METHOD FOR PRODUCING A COUNTER-FORM AND METHOD FOR MANUFACTURING A PART HAVING A COMPLEX SHAPE USING SUCH A COUNTER-FORM

Abstract

A method for producing a counter-form (20) for manufacturing a part having a complex shape (24) by pressure sintering densification. The counter-form (20) is formed from successive layers produced by numerically-controlled three-dimensional (3D) additive printing according to the following steps: numerically recording a three-dimensional negative of the part to be produced (24) in a control unit of a three-dimensional additive printing system in order to constitute the positive form of the counter-form to be produced; producing the counter-form (20) using a 3D additive printing technique. The part having a complex shape (24d) is then manufactured by pressure sintering, then separated from the counter-form which is also sintered (20).

Claims

1. A method for producing a counterform (20, 30a, 30b) for manufacturing a part of complex shape (1; 24d) by pressure sintering densification, the counterform (20; 30a, 30b) is formed of successive layers produced by digitally controlled three-dimensional (3D) additive printing, method comprising the following steps: digitally recording a three-dimensional negative (3) of the part to be produced (1; 24d) in a control unit of a three-dimensional additive printing system in order to make a print of the counterform (20; 30, 30b) to be produced, the rest of the counterform having faces of suitable shape for a mold for manufacturing the part (1; 24d); producing the counterform (30a, 30b) by means of a 3D additive printing technique, the size of the counterform (20; 30a, 30b) being increased by a density stretch factor that compensates for a shrinkage in the size of the part to be manufactured (1; 24d) in the direction of the uniaxial pressure (F) applied during the sintering densification of the part to be manufactured; and completing the additive printing of the counterform (20; 30a, 30b) by sintering.

2. The method for producing a counterform as claimed in claim 1, wherein the 3D additive printing technique is chosen from stereolithography, binder jetting, controlled extrusion, fused filament fabrication, inkjet printing, or aerosol jet printing.

3. The method for producing a counterform as claimed in claim 1, wherein the counterform (20; 30a, 30b) is produced from a porous material chosen from a ceramic, a silica, a metal silicate, or a composite material.

4. The method for producing a counterform as claimed in claim 1, wherein the printing is performed with a thickness of the walls of the counterform (20; 30a, 30b) that is less than or equal to five millimeters.

5. The method for producing a counterform (20, 30a, 30b) as claimed in claim 1, further including the step of removing the binder from the counterform (30a, 30b) at the output of the 3D additive printing by a heat treatment at a temperature of between 200 and 600° C. and rates of temperature rise of between 0.1 and 1° C./min.

6. The method for producing a counterform as claimed in claim 5, wherein the step of binder removal is followed by a step of pre-sintering by heat-treating the counterform (3a, 30b) at a temperature of between 600 and 1500° C.

7. The method for producing a counterform as claimed in claim 1, wherein said counterform is, in a subsequent step, divided into at least two portions (30a, 30b) that are joined along at least one joint plane (P) so as to eliminate at least one undercut, the joint plane (P) between the portions (30a, 30b) separating the complex shape into portions (30a, 30b) that can be removed from the mold directly.

8. A method for manufacturing a part of complex shape (1; 24d) by sintering using a counterform (20; 30a, 30b) produced by the method according to claim 7, wherein the method includes the following steps: bringing the counterform portions (20, 30a, 30b) together in a densification mold for sintering under uniaxial pressure; introducing a pulverulent or porous material to be densified into at least one duct (4) that passes through a counterform portion (30a); densifying the pulverulent or porous material for sintering under uniaxial pressure (F); and separating the counterform portions (30a, 30b) to release the part (1; 24d) thus manufactured.

9. The manufacturing method as claimed in claim 8, wherein the counterform (20; 30a, 30b) is produced from a porous material chosen so that the materials of the counterform (20; 30a, 30b) and of the part to be manufactured (1; 24d) exhibit the same behavior on sintering.

10. The manufacturing method as claimed in claim 8, wherein the sintering start temperature, or sintering end temperature, of a ceramic of the counterform (20; 30a, 30b) is higher than or equal to, or higher than, respectively, of the part to be manufactured (1; 24d).

11. The manufacturing method as claimed in claim 10, wherein the ceramic is chosen from YSZ, ATZ, ZTA and alumina powder exhibiting degrees of densification that may range from 40 to 80%.

12. The manufacturing method as claimed in claim 8, wherein at least one open-ended duct (4) for filling with a pulverulent or porous material intended for forming the part (1; 24d) is provided outside the counterform (20; 30a, 30b).

13. The manufacturing method as claimed in claim 8, wherein the sintering of the counterform (20; 30a, 30b) is applied at the same time as the sintering of the part to be manufactured (1; 24d).

14. The manufacturing method as claimed in claim 8, wherein the porous or pulverulent material of the part be manufactured (1; 24d) is chosen from a ceramic, a metal alloy, a polymer, or a composite material.

15. The manufacturing method as claimed in claim 14, wherein at least one of the outer walls of the counterform portion (30a, 30b) is voided and then filled with ceramic powder of which the sintering temperature is equal to that of the ceramic of the counterform portion (30a, 30b).

16. The manufacturing method as claimed in claim 8, wherein an interface of porous or pulverulent material (22; 42) is arranged between the counterform (20; 30a, 30b) and the material to be densified (24).

17. The manufacturing method as claimed in claim 16, wherein the interface (22; 42) is formed by at least one layer of material chosen from graphite, an yttrium oxide and boron nitride.

18. The manufacturing method as claimed in claim 17, wherein the interface layer (22; 42) is applied in a form chosen from a spray, a powder deposit, or a sheet of suitable shape.

Description

PRESENTATION OF THE FIGURES

[0041] 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:

[0042] FIG. 1a shows an exemplary part of complex shape to be produced according to the method of the invention;

[0043] FIG. 1b shows a digital model of a three-dimensional negative of the part to be produced of FIG. 1a;

[0044] FIG. 2 shows schematic views in section of the main steps 2a to 2e of the method for manufacturing a part of complex shape according to the invention by means of sintering using a counterform produced by means of the method according to the invention;

[0045] FIG. 3a shows a from view of a counterform produced in the context of manufacturing the part of FIGS. 1a and 1b;

[0046] FIG. 3b shows affront view of another counterform produced in the context of manufacturing the part of FIGS. 1a and 1b;

[0047] FIG. 3c showsa front view of the two counterforms of FIG. 3a-3b brought together in a mold for densification by SPS pressure sintering; and

[0048] FIG. 4, a perspective view of the manufactured part.

[0049] In the figures, identical elements are identified by the same reference sign which refers to the one or more passages of the description in which it is mentioned.

DETAILED DESCRIPTION

[0050] With reference to FIG. 1a, an exemplary part 1 of complex shape to be produced according to the manufacturing method of the invention is presented. The plane “P”—parallel to the reference plane XOZ) is the joint plane of two counterforms to be produced beforehand (as will be explained below) in order to allow easy removal of the part from the mold once produced: specifically, the part 1 has in particular a recess “C” forming an undercut, which makes removal from the mold difficult. According to the invention, the recess “C” is then entirely on the side of one counterform.

[0051] FIG. 1b shows a digital model 3 of the three-dimensional negative 10 of the part 1 of FIG. 1a. This digital model 3 is produced in a control unit of a three-dimensional additive printing system (not shown), in order to make the positive form of the portions of the counterform to be produced. For ease of removal from the mold, this positive form is divided into two portions, as shown in FIG. 1a. The subsequent step is the production of each counterform portion by means of a 3D additive printing technique, stereolithography in the example, the result being presented with reference to FIG. 3 with the two counterform portions 30a and 30b.

[0052] FIG. 2 shows schematic views in section of the means implemented in the main steps 2a to 2e of the method according to the invention for manufacturing a part of complex shape 24d by means of sintering under uniaxial pressure, this method using a counterform 20 produced (step 2a) according to the invention by means of a 3D additive printing technique, stereolithography in the example, from bound ceramic powder.

[0053] In the case illustrated, a single dihedral counterform suffices for easy removal from the mold of the prismatic part 24d (cf. step 2e) of which the shape is considered to be complex in this simplified example. A graphite interface layer 22 of constant thickness is then deposited on the counterform 20 (step 2b) by spraying, and then the material to be densified 24 is added onto this interface 22 (step 2c). This interface 22 serves to prevent interaction between the counterform 20 and the powder 24 of the part to be manufactured.

[0054] The materials to be densified used in the example for manufacturing the part are metal alloys, a TiAl alloy (titanium and aluminum alloy) and a nickel-based superalloy in the Rene family.

[0055] Advantageously, the material of the counterform 20 is chosen so that the materials of the counterform and of the part to be manufactured 24 have similar behavior on sintering, in terms of sintering start and end temperatures and of degree of densification.

[0056] In the case of the alloys used for the part to be manufactured, the ceramic used for the counterform is then ATZ (alumina-toughened zirconia) for a part made of TiAl, and YSZ (yttria-stabilized zirconia) for the nickel-based superalloy selected from the Rene family. More generally, the sintering start temperature (or sintering end temperature) of the ceramic used for the counterform is higher than or equal to (or higher than, respectively) that of the metal alloy of the part to be manufactured.

[0057] SPS sintering under uniaxial pressure of the material to be densified 24 also densifies the counterform 20 in this example (envisaging shrinkage of −10% to −45%), the material 24 and the counterform 20 being introduced into an SPS mold (not shown).

[0058] In envisaging this densification, the size of each counterform portion 20 is increased in order to anticipate the shrinkage of the part 24 in the direction of SPS sintering with the uniaxial pressure “F” exerted (step 2d). The geometry of the part 24 is thus “stretched” beforehand by a stretch factor “Fe” in order to compensate for this shrinkage in size of the part. The factor Fe is defined by the ratio of the density of the powder to be densified to the density of the densified powder. Advantageously, the simplified geometry of the counterform portions 20 may easily change in the case of a change in the value of the factor Fe.

[0059] Thus, in this exemplary embodiment, the uniaxial pressure “F” results in a decrease in the maximum height of the counterform 20 by 40%, this height going from a value “H” (step 2c) to a value “h” (step 2d). This decrease in height allows the part 24d to be manufactured with the intended height, the initial height “H” having been increased by applying the coefficient Fe. The condensed counterform and part, referenced 20d and 24d, are then easily separated (step 2e).

[0060] The views of FIGS. 3a and 3b present a counterform made of ATZ ceramic in the form of portions 30a and 30b, in the context of the example of manufacturing the part 1 made of TiAl according to FIGS. 1a and 1b, the ATZ ceramic and the TiAl alloy having similar behaviors on sintering. These counterform portions 30a and 30b have joining faces 40a and 40b in the joint plane “P” (cf. FIG. 1a).

[0061] Advantageously, removal of the binder from the counterform portions 30a, 30b is implemented by a 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 the organic compounds which may be introduced into the_ceramic powder during the 3D printing for producing the counterform portions.

[0062] Preferably, pre-sintering is also performed after removal of the binder. This pre-sintering consists in treating the counterform portions with binder removed 30a, 30b at even higher temperatures, for example 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.

[0063] The two half-impressions 41a and 41b of the part to be manufactured are covered with graphite 42 by spraying, and then with a layer based on yttrium oxide in order to prevent reaction between the ceramic and the material of the part to be manufactured, TiAl in the example. For the production of the counterform by means of stereolithography, the counterform divided into two portions allows unpolymerized paste to be removed. Additionally, the counterform portions 30a, 30b advantageously have a maximum thickness of 5 mm in order to avoid any risk of cracking during the sintering and the heat treatment for binder removal when recovering the part.

[0064] With reference to FIG. 3c, the two counterform portions 30a, 30b are joined together in an SPS sintering mold 2 so that the two half-impressions 41a, 41b form a single impression corresponding, in negative, to the part to be manufactured. The filling of this impression with TiAl powder is performed via the three hollow ducts 4. These ducts 4 pass through the face 42a opposite the joint face 40a of the counterform portion 30a (cf. FIG. 3a). The ducts 4 also allow any excess TiAl powder to be removed as necessary.

[0065] The outer walls of one or more counterform portions 30a, 30b may advantageously be voided, in order to facilitate their production by 3D printing. These voided spaces are then filled with YSZ (yttria-stabilized zirconia) powder which has a sintering temperature equivalent to that of the ATZ counterform ceramic used.

[0066] During the SPS sintering under uniaxial pressure, the ceramic and the metal alloy of the part to be manufactured will sinter simultaneously, the sintered ceramic covering the metal part. By virtue of the interface layers of graphite and of yttrium oxide 42 (cf. FIGS. 3a and 3b), the ceramic is easily separated from the part by freeing it mechanically and/or chemically. FIG. 4 illustrates the final part 1 obtained with some ceramic residues 43 still to be removed.

[0067] The invention is not limited to the exemplary embodiments described and shown. Thus, the counterform may be divided into a minimum number of portions in order to avoid undercuts in the part to be manufactured.

[0068] Furthermore, the counterform may be structured with localized regions of weakness without site restriction, in order to facilitate final removal from the mold.

[0069] Additionally, the part to be manufactured may be formed of a metal alloy powder, a ceramic, a composite material or any type of suitable material.