Multiple Welding Method

Abstract

In order to provide a multiple welding method using these melting electrodes 3A, 3B that enables a stable welding process with at least two melting electrodes 3A, 3B and a smaller heat input into the base material 6 compared to a multiple impulse welding method, it is proposed according to the present invention that a welding process having a short-circuit welding phase SPA1, SPB1 and a thermal welding phase SPA2, SPB2 that exhibits a higher heat input into the base material 6 compared to the short-circuit welding phase SPA1, SPB1 is respectively carried out with the at least two electrodes 3A, 3B, the short-circuit welding phases SPA1, SPB1 and the thermal welding phases SPA2, SPB2 periodically alternating and being time-synchronized based on at least one first synchronization event SEA1, SEB1 determined for each short-circuit welding phase SPA1, SPB1 and short-circuit welding phase SPA1, SPB1 of these welding processes of the at least two electrodes 3A, 3B.

Description

[Technical field]

[0001] The invention relates to a method for performing a multiple welding process on a base material by means of at least two melting electrodes, whereby with each electrode a welding step is performed after ignition of an arc between the electrode and the base material, whereby these welding steps of the at least two electrodes are time-synchronized. Furthermore, the invention relates to an installation for performing a multiple welding process. [Background technology]

[0002] Gas metal arc welding methods (MSG) have been known for many years in the prior art. For example, the metal inert gas (MIG) method or the metal active gas (MAG) method belong to gas metal arc (MSG) welding. In the case of gas metal arc (MSG) welding, a molten electrode consisting of a metallic electrode material is surrounded by a so-called shielding gas. Generally, gas metal arc welding methods are used to deposit a weld seam on a base material (build-up welding) or to join two base materials (joint welding). In both cases, an arc is ignited between the electrode and the base material by means of a welding voltage or a welding current resulting from the welding voltage, which melts the electrode and the area of ​​the base material surrounding the electrode. A strong joint is thereby achieved. Generally, the same or similar material as that for the base material is used as the electrode material. The electrode is fed to the weld point with a defined feed speed. In this case, the feed speed can be preset, for example during manual welding by hand or by settings on the welding device, or can depend on another parameter, for example the welding speed when the electrode is moved relative to the base material, or it can depend on the current, etc.

[0003] Compound welding methods are also known in which welding is performed simultaneously with at least two electrodes in order to improve the welding performance. For example, so-called tandem impulse welding methods, in which two impulse welding processes are performed simultaneously, belong to the category of compound welding methods. In this case, at least two electrodes as welding wires are melted in a common weld pool or in a separate weld pool respectively. For this, a separate welding device is generally used for each impulse welding process, i.e. a power source, a welding wire, a control and, if necessary, a welding wire feeder are respectively used. The impulse welding processes are performed with the respective welding devices, by the respective control appropriately controlling or adjusting the welding parameters, i.e. in particular the welding current, the welding voltage, the wire feed and possibly the amount of shielding gas. It is also known that in order to avoid possible mutually adverse effects of simultaneously running impulse welding processes (which may reduce the quality of the weld), both impulse welding processes can be synchronized in time. In this case, for example, the impulse frequency following the respective welding device is pre-set in one welding device. Both welding processes are therefore synchronized with one another and perform the welding with the same impulse frequency, so that the droplet breaks stably with both electrodes. Tandem welding processes with synchronized welding processes are disclosed, for example, in DE 112014001441 A1 and U.S. Pat. No. 8,946,596.

[0004] In the case of single-stage welding methods with only one molten electrode, the so-called CMT-Mix welding process is also known these days, as disclosed, for example, in EP 1 677 940. In this case, short-circuit welding phases, during which the welding wire moves in reverse, with a relatively small heat input into the base metal, alternate with impulse welding phases with a higher heat input compared to the short-circuit. The advantage of this method compared to conventional methods (e.g. simple impulse welding) is that, due to the controlled current supply and the assisted action of the wire movement during the material feed, only a very small amount of heat is penetrated into the base metal. The CMT-Mix welding process can therefore be used in particular for joining metals and alloys, for example for joining steel and aluminum. However, no multiple-stage welding process is known in the past in which the CMT-Mix welding process can be carried out with both electrodes, because the welding process can become unstable. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] DE 112014001441 A1 [Patent Document 2] U.S. Pat. No. 8,946,596 [Patent Document 3] European Patent No. 1677940 Summary of the Invention [Problem to be solved by the invention]

[0006] It is therefore an object of the present invention to provide a multiple welding method which allows a stable welding process with both electrodes and a smaller heat input into the base material compared to multiple impulse welding methods. [Means for solving the problem]

[0007] According to the invention, this problem is solved in that a respective welding process having a short circuit welding phase and a thermal welding phase exhibiting a higher heat input into the base metal compared to the short circuit welding phase is performed with the at least two electrodes, the short circuit welding phase and the thermal welding phase alternate periodically, and at least the short circuit welding phases of the welding processes of the at least two electrodes are time-synchronized based on at least one first synchronization event determined for each short circuit welding phase, so that the short circuit welding phases performed with the electrodes of the compound welding method have a specific time relationship, so that mutual adverse effects of the welding processes can be avoided.

[0008] In this case, in particular, a first phase shift is provided between the first synchronization events, so that the short circuit welding phases are synchronized in time. In this case, for example, the time of occurrence of a short circuit during the short circuit welding phase or the time of an increase in the feed speed performed to cause a short circuit can be used as the first synchronization event. This allows a constant time relationship between the short circuit welding phases to be easily set. In this case, the phase shift can be determined, for example, as a phase angle or a phase time.

[0009] In particular, at least one short circuit cycle is performed during a short circuit welding phase, during which the respective electrode is moved towards the base metal until a short circuit occurs and then moved in the opposite direction away from the base metal after the short circuit occurs, in particular 2 to 10 short circuit cycles are performed per short circuit welding phase. By the reversing wire feed, the break-off of the droplet from the electrode can be improved. By determining the number of short circuit cycles, the heat input into the base metal can be changed.

[0010] In particular, as thermal welding phase, a spray arc welding phase with a constant welding voltage is used or an impulse welding phase is carried out with a succession of impulse cycles with an impulse frequency, in which a ground current phase with a ground current alternates with an impulse current that is higher than the ground current, respectively. Thus, when using impulse welding phases, the known CMT-Mix welding process can be advantageously carried out with multiple electrodes in a multiple-path welding method.

[0011] Advantageously, the impulse welding phases of the welding processes of the at least two electrodes are time-synchronized based on at least one second synchronization event determined for each impulse welding phase, such that the impulse welding phases are in a determined time relationship and a respective CMT-Mix welding process can be performed with both electrode(s) of the compound welding method without the welding processes(s) adversely affecting each other.

[0012] In particular, a second phase shift is provided between the second synchronization events, so that the impulse welding phases are time-synchronized, in which case in particular characteristic times during the impulse welding phases are used as second synchronization events, for example the time of a change in a welding parameter or the time of break-off of a droplet from the electrode, so that a specific time relationship can be easily determined.

[0013] Furthermore, the object of the present invention is achieved by using the above-mentioned equipment, in which a plurality of said control units are configured to perform each one of the welding processes having periodically alternating short circuit welding phases and a thermal welding phase exhibiting a higher heat input into the base material compared to the short circuit welding phases, and the control unit of at least a first of said welding devices is configured to transmit at least one synchronization information regarding a determined first synchronization event of the short circuit welding phase of the welding process performed by the first of said welding devices to a control unit of at least a second of said welding devices via said communication link, and the control unit of at least a second of said welding devices is configured to time-synchronize the welding process performed by the second of said welding devices with the welding process of the first of said welding devices based on the determined first synchronization event of the short circuit welding phase of the welding process performed by the second of said welding devices using the received synchronization information.

[0014] Preferred configurations of the installation are set out in the dependent claims 10 to 15.

[0015] The present invention will now be described in detail with reference to the exemplary, schematic and non-limiting figures of Figures 1 to 5 which show preferred configurations of the present invention. [Brief description of the drawings]

[0016] [Figure 1] 1 shows a configuration of an installation for carrying out a compound welding method. [Diagram 2] 4 shows the time progression of multiple welding parameters in a multiple welding method according to a first preferred embodiment of the present invention. [Diagram 3] 6 shows changes over time of a plurality of welding parameters in a multiple welding method according to a second preferred embodiment of the present invention. [Figure 4] 13 shows changes over time of a plurality of welding parameters in a multiple welding method according to a third preferred embodiment of the present invention. [Diagram 5] 13 shows changes over time of a plurality of welding parameters in a multiple welding method according to a fourth preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] FIG. 1 shows a schematic diagram of an installation 1 for performing a compound welding method (for example MIG / MAG welding) by means of at least two melting electrodes 3A, 3B. Here, the installation 1 has two welding devices A, B which are independent of each other. A given welding process can be performed by the welding devices A, B on a common workpiece 6 consisting of a base metal 6. Of course, more than two welding devices A, B may be provided. However, for the understanding of the invention, only the arrangement of two welding devices A, B is sufficient. The welding devices A, B do not necessarily have to be configured as independent devices, but it is also conceivable that two (or more) welding devices A, B are arranged, for example, in a common housing. However, this does not mean that each welding device A, B is configured with its own welding circuit for performing the respective welding process.

[0018] As is known, the welding devices A, B (MIG / MAG welding devices) may each have one welding power source 2A, 2B, one welding wire feeder 14A, 14B and one welding torch 4A, 4B. The welding power sources 2A, 2B respectively provide the required welding voltages UA, UB, which are applied to the welding wire as the welding electrode 3A, 3B, respectively. The welding wire is fed by the welding wire feeder 14A, 14B to the respective welding torch 4A, 4B at a predefined feed speed vA, vB, which is preset according to the respective welding process. The feeding can be carried out, for example, inside or outside the hose packet 5A, 5B. The welding wire feeder 14A, 14B can be integrated in the welding device A, B, respectively, but can also be an independent device as shown in FIG. 1. For example, a wire roll 16A, 16B can be provided in the welding wire feeder 14A, 14B. The welding wire is wound on the wire roll 16A, 16B. However, for example, the welding wire may be disposed in a container, for example a drum, and fed from the drum to the welding torches 4A, 4B. Furthermore, suitable drives 17A, 17B driven by controls 9A, 9B may be provided to draw the welding wire from the welding wire 16A, 16B or the container and feed it to the welding torches 4A, 4B at feed rates vA, vB.

[0019] Furthermore, suitable drives 18A, 18B, which can also be controlled by corresponding controls 9A, 9B, may be provided in the welding torches 4A, 4B to generate the feed speeds vA, vB. In general, the drives 17A, 17B; 18A, 18B may be configured, for example, as a pair of drive rolls, between which the welding wire is transported. If the welding device A, B has only one drive 17A, 17B outside the welding torch, this is called the "push system". In this case, the welding wire is pushed approximately in the direction of the welding torch 4A, 4B. If the illustrated drives 18A, 18B are also provided in the welding torches 4A, 4B, this is called the "push-pull system". In this case, the welding wire can not only be pushed from the drives 17A, 17B in the direction of the welding torches 4A, 4B, but also pulled from the drives 18A, 18B in the direction of the welding torches 4A, 4B.

[0020] The "push-pull method" is used in particular in welding processes in which the feed speeds vA, vB and, if necessary, the feed direction can change relatively rapidly, for example in CMT welding processes. In the case of the "push-pull method", a suitable wire buffer may be provided, if necessary, for example as a known wire storage device. The wire buffer may be arranged between the (push-type) drives 17A, 17B present outside the welding torches 4A, 4B and the (pull-type) drives 18A, 18B provided inside the welding torches 4A, 4B.

[0021] To carry out the welding process, an arc is ignited between the electrodes 3A, 3B or the welding wire respectively and the base material 6 (= workpiece), here represented by a lightning-bolt arrow. On the one hand, the material of the base material 6 is locally melted by the arc, generating a so-called molten pool 15. On the other hand, in order to fuse the material of the molten electrodes 3A, 3B onto the workpiece 6, the welding wire is fed with a defined feed speed vA, vB into the molten pool 15 and melted by the arc. This allows a weld seam to be formed during a relative movement of the welding torches 4A, 4B with respect to the workpiece 6 (in FIG. 1, in the direction normal to the drawing).

[0022] For each hose packet 5A, 5B, if necessary, further cables (e.g. control cables or cooling water pipes, not shown) may be provided between the welding device A, B and the respective welding torch 4A, 4B. To protect the weld pool 15 from the atmosphere, in particular from the oxygen contained in the atmosphere, a shielding gas may be used to prevent oxidation. In this case, inert gases (e.g. argon), active gases (CO2) or mixtures of these gases are typically used, which can be supplied to the welding torches 4A, 4B via suitable shielding gas pipes 12A, 12B and also via the hose packets 5A, 5B. The shielding gas is typically stored in separate (pressure) tanks 7A, 7B. The shielding gas can be supplied to the welding devices A, B (or directly to the welding torches 4A, 4B), for example, via suitable piping. If the same shielding gas is used, one common tank may be provided for both (all) welding devices A, B. The hose packets 5A, 5B can be connected to the welding torches 4A, 4B of the welding devices A, B, for example via suitable connections.

[0023] To configure a welding circuit for each of the welding devices A and B, the welding power sources 2A and 2B can be connected to the base material 6 by means of ground cables 8A and 8B, respectively. One electrode, generally a negative pole, of the welding power sources 2A and 2B is connected to the ground cable 8A and 8B. The other electrode, generally a positive pole, of the welding power sources 2A and 2B is connected to the welding electrodes 3A and 3B via a suitable current cable 13A and 13B. Alternatively, one electrode, generally a negative pole, of the welding power sources 2A and 2B is connected to the welding electrodes 3A and 3B via a suitable current cable 13A and 13B. The other electrode, generally a positive pole, of the welding power sources 2A and 2B is connected to the ground cable 8A and 8B. Thus, for each welding process, a welding circuit is configured via the arc and the base material 6. A respective control unit 9A and 9B for controlling and monitoring the respective welding process including the feeding of the respective welding wire may be provided in the welding devices A and B. For this purpose, welding parameters required for the welding process, such as, for example, feed speeds vA, vB, welding currents IA, IB, welding voltages UA, UB, impulse frequencies fA, fB, etc., are predefined or can be defined in the control units 9A, 9B. To control the respective welding process, the control units 9A, 9B are connected to the welding power sources 2A, 2B and to the welding wire feeders 14A, 14B (e.g., in particular the drives 17A, 17B). To input or display certain welding parameters or welding states, user interfaces 10A, 10B connected to the control units 9A, 9B may be provided.

[0024] Furthermore, suitable interfaces (not shown) may be provided at the welding devices A, B, by means of which the welding devices A, B can be connected to a higher-level control capable of controlling all multiple welding methods. For example, a central control (not shown) may be provided, which is connected to both welding devices A, B (or to a number of welding devices A, B) and is capable of controlling the welding devices A, B. Naturally, the described welding devices A, B are well known and will not be described in further detail here.

[0025] The two welding torches 4A, 4B can be arranged close to each other so that the electrodes or welding wires 3A, 3B work in a common weld pool 15 in the workpiece 6 as shown in FIG. 1, instead of in two separate weld pools. However, the arrangement can also be variable. In such a variable arrangement, for example, each welding torch 4A, 4B is steered by a welding robot. Instead of a welding robot, naturally, another suitable steering device can be provided, for example of the portal crane type, which allows a movement in several axes, in particular in three axes. However, as shown by dashed lines in FIG. 1, a common welding torch can also be provided for both electrodes 3A, 3B. In this case, it is irrelevant whether joint welding or build-up welding or another welding method is performed by the welding torches 4A, 4B. Naturally, manual execution of a multiple welding method is also basically possible, for example by manually steering one or more welding torches 4A, 4B.

[0026] A number of control units 9A, 9B of a number of welding devices A, B can be linked by a communication link 11. Synchronization information Y can be transmitted and / or received via the communication link 11. Both welding processes can be time-synchronized by the synchronization information Y. In particular, the welding devices A, B are configured such that the synchronization information Y can be exchanged between the control units 9A, 9B, as indicated by the double arrow in FIG. 1. Thereby, both welding devices A, B can be used as "master" and as "slave". The "master" welding device A or B can transmit the synchronization information Y and the "slave" welding device A or B can use the synchronization information Y in order to synchronize the welding process performed by the "slave" welding device A or B to the "master" welding device A or B. The communication link 11 can be, for example, a wired or wireless link between the control units 9A, 9B or between the user interfaces 10A, 10B, for example a known data bus.

[0027] In the simplest case, the synchronization information Y can be, for example, a synchronization single pulse transmitted from one sending welding device A or B to at least one other (receiving) welding device A or B via the communication link 11. In this case, the synchronization pulse can be transmitted, for example, as a current or voltage pulse on the wired communication link 11 between the two welding devices A, B. However, it is also possible to configure the communication link 11 as a data bus, on which bus information is transmitted. In this case, the synchronization pulse can be transmitted as bus information. The transmission can be performed both wired (cable, optical fiber, etc.) and wired (WiFi, Bluetooth, etc.). At the receiving welding device A or B, the respectively performed welding process can be synchronized with the welding process of the sending welding device A or B by the receiving synchronization pulse.

[0028] According to the invention, it is proposed that the control units 9A, 9B are configured to perform a respective welding process having periodically alternating short-circuit welding phases SPA1, SPB1 and thermal welding phases SPA2, SPB2 exhibiting a higher heat input into the base material 6 compared to the short-circuit welding phases (see Figs. 2-5). Furthermore, it is proposed that at least the control unit 9A of the first welding device A is configured to transmit synchronization information Y on the determined first synchronization event SEA1 of the short-circuit welding phase SP1 of the welding process performed by the first welding device A to the control unit 9B of at least one second welding device B via the communication link 11 (Figs. 2-5). The control unit 9B of the at least one second welding device B is configured to time-synchronize the welding process performed by the second welding device B with the welding process of the first welding device A based on the determined first synchronization event SEB1 of the short-circuit welding phase SPB1 of the welding process performed by the second welding device B by the acquired synchronization information Y. Thus, the first welding device A functions as the "master" welding device and the second welding device B functions as the "slave" welding device.

[0029] As the synchronization events SEA1, SEB1, for example, a characteristic time point during the short-circuit welding phase SPA1, SPB1 of each executed welding process can be used, which is known or as easily detectable as possible. For example, an abrupt change, for example a rising edge or a falling edge during the time course of a welding parameter, such as the welding current I, the welding voltage U or the feed speed v, can be used as the first synchronization event SEA1, SEB1. In this case, the synchronization information Y can include, for example, a first phase shift φ1 between the first synchronization event SEA1 during the welding process of the first welding device A and the first synchronization event SEB1 during the welding process of the second welding device B. In this case, as the phase shift φ1, for example, an angle of 0-360° can be used for a cyclically repeated welding cycle or period, as will be explained in more detail below with reference to Figs. 2-5.

[0030] As is known, the short circuit welding phase SPA1, SPB1 is characterized in that a short circuit occurs when the respective electrodes 3A, 3B contact the base material 6. This characteristic time of the occurrence of the short circuit for the short circuit welding phase SPA1, SPB1 can therefore be provided as a first synchronization event SEA1, SEB1 of the short circuit welding phase SPA1, SPB1. The time of the occurrence of the short circuit can be ascertained on the basis of the course of the welding current I or the welding voltage U, as will be explained in more detail below on the basis of Figs. 2-5. Instead of the time of the actual occurrence of the short circuit, however, a known time of an increase in the feed speed v, which is intentionally performed in order to approximately force the occurrence of the short circuit, can also be used as the first synchronization event SEA1, SEB1. Alternatively, a known time of a reduction in the welding current IA, IB, which is intentionally performed in order to approximately force the occurrence of the short circuit, can also be used as the first synchronization event SEA1, SEB1. The arc energy of the arc can be reduced by the intentional reduction of the welding current IA, IB, so that a short circuit is generated. The increase in the feed speed v and the decrease in the welding currents IA, IB may be performed, for example, with a time lag. In this case, the time of the increase in the feed speed v or the time of the decrease in the welding currents IA, IB may be used as the first synchronization event SEA1, SEB1. However, the increase in the feed speed v and the decrease in the currents IA, IB may be performed simultaneously so that a common time may be used as the first synchronization event SEA1, SEB1.

[0031] To improve the cutting of the droplets during the short circuit welding phase SPA1, SPB1, it may be advantageous for at least one short circuit cycle ZKA, ZKB to be performed during the short circuit welding phase SPA1, SPB1. During this short circuit cycle ZKA, ZKB, the electrodes 3A, 3B are moved towards the base metal 6 until a short circuit occurs and then moved in the opposite direction away from the base metal 6 after the occurrence of the short circuit. The movement is performed in a known manner, by the respective welding wire feeders 14A, 14B being controlled by the respective controllers 9A, 9B. In this case, the duration of the short circuit welding phases SPA1, SPB1 (which exhibit a lower heat input into the base metal 6 compared to thermal welding) can be flexibly determined, for example by presetting a certain number of short circuit cycles ZKA, ZKB, for example by setting 2 to 10 short circuit cycles ZKA, ZKB for each short circuit welding phase SPA1, SPB1. In this case, in particular for each short-circuit cycle ZKA, ZKB, a reversible wire feed is performed, i.e. a movement towards the base material 6 up to the occurrence of a short circuit and a movement away from the base material 6 after said short circuit. Naturally, a reversible wire feed, i.e. a reversal of the direction of the feed speeds vA, vB, is only optional. The short-circuit welding phases SPA1, SPB1 may also be performed, for example, only with a variable feed speed v, without a change in the movement direction of the welding wire.

[0032] As the thermal welding phases SPA2, SPB2, for example, known impulse welding phases (FIGS. 2-5) can be used. Thereby, the above-mentioned CMT-Mix welding process can be performed in parallel by the two welding devices A, B, respectively. In the case of the CMT-Mix welding process, short-circuit welding phases SPA1, SPB1 and impulse welding phases SPA2, SPB2 alternate periodically. In this case, in the impulse welding phases, a number of successive impulse cycles ZPA, ZPB are typically performed with predefined impulse frequencies fA, fB. In the impulse cycles ZPA, ZPB, one ground current phase with a ground current IGA, IGB alternates with one impulse current IPA, IPB, which is higher than the ground current IGA, IGB, respectively. However, as the thermal welding, for example, known spray arc welding phases with substantially constant welding currents IA, IB (not shown) can also be used.

[0033] In particular, the same welding process is performed in parallel with both electrodes 3A, 3B by the control units 9A, 9B of both welding devices A, B adjusting the same welding parameters (U, I, v) f, etc., which are preset or can be preset. For example, if one impulse welding phase is performed by both welding devices A, B as thermal welding phases SPA2, SPB2, it is advantageous that the same impulse frequencies fA, fB are used in both impulse welding phases. However, the impulse frequencies fA, fB during the impulse welding phase of one welding device A, B may be integer multiples of the impulse frequencies fA, fB of the other welding device A, B, respectively.

[0034] If one impulse welding phase each is provided as a thermal welding phase SPA2, SPB2 (CMT-Mix welding process), it is advantageous for the welding processes performed with at least two electrodes 3A, 3B by at least two welding devices A, B to be time-synchronized for each impulse welding phase on the basis of at least one determined second synchronization event SEA2, SEB2, whereby at least two welding processes (CMT-Mix) performed in parallel can be time-synchronized such that both short-circuit welding phases and both impulse welding phases are in a determined time relationship to one another, as will be explained in more detail below on the basis of Figures 2-5.

[0035] The impulse welding phases SPA2, SPB2 can for example be synchronized in the same way as the short-circuit welding phases, by providing a second phase shift φ2, for example as a phase angle or a period, between the determined second synchronization events SEA2, SEB2. As the second synchronization event SEA2, SEB2, a characteristic time point can likewise be used in the impulse welding phases SPA2, SPB2, for example the time point at which the droplet breaks off from the respective electrode 3A, 3B, or a time point in the time course of a welding parameter, for example the welding current I, the welding voltage U or the feed speed v, for example a rising or falling edge changes abruptly can be used in the impulse welding phases SPA2, SPB2.

[0036] Thus, by the time synchronization of both (especially CMT-Mix) welding processes according to the invention, it is possible that (at least) two welding processes can be performed stably and with as little interaction as possible, since they proceed to each other with a determined time ratio. The respective time of the occurrence of a short circuit (or the time of the increase in the feed speed performed to initiate a short circuit or the time of the reduction in the welding current caused for the initiation of said short circuit) and / or the time of the breakage of the droplet can be detected, for example, by the respective control unit 9A, 9B. Or these times can be known, for example, if a predefined welding process is used with known welding parameters (known time progression of the welding current I, welding voltage U, feed speed v, etc.).

[0037] Predetermined welding parameters, such as a predetermined welding current IA, a welding voltage UA, and a predetermined feed rate vA, are set by the control unit 9A, so that for example the control unit 9A of the first welding device A can execute a first welding process (e.g. a preset CMT-Mix welding process having a short circuit welding phase SPA1 and an impulse welding phase as a thermal welding phase SPA2). Similarly, predetermined welding parameters, such as a predetermined welding current IB, a welding voltage UB, and a predetermined feed rate vB, are set by the control unit 9B, so that for example the control unit 9B of the second welding device B can execute a second welding process (e.g. a preset CMT-Mix welding process having a short circuit welding phase and an impulse welding phase as a thermal welding phase SPB2).

[0038] In this case, the control unit 9A of the first welding device A ("master") can transmit synchronization information Y regarding at least one first synchronization event SEA1 of the short circuit welding phase SPA1 of the first welding process (e.g. time of occurrence of a short circuit) and information regarding at least one second synchronization event SEA2 of the (optional) impulse welding phase SPA2 of the first welding process (e.g. time of break-off of a droplet from the electrode 3A) to the control unit 9B of the second control unit B via the communication link 11, for example as synchronization pulses or bus information. The control unit 9B of the second welding device B ("slave") can use the received synchronization information Y to synchronize the performed second (CMT-Mix) welding process with the first (CMT-Mix) welding process of the first welding device A. In particular, the control unit 9B of the second welding device B can time-synchronize the short circuit welding phase SPB1 with the short circuit welding phase SPA1 of the first welding device A based on the first synchronization event SEB1 (e.g. time of occurrence of a short circuit) by means of the synchronization information Y. Furthermore, if necessary, the control unit 9B of the second welding device B can time-synchronize the impulse welding phase SPB2 with the impulse welding phase SPA2 of the first welding device A based on a second synchronization event SEB2 (e.g., the time point at which the droplet breaks off from the electrode 3B) using the synchronization information Y.

[0039] For example, the synchronization information Y may include a predetermined first phase shift φ1. The short circuit welding phases SPA1, SPB1 are executed with a time shift from each other by the first phase shift φ1. The first phase shift φ1 may be preset, but may also be adjustable (for example, by the user interface 10A and / or 10B). Similarly, the synchronization information Y may include a predetermined second phase shift φ2. The short circuit welding phases SPA2, SPB2 are executed with a time shift from each other by the second phase shift φ2. As shown in FIG. 3, it is conceivable that the short circuit welding phases SPA1, SPB1 are executed synchronously, i.e. with a first phase shift φ1=0, and that the impulse welding phases SPA2, SPB2 are executed synchronously, i.e. with a second phase shift φ2=0. Naturally, however, another time synchronization may be selected. For example, φ1=0, φ2≠0 (FIG. 2) or φ≠0, φ2=0 (FIG. 5) or φ1=φ2≠0 (FIG. 4) (where φ1<φ2, φ1>φ2 or φ1=φ2) may be selected.

[0040] In the following, a preferred embodiment of the synchronization according to the invention is explained on the basis of the figures 2-5. In this case, the course of the welding currents IA, IB, the course of the welding voltages UA, UB and the course of the feed speeds vA, vB over time t are shown respectively at the top, the middle and the bottom for several welding processes carried out in parallel with (here two) electrodes 3A, 3B. In this case, the solid lines relate to a first welding process carried out, for example, with a first electrode 3A by a first welding device A, and the dashed lines relate to a second welding process of a compound welding method carried out with a second electrode 3B by a second welding device B. For example, here two CMT-Mix welding processes are shown as the first and second welding processes. Short-circuit welding phases SPA1, SPB1 and impulse welding phases SPA2, SPB2, respectively, alternate cyclically. Since the CMT-Mix welding processes are basically known from single-electrode welding processes (Einfach-Schweissverfahren) only the aspects that are important for the invention are explained in detail here. However, as mentioned above, spray arc welding phases with approximately constant welding currents IA, IB may also be used as thermal welding phases instead of impulse welding phases, in which case only the synchronization of the short circuit welding phases SPA1, SPB1 is sufficient.

[0041] As is known, in the impulse welding phase SPA2, SPB2, several successive impulse cycles ZPA, ZPB can be carried out with a preset or settable impulse frequency fPA, fPB. In this case, as illustrated in FIG. 2 on the basis of one impulse cycle ZPA, ZPB of the second (impulse) welding phase SPA2, SPB2, the impulse frequency fPA, fPB corresponds to the reciprocal of the period TZPA, TZPB of the impulse cycle ZPA, ZPB. In each impulse cycle ZPA, ZPB, a ground current phase with a ground current IGA, IGB generally alternates with an impulse current IPA, IPB that is higher than the ground current IGA, IGB. By generating such current impulses in each impulse cycle ZPA, ZPB, the droplet is purposefully cut off from the respective electrode 3A, 3B. As will be explained in more detail below, in order to time-synchronize the two impulse welding phases SPA2, SPB2 with one another, the time point of this droplet breaking can be used within the scope of the present invention as a characteristic second synchronization event SEA2, SEB2, for example for the impulse welding phases SPA2, SPB2.

[0042] In this case, the impulse frequencies fPA, fPB, the ground currents IGA, IGB and the impulse currents IPA, IPB can be selected to be the same, but may also be different. The time course of the welding voltages UA, UB, respectively shown in the central graph, approximately corresponds quantitatively to the course of the welding currents IA, IB, and will not be described in detail here. In general, the voltage U during the welding process is generated by the voltage drop in the arc and the voltage drop at the free wire end of the welding wire. The feed speeds vA, vB of the electrodes 3A, 3B are approximately constant during the impulse welding phases SPA2, SPB2 and change at the transition from or to the respective short-circuit welding phases SPA1, SPB1, respectively. However, non-constant feed speeds vA, vB during the impulse welding phases SPA2, SPB2 are naturally also conceivable. The overall duration of the impulse welding phase SPA2, SPB2 (derived from a number of impulse cycles ZPA, ZPB and the periods TZPA, TZPB of these impulse cycles ZPA, ZPB) can be set, for example, by presetting a period or by presetting a number of impulse cycles ZPA, ZPB and the periods TZPA, TZPB of these impulse cycles ZPA, ZPB.

[0043] In the example shown in Fig. 2-5, the magnitudes of the welding current IB, welding voltage UB and feed speed vB of the second electrode 3B are slightly smaller than the magnitudes of the welding current IA, welding voltage UA and feed speed vA of the first electrode 3A. This is due to the fact that the first electrode 3A is set as the main electrode and the second electrode 3B is set as the slave electrode. The main electrode precedes the slave electrode in the welding direction (in the direction of movement of the welding torches 4A, 4B to create the weld seam). This means that the slave electrode requires slightly less welding energy, since it operates in the molten pool already created by the main electrode. Naturally, this is only an example and the same welding parameters may be used for both welding processes.

[0044] As is known, in the short circuit welding phase SPA1, SPB1 at least one short circuit cycle ZKA, ZKB is carried out. As is evident from the feed rates vA, vB in the lower graph, in this short circuit cycle ZKA, ZKB the respective electrode 3A, 3B is moved towards the base metal 6 until a short circuit is formed and then moved in the opposite direction away from the base metal 6 after the short circuit. The time of occurrence of the short circuit is recognizable by the rise of the welding current IA, IB or in particular by the simultaneous drop of the welding voltage UA, UB. As will be explained further below, the time of occurrence of the short circuit can be advantageously used within the scope of the present invention as a characteristic first synchronization event SEA1, SEB1 of the short circuit welding phases SPA1, SPB1 in order to be able to time-synchronize the two short circuit welding phases SPA1, SPB1 with one another. However, instead of the time of occurrence of the actual short circuit as the characteristic first synchronization event SEA1, SEB1 of the short circuit welding phase SPA1, SPB1, the time of a short-term increase (illustrated in FIG. 5) of the feed speeds vA, vB may also be used, which is performed immediately before the time of occurrence of the actual short circuit in order to trigger the occurrence of said short circuit.

[0045] In the illustrated example, only a single short circuit cycle ZKA, ZKB is shown for each short circuit welding phase SPA1, SPB1, respectively, but naturally, several short circuit cycles ZKA, ZKB may be executed. For example, 2 to 10 short circuit cycles ZKA, ZKB may be executed for each short circuit welding phase SPA1, SPB1. By presetting the number of short circuit cycles ZKA, ZKB, the duration of the short circuit welding phase SPA1, SPB1 and therefore the period during which a small amount of heat must be input into the base material 6 (compared to the thermal welding phase SPA2, SPB2 or the impulse welding phase) can be determined. In the short circuit cycles ZKA, ZKB, the welding currents IA, IB may be changed, in particular a predefined course of the welding currents IA, IB may be controlled by the respective control units 9A, 9B. To assist in the cutting of the droplets, for example, the welding current IA, IB can be increased from a ground current (which may be equal to or different from the ground current IGA, IGB of the impulse welding phases SPA2, SPB2) to a boost current higher than the ground current (and lower than the impulse current IPA, IPB of the impulse welding phases SPA2, SPB2) in opposition to the wire feed speed vA, vB during the short-circuit cycle ZKA, ZKB, and then further decreased to the boost current.

[0046] In the example according to FIG. 2, the multiple short circuit welding phases SPA1, SPB1 are time-synchronized by a first phase shift φ1=0, i.e. both welding processes performed in parallel with the electrodes 3A, 3B are performed simultaneously. As already explained, the synchronization is performed on the basis of at least one first synchronization event SEA1, SEB1 for each short circuit welding phase SPA1, SPB1. Here, the time of occurrence of a short circuit during a short circuit cycle ZKA, ZKB is provided as the first synchronization event SEA1, SEB1. In the illustrated example, the impulse welding phases SPA2, SPB2 are time-synchronized by a second phase shift φ2=180°, so that they are recognizable on the basis of the welding currents IA, IB and the welding voltages UA, UB. That is, multiple impulse cycles ZPA, ZPB are performed with a time shift relative to one another. Similarly, the synchronization of the impulse welding phases SPA2, SPB2 is performed on the basis of at least one second synchronization event SEA2, SEB2 for each impulse welding phase SPA2, SPB2. In this case, the moment of breakage of the droplet, i.e. the rise from the ground current IGA, IGB to the impulse current IPA, IPB, is provided here as the second synchronization event SEA2, SEB2. As is evident in FIG. 2, the impulse frequencies fA, fB are in particular of the same magnitude. However, these impulse frequencies may also be of different magnitudes. In this case, each higher impulse frequency fA, fB is an integer multiple of each lower impulse frequency fA, fB.

[0047] In the example according to Fig. 3, the short circuit welding phases SPA1, SPB1 are time-synchronized by a phase shift φ1=0, and the impulse welding phases SPA2, SPB2 are also time-synchronized by a phase shift φ2=0. That is to say, the short circuit cycles ZKA, ZKB as well as the impulse cycles ZPA, ZPB are time-synchronized, so as to be recognizable on the basis of the welding currents IA, IB and the welding voltages UA, UB. Similarly, the synchronization is performed on the basis of the time of occurrence of a short circuit as a first synchronization event SEA1, SEB1 of the short circuit welding phases SPA1, SPB1, and on the basis of the breakage of a droplet as a second synchronization event SEA2, SEB2 of the impulse welding phases SPA2, SPB2. In the example according to Fig. 4, the short circuit welding phases SPA1, SPB1 are time-synchronized by a phase shift φ1=180°, and the impulse welding phases SPA2, SPB2 are also time-synchronized by a phase shift φ2=180°. This means that the short-circuit cycles ZKA, ZKB as well as the impulse cycles ZPA, ZPB are executed with a time stagger, so that they are recognizable on the basis of the welding currents IA, IB and welding voltages UA, UB, and for the short-circuit welding phases SPA1, SPB1 also on the basis of the feed rates vA, vB. Similarly, the synchronization is also executed on the basis of the time of occurrence of a short circuit as a first synchronization event SEA1, SEB1 for the short-circuit welding phases SPA1, SPB1 and on the basis of the breakage of the droplet as a second synchronization event SEA2, SEB2 for the impulse welding phases SPA2, SPB2. Naturally, other characteristic times may also be provided as the first and second synchronization events SEA1, SEB1, SEA2, SEB2.

[0048] Finally, in the example according to Fig. 5, the short circuit welding phases SPA1, SPB1 are time-synchronized by a phase shift φ1 = 180° and the impulse welding phases SPA2, SPB2 are time-synchronized by a phase shift φ = 0°. This means that the short circuit cycles ZKA, ZKB are executed with a time stagger and the impulse cycles ZPA, ZPB are executed synchronously, so as to be recognizable on the basis of the welding currents IA, IB and the welding voltages UA, UB, and for the short circuit welding phases SPA1, SPB1 also on the basis of the feed speeds vA, vB. Similarly, the synchronization is also executed on the basis of the time of occurrence of a short circuit as a first synchronization event SEA1, SEB1 for the short circuit welding phases SPA1, SPB1 and on the basis of the breakage of the droplet as a second synchronization event SEA2, SEB2 for the impulse welding phases SPA2, SPB2.

[0049] For completeness, the already explained short-term increases of the feed speeds vA, vB are furthermore shown (in dotted lines) in the lower graph of Fig. 5 as synchronization events SEA1', SEB1' instead of the short-circuit welding phases SPA1, SPB1. In this case, the feed speeds vA, vB are intentionally increased for a short period of time relative to a determined time point in order to generate a short circuit. The increase in the feed speed is shown in Fig. 5 as an irregular pulse. However, it can of course also be regular. In this case, the time point is of course also known by the known course of the welding parameters in time due to the known welding process performed.

[0050] The multiple welding steps of the multiple welding method performed in parallel can be adjusted in sequence as desired by the time synchronization of the present invention. As a result, two (or more) welding steps have as little influence on each other as possible. Finally, it is noted that the described embodiment is merely an example and does not limit the present invention, and a specific configuration may be realized by a person skilled in the art. The present application relates to the invention described in the claims, but may also include the following configurations as other aspects. 1. A method for performing a compound welding process on a base metal (6) by means of at least two molten electrodes (3A, 3B), comprising: With each electrode (3A, 3B), one welding process is performed after ignition of an arc between the electrode (3A, 3B) and the base material (6); The method in which these welding processes of at least two electrodes (3A, 3B) are time-synchronised, a respective welding process having a short circuit welding phase (SPA1, SPB1) and a thermal welding phase (SPA2, SPB2) exhibiting a higher heat input into the base material (6) compared to the short circuit welding phase (SPA1, SPB1) is performed with the at least two electrodes (3A, 3B); The short circuit welding phase (SPA1, SPB1) and the thermal welding phase (SPA2, SPB2) alternate periodically, The method, wherein at least the short circuit welding phases (SPA1, SPB1) of these welding processes of the at least two electrodes (3A, 3B) are time synchronized based on at least one first synchronization event (SEA1, SEB1) determined for each short circuit welding phase (SPA1, SPB1). 2. 2. The method according to claim 1, wherein a first phase shift (φ1) is provided between a plurality of said first synchronization events (SEA1, SEB1), thereby time-synchronizing said plurality of short circuit welding phases (SPA1, SPB1). 3. The method according to claim 1 or 2, wherein the first synchronization event (SEA1, SEB1) is the time of occurrence of a short circuit during the short circuit welding phase (SPA1, SPB1), or the time of an increase in the feed speed (vA, vB) performed to generate a short circuit, or the time of a decrease in the welding current (IA, IB) performed to generate a short circuit. 4. A method according to any one of 1 to 3 above, wherein at least one short circuit cycle (ZKA, ZKB) is performed during a short circuit welding phase (SPA1, SPB1), during which each of the electrodes (3A, 3B) is moved in the direction of the base material (6) until a short circuit occurs, and after the occurrence of the short circuit is moved in the opposite direction away from the base material (6), in particular 2 to 10 short circuit cycles (ZKA, ZKB) are performed for each short circuit welding phase. 5. As the thermal welding phase (SPA2, SPB2), an impulse welding phase or a spray arc welding phase is used; 5. The method according to any one of 1 to 4 above, wherein in the impulse welding phase, consecutive impulse cycles (ZPA, ZPB) are executed with an impulse frequency (fA, fB), and in these impulse cycles (ZPA, ZPB), a ground current phase having a ground current (IGA, IGB) alternates with an impulse current phase having an impulse current (IPA, IPB) higher than the ground current (IGA, IGB). 6. 6. The method according to claim 5, wherein the impulse welding phases (SPA1, SPB1) of the welding process of the at least two electrodes (3A, 3B) are time synchronized based on at least one determined second synchronization event (SEA2, SEB2) for each impulse welding phase (SPA2, SPB2). 7. 7. The method according to claim 6, wherein a second phase shift (φ2) is provided between said second synchronization events (SEA2, SEB2) such that said impulse welding phases (SPA2, SPB2) are time synchronized. 8. 8. The method according to claim 6 or 7, wherein as the second synchronization event (SEA2, SEB2) a characteristic time point during the impulse welding phase (SEA2, SEB2) is used, in particular the time point of a change in the welding parameters (U, I, v) or the time point of break-off of a droplet from the electrodes (3A, 3B). 9. An installation (1) for carrying out a compound welding method, comprising: In the facility, at least two welding devices (A, B) are provided for performing one welding process on one base material (6) by one molten electrode (3A, 3B), Each of the welding devices (A, B) has one control unit (9A, 9B) for controlling the respective welding processes, In the facility, a plurality of the control units (9A, 9B) of at least two of the welding devices (A, B) are connected via a communication link (11) in order to time-synchronize the plurality of welding processes, The control units (9A, 9B) are each configured to execute one welding process having periodically alternating short circuit welding phases (SPA1, SPB1) and thermal welding phases (SPA2, SPB2) exhibiting a higher heat input into the base material (6) than the short circuit welding phases, The control unit (9A) of at least a first of the welding devices (A) is configured to transmit at least one synchronization information (Y) relating to a determined first synchronization event (SEA1) of a short-circuit welding phase (SPA1) of a welding process performed by the first of the welding devices (A) to a control unit (9B) of at least one second of the welding devices (B) via the communication link (11), and the control unit (9B) of the at least one second of the welding devices (B) is configured to time-synchronize the welding process performed by the second of the welding devices (B) with the welding process of the first of the welding devices (A) based on the determined first synchronization event (SEB1) of the short-circuit welding phase (SPB1) of the welding process performed by the second of the welding devices (B) using the received synchronization information (Y). 10. The equipment described in claim 9, wherein the synchronization information (Y) includes at least one first phase shift (φ1) between a plurality of the first synchronization events (SEA1, SEB1). 11. The equipment described in 9 or 10 above, wherein the first synchronization event (SEA1, SEB1) is the time of occurrence of a short circuit during the short circuit welding phase (SPA1, SPB1), or the time of an increase in the feed speed (vA, vB) performed to generate a short circuit, or the time of a decrease in the welding current (IA, IB) performed to generate a short circuit. 12. Each of the welding devices (A, B) has a welding wire feeder (14A, 14B) that can be controlled by the control unit (9A, 9B), the control units (9A, 9B) are configured to execute at least one short circuit cycle (ZKA, ZKB) during the short circuit welding phase (SPA1, SPB1), and during the short circuit cycle (ZKA, ZKB), the welding wire feed units (14A, 14B) move the electrodes (3A, 3B) toward the base material (6) until a short circuit occurs, and then move the electrodes (3A, 3B) in the opposite direction away from the base material (6) after the short circuit occurs; 12. Installation according to claim 11, in particular in which 2 to 10 short circuit cycles (ZKA, ZKB) can be carried out per short circuit welding phase (SPA1, SPB1). 13. the plurality of control parts (9A, 9B) are configured to execute an impulse welding phase having a plurality of successive impulse cycles (ZPA, ZPB) with an impulse frequency (fA, fB) as a thermal welding phase (SPA2, SPB2), in which a ground current phase having a ground current (IGA, IGB) and an impulse current phase having a high impulse current (IPA, IPB) compared to the ground current (IGA, IGB) alternate with each other in the impulse cycles (ZPA, ZPB); or The installation according to claim 11 or 12, wherein the control units (9A, 9B) are configured to perform a spray arc welding phase having a constant welding current as a thermal welding phase (SPA2, SPB2). 14. The control unit (9A) of at least a first of the welding devices (A) is configured to transmit one piece of synchronization information (Y) relating to a determined second synchronization event (SEA2) of an impulse welding phase (SPA2) of a welding process performed by the first of the welding devices (A) to a control unit (9B) of at least one of the second of the welding devices (B) via the communication link (11), and the control unit (9B) of the at least one of the second of the welding devices (B) is configured to time-synchronize the welding process performed by the second of the welding devices (B) with the welding process of the first of the welding devices (A) based on the determined second synchronization event (SEB2) of the impulse welding phase (SPB2) of the welding process performed by the second of the welding devices (B) using the received synchronization information (Y). The facility described in any one of 10 to 13 above. 15. The synchronization information (Y) includes at least one phase shift (φ2) between a plurality of the second synchronization events (SEA2, SEB2); 15. Installation according to claim 14, wherein as second synchronization event (SEA2, SEB2) in particular a characteristic time point during the impulse welding phase (SEA2, SEB2) is provided, particularly preferably the time point of break-off of a droplet from the electrodes (3A, 3B) or the time point of a change in welding parameters (U, I, v). [Explanation of symbols]

[0051] 1 equipment 2A,2B welding power source 3A,3B Melting electrode 4A, 4B Welding torch 5A,5B Hose Packet 6 Workpiece, metal base material 7A, 7B (Pressure) Tank 8A, 8B Ground cable 9A, 9B Control section 10A, 10B User Interface 11 Communication Links 12A, 12B Shielding gas pipe 13A, 13B Current cable 14A, 14B Welding wire feed section 15 Molten Pool 16A, 16B Wire roll 17A, 17B Drive section 18A, 18B Drive section A,B Welding equipment UA,UB Welding voltage IA,IB Welding current vA,vB Feed speed fA,fB impulse frequency Y Synchronization information vA,vB Feed speed

Claims

1. A method for performing a compound welding process on a base material (6) by means of at least two melting electrodes (3A, 3B), comprising: With each electrode (3A, 3B), one welding process is carried out after ignition of an arc between the electrode (3A, 3B) and the base material (6); The method in which these welding processes of at least two electrodes (3A, 3B) are time-synchronised, a respective welding process having a short-circuit welding phase (SPA1, SPB1) and a thermal welding phase (SPA2, SPB2) exhibiting a higher heat input into the base material (6) compared to the short-circuit welding phase (SPA1, SPB1) is performed with the at least two electrodes (3A, 3B); The short circuit welding phase (SPA1, SPB1) and the thermal welding phase (SPA2, SPB2) alternate periodically; The method is characterized in that at least the short circuit welding phases (SPA1, SPB1) of these welding processes of the at least two electrodes (3A, 3B) are time synchronized based on at least one first synchronization event (SEA1, SEB1) determined for each short circuit welding phase (SPA1, SPB1).

2. 2. The method according to claim 1, characterized in that a first phase shift (φ1) is provided between a plurality of said first synchronization events (SEA1, SEB1), thereby time-synchronizing said plurality of short circuit welding phases (SPA1, SPB1).

3. 3. The method according to claim 1 or 2, characterized in that as the first synchronization event (SEA1, SEB1) the time of occurrence of a short circuit during the short circuit welding phase (SPA1, SPB1) or the time of an increase in the feed speed (vA, vB) performed to generate the short circuit or the time of a decrease in the welding current (IA, IB) performed to generate the short circuit is used.

4. 4. The method according to claim 1, wherein at least one short circuit cycle (ZKA, ZKB) is performed during the short circuit welding phase (SPA1, SPB1), during which the respective electrodes (3A, 3B) are moved towards the base material (6) until a short circuit occurs and then moved in the opposite direction away from the base material (6) after the occurrence of the short circuit.

5. The method according to claim 4, characterized in that 2 to 10 short circuit cycles (ZKA, ZKB) are performed during the short circuit welding phase.

6. As the thermal welding phase (SPA2, SPB2) an impulse welding phase or a spray arc welding phase is used, 6. The method according to claim 1, characterized in that during the impulse welding phase, a number of successive impulse cycles (ZPA, ZPB) are carried out with an impulse frequency (fA, fB), in which the impulse cycles (ZPA, ZPB) alternate with ground current phases having a ground current (IGA, IGB) and impulse current phases having a high impulse current (IPA, IPB) compared to the ground current (IGA, IGB).

7. 7. The method according to claim 6, characterized in that the impulse welding phases (SPA1, SPB1) of the welding process of the at least two electrodes (3A, 3B) are time synchronized based on at least one determined second synchronization event (SEA2, SEB2) for each impulse welding phase (SPA2, SPB2).

8. 8. The method of claim 7, wherein a second phase shift (φ2) is provided between the second synchronization events (SEA2, SEB2) such that the impulse welding phases (SPA2, SPB2) are time synchronized.

9. 9. The method according to claim 7 or 8, characterized in that as second synchronization event (SEA2, SEB2) a characteristic time point during the impulse welding phase (SEA2, SEB2) is used.

10. The method according to claim 9, characterized in that the time of change in the welding parameters (U, I, v) or the time of break-off of a droplet from the molten electrodes (3A, 3B) is used as a characteristic time during the impulse welding phase (SEA2, SEB2).

11. An installation (1) for carrying out a compound welding method, comprising: In the facility, at least two welding devices (A, B) are provided for performing one welding process on one base material (6) by one melting electrode (3A, 3B), Each of the welding devices (A, B) has one control unit (9A, 9B) for controlling the respective welding processes, In the facility, a plurality of the control units (9A, 9B) of at least two of the welding devices (A, B) are connected via a communication link (11) in order to time-synchronize a plurality of the welding processes, the control units (9A, 9B) are each configured to perform a welding process having periodically alternating short circuit welding phases (SPA1, SPB1) and thermal welding phases (SPA2, SPB2) exhibiting a higher heat input into the base material (6) compared to the short circuit welding phases, The control unit (9A) of at least a first of the welding devices (A) is configured to transmit at least one synchronization information (Y) relating to a determined first synchronization event (SEA1) of a short-circuit welding phase (SPA1) of a welding process performed by the first of the welding devices (A) to a control unit (9B) of at least one second of the welding devices (B) via the communication link (11), and the control unit (9B) of the at least one second of the welding devices (B) is configured to time-synchronize the welding process performed by the second of the welding devices (B) with the welding process of the first of the welding devices (A) based on the determined first synchronization event (SEB1) of the short-circuit welding phase (SPB1) of the welding process performed by the second of the welding devices (B) using the received synchronization information (Y).

12. 12. The installation according to claim 11, characterized in that the synchronization information (Y) comprises at least one first phase shift (φ1) between a plurality of the first synchronization events (SEA1, SEB1).

13. 13. The installation according to claim 11 or 12, characterized in that as a first synchronization event (SEA1, SEB1) the time of occurrence of a short circuit during the short circuit welding phase (SPA1, SPB1) or the time of an increase in the feed speed (vA, vB) performed to generate a short circuit or the time of a decrease in the welding current (IA, IB) performed to generate a short circuit is provided.

14. Each of the welding devices (A, B) has a welding wire feeder (14A, 14B) that can be controlled by the control unit (9A, 9B), 14. The installation according to claim 13, characterized in that the control unit (9A, 9B) is configured to perform at least one short circuit cycle (ZKA, ZKB) during the short circuit welding phase (SPA1, SPB1), and during said short circuit cycle (ZKA, ZKB), the welding wire feed unit (14A, 14B) moves the molten electrode (3A, 3B) towards the base material (6) until a short circuit occurs and then moves it in the opposite direction away from the base material (6) after the short circuit occurs.

15. The installation according to claim 14, characterized in that 2 to 10 short circuit cycles (ZKA, ZKB) are capable of being performed during the short circuit welding phase (SPA1, SPB1).

16. the plurality of control parts (9A, 9B) are configured to execute, as a thermal welding phase (SPA2, SPB2), an impulse welding phase having a plurality of successive impulse cycles (ZPA, ZPB) with an impulse frequency (fA, fB), in which a ground current phase having a ground current (IGA, IGB) and an impulse current phase having a high impulse current (IPA, IPB) compared to the ground current (IGA, IGB) alternate with each other; or The installation according to any one of claims 13 to 15, characterized in that the control units (9A, 9B) are configured to execute a spray arc welding phase with a constant welding current as a thermal welding phase (SPA2, SPB2).

17. 17. The installation according to claim 12, wherein the control unit (9A) of at least a first of the welding devices (A) is configured to transmit a piece of synchronization information (Y) relating to a determined second synchronization event (SEA2) of an impulse welding phase (SPA2) of a welding process performed by the first of the welding devices (A) to a control unit (9B) of the at least one second of the welding devices (B) via the communication link (11), and the control unit (9B) of the at least one second of the welding devices (B) is configured to time-synchronize a welding process performed by the second of the welding devices (B) with a welding process of the first of the welding devices (A) based on the determined second synchronization event (SEB2) of the impulse welding phase (SPB2) of a welding process performed by the second of the welding devices (B) using the received synchronization information (Y).

18. 18. The installation according to claim 17, characterized in that the synchronization information (Y) comprises at least one phase shift (φ2) between a plurality of the second synchronization events (SEA2, SEB2).

19. The equipment described in claim 18, characterized in that a characteristic time point during the impulse welding phase (SEA2, SEB2) is provided as a second synchronization event (SEA2, SEB2).

20. The equipment described in Claim 19, characterized in that as a characteristic time during the impulse welding phase (SEA2, SEB2), the time of breaking off of a droplet from the molten electrodes (3A, 3B) or the time of a change in welding parameters (U, I, v) is provided.

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