Method for reworking a defective weld joint of a hairpin winding for a stator of an electric machine

Abstract

Method for reworking a defective weld joint of a hairpin winding for a stator of an electric machine by re-welding, comprising the steps - Providing a stator with a hairpin winding inserted into the stator, in which at least one pair of two adjacent wire ends (1, 2) of the hairpin winding was defectively welded together in a previous welding process, - Clamping at least the wire ends (1, 2) of the hairpin winding to be re-welded in a clamping device (6), - Providing filler material (4) consisting of the same material as the at least one pair of wire ends (1, 2) to be re-welded and having at each pair of wire ends (1, 2) substantially the same quantity as any loss of wire material there due to the preceding faulty welding process, and arranging the filler material (4) at the pairs of wire ends (1, 2) to be re-welded, - wherein the filler material (4) in the arrangement on a pair of wire ends (1, 2) to be re-welded is flat at its end (8) facing away from the two wire ends (1, 2) to be welded and has essentially the same geometry there as the surfaces of the two wire ends (1, 2) facing away from the stator before the defective weld, and - the filler material (4) with its geometry at its end (9) facing the pair of wire ends (1, 2) to be welded again is adapted to the geometry (5) of the surfaces of the two wire ends (1, 2) after the faulty welding, - re-welding of at least one pair of adjacent wire ends (1, 2) by melting the filler material (4).

Description

[0001] The invention relates to a method for reworking a defective weld joint of a hairpin winding for a stator of an electric machine by re-welding, wherein a stator with a hairpin winding inserted into the stator is provided, in which at least one pair of two adjacent wire ends of the hairpin winding was defectively welded together in a previous welding process, at least the wire ends of the hairpin winding to be re-welded are clamped in a clamping device, filler material is provided which consists of the same material as the at least one pair of wire ends to be re-welded and which has substantially the same quantity at each pair of wire ends to be re-welded as a loss of wire material there due to the previous defective welding process, and the filler material is arranged at the pairs of wire ends to be re-welded.wherein the filler material in the arrangement on a pair of wire ends to be re-welded is flat at its end facing away from the two wire ends to be welded and has essentially the same geometry there as the surfaces of the two wire ends facing away from the stator before the defective weld, and the filler material with its geometry at its end facing the pair of wire ends to be re-welded is adapted to the geometry of the surfaces of the two wire ends after the defective weld, and at least one pair of adjacent wire ends is re-welded by melting the filler material.

[0002] It is known to manufacture stators for electric motors using so-called hairpin windings. In this process, U-shaped bent wire sections, particularly copper, are referred to as "hairpins" and inserted into the slots of the stator. To electrically form the windings from the individual hairpins, the wire ends of the hairpins must be welded together in pairs according to a predetermined pattern after being inserted into the stator. This can be done, in particular, by laser, electron beam, or TIG welding.

[0003] Welding defects can occur during welding, for example, due to explosions of residual insulating material that unintentionally remains on the wire ends after stripping. This causes some of the molten wire material to be flung away, resulting in an insufficient or even no electrically conductive weld between the wire pair being welded. Consequently, there is insufficient or no electrical contact, which impairs the current flow through the stator windings and thus the electrical properties of the stator, potentially leading to complete stator failure.

[0004] Since a hairpin stator can have several hundred, for example on the order of 200, pairs of wire ends to be welded, and thus a corresponding number of weld points, even a low rejection rate for individual welds can quickly lead to a high number of defective stators due to faulty welds. Because each stator already represents a significant investment in manufacturing and materials through the preceding production steps, the aim is to correct faulty welds by re-welding in order to reduce the rejection rate in stator production as much as possible.

[0005] DE 10 2020 210 778 A1 describes a method for monitoring a welding process of a hairpin winding, in which the geometry of the solidified weld bead is detected by means of an OCT measuring beam, compared with a target geometry and the quality of the weld bead is monitored based on the deviation and in the case of a weld bead classified as defective it is automatically re-welded.

[0006] DE 10 2018 200 035 A1 describes a method for electrically connecting hairpin ends in the manufacture of a rotor or stator with hairpin winding, wherein the connecting is carried out using a 3D printing process such that the hairpin ends to be connected are electrically conductively connected by printing metallic connecting elements.

[0007] From DE 10 2020 115 124 A1, a method for reworking a defective weld joint of a hairpin winding for a rotor or stator of an electric machine is known, in which the defective weld joint is first separated again by cutting off an area encompassing the defective weld joint from the conductor ends and thus shortening the conductor ends, and then the conductor ends are welded again, this time by a build-up welding process in which the welding electrode is partially melted and forms part of the weld joint.

[0008] A particular disadvantage here, besides the need to separate the area containing the faulty weld from the conductor ends and thus shorten the conductor ends, is that when re-welding without additional material and due to the shortened conductor ends, damage to the insulation edge can more easily occur due to heat input.

[0009] The invention is therefore based on the objective of providing a method for reworking a faulty weld joint of a hairpin winding for a stator of an electric machine by re-welding, in which the risk of damage to the wire insulation is reduced.

[0010] This problem is solved by a method for reworking a defective weld joint of a hairpin winding for a stator of an electric machine by re-welding with the features of claim 1. Further features of the invention are set forth in the dependent claims.

[0011] In the inventive method for reworking a defective weld joint of a hairpin winding for a stator of an electric machine by re-welding, a stator with a hairpin winding inserted into it is first provided. In this hairpin winding, at least one pair of adjacent wire ends was defectively welded together in a previous welding process.

[0012] At least the wire ends of the hairpin winding that need to be welded again are clamped in a clamping device.

[0013] Filler material is provided, consisting of the same material as the at least one pair of wire ends to be re-welded. This filler material is present at each pair of wire ends to be re-welded in essentially the same quantity as the loss of wire material at that pair due to the preceding faulty welding process. The filler material is placed (as individual units) at each pair of wire ends to be re-welded.

[0014] The additional material is geometrically adapted for re-welding a pair of wire ends that are to be welded again.

[0015] When positioned on a pair of wire ends to be re-welded, i.e., when it is placed in the position where it will later be melted during re-welding, the filler material is flat at its end facing away from the two wire ends to be welded (i.e., usually also the end facing away from the respective end face of the stator from which the wire pairs to be re-welded protrude). It has essentially the same geometry as the surfaces of the two wire ends facing away from the stator before the faulty weld. That is, the filler material is essentially flat on its side facing away from the two wire ends to be re-welded and has the same orientation as the wire ends of the hairpin pair before the faulty weld to avoid unwanted reflections.

[0016] Furthermore, the filler material, with its geometry at the end facing the pair of wire ends to be re-welded (i.e., usually also its end facing the stator face), is adapted to the geometry of the surfaces of the two wire ends after the faulty weld. This geometry is often funnel-shaped, conical, or semicircular / spherical due to ejection during welding explosions.

[0017] At least one pair of adjacent wire ends is then re-welded together by melting the filler material. In this process, the wire ends to be re-welded are also melted, either indirectly through heat conduction from the melted filler material, or through direct energy input into the wire ends, particularly after the filler material itself has been melted.

[0018] This ensures that the re-welded wire ends have the same length they would have had the first weld been flawless, or the same length as the adjacent, flawlessly welded pairs of wire ends. This allows the wire ends to be subsequently insulated uniformly, for example, by immersion. The risk of damaging the wire insulation is reduced, particularly compared to re-welding by electrode build-up, where the arc moves close to the insulation, at least initially, and can damage it. In contrast, the filler material in this process ensures a greater distance between the welding energy input and the wire insulation at all times.

[0019] In an advantageous embodiment of the method according to the invention, it is provided that at least the wire ends to be welded again, a subset or all wire ends of the hairpin winding are clamped in the clamping device, which was also used to clamp the wire ends in the preceding welding process, wherein after the preceding welding process the clamping device is first released and then clamped again, or the clamping is continued without interruption after the preceding welding process.

[0020] The subsequent welding can thus be carried out with the same welding equipment as the first weld. The tension from the first weld, in which usually all wire end pairs to be welded are tensioned, can be maintained; or the tension can be released from wire end pairs not to be welded again; or the tension can be completely released and re-tensioned, tensioning only the wire end pairs to be welded again; or additional wire end pairs can be tensioned, for example to stabilize the stator; or all wire end pairs can be re-tensioned.

[0021] This eliminates the need for additional clamping devices and the need to re-clamp between initial welding and subsequent welding.

[0022] In a further advantageous embodiment of the method according to the invention, the filler material is arranged on a pair of wire ends to be re-welded by a robot or manually. Since the geometry of the pair of wire ends to be re-welded is generally funnel-shaped, it is not necessary to fix the filler material during the re-welding process.

[0023] In a further advantageous embodiment of the method according to the invention, the melting is carried out using the same welding process that was also used in the preceding welding operation. The melting can also be carried out using the same welding device that was also used in the preceding welding operation. This eliminates the need for additional welding devices for subsequent welding.

[0024] In a particularly advantageous embodiment of the method according to the invention, the melting is carried out using a laser or electron beam. This allows the energy input to be controlled precisely, in particular to avoid damaging the wire insulation.

[0025] In a further advantageous embodiment of the method according to the invention, the geometry of the surfaces of the two wire ends after the defective weld is assessed, characterized, or measured by means of image processing. Based on the data thus obtained, the geometry of the filler material to be placed there during re-welding is selected at its end facing the pair of wire ends to be re-welded by choosing from a group of pre-formed geometries that are oriented towards geometries of wire end pairs due to typical welding defects. The surface of the defectively welded wire pair is often funnel-shaped, conical, or semi-circular or spherical due to the ejection during welding explosions, i.e., it frequently exhibits comparable geometries with regard to shape and size.It is therefore advantageous to provide supplementary material geometrically prepared and sorted into groups in order to cover the most common geometries at least approximately and to select suitable supplementary material from it when re-welding a wire end pair, instead of adapting it individually in each case.

[0026] In another advantageous embodiment of the method according to the invention, the geometry of the surfaces of the two wire ends after the defective weld is also assessed, characterized, or measured by image processing. Based on the data thus obtained, the geometry of the filler material at its end facing the pair of wire ends to be re-welded is then formed by an automated manufacturing device, for example, a milling device. This allows for the creation of a customized geometry.

[0027] An embodiment of the invention is described below with reference to the accompanying drawings.

[0028] They show: Fig. 1: Wire pairs of a hairpin stator before the subsequent welding according to the invention of a wire pair that was incorrectly welded in the previous welding process, Fig. 2: Wire pairs of a hairpin stator after the inventive re-welding of a wire pair that was incorrectly welded in the previous welding.

[0029] In Fig. Figure 1 shows two wire pairs from a multitude of wire pairs of a hairpin stator, whose electrical windings are formed by welding their wire ends 1, 2 together. On the right, a wire pair is shown before welding. On the left, a wire pair is shown after a faulty first weld. An explosion during the first weld, caused by heating and the resulting sudden vaporization of residual insulating material 3 left behind at the wire ends 1, 2 after stripping, ejected molten wire material from a laser or electron beam. As a result, the desired weld bead did not form when the two wire ends 1, 2 were welded together. Instead, a funnel or...Crater 5 was formed, and the two wire ends 1, 2 were not electrically connected to each other during the first welding, or only insufficiently, by molten wire material which subsequently solidified as a weld bead.

[0030] For re-welding to correct the unwanted defect, the wire ends 1, 2 in the illustrated embodiment remain clamped in the clamping device 6, by which they were already clamped during the first welding process, in order to press them together in a parallel butt joint during welding and to melt their wire ends by means of a laser or electron beam and thus weld them together in pairs.

[0031] For re-welding, filler material 4 is placed in the funnel 5 created by the faulty weld. On its side 9 facing the wire ends 1, 2 to be re-welded, this filler material is adapted to the shape of the funnel 5. This ensures that when the filler material 4 melts during re-welding, it fills the funnel 5 as completely as possible and simultaneously achieves a length of the re-welded wire ends 1, 2 with the added filler material 4 that corresponds to the length of pairs of wire ends 1, 2 that were correctly welded in the first welding process. Adapting the filler material 4 on its side 9 facing the wire ends 1, 2 to be re-welded to the shape of the funnel 5 can be achieved by creating a supply of units of filler material 4 in which the side 9 of the filler material 4 facing the wire ends 1, 2 to be re-welded is pre-shaped to the funnel shapes and depths typically formed during welding explosions.From these variants of prepared filler material units, a selection can then be made for the specific re-welding of pairs of wire ends 1 and 2. This can also be supported by image processing. It is also conceivable to use image processing to capture the funnel geometry and then to produce specific geometries of filler material 4 for the respective wire pair, e.g., automatically.

[0032] On its side 8 facing away from the wire ends 1, 2 to be welded again, the filler material 4 is flat or flattened, like the one on the right side of Fig. 1. A corresponding area of ​​two wire ends to be welded before the first welding. This prevents unwanted reflections of the laser or electron beam used for welding.

[0033] The additive material 4 and the wire ends 1, 2 are now (not shown) melted by a laser or electron beam. The result is in Fig. 2 shown on the left.

[0034] The molten filler material 4 forms a weld bead 7 after solidification, which corresponds at least largely to the one that should have formed during the first welding process. This also applies to the distance of the weld bead 7 from the stator end face, which corresponds to the distance between the wire end pairs that were welded correctly during the first welding process. That is, all welded wire ends protrude from the stator end face by essentially the same length.

[0035] The two wire ends 1, 2 are now connected by the weld bead 7 and reliably electrically contacted. The weld bead 7 is sufficiently spaced from the clamping device 6 and is not unintentionally welded to it. The stator can therefore be easily released by the clamping device 6. Since the heat input during re-welding occurs primarily in the filler material 4, no critical temperature is reached at the wire insulation 3 that would lead to its damage.

[0036] On the right side of Fig.Figure 2 shows the result of a re-welding process without the use of filler material. Here, the two wire ends 1 and 2, after a funnel formed due to the welding explosion during the first welding and a loss of wire material occurred, are re-welded without filler material by remelting the two remaining wire ends, for example, with a laser beam. This results in the wire ends being closer to the stator face after re-welding than the wire ends that were correctly welded in pairs during the first welding process. As shown, this can cause the resulting weld bead to rest on the clamping device and become difficult or impossible to remove, or even damage it.Furthermore, the heat input does not damage the additional material, but exclusively directly into the wires that have been shortened (due to the faulty first welding) and damages the wire insulation 3. REFERENCE MARK LIST 1 first wire end of a wire pair to be welded 2 second wire end of a wire pair to be welded 3 wire insulation 4 Additional material 5 Wire surface after a faulty weld 6 Clamping device 7 weld beads after re-welding 8 Side of the filler material facing away from the stator / wire pair 9 Side of the filler material facing the stator / wire pair

Claims

[1] Method for reworking a defective weld joint of a hairpin winding for a stator of an electric machine by re-welding, comprising the steps - Providing a stator with a hairpin winding inserted into the stator, in which at least one pair of two adjacent wire ends (1, 2) of the hairpin winding was defectively welded together in a previous welding process, - Clamping at least the wire ends (1, 2) of the hairpin winding to be re-welded in a clamping device (6), - Providing filler material (4) consisting of the same material as the at least one pair of wire ends (1, 2) to be re-welded and having at each pair of wire ends (1, 2) substantially the same quantity as any loss of wire material there due to the preceding faulty welding process, and arranging the filler material (4) at the pairs of wire ends (1, 2) to be re-welded, - wherein the filler material (4) in the arrangement on a pair of wire ends (1, 2) to be re-welded is flat at its end (8) facing away from the two wire ends (1, 2) to be welded and has essentially the same geometry there as the surfaces of the two wire ends (1, 2) facing away from the stator before the defective weld, and - the filler material (4) with its geometry at its end (9) facing the pair of wire ends (1, 2) to be welded again is adapted to the geometry (5) of the surfaces of the two wire ends (1, 2) after the faulty welding, - re-welding of at least one pair of adjacent wire ends (1, 2) by melting the filler material (4). [2] Method according to claim 1, characterized by , that at least the wire ends (1, 2) to be welded again, a subset or all wire ends of the hairpin winding are clamped in the clamping device (6) which was used to clamp the wire ends (1, 2) in the preceding welding process, wherein after the preceding welding process the clamping device (6) is first released and then re-tensioned, or the clamping is continued after the preceding welding process. [3] Method according to claim 1 or 2, characterized by, that the filler material (4) is positioned on a pair of wire ends (1, 2) to be re-welded by a robot or manually [4] Method according to any of the preceding claims, characterized by that the melting is carried out using the same welding process that was used in the previous welding process. [5] Method according to claim 4, characterized by that the melting is carried out using the same welding device that was used in the previous welding process. [6] Method according to one of the preceding claims 4 or 5, characterized by that the melting is done using a laser or electron beam. [7] Method according to any of the preceding claims, characterized by, that the geometry (5) of the surfaces of the two wire ends (1, 2) is assessed, characterized or measured by image processing after the defective welding and, based on the data obtained in this way, the geometry of the filler material (4) to be placed there during re-welding is selected at its end (9) facing the pair of wire ends (1, 2) to be welded again by selecting from a group of preformed geometries that are oriented to geometries of wire end pairs due to typical welding defects. [8] Method according to any of the preceding claims, characterized by, that the geometry (5) of the surfaces of the two wire ends (1, 2) is assessed, characterized or measured by image processing after the faulty welding and, based on the data obtained in this way, the geometry of the filler material (4) at its end (9) facing the pair of wire ends (1, 2) to be welded again is formed by an automated manufacturing device, for example by a milling device.

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