AUTOMATED CALIBRATION OF A DEVICE FOR FULLY PARALLELIZED ADDITIVE MANUFACTURING OF A COMPONENT WITH COMBINED WORK FIELDS

Description

FIELD OF THE INVENTION

[0001] The present invention relates to an arrangement and a method for powder bed-based additive manufacturing of a component, and in particular to the calibration and synchronization of several laser devices for the parallel production of the component with combined working fields. STATE OF THE ART

[0002] Additive manufacturing processes, in which a material is added layer by layer and thermally processed to create a component, are becoming increasingly important in industrial production compared to traditional subtractive manufacturing processes such as milling, drilling, and turning, in which material is removed to produce a component. The layer-based construction method that characterizes additive manufacturing processes enables the production of highly complex geometric structures with a high degree of design freedom that subtractive processes cannot achieve.

[0003] The increasing industrial importance of additive manufacturing processes is being driven by the increasing efficiency of laser sources used for thermal processing of materials. Accordingly, the market is currently undergoing a transition from the initial use of additive manufacturing processes solely for the production of prototypes ("rapid prototyping") to the mass industrial use of this technology for series production ("rapid manufacturing"). This development is evident in numerous sectors, such as the aerospace industry, the automotive industry, medical technology, and prosthetics.

[0004] A special type of additive manufacturing is powder-bed-based processes, in which a powdered starting material is applied layer by layer to the component to be manufactured and melted by laser light. The powder layers are typically in the micrometer range.

[0005] A key factor in increasing the efficiency of powder-bed additive manufacturing systems is the ability to process a component in parallel using multiple laser devices, enabling higher output rates. The combined use of multiple laser devices for the simultaneous production of a component absolutely requires precise calibration and synchronization of the individual laser devices. However, this is associated with difficulties for which no solution has yet been found. Common calibration systems for additive manufacturing systems rely on the adjustment of individual galvanometer scanners (so-called galvo motors) of the laser devices and cannot collectively account for temperature-related inaccuracies of the entire system.

[0006] WO 2017 / 085470 A1 discloses several methods for calibrating an optical module, in which uncalibrated optical modules are calibrated by comparison with a pre-calibrated optical module and / or using a calibration pattern. A calibration pattern can be generated from a single, already calibrated optical module.

[0007] EP 2 186 625 A2 describes a calibration method in which a calibration pattern is generated by a first device and / or a second device. The respective calibration pattern is captured by a camera and used as the basis for calibrating the associated device. The two devices are calibrated independently of each other.

[0008] Thus, there is a need for improvement in the additive manufacturing of components with regard to the calibration and synchronization of several laser devices operating in parallel. DESCRIPTION OF THE INVENTION

[0009] The present invention is based on the object of enabling the calibration, recalibration, and synchronization of one or more laser devices involved in parallel in the powder-bed-based additive manufacturing of a component. "Parallel" refers in particular to a fully parallelized manufacturing process in which several laser devices involved in the manufacturing process cooperate to produce the component by simultaneously processing a common build area. This object is achieved by an arrangement according to claim 1, a method according to claim 9, and a computer program product according to claim 15. Preferred embodiments and developments of the invention are specified in the dependent claims.

[0010] The present invention relates to an arrangement for powder bed-based additive manufacturing of a component. The arrangement comprises a housing that comprises a build volume, wherein the build volume comprises a build field. The build field is a 2-dimensional cross-sectional plane of the build volume and covers a surface of the housing on which the component can be produced layer by layer by successive powder bed applications and subsequent thermal processing. The build field typically corresponds to a vertical projection of the 3-dimensional build volume. This means, for example, that for a cylindrical build volume, the build field can correspond to a circular cross-sectional plane, and for a cubic build volume, the build field can correspond to a square cross-sectional plane, whereby any shape of the build volume is possible.The build volume can, for example, correspond to a separate volume subsection of the interior of the housing, and the build field can cover a corresponding surface section of a lower surface of the housing, which represents a 2-dimensional projection of the build volume onto the lower surface of the housing. The build field can also cover a movable surface on which a top powder bed layer of the starting material rests. In this case, the movable surface can be displaced along a direction after the laser processing of each powder bed layer such that a distance between the build field or the top powder bed layer of the starting material to be processed and the laser devices remains constant.

[0011] Please note, however, that both the build volume and the build area can be virtual geometric constructs that can cover a specific spatial area of ​​the assembly but do not necessarily have a physical nature. While the build area can, for example, extend over a separate surface section of the assembly's housing, it does not necessarily have to be identified with this separate surface section. The same applies to the build volume.

[0012] The housing can isolate the build volume from its surroundings, thereby avoiding disruptive interactions between the environment and the build volume, ensuring that the physical conditions required for additive manufacturing of the component in the build volume, such as pressure, temperature, humidity, atmospheric purity, etc., are maintained. However, the housing can enable optical interaction with the build volume from outside the housing, for example, through a translucent section of the housing. A translucent section of the housing can spatially coincide with the build volume or build field in order to enable visual observation of the manufacturing process in the build volume, as well as optical influence on the build volume from outside the housing.

[0013] The arrangement further comprises at least three marker devices mounted in or on the housing, each marker device being capable of projecting a light reference mark onto a component lying on the build field and / or onto the build field. The marker devices are preferably mounted on the housing in such a way that the marker devices can follow thermodynamically induced deformations of at least part of the housing. The marker devices can be arranged inside or outside the housing. However, when arranged outside the housing, the marker devices are arranged in such a way that they can establish optical contact with the build field and the component, for example, through a light-transmitting part of the housing.

[0014] By attaching the marker devices in or to the housing, it is possible to ensure that uncontrolled thermomechanical deformations of the housing or expansions of a part thereof have an equal impact on the build volume and the position of the light reference markings. Such deformations and expansions can occur, for example, during the manufacturing process as a result of temperature changes in the build volume. In this way, the problem of the positioning of the light reference markings on the build field or on the component being uncontrollably influenced by the aforementioned effects can be avoided or mitigated. Instead, in the event of expansions or deformations of the housing, the marker devices move at least partially with the housing, so that the relative positions of the light reference markings projected by the marker devices in relation to the build volume and / or the build field can be maintained.

[0015] The marker devices exhibit a very high pointing stability, so that apart from the aforementioned desired "drift" with the housing due to thermodynamically induced deformations or strains, no further drift affects the marker devices.

[0016] It goes without saying that the light reference markings are projected directly onto the build area when no component is contained or being manufactured within the build volume. If a component is on the build area, be it a finished component or a component that is currently being manufactured, the light reference markings can be projected both onto the component, i.e. onto a topmost powder layer of the component that may still be processed, and onto areas of the build area that are not shielded by the component. This also offers the advantage that the position of the light reference markings is independent of the development stage of the component during production, since the light reference markings can always be projected onto a topmost powder layer of the component.

[0017] The arrangement further comprises a plurality of laser devices for laser processing a powder bed to produce a component on the build field by means of additive manufacturing. Each laser device is configured to laser process an associated work field. The work fields of the respective laser devices cover a common overlap area. This common overlap area can correspond to the build field, i.e. can be congruent with the build field. This can be the case, for example, if the work fields of the individual laser devices cover a common square overlap area and the build field is a square build field. However, the common overlap area can encompass the build field without being congruent with it. This can be the case, for example, if the work fields of the individual laser devices cover a common square overlap area, but the build field is a circular build field.

[0018] Each of the laser devices can cover or process its own work area, which at least partially overlaps with the work areas of the remaining laser devices. The plurality of laser devices are configured for simultaneous, parallel laser processing of this common overlapping area, which corresponds to or encompasses the build area. The laser devices can be arranged above the housing and configured to optically interact with the build volume or the build area and / or with a component located within the build volume through a translucent part of the housing. This optical interaction can serve both for laser processing of a powder material for the purpose of additive manufacturing of the component and for calibrating and synchronizing the arrangement.

[0019] Herein, "laser device" is understood to mean a device suitable for laser processing the powder used to produce the component in the context of additive manufacturing. In particular, a laser device can comprise a deflection unit, also called a deflection head, which enables scanning of the entire build volume and can control the precise, laser-controlled melting of the powder used to produce the component. For the arrangement described herein, the deflection units that are the subject of patent application DE 10 2016 120 523 are particularly suitable as part of the laser devices, although the disclosure is not limited thereto, since the use of other laser devices or other deflection units is also possible.

[0020] Furthermore, each laser device comprises a detection device configured to detect the light reference markings. The detection of the light reference markings by the detection device can be achieved by optically detecting the light of the light reference markings reflected from the build area or from the component. This detection can comprise a mechanically controlled adjustment of the components of the laser device, such as mirrors, lenses, galvanometers, deflection units, or other optical and / or electronic elements. The light reference markings can be detected completely. Alternatively, the light reference markings can also be partially detected, so that only selected areas or parts of one or more of the light reference markings are detected. Both variants are covered by the term "detecting the light reference markings."

[0021] The detection of the light reference markings by the detection device and subsequent adjustment of the respective laser device to the light reference markings can be controlled by suitable software. The internal structure and operation of a laser device, including the aforementioned software, are known from the prior art and are not described in detail herein. Instead, reference is made to the aforementioned patent application DE 10 2016 120 523 for further details.

[0022] The arrangement further comprises a control unit which is configured to calibrate and / or synchronize the plurality of laser devices with one another based on the at least three light reference markings detected by the respective detection devices.

[0023] For this purpose, the control unit can comprise a processor on which suitable software can be executed, and a memory in which the software is stored. Based on this calibration, which is based on the light reference markings generated by the marker devices, the arrangement according to the invention enables precise operation of the laser devices for producing the component in additive manufacturing.

[0024] Operational temperature fluctuations of the laser devices can affect the accuracy of the laser devices in the form of offset drift and / or gain drift. These can cause a point determined by a laser device or the processor of a laser device to "wander" or change in relation to the build volume, so that the point of the build volume that is actually hit by the laser device when a specific point is targeted changes over time. Calibration adjusts the laser devices to actually hit a desired, targeted point of the build volume for the purpose of laser processing. In particular, calibration can compensate for or correct the effects of offset drift and / or gain drift.

[0025] The arrangement according to the invention allows for calibration of the laser devices, which takes into account the negative effects of operational sources of inaccuracy on the precision of the arrangement. This enables increased positional accuracy of the laser processing of the component by the laser devices in the arrangement, which ultimately results in increased quality of the manufactured component.

[0026] According to a preferred embodiment, at least three of the marker devices are each capable of projecting a linear light reference mark, wherein the linear light reference marks intersect in pairs at at least three associated intersection points. The detection device is configured to detect the at least three intersection points, and the control unit is further configured to calibrate the laser device (30) based on the at least three intersection points detected by the detection device. The use of intersection points for calibration at which linear light reference marks intersect enables improved drift behavior and improved image sharpness.

[0027] According to the invention, the control unit is configured to calibrate the plurality of laser devices and / or to synchronize different laser devices with one another based on the light reference markings and / or intersection points detected by the detection devices. Based on this synchronization, which is based on the light reference markings and / or intersection points generated by the marker devices, the arrangement according to the invention enables precise, simultaneous, parallel operation of the plurality of laser devices for the parallel production of the component within the framework of additive manufacturing. This results in improved synchronization of the laser devices with one another.

[0028] In a preferred embodiment, the arrangement further comprises a cover element suitable for covering the housing, wherein the at least three marker devices are preferably fastened in or on the cover element. "Covering" can refer to the creation of a fluid-tight connection between the cover element and the housing, which can prevent disruptive mechanical or chemical interactions of the environment with the build volume in order to ensure the maintenance of the physical or chemical conditions required for additive manufacturing of the component in the build volume. Nevertheless, the cover element enables optical interaction with the build volume from outside the housing.In particular, the cover element can be fully or partially translucent to enable visual observation and optical monitoring of the manufacturing process, as well as optical influence on the build volume from outside the housing. The cover element can, for example, comprise a glass window that spatially coincides with the build area and thus covers the entire build volume.

[0029] According to a preferred embodiment, the at least three marker devices are arranged outside the housing. The marker devices are then separated from the interior of the housing or the construction volume by the housing or by the cover element. This allows the operation of the marker devices to be stabilized. At the same time, the marker devices, which are nevertheless attached to the cover element, follow temperature-induced deformations of the cover element, which are expected to be similar to the deformations resulting from the construction volume.

[0030] InIn a preferred embodiment, the plurality of laser devices comprises at least four laser devices suitable for processing the entire construction field for producing the component in parallel. Accordingly, the number of marker devices can also be at least four, although the number of marker devices does not necessarily have to match the number of laser devices. The number of marker devices is two or more, preferably three or more. It should be noted that other configurations with any first number of laser devices and any second number of marker devices are also possible.

[0031] According to a preferred embodiment, the build field has one or more reference markings, and the detection device of at least one of the laser devices is further configured to detect the one or more reference markings. The reference markings can be markings of any type, for example, etched or chromated structures, but also optically generated markings. The reference markings can, for example, be markings formed on a surface of the housing that corresponds to the build field by etching, chromating, or the like.

[0032] The detection of the reference marks by the detection device of at least one of the laser devices can be carried out using the same mechanism used for detecting the light reference marks as described above. In particular, the same components of the detection device can be used for detecting the reference marks as for detecting the light reference marks.

[0033] The reference markings enable the marker devices to be aligned with the build area. The marker devices can, for example, be aligned such that the associated light reference marking assumes a predetermined spatial relationship to one or more of the reference markings. In particular, the marker devices can be aligned such that one or more of the light reference markings are aligned with one or more of the reference markings. This alignment can, for example, take place as part of a basic alignment prior to component manufacture. Accordingly, the marker devices are aligned with the build area using the reference devices before the first powder layer is applied. After the successive powder layers have been applied to the component in the build volume, the precise positioning of the reference markings and thus of the build area remains traceable thanks to the projected light reference markings.The basic setting just described can be repeated at a later time to readjust the arrangement.

[0034] Furthermore, the laser devices can be adjusted to the construction field using the reference markings, allowing the laser devices to detect the exact positioning and extent of the construction field and, if necessary, adjust the settings of their optical, mechanical, and / or electromagnetic components accordingly. Adjusting the laser devices to the construction field can include, for example, adjustments to focus, beam angle, or beam intensity.

[0035] In a preferred embodiment, the arrangement further comprises a removable reference marking plate that can be arranged in or on the build field and that comprises one or more reference markings. The reference marking plate can be suitable for being applied to the interior of the housing, for example, on a lower surface of the housing. The reference marking plate is preferably congruent with the build field. In the case of a circular build field, the reference marking plate can be a disk-shaped plate, for example. The reference markings can be markings of any type, for example, etched or chromated structures on the reference marking plate, but also optically generated markings.

[0036] Alternatively or additionally, at least three of the marker devices can comprise a laser light source configured to generate an associated light reference marking as a laser line, wherein the at least three laser lines intersect in pairs at a total of at least three associated intersection points. For example, three marker devices can generate three laser lines that intersect in pairs at three associated intersection points and project a laser marking triangle onto a component lying on the construction field and / or onto the construction field. Each corner point of the laser marking triangle corresponds to an intersection point of two of the laser lines. Similarly, four marker devices can, for example, generate four laser lines that intersect in pairs at four associated intersection points and form a laser marking quadrilateral, wherein each corner point of the laser marking quadrilateral corresponds to an intersection point of two of the laser lines.The four laser lines projected by the marker devices can, in particular, be perpendicular or parallel to each other in pairs, so that the projected laser marking quadrilateral is a rectangle or a square. The detection device and the control unit can then be configured such that the intersection points of the light reference markings can be used as the basis for calibration and / or synchronization.

[0037] Alternatively or additionally, at least one marker device is configured to generate light for generating the light reference marking, which light has one or more wavelengths between 405 nm and 850 nm, preferably between 490 nm and 640 nm, particularly preferably between 490 nm and 540 nm.

[0038] According to a further preferred embodiment, one or more of the marker devices are configured to project the associated light reference marking onto an outer edge line of the construction field, or at a distance from the outer edge line that does not exceed 10% of the diameter of the construction field. This proves particularly advantageous when the construction field is rectangular, since the light reference markings can then determine not only the positioning of the construction field, but also its exact dimensions and outer edges. In the case of a circular construction field, the light reference markings are preferably located within the construction field.

[0039] In a preferred embodiment, at least one of the laser devices comprises a laser light source configured to generate laser light for laser processing of a component, as well as a deflection unit configured to deflect and scan light. Furthermore, the at least one of the laser devices comprises a wavelength-selective optical element arranged between the deflection unit and the laser light source, which is at least partially reflective for one or more wavelengths of the laser light and at least partially transmissive for one or more wavelengths of the light reference markings.A reverse configuration, in which the wavelength-selective optical element is at least partially transmissive for one or more wavelengths of the laser light and at least partially reflective for one or more wavelengths of the light reference markings, is also possible, depending on the position of the laser light source and the detection device. The wavelength-selective optical element is further configured to decouple the light from the light reference markings and direct it onto the detection device.

[0040] The deflection unit can, for example, comprise a first scanning mirror and a second scanning mirror, wherein the first scanning mirror is configured to deflect and scan light in a first direction, and the second scanning mirror is configured to deflect and scan light in a second direction, wherein the first direction is perpendicular to the second direction. The detection device of the laser device is then arranged on a light path followed by light entering the laser device, downstream of the first scanning mirror, the second scanning mirror, i.e., downstream of the deflection unit, and the optical element. Note that this part of the light path can at least partially coincide with the light path taken by the light used for laser processing—in the opposite direction.

[0041] In some embodiments, light entering the laser device is deflected by the deflection unit toward the optical element. The light incident on the wavelength-selective optical element is transmitted or reflected by the element in whole or in part toward the detection device for detection. Light generated by the laser light source for laser processing of the component, however, is reflected by the wavelength-selective optical element and directed toward the build volume, so that at this point the light path for the laser light and the light path for detecting the light reference markings and / or the light reference markings separate.

[0042] Of course, it is also possible to use a wavelength-selective optical element that transmits the laser light and reflects the light to be detected by the detection device. Furthermore, the wavelength-selective optical element can deflect part of the light incident on the optical element in a direction other than the direction of the detection device, so that this part of the light can be detected in the laser device for other purposes. The detection device can, for example, comprise a monochromatic camera with a lens specially configured for detecting the light reference markings and / or the reference markings. The detection device can further comprise an autofocusing lens to enable a sharper detection of the light reference markings and / or the reference markings by the camera.

[0043] The present invention also relates to a method for calibrating and / or synchronizing the plurality of laser devices of an arrangement for powder bed-based additive manufacturing of a component according to claim 1.

[0044] The method comprises detecting at least three light reference marks with each of the laser devices. The method further comprises calibrating the individual laser devices and / or synchronizing the plurality of laser devices with one another based on the detected light reference marks. The method may thus comprise calibrating the plurality of laser devices, synchronizing the plurality of laser devices with one another, or both, wherein the calibration or synchronization is based on the detected light reference marks.

[0045] According to a preferred embodiment, at least three of the light reference markings are linear, with the linear light reference markings intersecting in pairs at at least three associated intersection points. In such embodiments, detecting the light reference markings comprises detecting the at least three intersection points. However, detecting the light reference markings in such embodiments can also consist of detecting the at least three intersection points. Calibrating the laser device or the individual laser devices and / or synchronizing the plurality of laser devices with one another is based on the at least three detected intersection points.

[0046] In a preferred embodiment, at least one of the laser devices comprises a deflection unit with which a laser beam generated by the associated laser device can be deflected to scan the construction volume. Calibration includes correcting an offset and / or compensating for a gain drift of the deflection unit. A person skilled in the art understands the "deflection unit offset" to be a constant difference between the actual deflection angle and an intended deflection angle of one or more deflection units, with the deflection angle of a deflection unit determining its beam direction. The offset arises from a deviation of the reference zero point of the galvanometers with respect to the actual center of the deflection angle range of a deflection unit. The term "gain drift" refers to a deviation between an intended change in the deflection angle and the actually achieved change in the deflection angle.This deviation can also be understood as a change in the size of the construction field by increasing or decreasing the deflection angle range of one or more deflection units.

[0047] According to a preferred embodiment, the method further comprises a step in which each of the marker devices is adjusted such that the associated light reference mark assumes a predetermined spatial relationship to one or more of the reference marks, in particular is brought into alignment with one of the reference marks.

[0048] In a preferred embodiment, the calibration of at least one of the laser devices is based on a selection among the light reference markings and / or intersection points, with preference given to light reference markings and / or intersection points that are further away from a center point of the working field of the associated laser device. Accordingly, the calibration is preferably based on light reference markings or intersection points that are at a greater distance from the center point of the working field of the associated laser device than a light reference marking or intersection point closest to these centers. In a further preferred embodiment, the calibration of the individual laser devices and / or synchronization of the plurality of laser devices is repeated during the additive manufacturing process. The repetition preferably takes place at regular intervals.This allows for continuous adjustment of the laser devices, taking into account changing conditions during the operation of the component manufacturing system. Calibration or synchronization can be repeated after each application of a new powder layer to the component. This allows for continuous adjustment or optimization of the laser device's operating settings to the current distance between the component and the respective laser devices.

[0049] A further aspect of the present invention relates to a computer program product comprising instructions which, when executed by a processor associated with an arrangement according to any one of claims 1 to 8, cause the processor to carry out the method according to any one of claims 9 to 14.

[0050] A computer-readable storage medium can store such a computer program product. BRIEF DESCRIPTION OF THE CHARACTERS

[0051] Fig. 1 shows an arrangement for powder bed-based additive manufacturing according to one embodiment of the invention. Fig. 2 shows an arrangement according to another embodiment of the invention. Fig. 3 shows a schematic structure of the components of a laser device of an arrangement according to one embodiment of the invention. Fig. 4 shows a schematic representation of the working fields of four laser devices of an arrangement according to one embodiment of the invention. Fig. 5 illustrates an exemplary spatial distribution of cross-shaped light reference markings or the reference markings on the build field according to one embodiment of the invention. Fig. 6 illustrates an exemplary spatial distribution of line-shaped light reference markings according to one embodiment of the invention. Fig. 7 shows a flowchart of a method for calibrating and synchronizing the plurality of laser devices of an arrangement according to one embodiment of the invention. DESCRIPTION OF PREFERRED EMBODIMENTS

[0052] Further advantages and features of the invention will become apparent from the following description, in which the invention is described using various embodiments with reference to the accompanying drawings.

[0053] The Fig. 1 shows an arrangement 10 for powder bed-based additive manufacturing of a component (cf. Fig. 2 ) according to an embodiment of the invention. The arrangement 10 comprises a housing 12, a construction volume 14, a construction field 16, four marker devices 20, four laser devices 30, a control unit 40 and a removable reference marking plate 50.

[0054] The build area 16 is a 2-dimensional cross-sectional plane of the build volume 14, which covers a portion of an inner floor surface of the housing 12. As shown in the Figure 1 shown, the construction area 16 corresponds to a vertical projection of the construction volume 14on the aforementioned bottom surface of the housing 12. The construction volume 14 corresponds to a volume subsection of the interior of the housing 12, which is marked with dashed lines in the figure.

[0055] The four marker devices 20 are attached to the housing 12 so that they can follow thermodynamically induced deformations of the housing 12. Each of the marker devices 20 is capable of projecting a light reference mark onto the build field 16 or onto a component lying on the build field 16. The marker devices 20 are arranged on an upper side of the housing 12 outside the housing.

[0056] The four laser devices 30 are arranged above the housing 12 and are suitable for processing the entire build area 16 in parallel to produce a component by additive manufacturing. The housing 12 has a translucent section 19 that spatially coincides with the build volume 14 and lies above the build area 16. Both the laser devices 30 and the marker devices 20 are in optical contact with the build volume 14 and the build area 16, respectively, through the translucent section 19 of the housing 12.

[0057] In the illustrated embodiment, the reference marking plate 50 is a glass plate that lies on the inner bottom surface of the housing 12 and is congruent with the build field 16. The reference marking plate 50 has four reference markings 52 etched onto an upper surface of the reference marking plate 50. The reference markings 52 lie on the build field 16 and can be considered reference markings of the build field 16.

[0058] The control unit 40 is functionally connected to the laser devices 30 and the marking devices 20 and is configured to calibrate and synchronize the laser devices 30 with each other.

[0059] The Fig. 2 shows an arrangement 10 for powder bed-based additive manufacturing of a component 100 according to another embodiment of the invention. Elements of the arrangement 10 which are shown in the Fig. 1 shown embodiment are marked with the same reference numerals as in the Fig. 1 . The elements that perform the same function in this embodiment as in the one with respect to the Fig. 1The details of the previously described embodiment will not be explained again. In the illustrated embodiment, the component 100 is formed on a movable support element 102 that can be displaced along a vertical direction and can move downward after each application of a layer of powder material, so that the distance between the uppermost layer of powder material and the laser devices remains constant.

[0060] Order 10 of the Fig. 2 differs from that of the Fig. 1 further in that it comprises a cover element 18 which covers the housing 12 and forms an upper side or upper outer wall of the housing 12. The cover element 18 has a light-transmitting portion 19 which corresponds to the light-transmitting portion 19 of the housing of the Fig. 1 The laser devices 30 are in optical contact with the construction volume 16 or the component 100 through the light-transmitting section 19 of the cover element 18.

[0061] Furthermore, in this embodiment, the marker devices 20 are attached to the cover element 18 within the housing 12. The figure also shows a component 100 being manufactured in the build volume 14. Each of the marker devices 20 projects a light reference mark 22 onto the component 100. In the embodiment shown, the marker devices 20 are configured to generate light for generating the light reference marks 22, said light having wavelengths in the range between 490 nm and 540 nm. The build field 16 has reference marks 17 that are chromatized on a bottom surface of the housing 12 and, in the illustrated situation, are covered by the component 100.

[0062] The Fig. 3shows a schematic representation of some of the components of one of the laser devices 30 of an arrangement according to an embodiment of the invention. The laser device 30 comprises a deflection unit with a first scanning mirror 35 and a second scanning mirror 36, as well as a wavelength-selective optical element 38 and a detection device 34. The laser device 30 further comprises a laser light source 33 for generating the laser light used for laser processing of the component. The wavelength-selective optical element 38 is arranged on the light path followed by the laser light generated by the laser light source 33 and / or the light to be detected by the detection device 34, between the deflection unit, i.e., the scanning mirrors 35 and 36, and the laser light source 33.

[0063] Light, in particular light reflected from the build field 16 of an arrangement or from a component 100 being produced in an arrangement, can enter the laser device 30. The deflection unit is configured to deflect and scan light. For this purpose, the first scanning mirror 35 is configured to deflect and scan light in a first direction, and the second scanning mirror 36 is configured to deflect and scan light in a second direction, wherein the first direction and the second direction are perpendicular to one another. The scanning mirrors 35 and 36 of the deflection unit are configured to reflect light entering the laser device 30 in the direction of the detection device 34 through the optical element 38.The wavelength-selective optical element 38 is configured to be transmissive to a wavelength range of the light from the light reference markings 22, which is reflected by the scanning mirrors 35 and 36 and enters the laser device 30 from the build volume, so that this light is transmitted toward the detection device 34 and is detected by it. This wavelength range of the light directed toward the detection device 34 is optimized for the detection settings of the detection device 34. As shown in FIG. Figure 3 As shown, the detection device 34 is arranged along the light path followed by the light entering the laser device 30 after the first scanning mirror 35, the second scanning mirror 36 and the optical element 38.

[0064] The wavelength-selective optical element 38 is further reflective for laser light generated by the laser light source 33 of the laser device 30 for laser processing a component, so that the laser light generated by the laser light source 33 is reflected by the first scanning mirror 35 and the second scanning mirror 36 in the direction of the build volume.

[0065] The positioning and / or angular settings of the first scanning mirror 35 and the second scanning mirror 36 can be adjusted, for example, by appropriate galvanometers to deflect the laser light toward a target point of the build volume and to deflect the light of the light reference marks 22 entering the laser device through the wavelength-selective optical element 38 toward the detection device.

[0066] The laser light is signaled in the figure by an arrow pointing downward from the laser light source 33. As shown in the figure, the light path of the laser light and the light path of the light detected by the detection device 34 overlap to the left of the optical element 38. In the embodiment shown, the detection device 34 comprises a camera 39 and a lens 37 specially configured for detecting the light reference marks and the reference marks and may include an autofocus lens configured to focus the light detected by the detection device 34. The camera 39 may be a monochromatic camera.

[0067] The Fig. 4 shows a schematic representation of the working fields of four laser devices 30 of an arrangement according to an embodiment of the invention. Each of the laser devices 30 of the arrangement of the Fig. 1 or 2The embodiment shown is configured for laser processing an associated square working field. First to fourth laser devices 30 are each configured for laser processing a first to fourth working field 32a-32d. Each of the working fields 32a-32d covers an area of ​​608 mm x 608 mm in the embodiment shown. The centers of adjacent working fields are offset by 202.63 mm in the embodiment shown.

[0068] The four work fields 32a-32d have a common overlapping area 32, which in the embodiment shown is congruent with the construction field 16. In other words, the square overlapping area 32 forms the square construction field 16. The construction field 16 covers an area of ​​approximately 402 mm x 402 mm in the embodiment shown. The four laser devices 30 are configured for simultaneous, parallel laser processing of the construction field 16. The marker devices 20 could, in the embodiment shown, be configured to project their associated light reference markings 22 onto an outer edge line of the construction field 16. The four marker devices 20 of the Fig. 1 and 2 The embodiments shown can, for example, be configured to project one of the light reference markings 22 onto one of the corners of the square construction field 16.

[0069] The Figure 5shows an exemplary distribution of the light reference markings 22 on a circular build field 16 according to another embodiment of the invention. In the embodiment shown, a square overlap area 32 of four laser devices 30 can be seen, which encompasses the circular build field 16 but is not completely congruent with it.

[0070] The Figure 6 shows an alternative embodiment in which instead of four cross-shaped light reference marks, as in the Fig. 5, four laser lines 22 are projected, which intersect in pairs at four intersection points 22'. The laser lines 22 can each be generated by a line laser light source. The four laser lines 22 projected by the marker devices are perpendicular or parallel to one another in pairs and form, as shown, a laser marking quadrilateral whose corner points correspond to the intersection points 22'. The intersection points 22' can be detected for calibration and / or synchronization purposes. The detection of the intersection points 22' of the laser lines 22 represents a special case of the detection of the light reference markings mentioned above. It is understood that the laser lines 22 do not need to be detected over their entire length, but only in the area of ​​the intersection points 22'.

[0071] It will be apparent to those skilled in the art that the embodiments of the Fig. 5 and 6can be combined so that, for example, three or four intersection points where three or four corresponding laser lines intersect, and one or more additional individual, for example point-shaped or shaped, light reference markings are used for calibration and / or synchronization. Any combination of point-shaped or cross-shaped and intersection points is possible, as long as at least three of the former or at least three of the latter are present.

[0072] The Fig. 7 shows a flowchart illustrating a method 200 for calibrating and synchronizing the laser devices of an arrangement according to an embodiment of the invention. The method 200 can be applied to an arrangement according to any embodiment of the invention. The method is described herein by way of example with reference to the Fig. 1 and 2 described in the embodiments shown.

[0073] The method 200 comprises a step 202 in which the marker devices 20 are adjusted such that the associated light reference marking 22 is brought into alignment with one of the reference markings 17 and 52, respectively.

[0074] The method 200 includes a step 204 in which each of the laser devices 30 detects at least three of the light reference marks 22 projected by the marker devices 20.

[0075] The method 200 further includes a step 206 in which the individual laser devices 30 are calibrated based on the detected light reference markings 22. The calibration includes, in particular, correcting an offset and compensating for a gain drift that may be present in a deflection unit (not shown in the figures) of the associated laser device 30. In the embodiment shown, the calibration is performed based on a selection among the light reference markings 22. In this selection, preference is given to the light reference markings 22 that are further away from a center point of the working field of the associated laser device.

[0076] This can be seen from the Figure 4better understand. A first laser device 30, which is configured for laser processing of the working field 32a, can be calibrated, for example, using the three light reference markings 22 that are further away from the center of the working field 32a than the light reference marking closest to this center. If the four marker devices 20 of the Fig. 1 and 2 For example, in the embodiments shown, project one of the light reference markings 22 onto one of the corners of the square construction field 16, the aforementioned nearest light reference marking lies on the upper left corner of the square construction field 16. The first laser device can then be calibrated in method step 206 using the other three light reference markings 22, namely the light reference markings top right, bottom left and bottom right.

[0077] The method 200 further includes a step 208 in which the four laser devices 30 of the array are synchronized with one another based on the detected light reference marks. This step 208 may be omitted for arrays that, according to some of the embodiments of the invention explained above, comprise only one laser device 30.

[0078] The process steps 206 to 208 can be carried out in any order, which does not necessarily correspond to the order in which Figure 7 must match the sequence shown. Furthermore, the method 200 may include a repetition of all method steps at regular intervals. LIST OF REFERENCE SYMBOLS

[0079] 10 Arrangement 12 Housing 14 Build volume 16 Build field 18 Cover element 19 Translucent part of the cover element 20 Marker devices 22 Light reference markings 22 Intersection points of the light reference markings 30 Laser device 32 Overlapping area of ​​the working fields 32a-32d Working fields 33 Laser light source 34 Detection device 35 First scanning mirror 36 Second scanning mirror 37 Lens 38 Wavelength-selective optical element 39 Camera 40 Control unit 50 Reference marking plate 52 Reference markings 100 Component 102 Movable holding element 200Procedures 202-208Procedure steps

Claims

1. An assembly (10) for powder bed based additive manufacturing of a component (100), the assembly (10) comprising: a housing (12) comprising a work volume (14), the workvolume (14) comprising a work field (16); at least three marker devices (20) mounted in or on the housing (12), each marker device (20) being adapted to project a light reference mark (22) onto a component (100) lying on the work field (16) and / or onto the work field (16); a plurality of laser devices (30), each laser device (30) being adapted for laser processing of a powder bed for producing a component (100) on the work field (16) by means of additive manufacturing, each of the laser devices (30) being adapted for laser processing of an associated working field (32a-32d), the working fields covering a common overlap area (32) corresponding to the work field (16) or comprising the work field (16), the plurality of laser devices (30) being adapted for simultaneous parallel laser processing of the work field (16), each laser device (30) comprising a detection device (34) adapted to detect the at least three light reference marks (22); and a control unit (40) adapted to calibrate and / or synchronize the plurality of laser devices (30) with each other based on the at least three light reference marks (22) detected by the detection devices (34).

2. The assembly (10) according to claim 1, wherein at least three of the marker devices (20) are adapted to each project a line-shaped light reference mark (22), the line-shaped light reference marks (22) crossing in pairs at at least three associated crossing points (22'); wherein the detection devices (34) are adapted to detect the at least three crossing points (22'); and wherein the control unit (40) is further adapted to calibrate the laser devices (30) based on the at least three crossing points (22') detected by the detection device (34).

3. The assembly (10) according to any one of the preceding claims, further comprising a cover element (18) adapted to cover the housing (12), wherein the at least two marker devices (20) are preferably mounted in or on the cover element (18).

4. The assembly (10) according to any one of the preceding claims, wherein the work field (16) comprises one or more reference marks (17), and wherein the detection device (34) of at least one of the laser devices (30) is further adapted to detect the one or more reference marks (17).

5. The assembly (10) according to claim 4, wherein the assembly (10) further comprises a removable reference mark plate (50) which can be arranged in or on the work field (16) and which comprises the one or more reference marks (52).

6. The assembly (10) according to any one of the preceding claims, wherein at least one of the marker devices (20) comprises a laser light source (33) and / or wherein at least one of the marker devices (20) is adapted to produce laser light for producing the light reference mark (22) having one or more wavelengths between 405 nm and 850 nm, preferably between 490 nm and 640 nm, more preferably between 490 nm and 540 nm.

7. The assembly (10) according to any one of the preceding claims, wherein one or more of the marker devices (20) are adapted to project the associated light reference mark (22) onto an outer edge line of the work field (16), or at a distance from the outer edge line which does not exceed 10% of the extension of the work field.

8. The assembly (10) according to any one of the preceding claims, wherein at least one of the laser devices (30) comprises: a laser light source (33) adapted to produce laser light for laser processing of a component (100); a deflection unit adapted to deflect and scan light; and a wavelength-selective optical element (38) which is arranged between the deflection unit and the laser light source (33) and which is at least partially reflective for one or more wavelengths of the laser light and is at least partially transmissive for one or more wavelengths of the light reference marks (22) or vice versa; wherein the wavelength-selective optical element (38) is further adapted to couple out the light of the light reference marks (22) and direct it to the detection device (34).

9. A method for calibrating and / or synchronizing the plurality of laser devices (30) of an assembly (10) for powder bed based additive manufacturing according to any one of the preceding claims, the method comprising: detecting at least three light reference marks (22) with each of the laser devices (30); and calibrating the individual laser devices (30) and / or synchronizing the plurality of laser devices (30) with each other based on the detected light reference marks (22).

10. The method according to claim 9, wherein at least three of the light reference marks (22) are line-shaped, the line-shaped light reference marks (22) crossing in pairs at at least three associated crossing points (22'), and wherein detecting the light reference marks (22) comprises or consists of detecting the at least three crossing points (22'); and wherein calibrating the individual laser devices (30) and / or synchronizing the plurality of laser devices (30) with each other is based on the at least three detected crossing points (22').

11. The method according to claim 9 or 10, wherein each of the laser devices (30) comprises a deflection unit with which a laser beam produced by the associated laser device (30) can be deflected for scanning the work field (16), and wherein the calibration comprises correction of an offset and / or compensation of a gain drift of the deflection unit.

12. The method according to any one of claims 9 to 11, further comprising a step in which each of the marker devices (20) is adjusted such that the associated light reference mark (22) assumes a predetermined spatial relationship to one or more of the reference marks (17; 52), and in particular is brought into registration with one of the reference marks (17; 52).

13. The method according to any one of claims 9 to 12, wherein the calibration of each of the laser devices (30) is based on a selection among the light reference marks (22) and / or the crossing points (22'), in which light reference marks (22) and / or crossing points (22') are preferred that are further away from a center point of the working field of the associated laser device (30).

14. The method according to any one of claims 9 to 12, wherein calibrating the individual laser devices (30) and / or synchronizing the plurality of laser devices (30) is repeated in the course of additive manufacturing, preferably at regular intervals.

15. A computer program product comprising instructions which, when the program is executed by a processor associated with an assembly according to any one of claims 1 to 8, cause the processor to carry out the method according to any one of claims 9 to 14.