Metal powder manufacturing method

Abstract

This invention provides a method for producing metal powders that exhibit good fluidity. [Solution] The metal powder manufacturing method comprises a compression step S30 and a cutting step S40. The compression step S30 compresses an aggregate 11 of foil-shaped metal pieces 10 in the compression direction to form a brick 12 of metal pieces 10 having sides 12a surrounding a central axis 12c parallel to the compression direction. The cutting step S40 cuts the sides 12a of the brick 12 to form fine particles 13 of metal powder.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a pulverization method for continuously producing fine powder from a raw material using a medium stirring type pulverizer. The pulverizer includes a horizontally arranged pulverization tank and an agitator shaft rotatably accommodated in the pulverization tank. An agitator arm is attached to the agitator shaft. The raw material introduced into the pulverization tank is agitated together with the media in the pulverization tank by the rotation of the agitator arm and is pulverized.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, there are several shaping methods for metal 3D printers, such as the powder bed method and the directed energy deposition method. In any method, appropriate fluidity is required for the metal powder. Therefore, it is desirable that the fine particles of the metal powder have a spherical shape or a shape close to a spherical shape.

[0005] On the other hand, when powders of metals with relatively high ductility such as aluminum and copper are produced using a medium stirring type pulverizer such as a ball mill, the shape of the produced fine particles tends to be scaly flat in one direction. The scaly fine particles have low sphericity and low fluidity. Since the metal powder with low fluidity has poor laying property, it is more likely to be difficult to perform precise shaping with a 3D printer of the powder bed method.

[0006] The present invention aims to provide a method for producing metal powders that can be manufactured with good fluidity. [Means for solving the problem]

[0007] A method for producing metal powder according to one aspect of the present invention comprises a forming step and a cutting step. The forming step involves compressing an aggregate of foil-shaped metal pieces in the compression direction to form a brick of the metal pieces having sides surrounding a central axis parallel to the compression direction. The cutting step involves cutting the sides of the brick to form fine particles of metal powder. [Effects of the Invention]

[0008] According to the present invention, a method for producing metal powders that have good fluidity can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view of an example of a metal piece applied to the metal powder manufacturing method according to the embodiment. [Figure 2] This is a flowchart showing an example of a metal powder manufacturing method according to an embodiment. [Figure 3] This is a diagram illustrating the compression process according to the embodiment. [Figure 4] An objective view of an example of a brick formed by the compression process. [Figure 5A] An objective view of an example of a brick formed by the compression process. [Figure 5B] An objective view of an example of a brick formed by the compression process. [Figure 6] This is a diagram illustrating a variation of the compression process. [Figure 7] This is a diagram illustrating the cutting process according to the embodiment. [Figure 8] This is a perspective view showing an example of the positional relationship between the cutting edge and the brick during the cutting process. [Figure 9] This is a diagram illustrating an example of a gripping method according to the embodiment. [Modes for carrying out the invention]

[0010] The metal powder manufacturing method according to this embodiment will be described below with reference to the drawings. For the sake of convenience, the metal powder manufacturing method according to this embodiment will be simply referred to as the manufacturing method. In addition, the same reference numerals will be used for the same elements shown in each figure, and redundant explanations will be omitted. Furthermore, the Z direction will be defined. The Z direction is, for example, the compression direction in the compression process described later.

[0011] The metal powder manufacturing method according to this embodiment produces metal powder by cutting a metal piece 10. In the following description, metal chips (metal chips) are given as an example of the metal piece 10. Metal chips are metal waste (chips) generated during the machining of a metal workpiece. However, the metal piece 10 is not limited to metal chips; for example, it may be a metal piece that is distributed on the market as a metal material.

[0012] Figure 1 is a perspective view of an example of a metal piece 10 applied to the manufacturing method according to this embodiment. As shown in Figure 1, the metal piece 10 is a foil-like metal having a predetermined thickness c. The shape of the metal piece 10 is arbitrary; for example, it may be a strip or a band stretched in one direction. The metal piece 10 may also be stretched linearly or curved. Furthermore, the metal piece 10 may be stretched in a spiral or helical shape. The width and length of the metal piece 10 are arbitrary as long as the metal piece 10 can be cut in the cutting process S40.

[0013] Figure 2 is a flowchart showing an example of a manufacturing method according to this embodiment. As shown in Figure 2, the manufacturing method comprises at least a compression step S30 and a cutting step S40. The compression step S30 compresses the aggregate 11 containing the metal pieces 10 in the Z direction (compression direction) to form a brick 12 of the metal pieces 10 (see Figure 4). The cutting step S40 cuts the side surface 12a of the brick 12 to form fine particles 13 of the metal powder (see Figure 8). As will be described later, the fine particles 13 have a higher degree of sphericity than the same volume of flake-shaped fine particles. Therefore, according to this embodiment, it is possible to obtain a metal powder with better fluidity than, at least, flake-shaped metal powder.

[0014] A specific example of the manufacturing method will be explained. As shown in Figure 2, the manufacturing method includes a washing step S10, a sorting step S20, a compression step S30 as a forming step (brick forming step), a cutting step S40, and a classification step S50. In the washing step S10, the metal pieces 10 are washed using a known cleaning agent and washing machine to remove contaminants such as oil and foreign matter attached to the metal pieces 10. However, if there are no contaminants attached to the metal pieces 10, or if the presence of contaminants does not affect subsequent processes, and intentional washing is considered unnecessary, the washing step S10 may be omitted.

[0015] The sorting step S20 selects metal pieces with dimensions suitable for use in the cutting step S40 from a group of metal pieces having various shapes. The sorting step S20 is performed after or before the washing step S10. The sorting step S20 performs the above sorting using, for example, at least one of several sieves with different mesh sizes. The sorting step S20 collects metal pieces 10 that are similar in size and shape. This reduces variations in the size and shape of the fine particles formed in the cutting step S40, thereby improving the yield in the production of metal powder. However, if the differences in the size and shape of the metal pieces are slight, the sorting step S20 may be omitted.

[0016] FIG. 3 is a diagram for explaining the compression step S30. The compression step S30 is executed after the cleaning step S10 and the sorting step S20. The compression step S30 compresses the aggregate 11 of the metal pieces 10 in the Z direction to form the brick 12 of the metal pieces 10. In this step, the mold 20 shown in FIG. 3 is used.

[0017] As shown in FIG. 3, the mold 20 includes a lower mold 21 and an upper mold 22. The lower mold 21 is a container and has a cavity 23 in which the metal pieces 10 are accommodated. The cavity 23 is a bottomed hole extending along the Z direction and opening toward the upper mold 22. The bottom surface 23a of the cavity 23 is a flat surface orthogonal to the Z direction. On the other hand, the upper mold 22 is a rod-shaped member inserted into the cavity 23. The upper mold 22 has a lower surface 22a facing the cavity 23. The lower surface 22a is a flat surface orthogonal to the Z direction. In a plane orthogonal to the Z direction, the cavity 23 and the upper mold 22 have complementary cross-sectional shapes. This cross-sectional shape is, for example, a circle or a polygon such as a rectangle.

[0018] In the compression step S30, first, the metal pieces 10 are put into the cavity 23. Next, the upper mold 22 is inserted into the cavity 23, and the aggregate 11 of the metal pieces 10 is pressed in the Z direction with the pressure required for the above-described compression. As a result, the aggregate 11 is compressed in the Z direction to become the brick 12. While the aggregate 11 is being compressed, the metal pieces 10 move or deform so as to expand (orient) in a direction orthogonal to the Z direction and are laminated in the Z direction (that is, in the thickness direction of the metal pieces 10 themselves). That is, inside the brick 12, the metal pieces 10 are laminated in the Z direction.

[0019] The compression in the compression step S30 is performed once or multiple times. For example, the compression in the compression step S30 may include a preliminary compression followed by a main compression. Both the preliminary and main compressions are performed at least once. The pressure of the main compression is higher than that of the preliminary compression. By performing a preliminary compression at a relatively low pressure before the main compression, the movement or deformation of the metal pieces 10 before the aggregate 11 is completely compressed can be promoted. This reduces the amount of metal pieces that do not unfold in a direction perpendicular to the Z direction, thereby reducing excess voids within the brick 12.

[0020] The maximum pressure during compression may be set to a value such that when the stacked metal pieces 10 are cut in the cutting process S40, fine particles 13 are individually formed from each of them. That is, even if the stacked metal pieces 10 are fixed together by compression, the maximum pressure during compression may be set to a value such that when they are cut, they are formed as multiple fine particles originating from each of the metal pieces 10. This setting value is appropriately determined according to the material, surface condition, etc., of the metal pieces 10.

[0021] Figure 4 is a perspective view of an example of a brick 12 formed in the compression process S30. In the compression process S30, the brick 12 is formed in a plate-like shape with thickness in the Z direction, or in a columnar shape extending in the same direction. The brick 12 also has a side surface 12a surrounding a central axis 12c parallel to the Z direction, and a pair of end surfaces 12b, 12b located on both sides in the Z direction. The cross-sectional shape of the brick 12 perpendicular to the Z direction depends on the cross-sectional shape of the cavity 23. That is, if the cross-sectional shape of the cavity 23 is circular, the brick 12 is formed in a disc-like or cylindrical shape with a similar cross-sectional shape centered on the central axis 12c (see Figure 5A). If the cross-sectional shape of the cavity 23 is polygonal, the brick 12 is formed in a rectangular disc-like or rectangular prism-like shape with a similar cross-sectional shape centered on the central axis 12c, and has a flat surface 12d on the side surface 12a (see Figure 5B).

[0022] Figure 6 illustrates a modified example of the compression process S30. As shown in Figure 6, the compression process S30 may include repeated steps of supplying the metal piece 10 to the cavity 23 and compressing the supplied metal piece 10 in the Z direction. In other words, the compression process S30 may alternately repeat the supply of the metal piece 10 and the compression of the metal piece 10. Furthermore, the compression in this case may also include the preliminary compression and final compression steps described above.

[0023] When a large amount of metal pieces 10 are supplied to the cavity 23, the pressure from the upper mold 22 becomes less effective in transmitting pressure to certain areas of the aggregate 11. In this case, the metal pieces 10 in those areas do not move or deform, and it becomes difficult for them to unfold in a direction perpendicular to the Z direction. As a result, the likelihood of not achieving stacking of metal pieces 10 in the Z direction in those areas increases.

[0024] In a modified version of the compression process S30, metal pieces 10 are supplied to the cavity 23 in stages, and compression is performed each time a metal piece 10 is supplied. As a result, pressure from the upper mold 22 is transmitted to each of the metal pieces 10 supplied to the cavity 23, causing the metal pieces 10 to move or deform during compression and unfold in a direction perpendicular to the Z direction. Therefore, the metal pieces 10 become easier to stack in the Z direction. Furthermore, it becomes easier to form long bricks 12 in the Z direction (see Figures 5A and 5B).

[0025] In the cutting process S40, the side surface 12a of the brick 12 formed in the compression process S30 is cut using a cutting tool 30 to form fine particles 13 of metal powder (see Figure 8). The cutting tool 30 is, for example, a face mill 31 as shown in Figure 7. However, the cutting tool 30 is not limited to a face mill 31 and may also be an end mill (not shown) or a metal saw (not shown). Alternatively, the brick 12 itself may be rotated using a lathe (not shown) and the side surface 12a may be cut with a cutting tool (not shown).

[0026] For the sake of explanation, we define the U, V, and W directions as mutually orthogonal to each other. The W direction is the cutting direction of the brick 12 by the cutting tool 30. The central axis 12c of the brick 12 is positioned parallel to the W direction. The brick 12 is also gripped from both sides in the W direction by the clamping mechanism 40 (see Figure 9). Therefore, the stacking direction of the metal pieces 10 within the brick 12 is approximately parallel to the W direction.

[0027] The rotational axis 31c of the face mill 31 is set, for example, to be parallel to the V direction. The relative movement direction (i.e., feed direction) between the face mill 31 and the brick 12 is set, for example, to the U direction. In this case, the cutting edge (tip) 32 of the face mill 31 moves on a circular orbit on the UW plane, centered on the rotational axis 31c.

[0028] Figure 8 is a perspective view showing an example of the positional relationship between the cutting edge 32 and the brick 12 during the cutting process S40. In this figure, for the sake of explanation, the circular trajectory of the cutting edge 32 is approximated by a linear trajectory. The angle of the cutting edge 32 (cutting edge angle) and the depth of cut are assumed to be 90°. However, these angles are not limited to 90°. As shown in Figure 6, the cutting edge 32 moves in the W direction while cutting into the side surface 12a of the brick 12. At this time, the metal piece 10 is partially cut, and the cut portion becomes fine particles 13. Most of the formed fine particles 13 are parallelepipeds such as the rectangle shown in Figure 6, or similar polyhedra.

[0029] For the sake of explanation, as an example of the formed fine particles 13, we assume a parallelepiped in which two of the three sides extending in three directions from one vertex form a right angle. Considering that the metal pieces 10 are stacked in the W direction, one of the three sides of the fine particles 13 will have a length approximately equal to the thickness c of the metal pieces 10. Furthermore, the length of one of the remaining two sides will be approximately equal to the feed rate a of the cutting edge 32 (cutting tool 30), and the length of the other will be approximately equal to the cutting depth b of the cutting edge 32. The feed rate is the relative distance traveled between the face mill 31 and the brick 12 when the rear cutting edge 32 reaches the position of the front cutting edge 32 of two adjacent cutting edges 32 in the rotational direction of the face mill 31.

[0030] In other words, the lengths of the three sides mentioned above can be adjusted by the thickness c of the metal piece 10, the feed rate a of the cutting tool 30 relative to the brick 12, and the cutting depth b of the cutting edge 32. Therefore, by setting these to roughly the same values, the shape of the microparticles 13 becomes close to a sphere of the same volume, and the sphericity of the microparticles 13 can be increased. For example, when the feed rate a, the cutting depth b, and the thickness c are all the same value, the shape of the microparticles 13 becomes a cube, and its sphericity, according to Wardell's definition (= surface area of ​​a sphere with the same volume as the particle / actual surface area of ​​the particle), is about 0.8, which is the highest among parallelepipeds.

[0031] Furthermore, the cutting of the brick 12 with the cutting tool 30 may be performed in an atmosphere of an inert gas such as a rare gas. For example, the gas in the space surrounding the cutting tool 30 may be replaced with an inert gas, or an inert gas may be locally blown onto the cutting location. Depending on the material of the brick 12, an oxide film may be formed during cutting. By cutting the brick 12 in an atmosphere of an inert gas, the formation of such an oxide film can be suppressed or avoided.

[0032] Figure 9 shows an example of a gripping method according to the embodiment. As described above, when cutting the side surface 12a of the brick 12, the brick 12 is gripped from both sides in the W direction by the clamping mechanism 40. Specifically, a pair of jaws 41, 41 of the clamping mechanism 40 grip the end faces 12b, 12b of the brick 12 facing the W direction.

[0033] During this gripping, as shown in Figure 9, the portion 12e of the brick 12 located on the virtual surface 14 may be gripped from the front and back in the W direction (cutting direction). The virtual surface 14 is located inside the brick 12 and is parallel to the cutting surface 15 formed by cutting. In this case, each jaw 41 has a projection 42 that protrudes toward the brick 12. The projection 42 extends in a direction parallel to the cutting surface 15 (i.e., the U direction), which is perpendicular to the W direction.

[0034] The end face 12b of the brick 12 is formed by the overlapping of numerous metal pieces 10 during compression. Consequently, the surface of the end face 12b is significantly uneven. Therefore, even when attempting to bring the die 41 into surface contact with the end face 12b, the unevenness of the end face 12b (in other words, the locally formed thicker portions of the brick 12 hinder the movement of the die 41) increases the likelihood that a portion of the die 41 will not make contact with the end face 12b. In particular, if the portion of the end face 12b that is not in contact with the die 41 is near the cutting surface 15, there is concern about the metal pieces 10 falling off or cutting defects occurring at that location.

[0035] On the other hand, when the jaw 41 having the protrusion 42 grips the brick 12, the jaw 41 contacts the end face 12b of the brick 12 in a state close to line contact. Therefore, the contact area between the jaw 41 and the end face 12b of the brick 12 is significantly reduced compared to when the jaw 41 without the protrusion 42 grips the brick 12. Also, the position where the protrusion 42 contacts the end face 12b is close to the cutting surface 15 of the brick 12. In other words, by providing the jaw 41 with the protrusion 42, the portion near the cutting surface 15 that is not gripped by the jaw 41 can be reduced, and problems such as metal piece 10 falling off and cutting defects can be suppressed.

[0036] Furthermore, the protruding portion 42 may have a curved surface 42a that protrudes toward the brick 12. In this case, the mouthpiece 41 and the end face 12b will be in contact with each other in a state close to line contact, which can further improve the poor contact described above.

[0037] Of the brick 12, the portion closest to the cutting surface 15 from the virtual surface 14 protrudes outward from the virtual surface 14. This protrusion is, for example, about 3 to 5 mm. Conversely, the portion of the brick 12 that protrudes about 3 to 5 mm from the virtual surface 14 can be cut stably without changing the position of the brick 12. However, this value may vary depending on the dimensions and material of the metal piece 10, the shape of the cutting edge 32, the cutting speed, etc.

[0038] The fine particles 13 formed in the cutting process S40 are classified in the classification process S50. The classification process S50 can be performed by known classification methods such as sieving or centrifugal classification. The classification process S50 selects only the fine particles 13 with a desired particle size range, resulting in metal powder that can be used in various devices. For example, considering metal powder used in a powder bed type 3D printer, the thickness of the powder layer formed (laid) in the recoating process is typically 50-100 μm. Therefore, the particle size of the fine particles 13 is smaller than this thickness.

[0039] As shown in Figure 2, the manufacturing method in this embodiment may further include a mixing step S60. The mixing step S60 involves mixing an auxiliary agent (not shown) with the metal piece 10. This step is performed before the cutting step S40. That is, the auxiliary agent is mixed with the metal piece 10 between the sorting step S20 and the cutting step S30.

[0040] The auxiliary agent may contain a component that is adhesive to the metal pieces 10. In this case, a known adhesive such as an epoxy adhesive or an acrylic adhesive can be used as the auxiliary agent. The adhesive auxiliary agent hardens before the cutting process S40, bonding the metal pieces 10 stacked in the Z direction together. This auxiliary agent may be removed after cutting using a solvent such as IPA (isopropyl alcohol).

[0041] The auxiliary agent may contain components that act during the processing of the metal powder. In this case, the auxiliary agent remains even after the cutting process S40 without being removed. For example, the auxiliary agent may contain components that function as a binder during the sintering of the brick 12. Known resins such as acrylic resin can be used as such an auxiliary agent. When mixed with the metal piece 10, the auxiliary agent may be in powder form or in liquid form mixed with a solvent.

[0042] (1) The manufacturing method according to this embodiment comprises the compression step and the cutting step described above. Fine particles 13, which become metal powder, are formed by cutting a foil-shaped metal piece. The fine particles 13 have dimensions derived from the thickness of the metal piece. Therefore, the degree of sphericity can be increased compared to flake-shaped fine particles of the same volume. In other words, it is possible to form metal powder with a higher degree of sphericity than by grinding using a medium such as a ball mill. The higher the degree of sphericity of the particles, the closer the fluidity of the powder containing the particles approaches the isotropic fluidity of powder with spherical particles. In other words, according to this embodiment, it is possible to manufacture metal powder with good fluidity. For example, it is possible to improve the packing ability of metal powder in a 3D printer and smoothly carry out precise molding.

[0043] Furthermore, in media-agitated grinders, particle size tends to asymptotically converge to a value of several hundred μm, and attempting to obtain a particle size smaller than that prolongs the grinding process and worsens production efficiency. In contrast, in the manufacturing method according to this embodiment, by adjusting the thickness of the metal piece 10, as well as the feed amount and cutting depth of the cutting edge 32 relative to the metal piece 10, it is possible to obtain a particle size of 100 μm or less in a single cutting pass. Therefore, it is more production efficient than grinding using a medium.

[0044] (2) The compression step S30 may be repeated, which includes supplying metal pieces 10 and compressing the supplied metal pieces 10 in the Z direction (compression direction). This makes it easier for the metal pieces 10 to unfold (orient) in a direction perpendicular to the Z direction over the entire Z direction, and makes it easier for the metal pieces 10 to be stacked in the Z direction. Therefore, it also becomes easier to form columnar bricks 12 that are long along the Z axis.

[0045] (3) The compression in the compression step S30 may include the preliminary compression and main compression described above. This can promote the movement or deformation of the metal pieces 10 before the aggregate 11 is completely compressed. It can also reduce the amount of metal pieces that do not unfold in the direction perpendicular to the Z direction, thereby reducing excess voids in the brick 12.

[0046] (4) The compression step S30 may form the brick 12 into a columnar shape extending along the central axis 12c. By forming the brick 12 into a relatively long columnar shape in the axial direction and then cutting the side surface 12a, a large amount of metal powder can be produced at once.

[0047] (5) In the compression step S30, the brick 12 may be formed into a prismatic shape with a flat surface 12d on its side surface 12a. By cutting the flat surface 12d with a cutting tool 30 such as a face mill 31, a large amount of metal powder can be produced from the initial stage of cutting, compared to the case where the brick 12 is cylindrical.

[0048] (6) The manufacturing method according to this embodiment may further include a mixing step S60 in which an auxiliary agent is mixed with the metal pieces 10. The auxiliary agent has, for example, an adhesive component. The adhesive auxiliary agent adheres the metal pieces 10 stacked in the Z direction to each other. This prevents the metal pieces 10 from falling off the brick 12 without being cut due to the cutting resistance during cutting. In other words, it is possible to suppress a decrease in yield in the production of metal powder.

[0049] (7) The auxiliary agent may remain after the cutting process and may contain components that act during the processing when the metal powder is used. This eliminates the need to add the same material as the auxiliary agent when using the metal powder.

[0050] (8) When cutting the side surface, the portion of the brick located on a virtual surface within the brick parallel to the cutting surface formed by the cutting may be gripped from the front and back in the cutting direction. This reduces the portion of the brick 12 that is not gripped near the cutting surface 15, thereby suppressing problems such as metal piece 10 falling off or cutting defects.

[0051] (9) The metal piece 10 may be metal chips. Normally, metal chips generated during machining are discarded as scrap iron. The manufacturing method of this embodiment reuses metal chips that were scheduled to be discarded as raw materials for metal powder. In other words, it can contribute to resource conservation.

[0052] The embodiments described above are merely illustrative examples provided to facilitate understanding of the invention. The technical scope of the invention is not limited to the specific technical matters disclosed in the embodiments described above, but also includes various modifications, changes, and alternative technologies that can be easily derived therefrom. [Explanation of symbols]

[0053] 10 metal pieces 11 Assemblage 12 Bricks 12a side 12b End face 12c center axis 12d plane 13 Fine particles 20 molds 30 cutting tools 40 Clamping mechanism S30 Compression process S40 cutting process

Claims

1. A forming step of forming a brick of metal pieces having sides surrounding a central axis parallel to the compression direction by compressing an aggregate of foil-like metal pieces in the compression direction, A cutting step in which the side surface of the brick is cut to form fine particles of metal powder, A method for producing metal powder, comprising the following features.

2. The forming step includes repeating the steps of supplying the metal piece and compressing the supplied metal piece in the compression direction. The method for producing metal powder according to claim 1.

3. The compression in the forming step includes a preliminary compression and a final compression performed after the preliminary compression, which is at a higher pressure than the preliminary compression. A method for producing metal powder according to claim 1 or 2.

4. The forming step involves forming the brick into a columnar shape extending along the central axis. A method for producing metal powder according to claim 1 or 2.

5. The forming step involves forming the brick into a prismatic shape having a flat surface on its side. The method for producing metal powder according to claim 4.

6. The process further comprises a mixing step of mixing an auxiliary agent with the metal piece, The aforementioned auxiliary agent has an adhesive component. The method for producing metal powder according to claim 1.

7. The process further comprises a mixing step of mixing an auxiliary agent with the metal piece, The aforementioned auxiliary agent has components that remain after the cutting process and act during the processing of the metal powder during use. The method for producing metal powder according to claim 1.

8. The method further includes gripping, from the front and rear in the cutting direction, a portion of the brick located on a virtual surface within the brick parallel to the cutting surface formed by the cutting, when cutting the aforementioned side surface. The method for producing metal powder according to claim 1.

9. The aforementioned metal piece is a metal chip. The method for producing metal powder according to claim 1.

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