Water atomized powder and additive manufacturing method

Abstract

This invention provides water-atomized powders and the like that can be used in powder deposition methods such as the DED method. [Solution] This is a water atomization powder for additive manufacturing containing metal particles. The water atomization powder has a flow energy of 30 mJ / cm³ normalized by the total volume of the metal particles when the air permeability is 4 mm / s. 3 It is less than [amount missing]. The water atomized powder of the present invention has high fluidity, so even when used in powder deposition methods such as the DED method, metal particles can be stably discharged from the nozzle. As a result, it is possible to form a molded object without density unevenness. Furthermore, by forming a molded object using the water atomized powder of the present invention, it is possible to manufacture the molded object at a lower cost than when using metal particles produced by gas atomization or plasma atomization methods.

Description

[Technical Field]

[0001] The present invention relates to a water atomized powder for additive manufacturing containing metal particles and a method for additive manufacturing. [Background technology]

[0002] Additive manufacturing (AM) technology is also known as 3D printing in Japan. Additive manufacturing methods include those using metal particles or metal wires as raw materials, those using resins as raw materials, and those using ceramics as raw materials. Among these, representative examples of metal additive manufacturing methods using metal particles as raw materials include powder bed fusion (PAD) and powder bed deposition (PAD).

[0003] Powder bed fusion is one example of a powder layer melting method. This method is further classified into methods such as selective laser melting (SLM) and electron beam melting (EBM).

[0004] In powder bed fusion fusion, metal particles are supplied to a stage to create a metal powder bed, which is then irradiated with a heat source to melt and solidify. This process is repeated, and the resulting object is built up in layers, thus performing additive manufacturing.

[0005] It is preferable that the metal powder bed on the stage is formed without any uneven distribution of metal particles. Forming the metal powder bed in this manner allows for the creation of highly homogeneous and densely sized molded objects.

[0006] In this powder bed fusion method, metal particles are used to create the structure. These metal particles are mainly produced by gas atomization or plasma atomization.

[0007] Because metal particles produced by gas atomization and plasma atomization are often expensive, powder materials produced by water atomization are being manufactured instead.

[0008] As an example of metal particles produced by the water atomization method, water atomized particles having a predetermined particle size distribution and a predetermined rotational angle of repose are disclosed in Patent Document 1. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2023-159851 [Overview of the project] [Problems that the invention aims to solve]

[0010] In powder deposition methods, there are methods such as Direct Energy Deposition (DED), which involves melting materials such as metal particles with a heat source and then depositing the molten materials.

[0011] In the DED (Digital-Emitted Deposition) method, additive manufacturing is performed by extruding metal particles from a nozzle. In the DED method, the stable extrusion of raw material powder from the nozzle allows for stable operation of the device, enabling manufacturing without density unevenness. Compared to powder bed bonding, the powder deposition method has the advantage of faster manufacturing speed, allowing for the rapid production of larger objects. Furthermore, since worn areas can be repaired by building up material, it can be used for repairing wear parts such as molds.

[0012] Metal particles produced by the water atomization method, as exemplified by Patent Document 1, contain many irregularly shaped particles. Therefore, when metal particles produced by the water atomization method are used in the DED system, the fluidity is insufficient, resulting in a problem where the metal particles cannot be stably discharged from the nozzle.

[0013] This invention has been made in view of the above-mentioned problems, and aims to provide water atomized powders and the like that can be used in powder deposition methods such as the DED method. [Means for solving the problem]

[0014] To solve the above problems, the present invention has the following features. [1] A water atomization powder for additive manufacturing containing metal particles, The fluid energy at an airflow rate of 4 mm / s, normalized by the total volume of the metal particles, is 30 mJ / cm³. 3 A water atomizing powder that is less than [amount missing]. [2] The water atomized powder according to [1], wherein the metal particles have a volume-based 10% cumulative particle diameter D10 measured by laser diffraction scattering method of 40 μm or more. [3] The water atomized powder according to [2], wherein the metal particles have a volume-based 90% cumulative particle size D90 measured by laser diffraction scattering method of 150 μm or less. [4] The metal particles are the water atomized powder according to [3], wherein the cumulative particle size D90 is 110 μm or less. [5] A water atomized powder as described in any of [1] to [4], having an average circularity of 0.80 or higher. [6] The metal particles are water atomized powder according to any one of [1] to [5], wherein the oxygen concentration is 7000 ppm or less. [7] The aforementioned metal particles are water atomized powder according to any one of [1] to [6], comprising an iron-based alloy. [8] A method for additive manufacturing that uses metal particles to create additive structures, A dispensing step in which the water atomized powder described in any of [1] to [7] is dispensed from a nozzle as the metal particles, A method for additive manufacturing, comprising a deposition step of depositing the metal particles discharged from the nozzle while melting them with a heat source.

Advantages of the Invention

[0015] According to the water atomized powder of the present invention, etc., since it has high fluidity, even when used in a powder deposition method represented by the DED method, metal particles can be stably discharged from the nozzle. As a result, it becomes possible to form a shaped object without density deviation. Further, by shaping a shaped object using the water atomized powder of the present invention, etc., it becomes possible to manufacture a shaped object at a lower cost than when using metal particles manufactured by a gas atomization method or a plasma atomization method.

Brief Description of the Drawings

[0016] [Figure 1] It is a flowchart showing a method for manufacturing water atomized powder. [Figure 2] It is a flowchart showing a laminated shaping method using water atomized powder.

Modes for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described. The water atomized powder for laminated shaping of the present invention is an aggregate of metal particles formed by the water atomization method.

[0018] For the water atomized powder of the present invention, the value obtained by normalizing the fluid energy (AE: mJ) at an air ventilation rate of 4 mm / s with the total volume of the metal particles is less than 30 mJ / cm 3 The fluid energy AE is the energy required to displace the powder in a predetermined flow pattern and flow rate in a state where air is introduced from the bottom of the container.

[0019] The value obtained by normalizing the fluid energy (AE: mJ) with the total volume of the metal particles is preferably less than 25 mJ / cm 3 and more preferably less than 20 mJ / cm 3 When the value is 30 mJ / cm 3By keeping the particle size below a certain level, metal particles can be stably ejected from the nozzle when creating objects using the powder deposition method. As a result, it becomes possible to obtain high-density, high-quality additively manufactured objects.

[0020] The fluid energy (AE: mJ), normalized by the total volume of metal particles, can be determined using a powder fluidity analyzer. While there are no particular limitations on the type of powder fluidity analyzer, one example is the Freeman Technology FT4 powder rheometer.

[0021] The fluid energy (AE: mJ), normalized by the total volume of metal particles, is calculated as follows: Metal particles are supplied to a container until they reach a predetermined position. Then, air at 4 mm / s is introduced from the bottom of the container, and a vane-shaped blade is moved from the top to the bottom of the container. The amount of work done by the blade as it moves through the metal particles is determined. This determined amount of work is defined as the fluid energy (AE: mJ). The total volume of metal particles is the volume of the container into which the metal particles were supplied until they reached the predetermined position.

[0022] It is more preferable that the metal particles have a volume-based 10% cumulative particle size D10 measured by laser diffraction scattering, which is 40 μm or larger. Note that the cumulative particle size D10 is the particle size corresponding to 10% of the cumulative particle size distribution of equivalent particle sizes. If the cumulative particle size D10 falls below 40 μm, the proportion of fine powder increases, resulting in decreased fluidity. Having a D10 of this value ensures appropriate fluidity of the water atomized powder.

[0023] Furthermore, the metal particles should preferably have a volume-based 90% cumulative particle size D90 measured by laser diffraction scattering, which is 150 μm or less, more preferably 110 μm or less, and more preferably 150 μm or less. Note that the cumulative particle size D90 is the particle size corresponding to 90% in the cumulative particle size distribution of equivalent particle size. Having a cumulative particle size D90 of this value makes it possible to ensure appropriate fluidity of the water atomized powder. If D90 is greater than 150 μm, the particle size distribution becomes wider and there are more coarse particles, which reduces the discharge performance from the nozzle.

[0024] Furthermore, it is preferable that the metal particles satisfy both the D10 and D90 requirements. For example, it is preferable that D10 is 40 μm or larger and D90 is 150 μm or smaller.

[0025] While there are no particular limitations on the laser diffraction particle size analyzer, examples include the LA-950V2 (model name) manufactured by Horiba, Ltd. For accurate measurements, it is preferable to use a laser diffraction particle size analyzer with a lower limit of 0.1 μm or less and an upper limit of 200 μm or more in the measurable particle size range. In a laser diffraction particle size analyzer, a laser beam is irradiated onto a solvent containing dispersed metal particles, and the particle size distribution of the metal particles is measured from the diffraction and scattering intensity of the laser beam.

[0026] The volume of metal particles with a circularity of 0.80 or higher is preferably 50% or more of the total volume of metal particles. Hereinafter, the volume of metal particles with the smallest circularity is calculated, and the circularity at which the volume sum reaches 50% is also referred to as the average circularity. The average circularity is more preferably 0.90 or higher. Having an average circularity of this value makes it possible to ensure the appropriate fluidity of the water atomization powder.

[0027] The average circularity can be determined by measuring multiple metal particles with a particle image analyzer, integrating their volumes starting with the particles with the lowest circularity, and using the circularity at which the integrated volume reaches 50%.

[0028] The circularity of a metal particle is calculated as [circumference of a circle with the same area as the projected figure] / [total length of the outline of the projected figure]. If the metal particle is a perfect sphere, the circularity is "1".

[0029] The oxygen concentration of the metal particles is preferably 7000 ppm or less, more preferably 5000 ppm or less, and more preferably 1500 ppm or less. By having an oxygen concentration of 7000 ppm or less in the metal particles, sputtering during additive manufacturing can be suppressed.

[0030] Furthermore, when oxygen in metal particles vaporizes, defects known as blowholes may occur in the fabricated object, and coarse oxides may form, potentially degrading its mechanical properties. By keeping the oxygen concentration of the metal particles below 5000 ppm, the occurrence of such blowholes and the degradation of mechanical properties in the fabricated object can be suppressed.

[0031] The oxygen concentration of metal particles is not particularly limited, but can be measured, for example, by the inert gas fusion method. An example of a device for measuring the oxygen concentration of metal particles is the oxygen and nitrogen analyzer (product name: ON736) manufactured by LECO Japan.

[0032] The metal particles preferably include those formed by the water atomization method of an iron-based alloy. More preferably, the metal particles consist solely of those formed by the water atomization method of the iron-based alloy.

[0033] Examples of iron-based alloys used for metal particles include SUS316L, SUS420J2, SUS630, maraging steel, carbon steel, pure iron, SKDSKH61, and SKD51. Since metal particles composed of these materials are particularly inexpensive among the metals used in water atomization powders, they can reduce manufacturing costs.

[0034] The method for producing the water atomized powder described above will now be explained. Figure 1 shows the process flow for the method of producing the water atomized powder. As shown in Figure 1, first, a particle formation step is performed in which metal particles are formed by the water atomization method (step S101).

[0035] Water atomization is a method of obtaining metal powder by injecting cooling water from a nozzle into a flow of molten metal, thereby breaking up the molten steel. Compared to gas atomization, water atomization uses only water, resulting in higher production capacity and lower costs. Therefore, it can reduce the manufacturing cost of metal particles.

[0036] In the water atomization method, the rapid cooling rate after fragmentation makes it difficult to ensure sufficient time for the molten steel to become spherical due to surface tension. As a result, metal particles formed by the water atomization method tend to have irregular shapes. In the particle formation step S101, it is preferable to adjust the spray pattern of the cooling water discharged towards the molten metal flow, and the convergence angle formed by the trajectory of the cooling water and the trajectory of the molten metal flow, to be within a predetermined range.

[0037] For example, it is preferable to inject cooling water at a spray pressure of 10 MPa or more with a spread angle in the range of 5 to 30°. Furthermore, the droplet diameter of the cooling water should be 100 μm or less. The convergence angle formed by the trajectory of the cooling water discharged toward the molten metal flow and the trajectory of the molten metal flow should be 5 to 10°. Additionally, the water / molten steel ratio (F / M), which is the amount of cooling water F (kg / min) discharged toward the molten metal flow and the amount of molten metal flow M (kg / min), should be 50 or more.

[0038] By adjusting the process in this way and forming metal particles using the water atomization method, the average circularity of the metal particles can be increased. Furthermore, it is preferable that the spray tank into which the cooling water is injected maintains an inert gas atmosphere. This inert gas atmosphere suppresses the oxidation of the metal particles.

[0039] Next, a drying process is carried out to dry the metal particles (step S102). In the drying process of step S102, drying is carried out by dewatering using, for example, a filter cloth. The dried metal particles are then subjected to a removal process to remove coarse particles and foreign matter (step S103). The removal process in step S103 is carried out by, for example, a sieve. The mesh size of the sieve should be, for example, about 180 μm to 250 μm.

[0040] Next, a reduction treatment step is performed to lower the oxygen concentration in the metal particles (step S104). The reduction treatment step in step S104 is performed, for example, by heat treatment in a reducing atmosphere such as hydrogen.

[0041] The reduction process in step S104 is not limited to this embodiment; for example, the metal particles can be efficiently reduced by performing the above process under reduced pressure. Performing the reduction process under reduced pressure allows for particularly efficient reduction when the metal particles contain large amounts of difficult-to-reduce elements such as Cr, Si, and Mn.

[0042] Next, a crushing process is performed in which the metal particles are crushed by impact (step S105). The crushing process in step S105 is not particularly limited, but can be carried out using a hammer mill or the like.

[0043] Next, a classification process is performed to adjust the metal particles to a predetermined particle size distribution (step S106). The classification process in step S106 is carried out, for example, using a sieve. The mesh size of the sieve can be adjusted as appropriate, for example, between 180 and 250 μm.

[0044] Preferably, the particle size distribution of the metal particles that have undergone the classification process in step S106 is measured using a particle size distribution analyzer that employs laser diffraction. In this way, the metal particles are adjusted to a predetermined particle size distribution. As a result, the fluidity of the water atomized powder can be made appropriate.

[0045] Furthermore, the drying step (S102), the removal step (S103), the reduction treatment step (S104), and the grinding step (S105) are optional steps depending on the implementation. In addition, if the reduction treatment step (S104) is performed, it is preferable to perform the grinding step (S105).

[0046] The additive manufacturing method using the water-atomized powder described above will now be explained. Figure 2 shows the flow chart of the additive manufacturing method using water-atomized powder. For example, a Direct Energy Deposition (DED) 3D printer can be used for additive manufacturing using water-atomized powder.

[0047] As shown in Figure 2, using the water atomized powder described above, an extrusion process is performed in which metal particles are ejected from the nozzle of the 3D printer toward a predetermined position (step S201).

[0048] In the extrusion process of step S201, the amount of water atomized powder extruded from the nozzle is preferably, for example, 0.5 to 20 g / min. By adjusting the extrusion amount in this way, molding can be performed while ensuring appropriate fluidity.

[0049] Next, a deposition process is performed in which the atomized powder is melted by irradiating it with a laser, and the molten water atomized powder is deposited (step S202). In the deposition process of step S2020, for example, the laser output should be set to 1000 to 2500 W. Also, the scanning speed should be set to 20 to 40 mm / s.

[0050] If the laser power is too low or the scanning speed is too high, defects will occur in the printed object due to insufficient melting of the powder. Conversely, if the laser power is too high or the scanning speed is too slow, over-melting will occur, disrupting the molten pool in the printed object and causing defects. In other words, by setting the laser power and scanning speed as described above, the occurrence of defects in the printed object can be suppressed. [Examples]

[0051] [Test Example 1: Nozzle Discharge Performance Evaluation Test Example] We conducted tests to evaluate the extrusion performance from the nozzle of a DED-type 3D printer by changing the properties of the water-atomized powder.

[0052] Water atomized powders were manufactured using the iron-based alloys shown in Table 1. All water atomized powders were subjected to the processes described above, from the particle formation step S101 to the classification step S106.

[0053] [Table 1]

[0054] In step S101, the particle formation process was carried out using the water atomization method in a high-frequency induction melting furnace. The high-frequency induction melting furnace was operated in an inert gas atmosphere, and the melting temperature was set to 1600°C or higher.

[0055] For each water atomized powder, the flow energy, particle size distribution, average circularity, and nozzle dispensing performance were evaluated. The results are shown in Table 2. The evaluation of each item was performed as follows.

[0056] (Measurement of fluid energy) The fluid energy was determined by dividing the fluid energy (AE: mJ), which represents the fluidity index of the powder material under conditions of air introduction from the bottom of the container, by the volume of the powder material.

[0057] The fluid energy was measured using a Freeman Technology "Powder Rheometer FT4". A 23.5 mm diameter blade and a 25 mm diameter cylindrical split container were used for the measurement.

[0058] Water atomization powder 25cm 3After filling the cylindrical split container, air at 4 mm / s was introduced from the bottom of the container. In this state, when moving the impeller-shaped blade in the powder material from the top to the bottom of the container, the flow energy was derived from the work done when moving the blade. Note that the normalized flow energy (mJ / cm 3 ) was obtained as follows. Normalized flow energy (mJ / cm 3 ) = Flow energy (mJ) at an air flow rate of 4 mm / s / Volume of water atomized powder (25 cm 3 )

[0059] (Evaluation of particle size distribution) The particle size distribution of the water atomized powder was measured by the above-mentioned laser diffraction method. As the laser diffraction particle size measuring device, LA-950V2 (model name) manufactured by Horiba, Ltd. was used.

[0060] (Measurement of average circularity) The average circularity of the powder particles was obtained by performing image analysis on 10,000 metal particles using Mophologi G3 manufactured by Malvern Panalytical. The average circularity was taken as the circularity of the particle whose volume integration reached 50% by integrating the volumes of particles with smaller circularities in the particle images.

[0061] (Evaluation of nozzle discharge performance) The discharge performance of the nozzle was evaluated by measuring the powder weight discharged from the nozzle 5 times in 1 minute. The average discharge amount was obtained from the 5 measured discharge amounts, and powders with a variation of ±1.5% or more from the average discharge amount among the 5 evaluations were rated as discharge performance "×", powders with a variation in the range of ±1.0 to 1.5% were rated as discharge performance "〇", and powders with a variation of less than ±1.0% were rated as discharge performance "◎".

[0062]

Table 2

[0063] As shown in Table 2, for No.1, 3, and 12, the flow energy (mJ / cm 3The value is 30 or higher. Therefore, the fluidity of the water atomized powder is not appropriate, and good nozzle dispensing performance could not be obtained.

[0064] In contrast, for Nos. 2, 4-11, and 13-24, the flow energy (mJ / cm) 3 The ratio is less than 30. Therefore, the fluidity of the water atomized powder is appropriate, and good nozzle dispensing performance was obtained.

[0065] [Test Example 2: Evaluation Test of Molded Objects] The water atomized powder used in the nozzle ejection performance evaluation test was used to fabricate objects, and their fabrication performance was evaluated. A laser-type DED 3D printer was used to fabricate the objects. The 3D printer used was a NIDEK Machine Tools LAMDA500 (DED type).

[0066] The 3D printer's laser output was set to 1600W, 20mm / s, and the water atomized powder discharge rate from the nozzle was set to 8g / min. The size of the printed object was 30mm square.

[0067] Regarding formability, the manner in which spatter occurred during printing and the relative density of the printed object were evaluated. Furthermore, to investigate the relationship with the manner in which spatter occurred, the oxygen concentration of metal particles was measured. The results are shown in Table 3. Each evaluation was performed as follows.

[0068] (Oxygen concentration of powder) The oxygen concentration of the powder was measured using the inert gas fusion method with an ON736 oxygen / nitrogen analyzer manufactured by LECO Japan.

[0069] (Evaluation of sputtering amount) The amount of spatter generated during the printing of objects using a 3D printer was visually evaluated. The spatter evaluation criteria were as follows: "○" for no spatter adhering to surrounding equipment, "△" for slight spatter adhering to surrounding equipment, and "×" for significant spatter adhering to surrounding equipment.

[0070] (Evaluation of form) The build quality was evaluated using nozzle ejection performance and sputter amount. The evaluation criteria were as follows: If at least one of the nozzle ejection performance or sputter amount evaluations was rated "×", it was marked "×", and if at least one was rated "△", it was marked "△". Furthermore, if both nozzle ejection performance and sputter amount evaluations were rated "〇", it was marked "〇", and if both nozzle ejection performance and sputter amount evaluations were rated "◎", it was marked "◎".

[0071] (Measurement of relative density) From the resulting fabricated objects, 20 mm square test specimens were taken, and the density of the fabricated objects was measured using the Archimedes method. The ratio of this density to the true density was defined as the relative density. The density of the bulk steel plate was used as the true density.

[0072] (Evaluation of the sculpture) The printed objects were evaluated according to their relative density. The evaluation criteria for relative density were as follows: 99.3% or higher was marked "◎", 98.8% or higher was marked "〇", and less than 98.8% was marked "×".

[0073] [Table 3]

[0074] For Nos. 4-6, 7-9, 15-19, 21, and 23, the object evaluation was "○" or higher, indicating favorable results. In contrast, for Nos. 1, 3, 12, 22, and 24, the object evaluation was "×", indicating unfavorable results.

[0075] Furthermore, for samples No. 22 and 24, where the oxygen concentration exceeded 7000 ppm, the sputtering amount was judged as "×". For samples No. 4, 5, 6, 15, 16, 21, and 23, where the oxygen concentration was between 1500 and 7000 ppm, the sputtering amount was judged as "△". For samples No. 1, 3, 7, 8, 9, 12, and 17-19, where the oxygen concentration was less than 1500 ppm, the sputtering amount was judged as "〇".

[0076] The embodiments and examples of the present invention have been described above. Because the water atomized powder of the present invention has excellent fluidity, it can be used in a powder volume method DED 3D printer to create high-quality additively manufactured objects.

Claims

1. A water atomization powder for additive manufacturing containing metal particles, The fluid energy at an airflow rate of 4 mm / s, normalized by the total volume of the metal particles, is 30 mJ / cm². ３ A water atomizing powder that is less than [amount missing].

2. The water atomized powder according to claim 1, wherein the metal particles have a volume-based 10% cumulative particle diameter D10 measured by laser diffraction scattering method of 40 μm or more.

3. The water atomized powder according to claim 2, wherein the metal particles have a volume-based 90% cumulative particle diameter D90 measured by laser diffraction scattering method of 150 μm or less.

4. The water atomized powder according to claim 3, wherein the metal particles have a cumulative particle diameter D90 of 110 μm or less.

5. The water atomized powder according to claim 1, wherein the average circularity is 0.80 or higher.

6. The water atomized powder according to claim 2, wherein the average circularity is 0.80 or higher.

7. The water atomized powder according to claim 3, wherein the average circularity is 0.80 or higher.

8. The water atomized powder according to claim 4, wherein the average circularity is 0.80 or higher.

9. The water atomized powder according to claim 1, wherein the metal particles have an oxygen concentration of 7000 ppm or less.

10. The water atomized powder according to claim 2, wherein the metal particles have an oxygen concentration of 7000 ppm or less.

11. The water atomized powder according to claim 3, wherein the metal particles have an oxygen concentration of 7000 ppm or less.

12. The water atomized powder according to claim 4, wherein the metal particles have an oxygen concentration of 7000 ppm or less.

13. The water atomized powder according to claim 5, wherein the metal particles have an oxygen concentration of 7000 ppm or less.

14. The water atomized powder according to claim 6, wherein the metal particles have an oxygen concentration of 7000 ppm or less.

15. The water atomized powder according to claim 7, wherein the metal particles have an oxygen concentration of 7000 ppm or less.

16. The water atomized powder according to claim 8, wherein the metal particles have an oxygen concentration of 7000 ppm or less.

17. The water atomization powder according to any one of claims 1 to 16, wherein the metal particles include an iron-based alloy.

18. A method for additive manufacturing that uses metal particles to perform additive manufacturing, A dispensing step of dispensing the water atomized powder according to any one of claims 1 to 16 as the metal particles from a nozzle, A method for additive manufacturing, comprising a deposition step of depositing the metal particles discharged from the nozzle while melting them with a heat source.

19. A method for additive manufacturing that uses metal particles to perform additive manufacturing, A dispensing step of dispensing the water atomized powder described in claim 17 as the metal particles from a nozzle, A method for additive manufacturing, comprising a deposition step of depositing the metal particles discharged from the nozzle while melting them with a heat source.

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