Method for Producing a Molded Product by Sintering

Abstract

The present invention relates to a method for producing a molded product from a blank, taking into account the sintering behavior thereof, and to a molded product produced by said method.

Claims

1. A process for preparing a shaped product, comprising the following steps: a) providing a blank, said blank having an inhomogeneous sintering behavior; b) processing the blank from step a) to obtain a shaped product; and c) sintering the shaped product from step b) to a desired final density; characterized in that the shrinkage of the blank is determined before the blank is processed, and the processing is performed in accordance with the spatially resolved scale-up factors obtained during the determination.

2. The process according to claim 1, characterized in that the blank has at least two components with different sintering behaviors, or one component with an inhomogeneous sintering behavior.

3. The process according to claim 1, characterized in that the blank comprises several components with different sintering behaviors, wherein the components are differently arranged between layers or gradually or in partial regions of the shape.

4. The process according to claim 1, characterized in that the blank comprises one or more materials selected from silicate raw materials or oxidic raw materials or non-oxidic raw materials.

5. The process according to claim 1, characterized in that the blank comprises at least one ceramic material, preferably selected from the group consisting of zirconium oxide (ZrO.sub.2), aluminum oxide (Al.sub.2O.sub.3), silicon carbide (SiC), silicon nitride (Si.sub.3N.sub.4), silicates, and mixtures thereof.

6. The process according to claim 1, characterized in that the shaped product is a dental restoration.

7. The process according to claim 1, characterized in that the blank provided in step a) is a presintered blank.

8. A kit, comprising: i) a blank; and ii) a set of spatially resolved scale-up factors, wherein said set of spatially resolved scale-up factors is obtained by determining the shrinkage of the blank.

9. A shaped product, characterized in that said shaped product has an inhomogeneous sintering behavior, and has a shape adapted to its sintering behavior.

10. The shaped product according to claim 9, characterized in that said shaped product is brought into a desired shape by sintering.

11. The shaped product according to claim 9, characterized in that the shape of the shaped product is predefined by spatially resolved scale-up factors.

12. The shaped product according to claim 9, characterized in that the shaped product comprises several components with different sintering behaviors, wherein the components are differently arranged between layers or gradually or in partial regions of the shape.

13. The shaped product according to claim 1, characterized in that the shaped product comprises one or more raw materials selected from silicate raw materials or oxidic raw materials or non-oxidic raw materials.

14. The shaped product according to claim 1, characterized in that the shaped product is a dental restoration.

15. The shaped product according to claim 14, characterized in that said dental restoration is selected from the group consisting of tooth restorations, bridge restorations, implants and implant abutments.

16. A shaped product obtainable by a process according to claim 1.

17. (canceled)

Description

EXAMPLES

1. Blank Consisting of One Component with an Inhomogeneous Shrinkage Behavior

Example 1 (Comparison)

[0055] In a first step, yttria-stabilized zirconia powder was pressed uniaxially from both sides to form a cuboid body. In this process, a density gradient forms within the body because of friction between the particles and the friction towards the pressing die wall in the pressing pressures necessary for such material, despite an optimized binder system and optimized flowability and slidability of the powder granules. The lowest density is found along the press-neutral zone. In this region, the lowest compaction of the powder granules occurs.

[0056] The pressed body was subjected to a thermal treatment at temperatures of up to 700 C. in order to remove organic additives. In a second thermal treatment, the body was presintered to from 50 to 60% of its maximum theoretical density at temperatures within a range of from 1000 C. to 1200 C.

[0057] A cuboid was milled from the presintered body. Its outer dimensions result from the sought intended geometry, i.e., the shrinkage occurring during the dense sintering was taken into account by enlarging the outer dimensions of the intended geometry using a uniform scale-up factor.

[0058] The milled-out cuboid was sintered to the desired final density at temperatures of from 1300 C. to 1600 C. The geometry of the sintered body was scanned and acquired using a profilometer. The dense-sintered body exhibits a deviation from the intended geometry. This is caused by the density gradient occurring in the body, which is maintained during the presintering of the blank, and leads to an inhomogeneous sintering behavior. Therefore, the sintered body shows a significant deviation from the intended geometry in the region of the press-neutral zone.

[0059] FIG. 1a shows the schematic representation of the milled-out body (bright) and of the dense-sintered body (dark), in which the deviation from the intended geometry is clearly seen.

[0060] FIG. 1b represents the profile measurement of the milled presintered body and of the dense-sintered body along the plane indicated in FIG. 1a. Here too, the significant deviation of the dense-sintered body from the sought cuboid intended geometry can be seen.

Example 2 (According to the Invention)

[0061] By analogy with Example 1, a presintered body was prepared from yttria-stabilized zirconia. From the presintered body, a cuboid blank was milled whose outer dimensions result from the intended geometry of the dense-sintered body. In contrast to Comparative Example 1, no uniform scale-up factor was used to consider the shrinkage occurring during the sintering. Rather, the inhomogeneous sintering behavior of the body was taken into account by scaling up the dimensions of the intended geometry in a spatially resolved manner in accordance with the density distribution. For this purpose, each coordinate point of the intended geometry was assigned its own scale-up factor, resolved in x, y, z coordinates, in order to obtain the geometry to be milled out.

[0062] By analogy with Example 1, the milled body was sintered to the desired final density, which is the same as that of the body described in Example 1, at temperatures within a range of from 1300 C. to 1600 C.

[0063] The dense-sintered body was scanned using a profilometer, in order to determine the outer dimensions.

[0064] FIG. 2a shows the schematic representation of the presintered milled body (bright) and of the dense-sintered body (dark), in which it is clearly seen that the dense-sintered body corresponds to the intended geometry.

[0065] FIG. 2b represents the profile measurement of the milled-out and of the dense-sintered body along the plane indicated in FIG. 2a. In contrast to Comparative Example 1, the dense-sintered body does not show any deviations from the intended geometry.

2. Blank Consisting of Four Layers with Different Compositions

Example 3 (Comparison)

[0066] Different yttria-stabilized zirconia powders were filled layer by layer into a press die, in which the powders respectively contained different additives in the form of iron oxide, cobalt oxide and erbium oxide. The layers were pressed uniaxially from both sides to form a cuboid blank. Because of the different compositions of the layers, different sintering behaviors are respectively obtained.

[0067] The pressed body was subjected to a thermal treatment at temperatures of up to 700 C. in order to remove organic additives. In a second thermal treatment, the body was presintered to from 50 to 60% of its maximum theoretical density at temperatures within a range of from 1000 C. to 1200 C.

[0068] A cuboid was milled from the presintered body. Its outer dimensions result from the sought intended geometry, i.e., the shrinkage occurring during the dense sintering was taken into account by enlarging the outer dimensions of the intended geometry using a uniform scale-up factor.

[0069] The milled-out cuboid was sintered to the desired final density at temperatures of from 1300 C. to 1600 C. The geometry of the sintered body was scanned and acquired using a profilometer. The dense-sintered body exhibits a deviation from the intended geometry. This is caused by the different sintering behaviors of the layers. The dense-sintered body clearly exhibits warping.

[0070] FIG. 3a shows the schematic representation of the presintered milled body (bright) and of the dense-sintered body (dark), in which the deviation from the intended geometry is clearly seen.

[0071] FIGS. 3b and 3c represent the profile measurement of the presintered milled body and of the dense-sintered body along the planes indicated in FIG. 3a. Here too, the significant deviation of the dense-sintered body from the sought cuboid intended geometry can be seen.

Example 4 (According to the Invention)

[0072] By analogy with Example 3, a multi-layered presintered body was prepared from yttria-stabilized zirconia. From the presintered body, a cuboid blank was milled whose outer dimensions result from the intended geometry of the dense-sintered body. In contrast to Comparative Example 3, no uniform scale-up factor was used to consider the shrinkage occurring during the sintering. Rather, the inhomogeneous sintering behavior of the body was taken into account by scaling up the dimensions of the intended geometry in a spatially resolved manner. For this purpose, each coordinate point of the intended geometry was assigned its own scale-up factor, resolved in x, y, z coordinates, in order to obtain the geometry to be milled out.

[0073] By analogy with Example 3, the milled body was sintered to the desired final density, which is the same as that of the body described in Example 3, at temperatures within a range of from 1300 C. to 1600 C.

[0074] The dense-sintered body was scanned using a profilometer, in order to determine the outer dimensions.

[0075] FIG. 4a shows the schematic representation of the presintered milled body (bright) and of the dense-sintered body (dark), in which it is clearly seen that the dense-sintered body corresponds to the intended geometry.

[0076] FIGS. 4b and 4c represent the profile measurement of the presintered milled body and of the dense-sintered body along the planes indicated in FIG. 4a. In contrast to Comparative Example 3, the dense-sintered body does not show any deviations from the intended geometry. The lateral faces of the cuboid are straight and plano-parallel in accordance with the intended geometry.

[0077] FIG. 5 demonstrates in an exemplary way the use of the spatially resolved scale-up factors in the determination of the distortion due to sintering. The process according to the invention allows for an individual adaptation of the scale-up factors. Thus, for example, the scale-up factor VGF2 at the lower plane 4 can be selected smaller than the scale-up factor VGF1 at the corner of plane 1 in each direction of space.

[0078] FIG. 6 also shows in an exemplary way a multi-layered shaped product whose planes exhibit different sintering behaviors. Here too, optimum adaptation can be achieved by selecting the scale-up factors that are individually adapted accordingly. Thus, in the present Example: [0079] VGF (x, E1; E5)<VGF (x, E3) [0080] VGF (y, E1; E5)<VGF (y, E3) [0081] VGF (z, E1; E5)<=>VGF (z, E3)

[0082] As the provided Examples and FIGS. 5 and 6 illustrate, the process according to the invention allows for the dimensionally accurate production of shape-structured inhomogeneous shaped products despite the different sintering behaviors of the individual partial regions of the shaped product, by using spatially resolved scale-up factors.