Machine parts, machine assemblies, and methods for manufacturing machine parts

Abstract

To provide a mechanical component that protects the opening edge of a hole from damage.SOLUTION: A mechanical component comprising sintered metal powder has a first face, a first hole formed in the first face, and an annular opening edge that connects the inner peripheral surface of the first hole to the first face. The opening edge includes a first edge constituting at least a part of the opening edge in the circumferential direction. The first edge includes a curved face smoothly connected to the inner peripheral surface. The first density within a specified range in a region below a depth of 0.6 mm from the curved face is higher than the second density within a specified range in a region beyond a depth of 1 mm from the curved face.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to machine parts, machine assemblies, and methods for manufacturing machine parts.

Background Art

[0002] Machine parts made of sintered compacts of metal powder are known. The sintered compact is produced by sintering a powder compact. The powder compact is obtained by pressure-forming metal powder. For example, Patent Document 1 discloses a gear as a machine part composed of a sintered compact of metal powder.

[0003] Some machine parts are combined with other machine parts to form a machine assembly. Such a machine assembly is, for example, a machine assembly including a machine part having a hole and a movable part that enters and exits the hole. In such a machine assembly, there is a risk that the movable part contacts the opening edge of the hole and the opening edge is damaged.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] If the density of the powder compact is increased, the fatigue strength of the machine part obtained by sintering the powder compact is improved, and it becomes difficult for the opening edge of the hole to be damaged. However, if the density of the powder compact is too high, defects such as cracking are likely to occur during the production and sintering of the powder compact.

[0006] One object of the present disclosure is to provide a machine part in which the opening edge of a hole is difficult to be damaged and a method for manufacturing the machine part. Another object of the present disclosure is to provide a machine assembly including the machine part of the present disclosure. [Means for solving the problem]

[0007] The machine parts disclosed herein are A mechanical part composed of a sintered body of metal powder, The first page, The first hole formed on the first surface, The first hole comprises an annular opening edge portion connecting the inner circumferential surface of the first hole and the first surface, The opening edge includes a first edge that constitutes at least a part of the circumferential direction of the opening edge, The first edge portion includes a curved surface that smoothly connects to the inner circumferential surface. The first density in a predetermined range in the region less than or equal to 0.6 mm deep from the curved surface is higher than the second density in a predetermined range in the region more than 1 mm deep from the curved surface.

[0008] The mechanical assembly disclosed herein is The machine parts disclosed herein and The device includes a movable part configured to move between a state in which it is positioned inside the first hole of the machine part and a state in which it is positioned outside the first hole.

[0009] The method for manufacturing machine parts disclosed herein is: Step A involves pressurizing metal powder to produce a compacted molded body having a first surface and a first hole formed on the first surface, Step B involves sintering the aforementioned compacted molded body to produce a sintered body, The process includes step C, which, after step B, applies pressure to at least a portion of the annular edge region surrounding the opening of the first hole using a jig to form a first edge connecting the first surface and the inner circumferential surface of the first hole, The first edge portion has a curved surface that smoothly connects to the inner circumferential surface. [Effects of the Invention]

[0010] The mechanical parts and mechanical assemblies of this disclosure are provided with opening edges that are less susceptible to damage.

[0011] The manufacturing method of the mechanical part of the present disclosure can manufacture a mechanical part having an opening edge that is difficult to be damaged.

Brief Description of the Drawings

[0012] [Figure 1] Figure 1 is a schematic configuration diagram of a mechanical assembly described in Embodiment 1. [Figure 2] Figure 2 is a partial cross-sectional view of the mechanical assembly shown in Figure 1. [Figure 3] Figure 3 is a cross-sectional view taken along the line III-III of the mechanical part shown in Figure 1. [Figure 4] Figure 4 is a cross-sectional view taken along the line IV-IV of the mechanical part shown in Figure 1. [Figure 5] Figure 5 is a cross-sectional photograph of a location corresponding to Figure 3. [Figure 6] Figure 6 is a schematic configuration diagram of a compacted powder compact for manufacturing the mechanical part described in Embodiment 1. [Figure 7] Figure 7 is a cross-sectional view taken along the line VII-VII of the compacted powder compact shown in Figure 6. [Figure 8] Figure 8 is a cross-sectional view taken along the line VIII-VIII of the compacted powder compact shown in Figure 6. [Figure 9] Figure 9 is a schematic explanatory diagram of a jig used for manufacturing the mechanical part described in Embodiment 1.

Modes for Carrying Out the Invention

[0013] [Description of Embodiments of the Present Disclosure] Hereinafter, embodiments of the present disclosure will be listed and described.

[0014] <1>The mechanical part according to the embodiment is a mechanical part composed of a sintered body of metal powder, a first surface, a first hole formed in the first surface, and an annular opening edge connecting the inner peripheral surface of the first hole and the first surface, where the opening edge includes a first edge portion that constitutes at least a part of the circumferential direction of the opening edge The first edge portion includes a curved surface that smoothly connects to the inner circumferential surface. The first density in a predetermined range in the region less than or equal to 0.6 mm deep from the curved surface is higher than the second density in a predetermined range in the region more than 1 mm deep from the curved surface.

[0015] As described later, the above mechanical component is combined with a movable part such as a pin that moves in and out of the first hole. In the above mechanical component, the opening edge surrounding the opening of the first hole has a first edge, and this first edge has a curved surface that smoothly connects to the inner circumferential surface of the first hole. Since there is no clear ridge between the smoothly connected curved surface and the inner circumferential surface, the movable part is smoothly guided into the first hole when it enters the hole. Moreover, in the above mechanical component, the density near the curved surface is higher than the density in other areas. Therefore, even if the movable part placed in the first hole comes into contact with the curved surface of the opening edge, the opening edge including the curved surface is less likely to be damaged.

[0016] In the above-described machine part, the location for measuring the second density can be any location within a region more than 1 mm deep from the curved surface. In other words, the second density can be considered to be the density of most of the machine part except for the vicinity of the curved surface. Therefore, in the above-described machine part, the vicinity of the curved surface is locally denser than other parts. Machine parts with such a configuration are less prone to defects such as cracking during manufacturing compared to machine parts where the overall density is equivalent to the first density.

[0017] <2> the above <1> In the machine parts described, The ratio of the first density to the true density of the sintered body may be 94% or more.

[0018] The ratio of the first density to the true density of the sintered body is the relative density of a local region with a depth of 0.6 mm or less from the curved surface. Local regions with a relative density of 94% or more exhibit excellent fatigue strength against surface pressure. Therefore, even if a movable part enters and exits the first hole, the opening edge is less likely to be damaged.

[0019] <3> the above <1> or <2> In the machine parts described, The ratio of the second density to the true density of the sintered body may be 86% or more and 92% or less.

[0020] As mentioned above, the second density can be considered to be the density of most of the mechanical part, excluding the vicinity of curved surfaces. Mechanical parts with a relative density of 86% or higher for the majority of the component have superior mechanical strength. Such mechanical parts are less likely to be damaged when incorporated into equipment. Furthermore, mechanical parts with a relative density of 92% or lower are less prone to defects such as cracking caused by excessively high density.

[0021] <4> the above <1> from <3> In any of the machine parts described above, The material of the sintered body may be an iron-based alloy.

[0022] Iron-based alloys have excellent strength and toughness. They also have the advantage of being inexpensive.

[0023] <5> the above <4> In the machine parts described, The iron-based alloy may contain at least one element selected from the group consisting of nickel, molybdenum, chromium, copper, and carbon.

[0024] Iron-based alloys containing the above elements possess excellent mechanical properties. Therefore, the above <5> The machine parts described can be suitably used for a variety of applications.

[0025] <6> the above <1> from <5> In any of the machine parts described above, The aforementioned opening edge further comprises a second edge portion that constitutes a part of the circumferential direction of the opening edge, The second edge portion may include a flat land surface connected to the inner circumferential surface and an inclined surface connecting the land surface and the first surface.

[0026] The second edge is positioned in a location where it is unlikely to come into contact with the movable parts. The first surface of a machine part is usually finished smoothly by polishing. When polishing, if the first surface and the inner surface of the first hole are connected at a right angle, burrs are likely to form at the joint between the first surface and the inner surface. On the other hand, the above <6> In this configuration, since the sintered body is manufactured through the molding of metal powder, the angle between the first surface and the inclined surface is usually obtuse, making it difficult for burrs to form at the joint between the first surface and the inclined surface. Therefore, it is suppressed that burrs that fall off from mechanical parts get into gaps in equipment containing mechanical parts. Fallen burrs can cause equipment failure.

[0027] <7> A machine assembly according to this embodiment is the above <1> from <6> The machine parts listed in any of the above, The device includes a movable part configured to move between a state in which it is positioned inside the first hole of the machine part and a state in which it is positioned outside the first hole.

[0028] In the above-described machine assembly, a movable part moves in and out of a first hole in the machine part. The opening edge of the first hole in the machine part is provided with a locally reinforced first edge. Therefore, the opening edge is less likely to be damaged by the movement of the movable part. As a result, the above-described machine assembly operates stably over a long period of time.

[0029] <8> the above <7> In the machine assembly described above, The aforementioned movable part is configured to be movable along a specific track, The aforementioned specific track extends in a direction along the first surface and intersects the first hole, The first edge portion may be provided in a position that overlaps with the specific track.

[0030] the above <8> In this configuration, when a movable part that moves along a specific track is positioned to correspond to the first hole, the movable part enters the first hole. At that time, the movable part enters the first hole while in contact with the opening edge. Therefore, if the point where the movable part makes contact, i.e., the point where it overlaps with the specific track of the movable part, is the locally reinforced first edge, the mechanical part is less likely to be damaged.

[0031] <9> The manufacturing method of a machine part according to the embodiment is: Step A involves pressurizing metal powder to produce a compacted molded body having a first surface and a first hole formed on the first surface, Step B involves sintering the aforementioned compacted molded body to produce a sintered body, The process includes step C, which, after step B, applies pressure to at least a portion of the annular edge region surrounding the opening of the first hole using a jig to form a first edge connecting the first surface and the inner circumferential surface of the first hole, The first edge portion has a curved surface that smoothly connects to the inner circumferential surface.

[0032] In this specification, the opening of the first hole is the entrance to the first hole on the first surface and is a non-substantial portion. In this specification, the edge region is a substantial portion that forms the contour of the opening. According to the above method for manufacturing a machine part, a machine part is produced in which at least a part of the edge region is locally densely densified. Therefore, when producing a powder compact, it is not necessary to make the overall density of the powder compact unnecessarily high. A powder compact that is not too dense is less prone to cracking during molding and during sintering after molding.

[0033] <10> the above <9> In the method for manufacturing machine parts described, In step A, a first chamfered portion and a second chamfered portion are formed in the edge region. In step C, the first chamfered portion is pressed by the jig, The first chamfered portion comprises a first land surface connected to the inner circumferential surface of the first hole, and a first inclined surface connecting the first land surface and the first surface. The second chamfered portion comprises a second land surface connected to the inner circumferential surface and a second inclined surface connecting the second land surface and the first surface. The depth of the first land surface along the axial direction of the first hole may be less than the depth of the second land surface.

[0034] The first chamfered portion becomes the first edge portion through pressurization using a jig. The depth of the first land surface of the first chamfered portion is smaller than the depth of the second land surface of the second chamfered portion. Therefore, the amount of deformation of the first chamfered portion due to pressurization is large, and the first edge portion tends to become denser.

[0035] The second chamfer becomes the second edge after the first surface is polished. The depth of the second land surface of the second chamfer is greater than the depth of the first land surface of the first chamfer. Therefore, after the first surface is polished, a portion of the second inclined surface and the second land surface remain. The second inclined surface becomes the inclined surface at the second edge, and the second land surface becomes the flat land surface at the second edge.

[0036] [Details of the embodiments of this disclosure] Hereinafter, embodiments of the sintered parts, methods for manufacturing sintered parts, and mechanical assemblies of this disclosure will be described with reference to the drawings. Identical reference numerals in the drawings indicate identical parts. The present invention is not limited to the configurations shown in the embodiments, but is intended to be limited to those shown in the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0037] <Embodiment 1> ≪Machine Assembly≫ The mechanical assembly 1 shown in Figures 1 and 2 comprises a mechanical part 2 and a movable part 3. The mechanical assembly 1 is, for example, a component of an automobile. The mechanical part 2 in the mechanical assembly 1 is made of a sintered metal powder body 20. The mechanical part 2 has a first hole 4. The movable part 3 is configured to move between a state in which it is positioned inside the first hole 4 and a state in which it is positioned outside the first hole 4. One of the features of this mechanical assembly 1 is that the density of at least a portion of the opening edge 5 of the first hole 4 is higher than the density of other parts. The components of the mechanical assembly 1 will be described in detail below.

[0038] Machine parts In this example, the machine part 2 is a block-shaped member composed of a sintered metal powder body 20. The shape of the machine part 2 is not particularly limited. For example, the machine part 2 may be a plate-shaped member or a disc-shaped member.

[0039] The material of the sintered body 20, i.e., the material of the metal powder, is, for example, an iron-based alloy mainly composed of iron (Fe). The iron-based alloy contains, for example, at least one element selected from the group consisting of nickel (Ni), molybdenum (Mo), chromium (Cr), copper (Cu), and carbon (C). For example, an iron-based alloy containing Cu and C described in ISO 5755:2012 is F-08C2. An iron-based alloy containing Mo, Cu, and C is, for example, FLA-07C2M. An iron-based alloy containing Ni, Mo, Cu, and C is, for example, FD-05N4C. An iron-based alloy containing Mo and Cr is, for example, FL-05Cr3M. These iron-based alloys containing at least one of the elements Ni, Mo, Cr, Cu, and C have excellent mechanical strength.

[0040] The machine part 2 has a first surface 21. In this example, the first surface 21 is a flat surface on the machine part 2. In this example, the first surface 21 is polished as described later. The arithmetic mean roughness Ra of the first surface 21 is, for example, 1.0 μm or less. The arithmetic mean roughness Ra is determined by a method in accordance with JIS B 0601:2001. The arithmetic mean roughness Ra of the first surface 21 may be, for example, 0.5 μm or less. In this example, the machine part 2 has a second surface 22 on the opposite side of the first surface 21.

[0041] The machine part 2 includes a first hole 4 provided on the first surface 21. In this example, the first hole 4 is a blind hole with a bottom. Unlike this example, the first hole 4 may also be a through hole opening to both the first surface 21 and the second surface 22.

[0042] The first hole 4 has an opening 4h. The opening 4h is the portion of the space enclosed by the inner circumferential surface 41 of the first hole 4 that is open to the first surface 21. The contour dimensions of the opening 4h of the first hole 4 as viewed from the first surface 21 side are not particularly limited as long as they are larger than the contour dimensions of the movable part 3. In this example, the contour shape of the opening 4h is a rectangular elongated hole that is long in the vertical direction of the paper.

[0043] The machine part 2 includes an annular opening edge 5 that connects the first surface 21 and the inner circumferential surface 41 of the first hole 4. The opening edge 5 is the portion that surrounds the opening 4h of the first hole 4 and is recessed compared to the first surface 21.

[0044] In this example, the opening edge 5 includes two first edges 51 and two second edges 52. In this example, the first edges 51 are positioned to intersect with a specific track 30 of the movable part 3. The specific track 30 extends in a direction along the first surface 21, as shown by the dashed line in Figure 1, and the movable part 3 moves along the specific track 30. When the movable part 3, having moved along the specific track 30, is positioned to correspond to the first hole 4, the movable part 3 fits into the first hole 4. Therefore, the movable part 3 may come into contact with the first edges 51. On the other hand, the movable part 3 does not come into contact with the second edges 52. Unlike this example, if the shape of the opening 4h of the first hole 4 substantially matches the outer shape of the movable part 3, the entire circumference of the opening edge 5 may be composed of the first edges 51.

[0045] [First edge] Figure 3 shows a cross-section of the first edge 51 along the axial direction of the first hole 4. In this example, the first edge 51 is composed of a curved surface 51c and an inclined surface 51s. The curved surface 51c smoothly connects to the inner circumferential surface 41 of the first hole 4. Therefore, there is no clear ridge between the curved surface 51c and the inner circumferential surface 41. The curved surface 51c protrudes convexly toward the corner connecting a virtual plane obtained by extending the first surface 21 toward the first hole 4 and a virtual curved surface obtained by extending the inner circumferential surface 41 toward upward. In the cross-section shown in Figure 3, the curved surface 51c forms a circular arc having a predetermined radius of curvature. The radius of curvature of the circular arc is, for example, 0.5 mm or more and 3.0 mm or less. The radius of curvature may also be 1.0 mm or more and 3.0 mm or less.

[0046] In the cross-section shown in Figure 3, the inclined surface 51s forms a straight line. The inclined surface 51s is not essential. That is, the first edge 51 may consist only of the curved surface 51c. In that case, the curved surface 51c may smoothly connect to the first surface 21. There is no clear ridge between the smoothly connected curved surface 51c and the first surface 21. On the other hand, there is a clear ridge between the inclined surface 51s and the first surface 21.

[0047] In this example of machine part 2, the first density in the local region 510 with a depth of 0.6 mm or less from the curved surface 51c is higher than the second density in the region with a depth of more than 1 mm from the curved surface 51c. The second density can be measured at any position within the region with a depth of more than 1 mm from the curved surface 51c. If the value of the second density is approximately the same regardless of the measurement position, the second density can be considered to be approximately the overall density of machine part 2.

[0048] The first and second densities are determined from cross-sectional photographs of machine part 2. Figure 5 is a cross-sectional photograph taken by SEM (Scanning Electron Microscope) of the part of machine part 2 corresponding to the part shown in Figure 3. In Figure 5, the white part is the solid part of machine part 2, and the gray part is the void formed inside machine part 2. The black part is the outer region of machine part 2. The dashed-dot arcs close to the curved surface 51c are lines 0.6 mm from the curved surface 51c. The dashed-dot arcs far from the curved surface 51c are lines 1 mm from the curved surface 51c.

[0049] The first density is determined as follows. First, in the cross-section shown in Figure 5, the first porosity of a first predetermined range in the region from the curved surface 51c to a depth of 0.6 mm or less is measured. In this example, the first predetermined range is the area inside the circle indicated by the dashed line. This circle is contained between the curved surface and the 0.6 mm line. The circle is selected at a position close to the inner circumferential surface 41 of the first hole 4. For example, the position of the circle is tangent to a line parallel to the first surface 21 that passes through the boundary between the curved surface 51c and the inner circumferential surface 41. The solid portion and the void portion within the circle are separated by image processing, and the area of ​​the circle and the area of ​​the void portion are determined. In this example, the ratio of the area of ​​the void portion to the area of ​​the circle is considered to be the first porosity of the first predetermined range. The unit of the first porosity is percent. The larger the first porosity, the lower the first density. That is, the smaller the first porosity, the higher the first density. The ratio of the area of ​​the solid portion to the area of ​​the circle may also be used as an indicator of the first density.

[0050] The ratio of the first density to the true density of the sintered body 20, i.e., the first relative density of the local region 510, is, for example, 94% or more. The true density of the sintered body 20 is the true density of the metal powder constituting the sintered body 20. The true density of the metal powder is calculated based on the composition of the metal powder. In this example, the ratio of the area of ​​the physical part within a first predetermined range of the cross-sectional photograph is considered to be the first relative density. Specifically, the first relative density is "(100 - first porosity)". If the ratio of the area of ​​the physical part within the first predetermined range is measured in the cross-sectional photograph, that ratio is considered to be the first relative density. A local region 510 with a first relative density of 94% or more exhibits high fatigue strength against the pressure of the movable part 3. The first relative density may also be 95% or more. The upper limit of the first relative density is, for example, 96%. The range of the first relative density is, for example, 94% or more and 96% or less, or 95% or more and 96% or less. The specific value of the first density can be determined by multiplying the true density of the metal powder constituting machine part 2 by the first relative density. For example, if the true density of the metal powder is 10 g / cm³ 3 If the first relative density is 95%, then the first density is 9.5 g / cm³. 3 That is the case.

[0051] The second density is determined as follows: In the cross-section shown in Figure 5, the second porosity of the second predetermined range in the region from the curved surface 51c to a depth of more than 1 mm is measured. The size and shape of the second predetermined range are the same as those of the first predetermined range. The porosity of the second predetermined range is determined by the same method as the porosity of the first predetermined range. That is, the ratio of the area of ​​the void portion to the area of ​​the second predetermined range is the second porosity of the second predetermined range. The larger the second porosity, the lower the second density. If the first porosity is smaller than the second porosity, it can be determined that the density of the local region 510 is higher than the density of the entire machine part 2.

[0052] The ratio of the second density to the true density of the sintered body 20, i.e., the second relative density of the portion excluding the area less than 1 mm deep from the curved surface 51c, is, for example, 86% to 92%. In this example, the ratio of the area of ​​the physical portion in the second predetermined range of the cross-sectional photograph is considered to be the second relative density. A machine part 2 with a second relative density of 86% or more has excellent strength. A machine part 2 with a second relative density of 92% or less has almost no cracks. The second relative density may also be, for example, 86% to 88%. The specific value of the second density can be obtained by multiplying the true density of the metal powder constituting the machine part 2 by the second relative density.

[0053] The first relative density is, for example, 3% or more higher than the second relative density. The first relative density may also be 5% or more higher than the second relative density.

[0054] [Second edge] Figure 4 shows a cross-section of the second edge 52 along the axial direction of the first hole 4. In this example, the second edge 52 comprises a land surface 52r and an inclined surface 52s. The land surface 52r is a flat surface connected to the inner circumferential surface 41. In this example, the land surface 52r is parallel to the first surface 21. The land surface 52r may also be inclined with respect to the first surface 21. The inclined surface 52s connects the land surface 52r and the first surface 21. The angle between the inclined surface 52s and the first surface 21 is obtuse. Burrs are less likely to form at the angle between the inclined surface 52s and the first surface 21, which are connected by an obtuse angle.

[0055] ≪Movable parts≫ The movable part 3 is a component configured to be movable relative to the mechanical part 2. In this example, the movable part 3 is a pin-shaped component. The configuration of the movable part 3 is not particularly limited. For example, the movable part 3 may be a projection provided on a block-shaped component.

[0056] In this example, the movable part 3 is configured to move freely relative to the mechanical part 2 by a rocking mechanism and a linear motion mechanism (not shown). The rocking mechanism moves the movable part 3 along a specific track 30 in the direction indicated by the white arrow. In this example, the specific track 30 is a straight line. Unlike this example, the specific track 30 may also be an arc.

[0057] The linear motion mechanism moves the movable part 3 along the axial direction of the first hole 4. When the movable part 3, having moved along the specific track 30, is positioned to correspond to the first hole 4, it is pushed into the first hole 4 by the linear motion mechanism. Unlike this example, the movable part 3 may also be manually inserted into and removed from the first hole 4 of the mechanical part 2.

[0058] The movable part 3 may be a sintered metal powder, a cast material, or a machined material obtained by processing a cast material. The material of the movable part 3 may be the same as or different from the material of the machine part 2.

[0059] As the movable part 3 moves along the specific track 30 and enters the first hole 4, the movable part 3 comes into contact with the first edge 51. In this example, the first edge 51 has a curved surface 51c that smoothly connects to the inner circumferential surface 41 of the first hole 4. Therefore, the movable part 3 is smoothly guided from the first edge 51 towards the interior of the first hole 4. When the movable part 3 enters the first hole 4, a strong stress acts on the curved surface 51c. Because the density of the local region 510 including the curved surface 51c is high, the curved surface 51c is rarely damaged.

[0060] ≪Manufacturing Method for Machine Parts≫ The manufacturing method of the machine part 2 according to this embodiment will be described mainly with reference to Figures 6 to 9. The manufacturing method in this example comprises the following steps. Process A: A process for producing a compacted molded body 6 having a first surface 6s and a first hole 4 formed on the first surface 6s by pressurizing and molding metal powder. • Process B: A process to produce a sintered body 7 by sintering the compacted powder molded body 6. • Step C: After step B, a step in which at least a portion of the edge region 4c surrounding the opening 4h of the first hole 4 is pressed with a jig to form the first edge 51. The following describes each step in detail.

[0061] [Process A] The metal powder in process A is the one described in section 2 of machine parts. The metal powder is filled into a mold and pressure-molded. In addition to the metal powder, a lubricant may be included in the mold. The lubricant may be, for example, lithium stearate or zinc stearate.

[0062] The pressure for compression molding is appropriately selected depending on the composition of the metal powder. For example, the pressure for compression molding a metal powder consisting of an iron-based alloy containing Cu and C is 500 MPa to 800 MPa. When the above iron-based alloy is compressed at the above pressure, a compacted body with a density of approximately 86% to 92% is obtained. If the pressure is 500 MPa or higher, it is easy to obtain a compacted body 6 with sufficient density. If the pressure is 800 MPa or lower, excessive load is less likely to be placed on the mold, and the density of the compacted body 6 does not become too high. If the density of the compacted body 6 is too high, defects such as cracking are likely to occur in the compacted body 6. The above pressure may also be 500 MPa to 600 MPa. In this case, the density of the compacted body is approximately 86% to 88%.

[0063] The compacted powder body 6 is provided with a first hole 4 formed by a mold. In this example, a first chamfered portion 61 and a second chamfered portion 62 are formed in the opening 4h of the first hole 4 and the surrounding annular edge region 4c. The first chamfered portion 61 and the second chamfered portion 62 are formed by a mold. Unlike this example, the edge region 4c may also be a corner where the first surface 6s and the inner circumferential surface 41 of the first hole 4 are connected at a right angle. Alternatively, the edge region 4c may consist of the above-mentioned right-angle corner and the second chamfered portion 62.

[0064] The first chamfered portion 61 comprises a first land surface 61r and a first inclined surface 61s, as shown in Figure 7. The first land surface 61r connects to the inner circumferential surface 41. In this example, the angle between the first land surface 61r and the inner circumferential surface 41 is 90°. The first land surface 61r is a plane parallel to the first surface 6s. The first land surface 61r may be inclined with respect to the first surface 6s.

[0065] The depth d1 of the first land surface 61r along the axial direction of the first hole 4 is, for example, greater than 0 mm and less than or equal to 0.15 mm. The depth d1 is the distance between the first land surface 61r and a virtual plane extended from the first surface 6s toward the first hole 4. The width w1 of the first land surface 61r is, for example, 0.1 mm or more and less than or equal to 0.3 mm. The width w1 is the length of the first land surface 61r in a direction perpendicular to the axial direction of the first hole 4.

[0066] The first inclined surface 61s connects to the first land surface 61r and the first surface 6s. In the cross-sectional view of Figure 7, the contour line of the first inclined surface 61s is a straight line, but it may also be a curved line that is convex upward and to the right.

[0067] The first chamfered portion 61 is compressed into a curved shape indicated by the dashed line by the machining process in step C described later. The compressed portion constitutes the first edge portion 51 of the machine part 2. In other words, the first chamfered portion 61 does not exist in the machine part 2. After the above pressurization, the first surface 6s is polished to the position of the horizontal line indicated by the dashed line. The newly exposed surface after polishing constitutes the first surface 21 of the machine part 2.

[0068] The second chamfered portion 62 comprises a second land surface 62r and a second inclined surface 62s, as shown in Figure 8. The second land surface 62r connects to the inner circumferential surface 41. In this example, the angle between the second land surface 62r and the inner circumferential surface 41 is 90°. The second land surface 62r is a plane parallel to the first surface 6s. The second land surface 62r may be inclined with respect to the first surface 6s.

[0069] The depth d2 of the second land surface 62r along the axial direction of the first hole 4 is, for example, 0.25 mm or more and 0.4 mm or less. The depth d2 is the distance between the first surface 6s and the extended surface of the second land surface 62r. ​​The width w2 of the second land surface 62r is, for example, 0.1 mm or more and 0.3 mm or less. The width w2 is the length of the second land surface 62r in the direction perpendicular to the axial direction of the first hole 4.

[0070] The second inclined surface 62s connects to the second land surface 62r and the first surface 6s. In the cross-sectional view of Figure 8, the contour line of the second inclined surface 62s is a straight line, but it may also be a curved line that convex diagonally upward to the right.

[0071] Here, the compacted molded body 6 is sintered in step B, which will be described later, to become a sintered body 7. The first surface 6s of the sintered body 7 is polished to the position of the horizontal line shown by the dashed line. The thickness to be polished is about 0.2 mm. Since the depth d2 of the second land surface 62r is greater than 0.2 mm, the second land surface 62r remains even after polishing. The second inclined surface 62s and the second land surface 62r that remain after polishing the first surface 6s constitute the second edge portion 52 of the machine part 2 (see Figure 4).

[0072] [Process B] In step B, the compacted body 6 is sintered. Sintering yields a sintered body in which the particles contained in the metal powder are bonded together. The compacted body 6 shrinks slightly during sintering, but the shape and size of the sintered body are approximately the same as those of the compacted body 6. Sintering is carried out based on known conditions according to the material of the metal powder. For example, in the case of a compacted body 6 made of iron-based alloy metal powder, the sintering temperature is, for example, 1000°C to 1400°C, or 1200°C to 1300°C. The sintering time is, for example, 15 minutes to 150 minutes, or 20 minutes to 60 minutes.

[0073] [Process C] In process C, at least a portion of the edge region 4c shown in Figure 6, in this example the first chamfered portion 61, is pressed by a jig. Figure 9 is an explanatory diagram showing an example of processing in process C. In the example shown in Figure 9, a backing plate 90 is placed on the first surface 6s of the sintered body 7. The backing plate 90 has a through hole 90h having a larger diameter than the first hole 4. Part of the jig 9 is inserted into the through hole 90h. The jig 9 comprises a columnar portion 9b, a tip portion 9c, a flange portion 9f, and a processing portion 9p. The flange portion 9f is located in the middle of the longitudinal direction of the columnar portion 9b. The portion of the columnar portion 9b below the flange portion 9f is inserted into the through hole 90h of the backing plate 90. The flange portion 9f contacts the upper surface of the backing plate 90 and restricts the movement of the jig 9. The tip portion 9c is a columnar body that is thinner than the columnar portion 9b. The tip portion 9c is inserted into the first hole 4. The machining section 9p is the part that connects the columnar section 9b and the tip section 9c. The machining section 9p contacts the edge region 4c and deforms the edge region 4c. Because the downward movement of the jig 9 is restricted by the flange section 9f, the machining section 9p does not press excessively against the edge region 4c.

[0074] The first chamfered portion 61 of the edge region 4c is compressed by the processing with the jig 9, thereby forming the first edge portion 51 of the machine part 2. In this example, the jig 9 is prismatic and does not come into contact with the second chamfered portion 62. Therefore, the second chamfered portion 62 is not processed by the jig 9 and becomes the second edge portion 52. As shown in Figure 7, in the first chamfered portion 61 of this example, the depth d1 of the first land surface 61r is very small. Therefore, because the amount of plastic deformation by the jig 9 is large, the density of the first edge portion 51 tends to be high. Unlike this example, if the edge region 4c has a corner where the first surface 6s and the inner circumferential surface 41 of the first hole 4 are connected at a right angle, the first edge portion 51 may be formed by the pressure applied to that corner by the jig 9.

[0075] [Other processes] The first surface 6s of the sintered body 7 may be polished. The polishing thickness is about 0.2 mm. The polishing thickness is less than the depth d2 of the second land surface 62r. ​​Therefore, the polishing jig will not reach the second land surface 62r. ​​Since the angle between the polished surface and the second inclined surface 62s is obtuse, burrs are unlikely to form at the corner between the polished surface and the second inclined surface 62s. Burrs can get into gaps in the device containing the mechanical parts 2 and may cause the device to malfunction. By making it difficult for burrs to form at the corner between the polished surface and the second inclined surface 62s, problems caused by burrs are suppressed.

[0076] <Example> In this example, mechanical parts for sample No. 1 and sample No. 2 were fabricated. The primary and secondary densities of the mechanical parts of each fabricated sample were then measured.

[0077] Sample No. 1 The machine part of sample No. 1 was manufactured by the machine part manufacturing method described in Embodiment 1. Specifically, a metal powder was prepared containing 2.0 mass% Cu, 0.8 mass% C, and the remainder being iron and an iron-based alloy, which is an unavoidable impurity. A compacted molded body 6, shown in Figure 6, was then produced. The true density of the metal powder was 7.85 g / cm³. 3 The pressure used to produce the compacted body 6 was 600 MPa. The depth d1 of the first land surface 61r of the compacted body 6 shown in Figure 7 was 0.1 mm and the width w1 was 0.2 mm. The depth d2 of the second land surface 62r shown in Figure 8 was 0.3 mm and the width w2 was 0.2 mm.

[0078] A compacted powder body 6 was sintered to produce a sintered body 7. The sintering temperature was 1130°C and the sintering time was 120 minutes. The first chamfered portion 61 of the sintered body 7 was processed using the jig 9 shown in Figure 9 to form the first edge portion 51. The radius of curvature of the curved surface 51c of the first edge portion 51 was 0.7 mm.

[0079] The first and second porosities of the sintered body 7 were measured by the method shown in Embodiment 1. The first porosity was 5.3%. The first relative density calculated from the first porosity was 100 - 5.3 = 94.7%. The true density of the metal powder was 7.85 g / cm³.3 Therefore, the primary density is 7.43 g / cm³. 3 On the other hand, the second porosity of the sintered body 7 was 11.1%, and the second relative density was 88.9%. The second density calculated from the second relative density was 6.98 g / cm³. 3 These results showed that the density of the first edge 51 was significantly higher.

[0080] Sample No. 2 Sintered body 7 was fabricated using the same method as sample No. 1. In this example, the first edge portion 51 was formed by processing the second chamfer portion 62 with a jig 9. The first and second porosity of sample No. 2 were measured. The first porosity was 11.6%, and the first relative density was 88.4%. The first density, calculated from the first relative density, was 6.94 g / cm³. 3 The second porosity was 11.5%, and the second relative density was 88.5%. The second density calculated from the second relative density was 6.90 g / cm³. 3 The first density was higher than the second density, but the difference between the two was small. This is presumed to be because even when processing areas with a large chamfer depth, such as the second chamfered portion 62, the amount of plastic deformation in the edge region 4c is small. [Explanation of Symbols]

[0081] 1. Machine Assembly 2 Machine parts 20 Sintered body, 21 First surface, 22 Second surface 3 Moving parts 30 Specific orbit 4 First hole 4c edge area, 4h opening 41 Inner surface 5. Opening edge 51 First edge, 51c Curved surface, 51s Inclined surface, 510 Local region 52 Second edge, 52r Land surface, 52s Inclined surface 6. Compacted Powder 6s front page 61 First chamfered section, 61r First land surface, 61s First inclined surface 62 Second chamfered section, 62r Second land surface, 62s Second inclined surface 7 Sintered body 9. Jig 9b columnar part, 9c tip part, 9f flange part, 9p processed part 90 backing plate, 90h through hole d1, d2 depth w1, w2 width

Claims

1. A mechanical part composed of a sintered body of metal powder, The first page, The first hole formed on the first surface, The first hole comprises an annular opening edge portion connecting the inner circumferential surface of the first hole and the first surface, The opening edge includes a first edge that constitutes at least a part of the circumferential direction of the opening edge, The first edge portion includes a curved surface that smoothly connects to the inner circumferential surface. The first density in a predetermined range in the region less than or equal to 0.6 mm from the curved surface is higher than the second density in a predetermined range in the region more than 1 mm from the curved surface. The ratio of the first density to the true density of the sintered body is 94.7% or more. Machine parts.

2. The mechanical part according to claim 1, wherein the ratio of the second density to the true density of the sintered body is 86% or more and 92% or less.

3. The mechanical part according to claim 1 or claim 2, wherein the material of the sintered body is an iron-based alloy.

4. The machine part according to claim 3, wherein the iron-based alloy comprises at least one element selected from the group consisting of nickel, molybdenum, chromium, copper, and carbon.

5. The aforementioned opening edge further comprises a second edge portion that constitutes a part of the circumferential direction of the opening edge, The mechanical part according to claim 1 or claim 2, wherein the second edge portion comprises a flat land surface connected to the inner circumferential surface and an inclined surface connecting the land surface and the first surface.

6. A machine part according to claim 1 or claim 2, The machine component comprises a movable part configured to move between a state in which it is positioned inside the first hole of the machine component and a state in which it is positioned outside the first hole. Machine assembly.

7. The aforementioned movable part is configured to be movable along a specific track, The aforementioned specific track extends in a direction along the first surface and intersects the first hole, The machine assembly according to claim 6, wherein the first edge portion is provided in a position that overlaps with the specific track.

8. Step A involves pressurizing metal powder to produce a compacted molded body having a first surface and a first hole formed on the first surface, Step B involves sintering the aforementioned compacted molded body to produce a sintered body, The process includes step C, which, after step B, applies pressure to at least a portion of the annular edge region surrounding the opening of the first hole using a jig to form a first edge connecting the first surface and the inner circumferential surface of the first hole, The first edge portion has a curved surface that smoothly connects to the inner circumferential surface, In step A, a first chamfered portion and a second chamfered portion are formed in the edge region. In step C, the first chamfered portion is pressed by the jig, The first chamfered portion comprises a first land surface connected to the inner circumferential surface of the first hole, and a first inclined surface connecting the first land surface and the first surface. The second chamfered portion comprises a second land surface connected to the inner circumferential surface and a second inclined surface connecting the second land surface and the first surface. The depth of the first land surface along the axial direction of the first hole is smaller than the depth of the second land surface. Manufacturing method for machine parts.

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