US20070071631A1

US20070071631A1 - Method for Producing Metallic Components, Corresponding Metallic Components and Kit for Carrying Out the Method

Info

Publication number: US20070071631A1
Application number: US11/463,699
Authority: US
Inventors: Helmut Laschutza; Thomas Wiest; Stephan Dierkes; Jan Eilers
Original assignee: Bego Bremer Goldschlaegerei Wilh Herbst & Co KG GmbH; Bego Bremer Goldschlagerei Wilh Herbst GmbH and Co KG
Current assignee: Bego Bremer Goldschlagerei Wilh Herbst GmbH and Co KG
Priority date: 2005-08-10
Filing date: 2006-08-10
Publication date: 2007-03-29
Also published as: EP1759682A3; DE102005038074A1; EP1759682A2

Abstract

A method is described for producing a metallic component, comprising the following steps: provision of a negative model for the component, which (i) is electrically: conductive or is rendered electrically conductive at least on the surface thereof or (ii) is porous and comprises an electrode inside, provision of a slip which comprises electrophoretically depositable metallic and optionally additionally ceramic particles, electrophoretic deposition of a layer of the particles from the slip onto the surface of the model, sintering or partial sintering of the deposited layer of particles.

Description

This application claims priority from German Patent Application 10 2005 038 074. 3-23 DE filed Aug. 10, 2005, the full disclosure of which is hereby incorporated by reference herein.
The present invention relates to a method for producing metallic components, in particular a metal-based dental restoration, to corresponding metallic components (in particular dental restorations) themselves and to a kit for carrying out the method according to the invention.
The invention is described hereinafter predominantly with regard to dental restorations, but also relates to other metallic components, c.f in this respect also Examples 2 and 3.
A metal-based dental restoration may in particular comprise a metallic dental article such as for example a cap, an inlay, only or a bridge.
The dental restoration is optionally fireable, i.e. suitable for having a ceramic coating fired on.
Metal-based dental restorations which are to be used as a metallic dental prosthesis are often obtained by the process of casting. In this process, the shape of the dental prosthesis is modeled in wax on a master model of the dental situation to be restored: the master model serves, relative to the wax modelling, as a negative model. The wax model is then embedded in an embedding material. The wax is removed from this embedding material by firing and in this way a mould is obtained into which molten metal is cast. The various stages of the method are carried out on-site in the dental laboratory, but are comparatively labour-intensive.
A less labour-intensive option for the dental technician is an alternative method in which the metallic dental prosthesis (as an example of a metal-based dental restoration) is produced in a CAD/CAM chain. In this connection, two alternative methods have come established in practice, both of which involve computer processing of the data obtained by scanning the model. In one case, the dental restoration is produced by material removal (milling) from a block of metal. In the other case, the dental restoration is built up in layers and subjected to local laser sintering. CAD/CAM chains entail a comparatively high level of technical complexity and the use of comparative costly equipment. When CAD/CAM chains are used, the dental restorations are often not produced on-site in the dental laboratory, but instead in special dental centres having the necessary CAD/CAM installations.
It is also already known to electrodeposit gold frameworks onto a plaster stump which has been rendered conductive by means of a conductive silver lacquer, which plaster stump as a negative model relative to the gold framework. A layer of god of a thickness of approx 0.2 to 0.3 mm is, for example, deposited over the course of a few hours. One disadvantage, other than the large amount of time required, is that a gold solutions is used, the handling and disposal of which is not unproblematic.
It was accordingly the object of the present invention to provide a method for producing a metallic component, in particular a metal-based dental restoration which, in comparison with the conventional casting method, is less labor-intensive, in comparison with the method using a CAD/CAM chain, requires a lower level of technical complexity and, in comparison with the method involving electrodeposition of a gold framework, is faster and less problematic with regard to the disposal of materials. Furthermore, in comparison with the conventional casting method and the CAD/CAM method, it was intended to dispense with modelling of the dental restoration (in wax or on the computer). In comparison with the electrodeposition of gold frameworks, the method to be stated should also permit the use of other metals and of alloys.
In addition to the above-discussed method for producing metal-based dental restorations, another method is known which is described in DE 35 32 331 A1. According to the method described therein, a dental prosthesis, suitable for overlaying, having a metallic structural matrix (i.e. a metal-based dental restoration) is produced by sinter metallurgy, by converting multimodal metal powder mixtures, optionally with the addition of glass and ceramic powders, into a slip with water, modelling the dental prosthesis with the slip and sintering the slip composition at a temperature which exceeds the solidus temperature of at least one powder constituent. The described method has, however, not gained any appreciable significance in practice, most probably because manual application of the slip comparatively complex.
Further documents of relevance to understanding the significance of the present invention are: DE 100 49 974 A1; DE 101 20 084 A1, DE 103 20 936 A1; U.S. Pat. No. 5,238,751 A.
The stated object is achieved according to the invention by a method for producing a metallic component, in particular a metal-based dental restoration, comprising the following steps:

- provision of a negative model for the component, which (i) is electrically conductive or is rendered electrically conductive at least on the surface thereof or (ii) is porous and, comprises an electrode inside,
- provision of a slip which comprises electrophoretically depositable metallic and optionally additionally ceramic particles,
- electrophoretic deposition of a layer of the particles from the slip onto the surface of the (negative) model,
- sintering or partial sintering of the deposited layer of particles.

In particular the invention relates to a method for producing a metal-based dental restoration, comprising the following steps:

- provision of a model of the dental situation to be restored (a positive model relative to the actual dental situation, but a negative model relative to the dental restoration). which (i) is electrically conductive or is rendered electrically conductive at least on the surface thereof or (ii) is porous and comprises an electrode inside,
- provision of a slip which comprises electrophoretically depositable metallic and optionally additionally ceramic particles,
- electrophoretic deposition of a layer of the particles from the slip into the surface of the model,
- sintering or partial sintering, of the deposited layer of particles.

The fraction of metallic particles, the slip used according to the invention preferably amounts to 50-100 wt. %, preferably, 75-100 wt. %, relative to the total mass of metallic and ceramic particles. The slip preferably contain no ceramic particles.
According to the invention, a layer of metallic and optionally (but not necessarily) ceramic particles is electrophoretically deposited onto the surface of a negative model, preferably a model of a dental situation to be restored. If such a deposition step is to be carried out, a negative model, for example a model of the dental situation to be restored, is required in which (i) at least the surface is electrically conductive or is rendered electrically conductive or (ii) is porous and comprises an electrode inside.
Negative models, for example models of a dental situation to be restored, which are electrically conductive on the surface thereof, may be made from conductive modelling materials, which may for example be obtained by adding a conductive material, for example silver, graphite, carbon black or platinum particles to conventional per se non-conductive modelling materials such as plaster, refractory materials, wax or plastics material. It is alternatively possible to use modelling materials which are intrinsically conductive.
A model of a dental situation to be restored, which has been rendered electrically conductive on the surface thereof and, relative to the finished dental restoration, may act as a negative model may, for example be obtained by applying a conductive coating onto a working model which is not per se conductive. Coating materials which may be used are in particular conductive silver lacquer, conductive graphite and platinum lacquer; alternatively, electrically conductive layers may, for example, be applied by metal sputtering. This applies correspondingly to other negative models.
The negative model (for example a dental working model) is produced using conventional methods, in particular rapid prototyping (milling, laser sintering, inkjet printing, stereo lithography, 3D printing) or casting methods, in particular using duplicate moulds.
A model of the dental situation to be restored which is porous and comprises an electrode inside, or another negative model (“negative” relative to the metallic component to be produced) is produced for example by rapid prototyping (milling, 3D printing) or casting methods, in particular using duplicating moulds. The recess within the model (or of the other negative model) which is required to accommodate the electrode, may either be introduced directly during production of the model or is introduced subsequently, for example, by drilling.
A model of a dental situation to be restored (or another negative model), which (i) is electrically conductive or is rendered electrically conductive at least on the surface thereof or (ii) is porous and comprises an electrode inside, may be used in an electrophoretic deposition method. For the purposes of the method according to the invention, the aim here is to deposit metallic particles onto the surface of the model, even the latter is porous and comprises an electrode inside; in the latter-stated case, deposition onto the surface of the model proceeds in the manner of membrane electrophoresis.
In a method according to the invention, a negative model is electrically conductive or is rendered electrically conductive at least on the surface thereof, for example a model of the dental situation to be restored, is preferably used which comprises:

- modeling material which is electrically conductive (thus for example a material rendered conductive by addition of silver, graphite, carbon black or platinum particles or a per se conductive material) or
- an electrically non-conductive modelling material having arranged on the surface thereof a coating of a conductive substance (thus in particular a conventional non-conductive material such as plaster, refractory material, wax of plastics material with a coating of for example silver, graphite or platinum).

If, alternatively, a negative model, in particular a model of a dental situation to be restored is used which is porous and comprises an electrode inside the pore size of the porous model is adapted to the particle size of the metallic and (if present) additional ceramic particles of the slip in such a manner that, during electrophoresis, the particles cannot reach as far as the electrode inside the model.
Such pore sizes adapted in this manner to the size of the particles are of great significance in achieving successful membrane electrophoresis.
According to a first alternative development of the method, the negative model (“negative” relative to the finished dental restoration) to be used in the method according to the invention has the dimensions of the dental situation to be restored, in particular is thus not enlarged relative to the dental situation to be restored. Sintering of the deposited layer of the (metallic and optionally additionally ceramic) particles then preferably proceeds on the model, the modelling material being selected such that, under the sintering conditions, the model undergoes a relative change in length of no more than 0.2%, preferably of no more than 0.05%, relative to the length before sintering. Thus, after sintering, the model still has (at least virtually) the dimensions of the dental situation to be restored. The external dimensions of the model (at least virtually) exactly predetermine the internal dimensions of the sintered layer of deposited metallic particles. Due to the retention of the dimensions of the model under sintering conditions, i.e. due to the absence of appreciable sintering shrinkage for the model, the internal geometry (internal dimensions) of the deposited layer of metallic and optionally ceramic particles cannot undergo significant change during the sintering process. A reduction in porosity within the layer of metallic particles and a reduction in layer thickness do, however, occur. The internal geometry (internal dimensions) of a crown, for example, which has been produced in this manner is retained during the sintering process, such that the accuracy of fit of the crown (or of another dental restoration) is particularly high. The sintered, thermally stable modelling material, which did not undergo any sintering shrinkage during sintering, may be removed from the sintered layer of metallic particles mechanically or chemically, for example by jet blasting or etching.
According to a second alternative development of the method, the model to be used in the method according to the invention has the dimensions of the dental situation to be restored, in particular is thus not enlarged relative to the dental situation to be restored. The layer of particles is, however, only partially sintered (subjected to a heat treatment) for the purpose of increasing strength, i.e. only slight relative changes in length (less than 0.1% change in length, preferably less than 0.05% change in length, relative to the length before partial sintering) of the molded article occur. There is additionally no or no substantial reduction in porosity (the change in porosity is preferably at most 5% relative to the porosity before partial sintering). In this development of the method the model is preferably selected such that it (i) may be removed from the molded article (the laser of metallic particles) by a (thermal, mechanical or chemical) pretreatment before partial sintering or (ii) shrinks away from the molded article during partial sintering.
A preferred method according to the invention is one in which the model has the dimensions of the dental situation to be restored, the deposited layer of the particles in question is partially sintered and optionally previously subjected to heat treatment, wherein, during partial sintering or the preceding heat treatment, the modelling material shrivels or is burnt out from the metallic layer.
According to a third alternative development of the method, the model to be used in the method according to the invention has larger dimensions than the dental situation to be restored. Sintering of the deposited layer of metallic particles then, proceeds on the model, the modeling material being, however, selected such that, under the sintering conditions the volume of the model reduces at least to the dimensions of the dental situation to be restored. During sintering, the porosity within the layer of deposited metallic and optionally ceramic particles falls, and since, under the sintering conditions, the volume of the model reduces at least to the dimensions of the dental situation to be restored, the deposited layer of particles also shrinks, the internal dimensions of the layer approaching the external dimensions of the dental situation to be restored.
According to a fourth alternative development of the method too, the model to be used in the method according to the invention has larger dimensions than the dental situation to be restored. Sintering of the deposited layer of metallic and optionally ceramic particles does not, however proceed on the model. The latter is instead removed by a suitable treatment before the actual sintering operation: see in this connection the comments made regarding the second alternative development of the method. For example, a wax model may be melted burnt away from the deposited layer of metallic and optionally ceramic particles by a brief heat treatment at a temperature which is lower than the subsequent sintering temperature. The prerequisite for the feasibility of the fourth alternative development of the method is, of course, that the green strength of the deposited layer of particles is sufficiently high for removal of the modelling material to be possible and not to lead to the immediate collapse of the structure of the metallic or metal/ceramic layer.
The slip of electrophoretically depositable metallic and optionally ceramic particles used in the method according to the invention comprises a powder with a monomodal, bimodal or higher modal particle size distribution. The slip additionally comprises a dispersant and optionally a stabilizer.
In a powder mixture which comprises metallic and additional ceramic particles, the ceramic powder gives rise, for example, to a comparatively high hardness of the finished component, or example the finished dental restoration.
The powder of metallic and optionally ceramic particles preferably has a bimodal or a higher modal particle size distribution.
Preferred metal powders are those for which the following possibilities for particle size distribution apply: 0.1 μm<d₅₀<20 μm, preferably 0.1 μm<d₅₀<10 μm.
If the slip of electrophoretically depositable particles comprises powder with the bimodal particle size distribution (as is preferred), the particle sizes at the locations of the two relative frequency maxima of the particle size distribution are preferably in a particle size ratio of greater than 5:1 to one another. The particles are for example, by means of laser diffraction.
In a preferred embodiment of such a slip, the slip comprises a powder with a fraction of metallic particles and a fraction of ceramic particles, wherein the smaller particles, i.e. the maximum on the particle size distribution curve which is associated with the smaller particle size, belong to the ceramic fraction.
Using such slips or powders gives rise to an electrophoretically deposited layer with particularly high green density (i.e. with particularly low porosity).
The electrophoretically deositable metallic particles may consist of alloys alternatively containing or not containing noble metals. Noble metals and other metals such as gold, titanium, iron, platinum, palladium, silver, cobalt, chromium etc. and the alloys thereof are, for example, used. The use of alloys containing gold is often preferred.
Electrophoretically depositable ceramic particles are for example alumina, zirconia, spinel etc.
During production of the slip of electrophoretically depositable particles, the person skilled in the art will take care to ensure that preferably no or only a slight change in slip composition occurs during electrophoretic deposition. He/she will take account of the fact that settling of the particles and thus separation of the slip is influenced by particle size, by the difference in density between the dispersant (liquid) and particles and by the viscosity of the slip. He/she will bear in mind that small particles within the slip settle more slowly than large ones and he/she will thus in particular select the particle size distributions which are characterised above as preferred. The person skilled in the art knows that a high density of the dispersant (the liquid) results in high buoyancy acting on the particles and thus in lower settling rates. The person skilled in the art is additionally aware that a high viscosity reduces the settling rate. The person skilled in the art will adjust the viscosity of the slip by suitably selecting the solids content and/or the initial viscosity of the dispersant. In preferably used slips, the solids content of the slip is in a range from 20 to 75 vol. %, preferably in the range from 30 to 60 vol. %, relative to the total volume of the slip.
In particular, in order to ensure an elevated filler content of the slip, the bimodal powder distribution which is stated further above to be preferred is used, preferably with powders which comprise metallic and ceramic particles.
The powders used may be monophasic (in the absence of ceramic particles), biphasic or multiphasic; in many cases it is also advantageous to use bi- or multiphase powders if no ceramic particles are used. Composites may be produced by using bi- or multiphase powders, i.e. components which, due to the use of different materials, combine the advantageous properties of the materials. The hardness and toughness of a component may also purposefully be influenced by the use of different material. The melting temperatures of the materials may, of course, furthermore differ. A higher melting or sintering metallic or ceramic material may thus be combined with a lower melting or sintering material and thus reduce the required sintering temperature.
It has proved advantageous to use a slip of electrophoretically depositable particles which comprises a powder with a bimodal or higher modal particle size distribution, wherein the powder fraction with the largest particle size comprises spherical particles or consists of spherical particles.
In one method according to the invention, sintering or partial sintering of the deposited layer of particles for increasing strength is preferably carried out at a temperature which is in the range from 0.45 to 0.9 times the melting temperature or solidus temperature of the lowest melting or the sole metallic phase of the layer. The melting or solidus temperature is here stated in Kelvin (K).
Sintering or partial sintering of the deposited layer of particles results in strengthening. The selected sintering temperature will be dependent on the material used and the desired result of the sintering operation. Conventional sintering temperature area the range from 600-1400° C.
If in addition to strengthening, porosity is to be reduced and thus the geometry of the layer of deposited particles is to be modified, when a monophasic powder is used, a sintering temperature is preferably selected which is in the range from 0.6 to 0.9 times the melting temperature or solidus temperature. In the case of multiphasic powders (powder mixtures), a sintering temperature is preferably selected in this case which is in the range from 0.6 to 0.9 times the melting temperature or solidus temperature of the lowest melting metallic phase of the layer (of powder). When multiphasic powders are used, sintering may, however, also be carried out above the melting temperature or solidus temperature of the lowest melting phase (liquid phase sintering).
The person skilled in the art can adjust the grain structure of the resultant sintered metallic layer by means of the sintering temperature. Grain growth is accelerated at elevated sintering temperatures, such that a comparatively coarse structure grain structure is obtained; at the same time, the required sintering time is very short. At lower sintering temperatures, exactly the opposite behavior is observed; the required sintering time is very high, but a finer grain structure is obtained.
If the heat treatment is merely intended to increase strength without being associated with a change in length of 0.1% or more, the heat treatment (partial sintering) of the deposited layer is preferably carried out at a temperature which is in the range of 0.45 to 0.6 times the melting temperature or solidus temperature of the lowest melting or the sole metallic phase of the layer. At such low temperatures, when an increase in strength is indeed obtained because adjacent metallic particles are joined together by sintered bridges, the geometry of the green body is retained. A partially sintered green body with remaining porosity is obtained.
The remaining porosity of partially sintered or sintered layers of deposited particles may then be filled with a low-melting material, preferably using a metal, for example a low-melting alloy, or using a preferably low-melting glass or a preferably low-melting resin or plastics material. In this way, composites, which are in many cases desired, may be produced. “Low-melting” are here materials whose melting point is no greater than 0.8 times the melting temperature or solidus temperature of the lowest melting or the sole metallic phase of the deposited layer.
Sintering or partial sintering of the deposited layer of the metallic and optionally ceramic particles may proceed under a normal atmosphere if noble metals or noble metal alloys have been used. If non-noble metals or alloys are used the person skilled in the art will purposefully select the sintering atmosphere. He/she will here bear in mind that oxygen, nitrogen and carbon are capable of reacting with non-noble metals or alloy constituents. In particular, the particle surfaces may be oxidized which gives rise to a molded article with impaired mechanical properties. It has proved advantageous to carry out sintering of the deposited layer of particles with the aim of reducing porosity or partially sintering the deposited layer of particles simply to increase strength in an oxygen-depleted atmosphere (the content of oxygen is below the content of oxygen in air). Depending on the affinity of the metal used or the alloy elements used, the nitrogen and/or carbon content in the sintering atmosphere is preferably also reduced. In many cases it is advantageous to flush the furnace chamber used for sintering or partial sintering with argon; it is in particular then possible to obtain a furnace chamber atmosphere containing little or no oxidizing gas (inert gas atmosphere).
In other cases, however, the person skilled in the art will, purposefully add oxidation gases in order to achieve formation of a composite.
Particularly preferred is a development of the method according to the invention, in which the fraction of metallic particles in the slip used amounts to 75-100 wt. %, preferably 100 wt. %, relative to the total mass of particles in the slip, wherein

(i) the metallic particles consist of alloys containing noble metal or of noble metals such as gold, platinum, palladium or silver
(ii) sintering of the deposited layer of metallic particles or partial sintering of the deposited layer of metallic particles is carried out in an oxygen-depleted atmosphere (this is important in particular when alloys containing no noble metals are used). Dispersants selected for use in a slip to be used according to the invention are preferably selected from the group consisting of water, alcohols and mixtures thereof. It is alternatively possible to use organic acids and the esters thereof, alcohol derivatives, organic nitrogen compounds (amides, nitro compounds, nitriles) aldehydes and ketones, organic sulfur compounds (sulfoxides, etc) and ethers. Since the deposition rate is inter alia dependent on the dielectric constant of the dispersant, a dispersant should have a dielectric index of at least 10 (for comparison: water (˜80), n-propanol (˜20) and should preferably be easily handled (no carcinogencity, no toxicity).

It is particularly preferred to use water, ethanol, isopropanol, n-propanol and mixtures thereof.
If a stabiliser is present in a slip to be used according to the invention, it is preferably selected from the group consisting of: electrostatically stabilising stabilisers, electrosterically stabilising stabilisers and mixtures thereof.
The aim of using stabilisers is to produce a stable dispersion, in which the particles exhibit a charge such that uniform electrophoretic deposition is possible. The cause of particle motion within the slip is here the interaction between the external electrical field and the charge of the particle.
The particle surfaces may be provided with electrical charges 1) by chemical reactions at the particle surface and 2) by specific adsorption/desorption of ions. In electrostatic stabilisation, the tendency of the dispersed metallic particles to coagulate due to van der Waals forces (dipole bonds) is counteracted by electrostatic repulsion. Electrosteric stabilisation likewise exploits the effect of electrostatic repulsion but additionally involves a steric hindrance effect which counteracts coagulation.
The electrostatically or electrosterically stabilising stabilisers are preferably selected from the group consisting of: organic and inorganic bases and acids, the salts thereof and the cations or anions thereof, complexing, agents, polymers (in particular as ions or in liquid form) and mixtures thereof.
Examples of suitable stabilisers are:
acetic acid (organic acid), 4-hydroxybenzoic acid (organic acid), ethylenediamine tetraacetate (dissociated, complex-forming residue of a salt of an organic acid), urea (organic compound of an inorganic base) triethanolamine (organic compound of an inorganic base, polyethyleneimine (polymer).
In the method according to the invention, it is in many cases advisable to add a binder to the slip, which binder is then deposited together with the metallic particle. Additionally or alternatively, a binder may be applied onto the deposited layer of particles before the thermal (sintering, partial sintering, heat treatment for removal of the model) or mechanical treatment. In such a development of the method, the binder contributes towards an increase in green body strength and hardness. Binders which may be used are in particular silicone resins, silanes, siloxanes, silicone esters, acrylates, polyvinyl alcohols or other polymers, for example binders conventionally used in paints, coatings and the building materials industry. The binders are of an inorganic or organic nature; organic binders are preferred because the do not remain in the sintered framework.
Using a binder reduces the risk of the green body's being destroyed or suffering damage during handling, further processing or during drying. After electrophoretic coating of a working model, the resultant dental restoration may be finished, for example with a scalpel or rotary multitool. Such preparation includes, for example, exposing the preparation border or reducing the layer thickness at desired points and a stable green body is advantageous for this purpose. Elevated green strength is likewise necessary for the method variant according to the invention in which the framework is separated from the model before sintering or partial sintering. In this case, the model and green body are subjected to thermal, mechanical or chemical treatment. The support which the green body received from the working model is then no longer present. After removal of the coated negative model from the slip, the deposited layer of metallic and optionally ceramic particle begins to dry. Depending on the particle size distribution, drying shrinkage may occur (more marked with small particle sizes than with large). In order to prevent cracking on drying, the strength of the layer is preferably enhanced by binders.
The invention also relates to a kit for carrying out a method according to the invention compromising:

- metal powder, dispersant and optionally stabilizer and/or binder and/or ceramic powder for producing a slip of electrophoretically depositable metallic particles;
- an electrophoresis apparatus for the electrophoretic deposition of metallic particles.

The statements made above relating to the method according to the invention apply correspondingly with regard to preferred developments.
The invention furthermore relates to the use of a metal powder or a slip comprising electrophoretically depositable metallic particles (and optionally ceramic particles) for the electrophoretic deposition of metallic (and optionally ceramic) particles onto the surface of a negative model, for example of the model of a dental situation to be restored. It is here again particularly preferred to use a metal powder in the absence of a ceramic powder or of a slip which contains no ceramic particles; c.f. in this connection the explanations relating to preferred methods according to the invention.
The statements made above in each case apply correspondingly with regard to preferred embodiments.
Further aspects and preferred developments of the invention emerge from the attached claims.
The invention is illustrated in greater detail below with reference to exemplary embodiments.

EXAMPLE 1

Production of a Sintered Metal Dental Layer
A duplicate stump is produced from a thermally stable impression material (phosphate-bound embedding material) and serves as a model of a dental situation be restored. A thin layer of conductive silver lacquer is applied onto the duplicate stump, so rendering the surface of the model electrically conductive. The surface of the duplicate stump which has been rendered conductive is electrically contacted and the duplicate stump is suspended in a slip of electrophoretically depositable metallic particles. The slip comprises 210 g of a dental alloy powder containing no noble metals, 20 g of ethanol as dispersant and 4.2 g of urea (stabilizer). The powder has a maximum particle size of 10 μm, a monomodal distribution and an average particle diameter of d50=5 μm. The dental alloy is a cobalt-chromium alloy containing molybdenum, tungsten, silicon and iron as further constituents. The quantity of urea used amounts to 2 wt. % relative to the mass of the dental alloy powder. A counter-electrode is also located in the slip. The smallest electrode gap of the electrodes is 15 mm. A 0.5 mm thick layer of metallic particles is formed within 45 seconds on the surface of the duplicate stump provided with conductive silver lacquer by applying a voltage of 40 V between the electrically conductive surface of the duplicate stump and the counter-electrode. The duplicate stump is subjected to thermal treatment in a kiln together with the deposited layer of the metallic particles. The sintering temperature is set at 900° C. for this purpose. The kiln is flushed with argon during this thermal treatment. The solidus temperature of the dental alloy used is at 1270° C. (liquidus temperature: 1380° C.). The ratio of sintering, temperature to solidus temperature is accordingly 0.76. The porosity of the metallic layer reduces during the sintering operation. Since the duplicate stump is a model made from a thermally stable impression material which is not subject to sintering shrinkage, the external geometry (external dimensions) of the stump is retained. The metallic layer accordingly retains its internal geometry, the layer thickness merely being reduced. The duplicate stump may be removed for the sintered metallic layer by jet blasting or etching. The sintered metal layer may be used as a dental crown.

EXAMPLE 2

Production of a Gearwheel
Example 2 relates to the production of a gearwheel in the form of a spur gear. The working diameter (reference diameter) of this spur gear is 48 mm, the number of teeth is z=24, so giving a modulus of m=2 mm. The gearwheel has an internal bore of 10 mm.
The data model for a subsequent rapid prototyping process for production of the gearwheel was generated by computer. Account was taken of the fact that the metallic green body produced on the basis of the data model shrinks on sintering. The data model was thus geometrically enlarged in accordance with this decrease in volume. A data negative of the gearwheel, enlarged by the sintering shrinkage and aligned such that its axis was perpendicular to the horizontal, was produced on a computer from the CAD data (data model) of the metallic green body of the gearwheel. This data negative was additionally divided into horizontal layers of equal thickness. The true negative was then produced by means of the stereolithographic rapid prototyping process. A light-curing resin, which was rendered electrically conductive by the addition of carbon black, was used for production. A first layer of the mixture of light-curing resin and carbon black was applied onto an electrically non-conductive substrate and completely cured. Further application then proceeded layer by layer with, subsequent, selective exposure to light in accordance with the generated data record.
Once the final layer had been built up and selectively cured, the substrate together with the rapid prototyping model were removed from the stereolithography apparatus. The rapid prototyping model was then removed from the excess, still liquid resin. The rapid prototyping model was obtained in the form of an electrically conductive negative mould of the gearwheel, enlarged by the anticipated sintering shrinkage, on the non-conductive substrate. This negative mould was electrically contacted and dipped in a metallic slip. The composition of the slip corresponded to that from Example 1.
After application of a voltage, the slip was deposited electrophoretically as a layer of metal onto the electrically conductive surface of the rapid prototyping model. Once the rapid prototyping model (negative) was filled with the metal layer, the rapid prototyping model was removed from the slip bath. The rapid prototyping model, together with the substrate to which the rapid prototyping model is joined, was clamped in a milling machine. Excess deposited slip was then milled away from the upward facing surface of the rapid prototyping model. The through-hole of the subsequent gearwheel was also produced during this milling operation and good parallelism of the tooth flanks was ensured. In a subsequent thermal treatment (see above), the rapid prototyping model was removed and the metallic component in the form of the gearwheel was dense sintered.

EXAMPLE 3

Production of a Gearwheel
In Example 3, the negative mould (as a negative model) of a gearwheel was produced in the manner described in Example 2, but in the size of the required component. Once a metallic green body had been produced in the manner described in Example 2, its metallic structure was only partially sintered. In order to increase strength and surface quality the component is infiltrated with epoxy resin. Infiltration with the epoxy resin proceeds in cycles and, due to the relatively high viscosity of the resin, is performed under a vacuum. Nevertheless, the metal sintering material is completely infiltrated only in the peripheral zones. Residual porosity of approx. 15% remains in the interior of the component. A temperature of only 160° C. is required for subsequent curing of the resin, such that no change in geometry occurs and the elevated accuracy of the construction process is maintained.
Comments Regarding Examples 2 and 3:
Other components may be produced in the described or a similar manner, such as for example injection moulds, mould cavities, mirrors, gold frameworks for dental applications, printing plates for applying a grain in the production of artificial leather and miscellaneous ceramic parts. The method according to the invention may particularly advantageously be used for producing ultra-short runs of components with complex geometry.

Claims

1. A method for producing a metallic component, comprising the following steps:

providing a negative model for the component, which is electrically conductive or is rendered electrically conductive at least on the surface thereof,

providing a slip which comprises electrophoretically depositable metallic and optionally additionally ceramic particles,

electrophoretically depositing a layer of the particles from the slip onto the surface of the model, and

at least partially sintering the deposited layer of particles.

2. A method according to claim 1, wherein the fraction of metallic particles in the slip amounts to 50-100 wt. %, preferably 75-100 wt. %, relative to the total mass of metallic and ceramic particles.

3. A method according to claim 1, wherein the fraction of metallic particles in the slip amounts to 100 wt. %, relative to the total mass of metallic and ceramic particles.

4. A method according to claim 1, wherein the negative model is made of a modelling material which is electrically conductive.

5. A method according to claim 1, wherein the negative model comprises an electrically non-conductive modelling material having arranged on the surface thereof a coating of a conductive substance.

6. A method according to claim 1, wherein the pore size of the porous model is adapted to the particle size of the metallic and optionally ceramic particles in such a manner that, during electrophoresis, the particles cannot reach as far as the electrode inside the model.

7. A method according to claim 1, wherein the slip of electrophoretically depositable particles comprises a dispersed powder with a monomodal, bimodal or higher modal particle size distribution, a dispersant and optionally a stabiliser.

8. A method according to claim 7, wherein the following applies regarding the particle size distribution of the powder: 0.1 μm<d₅₀<20 μm.

9. A method according to claim 7, wherein the stabiliser is selected from the group consisting of: electrostatically stabilising stabilisers, electrosterically stabilising stabilisers and mixtures thereof.

10. A method according to claim 7, wherein the stabiliser is selected from the group consisting of: organic and inorganic bases and acids, the salts thereof and the cations or anions thereof, complexing agents, polymers and mixtures thereof.

11. A method according to claim 1, wherein the slip of electrophoretically depositable particles comprises a powder with a bimodal particle size distribution, wherein the particle sizes at the locations of the two relative frequency maxima of the particle size distribution are preferably in a particle size ratio of greater than 5:1 to one another.

12. A method according to claim 1, wherein the metallic particles consist of gold, platinum, palladium, silver or alloys which contain noble metals.

13. A method according to claim 12, wherein sintering of the deposited layer of particles or partial sintering of the deposited layer of particles is carried out in an oxygen-depleted atmosphere.

14. A method according to claim 1, wherein sintering of the deposited layer of particles or partial sintering of the deposited layer of particles is carried out in an oxygen-depleted atmosphere.

15. The method according to claim 1, wherein the solids content of the slip is in a range from 20 to 75 vol. % relative to the total volume of the slip.

16. A method according to claim 1, wherein the solids content of the slip is in a range from 30 to 60 vol. %, relative to the total volume of the slip.

17. A method according to claim 1, wherein the slip of electrophoretically depositable particles comprises a powder with a bimodal or higher modal particle size distribution, whose fraction with the largest particle size comprises spherical particles or consists of spherical particles.

18. A method according to claim 1, wherein at least partially sintering the deposited layer of particles is carried out at a temperature which is in the range of 0.45 to 0.9 times the melting temperature or solidus temperature (in K) of the lowest melting or the sole metallic phase of the layer.

19. A method according to claim 1, wherein the at least partially sintering of the deposited layer of metallic particles

(i) in order to increase strength and reduce the porosity of the layer by at least 5%, relative to the porosity before at least partial sintering, is carried out at a temperature which is in the range of 0.6 to 0.9 times the melting temperature or solidus temperature of the lowest melting or the sole metallic phase of the layer or

(ii) in order to strength, while reducing the porosity of the layer by less than 5% relative to the porosity before at least partial sintering, is carried out at a temperature which is in the range of 0.45 to 0.6 times the melting temperature or solidus temperature of the lowest melting or the sole metallic phase of the layer.

20. A method according to claim 1, wherein any porosity remaining after the at least partial sintering is infiltrated with glass, resin, plastics material or metal.

21. A method according to claim 1, wherein a binder is added to the slip, which binder is deposited together with the particles, and/or a binder is applied onto the deposited layer of metallic particles before the thermal or mechanical treatment.

22. A method for producing a metal-based dental restoration, comprising the following steps:

provision of a negative model of the dental situation to be restored, which (i) is electrically conductive or is rendered electrically conductive at least on the surface thereof or (ii) is porous and comprises an electrode inside,

provision of a slip which comprises electrophoretically depositable metallic and optionally additionally ceramic particles,

electrophoretic deposition of a layer of the particles from the slip onto the surface of the model,

sintering or partial sintering of the deposited layer of particles.

23. A method according to claim 22, wherein the model has the dimensions of the dental situation to be restored, sintering of the deposited layer of the particles proceeds on the model and the modelling material is selected such that, under the sintering conditions, the model undergoes a relative change in length of no more than 0.2%.

24. A method according to claim 23, wherein the model is removed mechanically or chemically from the sintered layer of particles.

25. A method according to claim 22, wherein the model has the dimensions of the dental situation to be restored, the deposited layer of the particles in question is partially sintered and optionally previously subjected to heat treatment, wherein during partial sintering or the preceding heat treatment, the modelling material shrivels or is burnt out from the metallic layer.

26. A method according to claim 22 , wherein the model has larger dimensions than the dental situation to be restored, sintering of the deposited layer of particles proceeds on the model and the modelling material is selected such that, under the sintering conditions, the volume of the model reduces at least to the dimensions of the dental situation to be restored.

27. A component, in particular a dental restoration, comprising metal produced using a method according to claim 22.

28. A kit for carrying out a method according to claim 22 comprising:

metal powder, dispersant and optionally stabilizer and/or binder and/or ceramic powder for producing a slip of electrophoretically depositable particles;

an electrophoresis apparatus for the electrophoretic deposition of the particles.

29. A method for producing a metallic component, comprising the following steps:

providing a negative model for the component, which is porous and comprises an electrode inside,

electrophoretically depositing layer of the particles from the slip onto the surface of the model,

at least partial sintering of the deposited layer of particles.