APPARATUS FOR ADDITIVELY MANUFACTURING THREE-DIMENSIONAL OBJECTS

Apparatus (1) for additively manufacturing three-dimensional objects (2) by means of successive layerwise selective irradiation and consolidation of layers of a build material (3) which can be consolidated by means of an energy beam (5), wherein a determination device (6) is provided that is adapted to determine at least one parameter relating to a focal position (7) of the energy beam (5) and/or a deviation from a nominal focal position, wherein the determination is based on an angular deviation of at least one part of the energy beam (5) relative to a nominal angle.

The invention relates to an 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.

Apparatuses for additively manufacturing of three-dimensional objects are generally known from prior art. Such apparatuses typically use irradiation devices that are adapted to generate and/or guide an energy beam over a surface of build material, usually arranged in a build plane. Due to the selective irradiation of the build material, the build material may be selectively consolidated. By irradiating and thereby consolidating build material and alternatingly applying fresh layers of build material, the object may be layerwise built.

The consolidation behavior of the build material that is irradiated with the energy beam strongly depends on parameters of the energy beam, e.g. influencing the energy that is depleted in the build material. In other words, the parameters the control of the irradiation device is based on influence the consolidation behavior of the build material and thereby have an impact on the quality, in particular mechanical properties, of the object.

One of the key parameters is the focal position of the energy beam or, in other words, it is crucial to ensure that the energy beam is properly focused. As the spot size of the energy beam on the build material defines how much energy is depleted (per area) in the build material and also the spot size influences the structure or pattern that is irradiated in the build material, monitoring the spot size is important to ensure the object quality and/or a process quality is met, e.g. by ensuring the proper energy and/or intensity of the energy beam is used. For example, if the actual focal position of the energy beam deviates from a nominal focal position, a desired spot size is not met. Thus, the pattern that has to be irradiated in the build material will also deviate from the nominal pattern as structural elements of the object, e.g. line thicknesses, deviate from their nominal values. Additionally, the intensity or the energy per area deviates from the nominal energy per area, as the spot size, i.e. the area over which the energy of the energy beam is distributed, deviates from its nominal value, as well.

However, known approaches are limited by the response time of sensors, in particular on the conditions of rapid changing focal lengths of the optical systems used for additively manufacturing of three-dimensional objects. In known additive manufacturing apparatuses rapidly changing focal lengths may be misinterpreted as, e.g. thermal induced, focal shifts.

It is an object of the present invention to provide an apparatus for additively manufacturing of three-dimensional objects, wherein the determination of the focal position of the energy beam is improved.

The object is inventively achieved by an apparatus according to claim1. 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 selective layerwise consolidation of layers of a powdered build material (“build material”) which can be consolidated by means of an energy source, e.g. an energy beam, in particular a laser beam or an electron beam. A respective build material can be a metal, ceramic or polymer powder. A respective energy beam can be a laser beam or an electron beam. A respective apparatus can be a selective laser sintering apparatus, a selective laser melting apparatus, for instance.

The apparatus may comprise a number of functional units which are used during its operation. Exemplary functional units are a process chamber, an irradiation device which is adapted 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 adapted to generate a gaseous fluid 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.

As described before, the invention relates to an apparatus that is adapted to determine the focal position, i.e. in which the focal position may be monitored. The invention is based on the idea that a determination device is provided which is adapted to determine at least one parameter relating to a focal position of the energy beam and/or a deviation from a nominal focal position, wherein the determination is based on an angular deviation of at least one part of the energy beam relative to a nominal angle. Thus, a nominal angle can be defined under which the energy beam is incident on the determination device, for example on a beam splitter guiding the energy beam partially to the determination device, wherein the energy beam is incident under the nominal angle, if the energy beam is properly focused, i.e. the focal position meets a nominal focal position.

Hence, if the focal position of the energy beam deviates from a nominal focal position, the angle under which the energy beam is incident on the determination device will also deviate from the nominal angle that is defined for the properly focused energy beam. Therefore, it is possible to determine whether the energy beam is properly focused or whether a deviation from a nominal focal position is present by determining the angle under which the energy beam is incident, in particular determining the angular deviation of at least one part of the energy beam relative to the nominal angle. Thus, based on the determined nominal angle, it is possible to determine the at least one parameter relating to a focal position of the energy beam. In other words, the focal position and/or the deviation from a nominal focal position of the energy beam may be determined based on the determined angular deviation.

This allows for determining the at least one parameter relating to a focal position of the energy beam and/or a deviation from a nominal focal position without the need for monitoring the build plane and imaging at least one part of the build plane in which the energy beam is incident. Thus, the actual spot size of the energy beam on the build plane does not have to be compared with a nominal or defined spot size.

Further, the inventive apparatus advantageously allows for determining the at least one parameter relating to the focal position without the need for the energy beam being guided onto the build plane. Instead, the at least one parameter relating to the focal position of the energy beam may also be determined with the energy beam not being guided into the process chamber, as the determination can be performed with a (minor) part of the energy beam that is split off the energy beam, preferably before the energy beam is guided into the process chamber.

The determination device may be adapted to translate a focal position of the energy beam and/or a deviation from a nominal focal position into an angle and/or an angular deviation from a nominal angle. As described before, it is not necessary to measure the actual spot size of the energy beam on the build plane directly, for example via capturing an image of the energy beam being incident on the build plane. Instead, the at least one parameter relating to the focal position and/or a deviation from a nominal focal position, can be represented by an angle and/or an angular deviation from the nominal angle.

Of course, as many parameters may influence the focal position of the energy beam, such as focal lengths of the various optical components used in the additive manufacturing apparatus, the at least one determined parameter may include any of those factors contributing to/affecting the focal position of the energy beam. In particular, the focal position itself can be determined or the parameter can represent a deviation from the nominal focal position. Thus, it is possible to adjust the focal position in that the deviation from the nominal focal position may be reduced, in particular fully compensated to ensure that the nominal focal position is met. Thus, a closed loop control is feasible based on the determined parameter.

According to an embodiment of the inventive apparatus, a beam splitter may be provided that is adapted to split a sub-part off the energy beam and guide the sub-part towards the determination device. Thus, it is possible to split the sub-part off the energy beam and use the remaining (major) part of the energy beam to irradiate build material, as described before. For example, only a minor part of the energy beam may be split off as sub-part, for example less than 1%, preferably 0.3% of the energy beam, wherein the remaining (99% or 99.7%) of the energy beam may be used for processing in the additive manufacturing process. Preferably, the beam splitter is arranged on or attached to a focusing optical unit that is adapted to focus the energy beam onto the build plane.

The beam splitter further allows for a confocal set up of the determination device, wherein the sub-part may be split of the energy beam and guided towards the determination device. Further, it is possible to simultaneously irradiate build material, i.e. perform the additive manufacturing process, and determine the at least one parameter relating to the focal position and/or the deviation between the actual focal position and the nominal focal position. Thus, the focal position of the energy beam may be determined throughout the additive manufacturing process, wherein it is in particular not necessary to use the whole energy beam for the determination process. Instead, both the determination process and the additive manufacturing process can be performed in parallel. This allows for monitoring the behavior of the energy beam, in particular the focal position of the energy beam while the additive manufacturing process is performed. Thus, the deviations from a nominal focal position that occur during the additive manufacturing process can immediately be corrected via a corresponding adjustment and/or a calibration of the energy beam. In other words, a closed loop control can be performed.

The beam splitter may preferably be built as a cover glass, in particular an inclined cover glass, through which the energy beam may be guided into a process chamber of the apparatus. The cover glass may preferably be arranged between a focusing optical unit of the apparatus and a beam guiding unit, e.g. a scanner, such as one or more moveable mirrors. The beam guiding unit is used to guide the energy beam in the build plane. Hence, the energy beam is focused via the focusing optical unit and is subsequently incident on the beam splitter (cover glass). The part of the energy beam that passes the cover glass is preferably guided to (incident on) the beam guiding unit and is guided into the process chamber and onto the build plate. Another protective glass may be provided that is arranged between the beam guiding unit and the build plane, delimiting the process chamber and protecting the beam guiding unit from residues generated in the process. The protective glass therefore, delimits the process chamber and is used to couple the energy beam into the process chamber. Both, the cover glass (beam splitter) and the protective glass protect (optical) components of the apparatus from residues generated in the additive manufacturing process.

As a minor part, e.g. 0.3%, of the energy beam is reflected at the cover glass (beam splitter), the cover glass may be used as a beam splitter, as described before. The cover glass may further be inclined in that it encloses an angle with the energy beam, preferably deviant from 0°/90°. Thus, the cover glass may be arranged in an angle, e.g. 5°-85°, preferably 45°, with respect to the energy beam incident on the cover glass. As the energy beam is incident on the cover glass, a (major) part of the energy beam is transmitted through the cover glass, wherein a (minor) sub-part is reflected at the cover glass and guided towards the determination device.

Advantageously, by using the cover glass as beam splitter, it is not necessary to involve another optical element and further the reflection of the energy beam at the cover glass can be used and is not wasted in the optical system of the apparatus.

Further, a refractive element may be provided, in particular a wedge plate, which is adapted to guide the sub-part of the energy beam and adapted to increase an angular deviation of the sub-part of the energy beam. Thus, the sub-part that has been split off the energy beam may be transmitted through the refractive element, wherein an angular deviation may be increased to increase the effect and allow for an improved determination of the angular deviation from the nominal angle. Hence, angular deviations that are present may be amplified to improve the determination process.

According to another embodiment of the inventive apparatus, the determination device may comprise a focusing element adapted to image the sub-part onto a detector. The sub-part that has been split off the energy beam may be focused, e.g. via a refracting lens, onto a detector. The term “focusing” in this context does not require that the focus of the sub-part lies in the detector plane. The term is to be understood in that a collimated or diverging sub-part that is incident on the focusing unit is focused and that the sub-part that is transmitted through the focusing element further propagates towards the detector. Therefore, the focal plane of the sub-part may lie between the focusing element and the detector.

Further, the inventive apparatus, in particular the determination device, may comprise an optical filtering element, in particular an aperture, which is adapted to filter at least one part of the sub-part with a defined focal position deviant from a nominal focal position. A deviation from the nominal focal position will result in an angular deviation of the sub-part, which may preferably be increased via the refractive element, in particular the wedge plate. Afterwards, the sub-part is incident on the focusing element, which focuses the sub-part. For example, the focal position of the sub-part may lie in the plane of the optical filtering unit allowing the sub-part pass the optical filtering unit. If the focal position of the sub-part lies before or after the optical filtering unit, a part of the sub-part is filtered in that it is absorbed via the optical filtering unit. After the optical filtering unit has been passed, the sub-part is incident on the detector.

Preferably, the determination device may be adapted to perform the determination of the at least one parameter relating to the focal position and/or the deviation from a nominal focal position based a determination of a spot size of the sub-part of the energy beam on the detector, in particular a comparison of the spot size of the sub-part with a reference spot size. According to this embodiment, the determination device may be adapted to determine the at least one parameter relating to the focal position and/or the deviation from a nominal focal position by determining the spot size of the sub-part of the energy beam on the detector. As described before, the sub-part may be split off the energy beam via the beam splitter, in particular via a cover glass, wherein the sub-part is guided towards the detector. The sub-part may pass a refractive element, such as a wedge plate, to increase the angular deviation, as also described before. Between the beam splitter and the detector a focusing element is arranged that focuses the diverging sub-part.

As the focal position of the sub-part lies between the focusing unit and the detector, the sub-part meets the detector plane defocused. Thereby, the size of the spot of the sub-part is related to the angle under which the sub-part is reflected at the beam splitter. Therefore, the angular deviation that is caused by the deviation from the nominal focal position is (directly) related to the size of the spot of the sub-part that is imaged onto the detector. In particular, the greater the deviation from the nominal focal position, the greater the angular deviation and the larger is the size of the spot on the detector. Hence, the actual focal length and the actual focal position of the energy beam can be derived from the spot size of the sub-part on the detector.

In other words, the central part of the sub-part may be used as reference beam, for example a part of the energy beam that is on the optical axis of the energy beam. Further, the determination device may make use of the dependency between the angular deviation and the angle under which the sub-part is reflected at the beam splitter. As the focal length of the optical system, in particular of the focusing optical unit that is used to focus the energy beam on the build plane, directly defines the angle under which the energy beam is incident on the beam splitter, the focal length is related to the angle of incidence. The larger the focal length of the focusing optic unit the smaller is the angle of incidence on the beam splitter, wherein the angle of incidence is defined between an edge beam of the energy beam and the surface of the beam splitter. Hence, a nominal angle can be defined, wherein an energy beam focused with a nominal focal length, i.e. having a nominal focal position, is incident on the beam splitter under the nominal angle.

Thus, the angle of incidence is translated into the angular deviation as the sub-part is reflected at the beam splitter. Hence, an energy beam passing through the focusing optical unit having a comparatively larger focal length will be incident on the beam splitter under a comparatively smaller angle of incidence (compared to an energy beam that is properly focused). This will generate a corresponding angle of reflection. Thus, the angle of reflection will deviate from the angle of reflection and which a properly focused energy beam is reflected. The smaller angle of reflection causes due to passing the focusing element a larger spot on the detector. In comparison, an energy beam passing through the focusing optical unit with a comparatively smaller focal length, i.e. smaller than a nominal focal length, will be reflected at the beam splitter under a comparatively larger angle of reflection causing a comparatively smaller spot on the detector.

Thus, by taking the spot size on the detector into calculation, the focal length of the focusing optical unit can be derived. Further, a nominal focal length can be defined, wherein due to the determination of the spot size of the sub-part, it can be verified and/or monitored, whether the actual focal length matches the nominal focal length. Thereby, it is possible to determine, whether the focal position of the energy beam meets the nominal focal position.

According to another embodiment of the inventive apparatus, the detector may be built as or comprise a high repetition rate detector. Thus, sensors with high response times and/or high local resolutions may be used that can, for example, be driven by frequencies about 100 kHz or higher. This allows for determining the focal position (or deviations from a nominal focal position) in the rapid changing conditions in an additive manufacturing process. Therefore, even if the focal position of the energy beam changes rapidly, it is possible to determine the change of the focal position via the use of the high repetition rate sensor. The detector may in particular be built as or comprise at least two PSD-sensors (position sensitive device), preferably an arrangement of PSD-sensors and/or at least one line sensor. Each PSD-sensor may produce a signal, if the energy beam is incident on the PSD-sensor. By arranging multiple PSD-sensors in a defined spatial relation, e.g. in a row, it is possible to determine the size or changes in the size of the spot. Thus, the number of PSD-sensors generating a signal upon irradiation with the energy beam is related to the size of the spot of the energy beam and therefore, related to the angular deviation and the focal position or the deviation from a nominal focal position.

Preferably, the determination device may further be adapted to perform a power measurement of the energy beam. For example, the ratio between the sub-part and the whole energy beam may be known, wherein the power measurement of the sub-part may provide a conclusion on the power of the overall energy beam. The power/intensity of the energy beam, in particular the sub-part of the energy beam, may be determined via the detector.

According to another embodiment of the inventive apparatus, the apparatus may comprise a control unit, in particular an irradiation device, which is adapted to control the energy beam, wherein the determination device may be adapted to generate calibration data for controlling the energy beam, in particular for calibrating and/or adjusting the focal position of the energy beam. Thus, dependent on the at least one parameter relating to the focal position of the energy beam and/or a deviation from a nominal focal position, the determination device may generate calibration data that can be used for controlling the energy beam. Based on the calibration data, the control unit, in particular the irradiation device, may adjust the energy beam. For example, if a deviation from a nominal focal position occurs, the determination device may detect the deviation and generate calibration data. Subsequently, the control of the energy beam can be performed based on the calibration data in that the detected deviation can be reduced or compensated.

In particular, the apparatus may be adapted to control the energy beam in a closed loop. Thus, it is possible to continuously determine the at least one parameter relating to the focal position of the energy beam and/or the deviation from a nominal focal position, wherein the generated calibration data can be used in a feedback loop or closed loop, respectively. Thus, if a deviation from the nominal focal position occurs, the energy beam can be corrected immediately to avoid negative impacts on the additive manufacturing process.

Besides, the invention relates to a determination device for an apparatus for additively manufacturing of three-dimensional objects, in particular an inventive apparatus, as described before, which apparatus is adapted to generate an energy beam, wherein the determination device is adapted to determine at least one parameter relating to a focal position of the energy beam and/or a deviation from a nominal focal position, wherein the determination is based on an angular deviation of at least one part of the energy beam relative to a nominal angle.

Further, the invention may relate 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, in particular an inventive apparatus, as described before, wherein at least one parameter relating to a focal position of the energy beam and/or a deviation from a nominal focal position is determined via a determination device, in particular an inventive determination device, as described before, wherein the determination is based on an angular deviation of at least one part of the energy beam relative to a nominal angle.

Self-evidently, all details, features and advantages described with respect to the inventive apparatus are fully transferable to the inventive determination device and the inventive method. In particular, the inventive method may be performed on the inventive apparatus, preferably using the inventive determination device.

FIG. 1shows an apparatus1for additively manufacturing of three-dimensional objects2by means of successive layerwise selective irradiation and consolidation of layers of a build material3which can be consolidated by means of an energy beam5. The apparatus1comprises a determination device6which is adapted to determine at least one parameter relating to a focal position7of the energy beam5and/or a deviation from a nominal focal position, wherein the determination is based on an angular deviation of at least one part of the energy beam5relative to a nominal angle.

As can further be derived fromFIG. 1, an irradiation device is provided that is adapted to generate and guide the energy beam5. The irradiation device comprises, inter alia a focusing optical unit8that is adapted to focus the energy beam5onto a build plane9, in which build material3is arranged that can be selectively irradiated to consolidate the build material3and thereby build the three-dimensional object2. The energy beam5is incident on an inclined cover glass11that is used as a beam splitter12. The part of the energy beam5that passes the cover glass11is guided to a beam guiding unit26, such as a scanner. The energy beam5is coupled into a process chamber10of the apparatus1via protective glass (not shown). The splitting of the energy beam5at the cover glass11will be described with respect toFIG. 2.

FIG. 2shows the detail II ofFIG. 1, wherein the energy beam5is incident on the cover glass11that is used as beam splitter12. The energy beam5is transmitted through the cover glass11to a defined (major) part, for example to more than 99%, in particular to 99.7%. In other words, a sub-part13is split off the energy beam5and guided towards a detector14of the determination device6. As can further be derived fromFIG. 2, a central part15of the energy beam5is reflected at the beam splitter12and guided towards the detector14, wherein the central part15can be used as reference beam, as can be described in detail with reference toFIG. 3, 4. In detail, a first part16(e.g. right half of the energy beam5) of the energy beam5is reflected away from the detector14and a second part17(e.g. left half of energy beam5) is reflected towards the detector14.

In the situation that is depicted inFIG. 2, edge beams18are indicated that depict the limit of the second part17and the first part16of the energy beam5, wherein the other edge is delimited by the central part15. Of course, the major part of the first part16and the second part17is also transmitted through the beam splitter12as it is coupled through the cover glass11into the process chamber10to be focused on the build plane9. Thus, if a reflected part of the energy beam5is addressed, only the (minor) part of the energy beam5is to be understood that is reflected at the beam splitter12.

FIG. 2depicts that the edge beam18of the second part17and the central part15mark or delimit the sub-part13that is guided towards the detector14. In other words, the second part17of the energy beam5is partially reflected at the beam splitter12and guided as sub-part13towards the detector14. As can be derived fromFIG. 2, dependent on an angle of incidence19the edge beam18is incident on the beam splitter12, the edge beam18is reflected at the beam splitter12under an angle of reflection20. As the angle of incidence19under which the edge beam18is incident on the beam splitter12directly depends on the focal length of the focusing optical unit8that focuses the energy beam5on the build plane9, the focal position and/or the focal length and/or a deviation from a nominal focal position can be translated into an angular deviation. In particular, a reference angle21can be defined for the central part15that stays the same independent of the focal length with which the energy beam5is focused onto the build plane9.

FIG. 3shows the detail III with different energy beams5that are focused with different focal lengths and therefore, comprise different focal positions, wherein different edge beams18,18′ and18″are indicated. As the angles of incidence19,19′ and19″depend on the focal length of the focusing optical unit8that is used to focus the energy beam5, the focal lengths are translated into different angles of reflection20,20′ and20″ under which the different edge beams18,18′ and18″are reflected at the beam splitter12. Of course, the angle21for the central part15always stays the same as the central part15is the same for every focal length. As described before, the beam splitter12guides the reflected sub-part13to the detector14, as will be described with respect toFIG. 4.

FIG. 4shows the beam path of the sub-part13towards the detector14detail. Of course, although the three different energy beams5with different edge beams18,18′ and18″ are depicted, only one energy beam5is present at the same time, as the other edge beams18′ and18″only indicate the other energy beam or the change of focal lengths or the change of focal positions between the energy beams5. First, the sub-part13is guided through a refractive element22(optional), wherein the refractive element22increases the angular deviation of the sub-part13, as depicted via the edge beams18,18′ and18″. Afterwards, the sub-part13is transmitted through a focusing element23, for example a refracting lens, that focuses the sub-part13, wherein a focal position24of the sub-part13is arranged in a plane of an optical filtering unit25that is built as aperture.

Thus, dependent on the angle of incidence19,19′ and19″, the different edge beams18,18′ and18″ are reflected under different angles of reflection20,20′ and20″. Therefore, the spot size of the sub-part13on the detector14varies with the angle of incidence19,19′ in19″, as described before. Thus, dependent on the spot size d, d′ and d″ that are assigned to the different sub-parts13of the energy beams5with different edge beams18,18′ and18″ the focal length of the focusing optical unit8of the irradiation device can be derived. Hence, a comparison can be made between a nominal focal length and/or a nominal focal position and the actual focal position, as determined via the determination device6. Of course, the deviations from a nominal focal position can therefore be identified and compensated.

To compensate the present deviation from a nominal focal position, the determination device6may generate calibration data based on which the irradiation device can be controlled to adjust the focal length of the focusing optical unit8and therefore, adjust the focal position of the energy beam5. In other words, the determination device6may determine at least one parameter, for example the focal position of the energy beam5and/or a focal length of the focusing optical unit8and/or a deviation from a nominal focal position based on an angular deviation of at least one part of the energy beam5relative to a nominal angle. Dependent on which focal length and/or a focal position is desired and defined as nominal focal position or nominal focal length, respectively, an edge beam18may be defined. Thus, it is possible to compare the actual edge beam18,18′ or18″with the defined edge beam18. Dependent on the angular deviation between the actual edge beam18,18′ or18″with the defined edge beam18, the parameter relating to the focal position and/or the focal length can be determined.

As the spot sizes d, d′ and d″ directly relate to the corresponding focal length f, f′ and f″ that is used to focus the energy beam5and therefore, generate edge beams18,18′ and18″, a direct control of the focal position and/or the focal length can be performed dependent on the angular deviation that affects the spot size d, d′ and d″ on the detector14. Hence, the spot sizes d, d′ and d″ on the detector14are directly related to the focal length and therefore, to the focal position of the energy beam5. Thus, dependent on the signal generated via the detector14the focal length and/or the focal position can be controlled during an additive manufacturing process.

The detector14is built as or comprises a high repetition rate detector, for example a PSD-sensor (position sensitive device) and/or a line sensor. To control the energy beam5in a closed loop, the apparatus1preferably comprises a control unit (not shown), in particular integrated into the irradiation device, which is adapted to control the energy beam5based on calibration data that are generated via the determination device6.

Of course, the inventive method may be performed on the inventive apparatus1.