Method of fabricating a part by additive manufacturing

Abstract

A method is for fabricating a part by additive manufacturing while sparing certain particularly sensitive surfaces of the part, and in particular surfaces that have an influence on the aerodynamics of the final part. The method includes the following steps: providing a digital model of a part that is to be fabricated, the part that is to be fabricated including at least one surface that is to be spared, and orienting the digital model relative to a construction direction wherein the part is to be constructed in such a manner that the surface that is to be spared presents a construction angle greater than 30°, preferably greater than 50°.

Claims

1. A method of fabricating a bladed stator ring sector by additive manufacturing, the bladed stator ring sector including a surface to be spared, which is a surface of the bladed stator ring sector configured to be in contact with an air stream, the method comprising: providing a digital model of the bladed stator ring sector that is to be fabricated; orienting the digital model relative to a construction direction, said construction direction being a direction in which the bladed stator ring sector is to be constructed and in which fabrication layers are stacked on one another during additive manufacturing, in such a manner that the surface configured to be in contact with the air stream presents a construction angle greater than 30°, the construction angle being an angle between the surface configured to be in contact with the air stream and a plane orthogonal to the construction direction, and making the bladed stator ring sector layer by layer using an additive manufacturing technique based on the digital model, wherein making the bladed stator ring sector is performed by staking the fabrication layers during additive manufacturing such that the surface configured to be in contact with the air stream on the bladed stator ring sector presents an angle greater than 30° with the plane orthogonal to the direction in which the fabrication layers are stacked on one another during said additive manufacturing.

2. The method according to claim 1, wherein the surface configured to be in contact with the air stream is a surface of a vane portion, wherein the digital model of the bladed stator ring sector is oriented in such a manner that the main direction of said vane portion forms an angle greater than 30° relative to a plane orthogonal to the construction direction.

3. The method according to claim 1, wherein the surface configured to be in contact with the air stream is a surface of a passage portion, and wherein the digital model of the bladed stator ring sector is oriented in such a manner that the main direction of said passage portion forms an angle greater than 30° relative to a plane orthogonal to the construction direction.

4. The method according to claim 1, wherein the bladed stator ring sector includes at least one elongate portion having a front face and a side face, the front face being narrower than the side face, and wherein the digital model is oriented relative to a scanning direction corresponding to a travel direction of a spreader tool in such a manner that the front face of the elongate portion of the bladed stator ring sector is oriented substantially facing the spreader tool when the spreader tool moves in the scanning direction.

5. The method according to claim 4, wherein the elongate portion corresponds to a vane portion of the bladed ring stator sector and wherein the front face of the elongate portion corresponds to a leading edge or to a trailing edge of said vane portion.

6. The method according to claim 4, further comprising modifying the digital model wherein at least one edge of the digital model that is oriented facing the spreader tool when the spreader tool moves in said scanning direction is chamfered.

7. The method according to claim 1, further comprising adding support portions to the digital model in order to construct supports that are suitable for supporting the bladed stator ring sector while the bladed stator ring sector is being fabricated, and wherein the support portions are positioned in such a manner that no support portion comes into contact with the surface configured to be in contact with the air stream during fabrication, and wherein making the bladed stator ring sector with said additive manufacturing is performed without any physical support engaging the surface configured to be in contact with the air stream.

8. The method according to claim 7, wherein at least one inter-support reinforcing portion is added to the digital model to connect together at least two adjacent support portions, said inter-support reinforcing portion being disjoint from the surface configured to be in contact with the air stream.

9. The method according to claim 7, further comprising: removing the supports; and automatically polishing the surface configured to be in contact with the air stream.

10. The method according to claim 1, wherein the construction angle is greater than 50°.

11. The method according to claim 1, wherein, at a given point of the bladed stator ring sector, forming a portion of a given fabrication layer, the construction angle corresponds to an angle measured in a plane orthogonal to the construction plane between the construction plane and a straight line connecting the given point of the bladed stator ring sector through a closest point of the bladed stator ring sector forming a portion of an underlying fabrication layer.

12. The method according to claim 1, wherein the surface configured to be in contact with the air stream includes all of the surfaces of the part configured to be in contact with the air stream.

13. The method according to claim 1, wherein the bladed stator ring sector includes a plurality of vanes extending radially between an inner shroud and an outer shroud, and wherein the plurality of vanes, the inner shroud, and the outer shroud are free from any support during fabrication of the bladed stator ring sector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantages can be better understood on reading the following detailed description of various implementations of the invention given as non-limiting examples. The description refers to the accompanying sheet of figures, in which:

(2) FIG. 1 is an overall view of a device for additive manufacturing by selective melting of powder beds;

(3) FIGS. 2A and 2B are elevation views of an example model of a part that is to be fabricated;

(4) FIG. 3 is a perspective view of an example model of a part that includes an elongate portion;

(5) FIG. 4 is a perspective view of an example model of an aeronautic part that is to be fabricated; and

(6) FIG. 5 is a section view of the model of FIG. 4.

DETAILED DESCRIPTION OF IMPLEMENTATIONS

(7) FIGS. 2A and 2B are elevation views of a model 50 of a part that is to be fabricated on a construction platform 40 by an additive method of fabricating a part. The direction of construction, corresponding to the axis Z, is perpendicular to the construction plane that corresponds to the top surface 40a of the construction platform 40. A surface 50a of the model 50 of the part presents a construction angle β relative to the surface 40a of the construction platform. When this construction angle β is less than 30°, the surface 50a runs the risk of collapsing during fabrication: it is then preferable to arrange supports 60 for the surface 50a of the model 50 of the part in order to hold this surface 50a while the part is being fabricated.

(8) FIG. 3 is a perspective view of a model 70 of a portion that is elongate in the meaning of the present disclosure. The elongate portion has a front face 70b and a side face 70a, the front face 70b being narrower than the side face 70a. The construction direction, corresponding to the axis Z, is perpendicular to the top surface 40a of the construction platform 40, which extends in the X-Y plane, and the scanning direction corresponds to the travel direction of the spreader tool, e.g. a roller, that moves along the direction X. The side face 70a presents a construction angle β relative to the X-Y plane, and the direction in which the model 70 of the elongate portion extends in the X-Y construction plane presents an angle ε relative to the scanning direction X.

(9) As explained above, in the teaching of the present disclosure, the model 70 of the elongate portion is oriented in such a manner that the angle β is greater than 30° so as to avoid putting supports into place for holding the face 70a during fabrication of the part. Furthermore, in order to minimize the surface area of the part facing the spreader tool while it is moving in the scanning direction, it is preferable to minimize the angle F so that the elongate portion extends substantially in the scanning direction. Thus, when the spreader tool moves to deposit a top powder layer, it substantially faces the front face 70b. Since the front face 70b is small compared with the side face 70a, this minimizes any risk of the spreader tool becoming blocked by coming into abutment against said front face.

(10) With reference to FIGS. 4 and 5, there follows a description of an example method of fabricating a part by additive manufacturing. In this example, the part that is to be fabricated is a stator sector of a high-pressure compressor of a turbine engine, the sector having a plurality of vanes 170 extending radially between an inner shroud 181 and an outer shroud 182, these inner and outer shrouds 181 and 182 forming a passage in which the stream of working air flows when the turbine engine is in operation. This stator sector also has a ring sector 183 extending concentrically radially inwards from the inner shroud 181 and designed to carry an abradable track for providing sealing with the rotor. The stator sector has an axial direction A that is parallel to the central axis of the complete stator, and also a midplane M. The axial direction A corresponds substantially to the flow direction in operation of the stream of working air through the stator sector.

(11) A first step of the fabrication method seeks to model the part that is to be fabricated, or to acquire such a model that already exists and that is to be modified in accordance with the present disclosure. On this occasion, a holder block 110 is added to the model of the part at each of its circumferential ends, thereby serving to ensure cohesion for the inner and outer shrouds 181 and 182 and for the ring sector 183 during fabrication.

(12) This model is then placed in a fabrication space corresponding to the fabrication machine, and having three orthogonal directions X, Y, and Z. It also includes a model of the construction platform 140 lying in the X-Y plane, and a construction direction extending along the axis Z perpendicular to the X-Y plane and corresponding to the direction in which the successive powder layers are to be stacked during fabrication. Finally, it includes a scanning direction, extending along the axis X, that corresponds to the direction in which the roller used for depositing the powder layer by layer moves.

(13) Thereafter, surfaces that are to be spared are identified in the part that is to be fabricated. In the example of FIG. 4, the surfaces that are to be spared are the surfaces that come into contact with the air passing through the bladed stator ring, i.e. between the vanes 170, the inner shroud 181, and the outer shroud 182.

(14) Thereafter, a step of the fabrication method seeks to take the model 100 of the part as provided in the preceding step, and orient it relative to the X-Y construction plane, i.e. the top surface 140a of the construction platform 140. In this example, the model 100 is oriented in such a manner that the axial direction A of the sector forms an angle of about 55° (±10°) relative to the X-Y construction plane. By orienting the sector in such a manner, the main direction of the shrouds 181 and 182 forms an angle of 55° (±10°) relative to the X-Y construction plane; the main direction B of each of the vanes 170 forms an angle of 35° (±10°) relative to the X-Y construction plane.

(15) Once the model is oriented relative to the X-Y construction plane, it is then modified so as to have support portions 160 enabling the part to be held during fabrication. As a result of the above-mentioned orientation, it is possible to leave the vanes 170 and the shrouds 181 and 182 free from any support. In contrast, it is possible to provide support portions in association with zones other than those surfaces that are to be spared. More precisely, in this example, support portions 160 are arranged in association with the downstream end surface 182v of the outer shroud 182 and the downstream end surface 181v of the inner shroud 181 of the sector. Support portions 160 are also arranged in association with the downstream end surface 183v of the ring 183 and in association with the upstream inside surface 183m, given that the ring 183 is not designed to come into contact with the air stream. Naturally, it is possible to provide support portions 160 freely for the holder blocks 110, since those blocks are to be removed once the part has been fabricated.

(16) While designing the support portions, grooves or gaps 162 are also included so as to subdivide the support 160 into a plurality of segments. These grooves or gaps correspond to spaces that are not melted during fabrication.

(17) Furthermore, the support portions 160 are designed so as to include holes 120 giving easier access to zones of the part that are difficult to access, and also so as to be able to recover and recycle unused powder at the end of fabrication.

(18) Finally, while designing the support portions, inter-support reinforcing portions 164 are arranged transversely between adjacent support portions 160 and they are connected to those supports so as to reinforce the mechanical strength of the supports connected together in this way. These inter-support reinforcing portions 164 may also be provided under the vanes 170 and the shrouds 181 and 182 since they are disjoint from those surfaces, i.e. they do not touch the corresponding surfaces.

(19) Once these steps have been completed, a step is performed seeking to orient the model 100 about the axis Z so that the midplane M of the stator sector is in alignment with the scanning axis X. Thus, in the scanning plane, the chord of each of the vanes 170 forms an angle lying in the range 0° to 30° relative to the scanning axis X, so that the leading edge 170a of each vane 170 is substantially facing the roller when it moves in the scanning direction X.

(20) Once this orientation step has been performed, certain edges of the part facing the roller as it moves in the scanning direction X are then identified in the resulting model: these edges are then chamfered. Thus, in the model 100 for the stator sector, the edges 112 of the holder blocks 110 are chamfered. Without having such chamfers, the salient angles of the part might deform during fabrication under the effect of the heat generated by laser melting, thereby running the risk of blocking the spreader tool.

(21) Thereafter, the method includes a step of fabricating the part proper by additive manufacturing on the basis of the resulting modified model.

(22) Once the fabrication method has terminated and the raw fabricated part is obtained, the supports 160 are removed. The resulting part possesses vanes 170 and inner and outer shrouds 181 and 182 presenting a final surface state that is uniform. It is then possible to polish those parts automatically without any need for prior manual polishing, thereby making it possible to preserve the aerodynamic properties of the part.

(23) Although the present invention is described with reference to specific examples, it is clear that modifications and changes may be made to those examples without going beyond the general ambit of the invention as defined by the claims. In particular, individual characteristics of the various implementations shown and/or mentioned may be combined in additional implementations. Consequently, the description and the drawings should be considered in a sense that is illustrative rather than restrictive.

(24) It is also clear that all of the characteristics described with reference to a method can be transposed singly or in combination to a device, and vice versa, all of the characteristics described with reference to a device can be transposed, singly or in combination, to a method.