METHOD FOR FINISHING A PART MADE BY DEPOSIT AND SOLIDIFICATION OF SUCCESSIVE LAYERS OF POWDER AND THE PART OBTAINED BY THIS METHOD

Abstract

TITLE: METHOD FOR FINISHING A PART MADE BY DEPOSIT AND SOLIDIFICATION OF SUCCESSIVE LAYERS OF POWDER AND PART OBTAINED BY THIS METHOD. One aspect of the invention relates to a method for finishing a part made by depositing and solidifying successive layers of a powder, characterized in that it comprises: a roughing step (E1) by sandblasting a portion of a surface of the part with an initial roughness (Ra0) using a first sand (S1) having a rough grain size (G1) and projected at a rough sandblasting angle (A1) and a rough sandblasting pressure (P1) until a rough roughness (Ra1) of the portion of the surface of the part is achieved, and a finishing step (E2, E2') of the portion of the surface of the part until a Final roughness (Ra2) of the surface area of ​​the part, with the final roughness (Ra2) lower than the roughing roughness (Ra1). Figure to be published with the abbreviation: Figure 2

Description

Title of the invention: METHOD FOR FINISHING A PART PRODUCED BY DEPOSITION AND SOLIDIFICATION OF SUCCESSIVE LAYERS OF A POWDER AND PART OBTAINED BY THIS PROCESS TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of additive manufacturing and particularly to the powder bed laser fusion process.

[0002] The present invention relates more particularly to a method of finishing a part by depositing and solidifying successive layers of a powder, and a part obtained by this method. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] The laser powder bed fusion process, or Laser Beam Melting (LBM) or Laser Metal Deposition (LMD) in English terminology, is an additive manufacturing technology, also called three-dimensional (3D) printing involving the use of a 3D printer.

[0004] The powder bed laser fusion process allows the shaping of metal parts using metal powders. For example, direct metal laser sintering (DMLS) technology and electron beam melting (EBM) technology use metal powders such as aluminum, chromium, cobalt, etc. These different technologies of the powder bed laser fusion process allow the manufacturing of three-dimensional parts by adding material, that is to say by depositing and solidifying successive layers of a powder. This type of process differs from so-called "conventional" manufacturing processes, according to which the parts are produced by foundry and machining processes.

[0005] The powder bed laser fusion process is increasingly used for the manufacture of parts or tools in the aeronautical field and in particular for the production of turbomachine air veins or foundry molds.

[0006] Conventionally, the laser powder bed fusion process uses a 3D printer equipped with a laser to scan certain areas of a powder layer so as to fuse and solidify the powder particles of the layer to create a two-dimensional slice of the part. This step is repeated n times along a deposition axis Z until the final three-dimensional part 10 is created.

[0007] As shown in [Fig. 1], the final part 10 produced by a fusion process powder bed laser includes: - n layers of thickness e superimposed along a Z axis, including a first layer 100A, a last layer 100B opposite the first layer along the Z axis and n intermediate layers 100n, and - a first main surface 10A and a last main surface 10B connected to each other by a first and a second lateral surfaces 10C and 10D.

[0008] Generally, the surface condition of the parts 10 produced by a laser powder bed fusion process has defects and high roughness. For example, as illustrated in [Fig. 1], the superposition of the layers 100A, 100N, 100B of powder has an offset relative to each other causing a “staircase effect” of the first and second lateral surfaces 10C, 10D according to which the first lateral surface 10C is a supported surface (called up-skin surfaces in English terminology) and the second lateral surface D is an unsupported surface, called downskin. During the manufacture of the part 10 by laser powder bed fusion, the first lateral surface 10C faces the laser and the second lateral surface 10 is opposite the laser. Consequently, the second lateral surface 10D has a more unfavorable surface condition than that of the first lateral surface 10C. Further, as illustrated in [Fig.l], in certain cases, powder particles 12 bind to the second lateral surface 10D. These two phenomena depend on the orientation of the production of the part 10, that is to say on the orientation angle of the laser relative to the layer 100 of powder to be fused.

[0009] Consequently, the roughness of a part 10 produced by a laser powder bed fusion process is between 0.005 mm and 0.05 mm compared to a roughness between 0.001 mm and 0.004 mm for a part produced by a conventional manufacturing process such as by casting. Additive manufacturing by laser powder bed fusion does not make it possible to obtain surface conditions equivalent to those of a part produced by conventional manufacturing processes.

[0010] Furthermore, the surface condition inside the turbomachine veins directly influences the aerodynamics of the part and also the deposition capabilities of a protection against oxidation and / or corrosion on the surface. In addition, the surface condition of the foundry molds directly influences the roughness of the functional surfaces of the tools produced by casting. There are finishing processes also called finishing processes, making it possible to improve at least part of the surface condition of a part after its manufacture, for example by machining, milling or even robotic polishing. However, this type of finishing technique is not applicable to parts of the surface of a part that are difficult to access, such as the inside of a turbomachine vein, and does not make it possible to carry out a localized surface treatment of only a part of a surface of the part, in particular parts with a particularly unfavorable surface condition.

[0011] It is therefore important to find a solution to improve the surface condition of parts produced by additive manufacturing and more particularly by a laser fusion process on a powder bed, whatever the accessibility or complexity of the surface to be reworked. Summary of the invention

[0012] The invention offers a solution to the problems mentioned above, by proposing a method for finishing a part produced by depositing and solidifying successive layers making it possible to finish the surface condition of the part after its manufacture.

[0013] A first aspect of the invention relates to a method for finishing a part produced by depositing and solidifying successive layers of a powder comprising: - a roughing step by sandblasting a part of a surface of the part with initial roughness using a first sand having a roughing granulometry and projected at a roughing sanding angle and a sanding pressure to a roughing roughness of the part of the surface of the part, and - a step of finishing the part of the part of the surface of the part to a final roughness of the part of the surface of the part, with the final roughness lower than the roughing roughness.

[0014] The finishing method according to the invention makes it possible, thanks to the use of sandblasting as a finishing means, to reduce the roughness of a part of a surface of a part produced according to the laser powder bed fusion method by precisely targeting the parts of the part to be finished such as complex parts with low accessibility such as veins having heterogeneous roughness, but also the flat and accessible surfaces of unmachined parts such as functional surfaces of a tool or the surface of foundry molds. The roughing step makes it possible to reduce the roughness of the part of the surface in a homogeneous manner, then the finishing step makes it possible to reduce the roughness of the part of the surface again to a target roughness value.

[0015] Advantageously, the final roughness value is less than 0.003 mm corresponding to a target roughness value.

[0016] Preferably, the roughing sanding angle is between 45° and 90° and is preferably substantially equal to 80° so as to break the roughness peaks.

[0017] Advantageously, the value of the roughing grain size is between 0.10 mm and 0.50 mm so as to obtain a roughing roughness significantly lower than the initial roughness.

[0018] According to a first embodiment of the finishing step, the finishing step is carried out by sandblasting the part of the surface of the rough roughness part using a second sand having a final grain size and projected according to a final sandblasting angle and a sandblasting pressure, the value of the grain size of the first sand being less than the value of the grain size of the second sand.

[0019] Advantageously, according to the first embodiment of the finishing step, the final sanding angle is between 10° and 30° and is preferably substantially equal to 10°.

[0020] Preferably, according to the first embodiment of the finishing step, the value of the final grain size is between 0.045 mm and 0.10 mm so as to obtain a final roughness significantly lower than the roughness of the roughing.

[0021] According to a second embodiment of the finishing step, the finishing step is carried out by a superfinishing process such as machining by extrusion of abrasive paste, tribonfinishing, smirotropy, electrochemical polishing or chemical polishing.

[0022] According to a variant of the first embodiment of the finishing step, the sandblasting pressure values ​​of the roughing step and the finishing step are equal.

[0023] According to another variant of the first mode of the finishing step, the sandblasting pressure value of the roughing step is lower than the sandblasting pressure value of the finishing step in order to limit erosion phenomena.

[0024] Advantageously, according to the first and second embodiments of the finishing step, the sandblasting pressure value is between 1.5 and 3.5 bars, preferably substantially equal to 2.5 bars. A pressure value substantially equal to 2.5 makes it possible to reduce the phenomena of erosion and deformation of the material of the part of the surface of the part.

[0025] A second aspect of the invention relates to a part produced by deposition and solidification of successive layers of a powder obtained by the method according to any one of the preceding claims.

[0026] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0027] Other advantages and characteristics of the invention will appear on reading the following description, illustrated by the figures in which: - [Fig.l], already described, is a schematic representation of a part produced by a laser powder bed fusion process; - [Fig.2] is a block diagram representing the steps of a finishing process according to a first embodiment of the invention; - [Fig.3] is a block diagram representing the steps of a finishing process according to a second embodiment of the invention; - [Fig.4] is a schematic representation of the sanding of a roughing step of the finishing process according to the first and second embodiments of the invention; - [Fig.5] is a schematic representation of the sanding of a finishing step of the finishing process according to the first embodiment of the invention. DETAILED DESCRIPTION

[0028] An example of the manufacturing method according to the invention is described in detail below, with reference to the accompanying drawings. These examples illustrate the characteristics and advantages of the invention.

[0029] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0030] Figures 2 and 3 represent the steps of a method of finishing a part 10 (visible in [Fig.l]) produced by additive manufacturing and more particularly according to a laser fusion method on a powder bed by deposition and solidification of successive layers of powder, according to a first ([Fig.2]) and a second ([Fig.3]) embodiment.

[0031] The finishing method according to the first and second embodiments of the invention makes it possible to finish a portion of a surface of the part 10 in two steps. A first roughing step E1 of the surface with initial roughness Ra0 makes it possible to obtain the portion of the surface with a roughing roughness Ral lower than the initial roughness Ra0. A second finishing step E2 makes it possible to obtain the portion of the surface with a final roughness Ra2 lower than the roughing roughness Ral. The final roughness Ra2 of the portion of the surface of the part 10 is advantageously less than 0.003 mm.

[0032] The finishing method according to a first embodiment of the invention, as illustrated in [Fig.2] comprises: - a roughing step El by sandblasting a part of a surface of the part 10 of initial roughness RaO using a first sand SI having a roughing granulometry G1 and projected according to a roughing sanding angle Al and a roughing sanding pressure PI up to a roughing roughness Ral of the part of the surface, and - a finishing step E2 by sandblasting the part of the surface of the part 10 with roughness Ral using a second sand S2 having a final grain size G2 and projected according to a final sandblasting angle A2 and a final sandblasting pressure P2 up to a final roughness Ra2 of the surface part.

[0033] More particularly, the roughing steps E1 and final E2 according to the first embodiment of the invention correspond to two successive operations of sandblasting the part of the surface of the part 10 with two sands S1, S2 of generally different grain sizes G1, G2 and according to different sandblasting angles A1, A2 with G1 greater than or equal to G2 and A1 greater than A2. Advantageously, the roughing step E1 by sandblasting is carried out on the parts of the surface of the part 10 having initial roughnesses RaO greater than the other parts of the surface so as to obtain a roughing roughness Ral that is homogeneous between the different parts of the surface of the part 10.

[0034] As illustrated in [Fig.4], the sandblasting of the roughing step E1 is carried out by a sandblaster 20 comprising a sandblasting nozzle 22 projecting the sand S1, S2 onto a portion of at least one of the surfaces 10C, 10D of the part 10 (here onto a portion of the second lateral face surface 10D) according to the following parameters: - grain size of the Gl sand between 0.10 mm corresponding to F120 sand in FEPA-F unit and 0.50 mm corresponding to F36 sand in FEPA-F unit, - sandblasting angle Al between 45° and 90°, - PI sandblasting pressure between 1.5 and 3.5 bars, - DTI firing distance corresponding to the distance between the nozzle 22 of the sandblaster 20 and the second lateral surface lOC of the part 10, the firing distance being between 100mm and 200mm, - sandblasting flow rate between 1kg / min and 3kg / min, - exposure time of the nozzle 22 of the sandblaster on the part of the second lateral surface 10D of the part 10 between 2 and 25 seconds, - nozzle diameter 22 between 6.0 mm and 12.0 mm.

[0035] In order to determine the influence of the different parameters during sandblasting on the roughness of the part 10 produced by laser powder bed fusion, a first series of tests was carried out on parts 10 in the form of rectangular test pieces, constructed according to a laser orientation angle of 45°. The sandblasting was carried out on the part of the second lateral surface 10D having the most unfavorable surface condition.

[0036] The results of the first series of tests are presented in [Table 1] below: No. Gl PI (bar) Al (°) DTI (mm) Flow rate (kg / min) Ral 1 F220 3.5 10 150 1.5 1.5 2 F220 2.5 10 150 1.5 1.2 3 F150 3.5 10 150 2.8 1.2 4 F150 2.5 10 150 2.8 1.3 5 F120 3.5 10 150 3 1.2 6 F120 3.5 10 150 2 1.2 7 F120 3.5 20 150 3 2 8 F120 3.5 30 150 3 3

[0037] As illustrated in [Fig.5], the sanding of the finishing step E2 is carried out in the same way as for the roughing step E1. The sanding parameters of the finishing step E2 are as follows:

[0038]

[0039]

[0040] - G2 sand grain size between 0.045 mm and 0.10 mm (corresponding respectively to F220 to F120 sands in FEPA-F units), - A2 sanding angle between 10° and 30°, - P2 sandblasting pressure between 2.0 and 3.5 bars, - firing distance DT2 corresponding to the distance between the nozzle 22 of the sandblaster 20 and the part of the second lateral surface 10D of the part 10, the firing distance being between 100mm and 200mm, - sandblasting flow rate between 1kg / min and 3kg / min, - exposure time of the nozzle 22 of the sandblaster on the second lateral surface 10C of the part 10 between 5 and 40 seconds, - nozzle diameter 22 between 6.0 mm and 2.0 mm. In order to determine the influence of the different parameters during sandblasting on the roughness of part 10, a second series of tests was carried out on rectangular specimens by carrying out a first roughing step El by sandblasting and a second finishing step E2 by sandblasting. The nozzle diameter value is set to 8mm. The results of the second series of tests are presented in [Table 2] below: Stage El Stage E2 No. G1 PI Al DTI Flow rate Ral G2 P2 A2 DT2 Flow rate Ra2 9 F80 4 10 150 3 2.7 F120 4 10 150 3 1.1 10 F80 4 10 150 2.8 2.8 F150 4 10 150 2.8 1 11 F80 4 10 150 1.5 3.1 F220 4 10 150 1.5 1 12 F120 3.5 10 100 3 1.5 F120 3.5 10 100 3 0.95 13 F120 2.5 80° 150 3 2.9 F120 3.5 10° 150 3 1 14 F120 2.5 45° 150 3 3.1 F120 3.5 10° 150 3 1.1

[0041] According to the results of the second series of tests, for a test piece 10 having undergone a roughing step E1, the finer the sand S2 used during the finishing step E2, the more the roughness of the surface portion decreases. Consequently, the roughing step E1 uses a first sand SI with a roughing grain size G1 of between 0.10 mm and 0.50 mm (corresponding respectively to sands F120 to F36 in FEPA-F units). The finishing step E2 uses a second sand S2 finer than the first sand SI, with a final grain size G2 of between 0.045 mm and 0.10 mm (corresponding respectively to sands F220 to F120 in FEPA-F units).

[0042] The roughing sanding angle A1 of the roughing step E1 is between 45 and 90° in order to break the roughness peaks of the part of the surface of the part 10. The final sanding angle A2 of the finishing step E2 is said to be grazing, that is to say it is between 10° and 30° in order to erode the material of the part of the surface of the part 10 and thus reduce the average peaks to troughs. Advantageously, the final sanding angle A2 is substantially equal to 10° to obtain a low final roughness value Ra2 of the part of the surface of the part.

[0043] However, on a part 10 in which the part of its surface is complex, a sandblasting angle A1, A2 of 45° still makes it possible to obtain a roughness of the part of the surface of less than 0.003 mm.

[0044] The rough sandblasting pressure value PI is substantially equal to 3.5 bars and the final sandblasting pressure value P2 is substantially equal to 3.0 bars. Advantageously, the sandblasting pressure value PI, P2 of steps E1, E2 is substantially equal to 2.5 bars so as to reduce the phenomena of erosion and deformation of the material of the part of the surface of the part.

[0045] The finishing method according to a second embodiment of the invention, as illustrated in [Fig.3] comprises the following steps: - roughing El by sandblasting a part of a surface of the part with initial roughness RaO using a first sand S1 having a roughing grain size G1 and projected at a roughing sanding angle Al and a roughing sanding pressure PI to a roughing roughness Ral of the part of the surface, and - E2' finish by a superfinishing process up to a final roughness Ra2 of the surface part.

[0046] More particularly, the roughing step E1 according to the second embodiment of the invention is similar to the roughing step E1 of the first embodiment. The sanding is carried out on the parts of the surface of the part having initial roughnesses RaO greater than the other parts of the surface so as to obtain a roughing roughness Ral that is homogeneous between the different parts of the surface of the part 10.

[0047] Then, the finishing step E2' corresponds to a superfinishing process such as machining by extrusion of abrasive paste (called extrud-hone), tribofinishing, smi-rutropy, electrochemical polishing and chemical polishing. The superfinishing process is carried out on a set of parts of the surface of the part having a substantially homogeneous roughness Ral. Indeed, this type of superfinishing process is suitable for the treatment of parts of the surface of the parts 10 having a homogeneous roughness.

[0048] The finishing method according to the second embodiment, thanks to the combination of a sandblasting operation and a superfinishing process, makes it possible to make combinations of industrial ranges (use of machining by extrusion of abrasive paste called extrud-hone which is only effective on parts having homogeneous roughness) not previously possible, thanks to the adaptation of the exposure times of the nozzle of the sandblaster on the surface of the part making it possible to obtain a uniform roughness approximately equal to 0.004 mm over the entire part.

[0049] The method for finishing a part 10 according to the invention offers a solution for finishing the geometrically most complex and poorly accessible parts of a part of a surface of a part 10 having a high and / or heterogeneous initial roughness RaO thanks to the use of sandblasting.

Claims

Claims

1. Method for finishing a part (10) produced by depositing and solidifying successive layers of a powder, characterized in that it comprises: - a roughing step (El) by sandblasting a portion of a surface of the part (10) of initial roughness (RaO) using a first sand (SI) having a roughing granulometry (Gl) and projected according to a roughing sanding angle (Al) and a roughing sanding pressure (PI) to a roughing roughness (Ral) of the portion of the surface of the part (10), and - a finishing step (E2, E2') of the portion of the portion of the surface of the part (10) to a final roughness (Ra2) of the portion of the surface of the part (10), with the final roughness (Ra2) lower than the roughing roughness (Ral).

2. Finishing method according to claim 1, characterized in that the value of the final roughness (Ra2) is less than 0.003 mm.

3. Finishing method according to any one of the preceding claims, characterized in that the rough sanding angle (Al) is between 45° and 90° and is preferably substantially equal to 80°.

4. Finishing method according to any one of the preceding claims, characterized in that the value of the roughing grain size (Gl) is between 0.10 mm and 0.50 mm.

5. Finishing method according to any one of the preceding claims, characterized in that the finishing step (E2) is carried out by sandblasting the part of the surface of the part (10) of roughness (Ral) using a second sand (S2) having a final grain size (G2) and projected according to a final sandblasting angle (A2) and a final sandblasting pressure (P2), the value of the final grain size (G2) of the second sand (S2) being less than the value of the rough grain size (Gl) of the first sand (SI).

6. Finishing method according to claim 5, characterized in that the final sanding angle (A2) is between 10° and 30° and is preferably substantially equal to 10°.

7. Finishing method according to claim 5 or 6, characterized in that the value of the final granulometry (G2) is between 0.045 mm and 0.10 mm.

8. Finishing method according to any one of claims 1 to 3, characterized in that the finishing step (E2') is carried out by a superfinishing process such as machining by extrusion of abrasive paste, tribonfinishing, smirotropy, electrochemical polishing or chemical polishing.

9. Finishing method according to any one of the preceding claims, characterized in that the sandblasting pressure value (PI, P2) is between 1.5 and 3.5 bars, preferably substantially equal to 2.5 bars.

10. Part (10) produced by deposition and solidification of successive layers of a powder obtained by the method according to any one of the preceding claims.