Patent Description:
Welding transformers are used in welding devices for producing a connection of workpieces made from metal. The welding transformer is operated together with a welding tool, which is electrically connected to the secondary side of the welding transformer. Herein, the welding tool may be guided by hand or a robot.

The transformer is often attached to the welding tool to omit a bulky low-voltage cable. In such a case, the transformer needs to be optimized in weight and size to make the handling of the welding tool easy. This facilitates, too, to keep the power consumption of the welding tool low.

The transformer transforms a primary alternating current into a secondary alternating current with the desired voltage and time characteristics. The secondary side of the transformer is connected to a rectifier which rectifies the electric current output from the transformer and provides a direct electric current to at least one welding electrode of the welding tool. The transformer and the rectifier may form a transformer-rectifier-unit.

For producing a welding spot or a welding seam, electrode(s) of the welding tool contact(s) at least one workpiece. The welding transformer is controlled such that it produces electric current flowing via the electrode(s) into the workpieces to melt the metal such that the workpieces are connected by a welding spot or a welding seam.

In the operation of the welding device, high electric currents are produced, which heat up the transformer and the rectifier. To avoid overheating of the transformer, the transformer and the rectifier have to be cooled. The cooling may be accomplished by a cooling media flowing through cooling channels formed in the windings of the welding transformer.

The windings, in particular the secondary winding, of the welding transformer form a part having a rather complex geometry. The windings may be made from copper. For forming the cooling channel, the windings are machined to produce the required holes for the cooling channel. The holes comprise blind holes and through holes which cross each other. To prevent cooling media leaking from the cooling channels, the holes are to be sealed to the outside of the windings such that the sealed holes withstand a pressure of up to <NUM> bar, that is <NUM> * <NUM> kPa, without leakage.

Currently, sealing of the holes is made by soldering a plug into the holes by using a solder containing phosphorus. However, the soldering (brazing) process is time consuming and must be performed by a well-trained person. The quality of the soldered connection depends to a great extent on the skills of the person performing the soldering. To avoid these problems, glued grub screws are used for sealing the holes.

A further problem known for a long time in the technical field of welding transformers is that cooling media, especially aggressive cooling water, leads to corrosion destroying soldered/brazed connections of the copper material used for the windings and/or the sealed holes of the cooling channel of the windings. This affects especially plugs of the cooling channel as there is contact of three different materials, namely copper, brass and silver solder, with the cooling media. Phosphorous based solder material and/or zinc of the brass grub screws might get flushed by a high content of sulphur in the cooling media. High content of chlorine in the cooling media flushes the gluing from the glued grub screws.

As a result, cooling media, especially cooling water, is leaking from the cooling channels. Consequently, the cooling of the welding transformer cannot be secured. Moreover, the welding device may be damaged and/or polluted. Thus, the required quality of the welded products cannot be guaranteed. Due to a resulting failure of the welding device a machine breakdown may occur in a production line. Document <CIT> discloses a welding transformer with winding elements comprising cooling ducts. Openings in the cooling ducts are provided with recesses for receiving sealing elements.

All these difficulties are especially unacceptable for any production or processing line in which the welding device is to be used.

Therefore it is the object of the present invention to provide a method for producing a winding for a welding transformer and a winding for a welding transformer, which solve the above-mentioned problems and enable in particular to cool a welding transformer in a stable and reliable manner with low costs and which is thus usable in an industrial process of a production line.

This object is solved by a method for producing a cooling channel in a winding for a welding transformer according to claim <NUM>. In the method, a holder holds a winding module which comprises a first winding element, a second winding element and a base element, wherein each one of the first and second winding elements protrudes from the base element and wherein the first and second winding elements are positioned spaced to each other at the base element so that the winding module has a t-cross-section, wherein the first winding element comprises at least one window for accommodating a part of a core of the welding transformer, wherein the second winding element comprises at least one window for accommodating a part of a core of the welding transformer, and wherein the base element comprises grooves separating the base element into sections such that at least one of the sections is connected to the first and second winding elements and such that at least one of the sections is connected to only one of the first and second winding elements, and sealing a plug into a first hole of a cooling channel, which first hole is open to the outside of one of the elements, by controlling a movement of the plug relative to the first hole so that a solid-state welding joint is produced by material of the plug and material of the winding module, in which the first hole is positioned, wherein the holder holds the winding module such that a movement between the winding module and the holder is prevented while the step of sealing is performed.

The described method produces a winding which minimizes the risk of corrosion. This is achieved by producing the winding with joints/connections the stability of which is not affected by the chemical content of a cooling media contacting the joints/connections. The winding is produced preferably without soldered/brazed connections and/or without glued grub screws having contact to the cooling media of the cooling channel. Thus, leaking of the cooling channel is no problem anymore. This is also the fact, when aggressive cooling media is to be used in the cooling channels, as described with reference to the state of the art.

The resulting winding enables in particular to cool a welding transformer in a stable and reliable manner. Herein, the winding may be produced with higher process reliability, even if the shape or design of the winding is unchanged and thus still complex. This is very advantageous as regards a careful handling of resources.

A further advantage lies in that the described method uses a plug for sealing the holes of the cooling channel to the outside, wherein the plug has the same material as the cooling channel. Due to this, corrosion of the sealed holes of the cooling channel is prevented very effectively and securely.

In addition, the plug usable for sealing a hole of the cooling channel may have a less complex shape. The shape might be a rectangular shape, possibly comprising only one shoulder. Thus, the shape of the plug is less intricate than the shape of a screw and even the shape of a conventional plug used in soldering, for example. Consequently, the cost of the plug used in the described method is reduced.

Moreover, the holes of the cooling channel require no further preparation for securely sealing a hole with the plug. This results in further cost savings.

As a result, the winding can be produced less intricate than in the state of the art. Each one of the above-mentioned features contributes to perform the sealing of the holes of the cooling channel much faster than conventionally. Altogether, the described method is less time-consuming. This leads to reduction of costs, too.

Thus, the method for producing the described winding is very time-efficient and demands lower costs than known methods in this regard.

All these advantages result in a winding which is cost effective in production and maintenance. The same is valid for a welding tool, to which the winding is attached, and a generic welding device.

Altogether, the failure of the generic welding device can be minimized. This leads to a prolonged life time of the welding device, as well.

And, the use of the described winding in a welding device can contribute to a stable welding method in which the welding may be performed with high quality. This qualifies the winding to be used in a welding device applied in an industrial process of a production line.

Advantageous further developments of the method are given in the dependent claims.

In the method, the solid-state welding joint is produced by coalescence of contacting surfaces of the plug and the first hole below the melting point of the materials without supplying an additional joining material.

The solid-state welding joint may be produced by ultrasonic welding or rotation friction welding or friction welding.

Possibly, the movement of the plug relative to the first hole is controlled so that the hole sealed by the solid-state welding joint withstands without leakage a pressure of up to <NUM> * <NUM> kPa which is exerted by cooling media.

The material of the plug and the material, in which the first hole is positioned, is the same.

In one specific implementation form, the plug has a shoulder at the side of the plug which is inserted in the first hole before the step of sealing is performed.

The method may further comprising at least one step of the steps of milling the first holes into the first and second winding elements as well as the base element to form the cooling channel in the winding module, and providing each first hole with one solid-state welding joint for sealing the cooling channel to the outside of the winding module, and milling second holes into the base element, and providing at least one of the second holes with an insert for connecting the winding module with other parts of a transformer-rectifier-unit.

Sealing of a plug into a first hole according to the described method may be performed by a device for producing a welding joint in a cooling channel for a winding for a welding transformer, wherein the device comprises a control unit to control a movement of a plug in the first hole, and a holder for holding a winding module of the winding when sealing the plug into the first hole.

The above-described object is further solved by a winding for a welding transformer according to claim <NUM>. The winding comprises a winding module which comprises a first winding element framing at least one window for accommodating a part of a core of the welding transformer, a second winding element framing at least one window for accommodating a part of the core of the welding transformer, and a base element, wherein each one of the first and second winding elements protrudes from the base element, wherein the first and second winding elements are positioned spaced to each other at the base element so that the one-piece winding module has a t-cross-section, and wherein the base element comprises grooves which separates the base element into sections, and wherein at least one of the sections is connected to the first and second winding elements, wherein at least one of the sections is connected to only one of the first and second winding elements, wherein the first and second winding elements as well as the base element comprise a cooling channel for flowing a coolant through the first and second winding elements as well as the base element, and wherein a plug is sealed in a first hole of the cooling channel as a solid-state welding joint produced by the material of the plug and the material, in which the first hole is positioned.

The winding achieves the same advantages as they are mentioned above in respect of the method.

Advantageous further developments of the winding are given in the dependent claims.

Herein, each one of the first and second winding elements may comprise at least one hole to form the cooling channel, wherein at least one hole in the first and/or second winding elements is a blind hole and at least one hole in the first and/or second winding elements is a through hole so that the holes cross each other to form the cooling channel.

In one implementation form, the first winding element forms a frame for two windows, the windows of the first winding element are spaced from each other in the first winding element, the second winding element forms a frame for two windows, and the windows of the second winding element are spaced from each other in the second winding element.

The material of the winding module may be metal, in particular copper or aluminium.

The above-described winding may be part of a welding transformer which further comprises a core, and a primary winding, wherein the winding is positioned on the secondary side of the transformer, and wherein the primary winding is mounted to the core and to the secondary winding.

The above-described welding transformer may be part of a welding tool for producing an article. The welding tool may further comprise a control unit configured to adapt a welding current for forming the article by joining at least two parts of one workpiece and/or at least two workpieces by at least one welding joint.

The above-described welding tool may be part of a welding device. The welding device may further comprise a device for moving the welding tool according to a predetermined moving profile along the at least one workpiece, and wherein the article is a vehicle body.

Further possible implementations of the invention comprise also combinations of features or styles described above or in the following with reference to the embodiments, even if they are not explicitly mentioned. Herein, the person skilled in the art will also add single aspects as improvements or additions to the respective basic form of the invention.

In the following, the invention is described in more detail by means of embodiments and with reference to the appended drawing figures, wherein:.

In the drawing figures, the same or functionally same elements are provided with the same reference signs unless given otherwise.

<FIG> shows very schematically a plant <NUM> which comprises a welding device <NUM>, in particular a resistance welding device. The plant <NUM> is, for example, a production plant for producing articles <NUM> like vehicles, household devices, heaters, or the like.

In the plant <NUM>, metal workpieces <NUM>, <NUM> can be connected or joint by welding, especially resistance welding, so that a welded joint <NUM> is produced. For this purpose, the welding device <NUM> of <FIG> has a welding tool <NUM> in the form of a welding gun having two welding electrodes <NUM>, <NUM>. The welding device <NUM> further comprises a control device <NUM>, a welding transformer <NUM>, and a rectifier <NUM>. In the example of <FIG>, the welding device <NUM> further comprises a device <NUM> for guiding the welding tool <NUM>. The device <NUM> might be a robot.

The welding tool <NUM> may perform in particular resistance welding. The welding transformer <NUM> is possibly implemented as an intermediate frequency direct current transformer (MF-DC transformer). Herein, the rectifier <NUM> is mountable on the welding transformer <NUM>. Thus, a transformer-rectifier unit is formed.

The welding device <NUM> can use the welding tool <NUM> to produce the welded joint <NUM> under the control of the control device <NUM>. It is possible herein, for example, that two edges or corners of a single workpiece <NUM> are connected to one another by forming one or more welded joints <NUM>. Regardless of how many workpieces <NUM>, <NUM> are connected to each other by means of at least one welded joint <NUM>, the welded joint <NUM> can be implemented as a spot weld or a weld seam or a combination thereof. The device <NUM> may move the welding tool <NUM> according to a predetermined moving profile along the at least one workpiece <NUM>, <NUM>.

In a welding method for welding with the welding device <NUM>, at least one of the welding electrodes <NUM>, <NUM> contacts at least one workpiece <NUM>, <NUM>, and at least one welding transformer <NUM> is used to weld the at least one workpiece <NUM>, <NUM>.

On the secondary side of the welding transformer <NUM>, there is a first secondary voltage U21 between the first and second output terminals <NUM>, <NUM> of the welding transformer <NUM> in operation of the transformer <NUM>. In addition, a second secondary voltage U22 exists between the second and third output terminals <NUM> and <NUM> of the welding transformer <NUM> in operation of the transformer <NUM>. The first secondary voltage U21 and the second secondary voltage U22 form a welding voltage U23 at the output of the rectifier unit <NUM>, which results in a welding current I2.

The rectifier <NUM> has in the example of <FIG> first to fourth semiconductor devices <NUM> to <NUM>, for example transistors <NUM> to <NUM>.

The first semiconductor device <NUM> is connected to the first output terminal <NUM> of the welding transformer <NUM>. The second semiconductor device <NUM> is connected in series to the first semiconductor device <NUM>. Thus, the series connection composed of the first and second semiconductor devices <NUM>, <NUM> is connected between the welding transformer <NUM> and the welding tool <NUM>. More precisely, the series connection composed of the first and second semiconductor devices <NUM>, <NUM> is connected between the secondary side of the welding transformer <NUM> and the first welding electrode <NUM>.

The second welding electrode <NUM> is directly connected to the second output terminal <NUM> of the welding transformer <NUM>.

The third semiconductor device <NUM> is connected to the third output terminal <NUM> of the welding transformer <NUM>. The third semiconductor device <NUM> and the fourth semiconductor device <NUM> are connected in series. Thus, the series connection composed of the third and fourth semiconductor devices <NUM>, <NUM> is connected between the welding transformer <NUM> and the welding tool <NUM>. More precisely, the series connection formed by the third and fourth semiconductor devices <NUM>, <NUM> is connected between the welding transformer <NUM> and the first welding electrode <NUM>.

The control device <NUM> can also be configured to switch the polarity of the welding voltage U23 applied between the welding electrodes <NUM> and <NUM>. The polarity of the welding voltage U23 can be switched as desired by controlling the switching of the corresponding transistors <NUM>, <NUM>, <NUM>, <NUM>. According to one possibility for the polarity of the welding voltage U23, the electrode <NUM> is positively polarized and the electrode <NUM> is negatively polarized. Alternatively, the electrode <NUM> is negatively polarized and the electrode <NUM> is positively polarized.

The switching of the polarity of the welding voltage U23 by the welding device <NUM> can be used advantageously in sheet metal combinations, where undesirable burn-up or material migration of the welding electrode is caused in the welding gun. Furthermore, the resistance welding device <NUM> can be used particularly advantageously in welding chain links and/or in welding heating bodies.

If it is not required to switch the polarity of the welding voltage U23, which is applied between the welding electrodes <NUM> and <NUM>, one of the transistors of the series connection of the transistors <NUM>, <NUM> and one of the transistors of the series connection of the transistors <NUM>, <NUM> may be omitted.

<FIG> shows a specific example for building up a transformer-rectifier unit <NUM>, <NUM> according to the first embodiment. The transformer <NUM> comprises a primary winding <NUM>, a secondary winding <NUM>, a coating <NUM>, a core <NUM>, a first connecting block <NUM> and a second connecting block <NUM>. The core <NUM> is made from a soft-ferromagnetic or soft-ferrite material. The core <NUM> is can be made from iron, in particular from silicon-alloyed-iron. The coating <NUM> is illustrated as hachure.

The secondary winding <NUM> and the rectifier <NUM> may comprise a cooling channel <NUM> through which a coolant <NUM> may flow from an inlet to an outlet, as schematically shown in <FIG>. The inlet is indicated by an arrow for the coolant <NUM> flowing into the channel <NUM>. The outlet is indicated by an arrow for the coolant <NUM> flowing out of the channel <NUM>. The coolant <NUM> may be water or oil or gas or any other suitable coolant.

The primary winding <NUM> is mounted to connectors <NUM>, <NUM> for connecting the transformer <NUM>, in particular the primary side of the transformer <NUM>, to an electric power supply. The primary winding <NUM> may be made from a strap-like wire which is paint by synthetic resin. The primary winding <NUM> and the secondary winding <NUM> are wound around the core <NUM>. The primary winding <NUM> has more windings than the secondary winding <NUM>. Therewith, the electric current on the primary side of the transformer <NUM> is transformed to an electric current on the secondary side of the transformer <NUM> which has a higher electric current value than the electric current on the primary side.

The secondary winding <NUM> of the transformer <NUM> is mounted to the rectifier <NUM>. Herein, the cooling channel <NUM> may have parts in the rectifier <NUM>. Further, the secondary winding <NUM> is mounted to the first connecting block <NUM>. The first connecting block <NUM> is configured to mount the rectifier <NUM> to the welding tool <NUM> of <FIG>, in particular a robot. The first connecting block <NUM> and the secondary winding <NUM> are at least partly coated by the coating <NUM>. The second connecting block <NUM> is mounted to the rectifier <NUM>. The second connecting block <NUM> is configured to mount the rectifier <NUM> to the welding tool <NUM> of <FIG>. For example, the first connecting block <NUM> is used for connecting the transformer-rectifier unit <NUM>, <NUM> to the negative electrode of the welding tool <NUM>, whereas the second connecting block <NUM> is used for connecting the transformer-rectifier unit <NUM>, <NUM> to the positive electrode of the welding tool <NUM>.

<FIG> shows a winding module 35A for the secondary winding <NUM> of the welding transformer <NUM> of <FIG>. Basically, the winding module 35A has a T-cross-section. The winding module 35A builds a T with a double vertical stem. The winding module 35A may be made from an extruded profile. Alternatively, the winding module 35A may be a cast piece or made by another production method.

The winding module 35A may be constructed integrally, that is, the winding module 35A may be made from one piece of metal, in particular copper or aluminium. However, the winding module 35A may be constructed from more than one piece of metal. That is, instead of a monobloc construction, the winding module 35A may comprise at least two plates, which are connected to each other. Instead of metal, the winding module 35A may be made from another material which enables electric conduction. Copper and aluminium are advantageous as regards their comparable small electric resistance and simultaneously high thermic conductivity.

Possibly, the module 35A is coated by the coating <NUM>. The coating <NUM> may be provided only partly, as shown in <FIG> as hachure. The coating <NUM> may be performed in a step of coating after the profile <NUM> is milled into the form shown in <FIG>. The coating <NUM> may protect the module 35A against corrosion. For example, the coating <NUM> may be a coating for passivating the aluminium or an aluminium alloy. In particular, the coating <NUM> may be an anodization. Alternatively, the coating <NUM> may be a galvanic coating. Alternatively, the coating <NUM> may be a chemical coating of nickel. Alternatively, the coating <NUM> may be a cathodic dip coating. Alternatively, the coating <NUM> may be a plastic coating.

Alternatively or in addition, coolant <NUM> used in the cooling channel <NUM> of the module 35A may comprise a corrosion inhibitor.

The module 35A is designed such that it comprises a first winding element <NUM>, a second winding element <NUM> and a base element <NUM>. The base element <NUM> has several sections <NUM>, <NUM>, <NUM>, which are each connected with at least one of the winding elements <NUM>, <NUM>. The module 35A is divided by two grooves <NUM>, <NUM> so that the sections <NUM>, <NUM>, <NUM> are formed.

<FIG> shows a specific example for an outer contour <NUM> of the base element <NUM>. That is, the outer shape <NUM> of the base element <NUM> in <FIG> has bevelled edges and is almost rectangular, except for a recess in the section <NUM>.

The first winding element <NUM> protrudes from the base element <NUM>. The second winding element <NUM> protrudes from the base element <NUM>. The first and second winding elements <NUM>, <NUM> protrude from the same side of the base element <NUM>. The first winding element <NUM> and the second winding element <NUM> are positioned in parallel to each other. The first winding element <NUM> and the second winding element <NUM> are positioned spaced from one another by a space <NUM>. The first and second winding elements <NUM>, <NUM> are positioned side by side. Basically, the first and second elements <NUM>, <NUM> have identical shape or almost identical shape. The elements <NUM>, <NUM>, <NUM> each have a plate-like form.

The first winding element <NUM> has two windows <NUM>, <NUM> as openings for mounting the core <NUM> shown in <FIG>. The second winding element <NUM> has two windows <NUM>, <NUM> as openings for mounting the core <NUM> shown in <FIG>.

Each of the winding elements <NUM>, <NUM> and the base element <NUM> comprises first holes <NUM> for building up the cooling channel <NUM> in the elements <NUM> to <NUM>. The base element <NUM> comprises second holes <NUM> for mounting and fastening the module 35A to the other parts of the transformer-rectifier-unit <NUM>, <NUM>. Further, the base element <NUM> comprises third holes <NUM> for mounting and fastening the module 35A to the other parts of the transformer-rectifier-unit <NUM>, <NUM>. For the sake of a clear depiction, only some of the first holes <NUM>, only one of the second holes <NUM> and only one of the third holes <NUM> is/are provided with a reference sign in <FIG>.

The first winding element <NUM> basically has a rectangular shape. The first winding element <NUM> forms a frame around the two windows <NUM>, <NUM>. Each one of the windows <NUM>, <NUM> basically has a rectangular shape. The second winding element <NUM> basically has a rectangular shape. The second winding element <NUM> forms a frame around the two windows <NUM>, <NUM>. Each one of the windows <NUM>, <NUM> basically has a rectangular shape. The windows <NUM>, <NUM> are spaced from each other in a direction transverse to the direction in which the first and second winding elements <NUM>, <NUM> are positioned spaced to each other. The same is valid as regards the windows <NUM>, <NUM>. Thus, the windows <NUM>, <NUM> of the first and second winding elements <NUM>, <NUM> may be milled in one milling step. The same is valid as regards the openings <NUM>, <NUM>.

The primary winding <NUM> may be inserted into the module 35A of <FIG>, as shown in <FIG>. In particular, the primary winding <NUM> may be wound, and thus placed, beside the first winding element <NUM> and beside the second winding element <NUM> as well as in the space <NUM> between the first winding element <NUM> and the second winding element <NUM>. And, the core <NUM> may be inserted into the windows <NUM>, <NUM>, <NUM>, <NUM> of the first and second winding elements <NUM>, <NUM>. Thus, at least a part of the core <NUM> is accommodated in each one of the windows <NUM>, <NUM>, <NUM>, <NUM>.

At least one of the windows <NUM>, <NUM>, <NUM>, <NUM> may be produced by milling. At least one of the holes <NUM>, <NUM>, <NUM> may be produced by milling. At least one of the grooves <NUM>, <NUM> may be produced by milling. It is possible that at least one other technology, like water-cutting or laser-cutting and/or welding is used to form the module 35A as shown in <FIG>.

The holes <NUM> are blind holes and/or through holes which are connected with each other in the elements <NUM>, <NUM>, <NUM> to form the cooling channel <NUM> in the winding elements <NUM>, <NUM> and the base element 353B. Instead, the holes <NUM>, <NUM> are each through holes. The second holes <NUM> are additionally provided with a thread, as shown by two concentric rings in <FIG>. Thus, the second holes <NUM> are prepared as threaded holes <NUM>.

The groove <NUM> separates the sections <NUM>, <NUM>. The groove <NUM> separates the sections <NUM>, <NUM>. Thus, all of the sections <NUM>, <NUM>, <NUM> are positioned spaced from one another, namely by one of the grooves <NUM>, <NUM>. Each one of the grooves <NUM>, <NUM> is winding between the corresponding sections <NUM>, <NUM>, <NUM>. All of the sections <NUM>, <NUM>, <NUM> of the base element <NUM> differ in shape and form. Herein, the outer contour of all of the sections <NUM>, <NUM>, <NUM> of the base element 353B differ in shape. In other words, the sections <NUM>, <NUM>, <NUM> have varied shape and form.

The first section <NUM> is connected with the first winding element <NUM>, only. That is, the first section <NUM> is not connected with the second winding element <NUM>. The second section <NUM> is connected with the first and second winding elements <NUM>, <NUM>. The third section <NUM> is connected with the second winding element <NUM>, only. That is, the third section <NUM> is not connected with the first winding element <NUM>. As regards an intermediate frequency direct current transformer (MF-DC transformer) as the transformer <NUM>, the third section <NUM> may constitute a first positive conductive part of the MF-DC transformer, the first section <NUM> may constitute a second positive conductive part of the MF-DC transformer, and the second section <NUM> may constitute the negative conductive part of the MF-DC transformer.

The shape <NUM> may be milled in a next step following at least one of the steps of milling described-above. For this purpose, the milling tool mills recesses into the base element 353B as needed.

In case the winding module 35A is built by at least two parts, the parts may be formed into the shape as shown in <FIG>. Thereafter, the at least two parts may be joint to build the winding module 35A as shown in <FIG>.

<FIG> shows another example of a winding module 35B. In a second embodiment, the winding module 35B may be used for the secondary winding <NUM> of a transformer-rectifier unit <NUM>, <NUM>. The winding module 35B is configured like the winding module 35A shown in <FIG> except for the base element 353B, in particular the outer shape 3538B of the base element 353B and the positions of the holes <NUM>, <NUM>.

That is, also the section <NUM> of the module 35B has a recess in the outer shape 3538B. Further, the outer edge of the section <NUM> is inclined to build an angular rim. In addition, the position of the holes <NUM>, <NUM> in the sections <NUM>, <NUM>, <NUM> is adapted to the configuration of another transformer-rectifier unit which may differ from the configuration of the transformer-rectifier unit <NUM>, <NUM> shown in <FIG>.

At least one of the holes <NUM> of the cooling channel <NUM> of the module 35B shown in <FIG> may be sealed by performing a method as explained below by reference to <FIG>.

According to <FIG>, a plug <NUM> may be prepared and/or provided to seal a hole <NUM> of the module 35B, which is shown in <FIG> only partly. For this purpose, the plug <NUM> is positioned at least partly into the hole <NUM>. This is illustrated in <FIG> in a three-dimensional view of a part of the module 35B and in <FIG> in a cross section of the part of the module 35A. The plug <NUM> may be handled by a robot (not shown) for positioning the plug <NUM> at least partly into the hole <NUM>. As shown in <FIG> and <FIG> the plug <NUM> has smaller dimensions than the hole <NUM>. As a result, there is a movement space 355A, in which the plug <NUM> may move transvers to the hole <NUM> when the device <NUM> is used to set the plug <NUM> into the hole <NUM>.

The plug <NUM> has the same material like the module 35B. The material of the plug <NUM> may be metal, in particular copper or aluminium. The plug <NUM> has a rectangular shape. The plug <NUM> has a shape of a cylinder plate or disc. Thus, the shape of the plug <NUM> for sealing a hole <NUM> has a comparably and remarkably less complex shape than a conventional plug.

Before or after the steps illustrated by <FIG>, the module 35B is positioned in a holder <NUM>, as shown in <FIG>. The holder <NUM> is configured to hold, in particular grip, the module 35B. Thereafter, a sealing device <NUM> is used to seal the hole <NUM> with the plug <NUM>. Herein, the plug <NUM> is welded into the hole <NUM>. The holder <NUM> is adapted to the shape of the module 35B or the shape of at least one part of the module 35B. Herein, the holder <NUM> may be fastened to the frame of at least one of the windows <NUM>, <NUM>, <NUM>, <NUM>. The sealing device <NUM> and/or the holder <NUM> are configured to position the sealing device <NUM> and the module 35B relative to each other. The sealing device <NUM> may be moved by a moving device <NUM>, in particular a robot, around the module 35B held by the holder <NUM>. Additionally or alternatively, the holder <NUM> holding the module 35B is moved by the moving device <NUM>, in particular a robot, to position the module 35B relative to the sealing device <NUM> to seal one of the holes <NUM> with a plug <NUM>.

As shown in <FIG>, the sealing device <NUM> comprises an anvil <NUM>. The anvil <NUM> is movable transitionally in the direction of the axis of the anvil <NUM>. The anvil <NUM> is movable transitionally relative to the plug <NUM>. The anvil <NUM> has a face for contacting the plug <NUM>. The face for contacting the plug <NUM> has greater dimensions than the dimensions of a surface of the plug <NUM> which is faced to the anvil <NUM>. In addition, the sealing device <NUM> comprises a sonotrode <NUM>, a detecting unit <NUM> and a control unit <NUM>.

The sonotrode <NUM> is configured to exert an ultrasonic force F2 onto the plug <NUM>. The detecting unit <NUM> is configured to detect the value of the forces F1, F2. The control unit <NUM> is configured to control the operation of the anvil <NUM> and/or the operation of the sonotrode <NUM> and/or the operation of the detecting unit <NUM>. Therewith, the control unit <NUM> can control the method of setting a plug <NUM> in a hole <NUM> of a channel <NUM> (<FIG> or <FIG>) to seal the cooling channel <NUM> and/or the module 35B to the outside. In this method, the control unit <NUM> can use at least one detecting result transmitted by the detecting unit <NUM>.

For welding the plug <NUM> to the hole <NUM>, the anvil <NUM> is moved towards the plug <NUM> to exert a pressure force F1 onto the plug <NUM>. Additionally, the sonotrode <NUM> is activated to irradiate at least one ultrasonic frequency f. The at least one ultrasonic frequency f may be a sinusoidal frequency in the range of <NUM> to <NUM>, in particular a frequency in the range of <NUM> to <NUM>. Due to the at least one ultrasonic frequency f, the anvil <NUM> and the plug <NUM> vibrate with ultrasonic frequency f so that the plug <NUM> moves relative to the hole <NUM>. The vibrations are locally applied to the plug <NUM> which is held under pressure between the anvil <NUM> and the module 35B to create a solid-state weld. Herein, the holder <NUM> holds the module 35B such that the module 35B is not moved relative to the holder <NUM>, when the forces F1, F2 and a friction force F3 between the plug <NUM> and the hole <NUM> are applied. The holder <NUM> may be configured to exert a force F5 which counteracts the forces F1, F2.

The movement of the plug <NUM> causes the friction force F3 effective between the hole <NUM> and the plug <NUM>. As a result, the contact surfaces present between the plug <NUM> and the hole <NUM> join. Therewith, the material of the plug <NUM> and the material of the module 35B at the hole <NUM> is joint. The corresponding weld or welding joint <NUM> is shown in <FIG>.

The described solid-state welding produces coalescence of the faying or contacting surfaces of the plug <NUM> and the hole <NUM> at a temperature below the melting point of the material of the plug <NUM> and the material around the hole <NUM>. Thus, the material of the plug <NUM> and the material around the hole <NUM> can be joined without the addition of another material, like for example brazing or soldering filler material. Because solid-state welding does not melt the material of the plug <NUM> and the material around the hole <NUM>, which would be the case between <NUM> to <NUM> for copper, the effect of cuprous oxide does not occur.

In the ultrasonic welding performed by the device <NUM>, a pressure force F1 is applied to and/or between the plug <NUM> and the hole of the module 35B and an oscillating motion caused by at least one ultrasonic frequency f is used in a direction parallel to the contacting surfaces, as shown in <FIG>. The pressure force F1 may be comparably small, and thus moderate, due to the additional force F2 exerted by the vibration or oscillating motion caused by at least one ultrasonic frequency f.

To achieve a constant friction force F3, the detecting unit <NUM> may detect the thermal energy applied to the weld and/or the plug <NUM>. The detected energy may be used to control the above-described method. The welding operation of the device <NUM> is stopped when the detected thermal energy reaches a target value for the thermal energy. In addition, the detecting unit <NUM> may detect the position and/or the velocity of the plug <NUM> and/or the module 35B and/or the holder <NUM>. The detecting unit <NUM> may transmit the result(s) to the control unit <NUM>. However, it is possible that the velocity of the plug <NUM> and/or the module 35B and/or the holder <NUM> are/is set as a predefined parameter which is not controlled in a feedback loop by the control unit <NUM>.

The surface of the welding joint <NUM> may be a serrated surface, as illustrated in <FIG> in a top view of the module 35B. The serrated surface is formed corresponding to the contact surface of the anvil <NUM>. In case it is needed, the surface of the welding joint <NUM> may be smoothed to adjust the texture of the surface of the welding joint <NUM> to the texture of the surface of the module 35B. Such a smoothing or adjustment of the texture of the surface of the welding joint <NUM> might not be required, when the surface of the welding joint <NUM> and/or the surface of the transformer surrounding the welding joint <NUM> is not visible.

Thus, in operation, the sealing device <NUM> welds the plug <NUM> into the hole <NUM> by the use of the friction force F3 caused by the forces F1, F2. Preferably, the friction force F3 is positioned orthogonally to the pressure force F1. Preferably, the friction force F3 is positioned orthogonally to the force F2. Such a positioning of the forces F1 to F3 causes a very fast and robust joint of the materials of the plug <NUM> and the module 35B.

The sealing device <NUM>, in particular the control unit <NUM>, is configured to protocol the quality of each joint <NUM>. The protocol contains detecting results detected by the detecting unit <NUM> and related to the method performed to produce the joint <NUM>. The protocol may contain details, whether or not the joint <NUM> fulfils a predetermined quality standard. This is very advantageous for a proof as regards liability issues.

The sealing device <NUM> may produce the joints <NUM> much faster than by soldering. In addition, producing the joints <NUM> requires less cost than performing soldering instead. In addition, the quality of the joints <NUM> does not depend on the workers skill, since the method may be performed completely by the sealing device <NUM>. The worker does not need to know details about the method performed by the sealing device <NUM>. The worker only has to be trained to use the sealing device <NUM>.

<FIG> shows the resulting winding <NUM>, in which all of the holes <NUM> are sealed by a plug <NUM> to the outside for building the cooling channel <NUM>. The module 35B is thus provided by a plurality of plugs <NUM> to seal the cooling channel <NUM> of the module 35B to the outside of the module 35B.

For example, as shown in <FIG>, the cooling channel <NUM> formed in the module 35B has two inlets, namely one in the first section <NUM> of the base element 353B and one in the third section <NUM> of the base element 353B, but only one outlet in the second section <NUM> of the base element 353B. Thus, the coolant <NUM> can be guided from the rectifier <NUM> through the cooling channel <NUM> and back to the rectifier <NUM>, wherein the cooling channel <NUM> is built by the holes <NUM> in the module 35B, wherein the holes <NUM> are sealed to the outside of the elements <NUM> to <NUM> by the plugs <NUM>, where needed.

Thus, the welding joint <NUM> of the sealed holes <NUM> is configured to withstand the required pressure applied in a leakage test of the module 35B and/or the cooling channel <NUM>. Such a pressure is in particular a pressure of up to <NUM> bar, that is <NUM> * <NUM> kPa. Thus, the welding joint <NUM> and/or the holes <NUM> sealed with a plug <NUM>, respectively, as described above, contribute that the module 35B and/or the cooling channel <NUM> can withstand the required pressure, in particular a pressure of up to <NUM> bar, that is <NUM> * <NUM> kPa, so that no leakage of cooling media <NUM> occurs.

Further in <FIG>, the module 35B is provided by a plurality of thread inserts <NUM>. Each thread insert <NUM> is thread in one of the second holes <NUM>. Therewith, the second holes <NUM> are prepared for mounting the module 35B to the other parts of the transformer-rectifier-unit <NUM>, <NUM> shown in <FIG> and as described above. The third holes <NUM> may be used without inserts to mount the module 35B to the other parts of the transformer-rectifier-unit <NUM>, <NUM>.

Further in <FIG>, recesses <NUM>, <NUM> present in the bottom side of the base element 353B, for example by milling. The recess <NUM> is provided in the bottom side of the first and second sections <NUM>, <NUM> of the base element 353B. The recess <NUM> is provided in the bottom side of the second and third sections <NUM>, <NUM> of the base element 353B. Each recess <NUM>, <NUM> is positioned transverse to each one of the grooves <NUM>, <NUM> which the recess <NUM>, <NUM> crosses.

The, recesses <NUM>, <NUM> may be milled after or before the grooves <NUM>, <NUM> are milled.

Likewise, the module 35A of <FIG> may be produced as explained above by reference to <FIG> and <FIG>, except that the several sections <NUM>, <NUM>, <NUM> and the outer contour <NUM> of the base element <NUM> are formed for the module 35A, as shown in <FIG>. Then, the steps illustrated in <FIG> may be performed for the module 35A of <FIG> to build the winding <NUM>, as shown in <FIG>.

<FIG> show a plug 60A which may be used instead of the plug <NUM> shown in <FIG> to seal a hole <NUM> of the module 60A. As seen from the top, the plug 60A has an oval shape. The oval shape has a length L1 and an arc radius R1, as shown in <FIG>. As shown in a side view of the plug 60A in <FIG>, the plug 60A has a width W1, a height H1 and a symmetry axis <NUM>. The length L1 is smaller than the length L3 of the movement space 355A of the hole <NUM> shown in <FIG>.

As further shown in <FIG>, the length L3 of the movement space 355A of the hole <NUM>, and thus also the length L1 of the plug 60A, is smaller than the length L2 of the part of the module 35B in which the plug 60A is set and then welded. However, the length L3 of the movement space 355A of the hole <NUM>, and thus also the length L1 of the plug 60A, is greater than the width W2 of the module 35B. And, the length L3 of the movement space 355A of the hole <NUM>, and thus also the length L1 of the plug 60A, is greater than the diameter of the hole <NUM>.

The width W1 of the plug 60A is greater than the diameter of the hole <NUM>. However, the width W1 of the plug 60A is smaller than the width W2 of the module 35B.

As also shown in <FIG>, the plug 60A is positioned such that it does not protrude from the module 35B. The axis of the hole <NUM> is positioned transverse, in particular orthogonally, to the axis 35B1 of the module 35B. The symmetry axis <NUM> of the plug 60A is positioned to coincide with the axis 35B1 of the module 35B.

Instead of the plug 60A of <FIG> or the plug <NUM> shown in <FIG>, a plug 60B of <FIG> may be used to seal a hole <NUM> of the module 35B. According to <FIG>, the plug 60B has a shoulder <NUM> and a nipple <NUM>. The plug 60B basically has a T-form. The nipple <NUM> protrudes from the shoulder <NUM>, in a direction which is particular in parallel to the stem of the T-form. The nipple <NUM> protrudes from the shoulder <NUM> so that the nipple <NUM> projects in the direction of the module 35A, as shown in <FIG>. When using the device <NUM> for setting the plug 60B into the hole <NUM>, the nipple <NUM> scratches into the surface of the module 35B around the hole <NUM>. The nipple <NUM> increases the friction force F3 shown in <FIG>. The nipple <NUM> may have a pin shape or conical shape, as shown in <FIG>. However, the nipple <NUM> may have another shape as long as this shape has the function of increasing the friction force F3.

The shoulder <NUM> has a height H2. The plug 60B has at its first end the width W1. At its second end, the plug 60B has the width W3. The second end is to be faced to the hole <NUM>. For sealing the hole <NUM> with the plug 60B, the plug 60B is inserted into the hole <NUM> so that the shoulder <NUM> is positioned in the hole <NUM>, whereas the first end of the plug 60B may protrude from the hole <NUM>. The material of the shoulder <NUM> is thus welded at the hole <NUM> with the material of the module 35B. The shoulder <NUM> secures a still more robust connection between the plug 60B and the module 35B than the plug <NUM> or the plug 60A.

It is further conceivable that the plug 60B has more than one shoulder <NUM>. In addition, the plug 60B may be serrated in a region corresponding to the shoulder <NUM>. However, a cone shape is not advantageous, since the tool force is not perpendicular to the welding surface.

Alternatively to the shapes shown in <FIG>, at least one of the plugs 60A, 60B may be modified to have a rectangular or quadratic cross section or a cubical shape or any other shape suitable to achieve the sealing of the cooling channel <NUM> and/or the module 35B as described above.

<FIG> show a sealing device 80A for performing a method for sealing a hole <NUM> as regards a third embodiment. The method may be performed for sealing at least one of the holes <NUM> of the cooling channel <NUM> of the module 35A shown in <FIG>. Alternatively, at least one of the holes <NUM> of the cooling channel <NUM> of the module 35B shown in <FIG> may be sealed by performing the method as explained below by reference to <FIG>. In the following, a module 35B is used as an example.

Similar to the sealing device <NUM> of <FIG>, the sealing device 80A comprises a detecting unit 83A and a control unit 84A. The sealing device 80A of <FIG> is configured to perform rotation friction plug welding to seal a hole <NUM> of the module 35B. The sealing device 80A is configured to accommodate a plug 60C. The sealing device 80A is further configured to transitionally move the plug 60C along its axis. The sealing device 80A is further configured to rotate the plug 60C around its axis, as illustrated by the arrow marked with F4.

The plug 60C is an elongated plug having a length such that the sealing device 80A can clamp the plug 60C for accommodating the plug 60C. The plug 60C has a cylindrical shape. The plug 60C is made from the same material like the module 35B.

For performing a solid-state joining method to set the plug 60C into the hole <NUM>, the sealing device 80A moves the plug 60C to exert a compressive force or pressure force F1 onto the plug 60C, as shown in <FIG>. In addition, the sealing device 80A rotates the plug 60C around its axis, as shown by the rotation force F4. The detecting unit 83A is configured to detect the value of the forces F1, F4 and/or physical entities related thereto. For example, when the plug 60C is set into the hole <NUM>, the force F1 acts as a friction force between the plug 60C and the material surrounding the hole <NUM>. The friction force F1 is detected by the detecting unit 83A. The detecting result is used in a feedback loop performed by the control unit 84A. The rotation force F4 is caused by the rotational velocity of the plug 60C. The rotational velocity is regulated to achieve a constant force F1 in setting the plug <NUM> into the hole <NUM>.

The control unit 84A is configured to control the movement and/or clamping and/or rotation of the plug 60C and/or the operation of the detecting unit 83A. The control unit 84A can control the method of setting a plug 60C in a hole <NUM> of a channel <NUM> (<FIG> or <FIG>) to seal the cooling channel <NUM> and/or the module 35B to the outside. In this method, the control unit 84A can use at least one detecting result transmitted by the detecting unit 83A.

Due to the forces F1, F4, the plug 60C moves relative to the hole <NUM>. The movement of the plug 60C causes a friction force F3 effective between the surfaces of the hole <NUM> and the plug 60C, as already described with above. The friction force F3 is illustrated in <FIG> very simplified, since the friction force F3 effectively acts along the direction of rotation of the plug 60C. Also the friction force F3 is detected by the detecting unit 83A. The detecting result may be used in a feedback loop performed by the control unit 84A.

As a result, the contact surfaces present between the plug 60C and the hole <NUM> join in solid state. Therewith, the material of the plug 60C and the material around the hole <NUM> is fixed to each other. Thus, one end of the plug 60C is connected with the hole <NUM>, as shown in <FIG>. Copper scrap <NUM> produced by the above-described solid-state joining, is present on the surface of the module 35B. The copper scrap <NUM> is to be removed.

Coalescence is achieved by the heat of friction between the two surfaces. The described solid-state welding produces coalescence of the faying or contacting surfaces of the plug <NUM> and the hole <NUM> at a temperature below the melting point of the material of the plug <NUM> and the material around the hole <NUM>, as described above by reference to <FIG>. Thus, the material of the plug <NUM> and the material around the hole <NUM> can be joined without the addition of brazing or soldering filler material. And, the effect of cuprous oxide does not occur.

Additionally, the plug 60C is cut from the module 35B, so that the corresponding welding joint <NUM> and its surface is formed, as shown in <FIG>. The surface of the joint <NUM> may be smoothed to adjust the texture of the surface of the joint <NUM> to the texture of the surface of the module 35B.

Preferably, the plug 60C and the hole <NUM> in the module 35B are positioned relative to each other so that the friction force F3 is positioned orthogonally to the pressure force F1, as already described by reference to <FIG>.

The sealing device 80A provides the same advantages as mentioned for the sealing device <NUM>. However, the sealing device 80A is more expensive than the sealing device <NUM> even if no protocol can be provided as regards the sealing method performed for each joint <NUM> and the resulting quality. In addition, the produced copper scrap <NUM> has to be removed from the surface of the module 35B. And, smoothing the surface of the joint <NUM> to adjust the texture of the surface of the joint <NUM> to the texture of the surface of the module 35B is more intricate than for the joint <NUM>.

As shown in <FIG>, a sealing device 80B according to a fourth embodiment is configured to perform friction welding, in particular friction stir welding. Herein, the sealing device 80B comprises a detecting unit 83B, a control unit 84B and a tool <NUM>. The module 35B is held by the holder <NUM>, as detailed with regard to <FIG>. Alternatively, a tool 85A having a pin <NUM> may be used, as shown in <FIG> in a cross section and described later.

For performing friction welding with the tool <NUM>, the tool <NUM> according to <FIG> is rotated and traversed relative to a plug <NUM> set in the hole <NUM> of a part of module 35B. The movement of the tool <NUM> is shown in <FIG> by arrows. For coalescence, the tool <NUM> is controlled by the control unit 84B to exert mechanical pressure on the plug <NUM> and the material of the module 35B around the hole <NUM>. Therewith, the material of the plug <NUM> and the material of the module 35B around the hole <NUM> is warmed up and softened due to the mechanical pressure of the tool <NUM>. Thus, the tool <NUM> mechanically intermixes the material of the plug <NUM> and the material of the module 35B around the hole <NUM>. While the tool <NUM> is traversed along a joint line for joining the materials, the tool <NUM> mechanically intermixes the two pieces of metal of the plug <NUM> and the module 35B, and forges the hot and softened metal by the mechanical pressure.

Thus, a welding joint <NUM> of <FIG> similar to the welding joint <NUM> shown in <FIG> is formed in solid state. The surface of the welding joint <NUM> of <FIG> is serrated.

For performing the control, the control unit 84B may use at least one detecting result of the detecting unit 83B regarding the movement of the tool <NUM>. The detecting unit 83A may detect the position and/or the velocity of at least one of the tool <NUM> and/or the plug <NUM> and/or the module 35B and/or the holder <NUM>. The detecting unit 83A may transmit the result(s) to the control unit <NUM> for achieving the constant mechanical pressure.

In the mentioned modification of the tool <NUM>, the tool 85A of <FIG> has a pin <NUM> for performing friction stir welding. The pin <NUM> protrudes in the direction of the rotation axis of the tool <NUM>. In friction stir welding illustrated by <FIG> and <FIG>, the pin <NUM> contacts the surface of the plug <NUM>. Thus, due to the contacting pin <NUM>, the contact surface between the tool 85A and the plug <NUM> is smaller than when performing friction welding with the tool <NUM>. In addition, it is required to weld the recess in the welding joint <NUM>, which the pin <NUM> leaves in the welding joint <NUM>. Thus, like rotation friction welding, in which cutting the excess plug 60C is to be performed, friction (stir) welding requires additional processing after welding.

The friction (stir) welding has the same advantages as the rotation friction welding. However, like rotation friction welding, friction (stir) welding is more complex and slower than ultrasonic welding. In addition, the additional processing after welding required for rotation friction welding or friction (stir) welding is more intricate than for ultrasonic welding, since the texture of the surface of the welding joint <NUM> illustrated in <FIG> requires a comparably minimal additional processing.

All of the above-described implementations of the plant <NUM>, the device <NUM>, the transformer <NUM>, the transformer-rectifier-unit <NUM>, <NUM>, the winding <NUM>, the modules 35A, 35B, the devices <NUM>, 80A, 80B and the above-described methods can be used separately or in all possible combinations thereof. The features of the first and second embodiments and/or their modifications can be combined arbitrarily. Moreover, in particular, the following modifications are conceivable.

The elements shown in the figures are depicted schematically and can differ in the specific implementations from the forms shown in the figures provided that the above-described functions are ensured.

The shape of the elements <NUM>, <NUM>, <NUM>, especially the outer contour <NUM> of the base elements <NUM>, 353B, may be adapted to the specific requirements of the welding device <NUM>.

Additionally or alternatively, the dimensions of the elements <NUM>, <NUM>, <NUM> may be adapted to the specific requirements of the welding device <NUM>. That is, the thickness of the plate-like shape used for the elements <NUM>, <NUM>, <NUM> may differ from the thickness of the plate-like shape of the elements <NUM>, <NUM>, <NUM> shown in the drawings.

In case the transformer <NUM> has two cores <NUM>, the first and second winding elements <NUM>, <NUM> may each have only one window <NUM>, <NUM>. Each one of the two cores <NUM> may thus be mounted through the windows <NUM>, <NUM> and around one side of the frames of the winding elements <NUM>, <NUM>. The transformer <NUM> may have more than two cores, so that each one of the winding elements <NUM>, <NUM> may have more than two windows <NUM>, <NUM>.

Claim 1:
A method for producing a cooling channel in a winding (<NUM>) for a welding transformer (<NUM>), the method comprising the steps of
holding, by a holder (<NUM>), a winding module (35A; 35B) which comprises a first winding element (<NUM>), a second winding element (<NUM>) and a base element (<NUM>; 353B), wherein each one of the first and second winding elements (<NUM>; <NUM>) protrudes from the base element (<NUM>; 353B) and wherein the first and second winding elements (<NUM>; <NUM>) are positioned spaced to each other at the base element (<NUM>; 353B) so that the winding module (35A; 35B) has a t-cross-section, wherein the first winding element (<NUM>) comprises at least one window (<NUM>; <NUM>) for accommodating a part of a core (<NUM>) of the welding transformer (<NUM>), wherein the second winding element (<NUM>) comprises at least one window (<NUM>; <NUM>) for accommodating a part of the core (<NUM>) of the welding transformer (<NUM>), and wherein the base element (<NUM>; 353B) comprises grooves (<NUM>, <NUM>) separating the base element (<NUM>; 353B) into sections (<NUM>, <NUM>, <NUM>) such that at least one of the sections (<NUM>, <NUM>, <NUM>) is connected to the first and second winding elements (<NUM>; <NUM>) and such that at least one of the sections (<NUM>, <NUM>, <NUM>) is connected to only one of the first and second winding elements (<NUM>; <NUM>), and
sealing a plug (<NUM>; 60A, 60B, 60C) into a first hole (<NUM>) of the cooling channel (<NUM>), the cooling channel being provided in the first and second winding elements (<NUM>) as well as the base element (<NUM>; 353B) and being suitable for flowing a coolant (<NUM>) through the first and second winding elements (<NUM>; <NUM>) as well as the base element (<NUM>; 353B), which first hole (<NUM>) is open to the outside of one of the elements (<NUM>, <NUM>, <NUM>), by controlling a movement of the plug (<NUM>; 60A, 60B, 60C) relative to the first hole (<NUM>) so that a solid-state welding joint (<NUM>; <NUM>; <NUM>) is produced by material of the plug (<NUM>; 60A, 60B, 60C) and material of the winding module (35A; 35B), in which the first hole (<NUM>) is positioned,
wherein the holder (<NUM>) holds the winding module (35A; 35B) such that a movement between the winding module (35A; 35B) and the holder (<NUM>) is prevented while the step of sealing is performed.