workpiece (10, 10′), in particular a welding process with non-consumable electrodes (9), wherein the method has the following steps: outputting a reference signal (11) by means of a first welding current source (1), wherein the reference signal (11) contains synchronization information (13); measuring or receiving the reference signal (11) and evaluating the synchronization information (13) contained in the reference signal (11) by means of a second welding current source (2); synchronizing a second welding current (I.sub.2) of the second welding current source (2) with a first welding current (I.sub.1) of the first welding current source (1) on the basis of the synchronization information (13).
2. The method according to claim 1, wherein after the synchronization, the first (I.sub.1) and the second welding current (I.sub.2) are generated, and the welding process is performed.
3. The method according to claim 1, wherein the synchronization information (13) is contained in a time curve of the reference signal (11), in particular in a frequency, in a changing polarity, and/or in a phase angle (φ) of the reference signal (11).
4. The method according to claim 1, wherein the welding current sources (1, 2) are connected to a common alternating current network (3), in particular to a three-phase alternating current network (3), and that for synchronizing the welding current sources (1, 2) a phase conductor (12) of the alternating current network (3) is selected for the first welding current source (1), the reference signal (11) being generated on the basis of a voltage curve (U.sub.U,V,W) of the selected phase conductor (12), so that the synchronization information (13) provides for an identification of the selected phase conductor (12) by means of the second welding current source (2).
5. The method according to claim 4, wherein the first welding current (I.sub.1) and the second welding current (I.sub.2) are synchronized with the voltage curve (U.sub.U,V,W) of the selected phase conductor (12), preferably synchronized with a periodic synchronization point (15) in the voltage curve (U.sub.U,V,W) of the selected phase conductor (12), for example a periodic zero crossing (14).
6. The method according to claim 4, wherein the reference signal (11) has a time curve, in particular a frequency, a polarity, and a phase position, on the basis of which the selected phase conductor (12) can be uniquely identified.
7. The method according to claim 4, wherein the synchronization information (13) contained in the reference signal (11) provides for the identification of a periodic synchronization point (15), for example of a periodic zero crossing (14), in the voltage curve of the selected phase conductor (12).
8. The method according to claim 4, wherein the synchronization information (13) is derived from the voltage curve (U.sub.U,V,W) of the selected phase conductor (12), in particular from the frequency, the polarity, and/or the phase angle of the selected phase conductor (12).
9. The method according to claim 4, wherein a curve of the reference signal (11) is synchronized with the voltage curve (U.sub.U,V,W) of the selected phase conductor (12) in frequency, polarity, and/or phase angle.
10. The method according to claim 1, wherein the reference signal (11) is conducted directly or indirectly from the first welding current source (1) via a first welding torch (8), which is connected to the first welding current source (1), to a second welding torch (8), which is connected to the second welding current source (2), and further to the second welding current source (2).
11. The method according to claim 1, wherein the current intensity and the voltage level of the reference signal (11) are selected so that a melting of the workpiece (10, 10′), of a welding wire, or of electrodes (9) of a welding torch (8) is prevented.
12. The method according to claim 1, wherein the reference signal (11) is a voltage signal, preferably an alternating signal, in particular a square-wave signal.
13. A welding current source (1, 2) for performing a simultaneous welding process on at least one workpiece (10, 10′), in particular a welding process with non-consumable electrodes (9), wherein the welding current source (1, 2) has a synchronization unit (16), which, in a first mode for the synchronization with a further similar welding current source (1, 2), is configured to generate a reference signal (11) with synchronization information (13) prior to performing the welding process and to output the reference signal (11) to the further welding current source (2), and/or, in a second mode, to measure or to receive a reference signal (11) output by the further welding current source (1, 2), and to evaluate the synchronization information (13) contained in the reference signal (11), and, on the basis thereof, to synchronize a welding current (I.sub.1, I.sub.2) with a welding current (I.sub.1, I.sub.2) of the further welding current source (1, 2) prior to performing the welding process.
14. The welding current source (1, 2) according to claim 13, wherein in the first mode, the synchronization unit (16) is configured to generate the reference signal (11) on the basis of a voltage curve (U.sub.U,V,W) of a selected phase conductor (12) of an alternating current network (3).
15. A system consisting of at least two welding current sources (1, 2), wherein the welding current sources (1, 2) are each formed according to claim 13, and one of the two welding current sources (1) is operated in the first mode, and the other welding current source (2) is operated in the second mode.
Description
[0030] The invention will be described in more detail below on the basis of figures, to which it is not to be limited, however, in which:
[0031] FIG. 1 shows a first and a second welding current source;
[0032] FIG. 2A-B show, schematically, a simultaneous welding process with synchronized welding currents;
[0033] FIG. 3A-B show, schematically, a simultaneous welding process with welding currents, which are not synchronized; and
[0034] FIG. 4A-C show, schematically, the synchronization of welding currents with the phase conductor U.sub.u of a three-phase alternating current network, wherein the voltages of the phase conductors are illustrated against the neutral conductor; and
[0035] FIG. 5A and FIG. 5B show a process sequence for the synchronization of two welding current sources.
[0036] FIG. 1 shows a first welding current source 1 and a second welding current source 2, which are each connected to a symbolically illustrated common three-phase alternating current network 3 comprising three phase conductors 4. The two shown welding current sources 1, 2 are TIG-AC welding current sources for performing tungsten-inert gas welding processes with alternating currents (AC). It goes without saying that the current sources 1, 2 can also be used, for example, for pulse welding processes, which can be performed with direct current as well as with alternating current. The welding current sources 1, 2 are each electrically connected to a ground terminal 5 and thus to a workpiece 10 via a connecting line 6. A welding torch 8 comprising an electrode 9 is in each case furthermore connected to each welding current source 1, 2 via a supply line 7. The connecting lines 6 can be connected directly to one another or the workpieces 10 can be connected to one another via a common support (not illustrated).
[0037] The welding currents I.sub.1, I.sub.2 (see FIG. 2A, FIG. 3A), which are generated by welding current sources, are typically synchronized with the temporal voltage curve U.sub.U,V,W of a phase conductor 4 of the alternating current network 3, in particular with certain zero crossings 14 (which serve as periodic synchronization points 15) of a phase conductor 4. However, problems can arise when, as described above, several welding current sources 1, 2 are used during a welding process, and the generated welding currents I.sub.1, I.sub.2 are not synchronized. Then, it can happen that the arc LB is not directed as desired towards a workpiece 10, which is to be welded, during a welding process, but jumps from the workpiece 10 onto an electrode 9 of another welding torch 8 due to the resulting voltage difference (see FIG. 3A). The jump-over is in particular the case when—as illustrated—a gap is present between the workpieces 10, 10′. This results in a series connection of the welding current sources 1, 2 with a common electric circuit. This can interfere with the welding process or can even make it impossible, respectively. In the following, zero crossings 14 with a positive flank will be identified with a +, and zero crossings with a negative flank will be identified with a −.
[0038] A simultaneous welding process on two workpieces 10, 10′ is illustrated schematically in FIG. 2A. The two workpieces 10, 10′, for example the front sides of a pipe (not illustrated), are to be connected to one another with the help of the simultaneous welding process. Two welding current sources 1, 2 are used for this purpose, whereby the workpieces 10, 10′ are welded simultaneously on two opposite sides of the workpieces 10, 10′ by means of the welding torches 8. For this purpose, the workpieces 10, 10′ are connected to the negative poles of the welding current sources 1, 2 via the connecting lines 6. The positive poles of the welding current sources 1, 2 are connected accordingly by means of the welding torches 8. It goes without saying that the poles can also be switched or the polarity of the welding current changes periodically during AC welding processes, respectively—according to the polarity identifiers in brackets (FIG. 2A and FIG. 3A). As already mentioned, the generated welding currents I.sub.1, I.sub.2 are synchronized with a phase conductor 4 of the alternating current network 3 in the case of AC welding current sources. When the welding currents I.sub.1, I.sub.2 are synchronized with the same phase conductor 4 or the same periodic synchronization point 15, respectively, in the voltage curve U.sub.U,V,W of the phase conductor 4, the welding currents I.sub.1, I.sub.2 are also synchronous with one another. This case is illustrated schematically in FIG. 2B. FIG. 2B shows synchronized welding currents I.sub.1, I.sub.2 in amperes over time t in milliseconds. The welding currents I.sub.1, I.sub.2 are essentially synchronous in the frequency f and in the schematically illustrated phase angles φ.sub.1, φ.sub.2. The amplitude of the welding currents I.sub.1, I.sub.2 is adapted accordingly to the use, and it goes without saying that it can also be different, as illustrated. Only for the sake of better visualization, I.sub.2 is illustrated with dashed lines. It can be seen in FIG. 2A that the arcs LB are directed towards the workpieces 10, 10′ in order to attain a heat input there. However, the welding currents I.sub.1, I.sub.2 flow in separate electric circuits—as illustrated symbolically—via the respective connecting lines 6, 7 of the respective welding current source 1, 2.
[0039] FIG. 3A shows a welding process, during which the welding currents I.sub.1, I.sub.2 are not synchronized (for example due to a synchronization with different zero crossings 14 in the voltage curve U.sub.U,V,W of a phase conductor 4). It can be seen that the arcs LB are not directed towards the workpieces 10, 10′ in this case, but are at least intermittently directed towards the electrode 9 of the respective other welding torch 8. The heat input into the workpieces 10, 10′ is significantly reduced thereby, and a correct welding seam formation is prevented. The non-synchronized welding currents I.sub.1, I.sub.2 are illustrated schematically in FIG. 3B in amperes over time t in milliseconds. It can be seen that the welding currents I.sub.1, I.sub.2 run exactly out of phase in terms of time, thus φ.sub.1−φ.sub.2=180° electrically offset from one another. The polarities of the welding currents I.sub.1, I.sub.2 thus do not coincide. Only for the sake of better visualization, I.sub.2 is illustrated with dashed lines. The welding currents I.sub.1, I.sub.2 are synchronous in the frequency f, but not in the phase angles φ.sub.1, φ.sub.2 or in the polarity, respectively. The amplitudes of the welding currents I.sub.1, I.sub.2 are illustrated essentially identically here because the arcs LB burn relative to one another and a series connection of the welding current sources 1,2 results. Due to the series connection, one of the welding current sources 1, 2 takes over the impression of a welding current I.sub.1 or I.sub.2 into the common electric circuit. Symbolically, the welding current I.sub.1 is illustrated in the common electric circuit.
[0040] To synchronize the polarity of the welding currents I.sub.1, I.sub.2 of the welding current sources 1, 2 and to thus prevent a jump-over or a diversion, respectively, of the welding currents I.sub.1, I.sub.2 from the workpiece 10, 10′ onto the electrodes 9, it is provided to transmit a reference signal 11, for example from the first welding current source 1 to the second welding current source 2 prior to the welding process (thus prior to the output of the welding currents I.sub.1, I.sub.2). The synchronization, in particular the generation and evaluation of the reference signal 11, can take place with the help of synchronization units 16 (see FIG. 1), which are arranged in the welding current sources 1, 2. The welding currents I.sub.1, I.sub.2 can be synchronized with one another on the basis of the reference signal 11. In the case of the shown embodiment, the reference signal 11 specifies, with which phase conductor 4 and with which periodic synchronization points 15, which are contained in the voltage curve U.sub.U,V,W of the phase conductor 4, the polarity, the frequency, and the phase position of the welding currents I.sub.1, I.sub.2 are to be synchronized. The transmission of the reference signal 11 between the welding current sources 1, 2 can take place via the welding torches 8, for example prior to the welding process. For this purpose, the electrodes 9 of the welding torches 8 can be brought into contact, until the reference signal 11 has been transmitted, and the synchronization is concluded. The contact of the electrodes 9 is illustrated in FIG. 1. The reference signal 11 is therefore transmitted prior to the welding process.
[0041] The time sequence for synchronizing the welding currents I.sub.1, I.sub.2 with regard to the phase conductors is illustrated in FIG. 4A-C, whereby FIG. 4A illustrates the reference signal 11 of the master, FIG. 4B illustrates a non-synchronized state, and FIG. 4C illustrates a synchronized state of the two current sources 1, 2. The time sequence is illustrated as measurement between the phase conductors 4 and the neutral conductor. It goes without saying that the measurement can also take place between the phase conductors. It is the goal of the shown embodiment to inform the second welding current source 2, which acts as “slave”, with the help of the reference signal 11 prior to the welding process, with which phase conductor 4, in particular with which zero crossings 14 (more generally: periodic synchronization points 15) of the voltage curve U.sub.U,V,W of the selected phase conductor, the welding currents I.sub.1, I.sub.2 of the two welding current sources 1, 2 are to be synchronized in the future. Additional information, such as duty cycle and amplitude of the welding currents I.sub.1, I.sub.2 can also be reported to the second welding current source 2. The reference signal 11 to be transmitted is synchronized with the phase conductor 4, which is selected by means of the first welding current source 1, in frequency and period, whereby the phase conductor 4 can be identified on the basis of the reference signal. In the following, the selected phase conductor 4 will be identified with reference numeral 12. The welding currents I.sub.1, I.sub.2 can be kept synchronous during the subsequent welding/the welding process by means of the notification from the selected phase conductor 12 and the synchronization points 15, even if the welding current sources 1, 2 can no longer communicate with one another after conclusion of the transmission of the reference signal 11. The alternating current network 3 subsequently ensures the synchronicity in that the synchronization units 16 of the welding current sources 1, 2 were set to the synchronization points 15 of the alternating current network 3, which were reported by means of reference signal 11. The selected phase conductor 12, with which synchronization took place, is therefore stored in the welding current sources 1, 2. The synchronization information 13 is thus stored in the welding current sources 1, 2. The synchronicity of the welding currents I.sub.1, I.sub.2 is thus ensured for all welding processes, as long as the welding current sources 1, 2 remain connected to the alternating current network 3 and/or the phase sequence is not changed. The synchronization is to ensure that the welding currents I.sub.1, I.sub.2 are synchronous in frequency, phase angles, and polarity. The zero crossings 14 represent periodic synchronization points 15 in the voltage curve U.sub.U,V,W of the selected phase conductor 12, by means of which the welding currents I.sub.1, I.sub.2 can be synchronized. Due to its role in the process, the first welding current source 1 can also be referred to as “master” or “lead”. The selection as to which phase conductor 4 and which zero crossings 14 are to be used for the synchronization is made by the first welding current source 1. The voltage curve U.sub.U,V,W of the selected phase conductor 12 contains zero crossings 14+ with positive flanks as well as zero crossings 14− with negative flanks. In the shown exemplary embodiment, the zero crossings 14+ of the voltage curve U.sub.U with positive flanks are used as periodic synchronization points 15.
[0042] The selection of the phase conductor 12 can take place randomly, namely by means of the sequence of the connected phase conductors 4 during to the connection to the alternating current network 3. The second welding current source 2 is synchronized with the first welding current source 1 on the basis of the reference signal 11 in that the polarity and the phase position of the welding current 12, which is to be output but has not been generated yet, of the second welding current source 2 is switched through gradually to the zero crossings 14 of the phase conductors 4, until the welding current 12, which is to be generated, or the voltage curve thereof, respectively, is synchronous with the reference signal 11. At the end of the synchronization, both welding current sources 1, 2 synchronize their welding currents I.sub.1, I.sub.2, which are to be output, with the same phase conductor 4 and the same zero crossings 14+ of the voltage curve U.sub.U. The frequency and phase position of the welding currents I.sub.1, I.sub.2, which are to be generated, is taken over by the selected phase conductor 12. The welding currents I.sub.1, I.sub.2 are synchronous in frequency, phase position, and polarity due to the synchronization to the same periodic synchronization points 15, in particular zero crossings 14+, of the selected phase conductor 12. The welding currents I.sub.1, I.sub.2, which are to be output, do not have to actually be generated and output for synchronization purposes.
[0043] A reference signal 11 with synchronization information 13 is initially generated and output by means of the first welding current source 1 (FIG. 4A). The synchronization information 13 thereby contains, for example, the information as to which phase conductor 4 (the selected phase conductor 12) and which zero crossings 14+ (positive flank) or 14− (negative flank), respectively, are used for the synchronization. In the shown exemplary embodiment, the zero crossings 14+ of the voltage curve Uu with positive flanks are used as periodic synchronization points 15. The synchronization information 13 can further contain the amplitude of the welding current 12 and the form of the welding current 12. The reference signal 11 is thereby preferably not the welding current, but has a significantly lower level—for example 5 A. The synchronization information 13 can in particular be contained in the time curve of the reference signal 11, for example in the flanks or zero crossings 14′+ or 14′− of the reference signal. The reference signal 11 is adapted to the voltage curve U.sub.U,V,W of the selected phase conductor 12 with respect to the period duration or frequency, respectively, and is synchronized therewith. In the present case, the reference signal 11 is synchronous with the selected phase conductor 12 in the period T, as illustrated. A possible duty cycle of the reference signal 11, as illustrated in the figures, depends on user settings at the welding current sources 1, 2. The duty cycle can be different and has no impact on the synchronization. The duty cycle, thus the ratio of the duration of the positive and negative phase of the two welding currents 1, 2, is preferably set to be identical. The duty cycle of the welding currents I.sub.1, I.sub.2 impacts the heat input into the welding seam or on the cleaning zone of the welding seam, respectively, during the welding process. This is set accordingly by the user, depending on the use. This information is preferably contained in the reference signal 11, so that both welding current sources 1, 2 are set identically. In the shown case, the reference signal 11 is a square-wave signal, which coincides with the voltage curve of the selected phase conductor 12 with respect to the period duration and frequency, and which is thus synchronous. The zero crossings 14′+ of the reference signal 11 coincide with the zero crossings 14+ of the voltage curve of the selected phase conductor 12 in terms of time. The zero crossings 14′+ of the reference signal 11 mark periodic synchronization points 15 in the voltage curve of the selected phase conductor 12, with which the welding currents I.sub.1, I.sub.2 are to be synchronized. The phase positions of the voltage curve Uu of the selected phase conductor 12 and of the reference signal 11 thus coincide. With the reference signal 11, the selected phase conductor 12 can be uniquely identified by means of the second welding current source 2, can thus be differentiated from the other phase conductors 4. The reference signal 11 can be transmitted to the second welding current source 2 via the welding torches 8. The second welding current source 2 can evaluate the reference signal 11 and can determine, which phase conductor 4 and which zero crossings (in the present case the zero crossings 14+) was selected by the first welding current source 1 for synchronizing the welding currents I.sub.1, I.sub.2. The determination which phase conductor 4 or which zero crossings 14, respectively, were selected, can take place by comparing the reference signal 11 to the voltage curves U.sub.U,V,W of the phase conductors 4. The comparison can take place consecutively, thus phase conductor 4 by phase conductor 4. The reference signal 11 is thereby in each case compared with a voltage curve U.sub.U,V,W of a phase conductor 4. The comparison takes place at least once, for example five times. If the comparison is negative (as illustrated, e.g., in FIG. 4B), the next phase conductor 4 is used or a switch-over is made from the second welding current source 2 to the next phase conductor 4, respectively, and is compared to the reference signal 11. An error synchronization of the second welding current source 2 is illustrated on the bottom in FIG. 4B, in the case of which the second welding current source 2 is synchronized to the phase conductor 4 with the voltage U.sub.W. The phase conductor 4 with the voltage U.sub.W, however, is not synchronous with the reference signal 11. As soon as the correct phase conductor 4 was identified, a control can be performed several times, for example five times in a row, whether it is the correct phase conductor 4 and the correct zero crossings 14+. Error synchronizations are avoided thereby. Both welding currents I.sub.1, I.sub.2 are subsequently synchronized with the same phase conductor 4, in particular with the same periodic synchronization points 15 or zero crossings 14, respectively, but are not output yet. When a simultaneous welding process is started, the synchronized welding currents I.sub.1, I.sub.2 can be output. This is illustrated in FIG. 4C. In summary, the first welding current source 1 thus selected a phase conductor 12, and a reference signal 11 was generated, which is adapted to the selected phase conductor 12 and certain periodic synchronization points 15 (the zero crossings 14+) in the voltage curve U.sub.U,V,W of the selected phase conductor 12. The reference signal 11 was transmitted to the second welding current source 2, and the selected phase conductor 12 and the certain periodic synchronization points 15 in the voltage curve U.sub.U,V,W of the selected phase conductor 12 was identified by means of the second welding current source 2 on the basis of the reference signal 11. The welding currents of the first 1 and of the second welding current source 2 were subsequently synchronized with the selected phase conductor 12 and the periodic synchronization points 15 contained in the voltage curve U.sub.U,V,W. The welding currents I.sub.1, I.sub.2 can be output after the synchronization.
[0044] Two similar welding current sources 1, 2 can be used to perform the described method. They can in each case be capable of being switched over between a first mode and a second mode. In a first mode, the reference signal 11 can be generated and can be transmitted to a welding current source in the second mode. In the alternative, it can also be provided that the welding current sources cannot be switched over. A welding current source 1, which can be operated in the first mode, and a welding current source, which can be operated in the second mode, then has to be used to perform the method.
[0045] FIG. 5A shows the process sequence for synchronizing welding currents I.sub.1, I.sub.2, from the perspective of first welding current source 1 in the first mode. The method is started in step 101. In step 102, it is checked whether the welding torches 8 of the welding current sources 1, 2 are in electrical contact and whether an electrical current flows. In step 103, a reference signal 11 is output, which is essentially synchronous with the voltage curve of the selected phase conductor 12 in the period. A selected phase conductor 12 and periodic synchronization points 15 can be identified by the second welding current source 2 by means of the reference signal 11. The selection of the phase conductor 4 can take place randomly, for example by connecting the welding current source 2 to the alternating current network 3, or systematically. The reference signal 11 can be output, for example, for a certain time period. The method is ended on the part of the first welding current source 1 in step 104.
[0046] Parallel thereto, FIG. 5B shows the process sequence of the second welding current source 2 in the second mode. The method is started in step 201. It is checked in step 202, whether the welding torches 8 are in electrical contact and whether an electrical current flows. In step 203, the reference signal 11 is measured, evaluated, and compared with the voltage curve of a phase conductor 4. If the reference signal 11 is not synchronous with the compared phase conductor 4 (illustrated by means of the X), a switch-over to the next phase conductor 4 is performed in step 204, and step 203 is performed again. If the selected phase conductor 12 was identified (illustrated by means of the check mark), the method is also ended on the part of the second welding current source 2, optionally after repeated verification (step 205).
