Method and apparatus for additive manufacturing of a workpiece

Abstract

The present invention relates to a method and apparatus for additive manufacturing of a workpiece (14) using a dataset (34) that defines the workpiece (14) in multiple layers (16) arranged vertically above each other. A construction tool (24) moves a first energy beam (26) relative to a manufacturing platform (12) in a spatially resolved manner. A measuring device (36) determines various characteristics of the layer stack (20). The measuring device (36) includes an exciter (38) that excites the stack (20) by means of a second energy beam (42), and a detector (40) that detects the characteristics of the stack (20) as a result of the excitation in a spatially resolved manner. A controller (30) controls the second energy beam (42) and / or a detection path (44) to perform measurements along multiple measurement trajectories (46), which may differ from the trajectory (28) of the first energy beam (26). The first scanning unit (50) and the additional scanning unit (54) establish beam paths that are completely separate from each other for the first energy beam (26) and the second energy beam (42) and / or for the first energy beam (26) and the detection path (44).

Description

Technical Field

[0001] This invention relates to a method for additive manufacturing of workpieces, comprising the following steps:

[0002] - Receive a dataset that defines the workpiece in multiple layers arranged vertically above and below each other.

[0003] -Provide a manufacturing platform

[0004] - Provides a construction tool with a first scanning unit configured to move a first energy beam in a spatially resolved manner relative to a manufacturing platform.

[0005] - Multiple first trajectories are determined based on the dataset.

[0006] - In time-sequential steps, a first energy beam is moved relative to the manufacturing platform along one of the plurality of first trajectories, respectively, to produce a stack of workpiece layers arranged vertically to each other, corresponding to the first trajectories, in time-sequential steps.

[0007] - Determine various characteristics of the stack using a measuring device having an exciter that excites the stack with a second energy beam and a detector that detects the characteristics of the stack as a result of the excitation in a spatially resolved manner along a defined detection path, wherein the second energy beam and / or the detection path move relative to the manufacturing platform along a plurality of additional trajectories by means of an additional scanning unit, and wherein the additional trajectories are at least partially different from the first trajectory.

[0008] The present invention also relates to an apparatus for additive manufacturing of a workpiece, the apparatus having an interface for receiving a dataset defining the workpiece in multiple layers arranged vertically to each other; a manufacturing platform; a build tool having a first scanning unit configured to move a first energy beam relative to the manufacturing platform in a spatially resolved manner; and a controller, depending on the dataset, controlling the first scanning unit to move the first energy beam relative to the manufacturing platform along multiple first trajectories in temporally consecutive steps, wherein the build tool produces, in temporally consecutive steps, a stack having workpiece layers arranged vertically to each other, these workpiece layers corresponding to the first trajectories. ; and having a measuring device configured to determine various characteristics of the stack, wherein the measuring device has an exciter configured to excite the stack with a second energy beam, wherein the measuring device has a detector configured to detect, in a spatially resolved manner, the characteristics of the stack as a result of the excitation along a detection path, wherein the measuring device has additional scanning units, and wherein a controller is configured to control the additional scanning units separately from the first scanning unit, wherein the second energy beam and / or the detection path move relative to the manufacturing platform along multiple additional trajectories, wherein the additional trajectories may differ from the first trajectory. Background Technology

[0009] DE 10 2016 110 266 A1 discloses this method and the corresponding equipment.

[0010] Additive manufacturing methods used for producing workpieces are sometimes referred to as 3D printing. Different additive manufacturing methods exist. In so-called selective laser sintering (SLS), for example, a powder bed with a large number of metal powder particles is used. Selected powder particles on the upper side of the powder bed are spatially resolved, i.e., locally and selectively melted by means of a laser beam and thus bonded together. New powder layers are then applied to the workpiece structure, and the workpiece is thus produced layer by layer. Other additive manufacturing methods use electron beams instead of laser beams. Yet another method selectively applies powdered or filamentary material onto a manufacturing platform and selectively melts the material with an electron beam or laser beam. Electron beams or laser beams are examples of the first energy beam, which the build tool can use to produce material structures layer by layer, forming the workpiece after all layers have been completed. Individual workpiece layers are often produced from bottom to top on the manufacturing platform, where the manufacturing platform itself lowers the corresponding layer height after each workpiece layer.

[0011] Additive manufacturing of workpieces enables the production of highly complex individual workpieces at low material costs. However, significant challenges remain regarding workpiece quality because material inhomogeneities or anomalies can occur in each layer, negatively impacting workpiece quality. These inhomogeneities / anomalies can include porosity, cracks, and unmelted material. For this reason, numerous recommendations exist for detecting inhomogeneities / anomalies in additively manufactured workpieces as early as during layer production.

[0012] The following publication provides a review: Sarah K. Everton et al., “Review of in-situ process monitoring and in-situ Metrology for metal Additive Manufacturing,” Materials and Design, 95 (2016), pp. 431–445. According to one suggestion, the so-called molten pool, i.e., the area of ​​material melted by an energy beam, is recorded with a camera, and the average temperature on the molten pool is determined. The obtained data can be used to monitor the production process, but they do not provide any direct information about quality-related inhomogeneities / anomalies, some of which only appear after the molten pool has solidified.

[0013] In some proposals, a beam splitter is used to integrate the camera's observation beam path into the beam path of the construction tool. In contrast, US 2015 / 0375456 A1 proposes separate scanning units for monitoring the molten pool.

[0014] EP 1 815 936 B1 describes a method for additive manufacturing of a workpiece in which an ultrasonic pattern is excited in an upper layer of the workpiece by means of a second laser beam. The ultrasonic waves interact with inhomogeneities / anomalies and generate interference patterns, which can be determined based on the echo response from the surface. Furthermore, EP 1 815 936 B1 proposes eddy current analysis of the corresponding upper material layer and dimensional measurements using speckle interferometry, a laser scanner, or a stereo optical system. The laser used to generate the ultrasonic pattern should follow the laser of the building tool at a fixed distance of several centimeters. A similar proposal is disclosed in US 7,278,315 B1.

[0015] DE 10 2016 110 266 A1, mentioned in the introduction, proposes an optical unit that couples a beam for process monitoring into the processing beam. The measurement beam can be freely positioned within the working region of the processing beam using additional, separate scanning mirrors. However, process monitoring is spatially coupled into the working region of the processing beam. Summary of the Invention

[0016] Against this backdrop, the object of the present invention is to provide a method and apparatus of the type mentioned in the introduction, which enables improved monitoring of production processes closely related to manufacturing, so as to detect non-uniformities / abnormalities as early as possible, and, if necessary, to correct non-uniformities / abnormalities during the production process.

[0017] According to a first aspect of the invention, this object is achieved by a method of the type mentioned in the introductory section, wherein a first scanning unit and a further scanning unit establish completely separate beam paths for a first energy beam and a second energy beam and / or for the first energy beam and a detection path.

[0018] According to another aspect, this objective is achieved by a device of the type mentioned in the introduction, wherein a first scanning unit and a second scanning unit establish completely separate beam paths for the first energy beam and the second energy beam and / or for the first energy beam and the detection path.

[0019] Therefore, this novel device is capable of moving the first energy beam (write beam) and the second energy beam and / or detection path (one or more measurement beams) relatively independently of each other relative to the manufacturing platform and the workpiece surface disposed on the manufacturing platform. "Relatively independent" here means that the first scanning unit and the other scanning units are different from each other and can be controlled such that the second energy beam and / or detection path moves along a different trajectory than the first trajectory. Compared to the prior art described above, the first energy beam and the measurement beam therefore no longer need to move together and along a common trajectory. The first energy beam and the measurement beam can, in principle, move along a common trajectory through appropriate control of the first and other scanning units. However, the novel device is not limited to this, and the novel method advantageously utilizes the fact that the other trajectory can be at least partially and advantageously, even completely different from the first trajectory. In a preferred exemplary embodiment, trajectories that are spatially distant from each other and different from each other with respect to their respective instantaneous directions of motion and / or speeds of motion are implemented. The second energy beam and / or detection path can advantageously be positioned at any point during the production process at a lateral distance from the first energy beam, a lateral distance greater than half the diameter of the manufacturing platform in the corresponding distance direction. The practical result of this is that the layer stack can be inspected at a point “far” from the instantaneous processing position of the build tool on the layer stack. Therefore, the layer stack can advantageously be inspected while build is being performed simultaneously at a cooled measurement location. This is advantageously made possible by separate optical paths for the first and second energy beams or detection paths.

[0020] In the preferred exemplary embodiments and configurations discussed in more detail below, the "collision" between the second energy beam and / or the detection path and the first energy beam is avoided through appropriate control of the first and additional scanning units. Therefore, the preferred exemplary embodiments of this novel method and device involve considering the control of the first scanning unit when controlling the additional scanning units (and / or vice versa) to avoid energy beam "collisions" or overlap. However, the resulting dependence on the control of the first and additional scanning units does not conflict with the aforementioned ability to generate different trajectories in a manner separate from each other.

[0021] It is conceivable that in some exemplary embodiments of this novel method and device, the additional scanning unit moves only the second energy beam or only the detection path of the measuring device relative to the manufacturing platform. In principle, the second energy beam can excite a stack where the workpiece layers are generally arranged vertically relative to each other, i.e., arranged in a non-spatial-resolution manner, and spatial resolution detection of non-uniformity / abnormalities is essentially performed through appropriate movement of the detection path. Conversely, it is conceivable in principle that the spatial resolution of the detection is primarily achieved by locally selectively exciting the stack with the second energy beam, while the stack or its surface is acquired as a whole by a camera. However, in a preferred exemplary embodiment, the stack is excited and detected separately with the second energy beam in a locally selective manner. Therefore, the descriptions given above and below also apply to the detection path and the second energy beam.

[0022] This novel method and apparatus offer the following advantages: Inspection of the workpiece surface to detect any non-uniformities / anomalies can be performed simultaneously, without affecting the production of new workpiece layers (except for the advantageous avoidance of energy beam overlap). Specifically, the writing beam (first energy beam) and the measuring beam (second energy beam) can move simultaneously in areas as far apart as possible on the workpiece surface or manufacturing platform. As a result, for example, a new workpiece layer can be built on the "left" side of the workpiece, while the already constructed layer is inspected on the "right" side. Therefore, it is also possible to inspect the construction made in the workpiece area at the start of a manufacturing step and, if necessary, correct it immediately before starting the next workpiece layer (rework).

[0023] Therefore, this novel method and corresponding equipment enable flexible monitoring of manufacturing processes closely related to the process, as well as targeted detection of non-uniformity / abnormalities in already cured workpiece areas. Thus, the aforementioned objectives are fully achieved.

[0024] In a preferred configuration of the novel method and corresponding apparatus, the second energy beam and / or detection path moves along one of the plurality of additional tracks by means of an additional scanning unit in one of the time-sequential manufacturing steps, while the first energy beam moves along the first track.

[0025] In this configuration, the novel method and corresponding apparatus advantageously utilize the possibility of inspecting a stack of workpiece layers arranged vertically to each other while the upper workpiece layer is still being produced with the first energy beam. Therefore, the novel method and corresponding apparatus in this configuration benefit from two simultaneous, separate movements of the energy beam. This configuration facilitates the additive manufacturing of high-quality workpieces in a short time.

[0026] In another configuration, the second trajectory is determined based on the first trajectory, wherein, preferably, the overlap of the second energy beam and the first energy beam on the stack body is avoided.

[0027] This configuration involves the advantageous adaptation of the movement of the second energy beam (measurement beam) to the movement of the first energy beam (write beam) without resulting in rigid structural coupling. When determining the second trajectory, it is advantageous to consider that the energy input into the layer stack within a defined space and time interval remains below a defined threshold. In this configuration, the measurement beam advantageously excites the workpiece layer in a localized area only when the workpiece material has been sufficiently cooled and hardened, i.e., below a defined temperature threshold. This advantageously minimizes hot spots, internal stress, and delamination in the layer stack. Furthermore, the layers can be inspected more easily and accurately. The second energy beam (heating) via an additional scanning unit differs from the first energy beam (write beam) in the preferred exemplary embodiment in that it generates less energy than the first energy beam to remain below the melting temperature. Localized selective heating can also be considered when determining an additional trajectory for optimized workpiece production (“local preheating”). Both temperature limitations and elevation to a specific temperature can be advantageously used for process optimization.

[0028] In another configuration, the selected first trajectory is modified depending on the various characteristics of the stack.

[0029] In this configuration, the novel method and equipment benefit from the correction of non-uniformities / abnormalities in the ongoing manufacturing process. Specifically, non-uniformities / abnormalities in the upper workpiece layer are corrected before the production of the upper workpiece layer is fully completed. Therefore, this configuration advantageously contributes to the particularly efficient production of high-quality workpieces.

[0030] In another configuration, a second trajectory is repeatedly determined depending on the modified first trajectory.

[0031] In this configuration, the building tools and measuring devices interact with each other in an interdependent manner, and adapt their respective first trajectories and additional trajectories in an interdependent manner to achieve optimal workpiece production in the shortest possible time. Specifically, in this configuration, the additional trajectories can also be modified based on the modified first trajectory to recheck rework points and / or to restrict and / or change the energy input to specific points on the workpiece stack within defined time intervals.

[0032] In some preferred exemplary embodiments, the additional trajectory along which the measuring device moves the second energy beam and / or detects the path is determined based on a computer-aided simulation of the measurement process dependent on the first trajectory. Based on the scanning strategy of the construction tool, the optimal scanning strategy of the measuring device in the preferred exemplary embodiment is determined during possible repeated computer-aided simulations. The scanning strategy may include the density of the corresponding trajectory within a defined workpiece area, the direction of movement, the speed of movement, the energy or power of the corresponding energy beam, the pulse pause ratio, or other parameters. This simulation process preferably occurs before and / or during the manufacturing steps. Based on the various characteristics of the stack that can be determined by means of the measuring device during the manufacturing steps, the modified first trajectory is preferably determined in parallel with the writing process to rapidly correct non-uniformities / anomalies. For example, non-uniformities / anomalies can be corrected by updating the local selective melting of the near-surface workpiece layer. In a preferred exemplary embodiment, the points in the workpiece layer corrected in this way are re-examined by means of the measuring device to ensure that the non-uniformities / anomalies have been successfully eliminated. If necessary, the interdependent checks and corrections can be repeated multiple times, and the first trajectory and the additional trajectory can be determined accordingly in an interdependent manner. In some preferred exemplary embodiments, the parameters of the first energy beam can vary depending on individually determined characteristics during the interdependent processing and inspection of points on the workpiece layer. For example, one or more parameters mentioned below can vary depending on data from the measuring device: the power density of the first energy beam, the energy density of the first energy beam, the focusing of the first energy beam, and the distance between adjacent tracks of the first energy beam (track spacing). Furthermore, in some exemplary embodiments, additional workpiece material or special repair material can be supplied to non-uniform / abnormal areas to achieve correction based on data from the measuring device.

[0033] In another configuration of the novel method and corresponding device, the additional scanning unit moves the second energy beam and detection path together along the plurality of additional trajectories.

[0034] This configuration makes it possible to implement the measuring device within a single compact measuring module, and is therefore advantageous in terms of assembly and maintenance, as well as any replacement of the measuring device.

[0035] In another configuration, the additional scanning unit has a first additional scanning unit and a second additional scanning unit that is spatially distant and structurally separated, wherein the first additional scanning unit moves the second energy beam, and wherein the second additional scanning unit moves the detection path.

[0036] In this configuration, the actuator and detector of the measuring device can be advantageously arranged in separate housing modules, which are spatially distant from each other and, for example, arranged on different sides of the manufacturing platform. By dividing into multiple modules, the measuring device can be more easily integrated into this novel device. This arrangement is particularly advantageous if the measuring device detects near-surface deformation of the stack in a deflection measurement manner (i.e., via a detection path that includes the workpiece surface as a bundle forming or wavefront forming element).

[0037] In another configuration, the second energy beam and / or detection path moves continuously by means of an additional scanning unit, and the measuring device has a third scanning unit that moves to track the additional scanning unit.

[0038] In this configuration, the novel method and corresponding apparatus utilize a third scanning unit, which is advantageously positioned between the detector and the additional scanning unit. The third scanning unit can be advantageously used to reduce motion blur, which can occur with the continuous movement of the additional scanning unit. This configuration allows for very rapid determination of near-surface inhomogeneities / anomalies while still maintaining high spatial resolution.

[0039] In another configuration, the exciter selectively heats the stack and the measuring device detects deformation, particularly deformation contrast, within the stack. The detector can advantageously detect deformation contrast due to inhomogeneity using deflection and / or interferometric measurements. Compared to existing technologies, the targeted, locally selective heating (thermal excitation) of the stack, based on a second energy beam as an advantageous measuring device, is also an innovative development, independent of the aforementioned movements of the first and second energy beams occurring separately.

[0040] This configuration enables a very simple and cost-effective implementation of the measuring device. In some variations, a write laser, or more generally a build tool, can be used to thermally excite the near-surface workpiece layer for measurement / inspection. However, in a preferred exemplary embodiment of this novel method and device, the second energy beam preferably excites the workpiece layer over time intervals of a few microseconds to a maximum of 500 milliseconds, particularly preferably with the heating interval lasting between 0.5 and 5 milliseconds. In a preferred exemplary embodiment, the diameter of the second energy beam on the workpiece surface is in the range of a few millimeters to a few centimeters, that is, particularly on the order of 0.3 to 1.5 cm. In a preferred exemplary embodiment, the workpiece surface is locally heated by means of the second energy beam, wherein the temperature of the workpiece material is maintained below the melting temperature of the workpiece material. Typically, heating with the second energy beam results in a temperature increase of several Kelvin to 300 Kelvin, and in some cases up to 500 Kelvin.

[0041] In another configuration, the exciter generates ultrasonic waves within the stack.

[0042] In this configuration, the exciter excites the workpiece surface over time intervals on the order of picoseconds to nanoseconds, that is, over intervals lasting less than 1 microsecond. In a preferred exemplary embodiment of this configuration, the diameter of the second energy beam is on the order of several micrometers to several millimeters, preferably less than 10 mm, and particularly preferably less than 5 mm. An advantage of this configuration is that it allows for the effective detection and localization of near-surface inhomogeneities / anomalies hidden beneath the surface based on deformation contrast. In some exemplary embodiments, an ultrasonic detector can be positioned at the manufacturing platform and detect ultrasonic signals during layer production and / or measurement.

[0043] In another configuration, the measuring device detects temperature comparisons within the stack.

[0044] In a preferred exemplary embodiment of this configuration, the detector includes an infrared camera and / or a pyrometer. In some preferred exemplary embodiments, the pyrometer may be implemented with two separate cameras and upstream filters, each matched to a different wavelength transmission range. This configuration allows for monitoring of the molten pool in the first energy beam region with high local resolution, as an alternative to or supplement to detecting temperature contrast in the already solidified workpiece material.

[0045] It goes without saying that, without departing from the scope of the invention, the above features, as well as those to be explained below, can be used not only in their respective specified combinations, but also in other combinations or individually. Attached Figure Description

[0046] Exemplary embodiments of the present invention are shown in the accompanying drawings and described in more detail in the following description. In the drawings:

[0047] Figure 1 A simplified diagram illustrating an exemplary embodiment of the novel device is shown.

[0048] Figure 2 It shows according to Figure 1 A first variant of the measuring device in an exemplary embodiment,

[0049] Figure 3 A second variant of the measuring device according to an alternative exemplary embodiment is shown.

[0050] Figure 4 A third variant of the measuring device according to another exemplary embodiment is shown.

[0051] Figure 5 A fourth variant of the measuring device according to another exemplary embodiment is shown.

[0052] Figure 6 A fifth variant of the measuring device according to another exemplary embodiment is shown.

[0053] Figure 7 A sixth variant of the measuring device according to another exemplary embodiment is shown.

[0054] Figure 8 A seventh variant of the measuring device according to another exemplary embodiment is shown.

[0055] Figure 9 An eighth variant of the measuring device according to another exemplary embodiment is shown.

[0056] Figure 10 A ninth variant of the measuring device according to another exemplary embodiment is shown.

[0057] Figure 11 A tenth variant of the measuring device according to another exemplary embodiment is shown, and

[0058] Figure 12 A flowchart illustrating an exemplary embodiment of the novel method is shown. Detailed Implementation

[0059] exist Figure 1 In this diagram, an exemplary embodiment of the novel apparatus is generally indicated by reference numeral 10. The apparatus 10 has a manufacturing platform 12 on which workpiece 14 is additively manufactured according to an exemplary embodiment of the novel method. Workpiece 14 is constructed layer by layer from bottom to top in temporally consecutive steps. Figure 1The uppermost workpiece layer is indicated by reference numeral 16. After workpiece layer 16 is completed, in this exemplary embodiment, a new material layer made of powder material, such as metal and / or ceramic material, is distributed on the layer stack 20 by means of a scraper 18. For this purpose, the manufacturing platform 12 is typically lowered in the direction of arrow 22 to the height of the next material layer. Other exemplary embodiments may include applying workpiece material without a scraper, that is, for example, locally and selectively supplying workpiece material by means of a movable tool head.

[0060] Reference numeral 24 here schematically denotes a construction tool that, in the illustrated exemplary embodiment, generates a laser beam 26 and, by means of a first scanning unit ( Figure 1 (Not shown in the figure) The laser beam is moved relative to the manufacturing platform 12 and the material layer 16 to be constructed. Reference numeral 28 indicates a first trajectory along which the laser beam 26 moves on the layer 16 to locally and selectively melt the powder material particles along the trajectory 28.

[0061] In another exemplary embodiment, the build tool 24 may generate an electron beam to build a workpiece layer on the manufacturing platform 12. In another exemplary embodiment, the build tool 24 may also, as an alternative to or supplement to the energy beam 26, locally and selectively apply workpiece material to the manufacturing platform 12 or the uppermost workpiece layer 16, the workpiece material being, for example, in the form of material powder introduced into a molten pool and / or in the form of linear material placed on the upper workpiece layer 16. In another exemplary embodiment, the apparatus 10 may include more than one build tool 24, meaning the apparatus may use two, three, or more laser and / or electron beams to produce workpiece layers.

[0062] The build tool 24, sometimes simply referred to as the write laser, is connected to the controller 30, which controls the movement of the laser beam 26 along a first trajectory 28. The controller 30 has an interface 32 through which a dataset 34 is supplied, defining the workpieces to be produced in multiple layers arranged vertically to each other. In other words, the controller 30 controls the movement of the laser beam 26 based on the dataset 34, which describes a corresponding first trajectory generated by the dataset 34 in each workpiece layer 16 to be produced.

[0063] Reference numeral 36 indicates a measuring device, which here includes an actuator 38 and a detector 40. See below for further details. Figures 2 to 11 Further details of the measuring device 36 will be described with reference to various exemplary embodiments.

[0064] Exciter 38 generates a second energy beam 42, which in a preferred exemplary embodiment is also a laser beam. In some exemplary embodiments, the laser beam 42 is used to locally and selectively heat the upper workpiece layer 16 and, more preferably, an additional near-surface workpiece layer below the uppermost workpiece layer 16, to thermally induce local deformation of the workpiece layer 16 and the additional near-surface workpiece layers. In other exemplary embodiments, the laser beam 42 may be used to induce ultrasonic waves in the near-surface workpiece layer 16, which propagate in the workpiece layer 16 and the additional near-surface workpiece layers of the stack 20 and cause temporary deformation of the stack.

[0065] Reference numeral 44 indicates a detection path through which detector 40 can selectively detect near-surface deformation induced by laser beam 42. In some exemplary embodiments, the detector may additionally or alternatively selectively measure the temperature of the near-surface workpiece layer.

[0066] As shown below with reference to several exemplary embodiments Figures 2 to 11 As illustrated, the measuring device 36 has an additional scanning unit (not shown here) with which the laser beam 42 and / or detection path 44 can move along an additional trajectory 46. In this exemplary embodiment, the measuring device 36 is connected to the controller 30, so that the controller 30 can control not only the construction tool 24, but also the movement of the laser beam 42 and / or detection path 44.

[0067] Some exemplary embodiments of device 10 may include two separate controllers, wherein a first controller controls the construction tool 24, and a separate second controller controls the measuring device 36. In these exemplary embodiments, the two separate controllers are preferably connected via a bidirectional communication interface to coordinate the movement of the write beam 26 and the measurement beams 42, 44 in an interdependent manner, and in particular to avoid overlap of the laser beam 42 used for measurement with the write beam 26 on the workpiece layer 16. However, in all preferred exemplary embodiments, the laser beam 42 and / or the detection path 44 may be mechanically decoupled and thus move on the workpiece layer 16 separately from the write beam 26.

[0068] In the exemplary embodiment shown here, the construction tool 24 and the measuring device 36 are controlled by a shared controller 30. Preferably, a first control program for controlling the construction tool 24 and a separate second control program for controlling the measuring device 36 are executed on the controller 30. In a preferred exemplary embodiment, the two control programs exchange control data in a mutually dependent manner via an internal interface of the controller 30. The internal interface may be a purely software interface and / or may be implemented using a shared memory area within the controller 30, allowing both control programs to perform read and write access. For example, the internal interface may be a dual-port RAM.

[0069] In some preferred exemplary embodiments, the controller 30, or the corresponding controller for constructing the tool 24 and measuring device 36, is implemented using a commercially available personal computer with a commercially available operating system, such as Microsoft Windows, macOS, or Linux, and executing the aforementioned control program. In some cases, the controller 30 may be implemented as a software SPS on a commercially available PC. Alternatively or additionally, the controller may be implemented using dedicated control hardware in the form of one or more ASICs, FPGAs, microcontrollers, microprocessors, or equivalent logic circuits.

[0070] Figure 2 A first exemplary embodiment of the measuring device 36 is shown, which can be used in accordance with Figure 1 In device 10. The same reference numerals denote the same elements as before.

[0071] Here, the build tool 24 includes a laser 48 (write laser) and a first scanning unit 50 with a beamforming optics unit, which may include, for example, a movable deflector 52 or another scanning element. With the aid of the scanning unit 50, the controller 30 can move the laser beam 26 along a first trajectory 28 on the workpiece 14 to produce a new workpiece layer 16. As further noted above, an electron beam source may also be used instead of the write laser 48.

[0072] Here, the measuring device 36 comprises a compact integrated module 53, which includes an additional scanning unit 54 with additional beam-forming optics, using which both the laser beam 42 for exciting the workpiece stack 20 and the detection path 44 can move on the workpiece surface. The measuring device 36 here includes an additional laser as an exciter 38. For example, the additional laser (heating laser) could be a fiber laser with a collimator that generates a collimated laser beam 42. The collimated laser beam 42 is guided to the additional scanning unit 54 via one or more deflecting mirrors in the additional beam-forming optics. Thus, the laser beam 26 and the laser beam 42, that is, the first energy beam and the second energy beam, typically pass through completely separate beam paths.

[0073] Furthermore, the measuring device 36 includes a third laser 56, hereinafter referred to as the measuring laser. The measuring laser 56 generates a measuring laser beam 58, which is split into two partial beams by a beam splitter. The first partial beam is guided to a second scanning unit 54 and reflected from there, together with the laser beam 42, onto the workpiece surface. The second partial beam 60 is reflected via a mirror 62 in module 53 and forms a reference measuring beam for interferometric measurements. The reflection of the measuring laser beam 58 at the workpiece surface is acquired by another scanning unit 54 along a detection path 44 and superimposed with the reference measuring beam 60 reflected by the mirror 62. The optical sensor 64 may include a camera with a pixel array, a line scan camera, or an optical point sensor, detecting the superposition of the reflected measuring laser beam and the reflected reference measuring beam. As can be seen, the measuring laser beam 58 also passes through a beam path completely separate from the beam path of the laser beam 26.

[0074] In some exemplary embodiments, the measuring device 36 includes a speckle interferometer. Therefore, the measuring device 36 can operate according to the principles of electronic speckle pattern interferometry (ESPI) to detect small deformations of the workpiece stack 20 caused by the thermal excitation of the laser beam 42. In other words, in this exemplary embodiment, the measuring device 36 includes a speckle interferometer with a measuring laser 56, whose beam path 58 includes a path to the workpiece surface via an additional scanning unit 54. This exemplary embodiment is characterized in that the additional scanning unit 54 moves the laser beam 42 to heat the workpiece surface and moves the measuring laser beam 58 along a second trajectory 46 (…). Figure 1 The thermally induced deformation is detected together to detect non-uniformity / abnormality 66 in the upper workpiece layer. The heating energy of the heating laser is distributed from the excitation point on the upper side of the workpiece, and the non-uniformity / abnormality 66 "interferes" with this distribution. This "interference" can be detected in the form of deformation comparison by means of the measuring device 36. In particular, surface deformation perpendicular to the workpiece surface and parallel to the workpiece surface can be detected.

[0075] Figure 3 Another exemplary embodiment of the measuring device 36 is shown. In this exemplary embodiment, the measuring device 36 includes a first additional scanning unit 54a and a second additional scanning unit 54b. Scanning unit 54a moves the laser beam 42 of the heating laser 38, while scanning unit 54b moves the measuring laser beam 58. The scanning units 54a and 54b are preferably controlled synchronously with each other to locally and selectively guide the heating laser beam 42 and the measuring laser beam 58, or the detection path 44, to a common surface point of the stack 20. In another exemplary embodiment, the detection path 44 can track the heating beam 42 at a defined distance (not shown here), where this tracking is achieved only through appropriate control of the deflection units 50, 54a, and 54b. Figure 3As can be seen, the measuring device 36 in this exemplary embodiment includes two separate housing modules 53a, 53b, which can be arranged to be spatially separated from each other and, for example, opposite each other with respect to the manufacturing platform 12. Moreover, this exemplary embodiment of the measuring device 36 can also be based on the principle of speckle interferometry.

[0076] Figure 4 Another exemplary embodiment of the measuring device 36 is shown. The same reference numerals further denote the same elements as before. In this exemplary embodiment, the measuring device 36 includes a first additional scanning unit 54c that moves both the heating laser beam 42 and the measuring laser beam 58 along an additional trajectory 46. A second additional scanning unit 54d collects the reflection / scattering of the measuring laser beam 58 and superimposes the measuring laser beam with a reference measuring beam 60. In this exemplary embodiment, the measuring device 36 can also operate according to the principle of speckle interferometry, and the beam path of the measuring laser includes a path to the surface of the workpiece to be measured.

[0077] Figure 5 Another exemplary embodiment of the measuring device 36 is shown. In this exemplary embodiment, a first additional scanning unit 54a moves the heating laser beam 42 along an additional trajectory on the surface of the layer stack 20. Compared with the exemplary embodiment according to Figure 3 the measuring device 36 here has: a second additional scanning unit 54e that moves the measuring laser beam 58 on the surface of the layer stack 20; and a third additional scanning unit 54f that collects the reflection / scattering of the measuring laser beam from the surface along a detection path 44.

[0078] Figure 6 Another exemplary embodiment of the measuring device 36 is shown, which largely corresponds to the exemplary embodiment according to Figure 2 The same reference numerals denote the same elements as before. Compared with the exemplary embodiment according to Figure 2 the exemplary embodiment according to Figure 6 is based on the principle of shear interferometry. Thus, the measuring device 36 includes a shear element 68 instead of the beam splitter and mirror 62 in Figure 2 The shear element is typically a prism element that generates two slightly offset images of the surface of the layer stack 20 along the detection path 44, as a result of which interferometry becomes possible. According to Figure 6The measuring device 36 is highly insensitive to vibration because the interferometric subwaves used for interferometry are each guided on the surface of the stacked body 20. Furthermore, the shear interferometer can detect the gradient of surface deformation (compared to deformation in ESPI). Shear elements and shear interferometry based thereon can also be used in other exemplary embodiments.

[0079] Figure 7 Further exemplary embodiments of the measuring device 36 are shown, which largely correspond to those according to... Figure 2 An exemplary embodiment. And according to Figure 2 In contrast to the exemplary embodiment, the measuring device 36 includes a third scanning unit 70 located in the beam path upstream of the optical sensor 64. The third scanning unit 70 is synchronized with the additional scanning unit 54 and thus compensates for any motion blur that may occur, particularly if the scanning unit 54 moves continuously while an interference image of the surface of the workpiece stack 20 is recorded by the optical sensor 64. In this exemplary embodiment, the laser spot written to the laser 48 can move within the field of view, while the field of view is selectively kept stationary locally for measurement. Such use of the third scanning unit is also possible in other exemplary embodiments.

[0080] Figure 8 Another exemplary embodiment of the measuring device 36 is shown. The same reference numerals denote the same elements as before. In this exemplary embodiment, the measuring device 36 uses a short-pulse laser 72, the laser beam 42 of which excites ultrasonic waves in the workpiece stack 20. The laser beam 42 is selectively and locally focused at a location on the surface of the workpiece stack 20 by means of a first additional scanning unit 54a. From there, the ultrasonic waves propagate along the surface of the workpiece stack 20 (Rayleigh wave, sweeping mode) and enter the workpiece stack 20 (longitudinal wave and shear wave). Time-varying local deformation of the stack surface (acoustic near field) occurs at the location of the laser spot itself. The measuring laser 56 is used to measure the surface deflection and / or velocity change caused by the ultrasonic waves at a fixed or varying distance from the excitation point. Alternatively or additionally, the time-varying surface deflection can here be measured directly at the location of the excitation point. The position of the measuring laser beam 58 is varied here by means of a second additional scanning unit 54b. Therefore, the measuring laser beam 58 can be optionally guided to the excitation position (here indicated by reference numeral 58) or to a defined distance from the excitation position (here indicated by reference numeral 58') by means of an additional scanning unit 54b. In some advantageous variations, the controller 30 alternately controls the measuring laser beam 58 to the excitation position and at a defined distance from the excitation position during the measurement process.

[0081] The deflection amplitude is typically at 10. -10 up to 10-9 The speed ranges from the order of m and from mm / s to cm / s. Measurements can include the deflection of the stack surface in the normal direction (“out-of-plane”) or in the surface plane (“in-plane”), or both. Measurements can also be performed, as shown, in an interferometric and / or deflection measurement manner. The deflection measurement is based on the deflection of the measurement laser beam 58, caused by induced deformation of the stack surface and spatially resolved detection of the deflected measurement laser beam.

[0082] according to Figure 8 The measuring device 36 is based on interferometry, in which the illumination of the stack surface with the measuring laser beam 58 and the measurement of reflection and / or scattering are performed together via a second additional scanning unit 54b. Due to their high detection rate / sensitivity, interferometers based on photorefractive crystals 74, such as dual-wavelength hybrid interferometers or photoinduced EMF detectors, by means of which the reflected measuring laser beam and a portion of the beam 60 (reference beam) are superimposed, as are Fabry-Perot interferometers or fiber-optic Sagnac interferometers, which are also suitable for measuring the deformation of surfaces excited by ultrasonic propagation in a stack of workpieces. This measurement determines—depending on the design of the interferometer—the deformation (in-plane, out-of-plane) or the velocity (time-dependent deformation).

[0083] In a preferred exemplary embodiment, the first additional scanning unit 54a and the second additional scanning unit 54b are controlled synchronously relative to each other so as to optionally keep the distance between the laser spot's excitation for ultrasonic waves and the position used for measurement during movement above the workpiece stack 20 constant at 0, constant at a fixed value, and / or change it during measurement depending on the characteristics of the workpiece stack 20. At each measurement position, measurement data are recorded over a time period of several nanoseconds to several milliseconds, with a time resolution in the nanosecond range. This forms what is known as an A-scan. In some exemplary embodiments, the measurement data of the A-scan along trajectory 46 can be combined to form a B-scan. The entirety of all A-scans, i.e., the measurement data of all measurement positions at the workpiece stack 20, is typically referred to as a C-scan as is known per se to those skilled in the art of ultrasonic measurement.

[0084] In the case of identical or overlapping excitation and measurement locations, non-uniformity / anomaly 66 is examined in the region directly beneath the surface of the workpiece stack 20. In some advantageous exemplary embodiments, data from scan A is compared with a simulation of the surface laser excitation and its interaction with near-surface non-uniformity, providing information related to the non-uniformity / anomaly 66 directly beneath the corresponding measurement location. Scans B and C use image processing methods to provide further information related to the non-uniformity / anomaly, particularly information related to laterally propagating defects such as cracks.

[0085] When the distance between the excitation and measurement locations is fixed or variable, ultrasonic mode propagation models and their interactions with inhomogeneities / anomalies (e.g., reflection, scattering, Lamb models) are used and advantageously employed to evaluate the measurement data. Therefore, in some advantageous exemplary embodiments, the measuring device 36 is configured to use B-scans and / or C-scans to locate and / or quantify inhomogeneities / anomalies 66. In some exemplary embodiments, the measuring device 36 is advantageously configured to use machine learning methods to detect inhomogeneities / anomalies 66 and classify them regarding size, depth, and / or type. Analysis of the measurement data may include evaluation in both the time and frequency domains using Fourier methods.

[0086] Figure 9 Another exemplary embodiment of the measuring device 36 is shown, which is based on the excitation of ultrasound in the workpiece stack 20. According to Figure 9 The measuring device 36 includes three additional scanning units 54a, 54g, and 54h. The additional scanning unit 54a moves the laser beam 42 to excite ultrasonic waves along a separate trajectory. Here, the additional scanning unit 54g moves the measuring laser beam synchronously with respect to the scanning unit 54a, and the additional scanning unit 54h selectively detects reflections at the surface of the workpiece stack 20.

[0087] Similarly, in the exemplary embodiment based on ultrasonic excitation, a method corresponding to... Figure 7 The exemplary embodiment includes a third scanning unit 70 (not shown here) to reduce motion blur during continuous movement of the additional scanning units. In all preferred exemplary embodiments, the laser beam for inspection can be separated from the writing beam 26 along a trajectory 46 optimized for inspection of the workpiece stack 20 (see [link to documentation]). Figure 1 The movement may optionally include a jump from the measurement location to a spatially distant measurement location. Figures 2 to 7 In the exemplary embodiment, the heating laser 38 can operate continuously (continuous wave) or in pulses. In another exemplary embodiment not shown separately herein, the excitation of the workpiece stack 20 can be performed generally, and the detection of temperature contrast, deformation contrast, or deformation of the stack 20 is performed only in a spatially resolved manner.

[0088] Figure 10 Another exemplary embodiment of the measuring device 36 is shown. The same reference numerals continue to denote the same elements as before.

[0089] In this exemplary embodiment, the measuring device 36 includes a first camera 76a and a second camera 76b, as well as a first bandpass filter 78a and a second bandpass filter 78b. The bandpass filters 78a and 78b have different pass-through ranges, resulting in the cameras 76a and 76b acquiring different spectral bands. In some exemplary embodiments, the cameras 76a and 76b have sensitivity in the near-infrared range (NIR, λ < 1.1 µm) or the short-wave infrared range (SWIR). The temperature at the surface of the workpiece stack 20 can be determined in each pixel of the camera from the ratio of the radiation intensity reflected from and measured separately by the surface of the workpiece stack 20. Therefore, the measuring device 36 in this exemplary embodiment is configured to enable direct spatially resolved temperature measurement of the workpiece stack 20. In this exemplary embodiment, a heated laser 38 is used to induce a temperature contrast between non-uniformities / anomalies in the workpiece stack 20 and the surrounding surface of the workpiece stack 20.

[0090] Figure 11 Another exemplary embodiment of the measuring device 36 is shown, wherein an infrared camera 80 is used instead of two cameras 76a, 76b and separately assigned bandpass filters 78a, 78b.

[0091] It should be noted that the exemplary embodiments of the measuring device 36 can also be combined with each other, because the measuring device 36 can include, for example, according to Figure 10 and / or Figure 11 Temperature measurement and based on Figure 8 or Figure 9 Ultrasonic measurements and / or interferometric measurements and / or deflection measurements of thermally induced deformation.

[0092] Figure 12 A flowchart illustrating an exemplary embodiment of the novel method is shown. In step 82, a dataset is received that defines a workpiece to be produced in multiple layers arranged vertically to each other. According to step 84, based on the dataset from step 82, first trajectories are determined along which laser or electron beams are to be moved to construct the workpiece layers. According to step 86, depending on the dataset from step 82 and the first trajectories from step 84, second trajectories are determined along which spatially resolved measurements of the workpiece layers are to be performed. In some preferred exemplary embodiments, the measurements for each workpiece layer are simulated by means of a computer, particularly to avoid the overlap of the write beam and the measurement beam / detection path.

[0093] Here, a count variable is set in step 88 and incremented in each of the following manufacturing steps. According to step 90, the nth workpiece layer is then produced using a build tool. According to step 92, the nth layer is measured in parallel using a measuring device 36. In a preferred exemplary embodiment, the measurement of the nth layer begins with a time delay relative to the production of the nth layer according to step 90, wherein the area of ​​the nth workpiece layer 90 that has already been produced is measured while other areas of the nth workpiece layer are still being produced. As explained above, in this case, the measuring device uses one scanning unit 54 or multiple scanning units 54a, 54b, 54c, 54d, 54e, 54f, 54g, 54h, which are structurally separate from the scanning unit 50 and each establishes a beam path through which the write beam 26 of the build tool 24 does not travel.

[0094] According to step 94, the measurement data is evaluated and a decision is made as to whether correction of the nth workpiece layer is necessary. This is particularly true when the measurement data indicates non-uniformity / abnormality in the nth workpiece layer and / or the workpiece layers below it. If correction appears necessary, the first trajectory of the nth workpiece layer is modified here according to step 96, resulting in the non-uniformity / abnormality being corrected during the production process of the nth workpiece layer. In other words, the trajectory determined for the nth workpiece layer in step 84 is supplemented by additional motion, and / or a specific motion is modified in step 84 to make correction of the detected non-uniformity / abnormality possible. If correction appears unnecessary, step 96 can be omitted for the corresponding workpiece layer, and the "measurement path" of the method restarts in step 92.

[0095] When the production of the nth layer, including any corrections, is complete, a check is performed according to step 98 to determine whether additional workpiece layers should be produced. If so, the method returns to step 88 according to loop 100. When the production of all workpiece layers is complete, in some preferred variations of the method, the produced workpieces can be measured again as a whole according to step 102. For example, the workpieces can be measured in step 102 using X-rays and / or coordinate measurement methods conventional in the art to check for conformity with predetermined specifications.

Claims

1. A method for additive manufacturing of a workpiece (14), comprising the following steps: - Receive a dataset (34) that defines the workpiece (14) in multiple layers (16) arranged one above the other. - Provide a manufacturing platform (12). - Provide a construction tool (24) with a first scanning unit (50) configured to move a first energy beam (26) in a spatially resolved manner relative to the manufacturing platform (12). - Multiple first trajectories (28) are determined based on the dataset (34). - In the time-sequential steps (100), the first energy beam (26) is moved relative to the manufacturing platform (12) along one of the plurality of first trajectories (28) respectively, so as to produce a stack (20) having workpiece layers (16) arranged vertically to each other in these time-sequential steps, the workpiece layers corresponding to the first trajectories. - A measuring device (36) is used to determine various characteristics of the stack (20), the measuring device having an exciter (38) that excites the stack (20) with a second energy beam (42) and a detector (40) that detects the characteristics of the stack (20) as a result of the excitation in a spatially resolved manner along a defined detection path (44), wherein, The second energy beam (42) and the detection path (44) move relative to the manufacturing platform (12) along a plurality of additional trajectories (46) by means of an additional scanning unit (54), wherein the additional trajectories (46) are at least partially different from the first trajectories (28). The first scanning unit (50) and the other scanning unit (54) establish completely separate beam paths for the first energy beam (26), the second energy beam (42), and the detection path (44), and each of the first scanning unit (50) and the other scanning unit (54) has a beamforming optical unit.

2. The method as described in claim 1, characterized in that, The second energy beam (42) and / or the detection path (44) move along one of the plurality of additional trajectories (46) by means of the additional scanning unit (54) in one of these time-sequential steps, while the first energy beam (26) moves along the first trajectory (28).

3. The method as described in claim 1 or 2, characterized in that, The other trajectory (46) is determined based on these first trajectories (28).

4. The method as described in claim 3, characterized in that, This avoids the superposition of the second energy beam (42) and the first energy beam (26) on the stack.

5. The method as described in claim 1 or 2, characterized in that, The first trajectory selected is modified depending on the various characteristics of the stack (96).

6. The method as described in claim 5, characterized in that, These additional trajectories are determined repeatedly based on the modified first trajectory.

7. The method as described in claim 1 or 2, characterized in that, The additional scanning unit (54) moves the second energy beam (42) and the detection path (44) together along the multiple additional trajectories (46).

8. The method as described in claim 1 or 2, characterized in that, The additional scanning unit (54a) has a first additional scanning unit (54b) and a second additional scanning unit that is spatially and structurally separated, wherein the first additional scanning unit (54a) moves the second energy beam, and wherein the second additional scanning unit (54b) moves the detection path.

9. The method as described in claim 1 or 2, characterized in that, The second energy beam and / or the detection path move continuously by means of the additional scanning unit, and the measuring device (36) has a third scanning unit that moves to track the additional scanning unit (54).

10. The method as described in claim 1 or 2, characterized in that, The exciter (38) selectively heats the stack (20), and the measuring device (36) detects the deformation contrast in the stack (20).

11. The method as described in claim 1 or 2, characterized in that, The exciter (38) generates ultrasonic waves in the stack (20).

12. The method as described in claim 1 or 2, characterized in that, The measuring device (36) detects the temperature contrast within the stack (20).

13. An apparatus for additive manufacturing of a workpiece (14), the apparatus having an interface (32) for receiving a dataset (34) that defines the workpiece (14) in multiple layers (16) arranged vertically above each other; having a manufacturing platform (12); having a build tool (24) with a first scanning unit (50) configured to move a first energy beam (26) relative to the manufacturing platform (12) in a spatially resolved manner; having a controller (30) that controls the first scanning unit (50) to move the first energy beam (26) relative to the manufacturing platform (12) along multiple first trajectories (28) in temporally consecutive steps (100), wherein, The construction tool (24) produces a stack (20) having workpiece layers arranged vertically to each other in these time-sequential steps (100), these workpiece layers corresponding to these first trajectories (28); and has a measuring device (36) configured to determine various characteristics of the stack (20), wherein the measuring device (36) has an exciter (38) configured to excite the stack (20) with a second energy beam (42), and wherein the measuring device (36) has a detector (40) configured to detect, in a spatially resolved manner, the characteristics of the stack (20) as a result of the excitation along a detection path (44), wherein the measuring device (36) has an additional scanning unit. The unit (54), wherein the controller (30) is configured to control the additional scanning unit (54) separately from the first scanning unit (50), wherein the second energy beam (42) and the detection path (44) move relative to the manufacturing platform (12) along a plurality of additional tracks (46), wherein these additional tracks (46) may be different from these first tracks (28), characterized in that the first scanning unit (50) and the additional scanning unit (54) establish completely separate beam paths for the first energy beam (26) and the second energy beam (42) and the detection path (44), and the first scanning unit (50) and the additional scanning unit (54) each have a beamforming optical unit.

Images