Carbon material modified silica sand for fiber laser selective sintering forming, preparation method and application thereof

Abstract

The application provides a carbon material modified silica sand for fiber laser selective sintering forming, a preparation method and application thereof, and belongs to the technical field of additive manufacturing. The carbon material modified silica sand comprises silica sand, a composite binder, a coupling agent and a light absorber. The carbon material modification makes the material applicable to fiber laser SLS forming, reduces the problem of high cost caused by a carbon dioxide laser, optimizes laser quality and power by applying fiber laser, and improves forming efficiency and precision. The production and preparation of the material adopts a mechanical mixing method, avoids problems such as high cost and heavy pollution caused by a film coating process, and does not add urotropine during material mixing, thereby reducing safety hazards caused by the toxicity of urotropine.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology, and relates to a silica sand-based powder material suitable for selective laser sintering of fiber lasers, its preparation method and its application, especially to the forming of low-cost, high-quality selective fiber laser sintering sand molds for cast aluminum. Background Technology

[0002] Selective laser sintering (SLS) works by using a high-energy laser beam to irradiate the surface of a powder layer. The thermal effect of the laser on the powder causes the powder particles to adhere together. Two types of lasers are commonly used in this technology: a 10.6-micrometer wavelength carbon dioxide laser and a 1.06-micrometer wavelength fiber laser. Silica sand exhibits a strong thermal effect on the laser emitted by a carbon dioxide laser, but the photoelectric conversion efficiency of this type of laser is only 8%–12%, while fiber lasers achieve more than twice that of carbon dioxide lasers, reaching 25%–30%. Using fiber lasers in the selective laser sintering of silica sand can significantly reduce energy consumption. Fiber lasers also far surpass carbon dioxide lasers in terms of beam quality. For low-power Gaussian laser beams, with M… 2 The factor defines the beam quality, M. 2 The closer the value is to 1, the better the beam quality of the laser. Generally, for carbon dioxide lasers, M... 2The gain factor can be controlled below 5, while that of a fiber laser can reach below 1.3. In terms of lifespan, fiber lasers can reach approximately 100,000 hours, while CO2 lasers only reach about 30,000 hours. Furthermore, because CO2 lasers are gas-excited, requiring a gas reaction within a glass resonant cavity, the higher the power, the larger the required cavity and the larger the laser. Fiber lasers, using rare-earth-doped glass fiber as the gain medium, have a volume that doesn't change much with power; the volume of a 300W-2000W fiber laser remains essentially constant. In addition, the transmission of the laser beam from the laser to the scanning galvanometer system is much easier. Fiber lasers can propagate through a single fiber isolated from the outside air, minimizing the beam's susceptibility to environmental factors. The fiber itself is flexible, simplifying installation and maintenance. In contrast, CO2 lasers rely on multiple mirrors for propagation. In the dusty environment of selective laser sintering, mirrors are easily electrostatically attracted, leading to reduced laser quality and even damage to the mirrors. Therefore, the installation and maintenance of CO2 lasers are extremely difficult. Regarding cost, fiber lasers, driven by the development of metal 3D printing technology, have largely achieved domestic production, making their market price significantly lower than that of CO2 lasers. Because abrasive sand absorbs fiber lasers well, fiber lasers are generally used in 3D printing with abrasive sand as the matrix, while CO2 lasers are used in 3D printing equipment with silica sand. Abrasive sand has high refractoriness and is expensive, generally used for high-value castings such as cast steel and cast copper. Using abrasive sand in aluminum casting is a waste of materials, while inexpensive silica sand is a commonly used molding material for cast aluminum. Therefore, modifying silica sand to efficiently absorb fiber lasers for fiber laser 3D printing is of significant practical importance. This not only greatly saves costs but also allows for a wide range of selectable fiber laser power, making high-power laser printing easier and increasing forming efficiency.

[0003] Currently, most 3D printing molding materials used in casting are coated sand produced through a specific coating process. Coating processes are divided into thermal coating and wet coating. The thermal process involves preheating the sand to a certain temperature, adding resin to melt it, stirring to coat the sand grains with resin, adding a hexamethylenetetramine aqueous solution and lubricant, cooling, crushing, and sieving to obtain coated sand. The cold process involves dissolving resin in ethanol and adding hexamethylenetetramine during sand mixing, causing both to coat the sand grains. The ethanol then evaporates, resulting in coated sand. Both processes have drawbacks. Cold coating uses ethanol, posing significant safety risks and requiring large amounts of organic solvents, making it suitable only for small-scale production. Thermal coating is also more complex, requiring specialized large-scale sand mixing and crushing equipment. Mechanical mixing, however, avoids these drawbacks. It only requires mixing the necessary materials in a suitable order and process, making it suitable for production using selective laser sintering equipment. Furthermore, to maintain the thermoplastic characteristics of the resin before final molding and its thermosetting transition after molding, both thermal and cold coating processes require the addition of curing agents such as hexamethylenetetramine. Urotropine itself is toxic and reacts with thermoplastic phenolic resins to produce formaldehyde and ammonia, posing a significant health hazard. Thermosetting phenolic resins, on the other hand, can be directly added during mechanical mixing and act as a catalyst for the conversion of thermoplastic resins into thermosetting resins. Optimal 3D printing performance can be achieved through appropriate mechanical mixing in suitable proportions. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a silica sand molding material suitable for selective laser sintering (SLS) in metal casting. By modifying the material with carbon materials, it becomes suitable for fiber laser SLS molding, reducing the high cost associated with carbon dioxide lasers. Applying fiber lasers can also optimize laser quality and power, improving molding efficiency and precision. The material is produced using a mechanical mixing method, avoiding the high cost and heavy pollution associated with coating processes. No hexamethylenetetramine is added during material mixing, reducing safety hazards caused by its toxicity.

[0005] To achieve the above requirements, the technical solution adopted by the present invention is as follows:

[0006] A carbon-modified silica sand for selective sintering in fiber lasers, comprising: raw silica sand, a composite binder, a coupling agent, and a light absorber. Specifically:

[0007] The raw silica sand mainly uses silica sand of 50 mesh to 200 mesh, and the proportion of each particle size is reasonably configured according to the continuous gradation theory.

[0008] The composite adhesive is composed of thermoplastic resin and thermosetting resin. The thermosetting resin is type 2123, and the thermoplastic resin is type 2123F. Based on 100% of the total mass of the composite adhesive, the thermosetting resin accounts for 0.6% to 1.67% of the total mass.

[0009] The coupling agent is silane coupling agent HK550.

[0010] The light absorber should include flake graphite, granular graphite, graphene, or carbon nanotube high-strength fiber laser absorbing materials, preferably flake graphite; in addition to absorbing fiber laser light, it can also provide a lubricating effect. The material specifications of the light absorber are mainly selected between 1500 mesh and 2000 mesh.

[0011] The composite binder accounts for 2% to 4% of the mass of the raw silica sand. The coupling agent accounts for 5% of the mass of the composite binder. The light absorber accounts for 0.4% to 0.8% of the mass of the raw silica sand.

[0012] A method for preparing carbon-modified silica sand for fiber laser selective sintering includes the following steps:

[0013] This invention modifies the light absorption properties of silica sand primarily by leveraging the strong absorption characteristics of fiber lasers by light absorbers (such as graphite). Therefore, it is necessary to adsorb the light absorber onto the surface of the silica sand particles. The first step involves mechanically mixing the silica sand and the light absorber, and then modifying the surface of the silica sand particles using a silane coupling agent to enhance the graphite adsorption effect. The specific steps are as follows:

[0014] Step 1) Add the raw silica sand and light absorber into the sand mixer and rotate it at 60 revolutions per minute.

[0015] Step 2) Prepare a homogeneous silane coupling agent solution by mixing ethanol and silane coupling agent at a mass ratio of 1:2.

[0016] Step 3) Use a sprayer to add the uniform solution of silane coupling agent from step 2) into the sand mixer from step 1), and mix for 30 min to 55 min to allow the light absorber to stably adhere to the surface of the original silica sand particles, thus obtaining optically modified silica sand.

[0017] Step 4) Mix the thermoplastic resin and thermosetting resin at a weight ratio of 0.5 to 2 and stir evenly. Add the mixture to a sand mixer and mix at 60 revolutions per minute for 2 to 7 minutes to obtain carbon-modified silica sand.

[0018] Furthermore, this invention employs an image measuring instrument to sample and evaluate the mixing quality of the carbon-modified silica sand obtained from the mixing process.

[0019] An application of a silica sand-based powder material suitable for selective laser sintering using fiber lasers. Specifically:

[0020] Step 1) According to the dimensional requirements for the preparation of tensile strength test specimens in GB / T 2684-2009, use SolidWorks to draw a three-dimensional model of the figure-eight test specimen.

[0021] Step 2) Use Materialise Magics to slice the 3D model with a layer thickness of 0.3mm; fill the laser scanning path into each slice file with a 1.1mm spacing and a back-shaped filling method. This will result in a figure-eight shaped sample printing file.

[0022] Step 3) Upload the print file to the fiber laser 3D printing equipment, put the prepared carbon material modified silica sand into the powder supply box, and start printing by debugging the printing software.

[0023] Step 4) Adjust the fiber laser power and laser scanning speed to achieve a suitable sintering temperature, such as a fiber laser power of 550W and a laser scanning speed of 3000mm / s.

[0024] The carbon-modified silica sand, modified from graphite, can be used for fiber laser sintering. This material is characterized by its ability to uniformly heat the silica sand and resin materials by utilizing the large amount of heat converted from laser energy absorbed by the graphite when the fiber laser acts on the powder layer, causing the thermosetting and thermoplastic resins to melt and bond together. This material does not require complex coating processes and can be formed on 3D printing equipment using fiber lasers.

[0025] The innovative point of this invention is:

[0026] (1) By utilizing the properties of thermosetting resin and thermoplastic resin as catalysts, the molding and heat treatment of the molding material are guaranteed while the addition of toxic catalysts such as hexamethylenetetramine is eliminated.

[0027] (2) By utilizing the high absorption characteristics of carbon materials for fiber lasers, a mechanical mixing process and a silane coupling agent are used to make graphite uniformly adsorbed on the surface of silica sand, thereby improving the absorption capacity of silica sand for fiber lasers and making it suitable for fiber SLS 3D printing equipment.

[0028] The beneficial effects of this invention are as follows:

[0029] (1) The present invention uses fiber laser instead of carbon dioxide laser, which greatly reduces the cost of laser use and maintenance.

[0030] (2) With the use of fiber lasers, the laser quality is better, the power range available is wider, and the forming quality and efficiency are higher.

[0031] (3) The mechanical mixing process of the present invention can ensure the effect of graphite adhering to silica sand, ensure the uniformity of resin mixing, and avoid the problems of high cost and heavy pollution caused by the coating process.

[0032] (4) This invention utilizes the advantages of mechanical mixing process and the properties of thermosetting and thermoplastic as catalysts to optimize the composition, remove curing agent components such as hexamethylenetetramine, and reduce safety hazards.

[0033] (5) The components of the above materials are required to meet the casting sand mold standards and have great application value in the field of rapid casting. Attached Figure Description

[0034] Figure 1 Silica sand before graphite mixing;

[0035] Figure 2 It is silica sand mixed with graphite;

[0036] Figure 3 The microstructure of the composite powder particles after mixing;

[0037] Figure 4 The figure-eight shaped sample after sintering on a fiber laser device. Detailed implementation method:

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the operation process of this invention will be further described in detail below with reference to the accompanying drawings and specific examples. It should be noted that the specific examples described herein are only for explaining this invention, and the illustrations are illustrative in nature and are not intended to limit the scope of this invention.

[0039] Example 1:

[0040] Prepare raw materials with the following qualities: 10,000g silica sand, 400g phenolic resin (150g thermosetting phenolic resin, 250g thermoplastic phenolic resin), 40g flake graphite, and 20g silane coupling agent.

[0041] The preparation method of carbon-modified silica sand for fiber laser selective sintering is as follows:

[0042] (1) Take 10,000g of sieved 70-140 mesh silica sand, wash and dry it with water, and then put it into a sand mixer (e.g., Figure 1 Weigh 40g of graphite using an electronic balance and add it to the sand mixer.

[0043] (2) Mix the silane coupling agent and ethanol in a mass ratio of 1:2 to form a solution, and pour the solution into a spray bottle.

[0044] (3) Turn on the sand mixer and set it to rotate counterclockwise at 60 revolutions per minute. Mix for about ten seconds, then spray in 60g of solution. Stop mixing after 55 minutes.

[0045] (4) Take out a certain amount of graphite-modified silica sand and check the graphite adhesion. If the graphite does not fall off significantly, the requirements are met (e.g., Figure 2 ).

[0046] (5) Weigh 150g of thermosetting phenolic resin and 250g of thermoplastic phenolic resin using an electronic balance, add them to a measuring cup and mix evenly. Then pour the mixture into a sand mixer and mix for 4 minutes. The final product is a carbon-modified composite powder material suitable for SLS (such as...). Figure 3 ).

[0047] In application, the powder is sintered into mechanical samples using conventional fiber laser sintering technology, and then subjected to conventional SLS post-treatment for heat strengthening (such as...). Figure 4 The post-treatment involved heating in a 180°C drying oven for 3 hours. After post-treatment, the tensile strength was measured to be approximately 1.32 MPa, meeting the requirements for conventional foundry sand. Therefore, this powder can be used as a casting molding material suitable for fiber laser equipment.

[0048] Example 2:

[0049] Prepare the following raw materials in the following quantities: 10,000g silica sand, 400g phenolic resin (250g thermosetting phenolic resin and 150g thermoplastic phenolic resin), 40g flake graphite, and 20g silane coupling agent. This example differs from Example 1 in the proportions of the raw materials and the preparation process parameters.

[0050] The preparation method of carbon-modified silica sand for fiber laser selective sintering is as follows:

[0051] (1) Take 10,000g of sieved 70-140 mesh silica sand, wash and dry it with water, and put it into a sand mixer. Weigh 40g of graphite using an electronic balance and add it into the sand mixer.

[0052] (2) Mix the silane coupling agent and alcohol in a 1:2 ratio to form a solution, and pour the solution into a spray bottle.

[0053] (3) Turn on the sand mixer, set the parameters, and the speed is 60 revolutions per minute. Mix for about ten seconds, then spray in about 60g of solution. Stop mixing after 55 minutes.

[0054] (4) Take out a certain amount of graphite-modified silica sand and check the graphite adhesion. If the graphite does not fall off, the requirements are met.

[0055] (5) Weigh 250g of thermosetting phenolic resin and 150g of thermoplastic phenolic resin using an electronic balance, add them to a measuring cup and mix evenly, then pour into a sand mixer and mix for 4 minutes. Finally, carbon-modified SLS printing silica sand is obtained.

[0056] In application, the powder is sintered into mechanical samples using conventional fiber laser sintering technology, followed by conventional SLS post-treatment heating strengthening. The post-treatment heating strengthening involves baking at 180 degrees Celsius in a drying oven for 3 hours. The tensile strength, as tested, is approximately 1.45 MPa, meeting the requirements for conventional casting sand. Therefore, this powder can be used as a casting molding material suitable for fiber laser equipment.

[0057] Example 3:

[0058] Prepare the following raw materials with the following weights: 5000g silica sand, 150g phenolic resin (75g of which is thermosetting phenolic resin and 75g of which is thermoplastic phenolic resin), 40g granular graphite, and 7.5g silane coupling agent. This example differs from Example 1 in the proportions of the raw materials and the preparation process parameters; in this example, flake graphite is replaced with granular graphite.

[0059] The preparation method of carbon-modified silica sand for fiber laser selective sintering is as follows:

[0060] (1) Take 5000g of sieved 70-140 mesh silica sand, wash and dry it with water, and put it into a sand mixer. Weigh 40g of granular graphite using an electronic balance and add it into the sand mixer.

[0061] (2) Mix the silane coupling agent and alcohol in a 1:2 ratio to form a solution, and pour the solution into a spray bottle.

[0062] (3) Turn on the sand mixer and set it to rotate counterclockwise at 60 revolutions per minute. Mix for about ten seconds, then spray in about 22.5g of solution. Stop mixing after 30 minutes.

[0063] (4) Take out a certain amount of graphite-modified silica sand and check the graphite adhesion. If the graphite does not fall off, the requirements are met.

[0064] (5) Weigh 75g of thermosetting phenolic resin and 75g of thermoplastic phenolic resin using an electronic balance, add them to a measuring cup and mix evenly, then pour into a sand mixer and mix for 7 minutes. Finally, carbon-modified SLS printing silica sand is obtained.

[0065] In application, the powder is sintered into mechanical samples using conventional fiber laser sintering technology, followed by conventional SLS post-treatment heating strengthening. The post-treatment heating strengthening involves baking at 180 degrees Celsius in a drying oven for 3 hours. The tensile strength, as tested, is approximately 1.08 MPa, meeting the requirements for conventional casting sand. Therefore, this powder can be used as a casting molding material suitable for fiber laser equipment.

[0066] Example 4:

[0067] Prepare the following raw materials with the following weights: 5000g silica sand, 100g phenolic resin (50g of which is thermosetting phenolic resin and 50g of which is thermoplastic phenolic resin), 25g granular graphite, and 5g silane coupling agent. The difference between this example and Example 1 lies in the proportions of the raw materials and the preparation process parameters; in this example, flake graphite is replaced with granular graphite.

[0068] The preparation method of carbon-modified silica sand for fiber laser selective sintering is as follows:

[0069] (1) Take 5000g of sieved 70-140 mesh silica sand, wash and dry it with water, and put it into a sand mixer. Weigh 25g of granular graphite using an electronic balance and add it into the sand mixer.

[0070] (2) Mix the silane coupling agent and alcohol in a 1:2 ratio to form a solution, and pour the solution into a spray bottle.

[0071] (3) Turn on the sand mixer and set it to rotate counterclockwise at 60 revolutions per minute. Mix for about ten seconds, then spray in about 48g of solution. Stop mixing after 30 minutes.

[0072] (4) Take out a certain amount of graphite-modified silica sand and check the graphite adhesion. If the graphite does not fall off, the requirements are met.

[0073] (5) Weigh 50g of thermosetting phenolic resin and 50g of thermoplastic phenolic resin using an electronic balance, add them to a measuring cup and mix evenly, then pour into a sand mixer and mix for 2 minutes. Finally, carbon-modified SLS printing silica sand is obtained.

[0074] In application, the powder is sintered into mechanical samples using conventional fiber laser sintering technology, followed by conventional SLS post-treatment heating strengthening. The post-treatment heating strengthening involves baking at 180 degrees Celsius in a drying oven for 3 hours. The tensile strength, as tested, is approximately 0.71 MPa, meeting the requirements for conventional casting sand. Therefore, this powder can be used as a casting molding material suitable for fiber laser equipment.

[0075] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for preparing carbon-modified silica sand for selective sintering of fiber laser materials, characterized in that, Includes the following steps: Step 1) Add the raw silica sand and light absorber into the sand mixer and mix them evenly; Step 2) Prepare a homogeneous silane coupling agent solution by mixing ethanol and silane coupling agent at a mass ratio of 1:2; Step 3) Use a sprayer to add the uniform solution of silane coupling agent from step 2) into the sand mixer from step 1), and mix for 30 min to 55 min to allow the light absorber to be stably attached to the surface of the original silica sand particles, thus obtaining optically modified silica sand. Step 4) Mix thermoplastic phenolic resin and thermosetting phenolic resin in a weight ratio of 0.6 to 1.67 and stir evenly. Add the mixture to a sand mixer and mix at 60 revolutions per minute for 3 to 5 minutes to obtain carbon-modified silica sand. The light absorber is flake graphite, particulate graphite, graphene, or carbon nanotubes.

2. The method according to claim 1, characterized in that, The composite binder, composed of thermoplastic phenolic resin and thermosetting phenolic resin, comprises 2% to 4% of the mass of the original silica sand; the coupling agent comprises 5% of the mass of the composite binder; and the light absorber comprises 0.4% to 0.6% of the mass of the original silica sand.

3. The method according to claim 1, characterized in that, The silica sand used is 50-200 mesh silica sand, and the proportion of each particle size is reasonably configured according to the continuous gradation theory.

4. The method according to claim 1, characterized in that, The thermosetting phenolic resin is type 2123, and the thermoplastic phenolic resin is type 2123F.

5. The method according to claim 1, characterized in that, The coupling agent is a silane coupling agent KH550.

6. The method according to claim 1, characterized in that, The material specifications of the light absorber are selected between 1500 mesh and 2000 mesh.

7. A carbon-modified silica sand for selective sintering of fiber lasers, prepared by the preparation method according to any one of claims 1-6.

8. An application of the carbon-modified silica sand according to claim 7, characterized in that, The carbon-modified silica sand described above is used in fiber laser selective sintering molding.

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