Powder 3D printing lightweight high-precision magnesium phosphate cement-based material and preparation method thereof

Abstract

The invention relates to a powder 3D printing lightweight high-precision magnesium phosphate cement-based material and a preparation method thereof. The performance of magnesium phosphate cement is optimized by adopting fly ash floating beads extracted from industrial waste residues. The fly ash floating beads are screened in a stepped manner, a fly ash floating bead particle size distribution system with good grain composition is selected, magnesium phosphate cement is taken as a basic raw material, and the fly ash floating beads with good grain composition are added, so that a ball effect can be generated to improve the flatness of a powder bed, and a filling effect is generated to reduce recesses among hydration products; the temperature stress is absorbed to reduce cracks of a hydration product, a new product is generated through a micro reaction, finally, the apparent density of a concrete test piece is effectively reduced, the forming precision of a 3D printing test piece is improved, meanwhile, good mechanical strength is kept, and the method has wide application in the powder 3D printing technology aspect.

Description

Technical Field

[0001] The present invention relates to the technical field of powder 3D printing cement-based materials, and in particular to a powder 3D printing lightweight and high-precision magnesium phosphate cement-based material and a preparation method thereof. Background Art

[0002] Powder 3D printing technology is a layer-by-layer printing technology first proposed by SACHS et al. of MIT in 1993. It reacts powder materials with liquid materials to form a solid model, which can realize the construction of components from computer models to three-dimensional entities. In recent years, concrete has been widely used as a 3D printing material due to its low cost and rapid solidification. Powder 3D concrete printing has the advantages of fast molding and complex structure molding, and has broad application prospects in the production of cement products. Powder 3D printing technology has the potential to change the status quo of the construction industry, such as increasing the flexibility and functionality of existing building structures, reducing the use of building templates, and reducing construction costs. The technology has shown a relatively broad application prospect in the construction industry.

[0003] The printing material used by the powder 3D printer is composed of powder and binder. The working principle is to evenly lay the powder particles on the forming platform, selectively spray the binder and bond and solidify it, and the printed model is formed layer by layer. Therefore, the interlayer bonding strength of the printing material is required to be high. During printing, the previous layer must have a certain strength when solidifying to support the forming of the next layer, thereby realizing mold-free curing. Therefore, the powder material is required to have the advantages of high bonding strength, rapid hardening and low diffusion.

[0004] At present, gypsum powder is the most widely used material in powder 3D printing technology. For example, Chinese patent CN104230289A mentions a method for preparing gypsum powder 3D printing materials, but gypsum printed products generally have the disadvantages of low printed specimen strength and poor printing accuracy, which seriously limits its application scope; Chinese patent CN118084436A mentions a method for preparing high-toughness and fast-hardening sulphoaluminate cement-based materials. The printed specimens using this method have high strength, but the disadvantage is that the dimensional accuracy of the finished specimens is poor; in contrast, Chinese patent CN112759298A discloses a 3D printing material prepared from magnesium phosphate cement powder with higher compressive strength, but the molded specimens are heavy and the optimal accuracy is only 0.5 mm, requiring performance improvement.

[0005] Lightweighting is an important direction for the performance of concrete materials. By adding lightweight aggregates such as expanded perlite and ceramsite, the weight of the material can be reduced to a certain extent, but the mechanical properties and printing accuracy of the material are greatly affected, which makes lightness, mechanical properties and printing accuracy an irreconcilable contradiction. How to slow down the trend of mechanical properties degradation and improve printing accuracy while maintaining the lightweight of the material is an urgent problem to be solved in the current field of powder 3D printing building materials.

[0006] Therefore, the development of a powder 3D printed lightweight and high-precision magnesium phosphate cement-based material that can solve the above problems at the same time is of great significance to promoting the development of the construction industry. Summary of the invention

[0007] The purpose of the present invention is to provide a powder 3D printing lightweight high-precision magnesium phosphate cement-based material and a preparation method thereof. The cement-based material can achieve lightweight 3D printing cement-based materials, slow down the trend of material mechanical properties degradation, and improve printing accuracy, so that the three effects are achieved at the same time, and has good application prospects.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] In the first aspect, the present invention provides a powder 3D printing lightweight high-precision magnesium phosphate cement-based material, wherein the cement-based material is counted by weight ratio, and its composition and content are respectively:

[0010] Powder components: the molar ratio of magnesium oxide to phosphate is 4 / 1-10 / 1, the fly ash beads account for 10-40% of the total mass of magnesium oxide and phosphate, the quartz sand accounts for 2-20% of the total mass of magnesium oxide and phosphate, and the water reducer accounts for 1-5% of the total mass of magnesium oxide and phosphate;

[0011] Binder components: including deionized water, Surfynol465 surfactant and 1,2-propylene glycol, wherein the mass of Surfynol465 surfactant is 0.08-0.1% of the mass of deionized water, and the mass of 1,2-propylene glycol is 4-5% of the mass of deionized water;

[0012] The maximum particle size of the magnesium oxide, phosphate, quartz sand and water reducer is less than 100 microns; the particle size of the fly ash beads is between 10-70 microns, and the particle size distribution is normally distributed or approximately normally distributed, with a density of 400-450 kg / m 3 , the floating rate is more than 95%; the water-cement ratio of the powder component and the binder component is 0.14-0.16.

[0013] Furthermore, the particle size volume distribution of the fly ash floating beads meets the following requirements:

[0014] Particle size range (micrometers) 10-20 20-30 30-40 40-50 50-60 60-70 Volume ratio (%) 4-5 10-11 35-38 22-25 15-17 6-7 .

[0015] Furthermore, the phosphate is one or more of potassium dihydrogen phosphate or ammonium dihydrogen phosphate; the water reducer is one or more of lignin sulfonate, polycarboxylate, and naphthalene sulfonate; and the magnesium oxide is obtained by calcining magnesia ore at 1600-1800° C. for 30-60 minutes.

[0016] In the second aspect, the present invention protects a method for preparing the above-mentioned powder 3D printed lightweight and high-precision magnesium phosphate cement-based material, the process of the preparation method is:

[0017] (1) Screening powder: screening magnesium oxide, phosphate and quartz sand for particle size, and controlling the particle size of the powder materials to be less than 100 microns by a screening machine; step-screening fly ash floating beads, passing the fly ash floating beads through 1000 mesh, 800 mesh, 500 mesh, 400 mesh, 300 mesh, 240 mesh and 200 mesh sieves in sequence, and combining fly ash floating beads of different particle sizes in a manner such that the volume distribution obeys normal distribution or approximate normal distribution;

[0018] (2) Mixing powder: Put the sieved magnesium oxide, phosphate, quartz sand, water reducer and fly ash beads into a blender and mix them for not less than 5 minutes to obtain a mixed powder;

[0019] (3) Mixing the binder: Dissolve the Surfynol 465 surfactant and 1,2-propylene glycol in the binder component in deionized water, stir evenly, filter out the tiny residue and let it stand for at least 10 minutes, and then put it into the printer ink barrel for later use;

[0020] (4) Powder printing: The mixed powder is loaded into the printer feed bin, the mixed binder is poured into the printer ink barrel, the printing model is imported, the model is sliced, and the printer parameters and printing layer thickness are set; a layer of mixed powder is laid, and the mixed binder is sprayed onto the powder surface through the printer nozzle. The binder reacts with the powder quickly and hardens. The process of laying powder and spraying binder is repeated to obtain a printed specimen;

[0021] (5) Obtaining the test piece: After printing is completed, the test piece is immediately removed from the powder bed and the powder on the surface of the test piece is gently brushed off with a brush to obtain a lightweight, high-precision printed test piece.

[0022] Furthermore, in step (3), filtering the tiny residues is performed by using a 5-micron capsule filter to filter the mixed binder to prevent large particles in the binder from clogging the print head.

[0023] Preferably, the printed specimen has a dimensional error in the Z direction controlled within 0.5 mm while ensuring a 7d strength of 20-30 MPa.

[0024] Preferably, the mass of the fly ash floating beads accounts for 25-40% of the total mass of magnesium oxide and phosphate, and the dimensional errors in the three directions of X, Y and Z are all controlled within 0.5 mm, and preferably the dimensional error in the Z direction is controlled within 0.2 mm.

[0025] Preferably, the printing layer has a thickness of 100 microns.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The lightweight and high-precision magnesium phosphate cement-based material of the present invention can be used for printing of powder 3D printing physical experimental models, and can prepare a repeatable and controllable physical experimental model for powder 3D printing. Taking advantage of the rapid hardening and early strength of magnesium phosphate cement, by reasonably adding fly ash floating beads to improve its spreading performance and replace the hydration products of magnesium phosphate cement, the shortcomings of magnesium phosphate cement-based materials in powder 3D printing, such as large specimen weight and poor printing accuracy, are improved, which is conducive to obtaining a magnesium phosphate cement-based material printing physical model with the characteristics of light weight, high printing accuracy and high strength.

[0028] (2) The present invention uses magnesium phosphate cement as the basic raw material and adds fly ash beads with good particle size distribution, which has the following four advantages: 1) It can produce a ball effect to improve the flatness of the powder bed. This is because the fly ash beads have a spherical particle structure and can play the role of rolling bearings during the mixing process, reducing the friction between particles and optimizing the fluidity of magnesium phosphate cement; 2) It also produces a filling effect to reduce the depressions between hydration products. The hydration product of magnesium phosphate cement is struvite. There are a large number of depressions inside the struvite, and the fine fly ash beads can fill these depressions; 3) It can also absorb temperature stress and reduce the hydration product. The fly ash beads have the characteristics of high temperature resistance and low thermal conductivity, which can effectively reduce the hydration heat rise in the magnesium phosphate cement system and alleviate the stress concentration caused by temperature changes. The hollow structure and low thermal expansion coefficient of the beads enable them to absorb part of the stress when the temperature changes, thereby reducing the risk of cracks in the cement matrix caused by temperature differences; 4) It has certain chemical activity. During the hydration process, Al2O3, SiO2 and other components in the fly ash can participate in the reaction to form amorphous gels such as aluminum phosphate phase and magnesium silicate phase, which can effectively slow down the trend of reduced mechanical properties caused by the reduction of struvite.

[0029] The synergistic combination of the components in the cement-based material of the present invention ultimately effectively reduces the mass of the concrete specimen, improves the molding accuracy of the 3D printed specimen, and maintains good mechanical strength, and has a wide range of applications in powder 3D printing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a weighing comparison chart of Comparative Example 1 and Example 3. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0032] The powder 3D printing lightweight high-precision magnesium phosphate cement-based material of the present invention and the preparation method thereof, the cement-based material is counted by weight ratio, and its composition and content are respectively:

[0033] Powder components: the molar ratio of magnesium oxide / phosphate is 4 / 1-10 / 1, the mass of fly ash floating beads accounts for 10-40% of the total amount of magnesium oxide and phosphate, the mass of quartz sand particles accounts for 2-20% of the total amount of magnesium oxide and phosphate, and the mass of water reducer accounts for 1-5% of the total amount of magnesium oxide and phosphate;

[0034] Binder components: The base solution is composed of deionized water, the mass of Surfynol465 surfactant accounts for 0.08-0.1% of the mass of deionized water, and the mass of 1,2-propylene glycol accounts for 4-5% of the mass of deionized water;

[0035] The magnesium oxide is magnesia ore calcined at 1600-1800°C for 30-60 minutes, with a maximum particle size of less than 100 microns, a maximum particle size of phosphate less than 100 microns, and a molar ratio of magnesium oxide to phosphate of 4 / 1-10 / 1; a maximum particle size of quartz sand less than 100 microns; the particle size of the fly ash beads is between 10-70 microns, the particle size distribution is normally distributed or approximately normally distributed, and the density is 400-450 kg / m 3 , the floating rate is more than 95%; the phosphate can be one or more of potassium dihydrogen phosphate, ammonium dihydrogen phosphate, etc.; the water reducer is one or more of lignin sulfonate, polycarboxylate, naphthalene sulfonate, etc., the maximum particle size does not exceed 100 microns, and the water-cement ratio of the powder material to the binder is 0.14-0.16.

[0036] The binder component of the present invention comprises Surfynol 465 surfactant, 1,2-propylene glycol and deionized water, wherein the Surfynol 465 surfactant is used to adjust the surface tension of the binder solution, and the 1,2-propylene glycol is used to adjust the viscosity of the binder solution, so that the binder can flow smoothly in the inkjet tube and be ejected from the printing nozzle in a good droplet form.

[0037] The preparation method of the above material comprises the following steps:

[0038] (1) Screening powder: screening magnesium oxide, phosphate and quartz sand for particle size, and controlling the particle size of the powder materials to be less than 100 microns by a screening machine; step-screening fly ash floating beads, passing the fly ash floating beads through 1000 mesh, 800 mesh, 500 mesh, 400 mesh, 300 mesh, 240 mesh and 200 mesh sieves in sequence, and combining fly ash floating beads of different particle sizes in a manner such that the volume distribution obeys normal distribution or approximate normal distribution;

[0039] The specific implementation method of the step-by-step screening of fly ash floating beads in step (1) is: passing the fly ash floating beads through 1000 mesh, 800 mesh, 500 mesh, 400 mesh, 300 mesh, 240 mesh, and 200 mesh sieves in sequence. The screening machine consists of a sieve and a motor. The sieve is made of nylon and can be used to filter powder. The motor power is 1.5kW and plays a vibrating role.

[0040] (2) Mixing powder: Put the sieved magnesium oxide, phosphate, quartz sand, water reducer and fly ash beads into a blender and mix them for not less than 5 minutes to obtain a mixed powder;

[0041] (3) Mixing the binder: Dissolve the Surfynol 465 surfactant and 1,2-propylene glycol in the binder component in deionized water, stir evenly, filter out the tiny residue and let it stand for at least 10 minutes, and then put it into the printer ink barrel for later use;

[0042] (4) Powder printing: The mixed powder is loaded into the printer feed bin, the binder is poured into the printer ink barrel, the printing model is imported, the model is sliced, and the printer parameters are set; a layer of mixed powder is laid, and the mixed binder is sprayed onto the powder surface through the printer nozzle. The binder reacts with the powder quickly and hardens. The process of laying powder and spraying binder is repeated to obtain a printed specimen;

[0043] (5) Obtaining the test piece: After printing is completed, the test piece is immediately removed from the powder bed and the powder on the surface of the test piece is gently brushed off with a brush to obtain a lightweight, high-precision printed test piece.

[0044] Example 1

[0045] Step 1: ball milling magnesium oxide and ammonium dihydrogen phosphate at a ball milling speed of 1000r and a ball milling time of 10min, and controlling the particle size to be below 100 microns; ball milling quartz sand at a ball milling speed of 1000r and a ball milling time of 10min, and controlling the particle size to be below 100 microns;

[0046] Magnesium oxide and ammonium dihydrogen phosphate are mixed in a molar ratio of 6:1, quartz sand of 10% of the mass of the cementitious material (the total mass of magnesium oxide and ammonium dihydrogen phosphate) and a water reducer of 5% of the mass of the cementitious material are added, and fly ash floating beads with a particle size distribution that is approximately normally distributed and a mass of 10% of the mass of the cementitious material are added, and the mixture is stirred in a planetary mixer for 10 minutes to obtain a mixed powder;

[0047] Step 2: Add 0.1% Surfynol465 surfactant to the mass of deionized water, add 5% 1,2-propylene glycol to the mass of deionized water, stir evenly, filter out tiny residues and let stand for 10 minutes to obtain a mixed binder, so that the water-cement ratio of the powder material to the binder is 0.14;

[0048] Filtering tiny residues involves using a 5-micron capsule filter to filter the binder to prevent large particles in the binder from clogging the print head.

[0049] Step 3: Load the mixed powder into the printer feed bin, pour the mixed binder into the printer ink barrel, import the three-dimensional digital model of the printed specimen, and slice the digital model; then lay a layer of mixed powder material, and selectively spray the binder onto the powder surface through the printer nozzle. The binder reacts rapidly with the powder material to bond and harden, and the process of laying powder and spraying binder is repeated to obtain a printed specimen; the printer parameters of this embodiment are: the print head moving speed is 300mm / s, the powder wheel speed is 350r / min, the printing speed is 3L / h, the printing layer thickness is 100um, and the printing time of each layer is controlled to be about 30s.

[0050] Step 4: After printing is completed, remove the specimen from the powder bed immediately, use a brush to gently brush off the powder on the surface of the specimen, and finally obtain a powder 3D printed specimen.

[0051] Several specimens were printed in the above manner, cured for 7 days under natural conditions, and their apparent density, diffusion error and 7d compressive strength were tested.

[0052] Embodiment 2-4

[0053] The difference between Examples 2 to 4 and Example 1 is that the dosage of fly ash floating beads is changed, and the dosage of fly ash floating beads is 20%, 30%, and 40% respectively, and the preparation process and printing process of other component materials remain unchanged.

[0054] Comparative Example 1

[0055] This comparative example does not add fly ash floating beads based on Example 1.

[0056] Comparative Example 2

[0057] In this comparative example, the particle size and volume distribution of the fly ash floating beads are changed on the basis of Example 1, and an average distribution form is adopted, and the blending amount of the fly ash floating beads is 10%.

[0058] The specific ratios of all group experiments are shown in Table 1 (the table stipulates that the mass of magnesium oxide and diammonium phosphate is 100 parts):

[0059] Table 1

[0060]

[0061] The volume distribution percentage of fly ash floating beads in Comparative Example 2 and Example 1 is shown in Table 2

[0062] Table 2

[0063]

[0064] When printing, the experimental phenomena of different particle size distributions are shown in Table 3:

[0065]

[0066] It can be seen from Table 3 that in Comparative Example 1, the fluidity of the mixed powder is poor, there are depressions on the surface of the powder bed, and the diffusion area after the binder is sprayed is relatively large; in Comparative Example 2, due to the addition of fly ash floating beads with evenly distributed particle sizes, the fluidity of the powder is slightly improved, there are still depressions on the surface of the powder bed, and the diffusion area is reduced after the binder is sprayed; in Example 1, the particle size distribution of the fly ash floating beads is adjusted to an approximate normal distribution, so that the particle grading of the fly ash floating beads is uniform. After filling them into the material of step 2, the mixed powder has the best fluidity, the powder bed surface is laid the smoothest, and the diffusion area is the smallest after the binder is sprayed.

[0067] Therefore, it is beneficial to select fly ash floating beads with a particle size distribution that is approximately normal to improve printing accuracy.

[0068] The test results of apparent density, dimensional error and mechanical properties of each group of printed specimens are shown in Table 4:

[0069] Table 4

[0070]

[0071] In Table 4, the X direction is the moving direction of the print head, the Y direction is the moving direction of the powder spreader, and the Z direction is the powder stacking direction. The mechanical properties of the specimen are anisotropic. This is because when the previous layer of binder is sprayed onto the surface of the powder bed, the cement powder undergoes a hydration reaction in a short time to form struvite blocks. The binder that does not participate in the hydration reaction and the newly generated water in the hydration reaction will remain on the surface. After the next layer of powder is laid, the adjacent printed layers in the Z direction of the specimen will be tightly bonded into one, and there are interlayer textures in both the X and Y directions. In comparison, the Z direction is more tightly bonded, so the compressive strength in the Z direction is the highest; and the compressive strength in the X direction is slightly higher than that in the Y direction because the X direction is the moving direction of the print head. Due to the small pore gap between the two adjacent nozzles, the binder sprayed in the Y direction is not as uniform as in the X direction, and the cement hydration reaction in the X direction is more uniform, so the compressive strength in the X direction is greater than that in the Y direction. Similarly, the dimensional error is also anisotropic.

[0072] In the embodiment, adding fly ash floating beads with good particle size distribution can produce a ball effect to improve the flatness of the powder bed, can play the role of a rolling bearing during the mixing process, reduce the friction between particles, and optimize the fluidity of magnesium phosphate cement; at the same time, a filling effect is produced to reduce the depressions between hydration products. The hydration product of magnesium phosphate cement is struvite. There are a large number of depressions inside the struvite, and the fine fly ash floating beads can fill these depressions; in addition, temperature stress can be absorbed to reduce cracks in hydration products. Fly ash floating beads have the characteristics of high temperature resistance and low thermal conductivity, so that they can effectively reduce the hydration heat rise in the magnesium phosphate cement system and alleviate the stress concentration caused by temperature changes. The hollow structure and low thermal expansion coefficient of the floating beads enable them to absorb part of the stress when the temperature changes, thereby reducing the risk of cracks in the cement matrix caused by temperature differences; at the same time, they show a certain chemical activity. During the hydration process, Al2O3, SiO2 and other components in the fly ash can participate in the reaction to generate amorphous gels such as aluminum phosphate phase and magnesium silicate phase, which can effectively slow down the trend of reduced mechanical properties caused by the reduction of struvite.

[0073] In Example 3, 30% wt fly ash beads with good particle size distribution were added, and the particle size volume distribution was required to meet the requirements of approximate normal distribution. The specimen had the best performance in terms of apparent density and printing accuracy, and the apparent density reached 1.268 g / cm 3 The diffusion errors are 0.27mm in the X direction, 0.33mm in the Y direction, and 0.13mm in the Z direction. The compressive strength in the Z direction reaches 32.7MPa, which meets the performance requirements of powder 3D printing for lightweight, high printing accuracy, and high-strength magnesium phosphate cement-based materials.

[0074] The mass of the floating beads is 20-40% of the mass of the cementitious material, which can control the dimensional error in the Z direction within 0.5mm, and obtain higher printing accuracy while ensuring higher strength (20-30Mp). The mass of the fly ash floating beads accounts for 25-40% of the total mass of magnesium oxide and diammonium phosphate, and the dimensional errors in the three directions of X, Y and Z are all controlled within 0.5mm, preferably the dimensional error in the Z direction is controlled within 0.2mm.

[0075] The present application can effectively control the printing accuracy by controlling the added content and distribution state of the floating beads, and achieves the triple requirements of reducing density, improving accuracy, and ensuring high strength by adding floating beads, which is a significant improvement.

[0076] In order to more intuitively describe the innovation of the above-mentioned lightweight and high-precision material, the present invention uses the material parameters in Comparative Example 1 and Example 3 respectively, prints a "concrete plate" with a diameter of 210 mm and a thickness of 18 mm under the same external conditions, and weighs it. The comparison diagram is as follows: Figure 1 As shown, the "concrete plate" printed using the material in Comparative Example 1 weighs 1060g, and the "concrete plate" printed using the material in Example 3 weighs 840g, with a weight reduction of 220g, or 20.8%, and the effect is significant.

[0077] It can be clearly seen from the experimental results that within the scope of the requirements of this application, compared with traditional construction methods and cement-based 3D printing technology methods, the present invention has the advantages of light weight and high printing accuracy while ensuring high strength, and expands the application scope of powder 3D printed cement-based materials. The embodiments described in the present invention are easy to understand, and ordinary technicians in this technical field can normally prepare and use powder 3D printed lightweight and high-precision magnesium phosphate cement-based materials, which is convenient to implement and can be promoted and used in the field of new material technology.

[0078] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0079] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A powder 3D printing lightweight and high-precision magnesium phosphate cement-based material, characterized in that: The cement-based materials are counted by weight, and their composition and content are respectively: Powder components: the molar ratio of magnesium oxide to phosphate is 4 / 1-10 / 1, the fly ash beads account for 10-40% of the total mass of magnesium oxide and phosphate, the quartz sand accounts for 2-20% of the total mass of magnesium oxide and phosphate, and the water reducer accounts for 1-5% of the total mass of magnesium oxide and phosphate; Binder components: including deionized water, Surfynol465 surfactant and 1,2-propylene glycol, wherein the mass of Surfynol465 surfactant is 0.08-0.1% of the mass of deionized water, and the mass of 1,2-propylene glycol is 4-5% of the mass of deionized water; The maximum particle size of the magnesium oxide, phosphate, quartz sand and water reducer is less than 100 microns; the particle size of the fly ash beads is between 10-70 microns, and the particle size distribution is normally distributed or approximately normally distributed, with a density of 400-450 kg / m 3 , the floating rate is more than 95%; the water-cement ratio of the powder component and the binder component is 0.14-0.

16.

2. The cement-based material according to claim 1, characterized in that: The particle size volume distribution of the fly ash floating beads meets the following requirements: 。 3. The cement-based material according to claim 1, characterized in that: The phosphate is one or more of potassium dihydrogen phosphate or ammonium dihydrogen phosphate; the water reducer is one or more of lignin sulfonate, polycarboxylate, and naphthalene sulfonate; and the magnesium oxide is obtained by calcining magnesia ore at 1600-1800° C. for 30-60 minutes.

4. A method for preparing a powder 3D printed lightweight and high-precision magnesium phosphate cement-based material according to any one of claims 1 to 3, characterized in that: The process of the preparation method is: (1) Screening powder: screening magnesium oxide, phosphate and quartz sand for particle size, and controlling the particle size of the powder materials to be less than 100 microns by a screening machine; step-screening fly ash floating beads, passing the fly ash floating beads through 1000 mesh, 800 mesh, 500 mesh, 400 mesh, 300 mesh, 240 mesh and 200 mesh sieves in sequence, and combining fly ash floating beads of different particle sizes in a manner such that the volume distribution obeys normal distribution or approximate normal distribution; (2) Mixing powder: Put the sieved magnesium oxide, phosphate, quartz sand, water reducer and fly ash beads into a blender and mix them for not less than 5 minutes to obtain a mixed powder; (3) Mixing the binder: Dissolve the Surfynol 465 surfactant and 1,2-propylene glycol in the binder component in deionized water, stir evenly, filter out the tiny residue and let it stand for at least 10 minutes, and then put it into the printer ink barrel for later use; (4) Powder printing: Load the mixed powder into the printer feed bin, pour the mixed binder into the printer ink barrel, import the printing model, slice the model, set the printer parameters and printing layer thickness; Lay a layer of mixed powder, and spray the mixed binder onto the powder surface through the printer nozzle. The binder reacts with the powder quickly and hardens. Repeat the process of laying powder and spraying binder to obtain a printed specimen. (5) Obtaining the test piece: After printing is completed, the test piece is immediately removed from the powder bed and the powder on the surface of the test piece is gently brushed off with a brush to obtain a lightweight, high-precision printed test piece.

5. The preparation method according to claim 4, characterized in that: The filtering of the tiny residues in the step (3) is as follows: using a 5-micron capsule filter to filter the mixed binder.

6. The preparation method according to claim 4, characterized in that: The printed specimen has a dimensional error in the Z direction controlled within 0.5 mm while ensuring a 7d strength of 20-30 MPa.

7. The preparation method according to claim 6, characterized in that: The mass of the fly ash floating beads accounts for 25-40% of the total mass of magnesium oxide and phosphate, and the dimensional errors in the three directions of X, Y and Z are all controlled within 0.5 mm, and preferably the dimensional error in the Z direction is controlled within 0.2 mm.

8. The preparation method according to claim 4, characterized in that: The printing layer thickness is 100 microns.

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