JP2019135326A - Method for manufacturing sintered compact - Google Patents

Abstract

To provide a method for producing a sintered compact that facilitates machining of a pressed-powder molded body before sintering, and has excellent productivity.SOLUTION: A method for manufacturing a sintered compact has a preparation step for preparing a raw material powder including an iron-based metal powder, a molding step for fabricating a pressed-powder molded body having an average relative density of at least 93% overall by uniaxial pressing of the raw material powder using a mold, a processing step for mechanically processing the pressed-powder molded body to fabricate a processed molded body, and a sintering step for sintering the processed molded body to obtain a sintered compact.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing a sintered body that sinters a green compact formed by pressing metal powder, and a sintered body manufactured by the manufacturing method.

  Examples of metal members used in machines such as automobiles include sprockets, rotors, gears, rings, flanges, pulleys, vanes, and bearings. Examples of methods for producing these metal members include a casting method, a forging method, a metal injection molding (MIM) method, a powder metallurgy method, and a method of cutting a metal solidified body.

  In the casting method, an expensive casting mold is required, and it is difficult to obtain a metal member with sufficient dimensional accuracy. Further, since the dimensional accuracy of the cast body is poor, enormous amounts of post-processing and deburring are required to obtain a metal member having a desired size. Moreover, in order to reuse the processing waste generated during post-processing, the processing waste must be dissolved. The forging method has the same problem as the casting method.

  In the MIM method, it is necessary to add as much as about 20% of an organic binder to the molding material, and the degreasing process after molding is complicated and takes time. When the organic binder is removed, the shape change is large, and it is difficult to obtain a metal member having a desired dimensional accuracy. Further, since the MIM method is limited to the molding of small articles, there is a problem that a large metal member cannot be obtained.

  The powder metallurgy method in which a raw material powder containing metal powder is pressure-molded with a mold to produce a green compact, and this is sintered, is superior in dimensional accuracy to the above three manufacturing methods. However, it is difficult to obtain a metal member having a complicated shape by pressure molding using a mold, and it is necessary to post-process the sintered body in order to obtain a metal member having a complicated shape. If multi-stage forming is performed, a metal member having a complicated shape can be obtained. However, depending on the shape of the metal member to be manufactured, post-processing is required even for multi-stage forming. Further, in multi-stage molding, the metal powder cannot be uniformly filled in a cavity having a complicated shape, and local variation tends to occur in the molding density of the powder compact. When such a powder compact is sintered, there is a risk that the dimensional accuracy of the low density portion may be reduced or the mechanical strength of the low density portion may be reduced. Even in this powder metallurgy method, in order to reuse the processing waste generated in the post-processing, the processing waste must be dissolved.

  The method of cutting the metal solidified body has a problem that productivity is low. This is because the solidified metal has a high hardness, and thus the processing speed cannot be increased. In addition, a high-rigidity and expensive machining center is required for cutting a solidified metal having high hardness, and there is also a problem that the life of a processing tool provided in the machining center is shortened. Even in this method, in order to reuse the machining waste generated by cutting, the machining waste must be dissolved.

  In view of the above problems, in recent years, a metal member manufacturing method has been proposed in which a green compact before sintering is machined to sinter the green compact that has been processed into a predetermined shape. Since the green compact before sintering has a lower hardness than the sintered compact, a reduction in processing cost can be expected. However, since the compacted body that has been simply press-molded is brittle and has low mechanical strength, there are problems in terms of machinability, such as chipping and cracking that are likely to occur during machining.

  In order to solve the above-mentioned problem, Patent Document 1 discloses a method for producing a metal member (sintered body) that is pre-fired after a pre-fired molded body obtained by pressure-molding a metal powder and machined the pre-fired fired body. Manufacturing method). According to the manufacturing method of Patent Document 1, the pre-fired body obtained by pre-baking the formed body has higher mechanical strength than the pre-fired formed body, is difficult to be chipped when machined, and is easy to machine. become. Further, the temporarily fired body has a lower hardness than the sintered body after the main firing, and is easy to machine. In other words, the manufacturing method of Patent Document 1 proposes to solve the problem of machinability by pre-baking the green compact to increase the mechanical strength and machining the pre-fired body. ing.

JP 2007-77468 A

  In the method for producing a metal member of Patent Document 1, sintering of metal powder particles proceeds to some extent by pre-baking the green compact. For this reason, the temporarily fired body has a certain degree of hardness, although the hardness is lower than that of the sintered body after the main firing. Therefore, the technique of Patent Document 1 has room for improvement in terms of machinability. Moreover, since the metal powder particles are sintered by temporary sintering, the processing waste must be dissolved in order to reuse the processing waste.

  Moreover, in the manufacturing method of the metal member of patent document 1, pressure molding-> temporary baking-> machining-> main baking is performed, and there are many processes required in order to obtain a metal member. Therefore, the technique of Patent Document 1 has room for improvement in terms of productivity of metal members.

  The present invention has been made in view of the above circumstances, and one of its purposes is to provide a method for producing a sintered body that is easy to machine with respect to a green compact before sintering and is excellent in productivity. It is in.

A method for producing a sintered body according to one aspect of the present invention includes:
Preparing a raw material powder containing iron-based metal powder;
A molding step of producing a green compact having an overall average relative density of 93% or more by uniaxially pressing the raw material powder using a mold;
A processing step of machining the green compact to produce a processed compact; and
A sintering step of sintering the processed molded body to obtain a sintered body;
A method for producing a sintered body comprising:

The sintered body according to one aspect of the present invention is an iron-based sintered body,
The sintered compact whose average relative density of the said sintered compact is 93% or more.

  According to the method for manufacturing a sintered body according to one aspect of the present invention, since the machining of the green compact before sintering is easy, the sintered body according to one aspect of the present invention is manufactured with high productivity. be able to.

The upper diagram is a schematic diagram showing how a green compact is machined with a cutting tool, and the lower diagram is a schematic diagram showing how a metal solidified body is machined with a cutting tool. It is a schematic perspective view of the assembly of the planetary carrier and the planetary gear described in the production example. It is a schematic side view of the planetary gear as described in a manufacture example. The upper diagram is a schematic front view of the planetary carrier described in the production example, and the lower diagram is an AA cross-sectional view of the upper diagram.

-Description of embodiment of this invention <1> The manufacturing method of the sintered compact which concerns on embodiment is equipped with the following preparatory process, a formation process, a process process, and a sintering process.
In the preparation step, raw material powder containing iron-based metal powder is prepared.
In the forming step, the raw material powder is uniaxially pressed using a mold to produce a green compact having an overall average relative density of 93% or more.
In the processing step, the green compact is machined to produce a processed compact.
In the sintering step, the processed molded body is sintered to obtain a sintered body.

  In the method for producing a sintered body, a green compact is produced by uniaxial pressing using a mold. In uniaxial pressing, since the raw material powder can be molded by applying a very high surface pressure to the raw material powder, it is easy to obtain a compacted body having a high relative density and uniform density and no locally fragile portions. Therefore, the green compact obtained by uniaxial pressing is excellent in mechanical strength and is less likely to be chipped or cracked during machining. In other words, the compacted body obtained by uniaxial pressing can be used for the processing step without pre-sintering, so that the sintered body can be produced with high productivity according to the above-mentioned method for producing a sintered body. Can do.

  In the above method for producing a sintered body, a uniform green compact having a relative density of 93% or more is produced. Therefore, when a processed green body obtained by processing the green compact is sintered, the dimensions of the processed green body are measured. The way of change is stable. That is, the contraction degree of the processed molded body does not vary locally, and the entire processed molded body contracts almost uniformly. Therefore, it can suppress that the actual dimension of a sintered compact greatly deviates from a design dimension. The relative density is preferably 95% or more.

  In the method for producing a sintered body, since the green compact is subjected to a processing step without sintering, the processing resistance in the processing step is low. Therefore, compared with the case where a metal solid body is machined, the machining speed can be made 5 to 10 times faster, and the tool life used for machining can be extended to 10 to 100 times. Further, since the processing resistance of the green compact is low and the rigidity of the cutting tool or shank is small, a long or thin cutting tool or shank can be used during machining. Thus, since the freedom degree of selection of a cutting tool or a shank is high, there are few restrictions in the design of the shape of a metal member, ie, the freedom degree of the said design is high. For example, it is possible to produce a metal member that has been subjected to fine shaping such as hollow processing.

  Moreover, in the manufacturing method of the said sintered compact, the processing waste produced by machining can be reused, without melt | dissolving. Because it is compacted by cold molding to produce a compacted body, and since the compacted body is not sintered before machining, the metal powder contained in the processing waste is not altered. It is.

<2> As one form of the manufacturing method of the sintered compact which concerns on embodiment, the form which processes the said compacting body into a helical gear shape can be mentioned.

  In the sintered body manufacturing method according to the embodiment, since the green compact is machined before sintering, it can be easily formed into a complicated helical gear shape.

<3> As one form of the manufacturing method of the sintered compact which concerns on embodiment, the form whose pressure of the said uniaxial pressurization is 600 Mpa or more can be mentioned.

  By producing a green compact with a pressure in the above range, a green compact with high density and excellent machinability can be obtained.

<4> As one form of the manufacturing method of the sintered compact which concerns on embodiment, the said process process can mention the form performed using a cutting method.

  The cutting can be performed using at least one processing tool such as a milling cutter, a hob, a broach, and a pinion cutter. Since the green compact is excellent in workability, any of the above processing tools can easily perform high-precision cutting.

<5> As one form of the manufacturing method of the sintered compact which concerns on embodiment, the said process process compresses a compressive stress to the said compacting body in the direction which counteracts the tensile stress which acts on the said compacting body with a processing tool. The form performed while giving can be mentioned.

  By performing machining while applying a compressive stress to the green compact in a direction to cancel the tensile stress acting on the green compact, it is possible to effectively suppress the occurrence of cracks and chips in the green compact. The means for applying the compressive stress is exemplified in the embodiments described later.

The sintered body according to the <6> embodiment is an iron-based sintered body, and is a sintered body having an average relative density of 93% or more of the entire sintered body.

  The sintered body according to the embodiment having an average relative density of 93% or more is a novel sintered body that has never existed. In addition, since the sintered body of the embodiment has an average relative density of 93% or more, the sintered body has mechanical strength comparable to a processed product of a metal solidified body. And since the sintered compact of embodiment is manufactured by the manufacturing method of the sintered compact of embodiment, it is excellent in productivity rather than the processed product of a metal solidification body. The average relative density is preferably 95% or more.

<7> As one form of the sintered compact which concerns on embodiment, the said sintered compact can mention the form which is a helical gear.

  The sintered helical gear can be used as a component such as an automobile transmission. As already described, since the sintered body according to the embodiment has mechanical strength comparable to that of a processed product of a metal solidified body, it sufficiently functions as a component of an automobile that is subjected to a high load.

<8> As one form of the sintered body according to the embodiment having the helical gear shape, the helical gear teeth may be inclined at 30 ° or more with respect to the axis of the helical gear.

  Since the helical gear has excellent mechanical strength, even if the helical gear teeth are inclined at an angle of 30 ° or more with respect to the axis, the teeth are hardly damaged during use. As the angle with respect to the tooth axis increases, noise generated when the helical gear meshes with other gears can be reduced. The angle with respect to the tooth axis is preferably 50 ° or more.

-Details of embodiment of this invention The specific example of the manufacturing method of the sintered compact which concerns on embodiment of this invention is demonstrated referring drawings below. 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.

<Embodiment 1>
≪Summary of manufacturing method of sintered body≫
The method for manufacturing a sintered body according to the embodiment includes the following steps.
S1. Preparation step: preparing raw material powder containing iron-based metal powder.
S2. Molding step: A powder compact with an overall average relative density of 93% or more is produced by uniaxially pressing the raw material powder using a mold.
S3. Processing step: A green compact is machined to produce a processed compact.
S4. Sintering step: The processed molded body is sintered to obtain a sintered body.
S5. Finishing process: A finishing process is performed to bring the actual dimension of the sintered body closer to the design dimension.
Hereinafter, each process will be described in detail.

<< S1. Preparation process >>
[Metal powder]
The metal powder is a main material constituting the sintered body, and examples of the metal powder include iron or iron alloy powder containing iron as a main component. Typically, pure iron powder or iron alloy powder is used as the metal powder. Here, “an iron alloy containing iron as a main component” means that the element contains iron element in an amount of more than 50% by mass, preferably 80% by mass or more, and further 90% by mass or more. Examples of the iron alloy include those containing at least one alloying element selected from Cu, Ni, Sn, Cr, Mo, Mn, and C. The alloying element contributes to improvement of mechanical properties of the iron-based sintered body. Among the alloying elements, the contents of Cu, Ni, Sn, Cr, Mn and Mo are 0.5% by mass or more and 5.0% by mass or less, and further 1.0% by mass or more and 3.0% by mass. The following may be mentioned. The C content may be 0.2% by mass or more and 2.0% by mass or less, and further 0.4% by mass or more and 1.0% by mass or less. Alternatively, iron powder may be used as the metal powder, and the alloying element powder (alloyed powder) may be added thereto. In this case, the constituent component of the metal powder is iron in the raw material powder stage, but iron is alloyed by reacting with the alloying element by sintering in the subsequent sintering step. The content of metal powder (including alloyed powder) in the raw material powder is, for example, 90% by mass or more, and further 95% by mass or more. As the metal powder, for example, a powder prepared by a water atomizing method, a gas atomizing method, a carbonyl method, a reduction method, or the like can be used.

  The average particle diameter of the metal powder is, for example, 20 μm or more and 200 μm or less, and further 50 μm or more and 150 μm or less. By making the average particle diameter of the metal powder within the above range, it is easy to handle and pressure forming is easy in the subsequent forming step (S2). Furthermore, it is easy to ensure the fluidity of the raw material powder by setting the average particle size of the metal powder to 20 μm or more. By setting the average particle size of the metal powder to 200 μm or less, it is easy to obtain a sintered body having a dense structure. The average particle diameter of the metal powder is the average particle diameter of the particles constituting the metal powder. The particle diameter (D50) is such that the cumulative volume in the volume particle size distribution measured by a laser diffraction particle size distribution measuring device is 50%. To do. By using fine metal powder, the surface roughness of the metal member can be reduced and the corner edge can be sharpened.

[Others]
In press molding using a mold, it is common to use a raw material powder in which a metal powder and an internal lubricant are mixed in order to prevent the metal powder from sticking to the mold. However, in this example, the raw material powder does not contain an internal lubricant, or even if it is contained, the raw material powder content is 0.2% by mass or less. This is to suppress a reduction in the ratio of the metal powder in the raw material powder, and to obtain a green compact having a relative density of 93% or more in the molding step described later. However, it is permissible to include a small amount of internal lubricant in the raw material powder within a range in which a green compact having a relative density of 93% or more can be produced in the subsequent molding step. As the internal lubricant, a metal soap such as lithium stearate or zinc stearate can be used.

  An organic binder may be added to the raw material powder in order to prevent cracking and chipping from occurring in the green compact in the processing step described later. Examples of the organic binder include polyethylene, polypropylene, polyolefin, polymethyl methacrylate, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyamide, polyester, polyether, polyvinyl alcohol, vinyl acetate, paraffin, and various waxes. The organic binder may be added as necessary, and may not be added. When adding an organic binder, it is necessary to make it the addition amount of the grade which can produce a compacting body with a relative density of 93% or more by a subsequent shaping | molding process.

<< S2. Molding process >>
In the molding step, the green compact is produced by uniaxially pressing the raw material powder using a mold. A die that performs uniaxial pressing includes a die and a pair of punches that are fitted into upper and lower openings thereof, and compresses the raw material powder filled in the die cavity with an upper punch and a lower punch. This is a mold for producing a powder molded body. The green compact that can be molded with this mold has a simple shape. Examples of the simple shape include a columnar shape, a cylindrical shape, a prismatic shape, and a rectangular tube shape. Here, you may utilize the punch which equips a punch surface with a convex part and a recessed part, and the dent and protrusion corresponding to the said convex part and a recessed part are formed in the said compact powder compact in that case. The compacting body which has such a dent and a protrusion is also contained in the compacting body of a simple shape.

  The uniaxial pressure (surface pressure) may be 600 MPa or more. By increasing the surface pressure, the relative density of the green compact can be increased. A preferable surface pressure is 1000 MPa or more, and a more preferable surface pressure is 1500 MPa or more. There is no upper limit for the surface pressure.

[External lubricant]
In uniaxial molding, it is preferable to apply an external lubricant to the inner peripheral surface of the mold (the inner peripheral surface of the die or the pressing surface of the punch) in order to prevent the metal powder from sticking to the mold. As the external lubricant, for example, a metal soap such as lithium stearate or zinc stearate can be used. In addition, fatty acid amides such as lauric acid amide, stearic acid amide, and palmitic acid amide, and higher fatty acid amides such as ethylene bis stearic acid amide can be used as an external lubricant.

The overall average relative density of the green compact obtained by uniaxial pressing is 93% or more. The average relative density of the whole of the green compact is preferably 95% or more, more preferably 96% or more, and still more preferably 97% or more. The average relative density of the whole of the green compact is a cross-section (preferably orthogonal) at the position near the center in the pressure axis direction, near one end, and near the other end of the green compact. Can be obtained by taking an image analysis of each cross section. More specifically, first, images of a plurality of observation fields are obtained 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. It is preferable to acquire images of each observation field from positions dispersed as evenly as possible in the cross section. Next, the acquired image of each observation visual field is binarized to determine the area ratio of the metal particles in the observation visual field, and the area ratio is regarded as the relative density of the observation visual field. And the relative density calculated | required from each observation visual field is averaged, and the average relative density of the whole compacting body is computed. Here, the vicinity of the one end side (near the other end side) is, for example, a position within 3 mm from the surface of the green compact.

<< S3. Processing process >>
In the processing step, after the green compact is produced by uniaxial pressing, the green compact is machined without sintering. The machining is typically cutting, and the green compact is processed into a predetermined shape using a cutting tool. Examples of the cutting process include a turning process and a turning process, and the turning process includes a drilling process. Examples of the cutting tool include drilling, reamer, turning, milling, end mill, turning, cutting tool, and the like, in the case of drilling. In addition, cutting may be performed using a hob, broach, pinion cutter, or the like. Machining may be performed using a machining center capable of automatically performing a plurality of types of machining.

  An image of machining will be described based on the image diagram of FIG. The upper diagram in FIG. 1 schematically shows how the green compact 200 is machined with the cutting tool 100, and the lower diagram schematically shows how the metal solidified body 300 is machined with the cutting tool 100. ing. As shown in the upper diagram of FIG. 1, in the green compact 200 formed by pressing and solidifying the metal particles 202, machining is performed so that the metal particles 202 are peeled off from the surface of the green compact 200 by the cutting tool 100. Is given. Therefore, the processing waste 201 produced by machining is composed of metal powder formed by separating individual metal particles 202 constituting the green compact 200. The powdered processing waste 201 can be reused without dissolving. In the case where there are agglomerates in which the metal particles 202 are hardened, the agglomerates may be crushed as necessary. On the other hand, as shown in the lower diagram of FIG. 1, the metal solidified body 300 is machined so that the cutting tool 100 scrapes the surface of the metal solidified body 300. Since the processing waste 301 produced by machining is composed of a series of structures, it cannot be reused unless the processing waste 301 is dissolved.

  Before being subjected to machining, the surface of the compacted body is prevented from cracking or chipping by applying or immersing a volatile solution or plastic solution in which an organic binder is dissolved on the surface of the compacted body. It doesn't matter.

  Further, it may be possible to suppress the occurrence of cracks or chipping in the green compact by performing machining while applying a compressive stress to the green compact in a direction to cancel the tensile stress acting on the green compact. For example, when forming a processing hole in a green compact by broaching, a strong tensile stress acts near the exit of the processing hole when the broach penetrates the green compact. As a method for applying a compressive stress to cancel the tensile stress to the green compact, a plurality of green compacts can be stacked in multiple stages. It is preferable to dispose a dummy green compact or a plate material under the lowest green compact. If a plurality of green compacts are stacked in multiple stages, the lower surface of the green compact on the upper side is pressed against the upper surface of the lower green compact, and compressive stress acts on the lower surface. If broaching is performed from above the multi-stage stacked compacts, cracks and chips near the exit of the processed holes formed on the lower surface of the compact can be effectively prevented. Moreover, when forming a processing groove in a compacting body by milling, strong tensile stress acts in the vicinity of the exit of the processing groove. As a countermeasure, a configuration in which a plurality of powder compacts are arranged in the direction of milling and a compressive stress is applied to a portion serving as an exit of the processing groove can be mentioned.

<< S4. Sintering process >>
In the sintering step, the processed molded body obtained by machining the green compact is sintered. By sintering the green compact, a sintered body in which the metal powder particles are brought into contact with each other and bonded is obtained. For the sintering of the green compact, known conditions corresponding to the composition of the metal powder can be applied. For example, when the metal powder is iron powder or iron alloy powder, the sintering temperature is, for example, 1100 ° C. or higher and 1400 ° C. or lower, and 1200 ° C. or higher and 1300 ° C. or lower. Examples of the sintering time include 15 minutes to 150 minutes, and further, 20 minutes to 60 minutes.

  Here, the processing degree in the processing step may be adjusted based on the difference between the actual size and the design size of the sintered body. A processed molded body obtained by processing a high-density green compact with a relative density of 93% or more contracts almost uniformly during sintering. Therefore, the actual dimension of the sintered body can be made much closer to the design dimension by adjusting the processing degree of the processing step based on the difference between the actual dimension after sintering and the design dimension. As a result, it is possible to reduce labor and time for the next finishing process. When machining is performed at a machining center, the degree of machining can be easily adjusted.

<< S5. Finishing process >>
In the finishing step, the surface roughness of the sintered body is reduced by polishing the surface of the sintered body, and the dimensions of the sintered body are adjusted to the design dimensions.

≪Sintered body outline≫
According to the method for manufacturing a sintered body described above, a sintered body having an overall average relative density of 93% or more can be obtained. The overall average relative density of the sintered body is approximately equal to the overall average relative density of the green compact before sintering. The average relative density of the entire sintered body is preferably 95% or more, more preferably 96% or more, and further preferably 97% or more. The higher the average relative density, the higher the strength of the sintered body.

The average relative density of the entire sintered body is a cross-section (preferably a cross-section that intersects perpendicularly) in the vicinity of the center in the pressure axis direction, near one end side, and near the other end side of the sintered body. ) And image analysis of each cross section. More specifically, first, images of a plurality of observation fields are obtained 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. It is preferable to acquire images of each observation field from positions dispersed as evenly as possible in the cross section. Next, the acquired image of each observation visual field is binarized to determine the area ratio of the metal particles in the observation visual field, and the area ratio is regarded as the relative density of the observation visual field. And the relative density calculated | required from each observation visual field is averaged, and the average relative density of the whole sintered compact is computed. Here, since the pressing axis direction of the sintered body is uniaxially pressed in the production process of the sintered body, it can be easily grasped by observing the deformation state of the metal powder in the cross section of the sintered body. . Further, the vicinity of the one end side (near the other end side) is, for example, a position within 3 mm from the surface of the sintered body.

<Production example>
In the production example, the assembly 1 of the planetary gear 2 and the planetary carrier 3 shown in FIG. 2 was produced by the manufacturing method of the sintered body of the embodiment or the conventional manufacturing method of the sintered body. As shown in FIG. 3, the planetary gear 2 is a helical gear in which the teeth 20 are cut obliquely with respect to the axis (see the alternate long and short dash line). As shown in FIGS. 2 and 4, the planetary carrier 3 includes a disk-shaped first component 31 and a second component 32 in which three bridge portions 32 b are formed on a disc portion 32 s. .

<< Sample A; Method for Producing Sintered Body of Embodiment >>
First, the raw material powder which mixed 0.3 mass% C (graphite) powder with the alloy powder of Fe-2 mass% Ni-0.5 mass% Mo was prepared. The true density of the raw material powder is about 7.8 g / cm ³ .

Next, the raw material powder was press-molded by uniaxial pressing to produce the following three compacts. The molding pressure was 1200 MPa for all.
-A cylindrical compact for planetary gear 2 ... Diameter 50mm x Height 20mm
-Disc shaped compact for the first part 31 ... Diameter 130mm x Height 35mm
-Columnar compact for the second part 32 ... Diameter 130mm x Height 35mm

When the average relative density of the whole of the above three compacts was determined, all were 93% or more. The average relative density of the green compact is the above << S2. As described in the section of “Molding process”, a cross section is taken near the center and near both ends in the direction of the pressing axis, and 10 or more observation fields having an area of 300000 μm ² or more in each cross section are obtained by image analysis. It was. The average relative density of the specific green compact was about 96.2%. When the average relative density was corrected, the average bulk density of the green compact was 7.5 g / cm ³ .

  Subsequently, using the commercially available machining center, each produced compacting body was machine-processed, and the processing molded object of the desired shape was produced. In machining the green compact for the planetary gear 2, teeth 20 inclined by 50 ° with respect to the axis were formed. In the machining of the green compact for the first component 31, as shown in FIG. 1, a boss portion 31b is formed by machining, a hole is formed in the center of the boss portion 31b, and an internal part is formed inside the hole. Lugia teeth were formed. In the machining of the green compact for the second part 32, the bridge portion 32b is formed by cutting, and, as shown in the lower part of FIG. 4, the base portion of the bridge portion 32b is connected to the disc portion 32s. The inner peripheral surface portion (see the portion indicated by the black arrow) was formed in an R shape. By making the said inner peripheral surface part into R shape, the intensity | strength of the bridge part 32b can be improved. In the machining of any of the above green compacts, no cracks or chips were generated in the green compact. The processing waste generated by machining was a metal powder formed by separating individual particles constituting the green compact.

  Next, the processed molded body was sintered, and the planetary gear 2 and the planetary carrier 3 composed of the sintered body were produced. During the sintering, no cracks or chips occurred in the sintered body. Finally, the dimensions of the planetary gear 2 and the planetary carrier 3 were brought close to the design dimensions by polishing or the like, and the surface roughness was reduced.

When the average relative densities of the planetary gear 2 and the planetary carrier 3 of Sample A were determined, both were about 93% or more. The average relative density of the planetary gear 2 and the planetary carrier 3 (sintered body) is as follows. It calculated | required by image-analyzing the 10 or more observation visual field which has an area of 300000 micrometers ² or more of a cross section. Specifically, the average relative density of the planetary gear 2 and the planetary carrier 3 is about 96.2%. When the average relative density is adjusted to the average bulk density, the average bulk density of the planetary gear 2 and the planetary carrier 3 is 7.5 g / cm ^3. Met. Here, the observation visual field acquired from the cross section includes the portion of the teeth 20 of the planetary gear 2, and even if the relative density of the portion alone is obtained, the relative density of the portion is 96.2%. It was confirmed that

  The planetary gear 2 and the planetary carrier 3 of Sample A had a mechanical strength comparable to that of a planetary gear and a planetary carrier made of a solidified metal produced by a melting method. Therefore, it has been found that the planetary gear 2 and the planetary carrier 3 of the sample A can be sufficiently used as automobile components.

«Sample B; conventional method of manufacturing a sintered body»
The same raw material powder as that of Sample A was prepared, and a green compact having a shape close to the planetary gear 2 and a green compact having a shape close to the planetary carrier 3 were prepared by near net shape molding. Since the planetary gear 2 is a helical gear, a rotary press machine was used for forming the near-net shape of the planetary gear 2. In the rotary press, the inclination of the teeth 20 with respect to the axis cannot be 45 ° or more. Further, the molding pressure using a rotary press machine could only be much lower than 600 MPa.

The planetary gear 2 and the planetary carrier 3 according to the sample B were produced by sintering a compact molded body of a near net shape and performing a finishing process. With respect to the planetary gear 2 and the planetary carrier 3 of the sample B, the relative density of the observation field of the cross section was obtained by the same method as that of the sample A. As a result, the relative density of each observation field varied. Specifically, the average relative density of the teeth 20 portion of the planetary gear 2 is about 88.5% (average bulk density is 6.9 g / cm ³ ), and the average relative density of portions other than the teeth 20 is about 89.7. % (Average bulk density was 7.0 g / cm ³ ). Further, the average relative density of the entire sample B is about 89%.

  The mechanical strengths of the planetary gear 2 and the planetary carrier 3 of Sample B were significantly inferior to those of the planetary gear and the planetary carrier made of a solidified metal produced by a melting method. In particular, since the relative density of the teeth 20 of the planetary gear 2 to which high stress acts during use is low, the planetary gear 2 and the planetary carrier 3 of the sample B are considered to be inappropriate as components of an automobile.

  The method for producing a sintered body of the present invention can be suitably used for producing a sintered part having a complicated shape that is difficult to form only by pressure molding using a mold.

DESCRIPTION OF SYMBOLS 1 Assembly 2 Planetary gear 20 Tooth 3 Planetary carrier 31 1st part 31b Boss part 32 2nd part 32s Disk part 32b Bridge part 100 Cutting tool 200 Powder compacting body 201 Processing waste 202 Metal particle 300 Metal solid body 301 Processing waste

Claims (8)

Preparing a raw material powder containing iron-based metal powder;
A molding step of producing a green compact having an overall average relative density of 93% or more by uniaxially pressing the raw material powder using a mold;
A processing step of machining the green compact to produce a processed compact; and
A sintering step of sintering the processed molded body to obtain a sintered body;
A method for producing a sintered body comprising:   The method for manufacturing a sintered body according to claim 1, wherein in the processing step, the green compact is processed into a helical gear shape.   The method for producing a sintered body according to claim 1 or 2, wherein the pressure of the uniaxial pressurization is 600 MPa or more.   The said manufacturing process is a manufacturing method of the sintered compact of any one of Claims 1-3 performed using the cutting method.   The said processing process is performed while giving compressive stress to the said compacting body in the direction which cancels the tensile stress which acts on the said compacting body with a processing tool. The manufacturing method of the sintered compact of this. An iron-based sintered body,
The sintered compact whose average relative density of the said sintered compact is 93% or more.   The sintered body according to claim 6, wherein the sintered body is a helical gear.   The sintered body according to claim 7, wherein the teeth of the helical gear are inclined by 30 ° or more with respect to the axis of the helical gear.

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