WO2002045940A1

WO2002045940A1 - Method and device for making three-dimensional parts in fusible thermoplastic materials

Info

Publication number: WO2002045940A1
Application number: PCT/FR2001/003831
Authority: WO
Inventors: Hugues Goulesque
Original assignee: Hugues Goulesque
Priority date: 2000-12-04
Filing date: 2001-12-04
Publication date: 2002-06-13
Also published as: AU2002216169A1; FR2817493A1

Abstract

The invention concerns a method for making three-dimensional parts in fusible thermoplastic materials, by bonding and solidifying successive superimposed sections, each obtained by casting a binder (10) on a layer of particles (1). The binder (10) is heated before casting to a temperature both higher than its casting temperature and sufficiently high to produce surface melting of the particles (1) with which it is contacted, so as to produce its bonding with the latter after solidification. The bonding of two successive layers is carried out, by such a surface fusion and solidification process, between the particles (1) and each of the two successive layers (N-1 and N) of binder (10) and directly between the two successive layers (N-1 and N) of binder (10). The invention also concerns a device for making three-dimensional parts using said method.

Description

METHOD AND DEVICE FOR MANUFACTURING THREE-DIMENSIONAL PARTS FROM THERMOPLASTIC MATERIALS

FUSE

The present invention relates to a method for manufacturing three-dimensional parts, the basic materials of which are fusible thermoplastic materials, that is to say materials which have a low melting temperature, and whose physical structure is not modified. after partial or total merger and re-solidification. The invention thus applies in particular to materials of the plant, animal or mineral wax type such as paraffin.

Carrying out the process according to the invention involves the bonding and solidification of successive superposed parallel sections, and is based on the surface fusion of particles induced by contact with a molten binder. This surface melting phenomenon gives the part thus formed good mechanical strength.

The invention also relates to a device for manufacturing three-dimensional parts, the basic materials of which are fusible thermoplastic materials. This device is automated and includes computer control means.

The manufacture of three-dimensional objects is commonly carried out by rapid prototyping process. A wide variety of basic materials are used for this manufacturing, including metals, ceramics, plastics ...

However, the use, for the manufacture of three-dimensional objects, of basic materials such as wax and paraffin, has the advantage of having low material costs. All kinds of parts or molds, intended for multiple uses, can be manufactured with these materials. However, wax parts, because of their low temperature melting property, find a particularly advantageous use in foundry, or in similar activities applying the so-called "lost model" process.

This process consists in using a part obtained by rapid prototyping, called a model, and in making a mold, which is then used for the manufacture of a generally metallic part identical to the model. A self-hardening resin sand molding process can be used to make the mold. The last step in the manufacture of the mold is the evacuation of the model, by melting it. However, the mold does not withstand temperatures generally above 300 ° C which cause the combustion of the resin keeping the sand. It is therefore particularly suitable in this technique to use a model made of fusible materials such as waxes and paraffins, which makes it possible to effectively carry out the evacuation phase at satisfactory temperatures.

Today there are different rapid prototyping processes using fusible thermoplastics as the base material. We can quote for example:

- Modeling by deposition of molten material, or "Fused Deposition Mαdeling" (FDM), which operates from two nozzles respectively constructing a three-dimensional volume known as the support structure, and a volume corresponding to the part to be constructed. These two volumes, after solidification, are at the end of manufacture in "detachable" contact either mechanically or by dissolving the support structure. The part is therefore obtained after separation of these two volumes.

- Selective laser sintering, or "Selective Laser Sintering" (SLS), which operates from a laser which causes particles to agglomerate on the surface of a volume, according to zones determined by the geometric profile of the piece to be created. Layers of particles are successively applied and agglomerated on said volume. At the end of manufacture, a three-dimensional solid is formed from the different areas of the layers which have been hardened by the laser. The part is separated by evacuation of the non-agglomerated grains. - The "Shell Formation Topography" (TSF). It consists of superimposing successive layers of grains of sand stuck together by spraying molten paraffin at different heights depending on the area to be created. At the end of manufacture, the three-dimensional solid is formed from the different zones of the layers which have bonded between them.

These methods have the disadvantages of being long to implement for the manufacture of large parts, and of presenting high production costs, which become exorbitant if one seeks to adapt them to modern industrial conditions for models. large prototypes.

It is therefore desirable to have a process which can be implemented for large parts (for example larger than 3 m ³ ), at reduced production costs. It is further desirable, in this context, to lend itself to a definition of the shape of the pieces which passes through computer files of digital data as they are now commonly obtained by computer-aided design techniques and software.

The invention thus aims to propose a prototyping process for the manufacture of three-dimensional parts based on fusible thermoplastic materials, and a device suitable for the implementation of this process, which are such that they allow rapid, precise production. and inexpensive, large parts. It also aims to ensure that the method and the device according to the invention are particularly suitable for the manufacture of so-called prototyping models for use in the technique of manufacturing "lost model" molds used in foundries, it being understood that the invention can also be used, without modification other than those which are within the reach of those skilled in the art, for any similar application requiring the manufacture of three-dimensional parts made of fusible material.

To this end, the present invention proposes to have recourse to a process for manufacturing three-dimensional parts by bonding and solidification of different parallel two-dimensional sections of the part, defined as successive and superimposed sections, of the type comprising carrying out a repetitive cycle comprising depositing a layer of powder of a material in the form of grains or particles and casting on said layer, along a path predetermined by the shape of the part to be obtained, of a bonding material in liquid form so as to produce, after solidification of said binder, a section of the final part consisting of a layer of bonded particles , on which is deposited a new layer of particles for the realization of the next section of the part. The last step of such a process consists in evacuating unbound particles so as to release the formed part.

The techniques of this kind which are known are rather suitable for the production of foundry molds, and not prototype models. We can in particular refer here to patent application EP 0 431 924, which describes the manufacture of three-dimensional objects by superimposition and bonding of sections of different profiles, according to a method which uses a powder of grains or particles, spread out in layers successive, by planning to pour on each of them a binder in liquid form.

However, as illustrated by this document, the art prior to the present invention is not suited to the objectives which the latter has set for itself. The method described there is directed towards the manufacture of metal and / or ceramic molds, which can only be used directly as foundry molds. There is no question of taking advantage, as the present invention does, of the particular properties of the particles constituted by a fusible thermoplastic material of the type of waxes and paraffins.

The process according to the invention represents a notable improvement in known techniques of this kind by the fact that the particles and the binder are made of meltable chemically compatible thermoplastic materials, and that the binder material is heated before casting to a temperature which is at both higher than its drop pour point and sufficiently high, relative to the drop point of the powdered material, to cause the surface fusion of the particles with which it comes into contact, so as to achieve its connection with them after solidification.

According to the invention, the connection of two successive sections is thus achieved, by a similar process of surface fusion and solidification, acting at least either on the one hand between particles located at the interface of the two sections and the binder involved respectively. in each of the two successive layers, or on the other hand directly between the binder belonging to the two successive layers of binder. In preferred embodiments of the invention, the connection between two successive sections of the workpiece proceeds from one and from the other, so that each section of the piece is integral with the following d firstly because of the connection made between relatively large particles and the binder at the interface of two successive sections, secondly because of a connection made at least in places between the binder layer falling under a section of the room and that of the next section.

The bonding of the particles and the binder, carried out by surface fusion of the particles and. joint solidification with the binder, can be designated under the term of weld, although this term is normally used when it is about metals to be bonded. However, it is used here because it is very explicit when describing a connection of elements by local fusion of their respective surfaces in contact.

It should also be specified that by surface fusion of the particles is meant here any partial or total fusion starting on the surface of the particles. However, to ensure good mechanical resistance to the finished part, it is preferable that the fusion is deep enough to ensure an appropriate mechanical resistance bond, but that it does not go to the core in each particle of the powdered material. .

The invention advantageously takes advantage of the properties of the materials used, characterized by their fusible thermoplastic nature. Indeed, for fusible thermoplastic materials of type of waxes and paraffins, the transition between the solid state and the liquid state is not clear.

The melting point is commonly used to designate the temperature at which the material makes a transition from the solid or semi-solid phase to the liquid phase.

The following terms further characterize paraffins, and define its passage between the solid state and the liquid state, or vice versa: - the solidification point (or congealing point), defined by standard ASTM D938, is the temperature at which the material stops flowing when the temperature decreases,

- the dropping point, defined by standard ASTM D566, is the temperature at which the paraffin changes from the solid or semi-solid state to the liquid state when the temperature increases,

- the drop melting point, defined by standard ASTM D127, is the temperature at which the material begins to be sufficiently fluid to drip through an orifice.

These terms may be applicable to other fusible materials, for example hotmelt adhesives, and may in these cases be quantified and measured by methods comparable to the above-mentioned ASTM methods.

The choice of the binder heating temperature according to the method of the invention is thus linked, on the one hand to the drop pour point of the binder, to allow the latter to be in a sufficiently fluid form to flow from the nozzle onto the layer of particles, and on the other hand at the point of drop of the particles, so as to ensure the surface fusion of these. These properties, combined according to the invention with a relevant choice of the heating temperature of the binder, induce a particularly interesting result, namely an improved mechanical resistance of the finished part, because the surface melting of the particles provides better mechanical strength of each section, but also better strength of connections between successive sections.

According to another characteristic of the invention, the heating temperature and the volume of binder poured onto the layer of particles are chosen, in conjunction with the size of the particles and the thickness of the layer, so that the particles protrude part of the binder layer in each section after the binder has solidified, and the binder poured onto the next layer comes into contact with these particles at a temperature above the drop point of the material constituting them, or more precisely at a temperature sufficient to bringing them to the surface at a temperature above this drop point, so that the solidified connection stiffening the connection between two successive sections is produced, by surface fusion and solidification, between said particles and each of the two successive layers of binder.

In other particularly advantageous embodiments of the method according to the invention, the pouring conditions, in particular the heating temperature and the volume of binder poured onto the layer of particles, are adjusted so that the binder poured onto a layer of particles of powdered solid material is brought to a temperature sufficient for it to migrate through said layer until it comes into contact at least in places with the solidified binder of the previous section, and this so that contact occurs a temperature above the drop point of the binder, leading to a solid bond between the two successive sections by surface fusion and solidification directly between the two layers of binder. Better mechanical strength of the finished part is thus advantageously obtained.

Furthermore, all combinations of materials can be used for the particles and the binder, provided however that they are chemically compatible. However, according to a secondary characteristic of the invention, the particles and the binder are made of materials of the same kind. In preferred embodiments, the particles and the binder are made of wax. In some of these practical embodiments of the invention, the particles of powdered material consist of paraffin, as well as the binder.

The invention also provides a device for manufacturing parts particularly suitable for carrying out the process which it defines.

Such a device for manufacturing three-dimensional parts, by bonding and solidifying successive superposed sections, is characterized in that it comprises:

an enclosure for receiving successive layers of powder of a fusible thermoplastic material in the form of particles, the bottom of which is movable vertically along the Z axis of a XYZ trirectangle mark between each deposition of one of said layers, of a distance equal to the thickness of the next layer of particles,

- a system for depositing and distributing said powder on the surface of said enclosure, making it possible to obtain layers of regular thickness, - a pouring nozzle moving in an XY plane and depositing a binder, consisting of a thermoplastic material fuse chemically compatible with the material constituting said powder, and in liquid form, on said layer of particles, along a path predetermined by the shape of the part to be obtained, said pouring nozzle comprising at least one orifice of variable section,

a device for heating said binder supplying said pouring nozzle,

- And a computer control system for controlling the displacement of said nozzle and of the bottom of said enclosure, of said deposition and distribution system, of the temperature of said heating device and of the variation of said variable section.

In particular, the control system makes it possible to control, as a function of the fixed parameters inherent in the materials used and under predetermined conditions, all the variable parameters to regulate during the implementation of the method according to the invention, in its main and preferred embodiments as they have been defined above or that they will be described and illustrated later in the description.

In this way, depending on the shape of the workpiece and the degree of precision required, the size of the particles, the drop point of the material in the form of particles, the drop pour point and the solidification point of the material. binder material, ambient temperature and casting height, the control system controls the thickness of the particle layers, the heating temperature of the binder, the path and the speed of movement as well as the flow rate of the nozzle, and the width of the variable section.

The invention will now be further specified in its preferred characteristics, by the description of particular embodiments which are the subject of the examples below. Unless otherwise stipulated, all quantified quantities or other indications will be expressed in accordance with international standardization.

The materials chosen for the binder and the particles are fusible thermoplastics as defined above, of the wax or paraffin type.

One criterion for choosing the two fusible materials is their chemical compatibility. Any combination of compatible materials can be considered. However, it is preferable to use materials of the same kind, such as two microcrystalline waxes (for example the quality waxes M7387 and M0745 sold by Moore & Munger), or two polyethylene waxes (for example the waxes known under the trade names Polyflo200 and Polyflo300 sold by Moore & Munger), or the same synthetic paraffin for the powder particles and for the binder (for example the product sold by Schumann & Saso under the trade name Paaraflint H 1 N6). Furthermore, the choice of materials is also linked to the temperatures which govern their passage between the solid state and the liquid state.

Thus, for the binder, which provides the heat energy used to bond the particles and the sections between them, the parameters to be taken into account will be mainly:

- The solidification point, which determines in this application the limits of the migration of the binder in the layer of particles, that is to say the limits of the capillarity phenomenon. In fact, during the migration of the binder, it cools, and when its temperature reaches its solidification point, the flow between the particles is stopped,

- the drop pour point, which must be exceeded by the temperature of the binder in the nozzle in order to allow its flow.

With regard to particles, several characteristics must be considered:

- the drop point, which represents the temperature to be reached to cause their surface fusion,

- the particle size, in particular the average size of the particles and the size of the largest of them.

The application of the process according to the invention therefore involves a choice of materials whose characteristics mentioned above are compatible with the properties required for the particles on the one hand and the binder on the other hand.

According to a secondary characteristic of the invention, the heating temperature of the binder before casting, the casting height and the ambient temperature are chosen so that the temperature of the binder, when it is in contact with the powdered material, is greater than the latter's drop point.

This gives a completely advantageous solid weld of the particles with the binder. In general, and this in all the embodiments of the invention, it is preferable to keep a fixed casting height and low enough to avoid a significant heat loss of the binder during casting. The control of the temperature of the cast binder is thus facilitated. Likewise, the ambient temperature should ideally be fixed. Otherwise, the heating settings of the binder to be poured must be changed as a function of this temperature.

According to another secondary characteristic of the invention, the heating temperature of said binder before casting, the casting height and the ambient temperature are chosen, in conjunction with the particle size, in such a way that the particles do not melt. not to the core. In this way better resistance to the collapse of the part during manufacture, and therefore better dimensional stability of the finished part, are obtained.

Thus, for a casting without major loss of temperature between the outlet of the nozzle and the arrival on the layer of particles, it is advantageous to choose a heating temperature of the binder from 10 to 30 ° C higher than the drop point of the material. particles. This results in a surface fusion, but not at the core, of the particles, when in particular, according to preferred conditions for implementing the invention, the powder particles have dimensions of between 0.01 and 10 mm, and in particular of on the order of 0.01 to 2 mm and that they are at ordinary temperature (20 to 25 ° C).

For example, if one uses, for the particles and for the binder, the paraffin sold under the trade name Paraflint H 1 N6 mentioned above, which has a solidification point at 98 ° C, a drop pour point at 1 12 ° C and a drop point at 105 ° C, it will be optimal to pour the binder at a temperature of about 125 ° C, in order to effect the welding of the surface of the particles with the cast binder.

In preferred embodiments of the invention, the thickness of the layers of particles is chosen so as to be between 1 and 10 times, preferably between 2 and 5 times, the size larger particles, and small enough to ensure good dimensional accuracy. The optimal choice for the thickness of each layer is thus determined by the analysis of the granulometry of the powder and by the dimensional precision expected for the part manufactured.

If we take for example a powdered wax of the trade name Paraflint H 1 N6 with a particle size between 1 1 80 microns and 106 microns for an average grain size of 600 microns, it will be necessary to make thick layers at least equal to the size of the largest particles in order to prevent the layer deposition system from hitting the particles which could protrude from the last layer deposited. The precision obtained on the manufactured part could then be of the order of 0.6 mm after finishing.

If a powder wax of the trade name Acumist B-6 produced by Honeywell is used, with a particle size not exceeding 18 microns, the layer thickness can be reduced to a few hundredths of a millimeter and the precision of the parts optimized. These conditions can be advantageous, in particular, for producing topcoats for which precision and uniformity are essentially sought, although this is at the expense of dimensional tolerance when there is a core melting of the particles.

According to a secondary characteristic of the invention, the speed of displacement of the nozzle and the rate of pouring of the binder are regulated so that the volume of binder poured onto the layer of particles can fill a rate at least equal to 80% of the volume of air present between the particles, on the surface of the layer receiving the flow and over a thickness equal to that of the layer. In practice, this rate is between 85 and 98% of this volume.

In addition to the temperature and layer thickness adjustments, the flow rate of the binder as a function of the speed of movement of the nozzle is advantageously adjusted so that: - the binder can pass entirely through the powder layer to create the connection with the previous section, at least in places,

- The volume of binder poured is not excess and does not ultimately exceed the level of the surface of the layer, or does not spread over it.

If we consider a powder made up of spherical particles with an average radius equal to 300 microns such as paraffin with the trade name Paraflint H 1 N6, we can assess the volume of air left free between the grains at 40%. To fill it to 100% by producing a bead of 1 mm2 of average section from a nozzle moving at 100 mm / s, the flow rate of the nozzle should be 40 mm3 / s under optimal temperature conditions of casting and choice of the binder cast.

In preferred embodiments of the invention, the heating temperature of the binder before casting, the casting height and the ambient temperature are chosen so that the temperature of the binder material is higher than its drop pour point. when it comes into contact with said powder, and it reaches its solidification point immediately after the moment when the binder reaches the previous section.

In this way, the migration of the binder advantageously takes place over the entire thickness of the layer; the binder comes into contact with the previous section in order to ensure its connection, but it does not, however, extend beyond the layers of previous particles not linked to the solid state. This ensures that the parts of a section which are not supported by another solidified section, but by a layer of free particles, nevertheless have a thickness equal to the supported parts.

Furthermore, when choosing the binder heating temperature, it is desirable to take into account the fact that the binder material will cool quickly on contact with the particles, and much faster than on contact with air, so that at a given casting temperature the migration of the binder in the layer will be all the more quickly blocked. This is the case for example for a heating temperature of 120 ° C, and contact with particles at 25 ° C. The heating temperature of the binder must therefore be adapted as a function of the temperature of the particles, so that on the one hand the migration takes place over the entire thickness of the layer, and that on the other hand the binder is capable of causing the surface fusion of particles protruding from the previous section.

In addition, according to a particularly advantageous secondary characteristic, the binder material is chosen so that its solidification point is close to its drop pour point, and the heating temperature of said binder before casting, the casting height and the ambient temperature are chosen so that the temperature of the binder material when it comes into contact with the powder is just above its drop pour point, so that its migration into the powder layer is blocked quickly enough to obtain good dimensional accuracy.

This last point is to be combined with the choice of the thickness of the layers, which also allows to play on dimensional precision.

For example, one of the methods of implementing the method according to the invention uses a material in the form of particles, the drop point of which is relatively low compared to the temperature of the cast binder, in order to melt each more deeply. grains, and a binder poured at a temperature just above its drop pour point and such that its solidification point is close to its drop pour point in order to quickly block the migration of the binder in the layer and ensure dimensional accuracy. This small difference between solidification point and drop pour point is rather characteristic of paraffins, and therefore, in the case of this adjustment, it is possible for example to use a powder of the product sold by British Petroleum under the trade name Kérawax 3538 , having a drop point at 56 ° C, and pouring on it a paraffin of Kérawax 1301 quality, presenting a solidification point at 67 ° C and a drop flow at 71 ° C., which is heated to 73 ° C. In this case, the binder will solidify very quickly, but the surface of the particles will have been subjected to brutal heating at a temperature higher than the drop point of the material which constitutes them, and the welding will be correctly carried out.

According to a preferred embodiment of the invention, all the parameters defined above are combined and controlled so as to ensure the simultaneity of the following particularly advantageous conditions and results: - the binder material is found in the nozzle at a temperature above its drop pour point,

- there is a surface fusion and not at the heart of the particles on which the binder is poured,

- the migration of the binder is carried out through the entire thickness of the layer of particles,

- Partly of the particles protrude from each of the sections and their surface melting is caused by the coming into contact with the binder poured onto the next layer after migration of the latter through this layer, so that the connection between two sections successive is carried out, after solidification, between said particles and each of the two successive layers of binder,

- The binder poured on a layer of particles reaches the solidified binder of the previous section and causes its surface fusion, so that the connection between two successive sections is also carried out, after solidification, directly between the two successive layers of binder.

Preferably, at least in certain cases of application of the invention, it is also ensured that the binder occupies all the space present between the particles, in a volume corresponding to the surface of the layer receiving the casting on a thickness equal to that of said layer, in particular in order to achieve the best dimensional accuracy.

The invention will now be described further with reference to FIGS. 1 to 15, in which: FIGS. 1 to 9 illustrate the different sequences of the process for manufacturing a simple part in side view and in top view,

FIG. 10 shows diagrammatically the three-dimensional part obtained by carrying out the different sequences illustrated in FIGS. 1 to 9,

FIGS. 11 and 12 represent a sectional view of parts obtained according to the method according to the invention,

FIG. 13 illustrates a device according to the invention,

FIGS. 14. a to 14. c illustrate the binder castings produced by means of different nozzle orifices of various shapes,

- And Figure 15 shows an exploded view of the various elements of the device of Figure 13, detailing: the computer control system containing information on the part to be created, the binder heating device, the mechanism for moving the nozzle and the opening / closing of its pouring orifice, and the enclosure containing the particles and the powder deposition and distribution system.

Figures 1 to 9 illustrate the different stages of the manufacture of a simple part according to the method according to the invention. In accordance with this, the three-dimensional part is generated from the superposition and the connection by welding of successive sections of different profiles, determined by the shape of the part which one wishes to produce.

In FIG. 1, a layer of particles 1 made of fusible thermoplastic material is located in an enclosure 2, the bottom of which is movable. A binder 10 in fusion is deposited on this layer by a pouring nozzle 4. The device for heating the binder 10 is not shown in these figures.

The nozzle 4 moves in the XY plane, as illustrated in FIG. 2, so as to distribute the volume of binder 10 deposited over the entire desired surface. As it flows, the binder 10 migrates through the layer of particles 1. During its solidification, it attaches to the particles in contact with it by surface fusion of these particles due to the temperature of the binder. When the binder 10 has been poured over the entire surface to be solidified, as indicated in FIG. 3, the first cycle is finished. There is no need to wait any longer for the solidification of the formed section, since the various parameters are controlled in such a way that the time necessary for the edge 10 to reach its point of solidification is, at each point of the casting, equal to its migration time through the thickness of the layer.

All the steps are controlled by computer means, which are not shown here for the sake of clarity of the drawings, but which will be described later.

The bottom of the enclosure 2 then descends, to release, above the first layer, a space equal to the thickness of the second layer, as indicated in FIG. 4.

The particle deposition and distribution system 3 then fills this space with a layer of regular thickness of particles 1. This step is illustrated in FIG. 5. It results in a stable bed of particles for making a section of the assembly.

Thus, after each cycle, there is a descent of the bottom of the enclosure 2, and a volume of powder is mechanically distributed in the enclosure 2 using the system 3. The thickness of the layer of particles 1 as well deposited between two pouring levels is always equal to the descent height from the bottom of the enclosure 2, which makes it possible to adjust the distance between the top of the layers N and N-1.

FIG. 6 represents the assembly awaiting the second phase of casting the binder 10.

The second casting then takes place, with displacement of the nozzle 4 according to a profile different from the first, as illustrated in FIGS. 7 and 8. The binder 10 flows through the entire thickness of the layer, and reaches up to the level of the previous section to link it by thermoplastic welding phenomenon. When the second cycle is finished, the bottom of the enclosure 2 descends again to start the third cycle (Figure 9).

The process thus continues reiteratively.

The last step consists in removing the solid part from unbound particles 1. It is then necessary to clean the surfaces of the part of the particles which would have stuck there, and a finishing may be necessary if a smooth rendering is desired. The use of paraffins allows for example an easy finishing of the surface condition of the manufactured part.

During manufacture, if part of a section is not supported by another solidified part, it will not deform because it will cool and harden on a stable bed of unbound particles.

Finally, a part such as that shown in FIG. 10 is obtained, resulting from the implementation of the manufacturing process illustrated in FIGS. 1 to 9.

The connection of the different sections to each other is illustrated in FIGS. 1 1 and 12. Each of the sections binds to the previous one through particles 1 which are linked on the one hand to the binder 1 0 cast on the layer N and on the other share in the binder 10 poured onto the layer N-1, as illustrated in FIG. 1 1. In addition, the sections can also bond together directly, in places, by the binding of the binder 1 0 of the layer N to the binder 10 of the layer N-1. FIG. 12 represents the particularly advantageous case where the connection is made at the same time by these two phenomena. The best mechanical strength of the part is then reached. This is obtained by a suitable adjustment of the heating temperature of the binder 10 and of the thicknesses of the layers, as a function of the density, the shape and the drop point of the particles 1, the solidification point and the drop pour point. of the binder 10. Other conditions may also intervene in the settings, such as the ambient temperature or that of the enclosure. Depending on these parameters, optimal management of the volume of binder 10 deposited per unit of length also makes it possible to obtain precision on the dimensions of the finished part of the order of magnitude of the mean radius of the particles 1 used.

The various elements of the device according to the invention are shown in FIGS. 13 and 15.

The enclosure 2 receives the layers of particles 1. It only has the particularity of having a bottom which moves along the Z axis. This movement, produced by a defined and variable pitch, is controlled by a computer control system 6 after the end of the casting of the binder 10 on the layer of particles 1, in order to free up the space necessary for the distribution of the next layer.

The bottom of the enclosure 2 always remains parallel to its starting position, within tolerances such that the part being built is not subjected to unwanted distortions. It can be, for example, linked to a hydraulic cylinder controlled by a hydraulic distributor and an automaton, which allow its vertical and precise movement.

The system 3 for depositing and distributing the particles on the surface of the enclosure 2 is purely mechanical. At each crossing of the surface of the enclosure 2, it provides a sufficient volume of powder to create a flat layer of constant thickness which will accommodate the next pour.

This layer can completely cover the entire surface of the previous layer, it can also allow the top of the trail of binder 10 spilled on the previous layer to be exposed locally, if the latter has not completely infiltrated between the particles 1 and if it then creates an additional thickness relative to the surface of the particles. In this case, the connection between the sections will take place directly between the two successive binder flows. However, it should be recalled here that it is preferable to involve particles which are not completely melted in the connection between two successive layers in order to promote the cohesion of the whole. The system 3 may for example consist of a rolling roller resting on two parallel edges of the enclosure 2 and which will transport from one end to the other a surplus of powder so as to deposit one thickness equal to at most the distance between the top of the previous layer and the top of the parallel edges serving as support. Any other system which fulfills the function is of course usable. This system 3 is controlled by the computer control system 6.

The pouring nozzle 4 moves in the XY plane thanks to an assembly 7 and under the control of the computer control system 6. It makes it possible to channel the molten binder 10, which flows through it onto the layers of powder. The pouring nozzle 4 may include one or more orifices of different and / or variable sections. A preferred version of the nozzle 4 could be a nozzle with several orifices and controlled in rotation, which will make it possible to rapidly deposit a constant width of binder 10, and therefore in the end will make it possible to obtain a part having a constant material thickness, this which is often recommended in lost model foundries.

The flow rate of the nozzle 4 will be determined mainly by the thickness of the layers and the size of the particles 1: the greater the thickness of the layer, the more the flow rate of binder 10 will have to increase. This nozzle 4 is controlled in opening / closing, and its flow rate is preferably regulated by the computer control system 6, in particular by adjusting the pressure exerted on the binder 10. The number of orifices in play can be adjusted in the same way , as well as the shape and dimensions of the nozzle.

The assembly 7 which allows the displacement of the nozzle 4 may consist of a bracket articulated in rotation about the axis Z and whose horizontal arm allows the movement over a long distance of a carriage which contains the nozzle casting 4.

The heater 5 of the binder 10 feeds the pouring nozzle 4. It melts the binder 1 0 by heating to a temperature above its drop pour point. It's about, in a simplified version, of an electrically heated container for example, overhanging the nozzle 4 and connected to it by a pipe itself heated. It is controlled by the computer control system 6.

The computer control system 6 controls all the elements of the device. In a preferred embodiment of the invention, it is an electromechanical and / or electro-pneumatic control system and / or any other type of mechanism, which is controlled by a computer system holding the data on the part. to achieve. It can for example be made up of a computer whose analog and / or digital outputs are connected to automata which themselves control, for example pneumatic cylinders, or electric stepper motors combined with mechanical parts and systems, which coordinate the movements and openings of the nozzle 4 according to the path requested by the computer, which move the bottom of the enclosure 2 at the end of the cycle, which distribute the powder into layers of defined thickness and which control the heating of the binder 10.

The deposition of the binder 10 can take several forms depending on the orifice of the nozzle 4. Figures 14. a, 14. b and 14. c illustrate several types of deposition according to preferred embodiments of the device according to the invention , obtained respectively from a nozzle with a single round orifice, a nozzle with a triple orifice and controlled in rotation and a nozzle with a longitudinal orifice controlled in rotation.

The binder 10 can thus, depending on the case, be deposited in a simple net, or in several nets, or in a sheet, depending on the shape of the orifice. This allows large areas to be covered in a limited time. Shape and dimensions can be adjusted in conjunction with the binder flow and the nozzle displacement speed so as to always comply with the temperature conditions to be imposed on the binder deposited on the particle bed.

The nozzle 4 preferably has a variable section orifice, for example with a larger rectangular section. variable length. This means of adjusting the binder pouring conditions is particularly useful in the process according to the invention. It may indeed be sufficient to play on this parameter to cover surfaces with variable layers while maintaining the same conditions of punctual flow of binder as may be necessary, for a determined layer of particles, in order to ensure in a regular manner. a correct filling rate of the space between particles and the desired binding efficiency.

The foregoing description clearly explains how the invention achieves the objectives it has set for itself. In particular, it provides a method and a device for the precise manufacture of three-dimensional parts of good mechanical strength, made from fusible thermoplastic materials such as waxes and paraffins.

The main applications of the invention are the production of paraffin prototypes which will be molded in refractory plaster, in ceramic, or in foundry sand, in order to give rise after the paraffin is removed by fusion to a mold. foundry. The metal part thus cast in the mold will be the replica, near dimensional shrinkage, of the part made of paraffin. This application will particularly concern large parts, machine tool chassis, large casings and monumental art statues.

This new prototyping process, particularly suited to large parts, can also be applied to the production of molds for the manufacture of resin shells such as boat hulls, plastic bodywork for cars and others.

As a final example, the process according to the invention could be used for the low-cost manufacture of full-scale aesthetic models of prototypes such as a new car, household appliances, decorations, etc. The models can be painted and decorated.

Claims

1. Method for manufacturing three-dimensional parts by bonding and solidifying successive superposed sections,

comprising: carrying out a repetitive cycle comprising: - depositing a layer of powder of a material in the form of a bed of particles (1) of determined thickness,

- And the casting, on said layer of particles (1), along a path predetermined by the shape of the part to be obtained, of a binder material (10) in liquid form, to produce, after migration of said binder (1 0) through said layer and solidification of said binder (10), a section consisting of a layer of linked particles (1), on which the next layer of particles (1) is deposited, then the removal of said unbound particles (1) so as to ^'disengage said formed piece,

process characterized in that said particles (1) and said binder (10) consist of chemically compatible fusible thermoplastic materials and in that said binder material (10) is heated before casting to a temperature which is higher than its casting point drop and high enough to cause the surface fusion of the particles (1) with which it comes into contact, so as to achieve its connection with them after solidification, and in that the connection of two successive sections is achieved, by same process of surface fusion and solidification, between particles (1) located at the interface of the two sections and each of the two successive layers of binder, or directly between the two successive layers of binder (10).

2. Method according to claim 1, characterized in that the heating temperature of said binder (1 0) before casting, the casting height and the ambient temperature are chosen such that the temperature of said binder (10), when it is in contact with said powder material (1), is higher than the drop point of the latter.

3. Method according to claim 2, characterized in that the heating temperature of said binder (1 0) before casting, the casting height and the ambient temperature are chosen, in conjunction with the size of said particles (1), such so that the fusion of said particles (1) does not take place to the core.

4. Method according to any one of claims 1 to 3, characterized in that the thickness of each of said layers of particles (1) is chosen so as to be between 1 and 10 times, preferably between 2 and 5 times , the size of the largest particles, and small enough to ensure good dimensional accuracy.

5. Method according to any one of claims 1 to 4, characterized in that the speed of displacement of the casting and the rate of casting of said binder (10) are regulated so that the volume of said binder (10) poured onto said layer is at least equal to 80% of the volume of air present between said particles (1) on the surface of said layer receiving said flow and over a thickness equal to that of said layer.

6. Method according to any one of claims 1 to 5, characterized in that the heating temperature of said l iant (1 0) before casting, the casting height and the ambient temperature are chosen so that the temperature of said binder material (10) is greater than its drop pour point when it comes into contact with said powder (1), and that it reaches its solidification point immediately after the moment when said binder (1 0) reaches the section previous.

7. Method according to any one of claims 1 to 6, characterized in that said binder material (10) is chosen so that its solidification point is close to its drop pour point, and the heating temperature of said binder (10) before casting, the casting height and the ambient temperature are chosen so that the temperature of said binder material (10) when it comes into contact with said powder (1) is just above its pour point drop, so that its migration into said powder layer (1) is blocked quickly enough to obtain good dimensional accuracy.

8. Method according to any one of claims 1 to 7, characterized in that the heating temperature and the volume of said binder (10) poured onto said layer of particles (1) are chosen, in connection with the size of said particles ( 1) and the thickness of said layer of particles (1), so that particles (1) partly protrude from said section after solidification, and so that the binder (10) poured onto the next layer comes into contact with these particles (1) at a temperature higher than the drop point of the material constituting them, in such a way that the connection of two successive sections is achieved, by surface fusion and solidification, between said particles (1) and each of the two successive layers (N -1 and N) of binder (10).

9. Method according to claim 8, characterized in that the casting conditions, in particular the heating temperature and the volume of said binder (10) cast on said layer of particles (1), are such that said binder (10) cast on a layer also comes into contact with the binder material (1 0) solidified from the previous section, at a temperature above its drop point, so that the connection of two successive sections is also achieved, by surface fusion and solidification, directly between the two successive layers (N- 1 and N) of binder (10).

10. Method according to any one of claims 1 to 9, characterized in that said particles (1) and said binder (1 0) are made of materials of the same kind.

11. Method according to Claim 10, characterized in that the said particles (1) and the said binder (10) consist of wax, in particular paraffin.

12. Device for manufacturing three-dimensional parts, by bonding and solidifying successive superposed sections, characterized in that it comprises:

- An enclosure (2) for receiving successive layers of powder of a fusible thermoplastic material in the form of particles (1), the bottom of which is movable vertically along the Z axis of a XYZ cross-reference frame between each deposit of a said layers, by a distance equal to the thickness of the next layer of particles (1),

a system (3) for depositing and distributing said powder (1) on the surface of said enclosure (2), making it possible to obtain layers of regular thickness,

- a pouring nozzle (4) moving at least in an XY plane and depositing a binder (10), made of a fusible thermoplastic material chemically compatible with the material constituting said powder (1), and in liquid form, on said layer of particles (1), along a path predetermined by the shape of the part to be obtained, said pouring nozzle (4) comprising at least one orifice of variable section,

- a heating device (5) of said binder (10) supplying said pouring nozzle (4),

- a computer control system (6) for controlling the movement of said nozzle (4) and of the bottom of said enclosure (2), of said deposition and distribution system (3), of the temperature of said heating device (5) and the variability of said variable section,

said control system (6) being configured, according to parameters such as the shape of the part to be manufactured and the degree of precision required, the size of said particles (1), the drop point of said material in the form of particles ( 1), the drop pour point and the solidification point of the binder material (10), the ambient temperature and the casting height,

to control the casting conditions and in particular the thickness of said layers of particles (1), the heating temperature of said binder (10), the path and the speed of movement as well as the flow rate of said nozzle (4), and the width of said variable section,

so as to ensure that:

- said binder material (10) is located in said nozzle (4) at a temperature above its drop pour point,

- there is a surface fusion and not at the heart of the particles (1) on which said binder (10) is poured, without however the temperature of said particles (1) reaching their drop pour point,

the migration of said binder (10) is carried out through the entire thickness of said layer of particles (1), but does not exceed this thickness,

- relatively large particles partly protrude from each of said sections and their surface melting is caused by coming into contact with the binder (10) cast on the next layer after migration of the latter through this layer, so that the connection between two successive sections is carried out, after solidification, between said relatively large particles and each of the two successive layers (N-1 and N) of binder, - Said binder (10) cast on a layer of particles (1) reaches at least in places the binder (10) solidified from the previous section and causes its surface fusion, so that connection between two successive sections is also carried out, after solidification, directly between the two successive layers (N-1 and N) of binder (10).