Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/004—Photosensitive materials
  • G03F7/0047—Photosensitive materials characterised by additives for obtaining a metallic or ceramic pattern, e.g. by firing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
  • B22F1/103—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material containing an organic binding agent comprising a mixture of, or obtained by reaction of, two or more components other than a solvent or a lubricating agent
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
  • B22F10/10—Formation of a green body
  • B22F10/12—Formation of a green body by photopolymerisation, e.g. stereolithography [SLA] or digital light processing [DLP]
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
  • B29C64/10—Processes of additive manufacturing
  • B29C64/165—Processes of additive manufacturing using a combination of solid and fluid materials, e.g. a powder selectively bound by a liquid binder, catalyst, inhibitor or energy absorber
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y70/00—Materials specially adapted for additive manufacturing
  • B33Y70/10—Composites of different types of material, e.g. mixtures of ceramics and polymers or mixtures of metals and biomaterials
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/0037—Production of three-dimensional images
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y10/00—Processes of additive manufacturing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y80/00—Products made by additive manufacturing
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/09—Use of materials for the conductive, e.g. metallic pattern
  • H05K1/092—Dispersed materials, e.g. conductive pastes or inks
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/25—Process efficiency
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
  • Y10S430/145—Infrared
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
  • Y10S430/146—Laser beam

Definitions

• the present invention relates to a paste composition loaded with metallic powder, a method for obtaining metallic products from said composition, and a metallic product obtained according to said method.
• the invention relates more particularly to a paste composition intended for use in a rapid prototyping process, a rapid prototyping process of metallic products from said composition, and a metallic product obtained according to said process.
• pastes are obtained by mixing a solid filler in the form of a powder, for example an inorganic, metallic or ceramic powder, in a binder consisting of a photosensitive or thermosetting liquid resin, such as a photopolymerizable acrylic or epoxy resin traditionally used in stereolithography.
• a photosensitive or thermosetting liquid resin such as a photopolymerizable acrylic or epoxy resin traditionally used in stereolithography.
• the term paste includes in particular materials with very high viscosity, greater than 10,000 rnPa.s or so-called "marked threshold" materials.
• a “threshold” material is such that it does not flow (zero gradient) as long as the shear stress applied to it does not exceed a minimum value. It will be said that a material has a “marked threshold", when the value of this shear stress is greater than 20 Newton per square meter.
• a layer process is used for the shaping of three-dimensional parts using these pastes.
• the dough is spread out in thin layers, each layer being selectively solidified by a device emitting radiation, for example a laser, combined with galvanometric mirrors, as for stereolithography or powder agglomeration.
• a device emitting radiation for example a laser
• galvanometric mirrors as for stereolithography or powder agglomeration.
• Such pastes can be used for the manufacture of metallic products by carrying out an additional heat treatment after the above-mentioned shaping step.
• This treatment comparable to that of parts obtained by a metal injection molding type process (MIM), consists firstly in eliminating the organic part of the shaped part, namely the polymer part and any thermodegradable additives , this step being called hereinafter "debinding", then densifying the debinding piece in order to obtain the desired mechanical properties.
• the starting liquid composition comprises a photopolymerizable resin of low viscosity, of the order of 70 mPa.s for the resin used in Example 1 and of the order of 5 mPa.s for the resin used in Example 2, and must necessarily include a dispersant.
• the object of the present invention is to provide a paste composition making it possible to obtain, by a prototyping process, metal parts which have sufficient strength and low deformation, having substantially the properties of the metal initially in the form of powder.
• Another object of the present invention is to provide a process for obtaining metallic products from the paste composition according to the invention.
• Another object of the present invention is to provide a metallic product obtained according to the aforementioned process.
• a first object of the invention is a paste composition, comprising a binder loaded with metallic powder, intended to be used in a prototyping process, characterized in that it comprises:
• binder consisting of at least one photopolymerizable resin, having a viscosity of less than 4000 mPa.s measured at 25 ° C,
• a metal powder in a volume concentration greater than 40% relative to the composition having a minimum reactivity of the order of 5 mm 3 / s per watt of light power.
• the resin does not have a benzene cycle.
• the resin is a polyfunctional acrylate type resin, of functionality at least equal to three.
• the resin is the ditrimethylol propane tetraacrylate resin.
• the metal powder is present in a volume concentration greater than 50% relative to the composition and comprises at least 30% by volume of spherical particles.
• the metal powder is a powder of steel, stainless steel, titanium, titanium alloy, copper, tungsten, tungsten carbide, nickel alloy or a mixture of these. this.
• the powder has a particle size less than 45 ⁇ m.
• the composition comprises at least one of the following additives: - a rheological agent dissolved in the resin in a concentration of 2 to 15% by weight relative to the weight of resin,
• a wetting and / or dispersing agent in a concentration of less than 1% by weight relative to the metal powder
• a lubricating agent in a concentration of less than 0.5% by weight relative to the metal powder
• the particles forming the metal powder are covered with a coating layer, which has the particularity of being at least twice less absorbent than the metal powder.
• the coating layer consists of a wax or an oxidation layer formed by the oxidation of the particles forming the powder, improving the reactivity of the composition.
• the metal powder consists of a homogeneous mixture of metal powders, of the same nature or not, of at least two different particle sizes having a particle size ratio of between 1/10 and 1/5, preferably of the order 1/7.
• the photoinitiator is an ⁇ -amino ketone.
• the photoinitiator is 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone- 1.
• the composition comprises an activating agent such as isopropyl thioxanthone, l-chloro-4-propoxythioxanthone, or 4-benzoyl-4'-methyldiphenyl sulphide, or a mixture of at least two of these.
• an activating agent such as isopropyl thioxanthone, l-chloro-4-propoxythioxanthone, or 4-benzoyl-4'-methyldiphenyl sulphide, or a mixture of at least two of these.
• ci in combination with a co-initiator such as ethyl p-dimethylaminobenzoate.
• Another object of the invention is a process for obtaining metallic products from the paste composition as defined above, characterized in that it comprises: a) a step of shaping a product three-dimensional composite made up of thin layers of dough superimposed, obtained by repeating a cycle comprising the following steps:
• the layers of dough deposited have a thickness of less than 50 ⁇ m.
• the debinding step is carried out under neutral or reducing gas sweeping or under vacuum and may or may not be followed by an additional treatment for metering carbonaceous residues in the presence of oxygen, carbon monoxide or carbon dioxide to better control the final composition and structure of the sintered metal.
• the thermal cycle of the debinding step includes rapid heating ramps in the temperature zones where the binder degrades little or not and slow heating ramps and bearings in the zones where the binder degrades strongly , constituting a complete cycle lasting less than 48 hours.
• the sintering step induces the consolidation of the product by densification of the porous deliant product at a temperature lower than the melting temperature of the metal, for example 3/4 the melting temperature of the metal of the metal powder.
• the sintering step is carried out under gas sweeping (neutral or reducing) or under vacuum, under conditions such that the temperature uniformity is at most +/- 10 ° C.
• the thermal cycle includes rapid heating ramps, greater than or equal to 5 ° C./min, in the temperature zones where the unbinding product does not undergo transformation and slow heating ramps , less than or equal to 1 ° C / min, or stabilization stages of a duration of less than 1 hour, in areas where the debonding product undergoes physical transformations, and a sintering stage of duration between 30 minutes and 5 hours, preferably 1 hour.
• Another object of the invention is a deliant and sintered metal product obtained by the process according to the invention as defined above.
• the metal product has less than 2%, preferably less than 0.5%, by mass of carbonaceous residue relative to the mass of resin of the starting composition.
• the metal product has temporary support elements, produced in such a way that, within a radius of 1.5 mm, there are at least two distinct points belonging to two distinct support elements solidified on the same layer. in order to support cantilevered parts of the product.
• the paste composition according to the invention comprises a photopolymerizable or photosensitive resin, in combination with a photoinitiator, loaded with a metallic powder.
• the photopolymerizable resin used in the present invention preferably has a viscosity of less than 4000 mPa.s (at 25 ° C.) and the composition prepared from this resin and from the metal powder has a reactivity of at least 5 mm 3 / s / W with respect to an illumination, for example an ultraviolet type illumination.
• the reactivity of the composition is of course a function of the nature of the resin but also of that of the photoinitiator and that of the metal powder used.
• the reactivity of the composition varies from around 5 mm 3 / s / Wuv up to 40 mm 3 / s / W uv in the optimal wavelength range for the composition.
• acrylate type resins photopolymerizable by ultraviolet radiation
• a tetra-functional acrylate resin such as ditrimethylol propane tetraacrylate resin, sold by the company "Cray Valley” under the name commercial “Sartomer SR 355" hereinafter referred to as "SR355" resin. It is essential to reach high powder levels in the resin (at least 50% by volume but it is preferable to go up to 70% if this is possible) for better control of the geometry of the sintered parts and a accelerated sintering.
• This "SR 355" resin of the order of 700 mPa.s, makes it possible to achieve high loading rates of metallic powder and to increase the efficiency of various additives which will be described below, especially that of a rheological agent.
• the tetra-functional nature of this "SR 355" resin makes it very reactive to ultraviolet light, with an appropriate initiator, even when it is heavily loaded with metallic powder.
• a dipentaerythritol pentaacrylate resin sold by the company "Cray Valley” under the trade name “Sartomer SR 399” can also be used in the dough composition according to the invention.
• This resin has good reactivity, however its high viscosity (10 times more viscous than the above-mentioned “SR 355" resin) prevents its use in the case where the metal powder charge must exceed a certain percentage.
• diluent a more fluid resin
• This diluent preferably reactive (that is to say that it will create a crosslinked network, under the action of radiation like the resin), has a viscosity of less than 100 mPa.s and is incorporated in concentrations of 2 to 20% by mass relative to the resin. It makes it possible to increase the volume rate of powder (by a few percent) and improves the efficiency of a rheological agent which gives the dough a behavior of Bingham fluid type (at very high flow threshold).
• SR 355" resin In the case of a very reactive "SR 355" resin, this can be diluted with 2 to 20% of more fluid resins, such as those marketed by the company "Cray Valley” under the trade name "SR 256" (2- (2-ethoxyetoxy) ethyl acrylate) having a viscosity of 5 mPa.s or "SR 9003" (neopentyl glycol dipropoxylated diacrylate) having a viscosity of 17 mPa.s to give a resin which remains very reactive with a viscosity of the order of 400 mPa.s.
• SR 256 (2- (2-ethoxyetoxy) ethyl acrylate
• SR 9003 neopentyl glycol dipropoxylated diacrylate
• composition according to the invention may comprise a resin mixture containing at least 50% of "SR355" resin and at most 50% of more fluid resins used as diluent, including 2 to 20% of reactive resins such as those mentioned above, the remainder being made of non-reactive resin (s).
• the resin used in the compositions does not have a benzene ring.
• This absence of a benzene cycle has several beneficial effects. It facilitates the elimination of the polymer during debinding. Indeed, it would seem that this absence of cycle favors the decomposition into gaseous substances of small sizes (whereas on the contrary, the benzene cycle is not "broken" during the treatment and creates constraints during its diffusion through the product).
• a resin devoid of a benzene ring according to the invention makes it possible to obtain a low rate of carbon residues, less than 2%, preferably less than 0.5%, by mass relative to the mass of resin after thermal decomposition. during the debinding step.
• shrinking This property, which seems to be mainly due to the absence of aromatic cycle contributes strongly to a better control of deformations and better control of shrinkage during sintering.
• the reduction in the volume of the parts which accompanies their densification during sintering is called shrinking.
• the composition includes a priming system comprising a photoinitiator.
• the photoinitiator can be constituted by one of the photoinitiators absorbing in the wavelengths of the Argon laser (351-364nm) sold by the company Ciba-Geigy under the trade names "Irgacure 369” (2-benzyl-2-dimethylamino-l- (4-morpholinophenyl) - butanone-1), "Irgacure 651” (2, 2'-dimethoxy-2-phenylacetophenol), "Irgacure 1700", “Irgacure 819” or "Darocur 1173".
• the photoinitiator belongs to the family of amino ketones, the
• the priming system can also include an activating agent which makes it possible to move the activation wavelength of the photoinitiator, which once activated will react with the resin.
• an activating agent which makes it possible to move the activation wavelength of the photoinitiator, which once activated will react with the resin.
• the activating agent can be chosen from isopropyl thioxanthone, l-chloro-4-propoxythioxanthone, or 4-benzoyl-4'-methyldiphenyl sulphide, in combination with a co-initiator such as ethyl p-dimethylaminobenzoate.
• the volume concentration of the composition according to the invention in metal powder is preferably greater than 50%. Such a volume concentration is possible by the use of the resin as defined above, optionally with additives as described below. This high percentage allows sufficient dimensional control after sintering.
• the metal powder preferably comprises at least 30% by volume of spherical particles in order to make it possible to increase the limit volume concentration of powder in the composition and to promote densification during sintering.
• the limit volume concentration designates the powder concentration for which the viscosity of the composition becomes infinite. In practice, we talk about maximum volume concentration in powder, concentration from which it becomes difficult to achieve homogeneous mixing with conventional means (mixers) and taking into account the influence of the additives of the formulation.
• the powder has a particle size
• Such an increase can be obtained when the finest particles can be positioned in the interstices left by the largest particles, that is to say when the diameter ratio of the particles is of the order of 1/7.
• the use of a carbonyl iron powder with a much finer grain size than the usual grain sizes of steel, improves the densification thanks to the presence of fine particles and limits the deformations thanks to a higher concentration of steel. Furthermore, the resistance of the metal product can also be improved.
• composition of the powders referenced in% by mass is a composition of the powders referenced in% by mass:
• - 316L chromium (16.5 to 20%); nickel (8 to 14%); molybdenum (2.5-3.5%); carbon ⁇ 300 ppm; iron ( ⁇ 62.5 to 73%)
• TA6V aluminum (6%); vanadium (4%); titanium (90%)
• the theoretical limit volume concentration that can be obtained with a stack of perfect spheres is 74% by volume.
• this limiting concentration corresponds to a mass quantity of the order of 95% (this concentration depends on the density of the resin).
• the composition comprises 91% by weight, or 58% by volume, of stainless steel powder; this concentration can be increased up to the maximum volume concentration which is of the order of 63%.
• the limiting volume concentration represents a mass quantity of the order of 92%.
• the composition comprises 83% by weight, or 55% by volume, of titanium powder; this concentration can be increased up to the maximum volume concentration which is of the order of 60%.
• One of the conditions to be satisfied for a use of the composition in a rapid prototyping process as described in the present invention is the reactivity of the composition when the latter is subjected to ultraviolet type radiation.
• the introduction of fillers such as metal powders greatly reduces the penetration of light into the composition because part of this radiation is absorbed by the powder and is no longer available for the photopolymerization reaction.
• the volume reactivity goes from around 600 mm 3 / s / W for an uncharged liquid resin to around 5 mm / s / W for a composition based on the same resin and comprising approximately 58% by volume of spherical steel particles ( ⁇ 22 ⁇ m).
• the particles can be coated with a particular compound, which modifies the optical properties of the powder and the behavior of the paste vis-à-vis ultraviolet rays.
• This compound constituting a coating layer of determined thickness, must serve as a screen to avoid the absorption of light by the particle: for this, it must be less absorbent than the metallic particle which serves as its support (at minus twice less; it may not be absorbent at all); it can also have a refractive index such that the incident light is reflected and / or scattered within the dispersing medium (the resin).
• the role of this compound is to make it possible to "recover" the radiation normally absorbed by the powder and make it available for the resin (in fact the initiator) and the polymerization reaction. This contributes to significantly improving the reactivity of the composition.
• This compound can for example be a wax whose additional advantage is that it degrades completely without residue. This wax can be polyethylene or polyamide.
• the coating layer may also be an oxide layer formed on the surface of the metal particles.
• This oxide layer must be thick enough to modify the behavior of the ultraviolet powder. Of course, the importance of oxidation must be perfectly controlled because a powder that is too oxidized does not sinter well. Furthermore, this oxidation layer can contribute to a more efficient removal of carbon during debinding.
• the composition can also comprise a compound which increases its reactivity towards illumination. This compound can be added to the resin (dissolved or not in the resin) and / or, as described above, it can constitute a compound for coating the particles constituting the metal powder. This additive is for example a polyethylene wax.
• the nature of the powder is not limited to the aforementioned examples, and may for example consist of particles of carbon steels, tungsten, tungsten carbide, tungsten-cobalt carbide alloys, alloys nickel, chromium alloys, copper alloys ...
• the fact of adding fillers, in particular metallic fillers, in a liquid medium often induces problems of sedimentation of the powder particles.
• problems of sedimentation of the powder particles In the case of steel (density of the order of 8), this results in very rapid settling of the particles and prevents the use of the mixture in a process such as that described in the invention.
• sedimentation of the powder during storage of the dough or during shaping results in heterogeneity of the composition, mainly in the vertical direction, resulting during the heat treatment by differential shrinkages causing distortions or distortions.
• the composition according to the invention can comprise various additives which strongly limit sedimentation.
• Such an additive will have to modify the rheology of the mixture so that the paste obtained has a very high flow threshold and a low viscosity at high shear rates (behavior of Bingham fluid type or rheofluidifying fluid at threshold). Thus, sedimentation is limited when the dough is at rest while its viscosity decreases during manufacture to facilitate spreading of the layers.
• a rheological agent can be added to the resin, for example by dissolving with stirring and heating in the resin. This rheological agent can be chosen from compounds based on polyamide wax or hydrogenated castor oil or urea.
• a polyamide wax such as that marketed by the company "Kusomoto Chemicals” under the trade name “Disparlon 6650” or that marketed by the company Cray Valley under the trade name “Cray Vallac Super”.
• Concentrations of 2 to 15% by mass relative to the mass of resin lead to a fluid paste or to a gel to which the metal powder is added.
• the paste obtained has a very high flow threshold and a low viscosity at high shear rates.
• This rheological agent makes it possible to avoid sedimentation of the powder during storage or shaping which would lead to heterogeneity of the composition, mainly in the vertical direction, resulting in sintering by differential shrinkage at the source of distortions or distortions.
• paste compositions comprising powders of metals denser than steel of density 8 or copper of density 9, such as tungsten of density 19 or tungsten carbide of density 16 .
• This additive can be a so-called coupling agent compatible with the resin in order to avoid the formation of lumps. It is for example a silane coupling agent, such as that sold by the company "Witco” under the trade name “Silquest A-1120", in concentrations of 0.1 to 0.3% by mass relative to to the mass of metallic powder.
• This additive can also be a wetting and / or dispersing agent which modifies the surface tensions of the liquid and / or creates a screen (electrostatic or steric) around the particles to keep them away from each other and avoid the problems of agglomeration which induce both sedimentation of the particles and reduction of the maximum volume concentration.
• Such additives form strong interactions (such as chemical adsorption) between the liquid and the powder.
• it is a wetting and dispersing agent, present in a concentration of less than 1%, preferably less than 0.5% by weight relative to the weight of the metal powder, such as those sold by the company "Lucas Meyer "under the trade names Forbest H60 and Forbest 610 or that marketed by the company” Byk Chemie "under the trade name Disperbyk 111.
• This additive can also be a lubricating agent, as usually used in the metal injection molding (MIM) process, for example stearic acid or metal derivatives of stearic acid.
• MIM metal injection molding
• a lubricating agent which has an action close to that of a wetting / dispersing agent without however creating such strong interactions, makes it possible to increase the maximum volume concentration in powder of the composition. However, it should be noted that it significantly reduces the reactivity of the dough. It must be added in low concentration: less than 0.5% relative to the mass of metal powder.
• This additive can also be an adhesion agent, such as a resin having, in a known manner, an adhesion power on metal substrates. It can be added to the resin forming the binder in order to improve the wetting between the binder and the metal powder.
• this adhesion agent is one of the resins sold under the names "SR 705" (polyester acrylate), "SR 9050” (acid monoacrylate), "SR 9051” (acid triacrylate) or a mixture thereof.
• Additives in the form of metallic powder with melting points below the sintering temperature of the metallic powder can be added in order to induce sintering in the liquid phase. They contribute to the homogenization of the composition during sintering and lead to greater densification and better controlled shrinkage. The sintering temperature and / or the duration of the bearing are also reduced because the sintering process in the liquid phase is faster. Some of these additives can partially compensate for the shrinkage caused by densification (we speak of "swelling" due to the liquid phase) and lead to a shrinkage lower than it was in the absence of additive.
• this metallic additive can consist of a powder of copper, aluminum or boron for example.
• this additive lead to sintering with minimum shrinkage and / or improved properties and / or better dimensional control.
• this concentration can range from 0.2% by mass relative to the mass of steel for boron, up to 30% for copper or its derivatives such as bronze. Because of its homogenization role, sintering in the liquid phase can contribute to the formation of new alloys with new physical properties which can be adjusted according to the desired application.
• the shaping of a three-dimensional composite product from the dough according to the invention can be carried out by a prototyping machine (of the "Optoform" type) such as that described in the French patent application N ° 99 02719 filed by the plaintiff.
• the shaping of a three-dimensional product is obtained by the deposition by means of a scraper and the polymerization by means of an illumination of thin superposed layers of dough.
• the shaping of a composite product to starting from a paste composition according to the invention is produced with a layer thickness of less than 50 ⁇ m, varying for example from 25 to 50 ⁇ m depending on the metal powder used.
• the movement speed of the illumination can be similar to that used in stereolithography and thus reach several meters per second, since the fact of reducing the layer thickness does not prevent working at high speeds.
• the manufacturing times are comparable to those of other rapid prototyping techniques.
• the thermal cycle of debinding can be optimized according to the decomposition atmosphere by analyzes thermogravimetric.
• the degradation of the polymer can be spread over a temperature range ranging for example from 200 to 500 ° C., with one or more degradation zones depending on the nature of the degraded products. In areas of degradation, the temperature rise must be low and gradual to avoid the accumulation of stresses and overpressures in the parts which would lead to the formation of cracks, swelling, bubbles, distortions ...
• the speed of temperature rise called the heating ramp, also depends on the thickness of the walls of the rooms. Outside these degradation zones or in the temperature ranges where the loss in mass varies little (derivative with respect to the zero or low temperature), the heating can be accelerated.
• a debinding step may be provided under a sweep of reducing gas (hydrogen) in order to accelerate the degradation of the carbonaceous compounds or an additional treatment for metering the carbonaceous residues present: - oxygen; in this case, the quantity of oxygen introduced must be very precisely controlled to prevent oxidation of the metal
• sintering temperature at which it remains for a determined period
• Sintering makes it possible to densify the parts by eliminating the porosities left by the polymer once degraded. This densification is accompanied by a modification of the dimensions of the part called shrinkage, which is controlled by the sintering temperature and the duration of the bearing. This sintering temperature depends on the nature and granulometry of the powder and on the desired final properties.
• the sintering cycle includes at least one step in addition to the sintering step.
• a sintering cycle can be adapted (with several heating speeds and stabilization stages) in order to allow optimal dissolving of the carbon and a minimum formation of carbides which limits as much as possible the stresses due to densification and / or cooling.
• Mechanical resistance is directly linked to the density of the final part.
• the sintering temperature and the duration of the bearing can be adapted as a function of the resistance and / or shrinkage constraints during sintering.
• the heating rate is 5 ° C / min and the hold time 1 hour. This heating speed is relatively slow for sintering but allows good homogenization of the support and of the whole part.
• the sintering temperature is always lower than the melting temperature of the material and can, for example, correspond approximately to 3/4 of the melting temperature of the material used.
• the sintering step can be carried out at a temperature between 1150 and 1280 ° C.
• the temperature was between 1,200 ° C., with a linear shrinkage observed of 5 to 8%, and 1,250 ° C. with a linear shrinkage observed of 18%.
• sintering is carried out either under a neutral atmosphere, for example under argon or nitrogen, or under a reducing atmosphere, ideally under dry hydrogen or a nitrogen / hydrogen mixture, or under vacuum.
• the sintering step can be carried out under argon, a nitrogen / hydrogen mixture 90/10 or a primary vacuum.
• a partial pressure of argon or nitrogen prevents the vaporization of elements such as chromium, at high temperatures.
• Nitrogen is likely to create a nitrided layer on the surface of the parts, which when poorly controlled, can lead to a heterogeneous microstructure.
• the treatment is preferably carried out under secondary vacuum.
• Deformation problems vertical and horizontal distortions
• Particle oxidation during debinding for example, can also induce differential shrinkage resulting in stresses and deformations. Any problem attributable to the oven is avoided by working in a sealed oven and having a temperature uniformity of less than +/- 10 ° C, preferably less than +/- 5 ° C.
• stainless steel powders containing very little carbon such as the product referenced 316L in which [C] ⁇ 0.03% the amount of carbon or residue (in the form of a hydrocarbon), resulting from debinding, although limited to 0.4% by mass relative to the mass of resin of a paste according to the invention, is preponderant compared to that contained in the initial composition of the steel particles constituting the powder.
• This residual carbon is therefore all the more difficult to dissolve and the excess tends to form carbides, preferably chromium and molybdenum carbides which are distributed around the steel grains, thus modifying the composition of a microscopically and weakening the steel.
• a paste composition comprising a constituent additive may be provided, as described above.
• a carbon sensor such as titanium, niobium, tungsten, vanadium, molybdenum or tantalum, whether or not combined with a preliminary heat treatment, following the debinding step, for metering the residual carbon with monoxide carbon, carbon dioxide or oxygen, as mentioned above.
• the final composition and microstructure of the steel are less sensitive to the contribution of carbonaceous residues in small quantity such as that of the order 0.4% relative to the mass of resin contained in the composition from the use of the paste composition according to the invention.
• Composition A A:
• Composition B is a composition of Composition B:
• TA6V ⁇ 44 ⁇ m, melting temperature 1600-1650 ° C
• the above cycle takes account of an inertia of about 50 ° C between the set temperature taken in the oven enclosure and the actual temperature in the debinding enclosure.
• the rate of climb depends on the thickness of the walls of the rooms.
• the cycle described above is suitable for maximum thicknesses of 4-5 millimeters. Beyond that, it would be necessary to decrease the heating rate in the critical zone 270 ° C-520 ° C.
• Composition B sintering cycle
• the sintering step was carried out under secondary vacuum

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