Method and apparatus for monitoring a laser machining process by speckle photometry

Abstract

To provide a method and an apparatus for monitoring a laser processing process, guiding at least one processing laser beam over a processing object surface along one or more paths and locally melting the surface each time.SOLUTION: The method comprises: capturing irradiated and / or scattered rays reflected from a surface of a processing laser beam or an illumination laser in a spatial resolution and time resolution manner by a high-speed camera during a processing process; and automatically determining, as state variables, from an image, at least topography or roughness of a surface in one or more sections of interest, a size of a molten pool 14, and a porosity on or under the surface in each section of interest by means of static and time resolution speckle photometry. Thereby, the state variables of the surface to be processed is obtained in real time with the high resolution and the state variables can be used for adjustment of the processing process.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method and device for monitoring a laser machining process, in particular for additive manufacturing using a powder bed, in which at least one machining laser beam is guided along one or more paths over the surface to be machined, locally melting the surface in each case by forming a molten pool.

[0002] Additive manufacturing, or additive manufacturing, allows for the time- and resource-efficient production of components with nearly unlimited creative and structural freedom. This technique is particularly valued and promoted for its advantages in functional manufacturing, offering high innovation and applicability in the fields of tool-based manufacturing, aerospace, medical technology, and in lightweight construction and prototyping in general, for example in the production of conformally cooled turbine blades or personalized medical implants.

[0003] Although manufacturing processes are continuously being developed, these manufacturing processes must be properly monitored for quality assurance. Missetting process parameters or fluctuations in process conditions can lead to poor mechanical and technological properties of the resulting part or even to process interruptions. Reactive defect handling in parts is only partially possible and negates the advantages of additive manufacturing. Therefore, it is clear that a solution is needed for machine-integrated process monitoring that can detect defects as soon as they occur and stop the construction of the part to save material, time, and costs that could be incurred in further construction and processing. Alternatively, anomaly recognition can be used to control the manufacturing process and perform parameter adjustments without the need to interrupt the process.

[0004] Powder-bed additive manufacturing processes, such as selective laser melting (SLM) and laser powder bed fusion of metals (LPBF-M), represent a new class of manufacturing processes with a series of advantages over traditional manufacturing processes. Thus, for example, they can be used to produce finely detailed metal parts with significantly reduced weight that are not manufacturable by conventional casting, forging, and milling processes. These processes are particularly important industrially, especially because they allow for the relatively rapid and economical production of small quantities of spare parts.

[0005] However, powder-bed processes such as SLM or LPBF-M only produce high-quality parts with a low number of rejects when optimal process parameters are selected. However, the optimal process flow is often unknown, and there are no easy nondestructive testing methods that allow for simple, comprehensive testing of the components produced during the process. While there are up to 50 known factors that affect the process, these often have an unknown impact on process quality and can result in defects. These include, for example, poor bonding, material impurities, poor surface quality, porosity, or even lack of process continuity. Until now, it has not been possible to directly assess the causes of material, laser, and melt interactions in real time with high resolution. This is the only method that allows for the independent evaluation of process and material parameters to determine the extent to which the process produces defect-free components without the need for costly testing later. [Background technology]

[0006] The growing demand for better monitoring solutions and product documentation has led to the development of various methods in recent years. Thus, there are methods for determining the weld pool dimensions, similar to those already used in the field of laser welding. Using a beam splitter, the emitted radiation of the weld pool is detected by a photodiode and evaluated based on the gray value of a digital histogram. Based on the radiation intensity, an additional CMOS camera can be used to record and evaluate the characteristics of the weld pool.

[0007] US Patent No. 5,629,999 describes a method for coaxial monitoring of the weld pool using a high-resolution camera and a photodiode. A further development of this system, utilizing a thermographic detector, is described in US Patent No. 5,629,999. Here, the irradiation intensity of the weld pool is displayed as a function of the laser beam position in the x and y coordinates by a mapping algorithm. This procedure allows the creation of a composite image of the weld pool temperature, which generates an image of the image record. Dark spots in the image here represent signs of deviating process heat flow and may therefore indicate localized part bulging due to internal stress and heat accumulation in overhanging geometries.

[0008] Infrared pyrometer or thermography techniques are also used to examine the spatial and temporal evolution of the heat affected zone in the beam melting process, as for example in US Pat. No. 5,649,399.

[0009] Patent document 4 discloses an apparatus for spatially resolved temperature measurement in a laser processing method, in which an optical detector is arranged coaxially with the processing laser beam together with an optical filter that blocks the wavelength of the processing laser beam, and detects thermal radiation emitted from the processing area to determine the temperature.

[0010] In Patent Document 5, the exit velocity of the build material from the extrusion nozzle during 3D printing is monitored by laser speckle photometry. Patent Document 6 uses various methods, including laser speckle photometry, in combination with multiple light sources to monitor the machining process. Here, laser speckle photometry detects microvoids and unmelted metal. However, the details of the evaluation are not described.

[0011] Previous quality assurance methods, such as monitoring the weld pool or the build process with thermography or image-assisted methods, are not suitable for controlling high-speed processes in minimal space. All described methods are limited to monitoring individual process characteristics or defects during production, or utilize a combination of several methods. The large amount of data generated presents a further problem area for thermography and image-assisted monitoring methods, since real-time evaluation of the measurement data is not possible and significant recording capacity must be generated for product documentation in industrial environments. For example, in the aerospace industry, all quality-related data must be tracked for periods of up to five years. Infrared thermometers are suitable for deriving process parameters, such as the powder layer height. However, they are highly susceptible to noise during the process, making it impossible to make specific conclusions about the actual temperature. Furthermore, at temperatures of 500 μm, 2 For small target areas, only recording speeds as low as 50 ms (20 Hz) are achievable.

[0012] Previous methods evaluate the entire component layer and are very coarse and slow for individual laser points (approximately 30 μm to 80 μm). This method, which focuses on the region of the molten pool, specifically focuses on the melting process and expansion, but due to the amount of data, real-time evaluation or adequate detailed resolution of individual laser points is not possible. In particular, detailed thermal resolution (fine phase) of the molten pool is currently not available in any method. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] U.S. Patent Application Publication No. 2009 / 0206065 [Patent Document 2] European Patent No. 2598313 [Patent Document 3] German patent no. 102014212246 [Patent Document 4] European Patent No. 1693141 [Patent Document 5] U.S. Patent No. 9,527,240 [Patent Document 6] U.S. Patent Application Publication No. 2020 / 110025 Summary of the Invention [Problem to be solved by the invention]

[0014] It is an object of the present invention to provide a method and an apparatus for monitoring a laser machining process, in particular for additive manufacturing using a powder bed, which method and an apparatus allow in-line monitoring of the manufacturing process in real time with high detail resolution. [Means for solving the problem]

[0015] The above problem is solved by the method according to claim 1 and the method according to claim 2. to 11 The problem is solved by the device described. Advantageous configurations of the method and device are the subject of the dependent claims or can be found in the following description and examples.

[0016] The method monitors a laser processing process in which at least one processing laser beam is guided along one or more paths over the surface to be processed, locally melting the surface in each case by forming a molten pool. This can be, for example, a welding process, a smoothing process, or (in a preferred application) a powder bed additive manufacturing process in which a layer of powder is melted in each case corresponding to the cross-sectional area of ​​the part to be manufactured, thus building the part layer by layer.

[0017] In the proposed method, during the processing process, the laser radiation reflected and / or scattered from the surface of the processing laser beam is captured (detected) in a spatially and time-resolved manner by a camera with high temporal and spatial resolution, thereby obtaining a time-resolved and spatially resolved image suitable for laser speckle photometry. In an alternative embodiment, an additional laser is used to illuminate the surface, and the laser radiation reflected and / or scattered from the surface is captured in a spatially and time-resolved manner by a camera, thereby obtaining a time-resolved and spatially resolved image suitable for laser speckle photometry. In this case, it is preferable to use a suitable optical filter in front of the camera that only passes the respective laser radiation, i.e., has a corresponding small transmission bandwidth. The camera can be, for example, a CMOS camera or a CCD camera, and preferably, a lens or objective lens that images the processing surface is located upstream of this camera. In this case, it is preferable that the camera allows a recording frequency of up to 32 kHz. In the proposed method, during the machining process, several state variables of each currently machined surface area are automatically determined from images acquired by a camera by means of evaluation methods or algorithms of static and time-resolved laser speckle photometry, suitably displayed, compared with target variables, or even used to regulate the machining process. The state variables are at least the surface topography or roughness in one or more sections within the area of ​​the position of incidence of the machining laser beam on the surface, the size of the respective molten pool, and the surface or subsurface porosity in one or more sections within the area of ​​the position of incidence of the machining laser beam on the surface. Here, the capture of the reflected radiation and / or scattered radiation by the camera is preferably performed coaxially with respect to the machining laser beam.

[0018] Therefore, the proposed method and related device use a laser speckle photometry method for process monitoring. This optical method utilizes the heat generated during the processing or manufacturing process. If there is a defect in the ongoing melting or sintering process, the occurrence of material defects is estimated from changes in the interference pattern due to surface roughness and heat transport. If necessary, the process is then interrupted or adjusted based on the determined state variables. Image data for laser speckle photometry are acquired each time during the processing process. The speckle pattern, generated by the reflection and / or scattering of laser radiation (from the processing laser or additional illumination laser), is recorded by a camera and evaluated by a suitable computer algorithm. Here, for example, correlations between the statistically determined size of the speckle pattern and process parameters such as laser power, laser speed, and / or process energy density can be detected, and, in the case of manufacturing processes using powder beds, powder contamination can also be detected, if necessary.

[0019] In many laser processing processes, the processing laser beam is guided across the surface to be processed by one or more scanner mirrors, for example, a galvanometer scanner. The reflected radiation and / or scattered radiation is also preferably captured (detected) by a camera via these scanner mirrors, coaxially with the processing laser beam. Therefore, the incident position of the processing laser beam on the surface in each image acquired by the camera is at the same position within the image, and therefore the sections selected for evaluation of successive images in time are also at the same position within the image.

[0020] In principle, the reflected radiation and / or backscattered radiation can also be captured (detected) independently of the current position of the processing laser beam, i.e., non-coaxially with respect to the processing laser beam. The position of incidence of the processing laser beam relative to the surface must be detected in each individual image, since the position of incidence in each image varies. For this purpose, a laser beam tracking algorithm is preferably used. This algorithm recognizes the position of incidence of the processing laser beam in the image based on the presence of speckle dynamics in the speckle pattern, and only slight position changes from image to image are taken into account. Here, the filter used provides a list of possible positions, from which the one that best matches each acquired image is selected using information derived from the process parameters. These positions can then be combined into a corresponding smoothed path to define the respective scan line. Next, in relation to each current position of the laser beam in the image, a section is selected for evaluation, i.e., a section that determines the topography or roughness, the size and porosity of the molten pool, and possibly further state variables. Here, depending on the method, the evaluation of each of these sections can be carried out while the heating zone or the laser beam is just passing through these sections, or after the heating zone or the laser beam has already traversed these sections. This also applies to the selection of the sections to be evaluated in the case of coaxial illumination. In both alternatives, it is also possible to create a composite image of the heating zone characteristics of the entire surface to be processed, respectively.

[0021] In the proposed method, static and time-resolved laser speckle photometry algorithms are used to evaluate the acquired images. The surface topography or roughness in each evaluated section is determined by static analysis, i.e., by analyzing each individual image. For this purpose, the gray value distribution of the image is evaluated, and the topography is estimated from this gray value distribution. The size of the weld pool is determined by dynamic analysis. Here, the number of pixels affected by the thermal expansion of each target section, which are visible in the speckle pattern, is counted, since the number of pixels correlates with the size of the heated zone and thus the size of the weld pool. To determine the surface or subsurface porosity in each target section, a dynamic analysis is performed using a differential correlation function (DKF). This differential correlation function also allows for the recognition of possible surface or subsurface inhomogeneities. More details about this evaluation algorithm can be found in the examples below.

[0022] The apparatus used in this method accordingly preferably includes a high-resolution, high-speed camera equipped with an optical filter and a lens or objective. The lens or objective is integrated into the processing setup for the laser processing process and captures (detects) reflected radiation and / or scattered radiation from the surface in a spatially and time-resolved manner coaxially with the processing laser beam, and records time-resolved and spatially resolved images suitable for speckle photometry. For this purpose, a camera capable of recording images at a frame rate of more than 2000 frames per second is preferably used, particularly a camera capable of recording frequencies up to 32 kHz. In the proposed apparatus, the camera is connected to an evaluation device, which automatically determines from the images, by static and time-resolved laser speckle photometry evaluation methods, at least the surface topography or roughness in one or more sections within the region of the incident position of the processing laser beam on the surface, the size of the respective molten pool, and the surface or subsurface porosity in one or more sections within the region of the incident position of the processing laser beam on the surface as state variables. The evaluation device is preferably located directly next to the camera and includes at least one GPU module. The determined state variables can also be provided in various ways, for example in the form of one or more images or as a parameter list. The determined state variables can also be compared with target variables, and a signal can be generated if the respective state variable deviates from the target variable by more than a threshold value. The agreement or deviation can also be visualized, for example in the form of a traffic light display.

[0023] The proposed method and associated apparatus allow for in-line monitoring of the laser machining process or the surface being machined thereby based on many different characteristics. The method and apparatus provide high spatial resolution and higher recording speeds than conventional methods, while also allowing for adjustment of the machining process based on the determined state variables.

[0024] The proposed method and the associated device will now be explained in greater detail on the basis of examples in connection with the drawings. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 shows an overview of the algorithm used in the proposed method for determining the different state variables. [Figure 2] 1 is a schematic diagram of the use of the proposed device in the processing mechanism of a laser processing machine. [Figure 3] 1 is a diagram showing an example of the structure of the proposed device and its connection to a laser processing machine. FIG. [Figure 4] 10 is an exemplary diagram of a selection of sections for evaluation within an image recorded by a camera. DETAILED DESCRIPTION OF THE INVENTION

[0026] The proposed method and the associated device are described in more detail below, based on their application to monitoring additive manufacturing processes using powder beds. Here, speckle images recorded by a camera are evaluated both statically and dynamically in the method and device. The dynamic evaluation allows for the evaluation of the size of the heating zone or molten pool, open cavities, porosity, and even contamination of the powder used to build the part. To evaluate each state, algorithms are used to evaluate the thermal excitation after selective melting of the powder. This is related to the area of ​​the heating zone or molten pool and, if necessary, the cooling dynamics near the molten area. Figure 1 shows an exemplary overview of some of the algorithms that can be used in the proposed method.

[0027] Quantitative analysis of the part surface is based on evaluating the granularity of the speckle pattern in the acquired images. In additive manufacturing, topographical characteristics are important, starting from the powder state, through the newly produced layers, and all the way to the roughness of the finished part. For example, during LPBF-M, the short interaction time between the laser and the metal powder and the low viscosity of the metal melt place high demands on process control and often lead to the occurrence of the so-called "balling" phenomenon, in which the molten pool splits into multiple spherical molten beads. This results in undesirable surface topography and impacts further manufacturing processes.

[0028] Laser speckle photometry (LSP) allows the evaluation of topographical conditions through static images, with calibration in the measurement area. Differences in powder distribution can be seen, for example, in the gray value distribution. Furthermore, a visual inspection of the powder application can be performed separately. Images of the powder layer can also be used to recognize, for example, possible streaks in the powder, wear and damage to the coater (squeegee). This can be achieved with high temporal and spatial resolution.

[0029] Essential parameters for assessing surface topography or surface roughness from static images of LSP can be determined based on speckle size, statistical evaluation of gray value distribution (entropy of the image histogram) or by image processing algorithms of gray value transition matrices. The determined parameters can then be compared, for example, with reference values.

[0030] The speckle size is calculated by the half-width of the normalized autocorrelation function (Equation 1), which is defined by the intensity of the speckle pattern observed at the detection plane.

number

[0031] The autocorrelation function of a signal is the Fourier transform of the signal's power density. This phenomenon is called the Wiener-Khintchine theorem, whereby the power spectrum and inverse (inverse) power spectrum of the speckle image can be calculated, and then the autocorrelation can be obtained.

[0032] The entropy of the histogram of a still image is evaluated according to equation (2) as follows:

number

[0033] The evaluation of the gray value transition matrix (GLCM) is based on image processing methods for texture analysis. Typical features of this evaluation are:

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[0034] To evaluate the porosity, the differential correlation function (DKF) is used. This dynamic parameter is based on the evaluation of the gray value distribution with the time-dependent gray value change of individual pixels. This parameter is defined as follows:

number

[0035] This evaluation assumes that the thermomechanical properties of a material are characterized by optical images of dynamic speckle patterns caused by the target thermal expansion. In the case of additive manufacturing, the manufacturing process generates localized heating. Therefore, the LSP technique can detect heated areas in-line and evaluate strain changes locally. As a result of this analysis, trends in the correlation function values ​​can be observed.

[0036] Thus, for example, a locally heated surface above a defect will be hotter than a defect-free surface, despite the same optical absorption characteristics and surface topology, due to the lower relative density of the respective surface regions. This behavior is due to the reduced thermal conductivity within the cavity. Both boundary layers and defects result in heat accumulation and are considered insulating layers. The temperature increase results in material expansion, especially in the region of the treated surface. The scattering points that generate the speckle pattern shift, resulting in a visible speckle movement and change. This results in a slope of the detected DKF curve.

[0037] A further application of the LSP method is the detection of heterogeneities (inhomogeneities) based on DKFs. This relates to the classification of time signals of local temperatures or defect detection using discrete values ​​of DKFs. The representation of a discrete physical signal through time and space, such as a rapid time sequence of images or videos (up to 4 kHz) in the case of LSP, is equivalent to a representation by DKFs.

[0038] During the build process, the laser irradiation completely melts the powder, rapidly solidifying it and forming a strong bond with the underlying material layer. This process is repeated until the entire component is fabricated layer by layer. The hardening mechanism of the melt is essentially influenced by surface tension, viscosity, wetting, evaporation, oxidation, and thermocapillary effects. The typically high cooling rates in this process are problematic, especially for metallic materials, as they can result in high internal stresses, hot cracking, gas inclusions, and component deformation, depending on the alloy system and process strategy. Therefore, in-line measurements of the heating zone during the build process can be used to generate essential parameters for tuning internal stresses, component deformation, and the formation of gas inclusions.

[0039] The speckle pattern detects the local expansion of the material in the region of the molten pool, where it exhibits a characteristic speckle dynamics that differs from that of solidified material. Therefore, the count of pixels affected by thermal expansion in the speckle image correlates with the size of the heated zone, which in turn correlates with the energy input of the welding laser and the melt properties. The area of ​​the expanded zone is evaluated in each case by determining the number of pixels of the heated zone at the position of the laser beam, i.e., at the point of incidence of the laser beam on the surface. The number of pixels can be converted into meters.

[0040] Using the DKF algorithm, the heat conduction and absorption behavior of the material surface within the heating zone can be further evaluated. For this purpose, the DKF can be calculated locally for a specific heating zone in relation to the position of incidence of the processing laser beam. Special software allows for the local evaluation in graphical or tabular form. The software also knows or recognizes the position of the laser beam within the image and automatically determines the parameters relevant for the evaluation of the surface condition.

[0041] The speed of the algorithm allows for in-line measurements, which allow for local melting by the laser spot followed immediately by subsequent adjustments based on the evaluation results. This allows for defects to be removed before the melt completely solidifies or for defects to be adjusted in the current beam guidance. The method described herein is therefore suitable for powder bed additive manufacturing methods that respond in a geometry-adaptive manner to part geometry and the changing thermal behavior in the beam path.

[0042] 2 shows a schematic diagram of an example of a laser processing machine in which the proposed device (hereinafter referred to as LSP measurement system 1) is integrated. The laser processing machine comprises a processing laser 6, the laser beam of which is directed to the surface to be processed, i.e., a workpiece 13, by means of a scanner 5 in this illustration. In this example, the surface is additionally illuminated by an illumination laser (also referred to as LSP laser 7), and a suitable image of the surface is obtained from the reflected radiation and / or scattered radiation of the LSP laser 7 using the LSP measurement system 1, which performs speckle photometry. The coupling of the illumination laser beam and the acquisition of the image using the LSP measurement system 1 are each performed via a semi-transparent mirror 12, each coaxially aligned with the processing laser beam.

[0043] An example configuration of an LSP measurement system 1 is shown schematically in FIG. 3. In this example, the measurement system 1 includes a high-resolution image converter (CMOS / CCD) 2 with upstream optical filters 3 and lenses / objectives 4, as well as an energy-efficient chipset / electronics (not shown) for control of the measurement regime and sensor-related image processing. The illustrated module further includes one or more suitable interfaces 8, a power supply unit 9, and an evaluation unit 10. The evaluation unit 10 preferably includes a GPU for computation. The figure also shows an optional illumination laser 7, e.g., a laser diode, which can be used in addition to or instead of the processing laser 6 that excites the speckle pattern.

[0044] In a powder bed build process, a processing laser beam heats the powder based on a scan sequence defined by the AM machine (AM: Additive Manufacturing). When coaxially acquired (captured) by the LSP measurement system 1, as in Figure 2, one or more evaluation areas 11 are determined in the image by the software of the proposed machine relative to the laser beam's incidence position. Figure 4 explains the procedure based on the illustrated image. Here, the laser beam's incidence position in the form of a laser spot 15, the molten pool 14, the powder particles 16, and the evaluation area 11 are shown schematically. The scanning direction is also indicated by a left-pointing arrow. Disturbances, such as sparks and molten bead formation, are filtered out by specially developed filters to reduce the influence of interfering signals. This procedure also makes it possible to create and evaluate a composite image of the heating zone characteristics of a layer or an entire layer.

[0045] During the evaluation, for example, to determine the state of porosity based on the DKF, the evaluation area 11 is determined point by point or scanned across the image to locally approximate the heated zone of the newly melted material. The nature of the topography can be determined, for example, locally or across the entire layer. The calculation of the area of ​​the heated zone is performed continuously around the processing laser beam or laser spot 14. The determination of porosity, inhomogeneities, and contamination is performed within the rectangular evaluation area 11 shown in this example. The calculations are performed by the above-mentioned algorithms, and correlations are established between the state of the material, roughness, inhomogeneities, porosity, contamination, or the size of the heated zone.

[0046] When the image is acquired non-coaxially, the laser beam tracking already described above is performed to detect the position of the laser spot 14 in the speckle pattern. For this purpose, the laser position or the heating zone position is recognized based on the presence of speckle dynamics in the speckle pattern. Then, as in the description of FIG. 4, the position of the evaluation area 11 is selected relative to the detected position of the laser spot 14. [Explanation of symbols]

[0047] 1 LSP measurement system 2 Cameras 3. Filters 4 Lenses / Objectives 5. Scanner 6 Processing laser 7 LSP Laser 8 Interface 9 Power Supply Unit 10 evaluation units / GPU 11 Sections or evaluation areas within an image 12 Partially Transmitting Mirror 13 Materials 14 Molten pool 15 laser spot 16 powder

Claims

1. A method for monitoring a laser machining process, comprising directing at least one machining laser beam along one or more paths across a surface to be machined, locally melting said surface in each case by forming a molten pool (14); In the method, during the processing process: capturing reflected radiation and / or scattered radiation from said surface of said processing laser beam or of an additional laser (7) used to illuminate said surface by a high-speed camera (2) in a time-resolved and spatially resolved manner to obtain time-resolved and spatially resolved images suitable for laser speckle photometry; From said images, automatically by evaluation methods of static and time-resolved laser speckle photometry, at least the topography or roughness of the surface in one or more sections within the region of the incident position (15) of the processing laser beam on the surface; the size of each of the molten pools (14); porosity on or below the surface in one or more sections within the region of the incident position (15) of the processing laser beam on the surface; is determined as a state variable, A method wherein the porosity on the surface or below the surface is determined by a differential correlation function of each of the time-sequential images.

2. 2. A method according to claim 1, characterized in that the capturing of the reflected radiation and / or scattered radiation is performed by the camera (2) coaxially with respect to the processing laser beam.

3. 3. The method according to claim 2, characterized in that the processing laser beam is guided over the surface to be processed by one or more scanner mirrors, and the capturing of the reflected radiation and / or scattered radiation by the camera (2) also takes place via these scanner mirrors.

4. 2. The method of claim 1, wherein the position of incidence (15) of the processing laser beam relative to the surface in the image is determined by a tracking algorithm.

5. A method according to any one of claims 1 to 4, characterized in that the topography or roughness of the surface is determined by grey value distribution in each of the images.

6. The method according to any one of claims 1 to 5, characterized in that on the basis of the difference correlation function, the heterogeneity on or below the surface is also determined as a further state variable.

7. 7. The method according to claim 1, wherein the size of each of the molten pools (14) is determined by counting the number of pixels in each of the images that are affected by thermal expansion at the surface.

8. 8. Method according to any one of claims 1 to 7, characterized in that a filter (3) with a transmission bandwidth of 5 nm or less is used in front of the camera (2).

9. 9. Method according to any one of claims 1 to 8, characterized in that as camera (2) a camera is used which is capable of recording frequencies up to 32 kHz.

10. The method of any one of claims 1 to 9, wherein the laser machining process is adjusted based on one or more of the state variables.

11. An apparatus for monitoring a laser machining process, the apparatus comprising a machining mechanism for directing at least one machining laser beam along one or more paths across a surface to be machined, locally melting said surface in each case by forming a molten pool (14); The device comprises at least a high-speed camera (2) for capturing reflected and / or scattered radiation from the surface of the processing laser beam or of an additional laser (7) used to illuminate the surface during the processing process in a time-resolved and spatially resolved manner to obtain time-resolved and spatially resolved images suitable for laser speckle photometry; an evaluation device (10) connected to the camera (2); The evaluation device (10) automatically derives from the image by static and time-resolved speckle photometry evaluation methods at least the topography or roughness of the surface in one or more sections within the region of the location of incidence of the processing laser beam on the surface; the size of each of the molten pools; porosity on or below the surface in one or more sections within the region of the location of incidence of the processing laser beam on the surface; is determined as a state variable, the porosity on the surface or the subsurface is determined by a differential correlation function of each of the time-sequential images; The apparatus, wherein the camera (2) is integrated into the processing setup for the laser processing process so as to capture the reflected radiation and / or scattered radiation from the surface coaxially with respect to the processing laser beam.

12. 12. Device according to claim 11, characterized in that the camera (2) allows a recording frequency of up to 32 kHz.

Images