A method for inverse compensation of a forming surface model for light-cured ceramics

Abstract

The application provides a forming surface model reverse compensation method for photocured ceramics, comprising the following steps: carrying out slice processing on a ceramic structure model to obtain a gray scale image of each slice of the ceramic structure; taking each gray scale image as an exposure surface to obtain a profile point on an exposure profile of each exposure surface; calculating a light scattering influence value of all exposure points in a region with a distance of a maximum exposure influence range radius value from the profile point on each exposure surface; obtaining an equivalent circle curvature of the exposure profile, obtaining an actual over-curing size at the exposure profile according to the equivalent circle curvature, taking an over-curing size in a normal direction inward on all exposure profiles to obtain an over-curing exposure profile after single compensation; and adopting a dichotomy method to correct a model compensation coefficient to obtain a reverse compensation profile. The application can compensate precision errors caused by light scattering in a photocured ceramic manufacturing process, improve forming precision of a printing blank, and be used for high-quality manufacturing of photocured complex structure ceramics.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic light-curing printing, and particularly relates to a forming surface model reverse compensation method for light-cured ceramic. BACKGROUND

[0002] Digital light processing (DLP) ceramic 3D printing technology is a process of using ultraviolet or near-ultraviolet surface exposure to expose a photosensitive resin slurry with ceramic particles, the photosensitive resin is selectively cured according to the exposure shape, and the slurry is converted from a liquid state to a solid state layer by layer; a photosensitive resin body mixed with ceramic particles is obtained, and then the photosensitive resin is removed by degreasing; and sintering is performed to densify the ceramic pore structure.

[0003] The light scattering caused by ceramic particles in the slurry is the main reason for the decline in the printing process. Unlike pure photosensitive resin, the difference between the refractive index of the ceramic particles and the photosensitive resin causes a shift in the propagation direction of the ultraviolet light during propagation; for the surface exposure method of DLP printing, the complex scattering behavior of the surface exposure caused by the complex surface causes the actual solidification morphology to deviate from the original model size, thereby affecting the manufacturing precision of the DLP ceramic body and seriously restricting the application prospect of DLP ceramic. SUMMARY

[0004] The present application provides a forming surface model reverse compensation method for light-cured ceramic to manufacture high-precision light-cured ceramic according to the problems existing in the prior art.

[0005] The technical method adopted by the present application is: a forming surface model reverse compensation method for light-cured ceramic, comprising:

[0006] S1, establishing a ceramic structure model;

[0007] S2, performing slice processing on the ceramic structure model to obtain a gray scale image of each layer of the ceramic structure;

[0008] S3, taking each layer of the gray scale image as an exposure surface to obtain a contour point on an exposure contour of each exposure surface;

[0009] S4, determining an exposure maximum influence range radius value, and calculating a light scattering influence value of all exposure points in a region on each exposure surface with a distance from the contour point being the exposure maximum influence range radius value;

[0010] S5, obtaining an equivalent circle curvature of the exposure profile based on the light scattering influence value, obtaining an actual overcure size at the exposure profile according to the equivalent circle curvature, taking a normal inward overcure size on all the exposure profiles to obtain an overcured exposure profile after single compensation;

[0011] S6, presetting a model compensation coefficient, repeating steps S4 to S5, and correcting the model compensation coefficient by using a dichotomy method to obtain a counter-compensation profile.

[0012] In an embodiment of the present application, in step S4, the light scattering influence value is calculated as follows:

[0013]

[0014] wherein E0 is incident energy of a light source; A w is a width attenuation coefficient, which is related to light absorption and light scattering ability of each component in the slurry, l is a horizontal distance from any point in the exposure surface within the maximum influence range to the profile point, and S is a region with a distance of a radius value of the maximum influence range of the exposure from the profile point.

[0015] In an embodiment of the present application, in step S5, the actual overcure size at the exposure profile is obtained according to the equivalent circle curvature, which includes:

[0016] The actual overcure size w ex at the exposure profile is calculated by using the following empirical formula:

[0017] w ex = ξ k · w' ex

[0018] wherein ξ is a shape sensitivity coefficient, which is greater than 1, w' ex is the actual overcure size w ex , and k is the equivalent circle curvature.

[0019] In an embodiment of the present application, in step S6, the method for correcting the model compensation coefficient by using the dichotomy method includes:

[0020] If the overcured exposure profile of the compensated model is outside the theoretical exposure profile, then the corrected model compensation coefficient is taken downward according to the dichotomy method;

[0021] If the overcured exposure profile of the compensated model is inside the theoretical exposure profile, then the corrected model compensation coefficient is taken upward according to the dichotomy method;

[0022] The model compensation coefficient after iteration is calculated, and if it is within a preset confidence interval, then the calculation is ended.

[0023] In one embodiment of the present application, after step S6, further comprising:

[0024] S7, the photosensitive resin, dispersant and ceramic powder are sequentially added into the slurry tank in proportion, and after being stirred uniformly, they are poured into the ceramic material cylinder;

[0025] S8, after the printer obtains the exposure pattern of the compensated printing model, the printing platform is lowered into the ceramic material cylinder, and a shaped ceramic body is obtained by the method of photocuring molding;

[0026] S9, the ceramic body is subjected to a debinding process to obtain a ceramic green body, and the ceramic green body is subjected to a sintering process to obtain a densified ceramic.

[0027] In one embodiment of the present application, in step S7, the particle size of the ceramic powder is 1 μm.

[0028] In one embodiment of the present application, in step S7, the volume fraction of the ceramic powder is 30-60 vol%, the dispersant is polyvinylpyrrolidone with a volume fraction of 1-5 vol%, and the photosensitive resin is a compound prepared from bisphenol a epoxy acrylate as a raw material with a volume fraction of 35-69%.

[0029] In one embodiment of the present application, in step S8, the exposure energy is 5-25 mW / cm 2 , the exposure time is 4-40 s, and the printing layer thickness is 30-200 μm.

[0030] In one embodiment of the present application, in step S9, the debinding process comprises: the ceramic body is sequentially kept at 100℃, 237℃, 300℃ and 600℃ for 2-6 h, and the heating rate is 2℃ / min.

[0031] In one embodiment of the present application, in step S9, the sintering temperature of the sintering process is 1550℃, the heating rate is 2℃ / min, and the sintering time is 1-65 h.

[0032] The above technical solution of the present application has the following advantages compared with the prior art:

[0033] The forming surface model reverse compensation method for photocured ceramics of the present application can compensate the precision error caused by light scattering in the photocured ceramic manufacturing process, improve the forming precision of the printed body, and can be used for high-quality manufacturing of photocured ceramics with complex structures. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to make the content of the present application more easily understood, the present application will be further described in detail below according to specific embodiments of the present application and in conjunction with the drawings.

[0035] Figure 1a is a schematic diagram of light scattering affecting the shaping accuracy of a projection surface.

[0036] Figure 1b is a schematic diagram of the scattering effect of ultraviolet light on ceramic slurry.

[0037] Figure 2 is a schematic diagram of the estimation of accuracy error by equivalent curvature circle according to the present application.

[0038] Figure 3 is a schematic diagram of iteration according to the present application.

[0039] Figure 4a is a schematic diagram of the model and the model after reverse compensation (wherein a is a model structure diagram, a2 is a model slice before reverse compensation, and a3 is a model slice after optimization).

[0040] Figure 4b is a schematic diagram of model measurement before reverse compensation according to the present application.

[0041] Figure 4c is a schematic diagram of model measurement after reverse compensation according to the present application.

[0042] Figure 4d is a schematic diagram of a model slice before reverse compensation and a local enlarged view thereof (wherein b1 is a schematic diagram of a model slice before reverse compensation, and b2 is a local enlarged view).

[0043] Figure 4e is a schematic diagram of a model after reverse compensation according to the present application (wherein c1 is a schematic diagram of a model slice after reverse compensation, and c2 is a local enlarged view).

[0044] Figure 5 is a schematic diagram of a ceramic crown model.

[0045] Figure 6 is a comparison diagram of a single-layer exposure shape of a crown and an original model.

[0046] Figure 7 is a curve diagram of crown embryo defatting and sintering. DETAILED DESCRIPTION

[0047] The present application will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it.

[0048] The hardware basis of the present application is a DLP ceramic printer with a bottom-up structure. The DLP technology refers to the use of a digital micro-mirror unit (DMD) to selectively project the required exposure profile, and the use of ultraviolet (near-ultraviolet light) to cure a single layer of exposure surface with a specific shape, layer by layer, to form a three-dimensional structure with a specific shape. The size of a single exposure pixel can reach 2 microns.

[0049] The scattering effect of ultraviolet light in the ceramic slurry is the main cause of the accuracy error of the DLP ceramic green body. The strength of the scattering effect depends on the strength of the ultraviolet energy and the optical properties of the ceramic slurry in the ultraviolet band. As shown in Figure 1a 、 Figure 1b The refractive index contrast, particle size, and volume fraction of the ceramic slurry also have a significant impact on light scattering performance. The effects of particle size, volume fraction, and packing on the viscosity of the ceramic slurry and the forming quality should also be considered. Restricted by the above factors, the scattering effect of ultraviolet light on the ceramic slurry and the size deviation of the exposure profile are still unavoidable. Therefore, the present application corrects the exposure model through machine learning, based on the accuracy error empirical formula, to improve the forming accuracy of the printed blank in the xy plane, which can theoretically achieve the exposure accuracy of the light source.

[0050] Embodiment 1

[0051] Referring to Figure 3 A forming surface model counter-compensation method for light-cured ceramics includes the following steps:

[0052] S1, design a ceramic structure diagram with modeling software and save it as an STL format file;

[0053] S2, slice the STL format file through the printer software to obtain the slice grayscale image of each layer of printing;

[0054] S4, determine the appropriate maximum exposure range R according to the optical properties of the ceramic slurry itself and the exposure energy; the material can be determined according to the specific printer parameters; as shown in Figure 2 All profile points in the exposure surface are obtained, and the calculation formula of the influence E of all exposure points in the interval with a radius of R from the profile point is as follows:

[0055]

[0056] Wherein: E0 is the incident energy of the light source; A w is the width attenuation coefficient, which is related to the light absorption and light scattering ability of each component in the slurry, l is the horizontal distance from any point in the exposure surface within the maximum influence range to the profile point, and S is the area with a distance from the profile point of the maximum influence range radius value.

[0057] For any DLP exposure profile, the scattering energy at different profile positions is different. The actual light scattering influence range at all profile positions is calculated by the above formula, in addition, the light scattering influence values of 500 different curvature circles are also calculated in advance and stored in a list. By comparing the actual profile light scattering influence value with the values in the list, a curvature circle matching the exposure profile is obtained;

[0058] S5, such as Figure 2 As shown, based on the influence of all exposure points, the equivalent circular curvature k of all exposure profiles is calculated, and the actual over-curing dimension w at all exposure profiles is calculated using empirical formulas. ex Take the over-cured dimension in the normal direction on the outline to obtain the exposure outline after single compensation.

[0059] The actual over-curing dimension w at the exposure profile is calculated using the following empirical formula. ex :

[0060] w ex =ξ k ·w′ ex

[0061] Where: ξ is the shape sensitivity coefficient, its value is greater than 1, w′ ex For the actual overcured size w ex It was obtained from a sample with an equivalent circular curvature k of 0.

[0062] S6. For example Figure 3 As shown, through multiple iterations in steps S4 and S5, the bisection method is used to correct the model compensation coefficients, obtaining an accurate inverse compensation profile within a suitable confidence interval; specifically including:

[0063] If the over-cured exposure profile of the compensated model is outside the theoretical exposure profile, then the corrected model compensation coefficient is taken downward according to the dichotomy method.

[0064] If the over-cured exposure profile of the compensated model is within the theoretical exposure profile, then the compensation coefficient of the corrected model is taken upward according to the bisection method.

[0065] The calculation is completed by calculating the ratio of the over-cured exposure profile after iteration to the theoretical exposure profile. If the ratio is within the preset confidence interval, the calculation ends.

[0066] Understandably, if the model compensation coefficient is initially preset to 0.5, and the actual printed over-cured exposure profile after a single compensation is greater than the required profile (theoretical exposure profile, referring to the model profile being modeled), then it is corrected to 0.25; otherwise, it is corrected to 0.75. If the model compensation coefficient is 0.25, and the actual printed over-cured exposure profile after a single compensation is less than the required profile, then it is corrected to 0.375, and so on.

[0067] S7. Add the photosensitive resin, dispersant and yttrium-stabilized photocurable ceramic powder to the slurry tank in the following proportions. The ceramic powder has a particle size of 1 μm and a volume fraction of 55 vol%. The dispersant is polyvinylpyrrolidone with a volume fraction of 3 vol%. The photosensitive resin is a compound prepared from bisphenol A epoxy acrylate with a volume fraction of 42 vol%. Stir evenly and pour into the ceramic slurry tank.

[0068] S8. For example Figures 4a to 4e As shown, after the printer obtains the compensated print model exposure pattern, the printing platform moves down into the ceramic material cylinder, and the formed ceramic blank is obtained by photopolymerization molding.

[0069] S9. The ceramic green body is degreased to obtain a ceramic blank. The ceramic green body is then held at 100℃, 237℃, 300℃ and 600℃ for 4 hours in sequence, with a heating rate of 2℃ / min. The sintering process is carried out at a sintering temperature of 1600℃, a heating rate of 2.3℃ / min and a sintering time of 5 hours to obtain a dense ceramic core.

[0070] Example 2

[0071] The difference between Example 2 and Example 1 is that an all-ceramic crown model was selected as the implementation example of the anti-compensation model, such as... Figures 5 to 6 As shown in the figure. A comparison was made between the sliced ​​models of different layers and the model after inverse compensation. The model exhibited varying accuracy at different contour positions. After compensation using the method described above, a model structure with high accuracy and different compensation dimensions at different positions was obtained. After importing the compensated model into the printer, the printed blank was debound and sintered. The debinding and sintering curve is shown in the figure. Figure 6 As shown, a high-precision ceramic light-cured all-ceramic crown was obtained.

[0072] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for inverse compensation of a forming surface model for photocurable ceramics, characterized in that, include: S1. Establish a ceramic structure model; S2. Slice the ceramic structure model to obtain grayscale images of each slice of the ceramic structure. S3. Using each layer of grayscale image as an exposure surface, obtain the contour points on the exposure contour of each exposure surface; S4. Determine the maximum exposure influence range radius value, and calculate the light scattering influence value of all exposure points in the region of the maximum exposure influence range radius value within the area of ​​the contour point on each exposure surface; S5. Based on the light scattering influence value, the equivalent circular curvature of the exposure profile is obtained. The actual over-cured size at the exposure profile is obtained according to the equivalent circular curvature. The inward normal over-cured size is taken on all the exposure profiles to obtain the over-cured exposure profile after single compensation. S6. Preset the model compensation coefficient, repeat steps S4 to S5, and use the bisection method to correct the model compensation coefficient to obtain the inverse compensation profile. In step S4, the light scattering influence value is calculated as follows: , Where: E0 is the incident energy of the light source; is the width attenuation coefficient, which is related to the light absorption and light scattering capabilities of each component in the slurry; l is the horizontal distance from any point on the exposure surface within the maximum influence range to the contour point; and S is the region whose distance from the contour point is the radius of the maximum influence range of the exposure. In step S5, obtaining the actual over-curing dimension at the exposure contour based on the equivalent circular curvature includes: The actual over-curing size at the exposure profile is calculated using the following empirical formula. : , in: This is the shape sensitivity coefficient, whose value is greater than 1. Actual overcured dimensions Through equivalent curvature The sample with a value of 0 was obtained; In step S6, the method of correcting the model compensation coefficient using the bisection method includes: If the over-cured exposure profile of the compensated model is outside the theoretical exposure profile, then the corrected model compensation coefficient is taken downward according to the dichotomy method. If the over-cured exposure profile of the compensated model is within the theoretical exposure profile, then the compensation coefficient of the corrected model is taken upward according to the bisection method. Calculate the model compensation coefficients after iteration. If they are within the preset confidence interval, the calculation ends.

2. The method for inverse compensation of the forming surface model for photocurable ceramics according to claim 1, characterized in that, After step S6, the following is also included: S7. Add the photosensitive resin, dispersant and ceramic powder to the slurry tank in the correct proportions, stir evenly and then pour into the ceramic material tank. S8. After the printer obtains the compensated print model exposure pattern, the printing platform moves down into the ceramic material cylinder, and the formed ceramic blank is obtained by photopolymerization molding. S9. The ceramic blank is degreased to obtain a ceramic green body, and the ceramic green body is sintered to obtain a densified ceramic.

3. The method for inverse compensation of the forming surface model for photocurable ceramics according to claim 2, characterized in that, In step S7, the particle size of the ceramic powder is 1 μm.

4. The method for inverse compensation of the forming surface model for photocurable ceramics according to claim 2, characterized in that, In step S7, the ceramic powder has a volume fraction of 30-60 vol%, the dispersant is polyvinylpyrrolidone with a volume fraction of 1-5 vol%, and the photosensitive resin is a compound prepared from bisphenol A epoxy acrylate with a volume fraction of 35-69%.

5. The method for inverse compensation of the forming surface model for photocurable ceramics according to claim 2, characterized in that, In step S8, the exposure energy is 5-25 mW / cm². 2 The exposure time was 4-40 seconds and the printing layer thickness was 30-200 μm.

6. The method for inverse compensation of the forming surface model for photocurable ceramics according to claim 2, characterized in that, In step S9, the degreasing process includes: holding the ceramic blank at 100℃, 237℃, 300℃ and 600℃ for 2-6 hours in sequence, with a heating rate of 2℃ / min.

7. The method for inverse compensation of the forming surface model for photocurable ceramics according to claim 2, characterized in that, In step S9, the sintering temperature of the sintering process is 1550℃, the heating rate is 2℃ / min, and the sintering time is 1-65h.

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