Method for manufacturing a part of complex shape by pressure sintering starting from a preform

Abstract

This invention relates to a method for manufacturing a part of complex shape (3) by successive deposition of layers according to a technique of 3D additive printing and pressure sintering, comprising the following steps: an initial step of producing a model (1) from a material chosen from a porous or pulverulent material based on a metal alloy, a ceramic, a composite material and a lost material by formation of successive layers deposited according to the digitally controlled 3D additive printing technique, followed by a step of introducing a preform (1) made of porous or pulverulent material to be densified, derived from the model (1), into a mold (2) filled with a sacrificial porous or pulverulent material (13) in addition to the preform (1), the uniaxial densifying pressure sintering (10) then being applied to the mold (2) in order to form the part (3) which is finally extracted from the mold (2).

Claims

1. A method for manufacturing a part of complex shape by successive deposition of layers according to a technique of 3D additive printing and a pressure sintering, the method comprising the steps of: producing a model from a material chosen from porous or pulverulent materials based on a metal alloy, a ceramic, a composite material, or a lost material by formation of successive layers deposited according to a 3D additive printing technique which is digitally controlled; producing a preform from the model, the preform is made of porous or pulverulent material derived from the model, covering at least one face of the preform with a graphite layer to form an interface layer; introducing the preform covered with the graphite layer into a mold filled with sacrificial porous or pulverulent material; applying a pressure sintering under a uniaxial densifying pressure to the mold to form the part which is finally extracted from the mold; wherein pressure sintering is performed to a load between 50 MPa and 100 Pa and a direct current between 3000 A and 10000 A; wherein the 3D additive printing technique is chosen from stereolithography, binder jetting, controlled extrusion, fused filament fabrication, inkjet printing, or aerosol jet printing; and wherein the mold is filled with a pulverulent or porous sacrificial material before and after introduction of the preform, the sacrificial material being chosen from a ceramic, a silica, a metal silicate, or a composite material.

2. The method as claimed in claim 1, wherein the materials of the preform, of the interface layer, and of the sacrificial material have the same densifying behavior at a sintering start and end temperatures.

3. The method as claimed in claim 1, wherein the sacrificial material is a ceramic, the ceramic is chosen from YSZ, ATZ, ZTA and alumina powder exhibiting degrees of densification that range from 40 to 80%.

4. The method as claimed in claim 1, wherein the interface layer is applied in a form chosen from a spray, a powder deposit, and a sheet having a shape similar to a shape of the preform.

5. The method as claimed in claim 1, wherein the metal alloy of the part to be manufactured is chosen from a titanium alloy, a stainless steel, and a Ren nickel-based superalloy.

6. The method as claimed in claim 1, further including a step of removing a binder from the preform is performed at the output of the 3D additive printing by means of a heat treatment at temperatures of between 20 and 600 C. and rates of temperature rise of between 0.1 and 1 C./min.

7. The method as claimed in claim 6, wherein the step of binder removal is followed by a step of pre-sintering by heat-treating the preform at a temperature of between 60 and 1500 C.

8. The method as claimed in claim 1, wherein the model made of porous or pulverulent material constitutes the preform before the densification in the mold.

9. The method as claimed in claim 1, wherein the model is produced from lost material by additive printing, wherein a counterform made of porous or pulverulent material is formed around said model, wherein the lost material is removed, the counterform is then filled with the material to be densified which constitutes the preform corresponding to the model, before being introduced into the pressure sintering mold, and wherein the sacrificial material is added to the mold and in that, after application of the pressure sintering, the part is extracted from the counterform.

10. The method as claimed in claim 9, wherein the material of the counterform is chosen from a ceramic, a silica, a metal silicate, and a composite material, while exhibiting the same densifying behavior at the sintering start and end temperatures as that of the materials of the preform, of the sacrificial material and of the interface layer.

11. The method as claimed in claim 10, wherein the ceramic is chosen from powdered YSZ, ATZ, ZTA, or alumina having degrees of densification that range from 40 to 80%.

Description

PRESENTATION OF THE FIGURES

(1) Further information, features and advantages of the present invention will become apparent from reading the following non-limiting description given with reference to the attached figures which show, respectively:

(2) FIG. 1, perspective views of the main steps (1A to 1F) of one exemplary implementation of the method according to a first embodiment of the manufacture of a part of complex shape from a preform; and

(3) FIG. 2, schematic views in section of the main steps (2A to 2G) of one simplified exemplary implementation of the method according to a second embodiment of the manufacture of a part of complex shape from a preform.

DETAILED DESCRIPTION

(4) The main steps 1A to 1F of one example of the method for manufacturing a part of complex shape according to the invention are illustrated in FIG. 1 by views in section. In step 1A, a porous metal model 1 of the part to be manufactured is formed by jetting in successive layers according to a 3D additive printing technique, binder jetting in this example. The model reproduces a configuration pre-saved in the control unit of the jetting system (not shown) and constitutes the preform of the part to be obtained after sintering. This preform defines the geometry of the shape of the part to be manufactured in the manufacturing method according to the invention.

(5) The material of the part is initially in the form of a pulverulent or porous material, based on a metal alloy, in particular, in the examples illustrated, based on a titanium alloy, a titanium-aluminium alloy for example, a stainless steel or a nickel-based superalloy in the Ren family.

(6) Advantageously, removal of the binder from the preform in the form of a model 1 is implemented by heat treatment at temperatures of between 200 and 600 C., 400 C. in the example, with a rate of temperature rise of between 0.1 and 1 C./min, 0.5 C./min in the example. This step makes it possible to remove organic compounds which may be introduced into the ceramic powder during the 3D printing for producing the counterform portions.

(7) Preferably, pre-sintering is also performed after removal of the binder. This pre-sintering consists in treating the preform 1 at even higher temperatures, for example of between 600 C. and 1500 C. depending on the materials used, at 1200 C. in the example. This heat treatment makes it possible to start the densification of the counterform portions in order to give them mechanical strength and thus facilitate the application of the one or more interface layers, as described below.

(8) In step 1B, a graphite interface layer 11 is advantageously deposited uniformly by spraying onto the outer face 1e (see step 10) or the inner face 1i (see step 1A) of the preform 1. Alternatively, a graphite layer is sprayed onto both faces 1i, 1e of the preform 1. This graphite layer 11 makes it possible to prevent any interaction between the model 1 and the sacrificial pulverulent materialceramic in the examplewhich will be deposited later in order to facilitate final removal from the mold.

(9) With reference to step 1C, the preform 1 covered with the graphite layer 11 is introduced into the SPS pressure sintering mold 2 on a bed of sacrificial material of ceramic powder introduced beforehand (not visible). Next, the sacrificial powder 13 is also introduced into the mold 2 so that this mold 2 is filled with an assembly of materials to be densified (step 10). The sacrificial powder makes it possible to compensate for differences in densification during the subsequent sintering.

(10) SPS sintering is then applied to the mold 2 (load 10 of 50 MPa, direct current intensity of 3000 A, which results in the densification of the assembly of material contained in this mold 2 (step 1E). The densified part 3 is then removed from the mold 2 by unmolding and removing the portions of sacrificial material 13 which surround the part 3 (step 1F).

(11) According to another embodiment, as illustrated by the schematic views of steps 2A to 2G of FIG. 2, a lost-wax model 4 is first printed by stereolithography (step 2A). The model is cone-shaped in the example.

(12) A conical counterform 5 is then applied around the wax 4, in the form of a slip in the example illustrated (step 2B). Alternatively, the porous material forming the counterform may be a ceramic, a silica, a metal silicate, a composite material or the like.

(13) The wax 4 is then removed from the counterform 5 by way of suitable heating allowing this wax to be liquefied. The liquid escapes (arrow F1) through an opening 51 formed at the base of the counterform cone 5 which is thus completely emptied (step 2C).

(14) Advantageously, the counterform 5 is covered on its inner face 5i with a graphite interface layer 7 in order to facilitate removal from the mold and to prevent any interaction between the counterform and the material to be densified. Alternatively, a graphite layer is sprayed onto at least one of the faces 5i, 5e of the counterform 5.

(15) With reference to step 2D, the counterform 5 is filled with pulverulent material to be densified constituting the preform 6 of the part to be manufactured and corresponding to the wax model. The graphite layer 7 of the inner face 5i of the counterform 5 then covers the preform 6.

(16) Steps of binder removal and of pre-sintering are then advantageously implemented under the conditions of temperature and of rate of temperature rise described above.

(17) The counterform 5 and the preform 6 are then introduced into the SPS sintering mold 2 (step 2E) and sacrificial material 9 is additionally introduced into the mold 2. The sacrificial material is, in the examples illustrated, a material chosen from a ceramic, a silica, a metal silicate, a composite material or the like.

(18) The SPS densification is implemented by applying a load 10 and a direct current of 3000 A (step 2F). The sacrificial powder makes it possible to compensate for differences in densification during the sintering.

(19) The part 8 is then extracted from the mold 2 by unmolding, by removing the sacrificial material 9 and the counterform 5 (step 2G).

(20) The invention is not limited to the examples described and shown. Thus, the interface layers may be formed by a porous or pulverulent material other than graphite, in particular an yttrium oxide, boron nitride or the like.

(21) The first implementation is particularly suited to hollow parts, having convex and concave opposite faces, and the second implementation to solid, biconvex parts.

(22) Regardless of the implementation, the materials of the sacrificial material, of the counterform, of the preform and of the interface layers exhibit similar behavior with respect to the sintering start and end temperatures. The ceramic used is in the form of powder based on YSZ (yttria-stabilized zirconia), ATZ (alumina-toughened zirconia), ZTA (zirconia-toughened alumina), and alumina exhibiting degrees of densification that may range from 40 to 80%.

(23) In addition, the interface layers may be applied in a form chosen from a spray, a deposit of powder bound by a binder corresponding to the powder (aqueous solution, Rhodovil solution, etc.), a sheet of suitable shape or the like.

(24) Furthermore, in the first embodiment, the preform is directly the model in the example described. In general, this preform may also be derived from a base model by means of another 3D additive printing technique and/or by using another material, which makes it possible to change printing technique and printing material depending on the choice of the material for the part to be manufactured.