JP7221028B2 - Manufacturing method of sintered gear - Google Patents

Description

The present disclosure relates to a method for manufacturing sintered gears.

Conventionally, as metal gears, there are those made of sintered bodies (eg, Patent Document 1) and those made of wrought materials (eg, Patent Documents 2 to 4). Patent Document 1 discloses that, as a gear made of a sintered body (hereinafter referred to as a sintered gear), a compacted body before sintering is cut to form teeth and then sintered (specification [0059], [0060]).

JP 2017-186625 A Japanese Patent Application Laid-Open No. 2017-159400 Japanese Unexamined Patent Application Publication No. 2017-159401 JP 2017-226043 A

A further improvement in productivity is desired for sintered gears.
A sintered gear is superior in mass productivity compared to the method of manufacturing a gear by cutting out a molten material such as a round bar (Patent Documents 2 to 4). Furthermore, if the teeth are formed on the green compact before sintering as described in Patent Document 1, cutting can be performed more easily than when the teeth are formed on the sintered material after sintering. In this respect, the productivity of sintered gears can be improved.

However, as explained below, there is room for improvement in terms of productively manufacturing sintered gears with chamfered edges on each tooth.

Here, if the edges of each tooth of the gear remain sharp, for example, when carburizing is performed after sintering, localized excessive carburization may occur, or the edges may be chipped during use of the gear. . Therefore, it is desirable to chamfer the edges of each tooth. However, if the chamfering process is included between the sintering process and the carburizing process, for example, the materials will be repeatedly replaced with respect to the manufacturing equipment such as the heat treatment furnace and the chamfering device. Specifically, after sintering, the raw materials are taken out from the heat treatment furnace, and the taken-out raw materials are sequentially arranged in a chamfering device to be chamfered. After chamfering, the material is rearranged from the chamfering device to the heat treatment furnace and carburized. Such replacement of materials can be said to be one of the factors that cause a decrease in productivity.

Accordingly, one object of the present disclosure is to provide a method for manufacturing a sintered gear with excellent productivity.

The manufacturing method of the sintered gear of the present disclosure includes:
providing a gear-shaped powder compact comprising a plurality of teeth;
chamfering the edge of each tooth;
A step of sintering the chamfered green compact,
The edge chamfer of each tooth comprises:
By cutting the edge with a cutting tool with respect to the compacted body rotating around the axis of the gear,
The cutting tool is non-rotatably supported during cutting and is biased toward the edge by an elastic material.

The method for manufacturing a sintered gear of the present disclosure is excellent in productivity of sintered gears.

FIG. 1A is a schematic perspective view showing an example of a sintered gear. FIG. 1B is a partial perspective view showing an enlarged portion B surrounded by a broken line in the sintered gear shown in FIG. 1A. FIG. 2A is a partial perspective view showing an enlarged vicinity of the tip of a gear-shaped compacted body having a plurality of teeth. FIG. 2B is a partial perspective view showing an enlarged vicinity of the tip of a gear-shaped compacted body in which the edges of each tooth are chamfered. FIG. 3 is an explanatory diagram of the amount of chamfering.

[Description of Embodiments of the Present Disclosure]
In order to improve the productivity of sintered gears, the present inventors studied chamfering the edges of each tooth of the powder compact before sintering.

Conventionally, chamfering of the edges of each tooth of gears made from melted materials has been done by framing, cutting by moving a bit back and forth against each tooth at high speed, and profiling using rotary tools such as end mills. It's being used. In phrasing, the edges of the teeth are eliminated by plastic deformation that crushes the edges. In cutting work in which a cutting tool advances and retreats at high speed, the cutting tool is supported by a drive mechanism that advances and retreats along the axial direction of the shank portion of the cutting tool. Then, while rotating the gear around its axis, the cutting tool is advanced toward each tooth at high speed to bring the cutting edge into contact with the edge of the tooth to chamfer it. Rotate the gear while the bit is retracting to allow the next tooth edge to be chamfered. In profiling, the edges of the teeth are chamfered by moving the rotary tool so that the rotary tool follows along the edges of the teeth.

In the copying process described above, the processing time tends to be long. This is because the feed speed cannot be increased in order for the rotating tool to follow the shape of the gear. Moreover, when applying the above profiling processing to a green compact before sintering, it is necessary to make the processing speed slower than in the case of ingots. A green compact before sintering is inferior in mechanical strength to a wrought material. As a result, the rotary tool collides with the powder compact, causing chipping in the compact. Furthermore, the setting time of numerical control for following the rotary tool tends to be long. Even if the set shape of the gear is the same, a shape error occurs within the range of tolerance. Therefore, it is necessary to set follow-up conditions for each gear. For these reasons, applying the above profiling process to the powder compact requires a relatively long processing cycle time including the set time (for example, 3 minutes or more), and is not suitable for mass production. The machining cycle time is the time required to complete the chamfering of the tooth edges for one gear.

On the other hand, the above-described phrasing and cutting with a cutting tool generally require a relatively short processing cycle time (for example, 30 seconds or less) and are suitable for mass production. However, if the powder compact before sintering is subjected to the above-described phrasing process or the above-described cutting process in which the cutting tool is moved back and forth at high speed, chipping occurs in the powder compact. As described above, the powder compact is inferior in mechanical strength to ingot lumber. For this reason, chipping occurs in the powder compact due to pressing by a working tool for framing or collision with a cutting tool advancing at high speed. As a result, it is difficult to chamfer properly.

Based on the above, the inventors have found cutting conditions under which the edge of each tooth can be chamfered appropriately for the powder compact before sintering, and have completed the manufacturing method of the sintered gear of the present disclosure.
Embodiments of the present disclosure are listed and described below.

(1) A method for manufacturing a sintered gear according to an embodiment of the present disclosure includes:
providing a gear-shaped powder compact comprising a plurality of teeth;
chamfering the edge of each tooth;
A step of sintering the chamfered green compact,
The edge chamfer of each tooth comprises:
By cutting the edge with a cutting tool with respect to the compacted body rotating around the axis of the gear,
The cutting tool is non-rotatably supported during cutting and is biased toward the edge by an elastic member.

Here, the edge of each tooth includes the ridge line formed by the end surface (side surface) of the gear and the bottom surface, the ridge line formed by the end surface and tooth surface of the gear, and the ridge line formed by the end surface and the tip surface of the gear.

The manufacturing method of the sintered gear of the present disclosure is excellent in productivity of the sintered gear for the following reasons.
(a) A cutting tool used for chamfering is not rotated during cutting, but is supported in a state of being biased toward the tooth edge side by an elastic material. Therefore, the cutting edge of the cutting tool can move back and forth with respect to the edge of the tooth within the range of elastic deformation of the elastic material. By bringing the cutting tool so supported into contact with the rotating compact, the cutting edge of the cutting tool automatically follows the edge of each tooth. Even if the rotation speed of the powder compact is increased to some extent, it is easy to prevent chipping or the like from occurring in the powder compact or excessive local shaving. Therefore, even if the rotation speed is increased, the edges of each tooth can be properly chamfered. By increasing the processing speed, the processing cycle time can be shortened (see the test example described later). By shortening the machining cycle time, the productivity of sintered gears can be improved.
(b) When the carburizing process is performed after sintering, typically the sintering process and the carburizing process can be performed continuously. Therefore, it is possible to eliminate the need to replace the material in the heat treatment furnace. By omitting the exchange time, the manufacturing time can be shortened.

(c) The cutting applied to the powder compact before sintering can be said to be a process of separating and scraping off the powder particles constituting the powder compact. Therefore, substantially no burrs are generated due to plastic deformation of the material during cutting. Therefore, no burr removal work is required. Omitting the burr removal time reduces the manufacturing time. Note that when a molten material or a sintered material is cut, burrs are generated due to plastic deformation of the material during cutting. If burrs occur, removal work is required.
(d) Processing waste accompanying chamfering is typically in the form of powder. Therefore, the processing waste can be easily removed in a short time by using an air blow or the like. Moreover, if it is an air blow, it is difficult to damage the powder compact when removing the processing waste. The productivity of sintered gears can be improved in that the production of defective products due to damage can be reduced.
(e) Since the cutting resistance of the powder compact before sintering is lower than that of the melted material or the sintered material, the life of the cutting tool can be extended. Therefore, the cutting tool replacement frequency can be reduced. When mass-producing sintered gears, the manufacturing time can be shortened in that the cutting tool replacement time can be shortened.

(2) As an example of a method for manufacturing a sintered gear of the present disclosure,
chamfering the edge,
For each tooth, there may be mentioned a form including a process of sequentially and continuously cutting a tooth bottom edge, a tooth surface edge, and a tooth top edge located forward in the rotational direction of the powder compact.

In the above-described form, the chamfering time can be shortened compared to the case where the chamfering of the root edge, tooth surface edge, and tooth tip edge of each tooth is not performed continuously but performed separately. In this respect, the above embodiment is superior in productivity of sintered gears.

(3) As an example of a method for manufacturing a sintered gear of the present disclosure,
chamfering the edge,
After rotating the powder compact in one direction to perform the cutting process, the powder compact is rotated in the opposite direction to perform the cutting process.

When the green compact rotates in one direction, the front region of each tooth edge in the direction of rotation is defined as a first region, and the rear region is defined as a second region. In the above-described form, after chamfering the first region in order on the edge of each tooth, the powder compact is reversely rotated to chamfer the second region in order. That is, in the above embodiment, the chamfering of the first region and the chamfering of the second region are continuously performed by a simple operation of reversing the direction of rotation of the powder compact. Between the chamfering of the first area and the chamfering of the second area, there is no need to change the arrangement of the compact. In this regard, the above-described form is excellent in workability during chamfering, and tends to increase the productivity of sintered gears. Moreover, even if the top edge and bottom edge are overlapped by the chamfering of the first region and the chamfering of the second region, burrs are substantially generated on the top edge and its vicinity and on the tooth bottom edge and its vicinity. does not occur This is because the work material is a green compact before sintering. Since the step of removing burrs is not necessary, the above-described configuration can easily improve the productivity of the sintered gear. It should be noted that the processing debris generated on the tooth top edge and the tooth bottom edge can be easily removed by air blowing or the like as described above.

(4) As an example of a method for manufacturing a sintered gear of the present disclosure,
A form in which the average relative density of the powder compact is 93% or more is exemplified.

In the above-described mode, the relative density of the powder compact, which is the work material, is as high as 93% or more. Such dense powder compacts have excellent mechanical strength and are less likely to be chipped or cracked during chamfering. That is, the chamfering process can be performed satisfactorily, and the occurrence of defective products can be reduced. Also from the fact that the yield is high, the above-mentioned form tends to increase the productivity of the sintered gear.

(5) As an example of a method for manufacturing a sintered gear of the present disclosure,
Examples of the powder that constitutes the powder compact include a form containing iron powder and non-ferrous element powder, iron-based alloy powder and non-ferrous element powder, or iron-based alloy powder.

The above configuration can produce a sintered gear made of an iron-based alloy. Iron-based alloys are excellent in mechanical strength, rigidity, and wear resistance. Therefore, the above configuration can produce a sintered gear having excellent mechanical properties.

[Details of the embodiment of the present disclosure]
Hereinafter, embodiments of the present disclosure will be specifically described with reference to the drawings. The same reference numerals in the drawings indicate the same names.

[Sintered gear]
<overview>
A sintered gear 1 will be described mainly with reference to FIG.
The sintered gear 1 shown in FIG. 1A is a helical external gear. The sintered gear 1 is cylindrical with a through hole 2h and has a plurality of teeth 2 on its outer peripheral surface. Each end surface (side surface) 2e positioned on both sides in the axial direction of the sintered gear 1 (the axial direction of the through hole 2h) is a flat plane. The through hole 2h is provided so as to pass through the central portion of both end faces 2e. The gear shape shown in FIG. 1 is an example and can be changed as appropriate. Other shapes include cylindrical gears such as spur gears, bevel gears, and screw gears, and rod-shaped gears such as racks and helical racks. The cylindrical gear may be an internal gear.

As shown in an enlarged view in FIG. 1B, each tooth 2 provided in the sintered gear 1 is mainly composed of a tooth bottom surface 20, a tooth surface 21, and a tooth crest surface 22. As shown in FIG. The tooth bottom surface 20 is a surface forming the bottom of a space (tooth groove) provided between adjacent teeth 2 . The tooth crest surface 22 is a surface forming a region on the tip end side. The tooth bottom surface 20 and the tooth crest surface 22 are surfaces that rotate coaxially with the axis of the sintered gear 1 . The tooth surface 21 is a surface between the tooth bottom surface 20 and the tooth crest surface 22 . The tooth flank 21 is in contact with the tooth flank of another gear (not shown) that meshes with the sintered gear 1 . The tooth surface 21 in FIGS. 1A and 1B exemplifies a flat surface, but may be an involute curved surface.

Furthermore, the sintered gear 1 comprises a chamfer 3 on each tooth 2 near the boundary with the end face 2e. The chamfered portion 3 is formed in the manufacturing process of the sintered gear 1 by forming an edge 4 (FIG. 2A), which is a ridgeline between each surface (tooth bottom surface 20, tooth surface 21, tooth top surface 22) constituting each tooth 2 and the end surface 2e. is formed by chamfering Note that the chamfered portion 3 is omitted in FIG. 1A.

<composition>
The main constituent material of the sintered gear 1 is metal. The above metal is preferably an iron-based alloy. Here, the iron-based alloy is an alloy containing 80% by mass or more, preferably 90% by mass or more of Fe (iron). Such iron-based alloys are excellent in mechanical strength, rigidity, wear resistance, and the like. Therefore, the sintered gear 1 made of the iron-based alloy has excellent mechanical properties.

As a specific composition of the iron-based alloy, for example, from the group consisting of Cu (copper), Ni (nickel), Sn (tin), Cr (chromium), Mo (molybdenum), Mn (manganese) and C (carbon) Examples include those containing at least one selected nonferrous element and the balance being Fe (iron) and unavoidable impurities. A representative example of an iron-based alloy containing C is steel (carbon steel, alloy steel). Alloy steel, particularly alloy steel containing Ni, Mo and Mn is preferable because of its excellent mechanical strength.

The total content of nonferrous metal elements such as Cu, Ni, Sn, Cr, Mo, and Mn is 0.5% by mass or more and 5.0% by mass or less. Furthermore, the total content may be 1.0% by mass or more and 3.0% by mass or less.

The content of C is 0.2% by mass or more and 2.0% by mass or less. Furthermore, the content of C may be 0.4% by mass or more and 1.0% by mass or less.

It is preferable to adjust the composition of the raw material powder so as to obtain the sintered gear 1 having the desired composition.

<Relative Density>
The sintered gear 1 preferably has a high average relative density as a whole and is dense. It is because it is excellent in mechanical strength, rigidity, and abrasion resistance. For example, the average relative density of the whole is 93% or more. If the average relative density of the whole is 93% or more, the porous body is dense with very few pores and excellent in mechanical properties. The overall average relative density is preferably 95% or more, more preferably 96% or more, or 97% or more. Such a dense sintered gear 1 can be manufactured, for example, by using a dense powder compact in the manufacturing process.

The average relative density of the entire sintered gear 1 is obtained as follows.
For the tooth 2 of the sintered gear 1 and the region other than the tooth 2, cross sections are taken at the following three positions, image analysis is performed on each cross section, and this processed image is used. The three positions are near the center in the axial direction of the sintered gear 1, near one end face 2e, and near the other end face 2e. The vicinity of the end face 2e is, for example, a position within 3 mm from the end face 2e of the sintered gear 1. FIG. The cross-section is taken by cutting along a plane that intersects with the axial direction, typically a plane perpendicular to the axial direction.

More specific procedures are as follows.
(1) Collect images of a plurality of observation fields in each cross section. For example, 10 or more images of an observation field having an area of 500 μm×600 μm=300000 μm ² in each cross section are acquired. The image of each observation field of view is preferably obtained from each divided area by equally dividing the cross section, for example, in the circumferential direction or the longitudinal direction.
(2) binarize the acquired image of each observation field of view; In the binarized image, the area ratio of the metal particles occupying the observation field is obtained. This area ratio is regarded as the relative density of the observation field.
(3) Find and average the relative density of each observation field. Let this average value be the average relative density of the entire sintered gear 1 .

In the manufacturing process of the sintered gear 1, the pressurizing direction when forming the powder compact is typically parallel to the axial direction of the through holes 2h. In this case, the axial direction of the sintered gear 1 is substantially equal to the pressing direction mentioned above.

The sintered gear 1 allows inclusion of pores. However, as mentioned above, it is preferable that there are few pores. It can be said that the higher the overall average relative density mentioned above, the fewer the pores.

<Chamfer shape>
The chamfered portion 3 of the sintered gear 1 includes a tooth bottom chamfered portion 30 , a tooth surface chamfered portion 31 and a tooth top chamfered portion 32 . The tooth bottom chamfer 30 is provided near the boundary between the end surface 2 e and the tooth bottom surface 20 . The tooth chamfered portion 31 is provided near the boundary between the end surface 2 e and the tooth surface 21 . The tooth tip chamfered portion 32 is provided near the boundary between the end surface 2 e and the tooth tip surface 22 .

At least a part of the configuration surface of the chamfered portion 3 includes a flat surface. FIG. 1B illustrates a case in which all of the tooth bottom chamfered portion 30, the tooth surface chamfered portion 31, and the tooth top chamfered portion 32, which are the constituent surfaces of the chamfered portion 3, are flat surfaces. A chamfered portion 3 comprising a flat surface can be formed, for example, by cutting an edge 4 (FIG. 2A) of each tooth 2 during the manufacturing process with a cutting tool.

A corner portion between the tooth flank chamfered portion 30 and the tooth flank chamfered portion 31 and a corner portion between the tooth flank chamfered portion 31 and the tooth top chamfered portion 32 may include a curved surface 26 (FIG. 1(B)). mentioned. The chamfered portion 3 where the corner portion includes the curved surface 26 is cut continuously from the tooth root edge 40 to the tooth surface edge 41 or continuously from the tooth surface edge 41 to the tooth tip edge 42 in the manufacturing process. (see FIG. 2A for edge 4).

The solid line in FIG. 1B does not include a ridge line 25 connecting planes forming adjacent chamfered portions at the corners (for example, a constituent surface of the tooth flank chamfered portion 30 and a constituent surface of the tooth flank chamfered portion 31). Illustrate. The chain double-dashed line in FIG. 1B (see tooth 2 located on the right side of the paper surface of FIG. 1B) virtually shows the case where the corner portion includes curved surface 26 .

<Chamfering amount>
The chamfering amounts L1 to L3 will be described with reference to FIG.
FIG. 3 is a partial cross-sectional view schematically showing a state in which the vicinity of the chamfered portion 32 of the tooth 2 provided in the sintered gear 1 is cut along a plane parallel to the axial direction of the sintered gear 1. As shown in FIG. The following description will be given by taking the chamfered portion 32 as an example. Matters relating to the chamfering amounts L1 to L3 of the tooth tip chamfered portion 32 can also be applied to the tooth bottom chamfered portion 30 and the tooth surface chamfered portion 31 in the same manner.

The chamfering amount L1 at the chamfered portion 3 is the length along the creeping direction on the surface constituting the chamfered portion 3 (the surface constituting the tooth tip chamfered portion 32 in FIG. 3). The chamfering amount L2 is the length along the surface forming the tooth 2 (tooth top surface 22 in FIG. 3) at the chamfering portion 3 . The chamfering amount L3 is the length along the end face 2e at the chamfering location 3. As shown in FIG.

Specifically, the chamfering amount L1 is the distance between the following intersection point P1 and intersection point P2. The chamfering amount L2 is the distance between the following intersection point P1 and intersection point P3. The chamfering amount L3 is the distance between the following intersection point P2 and intersection point P3.
The intersection point P1 is a virtual plane (virtual surface 220 in FIG. 3) obtained by extending the constituent surface (tooth top surface 22) of the tooth 2 and a virtual surface (virtual surface 320 in FIG. 3) obtained by extending the constituent surface of the chamfered portion 3. intersection.
The intersection point P2 is the intersection point between the virtual plane 20e extending from the end face 2e and the virtual plane 320 of the chamfered portion 3 described above.
The intersection point P3 is the intersection point between the above-described virtual plane 220 and the virtual plane 20e.

The chamfering amounts L1 to L3 can be appropriately selected according to the size of each tooth 2 of the sintered gear 1. Also, the ratio of the large value of the chamfering amounts L2 and L3 to the smaller value (hereinafter referred to as the chamfering ratio) may be greater than one. In FIG. 3, the chamfering ratio is the ratio of the chamfering amount L3 to the chamfering amount L2, ie, L3/L2. Furthermore, the chamfering ratio may be 1.5 or more, 2 or more, or 3 or more. Although it depends on the reference value, the chamfering amount L3 tends to increase as the chamfering ratio increases. As the chamfering amount L3 increases, the sintered gear 1 can be formed such that the region near the boundary between the end face 2e and the forming surface of each tooth 2 is less likely to be chipped. When the green compact 10 before sintering is chamfered in the manufacturing process to form the chamfered portion 3, the ratio of the chamfered amounts L2 and L3 is easily set to more than one. This is because the powder compact 10 has a smaller cutting resistance than the sintered material after sintering, and the cutting length can be easily increased. The chamfering amounts L2 and L3 may be substantially equal. That is, the chamfer ratio may be 1.

<Surface texture>
When the sintered gear 1 is manufactured by chamfering the powder compact 10 before sintering to form the chamfered portions 3, the surfaces of the chamfered portions 3 are relatively rough. The chamfering scrapes off the powder particles that make up the powder compact 10, so that the processed surface after the chamfering tends to have unevenness based on the size of the powder particles. By sintering the powder compact 10 having such a rough machined surface, the surface of the chamfered portion 3 of the sintered gear 1 tends to be rough due to the unevenness.

[Manufacturing method of sintered gear]
<overview>
A method for manufacturing a sintered gear according to the embodiment will be described with reference to FIG. 2 as appropriate.
For example, the sintered gear 1 described above may be manufactured by a method for manufacturing a sintered gear according to the following embodiment. A method for manufacturing a sintered body according to an embodiment includes the following steps.
Step S1: A gear-shaped powder compact 10 having a plurality of teeth 2 is prepared.
Step S2: Chamfer the edge 4 of each tooth 2 .
Step S3: Sinter the chamfered compacted body 10 (hereinafter referred to as the processed body 11).
The edge 4 of each tooth 2 is chamfered by cutting the edge 4 with a cutting tool (not shown) with respect to the powder compact 10 rotating around the axis of the gear. The cutting tool is non-rotatably supported during cutting. Also, the cutting tool is biased toward the edge 4 of the tooth 2 by the elastic material.
Each step will be described in detail below.

<Step S1>
In this step, a gear-shaped powder compact 10 is prepared. The gear-shaped powder compact 10 can be produced, for example, by subjecting a powder compact having a predetermined shape to gear cutting such as hobbing. In this case, the compacted body before gear cutting can be made into a simple shape such as a cylindrical shape. Therefore, it is easy to form a compacted body with good shape accuracy and high dimensional accuracy before gear cutting. The excellent manufacturability of the powder compact contributes to the improvement of the productivity of the sintered gear 1 . Alternatively, the gear-shaped compacted body 10 may be formed using a mold.

<<Preparation of powder compact>>
A powder compact is an aggregate mainly composed of metal powder. Specifically, in the compacted body, each powder particle of the metal powder is plastically deformed to mesh with each other to maintain a lump state. Such a compacted body can be produced by filling a raw material powder, which is mainly composed of metal powder, into a mold having a predetermined shape and compressing the compacted product. A known pressing device such as a uniaxial pressing device can be used to manufacture the powder compact. The press device typically includes a die having a through hole, and upper and lower punches arranged at upper and lower openings of the through hole. A core rod may be used when producing a cylindrical powder compact.

≪Raw material powder≫
The content of the metal powder, which is the main component of the raw material powder, may be, for example, 90% by mass or more with respect to 100% by mass of the raw material powder. The content of the metal powder is 95% by mass or more, and may be 98% by mass or more. The higher the content of the metal powder in the raw material powder, the easier it is to obtain a compact powder compact. Here, the metal powder includes a powder made of a non-metal element which is a non-ferrous element powder used in an iron-based alloy described later.

The composition of the raw material powder may be adjusted according to the composition of the sintered gear 1 . For example, when manufacturing the sintered gear 1 made of an iron-based alloy, the powders constituting the powder compact may include iron powder and non-ferrous element powder, iron-based alloy powder and non-ferrous element powder, or iron-based alloy powder. is mentioned. In this case, the sintered gear 1 having excellent mechanical properties can be manufactured as described above. For details of the iron-based alloy, refer to the <Composition> section of the sintered gear described above.

The iron powder here is a powder made of pure iron. Pure iron is typically composed of Fe and impurities. The content of impurities in pure iron is, for example, 1% by mass or less in total. The content of C in pure iron is 0.02% by mass or less. The non-ferrous element powder is a powder made of a metal element other than Fe, or a powder made of a non-metal element. Metal elements other than Fe include the aforementioned Cu, Ni, Sn, Cr, Mo, Mn, and the like. C etc. are mentioned as a nonmetallic element. For example, when iron powder and non-ferrous element powder are used, although they are not iron-based alloys at the stage of raw material powders, the sintered gear 1 made of iron-based alloys can be manufactured by alloying them by sintering. The blending amounts of the iron powder or iron-based alloy powder (hereinafter referred to as iron-based powder) and the non-ferrous element powder should be adjusted so as to obtain an iron-based alloy with a desired composition. The mixing ratio (% by mass) of the iron-based powder and the non-ferrous element powder is, for example, iron-based powder: non-ferrous element powder of 99 or more: 1 or less. Further, the iron-based powder: non-ferrous element powder ratio may be 99.3 or more: 0.7 or less, and further 99.5 or more: 0.5 or less.

An iron-based alloy powder is a powder made of an iron-based alloy. When iron-based alloy powder is used, the composition of the metal powder contained in the raw material powder is substantially the same as the composition of the sintered gear 1 after sintering.

The above-mentioned iron powder, powder composed of non-ferrous metal elements, and iron-based alloy powder can be produced by, for example, a water atomization method, a gas atomization method, a carbonyl method, a reduction method, or the like. A commercially available powder may be used.

The average particle size of the above iron powder and iron-based alloy powder is, for example, 10 μm or more and 200 μm or less. When the average particle diameter is 10 μm or more and 200 μm or less, the powder is easy to handle and pressure-molded. Further, when the average particle size is 10 μm or more, the raw material powder has good fluidity and is easily filled into a mold. If the average grain size is 200 μm or less, the sintered gear 1 is excellent in sinterability and easy to obtain a dense sintered gear 1 . The smaller the average particle size, the easier it is to reduce the surface roughness. If improvement in moldability, denseness, surface properties, etc. is desired, the average particle size may be 40 μm or more and 150 μm or less. When multiple types of powders are used, the average particle size of each powder may be the same or different. The average particle size here is the particle size (D50) at which the cumulative volume in the volume particle size distribution measured by a laser diffraction particle size distribution analyzer is 50%.

In the case of producing a dense powder compact (for example, having an average relative density of 93% or higher, which will be described later), it is preferable that the metal powder content in the raw material powder is as high as described above. Therefore, the raw material powder may be, for example, substantially only metal powder. Alternatively, at least one of a lubricant and an organic binder may be included as long as a dense powder compact can be obtained. When the lubricant is included, it is possible to prevent seizure of the mold and the like. The content of the lubricant is preferably 0.2% by mass or less based on 100% by mass of the raw material powder. When the organic binder is included, it is easy to suppress the occurrence of chipping and cracking in the compact during molding. Known lubricants and organic binders can be used (see specifications [0040] and [0041] of Patent Document 1).

≪Molding conditions≫
As the mold for molding the powder compact, it is preferable to appropriately select a mold capable of molding a powder compact having a predetermined shape and size.

The pressure applied during molding is, for example, 600 MPa or higher. If the pressurizing pressure is 600 MPa or more, it is easy to make the powder compact compact. The higher the pressure, the easier it is to densify the powder compact. Therefore, the pressurization pressure is preferably 1000 MPa or more, more preferably 1500 MPa or more. Although there is no particular upper limit for the pressurizing pressure, if it is 3000 MPa or less, it is easy to prevent damage to the mold.

It is preferable to apply a lubricant to the inner peripheral surface of the mold (the inner peripheral surface of the die and the pressing surface of the punch described above). By applying a lubricant to the mold, even if the raw material powder does not contain the above-described lubricant, it is possible to prevent seizure of the mold and increase the content of the metal powder in the raw material powder. A known lubricant can be used (see specification [0044] of Patent Document 1).

≪Relative Density of Compacted Body≫
The average relative density of the entire powder compact is preferably 93% or more. The dense green body having an average relative density of 93% or more as a whole has excellent mechanical strength. Therefore, chipping, cracking, and the like are less likely to occur in the powder compact during chamfering, which will be described later, and also during gear cutting and other cutting processes. That is, cutting such as chamfering can be performed appropriately, and the occurrence of defective products can be reduced. The productivity of the sintered gear 1 can be improved by improving the yield. Further, by using a dense compacted body, a dense sintered gear 1 can be manufactured. A dense sintered gear 1 is preferable due to its excellent mechanical properties as described above.

The higher the average relative density of the entire green compact, the better the mechanical strength, which is preferable. Therefore, the overall average relative density is preferably 95% or more, more preferably 96% or more, or 97% or more. In order to increase the overall average relative density, it is possible to increase the content of the metal powder in the raw material powder, increase the molding pressure, finely and coarsely mix the metal powder, or use a powder with a large particle size. mentioned.

The average relative density of the entire compacted body is basically obtained in the same manner as the average relative density of the entire sintered gear 1 described above. The position of the cross-section taken from the compacted body includes the vicinity of the center in the pressurizing direction during molding, the vicinity of one end surface 2e, and the vicinity of the other end surface 2e. For the gear-shaped powder compact 10, it is preferable to take cross sections of the teeth 2 and regions other than the teeth 2 at the three positions described above. The cross section is taken by cutting along a plane that intersects with the direction of pressure, typically a plane that intersects perpendicularly. In addition, the method for determining the overall average relative density of the sintered gear 1 can be referred to, and detailed description thereof will be omitted.

≪Gear cutting≫
When gear-cutting is performed to produce the gear-shaped powder compact 10, a known gear-cutting tool can be used for the gear-cutting. Typical gear cutting tools include hobs, broaches, pinion cutters, and the like. Gear cutting may be performed using a machining center.

The following solution may be applied to the surface of the green compact before subjecting it to gear cutting. Alternatively, the surface of the green compact may be immersed in the following solutions. Examples of the solution include a volatile solution in which an organic binder is dissolved, a plastic solution, and the like. By coating or immersing the surface of the green compact with the solution, chipping and cracking of the surface layer of the green compact can be suppressed during gear cutting. In some cases, it is expected that chipping and cracking can be suppressed during the next chamfering process. Therefore, the application of the solvent or the immersion in the solvent contributes to the reduction of defective products due to chipping and cracking, thereby increasing the yield. The application of the solvent or the immersion in the solvent may be performed before chamfering or before cutting other than gear cutting and chamfering.

In addition to the gear cutting described above, other cutting processes may be applied to the powder compact before chamfering, which will be described later. This cutting may be either milling or turning. A machining center that can automatically perform multiple types of machining may be used. As a specific processing, for example, drilling processing and the like can be mentioned.

The above-mentioned gear cutting, chamfering, and other machining amounts may be adjusted by measuring the dimensions of the sintered material after sintering and feeding back the measured values. By adjusting the amount of processing according to actual measurements, it is easy to reduce the difference between the dimensions of the sintered material after sintering and the set dimensions. As a result, it is easy to shorten processing time such as finishing after sintering. This point contributes to improvement in productivity of the sintered gear 1 .

Processing scraps generated by the above-mentioned gear cutting, the below-described chamfering, and other cutting processes may be reused as the raw material powder. Here, when a compacted body is used as a work material, the processing waste generated by cutting is mainly powdery particles formed by separating the powder particles that constitute the compacted body. Such processing waste can be reused as raw material powder as it is without being re-dissolved and re-solidified. If there are agglomerates of solidified powder particles, the agglomerates may be appropriately pulverized. In addition, the compacted body that has chipped or cracked during cutting can be reused as the raw material powder if it is suitably pulverized and pulverized. When the compacted body is used as the work material in this way, it is easier to reuse processing scraps and defective products than when a sintered material is used as the work material. This point contributes to a reduction in material costs. Further, since the processing waste is in the form of powder, the processing waste can be easily removed from the compact by using an air blower or the like. Furthermore, if the processing waste is removed by an air blow, the powder compact is less likely to be damaged when the processing waste is removed. The fact that the occurrence of defective products due to damage can be reduced and the yield can be easily increased contributes to the improvement of the productivity of the sintered gear 1 .

<Step S2>
In this step, the edge 4 of each tooth 2 provided in a gear-shaped compacted body 10 (FIG. 2A) is chamfered by cutting to produce a processed body 11 (FIG. 2B). The edge 4 of each tooth 2 typically has a root edge 40 , a pair of tooth flank edges 41 ( 41 R and 41 L), and a tooth tip edge 42 . The bottom edge 40 is a ridge line formed by the end surface 2 e of the powder compact 10 and the bottom surface 20 . Each tooth surface edge 41 is a ridge formed by the end surface 2 e and each tooth surface 21 . The tip edge 42 is a ridge line formed by the end surface 2 e and the tip surface 22 .

《Working body》
The workpiece 11 has approximately the shape of the sintered gear 1 described above. The processed body 11 of this example is a helical external gear similar to the sintered gear 1 described above, and has a pair of end faces 2e and a plurality of teeth 2 provided on the outer peripheral side. In addition, this machined body 11 has a chamfered portion 3 near the boundary between the constituent surfaces of each tooth 2 (tooth bottom surface 20, tooth surface 21, tooth crest surface 22) and the end surface 2e. The chamfered portion 3 includes a tooth bottom chamfered portion 30 , a tooth surface chamfered portion 31 and a tooth top chamfered portion 32 .

The overall average relative density of the workpiece 11 substantially maintains the overall average relative density of the green compact 10 prior to chamfering. If the average relative density of the entire processed body 11 is 93% or more and dense, the sintered gear 1 can be made dense even after sintering as described above. Moreover, if the processed body 11 is dense in this way, shrinkage during sintering tends to be uniform. Therefore, it is easy to reduce the difference between the shape and dimensions of the workpiece 11 and the shape and dimensions of the sintered gear 1 . As a result, it is easy to shorten processing time such as finishing after sintering. This point contributes to improvement in productivity of the sintered gear 1 .

《Chamfering conditions》
As for the chamfering condition of the edge 4, it is desired that the green compact 10, which is fragile compared to the sintered material after sintering, does not suffer from chipping or cracking. Such conditions include satisfying the following.
(1) Cutting the edge 4 of each tooth 2 with a cutting tool while rotating the gear-shaped powder compact 10 around the axis of the gear.
(2) The cutting tool is non-rotatably supported during cutting.
(3) The cutting tool is supported while being biased toward the edge 4 side of the powder compact 10 by an elastic material.

By setting the above-described cutting tool in a specific supporting state, the following effects are obtained.
(1-1) Since the edge 4 of each tooth 2 is cut, defects such as chipping are less likely to occur in the powder compact 10 than when the edge 4 of each tooth 2 is crushed and plastically deformed.

(2-1) The cutting tool is supported so as not to rotate, and the workpiece is rotated. The rotation speed (number of rotations) of the work can be reduced to, for example, 200 rpm or less. Therefore, a drive mechanism (for example, a motor) with a large capacity is not required as a work rotation mechanism. In this respect, the costs associated with the chamfering device can be reduced.

(3-1) The cutting tool is biased toward the edge 4 side of the powder compact 10 by an elastic member (eg, a compression coil spring), so that it can be displaced within the range of elastic deformation of the elastic member. Therefore, the cutting tool can follow along the irregularities of the edge 4 from the tooth bottom edge 40 to the tooth tip edge 42 via the tooth surface edge 41 . Further, when the powder compact 10 is rotated around the axis of the gear, the cutting edge of the cutting tool contacting the edge 4 of the tooth 2 is pressed by the tooth 2, but is displaced by the above-described urging force so that the edge 4 can be maintained. As a result, the cutting edge can cut the edge 4 while being displaced along the edge 4 of the tooth 2 as the powder compact 10 rotates. That is, the cutting edge can automatically follow the movement of the teeth 2 accompanying the rotation of the green compact 10 to chamfer the edges 4 .

The chamfering operation will be described in detail by taking as an example the state in which the cutting edge of the cutting tool is arranged in contact with the edge 4 of the tooth 2A, for example the tooth root edge 40. FIG. In this arrangement state, when the powder compact 10 rotates in the direction of the black arrow (clockwise) in FIG. through to the tip edge 42 and can be cut. Further rotation of the compact 10 causes the cutting edge to move away from the tip edge 42 of the tooth 2A. However, as the powder compact 10 rotates, the cutting edge is arranged at the tooth bottom edge 40 between the tooth 2B adjacent to the tooth 2A in the rearward direction in the rotational direction, and the edge 4 of the tooth 2B is to cut Therefore, the edge 4 of each tooth 2 can be cut in turn.

Also, the cutting tool is displaced within the range of elastic deformation of the elastic material. Therefore, even if the rotational speed of the powder compact is increased to some extent, it is possible to prevent the edges 4 of the teeth 2 from being chipped or locally excessively shaved. Therefore, the rotation speed can be increased while the edges 4 of the teeth 2 can be satisfactorily chamfered. As a result, the processing speed during chamfering can be increased. The increased processing speed contributes to the improvement of the productivity of the sintered gear 1 . Furthermore, if the cutting tool is displaceably supported by the elastic material, a drive mechanism (eg, motor) for the cutting tool to follow along the edge 4 of each tooth 2 is not required.

≪Cutting tool≫
For example, the devices described in Patent Documents 2 to 4 can be used as cutting devices that satisfy the above conditions. This device includes a cutting tool (an example of a cutting tool) having a cutting edge, a holder that holds the cutting tool, and a jig that holds a gear as a work rotatably around its axis. The cutting tool is a rod-shaped body having a shaft portion and a cutting edge provided at the tip of the shaft portion. The cutting edge includes a first cutting edge that mainly cuts the tooth flank edge 41 and a second cutting edge that mainly cuts the tooth bottom edge 40 in succession. The holder supports the shaft portion so as not to rotate around the axis of the shaft portion. Further, the holder supports the cutting edge in a state of being biased toward the gear side along the axial direction of the shaft portion by a compression coil spring (an example of an elastic material).

The cutting tools provided in the devices of Patent Documents 2 and 3 are symmetrical about the axis of the shaft portion. The tip of the shaft portion is T-shaped. A T-shaped vertical bar corresponds to the axis of the shaft, and cutting edges are provided on each horizontal piece extending from the tip of the vertical bar to the left and right. A holder provided in this device supports the cutting tool in a state of being inclined at a certain angle with respect to the rotation axis of the gear.

The cutting tool provided in the device of Patent Document 4 has a conical tip. Near the apex of the cone is curved in a C shape, and this curved portion is the cutting edge.

≪Chamfering method≫
The edge 4 of each tooth 2 is chamfered, for example, by chamfering the edge 4 on one end face 2e side of the gear-shaped powder compact 10 and then chamfering the edge 4 on the other end face 2e side. Further, the chamfering of the edge 4 on the side of each end face 2e may be carried out by separately chamfering the tooth bottom edge 40, the tooth surface edge 41, and the tooth tip edge 42, for example, in the edge 4 of each tooth 2, but the chamfering may be performed continuously. By doing so, the chamfering time can be easily shortened. Shortening the chamfering time contributes to improving the productivity of the sintered gear 1 .

Here, when the powder compact 10 rotates in one direction, for example, in the direction of the black arrow in FIG. A second region 4L is defined as a region behind the . In FIG. 2A, the first region 4R of the tooth 2A is imaginarily indicated by hatching with two-dot chain lines. Moreover, the second region 4L is virtually indicated by cross-hatching with two-dot chain lines. In addition, in FIG. 2A, the boundary between both regions 4R and 4L is schematically indicated by a straight line.

It is efficient to continuously chamfer the first region 4R of each tooth 2 when the powder compact 10 rotates in one direction, for example, in the direction of the black arrow (clockwise) in FIG. 2A. Similarly, when the powder compact 10 rotates in the opposite direction (counterclockwise), it is efficient to chamfer the second region 4L of each tooth 2 continuously. As an example of such a chamfering method, the chamfering of the edge 4 of each tooth 2 is performed by: 42 may be continuously cut in order (hereinafter sometimes referred to as continuous processing). In this chamfering method, for example, if the powder compact 10 rotates in one direction (here, clockwise), for example, after chamfering the tooth bottom edge 40, the tooth surface edge 41R, and the tooth tip edge 42 of the tooth 2A in order, the tooth The root edge 40, the tooth surface edge 41R, and the tooth top edge 42 of another tooth 2B adjacent to 2A can be chamfered in order.

Furthermore, it is more efficient to continuously perform the chamfering of the first region 4R and the chamfering of the second region 4L. As an example of such a chamfering method, the edge 4 of each tooth 2 is chamfered by rotating the powder compact 10 in one direction and performing the above-described continuous treatment, and then rotating the powder compact 10 in the opposite direction. and performing the above-described continuous treatment.

In the chamfering method described above, for example, when shifting from the chamfering of the first region 4R in the edge 4 of each tooth 2 to the chamfering of the second region 4L, the rotation direction of the powder compact 10 is reversed. , chamfering of both regions 4R and 4L is continuously performed. Therefore, it is unnecessary to change the arrangement of the powder compact 10 between the chamfering of the first region 4R and the chamfering of the second region 4L. The fact that the replacement time of the powder compact 10 can be omitted contributes to the improvement of the productivity of the sintered gear 1 . In the chamfering method described above, for example, when the powder compact 10 is rotated in one direction, the bottom edge 40, the tooth surface edge 41R, and the tip edge 42 are cut in order, and when rotated in the opposite direction, The root edge 40, the tooth surface edge 41L, and the tooth top edge 42 are preferably cut in this order.

Chamfering of the first region 4R at the edge 4 of each tooth 2 can be performed by rotating the compact 10 in one direction. Further, the chamfering of the second region 4L at the edge 4 of each tooth 2 can be performed by rotating the powder compact 10 once in the opposite direction. The number of times of rotation in each direction of rotation may be one, but if it is set a plurality of times, the edge 4 of each tooth 2 can be chamfered more reliably. When the number of times of rotation is set to a plurality of times, if the number of rotations in one direction is performed a plurality of times and then the rotation in the opposite direction is performed a plurality of times, the number of times of changing the rotation direction is only one. As a result, it is easy to shorten the time required for changing the direction of rotation. This point contributes to improvement in productivity of the sintered gear 1 . Note that if the number of rotations is too large, the chamfering time will increase. Therefore, the number of rotations in one direction is preferably about 3 times or less (6 times or less in total for forward and reverse rotations).

In the chamfering method described above, the top edge 42 and the bottom edge 40 are allowed to be cut redundantly in the chamfering of the first region 4R and the chamfering of the second region 4L. Since the material to be cut is the powder compact 10, substantially no burrs are generated on the tip edge 42 and its vicinity and on the tooth bottom edge 40 and its vicinity even if the workpiece is cut in duplicate. Therefore, it is possible to reduce the step of removing burrs associated with overlapping cutting of the tooth tip edge 42 and the tooth bottom edge 40 . The fact that the number of steps can be reduced in this way contributes to the improvement in the productivity of the sintered gear 1 . It should be noted that processing chips may be generated on the tooth tip edge 42 and the tooth bottom edge 40 due to the above-described overlapping cutting. Since this processing waste is powdery as described above, it can be easily removed by an air blow or the like. Furthermore, if an air blow is used, it is possible to prevent damage to the machined surface after chamfering when removing machining waste.

≪Cutting conditions≫
Examples of the constituent material of the cutting tool include cemented carbide.
The cutting conditions for the chamfering are, for example, a workpiece rotational speed of 10 rpm or more and 200 rpm or less, further 150 rpm or less, and a cutting speed of 0.1 mm/rev. 2.5 mm/rev. These include:

《Other chamfering》
In the gear-shaped powder compact 10, portions other than the edge 4 of each tooth 2 may be chamfered. For example, the inner peripheral edge 4h (see FIG. 1A) of the through hole 2h of the powder compact 10 is chamfered. The inner peripheral edge 4h may be chamfered at the same time as the edge 4 of each tooth 2 is chamfered, or may be chamfered before or after the edge 4 is chamfered.

<Step S3>
In this step, the chamfered green compact 10 (processed body 11) is sintered. By sintering the workpiece 11 , a sintered gear 1 is obtained with a chamfer 3 on each tooth 2 .

The sintering conditions for the processed body 11 may be appropriately adjusted according to the composition of the raw material powder. Reference can be made to known sintering conditions. For example, when manufacturing a sintered gear 1 made of an iron-based alloy, the following sintering conditions may be used.
The sintering temperature is 1000° C. or higher and 1400° C. or lower. Furthermore, the sintering temperature may be 1100° C. or higher and 1300° C. or lower.
Sintering time is 10 minutes or more and 150 minutes or less. Furthermore, the sintering time may be 15 minutes or more and 60 minutes or less.

<Other processes>
Other steps include, for example, a step of carburizing the sintered material after sintering, and a step of finishing after carburizing. Known conditions can be referred to for carburizing treatment conditions, finishing conditions, and the like.

<Main effect>
The sintered gear manufacturing method of the embodiment can manufacture the sintered gear 1 with good productivity. The main reasons are as follows.
(a) The cutting tool used for chamfering is placed in the specific support state described above. Therefore, the cutting edge of the cutting tool can automatically follow the edge 4 of each tooth 2 of the rotating compact 10 . Furthermore, even if the rotational speed of the powder compact 10 is increased to some extent, the powder compact 10 is less likely to be chipped, and the edge 4 of each tooth 2 can be chamfered well. By increasing the machining speed, the machining cycle time can be shortened (see Test Example 1 below). In other words, high-speed copy processing can be performed.
(b) When the carburizing process is performed after sintering, typically the sintering process and the carburizing process can be performed continuously. Therefore, replacement of the materials in the heat treatment furnace, rearrangement of the materials, and the like can be eliminated. By omitting this replacement time, the manufacturing time can be shortened.

(c) Substantial burrs do not occur. Therefore, the burr removal time can be eliminated.
(d) Since the processing waste is mainly in the form of powder, it can be easily removed by an air blow or the like. Therefore, it is easy to shorten the time for removing processing waste.
(e) The cutting resistance of the powder compact 10, which is the work material, is lower than that of molten material or sintered material, so that the life of the cutting tool can be easily extended. Therefore, when a large number of sintered gears 1 are manufactured continuously, the cutting tool can be replaced less frequently. Therefore, it is easy to shorten the cutting tool replacement time during continuous production.
(f) The compacted body 10 before sintering is superior to the sintered material in machinability. Therefore, the processing speed such as gear cutting can be increased. Therefore, it is easy to shorten the processing time during cutting.
If the compacted body 10 before sintering is used as a work material for cutting including the above-described chamfering, the sintered gear 1 can be manufactured with higher productivity.

[Test Example 1]
The following sintered gears were produced and the machining cycle time for chamfering the edges of each tooth was investigated.

Here, a helical external gear made of an iron-based alloy was produced as a sintered gear. The gear specifications are as follows.
<Sintered gear>
Outer diameter: φ45mm, inner diameter: φ20mm, thickness 20mm
Module: 1.4
Torsion angle: 15.8°
Density: 7.71g/ ^cm3
Overall average relative density: 99.5%

The sintered gear was produced as follows.
A mixed powder of an iron-based powder and a carbon powder was prepared as a raw material powder. The composition of the iron-based powder is Fe-1.9Ni-0.2Mn-0.55Mo (additional element content: mass %). The average particle size of the iron-based powder is 42 μm. The average particle size of carbon powder is 8 μm. The mixing ratio (mass ratio) of the iron-based powder and the carbon powder was 99.6:0.4. Using the mixed powder, a cylindrical compact was produced by a uniaxial press. Molding pressure is 2000 MPa. The density of the green compact is 7.71 g/cm ³ . Moreover, the average relative density of the entire green compact is 99.5%, which is 93% or more. In addition, the average relative density of the entire sintered gear and the average density of the entire compacted compact were obtained by taking cross sections at three positions and measuring 10 At least one observation field of view is taken, image analysis is performed on each observation field of view, and this processed image is used to obtain the value. The size of each observation field is 500 μm×600 μm=300000 μm ² . For details, refer to the above-mentioned <Relative Density> section.

A gear-shaped powder compact was produced by subjecting the above cylindrical compact to gear cutting. A known hobbing machine was used for gear cutting. This gear cutting process did not cause chipping or cracking in the powder compact. In addition, the processing waste was powdery.

The edges of each tooth were chamfered for the gear-shaped powder compact described above. This chamfering was performed as follows. The powder compact is rotated around the axis of the gear. A cutting tool is used to cut the edge of the rotating powder compact. The cutting tool is non-rotatably supported during cutting. In addition, the cutting tool is supported by an elastic material so as to be biased toward the tooth edge side of the powder compact. A cutting tool made of cemented carbide was used.

In this test, the edge of each tooth was chamfered on one end face of the powder compact, and then the edge of each tooth was chamfered on the other end face. Each end face was chamfered by rotating the powder compact in one direction and performing the following continuous treatment, and then rotating the powder compact in the opposite direction to perform continuous treatment. The above-mentioned continuous processing is a processing in which the root edge, the tooth surface edge, and the tooth top edge, which are located forward in the rotational direction of the powder compact, are continuously cut in order for each tooth. Here, rotation in one direction was performed twice in succession, and then rotation in the opposite direction was performed two times in succession. Moreover, the rotation speed of the powder compact was set to 100 rpm. The cutting speed was 1.0 mm/rev. and

As described above, the chamfering was performed on both end surfaces of the powder compact. The time from the start to the end of the chamfering of both end faces was measured as the machining cycle time. The processing cycle time includes the time for changing the front and back of the powder compact and mounting it to the apparatus when performing the chamfering of one end face and the chamfering of the other end face.

As a result of the test, the processing cycle time was 20 seconds, which was very short. In this test, the tooth root edge, tooth flank edge, and tooth tip edge were chamfered in order, and it is considered that the machining cycle time could be shortened. In addition, the chamfering process did not cause chipping or cracking in the powder compact. Specifically, in each tooth of the powder compact, chipping, cracking, or the like did not occur on any of the machined surface, tooth bottom surface, tooth surface after chamfering, and the vicinity of the machined surface on the tooth top surface. The chamfering amount L3 (see FIG. 3) of each chamfered portion was measured for the green compact after chamfering. As a result, the chamfering amount L3 of the tooth bottom chamfered portion was 0.2 mm, the chamfering amount L3 of the tooth chamfered portion was 0.3 mm, and the chamfering amount L3 of the tooth top chamfered portion was 0.5 mm.

The chamfered compact was sintered. The sintering conditions are sintering temperature: 1150° C. and sintering time: 20 minutes. The sintered gear obtained after sintering had chamfers near the edges of each tooth. The chamfered portions of the sintered gear substantially maintained the chamfered portions of the powder compact described above.

The present invention is not limited to these examples, but is indicated by the scope of the claims, and is intended to include all modifications within the meaning and scope of equivalents of the scope of the claims.
For example, in Test Example 1, the composition of the sintered gear (raw material powder), the specifications of the sintered gear, the conditions for chamfering the edges of each tooth, etc. can be changed as appropriate.

Reference Signs List 1 sintered gear 10 compacted body 11 processed body 2, 2A, 2B tooth 2e end surface 2h through hole 20 tooth bottom surface 21 tooth surface 22 tooth top surface 220, 320, 20e virtual surface 25 ridge line 26 Curved surface 3 chamfered portion 30 tooth bottom chamfered portion 31 tooth surface chamfered portion 32 tooth top chamfered portion 4 edge 40 tooth bottom edge 41, 41R, 41L tooth surface edge 42 tooth top edge 4h inner peripheral edge 4R 1st area, 4L 2nd area

Claims (3)

providing a gear-shaped powder compact comprising a plurality of teeth;
chamfering the edge of each tooth;
A step of sintering the chamfered green compact,
The edge chamfer of each tooth comprises:
With respect to the powder compact that rotates about the axis of the gear, for each tooth, the tooth root edge, the tooth surface edge, and the tooth tip edge located forward in the rotation direction of the powder compact are connected in order. including cutting with a cutting tool,
After performing the cutting process by rotating the compacted body in one direction, performing the cutting process by rotating the compacted body in the opposite direction,
The cutting tool is non-rotatably supported during cutting and urged toward the edge by an elastic material.
A method for manufacturing sintered gears. 2. The method for manufacturing a sintered gear according to claim 1, wherein the powder compact has an average relative density of 93% or more. The method for manufacturing a sintered gear according to claim 1 or 2 , wherein the powder constituting the powder compact contains iron powder and non-ferrous element powder, iron-based alloy powder and non-ferrous element powder, or iron-based alloy powder. .

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