WO2015181247A1

WO2015181247A1 - Method for producing a three-dimensional object by solidifying powder

Info

Publication number: WO2015181247A1
Application number: PCT/EP2015/061740
Authority: WO
Inventors: Patrick Teulet
Original assignee: Phenix Systems
Priority date: 2014-05-28
Filing date: 2015-05-27
Publication date: 2015-12-03

Abstract

This production method, which cleverly combines quality and productivity, comprises a layering step, during which powder (P) is formed into a layer (C1 to C7), and a solidifying step, during which a laser beam scans and solidifies a portion (C1.O to C7.O) of the prepared layer of powder after the layering step, said solidified portion corresponding to a two-dimensional section of the object (1) to be produced, the layering step and then the solidifying step being repeated one after the other, by superposing the layers of powder until the object, which consists of the solidified layer portions, is obtained. The method further comprises a preparatory step, which is implemented before the layering and solidifying steps, and which involves determining a set of digitised superposed sections from a digital definition of the object to be produced, which correspond respectively to the solidified layer portions to be obtained, successively, through repetition of the layering and solidifying steps. The preparatory step involves identifying, from the set of sections, one or more so-called risk sections, each risk section being predisposed such that at least one so-called predictable fault (D) appears in the solidified layer portion corresponding to the risk section. The method further comprises at least one fault correction step, which is implemented both after the or each solidifying step following which the solidified layer portion corresponds to the or one of the risk sections, and before the layering step that follows said solidifying step, and during which a grinding tool (20) corrects the predictable fault in the solidified layer portion corresponding to said risk section.

Description

METHOD FOR MANUFACTURING THREE-DIMENSIONAL OBJECT

BY SOLIDIFICATION OF POWDER

The present invention relates to a method for manufacturing a three-dimensional object by solidification of powder.

In the field of the manufacture of three-dimensional objects, it is known to produce such objects by solidification, with the aid of a laser, of successively superimposed layers of powder: a pulverulent material, where appropriate mixing several powders and designated simply afterwards as powder, is layered, typically by display and compaction, then is scanned by the laser beam to be solidified, by sintering and / or melting, before being covered by a new layer of powder which in turn is solidified under the effect of a new scan of the laser and so on, until the complete object is obtained. This type of manufacturing makes it possible to increase the number of functions in one and the same three-dimensional object, via an increase in the complexity of the object's shapes, its surfaces, its volumes, the fineness of its details, its dimensions, the physico-chemical nature of its materials, etc. The prospects for this layer-by-layer additive manufacturing process are constantly pushing the limits of what is possible in terms of manufacturing capacity, generating an increase in creativity, and increasing the technological and economic stakes in terms of costs and deadlines. manufacture and frequency of renewal of designs.

This being so, one of the weaknesses of this type of manufacturing process lies in its originality, which consists in successively solidifying respective portions of powder layers, which respectively correspond to geometric sections of the three-dimensional object to be manufactured. Indeed, a three-dimensional object to manufacture is known in advance by its numerical definition: this numerical definition is processed using known algorithms, which slice the volume definition of the three-dimensional object, this slicing giving rise to the calculation of a set of geometric sections of the object to be manufactured. During the implementation of the manufacturing process, it acts by addition of material iteratively, in the sense of adding to each other solidified portions of powder layers respectively corresponding to the aforementioned geometric sections, according to the result of calculation of these sections previously established. According to this principle, it is understood that the iterative addition of material is intrinsically at the potential origin of a defect in the solidified part of each layer of powder. Indeed, the presence, in the portion of the powder layer that is solidified by laser scanning, of a local heterogeneity, such as a surplus of powder, spreading unevenness of the powder layer, or a variation of the physicochemical characteristics of the powder, in particular its chemical composition, its particle size and its granularity, leads to the solidified layer portion having a defect consisting of one or more overthicknesses. This defect alone does not call into question the local conformity of the object being manufactured, in the sense that, initially, the defect is negligible. On the other hand, this defect risks either leading to the manufacture of a non-compliant end-object, or, more frequently, inducing a stoppage of manufacture, that is to say that the manufacturing in progress will not not over, due to a "snowball effect": the consequences of the defect on the layers made over those with the defect are amplified as the manufacturing process progresses.

To circumvent this problem, it is known to put the powder in the form of thin layers: the more the layers of powder are thin, that is to say thin, the quality of manufacture of the object is good, especially in as regards the fineness and discretization of this object, in particular of its functional surfaces, while controlling the risk of appearance of defect. However, using layers of fine powder considerably increases the time required to manufacture the complete object, which greatly degrades the productivity of the manufacturing process. Conversely, by using layers of thick powder, which is made possible by the advent of lasers whose beams are more and more powerful, the productivity of the process can be increased, but by degrading the discretization of this fabrication. and therefore to the detriment of the fineness of the details of the manufactured object, while significantly increasing the risk of occurrence of defects in the portions of layer solidified by laser scanning.

According to another approach, US-A-2006/0208396, which may be considered as the state of the art closest to the invention, proposes to correct each defect immediately after its appearance, thanks to a grinding tool that resurface the solidified part of the layer, which has just been performed by laser scanning. In this way, once the correction is made by the grinding tool, the solidified portion, thus rectified, of the powder layer has characteristics consistent with those corresponding to the manufacture, without defect, of the object in progress. Manufacturing. However, again, the productivity of the manufacturing process is degraded. Indeed, it is understood that the systematic passage of the grinding tool on the recently solidified layer portion considerably extends the manufacturing time of the complete object. US-A-2006/0208396 proposes also to use the grinding tool after the actual detection of a defect, this detection being either optical, being implemented just after each laser scan, or by control of the resistance to advancement of a spreading blade powder on the last layer of solidified layer. However, at least as regards the optical detection, it is understood that its effectiveness may be doubtful because of the size of the defects to be detected and / or potential drifts of the optical detection system. In addition, in all cases, the systematic implementation of such a detection operation represents, as the object is manufactured, a considerable cumulative time, which degrades the productivity of the manufacturing process.

The object of the present invention is to provide a manufacturing method of the type defined above, which, while being reliable, cleverly reconciles quality and productivity.

To this end, the subject of the invention is a method for manufacturing a three-dimensional object by powder solidification, as defined in claim 1.

One of the ideas underlying the invention is to seek to ensure the complete and rapid manufacture of three-dimensional objects, which, where appropriate, have complex geometries, anticipating the appearance of defects, with prior identification of the layers predisposed to the appearance of these defects that can therefore be described as predictable defects. According to the invention, when, prior to obtaining the very first layer of powder, the digitized sections are determined which, during the iterative manufacture of the object, respectively correspond to the solidified parts of the layers of powder successively superimposed, identifies, among these digitized sections, the sections at risk, that is to say the sections whose corresponding solidified layer parts will predictably present defects. Therefore, as soon as, during the manufacture of the object, one of these solidified layer parts corresponding to one of the risk sections is obtained, a grinding tool is used to correct the foreseeable defect, without even elsewhere seek to verify the actual existence of this defect. Thus, the corresponding correction steps are implemented only when, in advance, the risk of presence of the foreseeable defects has been identified. This amounts, in a way, to pre-programming the correction of defects from a specific processing of the data relating to the digitized sections, making it possible to predict which sections are at risk according to pre-established conditions relating to the morphological characteristics. dimensions of the object to be manufactured and / or the manufacturing parameters of this object. It is understood that, thanks to this systematic control strategy, the manufacturing method according to the invention, taken as a whole, combines productivity and quality.

In practice, as explained in detail later, the identification of the risk sections advantageously relies on a strategy of selection of specific sections, in particular the juxtaposed multi-thickness zone sections, the large relative area sections and / or the undercut sections. Of course, the invention does not exclude that the manufacturing method optionally includes an in situ detection capability of defects, which are then described as unpredictable defects to differentiate predictable defects considered above. In this case, as explained in more detail later, this detection is advantageously integrated with the layering means of the powder.

Additional advantageous features of the method according to the invention are specified in the dependent claims.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the drawings in which:

- Figures 1 to 12 are schematic sections of a device used to implement the manufacturing method according to the invention, these Figures 1 to 12 respectively illustrating successive operations of a first example of this method;

- Figures 13 and 14 are elevational views of an object being manufactured according to a second manufacturing method according to the invention;

- Figures 15 and 16 are schematic sections similar to those of Figures 1 to 12, Figures 15 and 16 respectively illustrating successive operations of a third manufacturing method according to the invention; and

FIGS. 17 to 20 are diagrammatic sections similar to those of FIGS. 1 to 12, FIGS. 17 to 20 respectively illustrating successive operations of a fourth manufacturing method in accordance with the invention.

FIGS. 1 to 12 show a device 10 making it possible to manufacture, from a powder P, a three-dimensional object consisting of layers of solidified powder by sintering and / or melting.

The device 10 comprises a well 12 which is considered fixed relative to the rest of the device: this well 12 thus defines a three-dimensional coordinate system including a horizontal axis XX, an axis YY, both horizontal and perpendicular to the axis XX, and a ZZ axis both vertical and perpendicular to the XX and YY axes. The X-X and Z-Z axes belong to the section plane of FIGS. 1 to 12, while the Y-Y axis extends perpendicular to this section plane.

The device 10 comprises a piston 14, which is displaceable, in both directions, along a vertical axis Z14, parallel to the axis ZZ, and in a manner fitted inside the well 12. The piston 14 thus forms a support for the powder P, bordered around the axis Z14, by the well 12.

The device 10 further comprises a roller 16 which is displaceable relative to the well 12, both in rotation on itself, in both directions, around its central axis Y16 which is parallel to the axis YY, and in horizontal translation, in both directions, in a direction parallel to the axis XX. As explained below, the roller 16 is used to spread and compact the powder P on the piston 14. In practice, in a manner known per se, the movements of the roller 16 are controlled by means of ad hoc drive device 10, which are not shown in the figures and whose embodiment is not limiting of the invention.

The device 10 furthermore comprises laser emission means 18, which, for reasons of visibility, are only shown in certain figures, and which are designed, vertically above the piston 14, to scan by laser beam the P powder supported by this piston. Through arrangements known per se, the laser beam emitted by these means 18 is movable, relative to the well 12, along a controlled scanning path.

The device 10 further comprises a tool 20 for grinding powder P having been previously solidified by the laser emission means 18. For reasons of visibility, this tool 20 is only shown in FIG. only in dashed lines in Figure 1. The tool 20 acts by direct contact with the solidified powder to be grinded, typically by removal of material, in particular by abrasion. As a preferred non-limiting example, the grinding tool 20 is a milling cutter, a grinding wheel or, more generally, an abrasive and / or cutting tool.

As explained in more detail below, the tool 20 is movable, relative to the well 12, so as to act by mechanical interference with the solidified powder, resting on the piston 14. In the embodiment considered here, the tool 20 is thus displaceable, both in rotation about itself around its central axis Y20 which is parallel to the axis YY, in horizontal translation, in both directions, in a direction parallel to the axis XX, and in vertical translation, in both directions, in a direction parallel to the axis ZZ. In practice, the movements of the grinding tool 20 are controlled by ad hoc drive means of the device 10, which are not shown in the figures and whose embodiment is not limiting of the invention. This being so, according to a preferred embodiment, which is considered here without being limiting or obligatory, the drive means of the roller 16 and the drive means of the tool 20 are at least partially shared, this, inter alia, facilitates integration within the device 10, it being understood that the respective actuations of the roller 16 and the tool 20 are selective, that is to say can be achieved independently one of the other: in other words, the roller 16 and the tool 20 are preferably controlled by common means for selective actuation of this roller and this tool. Other features of the device 10 will appear below, in the context of the description of several examples of use of this device to manufacture the three-dimensional object 1 from the powder P, in other words, several examples of manufacturing process. of object 1

FIRST EXAMPLE OF MANUFACTURING PROCESS

This first example is decomposed into twelve successive times, respectively corresponding to FIGS. 1 to 12.

In FIG. 1, the device 10 is considered while the object 1 has already begun to be manufactured, by superposition of two layers of powder C1 and C2, the powder layer C1 covering the upper face of the piston 14 while the powder layer C2 covers the powder layer C1. Each of the powder layers C1 and C2 includes a solidified part C1 .0, C2.0, which in the layer C1, C2 forms a constitutive part of the object 1 during manufacture. In other words, at the time of manufacture shown in FIG. 1, the object 1, during manufacture, consists of the solidified portions C1 .0 and C2.0 of the powder layers C1 and C2.

In order to produce, as shown in FIG. 5, a third layer of powder C3, a part of which will be solidified, a layering step is successively carried out, during which powder P is put into the shape of the layer C3, then a solidification step, during which a portion C3.0 of the layer C3 is solidified by laser scanning. An example of implementation of these steps of layering and solidification is detailed below.

From its position in FIG. 1, the piston 14 is translated downwards along its axis Z14 to its position in FIG. 2, as indicated by the arrow F1 in FIG. 1, while additional powder P is reported. in the well 12, covering the layer C2. As shown in Figures 1, 2 and 3, this powder is spread over the entire powder layer C2, inside the well 12, by the roller 16. For this purpose, in a manner known per se, the roller 16 is here trained:

in horizontal translation in the direction of the axis XX, as indicated by the arrow F2 in FIGS. 1 to 3, the axis Y16 of the roll being thus translated horizontally from one axial end along the axis XX of the well; 12 at its opposite axial end, in this case from the left end to the right end of the well 12 in the figures, and

- Rotating on itself about its axis Y16 contrarotatively, that is to say in the opposite direction to that of its bearing on the powder disposed at the front of the roller 16 in the direction of its translation F2, as indicated by the arrow F3 in FIGS. 1 to 3. In this way, the contact caused by the outer surface of the roll 16 on the powder P located at the front of the roll 16 in the direction of its translation F2, opposes the displacement of the roll according to the translation F2, which improves the display of the powder, in a layer of controlled thickness. In practice, it will be understood that the drive means of the roller 16 are designed to apply to the latter a rectilinear force in the direction of the axis XX and a torque around the axis Y16, which are slaved to each other. other in a pre-established way to precisely control the spreading of the powder, depending, inter alia, on the nature of the object 1 to be manufactured, the finesse desired for the details of this object, the physicochemical nature of the powder, etc.

Once the roller 16 has spread powder P over the entire axial extent, along the axis XX, of the piston 14 inside the well 12 and the roller 16 thus occupies the translated position of FIG. 3, the piston 14 is translated upwards along its axis Z14, as indicated by the arrow F4 in FIG. 4, so as to project, with respect to the upper edge of the well 12, a portion of the layer of powder which has just been spread by the roller 16. Then, as shown in Figure 4, the roller 16 is driven, both in horizontal translation along the axis XX, from the axial end of the well 12, he at the end of the spreading of the powder, in other words from its translated position of FIG. 3, to the opposite axial end of the well 12, in other words to its initial position of FIG. indicated by the arrow F5 in FIGS. 4 and 5, and in rotation about itself around its axis Y16 in a controlled manner Arotative, as indicated by the arrow F6 in Figures 4 and 5. In this way, the roller 16 compact the layer of powder just spread, reducing the thickness, along the axis ZZ, to a predetermined value at the end of this compacting operation, the powder, spread and compacted, covering the powder layer C2, forms the powder layer C3.

As shown in FIG. 5, the laser emission means 18 are then actuated so that its beam, referenced 19A, partially scans the powder layer C3, solidifying, by sintering and / or melting, the part C3.0 of this powder layer C3, as indicated by the arrow F7 in FIG. 5. This solidified layer portion C3.0 is provided, with an appropriate definition of the trajectory of the beam 19A, to correspond to a two-dimensional section of the object to manufacture 1: in other words, in a manner known per se, the laser beam 19A gradually strikes a portion of the upper surface of the powder layer C3, this surface portion constituting a section of the object to be manufactured, calculated at the in the sense that, prior to the production of the first powder layer C1, a set of digitized superimposed sections is determined from a numerical definition of the object to be manufactured, these sectio overlapping ns corresponding to the layer parts of powder to successively solidify by laser scanning. In other words, before the implementation of the steps of layering of the layer C1 and solidification of the part C1 .0 of this layer C1, a preparatory step is implemented in which the digitized sections mentioned above. are determined, as explained above. Thus, it will be understood that, prior to the moment of manufacture shown in FIG. 1, powder P has been layered on the upper face of the piston 14, by spreading and then compacting using the roller 16 and the piston 14, then the powder layer C1 thus obtained was partially scanned by the laser beam 19A so as to solidify the part C1 .0 to correspond to the first of the pre-established sections of the object to be manufactured 1, then the powder P was layered on the powder layer C1, by spreading and then compaction with the aid of the roller 16 and the piston 14, then the thus obtained powder layer C2 was partially scanned by the laser beam 19A so as to solidify it part C2.0 to correspond to the second section of the object to be manufactured 1.

Once the solidified part C3.0 of the powder layer C3 is obtained, powder P is layered in the form of a fourth layer of powder C4, covering the powder layer C3, as shown in FIG. This layering of the powder layer C4 is carried out in a manner similar to the layering of the layers C1, C2 and C3. Then, also as shown in FIG. 6, the laser emission means 18 are actuated so that its beam 19A partially scans the powder layer C4, in order to solidify the latter throughout its thickness, by sintering and / or fusion. However, unlike the use of the laser beam 19A to completely solidify each of the parts C1 .0, C2.0, C3.0 of the preceding powder layers C1, C2 and C3, only a fraction C4.0.1 of a part C4.0, corresponding to a two-dimensional section of the object to be manufactured 1, of the layer C4 is solidified by laser scanning. In the embodiment considered in the figures, this fraction C4.0.1 of the part C4.0 of the powder layer C4 includes two portions C4.0.1 A and C4.0.1 B which are opposite each other in the direction of the axis XX, each of these portions C4.0.1 A and C4.0.1 B of the solidified fraction C4.0.1 being scanned by the laser beam 19A at different times, as illustrated by FIGS. 6 and 7, with an ad hoc setting of the operation and / or trajectory of this laser beam. In all cases, after the application on the fourth layer of powder C4 of the laser beam 19A, the portion C4.0 of this powder layer C4, corresponding to the two-dimensional section of the object to be manufactured 1 to level of this fourth layer of powder, is not solidified in its entirety, but only its C4.0.1 fraction is solidified, it being understood that, as shown in FIG. 7, this solidified fraction C4.0.1 extends over the entire thickness of the C4 powder layer. The remainder of the C4.0 portion of the C4 powder layer, which forms a C4.0.2 fraction of this C4.0 powder layer portion, is not solidified.

Then, as shown in FIG. 8, a fifth layer of powder C5 is layered, covering the fourth layer of powder C4, and, in the same way as for the layer of powder C4, only a fraction C5.0.1 d a part C5.0, corresponding to a new three-dimensional section of the object to be manufactured 1, of this fifth layer of powder C5 is solidified by scanning the laser beam 19A. Thus, as shown in FIG. 8, at the end of the laser scanning of the powder layer C5, the part of the latter corresponding to the two-dimensional section of the object to be manufactured 1 at the level of this powder layer C5, is only solidified for its C5.0.1 fraction, while its C5.0.2 fraction is not solidified.

Then, as shown in FIG. 9, in the same way as previously described for layering the powder layers C1, C2, C3, C4 and C5, a sixth layer of powder C6 is layered by covering the fifth layer of powder C5, then only a fraction C6.0.1 of a portion C6.0, corresponding to a new section of the object to be manufactured, of this sixth layer of powder C6 is solidified by scanning the laser beam 19A, while its fraction remaining C6.0.2 is not solidified.

Unlike the use of the laser emission means 18 described so far, these means 18 are then used to apply more laser energy to the powder P than during the solidification of the fractions C4.0.1, C5.0.1 and C6.0.1: to illustrate this aspect in the figures, the laser beam applying more energy is reference 19B. According to a preferred embodiment, this laser beam 19B differs from the laser beam 19A in that the power of the laser beam 19B is greater than that of the laser beam 19A.

In practice, the embodiment of the laser emission means 18 is not limiting, as long as these means 18 selectively apply two different laser energies, such as the laser beams 19A and 19B in the figures. By way of example, the laser emission means 18 includes two lasers whose respective sources have different powers or only one laser whose power of the source is adjustable in operation. In these two cases, the moving elements of the laser beams 19A and 19B, typically galvanometric mirrors, may be the same for the two beams 19A and 19B, which is to say that the characteristics, in particular the speed and accuracy respective scans by the beams 19A and 19B are the same for these two laser beams. An alternative is to use the same laser power but to play on the scanning speed to obtain that the beam 19B applies to the powder P more energy than the beam 19A. More generally, it is understood that it is the laser characteristics, respectively associated with the beams 19A and 19B, which are to be chosen or adjusted, and that depending on the powder thickness that is desired to solidify by laser scanning, as explained just after.

As shown in FIG. 9, because the beam 19B brings more laser energy, its application on the C6 powder layer induced by sintering and / or melting, at the same time, solidifies the fraction C6.0.2 of the part of the C6.0 powder layer which has not been solidified by the laser beam 19A and the solidification of the non-solidified fractions C4.0.2 and C5.0.2 of parts C4.0 and C5.0 of the underlying layers of powder C4 and C5. It is understood that the characteristics of the laser beam 19B are adapted to the need to jointly solidify, that is to say together and at the same time, the respective thicknesses of the three superimposed powder layers C4, 05 and 06.

At the end of the application of the laser beam 19B on the powder layer 06, as shown in FIG. 10, all the fractions C4.0.2, C5.0.2 and 06.0.2 of the powder layers 04, 05 and 06 are solidified. At this moment, it is understood that, in each of the layers of powder 04, 05 and 06, all of their portion C4.0, C5.0 and 06.0, corresponding to the two-dimensional sections associated with the object to be manufactured 1, is solidified. , with the advantage that, with regard to their fraction 04.0.2, C5.0.2 and 06.0.2, the solidification has been obtained productively thanks to the use of the beam 19B with high laser energy, while the solidarization of their fraction C4.0.1, 05.0.1 and 06.0.1 was obtained with finesse thanks to the use of the beam 19A with lower laser energy. As a result, the fractions C4.0.2, C5.0.2 and C6.0.2, which have been solidified together, form a solidified solid mass of powder, which is juxtaposed horizontally with the fractions C4.0.1, C5.0.1 and C6.0.1 which were individually solidified one after the other and one above the other, these fractions having a fine thickness compared to that of the above-mentioned cluster. It is understood that the fractions C4.0.1, 05.0.1 and C6.0.1 are advantageously provided at the edge of the object to be manufactured 1, to care for the quality of implementation, while the joint solidification of the fractions 04.0.2, C5. 0.2 and C6.0.2 promotes the manufacturing productivity of the object at heart.

As illustrated in FIG. 11, the grinding tool 20 is then actuated in order to correct defects D altering the surface state of the portion C6.0 of the powder layer 06. Indeed, at the end of the application of the laser beam 19B to the powder C6, the latter has, for example, as defects, extra thicknesses in the solidified layer portion C6.0, in particular in the fraction C6.0.2, projecting upwards from the upper surface of the rest of this solidified part C6.0. More generally, the defects D have been generated by the interaction between the powder layer C6 and the laser beam 19B, as shown schematically and exaggerated in FIG. 10. In fact, the solidified layer portion C6.0 corresponds to a digitized section that had been identified as being at risk, among all the digitized sections, when determining the latter from the numerical definition of the object 1 to be manufactured, in other words during the preparatory stage evoked upper. Indeed, as explained progressively above in connection with FIGS. 6 to 10, the digitized section corresponding to the solidified layer portion C6.0 is a juxtaposed multi-thickness zone section, in the sense that the solidified layer portion C6.0 includes both the fraction C6.0.1, which was solidified while covering the already solidified fraction C5.0.1 of layer C5 covered by layer C6, and the fraction C6.0.2 which was solidified together with the not yet solidified fraction C5.0.2 of the C5 layer. Such a juxtaposed multi-thickness zone section is predisposed to the appearance of defects in the corresponding solidified layer portion, as is the case for the defects of D of the solidified layer portion C6.0 shown in FIG. 10 In other words, since the solidified layer portion C6.0 corresponds to a risk section, these defects D are predictable.

In this respect, it will be noted that there is a direct relationship between the thickness of a layer of powder solidified by laser scanning and the quantity of powder necessary for producing this layer prior to its solidification: in fact, in a known manner in itself, the production of a layer of powder according to a given thickness implies that there is a distance between the generatrix of the layering roller, such as the roller 16 mentioned above, and the upper surface of the layer previously solidified, this distance increasing proportionally with the thickness of the solidified layer. This distance increases for at least two reasons: on the one hand, a dense structure of the solidified material is obtained at about 100% only from a density, of the order of 50%, for the powder deposited prior to solidification by laser scanning; on the other hand, the upper surface of the previously solidified layer is not, in reality, a strictly planar surface, but has an irregular surface condition, including peaks and valleys generated by the interaction of the laser beam with the powder layer. As a consequence of this situation, it is understood that it may be practically impossible to directly manufacture a layer of powder having, for example, a thickness of 15 μηι following the prior direct solidification of a layer of powder having for example a thickness of 60 μηι: indeed, to achieve the layer of 15 μηι, the generatrix of the roller will come into contact with the peaks of the upper surface of the 60 μηι layer, previously solidified. At least, this will cause crushing of material at the level of the previously solidified layer, with a risk of localized degradation of the structure, as well as a deterioration in the long term of the cylindrical surface of the roll, with loss of its mechanical, geometrical and surface condition. At worst, there will be interruption of the realization of the layer of 1 5 μηι, thus stopping the manufacturing process of the three-dimensional object. The preceding explanations also make it possible to understand why, in practice, it is impossible to provide, by the existing conventional methods, horizontally juxtaposed solidified layers having different respective thicknesses.

In order to eliminate the foreseeable defects D, a step of correcting these defects is implemented directly after the solidification step of the solidified layer portion C6.0, this step being preprogrammed because, as explained above, the digitized section corresponding to the solidified layer portion C6.0 has been identified as being at risk during the preparatory step mentioned above. To do this, the grinding tool 20 is, as shown in FIG. 11, actuated, for example, at the same time, rotated on itself about its central axis Y20, as indicated by the arrow F8 in FIG. 11, and close to the upper surface of the solidified part C6.0 of the powder layer C6, this approximation being made according to all conceivable kinematics: in the embodiment considered here, this approximation is realized by driving the tool 20 in horizontal translation in the direction of the axis XX, as indicated by the arrow F9 in FIG. 11, this translation F9 being preceded by a vertical offset, in the direction of the axis ZZ between the tool 20 and the piston 14, this offset resulting for example from the combination of a downward translation along the axis ZZ of the tool 20 and an upward translation along the axis ZZ of the piston 14. More generally, the piston 14 is ava ntageusement moved in a coordinated manner to the actuation of the grinding tool 20, in particular to enhance the action of this tool on defects D to eliminate.

When the outer face of the tool 20 interferes with each defect D, in particular their projecting portion, the tool eliminates the defect, by removal of material, in other words by removing, typically by abrasion and / or cutting, the corresponding excess thickness of this defect. This amounts to saying that the tool resurface the solidified part C6.0 of the powder layer C6. Of course, the operating conditions of the grinding tool 20, here the rotation speed F8 and the translation speed F9, are adapted to eliminate the excess thicknesses of the defects D in fine particles, which are detached from the solidified part C6.0, in particular of its fraction C6.0.2, of the layer of powder C6 and whose presence will not be sensitive thereafter of the implementation of the manufacture of the object 1.

Once the grinding tool 20 has processed the entire upper surface of the solidified layer portion C6.0 and thereby removed all projecting portions of the defects D, the actuation of this tool ceases. A layering step, aimed at forming a seventh layer of powder, covering the powder layer C6, can then be implemented without being impeded by the projecting portions of the defects D. As an example, FIG. this seventh layer of powder C7 whose part C7.0, corresponding to a two-dimensional section of the object to be manufactured 1, is solidified only fractionally, by scanning its corresponding fraction C7.0.1 by the laser beam 19A low power. Of course, rather than achieving this fractional joining of the C7.0 portion of the C7 powder layer, similar to what has been achieved for the C4 and C5 powder layers, the entire C7.0 portion of the layer C7 powder could have, by way of variant not shown, be solidified by scanning the laser beam 19A, similar to what has been achieved for the powder layers C1, C2 and C3. More generally, the operations just described so far are repeated to layer and partially solidify as many layers of powder as necessary to obtain the complete three-dimensional object 1, that is to say as much layers of powder only sections of this object previously determined during the preparatory stage, as explained above.

It should be noted that, in the embodiment considered in the figures, the various powder layers considered C1 to C7 have the same thickness, which, inter alia, facilitates the programming and actuation of the layering means which include the piston 14 and the roller 16. By way of non-limiting example, the aforementioned thickness is 10 or 15 μηι. This being the case, as a variant not shown, the layering of the powder layers can be provided so that these powder layers have respective different thicknesses: more precisely, because of the possibility of using the high energy beam 19B. laser, one or more layers of powder may be layered so as to have a greater thickness than the powder layers 01 to 07 considered in the figures, it being understood that this or these layers of thicker powder will be scanned exclusively by the laser beam 19B to solidify a portion corresponding to a two-dimensional section of the object to be made, occupying the entire thickness of this layer of thicker powder. Thus, more generally, the first example of the manufacturing method and the associated device allow:

to increase the productivity of manufacture by simultaneously solidifying several layers of powder, representing a stack of great thickness, in the same bed of powder to be solidified, in which layers of powder, of smaller thickness, are previously solidified by fractionally, and this by anticipating and correcting the foreseeable defects appearing during this simultaneous solidification; and

- to increase the surface quality of the functional surfaces of the three-dimensional objects that can be manufactured, by fractionally solidifying layers of thin powder, in the same bed of powder including a thick stack of layers of powder, solidified with a single a scanning blow of a beam applying more laser energy than that applied to solidify, layer after layer, the fractions of each of the layers of thin powder, without suffering from the presence of predictable defects due to their systematic correction as soon as 'They appear.

SECOND EXAMPLE OF MANUFACTURING PROCESS

This second example is illustrated by Figures 13 and 14.

The method of this second example uses the same layering and solidification steps as those explained in detail above in connection with FIGS. 1 to 5. For the rest of the presentation of this second example, it is considered that the process was thus implemented by repetition of the layering and solidification steps, until the solidified part of an nth layer of powder, which, in Figures 13 and 14, is observed vertically from above.

In the case of FIG. 13, this nth powder layer, referenced CN, includes a CN.sub.O solidified part which has a closed contour on itself, thus completely surrounding a non-solidified part CN.P.

In the case of FIG. 14, this nth powder layer, referenced CN ', includes a solidified part CN'.O which consists of strips parallel to each other and separated from each other by a non-solidified part CN'.P it also consists of parallel strips between them. In the example considered in FIG. 14, the strips of the solidified portion of layer CN'.O are of constant width and identical to each other, denoted by a. Similarly, the strips of the non-solidified layer portion CN'.P have a constant and identical width with each other, which is denoted by b and which, here, is equal to the width of the strips of the solidified layer portion CN '. O. By their structure, the solidified portions of CN.O and CN'.O layer correspond to sections, among those determined during the preparatory step mentioned above, potentially predisposed to a defect appears in the layer portion corresponding solidified CN.O, CN'.O. Indeed, these sections are potentially of large relative area, in the sense that, in horizontal geometric plane projection, the corresponding area of solidified layer portion is at least X% of the sum of the area of this layer part corresponding solidified surface and the area of the non-solidified layer portion CN.P, CN'.P while the latter is predominantly bordered by the solidified layer portion CN.O, CN'.O, X being strictly less than 100 Thus, for the examples considered in the figures and if X is set at 50, the section corresponding to the solidified layer part CN'.O is at risk, while the section corresponding to the solidified layer portion CN.O is not at risk. Of course, the section corresponding to the solidified portion CN.O layer will be considered at risk if X is chosen at a sufficiently large value, beyond 50. In practice, the value for X is chosen by the operator implementing the manufacturing method of the object 1, in particular as a function of the composition of the powder P and the morpho-dimensional characteristics of the object 1.

Thus, the second example of the manufacturing method provides, during the aforementioned preparatory step, to identify the sections with a large relative area, starting from a value pre-selected for the parameter X, as being at risk sections. i.e. sections predisposed to the appearance of a defect in the solidified layer portions corresponding to these sections. Just after the solidified layer portion corresponding to one of these risk sections is realized, a fault correction step, similar to that presented above in connection with FIG. 11, is implemented.

In practice, the correction step can thus be implemented, in a preprogrammed manner, after the completion of a solidified layer portion corresponding to each large relative area section. Alternatively, rather than providing that each large area section is a risk section whose corresponding solidified layer portion will be corrected, a large area section may be considered at risk only if it is the last of n sections with large relative area, n being a parameter chosen by programming, for example between 2 and 100.

THIRD EXAMPLE OF MANUFACTURING PROCESS

This third example is illustrated by Figures 15 and 16.

The method of the third example uses the same layering and solidification steps as those explained in detail above in connection with FIGS. 1 to 5. Thus, in FIG. 15, the object to be manufactured 1 has already begun to be manufactured, by superposition of the layers of powder C101 and C102 and the successive solidification of the respective portions C101 .O and C102.O of these layers C101 and C102. In addition, a third layer of powder C103 has been shaped and covers the layer C102. A beam 19 of the laser emission means 18 partially scans the powder layer C103, by solidifying a portion C103.0 of this layer C103, as indicated by the arrow F107 in FIG. 15. In other words, what has just been explained for the third example of the manufacturing process uses the explanations developed above for the previous examples.

As shown exaggerated in FIGS. 15 and 16, the solidified layer portion C103.O of the powder layer C103 has undercontained defects D that form this solidified layer portion C103.O with respect to the solidified part C102.O of the layer C102, in the sense that the solidified layer portion C103.O is partly overhanging on the non-solidified powder P of the layer C102.

Therefore, as shown in FIG. 16, at the end of the step of producing the solidified layer portion C103.O, the grinding tool 20 is used to correct the defects D, in particular in a similar manner to what had been explained with reference to FIG.

The implementation of this defect correction step D using the grinding tool 20 is preprogrammed in advance because, during the aforementioned preparatory step of determining the digitized sections of the object to be manufactured, the section corresponding to the solidified layer portion C3.0 has been identified as being at risk because this section is undercut, in the sense that, as explained above, the solidified layer portion C103.O includes an overhang on non-solidified powder of the layer C102 covered by the layer C103.

In practice, all digitized undercut sections can be considered as at risk and thus induce the implementation of the defect correction step just after the completion of the solidified layer portion corresponding to each of these sections against -bare. Alternatively, one or more criteria may be retained to characterize as being at risk or not the undercut sections of the object to be manufactured. In other words, among the various undercut sections of the object to be manufactured, only some will be identified as being at risk according to at least one of:

the particle size distribution of the powder P,

the chemical composition of the powder P, the thickness of the powder layer in which the portion of the solidified layer corresponding to the section is made, and

the angle formed, with respect to a horizontal geometrical plane, by the overhang of the corresponding solidified layer part.

FOURTH EXAMPLE OF MANUFACTURING PROCESS

This fourth example is illustrated by FIGS. 17 to 20.

The method of the fourth example is a variant of any one of the first, second and third examples described so far, in which, in addition to predicting and correcting the foreseeable defects D, the method provides for detecting and correcting defects other than predictable defects D, in other words, detecting and correcting unforeseeable defects d. Such unforeseeable defects d are likely to appear in solidified layer parts for various and non-limiting reasons, which, by definition, are either ignored or not sufficiently taken into account when the risk sections are identified during the step aforementioned preparatory process.

By way of example, as shown in an exaggerated manner in FIG. 17, the unpredictable defects d are undercuts which appear in a solidified part C103'.O of a powder layer C103 'corresponding to a section which does not was not characterized as being at risk during the preparatory stage. Also, in the exemplary embodiment considered in FIGS. 17 and following, once the solidified part C103'.O of the powder layer C103 'is obtained, the operations aiming at obtaining an additional layer of powder, covering the layer of Powder C103 ', begin to be implemented: similarly to what has been explained above, these operations consist, as shown in Figure 17, to translate downwardly the piston 14 along its axis Z14 similarly to the translation F1, as indicated by the arrow F1 'in FIG. 17, then beginning to spread on the layer of powder C103' additional powder P with the aid of the roller 16 driven simultaneously in translation and in rotation of similar to the translation F2 and the rotation F3, as indicated respectively by the arrows F2 'and F3' in FIG. 17.

However, this layering step to obtain an additional layer of powder is interrupted at the instant shown in FIG. 17, because of the detection of an unpredictable defect d of the solidified part C103'.O of the layer powder C103 ', by the roller 16, more precisely at the moment when this roller interferes with one of the unpredictable defects d. To do this, the drive means of the roller 16 are designed to control the kinematic behavior of the roller 16 for the purpose of spreading the powder to be layered, namely, its resistant torque, its translational speed and its angular position deviation from the predetermined initial setpoint. A variation measured on one of these parameters representative of the behavior of the roll indicates the presence of unpredictable defects d. In other words, more generally, in this variant, the device 10 makes it possible to control, in particular to measure, at least one parameter representative of the kinematic behavior of the roller 16 when it is used to layer the powder P and thus to observe a variation of this or these parameters, due to resistance to the spreading of this powder on the solidified portion of the powder layer to be covered by the powder P, because of the presence of the defects d of this solidified layer portion: for example in the case considered in the figures, during the spreading of the powder P by the roll 16, the driving torque in rotation of the roll 16 increases at the moment when the latter interferes with one of the defects d, which implies that the roll meets an obstacle resistant to its displacement.

Once the unpredictable defect d is detected and the layering operations are interrupted, the roll 16 is driven so as to be sufficiently separated from the defect d so that the latter can be treated by the grinding tool 20. In the exemplary embodiment considered in the figures, this clearance of the roll 16 consists of a horizontal translation in the direction of the axis XX and in the opposite direction to the translation F2 ', as indicated by the arrow F2 "in FIG. 18 In practice, the roller 16 thus finds, by the translation F2 ", its initial position, that is to say the position it occupied before the beginning of the layering operations to achieve the layer of powder covering the layer C103 '.

In order to eliminate the defects of the grinding tool 20 is then actuated as shown in Figure 19, and this, for example, similarly to what has been explained in detail with reference to Figure 1 1.

Advantageously, as shown in FIG. 20, the drive of the grinding tool 20 is held in such a way that the latter passes over the entire upper face of the solidified layer portion C103'.O: in this way, by in addition to correcting the unpredictable defect detected by the roller 16, the tool 20 corrects any other unforeseeable defects of the solidified part C103'.O. In the exemplary embodiment considered here, this amounts to translating the tool 20 from one of the axial ends, along the axis XX, of the well 12 to its opposite axial end, while the rotation of the tool 20 on itself is maintained.

It will be understood that, thanks to this fourth example of the manufacturing process of the object 1, the foreseeable defects D are systematically processed, without even seeking to detect them, which prevents, for these foreseeable defects D, the implementation of operations detection methods, such as those illustrated in FIGS. 17 and 18, while Unpredictable defects d, ie appearing in solidified layer parts corresponding to sections other than sections at risk, are still eliminated, after being detected.

As an advantageous optional arrangement, the method provides for the "capitalization" of information relating to unpredictable defects, in the sense that, by learning, the process progressively acquires the ability to identify as being at risk sections for which, when of similar past fabrications, the corresponding solidified layer parts have repeatedly presented unpredictable defects. In future manufacturing, these sections can be identified as being at risk.

OTHER EXAMPLES OF MANUFACTURING PROCESS

Other examples of method of manufacturing the object 1, using the device 10, consist in combining all or part of the method examples described so far. In particular, a particularly advantageous embodiment is that the manufacturing method provides, during the aforementioned preparatory step, to identify the risk sections as being one or more juxtaposed multi-thickness zone sections, one or more sections with large relative area and one or more undercut sections, advantageously by integrating in this method a possibility of detecting and correcting unforeseeable defects.

Claims

1. - A method of manufacturing a three-dimensional object (1) by powder solidification, which method comprises:

a layering step in the course of which powder (P) is formed into a layer (C1 to C7; CN; CN '; C101 to C103; C103'), and

a solidification step during which a laser beam (19A, 19B; 19) scans and solidifies a portion (C1.0 to C7.0; CN.O; CN'.O; C101.0 to C103.O; C103'.O) of the layer of powder prepared at the end of the layering step, this solidified part corresponding to a two-dimensional section of the object to be manufactured (1), the method in which the step of setting in a layer and then the solidification step are repeated one after the other, by superimposing the layers of powder, until the object which consists of the solidified layer parts,

which method further comprises a preparatory step, which is carried out before the layering and solidification steps, and during which a set of digitized superimposed sections is determined from a numerical definition of the object to be manufacturing, which respectively correspond to the solidified layer portions to successively obtain during the repetition of the layering and solidification steps,

characterized in that, during the preparatory step, is identified, among the set of sections, one or more so-called risk sections, each risk section being predisposed that at least one defect (D), said predictable, appears in the solidified layer portion corresponding to the risk section,

and in that the method further comprises at least one fault correction step:

- Which is implemented, at the same time, after the or each solidification step at the end of which the solidified layer portion corresponds to the one or one of the risk sections, and before the layering step following this solidification step, and

- During which a grinding tool (20) corrects the predictable defect (D) of the solidified layer portion corresponding to this risk section.

2. - Method according to claim 1, characterized in that, during the preparatory step, the or at least one of the risk sections is identified as being a section called multi-thickness zones juxtaposed, which corresponds to a part solidified (C6.0) of a layer of powder (C6), said upper, covering a layer of powder (C5), said lower, which portion of the solidified layer (C6.0) of the upper layer (C6) including two juxtaposed fractions, one of which (C6.0.1) is solidified by laser scanning while covering an already solidified fraction (C5.0.1) of the lower layer (C5) while the other fraction (C6.0.2) is to solidify by laser scanning together with a fraction not yet solidified (C5.0.2) of the lower layer (C5).

3. - Method according to one of claims 1 or 2, characterized in that, during the preparatory step, the or at least one of the risk sections is identified as being a section called large relative area, which corresponds to a solidified layer portion (CN.O; CN'.O) which, when projected on a horizontal geometric plane, has an area of at least X% of the sum of this area of the solidified layer portion and a area of a non-solidified layer portion (CN.P; CN'.P) predominantly bordered by the solidified layer portion, X being strictly less than 100.

4. - Method according to claim 3, characterized in that, during the preparatory step, the or at least one of the risk sections is identified as being the last of several sections with a large relative area.

5. - Method according to one of claims 3 or 4, characterized in that, during the preparatory step, the large relative area section is identified as being at risk when X is less than or equal to 50.

6. - Method according to any one of the preceding claims, characterized in that, during the preparatory step, the at least one of the layers at risk is identified as being a so-called undercut section, which corresponds to a solidified part (C103.O) of a layer of powder (C103), said upper, covering a layer of powder (C102), said lower, which portion of the solidified layer of the upper layer including an overhang on non-powder solidified from the lower layer.

7. - Method according to claim 6, characterized in that, during the preparatory step, the undercut section is identified as being at risk according to at least one of:

- the particle size distribution of the powder,

- the chemical composition of the powder,

the thickness of the corresponding powder layer, and

the angle formed, with respect to a horizontal geometrical plane, by the overhang of the solidified part of the associated upper layer.

Method according to one of the preceding claims, characterized in that, during the defect correction step, the grinding tool (20) is applied to the upper surface of the solidified layer portion and corrects the predictable defect (D) by removal of material.

9. - Process according to any one of the preceding claims, characterized in that, during each layering step, a piston (14) for supporting the layered powder is moved, and in that during the correction step, the piston is moved in a coordinated manner to the actuation of the grinding tool (20).

10. - Method according to any one of the preceding claims, characterized in that the grinding tool (20) is a milling cutter or grinding wheel.

1 1. - Process according to any one of the preceding claims, characterized in that, during the layering steps, controlling the solidified layer portion (C103'.O) obtained at the end of the solidification step which has preceded the current lay-up step, to detect a so-called unforeseeable defect (d), and, in case of detection of such an unpredictable defect (d), the current lay-up step is interrupted then the grinding tool (20) is used to correct this unforeseeable defect, and then the layering step is implemented again.

12. - Process according to claim 1 1, characterized in that, to implement each step of layering, using a spreading roller (16), which is driven simultaneously in rotation about itself around a central axis (Y16) of the roll and in translation perpendicular to this axis so as to spread the powder (P) to be layered, and of which at least one parameter of the kinematic behavior is measured so as to detect the unpredictable defect (d) by observing a variation of this parameter.

13. - A method according to claim 12, characterized in that the grinding tool (20) and the spreading roller (16) are controlled by common means of selective actuation of this grinding tool and of this roller. spreading.

14. - Process according to any one of the preceding claims, characterized in that the powder layers have substantially the same thickness.