Welding transformer, welding device and welding method for welding at least one component

Abstract

The invention provides a welding transformer, a welding device and a welding method for welding at least one component. The welding transformer comprises a primary winding for connection to an energy supply, a first secondary winding inductively coupled to the primary winding for connection to a first welding electrode of a welding tool, a second secondary winding and a third secondary winding, which are inductively coupled to the primary winding and connected to the first secondary winding, and are arranged for connection to a second welding electrode of the welding tool, with which at least one component is to be contacted, a first rectifying branch for rectifying a current flowing between the first secondary winding and the first welding electrode, a second rectifying branch for rectifying a current flowing between the second secondary winding and the second welding electrode, and a current-limiting element, which is connected to the third secondary winding in order to limit the current through the third secondary winding to a predetermined maximum value.

Description

Technical Field

[0001] The present invention relates to a welding transformer, welding equipment and welding method for welding, in particular resistance welding, at least one component. Background Technology

[0002] For example, welding, especially resistance welding, is used in automated production for assemblies of various plates. For instance, in production lines for furniture, radiators, etc., metal parts are joined by welding using welding tools on welding equipment. In automated vehicle manufacturing, welding equipment is used to create at least one welded connection on the body of vehicles such as motor vehicles, trucks, and airplanes.

[0003] Alternatively or additionally, resistance welding equipment can be used in single-piece production.

[0004] This welding equipment has a rectifier circuit for supplying direct current to the welding tool. The rectifier circuit can be constructed as a diode rectifier. To improve the efficiency of the rectifier circuit, four thyristors can be used alternatively. In this case, two anti-parallel thyristors are used instead of each diode in the diode rectifier. However, compared to a diode rectifier, a rectifier circuit with four thyristors requires twice the installation space.

[0005] Due to the direct current used during welding, magnetization may occur in the welded parts or components. This makes further processing of the welded metal parts difficult. The potential magnetization of system components can also lead to contamination and malfunctions in the welding machine.

[0006] For aluminum to be welded, it is essential to break through the corresponding alumina layer formed on the surface of the aluminum components. This requires a sufficiently high open-circuit voltage at the output of the welding transformer, ensuring sufficient current flow for welding even with the small current present in the alumina layer and the existing high contact resistance. Furthermore, the adhesive at the welding point also contributes to contact difficulties during welding. In addition, the increasingly shorter cycle times required for automated production must be met.

[0007] If welding is required on a combination of plates with different material thicknesses (e.g., thick / thin), additional problems arise. In this case, it's important to note that the welding clamp is always held onto the plate combination in the following direction for welding: the electrode that heats up more intensely is placed on the thicker plate. The electrode that heats up more intensely corresponds to the positive electrode. Therefore, positioning the welding clamp on the components for successive welding connections is often time-consuming.

[0008] To meet the required cycle time, two robots are often used, each guiding the welding gun. This increases the location requirements of the resistance welding equipment and the costs of supplying and operating it.

[0009] Furthermore, when welding aluminum, undesirable burn-off or material migration may occur on the welding electrodes, depending on the direction of the welding current. This is due to the various alloys and / or combinations of plate thicknesses being welded, and / or the Peltier effect. Summary of the Invention

[0010] Therefore, the object of the present invention is to provide a welding transformer, welding equipment, and welding method for welding at least one component, which can solve the problems mentioned above. In particular, it is to provide a welding transformer, welding equipment, and welding method for welding at least one component, wherein, in the welding process in which low current and high contact resistance exist, sufficient current is ensured to pass through for welding while the installation space for the welding transformer is small and efficient, and the cycle time for welding in automated production can be kept short while maintaining high production quality and low production cost.

[0011] The task is solved by a welding transformer for a welding apparatus used for welding at least one component, as described in claim 1. The welding transformer has a primary winding, a first-stage winding, a second-stage winding, and a third-stage winding, a first rectifier branch, a second rectifier branch, and a current-limiting element; the primary winding is connected to an energy supply device; the first-stage winding is inductively coupled to the primary winding and is connected to a first welding electrode of a welding tool; the second-stage and third-stage windings are inductively coupled to the primary winding and connected to the first-stage winding, and are provided for connection to a second welding electrode of the welding tool, wherein at least one component must contact the welding electrode for welding; the first rectifier branch is used to rectify the current flowing between the first-stage winding and the first welding electrode; the second rectifier branch is used to rectify the current flowing between the second-stage winding and the second welding electrode; the current-limiting element is connected to the third-stage winding to limit the current through the third-stage winding to a predetermined maximum value.

[0012] Existing auxiliary windings or inductors, which can be implemented as air-core coils, are particularly advantageous in welding processes where low current and high contact resistance are present. These conditions are especially present when welding, particularly resistance welding, at least one component with alumina and / or adhesive on its surface. Despite the low current and high contact resistance and / or contact difficulties in such components, the described welding transformer still ensures sufficient current flows through at least one welding electrode.

[0013] The welding transformer, due to its construction scheme combined with a rectifier, can commutate very quickly. This allows for the use of higher power on the secondary side of the welding transformer compared to conventional welding transformers combined with diode rectifiers.

[0014] The proposed design for the welding transformer can achieve lower grid power than conventional welding transformers combined with diode rectifiers. Here, lower grid power includes active power, reactive power, and phase current. This also results in CO2 savings during the operation of the welding transformer.

[0015] Furthermore, for the welding transformers requiring protection, only smaller converters and feeder components of a smaller fixed size, such as the main switch, are needed. This results in cost advantages in both the manufacturing and operation of the welding transformers.

[0016] In addition, the cooling requirements of welding transformers are reduced during operation. This also results in cost advantages in both the manufacturing and operation of welding transformers.

[0017] In summary, welding transformers advantageously contribute to keeping welding cycle times short in automated production, while ensuring high-quality and low-cost production. Furthermore, the welding transformer allows for faster current cut-off after the welding process compared to conventional welding equipment. This significantly reduces the time required to create welded joints. Consequently, even with only a single welding robot in operation, predetermined cycle times can be adhered to. This results in substantial advantages regarding the location requirements of welding equipment and its provision and operating costs.

[0018] Compared to the thyristor solutions described above, the welding transformer claimed in the claims has lower losses and a smaller installation space, while offering higher power. Furthermore, compared to the prior art MF-DC transformer with a diode rectifier, the welding transformer claimed in the claims has similar performance and a similar installation space, but with lower losses. These characteristics represent a significant advantage in terms of resource conservation. Moreover, the improved operating characteristics result in lower costs for the operators of resistance welding equipment.

[0019] Therefore, due to the often dominant ratio of constrained positions and for cost reasons, the welding transformer claimed in the claims, suitable for resistance welding, provides a very advantageous solution.

[0020] Other advantageous construction options for the welding transformer are described in the dependent claims.

[0021] The first and second rectifier branches may each have a series circuit consisting of two transistors connected between the welding tool and the output of the welding transformer, wherein the polarity of one transistor in the series circuit is reversed relative to the polarity of the other transistor in the series circuit.

[0022] These two transistors can be metal-oxide-semiconductor field-effect transistors, in which transistors with directional polarity are connected to the welding tool.

[0023] Additionally, a third rectifier branch may be provided for rectifying the current flowing between the primary winding and the first welding electrode. In one embodiment, the third rectifier branch has a series circuit consisting of two transistors connected between the welding tool and the output of the welding transformer, wherein the polarity of one transistor in the series circuit is reversed relative to the polarity of the other transistor in the series circuit.

[0024] In the construction scheme, the current limiting element is a controllable inductor and / or resistor connected between the secondary winding and the second welding electrode.

[0025] In another configuration, the current-limiting element is a semiconductor switch connected between the secondary winding and the second welding electrode. The semiconductor switch can be a bipolar transistor or a metal-oxide-semiconductor field-effect transistor. Alternatively, the semiconductor switch can be a thyristor, optionally connected in anti-parallel to another thyristor.

[0026] In another configuration, the current-limiting element is a series circuit consisting of a first tunnel diode and a semiconductor switch, with a second tunnel diode connected in anti-parallel to the first tunnel diode. The series circuit is connected between the second secondary winding and the second welding electrode, and the semiconductor switch is a bipolar transistor, a metal-oxide-semiconductor field-effect transistor, or a thyristor.

[0027] At least one of the welding transformers described above may be part of a welding apparatus for welding at least one component. The welding apparatus further includes a welding tool constructed as a welding clamp with two welding electrodes, between which at least one component is arranged during welding. At least one welding transformer may be used to supply welding current to the welding tool during the welding of at least one component.

[0028] The welding equipment may further include a control device for switching the series circuit consisting of two transistors in the rectifier branch during the inverter-controlled welding time in a first operating mode, and for switching the series circuit consisting of two transistors in the rectifier branch for a predetermined duration at the end of the inverter-controlled welding time in a second operating mode, which differs from the first operating mode. In this case, the first operating mode implements a polarity-reversible welding voltage and a polarity-reversible welding current on the welding transformer, while the second operating mode accelerates the current decay of the welding current already generated in the first operating mode.

[0029] The welding equipment described above can be part of a system configured to process objects. In this case, the resistance welding equipment can be configured to perform resistance welding on at least one component of at least one of the objects. Additionally or alternatively, the system can be constructed for producing a vehicle body, radiator, or chain as the object. Additionally or alternatively, the system can be constructed for producing an object from at least one component made of aluminum, on which adhesive may be present.

[0030] Furthermore, this task is solved by the resistance welding method for resistance welding at least one component according to claim 15. In this case, a welding tool is used that is electrically connected to a welding transformer having a primary winding, a first-stage winding, a second-stage winding, and a third-stage winding; the primary winding is used to connect to an energy supply device; the first-stage winding is inductively coupled to the primary winding and is used to connect to a first welding electrode of the welding tool; the second-stage winding and the third-stage winding are respectively inductively coupled to the primary winding and connected to the first-stage winding, and are provided to connect to a second welding electrode of the welding tool. In this case, the resistance welding method includes the steps of: contacting at least one component with the first and second welding electrodes of the welding tool; rectifying the current flowing between the first-stage winding and the first welding electrode using a first rectifier branch; rectifying the current flowing between the second-stage winding and the second welding electrode using a second rectifier branch; and limiting the current through the third-stage winding to a predetermined maximum value using a current-limiting element connected to the third-stage winding.

[0031] The welding method achieves the same advantages mentioned earlier regarding welding transformers and welding equipment.

[0032] Other possible embodiments of the invention also include combinations of features or embodiments not explicitly mentioned in the foregoing or hereinafter related to these embodiments. Individual aspects will also be added by those skilled in the art as improvements or supplements to the corresponding basic forms of the invention. Attached Figure Description

[0033] The invention will then be described in more detail with reference to the accompanying drawings and embodiments.

[0034] Figure 1 A block circuit diagram of a system having a welding apparatus according to a first embodiment is shown; Figure 2 The following graph shows the time variation of welding current: the welding current is generated when welding is performed using the welding equipment according to the first embodiment, and the welding current decays after the welding process compared with the welding current variation in the normal operation mode of the welding equipment; Figure 3 A block circuit diagram of a welding apparatus according to a second embodiment is shown; and Figure 4 A block circuit diagram of a welding apparatus according to a third embodiment is shown.

[0035] In these accompanying drawings, unless otherwise specified, the same or functionally equivalent elements are equipped with the same reference numerals. Detailed Implementation

[0036] Figure 1 A system 1 with welding equipment 2 is schematically shown, the welding equipment 2 being, in particular, resistance welding equipment 2. For example, system 1 could be a production system for objects 4 such as vehicles, furniture, radiators, etc.

[0037] In production system 1, metal parts 5 and 6 can be joined by welding, particularly resistance welding, to create a welded joint 7. For this purpose, welding equipment 2 includes at least one welding tool 10 in the form of a welding clamp, a control device 20, a converter 25, a welding transformer 30, a current-limiting element implemented as a controlled inductor 36, a rectifier circuit 40, and a device 50 for guiding the welding tool 10. The converter 25 and therefore the welding transformer 30 are supplied with electrical energy by an energy supply network 27.

[0038] exist Figure 1 In one example, the welding tool 10 has two welding electrodes 11 and 12.

[0039] The welding transformer 30 has a primary winding 31 on its primary side. On its secondary side, the welding transformer 30 has a first primary winding 32, a second primary winding 33, and an auxiliary winding 34, which is a third primary winding. The welding transformer 30 has four outputs, with windings 32 to 34 arranged between these outputs. The transformer 30, with a rectifier circuit 40 connected downstream, is a medium-frequency DC transformer, which can also be referred to as an MF-DC transformer. Furthermore, the welding transformer 30 has an auxiliary winding 34 as a third primary winding, as already mentioned.

[0040] The rectifier circuit 40 has a first rectifier branch 41, a second rectifier branch 42, and a third rectifier branch 43. The first rectifier branch 41 is constructed as a series circuit consisting of a first transistor and a second transistor. The second rectifier branch 42 is constructed as a series circuit consisting of a first transistor and a second transistor. The transistors in branches 41 and 42 are, in particular, metal-oxide-semiconductor field-effect transistors (MOSFETs). For example, the third rectifier branch 43 has at least one transistor. In particular, the third rectifier branch 43 has a series circuit consisting of transistors, especially MOSFETs, which can be operated in a synchronous circuit in a manner controlled by the control device 20.

[0041] Under the control of the control device 20, the welding equipment 2 can use the welding tool 10 to create a welded joint 7. For this purpose, at least one of the components 5 and 6 is arranged between the two welding electrodes 11 and 12, as described above and, for example, in... Figure 1 As shown in the diagram. In this case, it is particularly likely that components 5 and 6 have specific combinations, especially plate combinations. Such specific combinations are in particular combinations of plates with different material thicknesses, combinations of components with specific shapes, combinations with aluminum components and / or aluminum plates, etc. In order to weld the aluminum, the resistance welding equipment 2 is operated by means of the control device 20 so that the corresponding aluminum oxide layer on the relevant surface of the aluminum component is broken through.

[0042] Furthermore, if an adhesive is present at the location where the welded connection 7 is to be manufactured, the welded connection 7 can also be manufactured using the welding equipment 2 under the control of the control device 20. This will be described more precisely thereafter.

[0043] It is possible that, for example, the two sides of a single component 5 are connected to each other by resistance welding using one or more welded connections 7. Regardless of how many components 5 and 6 are connected to each other by welded connections 7, the (multiple) welded connections 7 can be spot welds, welds, or a combination thereof.

[0044] During normal welding operation, the welding transformer 30 converts the primary voltage U1 into the first to third stage voltages U. 21 U 22 U 23 In this case, the secondary voltage U 21 U 22 U 23 The sum of these values ​​is less than the value of the primary voltage U1. Furthermore, the welding transformer 30 transforms the primary current I1 on the primary side of the welding transformer 30 into a secondary current I2 on the secondary side of the welding transformer 30. The secondary current I2, which can also be referred to as the welding current, has a higher value than the primary current I1.

[0045] Therefore, in order to perform welding on the secondary side of the welding transformer 30 in the welding equipment 2, the primary voltage U 21 Attached to the primary winding 32 of the welding transformer 30. Secondary voltage U 21 It is attached between the first and second outputs of the welding transformer 30. Additionally, the second stage voltage U... 22 It is attached between the second and third outputs of the welding transformer 30. Furthermore, the third stage voltage U... 23 This current is applied between the second and fourth outputs of the welding transformer 30, causing a current I3 through the winding 34. The primary voltage U... 21 Secondary voltage U 22 and the third stage voltage U 23 Forming welding voltage U 21 U 22 U 23 The welding voltage U 21 U 22 U 23 This causes the welding current I2.

[0046] The first rectifier branch 41 is connected to the primary winding 32 of the welding transformer 30. In other words, the first rectifier branch 41 is connected to the first output of the welding transformer 30. The first rectifier branch 41 is connected between the welding transformer 30 and the welding tool. More precisely, the first rectifier branch 41 is connected between the welding transformer 30 and the first welding electrode 11.

[0047] The second welding electrode 12 is directly connected to the tap between the first auxiliary winding 32 and the second auxiliary winding 33. The tap between the first auxiliary winding 32 and the second auxiliary winding 33 is the second output of the welding transformer 30.

[0048] The second rectifier branch 42 is connected between the welding transformer 30 and the first welding electrode 11. Here, the third output of the welding transformer 30 is connected to one side of a controlled inductor 36, which in turn is connected to the second rectifier branch 42 on the other side. In other words, the second rectifier branch 42 is connected to the third output of the welding transformer 30. The second rectifier branch 42 is connected between the welding transformer 30 and the welding tool 10. More precisely, the second rectifier branch 42 is connected between the welding transformer 30 and the first welding electrode 11.

[0049] The auxiliary winding 34 is connected at one end to the second output of the welding transformer 30, or to a tap between the primary winding 32 and the secondary winding 33. The other end of the auxiliary winding 34 is connected to the controlled inductor 36. Furthermore, the controlled inductor 36 is connected to the third rectifier branch 43. In other words, the third rectifier branch 43 is connected to the third output of the welding transformer 30. The third rectifier branch 43 connects between the welding transformer 30 and the welding tool 10. More precisely, the third rectifier branch 43 connects between the welding transformer 30 and the first welding electrode 11.

[0050] During normal welding operation (as described above), control device 20 controls transformer 30 so that transformer 30 does not saturate when auxiliary winding 34 is operating on one side only. To this end, control device 20 controls controllable inductor 36 to limit the current I3 in auxiliary winding 34 to a predetermined current in primary winding 31 of transformer 30. Current I3 flows to first welding electrode 11 through rectifier branch 43. Third rectifier branch 43 has a corresponding series circuit composed of transistors, such as field-effect transistors, especially MOSFETs, to rectify the current in auxiliary winding 34. The series circuit composed of transistors, such as field-effect transistors, especially MOSFETs, can operate in a synchronous circuit, as described subsequently with respect to first rectifier branch 41 and second rectifier branch 42.

[0051] Therefore, when controlled by the control device 20, the controllable inductor 36 achieves current limitation on the auxiliary winding 34 and its components. Figure 1 In device 2, such components are the controllable inductor 36 and the third rectifier branch 43. Current limiting prevents the auxiliary winding 34 and its components from being damaged by excessive current I3. Alternatively, the third rectifier branch 43 is implemented as a diode.

[0052] By means of the auxiliary winding 34 on the secondary side of transformer 30, the output voltage of transformer 30 can be in no-load condition and increased under small welding current I2. This allows for better driving of welding current I2 at the start of welding time in the event of contact problems at the welding point (e.g., due to adhesive at the welding point).

[0053] The operation performed by the control device 20 described above corresponds to a transformer variant with a synchronous circuit of transistors in rectifier operation or rectifier branches 41, 42, 43.

[0054] Alternatively, in this location, the control device 20 can distinguish between two operating modes B1, B2 or B1, B2 for controlling the rectifier branches 41, 42. 20 Operating modes B1 and B2, and operating modes B1 and B 20 The effect on welding current I2 Figure 2 This is explained in the text. Additionally, control device 20 controls the third rectifier branch 43 as described above.

[0055] In the first operating mode B1, where welding or manufacturing of welding connection 7 is performed, energy is actively transferred from the primary side of welding transformer 30 to the secondary side of welding transformer 30 to generate welding DC current, or welding current I2. For this energy transfer from the primary side to the secondary side of welding transformer 30, control device 20 is configured to switch the polarity of the transistors in rectifier branches 41 and 42 as desired. Specifically, control device 20 is configured to turn on one of the transistors in rectifier branches 41 and 42 according to the output voltage and polarity pre-selection of welding transformer 30. Thus, when current is present, the series-connected transistors in rectifier branches 41 and 42 are turned on negatively during synchronous operation.

[0056] For example, based on the output voltage and polarity pre-selection, the control device 20 turns on the first transistor of the rectifier branch 41. When the welding current I2 is generated, the second transistor 42, which is connected in series, is then turned on negatively during synchronous operation.

[0057] In this way, two transistors are connected in series for each rectifier branch 41, 42 of the rectifier circuit 40.

[0058] In this way, a polarity-reversible welding voltage U can be achieved on the welding transformer 30. 21 U 22 And the welding current I2 with convertible polarity.

[0059] This enables the interchangeable polarity of the welding transformer 30 and the current direction of the welding current I2. Therefore, the magnetization effect described earlier can be avoided. Furthermore, in the case of components 5 and 6 with aluminum layers, the alumina layer can be cracked in a process-reliable manner, and / or problems caused by the presence of adhesive at the weld joint can be eliminated.

[0060] After time point t0 corresponding to the end of welding time T1, control device 20 switches to second operating mode B2, where the welding process is performed during welding time T1. In second operating mode B2, control device 20 actively switches the rectification operating mode on the secondary side, as described below.

[0061] For the second operating mode B2, the control device 20 controls the transistors in the rectifier branches 41 and 42 to achieve rapid current decay of the welding current I2, such as by means of... Figure 2 As explained.

[0062] exist Figure 2 The variation of the welding current I2 with time t is illustrated using a dashed curve, which occurs under standard rectification using a diode (not shown). Under such standard rectification, the energy from the secondary circuit of the welding transformer 30 decreases via ohmic losses in the diode after welding time T1 ends. In this case, the welding current I2 disappears at time t1.

[0063] Conversely, in this embodiment, in the second operating mode B2, in order to control the transistors in rectifier branches 41 and 42, at the end of the normally controlled welding time T1 of the converter, the welding current I2 decreases or its decay accelerates. To address this, in rectifier branches 41 and 42, the relevant transistors (whose pn junctions correspond to two diodes connected opposite each other) are removed from synchronous operation, and the decreasing welding current I2 is instead guided via the parallel diodes of the series-connected transistors in rectifier branches 41 and 42.

[0064] As a result, the welding current I2 has already disappeared at time point t2 or after duration T2, instead of disappearing after time t1 as usual, as in Figure 2 As explained in [the document / document].

[0065] Therefore, in the second operating mode B2, at the end of the inverter-controlled welding time T1, the control device 20 switches the corresponding series circuits of the rectifier branches 41 and 42, each consisting of two transistors, to continue for a predetermined duration T2 = t2 - t0. Thus, the first operating mode B1 and the second operating mode B2 are different from each other.

[0066] Therefore, in the second operating mode B2, by forcibly switching rectifier elements 41 and 42, additional energy is generated in the rectifier branch due to the current switching on the secondary side, thereby causing repeated magnetization on the secondary side of the welding transformer 30. This results in magnetization losses on the secondary side of the welding transformer 30, which together reduce the energy of the secondary circuit and thus cause the welding current I2 to decay more rapidly.

[0067] Therefore, the control device 20 is configured to actively switch the rectifier operation mode on the secondary side, which results in magnetization loss on the secondary side of the welding transformer 30.

[0068] Here, alternatively, but not necessarily due to the current limitation on current I3 described above, the control device 20 may also switch the transistors of rectifier branch 43 in the second operating mode as described above for the transistors of rectifier branches 41 and 42.

[0069] Furthermore, the aforementioned configuration, combining transformer 30 with rectifier branches 41 and 42 containing transistors and controlled by control device 20, has the following effect: the welding transformer 30 can have a smaller transformation ratio than a conventional welding transformer that operates using diodes in rectifier branches 41 and 42, while maintaining the same output power. In other words, if the welding transformer 30 described above has the same transformation ratio as a conventional welding transformer with the same output power, then the welding transformer 30 described above requires less input power than a conventional welding transformer 30. Therefore, compared to a conventional welding transformer with the same output power, the welding transformer 30, with a rectifier circuit 40 connected downstream, consumes less power supplied by converter 25. This is because the diodes in the rectifier branches 41 and 42 of a conventional welding transformer also operate synchronously during the time between welding processes. Consequently, the diodes also have power losses during idling, which ultimately leads to high internal losses in the conventional welding transformer.

[0070] For example, a welding transformer 30 with the previously described configuration, including an auxiliary winding 34, a controlled inductor 36, and a rectifier circuit 40 combined therewith, can have a transformation ratio of approximately 60:1. In a synchronous circuit, such a welding transformer 30 has a nominal current of approximately 6.5 kA, roughly the same as a conventional welding transformer according to industry standard DIN EN ISO 22829, which has a transformation ratio of 55:1. This welding transformer 30 with a transformation ratio of 60:1 can still drive a welding current I2 = 25 kA with a secondary resistance of 200 μOhm, as required by industry standard DIN EN ISO 22829 for a welding transformer with a transformation ratio of 55:1.

[0071] Compared with existing technologies, Figure 1 The welding transformer 30 thus has a smaller structural size, lighter weight, and cost advantages regarding the converter 25 and the main switch or welding equipment 2 for disconnecting the converter 25.

[0072] Welding equipment 2 can be particularly advantageously used in plate assemblies where undesirable burn-off or material migration of the welding electrodes 11, 12 occurs at the welding clamp, and / or when welding aluminum and / or where adhesive is present at the welding location, and / or where fast cycle times are required when using equipment 2. Furthermore, alloying of the electrode covers of the welding electrodes 11, 12 can be avoided. Additionally or alternatively, welding equipment 2 can be particularly advantageously used when welding chain links and when welding heat sinks.

[0073] Based on the modification scheme of the control device 20 to the previous control during welding, the control device 20 can take the following actions. In this case, in the second operating mode B2, the control device 20 alternately switches the welding current I2 back and forth in the two secondary branches of the transformer 30 via transistor control through rectifier branches 41 and 42, so as to achieve a faster current decay of the welding current I2, or to generate a faster current drop in the welding current I2.

[0074] In this scenario, in the second operating mode B2, the switching can be performed more quickly due to the higher primary voltage of transformer 30. This results in greater magnetization losses. Consequently, the welding current I2 decays at an even earlier point in time, between time t0 and time t2. Therefore, the welding current I2 decays even faster than in the first embodiment.

[0075] In this way, the advantages mentioned above regarding the first embodiment can also be achieved.

[0076] Figure 3 A welding apparatus 2A having a welding transformer 30A and a rectifier circuit 40A according to a second embodiment is shown.

[0077] Unlike the welding transformer 30 according to the previous embodiment, the welding transformer 30A according to this embodiment is constructed for a transformer variant with switching.

[0078] The welding transformer 30A has a resistor as a current-limiting element 37. This resistor may optionally be at least partially constructed in the auxiliary winding 34, or constructed through the auxiliary winding 34.

[0079] The third rectifier branch 43 has a series circuit composed of transistors, particularly MOSFETs, which are controlled by polarity-dependent control of the control device 20. Furthermore, the rectifier branch 43 can operate in a synchronous circuit, as described with respect to the preceding embodiments.

[0080] According to the modified second embodiment, the current-limiting element 37 of the welding transformer 30A is a semiconductor switch that turns off the auxiliary winding 34 from a predetermined value of current I3. The semiconductor switch can be a diode. This diode is combined with a rectifier branch 43, which is formed by a series circuit of transistors, particularly MOSFETs as described above, and controlled by polarity-dependent control of the control device 20. Furthermore, the rectifier branch 43 can operate in a synchronous circuit.

[0081] Welding equipment 2A in Figure 3 The circuit shown can be switched by the control device 20 in all variations for the current limiting element 37 according to the manner and method described with respect to one of the preceding embodiments.

[0082] In the transformer variant with two MOSFETs (synchronous circuits) for rectification in rectifier branches 41 and 42, the energy savings compared to conventional welding transformers operating with diodes in rectifier branches 41 and 42 are greater than in the transformer variant with switching.

[0083] In system 1 according to the preceding embodiment, welding equipment 2A may be used instead of welding equipment 2 according to the preceding embodiment.

[0084] Figure 4 A welding apparatus 2B having a welding transformer 30B and a rectifier circuit 40B according to a third embodiment is shown.

[0085] Unlike the welding transformers 30 and 30A according to the previous embodiments, the welding transformer 30B according to this embodiment is constructed for a transformer variant with pole switching.

[0086] The welding transformer 30B has two anti-parallel tunnel diodes as current-limiting elements 38, with a semiconductor switch connected in series with the tunnel diodes. The semiconductor switch is, for example, a MOSFET, a bipolar transistor, or a thyristor. The tunnel diodes limit the current I3 in the auxiliary winding 34 to a predetermined value.

[0087] In this case, no additional electrical components are required in the rectifier circuit 40 for rectifying the current I3.

[0088] Welding equipment 2B in Figure 4 The circuit shown can be switched by the control device 20 according to the manner and method described with respect to one of the preceding embodiments.

[0089] In system 1 according to the preceding embodiment, welding equipment 2B may be used instead of welding equipment 2 according to one of the preceding embodiments.

[0090] All the aforementioned configurations of System 1, welding equipment 2, 2A, 2B, control device 20, welding transformers 30, 30A, 30B, rectifier circuit 40, and resistance welding method can be applied individually or in all possible combinations. In particular, it is possible to arbitrarily combine all features and / or functions of the previously described embodiments. Additionally, the following modifications are particularly conceivable.

[0091] The parts shown in these figures are schematic and may deviate from the forms shown in these figures in an accurate construction scheme, provided that their functions as described above are maintained.

[0092] Alternatively, the transistors in rectifier branches 41, 42, and 43 are bipolar transistors, but preferably metal-oxide-semiconductor field-effect transistors (MOS-FETs).

[0093] Alternatively, welding transformers 30, 30A, and 30B can be established by a parallel circuit of two transformers.

[0094] The control device 20 may be able to control more than one welding tool 10, at least temporarily and / or simultaneously with at least one other welding tool 10.

Claims

1. A resistance welding apparatus (2; 2A, 2B) for resistance welding at least one component (5, 6), wherein the resistance welding apparatus comprises a welding transformer (30; 30A; 30B) and a rectifier (40). The welding transformers (30; 30A; 30B) described herein have: - Primary winding (31), for connection to energy supply device (27); - Four outputs, with a primary winding (32), a secondary winding (33), and a tertiary winding (34) arranged between the four outputs, wherein the primary winding (32) is inductively coupled to the primary winding (31) and is arranged between the first and second outputs of the welding transformer (30; 30A; 30B) to connect to the first and second welding electrodes (11, 12) of the welding tool (10), wherein the secondary winding (33) and the tertiary winding (34) are inductively coupled to the primary winding (31) respectively, and are ...2) and the tertiary winding (34) are inductively coupled to the primary winding (31) respectively, and are arranged between the first and second outputs of the welding transformer (30 Do not connect one of its terminals to the terminal of the first stage winding (32), which is the second output of the welding transformer (30; 30A; 30B) and is configured to connect to the second welding electrode (12) of the welding tool (10), wherein at least one component (5, 6) is in contact with the welding electrode (11, 12) for resistance welding, wherein the second stage winding (33) is connected to the third output of the welding transformer (30; 30A; 30B) by its other terminal; and The rectifier (40) described therein has: - A first rectifier branch (41) is used to rectify the current (I2) flowing from the primary winding (32) to the first welding electrode (11) via the first output of the welding transformer (30; 30A; 30B); and - A second rectifier branch (42) is used to rectify the current (I2) flowing from the second stage winding (33) to the first welding electrode (11) via the third output of the welding transformer (30; 30A; 30B); wherein at the fourth output of the welding transformer (30; 30A; 30B), current limiting elements (36, 37, 38) are connected to the third stage winding (34) to limit the current through the third stage winding (34) to a predetermined maximum value.

2. The resistance welding equipment (2; 2A, 2B) according to claim 1, wherein, The first rectifier branch (41) and the second rectifier branch (42) each have a series circuit consisting of two transistors connected between the output of the welding tool (10) and the welding transformer (30; 30A; 30B), wherein the polarity of one transistor in the series circuit is reversed relative to the polarity of the other transistor in the series circuit.

3. The resistance welding equipment (2; 2A, 2B) according to claim 2, wherein, The two transistors are metal-oxide-semiconductor field-effect transistors, and the transistors having reversed polarity are connected to the welding tool (10).

4. The resistance welding apparatus (2; 2A, 2B) according to any one of claims 1 to 3 further comprises a third rectifier branch (43) for rectifying the current (I3) flowing between the third stage winding (34) and the first welding electrode (11).

5. The resistance welding equipment (2; 2A, 2B) according to claim 4, wherein, The third rectifier branch (43) has a series circuit consisting of two transistors connected between the output of the welding tool (10) and the welding transformer (30; 30A); and the polarity of one transistor (42; 44) in the series circuit is reversed relative to the polarity of the other transistor (41; 43) in the series circuit.

6. The resistance welding equipment (2; 2A, 2B) according to any one of claims 1 to 3, wherein, The current limiting elements (36, 37, 38) are controllable inductors and / or resistors connected between the third winding (34) and the first welding electrode (11).

7. The resistance welding equipment (2; 2A, 2B) according to any one of claims 1 to 3, wherein, The current limiting elements (36, 37, 38) are semiconductor switches connected between the third winding (34) and the first welding electrode (11).

8. The resistance welding equipment (2; 2A, 2B) according to claim 7, wherein, The semiconductor switch is a bipolar transistor or a metal-oxide-semiconductor field-effect transistor.

9. The resistance welding equipment (2; 2A, 2B) according to claim 7, wherein, The semiconductor switch is a thyristor connected in anti-parallel to the thyristor.

10. The resistance welding equipment (2; 2A, 2B) according to any one of claims 1 to 3, wherein, The current limiting element (36, 37, 38) is a series circuit consisting of a first tunnel diode and a semiconductor switch, wherein the second tunnel diode is connected in antiparallel to the first tunnel diode, and wherein the series circuit is connected between the third stage winding (34) and the first welding electrode (11), and wherein the semiconductor switch is a bipolar transistor, a metal oxide field-effect transistor, or a thyristor.

11. The resistance welding apparatus (2; 2A, 2B) according to any one of claims 1 to 3, wherein the welding tool (10) is constructed as a welding clamp having two welding electrodes (11, 12), wherein, during welding, the at least one component (5, 6) is arranged between the two welding electrodes (11, 12).

12. The resistance welding apparatus (2; 2A, 2B) according to claim 11, subject to claim 2 or 3, further comprising a control device (20) for switching the series circuit consisting of two transistors in the rectifier branch (41; 42) during a converter-controlled welding time (T1) in a first operating mode (B1), and for switching the series circuit consisting of two transistors in the rectifier branch (41; 42) for a predetermined duration (T2) at the end of the converter-controlled welding time (T1), the second operating mode (B2) being different from the first operating mode (B1).

13. The resistance welding equipment (2; 2A; 2B) according to claim 12, wherein, The first operating mode (B1) achieves a polarity-reversible welding voltage (U) on the welding transformers (30; 30A, 30B). 21 U 22 U 23 The second operating mode (B2) accelerates the current decay of the welding current (I2) already generated in the first operating mode (B1) and the polarity-convertible welding current (I2).

14. A system (1) for processing an object (4) having a resistance welding apparatus (2; 2A; 2B) according to any one of claims 1 to 13, wherein the resistance welding apparatus (2; 2A; 2B) is configured to perform resistance welding on at least one component (5, 6) for at least one of the objects (4), wherein the system (1) is constructed for producing a vehicle body or radiator or chain as the object (4), and / or wherein the system (1) is constructed for producing the object (4) from at least one component (5, 6) made of aluminum, on which an adhesive can be present.

15. A resistance welding method for resistance welding at least one component (5, 6) using a welding tool (10), said welding tool (10) being electrically connected to a resistance welding apparatus (2; 2A; 2B) according to any one of claims 1 to 13; wherein said resistance welding method comprises the steps of: - To bring at least one component (5, 6) into contact with the first welding electrode (11) and the second welding electrode (12) of the welding tool (10), - The current (I2) flowing between the first primary winding (32) and the first welding electrode (11) is rectified using the first rectifier branch (41). - The current (I2) flowing between the second stage winding (33) and the first welding electrode (11) is rectified using the second rectifier branch (42), and - The current through the third winding (34) is limited to a predetermined maximum value by using current limiting elements (36, 37, 38), which are connected to the third winding (34) at the fourth output of the welding transformer (30; 30A; 30B).

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