LASER WELDING DEVICE AND METHOD FOR MONITORING, WITH A LASER WELDING HEAD AND A MONITORING DEVICE

Description

[0001] The invention relates to claim 1 to the use of a welding device instead of a resistance welding device for welding two workpieces, which has a first feeding device for feeding a first workpiece and a second feeding device for feeding a second workpiece, as well as a positioning device by which the two workpieces are aligned with each other in at least one defined welding position, and which has a welding device by which welding of the two workpieces positioned relative to each other is possible, such that the welding device includes a monitoring device that detects the reflected radiation in the range of the wavelength of the laser beam(s) emitted from the laser welding head, as well as in the infrared range, preferably in a range between 1200 and 1700 nm or in one or more sub-ranges, and / or in the visible light range.preferably detected and evaluated in a range between 450 and 850 nm or in one or more sub-ranges of the aforementioned range.

[0002] Such a welding device is known and is used in particular to produce miniature contacts by welding a sequence of contact elements onto a metal strip. The contact elements, which are to be applied to the metal strip in a periodic sequence, are manufactured by cutting them from a suitable metal wire or strip and then positioning them at the welding point in successive strokes of the device. The welding is carried out by a resistance welding process known per se. However, resistance welding has the disadvantage that the device is subject to high wear and contamination and can only operate at a low stroke rate.

[0003] DE 10 2016 203 511 A1 describes a resistance welding device comprising two welding electrodes arranged opposite each other, each connected or connectable to a welding power source via a separate power supply path, for welding the weld metal to be placed between the electrodes. At least one of the two electrodes can be moved relative to the other electrode from an electrode-distance position to a welding position by means of a feed device, in order to ensure proper welding of the weld metal located between the electrodes. This feed device for the movable electrode has an electric motor, wherein the electric motor is a linear motor with a stator and a rotor guided linearly along a linear axis of motion, and the rotor includes the first electrode.Such resistance welding devices are preferably used in automated systems for the mass production of welded parts, with controlled weld metal feeders ensuring a continuous or pulsed feed of the weld metal in accordance with the welding cycle. The weld metal consists, for example, of sheet metal parts, wire sections, or the like to be joined together. Welding contact material onto contact carrier surfaces and welding cable ends onto sheet metal parts or the like is also possible by resistance welding using a resistance welding device in a mass production process.

[0004] In the mass production of precision parts, when welding contact material onto substrates, precise adherence to specified process parameters, such as welding current, electrode force, welding duration, etc., is crucial. For producing precise welds, a well-defined feed procedure for the welding electrodes to the workpiece is particularly important. The moving first electrode should make contact with the workpiece as smoothly as possible, without any impact or bounce, and then reposition itself precisely as the workpiece softens at the weld point. A high feed rate is especially necessary when welding contact material onto a substrate to ensure the molten contact material is reliably joined and to achieve high-quality, spot welds.The quality of the resulting welds depends not only on the precise control of the welding current but also on the dynamic-mechanical properties of the machine, to which the tracking behavior of the electrode feeder contributes significantly. The dynamic-mechanical behavior of the feeder in the known resistance welding machine is particularly influenced by the welding current cables, which must also move and are routed directly from the welding power source to the electrodes. The welding current cable connected to the electrode must always move along with the electrode during its feed. Since welding current cables are relatively long when routed freely externally and must have relatively large cross-sections to conduct high currents, they have a relatively large mass that must be moved.This can be reflected in a lack of sufficient reproducibility of the welding results, which is particularly disadvantageous in the mass production of electrical contacts, especially miniature contacts.

[0005] German patent DE 10 2019 115 554 A1 describes a processing device for laser processing of a workpiece, which uses a laser processing head that directs a processing laser beam onto the workpiece. The laser processing device is designed to operate as autonomously and independently as possible, thus enabling its use in production with minimal or no operator intervention. In such cases, process monitoring with a control system is employed, which autonomously detects and ideally corrects undesirable process behavior during laser processing. A camera monitoring system coaxial with the processing laser beam of the workpiece's processing zone is one example of such process monitoring. This system uses a processing laser beam with a spectral range that includes a wavelength of 1070 nm.Alternatively, direct diode lasers (wavelength typically 940 to 980 nm) and other solid-state lasers (wavelength typically 1030 to 1080 nm) can be used. A detector system captures the laser radiation reflected from the workpiece. The disadvantage of the known device is that it provides only inadequate results with regard to monitoring the weld quality of the weld produced with the known laser welding head.

[0006] DE 10 2020 104 462 A1 (disclosing the preamble of claim 1) describes a laser welding device in which the laser welding device is provided to have sensors by means of which the reflected laser light is detected and analyzed in the process radiation range, in the infrared range and in the visible light range.

[0007] EP 4 173 749 A1, derived from WO 2022 / 004610 A1, describes a laser device in which a laser welding head is designed to perform a two-dimensional scan of the workpiece to be processed. For this purpose, three optical sensors are provided, which are arranged on the laser welding head.

[0008] EP 2 489 459 A1 describes a method for welding components using a laser beam, in which the laser beam is moved along a joining zone of the components, melting the material of the components, which are primarily made of metallic material, in the area of ​​the joining zone. This molten material solidifies in a trailing region of the laser beam at a distance from the laser beam to form a weld seam, the molten material in the trailing region of the laser beam being heated at least indirectly by means of a heat source.

[0009] EP 0 593 894 B1 describes a tool for a stamping press with a laser welding system. The stamping press has a frame in which an eccentric shaft is rotatably mounted in bearings. Two connecting rods are mounted on this driven eccentric shaft, their lower ends pivotally connected to a ram that carries an upper tool. The frame of the stamping press supports a lower tool. In the known stamping press, a punch is inserted in the upper tool, which interacts with a die in the lower tool to stamp sheet metal parts from a strip of sheet metal. These parts are then assembled into individual sheet metal stacks in the lower tool. A laser beam source is connected to the frame and communicates via optical conductors with a focusing device located on the lower tool.During operation, the eccentric shaft rotates, and via the connecting rods, the ram, along with the upper tool, punches the individual sheet metal parts. With each stroke of the ram, the die deposits another sheet metal part onto the existing part. As soon as the punch moves a short distance away from the die during its upward stroke, the laser welding system emits an extremely short laser beam at the point of contact between the deposited sheet metal and the part above it, welding the two parts together. Because the cutting edge of the die and / or punch wears down during operation, the corresponding working surface must be periodically ground to resharpen the die's cutting edge.This means that the respective weld point in the die is subject to a relative change in position, so that a readjustment of at least the focusing device of the laser welding system is generally necessary. The focusing device has a predetermined focal length and a predetermined focus point that defines the weld point of two sheet metal parts. It is mounted on a support block and has a point where it rests against one side of the support block. This side of the support block, which acts as a guide surface for the focusing device, runs exactly perpendicular to the optical axis of the focusing device. The support block is machined and positioned at such a precise distance from the weld point and connected to the body of the lower tool with such precise fasteners that the optics of the focusing device accurately maintain a specific weld point.The support block is a clamp-shaped component with two cheeks surrounding a through-hole for mounting the focusing device. The two cheeks are separated at the top by a slot and connected by a screw bolt. Tightening the screw bolt clamps the focusing device securely in the support block. The working surface of the lower tool body acts as a positioning surface for the support block, and this positioning surface is aligned with the cutting edge of the die inserted in the lower tool body. The lower side of the support block, where it rests on the working surface of the lower tool body, acts as a guide surface, defining at least one vertical position of the focusing device within the support block. The location and position of the focusing device in the support block, among other things, determine the weld point at the die.The horizontal distance of the support block from the welding point, and thus particularly from the side of the support block, is determined by two positioning pins inserted into bores in the support block and the body of the lower tool. The support block itself is connected to the body of the lower tool by means of a screw bolt. The positioning pins and the screw bolt are aligned along their longitudinal axes, thus defining a plane in which the optical axis of the focusing device lies. According to the aforementioned publication, this allows the support block to be built extremely narrow, making it possible to mount several focusing devices of the laser welding system, acting on the same die, in a confined space. This enables two sheet metal parts to be welded together at multiple points within the sheet metal stack simultaneously.If the cutting edge of the die needs resharpening, the lower tool is removed and, with the focusing device already removed, the support block is detached from the lower tool body by loosening the screw bolt. The working surface can then be ground in the usual way to resharpen the various cutting edges. It is crucial that the grinding process removes not only the area of ​​the lower tool body, but also, simultaneously and to the same extent, the area of ​​the lower tool body's positioning surface, which determines the height of the support block and consequently the focusing device. After this processing, the support block can be easily reattached to the lower tool body and the focusing device can be reinstalled.This eliminates the need for a time-consuming and costly realignment, especially of the support block, to the welding point, which has not shifted relative to the positioning surface.

[0010] The stamping press with laser welding system described in the aforementioned publication does allow for the stamping of one sheet metal part and its welding to another within a single device. However, a disadvantage is that adapting the laser welding system to changing operating conditions, which require realignment of the laser beam, is extremely difficult.

[0011] DE 10 2016 203 511 A1 describes a resistance welding device comprising two opposing welding electrodes for welding the weld metal positioned between the electrodes. It is provided that at least one of the two welding electrodes can be moved relative to the other electrode from an electrode spacing position to a welding position by means of a feed device, in order to weld the weld metal between the two electrodes. The feed device includes an electric motor for moving the first welding electrode, wherein the electric motor is a linear motor with a stator and a rotor guided linearly along a linear axis of motion, and the rotor incorporates the first electrode.

[0012] It is therefore an object of the invention to propose measures to replace the resistance welding described above.

[0013] This problem is solved according to the invention (see claim 1) in that a beam conditioning unit with an inlet area and an outlet area is arranged in the housing, wherein at least one laser beam exiting from the fiber end of the at least one optical fiber is directed to the inlet area of ​​the beam conditioning unit and at least one laser beam exits from the outlet area of ​​the beam conditioning unit, which is guided through an outlet opening from the housing of the laser welding head, and that the distance between the fiber end of the at least one optical fiber and the inlet area of ​​the beam conditioning unit is variable, and that an end area of ​​at least one optical fiber is arranged to be displaceable in an axial direction in the housing of the laser welding head.

[0014] According to the invention, a laser welding device is used which advantageously allows the resistance welding previously used for welding such workpieces to be replaced by laser welding. The measures according to the invention advantageously enable the welding of two workpieces, in particular a band- or strip-shaped workpiece with a thin second workpiece, such as a metallic wire, to be carried out by means of a laser welding process. Such a measure has the advantage that the laser welding of the two workpieces can be carried out at a high cycle rate. Furthermore, the welding process is relatively clean and involves little wear, especially compared to resistance welding.Furthermore, the measures according to the invention have the advantage that no damage occurs to the contact surface, since the welding energy required for welding two workpieces, in particular two electrical contacts, is applied from one side only. The invention provides that—and this is of independent patent-establishing importance—the welding device according to the invention has a monitoring device for detecting radiation emitted during laser exposure of a weld point. Such a measure has the advantage that the quality of the weld point produced by the at least one laser beam emerging from the laser welding head according to the invention can be checked in a simple manner—preferably continuously—and / or the at least one laser beam can be controlled.

[0015] In the measures according to the invention, a welding device is advantageously used which is characterized in that, by detecting and evaluating the light reflected from the workpiece in the range of process radiation, i.e., the laser light used, as well as in the visible light range, preferably in the range between 400 and 850 nm, and / or in the infrared range, preferably in the range between 1200 and 1700 nm, improved statements about the weld quality of the welds produced with the welding device according to the invention can be made. Such a measure has the advantage that the quality of the weld produced by the at least one laser beam emerging from the laser welding head according to the invention can be checked and / or the at least one laser beam can be controlled in a simple manner – preferably continuously.

[0016] An advantageous embodiment of the invention provides that radiation reflected by the monitoring device of the laser welding device according to the invention is detected and evaluated in the infrared range, particularly in the mid-infrared range, specifically in a wavelength range between 1200 and 1700 nm, or in one or more sub-ranges thereof. The higher the proportion of reflected infrared radiation, the larger the weld spots typically are.

[0017] A further advantageous embodiment of the invention provides that the monitoring device detects and evaluates the reflected radiation not only in the wavelength range of the laser light emitted by the laser welding head, but also in a region of the visible light spectrum, preferably in a range between 400 and 850 nm, or in one or more sub-regions of the visible spectrum. Such a measure has the advantage that the temperature of the weld can be determined in a simple manner by detecting the reflected radiation in a region of the visible light spectrum. This makes it possible to adjust the power of the laser radiation, particularly to reduce it, if the temperature is too high, especially if it is above the melting point of the molten material, in order to counteract porosity of the weld.

[0018] A further advantageous embodiment of the invention – which is of independent patent-establishing significance – provides that the beam preparation unit is designed as a galvanometric beam preparation unit, in particular as a galvanometer scanner. Such a measure has the advantage that it enables, in a particularly simple manner, flexible adaptation of at least one laser beam to the processing operations carried out by the welding device according to the invention.

[0019] A further advantageous embodiment of the invention – which is itself of independent patent-establishing significance – provides that the distance between the fiber end of the optical fiber and the entry area of ​​the beam conditioning unit of the laser welding head is variable. These measures according to the invention advantageously create a compact laser welding head for a laser welding device, which allows for easy adjustment of the focus position and / or the focus diameter of at least one laser beam.

[0020] A further advantageous embodiment of the invention provides that the laser welding head used in the welding device according to the invention has a housing in which at least one optical fiber opens, through which a laser beam generated by an external radiation source can be supplied to the laser welding head, that a beam conditioning unit with an inlet area and an outlet area is arranged in the housing, wherein at least one laser beam exiting from the fiber end of the at least one optical fiber is directed to the inlet area of ​​the beam conditioning unit, and at least one laser beam exits from the outlet area of ​​the beam conditioning unit, which is guided through an outlet opening from the housing of the laser welding head, and that the distance between the fiber end of the at least one optical fiber and the inlet area of ​​the beam conditioning unit is variable.It is therefore provided that the optical fibers, or at least one of them, through which the laser light generated by an external radiation source can be supplied to the laser welding head, and / or the beam conditioning unit are movably, and in particular displaceably, mounted in the housing. This measure has the advantage that the focus position and / or the focus diameter of at least one laser beam exiting the laser welding head according to the invention can be changed by simply altering the relative distance between the fiber end of the optical fiber and the entry area of ​​the beam conditioning unit. It is preferred that the optical fibers, or at least one of them, which open into the housing of the laser welding head according to the invention, are displaceably arranged within it, while the beam conditioning unit is fixedly mounted within the housing.Such a measure has the advantage of a particularly simple geometric-constructive design, so that a laser welding head designed in this way can be advantageously compact.

[0021] A further advantageous embodiment of the invention provides that two or more optical fibers are supplied to the housing of the laser welding head according to the invention, and that the relative distance between the beam conditioning unit and at least two of the optical fibers entering the housing can be changed, in particular by moving these optical fibers. It is preferred that each of the at least two optical fibers can be moved independently of the other optical fiber. This measure has the advantage that the focus position and / or the focus diameter of at least two laser beams emerging from the laser welding head according to the invention can be changed in a simple manner.Another advantage of using two or more optical fibers to supply the laser light is that this allows the triggering of the laser pulses emerging from the individual fiber ends to be controlled in time.

[0022] A further advantageous embodiment of the invention provides that the laser welding head has at least one clamping unit with a clamping sleeve and a clamping ring, by which the at least optical fibers in the laser welding head can be fixed in at least two positions. Such a measure has the advantage that the relative position between the beam conditioning unit and the fiber end can be easily changed.

[0023] A further advantageous embodiment of the invention provides that the beam conditioning unit is designed as a galvanometer scanner. Such a measure has the advantage that it enables a particularly simple and flexible adaptation of at least one laser beam to the processing operations carried out by the laser welding head according to the invention.

[0024] A further advantageous embodiment of the invention provides that the laser welding head has an inner tube which is rotatably arranged in the housing and which accommodates the beam conditioning unit. By rotating the inner tube and thus the beam conditioning unit housed within it, a pivoting movement of the laser beam(s) exiting the housing can be achieved.

[0025] A further advantageous embodiment of the invention provides that the laser welding head has a cooling device through which heat can be dissipated from its housing. According to a preferred embodiment of this cooling device, a cooling channel is provided in a holder that accommodates the inner tube, and this cooling channel encloses the inner tube at least over a portion of its circumference.

[0026] Further advantageous embodiments of the invention are the subject of the dependent claims.

[0027] Further details and advantages of the invention can be seen in the exemplary embodiment, which is described below with reference to the figures. The figures show: Figure 1 schematic representation of a welding device, Figure 2 an enlarged representation of the welding area of ​​the welding device Figure 1Figure 3 shows a perspective view of a first laser welding head, Figure 4 shows a top view of the first embodiment of the Figure 3 , Figure 5 a section along line AA of the Figure 3 , Figure 6 a section along line BB of the Figure 3 Figure 7 shows a perspective view of a second laser welding head, Figure 8 shows a top view of the second embodiment of the Figure 7 , and Figure 9 shows a section along line CC of the Figure 8 .

[0028] In the Figure 1 and 2 Figure 200 shows a welding device for welding two workpieces W1 and W2 using a laser welding head 1. Figures 3 to 6 show a first laser welding head 1 and the Figures 7 to 9 a second laser welding head 100.

[0029] In Figure 1The schematic diagram shows the structure of the welding device 200. This device has a first feeding device 210, by means of which a first workpiece W1, here a metal wire, in particular a silver wire, can preferably be fed to the device 200 intermittently. This device also has a second feeding device (not shown in the figures), by means of which a second workpiece W2, in particular a metal strip, can be fed. The two workpieces W1 and W2 are best made of the Figure 2 as can be seen. Furthermore, the welding device 200 has a laser welding head 1 or 100, which will be described in detail below. The welding device 200 also has a cutting device 230, by means of which workpiece pieces, in particular miniature contact elements K, can be successively cut off from the first workpiece W1. These are then - as is best done from Figure 2As can be seen, from a positioning device 240 at a welding position S (see also Figure 2) on the second workpiece W2. A laser beam L emanating from the laser welding head 1 or 100 illuminates both workpieces W1 and W2 at the welding point S. In the case described here of manufacturing contact elements, in particular miniature contact elements K, by means of laser welding, it is preferred that the laser illumination is effected from the side of the second workpiece W2 opposite the contact element K positioned at the welding position S by the positioning device 240. Such a measure has the advantage that a surface coating present on the contact element K is not destroyed or at least not significantly damaged. It can be provided that the second workpiece W2 has an opening O at this position through which the laser beam L can directly pass through the workpiece W2 and illuminate the first workpiece W1 and, in particular, the contact element K.However, it is evident to the expert from the following description that the two aforementioned measures - applying pressure from the side opposite the contact element K and providing an opening O - are not mandatory.

[0030] The Figure 1 Furthermore, a holder 250 for the laser welding head 1 or 100 is shown, which is not important for a further understanding of the welding device 200 and is therefore not described in more detail.

[0031] The laser welding heads 1 and 100 used in the welding device 200 are generally known and are therefore only described below to the extent necessary for understanding their construction and function.

[0032] The laser welding head 1 has a housing 2 into which at least one optical fiber 3 opens, through which a laser beam generated by a radiation source (not shown) can be supplied to the laser welding head 1. Only a single optical fiber 3 is shown in the figures. However, it will be apparent to those skilled in the art from the following description that it is also possible to supply more than two optical fibers to the housing 2 of the laser welding head 1, from the ends of which at least one laser beam L emerges. For the sake of simplicity, however, the following description of the figures assumes that only a single optical fiber 3 is supplied to the laser welding head 1. The laser beam L emerging from the optical fiber 3 reaches a beam conditioning unit 5, in which it is split into two laser beams L1 and L2 and processed accordingly.The two laser beams L1 and L2 then pass to a deflecting mirror 6 and exit the housing 2 of the laser welding head 1 through an opening 7. A protective glass 8 is provided in the opening 7.

[0033] The beam conditioning unit 5 serves to condition the laser beam supplied to it via the at least one optical fiber 3, in particular to split it into a number of n partial beams, e.g., into n = 2 partial beams in the case of a bifocal laser welding head 1. It will be apparent to those skilled in the art from the following description that the aforementioned case of a bifocal laser welding head is merely exemplary. It is, of course, also possible to design the laser welding head 1 as a monofocal laser welding head (n = 1) or as a bifocal or multifocal laser welding head 1, from whose opening 7 two or more than two laser beams emerge. To achieve this, the beam conditioning unit 5 has a corresponding number of optical elements, in particular lenses, beam splitters, etc. It may be provided that the beam conditioning unit 5 is arranged in the housing 2 of the laser welding head 1 in a replaceable manner.This measure has the advantage that the laser welding head 1 can be quickly converted, e.g., from a monofocal to a bifocal or multifocal laser welding head (or vice versa). It is also possible, of course, to modify the beam processing unit 5 housed in the casing 2 instead of replacing it, e.g., by replacing one lens pack with another and / or by adding or removing one or more lens elements.

[0034] It is preferred that the beam conditioning unit 5 be designed as a galvanometric beam conditioning unit, in particular as a galvanometer scanner. Such a measure has the advantage that the focus position and / or the focus diameter of one or more laser beams can be changed in a simple manner.

[0035] In order to use such a laser welding head 1 in a tool of a machine tool, in particular a tool that allows simultaneous punching and welding of workpiece parts, it is necessary that the focus position of the laser beam(s) exiting the laser welding head 1 be aligned with one or more welding points required for the welding process of the workpiece. This must be done in particular with regard to their focus position and their focus diameter, i.e., the diameter of the laser beam L1 or L2 appearing on the workpiece at the welding point.

[0036] To facilitate this, the described laser welding head 1 is designed so that the optical fiber 3 is movably mounted within it, and in particular, is displaceable in an axial direction relative to the beam processing unit 5. Changing the distance between a fiber end 3a of the optical fiber 3 and a front entry area 5a of the beam processing unit 5 causes a change in the focus position of the laser beam(s) exiting from an exit area 5b of the beam processing unit 5.

[0037] To enable this in a simple manner in the described embodiment of the laser welding head 1, it is provided that – as is best done from Figure 5As can be seen, the optical fiber 3 is slidably mounted in a clamping unit 4. The clamping unit 4 has a clamping sleeve 4a, which interacts with a clamping ring 4b. By tightening the clamping ring 4b, the optical fiber 3 is clamped in the clamping sleeve 4a and thus fixed in a specific position within the housing 2 of the laser welding head 1. By loosening the clamping ring 4b, this clamping is released, allowing the optical fiber 3 to be moved to change the distance between the fiber end 3a and the entry area 5b of the beam conditioning unit 5. After the optical fiber 3 has been positioned in its desired new position, the clamping ring 4b is tightened again, so that the optical fiber 3 is fixed in this position within the housing 2.

[0038] However, it is apparent to those skilled in the art that the change in the relative distance between fiber end 3a and entry region 5b can be achieved in a different way than the construction described above. For example, it is possible to arrange the front end region 3' of the optical fiber 3 on a slide that is movable within the housing 2. A combination of the two aforementioned measures – clamping unit 4 and movable slide – is also possible.

[0039] It is also conceivable that the beam conditioning unit 5 is slidably arranged within the housing 2, so that by moving the beam conditioning unit 5 – with the optical fiber 3 remaining stationary – a change in the focus position and / or focus diameter of the laser beam(s) exiting the housing 2 can be achieved. A combination of both measures – a slidable beam conditioning unit 5 and a slidable optical fiber 3 – is also possible.

[0040] It is evident to those skilled in the art from the foregoing description that the measures listed therein are merely exemplary. The essential point is that the distance between the fiber end 3a of the optical fiber 3 and the entry region 5a of the beam conditioning unit 5 can be changed to adjust the focus position and / or the focus diameter of the laser beam L supplied to the beam conditioning unit 5. Whether only the optical fiber 3 or only the beam conditioning unit 5 is moved within the housing 2 of the laser welding head 1, or whether both of these components are moved, is of secondary importance. However, it is preferred that the beam conditioning unit 5 remains stationary and that the change in the relative distance between its entry region 5a and the fiber end 3a of the optical fiber 3 is achieved by moving the optical fiber 3, in particular by shifting it in the axial direction.

[0041] As already explained above, the described laser welding head 1 is not limited to the configuration in which only a single optical fiber 3 is supplied to the housing 2. Rather, it is possible to use two or more optical fibers 3 to supply the laser light generated by an external radiation source to the laser welding head 1. It is then preferred that not only the relative distance between the entry region 5a of the beam conditioning unit 5 and the fiber end 3a of the optical fiber 3 can be changed, but that such a measure can be implemented for at least one further, and preferably all further, optical fibers. It is again preferred that at least one of the further optical fibers is movably arranged, in particular axially displaceable, in the housing 2 of the laser welding head 1, as described, for example, for the optical fiber 3.

[0042] Preferably, the laser beam(s) L1, L2 emerging from the laser welding head 1 are not only aligned with respect to their focus position, but their angular position is also variable. The following description assumes a bifocal laser welding head 1. However, it is clear to those skilled in the art that this does not limit the generality of the following descriptions.

[0043] In the functional diagram located in the lower left corner of the Figure 5 Two laser beams, L1 and L2, are schematically represented by circles P1 and P2. It is assumed that circles P1 and P2 represent the laser beams L1 and L2 emerging from the laser welding head 1 in its current configuration.

[0044] In order to align the laser beams L1 and L2 from the positions represented by circles P1 and P2 to the positions represented here by circles P1' and P2', the laser welding head 1 described above must be configured as follows: Figure 5 It is evident that an inner tube 9 is rotatably mounted in the housing 2. The beam conditioning unit 5 is arranged in the inner tube 9, so that a rotation of the inner tube 9 also rotates the beam conditioning unit 5, thereby achieving the change in the angular alignment of the laser beams L1, L2 described above.

[0045] Another preferred design now provides that – as can best be seen from the Figure 6As can be seen, the laser welding head 1 has a cooling device 10 which allows heat to be dissipated from the interior of the housing 2, in particular to cool the beam conditioning unit 5. For this purpose, it is preferably provided that the inner tube 9, which is held in a holder 11, is at least partially surrounded by a cooling medium K. The cooling medium K is supplied to the holder 11 through an inlet opening 11a and exits it through an outlet opening 11b. The cooling medium K enters through the inlet opening 11a and then flows through a cooling channel 11c of the holder 11, which extends from the inlet opening 11a to the outlet opening 11b. Preferably, the cooling channel 11c is continuous. Compressed air is preferably used as the coolant, but it is also possible to use a liquid or other gaseous coolant.

[0046] In the Figures 7 to 9A second laser welding device with a laser welding head 100 is now described, which corresponds to the basic structure of the first laser welding device. Corresponding components are therefore designated with the same reference numerals and are not described again with regard to their structure and function. The laser welding head 100 corresponds to the first laser welding head 1, but has a monitoring device, generally designated 110, for the processing quality, in particular the weld quality, which is achieved when a workpiece is exposed to at least one laser beam L1, L2 emerging from the housing 2 of the laser welding head 100. As can be seen from the Figure 6 and 7As can be seen, this monitoring device 110 is mounted on the housing 2 of the laser welding head 100. This has the advantage that a compact design of the laser welding device consisting of the laser welding head 100 and the monitoring device 110 can be achieved.

[0047] However, it is obvious to a person skilled in the art that such a mounting of the monitoring device 110 on the housing 2 of the laser welding head 100 is not mandatory. It is also possible to provide the monitoring device 110 externally to the welding head, so that a laser welding head 1 can also be used in accordance with the Figures 1 to 4 can be used in the described laser welding device.

[0048] The Figure 9 now shows a section along line CC of the Figure 6 The laser welding head 1 is again recognizable, as it is in Figure 3The details described for the design of the laser welding head 1 of the first embodiment apply accordingly to the laser welding head 100.

[0049] The laser welding head 100 differs from that of the first laser welding head in that a deflecting mirror 116 is semi-transparent, so that while the laser beams L1, L2 exiting the beam conditioning unit 5 are deflected – as with the deflecting mirror 6 of the first – radiation S reflected from the workpiece, which enters through the opening 7, passes through the deflecting mirror 116 and reaches an opening 118 of the housing 2 via a beam path 117 – which is not present in the first design. A measuring head 111 is arranged above this opening 118, which serves to detect the radiation emitted by the workpiece and, in particular, by the weld area. For this purpose, the described embodiment provides that the measuring head 111 has a deflecting mirror 126, which deflects the beams supplied to the measuring head 111 and directs them via a collimating lens 127 to a sensor arrangement 120.Signal lines 121 then carry the measurement signals from the sensor arrangement 120 to an evaluation unit (not shown).

[0050] It is preferred that the sensor arrangement 120 of the monitoring device 110 evaluates the radiation S reflected from the workpiece and, in particular, from the weld point in at least two different ranges, namely in the range of process radiation, i.e., the laser light used, e.g., in the wavelength range of 1460 nm for a YAG laser, and in the range of visible light, for example, in the wavelength range between 400 and 850 nm, and / or in the infrared range, i.e., for example, in the wavelength range between 1200 and 1700 nm. It is evident to those skilled in the art that the detection and / or evaluation of the reflected radiation S in the range of visible light and / or in the infrared range need not be carried out over the entire bandwidth of the aforementioned wavelength ranges, so that it is quite sufficient that the radiation S is detected in one or more sub-ranges of these wavelength ranges between 400 and 850 nm and / or 1200 nm, respectively.between 1200 and 1700 nm is recorded and evaluated.

[0051] A high intensity of reflected process radiation generally indicates that the weld points are insufficiently formed: A high proportion of reflected process radiation characterizes that a sufficient melt has not yet formed at the weld point.

[0052] The higher the infrared component of the reflected radiation S, the larger the weld points usually are.

[0053] Measuring the reflected radiation S in the visible range allows for a simple determination of the weld temperature. This helps to avoid excessively high temperatures, which can lead to porosity in the weld.

[0054] It is generally sufficient to detect and evaluate the reflected radiation S not only in the wavelength range of the process radiation but also in one of the other two ranges, i.e., either in the visible light range or in the infrared range. However, it is preferred that the reflected radiation S be detected and evaluated in all three of the aforementioned ranges: process radiation, visible light, and infrared radiation.

[0055] The currently detected values ​​are compared by the evaluation unit with previously acquired data. This makes it possible, in a simple manner and preferably continuously, to check the quality of the weld area produced by the at least one laser beam L1, L2 exiting the laser welding head 1 and / or to adjust the at least one laser beam L1, L2 accordingly. In particular, an improvement in weld quality can be achieved by changing the focus position and / or the focus diameter of at least one laser beam L1, L2.

Claims

1. Use of a welding device (200) instead of a resistance welding device for welding two workpieces, wherein a welding device (200) for welding a first workpiece (W1) and a second workpiece (W2) is used, wherein the welding device (200) comprises a first feeding device (210), by means of which a first workpiece (W1) can be fed to the welding device (200), and a second feeding device, by means of which a second workpiece (W2) can be fed to the welding device (200), wherein the welding device (200) has a welding system for welding the two workpieces (W1, W2), in that the welding device (200) has a laser welding head (1; 100), by means of which the welding energy required for welding the two workpieces (W1, W2) can be supplied, wherein the welding device (200) has got a controlling system (110) having a sensor arrangement (120), by which radiation (S), which is reflected by the workpiece (W) being impacted by one laser beam or the laser beams (L1, L2) exiting the laser welding head (1; 100), can be detected, and wherein the controlling system (110) evaluates the radiation (S) reflected by the workpiece (W) in at least two wavelength regions, wherein the controlling system (110) detects and evaluates the reflected radiation (S) in a region of the wavelength of the at least one laser beam (L1, L2) exiting the laser welding head (1; 100) as well as in an infrared region, in particular in the region between 1200 and 1700 nm or in one or several partial regions thereof, and / or in the region of visible light in particular in the region between 450 and 850 nm or in one or several partial regions, characterized in that the laser welding head (1; 100) has a housing (2), into which at least one optical fiber (3) is led, by means of which a laser beam (L) generated by an external radiation source can be fed to the laser welding head (1), that in the housing (2) a beam processing unit (5) having an entry region (5a) and an exit region (5b) is provided, whereby at least one laser beam exiting a fiber end (3a) of the at least one optical fiber (3) is guided to the entry region (5a) of the beam processing unit (5) and exits the laser beam processing unit (5) through the exit region (5b), said laser beam being led through an outlet opening (7b) of the housing (2) of the laser welding head (1), that the distance between the fiber end (3a) of the at least one optical fiber (3) and the entry region (5a) of the beam processing unit (5) can be altered, and that an end region (3') of at least one optical fiber (3) can be displaced in an axial direction in the housing (2) of the laser welding head (1).

2. Use of a welding device according to claim 1, characterized in that the laser welding head (100) has a deflection mirror (116) so that the radiation (S) reflected by the workpiece (W) reaches an opening (118) of the housing (2) via a beam path (117).

3. Use of a welding device according to one of the preceding claims, characterized in that a measuring head (111) is arranged above the opening (118) of the housing (2) of the laser welding head (100), and that the measuring head (111) has got a further deflection mirror (126), which deflects the beams supplied to the measuring head (111) and guides them to the sensor arrangement (120).

4. Use of a welding device (200) according to one of the previous claims, characterized in that the optical fiber (3) or at least one of the optical fibers (3) and / or the beam processing unit (5) are arranged in the housing (2) relatively movable to each other.

5. Use of a welding device (200) according to one of the previous claims, characterized in that the beam processing unit (5) is a galvanometric beam processing unit.

6. Use of a welding device (200) according to one of the previous claims, characterized in that the laser welding head (1; 100) comprises at least one clamping unit (4) by means of which at least one of the optical fibers (3) can be fixed in the housing (2) in at least two positions.

7. Use of a welding device (200) according to one of the previous claims, characterized in that an inner tube (9) is arranged in the housing (2), and that the beam processing unit (5) is accommodated in said inner tube (9), and that the inner tube (9) is arranged preferably rotably in the housing (2) of the laser welding head (1; 100).

8. Use of a welding device (200) according to one of the previous claims, characterized in that the laser welding head (1; 100) has a cooling system (10), through which heat can be dissipated from the interior of the housing (2), and that preferably in a holder (11) supporting the inner tube (9) at least one cooling channel (11c) of the cooling system (10) is arranged, to which a cooling medium (K) can be fed, and that further preferably the cooling channel (11c) extends around at least a part of the circumferential region of the inner tube (9) accommodating the beam processing unit (5).

9. Use of a welding device (200) according to one of the previous claims, characterized in that the welding device (200) comprises a positioning device (240), by means of which a portion separated from the first workpiece (W1) can be positioned at the welding point (S) on the second workpiece (W2).