Laser processing head and method for processing a workpiece

Abstract

The invention relates to a laser processing head and a method for processing a workpiece. A problem addressed by the invention is that of providing a laser processing head and a method for processing a workpiece by means of which a large number of possibilities for processing workpieces is achieved. For this purpose, a laser processing head for processing a workpiece by means of a laser beam is provided, comprising at least one scanning device for deflecting the laser beam and at least one collimator for collimating the laser beam, wherein during operation the at least one collimator can be moved in the propagation direction of the laser beam, whereby a diameter (D) of the laser beam incident on the workpiece can be changed.

Description

[0001] Laser processing head and method for processing a workpiece

[0002] The invention relates to a laser processing head and a method for processing a workpiece according to the preamble of the independent claims.

[0003] In the technical field of laser processing of workpieces, laser processing machines with controlled laser processing heads are widespread. These laser processing machines comprise a laser source for providing laser power, particularly for cutting or welding workpieces. The laser processing head usually includes various components and optics with which a controlled laser beam is precisely delivered to processing positions on the workpiece. Controlled deflection optics in the laser processing head are known. These can be quickly tilted or pivoted and deflect the processing laser beam along two vertical axes, allowing any two-dimensional cutting or welding geometries to be achieved on the workpiece. Sensor devices on the laser processing head are also known. These record the processed geometries on the workpiece for quality control and other functions, such as controlling the processing process.

[0004] An object of the invention is to provide a laser processing head and a method for processing a workpiece, with which a plurality of processing possibilities of workpieces are achieved.

[0005] This object is achieved according to the invention by a laser processing head and a method for processing a workpiece according to the independent patent claims.

[0006] A laser processing head is provided for processing a workpiece by means of a laser beam, comprising at least one scanning device for deflecting the laser beam and at least one collimator for collimating the laser beam, wherein the at least one collimator is movable during operation along the propagation direction of the laser beam, whereby a diameter D of the laser beam impinging on the workpiece can be changed.

[0007] Furthermore, a method for machining a workpiece by means of a laser beam is provided, comprising the following process steps:

[0008] - Providing a laser processing head comprising at least one scanning device for deflecting the laser beam and at least one collimator for collimating the laser beam;

[0009] - Changing a diameter D of the laser beam incident on the workpiece by moving the collimator during operation along the propagation direction of the laser beam.

[0010] Embodiments of the invention are described in the dependent claims.

[0011] In this case, a spot diameter can preferably be reduced from an initial diameter to an intended machining diameter at a starting point of a machining operation. Alternatively or simultaneously, the power of the laser beam can be increased from an initial power to a machining power intended for machining the workpiece. Furthermore, it is conceivable that at an end point of a machining operation, the spot diameter is increased from the machining diameter intended for machining the workpiece to a predetermined extension diameter. Alternatively or simultaneously, the power of the laser beam intended for machining the workpiece can be reduced from the machining power to an intended extension power.

[0012] In one example of the invention, the at least one scanning device has a first scanner mirror for scanning the laser beam in a first direction on the workpiece and a second scanner mirror for scanning the laser beam in a second direction on the workpiece. The term "scanning" by means of the scanning device refers to the controlled and targeted deflection or deflection of the laser beam from the incoming laser beam path. The scanning device is understood in particular to mean any apparatus designed to deflect the laser beam in a controlled manner. The processing laser beam can thus be applied to any variable positions on the workpiece.

[0013] In one example, the collimator comprises a convex lens system or a convex lens. Lens systems are particularly simple to construct and simultaneously capable of effectively shaping the laser beam. The convex lens system comprises at least one convex lens, optionally also additional optical lenses.

[0014] In a further example of the invention, the laser processing head comprises at least one deflecting mirror in the propagation direction of the laser beam behind the scanning device, at least one objective for focusing the laser beam onto the workpiece, and a sensor system for detecting radiation from the workpiece being processed. The deflecting mirror deflects the laser beam deflected by the scanning device in the laser processing head toward the workpiece, approximately in a perpendicular direction. The objective focuses the laser beam from the deflecting mirror in a suitable manner onto the workpiece, preferably into a focal plane that lies on the workpiece in a processing position. The sensor system detects the radiation, process radiation generated during processing of the workpiece, or other radiation, and provides data relating to the processing on the workpiece, such as the weld penetration depth, the seam position, or the seam geometry.The sensor system is advantageously used to monitor laser processing by the laser processing head and further provides data for controlling and regulating the laser processing. The sensor system can comprise a camera and / or an interferometer. The camera preferably detects the process radiation or the process light generated by the interaction of the laser beam with the workpiece material. The interferometer preferably detects radiation emitted by the interferometer itself and reflected by the workpiece. A beam splitter is provided to guide radiation to the sensor system. This beam splitter transmits the laser beam to the workpiece and deflects the radiation from the workpiece to the sensor system.

[0015] In a further example of the invention, the laser processing head has a rotatable process nozzle which supplies a process medium for adapting the process nozzle to a direction of movement of the laser beam along the workpiece.

[0016] In another example, a laser source delivers a variable laser power to the laser processing head via a laser light cable. The laser source typically generates the laser beam, which is then guided to the laser processing head via the laser light cable. In this example, the laser power at the laser source is controlled so that the laser beam has different intensities and the workpiece is exposed to correspondingly different energies, which influence the processing result. Furthermore, the beam movement of the laser beam, in combination with the diameter D controlled by the movable collimator, allows the intensity distributions of the laser radiation to be precisely adjusted on the workpiece.

[0017] Further advantages of the invention will become apparent from the description and the drawings. The embodiments shown and described are not intended to be exhaustive, but rather serve as examples for describing the invention.

[0018] The invention is described by way of example with reference to the following figures.

[0019] Fig. 1 shows a schematic perspective view of a laser processing head with a scanning device, a laser source connected via a laser light cable and a control device according to an example of the invention;

[0020] Fig. 2 shows a schematic side view of a laser processing head with a path of a laser beam to a workpiece according to an example of the invention; Fig. 3 shows various top views of geometries of laser beam spots, which are implemented with a laser processing head according to an example of the invention.

[0021] Fig. 1 shows a schematic perspective external view of a laser processing head 10 according to an example of the invention. The laser processing head 10 is an essential component of a laser processing machine and is controlled by robots. The laser processing head 10 comprises a coupler 17, which is connected to a fiber optic cable 16 for coupling laser power from a laser source 15 into the laser processing head 10. The laser source 15 can be designed in various ways, for example as a solid-state laser source, and generates a laser beam 12. The laser processing head 10 and the laser source 15 are signal-connected to at least one control device 50. Furthermore, the laser processing head 10 comprises a scanning device 22, which includes various optics for two-dimensionally deflecting the laser beam 12 in the laser processing head 10, i.e., for the simultaneous, controlled deflection of the laser beam in two spatial directions.This two-dimensional deflection or deflection of the laser beam 12 is referred to as wobbling. The laser processing head 10 further comprises a housing 36 connected to the scanning device 22, in which further optical elements are mounted. The scanning device 22 can also be integrated into the housing 36. The laser beam 12 is guided into the housing 36 of the laser processing head 10 and deflected to an exit opening 48. At the exit opening 48, the laser beam 12 leaves the laser processing head 10 during operation. In this example, the laser processing head 10 comprises a sensor system 40 connected to the scanning device 22. The sensor system 40 comprises a camera and / or an interferometer for detecting signals from a workpiece 14 to be processed. The camera detects process radiation from the workpiece 14, which is fed to the camera by the laser processing head 10.The camera has narrowband illumination for wavelength-selective recording, which is independent of process radiation or process lighting because it can be easily filtered, as well as for recording images of the workpiece 14, which are evaluated via subsequent image processing in the control device 50. The interferometer, which is alternatively or additionally included in the sensor system 40, typically transmits a low-power laser beam through the laser processing head 10, which is reflected by the workpiece 14, reflected back by the laser processing head 10 to the interferometer, and interferes with a reference beam. In particular, the low-power laser beam can be aligned coaxially with the laser beam 12 from the laser source 15. As an alternative to the interferometer, the sensor system 40 can comprise a line laser.With the line laser, the distance between the laser processing head 10 and the workpiece 14 is determined together with the camera using the triangulation principle. In all three cases, data relating to the processing process is determined, transmitted to the control device 50, and further processed. This data includes, for example, data on the weld seam, the penetration depth, and / or the weld geometry.

[0022] Fig. 2 shows a schematic side view of components of the laser processing head 10 to further explain its functionality. The divergent laser beam 12, shown in dashed lines, exits the fiber optic cable 16, shown in section, to a collimator 30, which is arranged in the laser processing head 10. The coupler 17 for connecting and coupling the laser beam 12 is not shown in Fig. 2. In this example, the collimator 30 is a convex lens, which provides a nearly parallel beam path of the laser beam 12 at the exit of the lens, in Fig. 2 below the collimator 30, in the direction of the path of the laser beam 12; the beam path or propagation of the laser beam 12 is changed from divergent to parallel to convergent. The collimator 30 can comprise additional lenses, such as a convex lens system consisting of several convex lenses. After the collimator 30, the laser beam 12 is fed to the scanning device 22, which is shown in Fig.2 is schematically shown as a dashed rectangle. The scanning device 22 comprises a first scanner mirror 24 and a second scanner mirror 26, from which the laser beam 12 is reflected one after the other. The first scanner mirror 24 and the second scanner mirror 26 are controlled by the control device 50, wherein the first scanner mirror 24 deflects the laser beam 12 in a first axis and the second scanner mirror 26 simultaneously deflects the laser beam 12 in a second axis perpendicular to the first axis. Consequently, the laser beam 12 is deflected by the scanning device 22 in two spatial dimensions. The first scanner mirror 24 and the second scanner mirror 26 are usually driven by fast galvanometer scanners with motors from the control device 50. The scanning device 22 can also be referred to as a 2D scanner.After the scanning device 22, the laser beam 12 strikes a deflection mirror 31 in the laser processing head 10, which deflects the laser beam 12 toward a beam splitter 38, in this case in a vertical direction. The deflection mirror 31 is installed immovably in the laser processing head 10. The laser beam 12, which strikes the beam splitter 38 from above in Fig. 2, passes through the beam splitter 38 essentially unhindered and is guided to an objective 42, which focuses the laser beam 12 onto the workpiece 14. The focal plane of the laser beam 12 is adjusted by the objective 42 approximately to the distance between a process nozzle 46 and the workpiece 14. Behind the lens 42 of the laser processing head 10, viewed in the direction of the laser beam 12, a protective glass 44 is arranged which protects the optics of the laser processing head 10 from external influences and ablation of the workpiece 14.The laser beam 12 exits the laser processing head 10 at the exit opening 48 and strikes the workpiece 14 to be processed. The process nozzle 46 is arranged rotatably, wherein the angle of rotation of the process nozzle 46 is controlled by the control device 50 such that the orientation of the process nozzle 46 corresponds to the impact positions of the laser beam 12 on the workpiece 14. The rotation of the process nozzle 46 consequently causes the process medium to strike the workpiece 14 at the same positions to which the laser beam 12 is directed. The laser beam 12 is shifted in the direction of its path along the workpiece 14 by an angle α corresponding to the controlled deflection of the first scanner mirror 24 and the second scanner mirror 26. Typically, there is a relative movement between the laser processing head 10 and the workpiece 14 during operation.The controlled pivoting of the first scanner mirror 24 and the second scanner mirror 26, approximately by an angle a, results in the processing positions being shifted accordingly by an angle a during the relative movement. A weld seam then runs offset by the angle a without pivoting. The control device 50 can specify any desired angle of rotation for the scanning device 22 and thus orient the laser beam 12 as desired on the workpiece 14.

[0023] Due to the described controlled deflection of the laser beam 12 in the scanning device 22, the laser beam can cover any two-dimensional geometries or shapes on the workpiece 14, for example, creating curved weld seams. A process medium, such as process gas, is supplied in a targeted manner using the controlled, rotatable process nozzle 46, which follows the laser beam 12 deflected in the scanning device 22.

[0024] The sensor system 40, which comprises at least one camera, detects radiation from the machined workpiece 14, which arises as an interaction of the laser beam 12 impinging on the material of the workpiece 14. Alternatively, the sensor system 40 comprises an interferometer, which receives the low-power laser beam emitted by the interferometer and reflected by the workpiece 14. In both cases, the radiation from the workpiece 14 travels in the direction of the beam splitter 38, through which the radiation is transmitted and reflected in the direction of the sensor system 40, approximately at a right angle in Fig. 2. Alternatively, the sensor system 40 is arranged near the deflection mirror 31, whereby the beam splitter 38 becomes obsolete. In this alternative, the reflected radiation or the process radiation from the workpiece 14 takes the same path as the laser beam 12 without beam splitting. The reflected radiation or the process radiation from the workpiece 14 is shown in Fig.2 is shown with dashed lines on an arrow pointing toward beam splitter 38 and an arrow pointing toward sensor system 40. Sensor system 40 is signal-connected to control device 50 and receives and processes the data from sensor system 40.

[0025] The collimator 30, located near the entrance of the laser processing head 10 behind the fiber optic cable 16, is movable along the propagation direction of the laser beam 12, in Fig. 2 in the vertical direction up and down. The control device 50 sends signals to a drive, a motor, on the collimator 30, which moves the collimator 30 accordingly. Due to the change in the position of the collimator 30, the beam path of the laser beam 12 impinging on the collimator 30 is changed in such a way that a diameter D of the laser beam 12 impinging on the workpiece 14 is changed. The diameter D of the laser beam 12 on the workpiece 14 is adjusted accordingly in a controlled manner. This controls not only the extent of the interaction area but also the energy input of the laser beam 12 into the workpiece 14.

[0026] The described combination of changing the diameter D of the laser beam 12, the beam diameter, at the surface of the workpiece 14 with the two-dimensional alignment of the laser beam 12 by the scanning device 22 enables more flexible applications of the laser processing head 10 with regard to the geometries and the course of weld seams and higher-frequency laser processing.

[0027] Fig. 3 shows various top views of geometries of spots or tracks of the laser beam 12 on the workpiece 14, which are produced with a laser processing head 10 according to an example of the invention. A spot is defined as an area of ​​a laser beam 12 impinging on the workpiece 14 at a given moment. A sequence of instantaneously recorded spots results in a seam profile during a welding process. The top row in Fig. 3 shows three different geometries of spots which are caused solely by changing the laser power at the laser source 15 by the control device 50. The higher the laser power or the amplitude of the laser power is set, the greater the extent a of the geometry, with the extent a being greatest on the right-hand side of the top row in Fig. 3.The processing direction by the laser processing head 10, the relative movement of the laser processing head 10 to the workpiece 14, is perpendicular to the extent a, i.e. the extent a refers to the width of the resulting weld seam at different laser powers. In the second row according to Fig. 3, three examples of a changed orientation of the laser beam 12 are shown. The extent a of the geometry is unchanged from the top row, so that the extents a in Fig. 3 correspond column by column with the smallest extent a of the laser power in the middle. The scanning device 22 has deflected the laser beam 12 by the same angle a for all three geometries in the second row, so that the alignment or orientation of the laser beam 12 on the workpiece 14 is changed by the angle a compared to the undeflected scanning device 22. In the third row according to Fig.3 shows the orientation of the geometry of the spots or tracks as in the first row without rotation by the first scanner mirror 24 and the second scanner mirror 26 of the scanning device 22 and the same extension a corresponding to an amplitude of a laser power at the laser source 15 as in the top two rows according to Fig. 3. In the three geometries in the third and fourth row, the collimator 30 is moved or displaced in a controlled manner compared to the two top rows, with the effect that the diameter D of the spots is increased. The diameter D is defined here as the length in the feed direction of the workpiece 14 perpendicular to the extension a. In the third row, three identical diameters D are shown corresponding to a position of the scanning device 22, with three different extensions a corresponding to three different laser powers.The fourth row shows the same diameters D and the same dimensions a of the geometries as in the third row, with the orientation of the geometries being changed compared to the geometries of the third row according to a controlled alignment of the laser beam 12 by the scanning device 22. Fig. 3 shows exemplary geometries achieved by combining the features of the laser processing head 10. The geometries according to Fig. 3 refer to individual spots and are continued arbitrarily along welding paths. During operation, the extent a and the diameter D of the spot, as well as the orientation with the angle a, can be changed independently of one another, individually or jointly, according to programmed instructions in the control device 50.

[0028] The laser processing head 10 and the method for processing the workpiece 14 enable switching from deep penetration welding to thermal conduction welding and vice versa during operation by changing the laser power at the laser source 15 and / or by changing the diameter D of the spot of the laser beam 12 on the workpiece 14 by moving the collimator 30. The control device 50 can dynamically adjust the spot of the laser beam 12 with oscillating movements of the spot at an adjustable frequency on the scanning device 22, which indicates the pivoting frequency of the first scanning mirror 24 and the second scanning mirror 26. The design of the seam path of the weld path is selected in the control device 50 by the operator of a laser processing machine. The seam path of the weld seam can, for example, be circular, loop-shaped, C-shaped, or triangular.

[0029] List of reference symbols

[0030] Laser processing head laser beam

[0031] Workpiece Laser source Fiber optic cable

[0032] Coupler Scanning device first scanner mirror second scanner mirror Collimator Deflecting mirror

[0033] Housing beam splitter sensor system

[0034] Lens Protective glass Process nozzle Outlet opening Control device

Claims

Claims: Laser processing head (10) for processing a workpiece (14) by means of a laser beam (12), comprising at least one scanning device (22) for deflecting the laser beam (12) and at least one collimator (30) for collimating the laser beam (12), characterized in that the at least one collimator (30) is movable during operation along the propagation direction of the laser beam (12), thereby allowing a diameter D of the laser beam (12) incident on the workpiece (14) to be changed. Laser processing head (10) according to claim 1, characterized in that a controlled or regulated actuator is associated with the collimator (30), which is configured for moving the collimator (30).A laser processing head (10) according to claim 1 or 2, characterized in that the at least one scanning device (22) comprises a first scanner mirror (24) for scanning the laser beam (12) in a first direction on the workpiece (14) and a second scanner mirror (26) for scanning the laser beam (12) in a second direction on the workpiece (14). A laser processing head (10) according to any one of the preceding claims, wherein the at least one collimator (30) comprises a convex lens system or a convex lens. A laser processing head (10) according to any one of the preceding claims, further comprising a deflecting mirror (31) in the propagation direction of the laser beam (12) behind the scanning device (22), at least one lens (42) for focusing the laser beam (12) onto the workpiece (14), and a sensor system (40) for detecting radiation from the processed workpiece. A laser processing head (10) according to claim 5, characterized by a beam splitter (38) behind the scanning device (22) for passing the laser beam (12) to the workpiece (14) and for reflecting the radiation from the workpiece (14) to the sensor system (40). A laser processing head (10) according to any one of the preceding claims, characterized in that the sensor system (40) comprises a camera and / or an interferometer. A laser processing head (10) according to any one of the preceding claims, characterized in that the laser processing head (10) has a rotatable process nozzle (46) for supplying a process medium and for aligning the process nozzle (46) with a direction of movement of the laser beam (12) along the workpiece (14). A laser processing head (10) according to any one of the preceding claims, characterized in that a laser source (15) supplies variable laser power to the laser processing head (10) via an optical fiber (16).Method for processing a workpiece (14) using a laser beam (12) comprising the following process steps:. - Providing a laser processing head (10) comprising at least one scanning device (22) for deflecting the laser beam (12) and at least one collimator (30) for collimating the laser beam (12); - Changing the diameter D of the laser beam (12) incident on the workpiece (14) by moving the collimator (30) during operation along the propagation direction of the laser beam (12). Method according to claim 10, comprising the method steps: - Providing a first scanner mirror (24) and a second scanner mirror (26) in the scanning device (22); - Scanning the workpiece (14) with the first scanner mirror (24) in a first direction and with the second scanner mirror (26) in a second direction. Method according to claim 10 or claim 11, comprising the method steps: - Providing a sensor system (40) on the laser processing head (10); - Detection of radiation from the workpiece (14) by the sensor system (40). Method according to one of claims 10 to 12, comprising the method steps: - Providing a rotatable process nozzle (46) on the laser processing head (10); - Supplying a process medium through the process nozzle (46) and rotating the process nozzle (46) to align the process nozzle (46) with a direction of movement of the laser beam (12) along the workpiece (14). Method according to any one of claims 10 to 13, comprising the process steps: - Providing a laser source (15) for coupling the laser beam (12) via a fiber optic cable (16) to the laser processing head (10); - Providing variable laser power at the laser source (15) for the laser processing head (10). Laser processing machine with a laser source (15) having a fiber optic cable (16) for delivering a laser beam (12) to a laser processing head (10) according to any one of claims 1 to 9.

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