Method for producing metal powder

Abstract

In order to suppress occurrence of excessive deformation of a material (1) being processed, this method for producing metal powder by cutting a surface of the metal material to be processed comprises: a first rolling step (P11) in which a first rolling die (21) is pressed against a first processed surface (S1) of the material being processed to perform rolling processing, thereby forming a second processed surface (S2) having a predetermined shape; a second rolling step (P12) in which a second rolling die (22) is pressed against the second processed surface to perform rolling processing, thereby forming a plurality of protrusion portions (11) on the surface of the material being processed. A pressing load (F2) of the second rolling die against the second processed surface is set to be smaller than a pressing load (F1) of the first rolling die against the first processed surface.

Description

Method for producing metal powder

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

[0002] As a method for producing this type of metal powder, there is known a metal powder forming method for forming metal powder by cutting a surface of a metallic workpiece, the method including: a plastic working step of forming, with a plastic working tool, a second surface having a plurality of protrusions aligned in at least one direction on a first surface of the workpiece; and a cutting step of forming metal powder by cutting the plurality of protrusions with a cutting tool (Patent Document 1).

[0003] WO2023 / 148980 pamphlet

[0004] However, in the above-mentioned conventional technology, when the second surface having a plurality of protrusions aligned in one direction on the first surface of the workpiece is plastically worked by the plastic working tool, the material forming the second surface escapes into the gap between the material and the rolling die and bulges up in the initial stage of the plastic working, and then excessive deformation occurs in which the apexes of the protrusions are crushed by the rolling die in the final stage of the plastic working.

[0005] The problem to be solved by the present invention is to provide a method for producing metal powder that can suppress the occurrence of excessive deformation of the workpiece.

[0006] The present invention solves the above problem by setting a lower pressing load when the second rolling die is pressed against the second processed surface that has been rolled by the first rolling die to perform rolling, compared with the pressing load when the first rolling die is pressed against the first processed surface of the metallic workpiece to perform rolling.

[0007] According to the present invention, the occurrence of excessive deformation of the workpiece can be suppressed.

[0008] This is a process diagram showing a method for producing metal powder according to one embodiment of the present invention. This is a schematic diagram showing the processing state in the plastic deformation process and cutting process according to one embodiment of the present invention. This is a view from arrow III in Figure 2. This is a schematic diagram showing the processing state in the plastic deformation process according to one embodiment of the present invention. This is a schematic diagram showing the processing state in the cutting process according to one embodiment of the present invention. This is a schematic diagram showing the processing state in the cutting process according to one embodiment of the present invention. This is a schematic diagram for explaining the problems that occur when a diagonal pattern is formed by rolling. This is a schematic diagram showing the relationship between the pressing loads of two rolling dies in the plastic deformation process according to one embodiment of the present invention. This is a schematic diagram showing the relationship between the pressing loads of two rolling dies in the plastic deformation process according to another embodiment of the present invention. This is a schematic diagram showing the relationship between the pressing loads of two rolling dies in the plastic deformation process according to yet another embodiment of the present invention. This is a schematic diagram showing the relationship between the pressing loads of two rolling dies in the plastic deformation process according to yet another embodiment of the present invention. This is a schematic diagram showing the relationship between the pressing loads of two rolling dies in the plastic deformation process according to yet another embodiment of the present invention.

[0009] Hereinafter, examples of embodiments for carrying out the present invention will be described with reference to the drawings. The method for producing metal powder in this embodiment involves cutting the surface of a workpiece 1 made of a metal material, and recovering the fine cutting powder generated by the cutting as a metal powder product. The material of the target metal powder is not particularly limited as long as it is a metal. For example, aluminum, aluminum alloys, copper, copper alloys, iron, stainless steel, titanium, titanium alloys, nickel, nickel alloys, cobalt alloys, etc., can be used as examples. The particle size of the fine metal powder produced in this embodiment is not particularly limited. For example, it is a metal powder with an average particle diameter of several tens of micrometers to about 500 micrometers.

[0010] The applications of the fine metal powder manufactured in this embodiment are not particularly limited. For example, it can be used as metal powder for metal 3D printing or as metal powder mixed into resin pellets. When the metal powder manufactured in this embodiment is used as metal for metal 3D printing, it can be used, for example, as metal powder for powder bed 3D printing. When the metal powder manufactured in this embodiment is used as metal for metal 3D printing, it can also be used in 3D printing methods called Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF), which involve mixing metal powder into resin filaments to form a laminate. Furthermore, when the metal powder manufactured in this embodiment is used as metal powder mixed into resin pellets, resin pellets containing the metal powder can be formed, and these pellets can be used for injection molding.

[0011] Furthermore, injection-molded parts and laminates 3D printed using the fused deposition modeling (FDM) or filament filament filament (FFF) methods described above can be degreased and fired to obtain metal parts from which the resin has been removed. For these applications, it is preferable that the aspect ratio of the particles (the ratio of the long axis to the short axis of the particles) is closer to 1, i.e., that the particles are spherical.

[0012] Figure 1 is a process diagram showing a method for manufacturing metal powder according to one embodiment of the present invention. In this embodiment, as shown in Figure 1, a metal workpiece 1 is prepared, a plurality of protrusions 11 are formed on the surface of the workpiece 1 (plastic deformation process P1), metal powder 4 is generated by cutting the plurality of protrusions 11 formed on the surface of the workpiece 1 using a cutting tool 3 (cutting process P2), and the generated metal powder 4 is recovered as a product (powder recovery process P3). After the cutting process P2 is completed and the plurality of protrusions 11 have been cut off the workpiece 1, the processing treatment of the plastic deformation process P1 and the cutting process of the cutting process P2 are performed on the cut surface of the workpiece 1 as needed. Plastic deformation is a process in which the surface of the workpiece 1 is plastically deformed by pressing a processing tool against the workpiece 1 with a predetermined pressure, without removing the base material. In particular, the plastic deformation process P1 in this embodiment consists of a first rolling process P11 and a second rolling process P12.

[0013] Figure 2 is a schematic diagram showing the processing state in the plastic deformation process P1 and cutting process P2 according to one embodiment of the present invention, Figure 3 is a view from arrow III in Figure 2, and Figure 4 is a schematic diagram showing the processing state in the plastic deformation process according to one embodiment of the present invention. The workpiece 1 in this embodiment shown in Figures 2 and 3 extends with a first axis A1 as its central axis and is circular or substantially circular in cross-section perpendicular to the first axis A1, so the workpiece 1 as a whole is cylindrical. However, the shape of the workpiece 1 is not limited to this, and for example, a part of the workpiece 1 may include a part that has a smaller radial dimension than other parts. Also, the workpiece 1 may be elliptical, polygonal, or the like. In the plastic deformation process P1 and cutting process P2 of this embodiment, one end 12 of the workpiece 1 is fixed to the chuck of a machining center or NC lathe, rotated in the direction of arrow H around the first axis A1, and while feeding the workpiece 1 in the direction of the first axis A1, rolling and cutting processes are continuously performed on the other end 13 of the workpiece 1.

[0014] In this embodiment, the workpiece 1 has a first surface S1 before the plastic deformation process P1 and the cutting process P2 are performed. The first surface S1 has an axisymmetric shape around the first axis A1. In the examples shown in Figures 2 and 3, the first surface S1 is formed on the outer circumferential surface of the workpiece 1. That is, the first surface S1 has the shape of a cylindrical surface with the first axis A1 as its central axis.

[0015] The plastic deformation process P1 of this embodiment includes a first rolling process P11 and a second rolling process P12, and is a process in which a two-step rolling process is performed on the workpiece 1 to form a diagonal pattern having a plurality of protrusions 11 on the surface of the workpiece 1, for example, as shown in Figures 4 to 6. In the following description, the surface of the workpiece 1 on which a diagonal pattern having a plurality of protrusions 11 has been formed by plastic deformation will be referred to as the third surface S3.

[0016] The rolling tool 2 of this embodiment includes a first rolling die 21 and a second rolling die 22, as shown in Figure 2. In the illustrated example, the first rolling die 21 is rotatable around a second axis A2 and is a roller-type tool with a disc shape when viewed in the axial direction of the second axis A2. The second rolling die 22 is rotatable around a third axis A3 and is a roller-type tool with a disc shape when viewed in the axial direction of the third axis A3. The first rolling die 21 rotates in the direction of arrow I in accordance with the rotation of the workpiece 1 (rotates together), and the second rolling die 22 rotates in the direction of arrow J in accordance with the rotation of the workpiece 1 (rotates together). The second axis A2 and third axis A3 illustrated in the figure extend parallel to the first axis A1, but the present invention is not limited to this. For example, the second axis A2 or the third axis A3 may extend in a direction inclined with respect to the first axis A1.

[0017] A processing surface is formed on the outer circumferential surface of the first rolling die 21. The processing surface of the first rolling die 21 is composed of a plurality of protrusions. In the example shown in Figure 3, each of these protrusions extends in a direction intersecting the second axis A2 when viewed radially from the first rolling die 21 and is arranged parallel to one another at equal intervals. Furthermore, the processing surface (not shown) formed on the outer circumferential surface of the second rolling die 22 is formed by extending a plurality of protrusions (not shown) in a direction intersecting the direction in which the protrusions of the first rolling die 21 extend.

[0018] Then, in the plastic deformation process P1 of this embodiment, as shown in Figure 4, first, in the first rolling process P11, the first rolling die 21 is pressed against the first surface S1 of the workpiece 1. As a result, the first surface S1 of the workpiece 1 is plastically deformed to conform to the shape of the processing surface of the first rolling die 21, and a second surface S2 is formed which has a plurality of convex portions extending in one direction and arranged at equal intervals.

[0019] In the subsequent second rolling process P12, the second rolling die 22 is pressed against the second surface S2 of the workpiece 1. As described above, the shape of the processing surface of the second rolling die has multiple convex ridges that extend in a direction intersecting one direction with respect to the shape of the processing surface of the first rolling die 21 and are arranged at equal intervals. As a result, the second surface S2 of the workpiece 1 is plastically deformed to conform to the shape of the processing surface of the second rolling die 22, and the third surface S3 is formed. In this way, by sequentially pressing the first rolling die 21 and the second rolling die 22, which have multiple convex shapes that extend in directions intersecting each other and are arranged at equal intervals, a third surface S3 is formed on the surface of the workpiece 1 with multiple convex portions 11 arranged regularly. The rolling conditions in the first rolling process P11 and the second rolling process P12 will be described later.

[0020] The material of the rolling tool 2, such as the first rolling die 21 and the second rolling die 22, should have a higher hardness than the workpiece 1. For example, the rolling tool 2 may be made of cemented carbide. Also, a sliding film (not shown) may be formed on the machined surfaces of the first rolling die 21 and the second rolling die 22. 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). The machined surface refers to a portion of the rolling tool 2 that has a predetermined shape and is formed on the surface to plastically deform the surface of the workpiece into a desired shape.

[0021] In this embodiment, a first rolling die 21 and a second rolling die 22 can be used as the rolling tool 2. Also, in this embodiment, a cutting tool 31 can be used as the cutting tool 3. In the example shown in Figures 2 and 3, the first rolling die 21 and the second rolling die 22, which are the rolling tool 2, are arranged on one radial side of the workpiece 1, and one cutting tool 31 is arranged on the other side. Note that the arrangement relationship between the workpiece 1, the rolling tool 2 (first rolling die 21 and second rolling die 22), and the cutting tool 3 (cutting tool 31) is not limited to the illustrated example, and can be appropriately set according to the shape and dimensions of the processing apparatus for carrying out the metal powder manufacturing method according to the embodiment.

[0022] The cutting process P2 is a process in which the multiple protrusions 11 of the diagonal pattern formed by the plastic deformation process P1 are cut with a cutting tool 3. When the multiple protrusions 11 are cut, metal powder 4 is obtained as cutting dust. In the following description, the surface of the workpiece 1 after the multiple protrusions 11 have been cut will also be referred to as the fourth surface S4.

[0023] The cutting tool 31 of this embodiment is equipped with a cutting edge 32. The cutting edge 32 has a flat blade shape that extends in a direction parallel to the first axis A1. As shown in Figure 3, the width of the cutting edge 32 of the cutting tool 31 and the width of the rolling tool 2 may be approximately equal in the direction parallel to the first axis A1.

[0024] Next, the operation will be explained. As shown in Figure 2, in the plastic deformation process P1 and cutting process P2 of this embodiment, one end 12 of the workpiece 1 is fixed to the chuck of a machining center or NC lathe, and the workpiece 1 is rotated in the direction of arrow H around the first axis A1, and rolling and cutting processes are continuously performed on the other end 13 of the workpiece 1 while feeding the workpiece 1 in the direction of the first axis A1.

[0025] As a result, the first surface S1 of the workpiece 1 becomes a third surface S3 with multiple protrusions 11 forming a diagonal pattern via the second surface S2, and then some or all of the protrusions 11 on the third surface S3 are cut away to become a fourth surface S4. Metal powder 4 is generated at this time. Furthermore, as the rotation of the workpiece 1 continues, the fourth surface S4 of the workpiece 1 becomes a third surface S3 with multiple protrusions 11 forming a diagonal pattern via the second surface S2, and then some or all of the protrusions 11 on the third surface S3 are cut away to become a fourth surface S4 again. This process is repeated thereafter.

[0026] Furthermore, when performing the rolling process, the pitch of the multiple protrusions 11 can be adjusted by adjusting the pitch of the protrusions of the first rolling die 21 or the pitch of the protrusions of the second rolling die 22. In addition, the height H1 of each of the multiple protrusions 11 in the radial direction of the workpiece 1 (see Figure 5) can be controlled by the pressing load of the first rolling die 21 in the first rolling process P11 and the pressing load of the second rolling die 22 in the second rolling process P12. For example, when performing the rolling process, the height H1 of the protrusions 11 can be made lower by reducing the pressing load of the first rolling die 21 or the second rolling die 22. Note that the height H1 refers to the distance between the top 11a and the first surface S1 (or fourth surface S4) in an axial view parallel to the first axis A1 in Figure 5.

[0027] Furthermore, when performing cutting, the cutting tool 31 shown in Figure 5 may be used to cut in the direction of arrow K with a predetermined depth of cut D. At this time, the movement of the cutting tool 31 in a direction perpendicular to the cutting direction may be restricted. The depth of cut D refers to the distance in the radial direction of the workpiece 1 between the top 11a of the protrusion 11 and the point P of the cutting blade 32 that is closest to the first axis A1, in the example shown in the figure. The depth of cut D may also be less than or equal to the height H1 of each of the multiple protrusions 11 in the radial direction of the workpiece 1. By cutting the cutting tool 31 into the third surface S3 having multiple protrusions 11, at least a portion of the multiple protrusions 11 is cut by the cutting blade 32, as illustrated in Figure 6, and metal powder 4 is generated as cutting chips.

[0028] Now, Figure 7 is a schematic diagram illustrating the problems that arise when a diagonal pattern is formed by a plastic deformation process P1 consisting of a first rolling process P11 and a second rolling process P12. When a diagonal pattern is formed by a plastic deformation process P1 consisting of a first rolling process P11 and a second rolling process P12, first, in the first rolling process P11, the first surface S1 of the workpiece 1 is rolled using the first rolling die 21 to form a second surface S2 having multiple convex ridges arranged at equal intervals in one direction. As a result, as shown in the lower left cross-sectional view of Figure 7, a second surface S2 having the desired convex ridges is formed.

[0029] In the subsequent second rolling process P12, the second surface S2 of the workpiece 1 is rolled to form multiple convex ridges arranged at equal intervals in a direction intersecting the multiple convex portions formed on the second surface S2. In the initial stages of the rolling process in this second rolling process P12, as shown in the lower center cross-sectional view of Figure 7, the material (thickness) forming the second surface S2 escapes into the gap with the second rolling die 22 and bulges out (the direction of bulging is indicated by the arrow). In the final stages of the rolling process, as shown in the lower right cross-sectional view of Figure 7, excessive deformation occurs where the apex of the convex ridges is crushed by the second rolling die 22 due to the bulging of the material (thickness). A cross-sectional photograph of this is shown in the lower right of Figure 7.

[0030] When such excessive deformation occurs, the desired square pyramidal protrusion 11, as shown in the upper right perspective view of Figure 7, cannot be obtained, and there is a problem in that the quality of the metal powder produced by cutting, such as the shape and particle size, is unstable. The main cause of such excessive deformation is that the stress generated on the second surface S2 by pressing with the second rolling die 22 is greater than the stress generated on the first surface S1 by pressing with the first rolling die 21.

[0031] In other words, the first rolling die 21 makes surface contact with the first surface S1 and presses against it, while the second surface S2 has multiple equally spaced protrusions formed thereon, so the second rolling die 22 makes point contact with the second surface S2 and presses against it. Therefore, when the first rolling die 21 and the second rolling die 22 are pressed with the same pressing load F, the stress σ = pressing load F / contact area A means that the stress generated on the second surface S2 by the second rolling die 22, which has a smaller contact area, is greater than the stress generated on the first surface S1 by the first rolling die 21, which has a larger contact area.

[0032] Therefore, in the plastic deformation process P1 of this embodiment, the pressing load F2 of the second rolling die 22 onto the second surface S2 is set to be smaller than the pressing load F1 of the first rolling die 21 onto the first surface S1 (F2 < F1). In other words, the pressing load F1 of the first rolling die 21 onto the first surface S1 and the pressing load F2 of the second rolling die 22 onto the second surface S2 are set so that the absolute value |σ1 - σ2| of the difference between the stresses σ1 and σ2 acting on the first surface S1 and the second surface S2, respectively, is less than or equal to a predetermined value a. Here, the predetermined value a is not particularly limited, but it is preferably close to 0, and more preferably 0. A predetermined value a of 0 means that the stresses σ1 and σ2 acting on the first surface S1 and the second surface S2, respectively, are equal.

[0033] Figure 8 is a schematic diagram showing the relationship between the pressing loads F1 and F2 of two rolling dies 21 and 22 in a plastic deformation process P1 according to one embodiment of the present invention. Since the pressing direction of the two rolling dies 21 and 22 is toward the center of the workpiece 1, the two pressing loads F1 and F2 also act toward the center of the workpiece 1.

[0034] When the pressing load F2 of the second rolling die 22 onto the second surface S2 is set to be smaller than the pressing load F1 of the first rolling die 21 onto the first surface S1 (F2 < F1), several embodiments are possible. These embodiments will be described below.

[0035] Figure 9 is a schematic diagram showing the relationship between the pressing loads F1 and F2 of two rolling dies 21 and 22 in a plastic deformation process according to another embodiment of the present invention. In this example, the first rolling die 21 and the second rolling die 22 are fixed to two different tool axes provided on a machining center and are structured to be independently controllable. The pressing load F1 of the first rolling die 21 onto the first surface S1 and the pressing load F2 of the second rolling die 22 onto the second surface S2 are controlled by the respective feed amounts m1 and m2 of the two tool axes set on the machining center.

[0036] In other words, if the feed rate m of the tool shaft is small, the pressing load F is also small, and if the feed rate m of the tool shaft is large, the pressing load F is also large. Therefore, the feed rate m2 of the tool shaft on which the second rolling die 22 is provided is set to be smaller than the feed rate m1 of the tool shaft on which the first rolling die 21 is provided (m2 < m1), and the first rolling process P11 and the second rolling process P12 are carried out. As a result, the pressing load F2 of the second rolling die 22 onto the second surface S2 is smaller than the pressing load F1 of the first rolling die 21 onto the first surface S1 (F2 < F1), and the first rolling process P11 and the second rolling process P12 can be carried out.

[0037] Figure 10 is a schematic diagram showing the relationship between the pressing loads F1 and F2 of two rolling dies 21 and 22 in a plastic deformation process according to yet another embodiment of the present invention. In this example, the first rolling die 21 is pressed against the first surface S1 via the first elastic member 23, and the second rolling die 22 is pressed against the second surface S2 via the second elastic member 24. The pressing load F1 of the first rolling die 21 against the first surface S1 and the pressing load F2 of the second rolling die 22 against the second surface S2 are controlled by the elastic force f1 of the first elastic member 23 and the elastic force f2 of the second elastic member 24.

[0038] In other words, the elastic force f2 of the second elastic member 24 is set to be smaller than the elastic force f1 of the first elastic member 23 (f2 < f1), and the first rolling process P11 and the second rolling process P12 are carried out. As a result, the pressing load F2 of the second rolling die 22 onto the second surface S2 is smaller than the pressing load F1 of the first rolling die 21 onto the first surface S1 (F2 < F1), and the first rolling process P11 and the second rolling process P12 can be carried out.

[0039] Figure 11 is a schematic diagram showing the relationship between the pressing loads F1 and F2 of two rolling dies 21 and 22 in a plastic deformation process according to yet another embodiment of the present invention. In this example, the first rolling die 21 and the second rolling die 22 are rotatably fixed to a single jig 25 that can move toward the workpiece 1, and rolling is performed by the first rolling die 21 and the second rolling die 22 by moving this jig 25 toward the workpiece 1. The approach direction V of the jig 25 is shown by a white arrow, and in this example, the approach direction of the jig 25 is parallel to the direction toward the center of the workpiece 1 from the contact surface between the first rolling die 21 and the workpiece 1. The pressing load F1 applied by the first rolling die 21 to the first surface S1 and the pressing load F2 applied by the second rolling die 22 to the second surface S2 are controlled by the positional relationship between the first rolling die 21, the second rolling die 22, and the workpiece 1, and the approaching movement direction V of the jig 25.

[0040] For example, as shown in Figure 11, when the jig 25 is brought close to the workpiece 1 along direction V, the pressing load F2 of the second rolling die 22 on the second surface S2 is equal to the pressing load F1 of the first rolling die 21 on the first surface S1, and the pressing load F2 of the second rolling die 22 on the second surface S2 is equal to F2 = F1cosθ from a geometric relationship (angle θ is the angle between the first rolling die 21 and the second rolling die 22). As a result, the pressing load F2 of the second rolling die 22 on the second surface S2 is smaller than the pressing load F1 of the first rolling die 21 on the first surface S1 (F2 < F1), and the first rolling process P11 and the second rolling process P12 can be carried out.

[0041] Although specific illustrations are omitted, before carrying out the first rolling process P11 and the second rolling process P12, the contact area A1 between the first rolling die 21 and the first surface S1, and the contact area A1 between the second rolling die 22 and the second surface S2 may be determined in advance using methods such as cross-sectional measurement or cross-sectional analysis. The pressing load F1 of the first rolling die 21 onto the first surface S1 and the pressing load F2 of the second rolling die 22 onto the second surface S2 may then be controlled according to these contact areas A1 and A2. In this case, it is more preferable to set the pressing load F1 of the first rolling die 21 onto the first surface S1 and the pressing load F2 of the second rolling die 22 onto the second surface S2 so that the absolute value |σ1-σ2| of the difference between the stresses σ1 and σ2 acting on the first surface S1 and the second surface S2, respectively, is less than or equal to a predetermined value a. Here, the predetermined value a is not particularly limited, but it is preferably close to 0, and more preferably 0.

[0042] Figure 12 is a schematic diagram showing the relationship between the pressing loads F1 and F2 of two rolling dies 21 and 22 in a plastic deformation process according to yet another embodiment of the present invention. In this example, before performing the first rolling process P11 and the second rolling process P12, the pressing load F1 of the first rolling die 21 onto the first surface S1 and the pressing load F2 of the second rolling die 22 onto the second surface S2 are measured in advance using a load cell or the like. Based on the measurement results of this measurement process, the contact area A1 between the first rolling die 21 and the first surface S1 and the contact area A2 between the second rolling die 22 and the second surface S2 are determined such that the absolute value |σ1 - σ2| of the difference in stress acting on the first surface S1 and the second surface S2 is less than or equal to a predetermined value a. Then, the die diameter D1 of the first rolling die 21 and the die diameter D2 of the second rolling die 22 are set so that the respective contact areas A1 and A2 are determined (D2 > D1), and the first rolling process P11 and the second rolling process P12 are carried out as shown in the figure. As a result, the pressing load F2 of the second rolling die 22 onto the second surface S2 is made smaller than the pressing load F1 of the first rolling die 21 onto the first surface S1 (F2 < F1), and the first rolling process P11 and the second rolling process P12 can be carried out.

[0043] As described above, the method for producing metal powder according to the present embodiment is a method for producing metal powder by cutting the surface of a metallic workpiece 1, comprising: a first rolling step P11 of pressing a first rolling die 21 against a first surface S1 of the workpiece 1 to perform rolling processing, thereby forming a second surface S2 of a predetermined shape; and a second rolling step P12 of pressing a second rolling die 22 against the second surface S2 to perform rolling processing, thereby forming a plurality of convex portions 11 on the surface of the workpiece 1. Since the pressing load F2 of the second rolling die 22 against the second surface S2 is set to be smaller than the pressing load F1 of the first rolling die 21 against the first surface S1, the stress σ2 acting on the second surface S2 can be reduced, and as a result, the occurrence of excessive deformation of the workpiece 1 can be suppressed.

[0044] Further, in the method for producing metal powder according to the present embodiment, the pressing load F1 of the first rolling die 21 against the first surface S1 and the pressing load F2 of the second rolling die 22 against the second surface S2 are set such that the absolute value of the difference between the stresses acting on the first surface S1 and the second surface S2, |σ1-σ2|, is equal to or less than a predetermined value a. Therefore, the stress σ2 acting on the second surface S2 and the stress σ1 acting on the first surface S1 are equal or approximate to each other, and as a result, the occurrence of excessive deformation of the workpiece 1 can be suppressed.

[0045] Further, in the method for producing metal powder according to the present embodiment, the first rolling die 21 and the second rolling die 22 are respectively fixed to two different tool shafts provided in a machining center, and the pressing load F1 of the first rolling die 21 against the first surface S1 and the pressing load F2 of the second rolling die 22 against the second surface S2 are controlled by the feed amounts m1 and m2 of the machining center. Therefore, the pressing load F2 of the second rolling die 22 against the second surface S2 can be set to be smaller than the pressing load F1 of the first rolling die 21 against the first surface S1, and as a result, the occurrence of excessive deformation of the workpiece 1 can be suppressed.

[0046] Furthermore, in the metal powder manufacturing method of the present embodiment, the first rolling die 21 is pressed against the first surface S1 via a first elastic member 23, and the second rolling die 22 is pressed against the second surface S2 via a second elastic member 24. The pressing load F1 of the first rolling die 21 against the first surface S1 and the pressing load F2 of the second rolling die 22 against the second surface S2 are controlled by the elastic force f1 of the first elastic member 23 and the elastic force f2 of the second elastic member 24. Therefore, the pressing load F2 of the second rolling die 22 against the second surface S2 can be set to be smaller than the pressing load F1 of the first rolling die 21 against the first surface S1, and as a result, the occurrence of excessive deformation of the workpiece 1 can be suppressed.

[0047] Furthermore, in the metal powder manufacturing method of the present embodiment, the first rolling die 21 and the second rolling die 22 are fixed to a single jig 25 that is movable toward the workpiece 1. The pressing load F1 of the first rolling die 21 against the first surface S1 and the pressing load F2 of the second rolling die 22 against the second surface S2 are controlled by the positional relationship (geometrical positional relationship) among the first rolling die 21, the second rolling die 22, and the workpiece 1, and the approaching movement direction V of the jig 25. Therefore, the pressing load F2 of the second rolling die 22 against the second surface S2 can be set to be smaller than the pressing load F1 of the first rolling die 21 against the first surface S1, and as a result, the occurrence of excessive deformation of the workpiece 1 can be suppressed.

[0048] Furthermore, in the metal powder manufacturing method of the present embodiment, a contact area A1 between the first rolling die 21 and the first surface S1, and a contact area A2 between the second rolling die 22 and the second surface S2 are obtained. The pressing load F1 of the first rolling die 21 against the first surface S1 and the pressing load F2 of the second rolling die 22 against the second surface S2 are controlled in accordance with these contact areas A1 and A2. Therefore, the pressing load F2 of the second rolling die 22 against the second surface S2 can be set to be smaller than the pressing load F1 of the first rolling die 21 against the first surface S1, and as a result, the occurrence of excessive deformation of the workpiece 1 can be suppressed.

[0049] Furthermore, in the metal powder manufacturing method of this embodiment, a measurement step is further included before the first rolling step P11 and the second rolling step P12 in which the pressing load F1 of the first rolling die 21 onto the first surface S1 and the pressing load F2 of the second rolling die 22 onto the second surface S2 are measured in advance. Based on the measurement results of the measurement step, the pressing load F1 of the first rolling die 21 onto the first surface S1 and the pressing load F2 of the second rolling die 22 onto the second surface S2 are set so that the absolute value |σ1-σ2| of the difference in stress acting on the first surface S1 and the second surface S2 is less than or equal to a predetermined value a. As a result, the pressing load F2 of the second rolling die 22 onto the second surface S2 can be set to be smaller than the pressing load F1 of the first rolling die 21 onto the first surface S1, and as a result, the occurrence of over-deformation of the workpiece 1 can be suppressed.

[0050] Furthermore, in the metal powder manufacturing method of this embodiment, before the first rolling step P11 and the second rolling step P12, the pressing load F1 of the first rolling die 21 onto the first surface S1 and the pressing load F2 of the second rolling die 22 onto the second surface S2 are measured in advance, and based on the measurement results, the contact area A1 between the first rolling die 21 and the first surface S1 is set such that the absolute value |σ1-σ2| of the difference in stress acting on the first surface S1 and the second surface S2 is less than or equal to a predetermined value a. The contact area A2 between the second rolling die 22 and the second surface S2 is determined, and the die diameter D1 of the first rolling die 21 and the die diameter D2 of the second rolling die 22 are set so that the respective contact areas A1 and A2 are determined. As a result, the pressing load F2 of the second rolling die 22 onto the second surface S2 can be set to be smaller than the pressing load F1 of the first rolling die 21 onto the first surface S1, and as a result, the occurrence of excessive deformation of the workpiece 1 can be suppressed.

[0051] The first surface S1 corresponds to the first workpiece surface according to the present invention, and the second surface S2 corresponds to the second workpiece surface according to the present invention.

[0052] 1…Workpiece 11…Protrusion 12…One end 13…Other end 2…Plastic deformation tool 21…First rolling die 22…Second rolling die 23…First elastic member 24…Second elastic member 25…Jig 3…Cutting tool 31…Cutting tool 32…Cutting blade 4…Metal powder P1…Plastic deformation process P11…First rolling process P12…Second rolling process P2…Cutting process P3…Powder recovery process H1…Height of protrusion S1…First surface (first workpiece surface) S2…Second surface (second workpiece surface) S3…Third surface S4…Fourth surface F1, F2…Pressing load A1, A2…Contact area σ1, σ2…Stress D1, D2…Die diameter

Claims

1. A method for manufacturing metal powder by cutting the surface of a metal workpiece, comprising: a first rolling step of pressing a first rolling die against a first workpiece surface of the workpiece to perform rolling and form a second workpiece surface of a predetermined shape; and a second rolling step of pressing a second rolling die against the second workpiece surface to perform rolling and form a plurality of protrusions on the surface of the workpiece, wherein the pressing load of the second rolling die against the second workpiece surface is set to be smaller than the pressing load of the first rolling die against the first workpiece surface.

2. The method for producing metal powder according to claim 1, wherein the pressing load of the first rolling die on the first workpiece and the pressing load of the second rolling die on the second workpiece are set such that the absolute value of the difference in stress acting on the first workpiece surface and the second workpiece surface is less than or equal to a predetermined value.

3. The method for manufacturing metal powder according to claim 1 or 2, wherein the first rolling die and the second rolling die are fixed to two different tool axes provided on a machining center, and the pressing load of the first rolling die against the first workpiece surface and the pressing load of the second rolling die against the second workpiece surface are controlled by the feed rate of the machining center.

4. The method for manufacturing metal powder according to claim 1 or 2, wherein the first rolling die is pressed against the first workpiece surface via a first elastic member, the second rolling die is pressed against the second workpiece surface via a second elastic member, and the pressing load of the first rolling die against the first workpiece surface and the pressing load of the second rolling die against the second workpiece surface are controlled by the elastic force of the first elastic member and the elastic force of the second elastic member.

5. The method for manufacturing metal powder according to claim 1 or 2, wherein the first rolling die and the second rolling die are fixed to a single jig that can move toward the workpiece, and the pressing load of the first rolling die on the first workpiece surface and the pressing load of the second rolling die on the second workpiece surface are controlled by the positional relationship between the first rolling die, the second rolling die and the workpiece, and the direction of the approaching movement of the jig.

6. The method for producing metal powder according to claim 1 or 2, wherein the contact area between the first rolling die and the first workpiece surface and the contact area between the second rolling die and the second workpiece surface are determined, and the pressing load of the first rolling die against the first workpiece surface and the pressing load of the second rolling die against the second workpiece surface are controlled according to these contact areas.

7. A method for producing metal powder according to claim 1 or 2, further comprising a measurement step prior to the first rolling step and the second rolling step, wherein the pressing load of the first rolling die onto the first workpiece surface and the pressing load of the second rolling die onto the second workpiece surface are measured in advance, and the pressing load of the first rolling die onto the first workpiece surface and the pressing load of the second rolling die onto the second workpiece surface are set based on the measurement results of the measurement step such that the absolute value of the difference in stress acting on the first workpiece surface and the second workpiece surface is less than or equal to a predetermined value.

8. The method for producing metal powder according to claim 1 or 2, wherein, prior to the first rolling step and the second rolling step, the pressing load of the first rolling die onto the first workpiece surface and the pressing load of the second rolling die onto the second workpiece surface are measured in advance; based on the measurement results, the contact area between the first rolling die and the first workpiece surface and the contact area between the second rolling die and the second workpiece surface are determined such that the absolute value of the difference in stress acting on the first workpiece surface and the second workpiece surface is less than or equal to a predetermined value; and the die diameter of the first rolling die and the die diameter of the second rolling die are set so that the respective contact areas are determined.

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