Method for manufacturing sintered member, mold, and sintered member

Abstract

This method for manufacturing a sintered member comprises: a step for pressure-molding a raw material powder packed in a cavity of a mold to produce a cylindrical powder compact; and a step for sintering the powder compact. This mold comprises: a die having a hollow part penetrating in a first direction; a core rod inserted into the hollow part along the first direction; a lower punch inserted between the die and the core rod; a first upper punch inserted into the hollow part so as to be in contact with the upper end surface of the core rod; and a second upper punch inserted between the die and the first upper punch. The side surface of the first upper punch has a plurality of tapered surfaces, the outer dimensions of which decrease toward the lower end surface, and one or more orthogonal surfaces orthogonal to the first direction. In the step of producing a powder compact, the raw material powder is pressure-molded by the upper end surface of the lower punch, the side surface including the plurality of tapered surfaces and one or more orthogonal surfaces of the first upper punch, and the lower end surface of the second upper punch.

Description

Method for manufacturing a sintered member, mold, and sintered member

[0001] The present disclosure relates to a method for manufacturing a sintered member, a mold, and a sintered member. This application claims priority based on Japanese Patent Application No. 2024-175021 filed on October 4, 2024. All the descriptions described in the Japanese application are incorporated herein by reference.

[0002] The powder molding die for stepped sintered parts disclosed in Patent Document 1 includes a die, a lower punch, a core rod, and an upper punch. The die forms the outer periphery of the molded body. The die has a molding hole penetrating vertically. The core rod is inserted into the molding hole of the die from below. The core rod includes a stepped portion forming portion that forms a stepped portion formed on the inner periphery of the molded body. The stepped portion forming portion is composed of one tapered surface whose outer diameter decreases toward the upper end surface of the core rod. The lower punch forms the lower end surface of the molded body. The lower punch is inserted from below between the die and the core rod. The upper punch forms the upper end surface of the molded body. The upper punch is inserted from above between the die and the core rod.

[0003] Japanese Unexamined Patent Application Publication No. 2017-94345

[0004] The method for manufacturing a sintered member of the present disclosure includes a step of filling a raw material powder into a cavity of a mold, a step of producing a cylindrical compacted body by press-molding the raw material powder in the cavity, and a step of producing a sintered member by sintering the compacted body. The mold includes a die having a hollow portion penetrating in a first direction, a core rod inserted into the hollow portion along the first direction, a lower punch inserted between the die and the core rod, a first upper punch inserted into the hollow portion so as to contact the upper end surface of the core rod, and a second upper punch inserted between the die and the first upper punch. The side surface of the first upper punch has a plurality of tapered surfaces whose outer dimensions decrease toward the lower end surface, and one or more orthogonal surfaces orthogonal to the first direction. The step of producing the compacted body press-molds the raw material powder by the upper end surface of the lower punch, the side surface including the plurality of tapered surfaces and the one or more orthogonal surfaces of the first upper punch, and the lower end surface of the second upper punch.

[0005] Figure 1 is a cross-sectional view illustrating step A in the manufacturing method of the sintered member of Embodiment 1. Figure 2 is a cross-sectional view illustrating the first step of step B in the manufacturing method of the sintered member of Embodiment 1. Figure 3 is a cross-sectional view illustrating the second step of step B in the manufacturing method of the sintered member of Embodiment 1. Figure 4 is a cross-sectional view taken along line IV-IV of Figure 3. Figure 5 is a perspective view showing the general outline of the sintered member of Embodiment 1. Figure 6 is a cross-sectional view taken along line VI-VI of Figure 5. Figure 7 is a cross-sectional view illustrating the manufacturing method of the sintered member of Embodiment 2. Figure 8 is a cross-sectional view taken along line VIII-VIII of Figure 7. Figure 9 is a perspective view showing the general outline of the sintered member of Embodiment 2. Figure 10 is a cross-sectional view taken along line X-X of Figure 9. Figure 11 is a cross-sectional view illustrating the manufacturing method of the sintered member of Embodiment 3. Figure 12 is a cross-sectional view taken along line XII-XII of Figure 11. Figure 13 is a cross-sectional view illustrating the manufacturing method of a comparative example of a sintered member.

[0006] When the core rod has the stepped molded portion as described in Patent Document 1, it is difficult to produce a compacted powder body with a complex shape by pressure molding without machining. A compacted powder body with a complex shape, as referred to here, is a cylindrical compacted powder body having an inner circumferential surface with an inner diameter that is not uniform along the central axis.

[0007] One of the purposes of this disclosure is to provide a method for manufacturing sintered members that facilitates the production of sintered members with complex shapes.

[0008] The method for manufacturing sintered members described herein facilitates the production of sintered members with complex shapes.

[0009] First, the embodiments of this disclosure will be listed and described.

[0010] (1) A method for manufacturing a sintered member according to one aspect of the present disclosure comprises the steps of: filling a cavity of a mold with raw material powder; producing a cylindrical compacted body by pressure molding the raw material powder in the cavity; and producing a sintered member by sintering the compacted body. The mold comprises a die having a hollow portion penetrating in a first direction; a core rod inserted into the hollow portion along the first direction; a lower punch inserted between the die and the core rod; a first upper punch inserted into the hollow portion so as to be in contact with the upper end surface of the core rod; and a second upper punch inserted between the die and the first upper punch. The side surface of the first upper punch has a plurality of tapered surfaces whose outer dimensions decrease towards the lower end surface, and one or more orthogonal surfaces perpendicular to the first direction. The step of producing the compacted body involves pressure molding the raw material powder with the upper end surface of the lower punch, the side surface of the first upper punch including the plurality of tapered surfaces and the one or more orthogonal surfaces, and the lower end surface of the second upper punch.

[0011] Although details will be described later, consider a comparative example in which the side surface of the core rod has multiple tapered surfaces that decrease in outer dimension as they approach the upper end surface of the core rod, and one or more orthogonal surfaces perpendicular to the first direction. In the above comparative example, the cavity into which the raw material powder is filled is formed by the upper end surface of the lower punch, the side surface of the core rod having multiple tapered surfaces and one or more orthogonal surfaces, and the inner circumferential surface of the die. In the above comparative example, the filling height of the raw material powder differs from one another at the locations corresponding to the upper end surface of the lower punch, each tapered surface, and each orthogonal surface. Furthermore, in the above comparative example, when the raw material powder is pressure-molded by the upper punch, there is no room for the raw material powder to escape. Therefore, in the above comparative example, the compression ratio cannot be made equal at the locations corresponding to the upper end surface of the lower punch, each tapered surface, and each orthogonal surface. That is, in the above comparative example, areas are formed in which the raw material powder cannot be sufficiently compacted. Thus, in the above comparative example, it is difficult to manufacture complex-shaped powder compacts, and by extension complex-shaped sintered members, without machining.

[0012] In the sintered member manufacturing method described in (1) above, the cavity is formed by the upper end surface of the lower punch, the side surface of the core rod which has a substantially uniform outer dimension, and the inner circumferential surface of the die. Therefore, the filling height of the raw material powder is uniform. In the sintered member manufacturing method described in (1) above, the side surface of the first upper punch has multiple tapered surfaces and one or more orthogonal surfaces. When the raw material powder is pressed by this first upper punch, a portion of the raw material powder tends to move away from the side surface of the first upper punch. Due to this movement of the raw material powder, in the sintered member manufacturing method described in (1) above, the compression ratio at the locations corresponding to each tapered surface and orthogonal surface tends to be equal compared to the comparative example. Therefore, in the sintered member manufacturing method described in (1) above, it is easier to produce a cylindrical compacted molded body whose inner circumferential surface has multiple tapered surfaces and one or more orthogonal surfaces compared to the comparative example. The method for manufacturing the sintered member described in (1) above makes it easy to produce a cylindrical sintered member having multiple tapered surfaces and one or more orthogonal surfaces on its inner circumferential surface without performing machining such as cutting, machining, grinding, and polishing on the powder compacted molded body. The method for manufacturing the sintered member described in (1) above makes it easy to produce a powder compacted molded body with small variations in molding density. Here, "cylindrical" includes a completely cylindrical shape with a wall extending around the entire circumference, such as a hollow shape, and a partially cylindrical shape with a wall extending only to a part of the circumference, such as a shape divided by a cross-section including the axis of a completely cylindrical shape. Completely cylindrical shapes include cylindrical, elliptical, and polygonal cylindrical shapes. The cross-sectional shapes of a completely cylindrical shape are circular, elliptical, and polygonal. Partially cylindrical shapes are not limited to semi-cylindrical shapes with a central angle of 180° in the cross-sectional shape. The cross-sectional shape of a partially cylindrical shape is C-shaped or U-shaped.

[0013] (2) In the method for manufacturing the sintered member described in (1) above, the angle between each of the plurality of tapered surfaces and the virtual surface perpendicular to the first direction may be 1° or more and less than 90°.

[0014] The method for manufacturing the sintered member described in (2) above makes it easy to produce a cylindrical powder compact having multiple tapered surfaces on its inner circumferential surface that satisfy the above angle. Therefore, the method for manufacturing the sintered member described in (2) above makes it easy to produce a cylindrical sintered member having multiple tapered surfaces on its inner circumferential surface that satisfy the above angle without having to perform the above machining on the powder compact.

[0015] (3) In the method for manufacturing a sintered member according to (1) or (2) above, the core rod may be inserted into the hollow portion such that the shape of the space surrounded by the inner circumferential surface of the die and the side surface of the core rod, when viewed in the first direction, is C-shaped.

[0016] In the manufacturing method of the sintered member described in (3) above, it is easy to produce a powder compact that is partially cylindrical, i.e., C-shaped when viewed in the first direction, and has multiple tapered surfaces and one or more orthogonal surfaces on its inner circumferential surface. Therefore, the manufacturing method of the sintered member described in (3) above makes it easy to produce a sintered member that is partially cylindrical, i.e., C-shaped when viewed in the first direction, and has multiple tapered surfaces and one or more orthogonal surfaces on its inner circumferential surface, without having to perform the above-mentioned machining on the powder compact.

[0017] (4) In the method for manufacturing the sintered member described in (1) or (2) above, the core rod may be inserted into the hollow portion such that the hollow portion is divided into a plurality of segments arranged in parallel in a direction perpendicular to the first direction. Each of the plurality of segments, when viewed from above, is C-shaped. Among the plurality of segments, adjacent segments with the core rod in between are formed such that C-shaped openings face each other.

[0018] The method for manufacturing sintered members described in (4) above allows for the production of multiple compacted molded bodies in a single pressure molding process. Therefore, the method for manufacturing sintered members described in (4) above offers superior productivity compared to the method for manufacturing sintered members described in (3) above.

[0019] In the manufacturing method of the sintered member described in (4) above, when the first upper punch is lowered and the side surface of the first upper punch pressurizes and molds the raw material powder, pressure is applied from the raw material powder of each segment to the first upper punch in a direction perpendicular to the first direction. The shape of each segment when viewed from above is C-shaped, and the C-shaped openings are formed to face each other. Therefore, the above pressure acts on the first upper punch in a way that sandwiches it. As a result, the above pressure is easily canceled out, and the first upper punch is less likely to shift in a direction perpendicular to the first direction, so it is easy to produce a compacted molded body with excellent dimensional accuracy. Thus, the manufacturing method of the sintered member described in (4) above makes it easy to produce a sintered member with excellent dimensional accuracy. In addition, in the manufacturing method of the sintered member described in (4) above, since the first upper punch is less likely to shift, seizure between the first upper punch and the die is less likely to occur.

[0020] (5) In any of the methods for manufacturing a sintered member described in (1) to (4) above, the timing at which the second upper punch press-moldes the raw material powder may be later than the timing at which the first upper punch is inserted into the hollow portion.

[0021] The manufacturing method of the sintered member described in (5) above has less restriction on the movement of the raw material powder compared to the case where the timing of the second upper punch press-molding the raw material powder and the timing of the first upper punch press-molding the raw material powder are the same. In the manufacturing method of the sintered member described in (5) above, the press-molding by the first upper punch makes it easier to move a portion of the raw material powder away from the side of the first upper punch along a direction perpendicular to the first direction. Therefore, it is easier to reduce the pressure acting from the raw material powder on the first upper punch in a direction perpendicular to the first direction. Thus, the lifespan of the first upper punch is less likely to decrease.

[0022] (6) A mold according to one aspect of the present disclosure is a mold for producing a cylindrical compacted body by pressurizing raw material powder. The mold comprises a die having a hollow portion penetrating in a first direction, a core rod inserted into the hollow portion along the first direction, a lower punch inserted between the die and the core rod, a first upper punch inserted into the hollow portion so as to be in contact with the upper end surface of the core rod, and a second upper punch inserted between the die and the first upper punch. The side surface of the first upper punch has a plurality of tapered surfaces whose outer dimensions decrease towards the lower end surface, and one or more orthogonal surfaces perpendicular to the first direction.

[0023] The mold described in (6) above can be used to manufacture a cylindrical sintered member having multiple tapered surfaces and one or more orthogonal surfaces on its inner circumferential surface.

[0024] (7) A sintered member according to one aspect of the present disclosure is a cylindrical sintered member. The inner circumferential surface of the sintered member has a plurality of tapered surfaces along the central axis of the sintered member, the inner dimensions of which decrease from the first end to the second end of the sintered member, and one or more orthogonal surfaces perpendicular to the central axis. None of the plurality of tapered surfaces and none of the one or more orthogonal surfaces have cut marks, machining marks, grinding marks, or polishing marks.

[0025] The above-described sintered member can be suitably used for machine parts and the like, which have multiple tapered surfaces and one or more orthogonal surfaces on their inner circumferential surface. Since each tapered surface and orthogonal surface does not have cutting marks, machining marks, grinding marks, or polishing marks, the above-described sintered member offers excellent productivity and makes it easy to reduce manufacturing costs.

[0026] The manufacturing method, mold, and embodiments of the sintered member described herein will be explained below with reference to the drawings. The same reference numerals in the drawings indicate the same parts. The shapes, sizes, and positional relationships shown in each drawing are for illustrative purposes only and do not necessarily represent the actual shapes, sizes, and positional relationships.

[0027] [Embodiment 1] <Method for Manufacturing a Sintered Member> The method for manufacturing a sintered member according to Embodiment 1 will be described with reference to Figures 1 to 4. The method for manufacturing a sintered member according to Embodiment 1 comprises the following steps A to C. Step A is a step of filling the cavity of the mold 1 with raw material powder 9. Step B is a step of producing a cylindrical compacted molded body by pressurizing the raw material powder 9 in the cavity. Step C is a step of producing a sintered member 10 shown in Figure 5 by sintering the compacted molded body. One of the features of the method for manufacturing a sintered member according to Embodiment 1 is that a compacted molded body is produced using a specific mold 1.

[0028] <<Mold>> Mold 1 produces a cylindrical powder compact. In this example, mold 1 produces a powder compact that becomes the cylindrical sintered member 10 shown in Figure 5. As shown in Figure 1, mold 1 comprises a die 2, a core rod 3, a lower punch 4, a first upper punch 5, and a second upper punch 6.

[0029] [Die] Die 2, together with the core rod 3 and the lower punch 4, forms a cavity into which the raw material powder 9 is filled. In this example, die 2 forms the outer circumferential surface 13 of the compacted molded body shown in Figure 5. Die 2 has a hollow portion 20 that penetrates in a first direction, as shown in Figure 1. The first direction is the vertical direction. The hollow portion 20 has an end that opens upwards and an end that opens downwards of die 2. The hollow portion 20 is a space with both ends open. In this example, the inner circumferential surface 25 of the hollow portion 20 corresponds to the outer shape of the compacted molded body to be produced. The shape of the inner circumferential surface 25 in this example, as viewed from above, is circular, as shown in Figure 4. Die 2 moves along the first direction by a drive mechanism (not shown).

[0030] [Core Rod] As shown in Figure 1, the core rod 3 is inserted into the hollow section 20 from below along the first direction. The core rod 3 is columnar in shape. The core rod 3 has an upper end surface 35 that faces the lower end surface 55 of the first upper punch 5. The shape of the upper end surface 35 of the core rod 3 when viewed from above corresponds to the inner circumference shape of the compacted molded body. The inner circumference shape of the compacted molded body referred to here is the inner circumference shape of the part of the compacted molded body where the inner diameter is smallest. In this example, the shape of the upper end surface 35 of the core rod 3 is circular. That is, the shape of the core rod 3 in this example is cylindrical. The diameter of the upper end surface 35 of the core rod 3 corresponds to the smallest inner diameter of the compacted molded body. The core rod 3 moves along the first direction by a drive mechanism (not shown). The core rod 3 moves independently of the die 2 by the drive mechanism. In this example, the core rod 3 is inserted into the hollow portion 20 such that the shape of the space enclosed by the inner circumferential surface 25 of the die 2 and the side surface of the core rod 3, when viewed from above, is annular.

[0031] [Lower Punch] The lower punch 4 has an upper end surface 45 that forms the lower end surface 12 of the compacted molded body shown in Figure 5. As shown in Figures 1 to 3, the lower punch 4 is inserted from below along the first direction between the die 2 and the core rod 3. In this example, there is one lower punch 4. Unlike this example, there may be multiple lower punches 4, similar to the second upper punch 6 described later. The lower punch 4 is cylindrical in shape. The shape of the upper end surface 45 of the lower punch 4 when viewed from above corresponds to the shape of the lower end surface 12 of the compacted molded body. In this example, the shape of the upper end surface 45 of the lower punch 4 is annular. The inner diameter of the upper end surface 45 of the lower punch 4 is the same as the inner diameter of the lower end surface 12 of the compacted molded body and corresponds to the diameter of the upper end surface 45 of the core rod 3. The outer diameter of the upper end surface 45 of the lower punch 4 is the same as the outer diameter of the lower end surface 12 of the compacted molded body and corresponds to the diameter of the inner circumferential surface 25 of the die 2. In this example, the lower punch 4 is fixed so as not to move along the first direction.

[0032] [First Upper Punch] The first upper punch 5 has a lower end surface 55 that faces the upper end surface 35 of the core rod 3, and a side surface 56 that forms the inner circumferential surface 14 of the compacted molded body shown in Figure 5. As shown in Figures 1 to 3, the first upper punch 5 is inserted into the hollow portion 20 from above along the first direction, facing the core rod 3. The shape of the first upper punch 5 is columnar. The shape of the lower end surface 55 of the first upper punch 5 when viewed from below corresponds to the inner circumferential shape of the compacted molded body. The inner circumferential shape of the compacted molded body referred to here is the inner circumferential shape with the smallest inner diameter of the compacted molded body. As shown in Figure 4, the shape of the lower end surface 55 of the first upper punch 5 in this example is circular. That is, the shape of the first upper punch 5 in this example is cylindrical. The diameter of the lower end surface 55 of the first upper punch 5 corresponds to the smallest inner diameter of the compacted molded body. In this example, the diameter of the lower end face 55 of the first upper punch 5 is the same as the diameter of the upper end face 35 of the core rod 3. The first upper punch 5 moves along the first direction by a drive mechanism (not shown). The first upper punch 5 moves independently of the die 2 by the drive mechanism.

[0033] The side surface 56 of the first upper punch 5 has a plurality of tapered surfaces 57 whose outer dimensions decrease towards the lower end surface 55, and one or more orthogonal surfaces 58 perpendicular to the first direction. The side surface 56 of the first upper punch 5 may further have parallel surfaces 59 parallel to the first direction. The number of parallel surfaces 59 may be one or more. In this example, there are two tapered surfaces 57. In this example, there are two orthogonal surfaces 58. In this example, there are five parallel surfaces 59. The side surface 56 of the first upper punch 5 is composed of, in order from top toward the lower end surface 55, a first parallel surface 591, a first orthogonal surface 581, a second parallel surface 592, a second orthogonal surface 582, a third parallel surface 593, a first tapered surface 571, a fourth parallel surface 594, a second tapered surface 572, and a fifth parallel surface 595. The fifth parallel surface 595 is connected to the lower end surface 55.

[0034] The angle θ between each tapered surface 571, 572 and a virtual surface perpendicular to the first direction is, for example, 1° or more and less than 90°. In this case, a cylindrical powder compact has an inner circumferential surface 14 with multiple tapered surfaces 15 that satisfy the above angle, and this can be easily manufactured. Therefore, a cylindrical sintered member 10 has an inner circumferential surface 14 with multiple tapered surfaces 15 that satisfy the above angle, and this can be easily manufactured without performing machining such as cutting, machining, grinding, and polishing on the powder compact. The angles θ may be 10° or more and 60° or less, or 30° or more and 45° or less. The angles θ may be the same as each other, or they may be different from each other.

[0035] Let us examine the comparative example shown in Figure 13. In the comparative example, the side surface 36 of the core rod 3 is composed of a first parallel surface, a first orthogonal surface, a second parallel surface, a second orthogonal surface, a third parallel surface, a first tapered surface, a fourth parallel surface, a second tapered surface, and a fifth parallel surface, in order from the bottom toward the upper end surface 35. The first parallel surface, first orthogonal surface, second parallel surface, second orthogonal surface, third parallel surface, first tapered surface, fourth parallel surface, second tapered surface, and fifth parallel surface in the above comparative example are the same as the first parallel surface 591, first orthogonal surface 581, second parallel surface 592, second orthogonal surface 582, third parallel surface 593, first tapered surface 571, fourth parallel surface 594, second tapered surface 572, and fifth parallel surface 595 in the present example in Figure 1. In the comparative example, the first upper punch 5 has a side surface 56 with a uniform outer dimension and a lower end surface 55 with the same outer dimension as the side surface 56. In the comparative example, the cavity into which the raw material powder 9 is filled is formed by the upper end surface 45 of the lower punch 4, the side surface of the core rod 3 having multiple tapered surfaces and multiple orthogonal surfaces, and the inner circumferential surface 25 of the die 2. In the comparative example, the filling height of the raw material powder 9 differs from that of the upper end surface 45 of the lower punch 4 at the locations corresponding to each tapered surface and each orthogonal surface. Furthermore, in the comparative example, when the raw material powder 9 is pressure-molded by the second upper punch 6, there is no relief for the raw material powder 9. Therefore, in the comparative example, the compression ratio at the locations corresponding to the upper end surface 45 of the lower punch 4 and each tapered surface and each orthogonal surface cannot be made equal. Consequently, in the comparative example, it is difficult to manufacture a compacted powder molded body, and by extension a sintered member 10, with a complex shape without performing the above machining.

[0036] In the example shown in Figure 1, the cavity is formed by the upper end surface 45 of the lower punch 4, the side surface of the core rod 3 with a uniform outer dimension, and the inner circumferential surface 25 of the die 2. Therefore, the filling height of the raw material powder 9 is uniform. In this example, the side surface 56 of the first upper punch 5 has multiple tapered surfaces 57 and one or more orthogonal surfaces 58. When the raw material powder 9 is pressed by the first upper punch 5, movement of the raw material powder 9 is likely to occur in the direction away from the side surface 56 of the first upper punch 5. In this example, due to the movement of the raw material powder 9, the compression ratio at the locations corresponding to each tapered surface 57, the orthogonal surface 58, and the lower end surface 611 of the second upper punch 6 is more likely to be equal compared to the comparative example above. Therefore, in this example, it is easier to produce a cylindrical compacted molded body having multiple tapered surfaces and one or more orthogonal surfaces on its inner circumferential surface compared to the comparative example above. Therefore, in this example, even without performing the above-mentioned machining on the compacted body, it is easy to produce a cylindrical sintered member 10 having multiple tapered surfaces 15 and orthogonal surfaces 16 on its inner circumferential surface 14, as shown in Figures 5 and 6.

[0037] [Second Upper Punch] The second upper punch 6 is inserted from above along the first direction between the die 2 and the first upper punch 5, as shown in Figures 1 to 3. In this example, there is one second upper punch 6. Unlike this example, there may be multiple second upper punches 6. In this example, the shape of the second upper punch 6 is cylindrical. The second upper punch 6 has a lower end surface 611 and an outer circumferential surface 612. The lower end surface 611 of the second upper punch 6 forms the upper end surface 11 of the compacted molded body shown in Figure 5. The outer circumferential surface 612 of the second upper punch 6 slides against the inner circumferential surface 25 of the die 2.

[0038] In this example, the shape of the lower end surface 611 (Figure 1) of the second upper punch 6, when viewed from below, is annular. In this example, the lower end surface 611 is an orthogonal surface perpendicular to the first direction. The inner diameter of the lower end surface 611 is the same as the inner diameter of the upper end surface 11 of the compacted body. The outer diameter of the lower end surface 611 is the same as the outer diameter of the upper end surface 11 of the compacted body and corresponds to the diameter of the inner circumferential surface 25 of the die 2.

[0039] The second upper punch 6 moves along the first direction by a drive mechanism (not shown). The second upper punch 6 moves independently of the first upper punch 5 by the drive mechanism.

[0040] <<Process A: Filling with raw material powder>> In Process A, as shown in Figure 1, the core rod 3 is inserted into the hollow section 20 by a drive mechanism to form a cavity. The upper end surface 45 of the lower punch 4 is positioned at a predetermined location in the hollow section 20. The core rod 3 is raised by the drive mechanism so that the upper end surface 35 of the core rod 3 is flush with the upper surface 26 of the die 2. In this example, an annular cavity is formed when viewed from above. In Process A, the raw material powder 9 is filled into the cavity formed by the die 2, the core rod 3, and the lower punch 4. In this example, the raw material powder 9 is filled until it is flush with the upper surface 26 of the die 2.

[0041] The raw material powder 9 includes known metal powders. These metal powders may be, for example, pure iron powder, iron alloy powder, copper powder, copper alloy powder, aluminum powder, or aluminum alloy powder. In addition to the above metal powders, the raw material powder 9 may also contain at least one of a known binder or a known lubricant. A lubricant may be applied to the inner surface 25 of the die 2 before filling the cavity with the raw material powder 9. If a lubricant is applied to the inner surface 25 of the die 2, the raw material powder 9 may not contain the lubricant.

[0042] <<Process B: Production of a Compacted Powder Body>> In Process B, the raw material powder 9 in the cavity is pressure-molded by the upper end surface 45 of the lower punch 4, the side surface 56 of the first upper punch 5 which includes multiple tapered surfaces 57 and one or more orthogonal surfaces 58, and the lower end surface 611 of the second upper punch 6. In this example, as shown in Figures 2 and 3, the timing at which the second upper punch 6 pressure-moldes the raw material powder 9 is later than the timing at which the first upper punch 5 is inserted into the hollow section 20. After the lower end surface 55 of the first upper punch 5 contacts the upper end surface 35 of the core rod 3 as the first upper punch 5 descends, the core rod 3 is lowered together with the first upper punch 5 as shown in Figure 2. This descent causes the side surface 56 of the first upper punch 5 to pressure-molde the raw material powder 9. Next, as shown in Figure 3, the second upper punch 6 is lowered and inserted into the hollow section 20. Then, the lower end surface 611 of the second upper punch 6 pressure-moldes the raw material powder 9.

[0043] Since the timing of the second upper punch 6 is later than that of the first upper punch 5, by the pressure forming with the first upper punch 5, a part of the raw material powder 9 moves in a direction away from the side surface 56, that is, in a direction approaching the inner peripheral surface 25 of the die 2. Further, as shown in FIG. 2, a part of the raw material powder 9 may overflow onto the upper surface 26 of the die 2. By this pressure forming, pressure in a direction orthogonal to the first direction acts on the raw material powder 9 with respect to the first upper punch 5. However, since a part of the raw material powder 9 overflows onto the upper surface 26, the pressure acting on the first upper punch 5 is likely to be reduced. In this example, since the cavity is annular as described above, the pressure is likely to act on the first upper punch 5 substantially evenly from around the first upper punch 5. Therefore, it is difficult for the first upper punch 5 to shift in a direction orthogonal to the first direction, and it is easy to produce a compacted body with excellent dimensional accuracy.

[0044] The produced compacted body is taken out of the mold 1. For example, with the first upper punch 5 and the second upper punch 6, and the core rod 3 and the lower punch 4 sandwiching the compacted body from above and below, the die 2 is lowered until the compacted body is exposed from the die 2. When the compacted body is exposed from the die 2, the first upper punch 5 and the second upper punch 6 are raised to take out the compacted body.

[0045] ≪Step C: Producing a sintered member≫ In step C, the compacted body is sintered. The sintering conditions can be appropriately selected according to the composition of the raw material powder 9. For example, when the raw material powder 9 contains at least one of pure iron powder and iron alloy powder, the sintering temperature is, for example, 1100 ° C or higher and 1400 ° C or lower, 1200 ° C or higher and 1300 ° C or lower. The sintering time is, for example, 15 minutes or longer and 150 minutes or shorter, 20 minutes or longer and 60 minutes or shorter. Known conditions can be applied as the sintering conditions.

[0046] After step C, no finishing process is performed on the sintered part. The finishing process is machining for removing a part of the sintered part or conforming the dimensions to the designed dimensions. The machining is, for example, cutting, cutting, grinding, or polishing.

[0047] <<Other Processes>> After Process C, carburizing quenching and tempering may be performed on the sintered member 10 as necessary. In this case, the mechanical properties of the sintered member 10, particularly hardness and toughness, are likely to be improved.

[0048] <Sintered Member> Referring to FIGS. 5 and 6, the sintered member 10 of Embodiment 1 will be described. The sintered member 10 is cylindrical. The sintered member 10 has an upper end surface 11, a lower end surface 12, an outer peripheral surface 13, and an inner peripheral surface 14. The shape of the upper end surface 11 as viewed from above and the shape of the lower end surface 12 as viewed from below are annular. In this example, the outer diameter of the upper end surface 11 is the same as the outer diameter of the lower end surface 12, and the inner diameter of the upper end surface 11 is larger than the outer diameter of the lower end surface 12. The outer peripheral surface 13 connects the outer peripheral edge of the upper end surface 11 and the outer peripheral edge of the lower end surface 12. The outer peripheral surface 13 is a cylindrical surface. The inner peripheral surface 14 connects the inner peripheral edge of the upper end surface 11 and the inner peripheral edge of the lower end surface 12.

[0049] The inner peripheral surface 14 has a plurality of tapered surfaces 15 whose inner dimensions become smaller from the upper end surface 11 to the lower end surface 12 of the sintered member 10 along the central axis of the sintered member 10 and one or more orthogonal surfaces 16 orthogonal to the central axis. The inner peripheral surface 14 may further have a parallel surface 17 parallel to the central axis. The number of parallel surfaces 17 may be single or plural. In this example, the number of tapered surfaces 15 is two. The number of orthogonal surfaces 16 in this example is two. The number of parallel surfaces 17 in this example is five.

[0050] In this example, the inner circumferential surface 14 is composed of, in order from the upper end surface 11 to the lower end surface 12, a first parallel surface 171, a first orthogonal surface 161, a second parallel surface 172, a second orthogonal surface 162, a third parallel surface 173, a first tapered surface 151, a fourth parallel surface 174, a second tapered surface 152, and a fifth parallel surface 175. The first parallel surface 171 is connected to the upper end surface 11. The fifth parallel surface 175 is connected to the lower end surface 12. Each of the parallel surfaces 171, 172, 173, 174, and 175 is a cylindrical surface. The first orthogonal surface 161 and the second orthogonal surface 162 are annular surfaces. The first tapered surface 151 and the second tapered surface 152 are cylindrical surfaces that taper from the upper end surface 11 to the lower end surface 12. The first parallel surface 171, the first orthogonal surface 161, the second parallel surface 172, the second orthogonal surface 162, the third parallel surface 173, the first tapered surface 151, the fourth parallel surface 174, the second tapered surface 152, and the fifth parallel surface 175 are formed by the first parallel surface 591, the first orthogonal surface 581, the second parallel surface 592, the second orthogonal surface 582, the third parallel surface 593, the first tapered surface 571, the fourth parallel surface 594, the second tapered surface 572, and the fifth parallel surface 595 of the first upper punch 5 shown in Figure 1.

[0051] Each of the inner circumferential surfaces 14, that is, each of the tapered surfaces 151, 152, each of the orthogonal surfaces 161, 162, and each of the parallel surfaces 171, 172, 173, 174, 175, does not have cutting marks, machining marks, grinding marks, or polishing marks. These processing marks are streaky irregularities that occur during processing.

[0052] [Embodiment 2] <Method for Manufacturing Sintered Member> The method for manufacturing a sintered member in Embodiment 2 will be described with reference to Figures 7 and 8. The method for manufacturing a sintered member in this example is the same as the method for manufacturing a sintered member in Embodiment 1, except that the shape of the mold 1 is different. The following description will focus on the differences from Embodiment 1.

[0053] <<Mold>> In this example, mold 1 produces a powder compacted body that will become a semi-cylindrical sintered member 10 as shown in Figure 9. Mold 1 comprises a die 2, a core rod 3, a lower punch 4, a first upper punch 5, and a second upper punch 6.

[0054] [Die] The hollow portion 20 of die 2 is semi-cylindrical in shape. When viewed from above, the hollow portion 20 is semi-circular in shape.

[0055] [Core Rod] The core rod 3 has a semi-cylindrical shape. When viewed from above, the core rod 3 has a semi-circular shape. The core rod 3 is inserted into the hollow portion 20 such that the space enclosed by the inner circumferential surface 25 of the die 2 and the side surface of the core rod 3 has a C-shape when viewed from above.

[0056] [Lower Punch] The upper end surface 45 of the lower punch 4 is formed in a C shape. In this example, the outer and inner surfaces of the lower punch 4 are composed of semicircular surfaces.

[0057] [First Upper Punch] The first upper punch 5 has a semi-cylindrical shape. When viewed from above, the first upper punch 5 has a semi-circular shape.

[0058] [Second Upper Punch] The lower end surface 611 of the second upper punch 6 is formed in a C shape. In this example, the outer circumferential surface 612 and the inner circumferential surface of the second upper punch 6 are composed of semicircular surfaces.

[0059] In step B of this example, when the first upper punch 5 is lowered and the side surface 56 of the first upper punch 5 pressurizes the raw material powder 9, a portion of the raw material powder 9 overflows onto the upper surface 26 of the die 2, similar to Embodiment 1. This pressurizing action causes pressure to act from the raw material powder 9 on the first upper punch 5 in a direction perpendicular to the first direction toward the inner surface 25 of the die 2. Because the cavity in this example is C-shaped, the above pressure makes it easy for the first upper punch 5 to slide against the inner surface 25 of the die 2. However, because a portion of the raw material powder 9 overflows onto the upper surface 26, the above pressure acting on the first upper punch 5 is easily reduced. Therefore, the first upper punch 5 is less likely to slide against the inner surface 25 of the die 2.

[0060] <Sintered Member> The sintered member 10 of Embodiment 2 will be described with reference to Figures 9 and 10. The sintered member 10 is semi-cylindrical. The shape of the upper end surface 11 of the sintered member 10 when viewed from above and the shape of the lower end surface 12 when viewed from below are C-shaped. The outer circumferential surface 13 of the sintered member 10 is a semi-circular arc surface. The inner circumferential surface 14 of the sintered member 10 is composed of the same as the inner circumferential surface 14 of Embodiment 1, in order from the upper end surface 11 to the lower end surface 12, a first parallel surface 171, a first orthogonal surface 161, a second parallel surface 172, a second orthogonal surface 162, a third parallel surface 173, a first tapered surface 151, a fourth parallel surface 174, a second tapered surface 152, and a fifth parallel surface 175. Each of the parallel surfaces 171, 172, 173, 174, and 175 is a semi-circular arc surface. Each of the orthogonal surfaces 161 and 162 is a semi-circular annular surface. Each tapered surface 151, 152 is a semicircular arc surface that tapers from the upper end surface 11 to the lower end surface 12.

[0061] [Embodiment 3] <Method for Manufacturing Sintered Member> The method for manufacturing a sintered member according to Embodiment 3 will be described with reference to Figures 11 and 12. The method for manufacturing a sintered member according to Embodiment 3 differs from the methods for manufacturing sintered members according to Embodiments 1 and 2 in that the hollow portion 20 is divided by the core rod 3 into a plurality of segments arranged in parallel in a direction perpendicular to the first direction. In the method for manufacturing a sintered member according to this example, a number of compacted molded bodies corresponding to the number of segments, i.e., a plurality of compacted molded bodies, can be manufactured in a single pressure molding. More specifically, two compacted molded bodies that become the sintered member 10 shown in Figures 9 and 10 can be manufactured in a single pressure molding.

[0062] ≪Mold≫ [Die] The hollow portion 20 of die 2 is composed of two first hollow portions 21 and one second hollow portion 22. In this example, one second hollow portion 22 is positioned between the two first hollow portions 21. The two first hollow portions 21 and the one second hollow portion 22 are in communication with each other. The shape of each first hollow portion 21 is the same semi-cylindrical shape as the hollow portion 20 of Embodiment 2. The shape of the second hollow portion 22 is a rectangular column. The shape of the second hollow portion 22 when viewed from above is rectangular. In this example, the diameter of the semicircular first hollow portion 21 is longer than the longer side of the rectangle of the second hollow portion 22. Two first hollow sections 21 and one second hollow section 22 are formed such that the semicircular diameter of one first hollow section 21, the rectangular long side of the second hollow section 22, and the semicircular diameter of the remaining first hollow section 21 face each other.

[0063] [Core Rod] The core rod 3 is composed of two first parts 31 and one second part 32. In this example, one second part 32 is positioned between the two first parts 31. The two first parts 31 and the one second part 32 are formed in a continuous line. The shape of each first part 31 is the same semi-cylindrical shape as the core rod 3 of Embodiment 2. The shape of the second part 32 is a rectangular column. The shape of the second part 32 when viewed from above is rectangular. In this example, the semicircular diameter of each first part 31 is shorter than the long side of the rectangle of the second part 32. The two first parts 31 and the one second part 32 are formed such that the semicircular diameter of one first part 31, the long side of the rectangle of the second part 32, and the semicircular diameter of the remaining first part 31 face each other.

[0064] The core rod 3 is inserted into the hollow section 20 such that it divides the hollow section 20 into two segments arranged in parallel in a direction perpendicular to the first direction. Each segment, when viewed from above, is C-shaped. Each segment is symmetrical with respect to the core rod 3. That is, each segment is the same size and shape as the others. Each segment is formed so that C-shaped openings face each other.

[0065] [First Upper Punch] The first upper punch 5 is composed of two first parts 51 and one second part 52. In this example, one second part 52 is positioned between the two first parts 51. The two first parts 51 and the one second part 52 are formed in a continuous manner. The shape of each first part 51 is the same semi-cylindrical shape as the first upper punch 5 in Embodiment 2. The shape of the second part 52 is a rectangular column. The shape of the second part 52 when viewed from above is rectangular. In this example, the semicircular diameter of the first part 51 is shorter than the long side of the rectangle of the second part 52. The two first parts 51 and the one second part 52 are formed such that the semicircular diameter of one first part 51, the long side of the rectangle of the second part 52, and the semicircular diameter of the remaining first part 51 face each other. One first upper punch 5 is inserted into the two segments.

[0066] [Lower Punch and Second Upper Punch] A lower punch 4 and a second upper punch 6 are inserted into each segment. The number of lower punches 4 and second upper punches 6 in this example corresponds to the number of segments. The lower punches 4 and second upper punches 6 are the same as those in Embodiment 2. In this example, a lower punch 4 and a second upper punch 6 are inserted into each segment. One compacted body is produced from one segment. In a mold 1 having two segments as in this example, two compacted bodies are produced. The compacted bodies produced have the same shape as the compacted bodies produced in Embodiment 2.

[0067] In step B of this example, when the first upper punch 5 is lowered and the side surface 56 of the first upper punch 5 pressurizes the raw material powder 9, a portion of the raw material powder 9 overflows onto the upper surface 26 of the die 2, similar to embodiments 1 and 2. This pressurizing process causes pressure to act on the first upper punch 5 from the raw material powder 9 of each segment in a direction perpendicular to the first direction. In this example, as described above, the shape of each segment when viewed from above is C-shaped, and they are symmetrical with respect to the core rod 3, with the C-shaped openings facing each other. Therefore, the above pressure acts on the first upper punch 5 in a way that sandwiches it. As a result, the above pressure is easily canceled out, and the first upper punch 5 is less likely to shift in a direction perpendicular to the first direction, so the first upper punch 5 does not shift to one side of the inner circumferential surface 25 of the die 2 and hit the inner circumferential surface 25. Therefore, the lifespan of the first upper punch 5 is less likely to decrease.

[0068] The present invention is not limited to the configurations shown in the embodiments, but is intended to include all modifications within the meaning and scope of the claims as indicated by the claims. It should be understood that at least one configuration or feature described in each embodiment can be combined with other embodiments or modified in various ways.

[0069] 1. Mold 2. Die 20. Hollow section, 21. First hollow section, 22. Second hollow section 25. Inner circumferential surface, 26. Top surface 3. Core rod 31. First section, 32. Second section 35. Upper end surface, 36. Side surface 4. Lower punch 45. Upper end surface 5. First upper punch 51. First section, 52. Second section 55. Lower end surface, 56. Side surface 57. Tapered surface 571. First tapered surface, 572. Second tapered surface 58. Orthogonal surface 581. First orthogonal surface, 582. Second orthogonal surface 59. Parallel surface 591. First parallel surface, 592. Second parallel surface, 593. Third parallel surface 594. Fourth parallel surface, 595. Fifth parallel surface 6. Second upper punch 611. Lower end surface, 612. Outer circumferential surface 9. Raw material powder 10. Sintered member 11 Upper end face, 12 Lower end face, 13 Outer circumference face, 14 Inner circumference face, 15 Tapered surface, 151 First tapered surface, 152 Second tapered surface, 16 Orthogonal surface, 161 First orthogonal surface, 162 Second orthogonal surface, 17 Parallel surface, 171 First parallel surface, 172 Second parallel surface, 173 Third parallel surface, 174 Fourth parallel surface, 175 Fifth parallel surface, θ Angle

Claims

1. A method for manufacturing a sintered member, comprising the steps of: filling a cavity of a mold with raw material powder; pressurizing the raw material powder in the cavity to produce a cylindrical compacted body; and sintering the compacted body to produce a sintered member, wherein the mold comprises: a die having a hollow portion penetrating in a first direction; a core rod inserted into the hollow portion along the first direction; a lower punch inserted between the die and the core rod; a first upper punch inserted into the hollow portion so as to contact the upper end surface of the core rod; and a second upper punch inserted between the die and the first upper punch, wherein the side surface of the first upper punch has a plurality of tapered surfaces whose outer dimensions decrease towards the lower end surface, and one or more orthogonal surfaces perpendicular to the first direction, and the step of producing the compacted body pressurizes the raw material powder with the upper end surface of the lower punch, the side surface of the first upper punch including the plurality of tapered surfaces and the one or more orthogonal surfaces, and the lower end surface of the second upper punch.

2. The method for manufacturing a sintered member according to claim 1, wherein the angle between each of the plurality of tapered surfaces and a virtual surface perpendicular to the first direction is 1° or more and less than 90°.

3. The method for manufacturing a sintered member according to claim 1 or claim 2, wherein the core rod is inserted into the hollow portion such that the shape of the space enclosed by the inner circumferential surface of the die and the side surface of the core rod, when viewed in the first direction, is C-shaped.

4. The method for manufacturing a sintered member according to claim 1 or 2, wherein the core rod is inserted into the hollow portion such that it divides the hollow portion into a plurality of segments arranged in parallel in a direction perpendicular to the first direction, each of the plurality of segments is C-shaped when viewed from above, and the segments adjacent to each other with the core rod in between are formed such that C-shaped openings face each other.

5. The method for manufacturing a sintered member according to any one of claims 1 to 4, wherein the timing at which the second upper punch press-moldes the raw material powder is later than the timing at which the first upper punch is inserted into the hollow portion.

6. A mold for producing a cylindrical compacted body by pressure molding raw material powder, comprising: a die having a hollow portion penetrating in a first direction; a core rod inserted into the hollow portion along the first direction; a lower punch inserted between the die and the core rod; a first upper punch inserted into the hollow portion so as to be in contact with the upper end surface of the core rod; and a second upper punch inserted between the die and the first upper punch, wherein the side surface of the first upper punch has a plurality of tapered surfaces whose outer dimensions decrease towards the lower end surface, and one or more orthogonal surfaces perpendicular to the first direction.

7. A cylindrical sintered member, wherein the inner circumferential surface of the sintered member has a plurality of tapered surfaces along the central axis of the sintered member, the inner dimension of which decreases from a first end to a second end of the sintered member, and one or more orthogonal surfaces perpendicular to the central axis, and each of the plurality of tapered surfaces and the one or more orthogonal surfaces are free from cutting marks, machining marks, grinding marks, and polishing marks.

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