JP6555679B2 - Manufacturing method of iron-based sintered parts and iron-based sintered parts - Google Patents

Description

  The present invention relates to a method for manufacturing a sintered part and a sintered part. In particular, the present invention relates to a method for manufacturing a sintered part having excellent productivity.

  Sintered bodies (sintered alloys) formed by sintering compacts of metal powders such as iron powder are used for automobile parts and machine parts. Examples of such sintered alloy parts (hereinafter simply referred to as “sintered parts”) include sprockets, rotors, gears, rings, flanges, pulleys, vanes, bearings, and the like. In general, sintered parts are manufactured by pressing a raw material powder containing metal powder to produce a green compact (green compact) and sintering it. Accordingly, machining is performed as a finishing process.

  By the way, some sintered parts have through holes. For example, there is a part in which a through hole (eg, an oil hole) extending from an outer peripheral surface to an end surface or an inner peripheral surface is formed. About such components, since a through-hole cannot be integrally formed with respect to a compacting body at the time of shaping | molding, it drills with a drill after sintering (refer patent document 1).

  A typical drill used for drilling has a V-shaped cutting edge at the tip. In the case of a cemented carbide drill, the tip angle of the cutting edge is often set to about 130 ° to 140 °.

JP 2006-336078 A

  When drilling a sintered part with a drill, drilling after sintering is difficult, and productivity is low.

  Sintered parts are hard because the metal powder particles are firmly bonded by diffusion bonding and alloying by sintering. Therefore, when drilling a sintered part with a drill, the cutting resistance is high and it is difficult for the drill to enter. Therefore, cutting is difficult, processing takes time, and the tool life is shortened. In addition, since the resistance when the drill bites is high, it is difficult to obtain a stable machining hole accuracy such as the drill is likely to swing. Further, since the cutting resistance is high and the thrust load is high, burrs are likely to occur along the opening edge on the outlet side from which the drill comes out when the through hole is formed. When the drill penetrates, the thickness of the bottom of the through-hole becomes thinner, so if the strength of the bottom cannot be maintained against the thrust load, the bottom will not be cut and will be deformed and pushed out to the outlet side. It occurs by being. The generated burrs need to be removed in a later process, and the work requires time and labor. Depending on the location of burrs, it may be difficult or impossible to remove. Therefore, in the production of sintered parts, improvement in productivity is desired from the viewpoint of reducing manufacturing costs.

  When a through hole is formed so as to pass through a curved surface of the sintered part and at least one opening (especially, an opening on the outlet side) is provided on the curved surface, the burr generated at the opening of the through hole Difficult to remove. Since burrs formed by drilling a sintered part are hard, deburring is usually performed by polishing. However, it is difficult to uniformly contact the polishing tool along the curved surface, and it is difficult to polish the curved surface uniformly.

In particular, deburring is difficult when the following through-hole is formed in the sintered part.
(A) When two or more through holes are formed, and at least one through hole is formed so as to pass through the inner peripheral surface of another through hole. (B) A groove or hole having a curved inner peripheral surface is sintered. (C) The sintered part is a cylindrical body having a curved inner peripheral surface, and the through hole is formed into a cylindrical body. When forming so as to come out on the inner peripheral surface of

  In any of the cases (A) to (C), at least one opening of the through hole is provided on the curved surface. In addition, in the case of (A), one opening of the through hole is provided on the inner peripheral surface (curved surface) of another through hole, and the burr is formed so as to protrude from the inner peripheral surface of the other through hole. If the opening of another through hole is small, or if the opening of the through hole is provided on the inner peripheral surface at a position away from the opening of another through hole, the polishing tool cannot be inserted or the polishing tool cannot reach. Deburring is difficult. In the case of (B), the opening of the through hole is provided on the inner peripheral surface (curved surface) of the groove or hole, and the burr is formed so as to protrude from the inner peripheral surface of the groove or hole. If the opening of the groove or hole is small, or if one opening of the through hole is provided on the inner peripheral surface at a position away from the opening of the groove or hole, deburring is difficult. In the case of (C), the opening of the through hole is provided on the inner peripheral surface (curved surface) of the cylindrical body, and the burr is formed so as to protrude from the inner peripheral surface of the cylindrical body. Deburring is difficult if the inner diameter of the cylindrical body is small or if one opening of the through hole is provided on the inner peripheral surface at a position away from the opening of the cylindrical body. Therefore, in the conventional manufacturing method, when the through holes as in the above (A) to (C) are formed in the sintered part, it is difficult to deburr, and a lot of burrs are likely to remain in the openings of the through holes.

  Then, one of the objectives of this invention is providing the manufacturing method of the sintered component which is excellent in productivity, being able to reduce the burr | flash of opening of a through-hole. Another object of the present invention is to provide a sintered part that has few burrs at the opening of the through hole and is excellent in productivity.

  The manufacturing method of the sintered component which concerns on 1 aspect of this invention is equipped with a formation process, a drilling process, and a sintering process. In the molding step, a green compact having a curved surface is produced through press molding of a raw material powder containing metal powder. In the drilling step, the green compact is drilled to form at least one through hole. A sintering process sinters the said compacting body after the said drilling process. In the method for manufacturing a sintered part, in the drilling step, at least one through hole is formed so as to pass through the curved surface of the green compact, and at least one opening of the through hole is provided on the curved surface. .

  A sintered part according to one embodiment of the present invention is a sintered part having a curved surface and having at least one through hole formed therein. As for the said sintered component, the internal peripheral surface of the said through-hole is a satin-like shape. Further, the sintered part is formed so that at least one of the through holes passes through the curved surface of the sintered part, and at least one opening of the through hole is provided on the curved surface.

  The method for manufacturing a sintered part is excellent in productivity while reducing the burr at the opening of the through hole. The sintered part has few burrs at the opening of the through hole, and is excellent in productivity.

It is process explanatory drawing explaining the manufacturing method of the sintered component which concerns on embodiment. It is the schematic explaining an example of R drill used for drilling by the manufacturing method of the sintered component which concerns on embodiment. It is a comparison explanatory drawing at the time of drilling with the R drill which has an arc-shaped cutting edge, and when drilling with the V drill which has a V-shaped cutting edge. It is the schematic explaining an example of the multi-angle drill used for drilling with the manufacturing method of the sintered component which concerns on embodiment. It is comparison explanatory drawing at the time of drilling with the case where it drills with a multi-angle drill, and the V drill which has a V-shaped cutting edge. It is the schematic explaining the manufacturing method of the sintered component which concerns on the modification 2, and a sintered component. It is the schematic explaining the manufacturing method of the sintered component which concerns on the modification 3, and a sintered component. It is the schematic explaining the manufacturing method of the sintered component which concerns on the modification 4, and a sintered component. 6 is a photomicrograph showing an outlet of a through hole when a through hole is formed using an R drill in Test Example 1. FIG. 4 is a photomicrograph showing an outlet of a through hole when a through hole is formed using a double angle drill in Test Example 1. FIG. 2 is a photomicrograph showing an outlet of a through hole when a through hole is formed using a V drill in Test Example 1. FIG. It is a graph which shows the relationship between the rake angle, thrust load, and torque at the time of forming a through-hole using R drill in Test Example 2. 4 is a photomicrograph showing an inner peripheral surface of a through hole of a green compact produced in Test Example 3. FIG.

[Description of Embodiment of the Present Invention]
As a result of diligent research on the technology for improving the productivity of sintered parts, the inventors of the present invention have achieved productivity by drilling with a green compact before sintering rather than after sintering. It was found that can be improved. The compacted body is only a material powder that has been hardened by molding and is in a state where the particles of the metal powder are in mechanical contact with each other, and thus is not firmly bonded as after sintering. Therefore, when drilling is performed on the green compact before sintering, compared to drilling after sintering, the metal powder particles are weakly bonded to each other, cutting is easy, and cutting resistance (thrust load) Is greatly reduced. Then, the present inventors can form a through-hole with high efficiency and few burrs by drilling in the green compact, and even if burrs occur, without using a polishing tool, The inventors have obtained knowledge that deburring can be easily performed, and have completed the present invention. First, embodiments of the present invention will be listed and described.

  (1) The manufacturing method of the sintered component which concerns on one form of this invention is equipped with a formation process, a drilling process, and a sintering process. In the molding step, a green compact having a curved surface is produced through press molding of a raw material powder containing metal powder. In the drilling process, the green compact is drilled with a drill to form at least one through hole. In the sintering step, the green compact is sintered after drilling. In the manufacturing method of the sintered part, in the drilling step, at least one through hole is formed so as to pass through the curved surface of the green compact, and at least one opening of the through hole is provided on the curved surface.

  According to the method for manufacturing a sintered part, since a drilling process is performed on a green compact before sintering, cutting is easy and cutting resistance (thrust load) is greatly reduced. Therefore, compared with the conventional manufacturing method which drills with a drill after sintering, processing time can be shortened, the hole accuracy can be improved, and the tool life can be greatly improved. In addition, burrs are unlikely to occur when a green compact is drilled with a drill. Even if burrs are generated, the burrs can be easily removed by, for example, air blowing, and the time and labor required for the deburring operation can be reduced.

  In particular, when manufacturing a sintered part in which through holes are formed so as to come out to the curved surface of the sintered part, even if the curved surface is not polished for deburring, there are few or no burrs in the opening of the through hole. A sintered part is obtained. Therefore, the method for manufacturing a sintered part is excellent in productivity while reducing the burr at the opening of the through hole. Here, the compacting body produced in the molding step includes not only one having a curved surface formed by molding, but also one having a curved surface formed by cutting after molding.

  (2) As one form of the manufacturing method of the sintered part, the drill used for drilling has an R drill having an arcuate cutting edge at the tip, or a plurality of cutting edges at the tip, and The tip angle of the cutting edge is a multi-angle drill that gradually decreases from the center side to the outer peripheral side.

  When drilling is performed on the green compact with a drill, when the through hole is formed, a so-called edge chipping occurs in which the opening edge on the outlet side from which the drill comes out is chipped. As a result of repeated studies by the present inventors, it has been found that by using the R drill or the multi-angle drill for drilling a green compact, it is possible to suppress the occurrence of edge chipping when forming a through hole. Obtained. The R drill is a drill whose shape of the cutting edge is an arc (R shape), and the multi-angle drill is a drill whose shape of the cutting edge gradually decreases from the center side to the outer peripheral side. is there. The “shape of the cutting edge” as used herein refers to the cutting edge when projected from a direction perpendicular to the parallel plane passing through the center axis of the drill, with the cutting edge parallel to the plane parallel to the axis. It is the projected shape of the blade. When the shape of the cutting edge is an arc, when the drill is rotated and the cutting edge is viewed from a direction orthogonal to the rotation axis of the drill, the rotation locus of the cutting edge appears to be an arc.

  (3) As one form of the manufacturing method of the said sintered component, in a drilling process, 2 or more through-holes are formed, and at least 1 through-hole is formed so that it may pass out to the internal peripheral surface of another through-hole. Can be mentioned.

  According to the method for manufacturing a sintered part, a sintered part can be manufactured in which two or more through holes are formed and at least one through hole passes through the inner peripheral surface of another through hole. According to the method for manufacturing a sintered part, a sintered part having few or no burrs at the opening of a through hole provided on the inner peripheral surface of another through hole, which is difficult to realize by a conventional manufacturing method. Can be obtained.

  (4) As one form of the manufacturing method of the said sintered component, the groove | channel or hole which has a curved inner peripheral surface is formed in the compacting body. And in a drilling process, forming a through-hole so that it may pass out to the inner peripheral surface of a groove | channel or a hole is mentioned.

  According to the method for manufacturing a sintered part, a groove or hole having a curved inner peripheral surface is formed, and a sintered part formed so that a through hole passes through the inner peripheral surface of the groove or hole can be manufactured. According to the above method for manufacturing a sintered part, a sintered part having few or no burrs in the opening of the through hole provided on the inner peripheral surface of the groove or hole, which is difficult to realize by the conventional manufacturing method, is obtained. be able to.

  (5) As one form of the manufacturing method of the said sintered component, let a compacting body be a cylindrical body which has a curved inner peripheral surface in a formation process. And in a drilling process, forming a through-hole so that it may pass out to the internal peripheral surface of a cylindrical body is mentioned.

  According to the method for manufacturing a sintered part, it is possible to manufacture a sintered part that is a cylindrical body having a curved inner peripheral surface and is formed so that a through hole passes through the inner peripheral surface of the cylindrical body. According to the method for manufacturing a sintered part, a sintered part having few or no burrs at the opening of the through hole provided in the inner peripheral surface of the cylindrical body, which is difficult to realize by the conventional manufacturing method, is obtained. be able to.

  (6) A sintered part according to an embodiment of the present invention is a sintered part having a curved surface and having at least one through hole formed therein. And the inner peripheral surface of a through-hole is satin-like. Further, at least one through hole is formed so as to pass through the curved surface of the sintered part, and at least one opening of the through hole is provided on the curved surface.

  As mentioned above, when drilling a green compact before sintering, the metal powder particles are weakly bonded, so the metal powder particles are cut off with a drill to form through holes. To go. Therefore, the inner peripheral surface of the through-hole formed in the green compact has a textured shape with the overall irregularities formed by the particles. Since the surface properties of the inner peripheral surface of the through hole are substantially maintained after sintering, the inner peripheral surface of the through hole is satin-finished even in sintered parts obtained by sintering the green compact formed with the through hole. It becomes a shape. In other words, the fact that the inner peripheral surface of the through hole formed in the sintered part has a satin shape indicates that the green compact before sintering has been drilled. Therefore, the sintered part is excellent in productivity as compared with a conventional sintered part in which a through hole is formed after sintering.

  Furthermore, according to the above sintered parts, since the through-holes are formed in the green compact before sintering and the through holes are formed at the stage of the green compact, burrs are generated at the openings of the through holes. It is difficult, and even if burrs are generated, they can be easily removed at the stage of the green compact, so that a sintered part with few or no burrs can be obtained at the openings of the through holes. In particular, even when the through-hole is formed so as to pass through the curved surface of the sintered part, it is not necessary to polish the curved surface for deburring. Therefore, the sintered part has fewer through-hole burrs and is excellent in productivity.

  In contrast, when drilling with a drill after sintering, the metal powder particles are firmly bonded together by sintering, so the metal powder particles are cut while being drilled to form through holes. To go. Therefore, the inner peripheral surface of the through-hole formed by drilling a sintered part with a drill is a smooth surface with little unevenness as a whole, and has gloss.

  (7) As one form of the sintered part, the ten-point average roughness Rz of the inner peripheral surface of the through hole is 20 μm or more.

  When forming a through-hole with a drill in a green compact before sintering and sintering, the ten-point average roughness Rz of the inner peripheral surface of the through-hole formed in the sintered part is the shape of the metal powder particles -Depending on the size, for example, it may be 20 μm or more. The upper limit of the ten-point average roughness Rz of the inner peripheral surface of the through hole is, for example, 150 μm or less. On the other hand, when a through-hole is formed with a drill after sintering, the ten-point average roughness Rz of the inner peripheral surface of the through-hole formed in the sintered part is usually less than 20 μm and further 15 μm or less.

  (8) As one form of the sintered component, two or more through-holes are formed, and at least one through-hole is formed so as to come out to the inner peripheral surface of another through-hole.

  The sintered component has few or no burrs at the opening of the through hole provided on the inner peripheral surface of another through hole.

  (9) As one form of the sintered part, a groove or a hole having a curved inner peripheral surface is formed, and the through hole is formed so as to come out to the inner peripheral surface of the groove or hole. .

  In the sintered part, there are few or no burrs at the openings of the through holes provided on the inner peripheral surface of the groove or hole.

  (10) As one form of the sintered component, it is a cylindrical body having a curved inner peripheral surface, and the through hole is formed so as to come out to the inner peripheral surface of the cylindrical body.

  In the sintered part, there are few or no burrs at the openings of the through holes provided on the inner peripheral surface of the cylindrical body.

[Details of the embodiment of the present invention]
A method for manufacturing a sintered part according to an embodiment of the present invention and a specific example of the sintered part will be described below with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

<Method for manufacturing sintered parts>
A method for manufacturing a sintered part according to an embodiment of the present invention includes a forming step for producing a green compact, a drilling step for drilling a green compact with a drill, and a green compact after drilling. And a sintering step of sintering. The method for producing a sintered part is characterized in that, in the drilling step, at least one through hole is formed so as to pass through the curved surface of the green compact, and at least one opening of the through hole is provided on the curved surface. . Hereinafter, each process of the manufacturing method will be described in detail with reference mainly to FIG.

(Molding process)
In the molding step, a green compact G having a curved surface is produced through press molding of a raw material powder containing metal powder (see the upper diagram of FIG. 1). The green compact G is a raw material of a sintered part, and is molded into a shape corresponding to the sintered part S to be manufactured (see the lower diagram of FIG. 1). Here, as the green compact G (sintered part S), a cylindrical one having a circular shaft hole 30 formed at the center is taken as an example. That is, the green compact G (sintered part S) illustrated in FIG. 1 is a cylindrical body (cylindrical body) having a cylindrical (curved surface) inner peripheral surface.

<Raw material powder>
The raw material powder contains a metal powder as a main component. The material of the metal powder can be appropriately selected according to the material of the sintered part to be manufactured, and typically includes an iron-based material. “Iron-based material” is iron or an iron alloy containing iron as a main component. Examples of the iron alloy include those containing one or more additive elements selected from Ni, Cu, Cr, Mo, Mn, C, Si, Al, P, B, N, and Co. Specific iron alloys include stainless steel, Fe-C alloy, Fe-Cu-Ni-Mo alloy, Fe-Ni-Mo-Mn alloy, Fe-P alloy, Fe-Cu alloy, Fe -Cu-C alloy, Fe-Cu-Mo alloy, Fe-Ni-Mo-Cu-C alloy, Fe-Ni-Cu alloy, Fe-Ni-Mo-C alloy, Fe-Ni-Cr Alloy, Fe-Ni-Mo-Cr alloy, Fe-Cr alloy, Fe-Mo-Cr alloy, Fe-Cr-C alloy, Fe-Ni-C alloy, Fe-Mo-Mn-Cr -C system alloy etc. are mentioned. An iron-based sintered part can be obtained by mainly using powder of iron-based material. When the powder of iron-based material is mainly used, the content is, for example, 90% by mass or more, and further 95% by mass or more when the raw material powder is 100% by mass.

  When iron-based material powder, particularly iron powder, is mainly used, metal powder such as Cu, Ni, and Mo may be added as an alloy component. Cu, Ni, and Mo are elements that improve the hardenability. The amount of addition is, for example, more than 0% by mass and 5% by mass or less, and further 0.1% by mass to 2% by mass when the raw material powder is 100% by mass. % Or less. Moreover, you may add nonmetallic inorganic materials, such as carbon (graphite) powder. C is an element that improves the strength of the sintered body and the heat-treated body, and the content thereof is, for example, more than 0% by mass and 2% by mass or less, further 0.1% by mass when the raw material powder is 100% by mass. For example, the content may be 1% by mass or less.

  The raw material powder preferably contains a lubricant. When the raw material powder contains a lubricant, when the raw material powder is press-molded to produce the green compact G, the lubricity at the time of molding is enhanced, and the moldability is improved. Therefore, even if the pressure of press molding is lowered, it is easy to obtain a dense green compact G, and by increasing the density of the green compact G, it is easy to obtain a high-density sintered part S. Further, when the lubricant is mixed with the raw material powder, the lubricant is dispersed in the green compact G, so that the green compact G is drilled with a drill 10 in the subsequent process (see the middle diagram in FIG. 1). It also functions as a drill lubricant. Therefore, cutting resistance (thrust load) can be reduced and tool life can be improved. Examples of the lubricant include metal soaps such as zinc stearate and lithium stearate, fatty acid amides such as stearic acid amide, and higher fatty acid amides such as ethylene bis stearic acid amide. The lubricant may be in the form of a solid, powder, liquid or the like. The content of the lubricant is, for example, 2% by mass or less, further 1% by mass or less when the raw material powder is 100% by mass. If the content of the lubricant is 2% by mass or less, the proportion of the metal powder contained in the green compact G can be increased. Therefore, even if the pressure of press molding is lowered, it is easy to obtain a dense green compact G. Furthermore, volume shrinkage due to the disappearance of the lubricant when the green compact G is sintered in the subsequent process can be suppressed, and the dimensional accuracy is high and the high-density sintered part S can be easily obtained. The content of the lubricant is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more from the viewpoint of obtaining an effect of improving lubricity.

  The raw material powder does not contain an organic binder. Since the ratio of the metal powder contained in the green compact G can be increased by not containing the organic binder in the raw material powder, it is easy to obtain a dense green compact G even if the pressure of the press molding is lowered. Furthermore, it is not necessary to degrease the green compact G in a subsequent process.

  The raw material powder is mainly composed of the above-described metal powder, and is allowed to contain inevitable impurities.

  As the metal powder, water atomized powder, reduced powder, gas atomized powder, and the like can be used, and among them, water atomized powder or reduced powder is preferable. Since the water atomized powder and the reduced powder have many irregularities formed on the particle surface, the irregularities between the particles are meshed during molding, and the shape retention of the green compact G can be increased. In general, with gas atomized powder, particles with less unevenness are easily obtained, whereas with water atomized powder or reduced powder, particles with more unevenness are more likely to be obtained. The average particle size of the metal powder is, for example, 20 μm or more and 50 μm or more and 150 μm or less. The “average particle diameter of the metal powder” is a particle diameter (D50) at which the cumulative volume in the volume particle size distribution measured by a laser diffraction particle size distribution measuring device is 50%. If the average particle diameter of the metal powder is within the above range, it is easy to handle and press forming.

<Press molding>
In press molding, a molding apparatus (molding die) that can be molded into a shape corresponding to a sintered part as a final product is used. In the green compact G illustrated in FIG. 1, the shaft hole 30 is integrally formed at the time of molding, and is formed into a cylindrical body (tubular body) having a cylindrical (curved surface) inner peripheral surface. The green compact G is inserted into, for example, upper and lower punches having annular press surfaces that form both end faces of the green compact G, and the upper and lower punches. It can be formed using a cylindrical inner die that forms a surface and an outer die that surrounds the outer peripheries of the upper and lower punches and is formed with circular insertion holes that form the outer peripheral surface of the green compact G. Both end surfaces in the axial direction of the green compact G are press surfaces pressed by upper and lower punches, the inner peripheral surface and the outer peripheral surface are slidable contact surfaces with the inner and outer dies, and the shaft hole 30 is formed integrally during molding. Is done. The press molding pressure is, for example, 250 MPa or more and 800 MPa or less.

(Drilling process)
In the drilling process, the green compact G is drilled with a drill 10 to form at least one through hole 50 (see the middle diagram of FIG. 1). Here, the drill 10 forms one through-hole 50 that passes from the outer peripheral surface of the green compact G to the inner peripheral surface (curved surface). That is, the shaft hole (molding hole) 30 formed in the green compact G is connected to the through hole (drill hole) 50 formed by the drill 10, and the opening on the outlet side of the through hole 50 is the green compact. It is provided on the inner peripheral surface of G (the inner peripheral surface of the shaft hole 30). In this example, the through hole 50 is formed at a location where the distance (thickness) between the inner peripheral surface of the through hole 50 and the outer surface (end surface) of the green compact G is equal to or larger than the diameter of the through hole 50. Yes.

<drill>
The drill 10 used for drilling the green compact G is not particularly limited as long as the green compact G can be drilled. From the viewpoint of suppressing the occurrence of edge chipping, the drill 10 described below is used. 2) or a multi-angle drill (see FIG. 4). The R drill and multi-angle drill will be described.

<R drill>
The R drill will be described with reference to FIG. The R drill 10 </ b> R is a drill having an arcuate cutting edge 110 at the distal end portion 100. The tip portion 100 is a portion from the tip (vertex) of the cutting edge 110 to the outer periphery corner 120. Here, the surface when the drill is arranged so that the cutting edge is parallel to the horizontal plane and viewed from the direction orthogonal to the horizontal plane is referred to as a plane. Further, a surface when the drill is arranged so that the cutting edge is parallel to the horizontal plane and is viewed from a direction orthogonal to the central axis of the drill and parallel to the horizontal plane is referred to as a side surface. 2 is a schematic plan view of the drill, the lower left diagram of FIG. 2 is a schematic front view of the drill viewed from the tip side, and the lower right diagram of FIG. 2 is a schematic side view partially showing the tip of the drill. FIG.

<Shape of cutting edge>
The R drill 10R illustrated in FIG. 2 has a cutting edge 110 parallel to a plane parallel to the central axis of the R drill 10R and is orthogonal to the parallel plane, as shown in the upper left diagram of FIG. When viewed in plan from the direction, the projected shape of the cutting edge 110 is arcuate. The central angle α of the arc forming the cutting edge 110 is, for example, 130 ° or more, preferably 135 ° or more and 180 ° or less, and more preferably 150 ° or more. In this example, the central angle α of the arc is 180 °. On the other hand, the radius R of the arc forming the cutting edge is, for example, not less than 0.4 times and not more than 0.6 times the diameter d of the drill, preferably 0.5 times the drill diameter d, that is, the radius of the drill diameter d ( d / 2). In this example, the shape of the cutting edge is semicircular, the center angle α of the arc is 180 °, and the radius R of the arc is equal to the radius of the drill diameter d. That is, the length h of the tip 100 along the axial direction of the drill is equal to the radius R of the arc. Although the diameter d of R drill 10R is not specifically limited, For example, they are 1.0 mm or more and 20.0 mm or less. The “drill diameter (drill diameter)” as used herein refers to the outer diameter of the portion where the cutting edge is formed (so-called blade portion).

<Rake angle of cutting edge>
The rake angle of the cutting edge 110 is, for example, 0 ° or more, preferably more than 0 ° and 10 ° or less, more preferably 5 ° or more and 8 ° or less. The “rake angle” here is an angle formed between the parallel surface and the rake surface when the cutting edge is made parallel to the surface parallel to the center axis of the drill. Specifically, as shown in the lower right diagram of FIG. 2, the rake angle of the cutting edge 110 is such that the cutting edge 110 is parallel to the plane parallel to the central axis of the R drill 10R, and the central axis of the R drill 10R. Is an angle γ formed by the plane P parallel to the axis and the rake face 111 constituting the cutting edge 110 when viewed from the side parallel to the horizontal plane. In this example, the rake angle of the cutting edge 110 is 7 °.

  Here, the reason why the occurrence of edge chipping can be suppressed by using the above-described R drill 10R having the arc-shaped cutting edge for drilling the green compact G is considered as follows.

  First, the mechanism of the occurrence of edge cracks is considered as follows. In the case of the green compact G, since the bond between the metal powder particles is weak, it is brittle. Therefore, when the drill 10 penetrates, the thickness of the bottom portion of the through hole 50 becomes thin, and when the strength of the bottom portion cannot be maintained against the thrust load, cutting cannot be performed before the drill 10 penetrates. The bottom part falls out to the outlet side (extruded). When the bottom portion of the through hole 50 falls out without being cut, the vicinity of the bottom portion collapses together, so that the opening edge on the outlet side through which the drill 10 comes out is chipped.

  The left diagram in FIG. 3 shows an R drill 10R whose cutting edge has an arc shape (semicircular shape) and a green compact G that has been drilled with the R drill 10R. The R drill 10 </ b> R shown in FIG. 3 is simply illustrated by omitting grooves and the like for easy understanding.

  In the R drill 10R, the shape of the cutting edge 110 is semicircular as shown in the upper diagram on the left side of FIG. As shown in FIG. 2 on the left side of FIG. 3, when the green compact G is drilled with an R drill 10R (the white arrow in the figure indicates the feed direction of the drill), the shape of the cutting edge 110 is Transferred to the green compact G, and the bottom surface has a circular arc shape (semicircle), that is, a semispherical hole is formed in the green compact G. In the R drill 10R, since the shape of the cutting edge 110 is a circular arc (semi-circular arc), the thrust load acts in a radially distributed manner as indicated by solid arrows in the figure. On the other hand, in the green compact G, the bottom surface of the hemispherical hole is supported by the side of the arc (hemispherical surface) with respect to the thrust load of the drill as indicated by the solid line arrow in the figure, so that it is strong against deformation and has high strength. high. That is, when the green compact G is drilled with the R drill 10R, the thrust load itself is low and the thrust load acting on the bottom is dispersed, so that stress concentration is small and the strength of the bottom is maintained. In addition, the maximum thickness Ht of the bottom surface of the hole is equal to the length h of the tip portion 100, and increases as the length h of the tip portion 100 increases. In the case of the R drill 10R, the maximum thickness Ht of the bottom surface of the hole can be increased, so that the strength of the bottom portion is increased by the thickness. Therefore, when the green compact G is drilled with the R drill 10R, even if the thickness of the bottom of the through hole is reduced when the drill penetrates, the bottom of the thrust load is reduced. The strength of the steel is easily maintained, and cutting is possible just before the drill penetrates. Therefore, since it can suppress that a bottom part collapses without being able to cut before a drill penetrates, generation | occurrence | production of an edge chip | tip can be suppressed.

  On the other hand, when using a drill having a V-shaped cutting edge that has been widely used in the past (hereinafter sometimes referred to as “V drill”), it is difficult to suppress the occurrence of edge chipping. The right view of FIG. 3 shows a V-shaped drill 11 having a V-shaped cutting edge and a green compact G that has been drilled with the V-drill 11. The V drill 11 illustrated in FIG. 3 is simply illustrated with grooves and the like omitted as in the R drill 10R. In this example, the V drill 11 has a tip angle β of the cutting edge 110 of about 130 ° to 140 ° and a drill diameter d equivalent to that of the R drill 10R.

  As shown in FIG. 2 on the right side of FIG. 3, when the green compact G is drilled with the V drill 11, the shape of the cutting edge 110 is transferred to the green compact G, and the bottom surface is triangular in shape, A conical hole is formed in the green compact G. In the V drill 11, since the shape of the cutting edge 110 is V-shaped (triangle), the thrust load acts in the direction orthogonal to the side (conical surface) of the triangle as indicated by the solid line arrow in the figure. On the other hand, in the green compact G, the bottom surface of the conical hole is supported by a triangular side (conical surface) with respect to the thrust load of the drill as indicated by the solid arrow in the figure. Compared with, stress is concentrated and the strength is low. That is, when the green compact G is drilled with the V drill 11, the thrust load acting on the bottom cannot be dispersed compared to the R drill 10R, and the strength of the bottom is difficult to be maintained. In addition, in the case of the V drill 11, since the maximum thickness Ht of the bottom surface of the hole is small, the strength of the bottom portion is lowered by the thickness. Therefore, when the green compact G is drilled with the V drill 11, the thickness of the bottom portion of the through hole is reduced when the drill penetrates, so that the bottom portion cannot be cut before the drill penetrates. Easy to collapse. Therefore, it is difficult to suppress the occurrence of edge chipping.

  For the above reasons, the occurrence of edge chipping can be effectively suppressed when the central angle of the arc forming the cutting edge is 135 ° or more and 180 ° or less. If the center angle of the arcuate cutting edge is 135 ° or more, the cutting edge shape approaches a semicircular shape, and the thrust load is greatly reduced by the radial distribution of the thrust load. Thrust load during drilling Can be distributed. In addition, since the shape of the bottom surface of the hole approaches a hemispherical shape, the strength against thrust load can be increased, and in addition, the maximum thickness Ht of the bottom surface of the hole (see the left figure in FIG. 3) is increased and the strength is improved. Therefore, the strength of the bottom can be sufficiently maintained. The central angle of the arc is more preferably, for example, 150 ° or more, and particularly preferably 180 ° so as to form a semicircular cutting edge. On the other hand, the radius of the arc that forms the cutting edge is preferably substantially equal to the radius of the drill diameter, and is preferably 0.4 times or more and 0.6 times or less of the drill diameter, for example. In particular, the shape of the cutting edge is preferably a semicircular shape, the center angle of the arc is 180 °, and the radius of the arc is preferably 0.5 times the drill diameter, that is, equal to the radius of the drill diameter d. .

  From the viewpoint of suppressing the occurrence of edge chipping, it is considered that a smaller cutting resistance (thrust load) is advantageous. Since the rake angle of the cutting edge is more than 0 ° and not more than 10 °, the thrust load can be reduced, so that the occurrence of edge chipping can be more effectively suppressed. When the rake angle is greater than 0 °, the cutting edge becomes sharp and the thrust load is reduced. On the other hand, when the rake angle is increased, the cutting edge becomes sharp and the cutting edge strength decreases. However, since the work material is a green compact, chipping due to a decrease in cutting edge strength is unlikely to occur. However, if the rake angle is more than 10 °, the thrust load increases, so the rake angle is preferably 10 ° or less. The rake angle is more preferably 5 ° or more and 8 ° or less, for example, from the viewpoint of reducing the thrust load.

<Multi-angle drill>
The multi-angle drill will be described with reference to FIG. The multi-angle drill 10 </ b> W is a drill having a plurality of cutting edges 110 at the tip portion 100, and the tip angle of the cutting edge 110 gradually decreases from the center side to the outer peripheral side. FIG. 4 is a schematic plan view of the drill.

<Shape of cutting edge>
The multi-angle drill 10W illustrated in FIG. 4 has two cutting edges 110a and 110b, and the cutting edge 110 is composed of a primary cutting edge 110a and a secondary cutting edge 110b from the center of the tip to the outer peripheral corner 120. . As shown in FIG. 4, when the cutting edge 110 is parallel to a plane parallel to the central axis of the multi-angle drill 10 </ b> W and viewed from a direction orthogonal to the parallel plane, the cutting edge 110 is viewed. Is a shape in which the tip angles (β1, β2) gradually decrease from the center side to the outer peripheral side. The tip angle β1 of the primary cutting edge 110a is, for example, not less than 100 ° and not more than 160 °, and preferably not less than 115 ° and not more than 145 °. The tip angle β2 of the secondary cutting edge 110b is, for example, 20 ° to 100 °, and preferably 40 ° to 80 °. However, the tip angle β2 is smaller than the tip angle β1 (β1> β2). In this example, the tip angle β1 is 135 ° and the tip angle β2 is 60 °. The multi-angle drill 10W shown in FIG. 4 is a so-called double-angle drill with two tip angles.

  The diameter d1 of the outermost peripheral portion of the primary cutting edge 110a is, for example, not less than 0.3 times and not more than 0.9 times the diameter d, preferably not less than 0.5 times and not more than 0.9 times the drill diameter d. is there. In this example, the diameter d1 of the outermost peripheral portion of the primary cutting edge 110a is 0.8 times the drill diameter d. The rake angle of the cutting edge 110 (the primary cutting edge 110a and the secondary cutting edge 110b) is, for example, 0 ° or more and 30 ° or less. In this example, the rake angle of the primary cutting edge 110a is 0 °, or the secondary cutting edge. The rake angle of the blade 110b is 0 °.

  Here, the use of the multi-angle drill 10W described above can suppress the occurrence of edge cracks as compared with the above-described V drill (see FIG. 3) having a single tip angle as follows. Conceivable.

  The left figure of FIG. 5 has shown the compacting body G which drilled with the multi-angle drill (double angle drill) 10W and the double angle drill 10W. The double angle drill 10 </ b> W shown in FIG. 5 is simply illustrated with grooves and the like omitted for easy understanding. The right diagram in FIG. 5 shows a case where a drilling process is performed with a V drill, which is the same as the right diagram in FIG.

  As shown in the upper diagram on the left side of FIG. 5, the double angle drill 10 </ b> W has a shape in which the tip angle of the cutting edge 110 decreases stepwise. The double angle drill 10W has a length h of the tip 100 when the tip angle β1 of the double angle drill 10W and the tip angle β of the V drill 11 are equal to those of the V drill 11 (see the right figure in FIG. 5). Becomes larger. Therefore, as shown in the lower two figures of FIG. 5, when drilling the green compact G with the double angle drill 10W, the maximum thickness Ht of the bottom surface of the hole can be increased compared to the V drill 11, so The strength of the bottom is increased by the thickness. Therefore, when the double-angle drill 10W is used, the strength of the bottom is easily maintained against the thrust load, and it is easy to cut until just before the drill penetrates. Moreover, in the double angle drill 10W, the thrust load acting on the bottom can be dispersed as shown by the solid line arrow in the figure by changing the tip angle. Therefore, as compared with the V drill 11, it is possible to suppress the bottom portion from collapsing without being cut before the drill penetrates, and thus it is possible to suppress the occurrence of chipping.

<Cutting conditions>
Cutting conditions such as the rotational speed and feed rate (feed amount) of the drill 10 may be set as appropriate according to the material of the green compact G (metal powder), the depth of the through-hole 50 to be formed, the diameter of the drill 10, and the like. . For example, the rotational speed is 1000 rpm or more, further 2000 rpm or more, the feeding speed is 100 mm / min or more, further 200 mm / min or more, and the feeding amount is 0.01 mm / rev. Further, 0.1 mm / rev. The above is mentioned. Through experiments, it has been found that processing at a compacted body can be performed at a higher speed than processing a sintered body.

  The inner peripheral surface of the through-hole 50 formed in the green compact G with the drill 10 is a satin finish. In the green compact G, since the bonding between the metal powder particles is weak, when drilling with a drill, the metal powder particles are cut off with the drill to form the through holes 50. Therefore, the inner peripheral surface of the through-hole 50 formed in the green compact G is formed into a satin-like shape as a whole with unevenness due to particles.

(Sintering process)
In the sintering step, the green compact G is sintered after drilling. For sintering, an appropriate sintering furnace (not shown) capable of controlling the temperature atmosphere is used. The sintering conditions may be set as appropriate according to the material of the green compact G (metal powder) and the like. The sintering temperature is, for example, 1000 ° C. or higher, further 1100 ° C. or higher and 1200 ° C. or higher, and is not higher than the melting point of the main metal powder (for example, 1400 ° C. or lower). Examples of the sintering time include 15 minutes to 150 minutes, and further, 20 minutes to 60 minutes. By sintering, a sintered part S having a curved surface and having a through hole 50S is obtained (see the lower diagram of FIG. 1). The sintered part S relates to the embodiment of the present invention.

<Sintered parts>
A through hole 50S is formed in the sintered part S. This through-hole 50S is the through-hole 50 formed with the drill 10 with respect to the compacting body G by the drilling process before sintering (refer the middle figure of FIG. 1). As above-mentioned, the internal peripheral surface of the through-hole 50 formed in the compacting body G with the drill 10 is a satin finish. Since the surface property of the inner peripheral surface of the through-hole 50 is substantially maintained even after sintering, the inner peripheral surface of the through-hole 50S of the sintered part S obtained by sintering the green compact G is also satin-like. It becomes. In other words, the fact that the inner peripheral surface of the through-hole 50S formed in the sintered part S is a satin finish indicates that the drilling process has been performed on the green compact G before sintering. Yes. In the sintered part S, the ten-point average roughness Rz of the inner peripheral surface of the through hole 50S is, for example, 20 μm or more and 150 μm or less.

  The through hole 50S is formed so as to pass from the outer peripheral surface of the sintered component S to the inner peripheral surface (curved surface), and the opening on the outlet side of the through hole 50S is the inner peripheral surface of the sintered component S (the shaft hole 30). (Inner peripheral surface). In this example, the through hole 50S is formed at a location where the distance (thickness) between the inner peripheral surface of the through hole 50S and the outer surface (end surface) of the sintered part S is equal to or larger than the diameter of the through hole 50S. Yes.

<Effect>
Since the method for manufacturing a sintered part according to the above embodiment performs drilling with a drill on the green compact before sintering, cutting is easy and cutting resistance (thrust load) is greatly reduced. The Therefore, compared with the conventional manufacturing method which drills with a drill after sintering, processing time can be shortened, the hole accuracy can be improved, and the tool life can be greatly improved. Furthermore, according to the method for manufacturing a sintered part according to the above embodiment, since the through hole is formed in the green compact, it is difficult for the burr to be generated at the opening of the through hole. Since it can be easily removed at the stage of the molded body, burrs at the opening of the through hole can be reduced. In particular, when manufacturing a sintered part in which through holes are formed so as to come out to the curved surface of the sintered part, even if the curved surface is not polished for deburring, there are few or no burrs in the opening of the through hole. A sintered part is obtained. Therefore, the method for manufacturing a sintered part is excellent in productivity while reducing the burr at the opening of the through hole.

  In the sintered part according to the above embodiment, a through hole is formed, and since the inner peripheral surface of the through hole is a satin-like shape, drilling is performed on the green compact before sintering, Excellent productivity. Furthermore, according to the sintered part, since the hole forming is performed on the green compact before sintering and the through hole is formed in the green compact, it is difficult for burrs to occur at the opening of the through hole. Even if burrs are generated, they can be easily removed at the stage of the green compact, so that sintered parts with little or no burrs can be obtained at the openings of the through holes. In particular, even when the through-hole is formed so as to pass through the curved surface of the sintered part, it is not necessary to polish the curved surface for deburring. Therefore, the sintered part has fewer through-hole burrs and is excellent in productivity.

[Modification 1]
In the above-described embodiment (see FIG. 1), the through-hole 50 that passes through the inner peripheral surface (curved surface) is formed on the green compact G of the cylindrical body (tubular body), and this is sintered. An example of manufacturing a sintered part S that is a cylindrical body (cylindrical body) and is formed so that the through hole 50S passes through the inner peripheral surface (curved surface) of the cylindrical body (cylindrical body) has been described. In the first embodiment, the case where one through hole 50 is formed in the green compact G has been described as an example, but a plurality of through holes 50 may be formed. In this case, a plurality of through holes 50S are formed. The sintered part S thus obtained is obtained. When the green compact G is a cylindrical body, the outer peripheral shape may be, for example, an elliptical shape or a polygonal shape other than a circular shape in the axial cross-sectional view. It is possible to form various cylindrical shapes whose shapes are circular or elliptical.

[Modification 2]
In the above-described embodiment (see FIG. 1), the case where the green compact G is a cylindrical body (cylindrical body) having a cylindrical (curved) inner peripheral surface has been described as an example. As another example, as shown in FIG. 6, two or more through holes 50 and 51 are formed in the green compact G, and the through hole 50 is formed so as to pass through the inner peripheral surface of another through hole 51. To do. The green compact G illustrated in FIG. 6 is formed in a columnar shape, and after forming the through hole 51 from one end surface toward the other end surface, the through hole is formed from the outer peripheral surface of the green compact G. A through hole 50 is formed so as to pass through the inner peripheral surface of 51. Not only the through hole 50 but also the through hole 51 is formed by drilling the green compact G with a drill (not shown), and the through hole 51 has a cylindrical (curved) inner peripheral surface. That is, the opening on the outlet side of the through hole 50 is provided on the inner peripheral surface (curved surface) of the through hole 51. In this example, the through hole 51 has a larger diameter than the through hole 50, and the drill diameter used for the through hole 51 is larger than the drill diameter used for the through hole 50.

  According to the second modified example, the sintered part S is obtained in which two or more through holes 50 and 51 are formed and the through hole 50 is formed so as to come out to the inner peripheral surface (curved surface) of the through hole 51.

[Modification 3]
As another example, as shown in FIG. 7, a groove 53 having a curved inner peripheral surface is formed in the green compact G, and the through hole 50 is formed so as to pass through the inner peripheral surface of the groove 53. To do. The green compact G illustrated in FIG. 7 is a quadrangular columnar body, and a groove 53 having a semicircular cross section in the longitudinal direction is formed on the upper surface from one end side to the other end side. The groove 53 has a semicylindrical (curved) inner peripheral surface. Here, the groove 53 is formed integrally with the green compact G at the time of molding, but the groove 53 can also be formed by cutting after the green compact G is formed into a quadrangular prism shape. And the compacting body G illustrated in FIG. 7 forms the through-hole 50 so that it may come out from the outer peripheral surface (side surface or lower surface) of the compacting body G to the inner peripheral surface (curved surface) of the groove 53, An opening on the outlet side of the through hole 50 is provided on the inner peripheral surface (curved surface) of the groove 53.

  According to the third modified example, the sintered part S is formed in which the groove 53 having the curved inner peripheral surface is formed and the through hole 50 is formed so as to come out to the inner peripheral surface (curved surface) of the groove 53.

[Modification 4]
As another example, as shown in FIG. 8, a hole 55 having a curved inner peripheral surface is formed in the green compact G, and the through hole 50 is formed so as to pass through the inner peripheral surface of the hole 55. To do. The green compact G illustrated in FIG. 8 is a quadrangular columnar body, in which a hole 55 having a circular cross section is formed from the upper surface to the lower surface, and the hole 55 does not penetrate to the lower surface. The hole 55 has a cylindrical (curved surface) inner peripheral surface. Here, the hole 55 is integrally formed in the green compact G at the time of molding. However, the hole 55 may be formed by cutting after the green compact G is formed into a quadrangular prism shape. And the compacting body G illustrated in FIG. 8 forms the through-hole 50 so that it may come out from the outer peripheral surface (side surface) of the compacting body G to the inner peripheral surface (curved surface) of the hole 55, and the through-hole 50 openings on the outlet side are provided on the inner peripheral surface (curved surface) of the hole 55.

  According to the modification 4, the hole 55 having the curved inner peripheral surface is formed, and the sintered part S formed so that the through hole 50 passes through the inner peripheral surface (curved surface) of the hole 55 is obtained.

[Test Example 1]
A raw powder containing metal powder was press-molded to produce a green compact, and a drilling test was performed on the green compact using a drill having a different cutting edge shape.

(Green compact)
Water atomized iron powder (average particle size (D50) 100 μm), water atomized copper powder (average particle size (D50) 30 μm), carbon (graphite) powder (average particle size (D50) 20 μm), and ethylene as a lubricant Bistearic acid amide was prepared and mixed to prepare a raw material powder.

The prepared raw material powder was filled into a predetermined molding die and press-molded at a pressure of 600 MPa to produce a plate-like compacted body of 50 mm long × 20 mm wide × 10 mm thick. The density of the green compact was 6.9 g / cm ³ . This density is an apparent density calculated from the volume and mass of the green compact.

  Next, the produced compacted body was drilled with a drill to form through holes in the thickness direction of the compacted body. And the opening part by the side of the exit of a through-hole was observed, and the generation | occurrence | production state of edge chipping was investigated.

  As the drill, an R drill having a semicircular cutting edge shape as shown in FIG. 2 was prepared. The prepared R drill has a drill diameter d of 8.0 mm, a center angle α of the arc forming the cutting edge is 180 °, and an arc radius R of 4.0 mm (0.5 times the drill diameter d). ). The rake angle of the cutting edge is 0 °. This R drill was produced by polishing the cutting edge of the tip of a drill (model number: MDW0800GS4, material: cemented carbide) manufactured by Sumitomo Electric Hardmetal Co., Ltd.

  Further, a double angle drill having two tip angles as shown in FIG. 4 was prepared. The prepared double angle drill has a drill diameter d of 4.0 mm, a primary cutting edge angle β1 of 135 °, and a secondary cutting edge angle β2 of 60 °. Moreover, the rake angle of the cutting edge (primary cutting edge and secondary cutting edge) is 0 °. This double angle drill was manufactured by polishing the cutting edge at the tip of a drill (model number: MDW0400HGS5, material: cemented carbide) manufactured by Sumitomo Electric Hardmetal Co., Ltd.

  Furthermore, a V drill having a V-shaped cutting edge was prepared. The prepared V drill is a drill (model number: 05WHNSB0400-TH, material: cemented carbide) manufactured by Hitachi Tool Co., Ltd. This V drill has a drill diameter d of 4.0 mm and a tip angle of the cutting edge of 140 °.

  Using the R drill, the double angle drill, and the V drill, the green compact was drilled to form a through hole. Cutting conditions when the R drill was used were a rotational speed of 4000 rpm and a feed rate of 1600 mm / min. The cutting conditions when using a double angle drill or V drill are as follows: the rotation speed is 4000 rpm, the feed speed is 800 mm / min until the hole depth reaches 5 mm from the inlet side, and the feed is made until the hole depth penetrates from the position of 5 mm. The speed was 1600 mm / min.

  After the drilling process, the opening on the outlet side of the through hole was observed with an optical microscope for the compacted body in which the through hole was formed with each drill. The results are shown in FIGS. 9 shows a case where an R drill is used, FIG. 10 shows a case where a double angle drill is used, and FIG. 11 shows a case where a V drill is used. In the micrographs of FIGS. 9 to 11, the central circular portion is a through hole. In FIG. 9, a black annular portion having a constant width that borders the central circular portion (through hole) is a portion where the inner peripheral surface of the through hole is visible. In FIG. 10, the gray portion around the through-hole and partially missing, and in FIG. 11, the gray portion spreading around the through-hole is chipped. As shown in FIG. 9, when the through-hole was formed with the R drill, there was very little edge chipping at the opening on the outlet side of the through-hole, and no edge chipping could be confirmed in this example. Moreover, as shown in FIG. 10, when a through-hole is formed with the said double angle drill, it turns out that an edge chip | tip is small in opening of the exit side of a through-hole. On the other hand, when the through-hole is formed with the V drill, it can be seen that a large chip is generated at the opening on the outlet side of the through-hole as shown in FIG. When the through-holes were formed using a double angle drill and a V drill, the edge chipping amount was 0.36 mm for the double angle drill and 1.55 mm for the V drill. The edge chipping amount is determined by measuring the distance from the micrographs of FIGS. 10 and 11 to the point farthest from the center of the through hole among the points located on the contour of the edge chipping part. It calculated | required by calculating the difference with a diameter. From this result, it can be seen that the occurrence of edge chipping can be suppressed by using an R drill or a multi-angle drill having an arcuate cutting edge. It turns out that generation | occurrence | production of a chipping edge can be suppressed more especially if R drill is used.

[Test Example 2]
Using R drills with different cutting edge rake angles, drilling was performed on the green compacts, and the thrust load when forming through holes was compared.

  The same compact as that of Test Example 1 was used as the green compact to be processed.

  The R drill used has a semi-circular cutting edge as in Test Example 1, and the cutting edge at the tip of a drill (model number: MDW0800GS4, material: cemented carbide) manufactured by Sumitomo Electric Hardmetal Co., Ltd. It was made by polishing. In this R drill, the drill diameter d is 8.0 mm, the center angle α of the arc forming the cutting edge is 180 °, and the radius R of the arc is 4.0 mm (0.5 times the drill diameter d). Three types of R drills with rake angles of 0 °, 7 °, and 10 ° were produced. R drills with a rake angle of 0 ° were R0, R drills with a rake angle of 7 ° were R7, and a rake angle was 10 °. The R drill was designated as R10.

  Each of the three types of drills (R0, R7, R10) was drilled three times in the green compact to form three through holes in the thickness direction of the green compact. The cutting conditions were a rotational speed of 2000 rpm and a feed rate of 200 mm / min (feed amount of 0.1 mm / rev.). And in each drilling process from the 1st time to the 3rd time, the thrust load and torque at the time of forming a through-hole were measured. The thrust load and torque were measured using a cutting dynamometer (manufactured by Nippon Kistler Co., Ltd., model number 9272) from the start of drilling until a through hole was formed, and the maximum value was obtained. Moreover, the average value was also calculated | required from each thrust load and torque in each drilling process.

  Tables 1 to 3 show thrust loads and torques when drilling is performed using drills R0, R7, and R10. For example, in Table 1, “R0-1” indicates the first drilling process using the drill of R0, the first half symbol is the drill used, and the second half number is the number of drilling. (Tables 2 and 3 are also the same). Further, FIG. 12 shows the relationship between the rake angle and the thrust load and torque based on the average value of the thrust load and torque in each drill. In the graph of FIG. 12, the horizontal axis indicates the rake angle (°), the left vertical axis indicates the thrust load (N), the right vertical axis indicates the torque (N · m), the ■ mark indicates the thrust load, and the ◇ mark Is the torque.

  From the results of Tables 1 to 3 and FIG. 12, it can be seen that the R load with a rake angle of 7 ° has a smaller thrust load than the R drill with a rake angle of 0 ° or 10 °. If the rake angle is in the range of more than 0 ° and not more than 10 °, it is considered that the thrust load can be reduced compared to the case where the rake angle is 0 °. Therefore, it is considered that the occurrence of edge chipping can be more effectively suppressed by using an R drill having a rake angle of more than 0 ° and not more than 10 °. On the other hand, it can be seen that the torque tends to decrease as the rake angle increases.

  Furthermore, as a reference, a double-angle drill was used to make a hole in the green compact, and in the same manner as in Test Example 2, the thrust load and torque when forming the through hole were examined.

  The used double angle drill has a drill diameter d of 8.0 mm, a primary cutting edge angle β1 of 135 °, and a secondary cutting edge angle β2 of 60 °. Moreover, the rake angle of the cutting edge (primary cutting edge and secondary cutting edge) is 0 °. This double angle drill was produced by polishing the cutting edge at the tip of a drill (model number: MDW0800GS4, material: cemented carbide) manufactured by Sumitomo Electric Hardmetal Co., Ltd. This double angle drill was designated as W0.

  With the double angle drill W0, the green compact was drilled three times to form three through holes in the thickness direction of the green compact. The cutting conditions were a rotational speed of 2000 rpm and a feed rate of 200 mm / min (feed amount of 0.1 mm / rev.). And in each drilling process from the 1st time to the 3rd time, similarly to Test Example 2, the thrust load and torque at the time of forming the through hole were measured. The results are shown in Table 4.

[Test Example 3]
After drilling the green compact using an R drill, the green compact with through holes formed by the R drill was sintered to produce a sintered part.

  The same compact as that of Test Example 1 was used as the green compact to be processed.

  Here, an R drill having a semi-circular cutting edge and a drill diameter d of 3.5 mm was used. This R drill was produced by polishing the cutting edge of the tip of a drill (model number: MDW0350GS4, material: cemented carbide) manufactured by Sumitomo Electric Hardmetal Co., Ltd. In this R drill, the central angle α of the arc forming the cutting edge is 180 °, the radius R of the arc is 1.75 mm (0.5 times the drill diameter d), and the rake angle is 0 °.

  Using the R drill, a hole was formed in the green compact to form a through hole in the thickness direction of the green compact. The cutting conditions were a rotational speed of 2000 rpm and a feed rate of 200 mm / min (feed amount of 0.1 mm / rev.). After drilling, the green compact formed with through holes was sintered at 1130 ° C. for 20 minutes to produce a sintered part.

  Similarly, the green compact formed with the through hole was cut in the thickness direction so as to pass through the central axis of the through hole, and the inner peripheral surface of the through hole was observed with an optical microscope. The cross-sectional photograph is shown in FIG. In FIG. 13, a central belt-like portion extending in the left-right direction is the inner peripheral surface of the through hole. As shown in FIG. 13, the inner peripheral surface of the through hole was a satin finish. Moreover, it was 40 micrometers when ten-point average roughness Rz of the internal peripheral surface of this through-hole was measured. Further, the sintered part produced above was cut in the thickness direction so as to pass through the central axis of the through hole, and the inner peripheral surface of the through hole was observed with an optical microscope. Similar to the surface properties of the peripheral surface, the ten-point average roughness Rz of the inner peripheral surface was also equivalent. The ten-point average roughness Rz is a value measured in accordance with “Product Geometric Specification (GPS) —Surface Properties: Contour Curve Method—Terminology, Definition and Surface Property Parameters JIS B 0601: 2013”.

  As a result of forming a through-hole with a drill in the sintered part after sintering and observing the inner peripheral surface of the through-hole in the same manner, the inner peripheral surface of the through-hole is smooth with few irregularities, although illustration is omitted. The surface was glossy. Further, the ten-point average roughness Rz of the inner peripheral surface of the through hole was measured and found to be 11 μm. The drill used for drilling the sintered parts is MDW0350GS4 manufactured by Sumitomo Electric Hardmetal Co., Ltd., and the shape of the cutting edge is V-shaped, the drill diameter d is 3.5 mm, and the tip angle of the cutting edge is 135 °. It is.

  The method for manufacturing a sintered part according to one aspect of the present invention is used for manufacturing various types of sintered parts such as automobile parts and machine parts (eg, sprockets, rotors, gears, rings, flanges, pulleys, vanes, bearings, etc.). Is possible. The sintered part which concerns on 1 aspect of this invention can be utilized for various sintered parts, such as a motor vehicle part and a machine part.

10 drill 10R R drill 10W multi-angle drill (double angle drill)
DESCRIPTION OF SYMBOLS 11 V drill 100 Tip part 110 Cutting edge 110a Primary cutting edge 110b Secondary cutting edge 111 Rake face 120 Outer periphery corner 30 Shaft hole 50 Through hole 51 Through hole 53 Groove 55 Hole 50S Through hole G Powder compact S Sintered part

Claims (7)

A molding process for producing a green compact having a curved surface through press molding of a raw material powder containing metal powder,
Drilling the green compact with a drill to form at least one through hole; and
A sintering step of sintering the green compact after the drilling process,
The raw material powder is
Contains no organic binder, contains 95% by mass or more of iron-based material as 100% by mass of the raw material powder,
The drill used for the drilling process is
R drill with an arcuate cutting edge at the tip, or a multi-angle drill with multiple cutting edges at the tip, and the tip angle of each cutting edge gradually decreases from the center to the outer periphery ,
The rake angle of the cutting edge is 0 ° or more and 10 ° or less,
A method of manufacturing an iron-based sintered part, wherein in the drilling step, at least one through hole is formed so as to pass through the curved surface of the green compact, and at least one opening of the through hole is provided on the curved surface. The iron-based material is mainly composed of iron powder, and includes at least one of a metal powder of an alloy component of more than 0% by mass and 5% by mass or less and a nonmetallic inorganic material of more than 0% by mass and 2% by mass,
The said raw material powder is a manufacturing method of the iron-type sintered component of Claim 1 containing 0.1 to 1 mass% of lubricants.   3. The iron-based firing according to claim 1, wherein in the drilling step, two or more through holes are formed, and at least one of the through holes is formed so as to pass through an inner peripheral surface of another through hole. A method of manufacturing a bonded part. A groove or hole having a curved inner peripheral surface is formed in the green compact,
The method for manufacturing an iron-based sintered component according to claim 1 or 2, wherein, in the drilling step, the through hole is formed so as to pass through the inner peripheral surface of the groove or hole. In the molding step, the green compact is a cylindrical body having a curved inner peripheral surface,
The method for manufacturing an iron-based sintered part according to claim 1 or 2, wherein, in the drilling step, the through hole is formed so as to pass through the inner peripheral surface of the cylindrical body. An iron-based sintered part having a curved surface and having two or more through-holes,
The inner peripheral surface of the through hole is satin-like,
The ten-point average roughness Rz of the inner peripheral surface of the through hole is 20 μm or more and 150 μm or less,
At least one of the through holes is formed so as to pass through the curved surface of the sintered part, and at least one opening of the through hole is provided in the curved surface ;
An iron-based sintered component in which at least one of the through holes is formed so as to pass out to an inner peripheral surface of another through hole .   The iron-based sintered part according to claim 6, comprising an Fe—Cu—C-based alloy.