Patent Application
20230271352
The invention relates to a method for producing a cold casting mold for producing molded parts, in particular dental molded parts, from a mixing compound, wherein the cold casting mold, having a cavity that corresponds geometrically to the molded part, in particular dental molded part, is additively constructed from a starting material by means of an additive material construction method, in particular a 3D printing method using a 3D printer, on the basis of a digital data set based on a three-dimensional model of the oral cavity of a patient and at least one first opening that opens into the cavity for filling with the mixing compound. The invention also relates to the use or the production of such an additively constructed cold casting mold for a method for producing molded parts, in particular dental molded parts, from a sinterable or a light-curing mixing compound.
The production of molded parts by means of computer-assisted methods (CAD/CAM) is known from a large number of technical fields. Dental molded parts, in particular dentures, such as crowns and bridges, but also dental implants and prostheses or parts relevant to orthodontics, such as brackets, are manufactured in many dental practices and dental laboratories by computer-assisted methods (CAD/CAM). First, a digital, three-dimensional model of the oral cavity of a patient is created. The required dentures are planned with the aid of software and the created data set is transferred to a milling machine, for example, which mills the finished dentures out of a blank. The blanks are usually produced according to a cold casting process, in which a mixing compound is first produced from a ceramic powder or metal powder suitable for dental technology. A pasty mass, a slurry, a suspension, or even a “dry” bulk powder can be used as the mixing compound. A method for producing dentures from dental metal powder is known from EP 2 470 113 B1. In this case, a CrCo dental metal powder is mixed into a slurry, poured cold into a mold, and dried therein. A binder added to the slurry provides sufficient dimensional stability after the drying, so that the dried slurry can be removed from the cold casting mold as a green body and milled into the desired three-dimensional shape using the transferred digital data set. Final (dense) sintering gives the dentures the required hardness and density. Material properties required for approval as dental molded parts are permanently defined on the basis of national and/or international standards. Such cold casting methods are only suitable for the production of blanks. The fine, complex shapes of the actual dentures are then milled out of the blank by machining. Teachings on metal or ceramic slurries for dental technology are prior art and can be found, for example, in the documents EP1658018 B1, EP1047355 B1, WO 2013007684 A, EP1558170 B1, and EP1885278 B1. Information on their conditioning can be found in the documents DE 10 2005 023 727 B4 and DE19801534 A1. Carrying out the final dense sintering is also adequately described in the prior art; corresponding methods and sintering furnaces can be found in EP 2765950 B1, EP 2844412 A1, WO2011020688 A1.
When using bulk powders as a mixing compound, an additional work step, carrying out isostatic pressing, is usually required to achieve sufficient dimensional stability. High pressure is applied evenly to all sides of the mixing compound for this purpose. Corresponding methods for the production of ceramic dentures from ceramic powders, for example zirconium oxide are also well known from the prior art. A method in which tooth parts are produced from ceramic powder is described in WO 2008/114 142 A1.
The digital, three-dimensional model of the oral cavity is also used for the production of temporary restorations made of plastic. Here, the data set created for the denture is passed on a 3D printer, which constructs the temporary restoration in layers by means of an additive material construction method (3D printing) from plastic starting material.
In the meantime, in addition to plastics, inorganic substances can also be used as starting materials in the field of additive material construction methods. Additive material construction methods such as SLM (selective laser melting), extrusion methods such as FDM (fused deposition molding) and FFF (fused filament fabrication) are known. Additive material construction methods that use the light-curing properties of the starting materials are also known, e.g.: SLA or STL (stereolithography), DLP (digital light processing), LCM (lithography-based ceramic manufacturing).
There have therefore already been initial attempts to produce dentures from metal or ceramic by means of additive material construction methods. A method in which a tooth crown is produced from zirconia by means of an additive material construction method is known from WO 2018/065856 A1. However, 3D printers for metal or ceramic objects are very expensive and/or the printed molded part does not meet the high material requirements to be approved for dental use. In particular, additive material construction methods require a very high proportion of binder in the starting material (approximately 30%), which is why the required final density or final hardness cannot be achieved or is extremely difficult to achieve. An economical implementation of the printing of dental molded parts made of ceramic or metal is not in sight.
WO 2019/210285 A2 discloses another possibility in which the digital, three-dimensional data of the oral cavity is to be used to produce densely sintered dental prostheses with a complex shape using a 3D printer. For this purpose, not the dentures, but a self-destructing mold is to be printed using a 3D printer. A powder mixture made of of two components, a sinterable alumina powder and a powdered binder having a high coefficient of thermal expansion (CTE), is used as the starting material for the printing process. The printed casting mold is filled with a sinterable, dry zirconia bulk powder as a mixing compound. The casting mold is then closed using a cover printed from the same material in order to isostatically press the casting mold together with the zirconia bulk powder located therein at a pressure of 400 MPa. In this method, it is crucial that the bulk powder is free of binders in order to enable uniform pressing. The bulk powder is compacted together with the casting mold and then sintered without removing the mold. During sintering, the binders contained in the mold expand, causing the mold to burst open. The sintering temperature of the mold has to be higher than the sintering temperature of the bulk powder so that the finished sintered molded part is released from the mold. A disadvantage of the disclosed method is, on the one hand, the high costs associated with the 3D printing of the ceramic starting material and the isostatic pressing at extremely high pressures of 400 MPa. However, the use of a ceramic starting material having a sintering temperature higher than that of the bulk powder is crucial for the method described. On the other hand, the possible uses of the method are also limited. The mixing compound used has to be free of binders in order to achieve uniform pressing. In addition, compacting pressing methods, especially isostatic pressing, in which the pressure is to act evenly on the molded part from all sides, are not suitable for mixing compounds having a moisture content of greater than 7%. Liquids are nearly incompressible. To carry out the isostatic pressing, it is necessary to completely enclose the bulk powder within the casting mold closed using the lid. For this reason, any moisture contained in the mixing compound cannot escape.
The object of the present invention is therefore to provide an additively constructed, in particular 3D-printed, cold casting mold which, in comparison to the prior art, is more cost-effective and enables mass production of dental molded parts having complicated anatomical shapes, colorations, and light-refracting surface structures, such as crowns, bridges, jaw implants, abutments, prostheses, etc. At the same time, the possible uses are to be expanded. In particular, the use of a wide variety of mixing compounds made of sinterable and non-sinterable metallic and/or ceramic materials or plastic, either in dry powder form or as a slurry, suspension, or pasty mass, is made possible.
The object is achieved by a method for producing a cold casting mold according to claim 1. A method for producing a cold casting mold of the type described in detail at the outset is characterized in that the cold casting mold is additively constructed having at least one second opening, which opens into the cavity and/or leads out of the cavity, for discharging gases, in particular air inclusions, and/or liquids, in particular diluents.
According to the invention, in addition to the first opening provided for filling the cavity with the mixing compound, at least one second opening is formed which, like the first opening, opens into the cavity or leads out of it in a fluid-conducting manner. In principle, it is conceivable to form the first opening and/or the second opening, in particular to drill it, after the additive construction of the cold casting mold has been completed. However, it is advantageous to form the first opening and/or the second opening directly during the additive material construction, so that an additional work step is avoided. Comparable with, for example, (vacuum) bottling systems, it is also conceivable to form the second opening (for venting) during the additive material construction and to form the first opening (for filling) by introducing a filling channel, in particular concentrically, into the second opening. The second opening makes it possible to discharge fluids, i.e., gases and/or liquids, even while the cold casting mold is being filled (comparable to a venting opening when pouring in using a TetraPak®). After filling, to cure and/or solidify the mixing compound, the at least one first opening and/or the at least one second opening remain unclosed, which allows fluids to escape. On the one hand, air inclusions caused by filling the cold casting mold with the mixing compound can thus be discharged, for example. On the other hand, liquids such as diluents contained in pasty, moist, or slurry-like mixing compounds or suspensions can also be discharged from the cavity of the cold casting mold, which enables the mixing compound to dry within the cold casting mold. Due to the formation of the at least one second opening, the cold casting mold constructed additively according to the method according to the invention can not only be used for mixing compound having any moisture content, the at least one second opening also allows venting when using a bulk powder, which can be supported, for example, by shaking.
According to one preferred embodiment of the invention, at least one wall of the cold casting mold that delimits the cavity is therefore completely or in regions additively constructed having a plurality of second openings that open into the cavity and penetrate this wall, for discharging gases, in particular air inclusions, and/or liquids, in particular diluents.
In that one or more walls of the cold casting mold are penetrated with a plurality of second openings adjacent to one another, a sieve-like surface may be formed which, on the one hand, enables the passage of liquids and gases, but on the other hand holds back solids. The diameter of the respective second openings is preferably smaller than the particle size and/or the size of particle agglomerates that form in the powder contained in the mixing compound, such as metal powder, ceramic-glass ceramic powder, or plastic powder.
In a refinement of this embodiment, the plurality of second openings are therefore also formed as pores and/or capillaries which penetrate the wall, so that the wall has porous and/or hygroscopic properties, either completely or in regions.
Such an embodiment also has the advantage that moisture contained in the mixing compound is taken up or absorbed by the adjoining porous and/or hygroscopic wall and is preferably transported away from the interior, in the direction of the atmosphere surrounding the cold casting mold or away. This effect can be aided by increasing the ambient temperature surrounding the cold casting mold or other measures to reduce the ambient humidity, by which drier ambient air is created.
It is also advantageous to produce the cold casting mold from different starting materials having physical properties differing from one another. For example, the ability of the porous and/or hygroscopic areas to absorb moisture can be increased by way of a suitable starting material. Other regions or structures of the cold casting mold, such as filling channels, compensating volumes, or support structures can be formed by selecting a different starting material having different properties, e.g., water solubility, color, transparency, etc.
In order to facilitate the filling of the cold casting mold, for example by means of a syringe or a cannula or a similar tool, the cold casting mold can be additively constructed having a filling channel adjoining the at least one first opening in a fluid-conducting manner.
The filling channel is preferably integrally formed with the cold casting mold. The filling channel enables in particular a pressurized filling of the cold casting mold, for example by injection molding.
In a refinement, the filling channel is connected in a fluid-conducting manner to at least one compensating volume for storing mixing compound.
The compensating volume is preferably also additively constructed integrally with the cold casting mold. In particular when using mixing compound having a higher moisture content and/or in the case of air inclusions, the compensating volume acts as a kind of reservoir and allows the mixing compound to run or trickle down to compensate for the volume loss caused by the escape of gases and/or liquids via the at least one second opening from the cavity.
According to an alternative variant of the invention, the cavity of the cold casting mold can be filled more quickly and/or more evenly by additively constructing the cold casting mold having two or more first openings, each opening into the cavity, for simultaneous or staggered filling with mixing compound.
Because two or more first openings provided for filling open into the cavity at different positions, filling with different mixing compounds can also take place at different positions of the cavity, for example. If the additional first openings are not used for filling, they can function as second openings for discharging fluids.
An organic material, in particular an organic wax and/or a polymer and/or a plastic, is particularly advantageously used as the starting material for additively constructing the cold casting mold, so that the cold casting mold can be plasticized and/or thermally and/or thermochemically decomposed.
Organic materials such as waxes and/or polymers and/or plastics are significantly easier and therefore more cost-effective to use in additive material construction methods, for example 3-D printing. The heat resistance of plastics is comparatively low, so that the additively constructed cold casting mold made of an organic material can be plasticized or even decomposed thermally and/or thermochemically, in particular by pyrolysis and/or combustion. For structures and/or walls of the cold casting mold that do not delimit or directly adjoin the cavity, in particular for support structures, filling channels, compensating volumes, etc., a starting material having a lower melting point, for example wax, can advantageously be used than for the walls of the cold casting mold that delimit the cavity, which are then additively constructed, for example, from polymers or plastics. In this way, during the plasticizing or decomposition of the cold casting mold, in particular stresses occurring as a result of heat, which could result in damage to the molded part, can be reduced or even completely avoided. The organic starting material can contain small additions of inorganic materials. For example, it is common to admix inorganic additives to plastics. However, the proportion of organic components is always higher than the proportion of inorganic components.
The organic material used for additively constructing the cold casting mold preferably has a melting point and/or a decomposition temperature in a temperature range from 40° C. to 300° C., preferably 60° C. to 300° C.
The melting temperature or the melting temperature range of the cold casting mold is therefore below the melting and/or sintering temperature of the mixing compounds typically used. The decomposition temperature, i.e., the temperature at which thermal and/or thermochemical decomposition of the cold casting mold begins, is also advantageously below the melting and/or sintering temperature of the mixing compound used.
In a refinement, the organic material used for additively constructing the cold casting mold can be plasticized by the action of heat, in particular at a temperature in a temperature range from 35° C. to 300° C., preferably 50° C. to 300° C., and/or can be decomposed thermally by pyrolysis and/or thermochemically by combustion by the action of heat, in particular at a temperature in a temperature range from 200° C. to 650° C. A material group having a particularly low heat resistance is represented, for example, by waxes. By using a waxy, organic material, a softening or plasticizing of the cold casting mold can already be achieved from a temperature of approximately 35° C.
The thermal and/or thermochemical decomposition can preferably be continued completely and/or at high temperatures in a sintering temperature range from 1300° C. to 2500° C., so that a residue-free or at least almost residue-free dissolution of the cold casting mold is made possible by the action of heat.
Alternatively, according to one advantageous embodiment, however, mechanical destruction of the cold casting mold can already be provided during the additive material construction method by additively constructing at least one wall delimiting the cavity of the cold casting mold having a predetermined breaking point, in particular having a reduced wall thickness in regions.
The proposed production method is based on three-dimensional, digital data, in particular of the oral cavity of a patient. The geometric shape data derived from this for molded parts, in particular for dental molded parts, are used directly in the additive material construction method in the geometric design of the cavity of the cold casting mold. In order, for example in dental technology, to guarantee a precise fit of dental molded parts, in particular crowns, bridges, dental implant parts, and/or prostheses in the oral cavity of the patient, the digital data set for the geometric design of the cavity of the cold casting mold therefore preferably includes a sintering and/or hardening-related volume shrinkage of the mixing compound. Depending on the mixing compound used, a corresponding volume shrinkage during curing or solidification and/or sintering of the mixing compound is to be taken into consideration, the cavity of the cold casting mold is to be designed having a correspondingly adapted (larger) initial geometry. For example, for mixing compounds containing ceramic powder, sintering shrinkage in a range from 25% to 50%, for mixing compounds containing sol and nano zirconium oxide particles in a range from 50% to 95% and for mixing compounds containing metal powder, sintering shrinkage in a range from 8% to 25% is to be taken into consideration, each in relation to the initial geometry. For the curing of the mixing compound by light and/or drying, a volume shrinkage of approximately 2% to 20% in relation to the initial geometry is to be taken into consideration. A volume shrinkage in a range from 1% to 10%, in relation to the initial geometry, can also be taken into consideration for the cold casting mold itself for the production of the molded part. The cold casting mold produced according to the method according to the invention enables molded parts, in particular dental molded parts, to be produced inexpensively from a wide variety of mixing compounds.
The cold casting mold according to the invention has at least one first opening opening into the cavity for filling with the mixing compound and is characterized by at least one second opening opening into the cavity for discharging gases, in particular air inclusions, and/or liquids, in particular diluents.
In one embodiment, the cold casting mold has an organic material, in particular an organic polymer or a plastic having a melting point and/or a decomposition temperature in a temperature range from 40° C. to 300° C., in particular from 60° C. to 300° C., so that the cold casting mold can be plasticized, in particular at a temperature in a temperature range from 35° C. to 300° C., in particular from 50° C. to 300° C. and/or can be thermally and/or thermochemically decomposed, in particular at a temperature in a temperature range from 200° C. to 650° C.
Filigree, thin-walled structures are often required in dental molded parts such as crowns, bridges, dental implant parts, and/or prostheses. High sintering temperatures are required especially for the production of dental molded parts made of ceramic or metal. In order to avoid damage to the molded part due to the thermal expansion of the cold casting mold, the linear, thermal expansion of the cold casting mold is advantageously at most 10%, preferably at most 3%, and particularly preferably at most 0.8% in relation to its initial geometry, wherein the maximum thermal expansion of the cold casting mold is reached at a temperature of less than or equal to 240° C., preferably less than or equal to 200° C., more preferably less than or equal to 150° C., and particularly preferably less than or equal to 100° C. Preferably, the coefficient of thermal expansion (CTE value) of the mixing compound can be adjusted, taking into consideration the respective CTE values of the metal, ceramic, or glass-ceramic powder used, by way of the proportions of polyelectrolytes and binders (polymers) and the CTE value of the cold casting mold, so that cold casting mold and mixing compound are subject to a similar or identical thermal expansion. Additionally or alternatively, the mechanical stability of the mixing compound (in the green body state) can be increased by increasing the proportion of binder.
In order to achieve the dimensional accuracy of the cold casting mold required for dental molded parts, even with pressure filling methods, the cold casting mold has a Shore hardness of at least 15 according to Shore A and/or of at least 10 Shore D and a modulus of elasticity of at least 5 MPa. The walls delimiting the cavity of the cold casting mold preferably each have a wall thickness of at least 0.01 mm. The Shore hardness is a material parameter for elastomers and plastics and is defined in the standards DIN EN ISO 868, DIN ISO 7619-1, and ASTM D2240-00. The modulus of elasticity, also referred to as tensile modulus or elasticity modulus, is defined for plastics in particular according to DIN EN ISO 527-1:2019-12.
An exemplary prototype of a cold casting mold according to the invention, suitable for the production of dental molded parts, was produced according to a stereolithography 3D printing method having the following PHYSICAL PROPERTIES:
By using a starting material for the additive construction of the cold casting mold, which makes one or more walls delimiting the cavity of the cold casting mold transparent and/or transmissive to UV radiation, optical monitoring of the filling of the cold casting mold is possible. For example, the mixing compound or different mixing compounds can be marked using optical markers, in particular using food coloring. The filling of the cold casting mold can then be monitored automatically using a camera.
In addition, the possible uses of the cold casting mold can also be extended to light-curing mixing compounds, which are light-cured in a correspondingly adapted method for the production of molded parts, in particular dental molded parts, in the interior of the cold casting mold.
The object of the invention stated at the outset is therefore also achieved by a method for producing molded parts, in particular dental molded parts, from a sinterable mixing compound according to claim 20 using a cold casting mold according to the invention according to one of the preceding embodiments, and by a method for producing molded parts, in particular dental molded parts from a light-curing mixing compound according to claim 30 using a cold casting mold according to the invention according to one of the preceding embodiments.
A method according to the invention for producing molded parts, in particular dental molded parts, in particular crowns, bridges, dental implant parts, prostheses, etc. from a sinterable mixing compound, such as dental ceramic or glass ceramic powders or slurries, dental metal powders or slurries, etc., using the cold casting mold according to the invention has the following method steps:
Gases and/or liquids contained and/or enclosed in the mixing compound are discharged from the cavity via the at least one second opening both during the filling and during the curing and/or solidifying of the mixing compound. Optionally and after the filling, gases and/or liquids contained and/or enclosed in the mixing compound can also escape via the at least one first opening, which remains unclosed throughout the course of the method.
Already during the curing and/or solidifying of the mixing compound, or optionally also only after the mixing compound is completely cured, in particular to green body hardness, a
According to the invention, the claimed production method is carried out using a cold casting mold having at least two openings connected to the cavity in a fluid-conducting manner, wherein the cavity of the cold casting mold is filled via one opening, the first opening, and fluids contained in the mixing compound, for example diluents or fluids enclosed by the mixing compound, for example air inclusions, are discharged from this mixing compound or from the cavity via another opening, the second opening. In the method according to the invention, the at least two openings enable curing and/or hardening even of binder-containing and/or moist or pasty mixing compounds, such as slurries or suspensions.
According to a refinement of the method, the mixing compound is therefore preferably provided as a slurry and/or pasty mass and contains a diluent, in particular water, wherein the mixing compound cures in the cavity of the cold casting mold by drying and a liquid component and/or moisture content of the mixing compound is discharged by means of the at least one or the plurality of second openings from the cold casting mold, in particular is withdrawn from the mixing compound.
In an advantageous method design, the mixing compound comprises a metal powder, in particular a CrCo powder or a ceramic powder, in particular a zirconium oxide powder and/or an aluminum oxide powder or a glass ceramic powder, in particular a lithium disilicate powder and a binder, wherein the mixing compound in a refinement of this method design cures to green body hardness in the cavity of the cold casting mold.
Binder-containing mixing compounds can be cured in the cold casting mold to green body hardness solely by drying, without applying pressure. The use of a binder means that the cost-intensive isostatic pressing known from the prior art can be dispensed with. In contrast to the method also described in the prior art, however, it is then necessary to carry out the curing of the mixing compound with the cold casting mold open (without a “lid”), wherein fluids are discharged via the at least one second opening and, if necessary, additionally also via the at least one first opening from the cavity of the cold casting mold.
Binders are known in many forms from the prior art and consist mainly of organic materials such as resins, surfactants, polyelectrolytes, polymers, and/or waxes, which result in a comparatively low melting point.
In order to achieve a gentle detachment of the cold casting mold from the mixing compound before debinding takes place or before the binder begins to melt, according to a variant of the method, the temperature resistance and/or heat resistance of the cold casting mold, in particular the melting point and/or the decomposition temperature of the cold casting mold, is below the melting point of the binder and/or below the sintering temperature of the metal powder or the ceramic powder.
The use of a thermally and/or thermochemically decomposable cold casting mold is provided for the method according to the invention. The thermal and/or thermochemical decomposition of the cold casting mold is preferably carried out in a sintering furnace, wherein the cold casting mold is opened and placed in the sintering furnace together with the mixing compound located therein. The decomposition of the cold casting mold can already be initiated or carried out completely at a temperature in a range from 200° C. to 650° C. The respective sintering temperatures of the ceramic powders or metal powders contained in the sinterable mixing compounds are in a range between 1200° C. and 2500° C., so that the cold casting mold is completely or almost completely thermally and/or thermochemically decomposed when the finished, i.e., densely sintered molded part, in particular dental molded part is obtained. In this way, the cold casting mold can be removed gently and without damaging the molded part without any additional work steps before or during the sintering process.
An optional method step provides for the mixing compound to be pre-sintered before the actual sintering, in particular at a temperature in a temperature range from 650° C. to 1300° C., in order to remove the binder components before the molded part is compacted to final hardness.
According to a method variant, the decomposition of the cold casting mold can be carried out pyrolytically under oxygen-free conditions. In particular, the cold casting mold is placed for this purpose in a sintering furnace together with the mixing compound contained therein, which enables sintering under vacuum and/or a protective atmosphere. This method variant is particularly suitable for the production of metallic, dental molded parts, for example made of a CrCo alloy, in order to avoid damage to the molded part due to oxidation.
According to another method variant, in particular in order to obtain ceramic, dental molded parts, decomposition of the cold casting mold with supply of oxygen by combustion is also possible.
A method according to the invention for producing molded parts, in particular dental molded parts, from a light-curing mixing compound using a cold casting mold according to the invention comprises the following steps:
wherein gases and/or liquids contained and/or enclosed in the mixing compound are discharged from the cavity via the at least one second opening. It is also provided according to the invention for producing molded parts, in particular dental molded parts from light-curing mixing compounds, that fluids contained therein can escape via the at least one second opening during the filling and/or curing or solidifying. Especially when using multi-component materials that have to be mixed together during filling, undesired air inclusions often occur. Such air inclusions can escape via the at least one second opening of the cold casting mold while it is still being filled with the mixing compound.
Optionally, thermal and/or thermochemical decomposition of the cold casting mold can be dispensed with. According to the invention, the cold casting mold is separated or detached from the mixing compound along one or more predetermined breaking points of the cold casting mold in order to obtain a ready-to-use molded part in particular, in particular a dental molded part, such as a denture. The predetermined breaking points have preferably already been formed during the production of the cold casting mold, in particular, they can be wall regions having a wall thickness that is less than that of the other wall regions. In particular, by blowing in compressed air or by using an eccentric tool, the cold casting mold can be “torn open” along the predetermined breaking points after the mixing compound has cured and/or solidified and can thus be detached from the molded part.
According to an advantageous design of the method, the mixing compound comprises an organic material, in particular a plastic or a plastic-based composite material, in particular a plastic-based hybrid composite material or nanohybrid composite material. Such composites have hitherto mostly been used in dental technology for fillings or temporary restorations. Especially with nanohybrid composite materials, having a high filler content of fibers or particles, having a particle size in the nanometer range, however, the material properties required for dental molded parts, such as dentures, with respect to hardness and tightness can also be achieved in principle.
In an advantageous variant of the method, the mixing compound cures in the cavity of the cold casting mold by way of a chemical reaction, for example by means of a two-component binder. The chemical reaction can be started by the action of heat and/or the removal of moisture. The chemical reaction is particularly preferably triggered by the action of light, wherein the walls delimiting the cavity of the cold casting mold are transparent and/or transmissive to UV radiation and the cold casting mold is irradiated using a light source, in particular a UV lamp.
The mixing compound in the cavity of the cold casting mold is preferably cured to the desired final hardness, i.e., the hardness of the finished molded part, before the cold casting mold is detached or removed.
The following description paragraphs contain advantageous method variants which can be used both for the production according to the invention of molded parts from sinterable mixing compounds and also the production according to the invention of molded parts from chemically-curing, in particular light-curing mixing compounds.
For example, the cold casting mold, in particular the walls of the cold casting mold delimiting the cavity, can be coated using a coating agent before the filling with the mixing compound in order to avoid a frictional and/or materially-bonded connection between the cold casting mold and the mixing compound.
It is conceivable to immerse the cold casting mold in a basin having an organic, oily liquid such as petroleum, or alternatively to rinse it using an organic, oily liquid such as petroleum, shortly before or immediately before it is filled with the mixing compound. In this way, a heat-resistant protective layer can be formed in a simple and uncomplicated manner between the walls of the cold casting mold delimiting the cavity and the mixing compound, without closing the first and/or the second opening.
The cavity of the cold casting mold is preferably filled under the action of pressure, wherein an internal pressure present in the cavity is lower than a filling pressure at which the mixing compound is supplied to the cavity.
In practical implementation, two fundamental variants are conceivable for this purpose. With a so-called vacuum filling (implemented in a similar way, for example, in filling systems for bottles), a negative pressure in relation to the environment or a vacuum (0.1 mbar to 0.5 mbar) can be generated within the cavity, due to which the mixing compound is “sucked” into the cavity. After filling, the vacuum or negative pressure is released, so that liquids and/or gases can escape from the at least one second opening and/or the at least one first opening. In this first variant, the filling pressure then corresponds to the ambient pressure. In the second variant, the mixing compound can be injected into the cavity, for example by means of a pump, a screw conveyor, or a simple syringe under pressure, with overpressure in a range, for example, between 1.5 mbar and 10 bar, wherein liquids and gases can already escape from the at least one second opening during the filling. A well-known pressure filling method is, for example, the injection molding method.
After filling, it is advantageous if the mixing compound cures in the cavity of the cold casting mold under the action of heat, wherein the cold casting mold filled with the mixing compound and opened is placed in a drying cabinet or climatic cabinet or a sintering furnace and a temperature is set in a temperature range from 35° C. to 120° C., preferably from 50° C. to 120° C. If necessary, the ambient humidity can also be set to a desired value. ambient humidity in a range from 1% to at most 50% has proven to be advantageous for gentle, uniform, and at the same time rapid drying.
The action of heat and, if necessary, reduced ambient humidity can accelerate the curing and/or solidifying of the mixing compound, for example in the case of a drying process. In particular, the atmosphere or ambient air present in the environment, thus in the drying cabinet or climatic cabinet or in the sintering furnace, is dried, due to which moisture and/or liquid contained in the mixing compound are transported away more quickly from the cavity into the environment. This effect can have considerable influence on the drying times, especially when the walls of the cold casting mold are designed having a porous and/or hygroscopic surface which is penetrated by a large number of second openings in the form of pores and/or capillaries.
According to one method option, the cold casting mold is plasticized after it has been filled with the mixing compound and preferably also after the mixing compound has cured, in order to facilitate detachment of the walls delimiting the cavity from the mixing compound located therein, wherein the cold casting mold filled with the mixing compound is placed in a drying cabinet or climatic cabinet or a sintering furnace and a temperature is set in a temperature range of 35° C. to 300° C., preferably 45° C. to 180° C. The material properties of organic materials or plastics can be utilized here. Before the melting point of the cold casting mold is reached, the organic material, in particular the plastic, begins to soften, as a result of which the cold casting mold can be plasticized or plastically deformed. By blowing in compressed air in a targeted manner, the soft, malleable cold cast mold can be detached from the preferably cured mixing compound.
A particularly fast and uniform filling can take place, for example, according to an embodiment variant of the method, in that the cavity of the cold casting mold is filled with the mixing compound via multiple first openings.
For example, mixing compounds consisting of two or more components can be filled into the cavity of the cold casting mold correspondingly via two or more first openings, for example to prevent premature (light-induced) curing and/or solidifying during filling.
In a refinement of this embodiment variant, the cavity of the cold casting mold is filled via the multiple first openings with respective mixing compounds containing additives for coloring and/or for producing opacity to produce a molded part, in particular a dental molded part having regions of differing coloring and/or opacity.
In this way, the natural appearance of a tooth can be simulated. For this purpose, the different mixing compounds can in particular have various additives, which result in a coloration in the finished molded part according to the standard color ring from Vita, Bad Säckingen, A1 to A4, B1 to B4, C1 to C4 and D1 to D4. A large number of corresponding additives are known from the prior art. Examples of suitable coloring elements are Fe, Mn, Cr, Ni, Co, Pr, Ce, Eu, Gd, Nd, Yb, Tb, Er, and Bi.
Finally, according to an advantageous method variant, the cold casting mold is produced according to one of the method variants of the production method for a cold casting mold described above.
Further details, features, feature (sub-)combinations, advantages, and effects on the basis of the invention will be apparent from the following description of a preferred exemplary embodiment and from the drawings. In the figures
The figures are merely of an exemplary nature and are used only to understand the invention. The same elements are provided with the same reference numerals and are therefore usually only described once.
A filling channel 130 having a compensating volume 131 adjoins the first opening 111 in a fluid-conducting manner. Filling means 400, for example injection syringes 420, in particular low-pressure injection syringes (see
A sectional representation of a third exemplary embodiment of a cold casting mold 100 according to the invention having a total of five filling channels 130 can be seen in
A fifth exemplary embodiment of a cold casting mold 100 according to the invention can be seen in
The mixing compound 200 cured to the final hardness required for dental molded parts 210 can be seen in
After the curing, the cold casting mold 100 can optionally be plasticized (3.1). For this purpose, the cold casting mold 100 is placed in a sintering furnace together with the hardened mixing compound 200 located therein and a temperature in a range from 35° C. to 300° C., in particular from 50° C. to 300° C., is set inside the sintering furnace. The plastic of the cold casting mold 100 softens and can, for example, be “inflated” by blowing in compressed air 232 and detached from the mixing compound 200. In the case of a dental plastic molded part 210, the cold casting mold 100 is opened by the action of mechanical force along one or more predetermined breaking points 124 formed during production (4.B) and the finished dental molded part 210 is removed.
For the production of ceramic or metallic dental molded parts 210, the cold casting mold 100 is thermally or thermochemically decomposed (4.A) before or while the mixing compound 200 cures to final hardness. For this purpose, the cold casting mold 100 is placed in a sintering furnace together with the mixing compound 200 located therein and thermal decomposition or pyrolysis in the absence of oxygen or thermochemical decomposition or combustion with oxygen at a temperature in a temperature range from 200° C. to 650° C. is initiated, during which the starting material 150 is completely or almost completely dissolved. At a temperature in a temperature range from 650° C. to 1300° C., the mixing compound 200 can optionally be pre-sintered (5.1), wherein the binder 206 evaporates. During the ultimate final or dense sintering (5), the mixing compound 200 is compacted to final hardness at a temperature in a temperature range from 900° C. to 2500° C. and can be removed from the sintering furnace as a finished dental molded part 210. Any remnants of the cold casting mold 100 that are not yet completely decomposed are also decomposed during pre-sintering or final sintering.
Alternatively or additionally, a vacuum can also be generated in the cavity 110 of the cold casting mold 100, as a result of which vacuum conveying or also suction conveying of the mixing compound 200 is implemented. A vacuum is generated centrally or decentrally using a vacuum generator 441 in order to suction in mixing compound 200 via the at least one first opening 111 and to transport it into the cavity 110 of the cold casting mold 100. The mixing compound 200 is held back in the interior of the cavity 110 via the plurality of second openings 112 or the wall sections lying between them. The conveying air 442 used to convey the mixing compound 200 passes through the plurality of second openings 112 and is supplied from the environment via a particle filter 443. The control of the filling is simplified via a bypass channel 444 which is connected in a fluid-conducting manner to the filling channel 130.
Finally,
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2019 128 336.1 | Oct 2019 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/079500 | 10/20/2020 | WO |
