Welding method for contiguous terminals of conductor elements of an inductive winding of an electrical machine and welding station therefor

Abstract

A welding method for windings (B) of electrical machines comprising hairpin-type conductor elements (C) positioned within respective longitudinal slots (D) of a ferromagnetic core (E). The welding method comprises the following steps: arranging the ferromagnetic core (E) that contains the conductor elements (C) in a welding area; mutually welding the terminals (A) of the conductors (C) by means of the welding device (2) with a laser beam (2a), so as to hit a front (H) of the contiguous terminals (A) for a time interval suitable to melt an end portion of the material that constitutes the same, generating a welding blob (L). According to the invention, the step of arranging the core (E) provides for arranging the core with its longitudinal axis (F) oriented in a horizontal direction. Moreover, the method comprises a step of emitting a gas jet (3a) toward the fronts (H) of the terminals (A) along a substantially vertical and bottom-up direction.

Description

[0001] WELDING METHOD FOR CONTIGUOUS TERMINALS OF CONDUCTOR ELEMENTS OF AN INDUCTIVE WINDING OF AN ELECTRICAL MACHINE AND WELDING STATION THEREFOR

[0002] The present invention relates to a welding method for welding contiguous terminals of conductor elements of an inductive winding of an electrical machine and to a welding station therefor.

[0003] In the present description, the term “conductor elements” is understood to comprise all portions of electrically conducting elements (electrical conductors) that can be used to provide an inductive winding of an electrical machine (such as, for example, an electric motor, an alternator, a dynamo, and others): therefore, so-called “hairpins”, “I-pins”, and any other type of portion of electrically conducting material that can be used to provide parts of the inductive winding of interest also fall within this definition.

[0004] The terminals of portions of conductor elements must be mutually coupled (by welding) in order to ensure the necessary electrical continuity of the inductive winding, in order to ensure that it can trigger the electromagnetic interactions that ensure the proper operation of the electrical machine; hence, the inductive windings of the stator of an electric motor, when carrying an appropriate electric current, generate on the rotor a traction force by electromagnetic induction, thus making the rotor rotate.

[0005] Welding of the terminals of the conductor elements is normally performed while keeping said conductor elements with their longitudinal axis arranged in a vertical direction, in particular with their respective terminals facing / pointing upward. In this way, the effect of gravity is to keep the blob of molten metal at the top of the two terminals (a small portion of the molten material may drip along a first short portion of the lateral walls of the terminals).

[0006] This well-established technique, which is in use in almost all apparatuses for welding the terminals of the conductor elements constituting inductive windings of electrical machines, has some problems since the welding step is generally carried out by means of a laser welding device facing from above the terminals of the conductor elements for the purpose of emitting the laser beam downward in a direction with a vertical component, so as to melt the metallic material of such terminals.

[0007] During the step of melting the metal of the terminals of the conductor elements, fumes are generated which, since they reach high temperatures, tend to rise with respect to the surface of the terminals, and, as a result, return toward the laser welding device located above the terminals, interfering with the laser beam: this can be problematic, since it might reduce the efficiency of the laser beam, causing irregularities in the melting of the material.

[0008] Moreover, following the melting of the metallic material provided by the laser beam, there is a step of solidification of the welding blob which is normally characterized by rapid cooling, during which the welding blob is subjected to physical instability and as a result sprays of molten metal, i.e., “welding spatter” in the jargon, may occur and may interfere with the laser beam or in any case compromise the quality of the surfaces that are contiguous to those being welded (surfaces on which the spatters of molten material may be deposited).

[0009] Moreover, the presence of large amounts of welding fumes in the vicinity of the blob during melting and during cooling increases the porosity of said welding blob and, once such blob has solidified, of the resulting welding joint. This effect, although only detected through microscopy, can considerably reduce the tolerable tear strength (maximum mutual tear force applied to the two distinct mutually welded conductor elements) of the welding joint of the terminals of the conductor elements.

[0010] The problems described, i.e., the presence of welding fumes and the generation of welding spatter, sometimes reduce the net area (and also the net volume) of the welding joint (understood as the difference between the total area or volume of the welding joint and the area or volume occupied by porosities) performed between the two terminals (in particular, it may happen that in a totally unpredictable manner some mutually welded terminals have a tear strength, understood as the force required to separate the two welded terminals through mutual spacing, that is lower than the required standards, due to such issues).

[0011] The aim of the present invention is to solve the above problems by providing a method for welding contiguous terminals of conductor elements of an inductive winding of an electrical machine that ensures that high values of tear strength of welded terminals are obtained.

[0012] Within this aim, an object of the invention is to provide a method for welding contiguous terminals of conductor elements of an inductive winding of an electrical machine that ensures that substantially constant values of tear strength of the welded terminals are obtained, even on very large samples of welds performed.

[0013] Another object of the invention is to provide a method for welding contiguous terminals of conductor elements of an inductive winding of an electrical machine wherein the quality of the welding joint is not affected by the presence of the fumes emitted by the molten metal.

[0014] Another object of the invention is to provide a method for welding contiguous terminals of conductor elements of an inductive winding of an electrical machine wherein the quality of the welding joint is not affected by the presence of welding spatter, since it may increase the porosity of the welding joint, reducing the tear strength, or may settle on some of the components of the welding station, such as the laser welding device, thus reducing the efficiency during the welding of subsequent pairs of terminals.

[0015] Another object of the invention is to provide a station for welding contiguous terminals of conductor elements of an inductive winding of an electrical machine that allows to obtain high tear strength values of the welded terminals. Another object of the invention is to provide a station for welding contiguous terminals of conductor elements of an inductive winding of an electrical machine that allows to obtain substantially constant values of tear strength of the welded terminals, even on very large samples of welds performed.

[0016] Another object of the invention is to provide a station for welding contiguous terminals of conductor elements of an inductive winding of an electrical machine that ensures a welding quality that is independent of the presence of the fumes emitted by the molten metal.

[0017] Another object of the invention is to provide a station for welding contiguous terminals of conductor elements of an inductive winding of an electrical machine that ensures a welding quality that is independent of the presence of welding spatter emitted by the molten metal.

[0018] A further object of the present invention is to provide a method for welding contiguous terminals of conductor elements of an inductive winding of an electrical machine and a corresponding welding station that have low costs, are relatively simple to provide in practice and are of assured application.

[0019] This aim and these objects are achieved by the method for welding contiguous terminals of conductor elements of an inductive winding of an electrical machine according to claim 1.

[0020] This aim and these objects are also achieved by means of a welding station for terminals of conductor elements of an inductive winding of an electrical machine according to claim 6.

[0021] Further characteristics and advantages of the invention will become better apparent from the description of a preferred but not exclusive embodiment of the welding method for contiguous terminals of conductor elements of an inductive winding of an electrical machine and of the welding station that performs it, illustrated by way of non-limiting example in the accompanying drawings, wherein: Figure 1 is a schematic front view of an incomplete inductive winding provided within the ferromagnetic core of an electrical machine;

[0022] Figure 2 is a schematic axonometric view of the incomplete inductive winding of Figure 1 and an illustrative block diagram of the station according to the invention suitable for performing the method according to the invention;

[0023] Figure 3 is an enlarged- scale view of the detail III identified in Figure 2, combined with an illustrative block diagram of part of the station according to the invention suitable for performing the method according to the invention;

[0024] Figure 4 is a schematic front view of an inductive winding provided within the ferromagnetic core of an electrical machine;

[0025] Figure 5 is a schematic axonometric view of the inductive winding of Figure 4;

[0026] Figure 6 is an enlarged-scale view of the detail VI identified in Figure 5;

[0027] Figure 7 is an enlarged- scale schematic axonometric view of a gas jet dispenser of a station according to the invention;

[0028] Figure 8 is a schematic side view of a group of terminals during a welding method with a vertical arrangement of the terminals, according to the prior art;

[0029] Figure 9 is a schematic side view of a group of terminals during a welding method with a horizontal arrangement of the terminals, according to the prior art;

[0030] Figure 10 is a schematic side view of a group of terminals during the welding method according to the invention.

[0031] With reference to the abovementioned figures, a welding station for contiguous terminals A of conductor elements C of an inductive winding B of an electrical machine suitable for performing the method according to the invention is generally designated by the reference numeral 1. The welding method according to the invention is suitable for completion (closure of the electrical circuit, aimed at providing continuity thereof) of windings B of electrical machines comprising conductor elements C of the hairpin type (i.e., constituted by a portion of conductor wire made of electrically conducting material and provided with an outer coating layer Ai made of dielectric material, bent with a substantially hairpin-like shape and provided with ends suited to be joined with corresponding ends of other conductor elements C to provide the electrical winding B). In particular, the conductor elements C are positioned within respective longitudinal slots D of a ferromagnetic core E of a winding B, stator or rotor, of an electrical machine.

[0032] In practice, the ferromagnetic core E might be the one of a stator (as in the example given by way of non-limiting example in the accompanying figures) or the one of a rotor of a rotating electrical machine, or the core of a static electrical machine (such as power and non-power transformers and / or autotransformers) .

[0033] The ferromagnetic core E of the electrical machines on which the assembly 1 according to the invention is able to operate comprises a longitudinal axis F which is perpendicular to two mutually opposite heads Ei and E2of said core E.

[0034] Specific end portions of the conductor elements C (which at least partially protrude from a respective head E1?E2of the ferromagnetic core E) comprise a respective terminal A (fully protruding from a respective head Ei, E2of the ferromagnetic core E) which is to be welded to at least one additional terminal A contiguously arranged, wherein the at least one additional terminal A also is equally fully protruding from the same head E E2of the ferromagnetic core E.

[0035] The terminals A are arranged contiguously in groups of at least two terminals A: all terminals A belonging to a respective group are suitable to be mutually welded. The welding method comprises a first step of arranging the ferromagnetic core E containing the conductor elements C in a welding area, according to a configuration in which the terminals A of the conductor elements C face a welding device 2 and are oriented toward it. The welding area corresponds to a compartment of a welding station 1 , better illustrated hereinafter, configured to accommodate the core E.

[0036] A second step of mutual welding of the terminals A by means of the welding device 2 is then provided. The welding device 2 is of the laser type and is configured to emit a laser beam 2a oriented substantially parallel to the terminals A of the conductors C. In the ferromagnetic core E, the terminals A are arranged with their longitudinal axis G parallel to the axis F of the ferromagnetic core E.

[0037] The second step of mutual welding consists of welding the terminals A to each other, with the laser beam 2a emitted by the device 2, wherein the laser beam 2a is oriented to hit a front H of the contiguous terminals A of a group: the emission of the beam 2a continues for a time interval suitable to melt an end portion (the one close to the front H) of the material constituting the terminals A, resulting in the formation of a welding blob L (blob of fused material).

[0038] According to the invention, the first step of arranging the core E advantageously provides for arranging the core E with its longitudinal axis F oriented in the horizontal direction.

[0039] In order to provide unambiguous identification of the terms "horizontal" and "vertical" used in the present description, it is specified that the vertical direction is to be understood as a direction parallel to the Earth's gravitational field: more precisely, the vertical direction shall be the direction of gravitational acceleration ag. Accordingly, a direction lying on a plane perpendicular to the vertical direction (and thus orthogonal to the direction of gravitational acceleration ag) is identified as the horizontal direction. The method according to the invention moreover conveniently comprises a step of emitting, by a specific dispenser 3 described better hereinafter, a gas jet 3a toward the fronts H of the terminals A along a substantially vertical direction and upward from below. This step of emitting a gas jet 3a is carried out so as to at least partially overlap the welding step.

[0040] This means that preferably the step of emitting the gas jet 3a is intended to begin before the emission of the laser beam 2a by the device 2 and to persist for the full duration of said laser emission, being interrupted only after the emission of the laser beam 2a has been interrupted.

[0041] It is not excluded to synchronize the emission of the laser beam 2a and the dispensing of the gas jet 3a or, in some cases related to specific applications, to anticipate and / or delay the start of the dispensing of the gas jet 3a with respect to the beginning or end of the emission of the laser beam 2a.

[0042] It is pointed out that, after the step of arranging the core E in the welding area and prior to the welding step, the method according to the invention may favorably comprise moreover a step of mutual alignment of the terminals A contiguously arranged, in order to ensure a stable mutual welding position. Such contiguously arranged terminals A belong to the same group of terminals A that will be welded together, thus the preliminary alignment will enhance the welding quality.

[0043] During this preliminary step of mutual alignment of the terminals A there may preferably be alignment operations, in translation and / or rotation, of the terminals A of each group to be welded, along at least one of the directions of a Cartesian reference system (shown in the accompanying figures and identified by the Cartesian tern of axes X, Y and Z) and / or according to at least one angle of rotation with respect to a corresponding X, Y, Z axis of said Cartesian system (tern of angles of rotation shown in the accompanying figures and identified by the angles a, 0 and y). With reference to the Cartesian tern shown in the accompanying figures, in order to unambiguously define the geometry of the constructive example shown in said figures, the X-axis and Z-axis lie on a horizontal plane, while the Y-axis has a vertical direction (i.e., corresponding to the direction of gravitational acceleration ag). Obviously, such a geometric configuration refers to one possible embodiment and does not define any limitation to any further variations in which the axes of the Cartesian reference system do not provide for the Y-axis to be arranged along the direction of gravitational acceleration ag.

[0044] By means of the preliminary step of alignment, it is possible to ensure that the terminals A of a same group are perfectly juxtaposed and overlapping. Considering the need to superimpose them in the vertical direction (so that each terminal A lies above or below another terminal A) so that the base surface of a first terminal A matches up with the top surface of another terminal A (likewise for any other terminals A forming the group of interest), it is also appropriate to provide for a further step of further orientation, by means of which the terminals A can be arranged, each time, so that they are correctly oriented with respect to the reference system and the laser welding device 2 (or with respect to the laser beam 2a): it is pointed out that the laser welding device 2 and the direction of the laser beam 2a are fixed, and therefore the only way to arrange the terminals A correctly with respect to the direction of the laser beam 2a is to orient the terminals A in space according to the specific requirements of mutual overlap in the vertical direction. However, it is not excluded that the terminals A can be juxtaposed by side-by-side arrangement (with their lateral surfaces matching up), although this is an embodiment of lower interest in application.

[0045] With reference to an embodiment according to the invention, during the step of arranging the core E, the core E is arranged with its axis F substantially in the horizontal direction. The substantial horizontality of the axis F can be identified as a geometric condition of said axis whereby it is arranged horizontally or is inclined with respect to the horizontal direction by an angle of small extent (for example, ±15° inclination with respect to the horizontal direction, or preferably ±10° inclination with respect to the horizontal direction).

[0046] In the case of a perfectly horizontal arrangement of the axis F of the core E, the gas jet 3a toward the terminals A has a substantially vertical direction, with a bottom-up direction, i.e., opposite to that of gravitational acceleration ag.

[0047] In a manner similar to what has been described with regard to the substantial horizontality of the axis F, the orientation of the gas jet 3a in the vertical direction can also have a tilt tolerance. If the axis F of the core E is tilted (as shown above by a small angle) with respect to the horizontality condition, the gas jet 3a may also be inclined by an angle of low extent with respect to the verticality condition (for example, ±15° inclination with respect to the vertical direction, or preferably ±10° inclination with respect to the vertical direction) or may be perfectly vertical, as a function of the specific requirements of application and depending on the goal to be achieved by virtue of said gas jet 3a.

[0048] The gas jet 3a produces a series of positive repercussions on the welding quality, which will be described in detail hereinafter.

[0049] First of all, the gas jet 3a, featuring a substantially vertical orientation with a direction opposite to that of gravitational acceleration ag, ensures a support of the type known in the art as “fluidized bed” or “gas cushion” of the molten blob L that would instead be attracted downward by the weight force due to its own weight (due to the gravitational acceleration ag).

[0050] These aspects are shown in Figures 8, 9 and 10. In particular, Figure 8 shows a welding step of a method of a conventional type in which the terminals A are arranged vertically and the molten blob L is supported by the terminals A which are below it. Besides, Figure 9 shows a welding step of a method of a conventional type in which the terminals A are arranged horizontally and the molten blob L is attracted downward by the force of gravity, having the orientation and direction of gravitational acceleration ag, assuming a deformed shape which entails the provision of a poor welded joint R. Likewise, Figure 10 shows the welding step of the method according to the invention, in which the molten blob L is supported by the gas jet 3a against the force of gravity, having the orientation and direction of gravitational acceleration ag). By calibrating the intensity of the gas jet 3a it is therefore possible to support the molten blob L, preventing it from deforming or moving downward, with respect to the terminals A of the group subjected to welding.

[0051] Moreover, in the course of welding, gas fumes M may be generated which in the prior art remain proximate to the molten blob L, interfering with the laser beam 2a and potentially reducing its effectiveness. Moreover, the fumes M can increase the porosity of the welding joint, compromising its mechanical properties (or in any case reducing them), with particular reference to mechanical strength.

[0052] By virtue of the presence of the gas jet 3a, instead, the fumes M are rapidly moved away from the molten blob L, ensuring that the laser beam 2a is not disturbed by them.

[0053] During the welding step and, in particular, during the cooling and solidification step following the melting of the material (i.e., during the transition of the molten material from the liquid state to the solid state), the emission of particles N of molten (or even solid) material from the molten blob L may also occur, which are normally termed welding spatter in the technical language of the industry. Obviously, the spatter N can be deposited anywhere, even proximate to the terminals A of the group that are being welded, compromising the quality of the entire method being carried out and, potentially, of the inductive winding B as well. In particular, the spatter N, coming from the molten blob L, may contribute to the increase of porosity of the welding joint, reducing the tear strength (welding quality) and possibly settling on components of the welding station 1, damaging them or reducing their effectiveness, thus leading to negative consequences on the subsequent welding operations to be carried out on other groups of terminals A.

[0054] For such reasons, it is preferable to reduce the spatter N that may be deposited on parts of the winding B and / or of the terminals A: the gas jet 3a enhances the removal of the spatter N from the terminals A and from the winding B, consequently improving the quality of the welding of the terminals A of the group and, potentially, the quality of the entire inductive winding B.

[0055] Finally, it should be pointed out that the gas jet 3a removes heat from the molten blob L: the cooling of the molten blob L (and the solidification thereof) is therefore modified (and more uniform) than it would be in the absence of the gas jet 3a.

[0056] It has been experimentally verified that the modified cooling and the removal of the fumes M and of the spatters N allow to obtain welds that are stronger (with high tear strength) and more stable, ensuring that welding joints R of the group of welded terminals A having a regular and substantially symmetrical shape are obtained. In fact, the gas jet 3a displaces the spatter N in a transverse direction with respect to the welding mask, increasing its lifespan since it does not suffer from the undesired sticking of weld spatter N, resulting in higher productivity, reduction of breakdowns in the operation of the plant that implements the method due to preventive / scheduled maintenance operations, as well as reducing breakdowns in the operation of the plant that implements the method and the associated “non-conformities” due to an excessive amount of spatter N deposited on the welding mask leading to a corrective maintenance operation.

[0057] Moreover, during welding operations, a plasma corona is generated around the molten blob L: such a plasma corona subtracts energy from the laser beam 2a and thus worsens the quality of the welding joint and / or requires more time to complete it. The gas jet 3a ensures that the plasma corona is removed (or otherwise displaced with respect to the laser beam 2a): this ensures that the maximum possible amount of energy, supplied by the laser beam 2a, is transferred to the terminals A for localized melting of their ends and their welding.

[0058] Positively, the method according to the invention furthermore comprises a step of orienting the ferromagnetic core E that allows to ideally align the groups of terminals A to be welded on top of each other, in mutual alignment, with respect to the vertical direction of the gas jet 3a.

[0059] With reference to an embodiment according to the invention, the method according to the invention may more specifically comprise a step of rotating the ferromagnetic core E about its longitudinal axis F so as to arrange, each time, the terminals A of the group to be welded one above the other, in mutual alignment, with respect to the vertical direction of the gas jet 3a.

[0060] The method according to the invention can comprise a step of mutual realignment of a new group of terminals A of a group to be welded which are present in respective slots D of the ferromagnetic core E to the laser welding device 2 (and to the dispenser 3 of the gas jet 3a) at the end of a welding step performed on a previous group of terminals A.

[0061] The movement of the ferromagnetic core E to allow the alignment of a new group of terminals A with the device 2 and with the dispenser 3 is intended to bring new terminals A of the group (not yet welded) into the correct position to be subjected to welding according to the correct alignment with respect to the gas jet 3a. This operation is less important if terminals A having a vertical longitudinal axis are welded by means of a laser beam 2a that is also arranged in a vertical direction: in fact, in such a case the molten blob L is not suspended and subject to the gravitational field, as it occurs in the case of welding along a horizontal direction of the laser beam 2a, but it is supported by the terminals A, which are arranged below the molten blob L in this case.

[0062] In this way, by means rotating the core E, it is thus possible to align with the welding device 2 (more precisely with the direction in which it emits the laser beam 2a) and with the dispenser 3 (more precisely with the direction in which it delivers the gas jet 3a) a new group of terminals A to allow their welding.

[0063] It should be specified that the method according to the invention may, moreover, efficiently comprise an additional preventive step of removing the coating Ai made of dielectric material of each conductor element C at its terminals A: the removal of the coating Ai is necessary to ensure that the welding quality is optimal, since the dielectric material, when hit by the laser beam 2a, might generate gaseous emissions (fumes) or solid residues that could worsen the welding quality of the terminals A of the group to be welded.

[0064] Preferably, the gas jet 3a may conveniently be a dry air flow, that is, air having a water vapor content of less than 1%, and preferably filtered beforehand.

[0065] The minimal content of water vapor and suspended particles in the air flow constituting the gas jet 3a ensure that said air flow does not interfere with the propagation of the laser beam 2a in the desired direction, thus avoiding undesirable phenomena such as, for example, refraction, scattering, absorption of the laser beam 2a due to the high presence of vapor: the gas jet 3a must therefore allow the laser beam 2a to be transmitted substantially completely when it passes through it.

[0066] The absence of humidity in the gas jet 3a is extremely advantageous, since the presence of vapor would have numerous negative effects on the molten blob L, resulting in increased porosity in the welding joint, worsening its mechanical performance (i.e.: tear strength). Advantageously, the gas jet 3a can be provided by adopting a gas of the type used as “shielding gas,” i.e., inert or semi-inert, such as nitrogen, carbon dioxide, helium, argon, etc.

[0067] Preferably, the gas jet 3a is advantageously dispensed through a plurality of nozzles connected to a compressed air supply line: it is specified that the compressed air supply line may be associated with a compressed air circuit of the known type.

[0068] The gas jet 3a may be validly dispensed at a pressure comprised between 100 kPa and 2 MPa (i.e., between 1 bar and 20 bar), preferably between 300 kPa and 1 MPa (i.e., between 3 bar and 10 bar), even more preferably between 500 kPa and 600 kPa (i.e., between 5 bar and 6 bar).

[0069] An embodiment for which unquestionable functionality has been verified experimentally provides for dispensing a gas jet 3a at a pressure of 570 kPa (corresponding to 5.7 bar); in this experimental verification, eight separate nozzles constituted by holes with a diameter of about 1 mm, provided on a common generatrix of a cylindrical tube having a diameter of about 8 mm, were adopted.

[0070] In the method according to the invention, which provides for horizontal welding (i.e., performed on terminals A having their respective axes G arranged in a substantially horizontal direction and performed by means of a laser beam 2a which also has a substantially horizontal direction), it is essential that the terminals A of the group to be welded are oriented mutually and with respect to the dispenser 3 (in particular to the direction of its gas jet 3a) in an ideal manner.

[0071] The rotation of the ferromagnetic core E is thus provided about its axis F, so that its heads Ei and E2each remain lying on a respective fixed plane.

[0072] Preferably, the orientation step provides for preparing the core E so that a vertical overlap occurs in the group of contiguous terminals A (i.e., the terminals are one above the other) with their respective axes G substantially horizontal; this is necessary to ensure the required welding quality. The vertical overlap of the contiguous terminals A of the group to be welded by rotation of the core about its axis F is extremely advantageous since it ensures homogeneity in the welding joint R, because of the effect that gravitational acceleration aghas: arranging the terminals A one above the other helps to have substantially constant tear strength for each welding joint R.

[0073] As shown above, the mutual realignment step may conveniently be carried out by means of specific displacements of the ferromagnetic core E. In particular, an embodiment that allows an effective realignment, illustrated by way of non-limiting example, may be achieved by means of a rotation of the ferromagnetic core E about the respective longitudinal axis F (of symmetry).

[0074] The protective scope of the present invention also extends to a welding station 1 for windings B of electrical machines having conductor elements C of the hairpin type.

[0075] In this station 1 the conductor elements C are placed within respective slots D of a ferromagnetic core E.

[0076] Said ferromagnetic core E shall comprise a longitudinal axis F perpendicular to two mutually opposite heads E E2of the core E.

[0077] Respective end portions of the conductor elements C comprise respective terminals A which, in order to be mutually welded, protrude at least from one of the two heads Ei, E2of the ferromagnetic core E.

[0078] The terminals A are arranged contiguously in groups of at least two terminals A for their mutual welding.

[0079] Advantageously, said station 1 according to the invention comprises a support 4 for locking the ferromagnetic core E: in Figure 2 the support 4 is shown merely by way of example as constituted by a pair of retention elements (represented by means of respective graphical symbols in use in physics and mechanics) that allow the core E to be rigidly locked, but also, if necessary, to be rotated about its own axis F. Obviously said graphical representation refers to one possible way of providing the support 4, which in practice may be provided according to completely different geometries and structures while still falling within the protective scope of the present invention.

[0080] Moreover, the station 1 comprises at least one welding device 2 configured to emit a laser beam 2a directed in a direction that is substantially parallel to the direction of the longitudinal axes G of the terminals A of the group to be welded. With reference to an embodiment according to the invention, illustrated by way of non-limiting example, it is specified that the direction of the longitudinal axes G of the terminals A and the direction of the axis F of the core E may be parallel.

[0081] The laser beam 2a is sized for localized melting of an end portion (close to the front H) of the material that constitutes the terminals A of the group, with consequent mutual welding thereof.

[0082] As previously mentioned, the support 4 for locking the core E has to ensure a removable locking, so as to allow the extraction of a core in which all the welds necessary for the completion of the inductive winding B have been performed, configured to arrange the core E so that its longitudinal axis F is substantially horizontal.

[0083] Moreover, it is specified that the station 1 according to the invention further comprises a gas dispenser 3 configured and oriented to emit a gas jet 3a toward the terminals A, at end fronts H thereof, along a substantially vertical orientation and with a bottom-up direction.

[0084] It is moreover advantageously provided that the station 1 may comprise an alignment mask, not shown in the accompanying figures but nevertheless conforming to the teachings of international patent applications WO2023083714 and W02023088802 in the name of the same Applicant.

[0085] This mask allows to perform alignment operations in translation and / or rotation of terminals A of at least one respective group. In particular, the mask is advantageously configured to provide an alignment of the terminals A of each group to be welded along at least one of the directions of a Cartesian reference system (shown in the accompanying figures and identified by the Cartesian tern of axes X, Y and Z) and / or according to at least one angle of rotation with respect to a corresponding axis X, Y, Z of said Cartesian system (tern of angles of rotation shown in the accompanying figures and identified by the angles a, 0 and y).

[0086] By means of the preliminary alignment step it is possible to ensure that the terminals A of a same group are perfectly juxtaposed and overlapping. Preferably, they are overlapping in the vertical direction, so that each terminal A is above or below another terminal A, so that the base surface of a first terminal A matches up with the top surface of another terminal A or any other terminals A forming the group of interest. Nevertheless, it is not excluded that the terminals A may be juxtaposed in a mutually side-by-side arrangement, with their lateral surfaces matching up in a horizontal direction, although this is an embodiment of lower interest in application.

[0087] The locking support 4 is configured for the indexed rotation of the core E about its own longitudinal axis F, so as to orient, each time, a new group of terminals A to be mutually welded in which one terminal A is arranged above another terminal A of the same group in the vertical direction (i.e., superimposed vertically so that the base of one terminal A is juxtaposed against the top of another terminal A of the group, as shown above).

[0088] The gas dispenser 3 may be configured to dispense compressed air: in this case, the dispenser 3 is connectable to means for supplying compressed air (which are of a known type and, generally, independent of the station 1 with respect to which they supply only compressed air). As an alternative to compressed air, the use of inert gas cylinders (shielding gas), such as for example, nitrogen, CO2, helium, argon, etc., is provided.

[0089] Moreover, it should be noted that the gas dispenser 3 may comprise a plurality of contiguous nozzles configured and sized for generating a compressed gas jet 3a that is wider than the width S of the group of contiguous terminals A to be mutually welded.

[0090] The dispenser 3 of compressed gas may be constituted by a pipe 4 provided with holes 5 substantially distributed along a directrix of its lateral surface, along a portion that is longer than the width S of the group of contiguous terminals A to be subjected to mutual welding.

[0091] It is specified that, in the station 1 according to the invention, the core E may be arranged in a configuration in which its longitudinal axis F, corresponding to the axis G of the terminals A of the conductor elements C accommodated within the respective slots D of the core E, is substantially horizontal, with a tolerance of about ±15° with respect to horizontality, preferably ±10° with respect to horizontality.

[0092] The compressed gas dispenser 3 in this case is configured to emit a gas jet 3a toward the terminals A, at their end front H, along a direction close to the one that is perpendicular to the direction of the longitudinal axis F of the core E, with a tolerance of about ±15° with respect to orthogonality, preferably ±10° with respect to orthogonality, and with a bottom-up direction, i.e., substantially opposite to the direction of gravitational acceleration ag.

[0093] According to embodiments according to the invention, the holes 5 present on the tube 4 may be at least two, preferably at least 4, even more preferably at least 6.

[0094] A preferred embodiment, illustrated by way of non-limiting example in Figure 7, provides for the adoption of a tube 4 provided with 8 holes 5 which are laterally adjacent and arranged along a generatrix of the lateral surface of said tube 4.

[0095] Each hole 5 constitutes a dispensing nozzle and has a diameter comprised between 0.05 mm and 10 mm, preferably between 0.5 mm and 3 mm, even more preferably close to 1 mm.

[0096] All the embodiments illustrated so far have been found to be adapted to different hairpin sizes (which comprise a different amount of molten blob L, to be supported with a specific gas jet 3a, depending on the width of terminal A). It is not excluded that, upon further different application requirements, it may be convenient to resort to further different embodiments which are however within the inventive concept of the present invention.

[0097] Moreover, it is specified that the support 4 may usefully comprise supporting means for locking the core E which are configured for the arrangement of said core E with its longitudinal axis perfectly horizontal, with a corresponding perfectly horizontal arrangement of the axes G of the terminals A.

[0098] In this case, the at least one welding device 2 is configured to emit a laser beam 2a having a direction that is substantially parallel to the direction of the longitudinal axes G of the terminals A to be welded, i.e., horizontal.

[0099] Furthermore, the gas dispenser 3 is configured in this case to emit a gas jet 3a in an orientation which is perpendicular to the direction of the axes G of the terminals A of the group to be welded, therefore substantially vertical, having a direction opposite to the direction of gravitational acceleration ag.

[0100] This results in the consequences listed hereafter:

[0101] - the gas jet 3a ensures at least partial support of the molten blob L of the end region of the terminals A of the group subjected to the incidence of the laser beam 2a,

[0102] - the gas jet 3a removes any liquid effusions, such as spatter N, and gaseous effusions, such as the fumes M, that originate from the molten blob L;

[0103] - the gas jet 3a optimizes / conditions the forced convection heat transfer of the molten blob L during the cooling / solidification step of the welding joint R when the emission of the laser beam 2a incident on the terminals A ceases, with a consequent increase in the tear strength and stability of the welding joint.

[0104] In particular, it has been verified that terminals A mutually welded in a station 1 according to the invention and / or by applying a method according to the invention have a tear strength on the order of about 400 N, thus higher than the tear strength achievable with a traditional welding method with terminals A and laser beam 2a in a vertical direction (which has values on the order of approximately 260 N).

[0105] Tear strength may be measured in accordance with the standards given in UNI EN ISO 4136 ("Destructive tests on welds of metallic materials. Transverse tensile test").

[0106] Advantageously, the present invention solves the problems set forth above by providing a welding method for contiguous terminals A of conductor elements C of an inductive winding B of an electrical machine that ensures that high tear strength values of the welded terminals A are obtained.

[0107] Conveniently, the method according to the invention guarantees the obtainment of substantially constant values of tear strength (in particular, always higher than the average value obtainable with a welding joint according to the background art performed with the terminals arranged in a vertical direction) of the welded terminals A, even on very large samples of welds performed.

[0108] The method according to the invention ensures that the quality of the welding joint is not affected by the presence of the fumes M emitted by the molten metal.

[0109] The method according to the invention ensures higher productivity in a welding plant for windings of electrical machines by reducing the spatter N deposited on the device 2 or on the alignment mask for welding. The method according to the invention ensures that welding quality is not affected by the presence of the spatter N emitted by the molten metal. In particular, since the spatters N can increase the porosity of the welding joint R (reduction of tear strength) due to uncontrolled implosions during rapid cooling during solidification, eliminating and / or reducing them influences an increase in mechanical strength at the layer of the welding joint R. Moreover, the gas jet 3a also results in a reduction of the spatter N that might deposit on the welding mask, since said spatter N are pushed at right angles to the direction of the terminals A and, when outside the range of action of the gas jet 3a, are subject to gravitational acceleration ag, which moves them away from the region of the station 1 where welding is performed, promoting greater cleanliness. Moreover, reducing the spatter N leads to a reduction in the maintenance requirements of the welding station 1 and increases its productivity: the welding mask is in fact less subjected to the deposition of spatter N. This reduces the need for scheduled / preventive maintenance operations and also the cost of spare parts, which are needed to replace components damaged by the accumulation of spatter N.

[0110] The welding station 1 for terminals A of conductor elements C of an inductive winding B of an electrical machine according to the invention allows to obtain high tear strength values of welded terminals A.

[0111] The station 1 according to the invention allows to obtain substantially constant values of tear strength of the welded terminals A (in particular, always higher than the average value obtainable with a welding joint according to the background art performed with the terminals A arranged in a vertical direction), even on very large samples of welds performed.

[0112] The station 1 according to the invention ensures a welding quality that is independent of the presence of the fumes M emitted by the molten metal.

[0113] The station 1 according to the invention ensures a welding quality that is independent of the presence of the spatters N emitted by the molten metal.

[0114] The welding method according to the invention and the welding station 1 therefor are relatively simple to provide in practice and of low cost: these characteristics make the welding method and the welding station according to the invention innovations of assured application.

[0115] The invention thus conceived is susceptible of numerous modifications and variations, all within the scope of the inventive concept; all the details may furthermore be replaced with other technically equivalent elements.

[0116] In the embodiments shown, individual characteristics, given in relation to specific examples, may actually be interchanged with other different characteristics that exist in other embodiments.

[0117] In practice, the materials used, as well as the dimensions, may be any according to the requirements and the state of the art.

[0118] The disclosures in Italian Patent Application No. 102023000025227 from which this application claims priority are incorporated herein by reference.

[0119] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

CLAIMS1. A welding method for welding hairpin-type conductor elements (C) inserted within respective longitudinal slots (D) of a ferromagnetic core (E), wherein- said ferromagnetic core (E) comprises a longitudinal axis (F) perpendicular to two opposing ends (El, E2) of said core (E);- each end portion of said conductor elements (C) comprises respective terminals (A) protruding from one of the two heads (El, E2) of said ferromagnetic core (E);- said terminals (A) are arranged contiguously in groups of at least two terminals (A) of different conductor elements (C); said welding method comprising the following steps:- arranging said ferromagnetic core (E) provided with said conductor elements (C) in a welding area according to a configuration wherein the terminals (A) of the conductor elements (C) face and are oriented towards a welding device (2);- welding the terminals (A) to each other with said welding device (2) by means of a laser beam (2a) oriented to hit a front (H) of the contiguously grouped terminals (A) for a time interval suitable for producing on said end portion a blob (L) of fused material; said method being characterized in that said arranging step provides positioning said core (E) with its longitudinal axis (F) oriented in a horizontal direction, and in that said method further comprises a step of emitting a gas jet (3a) towards the blob (L) of fused material along a substantially vertical and bottom-up direction, and with a pressure configured to sustain said blob (L) avoiding its separation from the contiguously grouped terminals (A) due to gravity (ag), said step of emitting a gas jet (3a) being carried out at least partially overlapping the welding step.

2. The welding method according to the previous claim, characterizedin that after said arranging step and before said welding step, said method further comprises a step of mutually aligning the contiguously arranged terminals (A) defining said group, so as to guarantee a stable mutual welding position, said aligning step comprising mutual alignment operations, in translation and / or rotation, of the said terminals (A) of each said group to be welded, according to at least one of the directions of a Cartesian reference system and / or according to at least one rotation angle with respect to a corresponding axis of said Cartesian system.

3. The welding method according to one or more of the previous claims, characterized in that said gas jet (3a) is delivered through a plurality of nozzles connected to a supply piping of compressed air.

4. The welding method according to one or more of the previous claims, characterized in that it comprises a step of mutual realigning said ferromagnetic core (E) and said welding device (2) so as to arrange, each time, a new group of terminals (A) to be welded aligned with said welding device (2).

5. The welding method according to the previous claim, characterized in that said step of mutual realigning is carried out by rotating said ferromagnetic core (E) about its longitudinal axis (F).

6. A welding station for welding hairpin-type conductor elements (C), wherein- said conductor elements (C) are positioned within respective slots (D) of a ferromagnetic core (E);- said ferromagnetic core (E) comprises a longitudinal axis (F) perpendicular to two opposing ends (El, E2) of said core (E);- each end portion of said conductor elements (C) comprises respective terminals (A) protruding from one of the two heads (El, E2) of said ferromagnetic core (E);- said terminals (A) are arranged contiguously in groups of at least two terminals (A) of different conductor elements (C);said welding station (1) comprising:- a support (4) for fixing said ferromagnetic core (E) provided with said conductor elements (C);- at least one laser welding device (2) configured to emit a laser beam (2a) directed in a direction substantially parallel to the direction of the longitudinal axes (G) of said terminals (A) to be welded, said laser beam (2a) being dimensioned for producing on said end portion a blob (L) of fused material, with the consequent mutual welding thereof; said station (1) being characterized in that said fixing support (4) is of the removable type and is configured to arrange said core (E) with its longitudinal axis (F) substantially horizontal, and in that said station (1) further comprises a gas dispenser (3) configured and oriented to emit a gas jet (3a) towards the blob (L) of fused material created on said terminals (A), according to a substantially vertical and bottom-up direction, said gas jet (3a) being dimensioned with a pressure suitable for sustaining said blob (L) to avoid its separation from the contiguously grouped terminals (A) due to gravity (ag).

7. The welding station according to the previous claim, characterized in that it comprises an alignment mask, for the translation and / or rotation of the terminals (A) of at least one respective group of terminals (A), said mask being configured to achieve a mutual alignment of said terminals (A) of each said group to be welded according to at least one of the directions of a Cartesian reference system and / or according to at least one rotation angle with respect to a corresponding axis of said Cartesian system.

8. The welding station according to at least one of claims 6 and 7, characterized in that said fixing support (4) is configured to rotate said core (E) around its own longitudinal axis (F), so as to arrange, each time, a new group of contiguous terminals (A) to be welded to each other, wherein one terminal (A) is arranged on top of the other in the vertical direction.

9. The welding station according to at least one of claims 6, 7 and 8,characterized in that said gas dispenser (3) is configured to supply compressed air, said gas dispenser (3) being connectable to means of compressed-air supply.

10. The welding station according to at least one of claims 6 to 9, characterized in that said gas dispenser (3) comprises a plurality of contiguous nozzles (5) configured and dimensioned to generate a gas jet (3a) with a width greater than the width of the group of said contiguous terminals (A) to be subjected to mutual welding so that said blob (L) can be properly sustained with the stream of gas jet (3a).

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