Apparatus and method for performing a welding process - Patents.com

Abstract

In order to provide a welding apparatus 1 for performing a WIG welding process which allows an improved control of the welding process, it is proposed that a measurement winding 24 is provided in the ignition device 18 and that a second voltage measuring device 25 is provided in the welding apparatus 1 for detecting a measured winding voltage U_MESS at the measurement winding 24 and / or that a measurement winding simulation device is provided in the welding apparatus 1 for simulating a virtual measurement winding 24 of the ignition device 18 and calculating a measured winding voltage U_MESS at this virtual measurement winding 24, and that the control device 5 is configured to use the power supply voltage U_SQ and the measured winding voltage U_MESS detected by the second voltage measuring device 25 or the measured winding voltage U_MESS calculated by the measurement winding simulation device for calculating a WIG arc voltage U_LB_WIG at the WIG arc LB and to use the calculated WIG arc voltage U_LB_WIG for controlling the WIG welding process.

Description

[Technical field]

[0001] The present invention relates to a welding apparatus for performing a WIG welding process on a workpiece. In this case, a welding power source having a first pole and at least one second pole is provided in the welding apparatus. In this case, the first pole is electrically connected to a WIG welding torch including a non-consumable electrode, and the second pole is electrically connectable to the workpiece. In this case, the welding apparatus is provided with an ignition device for non-contact ignition of a WIG arc between the non-consumable electrode and the workpiece, the ignition device having a secondary winding for supplying an ignition voltage to a WIG welding cable. In this case, the welding apparatus is provided with a first voltage measuring device for detecting a source voltage between the first pole and the second pole of the welding power source. In this case, the welding apparatus is provided with a control device configured to use the source voltage for controlling the WIG welding process. Furthermore, the present invention relates to a method for performing a WIG welding process on a workpiece by a non-consumable electrode. [Background technology]

[0002] In the case of conventional WIG (Tungsten Inert Gas) or multi-process machines (Metal Shielding Gas - SMG and WIG), a voltage measuring device is required to measure the arc voltage. Typically, this voltage measuring device is installed in the welding machine and measures the voltage between the connector for the WIG welding torch, possibly the connector for the MSG welding torch and the connector for the ground cable. The measured voltage can be used approximately as the arc voltage and can be used to control the welding process. To ignite the arc contactlessly between the WIG electrode and the workpiece, so-called HF (High Frequency) ignition is often used. In this case, a so-called HF ignition device is integrated in the WIG cable, which generally comprises a coil device that converts a pulsed (for example below 2500 V) voltage into a (high) ignition voltage. The ignition voltage ionizes the gas section between the electrode and the workpiece. As a result, an arc is ignited. In this case, the ignition voltage can reach within the range of several kV to 20 kV depending on the electrode spacing.

[0003] However, since the voltage is measured at these connectors, the measured voltage (used as the arc voltage) includes the voltage drop at the HF igniter and possibly also at the welding cable that is laid up to the welding torch. The coil arrangement of the HF igniter generally has a non-linear inductance-current characteristic and has a very high inductance at small currents in the range of a few amperes. With increasing current, the inductance starts to saturate. Due to the relatively high voltage drop at small currents, this non-linear behavior has a detrimental effect on the voltage measurement. This leads to inaccurate measurement results. As a result, the measured voltage may deviate significantly from the actual arc voltage. Furthermore, this has a detrimental effect on the control of the welding process and possibly also on the weld seam that is produced. Therefore, in order to be able to detect the exact arc voltage during WIG welding, the welding voltage must be detected immediately behind the HF igniter. However, in this case, the problem is that the potential of the ignition voltage may reach 10 kV or more, and therefore the realization of a measuring circuit is not easily possible.

[0004] EP 1021269 discloses a WIG welding device with an HF ignition device and an independent voltage measuring device at the electrode to detect the arc voltage. The HF ignition device is provided with a secondary winding for supplying the HF voltage to the welding cable and a measuring winding integrated in the measuring cable. The measuring winding is used to avoid the HF voltage being applied to the power section of the welding power source. The measuring winding consists of a thin, well-insulated cable which is wound together with the secondary winding. The measuring winding and the secondary winding have the same winding direction and the same number of turns. The same voltage is induced in the measuring winding and the secondary winding, respectively.

[0005] US 2561995 A1 discloses an arc ignition and stabilization system including a coupling transformer. A secondary winding for supplying voltage to a welding circuit, a first primary winding having a relatively small number of turns and a second primary winding having a relatively large number of turns are provided in the coupling transformer. A voltage step-up and voltage step-down behavior for the arc welding circuit is described. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] European Patent No. 1021269 [Patent Document 2] US Patent Publication No. 2,561,995 Summary of the Invention [Problem to be solved by the invention]

[0007] It is an object of the present invention to provide a welding apparatus and method for performing a WIG welding process which allows for improved control of the welding process. [Means for solving the problem]

[0008] According to the present invention, this problem is solved by the fact that a measurement winding is provided in the ignition device, a second voltage measurement device is provided in the welding device for detecting a measurement winding voltage at the measurement winding, and / or a measurement winding simulation device is provided in the welding device for simulating a virtual measurement winding of the ignition device and calculating a measurement winding voltage at the virtual measurement winding, and the control device is configured to use the power supply voltage and the measurement winding voltage detected by the second voltage measurement device or the measurement winding voltage calculated by the measurement winding simulation device to calculate a WIG arc voltage at the WIG arc and to use the calculated WIG arc voltage to control the WIG welding process. As a result, a more accurate calculation of the WIG arc voltage can be performed during WIG welding. As a result, the control of the welding process and therefore the welding quality can be improved.

[0009] Preferably, the control device is configured to calculate a voltage drop on the secondary winding of the ignition device from the measurement winding voltage and a constant proportionality factor, and to calculate the arc voltage from the difference between the supply voltage and the voltage drop, so that the voltage sensed on the measurement winding can be used to simply calculate the WIG arc voltage of interest.

[0010] Preferably, a coil arrangement with a coil core is provided in the ignition device, and the secondary winding and the measurement winding are arranged on the coil core. In this case, the secondary number of turns of the secondary winding and the measurement number of turns of the measurement winding are different. In this case, the measurement number of turns is preferably smaller than the secondary number of turns. In this case, the secondary number of turns is, for example, 5 to 10, particularly preferably 7, and / or the measurement number of turns is preferably at most 2, in particular 1. Preferably, a primary winding with a primary number of turns is arranged on the coil core of the coil arrangement. In this case, the primary number of turns is smaller than the secondary number of turns and is equal to or greater than the measurement number of turns, in which case the primary number of turns is preferably 2 to 4, in particular 2. This provides an ignition device configuration in which a beneficial ratio is fixed between the numbers of turns.

[0011] Preferably, the control device is configured to use a transformation ratio between the number of secondary turns and the number of measured turns as a proportionality factor for calculating the voltage drop of the secondary winding, so that the WIG arc voltage can be calculated depending on the configuration of the ignition device.

[0012] It may further be advantageous if the welding device is adapted to perform an MSG welding process, in which case the first pole of the welding power source is connected or connectable to an MSG welding torch, preferably comprising a consumable electrode, via a third connector. In addition to WIG welding processes, MIG / MAG welding processes can thus also be performed by the welding device. Thus, a welding device is provided which is very flexibly usable.

[0013] An analog or digital measuring circuit may be provided in the control device to calculate the WIG arc voltage. In this case, in particular, a filter is provided in the measuring circuit to filter at least one voltage signal. By calculating the WIG arc voltage based on a comparatively small measuring winding voltage according to the invention, the measuring circuit can be configured for smaller potentials. This allows the measuring circuit to be constructed more simply and requires a narrower measuring range, so that a more accurate calculation of the measuring winding voltage, i.e. of the WIG arc voltage, can be performed.

[0014] It may be further advantageous that the control device is configured to store a welding current circuit model including a model of a WIG welding cable and / or a model of an MSG welding cable and / or a model of a ground cable and / or a model of a workpiece, and to calculate a voltage drop in the WIG welding cable and / or a voltage drop in the MSG welding cable and / or a voltage drop in the ground cable M and / or a voltage drop in the workpiece W by the welding current circuit model and to take the calculated voltage drops into account when calculating the WIG arc voltage at the WIG arc and / or the MSG arc voltage at the MSG arc. In this case, the model of the WIG welding cable and / or the model of the MSG welding cable preferably includes at least one ohmic resistance and at least one inductance. This allows the target WIG arc voltage to be calculated even more accurately, since possible voltage drops can be taken into account.

[0015] Preferably, the welding device may be provided with an additional auxiliary power source for generating an auxiliary voltage for re-igniting the WIG arc during the WIG welding process, in particular during an AC welding process, and the control device may be configured to detect the re-ignition of the WIG arc based on the calculated WIG arc voltage and to shut down the auxiliary power source upon detection of the WIG arc. In this case, the re-ignition of the WIG arc is preferably detected based on a preset voltage threshold. Thus, the arc voltage calculated according to the invention may be advantageously used as an indicator for identifying the WIG arc and then shutting down the auxiliary power source. Thus, an undesired overshoot of the welding current may be avoided during a polarity reversal process during an AC welding process. Thus, an unpleasant loud noise may be avoided.

[0016] Furthermore, the problem is solved by a method according to claim 11. Preferred embodiments of the method are set forth in the dependent claims 12-15.

[0017] The invention will now be described in more detail with reference to the following figures 1 to 8, which show, by way of example, schematic and non-limiting example, preferred configurations of the invention. [Brief description of the drawings]

[0018] [Figure 1] 1 shows a welding device for performing WIG welding on a workpiece. [Diagram 2] 1 shows a schematic diagram of an ignition device. [Diagram 3] 1 shows the L / I characteristic curve of the secondary winding of the ignition device. [Figure 4] FIG. 2 is an electrical equivalent circuit diagram of a welding current circuit of the welding device according to FIG. 1. [Diagram 5] 4 shows the time course of electric welding parameters during a polarity reversal step of an AC welding process. [Figure 6] 1 illustrates a current-voltage characteristic curve of an auxiliary power supply. [Figure 7] 1 shows the time evolution of electric welding parameters during re-ignition of a WIG arc during an AC welding process under the use of an auxiliary power source according to the prior art. [Figure 8] 4 illustrates the time course of electric welding parameters during re-ignition of a WIG arc during an AC welding process under the use of an auxiliary power supply according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] FIG. 1 illustrates the configuration of a welding device 1 according to the invention for performing a welding process. The illustrated welding device 1 is configured at least for performing a welding process with a non-consumable electrode, i.e. the known WIG (WIG = tungsten inert gas) welding. In this case, a so-called tungsten electrode E1 or a WIG electrode E1 is used as the non-consumable electrode. Optionally, however, as shown by dashed lines in FIG. 1, the device 1 may also be configured for performing a MIG / MAG welding process or a conventional metal-shielded gas welding (MSG) process with a molten MSG electrode E2 as the welding wire. Thus, a MIG / MAG welding process or a WIG welding process can be performed by the welding device 1. In this case, both of these different welding processes are usually not performed simultaneously. The WIG electrode E1 is arranged in a WIG welding torch 6, and the optional MSG electrode E2 (welding wire) is arranged in a MSG welding torch 14. The illustrated welding device 1 is configured for performing a manual welding process. In this welding process, the WIG welding torch 6 (or the MSG welding torch 14) is manually operated by a welder. However, a welding robot (not shown) may of course be provided. The WIG welding torch 6 and / or the MSG welding torch 14 can be moved automatically by the welding robot according to a preset movement sequence. The use of a welding robot is known, so this will not be described in detail any further. The main part of the present invention relates to WIG welding. Therefore, in the following, no detailed reference will be made to MSG welding.

[0020] As is known, the illustrated welding device 1 comprises a welding power source 2, which may for example be provided on a mobile or stationary welding machine 3. The required power can be supplied to the welding power source 2 from a power source Q, for example a three-phase AC power source, via suitable electrical terminals 4. As is known, the welding power source 2 has a first pole P1 and a second pole P2. The first pole P1 is electrically connected to a first connector AB1 and the second pole P2 is electrically connected to a second connector AB2. A WIG welding torch 6 comprising a WIG electrode E1 can be connected to the first connector AB1 by means of a welding cable 7. The second connector AB2 can be connected via a ground cable M to a workpiece W, on which the welding process has to be performed.

[0021] Furthermore, if the welding station 1 is also configured for carrying out an MSG welding process, then similar to the first connector AB1 for the WIG welding torch 6, a third connector AB3 is also provided for connecting an MSG welding torch 14. In FIG. 1, the third connector AB3 is arranged, for example, on the welding machine 3. Within the scope of the present invention, these connectors AB1, AB2, AB3 refer to both removable and fixed, i.e. non-removable connections. However, in general, removable, in particular standardized connectors are used as connectors AB1, AB2, AB3.

[0022] As shown by the positive and negative signs in FIG. 1, the first pole P1 of the welding power source 2 is generally configured as a positive pole and the second pole P2 of the welding power source 2 is generally configured as a negative pole. In principle, however, the opposite pole or a reversal of the poles P1, P2 is also possible by the welding power source 2 during operation of the welding device 1. As is known, the welding current required for the welding process is supplied from the welding power source 2 via a welding cable 7 to the WIG welding torch 6 and to the WIG electrode E1 provided on said WIG welding torch 6. As is known, the welding cable 7 can be laid in a hose packet 8. In addition to the welding cable 7, further cables and / or pipes and / or hoses that are necessary or useful for the welding process can also be provided in said hose packet 8.

[0023] To perform the WIG welding process, a first potential is applied to the workpiece W (usually negative in the case of DC-WIG welding) by means of an earth cable M, and a second potential is applied to the WIG electrode E1 (usually positive in the case of DC-WIG welding) via a welding cable 7. In contrast, in the case of AC-WIG welding, the polarity alternates between the workpiece and the electrode E1 depending on the frequency of the welding current. Said polarity alternation is performed in an inverter 29 by means of semiconductor technology. In the case of a polarity reversal process (polarity alternation), the arc is temporarily extinguished during the zero passage (welding current I=0). To make it possible to re-ignite the arc in the case of AC-WIG welding, an additional voltage is applied between the workpiece and the electrode E1 by means of an auxiliary voltage source 27. Typically, such an additional auxiliary voltage is between 90V and 500V. After ignition of the arc LB_WIG between the free end of the WIG electrode E1 and the welding position 12, the welding current path is closed and the welding current I is passed through. Due to the non-consumable electrode E1, to perform the WIG welding process it may furthermore be necessary (unlike MIG / MAG welding with a fusible electrode E2) to supply a separate additive Z to the welding position 12. This additive can be supplied either manually or mechanically by a feed device 13a. The additive Z and a part of the workpiece W are melted by the arc LB_WIG. This forms the weld seam N.

[0024] In order to shield the molten pool against the surroundings and thus avoid oxidation, a (active or inert) shielding gas SG is often also used to carry out the welding process. The shielding gas SG can be supplied to the WIG welding torch 6 (and optionally to the MSG welding torch 14) via a suitable shielding gas pipe 10, for example, from a suitable shielding gas container 9. The shielding gas pipe 9 can also be laid, for example, in the hose packet 8 towards the WIG welding torch 6 (or in the hose packet 16 towards the MSG welding torch 14). However, an independent supply of the shielding gas SG is naturally also possible. In this case, a pressure regulator 11 can be provided, for example as a pressure regulating valve arranged in the shielding gas container, to control the flow rate of the shielding gas SG. Furthermore, possibly, a cooling medium can be supplied via the hose packet 8 to cool the WIG welding torch 6 (and possibly, a cooling medium can be supplied via the hose packet 16 to cool the MSG welding torch 14).

[0025] Furthermore, a control device 5, which may be configured, for example, as suitable hardware and / or software, is provided in the welding device 1. The control device 5 is connected to the welding power source 2 and is configured to control the welding power source 2 in order to perform a desired welding process. The control device 5 controls the welding power source 2 during the welding process in order to adjust certain welding parameters, e.g. electrical welding parameters such as the welding voltage U, the welding current I, the frequency f of the welding current I, etc. Furthermore, the control device 5 may also control other units present in the welding device 1 in order to adjust non-electrical welding parameters. For example, the control device 5 may control a pressure regulator 11 of the shielding gas container 9 in order to open-loop or closed-loop control the amount of shielding gas supplied to the welding position 12.

[0026] The control device 5 can also control the feed device 13a for the optional additive Z for open-loop or closed-loop control of the feed rate of the additive Z. The control device 5 can also control the optional feed device 13b at the MSG welding torch 14. As is known, the welding wire can be fed to the feed devices 13a / 13b, for example, from a wire store 13c. In FIG. 1, the feed device 13a / 13b including the wire store 13c is shown here, for example, as an independent unit, but the feed device 13a / 13b can naturally also be part of the welding machine 3. In general, the welding parameters to be adjusted, which mainly depend on the welding process to be performed, can be considered as known. Depending on the welding process to be performed, the welding parameters can naturally be changed qualitatively and quantitatively. The control device 5 can, for example, adjust the time course of various welding parameters (for example, welding current I, welding voltage U, frequency f of the welding current I, etc.) depending on the pre-set welding process. To this end, the control device 5 may for example comprise one or more suitable controllers for controlling one or more welding parameters to preset target values.

[0027] The welding device 1, e.g. the welder 3, may be provided with a user interface 15 which appropriately communicates with the control device 5. A user may perform certain adjustments via this user interface 15. For example, a certain welding process may be selected and certain welding parameters may be selected and / or adjusted. For example, a predefined welding program with predetermined certain welding parameters may also be stored in the control device 5 which may be selected by the user via the user interface 15. If a welding robot is provided in the welding device 1, the control device 5 may for example communicate with a robot control device in order to synchronize the welding process with the movement of the WIG welding torch 6 (or the MSG welding torch 14). The communication may for example be performed by a higher-level control device (not shown).

[0028] The welding apparatus 1, here the welding machine 3, is further provided with a first voltage measuring device 17 for detecting a current source voltage U_SQ between the first pole P1 and the second pole P2 of the welding power source 2. The first voltage measuring device 17 may be configured as an independent unit, for example as a voltmeter, as shown in Fig. 1, but may also be suitably integrated into the control device 5. The control device 5 is configured to use the current source voltage U_SQ for an open-loop or closed-loop control of the welding process. For example, the control device 5 can calculate one or more control parameters depending on the obtained current source voltage U_SQ and can control the welding power source 2 by means of said one or more control parameters.

[0029] Conventionally, the control device 5 uses the current source voltage U_SQ, for example approximately, as a guide for the target arc voltage U_LB at the arc LB_WIG, which is used, for example, to adjust the arc voltage U_LB as actual value. As setpoint value, for example, a welding voltage U or the time course of the welding voltage U, which is preset depending on the desired welding process, can be used. A suitable controller of the control device 5 can calculate an adjustment variable as control parameter from the actual value and the setpoint value according to a predefined adjustment rule. The control device 5 can then control the welding power source 2 with the calculated adjustment variable, for example, to adjust the setpoint values ​​of the welding voltage U and / or the welding current I and / or variables derived therefrom.

[0030] Furthermore, the welding device 1 is provided with a (high frequency) ignition device 18 for generating an ignition voltage U_Z in order to ignite an arc LB_WIG between the non-consumable electrode E1 and the workpiece W in a non-consumable manner. In this case, the ignition means re-ignition during the welding process. The ignition device 18 is arranged on the cable between the first pole P1 of the welding power source 2 and the WIG welding torch 6 or the WIG electrode E1. In the illustrated example, the ignition device 18 is arranged on the welding machine 3 between the welding power source 2 and the first connector AB1. However, basically, the ignition device 18 may also be arranged between the first connector AB1 and the WIG welding torch 6, i.e. outside the welding machine 3. In this case, the first voltage measuring device 17 may directly detect the current source voltage U_SQ between the first connector AB1 and the second connector AB2.

[0031] In Fig. 2, the ignition device 18 is shown in a simplified form. The ignition device 18 is provided with a coil arrangement 20 having a coil core 21. A primary winding 22, a secondary winding 23 and, according to a preferred embodiment of the invention, an additional measurement winding 24 are arranged on the coil core 21. In particular, the primary winding 22 is connected to an independent ignition voltage source 19, which can be supplied with the necessary power, for example, from the power source Q shown in Fig. 1. Furthermore, according to the invention, a second voltage measuring device 25 is provided for detecting the measurement winding voltage U_MESS at the measurement winding 24. The secondary winding 23 is arranged between the first pole P1 of the welding power source 2 and the WIG electrode E1, for example between the first pole P1 and the first connector AB1 in Fig. 1. The primary winding 22 has a constant primary winding number N1 and the secondary winding 23 has a constant secondary winding number N2, which is equal to or greater than the primary winding number N1. The measurement winding 24, which will be described in more detail below, has a fixed measurement winding number N_MESS that is less than or equal to the primary winding number N1.

[0032] Therefore, the coil device 20 has the function of a transformer. When a pulse voltage U_PULS is applied from the ignition voltage source 19 to the primary winding 22, a magnetic flux is generated in the common coil core 21. The time-varying magnetic flux induces an ignition voltage U_Z in the secondary winding 23, which is proportional to the number of secondary turns N2 of the secondary winding 23. Thus, for example, the ratio between the ignition voltage U_Z and the pulse voltage U_PULS corresponds to the ratio between the number of secondary turns N2 and the number of primary turns N1. That is,

[0033]

number

[0034]

number

[0035] The ignition voltage U_Z is input to the welding cable 7. As a result, the gas is ionized between the WIG electrode E1 and the workpiece W and an arc LB_WIG is ignited. For the ionization of the gas section, a high voltage must be generated, as known, for example in the range of 5 kV to 15 kV, depending on the distance between the WIG electrode E1 and the workpiece W. After the ignition of the arc, the ignition voltage U_Z is further switched off and the welding process is started or continued. According to a preferred configuration of the ignition device 18, the number of secondary turns N2 is, for example, 5 to 10, in particular 7, the number of primary turns N1 is, for example, 2 to 4, in particular 2, and the number of measuring turns N_MESS is at most 2, in particular 1. With a pulse voltage U_PULS=2600 V, the number of secondary turns N2=7, the number of primary turns N1=2 and the number of measuring turns N_MESS=1, for example an ignition voltage U_Z=9100 V can be generated, and the measuring winding voltage U_MESS is U_MESS=1300 V according to the above relationship. The ignition device 18, in particular the secondary winding 23, acts as a damping choke in the direction of the welding power source 2. As a result, the high voltage U_Z cannot damage sensitive power electronics and sensors (e.g. the first voltage measuring device 17).

[0036] Due to the above-mentioned problems with the voltage drop at the ignition device 18, in particular at the secondary winding 23, the current source voltage U_SQ, when used to control the welding process, conventionally produces unsatisfactory results. This is due to the non-linear inductance characteristic of the ignition device 18, in particular at the secondary winding 23. For the purpose of this explanation, a typical characteristic curve is shown in FIG. 3. In this case, the differential inductance of the secondary winding 23 is plotted against the current I. It can be seen that the inductance L assumes high values ​​in the range of more than 200 to 500 μH at relatively small currents, for example 1 to 3 amperes, and that at higher currents the inductance begins to saturate. As a result, at low (welding) currents I in the WIG welding cable 7, a relatively high voltage drop occurs at the secondary winding 23. As a result, the current source voltage U_SQ detected by the first voltage measuring device 17 differs, in some cases, significantly from the actual arc voltage U_LB at the arc LB_WIG. This is detrimental to the control of the welding process.

[0037] In Fig. 4, an equivalent circuit diagram of the welding current circuit of the welding device 1 according to Fig. 1 is shown. In this case, the welding power source 2 may include an auxiliary power source 27 and an inverter 29 (not shown). The primary winding 22 of the ignition device 18 is shown here as inductance L1, the secondary winding 23 as inductance L2 and the measurement winding 24 as inductance L_MESS. The WIG welding cable 7 is modeled by an ohmic resistance R_WIG and an inductance L_WIG. Similarly, the WIG arc LB_WIG is modeled by an ohmic resistance R_LB_WIG. The optional MSG welding cable 16 is modeled by an ohmic resistance R_MSG and an inductance L_MSG, and similarly the MSG arc LB_MSG is modeled by an ohmic resistance R_LB_MSG.

[0038] Based on the position of the voltage measuring device 17 in Fig. 4, it can be recognized that the detected current source voltage U_SQ does not only include the voltage drop in the WIG welding cable 7, but also in particular the voltage drop in the secondary winding 23 of the ignition device 18, here the inductance L2. However, in order to control the welding process as precisely as possible, the arc voltage U_LB_WIG at the arc LB is of value. It therefore turns out that the use of the source voltage U_SQ to control the welding process may lead to unsatisfactory results in some cases.

[0039] In order to avoid such unsatisfactory results, it is indeed possible, as shown in FIG. 4 based on the dashed voltage measuring device 26, to measure the arc voltage U_LB_WIG closer to the WIG arc LB_WIG, for example directly behind the ignition device 18. However, it is not easily possible to measure the arc voltage U_LB_WIG directly, since conventional measuring circuits are not designed for high voltages in the range of the ignition voltage U_Z. On the one hand, such high voltages can cause damage to the measuring circuit. On the other hand, a measurement as accurate as possible of the arc voltage U_LB_WIG during the welding process (i.e. after the ignition has already been carried out), which can be in the range of several hundred volts, is not possible, since the measuring range for the ignition voltage U_Z must be designed for an ignition voltage U_Z in the range of several kV as described above.

[0040] Therefore, according to a preferred embodiment of the invention it is proposed that a measured winding voltage U_MESS at the measurement winding 24 is calculated by the second voltage measuring device 25 and that the control device 5 uses the supply voltage U_SQ and the measured winding voltage U_MESS to calculate the arc voltage U_LB_WIG of the arc LB_WIG. Instead of the supply voltage U_SQ, said calculated arc voltage U_LB_WIG can then be used for controlling the welding process.

[0041] According to another embodiment of the invention, instead of the measurement winding 24 arranged in the ignition device 18, a measurement winding simulation device (not shown) is provided to simulate a virtual measurement winding 24 of the welding device 1. In this case, the second voltage measurement device 25 can be omitted and the measurement winding voltage U_MESS at the virtual measurement winding 24 can be calculated by the measurement winding simulation device. The control device 5 then calculates the arc voltage U_LB_WIG of the arc LB_WIG. The supply voltage U_SQ and the simulated measured winding voltage U_MESS can be used.

[0042] The measurement winding simulation device is configured to simulate a "real" measurement winding 24, which does not exist physically, by means of a virtual measurement winding 24 and to determine from the simulation a measurement winding voltage U_MESS at the virtual measurement winding 24. In this case, the simulation is carried out in particular on the basis of the current flowing through the secondary winding 23. In a simple configuration, the measurement winding simulation device may for example comprise a characteristic curve, in which the measurement winding voltage U_MESS is plotted as a function of the current at the secondary winding 23. However, the measurement winding simulation device may also comprise a characteristic curve, in which the measurement winding voltage U_MESS is plotted as a function of the current at the secondary winding 23 and further input variables. The characteristic curve or the cause and effect diagram may for example be implemented in the control device 5 as a look-up table. The characteristic curve or the cause and effect diagram may be calculated from measurements previously performed on a real ignition device 18, which includes the "real" measurement winding 24. However, in order to analyze the measurement winding voltage U_MESS on the basis of physical relationships, the measurement winding simulation device may also comprise a physical model of the "real" measurement winding 24.

[0043] Naturally, however, the measurement winding simulation device may also be provided in conjunction with the "real" measurement winding 24 and the second voltage measurement device 25. This allows, for example, the plausibility of the measurement winding voltage U_MESS calculated by the second voltage measurement device 25 to be checked or the measurement winding voltage U_MESS to be calculated redundantly. The measurement winding simulation device may, for example, be integrated into the welding device 1 as separate hardware and / or software and be able to communicate appropriately with the control device 5. In particular, however, the measurement winding simulation device is integrated into the control device 5.

[0044] In this case, in particular, the voltage drop U2 of the ignition device 18, in particular the voltage drop U2 on the secondary winding 23, is calculated by the control device 5 from the measured winding voltage U_MESS detected by the second voltage measuring device 25 or the measured winding voltage U_MESS simulated by the measuring winding simulation device and a constant proportionality factor φ, and the arc voltage U_LB_WIG at the WIG arc LB_WIG is calculated as

[0045]

number

[0046] As already explained, the primary number of turns N1 of the primary winding 22, the secondary number of turns N2 of the secondary winding 23 and the measurement number of turns N_MESS of the measurement winding 24 are different from each other. In this case, the measurement number of turns N_MESS is in particular smaller than the primary number of turns N1, which in turn is smaller than the secondary number of turns N2. In a preferred embodiment, the measurement number of turns N_MESS=1, the primary number of turns N1=2 and the secondary number of turns N2=7. Preferably, the control device 5 is

[0047]

number

[0048] However, the WIG arc voltage U_LB_WIG calculated according to the invention further includes the voltage drop in the WIG welding cable 7 and therefore corresponds to the voltage detected by the voltage measuring device 26 shown in dashed line in FIG. 4. It may therefore be advantageous if a welding current circuit model of the welding current circuit is stored in the control device 5 in order to calculate at least the voltage drop in the WIG welding cable 7 and take it into account when calculating the WIG arc voltage U_LB_WIG. In this case, in particular, the welding current circuit model includes at least a model of the WIG welding cable and possibly also a model of the MSG welding cable. In particular, these models include at least one ohmic resistance R, here R_WIG, R_MSG, respectively, and at least one inductance L, here L_WIG, L_MSG. This allows the control device 5 to calculate these voltage drops and take them into account when calculating the WIG arc voltage U_LB_WIG or possibly the MSG arc voltage U_LB_MSG.

[0049] Furthermore, in order to calculate the voltage drop in the ground cable M and / or the workpiece W, the welding current circuit model may include a model of the ground cable M and / or a model of the workpiece W, which can be taken into account when calculating the arc voltage U_LB_WIG or possibly the MSG arc voltage U_LB_MSG. Naturally, the modeling of the welding current circuit in FIG. 4 is shown as an example only and in a simplified manner. Naturally, the welding current circuit can be configured more complexly in order to depict as accurately as possible the actual configuration of the welding device 1. For example, model parameters of the welding current circuit model may be changeable and can be adjusted, for example by a user, for example via the user interface 15.

[0050] The advantage of the inventive calculation of the WIG arc voltage U_LB_WIG is that the measurement circuit only needs to be designed for the potential at the measurement winding and does not have to be adapted to the potential of the secondary winding 23, which as mentioned above is in the range of several kV and can reach, for example, 10 kV. With a suitable design of the ignition device 18 (for example N2=7, N_MESS=1), the maximum measurement winding voltage U_MESS at the ignition of the WIG arc LB_WIG and the ignition voltage U_Z=9100 V can be limited, for example, to 1300 V. In normal operation during the welding process (after ignition or between re-ignitions), the welding voltage U at the WIG welding cable can reach, for example, 437.5 V. Thus, the measurement winding voltage U_MESS can reach 62.5 V according to a transformation ratio of j=7 and the voltage at the primary winding 22 with the number of primary turns N1=2 can reach, for example, 125 V.

[0051] Due to the potential at the measuring winding 24, for example 1300 V, being much smaller than the ignition voltage U_Z at the secondary winding 23 during ignition of the WIG arc LB_WIG, a relatively simply constructed circuit with a narrower measurement range can be provided, for example in the control device 5, for calculating the WIG arc voltage U_LB_WIG. In this case, the measuring circuit can be configured, for example, as a digital or analog measuring circuit. In the case of a digital measuring circuit, the signal of the supply voltage U_SQ and the signal of the measuring winding voltage U_MESS are digitized by an analog / digital (A / D) converter and subsequently digitally subtracted, for example by a suitable subtractor. In this case, the calculation of the voltage drop U2 from the measuring winding voltage U_MESS can be carried out before or after the digitization.

[0052] However, preferably, the calculation of the WIG arc voltage U_LB_WIG can also be performed by an analog measuring circuit, which may for example comprise several operational amplifiers (OPVs), subtractors and filters. As is known, OPVs have a maximum input current and / or input voltage that is preset by the manufacturer. In order not to exceed these preset input currents and / or input voltages, as is known, one or more ohmic resistors, so-called compensation resistors, can be connected in series with the respective inputs of an OPV. Due to the detection according to the invention of the measuring voltage U_MESS at the measuring winding 24, smaller compensation resistors are required due to the smaller potential at the measuring winding 24, which has the advantage that the analog measuring circuit can be constructed more simply. The construction and functioning of such measuring circuits are basically known and will not be described in further detail here.

[0053] FIG. 5 shows the time course of the welding parameters welding voltage U and welding current I during a polarity reversal process of an alternating current (AC) welding process. The advantages of the invention are explained again on the basis of the time course. As is known, in the case of AC welding, the polarity of the welding current I alternates between positive and negative during the welding process, as shown by the solid line with circles. The source voltage U_SQ detected by the first voltage measuring device 17 is shown by a solid line without marks. The voltage drop U2 calculated by the secondary winding 23 of the ignition device 18 on the basis of the measured winding voltage U_MESS (detected from the voltage measuring device 25) is shown by a solid line with triangles. The WIG arc voltage U_LB_WIG′ detected by the measuring device 26 (see FIG. 4) is shown by a solid line with crosses, and the WIG arc voltage U_LB_WIG calculated according to the invention is shown by a dashed line. In this case, the measured WIG arc voltage U_LB_WIG′ is shown exclusively for comparison purposes and is not actually measured due to the disadvantages already explained in detail. Within the time range T_Z, the arc LB restrikes as evidenced by a steep drop in the measured WIG arc voltage U_LB_WIG'.

[0054] It is easily discernible on the basis of the time course of FIG. 5 that during the polarity reversal process, due to small welding currents I (e.g. 1-5 A) in the zero crossing region, the source voltage U_SQ differs significantly from the measured WIG arc voltage U_LB_WIG'. This is due to the non-linear relationship between the inductance I2 of the secondary winding 23, the welding current I and the resulting voltage drop U1, as already explained on the basis of the characteristic curve of FIG. 3. In contrast, for numerically larger currents I, e.g. greater than 10 A, the non-linear characteristic curve of the secondary winding 23 is much smaller, because the inductance I2, i.e. the voltage drop U2, is much smaller due to saturation. As shown in FIG. 5, it was confirmed during the measurement that the deviation Δ_MESS between the measured source voltage U_SQ and the measured WIG arc voltage U_LB_WIG' correlates very well with the voltage drop U2 in the secondary winding 23.

[0055] As can be seen on the basis of the dashed line, the difference between the measured source voltage U_SQ and the calculated voltage drop U2 therefore correlates very well with the measured WIG arc voltage U_LB_WIG'. The arc voltage U_LB_WIG thus calculated can be used as the critical WIG arc voltage U_LB_WIG for controlling the welding process. In this case, as described above, the WIG arc voltage U_LB_WIG is calculated on the basis of the measured winding voltage U_MESS at the measuring winding 24, detected by the second voltage measuring device 25, and the proportionality factor φ. In this case, the proportionality factor φ corresponds in particular to the transformation ratio i.

[0056] According to another preferred embodiment, an additional auxiliary power supply 27 is provided in the welding device 1 for generating an auxiliary voltage U_H. In this case, the auxiliary power supply 27 can be configured as an (ideal) voltage source or as an (ideal) current source. In this case, the auxiliary voltage U_H is used for re-igniting the WIG arc LB_WIG during the WIG welding process being performed. Typically, such an auxiliary power supply 27 is used during an AC welding process for generating a relatively high welding voltage in the range of 90V-500V in the welding current circuit for a short period of time at the zero crossing of the welding current I during the polarity reversal process. This allows or supports the re-ignition of the WIG arc LB_WIG. After the re-ignition of the WIG arc LB_WIG, the auxiliary voltage is switched off again as quickly as possible.

[0057] As is known, a welding transformer (not shown) can be provided in the welding power source 2 for generating the welding voltage required for the welding process, within the scope of the present description, for example for generating a power supply voltage U_SQ between the first pole P1 and the second pole P2. In this case, the auxiliary power source 27 can be configured, for example, as an additional winding with a different transformation ratio of the welding transformer. An auxiliary voltage U_H, which is comparatively higher than the welding voltage U or the power supply voltage U_SQ, can be generated by said transformation ratio. After a rectifier and, for example, a switchable IGBT (insulated gate bipolar transistor) or MOSFET (metal oxide semiconductor field effect transistor), the auxiliary voltage U_H can be supplied, for example, to the connectors AB1, AB2 of the welding device 1. A current-voltage characteristic curve of the auxiliary power source 27 is illustrated by way of example in FIG. 6. In said characteristic curve, an approximately linear relationship is obtained between the auxiliary voltage U_H and the auxiliary current I_H. The maximum auxiliary voltage U_Hmax at an auxiliary current of I_H=0 can reach, for example, in the range of 270 V, and the maximum auxiliary current I_Hmax at an auxiliary voltage U_H=0 can reach, for example, in the range of 300 A or more. The configuration and function of such an auxiliary power source 27 is basically known in the prior art, so a detailed description thereof will be omitted. In FIG. 1, the auxiliary power source 27 is shown only diagrammatically as part of the welding power source 2.

[0058] FIG. 7 shows a graph of the time course of the welding current I_WIG, the arc voltage U_LB_WIG at the WIG arc and the auxiliary voltage U_H during the polarity reversal process of the AC welding process under the use of the auxiliary power source 27. This illustrated time course corresponds to the prior art. The solid line without marks shows the arc voltage U_LB_WIG at the WIG arc LB_WIG, the solid line with cross marks shows the auxiliary current I_H of the auxiliary power source 27, and the solid line with circles shows the welding current I_WIG. Within the illustrated auxiliary energy time range T_H, the auxiliary power source 27 is in operation. In this case, the arc is still not ignited. That is to say, a very large ohmic resistance is present in the welding current circuit. The auxiliary energy time range T_H can reach, for example, within the range of 250 μs. Thus, within the auxiliary energy time range T_H, the arc voltage U_LB_WIG approximately corresponds to the maximum auxiliary voltage U_Hmax of the auxiliary power source 27, for example, within the range of 270 V.

[0059] At the end of the auxiliary energy time range T_H, within the (re)ignition time range T_WZ shown here, the arc LB_WIG is ignited. This is recognizable by a very steep drop in the arc voltage U_LB_WIG, for example below 30 V. At the same time, the welding current I_WIG and the auxiliary current I_H rise steeply. The task is to interrupt the auxiliary voltage U_H as quickly as possible after the ignition of the arc LB_WIG, by switching off the auxiliary power supply 27. Conventionally, a constant (re)ignition current level I_WZ is used to detect the arc LB_WIG, and the auxiliary power supply 27 is switched off when the ignition current level I_WZ is reached. FIG. 7 illustrates an ignition current level I_WZ, which can reach, for example, 35 A. The welding current I_WIG can be detected, for example, by a current measuring device 28 shown in Figures 1 and 4, and the control device 5 can shut down the auxiliary power supply depending on the detected welding current I_WIG and the preset ignition current level I_WZ.

[0060] In FIG. 7 it can be seen that, despite the selected interruption criterion of I_Z=35 A to, for example, 42 A, the welding current I_WIG overshoots with a very high current rise rate. This steep current rise causes an acoustically very loud polarity reversal step, which is generally perceived as unpleasant by the welder. This relationship can be derived from the U / I characteristic curve of the auxiliary power supply 27 (FIG. 6). In FIG. 6 it can be seen that for a low auxiliary voltage U_H, for example of 20 V, a very high auxiliary current I_H, for example of 285 A, occurs after the ignition of the arc LB_WIG, which causes a steep current rise of the welding current I_WIG. It is therefore evident that it is beneficial to detect the ignition of the arc LB_WIG as early as possible in order to be able to shut down the auxiliary power supply 27 as quickly as possible. However, it is not advisable to further reduce the ignition current level I_WZ to a smaller value, since this would in some cases not ensure a stable (re)ignition of the arc LB_WIG.

[0061] Therefore, according to a preferred embodiment of the invention, the welding current I_WIG is no longer used to detect the arc LB_WIG, but the arc voltage U_LB_WIG calculated according to the invention, as explained on the basis of Fig. 8. Fig. 8 shows, similarly to Fig. 7, a graph of the welding current I_WIG (solid line with circles), the arc voltage U_LB_WIG at the WIG arc (solid line without marks) and the auxiliary current I_H of the auxiliary power supply 27 over time during the polarity reversal phase (solid line with crosses) of the AC welding process. Similarly, the arc LB_WIG is (re)ignited within the (re)ignition time range T_WZ. This is recognizable by a steep drop in the arc voltage U_LB_WIG.

[0062] In this case, unlike the prior art according to FIG. 7, the (re)ignition of the arc voltage LB_WIG is detected based on the arc voltage U_LB_WIG of the arc LB_WIG calculated (based on the measured winding voltage U_MESS) and no longer based on the welding current I_WIG. The arc voltage U_LB_WIG can be used as a more accurate indicator for ionizing the gas section between the WIG electrode E1 and the workpiece W. The control device 5 can detect the (re)ignition of the WIG arc LB_WIG based on a (re)ignition voltage level U_WZ, which is, for example, preset and can be in the range of, for example, 10 V to 113 V. In FIG. 8, the ignition voltage level U_WZ=45 V is illustrated as a dashed horizontal line. It is clear that the auxiliary power supply 27 is detected in this case already much earlier, i.e. at a clearly smaller welding current I_WIG of, for example, 3.5 A. This prevents a large overshoot of the welding current I_WIG as in FIG. 7 from occurring. Thereby, the polarity reversal process is no longer perceived as unpleasant by the welder. Instead of detecting the restrike of the WIG arc LB_WIG based on a preset ignition voltage level U_WZ, for example a preset time gradient dU_LB_WIG / dt may be used as a requirement for detecting the restrike of the WIG arc LB_WIG.

[0063] However, in some cases, the preset ignition voltage level U_WZ may be reached or exceeded, for example in an undesired manner. As a result, the ignition voltage level U_WZ may be insufficient as an independent indicator for re-ignition of the WIG arc LB_WIG. This situation may arise, for example, when a self-induced voltage is induced in the welding current circuit. This may be, for example, a situation in which the WIG welding cable 7 and / or the ground cable M are crossed with a welding cable (or another current-carrying cable) of another welding device or are arranged spatially close to said cable, for example partially parallel. In this case, a voltage, a so-called self-induced voltage, may be induced in the WIG welding cable 7 and / or the ground cable M of the welding device 1 under consideration, due to the time-varying current in said other welding cable (or another current-carrying cable). If this self-induced voltage reaches or exceeds the preset ignition voltage level U_WZ, a re-ignition of the WIG arc LB_WIG may be erroneously detected, without any re-ignition of the WIG arc LB_WIG actually occurring at all. This can be advantageously avoided if, in addition to the preset ignition voltage level U_WZ, a preset (re-)ignition current level I_WZ of the auxiliary power supply 27 (as explained with reference to Fig. 7) is used, whereby the ignition current level I_WZ can be used to verify the re-ignition of the WIG arc LB_WIG. The present application relates to the invention described in the claims, but may also include the following configurations as other aspects. 1. A welding device (1) for performing a WIG welding process on a workpiece (W), A welding power source (2) having one first pole (P1) and at least one second pole (P2) is provided in the welding device (1), The first pole (P1) is electrically connected to a WIG welding torch (6) including a non-consumable electrode (E1), and the second pole (P2) can be electrically connected to the work (W); In the welding device (1), an ignition device (18) for igniting a WIG arc (LB_WIG) in a non-contact manner is provided between the non-consumable electrode (E1) and the work (W), and the ignition device (18) has a secondary winding (23) for supplying an ignition voltage (U_Z) to a WIG welding cable (7); The welding device (1) includes a first voltage measuring device (17) provided between the first pole (P1) and the second pole (P2) of the welding power source (2) for detecting a power source voltage (U_SQ), The welding apparatus (1) is provided with a control device (5) configured to use the power supply voltage (U_SQ) to control the WIG welding process. In the welding apparatus (1), a measurement winding (24) is provided in the ignition device (18) and a second voltage measurement device (25) is provided in the welding device (1) for detecting a measurement winding voltage (U_MESS) at the measurement winding (24); and / or a measurement winding simulation device is provided in the welding device (1) for simulating a virtual measurement winding (24) of the ignition device (18) and for calculating a measurement winding voltage (U_MESS) at the virtual measurement winding (24); and The control device (5) is configured to use the power supply voltage (U_SQ) and the measured winding voltage (U_MESS) detected by the second voltage measurement device (25) or the measured winding voltage (U_MESS) calculated by the measurement winding simulation device to calculate a WIG arc voltage (U_LB_WIG) at the WIG arc (LB), and to use the calculated WIG arc voltage (U_LB_WIG) to control the WIG welding process of the welding device (1). 2. The welding device (1) described in claim 1, wherein the control device (5) is configured to calculate a voltage drop (U2) in the secondary winding (23) of the ignition device (18) from the measured winding voltage (U_MESS) and a constant proportionality coefficient (φ), and to calculate the arc voltage (U_LB_WIG) from the difference between the power supply voltage (U_SQ) and the voltage drop (U2). 3. A coil device (20) having a coil core (21) is provided in the ignition device (18), and the secondary winding (23) and the measurement winding (24) are arranged in the coil core (21), 3. The welding device (1) according to claim 2, wherein the number of secondary turns (N2) of the secondary winding (23) and the number of measurement turns (N_MESS) of the measurement winding (24) are different. 4. the measurement number of turns (N_MESS) is less than the secondary number of turns (N2); The welding device (1) according to claim 3, wherein the number of secondary turns (N2) is preferably 5 to 10, particularly preferably 7, and / or the number of measurement turns (N_MESS) is preferably at most 2, particularly 1. 5. a primary winding (22) having a primary winding number (N1) is disposed on the coil core (21) of the coil device (20); the primary winding number (N1) is smaller than the secondary winding number (N2) and is equal to or larger than the measurement winding number (N_MESS); The welding device (1) according to the above 3 or 4, wherein the number of primary turns (N1) is preferably 2 to 4, and particularly preferably 2. 6. The welding device (1) according to any one of claims 3 to 5, wherein the control device (5) is configured to use a transformation ratio (j) between the number of secondary turns (N2) and the number of measured turns (N_MESS) as a proportionality coefficient (φ) for calculating a voltage drop (U2) in the secondary winding (23). 7. The welding device (1) is configured to perform an MSG welding process, 7. The welding device (1) according to any one of claims 1 to 6, wherein the first pole (P1) of the welding power source (2) is connected or connectable to an MSG welding torch (14) including a consumable electrode (E2). 8. An analog or digital measuring circuit is provided in the control device (5) for calculating the WIG arc voltage (U_LB_WIG), 8. The welding device (1) according to any one of claims 1 to 7, in particular a filter is provided in the measuring circuit for filtering at least one voltage signal. 9. A welding current circuit model including a model of a WIG welding cable (7) and / or a model of an MSG welding cable (16) and / or a model of a ground cable (M) and / or a model of a work (W) is stored in the control device (5); and the control device (5) is configured to calculate a voltage drop in the WIG welding cable (7) and / or a voltage drop in the MSG welding cable (16) and / or a voltage drop in the ground cable M and / or a voltage drop in the workpiece W by the welding current circuit model, and to take the calculated voltage drops into consideration when calculating a WIG arc voltage (U_LB_WIG) in the WIG arc (LB_WIG) and / or a MSG arc voltage (U_LB_MSG) in the MSG arc (LB_MSG), The welding device (1) described in any one of claims 1 to 8, wherein the model of the WIG welding cable (7) and / or the model of the MSG welding cable (16) preferably includes at least one ohmic resistance (R_WIG, R_MSG) and at least one inductance (L_WIG, L_MSG). 10. the welding device (1) is provided with an additional auxiliary power source (27) for generating an auxiliary voltage (U_H) for re-igniting the WIG arc (LB_WIG) during a WIG welding process, in particular an AC welding process, being performed; and the control device (5) is configured to detect re-ignition of the WIG arc (LB_WIG) based on the calculated WIG arc voltage (U_LB_WIG) and to stop the auxiliary power supply (27) when the WIG arc (LB_WIG) is detected, 10. The welding device (1) as set forth in any one of claims 1 to 9, wherein the restrike of the WIG arc (LB_WIG) is preferably detected based on a preset voltage threshold (U_WZ). 11. A method for performing a WIG welding process on a workpiece (W) by means of a non-consumable electrode (E1), comprising: The non-consumable electrode (E1) is electrically connected to a first pole (P1) of a welding power source (2) via a WIG welding cable (7), the work (W) is electrically connected to a second pole (P2) of the welding power source (2), and an ignition voltage (U_Z) is supplied to the WIG welding cable (7) by a secondary winding (23) of an ignition device (18) to ignite a WIG arc (LB_WIG) between the non-consumable electrode (E1) and the work (W) in a non-contact manner; A power supply voltage (U_SQ) is detected between the first pole (P1) and the second pole (P2) of the welding power supply (2); The method, wherein the detected power supply voltage (U_SQ) is used by a control device (5) to control the WIG welding process, A measurement winding voltage (U_MESS) is detected by a measurement winding (24) provided on the ignition device (18), or a virtual measurement winding (24) of the ignition device (18) is simulated by a measurement winding simulation device, and a measurement winding voltage (U_MESS) is calculated at the virtual measurement winding (24); and The control device (5) uses the source voltage (U_SQ) and the detected or calculated measured winding voltage (U_MESS) to calculate a WIG arc voltage (U_LB_WIG) at the WIG arc (LB_WIG), and uses the calculated WIG arc voltage (U_LB_WIG) to control the WIG welding process. 12. The method according to claim 11, wherein the control device (5) calculates a voltage drop in the secondary winding (23) from the measured winding voltage (U_MESS) and a proportionality coefficient (φ), and calculates the WIG arc voltage (U_LB_WIG) from the power supply voltage (U_SQ) and the voltage drop (U2). 13. the control device (5) uses a transformation ratio between the number of secondary turns (N2) of the secondary winding (23) and the number of measurement turns (N_MESS) of the measurement winding (24) as a proportionality coefficient (φ) to calculate the voltage drop (U2); 13. The method according to claim 12, wherein the WIG arc voltage (U_LB_WIG) is calculated by the control device (5), preferably by an analog or digital circuit. 14. A welding current circuit model stored in the control device (5) calculates a voltage drop in the WIG welding cable (7) and / or a voltage drop in a ground cable (M) and / or a voltage drop in the work (W); and The control device (5) takes the calculated voltage drop into consideration when calculating the WIG arc voltage (U_LB_WIG), 14. The method according to any one of claims 11 to 13, wherein the welding current circuit model preferably includes at least one ohmic resistance (R_WIG) and at least one inductance (L_WIG). 15. an auxiliary voltage (U_H) is generated by an additional auxiliary power source (27) for re-igniting the WIG arc (LB_WIG) during the WIG welding process being performed; and the control device (5) detects re-ignition of the WIG arc (LB_WIG) based on the calculated WIG arc voltage (U_LB_WIG), and stops the auxiliary power supply (27) when the WIG arc (LB_WIG) is detected; 15. The welding device (1) as set forth in any one of the above items 11 to 14, wherein the restrike of the WIG arc (LB_WIG) is preferably detected based on a preset voltage threshold (U_WZ).

Claims

1. A welding device (1) for performing a WIG welding process on a workpiece (W), comprising: A welding power source (2) having one first pole (P1) and at least one second pole (P2) is provided in the welding device (1), The first pole (P1) is electrically connected to a WIG welding torch (6) including a non-consumable electrode (E1), and the second pole (P2) is electrically connectable to the work (W); The welding device (1) is provided with an ignition device (18) for igniting a WIG arc (LB_WIG) in a non-contact manner between the non-consumable electrode (E1) and the work (W), the ignition device (18) having a secondary winding (23) for supplying an ignition voltage (U_Z) to a WIG welding cable (7); The welding device (1) is provided with a first voltage measuring device (17) for detecting a power supply voltage (U_SQ) between the first pole (P1) and the second pole (P2), The welding apparatus (1) is provided with a control device (5) configured to use the power supply voltage (U_SQ) to control the WIG welding process. a measuring winding (24) is provided in the ignition device (18) and a second voltage measuring device (25) is provided in the welding device (1) for detecting a measuring winding voltage (U_MESS) at the measuring winding (24); and / or a measurement winding simulation device is provided in the welding device (1) for simulating a virtual measurement winding (24) of the ignition device (18) and for calculating a measurement winding voltage (U_MESS) at the virtual measurement winding (24); and The control device (5) is configured to use the power supply voltage (U_SQ) and the measured winding voltage (U_MESS) detected by the second voltage measurement device (25) or the measured winding voltage (U_MESS) calculated by the measurement winding simulation device to calculate a WIG arc voltage (U_LB_WIG) at the WIG arc (LB), and to use the calculated WIG arc voltage (U_LB_WIG) to control the WIG welding process.

2. 2. The welding device (1) according to claim 1, characterized in that the control device (5) is configured to calculate a voltage drop (U2) in the secondary winding (23) of the ignition device (18) from the measured winding voltage (U_MESS) and a constant proportionality coefficient (φ) and to calculate the arc voltage (U_LB_WIG) from the difference between the power supply voltage (U_SQ) and the voltage drop (U2).

3. A coil device (20) having a coil core (21) is provided in the ignition device (18), the secondary winding (23) and the measurement winding (24) are arranged in the coil core (21), 3. The welding device (1) according to claim 2, characterized in that the number of secondary turns (N2) of the secondary winding (23) and the number of measurement turns (N_MESS) of the measurement winding (24) are different.

4. the measurement number of turns (N_MESS) is less than the secondary number of turns (N2); 4. The welding device (1) according to claim 3, characterized in that the number of secondary turns (N2) is preferably 5 to 10, particularly preferably 7, and / or the number of measurement turns (N_MESS) is preferably at most 2, in particular 1.

5. A primary winding (22) having a primary winding number (N1) is disposed on the coil core (21) of the coil device (20), the primary winding number (N1) is less than the secondary winding number (N2) and is greater than or equal to the measurement winding number (N_MESS); Welding device (1) according to claim 3 or 4, characterized in that the number of primary turns (N1) is preferably between 2 and 4, in particular 2.

6. 5. The welding device (1) according to claim 3 or 4, characterized in that the control device (5) is configured to use a transformation ratio (j) between the number of secondary turns (N2) and the number of measured turns (N_MESS) as a proportionality coefficient (φ) for calculating the voltage drop (U2) in the secondary winding (23).

7. The welding device (1) is configured to perform an MSG welding process, 2. The welding device (1) according to claim 1, characterized in that the first pole (P1) of the welding power source (2) is connected or connectable to a MSG welding torch (14) including a consumable electrode (E2).

8. an analog or digital measuring circuit is provided in the control device (5) for calculating the WIG arc voltage (U_LB_WIG), 8. Welding device (1) according to claim 1 or 7, characterized in that in particular a filter is provided in the measuring circuit for filtering at least one voltage signal.

9. a welding current circuit model including a model of a WIG welding cable (7) and / or a model of an MSG welding cable (16) and / or a model of a ground cable (M) and / or a model of a work (W) is stored in the control device (5); and the control device (5) is configured to calculate a voltage drop in the WIG welding cable (7) and / or a voltage drop in the MSG welding cable (16) and / or a voltage drop in the ground cable (M) and / or a voltage drop in the work W using the welding current circuit model, and to take the calculated voltage drops into consideration when calculating a WIG arc voltage (U_LB_WIG) at the WIG arc (LB_WIG) and / or a MSG arc voltage (U_LB_MSG) at the MSG arc (LB_MSG); 8. The welding device (1) according to claim 1 or 7, characterized in that the model of the WIG welding cable (7) and / or the model of the MSG welding cable (16) preferably comprises at least one ohmic resistance (R_WIG, R_MSG) and at least one inductance (L_WIG, L_MSG).

10. the welding device (1) is provided with an additional auxiliary power source (27) for generating an auxiliary voltage (U_H) for re-igniting the WIG arc (LB_WIG) during a WIG welding process, in particular an AC welding process, being performed; and the control device (5) is configured to detect restrike of the WIG arc (LB_WIG) based on the calculated WIG arc voltage (U_LB_WIG) and to stop the auxiliary power supply (27) when the WIG arc (LB_WIG) is detected, 2. The welding device (1) according to claim 1, characterized in that the restrike of the WIG arc (LB_WIG) is detected preferably on the basis of a predefined voltage threshold (U_WZ).

11. A method for performing a WIG welding process on a workpiece (W) by means of a non-consumable electrode (E1), comprising: The non-consumable electrode (E1) is electrically connected to a first pole (P1) of a welding power source (2) via a WIG welding cable (7), and the work (W) is electrically connected to a second pole (P2) of the welding power source (2). An ignition voltage (U_Z) is supplied to the WIG welding cable (7) by a secondary winding (23) of an ignition device (18) to ignite a WIG arc (LB_WIG) between the non-consumable electrode (E1) and the work (W) in a non-contact manner. A power supply voltage (U_SQ) is detected between the first pole (P1) and the second pole (P2) of the welding power supply (2); The method, wherein the detected power supply voltage (U_SQ) is used by a control device (5) to control the WIG welding process, A measurement winding voltage (U_MESS) is detected at a measurement winding (24) provided on the ignition device (18), or a virtual measurement winding (24) of the ignition device (18) is simulated by a measurement winding simulation device, and a measurement winding voltage (U_MESS) is calculated at the virtual measurement winding (24); and the control device (5) uses the source voltage (U_SQ) and the detected or calculated measured winding voltage (U_MESS) to calculate a WIG arc voltage (U_LB_WIG) at the WIG arc (LB_WIG), and uses the calculated WIG arc voltage (U_LB_WIG) to control the WIG welding process.

12. 12. The method according to claim 11, characterized in that the control device (5) calculates the voltage drop in the secondary winding (23) from the measured winding voltage (U_MESS) and a proportionality factor (φ) and calculates the WIG arc voltage (U_LB_WIG) from the power supply voltage (U_SQ) and the voltage drop (U2).

13. The control device (5) uses a transformation ratio between the number of secondary turns (N2) of the secondary winding (23) and the number of measurement turns (N_MESS) of the measurement winding (24) as a proportionality coefficient (φ) to calculate the voltage drop (U2); 13. The method according to claim 12, characterized in that the WIG arc voltage (U_LB_WIG) is calculated by the control device (5), preferably by an analog or digital circuit.

14. A welding current circuit model stored in the control device (5) calculates a voltage drop in the WIG welding cable (7) and / or a voltage drop in a ground cable (M) and / or a voltage drop in the work (W); and The control device (5) takes the calculated voltage drop into consideration when calculating the WIG arc voltage (U_LB_WIG), 12. The method of claim 11, wherein the welding current circuit model preferably includes at least one ohmic resistance (R_WIG) and at least one inductance (L_WIG).

15. an auxiliary voltage (U_H) is generated by an additional auxiliary power source (27) for re-igniting the WIG arc (LB_WIG) during the WIG welding process being performed; and the control device (5) detects restrike of the WIG arc (LB_WIG) based on the calculated WIG arc voltage (U_LB_WIG), and stops the auxiliary power supply (27) when the WIG arc (LB_WIG) is detected; 12. The method of claim 11, wherein restrike of the WIG arc (LB_WIG) is detected based on a preferably pre-set voltage threshold (U_WZ).

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