Patent Application
20190060999
This application claims priority to European Patent Application serial no. 17 187 997.6 filed Aug. 25, 2017, the contents of which are incorporated herein by reference in their entirety as if set forth verbatim.
The invention relates to an apparatus for additively manufacturing of three-dimensional objects by means of successive layerwise selective irradiation and consolidation of layers of a build material which can be consolidated by means of an energy beam, with an irradiation device configured to generate the energy beam, wherein the energy beam propagates along an optical beam path onto a build plane, wherein the energy beam irradiates build material in at least one consolidation zone.
Such apparatuses are well-known from prior art, wherein an energy beam selectively irradiates layers of a build material, wherein the build material is consolidated by irradiation with the energy beam. The energy beam is generated via an irradiation device and guided onto a build plane along an optical beam path. In other words, the energy beam is selectively guided onto a surface of build material located in a build plane, wherein the parts of the surface of the build material the energy beam is guided on are irradiated and thereby, consolidated. By selectively irradiating several layers in succession the three-dimensional object is additively built. The path in the build plane the energy beam is guided along is referred to as energy beam path (“writing path”), whereas the optical beam path refers to the path the energy beam travels along from the irradiation device, in particular from a beam source of the irradiation device through optical elements, to the build plane. In other words, the energy beam path is the variation of the position of the energy beam in the build plane.
Further, it is known from prior art to detect the temperature in the consolidation zone to generate information relating to a quality of the manufacturing process, in particular whether the irradiated build material is properly consolidated. The process quality and/or structural parameters of the object built in the manufacturing process additionally depend on the temperature in zones adjacent to the consolidation zone. In particular, if a temperature gradient between the consolidation zone and adjacent zones exceeds a defined value, negative impacts on the quality of the built object can occur, e.g. cracks in the volume of the built object.
Therefore, it is an object to provide an apparatus, wherein the manufacturing process is improved.
The object is inventively achieved by an apparatus according to the claims. Advantageous embodiments of the invention are subject to the dependent claims.
The apparatus described herein is an apparatus for additively manufacturing three-dimensional objects, e.g. technical components, by means of successive layerwise selective irradiation and consolidation of layers of a powdered build material (“build material”) which can be consolidated by means of an energy beam. A respective build material can be a metal, ceramic or polymer powder. A respective energy beam can be a laser beam or an electronic beam. A respective apparatus can be a selective laser sintering apparatus, a selective laser melting apparatus or a selective electron beam melting apparatus, for instance.
The apparatus comprises a number of functional units which are used during its operation. Exemplary functional units are a process chamber, an irradiation device which is configured to selectively irradiate a build material layer disposed in the process chamber with at least one energy beam, and a stream generating device which is configured to generate a gaseous fluid stream, e.g. a gas stream, at least partly streaming through the process chamber with given streaming properties, e.g. a given streaming profile, streaming velocity, etc. The gaseous fluid stream is capable of being charged with non-consolidated particulate build material, particularly smoke or smoke residues generated during operation of the apparatus, while streaming through the process chamber. The gaseous fluid stream is typically inert, i.e. typically a stream of an inert gas, e.g. argon, nitrogen, carbon dioxide, etc. The detection device may comprise a scanning unit that is configured to guide radiation emitted from the build plane to at least one sensor, in particular a camera, of the detection device.
The invention is based on the idea that a detection device is provided that is configured to detect radiation emitted from at least one adjacent zone that is located adjacent to the consolidation zone or to detect radiation emitted from the consolidation zone and radiation emitted from the adjacent zone. Thus, the apparatus allows for a detection of the radiation that is emitted from a zone adjacent to the consolidation zone so as to generate information relating to the effects of the manufacturing process on the build material adjacent to the build material in the consolidation zone. Thus, it is possible to generate information that is linked directly to the adjacent zone, whereas in prior art it is only possible to acquire information relating to the consolidation zone and to estimate the effect on the zones adjacent to the consolidation zone.
The zone in which the energy beam directly irradiates the build material is referred to as “consolidation zone” in the scope of this application. A zone adjacent to the consolidation zone (“adjacent zone”) is in particular in thermal contact with the consolidation zone in that an irradiation of the consolidation zone with the energy beam increasing the temperature of the build material in the consolidation zone leads to an increase of the temperature in the adjacent zone due to the thermal contact. For example, the adjacent zone directly contacts or surrounds the consolidation zone. The term “emit” or “emission” in the scope of this application refers to the reflection of radiation at a surface as well as the generation and the release of radiation by an object or volume, for example a volume of build material, e.g. thermal radiation due to heating the object.
In particular, an optical beam path of the detected radiation, the detected radiation travels along is different from the energy beam path. The optical beam path of the detected radiation refers to the path the radiation travels along that is emitted from the build material in the build plane. In particular, the emitted radiation travels from the build plane to the detection device, e.g. an optical sensor of the detection device. The apparatus therefore, is designed in that, unlike in prior art, the radiation used to acquire the information, i.e. the detected radiation, is not reflected at or generated in the build plane and travels the same optical beam path as the energy beam used to irradiate the build material in reverse direction. Instead, the detection device is arranged in that the optical beam path of the detected radiation differs from the optical beam path of the energy beam. Thus, the detected radiation does not travel through the optical components of the irradiation device, e.g. optical components used to collimate and/or focus the energy beam onto the build plane. Such optical components of typical irradiation devices comprise filter units, e.g. antireflection coatings, that filter a wide range of the wavelength spectrum so as to predominantly allow radiation with the wavelength of the energy beam or close to the wavelength of the energy beam to pass. Detected radiation refers to radiation that has been emitted by the build plane, in particular thermal radiation and reflected radiation, and guided towards the detection device or detected via the detection device, respectively.
This implies filtering of a wide range of the wavelength spectrum in that information is lost in apparatuses in which the detected radiation travels the same optical beam path as the energy beam used to irradiate the build material. According to this embodiment of the apparatus, the detected radiation does not travel the same optical beam path as the energy beam allowing for optical components without or with other filter units (coatings) to be used that allow radiation of a wider wavelength spectrum to pass. Further, radiation can be detected without the need of the detection device interfering with the optical beam path of the energy beam.
According to an embodiment of the apparatus, the detection device is configured to detect a temperature of at least one consolidation zone and/or at least one adjacent zone and/or to determine a temperature gradient between at least one consolidation zone and at least one adjacent zone. Of course, dependent on the object to be built, multiple consolidation zones and multiple adjacent zones can be present. The detection device enables a detection of the temperature not only in the consolidation zone but additionally, in at least one adjacent zone. This enables the generation of information relating to the effects of the irradiation with the energy beam on build material in adjacent zones.
In particular, it is possible to directly detect the temperature of an adjacent zone and therefore, determine the temperature flux between the consolidation zone and the adjacent zone. The adjacent zone is thereby, heated due to the thermal contact with the consolidation zone that is directly irradiated with the energy beam. Based on the detected temperature of the adjacent zone and the temperature of the consolidation zone or for example, two adjacent zones, thermal strains and/or mechanical stress in the build material and in the object can be determined. Further, a tendency of the build material and/or the object to develop defects, e.g. cracks, can be estimated.
The detection of the temperature and/or the temperature gradient allows a user of the apparatus to adjust various parameters, in particular beam parameters such as the intensity and/or the power of the energy beam so as to avoid temperature gradients above a predefined value leading to stress in the build material.
The apparatus can further be improved by providing a control unit that is configured to adjust or set at least one process parameter dependent on the detected temperature and/or the determined temperature gradient. Thus, the control unit may set or adjust various process parameters based on the detected temperature and/or the determined temperature gradient. The control of the process parameter by the control unit allows for an at least semi-automated process control, wherein the respective process parameters may be automatically controlled by the control unit dependent on the detected temperature and/or the determined temperature gradient. The process parameters may be controlled in that the process quality is enhanced, in particular that negative impacts on the build material and/or the object are reduced or avoided.
Particularly, the control unit may be configured to control, in particular to reduce, the temperature in at least one consolidation zone and/or to control, in particular to increase, the temperature in at least one adjacent zone and/or to reduce the temperature gradient between at least one consolidation zone and at least one adjacent zone dependent on the detected temperature and/or the determined temperature gradient, in particular exceeding a predefined threshold value. Hence, it is possible to reduce mechanical stress or thermal strains in the object by directly controlling the temperature in the consolidation zone and directly or indirectly control the temperature of the at least one adjacent zone. Due to the thermal contact the adjacent zone can indirectly be heated by heating the consolidation zone. Besides, the adjacent zone can be heated via the energy beam or a respective temperature element, e.g. a radiant heater or a water heater. The respective temperature may be controlled directly dependent on the detected temperatures and/or the determined temperature gradients. For example, if the temperature gradient is below a defined threshold value, it is possible to increase the temperature of the consolidation zone. If the temperature gradient is above a defined threshold value, the control unit may reduce a specific process parameter, e.g. the intensity or the power of the energy beam, to reduce the temperature in the consolidation zone.
Further, it is possible to directly control the temperature in the adjacent zone or the adjacent zones, for example by a heating the adjacent zone with a heating element, for example a radiant heater or a fluid heater. Besides, the adjacent zone can also be heated via the energy beam. By heating the adjacent zone a current temperature gradient can be reduced, as the temperature of the adjacent zone is at least partially adapted to the temperature in the consolidation zone. Of course, every combination of increasing or reducing the temperature in the consolidation zone or various adjacent zones is possible. The control unit may control the respective temperature or temperature gradient, if the temperature gradient exceeds a predefined threshold value. The threshold value may be defined regarding at least one property of the build material, for example an evaporation temperature or a melting temperature or the thermal expansion of the build material.
According to another embodiment of the apparatus, the control unit is configured to control the temperature and/or the temperature gradient dependent on an ambient parameter and/or a path velocity of the energy beam and/or a condition of the build material. Therefore, the respective temperature and/or temperature gradient is controlled dependent on an ambient parameter, e.g. an ambient temperature in the process chamber and/or a property of a gas stream. Additionally or alternatively, it is possible to control the temperature and/or the temperature gradient dependent on the energy depleted in the build material, for example corresponding to a path velocity of the energy beam, as the duration the energy beam irradiates a volume of build material directly affects the energy that is depleted in the respective volume of build material. By moving the energy beam slower or faster over the build plane more or less energy may be depleted in the build material.
Further, the temperature and/or the temperature gradient may be controlled with respect to a condition of the build material. The condition of the build material may be detected with a suitable sensor in that a relation of the condition of the build material and the temperature or the temperature gradient the build material can tolerate is taken into account. The sensor may for example be configured to detect a humidity of the build material.
The apparatus can further be improved in that a data storage is provided that is configured to store at least one parameter, in particular a temperature and/or a temperature gradient. The storage of at least one parameter allows for a documentation and enhanced quality management of the manufacturing process. Thereby, a relation between the parameters present in the manufacturing process, for example a temperature of the consolidation zone and/or the temperature in adjacent zones, and properties of the built object is possible. In particular, specific properties or features of the object can be linked to the stored parameter that was present during the manufacturing of the object. Present mechanical properties or features of the object can therefore be traced back to the manufacturing process, wherein positive and negative impacts on the object can be documented, wherein the documentation can also be used for future manufacturing processes.
Further, a scanning unit can be provided that is configured to guide the radiation that is emitted from the at least one consolidation zone and/or the at least one adjacent zone to the detection device. The scanning unit therefore, basically functions like a beam deflection unit of the irradiation device in that radiation emitted from a source, e.g. build material in the build plane, is guided to a defined position, i.e. a defined plane, for example a sensor surface of a sensor of the detection device. The scanning unit allows for an imaging of the consolidation zone and/or at least one adjacent zone onto the sensor, wherein, of course, the position of the consolidation zone varies with the current position of the energy beam on the build plane. Thus, it is possible to follow the position of the energy beam traveling the energy beam path in the build plane and to image the consolidation zone and/or the at least one adjacent zone onto a sensor of the detection device. As the scanning unit is configured to guide emitted radiation to the detection device it is possible to monitor radiation that is emitted from an arbitrary position of the build plane.
It is also possible to detect radiation that is emitted from a defined position relative to the consolidation zone, e.g. a zone with a defined distance to a current position of the energy beam in the build plane. As the energy beam travels over the build plane along the energy beam path, the radiation emitted from the defined position is being guided to the detection device.
In particular, the scanning unit may be synchronized with the irradiation device, in particular with at least one beam deflection unit of the irradiation device configured to guide the energy beam over the build plane, in that the at least one consolidation zone and/or the at least one adjacent zone is imaged onto a measuring unit of the detection device. The synchronization of the scanning unit with the irradiation device or particularly, the beam deflection unit, allows for a synchronized monitoring of the consolidation zone as the current position of the energy beam on the build plane can be imaged to the detection device via the scanning unit. A variation in the position of the energy beam on the build plane leads to an update of the position that is monitored via the detection device. Hence, an “online-” monitoring is enabled.
The detection device may comprise at least one optical element configured to image the at least one consolidation zone and/or the at least one adjacent zone onto the measuring unit, wherein the optical element is an apochromat. The use of an apochromat is advantageous, as the focal length only slightly varies when the wavelength of the radiation through the optical element is changed. Imaging errors can therefore be reduced.
According to another embodiment of the apparatus, the measuring unit comprises at least one pyrometer camera, in particular a ratio pyrometer camera. The use of a pyrometer camera allows for a local resolution of the temperature of at least one zone on the build plane. Further, the detection of the temperature of at least one consolidation zone and/or one adjacent zone may be performed time resolved. Thus, the detection of local varying temperatures and therefore, temperature gradients is possible. Hence, the temperatures and temperature gradients may be detected/determined locally and timely resolved. This leads to an improved detection or determination of possible thermal strains or mechanical stress in the object.
Further, the apparatus can be improved by providing a protective glass that is arranged between the build plane and the detection device, wherein a transmittance spectrum of the protective glass ranges from 170 nm to 5000 nm, preferably from 400 nm to 2000 nm. The protective glass used is unlike in prior art configured to let pass radiation from a wide wavelength spectrum. This enables the analysis of adjacent zones, in particular zones imaging radiation that differs from the radiation of the energy beam. The arrangement of the detection device as described above together with the use of the protective glass is advantageous, since a regular irradiation device can be used. Further, no changes in an existing irradiation device have to be made, wherein in particular a change of optical components of the irradiation device can be omitted, so that optically effective surfaces of every component of the irradiation device can be anti-reflection coated as usual. This allows for an efficient set up requiring low effort.
Besides, the invention relates to a detection device, in particular a detection device for an apparatus as described above, wherein the detection device is configured to detect radiation emitted from at least one adjacent zone adjacent to the consolidation zone or radiation emitted from the consolidation zone and radiation emitted from the adjacent zone. Self-evidently, all advantages, features and details described with respect to the apparatus are fully transferable to the detection device.
Additionally, the invention relates to a method for operating at least one apparatus for additively manufacturing three-dimensional objects by means of successive layerwise selective irradiation and consolidation of layers of a build material which can be consolidated by means of an energy beam, wherein the energy beam propagates along an optical beam path of the energy beam onto a build plane, wherein the energy beam irradiates build material in at least one consolidation, wherein radiation emitted from at least one adjacent zone adjacent to the consolidation zone or radiation emitted from the consolidation zone and radiation emitted from the adjacent zone is detected.
Further, the invention relates to a protective glass for an additive manufacturing apparatus, in particular an apparatus as described before, which protective glass arrangable between a build plane and a detection device of the apparatus, wherein a transmittance spectrum of the protective glass ranges from 170 nm to 5000 nm, preferably from 400 nm-2000 nm.
Of course, all advantages, features and details described with respect to the apparatus and the detection device are fully transferable to the method. In particular, the method may be performed on an apparatus as described above.
According to an embodiment, the method comprises the following steps:
The method according to this embodiment allows for the detection of radiation from the consolidation zone as well as from an adjacent zone. The radiation in the consolidation zone comprises thermal radiation due to heating the build material and radiation of the energy beam that is reflected on the metallic surface of build material that has been consolidated in the consolidation zone. Due to the thermal contact of the adjacent zone with the consolidation zone the build material in the adjacent zone is heated as well, wherein radiation emitted from the adjacent zone is mainly thermal radiation that can be detected.
By detecting the radiation from the consolidation zone and/or the adjacent zone the temperatures of the various zones are detected and a temperature gradient can be determined. Based on the temperature gradient it is possible to estimate whether negative impacts on the object are present, in particular whether thermal strain or mechanical stress in the object may be present. Dependent on the determined temperature gradient and/or the detected temperature at least one process parameter can be controlled to avoid inducing mechanical stress or thermal strain in the object.
An exemplary embodiment of the invention is described with reference to
The apparatus 1 comprises a detection device 11 that is configured to detect radiation 12a, 12b emitted from the adjacent zones 9, 10 and the consolidation zone 8 traveling an optical beam path 12 of the emitted radiation 12a, 12b. In
The detection device 11 comprises a scanning unit 13 configured to guide radiation 12a, 12b emitted from the build plane 7 to a measuring unit 14 comprising an optical sensor, for example a CMOS or CCD sensor. In particular, the measuring unit 14 may be built as or comprise a pyrometer camera configured to provide suitable local resolution to detect the temperature of the single zones 8 to 10. Radiation 12a emitted from the consolidation zone 8 and radiation 12b emitted from the adjacent zones 9, 10 is transmitted through a protective glass 15 that is transparent in a wavelength spectrum e.g. of 400 nm to 2000 nm. Thus, nearly the entire radiation 12a, 12b emitted from the build plane 7 and traveling along the optical beam path 12 of the emitted radiation 12a, 12b can pass the protective glass 15.
The scanning unit 13 guides the radiation 12a, 12b to the measuring unit 14, wherein the radiation 12a, 12b passes through an optical element 16 that is built as an apochromat.
Hence, the detection device 11 is configured to detect radiation 12a, 12b and thereby detect the temperature of the consolidation zone 8 and the adjacent zones 9, 10. By detecting the temperature it is possible to determine a temperature gradient between the adjacent zone 9 and the consolidation zone 8 and between the consolidation zone 8 and the adjacent zone 10. Further, respective information can be generated dependent on the detected temperatures and the determined temperature gradients relating to properties of the object 2.
The apparatus 1 further comprises a control unit 17 that is configured to control various process parameters, for example beam parameters such as a power and/or an intensity of the energy beam 4. Thus, the control unit 17 may control the irradiation device 5, for example the beam velocity of the energy beam 4, e.g. the velocity of the variation of the position of the energy beam 4 in the build plane 7 traveling along the energy beam path.
As can be derived from
The control unit 17 further is configured to control the temperature and the temperature gradient in or between the respective zones 8 to 10. In particular, if a defined threshold of the temperature gradient is exceeded, the control unit 17 may control the respective process parameter, in particular an energy beam power or an energy beam intensity of the energy beam 4 to avoid negative impacts on the object 2 such as mechanical stress or thermal strain that may lead to cracks in the object 2.
Further, the apparatus 1 can comprise a heating element (not shown), e.g. a water heater located below the build plane 7 or a radiant heater, configured to heat the adjacent zones 9, 10 to reduce a temperature gradient between the adjacent zones 9, 10 and the consolidation zone 8 by heating the adjacent zones 9, 10. The method described above may be performed on the apparatus 1 depicted in
| Number | Date | Country | Kind |
|---|---|---|---|
| 17187997.6 | Aug 2017 | EP | regional |
