Device for additive manufacturing of three-dimensional objects

Abstract

The invention relates to a device (1) for additive production of a three-dimensional object (2) by successive, layer-by-layer selective irradiation and solidification of layers of a construction material (3) which can be solidified by means of an energy beam (4), a measuring unit (5) being provided, the measuring unit (5) is configured to generate information relating to a collimated portion (6) of the energy beam (4) and information relating to a focused portion (7) of the energy beam (4).

Description

[0001] This application is a divisional application of the invention patent application with application number 201711238412.9 filed on November 30, 2017, and the invention name is “Device for additively manufacturing three-dimensional objects”. Technical Field

[0002] The invention relates to a device for the additive production of three-dimensional objects by selectively irradiating and curing layers of a building material curable by means of an energy beam in succession, layer by layer. Background Art

[0003] Devices in which an energy beam is used to selectively irradiate layers of building material, thereby solidifying the building material due to the irradiation with the energy beam, are well known in the prior art. To ensure or maintain a constant process quality, it is necessary to monitor various process parameters, such as the power of the energy beam or the energy dissipated by the energy beam in the building material.

[0004] For example, the focus position of the energy beam may shift due to variations in process temperature, such as the temperature of at least one component of the apparatus. Such temperature-induced focus position shifts need to be corrected; otherwise, irradiating the build material with a defocused energy beam results in deviations in the object. Therefore, it is preferable to monitor and control various process parameters to ensure consistent process quality. Summary of the Invention

[0005] It is therefore an object of the present invention to provide a device which improves the control of process parameters.

[0006] This object is inventively achieved by a device according to claim 1. Advantageous embodiments of the invention are provided by the dependent claims.

[0007] The apparatus described herein is an apparatus for additively manufacturing three-dimensional objects, such as technical components, by sequentially and layer by layer selectively irradiating and solidifying layers of a powdered building material ("building material") that can be solidified using an energy beam. The building material can be metal, ceramic, or polymer powder. The energy beam can be a laser beam or an electron beam. The apparatus can be, for example, a selective laser sintering apparatus, a selective laser melting apparatus, or a selective electron beam melting apparatus.

[0008] The apparatus comprises a plurality of functional units used during its operation. Exemplary functional units are a process chamber, an irradiation device configured to selectively irradiate a layer of building material arranged in the process chamber with at least one energy beam, and a flow generation device configured to generate a flow of a gaseous fluid at least partially flowing through the process chamber with given flow characteristics, such as a given flow profile, flow velocity, etc.

[0009] The present invention is based on the idea of providing a measuring unit comprising at least one measuring device configured to generate information relating to a collimated portion of the energy beam and information relating to a focused portion of the energy beam. Thus, multiple process parameters can be monitored, since information relating not only to the focused portion of the energy beam, for example the portion between the focusing optics and the build plane, but also to the collimated portion of the energy beam, for example the portion between the collimating optics and the focusing optics, is generated. Consequently, a shift in the focal position of the energy beam or a shift in the focal length of at least one optical device or optical element can be determined. This allows, for example, the adjustment of at least one process parameter to at least partially compensate for a shift in the focal position or the focal length.

[0010] Thus, by means of the present invention, it can be ensured that a constant process quality is met, since, for example, the focus position of the energy beam can be kept constant, thereby allowing a constant energy input into the building material that has to be irradiated.

[0011] According to an advantageous embodiment, the device comprises:

[0012] a first beam splitter located between the collimating optics and the focusing optics, wherein a first beam path extends from the collimating optics through the focusing optics to the build plane, a second beam path extends from the collimating optics to the first measuring device, and a third beam path extends from the build plane and / or from a surface between the build plane and the focusing optics through the focusing optics to the second measuring device, wherein

[0013] - the first measuring device is configured to generate information about the collimated portion of the energy beam, and

[0014] The second measuring device is configured to generate information about the radiation emitted from the region of the build plane and / or to generate information about the focused portion of the energy beam.

[0015] Thus, a first beam splitter is used to split the energy beam exiting the collimating optics into a first beam path and a second beam path, wherein the first beam path extends from the collimating optics through the focusing optics to the build plane for irradiating the build material. The second beam path branches off from the energy beam and extends from the collimating optics to the first measuring device. Furthermore, a third beam path extending from the build plane and / or from a surface between the build plane and the focusing optics is guided to the second measuring device via the first beam splitter. This embodiment allows monitoring of various portions of the energy beam, wherein in particular, the collimated portion of the energy beam between the collimating optics and the focusing optics and the focused portion between the focusing optics and the build plane can be evaluated, as well as the radiation emitted from at least one region of the build plane and / or from a surface between the focusing optics and the build plane.

[0016] The term "emission" or "emitted" within the scope of this application refers to the reflection or generation or similar formation of radiation, wherein the radiation is released from the corresponding object or surface. Therefore, "emission" is not limited to the generation of radiation with respect to a beam source, but can also be understood as the reflection of radiation at a surface or the emission of (thermal) radiation by an object of a defined temperature.

[0017] According to another advantageous embodiment, the first measuring device includes a second beam splitter, which is configured to split the second energy beam traveling along the second beam path into two sub-portions, and / or the second measuring device includes a second beam splitter, which is configured to split the third energy beam traveling along the third beam path into two sub-portions.

[0018] By dividing the second energy beam traveling along the second beam path into two sub-portions and / or dividing the third energy beam traveling along the third beam path into two sub-portions, it is possible to determine or measure whether each energy beam is collimated. In other words, the angle at which the light of a single energy beam reaches the detector assigned to the corresponding measuring device can be detected. Therefore, the diameter of the corresponding energy beam is measured at two different positions along the corresponding beam path traveling along the energy beam. By comparing the two diameters measured at the two different positions, information related to the collimation state of the energy beam can be generated.

[0019] Thus, it is possible to have a single detector or two detectors, wherein the two subsections are sequentially imaged on the detector, for example using a shutter unit that is configured to disable one of the subsections, thereby allowing the measurement of the other subsection of the energy beam, and vice versa. For example, a single detector can be moved between at least two measurement positions, wherein the diameters of the respective energy beams are measured at the two positions and subsequently compared, thereby generating information about the collimation state of the respective energy beams. Thus, the optical path lengths of the two subsections traveling to the different measurement positions can be varied.

[0020] The device can be further improved in that the first measuring device and / or the second measuring device comprises two optical sensors, wherein the first sub-portion is measured via the first optical sensor and the second sub-portion is measured via the second optical sensor.

[0021] According to this embodiment, the energy beam, which has been split into two sub-portions, is measured using different optical sensors, which are arranged at different locations, i.e., at different distances from the second beam splitter. In other words, the distances traveled by the sub-portions of the respective energy beams are different, i.e., the beam lengths or optical path lengths are different for the two sub-portions. Therefore, if the respective energy beams are not properly collimated, the beam diameters of the two sub-portions are different. By providing this configuration, information can be generated regarding the collimation state of the respective energy beams and the parameters of optical components such as lenses, in particular, the focal length of the collimating or focusing optics.

[0022] Advantageously, the second measuring device comprises a dichroic beam splitter configured to split the third beam path into a first sub-path extending from the irradiation area of the build plane to the melt pool monitoring unit and a second sub-path reflected from a surface between the focusing optics and the build plane, in particular a cover glass of the focusing optics, to the second beam splitter of the second measuring device.

[0023] The dichroic beam splitter is configured to split an energy beam or electromagnetic radiation incident on the dichroic beam splitter, generally according to the wavelength of the electromagnetic radiation. Advantageously, the dichroic beam splitter can be configured to split off only a small portion or a defined amount of the third energy beam resulting from reflection of the energy beam, such as that occurring in the curing area or at a surface between the build plane and the focusing optics. The main portion of the energy beam is able to pass through the dichroic filter and travel to the second measurement unit.

[0024] Radiation emitted from adjacent areas around the solidification area is largely separated from the third energy beam, for example, radiation generated indirectly by areas adjacent to the solidification area due to thermal contact. For example, the dichroic beam splitter can be configured to selectively separate or reflect (thermal) radiation emitted from the build plane, for example in the wavelength spectrum from 250 nm to 3000 nm, wherein radiation with a wavelength of about 1070 nm is reflected only to a lesser extent. Thus, if the energy beam is generated at a wavelength of about 1070 nm, the energy beam can essentially pass through the dichroic beam splitter, wherein only a small amount of the energy beam is reflected by the dichroic beam splitter. Radiation emitted from the build plane, in particular radiation emitted from areas adjacent to the solidification area (wherein the radiation is in the wavelength spectrum from 250 nm to 3000 nm), passes through the dichroic beam splitter only to a lesser extent, wherein a larger amount is reflected by the dichroic beam splitter and is directed to the melt pool monitoring unit, wherein the radiation emitted from the build plane (i.e., the area adjacent to the solidification area) can be measured or analyzed.

[0025] The apparatus may be further improved so that the information generated by the first measuring device includes or relates to:

[0026] - current beam power,

[0027] - The current focal length of the collimating optics.

[0028] Thus, by measuring or analyzing the portion of the energy beam extending along the second beam path, the current beam power of the energy beam, which has been collimated by the collimating optics and directed to the first measurement unit, can be characterized. Furthermore, the current focal length of the collimating optics can be monitored or characterized, as well as the effects of temperature variations on the collimating optics. Thus, this embodiment allows monitoring the collimation of the energy beam, or in other words, monitoring whether it is necessary to correct the current focal length or current focal position of the energy beam, for example due to temperature-induced deviations.

[0029] According to another embodiment of the apparatus, the information generated by the second measuring device comprises or relates to:

[0030] - the current focus position,

[0031] - the temperature in the irradiated area of the building plane,

[0032] - Optical parameters of the focusing optics, in particular the focal length.

[0033] Similar to the information described previously, monitoring performed by the second measuring device allows the determination of the current focal position or current optical parameters of the focusing optics, in particular the focal length of the focusing optics. Together with the determined focal length of the collimating optics, the focal length of the optical system comprising the focusing optics and the collimating optics can be determined. Furthermore, the temperature of a region of the build plane can be determined. This region can be a curing region, where the energy beam directly irradiates the build material to cure it, or a region adjacent to the curing region, which is in thermal contact with the curing region and is thus indirectly heated by the energy beam.

[0034] By monitoring the temperature of the irradiated area, the quality of the object being built can be indicated, and by monitoring and individually controlling process parameters to avoid high temperature gradients or temperature differences between adjacent areas of the object, defects in the object can be avoided.

[0035] Another embodiment of the apparatus provides a cover glass disposed between the focusing optics and the build plane, wherein the cover glass is configured to reflect at least a portion of the energy beam. The cover glass provides a surface from which the energy beam is partially reflected along the third beam path. Therefore, the reflection of the energy beam at the cover glass can be used to monitor process parameters, as the reflected portion of the energy beam can be evaluated by a second measuring device. This allows for characterization of the properties of the focused portion of the energy beam, as the portion of the energy beam reflected at the cover glass has already passed through the collimating optics and the focusing optics.

[0036] The previously described embodiment can be modified to include an optical diaphragm positioned at the focal point of the portion of the energy beam reflected by the protective glass. This embodiment enables filtering of different portions of the energy beam or light extending along undesirable beam paths. Only a portion of the reflected energy beam from the protective glass passes through the optical diaphragm, which can be adjusted accordingly. Thus, radiation emitted from surfaces or areas of no interest, as well as scattered radiation, can be separated from the portion of the energy beam that requires evaluation by the diaphragm.

[0037] Another embodiment of the device advantageously provides that at least one information item generated by the measuring unit can be transmitted to a quality management system. Thus, the information item generated by the measuring unit can be stored in a data memory of the quality management system and / or further processed, for example to characterize the object to be manufactured and / or to record process parameters during the object's manufacturing process. This allows correspondingly linking object characteristics with corresponding manufacturing processes or parameters during the manufacturing process.

[0038] According to another advantageous embodiment, a control unit is provided, which is configured to control at least one process parameter of the energy beam, in particular the focal position, based on at least one information generated by the measuring unit. Thus, by monitoring the individual parts of the energy beam as described above, at least one process parameter can be evaluated and controlled ("online"). By monitoring the relevant process parameters during the manufacturing process of the object, the process parameters can be corrected or adjusted before changes in the process parameters, such as changes in the focal position, lead to deviations in the object currently being manufactured. Thus, by evaluating the individual parts of the energy beam, such as the focused part, the reflected part and the collimated part, the corresponding components can be adjusted and thus the corresponding parameters corrected before deviations occur. Thus, the position or relative position of optical devices, such as lenses, can be adjusted to compensate for shifts in the focal length or the focal position due to temperature changes.

[0039] Furthermore, the present invention relates to a method for operating an apparatus for additively manufacturing a three-dimensional object by selectively irradiating and curing layers of a building material, layer by layer, which building material can be cured by an energy beam, wherein information related to a collimated portion of the energy beam and information related to a focused portion of the energy beam is generated.

[0040] It is obvious that all features, advantages and details described with respect to the device are fully transferable to the method and vice versa. The method is preferably carried out on a device as described above.

[0041] According to one embodiment of the method, the energy beam is split between the collimating optics and the focusing optics into a first beam path, a second beam path, and a third beam path, the first beam path extending from the collimating optics through the focusing optics onto the build plane, the second beam path extending from the collimating optics to a first measuring device, and the third optical path extending from the build plane and / or from a surface between the focusing optics and the build plane through the focusing optics to a second measuring device, wherein information about the collimated portion of the energy beam is generated by the first measuring device, and information about radiation emitted from the region of the build plane and / or from the surface between the focusing optics and the build plane and / or information about the focused portion of the energy beam is generated by the second measuring device.

[0042] Thus, the energy beam leaving the collimating optics is split by a beam splitter before passing through the focusing optics and being directed to the first measurement device. Radiation reflected at the build plane and / or at surfaces arranged behind the focusing optics is directed by the beam splitter to the second measurement unit. This allows monitoring of relevant beam portions, in particular the collimated portion, the focused portion, and radiation emitted from the region of the build plane and / or from surfaces between the build plane and the focusing optics. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Exemplary embodiments of the present invention are described with reference to the accompanying drawings. Figure 1 is a schematic diagram and illustrates the apparatus of the present invention. DETAILED DESCRIPTION

[0044] The figure shows an apparatus 1 for additively manufacturing a three-dimensional object 2 by selectively irradiating and curing layers of a building material 3, which can be cured by an energy beam 4, in succession, layer by layer. The apparatus 1 comprises a measuring unit 5 having two measuring devices 14, 16, which are configured to generate information relating to a collimated portion 6 of the energy beam 4 and information relating to a focused portion 7 of the energy beam 4. The measuring devices 14, 16 are thus configured to simultaneously measure different portions 6, 7 of the energy beam 4, enabling the measuring unit 5 to generate information relating to the different portions 6, 7 of the energy beam 4.

[0045] Measuring unit 5 comprises a first beam splitter 8 for splitting energy beam 4, wherein a first beam path 9 extends from collimating optics 10 through first beam splitter 8 and focusing optics 11 to a building plane 12. The portion of energy beam 4 extending along first beam path 9 is therefore not reflected by first beam splitter 8 and is used to illuminate building material 3 in building plane 12.

[0046] The first beam splitter 8 splits off a portion of the energy beam 4 that extends along a second beam path 13 from the collimating optical device 10 to the first measuring device 14. In addition, the first beam splitter 8 reflects the reflected portion of the energy beam 4, which extends along a third beam path 15 from the build plane 12 or from a surface between the build plane 12 and the focusing optical device 11 through the focusing optical device 11 to the second measuring device 16. Thus, the first beam splitter 8 serves to split the energy beam 4, wherein the first beam path 9 passes through the first beam splitter 8, and the second energy beam path 13 is reflected by the first beam splitter 8 to the first measuring device 14, and wherein the third energy beam path 15 is reflected by the first beam splitter 8 to the second measuring device 16.

[0047] The first measuring device 14 comprises a second beam splitter 17, which splits the portion of the energy beam 4 extending along the second beam path 13 into a first sub-portion 18 and a second sub-portion 19, wherein the first sub-portion 18 is imaged on a first optical sensor 20 and the second sub-portion 19 is measured via a second optical sensor 21. The first optical sensor 20 and the second optical sensor 21 are arranged at different distances from the second beam splitter 17. As a result, the optical path lengths of the sub-portions 18, 19 of the portion of the energy beam 4 extending along the second beam path 13 are different. This makes it possible to measure whether the collimated portion 6 of the energy beam 4 is properly collimated or whether the focal length of the collimating optics 10 must be adjusted. Other parameters of the energy beam 4 and / or the collimating optics 10, such as the power of the energy beam 4, can be measured via the optical sensors 20, 21.

[0048] The second measurement device 16 is configured similarly to the first measurement device 14. Therefore, the same reference numerals are used for identical components. The second measurement device 16 also includes a second beam splitter 17 and two optical sensors 20 and 21, wherein the two optical sensors 20 and 21 are arranged at different distances from the second beam splitter 17. The second beam splitter 17 of the second measurement device 16 also splits the portion of the energy beam 4 incident on the second beam splitter 17 into a first sub-portion 18 and a second sub-portion 19.

[0049] In addition, the second measuring device 16 includes an optical diaphragm 22, which is arranged at the focal position of the portion of the energy beam 4 reflected by the protective glass 23. The diaphragm 22 allows filtering of radiation, wherein only the portion of the energy beam 4 reflected by the protective glass 23 is allowed to pass through the optical diaphragm 22 and pass to the second beam splitter 17 of the second measuring device 16. Radiation other than the portion of the energy beam 4 reflected by the protective glass 23 is blocked by the optical diaphragm 22.

[0050] Measuring unit 5 further includes a dichroic beam splitter 24 assigned to second measuring device 16, wherein dichroic beam splitter 24 is configured to selectively filter (reflect) or pass radiation through dichroic beam splitter 24 depending on its wavelength. In particular, the portion of energy beam 4 emitted from the region of build plane 12 or reflected at protective glass 23—i.e., extending along third beam path 15—is filtered by dichroic beam splitter 24 depending on wavelength. This allows filtering of two different portions of energy beam 4: the portion reflected at protective glass 23 or build plane 12, or the portion emitted from the region of build plane 12, in particular thermal radiation. Thus, it is possible to measure radiation emitted by build plane 12, in particular from the region adjacent to the curing area, where energy beam 4 directly irradiates build material 3.

[0051] In particular, the dichroic beam splitter 24 can be designed so that the wavelength of the energy beam 4 is reflected only to a small extent, or in other words, the radiation having the wavelength of the energy beam 4 can pass through the dichroic beam splitter 24 to the greatest extent. Therefore, the portion 25 of the energy beam 4 that passes through the dichroic beam splitter 24 is mainly the portion of the energy beam 4 that is reflected at the protective glass 23 or the curing area, passes through the focusing optical device 11, and is reflected at the first beam splitter 8. The portion 25 of the energy beam 4 is guided to the second measuring device 16, is filtered again by the optical diaphragm 22, and is subsequently divided into two sub-portions 18, 19 by the second beam splitter 17 and imaged onto the optical sensors 20, 21.

[0052] Furthermore, portion 26 (the thermal radiation emitted by the region of build plane 12) is primarily reflected by dichroic beam splitter 24, since the wavelength of portion 26 is different from the wavelength that dichroic beam splitter 24 is designed to pass. Portion 26 is primarily emitted by build plane 12, in particular by the region adjacent to the solidification region. Consequently, portion 26 is emitted by build plane 12 and passes through protective glass 23 and focusing optics 11. Subsequently, portion 26 is reflected by first beam splitter 8 and dichroic beam splitter 24 and directed to melt pool monitoring unit 27. Melt pool monitoring unit 27 is configured to measure portion 26. In particular, melt pool monitoring unit 27 includes at least one optical sensor (not shown), for example, in order to determine the temperature of the region of build plane 12 from which portion 26 is emitted.

[0053] As can be seen from the single figure, device 1, in particular measuring unit 5, allows for the determination of individual portions of energy beam 4 and of the radiation emitted from build plane 12. In particular, information can be generated regarding collimation portion 6 and focusing portion 7, as well as portion 26 of the radiation emitted from build plane 12. This allows for the adjustment of various process parameters, in particular the focal lengths of collimation optics 10 and focusing optics 11, to avoid or correct focus shifts of energy beam 4, such as those caused by temperature differences. Furthermore, the temperature gradient between the curing area and the adjacent areas can be determined by measuring the temperature in the curing area and the adjacent areas. Consequently, if the determined temperature gradient exceeds a predetermined value, the corresponding process parameters, in particular the power of energy beam 4, can be adjusted, in particular reduced.

[0054] Obviously, the above method can be used in Figure 1 Executed on device 1 as shown.

Claims

1. A device (1) for the additive production of three-dimensional objects (2) by selectively irradiating and curing layers of a building material (3) curable by means of an energy beam (4) in succession, layer by layer, characterized in that The device comprises a measuring unit (5), the measuring unit (5) comprising: collimating optics (10), focusing optics (11) and a first beam splitter (8) located between the collimating optics (10) and the focusing optics (11); a first measurement device (14) configured to generate information related to the collimated portion (6) of the energy beam (4); and a second measuring device (16) configured to generate information related to the focused portion (7) of the energy beam (4); The first beam splitter (8) is configured to reflect a portion of the energy beam (4) that has extended through the collimating optical device (10) to provide the collimated portion (6) of the energy beam (4), and is configured to extend a portion of the energy beam through the focusing optical device (11) to provide the focused portion (7) of the energy beam (4).

2. The device according to claim 1, characterized in that wherein at least a portion of the focused portion (7) of the energy beam (4) defines a first beam path (9) extending through the focusing optics (11) onto a build plane (12), and wherein at least a portion of the collimated portion (6) of the energy beam (4) defines a second beam path (13) extending to the first measuring device (14), and wherein a third beam path (15) extends from the build plane (12) and / or a surface between the build plane (12) and the focusing optics (11) through the focusing optics (11) to the second measuring device (16), The second measuring device (16) is configured to generate information related to radiation emitted from the region of the building plane (12) and / or to generate information related to the focused portion (7) of the energy beam (4).

3. The device according to claim 2, characterized in that The first measuring device (14) comprises a second beam splitter (17) configured to split the second energy beam (4) travelling along the second beam path (13) into two sub-portions (18, 19), and / or the second measuring device (16) comprises a second beam splitter (17) configured to split the portion of the energy beam (4) travelling along the third beam path (15) into two sub-portions (18, 19).

4. The device according to claim 3, characterized in that The first measuring device (14) and / or the second measuring device (16) comprises two optical sensors (20, 21), wherein the first sub-portion (18) is measured by the first optical sensor (20) and the second sub-portion (19) is measured by the second optical sensor (21).

5. The device according to claim 4, characterized in that At least two optical sensors (20, 21) of the same measuring device (14, 16) are arranged at different distances from the second beam splitter (17) and / or are movable.

6. The device according to claims 2 to 5, characterized in that The second measuring device (16) comprises a dichroic beam splitter (24) configured to split radiation travelling along the third beam path (15) into a first subpath and a second subpath, the first subpath extending from the region of the build plane (12) to a melt pool monitoring unit (27), the second subpath being reflected from a surface between the focusing optics (11) and the build plane (12) to the second beam splitter (17) of the second measuring device (16).

7. The device according to any one of claims 1 to 6, characterized in that wherein the information generated by the first measuring device (14) includes or relates to: Current beam power; and / or The current focal length of the collimating optics (10).

8. The device according to any one of claims 1 to 7, characterized in that wherein the information generated by the second measuring device (16) includes or relates to: Current focus position; the temperature in the irradiated area of the build plane (12); and / or Optical parameters of the focusing optical device (11).

9. The device according to any one of claims 1 to 8, characterized in that include: A protective glass (23) is arranged between the focusing optics (11) and the building plane (12), wherein the protective glass (23) is configured to reflect at least a portion of the energy beam (4).

10. The device according to claim 9, characterized in that include: An optical film (22) is located at a focal position of the energy beam (4) reflected by the protective glass (23).

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