Metal powder formation method

Abstract

A metal powder forming method for forming a metal powder (M1) by cutting the surface of a metal material (1) to be processed, the metal powder forming method comprising: a plastic working step for using a plastic working tool (10) to form a second surface (S2) that has multiple protrusions (30) side-by-side in at least one direction on a first surface (S1) of the material (1) being processed; and a cutting step for forming the metal powder (M1) by cutting the multiple protrusions (30) using a cutting tool (20).

Description

[Technical Field]

[0001] The present invention relates to a method for forming metal powders. [Background technology]

[0002] In the method for manufacturing a molded body disclosed in Patent Document 1 below, the molding material contains metal microparticles formed into a scale-like shape by cutting metal, and a resin. This molding material is shorter than the maximum length of the scale-like metal microparticles contained in the molding material. The molded body is formed by ejecting the metal microparticles into a mold from an injection port that can inject the metal microparticles into the mold in the same direction. This aligns the direction of the metal microparticles, allowing the production of a molded body with oriented thermal conductivity and electrical conductivity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-206728 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional methods for obtaining metal powder by cutting metal, the resulting metal powder contains metal particles with a variety of shapes, particle sizes, aspect ratios, etc. In other words, it is sometimes impossible to control the shapes of the metal particles contained in the resulting metal powder. As a result, the resulting metal powder contains metal particles that cannot be used in subsequent molding processes, and metal particles with the desired shapes, etc. must be selected from the resulting metal powder.

[0005] An object of the present invention is to control the shape of metal particles contained in metal powder formed by cutting a workpiece. [Means for solving the problem]

[0006] A metal powder forming method according to one embodiment of the present invention is a metal powder forming method for forming metal powder by cutting the surface of a metallic workpiece, and includes a plastic processing step for forming a second surface having a plurality of convex portions on a first surface of the workpiece, and a cutting step for forming metal powder by cutting the plurality of convex portions. [Effects of the Invention]

[0007] According to the present invention, it is possible to control the shape of metal particles contained in metal powder formed by cutting a workpiece. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic side view showing the arrangement relationship between a workpiece, a rolling tool, and a cutting tool in a metal powder forming method according to a first embodiment. FIG. [Figure 2] 2 is a diagram for explaining the metal powder forming method according to the first embodiment, and is a schematic side view corresponding to the view taken along the arrow II in FIG. 1. FIG. [Figure 3A] FIG. 1 is a schematic side view showing a rolling tool according to a first embodiment. [Figure 3B] 3B is a schematic cross-sectional view taken along line IIIB-IIIB in FIG. 3A, showing the rolling tool according to the first embodiment. [Figure 4] FIG. 4 is a diagram for explaining a rolling step according to the first embodiment, and is a schematic partial cross-sectional view taken along line IV-IV in FIG. [Figure 5] 1 is a schematic side view showing a cutting tool according to a first embodiment and a second embodiment. FIG. [Figure 6] FIG. 6 is a diagram for explaining a cutting step according to the first and second embodiments, and is a schematic partial cross-sectional view taken along line VI-VI in FIG. 2. [Figure 7] FIG. 1 is a diagram for explaining a cutting step according to the first and second embodiments, and is a schematic partial cross-sectional view showing an example of how metal powder is formed from a workpiece. [Figure 8A] FIG. 10 is a schematic side view showing a rolling tool according to a second embodiment. [Figure 8B] 8B is a schematic cross-sectional view taken along line VIIIB-VIIIB in FIG. 8A, showing the rolling tool according to the second embodiment. [Figure 9] FIG. 5 is a schematic partial cross-sectional view corresponding to FIG. 4, illustrating a rolling step according to the second embodiment. [Figure 10] 10 is a diagram for explaining the action and effect of the metal powder forming method according to the second embodiment, and is a schematic partial cross-sectional view corresponding to FIG. 9 showing a plurality of protrusions after being unloaded in the rolling process. FIG. [Figure 11] 10 is a schematic side view showing the arrangement relationship between a workpiece, a rolling tool, and a cutting tool in a metal powder forming method according to a third embodiment. FIG. [Figure 12] 12 is a diagram for explaining a metal powder forming method according to a third embodiment, and is a schematic plan view corresponding to the view seen from the arrow XII in FIG. 11. FIG. [Figure 13] 13 is a diagram for explaining a cutting step according to the third embodiment, and is a schematic partial side view corresponding to the view seen from the arrow XIII in FIG. 12. FIG. [Figure 14] FIG. 10 is a diagram for explaining a cutting step according to a third embodiment, and is a schematic partial perspective view showing an example of a mode in which metal powder is formed from a workpiece. [Figure 15] FIG. 2 is a diagram for explaining a spheroidizing step according to the embodiment, and is a schematic side view showing the arrangement relationship between a first plate member, a second plate member, and metal powder. [Figure 16] 5A and 5B are schematic plan views showing the movement of a second plate member relative to a first plate member in a spheroidizing step according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The average aspect ratio or average particle size of the metal powder M1 formed by the metal powder forming method according to the embodiment was measured using a particle image analyzer (product name: Morphologi 4, manufactured by Malvern Panalytical). More specifically, the metal powder M1 containing thousands to tens of thousands of metal particles M2 was dispersed on a glass plate using a powder dispersion unit, photographed with an objective lens of a predetermined magnification, and the average aspect ratio or average particle size was calculated using image analysis software. The magnification of the objective lens can be appropriately set depending on the shape, etc., of the metal powder M1. The aspect ratio is the ratio of the length of the major axis to the length of the minor axis of a particle when photographed from a predetermined direction. The particle size is the circle-equivalent diameter of the particle. The circle-equivalent diameter is the diameter of a circle having an area equal to the projected area of ​​the photographed particle. In the following description, the average aspect ratio and average particle size of the metal powder M1 will be simply referred to as the aspect ratio and particle size, respectively.

[0010] The metal powder forming method according to the embodiment can form metal powder M1 having a particle size of, for example, 1 μm to 500 μm. The metal powder M1 may also be used as a molding material in a metal 3D printer (not shown). In this case, the particle size of the metal powder M1 may be, for example, 1 μm to 100 μm. The mode diameter of the metal powder M1 may be 25 μm to 75 μm. The mode diameter refers to the particle size or particle size range most frequently found in a measurement sample. The metal powder M1 can be used, for example, as a powder material supplied to a powder bed in powder bed 3D printing. The metal powder M1 may also be used in other types of metal 3D printers. For example, the metal powder M1 may be used as a powder material to be mixed with a thermoplastic resin in a fused deposition modeling (FDM) 3D printer.

[0011] Hereinafter, a metal powder forming method according to an embodiment will be described with reference to the drawings. The metal powder forming method according to the embodiment is a metal powder forming method for forming metal powder M1 by cutting the surface of a metallic workpiece 1, and includes a plastic processing step and a cutting step. The metal powder M1 is composed of a large number of metal particles M2. In the following description, elements having the same function are assigned the same reference numerals, and duplicated explanations will be omitted.

[0012] The workpiece 1 is a component that will be the material for the metal powder M1, and may be made of, for example, aluminum, an aluminum alloy, copper, a copper alloy, or the like. In the example shown in FIGS. 1 and 2, the workpiece 1 extends about a first axis A1 as its central axis, and has a substantially circular shape in a cross section perpendicular to the first axis A1. Therefore, the workpiece 1 has an overall cylindrical shape. However, the shape of the workpiece 1 is not limited to this; for example, the workpiece 1 may have a portion that is smaller in radial dimension than the other portions. Furthermore, the workpiece 1 may have a shape such as an elliptical cylinder or a polygonal cylinder.

[0013] The workpiece 1 has a first surface S1 before the plastic working process and the cutting process are performed. The first surface S1 has an axisymmetric shape about a first axis A1. In the example shown in FIG. 1, the first surface S1 forms the outer circumferential surface of the workpiece 1. In other words, the first surface S1 may have the shape of a cylindrical surface with the first axis A1 as the central axis.

[0014] The plastic processing step is a step of forming a plurality of convex portions 30, such as the example shown in FIG. 4, on the first surface S1 of the workpiece 1 by plastic processing. In the following description, the surface of the workpiece 1 on which the plurality of convex portions 30 are formed by plastic processing is referred to as the second surface S2. In the plastic processing step, the workpiece 1 is plastically deformed by pressing a plastic processing tool 10 against the first surface S1, thereby forming a plurality of convex portions 30. The plurality of convex portions 30 are formed aligned in at least one direction. Note that the material of the plastic processing tool 10 only needs to have a higher hardness than the workpiece 1. For example, the plastic processing tool 10 may be made of cemented carbide. A sliding film (not shown) may be formed on the working die of the plastic processing tool 10. The sliding film may be, for example, a diamond-like carbon (DLC) coating. The sliding film may be formed by a known film formation method such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). The processing mold refers to a mold having a predetermined shape formed on the surface of a plastic processing tool in order to plastically deform the surface of an object to be processed into a desired shape.

[0015] Plastic processing is a process in which a processing die is pressed against the workpiece 1 with a predetermined pressure to cause plastic flow of the first surface S1 of the workpiece 1, thereby plastically deforming the base material without removing it. Below, a case in which the first surface S1 is plastically deformed by rolling as an example of plastic processing to form multiple protrusions 30 will be described, but this is not limiting. For example, the multiple protrusions 30 may be formed by press processing. Furthermore, the rolling process described below is an example of a plastic processing process, and is not limited to this. For example, the plastic processing process may be a press processing process.

[0016] The cutting step is a step of cutting the plurality of protrusions 30 formed by plastic working with a cutting tool 20. When the plurality of protrusions 30 are cut, metal powder M1 is obtained as cutting powder. In the following description, the surface of the workpiece 1 after the plurality of protrusions 30 have been cut is referred to as a third surface S3.

[0017] (First embodiment) Next, a metal powder forming method according to a first embodiment will be described with reference to Figures 1 to 7. In the example shown in Figure 1, a plastic processing tool 10 is arranged on one radial side of a workpiece 1, and a cutting tool 20 is arranged on the other side. In this embodiment, a rolling tool 10a can be used as the plastic processing tool 10. In addition, a rotary tool 20a can be used as the cutting tool 20. The arrangement of the workpiece 1, the plastic processing tool 10, and the rotary tool 20a is not limited to the example shown in the figures, and can be set appropriately depending on the processing device that performs the metal powder forming method according to the embodiment, and the shape, dimensions, etc. of the workpiece 1.

[0018] Next, the rolling tool 10a will be described. The rolling tool 10a is a tool that can rotate around the second axis A2, and in the example shown in Figures 3A and 3B, has a disk-like shape when viewed in an axial direction parallel to the second axis A2. The second axis A2 may extend in a direction inclined with respect to the first axis A1 when viewed in an axial direction parallel to a direction perpendicular to the first axis A1 and the second axis A2.

[0019] As shown in the example, the outer peripheral portion 11 of the rolling tool 10a is configured so that its width dimension decreases as it moves radially outward of the rolling tool 10a. As a result, rolling blades 12 extending in the circumferential direction of the rolling tool 10a are formed on the outer peripheral portion 11. The rolling blades 12 correspond to the processing dies of the rolling tool 10a. The outer peripheral portion 11 is a portion extending in the circumferential direction on the radially outer side of the rolling tool 10a. The radially outward direction of the rolling tool 10a is the direction opposite to the second axis A2 in the radial direction of the rolling tool 10a. The width direction of the rolling tool 10a is a direction parallel to the second axis A2.

[0020] The cross section shown in FIG. 3B is a cross section perpendicular to the circumferential direction of the rolling tool 10a. In this cross section, a tip angle θ1 is formed at the tip 13 of the rolling blade 12. The rolling blade 12 is pressed against the workpiece 1 in the rolling process described below, plastically deforming the workpiece 1. The tip 13 constitutes the radially outer side of the rolling blade 12. The tip angle θ1 may be 30 degrees or more and 90 degrees or less. Alternatively, the tip angle θ1 may be 60 degrees. Furthermore, in this cross section, the radially outer end of the tip 13 may be curved so as to be convex radially outward with a predetermined curvature radius R1. The curvature radius R1 may be set to a value equal to or less than the particle size of the metal powder M1 to be obtained by the metal powder forming method according to the embodiment. For example, if a metal powder M1 with a particle size of 50 μm is to be formed, the curvature radius R1 may be set to be 1 μm or more and 50 μm or less. This makes it possible to more reliably form the metal powder M1 with the desired particle size.

[0021] The arithmetic mean roughness Ra of the surface of the rolling blade 12 may be 0.01 μm or more and 0.1 μm or less. This makes it possible to prevent excessive friction between the rolling blade 12 and the workpiece 1 during the rolling process described below. This reduces wear on the rolling blade 12 and more reliably controls the shape of the convex portions 30 formed during the rolling process. The maximum height roughness Rz of the surface of the rolling blade 12 may be 0.1 μm or more and 1.0 μm or less. The arithmetic mean roughness Ra and the maximum height roughness Rz are indicators of surface roughness specified in the Japanese Industrial Standards' "Geometrical Product Specifications (GPS) - Surface Texture: Profile Curve Method - Terms, Definitions, and Surface Texture Parameters" (JIS B0601:2013).

[0022] Next, the rotary tool 20a will be described. The rotary tool 20a may be, for example, an end mill equipped with a cutting blade 21. In the example shown in FIG. 5, the cutting blade 21 is disposed at one end of the rotary tool 20a. A plurality of nicks 22 are formed in the cutting blade 21, and the cutting blade 21 has an overall comb-like shape. In the example shown, a plurality of nicks 22 are formed in the cutting blade 21 in a direction parallel to the third axis A3. By rotating the rotary tool 20a around the third axis A3, the surface of the workpiece 1 can be cut with the plurality of nicks 22. Note that the rotary tool 20a is not limited to the example shown in the figure, and may be, for example, a roughing end mill (not shown) having a peripheral cutting edge formed in a wavy shape.

[0023] As shown in FIG. 6 , a tip angle θ2 is formed at the tip 23 of each nick 22 when viewed in the circumferential direction of the rotary tool 20a. The circumferential direction of the rotary tool 20a is the direction around the third axis A3 of the rotary tool 20a. The tip 23 constitutes the radially outer side of the nick 22 relative to the rotary tool 20a. The tip angle θ2 may be 45 degrees or greater and 90 degrees or less. The tip angle θ2 may also be 60 degrees. When viewed in the circumferential direction, the radially outermost portion of each nick 22 on the rotary tool 20a may be curved with a predetermined radius of curvature R2 so as to be convex radially outward. The radius of curvature R2 may be 1 μm or greater and 100 μm or less. When viewed in the circumferential direction, the pitch Pi2 between the multiple nick 22 may be 10 μm or greater and 100 μm or less. The height H2 of each nick 22 may be 10 μm or greater and 100 μm or less. The height H2 is the radial distance between the portion of the nick 22 that is located most radially outward of the rotary tool 20a and the bottom 24. The bottom 24 is a portion formed between the multiple nicks 22.

[0024] The ratio of the tip angle θ1 of the rolling blade 12 to the tip angle θ2 of the nicks 22 may be configured to be within a predetermined range. For example, the tip angle θ1 may be 0.7 to 1.5 times the tip angle θ2. This allows the aspect ratio of the metal powder M1 to be further reduced. The tip angle θ1 and the tip angle θ2 may be equal to each other.

[0025] Next, a rolling process using a rolling tool 10a will be described with reference to the examples shown in Figures 1, 2, and 4. One side end 2 of the workpiece 1 is fixed to the chuck of a numerically controlled (NC) lathe (not shown), for example, and the rolling process can be performed while the workpiece 1 is rotated around a first axis A1. In the rolling process, rolling is performed on the workpiece 1 rotating in the direction of arrow A with the first axis A1 as the central axis.

[0026] In the rolling process, first, the rolling blade 12 of the rolling tool 10a is pressed with a predetermined pressing load against the first surface S1 of the workpiece 1 rotating around the first axis A1. In the example shown in FIG. 1, the rolling tool 10a is pressed by moving it in the direction of arrow B. Then, while the workpiece 1 is rotating, the rolling tool 10a is moved in the feed direction. As a result, as shown in FIGS. 2 and 4, grooves 5 are formed on the first surface S1, and a portion of the workpiece 1 is plastically deformed around the rolling blade 12 to form a protrusion 30. Note that at this time, the rolling tool 10a may rotate in the direction of arrow C (see FIG. 1) around the second axis A2 as the workpiece 1 rotates. Note that the feed direction is the direction in which the rolling tool 10a is moved to form a plurality of protrusions 30 aligned in one direction on the first surface. 4, the feed direction is the direction of arrow D, and the rolling tool 10a is fed from the other end 3 of the workpiece 1 toward the one end 2. The feed direction may be parallel to the first axis A1 of the workpiece 1.

[0027] By the rolling process, the surface of the workpiece 1 is plastically deformed so as to rise along the path of the rolling blade 12, and convex portions 30 are formed continuously in the circumferential direction of the workpiece 1. Furthermore, during the rolling process, the rolling tool 10a is moved in the feed direction while the workpiece 1 is rotated. Therefore, the rolling blade 12 moves relatively along a spiral path on the first surface S1 of the workpiece 1. As a result, a spiral groove 5 is formed on the first surface S1 as shown in FIG. 2. Each of the widthwise sides of the groove 5 formed in this way is defined by a convex portion 30. Therefore, a second surface S2 is formed on the surface of the workpiece 1, which has a plurality of convex portions 30 aligned at least in a direction parallel to the first axis A1.

[0028] As shown in the example in FIG. 4, the grooves 5 are formed by transferring the shape of the tip 13 of the rolling blade 12 to the first surface S1. Therefore, in a cross section perpendicular to the circumferential direction of the second surface S2 of the workpiece 1, the tip angle θ3 of the convex portion 30 and the tip angle θ1 of the rolling blade 12 are approximately equal. The tip angle θ3 is the angle of the tip 33 of each of the multiple convex portions 30. Therefore, the tip angle θ3 may be 0.7 to 1.5 times the tip angle θ2 of the nick 22. The tip angles θ3 and θ2 may be equal. Note that the portion of the second surface S2 formed by the bottom 34 may be curved with a predetermined radius of curvature so as to be convex toward the first axis A1 in a cross section perpendicular to the circumferential direction of the workpiece 1. The bottom 34 defines the first axis A1 side of the groove 5. The radius of curvature may be approximately equal to the radius of curvature R1 of the tip 13.

[0029] The protrusions 30 have tip portions 33 formed by the workpiece 1 being raised. The tip portions 33 are the portions of the protrusions 30 that form the radially outer side of the workpiece 1. The pitch Pi1 between the multiple grooves 5 in the direction parallel to the first axis A1 can be controlled by the feed speed of the rolling tool 10a. Therefore, the pitch Pi3 between the multiple protrusions 30 in the direction parallel to the first axis A1 can be controlled by the feed speed of the rolling tool 10a. The feed speed of the rolling tool 10a is the moving speed of the rolling tool 10a in the feed direction.

[0030] In the illustrated example, pitch Pi1 is the distance between points P1 and P2 in a direction parallel to the first axis A1. Points P1 and P2 are the portions of adjacent bottom portions 34 that are located closest to the first axis A1. Furthermore, pitch Pi3 is the distance between points P3 and P4 in a direction parallel to the first axis A1. Points P3 and P4 are the portions of adjacent protrusions 30 that are located closest to the radially outer side of the workpiece 1. Furthermore, as illustrated in the figure, the feed speed of the rolling tool 10a may be controlled so that pitch Pi1 and pitch Pi3 are approximately equal values.

[0031] The height H3 of the protrusions 30 can be controlled by the indentation load when pressing the rolling tool 10a against the workpiece. The height H3 is the height of each of the multiple protrusions 30 in the radial direction of the second surface S2 of the workpiece 1. For example, the height H3 can be increased by increasing the indentation load. In the illustrated example, the height H3 is the distance between points P1 and P3 in the radial direction of the workpiece 1. The indentation load and the height H3 may satisfy the relationship shown in Equation 1 below. X in Equation 1 is the Brinell hardness (HB) of the workpiece 1, which is the hardness specified in the Japanese Industrial Standards "Brinell Hardness Test - Part 1: Test Method" (JIS Z 2243-1:2018) and "Brinell Hardness Test - Part 2: Hardness Value Table" (JIS Z 2243-2:2018). Height H3 [unit: μm] = (-0.022X + 2.137) x indentation load [unit: N]... (Equation 1)

[0032] The height H3 may be 0.7 to 1.3 times the width of each of the plurality of protrusions 30 in the direction parallel to the first axis A1. Furthermore, the height H3 and the width may be approximately equal. For example, the distance between points P1 and P3 in the radial direction of the workpiece 1 may be equal to the distance between points P1 and P2 in the direction parallel to the first axis A1. In the illustrated example, the width of each of the plurality of protrusions 30 corresponds to the pitch Pi1 of the grooves 5.

[0033] Next, a cutting step in which cutting is performed using the rotary tool 20a will be described. In the example of cutting shown in FIGS. 1 and 2, the rotary tool 20a cuts multiple protrusions 30 formed by rolling. In this cutting, the rotary tool 20a is rotated in the direction of arrow E around the third axis A3 as its central axis, cuts in the direction of arrow G to a predetermined cutting depth D1, and then moved in the direction of arrow F. In the illustrated example, the direction of arrow F is parallel to the first axis A1, but is not limited to this. The direction in which the rotary tool 20a is moved may be a direction that obliquely intersects the first axis A1 when viewed in an axial direction perpendicular to the first axis A1 and the third axis A3. Alternatively, the rotary tool 20a may be configured to move in the opposite direction to the direction of arrow F.

[0034] The cutting depth D1 is the cutting depth of the rotary tool 20a into the second surface S2 of the workpiece 1. In the example shown in FIG. 1, the rotary tool 20a cuts in the direction of arrow G, which is perpendicular to the first axis A1 and the third axis A3. In the example shown in FIG. 6, the cutting depth D1 is the radial distance of the workpiece 1 between points P5 and P6 on a cross section perpendicular to the first axis A1 and passing through the third axis A3. Point P5 is the portion of the protrusion 30 that is closest to the third axis A3. Point P6 is the portion of each of the tip portions 23 of the multiple nicks 22 that is closest to the first axis A1.

[0035] As shown in FIG. 7, the rotary tool 20a is rotated and fed in the direction of arrow F at a cutting depth D1, whereby the protrusions 30 are cut by the nicks 22. This process produces a plurality of metal particles M2, which are cutting powder. The metal powder M1 is composed of these metal particles M2. The dashed-dotted lines in the figure schematically show the trajectories of the tips of the nicks 22. Because the metal particles M2 have, for example, a substantially regular tetrahedron shape, the aspect ratio of the metal powder M1 can be made close to 1. In other words, by controlling the shape of the metal particles M2, the aspect ratio, particle size, and the like of the metal powder M1 can be controlled. In the illustrated example, a portion of each of three protrusions 30 aligned in one direction is cut by the nicks 22, but this is not limiting. Four or more protrusions aligned in one direction may also be cut substantially simultaneously.

[0036] In the metal powder forming method according to this embodiment, the cutting process can be performed while the rolling process is being performed. For example, while the workpiece 1 is being rotated, the first surface S1 is rolled using the rotary tool 20a, and the convex portions 30 formed by the rolling process can be cut using the rotary tool 20a at the same time. That is, while the workpiece 1 is being rotated around the first axis A1, the formation of the convex portions 30 by the rolling process and the cutting of the convex portions 30 by the cutting process can be performed simultaneously.

[0037] In the example shown in FIGS. 1 and 2, the workpiece 1 rotates in the direction of arrow A and the rotary tool 20a moves in the direction of arrow F simultaneously. Therefore, as shown in FIG. 2, the relative trajectory 22a of the nicks 22 with respect to the workpiece 1 is inclined with respect to the first axis A1 when viewed in the axial direction perpendicular to the first axis A1 and the third axis A3. Here, when obtaining the metal powder M1, the extension direction of the trajectory 22a does not have to be parallel to the extension direction of the grooves 5. That is, the extension direction of the trajectory 22a and the extension direction of the protrusions 30 need only intersect. However, the extension direction of the trajectory 22a and the extension direction of the grooves 5 may be perpendicular to each other. That is, the extension direction of the trajectory 22a and the extension direction of the protrusions 30 may be perpendicular to each other. This allows the protrusions 30 to be cut in a direction perpendicular to the extension direction, thereby more reliably controlling the shape of the metal particles M2.

[0038] After cutting the multiple convex portions 30 from the other end 3 to the one end 2 of the workpiece 1, the rotary tool 20a may be returned to the other end 3 side while preventing contact between the rotary tool 20a and the workpiece 1. Then, the rotary tool 20a may again be caused to cut to a cutting depth D1 and fed in the direction of arrow F to cut the multiple convex portions 30 and form metal powder M1. In this case, the rotation of the workpiece 1 can be controlled so that the cutting blade 21 cuts the uncut portions of the multiple convex portions 30.

[0039] (Second embodiment) Next, a metal powder forming method according to a second embodiment will be described with reference to Figures 8A to 10. In the second embodiment, a rolling tool 10b is used as the plastic processing tool 10, instead of the rolling tool 10a used in the first embodiment. The workpiece 1 and cutting tool 20 are configured similarly to those in the first embodiment.

[0040] The rolling tool 10b is a tool that can rotate around the second axis A2, and in the example shown in FIGS. 8A and 8B , it has a disk-like shape when viewed in an axial direction parallel to the second axis A2. The rolling tool 10b has an outer peripheral surface 15, a ridge portion 16, and a bottom portion 17. The outer peripheral surface 15 is the radially outer surface of the rolling tool 10b and extends in the circumferential direction of the rolling tool 10b with the second axis A2 as its central axis. A plurality of ridge portions 16 extending in the circumferential direction are formed on the outer peripheral surface 15. Therefore, in a cross section perpendicular to the circumferential direction of the rolling tool 10b, the outer peripheral surface 15 has a wavy shape. The outer peripheral surface 15 corresponds to the processing die of the rolling tool 10b. The bottom portion 17 is a portion formed between each of the plurality of ridge portions 16. In the illustrated example, three ridge portions 16 are formed on the outer peripheral surface 15, but this is not limited thereto. The number of ridge portions can be set appropriately depending on the dimension of the workpiece 1 in the first axis A1 direction, the processing time of the rolling step, etc. For example, two ridge portions 16 or four or more ridge portions 16 may be formed on the outer circumferential surface 15.

[0041] In a cross section perpendicular to the circumferential direction of the rolling tool 10b shown in Figures 8B and 9, the dimension of the ridge portion 16 in the width direction of the rolling tool 10a decreases radially outward. Therefore, in this cross section, the ridge portion 16 is formed with a tip angle θ4. The tip angle θ4 may be 30 degrees or more and 90 degrees or less. The tip angle θ4 may also be 60 degrees. In this cross section, the radially outer side of the ridge portion 16 may be curved with a radius of curvature R3 so as to be convex radially outward. The radius of curvature R3 may be 1 µm or more and 100 µm or less.

[0042] In the radial direction of the rolling tool 10b, the height H1 of each of the multiple ridge portions 16 is set to a value equal to or greater than the particle size of the metal powder M1 to be formed in this embodiment. In the cross section shown in Figure 9, the height H1 is the distance between points P7 and P8 in the radial direction of the rolling tool 10b. Point P7 is the portion of the ridge portion 16 located most radially outward. Point P8 is the portion of the bottom portion 17 located most toward the second axis A2.

[0043] The pitch Pi4 of the ridge portions 16 may be set to a value 0.7 to 1.3 times the particle size of the metal powder M1 to be formed in this embodiment. Alternatively, the pitch Pi4 may be set to a value equal to the particle size of the metal powder M1. The pitch Pi4 is the pitch of the ridge portions 16 in the direction of the second axis A2. In the cross section shown in FIG. 9, the pitch Pi4 is the distance between points P7 and P9. Points P7 and P9 are the portions of adjacent ridge portions 16 that are located furthest radially outward from the rolling tool 10b.

[0044] 8B and 9, the bottom 17 may be curved with a radius of curvature R4 so as to be convex toward the second axis A2. The radius of curvature R4 may be set to a value equal to or less than the particle size of the metal powder M1 to be formed in this embodiment. For example, when forming metal powder M1 with a particle size of 50 μm using the metal powder forming method according to this embodiment, the radius of curvature R4 may be set to be equal to or greater than 1 μm and equal to or less than 50 μm.

[0045] Next, a rolling step will be described in which the workpiece 1 is rolled using the rolling tool 10b. As in the first embodiment, in the rolling step, the outer peripheral surface 15 of the rolling tool 10b is pressed with a predetermined indentation load against the first surface S1 of the workpiece 1 rotating around the first axis A1. Then, while the workpiece 1 is rotating, the rolling tool 10a is moved in the feed direction (direction of arrow D). As a result, multiple grooves 5 are formed on the first surface S1, and a portion of the workpiece 1 around the ridge portion 16 is plastically deformed so as to rise, forming multiple protrusions 30. At this time, the rolling tool 10b may rotate around the second axis A2 as the workpiece 1 rotates.

[0046] In the example shown in FIG. 9, the outer peripheral surface 15 is pressed against the workpiece 1 with a predetermined indentation load, thereby bringing the tip 33 into contact with the bottom 17. That is, when performing rolling, the indentation load of the rolling tool 10b may be set so that the protrusions 30 come into contact with the bottom 17. In this case, the radius of curvature of the tip 33 in a cross section perpendicular to the circumferential direction of the workpiece 1 is approximately equal to the radius of curvature R4 of the bottom 17. The indentation load and the height H3 of the protrusions 30 satisfy the relationship in Equation 2 below. In Equation 2, X is the Brinell hardness (HB) of the workpiece 1, and n is the number of ridges 16 formed on the outer peripheral surface 15 of the rolling tool 10b. n is an integer of 2 or more, and in the illustrated example, n=3. Height H3 [unit: μm] = (-0.022X + 2.137) x indentation load [unit: N] / n... (Equation 2)

[0047] When performing the rolling process, the protrusions 30 may be formed so that the height H3 is equal to or greater than the particle size of the metal powder M1 to be formed in this embodiment. That is, the pressing load of the rolling tool 10b may be set so that the second surface S2 of the workpiece 1 is raised to a height equal to or greater than the particle size of the metal powder M1 in the radial direction of the workpiece 1.

[0048] The cutting step according to this embodiment is performed using the rotary tool 20a in the same manner as in the first embodiment, and therefore a description thereof will be omitted.

[0049] (Third embodiment) Next, a metal powder forming method according to a third embodiment will be described with reference to Figs. 11 to 14. In the third embodiment, a knurling tool 10c can be used as the plastic processing tool 10. The knurling tool 10c is one form of a rolling tool. Also, a cutting tool 20b can be used as the cutting tool 20. The workpiece 1 illustrated in the figures has the same configuration as in the first embodiment.

[0050] 11 and 12, the knurling tool 10c is disposed on one radial side of the workpiece 1, and the cutting tool 20b is disposed on the other radial side. The arrangement of the workpiece 1, the knurling tool 10c, and the cutting tool 20b is not limited to the illustrated example, and can be set appropriately depending on the shape, dimensions, etc. of the processing device that performs the metal powder forming method according to the embodiment.

[0051] The knurling tool 10c may include a first knurling tool 10c1 and a second knurling tool 10c2. In the illustrated example, the first knurling tool 10c1 is a roller-type tool that is rotatable about a fourth axis A4 and has a disk-like shape when viewed in an axial direction parallel to the fourth axis A4. The second knurling tool 10c2 is a roller-type tool that is rotatable about a fifth axis A5 and has a disk-like shape when viewed in an axial direction parallel to the fifth axis A5. The fourth axis A4 or the fifth axis A5 illustrated in the figure extends parallel to the first axis A1, but is not limited to this. The fourth axis A4 or the fifth axis A5 may extend in a direction inclined relative to the first axis A1.

[0052] A processing die 18 is formed on the outer peripheral surface of the first knurling tool 10c1. The processing die 18 may be configured by a plurality of ridge portions. In the example shown in FIG. 12, each of the plurality of ridge portions extends in a direction intersecting with the fourth axis A4 when viewed in the radial direction of the first knurling tool 10c1, and is arranged parallel to one another. In addition, the processing die formed on the outer peripheral surface of the second knurling tool 10c2 may be configured by providing a plurality of ridge portions (not shown) extending in a direction intersecting with the extending direction of the ridge portions of the first knurling tool 10c1.

[0053] The knurling tool 10c illustrated in the drawings includes two roller-type tools, a first knurling tool 10c1 and a second knurling tool 10c2, but is not limited to this. For example, the knurling tool 10c may include only one roller-type tool. In this case, a plurality of recesses having a shape such as a quadrangular pyramid or a hemisphere may be formed on the outer circumferential surface of the roller-type tool.

[0054] The cutting tool 20b has a cutting blade 25. The cutting blade 25 has a flat blade shape extending in a direction parallel to the first axis A1. As shown in FIG. 12, the width of the cutting blade 25 of the cutting tool 20b and the width of the knurling tool 10c in the direction parallel to the first axis A1 may be approximately equal. Furthermore, the center of the end of the cutting blade 25 on the workpiece 1 side and the center of the end of the knurling tool 10c on the workpiece 1 side may be disposed at the same position in the direction parallel to the first axis A1.

[0055] In the rolling process according to this embodiment, as in the first embodiment, one side end 2 of the workpiece 1 is fixed to the chuck portion of an NC lathe, and rolling is performed while rotating around the first axis A1 in the direction of arrow H (see FIG. 11). In the rolling process, a knurling tool 10c is pressed against a first surface S1 of the workpiece 1 rotating around the first axis A1 with a predetermined pressing load. This causes the first surface S1 to rise into a shape corresponding to the processing mold of the knurling tool 10c, and multiple protrusions 40 are formed. Note that at this time, the first knurling tool 10c1 may rotate in the direction of arrow I in accordance with the rotation of the workpiece 1. Furthermore, the second knurling tool 10c2 may rotate in the direction of arrow J. The multiple protrusions 40 are one aspect of the multiple convex portions 30 formed by the rolling process.

[0056] In the illustrated example, the multiple ridges of the first knurling tool 10c1 and the multiple ridges of the second knurling tool 10c2 are transferred to the first surface S1, forming multiple protrusions 40 having a substantially quadrangular pyramid shape (see FIGS. 13 and 14). Therefore, the multiple protrusions 40 are periodically arranged in the direction in which the grooves formed by transferring the ridges of the first knurling tool 10c1 extend, and in the direction in which the grooves formed by transferring the ridges of the second knurling tool 10c2 extend. That is, multiple protrusions 40 arranged two-dimensionally are formed on the first surface S1 by rolling. The shape of the protrusions 40 is not limited to the illustrated example. The protrusions 40 may have a hemispherical shape, for example.

[0057] When performing the rolling process, the pitch of the multiple protrusions 40 can be adjusted by adjusting the pitch of the ridges of the first knurling tool 10c1 or the pitch of the ridges of the second knurling tool 10c2. That is, the pitch of the multiple protrusions 40 can be controlled by the pitch of the processing mold formed on the knurling tool 10c. The pitch of the multiple protrusions 40 is the distance between the apexes 41 of adjacent protrusions 40. The apex 41 is the part of each of the multiple protrusions 40 that is located most radially outward in the radial direction of the workpiece 1.

[0058] Furthermore, the height H4 of each of the multiple protrusions 40 in the radial direction of the workpiece 1 can be controlled by the pressing load of the knurling tool 10c in the rolling process. For example, the height H4 of the protrusions 40 can be reduced by reducing the pressing load of the knurling tool 10c during rolling. In the example shown in Fig. 13, the height H4 is the distance between the apex 41 and the first surface S1 when viewed in the axial direction parallel to the first axis A1.

[0059] Next, a cutting process using the cutting tool 20b will be described. In the cutting example shown in FIG. 13, the cutting tool 20b cuts the multiple protrusions 40 formed by the knurling tool 10c. In this cutting process, the cutting tool 20b may be fixed in place by cutting to a predetermined cutting depth D2 in the direction of arrow K. At this time, movement of the cutting tool 20b in a direction perpendicular to the cutting direction may be restricted. That is, when cutting the multiple protrusions 40 with the cutting tool 20b, the cutting tool 20b may be configured to be movable only in the cutting direction. However, the configuration of the cutting tool 20b is not limited thereto. For example, the cutting tool 20b may be configured to be movable in a direction parallel to the first axis A1 of the workpiece 1 while cutting. In this case, the feed speed of the cutting tool 20b in a direction parallel to the first axis A1 may be set according to the rotation speed of the workpiece 1 about the first axis A1. For example, the feed speed of the cutting tool 20b may be set to be greater than the rotation speed of the workpiece 1. In the example shown in the figure, the depth of cut D2 is the distance in the radial direction of the workpiece 1 between the apex 41 of the protrusion 40 and a point P10 of the cutting blade 25 that is closest to the first axis A1. The depth of cut D2 may be equal to or less than the height H4 of each of the multiple protrusions 40 in the radial direction of the workpiece 1. The depth of cut D2 may also be equal to the height H4. This more reliably forms metal particles M2 that correspond to the shape of the protrusions 40, and further prevents irregularities from being formed on the third surface S3 of the workpiece 1. As in the examples shown in FIGS. 11 and 12, the direction of the arrow K may be perpendicular to the first axis A1.

[0060] By cutting the cutting tool 20b into the second surface S2, at least some of the protrusions 40 are cut by the cutting blade 25, as shown in FIG. 14, and metal particles M2 are formed as cutting powder.

[0061] In the first to third embodiments described above, an example has been given in which the first surface S1 of the workpiece is rolled to form the second surface S2, and then the second surface S2 is cut. However, the surface of the workpiece 1 after cutting may be further rolled and cut. That is, a second rolling step may be performed to form a plurality of protrusions 30 on the third surface S3 of the workpiece 1 after the plurality of protrusions 30 formed in the rolling step are cut in the cutting step. Then, a second cutting step may be performed to form the metal powder M1 by cutting the plurality of protrusions 30 formed in the second rolling step with a cutting tool 20.

[0062] The metal powder M1 obtained by the above embodiment may further be subjected to a spheroidizing process. The spheroidizing process is a process for further reducing the aspect ratio of the metal powder M1. As illustrated in FIGS. 15 and 16, a first plate member 50 and a second plate member 51 are used in the spheroidizing process. In the illustrated example, the first plate member 50 and the second plate member 51 are disk-shaped members having a substantially circular shape in a planar view, but this is not limited thereto. The first plate member 50 and the second plate member 51 may also be members having a substantially rectangular or polygonal shape in a planar view. The materials of the first plate member 50 and the second plate member 51 can be appropriately selected depending on the material of the metal powder M1. For example, at least the surfaces of the first plate member 50 and the second plate member 51 that sandwich the metal powder M1 in the spheroidizing process described below may be made of a metal such as stainless steel or a diamond sintered body such as PCD (Polycrystalline Diamond). Furthermore, a sliding film may be formed on the surfaces. The sliding film may be, for example, a DLC coating.

[0063] In the spheroidizing process, first, the metal powder M1 is placed between the upper surface of the first plate member 50 and the lower surface of the second plate member 51. Next, the second plate member 51 is pressed against the first plate member 50 while applying a predetermined load. In the example shown in FIG. 15, the second plate member 51 is pressed against the first plate member 50 in the direction of arrow L. As a result, the metal powder M1 is sandwiched between the first plate member 50 and the second plate member. Next, the first plate member 50 and the second plate member are slid while the predetermined load is being applied. In the example shown in FIG. 16, the second plate member 51 is slid in the direction of arrow M relative to the first plate member 50 so as to form a substantially circular orbit in a plan view. As a result, the metal powder M1 is rolled between the first plate member 50 and the second plate member 51, and plastic deformation can be performed so that the aspect ratio approaches 1. The predetermined load can be set appropriately depending on the material and hardness of the metal powder M1 and the material, hardness, mass, etc. of the first plate member 50 and the second plate member 51. As in the illustrated example, the second plate member 51 may be slid within a range that overlaps with the first plate member 50 in a plan view.

[0064] In one embodiment, the spheroidizing process may be applied to metal powder M1 having an aspect ratio of 2 or more. This allows the aspect ratio of metal powder M1 to be closer to 1. Alternatively, the spheroidizing process may be applied to metal powder M1 having an aspect ratio of 2 or more and 5 or less. This allows metal powder having an aspect ratio of 1 or more and less than 2 to be formed.

[0065] The arithmetic mean roughness Ra of the upper surface of the first plate member 50 and the lower surface of the second plate member 51 may be 1.0 μm or more. This allows the aspect ratio of the metal powder M1 to be reduced more reliably. The arithmetic mean roughness Ra may be set depending on the material of the metal powder M1. For example, when the metal powder M1 is copper or a copper alloy, the arithmetic mean roughness Ra may be 1.0 μm or more and 3.0 μm or less. When the metal powder M1 is aluminum or an aluminum alloy, the arithmetic mean roughness Ra may be 1.0 μm or more and 2.5 μm or less. This allows the aspect ratio of the metal powder M1 to be reduced more reliably. The arithmetic mean roughness Ra may be set to fall within a desired numerical range regardless of the direction in which the surface roughness is measured. This allows the aspect ratio of the metal powder M1 to be reduced more reliably regardless of the sliding direction between the first plate member 50 and the second plate member 51.

[0066] (1) The metal powder forming method according to the embodiment is a metal powder forming method for forming metal powder M1 by cutting the surface of a metal workpiece 1, and includes a plastic processing step for forming a second surface S2 having a plurality of convex portions 30 aligned in at least one direction on a first surface S1 of the workpiece 1 using a plastic processing tool 10, and a cutting step for forming metal powder M1 by cutting the plurality of convex portions 30 with a cutting tool 20.

[0067] According to the metal powder forming method of the embodiment, it is possible to form a plurality of convex portions 30 aligned in one direction by plastic processing. Therefore, it is possible to form a plurality of convex portions 30 by plastically deforming the workpiece 1, and it is possible to suppress the generation of metal scraps when forming the plurality of convex portions 30. In other words, it is possible to improve the material yield rate. Furthermore, in the cutting process, the plurality of convex portions 30 are cut to form the metal powder M1. Therefore, it is possible to form the metal powder M1 with a more uniform aspect ratio, particle size, etc. In other words, it is possible to control the shape of the metal particles M2 contained in the metal powder M1 formed by cutting the workpiece 1.

[0068] (2) The plastic processing tool 10 may be a rolling tool 10a, 10b, or 10c, and the plastic processing process may be a rolling process in which the rolling tool 10a, 10b, or 10c is used to form a second surface S2 having a plurality of protrusions 30 on a first surface S1 of the workpiece 1.

[0069] According to the metal powder forming method of the embodiment, the rolling tools 10a, 10b, and 10c can be used to form the plurality of protrusions 30 by rolling. Therefore, the plurality of protrusions 30 can be formed more easily.

[0070] (3) The first surface S1 of the workpiece 1 has an axisymmetric shape around the first axis A1, and the cutting process may be performed while the workpiece 1 is rotated around the first axis A1 during the rolling process.

[0071] This allows the rolling process and the cutting process to be performed while rotating the workpiece 1, which has an axisymmetric shape about the first axis A1, around the first axis A1. That is, while rotating the workpiece 1 around the first axis A1, the formation of the convex portions 30 by the rolling process and the cutting of the convex portions 30 by the cutting process can be performed simultaneously. This allows the processing time for forming the metal powder M1 to be shortened.

[0072] (4) In the rolling process, the rolling tools 10a, 10b may be moved in the feed direction while being pressed against the first surface S1 of the workpiece 1 rotating around the first axis A1, and a spiral groove 5 may be formed on the first surface S1, thereby forming a plurality of convex portions 30 aligned at least in a direction parallel to the first axis A1.

[0073] As a result, by moving the rolling tools 10a, 10b in the direction of the first axis A1 while pressing them against the workpiece 1 rotating around the first axis A1, it is possible to form the multiple protrusions 30. Therefore, it is possible to form the multiple protrusions 30 more easily.

[0074] (5) In the rolling process, the pitch Pi3 of the plurality of protrusions 30 in the direction parallel to the first axis A1 may be controlled by the feed speed of the rolling tools 10a and 10b.

[0075] This makes it easier to control the pitch Pi3 of the multiple protrusions 30. Therefore, when forming the metal powder M1 by cutting the multiple protrusions 30, it is easier to form the metal powder M1 with a uniform particle size and the like.

[0076] (6) The height H3 of each of the plurality of protrusions 30 may be controlled by the pressing load of the rolling tools 10a and 10b.

[0077] This makes it easier to control the height H3 of the plurality of protrusions 30. Therefore, when forming the metal powder M1 by cutting the plurality of protrusions 30, it is easier to form the metal powder M1 with a uniform particle size and the like.

[0078] (7) The cutting tool 20 may be a rotary tool 20a having a plurality of nicks 22 formed on the cutting blade 21, and in the cutting process, the rotary tool 20a may be rotated to cut the plurality of protrusions 30 with the plurality of nicks 22.

[0079] As a result, each of the multiple protrusions 30 formed on the workpiece 1 can be cut by the nicks 22 formed on the rotary tool 20a. As a result, metal particles M2 are formed according to the shape of the nicks 22. Therefore, the shape of the metal particles M2 can be more reliably controlled.

[0080] (8) The rolling tool 10a is rotatable around a second axis A2 different from the first axis A1, and has an outer peripheral portion 11 with the second axis A2 as its central axis, and a rolling blade 12 provided on the outer peripheral portion 11 and extending in the circumferential direction, and the angle θ1 of the tip 13 in a cross section perpendicular to the circumferential direction of the rolling blade 12 may be 0.7 to 1.5 times the angle θ2 of the tip 23 of the nick 22 when viewed in the circumferential direction of the rotating tool 20a.

[0081] In the rolling process, the multiple protrusions 30 are formed by pressing the rolling blade 12 of the rolling tool 10a. Therefore, the angle θ3 of the tip 33 of the protrusion 30 can be set to a value close to the angle θ2 of the tip 23 of the nick 22. This allows the aspect ratio of the formed metal powder M1 to be closer to 1.

[0082] (9) The rolling tool 10b is rotatable around a second axis A2 different from the first axis A1, and has an outer peripheral surface 15 with the second axis A2 as its central axis, a plurality of circumferentially extending convex rib portions 16 provided on the outer peripheral surface 15, and a bottom portion 17 between each of the plurality of convex rib portions 16. During the rolling process, the rolling tool 10b may be rotated around the second axis A2 while pressing the outer peripheral surface 15 against the first surface S1 of the workpiece 1 rotating around the first axis A1.

[0083] This allows the rolling step to be performed using the rolling tool 10b having the plurality of ridge portions 16 formed on the outer peripheral surface 15. Therefore, by pressing the plurality of ridge portions 16 against the first surface S1 of the workpiece 1, the plurality of ridge portions 30 are formed, and the processing time for the rolling step can be further shortened.

[0084] (10) In the rolling step, the pressing load of the rolling tool 10b may be set so that the portion of the second surface S2 that is raised by pressing the rolling tool 10b comes into contact with the bottom 17 of the rolling tool 10b.

[0085] In the rolling process, by pressing the rolling tool 10b, the workpiece 1 is deformed so as to bulge between the multiple convex streak portions 16, thereby forming multiple convex portions 30. Then, the portion of the second surface S2 that is bulged by pressing the rolling tool 10b comes into contact with the bottom portion 17 of the rolling tool 10b. Therefore, the shape of the outer peripheral surface 15 of the rolling tool 10b can be more reliably transferred to the workpiece 1, and the shape of the multiple convex portions 30 can be more reliably controlled.

[0086] (11) In the radial direction of the rolling tool 10b, the height H1 of each of the multiple convex rib portions 16 is equal to or greater than the particle size of the metal powder M1, and in the rolling process, a load may be input so that the second surface S2 of the workpiece 1 rises to a height equal to or greater than the particle size of the metal powder M1 in the radial direction of the workpiece 1.

[0087] After forming multiple protrusions 30 on the first surface S1 of the workpiece 1 by pressing the rolling tool 10b, the load input to the workpiece 1 from the rolling tool 10b is reduced. At this time, the height of the protrusions 30 may decrease due to a restoring force generated in the protrusions 30. That is, when the load is removed during the rolling process, the height of the protrusions 30 may decrease. In the example shown in FIG. 10, after the load is removed, the protrusions 30 contract in the direction of the first axis A1 due to the restoring force, reducing their height. Therefore, the height H3 of the protrusions 30 after the load is removed is lower than the height of the protrusions 30 before the load is removed. Note that the shape of the protrusions 30 before the load is removed is indicated by a dashed line in FIG. 10. In the metal powder forming method according to the embodiment, the height H1 of each of the multiple protrusions 16 is set to a value equal to or greater than the particle size of the metal powder M1. Therefore, the workpiece 1 can be raised by pressing the rolling tool 10b so that the height H3 is equal to or greater than the particle size of the metal powder M1 to be formed. Therefore, even if the height of the protrusions 30 decreases when the load is removed, the height H3 of the protrusions 30 can be prevented from becoming too small compared to the particle size of the metal powder M1 to be formed, thereby making it possible to more reliably control the shape of the metal particles M2.

[0088] (12) In a cross section perpendicular to the circumferential direction of the outer surface 15 of the rolling tool 10b, the bottom 17 is curved with a predetermined radius of curvature R4 so as to be convex toward the second axis A2, and the predetermined radius of curvature R4 may be a value less than the particle size of the metal powder M1.

[0089] 10, when the load is removed in the rolling process, the height of the convex portion 30 may decrease due to the restoring force, and the radius of curvature of the tip portion 33 in a cross section perpendicular to the circumferential direction of the workpiece 1 may increase. Even in such a case, the metal powder forming method according to the embodiment can prevent the radius of curvature of the tip portion 33 of the convex portion 30 after the load is removed in a cross section perpendicular to the circumferential direction of the workpiece 1 from becoming excessively large. Therefore, the shape of the metal particles M2 can be more reliably controlled.

[0090] (13) The pitch Pi4 of the ridge portions 16 in the direction of the second axis A2 of the rolling tool 10b may be 0.7 to 1.3 times the particle size of the metal powder M1.

[0091] This prevents the width of each of the plurality of protrusions 30 in the direction of the first axis A1 from being too small compared to the particle size of the metal powder M1 to be formed, thereby more reliably controlling the shape of the metal particles M2.

[0092] (14) The height of each of the multiple protrusions 30 in the radial direction of the second surface S2 of the workpiece 1 may be 0.7 to 1.3 times the width of each of the multiple protrusions 30 in a direction parallel to the first axis A1, and the angle θ3 of the tip 33 of each of the multiple protrusions 30 in a cross section perpendicular to the circumferential direction of the second surface S2 of the workpiece 1 may be 0.7 to 1.5 times the angle θ2 of the tip 23 of the nick 22 when viewed in the circumferential direction of the rotary tool 20a.

[0093] This allows the aspect ratio of the metal powder M1 to be closer to 1. In other words, the shape of the metal particles M2 contained in the metal powder M1 formed by cutting the workpiece 1 can be more reliably controlled.

[0094] (15) The first surface S1 of the workpiece 1 has a cylindrical surface shape with the first axis A1 as the central axis, the rolling tools 10a, 10b, 10c are knurling tools 10c, and the multiple convex portions 30 formed in the rolling process may be multiple protrusions 40 arranged two-dimensionally on the first surface S1, formed by pressing the knurling tool 10c against the first surface S1 of the workpiece 1 rotating around the first axis A1.

[0095] In the rolling process, a plurality of protrusions 40 can be formed on the first surface S1 by pressing the knurling tool 10c against the workpiece 1. Then, the plurality of protrusions 40 can be cut to form the metal particles M2. Therefore, the shape of the metal particles M2 can be more reliably controlled.

[0096] (16) In the rolling process, the pitch between each of the multiple protrusions 40 may be controlled by the pitch of the processing mold formed on the knurling tool 10c, and the height H4 of each of the multiple protrusions 40 in the radial direction of the workpiece 1 may be controlled by the pressing load of the knurling tool 10c in the rolling process.

[0097] As a result, by adjusting the pitch of the processing die formed on the knurling tool 10c, the pitch between each of the multiple protrusions 40 formed in the rolling process can be adjusted. Therefore, the pitch between each of the multiple protrusions 40 can be more easily controlled. Furthermore, by adjusting the pressing load of the knurling tool 10c, the height H4 of each of the multiple protrusions 40 formed on the workpiece 1 can be adjusted. Therefore, the height H4 can be more easily controlled. Therefore, the shape of the metal particles M2 can be more reliably controlled.

[0098] (17) The cutting tool 20 is a cutting tool 20b having a cutting blade 25 parallel to the first axis A1, and the cutting depth D2 of the cutting tool 20b during the cutting process may be less than the height H4 of each of the multiple protrusions 40 in the radial direction of the second surface S2 of the workpiece 1.

[0099] This allows the protrusions 40 to be cut with the cutting tool 20b so as to maintain the shape of each of the multiple protrusions 40. Furthermore, in the cutting process, the protrusions 40 can be cut so that each of the multiple protrusions 40 is more reliably separated. Therefore, it is possible to more reliably form metal particles M2 that correspond to the shape of the protrusions 40. In other words, it is possible to more reliably control the shape of the metal particles M2.

[0100] (18) In the cutting step, the cutting tool 20b can move only in the cutting direction, and the width of the cutting edge 25 of the cutting tool 20b and the width of the knurling tool 10c in the direction of the first axis A1 may be equal.

[0101] This allows the cutting tool 20b to cut only the protrusions 40 of the workpiece 1. This makes it possible to more reliably form metal particles M2 that correspond to the shape of the protrusions 40. This allows for more reliably controlling the shape of the metal particles M2.

[0102] (19) After the plurality of protrusions 30 formed in the rolling process are cut in the cutting process, a second rolling process may be performed on the third surface S3 of the workpiece 1 to form a plurality of further protrusions 30, and a second cutting process may be performed to form metal powder M1 by cutting the plurality of protrusions 30 formed in the second rolling process with a cutting tool 20.

[0103] This allows the third surface S3 of the workpiece 1 that has been cut in the cutting step to be further subjected to the rolling step and cutting step, thereby further improving the material yield rate and shortening the processing time required to form a desired amount of metal powder M1.

[0104] (20) A sliding film may be formed on the surface of the working mold of the rolling tools 10a, 10b, and 10c.

[0105] This reduces the frictional resistance that occurs between the rolling tools 10a, 10b, and 10c and the workpiece 1 during the rolling process. Therefore, it is possible to prevent the plurality of protrusions 30 formed on the workpiece 1 from being deformed due to the frictional resistance. That is, it is possible to more reliably control the shapes of the plurality of protrusions 30. This allows more reliably control the shapes of the metal particles M2. [Explanation of symbols]

[0106] 1 workpiece, 5 groove, 10 plastic processing tool, 10a rolling tool, 10b rolling tool, 10c knurling tool, 11 outer periphery, 12 rolling blade, 13 tip, 15 outer periphery, 16 convex portion, 17 bottom, 20 cutting tool, 20a rotating tool, 20b cutting tool, 21 cutting blade, 22 nick, 23 tip, 25 cutting blade, 30 convex portion, 33 tip, 40 protrusion, A1 first axis, A2 second axis, D2 cutting depth, S1 first surface, S2 second surface, S3 third surface, θ1 tip angle, H1 height, H3 height, H4 height, M1 metal powder, Pi3 pitch, Pi4 pitch, R4 radius of curvature, θ2 tip angle (angle), θ3 tip angle (angle)

Claims

1. A metal powder forming method for forming metal powder by cutting the surface of a metal workpiece, a rolling step of forming a second surface having a plurality of protrusions on a first surface of the workpiece using a rolling tool; a cutting step of forming metal powder by cutting the plurality of convex portions with a cutting tool, the first surface of the workpiece has an axisymmetric shape about a first axis; The cutting step is performed while the rolling step is performed while the workpiece is rotated around the first axis, In the rolling process, the rolling tool is moved in a feed direction while being pressed against the first surface of the workpiece rotating around the first axis, thereby forming a spiral groove on the first surface, thereby forming the plurality of convex portions aligned in at least a direction parallel to the first axis.

2. The metal powder forming method according to claim 1 , wherein in the rolling step, the pitch of the plurality of protrusions in the direction parallel to the first axis is controlled by a feed speed of the rolling tool.

3. The metal powder forming method according to claim 1 or 2, wherein the height of each of the plurality of protrusions is controlled by a pressing load of the rolling tool.

4. The cutting tool is a rotary tool having a plurality of nicks formed on a cutting blade, The metal powder forming method according to any one of claims 1 to 3, wherein in the cutting step, the plurality of convex portions are cut by the plurality of nicks while the rotary tool is rotated.

5. the rolling tool is rotatable around a second axis different from the first axis, and includes an outer circumferential portion having the second axis as a center axis, and a rolling blade provided on the outer circumferential portion and extending in a circumferential direction; The metal powder forming method according to claim 4, wherein the angle of the tip of the rolling blade in a cross section perpendicular to the circumferential direction is 0.7 to 1.5 times the angle of the tip of the nick when viewed in the circumferential direction of the rotary tool.

6. the rolling tool is rotatable around a second axis different from the first axis, and includes an outer circumferential surface having the second axis as a center axis, a plurality of circumferentially extending convex ridge portions provided on the outer circumferential surface, and bottom portions between each of the plurality of convex ridge portions; The metal powder forming method according to claim 4, wherein in the rolling process, the rolling tool is rotated around the second axis while pressing the outer surface against the first surface of the workpiece rotating around the first axis.

7. 7. The metal powder forming method according to claim 6, wherein in the rolling process, the pressing load of the rolling tool is set so that the portion of the second surface that is raised by pressing the rolling tool comes into contact with the bottom of the rolling tool.

8. a height of each of the plurality of protruding portions in a radial direction of the rolling tool is equal to or greater than a particle size of the metal powder; The metal powder forming method according to claim 6 or 7, wherein in the rolling process, a load is input so that the second surface of the workpiece rises in the radial direction of the workpiece to a height equal to or greater than the particle size of the metal powder.

9. In a cross section perpendicular to the circumferential direction of the outer circumferential surface of the rolling tool, the bottom portion is curved with a predetermined radius of curvature so as to be convex toward the second axis, The metal powder forming method according to any one of claims 6 to 8, wherein the predetermined radius of curvature is equal to or smaller than the particle size of the metal powder.

10. The metal powder forming method according to any one of claims 6 to 9, wherein the pitch of the ridge portion in the direction of the second axis of the rolling tool is 0.7 to 1.3 times the particle size of the metal powder.

11. a height of each of the plurality of protrusions in a radial direction of the second surface of the workpiece is 0.7 to 1.3 times a width of each of the plurality of protrusions in a direction parallel to the first axis, The metal powder forming method according to any one of claims 4 to 10, wherein the angle of the tip of each of the plurality of protrusions in a cross section perpendicular to the circumferential direction of the second surface of the workpiece is 0.7 to 1.5 times the angle of the tip of the nick when viewed in the circumferential direction of the rotary tool.

12. 12. The metal powder forming method according to claim 1, further comprising: performing a second rolling process to form a plurality of convex portions on a third surface of the workpiece after the plurality of convex portions rolled in the rolling process have been cut in the cutting process; and performing a second cutting process to form the metal powder by cutting the plurality of convex portions formed in the second rolling process with the cutting tool.

13. The metal powder forming method according to any one of claims 1 to 12, wherein a sliding film is formed on the surface of the working die of the rolling tool.

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