Method for laser welding bent metal-containing bar-type conductors with strength redistribution in the start and end phases, corresponding bar-type conductor arrangement, and use of such a bar-type conductor arrangement

Abstract

The present invention relates to a method for laser welding bar-type conductors (1a, 1b), the bar-type conductors (1a, 1b) being made of an aluminum-containing rod-shaped conductor material with an aluminum content of at least 75% by weight. The two bar-type conductors (1a, 1b) are arranged adjacent to each other with at least a partial overlap and are welded by a processing laser beam (11). A weld bead (19) is formed on a common base surface (7) of the adjacent bar-type conductors (1a, 1b), the weld bead connecting the bar-type conductors (1a, 1b) to each other. The present invention provides that the processing laser beam (11) is guided while the bar-type conductors (1a, 1b) are laser welded such that a weld contour (12) of the processing laser beam (11) is arranged relative to the bar-type conductors (1a, 1b). A speed of advancement v of the processing laser beam (11) along a weld contour (12) for the bar-type conductors (1a, 1b) is selected while the bar-type conductors (1a, 1b) are being laser welded, the weld bead (19) has a non-liquid oxide layer (14) on which liquid bar-type conductor material (15) accumulates, and while the bar-type conductors (1a, 1b) are being laser welded, the non-liquid oxide layer (14) is formed by a weld contour (12) that is aligned with the weld contour (12). In a manner corresponding to the above, the non-liquid oxide film (14) is partially broken only at the end face (20) of the weld bead (19) facing upward by the processing laser beam (11), and while the bar-shaped conductors (1a, 1b) are being laser welded, the non-liquid oxide film (14) remains undamaged in the peripheral region (21) of the weld bead (19), which peripheral region extends away from the upper end face (20) downward towards the bar-shaped conductors (1a, 1b) and extends around the entire weld bead (19).

Description

[Technical field]

[0001] The present invention relates to a method for laser welding bar-type conductors, preferably bent bar-type conductors, in particular hairpins for electric motors or generators, comprising the steps of: the bar-type conductor is made of an aluminum-containing bar-type conductor material having an aluminum content of at least 75% by weight, preferably at least 90% by weight; The two bar-type conductors are disposed adjacent to each other with partial overlapping portions, and are welded to each other by a processing laser beam, and a weld bead connecting the bar-type conductors to each other is formed on a common base surface of the adjacent bar-type conductors; In particular, the common base surface is horizontally aligned It concerns the method. [Background technology]

[0002] Such a method is disclosed by an online publication (Non-Patent Document 1).

[0003] In the manufacture of electric motors or electronic generators, in addition to wound stators, nowadays also stators are used that are made of metal, usually bent bar-shaped conductors ("bar-type conductors"), in particular so-called hairpins. The bar-type conductors are arranged to correspond to the intended electrical connections and are then welded together, thus forming electromagnets. In contrast to wound stators, the hairpin technology allows advantages in terms of weight, cost and efficiency.

[0004] Bar-type conductors are often welded using a laser beam. For this purpose, a laser beam is typically directed at the front end faces of two overlapping bar-type conductors, which are often placed against each other. As a result, heat is introduced into the bar-type conductors, which melt and, after solidification, are connected to each other by a solidified weld bead.

[0005] During welding, it is necessary to create a sufficiently large cross-sectional area through which the current can flow between the two bar-shaped conductors. If the welding is not performed properly, ohmic heating, loss of effectiveness or unusable electromechanical machines may occur during operation.

[0006] Up until now, copper bar-type conductors have been mainly used, and an example of welding of copper-containing bar-type conductors was disclosed in a subsequently published patent application (Patent Document 1).

[0007] In the aforementioned online publication, Clean-Lasersysteme proposes directly machining aluminum hairpins instead of copper. For this purpose, aluminum hairpins are welded together in a vacuum. The use of aluminum hairpins should offer, among other things, cost advantages. No further details about the method are mentioned.

[0008] However, welding aluminum hairpins turns out to be difficult in practice: the weld bead created by the laser beam can easily flow during the welding operation, and thus often results in an insufficient cross-sectional area for the conduction of electric current, making the weld unusable. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] DE 10 2020 113 179.8 [Non-patent literature]

[0010] [Non-Patent Document 1] “STATOR HAIRPINS AUS ALUMINUM ENTLACKEN UND SCHWEISSEN-GROSSES EINSPARPOTENZIAL”[“Stripping and welding stator hairpins of aluminum - great savings potential”]by Clean-Lasersysteme,Herzogenrath(North Rhine-Westphalia,DE),cf.https: / / www.cleanlaser.de / de / news / hairpins-aluminium / ,dated 05.03.2021 Summary of the Invention [Problem to be solved by the invention]

[0011] It is an object of the present invention to provide a method for laser welding bar-type conductors of aluminum-containing alloys in order to reliably produce a usable welded connection, in particular to obtain a sufficiently large cross-sectional area for the conduction of electric current. [Means for solving the problem]

[0012] This object is achieved according to the invention by a method of the type mentioned in the introduction, which method comprises the steps of: During the laser welding of the bar-shaped conductor, the processing laser beam is guided, in which in the process the welding contour of the processing laser beam is arranged relative to the bar-shaped conductor, and the advance speed v of the processing laser beam along the welding contour relative to the bar-shaped conductor is - during the laser welding of the bar-type conductor, the weld bead has a non-liquid oxide film, and during the laser welding of the bar-type conductor, liquid bar-type conductor material accumulates inside the non-liquid oxide film; During laser welding of bar-shaped conductors, the non-liquid oxide film is partially broken open by the processing laser beam only on the upward end face of the weld bead, so as to correspond to the weld contour; During laser welding of bar-type conductors, the non-liquid oxide film remains intact in the peripheral region of the weld bead extending from the top surface downwards towards the bar-type conductor and around the entire weld bead It is permitted that the selection be made as follows.

[0013] Within the context of the method according to the invention, it is proposed to use a suitable technique for carrying out the process of welding two aluminum-containing bar-type conductors, to have the effect that a non-liquid oxide film ("oxide film") is formed in the region of the process zone and remains stable during the method. A liquid bar-type conductor material is then formed underneath the oxide film, which is held by the oxide film in the defined form of a weld bead, thereby making it possible to reliably produce a usable welded connection.

[0014] When welding two metal-containing bar-type conductors, it is important to create a dimensionally stable weld bead, since the quality of the resulting weld bead affects the current conduction characteristics between the bar-type conductors. Aluminum has a significantly lower viscosity and surface tension than copper at its melting temperature. For this reason, during welding, the low-viscosity melt of the aluminum-containing alloy tends to flow out of the area of ​​the process zone where the weld is performed in an uncontrolled manner. This can lead to a large deformation or incomplete formation of the weld bead and thus a reduction in the cross-sectional area between the bar-type conductors through which the current can flow.

[0015] Thus, in addition to the cost savings already mentioned above, there is also a weight reduction (density of copper in elemental form is 8.96 g / cm 3 is the density of elemental aluminum, 2.7 g / cm 3 The advantages derived from the use of aluminum-containing bar-type conductors, such as conductor widths of 100 mm or less (more than three times that of 100 mm), may be offset by the disadvantages of defects or excessively small cross-sectional areas between the bar-type conductors.

[0016] In the method according to the invention, the way in which the process is carried out is selected so that during the laser welding of the bar-type conductors, a non-liquid oxide film ("oxide film") is present in the area of ​​the process zone. The oxide film avoids the disadvantages of the low viscosity and surface tension of the melt of aluminum-containing alloys. The oxide film keeps the shape of the melt uniform, aligns it upwards and forms a peripheral area ("flank") bounded by the sides. This creates a uniform weld bead and prevents the melt from flowing to the sides. The viscosity and surface tension of the melt are therefore no longer an issue.

[0017] Aluminum in air spontaneously forms a thin layer of aluminum oxide (self-passivation) to protect the bar-shaped conductor material from corrosion. Thus, at the start of the welding method, the bar-shaped conductor material is already covered by an oxide film, under which liquid melt can form and accumulate. As a result of the temperatures reached during laser welding, in particular during laser welding, the thickness of the oxide film can be increased compared to that of a conventional solid bar-shaped conductor. Furthermore, during the method, new aluminum oxide can spontaneously form at the locations where the molten aluminum is exposed, in particular at the locations of the oxide film that is broken open by the processing laser beam. During the method, the oxide film remains for substantially the entire time in order to demarcate the weld bead that is formed or grows, using the oxide film that is present before the start of the laser welding and / or the oxide film that is newly formed during the laser welding.

[0018] The process is carried out in the context of the present invention in such a way that the dynamics of the melt are limited, especially in the vicinity of the peripheral region, and that cracks from which the melt can exit in an uncontrolled manner are prevented from forming in the peripheral region, which would result in an uneven weld bead. In order to limit the dynamics of the melt pool, the processing laser beam can follow the weld contour, especially with a sufficiently low advance speed. Furthermore, in order to avoid cracks in the peripheral region of the oxide film of the weld bead, the weld contour can be selected to be sufficiently spaced from the periphery of the bar-shaped conductor (or from the periphery of the "end face", which is the face of the bar-shaped conductor facing the laser beam). The stability of the oxide film is promoted under these conditions.

[0019] In the process of laser welding of bar-shaped conductors, a molten pool is created under the oxide film. This is possible because the melting temperature of aluminum in elemental form, about 660 °C, is significantly lower than that of aluminum oxide, about 2070 °C (depending on atmospheric conditions, the processing laser beam may also cause separation of Al2O3 instead of melting). The molten pool is heated until the desired amount of liquid aluminum is obtained. This ensures that the cross-sectional area between the bar-shaped conductors at the final solidification is large enough to obtain a sufficiently high conduction of electric current.

[0020] The processing laser beam interacts with the oxide film substantially only in the area where the processing laser beam is incident on the oxide film. The processing laser beam breaks open the oxide film only along its weld contour, so the weld contour creates a broken open (i.e., liquid) trajectory and possibly also has broken open (or liquid) areas inside the weld contour. At all other points, the oxide film is maintained, holding the molten bar conductor material together and maintaining its shape.

[0021] After the action of the working laser beam is completed, the molten pool, still held in shape by the oxide film, is cooled down, so that on solidification the connected bar-shaped conductors have a sufficiently large cross-sectional area resulting in a defined weld bead that ensures a sufficiently good conduction of the electric current, and a usable weld connection is reliably created.

[0022] Preferred variants of the invention In a preferred variant of the method according to the invention, the welding contour of the working laser beam is arranged with respect to the bar-shaped conductor in such a way that, with respect to the minimum distance d of the welding contour from the periphery of the common base surface and the extent L of the common base surface along the direction in which the minimum distance d lies, d ≥ 0.15*L, preferably d ≥ 0.20*L, particularly preferably d ≥ 0.25*L, this has proven successful in practice, with a distance d that minimizes the probability of damage to the oxide film, especially in the surrounding area.

[0023] Particularly preferred is a variant in which the weld contour of the processing laser beam is arranged with respect to the bar-shaped conductor in such a way that, with respect to the minimum distance d of the weld contour from the outer periphery of the common base surface, d≧0.6 mm, preferably d≧0.8 mm, particularly preferably d≧1.0 mm, applies, which has also proven successful in practice and involves a distance d at which the probability of damage to the oxide film, especially in the surrounding area, is minimized.

[0024] In an advantageous variant, the following applies with respect to the advance speed v of the processing laser beam along the weld contour of the processing laser beam for the bar-shaped conductor: v≦1600 mm / s, preferably v≦1200 mm / s, particularly preferably v≦800 mm / s. The advance speed v influences the dynamics of the melt generated under the non-liquid oxide film. With the specified advance speed, in fact, the oxide film exhibits good stability and a weld bead of uniform shape is formed.

[0025] A variant in which the laser welding is carried out in an oxygen-containing atmosphere, in particular in air, is preferred. The oxygen-containing atmosphere stabilizes the oxide film of the weld bead and promotes the rapid reconstruction of aluminum oxide, for example on exposed aluminum melt in the trajectory of the processing laser beam. Furthermore, the oxygen-containing atmosphere can be easily set up, especially if air is used, and no additional structures are required.

[0026] In a preferred variant of the method according to the invention, at least in the second half of the laser welding of the bar-shaped conductors, the peripheral area in which the non-liquid oxide film remains intact extends over at least 3 / 4 of the height of the weld bead, preferably over at least 9 / 10 of the height of the weld bead, thus ensuring the formation of a dimensionally stable and uniform weld bead with a height that establishes a practically sufficient electrical conduction of the current between the bar-shaped conductors over the available cross-sectional area of ​​the weld bead. Usually, the peripheral area extends over practically the entire height of the weld bead.

[0027] A variant is also preferred in which two bar-shaped conductors are arranged with their end regions parallel to one another, in particular the end regions of the bar-shaped conductors are widely pressed against one another, the front end faces of the bar-shaped conductors are located at approximately the same height relative to the direction of the longitudinal extent of the end regions of the bar-shaped conductors, and the processing laser beam is directed at the front end faces of the bar-shaped conductors, which thus provide a common base surface on which the weld bead is formed. Arranging the end faces at approximately the same height has the effect that the respective melts formed on the end faces by the processing laser beam can be combined without problems to form a common uniformly shaped (spherical) weld bead, in particular the common weld bead does not have to form a bevel. The end regions placed against one another reduce the risk that the melt of the common weld bead will flow out between the bar-shaped conductors. By pressing the end regions against one another, the gaps remaining between the end regions placed against one another can be minimized.

[0028] Advantageous is a further development of this variant in which the end regions of the bar-shaped conductors are directed approximately vertically upwards, in particular the front end faces being aligned approximately horizontally. In this arrangement, the end faces can be easily accessed by the processing laser beam. The horizontal alignment of the end faces has the effect that the melt formed is not subjected to any downhill-slope forces, and the weld bead can be stabilized.

[0029] Also preferred is a further development in which the processing laser beam is incident on the front end face approximately perpendicularly. This has a particularly stable vapor capillary effect and reduces the dynamics of the molten pool. A defined weld bead can be formed more easily.

[0030] Preferably, the bar-shaped conductors have, at least in the vicinity of the common base surface, in particular in each end region, a rectangular cross section with an edge length of 0.2 mm to 10 mm, preferably 1 mm to 8 mm, particularly preferably 2 mm to 6 mm, and in particular for each bar-shaped conductor, the length L2 of the long edge is less than the length L of the short edge. kurz A variant in which the cross section of the two bar-shaped conductors to be welded together is twice as long as the short edge, and the cross section of the two bar-shaped conductors to be welded together is the same. These dimensions have proven successful in practice, particularly for the construction of electric motors. Typically, the long edges of the bar-shaped conductors are placed against each other, thus maximizing the cross-sectional area of ​​the weld bead with which the bar-shaped conductors can be connected to each other. If the long edges are selected to be twice as long as the short edges, a square base surface with the same cross section can be provided for the bar-shaped conductors. A particularly circular weld contour allows the energy from the processing laser beam to be introduced particularly uniformly into this base surface.

[0031] Further preferred is a variant in which the minimum distance d2 between the weld contour and the periphery of the common base surface in the direction of each long edge is 20% to 40%, preferably 25% to 35%, of the length L2 of the corresponding long edge, and the minimum distance d1 between the weld contour and the periphery of the common base surface in the direction of each short edge is 20% to 40%, preferably 25% to 35%, of twice the length L1 of the short edge, with distances d2 and d1 that have proven successful in practice and minimize the probability of damage to the oxide film, especially in the surrounding area.

[0032] In an advantageous variant, the processing laser beam is 0.5kW≦P≦20kW, Preferably, 2 kW ≦ P ≦ 10 kW; Particularly preferably, 4 kW≦P≦8 kW and a laser output P of and / or the wavelength of the processing laser beam is between 400 nm and 1200 nm. These laser powers and wavelengths of the processing laser beam have proven particularly successful in practice for the method according to the invention. In particular, it is possible to obtain a uniform formation of the weld bead during the welding process.

[0033] Particularly preferred are variants in which the weld contour is selected to be linear, circular or elliptical and is passed multiple times during the laser welding of the bar-type conductor. In particular, the weld contour is generated by a scanner optical unit. The multiple passes of the weld contour during the laser welding of the bar-type conductor allow for a uniform distribution of the energy from the processing laser beam and for the process to introduce virtually any desired amount of energy into the bar-type conductor by the corresponding number of passes. Local overheating is avoided. Overall, a particularly uniform formation of the weld bead can be achieved. The scanner optical unit, typically formed with a mirror and two piezo actuators, allows for a low-cost establishment of the weld contour on the bar-type conductor or weld bead and for the weld contour to be passed accurately, in particular also at speeds that are impossible to reach or can only be reached with difficulty by mechanically moving the workpiece or the laser. The shape of the weld contour can be adapted to the shape and alignment of the bar-type conductor to be welded.

[0034] Further preferred is a variant in which a shaped laser beam having a core portion and a ring portion annularly surrounding the core portion is at least temporarily selected as the processing laser beam, in particular the variant in which the shaped laser beam is generated by a 2-in-1 fiber with a core fiber diameter KFD of 11 μm≦KFD≦300 μm, preferably 50 μm≦KFD≦100 μm, and a ring fiber diameter RFD of 50 μm≦RFD≦1000 μm, preferably 200 μm≦RFD≦400 μm. The use of a shaped laser beam makes it possible to reduce the dynamics of the molten pool overall, which minimizes welding defects such as spatter formation or porosity formation, in particular at the beginning and end of the method. The power component of the laser output portion of the core may be selected or varied between 20% and 100%, preferably between 20% and 80%, particularly preferably between 40% and 60%. The distribution of the laser power between the core portion and the ring portion may be selected to be constant throughout the entire welding process, if necessary. In that case, typically the power component P of the core portion is kern is 40-60%. Alternatively, the power component P kern If necessary, in the main phase of laser welding (between the initial and final phases), the power component P of the core part at 100% can be selected to increase the process speed. kern In the first stage (initial stage) and / or the last stage (final stage), the output component P of the core part can be selected to minimize defects in the weld. kern can be chosen to be small, and in particular to vary continuously.

[0035] In a preferred further development of this variant, the power component P of the laser output of the core section kern is selected to be smaller during the first phase of laser welding of the bar-type conductor than during the main phase of laser welding of the bar-type conductor, in particular the power component P of the laser power of the core part kernincreases continuously during the first stage, in particular the first stage has a duration of 1 ms to 30 ms. The power component P is selected to be small when the processing laser beam passes (start of the initial stage). kern This ensures a reduction in spatter formation and thus prevents a relatively large amount of liquid melt and non-liquid oxide film from being prematurely ejected from the process zone at the beginning of the initial stage, which would make it more difficult to form a uniform weld bead. After the passage, the power component P kern can be continuously increased up to the desired power of the main phase. Typically, the first phase (initial phase) comprises a proportion of 10-30% of the total welding duration. During the first phase, a vapor capillary is formed. The first phase typically lasts at least as long as it takes for the vapor capillary to reach at least 30% of its maximum capillary depth during laser welding of bar-type conductors.

[0036] Also preferred is a power component P of the laser output of the core portion. kern is selected to be smaller during the last phase of laser welding of the bar-type conductor than during the main phase of laser welding of the bar-type conductor, and in particular the power component P of the laser power of the core part kern is continuously decreased during the last stage, in particular in the further development form where the last stage has a duration of 1 ms to 30 ms. In the last stage (final stage), the output component P kern ensures that the vapor capillary can be reduced in a controlled manner, and the output component P kern This allows a particularly gradual retreat of the vapor capillary, which has the effect that no or only few small pores are formed in the weld bead, thus ensuring a reliably usable weld connection. Typically, the last stage comprises 10-30% of the total welding duration.

[0037] A bar-type conductor arrangement comprising at least two bar-type conductors welded by the above-mentioned method according to the invention is also included within the context of the present invention. The weld bead formed during welding is of uniform shape and ensures a sufficient cross-sectional area for the current to flow between the welded bar-type conductors. Typically, multiple bar-type conductors are welded in series (e.g. in a stator carrier), and a bar-type conductor is welded at both legs to further bar-type conductors (or to power connections in the case of terminal bar-type conductors).

[0038] Furthermore, the invention comprises the use of a bar-type conductor arrangement, each made by welding two respective bar-type conductors by the method according to the invention described above, the bar-type conductor arrangement being attached to an electric motor or generator. The welded connections of the bar-type conductors are particularly reliable and therefore easily adaptable to the high current intensities occurring in electric motors and generators. In the case of electric motors provided for mobile applications (e.g. electric vehicles), the inherent low weight of the bar-type conductors of aluminium-containing bar-type conductor materials is particularly advantageous.

[0039] Further advantages of the invention will become apparent from the description and the drawings. Likewise, according to the invention, the features mentioned above and those to be detailed hereafter can in each case be used alone and separately or together in any desired combination. The illustrated and described embodiments should not be understood as an exhaustive enumeration, but rather as exemplary features for outlining the invention.

[0040] The invention is illustrated in the drawings and will be explained in more detail on the basis of exemplary embodiments. [Brief description of the drawings]

[0041] [Figure 1] FIG. 2 shows a schematic side view of two bent bar-type conductors in a partially overlapping arrangement that are to be welded together within the context of the present invention. [Diagram 2]2 shows a schematic perspective view of the end regions of two bar-shaped conductors of FIG. 1 placed against each other before starting the laser welding according to the invention; [Diagram 3] 3 shows a schematic side view of the two bar-shaped conductors of FIG. 2 during laser welding according to the present invention, along with the weld bead being formed. [Figure 4] 3 shows a schematic plan view of the end regions of the two bar-shaped conductors of FIG. 2; [Diagram 5] 1 shows a schematic plan view of the end regions of two bar-shaped conductors in a variant in which the common base surface is square. [Figure 6a] 1 shows a schematic diagram of a cross section of a processing shaped laser beam of the present invention having a core portion and a ring portion. [Figure 6b] FIG. 2 shows a schematic diagram of a cross section of an exemplary 2-in-1 fiber of the present invention having a core fiber and a ring fiber, which allows for providing a shaped laser beam for laser welding according to the present invention. [Figure 7] 1 shows a diagram of the core portion of the laser output of a shaped working laser beam of the present invention during laser welding of two bar-shaped conductors as a function of time. [Figure 8a] 1 shows images from an experiment immediately after the completion of laser welding of two aluminum-containing bar-type conductors under conditions where the oxide film of the weld bead repeatedly cracks open, forming an uneven weld bead. [Figure 8b] 1 shows an image of an experiment immediately after the completion of laser welding of two aluminum-containing bar-type conductors under conditions of the method according to the invention, in which the oxide film of the weld bead in the surrounding area remains intact and a uniform weld bead is formed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Figure 1 shows a schematic side view of two bent aluminum-containing bar-type conductors 1a, 1b, which are of a configuration known as hairpins and are used in the manufacture of electrodynamic machines such as electric motors or generators. Each of the bar-type conductors 1a, 1b is generally U-shaped and has two legs 2a, 3a and 2b, 3b, respectively, and an intermediate piece 4a, 4b connecting each pair of legs to each other.

[0043] The bar-shaped conductors 1a, 1b are intended to be conductively connected to one another. For this purpose, according to the invention, the bar-shaped conductors 1a, 1b are welded to one another in their end regions 5a, 5b. For the welding, the leg 3a of the first bar-shaped conductor 1a and the leg 3b of the second bar-shaped conductor 1b are arranged with an overlap and, in the variant shown, rest against one another.

[0044] For the bar-shaped conductors 1a, 1b, aluminum-containing bar-shaped conductor materials are used having an aluminum content of at least 75% by weight, preferably at least 90% by weight. Possible aluminum-containing bar-shaped conductor materials that come into consideration are, for example, the aluminum alloy group of the 1000-6000 series (for example the material EN AW-1050A).

[0045] FIG. 2 shows a schematic perspective view of the end regions 5a, 5b of the bar-shaped conductors 1a, 1b before starting the laser welding according to the invention. The coordinate system is selected such that the x-axis points to the right, the y-axis points into the plane of the drawing and the z-axis points up. Here, the front end faces 6a, 6b of the two bar-shaped conductors 1a, 1b are at approximately the same height and are horizontally aligned. The front end faces 6a, 6b of the two bar-shaped conductors 1a, 1b together form a common base surface 7. The end regions 5a, 5b of the bar-shaped conductors 1a, 1b each have a rectangular cross section in the xy-plane. The long sides 8a, 8b of the cross sections of the bar-shaped conductors 1a, 1b rest against each other in the end regions 5a, 5b of the legs 3a, 3b, which are pressed against each other (not shown in detail). The legs 3a, 3b are vertically aligned and parallel to one another such that the two end faces 6a, 6b, and thus the common base surface 7, are aligned upwards.

[0046] The two end regions 5a, 5b are welded using a processing laser beam 11. For this purpose, a welding contour 12 is defined on the common base surface 7, through which the processing laser beam 11 is then passed several times. In the embodiment shown here, the welding contour 12 is selected to be elliptical. Depending on how the bar-shaped conductors are to be dimensioned and what the envisaged welding requirements are, it is also possible to select a linear welding contour (not shown here) or a circular welding contour (see FIG. 5). The dotted region 13 indicates the region of the bar-shaped conductors 1a, 1b that will be melted by the action of the processing laser beam 11. In an advantageous embodiment, the beam of the processing laser beam 11 can be guided along the welding contour 12 by a scanner optical unit (not shown in detail).

[0047] The processing laser beam 11 is incident almost perpendicularly on the common base surface 7. It should be noted that during the manufacture of the different pairs of bar-type conductors 1a, 1b, the angle of incidence of the processing laser beam 11 can usually be changed slightly so that the bar-type conductors 1a, 1b, which are usually arranged in a stator carrier (not shown in detail), do not have to be moved too frequently. The processing laser beam 11 typically does not deviate from the perpendicular incidence on the base surface 7 by more than 40°, preferably by no more than 20°.

[0048] The laser power P of the processing laser beam 11 may be selected such that 0.5kW≦P≦20kW, preferably 2kW≦P≦10kW, particularly preferably 4kW≦P≦8kW. In practice, this allows good results to be obtained. For example, a power P of 6kW can be used to weld two aluminum-containing bar-shaped conductors 1a, 1b. The wavelength of the processing laser beam 11 may be 400nm to 1200nm. Examples of this are wavelengths of 450nm (blue), 515nm (green), 900±100nm (diode, NIR), 1030nm (NIR), 1064nm (NIR), and 1070nm (NIR).

[0049] Figure 3 shows a schematic side view of two bar-type conductors 1a, 1b of Figure 2 according to the invention with a weld bead 19 at the latter stage of laser welding. The coordinate system is chosen such that the x-axis points out of the plane of the drawing, the y-axis points to the right and the z-axis points up. Shown are end regions 5a, 5b of the bar-type conductors 1a, 1b during laser welding, with a weld bead 19 formed at the end of the end regions 5a, 5b, in this case the top end.

[0050] The processing laser beam 11 is intended to move along the weld contour 12 located on the upper end surface 20 of the weld bead 19. This introduces heat into the aluminum-containing bar-type conductor material. In this process, the liquid bar-type conductor material 15 (dashed reference line, since the liquid bar-type conductor material 15 is hidden under the non-liquid oxide film 14), i.e., the aluminum-containing melt, is formed and accumulated under the non-liquid oxide film 14. The non-liquid oxide film 14 then forms the boundary of the weld bead 19, ensuring that the shape of the liquid bar-type conductor material 15 is maintained and preventing the liquid bar-type conductor material 15 from flowing. The non-liquid oxide film 14 is locally broken and opened by the processing laser beam 11, which, in the illustrated variant, leaves a broken and opened track 12a along the weld contour 12. This temporarily exposes the liquid bar-type conductor material 15 along the track 12a in the broken and opened area. Behind the working laser beam 11, the liquid bar-shaped conductor material 15 starts to oxidize again, as a result of which a new oxide film 14 is formed and the tracks 12a close again. In the illustrated variant, the tracks 12a extend over about 1 / 3 of the circumference of the weld contour 12 before the non-liquid oxide film 14 grows completely over the tracks 12a again. The method according to the invention is typically carried out in an oxygen-containing atmosphere (e.g. air), so that the non-liquid oxide film 14 can be regenerated particularly quickly by oxidation in the broken open areas.

[0051] The non-liquid oxide film 14 extends from the top surface 20 down to the still solid end regions 5a, 5b of the bar-shaped conductors 1a, 1b and into the peripheral region 21 of the weld bead 19 around the entire weld bead 19. In the variant shown here, the non-liquid oxide film 14 is broken open along the weld contour 12, and the processing laser beam 11 moves along the weld contour 12 in the region of the trajectory 12a (shown in black). The exposed liquid bar-shaped conductor material 15 is oxidized again by the oxygen-containing atmosphere (unfilled region of the black contour 12 in FIG. 3). In the variant shown here, the non-liquid oxide film 14 on the top surface 20 remains intact. In other variants, it is also possible that the entire inner region of the weld contour 12 is broken open and remains substantially broken open during the welding process (this possibility is not shown here).

[0052] The weld bead 19 has a total height H sp and the surrounding area 21 of the weld bead 19 where the non-liquid oxide film 14 remains intact has a height H unv It has a height H unv generally extends from the lower end of the weld bead 19 to the area where the working laser beam 11 moves along the weld contour 12. The working laser beam 11 partially breaks open the non-liquid oxide film 14, thereby exposing the liquid bar-shaped conductor material 15, so that the area of ​​the upper end surface 20 inside the weld contour 12 is no longer considered to be an intact part of the surrounding area 21. In the variant shown here, H unv is H sp In order to be able to form a defined weld bead 19, the height H unv is the height H sp Preferably, at least 3 / 4 of the height H sp It has been shown to be advantageous for the weld bead 19 to extend over at least 9 / 10 of the end face 20. In many applications, for a weld bead 19 having a generally flat configuration at the end face 20, H unv is effectively the height H sp (not shown in detail).

[0053] At the end of the welding, after the action of the working laser beam 11 is completed, the liquid bar-type conductor material 15 cools and finally solidifies while continuing to maintain its shape due to the non-liquid oxide film 14. The bar-type conductors 1a, 1b are then conductively connected to each other by a weld bead 19. In this process, the weld bead 19 is placed on both bar-type conductors 1a, 1b, covering them over the entire surface area of ​​their ends. The quality of the conductive connection between the two bar-type conductors 1a, 1b is substantially determined by the connection cross-sectional area 22. The connection cross-sectional area 22 is the surface area that allows the conduction of current from the first bar-type conductor 1a to the second bar-type conductor 1b. In the case of the well-defined weld bead 19 shown in FIG. 3, the connection cross-sectional area 22 corresponds to the cross-sectional area of ​​the weld bead 19 at the contact surfaces of the long sides of the legs 3a, 3b of the bar-type conductors 1a, 1b that are placed against each other.

[0054] FIG. 4 shows a schematic plan view of the end regions 6a, 6b of the two bar-shaped conductors 1a, 1b of FIG. 2. The coordinate system is selected such that the x-axis points to the right, the y-axis points up and the z-axis points out of the plane of the drawing. The front end faces 6a, 6b form a common base surface 7 on which an elliptical weld contour 12 is shown. The bar-shaped conductors 1a, 1b each form a respective rectangular cross section 9a, 9b corresponding to each end face 6a, 6b visible here in the end region 5a, 5b. In this variant, the rectangular cross sections 9a, 9b of the end regions 5a, 5b of the two bar-shaped conductors 1a, 1b are identical. In practice, the edge length of the cross sections 9a, 9b is usually between 0.2 mm and 10 mm, preferably between 1 mm and 8 mm, particularly preferably between 2 mm and 6 mm.

[0055] The rectangular front end faces 6a and 6b each have a long edge length L2 and a short edge length L kurz The common base surface 7 is represented by the length of the long edge L2 and twice the length of the short edge L1. Note that for more clarity, a narrow gap is shown between the front end faces 6a and 6b in FIG. 3. In reality, the bar-shaped conductors 1a, 1b rest against each other, so that the distance is practically zero, and therefore 2*Lkurz =L1.

[0056] The minimum distance between the weld contour 12 in the direction of the short edge 17 and the outer periphery 18 of the common base surface 7 is called the minimum distance d1. The minimum distance between the weld contour 12 in the direction of the long edge 16 and the outer periphery 18 of the common base surface 7 is called the minimum distance d2. In practice, it has been shown that the flanks of the non-liquid oxide film remain substantially intact during welding if d1 is selected to be 20%-40% of the length of L1, preferably 25%-35% of the length of L1, and d2 is selected to be 20%-40% of the length of L2, preferably 25%-35% of the length of L2.

[0057] FIG. 5 shows a schematic plan view of the front end faces 6a, 6b of two bar-shaped conductors 1a, 1b similar to those shown in FIG. 4, in a variant in which the common base surface 7 has a square shape. The coordinate system is selected such that the x-axis points to the right, the y-axis points up and the z-axis points out of the plane of the drawing. The front end faces 6a, 6b are arranged in close contact with each other at their long edges 8a, 8b. The minimum distance between the circular weld contour 12 and the outer edge 18 of the common base surface 7 is called the minimum distance d. The common base surface 7 has an extent L along the direction in which the minimum distance d lies. In the variant shown here, d=0.25*L approximately holds. In practice, the minimum distance d between the weld contour 12 and the outer periphery 18 of the common base surface 7 is selected such that d is at least 15% of the length of L, preferably at least 20% of the length of L, particularly preferably at least 25% of the length of L. This minimizes the risk of the non-liquid oxide film tearing open in the surrounding area during welding. For example, if a pair of bar-type conductors 1a, 1b is selected having a range L=4 mm (which in practice corresponds to conventional dimensioning), the minimum distance d may be 0.6 mm or more, preferably 0.8 mm or more, particularly preferably 1 mm or more.

[0058] 5 also shows the processing laser beam 11 on the weld contour 12. The laser beam moves with a travel speed v along the weld contour 12. In practice, it has been shown that for the processing laser beam 11, the travel speed v can be advantageously selected such that v is less than or equal to 1600 mm / s, preferably less than or equal to 1200 mm / s, particularly preferably less than or equal to 800 mm / s. With such a selected travel speed v (for example 800 mm / s), the dynamics of the liquid bar-type conductor material in the non-liquid oxide film are small and the risk of cracks forming in the surrounding area of ​​the non-liquid oxide film is particularly low.

[0059] Within the context of the method according to the invention, it is advantageous to select the processing laser beam 11 as a shaped laser beam 11a, at least temporarily, having a core portion 23 and a ring portion 24. Fig. 6a shows an example of a beam cross section of such a shaped laser beam 11a. The ring portion 24 surrounds the core portion 23. This makes it possible to reduce welding defects, in particular at the beginning and end of the laser welding.

[0060] The shaped laser beam 11a is generated, for example, by a 2-in-1 fiber 27. Fig. 6b shows a cross section of an exemplary 2-in-1 fiber 27 that can provide a shaped laser beam for the method according to the invention. The 2-in-1 fiber 27 has a core fiber 25 and a ring fiber 26 surrounding the core fiber. For the core fiber diameter KFD of such a 2-in-1 fiber 27, it is possible to select, for example, 11 μm≦KFD≦300 μm, preferably 50 μm≦KFD≦100 μm, and for the ring fiber diameter RFD of such a 2-in-1 fiber 27, it is possible to select, for example, 50 μm≦RFD≦1000 μm, preferably 200 μm≦RFD≦400 μm.

[0061] Core output component P kern and the output component P of the ring part ringcan be set so that the original laser beam is partially fed into the core fiber 25 and partially into the ring fiber 26, for example by pushing an optical wedge (not shown in detail) partially into the original laser beam. Within the context of the present invention, the power distribution between the core and ring portions can be chosen to be constant throughout the duration of the laser welding of the bar-type conductors or can be varied. Typically, P kern is the total laser power P of the processing laser beam ges The output component P kern , P ring Typically, the total laser power P ges =P kern +P ring is selected to be constant throughout the duration of the weld.

[0062] Constant total power P as a function of time t ges The output component P kern In an advantageous variant of laser welding according to the invention, which is shown in the form of a schematic diagram in FIG. 7, the following procedure is taken:

[0063] The laser welding of two bar-type conductors includes a first phase (initial phase) EP, a main phase HP and a last phase (final phase) LP during which the movement is performed along the weld contour (e.g., multiple passes through an elliptical or circular path). Here, the advance speed can typically be selected to be constant throughout the entire welding duration GD. In the first phase EP (between instants t0 and t1) and the last phase LP (between instants t2 and t3) of the laser welding of the bar-type conductors, the power component P of the laser output of the core kern is chosen to be lower than the intermediate (between instant t1 and instant t2) main phase HP.

[0064] When the shaped laser beam 11a passes at the beginning of the first phase EP in time (time t0), the laser power P kern A low P reduces spatter formation and therefore prevents relatively large amounts of non-liquid oxide film (and liquid melt) from being ejected. kern starts here at 30% and then increases (linearly in this example) within the first phase EP in time until it reaches the target value of the main phase HP. For example, the selection of the duration of the first phase EP may depend on whether the vapor capillary generated by the shaped laser beam has reached a certain capillary depth (e.g., 30% of its maximum capillary depth). The first phase EP in time of laser welding often includes a component of 10-30% of the total welding duration GD of the welding of two bar-type conductors and may last, for example, 1 ms to 30 ms.

[0065] Then, during the main phase HP (between time t1 and time t2), the desired component P kern Then, a movement is again performed along the welding contour 12. In the illustrated variant, in the main phase, P kern is 100%, i.e. no ring components are irradiated. Alternatively, P kern However, it is also possible to select it to be, for example, 60% to 90%.

[0066] After the main phase HP (from time t2), the component P of the laser power of the core kern is decreased again (in this case linearly) until it reaches the target value (in this case subsequently 30%). The effect achieved hereby is that the vapor capillary generated by the shaped laser beam is uniformly decreased, so that only few, if any, porosity is obtained in the cooled bar-shaped conductor material. The temporally last phase LP of laser welding often comprises a component of 10-30% of the total welding duration GD of the weld and may last from 1 ms to 30 ms.

[0067] FIG. 8a shows an experimental image of two aluminum-containing bar-shaped conductors immediately after the end of the laser welding (i.e. before the weld bead solidifies and after the working laser beam has acted), in which an inhomogeneous weld bead is formed. In this example, v=3200 mm / s was selected for the advance speed v of the working laser beam, and P=6 kW for the laser power P of the working laser beam. The laser wavelength is 1030 nm, the total welding time is 85 ms, the bar-shaped conductors are manufactured from the aluminum alloy EN AW-1050A, the cross section of the individual hairpins is 2x4 mm, a circular weld contour with a diameter of 2 mm is in the middle of the end faces of the hairpins that are placed against each other. The high advance speed v causes high dynamics of the melt, which breaks and opens the oxide film in multiple places, destroys its cohesion and allows the low-viscosity melt to flow in an uncontrolled manner. In this way, a defined weld bead with an approximately spherical shape cannot be obtained. This can be seen in FIG. 8a by the irregularly shaped weld bead and the messy end surface.

[0068] In contrast, FIG. 8b shows an experimental image of two aluminum-containing bar-shaped conductors immediately after the end of laser welding (before the weld bead solidifies and after the working laser beam has acted) under the conditions of the method according to the invention, in which a uniform weld bead is formed. In this example, v=800 mm / s was selected for the advance speed v of the working laser beam and P=6 kW was selected for the laser power P of the working laser beam. The laser wavelength is 1030 nm, the total welding time is 85 ms, the bar-shaped conductors are made of aluminum alloy EN AW-1050A, the cross section of the individual hairpins is 2x4 mm, a circular weld contour with a diameter of 2 mm is in the middle of the end faces of the hairpins placed against each other. At the advance speed v selected here, the non-liquid oxide film in the surrounding area remains intact when processed by the working laser beam. Finally, the non-liquid oxide film is partially broken open in the trajectory of the working laser beam. In this way, an intact non-liquid oxide film and a defined weld bead with an approximately spherical shape can be obtained, as can be clearly seen in FIG. 8b. [Explanation of symbols]

[0069] 1a, 1b Bar type conductor 2a, 2b (outside) legs 3a, 3b (inside) legs 4a, 4b Intermediate parts 5a, 5b end area 6a, 6b Front end 7 Common Base Surface 8a, 8b long side 9a, 9b cross section 11 Laser beam for processing 11a Shaped laser beam 12 Welding Profile 13 areas 14 Non-liquid oxide films 15 Liquid bar-type conductor material 16 Long Edge 17 Short Relationship 18 Outer periphery 19 Weld Bead 20 Front end side 21 Surrounding Area 22 Connected cross-sectional area 23 Core part 24 Ring part 25 core fiber 26 Ring Fiber 27 2-in-1 Fiber d minimum distance d1 Minimum distance (in the direction of the short edge) d2 minimum distance (towards the long edge) EP First Stage (Early Stage) HP Main Phase H sp Weld bead height H unv Height of intact surrounding area KFD Core Fiber Diameter LP Last Stage (Final Stage) L range (in the direction of the minimum distance d) Twice the length of the L1 short edge L2 long edge length L kurz Short edge length P Laser power Pges Total Laser Power P kern Core laser power P ring Laser output of the ring RFD Ring Fiber Diameter v Progress speed

Claims

1. A method for laser welding bar-type conductors (1a, 1b), preferably bent bar-type conductors (1a, 1b), in particular hairpins for electric motors or generators, comprising the steps of: said bar-type conductors (1a, 1b) consist of an aluminum-containing bar-type conductor material having an aluminum content of at least 75% by weight, preferably at least 90% by weight; Two bar-type conductors (1a, 1b) are arranged next to each other with a partial overlap and are welded to each other by a processing laser beam (11), and a weld bead (19) connecting the bar-type conductors (1a, 1b) to each other is formed on a common base surface (7) of the adjacent bar-type conductors (1a, 1b); In particular, said common base surface (7) is horizontally aligned, During the laser welding of the bar-shaped conductors (1 a, 1 b), the working laser beam (11) is guided, in the process a welding contour (12) of the working laser beam (11) is arranged relative to the bar-shaped conductors (1 a, 1 b), and the advancement speed v of the working laser beam (11) along the welding contour (12) relative to the bar-shaped conductors (1 a, 1 b) is during said laser welding of said bar-shaped conductors (1a, 1b), said weld bead (19) has a non-liquid oxide film (14) inside which liquid bar-shaped conductor material (15) accumulates; during the laser welding of the bar-shaped conductors (1a, 1b), the non-liquid oxide film (14) is partially broken open by the working laser beam (11) only on the upwardly facing end face (20) of the weld bead (19) in a manner that corresponds to the weld contour (12); - during the laser welding of the bar-shaped conductors (1a, 1b), the non-liquid oxide film (14) remains intact in a peripheral region (21) of the weld bead (19) extending from the upper end surface (20) downwards towards the bar-shaped conductors (1a, 1b) and around the entire weld bead (19); Selected to be method.

2. The welding contour (12) of the processing laser beam (11) has a minimum distance d of the welding contour (12) from the outer periphery (18) of the common base surface (7) and a range L of the common base surface (7) along which the minimum distance d lies:

2. The method according to claim 1, wherein the bar-shaped conductors (1a, 1b) are arranged such that d≧0.15*L, preferably d≧0.20*L, particularly preferably d≧0.25*L.

3. The weld contour (12) of the working laser beam (11) has a minimum distance d of the weld contour (12) from the outer periphery (18) of the common base surface (7): d≧0.6 mm, preferably d≧0.8 mm, particularly preferably d≧1.0 mm 3. The method according to claim 1, wherein the bar-shaped conductors (1a, 1b) are arranged such that:

4. With respect to the advance speed v of the working laser beam (11) along the welding contour (12) of the working laser beam (11) relative to the bar-shaped conductors (1a, 1b), v≦1600 mm / s, preferably v≦1200 mm / s, particularly preferably v≦800 mm / s The method according to claim 1 or 2, wherein

5. 3. The method according to claim 1 or 2, wherein the laser welding is carried out in an oxygen-containing atmosphere, in particular in air.

6. At least in the latter part of the laser welding of the bar-type conductors (1a, 1b), the peripheral area (21) where the non-liquid oxide film (14) remains intact is larger than the height (H) of the weld bead (19). ｓｐ ) of the weld bead (19), preferably over at least 3 / 4 of the height (H ｓｐ 3. The method of claim 1 or 2, wherein the length of the first and second electrodes extends over at least 9 / 10 of the first and second electrodes.

7. the two bar-shaped conductors (1a, 1b) are arranged with their end regions (5a, 5b) parallel to one another and resting against one another, In particular, the end regions (5a, 5b) of the bar-shaped conductors (1a, 1b) are extensively pressed against one another, the front end faces (6a, 6b) of the bar-type conductors (1a, 1b) are located at approximately the same height in the direction of the longitudinal extent of the end regions (5a, 5b) of the bar-type conductors (1a, 1b); The processing laser beam (11) is directed at the front end faces (6a, 6b) of the bar-shaped conductors (1a, 1b), which thus provide the common base surface (7) on which the weld bead (19) is formed. The method according to claim 1 or 2.

8. The end regions (5a, 5b) of the bar-shaped conductors (1a, 1b) are directed substantially vertically upwards; In particular, the front end faces (6a, 6b) are aligned substantially horizontally. The method according to claim 7.

9. 8. The method according to claim 7, wherein the processing laser beam (11) is incident on the front end faces (6a, 6b) substantially perpendicularly.

10. The bar-shaped conductors (1a, 1b) have an edge length (L ｋｕｒｚ , L ２ ) has a rectangular cross section (9a, 9b) of 0.2 mm to 10 mm, preferably 1 mm to 8 mm, particularly preferably 2 mm to 6 mm, In particular, for each bar-type conductor (1a, 1b), the length L of the long edge ２ is the length of the short edge L ｋｕｒｚ and the cross sections (9a, 9b) of the two bar-type conductors (1a, 1b) that are welded together are the same. The method according to claim 1 or 2.

11. The minimum distance d between the welding contour (12) and the outer periphery (18) of the common base surface (7) in the direction of each long edge (16) ２ is the length L of the corresponding long edge ２ 20% to 40%, preferably 25% to 35%, of the minimum distance d between the welding contour (12) and the outer periphery (18) of the common base surface (7) in the direction of each short edge (17). １ is the length L of the short edge １ The method according to claim 10, wherein the concentration of the stoichiometric amount ...

12. The processing laser beam (11) 0.5kW≦P≦20kW, Preferably, 2 kW≦P≦10 kW, Particularly preferably, 4 kW≦P≦8 kW and having a laser power P of And / or the wavelength of the processing laser beam (11) is 400 nm to 1200 nm; The method according to claim 1 or 2.

13. the weld profile (12) is selected to be linear, circular or elliptical and is passed multiple times during the laser welding of the bar-type conductors (1a, 1b); In particular, the welding contour (12) is generated by a scanner optical unit. The method according to claim 1 or 2.

14. A shaped laser beam (11a) having a core portion (23) and a ring portion (24) annularly surrounding the core portion (23) is at least temporarily selected as a processing laser beam (11); 3. The method according to claim 1 or 2, wherein the shaped laser beam (11a) is generated by a 2-in-1 fiber (27) having a core fiber diameter KFD with 11 μm≦KFD≦300 μm, preferably 50 μm≦KFD≦100 μm, and a ring fiber diameter RFD with 50 μm≦RFD≦1000 μm, preferably 200 μm≦RFD≦400 μm.

15. The output component P of the laser output of the core portion (23) ｋｅｒｎ is selected to be smaller during a first phase (EP) of the laser welding of the bar-type conductors (1a, 1b) than during a main phase (HP) of the laser welding of the bar-type conductors (1a, 1b), In particular, the output component P of the laser output of the core portion (23) ｋｅｒｎ increases continuously during the first phase (EP), In particular, the first phase (EP) has a duration of 1 ms to 30 ms; The method of claim 14.

16. The output component P of the laser output of the core portion (23) ｋｅｒｎ is smaller during the last phase (LP) of the laser welding of the bar-type conductors (1a, 1b) than during the main phase (HP) of the laser welding of the bar-type conductors (1a, 1b), In particular, the output component P of the laser output of the core portion (23) ｋｅｒｎ decreases continuously during the last phase (LP), In particular, the last phase (LP) has a duration of 1 ms to 30 ms; The method of claim 14.

17. A bar-type conductor comprising at least two bar-type conductors (1a, 1b) welded by the method according to claim 1 or 2.

18. Use of a bar-type conductor arrangement, said bar-type conductor arrangement being produced by welding two respective bar-type conductors (1a, 1b) by the method according to claim 1 or 2, said bar-type conductor arrangement being mounted in an electric motor or generator. Use of a bar-type conductor arrangement.

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