JP2011089178A - Re-pressurization method for sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a re-pressurization method for a sintered compact by which, when a sintered compact subjected to sizing is re-pressurized by a pressing punch and a counter punch in a sizing die, the occurrence of burrs at an edge part on the pressing-direction distal end side of the re-pressurized sintered compact can be prevented, and to provide a sizing die which is suitable for the method. <P>SOLUTION: Upon the re-pressurization of the sintered compact 40, a sizing die 10 provided with the following constitution is used. The sizing die 10 to be used has in the axial direction thereof a bottom dead center region 3 having a length equal to the thickness of a sintered compact 40 subjected to sizing and a pore region 4 whose inside diameter is smaller than that of the bottom dead center region 3. Then, in the pore region 4, a clearance is prevented from being formed between the extended surface of the circumferential face of the sintered compact 40 subjected to sizing and the inner circumferential face of the sizing die 10. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for repressurizing a sintered body for correcting the flatness of a sintered body subjected to sizing for densifying the surface of the sintered body, and a sizing suitable for the repressurizing method. It is about the die.

  2. Description of the Related Art Conventionally, sintered bodies formed by sintering metal powder compacts have been used for automobile parts, general machine parts, and the like. Among such parts, parts such as sprockets and various gears are contacted with other parts such as a chain or another gear during use and receive contact stress (Hertz stress). In such parts, in order to increase the fatigue strength at the contact point with other parts and the vicinity thereof, the pores in the surface side region of the contact point (typically, in the case of gears, tooth surface and tooth bottom surface) are reduced. And densification is performed. This densification includes rolling, sizing, and forging as described in Patent Document 1.

  Of the methods for densification, sizing is a method conventionally used for correcting the dimensions of a sintered body. By diverting or partially changing this equipment, densification can be easily performed, and productivity is excellent.

  FIG. 3 is an explanatory view schematically showing a procedure for sizing a cylindrical sintered body, and is a center line of a cross section cut in parallel to a center line (shown by a one-dot chain line) of a sizing die 100 used for sizing. It is a figure which shows only the left half from. A specific method of sizing will be described with reference to FIG.

  In order to size the sintered body, first, as shown in FIG. 3I, a sizing die 100 having a sizing projection 11 on the inner peripheral surface is prepared, and a pressing punch 20 is used in the sizing die 100. The sintered body 40 is pushed in. The sintered body 40 is supported by the core rod 30 inserted into the central hole. Then, as shown in FIG. 3 (II), the sintered body 40 is sized by the sizing protrusion 11 when passing through the sizing protrusion 11. More specifically, the peripheral surface of the sintered body 40 is pressed from the outer peripheral side by the sizing protrusion 11, and as a result, the surface side region of the peripheral surface of the sintered body 40 is densified. As shown in FIG. 3 (III), the pressed sintered body 40 is finally held against the opposing punch 21 inserted into the sizing die 100 from the side opposite to the pressing punch 20.

  By the way, since the force which bends when the sintered compact 40 pushed in with the push punch 20 passes the sizing protrusion 11 acts, the flatness of the sintered compact 40 falls a little. Therefore, in order to correct the flatness of the sintered body 40 after sizing, re-pressurization may be performed in which the sintered body 40 after sizing is pressed and compressed by the punch 20 and the opposing punch 21.

JP 2004-010906 A

  However, when the sintered body after sizing is re-pressurized, as shown in FIG. 3 (III), a burr 41 may be generated at the edge of the sintered body 40 on the front side in the pushing direction.

The reason for the occurrence of burrs is that, as shown in FIG. 4 (partially enlarged view of FIG. 3 (III) above), in the sizing die 100, the insertion region 1, the sizing region 2, and the bottom dead center region 3 are defined in the axial direction. It is thought that there is a cause in the shape of the bottom dead center region 3. The definition of these areas is as follows.
Insertion area 1 ... Area from the insertion end of the sintered body 40 to the sizing protrusion 11 Sizing area 2 ... Area where the sizing protrusion 11 exists Bottom dead center area 3 ... When the sintered body 40 is re-pressurized, the sintered body Area to keep 40

  The bottom dead center region 3 will be specifically described. The length of the bottom dead center region 3 is formed to have a margin with respect to the thickness of the sintered body 40 after sizing. This is because it is assumed that the sintered body 40 having various thicknesses is sized. According to the shape of the bottom dead center region 3 as described above, the sintered body 40 not only spreads radially outward (leftward on the paper) during re-pressurization, but also toward the front end side in the pushing direction (lower on the paper). And a part of the expanded sintered body 40 becomes a burr 41 and is formed in the sintered body 40.

  The present invention has been made in view of the above circumstances, and one of its purposes is to re-pressurize a sintered body after sizing with a pressing punch and a counter punch in a sizing die. An object of the present invention is to provide a method for repressurizing a sintered body capable of preventing burrs from occurring at the edge on the front end side in the pressing direction of the sintered body, and a sizing die suitable for the repressurizing method.

  The method for repressurizing the sintered body of the present invention relates to a method for repressurizing the sintered body after sizing the sintered body obtained by sintering a compact of metal powder. Sizing is a surface side region including the peripheral surface by pressing the peripheral surface of the sintered body from the outer peripheral side by pressing the sintered body into the sizing die with a pressing punch and sizing protrusions formed on the inner peripheral surface of the sizing die. This is an operation to refine the process. The re-pressurization is performed at a position immediately after the sizing sintered body passes through the sizing projection in the sizing die, and the sizing body is squeezed between the pressing punch and an opposing punch facing the pressing punch. This is an operation to compress. And the re-pressurization method of the present invention was re-pressurized by re-pressurizing the sintered body after sizing with an indentation punch and a counter punch using a sizing die having the following configuration. It is characterized by suppressing generation | occurrence | production of the burr | flash at the edge part of the pressing direction in a sintered compact.

  The sizing die used in the method for repressurizing the sintered body of the present invention has a bottom dead center region having a length corresponding to the thickness of the sintered body after sizing on the axial direction side of the sizing protrusion in the axial direction. And a pore region having a predetermined length on the pushing direction side of the bottom dead center region and having a smaller inner diameter than the bottom dead center region. Among these regions, in the bottom dead center region, a first clearance is formed between the peripheral surface of the sintered body after sizing and the inner peripheral surface of the sizing die. In the pore region, a second clearance is formed between the inner peripheral surface of the sizing die and the outer peripheral surface of the opposing punch, and the extended surface of the peripheral surface of the sintered body after sizing and the inner periphery of the sizing die It is comprised so that a clearance may not be formed between surfaces.

  According to the method for repressurizing a sintered body having the above-described configuration, when the sintered body after sizing is repressurized, burrs are generated at the edge on the front end side in the pressing direction of the repressurized sintered body. This can be suppressed. This is because the protrusion of the compressed sintered body toward the front end side in the pressing direction can be physically pressed by the step formed near the boundary between the bottom dead center region and the pore region.

  In the repressurization method for the sintered body of the present invention, the first clearance and the second clearance are preferably set to predetermined values.

  First, the first clearance A is preferably 0.1 mm ≦ A ≦ 0.3 mm. The first clearance A is the clearance between the inner peripheral surface of the sizing die and the outer peripheral surface of the sintered body after sizing in the bottom dead center region, and when the sintered body after sizing is re-pressurized, It is a part which allows the spread when it spreads outward in the radial direction. For this reason, the first clearance A is required to have a certain size. Although the spread of the sintered body in the radial direction varies depending on the size of the sintered body, if the first clearance A is in the above range, the sintered body and the sizing die can be prevented from being seized. More preferably, the first clearance A is 0.1 mm ≦ A ≦ 0.2 mm.

  Next, the second clearance B is preferably 0 <B ≦ 0.02 mm. Since the second clearance is a clearance between the inner peripheral surface of the sizing die and the outer peripheral surface of the opposing punch in the pore region, it is preferably as small as possible. If it is the 2nd clearance B of the said range, the movement of the opposing punch within a sizing die can be made smooth. In addition, the small second clearance B means that the difference between the inner diameter of the sizing die in the bottom dead center region and the inner diameter of the sizing die in the pore region is large, and the firing at the time of re-pressurization is caused by the step formed between the two regions. The effect of suppressing the occurrence of burrs in the body is also enhanced. The more preferable second clearance B is 0.01 mm ≦ B ≦ 0.02 mm.

  Further, the sizing die of the present invention is used for sizing to make a surface side region including a peripheral surface of a sintered body obtained by sintering a compact of a metal powder, and is formed on an inner peripheral surface of a space into which the sintered body is pushed. The present invention relates to a sizing die having a sizing projection for pressing the peripheral surface of the sintered body from the outer peripheral side. This sizing die of the present invention has a bottom dead center region having a length corresponding to the thickness of the sintered body after sizing on the axial direction side with respect to the sizing projection in the axial direction, and a pushing direction from the bottom dead center region. And a pore region having a predetermined length on the side and having a smaller inner diameter than the bottom dead center region. The sizing die of the present invention is configured such that a first clearance is formed between the peripheral surface of the sintered body after sizing and the inner peripheral surface of the sizing die in the bottom dead center region, and the pores In the region, a second clearance is formed between the inner peripheral surface of the sizing die and the outer peripheral surface of the opposing punch, and between the extended surface of the peripheral surface of the sintered body after sizing and the inner peripheral surface of the sizing die It is characterized by not being formed in a clearance.

  The sizing die of the present invention can be suitably used for the above-described method for repressurizing the sintered body of the present invention. Of course, this sizing die may be used only for sizing the sintered body and not for repressurizing the sintered body.

  In the method of repressurizing the sintered body of the present invention, even if the sintered body is repressurized in the sizing die in order to correct the flatness of the sintered body after sizing, Burr is unlikely to occur. As a result, it is possible to reduce the effort of removing burrs from the sintered body after re-pressurization, and to reduce the physical properties of the sintered body due to the formation of burrs, for example, mechanical characteristics and electromagnetic characteristics Can be suppressed.

It is process explanatory drawing which shows typically the procedure which performs sizing and re-pressurization to a sintered compact using the sizing die of this invention, Comprising: The cross section cut | disconnected in parallel with the centerline (it shows with a dashed-dotted line) of a sizing die It is a figure which shows only the left half from the centerline. It is the elements on larger scale of this invention sizing die in the state by which the repressurized sintered compact is arrange | positioned. It is explanatory drawing which shows typically the procedure which performs sizing and re-pressurization to a sintered compact using the conventional sizing die, Comprising: The center of the cross section cut | disconnected in parallel with the centerline (it shows with a dashed-dotted line) of a sizing die It is a figure which shows only the left half from a line. It is the elements on larger scale of the conventional sizing die in the state by which the re-pressurized sintered compact is arranged.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2.

  The method for repressurizing the sintered body of the present invention is to correct the flatness of the sintered body in the sizing die used for sizing after performing sizing to densify the surface side region of the peripheral surface of the sintered body. belongs to. First, sizing will be briefly described, and then the method for repressurizing the sintered body of the present invention will be described in detail.

[Sizing]
In order to size the sintered body, the sintered body 40 supported by the core rod 30 is pushed into the through-hole of the sizing die 10 using the pushing punch 20 as shown in FIG. A sizing projection 11 for pressing the peripheral surface of the sintered body 40 from the outer peripheral side is provided on the inner peripheral surface of the through hole. Therefore, as shown in FIG. 1 (II), the peripheral surface of the sintered body 40 that moves to the back of the through hole by the pressing punch 20 is pressed toward the inside in the radial direction of the sintered body 40, The surface side region is densified. Then, as shown in FIG. 1 (III), the sintered body 40 pushed by the pushing punch 20 is finally stopped against the opposing punch 21 that has been fitted in the sizing die 10 in advance. Here, after the densified sintered body 40 passes through the sizing protrusions 11, it slightly springs back radially outward.

[Method of Repressurizing the Sintered Body of the Present Invention]
Next, in order to re-pressurize the sintered body 40 after sizing, as shown in FIG. 1 (III), the pressing punch 20 and the opposing punch 21 are placed with the sintered body 40 held inside the sizing die 10. The sintered body 40 is compressed between the punches 20 and 21 by being driven toward each other. That is, the method for repressurizing the sintered body of the present invention is performed by diverting the sizing die 10 used when sizing the sintered body 40. Here, the sizing die 10 used in the method for repressurizing the sintered body of the present invention is the sizing die of the present invention in which a design change is applied to a part of a conventional sizing die. This design change does not affect the sizing of the sintered body differently from the conventional sizing die.

<Sizing Die>
The sizing die 10 of the present invention shown in FIG. 2 (partially enlarged view of FIG. 1 (III)) is similar to the conventional sizing die described with reference to FIG. 4 in the insertion region 1, the sizing region 2, and the bottom dead center region. 3. The most characteristic features of the sizing die 10 are that the length of the bottom dead center region 3 (the axial direction of the sizing die 10) is shorter than that of the conventional sizing die and the pushing direction of the bottom dead center region 3 The pore region 4 having a predetermined length on the side and having a smaller inner diameter than the bottom dead center region 3 is defined.

  First, the bottom dead center region 3 is a region for retaining the sintered body 40 after sizing. The length of the bottom dead center region 3 is formed to a length corresponding to the thickness of the sintered body 40 to be repressed, that is, approximately the same as the length in the thickness direction of the sintered body 40 after sizing. . Further, the inner diameter of the bottom dead center region 3 is formed larger than the inner diameter of the sizing region 2.

  The first clearance A between the inner peripheral surface of the sizing die 10 and the outer peripheral surface of the sintered body 40 after sizing in the bottom dead center region 3 is preferably 0.1 mm ≦ A ≦ 0.3 mm. A more preferable first clearance A is 0.1 mm ≦ A ≦ 0.2 mm. The first clearance A is for allowing the sizing body 40 to expand when it springs back and expands radially outward. In addition, the first clearance A is a portion that allows the spread when the sintered body 40 spreads radially outward when the sintered body 40 after sizing is re-pressurized.

  On the other hand, the pore region 4 is a region having a smaller inner diameter than the bottom dead center region 3. In the pore region 4, a second clearance B is formed between the inner peripheral surface of the sizing die 10 and the outer peripheral surface of the opposing punch 21, and the extended surface of the peripheral surface of the sintered body 40 after sizing and the sizing A clearance is not formed between the inner peripheral surface of the die 10.

  First, the significance of the second clearance B will be described. The second clearance B is a clearance for smoothly moving the opposing punch 21 fitted in the sizing die 10 so as not to easily come out of the sizing die 10. is there. For this reason, the second clearance B is preferably as small as possible. Specifically, the second clearance B is preferably 0 <B ≦ 0.02 mm. The more preferable second clearance B is 0.01 mm ≦ B ≦ 0.02 mm.

  Next, the significance of preventing a clearance from being formed between the extended surface of the peripheral surface of the sintered body 40 and the inner peripheral surface of the sizing die 10 will be described. With such a configuration, as shown in FIG. 2, a step due to the difference in inner diameter between the bottom dead center region 3 and the pore region 4 is formed, and the step is a sintered body at the front end side in the pushing direction. It can be set as the structure distribute | arranged to 40 surfaces. As a result, even if the compressed sintered body 40 tries to spread toward the front end side in the pushing direction, the spread can be physically suppressed by the step.

[Effect of repressurizing method of sintered body]
According to the method for repressurizing the sintered body of the present invention, as described above, when the sintered body 40 is repressurized in the bottom dead center region 3 of the sizing die 10, It is possible to suppress the sintered body 10 from spreading to the side. Therefore, even if the sintered body 40 is re-pressurized to correct the flatness of the sintered body 40 after sizing, burrs are unlikely to occur at the edge of the sintered body 10 on the front side in the pushing direction.

  Incidentally, since the sizing projection 11 mechanically suppresses the re-pressurized sintered body 10 from spreading in the opposite direction at the edge portion in the direction opposite to the pushing direction of the sintered body 10, The burrs are of such a degree that they can be easily removed even if they occur.

  In this embodiment, first, a plurality of compacts of metal powder were prepared, and a plurality of sintered bodies were prepared by sintering them. And after performing the sizing for densifying the surrounding surface of a sintered compact with respect to this sintered compact, the repressurization which corrects the flatness of the sintered compact after a sizing was performed. At the time of re-pressurization, either the re-pressurization method of the sintered body of the present invention described with reference to FIGS. 1 or 2 or the conventional re-pressurization method of the sintered body described with reference to FIGS. The burrs were examined for the samples obtained through the respective methods.

A mixed powder prepared by mixing an Fe-based alloy powder and a lubricant was prepared as a raw material for a molded body that became a sintered body by sintering. This mixed powder was compression-molded with a cold mold to obtain a cylindrical molded body. The obtained molded body was placed in a pusher-type furnace and sintered in a nitrogen (N ₂ ) atmosphere to obtain a sintered material. Next, cutting was performed to form a through hole in the center of the sintered material, and a cylindrical material was obtained. This material was sized for densification. In addition, as already explained for sizing, there is no significant difference in the degree of densification of the sintered body even if the sizing die of the present invention or the conventional sizing die is used.

  Next, the sintered compact after the sizing was placed in the sizing die, and the sintered compact was re-pressurized between the pressing punch and the opposing punch.

  When the sintered body after re-pressurization obtained as described above was visually confirmed, in the sintered body re-pressurized by using a conventional sizing die, the edge on the front side in the indentation direction of the sintered body Burr was generated at the portion, and the burr could not be removed by rubbing with a resin brush. On the other hand, in the sintered body re-pressurized using the sizing die of the present invention, burrs were generated at the edge of the sintered body in the pushing direction, but the burrs were easily removed with a resin brush. . Therefore, the removal of burrs after re-pressurization does not require a separate process such as cutting, and can be handled only by brushing.

  The above-described embodiment can be appropriately changed without departing from the gist of the present invention, and is not limited to the above-described configuration. For example, the composition of the sintered body and the shape of the sintered body can be changed as appropriate.

  The method of repressurizing the sintered body of the present invention is reduced by sizing a member made of a sintered body obtained by sintering various types of gears such as wheel gears, sprockets, and other parts, which are formed by sintering a metal powder compact. This can be suitably used to correct the flatness of the sintered body.

DESCRIPTION OF SYMBOLS 10,100 Sizing die 11 Sizing protrusion 1 Insertion area 2 Sizing area 3 Bottom dead center area 4 Pore area 20 Push punch 21 Opposing punch 30 Core rod 40 Sintered body 41 Burr A 1st clearance B 2nd clearance

Claims (4)

A sintered body obtained by sintering a compact of a metal powder is pressed into a sizing die with a pressing punch, and the peripheral surface of the sintered body is pressed from the outer peripheral side by a sizing projection formed on the inner peripheral surface of the sizing die. After sizing the surface side area including the surface,
At the position immediately after the sintered body after sizing passes through the sizing projection in the sizing die, the sintered body is compressed by the pressing punch and the opposing punch opposite to the pressing punch. Pressurizing method,
The sizing die is
In the axial direction, a bottom dead center region having a length corresponding to the thickness of the sintered body after sizing on the push direction side with respect to the sizing projection, and a predetermined length on the push direction side with respect to the bottom dead center region. And a pore region having an inner diameter smaller than the bottom dead center region,
In the bottom dead center region, a first clearance is formed between the peripheral surface of the sintered body after sizing and the inner peripheral surface of the sizing die,
In the pore region, a second clearance is formed between the inner peripheral surface of the sizing die and the outer peripheral surface of the opposing punch, and the extended surface of the peripheral surface of the sintered body after sizing and the inner peripheral surface of the sizing die Configured so that no clearance is formed between
Using a sizing die with the above configuration, re-pressurize the sintered body after sizing with an indentation punch and a counter punch, and burrs are generated at the edge on the tip side in the indentation direction of the re-pressurized sintered body. A method for repressurizing a sintered body, characterized in that the suppression is performed.   2. The method for repressurizing a sintered body according to claim 1, wherein the first clearance A satisfies 0.1 mm ≦ A ≦ 0.3 mm.   3. The method for repressurizing a sintered body according to claim 1, wherein the second clearance B satisfies 0 <B ≦ 0.02 mm. Used for sizing the surface side region including the peripheral surface of the sintered body obtained by sintering the compact of the metal powder, and the peripheral surface of the sintered body is formed on the inner peripheral surface of the space into which the sintered body is pushed. A sizing die having a sizing projection to be pressed from the outer peripheral side,
The sizing die is
In the axial direction, a bottom dead center region having a length corresponding to the thickness of the sintered body after sizing on the push direction side with respect to the sizing projection, and a predetermined length on the push direction side with respect to the bottom dead center region. And a pore region having an inner diameter smaller than the bottom dead center region,
In the bottom dead center region, a first clearance is formed between the peripheral surface of the sintered body after sizing and the inner peripheral surface of the sizing die,
In the pore region, a second clearance is formed between the inner peripheral surface of the sizing die and the outer peripheral surface of the opposing punch, and the extended surface of the peripheral surface of the sintered body after sizing and the inner peripheral surface of the sizing die A sizing die characterized in that a clearance is not formed between the two.

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