CN114262518B - Nylon powder material for selective laser sintering and preparation method thereof - Google Patents
Nylon powder material for selective laser sintering and preparation method thereof Download PDFInfo
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Abstract
The invention provides a preparation method of nylon powder material for selective laser sintering, which comprises the following steps: after the nylon granules undergo a cryogenic grinding process and a classifying and sieving process, nylon powder with the average particle diameter of 50-75 mu m and the diameter distance of 0.6-1.5 is prepared; the high polymer powder is added from the top end of a heat treatment tower, the heat treatment tower is vertically arranged, the heat treatment tower comprises three sections of areas, namely a heating area, a heat preservation area and a cooling area which are sequentially arranged from top to bottom, the cooling area adopts a five-section cooling process, and nylon powder with the average particle diameter of 50-75 mu m and the diameter distance of 0.6-1.5 is prepared after passing through the three sections of areas; and adding a flow aid into the nylon powder after the nylon powder is subjected to a grading sieving process, so as to obtain the nylon powder for selective laser sintering. The nylon powder material prepared by the invention has moderate average particle size, narrow particle size distribution, high sphericity, high enthalpy value and wide sintering window.
Description
Technical Field
The invention belongs to the technical field of additive manufacturing, and particularly relates to a nylon powder material for selective laser sintering and a preparation method thereof.
Background
Selective laser sintering technology is currently a commonly used rapid prototyping technology that allows for the creation of a computer three-dimensional model of a target part without tooling, slicing the three-dimensional model with layering software, and finally obtaining a three-dimensional body from multiple stacks of laser sintered powder.
The polymer materials mainly used for the selective laser sintering technology at present are thermoplastic materials, such as nylon 612, polyurethane, polyamide, polyether-ether-ketone and other powder materials. The main methods for preparing the powder on the market are a solvent precipitation method and a cryogenic grinding method, wherein the powder prepared by the solvent precipitation method has high sphericity, good fluidity, high enthalpy value and wide sintering window, but the manufacturing price is high; the powder prepared by the cryogenic grinding method has low price, but has irregular sphericity, poor sphericity, low enthalpy value and narrow sintering window. Powder with poor sphericity leads to flowability of the powder, which can affect powder spreading during sintering. The powder with low enthalpy value is easy to melt unsintered powder by self heat of the melted body in the sintering process, so that the surface of a workpiece is poor, the roughness of the workpiece is high, and the workpiece is easy to warp due to the powder with narrow sintering window in the sintering process. Therefore, the polymer powder prepared by cryogenic grinding has poor morphology regularity, wide particle size distribution, poor fluidity, low enthalpy value and narrow sintering window, which affects the application of the polymer powder to the selective laser sintering technology and the application scene of the selective laser sintering technology, while most of thermoplastic powder cannot be prepared by a solvent precipitation method, and is generally prepared by a deep powder grinding method.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a preparation method of nylon powder for selective laser sintering, which is used for preparing polymer powder for selective laser sintering with low price and wide application range and improving sphericity, enthalpy value and sintering window of nylon powder material prepared by a cryogenic grinding method. The method comprises the steps of carrying out cryogenic grinding on a nylon material, optimizing the nylon powder material subjected to cryogenic grinding through a heat treatment tower process, and finally obtaining the nylon powder with moderate average particle size, narrow particle size distribution, high sphericity, high enthalpy value and wide sintering window.
The invention provides a preparation method of nylon powder material for selective laser sintering, which comprises the following steps:
step one: after the nylon granules undergo a cryogenic grinding process and a classifying and sieving process, nylon powder with the average particle diameter of 50-75 mu m and the diameter distance of 0.6-1.5 is prepared;
step two: adding the polymer powder from the top end of a heat treatment tower, wherein the heat treatment tower is vertically arranged, the heat treatment tower comprises three sections of areas, namely a heating area, a heat preservation area and a cooling area which are sequentially arranged from top to bottom, the cooling area adopts a five-section cooling process, and nylon powder with the average particle diameter of 50-75 mu m and the diameter distance of 0.6-1.5 is prepared after passing through the three sections of areas;
step three: and (3) adding a flow aid into the nylon powder prepared in the step (II) after a classifying and sieving process to prepare the nylon powder for selective laser sintering.
Further preferably, the total height of the powder in the heating area is 1m, the heating temperature is 200-300 ℃, and the powder falling speed is 0.5-1.5 m/h; the total height of the powder in the heat preservation area is 20m, the heat preservation temperature is 200-300 ℃, and the powder falling speed is 3-10 m/h.
Further preferably, the total height of the powder in the cooling zone is 10m and the powder falling speed is 3-40 m/h.
Further preferably, the five-stage cooling process adopted by the cooling area specifically comprises the following steps: the descending speed of the powder in the first stage of cooling is 15-20 m/h, and the total height of the powder is 2m; the descending speed of the powder in the second cooling section is 12-15 m/h, and the total height of the powder is 2m; the descending speed of the powder in the third section of cooling is 9-12 m/h, and the total height of the powder is 2m; the descending speed of the powder in the fourth stage of cooling is 6-9 m/h, and the total height of the powder is 2m; the descending speed of the powder in the fifth stage of cooling is 3-6 m/h, and the total height of the powder is 2m.
Further preferably, the nylon pellets are nylon 1212, nylon 12, nylon 1010, nylon 11, nylon 612, nylon 610, nylon 6 or nylon 66 pellets.
Further preferably, the cryogenic grinding process is as follows: the nylon granules are added into a cryogenic pulverizer, liquid nitrogen is introduced, the cryogenic pulverizer is started, the pulverizing temperature is between-120 ℃ and-80 ℃, and the stirring speed is between 1500r/min and 3000r/min.
Further preferably, the nylon powder produced in the first step has a bulk density of 0.38 to 0.45g/cc, a enthalpy value of 30 to 50J/g, and a sintering window of 20 to 30 ℃.
Further preferably, the nylon powder obtained in the second step has a bulk density of 0.45 to 0.52g/cc, a enthalpy value of 80 to 120J/g, and a sintering window of 30 to 50 ℃.
Further preferably, the flow aid may be fumed silica, fumed alumina or nano-titania.
The invention also provides a nylon powder material for selective laser sintering, which is characterized by being prepared by adopting the preparation method of the nylon powder material for selective laser sintering.
In the field of selective laser sintering, nylon powder needs to be paved from a powder supply system to molding through a scraper or a roller, so that the flowability of nylon is important, and the flowability of the nylon is mainly related to the morphology, the average particle size and the particle size distribution of the powder. If the nylon powder has a higher sphericity, the average particle diameter is in a suitable range, the particle diameter distribution is narrower, and the powder has better fluidity, which is more advantageous for application to equipment for selective laser sintering. If the nylon powder is crystallized at a slower crystallization speed in the cooling process, the more stable the crystallization, the higher the melting point of the nylon powder, the wider the sintering window (the sintering window is the difference between the starting point of the melting point of the powder and the ending point of the crystallization point of the powder), the higher the sintering temperature can be set when sintering the nylon powder, and the more complete the nylon powder is melted. If the crystal form of the nylon powder is more stable, the enthalpy value of the nylon powder is higher, and the thermal performance of the nylon powder is more stable, the nylon powder is less prone to be melted when being contacted with a melt melted by laser, and the workpiece surface prepared in this case is better.
After the nylon powder is subjected to a proper cryogenic grinding process, the nylon powder with proper particle size is obtained. But the nylon powder prepared by cryogenic grinding has irregular shape, poor sphericity, wide particle size distribution, wide diameter distance and narrow sintering window, thereby limiting the application of the nylon powder in the selective laser sintering technology. The invention screens and classifies the deeply cooled nylon powder to obtain micron-sized powder. After the heat treatment tower, the sphericity of the powder is improved, the diameter distance of the nylon powder is reduced, the fluidity of the powder is increased, the crystallization performance of the nylon powder is improved, and the enthalpy value and sintering window of the nylon powder are improved. In the heat treatment tower, when the nylon powder in the heating area is heated to a higher temperature than the melting point, the nylon powder surface is Cheng Nian in a high-temperature state, and in this state, the nylon powder surface is in a form capable of undergoing plastic irreversible deformation under the action of external force. The viscous state of nylon has similar fluidity of low molecular liquid, so that the pressure difference can be formed on the upper surface and the lower surface of the nylon powder under the action of surface tension in the descending process of the nylon powder. So that irregular upper and lower portions of the nylon powder surface are subjected to different forces, the nylon powder surface tends to be a smooth surface, and finally the powder is changed from irregularly shaped powder to nearly spherical or spherical powder. When the temperature of the thermal insulation area is high, isothermal crystallization can occur, meanwhile, in the cooling process of the cooling area, the process is very slow, a five-section cooling process is adopted, and the nylon powder can be crystallized more completely in the whole process, so that a more stable crystal form is formed. The melting point of the nylon powder can be improved, the sintering window of the nylon powder is improved, the enthalpy value of the nylon powder is also improved, and the nylon powder is more suitable for the field of selective laser sintering.
The invention provides a nylon powder material for selective laser sintering and a preparation method thereof, which have the following beneficial effects: the nylon powder with moderate grain diameter, narrow grain diameter distribution, high sphericity and good fluidity is obtained after the nylon granules are subjected to cryogenic crushing and heat treatment in a heat treatment tower. Meanwhile, five sections of cooling are carried out in the cooling stage of the heat treatment tower, so that the enthalpy value and the sintering window of the nylon powder can be improved, the nylon powder is suitable for the field of selective laser sintering, and the workpiece prepared from the nylon powder has good performance and good surface.
Drawings
FIG. 1 is a DSC of a comparative example of a process for preparing a nylon powder material for selective laser sintering in accordance with the present invention;
FIG. 2 is a DSC of an embodiment of a method of preparing a nylon powder material for selective laser sintering according to the present invention.
Detailed Description
The present invention will be described in further detail by the following embodiments.
Comparative example one
Step one: adding nylon 1212 granules into a cryogenic pulverizer, introducing liquid nitrogen, starting the cryogenic pulverizer, and stirring at a speed of 2000r/min at a pulverizing temperature of-100 ℃. Then sieving and grading to obtain nylon 1212 powder for selective laser sintering with average particle diameter of 60 μm, diameter distance of 1.9 and apparent density of 0.39 g/cc. The enthalpy value of the nylon powder is 40J/g, the first melting point is 178 ℃, and the sintering window is 22 ℃.
Example 1
Step one: adding nylon 1212 granules into a cryogenic pulverizer, introducing liquid nitrogen, starting the cryogenic pulverizer, and stirring at a pulverizing temperature of-100deg.C at a stirring rate of 2000r/min to obtain nylon 1212 powder with average particle diameter of 60 μm, diameter distance of 1.9 and apparent density of 0.39 g/cc. The enthalpy value of the nylon 1212 powder is 40J/g, the first melting point is 178 ℃, and the sintering window is 22 ℃.
Step two: the cryogenic crushed nylon 1212 powder is added from the top end of a heat treatment tower which is vertically arranged, and each section of the heat treatment tower comprises three sections of areas, and the descending speed of the powder and the temperature of the powder can be controlled by each section of area. A first zone heating stage, wherein the total height of the powder is 1m, the temperature is set at 208 ℃, and the descending speed of the powder is 1m/h; the second zone heat preservation stage, wherein the total height is 20m, the temperature is set at 213 ℃, and the powder falling speed is 8m/h; the third zone cooling stage, the height is 10m, the cooling first section is 20m/h, and the height is 2m; the second cooling section is 15m/h and the height is 2m; the third cooling section is 12m/h, and the height is 2m; the second cooling section is 9m/h and the height is 2m; the second cooling section is 6m/h and the height is 2m. The nylon 1212 powder obtained had an average particle diameter of 58 μm, a gauge of 0.8 and a bulk density of 0.5g/cc. The enthalpy value of the nylon 1212 powder is 96J/g, the second melting point is 187 ℃, and the sintering window is 31 ℃.
Step three: and sieving and grading the nylon 1212 powder, and then adding a fumed silica flow aid to obtain the nylon 1212 powder for selective laser sintering.
Example two
Step one: adding nylon 12 into a cryogenic pulverizer, introducing liquid nitrogen, starting the cryogenic pulverizer, and stirring at a temperature of-120 ℃ and a stirring rate of 3000r/min to obtain polyurethane powder. Then, the polyurethane powder having an average particle diameter of 45 μm, a gauge of 2.1 and a bulk density of 0.38g/cc was obtained by sieving and classifying. The enthalpy value of the nylon 12 powder is 30J/g, the first melting point is 177 ℃, and the sintering window is 21 ℃.
Step two: the deeply-cooled crushed nylon 12 powder is added from the top end of a heat treatment tower which is vertically arranged, and each section of the heat treatment tower comprises three sections of areas, wherein the dropping speed of different powder and the temperature of the powder can be controlled by each section of area. A first zone heating stage, wherein the total height of the powder is 1m, the temperature is set at 207 ℃, and the descending speed of the powder is 1.5m/h; the second zone heat preservation stage, wherein the total height is 20m, the temperature is set at 212 ℃, and the powder falling speed is 10m/h; the third zone cooling stage, the height is 10m, the cooling first section is 18m/h, and the height is 2m; the second cooling section is 14m/h, and the height is 2m; the third cooling section is 11m/h, and the height is 2m; the second cooling section is 8m/h, and the height is 2m; the second cooling section is 5m/h and the height is 2m. The nylon 12 powder obtained had an average particle diameter of 42. Mu.m, a gauge of 0.9, a bulk density of 0.45g/cc, a heat content of 98J/g, a second melting point of 186℃and a sintering window of 30 ℃.
Step three: and sieving and grading nylon 12 powder, and adding a fumed silica flow aid to obtain the nylon 12 powder for selective laser sintering.
Example III
Step one: adding the nylon 1010 granules into a cryogenic pulverizer, introducing liquid nitrogen, starting the cryogenic pulverizer, and stirring at the pulverizing temperature of-100 ℃ and the stirring speed of 3000r/min to obtain nylon 1010 powder. And sieving and grading to obtain nylon 1010 powder with average particle diameter of 50 μm and diameter distance of 1.9. The enthalpy value of the nylon 1010 powder is 36J/g, the first melting point is 195 ℃ and the sintering window is 23 ℃.
Step two: the deeply-cooled crushed nylon 1010 powder is added from the top end of a heat treatment tower, the heat treatment tower is vertically arranged, and comprises three sections of areas, and each section of area can control the falling speed of different powder and the temperature of the powder. A first zone heating stage, wherein the total height of the powder is 1m, the temperature is set to 225 ℃, and the descending speed of the powder is 1.3m/h; the second zone heat preservation stage, wherein the total height is 20m, the temperature is set at 230 ℃, and the powder descending speed is 8m/h; the third zone cooling stage, the height is 10m, the cooling first section is 17m/h, and the height is 2m; the second cooling section is 13m/h and the height is 2m; the third cooling section is 10m/h and the height is 2m; the second cooling section is 8m/h, and the height is 2m; the second cooling section is 4m/h and the height is 2m. The nylon 1010 powder obtained had an average particle diameter of 48. Mu.m, a gauge of 0.8 and a bulk density of 0.46g/cc. The enthalpy value of the nylon 1010 powder is 80J/g, the second melting point is 205 ℃, and the sintering window is 33 ℃.
Step three: and sieving and grading the nylon 1010 powder, and adding a fumed silica flow aid to obtain the nylon 1010 powder for selective laser sintering.
Example IV
Step one: adding the nylon 11 granules into a cryogenic pulverizer, introducing liquid nitrogen, starting the cryogenic pulverizer, and stirring at the pulverizing temperature of-100 ℃ and the stirring speed of 2500r/min to obtain nylon 11 powder. Then, the nylon 11 powder having an average particle diameter of 70 μm, a diameter distance of 1.8 and a bulk density of 0.42g/cc was obtained by sieving and classifying. The enthalpy value of the nylon 11 powder is 42J/g, the first melting point is 192 ℃, and the sintering window is 27 ℃.
Step two: the deeply-cooled crushed nylon 11 powder is added from the top end of a heat treatment tower, the heat treatment tower is vertically arranged, and comprises three sections of areas, and each section of area can control the falling speed of different powder and the temperature of the powder. A first zone heating stage, wherein the total height of the powder is 1m, the temperature is set at 222 ℃, and the descending speed of the powder is 1.1m/h; the second zone heat preservation stage, wherein the total height is 20m, the temperature is set at 227 ℃, and the powder falling speed is 7m/h; the third zone cooling stage, the height is 10m, the cooling first section is 15m/h, and the height is 2m; the second cooling section is 12m/h, and the height is 2m; the third cooling section is 9m/h and the height is 2m; the second cooling section is 6m/h and the height is 2m; the second cooling section is 3m/h and the height is 2m. The nylon 11 powder obtained had an average particle diameter of 67 μm and a gauge of 0.7. The enthalpy value of the nylon 11 powder is 93J/g, the second melting point is 215 ℃, and the sintering window is 50 ℃.
Step three: and sieving and grading nylon 11 powder, and adding a fumed silica flow aid to obtain the nylon 11 powder for selective laser sintering.
Example five
Step one: adding nylon 612 granules into a cryogenic pulverizer, introducing liquid nitrogen, starting the cryogenic pulverizer, pulverizing at-80deg.C, and stirring at 1500r/min to obtain nylon 612 powder. Then sieving and classifying to obtain nylon 612 powder with average particle diameter of 80 μm, diameter distance of 1.5 and apparent density of 0.45 g/cc. Nylon 612 powder has a heat content of 50J/g, a first melting point of 203 ℃, and a sintering window of 27 ℃.
Step two: the cryogenically crushed nylon 612 powder is added from the top of a heat treatment tower which is vertically arranged and comprises three sections of areas, and each section of area can control the falling speed of different powder and the temperature of the powder. A first zone heating stage, wherein the total height of the powder is 1m, the temperature is set at 233 ℃, and the descending speed of the powder is 0.9m/h; the second zone heat preservation stage, wherein the total height is 20m, the temperature is set at 238 ℃, and the powder falling speed is 6m/h; the third zone cooling stage, the height is 10m, the cooling first section is 18m/h, and the height is 2m; the second cooling section is 14m/h, and the height is 2m; the third cooling section is 11m/h, and the height is 2m; the second cooling section is 8m/h, and the height is 2m; the second cooling section is 5m/h and the height is 2m. The nylon 612 powder obtained had an average particle diameter of 75 μm, a gauge of 0.6 and a bulk density of 0.52g/cc. Nylon 612 powder has a enthalpy value of 102J/g, a second melting point of 217 ℃, and a sintering window of 41 ℃.
Step three: the nylon 612 powder is sieved and graded, and then fumed silica flow aid is added to obtain the nylon 612 powder for selective laser sintering.
Example six
Step one: adding nylon 610 granules into a cryogenic pulverizer, introducing liquid nitrogen, starting the cryogenic pulverizer, and stirring at a speed of 2000r/min at a pulverizing temperature of-100 ℃ to obtain nylon 610 powder. Then, the nylon 610 powder having an average particle diameter of 60 μm, a diameter distance of 1.7 and a bulk density of 0.4g/cc was obtained by sieving and classifying. The enthalpy value of the nylon 610 powder is 38J/g, the first melting point is 211 ℃, and the sintering window is 27 ℃.
Step two: the cryogenic crushed nylon 610 powder is added from the top end of a heat treatment tower which is vertically arranged, and the heat treatment tower comprises three sections of areas, wherein each section of area can control the falling speed of different powder and the temperature of the powder. A first zone heating stage, wherein the total height of the powder is 1m, the temperature is set to 241 ℃, and the descending speed of the powder is 0.7m/h; the second zone heat preservation stage, wherein the total height is 20m, the temperature is set at 246 ℃, and the powder falling speed is 5m/h; the third zone cooling stage, the height is 10m, the cooling first section is 17m/h, and the height is 2m; the second cooling section is 13m/h and the height is 2m; the third cooling section is 10m/h and the height is 2m; the second cooling section is 7m/h and the height is 2m; the second cooling section is 4m/h and the height is 2m. The nylon 610 powder obtained had an average particle diameter of 58. Mu.m, a gauge of 0.8 and a bulk density of 0.51g/cc. The enthalpy value of the nylon 610 powder is 108J/g, the second melting point is 218 ℃, and the sintering window is 34 ℃.
Step three: and sieving and grading the nylon 610 powder, and adding a fumed silica flow aid to obtain the nylon 610 powder for selective laser sintering.
Example seven
Step one: adding the nylon 6 granules into a cryogenic pulverizer, introducing liquid nitrogen, starting the cryogenic pulverizer, and stirring at the pulverizing temperature of-100 ℃ and the stirring speed of 2000r/min to obtain nylon 6 powder. Then, the nylon 6 powder having an average particle diameter of 60 μm, a gauge of 1.7 and a bulk density of 0.4g/cc was obtained by sieving and classifying. The enthalpy value of the nylon 6 powder is 39J/g, the first melting point is 219 ℃, and the sintering window is 28 ℃.
Step two: the deeply-cooled crushed nylon 6 powder is added from the top end of a heat treatment tower, the heat treatment tower is vertically arranged, and comprises three sections of areas, and each section of area can control the falling speed of different powder and the temperature of the powder. A first zone heating stage, wherein the total height of the powder is 1m, the temperature is set to 249 ℃, and the descending speed of the powder is 0.5m/h; the second zone heat preservation stage, wherein the total height is 20m, the temperature is set at 254 ℃, and the powder falling speed is 3m/h; the third zone cooling stage, the height is 10m, the cooling first section is 17m/h, and the height is 2m; the second cooling section is 13m/h and the height is 2m; the third cooling section is 10m/h and the height is 2m; the second cooling section is 7m/h and the height is 2m; the second cooling section is 4m/h and the height is 2m. The nylon 6 powder obtained had an average particle diameter of 59. Mu.m, a gauge of 0.9 and a bulk density of 0.52g/cc. The enthalpy value of the nylon 6 powder is 114J/g, the second melting point is 226 ℃, and the sintering window is 35 ℃.
Step three: and sieving and grading the nylon 6 powder, and then adding the fumed silica flow aid to obtain the nylon 6 powder for selective laser sintering.
Example eight
Step one: and (3) adding the nylon 66 granules into a cryogenic pulverizer, introducing liquid nitrogen, starting the cryogenic pulverizer, and stirring at the pulverizing temperature of-100 ℃ and the stirring speed of 2000r/min to obtain nylon 66 powder. Then, the nylon 66 powder with an average particle diameter of 60 μm, a diameter distance of 1.7 and a bulk density of 0.4g/cc was obtained by sieving and classifying. The enthalpy value of the nylon 66 powder is 40J/g, the first melting point is 256 ℃ and the sintering window is 30 ℃.
Step two: the deeply-cooled crushed nylon 66 powder is added from the top end of a heat treatment tower which is vertically arranged, and each section of the heat treatment tower comprises three sections of areas, and the descending speed of the powder and the temperature of the powder can be controlled by each section of area. A first zone heating stage, wherein the total height of the powder is 1m, the temperature is set at 300 ℃, and the descending speed of the powder is 1m/h; the second zone heat preservation stage, wherein the total height is 20m, the temperature is set at 300 ℃, and the powder falling speed is 8m/h; the third zone cooling stage, the height is 10m, the cooling first section is 17m/h, and the height is 2m; the second cooling section is 13m/h and the height is 2m; the third zone cooling stage, the height is 10m, the cooling first section is 17m/h, and the height is 2m; the second cooling section is 13m/h and the height is 2m; the third cooling section is 10m/h and the height is 2m; the second cooling section is 7m/h and the height is 2m; the second cooling section is 4m/h and the height is 2m. The nylon 66 powder obtained had an average particle diameter of 58. Mu.m, a gauge of 0.8 and a bulk density of 0.49g/cc. The enthalpy value of the nylon 66 powder is 120J/g, the second melting point is 266 ℃, and the sintering window is 40 ℃.
Step three: and sieving and grading the nylon 66 powder, and adding a fumed silica flow aid to obtain the nylon 66 powder for selective laser sintering.
The diameter distance in the embodiment of the invention is = (D90-D10)/D50, and the representative meaning of the diameter distance is the distribution of powder particle size. Sintering window = melting point peak start point-crystallization peak end point, which represents a range of values where the sintering temperature can be set, the wider the sintering window, the more favorable the sintering of the powder, the specific parameters of the preparation method of the nylon powder material prepared by the present invention are shown in table 1-2, fig. 1 is a DSC diagram of a comparative example one, and fig. 2 is a DSC diagram of an example one.
TABLE 1 Nylon powder parameter table prepared in step one of the preparation methods of nylon powder material for selective laser sintering of the present invention
TABLE 2 parameter Table of Nylon powder prepared in step two of the preparation method of Nylon powder material for selective laser sintering of the present invention
Claims (7)
1. The preparation method of the nylon powder material for selective laser sintering is characterized by comprising the following steps of:
step one: after the nylon granules undergo a cryogenic grinding process and a classifying and sieving process, nylon powder with the average particle diameter of 50-75 mu m and the diameter distance of 0.6-1.5 is prepared; the bulk density of the nylon powder prepared in the first step is 0.38-0.45 g/cc, the enthalpy value is 30-50J/g, and the sintering window is 20-30 ℃;
step two: the nylon powder is added from the top end of a heat treatment tower, the heat treatment tower is vertically arranged, the heat treatment tower comprises three sections of areas, the three sections of areas are a heating area, a heat preservation area and a cooling area which are sequentially arranged from top to bottom, the cooling area adopts a five-section cooling process, and the nylon powder is prepared into nylon powder with the average grain diameter of 50-75 mu m and the diameter distance of 0.6-1.5 after passing through the three sections of areas; the bulk density of the nylon powder prepared in the second step is 0.45-0.52 g/cc, the enthalpy value is 80-120J/g, and the sintering window is 30-50 ℃;
step three: and (3) adding a flow aid into the nylon powder prepared in the step (II) after a classifying and sieving process to prepare the nylon powder for selective laser sintering.
2. The method for producing nylon powder material for selective laser sintering according to claim 1, wherein the total height of the powder in the heating region is 1m, the heating temperature is 200 to 300 ℃, and the powder falling speed is 0.5 to 1.5m/h; the total height of the powder in the heat preservation area is 20m, the heat preservation temperature is 200-300 ℃, and the powder falling speed is 3-10 m/h.
3. The method for producing nylon powder material for selective laser sintering according to claim 1, wherein the total height of the powder in the cooling zone is 10m and the falling speed of the powder is 3 to 40m/h.
4. The method for preparing nylon powder material for selective laser sintering according to claim 3, wherein the five-stage cooling process adopted by the cooling area is specifically as follows: the descending speed of the powder in the first stage of cooling is 15-20 m/h, and the total height of the powder is 2m; the descending speed of the powder in the second cooling section is 12-15 m/h, and the total height of the powder is 2m; the descending speed of the powder in the third section of cooling is 9-12 m/h, and the total height of the powder is 2m; the descending speed of the powder in the fourth stage of cooling is 6-9 m/h, and the total height of the powder is 2m; the descending speed of the powder in the fifth stage of cooling is 3-6 m/h, and the total height of the powder is 2m.
5. The method for preparing nylon powder material for selective laser sintering according to claim 4, wherein the nylon pellets are nylon 1212, nylon 12, nylon 1010, nylon 11, nylon 612, nylon 610, nylon 6 or nylon 66 pellets.
6. The method for preparing nylon powder material for selective laser sintering according to claim 5, wherein the cryogenic pulverizing process is as follows: the nylon granules are added into a cryogenic pulverizer, liquid nitrogen is introduced, the cryogenic pulverizer is started, the pulverizing temperature is between-120 ℃ and-80 ℃, and the stirring speed is between 1500r/min and 3000r/min.
7. The method for preparing nylon powder material for selective laser sintering according to claim 1, wherein the flow aid is fumed silica, fumed alumina or nano-titania.
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