WO1993025377A1

WO1993025377A1 - Method and device for making an industrial part model in order to achieve a partial transformation of a liquid under the action of the light

Info

Publication number: WO1993025377A1
Application number: PCT/FR1993/000538
Authority: WO
Inventors: Claude Medard; André Luc ALLANIC; Philippe Schaeffer
Original assignee: Laser 3D
Priority date: 1992-06-05
Filing date: 1993-06-04
Publication date: 1993-12-23
Also published as: FR2692066A1

Abstract

The method comprises the automatic creation of a part model by means of successive elementary volumes previously defined by means of a data processing system. This method is characterized by means providing for the progressive covering of the created elementary volumes with a thin planar liquid sheet owing to the implementation of a device using the action of a flexible thin film whose lower portion is in contact with the liquid. Application to the automatic making of an industrial part model whose shape has been stored in a memory of a data processing system.

Description

Method for producing a model of an industrial part by partial transformation of a liquid under the action of light and device for implementing this method.

The present invention relates to a method and a device for the production of industrial objects or models of parts, by the action of light and in particular by photo-transformation of a plastic or composite material. It is desirable to be able to have an industrial part, such as in particular a mechanical part, before launching mass production. Currently, to make models of such parts, it is necessary to first carry out dimensioned plans at the design office from quantified data which define the shape of the part. For several years, the "Computer Aided Design" (CAD) method has been used to define the shape of this part.

It is known to provide a method and a device for producing models of industrial parts by using the figures available in the output memories of the computer, directly to produce the models of parts without having to go through the intermediate plans or, having to involve machining machines with numerical controls such as milling machines, lathes, etc ...

Methods and devices proposed for the realization of models using CAD are based on a chemical polymerization induced by LASER. The controlled movement of one or more laser beams possibly concentrated at the same point, allows the local polymerization of an advantageously polyfunctional monomer and, step by step, the production of the part.

In particular, the document FR-A-2,567,668 describes a process whose general principle of producing a part is based on the use of an apparatus comprising a tank which contains the monomer (or the oligomer or the mixture of two) liquid photopolymerizable (which will be called more simply "monomer", or even simply "resin") at the

REPLACEMENT SHEET level from which a mobile platform outcrops step by step during the operation. The UV laser beam traces on the surface of the liquid successive sections of the object to be produced, thanks to a set of mirrors with electronic deflection, controlled by the database of the CAD system. The software previously subdivided the virtual model of the object into a multitude of thin parallel sections. As each slice solidifies, the "sculpted" model dives slowly into the tank: with a 10 mW laser, this system makes it possible to create a part 30 mm high in 50 minutes, with a precision of the order of 1 / 10th of a millimeter. The model can be created in all kinds of materials (plastics), in a wide variety of colors, with different hardnesses and a whole range of abrasion resistance (SCIENCE AND TECHNOLOGY N ° 2, February 1988 / INDUSTRIAL LASER REVIEW, vol 2, No. 8, January 1988). This type of process for manufacturing three-dimensional models, which uses the principle of single-photon absorption of light by photoinitiators of polymerization or crosslinking, has the disadvantage of requiring the superimposition of the monomer (or of an oligomer or of a mixture) on already polymerized parts; to obtain good model accuracy, a considerable number of liquid or pasty layers of monomer must be superimposed, which can lead to fairly long manufacturing times.

The duration of installation of the layers is substantially increased by the problems of wettability (cf. FIG. 2) of the polymer with a monomer. Indeed, to produce layers of the order of 500 micrometers thick or less, current machines systematically perform a relative movement of the part already solidified with respect to the surface of the resin of amplitude greater than the thickness of the desired layer. This movement is carried out in two distinct phases: - descent of the platform causing in its movement the part of the part already created so as to establish an altitude difference between the level of the liquid and the last solidified layer, sufficient

REPLACEMENT SHEET to cause spontaneous covering of this last layer by the liquid; - rise of the platform driving in its movement the part of the part already created so as to establish an altitude difference between the level of the liquid and the last solidified layer equal to the thickness of the next layer which is wishes to solidify. These two successive movements give rise to disturbances in the flatness of the liquid which stabilize after a considerable time, all the longer as the resin is viscous, the layer is thin, and the surface of the last solidified layer is large. .

In order to reduce these non-productive relaxation times, 3D Systems, the world leader in the market for machines operating according to the principle described above, uses a "scraper". This scraper is a rod or a rigid blade which carries out a translational movement parallel to the surface of liquid resin, thus causing by liquid / solid mechanical interaction forced flows having as a consequence a notable reduction in the amplitude of the deformations of the surface of the liquid. For more details, the reader will refer to FIG. 3.

This device has a certain number of drawbacks both by its difficulty of implementation and by its efficiency. In fact, the mechanical precision of the guide of the scraper is directly linked to the thickness of the desired layer, any guide error being able to cause scraper / part interference that is fatal to the good progress of the manufacture (see FIG. 4). This is even more true if one wishes to insert objects (for example metallic) in the part during its manufacture. Consequently, the rigid scraper system is particularly delicate to use when seeking to produce very thin layers (a few tens of micrometers) on large surfaces. To partially overcome this drawback, competing systems propose to use semi-rigid scrapers

(see figure 5).

REPLACEMENT SHEET Another disadvantage of this rigid or semi-rigid scraping system is that deformations of the surface of the liquid (wave, drag) are induced upstream and downstream of the scraper during its movement, giving rise to relaxation times. inevitable, all the more important as the resin is viscous and the speed of movement of the scraper is high. We thus manage to define an optimal speed, very limited by the viscosity of the resin and the mechanical coefficients of the fluids characteristic of the forced flows mentioned above.

In addition to the two disadvantages which we have just mentioned, the use of a rigid or semi-rigid scraper poses a problem which we will call the "problem of bowls" (cf. FIG. 6). When it is desired to manufacture parts having closed wells in which the liquid cannot circulate towards the rest of the tank, a meniscus appears above the well. This meniscus is a direct consequence of the round-trip movement described above, which creates a local excess thickness relative to the level of the liquid. It is very difficult to remove this meniscus by the use of a scraper: the meniscus reappears after its passage, barely diminished. However, several successive passes make it possible to reach a final flatness accepted today as a limit of current technology, but hardly acceptable for an intensive industrial use of the process, because it is at the cost of a substantial increase in setting time. in place of the layer, therefore a drop in production yield, that this problem can be minimized. It should be noted that it is further aggravated with a semi-rigid type scraper, sometimes used for its other advantages.

We find in the French patent application (9107983 of 06/27/91, not yet published to date) the description of a process making it possible to elegantly overcome some of the problems associated with the implementation of a layer. The process differs essentially from that implemented for example in machines marketed by 3D Systems by the fact that the platform is set in helical movement. So, the part of the piece that has just been

REPLACEMENT SHEET polymerized induces a shearing of the liquid in the vicinity of the surface which may be sufficient to obtain, despite the wettability problems, recovery of the solid by the liquid. However, such a method has a certain number of limitations; it does not in particular allow thin layers to be produced with viscous resins. This drawback can be offset by the use of a system comparable to the scraper, but here advantageously fixed relative to the tank, without however overcoming the drawbacks mentioned above (mechanical difficulty, disruption of the surface of the liquid time etc.).

To date, we believe that the methods of placing the layers currently used, making it advantageous to use a scraper, rigid or semi-rigid, significantly limit the performance of a machine for producing three-dimensional parts by photo-solidification. of a liquid resin.

The object ^'of the present invention is to provide a method belonging to the category as described above, but which allows to significantly reduce the time of establishment of the layers, which improves the yield of three-dimensional parts production machines by photo¬ solidification of a liquid, and therefore which reduces the manufacturing cost of the parts produced considerably. To achieve this result, the invention proposes to rely on different physical phenomena for the establishment of the layers, ie to replace the large amplitude movements necessary for spontaneous recovery of the solid by the liquid, as well as the scraper which works by forcing a flow of resin by mechanical means, by a simplified process using a device which we will call "wetting", which works, him, by using the properties of capillarity induced by the surface tension of the resin to overcome the forces of interfacial tension (triple interface liquid resin / solid polymer / gaseous air) which oppose spontaneous covering of the polymer by the resin.

REPLACEMENT SHEET A wetting agent is a flexible elongated film the lower part of which is partially in contact with the resin. The upper part of this film is fixed to a mechanical arm allowing it to be moved at a constant altitude above the liquid. This film may advantageously be made of a material with a density lower than that of the resin to prevent it from penetrating below the surface thereof, although the thinness of the film combined with the surface tension phenomena can eliminate this problem. It suffices to lower the part or to raise the level of the liquid (even from an extremely low height) and to move the wetting machine, simultaneously or not, so that the monomer is transported by capillarity over the already polymerized portions of the part, which ensures both correct wetting and excellent flatness of the liquid (no scraper therefore no wave, no drag), that is to say a practically zero relaxation time (see FIG. 7).

In addition, the minimum layer thickness is particularly low compared to the traditional process: it is reasonable to manufacture on an industrial machine using this device layers of 25 micrometers thick, while current machines do not go below 100 micrometers . On an experimental basis, layers of 5 micrometers were actually made with this device during feasibility tests. This means that the method relating to the invention allows the production of parts having a much better surface condition than by the previous methods: the "staircase effect" induced by a manufacturing by layers is all the more reduced as the layers are thin.

The fineness limit accessible thanks to a wiper scan is no longer linked to mechanical guidance problems, but rather to the molecular structure of the monomer, that is to say this limitation is practically negligible compared to the other process parameters. (polymerized depth, etc.). Indeed, the connection between the mechanical arm located above the liquid and the solid part in contact with it is made extremely flexible by the

REPLACEMENT SHEET nature of the film, low quality guidance largely sufficient insofar as it simply ensures permanent contact of the lower end of the film with the liquid and the non-penetration of the mechanical arm in the liquid. This mechanical flexibility also offers the advantage of not causing damage to the part when small asperities (linked to the deformations induced by the withdrawal or the insertion of loads or mechanical parts within the part during its creation ) appear above the last layer formed.

In addition, the rigidity of this mechanical arm can be very low, thus offering the possibility of using inexpensive and light materials, and therefore an equally inexpensive motorization. Let us add that in principle, the "wetting" causes only very small disturbances of the surface of the resin, which allows effective scanning speeds much higher than the technical limits generated by the use of scrapers (rigid or semi- rigid). Given the nature of the physical phenomena involved, this scanning speed limit is practically independent of the thickness of the layer to be produced, as well as, to a lesser extent, the viscosity of the resin. Knowing that one of the fundamental problems of this process resides in the fact that, under the effect of the shrinkage due to solidification, the part undergoes global deformations linked to the appearance of internal tensions, the advantage of the wetting agent: the shrinkage decreases notably when high viscosity resins are used (which generally have a low shrinkage on polymerization), resins which hitherto have been abandoned due to the time taken to set up the prohibitive layers which they induced .

At this stage of the presentation, we can therefore affirm that the fact of carrying out a positioning of the layers by means of a "wetting agent" has the following advantages compared to the prior art: saving in setting time in place of the layers, due to:

REPLACEMENT SHEET the amplitude of the movement of the platform (or of the surface of the resin) limited to its minimum value, that is to say the thickness of the layer, this movement also being able to be carried out in "masked time" during that of the moistener

- significantly higher maximum scanning speed relaxation time of practically canceled surface deformations - possibility of making very thin layers (25 micrometers instead of 100) without increasing the installation time

- possibility of using low shrinkage resins

(in general very viscous) without prohibitive increase in the time of installation of the layers

- complete cancellation of the "bowl problem" previously described.

Unlike the scraper, the moistener, due to its great flexibility, can lead to minor inconveniences for movements requiring a change of direction (see Figure 8). It is interesting, in fact, to carry out a sweep in one direction for one layer, then in the other for the next, etc. The advantage of such a movement is simply to limit the amplitude of the stroke of the device to save time. However, it is possible that the reversal of the film caused by the inversion of the movement of the mechanical arm may cause local deformation of the liquid surface, which it is desirable to avoid. To overcome this problem, it is advantageous to take advantage of the laser scanning time (solidification of the layer which has just been put in place) so that the mechanical arm makes a return path to the starting position following a path outside the surface. working, said path can advantageously be in the form of a gutter (see Figure 9) containing resin and communicating with the tank itself. This solution has the advantage of avoiding reversing the wiper direction of scanning, but it involves poorly optimized machine ergonomics. Another solution is to use

REPLACEMENT SHEET a film folded in the shape of a U (see Figure 10) which makes the damper symmetrical, thus limiting the harmful effects of turning over a simple film. It may also be advantageous for this purpose to reduce the length of contact of the film with the liquid, without however losing the advantage mentioned above concerning the ease of implementation of the mechanical guidance.

Another problem consequent to the use of a moistener can also arise when the solidified part to be covered represents a large fraction of the working surface; this is what we will call the problem of "liquid supply". Indeed, it is easily understood that in the extreme case where the solidified part represents the entire working surface, the wetting machine cannot fully perform its function since it only distributes the volume of liquid located on the surface to the exterior of the polymerized surfaces (which is zero in said extreme case). It is therefore necessary to anticipate situations where the problem of supplying liquid can become prohibitive. We therefore propose in the following a number of solutions which make it possible to overcome them.

One could imagine a first solution consisting in supplying the wetting agent with resin by an external device, all along its path. The realization of such a device faces various technical difficulties:

- problem of flow of the resin (pressure drop) within the wetting device supply;

- problem of regulating the quantity of liquid to be supplied to the moistener; - problem of regulation of the level of the liquid in the tank; etc ... The present invention is characterized in that, for the sake of simplification, the "wetting" used does not require a supply of liquid to fulfill its function. Here we give ways to achieve it.

First of all, it is advantageous to carry out a wiper sweep such that the swept area is greater than

REPLACEMENT SHEET the work surface (see Figure 11), which allows on the one hand to reduce the disadvantage of the liquid supply, and on the other hand to postpone any disturbances due to edge effects (ends of the wetters) in outside the work surface. Advantageously, the mechanical arm may be given a non-rectilinear shape of the concave type for example, in order to take optimal advantage of the supply of potential liquid offered by the part of the surface swept by the wiper external to the working field. It is also advantageous under these conditions to give the tank a flared shape in its upper part (see Figure 11) to allow a large surface area of liquid without substantially increasing the amount of resin (fairly heavy initial investment) necessary to fill said tank.

To this first solution can be added a sweep carried out by at least two successive wetters (cf. FIG. 12). The advantage is twofold: risk of non-recovery of the part divided by at least two, and attenuation of residual flatness defects after the passage of the first damper.

In addition, still to overcome the problem of supplying liquid, the wetting machine may be composed of several flexible films separated by one or more resin interfaces maintained by capillarity (see FIG. 13). According to this same solution, variants may consist in using for the film (s) materials capable of absorbing resin, such as for example films, braided or not.

Finally, in addition to the solutions relating to the moistener itself, it is advantageous to have recourse to a radical modification of the prior methods. Indeed, the problem of "liquid supply" becomes critical when at least one of the layers to be solidified has a related area of large area. This problem can be overcome by performing an original breakdown of the volume occupied by the part (s) to be manufactured.

The classic method in the process of manufacturing objects by layer is to decompose the object into layers

REPLACEMENT SHEET successive parallel horizontal lines (see Figure 14). Here, we rather wish to divide it into elementary volumes whose upper face is flat and horizontal.

The manufacturing phase, after this division into elementary volumes, will include the following stages:

(1) Classify said elementary volumes in ascending order of altitude of their upper face, thus defining a series of horizontal planes of increasing altitude (2) Make the level of the liquid coincide with the first plane of the series of planes defined in l '' step (1) (3) Solidify by phototransformation of the liquid each elementary volume whose upper face corresponds to the altitude of the plane selected in step (2) (4) Cover with liquid the or all the elementary volumes just d '' be solidified

(5) Make the level of the liquid coincide with the following plane of the series of plans defined in step (1)

(6) Solidify by phototransformation of the liquid each elementary volume, the upper face of which corresponds to the altitude of the plane selected in step (5)

(7) Repeat operations (4), (5) and (6) until the elementary volumes are all solidified.

The division into elementary volumes can be carried out in such a way as to considerably limit the surface of the zones to be solidified, these then being solidified in a fragmented manner in several successive stages (cf. FIG. 15) interspersed with a sweep of the wetting agent in order to obtain liquid covering of solidified areas. Advantageously, the zones solidified in each of said successive stages will be separated in order to offer the possibility for the liquid to circulate between these zones. We could for example perform strip type cuts (see Figure 15) or checkerboard (see Figure 17). It is clear that by such a method, it is not possible to produce parts comprising horizontal faces of large dimension perfectly flat without being in the delicate situation mentioned above.

REPLACEMENT SHEET On the other hand, given the very small thicknesses of layer which can easily be obtained by the use of a wetting machine, the defect in flatness consecutive to a solidification fragmented by blocks of different altitude can be limited in amplitude, so to make the roughness of a flat surface practically imperceptible (see Figure 15).

In addition, if however it is desired to obtain horizontal surfaces of large surface area without notable roughness, it is possible to produce a finishing layer on the lower, rough part, in order to eliminate the flatness defects.

(see figure 16). We are then faced with the initial problem

"liquid supply" (large related surface to be covered), limited however to the topcoat. It is clear that at the next layer, perfect recovery will be unlikely, it will however be obtained a few steps later (several passes of the moistener).

In summary, we see that the use of wetters has many advantages, and that a particular cutting of the volume to be polymerized no longer in layers but in elementary volumes of variable depth with flat and horizontal upper face makes it possible to use these wetters. simple (no complex device for supplying and regulating the liquid level) and reliable (without risk of "dewetting").

The description which follows with reference to the appended drawings will explain in more detail the drawbacks of conventional systems and how the invention can be implemented.

Figure 1 schematically shows an embodiment of the device according to the invention.

Figure 2 shows the difficulty of obtaining a recovery by the liquid of the parts which have just been solidified.

Figure 3 are shown the steps of setting up a layer of planar liquid on the part of the part already solidified. Figure 4 illustrates the drawbacks associated with the use of a rigid scraper poorly guided mechanically.

Figure 5 shows that the use of a semi-rigid scraper can limit the risk described in Figure 4.

REPLACEMENT SHEET Figure 6 illustrates the "bowl problem".

Figure 7 illustrates the innovation relating to the claimed process.

Figure 8 illustrates the risk of causing local deformation of the liquid when the wiper direction is reversed.

Figure 9 illustrates a device making it possible to avoid reversing the direction of scanning of the film.

Figure 10 illustrates a solution of using a U-shaped film.

Figure 11 illustrates a device making it possible to carry out a particular sweeping by the moistener.

Figure 12 illustrates a sweep carried out by several successive wetters. Figure 13 illustrates a device for taking advantage of the surface tension of the liquid to overcome the problem of supplying liquid.

Figure 14 represents the successive stages of creation of a part by the traditional process. Figure 15 represents the successive stages of creation of a part by a process consisting in solidifying elongated volumes (bands).

Figure 16 shows how one can obtain a suitable flatness following the operations described in Figure 15.

Figure 17 represents the successive stages of creation of a part, consisting in solidifying unelongated volumes.

FIG. 1 schematically represents an embodiment of the device according to the invention. In Figure 1, a memory system 1 is shown, arranged at the output of a computer not shown, which was used to determine by the CAD method, the geometric characteristics of a part. A light generator 2 is connected to the output of the system 1 through a processing circuit 3 and emits radiation 4.

The radiation 4 is shaped by an optical system 7 then is deflected by another optical system 8 on a portion 9 of the surface of the liquid 5, contained in a tank 6. SUBSTITUTE SHEET 14

A motorized system 9bis, connected to 3 allows control of 7 and 8.

The device further comprises a mechanical system 10, controlled by a motorized system 11, connected to 3, which makes it possible to move a plate 12 in the liquid, by means of a mechanical part 13 ensuring a rigid connection between 10 and 12 .

Another mechanical system 14, controlled by a motorized system 15, connected to 3, makes it possible to move a scraper 16 parallel to the surface of the liquid.

In this figure, we can see an object 17 during manufacture. This production is carried out by repeating the following operations:

solidification of the layer in progress by scanning the light beam 4 at the surface of the liquid,

- placement of a new layer of liquid above the layer which has just been solidified.

In FIG. 2 is shown the difficulty of obtaining recovery by the liquid of the parts which have just been solidified. Step A represents the situation just after partial solidification of a layer. The part which has just been solidified 18 under the action of light from the surface 20 of the liquid 5 adheres to the previously solidified layers 19. Step B represents the situation after a relative movement of the part being created (18 + 19) with respect to the surface 20 of the liquid, carried out vertically, of amplitude equal to the desired thickness "e" of the next layer. It is found that the liquid 5 does not manage to cover 18 for reasons of problems of interfacial tension (insufficient wettability). A dead volume W appears, no longer allowing proper continuation of operations.

In FIG. 3 are shown the steps for placing a layer of plane liquid on the part of the part already solidified, making it possible to overcome the problem illustrated in FIG. 2.

REPLACEMENT SHEET Step A shows a relative movement of the part (18 + 19) with the surface 20 of the liquid 5, of amplitude "a" greater than the thickness "e" of the desired layer. This movement, by its large amplitude, makes it possible to obtain a forced covering of the part (18 + 19) by the liquid 5, involving flows caused by the forces of gravity.

After covering, the movement is reversed so as to position the part at the appropriate altitude allowing the desired thickness of the layer to be obtained.

Step B shows the shape of the deformations of the surface 21 of the liquid following the round-trip movement described above (page ??, lines ??). In order to achieve the desired surface flatness 22, it is necessary to wait for the liquid to stabilize, this time being all the more important when it is desired to produce thin layers.

Step C shows the action of a rigid scraper 23 moving so as to cause forced flows, resulting in a significant reduction in the surface deformations mentioned above. Line 21 bis recalls the shape taken by the surf ace of the liquid at the end of step B.

Stage D finally shows the residual deformations of the surface:

- 25: upstream and downstream of the scraper, - and 24: low amplitude wave left above the solidified parts. Consequently, this method of placing a layer involves several distinct phases, during which the forces brought into play are essentially linked to the action of gravity and to forced flows caused by a liquid / solid interaction, the surface tension of the liquid having negligible effects compared to other physical phenomena involved.

FIG. 4 illustrates the drawbacks associated with the use of a rigid scraper poorly guided mechanically. When the guidance is not precise enough to respect the ideal trajectory given by the path I, situations may arise such that the rigid scraper 23 comes into contact

REPLACEMENT SHEET (point 26) with the part, at the risk of causing for example the tearing of a part 27 of it.

FIG. 5 shows that the use of a semi-rigid scraper 28 can limit the risk described in FIG. 4. It is indeed observed that due to poor mechanical guidance (path II instead of path I), when a semi-scraper -rigid comes into contact with the part, it deforms (28 bis) without damaging it.

Figure 6 illustrates the "bowl problem" cited above. Step A shows the situation after the back-and-forth movement described in Figure 3 (steps A and B) for a part 29 having the shape of a closed well, or of a U if one is satisfied a two-dimensional representation. The return to the flatness 22 of the deformed liquid surface 20 imposes flow which can only occur in zones 30 and 31. The thickness of liquid remaining small (of the order of e) in these zones, the speed d The flow of liquid is very limited, and therefore the meniscus cannot disappear quickly. Step B of this figure illustrates the fact that the passage of a scraper 23 in such a situation causes movements of liquid essentially confined in the volume V. Consequently, as shown in step C, the meniscus present at the step A cannot be completely reduced by the passage of a scraper. Line 20bis recalls the situation in step A.

FIG. 7 illustrates the innovation relating to the claimed process. The recovery is carried out firstly by a relative movement of the resin surface with respect to the piece of amplitude e equal to the thickness of the desired layer. The situation is then similar to that described by step B of FIG. 2; this is represented by step A of FIG. 7. The covering of the already polymerized part (18 + 19) is obtained by setting in motion a mechanical arm 32 parallel to the surface of the liquid 20, which arm causes a flexible film 33, the lower part of which rests on the surface of the liquid. The successive steps B and C show how, thanks to the surface tension of the liquid, said

REPLACEMENT SHEET film overcomes the wettability problems illustrated in Figure 2.

The situation in step C also illustrates the small difference in flatness 34 after passage of the moistener, in contrast to the deformations 24 and 25 (of FIG. 3) induced by the use of a scraper.

FIG. 8 illustrates the risk of causing local deformation of the liquid when the wiper direction of the wiper is reversed. When the arm changes the direction of movement, the flexible film 33 gradually turns over, leaving behind a deformation of the surface 35.

FIG. 9 illustrates a device making it possible to avoid reversing the direction of scanning of the film. The useful surface S of the liquid located above the tank is swept by the moistener (composed of the mechanical arm 32 and the film 33) by a movement allowing it to pass from position I to position II. During the solidification time of the layer which has just been formed, the wetting agent makes a return movement to position I (successive positions III, IV, V) by sweeping the surface T of the liquid contained in a gutter.

36 in the form of a loop. The depth q of the gutter 36 is advantageously less than that p of the tank 6, which limits the amount of liquid present in said gutter. FIG. 10 illustrates a solution consisting in using a U-shaped film 37 in order to limit the possible problems due to a reversal of the direction of movement of the moistener: when moving from direction I to direction II, the part of film located between points 38 and 39 always remains in contact with the liquid, which means that the problem linked to the turning of the film (cf. fig 8) is avoided.

FIG. 11 illustrates a device making it possible to carry out a sweep by the moistener such that the swept surface SB is greater than the working surface SV. In the front view is illustrated the flared shape of the tank leading to two depths of liquid p and q.

FIG. 12 illustrates a sweep carried out by several successive wetters.

REPLACEMENT SHEET FIG. 13 illustrates a device making it possible to take advantage of the surface tension of the liquid to overcome the problem of the supply of liquid mentioned above. The moistener consists of several films 40, 41, 42, 43 and 44 attached to the same mechanical arm 32, between which a reserve of liquid 45 is maintained by capillarity.

FIG. 14 represents a part to be produced PIE, of parallelepiped shape and having a large surface in the XY plane. The successive stages of creation of this part by the conventional process, that is to say by stacking successive horizontal layers are represented by stages A to D. The top view shows for each stage the solidified surface to be covered, it can be seen that at each stage it is large and corresponds to the entire surface of the part (in the XY plane corresponding to the altitude of the selected layer).

Note: In the description of Figures 15 to 17, the expression "solidify a volume" means the fact of "solidifying the parts of the part located in the volume".

FIG. 15 represents the successive stages of creation of a part by a process consisting in solidifying elongated volumes (strips). As can be seen in the top views, the solidified surfaces to be covered are fractions of the overall surface of the part (XY), disjoint, so as to facilitate the flow of liquid.

The figure represents an exemplary embodiment of a piece by strips but it does not constitute a generality in any case.

In this figure are also indicated the different altitudes H ^ ... H4 with which the liquid level must be made to coincide for each step. It can be seen in this figure that the thickness of the solidified strips is not necessarily equal to the difference in height H ^ - H ^ _ ι separating two stages. Thus, the upper face of the part may have flatness defects linked to the very low amplitude process (H4-H3) even if very thick strips are solidified.

REPLACEMENT SHEET FIG. 16 shows how a suitable flatness can be obtained following the operations described in FIG. 15, for the upper face of a part.

FIG. 17 represents the successive stages of creation of a part, consisting in solidifying unelongated volumes. The example described in no way constitutes a generality. It can be seen on the top views that the surfaces to be covered for each step each time represent a small fraction of the total surface of the part, these surfaces are separated to allow good circulation of the liquid during recovery. It can also be seen that the final upper face is not perfectly flat.

By a process analogous to that described in FIG. 16 to correct the flatness defects resulting from a manufacturing based on the principle described in FIG. 15, the manufacturing defects based on FIG. 17 can be corrected by adding a finishing layer, the depth at each point is judiciously chosen to complete the volume previously solidified.

REPLACEMENT SHEET

Claims

1) Method for manufacturing one or more solid three-dimensional part (s) by phototransformation of liquid, comprising the following steps:

(a) Decompose the volume of the part (s) into elementary volumes whose upper face is flat and horizontal

(b) Classify said elementary volumes in ascending order of altitude of their upper face, thus defining a series of horizontal planes of increasing altitude

(c) make the level of the liquid coincide with the first plane of the series of planes defined in step (b) (d) solidify by phototransformation of the liquid each elementary volume whose upper face corresponds to the altitude of the plane selected in step (c) (e) Cover with liquid the elementary volumes which have just been solidified (f) Make the level of the liquid coincide with the following plane of the series of plans defined in step (b) (g) Solidify by phototransformation of the liquid each elementary volume, the upper face of which corresponds to the altitude of the plane selected in step (g) (h) Repeat operations (e), (f) and (g) until the elementary volumes are all solidified.

characterized in that it uses means essentially taking advantage of the surface tension of the liquid to cover the already polymerized part of the part with a thin layer of said liquid, without resorting either to an external supply of liquid, or to forced flows by gravity or by mechanical interaction.

2) Method according to claim 1 characterized in that the liquid is contained in a flared tank in its upper part.

REPLACEMENT SHEET 3) Method according to claim 1 characterized in that the volumes solidified during one of the phases (d) or (g) are disjoint.

4) Method according to claim 1 characterized in that the means for setting up thin layers of liquid comprise moving mechanical parts traversing a trajectory without reversing the direction of travel.

5) Method according to claim 1 characterized in that the means for positioning the thin layers of liquid comprise moving mechanical parts traversing a path alternately in one direction then in the opposite direction.

6) Device according to claim 1 characterized in that the thin flat layers of liquid are put in place by setting in motion a thin flexible film whose lower part is in contact with the liquid.

7) Device according to claims 1 and 5 characterized in that the thin flexible film is folded back on itself in a U shape.

8) Device according to claims 1 and 5 characterized in that the thin flexible film consists of fibers.

9) Device according to claims 1 and 5 characterized in that the thin flexible film consists of several layers of material capable of retaining liquid by capillarity.

10) Device according to claim 1 characterized in that the thin layers of liquid are put in place by the passage of at least two successive flexible thin films.

REPLACEMENT SHEET