US20100224146A1

US20100224146A1 - Method for manufacturing a shaft member having a sintered part bonded thereto and a camshaft for an internal combustion engine

Info

Publication number: US20100224146A1
Application number: US12/159,448
Authority: US
Inventors: Takeshi Kuwahara; Atsuya Aoki; Masahiro Shinzawa; Hiroshi Takiguchi
Original assignee: Nippon Piston Ring Co Ltd
Current assignee: Nippon Piston Ring Co Ltd
Priority date: 2005-12-28
Filing date: 2006-12-27
Publication date: 2010-09-09
Also published as: JPWO2007077880A1; WO2007077880A1; KR20080066079A

Abstract

A method for manufacturing a shaft member having a sintered part bonded thereto is simple and provides an increased process yield and a high accuracy in position and angle of the sintered part. A green compact is prepared by subjecting a metal or alloy powder to a compression molding. A projection formed on an outer peripheral surface of the shaft member is embedded into the green compact, while chipping partially the green compact with the projection, to combine the green compact with the shaft member. Then, a sintering is carried out.

Description

TECHNICAL FIELD

The present invention relates to a method for manufacturing a shaft member having a sintered part bonded thereto. More specifically, the present invention relates to a manufacturing method, which is applicable to manufacture of for example a so-called “assembled camshaft”.

BACKGROUND OF THE INVENTION

A camshaft used for an internal combustion engine such as, for example, an automobile engine has been manufactured by compression-molding a metal or alloy powder into a cam lobe shape, placing same onto a shaft serving as a shaft member, and then sintering them to bond the sintered cam lobe integrally to the shaft through a sinter-diffusion bonding.
In such a method for manufacturing a so-called “assembled camshaft”, there is a need to carry out a sintering step, while stationarily placing the sintered cam lobe in a predetermined position and at a predetermined angle on the shaft serving as the shaft member. Various methods of stationarily placing the cam lobe have conventionally been developed.
For example, Patent Document 1 and Patent Document 2 disclose that a recess (groove) is formed on an outer peripheral surface of a shaft serving as a shaft member, on the one hand, and a projection corresponding to the above-mentioned recess is formed on a cam lobe, on the other hand.
In addition, Patent Document 3 discloses that a recess is formed on an outer peripheral surface of a shaft and another recess is formed in a cam lobe, and a pin is inserted into a space, which is defined by these two recesses, to secure a cam lobe to the shaft.
Further, Patent Document 4 discloses that a striking step is applied to an outer peripheral surface of a shaft with the use of a chisel to form a projection thereon, and a cam lobe and the shaft are temporarily secured to each other, utilizing the above-mentioned projection.
Patent Document 1: Japanese Patent Provisional Publication No. S54-041266
Patent Document 2: Japanese Patent Provisional Publication No. S60-033302
Patent Document 3: Japanese Patent Provisional Publication No. H08-210110
Patent Document 4: Japanese Patent Provisional Publication No. H03-168305

DISCLOSURE OF THE INVENTION

Subject to be Solved by the Invention

However, in the method disclosed in the above-mentioned Patent Document 1 and Patent Document 2, the projection and recess, which are required to be formed, are not essential to the camshaft in its primary functions, with the result that degree of freedom in design may be decreased. In case where the recesses (i.e., the grooves) are continuously formed on the outer peripheral surface of the shaft in its axial direction, a gap may be formed between the cam lobe and the portion of the shaft, on which the recesses are formed, thus causing problems in strength.
Also in the method disclosed in the above-mentioned Patent Document 3, the recess is required to be formed in the same manner as the above-mentioned Patent Document 1, thus causing problems on decrease in degree of freedom in design and strength. Further, in addition to the cam lobe and shaft, the pin is required to be used, thus complicating the manufacturing process, decreasing process yield and increasing the manufacturing costs.
In the method disclosed in the above-mentioned Patent Document 4, a bonding method by which the cam lobe and the shaft are bonded to each other is a welding. The invention disclosed therein has no fundamental concept of bonding them through a sinter-diffusion bonding in the same manner as the invention of the present application. When studying the contents of Patent Document 4, this document describes that the projection formed by the chisel is pressed, when fitting the cam lobe onto the shaft, by the cam lobe to be plastically deformed. It is clearly judged from this description that the cam lobe is entirely distinct from a green compact, which is prepared by subjecting a metal or alloy powder to a compression molding, and that, when comparing the cam lobe and the shaft in hardness, the cam lobe is harder than the shaft. In addition, according to the description of Patent Document 4, after fitting the cam lobe onto the shaft, the projection has already been crushed to disappear. At this moment, the cam lobe may not be fixed to the shaft, or even if fixed, they are fixed to each other by an extremely small connection strength. It is therefore considered that, when a sintering step is carried out in the same manner as the present invention, the cam lobe may rotate, thus making it impossible to secure the cam lobe to the shaft at the desired angle in an accurate manner.
A primary object of the present invention, which was made to solve the above-mentioned problems, is to provide a method for manufacturing a shaft member having a sintered part bonded thereto, which method is simple and provides an increased process yield and a high accuracy in position and angle of the sintered part, as well as a cam shaft for an internal combustion engine, manufactured by the above-mentioned method.

Means to Solve the Subject

In order to attain the aforementioned object, the method for manufacturing a shaft member having a sintered part bonded thereto, which comprises: a green compact preparation step of subjecting a metal or alloy powder to a compression molding to prepare a green compact; a projection formation step of pressing a pressing device onto an outer peripheral surface of a shaft member at a predetermined position to deform the outer peripheral surface of the shaft member to form a projection having a height of from 0.03 mm to 0.25 mm at the predetermined position; a combination step of embedding the projection formed on the outer peripheral surface of the shaft member into the green compact, while chipping partially the green compact with the projection, to combine the green compact with the shaft member; and a sintering step of sintering the green compact to convert same into a sintered part and bond the sintered part integrally to the shaft member through a sinter-diffusion bonding.
In the present invention, a temporary bonding step of temporarily bonding the green compact to the shaft member by an adhesive agent may be carried out after the combination step before the sintering step.
In the present invention, the sintered part may comprise a cam lobe or the cam lobe and a journal, and the shaft member may comprise a shaft.
In order to attain the aforementioned object, a camshaft for an internal combustion engine is manufactured by the method for manufacturing a shaft member.

EFFECT OF THE INVENTION

According to the present invention, in the method for manufacturing a shaft member having a sintered part bonded thereto, wherein a green compact made of a metal or alloy powder is placed on a shaft member and then sintered to prepare an integral body through a sinter-diffusion bonding, a fine projection is formed on the surface of the shaft member before placing the green compact on the shaft member, so that such a projection is utilized to ensure a stationarily combined state of the green compact and the shaft member. Therefore, there is no need to apply, in the same manner as the above-mentioned Patent Documents 1 and 2, a working step to both of the green compact (the cam lobe in Patent Documents 1 and 2) and the shaft member (the shaft in Patent Documents 1 and 2), and applying a working step only to the shaft member suffices, this making it possible to increase process yield and degree of freedom in design. In addition, the working step to be applied to the shaft member in the manufacturing method of the present invention is only to pressing a pressing device onto the surface of the shaft member to form a fine projection, and the projection is embedded eventually into the green compact at the contact portion therewith, with the result that such a working step does not decrease the strength unlike the above-mentioned Patent Documents 1 and 2.
In the manufacturing method of the present invention, there is no need to use an additional member typified as the pin described in Patent Document 3, thus making it possible to reduce costs.
In the manufacturing method of the present invention, the fine projection formed on the outer peripheral surface of the shaft member is embedded into the green compact, so as to ensure a stationarily combined state of the shaft member and the green compact. It is therefore possible to prevent the cam lobe from shifting unfavorably in the axial direction or rotating in a manner as described in Patent Document 4, thus improving accuracy in position and angle of the sintered part.
In the conventional method wherein the groove is formed on the shaft and the projection is formed on the cam lobe, the cam lobe is fitted on the shaft and then sintered, shrinkage occurs only in the cam lobe during a sintering step, a clearance between the cam lobe and the shaft is increased, thus causing a large deviation in mounting angle between them. To the contrary, according to the present invention, the projection is formed on the shaft and the green compact for the cam lobe shrinks during the sintering step so that the projection is embedded into the cam lobe, thus improving accuracy in mounting angle of the cam lobe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing respective steps of a manufacturing method of the present invention.

FIG. 2 includes descriptive views of a projection formation step of the manufacturing method of the present invention, and more specifically, FIG. 2( a) is a schematic cross sectional view showing how to carry out this step and FIG. 2( b) is an enlarged cross sectional view showing an outer peripheral surface of a shaft on which a projection is formed.

FIG. 3 includes descriptive views showing a combination step of the manufacturing method of the present invention.

EXPLANATION OF THE REFERENCE NUMERALS

- 20—shaft
- 21—pressing device
- 22—projection

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the manufacturing method of the present invention will be described in more detail with reference to drawings.
FIG. 1 is a flow chart showing respective steps of a manufacturing method of the present invention.
The present invention is not limited only to a method for manufacturing a camshaft, but is applicable to manufacture of a product having a sintered part and a shaft member, which are bonded integrally with each other through a sinter-diffusion bonding. In order to give more specific description of the invention, there is provided a typical example case where a so-called “assembled camshaft” in which sintered parts such as a cam lobe and a journal, which are discrete parts relative to a shaft, are bonded to the shaft, and the present invention will be described below on the premise that the sintered part is a cam lobe and the shaft member is a shaft.
As shown in FIG. 1, the manufacturing method of the present invention comprises a green compact preparation step S1 of subjecting a metal or alloy powder to a compression molding to prepare a green compact; a projection formation step S2 of pressing a pressing device onto an outer peripheral surface of a shaft member at a predetermined position to deform the outer peripheral surface of the shaft member to form a fine projection at the predetermined position; a combination step S3 of combining the green compact with the shaft member; a temporary bonding step S4 of temporarily bonding the green compact to the shaft member; and a sintering step S5 of sintering the green compact to convert same into a sintered part and bond the sintered part integrally to the shaft member through a sinter-diffusion bonding.
The respective steps will be described in detail below.

(1) Green Compact Preparation Step

The purpose of the green compact preparation step S1 of the manufacturing method of the present invention is to subject material of a metal or alloy powder to a compression molding to prepare a green compact. An appropriate design of the green compact to be made taking into consideration a shape and the other parameters of a finished product suffices and there is no specific additional limitation in shape of the green compact. In case where a camshaft is for example manufactured, the green compact has a shape of a cam lobe.
Any conventionally known metal or alloy powder may be used as the metal or alloy powder in the above-mentioned step S1 and there is no specific additional limitation in material of the green compact. However, for example, a stainless alloy powder is preferably used so that shrinkage ratio of the green compact after completion of the sintering step ((Green Compact Dimension-Sintered Part Dimension)/Green Compact Dimension×100) becomes 4 to 7%.
The projection formed on the shaft member (e.g., the shaft) is embedded into the green compact prepared by the step S1, when carrying out the combination step S3 described later, and more specifically, a certain amount of load is applied to the green compact. Accordingly, the green compact is required to have a certain hardness, which provides endurance against the load applied in the combination step S3. More specifically, the green compact is preferably prepared at a pressure of from 440 to 690 MPa. The green compact preferably has a relative density of at least 70%.

(2) Projection Formation Step

The purpose of the projection formation step S2 of the manufacturing method of the present invention is to press a pressing device onto an outer peripheral surface of the shaft member at a predetermined position to deform the outer peripheral surface of the shaft member to form a fine projection at the above-mentioned predetermined position.
FIG. 2 includes descriptive views of the projection formation step, and more specifically, FIG. 2( a) is a schematic cross sectional view showing how to carry out this step and FIG. 2( b) is an enlarged cross sectional view showing an outer peripheral surface of the shaft on which the projection is formed.
In this step, the pressing device is pressed on the outer peripheral surface of the shaft 20 serving as the shaft member at the predetermined position. After completion of this step, the shaft 20 is deformed on its peripheral surface to form the fine projection 22 on the above-mentioned position, as shown in FIG. 2( b).
The fine projection 22 is used in combination of the shaft 20 and the green compact having the shape of the cam lobe in the combination step S3 described later.
The fine projection 22 may have a height “h” to such an extent that the projection is embedded into the green compact as described above to stationarily secure the green compact in the combination step S3 described later. The height of the projection may appropriately be determined so that as the above-mentioned object is achieved. However, an excessively increased height may lead to an obstacle to the fitting of the green compact onto the shaft, and may cause an excessively high load to be applied to the green compact during the combination step to break the green compact, thus causing unfavorable problems. In addition, such an excessively increased height needs a large impact force, leading to an decreased service life of the pressing device, an increased force for forming the projection and an increased power of manufacturing facilities due to an increased force required for carrying the combination step, thus causing additional unfavorable problems. In a specific example, the height of the projection is preferably within the range of from 0.03 to 0.25 mm. In case where three projections are provided, the height of from 0.03 to 0.2 mm is preferable, two projections, from 0.05 to 0.2 mm, and five projections, from 0.03 to 0.1 mm.
On the other hand, a recess 23, which is inevitably formed by the formation of the fine projection 22, is not utilized in the manufacturing method of the present invention. Therefore, there is no specific limitation in shape (depth and size) of the recess. However, the recess 23 is preferably as small as possible, with the result that the tip of the pressing device 21 preferably has an improved shape.
In the method of the present invention, there is used the pressing device having appropriately selected requirements so as to permit an effective formation of the fine projection 22 in the above-mentioned manner, and there is no specific additional limitation. More specifically, the tip of the pressing device preferably has a conical shape with a preferable cone angle of 40 to 80 degrees. In addition, the tip of the pressing device preferably has a radius of curvature “R” of up to 1 mm and more preferably of 0.05 to 0.5 mm. The cone angle of under 40 degrees may decrease the service life of the pressing device 21. On the other hand, the cone angle of over 80 degrees may lead to difficulty in formation of the appropriate projection 22. In addition, The radius of curvature “R” of over 1 mm may lead to difficulty in formation of the appropriate projection 22 and a larger force for pressing the pressing device 21 is required.
In order to carry out the method of the present invention, the pressing device 21 preferably has a hardness, which is equal to or larger than that of the shaft serving as the shaft member. For example, carbide steel or high-speed tool steel may be used.
On the other hand, the hardness of the shaft member, which is typified as the shaft, may appropriately be determined in accordance with use and required performance of a finished product to be manufactured by the method of the present invention. However, it is necessary to form the fine projection 22 and put the thus formed projection 22 into the green compact as described above, with the result that the shaft member is required to have a certain hardness. In an example case of the shaft for the camshaft, the surface hardness of the shaft is preferably HRB75 to 105. The surface hardness of under HRB75 may make it difficult to form the projection 22 having the desired height “h”, even when the pressing force is applied with the use of the pressing device. On the other hand, the surface hardness of over HRB105 may decrease the service life of the pressing device 21. Material having such a hardness may include for example material of S45C, STKM13 and SUJ2.
A pressure at which the pressing device 21 is pressed onto the surface of the shaft in the above-mentioned step S2, may appropriately determined so as to permit the formation of the projection 22 having the above-mentioned desired height “h”, taking into consideration balance between the hardness of the pressing device 21 and the hardness of the shaft 20, and there is no specific additional limitation. In an example case, the pressure is preferably 490 to 2450 N. The pressure of less than 490 N may not provide the projection with the desired height “h”. On the other hand, the pressure of over 2450 N may increase the depth of the recess 23, which is utilized in the present invention, and may deform generally the shaft, if the thickness of the shaft is small.
In the step S2, at least one projection 22 is formed for each green compact and there is no specific limitation in number of the projection, and five projections may be formed. When the present invention is applied to manufacture for example of the assembled camshaft in which a single projection 22 is formed for each of the cam lobes, such a projection 22 is preferably formed in a position (a predetermined central angle), which corresponds to a nose portion (a portion having the maximum thickness) of the cam lobe. In case where two projections 22 are formed for each of the cam lobes, these projections 22 are preferably formed on the shaft in a position between 0° and +35° and in another position between 0° and −35° with reference to the position corresponding to the nose portion of the cam lobe, and more preferably in a position of +25±10° and −25±10°, and more preferably in a position of +25±7° and −25±7°. In case where three projections are formed for each of the cam lobes, these projections 22 are preferably formed on the shaft in a position between 0° and +35° with reference to the position corresponding to the nose portion of the cam lobe, in another position of 0° and in the other position between 0° and −35°, or preferably formed thereon in a position between 0° and +35° with reference to the position corresponding to the nose portion of the cam lobe, in another position of +180° and in the other position between 0° and −35°. In case where four projections are formed for each of the cam lobes, these projections 22 are preferably formed on the shaft in a position between 0° and +35° with reference to the position corresponding to the nose portion of the cam lobe, in another position of 0°, in the other position between 0° and −35° and in the other position of +180°. In case where five projections are formed for each of the cam lobes, these projections 22 are preferably formed on the shaft in a position between 0° and +35° with reference to the position corresponding to the nose portion of the cam lobe, in another position of 0°, in the other position between 0° and −35°, in the other position of +150°, and in the other position of −150°, or preferably formed in a position between 0° and +35° with reference to the position corresponding to the nose portion of the cam lobe, in another position of 180°, in the other position between 0° and −35°, in the other position of +150°, and in the other position of −150°.
High accuracy is not required in determination of the above-mentioned angular positions for the projections. When the method of the present invention is applied to manufacture of the assembled camshaft, the number and position of the projections formed on the shaft member are preferably determined based on the above-described combination of the number and position of the projections. However, when a sinter-diffusion bonding is applied to bond the sintered parts integrally to the shaft member, these matters may be determined taking into consideration a shape and strength of the green compact, and there is no specific additional limitation.

(3) Combination Step

The purpose of the combination step S3 of the manufacturing method of the present invention is to embed the projection formed on the outer peripheral surface of the shaft member into the green compact, while chipping partially the green compact with the projection, to combine the green compact with the shaft member.
FIG. 3 includes descriptive views showing the combination step S3 of the manufacturing method of the present invention.
In the step S3, the green compact is combined with the shaft member by fitting the green compact for the cam lobe onto the shaft having the fine projection, which has been formed in accordance with the above-described projection formation step S2, from its one end, and embedding the projection 22 into the green compact, while chipping, with the projection, the inner surface portion of the green compact, which defines a shaft insertion hole, as shown in FIGS. 3( a) and 3(b). The green compact may be elastically deformed during the fitting of the green compact onto the shaft, thus preventing the green compact from shifting in either a fitting direction or an opposite direction thereto.
The projection formed on the shaft member (the shaft) is embedded into the green compact, while chipping partially the green compact (the cam lobe) with the projection, in this manner, thus making it possible to secure the green compact to the shaft member in an more accurate manner than the conventional method.
In this step, it is preferable to embed the projection 22 into the green compact by a distance, which is substantially equal to half of a thickness W of the green compact in the fitting direction thereof. However, in case where the green compact has a thickness W of over 20 mm, it is preferable to determine the fitting distance to be about 10 mm.
A clearance (i.e., a gap) between the green compact (the cam lobe) and the shaft member (the shaft) may be determined appropriately based on the height “h” of the projection 22 formed on the outer peripheral surface of the shaft member in the above-mentioned projection formation step S2. Such a clearance is preferably determined to be about 0.05 to 0.2 mm. A clearance of under 0.05 mm would make it difficult to fit the green compact on the shaft member, thus causing problems on decrease in process yield. On the other hand, a clearance of over 0.2 mm would cause an embedded amount of the projection 22 into the green compact to be decreased, thus making it difficult to secure the green compact to the shaft member. It is preferable to determine, from this standpoint, the clearance so that the projection 22 of the shaft member is embedded into the green compact by at least 0.01 mm.
FIGS. 3( c) and 3(d) show procedures of the combination step S3 applied when a plurality of the green compacts for the cam lobe are fitted on the shaft. As shown in these figures, when the plurality of the green compacts for the cam lobe are fitted on the shaft, it is preferably to carry out the projection formation step S2 and the combination step S3 and then repeat these steps. Because, when the same projection formation step S2 is continuously repeated, the green compact for the cam lobe is fitted onto the shaft from its one end and moved beyond the projection formed on the side of the one end of the shaft, with the result that the green compact for the cam lobe is chipped off in an undesirable manner, thus causing problems on decrease in strength.

(4) Temporary Bonding Step

The purpose of the temporary bonding step S4 of the manufacturing method of the present invention is to temporarily bond, before the sintering step, the green compact for the cam lobe, which has been fitted onto the shaft member (the shaft) in accordance with the above-described combination step S3.
The above-mentioned step S4 is not essential to the manufacturing method of the present invention. However, it is preferable to carry out this step for the purpose of improving accuracy.
As is clear from the description of the combination step S3, in the method of the present invention, the combination step is carried out so as to chip partially the green compact with the projection formed on the shaft member, with the result that the green compact may not easily be shifted further in the fitting direction thereof. However, it may be conceivable that retention of the green compact against a force applied in the opposite direction to the fitting direction of the green compact is smaller than that against a force applied in the fitting direction thereof. These descriptions are based on a merely theoretical comparison. The projection is embedded into the green compact, while the green compact is actually elastically deformed, and the green compact is retained even against the force applied in the opposite direction to the fitting direction of the green compact. In view of these respects, when a higher accuracy is desired, it is preferable to carry out the temporary bonding step.
Concerning a means actually used in the step S4, various kinds of means used in the conventional method for manufacturing an assembled camshaft may be selected appropriately and used, and there is no specific additional limitation. For example, adhesive may be applied to combined portions of the shaft member and the green compact. In this case, the adhesive may include α-cyanoacrylate adhesive.

(5) Sintering Step

The purpose of the sintering step S5 of the manufacturing method of the present invention is to sinter the green compact for the cam lobe, which has been fitted onto the shaft member (the shaft), and temporarily bonded thereto, where appropriate, to convert same into a sintered part and bond the sintered part integrally to the shaft member through a sinter-diffusion bonding.
The conventional sintering step is carried out as the step S5 and there is no specific additional limitation in the manufacturing method of the present invention.
More specifically, it is preferable to carry out the sintering step at a temperature of from 1100 to 1200° C. A sintering time is preferably determined as about 0.5 to 2 hours, although it depends upon a size of a sintered part to be prepared and a kind of metal or alloy powder as used. When the sintering step is carried out at a temperature of at least 1200° C., an excessively large deformation may occur or fine “blisters” may be generated, thus causing unfavorable problems.
It is preferable to determine a shrinkage ratio of the green compact due to the sintering step to be within a range of from about 4 to about 7%. A lower shrinkage ratio than the above-mentioned range may lead to insufficient diffusion bonding.

EXAMPLES

The manufacturing method of the present invention will be described more in detail based on examples.

Example 1

Ten camshafts (each shaft having a single cam lobe) were prepared in accordance with the manufacturing method of the present invention, as shown in FIG. 1. These camshafts will be hereinafter referred to as “Sample Nos. 1 to 10”, respectively.
A position and height of the projection formed on each shaft of the sample are shown in Table 1 below. Each of Sample Nos. 1 to 4 has two projections, each of Sample Nos. 5 to 7 has three projections and each of Sample Nos. 8 to 10 has five projections.
Fe-8Cr-1.9Ni-2Mo-2.7C was used as an alloy powder. A cold-drawn pipe was used as the shaft.
The pressing device had a tip portion made of diamond. The tip portion had a conical shape having an cone angle of 60 degrees and a radius of curvature “R” of 0.2 mm.
A misalignment angle indicating an amount of deviation in an angular position of the cam lobe after completion of the sintering step from the green compact for the cam lobe immediately after completion of the temporary bonding step, which position served as a reference angular position of “0” degrees on the periphery of the shaft, was measured for each of the samples as prepared. The clockwise deviation as viewed from the fitting direction of the green compact is indicated as “plus (+)” and the counter-clockwise deviation, as “minus (−)”.
The measurement results are shown in Table 1.

Comparative Example 1

Two camshafts were prepared in accordance with the same method as Example 1, except that projections had the size standing outside the scope of the manufacturing method of the present invention. These camshafts will be hereinafter referred to as “Sample Nos. 11 and 12”, respectively.
The measurement results for these samples are also shown in Table 1 in the same manner as the above-mentioned Example 1.

Conventional Example 1

The camshafts (each shaft having a single cam lobe) were prepared in accordance with the conventionally known method for manufacturing an assembled camshaft. These camshafts will be hereinafter referred to as “Sample Nos. 13 to 15”, respectively.
The same conditions of the alloy powder and the shaft as the above-mentioned example were applied.
The conventionally known method for manufacturing an assembled camshaft comprised the steps of forming a groove extending along the axial direction of a shaft on the outer peripheral surface thereof, forming a projection on an inner peripheral surface of a green compact for a cam lobe, which was to be fitted onto the shaft, fitting the green compact for the cam lobe onto the shaft so as to fit the projection into the groove, and sintering them to bond the cam lobe to the shaft (see FIGS. 1 to 3 of Patent Document 2 as mentioned above).
Evaluation was made in the same manner as Example 1 as described above. The results are also shown in Table 1.

TABLE 1

First Projection	Second Projection	Third Projection	Fourth Projection	Fifth Projection	Misalignment

Sample No.	Position	Height	Position	Height	Position	Height	Position	Height	Position	Height	Angle

1(Example)	+30°	0.12	−30°	0.12							0.55
2(Example)	+30°	0.16	−30°	0.16							0.32
3(Example)	+30°	0.20	−30°	0.20							0.17
4(Example)	+30°	0.24	−30°	0.24							0.03
5(Example)	+30°	0.08	−30°	0.08	180°	0.08					0.50
6(Example)	+30°	0.12	−30°	0.12	180°	0.12					0.23
7(Example)	+30°	0.18	−30°	0.18	0°	0.18					0.03
8(Example)	+30°	0.03	−30°	0.03	180°	0.03	+150°	0.03	−150°	0.03	0.93
9(Example)	+30°	0.06	−30°	0.06	180°	0.06	+150°	0.06	−150°	0.06	0.45
10(Example)	+30°	0.09	−30°	0.09	0°	0.09	+150°	0.09	−150°	0.09	0.07
11(Comparative)	+30°	0.26	−30°	0.26							Cracks
											occurred
12(Comparative)	+30°	0.02	−30°	0.02	180°	0.02	+150°	0.02	−150°	0.02	3.00
13(Conventional)											1.95
14(Conventional)											2.00
15(Conventional)											1.98

Comparison Among Example 1, Comparative Example 1 and Conventional Example 1

As is clear from Table 1 as indicated above, it is recognized that the amount of deviation in an angular position of the cam lobe after completion of the sintering step from the position (0 degrees) the green compact for the cam lobe immediately after completion of the temporary bonding step in Example 1 is small in comparison with Comparative Example 1 and Conventional Example 1, thus being excellent in accuracy.
Specifically, comparing Sample No. 8 of the present invention provided with the projection having a height of 0.03 mm with Sample No. 12 of the comparative example provided with the projection having a height of 0.02 mm, they are quite different from each other in a misalignment angle, thus proving that determining the height of the projection within the range of the present invention is effective.

Claims

1. A method for manufacturing a shaft member having a sintered part bonded thereto, which comprises:

a green compact preparation step of subjecting a metal or alloy powder to a compression molding to prepare a green compact;

a projection formation step of pressing a pressing device onto an outer peripheral surface of a shaft member at a predetermined position to deform the outer peripheral surface of said shaft member to form a projection having a height of from 0.03 mm to 0.25 mm at said predetermined position;

a combination step of embedding said projection formed on the outer peripheral surface of the shaft member into the green compact, while chipping partially the green compact with the projection, to combine the green compact with the shaft member; and

a sintering step of sintering said green compact to convert same into a sintered part and bond the sintered part integrally to the shaft member through a sinter-diffusion bonding.

2. The method for manufacturing a shaft member having a sintered part bonded thereto, as claimed in claim 1, wherein:

a temporary bonding step of temporarily bonding the green compact to the shaft member by an adhesive agent is carried out after said combination step before said sintering step.

3. The method for manufacturing a shaft member having a sintered part bonded thereto, as claimed in claim 1, wherein:

said sintered part comprises a cam lobe and said shaft member comprises a shaft.

4. A camshaft for an internal combustion engine, manufactured by the method for manufacturing a shaft member, as claimed in claim 1.

5. The method for manufacturing a shaft member having a sintered part bonded thereto, as claimed in claim 2, wherein:

6. A camshaft for an internal combustion engine, manufactured by the method for manufacturing a shaft member, as claimed in claim 2.

7. A camshaft for an internal combustion engine, manufactured by the method for manufacturing a shaft member, as claimed in claim 3.