Methods for monitoring laser processing processes and related laser processing systems

Abstract

This invention relates to a method for determining the depth of a steam capillary during a laser processing procedure. The method includes: irradiating a processing laser beam onto at least one workpiece to form a steam capillary, wherein the processing laser beam is deflected on the workpiece along a processing path within a first scanning field by a first deflection device; irradiating an optical measurement beam onto the workpiece, wherein the optical measurement beam is deflected relative to the processing laser beam along a detection path within a detection region on the workpiece by a second deflection device, and subsequently deflected together with the processing laser beam by the first deflection device; detecting a distance measurement value along the detection path based on the fraction of the optical measurement beam reflected by the workpiece; and determining the depth and / or position of one of the steam capillaries based on the detected distance measurement value, wherein the size of the detection region is determined based on the position of the processing laser beam and / or based on the deflection of the processing laser beam and / or based on the deflection of the processing laser beam by the first deflection device. Furthermore, a laser processing system is proposed.

Description

Technical Field

[0001] This invention relates to a method for monitoring laser processing, particularly laser welding, and a laser processing system for monitoring laser processing, particularly laser welding. Background Technology

[0002] In a laser processing system (also known as a laser processing apparatus or simply an apparatus), a processing laser beam emitted from a laser beam source or the end of a laser optical fiber is focused onto the workpiece to be processed in order to process it. Processing can include laser beam welding. A laser processing system can include a laser processing head, such as a laser welding head, in which beam-guiding optics are integrated. For processing, the laser beam is irradiated onto the surface of the workpiece, whereby the laser beam moves along a so-called processing path on the surface. Here, vapor capillaries, also known as keyholes, are formed in the region between the workpiece surfaces (on which the laser beam irradiates) up to a certain depth within the workpiece. In the region of the vapor capillaries, the material of the workpiece is so intensely heated by the irradiated laser power that the material evaporates. The vapor capillaries are surrounded by regions where the material is in a molten state. This region is called the molten pool.

[0003] The depth of the steam capillary, i.e., the distance between the (unprocessed) surface of the workpiece and the deepest part of the steam capillary, is of great significance. The depth of the steam capillary is related, for example, to the weld penetration depth, i.e., the depth to which the workpiece material has melted during processing. On the one hand, knowing the depth of the steam capillary or weld penetration allows for the estimation of the strength of the weld joint, i.e., whether it has penetrated sufficiently; on the other hand, knowing the depth of the steam capillary ensures that the weld is not visible underneath, i.e., there is no undesirable burn-through. Therefore, the depth of the steam capillary, also known as the keyhole depth, is a decisive factor for the weld quality produced in laser beam welding. The deepest part of the steam capillary is also called the keyhole bottom or the processed substrate.

[0004] For this reason, measuring the depth of the steam capillary during laser beam welding is of great significance. Recently, depth or distance measurement has been achieved non-contactly using optical coherence tomography (OCT). To do this, the optical measurement beam of the OCT apparatus (also called the OCT measurement beam) illuminates the workpiece, and a portion of the beam is reflected back into the OCT apparatus. However, to reliably measure the depth of the steam capillary, it is essential to ensure that the optical measurement beam enters the steam capillary at its deepest point and that the light reflected from there returns to the OCT apparatus.

[0005] Typically, the location of the deepest part of the steam capillary does not coincide with the location of the processing laser beam. The position, shape, and size of the steam capillary on the workpiece surface depend on the current parameters of the laser processing. These parameters include, for example, the processing speed (also known as the feed rate), the processing direction, the power of the processing laser beam, the focal size of the processing laser beam, and the material of the workpiece. For instance, increasing the processing speed leads to a greater distance between the location of the steam capillary and the location of the processing laser beam.

[0006] For this reason, positioning the OCT measurement beam on the workpiece in such a way that reliably determining the deepest part of the steam capillary is one of the greatest challenges. This problem is amplified again when using a so-called scanning system as a laser processing system for laser beam welding, in which the processing laser beam is moved across the processing path by means of a scanning mirror or other deflection unit. This is because chromatic aberration and angular variations between the processing laser beam and the OCT measurement beam relative to the objective lens and workpiece cause the OCT measurement beam to be located at a different position on the workpiece than the processing laser beam. Furthermore, in scanning systems, especially scanner-based welding systems, high processing speeds are often used, so the deviation between the position of the steam capillary and the position or focus of the processing laser is typically significantly greater than in fixed optical systems. This problem is exacerbated by frequent changes in welding direction and speed.

[0007] In addition, other effects may occur, such as the polarization dependence of mirror reflections of the scanning system, thermal effects, the motion of the external axis of the scanning system or workpiece and the associated vibrations, and the material properties of the mating parts, which may adversely affect the measurement.

[0008] A typical scanning system for measuring keyhole depth using optical coherence tomography (OCT) attempts to "randomly" illuminate the keyhole by scanning the OCT measurement beam with the location of the machining laser beam on the workpiece as the center. This scanning typically has a fixed pattern (e.g., a circle, a flat figure-eight, a spiral). This means that in most measurements (typically in the range of 10 kHz to 500 kHz), the OCT measurement beam does not illuminate the keyhole, and a small number of measurements from the keyhole must be filtered out from the set of all measurements. Because the scanning pattern is fixed and pre-defined, the size of the scanning pattern, i.e., the scanning area, must match the least certain process conditions regarding the keyhole location. Therefore, a large scanning area is usually pre-defined for the scanning pattern, which must be scanned by the measurement beam in a short time. This results in the portion of the measurement from the keyhole decreasing with the increase in the scanning area size. This ratio worsens further if welding that only forms small keyhole diameters is now performed.

[0009] The degradation in measurement quality stems from two main factors: firstly, the limited measurement frequency of the optical coherence tomography (OCT) device, and secondly, the limited intensity of the OCT measurement beam. Both factors result in less signal generation from the deepest part of the keyhole as the scanning area used for the OCT measurement beam increases. Ultimately, starting from a specific size of the scanning area, sufficient measurements from the keyhole are no longer obtained to draw sufficiently accurate conclusions about its depth. Summary of the Invention

[0010] The objective of this invention is to provide a system and method that improves the reliability, speed, and accuracy of determining the depth and / or position of a vapor capillary during laser processing.

[0011] This task is solved by the technical solution according to the present invention. Advantageous configurations and extensions are described later.

[0012] The basic concept of this invention is to define or limit a region of the workpiece during the laser processing procedure that must be probed or scanned by an optical measurement beam (e.g., for optical coherence tomography) for interferometry or optical ranging. This region (hereinafter also referred to as the probe region) is determined or matched based on at least one current (process) parameter of the laser processing procedure. In particular, the probe region can be matched based on the position of the laser processing beam within a first scanning field of a first deflection device, where the optical measurement beam probes the workpiece surface to deflect the laser processing beam along a pre-given processing path. This reduces the probability of erroneous measurements, i.e., measurements taken outside the vapor capillary.

[0013] The detection area, also known as the search area or scanning area, can be defined as the region on the workpiece in which it is detected by an optical measuring beam to determine the position and depth of the steam capillary. The detection area can be stationary relative to the laser processing beam. Therefore, the detection area can follow the processing beam offset along the processing path. Detection is achieved by illuminating and deflecting the optical measuring beam along a detection path within the detection area and by detecting distance measurements along the detection path based on the portion reflected back from the workpiece. The position and / or depth of the steam capillary can then be determined based on the detected distance measurements. The position of the steam capillary can be defined as the location of its deepest point, while the depth can be defined as the distance between the (unprocessed) surface of the workpiece and the deepest point of the steam capillary.

[0014] The size of the detection area can represent the area of ​​the detection region on the workpiece. The shape of the detection area can represent its geometry, meaning that the shape can remain unchanged when the size is changed. The location of the detection area can be defined as the location of the center point or the centroid of the surface of the detection area on the workpiece.

[0015] Instead of using an optical measuring beam to move or probe the area surrounding the processing laser beam (also known as the processing field) with a fixed, pre-defined scanning pattern, the detection area for searching the steam capillary is thus significantly reduced in this invention. Furthermore, the focal position of the optical measuring beam can be matched, for example, based on its position on the workpiece or within the first and / or second scanning field. With the interferometric ranging parameters unchanged, a higher signal intensity is first obtained for the portion of the optical measuring beam reflected by the steam capillary, resulting in a better signal-to-noise ratio. Secondly, significantly more distance measurements "from the steam capillary" are obtained because the optical measuring beam passes through the steam capillary more frequently. This is particularly evident in laser welding processes, yielding more measurements per unit length of the resulting weld from the steam capillary.

[0016] According to a first aspect of the invention, a method is provided for monitoring a laser processing process or determining the depth and / or position of a steam capillary during a laser processing procedure. The method comprises: irradiating a processing laser beam onto at least one workpiece for forming a steam capillary, wherein the processing laser beam is deflected on the workpiece along a processing path within a first scanning field by a first deflection device; irradiating an optical measurement beam onto the workpiece, wherein the optical measurement beam is deflected on the workpiece relative to the processing laser beam along a detection path by a second deflection device, and subsequently deflected together with the processing laser beam by the first deflection device; detecting distance measurements along the detection path based on a portion of the optical measurement beam reflected by the workpiece, particularly by means of optical coherence tomography; and determining the depth and / or position of the steam capillary based on the detected distance measurements, wherein the size of a detection area is determined or matched based on at least one parameter. In other words, the detection area for the measurement beam can be matched to the corresponding processing condition such that, based on at least one parameter, the detection area is minimized.

[0017] Here, the size of the detection area is determined or matched based on at least one of the following parameters: the position of the processing laser beam on the workpiece, the position of the processing laser beam within the first scanning field, the angle or orientation of the processing laser beam about the workpiece, the deflection of the processing laser beam through the first deflection device, the processing direction, the processing speed, the processing speed vector or the velocity vector of the processing beam, the power of the processing laser beam, the material and / or thickness of at least one workpiece, the deflection angle of the first deflection device, the optical path length of the processing laser beam between the laser source used for processing the laser beam and at least one workpiece, the optical path length of the optical measuring beam between the radiation source of the optical measuring beam and at least one workpiece, the focal position of the processing laser beam, the focal position of the optical measuring beam, the cross-sectional shape of the processing laser beam, especially the cross-sectional shape of the processing laser beam at the focal point, the cross-sectional shape of the optical measuring beam, especially the cross-sectional shape of the optical measuring beam at the focal point, and the orientation of the laser processing system, especially the laser processing head and the workpiece relative to each other.

[0018] According to a second aspect of the invention, a laser processing system, particularly a laser welding system, is provided. The laser processing system includes: a laser processing head for irradiating at least one workpiece with a processing laser beam to form a steam capillary, wherein the laser processing head includes a first deflection device for deflecting the processing laser beam on the workpiece along a processing path within a first scanning field; a measuring device for interferometric ranging, particularly by means of optical coherence tomography, the measuring device being configured to irradiate at least one workpiece with an optical measuring beam and including a second deflection device for deflecting the optical measuring beam on the workpiece relative to the processing laser beam along a detection path within a detection region; and a coupling device for coupling the optical measuring beam into the laser processing head, the coupling device being arranged prior to the first deflection device in the beam propagation direction of the processing laser beam such that the optical measuring beam can be deflected together with the processing laser beam by the first deflection device, wherein the measuring device is configured to detect distance measurements along the detection path based on a portion of the optical measuring beam reflected by the workpiece, for determining the depth and / or position of the steam capillary.

[0019] The measuring device can be configured to determine or match the size of the detection area based on at least one of the parameters mentioned above.

[0020] The laser processing system or the control unit contained therein may be configured to perform a method for determining the depth of a steam capillary according to an embodiment.

[0021] These parameters can be current parameters during the laser welding process. This method can be executed during the laser processing. In particular, it can be executed as an inline method. The probe area can be determined or matched in real time. This allows the position, size, and shape of the probe area to be determined at any point during the laser processing, based on the current parameters.

[0022] The detection area can be arranged closely following the laser processing beam. The detection area is preferably determined relative to the (current) position of the laser processing beam, and therefore the laser processing beam can be stationary. In other words, the detection area can follow the movement of the laser processing beam. Preferably, the laser processing head and the workpiece are arranged relatively stationary to each other at least during the laser processing process, i.e., during weld formation, with the laser processing beam irradiating the workpiece through the laser processing head. Therefore, during the laser processing process, the laser processing beam is preferably deflected only by the first deflection device along the processing path. The processing path can correspond to the desired weld orientation. However, the invention can also be applied to laser processing systems where the workpiece moves, for example, via an axis system during processing. Another possibility is that the laser processing head is fixed to a robot. In this case, the first deflection device deflects the laser processing beam, wherein the robot moves simultaneously or synchronously. This can save cycle time. In this case, there is a higher-level control device that coordinates the movement of the robot and the first and / or second deflection units. The movement of the laser processing beam is preferably carried out without superimposed oscillating motion or so-called oscillating motion. However, if the movement of the laser processing beam along the processing path is superimposed with a small-amplitude oscillating motion, i.e., a so-called oscillating motion, the position of the detection area can follow the movement of the laser processing beam along the processing path, preferably without considering the oscillating motion.

[0023] Laser processing can be laser welding or laser beam welding, especially laser beam scanning welding. A laser processing system can be configured to perform the laser processing process by directing a processing laser beam onto the workpiece.

[0024] The first and second deflection devices can also be called scanning devices or scanners. Laser processing systems can also be called scanning systems.

[0025] One or more of the aforementioned aspects may include one or more of the following optional features:

[0026] According to the implementation, the position and / or shape of the detection area can be determined based on the position of the processing laser beam, particularly based on the position of the processing laser beam within the first scanning field. Alternatively or additionally, the position, size, and / or shape of the detection area can be determined based on the processing speed along the processing path and / or based on the processing direction and / or based on the processing speed vector, i.e., based on the speed vector of the processing laser beam.

[0027] According to the implementation method, the theoretical position of the steam capillary can be determined, and the position of the detection area can be determined based on the determined theoretical position of the steam capillary, such that the determined theoretical position is included within the detection area. Specifically, the position of the detection area can be determined based on the determined theoretical position of the steam capillary, such that the determined theoretical position of the steam capillary corresponds to the center point or centroid of the detection area. The theoretical position of the steam capillary can be determined based on current process parameters. Multiple theoretical positions of the steam capillary can be stored in a table, for example, for different process parameters.

[0028] The detection path can be determined in such a way that the start or origin of the detection path corresponds to the theoretical position of the steam capillary.

[0029] The method can be performed continuously and / or repeatedly and / or iteratively during the laser processing. For example, a center point or centroid of the probe area can be determined such that this center point or centroid corresponds to a position of the vapor capillary previously determined by distance measurements.

[0030] The size of the determined or matched detection area can be smaller than the size of the second scanning field. The size of the detection area can be determined such that it is equal to or greater than five times the (theoretical) size of the steam capillary. The size of the steam capillary can substantially correspond to the area of ​​the steam capillary on the workpiece surface.

[0031] The closer the processing laser beam is to the edge of the first scanning area and / or the higher the processing speed, the larger the size of the detection area can be determined. The stronger the laser processing beam is deflected by the first deflection device, for example, from a zero-position state, the larger the size of the detection area can be determined. The zero-position state can represent the undeflected orientation of the laser processing beam, i.e., the laser processing beam is not deflected by the first deflection device. Preferably, in the zero-position state, the laser processing beam extends coaxially with the optical axis of the laser processing head or the optical axis of the focusing optics.

[0032] The higher the processing speed, the greater the distance between the position of the detection area on the workpiece surface and the position of the processing laser beam on the workpiece surface can be determined.

[0033] The location, shape, and / or size of the detection area can be determined such that the processing laser beam is located outside the detection area. The detection area can be arranged along the processing path and / or in the processing direction, closely following the position of the processing laser beam.

[0034] The shape of the detection area can be matched and / or oriented based on the processing direction. For example, a circular or droplet shape can be determined as the shape of the detection area based on the processing direction. In the case of non-point-symmetric shapes, such as droplet, trapezoidal, or triangular shapes, the shape can be oriented according to the processing direction or the velocity vector of the processing beam.

[0035] The detection path or a portion thereof may have the shape of a figure eight, a flat figure eight, a dumbbell, a peanut, a spiral, a circle, and / or an arc. The detection path or a portion thereof may have the shape of a zigzag, a sawtooth, a rectangle, and / or a meander.

[0036] The detection region can be determined based on table values ​​and / or, in the case of using an artificial neural network. Alternatively or additionally, the detection region can be matched based on a functional relationship of the parameters. Table values ​​can be obtained based on experiments and / or simulations. The detection region can be determined or stored alternatively or additionally based on theoretical values ​​and / or experimental values ​​and / or analytical values ​​or combinations thereof. Depending on the implementation, interpolation or extrapolation can be performed on non-existent table values. The artificial neural network can be trained based on experimental data.

[0037] Furthermore, the location, shape, and / or size of the detection area and / or the theoretical location of the vapor capillary can be determined based on at least one additional parameter of the laser processing system, such as the orientation of the mirrors of the first and / or second deflection devices relative to each other, and / or the parameters of the gantry or robot, especially the robot arm, by means of which the relative position between the laser processing head and the workpiece is changed.

[0038] The coupling of the optical measurement beam can be performed before the first deflection device in the beam propagation direction of the processing laser beam. The coupling device, such as a beam splitter or dichroic mirror, can be arranged before the first deflection device in the beam propagation direction.

[0039] The first deflection device may be configured to deflect the processing laser beam along a first axis by at least a first deflection angle. Preferably, the first deflection device is additionally configured to deflect the processing laser beam along a second axis by a second deflection angle, wherein the first axis and the second axis are arranged at an angle relative to each other, for example, perpendicular to each other. The first maximum deflection angle and / or the second maximum deflection angle of the first deflection device may be equal to or greater than 10 degrees, particularly 10 to 20 degrees. These deflection angles correspond to a mirror angle of at least + / - 5 degrees, particularly + / - 10 degrees, since the beam is deflected by twice the mirror angle.

[0040] The second deflection device may be configured to deflect the measuring beam along the first axis by at least a first deflection angle. Preferably, the second deflection device is additionally configured to deflect the measuring beam along the second axis by a second deflection angle, wherein the first axis and the second axis are arranged at an angle relative to each other, for example, perpendicular to each other. The first maximum deflection angle and / or the second maximum deflection angle of the second deflection device may each be less than 10 degrees, and preferably less than 3 degrees, especially about 2 degrees.

[0041] The first scanning field of the first deflection device can be defined as a region on the workpiece, particularly on the surface of the workpiece, and / or predetermined by the first and second maximum deflection angles of the first deflection device. The second scanning field of the second deflection device can be defined as a region on the workpiece, particularly on the surface of the workpiece, and / or predetermined by the first and second maximum deflection angles of the second deflection device. The length and / or width of the first scanning field can be equal to or greater than 50 mm. The first scanning field can, for example, have a size greater than 50 x 50 mm on the workpiece, particularly equal to or greater than about 100 x 200 mm or 250 x 150 mm. The length and / or width of the second scanning field on the workpiece can be less than 30 mm, preferably less than 15 mm, for example, about 10 mm. According to an embodiment, the first and / or second scanning fields have an elliptical shape. In this case, the length of the scanning field can describe the length of the major axis of the ellipse, while the width of the scanning field can describe the length of the minor axis of the ellipse.

[0042] The second deflection device may have a second scanning field smaller than the first scanning field. The first deflection device may be configured as a large-field scanner and / or the second deflection device may be configured as a small-field scanner.

[0043] To induce deflection of the processing laser beam, the first deflection device may have a first movable mirror and a second movable mirror. The first movable mirror can rotate about a first axis of rotation, and the second movable mirror can rotate about a second axis of rotation, wherein the first and second axes of rotation are at an angle relative to each other, for example, between 45° and 135°, particularly about 75° or 90°. For this purpose, the mirrors, or the first and second mirrors, can be configured as a galvanometer-spiegel, or simply a galvanometer-spiegel. Alternatively, the first deflection device may have movable mirrors that can rotate or pivot about at least two axes. Accordingly, the first deflection device can be configured as a galvanometer scanner or a galvanometer scanner. Alternatively, the first deflection device can be configured as a prism scanner or a lens scanner.

[0044] To induce deflection of the measuring beam, the second deflection device may have a first movable mirror and a second movable mirror. The first movable mirror may rotate about a first axis of rotation, while the second movable mirror may rotate about a second axis of rotation, wherein the first and second axes of rotation are at an angle relative to each other, for example, between 45° and 135°, particularly about 75° or 90°. Alternatively, the second deflection device may have movable mirrors capable of rotating or pivoting about at least two axes. To move the mirrors, or the first and second mirrors, the second deflection device may include at least one corresponding galvanometer actuator. Thus, the first and second mirrors may be configured as galvanometer mirrors, or simply galvanometer mirrors. Correspondingly, the second deflection device may be configured as a galvanometer scanner or galvanometer scanner. Alternatively, the second deflection device may be configured as a prism scanner or lens scanner.

[0045] The first deflection device and / or the second deflection device may alternatively have MEMS-based drivers, piezoelectric drivers, and / or inductive drivers.

[0046] Furthermore, the focal position of the optical measurement beam can preferably be adjusted independently of the focal position of the laser processing beam. The focal position of the optical measurement beam can be matched according to the position of the laser processing beam and / or the optical measurement beam in the first scanning field. In particular, the optical measurement beam can be focused onto the workpiece, especially its surface. Focusing the optical measurement beam onto the workpiece or its surface has the advantage of obtaining a higher signal intensity from the portion of the optical measurement beam reflected from the steam capillary and thus a better signal-to-noise ratio.

[0047] To adjust the focal position of the optical measurement beam, the laser processing system may have a collimating device for collimating the optical measurement beam. This collimating device may include collimating optics. These collimating optics can be adjusted along the optical axis of the collimating device and / or along the beam propagation direction of the optical measurement beam. This adjustment may be, for example, performed by a motor. The measuring device may be configured to control the collimating device such that the focal position of the optical measurement beam is adjusted based on the position of the optical measurement beam in a first scanning field and / or based on the position of the optical measurement beam in a second scanning field. This allows the focusing of the optical measurement beam to be matched according to the orientation of the processing laser beam and / or the optical measurement beam in the first scanning field and / or according to the orientation of the optical measurement beam in the second scanning field.

[0048] The collimating device for the optical measurement beam can be arranged in front of the coupling device in the beam propagation direction of the optical measurement beam.

[0049] The laser processing system may also include a collimating device for collimating the processing laser beam. The collimating device for the processing laser beam may be arranged before the coupling device in the beam propagation direction of the processing laser beam. The collimating device for the processing laser beam or a portion thereof may be adjusted along the optical axis of the collimating device and / or along the beam propagation direction of the processing laser beam to adjust the focal position of the processing laser beam. The collimating device may include two or more lenses, the distance between which is at least partially variable. This adjustment may be, for example, motor-driven. The control unit of the laser processing system may be configured to control the collimating device such that the focal position of the processing laser beam is adjusted based on the position of the processing laser beam within a first scanning field.

[0050] Furthermore, the laser processing system may include a focusing device for focusing the processing laser beam and / or the optical measurement beam. The focusing device may include two or more lenses, the distance between which is at least partially variable to adjust or change the focal point position. The focusing device may be configured, in particular, to focus the processing laser beam onto the workpiece, especially onto the surface of the workpiece. The focusing device may be arranged after the first deflection device in the beam propagation direction of the processing laser beam.

[0051] Preferably, the focusing of the optical measurement beam and / or the laser processing beam is achieved through an F-θ objective. This F-θ objective is preferably designed not only for the wavelength of the optical measurement beam but also for the wavelength of the laser processing beam. The F-θ objective can be telecentrically positioned.

[0052] The measuring device can be configured as an optical coherence tomography (OCT) device or include such an OCT device. A measuring device configured as an OCT device can have a dynamic reference beam splitter to extend the measurement range.

[0053] Furthermore, the offset used to deflect the optical measurement beam can be determined by a second deflection device to compensate for chromatic aberration of the optical measurement beam relative to the processing laser beam. The optical measurement beam can be deflected along the detection path taking into account the determined offset. This offset can also be referred to as deviation. According to an embodiment, the offset can be determined based on table values. These table values ​​can be stored in the control unit of the laser processing system. Here, interpolation or extrapolation can be performed for non-existent table values.

[0054] The laser processing system may also include a control unit configured to control the laser processing system and / or its components to perform a laser processing process or to monitor the laser processing process or to determine the depth and / or position of a steam capillary. The control unit may particularly be configured to control a laser processing head, a first deflection device, a second deflection device, a collimation device for optically measuring the beam, and / or a collimation device for processing the laser beam. The functions of the measuring device may be integrated into the control unit, or the measuring device itself may be integrated into the control unit.

[0055] The laser processing system may also include a laser source for generating the processing laser beam, or be configured to couple the processing laser beam from the laser source for generating the processing laser beam, for example, via a fiber coupler, to the processing head. The laser source may also be simply referred to as a laser. A laser can be constructed as a single-mode laser, a multimode laser, a solid-state laser, and / or a fiber laser. The laser processing system may include optical fibers for guiding the laser beam from the laser source to the laser processing head. The laser processing system may include other sensors, such as photodiodes, pyrometers, and / or cameras. These other sensors can be used to determine values ​​representing the depth of the steam capillary from distance measurements. The laser processing system may also include an interface for transmitting data to external systems.

[0056] The at least one workpiece may include a battery cell. Irradiation by the processing laser beam can achieve contact for the battery cell. Alternatively or additionally, the at least one workpiece may include a power electronic component. Irradiation by the processing laser beam can achieve welding for the power electronic component. Alternatively or additionally, the at least one workpiece may include a mobile phone component. Irradiation by the processing laser beam can achieve welding for components used in mobile phones. Attached Figure Description

[0057] The invention is described in detail below with reference to the accompanying drawings.

[0058] Figure 1A Block diagram of a laser processing system according to an embodiment of the present invention;

[0059] Figure 1B A schematic diagram of a laser processing system according to an embodiment of the present invention;

[0060] Figure 2 A schematic diagram illustrating the first scanning field of a first deflection device for a laser processing system according to an embodiment of the present invention;

[0061] Figure 3 A flowchart of a method for determining the depth of a vapor capillary during a laser processing procedure according to an embodiment of the present invention;

[0062] Figures 4A-4DA schematic diagram of the workpiece surface, used to illustrate the detection area defined according to the embodiment;

[0063] Figure 5 A schematic diagram used to visually illustrate the detection path within the detection area according to the implementation method.

[0064] Unless otherwise stated, the same reference numerals are used for elements that are the same and have the same function. Detailed Implementation

[0065] Figure 1A This is a block diagram of a laser processing system according to an embodiment of the present invention. Figure 1B This is a schematic diagram.

[0066] The laser processing system 10 can be coupled to a laser source 12 for generating a processing laser beam 14 (also simply referred to as a processing beam or laser beam) so as to couple the processing laser beam 14 into a laser processing head 16 of the laser processing system 10. The laser processing system 10 includes a laser processing head 16 for irradiating and directing the processing laser beam 14 onto and towards at least one workpiece 18a, 18b. The laser source 12 can be configured as a single-mode laser, a solid-state laser, or a fiber laser.

[0067] The laser processing system 10 can be configured to perform a laser welding process for welding at least one workpiece 18a, 18b. In this case, the laser processing system 10 can be constructed as a laser welding system and the laser processing head 16 can be constructed as a laser welding head. For example, the laser processing system 10 can be configured to weld two workpieces 18a, 18b to each other. Figure 1B As shown, the two workpieces 18a and 18b are arranged with an lap joint, but the invention is not limited thereto. The workpieces may also be arranged with parallel joints or butt joints, for example.

[0068] Welding of the at least one workpiece 18a, 18b is achieved by irradiating the at least one workpiece 18a, 18b with a processing laser beam 14 along a processing path for forming a weld (see [link]). Figures 4A to 4D When the processing laser beam 14 irradiates at least one workpiece 18a, 18b, the material of the workpieces 18a, 18b is heated so intensely that it evaporates. This creates a vapor capillary (not shown) in the region between the surfaces of the workpieces 18a, 18b, extending to a certain depth within the workpieces 18a, 18b. The depth of the vapor capillary is of paramount importance for evaluating the quality of the laser welding process, as this depth allows for the derivation of conclusions regarding the weld strength. The laser processing system 10 is configured to determine the depth and / or location of the vapor capillary.

[0069] The processing laser beam 14 is transmitted from the laser source 12 to the laser processing head 16 via the optical fiber 20 of the laser processing system 10 and coupled to the laser processing head 16 from one end of the optical fiber 20, for example, by means of a fiber coupler. A collimating device 21, connected to the fiber coupler, has a collimating optics 22 for collimating the processing laser beam 14, which diverges from the end of the optical fiber 20. The focal position of the processing laser beam 14 can be adjusted or corrected by means of the collimating device 21. The axis along which the focal position of the processing laser beam 14 can be adjusted may correspond to the optical axis of the laser processing head 16, particularly the optical axis of the focusing optics 24. This axis may also be referred to as the z-axis. Therefore, the collimating optics 22 may be referred to as a z-collimating optics or simply z-collimating. The focal position can be adjusted by adjusting the collimating optics 22 along its optical axis or the beam axis of the processing laser beam 14. The collimating device 21 may have a motor unit for adjusting the collimating optics 22.

[0070] Furthermore, the laser processing head 16 includes a focusing device 23 with a focusing optics 24 for focusing the processing laser beam 14 onto the workpieces 18a and 18b. The focusing optics 24 may be configured as an F-θ optics or include such an F-θ optics.

[0071] To change the position of the processing laser beam 14 on the workpieces 18a and 18b, and specifically to irradiate the processing laser beam 14 along the processing path, the laser processing system 10 further includes a first deflection device 26 for deflecting or shifting the processing laser beam 14 relative to the workpieces 18a and 18b. The first deflection device 26 is configured to deflect or shift the processing laser beam 14 about the workpieces 18a and 18b along two axes x and y (see...). Figure 2 Movement and deflection. According to the embodiment, the two axes x and y can be perpendicular to each other and parallel to the surfaces of workpieces 18a and 18b, but are not limited thereto. The first deflection device 26 can also be called a scanner. With the aid of the first deflection device 26, the processing path can be moved by the processing laser beam 14.

[0072] The first deflection device 26 is configured to deflect the processing laser beam 14 along the x-axis by a first deflection angle and along the y-axis by a second deflection angle. The deflection device 26 includes zero positions about the x-axis and about the y-axis, respectively, for which the processing laser beam 14 occupies a zero position along the corresponding axis (see [reference]). Figure 2The zero position of the x-axis and the zero position of the y-axis can be considered together as the center point or center 30 of the first scanning field 64 of the first deflection device 26. The center 30 of the first scanning field 64 can correspond to the non-deflection state of the processing laser beam 14, i.e., the (general) zero state of the processing laser beam 14. In the non-deflection state of the processing laser beam 14, the processing laser beam 14 can extend coaxially with the optical axis of the laser processing head 16 and / or the optical axis of the focusing optics 24 between the laser processing head 16 and the workpieces 18a, 18b.

[0073] A first maximum deflection angle 28 along the x-axis (i.e., rotating about the y-axis) and a second maximum deflection angle 29 along the y-axis (i.e., rotating about the x-axis) are predefined at the edge of a first scanning field 64 on the surfaces of workpieces 18a and 18b, within which the first deflection device 26 can deflect the processing laser beam 14 relative to workpieces 18a and 18b. According to an embodiment, the first deflection device 26 is configured as a large-field scanner. For example, the first maximum deflection angle 28 and / or the second maximum deflection angle 29 can be greater than 10 degrees. The first and second maximum deflection angles can be predefined in the construction technique. Alternatively, an F-θ objective lens used as a focusing device can limit the maximum deflection angle.

[0074] exist Figure 2 In the diagram, the first scanning field 64 is shown in a rectangular shape, but the invention is not limited thereto. The first scanning field 64 may also have a circular or elliptical shape. In this case, in Figure 2 The rectangle shown can be considered as the rectangle with the largest area inscribed in the first scan field 64 of the ellipse.

[0075] According to one embodiment, the first deflection device 26 includes two movable mirrors 32a and 32b, which are rotatable about different axes of rotation. These two mirrors 32a and 32b can be configured as galvanometer mirrors. In this case, the first deflection device 26 can be referred to as a galvanometer scanner or galvanometer scanner.

[0076] According to the embodiments, the laser processing head 16 and / or workpieces 18a, 18b can additionally move relative to each other, preferably between two successive laser processing processes. For example, workpieces 18a, 18b can be moved relative to the laser processing head 16 by a first motion unit (not shown). Alternatively or additionally, the laser processing head 16 can be moved relative to the workpieces 18a, 18b by a second motion unit (not shown). The second motion unit can be configured as a robot, for example, and the laser processing head 16 can be fixed to the robot. During the laser processing process, i.e., during weld formation, the laser processing head 16 or the laser processing system 10 preferably remains stationary (relative velocity zero) relative to the workpieces 18a, 18b.

[0077] The laser processing system 10 also includes a measuring device 34 for interferometry or optical ranging by means of an optical measuring beam 36. The measuring device 34 is configured, for example, to measure the distance between the laser processing head 16 and the workpieces 18a and 18b.

[0078] The measuring device 34, according to embodiments, includes or may be configured as an optical coherence tomography (OCT) device. In other words, ranging can be based on optical coherence tomography (OCT). The measuring device 34 includes an analysis and evaluation unit 38 having a broadband light source, such as a superluminescent diode, abbreviated as SLD. The light source 39 couples the measurement light into an optical fiber 40. In a beam splitter 42, preferably configured as a fiber coupler, the measurement light is divided into a reference beam 44 and a measurement beam 46. The measurement light of the measurement beam 46 is transmitted as an optical measurement beam 36 through the optical fiber to a collimating device 48 and coupled from the end of the optical fiber into the collimating device 48 so as to be illuminated onto the workpieces 18a, 18b.

[0079] The collimating device 48 has a collimating optics 50 for collimating the optical measurement beam 36 that diverges from the end of the optical fiber. The focal position of the optical measurement beam 36 can be adjusted by means of the collimating optics 50. The axis along which the focal position of the optical measurement beam 36 can be adjusted corresponds to the optical axis of the laser processing head 16, and in particular the optical axis of the focusing optics 24. This axis can also be referred to as the z-axis. Therefore, the collimating optics 50 can be called the z-collimating optics 50 or simply z-collimating. The focal position can be adjusted by adjusting the collimating optics 50 along its optical axis or the beam propagation direction of the optical measurement beam 36. This adjustment can be performed by a motor.

[0080] According to the implementation, the reference beam 44 can be configured as a dynamic reference beam. This can extend the measurement range of the measuring device 34.

[0081] The distance measurement principle described here is based on optical coherence tomography, which utilizes the coherent properties of light using an interferometer. For distance measurement, an optical measuring beam 36 is projected onto the surfaces of workpieces 18a and 18b. A portion of the optical measuring beam 36 reflected from the surface is imaged onto the fiber optic end of the measuring beam splitter 46, where it is superimposed with a portion of the measuring light reflected from the reference beam splitter 44 in the beam splitter 42, resulting in interference. The superimposed light contains information about the displacement length difference between the reference beam splitter 44 and the measuring beam splitter 46. This information is analyzed and evaluated by the analysis and evaluation unit 38. Information about the distance to workpieces 18a and 18b, or the distance between workpieces 18a and 18b and the laser processing head 16, can thus be obtained.

[0082] To determine the depth of the steam capillary, the optical measuring beam 36 must be pointed into the steam capillary and reflected back to the measuring device 34 or analysis and evaluation unit 38 from the bottom of the steam capillary. If the distance to the surfaces of workpieces 18a and 18b is additionally known, the measuring device 34 or analysis and evaluation unit 38 can determine the depth of the steam capillary, i.e., the distance from the deepest part of the steam capillary to the surface of workpieces 18a and 18b. However, since the exact location of the deepest part of the steam capillary is unknown, the measuring beam 36 moves along the detection path within the detection area to detect or scan the workpiece surface within that area.

[0083] To change the position of the measuring beam 36 on the workpieces 18a and 18b, thereby measuring the distance to the workpieces 18a and 18b at different locations, the measuring device 34 includes a second deflection device 52 for deflecting or offsetting the optical measuring beam 36 relative to the workpieces 18a and 18b. Measuring the distance to the workpieces 18a and 18b at different locations can also be referred to as workpiece detection. The second deflection device 52 is configured to move and deflect the measuring beam 36 relative to the workpieces 18a and 18b along two axes. These two axes may correspond to the x and y axes of the first deflection device 26, but the invention is not limited thereto. The second deflection device 52 can also be referred to as a scanner. By means of the second deflection device 52, the surfaces and vapor capillaries of the workpieces 18a and 18b can be detected.

[0084] The second deflection device 52 has a first maximum deflection angle and a second maximum deflection angle. Based on the first maximum deflection angle and the second maximum deflection angle of the second deflection device 52, the second deflection device 52 has a second scanning field 66 (see...). Figures 4A-4D Within this second scanning field, the second deflection device 52 can maximize the deflection of the optical measuring beam 36 about the workpieces 18a and 18b. According to an embodiment, the second deflection device 52 is configured as a small-field scanner. For example, the first maximum deflection angle and / or the second maximum deflection angle of the second deflection device 52 can be less than 10 degrees. Therefore, the area or size of the second scanning field 66 can be smaller than the area or size of the first scanning field 64. The second scanning field 66 can have a rectangular, circular, or elliptical shape. The first and second maximum deflection angles can be predetermined in the construction technique.

[0085] According to one embodiment, the second deflection device 52 includes two movable mirrors 54a and 54b, which are rotatable about different axes of rotation. Mirrors 54a and 54b can be configured as galvanometer mirrors. In this case, the second deflection device 52 can be referred to as a galvanometer scanner or galvanometer scanner.

[0086] The laser processing head 16 also includes a coupling device 56 for coupling the optical measurement beam 36 into the laser processing head 16. The coupling device 56 is configured to superimpose the processing laser beam 14 with the measurement beam 36. The coupling device 56 includes, for example, a beam splitter 58. According to an embodiment, the beam splitter 58 may be implemented as a dichroic mirror or include a dichroic mirror. The beam splitter 58 allows the light from the measurement beam 36 to pass through and reflects the light from the processing laser beam 14. According to an embodiment, the (unoffset) optical measurement beam 36 and the (unoffset) processing laser beam 14 may extend at least sectionally parallel and / or coaxially with each other.

[0087] The optical measurement beam 36 is coupled into the laser processing head 16 via the coupling device 56 before the first deflection device 26 in the beam propagation direction of the optical measurement beam 36 or the processing laser beam 14. Specifically, the optical measurement beam 36 and the processing laser beam 14 pass not only through the first deflection device 26 but also through the focusing device 23. Therefore, the optical measurement beam 36 is deflected together with the processing laser beam 14 by the first deflection device 26. Ignoring chromatic aberration, the center of the second scanning area 66 of the second deflection device 52 can correspond to the position of the processing laser beam 14 on the workpieces 18a and 18b. The measurement beam 36 is then focused together with the processing laser beam 14 by the focusing optics 24 of the focusing device 23.

[0088] Because only the measuring beam 36 extends through the second deflection device 52, the optical measuring beam 36 is deflected relative to the processing laser beam 14 by the second deflection device 52 and is independent of the deflection of the processing laser beam 14 by the first deflection device 26.

[0089] The laser processing system 10 also includes a central control unit 60. According to an embodiment of the invention, the central control unit 60 is configured to control the laser processing system 10 or its components to perform a laser processing procedure and to perform methods for determining the depth and / or position of the steam capillary. For example, the central control unit 60 is configured to control the laser source 12 to turn the processing laser beam 14 on and off (laser control on / off) or to adjust or modulate the power of the processing laser beam 14 (power modulation). Furthermore, the central control unit 60 may be configured to control the focusing device 23 to adjust or correct the focal position of the processing laser beam 14. The central control unit 60 may also be configured to control the first deflection device 26 to deflect the processing laser beam 14 on the workpieces 18a, 18b and, in particular, as the processing laser beam 14 moves through the processing path. Additionally, the central control unit 60 is configured to transmit information about the position of the processing laser beam 14 in the first scanning field and the current power of the processing laser beam 14 to the control unit 62 of the measuring device 34.

[0090] The control unit 62 is configured to control the analysis and evaluation unit 38, the collimation device 48, and the second deflection device 52. For example, the control unit 62 is configured to output a signal to the analysis and evaluation unit 38 for controlling the dynamic reference beam splitter 44. Furthermore, the control unit 62 is configured to control the collimation device 48 to adjust or correct the focal position of the optical measurement beam 36, and particularly to adjust the focal position of the optical measurement beam 36 in the z-direction. Additionally, the control unit 62 may be configured to output a control signal to the second deflection device 52 to adjust the position of the measurement beam 36.

[0091] The control unit 62 can also be configured to determine chromatic aberration corrections for the optical measuring beam 36, particularly as a function of the position of the processing laser beam 14. The corrections can be determined along the x, y, and / or z axes. Furthermore, the control unit 62 can be configured to correct for possible deviations between the position of the steam capillary along the x and y axes and the processing laser beam 14 for the optical measuring beam 36. Finally, the control unit 62 can be configured to determine the detection area and scanning strategy of the measuring beam 36, as described in detail below. In particular, the detection area can be determined around the theoretical position of the steam capillary.

[0092] One or more of the functions of the control unit 62 can be implemented by the central control unit 60 and / or the control unit 62 can be integrated into the central control unit 60.

[0093] As described above, since the exact location (deepest part) of the steam capillary is unknown, the workpiece surface is probed within the detection area 76 using the measuring beam 36. Here, according to the invention, the frequency of erroneous measurements, or measurements at locations not corresponding to the (deepest part) of the steam capillary, can be reduced by matching the detection area 76 based on at least one parameter or by determining the detection area 76 to be as small as possible. The measuring device 34 or control unit 62 is therefore configured to determine the detection area 76 for the optical measuring beam 36 (see...). Figures 4A-4D The detection area 76 for the optical measuring beam 36 represents a region on the surface of workpieces 18a and 18b, within which the optical measuring beam 36 is oriented and deflected to different positions on workpieces 18a and 18b. At different positions, the distance to workpieces 18a and 18b can be detected or measured based on the portion of the optical measuring beam 36 reflected from the surface of workpieces 18a and 18b as previously described, in order to obtain the corresponding distance measurement value. The optical measuring beam 36 irradiating different positions within the detection area 76 can be done along the detection path 82 (see [link to relevant documentation]). Figure 5 The detection path 82 can, for example, have a spiral or zigzag shape. The determination of the detection path 82 within the detection area 76 can also be referred to as the determination of the scanning strategy.

[0094] Subsequently, based on the distance measurements detected along the detection path 82 within the detection area 76, the location 78 of the steam capillary can be determined (see [reference]). Figures 4A-4D , Figure 5 The detection area can also be referred to as the search area for the location 78 of the steam capillary, since the location 78 of the steam capillary is determined based on the distance measurements detected within the detection area 76. For example, the location where the maximum distance measurement is found is determined as the location 78 of the steam capillary.

[0095] Therefore, matching the detection area with the instantaneous process conditions is also necessary, because the (actual) position 78 of the steam capillary may not necessarily coincide with or have a constant deviation from the position of the processing laser beam 14 on the workpieces 18a and 18b. This depends on the different parameters of the laser processing process. Therefore, a gap or deviation may exist between the position 78 of the steam capillary and the position 68 of the processing laser beam 14, and this gap or deviation can be variable. This is in Figures 4A-4D The diagram visually illustrates that the position 78 of the steam capillary is arranged along the processing path 70, closely following the position 68 of the processing laser beam 14 on the workpieces 18a and 18b. This deviation depends particularly on the parameters of the laser processing procedure, also known as process parameters. These include the position 68 of the processing laser beam 14 on and / or with respect to the first scanning field, the angle of the processing laser beam 14 relative to the workpieces 18a and 18b, the deflection angle or current offset of the processing laser beam 14 through the first deflection device, the processing speed along the processing path 70, the processing vector or velocity vector of the processing beam, the power of the processing laser beam 14, and the material and thickness of the workpieces 18a and 18b.

[0096] The influence of these parameters on the deviation between the position of the processing laser beam and the position of the steam capillary, especially the deepest part of the steam capillary, can be related to the configuration of the laser processing system, such as the focal length and the optics used, and must be determined individually for the specific system if necessary. This can be done, for example, through simulation, experimentation, and measurement. To determine the (theoretical) position of the steam capillary during a defined or pre-given laser processing procedure, information about the influence of process parameters on the position of the steam capillary is stored in the control unit of the laser processing system as tabular values ​​or functional relationships for subsequent, similar, or identical laser processing procedures. Alternatively or additionally, this determination can also be made using an artificial neural network trained with said information.

[0097] Therefore, the actual position of the vapor capillary is not easily known during the laser processing. Furthermore, the measurement frequency of the measuring device is limited. That is, only a limited number of distance measurements can be obtained per unit time. If the workpiece surface is probed across the entire second scanning area of ​​the second deflection device using an optical measuring beam, relatively few distance measurements are detected from the deepest part of the vapor capillary. Thus, the depth of the vapor capillary cannot be determined with sufficient accuracy.

[0098] This invention is based on the following fundamental idea: during laser processing, the detection area for probing the workpiece is matched or optimized using an optical measurement beam based on the current process parameters during the laser processing. This allows the detection area to be determined according to the current and changing position of the processing laser beam during the laser processing.

[0099] Therefore, instead of probing the workpiece within a fixed, pre-defined detection area or around the position of the processing laser beam within the entire second scanning field of the second deflection device, as in the prior art, the detection area for probing the workpiece and searching for the steam capillary is significantly limited in this invention. This increases the probability that the optical measuring beam will irradiate the steam capillary during detection within the detection area along the detection path. Consequently, more distance measurements from the steam capillary are obtained. In particular, this results in more distance measurements from the steam capillary per unit time or per unit length of the detection or processing path. Therefore, the depth of the steam capillary can be detected more efficiently, quickly, and accurately.

[0100] Figure 3 A flowchart illustrating a method for determining the position and depth of a vapor capillary during a laser processing procedure according to an embodiment of the present invention is shown. This method can be referenced previously. Figure 1A and 1B The laser processing system 10 described herein is used to perform this process.

[0101] Figures 4A-4D A schematic diagram of the surface of a workpiece according to an embodiment is shown to visually illustrate the determination and matching of the detection area.

[0102] The method begins by irradiating the processing laser beam 14 onto... Figure 1A , 1B Laser processing, such as laser welding, is performed on workpieces 18a and 18b to form a steam capillary (S1). Here, the processing laser beam 14 is deflected on the workpiece 18a above by the first deflection device 26 along the processing path 70 within the first scanning field 64 of the first deflection device 26.

[0103] Furthermore, during the laser processing, an optical measuring beam 36 is irradiated onto the workpiece 18a so that a distance measurement value (S2) is detected along the detection path 82 based on the portion of the optical measuring beam 36 reflected by the workpiece 18a. Here, the optical measuring beam 36 is deflected on the workpiece 18a relative to the processing laser beam 14 along the detection path within the detection area by a second deflection device 52. Additionally, the optical measuring beam 36 is deflected together with the processing laser beam 14 by a first deflection device 26. Here, the size of the detection area 76, and particularly the size of the detection area 76, is determined and matched within the second scanning field 66 based on the current parameters of the laser processing. This can be achieved, for example, based on information about the influence of process parameters on the position of the steam capillary relative to the position of the processing laser beam. This information can be stored as tabular values ​​in the central control unit 60 or control unit 62. According to an embodiment, the determination and matching of the detection area can be achieved using an artificial neural network.

[0104] In the final step S3, the depth and / or location of the steam capillary is determined based on the detected distance measurements.

[0105] exist Figures 4A-4D The diagram shows a first scanning area 64 of the first deflection device 26 on the workpiece 18a. Furthermore, a second scanning area 66 of the second deflection device 52 is shown, used to deflect the measuring beam 36 relative to the processing laser beam 14 and independent of the processing laser beam. The area or size of the second scanning area 66 is smaller than that of the first scanning area 64.

[0106] In addition, Figures 4A-4D The image shows the position 68 of the processing laser beam 14 in the first scanning field 64. The position 68 of the processing laser beam 14 can be defined as the center point of a spot on the workpiece surface, such as the centroid of the surface, which is generated when the processing laser beam 14 irradiates the workpiece 18a. According to an embodiment, the spot is circular, but the invention is not limited thereto.

[0107] The position 68 of the processing laser beam 14 can be defined as the position of the processing laser beam 14 on the surface of the workpiece 18a. Correspondingly, the position 83 of the optical measuring beam 36 can be defined (see...). Figure 5 The location of the detection area 76 can be defined as the location of the center point or the centroid of the surface of the detection area 76 on the workpiece surface.

[0108] Ignoring chromatic aberration, the second scanning area 66 of the second deflection device 52 for the optical measurement beam 36 always includes the position 68 of the processing laser beam 14, and the position 68 of the processing laser beam 14 can correspond to the center point of the second scanning area 66. This is because, after being deflected by the second deflection device 52, the optical measurement beam 36 is subsequently superimposed on the processing laser beam 14 and can be deflected together with the processing laser beam 14 by the first deflection device 26.

[0109] exist Figures 4A-4D The image also visually illustrates the processing path 70 and the weld 72 formed thereafter, along which the processing laser beam 14 is guided during the laser welding process. Furthermore, a processing speed vector 74 is shown. The processing speed vector 74 can also be a two-dimensional vector parallel to the workpiece surface. The processing speed vector 74 is tangent to the processing path 70. The processing speed is the magnitude of the processing speed vector 74.

[0110] Therefore, the processing speed can be defined as the speed at which the processing laser beam 14 irradiates and deflects along the processing path 70. The possible superimposed oscillating motion of the processing laser beam 14 can be ignored here. Oscillating motion generally refers to oscillating motion about the actual processing position, the amplitude of which typically corresponds approximately to the width of the resulting weld. When the processing laser beam 14 performs oscillating motion, the processing speed can be referred to as the average speed of the processing laser beam 14 along the processing path 70. However, preferably, the deflection of the processing laser beam 14 along the processing path 70 is not superimposed on the oscillating motion.

[0111] In addition, Figures 4A-4D The actual position 78 of the steam capillary and the theoretical or desired position 80 of the steam capillary are plotted. According to the embodiment, the theoretical position 80 can first be determined based on the aforementioned current process parameters. Alternatively or additionally, the theoretically desired deviation between the position of the steam capillary and the position 68 of the processing laser beam 14 can be determined. Subsequently, the detection region 76 can be determined based on the theoretical position 80 and the theoretical deviation. For example, the detection region 76 can be determined such that the center point of the detection region 76 corresponds to the desired position 80.

[0112] As in Figure 4A As shown, the detection region 76 is defined as circular, for example. Furthermore, the area of ​​the detection region 76 is smaller than the area of ​​the second scanning region 66 used to measure the beam 36. Therefore, compared to searching using the entire second scanning region 66, the area searched for the steam capillary can be limited, and the search can be accelerated.

[0113] Figure 4B This shows the alignment of the detection area 76 with the position 68 of the processing laser beam 14. Compared to Figure 4AThe processing laser beam 14 is further deflected along the processing path 70. As a result, the position 68 and processing direction 74 of the processing laser beam 14 change. In particular, the position 68 of the processing laser beam 14 is closer to the right edge of the first scanning area 64.

[0114] and Figure 4A In contrast, the position of the detection area 76 is matched based on the changed position of the processing laser beam 14 and the changed processing direction 74. Furthermore, compared to Figure 4A The detection area 76 increases. This requires that the optical errors and effects of the first deflection device 26 and focusing optics 24 on the measuring beam 36 at the edge of the first scanning area 64 are increased, and these optical errors and effects are typically optimized only for the processing laser beam 14. To ensure that the actual position 78 of the steam capillary is always within the detection area 76, the size of the detection area 76 can be increased as the distance between the position 68 of the processing laser beam 14 and the edge of the first scanning area 64 decreases. However, the size of the detection area 76 is still smaller than the size of the second scanning area 66. According to an embodiment, the size of the detection area 76 can also be increased as the processing laser beam 14 is deflected by the first deflection device 26, i.e., as the deflection angle along the x and / or y axes increases.

[0115] exist Figure 4C In this process, the processing speed is increased. In other words, the magnitude of the processing speed vector 74 increases. As can be seen, compared to Figure 4A In this situation, the area of ​​detection region 76 becomes larger. However, in Figure 4C In the process, the detection area 76 is still smaller than the second scanning area 66. Furthermore, due to the higher processing speed, the distance between the position of the detection area 76 and the position 68 of the processing laser beam 14 increases. This is based on the understanding that as the processing speed increases, the distance or deviation between the theoretical position 80 of the steam capillary and the position 68 of the processing laser beam 14 increases.

[0116] Figure 4D Showing compared to Figure 4C The detection area 76' is matched to the shape or geometry. Figure 4D In this embodiment, the detection region 76' has a droplet shape. According to other embodiments, the detection region may have an oval, elliptical, trapezoidal, or triangular shape. Figure 4D Additional drawing Figure 4C The detection region 76. Although the detection region 76' has essentially the same length as the detection region 76, the width of the detection region 76' is reduced relative to the detection region 76. Therefore, the area to be searched for detecting the position and depth of the steam capillary can be further optimized and reduced.

[0117] Figure 5Visually shown in Figure 4A The detection path 82 is defined within the identified or matched detection area 76. Starting from the theoretical position 80 of the steam capillary, the surface of workpiece 18a is detected by deflecting the position 83 of the optical measuring beam 36 on workpieces 18a and 18b along the zigzag detection path 82 to detect distance measurements used to determine the position 78 and depth of the steam capillary. Therefore, the detection path begins, for example, at the theoretical position 80 of the steam capillary. The detection path may also extend outward in a spiral shape, preferably starting from the theoretical position 80 of the steam capillary.

[0118] According to an embodiment, the method for determining the position or depth of a vapor capillary during laser processing can be performed repeatedly or iteratively to reliably determine the position or depth of the moving vapor capillary. For example, the vapor capillary may follow the processing laser beam along the processing path. For this purpose, the position of the vapor capillary is determined, for example, in a first step as described above. In a subsequent second step, the position of the vapor capillary determined in the first step is used as the center point of a detection area for determining the position and / or depth of the vapor capillary in the second step. Therefore, according to an embodiment, the position of the detection area follows the position of the processing laser beam along the processing path, wherein the detection area is arranged immediately following the processing laser beam.

[0119] According to the implementation method, after batch switching (Chargenwechsel) of workpieces 18a and 18b, the detection area can be increased first. This allows for consideration of possible changes in the thickness, material, or other parameters of workpieces 18a and 18b between batches.

[0120] According to the embodiment, when the optical measuring beam 36 is irradiated and deflected on the workpiece 18a by the second deflection device 52, that is, when the optical measuring beam 36 is positioned on the workpieces 18a and 18b, the color deviation between the optical measuring beam 36 and the processing laser beam 14 is considered and maintained by the control unit 62 or by the central control unit 60. This can occur, for example, by determining and storing in the control unit, as a function of the wavelengths of the processing laser beam and the optical measuring beam and the position of the optical measuring beam 36 in the first scanning field 64, through measurement or simulation, for example, as a table or functional relationship. Subsequently, when the optical measuring beam 36 deflects along the detection path 82, this deviation can be considered and corrected. The color deviation can also be referred to as the chromatic aberration of the measuring beam 36 relative to the processing laser beam 14, and means the chromatic aberration of the measuring beam 36 caused by the elements of the laser processing head 16 designed and manufactured for the processing laser beam 14. The chromatic aberration of the measuring beam 36 is based on the difference between the wavelength of the measuring beam 36 and the wavelength of the processing laser beam 14. The chromatic aberration of the optical measurement beam 36 can be caused, for example, by the focusing optics 24.

[0121] According to other embodiments, the focus of the optical measuring beam 36 is matched or corrected based on its position in the first scanning field 64. This can be achieved, for example, by the movement of the collimating optics 50. This can be achieved, in particular, by so-called motor-driven collimation. The focus matching or motor-driven collimation can also be controlled as a function of process parameters. This process is also advantageous for the focusing optics 22 when using F-θ optics, since such optics are typically designed and optimized only for the wavelength of the processing laser beam 14.

[0122] Preferably, the laser processing system 10 includes additional sensors, such as photodiodes, pyrometers, and / or cameras. These can be used to determine or filter parameters indicating the distance from the bottom of the keyhole or the deepest part of the steam capillary based on distance measurements detected by the measuring device 34. For this purpose, artificial intelligence methods can also be used if necessary; for this, a neural network should be mentioned as an example, which is trained using experimental data.

[0123] According to an embodiment, the laser processing system 10 also includes an interface for transmitting data, such as the determined position 78 and / or depth of the steam capillary, to an external system.

[0124] This invention includes a method and a laser processing system for laser beam welding using a scanning system, wherein the depth and position of a steam capillary are determined by means of OCT measurement during the laser beam welding process. The scanning system includes a first scanner for deflecting the processing laser beam and the OCT measurement beam, a second scanner for deflecting the OCT measurement beam, and a control unit for the second scanner, which determines the scanning area of ​​the OCT measurement beam based on different process parameters.

Claims

1. A method for monitoring a laser processing process, comprising: - A processing laser beam (14) is irradiated onto at least one workpiece (18a, 18b) to form a steam capillary, wherein the processing laser beam (14) is deflected on the workpiece (18a, 18b) along the processing path (70) by a first deflection device (26) within a first scanning field (64) of the first deflection device (26). - An optical measurement beam (36) is irradiated onto the workpieces (18a, 18b), wherein the optical measurement beam (36) is deflected relative to the processing laser beam (14) by a second deflection device (52), and subsequently deflected together with the processing laser beam (14) by a first deflection device (26), wherein the optical measurement beam (36) is deflected on the workpieces (18a, 18b) along a detection path (82) within a detection area (76) by the second deflection device (52), wherein the second deflection device (52) has a second scanning field (66). - Based on the portion reflected by the workpiece (18a, 18b) from the optical measuring beam (36), the distance measurement value is detected along the detection path (82). - Determine the depth and / or location of the steam capillary based on the detected distance measurements. The position (68) of the processing laser beam (14) in the first scanning field (64) is matched with the area of ​​the detection area (76) on the workpiece (18a, 18b) and the position of the detection area (76), wherein the area of ​​the detection area (76) is smaller than the area of ​​the second scanning field (66) of the second deflection device (52).

2. The method according to claim 1, wherein, The shape of the detection area (76) is also matched based on the position (68) of the processing laser beam (14) in the first scanning field (64), and / or The position, area and / or shape of the detection area (76) are matched based on the processing speed along the processing path (70).

3. The method according to claim 1 or 2 further includes determining the theoretical position (80) of the steam capillary and determining the position of the detection area (76) based on the determined theoretical position (80) of the steam capillary.

4. The method according to claim 1 or 2, wherein, The processing laser beam (14) moves along the processing path (70) without superimposed oscillating motion, and / or, The processing laser beam (14) moves along the processing path (70) solely by means of deflection by the first deflection device (26), and / or, The laser processing head remains stationary relative to the workpiece during the laser processing process, and the processing laser beam (14) is irradiated onto the workpiece through the laser processing head.

5. The method according to claim 1 or 2, wherein, The closer the position (68) of the processing laser beam (14) is to the edge of the first scanning field (64) and / or the greater the processing speed, the larger the area of ​​the detection region (76) will be.

6. The method according to claim 1 or 2, wherein, The higher the processing speed, the greater the distance between the position of the detection area (76) and the position (68) of the processing laser beam (14).

7. The method according to claim 1 or 2, wherein, The position, shape and / or area of ​​the detection area (76) are determined such that the position (68) of the processing laser beam (14) is outside the detection area (76).

8. The method according to claim 1 or 2, wherein, The second scan field (66) is smaller than the first scan field (64).

9. The method according to claim 1 or 2, wherein, The position (68) of the processing laser beam (14) is the current position of the processing laser beam (14) during the laser processing process, and / or The detection area (76) is determined in real time.

10. The method according to claim 1 or 2, wherein, The detection area (76) and / or the theoretical location (80) of the steam capillary are determined based on at least one of the following parameters: The processing direction (74) of the processing laser beam, the velocity vector of the processing laser beam, the power of the processing laser beam (14), the material and / or thickness of the at least one workpiece (18a, 18b), the deflection angle of the first deflection device (26), the optical path length of the processing laser beam (14) between the laser source (12) for the processing laser beam (14) and the at least one workpiece (18a, 18b), the optical path length of the optical measurement beam (36) between the radiation source of the optical measurement beam (36) and the at least one workpiece (18a, 18b), the focal position of the processing laser beam (14), the focal position of the optical measurement beam (36), the cross-sectional shape of the processing laser beam (14) at the focal point, the cross-sectional shape of the optical measurement beam (36) at the focal point, and the orientation of the laser processing system (10) and the at least one workpiece (18a, 18b) relative to each other.

11. The method according to claim 1 or 2, wherein, The detection path (82) has the shape of the number "8", spiral, circle, arc, zigzag and / or meander within the detection area (76).

12. The method according to claim 1 or 2, wherein, The detection region is determined based on table values ​​and / or, in the case of using an artificial neural network and / or based on functional relationships (76).

13. The method according to claim 1 or 2, wherein, The at least one workpiece (18a, 18b) comprises a battery cell and the irradiation by the processing laser beam (14) enables contact for the battery cell.

14. The method according to claim 1, wherein, The laser processing process is a laser welding process.

15. The method according to claim 10, wherein, The determination of the detection area (76) includes the determination of the location, shape and / or area of ​​the detection area (76).

16. The method of claim 10, wherein, The orientation of the laser processing system (10) and the at least one workpiece (18a, 18b) relative to each other includes the orientation of the laser processing head (16) of the laser processing system (10) and the at least one workpiece (18a, 18b) relative to each other.

17. A laser processing system (10), comprising: - A laser processing head (16) for irradiating a processing laser beam (14) onto at least one workpiece (18a, 18b) for forming a steam capillary, wherein the laser processing head (16) includes a first deflection device (26) for deflecting the processing laser beam (14) on the workpiece (18a, 18b) along a processing path (70) within a first scanning field (64); - A measuring device (34) for interferometric ranging, the measuring device being configured to irradiate the at least one workpiece (18a, 18b) with an optical measuring beam (36), and including a second deflection device (52) for deflecting the optical measuring beam (36) on the workpiece (18a, 18b) relative to the processing laser beam (14) along a detection path (82) within a detection area (76), wherein the second deflection device (52) has a second scanning field (66). - A coupling device (56) for coupling the optical measurement beam (36) to the laser processing head (16), the coupling device being arranged before the first deflection device (26) in the beam propagation direction of the processing laser beam (14), such that the optical measurement beam (36) can be deflected by the first deflection device (26) together with the processing laser beam (14). The measuring device (34) is configured to detect distance measurements along the detection path (82) based on the portion of the optical measuring beam (36) reflected by the workpiece (18a, 18b), to determine the depth and / or position (78) of the steam capillary, and to match the area of ​​the detection region (76) on the workpiece (18a, 18b) and the position of the detection region (76) based on the position (68) of the processing laser beam (14) within the first scanning field (64), wherein the area of ​​the detection region is smaller than the area of ​​the second scanning field (66) of the second deflection device (52).

18. The laser processing system according to claim 17, wherein, The first deflection device (26) is configured to deflect the processing laser beam (14) along a first axis (x) by a first maximum deflection angle (28) and to deflect the processing laser beam (14) along a second axis (y) by a predetermined second maximum deflection angle (29), wherein the first axis and the second axis (x, y) are perpendicular to each other. The first scanning field (64) is pre-given by the first maximum deflection angle (28) and the second maximum deflection angle (29), wherein the first maximum deflection angle (28) and / or the second maximum deflection angle (29) are equal to or greater than 10 degrees.

19. The laser processing system according to claim 17 or 18, wherein, The measuring device (34) includes a collimation device (48) for adjusting the focal position of the optical measuring beam (36). The measuring device (34) is configured to control the collimation device (48) to adjust the focal position of the optical measuring beam (36) based on the position of the optical measuring beam (36) in the first scanning field (64) and / or in the second scanning field (66) of the second deflection device (52).

20. The laser processing system according to claim 17 or 18, wherein, The measuring device (34) is an optical coherence tomography device or includes such an optical coherence tomography device.

21. The laser processing system according to claim 17, wherein, The laser processing system (10) is a laser welding system.

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