Method for manufacturing pieces made of ceramic material by the technique of additive manufacturing

Abstract

On a working platform of a stereolithography machine, is manufactured, by the technique of additive manufacturing, simultaneously but separately, from a same pasty photocurable ceramic composition: a green assembly made up of a support of the green piece and of the green piece on the support, the free surface of the latter imprinted by a first face of the green piece; and a green ceramic shaper whose free surface bears the imprint of a second face of the green piece opposed to the first face; in a kiln, is placed, on the green shaper thus obtained with its imprint turned upwards, the green assembly thus obtained with its green piece turned downwards in order for it to be received in the imprint of the shaper, and the green piece thus held between the shaper and the support is subjected to debinding and to sintering.

Claims

1. A method for manufacturing a piece made of ceramic material by additive manufacturing or stereolithography, comprising: forming said piece in a green state from a photocurable ceramic composition comprising a ceramic powder and an organic portion able to be destroyed by heating during debinding and including at least one photocurable monomer and/or oligomer and at least one photoinitiator; manufacturing, on a working platform (1) of a stereolithography machine by additive manufacturing, simultaneously but separately, and from a pasty photocurable ceramic composition: a green assembly, formed of a support (2) of the green piece and of said green piece located on the support (2), a free surface of the support bearing a first imprint (2a) of a first face of said green piece, said first imprint (2a) being shifted in space but equivalent to said first face of said green piece so as to allow said first face to be received in said support (2), and a spacing between the first face and the support being filled with pasty material able to be removed once said green assembly is formed, and a green shaper (4) formed of a piece made of ceramic material that has a free surface that bears a second imprint (4a) of a second face of said green piece opposed to said first face, said second imprint (4a) having a surface shifted in space but equivalent to said second face of said green piece so as to allow said second face to be received in said shaper (4); placing, in an oven, and on said green shaper (4) thus obtained with the second imprint (4a) turned upwards, said green assembly thus obtained with the green piece turned downwards in order for the green piece to be received in the second imprint (4a) of said shaper (4); and subjecting the green piece thus held between the shaper (4) and the support (2) to debinding and sintering operations, the first and second imprints being such that the piece is completely enclosed between them during the debinding and sintering operations, wherein the support (2) includes at least one hole (5) passing through the support (2) to the first imprint (2a) for allowing passage of a solvent for removal of uncured pasty material after the formation of the support-green piece assembly, the at least one hole (5) having a circular cross section.

2. The method according to claim 1, wherein the first imprint (2a) of the support (2) corresponds to a surface shifted by 100 to 600 μm in space of said first face of the green piece.

3. The method according to claim 1, wherein the second imprint (4a) of the shaper (4) corresponds to a surface shifted by 20 to 80 μm in space of said second face of the green piece.

4. The method according to claim 1, wherein the green piece is manufactured at an angle on the support (2), the angle of inclination of the support with respect to the platform (1) being between 1 and 45°.

5. The method according to claim 1, wherein the support (2) is formed so as to be provided with at least one cavity (6) in a wall of the support, said wall being opposite to a wall of the support that bears the first imprint (2a) of the green piece in order to be filled with a ballast material when the support (2) is in a firing position.

6. The method according to claim 1, wherein the support (2) and the green piece and/or the platform (1) and the support (2) are linked by anti-curling studs (7) formed during manufacturing in areas of the green piece which are inclined to curling, the studs (7) having a diameter between 50 and 800 μm.

7. The method according to claim 1, wherein, during the manufacturing step, successive layers of photocurable ceramic composition are formed, each layer caused to be cured by irradiation according to a pattern previously defined from a model for said layer, and after the manufacturing step, the green assembly and the green shaper (4) are subjected to a cleaning step so as to remove uncured photocurable composition.

8. The method according to claim 1, wherein, during the manufacturing step, the following steps are carried out to form hollow parts of the green assembly as space between the support and the piece and hollow parts within the piece: forming, through machining, at least one recess (Re) in at least one cured photocurable ceramic composition layer from an upper surface thereof; depositing in said recess to fill the recess with a sacrificial organic material able to be cured and to be destroyed by heating during the debinding; and curing the sacrificial organic material to obtain a horizontal surface at a same level as a cured ceramic composition layer, wherein each time the at least one recess is formed, the at least one recess being delimited according to one or more patterns previously defined from a computer model, and a depth is selected to ensure continuity of the piece to be manufactured, and wherein once the cured layers are stacked up, a green support-piece assembly is obtained, and the green piece being detached from its support during the debinding.

9. The method according to claim 1, wherein, at the manufacturing step, a stack of plural supports and green pieces is formed, and a shaper is formed, and at the firing step, a stack of plural shapers, green pieces, and supports is formed, opposite faces of each support configured to cooperate with corresponding green pieces.

10. The method according to claim 1, wherein the green piece is a foundry core.

11. The method according to claim 2, wherein the second imprint (4a) of the shaper (4) corresponds to a surface shifted by 20 to 80 μm in space of said second face of the green piece.

12. The method according to claim 4, wherein the angle of inclination of the support with respect to the platform (1) is between 15 and 25°.

13. The method according to claim 4, wherein the angle of inclination of the support with respect to the platform (1) is 20°.

14. The method according to claim 1, wherein the at least one hole (5) has a diameter between 2 and 8 mm.

15. The method according to claim 6, wherein the studs have a diameter between 300 and 400 μm.

16. The method according to claim 2, wherein the green piece is manufactured at an angle on the support (2), the angle of inclination of the support with respect to the platform (1) being between 1 and 45°.

17. The method according to claim 3, wherein the green piece is manufactured at an angle on the support (2), the angle of inclination of the support with respect to the platform (1) being between 1 and 45°.

Description

(1) In this drawing:

(2) FIGS. 1 and 2 are, respectively, simplified and schematic representations of a foundry core having a complex and precise shape and a smooth surface, such a core being used for the casting of a turbine blade;

(3) FIG. 3 is a diagram illustrating the curling phenomenon, phenomenon which can be observed in the known upright manufacturing of cores;

(4) FIG. 4 is a diagram illustrating the detachment and sliding phenomenon of the core, phenomenon which can be observed in some cases, for example, when the irradiation energy becomes too high;

(5) FIG. 5 is an exploded perspective schematic view of a support having an angled upper surface and of a foundry core intended to be placed on its imprint formed in the angled upper surface;

(6) FIG. 6 is a view corresponding to FIG. 5 with the core placed on its support;

(7) FIG. 7 shows, from the side, a support having an angled surface forming an imprint having received the foundry core, which one bent during the firing because of the uncontrolled creeping on the upper face of the green piece;

(8) FIG. 8 shows, in perspective, a manufacturing platform of a stereolithography machine on which a support-piece assembly and a shaper were manufactured simultaneously, according to the invention;

(9) FIG. 9 is an exploded perspective view showing the piece and the shaper;

(10) FIGS. 10 and 11 are exploded perspective views of the support, the piece and the shaper in inverted positions;

(11) FIG. 12 is a side cross-sectional view of the piece on its support;

(12) FIG. 13 illustrates the positioning of the support, the piece and the shaper for the firing;

(13) FIG. 14 shows, in its left part, the rear face of a support made according to a particular embodiment of the present invention, and, in its right part, in an exploded view, said support viewed in its front part and the piece;

(14) FIG. 15 is a view similar to the right part of FIG. 13, with the support of FIG. 14;

(15) FIG. 16A shows the support substantially as shown as in the right part of FIG. 14 but made according to a variant; and

(16) FIG. 16B is, on a larger scale, a view of the detail of FIG. 16A which constitutes the variant in question.

(17) When referring to FIG. 5, it can be seen that a support S and a foundry core NF are shown in an exploded view. The support S has an upper surface which is tilted at an angle α with respect to the horizontal plane and in which an imprint E is formed for the lower face of the foundry core NF.

(18) For the CAD manufacturing of the support S, the lower surface of the foundry core NF is transferred onto the angled face of the support S so as to create an imprint E; an “offset” operation in XYZ, that is to say a shift in the directions X, Y, Z, by 400 μm for example, is carried out on such a face; the foundry core is then placed at a distance in Z or a space between the support S and the lower face of the foundry core which can be 135 μm plus the polymerization depth, the polymerization depth being the paste depth which will be polymerized by a passage of the laser. The polymerization depth depends on the paste which is used as well as on the laser parameters: power, hatching gap, laser scanning speed. In order to manufacture foundry cores made of alumina, the polymerization depth is generally 125 μm or about 125 μm.

(19) FIG. 6 shows the foundry core NF, with recesses Re formed upon the foundry core NF through machining, in place on its support S.

(20) FIG. 7 illustrates that, during the firing, the foundry core NF bent because of the uncontrolled creep on its upper face.

(21) FIG. 8 shows a manufacturing platform 1 of a stereolithography machine on which were simultaneously manufactured, according to the invention: a support 2—foundry core 3 assembly; and a shaper 4.

(22) Thus, the shaper 4 according to the invention is manufactured next to the support 2 and to the foundry core 3. The manufactured foundry core 3—support 2 combination is only used once, having no role when manufacturing the foundry core 3. It allows to handle and to fire the foundry core 3 with no distortion or breakage.

(23) In FIG. 9, it can be seen the shaper 4 which takes the same form as the support 2 with an angled face in which an imprint 4a is formed for the upper face of the foundry core 3.

(24) For the CAD manufacturing of the shaper 4, the upper surface of the foundry core 3 is transferred onto the angled face of the shaper 4 so as to create the imprint 4a; an “offset” operation in XYZ, that is to say a shift in the directions X, Y, Z, by 50 μm for example, is carried out on such a face, the offset being less important than for the creation of the support 2. The shaper 4 therefore has a surface which is closer to the surface of the foundry core 3.

(25) FIGS. 10 and 11 show in an exploded view and in two different directions: the support 2 with its imprint 2a (which can be seen in FIG. 10) for the lower face of the core; the foundry core 3; the shaper 4 with its imprint 4a (which can be seen in FIG. 11) for the upper face of the foundry core.

(26) It can be seen that such a configuration according to the invention comprising the firing shaper 4 allows the foundry core 3 to be protected both by the support 2 and the shaper 4 when cleaning and handling, the distortions of the foundry core 3 during such steps being alleviated.

(27) FIG. 12 shows, on a larger scale, a cross-sectional view of the foundry core 3 during the manufacturing on its support 2, the space between the support 2 and the lower face of the foundry core 3 having been deliberately exaggerated in this view. Such a space is as described when referring to FIG. 5.

(28) As illustrated in FIG. 13, for the firing, the foundry core 3 is detached from its support 2 by debinding and sintered in a clamped way between the shaper 4 and the support 2, the shaper 4 being down, the foundry core 3, placed on the latter, and the support 2, placed on the foundry core 3 as it can be seen in the right part of FIG. 13.

(29) The foundry core is thus maintained in the right shape thanks to the pressure applied by the support 2 and the shaper 4.

(30) By placing the foundry core 3 on the shaper 4 and the support 2 on top thereof, the foundry core 3 is compressed on the face of the shaper 4 which is more “precise” than that of the support 2.

(31) The foundry core 3 keeps its dimensions after sintering, because the three pieces 2, 3 and 4 have the same shrinking, being made of the same material.

(32) With such a technique, the difference with respect to the dimensions is reduced to more or less 0.2 mm.

(33) Furthermore, with such a technique, low rigidity pieces can be distorted without breaking.

(34) When referring to FIG. 14, it can be seen that the support 2 was made according to a variant which comprises holes 5 which go through it in several places, leading to the imprint 2a. The diameter of such holes 5 can be between 2 and 8 mm, being for example 4 mm.

(35) When cleaning, the operator can pass cleaning solvent through such holes 5, the paste comprised between the foundry core 3 and the support 2 beginning to partially solubilize, facilitating the detachment of the foundry core 3.

(36) As it can also be seen in FIG. 14 and also in FIG. 15, the support 2 can be made according to another variant which comprises, in its surface which is opposed to the angled surface and which is intended to be on top thereof during the firing (FIG. 15), cavities 6, here three in number and with a square shape, which are intended to receive beads or sand during the firing in order to provide an additional pressure on the foundry core 3, and thus to control the creeping of the latter during the firing.

(37) The support 2 shown in FIGS. 14 and 15 also comprises holes 5, which ones lead to the bottom of the cavities 6.

(38) The beads inserted into the cavities 6 should have a diameter greater than that of the holes 5. If sand or small beads are used, the holes 5 should be plugged.

(39) The shape and the number of cavities 6 can vary. The cavities 6 can be filled unequally if the creeping of the foundry core 3 on only certain areas thereof is desired to be controlled.

(40) If cleaning holes 5 remain free during the sintering, they will serve as a chimney to facilitate the discharge of organic materials.

(41) Now, when referring to FIGS. 16A and 16B, it can be seen that is shown a variant of the support 2 which comprises, in the bottom of the imprint 2a, an area comprising anti-curling studs 7, such studs linking the foundry core 3 being manufactured and the support 2 and being intended to prevent the flat surfaces of the foundry core 3 from bending. Their diameter can be between 50 and 800 μm, especially between 300 and 400 μm. The studs 7 are broken when the foundry core 3 is detached from the support 2.

(42) In FIGS. 10 and 11 as well as 13 (right part), it can be seen that the shaper 4 has, in its base, cavities of the type of the cavities 6 of the support 2. Such cavities shown in the shaper 4 only have the function to limit the ceramic thicknesses with a view to facilitating the firing. Here, they are optional.