Method and casting mold, in particular for use in cold casting methods

Abstract

The invention relates to a casting mold, in particular for use in cold casting methods, which is produced with the aid of a powder-based layering method, the final casting mold having a treated surface.

Claims

1. A method comprising the steps of: producing a casting molds for use in cold casting methods at temperatures where the casting mold is not destroyed, wherein the casting mold is built with the aid of a powder-based layering method and has a porous molded body, treating a porous surface of the casting mold with a sealant which closes pores of the molded body and seals the surface water-tight, cold casting a part at a temperature where the casting mold is not destroyed, and removing the part from the casting mold; wherein the layering method is a powder bed-based 3D printing method and includes: applying a powder-based layer using a coater, wherein the powder-based layer includes a particle precoated with an activator; and selectively printing a fluid on the powder-based layer with a print head.

2. The method of claim 1, wherein the porosity of the surface is modified by an epoxy resin, a polyurethane, an unsaturated polyester, a phenol/resol resin, an acrylate and/or a polystyrene.

3. The method of claim 1, wherein the porous surface is modified by a black wash or dispersion prior to the step of treating with a sealant, wherein the black wash includes a zirconium oxide, aluminum oxide-, calcium oxide-, titanium oxide-, chalk- or silicic acid-based black wash and the dispersion includes a plastic, cellulose, sugar-, flour and/or salt-based solution.

4. The method of claim 1, wherein the porosity of the sealant includes a grease, an oil, a wax, or a hot water-soluble substance.

5. The method of claim 1, wherein a cold resin binding system is used for the layering method.

6. The method of claim 5, wherein the surface is sealed with a hydrophobic material.

7. The method of claim 5, wherein the porosity of the surface is modified by an infiltrate prior to the step of treating with a sealant.

8. The method of claim 5, wherein the porosity of the surface is modified by an epoxy resin, a polyurethane, an unsaturated polyester, a phenol/resol resin, an acrylate and/or a polystyrene.

9. The method of claim 5, wherein the porosity of the surface is modified by a zirconium oxide-, aluminum oxide-, calcium oxide-, titanium oxide-, chalk- or silicic acid-based black wash prior to the step of treating with a sealant.

10. The method of claim 5, wherein the porosity of the surface is modified or sealed by means of a hot water-soluble substance.

11. The method of claim 1, wherein the cold casting methods is for producing a concrete cast part.

12. The method of claim 1, wherein the cold casting method is for producing a cold-cast polymer component.

13. The method of claim 1, wherein the particle is a sand particle.

14. The method of claim 13, wherein the fluid reacts with the activator on the powder-based layer to form a polymer that binds the sand particles together.

15. A method comprising the steps of: producing a casting molds for use in cold casting methods at temperatures where the casting mold is not destroyed, wherein the casting mold is built with the aid of a powder-based layering method, treating a porous surface of the casting mold, cold casting a part at a temperature where the casting mold is not destroyed, and removing the part from the casting mold; wherein the layering method includes applying a powder-based layer using a coater, wherein the powder-based layer includes a sand particle precoated with an activator; and selectively printing a fluid on the powder-based layer with an ink jet print head; wherein the fluid reacts with the activator on the powder-based layer to form a polymer that binds the sand particles together.

16. The method of claim 15, wherein the casting mold includes a surface modified by an epoxy resin, a polyurethane, an unsaturated polyester, a phenol/resol resin, an acrylate, or a polystyrene, for reducing the porosity of the surface.

17. The method of claim 15, wherein the casting mold includes a surface modified by a black wash or a dispersion, for reducing the porosity of the surface, wherein the black wash includes a zirconium oxide, aluminum oxide, calcium oxide, titanium oxide, a chalk, or a silicic acid, and the dispersion includes a plastic, a cellulose, sugar, flour, or a salt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Brief description of the figures, which represent preferred specific embodiments:

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

(3) FIG. 2: shows a representation of a simple cast part without undercuts;

(4) FIG. 3: shows a representation of a complex cast part, including undercuts;

(5) FIG. 4: shows a representation of a set of multiple-use molds for producing the simple cast part;

(6) FIG. 5: shows a sectional representation of ejectors and assembly aids for a multiple-use casting mold;

(7) FIG. 6: shows a representation of a set of single-use molds for producing the complex cast part;

(8) FIG. 7: shows a sectional view of a component treated according to the invention;

(9) FIG. 8: shows an illustration of the mold breakout process with a treatment according to the invention.

DETAILED DESCRIPTION

(10) One example of a device for producing a molded part according to the present invention includes a powder coater (101). Particulate material is applied thereby to a building platform (102) and smoothed (FIG. 1). The applied particulate material may be made from a wide range of materials; according to the invention, however, sand is preferred for reasons of its low cost. This sand is precoated, for example, with an activator component. The height of powder layers (107) is determined by the building platform (102). 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.

(11) After a coating process, a fluid is printed onto the layer with the aid of an ink-jet print head (100). The print image corresponds to the section of the component in the present build height of the device. The fluid strikes and slowly diffuses into the particulate material.

(12) The fluid reacts with the activator in the particulate material to form a polymer. The latter binds the particles to each other.

(13) In the next step, the building platform (102) is lowered by the distance of one layer thickness. The steps of layer construction, printing and lowering are now repeated until the desired component (103) is completely produced.

(14) The component (103) is now complete, and it is located in the powder cake (114). In the final step, the component is freed of the loose particulate material and cleaned with compressed air.

(15) A component produced in this manner forms the basis for the present invention. The use of these molds may be divided into two areas: single-use molds and multiple-use molds. According to the present invention, they may be used in cold-casting methods.

(16) FIG. 2 shows a simple cast part (200). It is economical to achieve multiple castings with the aid of one mold. A larger and more complex component is represented, for example, by a sink (300) in FIG. 3. The sink has a bowl-shaped formation (301) in its middle. An opening (303) for the later drain is situated in its center. Another opening (302) for the faucet is situated in the rectangular part of the basin.

(17) As a single-use mold (600), breakout is achieved by destroying the mold. The mold is expediently produced as a thin bowl. The structure is additionally reinforced by means of ribbing to withstand the hydrostatic pressures. FIG. 6 shows a mold of this type. The mold is designed in two parts (600, 601).

(18) FIG. 4 shows a multiple-use mold. It comprises two halves (400, 401), each of which has a thick-walled design, and into which the cavity (402) for the casting material is introduced. A sprue (403) is also provided.

(19) The mold (400, 401; 600, 601) may be produced, for example, from a sand having an average grain size of 140 m, which was premixed with a hardener for a so-called cold resin in the amount of 0.3 wt %. The binding process preferably takes place with a concentration of cold resin in the range of 1.0 to 2.5 wt %.

(20) After the printing process, the mold may be removed from the loose sand and cleaned.

(21) Different methods may be used to modify the pore size. For example, an infiltration with a two-component polymer is possible. However, the material must be used in such a way that, according to the invention, pores which facilitate easy mold breakout remain on the surface after treatment. For this purpose, the mold is treated, for example, with an adapted seal, which is processed at room temperature and does not develop high strengths.

(22) It is likewise possible to additionally use a black wash from the metal casting field. Smaller particles are applied to the surface in this case. The effective pore cross section is modified thereby. As a result, it is possible to prevent, for example, the mechanically weak seal according to the invention from being pressed into the mold due to high hydrostatic pressures.

(23) Grease may be used as a simple seal according to the invention. The grease may be applied to the mold by spreading or spraying it on. The grease muse be suitably selected for the task. Too heavy a grease may be difficult to process. Too thin a grease or oil infiltrates the mold and thus no longer provides a sealing function.

(24) After spreading or brushing, the grease may be additionally smoothed. A superficial application of heat is suitable for this purpose. This may be done, for example, with a hot air gun or a blowtorch. Thoroughly heating the mold is not desirable, since this may lead to the possibility of leaks in the seal.

(25) The use of wax is also possible according to the invention. The wax is expediently liquefied by heating for processing. The low viscosity must be increased by means of a thickener; for example, polystyrene microgranulates may be used for this purpose. It is also possible to use hydrophobic solvents, such as the alkanes or benzine, to create a wax solution whose viscosity may be effectively adjusted.

(26) A seal made from hot water-soluble polyvinyl alcohol may also be created. This material is dissolved in hot water and applied to the preheated mold. The mixing water of a concrete is unable to attack the seal.

(27) FIG. 7 shows the process on the microscopic level. The molded body is constructed with the aid of particles (700), which are bonded to each other. Fine particles (702) collect on the geometric component boundary (701) in the event of a black-washed component. The seal (703) seals the surface water-tight.

(28) The molds prepared in this manner are subsequently equipped with additional function components.

(29) For example, ejectors (500, 501) may be inserted into multiple-use molds for easier breakout from the mold. Depending on the expected breakout forces, the seat of the ejectors in the printed mold was reinforced in advance, e.g., using an epoxy resin infiltration. The ejectors may be designed as bolts (501), which engage with a nut (500), which may be countersunk into the printed part. A force is then generated between the mold and the cast part by applying a torque to the bolt.

(30) The mold may also be provided with centering pins. These pins minimize the offset between the mold halves and thus ensure a precise cast part.

(31) Some structures known from metal casting molds may be provided directly on the printed part. Thus, centering elements (603) may be implemented, and labyrinth seals (502) may be mounted for a better sealing action between the mold halves.

(32) The reinforcement is inserted into the mold cavity (402) before the molds are closed. It is expediently held at a distance relative to the mold with the aid of plastic or concrete supports. In this state, empty conduits may also be inserted into the mold for later introduction of electric lines or other media.

(33) The assembly of the molds may be facilitated by bores (503) in the molds. Bolts, which apply the compressive forces onto critical mold areas in a targeted manner, may be guided through these bores. Additional plates may also be screwed on, which reinforce the mold against the casting forces.

(34) Casting takes place through mounted sprues (403) or material shafts. Depending on the technique and casting material used, additional ventilation bores (602) may also be introduced. If a vibrator is to be inserted after casting to compress the casting material, an access is provided in the mold. Mold parts (e.g. 601), which are able to float, due to the pressure of the casting material, must be prevented from changing position, e.g. by being weighted down.

(35) After the casting process, the part rests for up to several days, depending on the binding time of the casting material. The demolding process then takes place.

(36) Due to the low strength of the seal, the latter is easily removed from the pores of the mold during breakout (see FIG. 8). This process may be assisted by heating the mold together with the cast part. As a result of the low separating forces, even delicate cast parts may be safely broken out of the mold.

(37) If a single-use mold is used, the mold may be pre-damaged by hitting it with a hammer in a targeted manner. Depending on the wall thickness of the mold, the actual separation process is carried out with the aid of a putty knife or another flat tool. The mold may also be separated from the cast body by means of sand blasting. The selection of the blasting material and the pressure must be adapted according to the hardness of the casting material, so that the casting material is not damaged.

(38) The multiple-use mold is preferably placed in a furnace before breakout and heated overnight to a temperature of, for example, 60 C. Air circulation should be avoided to prevent drying out if concrete is used as the casting material.

(39) After the furnace process, the bond between the mold and cast part is stressed by tightening the bolts on the ejectors. The mold then usually opens with the aid of slight vibrations or hammer blows.

(40) After the casting process, the sealing medium (801) must be removed from the cast part (800). If grease is used, soaps and washing pastes for cleaning oils and greases are helpful. Hand washing paste that includes cleansing particles is particularly preferred in this case.

(41) After casting, the parts are further processed as in the case of conventional production methods. The usual methods such as grinding or sand blasting are used for surface modification.

LIST OF REFERENCE NUMERALS

(42) 100 Print head 101 Coater 102 Building platform 103 Component 104 Build container 105 Print head path 106 Coater path 107 Powder layers 108 Direction of building platform movement\ 109 Dosed droplets 110 Powder roll 111 Build space boundary 112 Coater gap 113 Coater stock 114 Powder Cake 200 Simple cast part 300 Complex cast part, sink 301 Bowl-shaped sink area 302 Hole for faucet 303 Hole for drain 400 Casting mold, top box 401 Casting mold, bottom box 402 Cavity for casting material 403 Sprue 500 Nut 501 Bolt 502 Labyrinth seal 503 Bore for assembly bolts 600 Sink mold, bottom box 601 Sink mold, top box 602 Ventilation bores 603 Mold centering element and contact point 604 Mold core for drain 605 Mold core for faucet 606 Mold cores for wall mounting 700 Particle 701 Geometric mold boundary 702 Particle of the black wash 703 Seal 800 Cast part 801 Drawn-out seal