FR2654538A1 - Method and device for producing a model of an industrial part by polymerisation of a monomer liquid - Google Patents

Abstract

This method comprises n successive steps, each step consisting in introducing into a vat (6), at increasing levels from one step to the other, the monomer liquid and a support liquid of greater density, then in illuminating a part of the equilibrium surface of the monomer liquid by radiation capable of polymerising it. A system of memories (1) is provided, linked to a radiation generator (2) by a processing circuit (3) and means for introducing the monomer liquid (11-13) and the support liquid (16-18) into the vat. Thus it is possible to keep the object produced in a gravity situation practically identical to that which existed in the preceding steps and to permit, by use in the said carrier liquid of diffusing and luminescent substances, homogeneous polymerisation of the part by the use of traditional UV sources (37).

Description

 The present invention relates to a method and a device for producing an industrial part model by polymerization of a monomer liquid.

 This technique, as well as various methods for its implementation, is described in particular in the Acts of the School of Industrial Photochemistry of Nancy, December 1988, CPIC editor, pages 542 to 567, and whose teachings will be considered as part of this description.

 One of the methods, which is of a type to which the invention belongs, comprises n successive stages, each stage successively comprising - introduction of a monomer liquid into a tank up to a predetermined level, the predetermined levels h1, h2 hn of the n steps forming an increasing sequence - and an exposure of the monomer liquid contained in the tank to radiation capable of polymerizing the monomer liquid in a flattened volume whose surface extends over part of the equilibrium surface of the liquid monomer and whose thickness extends to the predetermined level of the previous step, the shape of the industrial part being determined by information representative of the shape of n sections of the part by n parallel planes and of the mutual arrangement of these n sections, this radiation being directed according to said information so that the profiles of the surfaces of the n flattened solidified volumes are respectively t identical to the profile of the n sections of the part and that these surfaces are superimposed according to said mutual arrangement.

 This process has a drawback. In fact, it can be seen that the models produced using this process have surface defects in certain cases.

 The object of the present invention is to overcome this drawback.

 It relates to a process of the type mentioned above, characterized in that each step of rank p further comprises, before said exposure, the introduction into the tank of a support liquid which cannot be polymerized by said radiation, this support liquid having a density greater than that of the monomer liquid and that of the solidified monomer, this support liquid rising in the tank at each step of rank p to a level h 1 equal to that of the monomer liquid in the previous step, so to support the monomer liquid of level hp, p being an integer successively taking the values 2, 3 ------ n.

 In an embodiment of the method according to the invention, the exposure of the monomer liquid to radiation comprises, at each step - a first exposure of a closed peripheral cord running along the profile of the surface of said flattened volume, this first exposure taking place by not necessarily continuous displacement of a beam of radiation on the equilibrium surface of the monomer liquid in the tank, - an evacuation of the support liquid and of the monomer liquid from the tank located outside said bead, - and a second exposure of the monomer liquid surrounded by said bead, this exposure taking place overall by another radiation fixed relative to the tank.

 In various embodiments of the method according to the invention, the monomer liquid is either of the unifunctional type, or of the polyfunctional type, or a mixture of monomeric and polyfunctional liquid monomer. The monomer liquid can also contain a sensitizing additive capable of increasing the rate of polymerization or one of the luminescent additives.

 The support liquid is preferably immiscible with the monomer liquid, but it can contain a fluid additive miscible both with the support liquid and with the monomer liquid.

 According to another aspect of the present invention, in a process of the aforementioned generic type, a non-polymerizable support liquid is introduced into the tank, this support liquid having a density greater than that of the monomer liquid, so as to remove the excess monomer liquid .

 The present invention also relates to a device for producing an industrial part model by polymerization of a monomer liquid, comprising - a tank, - means for introducing a monomer liquid into the tank, - a memory system containing information representative of the shape of the industrial part, - a processing circuit connected to the memory system and capable of delivering, from this information, signals representative of the position of elements of the volume of the part, these signals being delivered in a first scan taking place in n successive parallel planes, - a generator of a radiation beam connected to the output of the treatment circuit, this beam being capable of causing solidification of the monomer liquid by polymerization, - connected means to the processing circuit to direct the beam towards successive portions of the equilibrium surface of the monomer liquid in the tank following a second scan, this second scan taking place along n successive horizontal planes the level of which rises progressively above the bottom of the tank, - control means connected to the processing circuit and to the introduction means of the monomer liquid, to adjust the level of the monomer liquid in the tank to increasing predetermined values hl, h2 hn corresponding to the n successive horizontal planes, device characterized in that it further comprises - means for introduction into the tank, under the monomer liquid, a support liquid with a density greater than that of the monomer liquid - and a control system connected to the processing circuit and to the means for introducing the support liquid, for adjusting the level of this support liquid at predetermined values lower than the values of the level of the monomer liquid.

 In one embodiment of the device according to the invention, it comprises means connected to the treatment circuit for removing from the tank the support liquid and a first part of the monomer liquid through an opening made in the bottom of the tank, and a source of radiation fixed with respect to the tank, this source being connected to the treatment circuit to irradiate the entire second part of the monomer liquid remaining in the tank after the removal of said first part.

 In another embodiment of the generator according to the invention, the generator of the radiation beam comprises a laser emitter, and, said means for directing the beam towards the equilibrium surface of the monomer liquid in the tank comprising a mobile converging optical system , means for moving the optical system converge above the tank, and means for adjusting the focusing distance of the optical system.

 In another embodiment of the device according to the invention, said means for directing the optical beam towards the equilibrium surface of the monomeric liquid in the tank comprise a rotating reflector disposed at the outlet of the converging optical system and capable of modifying the inclination of the beam relative to the vertical.

 Particular embodiments of the object of the present invention are described below by way of example, with reference to the accompanying drawings in which - Figure 1 schematically shows an embodiment of the device according to the invention, - Figure 2 is a perspective view of part of the device illustrated in Figure I, - Figure 3 shows a modification of detail of the device illustrated in Figure 2, - and Figure 4 schematically shows another embodiment of the device according to the invention.

 In FIG. 1, a memory system 1 is shown, arranged at the output of a computer, not shown, which has been used to determine by the computer-aided design (CAD) method the characteristics of a part such as a connecting rod. An optical generator 2 is connected to the output of the system 1 through a processing circuit 3. The generator 2 can be a laser generator, for example of the excimer type. It can also be a source of X-rays, gamma rays or electrons.

 The generator 2 emits radiation 4 which is concentrated on a portion 5 of the internal volume of a tank 6 by a converging optical system 7. A control system 8, connected between the output of the circuit 3 and the optical system 7, makes it possible to adjust the focusing distance of the optical system 7.

 The device comprises means for moving the optical system 7 above the tank 6 in a horizontal plane 9. These means include motors such as 10 connected to the outlet of the circuit 3. A system for supplying the tank 6 in a monomer liquid comprises a pipe 11 connecting a reservoir 12 of this liquid inside the tank 6. An electric pump 13, controlled by a servo system 14 for the level 15 of monomer liquid in the tank 6, is placed in series on the pipe 11. The input of the system 14 is electrically connected to the output of the processing circuit 3.

 Another system for supplying the tank 6 with a support liquid, denser than the monomer liquid, comprises a pipe 16 connecting a reservoir 17 of the support liquid to an opening formed in the bottom of the tank 6. An electric pump 18 controlled by a servo system 19 of the level 20 of the support liquid in the tank 6, is placed in series on the pipe 16.

 FIG. 2 shows in perspective the tank 6, its means for supplying liquid as well as a preferred embodiment of the means of displacement of the optical system 7. These means of displacement comprise two motors 23 and 24 integral with two rails 25 and 26 fixed longitudinally on two parallel upper edges of the tank 6. The output shafts of the motors 23 and 24 are connected, by worm gear systems, to two mobile carriages 27 and 28 sliding along the rails 25 and 26. A third rail 29 is fixed transversely to carriages 27 and 28. A motor 30 fixed to one end of the rail 29 is connected by a worm gear system, to a carriage 31 sliding along the rail 29. The laser generator 2 is arranged so as to deliver a beam 32 parallel to the rail 25 towards a reflector 33 fixed on the carriage 28. The reflector 33 deflects the beam 32 parallel to the rail 29 towards another reflector 34 fixed on the carriage 31. The reflector 34 vertically reflects the beam it receives towards the optical system 7 also fixed on the carriage 31. The optical system 7, with vertical axis and at variable focusing distance, concentrates the laser energy on a surface portion 5 of the liquid contained in the tank 6.

 FIG. 2 also shows the reservoir 12 of monomer liquid, connected to the interior volume of the tank by the pipe II on which the pump 13 is arranged. This figure also shows the reservoir 17 of support liquid, connected to an opening in the bottom of the tank 6 via the pipe 16 on which the pump 18 is arranged.

 FIG. 3 represents a detail of a variant of the embodiment illustrated by FIG. 2. In this variant, the carriage 31 comprises, in addition to an optical system 7 with variable focus, a complementary device composed of one or more rotating mirrors 35 arranged at the output of the optical system 7. These mirrors make it possible to tilt the focused laser beam relative to the vertical 38; the rotation of these mirrors is ensured by motors 36 also fixed on the carriage 31. The motors 36 are electrically connected to the processing circuit 3 (FIG. 1).

 The device illustrated in Figures 1, 2 and 3 operates as follows.

 The memories of the system 1 contain information, for example digital, representative of the shape of the part to be reproduced, the characteristics of which have been determined using the computer according to the C.A.O.

 The volume of the part is divided into a certain number of elements and the information from system 1 determines the position of the different elements of the part with respect to a reference system such as a system of xyz trirectangles. The processing circuit 3 makes it possible to classify this information in the order of a scan of the volume of the part and to deliver corresponding positioning signals. These signals are representative on the one hand of the form of n sections of the part by n parallel planes and on the other hand of the mutual arrangement of these n sections.

 The method for producing the part comprises n successive steps which are first described in the case where the device illustrated in FIGS. 1 and 2 is used.

In a first step, the signals of the circuit 3 are transmitted to the pump 13 which pours into the tank 6, initially empty, of the monomer liquid stored in the reservoir 12. The flow of the liquid is stopped by the servo system 14 when the level above the bottom of the tank reaches a predetermined value hl relatively low; the control system 8 adjusts the focusing distance of the optical system 7 so that the focal point of the laser beam is located in the tank a little below the level h1, for example at the level h2. The
2 signals from circuit 3 are also transmitted to motors 23 and 24 which operate in synchronism so as to keep rail 29 perpendicular to rails 26 and 27. These signals are also transmitted to motor 30. The optical system 7 is thus moved horizontally in the plane 9 following the scanning of the part to be reproduced so as to expose to laser radiation successive portions of a part of the equilibrium surface of the liquid, this part corresponding to a first section of the part by the first of the n parallel planes . The portions of the monomer liquid thus exposed are polymerized and solidified in a flattened volume whose surface extends over said equilibrium surface part and whose thickness corresponds to the level h. A first section of the model is thus obtained, resting on the bottom of the tank.

 In a second step, the pump 18 introduces into the tank 6 the support liquid stored in the tank 17. This liquid spreads in the tank under the monomer liquid, so as to slightly raise the level of the monomer liquid above the level hl and to form an underlying layer of support liquid. The control circuit 19 stops the flow of the support liquid when the level of the underlying layer reaches the level h1 of the monomer liquid in the previous step.

Then the pump 13 is started in order to bring the level of the monomer liquid to a predetermined value h2 greater than hl. The focal point of the optical system 7 is adjusted a little below the level h2, for example at the level h1 2. The optical system 7 is then
2 moved horizontally so as to expose to laser radiation successive portions of another part of the equilibrium surface of the liquid, this other part corresponding to a second section of the part by the second of said n parallel planes. The monomer liquid is thus solidified according to another flattened volume whose thickness is equal to h2 hl. A second slice of the model is thus obtained which adheres by its lower surface to the upper surface of the first slice.

 It is found that the material polymerized by the action of laser radiation has a density greater than that of the monomer liquid from which it comes.

The underlying layer of support liquid has a density greater than that of this polymerized material, which allows it to support the solidified portions which are not located directly on the volume solidified in the previous step, and to prevent these portions do not fall to the bottom of the tank due to their density greater than that of the monomer liquid. The latter undesirable phenomenon can occur in particular, using the method according to the prior art, when the surface of the model has a shape which widens when going from one step to the next. This phenomenon then leads to a deterioration of the surface condition of the model. The layer of the underlying support liquid according to the present invention thus plays a role analogous to that of the already solidified volume on which the new polymer material can be fixed.

 The following steps are completely analogous to the second step which has just been described, it being understood that at each step of rank p where the level 15 of the monomer liquid is adjusted to a value hp, of level 20 of the support liquid is set to a value hp 1 equal to that of the level of the monomer liquid in the previous step.

 When using the device illustrated in Figures 1 and 2, it is clear that each solidified portion has the shape of a small vertical cylinder.

These cylinders are connected to each other in the solid part of the model, but give the exterior surface of the model a shape which moves further from reality the greater the difference between the successive levels hl h. The use of the device illustrated in FIG. 3 makes it possible to improve the surface quality of the model by giving the focused laser beam, for the production of the surface portions of the model, an inclination A relative to the vertical 38, identical to the inclination of the plane tangent to the surface of the corresponding elements of the part to be reproduced. The model thus produced thus has a shape closer to that of the part to be reproduced.

 The monomeric liquids which can be used in the device according to the present invention can be classified into two main categories: the unifunctional monomers and the polyfunctional monomers. Unifunctional monomers polymerize by chain reaction under the effect of radiation, while polyfunctional monomers polymerize by branching reactions or by crosslinking. With a polyfunctional monomer, the higher the intensity of the radiation, the higher the hardness of the solidified material. However, for polyfunctional monomers formed from small molecules, the presence of a high excitation flux leads to the formation of free radicals or other reactive species in large quantities which then disappear as a result of radical recombination processes: this results in the formation of resins of low masses with internal tensions likely to make the model fragile.

 In order to be able to expose the monomeric liquids to high excitatory fluxes, it is possible to use either polyfunctional monomers formed from larger molecules, or mixtures of unifunctional and polyfunctional monomers. In general, solidified substances formed by crosslinking from polyfunctional monomers are insoluble in monomeric liquids, which is not always the case for substances polymerized from unifunctional monomers.

 The photopolymerizable liquid is always made up of two systems: the initiator system and the "resin" system, each of which can be made up of one or more types of molecules.

 The initiator system can very simply consist of a single type of molecule which, after absorption of an excitation photon, will decompose directly by homolytic scission into priming free radical species in the case of radical polymerization, strong acids in the case of cationic polymerization.

 These initiators are substituted acetophenones (haloacetophenones, alkoxyacetophenones), benzolines and benzoin ethers, benzoyl oxine derivatives, phosphene oxides, aromatic ketones containing a carbon-sulfur bond (sulfides, sulfoxides, sulfones) azo compounds or substituted α-amino ketones in the case of radical polymerization and of the diazonium, dialkyl-4-hydroxyaryl-sulfonium or dialkylphenacyl-sulfonium salts in the case of cationic polymerization.

 The initiator system can also contain an electron or hydrogen transferer in the case where the initiator alone does not allow the formation of the initiating species. The initiators used in this case are diarylketones (derivatives of benzophenone, fluorenone, anthrone, xanthone, acridone or thioxanthone), derivatives of benzile (or diphenylethanedione) or ketocoumarins in the case of radical polymerization and of diaryliodonium, triarylsulfonium, triarylselenonium or ferrocenium salts in the case of cationic polymerization. The most reactive hydrogen donors are those carrying the hydrogen atom in the form of an oxygen (aliphatic ethers) and nitrogen (aliphatic amines and more particularly tertiary amines) or directly attached to a sulfur (thiols and thioethers). Alcohols and aliphatic hydrocarbons, although less reactive, can also play this role. Tertiary amines are the best electron donors.

 The initiator system may contain a photosensitizer in case the absorption spectrum of the initiator does not coincide with the wavelength of the irradiation source or to accelerate the rate of polymerization.

 Photosensitization of radical initiators is done by energy transfer - with thioxanthone derivatives (isopropylthioxanthone for example) - or by electron transfer. The photosensitization of cationic initiators is essentially done by electron transfer, either directly with arene type molecules (anthracene, perylene for example) or phenothiazine, or indirectly after hydrogen transfer with aromatic ketone type derivatives (thioxanthone , acetophenone, benzophenone).

 The "resin" system can consist either of a single type of monomer or of a mixture of mono, di, tri or even tetrafunctional monomers. The choice is dictated by the desired characteristics of the material before polymerization (viscosity, vapor pressure), of the material after polymerization (insolubility in the starting liquid, solid physical state) and of the polymerization reaction (kinetics, shrinkage or relative difference between the densities of the material before and after polymerization). The choice generally results from a compromise between the properties having an advantage and those having a disadvantage.

 In the case of radical polymerization, acrylate resins, unsaturated polyesters, thiol-enes or urethanes are generally used. In the case of cationic polymerization, epoxy resins (cycloaliphatic, aromatic or aliphatic diglycidyl ethers), divinyl ethers, spiroorthoester or spiroorthocarbonate are generally used.

 It is also possible to use a mixed system consisting of polymerizing monomers cationically and radically. Both types of initiator systems must be present.

 It may also be useful, in certain cases, to add a luminescent additive to the monomer liquid, for example to perform certain optical measurements on the model.

 Can be used as carrier liquid, for example water laden with salts. However, since the support liquid is not miscible with the monomer liquid, the level of the support liquid in the tank is not always perfectly constant and the layer of monomer liquid does not always have a constant thickness. To overcome this possible difficulty, it may be advantageous to add to the support liquid, in a small amount, a substance soluble both in the monomer liquid and in water. This substance can be, for example, an alcohol, an acetone, or a surfactant. Under these conditions, the distance between the interfaces 15 and 20 is substantially independent of the region of the tank where it is measured.

 A small object with a surface area of 5 cm2 and a height of 1.5 cm representing a bridge comprising square piles of 1 cm side, surmounted by a crosspiece resting on these piles, of length 5 cm, was produced with using a device similar to that shown in FIGS. 1 and 2. The radiation generator was a high pressure mercury vapor lamp, of power 500 W, delivering a parallel beam capable of being focused.

 Another embodiment of the device according to the invention is shown in Figure 4. This embodiment has the same elements as that illustrated in Figure 1, designated by the same reference numerals. The device illustrated in Figure 4 further comprises a pipe 21 for discharging the tank, connected to an opening in the bottom of the tank 6, and a pump 22 inserted in the pipe 21 and connected to the outlet of the circuit. treatment 3. The device in FIG. 4 also includes sources 37 of radiation fixed relative to the tank, arranged so as to radiate the interior of the tank 6 overall.

 The operation of the device illustrated in Figure 4 is changed from that of Figure 1 as explained below.

 At each step, the movement of the optical system 7 is controlled by the circuit 3 only to solidify a closed peripheral bead along the profile of the surface part to be irradiated. The monomer liquid then contained in the tank has a first part outside the cord and a second part surrounded by the cord.

 The circuit 3 then starts the pump 22 so as to remove from the tank the support liquid (if it is a step of order at least equal to 2) and the first part of the monomer liquid.

 Then the circuit 3 triggers the operation of the radiation sources 37, so as to solidify in a short instant the entire surface located inside the bead.

 This solidification in two successive phases makes it possible to reduce the total solidification time and to increase the homogeneity of the material of the model.

 In the next step of the process, monomer liquid and support liquid are introduced into the tank so as to allow the polymerization of another section of the model.

 Of course, contrary to what is shown diagrammatically in FIG. 4, the stationary sources of radiation 37 that are not very stigmatic are arranged above the tank so as to be able to illuminate its internal volume without hampering the movement of the optical system 7. In addition , the device may include means not shown for moving the mobile carriage 31 away from the tank during the irradiation carried out by the sources 37, so that this carriage and its accessories cannot be interposed on the path of the fixed radiation.

 It is possible to adapt without difficulty to the device illustrated in Figure 4 of the additional systems. This is how it is possible to set up a system for draining the monomer liquid surrounded by the cord, so as to obtain a hollow model.

 Finally, according to a last embodiment of the invention, a carrier liquid is not used, such as for example salt water, which was mentioned above. The part is therefore produced by its surface as has also been specified by a traditional layering method, in itself known.

 In these known methods, the volume part containing unpolymerized monomer is taken out of the tank containing said monomer to be mass polymerized by photopolymerization using UV sources.

 conventional. However, for the production of large parts, the presence of liquid inside the part induces, when the latter is no longer immersed in its monomer bath, deformations linked to gravitational effects.

 The use of the process described here overcomes this major drawback by replacing the monomer with a non-miscible carrier liquid, not layer by layer, but once after the part has been made by its surface. Under these conditions, the object produced is maintained practically in the absence of gravitational effects and no longer deforms.

 The carrier liquid can advantageously be obtained from water added with salts, the density of which is adapted to enable the monomer to be removed, which must have a density lower than that of the carrier liquid. The use of such a fluid, transparent to UV radiation.

conventionally used to mass polymerize the object in a subsequent step, further allows a limitation of the thermal effects induced by this photochemical crosslinking.

 This carrier liquid can finally have other peculiarities - contain light-diffusing substances, such as particles of divided solids: alumina, titanium oxide, etc. which allow the light coming from UV sources to be diffused throughout the reactor, allowing hidden areas to be reached.

 - contain luminescent and in particular fluorescent substances.

The use in the medium carrying such substances allows, by the emission at a suitable wavelength, a homogeneous or almost homogeneous absorption of light in the room and, more precisely, in the liquid monomer. Under these conditions, the polymerization is isotropic and the part undergoes only an isotropic deformation. On the other hand, in traditional methods, the absorption of light takes place at shallow depths and is capable of inducing, by a polymerization spatially resolved over time, deformations incompatible with the specifications of the designer of the part.

Claims (19)

 1. Method for producing an industrial part model by polymerization of a monomer liquid, comprising n successive stages, each stage successively comprising - introduction of a monomer liquid into a tank up to a predetermined level, the predetermined levels h1, h2 hn of the n steps forming an increasing sequence - and an exposure of the monomer liquid contained in the tank to radiation capable of polymerizing the monomer liquid in a flattened volume whose surface extends over part of the equilibrium surface of the liquid monomer and whose thickness extends to the predetermined level of the previous step, the shape of the industrial part being determined by information representative of the shape of n sections of the part by n parallel planes and of the mutual arrangement of these n sections, this radiation being directed according to said information so that the profiles of the surfaces of the n volumes ap solidified latis are respectively identical to the profile of the n sections of the part and that these surfaces are superimposed according to said mutual arrangement, characterized in that each step of row p further comprises, before said exposure, the introduction into the tank (6) of a support liquid that cannot be polymerized by said radiation, this support liquid having a density greater than that of the monomer liquid and that of the solidified monomer, this support liquid rising in the tank at each step of rank p at a hop 1 level (20) equal to that of the monomer liquid in the previous step, so as to support the monomer liquid of level h (15), p being a  p integer successively taking the values 2, 3 ------- n.  2. Method according to claim 1, characterized in that the exposure of the monomer liquid to radiation comprises, at each step - a first exposure of a closed peripheral cord along the profile of the surface of said flattened volume, this first exposure s 'effecting by displacement of a beam of radiation on the equilibrium surface of the monomer liquid in the tank, - an evacuation of the support liquid and the monomer liquid from the tank (6) located outside said bead - and a second exposure of the monomer liquid surrounded by said bead, this exposure taking place globally by another radiation fixed relative to the tank.  3. Method according to claim I, characterized in that the monomer liquid is of the unifunctional type.  4. Method according to claim 1, characterized in that the monomer liquid is of the polyfunctional type.  5. Method according to claim 1, characterized in that the monomer liquid is a mixture of unifunctional monomer liquid and polyfunctional monomer liquid.  6. Method according to claim 1, characterized in that the monomer liquid contains a sensitizing additive capable of increasing the rate of polymerization.  7. Method according to claim 1, characterized in that the monomer liquid contains a luminescent additive.  8. Method according to claim 1, characterized in that the support liquid is immiscible with the monomer liquid.  9. Method according to claim 1, characterized in that the support liquid contains a fluid additive miscible both with the support liquid and with the monomer liquid.  10. Method for producing an industrial part model by polymerization of a monomer liquid comprising n successive stages, each stage comprising successively - introduction of a monomer liquid into a tank up to a predetermined level, the predetermined levels h1, h2 h n stages forming  n an increasing sequence - and exposure of the monomer liquid contained in the tank to radiation capable of polymerizing the monomer liquid in a flattened volume whose surface extends over part of the equilibrium surface of the monomer liquid and whose thickness extends to the predetermined level of the previous step, the shape of the industrial part being determined by information representative of the shape of n sections of the part by n parallel planes and of the mutual arrangement of these n sections, this radiation being directed according to said information so that the profiles of the surfaces of the n flattened solidified volumes are respectively identical to the profile of the n sections of the part and that these surfaces are superimposed according to said mutual arrangement, characterized in that, after execution n successive stages, a non-polymerizable support liquid is introduced into the tank (6), this support liquid having a e density greater than that of the monomer liquid, so as to remove the excess monomer liquid.  11. The method of claim 10, characterized in that the exposure of the monomer liquid to radiation comprises, at each step - a first exposure of a closed peripheral cord along the profile of the surface of said flattened volume, this first exposure s 'effecting by a not necessarily continuous displacement of a beam of radiation on the equilibrium surface of the monomer liquid in the tank, - a formation, above the object being manufactured, of a layer of monomer of known height, and in that, after the final step of removing excess monomer liquid by introduction of the non-polymerizable support liquid, the monomer liquid contained within the volume defined by the previously peripheral cords is polymerized exposed.  12. Method according to claim 11, characterized in that the final polymerization step is carried out by activation of an external UV light source.  13. The method of claim 12, wherein a liquid transparent to active radiation is used to perform the volume polymerization.  14. The method of claim 12, wherein one uses, for the volume polymerization, a liquid containing diffusing substances.  15. The method of claim 12, wherein is used for the volume polymerization of luminescent substances capable of allowing a more homogeneous absorption of the light re-emitted inside the volume to be polymerized.  16. Device for producing an industrial part model by polymerization of a monomer liquid, comprising - a tank (6), - means (11, 12, 13) for introducing a monomer liquid into the tank, - a memory system (1) containing information representative of the shape of the industrial part, - a processing circuit (3) connected to the memory system (I) and capable of delivering, from this information, signals representative of the position of elements of the volume of the room, these signals being delivered according to a first scan taking place in n successive parallel planes, - a generator (2) of a radiation beam connected to the output of the processing circuit (3) , this beam being capable of causing solidification of the monomer liquid by polymerization, - means (10) connected to the processing circuit for directing the beam towards successive portions of the equilibrium surface of the monomer liquid in the tank following a second scan, this second scan taking place along n successive horizontal planes the level of which rises progressively above the bottom of the tank, - control means (14) connected to the treatment circuit (3 ) and to the means (11, 12, 13) for introducing the monomer liquid, to adjust the level of the monomer liquid in the tank (6) to increasing predetermined values hl, h2 h corresponding to the n successive horizontal planes,  n characterized in that it further comprises - means (16, 17, 18) for introducing into the tank (6), under the monomer liquid, a support liquid with a density greater than that of the monomer liquid - and a servo system (19) connected to the treatment circuit (3) and to the means (16, 17, 18) for introducing the support liquid, for adjusting the level of this support liquid to predetermined values lower than the level values monomer liquid.  17. Device according to claim 16, characterized in that it comprises means (21, 22) connected to the treatment circuit (3) for removing from the tank (6) the support liquid and a first part of the monomer liquid by a opening in the bottom of the tank, and a source (37) of radiation fixed relative to the tank, this source being connected to the treatment circuit (3) to irradiate all the second part of the monomer liquid remaining in the tank after the removal of said first part.  18. Device according to claim 16, characterized in that the generator of the radiation beam comprises a laser emitter, and, said means for directing the beam towards the equilibrium surface of the monomer liquid in the tank comprising a converging optical system (7 ) mobile, means (10) for moving the converging optical system above the tank, and means (8) for adjusting the focusing distance of the optical system (7).  19. Device according to claim 18, characterized in that said means for directing the beam towards the equilibrium surface of the monomer liquid in the tank (6) comprise a rotating reflector (35) disposed at the outlet of the converging optical system (7 ) and capable of modifying the inclination of the beam relative to the vertical (38).