Patent Publication Number: US-2020276640-A1

Title: Apparatus and method for producing a three-dimensional work piece

Description:
The present invention relates to an apparatus and a method for producing a three-dimensional work piece. 
     Powder bed fusion is an additive layering process by which pulverulent, in particular metallic and/or ceramic raw materials can be processed to three-dimensional work pieces of complex shapes. To that end, a raw material powder layer is applied onto a carrier by a powder application device. The raw material powder is than subjected to radiation (e.g., laser or particle radiation) in a site-selective manner in dependence on the desired geometry of the work piece that is to be produced. The radiation penetrating into the powder layer causes heating and consequently melting or sintering of the raw material powder particles. Further raw material powder layers are then applied successively to the layer on the carrier that has already been subjected to radiation treatment, until the work piece has the desired shape and size. Powder bed fusion may be employed for the production of prototypes, tools, replacement parts, high value components or medical prostheses, such as, for example, dental or orthopedic prostheses, on the basis of CAD data. Examples for powder bed fusion techniques include Selective Laser Melting (SLM) and Selective Laser Sintering (SLS). 
     In order to maintain a high process quality, it is crucial that a location where the radiation beam impinges onto the raw material powder can be precisely controlled, in particular with regard to the preceding layers, which have already been solidified. The best results can be achieved when this location is not only controlled with regard to directions parallel to an uppermost layer of raw material (i.e., with regard to an x-y-plane) but also with regard to a direction perpendicular to the uppermost layer of raw material powder (i.e., a focus direction or z-direction). 
     In known apparatuses for producing a three-dimensional work piece, it is difficult to control a location where the radiation beam impinges onto the raw material powder over the entire manufacturing process, in particular due to thermal deformations of various structures and components of the apparatus. 
     The invention is directed at the object of providing an apparatus and a method, which solve the above-described problems and/or other related problems. 
     This object is addressed by an apparatus according to claim  1  and by a method according to claim  15 . 
     According to a first aspect, an apparatus for producing a three-dimensional work piece is provided. The apparatus comprises a carrier configured to receive multiple layers of raw material powder, an irradiation unit configured to direct a radiation beam to predetermined sites of an uppermost layer of the raw material powder in order to solidify the raw material powder at the predetermined sites, a process chamber defining a volume through which the radiation beam is directed from the irradiation unit to the raw material powder, and a support structure provided outside the process chamber and supporting the irradiation unit. 
     According to the present disclosure, a plane parallel to a surface of the carrier of the apparatus (and, therefore, parallel to an uppermost layer of raw material powder) is defined to be an x-y-plane of a Cartesian coordinate system used herein. Further, a direction perpendicular to this plane is defined as a z-direction. 
     The carrier may have a rectangular cross-section in the x-y-plane. The carrier may further be movable in the z-direction in order to be lowered after an Irradiation process of an uppermost layer of raw material powder is finished, such that a new layer of raw material powder can be applied by a powder application device. The irradiation unit may comprise a radiation source such as, e.g., a laser. As an alternative to a laser, also a particle source, such as an electron source, may be provided. In order to be able to direct the radiation beam in the x-y-plane, the irradiation unit may comprise at least one scanning unit. The scanning unit may comprise at least one movable mirror configured to direct the radiation beam to a desired location in the uppermost layer of raw material powder. The scanning unit may be controlled by a control unit. Further, the irradiation unit may comprise a focus unit configured to change a focus position along the beam path of the radiation beam (substantially along the z-direction). 
     The irradiation unit may be configured to generate and control the direction of more than one radiation beam. For example, at least two scanning units may be provided, wherein each of the scanning units is configured to control the direction of a corresponding radiation beam. Thereby, two or more melting pools can be formed at the same time. In case more than one radiation beam can be emitted, a surface of an uppermost layer of raw material powder may be subdivided into two or more irradiation areas, wherein each of the radiation beams can be scanned over a corresponding one of the irradiation areas. An overlap zone may exist, in which two or more adjacent irradiation areas overlap. 
     The process chamber defines a volume, which does not necessarily mean that the process chamber is hermetically sealed with regard to the exterior. The process chamber may be defined, e.g., by sidewalls of the process chamber, wherein four sidewalls may be provided, each sidewall extending substantially perpendicular to the x-y-plane. The sidewalls may comprise at least one opening for forming an inlet or outlet (e.g., for gas) and/or at least one attachment member for attaching an element of the apparatus to a corresponding one of the sidewalls. The volume of the process chamber may be limited in the z-direction to a bottom side by the carrier and/or by an uppermost layer of the raw material powder. As described later, a build cylinder may be attached or may be attachable to the bottom side of the process chamber. The volume of the process chamber may be limited to an upper side by a top wall having an opening for the one or more radiation beams. Alternatively, the upper side of the process chamber may be limited by a thermal isolation layer comprising a thermally isolating gas. Further, the upper side of the process chamber may also be limited by the irradiation unit, wherein the irradiation unit itself is not part of the process chamber. In other words, the process chamber may be defined as a wall structure providing a housing for a spatially, atmospherically, and fluidically closed process environment. 
     The support structure may comprise a support frame. The support structure may be arranged outside the process chamber such that no parts of the support structure are arranged within the process chamber. In other words, the support structure may be arranged such that it is not influenced by process heat generated in the process chamber, e.g., by a building process performed within the process chamber. The support structure may, e.g., comprise a support frame configured to independently stand on a ground (e.g., a ground plate). The support structure supports the irradiation unit, e.g., by providing a mechanical support for the irradiation unit. In other words, the irradiation unit may be mounted to the support structure. The irradiation unit may be mounted to the support structure by appropriate mounting means, such as screws, pins, bolts, etc. Further, the irradiation unit may be mounted to the support structure via one or more attachment members having mechanically and/or thermally decoupling properties. The support structure may comprise one or more support frames. In case the support structure comprises more than one support frame, the individual support frames may be releasably or non-releasably attached to each other. For example, each support frame of the support structure can be individually placed onto a common ground or a common base plate. The individual support frames may be nested. Each support frame of the support structure can support one or more components of the apparatus (such as the irradiation unit). 
     By supporting the irradiation unit by the support structure, which is provided outside the process chamber, it can be ensured that process heat generated within the process chamber has no influence on a position (i.e., a dislocation) of the irradiation unit with regard to the support structure. The position of the irradiation unit with regard to the support structure (which may be regarded as a reference coordinate system of the apparatus) thereby can be maintained unchanged. In examples in which further components are supported by the support structure, it can be ensured that the position of the irradiation unit with regard to these further components is maintained unchanged. Further, since the irradiation unit is not affected (or less affected) by process heat generated within the process chamber, positions of individual optical components within the irradiation unit with regard to each other and/or optical properties (e.g., focal length, etc.) of these optical components stay constant. 
     The support structure may be thermally decoupled from the process chamber, such that process heat inside the process chamber causes no substantial thermal deformation of the support structure. 
     According to the present disclosure, the expression “thermally decoupled” may mean that there is no (or almost no) heat transport between the two thermally decoupled elements. In other words, there is (almost) no thermal conduction between the two thermally decoupled elements and the thermal conductivity of a material provided between the two thermally decoupled elements is low. The process heat may be heat generated by the laser beam when it impinges onto and melts the raw material powder. For example, the process chamber may be attached to the support structure via one or more attachment members having thermally decoupling properties. When the process heat inside the process chamber causes no substantial thermal deformation of the support structure, a spatial relationship between the process chamber and the support structure may be maintained. 
     The irradiation unit may be mechanically decoupled from the process chamber, such that thermal deformation of the process chamber due to process heat inside the process chamber causes no substantial dislocation of the irradiation unit with regard to the support structure. 
     According to the present disclosure, the expression “mechanically decoupled” may mean that thermal deformation of a first element causes no (or almost no) mechanical dislocation of a second element with regard to the first element, when the first and second elements are mechanically decoupled from each other. For example, the irradiation unit and the process chamber may both be attached to the support structure. The support structure may comprise a rigid support frame, wherein the coefficient of thermal expansion of the support frame may be very low. In addition or alternatively, the irradiation unit may be thermally decoupled from the support structure and/or the process chamber may be thermally decoupled from the support structure. When the process heat inside the process chamber causes no substantial dislocation of the irradiation unit with regard to the support structure, it can be ensured that a spatia relationship between the irradiation unit and the support structure can be maintained. 
     An air gap may be provided between the support structure and a side wall of the process chamber. The air gap may enhance a thermal decoupling between the support structure and the process chamber, because air has a low thermal conductivity. 
     The support structure may comprise at least two feet configured to be placed on a ground plate. Thereby, the support structure may be configured to independently stand on a ground. 
     The apparatus may further comprise a build cylinder having at least one side wall configured to be in contact with the raw material powder applied onto the carrier. The at least one side wall of the build cylinder my thereby support the raw material powder, such that the raw material powder is kept in a predefined shape (e.g., a cuboid shape). The build cylinder may form a volume having a cross section substantially corresponding to a cross section of the carrier in top view. In other words, the carrier can move through the build cylinder, wherein a distance between edges of the carrier and the side walls of the build cylinder stays substantially constant. This distance may be very small and/or sealed by a sealing member, such that no raw material powder can pass through a slit between edges of the carrier and the build cylinder. For example, a cross section of the volume defined by the build cylinder may be, e.g., circular, rectangular (e.g., square-shaped), or rectangular with rounded edges. The build cylinder may be attached to a bottom side of the process chamber. Further, the build cylinder may be releasably attachable to a bottom side of the process chamber. As described later, the build cylinder may also be attached to a build cylinder movement unit configured to vertically move the build cylinder with regard to the support structure and with regard to the carrier. 
     The apparatus may further comprise a carrier movement unit configured to vertically move the carrier with regard to the process chamber and with regard to the build cylinder and within the build cylinder, the carrier movement unit being supported by the support structure. 
     Thereby, the carrier may be supported by the support structure via the carrier movement unit. By supporting the carrier movement unit by the support structure, it can be ensured that the carrier is thermally and/or mechanically decoupled from the process chamber and, thereby, a spatial relationship between the carrier and the irradiation unit can be maintained and controlled. Since the carrier can vertically move within the build cylinder, a volume filled with raw material powder can be increased or decreased by the movement of the carrier. The carrier movement unit can be configured to move downwards within the build cylinder after an irradiation process of an uppermost layer of raw material powder has been finished, such that a new layer of raw material powder can be applied on the previous uppermost layer. As mentioned above, the support structure may comprise a plurality of support frames. For example, the irradiation unit may be attached to a first one of these support frames and the carrier movement unit may be attached to a second one of the support frames. For example, the first and the second support frame of the support structure can be individually placed onto a common ground or a common base plate. The Individual support frames may be nested. 
     The carrier movement unit may be mechanically decoupled from the process chamber, such that thermal deformation of the process chamber due to process heat inside the process chamber causes no substantial dislocation of the carrier movement unit with regard to the support structure. 
     For example, when each of the process chamber, the irradiation unit, and the carrier movement unit are independently supported by the support structure, these three elements of the apparatus can be thermally and/or mechanically decoupled from each other. 
     The apparatus may further comprise a build cylinder movement unit configured to vertically move the build cylinder with regard to the support structure. The build cylinder movement unit may be supported by the support structure. Further, the process chamber may be supported by the support structure and the build cylinder can be vertically moved with regard to the process chamber. For example, the build cylinder may be moved downwards after a building process of a work piece is completed, such that the work piece is accessible from its side and the raw material powder can be removed from the work piece. 
     The process chamber may be supported by the support structure at a ground level of the process chamber. 
     In other words, one or more attachment members via which the process chamber is attached to the support structure are arranged in an area of the ground level of the process chamber. Thereby, a location of the ground level of the process chamber can be predefined with regard to the support structure. In case the process chamber expands due to process heat generated within the process chamber, the location of the ground level of the process chamber does not change. The ground level of the process chamber may correspond to an uppermost layer of raw material powder provided on the carrier. 
     The apparatus may further comprise a powder application device supported by the support structure. In other words, the powder application device may be independently supported by the support structure, such that the powder application device is mechanically and/or thermally decoupled from other components of the apparatus, such as the process chamber, the irradiation unit, and the carrier. 
     The apparatus may further comprise a thermal isolation layer provided between the irradiation unit and the process chamber. The thermal isolation layer may be filled with thermally isolating gas. Further, at least one gas inlet may be provided configured for filling the thermal isolation layer with thermally isolating gas. The thermal isolation layer may be configured such that the radiation beam passing the thermal isolation layer is not influenced (i.e., deflected or absorbed) by the thermal isolation layer. 
     The apparatus may further comprise a vertical location measurement device configured to determine a vertical location of the carrier with regard to the support structure. 
     By determining the vertical location of the carrier with regard to the support structure, a location of an uppermost layer of raw material powder may be precisely estimated. 
     The vertical location measurement device may comprise a glass scale. By providing a glass scale it can be ensured that the vertical location measurement is not affected by thermal influences and, in particular by process heat generated within the process chamber. 
     According to a second aspect, a method for producing a three-dimensional work piece is provided. The method comprises applying a layer of raw material powder onto a carrier, directing, by an irradiation unit, a radiation beam to predetermined sites of the layer of the raw material powder in order to solidify the raw material powder at the predetermined sites, wherein the radiation beam is directed from the irradiation unit to the raw material powder through a volume defined by a process chamber, and wherein a support structure is provided outside the process chamber and supports the irradiation unit. 
     The details set out above with regard to the first aspect may also apply to the second aspect, where appropriate, In particular, the method of the second aspect may be carried out by the apparatus of the first aspect. 
    
    
     
       Preferred embodiments of the invention are described in greater detail with reference to the appended schematic drawing, wherein 
         FIG. 1  shows a schematic side view of an apparatus according to the present disclosure. 
     
    
    
     In known apparatuses for producing three-dimensional work pieces, a mechanical coupling and thermal expansion and deformation of machine components with regard to each other leads to variations in the process conditions and, thereby, to inaccuracies in a generation process. 
     More precisely, the simultaneous arrangement of three critical layers with regard to each other determines the process quality within a layer to be irradiated, These layers are an irradiation area (focal-/0-layer), a powder application layer, and an optics/scanner layer. In addition, controlling a position of a vertical movement unit (e.g., a carrier movement unit) is crucial In order to maintain a homogeneous layer-wise movement of the carrier. 
     In an ideal case, these layers have to be aligned with regard to each other during the entire building process, namely translational and rotational in x-y-direction and translational in z-direction. Tolerances in this alignment determine or at least have an influence on the quality of the work piece. 
     In known apparatuses, components determining these layers (irradiation unit, powder application device, carrier movement unit) are indirectly via other central machine components or even directly mechanically coupled to each other, Thermal deformations (and, in particular, thermal expansion) and static loads have a negative influence on the tolerances. 
     In other words, in order to achieve a high quality of a produced work piece, it is necessary that a (three-dimensional) position of the uppermost layer of raw material powder with regard to the irradiation unit is known, such that the radiation beam can be directed to predetermined locations of the raw material powder. One possibility of obtaining knowledge of the spatial relationship between the raw material powder and the irradiation unit is to perform periodic calibration measurements during a production process, Another option is to try to maintain the spatial relationship between the raw material powder and the irradiation unit as constant as possible, such that no calibration measurements during the production process are necessary. 
     According to the present disclosure, a solution to the aforementioned problem comprises providing a support structure supporting the irradiation unit, wherein the support structure is provided outside the process chamber. According to an embodiment, components determining the aforementioned layers (such as irradiation unit, a powder application device, and carrier movement unit) are mechanically and, more advantageous, mechanically and thermally decoupled from each other. 
     Components bearing thermal load, such as the process chamber, are thereby mechanically and/or thermally decoupled from the aforementioned components determining the layers. A thermal influence on the components determining the layers can therefore be prevented. This may firstly mean, that a direct thermal influence via heat transfer and, thereby, deformation of a component determining one of the aforementioned layers can be prevented (thermal decoupling). Secondly, that may mean that indirect thermal influence in the form of mechanical influence caused by thermal deformation of the process chamber can be prevented (mechanical decoupling). Hence, thermal and/or mechanical decoupling can be implemented in order to improve the quality of a building process. 
     The above advantages can be achieved by using a support structure, such as an external support structure, which may also be referred to as exoskeleton. This is support structure may represent an external support frame, which supports one or more of the components defining the aforementioned layers. By individually mounting each of the components to the support structure, the components have a fixed spatial relationship with regard to each other. Due to the mechanical and/or thermal decoupling of the components, this spatial relationship maintains fixed during an entire building process. Examples of the components are, e.g., a process chamber, a carrier, a carrier movement unit, a powder application device, an irradiation unit, and a process chamber movement unit. 
       FIG. 1  shows a schematic side view of an apparatus for producing three-dimensional work pieces according to the present disclosure. The apparatus comprises a carrier  2 , which is configured to receive multiple layers of raw material powder  4 . During a building process, a first layer of raw material powder  4  is applied onto the carrier  2  by means of a powder application device  6  of the apparatus. The raw material powder  4  (e.g., metal powder) can be melted and solidified by a radiation beam  8 . 
     The radiation beam  8  is directed to the first layer of raw material powder  4  in order to solidify the raw material powder  4  in a site-selective manner according to CAD data of a work piece  10  to be produced. The locations on the uppermost layer of the raw material powder  4  to which the radiation beam  8  is directed therefore correspond to a geometry of the work piece  10  to be produced. The carrier  2  is movable along the z-direction (indicated by an arrow in  FIG. 1 ) in order to lower the carrier  2  after a solidification process of a layer of raw material powder  4  is finished. 
     For enabling this vertical movement of the carrier  2 , the apparatus comprises a carrier movement unit  12 . After the carrier  2  has been lowered, a new layer of raw material powder  4  is applied and a solidification process (i.e, an irradiation process) of this new layer begins. Thus, layer by layer, the work piece  10  is built up on the carrier  2 . 
     For housing the raw material powder  4  and, optionally, for guiding the movable carrier  2 , the apparatus comprises a build cylinder  13  having at least one side wall configured to be in contact with the raw material powder  4 . In the embodiment shown in  FIG. 1 , the build cylinder  13  has four side walls defining a cuboid volume in which the raw material powder  4  is located. This volume is limited to its lower side by the carrier  2  having a rectangular cross-section. The side wall of the build cylinder  13  are in contact with the raw material powder  4  applied onto the carrier  2  and are configured to support the raw material powder  4 , such that the raw material powder  4  maintains its (cuboid) shape. A distance between the side walls of the build cylinder  13  and corresponding edges of the carrier  2  is very small or even negligible, such that no raw material powder  4  can pass through a slit between the carrier  2  and the build cylinder  2 . Additionally, the carrier  2  may comprise a sealing member arranged at its edges. After one layer of raw material powder  4  has been completely irradiated (according to a geometry of the desired work piece  10 ), the carrier  2  is lowered within the build cylinder  13 , such that a new layer of raw material powder  4  can be applied. 
     The apparatus further comprises an irradiation unit  14  comprising one or more radiation sources. In the embodiment shown in  FIG. 1 , the irradiation unit  14  is configured to generate two independent radiation beams  8 . Each of the radiation beams  8  can be controlled and directed to a desired location by means of a corresponding scanning unit. Each of the scanning units comprises at least one movable mirror, which is configured to deflect the respective radiation beam to the desired location on the uppermost layer of the raw material powder. The two radiation beams can be generated, e.g., by using only one radiation source, dividing the beam emitted by the radiation source by means of a beam splitter into two sub-beams and by directing each of the sub-beams to one of the scanning units. As an alternative, two radiation sources may be provided, wherein each radiation source emits a beam which is directed to one of the scanning units. 
     As shown in  FIG. 1 , each of the two radiation beams  8  defines an irradiation area on a surface of an uppermost layer of the raw material powder  4 . An overlap area is provided, in which the irradiation area of a first scanning unit and the irradiation area of a second scanning unit overlap. 
     Further, the irradiation unit  14  comprises, for each of the radiation beams  8 , a focus unit configured to change a focus position of the respective radiation beam  8  in a direction along a beam path of the corresponding radiation beam  8 . By means of the focus unit, a position of a focus point of the respective laser beam may be adjusted in a depth direction (z-direction). 
     According to the present embodiment, the radiation sources of the irradiation unit  14  are lasers and the emitted radiation beams  8  are laser beams. More precisely, the radiation sources may, for example, comprise a diode pumped Ytterbium fiber laser emitting laser light having a wavelength of approximately 1070 to 1080 nm. The irradiation unit  14  is configured to selectively irradiate each of the radiation beams  8  onto the raw material  4  on the carrier  2 . By means of the irradiation unit  14 , the raw material powder  4  may be subjected to laser radiation in a site-selective manner in dependence on the desired geometry of the work piece  10  that is to be produced. 
     Each of the scanning units comprises movable mirrors for directing the radiation beams  8  in directions parallel to the carrier  2 , i.e., directions parallel to the uppermost layer of raw material  4 . In other words, a location of the radiation beams  8  can be varied both in the x-direction and the y-direction. 
     In addition to the scanning units and the focus units, the irradiation unit  14  may comprise further optical components for guiding and/or processing the radiation beams  8 . For example, a beam expander may be provided for expanding the radiation beams  8 . Further, object lenses may be provided behind each of the scanning units. The object lenses may be f-theta object lenses. 
     The apparatus further comprises a control unit (not shown) for controlling functionalities of the apparatus before, during, and after a building process. In particular, the control unit is configured to control the functionalities of the apparatus, such as the vertical movement of the carrier  2  via the carrier movement unit  12 , the vertical movement of the build cylinder  13  via the build cylinder movement unit  16  (if applicable), the raw material powder application by the powder application device  6 , the scanning of the scanning units, the radiation source of the irradiation unit  14 , etc. 
     A volume through which the radiation beams  8  are directed from the irradiation unit  14  to the uppermost layer of raw material powder  4  is defined by the process chamber  18 . As shown in  FIG. 1 , the process chamber  18  has side walls extending perpendicular to the x-y-plane and a bottom wall and a top wall extending parallel to the x-y-plane. Although the process chamber  18  thereby represents a box structure (or cuboid structure), the process chamber  18  is not limited to such a cuboid. The process chamber may have other forms, such as, e.g., a cylindrical form, a form of a pyramid, etc. Further, the process chamber is not necessarily hermetically sealed to the exterior. For example, openings may be provided in the sidewalls of the process chamber  18 , which may serve, e.g., as gas inlets and/or gas outlets. The top wall and/or the bottom wall of the process chamber  18  may be omitted or large openings may be provided in the top wall and/or the bottom wall. For example, the top wall comprises an opening through which the laser beams  8  can enter the process chamber  18 , Further, in addition to or as an alternative to a top wall of the process chamber  18 , a thermal isolation layer  20  may be provided at an interface between the process chamber  18  and the irradiation unit  14  as shown in  FIG. 1 , The process chamber  18  is limited to a bottom side by the raw material powder  4  in case raw material powder  4  is applied to the carrier  2 . Otherwise, the process chamber  18  is limited to its bottom side by the carrier  2 . The build cylinder  13  directly adjoins the process chamber  18 . In one example, the build cylinder  13  is attached (i.e., permanently affixed) to the process chamber  18 . In another example, the build cylinder  13  is releasably attached to the process chamber  18 . Further, the build cylinder  13  can be movable with regard to the process chamber by means of a build cylinder movement unit  16  as described below. 
     As explained above, the process chamber  18  fulfills a housing function for maintaining a spatially, atmospherically, and fluidically closed (or substantially closed) process environment. 
     During a building process, process heat is generated within the process chamber  18 , in particular in a lower area of the process chamber  18 , where the radiation beams  8  impinge onto the raw material powder  4  and form melting pools in the raw material powder  4 . By means of the walls of the process chamber  18 , the generated process heat stays inside the process chamber  18 . In other words, the walls of the process chamber  18  provide a thermal isolation to the exterior. However, the process heat generated within the process chamber  18  may cause thermal deformations of the process chamber  18  and, in particular of walls of the process chamber  18 . 
     s As shown in  FIG. 1 , the apparatus comprises a support structure  22  in the form of an external support frame (exoskeleton). The irradiation unit  14  is supported by the support structure  22  via attachment members  24 . The attachment members  24  provide a stable mechanical connection between the support structure  22  and the irradiation unit  14 . In addition to that, the attachment members  24  may have thermally decoupling properties, which means that heat transport through the attachment members  24  is suppressed. In other words, a thermal conductivity of the attachment members  24  may be low, This also holds for each of the attachment members  24  described in the following. 
     The support structure  22  is provided outside the process chamber  18  and, therefore, the support structure  22  is not directly influenced by process heat generated within the process chamber  18 . As shown in  FIG. 1 , an air gap is provided between the process chamber  18  and the support structure  22 , such that the process chamber  18  and the support structure  22  are thermally isolated from each other. 
     The process chamber  18  Is supported by the support structure  22  via attachment members  24 , As shown in  FIG. 1 , the process chamber  18  is supported from the outside, such that the support structure  22  does not extend into the process chamber  18 . The process chamber  18  is thermally decoupled from the support structure  22 . That means, that process heat generated within the process chamber  18  is not transported to the support structure  22 , e.g., because the attachment members  24  have a low thermal conductivity. Further, an air gap is provided between the support structure  22  and the process chamber  18 , which represents a thermal isolation layer. The process chamber  18  is also mechanically decoupled from the support structure  22 . That means that a thermal deformation of the process chamber  18  caused by process heat generated within the process chamber  18  does not cause a deformation of the support structure  22 . This behavior can be achieved by providing a rigid structure for the support structure  22 . In other words, the support structure  22  is made of rigid material, such as metal, which is not deformed by forces caused by deformations of the process chamber  18 . Further, the attachment members  24  may have mechanically decoupling properties, which means that the attachment members  24  can absorb deformations of the process chamber  18 . 
     The process chamber  18  is attached to the support structure  22  in a lower area of the process chamber  18  as shown in  FIG. 1 . For example, the process chamber  18  can be supported by the support structure  22  in the height of a 0-level (see dashed line in Fig,  1 ). This 0-level can be used as reference plane, which coincidences with an uppermost layer of raw material powder  4 . By attaching the process chamber  18  to the support structure  22  close to a bottom wall of the process chamber  18 , thermal deformations that occur within the process chamber  18  have no or almost no influence on a position of the 0-level mentioned above. Therefore, the 0-level maintains its position with regard to the support structure  22 . 
     By arranging the process chamber  18  and the irradiation unit  14  as described above, i.e., by individually supporting the process chamber  18  and the irradiation unit  14  on the support structure  22 , the process chamber  18  and the irradiation unit  14  can be thermally and mechanically decoupled from each other. With regard to the thermal decoupling, that means that process heat generated within the process chamber  18  is not transported to the irradiation unit  14  and, therefore, does not cause a thermal deformation or thermal displacement of the irradiation unit  14  with regard to the process chamber  18 . Further, since the irradiation unit  14  is not affected (or less affected) by process heat generated within the process chamber  18 , positions of individual optical components within the irradiation unit  14  with regard to each other and/or optical properties (e.g., focal length, etc.) of these optical components stay constant, With regard to the mechanical decoupling, that means that thermal deformations of the process chamber  18  do not cause deformations or dislocations of the irradiation unit  14 . Hence, It can be ensured that a spatial relationship between the process chamber  18  (in particular, a bottom region of the process chamber  18  where the raw material powder  4  is provided) and the irradiation unit  14  is maintained during a building process. In other words, the irradiation unit  14  does not move with respect to the process chamber  18  during the building process, which improves the precision of the building process and, therefore, the quality of the produced work piece  10 . 
     In an embodiment, the thermal isolation layer  20  is provided between the process chamber  18  and the irradiation unit  14  in order to enhance the thermal decoupling of the two components. The thermal isolation layer  20  may comprise a thermally isolating gas. 
     The powder application device  6  is also individually supported by the support structure  22  via corresponding attachment members  24  (not shown). Thereby, the powder application device  6  can be mechanically decoupled from the process chamber  18 , such that thermal deformations of the process chamber  18  do not cause any deformations or dislocations of the powder application device  6 . 
     Optionally, the apparatus may comprise a build cylinder movement unit  16  as indicated by arrows in  FIG. 1 . In that case, the build cylinder movement unit  16  is either directly supported by the support structure  22  via corresponding attachment members (not shown) or the build cylinder movement unit  16  is attached to the process chamber  18 , e.g., to a side wall or a bottom wall of the process chamber  18 . The build cylinder movement unit  16  is configured to move the build cylinder  13  in a vertical direction (z-direction) with regard to the support structure  22 . Since the process chamber  18  is supported and affixed to the support structure  22 , the build cylinder movement unit  16  is configured to vertically move the build cylinder  13  with regard to the process chamber  18 . For example, the control unit may be configured to vertically move the build cylinder  13  downwards after a building process of the work piece  10  is completed, such that the work piece  10  is accessible from its sides and raw material powder  4  can be removed from the work piece  10 . 
     The apparatus comprises the carrier movement unit  12 , which is configured to move the carrier  2  in a vertical direction (z-direction). The carrier movement unit  12  is supported by the support structure  22  via attachment members  24 . By individually supporting the carrier movement unit  12  to the support structure  22 , the carrier movement unit  12  can be mechanically and thermally decoupled from the other components of the apparatus and, In particular, from the process chamber  18 . Hence, the carrier movement unit  12  is thermally and mechanically decoupled from the process chamber  18 . Therefore, process heat generated within the process chamber  18  does not lead to a displacement of the carrier movement unit  12  or the carrier  2  coupled to the carrier movement unit  12 . 
     Optionally, a vertical location measurement device  26  may be provided in the form of a glass scale. The vertical location measurement device  26  is configured to measure a vertical location of the carrier  2  with regard to the carrier movement device  12  and, therefore, with regard to the support structure  22 . Based on measurement results of this vertical location measurement device  26 , a location of the carrier  2  and a location of an uppermost layer of raw material powder  4  can be determined by the control unit. 
     The support structure  22  comprises at least two feet  28  configured to be placed onto a ground plate. By means of the feet  28  the support structure  22  can stably be placed onto a ground such that deformations and vibrations can be avoided. 
     Although the support structure  22  of the embodiment shown in  FIG. 1  consists of one single support frame, the support structure may comprise more than one support frame. These support frames can be releasably or non-releasably attached to each other. Further, a plurality of support frames can be provided and each support frame supports one or more of the components  14 ,  18 ,  6 ,  16 , and  12 . For example, the support structure can comprise a first support frame for supporting the irradiation unit  14  and a second support frame for supporting the carrier movement unit  12 . The individual support frames of the support structure can be placed (e.g., attached) on a common ground or a common base plate. The support frames can be nested or arranged next to each other. In any case, the support structure provides a structure, where the individual components are supported and attached and a location of the components with regard to a common reference does not change. This common reference can be the support structure itself or a common ground or a common base plate. In particular, a position of the components with respect to each other does not change. 
     As described above and as shown in  FIG. 1 , each of the components  14 ,  18 ,  6 ,  16 , and  12  are individually supported by the support structure  22  via corresponding attachment members  24 . By individually supporting these components to the support structure  22 , the components can be mechanically and thermally decoupled from each other. In particular, the components can be placed in a spatial relationship to each other which is independent of process heat generated within the process chamber  18  and/or independent of mechanical deformations of the process chamber  18  caused by process heat generated within the process chamber  18 . Although it is advantageous to support all of the components  14 ,  18 ,  6 ,  16 , and  12  by the support unit  22 , the advantages of the present disclosure can also be achieved if one or more of the aforementioned components is not individually supported by the support structure. However, it is advantageous that at least the irradiation unit  14  and the process chamber  18  are individually supported by the support structure  22 . 
     In one embodiment, process heat may be directed into the support structure  22  but this process heat does not cause any dislocation (or no substantial dislocation) of the individual components  14 ,  18 ,  6 ,  16 , and  12  with respect to each other, because a coefficient of thermal expansion of the support structure  22  is very low. In that case, the components are at least mechanically decoupled from each other. 
     Since a spatial relationship between the individual components can be maintained, a process precision can be improved, which leads to a higher quality of a generated work piece  10 . 
     Further, a preheating time can be reduced, which is needed for calibrating and for starting the building process in order to work under stable thermal conditions. 
     Another advantage of the structure described above is that individual components can be easily exchanged and replaced without negative Influence on the rest of the apparatus.