WO2014156979A1

WO2014156979A1 - Sintered machine part and process for producing same

Info

Publication number: WO2014156979A1
Application number: PCT/JP2014/057816
Authority: WO
Inventors: 豪萩本; 勝彦上田; 偉樹中久木; 清彰入江
Original assignee: 日立化成株式会社
Priority date: 2013-03-25
Filing date: 2014-03-20
Publication date: 2014-10-02
Also published as: CN105358274B; JP6065105B2; CN105358274A; JPWO2014156979A1

Abstract

Provided are: a sintered machine part which is composed of a sintered alloy and which comprises both a body that has a working surface and a pin that is formed integrally with the body and that protrudes from the working surface; and a process for producing the same. The root of the pin is enlarged so that the side surface of the pin curves in the neighborhood of the root and thus connects smoothly with the working surface of the body. The sintered alloy has a metal structure which comprises a matrix having a density ratio of 80 to 96% and a densified layer having a density ratio that is 96% or more and that is higher than the density ratio of the matrix, while the densified layer is provided in the side of the pin so as to exhibit a depth of 0.3mm or more at the maximum-stress position at which the stress due to the bending load applied to the pin is the maximum. This process includes: prescribing a net shape of a sintered machine part which has a pin having a shape described above; preparing a sintered body of a sintered alloy having a density ratio of 80 to 96%, the side of the sintered body having a bulge which protrudes from the net shape and which is formed by the addition of excess alloy in a region such that the stress in the region due to the bending load applied to the pin is estimated to be high; cold-repressing the excess alloy of the sintered body so as to form the net shape; and thus forming a densified layer in the side of the pin.

Description

Sintered machine parts and manufacturing method thereof

The present invention relates to a sintered machine part having a pin projecting from one surface of a main body and a method for manufacturing the same, and more particularly to a sintered machine part in which breakage due to a load acting on the pin is suppressed and a method for manufacturing the same.

Powder metallurgy is a technology for manufacturing metal products by solidifying powder powders made of metal powders into a predetermined shape and dimensions and heating them at a temperature that does not melt them, thereby bonding powder particles firmly. Therefore, it is being applied to automobile machine parts and various industrial machine parts because it can be shaped into a near net shape and is suitable for mass production.

Sintered parts by the powder metallurgy method generally have a drawback in that the strength between the powder particles when the raw material powder is compression-molded remains as pores after sintering, so that the strength is lower than that of the melted material. For this reason, when a mechanical part having a pin protruding from the body is manufactured by the powder metallurgy method, when a high load acts on the pin and stress concentrates on the root of the pin, the pin is rooted due to its low strength. Break from. For example, a gear change cam part constituting a transmission mechanism of a motorcycle is a machine part 1 as shown in FIG. 1, and has six pins 2 projecting from one surface of a substantially hexagonal main body 3. The six pins 2 receive a high load at the time of gear change.

In order to prevent the breakage of the pin while applying the powder metallurgy method to the manufacture of a machine part in which a high load acts on such a pin, the pin 2 made of molten steel is press-fitted into the main body 3 made of a sintered body. The machine part 1 is configured. That is, the mechanical component 1 as shown in FIG. 1 includes a step of forming each pin 2 from molten steel, a step of forming a main body 3 made of a sintered body, and a step of press-fitting the pin 2 into the hole 4 of the main body 3. And manufactured by.
In the manufacture of mechanical parts as described above, it is necessary to separately prepare pins manufactured from molten steel, and since a process of pressing the pins into the main body made of a sintered body is added, it takes time and effort. Cost increases. That is, the advantage of the powder metallurgy method that can be formed into a near net shape with few steps and is suitable for mass production is impaired.

On the other hand, as an example of manufacturing a machine part as shown in FIG. 1 with a sintered body without using molten steel, the sintered body formed by sintering and sintering the raw material powder to a high temperature is heated to a high temperature. It is known that pins are formed by plastic flow by forging (so-called sintered forging) (see Non-Patent Document 1 below).

In the forming method in which the pins are formed by such metal flow (plastic flow) by sintering forging, the density ratio of the entire pins can be increased to the same level as that of the molten steel, so that breakage from the root of the pin portion is prevented.
However, such a method requires equipment for heating a sintered body to be a forging material and equipment for heating a mold, and requires heating costs for the sintered body and the mold. In addition, the mold used for hot forging is expensive and has a short life, which increases the manufacturing cost accordingly.

As described above, in a mechanical component in which a high load acts on a pin protruding from the main body, the entire mechanical component including the pin is composed of a sintered body, and a sintered mechanical component in which breakage of the pin is suppressed is obtained. It is desired. In addition, a manufacturing method that can obtain such a sintered machine component at a low cost without heating the sintered body and the mold is desired.
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, have a pin protruding from the main body, and have a sintered machine part in which the breakage of the pin is suppressed while being entirely composed of a sintered body, and such a sintered machine It is to realize a manufacturing method capable of providing parts at low cost without using expensive equipment.

In order to solve the above problems, the present inventors have examined, in a mechanical component in which the pin protrudes from the main body and a high load acts on the pin, even if the entire pin is not formed at a high density, It has been found that breakage of the pin can be suppressed if the density is increased by locally densifying only a specific part of the pin.

According to one aspect of the present invention, a sintered machine component is composed of a sintered alloy and has a main body having a working surface and a pin formed integrally with the main body and protruding from the working surface. The pin has an axial shape that expands at the base so that the side surface of the pin smoothly curves near the base and continues to the working surface of the main body, and constitutes the sintered machine part The sintered alloy has a metallographic structure having a matrix having a density ratio of 80 to 96% and a densified layer having a density ratio of 96% or more and a higher density ratio than the matrix, and the densified layer includes: The gist is that the pin is provided on the side surface of the pin so that the depth is 0.3 mm or more at the maximum stress position where the stress generated from the bending load applied to the pin is maximum.

The pin protrudes perpendicularly from the working surface and is positioned between the pin main portion and the pin main portion and the main body so that the side surface of the pin main portion and the working surface are continuous. A flare base having a concavely curved side surface, wherein the stress maximum position is on the side surface of the flare base, and the region where the densified layer is formed is at least one of the side surfaces of the flare base. Part. The entire portion excluding the densified layer is composed of the matrix, and the density ratio of the outermost surface of the densified layer is preferably 97% or more, and the flare base is curved on the side surface in the axial cross section of the pin. It has the shape of a curved rotating body showing
The flare base may be configured to have a shape of an arc rotator or an elliptic arc rotator whose side faces indicate an arc or an elliptic arc in the axial section of the pin, or the flare base may be in the axial section of the pin. The side surface may partially include a truncated cone portion having a straight line, and the side surface of the flare base portion may be configured to exhibit a curve partially including the linear portion in the axial cross section of the pin. The angle between the straight line indicated by the side surface of the truncated cone part and the axial direction of the pin in the axial cross section of the pin is preferably 45 ° or less.
When the main body has a substantially flat plate shape with the working surface being flat and has a back surface formed with a recess at a position corresponding to the pin on the opposite side of the working surface, a uniform sintered body is obtained. It is effective for formation, and the depth of the recess is preferably 10 to 70% of the thickness of the main body.

According to another aspect of the present invention, there is provided a method for manufacturing a sintered machine component, comprising: a main body having a working surface; and a pin that is integrally formed with the main body at a base and protrudes from the working surface. Stipulates the net shape of the sintered machine part with an axial shape that expands at the base, and the side surface of the pin smoothly curves near the base and is continuous with the working surface of the body In the net shape, there is a shape in which surplus thickness is added to a region including the maximum stress position where the stress generated from the bending load applied to the pin is highest, and the side surface of the pin bulges from the net shape, A sintered body composed of a sintered alloy having a density ratio of 80 to 96% is prepared, and the excess thickness of the sintered body is recompressed in the cold and formed into the net shape. Density ratio is 96% or more at high density ratio The densified layer, the depth in the stress maximum position is summarized in that with the formation on the side surface of the pin so that the above 0.3 mm.

The re-compression of the surplus is preferably performed at a pressure of 50 to 1200 MPa. The main body has a substantially flat plate shape with the working surface being flat, and the sintered body has a back surface formed with a recess at a position corresponding to the pin on the opposite side of the working surface. It is advantageous for uniform molding. The depth of the recess is preferably 10 to 70% of the thickness of the main body.

According to the configuration of the present invention, in a mechanical component in which a high load acts on a pin protruding from the main body, the entire mechanical component including the pin is made of a sintered material, and only a portion where stress is concentrated is made dense. It is possible to suppress breakage of the pins and to supply machine parts at low cost. In addition, in the manufacturing method of the present invention, the surplus is densified by plastic working that is recompressed in the cold, so there is no need for equipment for heating the sintered body and the mold, and the manufacturing cost is greatly reduced. it can.

It is a schematic diagram which shows an example of the conventional sintering machine component used as a gear change component in the transmission mechanism of a motorcycle, and (a) is a top view of the sintering machine component in which the plane from which the pin protrudes is arranged on the upper side. , (B) is a cross-sectional view taken along line AA in FIG. 1 (a), and (c) is a perspective view. It is a schematic diagram showing an example of a sintered machine component of the present invention used as a gear change component in a transmission mechanism of a motorcycle, and (a) is an upper surface of a sintered machine component in which a plane from which a pin protrudes is arranged on the upper side. FIG. 2B is a cross-sectional view taken along the line BB in FIG. 2A, and FIG. FIG. 2 shows an example in which the side surface of the flare base of the pin in the sintered machine part of FIG. 2 shows an arc in the axial cross section, and (a) and (b) are schematic diagrams in which the portion C of FIG. 2 (b) is enlarged. FIG. 3C is a graph of stress distribution showing the relationship between the distance x from the main body on the side surface of the pin and the stress σx, corresponding to FIG. 3B. FIG. 2 shows another example in which the side surface of the flare base portion of the pin in the sintered machine part of FIG. 2 shows an arc in the axial cross section, and (a) and (b) are schematic diagrams showing an enlarged portion C of FIG. FIG. 4C is a stress distribution graph showing the relationship between the distance x from the main body on the pin side surface and the stress σx in correspondence with FIG. FIG. 2 shows an example in which the side surface of the flare base of the pin in the sintered machine part of FIG. 2 shows an elliptical arc in the axial cross section, and (a) and (b) are schematic diagrams in which the portion C of FIG. FIG. 5C is a stress distribution graph showing the relationship between the distance x from the body on the side surface of the pin and the stress σx in correspondence with FIG. FIG. 2 shows another example in which the side surface of the flare base of the pin in the sintered machine part of FIG. 2 shows an elliptical arc in the axial cross section, and (a) and (b) are enlarged views of part C of FIG. FIG. 6C is a graph of stress distribution showing the relationship between the distance x from the main body on the side surface of the pin and the stress σx in correspondence with FIG. FIG. 2 shows still another example in which the side surface of the flare base portion of the pin in the sintered machine part shown in FIG. 2 shows an elliptical arc in the axial section, and (a) and (b) show an enlarged portion C in FIG. 2 (b). (C) is a graph of stress distribution showing the relationship between the distance x from the main body on the side surface of the pin and the stress σx in correspondence with FIG. 7 (b). 2 shows an example in which the side surface of the flare base portion of the pin in the sintered machine part of FIG. 2 shows a curve including a straight line in part in the axial cross section, and (a) and (b) show part C of FIG. FIG. 8C is a stress distribution graph showing the relationship between the distance x from the body on the side surface of the pin and the stress σx, corresponding to FIG. 8B. (A) is a schematic diagram which shows the example of a shape of a sintered compact raw material, (b) is an enlarged view of the part D in Fig.9 (a). (A) is a schematic diagram which shows an example of a structure of the metal mold | die apparatus which recompresses a sintered compact raw material, (b) is an enlarged view of the part E in Fig.10 (a). (A), (b) is a schematic diagram explaining the recompression state of a sintered compact raw material.

(Convention points of the invention)
In a machine part in which a columnar pin projects vertically from a flat working surface, when a load is applied to the pin, the bending moment due to the load applied to the pin is maximized at the base of the pin, and the bending moment is opposite to the bending direction. Acts as a tensile stress on the side of the pin on the side. As a result, the tensile stress acts intensively on the corners of the pin base where the pin side surface and the action surface are discontinuous, and the fracture proceeds from the surface of the root.
Therefore, in the present invention, first, a pin is formed in an axial shape that expands at the base, and the diameter of the columnar pin main portion having a constant diameter increases from the pin main portion side toward the main body side. The pin is configured to have a flare base. By enlarging the base portion in this way, the volume at the base of the pin is increased, and the strength at the base of the pin is increased accordingly. Further, the flare base is formed in a shape that expands in a morning glory shape so that the side surface of the pin and the working surface of the main body are smoothly continuous. As a result, the stress acts in the flare base and its surrounding area (that is, including the boundary area of the main body adjacent to the flare base and the boundary area of the pin main part adjacent to the flare base). It works effectively to prevent stress concentration at the base of the pin.

Tensile stress increases at the surface of the flare base and the surrounding area. Therefore, in the present invention, secondly, after providing the flare base as described above, the surface is densified in a region where the stress due to the bending load is high, and a high-density layer having a high density is provided. In addition, the strength is higher than the strength of the sintered body determined by the shape. Thereby, it is possible to resist the progress of fracture due to tensile stress. When the flare base is configured so as to have the densified layer as described above, the breakage at the flare base can be avoided.

Based on the above findings, the sintered machine part of the present invention specifically has a main body with a density ratio of 80 to 96% and at least one pin protruding on the flat working surface of the main body. The side surface of the pin is formed so as to be smoothly curved into a concave curved surface near the base and to be continuous with the working surface of the main body. Further, in the region where the stress due to the bending load applied to the pin is high, that is, the region including at least a part of the side surface of the flare base, a highly densified layer having a density ratio of 96% or more is formed. The The densified layer is formed so that the depth from the surface is at least 0.3 mm at a position where the stress due to the bending load is highest.

In addition, the method for manufacturing a sintered machine part of the present invention includes a main body and a pin protruding from the working surface of the main body, and the pin has an axial shape with an enlarged base, and the side surface of the pin and the working surface of the main body The net shape of the sintered machine part is set as a shape that curves smoothly so that it is smoothly continuous. It is made of sintered material with a density ratio of 80 to 96%. ) In the flare base, and a sintered body having a shape expanded from the net shape is prepared, and the excess thickness of the sintered body is recompressed in the cold and formed into a net shape. A highly densified layer having a high density ratio and a density ratio of 96% or more is formed. By this recompression, the root is formed into a curved surface that smoothly connects the side surface of the pin and the working surface of the main body, and at the same time, a densified layer is formed at the position of the surplus. The depth of the densified layer can be adjusted by the thickness of the surplus, and the surplus thickness of the sintered body is adjusted so that the depth of the densified layer is 0.3 mm or more at least at the position where the stress due to bending load is highest. The thickness is adjusted.

Generally, sintered machine parts having a density ratio of 80 to 96% are used, and most of the main body and pins of the sintered machine parts of the present invention are also sintered with such a general density ratio of 80 to 96%. Composed of bond money. Then, a densified layer is provided by recompressing the surface at the flare base, and the side surface of the pin and the working surface of the main body are formed into a smooth concave curved surface so as to continue through the flare base as described above. Accordingly, when local recompression is applied to the sintered material, the metal structure becomes a multiphase structure having a matrix composed of the original sintered material and a compressed densified layer.
The formation of the densified layer does not produce a clear boundary between the matrix and the densified layer, which are continuous with the same sintered composition and are not discontinuous. The densified layer is determined as a portion where the density ratio calculated from the porosity is higher than that of the matrix and is 96% or more based on the porosity in the metal structure cross section of the sintered machine part. That is, when the density ratio in the matrix is less than 96%, the densified layer is a portion where the density ratio is 96% or more, and when the density ratio of the matrix is 96%, the density ratio range is higher than 96%. It is a densified layer. The densified layer is formed so that the depth from the surface is at least 0.3 mm at a position where the stress due to the bending load is highest. A highly densified layer having a depth of 0.3 mm or more has a remarkable improvement in durability against stress. When the depth of the densified layer is less than 0.3 mm from the surface, or the density ratio is 96%. If it is smaller, the durability against the tensile stress on the surface of the flare base caused by the bending load is lowered. Accordingly, it is extremely preferable to form the film so that the depth is 0.3 mm or more in a band having a certain width including the position where the stress due to the bending load is maximized.

The greater the depth of the densified layer, the greater the strength of the flare base, and there is no upper limit. That is, the case where the flare base is densified to the center of the pin is also within the scope of the present invention. However, if the densified layer is to be formed deeply, the machining cost increases accordingly, and the machining cost increases. Further, it is not necessary to strengthen beyond the minimum strength that can resist the bending moment generated by the load applied to the pin. The depth of the densified layer may be up to about 75% of the radius of the pin.

The densified layer may be formed over the entire area of the flare base and its periphery, but at least the region including the position where the tensile stress due to the bending load is the highest among the flare base and its periphery (for example, FIGS. 3 to 8). (B), the region shown as the region S) may be formed. The stress due to the bending load can be obtained by a calculation method generally used in material mechanics (details will be described later), and by obtaining the stress distribution on the side surface of the pin, the position where the stress is highest (hereinafter, the maximum stress position) And indicated by a symbol P in the figure). The stress distribution and the maximum stress position on the side surface of the pin vary depending on the shape of the flare base. As can be understood from FIGS. 3C to 8C, the maximum stress position has a circular shape that has a constant axial height and circulates around the side surface of the pin, and the densified layer has the maximum stress position. It is formed on the side surface of the pin in the shape of a band including it. For example, when the spread in the radial direction is larger than the height of the enlarged bottom portion as shown in FIG. 6, the maximum stress position is located near the upper end of the flare base and very close to the pin main portion, but the stress maximum The position is always on the side of the flare base. Accordingly, the region where the densified layer is formed includes at least a part of the side surface of the flare base.

Since the stress due to the bending load acts in a distributed manner throughout the flare base, as the height of the flare base (the length in the axial direction) increases, the stress is widely distributed and the maximum value of stress (at the maximum stress position) (Stress value) decreases. On the contrary, when the height of the flare base is small, the stress is not dispersed so much, so the maximum value of the stress becomes high, and high stress acts around the stress maximum position (see FIGS. 3 and 4). That is, when the flare base is lowered, the range in which a stress of a certain level or more acts is widened. In this case, even if a densified layer is formed over the entire side surface of the flare base, if the bending moment is greater than the strength at the neck (the lower end of the pin main part including the boundary with the flare base) connected from the flare base to the pin main part, The action of tensile stress at the neck of the pin increases and breaks.
Therefore, it is recommended that the flare base is provided to have a certain height or more, preferably 0.1 mm or more. Alternatively, as another countermeasure, breakage of the pin can be suppressed by forming a densified layer on the neck. When a densified layer is formed on the neck, if the densified layer on the flare base and the densified layer on the neck are formed separately, the stress acts between the densified layer on the flare base and the densified layer on the neck. Therefore, it is formed so that the densified layer of the flare base and the densified layer of the neck are continuous. Note that, at the position where the distance from the boundary with the flare base portion exceeds 0.5 mm on the pin main portion side, the bending moment becomes small and the strength of the sintered material matrix can be resisted. Accordingly, the range in which the densified layer is formed on the neck may be a range up to 0.5 mm from the boundary with the flare base.

As shown in FIG. 5, when the flare base is formed to be long in the axial direction, the stress is widely dispersed, so the maximum value of the stress decreases. On the other hand, since the bending moment increases as the distance (height) from the main body decreases, if the flare base spreads small, the increase in strength at the base is small, so that high stress is generated on the main body side where the bending moment is large. . Therefore, the stress maximum position shifts from the pin main part side to the main body side, and in FIG. 5, approaches the middle of the flare base part. As shown in FIG. 7, when the length is longer in the axial direction and the spread in the radial direction is smaller, the stress distribution is further widened and deflected toward the main body as a whole, and the maximum stress position is on the main body side from the middle of the flare base. Therefore, the densified layer may be formed in a region of the flare base that is deflected toward the main body.

As shown in FIG. 6, when the flare base is formed so as to spread greatly toward the main body, the radius and the radial cross-sectional area of the flare base suddenly increase toward the main body, so that the strength of the portion adjacent to the main body increases. And the stress concerning a pin becomes small in the main body side. In such a case, the stress maximum position is close to the pin main part, so if the densified layer is formed by deflecting to the pin main part side, the densified layer is formed in the region on the main body side where the thickness has increased dramatically. Even if it is not done, the breakage of the pin can be suppressed.
As described above, the densified layer is formed in a band shape in a region where a high stress of a predetermined level or more acts around the maximum stress position in the flare base and its surrounding region. The width of the band-shaped region forming the densified layer can be appropriately changed according to the durability required for the pin, and is determined based on the stress distribution obtained from the pin mechanics in terms of material mechanics. In order to particularly enhance the durability along the direction in which the bending load is applied to the pins, the width in the load direction of the band-like region forming the densified layer may be partially expanded.

Since the tensile stress is maximized at the outermost surface in the flare base and its surrounding area, the densified layer preferably has the highest density ratio at the outermost surface. The method of providing a densified layer by recompression of surplus is a preferable method because such a densified layer having the highest density ratio at the outermost surface is formed. In the formation of the densified layer, the densification may be performed so that the density ratio at least on the outermost surface at the maximum stress position in the flare base and its peripheral region is preferably 97% or more, more preferably 98% or more. Of course, the portion of the pin other than the densified layer (that is, the matrix) has a density ratio of 80 to 96%.

The shape of the flare base is not particularly limited as long as the side surface of the pin and the action surface of the main body are smoothly continuous. That is, the side surface of the flare base has a curved shape (that is, a curved rotating body) in the axial cross section of the pin, and the straight line indicated by the pin main portion side surface and the working surface of the main body is tangent at both ends of the curve. . For example, in the axial cross section of the pin, the side surface of the flare base may have a shape such as an arc rotator or an elliptic arc rotator showing a concave curve such as an arc or an elliptical arc. In these, the side surface of the flare base is an arc rotation surface It becomes a morning glory-like concave curved surface such as an elliptical arc rotation surface. When the shape of the flare base is an arc rotating body, stress concentration is likely to occur when the arc has a small radius. Therefore, the curvature is preferably such that the radius becomes an arc of 0.1 mm or more. On the other hand, if the flare base is excessively formed, the function as a pin becomes difficult. Therefore, the curvature is preferably such that the radius (the height of the flare base) becomes an arc of 30% or less of the height of the pin.

Further, as another flare base shape, as shown in FIG. 8, it may be formed so as to include one or a plurality of truncated cone parts between the pin main part and the main body. The truncated cone has a shape in which the side surface is a straight line in the axial cross section. That is, the flare base may have a shape such that the side surface of the flare base in the axial section shows a curve partially including one or more straight portions. However, since the side surface of the flare base portion is continuous with the side surface of the pin main portion and the action surface of the main body, the upper and lower end portions of the side surface of the flare base portion are configured as curves in contact with the side surface of the pin main portion and the action surface in the axial section. . That is, the flare between the pin main portion and the truncated cone portion and between the truncated cone portion and the main body is smoothly continuous with a concave curved surface portion having a curved surface such as an arc in the axial cross section of the pin. It is necessary to configure the base so that stress concentration does not occur between the pin main part and the truncated cone part and between the truncated cone part and the main body. In addition, in the case of providing a plurality of truncated cone parts, it is necessary to smoothly connect with a concave curved surface part that is a curved line such as an arc in the axial section so that stress concentration does not occur between the truncated cone parts. . Accordingly, the flare base in this case has a shape in which the upper and lower sides of each of the one or more truncated cones are sandwiched between curved rotating bodies. When the truncated cone portion is formed, if the angle of the inclined surface with respect to the pin becomes excessive, it becomes difficult to form a densified layer on the pin main portion side due to recompression of the surplus. Therefore, the angle of the slope is preferably 45 ° or less with respect to the axial direction. In the flare base having the above-described shape, the stress due to the bending load is high near the upper end of the flare base and the neck of the pin main part, and the maximum stress position is on the curved rotating body adjacent to the pin main part.
As described above, in any of the pins having various shapes of the flare base, the stress maximum position is located on the flare base. Therefore, the region where the densified layer is formed always includes the side surface of the flare base.

In the above-described configuration, only the flare base and its peripheral surface are densified, so the other parts (most of the main body and pins) are composed of a sintered alloy matrix of a raw material sintered body, and the density is The density of the raw material sintered body is maintained.

A sintered machine part having a flare base in which the side surface of the pin and the working surface of the main body as described above are smoothly continuous and having a densified layer formed in a region where stress is increased is manufactured as follows. be able to.

First, the net shape of sintered machine parts is specified. In other words, it has a main body having a working surface and a pin that is formed integrally with the main body at the base and protrudes from the working surface so that the side surface of the pin is smoothly curved near the base and is continuous with the working surface of the main body. The net shape is defined as a shape that forms a pin having an axial shape that expands at the base. Then, a sintered body is prepared which is formed of a sintered alloy matrix that constitutes a large part of the sintered machine part and substantially has a shape in which a net shape is added with extra densification surplus. In other words, this sintered body is prepared to a density ratio of 80 to 96%, and a shape obtained by adding a surplus for forming a densified layer to the net shape of the sintered machine part is added in advance. Specifically, the sintered body has a main body and a pin protruding from the working surface of the main body, and the pin includes a pin main portion and a flare base that expands toward the main body, and further includes a flare base. In addition, the peripheral side surface has a surplus corresponding to the depth of the densified layer to be formed in the range where the densified layer is formed, as compared to a curved surface in which the side surface of the pin main part and the working surface of the main body are smoothly continuous. Is formed into a shape that expands (see, for example, FIG. 9B). The surplus is provided in a region including the stress maximum position where the stress due to the bending load increases, and the thickness of the surplus is determined so that the depth of the densified layer formed by subsequent recompression is at least at the stress maximum position. The thickness is set to be 0.3 mm or more. Since the depth and density ratio of the densified layer to be formed vary depending on the thickness of the surplus, the surplus thickness is set so that a portion where the density ratio is compressed to 96% or more has a suitable depth. It is appropriately set, and is generally about 30 to 150% of the depth of the densified layer to be provided.

Next, when the surplus of the sintered body is recompressed to form the flare base and its peripheral side into a shape in which the side surface of the pin and the working surface of the main body are smoothly continuous (ie, net shape), Is plastically deformed so as to be pushed toward the inside of the sintered body, whereby the pressed surface is compressed and densified from the matrix to form a highly densified layer. The means used for recompression should just be what can press the surplus of a sintered compact. Since the use of the mold apparatus is advantageous in terms of machining accuracy and workability, in this case, when the net shape is defined, a mold (see FIG. 10) in which the net shape is reflected in the cavity shape is prepared in advance. To do. Since the sizing mold is a mold that constitutes a cavity of the net shape, it is suitable for recompression of excess wall.
In this way, by preparing a sintered body having a surplus and recompressing the surplus, a sintered machine part having the above-described densified layer can be obtained. The sintered machine part has a metal structure in which all parts except the densified layer are formed of a sintered alloy matrix. When the density ratio of the sintered body is 96%, the density ratio of the portion densified by re-compression of the surplus is always higher than the density ratio of the sintered body of 96%. In the case of less than 96%, if the surplus is thin, the density ratio may be less than 96% even when densified. That is, the lower the density ratio of the starting sintered body, the thicker the surplus thickness provided.

Due to the recompression of the surplus, the surplus surface becomes at least part of the surface of the densified layer, that is, the surface of the region including the flare base and its periphery. Since this surface has the highest degree of processing and is in the most dense state, the densified layer formed by recompression is extremely effective in adding tensile strength against bending loads.

When recompressing the sintered body provided with the surplus, the punch is first brought into contact with the surplus, and when the surplus is pressed and compressed by plastic deformation, the punch comes into contact with the main body of the sintered body ( (See FIG. 11). That is, the pressing area to which the punch applies pressure differs between the initial stage and the final stage of recompression. Even if the pressure per unit area by the punch is small, when the punch pressing area is small, the press load as the whole punch is concentrated on the small pressing area. Therefore, at the initial stage of re-compression where the press load is intensively applied to the surplus wall with a small area, even if the pressure per unit area is a small pressure of about 50 MPa, the plastic deformation of the surplus is sufficiently performed at room temperature. Can do. However, if the surplus area is not so small compared to the maximum pressing area of the punch, a high pressure of about 1200 MPa may be required to perform plastic deformation of the surplus.

Generally, the pressure required for cold forging with large work deformation is 1500 to 2500 MPa, and machining the entire part at a pressure lower than this is limited to work with extremely small deformation such as dimensional correction. In contrast, the densification in the vicinity of the flare base in the present invention is a partial recompression process, and only a surplus formed in a part of the sintered body is locally plastically processed to be a densified layer. Therefore, even if the deformation near the surplus is large, the process can be performed at a low pressure of about 50 to 1200 MPa. In the manufacture of sintered machine parts, generally, after the sintering process, cold recompression including sizing (deformation of about 0.1 mm or less) for dimensional correction or the like is performed. It can be easily carried out at room temperature using a mold, and no conventional equipment for heating a sintered body or equipment for heating a mold is required. Moreover, it can be executed in parallel when performing cold compression such as sizing.

In the case of the gear change cam part for the transmission mechanism of the motorcycle described above, it is possible to re-compress the surplus with a low pressure of about 200 to 800 MPa, which is generally used in the sizing process of sintered parts. Cost can be extremely low.

Since the above-mentioned recompression process only densifies the location where the surplus is provided, except for the location where the densified layer is formed, it is the same as the sintered body density of the main body, compared to the case of processing the entire pin, There is much less labor and cost.

The process of recompressing the above surplus at room temperature can be carried out without using a sizing mold. For example, the surplus is pushed toward the inside of the sintered body by pressing a rotating or vibrating roller or the like. You may process so that it may push.

As a material composition constituting the sintered body, a composition of various iron-based sintered materials for machine structural parts that can be re-compressed such as sizing is suitable. For example, SMF type 1 (pure iron type), SMF type 2 (iron-copper type), SMF type 3 (iron-carbon type), SMF type 4 (iron-copper-carbon type) as defined in Japanese Industrial Standard (JIS) Z2550 , SMF5 (iron-nickel-copper-carbon), SMF6 (iron-carbon (copper infiltration)), SMF7 (iron-nickel), SMF8 (iron-nickel-carbon), SMS1 (Austenitic stainless steel), SMS2 (ferritic stainless steel), etc., 4100 (iron-chromium-manganese) and 4600 (iron-nickel-molybdenum) of the American Iron and Steel Institute standard (AISI) Examples include iron-based alloy compositions.

In preparing the sintered body, first, a raw material powder having the above material composition is prepared. The raw material powder may be in any form of a mixture of plain metal powder, a mixture of plain metal powder and alloy powder, and alloy powder, for example, iron powder, Single powder of alloying element, mixed powder mixed with graphite powder, etc., iron alloy powder alloyed with each alloying element, and simple powder of alloying element and graphite powder mixed with iron alloy powder A mixed powder or the like is used as a raw material powder.

Using the raw material powder as described above, a green compact having a shape corresponding to the external shape of the above-described sintered body (a shape obtained by adding extra thickness to the net shape) is compression-molded. That is, a green compact is formed in which a pin protrudes from the working surface of the main body, and a surplus is added in the vicinity of the flare base that expands at the base of the pin so that the side surface of the pin and the working surface of the main body are smoothly continuous. . For example, a die having a die hole that forms the outer peripheral shape of the main body, a lower outer punch that has a hole that molds the outer periphery (side surface) of the pin and is fitted into the die hole of the die to mold the working surface of the main body, The space formed by the lower inner punch that is slidably fitted into the hole of the lower and outer punches and forms the top of the pin is filled with the raw material powder to form a flat rear surface opposite to the working surface. The green compact is formed by compressing the raw material powder with the punch, the inner lower punch and the outer lower punch. With respect to the molding conditions at this time, the molding can be performed at a molding pressure of about 400 to 800 MPa, similarly to the molding conditions in the production of general sintered machine parts.
If there is substantially no dimensional change before and after sintering the green compact, the difference in the cavity between the green compact mold and the sintered compact recompression mold (sizing mold) Only meat related parts. In this case, since the molding pressure at the time of compacting is not so different from the pressure for recompressing the sintered body, it is possible to use the mold together by exchanging only the punch for the surplus portion.

In general, while the molding pressure applied to the raw material powder propagates, pressure energy is consumed while the raw material powder is rearranged and plastically deformed, so the density is lowered at the center of the molded body and a so-called neutral zone occurs. It becomes easy. The shape having a pin protruding from the working surface of the main body is a shape in which the height of the main body and the portion having the pin are different and the height of the pin is high, so that the density of the pin is likely to be smaller than that of the main body. For this reason, when the green compact is formed using an upper punch having a shape having a protrusion so that a recess is formed at a position corresponding to the pin on the back surface opposite to the working surface from which the pin protrudes, This is preferable because the thickness of the main body at the protruding position is reduced and the molding density of the pins can be increased. The depth of the recess on the back surface is preferably about 10 to 70% of the thickness of the main body.

The green compact can be sintered under the same conditions as those used in the production of general sintered machine parts. However, when oxidation occurs in the sintering process, the sintered body becomes hard and plastically deforms. Since it becomes difficult, it is preferable to use a non-oxidizing gas atmosphere or a vacuum atmosphere as a sintering atmosphere as a processing material for sintered machine parts. Examples of the non-oxidizing gas include nitrogen gas, nitrogen-hydrogen mixed gas, ammonia decomposition gas, butane-modified gas, and inert gas such as argon. The sintering temperature can be set to about 1000 to 1250 ° C.

In the production of the sintered machine parts of the present invention, after cold recompression processing, quenching treatment such as carburizing quenching and bright quenching is performed as necessary, as is done in ordinary sintered machine parts. , And subsequent heat treatment such as tempering. When quenching is performed, the sintered machine parts are heated above the austenitizing temperature region of the sintered material, so that the close particles around the closed pores are metallurgically bonded in the plastically densified layer. Thus, the strength can be further improved.

(1) Specific example of sintered machine part An example of the shape of the sintered machine part of the present invention is shown in FIG. FIG. 2 shows application to a gear change part used in a transmission mechanism of a motorcycle as an example of a machine part in which a high load acts on a pin protruding from a main body. 2 (a) and 2 (c) are a top view and a perspective view in a state where the working surface of the main body from which the pin protrudes is arranged on the upper side, and FIG. 2 (b) is a cross-sectional view taken along line AA in FIG. FIG. As shown in FIG. 2B, the sintered machine part 10 has a substantially hexagonal star shape with rounded apex angles, and one of the six apex angles has a main body with an apex missing in an arc shape. 11 and six pins 12, and the pins 12 project vertically from a flat working surface 13 (upper surface) on one side of the flat plate-like body 11. The present invention can be applied to a machine part having one or more such protruding pins. The sintered machine component 10 of the present invention has a shape in which each of the pins 12 expands at the base so that the side surface 14 (outer peripheral surface) of the pin 12 and the working surface 13 of the main body 11 are smoothly continuous. It is comprised by the columnar pin main part 12a and the flare base 12b expanded at the root. In addition, the recessed part 16 which has in the back surface on the opposite side to the action surface 13 of the main body 11 is for preventing that a neutral zone produces | generates at the time of compacting.

FIGS. 3 to 7 are enlarged sectional views of part B of FIG. 2B, and show various examples of formation of a densified layer. In these drawings, (a) is a schematic diagram of pore distribution, (b) is a schematic diagram showing formation of a densified layer (area indicated by hatching) having a density ratio of 96% or more, and (c) is a pin 12. 6 is a graph showing the relationship between the axial distance x of the pin 12 and the cross-sectional stress σx when a bending load is applied to.

FIG. 3 shows an example of a flare base 12 b that connects the working surface 13 of the main body 11 and the side surface 14 of the pin 12, and the side surface 14 b of the flare base 12 b is a curved surface showing an arc having a radius R 1 in the axial section of the pin 12. The form is shown. As shown in FIG. 3A, pores are dispersed in the matrix of the sintered body constituting most of the main body 11 and the pin 12, but the densified layer 15 formed on the flare base 12b is plastically deformed. The pores are shrunk or vanished and densified. However, since the sintered body matrix and the densified layer 15 are continuous, the densified layer 15 is expressed as shown in FIG. 3B with a density ratio of 96% as a boundary.

When the side surface 14b of the flare base 12b of the pin 12 is a curved surface showing an ellipse in the axial section (the diameter of the pin in the axial direction is Ra and the diameter of the pin in the radial direction (direction of the working surface 13) is Rb) The stress σx of the cross section of the pin 12 at the axial distance x from the main body 11 when the bending load W is applied to the position of the axial distance L from 11 can be obtained as follows (formula Middle, x: axial distance from the body 11, r: pin radius).
A) At 0 ≦ x <Ra, stress σx = 4 W (L−x) /
π [r + Rb-Rb [1- (x-Ra) ² / Ra ² ] ^1/2 ] ³
B) At Ra ≦ x ≦ L, stress σx = 4 W (L−x) / πr ³

As shown in FIG. 3, when the flare base 12b is formed so that the side surface is a curved surface showing an arc having a radius R1 in the axial section (Ra = Rb = R1 in the above formula), the tensile stress (hereinafter referred to as the bending stress) The region S in which the stress (simply referred to as “stress”) is higher than a certain level is distributed in the upper half of the flare base 12b and the neck of the pin main portion 12a as shown in FIG. 3B, and on the main body 11 side of the flare base 12b. The lower end portion is out of the region S. The maximum stress position P where the stress σx is the highest (the position at the distance x = Xp in FIG. 3C) is on the flare base 12b, and the position is close to the upper end of the flare base 12b and the boundary with the pin main portion 12a. Located slightly below (0.5R1 <Xp <R1).
Therefore, the densified layer 15 having a density ratio of 96% or more is formed on the side surface of the region S where the stress is increased so that at least the depth from the surface of the densified layer 15 at the maximum stress position P is d (0.3 mm) or more. When the is formed, the strength of the base of the pin 12 is improved and breakage of the pin 12 is suppressed. The formation range of the densified layer 15 is, as shown in FIG. 3 (b), a side surface in a range including the upper most part of the flare base part 12b and the lower end part of the pin main part 12a among the flare base part 12b and its periphery. Become. As shown in FIG. 3B, when the densified layer 15 is formed so that the depth of the densified layer 15 is not less than d in all areas S where stress is high, it is very good and the durability is further improved. .

FIG. 4 is an example in which the side surface of the flare base 12b that connects the working surface 13 of the main body 11 and the side surface 14 of the pin 12 is formed so as to show an arc having a radius R2 smaller than the radius R1 in FIG. The region S in FIG. 4B is a region where the stress σx reaches the same level as the region S in FIG.
Even when the flare base 12b is formed as shown in FIG. 4, the stress maximum position P is on the flare base 12b, and the position is close to the upper end of the flare base 12b and slightly below the boundary with the pin main portion 12a. (0.5R2 <Xp <R2). However, since the radius R2 of the arc (that is, the height of the flare base 12b) is small, the stress maximum positions P and Xp are lower than in the case of FIG. 3, and the stress distribution is concentrated in a narrow range near the root of the pin 12. For this reason, the maximum stress σx increases, and the region S where the stress increases becomes wider than in the case of FIG. 3 and reaches the entire area and the neck of the flare base 12b as shown in FIG. 4B. Also in this case, the densified layer 15 has a depth from the surface of the densified layer 15 at least at the maximum stress position P corresponding to the distribution of the region S in which the stress becomes high so that the depth is d (0.3 mm) or more. By forming, the strength of the base of the pin 12 is improved and breakage of the pin 12 is suppressed. Based on the shape of the flare base 12b in FIG. 4, in order to impart durability equivalent to that of the pin 12 in FIG. 3 (b) by forming the densified layer 15, the stress is high as shown in FIG. 4 (b). In the entire region S, the densified layer 15 is formed so that the depth of the densified layer 15 is not less than d, and the range of the densified layer 15 is wider and deeper than in the case of FIG.

5 and 6 show an example in which the flare base 12b is formed so that the side surface 14b of the flare base 12b shows an elliptical arc (major axis R3 / minor axis R4 = 3/2) in the axial section. The ellipse diameter Ra (the height of the flare base 12b) is the major axis R3 in FIG. 5, and the minor axis R4 in FIG. FIG. 7 shows an example in which the flare base 12b is formed so that the side surface 14b of the flare base 12b has a vertically longer elliptical arc (long diameter R3 / short diameter R4 = 4/1) in FIG. The region S in FIGS. 5 to 7 is also a region where the stress σx reaches the same level as the region S in FIG.
In the case of FIG. 5, the region S in which the stress is increased is distributed in the flare base 12 b in the upper portion excluding a part on the lower side (main body 11 side) as shown in FIG. It is biased to the upper side (pin main portion 12a side). Although the stress maximum position P is on the flare base 12b, the position shifts downward toward the main body 11 as compared with the case of FIG. 3, and the boundary (flare base) from the middle of the flare base 12b to the pin main portion 12a. 12b (upper end) (that is, 0.5Ra ≦ Xp <Ra).
In the case of FIG. 6, the region S where the stress increases is distributed in the upper part of the flare base 12b and the neck of the pin main part 12a as shown in FIG. 6B, and the lower part (the main body 11 side) of the flare base 12b. Part) is out of region S. The maximum stress position P is close to the upper end of the flare base 12b and slightly below the boundary with the pin main portion 12a (0.5Ra <Xp <Ra).

In the case of FIG. 7, the stress maximum position P moves further downward as compared with the case of FIG. 5, and is located below the middle of the flare base 12b (that is, 0 <Xp <0.5Ra). The region S where the stress increases is distributed near the center of the flare base 12b, and the upper portion (pin main portion 12a side) and the lower portion (main body 11 side) of the flare base 12b deviate from the region S.

As understood from FIGS. 5 to 7, as the diameter Ra (the axial height of the flare base 12b) increases, the maximum stress position P shifts from the vicinity of the upper end of the flare base 12b to the main body 11 side, and the pin main portion The need to form a densified layer at the lower end (neck) of 12a is reduced. Further, as the diameter Rb (the increase in the radius of the flare base 12b) increases, the stress maximum position P shifts to the pin main portion 12a side, and the necessity of forming a densified layer near the main body 11 decreases. That is, the stress maximum position P is determined by the balance of the diameters Ra and Rb within the range of the flare base 12b. Also in the cases as shown in FIGS. 5 to 7, the depth from the surface of the densified layer 15 is d (0.3 mm) or more at least in the stress maximum position P, preferably in the entire region S where the stress is high. As described above, by forming the densified layer 15 in the region S where the stress becomes high, the strength of the base of the pin 12 is improved and breakage of the pin 12 is suppressed. The region S where the stress becomes high is determined based on the stress distribution as a region where the stress becomes a desired level or more in the stress distribution according to the durability required for the pin 12.

FIG. 8 shows an example in which the side surface 14b of the flare base 12b that connects the main body 11 and the pin 12 partially includes a straight line in the axial section and shows a curve as a whole. In this example, the flare base portion 12b has a shape partially including the truncated cone portion 12c, and as shown in FIG. 8A, the upper portion 12d in which the side surface 14d shows an arc having a radius R5 in the axial cross section, and the truncated cone shape. The part 12c and the lower surface 12e in which the side surface 14e indicates an arc of radius R6 in the axial cross section are constituted. In the axial cross section, the side surface 14c of the truncated cone part 12c shows a straight line, and the side surface 14c of the truncated cone part 12c and the side surface 14a of the pin main part 12a are smoothly continuous via an arcuate side surface 14d having a radius R5. The side surface 14c of the truncated cone part 12c and the working surface 13 of the main body 11 are formed so as to be smoothly continuous via an arcuate side surface 14e having a radius R6. The side surface 14 c of the truncated cone part 12 c is inclined at an angle θ with respect to the axial direction of the pin 12.

In this embodiment, the stress σx of the cross section of the pin 12 at the axial distance x from the main body 11 when a bending load W is applied to the position of the axial distance L from the main body 11 is obtained as follows. (Where x is the axial distance from the body 11, r is the radius of the pin main portion 12a, b is the radius of the bottom of the cone (on the working surface 13) formed by the extension of the side surface 14c and the pin. Difference from the radius r of the main portion 12a, x1: axial height of the upper end of the lower portion 12e, x2: axial height of the upper end of the truncated cone portion 12c, x3: axial height of the upper end of the flare base 12b). The stress distribution is as shown in FIG. 8C, and the region S in FIG. 8 is also a region where the stress σx reaches the same level as the region S in FIG.

a) When 0 ≦ x <x1, σx = 4W (L−x) {R6 (1-sinθ) / cosθ +
r + b- [R6 ^2- (x-R6) ² ] ^0.5 } ^-3 / π
b) When x1 ≦ x <x2, σx = 4 W (L−x) [(−tan θ) x + r + b] ⁻³ / π
c) x2 in ≦ x <x3 σx = 4W ( L-x) {r + R5- [R5 ² - {x-
[R5 (1-cosθ) + bcosθ] / sinθ} ² ] ^−0.5 } ⁻³ / π
d) When x3 ≦ x ≦ L, σx = 4 W (L−x) / (πr ³ )

The form of FIG. 8 is designed so that the angle θ at which the side surface 14c of the truncated cone part 12c is inclined is 30 °. In this case, as shown in FIGS. 8B and 8C, the stress maximum position P Is located near the upper end of the flare base 12b, and the region S where the stress is high is the lower end including the flare base 12b (the truncated cone part 12c, the upper part 12d) and the neck of the pin main part 12a (the boundary with the flare base 12b) ) And the lower part of the flare base 12b (the lower part 12e, the lower part of the truncated cone part 12c) is out of the region S. Even in such a form, the densified layer 15 is formed so that the depth from the surface of the densified layer 15 at least at the maximum stress position P is d (0.3 mm) or more in the region S where the stress is increased. As a result, the strength of the base of the pin 12 is improved and breakage of the pin 12 is suppressed.

As described above, the densification layer 15 has all or part of the flare base 12b and its surrounding area, that is, bending load, so that at least the depth at the maximum stress position P is d (0.3 mm) or more. It is formed in the region S where the stress due to is increased to a certain level or more. The sintered machine component of the present invention is not limited to the above-described embodiment, but in many cases, it is effective to form the densified layer 15 in a range including the boundary between the pin main portion 12a and the flare base portion 12b. It is necessary to form the densified layer 15 near the main body 11 of the flare base 12b when the height of the flare base 12b is small as shown in FIG. Therefore, when the height of the flare base 12b is set to about 1 mm or more, the densified layer 15 is generally formed on the neck of the pin main portion 12a (range from the boundary to 0.5 mm) and most of the flare base 12b. It is possible to cope with it, and the breakage of the pin can be preferably suppressed. In the above-described embodiment, the case where the shape of the pin main portion 12a is a cylindrical shape will be described. However, the present invention can also be applied to a pin having an elliptical column shape or a polygonal column shape. By providing the base, durability against bending load can be imparted.

(2) Specific Example of Method for Manufacturing Sintered Machine Part First, as described above, the net shape of the sintered machine part is formed integrally with the main body having the action surface and the base at the base and protrudes from the action surface. The pin is defined as a shape having an axial shape that expands at the root so that the side surface of the pin bends smoothly in the vicinity of the root and is continuous with the working surface of the main body. Then, a sintered body 10 ′ substantially having a shape obtained by adding the extra thickness 20 to the net shape is prepared.

FIG. 9 shows an example of the shape of a sintered body used as a raw material in the method for manufacturing a sintered machine part of the present invention. The sintered body 10 ′ is formed entirely by a sintered alloy that forms a matrix of the sintered machine part 10, and substantially has a shape obtained by adding the extra thickness 20 to the net shape of the sintered machine part 10. Have. Specifically, the sintered body 10 ′ has a shape in which the pin 12 ′ protrudes from a flat lower surface 13 ′ (corresponding to the working surface 13) on one side of the main body 11 ′, similar to the main body 11 of the sintered machine component 10. The pin 12 ′ includes a pin main portion 12 a ′ and a flare base portion 12 b ′, and a surplus 20 added to the neck portion of the pin main portion 12 a ′ and the side portion of the flare base portion 12 b ′. The pin main portion 12a ′ and the flare base portion 12b ′ are the same as the pin main portion 12a and the flare base portion 12b of the sintered machine part 10 except that the pin main portion 12a ′ and the flare base portion 12b ′ have a single structure without a densified layer. As shown in b), the side surfaces of the pin main portion 12a ′ and the flare base portion 12b ′ are formed so as to bulge by an amount corresponding to the surplus thickness 20. In FIG. 9 (b), the dotted line shows the shape of the flare base 12b of the sintered machine part after recompressing the surplus material 20, that is, the net shape. The surplus thickness 20 is provided in a thickness corresponding to the depth of the densified layer 15 corresponding to the position where the densified layer 15 is formed. Regarding the sintered body 10 ′, the net shape is considered to include a minute error that can be corrected by sizing. The upper surface of the sintered body 10 ′ has a recess 16 ′ corresponding to the recess 16 of the sintered machine part 10.

FIG. 10A shows an example of a mold apparatus for recompressing the sintered body 10 ′ having a shape as shown in FIG. The recompression mold apparatus can be composed of the same parts as the mold used for sizing. Specifically, as shown in FIG. 10A, the mold apparatus includes a die 30 having a mold hole 31 that defines the outer peripheral shape of the sintered body 10 ′, and a lower surface of the main body 11 ′ of the sintered body 10 ′. A lower outer punch 40 having a punch surface 41 defining 13 ′ (corresponding to the working surface 13) and a lower inner punch having a punch surface 46 defining the lower end surface (top surface) of the pin 12 ′ of the sintered body 10 ′. A punch 45, a core rod 50 having an outer periphery 51 that defines the shape of the center hole of the sintered body 10 ', and an upper punch 60 having a punch surface 61 that defines the upper surface of the main body 11' of the sintered body 10 '. . The upper punch 60 has a side surface 62 slidably fitted into the mold hole 31 of the die 30, and the punch surface 61 has a convex portion that defines the concave portion 16 of the sintered machine component 10. The lower outer punch 40 has an outer peripheral surface 44 that is slidably fitted to the die hole 31 of the die 30, and further has a hole 42 that is slidably fitted to the lower inner punch 45 on the outer periphery 47. .

10A forms a net shape of the sintered machine component 10, and the flare base molding surface that defines the side surface of the flare base 12b is formed at the upper end of the hole 42 of the lower outer punch 40. 43. FIG.10 (b) is an enlarged view of the part E which has the flare base shaping | molding surface 43 in Fig.10 (a). The flare base molding surface 43 is shaped into a shape corresponding to the flare base 12b in order to give the sintered body 10 'the shape of the flare base 12b of the sintered machine component 10 by cold compression. That is, the cylindrical hole 42 in contact with the side surface of the pin main portion 12a ′ of the sintered body 10 ′ expands at the upper end portion, and the inner surface of the hole 42 is in contact with the lower surface of the sintered body 10 ′. The flare base molding surface 43 is formed so as to be smoothly curved near the upper end so as to be continuous.

FIG. 11 shows a deformation of the surplus wall 20 when the sintered body 10 ′ is cold-recompressed using a mold apparatus as shown in FIG. 10. When the sintered body 10 ′ is inserted into the cavity of the die 30 of the mold apparatus, the surplus thickness 20 of the sintered body 10 ′ contacts the flare base molding surface 43 of the lower outer punch 40 as shown in FIG. Touch. When the sintered body 10 ′ in this state is pressurized in the vertical direction by the upper punch 60 and the lower inner punch 45, the surplus thickness 20 is pressed by the flare base molding surface 43 of the lower outer punch 40 and enters the sintered body 10 ′. As shown in FIG. 10B, the side surface of the surplus wall 20 is formed on the side surface 14b of the flare base 12b, and the density of the pressed surface is increased to increase the density of the densified layer 15. A flare base portion 12b and a neck portion are formed on the sides. Thereby, the sintered machine part 10 is obtained from the sintered body 10 ′, and the density of the densified layer 15 is highest on the outermost surface. The side surface shape of the flare base 12b of the sintered machine component 10 is determined by the flare base molding surface 43 of the lower outer punch 40, and the range and depth in which the densified layer 15 is formed are the surplus of the sintered body 10 '. 20 corresponds to the range and size (thickness) provided, so that the flare base 12b of the sintered machine component 10 and the state in the vicinity thereof can be arbitrarily determined by the flare base molding surface 43 and the surplus wall 20 of the sintered body 10 ′. Can be controlled.

The above-described manufacturing method is an example of a form in which the surplus meat 20 is recompressed using a sizing process, and this form contributes to an improvement in cost performance in that an additional recompression process is unnecessary. However, the manufacturing method of the present invention is not necessarily limited to the above-described form. For example, a method (so-called rolling or the like) that causes a plastic deformation of the surplus by pressing a rotating or vibrating roller or the like against the surplus 20 is used. Can be implemented.

Hereinafter, the present invention will be described in more detail by way of examples.
In an iron-based alloy powder having a composition consisting of Ni: 2%, Mo: 1.5%, balance: Fe and unavoidable impurities, the graphite powder is 0.3% of the total amount and the zinc stearate powder is the total amount. The raw material powder was prepared by mixing the graphite powder and the zinc stearate powder so as to be 0.6%.

The flare base 12b of the pin (length: 6 mm, pin main portion 12a radius r: 2 mm) is an arc rotating body whose side surface shows an arc (radius R1 = 2 mm) in the axial section as shown in FIG. 9 is defined as a net shape of a sintered machine part, and a compacting die for preparing a green compact having a shape obtained by adding the surplus wall 20 to the net shape as shown in FIG. Five types of thicknesses (at the stress maximum position P) were prepared in a range of 0 to 0.6 mm.
For each mold, the raw material powder in an amount that gives a compact density of 7.15 Mg / m ³ is weighed and filled, and compacted to produce a green compact, which is repeated to obtain sample numbers 1 to 4 A plurality of green compacts were prepared. The obtained green compact was put into a sintering furnace having an atmosphere of H ₂ : 5% by volume and N ₂ : 95% by volume, heated at 1195 ° C. for 120 minutes for sintering, and then the sintering furnace was cooled. The sintered body was taken out.

Furthermore, as a recompression mold apparatus that constitutes the cavity of the net shape, a mold apparatus having a configuration as shown in FIG. 10 is prepared, and by using this, sintering of sample numbers 1 to 4 obtained above is performed. By performing cold recompression of the body surplus at a pressure of 250 MPa, molding the side surfaces of the pins and forming a densified layer, a plurality of sintered machine parts of sample numbers 1 to 4 were produced. . For each sample, using one sintered machine part, the density ratio in the vicinity of the flare base is obtained based on the pore distribution in the axial section of the pin, and the stress maximum position P (axial distance x from the body x = about 1). .6 mm), the depth of the densified layer was measured. As a result, a densified layer similar to FIG. 11B is formed, and the depth of the densified layer of the sintered machine part depends on the size of the surplus of the sintered body as shown in Table 1. It was 0 to 1.0 mm.
Moreover, when another sintered machine part was prepared for each sample, a load was applied to the tip of the pin using an autograph, and the breaking load of the pin was measured, the results shown in Table 1 were obtained.

(Table 1)
Sample number Depth of densified layer (mm) Breaking load of pin (kN)
1 0.0 3.8
2 0.1 4.1
3 0.3 6.0
4 0.5 6.1
5 1.0 6.3

From Table 1, the sintered machine part of Sample No. 1 that does not form a densified layer on the side surface of the flare base has a pin breaking load of 3.8 kN, but the depth of the densified layer as in Sample Nos. 2 to 4 It can be seen that the breaking load increases as the thickness increases, and in particular, when the depth of the densified layer increases from 0.1 mm to 0.3 mm, the breaking load significantly increases. Moreover, the increase in the breaking load is moderate in the region where the depth of the densified layer is 0.3 mm or more. From this, it is understood that a densified layer having a densified layer depth of 0.3 mm or more is very effective in suppressing pin breakage.

When the sintered machine part of the present invention is used as a machine part in which a high load acts on a pin protruding from the main body, such as a gear change part constituting a transmission mechanism of a motorcycle, breakage of the pin is suppressed. Therefore, it contributes to the supply of machine parts with excellent durability. In addition, since the densified layer is formed only in a portion having high stress and the structure is densified, it can be easily manufactured, and an inexpensive mechanical component having excellent durability can be provided.

Claims

A sintered machine component comprising a sintered body and having a working surface and a pin integrally formed with the body and projecting from the working surface,
The pin has an axial shape that expands at the base so that the side surface of the pin is smoothly curved near the base and is continuous with the working surface of the main body,
The sintered alloy constituting the sintered machine part has a metallographic structure having a matrix with a density ratio of 80 to 96% and a densified layer with a density ratio of 96% or more and a higher density ratio than the matrix. The densified layer is a sintered machine part provided on the side surface of the pin so that the depth is 0.3 mm or more at the maximum stress position where the stress generated from the bending load applied to the pin is maximum.
The pin protrudes perpendicularly from the working surface and is positioned between the pin main portion and the pin main portion and the main body so that the side surface of the pin main portion and the working surface are continuous. A flare base having a concavely curved side surface,
2. The sintered machine part according to claim 1, wherein the stress maximum position is on a side surface of the flare base, and the region where the densified layer is formed includes at least a part of the side surface of the flare base.
The entire portion excluding the densified layer is composed of the matrix, and the density ratio of the outermost surface of the densified layer is 97% or more,
3. The sintered machine part according to claim 2, wherein the flare base portion has a shape of a curved rotating body in which the side surface is curved in an axial section of the pin.
3. The sintered machine part according to claim 2, wherein the flare base has a shape of an arc rotator or an elliptic arc rotator whose side faces indicate an arc or an elliptic arc in an axial section of the pin.
The flare base portion partially includes a truncated cone portion having a straight side surface in the axial cross section of the pin, and the side surface of the flare base portion exhibits a curve partially including the linear portion in the axial cross section of the pin. The sintered machine part according to claim 2.
The sintered machine part according to claim 5, wherein an angle between a straight line indicated by a side surface of the truncated cone part and an axial direction of the pin in an axial section of the pin is 45 ° or less.
7. The main body according to claim 1, wherein the main body has a substantially flat plate shape with the working surface being flat, and has a back surface formed with a recess at a position corresponding to the pin on the opposite side of the working surface. 2. A sintered machine part according to item 1.
The sintered machine part according to claim 7, wherein the depth of the recess is 10 to 70% of the thickness of the main body.
A main body having a working surface; and a pin formed integrally with the main body at the base and projecting from the working surface, the pin having an axial shape expanding at the base, and a side surface of the pin is rooted As a shape that smoothly curves in the vicinity and is continuous with the working surface of the main body, the net shape of the sintered machine part is defined,
In the net shape, there is a shape in which surplus thickness is applied to a region including the maximum stress position where the stress generated from the bending load applied to the pin is highest, and the side surface of the pin bulges from the net shape, and the density ratio Prepared a sintered body composed of 80-96% sintered alloy,
The excess thickness of the sintered body is recompressed cold and formed into the net shape, and a dense layer having a density ratio of 96% or more than that of the sintered body is deepened at the maximum stress position. A method for manufacturing a sintered machine component, comprising forming the pin on a side surface so that the thickness is 0.3 mm or more.
The method for manufacturing a sintered machine part according to claim 9, wherein the recompression of the surplus is performed at a pressure of 50 to 1200 MPa.
The main body has a substantially flat plate shape with the working surface being flat, and the sintered body has a back surface formed with a recess at a position corresponding to the pin on the opposite side of the working surface. A method for producing a sintered machine part according to 9 or 10.
The method for manufacturing a sintered machine part according to claim 11, wherein the depth of the recess is 10 to 70% of the thickness of the main body.