METHOD FOR ADDITIVE MANUFACTURING OF AT LEAST ONE PART BY LASER POWDER BED FUSION

Abstract

An additive manufacturing process (10) for at least one part (12) by laser powder bed fusion, comprising the following steps: a) producing the part(s) (12) by laser powder bed fusion, layer by layer, the part(s) thus produced having first surfaces (14) having nominal dimensions that do not require adjustment and second surfaces (16) having non-nominal dimensions that require adjustment; b) machining said second surfaces (16) to give them nominal dimensions, characterized in that, to facilitate step b), the process includes, during step a), marking said second surfaces (16). Figure for the abstract: Figure 2

Description

Title of the invention: METHOD FOR ADDITIVE MANUFACTURING OF AT LEAST ONE PART PER LASER POWDER BED FUSION Technical field of the invention

[0001] The present invention relates to the field of additive manufacturing.

[0002] More particularly, the present invention relates to a method of additive manufacturing of at least one part by laser powder bed fusion. Technical background

[0003] It is known to produce a part, in particular for an aircraft turbomachine, by additive manufacturing.

[0004] Several additive manufacturing technologies exist, and this application relates in particular to powder bed fusion additive manufacturing. The powder is melted using a high-energy beam, such as a laser beam (SLM, or Laser Beam Melting). In practice, a bed of powder is deposited on a support platform and scanned by the laser beam to build the part layer by layer, with a third layer of fused powder being placed on top of a second layer of powder, which is itself placed on top of a first layer of powder.

[0005] Figure 1 illustrates an example of an additive manufacturing apparatus 10 comprising: - a build platform 2 serving as a support for the production of a part 1, - a powder feeding device 5 for a desired material onto the build platform 2, - a scraper 3 allowing the powder P to be spread on the manufacturing tray 2 in a layer of Cb C2 powder, - a powder recovery unit 6 P allowing the recovery of excess powder, and - a laser beam generator 4 configured to generate a laser beam 40 intended to scan the powder layer(s) Ci, C2 for the purpose of localized powder melting and the manufacture of the part 1 layer by layer.

[0006] The device 10 also includes a control device 7 located at the generator 4. This control device 7 allows various characteristics of the part 1 to be checked during the layer-by-layer manufacturing process.

[0007] A powder bed fusion additive manufacturing process generally comprises two successive steps. In a first step, the part or parts to manufacturing is carried out by laser powder bed fusion, layer by layer, as mentioned above.

[0008] In general, the part or parts thus produced comprise first surfaces having nominal dimensions which therefore do not need to be adjusted, and second surfaces which have non-nominal dimensions, such as an overthickness, and which need to be adjusted.

[0009] In this application, "nominal dimensions" means dimensions that conform to a specification, and "non-nominal dimensions" means dimensions that do not conform to the specification.

[0010] The second surfaces are, for example, surfaces which are connected to supports of the part, these supports being made layer by layer at the same time as the part to support parts of the part during manufacturing.

[0011] During a second step of the process, the second surfaces are adjusted by machining to give them nominal dimensions and in particular to remove the aforementioned excess thickness.

[0012] Since this adjustment is a manual operation, it is essential to ensure the repeatability of the adjustments on the parts to avoid generating defects (tool marks, impacts, etc.) that would lead to scrap or non-conformities. Furthermore, in practice, it is not easy for an operator to identify excess thickness that needs to be removed.

[0013] The present invention proposes a simple, effective, and economical solution for facilitating the second adjustment step of a process of the aforementioned type. Summary of the invention

[0014] The invention relates to an additive manufacturing process for at least one part by laser powder bed fusion, comprising the following steps: a) producing the part or parts by laser powder bed fusion, layer by layer, the part or parts thus produced having first surfaces having nominal dimensions that do not need to be adjusted and second surfaces that have non-nominal dimensions and that need to be adjusted,

[0015] b) to adjust said second surfaces by machining to give them nominal dimensions,

[0016] characterized in that, to facilitate step b), the process includes during step a) marking said second surfaces.

[0017] The invention thus proposes to mark the second surfaces in such a way as to facilitate their adjustment. The operator who will perform the adjustment of the second surfaces can thus easily identify them and machine these surfaces without risk of overlapping onto adjacent surfaces.

[0018] The method according to the invention may comprise one or more of the following features or steps, considered independently of each other or in combination with each other: - the marking is achieved by burning said second surfaces, this burning generating a difference in appearance between the first and second surfaces; - burning generates a blackening of the secondary surfaces; - the burning is carried out by further heating the powder using the laser level of said second surfaces; - the marking is achieved by texturing said second surfaces, this texturing being achieved by an extra thickness of molten material in step a); - the texturing includes a repetition of geometric patterns; - the patterns are chosen from lines, dots, crosses, stars, pegs in the form of pyramids for example, and geometric figures; - the patterns are regularly distributed; - the texturing is completely removed in step b) so that the second surfaces are smooth at the end of step b); - the texturing has a height equal to said overthickness; - The marking is carried out by forming machining indicators and / or markers on said second surfaces; - after step a), the machining markers are visible, and in which step b) is carried out until the machining markers disappear; - after step a), the machining indicators are invisible, and in which step b) is carried out until the machining indicators appear; - said second surfaces are connected to supports made by additive manufacturing during step a), these supports being removed before or during step b); - the part is bladed; it therefore includes at least one blade; it is preferably a part for a turbomachine, in particular for an aircraft; - the marking forms a grid or one or more series of lines. Brief description of the figures

[0019] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the accompanying drawings in which:

[0020] [Fig. 1] Fig. 1, already described, is a schematic perspective view of an additive manufacturing apparatus for a part by laser powder bed fusion according to the prior art,

[0021] [Fig.2] [Fig.2] is a schematic perspective view of parts, one of which is produced using the method according to the invention and comprises a second marked surface,

[0022] [Fig. 3a-3d] Figures 3a to 3d are very schematic views of a work in progress adjustment.

[0023] [Fig.4] [Fig.4] is a schematic perspective view of a part marked according to the invention,

[0024] [Fig. 5] [Fig. 5] is a schematic perspective view of a part produced by additive manufacturing, which includes an adjustable overhang.

[0025] [Fig.6] [Fig.6] is a schematic perspective view of a part made by additive manufacturing according to the invention, and which includes an adjustable overthickness

[0026] [Fig.7] [Fig.7] is a larger-scale view of a detail of [Fig.6], and

[0027] [Fig.8a-8c] Figures 8a to 8c are schematic views of geometric patterns for marking the extra thickness. Detailed description of the invention

[0028] Fig. 1 has been described in the technical background of this application and illustrates an additive manufacturing apparatus according to the prior art.

[0029] There are at least two types of additive manufacturing of a part: either the part is made by successive deposits of molten material, or the part is made by selective laser melting on a powder bed (SLM or LBM).

[0030] The present invention relates to a method of additive manufacturing of the part by laser powder bed fusion.

[0031] A method of this type can be described as follows.

[0032] A digital production file is created using suitable software. This file is generated following the slicing of a part to be manufactured into slices of given thicknesses from the CAD (Computer-Aided Design). The production file includes all the necessary instructions (laser paths so that the machine can produce the part, slice by slice).

[0033] The build platform serves as the base for manufacturing the part. The powder spreading device allows a layer of powder of the desired material to be spread onto the build platform, to a desired thickness. This device can be a roller or a scraper that moves in translation along an axis on either side of the powder bed.

[0034] Once the powder layer is deposited, at least one laser beam selectively scans certain areas of the powder bed, corresponding to a slice of the part to be produced. The scanning pattern and all laser parameters (such as laser power, scanning speed, spacing between two laser passes, etc.) are dictated to the device by the production file. The laser's passage over the powder bed raises the powder to a temperature above its melting point. A molten pool is thus created. Upon cooling, this pool solidifies and forms a solid bead. At the end of the laser scanning of a powder layer, a two-dimensional cross-section of the desired object is therefore obtained.

[0035] The powder spreading device then deposits a new layer of powder on top of the previous one. A new laser scan is performed to consolidate a new section of the part.

[0036] Thus, iteratively, a three-dimensional object is reconstituted by successive consolidation of two-dimensional sections, or slices.

[0037] To facilitate the casting of a part, it is often necessary to generate supports to enable the part to be manufactured. These supports are to be removed by machining later in the process, and the surfaces on which the supports rest must be adjusted. These surfaces are distinct from the other surfaces of the part, which do not need to be adjusted.

[0038] In the present invention, a distinction is therefore made between first surfaces of the part which have nominal dimensions and which do not need to be adjusted, and second surfaces of the part which have non-nominal dimensions and which need to be adjusted.

[0039] The process according to the invention essentially comprises two steps, namely: a) producing the part or parts by laser powder bed fusion, layer by layer, and

[0040] b) adjust by machining the aforementioned second surfaces of the or each part.

[0041] As mentioned above, these second surfaces are for example surfaces of the part connected to supports at the end of step a), these supports being removed before or during step b).

[0042] The invention proposes a parametric or geometric strategy for identifying the second surfaces to be adjusted.

[0043] The idea, in order to compensate for defects, is to make the secondary surfaces requiring adjustment more visible and thus visually limit the operator's focus to the secondary surfaces that need reworking. The technical solution that allows for visually differentiating the secondary surfaces from the primary surfaces of the same part is the "marking" of the secondary surfaces.

[0044] Three marking variants are possible according to the invention.

[0045] Burning

[0046] According to a first embodiment, the marking is carried out by burning the second surfaces, this burning generating a difference in appearance between the first and second surfaces.

[0047] Fig. 2 shows several parts 11, 12 produced by additive manufacturing.

[0048] Part 11 on the left in the drawing is produced by a process of the prior art and comprises first surfaces 14 and second surfaces 16 which are in appearance identical and cannot be visually distinguished from one another.

[0049] Part 12 on the right in the drawing is made by a process according to the invention and comprises first surfaces 14 similar to those of the prior art, and second surfaces 16 which are marked.

[0050] The marking is carried out by burning. The burning preferably generates a color change, such as blackening, of the second surfaces 16 compared to the first surfaces 14 of the part 12.

[0051] This burning is achieved by further heating the powder with the laser at the level of the second surfaces 16.

[0052] The part is manufactured using a laser that fuses the part or material. The first embodiment uses this laser with a contour parameter that is more energetic than the usual contour parameter in order to "burn" the desired surface. This gives it a different visual appearance without degrading the mechanical properties of the part, as it is purely a surface effect that can then be refined through adjustments. In terms of fusion parameters, a faster and more energetic parameter than the usual contour parameter (appropriate for the material) can be used to deliver more energy, which will have the desired effect of changing the surface appearance.

[0053] Machining marks or indicators

[0054] According to a second embodiment, the marking is carried out by forming machining marks and / or indicators on the second surfaces.

[0055] Figures 3a to 3d show a part 12 which is made by a process according to the invention and which includes a second surface 16 having witnesses 20 and markers 22.

[0056] After step a), the machining markers 20 are apparent and are intended to be removed by machining during step b).

[0057] After step a), the machining witnesses 22 are invisible because they are integrated into the material. These witnesses 22 are then intended to be revealed during step b) to make them visible.

[0058] The third embodiment can therefore be achieved by adding to the 3D model indicators or markers embedded in the material which will either disappear or appear During surface reworking, the operator will consume both the material and the indicator simultaneously. The disappearance of the marker or the appearance of the indicator signals that the material has been consumed and that reworking the surface should stop before generating non-conformities. These markers / indicators can also serve as indicators of proper material removal (neither too much nor too little).

[0059] In figure 3a, the markers 20 are visible on the surface 16 and the witnesses 22 (represented in dotted lines) are invisible because they are contained in the material.

[0060] In Figure 3b, the markers 20 are partially machined during the fitting step. The guides 22 (shown as dashed lines) remain invisible.

[0061] In Figure 3c, the markers 20 are completely machined and were removed by machining during the fitting step. The test pieces 22 (shown as solid lines) are, however, revealed and are now visible. It is therefore not necessary to continue fitting the part.

[0062] If the adjustment is continued, there is a risk of removing the witnesses 22 as seen in figure 3d. In this case, the part would no longer conform and would have to be scrapped.

[0063] Texturing - Thickness

[0064] According to a third embodiment, the marking is achieved by texturing the second surfaces, this texturing being achieved by an excess thickness of melted material in step a).

[0065] The laser melting process can generate degraded surface conditions on the manufactured parts, including greater roughness and numerous surface porosities.

[0066] These areas are thus often supported to limit these degradations, the supports then being removed manually and the interface surface adjusted manually in order to achieve the desired surface condition.

[0067] However, the finer the desired surface finish, the more adjustments are required, and therefore the more material is consumed on the part. Since manual adjustment is neither repeatable nor industrially feasible, it is difficult to guarantee both surface finish and dimensional conformity with current state-of-the-art support technology.

[0068] One solution is to add an extra thickness of material to be adjusted, but the boundary between the extra thickness and the part is not visually identifiable, so the fitter cannot know where to stop in the prior art.

[0069] In the present invention, a distinction is therefore made between first surfaces of the part which have nominal dimensions and which do not need to be adjusted, and second surfaces of the part which have an extra thickness and which need to be adjusted.

[0070] Figure 4 shows a part 12 which is produced by a process according to the invention and which includes a first surface 14 similar to that of the previous technique, and a second surface 16 which is marked by a texture 18.

[0071] The texture 18 comprises a repetition of geometric patterns in the example shown. The patterns here are dots in the form of pyramids, for example.

[0072] The texture 18 is preferably completely removed in step b) so that the second surfaces 16 are smooth at the end of step b).

[0073] The texturing can have a height equal to the thickness.

[0074] The second embodiment can therefore include adding to the 3D model a A 3D-drawn texture. It can take the form of knurling, allowing the fitter to easily identify which surface needs adjusting. Figure 5 shows a prior art part 12 with surfaces 16 exhibiting raised areas that are difficult to identify and locate. In the example shown, this part 12 is a distributor sector comprising a series of vanes, with the raised areas on the surfaces 16 located at the trailing edges of these vanes.

[0075] The idea, in order to address quality defects, is to make the excess thickness to be adjusted more visible and thus visually indicate to the operator this excess thickness that he must correct. The technical solution that allows the excess thickness to be visually differentiated from the first surfaces of the same part is the "marking" of the excess thickness.

[0076] The solution is to be able to visually identify the boundary between the part and the machining over-thickness and therefore more generally the material in excess thickness.

[0077] And this is possible if on each fused layer of machining overstuffing a pattern clearly identifiable by over-machining the layer is marked in a second step.

[0078] For over-lasing, the idea is to use a specific parameter setting which generates a difference in coloration between areas lasered twice and those lasered only once. Overheating, which could have harmful consequences, is also avoided.

[0079] The advantage of over-etching each layer of material is that it allows the pattern to be embedded in the volume and not just on the surface. Thus, when the pattern disappears, there is no longer any need to adjust the material and the part is geometrically preserved.

[0080] Different patterns can be used and laser marked (the design is easily produced in CAD).

[0081] Advantageously, the marking is achieved by forming a repetition of geometric patterns on the overthickness.

[0082] Figures 6 and 7 show, for example, a part 12 obtained by the process according to the invention, after step a). This part 12 has an increased thickness on a surface 16, which is marked. In the example shown, this part 12 is also a distributor sector which includes a series of blades, the 16 surfaces with overthicknesses being located at the trailing edges of these blades.

[0083] The marking can form a grid as illustrated in figures 6 and 7.

[0084] The patterns can be chosen from lines, dots, crosses, stars, and geometric figures (figures 8a-8c). The patterns are preferably regularly distributed.

[0085] The marking may comprise one or more series of lines. In Figure 8a, several non-straight lines extend alongside each other. In Figure 8b, several series of dotted lines extend alongside each other. In Figure 8c, several series of star lines extend alongside each other.

[0086] This invention makes it possible to guarantee the double conformity of surface condition / dimension following the adjustment operation.

[0087] It also allows the production by laser fusion of parts with very demanding surface finish / dimensional specifications, in particular aerodynamic duct parts.

Claims

Demands

1. An additive manufacturing method (10) for at least one part (12) by laser powder bed fusion, comprising the following steps: a) producing the part or each part (12) by laser powder bed fusion, layer by layer, the part or each part thus produced having first surfaces (14) having nominal dimensions which do not need to be adjusted and second surfaces (16) which have non-nominal dimensions which need to be adjusted, b) adjusting said second surfaces (16) by machining to give them nominal dimensions, characterized in that, to facilitate step b), the method comprises during step a) marking said second surfaces (16).

2. A method according to claim 1, wherein the marking is carried out by burning said second surfaces (16), this burning generating a difference in appearance between the first and second surfaces (14, 16).

3. Method according to claim 2, wherein the burning generates a blackening of the second surfaces (16).

4. A method according to claim 2 or 3, wherein the burning is carried out by further heating the powder by means of the laser at said second surfaces (16).

5. A method according to claim 1, wherein the marking is achieved by texturing (18) said second surfaces, this texturing (18) being achieved by an excess thickness of molten material at the step

6. dj. Method according to claim 5, wherein the texturing (18) comprises a repetition of geometric patterns.

7. A method according to claim 6, wherein the patterns are chosen from lines, dots, crosses, stars, spikes in the form of pyramids for example, and geometric figures.

8. A method according to claim 6 or 7, wherein the patterns are regularly distributed.

9. A method according to any one of claims 5 to 8, wherein the texturing (18) is completely removed in step b) so that the second surfaces are smooth at the end of step b).

10. Method according to claim 9, wherein the texturing (18) has a height equal to said overthickness.

11. Method according to claim 1, wherein the marking is carried out by forming machining witnesses (20) and / or markers (22) on said second surfaces.

12. A method according to claim 11, wherein, after step a), the machining markers (20) are apparent, and wherein step b) is carried out until the machining markers (20) disappear.

13. A method according to claim 11 or 12, wherein, after step a), the machining witnesses (22) are invisible, and wherein step b) is carried out until the machining witnesses (22) appear.

14. A method according to any one of the preceding claims, wherein said second surfaces (16) are connected to supports produced by additive manufacturing during step a), these supports being removed before or during step b).

15. A method according to any one of the preceding claims, wherein the marking forms a grid or one or more series of lines.

16. Method according to any one of the preceding claims, wherein the part is bladed.

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