A method for selecting ultraviolet light energy density in quartz glass additive manufacturing

Abstract

The present invention discloses a method for selecting ultraviolet light energy density in quartz glass additive manufacturing. The method first performs a curing test on a preset composite material formula to obtain an energy density-curing depth curve and an energy density-monomer conversion rate curve; for a selected slice layer thickness, the energy density difference received by the upper and lower surfaces of the single cured layer is calculated, and the optimal energy density is selected according to the principle that the monomer conversion rate of the material in the most area from bottom to top in 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. By selecting the optimal energy density, the present invention can effectively improve the interlayer bonding effect and overall uniformity, improve the strength of the printed part and alleviate the anisotropy of the overall structural performance, reduce the internal stress of the printed part and the sintered part, reduce the defects inside and on the surface of the sintered part, improve the surface quality and light transmittance, and achieve the optimization of the molding quality.

Description

Technical Field

[0001] The present invention belongs to the field of silicon oxide photocuring composite material additive manufacturing, and in particular relates to a method for selecting ultraviolet light energy density in quartz glass additive manufacturing. 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 and high-temperature resistance, and electrical insulation. With the rapid development of additive manufacturing technology, the difficulties faced in processing micro-glass components with complex geometries, such as high melting point, high brittleness, and low molding quality, have been effectively addressed. There are many types of existing quartz glass additive manufacturing technologies, mainly including Laser Powder Bed Fusion (LPBF), light-curing-based technologies including stereolithography (SLA), Digital Light Processing (DLP) and Two-photon Polymerization (2PP), and material extrusion-based technologies including Directed Energy Deposition (DED), Direct Ink Writing (DIW) and Fused Deposition Modeling (FDM). Among them, Digital Light Processing (DLP) technology has become a hot spot in the current research of quartz glass additive manufacturing technology due to its high molding precision, fast molding speed, low cost and high surface quality, and is widely used in the fields of optics and microfluidics.

[0003] DLP photocuring technology obtains the target component by stacking printing layers of fixed thickness layer by layer. This process has high requirements on the rheological properties and curing properties of liquid composite materials. In order to obtain photocured prints and quartz glass sintered parts with excellent overall performance, the adjacent cured layers must have good interlayer bonding quality. The energy density of ultraviolet light is a key parameter affecting the monomer conversion rate and curing depth of the material, which in turn 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 silicon oxide composite materials: 1) The optimal energy density is difficult to determine, which leads to uncontrollable monomer conversion rate in the cured layer. Excessive energy density leads to an overall high conversion rate and high strength of the single layer, weakened interlayer bonding between adjacent layers, increased stress in the cured layer, and easy phenomenon of reduced overall strength of the printed part or molding failure, more defects inside the sintered part or cracking due to excessive stress, anisotropy of the overall performance of the structure, etc.; too low energy density leads to low single layer conversion rate and low strength, insufficient overall mechanical strength of the printed part, reduced surface quality of the sintered part, and significantly reduced light transmittance; 2) The correspondence between different slice layer thicknesses and the optimal energy density is unclear. Since it is difficult to achieve the optimal molding efficiency and molding accuracy at the same time, the slice layer thickness often needs to be adjusted according to actual needs, and its corresponding optimal energy density also needs to be adjusted. Most of the existing adjustment methods rely on process experience and are not accurate. Multiple photocuring experiments at different energy densities are required and the molding effect must be observed by the naked eye. There is a lack of an efficient, systematic and scientific adjustment method to determine the correspondence between slice layer thickness and optimal energy density. Summary of the Invention

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

[0005] The technical solutions of the present invention are as follows:

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

[0007] 1) According to the preset composite material formula, the polymer monomer, plasticizer, surfactant, nano-silica powder, photoinitiator, polymerization inhibitor and light absorber are mixed evenly, and the prepared composite material is vacuum defoamed;

[0008] 2) According to the fixed light intensity (unit: mW / cm 2 ) and different exposure times (unit s) to test the curing performance of the composite material, and record the curing performance of the composite material at different energy densities (unit mJ / cm 2 ) and plotted as a graph of energy density-curing depth;

[0009] 3) Performing Fourier transform infrared spectroscopy on the composite material before curing and the material after the curing depth test in step 2), recording the absorption intensities of the C=C bond characteristic peak and the C=O bond characteristic peak, calculating the monomer conversion rate, and plotting an energy density-monomer conversion rate curve;

[0010] 4) During the additive manufacturing process, for a slice layer of a predetermined thickness, the material layer cured by the printing device during a single photocuring process corresponds to the corresponding single cured layer. The difference in energy density received by the upper and lower surfaces of the single cured layer is calculated. The optimal energy density is selected based on the principle that the monomer conversion rate of the material in the majority of the area from bottom to top within the single cured layer reaches the conversion rate threshold, while the monomer conversion rate of the material in a small area of ​​the upper layer is lower than the conversion rate threshold.

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

[0012] The composite material is prepared by mixing a monofunctional monomer 4-HBA, a difunctional monomer HDDA, a plasticizer DEDB, and a surfactant POE, then adding nano-silica powder thereto, and after mixing evenly, adding a photoinitiator I819, an inhibitor hydroquinone, and a light absorber Sudan Orange G, respectively, to obtain the composite material.

[0013] Preferably, the composite material is prepared as follows: first, the monofunctional monomer 4-HBA, the difunctional monomer HDDA, the plasticizer DEDB and the surfactant POE are mixed in a volume fraction ratio of 6:1:2:1, and then the nano-silica powder is added thereto in portions, with a single addition amount of 2wt% of the total addition amount. After mixing evenly, 0.2wt% of the photoinitiator I819, 0.1wt% of the polymerization inhibitor hydroquinone and 0.05wt% of the light absorber Sudan Orange G are added to the total mass of the polymer monomer to obtain the composite material.

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

[0015] According to a preferred embodiment of the present invention, step 2) is specifically as follows: adding the prepared composite material to the material table, inputting a specific energy density, after the exposure is completed, shoveling out the cured layer and using a cleaning agent to clean the uncured material on the surface, using a screw micrometer to measure and record the curing depth; keeping the light intensity constant and changing the exposure time, repeating multiple groups of experiments to obtain curing depth data under different energy densities, and finally fitting the energy density-curing depth curve according to the Jacobs working curve to determine the critical energy density. and penetration depth ; The critical energy density refers to the minimum energy density threshold required for the material to begin 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), the energy density difference received by the upper and lower surfaces of the single solidified layer is calculated as follows:

[0017] Assume the slice thickness is L t , calculated when the slice thickness is L t The energy density difference between the upper and lower surfaces of the single solidified layer is: ,in, 、 Represent the energy density of the lower and upper surfaces of a single solidified layer respectively; the slice thickness L t and penetration depth is a known parameter, according to the energy density Get the specific energy density difference.

[0018] According to a preferred embodiment of the present invention, in step 4), the monomer conversion rate of the material in the majority of the regions from bottom to top within the single solidified layer reaches the conversion rate threshold, and the monomer conversion rate of the material in a small portion of the upper region is lower than the conversion rate threshold. Specifically, the monomer conversion rate of the material in a% of the region from bottom to top within the single solidified layer reaches the conversion rate threshold; and the monomer conversion rate of the material in the remaining region of the upper layer is lower than the conversion rate threshold.

[0019] That is, when the layer thickness is L t When the energy density of a% area from bottom to top in a single solidified layer is ensured The corresponding monomer conversion rate just reaches the conversion rate threshold. Preferably, the a% can be 80% to 90%, and more preferably, a% can be 85%.

[0020] Based on this, the method for selecting the optimal energy density is: determine the monomer conversion rate threshold α according to the energy density-monomer conversion rate curve max And the energy density E corresponding to the threshold value max , making , where the slice thickness Lt and penetration depth is a known parameter, a is a specific value selected, the selection range is 80~90, and the most preferred value is 85; the calculated This is the optimal energy density.

[0021] Compared with the existing technology, the method for selecting ultraviolet light energy density in quartz glass additive manufacturing proposed in this invention can effectively solve the problems of the difficulty in determining the optimal energy density in the existing quartz glass photocuring additive manufacturing process and the unclear correspondence between the slice thickness and the optimal energy density. The main performance is as follows:

[0022] 1) Determining the optimal energy density effectively improves interlayer bonding and overall uniformity, increases the strength of printed parts, alleviates the anisotropy of the overall structural performance, reduces internal stress in printed and sintered parts, reduces defects inside and on the surface of sintered parts, improves surface quality and light transmittance, and achieves optimal molding quality.

[0023] 2) Scientifically and accurately adjust the energy density for different slice layer thicknesses, ensuring successful molding and achieving high molding quality under different slice layer thickness requirements; BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 It is the structural formula of the compound in the silicon oxide photocurable composite material system.

[0026] Figure 3 Schematic diagram of the changes in energy density and monomer conversion rate in a single solidified layer.

[0027] Figure 4 This is the energy density-curing depth curve.

[0028] Figure 5 This is the energy density-monomer conversion rate curve. DETAILED DESCRIPTION

[0029] The present invention will be further described and illustrated below in conjunction with specific embodiments. The embodiments are merely illustrative of the present disclosure and do not limit its scope. The technical features of the various embodiments of the present invention may be combined accordingly, provided that there is no conflict between them.

[0030] Before introducing the energy density selection method of the present invention, the principle and equipment of DLP photo-curing molding are first explained. Figure 1As shown, the DLP light-curing molding equipment mainly includes a lifting mechanism 1, a molding platform 2, a printing part 3, a composite material 4, a material table 5, ultraviolet light 6, and a digital micromirror device 7 arranged from top to bottom.

[0031] The principle of photocuring is as follows: Before photocuring begins, the silica nanocomposite material 4 to be printed is placed on the material platform 5. After the material self-levels, the curing parameters are set on the device control panel. After the curing parameters are set, the lifting mechanism 1, along with the building platform 2, moves downward until the bottom of the building platform 2 is one slice layer thick from the top of the material platform 5. The digital micromirror device 7 controls the projection of ultraviolet light 6 from bottom to top according to the slice model data, ensuring that the shape projected onto the bottom of the material platform 5 is consistent with the first slice layer. After the first layer is cured, the building platform 2 slowly moves upward along with the lifting mechanism 1 for a certain distance and remains there for a certain period of time, separating the single cured layer from the material platform 5. After the material on the material platform 5 has self-leveled, the lifting mechanism 1, along with the building platform 2, moves downward again, curing, bonding, and separating the corresponding number of layers according to the corresponding slice parameters, ultimately achieving the desired structure, i.e., the printed part 3. During the photocuring process, the only moving mechanisms are the lifting mechanism 1 and the building platform 2; the rest of the mechanisms remain stationary.

[0032] The method of the present invention studies the method for selecting the optimal energy density under a preset composite material formula. Therefore, during the implementation of the method of the present invention, the silicon oxide nanocomposite material formula is known and has been given. It should be noted that the silicon oxide nanocomposite material formula is not limited to the formula given in the embodiments of the present invention. As can be seen from the implementation process of the present invention, the method of the present invention is applicable to the selection of the optimal energy density in DLP photocuring molding of any silicon oxide nanocomposite material. Therefore, the present invention does not make specific requirements on the silicon oxide nanocomposite material formula.

[0033] Typically but not limiting, the embodiment provides a silicon oxide photocurable composite material formulation system, the compound structure involved in the formulation system is as follows Figure 2As shown, the main components of the photopolymerization system include 4-hydroxybutyl acrylate (4-HBA), 1,6-hexanediol diacrylate (HDDA), diethylene glycol dibenzoate (DEDB), phenoxyethanol (POE), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (I819), hydroquinone (Hyd), and Sudan Orange G (SOG). 4-HBA is a monofunctional monomer, and HDDA is a difunctional monomer. Both are the main components of the photopolymerization reaction, forming a dense cross-linked network after the reaction. DEDB is mainly a plasticizer in the material system, improving the flexibility and ductility of the printed part 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, triggering the photopolymerization reaction under 405nm UV light. Hydroquinone is a stabilizer in the system, ensuring the stability of various material properties after standing. Sudan Orange G is a light absorber in the system, effectively controlling over-curing and improving Z-axis printing accuracy.

[0034] Under the stimulation of incident UV light, photoinitiator I819 absorbs light energy and undergoes a cleavage reaction, generating highly reactive free radicals. These free radicals rapidly undergo addition reactions with the unsaturated monomers 4-HBA and HDDA, which contain carbon-carbon double bonds, in the system, initiating free radical polymerization. Guided by the free radicals, the polymer chain continues to extend toward other monomers, forming linear or branched chains. When two free radicals meet, a chain termination reaction occurs, ending the chain growth process. Because both 4-HBA and HDDA contain functional groups, the polymerization reaction is not merely linear but also accompanied by numerous cross-linking reactions. The uneven spatial distribution and varying reactivity of the different monomers contribute to the randomness and localized density of the polymerization process. As the reaction proceeds, the monomers connect through covalent bonds, gradually building a three-dimensional cross-linked network structure, transforming the material from a liquid to a solid state, resulting in a dense printed part with excellent mechanical properties. The hydroxyl groups on both sides of POE and the hydroxyl groups at the end of 4-HBA can combine with the silanol groups on the surface of nano-silica powder through hydrogen bonds to form a dissolution layer, reducing the effect of increased viscosity due to agglomeration of nano-powder on the fluidity of the composite material and improving the printability of the material.

[0035] The following is combined with Figures 3 to 5 The principle of the energy density selection method of the present invention is explained, wherein Figures 3 to 5 They are respectively in a single solidified layer (thickness is slice layer thickness L t ) Schematic diagram of energy density and monomer conversion rate changes, energy density-curing depth curve and energy density-monomer conversion rate curve.

[0036] During the DLP stereolithography process, UV light undergoes significant attenuation as it propagates within the composite material, with its intensity decreasing exponentially with increasing penetration depth. This process can be described by the Beer-Lambert law, as shown in Equation (1).

[0037] (1)

[0038] Where: Represents the energy density of light when it propagates to depth z in the material; (mJ / cm 2 ) is the initial energy density of the incident ultraviolet light on the surface of the material, and is the light intensity I (mW / cm 2 ) and the product of exposure time t (s); is the absorption coefficient of the material for the wavelength of light, which usually depends on the composition, structure and wavelength of the material; 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 photocurable material, Jacobs proposed a method to describe the curing depth of the material during the photocuring process. and energy density The empirical model of the relationship between is called the Jacobs working curve, as shown in formula (2).

[0039] (2)

[0040] Where: Represents the depth of cure achieved by a material under specific exposure conditions; The penetration depth of light, that is, the depth at which the energy density decays to 1 / e of the initial energy density on the surface of the material, is defined as , so formula (1) can also be expressed as ; It 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 begin gelation.

[0041] The energy density-curing depth curve and energy density-monomer conversion rate curve obtained based on experimental data are as follows: Figure 4 and Figure 5 As shown, it is first assumed that point M corresponds to the optimal energy density, point K corresponds to low energy density, that is, the monomer conversion rate corresponding to the energy density on the lower surface of the single solidified layer is lower than the threshold value of the monomer conversion rate, and point N corresponds to high energy density, that is, the monomer conversion rate corresponding to the energy density on the upper surface of the single solidified layer reaches the threshold value of the monomer conversion rate, where the threshold value of the monomer conversion rate corresponds to Figure 5 The maximum conversion rate α max .according to Figure 4 and Figure 5, the energy density of the material surface corresponding to point K is E K , the curing depth is h K , during the light curing process, when Figure 1 When the forming platform 2 moves to a distance of one slice layer thickness from the bottom of the material table 5, the ultraviolet light 6 is set according to the energy density E K When projected onto the lower surface of the material, according to the Beer-Lambert law, light propagates inside the material and exhibits significant attenuation. The energy density of light when it reaches the upper surface of the solidified 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 With α K’ ,like Figure 3 The monomer conversion rate reflects the completeness of the polymerization reaction. A high conversion rate generally means a denser cured cross-linked network structure and less residual uncured monomer, which helps improve the material's mechanical properties and dimensional accuracy. The K point corresponds to a point where both the upper and lower surfaces of the material do not reach the monomer conversion threshold. This indicates that the single layer of material is not fully cured, the cross-linked network is not dense enough, and the overall mechanical strength of the printed part obtained at this energy density is insufficient.

[0042] according to Figure 4 and Figure 5 , the energy density of the material surface corresponding to point N is E N , the curing depth is h N , light attenuates after passing through the material, and the energy density obtained on the 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 With α N’ ,like Figure 3 As shown. The monomer conversion rates on the upper and lower surfaces of the material corresponding to point N have both reached the conversion rate threshold. The overall conversion rate of the single-layer material is too high, and the strength is too large. During the layer-by-layer stacking process of photocuring, a small amount of incompletely converted (i.e., material that has not reached the monomer conversion rate threshold) material on the upper surface of the newly cured layer must act as an adhesive to ensure that the cured layer can effectively bond 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. Poor interlayer bonding can easily lead to the cured layer falling off, resulting in 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, light propagates inside the material and shows obvious attenuation. The energy density of light when it reaches the upper surface of the solidified 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 With α M’ ,like Figure 3 As shown, the monomer conversion rate of the lower half including the lower surface reaches the threshold of the monomer conversion rate of the material, the overall cross-linking network is relatively dense, and a small part of the incompletely converted material exists on the upper surface of the layer, which can act as an adhesive to improve the interlayer bonding effect between adjacent solidified layers, ensuring the smooth progress of the printing process while improving the mechanical strength and mechanical properties of the structure. In summary, the energy density E M The optimal energy density can be selected based on the principle that the monomer conversion rate of the material in the majority of the upper regions within a single solidified layer reaches the conversion rate threshold, while the monomer conversion rate of the material in a small portion of the upper region is below the conversion rate threshold. Based on the above analysis and further research in the present invention, it was determined that when the monomer conversion rate of the material in 80%-90% (preferably 85%) of the upper region within a single solidified layer reaches the conversion rate threshold, and the monomer conversion rate of the material in the remaining upper region (i.e., the upper 10%-20%) is below the conversion rate threshold, the interlayer bonding effect between adjacent solidified layers is more ideal. In subsequent embodiments, to optimize the interlayer bonding effect between solidified layers, the optimal energy density is selected based on the principle that the monomer conversion rate of the material in 85% of the upper region within a single solidified layer reaches the conversion rate threshold, while the monomer conversion rate of the material in the upper 15% is below the conversion rate threshold.

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

[0045] Step 1: Prepare a composite material. 4-HBA, HDDA, DEDB, and POE were uniformly mixed using a magnetic stirrer at a volume fraction of 6:1:2:1. Nano-silica powder was then added to the mixed monomer solution in portions, with the total amount of powder added accounting for 55wt% of the total mass of the composite material, and the single addition amount was 2wt% of the total amount. The mixture was uniformly mixed using a suspended mechanical stirrer. Finally, 0.2wt% of the photoinitiator I819, 0.1wt% of the polymerization inhibitor hydroquinone, and 0.05wt% of the light absorber Sudan Orange G were added in sequence, accounting for the total mass of the polymer monomers. Mixing was continued using a suspended mechanical stirrer, and bubbles introduced into the material were eliminated using a vacuum defoamer to obtain a uniform silica nanocomposite material.

[0046] Step 2: Test the curing depth. Add the prepared composite material to the material table 5 and input a specific energy density. After the exposure is completed, 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 screw micrometer to measure the curing depth and record it. Keep the light intensity constant and change the exposure time. Repeat multiple sets of experiments to obtain the curing depth data under different energy densities. Finally, according to the Jacobs working curve, fit the energy density-curing depth curve to determine the critical energy density. and penetration depth .

[0047] Step 3: Test the monomer conversion rate. Perform Fourier transform infrared spectroscopy on the nanocomposite material after mixing evenly, and record the absorption intensity of the C=C bond characteristic peak and the C=O bond characteristic peak, which are A 01 and A 02 The lower surface of the solidified layer obtained in step 2 under different energy densities was tested by Fourier transform infrared spectroscopy, and the absorption intensities of the characteristic peaks of C=C bond and C=O bond were also recorded, which were A t1 and A t2 According to the monomer conversion calculation formula The monomer conversion rate under different energy densities was calculated and an energy density-monomer conversion rate curve was drawn.

[0048] Step 4: Select the optimal energy density. Here we use the slice thickness commonly used in the light curing process. As an example, the material penetration depth obtained by fitting in step 2 is According to formula (1), at the optimal energy density point M, the energy density at 85% of the area from bottom to top in the single solidified layer is: ; It can also be concluded that the difference in energy density received by the upper and lower surfaces is ,Right now Figure 3 E in M -E M’ Determine the monomer conversion rate threshold α based on the energy density-monomer conversion rate curve max And the energy density E corresponding to the threshold value max , making , calculate the energy density E M This is the optimal energy density. At this time, the energy density E M The value of satisfies the monomer conversion rate α of most (85% area) materials on the lower surface of the single solidified layer M Reaching the monomer conversion rate threshold α max At the same time, ensure that the monomer conversion rate of a small part (15% area) of the upper surface material is α due to ultraviolet light attenuation and other reasons. M’ Slightly below the threshold α max, acts as an adhesive between adjacent solidified layers to improve the interlayer bonding effect, energy density E M That is, the slice thickness Optimal energy density for photocuring of silica nanocomposites.

[0049] In the process of stereolithography, the selection of slice layer thickness has a significant impact on the molding accuracy and molding efficiency, so the slice layer thickness needs to be adjusted according to the actual process. For different slice layer thicknesses, the method in step 4 can be used to select the corresponding optimal energy density, thereby achieving 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, the energy density at 85% of the area from bottom to top in the single solidified layer is calculated as The difference in energy density received by the upper and lower surfaces is , where D p and L t All of them are known parameters. The monomer conversion rate threshold α is determined according to the energy density-monomer conversion rate curve. max And the energy density E corresponding to the threshold value max , making , calculate the energy density E M This is the optimal energy density. At this time, the energy density E M The value of satisfies the monomer conversion rate α of most (85% area) materials on the lower surface of the single solidified layer M Reaching the monomer conversion rate threshold α max At the same time, ensure that the monomer conversion rate of a small part (15% area) of the upper surface material is α due to ultraviolet light attenuation and other reasons. M’ Slightly below the threshold α max , acts as an adhesive between adjacent solidified layers to improve the interlayer bonding effect, energy density E M That is, for slice thickness Optimal energy density for photocuring of silica nanocomposites.

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

[0051] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. Persons skilled in the art will readily appreciate that variations and modifications may be made without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A method for selecting ultraviolet light energy density in quartz glass additive manufacturing, characterized in that: The following steps are involved: 1) According to the preset composite material formula, the polymer monomer, plasticizer, surfactant, nano-silica powder, photoinitiator, polymerization inhibitor and light absorber are mixed evenly, and the prepared composite material is vacuum defoamed; 2) Test the curing performance of the composite material at a fixed light intensity and different exposure times, record the curing depth of the composite material at different energy densities, and plot an energy density-curing depth curve; 3) Performing Fourier transform infrared spectroscopy on the composite material before curing and the material after the curing depth test in step 2), recording the absorption intensities of the C=C bond characteristic peak and the C=O bond characteristic peak, calculating the monomer conversion rate, and plotting an energy density-monomer conversion rate curve; 4) During the additive manufacturing process, for a slice layer of a predetermined thickness, the material layer cured by the printing device during a single photocuring process corresponds to the corresponding single cured layer. The difference in energy density received by the upper and lower surfaces of the single cured layer is calculated. The optimal energy density is selected based on the principle that the monomer conversion rate of the material in the majority of the area from bottom to top within the single cured layer reaches the conversion rate threshold, while the monomer conversion rate of the material in a small area of ​​the upper layer is lower than the conversion rate threshold.

2. The method for selecting ultraviolet light energy density in quartz glass additive manufacturing according to claim 1, characterized in that: In step 1), in the preset composite material formula, the polymer monomers are the monofunctional monomer 4-HBA and the difunctional 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 composite material is prepared by mixing a monofunctional monomer 4-HBA, a difunctional monomer HDDA, a plasticizer DEDB, and a surfactant POE, then adding nano-silica powder thereto, and after mixing evenly, adding a photoinitiator I819, an inhibitor hydroquinone, and a light absorber Sudan Orange G, respectively, to obtain the composite material.

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

4. The method for selecting ultraviolet light energy density in quartz glass additive manufacturing according to claim 1, characterized in that: The step 2) is specifically as follows: adding the prepared composite material to the material table, inputting a specific energy density, after the exposure is completed, scraping out the cured layer and using a cleaning agent to clean the uncured material on the surface, using a screw micrometer to measure and record the curing depth; keeping the light intensity constant and changing the exposure time, repeating multiple groups of experiments to obtain curing depth data under different energy densities, and finally fitting the energy density-curing depth curve according to the Jacobs working curve to determine the critical energy density. and penetration depth ; The critical energy density refers to the minimum energy density threshold required for the material to begin 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 ultraviolet light energy density in quartz glass additive manufacturing according to claim 4, characterized in that: The cleaning agent is isopropyl alcohol, phenoxyethanol and water in a volume ratio of 1:1:

1.

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

7. The method for selecting ultraviolet light energy density in quartz glass additive manufacturing according to claim 4, characterized in that: In step 4), the energy density difference received by the upper and lower surfaces of the single solidified layer is calculated as follows: Assume the slice thickness is L t , calculated when the slice thickness is L t The energy density difference between the upper and lower surfaces of the single solidified layer is: ,in, 、 Represent the energy density of the lower and upper surfaces of a single solidified layer respectively; the slice thickness L t and penetration depth is a known parameter, according to the energy density Get the specific energy density difference.

8. The method for selecting ultraviolet light energy density in quartz glass additive manufacturing according to claim 7, characterized in that: In step 4), the monomer conversion rate of the material in the majority of the regions from bottom to top in the single solidified layer reaches the conversion rate threshold, while the monomer conversion rate of the material in a small portion of the upper region is lower than the conversion rate threshold. Specifically, the monomer conversion rate of the material in a region of a% from bottom to top in the single solidified layer reaches the conversion rate threshold; the monomer conversion rate of the material in the remaining region of the upper layer is lower than the conversion rate threshold; the a% is 80% to 90%; That is, when the layer thickness is L t When the energy density of a% area from bottom to top in a single solidified layer is ensured The corresponding monomer conversion rate just reaches the conversion rate threshold.

9. The method for selecting ultraviolet light energy density in quartz glass additive manufacturing according to claim 8, characterized in that: In step 4), the method for selecting the optimal energy density is: determine the monomer conversion rate threshold α according to the energy density-monomer conversion rate curve max And the energy density E corresponding to the threshold value max , making , where the slice thickness L t and penetration depth D p is a known parameter, a is a selected specific value, and the selection range is 80~90; the calculated E M This is the optimal energy density.

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