Method for the layered manufacturing of at least one object on a roughened base element
Patent Information
- Application Number
- EP2023716611
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-05-12
- Filing Date
- 2023-04-06
- Publication Date
- 2025-03-19
Smart Images
Figure 1.1
Abstract
Description
[0001] Method for the layer-by-layer production of at least one object on a roughened base element
[0002] The invention relates to a method for operating a system for layer-by-layer production of at least one object on a base element by local solidification of powdered material in a respective layer with a working laser, comprising the following steps: Step A) the base element is arranged on a movable piston plate,
[0003] Step B) a preliminary measurement is carried out in the system, whereby a measuring device is used to measure a measuring pattern on the top side of the base element,
[0004] Step C) Based on data from the preliminary measurement, the layer-by-layer production of at least one object on the base element is prepared and carried out.
[0005] Such a process is known, for example, from WO 2019 / 086250 Al.
[0006] By locally solidifying powdered material using high-energy beams (usually laser beams or electron beams), three-dimensional objects can be manufactured relatively easily and quickly. Geometric limitations of conventional manufacturing processes such as milling or injection molding can be overcome. Layer-by-layer manufacturing is often used for prototypes or for objects that are only produced in small quantities.
[0007] The object(s) are grown on a base element mounted on a movable piston plate of a piston. After each layer of powdered material has been applied to the base element, the powdered material is locally solidified using one or more high-energy beams. The piston plate and piston are then lowered by one layer thickness, a new layer of powdered material is applied and locally solidified, and so on.
[0008] To ensure good manufacturing quality during layer-by-layer production, it is crucial that the base element on which the object(s) are manufactured is correctly aligned. It is also necessary that the high-energy beams are correctly aligned to the base element. Therefore, a preliminary measurement is usually performed before production begins, in which a sample is measured on the top side of the base element.
[0009] For example, as described in WO 2019 / 086250 A1, a measuring laser can be used to generate a measurement pattern of laser light on the base element, which is embodied there as a flat substrate plate. This pattern is then measured with a camera. Using the data from this preliminary measurement, the position and / or orientation of the base element can be corrected, for example, in order to prepare for the subsequent production of the object(s). From DE 10 2018 219 301 A1, it is known to measure the position of a base element embodied there as a preform by scanning the working beam over the preform with a scanner and detecting light scattered back into the scanner along the optical axis in a location-dependent manner. This makes it possible to obtain an image of the preform. Using this image, the working beam can then be correctly aligned to the preform during layer-by-layer production.
[0010] The basic elements, such as substrate plates or preforms, for the layer-by-layer production of three-dimensional objects are often made of metal. Metals often have shiny (reflective) surfaces on which projected light patterns are often difficult to see and just as difficult to capture with a camera. When scanning the surface of a preform with a working laser that predominantly does not hit the surface perpendicularly, the amount of backscattered laser light along the optical axis is also quite small. In addition, unintentional light reflections on the reflective surface can overlay the measurement patterns and thus disrupt their capture. Accordingly, with reflective surfaces of the base element, the measurement patterns can often only be captured with insufficient contrast or incompletely, and preparation for layer-by-layer production is not reliably possible.
[0011] In the case of base elements with reflective surfaces, it is common practice to pretreat them before the base element is placed on the piston platform in the layer-by-layer production system. Typical pretreatments include sandblasting or brushing. This roughens the surface of the base element, significantly increasing light scattering at the surface. The contrast in preliminary dimensions is then improved, and layer-by-layer production can be easily prepared. However, sandblasting or brushing the surface is comparatively complex and increases the cost of production.
[0012] WO 2015 / 040185 A1 also discloses applying reference markings to a calibration plate, forming laser markings on the calibration plate using the working laser of a 3D printing system, and imaging the calibration plate with a camera. Scanner corrections are determined from the relative position of the laser markings to the reference markings.
[0013] Object of the invention
[0014] The object of the invention is to enable an improved contrast in the preliminary measurements in a simple manner.
[0015] Description of the invention
[0016] This object is achieved according to the invention by a method of the type mentioned at the outset, which is characterized in that after step A) and before step B) a step A') takes place, with
[0017] Step A') in a treatment area of the base element, a surface of the base element facing the working laser is roughened with the working laser in the system, wherein the treatment area comprises at least a part of the upper side of the base element, and that in step B) the measurement pattern to be measured
[0018] - comprises a light pattern which is projected at least partially into the roughened treatment area on the upper side of the base element, and / or
[0019] - an edge structure of the base element on the upper side of the base element with a plurality of edges, wherein at least a part of the edges of the edge structure lies in the roughened processing area.
[0020] The invention provides for pretreating the base element with the working laser in the layer-by-layer manufacturing system (also called a 3D printing system). The working laser roughens the surface of the base element in a treatment area, at least over a portion of the upper side of the base element, thereby increasing diffuse light scattering in the treatment area. The measurement pattern to be measured is more visible on the roughened surface of the treatment area, or against the background of the roughened surface of the treatment area, than on an untreated, particularly reflective, surface.
[0021] Light patterns projected onto the roughened surface are clearly visible from a wide solid angle and, in particular, are easily captured with a camera. Likewise, edges of any edge structure of the base element in front of the roughened surface become more visible and easier to capture. Another advantage is that highlights on the surface of the base element are avoided, which can impair the contrast when capturing the measurement pattern during preliminary measurement.
[0022] Overall, improved pattern recognition, particularly shape recognition and edge detection, can be achieved through the invention. Within the scope of the invention, the measurement of the measurement patterns can be carried out with high contrast and thus very reliably and reproducibly.
[0023] Within the scope of the invention, the roughening of the surface of the processing area is carried out using the working laser (or possibly multiple working lasers, if available). The working laser is used for the local solidification of the powder layers during layer-by-layer production and, within the scope of the invention, also for roughening the surface of the base element in the treatment area for preliminary measurements, and is therefore used twice. A separate device for roughening the surface of the base element (such as a sandblasting station or a brushing station) is not necessary, making the inventive process particularly simple and cost-effective.
[0024] In addition, it is possible to easily adapt the roughening with the working laser to a specific type of base element, for example to the material (often copper, steel, aluminum, etc.) or the preceding production steps (often milling, sawing, etc., followed by polishing), or the surface geometry (flat substrate or preform with edge structure). For this purpose, the laser power or feed rate of the working laser or the melt trace spacing can be adjusted. Since the 3D printing system also has the equipment to observe the measurement pattern, the treatment success (detectable by the contrast of the measurement pattern) can be checked immediately after the surface is roughened, thus enabling particularly quick and easy feedback for optimizing the laser parameters for roughening the base element in the treatment area.
[0025] Using the data from the preliminary measurement, the position and / or orientation (tilt) of the base element can be recorded, thus initiating a corresponding position and / or orientation correction of the base element, and / or adjusting (calibrating) the scanner of the working laser (or the scanners of multiple working lasers, if available). This prepares for the layer-by-layer production of at least one object. Subsequently, the actual layer-by-layer production of the object (each with application of a powder layer, local solidification with the working laser, lowering the piston by one layer height, application of the next powder layer, etc.) can take place using the working laser (or working lasers, if available).
[0026] The measurement pattern can, in particular, comprise a projected triangulation pattern. A light pattern as a measurement pattern is typically generated by a dedicated measuring laser (usually a laser diode); however, it is also possible to generate a light pattern with the working laser. During the projection of the light pattern, the surface of the base element is not altered (in particular, it is not melted).
[0027] The base element (also called a build platform) is typically a flat substrate plate or a preform with a preform structure that forms a relief on the top side of the base element. During step A'), the surface of the base element is melted, in particular, creating a multitude of small melt beads on the surface, which collectively cause diffuse light scattering.
[0028] Preferred variants of the invention
[0029] A variant of the process according to the invention is preferred which provides that after step B) a step B') takes place, with
[0030] Step B') to an image information of the measured measurement pattern, which is contained in the data of the preliminary measurement, a contrast measurement value KMW is determined and compared with a contrast limit value KGW, and that steps A'), B) and B') are repeated if: KMW <KGW. Dadurch kann ein ausreichender Kontrast des Messmusters für die Vorbereitung der schichtweisen Fertigung auf einfache Weise sichergestellt werden. Der Kontrastwert kann insbesondere einen Helligkeitsunterschiedswert am Rand eines Lichtmusters (beleuchteter Bereich vs. nicht beleuchteter Bereich) oder an einer Kante (Kantenlinie vs. benachbarter Bereich) umfassen oder einen Mittelwert solcher Helligkeitsunterschiedswerte. Man beachte, dass im Allgemeinen die ungefähre Lage des Messmusters auf dem Basiselement vorbekannt ist, sodass entsprechende Ränder oder Kanten meist leicht aufzufinden und zu identifizieren sind.
[0031] A preferred further development of this variant is one in which, by repeating steps A'), B', and B'), feedback control of laser parameters of the working laser is carried out during roughening of the surface facing the working laser in step A'). Within the scope of the feedback control, optimization of the laser parameters or the contrast (determined based on the contrast measurement value) is easily possible within the scope of the invention. The treatment of the surface and the contrast determination can be carried out using the means of the 3D printing system; in particular, no insertion or removal of the base element is necessary for the feedback. A further development is also preferred which provides that, when step A') is repeated, a laser speed VL and / or a laser power PL and / or a melt track distance AL of the working laser is changed compared to a previous step A').These laser parameters are easy to control and usually allow good influence on the roughening of the surface of the base element.
[0032] A further preferred variant provides that the system has a heating device for the base element, with which the base element is preheated before the start of the layer-by-layer production of the at least one object, and that steps A') and B) take place while the base element is being preheated by the heating device. This allows step A') and step B) (and possibly also step B') to be carried out in a time-saving manner and, in particular, without extending the downtime.
[0033] Also advantageous is a variant that provides for the system to have a gas-tight build chamber in which a protective gas atmosphere is established before the start of layer-by-layer production of the at least one object, and that steps A') and B) take place while the protective gas atmosphere is being established. This also allows steps A') and B) (and possibly also a step B') to be performed in a time-saving manner, in particular without extending the downtime.
[0034] Another advantageous variant is one in which the measuring device includes a camera that captures at least one image of the measurement pattern on the top side of the base element during the preliminary measurement. This variant is easy to implement and has been proven in practice. The camera allows light patterns, in particular, to be captured quickly and easily.
[0035] In an alternative variant, it is provided that the measuring device comprises a zero-dimensional photodetector, in particular a photodiode, that the measuring device further utilizes the working laser and a scanner device of the working laser, and that at least one image of the measurement pattern on the upper side of the base element is recorded by scanning the upper side of the base element with a measuring laser beam generated by the working laser and detecting laser light that is backscattered from an impact point of the measuring laser beam on the upper side of the base element through the scanner device into the zero-dimensional photodetector. This procedure ("laser camera") can generate a highly accurate image of the upper side of the base element. A separate conventional camera is not necessary. In particular, preform structures can be imaged with high accuracy and with reference to the scanner coordinate system.When the surface is scanned with the working laser during the preliminary measurement, the surface of the base element is not changed, and in particular, it is not melted.
[0036] A variant is also preferred in which the data from the preliminary measurement provides information about
[0037] - a position of the base element relative to the piston plate or the rest of the system and / or
[0038] - tilting of the base element relative to the piston plate or the rest of the system and / or
[0039] - three-dimensional structures of the base element, in particular the position of the three-dimensional structures relative to the piston plate or the rest of the system. With this information, the layer-by-layer production on the base element can generally be adequately prepared, in particular so that the three-dimensional objects grow correctly on the base element in terms of position and orientation. The data from the preliminary measurement can be used in particular for calibrating or adjusting the scanner system of the working laser (or the scanner systems of the working lasers). A variant in which the base element is designed as a flat substrate plate is also preferred. In this variant, the measurement pattern is typically selected as a light pattern. The base plate can be checked or corrected for correct position and / or suitable orientation (tilt position) as part of the preliminary measurement.Universal three-dimensional objects can be grown on the flat substrate plate, if necessary also on supports.
[0040] Also preferred is a variant in which the base element is designed as a preform, wherein a preform structure with a plurality of edges is incorporated into the preform on the upper side of the base element, in particular wherein the preform structure serves at least partially as the edge structure of a measurement pattern to be measured. This allows complex structures to be manufactured for many applications. The preform is manufactured conventionally (not via 3D printing), for example, by bending processes and / or cold forming and / or casting processes and / or milling processes.
[0041] Also within the scope of the present invention is a system for the layer-by-layer production of at least one object on a base element by locally solidifying powdered material in a respective layer using a working laser, configured to carry out a method according to the invention described above, in particular wherein the system is configured to automatically carry out at least steps A'), B) and C). With the system, a preliminary measurement with good contrast can be carried out in a simple and cost-effective manner, even if the base part is still highly reflective (glossy) after previous production steps that took place outside the system, and a reliable 3D print with high production accuracy can be carried out. For the automated execution of process steps, the system typically has an electronic control device.The use of a device according to the invention described above in a method according to the invention described above also falls within the scope of the present invention. In the system, the roughening of the surface of the base element in the treatment area can be carried out using the working laser, and subsequently, the layer-by-layer production of the at least one three-dimensional object can be carried out in the system using the working laser for the local solidification of the powdered material.
[0042] Further advantages of the invention will become apparent from the description and the drawings. Likewise, the above-mentioned and further-described features can be used individually or in combination in any desired manner. The embodiments shown and described are not intended to be exhaustive, but rather are exemplary in nature for describing the invention.
[0043] Detailed description of the invention and drawing
[0044] The invention is illustrated in the drawing and is explained in more detail using exemplary embodiments.
[0045] Fig. 1 shows a schematic view of a first embodiment of a system for the layer-by-layer production of an object with a measuring device comprising a camera for carrying out the method according to the invention;
[0046] Fig. 2 shows a schematic view of a second embodiment of a system for the layer-by-layer production of an object with a measuring device comprising a zero-dimensional photodetector for carrying out the method according to the invention; Fig. 3 illustrates, using a flowchart, a first variant of the method according to the invention, in which, after a preliminary measurement, the layer-by-layer production of the object is prepared and carried out;
[0047] Fig. 4 uses a flow chart to explain a second variant of the method according to the invention, in which a feedback control is carried out after a preliminary measurement;
[0048] Fig. 5 shows an experimental image of a flat substrate plate whose surface has been partially roughened with the working laser, with a light pattern projected onto the substrate plate;
[0049] Fig. 6 shows an experimental image of a preform whose surface was partially roughened with the working laser.
[0050] Fig. 1 shows a schematic side view of a first embodiment of a system 1 for the layer-by-layer production of an object (not shown in detail), the system 1 being suitable for carrying out the method according to the invention.
[0051] System 1 comprises a gas-tight build chamber 2. A protective gas atmosphere (inert gas atmosphere) can be created in the gas-tight build chamber 2. The protective gas atmosphere is created before the layer-by-layer production of the object begins. The protective gas (inert gas) can be nitrogen or a noble gas such as argon, for example.
[0052] A powder cylinder arrangement 3 is connected to the gas-tight build chamber 2. The powder cylinder arrangement 3 has a powder cylinder 4 for a powdered material 5 (area shown in dotted lines). The object is manufactured from the powdered material 5, for example by sintering or melting. By gradually raising a powder piston 6 with a first lifting device 7, a small amount of the powdered material 5 is raised above the level of a floor 8 of the gas-tight build chamber 2. With a slide 9, this small amount of powdered material 5 can be transferred to a build cylinder arrangement 10. Excess powdered material 5 can be swept into a collection container 11 connected to the gas-tight build chamber 2 using the slide 9.
[0053] The build cylinder assembly 10 is also connected to the gas-tight build chamber 2. The build cylinder assembly 10 has a movable piston plate 12, on top of which a base element 13, in the embodiment shown here a flat substrate plate 13a, is arranged. The object is manufactured on the base element 13. In the embodiment shown here, a heating device 14 is arranged in the movable piston plate 12. The heating device 14 is designed here with electrical heating coils 14a. The heating device 14 can be used to preheat the base element 13 before the layer-by-layer production of the object. The base element 13, together with the movable piston plate 12, can be moved vertically in a base body 15 via a second lifting device 16.
[0054] The system 1 further comprises a working laser 17. The working laser 17 can provide laser beams 18 for different purposes. In the embodiment shown here, the working laser 17 provides a preparation laser beam 18a (solid line) and a processing laser beam (not shown in detail here). The preparation laser beam 18a can be used to prepare the base element 13 for preliminary measurements. The processing laser beam can be used to produce the object layer by layer. The laser beam 18 is guided onto a scanner device 19 of the working laser 17. The scanner device 19 can direct the laser beam 18 onto the base element 13. The scanner device 19 can comprise one or more movable mirrors 19a, with which the orientation of the laser beam 18 onto the base element 13 can be changed. The laser beam 18 is guided into the gas-tight build chamber 2 via a window 20.According to the invention, before the start of the layer-by-layer production of the object on the base element 13, the base element 13 is roughened with the working laser 17 on an upper side 23 of the base element 13. For this purpose, the base element 13 is roughened with the processing laser beam 18a in a treatment area 21 on a surface 22 facing the preparation laser beam 18a on the upper side 23 of the base element 13. In the example illustrated here, only a portion of the upper side 23 of the base element 13 is encompassed by the roughened treatment area 21 of the base element 13.
[0055] Furthermore, after roughening the treatment area 21 of the base element 13, a measurement pattern 24 is measured as part of a preliminary measurement (before starting production of the layers). In the example illustrated here, the measurement pattern 24 is irradiated (projected) as a light pattern 24a into the roughened treatment area 21 onto the upper side 23 of the base element 13. Only by roughening the surface 22 of the flat substrate plate 13a does the light pattern 24a become sufficiently clearly visible on the base element 13 (in other words, the contrast of the light pattern 24a improves as a result of the roughening), so that the light pattern 24a can be clearly captured and processed, for example, by an image processing algorithm. The light pattern 24a is generated by means of a projector 25 (for example, a measuring laser comprising a laser diode). In the preliminary measurement, the measuring pattern 24 on the upper side 23 of the base element 13 is measured using a measuring device 26.In the embodiment shown here, the measuring device 26 comprises a camera 27. For the preliminary measurement, the camera 27 takes at least one image of the light pattern 24a.
[0056] The image data from camera 27 is transmitted to a control unit 28 and processed. In particular, the preliminary measurement data can include information about the position and tilt of the base element 13 relative to the piston plate 12 or to the system 1. The preliminary measurement data serves as the basis for preparing and implementing the layer-by-layer production of the object on the base element 13. The control unit 28 forwards control commands to connected components that take the preliminary measurement data into account, and the layer-by-layer production of the object on the base element 13 can be carried out. In Fig. 1, transmission lines leading from the working laser 17, the scanner device 19, the projector 25, and the measuring device 26 to the control unit 28 are shown as dashed lines.It should also be noted that the control unit 28 also controls the first lifting device 7, the slide 9, the heating device 14 and the second lifting device 16 (the transmission lines are not shown in detail here for the sake of clarity).
[0057] Fig. 2 shows a schematic side view of a second embodiment of a system 1 for the layer-by-layer production of an object (not shown in detail), wherein the system 1 is suitable for carrying out the method according to the invention. The second embodiment of the system 1 shown here is constructed similarly to the first embodiment of the system 1 in Fig. 1, which is why only the essential differences in Fig. 2 are explained.
[0058] In the embodiment shown here, the base element 13 is formed as a preform 13b. A plurality of edges 29 are incorporated into the preform 13b. The edges 29 form a preform structure 30 (relief) on the upper side 23 of the preform 13b. In the embodiment shown, the heating device 14 is formed with radiant heaters 14b. The radiant heaters 14b are arranged in the gas-tight build chamber 2 and directed toward the upper side 23 of the base element 13. The radiation (infrared radiation) of the radiant heaters 14b is depicted as wavy curves.
[0059] In the embodiment of Fig. 2, the working laser 17 can provide a measuring laser beam 18b (solid line) as laser beam 18 in addition to the preparation laser beam (not shown in detail here) and the processing laser beam (also not shown in detail). The measuring laser beam 18b can be used to scan the upper side 23 of the base element 13. In the embodiment shown here, the laser beam 18 is guided over a semi-transparent mirror 31 and from there to the scanner device 19 of the working laser 17. According to the invention, before the start of the layer-by-layer production of the object on the base element 13, the surface 22 is roughened with the working laser 17 on the upper side 23 of the base element 13 in the treatment area 21.
[0060] Furthermore, according to the invention, after roughening the treatment area 21 of the base element 13, the measurement pattern 24 is measured. In the example shown here, an edge structure 24b of the base element 13 serves as the measurement pattern 24. The edge structure 24b here corresponds to a part of the preform structure 30. The edges 29 of the edge structure 24b are all encompassed (enclosed) by the roughened treatment area 21 of the base element 13. Only by roughening the surface 22 of the preform 13b does the edge structure 24a become sufficiently clearly visible (in other words, the contrast of the edge structure 24a improves), so that the edge structure 24b can be clearly detected and processed, for example, by an image processing algorithm. In the preliminary measurement, the measurement pattern 24 on the upper side 23 of the base element 13 is measured using the measuring device 26.In the embodiment shown here, the measuring device 26 comprises a zero-dimensional photodetector 32, which is designed as a photodiode 32a.
[0061] For the preliminary measurement, the measuring laser beam 18b is guided via the scanner device 19 of the working laser 17 to the upper side 23 of the base element 13. The measuring laser beam 18b impinges there on an impact point 33. From the impact point 33, laser light 34 (dotted lines) is backscattered into the scanner device 19 of the working laser 17. From there, the backscattered laser light 34 is guided to the semi-transparent mirror 31. The semi-transparent mirror 31 is partially transparent to the backscattered laser light 34, so that a portion of the backscattered laser light 34 passes through the semi-transparent mirror 31 and strikes a focusing lens 35. The focusing lens 35 focuses the backscattered laser light 34 onto the zero-dimensional photodetector 32.The upper surface 23 of the base element 13 can be scanned by a plurality of repetitions of these individual measurements at further impact points 33 (corresponding to different positions of the movable mirror 19a of the scanner device 19), and an image of the measurement pattern 24 can be obtained by composing these individual measurements.
[0062] The measurement data from the photodetector 32 are transmitted to the control unit 28 and processed. In particular, the preliminary measurement data can include information about the three-dimensional structures of the base element 13 or about the position of the three-dimensional structures relative to the piston plate 12 or the system 1.
[0063] Fig. 3 explains in a flow chart the sequence of a first variant of the method according to the invention for the layer-by-layer production of an object on a base element, as can be carried out, for example, on the system of the first embodiment in Fig. 1.
[0064] Initially, in step Aj, the base element is placed on a movable piston plate of the system. The movable piston plate and the base element can be arranged in a gas-tight construction chamber of the system.
[0065] In the next step A'j, a treatment area of the base element is roughened. The roughening of the treatment area is performed using a working laser, which provides a preparatory laser beam with which the treatment area of the base element can be roughened.
[0066] In a subsequent step Bj, a preliminary measurement is carried out in the system. For this purpose, a measurement pattern is measured on the top side of the base element. The measurement is carried out using a measuring device, for example a camera or a photodiode. Only the roughening of the surface of the base element makes it possible for the measurement pattern to be projected either as a clearly recognizable light pattern onto the top side of the base element and measured with the measuring device, or for the measurement pattern to be measured as a clearly recognizable edge structure of the base element with the measuring device. Please note that during steps A') and B), the base element can be preheated using a heating device. Likewise, if the system has a gas-tight build chamber, a protective gas atmosphere can be created in the gas-tight build chamber during steps A') and B).
[0067] In a final step (C), the layer-by-layer fabrication of the object is prepared and carried out. This preparation and execution is based on the data from the preliminary measurements.
[0068] Fig. 4 illustrates, in a flowchart, the sequence of a second variant of the method according to the invention for layer-by-layer production of an object on a base element, as can be carried out, for example, on the system of the first embodiment in Fig. 1. Steps A), A'), B), and C) are identical to the flowchart in Fig. 3. Therefore, only the differences are explained in Fig. 4.
[0069] In the variant shown here, between step B) and step C) there is another
[0070] Step B' takes place. The data from the preliminary measurement contains image information of the measured sample. In step B'), a contrast measurement value KMW is determined for the image information of the measured sample, after which a comparison of the contrast measurement value KMW with a contrast limit value KGW is made. In this way, it can be determined whether the contrast of the measured sample and thus the data from the preliminary measurement are good enough for, for example, an image processing algorithm to process the data from the preliminary measurement to prepare and carry out the production of at least one object on the base element. If KMW>KGW, the process continues with step C). If, however, KMW <KGW, wird mit einem Schritt Z) fortgefahren.
[0071] In step Z), a feedback check is carried out. During the feedback check, the data from the current preliminary measurement (for example, at the level of image information or the contrast measurement value) is compared with a reference value (e.g., from previous preliminary measurements, or the specified contrast limit KGW) and an assessment is made as to whether the last selected production parameters or the last applied change to the production parameters has brought about a (desired) improvement or not. If necessary, the production parameters are then changed to further improve the contrast measurement value in a next step A'). In particular, a laser speed VL and / or a laser power PL and / or a melt track distance AL of the working laser can then be changed.After setting the laser parameters, steps A'), B) and B') are carried out again and at the end of step B') it is checked whether step C) can be continued or whether steps Z), A'), B) and B') must be repeated.
[0072] Fig. 5 shows an experimental photograph of a base element 13, which is formed as a flat substrate plate 13a and arranged on a piston plate 12. According to the method according to the invention, the left half of the flat substrate plate 13a (shown in Fig. 5) was roughened with the working laser. The measurement pattern 24 to be measured is projected as a (here square) light pattern 24a onto the top side of the flat substrate plate 13a. On the left half of the flat substrate plate 13a, the light pattern 24a is clearly visible. On the right half of the flat substrate plate 13a, which was not roughened, the light pattern is largely not visible at all or only very faintly visible.
[0073] Fig. 6 shows an experimental photograph of a base element 13, which is formed as a preform 13b with a preform structure. According to the method according to the invention, a section of the preform 13b in the left area was roughened with the working laser. The measurement pattern 24 to be measured here comprises an edge structure 24b, with the preform structure partially serving as the edge structure 24b. The edge structure 24b is clearly visible in the left area of the preform 13b, which was roughened by the working laser. In the areas that were not roughened, the edge structure 24b is difficult to discern, and highlights (light reflections) and other reflections overshadow the contrast. In addition, the roughening leads to the disappearance of the milling marks on the base element 13, which is advantageous for image processing applications, even independent of highlights.
[0074] 1 system
[0075] 2 gas-tight construction chamber
[0076] 3 Powder cylinder arrangement
[0077] 4 powder cylinders
[0078] 5 powdered material
[0079] 6 powder flasks
[0080] 7 first lifting device
[0081] 8 Floor (of the gas-tight construction chamber)
[0082] 9 sliders
[0083] 10 Construction cylinder arrangement
[0084] 11 collection containers
[0085] 12 (movable) piston plate
[0086] 13 Basic element
[0087] 13a flat substrate plate
[0088] 13b Preform
[0089] 14 Heating device
[0090] 14a Heating coil
[0091] 14b Radiant heater
[0092] 15 basic bodies
[0093] 16 second lifting device
[0094] 17 working lasers
[0095] 18 laser beam
[0096] 18a Preparation laser beam
[0097] 18b Measuring laser beam
[0098] 19 Scanner setup
[0099] 19a movable mirror
[0100] 20 windows
[0101] 21 Treatment area
[0102] 22 Surface (of the base element) 23 Top (of the base element)
[0103] 24 measurement patterns
[0104] 24a light pattern
[0105] 24b Edge structure
[0106] 25 projectors
[0107] 26 Measuring device
[0108] 27 Camera
[0109] 28 Control unit
[0110] 29 edge
[0111] 30 Preform structure
[0112] 31 semi-transparent mirror
[0113] 32 zero-dimensional photodetector
[0114] 32a Photodiode
[0115] 33 Point of impact
[0116] 34 (backscattered) laser light
[0117] 35 focusing lens
[0118] AL melting track distance (of the working laser)
[0119] KGW contrast limit
[0120] KMW contrast measurement value
[0121] PL Laser power (of the working laser)
[0122] VL laser speed (of the working laser)
Claims
Patent claims Method for operating a system (1) for the layer-by-layer production of at least one object on a base element (13) by local solidification of powdered material (5) in a respective layer with a working laser (17), comprising the following steps: Step A) the base element (13) is placed on a movable piston plate (12) ordered, Step B) in the system (1) a preliminary measurement is carried out, whereby a measuring device (26) is used to measure a measurement pattern (24) on the top (23) of the base element (13), Step C) based on data from the preliminary measurement, the layer-by-layer manufacturing of the at least one object on the base element (13) is prepared and carried out, characterized in that a step A') takes place after step A) and before step B), with Step A') in a treatment area (21) of the base element (13) a surface (22) of the base element facing the working laser (17) is (13) roughened with the working laser (17) in the system (1), wherein the treatment area (21) includes at least a part of the top surface (23) of the base element (13), and that in step B) the measurement pattern (24) to be measured - comprises a light pattern (24a) which is projected at least partially into the roughened treatment area (21) on the top surface (23) of the base element (13), and / or - an edge structure (24b) of the base element (13) on the top surface (23) of the base element (13) comprising a plurality of edges (29), wherein at least a portion of the edges (29) of the edge structure (24b) lie within the roughened machining area (21). The method according to claim 1, characterized in that, following step B), a step B') takes place, with In step B') of an image information of the measured measurement pattern (24) contained in the data of the pre-measurement, a contrast measurement value KMW is determined and compared with a contrast limit value KGW, and steps A'), B) and B') are repeated if: KMW <KGW. Verfahren nach Anspruch 2, dadurch gekennzeichnet, dass über die Wiederholung der Schritte A'), B) und B') eine Feedback-Kontrolle (Z)) von Laserparametern des Arbeitslasers (27) beim Aufrauen der dem Arbeitslaser zugewandten Oberfläche in Schritt A') erfolgt. Verfahren nach Anspruch 2 oder 3, dadurch gekennzeichnet, dass bei einer Wiederholung von Schritt A') eine Lasergeschwindigkeit VL und / oder eine Laserleistung PL und / oder ein Schmelzspurenabstand AL des Arbeitslasers (17) gegenüber einem vorhergehenden Schritt A') geändert wird.Method according to one of the preceding claims, characterized in that the system (1) has a heating device (14) for the base element (13) with which the base element (13) is preheated before the start of the layer-by-layer production of the at least one object, and that steps A') and B) take place during the preheating of the base element (13) with the heating device (14). A method according to any one of the preceding claims, wherein the system (1) comprises a gas-tight build chamber (2) in which a protective gas atmosphere is established before the start of the layer-by-layer production of the at least one object, and wherein steps A') and B) take place during the establishment of the protective gas atmosphere. A method according to any one of claims 1 to 6, characterized in that the measuring device (26) comprises a camera (27) which, during the preliminary measurement, captures at least one image of the measurement pattern (24) on the top surface (23) of the base element (13).A method according to any one of claims 1 to 6, characterized in that the measuring device (26) comprises a zero-dimensional photodetector (32), in particular a photodiode (32a), that the measuring device (26) further utilizes the working laser (17) and a scanner device (19) of the working laser (17), and that at least one image of the measurement pattern (24) on the top surface (23) of the base element (13) is recorded by scanning the top surface (23) of the base element (13) with a measuring laser beam (18b) generated by the working laser (17) and detecting laser light (34) which is backscattered from an impact point (33) of the measuring laser beam (18b) on the top surface (23) of the base element (13) through the scanner device (19) into the zero-dimensional photodetector (32). A method according to any one of the preceding claims, characterized in that the data of the preliminary measurement contain information about. - a position of the base element (13) relative to the piston plate (12) or to the rest of the system (1) and / or - a tilting of the base element (13) relative to the piston plate (12) or to the rest of the system (1) and / or - three-dimensional structures of the base element (13), in particular the The method comprises the position of the three-dimensional structures relative to the piston plate (12) or to the rest of the system (1). A method according to any one of claims 1 to 9, characterized in that the base element (13) is designed as a flat substrate plate (13a). A method according to any one of claims 1 to 9, characterized in that the base element (13) is designed as a preform (13b), wherein a preform structure (30) with a plurality of edges (29) is incorporated into the preform (13b) on the top surface (23) of the base element (13), in particular wherein the preform structure (30) serves at least partially as an edge structure (24b) of a measurement pattern (24) to be measured.A system (1) for the layer-by-layer fabrication of at least one object on a base element (13) by local solidification of powdered material in each layer using a working laser (17), configured for carrying out a method according to any one of claims 1 to 11, in particular wherein the system (1) is configured for the automatic execution of at least steps A'), B) and C). Use of a device according to claim 12 in a method according to any one of claims 1 to 11.