JP4282084B2 - Method for manufacturing sintered parts - Google Patents

Description

  The present invention relates to a method for manufacturing sintered parts such as various gears and annular parts made of sintered metal manufactured by powder metallurgy, and relates to an improved technique for improving wear resistance.

Many of these types of sintered parts are iron-based alloys, and the density obtained by compressing and sintering the powder is about 6.8 to 7.2 Mg / m ³ . In sprockets (chain gears), gears with a large load, and the like, the wear resistance of the tooth surface is required more than other parts, and high density is effective as one means for that purpose. As a method for increasing the density, in the case of an iron-based sintered body, hot forging can be mentioned. Hot forging can produce high-density parts with almost no pores, but sintered parts that do not need to be densified as a whole will be over-quality and heavy, and vibration damping There is a disadvantage that the advantages of the porous body such as action and oil impregnation are impaired. In addition, hot forging requires a device that compresses the workpiece at a high temperature, and because it requires consideration to prevent oxidation of the workpiece being heated, it is cumbersome and expensive. There is.

  As another method for increasing the density, there is cold forging of the sintered body as described in Patent Document 1, and in particular, as a method for increasing the density (densification) of the tooth surfaces of the sintered gear. As described in Patent Document 2, there is gear rolling. In the rolling of the sintered body, the internal pores are the same as before rolling, and only the surface layer of the rolled tooth surface is densified, and the pitching wear resistance is improved, and a sintered gear with good gear accuracy is obtained. It is supposed to be done.

JP 2003-253372 A Japanese Patent Publication No. 48-33137

  The cold forging described in Patent Document 1 has a feature that gears can be densified by compression at room temperature. However, since a material made of a tablet-like sintered body (hereinafter referred to as a sintered material) is compressed and expanded in a mold and is closely attached to a die to form a tooth profile, a high pressure is required, A gear having a high tooth height has a disadvantage that the tooth tip density tends to be low. Further, when compressing to a state close to the true density by cold forging, there is a case where a sintered material having a weight larger than a predetermined value is compressed to a predetermined size because the weight of the sintered material varies. This must be avoided because the mold is likely to break, and therefore, as with hot forging, a larger mold that can create burrs and surplus will be used. The removal process is required, resulting in an increase in the number of processes.

  On the other hand, the rolling of the sintered gear described in Patent Document 2 is characterized in that the tooth surface and the tooth bottom surface of the gear can be densified and finished with high dimensional accuracy and can be provided with wear resistance. There is. However, there is a problem that it takes a relatively long time for rolling. In addition, with a gear having a relatively small module, the rolling allowance may not be large, so that uniform densification is difficult, and it is not suitable for densification of tooth portions and shaft hole portions.

  Therefore, in the case of a sintered gear, as shown in FIGS. 7 to 9, as shown in FIGS. 7 to 9, the thickness of only the tooth portion is increased, and the portion is compressed in the thickness direction in the re-pressing process to increase the tooth portion. A method of increasing the density was considered. This method is based on the same principle as the cold forging described above, but has the advantage that the pressing force of the punch can be reduced and the burden on the die can be reduced because only the tooth portion is compressed. FIGS. 7A and 7B show a side view and a cross-sectional view of a sprocket 31 made of a sintered body to be manufactured. As shown in FIG. In the sintered material 41, surplus portions 45a having a predetermined thickness are formed in advance on both sides in the thickness direction of the tooth portion forming portion 45 corresponding to the tooth portion 35, and the tooth surface of the sintered material 41 is formed. The inner peripheral surface 42a of the shaft hole 42 is restrained by the die 51 and the core rod 52, respectively, and the surplus portion 45a is compressed by the upper and lower punches 53 and 54 as shown in FIG. Then, as shown in FIGS. 9B to 9C, the surplus portion 45a is crushed and the tooth portion molding portion 45 is compressed, and the compressed tooth portion 35 is densified.

  However, in this method, as shown in FIG. 9C, in the tooth portion, the meat is not only crushed in the compression direction in the direction of the arrow A but also squeezed out radially inward in the direction of the arrow A ′. There is a behavior that plastic flow occurs, and for this reason, no matter how much it is compressed in the thickness direction, the meat to be compressed flows out radially inward, and there is a limit to increasing the density. FIG. 9D shows an example of the density distribution of the sprocket 31 when the tooth portion 35 is densified by this method. From the densified tooth portion 31, the inner peripheral portion without the tooth portion 31. In the region 33, there is a relatively wide region where the density gradually slopes, which indicates that the amount of meat that plastically flows from the tooth portion 31 toward the inner peripheral portion 33 is large.

  The present invention has been made in view of the above circumstances. In compression molding of a sintered part having a high density portion and a low density portion, the outflow of meat from the high density portion to the low density portion is suppressed. It is an object of the present invention to provide a method for manufacturing a sintered part, which can further increase the density of the density part and thereby form the high-density part and the low-density part relatively clearly.

  The present invention is a method for producing a sintered part comprising a high-density part, a low-density part having a lower density than the high-density part, and a step part connecting the high-density part and the low-density part. The compression direction is a direction that intersects the direction in which the high-density portion and the low-density portion are arranged, and as a material before compression, a high-density side surplus portion is formed on both sides of the compression direction, and is compressed and molded. A high-density molded part that forms a high-density part, a low-density molded part that is arranged in a state displaced in one direction of compression with respect to the high-density molded part, and that becomes the low-density part after compression molding, and these The high-density molded part and the low-density molded part are connected, and the thickness gradually increases from the low-density molded part side toward the high-density molded part side on the other side opposite to the one direction in the compression direction. A step portion side surplus portion is formed, and has a step portion forming portion that forms the step portion after compression molding A sintered material composed of a bonded body is prepared, and the high-density portion is molded by compressing the high-density molded portion and crushing the high-density side surplus portion in a state where the outer periphery of the sintered material is constrained. A step portion is formed between the high density portion and the low density portion by compressing and crushing at least the step portion side surplus portion of the step portion forming portion, and the high density portion, It is characterized in that a sintered part having the low density part and the step part connecting the high density part and the low density part is obtained.

  According to the present invention, for example, when manufacturing a sprocket as shown in FIG. 7, the tooth portion is a high-density portion, and the inner peripheral portion of the tooth portion on the inner peripheral side is a low-density portion. A sprocket having a stepped portion will be manufactured. In that case, when the high-density formed portion of the sintered material is compressed in the thickness direction and the surplus portion is crushed, as shown in FIG. 9C, in the tooth portion, in the inner peripheral direction, that is, in the low-density portion direction. In the case of the present invention, the meat that flows out flows out in the direction of the stepped portion opposite to the restrained side surface.

  However, the sintered material of the present invention has a stepped portion surplus portion on the side opposite to one direction (one thickness direction) in which the low density formed portion is shifted with respect to the high density formed portion of the step formed portion. This step-side surplus part is compressed at the same time, so that in the step-forming part, in addition to the meat that plastically flows straight in the compression direction, according to the shape of the step, high-density forming Meat that plastically flows in the direction of the part is produced. That is, in the stepped portion forming portion, the movement of the meat facing the meat flowing out from the high density formed portion to the stepped portion forming portion occurs. Due to the flow of this part of the meat, the movement of the meat flowing out from the high-density molded part to the stepped molded part is suppressed, and as a result, the degree of compression of the high-density molded part increases, The high density portion is effectively densified.

  Even in the conventional method as shown in FIG. 9, if the thickness of the surplus portion of the tooth portion is increased, although the meat flows out to the inner peripheral portion, the degree of compression increases and the densification of the tooth portion is not possible. is there. However, when such a method is adopted, the burden on the mold is large, which causes a problem that the burden on the apparatus increases, such as an increase in the size of the mold and an increase in compression capacity. However, in the case of the present invention, a stepped portion is provided in the sintered material and a stepped portion side surplus portion is formed, which suppresses the outflow of meat from the high density portion formed portion toward the stepped portion formed during compression. Since the high-density part can be made into a high-density part without increasing the compression capacity, there is an advantage that an increase in production burden such as an increase in the size of the mold can be suppressed.

  In the present invention, a part of the meat of the compressed stepped part flows in the direction of the high density formed part, and the high density formed by effectively preventing the meat flowing from the high density formed part in the direction of the step formed part. In order to increase the degree of compression of the part, the thickness h1 corresponding to the compression direction dimension of the high-density part in the sintered part after molding, and the step amount h2 with respect to the high-density part of the low-density part due to the formation of the step part, Ratio: h2 / h1 is preferably ¼ or more.

  Moreover, as an example of the cross-sectional shape of the step part of the sintered part after shaping | molding, linear shape, arc shape, etc. are mentioned. In the case of a straight line, it is desirable that the inclination angle of the step portion with respect to the high-density portion is 10 ° or more and less than 90 °.

  According to the present invention, when the high-density portion is compression-molded, the sintered material is formed in a shape that suppresses the outflow of meat that impairs the improvement in the degree of compression of the high-density portion. As a result, the density of the portion is effectively increased, and a sintered part in which the high-density portion and the low-density portion are relatively clearly separated can be easily manufactured.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a sprocket (sintered part) 1A made of a sintered body manufactured by the manufacturing method of one embodiment, and this sprocket 1A is formed around a shaft hole 2 into which a shaft is fitted and fixed. An annular inner peripheral portion (low density portion) 3, a cap-shaped step portion 4 formed around the inner peripheral portion, and a tooth portion (high density portion) formed around the step portion 4 5 having a uniform thickness. In the tooth portion 5, a large number of teeth 5a are formed at equal intervals in the circumferential direction, and a tooth gap 5b exists between the teeth 5a.

The sprocket 1A is obtained by re-pressing a sintered material made of a sintered body in the thickness direction. The tooth portion 5 has a high density (7.6 Mg / m ³ or more), and the inner peripheral portion 3 has a tooth. It is molded at a lower density (about 7.2 Mg / m ³ ) than part 5. The inner peripheral portion 3 is displaced in one thickness direction (upward in FIG. 1B) with respect to the tooth portion 5 due to the formation of the step portion 4, and the surfaces of the tooth portion 5 and the inner peripheral portion 3 The directions are parallel.

  As shown in FIG.1 (c), the step part 4 which connects the tooth | gear part 5 and the inner peripheral part 3 has a linear cross-sectional shape, and the inclination | tilt angle (theta) with respect to the tooth | gear part 5 is 10 degrees or more, and It is set within a range of less than 90 °. Further, the ratio of the thickness h1 of the tooth portion 5 (though the thickness of the entire sprocket 1A) and the step amount h2 of the inner peripheral portion 3 is set to 1/4 or more. In the case of this sprocket 1A, the radial lengths of the inner peripheral portion 3 and the tooth portion 5 are approximately the same, and the radial length of the step portion 4 is, for example, about half of the inner peripheral portion 3.

Next, the re-pressure process for manufacturing the sprocket 1A will be described.
FIG. 2 shows a preparation stage before a material (hereinafter referred to as a sintered material) 11A made of a sintered body before being re-press-molded into the sprocket 1A is compressed in the thickness direction by the mold 20. The sintered material 11A has a shape similar to that of the sprocket 1A, and is formed around the inner periphery molding portion (low density molding portion) 13 formed around the shaft hole 12 and the inner periphery molding portion 13. This is a sintered body in which a shade-shaped stepped portion forming portion 14 and a tooth portion forming portion (high density forming portion) 15 formed around the stepped portion forming portion 14 are integrally formed. A large number of teeth are formed in the tooth portion molding portion 15 at equal intervals in the circumferential direction. The step forming portion 14 linearly extends from the inner peripheral end of the tooth forming portion 15 to the inner peripheral side while rising in one thickness direction (upward in FIG. 2), and the inner periphery of the step forming portion 14. From the end, the inner peripheral portion molding portion 13 extends in parallel with the tooth portion molding portion 15 toward the inner peripheral side. It can be said that the inner peripheral portion molding portion 13 is arranged in a state shifted in one thickness direction (upward in FIG. 2) with respect to the tooth portion molding portion 15 due to the stepped portion molding portion 14.

  On both surfaces of the tooth forming portion 15, that is, on the upper and lower end surfaces in FIG. 2, tooth portion surplus portions (high density side surplus portions, thickness portions on the outer surface side from the broken line) 15a having a certain thickness are formed. The tooth part molding part 15 is formed thicker than the other parts. Further, in the stepped portion forming portion 14 in the direction of rising from the tooth portion forming portion 15 to the inner peripheral portion forming portion 13, that is, on the lower surface that is the surface opposite to the upper side, the tooth portion forming from the inner peripheral portion forming portion 13 side. The thickness gradually increases toward the portion 15, and a step-side surplus portion 14 a having a triangular cross section that is continuous without a step is formed on the lower surface of the tooth-forming portion 15. In this case, the thickness of the inner peripheral portion molding portion 13 is substantially the same as that of the inner peripheral portion 3 after re-pressing.

  The mold 20 is coaxially fitted in the die 21 and a die 21 having a cylindrical inner wall surface 21a in which a tooth surface (side surface on the opposite side) which is an outer peripheral surface of the sintered material 11A is slidably fitted. A core rod 22 that is slidably inserted into the shaft hole 12 of the sintered material 11A, and upper and lower cylindrical punches 23 that press the upper and lower end faces of the sintered material 11A to compress the sintered material 11A in the thickness direction; 24. The punch surfaces of the upper and lower punches 23 and 24 have dimensions and shapes corresponding to the upper and lower end surfaces of the sprocket 1A after re-pressing.

  As shown in FIG. 2, in the sintered material 11A, the inner peripheral portion molding portion 13 projects upward in the die 21, and the tooth surface fits into the cylindrical inner wall surface 21a so that it cannot move in the radial direction. It is restrained like this. Further, the core rod 22 is inserted into the shaft hole 12, and the inner peripheral surface 12a is restrained so as not to move in the radial direction. From such a set state, the sintered material 11A is re-pressurized when the upper and lower punches 23, 24 move to the sintered material 11A side. The punch surfaces of the upper and lower punches 23 and 24 have the same size and shape as the upper and lower surfaces of the sprocket 1A after re-pressing. Therefore, the upper and lower punches 23 and 24 contact the sintered material 11A. As a result of the contact, the upper punch 23 is formed only on the upper surface of the tooth surplus part 15a of the tooth part molding part 15 because the tooth part surplus part 15a is formed on the upper and lower end surfaces of the tooth part molding part 15. The lower punch 24 hits only the lower surface of the tooth part surplus part 15 a of the tooth part forming part 15, and a gap is formed between the step part forming part 14 and the inner peripheral part 3.

  As shown in FIG. 3 (a), when the compression operation in which the upper and lower punches 23 and 24 approach each other starts, first, the tooth side surplus portion 15a is crushed, and as shown in FIG. 3 (b), The lower punch 24 causes the stepped portion surplus portion 14a of the stepped portion forming portion 14 to be crushed from the outer peripheral side. Then, as shown in FIGS. 3C to 3D, the tooth side surplus portion 15a is further crushed and the step side surplus portion 14a is further crushed, so that the upper and lower punches 23 and 24 are fired. The bonded material 11A is in close contact with the entire upper and lower end faces, or is further slightly compressed, and then the recompression of the sintered material 11A is completed, and the sprocket 1A shown in FIG. 1 is obtained.

  In such a compression operation, when the tooth portion forming portion 15 is compressed in the thickness direction as indicated by an arrow A in FIGS. 3A to 3C, the tooth portion surplus portion 15a is crushed. In the part forming part 15, the tooth surface is restrained by the die 21 so that the plastic flow of the meat does not occur in the outer circumferential direction, but the meat flows out in the direction of the stepped part forming part 14 opposite to the tooth surface. To go. On the other hand, when the stepped portion surplus portion 14a inclined with respect to the toothed portion forming portion 15 is compressed, the stepped portion forming portion 14 has a compression direction B as shown in FIGS. Then, a phenomenon occurs in which the meat plastically flows in the direction of the component force D, which is orthogonal to the direction C toward the outer peripheral side.

  As shown in FIG. 3 (d), the flow of the meat in the direction of the component force D of the meat is a direction D ′ opposite to the meat flowing out in the direction A ′ from the tooth forming part 15 to the step forming part 14. Acts as a meat flow. Due to the flow of the meat in the facing direction D ′, the movement of the meat flowing out from the tooth forming part 15 to the step forming part 14 is suppressed. As a result, the degree of compression of the tooth forming part 15 is increased and the compression is performed. The densified tooth portion 5 is effectively densified. FIG. 3 (e) shows an example of the density distribution of the sprocket 1 </ b> A obtained in this embodiment, and the density distribution in the stepped portion 4 between the high-density tooth portion 5 and the low-density inner peripheral portion 3. The inclined region is formed in a narrow range, and the high-density tooth portion 5 and the low-density inner peripheral portion 3 are relatively clearly separated.

  In the sprocket 1A, the cross-sectional shape of the step portion 4 is linear. However, in the present invention, the sprocket 1B can be applied to a sprocket 1B having a circular cross-section of the step portion 4 as shown in FIG. FIG. 5 shows a sintered material 11B before re-pressing the sprocket 1B and a re-pressing die 20. The sintered material 11B in this case also has a tooth part molding part 15, a step part molding part 14, and an inner peripheral part molding part 13, and the tooth part side margin of uniform thickness is provided on both surfaces of the tooth part molding part 15. A meat portion 15a is formed, and a step portion side surplus portion 14a whose lower surface is linearly inclined is formed on the lower surface side of the step portion forming portion 14. As the mold 20, the die 21 and the core rod shown in FIG. 2 are used, but the upper and lower punches 23, 24 corresponding to the upper and lower end faces of the sprocket 1B are used, and in particular, the step portion 4 can be formed. It has a shape. In the sprocket 1B in this case, the ratio h2 / h1 between the thickness h1 of the tooth portion 5 and the stepped amount h2 of the inner peripheral portion 3 is set to 1/4 or more, similarly to the sprocket 1A. .

  FIGS. 6A to 6C show a state in which the sintered material 11B is compressed in the thickness direction by the upper and lower punches 23 and 24. In this case, as shown in FIG. First, the upper punch 23 compresses the upper tooth portion side surplus portion 15a of the tooth portion 5 forming portion, and the lower punch 24 compresses the step portion side surplus portion 14a. Subsequently, FIG. As shown to b), the tooth | gear part shaping | molding part 15 is compressed from the upper and lower sides, and the step part side surplus part 14a is compressed further.

  Also in this case, in the process in which the stepped portion surplus portion 14a is compressed, as shown in FIGS. 6 (a) and 6 (b), the stepped portion forming portion 14 is orthogonal to the compression direction B. Thus, a phenomenon occurs in which the meat plastically flows in the direction of the component force D with the direction C toward the outer peripheral side. As shown in FIG. 6C, the flow of the meat in the direction of the component force D is in the direction D ′ facing the meat flowing out from the tooth forming part 15 in the direction A ′ of the stepped part forming part 14. The movement of the meat that acts as a flow of meat and flows out from the tooth forming part 15 to the step forming part 14 is suppressed, and as a result, the densified tooth part 5 is effectively densified. FIG. 6D shows an example of the density distribution of the sprocket 1B obtained in this embodiment, and the density distribution in the stepped portion 4 between the high-density tooth portion 5 and the low-density inner peripheral portion 3 is shown. The inclined region is formed in a narrow range.

  In addition to the sprocket as in the above embodiment, the present invention is applied when manufacturing a sintered part having a high-density portion at a necessary portion, such as an oil pump rotor, a gear for a speed reducer, and a toothed belt pulley. Can do.

It is (a) side view, (b) sectional drawing, and (c) expanded sectional view of the sprocket manufactured with the manufacturing method of one embodiment of the present invention. It is sectional drawing which shows the state by which the sintering raw material used by one Embodiment was set to the metal mold | die. (A)-(d) is sectional drawing which shows the compression process in the manufacturing method of one Embodiment, (e) is sectional drawing which shows the density distribution of the sprocket after manufacture. It is (a) side view, (b) sectional drawing, (c) expanded sectional view of the sprocket of other embodiments of the present invention. It is sectional drawing of the state by which the sintering raw material of other embodiment was set to the metal mold | die. (A)-(c) is sectional drawing which shows the compression process in the manufacturing method of other embodiment, (d) is sectional drawing which shows the density distribution of the sprocket after manufacture. It is the (a) side view and (b) sectional view of the sprocket manufactured by one conventional method. It is sectional drawing which shows the state by which the sintering raw material used with one conventional method was set to the metal mold | die. (A)-(c) is sectional drawing which shows the compression process by one conventional method, (d) is sectional drawing which shows the density distribution of the sprocket after manufacture.

Explanation of symbols

1A, 1B ... Sprocket (sintered parts)
3 ... Inner circumference (low density part)
4 ... Step part 5 ... Tooth part (high density part)
11A, 11B ... Sintered material 13 ... Inner circumference molding part (low density molding part)
14a ... Step side surplus part 14 ... Step part forming part 15a ... Tooth part side surplus part (high density side surplus part)
15 ... Tooth part molding part (high density molding part)
h1 ... thickness h2 ... level difference

Claims (4)

A method for producing a sintered part comprising a high-density part, a low-density part having a lower density than the high-density part, and a step part connecting the high-density part and the low-density part,
The compression direction is a direction that intersects the direction in which the high-density portion and the low-density portion are arranged,
As a material before compression, a high-density side surplus part is formed on both sides in the compression direction, and a high-density molded part that is compression-molded to form the high-density part,
A low-density molded part that is arranged in a state shifted in one direction of compression with respect to the high-density molded part, and is the low-density part after compression molding,
The high-density molded part and the low-density molded part are connected, and the thickness gradually increases from the low-density molded part side toward the high-density molded part side on the other side opposite to the one direction in the compression direction. A stepped portion surplus portion is formed, and a sintered material made of a sintered body having a stepped portion forming the stepped portion after compression molding is prepared,
In a state where the outer periphery of the sintered material is constrained, the high-density part is compressed to crush the high-density side surplus part and to form the high-density part,
By compressing and crushing at least the step portion side surplus portion of the step portion forming portion, a step portion is formed between the high density portion and the low density portion,
A method for producing a sintered part, comprising: obtaining a sintered part having the high-density part, the low-density part, and the step part connecting the high-density part and the low-density part.   The ratio of the thickness h1 corresponding to the compression direction dimension of the high-density part in the sintered part and the step amount h2 to the high-density part of the low-density part due to the formation of the step part: h2 / h1 It is 1/4 or more, The manufacturing method of the sintered component of Claim 1 characterized by the above-mentioned.   The cross-sectional shape of the step portion of the sintered part is linear, and an inclination angle of the step portion with respect to the high-density portion is 10 ° or more and less than 90 °. Manufacturing method of sintered parts.   The method for manufacturing a sintered part according to claim 1 or 2, wherein the stepped portion of the sintered part has an arcuate cross-sectional shape.

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