Metal powder formation method

Abstract

To control a shape of metal particles contained in a metal powder formed by cutting a workpiece.SOLUTION: A method for forming a metal powder, in which the metal powder is formed by cutting a surface of a metal workpiece, includes: a plastic working step of forming a second surface having a plurality of convex portions on a first surface of the workpiece; and a cutting step of forming the metal powder by cutting the plurality of convex portions.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for forming metal powder.

Background Art

[0002] In the method for manufacturing a molded body disclosed in Patent Document 1 below, the molding material contains metal fine particles obtained by cutting a metal and formed into a flaky shape, and a resin. This molding material is shorter than the maximum length of the flaky metal fine particles contained in this molding material. Further, the metal fine particles are discharged from an injection port capable of injecting the metal fine particles into the mold in the same direction, and a molded body is formed. Thereby, the directions of the metal fine particles are aligned, and a molded body having orientation in heat conductivity and electrical conductivity can be manufactured.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the conventional method of obtaining metal powder by cutting a metal, the formed metal powder contained metal particles having various shapes, particle sizes, aspect ratios, etc. That is, there were cases where the shape of the metal particles contained in the formed metal powder could not be controlled. Therefore, the formed metal powder contained metal particles that could not be used for subsequent molding processes, and there were cases where metal particles having a desired shape or the like were selected from the 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 Problems

[0006] A metal powder forming method according to one aspect of the present invention is a metal powder forming method for forming metal powder by cutting the surface of a metal workpiece, comprising a plastic deformation step of forming a second surface having a plurality of protrusions on a first surface of the workpiece, and a cutting step of forming metal powder by cutting the plurality of protrusions. [Effects of the Invention]

[0007] According to the present invention, the shape of metal particles contained in metal powder formed by cutting a workpiece can be controlled. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic side view showing the arrangement relationship between the workpiece, the rolling tool, and the cutting tool in a metal powder forming method according to the first embodiment. [Figure 2] This figure illustrates a metal powder formation method according to the first embodiment, and is a schematic side view corresponding to the view taken by arrow II in Figure 1. [Figure 3A] This is a schematic side view showing a rolling tool according to the first embodiment. [Figure 3B] This is a schematic cross-sectional view along the line IIIB-IIIB in Figure 3A, showing a rolling tool according to the first embodiment. [Figure 4] This is a diagram illustrating the rolling process according to the first embodiment, and is a schematic partial cross-sectional view along the line IV-IV in Figure 1. [Figure 5] This is a schematic side view showing a cutting tool according to the first and second embodiments. [Figure 6] This figure illustrates the cutting process according to the first and second embodiments, and is a schematic partial cross-sectional view along the line VI-VI in Figure 2. [Figure 7] This figure illustrates the cutting process 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] This is a schematic side view showing a rolling tool according to the second embodiment. [Figure 8B] This is a schematic cross-sectional view along the line VIIIB-VIIIB in Figure 8A, showing a rolling tool according to the second embodiment. [Figure 9] This is a diagram illustrating the rolling process according to the second embodiment, and is a schematic partial cross-sectional view corresponding to Figure 4. [Figure 10] This figure illustrates the effects of the metal powder formation method according to the second embodiment, and is a schematic partial cross-sectional view corresponding to Figure 9, showing multiple protrusions after unloading in the rolling process. [Figure 11] This is a schematic side view showing the arrangement relationship between the workpiece, the rolling tool, and the cutting tool in a metal powder forming method according to the third embodiment. [Figure 12] This figure illustrates a metal powder formation method according to a third embodiment, and is a schematic plan view corresponding to the view taken by arrow XII in Figure 11. [Figure 13] This figure illustrates the cutting process according to the third embodiment and is a schematic partial side view corresponding to the view taken by arrow XIII in Figure 12. [Figure 14] This figure illustrates the cutting process according to the third embodiment and is a schematic partial perspective view showing an example of how metal powder is formed from a workpiece. [Figure 15] This figure illustrates the spheroidizing process according to the embodiment, and is a schematic side view showing the arrangement relationship between the first plate member, the second plate member, and the metal powder. [Figure 16] This is a schematic plan view showing the movement of the second plate member relative to the first plate member in the spheroidizing process according to the embodiment. [Modes for carrying out 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 at 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 according to the shape of the metal powder M1 and the like. The aspect ratio is the ratio of the length of the long axis to the length of the short axis of the particle in imaging from a predetermined direction. The particle size is the equivalent circle diameter of the particle. The equivalent circle 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 are simply referred to as aspect ratio and particle size, respectively.

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

[0011] Hereinafter, a method for forming metal powder according to an embodiment will be described with reference to the drawings. The method for forming metal powder according to the embodiment is a method for forming metal powder M1 by cutting the surface of a workpiece 1 made of metal, and includes a plastic working 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 denoted by the same reference numerals, and redundant descriptions are omitted.

[0012] The workpiece 1 is a member that becomes the material of the metal powder M1, and may be composed of, for example, aluminum, an aluminum alloy, copper, a copper alloy, or the like. In the example shown in FIGS. 1 to 2, the workpiece 1 extends with the first axis A1 as the central axis and has a substantially circular shape in a cross section perpendicular to the first axis A1. Therefore, the workpiece 1 has a cylindrical shape as a whole. Note that the shape of the workpiece 1 is not limited to this, and for example, a portion of the workpiece 1 may have a smaller dimension in the radial direction than other portions. Further, the workpiece 1 may have a shape such as an elliptical column shape or a polygonal column shape.

[0013] The workpiece 1 includes a first surface S1 in a state before the plastic working step and the cutting step are performed. The first surface S1 has an axially symmetric shape around the first axis A1. In the example shown in FIG. 1, the first surface S1 constitutes the outer peripheral surface of the workpiece 1. That is, the first surface S1 may have a shape of a cylindrical surface with the first axis A1 as the central axis.

[0014] The plastic deformation process is a process in which a workpiece 1 is plastically deformed to form a plurality of protrusions 30 on the first surface S1, such as the example shown in Figure 4. In the following description, the surface of the workpiece 1 on which the plurality of protrusions 30 have been formed by plastic deformation will be referred to as the second surface S2. In the plastic deformation process, the workpiece 1 is plastically deformed by pressing the plastic deformation tool 10 against the first surface S1, thereby forming a plurality of protrusions 30. The plurality of protrusions 30 are formed in a state where they are aligned in at least one direction. The material of the plastic deformation tool 10 only needs to have a higher hardness than the workpiece 1. For example, the plastic deformation tool 10 may be made of cemented carbide. In addition, a sliding film (not shown) may be formed on the processing die of the plastic deformation tool 10. This sliding film may be, for example, a DLC (Diamond Like Carbon) coating. Furthermore, this sliding film may be formed by known film formation methods such as PVD (Physical Vapor Deposition) or CVD (Chemical Vapor Deposition). A processing die refers to a die with a predetermined shape formed on the surface of a plastic working tool in order to plastically deform the surface of a workpiece into a desired shape.

[0015] Plastic deformation is a process in which a workpiece 1 is pressed with a predetermined pressure using a die, causing the first surface S1 of the workpiece 1 to undergo plastic flow and deform plastically without removing any material from the base material. Below, we will describe a case in which the first surface S1 is plastically deformed by rolling as an example of plastic deformation to form a plurality of protrusions 30, but we are not limited to this. For example, the plurality of protrusions 30 may be formed by press working. Furthermore, the rolling process described below is just one example of a plastic deformation process and is not limited to this. For example, the plastic deformation process may be a press working process.

[0016] The cutting process involves cutting off multiple protrusions 30 formed by plastic deformation using a cutting tool 20. When the multiple protrusions 30 are cut off, metal powder M1 is obtained as cutting dust. In the following description, the surface of the workpiece 1 after the multiple protrusions 30 have been cut off will be referred to as the third surface S3.

[0017] (First Embodiment) Next, a metal powder formation method according to the first embodiment will be described with reference to Figures 1 to 7. In the example shown in Figure 1, a plastic deformation tool 10 is arranged on one radial side of the 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 deformation tool 10. A rotary tool 20a can be used as the cutting tool 20. The arrangement of the workpiece 1, the plastic deformation tool 10, and the rotary tool 20a is not limited to the illustrated example, and can be appropriately set according to the processing apparatus for implementing the metal powder formation method according to the embodiment, as well as 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, it has a disc-shaped form when viewed in the 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 the axial direction parallel to the direction perpendicular to the first axis A1 and the second axis A2.

[0019] As shown in the example in the figure, the outer circumference 11 of the rolling tool 10a is configured such that its width decreases as it extends radially outward. As a result, rolling blades 12 extending in the circumferential direction of the rolling tool 10a are formed on the outer circumference 11. The rolling blades 12 correspond to the processing die in the rolling tool 10a. The outer circumference 11 is the part that extends circumferentially on the radially outward side of the rolling tool 10a. Radially outward 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 parallel to the second axis A2.

[0020] The cross-section shown in Figure 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 portion 13 of the rolling blade 12. The rolling blade 12 is the part that is pressed against the workpiece 1 in the rolling process described later, causing the workpiece 1 to plastically deform. The tip portion 13 is the part that constitutes the radially outward side of the rolling blade 12. The angle of the tip angle θ1 may be 30 degrees or more and 90 degrees or less. Alternatively, the angle of the tip angle θ1 may be 60 degrees. Furthermore, in this cross-section, the radially outward end of the tip portion 13 may be curved to be convex radially outward with a predetermined radius of curvature R1. The radius of curvature R1 may be set to a value less than or equal to the particle size of the metal powder M1 to be obtained by the metal powder forming method according to the embodiment. For example, if it is desired to form metal powder M1 with a particle size of 50 μm, the radius of curvature R1 may be set to 1 μm or more and 50 μm or less. This makes it possible to more reliably form metal powder M1 with the desired particle size.

[0021] Furthermore, 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 suppresses excessive frictional force between the rolling blade 12 and the workpiece 1 during the rolling process described later. As a result, wear of the rolling blade 12 is suppressed, and the shape of the protrusions 30 formed in the rolling process can be controlled more reliably. Furthermore, 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 indices indicating surface roughness as defined in the Japanese Industrial Standard "Geometric Product Specifications (GPS) - Surface Texture: Profile 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 Figure 5, the cutting blade 21 is disposed at one end of the rotary tool 20a. Multiple nicks 22 are formed on the cutting blade 21, giving it a comb-like shape overall. In the illustrated example, multiple nicks 22 are formed on 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 multiple nicks 22. Note that the rotary tool 20a is not limited to the illustrated example, and may be, for example, a roughing end mill (not shown) having a wavy outer edge.

[0023] As shown in Figure 6, a tip angle θ2 is formed at the tip portion 23 of the nick 22 in a circumferential view 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 portion 23 constitutes the radially outward side of the nick 22 of the rotary tool 20a. The angle of the tip angle θ2 may be 45 degrees or more and 90 degrees or less. Alternatively, the angle of the tip angle θ2 may be 60 degrees. In the circumferential view, the radially outward portion of the nick 22 of 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 more and 100 μm or less. Also, in the circumferential view, the pitch Pi2 between multiple nicks 22 may be 10 μm or more and 100 μm or less. Also, the height H2 of the nick 22 may be 10 μm or more and 100 μm or less. The height H2 is the radial distance between the outermost radially outward portion of the nick 22 on the rotating tool 20a and the bottom 24. The bottom 24 is the portion formed between multiple nicks 22.

[0024] Furthermore, the ratio of the tip angle θ1 of the rolling blade 12 to the tip angle θ2 of the nick 22 may be configured to be within a predetermined range. For example, the angle of tip angle θ1 may be 0.7 to 1.5 times the angle of tip angle θ2. This can further reduce the aspect ratio of the metal powder M1. Note that tip angles θ1 and θ2 may be equal.

[0025] Next, the rolling process using the rolling tool 10a will be described with reference to the examples shown in Figures 1, 2, and 4. One end 2 of the workpiece 1 is fixed, for example, to the chuck of an NC (numerically controlled) lathe (not shown), and the rolling process can be performed while the workpiece 1 is rotated around the first axis A1. In the rolling process, the rolling process is performed on the workpiece 1 which is 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 against the first surface S1 of the workpiece 1, which is rotating around the first axis A1, with a predetermined pressing load. In the example shown in Figure 1, the rolling tool 10a is pressed by moving it in the direction of arrow B. Then, while the workpiece 1 is still rotating, the rolling tool 10a is moved in the feed direction. As a result, as shown in Figures 2 and 4, grooves 5 are formed on the first surface S1, and a part of the workpiece 1 around the rolling blade 12 undergoes plastic deformation so that it bulges out, forming a convex portion 30. At this time, the rolling tool 10a may rotate in the direction of arrow C (see Figure 1) with the second axis A2 as its central axis, following the rotation of the workpiece 1. The feed direction is the direction in which the rolling tool 10a is moved to form multiple convex portions 30 aligned in one direction on the first surface. In the example shown in Figure 4, the feed direction is in the direction of arrow D, and the rolling tool 10a is fed from the other end 3 side of the workpiece 1 toward the one end 2 side. This feed direction may also be parallel to the first axis A1 of the workpiece 1.

[0027] During the rolling process, the surface of the workpiece 1 undergoes plastic deformation, causing it to bulge along the trajectory of the rolling blade 12, and convex portions 30 are continuously formed in the circumferential direction of the workpiece 1. In addition, 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 helical trajectory on the first surface S1 of the workpiece 1. As a result, a helical groove 5 is formed on the first surface S1, as shown in Figure 2. Each side of the widthwise direction of the groove 5 thus formed 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 arranged in a direction parallel to the first axis A1.

[0028] As shown in the example in Figure 4, the groove 5 is formed by transferring the shape of the tip 13 of the rolling blade 12 onto the first surface S1. Therefore, the tip angle θ3 of the convex portion 30 and the tip angle θ1 of the rolling blade 12 are approximately equal in a cross section perpendicular to the circumferential direction of the second surface S2 of the workpiece 1. The tip angle θ3 is the angle of the tip 33 of each of the multiple convex portions 30. Accordingly, the tip angle θ3 may be 0.7 to 1.5 times the tip angle θ2 of the nick 22. Also, the tip angle θ3 and the tip angle θ2 may be equal. Furthermore, the portion of the second surface S2 composed of 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 is the portion that defines the groove 5 on the first axis A1 side. This radius of curvature may be approximately equal to the radius of curvature R1 of the tip 13.

[0029] The protrusion 30 includes a tip portion 33 formed by a raised section of the workpiece 1. The tip portion 33 is the part of the protrusion 30 that constitutes the radially outward side of the workpiece 1. Furthermore, the pitch Pi1 between the multiple grooves 5 in the direction parallel to the first axis A1 can be controlled by the feed rate of the rolling tool 10a. Therefore, the pitch Pi3 of the multiple protrusions 30 in the direction parallel to the first axis A1 can be controlled by the feed rate of the rolling tool 10a. The feed rate of the rolling tool 10a refers to the movement 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 parts of adjacent bottom portions 34 that are closest to the first axis A1. 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 parts of adjacent protrusions 30 that are furthest radially outward from the workpiece 1. As illustrated in the figure, the feed rate of the rolling tool 10a may also be controlled so that pitches Pi1 and Pi3 are approximately equal.

[0031] The height H3 of the protrusions 30 can be controlled by the pressing load when the rolling tool 10a is pressed 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 pressing 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 pressing load and the height H3 may also satisfy the following relationship Equation 1. In Equation 1, X 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" (Z 2243-2:2018). Height H3 [unit: μm] = (-0.022X + 2.137) × Indentation load [unit: N] ... (Equation 1)

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

[0033] Next, a cutting process using a rotary tool 20a will be described. In the example of cutting shown in Figures 1 and 2, a plurality of protrusions 30 formed by rolling are cut by the rotary tool 20a. In this cutting process, the rotary tool 20a is rotated in the direction of arrow E with the third axis A3 as the central axis, cut 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 it is not limited to this. The direction in which the rotary tool 20a is moved may be a direction that intersects the first axis A1 diagonally in an axial view perpendicular to the first axis A1 and the third axis A3. Furthermore, the rotary tool 20a may be configured to move in the opposite direction to 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 Figure 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 Figure 6, the cutting depth D1 is the distance in the radial direction of the workpiece 1 between points P5 and P6 in a cross section perpendicular to the first axis A1 and passing through the third axis A3. Point P5 is the part of the protrusion 30 closest to the third axis A3. Point P6 is the part of each of the multiple nicks 22 tips 23 closest to the first axis A1.

[0035] By rotating the rotary tool 20a at a cutting depth D1 and feeding it in the direction of arrow F, the protrusions 30 are cut by the nicks 22, as illustrated in Figure 7. During this process, multiple metal particles M2, which constitute cutting chips, are formed. The metal powder M1 is composed of these multiple metal particles M2. The dashed line shown in the figure schematically represents the trajectory of the tip of the nicks 22. Since the metal particles M2 have, for example, a roughly tetrahedral shape, the aspect ratio of the metal powder M1 can be brought close to 1. That is, by controlling the shape of the metal particles M2, the aspect ratio, particle size, etc., of the metal powder M1 can be controlled. In the illustrated example, a portion of each of the three protrusions 30 aligned in one direction is cut by multiple nicks 22, but this is not limited to this. Four or more protrusions aligned in one direction may be cut almost simultaneously.

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

[0037] In the examples shown in Figures 1 and 2, the rotation of the workpiece 1 in the direction of arrow A and the movement of the rotary tool 20a in the direction of arrow F occur simultaneously. Therefore, the relative trajectory 22a of the nick 22 with respect to the workpiece 1 is inclined with respect to the first axis A1 in an axial view perpendicular to the first axis A1 and the third axis A3, as shown in Figure 2. Here, in order to obtain metal powder M1, the extension direction of the trajectory 22a does not need to be parallel to the extension direction of the groove 5. That is, the extension direction of the trajectory 22a and the extension direction of the protrusion 30 do need to intersect. The extension direction of the trajectory 22a and the extension direction of the groove 5 may be perpendicular. That is, the extension direction of the trajectory 22a and the extension direction of the protrusion 30 may be perpendicular. This allows the protrusion 30 to be cut in a direction perpendicular to its extension direction, and the shape of the metal particles M2 can be controlled more reliably.

[0038] Alternatively, after cutting multiple protrusions 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 ensuring that the rotary tool 20a does not come into contact with the workpiece 1. Then, the rotary tool 20a may be made to cut again to a cutting depth D1 and fed in the direction of arrow F to cut the multiple protrusions 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 protrusions 30.

[0039] (Second Embodiment) Next, a metal powder formation method according to the 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 deformation tool 10 instead of the rolling tool 10a used in the first embodiment. The workpiece 1 and cutting tool 20 are configured in the same way as 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 Figures 8A and 8B, it has a disc-shaped form when viewed in the axial direction parallel to the second axis A2. The rolling tool 10b comprises an outer circumferential surface 15, a ridge portion 16, and a bottom portion 17. The outer circumferential surface 15 is the radially outward surface of the rolling tool 10b and extends in the circumferential direction of the rolling tool 10b with the second axis A2 as the central axis. Multiple ridge portions 16 extending in the circumferential direction are formed on the outer circumferential surface 15. Therefore, in a cross-section perpendicular to the circumferential direction of the rolling tool 10b, the outer circumferential surface 15 has a wavy shape. The outer circumferential surface 15 also corresponds to the processing die of the rolling tool 10b. The bottom portion 17 is the part formed between each of the multiple ridge portions 16. In the illustrated example, three ridge portions 16 are formed on the outer circumferential surface 15, but it is not limited to this. The number of raised ridges can be appropriately set according to the dimensions of the workpiece 1 in the direction of the first axis A1, the processing time of the rolling process, etc. For example, two raised ridges 16 or four or more raised ridges 16 may be formed on the outer surface 15.

[0041] In the cross-section perpendicular to the circumferential direction of the rolling tool 10b shown in Figures 8B and 9, the dimension of the protruding ridge portion 16 in the width direction of the rolling tool 10a is configured to decrease as it extends radially outward. Therefore, a tip angle θ4 is formed on the protruding ridge portion 16 in this cross-section. The angle of the tip angle θ4 may be between 30 degrees and 90 degrees. Alternatively, the angle of the tip angle θ4 may be 60 degrees. Furthermore, the radially outward side of the protruding ridge portion 16 in this cross-section may be curved with a radius of curvature R3 so as to be convex radially outward. The radius of curvature R3 may be between 1 μm and 100 μm.

[0042] In the radial direction of the rolling tool 10b, the height H1 of each of the multiple protrusions 16 is set to be greater than or equal to 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 part of the protrusion 16 that is located on the radially outer side. Point P8 is the part of the bottom 17 that is located on the second axis A2 side.

[0043] The pitch Pi4 of the raised ridge portion 16 may be set to a value of 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. Note that the pitch Pi4 is the pitch of the raised ridge portion 16 in the direction of the second axis A2. In the cross-section shown in Figure 9, the pitch Pi4 is the distance between point P7 and point P9. Points P7 and P9 are the portions of adjacent raised ridge portions 16 that are located furthest radially outward from the rolling tool 10b.

[0044] In the cross-sections shown in Figures 8B and 9, the bottom portion 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 less than or equal to 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 between 1 μm and 50 μm.

[0045] Next, a rolling process in which the workpiece 1 is rolled using a rolling tool 10b will be described. Similar to the first embodiment, in the rolling process, the outer surface 15 of the rolling tool 10b is pressed against the first surface S1 of the workpiece 1, which is rotating around the first axis A1, with a predetermined pressing load. Then, while the workpiece 1 is still rotating, the rolling tool 10a is moved in the feed direction (arrow D direction). As a result, multiple grooves 5 are formed on the first surface S1, and a part of the workpiece 1 is plastically deformed so that it bulges around the raised ridges 16, forming multiple protrusions 30. Note that at this time, the rolling tool 10b may rotate around the second axis A2 as its central axis in accordance with the rotation of the workpiece 1.

[0046] In the example shown in Figure 9, the tip 33 and the bottom 17 are in contact when the outer circumferential surface 15 is pressed against the workpiece 1 with a predetermined pressing load. That is, when performing the rolling process, the pressing load of the rolling tool 10b may be set so that the protrusion 30 and the bottom 17 are in contact. In that 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 relationship between the pressing load and the height H3 of the protrusion 30 satisfies the following equation 2. In equation 2, X is the Brinell hardness (HB) of the workpiece 1, and n is the number of protrusions 16 formed on the outer circumferential 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) × Indentation load [unit: N] / n ... (Equation 2)

[0047] When performing the rolling process, the protrusions 30 may be formed such that the height H3 is greater than or equal to 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, in the radial direction of the workpiece 1, the second surface S2 of the workpiece 1 is raised to a height greater than or equal to the particle size of the metal powder M1.

[0048] The cutting process according to this embodiment is performed using the rotary tool 20a in the same manner as in the first embodiment, so its description is omitted.

[0049] (Third embodiment) Next, a metal powder formation method according to the third embodiment will be described with reference to Figures 11 to 14. In the third embodiment, a knurling tool 10c can be used as the plastic working tool 10. The knurling tool 10c is a form of a rolling tool. In addition, a cutting tool 20b can be used as the cutting tool 20. The workpiece 1 illustrated in the figure is configured in the same way as in the first embodiment.

[0050] In the examples shown in Figures 11 and 12, the knurling tool 10c is positioned on one side of the workpiece 1 in the radial direction, and the cutting tool 20b is positioned on the other side. The arrangement of the workpiece 1, the knurling tool 10c, and the cutting tool 20b is not limited to the illustrated examples and can be appropriately set according to the shape, dimensions, etc., of the processing apparatus used to implement 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 around the fourth axis A4 and has a disc shape when viewed in the axial direction parallel to the fourth axis A4. The second knurling tool 10c2 is a roller-type tool that is rotatable around the fifth axis A5 and has a disc shape when viewed in the axial direction parallel to the fifth axis A5. The fourth axis A4 or fifth axis A5 illustrated in the figure extends parallel to the first axis A1, but is not limited thereto. The fourth axis A4 or fifth axis A5 may extend in a direction inclined with respect to the first axis A1.

[0052] A machining die 18 is formed on the outer circumferential surface of the first knurling tool 10c1. The machining die 18 may be composed of a plurality of protrusions. In the example shown in Figure 12, each of the plurality of protrusions extends in a direction intersecting the fourth axis A4 in a radial view of the first knurling tool 10c1 and is arranged parallel to each other. Furthermore, the machining die formed on the outer circumferential surface of the second knurling tool 10c2 may be formed by extending a plurality of protrusions (not shown) in a direction intersecting the extending direction of the protrusions of the first knurling tool 10c1.

[0053] The knurling tool 10c illustrated in the figure comprises 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 comprise only one roller-type tool. In that case, multiple recesses with shapes such as a square pyramidal shape or a hemispherical shape may be formed on the outer surface of the single roller-type tool.

[0054] The cutting tool 20b is equipped with a cutting edge 25. The cutting edge 25 has a flat blade shape that extends in a direction parallel to the first axis A1. As shown in Figure 12, the width of the cutting edge 25 of the cutting tool 20b and the width of the knurling tool 10c may be approximately equal in the direction parallel to the first axis A1. Also, in the direction parallel to the first axis A1, the center of the end of the cutting edge 25 on the workpiece 1 side and the center of the end of the knurling tool 10c on the workpiece 1 side may be located at the same position.

[0055] In the rolling process according to this embodiment, one end 2 of the workpiece 1 is fixed to the chuck of the NC lathe, similar to the first embodiment, and the rolling process is performed while rotating the workpiece around the first axis A1 in the direction of arrow H (see Figure 11). During the rolling process, the knurling tool 10c is pressed against the first surface S1 of the workpiece 1, which is rotating around the first axis A1, with a predetermined pressing load. As a result, the first surface S1 is raised in a shape corresponding to the processing die of the knurling tool 10c, and a plurality of protrusions 40 are formed. 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. The second knurling tool 10c2 may also rotate in the direction of arrow J. The plurality of protrusions 40 are one form of the plurality of convex portions 30 formed by the rolling process.

[0056] In the illustrated example, multiple protrusions of the first knurling tool 10c1 and multiple protrusions of the second knurling tool 10c2 are transferred to the first surface S1, forming multiple roughly square pyramidal projections 40 (see Figures 13 and 14). Therefore, the multiple projections 40 are periodically arranged in the direction in which the grooves formed by the transfer of the protrusions of the first knurling tool 10c1 extend, and in the direction in which the grooves formed by the transfer of the protrusions of the second knurling tool 10c2 extend. That is, multiple projections 40 arranged in two dimensions are formed on the first surface S1 by the rolling process. Note that the shape of the projections 40 is not limited to the illustrated example. The projections 40 may be, for example, hemispherical in shape.

[0057] When performing a rolling process, the pitch of the multiple protrusions 40 can be adjusted by adjusting the pitch of the protrusions of the first knurling tool 10c1 or the pitch of the protrusions of the second knurling tool 10c2. In other words, the pitch of the multiple protrusions 40 can be controlled by the pitch of the processing die formed on the knurling tool 10c. The pitch of the multiple protrusions 40 is the distance between the tops 41 of adjacent protrusions 40. The top 41 is the part of each of the multiple protrusions 40 that is located furthest 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 during the rolling process. For example, by reducing the pressing load of the knurling tool 10c during rolling, the height H4 of the protrusions 40 can be made lower. In the example shown in Figure 13, the height H4 is the distance between the top 41 and the first surface S1 in an axial view parallel to the first axis A1.

[0059] Next, a cutting process using the cutting tool 20b will be described. In the example of cutting shown in Figure 13, a plurality of protrusions 40 formed by the knurling tool 10c are cut by the cutting tool 20b. In this cutting process, the cutting tool 20b may be fixed in place after cutting to a predetermined 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 a plurality of protrusions 40 with the cutting tool 20b, the cutting tool 20b may be configured to move only in the cutting direction. However, the configuration of the cutting tool 20b is not limited to this. For example, the cutting tool 20b may be configured to move in a direction parallel to the first axis A1 of the workpiece 1 while it is cut. In that case, the feed rate of the cutting tool 20b in the direction parallel to the first axis A1 may be set according to the rotational speed of the workpiece 1 around the first axis A1. For example, the feed rate of the cutting tool 20b may be set to be greater than the rotational speed of the workpiece 1. In the example shown in the figures, the cutting depth D2 is the radial distance of the workpiece 1 between the top 41 of the projection 40 and the point P10 of the cutting blade 25 that is closest to the first axis A1. The cutting depth D2 may also be less than or equal to the height H4 of each of the multiple projections 40 in the radial direction of the workpiece 1. The cutting depth D2 may also be equal to the height H4. This makes it possible to more reliably form metal particles M2 according to the shape of the projection 40, and furthermore, it is possible to suppress the formation of irregularities on the third surface S3 on the workpiece 1 side. In addition, as shown in the examples in Figures 11 and 12, the direction of arrow K may be perpendicular to the first axis A1.

[0060] By cutting into the second surface S2 with the cutting tool 20b, at least a portion of the multiple protrusions 40 is cut by the cutting blade 25, as illustrated in Figure 14, and metal particles M2 are formed as cutting chips.

[0061] In the first to third embodiments described above, an example was taken in which a first surface S1 of the workpiece is rolled to form a second surface S2, and then the second surface S2 is cut. However, further rolling and cutting processes may be performed on the surface of the workpiece 1 after cutting. That is, a second rolling process 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 rolled in the rolling process have been cut in the cutting process. Then, 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.

[0062] The metal powder M1 obtained by the above embodiments may be further subjected to a spheroidizing process. The spheroidizing process is a process to further reduce the aspect ratio of the metal powder M1. As illustrated in Figures 15 and 16, the spheroidizing process uses a first plate member 50 and a second plate member 51. In the illustrated examples, the first plate member 50 and the second plate member 51 are disc-shaped members having a substantially circular shape in plan view, but are not limited to this. The first plate member 50 and the second plate member 51 may be members having shapes such as a substantially rectangular or substantially polygonal shape in plan view. The material of the first plate member 50 and the second plate member 51 can be appropriately set according to the material of the metal powder M1. For example, of the first plate member 50 and the second plate member 51, at least the surface that holds the metal powder M1 in the spheroidizing process described later may be made of a metal such as stainless steel or a diamond sintered body such as PCD (Polycrystalline Diamond). A sliding film may also be formed on the surface. The sliding film may be, for example, a DLC coating.

[0063] In the spheroidizing process, first, 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 Figure 15, the second plate member 51 is pressed against the first plate member 50 in the direction of arrow L. This causes the metal powder M1 to be sandwiched between the first plate member 50 and the second plate member. Next, while maintaining the predetermined load, the first plate member 50 and the second plate member are slid. In the example shown in Figure 16, the second plate member 51 is slid in the direction of arrow M so as to form a substantially circular trajectory in plan view relative to the first plate member 50. This causes the metal powder M1 to roll between the first plate member 50 and the second plate member 51, allowing for plastic deformation so that the aspect ratio approaches 1. The predetermined load can be appropriately set according to 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. In addition, as shown in the illustrated example, the second plate member 51 may be slid within the range that overlaps with the first plate member 50 in a plan view.

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

[0065] The arithmetic mean roughness Ra value 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 for a more reliable reduction of the aspect ratio of the metal powder M1. Furthermore, the arithmetic mean roughness Ra value may be set according to the material of the metal powder M1. For example, if the metal powder M1 is copper or a copper alloy, the arithmetic mean roughness Ra value may be 1.0 μm or more and 3.0 μm or less. Also, if the metal powder M1 is aluminum or an aluminum alloy, the arithmetic mean roughness Ra value may be 1.0 μm or more and 2.5 μm or less. This allows for a more reliable reduction of the aspect ratio of the metal powder M1. Note that the arithmetic mean roughness Ra value may be set to be within a desired numerical range regardless of the measurement direction of the surface roughness. This allows for a more reliable reduction of the aspect ratio of the metal powder M1 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, comprising a plastic deformation step of forming a second surface S2 having a plurality of protrusions 30 arranged in at least one direction on a first surface S1 of the workpiece 1 with a plastic deformation tool 10, and a cutting step of forming metal powder M1 by cutting the plurality of protrusions 30 with a cutting tool 20.

[0067] According to the metal powder formation method of the embodiment, a plurality of protrusions 30 aligned in one direction can be formed by plastic deformation. Therefore, a plurality of protrusions 30 can be formed by plastically deforming the workpiece 1, and the generation of metal scrap when forming the plurality of protrusions 30 can be suppressed. In other words, the material yield can be improved. Furthermore, in the cutting process, metal powder M1 is formed by cutting the plurality of protrusions 30. Therefore, metal powder M1 with a more uniform aspect ratio, particle size, etc. can be formed. In other words, the shape of the metal particles M2 contained in the metal powder M1 formed by cutting the workpiece 1 can be controlled.

[0068] (2) The plastic working tool 10 is a rolling tool 10a, 10b, 10c, and the plastic working step may be a rolling step in which a second surface S2 having a plurality of protrusions 30 is formed on the first surface S1 of the workpiece 1 using the rolling tools 10a, 10b, 10c.

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

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

[0071] This allows a workpiece 1, which has an axisymmetric shape around the first axis A1, to undergo both a rolling process and a cutting process while rotating it around the first axis A1. In other words, the formation of the protrusions 30 by rolling and the cutting of the protrusions 30 by cutting can be performed simultaneously while the workpiece 1 is rotating around the first axis A1. Therefore, the processing time required to form the metal powder M1 can be shortened.

[0072] (4) In the rolling process, the rolling tools 10a and 10b are pressed against the first surface S1 of the workpiece 1 which is rotating around the first axis A1 and moved in the feed direction, thereby forming a spiral groove 5 on the first surface S1, and a plurality of protrusions 30 arranged in a direction parallel to the first axis A1 may be formed.

[0073] This allows for the formation of multiple protrusions 30 by pressing the rolling tools 10a and 10b against the workpiece 1 rotating around the first axis A1 and moving them in the direction of the first axis A1. Therefore, multiple protrusions 30 can be formed more easily.

[0074] (5) In the rolling process, the pitch Pi3 of the multiple protrusions 30 in a direction parallel to the first axis A1 may be controlled by the feed rate 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 metal powder M1 by cutting the multiple protrusions 30, it becomes easier to form metal powder M1 with uniform particle size and other characteristics.

[0076] (6) The height H3 of each of the multiple 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 multiple protrusions 30. Therefore, when forming metal powder M1 by cutting the multiple protrusions 30, it becomes easier to form metal powder M1 with uniform particle size and other characteristics.

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

[0079] This allows each of the multiple protrusions 30 formed on the workpiece 1 to 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 controlled more reliably.

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

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

[0082] (9) The rolling tool 10b is rotatable around a second axis A2 which is different from the first axis A1, and comprises an outer circumferential surface 15 with the second axis A2 as its central axis, a plurality of circumferentially extending protrusions 16 provided on the outer circumferential surface 15, and a bottom portion 17 between each of the plurality of protrusions 16, and in the rolling process, the outer circumferential surface 15 may be pressed against the first surface S1 of the workpiece 1 which is rotating around the first axis A1 while the rolling tool 10b is rotating around the second axis A2.

[0083] This allows the rolling process to be performed using a rolling tool 10b having multiple protrusions 16 formed on its outer surface 15. Therefore, by pressing the multiple protrusions 16 against the first surface S1 of the workpiece 1, multiple protrusions 30 can be formed, further shortening the processing time of the rolling process.

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

[0085] In the rolling process, by pressing the rolling tool 10b against the workpiece 1, the workpiece 1 is deformed so that it bulges between the multiple protrusions 16, thereby forming multiple protrusions 30. The bulging portion of the second surface S2 caused by pressing the rolling tool 10b comes into contact with the bottom 17 of the rolling tool 10b. As a result, the shape of the outer surface 15 of the rolling tool 10b can be more reliably transferred to the workpiece 1, and the shape of the multiple protrusions 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 protrusions 16 is equal to or greater than the particle size of the metal powder M1, and in the rolling process, a load may be applied such 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] By pressing the rolling tool 10b against the workpiece 1, a plurality of protrusions 30 are formed on the first surface S1 of the workpiece 1. After this, the load applied to the workpiece 1 from the rolling tool 10b is reduced. At this time, the height of the protrusions 30 may decrease due to the restoring force generated in the protrusions 30. That is, the height of the protrusions 30 may decrease when the load is removed during the rolling process. In the example shown in Figure 10, after removal, the protrusions 30 contract in the direction of the first axis A1 due to the restoring force, and the height of the protrusions 30 decreases. Therefore, the height H3 of the protrusions 30 after removal is lower than the height of the protrusions 30 before removal. Note that in Figure 10, the shape of the protrusions 30 before removal is shown by a dashed line. In the metal powder forming method according to this embodiment, the height H1 of each of the plurality of protrusions 16 is set to a value greater than or equal to 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 greater than or equal to the particle size of the metal powder M1 to be formed. Therefore, even if the height of the protrusion 30 decreases when the load is removed, it is possible to prevent the height H3 of the protrusion 30 from becoming too small compared to the particle size of the metal powder M1 to be formed. This allows for more reliable control of 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 portion 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 or equal to the particle size of the metal powder M1.

[0089] As shown in the example in Figure 10, when the load is removed during the rolling process, the height of the protrusion 30 decreases 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 cases, the metal powder forming method according to the embodiment can suppress the excessive radius of curvature of the tip portion 33 of the protrusion 30 in a cross section perpendicular to the circumferential direction of the workpiece 1 after the load has been removed. Therefore, the shape of the metal particles M2 can be controlled more reliably.

[0090] (13) The pitch Pi4 of the raised ridges 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 multiple protrusions 30 in the direction of the first axis A1 from becoming too small compared to the particle size of the metal powder M1 to be formed. Therefore, the shape of the metal particles M2 can be controlled more reliably.

[0092] (14) The height of each of the multiple protrusions 30 in the radial direction of the second surface S2 of the workpiece 1 is 0.7 to 1.3 times the width of each of the multiple protrusions 30 in the 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 in a circumferential view of the rotary tool 20a.

[0093] This makes it possible to bring the aspect ratio of the formed metal powder M1 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 controlled more reliably.

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

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

[0096] (16) In the rolling process, the pitch between each of the multiple protrusions 40 may be controlled by the pitch of the processing die 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] This allows the pitch between each of the multiple protrusions 40 formed in the rolling process to be adjusted by adjusting the pitch of the processing die formed on the knurling tool 10c. Therefore, the pitch between each of the multiple protrusions 40 can be controlled more easily. In addition, the height H4 of each of the multiple protrusions 40 formed on the workpiece 1 can be adjusted by adjusting the pressing load of the knurling tool 10c. Therefore, the height H4 can be controlled more easily. Consequently, the shape of the metal particles M2 can be controlled more reliably.

[0098] (17) The cutting tool 20 is a tool bit 20b equipped with a cutting edge 25 parallel to the first axis A1, and the depth of cut D2 of the tool bit 20b in the cutting process may be less than or equal to the height H4 of each of the plurality of 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 while maintaining the shape of each of the multiple protrusions 40. Furthermore, during the cutting process, the protrusions 40 can be cut in such a way that each of the multiple protrusions 40 is separated more reliably. As a result, metal particles M2 corresponding to the shape of the protrusions 40 can be formed more reliably. In other words, the shape of the metal particles M2 can be controlled more reliably.

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

[0101] This allows only the multiple protrusions 40 of the workpiece 1 to be cut by the cutting tool 20b. Therefore, metal particles M2 corresponding to the shape of the protrusions 40 can be formed more reliably. Consequently, the shape of the metal particles M2 can be controlled more reliably.

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

[0103] This allows for further rolling and cutting processes to be performed on the third surface S3 of the workpiece 1 after it has been cut in the cutting process. As a result, the material yield can be further improved, and the processing time required to form the desired amount of metal powder M1 can be further shortened.

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

[0105] This reduces the frictional resistance generated between the rolling tools 10a, 10b, and 10c and the workpiece 1 during the rolling process. As a result, deformation of the multiple protrusions 30 formed on the workpiece 1 due to this frictional resistance can be suppressed. In other words, the shape of the multiple protrusions 30 can be controlled more reliably. This allows for more reliable control of the shape of the metal particles M2. [Explanation of Symbols]

[0106] 1 Workpiece, 5 Groove, 10 Plastic deformation tool, 10a Rolling tool, 10b Rolling tool, 10c Knurling tool, 11 Outer circumference, 12 Rolling blade, 13 Tip, 15 Outer surface, 16 Rib, 17 Bottom, 20 Cutting tool, 20a Rotary tool, 20b Turning tool, 21 Cutting blade, 22 Nick, 23 Tip, 25 Cutting blade, 30 Rib, 33 Tip, 40 Projection, A1 First axis, A2 Second axis, D2 Depth of cut, 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 method for forming metal powder by cutting the surface of a metal workpiece, A rolling process in which a second surface having a plurality of protrusions is formed on the first surface of the workpiece using a rolling tool, A cutting step in which metal powder is formed by cutting the aforementioned multiple protrusions with a cutting tool, Equipped with, The first surface of the workpiece has an axisymmetric shape around the first axis, The cutting process is performed while the workpiece is rotated around the first axis, A method for forming metal powder, wherein in the rolling process, the rolling tool is pressed against the first surface of the workpiece which is rotating around the first axis, thereby forming a plurality of first grooves extending in one direction, a plurality of second grooves extending in a direction intersecting the plurality of first grooves, and a plurality of protrusions arranged in the direction in which the plurality of first grooves and the plurality of second grooves extend, respectively.

2. The metal powder forming method according to claim 1, wherein the rolling tool is a roller-type tool having a plurality of recesses corresponding to the plurality of protrusions formed on its outer surface.

3. The aforementioned rolling tool comprises a first rolling tool and a second rolling tool, The plurality of first grooves are formed by the first rolling tool, The metal powder forming method according to claim 1, wherein the plurality of second grooves are formed by the second rolling tool.

4. A method for forming metal powder according to any one of claims 1 to 3, comprising: a second rolling step in which a plurality of protrusions formed in the rolling step are cut in the cutting step, and a second cutting step in which the plurality of protrusions formed in the second rolling step are cut with the cutting tool to form the metal powder.

5. A method for forming metal powder according to any one of claims 1 to 4, wherein a sliding film is formed on the surface of the processing die of the rolling tool.

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