METHOD FOR JOINING COPPER HAIRPINS AND STATOR

Abstract

A method for joining copper hairpins includes providing at least two ends to be joined to one another of the copper hairpins, and joining the copper hairpins. The copper hairpins are joined by laser beam welding with a machining beam having a wavelength of less than 1000 nm.

Claims

1.-12. (canceled)

13. A method for joining copper hairpins, the method comprising: providing at least two ends of the copper hairpins to be joined to one another; and joining the copper hairpins to be joined by laser beam welding with a machining beam having a wavelength of less than 1000 nm.

14. The method according to claim 13, which comprises using a green machining beam or a blue machining beam.

15. The method according to claim 14, which comprises using a green laser beam having a wavelength of 500 nm to 550 nm or a blue laser beam having a wavelength of 425 nm to 475 nm.

16. The method according to claim 14, which comprises using a green laser beam having a wavelength of 510 nm to 520 nm or a blue laser beam having a wavelength of 440 nm to 450 nm.

17. The method according to claim 13, which comprises welding the copper hairpins to one another by way of heat conduction welding, and selecting an intensity of the machining beam to substantially avoid deep welding and/or a formation of a vapor capillary.

18. The method according to claim 13, which comprises impinging the machining beam on end faces of the ends of the hairpins to be joined and radiating the machining beam in a longitudinal direction of the hairpins.

19. The method according to claim 13, which comprises forming the machining beam to take up a cross-sectional geometry of an end side of the hairpins, and impinging a cross section of the machining beam completely on an end face of the hairpins.

20. The method according to claim 13, which comprises forming the machining beam to impinge on a cross-sectional geometry of an end side of the hairpins with at least two different intensities.

21. The method according to claim 20, which comprises causing the machining beam to impinge with a first intensity in a first region of the end side and with a second intensity in a second region of the end side.

22. The method according to claim 13, which comprises configuring the machining beam with a different intensity in a center thereof than in an edge region thereof.

23. The method according to claim 22, which comprises delivering the machining beam via a core fiber and a ring fiber and coupling into the core and ring fibers mutually different intensities and/or different wavelengths.

24. The method according to claim 13, which comprises selecting an intensity of the machining beam to prevent evaporation of a material of the copper hairpins from occurring.

25. The method according to claim 13, which comprises selecting an intensity of the machining beam to substantially prevent evaporation of a material of the copper hairpins from occurring.

26. The method according to claim 13, which comprises providing the hairpins with a substantially rectangular cross-sectional contour having a width dimension and a depth dimension.

27. The method according to claim 26, wherein the width dimension is 1 mm to 10 mm and the depth dimension is 1 mm to 10 mm.

28. The method according to claim 26, wherein the width dimension is 0.5 mm to 1.5 mm and the depth dimension is 0.5 mm to 1.5 mm.

29. The method according to claim 26, wherein at least one of the width dimension or the depth dimension lies between 1.5 mm and 6 mm or between 6 mm and 10 mm.

30. The method according to claim 13, which comprises providing the hairpins with a coating for at least one of a mechanical protection, chemical protection, or electrical insulation.

31. The method according to claim 30, wherein the coating is composed of a polymer selected from the group consisting of polyamide-imide, polyether ether ketone, polyesterimide, and polyimide.

32. The method according to claim 30, wherein the coating is composed of Kapton®.

33. A stator for an electric motor, comprising a stator winding formed from joined-together copper hairpins that are joined together by the method according to claim 13.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0045] Preferred further embodiments of the invention will be explained in more detail by the following description of the figures. In the figures:

[0046] FIG. 1 shows a schematic side view of two copper hairpins to be joined to one another, which are impinged on by a machining beam;

[0047] FIG. 2 shows a schematic plan view of the end faces of the two copper hairpins to be joined to one another of FIG. 1, and also of a machining beam; and

[0048] FIG. 3 shows a further schematic plan view of two copper hairpins to be joined to one another with a further machining beam which has two different intensity ranges.

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

[0049] In the following text, preferred exemplary embodiments will be described with reference to the figures. Here, elements that are identical, similar or have the same effect are provided with identical reference designations in the various figures, and a repeated description of these elements is in some cases dispensed with in order to avoid redundancies.

[0050] FIG. 1 schematically shows the respective ends of two hairpins 10, 12 which are already in a joining position. For this purpose, in the embodiment shown, the two ends of the hairpins 10, 12 have already been shortened and placed against one another such that joining by means of laser beam welding is made possible.

[0051] In FIG. 1, end faces 114, 124 of the ends of the hairpins 10, 12 point upward toward a machining beam 2.

[0052] In order to be able to join the ends of the hairpins 10, 12 by means of laser welding, the ends to be joined of the hairpins 10, 12 correspondingly bear against one another at least in a jointly formed plane 3, wherein the gap between the two ends of the hairpins 10, 12 should be kept as small as possible and a gap is preferably not present. The contact area between the two ends of the hairpins 10, 12 that is present in the common plane 3 is thus as large as possible.

[0053] Furthermore, it is preferable for a lateral offset with respect to the common plane 3 of the two ends of the hairpins 10, 12 to be minimized or preferably to be avoided. Furthermore, a height offset with respect to the respective end faces 114, 124 of the two ends of the hairpins 10, 12 is preferably also kept very small or preferably avoided, and an angular position between the ends of the two hairpins 10, 12 is preferably also kept particularly small or preferably avoided.

[0054] In order to achieve the aforementioned preferred orientation in particular also of the end faces 114, 124 before the actual joining of the two ends of the hairpins 10, 12 and to be able to also maintain said orientation during the joining, use is for example made of mechanical clamps in order to gather together the ends of the hairpins 10, 12.

[0055] The hairpins 10, 12 each have a mechanically and chemically protective and electrically insulating coating 110, 120, which can be provided for example in the form of a plastics coating. In a prepared region 112, 122, which comprises the ends to be joined of the hairpins 10, 12, the respective coating is removed from the hairpins 10, 12 such that only the bare copper material without further coating remains in these prepared regions.

[0056] In this way, as a result of the provision of the prepared regions 112, 122 of the ends of the hairpins 10, 12, the bare copper material of the two hairpins 10, 12 also bears against one another in the jointly formed plane 3. The joining by laser beam welding is also intended to take place in this region, such that the material melted for the welding is then free of impurities.

[0057] The coating 110, 120 is removed from the ends of the hairpins 10, 12 in order to avoid impurities being introduced into the melt during the welding process, said impurities possibly leading, for example, to an indefinable strength of the re-solidified material and/or to defects in the microstructure of the re-solidified material and/or to fluctuations in the conductivity of the re-solidified material at the joining point. Furthermore, by removing the coating 110, 120, the formation of toxic vapors during laser beam welding is avoided.

[0058] The prepared regions 112, 122 are oriented relative to one another such that the joining of the two copper hairpins 10, 12 by laser beam welding is reliably made possible.

[0059] The cleaning or the removal of the coating 110, 120 from the hairpins 10, 12 in the prepared regions 112, 122 can be carried out, for example, by laser machining or by known mechanical or chemical cleaning operations, in order to prepare the hairpins 10, 12 for the actual joining.

[0060] The process of preparing, orienting, forming and gathering-together two ends of copper hairpins 10, 12 is known in principle and is not specified further here.

[0061] FIG. 2 shows a plan view of two hairpins 10, 12 which have already been prepared, oriented relative to one another and gathered together and which are intended to be joined to one another.

[0062] As can readily be seen from the plan view, the hairpins 10, 12 each have a substantially rectangular cross-sectional contour having in each case a width X and a depth Y. This cross-sectional contour of the hairpins 10, 12 also corresponds to the contour of the end face 114, 124 of the hairpins 10, 12, which is then effectively impinged upon by the machining beam 3. In the exemplary embodiment shown, the common plane 3, in which the two ends of the hairpins 10, 12 bear against one another, is produced along the depth extent Y (that is to say perpendicular to the width X).

[0063] Typical dimensions of a hairpin 10, 12 are for example a width X of 1 mm to 10 mm and a depth of 1 mm to 10 mm. Small hairpins can preferably have a width and/or a depth of 0.5 mm to 1.5 mm, medium-sized hairpins can preferably have a width and/or depth of 1.5 mm to 6 mm and large hairpins can have a width and/or depth of 6 mm to 10 mm. The specific dimensioning of the copper hairpins 10, 12 is produced on the basis of the respective application.

[0064] The base material of a copper hairpin 10, 12 is for example copper, for example oxygen-free copper (ETP—electrolytic tough pitch) for electrical applications.

[0065] The coating 110, 120 of the hairpins can be present for example in the form of a coating composed of PAI (polyamide-imide), PEEK (polyether ether ketone), PEI (polyesterimide) or PI (polyimide such as for example Kapton), in order to mechanically and chemically protect the base material of the copper hairpins 10, 12 and to provide electrical insulation.

[0066] The ends of the hairpins 10, 12, which are provided for the construction of a stator winding of a stator for an electric motor, accordingly also have this rectangular or else square cross-sectional contour, which accordingly enables areal abutment of the ends to be joined of the hairpins 10, 12 in the common plane 3.

[0067] The joining of the copper hairpins 10, 12 can then be carried out by means of a machining beam 2, which is schematically indicated in FIGS. 1 and 2.

[0068] As can be seen for example in FIG. 2, the machining beam 2 is preferably formed such that it impinges on the total end face of the ends to be joined of the hairpins 10, 12. The total end face is formed from the end faces 114, 124 of the respective ends of the copper hairpins 10, 12, which are correspondingly directed upward in FIG. 1 and which are shown in plan view in FIG. 2.

[0069] In a preferred alternative, which is shown further below in relation to FIG. 3, the machining beam may also impinge only partially on the end faces 114, 124 of the hairpins 10, 12 to be joined to one another.

[0070] The machining beam 2 is a laser beam by means of which the two hairpins 10, 12 can be joined by laser beam welding.

[0071] The wavelength of the machining beam 2 used here is less than 1000 nm.

[0072] In the exemplary embodiment shown in FIGS. 1 and 2, the machining beam 2 is preferably a green machining beam 2, which is formed by a laser beam having a wavelength of 500 nm to 550 nm, particularly preferably having a wavelength of 510 nm to 520 nm. Or the machining beam 2 is a blue machining beam 2, which is formed by a laser beam having a wavelength of 425 nm to 475 nm, particularly preferably having a wavelength of 440 nm to 450 nm.

[0073] What is achieved by the selected wavelength range of the machining beam 2 is that the energy of the machining beam 2 is well absorbed by the hairpins 10, 12, and in particular by their base material in the form of the copper material. In this way, an efficient input of laser energy and thus of heat energy into the hairpins 10, 12 is possible, such that laser beam welding by means of heat conduction welding is made possible. Due to the increased absorption of the energy of the machining beam 2 in the copper material, the formation of a vapor capillary can be dispensed with.

[0074] Whether a welding process is a heat conduction process or a deep welding process is largely dependent on the energy density or the intensity of the machining beam 2 impinging on the copper hairpins 10, 12 to be joined to one another. Exceeding a so-called threshold intensity, from which the heat conduction process changes into a deep welding process, should ideally be avoided.

[0075] However, the use of high machining energies is also conceivable as long as the machining energy is distributed over a large area, for example in the case of hairpins which have an above-average-sized diameter or an above-average-sized end face 114, 124. Owing to the large machining area, the achieved energy density or intensity of the machining beam is then preferably to be adjusted again such that the threshold intensity, from which the heat conduction process changes into a deep welding process, is not exceeded.

[0076] If the machining beam 2 applies laser energy to substantially the total end face 114, 124 of the hairpins 10, 12 to be joined to one another, heat conduction takes place within the hairpins 10, 12 from this end face 114, 124 in the longitudinal direction, which is indicated by the longitudinal direction Z in FIG. 1. Correspondingly, heat conduction takes place in the hairpins 10, 12 in an essentially one-dimensional manner, namely along the longitudinal direction Z, which is also the heat conduction direction.

[0077] The machining beam 2 is preferably oriented such that, on the one hand, it impinges with the machining beam on the respective end faces 114, 124 of the hairpins 10, 12. At the same time, the machining beam 2 is preferably also oriented such that it extends substantially in the longitudinal direction Z of the hairpins 10, 12. Accordingly, a melt bead formed by the melted material remains in the region of influence of the machining beam 2 during laser beam welding of the hairpins 10, 12 even if the melt bead moves in the direction of heat propagation, i.e. longitudinal direction Z of the hairpins 10, 12.

[0078] The orientation of the cross section of the machining beam 2 is preferably also oriented according to the orientation of the end faces 114, 124 of the ends of the hairpins 10, 12 and in particular the dimensions and rotational orientation relative to the axis of the machining beam 2. The implementation of such a dimensioning and rotational orientation of the machining beam 2 is known in principle, such that it will not be discussed further here.

[0079] An alternative refinement of the machining beam 2 is now shown in FIG. 3, the machining beam 2 being divided and applying a different intensity to the end face 114, 124 of the hairpins 10, 12 in a central region 20 than in its edge region 22, which surrounds the central region 20.

[0080] In other words, the machining beam 2 may for example not apply any intensity at all to the central region 20, such that the intensity of the machining beam 2 in the central region 20 is equal to 0. That edge region 22 of the end face 114, 124 on which the machining beam 2 impinges is correspondingly configured for example in the form of a frame or ring.

[0081] In a further preferred alternative, it is also possible for a machining beam 2 having a first intensity in a first region 22 and a second intensity in a second region 20 to impinge on the end faces 114, 124. In the first region 22 and in the second region 20, it is alternatively or additionally also possible for the end faces 114, 124 to be impinged upon with different wavelengths of the machining beam 2.

[0082] In other words, a higher intensity can be applied to the end faces 114, 124 for example in a first region 22, which is configured for example in the form of a ring or frame, and a lower intensity can be applied in the second region 20 which is then located in the central region.

[0083] This can be achieved, for example, by making the machining beam 2 impinge on the end faces 114, 124 for example by means of a so-called “2-in-1” fiber which has a core fiber and a ring fiber, into which different laser power can be coupled. In this way, the power in the core fiber can be reduced so that the machining beam has a lower intensity in the center than in the edge region. If the power in the core fiber is equal to 0 and laser power is only coupled into the ring fiber, then no energy at all will be applied in the center of the end face 114, 124 of the hairpins 10, 12 and the intensity of the machining beam 2 in the center would accordingly be equal to 0.

[0084] These above-mentioned impingements with different intensities of the machining beam 2 in the plane of the end faces 114, 124 take into account in particular the fact that in the edge region of the machining beam 2, which also strikes the edge region of the cross section of the hairpin 10, 12, heat diffusion takes place through the outer walls of the hairpins, which does not occur in the central region since the latter is enclosed by the edge region. Correspondingly, the inhomogeneous input of machining energy by the machining beam 2 nevertheless achieves substantially homogeneous heating of the cross section of the hairpin 10, 12.

[0085] Since the machining beam 2 strikes the end face 114, 124 of the hairpins 10, 12 and is also oriented in the longitudinal direction Z of the hairpins 10, 12, it is the case that one-dimensional heat conduction, and thus also an extension of the heat conduction in the direction of the welding depth, occurs in principle. This also results in the possibility of a virtually infinite welding depth in the hairpins 10, 12, which is theoretically limited only by the extent of the hairpins 10, 12 in the longitudinal direction Z.

[0086] In practice, however, the aim is to achieve a significantly more limited welding depth, which results in a melt bead that has no tendency to flow away, in order to avoid uncontrolled distribution of the melted material. In other words, the welding depth is limited by the surface tension of the melt, since it is undesirable for the melted material of the melt bead to flow away.

[0087] Furthermore, both a mechanically and electrically reliable connection of the two hairpins 10, 12 can be established in this way, in order to in this way achieve a mechanically and electrically reliable joining of the hairpins 10, 12 and to thus provide a reliable formation of a stator winding of a stator for an electric motor.

[0088] As far as applicable, all of the individual features illustrated in the exemplary embodiments can be combined with one another and/or exchanged without departing from the scope of the invention.

LIST OF REFERENCE SIGNS

[0089] 10 Copper hairpin

[0090] 12 Copper hairpin

[0091] 110 Coating

[0092] 112 Prepared region

[0093] 114 End face

[0094] 120 Coating

[0095] 122 Prepared region

[0096] 124 End face

[0097] 2 Machining beam

[0098] 20 Central region

[0099] 22 Edge region

[0100] 3 Common plane

[0101] X Width of the hairpin

[0102] Y Depth of the hairpin

[0103] Z Longitudinal direction of the hairpin