MACHINE FOR THE PRODUCTION OF RAW PARTS FROM CERAMIC OR METAL MATERIAL

Description

[0001] The present invention relates to a machine for manufacturing raw parts in ceramic or metallic material by stereolithography, such raw parts being intended to be subjected to cleaning, debinding and sintering operations to obtain finished ceramic or metallic parts.

[0002] Stereolithography generally includes the following steps to obtain these raw parts: A computer-aided design constructs a computer model of the part to be manufactured, the dimensions of which are slightly larger than those of the part to be manufactured in order to allow for shrinkage of the ceramic or metallic material during the manufacture of the part;and the part is manufactured in the following manner: a first layer of a hardenable composition comprising said ceramic or metallic material formed by at least one ceramic or metallic powder respectively, and an organic part comprising at least one monomer and / or oligomer and at least one initiator of the polymerization of said monomer(s) and / or oligomer(s), and, where appropriate, at least one of a plasticizer, a solvent, a dispersant and a polymerization inhibitor, is hardened the first layer of the photocurable composition by irradiation (for example by laser scanning of the free surface of said layer or by diode projection system) according to a pattern defined from the model for said layer, forming a first stage; a second layer of the hardenable composition is formed on the first stage;The second layer of the hardenable composition is hardened by irradiation according to a pattern defined for said layer, forming a second stage; this irradiation is carried out in the same way as for the first layer; optionally, the above steps are repeated to obtain the part in its raw state.

[0003] Then, as noted above, to obtain the finished part, the raw part is cleaned to remove the uncured composition; the cleaned raw part is unbound; and the cleaned and unbound raw part is sintered to obtain the finished part.

[0004] The curable composition can be in the form of a suspension. The rigid support is a work platform that supports the various layers of the part being built, as well as the suspension. Each layer is generally formed by lowering the work platform and spreading a predetermined thickness of suspension. A reservoir of suspension is stored in tanks (trays, cartridges, or pressurized containers) which are automatically emptied of a predetermined quantity of suspension for each layer. This creates a bead or ridge of suspension to be spread onto the top layer of the part being manufactured, which has been previously lowered by the work platform. Each layer is generally spread by a scraper that sweeps across the work platform's surface, for example, by moving forward in a straight horizontal direction.

[0005] At each layer formation, the sausage comes out of its reservoir to extend over the width of the plate between the latter and the scraper to a height calculated so that the latter can be covered with suspension forming the layer when the scraper advances.

[0006] This system is not feasible for large machines because: The suspension bead, pushed by the scraper along the entire length of the build plate, will strike the polymerized parts, which are fragile, generating excessive stress on the parts. It is very difficult to ensure a uniform bead height across its entire width, so the build plate may not be properly covered, leading to the use of a much larger quantity of suspension than necessary to avoid this risk. This generates additional stress.

[0007] The applicant company proposed delivering the suspension via a nozzle in front of the scraper, across its entire width. While this solution resolves the issue of widthwise distribution, the problem of lengthwise distribution remains unresolved for large platens, as the continuous delivery of suspension during scraper movement becomes more complex. Indeed, if l'on Stopping the scraper at certain times to deposit a new suspension bead generates surface defects on the parts, namely marks at the stops; and if a continuous suspension bead is deposited in front of the scraper, this operation is difficult to control over the entire width during the entire advance of the scraper, leading to the depositing of a greater quantity of suspension than necessary, generating additional effort.

[0008] US 5,980,812 relates to a method for manufacturing models, molds, parts and other objects based on the homogenization of the components of the dispersion to form an alloy which has properties different from the properties of the dispersion or of its individual components.

[0009] US 5,922,364 relates to control systems for producing successive contiguous layers to form a three-dimensional object on a part support surface. US 5,902,537 A relates to a stereolithography system in which the spreading device has an external reservoir and a vacuum forming device.

[0010] To overcome these drawbacks, the Applicant proposed that the delivery and spreading of suspension onto the horizontal receiving surface for the first layer and onto each previously cured pattern layer for each subsequent layer be carried out by a suspension reservoir applicator system supplied by an external tank, with the stacking of layers taking place in a tray that fills with suspension at each layer formation.

[0011] Thus, according to the invention, the suspension deposition can be carried out in a controlled manner advantageously over the entire width and length of the layers without excess suspension as in the previously described situations of the prior art.

[0012] Furthermore, the progressive filling of the tank offers advantages compared to the case where one would work with a tank initially filled with the suspension, into which a tray is lowered step by step with each layer formation. This tray supports the stacking of the hardened patterned layer to cover the new layer to be irradiated. These advantages are those d'éviter a decrease in the responsiveness of the suspension as a result d'un exchange with ambient temperature, d'éviter sedimentation at the bottom of the tank of the ceramic or metallic part of the suspension, and to avoid a high shear stress which would be necessary to lower an excessively high viscosity level of the suspension to allow it to properly coat the layers to be irradiated.

[0013] The present invention therefore relates to a machine for manufacturing parts using the stereolithography technique, according to which layers of radiation-curable suspension are successively hardened one above the other by irradiation according to a pattern defined for each layer, said machine comprising: a horizontal receiving surface, configured to receive the first layer and subsequent layers formed one on top of the other from the first layer; a feeding and spreading device configured to, at each layer formation, feed a quantity of suspension and spread it onto said horizontal receiving surface for the first layer, and onto each previously cured patterned layer for each of the subsequent layers, the feeding and spreading device and the horizontal receiving surface being movable relative to each other in the direction of layer stacking; and an irradiation device to irradiate each layer once spread to cure it in the previously defined pattern, characterized by the fact that the horizontal receiving surface is constituted by the bottom of a tray, said tray having a length and a width, and that said device the supply and spreading system includes a suspension applicator and an external reservoir, the suspension applicator comprising a suspension reservoir supplied by the external reservoir, at least one vacuum forming device in the suspension reservoir and at least one hole connected to the suspension reservoir and formed opposite the horizontal receiving surface, said at least one vacuum forming device being controlled to regulate the quantity of suspension released by said at least one hole, the suspension applicator being arranged according to the width of the tray and having at least the printing width and being configured to move in translation along the length of the tray to be able to apply suspension through said at least one hole onto the receiving surface and that it includes a device for controlling the supply of suspension to the suspension reservoir cavity during the translational movement of the applicator.

[0014] According to a particular embodiment of the machine according to the invention, said at least one vacuum forming device is connected to a vacuum tap to control the amount of suspension released by said at least one hole.

[0015] The applicator can be a rectangular parallelepiped, the active face opposite the horizontal receiving surface being the release face of the applicator in which said at least one hole is formed.

[0016] Said at least one hole formed, which is formed in the active face, may consist of a single slit formed over the entire width of the active face of the applicator or of a plurality of holes uniformly distributed over the entire width of the active face of the applicator.

[0017] The suspension can be brought to the reservoir cavity by several feeds from the external reservoir, evenly distributed over the width of the applicator, with internal suspension distribution tubes being mounted plunging into the reservoir cavity.

[0018] The suspension reservoir can advantageously be divided into compartments, each associated with a vacuum-generating device via at least one vacuum port and at least one suspension supply from the reservoir. Thus, each compartment has its own supply and vacuum system. The advantage lies in the fact that if one compartment loses suspension for any reason, it does not affect the others. It has also been found that this arrangement allows for better control of the suspension level in the suspension applicator.

[0019] The advantage of adding suspension during the movement of the applicator is to minimize the amount of suspension in front of the applicator, which can induce mechanical stress phenomena on the parts or bead problems during hardening, subsequently generating interference with the applicator.

[0020] The machine according to the invention may include a sensor for the quantity of uncured suspension in the tray, and an automaton regulating for each layer the supply of suspension by the applicator according to the level of uncured suspension detected in the tray by the suspension quantity sensor.

[0021] The suspension quantity sensor can be one of a level sensor and a volume sensor.

[0022] The active face of the applicator may carry at least one blade configured to allow scraping of the suspension deposited by said at least one hole, said blade being located behind said at least one hole in the direction of movement of the applicator.

[0023] The front face of the applicator in the direction of travel may have a thrust shield shape.

[0024] The tank can be equipped with an overflow to remove excess uncured suspension. The overflow can be controlled according to the suspension level detected by the sensor measuring the quantity of uncured suspension in the tank.

[0025] To better illustrate the object of the present invention, a particular embodiment will be described below, by way of indication and not limitation, with reference to the attached drawing.

[0026] In this drawing: [ Fig. 1 ] is a front elevation view of a suspension applicator for a machine according to the invention; [ Fig. 2 ] is a top view of the device of the Figure 1 ; Fig. 3 ] is a cross-sectional view along III-III of the Figure 1 ; Fig. 4 ] is a longitudinal cross-sectional view along IV-IV of the Figure 2 ; Fig. 5 ] is a front view of the applicator of the Figure 1 in place in the machine according to the invention; [ Fig. 6 [ ] is a schematic view illustrating the operation of the machine according to the invention. Fig. 7a ] illustrates the formation of a layer during the advance of the suspension applicator; [ Fig. 7b ] illustrates the formation of a layer seen in the machine's tank; [ Fig. 7c ] illustrates the formation of a layer with the addition of extra material; [ Fig. 7d ] illustrates the formation of a layer with aspiration of excess material d). [ Fig. 8 ] is an exploded perspective view of a suspension applicator for a machine according to the invention, said applicator conforming to a variant of that shown in the Figures 1 à 4 .

[0027] If we refer to Figures 1 à 5 We can see that we have represented a suspension applicator 1 having the general shape of a rectangular parallelepiped formed by an elongated upper plate 2, horizontal in the position of use, folded downwards at each of its ends to form transverse plates 3 of greater thickness. On each side of these walls 2 and 3, a lateral plate 4 is fixed by screws 5.

[0028] A suspension reserve of 6 is thus established ( Fig. 4 ) delimited by plates 2, 3 and 4, the lower face or release face (FL) being formed by the edges of plates 3 and 4 and having a slotted T-shaped hole (see Fig. 3 ).

[0029] The cross plates 3 have holes 7 for the passage of fixing screws onto an applicator holder 8. This holder, fitted with its applicator 1, is mounted to slide on rails 9 which frame a horizontal receiving surface 10 (see Fig. 5 ).

[0030] In the upper plate 2 are recesses 11, each adapted to receive an end fitting 12 of a pipe 13. The pipes 13 are connected to an intermediate fitting 14 from which a pipe 15 extends. The two pipes 15 are joined at an intermediate fitting (not shown) from which a connecting pipe extends to an external suspension reservoir (R on the Fig. 6 ).

[0031] The recesses 11 are each connected to an internal suspension distribution tube 16 plunging into the reservoir 6.

[0032] The supply of suspension into reservoir 6 is controlled by a device (not shown) which is programmed to open one or more distribution valves to address suspension, for example, while applicator 1 is stopped, in particular at a transverse edge of the receiving surface.

[0033] In plate 2, there are also vacuum connections 17 connected in pairs by pipes 18 to an intermediate fitting 19 from which a connection leads to a vacuum forming device (not shown).

[0034] Each of the plates 4 has a scraping blade L along its lower edge in the example shown, this having here the shape of a thrust shield ( Fig. 3 Details concerning this shape can be found in the French patent application filed on July 8, 2019, in the name of the present applicant, entitled "Device for applying layers of paste for an apparatus for manufacturing ceramic parts by stereolithography." Other shapes of scraping blades can be used, such as beveled blades, for example with a high entry angle (e.g., 45°) or, if laminar flow is desired, with a smaller entry angle.

[0035] In the example shown, the suspension applicator comprises two blades L, each active in one of two directions of movement. The machine according to the invention operates as follows: (a) formation of a first layer C of suspension in the bottom of a container (B) ( Fig. 6 (a) by moving the applicator 1, whose reservoir 6 has been previously filled from the reservoir R; a vacuum (depression) is necessary in this operation to prevent any unwanted deposition of suspension and to regulate this deposition; (b) hardening of the first layer according to the desired pattern; (c) raising the applicator 1 by one layer height; (d) formation of the second layer C by moving the applicator 1 in the opposite direction; (e) hardening of the second layer C; with the repetition of steps (c) and (e) for the construction of the piece in its raw state.

[0036] There Figure 6 represents a machine according to the invention in which the applicator 1 rises each time by the height of one layer from the bottom of the tray B.

[0037] It is also possible to anticipate that the work surface will descend, as illustrated in the Figure 7b, 7c ou 7d In other words, it is the bottom of the tank that sinks with each layer formation.

[0038] If we now refer to the Figure 7a , we can see that as applicator 1 deposits suspension onto the previous layer which comes from suspension reservoir 6, a V wave forms in front of the applicator which is scraped by the front blade.

[0039] If we refer to the Figure 7b The diagram, showing applicator 1 in its initial position (filling reservoir 6), in an intermediate position (during the actual application), and in its final position (after application), reveals an overflow TP on the edge of the tank opposite the initial position. The suspension that falls into the overflow TP can advantageously be returned to the external reservoir R.

[0040] If we refer to the Figure 7c We can see that we have represented the situation in which the level of a previous layer in an uncured location is too low compared to the rest of the layer. In this case, we command the addition of the missing suspension material.

[0041] If we refer to the Figure 7d We can see that we have represented the situation in which the level of a previous layer in an uncured location is too high relative to the rest of the layer. In this case, the suction of the excess suspended material is triggered.

[0042] If we refer to the Figure 8 , we can see that we have represented an applicator 1' which differs from applicator 1 in that the suspension reservoir 6 is divided into compartments (four in the example shown) by three partitions 20 perpendicular to the upper plate 2 and extending downwards to the vicinity of the suspension outlet slot T.

[0043] Elements of applicator 1' identical to those of applicator 1 are designated by the same reference numbers.

[0044] The compartments formed by the partitions 20 are approximately the same volume and each is supplied with suspension by a pipe similar to a pipe 13 as shown on the Figure 5 , and is connected to a vacuum forming device by a vacuum connection 17.

[0045] In the example shown, the partitions 20 are beveled at their lower part, which makes it easier to exit the suspension from each of the compartments.

[0046] On the Figure 8 , have not been shown the internal distribution tubes 16 mounted internally in the recesses 11 receiving an end fitting 12 of a pipe 13.

[0047] Thus each compartment has its own supply and vacuum system, allowing control of the supply and vacuum system compartment by compartment.

[0048] On the Figure 8 We have also shown control windows 21 which can, if desired, be made in the front wall 4 to observe the behavior of the suspension during its deposition.

Claims

1. - A machine for manufacturing parts by the stereolithography technique, according to which layers of radiation-curable suspension are successively cured one on top of the other by irradiation according to a pattern defined for each layer, said machine comprising: - a horizontal receiving surface (10), configured to receive the first layer and subsequent layers formed on top of each other from the first layer; - a supply and spreading device configured to, at each layer formation, supply a quantity of suspension and spread it on said horizontal receiving surface (10) for the first layer, and on each previously cured patterned layer for each of the subsequent layers, the supply and spreading device and the horizontal receiving surface (10) being movable relative to each other in the direction of layer stacking; and - an irradiation device for irradiating each layer after it has been spread to cure it in the previously defined pattern, characterized in that the horizontal receiving surface (10) is constituted by the bottom of a vat (B), said vat (B) having a length and a width, and in that said supply and spreading device comprises a suspension applicator (1) and an external tank (R), the suspension applicator (1) comprising a suspension reserve (6) fed from the external tank (R), at least one vacuum forming device in the suspension reserve (6) and at least one hole (T) connected to the suspension reserve (6) and formed facing the horizontal receiving surface (10), said at least one vacuum forming device being controlled to regulate the amount of suspension released from said at least one hole (T), the suspension applicator (1) being disposed along the width of the vat (B) and having at least the printing width and being configured to translate along the length of the vat (B) to be able to apply suspension through said at least one hole (T) onto the receiving surface (10), and in that it comprises a device for controlling the supply of suspension to the suspension reserve cavity (6) during the translational movement of the applicator (1).

2. - Machine according to claim 1, characterized in that said at least one vacuum forming device is connected to a vacuum tapping (17) to control the amount of suspension released from said at least one hole (T).

3. - Machine according to one of claims 1 and 2, characterized in that the applicator (1) is a rectangular parallelepiped, the active face facing the horizontal receiving surface (10) being the release face (FL) of the applicator (1) in which said at least one hole (T) is formed.

4. - Machine according to claim 3, characterized in that said at least one hole (T) which is formed in the active face is constituted by a single slit formed over the entire width of the active face of the applicator (1) or by a plurality of holes uniformly distributed over the entire width of the active face of the applicator (1).

5. - Machine according to one of claims 3 and 4, characterized in that the suspension is supplied to the suspension reserve (6) by several supplies from the external tank (R), uniformly distributed over the width of the applicator (1), internal suspension distribution tubes (16) being able to be mounted dipping into the suspension reserve.

6. - Machine according to one of claims 1 to 5, characterized in that the suspension reserve (6) is divided into compartments each associated with a vacuum formation device by at least one vacuum tapping (17) and with at least one supply of suspension from the external tank (R).

7. - Machine according to one of claims 1 to 6, characterized in that it also comprises a sensor for the quantity of uncured suspension in the vat (B), and a controller regulating, for each layer, the supply of suspension by the applicator as a function of the level of uncured suspension detected in the vat (B) by the suspension quantity sensor.

8. - Machine according to claim 7, characterized in that the suspension quantity sensor is one of a level sensor and a volume sensor.

9. - Machine according to one of claims 4 to 8, characterized in that the active face of the applicator (1) carries at least one blade (L) configured to allow scraping of the suspension deposited through the said at least one hole (T), the said blade (L) being located set back from the said at least one hole (T) in the direction of movement of the applicator (1).

10. - Machine according to one of claims 4 to 8, characterized in that the front face (4) of the applicator (1) in the direction of movement has the form of a pushing shield.

11. - Machine according to one of claims 1 to 10, characterized in that the vat (B) is equipped with an overflow for discharging excess uncured suspension.

12. - Machine according to claim 10 taken in combination with claims 7 to 10, characterized by the fact that the overflow is controlled as a function of the level of suspension detected by the sensor of the quantity of uncured suspension in the vat (B).