JP2003286504A - Method for manufacturing sintered member with bore superior in coaxiality accuracy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a sintered member with a bore superior in coaxiality accuracy. <P>SOLUTION: In a process of manufacturing the sintered member with the bore, when performing a primary compression molding and a secondary compression molding with the use of a compacting mold consisting of a die, a core rod inserted in the central part inside a die hole of the die, an upper punch, and a lower punch, the manufacturing method employs the mold having chamfering protrusions on the inner and/or outer circumferential parts of the upper and/or lower punches, wherein the chamfering protrusion of the upper punch or the lower punch used for the secondary compression molding is equal to or larger than that used for the primary compression molding. Thereby, the coaxiality accuracy of the inside and outside perimeters is improved. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a sintered member having an inner hole, which includes compression molding a plurality of times, and more particularly to improvement of coaxiality accuracy of inner and outer circumferences.

[0002]

2. Description of the Related Art Powder metallurgical products can be processed into shapes close to those of parts, and cutting costs can be reduced. In recent years, many have been used as parts for internal combustion engines from the viewpoint of reducing the manufacturing cost of internal combustion engines. Has been done. Since a considerable load is applied to parts for internal combustion engines, materials having high strength and excellent slidability are required.

As a method for obtaining a material having a high strength, that is, a high density, a warm compaction, a double compression and a double sintering method (2P2S
Method), or a sintering forging method is generally known.
However, for example, in the powder metallurgy product manufactured by using the 2P2S method, the dimensional accuracy is insufficient to completely omit the cutting process, and therefore, the sizing treatment or the like is added to improve the dimensional accuracy. . However, the amount of deformation due to the sizing process is naturally limited, and the dimensional accuracy of the product may be insufficient depending on the dimensional accuracy before the sizing process.

For example, as a sintered body having an inner hole, a mold having a core rod inserted into a mold hole (die hole) of a molding die is used, raw material powder is filled in a die hole around the core rod, and the raw material powder is punched. Compress in the length direction of the core rod using
It has been manufactured by forming a molded product having a temporary inner hole, further subjecting it to sizing treatment to correct the shape, and sintering. However, in the sintered body manufactured by such a technique, when the height is larger than the inner hole diameter, there is a problem that the inner hole diameter near the opening is smaller than the inner hole diameter in the central portion.

To address such a problem, for example, Japanese Patent Laid-Open No. 61
-210102 proposes a high-precision manufacturing method of a sintered body having an inner hole (hollow hole) using a core rod whose outer peripheral wall tapers toward the opening side of the hollow hole (inner hole). Is proposed. The sintered body manufactured by the technique described in JP-A-61-210102 is said to have inner holes (hollow holes) with high circularity.

Further, in Japanese Patent Application Laid-Open No. 61-210106, a compact obtained by compacting raw material powder is subjected to induction hardening treatment to form a quenching layer on the surface layer of the compact, and then sizing. A method of obtaining a highly accurate sintered body by performing treatment has been proposed. In the technique described in Japanese Patent Laid-Open No. 61-210106, the deformation caused by the sizing treatment can be absorbed by the porous portion inside the quenching layer, and the dimensional accuracy is improved. However, there is a limit to the increase in the porosity of the porous portion, and naturally there is a limit to the improvement of the accuracy of hollow holes (inner holes) by the technique described in JP-A-61-210106.

Although the dimensional accuracy of the inner diameter and the outer diameter of the sintered body having the inner hole is considerably improved by the technique as described above, the difference between the inner diameter-based axis center and the outer diameter-based axis center (of the inner and outer circumferences) The coaxial precision) is usually determined by the precision during molding. In manufacturing a camshaft that assembles multiple sintered bodies (cams) with inner holes onto a shaft, in addition to the dimensional accuracy of the inner diameter of the sintered body (cam), the outer diameter of the outer peripheral portion of the sintered body (cam) It is required to improve the accuracy of coaxiality between the shaft center based on the axis and the shaft center based on the inner diameter of the inner peripheral portion of the sintered body (cam). In particular, recently, sintered bodies (cams) made of different materials may be assembled on the same shaft, and further improvement of coaxiality accuracy is demanded.

In response to such a demand, for example, Japanese Patent Laid-Open No. 2001-2001
-293531 discloses a work (sintered body) having an inner peripheral portion and an outer peripheral portion that define a hole, and a die having a die hole and a core rod arranged in the die hole is used. The inner periphery of the work is squeezed by the outer periphery of the core rod while the outer periphery of the work is constrained by the inner periphery of the die hole. There has been proposed a method for improving the inner diameter accuracy of a work, which includes an ironing step for increasing the coaxiality with the axis center based on the outer diameter of the workpiece.

Further, in Japanese Patent Laid-Open No. 2001-198645, a material having a thickness larger than that of a cam lobe to be manufactured, a small outer shape, and an axial hole slightly larger than the shape of the axial hole is manufactured. An outer mold having a wall surface complementary to the contour shape of the cam lobe to be formed, a middle mold having a wall surface complementary to the shape of the axial hole of the cam lobe, and a lower mold having a receiving hole for engaging the bottom surface and the middle mold. There has been proposed a method of manufacturing a cam lobe for an assembly type cam shaft, which is placed in a mold and cold pressed in the thickness direction with a pressing die having the same cross-sectional shape as the cam lobe.

[0010]

[Problems to be Solved by the Invention]
In the technology described in the 01-198645 publication, the manufactured cam lobe (sintered body) lacks the coaxiality accuracy and often requires finishing, which complicates the process and increases the manufacturing cost. There was a problem of inviting. In addition, JP 2001-2
The technique described in Japanese Patent No. 93531 requires ironing of the inner peripheral surface of the sintered body and may not always achieve the desired coaxiality accuracy, often requiring finishing. There is a problem that the process becomes complicated and the manufacturing cost rises.

It is an object of the present invention to advantageously solve the above-mentioned problems of the prior art, and to propose a method for manufacturing a sintered member with an inner hole, which has excellent coaxiality accuracy of the inner and outer circumferences. The term "excellent in coaxiality accuracy" as used in the present invention refers to an axial center based on the outer diameter of the outer peripheral portion and an axial center based on the inner diameter of the inner peripheral portion of the sintered body (cam). The average deviation (difference) is within 0.04 mm.

[0012]

In order to achieve the above-mentioned object, the present inventor has further diligently studied the factors affecting the accuracy of coaxiality. As a result, in the method for producing a sintered body including the recompression step, a clearance is required between the die and the pre-sintered body (workpiece) at the time of recompression. It has been found that there is a degree of freedom in the loading position of the body (workpiece), which causes a deviation (difference) between the shaft center based on the outer diameter and the shaft center based on the inner diameter, resulting in a decrease in the coaxiality accuracy. It was The present inventor has realized that the precision of coaxiality is remarkably improved by adjusting the die shape so that the pre-sintered body (work) is inserted into a fixed position during recompression. completed.

That is, according to the present invention, a die, a core rod inserted into the center of the die hole of the die, an upper punch,
In a method for producing a sintered member with an inner hole, which comprises a step of at least primary compression molding and secondary compression molding using a molding die including a lower punch, the molding die includes an upper punch and / or The lower punch has chamfered protrusions on the inner peripheral side and / or the outer peripheral side, and the chamfered protrusion of the upper or lower punch used for the secondary compression molding is the chamfered protrusion of the upper or lower punch used for the primary compression molding. A method of manufacturing a sintered member with an inner hole, which is excellent in coaxial precision of the inner and outer circumferences, characterized in that the mold is the same as or larger than the above.

Further, according to the present invention, a die for primary molding comprising a die, a core rod inserted into the center of the die hole of the die, an upper punch and a lower punch is used. Of the raw material powder is filled in the die hole between the die and the core rod, and the raw material powder is primarily compression-molded by the upper punch and the lower punch, and then temporary sintering is performed to form a temporary hole having an inner hole. Primary forming step of forming a sintered body, a die for forming the pre-sintered body, a core rod inserted into the center of the die hole of the die, an upper punch, and a lower punch, and a secondary forming die. Secondary molding step in which the pre-sintered body is secondarily compression-molded by the upper punch and the lower punch and then main-sintered to obtain a sintered body having an inner hole. In the method for producing a sintered member with an inner hole, the upper pan of the die for primary molding is And / or the lower punch of the primary molding die, and the upper punch of the secondary molding die and / or the lower punch of the secondary molding die are on the inner peripheral side and / or the outer peripheral portion. A chamfered protrusion on the side, and the chamfered protrusion of the upper or lower punch used for the secondary compression molding is equal to or larger than the chamfered protrusion of the upper or lower punch used for the primary compression molding. It is a method of manufacturing a sintered member with an inner hole having excellent degree of accuracy.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention uses a molding die composed of a die, a core rod inserted into the center of the die hole of the die, an upper punch and a lower punch, and uses at least raw material powder as a raw material powder. A method of manufacturing a sintered member with an inner hole, comprising: a primary molding step of performing primary compression molding; and a secondary molding step of performing secondary compression molding (recompression molding) on the primary molded body that has undergone the primary molding step. Is. In the present invention, the primary molding step includes a step of performing primary compression molding to form a primary molded body and then performing preliminary sintering to form a temporary sintered body, and further, in the secondary molding step, obtained in the primary molding step. It is preferable to use a so-called 2P2S method, which comprises a step of subjecting the thus-prepared temporary sintered body to recompression molding (secondary compression molding) and further performing main sintering to obtain a sintered body. Hereinafter, description will be made based on the case where the 2P2S method is used, but it goes without saying that the present invention is not limited to this.

First, in the present invention, in order to manufacture a sintered member with an inner hole, a die 11, a core rod 14 inserted into the center of the die hole of the die 11, an upper punch 12, and a lower punch 13 are formed.
A molding die consisting of and is used. The raw material powder 1 is filled in the die hole around the core rod 14 and compression-molded by the upper punch 12 and the lower punch 13 to obtain a primary compact. It should be noted that the upper punch 12 or the lower punch 13 has holes 122 and 132 in the central portion so that the core rod 14 can slide. Upper punch 12
The lower punch 13 has an inner peripheral portion that defines a hole and an outer peripheral portion that defines an outer peripheral surface that slides with the inner peripheral surface of the die. Further, the raw material powder used is not particularly limited,
It is preferable to select the sintered member as a product depending on the intended use. For example, in the case of an iron-based sintered member, it is preferable to use, as a raw material powder, a mixed powder obtained by mixing iron-based powder such as iron powder with graphite powder, alloy powder, lubricant and the like.

In the primary molding die used for the primary compression molding of the present invention, either one or both of the upper punch 11 and the lower punch 12 have chamfered protrusions 121, 131 on the inner peripheral side and / or the outer peripheral side. To provide. The chamfered protrusions 121 and 131 are
It is preferable to attach it over the entire circumference of the inner peripheral portion or the outer peripheral portion. FIG. 1 shows an example of a primary molding die in which a chamfered protrusion 131 is provided on the inner peripheral side of the lower punch 13. Using the die for primary molding as shown in FIG. 1, the raw material powder 1 was compression-molded to form a primary compact, which was then provisionally sintered. It will be chamfered. In the present invention, the pre-sintering conditions are not particularly limited. It is preferable to carry out under the conditions determined according to the raw material powder used.

As described above, by chamfering the inner peripheral portion or the outer peripheral portion of the pre-sintered body and the chamfered protrusions attached to the secondary molding die, which will be described later, are used together, the subsequent secondary molding is performed. In the secondary molding die at
The charging position of the (temporary sintered body) can be fixed. As described above, in the primary forming step, the temporary sintered body 2 having one or both of the inner peripheral side and the outer peripheral side along the inner hole chamfered is then charged into the secondary forming die. Then, secondary compression molding is performed, and then main sintering is performed to perform a secondary molding step of forming a sintered body.

In the secondary compression molding, as shown in FIG. 2, as in the primary compression molding, the lower punch 23 is inserted into the die hole of the die 21.
, The core rod 24 is inserted into the center of the die hole, and the core rod 24 is inserted into the inner hole 232 of the lower punch 23. The lower punch 23 descends while the die 21 is fixed, and the inner peripheral surface of the die 21, the outer peripheral surface of the core rod 24, and the lower punch 23 are lowered.
The pre-sintered body (workpiece) 2 is charged into the portion (die hole) surrounded by 23.

As the secondary molding die used in the secondary compression molding, as in the case of the primary molding die, one or both of the upper punch 22 and the lower punch 23 is provided on the inner peripheral side and / or A mold provided with chamfered protrusions 221, 231 on the outer peripheral side is used. The chamfered protrusions 221 and 231 are preferably provided along the entire circumference of the inner peripheral portion or the outer peripheral portion.

Further, the chamfered protrusions 221 and 231 of the upper or lower punch used in the secondary compression molding are chamfered protrusions having a size equal to or larger than that of the chamfered protrusions 121 and 131 of the upper or lower punch used in the primary compression molding. With this chamfer protrusion,
By chamfering the temporary sintered body formed by the primary compression molding, the charging position of the work (temporary sintered body) 2 at the time of the secondary compression molding can be set to a constant position without variation.

The temporary sintered body (workpiece) 2 charged in the inner peripheral surface of the die 21, the outer peripheral surface of the core rod 24, and the portion surrounded by the lower punch 23 (die hole) is the lower side of the temporary sintered body. By the chamfering of the inner peripheral portion and the chamfering protrusion 231 attached to the inner peripheral portion side of the lower punch, the clearance between the core rod 21 and the work 2 is fixed so as to be uniform over the entire circumference. Thereby, the accuracy of coaxiality can be remarkably improved after the recompression molding and the main sintering.

FIG. 2 shows an example of a secondary molding die in which a chamfered protrusion is provided on the inner peripheral side of the lower punch in a state immediately before secondary compression molding (recompression molding). Similarly, FIG. 3 similarly shows an example of a secondary molding die in which chamfered protrusions are provided on the inner peripheral side and the outer peripheral side of the lower punch and the upper punch. The temporary sintered body (workpiece) 2 fixed at a fixed position in the die hole is compressed by the lowered upper punch 22 to be a secondary compact (recompression compact). After that, the upper punch 22 and the lower punch 23 are raised to take out the secondary molded body from the die 21.

The secondary compact taken out from the die is further subjected to main sintering to obtain a sintered member (sintered body) having an inner hole. The present sintering conditions are not particularly limited in the present invention.
It is preferable to carry out under the conditions determined according to the raw material powder used.

[0025]

[Example] After sintering graphite powder and copper powder to iron powder, C: 0.8 quality
%, Cu: 1.5% by mass, and further lubricated
Zinc stearate as an agent is the sum of iron powder, graphite powder and copper powder.
1 part by weight is mixed with 100 parts by weight and mixed to form a mixed powder.
did. Using this mixed powder as the raw material powder, the primary composition shown in FIG.
Filling the die hole of the forming die, surface pressure: 6-7ton / cm ²so
Primary compression molding was performed to obtain a primary molded body. For primary molding
The mold has chamfered protrusions (C: 0.5 mm) on the inner circumference of the lower press.
After pre-sintering, the outer diameter is 40 mm × inner diameter 30 mm × thickness 15 mm.
The mold was designed to be.

These primary compacts were placed in a vacuum sintering furnace at 60
A temporary-sintered body was obtained by a primary forming step in which temporary-sintering was performed within a temperature range of 0 to 900 ° C. Then, a surface pressure of 7 to 10 ton / cm ² was applied to these temporary sintered bodies by using a secondary molding die shown in FIG.
After performing secondary compression molding with to make a secondary molded body, 1100 ~
A second molding process in which main sintering was performed at a temperature of 1200 ° C. was used as a sintered member with an inner hole, and the present invention example 1 was obtained. The secondary molding die is a die designed to be a member having an outer diameter of 40 mm × an inner diameter of 30 mm × a thickness of 15 mm after the main sintering, and a temporary sintered body is formed on the inner peripheral portion of the lower punch. A metal mold provided with a chamfered protrusion (C: 0.5 mm) having a size larger than the chamfer provided on the lower inner peripheral portion of the mold. The clearance between the secondary molding die and the pre-sintered body was set to 0.1 mm (one side).

Further, a raw material powder having the same composition as that of Inventive Example 1 was used as a primary molding die, and a lower punch having chamfered protrusions (C: 0.5 mm) provided on both sides of the inner peripheral side and the outer peripheral side, Chamfered protrusions (C: on both sides of the inner peripheral side and the outer peripheral side)
0.5mm) is used for the upper punch, and as a secondary molding die, chamfered protrusions are attached on both inner and outer peripheral sides as shown in Fig. 3. The primary molding step and the secondary molding step were performed under the same conditions as in Invention Example 1 except that a punch and a die using an upper punch provided with chamfered protrusions on both the inner peripheral side and the outer peripheral side were used. Example 2 of the present invention was carried out to obtain a sintered member having an inner hole. In addition,
In the secondary molding die, the chamfered protrusions attached to the lower punch and the upper punch had a larger dimension (C: 0.6 mm) than the chamfer imparted to the pre-sintered body by the primary molding die.

In addition, as a comparative example, the present invention is used except that a mold in which neither the lower punch nor the upper punch is provided with a chamfered protrusion is used as the primary molding die and the secondary molding die. A raw material powder having the same composition as in Example 1 was subjected to a primary molding step and a secondary molding step under the same conditions as those of Example 1 of the present invention to obtain a sintered member with an inner hole, and a comparative example was prepared. For these sintered members, the amount of deflection of the entire outer circumference is measured with the inner circumference as a reference,
The difference (mm) between the shaft center based on the outer diameter of the outer circumference and the shaft center based on the inner diameter of the inner circumference was obtained, and the coaxiality accuracy was evaluated. The accuracy of the coaxiality is improved as the difference between the axes is smaller.

The obtained results are shown in FIG. From FIG. 4, the coaxiality of each of Inventive Example 1 and Inventive Example 2 is 0.04 mm.
It can be seen that the accuracy of the coaxiality is remarkably improved as compared with the comparative example of 0.05 mm.

[0030]

EFFECTS OF THE INVENTION According to the present invention, a sintered member with an inner hole, which is excellent in dimensional accuracy such as inner diameter and outer diameter, and is remarkably excellent in concentricity accuracy, can be manufactured inexpensively and stably by a simple method. It has a remarkable industrial effect that it can be manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing an example of the configuration of a primary molding die suitable for the present invention.

FIG. 2 is a cross-sectional view schematically showing an example of the configuration of a secondary molding die suitable for the present invention.

FIG. 3 is a cross-sectional view schematically showing an example of the configuration of a secondary molding die suitable for the present invention.

FIG. 4 is a graph showing the coaxiality accuracy of the example of the present invention.

[Explanation of symbols]

Raw material powder 11 die (for primary molding) 12 Upper punch (for primary molding) 13 Lower punch (for primary molding) 14 Core rod (for primary molding) 15 Core rod receiving jig 121 Upper punch chamfer protrusion (for primary molding) 122 Upper punch inner hole (for primary molding) 131 Lower punch chamfer protrusion (for primary molding) 132 Lower punch inner hole (for primary molding) 2 work (temporary sintered body) 21 dies (for secondary molding) 22 Upper punch (for secondary molding) 23 Lower punch (for secondary molding) 24 core rod (for secondary molding) 25 Core rod receiving jig 221 Upper punch chamfer protrusion 222 Upper punch inner hole 231 Lower punch chamfer protrusion 232 Lower punch inner hole

Claims (2)

[Claims] 1. A molding die comprising a die, a core rod inserted into the center of the die hole of the die, an upper punch and a lower punch, and at least primary compression molding and secondary compression molding are performed. In the method for producing a sintered member with an inner hole, which comprises the step of including, in the molding die, the upper punch and / or the lower punch has chamfered protrusions on the inner peripheral side and / or the outer peripheral side, and The inner and outer circumferences are excellent in coaxiality accuracy, characterized in that the chamfered protrusion of the upper or lower punch used in the secondary compression molding is the same or larger than the chamfered protrusion of the upper or lower punch used in the primary compression molding. Manufacturing method of sintered member with holes. 2. A die for primary molding, comprising a die, a core rod inserted into the center of the die hole of the die, an upper punch and a lower punch, and the die of the primary molding die is used. Filling the raw material powder in the die hole between the core rod,
After primary compression molding of the raw material powder by the upper punch and the lower punch, a primary molding step of performing temporary sintering to form a temporary sintered body having an inner hole, the temporary sintered body, a die, The core rod inserted into the center of the die hole of the die, an upper punch, and a lower punch are inserted into the die hole of a secondary molding die, and the temporary punch is performed by the upper punch and the lower punch. In the method for producing a sintered member with an inner hole, which comprises a secondary compression step of subjecting a sintered body to a secondary compression molding and then performing a main sintering to obtain a sintered body having an inner hole in a central portion, The upper punch of the mold and / or the lower punch of the primary molding die, the upper punch of the secondary molding die and / or the lower punch of the secondary molding die, and the inner peripheral side and / or Or has a chamfered protrusion on the outer peripheral side and is used for the secondary compression molding or A method for producing a sintered member with an inner hole having excellent coaxiality accuracy, wherein the chamfered protrusion of the lower punch is equal to or larger than the chamfered protrusion of the upper or lower punch used in the primary compression molding.