Method for selecting ultraviolet light energy density in quartz glass additive manufacturing

Abstract

The invention discloses a method for selecting ultraviolet light energy density in quartz glass additive manufacturing. The method comprises the following steps: firstly, carrying out curing test on a preset composite material formula to obtain an energy density-curing depth curve graph and an energy density-monomer conversion rate curve graph; for the selected slice layer thickness, the energy density difference value received by the upper surface and the lower surface of the single curing layer is calculated, and the optimal energy density is selected according to the principle that the monomer conversion rate of most area materials in the single curing layer from bottom to top reaches a conversion rate threshold value and the monomer conversion rate of small area materials in the upper layer is lower than the conversion rate threshold value. Through the selection of the optimal energy density, the interlayer bonding effect and the overall uniformity can be effectively improved, the strength of a printed piece is improved, the anisotropy of the overall performance of the structure is relieved, the internal stress of the printed piece and a sintered piece is reduced, the defects of the interior and the surface of the sintered piece are reduced, the surface quality and the light transmittance are improved, and the forming quality optimization is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of additive manufacturing of silica photocurable composites, and particularly relates to a method for selecting the ultraviolet light energy density in the additive manufacturing of quartz glass. Background Art

[0002] Quartz glass is widely used in scientific research, industrial production and daily life due to its excellent optical properties, mechanical strength, chemical corrosion resistance, high temperature resistance and electrical insulation. With the rapid development of additive manufacturing technology, the difficulties faced in the processing of micro-complex geometric structure glass components, such as high melting point, high hardness and brittleness, and low forming quality, have been well solved. There are a rich variety of existing quartz glass additive manufacturing technologies, mainly including Laser Powder Bed Fusion (LPBF), light-curing-based technologies such as Stereolithography (SLA), Digital Light Processing (DLP) and Two-photon Polymerization (2PP), and material extrusion-based technologies such as Directed energy deposition (DED), Direct Ink Writing (DIW) and Fused Deposition Modelling (FDM). Among them, the Digital Light Processing (DLP) technology has become a hot topic in the current research of quartz glass additive manufacturing technology due to its high forming accuracy, high forming speed, low cost and high surface quality, and is widely used in the fields of optics and microfluidics.

[0003] The DLP stereolithography technology obtains the target component by stacking printing layers with a fixed layer thickness layer by layer. This process has high requirements for the rheological properties and curing properties of the liquid composite material. To obtain a stereolithography printed part and a sintered quartz glass part with excellent overall performance, good interlayer bonding quality is required between adjacent cured layers. The energy density of ultraviolet light is a key parameter affecting the monomer conversion rate and curing depth of the material, and thus has a significant impact on the interlayer bonding effect. However, there is currently a lack of systematic research to clarify the selection method of the optimal energy density and its matching relationship with the slice layer thickness. Therefore, there are the following technical difficulties in the photocuring process of silica composites: 1) It is difficult to determine the optimal energy density, which leads to uncontrollable monomer conversion rate in the cured layer. Too high energy density results in too high overall monomer conversion rate and too large strength in a single layer, weakening the interlayer bonding force between adjacent layers, increasing the stress in the cured layer, and prone to phenomena such as overall reduction of the strength of the printed part, failure of forming, more defects inside the sintered part, or cracking due to excessive stress, and anisotropy of the overall performance of the structure; too low energy density results in too low monomer conversion rate and too small strength in a single layer, insufficient overall mechanical strength of the printed part, poor surface quality of the sintered part, and significantly reduced light transmittance; 2) The corresponding relationship between different slice layer thicknesses and the optimal energy density is not clear. Since it is difficult to simultaneously achieve the optimal between forming efficiency and forming accuracy, the slice layer thickness often needs to be adjusted according to actual requirements, and the corresponding optimal energy density also needs to be adjusted. Most of the existing adjustment methods rely on process experience and are not accurate. It is necessary to conduct photocuring experiments under different energy densities and observe the forming effect with the naked eye. There is a lack of an efficient, systematic and scientific adjustment method to determine the corresponding relationship between the slice layer thickness and the optimal energy density. Summary of the Invention

[0004] To solve the problems in the prior art, the present invention proposes a method for selecting the energy density of ultraviolet light in the additive manufacturing of quartz glass.

[0005] The technical solution of the present invention is as follows:

[0006] The present invention provides a method for selecting the energy density of ultraviolet light in the additive manufacturing of quartz glass, which includes the following steps:

[0007] 1) Mix the polymer monomer, plasticizer, surfactant, nano-silica powder, photoinitiator, inhibitor and light absorber evenly according to the preset composite material formula, and defoam the prepared composite material under vacuum;

[0008] 2) Test the curing performance of the composite material according to a fixed light intensity (unit: mW / cm 2 ) and different exposure times (unit: s), record the curing depth of the composite material under different energy densities (unit: mJ / cm 2 ), and plot an energy density - curing depth curve graph;

[0009] 3) Fourier transform infrared spectroscopy tests are respectively carried out on the composite material before curing and the material after the curing depth test in step 2). The absorption intensities of the characteristic peaks of C=C bonds and C=O bonds are respectively recorded, the monomer conversion rate is calculated, and an energy density - monomer conversion rate curve is plotted;

[0010] 4) During the additive manufacturing process, for a sliced layer with a certain determined layer thickness, the material layer cured by the printing device in one photocuring process is the corresponding single-cured layer. Calculate the difference in energy density received on the upper and lower surfaces of the single-cured layer. According to the principle that the monomer conversion rate of the material in most regions from bottom to top within the single-cured layer reaches the conversion rate threshold, and the monomer conversion rate of the material in a small part of the upper region is lower than the conversion rate threshold, select the optimal energy density.

[0011] According to the preferred solution of the present invention, in step 1), in the preset composite material formula, the polymer monomer is the monofunctional monomer 4-HBA and the bifunctional monomer HDDA, the plasticizer is DEDB, the surfactant is POE, the photoinitiator is I819, the inhibitor is hydroquinone, and the light absorber is Sudan Orange G;

[0012] The preparation method of the composite material is as follows: First, mix the monofunctional monomer 4-HBA, the bifunctional monomer HDDA, the plasticizer DEDB, and the surfactant POE, then add nano-silica powder thereto. After mixing evenly, add the photoinitiator I819, the inhibitor hydroquinone, and the light absorber Sudan Orange G respectively to obtain the composite material.

[0013] Preferably, the preparation method of the composite material is as follows: First, mix the monofunctional monomer 4-HBA, the bifunctional monomer HDDA, the plasticizer DEDB, and the surfactant POE according to a volume fraction ratio of 6:1:2:1, then add nano-silica powder thereto in portions, and the single addition amount is 2 wt% of the total addition amount. After mixing evenly, add 0.2 wt% of the photoinitiator I819, 0.1 wt% of the inhibitor hydroquinone, and 0.05 wt% of the light absorber Sudan Orange G based on the total mass of the polymer monomer to obtain the composite material.

[0014] According to the preferred solution of the present invention, in step 2), the energy density is the product of the light intensity and the exposure time.

[0015] According to a preferred embodiment of the present invention, step 2) is specifically as follows: Add the prepared composite material to the material table, input a specific energy density. After the exposure is completed, shovel out the cured layer and use a cleaning agent to clean the uncured material on the surface, measure the curing depth using a micrometer and record it; Keep the light intensity unchanged and change the exposure time, repeat multiple groups of experiments to obtain the curing depth data under different energy densities. Finally, fit the energy density-curing depth curve according to the Jacobs working curve to determine the critical energy density. and the penetration depth ; The critical energy density refers to the minimum energy density threshold required for the material to start gelation, and the penetration depth refers to the depth corresponding to when the energy density decays to 1 / e of the initial energy density on the material surface.

[0016] According to a preferred embodiment of the present invention, in step 4), calculating the energy density difference received by the upper and lower surfaces of a single cured layer is specifically as follows:

[0017] Let the slice layer thickness be L t , calculate the energy density difference received by the upper and lower surfaces of a single cured layer when the slice layer thickness is L t , that is , where , respectively represent the energy densities of the lower and upper surfaces of a single cured layer; The slice layer thickness L t and the penetration depth are known parameters, and the specific energy density difference is obtained according to the energy density .

[0018] According to a preferred embodiment of the present invention, in step 4), the principle that the monomer conversion rate of most of the material in a single cured layer from bottom to top reaches the conversion rate threshold and the monomer conversion rate of a small part of the material in the upper layer is lower than the conversion rate threshold is specifically as follows: In a single cured layer, the monomer conversion rate of a% of the material from bottom to top reaches the conversion rate threshold; The monomer conversion rate of the remaining material in the upper layer is lower than the conversion rate threshold;

[0019] That is, when the layer thickness is L t , ensure that the energy density at a% of the area from bottom to top in a single cured layer corresponds to the monomer conversion rate just reaching the conversion rate threshold. Preferably, a% can be taken as 80% - 90%, and more preferably, a% can be taken as 85%.

[0020] Based on this, the method for selecting the optimal energy density is: Determine the monomer conversion rate threshold α max and the energy density E max corresponding to just reaching the threshold according to the energy density - monomer conversion rate curve, so that , where the slice layer thickness Lt and penetration depth are known parameters, a is a specific selected value, and the selection range is 80-90, and the most preferred value is 85; the calculated is the optimal energy density.

[0021] Compared with the prior art, a method for selecting the ultraviolet light energy density in the additive manufacturing of quartz glass proposed by the present invention can effectively solve the problems such as the difficulty in determining the optimal energy density and the unclear corresponding relationship between the slice layer thickness and the optimal energy density in the existing photo-curing additive manufacturing process of quartz glass, and the main manifestations are as follows:

[0022] 1) The determination of the optimal energy density effectively improves the interlayer bonding effect and overall uniformity, improves the strength of the printed parts and alleviates the anisotropy of the overall structure performance, reduces the internal stress of the printed parts and sintered parts, reduces the defects inside and on the surface of the sintered parts, improves the surface quality and light transmittance, and realizes the optimization of the forming quality;

[0023] 2) Scientifically and accurately adjusting the energy density for different slice layer thicknesses, and realizing high forming quality under different slice layer thickness requirements on the basis of ensuring successful forming; BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic diagram of the DLP photocuring forming principle; in the figure, 1 - lifting mechanism, 2 - forming platform, 3 - printed part, 4 - composite material, 5 - material table, 6 - ultraviolet light, 7 - digital micromirror device.

[0025] Figure 2 is the structural formula of the compound in the silica photocuring composite material system.

[0026] Figure 3 is a schematic diagram of the change of energy density and monomer conversion rate in a single cured layer.

[0027] Figure 4 is an energy density - curing depth curve graph.

[0028] Figure 5 is an energy density - monomer conversion rate curve graph. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will be further described and explained below in conjunction with the specific embodiments. The embodiments are only examples of the present disclosure and do not delimit the scope of limitation. The technical features of each embodiment of the present invention can be combined correspondingly without conflict.

[0030] Before introducing the energy density selection method of the present invention, the DLP photocuring forming principle and equipment will be described first. As Figure 1As shown in the figure, the DLP stereolithography equipment mainly includes a lifting mechanism 1, a forming platform 2, a printed part 3, a composite material 4, a material table 5, ultraviolet light 6, and a digital micromirror device 7, which are arranged from top to bottom.

[0031] The principle of stereolithography is as follows: Before the stereolithography starts, the silica nanocomposite material 4 to be printed is added to the material table 5. After the material self-levels, the curing parameters are set on the equipment control panel. After the curing parameters are set, the lifting mechanism 1 drives the forming platform 2 to move downward until the bottom surface of the forming platform 2 is at a height of one slice layer thickness from the top surface of the material table 5. The digital micromirror device 7 controls the ultraviolet light 6 to project from bottom to top according to the data of the slice model, ensuring that the shape projected onto the bottom surface of the material table 5 is consistent with the first slice layer. After the first layer is cured, the forming platform 2 slowly moves upward a certain distance and stays for a certain time with the lifting mechanism 1 to separate the single cured layer from the material table 5. After the material on the material table 5 self-levels, the lifting mechanism 1 drives the forming platform 2 to move downward again, and the corresponding number of layers are cured, combined, and separated according to the corresponding slice parameters, finally realizing the curing and forming of the target structure, that is, the printed part 3. During the stereolithography process, the motion mechanism only includes the lifting mechanism 1 and the forming platform 2, and the rest of the mechanisms remain stationary.

[0032] In the method of the present invention, the optimal energy density selection method under a preset composite material formula is studied. Therefore, during the implementation of the method of the present invention, the silica nanocomposite material formula is known and has been given. It should be noted that the silica nanocomposite material formula is not limited to the formula given in the embodiments of the present invention. From the implementation process of the present invention, it can be seen that the method of the present invention is applicable to the selection of the optimal energy density in the DLP stereolithography of any silica nanocomposite material. Therefore, the present invention does not make specific requirements for the silica nanocomposite material formula.

[0033] Typical but not limiting, the embodiment provides a silica photocurable composite material formula system, and the chemical compound structural formulas involved in the formula system are as Figure 2As shown, it mainly includes 4-hydroxybutyl acrylate (4-HBA), 1,6-hexanediol diacrylate (HDDA), diethylene glycol dibenzoate (DEDB), phenoxyethanol (POE), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (I819), hydroquinone (Hyd), and Sudan Orange G (SOG). 4-HBA is a monofunctional monomer, and HDDA is a bifunctional monomer. Both are the main bodies of the photocuring reaction and form a tight crosslinked network after the reaction; DEDB is mainly a plasticizer in the material system, improving the flexibility and ductility of the printed parts and reducing the brittleness of the structure; POE is a surfactant in the material system, improving the fluidity and printability of the composite material system; I819 is a photoinitiator in the material system, initiating the photocuring reaction under the irradiation of 405 nm ultraviolet light; hydroquinone is a stabilizer in the system, ensuring the stability of each property of the material after standing; Sudan Orange G is a light absorber in the system, which can effectively control the over-curing phenomenon and improve the printing accuracy of the Z-axis.

[0034] Under the excitation of the incident ultraviolet light, the photoinitiator I819 absorbs light energy and undergoes a cleavage reaction to generate highly active free radicals. These free radicals can rapidly undergo an addition reaction with the unsaturated monomers 4-HBA and HDDA containing carbon-carbon double bonds in the system, initiating the free radical polymerization process. The polymerization chain continuously extends to other monomers under the guidance of free radicals, forming linear or branched polymerization chains. When two free radicals meet, a chain termination reaction occurs, thus ending the chain growth process. Since both 4-HBA and HDDA have functional groups, the polymerization reaction is not only linear growth but also accompanied by a large number of crosslinking reactions. The uneven distribution and different reaction activities of different monomers in space make the polymerization process show randomness and local denseness. As the reaction proceeds, the monomers are connected to each other through covalent bonds, gradually constructing a three-dimensional crosslinked network structure, transforming the material from a liquid state to a solid state, and forming a dense printed part with good mechanical properties. The hydroxyl groups on both sides of POE and the hydroxyl group at the end of 4-HBA can form a dissolution layer by hydrogen bonding with the silanol groups on the surface of the nano-silica powder, reducing the increase in viscosity caused by the agglomeration of nano-powders and the impact on the fluidity of the composite material, and improving the printability of the material.

[0035] The following combines the attached Figures 3 to 5 Elaborate on the principle of the energy density selection method of the present invention, where Figures 3 to 5 are respectively the schematic diagram of the change in energy density and monomer conversion rate in a single curing layer (the thickness is the slice layer thickness L t ), the energy density-curing depth curve, and the energy density-monomer conversion rate curve.

[0036] When ultraviolet light propagates inside the composite material during the DLP stereolithography process, significant attenuation will occur, and its intensity decreases exponentially with the increase of the penetration depth. This process can be described by the Beer-Lambert law, as shown in Equation (1).

[0037] (1)

[0038] In the formula: represents the energy density when light propagates to depth z in the material; (mJ / cm 2 ) is the initial energy density of the incident ultraviolet light on the material surface, which is the product of the light intensity I (mW / cm 2 ) and the exposure time t (s); is the absorption coefficient of the material for light of this wavelength, which usually depends on the composition, structure of the material and the wavelength of the ultraviolet light; z is the propagation depth of light in the material. Based on the Beer-Lambert law and combined with the curing threshold characteristics of the photocuring material, Jacobs proposed an empirical model describing the relationship between the curing depth of the material and the energy density during the photocuring process, which is called the Jacobs working curve, as shown in Equation (2).

[0039] (2)

[0040] In the formula: represents the curing depth reached by the material under specific exposure conditions; is the penetration depth of light, that is, the depth corresponding to the energy density decaying to 1 / e of the initial energy density on the material surface, defined as , so Equation (1) can also be expressed as ; represents the critical energy density required for the material to undergo a curing reaction, that is, the minimum energy density threshold required for the material to start gelation.

[0041] Based on the energy density-curing depth curve and the energy density-monomer conversion rate curve obtained from experimental data testing, as shown in Figure 4 and Figure 5 respectively, it is first assumed that point M corresponds to the optimal energy density, point K corresponds to a low energy density, that is, the monomer conversion rate corresponding to the energy density on the lower surface of the single cured layer is lower than the threshold of the monomer conversion rate, and point N corresponds to a high energy density, that is, the monomer conversion rate corresponding to the energy density on the upper surface of the single cured layer reaches the threshold of the monomer conversion rate, where the threshold of the monomer conversion rate corresponds to Figure 5 the maximum conversion rate α max in. According to Figure 4 and Figure 5, the energy density of the lower surface of the material corresponding to point K is E K , the curing depth is h K , during the photocuring process, when Figure 1 the forming platform 2 in K moves to a distance of one slice layer thickness from the bottom of the material table 5, the ultraviolet light 6 projects onto the lower surface of the material according to the set energy density E K’ , according to the Beer-Lambert law, the light attenuates significantly during propagation inside the material, and the energy density of the light when it reaches the upper surface of the cured layer is E K , the monomer conversion rates corresponding to the energy densities obtained on the lower and upper surfaces of the material are α K’ and α Figure 3 as shown. The monomer conversion rate reflects the degree of completion of the polymerization reaction. A high conversion rate usually means a denser cured crosslinked network structure and fewer remaining uncured monomers, which helps to improve the mechanical properties and dimensional accuracy of the material. The monomer conversion rate thresholds are not reached on both the upper and lower surfaces of the material corresponding to point K, the curing degree of the single-layer material is insufficient, and the density of the crosslinked network is insufficient. The overall mechanical strength of the printed part obtained based on this energy density is insufficient.

[0042] According to Figure 4 and Figure 5 , the energy density of the lower surface of the material corresponding to point N is E N , the curing depth is h N , the light attenuates after passing through the material, and the energy density obtained on the upper surface of the material is E N’ , the monomer conversion rates corresponding to the energy densities obtained on the lower and upper surfaces of the material are α N and α N’ as shown. Figure 3 The monomer conversion rates on both the upper and lower surfaces of the material corresponding to point N have reached the conversion rate thresholds. The overall conversion rate of the single-layer material is too high and the strength is too large. During the forming process of photocuring layer-by-layer stacking, a small part of the material that is not fully converted (i.e., does not reach the monomer conversion rate threshold) on the upper surface of the newly cured layer must act as an adhesive to ensure that this cured layer can be effectively bonded to the already cured layer. The high monomer conversion rate on the upper surface of the material corresponding to point N affects the bonding effect between adjacent cured layers, and the poor interlayer bonding effect easily leads to the detachment of the cured layer and printing failure.

[0043] According to Figure 4 and Figure 5 , the energy density of the lower surface of the material corresponding to point M is E M , the curing depth is h M , according to the Beer-Lambert law, the light attenuates significantly during propagation inside the material, and the energy density of the light when it reaches the upper surface of the cured layer is E M’, the monomer conversion rates corresponding to the energy densities obtained on the lower and upper surfaces of the material are α M and α M’ , as Figure 3 shown, where the lower half includes that the monomer conversion rate of the lower surface reaches the threshold value of the monomer conversion rate of the material, the overall crosslinked network is relatively dense, and there is a small part of the material on the upper surface that is not completely converted, which can act as an adhesive to improve the interlayer bonding effect between adjacent cured layers, ensure the smooth progress of the printing process, and improve the mechanical strength and mechanical properties of the structure. In summary, the energy density E M is the optimal energy density, and the optimal energy density can be selected based on the principle that the monomer conversion rate of most of the material from bottom to top in a single cured layer reaches the conversion rate threshold, and the monomer conversion rate of a small part of the material in the upper layer is lower than the conversion rate threshold. Based on the above analysis and further research of the present invention, it is obtained that when the monomer conversion rate of the material in the 80%-90% (preferably 85%) area from bottom to top in a single cured layer reaches the conversion rate threshold, and the monomer conversion rate of the remaining area in the upper layer (i.e., the 10%-20% area in the upper layer) is lower than the conversion rate threshold, the interlayer bonding effect between adjacent cured layers is relatively ideal. In the subsequent embodiments, in order to optimize the interlayer bonding effect between the cured layers, the principle that the monomer conversion rate of the material in the 85% area from bottom to top in a single cured layer reaches the conversion rate threshold and the monomer conversion rate of the material in the 15% area in the upper layer is lower than the conversion rate threshold is used to select the optimal energy density.

[0044] Based on the foregoing analysis, the implementation details of each step of a method for selecting the ultraviolet light energy density in the additive manufacturing of quartz glass involved in the present invention are as follows.

[0045] Step 1: Prepare a composite material. 4-HBA, HDDA, DEDB, and POE are uniformly mixed by a magnetic stirrer according to a volume fraction of 6:1:2:1. Then, nano-silica powder is added to the mixed monomer solution in portions. The total addition amount of the powder accounts for 55wt% of the total mass of the composite material, and the single addition amount is 2wt% of the total addition amount. It is mixed evenly by a suspended mechanical stirrer. Finally, photoinitiator I819 accounting for 0.2wt% of the total mass of the polymer monomer, inhibitor hydroquinone accounting for 0.1wt%, and light absorber Sudan Orange G accounting for 0.05wt% are added in sequence. The suspended mechanical stirrer is used to continue mixing, and a vacuum defoamer is used to eliminate the bubbles introduced into the material. Finally, a uniform silica nanocomposite material is obtained.

[0046] Step 2: Test the curing depth. Add the prepared composite material to the material table 5, input a specific energy density. After the exposure ends, use a silicone spatula to scrape out the cured layer and use a cleaning agent to clean the uncured material on the surface. Use a micrometer to measure the curing depth and record it. Keep the light intensity unchanged and change the exposure time. Repeat multiple groups of experiments to obtain the curing depth data at different energy densities. Finally, fit the energy density-curing depth curve according to the Jacobs working curve to determine the critical energy density and the penetration depth .

[0047] Step 3: Test the monomer conversion rate. Conduct Fourier transform infrared spectroscopy (FTIR) tests on the uniformly mixed nanocomposite material, and record the absorption intensities of the characteristic peaks of the C=C bond and the C=O bond, which are A 01 and A 02 . Conduct FTIR tests on the lower surface of the cured layers obtained at different energy densities in Step 2. Similarly, record the absorption intensities of the characteristic peaks of the C=C bond and the C=O bond, which are A t1 and A t2 . Calculate the monomer conversion rates at different energy densities according to the monomer conversion rate calculation formula and plot the energy density-monomer conversion rate curve

[0048] Step 4: Select the optimal energy density. Here, taking the commonly used slice layer thickness in the photocuring process as an example, according to the material penetration depth fitted in Step 2 and formula (1), it can be obtained that at the optimal energy density point M, the energy density at the 85% area from bottom to top in a single cured layer is ; it can also be obtained that the difference in the energy density received by the upper and lower surfaces is , that is Figure 3 the E M - E M’ in max . Determine the monomer conversion rate threshold α max and the energy density E max corresponding to just reaching the threshold according to the energy density-monomer conversion rate curve, such that , calculate the energy density E M which is the optimal energy density. At this time, the value of the energy density E M satisfies that the monomer conversion rate α M of most (85% area) of the material on the lower surface of a single cured layer reaches the monomer conversion rate threshold α max , while ensuring that the monomer conversion rate α M’ of a small part (15% area) of the material on the upper surface is slightly lower than the threshold α max due to reasons such as ultraviolet light attenuation., acting as an adhesive between adjacent cured layers to enhance the interlayer bonding effect, energy density E M is for the slice layer thickness which is the optimal energy density of the photocured silica nanocomposite at that time.

[0049] During the photocuring forming process, the choice of slice layer thickness has a significant impact on the forming accuracy and forming efficiency. Therefore, the slice layer thickness needs to be adjusted according to the actual process. For different slice layer thicknesses, the corresponding optimal energy density can be selected by referring to the method in step 4, so as to realize the selection of the optimal energy density in the additive manufacturing process. Specifically, for different slice layer thicknesses L t , according to the selection method in step 4, calculate the energy density at the 85% area from bottom to top in a single cured layer as and the energy density difference received by the upper and lower surfaces is , where D p and L t are both known parameters. Determine the monomer conversion threshold α max and the energy density E corresponding to just reaching the threshold max , such that , calculate the energy density E M which is the optimal energy density. At this time, the value of the energy density E M satisfies that the monomer conversion rate α M of most of the material (85% area) on the lower surface of a single cured layer reaches the monomer conversion threshold α max , while ensuring that the monomer conversion rate α M’ of a small part of the material (15% area) on the upper surface is slightly lower than the threshold α max , acting as an adhesive between adjacent cured layers to enhance the interlayer bonding effect, energy density E M is the optimal energy density of the photocured silica nanocomposite when the slice layer thickness is at that time.

[0050] The energy density selection method proposed by the present invention can effectively solve the problems such as the difficulty in determining the optimal energy density and the unclear corresponding relationship between the slice layer thickness and the optimal energy density in the existing photocuring additive manufacturing of quartz glass. It shows great advantages in improving the mechanical strength and crosslinking density of the formed parts, alleviating anisotropy, and reducing internal stress, providing an efficient and reliable solution for the photocuring additive manufacturing of quartz glass.

[0051] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. For those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention.

Claims

1. A method for selecting the ultraviolet light energy density in the additive manufacturing of quartz glass, characterized in that, It includes the following steps: 1) Mix the polymer monomer, plasticizer, surfactant, nano-silica powder, photoinitiator, inhibitor and light absorber evenly according to a preset composite material formula, and degas the prepared composite material under vacuum; 2) Test the curing performance of the composite material according to a fixed light intensity and different exposure times, record the curing depth of the composite material at different energy densities, and draw an energy density - curing depth curve; 3) Perform Fourier transform infrared spectroscopy tests on the composite material before curing and the material after the curing depth test in step 2), record the absorption intensities of the characteristic peaks of C=C bonds and C=O bonds respectively, calculate the monomer conversion rate, and draw an energy density - monomer conversion rate curve; 4) During the additive manufacturing process, for a sliced layer with a certain determined layer thickness, the material layer cured by the printing device in one photo-curing process is the corresponding single-cured layer. Calculate the difference in energy density received by the upper and lower surfaces of the single-cured layer. According to the principle that the monomer conversion rate of the material in most areas from bottom to top within the single-cured layer reaches the conversion rate threshold, and the monomer conversion rate of the material in a small part of the upper area is lower than the conversion rate threshold, select the optimal energy density.

2. The method for selecting the ultraviolet light energy density in the additive manufacturing of fused silica glass according to claim 1, characterized in that In step 1), in the preset composite material formula, the polymer monomer is the monofunctional monomer 4-HBA and the bifunctional monomer HDDA, the plasticizer is DEDB, the surfactant is POE, the photoinitiator is I819, the inhibitor is hydroquinone, and the light absorber is Sudan Orange G; The preparation method of the composite material is as follows: First, mix the monofunctional monomer 4-HBA, bifunctional monomer HDDA, plasticizer DEDB and surfactant POE, then add nano-silica powder thereto. After mixing evenly, add photoinitiator I819, inhibitor hydroquinone and light absorber Sudan Orange G respectively to obtain the composite material.

3. The method for selecting the ultraviolet light energy density in the additive manufacturing of fused silica glass according to claim 1, wherein In step 2), the energy density is the product of the light intensity and the exposure time.

4. The method for selecting the ultraviolet light energy density in the additive manufacturing of fused silica glass according to claim 1, wherein The specific steps of step 2) are as follows: Add the prepared composite material to the material table, input a specific energy density. After the exposure is completed, shovel out the cured layer and use a cleaning agent to clean the uncured material on the surface. Use a micrometer to measure the curing depth and record it. Keep the light intensity unchanged and change the exposure time. Repeat multiple groups of experiments to obtain the curing depth data at different energy densities. Finally, fit the energy density-curing depth curve according to the Jacobs working curve to determine the critical energy density and the penetration depth ; The critical energy density refers to the minimum energy density threshold required for the material to start gelation, and the penetration depth refers to the depth corresponding to when the energy density decays to 1 / e of the initial energy density on the material surface.

5. The method for selecting the ultraviolet light energy density in the additive manufacturing of fused silica glass according to claim 4, characterized in that, The cleaning agent is isopropyl alcohol, phenoxyethanol and water with a volume ratio of 1:1:

1.

6. The method for selecting the ultraviolet light energy density in the additive manufacturing of fused silica glass according to claim 1, characterized in that, In step 3), the calculation formula for the monomer conversion rate is: ； Among them, A 01 and A 02 are the absorption intensities of the characteristic peaks of C=C bonds and C=O bonds in the Fourier transform infrared spectroscopy test of the composite material before curing, respectively; A t1 and A t2 are the absorption intensities of the characteristic peaks of C=C bonds and C=O bonds in the Fourier transform infrared spectroscopy test of the lower surface of the cured layer after the curing depth test, respectively.

7. The method for selecting the ultraviolet light energy density in the additive manufacturing of fused silica glass according to claim 1, wherein In step 4), the calculation of the difference in energy density received by the upper and lower surfaces of the single-cured layer is specifically: Set the slice layer thickness as L t , calculate the difference in energy density received by the upper and lower surfaces of a single cured layer when the slice layer thickness is L t , that is , where 、 represent the energy density of the lower surface and the upper surface of a single cured layer respectively; the slice layer thickness L t and the penetration depth are known parameters, and the specific energy density difference is obtained according to the energy density .

8. The method for selecting the ultraviolet light energy density in the additive manufacturing of fused silica glass according to claim 1, wherein In step 4), the principle that the monomer conversion rate of the material in most areas from bottom to top within the single-cured layer reaches the conversion rate threshold, and the monomer conversion rate of the material in a small part of the upper area is lower than the conversion rate threshold is specifically: the monomer conversion rate of the material in a% area from bottom to top within the single-cured layer reaches the conversion rate threshold; the monomer conversion rate of the material in the remaining upper area is lower than the conversion rate threshold; the a% is 80% - 90%; That is, when the layer thickness is L t Ensure that the energy density at the a% area from bottom to top within a single cured layer corresponds to a monomer conversion rate that just reaches the conversion rate threshold.

9. The method for selecting the ultraviolet light energy density in the additive manufacturing of fused silica glass according to claim 8, wherein In step 4), the method for selecting the optimal energy density is as follows: determine the monomer conversion threshold α according to the energy density - monomer conversion rate curve max and the energy density E corresponding to just reaching the threshold max , such that , where the slice layer thickness L t and the penetration depth D p are known parameters, a is a specific value selected, and the selection range is 80 - 90; the calculated E M is the optimal energy density.

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