3D reverse printing method and device

Abstract

The present invention relates to a method and a device for producing three-dimensional models, wherein binding/bonding material is applied in layers to a building platform and media are selectively applied which delay or completely prevent the binding of the applied material.

Claims

1. A material system for 3D printing wherein the material system comprises: a particulate build material for applying to a build space in a defined layer thickness in the form of a powder or a dispersion, and a liquid for selectively applying via a print head to the particulate build material in one or more areas in which the particulate build material is not to be solidified by a solidification reaction; wherein the particulate build material is selected so that a solidification reaction of the particulate build material has already started, starts or may be started by introducing energy upon the application of the particulate build material, and the liquid is selected for inhibiting or stopping the solidification reaction; wherein the particulate build material is selected from the group consisting of a freshly mixed concrete or mortar, a mixture of a filler and a reactive resin system, a mixture of a foundry molding material and a reactive resin system common in foundries, a mixture of a filler and water glass, and a mixture of particles and a meltable material; with the proviso that the mixture of particles and the meltable material is heated to a temperature above the melting temperature of the meltable material prior to application.

2. The material system of claim 1, wherein the particulate build material is a mixture of a foundry molding material and a reactive resin system common in foundries, or a mixture of a filler and water glass.

3. The material system of claim 2, wherein the liquid is a reaction-inhibiting liquid.

4. The material system of claim 3, wherein the liquid is a reaction-stopping liquid.

5. A material system for 3D printing wherein the material system comprises: a particulate build material for applying to a build space in a defined layer thickness in the form of a powder or a dispersion, wherein the particulate build material solidifies by a salification reaction including a hydration, and a liquid for selectively applying via a print head to the particulate build material in one or more areas in which the particulate build material is not to be solidified by a solidification reaction; wherein the particulate build material is selected so that a solidification reaction of the particulate build material has already started, starts or may be started by introducing energy upon the application of the particulate build material, and the liquid is selected for inhibiting or stopping the hydration.

6. The material system of claim 1, wherein the particulate build material solidifies by a solidification reaction including a polymerization.

7. The material system of claim 1, wherein the particulate build material solidifies by a phase transition.

8. The material system of claim 1, wherein the particulate build material includes a powder material and a binding agent, wherein the powder material includes a sand, a ceramic powder, a metal powder, a wood particle, a fibrous material, a cellulose, or a lactose powder.

9. The material system of claim 8, wherein the binding agent includes an acrylate, a styrene, a polyurethane, an epoxy resin, a polyester or a polyamide.

10. The material system of claim 9, wherein particulate build material includes products of a solidification reaction of the particulate build material.

11. A material system of claim 1, for 3D printing wherein the material system comprises: a particulate build material for applying to a build space in a defined layer thickness in the form of a powder or a dispersion, and a liquid for selectively applying via a print head to the particulate build material in one or more areas in which the particulate build material is not to be solidified by a solidification reaction; wherein the particulate build material is selected so that a solidification reaction of the particulate build material has already started, starts or may be started by introducing energy upon the application of the particulate build material, and the liquid is selected for inhibiting or stopping the solidification reaction; wherein the liquid includes a monofunctional reactant.

12. A material system for 3D printing wherein the material system comprises: a particulate build material for applying to a build space in a defined layer thickness in the form of a powder or a dispersion, and a liquid for selectively applying via a print head to the particulate build material in one or more areas in which the particulate build material is not to be solidified by a solidification reaction; wherein the particulate build material is selected so that a solidification reaction of the particulate build material has already started, starts or may be started by introducing energy upon the application of the particulate build material, and the liquid is selected for inhibiting or stopping the solidification reaction; wherein the particulate build material is a self-hardening material mixture.

13. The material system of claim 12, wherein the liquid slows down or prevents a self-hardening reaction of the particulate build material.

14. A material system for 3D printing wherein the material system comprises: a particulate build material for applying to a build space in a defined layer thickness in the form of a powder or a dispersion, and a liquid for selectively applying via a print head to the particulate build material in one or more areas in which the particulate build material is not to be solidified by a solidification reaction; wherein the particulate build material is selected so that a solidification reaction of the particulate build material has already started, starts or may be started by introducing energy upon the application of the particulate build material, and the liquid is selected for inhibiting or stopping the solidification reaction; wherein the liquid includes an acidic sugar solution, an acid, or a hydrophobic solution.

15. A material system for 3D printing wherein the material system comprises: i) a build material for applying to a build space in a defined layer thickness in the form of a paste-like substance, wherein the build material includes an aggregate material, a paste, water, and optionally additives; and ii) a liquid for selectively applying via a print head to the build material in one or more areas in which the particulate build material is not to be solidified, wherein the liquid interferes with a hydration of the build material or interferes with a solidification reaction of the build material.

16. The material system of claim 15, wherein the aggregate includes a metal or a ceramic, optionally wherein a solidification reaction of the build material has started prior to applying to a build space and/or prior to introduction of energy.

17. The material system of claim 15, wherein the paste is a cement paste and the liquid includes an acidic sugar solution that interferes with hydration of the cement; optionally wherein a solidification reaction of the build material has started prior to applying to the build space and/or prior to introduction of energy.

18. A material system for 3D printing wherein the material system comprises: i) a build material for applying to a build space in a defined layer thickness including a powder material and a phase change material, wherein the build material is above a melting temperature of the phase change material; and ii) a liquid for selectively applying via a print head to the build material in one or more areas in which the particulate build material is not to be solidified, wherein the liquid interferes with the solidification of the phase change material.

19. The material system of claim 18, wherein the build material is in a coater device and the build material has a temperature above the melting temperature of the phase change material prior to application by the coater device to the build space.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The figures describe 3D printers from the prior art as well as preferred specific embodiments of the invention.

(2) FIG. 1: shows a schematic representation of the components of a powder-based 3D printer in an isometric view.

(3) FIG. 2: shows a sequence of a conventional 3D printing process with the use of a layered radiation hardening technique.

(4) FIG. 3: shows a diagram of the unpacking of components from a reaction-inhibited material which may be used according to the invention.

(5) FIG. 4: shows a diagram of an inhibited phase transition reaction which may be used according to the invention.

(6) Reaction Schemata:

(7) Schema 1: Chemical reaction of a reaction-inhibited cold resin method which may be used according to the invention.

(8) Schema 2: Chemical reaction of a reaction-inhibited cold-box method which may be used according to the invention.

PREFERRED EMBODIMENTS OF THE INVENTION

(9) In a first step, a liquid or powdered material (build material) is applied to a building platform and smoothed with the aid of a coater. This material solidifies on its own over time or preferably by means of an activation process. The material may solidify, for example, by means of drying. A chemical reaction that progresses slowly is also conceivable. Physical processes, such as a phase transition, are also conceivable.

(10) A liquid substance, or a substance located in a liquid, which slows down or blocks the particular solidification mechanism, is then applied via an ink jet print head (print head) before or after an optional solidification step.

(11) A solidification step may be, e.g., a drying process following the print process. However, a UV activation of a hardenable polymer is also conceivable.

(12) The building platform is subsequently lowered by one layer thickness.

(13) The aforementioned steps are repeated until the desired body has been created.

(14) In the end, the material surrounding the component and the deposits are removed. This may take place by brushing, blasting or rinsing, depending on the type of the mechanism.

(15) The advantages of this method are that the slowing down or blocking of the solidification mechanism may usually be achieved using a very small amount of an inhibiting medium. This medium is usually easier to dose than the solidifying materials.

(16) In addition, intimate mixtures may be achieved in this manner. The material may be intensively prepared using the customary mixing tools. Powerful mixing energies may be used.

(17) The third aspect relates to the introduction of reinforcements into the component. Due to the premixing, much more complex materials may be processed as a layer than when using prior-art methods.

(18) The consolidation of the base material is likewise influenced. Methods for the liquid dispensing of powder materials may be used, which advantageously influence an efficient particle packing.

(19) In summary, the inventors have developed a means for advantageously making the use of materials accessible to 3D printing methods which were previously unusable for 3D printing. For example, a conventional concrete may be processed.

(20) The result is a component which is in no way inferior to a cast quality. For example, a plastic component may likewise be produced from highly viscous reactive resins. Strengths that are excellent for additively produced components are associated therewith.

OTHER PREFERRED EMBODIMENTS OF THE INVENTION

(21) The system according to the invention draws heavily on powder-based 3D printing. The mechanical engineering is augmented to meet the requirements according to the invention.

(22) The device according to the invention includes a coater (2). This coater is used to apply and smooth premixed particulate material or a liquid containing particulate material onto a building platform (3) (FIG. 2(a)). The applied particulate material may consist of a wide range of materials. For example, sands, ceramic powders, metal powders, plastic, wood particles, fibrous materials, celluloses, lactose powders, etc. may be used. The flow characteristics of these materials may vary enormously. Different coater techniques permit layering from dry, free-flowing powders and cohesive, firm powders to liquid-based dispersions. The height of powder layers (4) is determined by building platform (3). It is lowered after one layer has been applied. During the next coating operation, the resulting volume is filled and the excess smoothed. The result is a nearly perfectly parallel and smooth layer of a defined height.

(23) According to the invention, the solidification process of the applied build material begins before the application, since all components needed for the reaction have been recently mixed intimately in a mixing means. The build material is thus produced in a preparation means prior to dispensing and quickly fed to the coater. The transport times and flow rates are monitored. If an error occurs, the material is not supplied to the machine, and the machine is rinsed with neutral material. The neutral material may comprise, for example, a passive component of the build material.

(24) The material feed is structurally carried out without any dead space. I.e., the material flow always carries along all material quantities located in the feed laminarly.

(25) After a coating process, the layer is printed with a liquidthe so-called retarding agentwith the aid of an ink jet print head (1) (FIG. 2(b)). The print image corresponds to the inverted section of the component in the present build height of the device. The liquid slowly and diffusively penetrates the particulate material.

(26) Following the method according to the invention, the retarding agent solidifies the layer during or shortly after printing (FIG. 2(c)). To speed up this process, or to initiate the hardening, an IR radiator (5), for example, may be additionally passed over the build space in one preferred embodiment. This IR radiator may be coupled with the axis of the coating system. The solvent evaporates during heating. In the case of liquids that present a fire hazard, the evaporating material is extracted immediately (7).

(27) This process may be used to influence, and preferably to speed up, the time sequences of the solidification reaction. The period of time until the parts are unpacked may be shortened thereby.

(28) In the method according to the invention, a job block (300) is generally produced by the build process, from which the embedded components (301) must be removed following the build process. This procedure may take place, e.g., by rinsing with a liquid (302, 303). Likewise or additionally, the component may be exposed by scrubbing or brushing manually (305).

(29) Brief descriptions of preferred material systems are provided below. In each case, the overall process is briefly illustrated.

(30) Cement-bound material An aggregate, such as sand, is mixed with a cement paste, water and additives. This paste-like substance is applied to a building platform with the aid of a special coater.

(31) An acidic sugar solution is dispensed as the reaction-retarding substance onto the areas that are not to be solidified. This combination interferes with the hydration of the cement and thus the solidification.

(32) After a certain binding time, the resulting job block may be detached with the aid of water. The retarded material is then brushed off under the action of water. The rinsing solution is environmentally safe, since it is non-toxic.

(33) The component produced in this manner is comparable to a cement component produced by casting in terms of its condition and strength characteristics.

(34) Polymer Synthesis Reaction (Cold Resin)

(35) A reaction-retarded cold resin binding agent for metal casting applications is mixed with a hardener and sand as a batch and fed into the coater. The latter applies the build material as a layer. Compared to the prior art, a special coater is used, which is able to process very cohesive sand mixtures.

(36) An ink-jet print head prints a basic substance in the area in which the sand is to be removed later on. Only a small quantity of a highly basic-acting substance must be applied.

(37) The build material completely solidifies in this process without a substance being printed thereon. Special measures must be taken to protect the mixer, coater and build container.

(38) The result of this process is a porous mold or a core having a cold resin binding, which may be used in metal casting in the known manner.

(39) Polymer Synthesis Reaction (Polyurethane)

(40) An at least difunctional prepolymer isocyanate is mixed with at least difunctional phenol-containing polyol and other additives and with foundry sand. The mixture is set in such a way that the polymerization reaction takes multiple tens of minutes or sets in only after at least this dwell time.

(41) In the area where the sand is to be removed later on, an ink-jet print head prints a substance which, on the one hand, is monofunctional and, on the other hand, reacts with a reactive component much faster than with the multifunctional reactant. The reactive groups needed for a polymerization are reduced thereby. In this system, for example, a printing of compounds with the formula ROH or R1-NHR2 is efficacious, short-chain alcohols, such as ethanol or 2-propanol being preferred with regard to the resulting reaction products. Isocyanate groups are effectively and irreversibly deactivated with these substances.

(42) For unpacking, the loose sand is brushed and blasted off.

(43) The result is a casting mold for metal casting applications of the cold box type known in this field.

(44) Polymer Synthesis Reaction (Polyacrylate)

(45) A base material, such as expanded glass or a polymer, is mixed with radically polymerizable acrylates. A photoinitiator is also added to the system.

(46) In the area where the base material is to be removed later on, an ink-jet print head prints a substance which interferes with the further concatenation or deactivates the photoinitiator. These may be known inhibitors such as TEMPO or hydroquinone.

(47) The printing process is followed by an exposure to light using a UV lamp. Due to the deactivated photoinitiator, either no radicals for the polymerization, or only as many radicals as can be immediately absorbed by the added inhibitors, are formed in the printed areas. As a result, no solidity may build up in the printed areas.

(48) The result of this process is a filled plastic component. The latter may be used as a function component in industrial applications or as a visual aid.

(49) Phase Change

(50) A base material (600), e.g. polystyrene powder, is mixed with a wax (601) and heated to a temperature above its melting point (FIG. 4a). In the hot state, it is applied to the building platform with the aid of the coater. The temperature in the build space is maintained above the melting point of the wax.

(51) This layer is printed with oil drops (602), e.g., paraffin oil (FIG. 4b). This oil is mixable with the hot wax. This mixture (603) is located between the particles in the outer area.

(52) During the slow cooling process, a solidity forms in the unprinted area, due to the cooled particle bridges (604). In the printed area, the oil interferes with the formation of solidity. The particles in this area (outside component contour 605) may subsequently be easily brushed off.

(53) The component produced in this manner may be used as a so-called wax model for investment casting applications.

(54) To simplify the separation of the desired component and the surrounding material, printing the retarding agent only linearly along the outer contour of the particular layer cross section and printing the areas outside the component contour with a grid are expedient for reasons of material economy. If all-over separating planes are now inserted in a certain order, a cube structure arises around the component, which may be easily removed, even from complex geometric sections. The size of the cube geometry may be either set as standard, or it may automatically adapt to the component contour with the aid of corresponding algorithms.

(55) A number of reaction schemata are furthermore illustrated for the material systems according to the invention:

(56) Reaction schema 1 (chemical reaction, cold resin/reaction stop):

(57) ##STR00001##

(58) Reaction of furfuryl alcohol with condensation under acidic conditions; increase in pH value prevents the reaction from taking place.

(59) Reaction schema 2 (chemical reaction, cold box):

(60) ##STR00002##

(61) Polymerization is prevented by a competition reaction of the isocyanate with 2-propanol.

LIST OF REFERENCE NUMERALS

(62) 100 Ink-jet print head 101 Powder coater 102 Building platform 103 Component 104 Build space boundary 107 Powder layers 200 Solidifying unit 300 Job block 301 Embedded component 302 Rinsing nozzle 303 Dripping material in the outer area 304 Exposed component 305 Brush 600 Base particles 601 Liquid wax 602 Oil drops 603 Bridge of wax/oil 604 Solidified wax 605 Component contour