DE102020120643A1 - Process for laser welding of electrodes - Google Patents

Abstract

The invention relates to a method for welding two rod-shaped electrodes by means of a laser beam, comprising: detecting the positions of the rod-shaped electrodes and determining a processing point on each of the rod-shaped electrodes; splitting the laser beam into two sub-beams; and Radiating the two partial beams onto one of the processing points of the two rod-shaped electrodes and forming a common molten pool for welding the rod-shaped electrodes.

Description

technical field

The present invention relates to a method for the integral connection, in particular for laser welding, of electrodes, in particular rod-shaped electrodes, also called rod electrodes, and a processing device that is set up to carry out the method.

background

In a laser processing system for processing a workpiece using a laser beam, the laser beam emerging from a laser beam source or from one end of a laser conducting fiber is focused or bundled onto a workpiece to be processed with the aid of beam guidance and focusing optics in order to locally heat the workpiece to melting temperature. The processing can in particular include laser welding. The laser processing system can include a laser processing device, for example a laser processing head, in particular a laser welding head.

In the field of electromobility, the manufacture of electric motors, in particular the manufacture of stators for electric motors, plays a central role. In order to simplify the complex and difficult-to-automate winding process for manufacturing the stator coil, winding segments, so-called hairpins or rod electrodes, are shot from rectangular copper wire into the stator slot. The ends of these hairpins are then connected to one another, for example by clamping or twisting. However, this is just as time-consuming as it is imprecise. Therefore, a scanner laser welding method has recently been used to connect the hairpins. The welding of hairpins is one of the main joining tasks in connection with the electrification of the transport system. For the connection of the hairpins and thus for the successful manufacture of a stator coil, it is essential that there is electrical contact between the welded hairpins, i.e. that current can flow between the welded parts or via the welded joint. These copper contacts should be welded spatter-free with the lowest possible contact resistance between the individual hairpins. In addition, it is a challenge to hit the individual hairpins and to ensure a homogeneous joining process.

In a conventional scanner laser welding process, as in 1 1, a laser beam 10 is directed at ends 1a, 2a of two adjacent hairpins 1, 2 and scanned with a 2D scanner in a circular path (dashed arrow) over both ends 1a, 2a to form a common weld pool. However, when the laser beam hits the gap 30 between the two adjacent hairpins 1, 2, insulation material 3 surrounding a lower part of the hairpins for insulation can be melted. If, in addition, the adjacent hairpins 1, 2 are at different heights or z-positions, ie if the distance from the laser processing head is different, the ends 1a, 2a of the two adjacent hairpins are melted unevenly. This can cause spatter and pinholes, resulting in poor electrical connection or high resistance. In addition, the 2D scanner required for this is relatively expensive.

Welding highly reflective materials, such as copper, with a laser beam with a wavelength in the micrometer range, i.e. in the infrared (IR) range, is inherently challenging. For this reason, laser sources with shorter wavelengths have also recently been used, for example in the blue or green range, although these are significantly more expensive than IR laser sources.

Summary of the Invention

It is an object of the present invention to specify a method for materially connecting, in particular for welding, two electrodes using a high-energy machining beam, in particular an electron beam or laser beam, which enables precise and reliable contacting of the electrodes at low cost. Furthermore, it is an object of the present invention to specify a processing device for the integral connection, in particular for welding, of two electrodes using a high-energy processing beam, in particular an electron or laser beam, which enables precise and reliable contacting of the electrodes at low cost.

The object is solved by the features of the independent claim. Features of preferred embodiments are given in the subclaims.

The present invention is based on the idea of generating a separate weld pool on at least two electrodes to be connected to one another by a so-called twin or multi-spot welding process in which the laser beam is divided into at least two partial beams. These separate weld pools then combine to form a common weld pool in order to create the material connection or the electrical contact. Instead of a laser beam any other high-energy processing beam, such as an electron beam, can also be used. The present invention is described below using the example of welding by means of a laser beam, but is not limited to this.

According to one aspect, a method for cohesively connecting at least two electrodes using a high-energy processing beam, in particular for welding at least two electrodes using an electron beam or laser beam, comprises: determining a processing point on each of the electrodes; Splitting the processing beam into at least two partial beams, and irradiating the at least two partial beams onto one of the processing points of the at least two electrodes in order to form a common melt pool for welding the electrodes or for establishing an electrical connection between the electrodes. The number of partial beams preferably corresponds to the number of electrodes. Furthermore, a step of detecting the positions of the electrodes can be carried out before the machining points are determined.

According to a further aspect, a processing device for materially connecting two electrodes by means of a high-energy processing beam, in particular a laser processing device for welding at least two electrodes by means of a laser beam, comprises: a detection unit for determining a processing point on each of the electrodes; and a processing head for radiating at least two partial beams onto one of the processing points, the processing head comprising splitting optics for splitting the processing beam into the at least two partial beams. The splitting optics can also be referred to as multi-spot optics. The processing device can also include a control unit that is set up to carry out a method according to one of the embodiments described in this disclosure. The number of partial beams preferably corresponds to the number of electrodes. The detection unit can also be set up to detect the positions of the electrodes.

The method and the processing device can have one or more of the following preferred features.

Each of the processing points preferably lies on a surface of the respective electrode. The point on the respective electrode to which a partial beam is directed (at least temporarily or at the beginning of the irradiation process) can be designated as the processing point. Preferably, the processing point on each of the electrodes is determined such that the processing point is at the center of a surface of the electrode facing the laser processing device. At least one of the partial beams can be radiated perpendicularly onto the corresponding electrode or onto its surface containing the processing point.

The position of each electrode can be sensed to determine the corresponding processing point. The position of the electrode may include a position of the electrode in a plane perpendicular to a laser beam propagating direction, i.e., x- and y-directions. Alternatively or additionally, the position of the electrode can be a position of the electrode in a laser beam propagation direction (i.e. in the z-direction) and/or a distance between a surface of the electrode and a laser processing device executing the method, and/or a location or position of the electrode in three-dimensional space encompass space.

The positions of the electrodes can be detected by optical coherence tomography and/or by a camera and/or by at least one photodiode. For example, the detection unit can include a scanning device for surface scanning, an optical coherence tomograph or a camera, or can include a photodiode sensor that is sensitive to a wavelength of the laser beam. Detecting the positions of the electrodes can include irradiating the laser beam or the at least two partial beams onto the electrodes along a measurement path and detecting a reflected portion of the irradiated laser beam or the irradiated partial beams, in particular by means of a photodiode. The positions of the electrodes can then be determined based on the detected reflected portion. The laser beam or the at least two partial beams can be radiated onto the electrodes along at least one first measuring path and along at least one second measuring path. The first measurement path can have a predetermined angle to the second measurement path. The positions of the at least two electrodes in a plane perpendicular to the laser beam propagation direction, ie in the x and y plane, can be detected or determined based on the reflected portion of the irradiated laser beam or the irradiated partial beams. The method may further include positioning the electrodes in a positioning device, wherein a reflectivity of the positioning device differs from a reflectivity of the electrodes. In this case, the measuring path preferably comprises a first and a second area, which lie on the positioning device, as well as an area on at least one of the electrodes between the first and the second area. The positioning device and the electrodes can be made of different materials and/or have a different liche surface roughness, so that they have different reflectivities. For example, the surface of the positioning device can consist of brushed, sandblasted and/or matt metal, in particular aluminum, and the surface of the electrodes can consist of smooth, shiny or polished metal, in particular copper. For detecting the positions, a laser power of the irradiated laser beam can be selected that is lower than a laser power for welding the electrodes and/or a speed that is higher than a speed during the formation of melt pools on the electrodes. Accordingly, the laser power or the speed can be selected in such a way that the laser beam is not coupled into the material of the electrodes, but is only reflected. In other words, a power density of the laser beam on a surface of the electrodes and/or the positioning device can be selected such that it is below a threshold value at which the laser beam couples into the electrodes or the positioning device.

The electrodes can be illuminated to detect the positions. For this purpose, the detection unit can include at least one light source, such as a VCSEL or a laser diode. The VCSEL can emit light at a wavelength of e.g. 680nm, 850nm or 940nm. For example, the laser diode can have a wavelength of 630nm-640nm or 808nm-810nm.

In addition to detecting the positions of the electrodes, at least one of the following parameters can also be detected: a size of the surface on which the processing point lies; a distance between the electrodes (i.e. in a plane perpendicular to the beam propagation direction of the laser beam or the partial beams or perpendicular to an optical axis of the laser processing head or the focusing optics); and a size and/or depth of the separate melt pools and/or the common melt pool.

A distance (ie on the electrodes) and/or an angle and/or an intensity distribution between the partial beams can be adjustable, for example depending on a distance between the processing points in a plane perpendicular to the optical axis of the laser beam or the partial beams or to an optical axis Axis of the focusing optics. For example, the intensity of the laser beam can be divided unequally among the partial beams. So if the processing point of one electrode is closer to the laser processing head than the processing point of the other electrode, the intensity of one partial beam that is directed at one electrode can be lower than the intensity of the other partial beam that is directed at the other electrode that is further away is directed. The intensities of the two partial beams can preferably be changed steplessly in a ratio of 80:20 to 50:50.

The distance between the processing points is preferably larger than a focus diameter of at least one of the partial beams or larger than a diameter of at least one of the partial beams on the respective electrode or larger than a narrow side of one of the electrodes. The distance between the processing points can be between 0.3 mm and 3 mm, for example. Each partial beam is therefore preferably directed onto the processing point of one of the electrodes, so that the partial beams or points of impingement of the partial beams on the electrodes are spaced apart or separated from one another.

The splitting optics or multi-spot optics can comprise at least one beam-shaping optics, at least one diffractive optical element, at least one free-form optics, at least one wedge plate and/or at least one mirror. In particular, the splitting optics can be set up to set a distance and/or an angle and/or an intensity distribution between the partial beams. The splitting optics can be insertable into the beam path of the laser beam and removable from the beam path of the laser beam. In other words, the division of the laser beam into a plurality of partial beams can be switched on and off.

The laser processing device can also contain collimation optics for collimating the laser beam and/or focusing optics for focusing the partial beams. The splitting optics can be arranged before or after the focusing optics in the beam propagation direction. The splitting optics can be arranged between the collimating optics and the focusing optics. In other words, the collimated laser beam is preferably divided into the partial beams. The partial beams can be focused by common focusing optics or by separate focusing optics. Accordingly, a focal position can be set jointly for the two partial beams or separately for each partial beam.

The focus position is preferably set separately for each partial beam. As a result, the necessary power density can also be generated at different levels, for example if the electrodes have a different position in the beam propagation direction of the laser beam or the partial beams or along an optical axis of the focusing optics.

A focal position of the at least two partial beams and/or at least one partial beam can be adapted to the detected position of the respective electrode or to the position of the respective processing point. During the irradiation of the partial beams, the focus of at least one of the partial beams can be at least temporarily on the processing point and/or on the surface of the respective electrode.

The focal position of the at least two partial beams or of at least one partial beam is preferably changed during the irradiation of the partial beams, in particular continuously or in steps. In one embodiment, at least one of the partial beams can be directed onto the respective electrode in a defocused manner during the irradiation of the partial beams in a first step. In a subsequent second step, the focus position of the at least one partial beam can be adjusted. For example, the focus position of the at least one partial beam can be approached or removed from the processing point on the respective electrode, in particular continuously or step by step. As a result, a joint of the electrodes or the separate weld pool or the common weld pool can be modified in such a way that the coupling of the laser beam is improved. The respective electrode surface is heated by the defocused irradiation of the partial beam(s), so that the coupling of the laser beam is also improved for long wavelengths, e.g. in the IR range. For example, the absorption of IR laser radiation by copper in the molten phase is almost identical to that at shorter wavelengths.

At the end of the irradiation of the partial beams or after formation of the common weld pool, at least one of the partial beams can be directed onto the respective electrode in a defocused manner. In this way, a smoothing of the welded connection or weld seam can be achieved. At least one of the partial beams is preferably directed onto the respective electrode in a defocused manner at the beginning and at the end of the irradiation of the partial beams.

Each partial beam preferably remains on the respective electrode during irradiation. In other words, in the case of two sub-beams and two electrodes, a first of the two sub-beams preferably remains directed only at a first of the two electrodes, and the second of the two sub-beams only at the second of the two electrodes. In this way it can be avoided that a partial beam falls into an intermediate space or gap between the electrodes and heats up insulation or other material there. In addition, separate melt pools can be generated as a result. Once the electrode material, e.g. the copper, has been brought into the molten phase, the separate melt pools flow together to form a common melt pool. As a result, the formation of pores in the materially bonded connection or in the weld seam can be reduced.

The partial beams can preferably be deflected on the respective electrode, in particular linearly. The deflection can be parallel to or along an edge or side of the electrode. The partial beams can be moved back and forth on the respective electrode, for example in a direction perpendicular to a straight line connecting the electrodes or parallel to the opposite sides of the electrodes. For example, each sub-beam can be moved back and forth or oscillated along a predetermined path on the corresponding electrode. The oscillating movement or the predetermined path can be linear, circular, zig-zag, wavy, helical, 8-shaped or the like. The partial beams can be deflected by deflecting the laser beam before it is divided into the two partial beams. Alternatively, the partial beams can be deflected after the laser beam has been divided. For this purpose, the laser processing device can comprise a deflection unit for deflecting the laser beam and/or the partial beams. The deflection unit is preferably a linear or 1D deflection unit, ie set up for a linear deflection in only one direction. A one-dimensional (1D) deflection unit is significantly less expensive and more compact than a deflection unit that is set up for a 2D deflection or for a deflection in two mutually perpendicular directions. To deflect the laser beam, the deflection unit can be arranged between the collimation optics and the splitting optics. Alternatively, the deflection unit can be arranged between the splitting optics and the focusing optics in order to deflect the partial beams directly. In this case, the partial beams can be deflected independently of one another. The deflection unit can, for example, be an oscillation module, an ID scanner or a 2D scanner and/or comprise at least one mirror, in particular a galvanometer mirror. The deflection of the partial beams is preferably repeated regularly or periodically. The deflection of the partial beams can be referred to as position modulation of the partial beams. A position modulation amplitude or deflection amplitude and/or a position modulation frequency or deflection frequency and/or a position modulation speed or deflection speed can be set based on at least one of the following parameters: the positions of the electrodes; a size of the surface on which the edit point lies; a gap between the electrodes; a size and / or depth of the separate melt pools and / or the common seed melt pool; a radiation duration of the partial beams on the electrodes; a wavelength of the laser beam; and a power of the laser beam.

The electrodes are preferably arranged in such a way that the processing points or the surfaces of the electrodes which comprise the processing points lie on a plane perpendicular to the beam propagation direction of the laser beam. The electrodes can be arranged parallel or antiparallel to one another. In particular, in the case of a parallel arrangement of the electrodes, ends of the electrodes can point in the same direction, but in the case of an anti-parallel arrangement, ends of the electrodes can point in opposite directions. Ends of the electrodes are preferably arranged next to and/or adjacent to one another. The partial beams can be radiated onto the ends of the electrodes at the front. For example, a beam propagation direction of the partial beams can be arranged essentially parallel to the longitudinal axis of the electrodes.

The electrodes are preferably rod-shaped electrodes. The electrodes can have at least one flat side or plane surface and/or have a rectangular or square cross-section. Preferably, two flat sides of the electrodes are arranged opposite each other. For example, one end or a cross-section of the electrodes can have a width (or narrow side) of about 1 mm and a length (or long side) of about 5 mm.

The electrodes can be made of copper and/or aluminum or contain copper and/or aluminum. For example, the electrodes are or include hairpins or winding segments of a stator coil or a stator winding.

The laser beam preferably has wavelengths in the infrared range, for example between 780 nm and 1400 nm, in particular between 1000 nm and 1100 nm. This has the advantage that an inexpensive IR laser source can be used. However, the laser beam can also have a wavelength in the visible green or blue range, in particular in the range between 400 nm and 450 nm or between 510 nm and 550 nm.

An irradiated power of the two partial beams, i.e. the power of the laser beam, can be modulated or set based on at least one of the following parameters: a position modulation amplitude or deflection amplitude, a position modulation frequency or deflection frequency, a position modulation speed or deflection speed, the positions of the electrodes; a size of the surface on which the edit point lies; a gap between the electrodes; a size and/or depth of the separate weld pools and/or the common weld pool; a radiation duration of the partial beams on the electrodes; a wavelength of the laser beam; and a power of the laser beam.

character list

• 1 zeigt schematisch ein herkömmliches Scanner-Laserschweißverfahren;
• 2 zeigt schematisch eine Bearbeitungsvorrichtung gemäß einer Ausführungsform der vorliegenden Erfindung;
• 3 zeigt ein Diagramm eines Verfahrens gemäß einer Ausführungsform der vorliegenden Erfindung;
• 4 zeigt schematisch eine Bearbeitungsvorrichtung mit einem 1D Scanner gemäß einer Ausführungsform der vorliegenden Erfindung; und
• 5A und 5B zeigen schematisch alternative Anordnungen der beiden Elektroden.

The invention is described in detail below with reference to figures.

• 1 12 schematically shows a conventional scanner laser welding method;
• 2 shows schematically a processing device according to an embodiment of the present invention;
• 3 Figure 12 shows a diagram of a method according to an embodiment of the present invention;
• 4 shows schematically a processing device with a 1D scanner according to an embodiment of the present invention; and
• 5A and 5B show schematically alternative arrangements of the two electrodes.

Detailed description of the embodiments

Unless otherwise noted, the same reference numbers are used below for the same elements and those with the same effect.

2 shows a processing device for materially connecting workpieces with a high-energy processing beam according to an embodiment of the present invention. The invention is explained below using the example of a laser processing device for laser welding of two rod-shaped electrodes, but is not limited to this. The processing device can also use an electron beam for the material connection. Likewise, the electrodes can have a different shape.

The laser processing device comprises a laser processing head 100 for radiating a laser beam 10 onto the workpieces 1, 2. For example, the laser beam 10 generated by a laser source can be coupled into the laser processing head 100 via an optical fiber 11. The laser beam 10 is divided into two partial beams 10a, 10b by a splitting optics 50 arranged in the laser processing head 100, for example at least one optical wedge plate, at least one diffractive optical element, at least one freeform optics or at least one beam shaping optics. Preferably, the splitting optics 50 is collimated th laser beam 10 arranged so that the division into the two partial beams 10a, 10b based on the collimated laser beam 10 takes place. In other words, the splitting optics 50 can be arranged after a collimation optics 20 of the laser processing head 100 in the laser beam propagation direction. The two partial beams 10a, 10b can then be focused by focusing optics 60 for the machining process or the laser welding. Alternatively, separate focusing optics 60 can be provided for each partial beam 10a, 10b in order to set the focal positions of the two partial beams 10a, 10b independently of one another. The focusing optics 60 can also be arranged in front of the splitting optics 50 in the laser beam propagation direction, so that the splitting into the two partial beams 10a, 10b takes place based on the focused laser beam 10. Even if a division of the laser beam into exactly two partial beams 10a, 10b is described here, the disclosure is not limited to this. The laser beam 10 can be divided into two or more partial beams. Also, the number of electrodes is not limited to two, but the method can be used for welding two or more electrodes. The number of partial beams preferably corresponds to the number of electrodes to be welded to one another.

The focal position of the two partial beams 10a, 10b is preferably adjustable. The focal position can be adjusted, for example, by moving at least one of the following elements: the optical fiber 11, the collimating optics 20 and the focusing optics 60. The focal positions of the two partial beams 10a, 10b can be set together, i.e. both partial beams 10a, 10b can have the same focal position . Preferably, however, the focal positions of the two partial beams 10a, 10b can be set independently of one another, i.e. the focal positions of the two partial beams 10a, 10b can be different. In this way, a different distance between the electrodes and the laser processing head 100 can be compensated for.

The laser processing device also includes a detection unit 40 for detecting positions of the two electrodes 1, 2. For this purpose, the detection unit 40 can include, for example, an optical sensor, a photodiode, a camera and/or an optical coherence tomograph. The detection unit 40 can detect the position of the two electrodes 1, 2 in at least one direction perpendicular to the optical axis of the focusing optics 60 or perpendicular to a laser beam propagation direction. In the examples shown, the optical axis of the focusing optics 60 or the laser beam propagation direction extends in the z direction. An optical beam path of the detection unit 40 can be coupled into the laser beam path of the laser processing head 100 via a beam splitter 30, for example. Alternatively, the optical beam path of the detection unit 40 can be arranged outside of the laser processing head 100 and run at least partially inclined or parallel to the laser beam propagation direction. Preferably, the detection unit 40 can also detect a position of the electrodes 1, 2 along the optical axis of the focusing optics 60 or in the laser beam propagation direction (z-direction). In other words, a distance from each of the electrodes 1, 2 to the laser processing head 100 can be determined, for example in order to set a laser power or a focus position of the partial beams 10a, 10b based thereon. The detection unit 40 can be set up for process observation or monitoring, e.g. for pre-process or post-process monitoring.

In order to improve the position detection, an illumination unit (not shown) can also be provided. The lighting unit can be arranged on the detection unit 40 in order to couple light coaxially into the optical beam path of the detection unit. Alternatively, the electrodes are illuminated by the illumination unit independently of or outside of the laser processing head and/or the detection unit.

The two partial beams 10a, 10b are each directed onto one of the two rod-shaped electrodes 1, 2. The rod-shaped electrodes 1, 2 can in particular be hairpin electrodes or winding segments of a stator coil for an electric motor. The rod-shaped electrodes 1, 2 can be made of copper and/or aluminum. The rod-shaped electrodes 1, 2 are in 2 arranged parallel to one another, ie the end faces or the ends 1a, 2a of the rod-shaped electrodes 1, 2 point in the same direction. As a rule, there is a gap 30 between the rod-shaped electrodes 1, 2, for example due to insulating material 3 surrounding the rod-shaped electrodes 1, 2 in a lower region, or an imprecise arrangement, or the like. Each rod-shaped electrode is melted separately by the two partial beams 10a, 10b in order to form a separate melt pool on each rod-shaped electrode 1, 2. Due to the high surface tension of the electrode material, in particular copper, the two separate molten pools combine to form a common molten pool above a certain size, without essentially flowing into the gap 30 . In this way, an integral connection or a conductive contact between the rod-shaped electrodes can be produced with little formation of pores and without spatter.

The detection unit 40 is set up to determine a respective processing point A, B on each of the electrodes, onto which the respective partial beam 10a, 10b is directed. The processing point A, B can be determined on the respective electrode 1, 2 in such a way that it lies centrally on a surface of the electrode facing the laser processing head 100, in particular an end face. The processing points A and B are determined based on the detected position of the respective electrode 1, 2.

The laser processing device also includes a control unit 90 for controlling the laser processing device, ie for controlling at least one of the following components of the laser processing device: the laser processing head 100, a laser source, and the detection unit 40. The control unit 90 and the detection unit 40 can be integrated in one unit or separately be provided. The control unit 90 can receive data from or send data to the laser processing head 100 and the detection unit 40 . The control unit 90 is set up in particular to carry out a method according to embodiments of the present invention. The control unit 90 can exchange data with the detection unit 40 and/or the laser processing head (double arrow).

3 FIG. 12 schematically shows a flow chart of a method for the integral connection or welding of two electrodes according to embodiments of the present invention. In step S1, the positions of the electrodes 1, 2 are detected and a processing point A, B on each electrode 1, 2 is determined. In step S2, a laser beam 10 is divided into two partial beams 10a, 10b. In step S3, each partial beam 10a, 10b is directed onto the respective processing point A, B of the electrodes 1, 2 in order to form a separate melt pool on each electrode. The separate melt pools then combine to form a common melt pool. After solidification or cooling of the shared melt pool, there is a conductive contact with low resistance between the two electrodes.

The detection of the positions of the electrodes 1, 2 in step S1 preferably includes the detection of a lateral position of the two electrodes 1, 2 in at least one direction perpendicular to the optical axis of the focusing optics 60 or perpendicular to a laser beam propagation direction. In other words, the position and extent of a surface facing the laser processing head can be determined for each electrode. The examples shown are rod-shaped electrodes with a rectangular cross section. In order to detect the positions of the electrodes 1, 2, step S1 can additionally include irradiating the laser beam 10 along a measurement path and detecting a portion of the laser beam reflected by the electrodes. The detection of the positions of the electrodes 1, 2 in step S1 takes place here based on an intensity of the reflected portion of the laser beam detected along the measurement path. Optionally, the electrodes 1, 2 are arranged in a positioning device. The positioning device has a different reflectivity than the electrodes, so that based on the intensity of the reflected portion, it can be distinguished whether the laser beam is on the positioning device or on one of the electrodes.

After detecting the positions of the electrodes 1, 2, the processing points A, B can be defined on the surface. Advantageously, the processing point A, B is fixed centrally on the surface of the electrode 1, 2 facing the laser processing head 100.

Alternatively or additionally, when detecting the positions of the electrodes 1, 2 in step S1, an axial position of the electrodes 1, 2 along the optical axis of the focusing optics 60 or in the laser beam propagation direction (z-direction) can also be detected. In other words, detecting the positions of the electrodes 1, 2 in step S1 can include determining a distance from the respective electrode 1, 2 or from the respective processing point A, B. A focal position of at least one of the partial beams 10a, 10b can be set based on the axial positions of the electrodes 1, 2, which can differ from one another.

The laser beam 10 or the partial beams 10a, 10b preferably have a wavelength in the infrared range, in particular 1 μm. Although IR laser radiation couples less well into reflective materials such as copper or aluminum at room temperature than laser radiation with shorter wavelengths, e.g. in the visible range, they are much cheaper. In the molten phase, the absorption of IR laser radiation is comparable to laser radiation with shorter wavelengths.

During the irradiation of the two partial beams 10a, 10b in step S2, preferably at the beginning of the irradiation, a focal position of at least one of the partial beams 10a, 10b can be changed. For example, the focal position can be moved from a first position, in which the partial beam is defocused on the electrode, to a second position, in which the partial beam is focused on the electrode, ie the focus of the partial beam is on the electrode. The focal position at the first position, ie the defocused focal position, can be a focal position between the electrode and the laser processing head, ie above the electrode, or a focus position within the electrode. The focal position of the partial beams 10a, 10b can be the same and can be adjusted together. For example, a rapid focusing movement can generate the necessary laser power density at different levels in order to increase the surface temperature of the electrodes for better coupling of the laser beam or to compensate for different distances between the electrodes and the laser processing head 100 .

At the end of the irradiation, another focusing movement can take place. At the end of step S2, the focus position of at least one of the partial beams 10a, 10b is preferably changed from a position that is focused on the respective electrode to a defocused position. In this way, a surface of the welded connection can be smoothed.

In 4 a processing device according to a further exemplary embodiment is shown. The processing device of 4 essentially corresponds to the machining device 2 , except for the following differences. In contrast to the in 2 shown processing device, the laser beam is 10 in 4 laterally coupled into the processing head 100. Neither the in 2 processing head shown, nor the in 4 However, the processing head shown is limited to the respective coupling arrangement of the laser beam 10 .

As in 4 shown, the processing device according to a further exemplary embodiment comprises a deflection unit 70 for deflecting the laser beam 10 so that the partial beams 10a, 10b can be moved back and forth on the electrodes 1, 2 (see arrows in 4 ). The deflection unit 70 can include a 1D or 2D scanner. As a rule, however, a 1D scanner is preferred because it is cheaper and a linear deflection is usually sufficient. For example, the partial beams can be directed onto the respective processing points A, B in step S3 and then linearly deflected around the processing points A, B on the respective electrodes 1, 2. The linear deflection can take place parallel to or along an edge or side, in particular parallel to a longitudinal side or longitudinal axis, of a surface of the electrode 1, 2. The linear deflection preferably takes place parallel to opposite sides or surfaces of the electrodes or perpendicular to an imaginary connecting line between the two electrodes 1, 2. Each of the two rod-shaped electrodes preferably has at least one flat or level side on which the two electrodes 1, 2 opposite.

The deflection unit 70 can be arranged in front of the focusing optics 60 or in front of the splitting optics 50 in the laser beam propagation direction. In particular, the deflection unit 70 can be used as in 4 be arranged between the collimating optics 20 and the splitting optics 50 in order to deflect the laser beam 10 . In this case, the partial beams are deflected synchronously or parallel to one another on the respective electrodes 1, 2. However, the deflection unit 70 can also be arranged after the splitting optics 50 in the laser beam propagation direction, in particular between the splitting optics 50 and the focusing optics 60 . In this case, the deflection unit 70 can be set up to deflect the two partial beams 10a, 10b independently of one another.

Preferably, the two rod-shaped electrodes 1, 2, as in 2 and 4 shown, arranged so that their longitudinal axes are parallel to the laser beam propagation direction or to the optical axis of the focusing optics 60. In this case, the partial beams 10a, 10b are directed onto the electrodes 1, 2 at the front. In other words, the partial beams 10a, 10b can be radiated onto an end face or end face of the electrodes 1, 2.

As in 5A and 5B shown, the longitudinal axes of the two rod-shaped electrodes 1, 2 can also be aligned perpendicular to the laser beam propagation direction or to the optical axis of the focusing optics 60. In this case, the processing points A, B can be set on side faces of the rod-shaped electrodes, not on the end faces. In 2 and 4 the rod-shaped electrodes 1, 2 are aligned parallel to one another, so that their ends 1a, 2a point in the same direction. In 5A an alternative arrangement of the two rod-shaped electrodes 1 and 2 is shown. In 5A an anti-parallel arrangement of the electrodes is shown, with the ends 1a, 2a pointing in opposite directions. In 5B the rod-shaped electrodes 1, 2 are arranged parallel to each other, but the processing points A, B lie on side faces of the rod-shaped electrodes 1, 2.

According to the present invention, in a method for welding two electrodes, in particular rod-shaped electrodes, such as hairpins or winding segments of a stator coil, a partial beam of a machining beam is irradiated separately on each electrode. This allows a separate weld pool to be formed on each electrode. Due to the surface tension, the molten pools can combine to form a common molten pool and thus create a welded connection or weld seam. In this way spatter formation can be avoided and a pore-free welded connection can be achieved low contact resistance between the electrodes. In addition, the method according to the invention can be provided inexpensively. In particular, a deflection unit or at least a 2D scanner can be dispensed with. An IR laser source can also be used.

Claims (15)

Method for welding at least two electrodes (1, 2) by means of a laser beam (10), comprising: determining a processing point (A, B) on each of the electrodes (1, 2); Splitting the laser beam (10) into at least two partial beams (10a, 10b); and Radiating the partial beams (10a, 10b) onto one of the processing points (A, B) of the electrodes (1, 2) and forming a common molten pool for welding the electrodes (1, 2). procedure after claim 1 , wherein the electrodes (1, 2) are rod-shaped electrodes, hairpins or winding segments of a stator winding. A method according to any one of the preceding claims, wherein the electrodes (1, 2) are arranged substantially parallel to each other, and/or wherein the electrodes (1, 2) each have at least one flat side and are arranged with the flat sides facing each other lie. Method according to one of the preceding claims, in which the partial beams (10a, 10b) are radiated onto the ends (1a, 2a) of the electrodes (1, 2) at the front. Method according to one of the preceding claims, further comprising: detecting the positions of the electrodes (1, 2) before determining the machining points (A, B). procedure after claim 5 , wherein the positions of the electrodes (1, 2) include positions perpendicular to the laser beam propagation direction and the detection of the positions includes: - irradiating the laser beam (10) onto the electrodes (1, 2) along a measurement path; - detecting a portion of the laser beam reflected by the electrodes along the measuring path; and - determining the positions of the electrodes (1, 2) based on the reflected portion detected along the measurement path. procedure after claim 5 or 6 , wherein the detected positions of the electrodes (1, 2) include positions in the laser beam propagation direction and a focal position of at least one partial beam (10a, 10b) is adjusted based on the detected position of the respective electrode (1, 2). Procedure according to one of Claims 5 , 6 or 7 , The positions of the electrodes (1, 2) being detected by means of optical coherence tomography and/or by means of a camera and/or by means of image recognition and/or by means of photodiodes. Method according to one of the preceding claims, in which the partial beams (10a, 10b) are each moved on one of the electrodes (1, 2) during the irradiation. Method according to one of the preceding claims, in which the laser beam (10) and/or the partial beams (10a, 10b) are linearly deflected by a deflection unit (70) during the irradiation of the partial beams. Method according to one of the preceding claims, wherein during the irradiation of the partial beams (10a, 10b) in a first step at least one of the partial beams is directed defocused onto the respective electrode (1, 2) and in a subsequent second step the focal position of the at least one partial beam the processing point (A, B) on the respective electrodes (1, 2) is approached. Method according to one of the preceding claims, in which the electrodes (1, 2) consist of copper and/or aluminum or contain copper and/or aluminum. Method according to one of the preceding claims, wherein a wavelength of the laser beam (10) is in the infrared range, in particular in a range between 1030 nm and 1070 nm, or in the visible green range, in particular in a range between 505 nm and 570 nm, preferably at 515 nm, and/or in the visible blue range, in particular in a range from 405 nm to 500 nm or in a range between 440 nm and 460 nm, preferably at 450 nm. Method according to one of the preceding claims, in which the splitting of the laser beam (10) into the at least two partial beams (10a, 10b) takes place by splitting optics (40). Laser processing device for welding at least two electrodes (1, 2) by means of a laser beam (10), comprising: a detection unit (40) for determining a processing point (A, B) on each of the electrodes (1, 2), a laser processing head (100) to radiate of at least two partial beams (10a, 10b) each onto one of the processing points (A, B) of the at least two electrodes (1, 2), the laser processing head having splitting optics (30) for splitting the laser beam (10) into the at least two partial beams ( 10a, 10b); and a control unit configured to carry out a method according to any one of the preceding claims.

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