WO2016021362A1

WO2016021362A1 - Method for manufacturing composite sintered body

Info

Publication number: WO2016021362A1
Application number: PCT/JP2015/069719
Authority: WO
Inventors: 孝洋奥野; 雄太伊藤; 大平　晃也
Original assignee: Ntn株式会社; 孝洋奥野; 雄太伊藤; 大平　晃也
Priority date: 2014-08-05
Filing date: 2015-07-09
Publication date: 2016-02-11

Abstract

A method for manufacturing a composite sintered body is carried out through: a step for forming an inner green compact (12) by compressing metal powder using a mold provided with a die (21) and upper and lower punches (22, 23); a step for removing the inner green compact (12) from the inner periphery of the die (21) and inserting the same into an outer green compact (13) by making the die (21) and another member (outer green compact (13)) disposed adjacent thereto on the upper side move as a unit downward with respect to the inner green compact (12); and a step for sintering an integrated product (11) of the inner green compact (12) and the outer green compact (13).

Description

Method for producing composite sintered body

The present invention relates to a method for producing a composite sintered body.

In recent years, in machine parts such as automobile parts, there are increasing demands for cost reduction, omission of processing steps, energy saving and resource saving by near net shape. In order to respond to such a request, mechanical parts made of sintered metal are sometimes employed.

A sintered metal mechanical part is formed by sintering a green compact obtained by compression-molding metal powder at a predetermined temperature. However, in the case of a machine part having a complicated shape, there is a possibility that the green compact cannot be molded with a desired accuracy. Therefore, a complex shaped machine part may be configured by a composite sintered body in which a plurality of green compacts and sintered bodies are prepared in advance and joined together.

Examples of the method for producing a composite sintered body include a method of forming a plurality of sintered bodies in advance and then joining them by a method such as press fitting or caulking. However, with such a method, it cannot be said that sintered bodies can be joined with sufficient strength.

As another method for producing a composite sintered body, a plurality of green compacts are formed and fired in an integrated state to sinter each green compact to form a sintered body. There is known a method of joining the two. As such a method, there is a method using a low melting point metal (for example, a copper infiltration joining method or a brazing method). Specifically, a plurality of green compacts containing low melting point metal powders are prepared and fired in an integrated state, whereby each green compact is sintered and the low melting point metal melts. Thereby, liquid phase sintering is accelerated | stimulated and several sintered compact is joined. However, in this case, since a plurality of sintered bodies are joined with a low-melting-point metal having low strength, there is a fear that the joining strength is insufficient.

Therefore, as a method for firmly joining a plurality of sintered bodies, there is a sintered diffusion bonding technique in which the joining surfaces are diffusion-bonded by sintering in a state where sufficient pressure is applied to the joining surfaces of the plurality of green compacts. Are known. For example, in Patent Document 1 below, an inner green compact and an outer green compact are fitted with an interference fit and sintered in this state, whereby both are sintered and diffusion bonded. *

When forming a composite sintered body using the above-mentioned sintered diffusion bonding, it is necessary to press the inner green compact into the inner periphery of the outer green compact before the sintering step. Because it is brittle, it is easily damaged during press-fitting. For example, in Patent Document 2 below, in order to facilitate press-fitting, a small diameter slightly smaller than the inner diameter of the outer green compact O is provided at the tip of the outer peripheral surface of the inner green compact I as shown in FIG. A portion I1 is provided, and a tapered surface I2 is provided above the small diameter portion I1 (reference numerals I1 and I2 in FIG. 6 are added in this document).

Japanese Patent No. 3246574 Japanese Examined Patent Publication No. 62-57682 JP 58-193304 A Japanese Patent No. 3045460

However, when the configuration as shown in FIG. 6 is adopted, minute protrusions for forming the small diameter portion I1 and the tapered surface I2 are provided on the outer diameter portion of the mold (punch) for forming the end surface of the inner green compact I. Since it is necessary, this minute protrusion is easily damaged during molding. Moreover, since the shape of the front-end | tip part of the inner green compact I is restrict | limited, the freedom degree of design will be lost.

Such a problem occurs not only when the green compacts are pressed into each other but also when the green compact and a member made of another material (for example, a melted material) are pressed in.

From the above, the first technical problem to be solved by the present invention is that, in the manufacturing process of the composite sintered body, when the green compact and other members are press-fitted, mold damage and green compact design freedom are achieved. The purpose is to prevent damage during press-fitting of the green compact without causing a decrease in the degree.

In addition, the sintered body is usually manufactured through a compacting process in which a powder mixture containing metal powder is compression-molded to form a compact and a sintering process in which the compact is sintered at a predetermined temperature. The Since the compacting process is often performed using a uniaxial press, if the compact has an undercut shape, the compact cannot be removed from the mold. For this reason, there is a limit to the shape of a product made of a sintered body.

For example, in the case of a composite sintered body formed by joining a plurality of sintered bodies, it is possible to manufacture a product having a complicated shape having an undercut shape. In manufacturing such a composite sintered body, a sintered diffusion bonding technique as described above is known as a method of joining a plurality of sintered bodies. In order to increase the bonding force by sintering diffusion bonding, for example, the interference between the green compacts may be increased. However, since the green compact is very fragile, there is a high risk of breakage if the tightening margin is simply increased.

For example, in Patent Document 3 described above, the carbon amount of the green compact (inner) having the shaft portion is set to be 0.2% or more higher in weight ratio than the carbon amount of the green compact (outer) having the hole portion. Thus, a method is shown in which the amount of expansion of the inner due to sintering is made larger than the amount of expansion of the outer to increase the joining force between the two members.

Moreover, in said patent document 4, in sintering and joining copper-type material to the hole part of iron-type material, while specifying the composition of copper-type material and sintering on predetermined conditions, copper-type material is obtained. A method of expanding and bonding to a ferrous material is shown.

However, both methods of Patent Documents 3 and 4 increase the tightening allowance by making the difference in expansion amount between the inner and outer different, but there is a limit to improving the bonding strength by such a method. . Moreover, in the method of patent document 4, when the ratio of copper is increased and the amount of expansion is enlarged, the density of a sintered compact will fall and intensity | strength will fall.

Such a problem is not limited to a composite sintered body formed by joining sintered bodies, but a composite sintered body formed by joining a sintered body and a member made of another metal material (for example, a melted material). Also occurs in the same way.

From the above, the second technical problem to be solved by the present invention is to increase the bonding strength of a plurality of members constituting the composite sintered body.

In order to solve the first problem, the first invention of the present application includes a step of forming an inner green compact by compressing metal powder using a die and a die having upper and lower punches, the die and the die The other member disposed adjacent to one side in the axial direction is integrally moved to the other side in the axial direction with respect to the inner green compact, thereby taking out the inner green compact from the inner periphery of the die. Provided is a method for producing a composite sintered body that is subjected to a step of press-fitting into the inner periphery of another member and a step of sintering an integrated product of the inner green compact and the other member.

¡When the inner green compact is removed from the inner periphery of the die, the outer peripheral surface of the inner green compact attempts to expand its diameter by releasing stress (spring back). In the present invention, as described above, the other member is disposed adjacent to one side in the axial direction of the die, and these are integrally moved to the other side in the axial direction with respect to the other member. Move from the inner circumference to the inner circumference of the other member. Thus, since the inner green compact can be press-fitted into the inner circumference of the other member before the inner green compact has completely expanded, the inner compact of the other member is expanded after the inner green compact has been completely expanded. The press-fitting resistance can be reduced as compared with the case of press-fitting around. Thereby, damage to the inner green compact can be prevented without changing the shape of the green compact or the mold.

Further, the present invention can be applied not only when the inner green compact is pressed into the inner circumference of the other member as described above, but also when the other member is press-fitted into the inner circumference of the outer green compact. That is, the present invention includes a step of forming an outer green compact by compressing a metal powder using a die, an upper and lower punch, and a mold including a core rod, and adjacent to the core rod and one axial side thereof. The core rod is taken out from the inner periphery of the outer powder compact by integrally moving the other member arranged to the other side in the axial direction with respect to the outer powder compact, and the inner periphery of the outer powder compact. It can also be characterized as a method for producing a composite sintered body through a step of press-fitting the other member and a step of sintering an integrated product of the outer green compact and the other member.

The present invention can be applied regardless of whether the other member is a green compact obtained by compression-molding a metal powder or a member made of a melted material or a sintered metal.

The second invention of the present application made to solve the second problem includes a first member made of a sintered metal containing iron and copper, and a second member made of a sintered metal or another metal material. In the composite sintered body bonded by diffusion bonding, the ratio of copper in the bonding surface between the first member and the second member is higher than the ratio of copper in the first member.

Further, the second invention of the present application compresses and molds a raw material powder containing iron-based powder and copper-based powder to form a first green compact, and compresses and molds a raw material powder having the same or different composition as the raw material powder. A step of forming the second green compact and heating the first green compact and the second green compact in a pressed state to sinter the first green compact and the second green compact. And obtaining the first member and the second member made of sintered metal, and joining the first member and the second member by diffusion bonding. Among the green compacts, the ratio of copper on the joint surface with the second green compact is higher than the ratio of copper inside the first green compact.

In addition, the second invention of the present application includes a step of compression-molding a raw material powder containing iron-based powder and copper-based powder to form a first green compact, and forming a second member with a metal material, and the first pressure By heating the powder and the second member in pressure contact with each other, the first green compact is sintered to obtain a first member made of sintered metal, and the first member and the second member. In the method for manufacturing a composite sintered body having a step of bonding the first green compact by diffusion bonding, the ratio of copper in the bonding surface with the second member of the first green compact is a ratio of the first green compact. It is characterized by being higher than the proportion of copper in the interior.

As described above, the ratio of the liquid phase (molten copper) intervening in the joint surfaces of both members increases during sintering by increasing the proportion of copper in the joint surfaces of the first member and the second member. As the molten copper solidifies, the joint strength between the two members is increased. In addition, since the iron contacted with the molten copper has improved sinterability, the ratio of the molten copper on the joint surface is increased, so that the sinterability of the iron-based powder exposed on the surface of the first member is improved. Bonding strength with the member is increased. At this time, the ratio of copper in the first member is made lower than the ratio of copper in the joining surface, thereby suppressing the expansion of the first member (sintered body) during sintering and preventing the strength from being lowered. Can do.

As described above, according to the manufacturing method of the first invention of the present application, when the green compact and other members are press-fitted, the green compact is not caused without causing damage to the mold or a reduction in the degree of freedom in designing the green compact. The body can be prevented from being damaged during press-fitting.

As described above, according to the second invention of the present application, the bonding strength of the first member and the second member constituting the composite sintered body can be increased.

It is sectional drawing of the machine component which consists of a composite sintered compact. It is sectional drawing which shows the procedure of the manufacturing method of the said mechanical component which concerns on embodiment of this invention 1st invention. It is sectional drawing which shows the procedure which shape | molds an inner green compact and integrates with the outer compact | molding previously shape | molded. It is sectional drawing which shows the procedure of the manufacturing method of the said mechanical component which concerns on other embodiment. It is sectional drawing which shows the procedure which shape | molds an outer compact and integrates with the preformed inner compact. It is sectional drawing which shows the conventional method of press-fitting inner green compact to the inner periphery of outer green compact. It is sectional drawing of the composite sintered compact which concerns on one Embodiment of this-application 2nd invention. It is sectional drawing which shows the procedure of the manufacturing method of the said composite sintered compact. The upper part is a side view of the flat copper powder, and the lower part is a plan view.

Hereinafter, an embodiment of the first invention of the present application will be described with reference to FIGS.

FIG. 1 shows a mechanical part 1 made of a composite sintered body. The mechanical component 1 includes an inner member 2 and an outer member 3. The outer peripheral surface 2a of the inner member 2 and the inner peripheral surface 3a of the outer member 3 have the same cross-sectional shape in the entire axial direction, and are cylindrical surfaces in this embodiment. In the illustrated example, the inner member 2 is a cylindrical shaft, and the outer member 3 is a gear having teeth 3b on the outer periphery. The outer peripheral surface 2a of the inner member 2 and the inner peripheral surface 3a of the outer member 3 are fitted with an interference fit and are diffusion bonded. The outer peripheral surface 2a of the inner member 2 and the inner peripheral surface 3a of the outer member 3 are not limited to cylindrical surfaces, and for example, splines may be formed on these surfaces and these may be fitted.

In the present embodiment, the inner member 2 and the outer member 3 are formed of sintered metal, for example, containing iron as a main component (that is, iron is contained most in a weight ratio, for example, 50 wt% or more, preferably 90 wt% or more). Made of ferrous sintered metal. In addition, copper-based sintered metal containing copper as a main component (that is, containing copper in the most by weight ratio, for example, containing 50 wt% or more), iron and copper as main components (that is, iron and copper in weight ratio). The inner member 2 and the outer member 3 may be formed of a copper-iron-based sintered metal, which is the most common two components (for example, each containing 25 wt% or more). Moreover, in this embodiment, although the inner member 2 and the outer member 3 are formed with the sintered metal of the same composition, you may form the inner member 2 and the outer member 3 with the sintered metal of a different composition.

The machine part 1 is manufactured by a method according to an embodiment of the present invention. Specifically, as shown in FIG. 2, a step of molding an outer green compact 13 as another member (see the left diagram of FIG. 2), an inner green compact 12, The mechanical component 1 is manufactured through a process of integrating 13 (see the center diagram in FIG. 2) and a process of sintering the integrated product 11 of the green compacts 12 and 13 (see the right diagram in FIG. 2).

The outer green compact 13 is formed by compression molding a raw material powder containing a metal powder. The raw powder of the outer green compact 13 is, for example, a mixture of iron powder, graphite powder, and a lubricant. In this embodiment, pure iron powder having a purity of 98% or more is used as iron powder, artificial graphite is used as graphite powder, and metal soap or amide wax is used as a lubricant. As for the composition of the raw material powder, for example, the graphite powder is 0.2 wt%, the lubricant is 0.3 wt%, and the balance is iron powder. By compressing the mixed powder with a mold, an outer green compact 13 having substantially the same shape as the outer member 3 shown in FIG. 1 is formed. In the present embodiment, compression molding of the outer green compact 13 is performed at room temperature. *

The inner green compact 12 is formed by compression molding a raw material powder containing a metal powder. In the present embodiment, the raw material powder of the inner green compact 12 is the same as the raw material powder of the outer compact 13 described above. As shown in FIG. 3, the mold for molding the inner green compact 12 includes a die 21, a lower punch 22, an upper punch 23, and a pressing member 24. In the present embodiment, the lower punch 22 is fixed on the base 25, and the die 21, the upper punch 23, and the pressing member 24 can be moved up and down with respect to the lower punch 22. In this embodiment, the compression molding of the inner green compact 12 is performed at room temperature. The compression molding of the inner green compact 12 may be performed with the mold heated.

In the molding process of the inner green compact 12, first, as shown in the upper left diagram of FIG. 3, the raw material powder M is filled into the cavity formed by the die 21 and the lower punch 22. In this state, as shown in the upper right diagram of FIG. 3, the inner powder compact 12 is formed by lowering the upper punch 23 and compressing the raw material powder M. At this time, by lowering the upper punch 23 and simultaneously lowering the die 21 by a predetermined distance (for example, half the compression stroke of the upper punch 23), the inner green compact 12 is relatively compressed from both the upper and lower sides, and the inner The density of the green compact 12 can be made uniform (floating die method).

Thereafter, as shown in the lower left diagram of FIG. 3, the outer green compact 13 is disposed adjacent to the upper side of the die 21. Specifically, the outer green compact 13 is placed on the die 21 while the inner peripheral surface 13 a of the outer green compact 13 is fitted to the outer peripheral surface 23 a of the upper punch 23. At this time, the inner diameter of the outer green compact 13 and the inner diameter of the die 21 are the same, and the inner peripheral surface 13 a of the outer green compact 13 is continuously provided above the inner peripheral surface 21 a of the die 21. The inner diameter of the outer compact 13 is not limited to the same as the inner diameter of the die 21 and may be slightly larger or smaller than this. Further, a chamfered portion may be provided on one or both of the lower end of the inner peripheral surface 13 a of the outer green compact 13 and the upper end of the inner peripheral surface 21 a of the die 21.

In this state, as shown in the lower right diagram in FIG. 3, the outer green compact 13 is pushed downward by the pressing member 24, and the outer green compact 13 and the die 21 are integrally lowered. Thereby, the inner green compact 12 is taken out from the inner periphery of the die 21 and inserted into the inner periphery of the outer green compact 13. At this time, the inner green compact 12 taken out from the inner periphery of the die 21 tries to expand the outer diameter by the spring back, but by arranging the die 21 and the outer green compact 13 adjacently, The inner green compact 12 can be press-fitted into the inner periphery of the outer green compact 13 before the inner green compact 12 is completely expanded in diameter. Specifically, when the upper end portion of the inner green compact 12 protrudes upward from the inner periphery of the die 21, most of the outer peripheral surface 12 a of the inner green compact 12 is restrained by the die 21. The diameter expansion amount at the upper end of 12 is very small. In this state, the upper end of the inner green compact 12 is inserted into the inner peripheral surface 13a of the outer green compact 13 from below so that the inner green compact 12 is fully expanded in diameter. Compared with the case of press-fitting, the press-fitting resistance can be greatly reduced. Thereby, since the inner green compact 12 can be smoothly press-fitted into the inner periphery of the outer green compact 13, damage to both the

green compacts

12 and 13 can be prevented.

At this time, the amount of spring back of the inner green compact 12 is adjusted by adjusting the molding pressure at the time of molding the inner green compact 12 (that is, the descending amount of the upper punch 23). The tightening allowance with the outer green compact 13 can be controlled. According to the verification by the present inventors, by setting the tightening margin to 10 μm or more, preferably 20 μm or more, the bonding strength of the two

green compacts

12 and 13, and consequently the bonding strength of the inner member 2 and the outer member 3 is sufficient. It turns out that it can be raised.

Thereafter, the integrated product 11 of the inner compact 12 and the outer compact 13 is taken out of the mold and carried into a heating device, and the integrated product 11 is fired at a predetermined temperature for a predetermined time. In the present embodiment, the integrated product 11 is baked in a vacuum pressure sintering furnace under an argon atmosphere. Specifically, the integrated product 11 was heated at 800 ° C. for 2.5 hours, further heated at 1300 ° C. for 3.3 hours, and then cooled in a furnace at 25 ° C. By firing the integrated product 11 in this way, the inner green compact 12 and the outer green compact 13 are sintered to form the inner member 2 and the outer member 3, respectively, and the outer peripheral surface 2a of the inner member 2 and the outer member 3 is diffusion-bonded to the inner peripheral surface 3a. Thus, the machine part 1 is completed.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the case where the two

green compacts

12 and 13 are integrated using a mold for molding the inner green compact 12 is shown, but the present invention is not limited to this, and the outer green compact 13 Both

green compacts

12 and 13 can also be integrated using the metal mold | die to shape | mold. For example, in the embodiment shown in FIG. 4, the inner green compact 12 formed in advance is arranged in a mold for molding the outer green compact 13, and the outer green compact 13 is separated from the mold, and at the same time, the outer green compact is formed. An inner green compact 12 is press-fitted into the inner periphery of the body 13. Specifically, the step of molding the inner green compact 12 as the other member (see the left figure in FIG. 4), the step of molding the outer green compact 13 and integrating the two green compacts 12 and 13 ( The center part of FIG. 4), the process of sintering the integrated article 11 of the green compacts 12 and 13 (see the right figure of FIG. 4), and the machine part 1 are manufactured. Hereinafter, the procedure of this manufacturing method will be described in detail.

First, the inner green compact 12 is compression molded using the same raw material powder as in the above embodiment (not shown). Thereafter, the outer green compact 13 is compression-molded using the same raw material powder as in the above embodiment. As shown in FIG. 5, the mold for molding the outer green compact 13 includes a die 31, a lower punch 32, an upper punch 33, a pressing member 34, and a core rod 35. In this embodiment, the lower punch 32 is fixed on the base 36, and the die 31, the upper punch 33, the pressing member 34, and the core rod 35 can be moved up and down with respect to the lower punch 32.

First, as shown in the upper left diagram of FIG. 5, a raw material powder M is filled into a cavity formed by a die 31, a lower punch 32, and a core rod 35. In this state, as shown in the upper right view of FIG. 5, the upper punch 33 is lowered to form the outer green compact 13. At this time, the outer green compact 13 is compression-molded by the floating die method in which the die 31 is lowered simultaneously with the compression by the upper punch 33 as in the above embodiment. In addition, although the shaping | molding die for shape | molding the teeth 13b (refer FIG. 1) to the outer peripheral surface of the outer compact 13 is provided in the inner peripheral surface of the die | dye 31, FIG. Omitted.

Thereafter, as shown in the lower left diagram of FIG. 5, the inner green compact 12 is disposed adjacent to the upper portion of the core rod 35. Specifically, the inner green compact 12 is placed on the core rod 35 while the outer peripheral surface 12 a of the inner green compact 12 is fitted to the inner peripheral surface 33 a of the upper punch 33. At this time, the outer diameter of the inner green compact 12 and the outer diameter of the core rod 35 are the same, and the outer peripheral surface 12 a of the inner green compact 12 is continuously provided above the outer peripheral surface 35 a of the core rod 35. The outer diameter of the inner green compact 12 is not limited to the same as the inner diameter of the core rod 35, and may be slightly larger or smaller than this. Further, a chamfered portion may be provided on one or both of the lower end of the outer peripheral surface 12 a of the inner green compact 12 and the upper end of the outer peripheral surface 35 a of the core rod 35.

In this state, as shown in the lower right diagram of FIG. 5, the inner green compact 12 is pushed downward by the pressing member 34, and the inner green compact 12 and the core rod 35 are integrally lowered. Thereby, the core rod 35 is taken out from the inner periphery of the outer powder compact 13 and the inner powder compact 12 is press-fitted into the inner periphery of the outer powder compact 13. Then, the integrated part 11 of the inner green compact 12 and the outer green compact 13 is taken out from the mold, and this is carried into a heating device and sintered to complete the mechanical component 1.

In the above embodiment, the case where the green compacts are press-fitted is shown. However, the present invention is not limited to this, and the above manufacturing method can be used even when the green compact and other members made of a molten material or sintered metal are press-fitted. Can be applied. Specifically, for example, in the embodiment shown in FIG. 3, the outer member 3 made of a molten material or a sintered metal may be disposed adjacent to the die 21 instead of the outer green compact 13. In the embodiment shown in FIG. 5, the inner member 2 made of a molten material or a sintered metal may be disposed adjacent to the core rod 35 instead of the inner green compact 12.

In the embodiment shown in FIG. 3, the outer green compact 13 is lowered after the outer green compact 13 is disposed adjacently above the die 21 (see the lower left diagram in FIG. 3). The inner green compact 12 may be raised from the state shown in the lower left diagram of FIG. Further, in the embodiment shown in FIG. 5, after the inner green compact 12 is disposed adjacently above the core rod 35 (see the lower left figure in FIG. 5), the inner green compact 12 is lowered, but this is not restrictive. The outer green compact 13 may be raised from the state shown in the lower left diagram of FIG.

Further, in the embodiment shown in FIG. 3, after the outer green compact 13 is disposed adjacent to the upper side of the die 21, the die 21 and the outer green compact 13 are integrally lowered. After the outer green compact 13 is disposed adjacent to the lower side of the die 21, the die 21 and the outer green compact 13 may be raised integrally. Further, in the embodiment shown in FIG. 5, after the inner green compact 12 is disposed adjacently above the core rod 35, the core rod 35 and the inner green compact 12 are integrally lowered. The core rod 35 and the inner green compact 12 may be integrally raised after the inner green compact 12 is disposed adjacently below the core rod 35.

Moreover, the manufacturing method of the present invention can be applied not only to mechanical parts made of a composite sintered body but also to parts for other uses made of a composite sintered body.

It goes without saying that the present invention is not limited to the above embodiment and can be applied without departing from the gist of the present invention.

Hereinafter, an embodiment of the second invention of the present application will be described with reference to FIGS.

FIG. 7 shows a composite sintered body 101 according to an embodiment of the present invention. The composite sintered body 101 is a gear provided with an outer member 103 as a first member and an inner member 102 as a second member. The inner member 102 is a cylindrical solid shaft. The outer member 103 has a cylindrical shape and has teeth 103b on the outer periphery. The outer peripheral surface 102a of the inner member 102 and the inner peripheral surface 103a of the outer member 103 are not limited to cylindrical surfaces, and for example, splines may be formed on these surfaces, and these may be fitted.

As shown in FIG. 8, the composite sintered body 101 is a step of forming an outer green compact 113 as a first green compact and an inner green compact 112 as a second green compact (the left figure of FIG. 8). Reference), a step of integrating the green compacts 112 and 113 (see the center diagram of FIG. 8), and a step of sintering the integrated product 111 of the green compacts 112 and 113 (see the right diagram of FIG. 8). Manufactured.

The outer green compact 113 is formed by mixing a raw material powder containing an iron-based powder and a copper-based powder and then compression-molding the raw material powder. In this embodiment, iron powder (pure iron powder) as iron-based powder, copper powder (pure copper powder) as copper-based powder, graphite powder, and solid lubricant are mixed as the raw powder of the outer green compact 113. Things are used. The iron-based powder is not limited to pure iron powder, and may be iron-based alloy powder containing an alloy additive element. Similarly, the copper-based powder is not limited to pure copper powder, and may be a copper-based alloy powder containing an alloy additive element.

As the iron powder, reduced iron powder, atomized iron powder, or the like can be used. In this embodiment, reduced iron powder is used as the iron-based powder.

Two types of copper powder are used: flat copper powder and normal copper powder. In addition, it is not always necessary to use a mixture of two types of copper powder. For example, all of the copper powder may be composed of only flat copper powder.

The flat copper powder is flattened by stamping or pulverizing electrolytic copper powder or atomized copper powder. The flat copper powder has a foil shape. Specifically, for example, the aspect ratio L / t between the length L and the thickness t is 10 or more. In the present embodiment, as the flat copper powder, one having a length L of 20 μm to 80 μm and a thickness t of 0.5 μm to 1.5 μm (aspect ratio L / t = 13.3 to 160) is mainly used. Here, “length” and “thickness” refer to the geometric maximum dimension of each flat copper powder 120 as shown in FIG. The apparent density of the flat copper powder is 1.0 g / cm ³ or less.

Usually, copper powder is copper powder (electrolytic copper powder or atomized copper powder) that has not been crushed or crushed. Usually, copper powder is granular and is clearly distinguished from flat copper powder in the form of foil. In this embodiment, electrolytic copper powder is usually used as the copper powder.

As the graphite powder, artificial graphite, natural graphite, graphite or the like can be used, and artificial graphite is used in this embodiment. As the solid lubricant, for example, wax or metal soap can be used, and in this embodiment, ethylene bisstearamide is used.

The composition of the raw material powder is such that the copper powder is 0.8 to 12.0 wt%, the graphite powder and the lubricant are 1.0 wt% or less, and the balance is iron powder. Further, the ratio of the flat copper powder in the raw material powder is set to 0.4 to 4.0 wt%. Note that one or both of the graphite powder and the lubricant may be omitted unless particularly necessary.

充填 Fill the powder mold cavity with the above mixed powder. At this time, since the raw material powder contains flat copper powder, the flat copper powder adheres to the mold surface. In addition, if a fluid lubricant is previously attached to the flat copper powder, the flat copper powder is easily attached to the mold surface. The adhesion of the fluid lubricant to the flat copper powder is preferably performed before mixing with the raw material powder. As the fluid lubricant, fatty acids, particularly linear saturated fatty acids can be used, for example, stearic acid can be used.

Compressing the mixed powder in this state forms the outer green compact 113 in a state where the flat copper powder 120 is segregated on the surface (see the upper part of the left diagram in FIG. 8). In the outer green compact 113 thus molded, the ratio of copper on the surface (in particular, the inner peripheral surface 113a) is higher than the ratio of copper in the interior (for example, a region having a depth of 100 μm or more from the surface).

The inner green compact 112 is formed by compression molding a raw material powder containing a metal powder. As the raw material powder of the inner green compact 112, for example, a powder mainly composed of iron-based powder is used, and in this embodiment, a raw material powder having the same composition as the raw material powder of the outer green compact 113 is used. For this reason, like the outer green compact 113, the inner green compact 112 is also formed with the flat copper powder 120 segregated on the surface, and the ratio of copper on the surface (particularly the outer peripheral surface 112a) is internal (for example, It is higher than the ratio of copper in the region having a depth of 100 μm or more from the surface (see the lower part of the left figure in FIG. 8).

In the present embodiment, the compression molding of the outer green compact 113 and the inner green compact 112 is performed at room temperature (about 25 ° C.). However, compression molding of one or both of the outer green compact 113 and the inner green compact 112 may be performed with the mold heated.

Next, the inner green compact 112 is press-fitted into the inner periphery of the outer green compact 113 (see the center diagram in FIG. 8). The interference between the inner peripheral surface 113a of the outer green compact 113 and the outer peripheral surface 112a of the inner green compact 112 is 5 to 10 μm. At this time, the flat copper is segregated on the outer peripheral surface 112a of the inner green compact 112 and the inner peripheral surface 113a of the outer green compact 113, so that the ratio of copper in the joint surfaces of the two

green compacts

112 and 113 is It is higher than the ratio of copper in the outer green compact 113 and the inner green compact 112.

Then, the integrated product 111 of the inner green compact 112 and the outer green compact 113 is carried into a heating device and fired for a predetermined time at a temperature equal to or higher than the melting point of copper (see the right figure in FIG. 8). This step is performed, for example, in a vacuum pressure sintering furnace under an argon atmosphere. By firing the integrated product 111 in this manner, the inner green compact 112 and the outer green compact 113 are sintered to form the inner member 102 and the outer member 103, and the outer peripheral surface 102a of the inner member 102 and the outer member are formed. The inner peripheral surface 103a of 103 is diffusion bonded. Specifically, the iron powders are joined to each other in both the

green compacts

112 and 113 to form a sintered body (the inner member 102 and the outer member 103) and exposed to the outer peripheral surface 102a of the inner member 102. The iron powder and the iron powder exposed on the inner peripheral surface 103a of the outer member 103 are diffusion bonded.

At this time, the copper contained in the

green compacts

112 and 113 is melted by firing the integrated product 111. As a result, when the molten copper enters (wet) between the iron powders on the surfaces of the

powder compacts

112 and 113, the force acting between the powders via the molten copper acts and sintering is likely to occur. Improves. Also, the diffusion of iron atoms is likely to occur due to the action of molten copper, and a copper-iron alloy layer is generated. As described above, a copper-iron alloy having high sinterability is generated on the surfaces of the inner member 102 and the outer member 103, so that the copper-iron alloy is strongly diffusion-bonded to each other, so that the inner member 102 and the outer member 103 are joined. The joint strength with is increased. In the present embodiment, as described above, the copper 130 is unevenly distributed on the surfaces of the inner green compact 112 and the outer green compact 113, and a relatively large amount of copper is present on the joint surfaces of the two

green compacts

112 and 113. Therefore, the effect of improving the joining force between the inner member 102 and the outer member 103 by the molten copper 130 (see the right figure in FIG. 8) is great, and both the

members

102 and 103 are firmly joined. Thus, the composite sintered body 101 is completed.

The composite sintered body 101 manufactured by the method as described above has the following configuration.

The outer member 103 is formed of a sintered metal, particularly, an iron-based sintered metal including iron and copper. The sintered metal constituting the outer member 103 is mainly composed of iron (that is, iron is contained most in a weight ratio). The outer member 103 of this embodiment contains 0.8 to 12.0 wt% of copper and 0 to 1.0 wt% of graphite, with the balance being iron and inevitable impurities.

The inner member 102 is formed of a sintered metal, for example, an iron-based sintered metal, particularly, an iron-based sintered metal containing copper. In this embodiment, the inner member 102 is formed of an iron-based sintered metal having the same composition as the outer member 103.

The outer peripheral surface 102a of the inner member 102 and the inner peripheral surface 103a of the outer member 103 are fitted with an interference fit and diffusion bonded. Specifically, the iron structure of the inner member 102 and the iron structure of the outer member 103 are diffusion bonded. More specifically, the copper-iron alloy layer formed on the iron structure of the outer peripheral surface 102a of the inner member 102 and the copper-iron alloy layer formed on the iron structure of the inner peripheral surface 103a of the outer member 103 are diffusion bonded. ing.

The ratio (area ratio) of copper in the joint surface between the outer member 103 and the inner member 102 is higher than the ratio (area ratio) of copper inside the outer member 103 and the inner member 102. That is, in the composite sintered body 101, copper is unevenly distributed in the vicinity of the joint surface between the outer member 103 and the inner member 102. Specifically, for example, the ratio of copper in the joint surface between the outer member 103 and the inner member 102 is 5 to 15% in terms of area ratio. On the other hand, the ratio of copper in the outer member 103 and the inner member 102 is 0.8 to 12% in terms of area ratio. Note that the ratio of copper in the joint surface between the outer member 103 and the inner member 102 and the ratio of copper in the outer member 103 and the inner member 102 are EPMA (electron beam microanalyzer) or EDX (energy dispersive X-ray spectroscopy). Method), etc., can be measured by line analysis using a quantitative analyzer.

The present invention is not limited to the above embodiment. Hereinafter, although other embodiment of this invention is described, the same code | symbol is attached | subjected to the location which has the same function as said embodiment, and duplication description is abbreviate | omitted. *

In the above embodiment, the case where the inner member 102 as the second member is formed of an iron-based sintered metal having the same composition as that of the outer member 103 is shown, but the present invention is not limited thereto. For example, the inner member 102 is made of an iron-based sintered metal having a composition different from that of the outer member 103, another sintered metal (copper-based or copper-iron-based sintered metal), or a metal material other than the sintered metal (for example, a steel material). Etc.).

For example, when the inner member 102 as the second member is formed of a steel material, the composite sintered body is manufactured through the following steps. First, the raw material powder containing iron-based powder and copper-based powder is compression-molded to form the outer green compact 113, and the steel member is machined to form the inner member 102. Next, the inner member 102 made of a steel material is press-fitted into the inner periphery of the outer green compact 113 to integrate them. Then, by heating an integrated product of the outer green compact 113 and the inner member 102, the outer green compact 113 is sintered to form the outer member 103 made of sintered metal, and the inner member 102 and the outer member are also formed. 103 is bonded by diffusion bonding.

Also in this case, since copper is unevenly distributed on the surface of the outer green compact 113, a relatively large amount of molten copper is generated between the outer green compact 113 and the inner member 102 by heating. The molten copper is solidified at the joint surface between the inner member 102 and the outer member 103, whereby the joining force between the

members

102 and 103 is increased. In addition, when the molten copper touches the iron powder on the surface of the outer green compact 113 or the surface of the inner member 102 made of steel, the sinterability of iron exposed on these surfaces is enhanced, and the outer member 103 and The joining force with the inner member 102 is further increased.

In addition, the inner member 102 may be formed of an iron-based sintered metal containing copper, and the outer member 103 may be formed of another metal material (sintered metal other than the iron-based material, melted material, or the like).

In the above embodiment, the case where the first member (inner member 102) is press-fitted into the inner periphery of the second member (outer member 103) has been described. You may manufacture a composite sintered compact by sintering in the state which pressed the end surfaces of the member.

Further, the composite sintered body of the present invention can be applied not only to gears but also to other machine parts. For example, a bearing, a cam, or the like may be configured by the composite sintered body of the present invention. The composite sintered body of the present invention can be applied not only to mechanical parts but also to parts for other uses.

The configurations of the first embodiment of the present invention and the second embodiment of the present invention described above can be combined as appropriate. For example, in the embodiment shown in FIGS. 2 and 3, the proportion of copper on the outer peripheral surface 12 a of the inner green compact 12 may be higher than the proportion of copper in the inner green compact 12. Alternatively, in the embodiment shown in FIGS. 4 and 5, the proportion of copper in the inner peripheral surface 13 a of the outer green compact 13 may be higher than the proportion of copper in the outer green compact 13.

In order to confirm the effect of the second invention of the present application, the following test was performed. First, a plurality of types of raw material powders having different compositions are prepared, and each raw material powder is compression-molded at a molding pressure of 1176 MPa at room temperature, and a cylindrical outer green compact having an outer diameter of 23 mm, an inner diameter of 16 mm, and an axial width of 7 mm. The body and a cylindrical inner green compact having an outer diameter of φ16 mm were formed. Then, the inner green compact was pressed into the inner periphery of the outer green compact. The clamping allowance for both compacts was 8 μm. This integrated product was sintered at 1130 ° C. for 60 minutes to form a composite sintered body. In a plurality of types of composite sintered bodies formed in this way, the bonding strength between the inner member and the outer member was investigated. With respect to the bonding strength, with one end face in the axial direction of the outer member supported by a jig, only the inner member was pushed in from the other axial side to apply a load, and the composite sintered body was broken at the bonding face. The bonding strength was a value obtained by dividing the maximum load at the time of breaking by the side area of the bonding surface between the inner member and the outer member. The evaluation criteria of the bonding strength were ◎ at 200 MPa or more, ◯ at 150 to 200 MPa, Δ at 100 to 150 MPa, and × at less than 100 MPa.

First, the bonding strength when the ratio of the copper powder in the raw material powder was changed was investigated. At this time, the ratio of the flat copper powder in the raw material powder was constant at 0.5 wt%. Table 1 shows the evaluation results of the composition and bonding strength of each test piece.

From the results shown in Table 1, the ratio of the copper powder in the raw material powder of the green compact (that is, the ratio of copper in the sintered body) is 0.8 wt% or more, desirably 1.0 wt% or more, more desirably 2 It can be said that it is preferably 0.0 wt% or more. This is presumably because when the proportion of copper in the sintered body is too small, the molten copper on the joining surface is insufficient, and the effect of improving the joining strength between the inner member and the outer member is reduced. From the results shown in Table 1, it can be said that the ratio of copper in the sintered body is 12.0 wt% or less, desirably 10.0 wt% or less, and more desirably 5.0 wt% or less. This is considered to be because when the proportion of copper in the sintered body is excessive, expansion during sintering of the sintered body by copper becomes too large, resulting in a decrease in density and a decrease in strength of the sintered body. .

Next, in order to confirm the effect of the addition of the flat copper powder, the addition amount of the copper powder in the raw material powder is made constant at 2.0 wt% (Table 2) or 5.0 wt% (Table 3). The bonding strength was measured by changing the ratio of.

From the results of Table 2 and Table 3, the ratio of the flat copper powder in the raw material powder of the green compact is 0.4 wt% or more, desirably 0.5 wt% or more, more desirably 1.0 wt% or more. It can be said that it is preferable. This is presumably because if the proportion of the flat copper powder is too small, the molten copper on the joint surface is insufficient, and the effect of improving the joint strength between the inner member and the outer member is reduced. Further, from the results of Table 2 and Table 3, the ratio of the flat copper powder in the raw material powder of the green compact is 4.0 wt% or less, desirably 3.0 wt% or less, more desirably 2.0 wt% or less. It can be said that it is preferable. This is considered to be because when the ratio of the flat copper powder is excessive, expansion during sintering of the sintered body with copper becomes too large, resulting in a decrease in density and a decrease in strength of the sintered body.

DESCRIPTION OF SYMBOLS 1 Mechanical component 2 Inner member 3 Outer member 11 Integral product 12 Inner compact 13 Outer compact 21 Die 22 Lower punch 23 Upper punch 24 Press member 31 Die 32 Lower punch 33 Upper punch 34 Press member 35 Core rod M Raw material powder

Claims

Forming an inner green compact by compressing metal powder using a die and a die having upper and lower punches; and
The inner green compact is moved to the inner periphery of the die by integrally moving the die and the other member arranged adjacent to the one side in the axial direction to the other side in the axial direction with respect to the inner green compact. Taking out from the inner circumference of the other member,
A method for manufacturing a composite sintered body, which is performed through a step of sintering an integral product of the inner green compact and the other member.
Forming an outer green compact by compressing metal powder using a die, upper and lower punches, and a mold provided with a core rod;
The core rod and the other member disposed adjacent to one side in the axial direction thereof are integrally moved to the other side in the axial direction with respect to the outer green compact so that the core rod is removed from the inner periphery of the outer green compact. And the step of press-fitting the other member into the inner periphery of the outer green compact,
The manufacturing method of the composite sintered compact performed through the process of sintering the integral product of the said outer green compact and the said other member.
The method for producing a composite sintered body according to claim 1 or 2, wherein the other member is a green compact obtained by compression-molding metal powder.
The method for producing a composite sintered body according to claim 1 or 2, wherein the other member is a member made of a molten metal or a sintered metal.
The method for producing a composite sintered body according to claim 1, wherein a ratio of copper in the joint surface with the other member in the inner green compact is higher than a ratio of copper in the inner green compact.
3. The method for producing a composite sintered body according to claim 2, wherein a ratio of copper in the joint surface with the other member in the outer green compact is higher than a ratio of copper in the outer green compact. *