Preparation method of composite metal powder for cold metal melting additive manufacturing

Abstract

The invention discloses a preparation method of composite metal powder for cold metal melting additive manufacturing, which comprises the following steps: S1, adding a low-temperature binder, a thickening agent and metal powder into a solvent, and gradually separating out the binder to the surface of the metal powder through a solvent precipitation method, so as to form composite metal powder with the metal powder as an inner core and the metal powder as an outer core; the composite powder takes a binding agent to coat a thin layer as a shell; s2, the composite powder is subjected to spray drying, spherical powder with the uniform surface is formed, and composite metal powder is prepared; a precipitation method and a thickening agent are adopted to increase the viscosity of the solution, metal sedimentation is prevented, the metal powder can be fully coated with the binder, and then spray drying is directly adopted. The prepared composite metal powder is regular in shape, high in sphericity degree, uniform in surface, good in powder fluidity and high in apparent density, the powder can be evenly spread on a powder bed in the printing process, and a printed product is high in density. Meanwhile, according to the preparation method, the utilization degree of the binder is high, and the discharge amount of waste liquid is small.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing, and more specifically to a method for preparing composite metal powder for cold metal melting additive manufacturing. Background Technology

[0002] Metal additive manufacturing technology is characterized by high complexity, lightweight, and customization, and has been widely used in aerospace, medical, and automotive fields. Currently common metal additive manufacturing technologies include selective laser melting (SLM), selective electron beam melting (EBM), and laser metal deposition. These technologies all utilize high-energy sources to melt metal, and the accumulation of localized thermal stress during the melting and cooling process can easily lead to deformation and cracking. To avoid defects caused by thermal stress, cold metal melting (CMF) technology has emerged. CMF is a novel metal 3D printing technology that combines existing metal manufacturing processes with selective laser sintering (SLS). Its core process involves mixing a plastic binder into metal powder to form a metal-binder composite powder. Then, an energy source is used to melt the metal-binder composite powder to prepare a preform, which is subsequently debonded and sintered to obtain the final part. The most crucial step in the entire process is the metal binder composite powder. The binder needs to coat the metal surface while possessing a low melting point and good adhesion. Low-temperature melting avoids deformation and minimal dimensional changes during green body preparation, providing the green body with a certain strength. Traditional metal powder coating methods (dry mixing, solvent precipitation) easily lead to uneven binder distribution and irregular particle shapes, affecting the strength of the subsequently formed green body. For example, a method for preparing coated powder for cold metal melting additive manufacturing, as described in application number 202510252170.7 (CN120002004A), although it can achieve polymer-coated powder, results in uneven polymer coating on the metal surface during precipitation. Furthermore, because the polymer cannot completely precipitate from the solution during precipitation, and the solution has a certain viscosity, the coated powder adheres to each other after drying. Therefore, grinding is necessary; otherwise, the metal powder will agglomerate. However, the grinding process damages the polymer coating on the metal surface, resulting in irregular powder shapes, poor sphericity, and uneven surface (e.g., ...). Figure 12 As shown, poor powder flowability and low loose powder density will affect powder spreading during printing, as well as the compactness of the printed preform, ultimately affecting print quality.

[0003] Therefore, it is necessary to solve the technical problems of irregular powder shape, poor sphericity, uneven surface, poor powder flowability, and low loose powder density in metal binder composite powder produced by cold metal melting additive manufacturing, in order to improve the quality of 3D printing. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for preparing composite metal powder for cold metal melting additive manufacturing, which solves the technical problems of irregular powder shape, poor sphericity, uneven surface, poor powder flowability, and low loose powder density, so as to improve the quality of 3D printing.

[0005] The method for preparing composite metal powder for cold metal melting additive manufacturing of the present invention includes the following steps:

[0006] S1, low-temperature binder, thickener and metal powder are added to solvent, and the binder is gradually precipitated to the surface of metal powder by solvent precipitation method to form a composite powder with metal powder as the core and a thin layer of binder as the shell;

[0007] S2, the solution is spray-dried to form spherical powder with uniform surface coating, thus obtaining composite metal powder;

[0008] Furthermore, in step S1, the binder is first added to the solvent and heated and stirred until dissolved, then the thickener is added and stirred until completely dissolved, and finally the metal powder is added, heated and stirred, cooled to room temperature and stirred again, so that the binder gradually precipitates onto the surface of the metal powder to form a thin coating layer.

[0009] Further, in step S1, by mass percentage, the ratio of metal powder to low-temperature binder is 85:15 to 99.5:0.5; the ratio of metal powder to solvent is 0.5:1 to 5:1; and the mass of thickener is 0.1% to 5% of the mass of solvent.

[0010] Further, in step S1, the thickener is one or a mixture of two or more of the following: polyvinylpyrrolidone, hydroxymethyl cellulose, ethyl cellulose, phosphate esters, sodium polystyrene sulfonate, glycerin, polyamide wax, citric acid, and polymethyl methacrylate.

[0011] Further, in step S1, the low-temperature binder is one or a mixture of two or more of the following: rosin, paraffin wax, microcrystalline wax, ethylene-vinyl acetate copolymer, epoxy resin, phenolic resin, polyethylene glycol, polyaldehyde resin, and polyethylene oxide.

[0012] Furthermore, in step S2, a spray dryer is used for spray drying. The inlet air temperature of the spray dryer is set to 40-150℃, the air supply rate is 20-40Hz, the exhaust air rate is 20-40Hz, the peristaltic pump speed is 20-100r / min, and the nozzle speed is 10000-20000r / min.

[0013] Furthermore, after spray drying, powder with a particle size of less than 80 μm is screened.

[0014] The beneficial effects of this invention are as follows: The method for preparing composite metal powder for cold metal melting additive manufacturing employs a precipitation method with the aid of a thickener to increase the viscosity of the solution, preventing metal sedimentation and ensuring that the binder can fully coat the metal powder. Then, direct spray drying is used to uniformly coat the metal powder with the binder, forming a core-shell structure with the metal powder as the core and a thin layer of binder as the outer shell. Simultaneously, spray drying also coats all remaining binder in the solution onto the metal powder, resulting in more uniform coating and better sphericity of the composite powder. The prepared composite metal powder has a regular shape, high sphericity, uniform surface, good powder flowability, and high loose density, which facilitates uniform powder spreading on the powder bed during printing, and results in high-density printed products. Furthermore, the preparation method of this invention has high binder utilization and low wastewater discharge. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0016] Figure 1 This is a schematic diagram of the process for preparing the "core-shell" structured coated powder according to the present invention;

[0017] Figure 2 This is a scanning electron microscope image of epoxy resin-coated 316L composite powder from Example 1.

[0018] Figure 3 This is a scanning electron microscope image of the polyoxyethylene-coated CuGrZr copper alloy composite powder from Example 2.

[0019] Figure 4 This is a scanning electron microscope image of the microcrystalline wax-coated AlSi10Mg aluminum alloy composite powder from Example 3.

[0020] Figure 5 This is a scanning electron microscope image of the polyaldehyde resin-coated CoCrMoW cobalt-chromium alloy composite powder from Example 4.

[0021] Figure 6 This is a scanning electron microscope image of polyethylene glycol-coated 316L stainless steel composite powder from Example 5.

[0022] Figure 7 Scanning electron microscope image of uncoated 316L metal powder;

[0023] Figure 8 , Figure 9 Images of cylindrical samples prepared by laser sintering of powder prepared in Example 1 and samples after degreasing and sintering are shown.

[0024] Figure 10 TEM images of the composite powders from Examples 1 and 2;

[0025] Figure 11TEM images of the composite powders from Examples 3 and 4;

[0026] Figure 12 TEM image of the composite powder in Example 5;

[0027] Figure 13 Scanning electron microscope image of the composite powder prepared for application number 202510252170.7. Detailed Implementation

[0028] The method for preparing composite metal powder for cold metal melting additive manufacturing in this embodiment includes the following steps:

[0029] S1 involves adding a low-temperature binder, thickener, and metal powder to a solvent. The binder is then gradually precipitated onto the surface of the metal powder using a solvent precipitation method, forming a composite powder with the metal powder as the core and a thin layer of binder as the outer shell. Because the metal powder has a high density, it is prone to settling during pipeline flow, affecting the coating effect. Therefore, a thickener is used to increase the viscosity of the solution and prevent metal settling. The metal powder can be selected from common additive manufacturing metal powders or modified powders such as titanium alloys, nickel-based alloys, copper alloys, aluminum alloys, stainless steel alloys, tungsten alloys, and cobalt-chromium alloys, with a particle size range of 0–80 μm. The solvent can be one of water, alcohol, ethyl acetate, acetone, methanol, acetic acid, tetrahydrofuran, etc., determined based on the selected low-temperature binder to ensure the binder has a certain solubility in the solvent; for example, if the low-temperature binder is water-based epoxy resin, then water is selected as the solvent.

[0030] S2, the composite powder is spray-dried to form a uniformly shaped spherical powder, thus obtaining composite metal powder. In step S1, since both the binder and the metal powder are distributed in the solution, the binder cannot completely coat the metal powder, leaving binder and metal powder residues in the solution. Therefore, directly spray-drying the composite powder can completely coat the metal powder with the remaining binder in the solution, resulting in more uniform coating, better sphericity of the composite powder, and higher effective utilization of the binder. Simultaneously, the prepared composite metal powder has a regular shape, high sphericity, uniform surface, good powder flowability, and high loose density. During spray drying, the spray drying equipment is turned on, and parameters such as inlet air temperature, air supply rate, induced draft rate, peristaltic pump speed, and nozzle speed are set. Once the inlet air temperature, air supply rate, induced draft rate, and nozzle speed reach the set values, the peristaltic pump pipeline is connected to the solution, and the peristaltic pump is turned on for spraying.

[0031] In a preferred embodiment, a spray dryer is used for spray drying. The inlet air temperature of the spray dryer is set to 40–150°C, the air supply rate is 20–40 Hz, the exhaust air rate is 20–40 Hz, the peristaltic pump speed is 20–100 r / min, and the nozzle speed is 10,000–20,000 r / min. After spray drying, powder with a particle size of less than 80 μm is screened. The spray dryer includes an aqueous spray dryer, an organic spray dryer, and a low-temperature spray dryer. If an organic solvent is used in step S1, an organic spray dryer is selected. If the selected binder has a low melting point temperature, a low-temperature spray dryer can be used.

[0032] In this embodiment, in step S1, the binder is first added to the solvent and heated and stirred until dissolved. Then, a thickener is added and stirred until completely dissolved. Finally, metal powder is added, heated and stirred, then cooled to room temperature and stirred again, allowing the binder to gradually precipitate onto the surface of the metal powder to form a thin coating layer. The heating temperature is determined based on the minimum of the solvent boiling point and the low-temperature binder melting point, and is generally 5-20°C below the minimum. During heating, the solvent evaporates and the temperature drops to room temperature, reducing the amount of binder dissolved in the solvent, allowing it to gradually precipitate onto the surface of the metal powder and initially form a thin binder coating layer.

[0033] In this embodiment, in step S1, by mass percentage, the ratio of metal powder to low-temperature binder is 85:15-99.5:0.5; the ratio of metal powder to solvent is 0.5:1-5:1; the mass of thickener is 0.%-5% of the solvent mass; the thickener is one or a mixture of two or more of polyvinylpyrrolidone, hydroxymethyl cellulose, ethyl cellulose, phosphate esters, sodium polystyrene sulfonate, glycerin, polyamide wax, citric acid, and polymethyl methacrylate; the low-temperature binder is one or a mixture of two or more of rosin, paraffin wax, microcrystalline wax, ethylene-vinyl acetate copolymer, epoxy resin, phenolic resin, polyethylene glycol, polyaldehyde resin, and polyethylene oxide; the solvent is determined according to the selected low-temperature binder to ensure that the binder has a certain solubility in the solvent.

[0034] After spray drying is complete, collection and sieving are carried out: After the solution is completely spray dried, the air hammer of the equipment is turned on to collect the powder in the tank, and then the powder with a particle size of less than 80μm is selected by sieving with a vibrating screen.

[0035] Example 1

[0036] The composite metal powder used in this embodiment is 316L stainless steel powder with a particle size distribution of 15–28 μm; the low-temperature polymer is epoxy resin with a softening point of 85–95°C; the solvent is ethyl acetate; and the thickener is glycerol. The preparation process is as follows:

[0037] (1) The following ratios are mass ratios, where 316L stainless steel powder: epoxy resin = 100:5, 316L stainless steel powder: ethyl acetate = 1:1, and the mass of glycerol is 1% of the mass of ethyl acetate. Weigh out 316L powder, epoxy resin, ethyl acetate and glycerol respectively.

[0038] (2) Pour the weighed epoxy resin into ethyl acetate, stir and heat to completely dissolve the epoxy resin, then add glycerin. After the glycerin is dissolved and evenly dispersed, add 316L stainless steel powder, heat and stir at 60℃ for 2 hours, and finally stir at room temperature for 1 hour.

[0039] (3) Turn on the organic spray drying equipment and set the equipment parameters as follows: air inlet temperature 80℃, air supply rate 30HZ, air exhaust rate 29.5HZ, nozzle speed 18000r / min, peristaltic pump speed 40r / min. After the air inlet temperature, air supply rate, air exhaust rate and nozzle speed reach the set values, connect the peristaltic pump pipeline to the solution and turn on the peristaltic pump for spray drying.

[0040] (4) After the solution is completely spray dried, turn on the air hammer to make the coated powder on the surface of the spray drying chamber fall into the bottom collection tank. Pour the powder in the collection tank into the vibrating sieve and sieve it to select powder with a particle size of less than 80μm.

[0041] Example 2

[0042] In this embodiment, the composite metal powder used is CuGrZr copper alloy powder with a particle size distribution of 15–60 μm; the low-temperature polymer is polyethylene oxide with a melting point of 65–67 °C; the solvent is distilled water; and the thickener is hydroxyl cellulose. The preparation process is as follows:

[0043] (1) The following are the mass ratios, where CuGrZr powder: polyethylene oxide = 100:3, CuGrZr powder: distilled water = 2:1, and the mass of hydroxy cellulose is 0.5% of the distilled water. Weigh out polyethylene oxide, CuGrZr, distilled water and hydroxy cellulose respectively.

[0044] (2) Pour the weighed polyethylene oxide into distilled water, heat and stir to completely dissolve the polyethylene oxide, then add hydroxy cellulose. After the hydroxy cellulose is dissolved and evenly dispersed, add CuGrZr powder, heat and stir at 80℃ for 1 hour, and finally stir at room temperature for 1 hour.

[0045] (3) Turn on the low temperature spray drying equipment and set the equipment parameters as follows: air inlet temperature 50℃, air supply rate 40HZ, air exhaust rate 39HZ, nozzle speed 15000r / min, peristaltic pump speed 40r / min. After the air inlet temperature, air supply rate, air exhaust rate, and nozzle speed reach the set values, connect the peristaltic pump pipeline to the solution and turn on the peristaltic pump for low temperature spray drying.

[0046] (4) After the solution is completely spray dried, turn on the air hammer to make the coated powder on the surface of the spray drying chamber fall into the bottom collection tank. Pour the powder in the collection tank into the vibrating sieve and sieve it to select powder with a particle size of less than 80μm.

[0047] Example 3

[0048] The composite metal powder used in this embodiment is AlSi10Mg aluminum alloy powder with a particle size distribution of 0–53 μm; the low-temperature polymer is microcrystalline wax with a softening point of 72–80 °C; the solvent is tetrahydrofuran; and the thickener is polymethyl methacrylate. The preparation process is as follows:

[0049] (1) The following are mass ratios, in which AlSi10Mg: microcrystalline wax = 100: 4, AlSi10Mg: tetrahydrofuran = 3: 1, and the mass of polymethyl methacrylate is 1.5% of tetrahydrofuran. Weigh out microcrystalline wax, AlSi10Mg, tetrahydrofuran and polymethyl methacrylate respectively.

[0050] (2) Pour microcrystalline wax into tetrahydrofuran, heat and stir to completely dissolve the microcrystalline wax, then add polymethyl methacrylate. After the polymethyl methacrylate is dissolved and evenly dispersed, add AlSi10Mg powder, heat and stir at 50°C for 1.5 h, and finally stir at room temperature for 0.5 h.

[0051] (3) Turn on the organic spray drying equipment and set the equipment parameters as follows: air inlet temperature 60℃, air supply rate 35HZ, air exhaust rate 34.5HZ, nozzle speed 18000r / min, peristaltic pump speed 30r / min. After the air inlet temperature, air supply rate, air exhaust rate and nozzle speed reach the set values, connect the peristaltic pump pipeline to the solution and turn on the peristaltic pump for spray drying.

[0052] (4) After the solution is completely spray dried, turn on the air hammer to make the coated powder on the surface of the spray drying chamber fall into the bottom collection tank. Pour the powder in the collection tank into the vibrating sieve and sieve it to select powder with a particle size of less than 80μm.

[0053] Example 5

[0054] The composite metal powder used in this embodiment is CoCrMoW cobalt-chromium alloy powder with a particle size distribution of 0–53 μm; the low-temperature polymer is polyaldehyde resin with a softening point of 80–95 °C; the solvent is ethanol; and the thickener is polyvinylpyrrolidone. The preparation process is as follows:

[0055] (1) The following are mass ratios, where cobalt-chromium alloy powder: polyaldehyde resin = 100:5, cobalt-chromium alloy powder: ethanol = 1:1, and polyvinylpyrrolidone is 1% of ethanol. Weigh out polyaldehyde resin, cobalt-chromium alloy, ethanol and polyvinylpyrrolidone respectively.

[0056] (2) Pour the weighed polyaldehyde resin into ethanol, heat and stir to completely dissolve the polyaldehyde resin, then add polyvinylpyrrolidone. After the polyvinylpyrrolidone is dissolved and evenly dispersed, add cobalt chromium alloy powder, heat and stir at 65°C for 2 hours, and finally stir at room temperature for 0.5 hours.

[0057] (3) Turn on the organic spray drying equipment and set the equipment parameters as follows: air inlet temperature 80℃, air supply rate 30HZ, air exhaust rate 29.5HZ, nozzle speed 18000r / min, peristaltic pump speed 25r / min. After the air inlet temperature, air supply rate, air exhaust rate and nozzle speed reach the set values, connect the peristaltic pump pipeline to the solution and turn on the peristaltic pump for low temperature spray drying.

[0058] (4) After the solution is completely spray dried, turn on the air hammer to make the coated powder on the surface of the spray drying chamber fall into the bottom collection tank. Pour the powder in the collection tank into the vibrating sieve and sieve it to select powder with a particle size of less than 80μm.

[0059] Example 6

[0060] In this embodiment, the composite metal powder used is 316L alloy powder with a particle size distribution of 0–53 μm; the low-temperature polymer used is polyethylene glycol with a melting point of 65°C; the solvent used is distilled water; and the thickener used is hydroxymethyl cellulose. The preparation process of this embodiment is as follows:

[0061] (1) The following are the mass ratios, where 316L: polyethylene glycol = 100:8, 316L: distilled water = 1:1, and the mass of hydroxymethyl cellulose is 1.5% of the mass of distilled water; weigh out polyethylene glycol, 316L powder, distilled water and hydroxymethyl cellulose respectively;

[0062] (2) Pour the weighed polyethylene glycol into distilled water, heat and stir to completely dissolve the polyethylene glycol, then add hydroxymethyl fiber bundles. After the hydroxymethyl fiber bundles are dissolved and evenly dispersed, add 316L powder, heat and stir at 60°C for 3 hours, and finally stir at room temperature for 1 hour.

[0063] (3) Turn on the low temperature spray drying equipment and set the equipment parameters as follows: air inlet temperature 55℃, air supply rate 35HZ, air exhaust rate 34.5HZ, nozzle speed 15000r / min, peristaltic pump speed 25r / min. After the air inlet temperature, air supply rate, air exhaust rate and nozzle speed reach the set values, connect the peristaltic pump pipeline to the solution and turn on the peristaltic pump to carry out low temperature spray drying.

[0064] (4) After the solution is completely spray-dried, turn on the air hammer to make the coated powder on the surface of the spray drying chamber fall into the bottom collection tank. Pour the powder in the collection tank into the vibrating sieve and sieve it to select powder with a particle size of less than 80μm.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing composite metal powder for cold metal melting additive manufacturing, characterized in that: Includes the following steps: S1, low-temperature binder, thickener and metal powder are added to solvent, and the binder is gradually precipitated to the surface of metal powder by solvent precipitation method to form a composite powder with metal powder as the core and a thin layer of binder as the shell; S2, the composite powder is spray-dried to form spherical powder with a uniform surface, thus obtaining composite metal powder.

2. The method for preparing composite metal powder for cold metal melting additive manufacturing according to claim 1, characterized in that: In step S1, the binder is first added to the solvent and heated and stirred until dissolved. Then, the thickener is added and stirred until completely dissolved. Finally, the metal powder is added, heated and stirred, cooled to room temperature, and stirred again, so that the binder gradually precipitates onto the surface of the metal powder to form a thin coating layer.

3. The method for preparing composite metal powder for cold metal melting additive manufacturing according to claim 1, characterized in that: In step S1, by mass percentage, the ratio of metal powder to low-temperature binder is 85:15 to 99.5:0.5; the ratio of metal powder to solvent is 0.5:1 to 5:1; and the mass of thickener is 0.% to 5% of the mass of solvent.

4. The method for preparing composite metal powder for cold metal melting additive manufacturing according to claim 1, characterized in that: In step S1, the thickener is one or a mixture of two or more of the following: polyvinylpyrrolidone, hydroxymethyl cellulose, ethyl cellulose, phosphate esters, sodium polystyrene sulfonate, glycerin, polyamide wax, citric acid, and polymethyl methacrylate.

5. The method for preparing composite metal powder for cold metal melting additive manufacturing according to claim 1, characterized in that: In step S1, the low-temperature binder is one or a mixture of two or more of the following: rosin, paraffin wax, microcrystalline wax, ethylene-vinyl acetate copolymer, epoxy resin, phenolic resin, polyethylene glycol, polyaldehyde resin, and polyethylene oxide.

6. The method for preparing composite metal powder for cold metal melting additive manufacturing according to claim 1, characterized in that: In step S2, a spray dryer is used for spray drying. The inlet air temperature of the spray dryer is set to 40-150℃, the air supply rate is 20-40Hz, the exhaust air rate is 20-40Hz, the peristaltic pump speed is 20-100r / min, and the nozzle speed is 10000-20000r / min.

7. The method for preparing composite metal powder for cold metal melting additive manufacturing according to claim 6, characterized in that: After spray drying, powder with a particle size of less than 80 μm is screened.

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