WELDING PROCESS AND WELDING EQUIPMENT

Description

[0001] The invention relates to a welding process in which energy is introduced onto a workpiece in the area of ​​a welding point by means of a non-consumable electrode as a heat source in order to create a melt pool, wherein a welding wire separate from the heat source is supplied to the melt pool and wherein the welding wire is melted by the introduced energy in the area of ​​the melt pool in order to create a weld seam on the workpiece.The invention further relates to a welding device comprising a welding torch with a non-consumable electrode as a heat source for supplying energy to a welding point on a workpiece to generate a weld pool, comprising a feed device for supplying a welding wire separate from the heat source to the weld pool, wherein the welding wire can be melted in the area of ​​the weld pool by the energy supplied by the heat source in order to generate a weld seam on the workpiece, and comprising a control unit for controlling the feed device.

[0002] The invention generally relates to a welding device known from DE 10 2015 210741, comprising a welding torch with a heat source for supplying energy to a welding point on the workpiece to generate a weld pool, wherein a separate filler material in the form of a welding wire is supplied to the weld pool independently of the heat source. The welding wire is also melted by the energy of the heat source to create a weld seam on the workpiece. Examples include, for instance, the known TIG welding (tungsten inert gas welding), in which a non-consumable electrode made of tungsten or a tungsten alloy is used as a heat source, or the known plasma welding, in which a non-consumable electrode is also used.

[0003] In TIG welding, an arc is generated between the electrode and the workpiece, which on the one hand creates the weld pool on the workpiece and on the other hand melts the welding wire.

[0004] A combination of TIG welding and laser welding is also known; this is referred to as TIG / laser hybrid welding. In this process, the weld pool is created by the energy of the electric arc on the one hand and by the energy of the laser beam on the other. In all cases, the filler material, in the form of a welding wire, is fed separately, usually by a wire feeder.

[0005] The welding processes mentioned above should be distinguished from welding processes using a consumable electrode, in which the welding wire is used directly as the electrode, such as the well-known MIG / MAG welding. In this case, no separate filler material is required; the electrode itself forms the welding wire. These welding processes are not covered by the invention.

[0006] In TIG welding, a welding current is passed through the electrode to establish and maintain the arc between the electrode and the workpiece. An inert shielding gas (usually argon or helium) is typically used to prevent contact between the molten metal and the surrounding air. Additionally, an electric heating current can be applied to the welding wire to heat it and facilitate the melting of the filler material.

[0007] The welding wire is usually fed to the weld pool using a wire feeder. This typically involves using a preset or adjustable, usually constant, feed rate, which may depend on the set welding current. However, it frequently happens that the welding wire dips too deeply into the weld pool or loses contact with it and moves too far away. In both cases, this degrades the welding result and can lead to uneven welds or defects. This is especially true when the welding torch is operated manually, as the welder cannot always precisely control certain parameters that influence the energy applied to the welding wire.These influencing parameters include, for example, the distance between the welding torch and the workpiece or the angle between the welding wire and the electrode. This can also occur with robot-guided welding torches, for example when welding more complex geometries and / or at different welding speeds.

[0008] To eliminate this problem, it is already known from WO 2010 / 082081 A1 to use the heating current through the welding wire to detect changes in the voltage between the welding wire and the workpiece. If the voltage change exceeds a predefined limit, the heating current is reduced to a very low value for a defined period to prevent the welding wire from melting rapidly. The remaining low heating current detects when the welding wire makes renewed contact with the workpiece (more precisely, with the weld pool). Such contact creates a short circuit, causing the voltage between the welding wire and the workpiece to drop to near zero. If renewed contact is detected, the heating current through the welding wire is increased again.This method is therefore only applicable to hot wire applications (with additional heating of the welding wire by a heating current), but not to cold wire applications (without such a heating current).

[0009] In the JP 60-036860 B, the electrical potential around the electrode is evaluated to adjust the position of the welding wire relative to the workpiece. This electrical potential can be measured as the voltage between the welding wire and the workpiece and is used to determine the immersion depth of the welding wire in the weld pool. This allows the position of the welding wire relative to the workpiece—specifically, the distance between the welding wire and the workpiece—to be controlled, ensuring an optimal immersion depth. This method relies on the assumption that there is always contact between the weld pool and the welding wire. However, this practically always results in a short circuit between the welding wire and the workpiece, and the detectable voltages are very small and within a very narrow range, making the method susceptible to interference and unreliable.Apart from that, an additional regulator and actuator are needed to adjust the position of the welding wire relative to the workpiece and also relative to the welding torch.

[0010] Document US 2020 / 246902 A1 further concerns a MIG / MAG welding process in which a sum of time durations is varied during welding. Since it deals with a MIG / MAG welding process, the specifics and particular problems of TIG welding processes are only inadequately addressed.

[0011] It is therefore an object of the present invention to provide a welding process and a corresponding welding device, with a heat source and a welding filler material in the form of a welding wire, with which the highest possible and most consistent welding quality can be achieved in a simple manner and regardless of the skill of the welder.

[0012] This problem is solved according to the invention with the welding process mentioned at the outset by feeding the welding wire to the weld pool in intermittent feed cycles, preferably with a reversing feed rate, by determining an actual value of the duration of a first period of each feed cycle in which the welding wire does not touch the weld pool and / or by determining an actual value of the duration of a second period of each feed cycle in which the welding wire touches the weld pool, and by changing at least one defined parameter of the feed rate of the welding wire in the feed cycles depending on the determined actual value and a predetermined target value.Preferably, the feed rate parameter used is the average feed rate of an entire feed cycle, and / or the average positive feed rate of a feed cycle, and / or the average negative feed rate of a feed cycle. A feed cycle consists of a first period with a positive feed rate of the welding wire and a subsequent second period with a feed rate of zero or a negative feed rate. With the welding process according to the invention, the feed rate parameter can thus be continuously adjusted to set the target value. This allows a uniform weld seam of high quality to be produced essentially independently of the aforementioned variable parameters. Several of the aforementioned parameters can also be changed.

[0013] According to the invention, the actual value is determined as the duration of the first period of each feed cycle, and a target value for the first period is used as the setpoint. Alternatively, the actual value is determined as the duration of the second period of each feed cycle, and a target value for the second period is used as the setpoint. Finally, the actual value is determined as the sum of the duration of the first period and the duration of the second period of each feed cycle, and a target value for a droplet transfer frequency is used as the setpoint. If, for example, it is detected that the current duration of the first period is longer than the specified setpoint, the parameter of the welding wire feed rate is changed to adjust the setpoint. For example, the average feed rate per cycle or the average positive feed rate per cycle can be changed, in particular increased.Conversely, if it is detected that the current duration of the first period is shorter than the specified target value, then the average feed rate of the welding wire or the average positive feed rate is reduced. This makes it possible to keep the duration of the first period, in which the welding wire does not touch the weld pool, essentially constant throughout the entire welding process. Alternatively, the second period, in which the welding wire does touch the weld pool, can also be used. The second period essentially corresponds to the period between two consecutive first periods. A sum of the duration of the first period and the duration of the second period, corresponding to a droplet transfer frequency, can also be used.

[0014] The average feed rate or average positive feed rate can be changed, for example, by setting the feed rate to a defined first positive value for a specified boost time at the beginning of each feed cycle and then reducing it from the first value to a defined second positive value after the boost time has elapsed. The first value, a ratio between the first and second values, and / or the length of the boost time can preferably be determined based on an error between the measured actual value and the specified target value. This allows the average feed rate or average positive feed rate to be easily changed and advantageously reduces adverse effects due to the inertia of the welding wire.

[0015] Preferably, the energy is introduced into the workpiece via an electric arc generated between a non-consumable electrode and the workpiece. This allows the invention to be used in the known TIG welding process. Additionally, the energy can also be introduced into the workpiece by a laser beam generated by a laser optic. This allows the invention to be used in the laser hybrid welding process.

[0016] The actual value of the duration of the first period and / or the actual value of the duration of the second period can be determined continuously or discretely over time. For example, a discrete determination can be performed only in the time steps of the rule described below, thus eliminating the need for continuous determination.

[0017] The specified target value is preferably adjusted by changing at least one parameter of the feed rate. This allows for the use of feedback control, enabling very precise setting of the target value. This ensures consistent weld quality regardless of disturbances.

[0018] The target value can be defined, for example, based on the diameter of the welding wire, the material of the welding wire, an electrical welding parameter, particularly the welding current, and / or the weld geometry. This allows various influencing parameters to be considered when selecting the target value, enabling the process to be flexibly adapted to specific boundary conditions. The welder can set the target value, for example, via a user interface or select it from existing values.

[0019] Preferably, an electrical potential is measured at the welding wire, and the actual value of the duration of the first period and / or the actual value of the duration of the second period are determined from the time course of the measured electrical potential. This allows for a simple detection of when and for how long the welding wire is in contact with the workpiece.

[0020] The electrical potential can be measured, for example, by measuring an electrical voltage between the welding wire and the workpiece and / or an electrical current flowing through the welding wire, and determining the actual value of the duration of the first period and / or the actual value of the duration of the second period from a time course of the measuring voltage and / or the measuring current.

[0021] Optionally, an additional electrical base potential could be generated between the welding wire and the workpiece to enable measurement at any time, even if there is no electrical potential around the welding wire.

[0022] The problem is further solved with the aforementioned welding device by the fact that the control unit is designed to control the feed device in such a way that the welding wire can be fed to the weld pool in intermittent feed cycles, preferably with a reversing feed rate; that a detection unit is provided which is designed to determine, during a welding process carried out with the welding device, an actual value of the duration of a first period of each feed cycle in which the welding wire does not touch the weld pool and / or an actual value of the duration of a second period of each feed cycle in which the welding wire touches the weld pool; and that the control unit is designed to control the feed device.to change at least one defined parameter of the welding wire feed rate in the feed cycles depending on the determined actual value and a predetermined target value.

[0023] Advantageous embodiments of the welding device are specified in claims 10 to 14.

[0024] The present invention is described below with reference to the Figuren 1 bis 4 In more detail, the invention is explained, and exemplary, schematic, and non-restrictive embodiments are shown. This includes showing Fig.1 a welding device with a welding torch with a non-consumable electrode, Fig.2 a non-consumable electrode with a potential field around the arc caused by the welding current, Fig.3 an advantageous embodiment of the welding device according to the invention, Fig.4 Time profiles of an actual value of the potential, a target value of the potential and a feed rate of the welding wire.

[0025] In Fig.1 A welding device 1 in the form of a TIG welding device is shown. The welding device 1 has a welding power source 2 and a welding torch 3, on which a heat source 4 in the form of a non-consumable electrode 4a, e.g., a tungsten electrode, is arranged. Within the scope of the invention, the heat source 4 could, in addition to the non-consumable electrode 4a, also include a laser optic (not shown). For the sake of simplicity, the invention will below be described only with reference to TIG welding, but is of course also applicable in an analogous manner to the aforementioned TIG / laser hybrid welding.

[0026] In the illustrated example, the welding torch 3 is connected to the welding power source 2 by means of a hose assembly 5. A shielding gas cylinder 6 is also provided. Typical cylinder fittings on the shielding gas cylinder 6, for example for adjusting the shielding gas flow rate, are not shown. Furthermore, a wire feeder 7 is provided to supply a welding wire 8 as filler material to the weld point 25. The wire feeder 7 can be part of the welding power source 2 or can be designed as a separate unit. A welding wire spool 12 is arranged in the wire feeder 7, from which the welding wire 8 is unwound during welding and fed to the weld point 25 at a feed rate v. To generate the feed rate v, the wire feeder 7 has a suitable and sufficiently powerful drive unit 7a.

[0027] Furthermore, a control unit 13 is provided for controlling the welding device 1. Within the scope of the invention, the control unit 13 is configured at least to control the feed unit 7, in particular the drive unit 7a, in order to set the feed rate v of the welding wire 8 to a desired value. Within the scope of the invention, the welding wire 8 is fed to the weld area in intermittent feed cycles, as shown below with reference to Fig.3 This will be explained in more detail later. A feed cycle C has a first period with a positive feed rate v and a second period Z2 with a feed rate of zero or a negative feed rate (in the case of reversing wire feed). The control unit 13 can have suitable hardware and / or software in a known manner. Preferably, however, the control unit 13 is also designed to control the welding process carried out with the welding device 1. In addition to controlling the feed rate v, the control unit 13 can thus also control or regulate the welding parameters of a welding process, e.g., the welding current I_s, the welding voltage U_s, a frequency of the welding current I_s or the welding voltage U_s, the amount of shielding gas supplied, etc.Of course, several separate control units could also be provided, communicating with each other via a suitable communication link to exchange control parameters. However, the control of the feed rate v is essential to the invention, so the following discussion will mainly refer to control unit 13.

[0028] The welding device 1 may also include a user interface 14, which communicates appropriately with the control unit 13. Via the user interface 14, a welder can, for example, select a welding program or a specific welding process with predefined welding parameters (e.g., a pulse welding process with a specific welding current I_s and a specific frequency). Certain settings can also be selected or changed manually. For example, the feed rate v of the welding wire 8 was previously usually specified by the welder or selected from available values ​​and was generally constant.

[0029] The hose assembly 5 can transmit all necessary media, energy, and control signals to the welding torch 3, such as electrical energy (current, voltage), a cooling medium (if the welding torch 3 is cooled), control lines for controlling the welding process, the shielding gas from the shielding gas cylinder 6, or the welding wire 8. Typically, the hose assembly 5 consists of a single hose containing the individual lines and media. However, multiple separate hoses or lines can also be used.

[0030] The workpiece 10 to be welded is connected to the opposite electrical pole (usually the positive pole) via a contact wire 9. The contact wire 9 is often also referred to as the ground wire. A welding wire feeder 11 can also be arranged on the welding torch 3 to supply the welding wire 8 in a desired position and direction relative to the electrode 4a at the weld point 25. The welding wire feeder 11 can also be connected to a welding wire line 22, in which the welding wire 8 is guided separately, i.e., outside the hose assembly 5, to the welding wire feeder 11. However, the welding wire feeder 11 does not necessarily have to be arranged on the welding torch 3, but can also be arranged at any other suitable location, for example, on a welding robot.The feed unit 7 does not necessarily have to be located at the welding power source 2, but can also be located at any other suitable location, for example on a welding robot.

[0031] A contact sleeve (not shown) is typically arranged on the welding torch 3. This sleeve surrounds and electrically contacts the electrode 4a and is connected to the welding power source 2 (usually to the negative terminal) via a welding current cable 24, which is usually routed within the hose assembly 5. The electrode 4a protrudes from the welding torch 3 at one end. Shielding gas can escape from the welding torch 3 around the electrode 4a, surrounding the weld area 25 with the weld pool 26 and shielding it from the ambient atmosphere (as in Fig.3 (as indicated). The welding wire 8 is fed to the weld point 25 during welding in intermittent feed cycles C, optionally with reversing wire feed. Reversing wire feed means that a positive feed rate is used in the first period Z1 and a negative feed rate in the second period Z2. Since the basic structure and function, and the various modifications thereof, of such a welding device 1 are known, they will not be discussed in detail here.

[0032] As already mentioned, in addition to the electrode 4a shown, a laser optic (not shown) could also be provided as a heat source 4. The heat is supplied in addition to the electric arc 27 (see Fig.2 ) introduced into the workpiece 10 by a laser beam.

[0033] Fig.2 Figure 1 shows a more detailed view of the welding torch 3 in the area of ​​the tip of the non-consumable electrode 4a, which is located at a weld point 25 on the workpiece 10. A welding current I_s (e.g., in the range of 100 A) is generated by the welding power source 2 and conducted through the electrode 4a via the welding lead 24 to generate and maintain an arc 27 between the electrode 4a and the workpiece 10. Known methods can be used to ignite the arc 27, for example, high-frequency ignition or ignition by touching the workpiece 10 with the electrode 4a and subsequently lifting the electrode 4a. When the welding current I_s flows through the electrode 4a, a quasi-static electric field 28 is formed around the electrode 4a in a known manner, as shown in Figure 2. Fig.2 as indicated.

[0034] This quasi-static electric field 28 leads to a potential distribution in the vicinity of the electrode 4a, as shown in Fig.2 This is exemplified by equipotential lines 28a. The values ​​depend on factors such as welding current, electrode cooling, shielding gas, arc length (distance A), etc., but can be assumed to be known. This potential P can be detected as an electrical quantity, e.g., as an electrical measuring voltage U_m or as an electrical measuring current I_s, by a suitable potential detection unit 30. The potential detection unit 30 can, for example, include a voltmeter 29 with which the measuring voltage U_m can be measured against a reference potential. Fig.2 Exemplary voltage values ​​relative to the potential P of the workpiece 10 as a reference potential are shown on the equipotential lines 28a. This electrical potential P is measured via the welding wire 8, which is fed to the weld point 25 and is therefore located in the quasi-static electric field, and is recorded with the voltmeter 29. No separate measuring current needs to be passed through the welding wire 8. Likewise, a possible heating current for heating the welding wire 8 does not interfere with the measurement of the potential P. The potential P can therefore be measured in both cold wire and hot wire applications.

[0035] Instead of an electrical measuring voltage U_m, an electrical measuring current I_m flowing through the welding wire 8, caused by the potential P, can also be measured in an analogous manner, as exemplified in Fig.3 This is illustrated. For this purpose, for example, a terminating resistor 34 can be connected between the welding wire 8 and the workpiece 10, through which an electric current flows, which can be measured as a measuring current I_m to detect the potential P. The potential detection unit 30 includes a suitable current measuring device 33, as shown in Fig.3 This is illustrated. Of course, instead of measuring current I_m and measuring voltage U_m, another electrical quantity related to the potential distribution could be measured or determined in the same way; for example, a resistance or power could be determined from the measuring voltage U_m and the measuring current I_m. Within the scope of the invention, therefore, all these possibilities are encompassed by tapping the electrical potential P.

[0036] As in Fig.3 As indicated, the potential sensing unit 30 can, for example, be arranged in the welding power source 2, where the reference potential of the workpiece 10 is already present, for example via the contact line 9 or a separate line for contacting the workpiece 10. Using the contact line 9 is advantageous because it eliminates the need for an additional line. When using the contact line 9, the potential sensing unit 30 can, for example, be connected to the contact line 9 (ground socket) on the welding device 1. The only additional requirement in the welding device 1 is the potential sensing unit 30 to detect an electrical quantity representing the electrical potential P, for example, the electrical measuring voltage U_m. This can be achieved simply by implementing an electrical contact on the welding wire 8, for example, as a sliding contact in the feed unit 7.If necessary, a terminating resistor 34, which may also be part of the potential detection unit 30, may be provided between the welding wire 8 and the workpiece, or the contact line 9, or another reference potential.

[0037] From the electrical quantity representative of the potential P (measuring voltage U_m, measuring current I_m, etc.), it can be easily determined, based on the resulting potential distribution, whether the welding wire 8 is touching the weld pool 26 produced by the electrode 4a via the arc 27, or whether the welding wire 8 is too far from the weld pool 26 and is not touching it. If the welding wire 8 is touching the weld pool 26, a short circuit occurs, causing the measuring voltage U_m measured by the voltmeter 29 to drop to zero (or essentially zero), or the measuring current I_m measured by the current measuring unit 33 to drop to zero (or essentially zero). The same applies to any quantities derived from these. Conversely, if the welding wire 8 is not touching the weld pool 26, a certain measuring current I_m or a certain measuring voltage U_m will be measured, which depend on the magnitude of the potential P.

[0038] An additional auxiliary energy source (not shown) may also be provided in the measuring circuit of the potential detection unit 30 to generate a specific base potential. This is advantageous for applications where no or only a weak electric field forms around the heat source 4, such as in pure laser welding, where the heat source 4 has a laser optic 4a. The auxiliary energy source provides a measurable electric potential at all times, independent of the potential P of the electric field, which can be used for measurement. The auxiliary energy source can, for example, be designed as a high-impedance voltage source with which an auxiliary voltage can be applied to the welding wire 8. This could be used, for example, in TIG welding.A potential P can also be detected before the ignition of the arc 27, and it can be used to determine whether the welding wire 8 is in contact with the workpiece 10, in particular whether a short circuit is present.

[0039] According to the invention, a detection unit 31 is further provided, which is configured to determine an actual value t1_ist for a duration t1 of a first period Z1 of each feed cycle C during the execution of the welding process, in which the welding wire 8 does not touch the weld pool 26 or the workpiece 10. Alternatively or additionally, the detection unit 31 could also be configured to determine an actual value t2_ist for a duration t2 of a second period Z2 of each feed cycle C, in which the welding wire 8 touches the weld pool 26 or the workpiece 10. The durations t1, t2 and the periods Z1, Z2 are defined in Fig.4 depicted.

[0040] Investigation Unit 31 can be designed as a separate unit, equipped with suitable hardware and / or software, and communicating with Control Unit 13 via a suitable communication link, as described in Fig.2 As indicated. Advantageously, however, investigation unit 31 is integrated into control unit 13, as shown in Fig.3 The control unit 13 is designed according to the invention to control the feed device 7, in particular the drive unit 7a, in order to set at least one defined parameter of the feed rate v of the welding wire 8 depending on the determined actual values ​​t1_actual and / or t2_actual and a predetermined setpoint.

[0041] The measuring unit 31 can easily determine, based on the electrical quantity representative of the potential P (measuring voltage U_m, measuring current I_m, etc.), whether the welding wire 8 is touching the weld pool 26 produced by the electrode 4a via the arc 27 (short circuit) or whether the welding wire 8 is too far from the weld pool 26 (no short circuit). The time t1 of the first period Z1 (no short circuit) or the time t2 of the second period Z2 (short circuit) can be determined from the time course of the electrical quantity representative of the potential P, as shown by… Fig.4 shown.

[0042] In Fig.4 The upper diagram shows an example of the time course of a detected potential P. This course corresponds to the actual value P_actual of the potential P measured by the potential detection unit 30. Depending on the measured quantity, this could be, for example, the course of the measuring current I_m or the course of the measuring voltage U_m. The middle diagram shows a correlating time course of a setpoint P_setpoint of the potential P. The lower diagram shows a correlating time course of the feed rate v of the welding wire 8. This shows that the welding wire 8 is fed to the weld pool 26 in intermittent feed cycles C with a time-varying feed rate v. The feed rate v is set to a specific positive value in the first period Z1 of each cycle C; here, the values ​​v1 and v2 are shown. Fig.4 (For simplicity, only the first cycle C is shown). In the subsequent second period Z2 of cycle C, a feed rate v=0 is used in the example shown. Alternatively, a reversing wire feed can also be used, in which a negative feed rate v is used in the second period Z2, as indicated by the dashed line for two feed cycles C. A negative feed rate v corresponds to moving the welding wire back away from the weld pool 26, and a positive feed rate v corresponds to moving it towards the weld pool 26.

[0043] During the first two periods Z1, the welding wire 8 is not in contact with the weld pool 26. These first periods Z1 thus correspond to a short-circuit-free period, during which the potential P_actual measured by the potential detection unit 30 is greater than zero or greater than a defined value representing the short circuit. The second periods Z2, located between each pair of first periods Z1, correspond to a short-circuit period, during which the potential P_actual measured by the potential detection unit 30 is zero or reaches a value representing a short circuit. The detection unit 31 can determine the current duration t1_actual of the first periods Z1 from the actual value curve P_actual, i.e., the length of the short-circuit-free period. Alternatively, the detection unit 31 can also determine the current duration t2_ist of the second periods Z2 from the actual value curve P_ist, i.e., the length of the short-circuit period.The duration of an entire feed cycle C can also be determined, which corresponds to the sum of the duration t1_ist of the first period Z1 and the duration t2_ist of the second period Z2. This is also referred to as the droplet detachment frequency f. Fig.3 The current droplet detachment frequency f_is and the desired target value f_is shown as an example for a feed cycle C.

[0044] For example, a specific threshold value P_sw could be set for the potential P, representing a short circuit. The threshold value P_sw could be, for example, zero or slightly above it. Fig.4 An example threshold value P_sw, slightly greater than zero, is shown. The actual value t1_ist for the duration t1 can then be determined, for example, by measuring the time between a time ZPa, at which the measured potential P_ist (e.g., welding current I_s or welding voltage U_s) exceeds the defined threshold value P_sw, and a subsequent time ZPb, at which the measured potential P_ist falls below the defined threshold value P_sw again. Similarly, the duration t2 can be measured between a time ZPb, at which the measured potential P_ist falls below the defined threshold value P_sw, and a subsequent time ZPc, at which the measured potential P_ist exceeds the defined threshold value P_sw again. The times ZPa and ZPc are shown in Fig.4 The diagram above illustrates the first cycle, consisting of an initial period Z1 and a subsequent second period Z2. However, the measurement is continuously performed throughout the welding process, i.e., for a multitude of feed cycles C. The actual value f_ist of the droplet detachment frequency f corresponds to the time between time ZPa and time ZPc.

[0045] The determination of the actual values ​​t1_actual, t2_actual at times t1, t2 is preferably performed continuously over time, but could also be performed discretely over time, i.e., at certain fixed intervals. The acquisition of the actual value P_actual, i.e., the measurement of the measuring voltage U_m or the measuring current I_m, is preferably also performed continuously or discretely over time. Discrete-over-time acquisition can, for example, be performed in the time steps of the control system described in more detail below. The middle diagram shows that a specific constant time t1_setpoint (or t2_setpoint) is specified as the setpoint. According to the invention, the control unit 13 is designed to control the feed unit 7 accordingly, such that at least one defined parameter of the feed rate v of the welding wire 8 is adjusted in the feed cycles C during the welding process so that the desired setpoint t1_setpoint, t2_setpoint, or f_setpoint is reached.

[0046] The feed rate parameter v can be, for example, the average feed rate vm of an entire feed cycle C, and / or the average positive feed rate vmZ1 of a feed cycle C, and / or the average negative feed rate vmZ2 of a feed cycle C (in the case of reversing wire feed). The average feed rate vm, the average positive feed rate vmZ1, and the average negative feed rate vmZ2 are in Fig.3 The first feed cycle C is shown as an example.

[0047] For example, the actual value t1_is can be determined as the duration t1 of the first period Z1 of each feed cycle C, where a target value t1_should be used for the first duration t1. Similarly, the actual value t2_is can be determined as the duration t2 of the second period Z2 of each feed cycle C, and a target value t2_should be used for the second duration t2. An actual value f_is of the droplet transfer frequency f can also be determined, which corresponds to the sum of the duration t1 of the first period Z1 and the duration t2 of the second period Z2 of each feed cycle C. Here, a target value f_should for the droplet transfer frequency f can be used as the target value. In all three cases, one or more of the aforementioned influencing parameters of the feed rate v can be changed to adjust the respective target value.

[0048] The control unit 13 can advantageously incorporate a suitable controller, e.g., a PI controller or PID controller. The controller is configured to determine a manipulated variable S for the feed unit 7, particularly for the drive unit 7a, from the respective determined actual value, e.g., the actual value t1_actual for the duration t1 of the first time periods Z1 (or the determined actual values ​​t2_actual for the duration t2 of the second time periods Z2), and from the specified, preferably constant, setpoint, e.g., t1_setpoint, t2_setpoint, or f_setpoint. The control unit 13 then controls the feed unit 7 accordingly with the determined manipulated variable S to regulate the feed rate v, as shown in Fig.3 is shown.

[0049] This allows the short-circuit time t2 or the short-circuit-free time t1 to be adjusted to a desired value by continuously adapting the defined parameter, e.g., the average feed rate vm and / or the average positive feed rate vmZ1 and / or, if applicable, the average negative feed rate vmZ2. Thus, the variable influencing parameters mentioned above (e.g., variable distance X between electrode 4a and workpiece 10, variable angle α between electrode 4a and welding wire 8 - see [reference]) can be automatically taken into account. Fig.2 , or variable welding speed G in the direction of the weld seam 32 - see Fig.3 This allows the welder to react to changes in welding speed, which leads to improved weld quality, particularly in manual welding. For example, if the welding speed G is unintentionally increased by the welder, this usually results in an automatic increase in the short-circuit-free time t1 because there is less filler material in the weld pool 26. The control system according to the invention, for example, increases the average feed rate vm and thus automatically adjusts it to the increased welding speed G (and vice versa).

[0050] The setpoint t2_setpoint for the short-circuit time t2, the setpoint t1_setpoint for the short-circuit-free time t1, and the setpoint f_setpoint for the droplet detachment frequency f can be assumed to be known and, for example, stored as a fixed value in the control unit 13. The setpoint can also depend on the diameter of the welding wire 8 and / or the material of the welding wire 8 and / or an electrical welding parameter (e.g., the welding current I_s or the welding voltage U_s). Depending on the current welding parameter (which can be considered known due to the selected welding program), a corresponding setpoint can therefore be automatically set. Furthermore, the setpoint can also depend on the weld geometry (fillet weld, V-weld, etc.) of the weld 32 to be produced.

[0051] For example, a function for the setpoint, dependent on at least one parameter (e.g., the welding voltage I_s), can be stored in control unit 13. Control unit 13 can then determine the setpoint from this function. If the setpoint depends on a single parameter, the function could, for example, be stored in the form of a characteristic curve. If the setpoint depends on multiple parameters, the function could, for example, be stored as a characteristic map. Of course, the welder can also make additional manual adjustments, for example, via user interface 14. For instance, the welder could increase or decrease the preset setpoint based on a predefined range, such as a percentage.

[0052] In Fig.4 It is evident that the duration of the individual feed cycles C and the feed rate v in the respective feed cycles C change automatically during the course of the control process, in particular decreasing. While in the first cycle shown the error, i.e., the difference Δt1 between the actual value t1_actual and the setpoint t1_target, is still relatively large, the error is reduced by adjusting the feed rate v until the actual value t1_actual, t2_actual adjusts to the specified setpoint t1_target, t2_target. This is exemplified in the last and penultimate cycles in Fig.4 shown where the error was reduced to a sufficiently small value, preferably zero.

[0053] As shown in the diagram below Fig.4As shown, to change the mean feed rate vm or the mean positive feed rate vmZ1, it can be advantageous if, at the beginning of each feed cycle C, the feed rate v is initially set to a higher first positive value v1 for a certain boost time tu and, after the boost time tu has elapsed, is reduced to a relatively lower second positive value v2 < v1. This has also proven advantageous due to the inertia of the welding wire 8 and the welding torch 3. The first value v1 and / or the ratio between the first value v1 and the second value v2 and / or a length of the boost time tu can, for example, depend on the error Δt1 determined at the current time or in the current time step between the actual value t1_ist and the target value t1_soll (or on the error Δt2 between the determined actual value t2_ist and the target value t2_soll).The greater the respective difference Δt1, Δt2, the higher the first value v1 and / or the longer the time tu, as can be seen from the cycles shown. The ratio between the first value v1 and the second value v2 can therefore change, for example, depending on the error Δt1 (or error Δt2) during the course of the control process.

[0054] However, providing a boost time tu with increased feed rate v1 is of course only optional, and the average feed rate vm or the average positive feed rate vmZ1 could, for example, also be changed simply by changing the value v2.

[0055] As already mentioned, the invention is not limited to the described TIG welding, but can also be applied to TIG / laser hybrid welding or plasma welding.

Claims

1. A welding method, wherein energy is introduced into a workpiece (10) in the region of a welding point (25) by means of a non-consumable electrode (4a) as a heat source (4) in order to produce a molten bath (26), wherein a welding wire (8) separate from the heat source (4) is fed to the molten bath (26) and wherein the welding wire (8) is melted by the introduced energy in the region of the molten bath (26) in order to produce a weld seam (32) on the workpiece (10), characterized in that the welding wire (8) is fed to the molten bath (26) in intermittent feed cycles (C), preferably with a reversing feed speed (v), in that, while the welding method is being carried out, an actual value (t1_ist) of a duration (t1) of a first time period (Z1) of a feed cycle (C) is determined in each case, in which first time period (Z1) the welding wire (8) does not come into contact with the molten bath (26) and / or an actual value (t2_ist) of a duration (t2) of a second time period (Z2) of a feed cycle (C) is determined in each case, in which second time period (Z2) the welding wire (8) does come into contact with the molten bath (26), and in that at least one specified parameter of the feed speed (v) of the welding wire (8) is changed in the feed cycles (C) depending on the determined actual value and a predefined target value, wherein the duration (t1) of the first time period (Z1) of a feed cycle (C) is determined as the actual value (t1_ist) and a target value (t1_soll) for the first duration (t1) is used as the target value, or the duration (t2) of the second time period (Z2) of a feed cycle (C) is determined as the actual value (t2_ist) and a target value (t2_soll) for the second duration (t2) is used as the target value, or a sum of the duration (t1) of the first time period (Z1) and the duration (t2) of the second time period (Z2) of a feed cycle (C) is determined as the actual value (f_ist) and a target value (f_soll) for a drop transfer frequency (f) is used as the target value.

2. The welding method according to claim 1, characterized in that an average feed speed (vm) of an entire feed cycle (C) and / or an average positive feed speed (vmZ1) of a feed cycle (C) and / or an average negative feed speed (vmZ2) of a feed cycle (C) is used as a parameter of the feed speed (v).

3. The welding method according to claim 1 or 2, characterized in that the average feed speed (vm) or the average positive feed speed (vmZ1) is changed by setting the feed speed (v) to a defined first value (v1) for a defined boost time (tu) at the beginning of each feed cycle (C) and by reducing it from the first value (v1) to a defined second value (v2) after the boost time (tu) has elapsed, wherein the first value (v1) and / or a ratio between the first value and the second value (v2) and / or a length of the boost time (tu) can preferably be set as a function of an error (Δt1, Δt2) between the determined actual value (t1_ist, t2_ist) and the predefined target value (t1_soll, t2_soll).

4. The welding method according to one of claims 1 to 3, characterized in that the energy is introduced into the workpiece (10) via an electric arc (27) produced between a non-consumable electrode (4a) and the workpiece (10) and via a laser beam generated by a laser optics.

5. The welding method according to one of claims 1 to 4, characterized in that the actual value (t1_ist) of the duration (t1) of the first time period (Z1) and / or the actual value (t2_ist) of the duration (t2) of the second time period (Z2) are determined continuously or discretely and / or in that the predefined target value is adjusted by changing at least one parameter of the feed speed (v).

6. The welding method according to one of claims 1 to 5, characterized in that the target value is determined as a function of a diameter of the welding wire (8) and / or of a material of the welding wire (8) and / or of an electrical welding parameter, in particular of a welding current (I_s), and / or of a seam shape of the weld seam (32).

7. The welding method according to one of claims 1 to 6, characterized in that an electrical potential (P_ist) is tapped at the welding wire (8) and in that the actual value (t1_ist) of the duration (t1) of the first time period (Z1) and / or the actual value (t2_ist) of the duration (t2) of the second time period (Z2) is determined from a time profile of the detected electrical potential (P_ist), wherein the electrical potential (P_ist) is preferably tapped by measuring a measuring voltage (U_m) between the welding wire (8) and the workpiece (10) and / or an electric measuring current (I_m) flowing through the welding wire (8), and the actual value (t1_ist) of the duration (t1) of the first time period (Z1) and / or the actual value (t2_ist) of the duration (t2) of the second time period (Z2) is determined from a time profile of the measuring voltage (U_m) and / or of the measuring current (I_m), wherein, preferably, an electrical ground potential is generated between the welding wire (8) and the workpiece (10).

8. A welding device (1) comprising a welding torch (3) with a non-consumable electrode (4a) as a heat source (4) for introducing energy at a welding point (25) on a workpiece (10) in order to produce a molten bath (26), comprising a feed device (7) for feeding a welding wire (8) separate from the heat source (4) to the molten bath (26), wherein the welding wire (8) can be melted in the region of the molten bath (26) by the energy introduced by the heat source (4) in order to produce a weld seam (32) on the workpiece (10) and comprising a control unit (13) for controlling the feed device (7), characterized in that the control unit (13) is designed to control the feed device (7) in such a way that the welding wire (8) can be fed to the molten bath (26) in intermittent feed cycles (C), preferably with a reversing feed speed (v), in that a determination unit (31) is provided which is designed to determine, during a welding method carried out with the welding device (1), an actual value (t1_ist) of a duration (t1) of a first time period (Z1) of a feed cycle (C) in each case, in which first time period (Z1) the welding wire (8) does not come into contact with the molten bath (26) and / or to determine an actual value (t2_ist) of a duration (t2) of a second time period (Z2) of a feed cycle (C) in each case, in which second time period (Z2) the welding wire (8) does come into contact with the molten bath (26), and in that the control unit (13) is designed to control the feed device (7) in order to change at least one specified parameter of the feed speed (v) of the welding wire (8) in the feed cycles (C) depending on the determined actual value and on a predefined target value, wherein the actual value (t1_ist) is the duration (t1) of the first time period (Z1) of a feed cycle (C) and the target value is a target value (t1_soll) for the first duration (t1) or the actual value (t2_ist) is the duration (t2) of the second time period (Z2) of a feed cycle (C) and the target value is a target value (t2_soll) for the second duration (t2) or the actual value (f_ist) is a sum of the duration (t1) of the first time period (Z1) and the duration (t2) of the second time period (Z2) of a feed cycle (C) and the target value is a target value (f_soll) for a drop transfer frequency (f).

9. The welding device (1) according to claim 8, characterized in that the parameter of the feed speed (v) comprises an average feed speed (vm) of an entire feed cycle (C) and / or an average positive feed speed (vmZ1) of a feed cycle (C) and / or an average negative feed speed (vmZ2) of a feed cycle (C).

10. The welding device (1) according to claim 8 or 9, characterized in that the control unit (13) is designed to set the feed speed (v) to a defined first value (v1) for a defined boost time (tu) at the beginning of each feed cycle (C) and to reduce the feed speed (v) from the first value (v1) to a defined second value (v2) after the boost time (tu) has elapsed in order to change the average feed speed (vm) or the average positive feed speed (vmZ1), wherein the first value (v1) and / or a ratio between the first value and the second value (v2) and / or a length of the boost time (tu) are preferably defined as a function of an error (Δt1, Δt2) between the determined actual value (t1_ist, t2_ist) and the predefined target value (t1_soll, t2_soll).

11. The welding device (1) according to one of claims 8 to 10, characterized in that the heat source (4) comprises the non-consumable electrode (4a) for generating an electric arc (27) between the electrode (4a) and the workpiece (10) and a laser optics for generating a laser beam.

12. The welding device (1) according to one of claims 8 to 11, characterized in that the determination unit (31) is designed to determine the actual value (t1_ist) of the duration (t1) of the first time period (Z1) and / or the actual value (t2_ist) of the duration (t2) of the second time period (Z2) continuously or discretely, wherein the determination unit (31) is preferably integrated in the control unit (13), and / or in that the control unit (13) has a controller which is designed to determine a manipulated variable (S) for the feed unit (7) from the determined actual value and the predefined target value, and in that the control unit (13) is designed to control the feed unit (7) with the determined manipulated variable (S) in order to realize the target value.

13. The welding device (1) according to one of claims 8 to 12, characterized in that the determination unit (31) comprises a potential detection unit (30) which is designed to tap an electrical potential (P) on the welding wire (8) which arises around the heat source (4), and in that the determination unit (31) is designed to determine the actual value (t1_ist) of the duration (t1) of the first time period (Z1) and / or the actual value (t2_ist) of the duration (t2) of the second time period (Z2) from a time profile of the detected electrical potential (P_ist), wherein the potential detection unit (30) preferably comprises a voltage measuring device (29) for detecting a measuring voltage (U_m) between the welding wire (8) and the workpiece (10) and / or a current measuring device (33) for detecting an electrical measuring current (I_m) flowing through the welding wire (8), wherein the determination unit (31) is designed to determine the actual value (t1_ist) of the duration (t1) of the first time period (Z1) and / or the actual value (t2_ist) of the duration (t2) of the second time period (Z2) from a time profile of the measuring voltage (U_m) or measuring current (I_m), wherein particularly preferably an auxiliary energy source is provided by means of which an electrical ground potential can be generated between the welding wire (8) and the workpiece (10).

14. The welding device (1) according to one of claims 8 to 13, characterized in that the target value depends on a diameter of the welding wire (8) and / or on a material of the welding wire (8) and / or on an electric welding parameter (I_s, U_s), and / or on a seam shape of the weld seam (32).