DE102005058118A1 - Method for producing ceramic components, in particular casting molds - Google Patents

Abstract

The invention relates to a method for producing ceramic components, the green compact being produced from a suspension of ceramic particles by means of a stereolithography method. For this purpose, this suspension has a radiation-curable binder which is cured locally, for example with a laser. The green body is then subjected to a heat treatment in order to remove the binder from the green body. It is provided according to the invention that the suspension is essentially solvent-free and the low viscosity required for processing by means of stereolithography is influenced by varying the concentration of a dispersant for the ceramic particles. In this way, thermally stressed components can be produced from the ceramic, which due to their high density also have a high temperature resistance. For example, a mold (11) with a core (13) can be produced as a ceramic component.

Description

The The invention relates to a method for producing a ceramic Component in which a green body from a suspension containing at least 45% by volume of ceramic powder with an organic, hardenable Component is obtained as a binder by passing the suspension through local introduction of radiant energy to form the geometric Structure of greenware hardened and the green taken from the suspension and a heat treatment for removal supplied to the binder is, wherein the temperature is below the sintering temperature but high enough for thermal decomposition of the organic components of the green body he follows.

The method described above may, for example, the US 6,117,612 be removed. The aim is to have a process for the production of green compacts for ceramic components available, in which the green compact with a rapid prototyping method, eg. B. the method of stereolithography, can be produced. Areas of application for this process can be found not only in prototype construction but also in small series, where the production of molds for the green product is not worthwhile.

In order to be able to process the ceramic particle-produced suspensions with fill levels above 40% by volume of ceramic particles by means of rapid prototyping methods, they must have a sufficiently low viscosity. According to the US 6,117,612 the viscosity is reduced by the fact that the suspension, which must also contain components of a thermosetting resin for the generation of a preliminary bond in the green compact, is prepared on an aqueous basis. The water thus serves as a dilution for the per se viscous resin, so that the suspension to be processed, despite the high degree of filling of ceramic particles remains sufficiently fluid to be processed by rapid prototyping.

The The object of the invention is a method for manufacturing of ceramic components from green bodies indicate, in which the greenlings with a rapid prototyping process can be produced and the application of the rapid prototyping method comparatively can be done without problems.

These The object is achieved with the initially described method according to the invention thereby solved, that the suspension is substantially solvent-free, wherein the viscosity the suspension by varying the concentration of a dispersant less than 20,000 mPa · s is reduced and wherein it is the ceramic component to is a thermally stressed component. After the invention is the viscosity the suspension over adjusted the concentration of the added Disperpators, thereby achieved a setting of the required viscosity of less than 20,000 mPa · s can be. With this viscosity is a processing of the suspension, for example, in commercial Stereolithography systems possible.

On an addition of diluents like Water or organic solvents can in the suspension according to the invention be waived. It has become shown that the addition of solvents to reduce the viscosity limits the processability of the suspensions thus produced. By the energy input into the suspension to produce the desired Namely, it can evaporate locally because of its three-dimensional structure of solvents in the suspension come with the effect that there is the viscosity of the suspension increases. As a result, however, the desired result, a Greenfinch with a high degree of filling on ceramic particles, endangered. The high degree of filling is but especially for ceramic components with high thermal Stress required so that the component to be produced from the green compact a sufficient one Has density.

According to one Embodiment of the method is provided that the green compact for a casting tool will be produced. Casting tools are made with molten materials which raises the requirement for high temperature resistance results. Therefore, ceramic materials are particularly suitable for the production of molds. With the help of rapid prototyping methods like the Stereolithography can advantageous without much effort green compacts for complex housing structures getting produced. It is also the production of lost forms possible, being for possibly trainee inner contours no cores are necessary.

Indeed can according to a further embodiment of the invention, the green body itself be designed as a casting core, that without a previous sintering heat treatment or after one completed sintering heat treatment for Use is provided. If you have a green or one only incomplete sintered green compact used as a core, so is the subsequent destruction of the Kernes advantageous after the casting process substantially simplified. The greenling just needs a sufficient stability exhibit the casting process to survive safely. Against this background it can be decided how far the sintering process should drive before, or if the sintering process is not required is.

Another embodiment of the invention provides that the component is produced in one piece as a casting mold with internal structures replacing the casting core. This is advantageously made possible by the characteristics of the manufacturing process, for example by means of stereolithography, since the layered structure of the green compact also enables the creation of complex internal structures. In the destruction of the casting core replacing inner structures, however, the mold will usually be destroyed, so that in this embodiment of the invention are lost forms.

According to one particular embodiment of the invention it is provided that the Casting core or the internal structures of the mold with a cavity getting produced. This cavity can also be advantageous without major problems for example, produce by stereolithography. The cavity facilitates the demolition of the casting when removing the casting Casting and especially the removal of the destroyed Gusskernmaterials the cavity formed in the casting.

Especially It is advantageous if the casting tool after completion of the Heat treatment one Fed casting process before it has cooled to room temperature. This can be a Cooling up to the desired Temperature of the casting tool for the casting process to be awaited. Technically, there is the advantage that the mold for then the subsequent casting process does not have to be preheated. This is an energy saving possible. Furthermore The risk is reduced due to a cooling and subsequent heating the mold may encounter errors such as tensions, cracks or distortion.

According to one particular embodiment of the invention is a dispersant Alkylolammmoniumsalz used a copolymer having acidic groups. This is a so-called steric dispersant, which causes an effective separation of the powder particles from each other. This is achieved by the long-chain polymer molecules of the dispersant act as a separating layer between the individual powder particles. As a result, the mobility of the powder particles to each other guaranteed whereby the fluidity of the Suspension is maintained. This can be the required low viscosity to reach. Alkylolammmoniumsalze of copolymers having acidic groups for example, by the company Byk Chemie GmbH under the trade name Disperbyk 154, Disperbyk 180 or Disperbyk 190 offered.

When Advantageously, it has been found, if the above Dispersants in a concentration between 2 and 5% by weight added become. It has been shown that in this concentration range the viscosity is advantageously adjusted by targeted variations of the concentrations can, without the concentration of the dispersant other properties negatively affected by the suspension.

Farther it is advantageous if an acrylic resin is used as binder comes. Acrylic resins have in comparison to also eligible epoxy resins the advantage that they have a lower viscosity. Consequently let yourself also for the suspension achieve a relatively lower viscosity. However, when using acrylate resins, a photoinitiator must also be used for toasting the curing reactions be added. Upon irradiation of the suspension with UV radiation are formed from the photoinitiator free radicals, which subsequently a Initiate polymerization of the acrylate monomers. For example, when using a UV laser with the wavelength of 365 nanometers can be a liquid Photoinitiator from Ciba Ltd. with the trade name Darocur 4265 be used.

A additional Viscosity reduction can be achieve advantageous when the particles of ceramic powder coated before being introduced into the suspension with that of the disperser become. In this case, the dispersant does not become the suspension directly added, but with the dispersant coated particles guarantee the introduction of the dispersant in the suspension. The coating The powder particles with the disperser has the advantage that this when introducing the particles into the suspension already at his Place of action is located. This prevents, for example, clumping the powder particles during of introduction into the suspension. In addition, so is the best Ensures efficiency of Dispersatormoleküle.

One A particularly suitable method for curing the binder is the stereolithography method. This can be used advantageously on a proven technology become. The adjusted viscosities in the processed Ensure suspensions advantageous in that the production of green compacts without modification with commercial Stereolithography systems can be done.

According to a particular embodiment of the method, it is provided that the heat treatment to remove the binder with completion of oxygen at temperatures up to 600 ° C. By the conclusion of oxygen during the heat treatment, the removal of the binder, also called debinding, advantageously carried out particularly gently. It is namely prevented that an oxidation of the binder components takes place in the green compact. Due to such an exothermic reaction, thermal energy would otherwise be released, which could lead to tensions, cracks, delaminations and delays due to local overheating of the green body.

Farther It is beneficial if the heat treatment for removing the binder in an oxygen-containing atmosphere at temperatures up to 1150 ° C takes place. This heat treatment is particularly advantageous downstream of the latter. The debinding in an oxygen-containing atmosphere has namely the Advantage that this is more effective and therefore shorter treatment times higher Debinding effects achieved. Is the debinding under oxygenated the atmosphere only applied in a subsequent step, so is the concentration of the binder in the green already fallen so much by the first debinding step, that local overheating effects in the green can be excluded. The mentioned quality problems can therefore no longer occur.

Further Details of the invention are described below with reference to the drawing described. Show it

1 schematically the temperature profile during debindering according to an embodiment of the method according to the invention and

2 a ceramic housing component, which is produced according to an embodiment of the method according to the invention.

in the The method parameters are given below by way of example. the for the production of a green body successfully used. For this, the manufactured green has as Layered model with a layer thickness between 20 and 200 μm as digital Dataset available.

In the preparation of the suspensions, a commercially available Al ₂ O ₃ powder (alumina) having a mean particle diameter of 0.8 μm was used. Alternatively, powders of zirconia (ZrO ₂ ) or silica (SiO ₂ ) may also be used. With melting points of 1720 ° C (SiO ₂ ), 2050 ° C (Al ₂ O ₃ ) and 2480 ° C (ZrO ₂ ) these ceramic materials are resistant to high temperatures and are therefore suitable for use as molds for refractory materials (such as metals).

Around a degree of filling to achieve the suspension of ceramic particles of greater than 45% by volume and while a relatively low Viscosity of less than 20,000 mPa · s to ensure, the ceramic particles were in the suspension before admixture with the steric dispersant from Byk Chemie GmbH with the Trade name Disperbyk 180 coated. In order to have an optimal dispersing effect To achieve the dispersant was dissolved in a solvent and then with homogenized to the powder. This suspension was in a drying oven at 60 to 80 ° C dried until all the solvent had evaporated. The dried powder was additionally ground and sieved.

in the next Step, the pretreated ceramic powder was an acrylate resin added and by intensive stirring dispersed. This suspension was additionally ground with a ball mill to any remaining Aglomarate of ceramic particles to destroy. The thus prepared suspensions are also over a period of several weeks stable.

at an input of 4% by mass of the already mentioned dispersant at a degree of filling of ceramic particles of 45% by volume a viscosity of 2000 mPa · s. Due to the ratio moderately low viscosity the suspensions could the degree of filling be increased to ceramic powder to 55% by volume, without the maximum allowable viscosity exceeded 20,000 mPa · s was (the specified dispersant content is based on the mass of Ceramic powder covered).

In front the production of the green body in a stereolithography plant was the photoinitiator Darocur 4265 of the company Ciba Ltd. added. The proportion of photoinitiator based on the amount of suspension can be between 0.3 and 2% by mass lie, with the optimal amount in relation to the current composition the suspension is to be determined experimentally in each case. The laser power for the curing was varied between 5 and 14 mW. The hardening depth was 100 to 500 μm. Herewith could reach layer thicknesses between 50 and 100 microns.

The next step in debinding (binder removal) is in 1 shown schematically. A two-step debinding technique has been developed. First, the green compact was heated at K per minute in N ₂ atmosphere to 600 ° C (T ₁ ), and this temperature was maintained for one hour. This process took approximately 10 hours (t ₁ ). In a second step, the samples were further heated up to a temperature of 1150 ° C. (T ₂ ) in air or in an O ₂ atmosphere, and this temperature was also maintained for one hour. The second treatment step was also stopped after about 10 hours (t ₂ ), after which the green compact cooled to room temperature. Debinding errors such as distortion, cracks, delamination and the like could be avoided with this two-step process.

Subsequent sintering took place in known manner at 1800 ° C in H ₂ atmosphere. The finished ceramic reached 99.8% of the theoretical density, so that the ceramic structure contained hardly any pores.

Further Attempts to produce green bodies yielded more possible Variations of the above-mentioned process parameters. Instead of already mentioned Acrylate resin monomer 4017 may also include the acrylate resin monomer 4006 of Cognis GmbH be used. However, this has a higher viscosity, therefore lower filling levels Ceramic powder can be achieved. The process parameters in stereolithography can within the following areas on the particular application to be optimized: Penetration depth between 150 and 400 μm, laser power between 2 mW and 13 mW (using a 325 nm He-Cd laser) Wavelength), Focusing range of laser radiation between 45 and 90 μm and scanning speed between 50 and 200 mm / s. The stereolithographically obtained structures can in addition be exposed to an irradiation with UV light in order to improve curing to reach the binder.

In 2 an example of a casting tool is shown, which was produced with the described method of ceramic powder. This is executed to the right and left of the broken line in two variants. The casting tool consists of a mold 11 that a cavity 12 for the casting to be produced. The material of the form 11 is alumina. The cavity 12 is in the interior through a core 13 limited, which by means of a suitable recording 14 into the mold 11 can be inserted. For this purpose, the mold must be divisible in a manner not shown, so that the core 13 into the mold 11 can be inserted.

Alternatively, instead of the core 13 also an interior structure 15 be provided, which is integral with the rest of the form 12 will be produced. In fact, due to the nature of the stereolithographic manufacturing process, it is possible to manufacture the mold in one piece, including all the undercuts to be imaged. Therefore, assuming that it is a lost form, the shape 11 according to the variant left of the fracture line can also be produced without shaping division.

In the inner structure 15 or the core 13 is still a cavity 16 provided after the production of the casting in the cavity 12 a destruction of the core 13 or the internal structure 15 facilitated. The removal of the core can be further facilitated if it is not sintered, but as a green body in the mold 11 is inserted. The structure is then easier to destroy, because the adhesion of the ceramic particles with each other is limited.

Claims (13)

A method for producing a ceramic component, in which - a green compact is obtained from a suspension containing at least 45% by volume of ceramic powder with an organic, curable component as binder, by hardening the suspension by locally introducing radiant energy to form the geometric structure of the green compact and - the green compact is taken from the suspension and fed to a heat treatment to remove the binder, the temperature being below the sintering temperature but high enough for thermal decomposition of the organic constituents of the green compact, characterized in that the suspension is substantially solvent-free wherein the viscosity of the suspension is reduced by varying the concentration of a dispersing agent to less than 20,000 mPa · s, and wherein the ceramic component is a thermally stressed component. A method according to claim 1, characterized in that the green compact for a casting tool ( 11 . 13 ) will be produced. A method according to claim 2, characterized in that the green compact as a casting core ( 13 ), which is intended for use without a preceding sintering heat treatment or after an incomplete sintering heat treatment. A method according to claim 2, characterized in that the component as a casting mold ( 11 ) with the casting core ( 13 ) replacing interior structures ( 15 ) is made in one piece. Method according to claim 3 or 4, characterized in that the casting core ( 13 ) or the internal structures ( 15 ) of the mold with a cavity ( 16 ) getting produced. Method according to one of claims 2 to 5, characterized in that the casting tool ( 11 . 13 ) after completion of the heat treatment is fed to a casting process, before it has cooled to room temperature. Method according to one of the preceding claims, characterized in that the dispersant used is an alkylolammonium salt of a Copolymers with acidic groups is used. Method according to claim 7, characterized in that the dispersant has a concentration between 2 and 4% by mass is added. Method according to one of the preceding claims, characterized characterized in that the binder used is an acrylate resin, the suspension further comprising a photoinitiator for initiating the curing reaction is added. Method according to one of the preceding claims, characterized characterized in that the particles of the ceramic powder before coated in the dispersion with the dispersing agent become. Method according to one of the preceding claims, characterized characterized in that for curing the binder is a stereolithography method is applied. Method according to one of the preceding claims, characterized characterized in that the heat treatment for removal of the binder with completion of oxygen at temperatures up to 600 ° C he follows. Method according to one of the preceding claims, characterized characterized in that the heat treatment for removing the binder in an oxygen-containing atmosphere at temperatures up to 1150 ° C he follows.