Welding method and welding device

Abstract

The invention relates to a welding method and to a corresponding welding device (1), comprising a heat source (4) and a welding additive in the form of a welding wire (8), by means of which welding quality as high as possible and constant can be achieved in a simple manner independently of the skills of the welder. According to the invention, the welding wire (8) is fed to the weld puddle (26) with an intermittent feed cycle (C), preferably with a reversing feed speed (v), an actual value (t1ist) of a duration (t1) of a first time period (Z1) of the feed cycle (C) is determined and / or an actual value (t2ist) of a duration (t2) of a second time period (Z2) of the feed cycle (C) is determined during the execution of the welding method, and the actual value (t1ist) of the duration (t1) of the first time period (Z1) of the feed cycle (C) and / or the actual value (t2ist) of the duration (t2) of the second time period (Z2) of the feed cycle (C) is determined. A first period of time in which the welding wire (8) is not in contact with the weld puddle (26) and a second period of time in which the welding wire (8) is in contact with the weld puddle (26) are determined, and at least one specified parameter of the feed speed (v) of the welding wire (8) in the cycle (C) is further modified as a function of the determined actual value and a specified setpoint value.

Description

Technical Field

[0001] The invention relates to a welding method, in which energy is introduced into a workpiece in the region of a welding point by means of a non-consumable electrode as a heat source to produce a weld pool, wherein a welding wire separate from the heat source is fed to the weld pool and the welding wire melts in the region of the weld pool by the energy introduced to produce a weld seam on the workpiece. In addition, the invention relates to a welding device, comprising a welding torch having a non-consumable electrode as a heat source for introducing energy at a welding point on the workpiece to produce a weld pool, the welding device comprising a feed device for feeding a welding wire separate from the heat source to the weld pool, wherein the welding wire can be melted in the region of the weld pool by the energy introduced from the heat source to produce a weld seam on the workpiece, and the welding device comprises a control unit for controlling the feed device.

[0002] The invention generally relates to a welding device comprising a welding torch with a heat source for introducing energy at a welding point on a workpiece to produce a weld pool, wherein a separate additional material in the form of a welding wire is supplied to the weld pool independently of the heat source. The welding wire is likewise melted by the energy of the heat source to produce a weld seam on the workpiece. Examples of this are, for example, known WIG welding (tungsten inert gas welding) using a non-consumable electrode made of tungsten or a tungsten alloy as a heat source, known plasma welding also using a non-consumable electrode, or known laser welding using laser optics as a heat source. Background Art

[0003] In WIG welding, an arc is generated between the electrode and the workpiece, by which, on the one hand, a weld pool is generated on the workpiece and, on the other hand, the welding wire is melted. In laser welding, a laser is generated by laser optics, by which the weld pool is generated and the supplied welding wire is melted. Combinations of WIG welding and laser welding are also known, which are also referred to here as WIG / laser hybrid welding.

[0004] Here, the welding pool is generated by the energy of the arc on the one hand and by the energy of the laser beam on the other hand. In all cases, the additional material in the form of welding wire is fed separately, usually by a feed unit.

[0005] Different from the above-mentioned welding methods are welding methods with consumable electrodes, in which the welding wire is used directly as an electrode, such as the known metal inert gas welding (MIG) / metal active gas welding (MAG). In this case, no separate additional material is required, but the electrode simultaneously constitutes the welding wire. The present invention does not include these welding methods.

[0006] In WIG welding, the welding current is delivered through the electrode to form and maintain an arc between the electrode and the workpiece. Usually, an inert shielding gas (usually argon or helium) is used to prevent the melt from coming into contact with the surrounding air. In addition, a heating current can be introduced into the welding wire to electrically heat it and promote the melting of the added material.

[0007] Usually, the welding wire is fed to the welding point by a feed unit. In this case, the feed speed usually assumes a preset or adjustable, usually constant value, which can depend on the set welding current level as the case may be. However, it can always happen that the welding wire dips too deep into the weld pool or that the welding wire loses contact with the weld pool and is too far away from the weld pool. In both cases, the welding result is therefore impaired and can result in uneven welds or weld defects. This occurs in particular when the welding torch is guided manually, since the welder cannot always precisely comply with certain influencing parameters that influence the energy acting on 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. However, this can also happen in the case of robot-operated welding torches, for example when welding more complex geometries and / or different welding speeds.

[0008] In order to eliminate this problem, WO 2010 / 082081 A1 has already known to use the heating current flowing through the welding wire to detect the voltage change between the welding wire and the workpiece. If the voltage change exceeds a predetermined limit value, the heating current is reduced to a very small value for a certain time to prevent the welding wire from melting quickly. By maintaining a constant small heating current, the welding wire is detected to be in contact with the workpiece (more precisely, with the welding pool) again. This contact forms a short circuit, so that the voltage between the welding wire and the workpiece drops to zero. If contact is detected again, the heating current flowing through the welding wire is increased again. Therefore, this method can only be applied to the application of heating wire (having the function of auxiliary heating of the welding wire by the heating current), but is not applicable to the application of cold welding wire (without such heating current).

[0009] In JP 60-036860 B, the potential generated around the electrode is analyzed in order to change the position of the welding wire relative to the workpiece. The potential can be measured as a voltage between the welding wire and the workpiece and used to determine the immersion position of the welding wire in the weld pool. The position of the welding wire relative to the workpiece, more specifically the distance between the welding wire and the workpiece, is thereby adjusted in order to achieve the optimum immersion position. The basis of this method is that the welding pool and the welding wire are always in contact. Therefore, there is actually always a short circuit between the welding wire and the workpiece, and the detectable voltage is very small and within a very narrow range, which makes the method susceptible to interference and unreliable. In addition, an additional controller and actuator are required to be able to adjust the position of the welding wire relative to the workpiece and to the welding torch.

[0010] In addition, document US 2020 / 246902 A1 also relates to a MIG / MAG welding method, in which the sum of the durations is changed during the welding method. However, since this involves a MIG / MAG welding method, the details and unique problems of the WIG welding method are not fully explored. Summary of the invention

[0011] The object of the present invention is therefore to provide a welding method and a corresponding welding device having a heat source and a welding filler in the form of a welding wire, with which a welding quality which is as high as possible and constant can be achieved in a simple manner, regardless of the skill of the welder.

[0012] According to the invention, this object is achieved with the welding method described in the introduction in that the welding wire is fed to the weld pool in intermittent feed cycles, preferably with a reversing feed speed, and during the execution of the welding method, an actual value for the duration of a first period of a respective feed cycle, in which the welding wire is not in contact with the weld pool, and / or an actual value for the duration of a second period of a respective feed cycle, in which the welding wire is in contact with the weld pool, is determined, and at least one predetermined parameter of the feed speed of the welding wire in the feed cycle is changed as a function of the determined actual value and a previously defined setpoint value. Preferably, the average feed speed of an entire feed cycle and / or the average positive feed speed of a feed cycle and / or the average negative feed speed of a feed cycle are used as parameters for the feed speed. In this case, the feed cycle consists of a first period of time in which the welding wire feed speed is positive and a subsequent second period of time in which the feed speed is zero or negative. Thus, with the welding method according to the invention, the parameters of the feed speed can be continuously adjusted to adjust to the setpoint value. Thus, a high-quality, uniform weld seam can be produced substantially independently of the variable parameters described in the introduction. It is also possible to change several of the parameters mentioned.

[0013] According to the invention, the duration of the first time period of a corresponding feed cycle is determined as an actual value and the rated value of the first duration is used as the rated value, or the duration of the second time period of a corresponding feed cycle is determined as an actual value and the rated value of the second duration is used as the rated value, or the sum of the duration of the first time period of a corresponding feed cycle and the duration of the second time period is determined as an actual value and the rated value of the droplet transfer frequency is used as the rated value. For example, when it is recognized that the current duration of the first time period is longer than a previously specified rated value, the parameters of the wire feed speed are then changed to adjust to the rated value, for example, the average feed speed per cycle or the average positive feed speed per cycle can be changed, in particular, increased. Conversely, for example, when it is recognized that the current duration of the first time period is shorter than a previously specified rated value, the average feed speed or the average positive feed speed of the wire is then reduced. Thus, the duration of the first time period in which the wire is not in contact with the weld pool can be kept substantially constant throughout the welding method. As an alternative to the first time period, of course, a second time period in which the wire is in contact with the weld pool can also be used. The second time period substantially corresponds to the time period between two consecutive first time periods. It is also possible to use the sum of the duration of the first period and the duration of the second period, which corresponds to the droplet transfer frequency.

[0014] For example, the average feed speed or average positive feed speed can be changed by adjusting the feed speed to a first positive value within a specified boost time at the beginning of each feed cycle and reducing it from the first value to a second positive value after the boost time has ended, wherein the first value and / or the ratio between the first value and the second value and / or the length of the boost time can preferably be determined based on the error between the determined actual value and a previously specified setpoint value. Thus, the average feed speed or average positive feed speed can be easily changed and the adverse effects caused by the inertia of the welding wire can be reduced in an advantageous manner.

[0015] The energy is preferably introduced into the workpiece via an arc generated between a non-consumable electrode and the workpiece. The invention can therefore be applied to known WIG welding methods. As an alternative or in addition, the energy can also be introduced into the workpiece via a laser beam generated by laser optics. The invention can therefore be applied to laser welding processes or laser hybrid welding processes.

[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 time-continuously or time-discretely. For example, a time-discrete determination can be performed only with the time step of the control described below, so that a continuous determination is not required.

[0017] Preferably, the feed speed is adjusted to a previously defined setpoint value by changing the at least one parameter of the feed speed. Thus, a feedback control can be used, so that the setpoint value can be adjusted very accurately. Thus, a constant welding quality can be achieved without being affected by interference.

[0018] The setpoint value can be determined, for example, as a function of the diameter of the welding wire and / or as a function of the material of the welding wire and / or as a function of electric welding process parameters, in particular the welding current, and / or as a function of the weld seam shape of the weld seam. Thus, different influencing parameters can be taken into account when selecting the setpoint value, so that the process can be flexibly adapted to specific boundary conditions. The welder can, for example, determine the setpoint value via a user interface or select it from the available values.

[0019] Preferably, a potential is detected on the welding wire, and the actual value of the duration of the first time period and / or the actual value of the duration of the second time period is determined from the time curve of the detected potential. It is thus possible to detect in a simple manner when and for how long the welding wire touches the workpiece.

[0020] For example, the potential can be detected by measuring an electrical measurement voltage between the welding wire and the workpiece and / or an electrical measurement current flowing through the welding wire and determining an actual value of the duration of the first time period and / or an actual value of the duration of the second time period from the time profile of the measurement voltage and / or the measurement current.

[0021] As an option, an additional base potential can be generated between the welding wire and the workpiece, so that measurements can be made at any time, even if there is no potential around the welding wire.

[0022] Furthermore, the object is achieved using the welding device described at the outset in that the control unit is configured 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 at a reversing feed speed, and a determination unit is provided, which is configured to determine an actual value of the duration of a first time period of a respective feed cycle (in which the welding wire is not in contact with the weld pool) and / or an actual value of the duration of a second time period of a respective feed cycle (in which the welding wire is in contact with the weld pool) during the performance of a welding method using the welding device, and the control unit is configured to control the feed device so as to change at least one specified parameter of the feed speed of the welding wire in the feed cycle as a function of the determined actual value and a predetermined setpoint value.

[0023] Advantageous embodiments of the welding device are specified in claims 10 to 14 . BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The following is an exemplary, schematic and non-limiting description of advantageous constructional designs of the invention. Figures 1 to 4The present invention is described in detail. The accompanying drawings show:

[0025] Figure 1 is a welding device having a welding torch with a non-consumable electrode;

[0026] Figure 2 It is a non-consumable electrode having a potential field around the arc caused by the welding current;

[0027] Figure 3 It is an advantageous embodiment of the welding device of the present invention;

[0028] Figure 4 It is the time variation curve of the actual potential value, the rated potential value and the wire feed speed. DETAILED DESCRIPTION

[0029] exist Figure 1 , a welding device 1 is shown in the figure, in the form of a WIG welding device. 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, for example a tungsten electrode, is arranged. However, within the scope of the invention, as an alternative or in addition to the non-consumable electrode 4a, the heat source 4 can also have a (not shown) laser optical device. However, for the sake of simplicity, the invention is described below only with reference to WIG welding, but it can of course also be applied in a similar manner to laser welding or the WIG / laser hybrid welding described at the beginning.

[0030] In the example shown, the welding torch 3 is connected to the welding power source 2 via a hose assembly 5. In addition, a shielding gas container 6 is provided. Conventional gas cylinder attachments to the shielding gas container 6, such as for regulating the shielding gas flow, are not shown. In addition, a feed unit 7 is provided for conveying a welding wire 8 as a welding additive to the welding point 25. The feed unit 7 can be a component of the welding power source 2, but can also be designed as a separate unit. A wire roller 12 is arranged in the feed unit 7, from which the welding wire 8 is unwound during the welding process and conveyed to the welding point 25 at a feed speed v. In order to generate the feed speed v, the feed unit 7 has a suitable and sufficiently powerful drive unit 7a.

[0031] Furthermore, a control unit 13 is provided for controlling the welding device 1. The control unit 13 is designed within the scope of the invention at least to control the feed unit 7, in particular the drive unit 7a, in order to adjust the feed speed v of the welding wire 8 to a desired value. The welding wire 8 is fed to the welding point in an intermittent feed cycle within the scope of the invention, which will be referred to below. Figure 3Detailed description. Here, the feed cycle C has a first time period in which the feed speed v is positive and has a second time period Z2 in which the feed speed is zero or the feed speed is negative (in the case of a reversing wire feed). The control unit 13 can have suitable hardware and / or software in a known manner. However, the control unit 13 is preferably also configured to control a welding method performed using the welding device 1. Therefore, in addition to controlling the feed speed v, the control unit 13 can also control or adjust welding process parameters of the welding process performed, such as welding current I_s, welding voltage U_s, frequency of welding current I_s or welding voltage U_s, shielding gas delivery, etc. Of course, multiple independent control units can also be provided, which communicate with each other via a suitable communication connection to exchange control variables. However, controlling the feed speed v is crucial to the present invention, so that the following mainly only relates to the control unit 13.

[0032] In the welding device 1, a user interface 14 may also be provided, which communicates with the control unit 13 in a suitable manner. The welder can select, for example, a welding program or a specific welding process with predefined welding process parameters (e.g. a pulse welding process with a specific welding current I_s and a specific frequency) via the user interface 14. Likewise, certain settings can also be selected or changed manually. For example, the feed speed v of the welding wire 8 is usually set by the welder or selected from available values ​​and is usually constant.

[0033] All required media, energy and control signals can be conveyed to the welding torch 3 in the hose assembly 5, such as electrical energy (current, voltage), coolant (if the welding torch 3 is cooled), control lines for controlling the welding process, shielding gas container 6 or shielding gas for welding wire 8. Usually a hose is provided as hose assembly 5, in which the individual lines and media are guided. However, it is of course also possible to provide a plurality of separate hoses or lines.

[0034] The opposite electrode (usually the positive electrode) contacts the workpiece 10 to be welded via a contact wire 9. The contact wire 9 is also usually referred to as a ground wire. A wire feeder 11 can also be provided on the welding torch 3 to be able to feed the welding wire 8 to the welding point 25 in a desired position and direction relative to the electrode 4a. The wire feeder 11 can also be connected to a wire guide tube 22, in which the welding wire 8 is guided separately - that is, outside the hose assembly 5 - to the wire feeder 11. However, the 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 also does not necessarily have to be arranged on the welding power source 2, but can also be arranged at any other suitable location, for example, on a welding robot.

[0035] A contact sleeve (not shown) is usually arranged on the welding torch 3, which surrounds the electrode 4a and is in electrical contact with it and is connected to the welding power source 2 (usually to the negative pole) via a welding power line 24 (usually guided in the hose assembly 5). The electrode 4a extends out of the welding torch 3 at one end of the welding torch 3. The shielding gas can be discharged from the welding torch 3 around the electrode 4a, and the shielding gas surrounds the welding point 25 together with the welding pool 26 and isolates it from the surrounding environment (such as in Figure 3 ). During welding, the welding wire 8 is fed to the welding point 25 in an intermittent feeding cycle C (optionally in a reversing wire feeding). Reversing wire feeding means that a positive feeding speed is used in a first time period Z1 and a negative feeding speed is used in a second time period Z2. Since the basic structure and basic functions of such a welding device 1 and various modifications thereof are known, they will not be described in detail here.

[0036] As mentioned above, in addition to the electrodes 4a shown, a laser optical system (not shown) can also be provided as a heat source 4. In this case, the heat is provided in addition to or instead of the arc 27 (see Figure 2 ) is introduced into the workpiece 10 by means of a laser beam. In pure laser welding (i.e. without electrode 4a), as is known, no wires 24, 9 are required, since no arc has to be ignited. Apart from this, however, the structure of the welding device 1 is essentially the same. In particular, in the case of laser welding, the welding wire 8 is also fed to the welding point 25 by means of the feed unit 7.

[0037] Figure 2 A more detailed view of the welding torch 3 in the area of ​​the tip of the non-consumable electrode 4a is shown, which is located at the welding point 25 on the workpiece 10. The welding current I_s (e.g. in the range of 100A) generated by the welding power source 2 is delivered through the electrode 41 via the welding line 24 to generate or maintain an arc 27 between the electrode 4a and the workpiece 10. The arc 27 can be ignited by known methods, such as high frequency ignition, or by bringing the workpiece 10 into contact with the electrode 4a and then lifting the electrode a for ignition. 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, such as in Figure 2 as shown in .

[0038] This quasi-static electric field 28 results in a potential distribution around the electrode 4a, as shown in Figure 2, as shown by way of example by the equipotential lines 28a. These values ​​depend essentially on the welding current, electrode cooling, shielding gas, arc length (distance A) etc., but can be assumed to be known. This potential P can be measured as an electrical variable, for example as an electrical measurement voltage U_m or as an electrical measurement current I_s, by a suitable potential detection unit 30. For this purpose, the potential detection unit 30 can have, for example, a voltage measuring device 29, with which the measurement voltage U_m can be detected relative to a reference potential. Figure 2 , exemplary voltage values ​​are indicated on the equipotential lines 28a relative to the potential P of the workpiece 10 as a reference potential. This potential P is measured via the welding wire 8, which is supplied to the welding point 25 and is therefore in a quasi-static electric field, and is detected by means of a voltage measuring device 29. For this purpose, it is not necessary to supply a separate measuring current via the welding wire 8. A possible heating current for heating the welding wire 8 also does not hinder the measurement of the potential P. The potential P can thus be detected both when using a cold welding wire and when using a hot welding wire.

[0039] Instead of the electrical measuring voltage U_m, the electrical measuring current I_m flowing through the welding wire 8 and caused by the potential P can also be measured in a similar manner, as exemplified in Figure 3 For this purpose, for example, a terminating resistor 34 can be connected between the welding wire 8 and the workpiece 10, through which a current to be measured as a measuring current I_m can flow in order to measure the potential P. In this case, Figure 3 As shown, the potential detection unit 30 has a suitable ammeter 33. Of course, in the same way, other electrical variables related to the potential distribution can be measured or determined instead of measuring the current I_m and the voltage U_m, for example, the resistance or power can be determined from the voltage U_m and the current I_m. Therefore, within the scope of the present invention, the detection of the potential P includes all these possibilities.

[0040] like Figure 3As shown in FIG. 1 , the potential detection unit 30 can be arranged, for example, in a welding power source 2 in which a reference potential of the workpiece 10 already exists, for example, via a contact wire 9 or a separate line for contacting the workpiece 10. The use of the contact wire 9 is advantageous because it can save additional lines. In the case of using the contact wire 9, the potential detection unit 30 can be connected to an interface (ground socket) of the contact wire 9 on the welding device 1, for example. In order to measure an electrical variable representing the potential P, such as an electrical measurement voltage U_m, it is only necessary to additionally provide the potential detection unit 30 in the welding device 1. For this purpose, an electrical contact on the welding wire 8 can be easily realized, for example as a sliding contact in the feed unit 7. Optionally, a terminating resistor 34 can be provided between the welding wire 8 and the workpiece or the contact wire 9 or another reference potential, which terminating resistor can also be a component of the potential detection unit 30.

[0041] From the electrical variables representing the potential P (measured voltage U_m, measured current I_m, etc.), based on the generated potential distribution, it can be easily recognized whether the welding wire 8 is in contact with the welding pool 26 generated by the electrode 4a via the arc 27, or whether the welding wire 8 is too far away from the welding pool 26 and is not in contact with the welding pool 26. When the welding wire 8 is in contact with the welding pool 26, a short circuit is formed, so that the measured voltage U_m measured by the voltage measuring device 29 drops to zero (or substantially zero), or the measured current I_m measured by the current measuring unit 33 drops to zero (or substantially zero). The same applies to the possible variables determined therefrom. On the contrary, when the welding wire 8 is not in contact with the welding pool 26, a certain measured current I_m or a certain measured voltage U_m is measured, which depends on the height of the potential P.

[0042] Optionally, an additional auxiliary energy source (not shown) can also be provided in the measuring circuit of the potential detection unit 30 in order to generate a defined basic potential. This is advantageous for applications in which no or only a small electric field is formed around the heat source 4, such as in the case of pure laser welding in which the heat source has a laser optical device 4a. Due to the auxiliary energy source, a measurable potential that can be used for measurement is always present, regardless of the potential P of the electric field. The auxiliary energy source can be designed, for example, as a high-impedance power source, with which an auxiliary voltage can be applied to the welding wire 8. Thus, in the case of WIG welding, for example, the potential P can also be measured before the arc 27 is ignited, and it can be determined from this potential whether the welding wire 8 is in contact with the workpiece 10, in particular whether a short circuit is present.

[0043] Furthermore, according to the present invention, a determination unit 31 is provided, which is configured to determine an actual value t1_ist of a duration t1 of a first time period Z1 of a respective feed cycle C during the execution of the welding method, during which the welding wire 8 is not in contact with the weld pool 26 or the workpiece 10. As an alternative or in addition, the determination unit 31 may also be configured to determine an actual value t2_ist of a duration t2 of a second time period Z2 of a respective feed cycle C, during which the welding wire 8 is in contact with the weld pool 26 or the workpiece 10. Figure 4 The durations t1 , t2 and the time periods Z1 , Z2 are shown in .

[0044] The determination unit 31 can be constructed as an independent unit, which has suitable hardware and / or software and communicates with the control unit 13 via a suitable communication connection, such as in Figure 2 However, it is advantageous if the determination unit 31 is as shown in Figure 3 1 and 2. As shown in FIG. 1 , the control unit 13 is integrated in the control unit 13. 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 adjust at least one specific parameter of the feed speed v of the welding wire 8 according to a specific actual value t1_ist and / or t2_ist and a previously defined setpoint value.

[0045] The determination unit 31 can recognize in a simple manner from the electrical variables (measured voltage U_m, measured current I_m, etc.) representing the potential P based on the generated potential distribution whether the welding wire 8 is in contact with the welding pool 26 generated by the electrode 4a via the arc 27 (short circuit) or whether the welding wire 8 is too far away from the welding pool 26 (no short circuit). Figure 4 As shown, the duration t1 of the first time period Z1 (no short circuit) or the duration t2 of the second time period Z2 (short circuit) can be determined from the time profile of the measured electrical variable representing the potential P.

[0046] exist Figure 4 In the upper graph, an exemplary time profile of a measured potential P is shown. This profile therefore corresponds to the profile of an actual value P_ist of the potential P measured by the potential detection unit 30. Here, depending on the measured variable, it can be, for example, a profile of a measured current I_m or a profile of a measured voltage U_m. In the middle graph, the associated time profile of a rated value P_soll of the potential P is shown. In the lower graph, the associated time profile of the feed speed v of the welding wire 8 is shown. It can be seen from this that the welding wire 8 is fed to the welding pool 26 with an intermittent feed cycle C at a feed speed v that varies over time. The feed speed v is adjusted to a specific positive value in each cycle C within the corresponding first time period Z1, here the values ​​v1, v2 (in Figure 4 In the example shown, only the first cycle C is shown for the sake of simplicity). In the subsequent second time segment Z2 of the cycle C, a feed speed v=0 is used. As an alternative, a reversing wire feed can also be used, wherein a negative feed speed v is used in each second time segment Z2, as shown by a dashed line for two feed cycles C. In this case, a negative feed speed v corresponds to a displacement of the welding wire from the weld pool 26, while a positive feed speed v corresponds to a displacement in the direction of the weld pool 26.

[0047] During each first time period Z1, the welding wire 8 is not in contact with the welding pool 26. Therefore, the first time period Z1 corresponds to a short-circuit-free time, during which the potential P_ist measured by the potential detection unit 30 is greater than zero or greater than a specified value representing a short circuit. Each second time period Z2 located between two first time periods Z1 corresponds to a short-circuit time, during which the potential P_ist measured by the potential detection unit 30 is zero or has a value representing a short circuit. The determination unit 31 can determine the current duration t1_ist of the first time period Z1, that is, the length of the short-circuit-free time, from the actual value change curve P_ist. As an alternative, the determination unit 31 can also determine the current duration t2_ist of the second time period Z2, that is, the length of the short-circuit time, from the actual value change curve P_ist. 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 time period Z1 and the duration t2_ist of the second time period Z2. In this case, it is also called the so-called droplet separation frequency f. Figure 3 In FIG. 1 , the current droplet detachment frequency f_ist and the desired setpoint value f_setpoint of the droplet detachment frequency f are shown taking a feed cycle C as an example.

[0048] For example, a specific threshold value P_sw can be determined for the potential P, which represents a short circuit. The threshold value P_sw can be zero or slightly higher, for example. Figure 4 For example, a threshold value P_sw slightly greater than zero is marked in it. Thus, for example, the actual value t1_ist of the duration t1 can be determined in the following way, namely measuring the time between the time point ZPa when the measured potential P_ist (for example, welding current I_s or welding voltage U_s) exceeds the specified threshold value P_sw and the subsequent time point ZPb when the measured potential P_ist is again below the specified threshold value P_sw. The duration t2 between the time point ZPb when the measured potential P_ist is below the specified threshold value P_sw and the subsequent time point ZPc when the measured potential P_ist again exceeds the specified threshold value P_sw can be measured in a similar manner. Figure 4In the upper graph of FIG. 1 , the time points ZPa to ZPc are shown taking the first cycle consisting of a first time period Z1 and a subsequent second time period Z2 as an example. However, the determination can of course be carried out continuously during the execution of the welding process, i.e. during a number of feed cycles C. The actual value f_ist of the droplet separation frequency f corresponds to the time between the time point ZPa and the time point ZPc.

[0049] Here, the actual values ​​t1_ist, t2_ist at the times t1, t2 are preferably measured continuously in time, but can also be measured discretely in time (i.e., at a predetermined interval). The actual value P_ist is preferably also measured continuously or discretely in time, i.e., for example, the measurement voltage U_m or the measurement current I_m is measured. For example, the time-discrete measurement can be performed with a controlled time step that will be described in detail below. It can be seen in the middle curve diagram that a specific constant time t1_soll (or t2_soll) is specified as the setpoint value. According to the invention, the control unit 13 is configured to control the feed unit 7 accordingly, so that in the welding method, at least one specified parameter of the feed speed v of the welding wire 8 in the feed cycle C is adjusted so that the desired setpoint value t1_soll, t2_soll or f_soll is reached.

[0050] For example, the average feed speed vm of an entire feed cycle C, and / or the average positive feed speed vmZ1 of a feed cycle C, and / or the average negative feed speed vmZ2 of a feed cycle C (in the case of reversing wire feeding) can be used as parameters for the feed speed v. Figure 3 In FIG. 1 , taking the first feed cycle C as an example, the average feed speed vm, the average positive feed speed vmZ1 and the average negative feed speed vmZ2 are shown.

[0051] For example, the duration t1 of the first time period Z1 of a corresponding feed cycle C can be determined as an actual value t1_ist, wherein the rated value t1_soll of the first duration t1 is used as the rated value. Similarly, the duration t2 of the second time period Z2 of a corresponding feed cycle C can be determined as an actual value t2_ist, and the rated value t2_soll of the second duration t2 is used as the rated value. The actual value f_ist of the droplet transfer frequency f can also be determined, which corresponds to the sum of the duration t1 of the first time period Z1 of a corresponding feed cycle C and the duration t2 of the second time period Z2. In this case, the rated value f_soll of the droplet transfer frequency f can be used as the rated value. In all three cases, one or more of the above-mentioned influencing parameters of the feed speed v can be changed to adjust to the corresponding rated value.

[0052] For this purpose, a suitable controller, such as a PI controller or a PID controller, can be advantageously provided in the control unit 13. The controller is designed to determine the manipulated variable S of the feed unit 7, in particular the manipulated variable S of the drive unit 7a, from the respectively determined actual values, such as the actual value t1_ist of the duration t1 of the first time period Z1 (or the determined actual value t2 of the duration t2 of the second time period Z2) and from a previously specified (preferably constant) setpoint value, such as t1_setpoint, t2_setpoint or f_setpoint. The control unit 13 then uses the determined manipulated variable S to control the feed unit 7 accordingly, so that Figure 3 The feed speed v is adjusted as shown.

[0053] Thus, by continuously adjusting the specified parameters, such as the average feed speed vm and / or the average positive feed speed vmZ1 and / or the optional average negative feed speed vmZ2, the short-circuit time t2 or the non-short-circuit time t1 can be adjusted to the desired value. Thus, the variable influencing parameters mentioned at the beginning (such as the variable distance X between the electrode 4a and the workpiece 10, the variable angle α between the electrode 4a and the welding wire 8 - see Figure 2 , or a variable welding speed G in the direction of the weld seam 32 - see Figure 3 ) automatically reacts, which can improve the welding quality, especially in the case of manual welding. For example, if the welder unintentionally increases the welding speed G, this usually leads to an automatic extension of the short-circuit-free time t1, because less additional material is present in the weld pool 26. By means of the control according to the invention, in this case, for example, the average feed speed vm is increased and thus automatically adapted to the increased welding speed G (and vice versa).

[0054] The setpoint value t2_setpoint for the short-circuit time t2, the setpoint value t1_setpoint for the non-short-circuit time t1, and the setpoint value f_setpoint for the droplet separation frequency f can be assumed to be known and stored, for example, as fixed values ​​in the control unit 13. The setpoint values ​​can also depend on the diameter of the welding wire 8 and / or the material of the welding wire 8 and / or the electric welding process parameters (for example, the welding current I_s or the welding voltage U_s). Depending on the current welding process parameters (which can be regarded as known due to the selected welding program), a corresponding setpoint value can be automatically set. In addition, the setpoint value can also depend on the weld shape of the weld seam 32 to be produced (fillet weld, V-weld, etc.).

[0055] For example, a function that relates the setpoint value to at least one variable, such as the welding voltage I_s, can be stored in the control unit 13. The control unit 13 can then determine the setpoint value from the function. In the case where the setpoint value is related to one variable, the function can be stored, for example, in the form of a characteristic curve. In the case where the setpoint value is related to a plurality of variables, the function can be stored, for example, as a family of characteristic curves. Of course, the welder can optionally additionally make manual settings, for example via the user interface 14. The preset setpoint value can, for example, be increased or reduced by the welder according to a previously specified bandwidth, for example in percentage.

[0056] exist Figure 4 It can be seen that the duration of each feed cycle C and the size of the feed speed v in the corresponding feed cycle C can be automatically changed, and in particular reduced, during the control process. In the first cycle shown, the error, that is, the difference △t1 between the actual value t1_ist and the setpoint value t1_soll, is still relatively large, but this error is reduced by adjusting the feed speed v until the actual values ​​t1_ist, t2_ist are adjusted to the previously specified setpoint values ​​t1_soll, t2_soll. Figure 4 This is shown, for example, in the last and second to last cycle, where the error has been controlled to a sufficiently small value, preferably zero.

[0057] As in Figure 4 As shown in the lower graph of , it is advantageous to change the average feed speed vm or the average positive feed speed vmZ1 if the feed speed v is first adjusted to a higher first positive value v1 within a certain ramp-up time tu at the beginning of each feed cycle C and then reduced to a relatively lower second positive value v2<v1 after the ramp-up time tu. This has proven to be advantageous due to the inertia of the welding wire 8 and the welding torch 3. In this case, the first value v1 and / or the ratio between the first value v1 and the second value v2 and / or the length of the ramp-up time tu can depend, for example, on the error Δt1 between the actual value t1_ist and the setpoint value t1_setpoint determined at the respective current point in time or in the current time step (or on the error Δt2 between the determined actual value t2_ist and the setpoint value t2_setpoint). As can be seen with reference to the illustrated cycles, the greater the respective differences Δt1, Δt2, the higher the first value v1 and / or the longer the time tu. Therefore, the ratio between the first value v1 and the second value v2 may be changed, for example, according to the error Δt1 (or the error Δt2 ) in the control process.

[0058] However, providing an increased feed speed v1 for the lifting time tu is of course only an option, and it is also possible, for example, to modify the average feed speed vm or the average positive feed speed vmZ1 simply by changing the value v2.

[0059] As already mentioned, the invention is not limited to the described WIG welding, but can also be used in laser welding or WIG / 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) to produce a weld pool (26), wherein a welding wire (8) separate from the heat source (4) is fed to the weld pool (26) and the welding wire (8) is melted in the region of the weld pool (26) by the introduced energy to produce a weld seam (32) on the workpiece (10), characterized in that: The welding wire (8) is fed to the welding pool (26) in an intermittent feed cycle (C), preferably at a reversing feed speed (v), and during the execution of the welding method, an actual value (t1_ist) of the duration (t1) of a first time period (Z1) of a respective feed cycle (C) is determined and / or an actual value (t2_ist) of the duration (t2) of a second time period (Z2) of a respective feed cycle (C) is determined, during which the welding wire (8) is not in contact with the welding pool (26) and during which the welding wire (8) is in contact with the welding pool (26), and at least one specified parameter of the feed speed (v) of the welding wire (8) in the feed cycle (C) is changed according to the determined actual value and a previously specified setpoint value, The duration (t1) of the first time period (Z1) of a corresponding feed cycle (C) is determined as an actual value (t1_ist) and the rated value (t1_soll) of the first duration (t1) is used as the rated value, or the duration (t2) of the second time period (Z2) of a corresponding feed cycle (C) is determined as an actual value (t2_ist) and the rated value (t2_soll) of the second duration (t2) is used as the rated value, or the sum of the duration (t1) of the first time period (Z1) and the duration (t2) of the second time period (Z2) of a corresponding feed cycle (C) is determined as an actual value (f_ist) and the rated value (f_soll) of the droplet transfer frequency (f) is used as the rated value.

2. The welding method according to claim 1, characterized in that: The average feed speed (vm) of an entire feed cycle (C) and / or the average positive feed speed (vmZ1) of a feed cycle (C) and / or the average negative feed speed (vmZ2) of a feed cycle (C) are used as parameters for 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 in such a way that at the beginning of each feed cycle (C) the feed speed (v) is adjusted to a specified first value (v1) within a specified lifting time (tu) and is reduced from the first value (v1) to a specified second value (v2) after the lifting time (tu) has expired, wherein the first value (v1) and / or the ratio between the first value and the second value (v2) and / or the length of the lifting time (tu) are preferably determined as a function of an error (Δt1, Δt2) between a determined actual value (t1_ist, t2_ist) and the previously specified setpoint value (t1_setpoint, t2_setpoint).

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

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

6. The welding method according to any one of claims 1 to 5, characterized in that: The setpoint value is determined as a function of the diameter of the welding wire (8) and / or the material of the welding wire (8) and / or electric welding process parameters, in particular the welding current (I_s), and / or the weld seam shape of the weld seam (32).

7. The welding method according to any one of claims 1 to 6, characterized in that: A potential (P_ist) is detected on the welding wire (8), and an actual value (t1_ist) of the duration (t1) of the first time period (Z1) and / or an actual value (t2_ist) of the duration (t2) of the second time period (Z2) is determined from the time variation curve of the measured potential (P_ist), wherein the potential (P_ist) is preferably detected in the following manner, i.e., an electrical measurement voltage (U_m) between the welding wire (8) and the workpiece (10) and / or an electrical measurement current (I_m) flowing through the welding wire (8), and an actual value (t1_ist) of the duration (t1) of the first time period (Z1) and / or an actual value (t2_ist) of the duration (t2) of the second time period (Z2) is determined from the time variation curve of the measurement voltage (U_m) and / or the measurement current (I_m), wherein preferably a base potential is generated between the welding wire (8) and the workpiece (10).

8. A welding device (1) comprising a welding torch (3) having a non-consumable electrode (4a) as a heat source (4) for introducing energy at a welding point (25) on a workpiece (10) to produce a weld pool (26), the welding device comprising a feed device (7) for feeding a welding wire (8) separate from the heat source (4) to the weld pool (26), wherein the welding wire (8) can be melted in the region of the weld pool (26) by the energy introduced from the heat source (4) to produce a weld seam (32) on the workpiece (10), and the welding device comprising a control unit (13) for controlling the feed device (7), characterized in that: The control unit (13) is configured to control the feed device (7) so that the welding wire (8) can be fed to the welding pool (26) with an intermittent feed cycle (C), preferably with a reversing feed speed (v), and is provided with a determination unit (31), which is configured to determine an actual value (t1_ist) of a duration (t1) of a first time period (Z1) of a corresponding feed cycle (C) and / or determine an actual value (t2_ist) of a duration (t2) of a second time period (Z2) of a corresponding feed cycle (C) during a welding method performed using the welding device (1), in which the welding wire (8) is not in contact with the welding pool (26) and in which the welding wire (8) is in contact with the welding pool (26), and the control unit (13) is configured to control the feed device (7) so as to determine the actual value (t1_ist) of a duration (t1) of a first time period (Z1) of a corresponding feed cycle (C) and / or determine the actual value (t2_ist) of a duration (t2) of a second time period (Z2) of a corresponding feed cycle (C) during a welding method performed using the welding device (1), and the control unit (13) is configured to control the feed device (7) so as to determine the actual value (t1_ist) of a duration (t2) of a second time period (Z2) of a corresponding feed cycle (C) according to the determined At least one specified parameter of the feed speed (v) of the welding wire (8) in a feed cycle (C) is changed by a predetermined actual value and a predetermined setpoint value, wherein the actual value (t1_ist) is the duration (t1) of a first time period (Z1) of a corresponding feed cycle (C) and the setpoint value is the setpoint value (t1_setpoint) of the first time period (t1), or the actual value (t2_ist) is the duration (t2) of a second time period (Z2) of a corresponding feed cycle (C) and the setpoint value is the setpoint value (t2_setpoint) of the second time period (t2), or the actual value (f_ist) is the sum of the duration (t1) of the first time period (Z1) and the duration (t2) of the second time period (Z2) of a corresponding feed cycle (C) and the setpoint value is the setpoint value (f_setpoint) of the droplet transfer frequency (f).

9. The welding device (1) according to claim 8, characterized in that: The parameters of the feed speed (v) include 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 adjust the feed speed (v) to a specified first value (v1) within a specified lifting time (tu) at the beginning of each feed cycle (C) in order to change the average feed speed (vm) or the average positive feed speed (vmZ1), and to reduce the feed speed (v) from the first value (v1) to a specified second value (v2) after the lifting time (tu) has expired, wherein the first value (v1) and / or the ratio between the first value and the second value (v2) and / or the length of the lifting time (tu) are preferably determined as a function of an error (Δt1, Δt2) between a determined actual value (t1_ist, t2_ist) and the previously specified setpoint value (t1_setpoint, t2_setpoint).

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

12. The welding device (1) according to any one of claims 8 to 11, characterized in that: The determination unit (31) is configured to determine an actual value (t1_ist) of the duration (t1) of a first time period (Z1) and / or an actual value (t2_ist) of the duration (t2) of a second time period (Z2) in a time-continuous or time-discrete manner, wherein the determination unit (31) is preferably integrated in a control unit (13), and / or the control unit (13) has a controller configured to determine a manipulated variable (S) for a feed unit (7) from the determined actual value and the predetermined setpoint value, and the control unit (13) is configured to control the feed unit (7) using the determined manipulated variable (S) to adjust to the setpoint value.

13. The welding device (1) according to any one of claims 8 to 12, characterized in that: The determination unit (31) has a potential detection unit (30) which is configured to detect a potential (P) generated around a heat source (4) on the welding wire (8), and the determination unit (31) is configured to determine an actual value (t1_ist) of a duration (t1) of a first time period (Z1) and / or an actual value (t2_ist) of a duration (t2) of a second time period (Z2) from a time curve of the measured potential (P_ist), wherein the potential detection unit (30) preferably has a device for measuring an electrical measurement voltage (U_ist) between the welding wire (8) and the workpiece (10). _m) and / or a current measuring device (33) for measuring an electrical measuring current (I_m) flowing through a welding wire (8), wherein the determination unit (31) is configured to determine an actual value (t1_ist) of the duration (t1) of a first time period (Z1) and / or an actual value (t2_ist) of the duration (t2) of a second time period (Z2) from a time variation curve of the measuring voltage (U_m) or the measuring current (I_m), wherein an auxiliary energy source is particularly preferably provided, by means of which a basic potential can be generated between the welding wire (8) and the workpiece (10).

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

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