A multiple combined surface exposure manufacturing method for high-precision molding of ceramic cores

Abstract

The present invention provides a method for manufacturing a ceramic core using multiple combined surface exposures for high-precision molding, comprising the following steps: S1. Designing a ceramic core structure diagram using modeling software and saving it as an STL file; S2. Slicing the STL file to obtain a grayscale image of each printed slice layer, calculating a threshold k for multiple exposures, and measuring the actual threshold kn of the model; S3. Importing the slice grayscale image into a light-curing 3D printer, performing a single exposure or n+1 slice grayscale image processing and combined surface exposure; S4. Adding a photosensitive resin, a dispersant, and ceramic powder to a slurry tank and pouring it into a ceramic material cylinder; S5. After the printer obtains the exposure pattern of the printed model, a formed ceramic body is obtained by light-curing molding; S6. Degreasing the ceramic body to obtain a ceramic green body, which is then sintered to obtain a ceramic core. The present invention can improve the curing performance of the ceramic slurry, reduce structural defects in the printed body, and can be used to manufacture high-precision ceramic core bodies.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic DLP printing, in particular to a multiple combined surface exposure manufacturing method for high-precision molding of ceramic cores. Background Art

[0002] Digital light processing ceramic 3D printing technology is a process that uses digital micromirror units to selectively expose ceramic slurry through a specific wavelength. The photosensitive resin absorbs energy and undergoes a cross-linking reaction, transforming the slurry from liquid to solid. At this time, the ceramic particles are dispersed in the solidified photosensitive resin. The photosensitive resin is then removed through a degreasing process, and the ceramic particles are densified through a sintering process.

[0003] The ceramic core is an internal cooling structure used to form hollow blade castings. Its performance and quality greatly affect the qualification rate and cost of casting production. The ceramic core must have sufficient room temperature strength and high temperature strength to withstand the impact of molten metal during pouring. At present, the internal cooling structure of the blade has developed from single convection air cooling to double-wall super air cooling. For the development of turbine blades with new cooling structures, the traditional ceramic core preparation method is complicated, mainly through hot pressing and gel injection molding, and multiple sets of molds need to be prepared in advance. After the blade design is changed, the mold needs to be re-prepared, resulting in a long blade development and production cycle. The mold opening process will also cause varying degrees of damage to the surface of the core blank. Correspondingly, ceramic DLP technology does not require molds, can accelerate the research and development of new products, shorten the manufacturing cycle, meet personalized needs, and has the advantages of high manufacturing precision and high degree of freedom in forming structure. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a multiple combined surface exposure manufacturing method for high-precision molding of ceramic cores, which is used to manufacture high-precision, defect-free alumina ceramic cores.

[0005] The technical solution adopted in the present invention is:

[0006] A multiple combined surface exposure manufacturing method for high-precision molding of ceramic cores, comprising the following steps:

[0007] S1. Design the ceramic core structure using modeling software and save it as an STL file.

[0008] S2. Slice the STL file using the printer software to obtain a grayscale image of each printed slice. Calculate the multiple exposure threshold k and the actual threshold kn of the measurement model. Compare k and kn. If k > kn, perform n exposures. If k < kn, perform n+1 exposures.

[0009] S3. When n=1 and k>k1, the slice grayscale image obtained in step S2 is imported into the light-curing 3D printer. After the printer obtains the slice grayscale image of each layer of the printed model, it performs a single exposure to obtain an exposure pattern of a single combined surface exposure. When n≥1 and k<k1, the exposure pattern of the single combined surface exposure is subjected to n or n+1 slice grayscale image processing and combined surface exposure by the slice image secondary processing module to obtain an exposure pattern of n or n+1 combined surface exposures.

[0010] S4. The photosensitive resin, dispersant and ceramic powder are sequentially added to the slurry tank in proportion, stirred and poured into the ceramic material tank;

[0011] S5. After the printer obtains the exposure pattern of the print model, the printing platform is moved down to the ceramic material cylinder, and a formed ceramic body is obtained by a photocuring method;

[0012] S6. Degreasing the ceramic body to obtain a ceramic green body, and sintering to obtain a densified ceramic core.

[0013] Preferably, in the above-mentioned method for manufacturing ceramic cores by multiple combined surface exposures with high precision molding, in step S2, the calculation formulas for the multiple exposure threshold k and the actual threshold kn of the measurement model are as follows:

[0014]

[0015] Where: Cd is the thickness of the solidified layer at any position of the slurry, which can reflect the forming quality of the material; k is the shape influence coefficient of the solidified layer thickness of the slurry; S is the entire exposure surface; L is the horizontal distance from any point on the exposure surface to the solidified layer thickness test point.

[0016] Preferably, in the multiple combined surface exposure manufacturing method for high-precision molding of ceramic cores, the grayscale image processing of the slice in step S3 is specifically as follows: the inner and outer contours of the grayscale image are found through the contour selection function of Python, and a compensation calculation is performed on the contour in the normal direction inside the contour, and the compensation size of the compensation calculation is 100 μm.

[0017] Preferably, in the above-mentioned method for manufacturing ceramic cores by multiple combined surface exposures with high precision, the exposure energy in the first combined surface exposure, the nth or n+1th combined surface exposure in step S3 is 5-25 mW / cm 2 , the exposure time is 4-40s, and the printing layer thickness is 50-200μm.

[0018] Preferably, in the multiple combined surface exposure manufacturing method for high-precision molding of ceramic cores, the ceramic powder in step S4 is 5μm spherical α-alumina with a volume fraction of 30-60vol%, the dispersant is polyvinyl pyrrolidone with a volume fraction of 1-5vol%, and the photosensitive resin is a compound prepared with bisphenol A epoxy acrylate as raw material, with a volume fraction of 35-69%.

[0019] The photosensitive prepolymer is a compound prepared from bisphenol A epoxy acrylate (BAEA) as a raw material, the photosensitive prepolymer 1,6-hexanediol diacrylate (HDDA), methyl propane triacrylate (TMPTA) as a diluent monomer, 2-hydroxy-2-methylpropionic acid (1173) and diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) as a photoinitiator.

[0020] Preferably, in the multiple combined surface exposure manufacturing method for high-precision molding of ceramic cores, the degreasing process in step S6 is specifically as follows: the ceramic body is kept at 100°C, 237°C, 300°C, and 600°C for 2-6 hours, with a heating rate of 2°C / min, the sintering temperature of the sintering process is 1550°C, the heating rate is 2°C / min, and the sintering time is 1-65 hours.

[0021] Advantages of the present invention:

[0022] (1) The multiple combined surface exposure manufacturing method for high-precision molding of ceramic cores of the present invention, after the completion of one exposure, is affected by the uneven scattering of the energy of the DLP surface exposure light source, and the position where the printing quality deteriorates is subjected to a second exposure. In a single cycle, the exposure grayscale image is processed twice, and the compensation size is taken inward along the normal vector of the exposure profile. At the position with lower printing accuracy, a selective second exposure is performed, and the second exposure uses the processed grayscale image. After the weak layer is printed, the printer starts printing the next layer until the printing is completed. The multiple combined surface exposure manufacturing method of the present invention can improve the curing performance of the ceramic slurry, reduce the structural defects of the printed body, and can be used for the manufacture of high-precision ceramic core bodies. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Figure 4. Differences in forming performance of the refined structure of the present invention.

[0024] Figure 2 Schematic diagram of the multiple exposure process flow of the present invention.

[0025] Figure 3 Process flow chart of the present invention.

[0026] Figure 4 FIG. 4 is a diagram showing the process of determining the number of exposures according to the present invention.

[0027] Figure 5 This is a comparison diagram of Examples 1-3 of the present invention.

[0028] Figure 6 This is the debinding-sintering process curve of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to specific drawings and embodiments.

[0030] The printer uses a DLP ceramic printer. DLP technology uses photons to solidify photosensitive materials, forming complex structures layer by layer using a high-precision light source. Ultraviolet / UV light is used to solidify ceramic slurry layer by layer, and then the layers are accumulated and stacked to form the finished product. DLP uses a DMD (Digital Micromirror Device) to adjust the shape of the entire cross-section, forming the entire cross-section in one go. The DMD resolution can reach 2 million pixels.

[0031] Affected by the exposure energy of the light source and the changes in the printing structure, the printing quality of different exposure structures at different positions is different, such as Figure 1 Under different exposure areas, affected by the light scattering and light absorption properties of the ceramic slurry, when the exposure energy is the same, the curing depth of the slurry gradually decreases, thereby reducing the curing performance of the slurry, and ultimately leading to the unevenness of the displayed printing parameters caused by the structure. From this, we can find that it is inappropriate to select the same exposure energy parameters for different exposure sections.

[0032] like Figure 2-3 Generally speaking, the finer the structure, the worse the printing quality, which limits the forming quality of DLP. The slice image secondary processing module is used to obtain the exposure pattern of multiple combined surface exposures. The printing platform precession module controls the coordinated movement of the printing platform motor, the platform scraper motor and the peeling motor. The printing platform motor is used to control the Z-axis movement of the printing platform, the platform scraper motor is used to control the scraper to scrape a sufficient amount of ceramic slurry, and the peeling motor is used to control the single-layer peeling of the printing cylinder.

[0033] The slice image secondary processing module is used to obtain the exposure pattern of secondary combined surface exposure. The image of multiple combined surface exposure comes from the processed slice grayscale image. The multiple combined surface exposure position is located in the area with poor printing quality.

[0034] like Figure 3After the printer obtains the slice grayscale image of each layer of the printed model, the printing platform moves down to the ceramic material tank, and the slice image is selectively exposed on the printing platform. The printing platform moves up, and the image of the multiple combined surface exposure comes from the processed slice grayscale image. The processed slice grayscale image is obtained by taking the compensation size inward along the contour normal direction to obtain a grayscale image for multiple combined surface exposure, where the compensation size is used to compensate for the precision error caused by the optical effect. After the multiple combined surface exposure is completed, the printing platform moves up, the peeling motor peels off the single layer, the scraper scrapes a new layer of ceramic slurry, and then starts printing the next layer, accumulating layer by layer, and repeating the cycle until the ceramic body structure is formed.

[0035] Example 1

[0036] A multiple combined surface exposure manufacturing method for high-precision molding of ceramic cores, comprising the following steps:

[0037] S1. Design the ceramic core structure using modeling software and save it as an STL file;

[0038] S2. Slice the STL file using the printer software to obtain a grayscale image of each printed slice layer. Calculate the multiple exposure threshold k and the actual threshold kn of the measurement model, and compare k and kn.

[0039] The calculation formulas for the multiple exposure threshold k and the actual threshold kn of the measurement model are as follows:

[0040]

[0041] Where: Cd is the thickness of the solidified layer at any position of the slurry, which can reflect the forming quality of the material; k is the shape influence coefficient of the solidified layer thickness of the slurry; S is the entire exposure surface; L is the horizontal distance from any point on the exposure surface to the solidified layer thickness test point;

[0042] During DLP printing, since the scattered energy of the surface exposure at different exposure positions of different exposure patterns is non-uniform, we use the above calculation formula to determine the threshold value for double exposure or even multiple exposures. The formula is the surface integral of the energy attenuation of any exposure pattern on the xy axis based on the Beer-Lambert law, which can well describe the non-uniformity of the light source energy during the exposure process. In particular, the non-uniformity leads to the curing layer thickness C d The decrease in value can therefore be expressed as a function of the d The k value is used as the threshold value for print quality degradation. The specific method for determining the number of exposures is as follows: Figure 4 The threshold k calculated according to the formula is compared with k1, k2, and k3 to determine whether multiple exposures are needed. Here, k1, k2, and k3 come from the actual measurement results of the influence of k value on the thickness of the cured layer.

[0043] S3.n=1, and k>k1. Import the sliced ​​grayscale image obtained in step S2 into the light-curing 3D printer. After the printer obtains the sliced ​​grayscale image of each layer of the printed model, it performs a single exposure to obtain an exposure pattern for a combined surface exposure. During a single combined surface exposure, the exposure energy is 5mW / cm 2 , exposure time is 4s, and printing layer thickness is 100μm;

[0044] S4. The photosensitive resin, dispersant and ceramic powder are sequentially added to the slurry tank in proportion. The ceramic powder is 5μm spherical α-alumina with a volume fraction of 55vol%. The dispersant is polyvinyl pyrrolidone with a volume fraction of 3vol%. The photosensitive resin is a compound prepared from bisphenol a epoxy acrylate with a volume fraction of 42vol%. Stir well and pour into the ceramic material tank.

[0045] S5. After the printer obtains the exposure pattern of the print model, the printing platform is moved down to the ceramic material cylinder, and a formed ceramic body is obtained by a photocuring method;

[0046] S6. The ceramic body is subjected to a degreasing process to obtain a ceramic green body, and the ceramic body is kept at 100°C, 237°C, 300°C, and 600°C for 2 hours, with a heating rate of 2°C / min. The sintering temperature of the sintering process is 1550°C, the heating rate is 2°C / min, and the sintering time is 5 hours. A densified ceramic core is obtained by sintering.

[0047] Example 2

[0048] The difference between Example 2 and Example 1 is that: n=1, and k<k1, the slice grayscale image obtained in step S2 is imported into the light-curing 3D printer, and after the printer obtains the slice grayscale image of each layer of the printed model, it performs a single exposure to obtain an exposure pattern for a single combined surface exposure, and the exposure pattern for the single combined surface exposure is subjected to a second slice grayscale image processing and a combined surface exposure processing by the slice image secondary processing module to obtain an exposure pattern for a second combined surface exposure;

[0049] When the first combined surface is exposed, the exposure energy is 5mW / cm 2 , the exposure time is 4s, the printing layer thickness is 100μm; during the second combined surface exposure, the exposure energy is 5mW / cm 2 , the exposure time is 7s, the printing layer thickness is 100μm, and the compensation calculation of the normal to the contour is performed on the contour, and the compensation size is selected as 100μm.

[0050] Example 3

[0051] The difference between Example 3 and Example 1 is that: n=2, and k<k2, three exposures are performed, the slice grayscale image obtained in step S2 is imported into the light-curing 3D printer, and after the printer obtains the slice grayscale image of each layer of the printed model, it performs one exposure to obtain an exposure pattern of a first combined surface exposure, and the exposure pattern of the first combined surface exposure is subjected to a second slice grayscale image processing and a combined surface exposure processing by the slice image secondary processing module to obtain an exposure pattern of a second combined surface exposure, and finally, the exposure pattern of the second combined surface exposure is subjected to a third slice grayscale image processing and a combined surface exposure processing by the slice image secondary processing module to obtain an exposure pattern of a third combined surface exposure;

[0052] When the first combined surface is exposed, the exposure energy is 5mW / cm 2 The exposure time is 4s, the printing layer thickness is 100μm, and the exposure energy is 5mW / cm during the second combined surface exposure. 2 The exposure time is 7s, the printing layer thickness is 100μm, and the compensation calculation is performed on the contour. The compensation size is selected as 100μm. When the third combined surface is exposed, the exposure energy is 5mW / cm 2 , exposure time is 10s, printing layer thickness is 100μm, compensation calculation is performed on the contour in the normal direction, and the compensation size is selected as 100μm.

[0053] The printing effects of Examples 1-3 are as follows: Figure 5 , under the premise of different printing layer thicknesses, the printing quality is quite different. This step effect will lead to a significant decline in the final forming quality, seriously restricting the forming quality of the ceramic core and limiting the quality of the blades cast by the ceramic core in the subsequent casting; through multiple combined surface exposures, although the structure we selected is the same, under the premise of different printing layer thicknesses, the printing quality is quite different. This step effect will lead to a significant decline in the final forming quality, seriously restricting the forming quality of the ceramic core and limiting the quality of the blades cast by the ceramic core in the subsequent casting. Through the multiple surface exposure process, we can improve the light curing performance of weak positions, thereby improving the printing quality; compared with Example 2, Example 3 uses three exposures, and the step effect is less obvious at the fine structure, and the blank has better forming quality.

[0054] Figure 6 This is the debinding and sintering curve used in Examples 1-3. The debinding process adopts vacuum-air two-stage debinding, and the sintering adopts conventional sintering. The debinding process is kept at 100°C, 237°C, 300°C, and 600°C for two hours in sequence, with a heating rate of 2°C / min. The sintering temperature of the sintering process is 1550°C, and the heating rate is 2°C / min.

[0055] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for manufacturing ceramic cores by multiple combined surface exposures for high-precision molding, characterized in that: The following steps are involved: S1. Design the ceramic core structure using modeling software and save it as an STL file; S2. Slice the STL file using the printer software to obtain a grayscale image of each printed slice. Calculate the multiple exposure threshold k and the actual threshold kn of the measurement model. Compare k and kn. If k > kn, perform n exposures. If k < kn, perform n+1 exposures. S3. When n=1 and k>k1, the slice grayscale image obtained in step S2 is imported into the light-curing 3D printer. After the printer obtains the slice grayscale image of each layer of the printed model, it performs a single exposure to obtain an exposure pattern of a single combined surface exposure. When n≥1 and k<k1, the exposure pattern of the single combined surface exposure is subjected to n or n+1 slice grayscale image processing and combined surface exposure by the slice image secondary processing module to obtain an exposure pattern of n or n+1 combined surface exposures. S4. The photosensitive resin, dispersant and ceramic powder are added to the slurry tank in proportion, stirred and poured into the ceramic material tank; S5. After the printer obtains the exposure pattern of the print model, the printing platform is moved down to the ceramic material cylinder, and a formed ceramic body is obtained by a photocuring method; S6. The ceramic body is subjected to a degreasing process to obtain a ceramic green body, which is sintered to obtain a densified ceramic core; In step S2, the calculation formulas for the multiple exposure threshold k and the actual threshold kn of the measurement model are as follows: ， Where: Cd is the solidified layer thickness at any position of the slurry, reflecting the forming quality of the reaction material, k is the shape influence coefficient of the solidified layer thickness of the slurry; S is the entire exposure surface, and L is the horizontal distance from any point on the exposure surface to the solidified layer thickness test point.

2. The method for manufacturing a ceramic core by multiple combined surface exposures for high-precision molding according to claim 1, characterized in that: The grayscale image processing of the slice in step S3 is specifically as follows: finding the inner and outer contours of the grayscale image through the contour selection function of Python, and performing compensation calculation on the contour in the normal direction of the contour, and the compensation size of the compensation calculation is 100 μm.

3. The method for manufacturing a ceramic core by multiple combined surface exposures for high-precision molding according to claim 1, characterized in that: In step S3, the exposure energy during the first combined surface exposure, nth or n+1th combined surface exposure is 5-25 mW / cm 2 , the exposure time is 4-40s, and the printing layer thickness is 50-200μm.

4. The method for manufacturing a ceramic core by multiple combined surface exposures for high-precision molding according to claim 1, characterized in that: In step S4, the ceramic powder is 5 μm spherical α-alumina with a volume fraction of 30-60 vol%. The dispersant is polyvinyl pyrrolidone with a volume fraction of 1-5 vol%. The photosensitive resin is a compound prepared from bisphenol A epoxy acrylate with a volume fraction of 35-69%.

5. The method for manufacturing a ceramic core by multiple combined surface exposures for high-precision molding according to claim 1, characterized in that: The degreasing process in step S6 is as follows: the ceramic body is kept at 100°C, 237°C, 300°C, and 600°C for 2-6 hours, with a heating rate of 2°C / min. The sintering temperature of the sintering process is 1550°C, the heating rate is 2°C / min, and the sintering time is 1-65 hours.

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