Method of Forming Member, Valve Guide and Method of Forming the Same, and Method of Forming Tubular Member

Abstract

There is provided a method by which a member having an undercut in the inner peripheral portion thereof can be formed readily. To form a material (1) formed with a recess (2) and the undercut (3) by using a swaging device, while the material (1) is first gripped by a damper (11), and a mandrel (12) is inserted into the recess (2) of the material (1). The mandrel (12) used has an outside diameter equal to the inside diameter of a blind hole of an aimed product (fuel injection nozzle). Then, the material (1) is pushed in by the mandrel (12) to a position at which the material (1) abuts on a stopper (13), and the outside surface of the material (1) is struck by swaging dies (8) to perform a swaging operation. This swaging operation reduces the inside diameter of the recess (2) to the outside diameter of the mandrel (12), with the undercut (3) left.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram for illustrating a forming process in accordance with a first invention;

FIG. 2 is a front view of a device used for swaging in a forming process in accordance with a first invention;

FIG. 3 is views for illustrating the details of swaging operation in a forming process in accordance with a first invention;

FIG. 4 is a view for illustrating an improvement left in a first invention;

FIG. 5 is a block diagram for illustrating a forming process in accordance with a second invention;

FIG. 6 is views for illustrating the details of swaging operation in a forming process in accordance with a second invention;

FIG. 7( a) is a sectional view of a material formed with a positioning hole, and FIG. 7(b) is a view for illustrating an unfavorable positioning hole;

FIG. 8 is a view for illustrating a process for forming a positioning hole by forging;

FIGS. 9( a) and 9(b) are sectional views of materials in which an excess thickness portion is formed;

FIG. 10 is views for illustrating an improvement left in a first invention;

FIG. 11 is a block diagram for illustrating a forming process in accordance with a third invention;

FIGS. 12( a) and 12(b) are sectional views of materials;

FIG. 13 is a view for illustrating a process for forming a recess in a material by forging;

FIGS. 14( a) to 14(c) are views for illustrating the details of swaging operation in a forming process in accordance with the present invention;

FIG. 15 is a view for illustrating an improvement left in a first invention;

FIG. 16 is a block diagram for illustrating a forming process in accordance with a fourth invention;

FIG. 17 is a view for illustrating a process for forming an excess thickness portion;

FIG. 18 is a view for illustrating a process for forming an excess thickness portion;

FIG. 19 is views for illustrating the details of swaging operation in a forming process in accordance with a fourth invention;

FIG. 20 is a block diagram for illustrating a forming process in accordance with a fifth invention;

FIG. 21 is a view for illustrating a process for forming a recess in a material by forging;

FIGS. 22( a) to 22(c) are views for illustrating the details of swaging operation in a forming process in accordance with a fifth invention;

FIGS. 23( a) to 23(b) are views for illustrating another example;

FIGS. 24( a) to 24(e) are block diagrams for illustrating a forming process in accordance with a sixth invention;

FIGS. 25( a) to 25(c) are views for illustrating the details of swaging operation in a forming process in accordance with the present invention; and

FIG. 26 is a sectional view of a conventional fuel injection nozzle.

BEST MODE FOR CARRYING OUT THE INVENTION

Specific examples will now be described with reference to the accompanying drawings.

First Invention

First, a rod-shaped material 1 is prepared by cutting a billet shown in FIG. 1(a). As this rod-shaped material, SCM415 etc. are suitable.

Subsequently, as shown in FIG. 1 (b), a recess 2 is formed in the rod-shaped material 1 by cold forging (forward extrusion or backward extrusion). This recess 2 is a portion that forms the inner peripheral portion of product subsequently. The recess 2 is formed so as to have a diameter larger than that of the inner peripheral portion of product and have a diameter so large that the recess 2 can be machined satisfactorily (not smaller than 10 mm).

Next, as shown in FIG. 1(c), an undercut 3 is formed in the recess 2, and successively, as shown in FIG. 1(d), the recess 2 is formed into a blind hole 4 having an inside diameter of 2 to 4 mm by cold swaging. Further, the outer peripheral surface is machined by turning to obtain a product (fuel injection nozzle) shown in FIG. 1(e).

The machining method for the material is not limited to plunge machining in which a tool is moved in the radial direction as shown in the figure, and infeed machining in which the material is moved in the axial direction may be performed. Also, the turning can be omitted by forming the tip end portion of the swaging die into a predetermined shape in advance.

Now, a device for performing the swaging operation is explained. As shown in FIG. 2, a swaging device has an inside rotor 5 and an outside rotor 6. In the inside rotor 5, through holes 7 extending in the radial direction are formed at 90° intervals, and a swaging die 8 and a striker 9 are slidably fitted in each of the through holes 7 in the named order from the inside. On the other hand, in the outside rotor 6, twelve pins 10 are rotatably held at equal intervals in the circumferential direction.

In the above-described swaging device, when the inside rotor 5 is turned clockwise and the outside rotor 6 is turned counterclockwise, the swaging die 8 and the striker 9 that are held in the inside rotor 5 are urged to the outside in the radial direction by a centrifugal force. Since the outside rotor 6 turns on the outside and a part of each of the pins 10 held in the outside rotor 6 projects to the inside from the outside rotor 6, the pin 10 pushes the striker 9 inward in the radial direction each time the pin 10 passes through the outer end portion of the striker 9. Accordingly, the swaging die 8 is also pushed inward in the radial direction to strike the surface of the material set in the center of the four swaging dies 8 at a rate of several thousand cycles per minute to perform swaging operation.

In order to form the material 1 formed with the recess 2 and the undercut 3 by using the above-described swaging device, first, as shown in FIG. 3(a), the material 1 is gripped by a damper 11, and a mandrel 12 is inserted into the recess 2 of the material 1. This mandrel 12 is configured so as to have an outside diameter equal to the inside diameter of the blind hole in an aimed product (fuel injection nozzle).

As shown in FIG. 3(b), the material 1 is pushed in to a position at which the material 1 abuts on a stopper 13 by using the mandrel 12, and the outside surface of the material 1 is struck by the swaging dies 8 as described above to perform swaging operation. The inside diameter of the recess 2 is decreased to the outside diameter of the mandrel 12 by this swaging operation with the undercut 3 being left. The machining method for the material is not limited to plunge machining in which a tool is moved in the radial direction as shown in the figure, and infeed machining in which the material is moved in the axial direction may be performed.

Thereafter, the external shape of product (fuel injection nozzle) is formed by turning. However, the turning can be omitted by forming the tip end of the swaging die 8 into a predetermined shape.

Second Invention

Next, an example of a second invention will be explained. The second invention is an improvement on the first invention; specifically, in the first invention, the large-diameter recess is formed in the material by forging (forward extrusion or backward extrusion), and after the undercut has been formed at the inner periphery of the recess, the mandrel having a diameter equal to the diameter of the inner peripheral portion of an aimed member is inserted into the recess, and then the material is swaged from the outside. Thereafter, the nozzle shape is formed, for example, by grinding the outside surface.

The method of the first invention is very effective in forming a fuel injection nozzle etc. However, since the ordinary mandrel used for swaging has a flat tip end portion, the machining of the female tapered tip end portion of a hollow hole must be performed subsequently, so that the machining operation is troublesome. Also, even if the female tapered tip end portion is formed by post-machining, it is impossible to exactly know the length of the female tapered tip end portion. Therefore, it is impossible to exactly know a grinding allowance at the time when the final external dimensions are obtained, so that the thickness of the tip end portion is liable to vary.

Also, it is necessary to use a very thin mandrel in forming a fuel injection nozzle etc. In the case where the very thin mandrel is used, if the tip end of the mandrel shifts from the recess center as shown in FIG. 4, the material tilts when it abuts on the stopper, so that a high load is applied to the mandrel, and hence buckling may occur. Also, the tilt of material results in the impossibility of obtaining the depth accuracy of a hollow hole.

Accordingly, in the second invention, first, a rod-shaped material 21 shown in FIG. 5(a) is prepared by cutting a billet. As this rod-shaped material, SCM415 etc. are suitable. Subsequently, as shown in FIG. 5(b), a recess 22 is formed in the rod-shaped material 21 by cold forging (forward extrusion or backward extrusion). This recess 22 is a portion that forms the inner peripheral portion of product subsequently. The recess 22 is formed so as to have a diameter larger than that of the inner peripheral portion of product and have a diameter so large that the recess 22 can be machined satisfactorily (not smaller than 10 mm).

After the rod-shaped material 21 has been cold forged, as shown in FIG. 5(c), an undercut 23 is formed in the recess 22, and successively, as shown in FIG. 5(d), the recess 22 is formed into a blind hole 24 having an inside diameter of 2 to 4 mm by cold swaging. Further, the outer peripheral surface is machined by turning to obtain a product (fuel injection nozzle) shown in FIG. 5(e).

The machining method for the material is not limited to plunge machining in which a tool is moved in the radial direction as shown in the figure, and infeed machining in which the material is moved in the axial direction may be performed. Also, the turning can be omitted by forming the tip end portion of the swaging die into a predetermined shape in advance.

The swaging device is the same as the device used in the first invention. Specifically, as shown in FIG. 2, the swaging device has an inside rotor 5 and an outside rotor 6. In the inside rotor 5, through holes 7 extending in the radial direction are formed at 90° intervals, and a swaging die 8 and a striker 9 are slidably fitted in each of the through holes 7 in the named order from the inside. On the other hand, in the outside rotor 6, twelve pins 10 are rotatably held at equal intervals in the circumferential direction.

In the above-described swaging device, when the inside rotor 5 is turned clockwise and the outside rotor 6 is turned counterclockwise, the swaging die 8 and the striker 9 that are held in the inside rotor 5 are urged to the outside in the radial direction by a centrifugal force. Since the outside rotor 6 turns on the outside and a part of each of the pins 10 held in the outside rotor 6 projects to the inside from the outside rotor 6, the pin 10 pushes the striker 9 inward in the radial direction each time the pin 10 passes through the outer end portion of the striker 9. Accordingly, the swaging die 8 is also pushed inward in the radial direction to strike the surface of the material set in the center of the four swaging dies 8 at a rate of several thousand cycles per minute to perform swaging operation.

In order to form the material 21 formed with the recess 22 and the undercut 23 by using the above-described swaging device, first, as shown in FIG. 6(a), the material 21 is gripped by a damper 11, and a mandrel 12 is inserted into the recess 22 of the material 21. This mandrel 12 is configured so that the outside diameter thereof is equal to the inside diameter of the blind hole 24 in an aimed product (fuel injection nozzle), and a tip end portion 12a thereof has a conical shape to form a female tapered portion 24a at the tip end of the blind hole 24 of an aimed product.

As shown in FIG. 6(b), the material 21 is pushed in to a position at which the material 21 abuts on a stopper 13 by using the mandrel 12, and the outside surface of the material 21 is struck by the swaging dies 8 as described above to perform swaging operation. The inside diameter of the recess 22 is decreased to the outside diameter of the mandrel 12 by this swaging operation with the undercut 23 being left. With decreasing diameter, a material in the bottom portion of the material 21 also moves to the inside as indicated by the arrow marks so as to wrap the tip end portion 12a of the mandrel, by which the female tapered portion 24a is formed as shown in FIG. 6(c).

The position of the female tapered portion 24a is consistent with the tip end portion 12a of the mandrel. Also, the length of the mandrel 12 and the position of the end portion of the material 21 can be measured by a sensor or the like. Therefore, it is possible to exactly know the thickness (t0) of the bottom portion of the material 27, so that a grinding allowance (t1) can be determined from this thickness (t0). That is to say, the tip end portion 12a of the mandrel can be used as a machining allowance in the lengthwise direction.

FIG. 7( a) is a view showing an example in which a positioning hole 25 is formed in the center of the recess 22 of the material 21. By inserting the tip end portion 12a of the mandrel into the positioning hole 25, the material 21 is prevented from being tilted by the shift of the mandrel 12 at the time of swaging operation.

If the opening angle of the positioning hole 25 is smaller than the angle of the tip end portion 12a of the mandrel as shown in FIG. 7(b), a deficient thickness may be produced after the swaging operation. Therefore, the positioning hole 25 is formed so that the depth thereof is equal to or shallower than the length of the mandrel tip end portion, and the opening angle thereof is equal to or larger than the angle of the mandrel tip end portion.

It is advantageous in terms of process that the positioning hole 25 be formed by forging (forward extrusion) as shown in FIG. 8 at the same time that the recess 22 is formed. Also, the recess 22 and the positioning hole 25 may be formed at the same time by backward extrusion in place of the forward extrusion.

FIGS. 9( a) and 9(b) each show examples in which in addition to the positioning hole 25, an excess thickness portion 21a or 21b is provided in the outer peripheral portion of the material 21 or in the inner peripheral portion of the recess 22 in a predetermined range from the bottom of the recess 22 at the time of forging operation. At the time of swaging operation, since the material of the material 21 moves in the opening direction along the axial direction, the material runs short near the bottom of the recess 22. However, the provision of the excess thickness portion 21a or 21b can compensate this shortage.

Third Invention

Next, an example of a third invention will be explained. The third invention is an improvement on the first invention; specifically, in the first invention, the large-diameter recess is formed in the material by forging (forward extrusion or backward extrusion) as described above, and as shown in FIG. 10(a), after the undercut has been formed at the inner periphery of the recess, the mandrel having a diameter equal to the diameter of the inner peripheral portion of an aimed member is inserted into the recess, and then the material is swaged from the outside. Thereafter, the nozzle shape is formed, for example, by grinding the outside surface.

The method of the first invention is very effective in forming a fuel injection nozzle etc. However, when the forming ratio is high, the material flows in the opening direction along the lengthwise direction at the time of swaging operation. At this time, the corner portion of the recess is left behind as shown in FIG. 11(b), and finally a deficient thickness may be produced as shown in FIG. 10(c).

Accordingly, in the third invention, first, a rod-shaped material 31 shown in FIG. 11(a) is prepared by cutting a billet. As this rod-shaped material, SCM415 etc. are suitable. Subsequently, as shown in FIG. 11(b), a recess 32 is formed in the rod-shaped material 31 by cold forging (forward extrusion or backward extrusion). This recess 32 is a portion that forms the inner peripheral portion of product subsequently. The recess 32 is formed so as to have a diameter larger than that of the inner peripheral portion of product and have a diameter so large that the recess 32 can be machined satisfactorily (not smaller than 10 mm).

A chamfered portion 32a is formed in the corner portion of the bottom of the recess 32. As shown in FIG. 12(a), the chamfered portion 32a is R-chamfered, and the formation region thereof is a region that provides a clearance between the swaging mandrel and the inner peripheral surface of the recess 32. The whole of this clearance region may be chamfered. However, if 35% or more of the clearance region is chamfered, there is no fear of producing a deficient thickness.

Also, the chamfered portion 32a is not limited to R-chamfer, and may be C-chamfered as shown in FIG. 12(b). Further, as shown in FIG. 12(b), a positioning hole 34 in which the conical tip end portion of the mandrel is inserted is formed in advance in the center of the recess 32, by which the material 31 is prevented from being tilted by the shift of the mandrel at the time of swaging operation.

It is advantageous in terms of forming efficiency that the recess 32, the chamfered portion 32a, and the positioning hole 34 be formed at the same time by cold forging (forward extrusion) shown in FIG. 13. The forging may be performed by backward extrusion. However, since the backward extrusion buckles the punch easily, forward extrusion is more advantageous.

Returning to FIG. 11, after the rod-shaped material 31 has been cold forged, as shown in FIG. 11(c), an undercut 33 is formed in the recess 32, and successively, as shown in FIG. 11(d), the recess 32 is formed into a blind hole 34 having an inside diameter of 2 to 4 mm by cold swaging. Further, the outer peripheral surface is machined by turning to obtain a product (fuel injection nozzle) shown in FIG. 11(e).

The swaging device is the same as the device used in the first invention. Specifically, as shown in FIG. 2, the swaging device has an inside rotor 5 and an outside rotor 6. In the inside rotor 5, through holes 7 extending in the radial direction are formed at 900 intervals, and a swaging die 8 and a striker 9 are slidably fitted in each of the through holes 7 in the named order from the inside. On the other hand, in the outside rotor 6, twelve pins 10 are rotatably held at equal intervals in the circumferential direction.

In the above-described swaging device, when the inside rotor 5 is turned clockwise and the outside rotor 6 is turned counterclockwise, the swaging die 8 and the striker 9 that are held in the inside rotor 5 are urged to the outside in the radial direction by a centrifugal force. Since the outside rotor 6 turns on the outside and a part of each of the pins 10 held in the outside rotor 6 projects to the inside from the outside rotor 6, the pin 10 pushes the striker 9 inward in the radial direction each time the pin 10 passes through the outer end portion of the striker 9. Accordingly, the swaging die 8 is also pushed inward in the radial direction to strike the surface of the material set in the center of the four swaging dies 8 at a rate of several thousand cycles per minute to perform swaging operation.

In order to form the material 31 formed with the recess 32 and the undercut 33 by using the above-described swaging device, first, as shown in FIG. 14(a), the material 31 is gripped by a damper 11, and a mandrel 12 is inserted into the recess 32 of the material 31. This mandrel 12 is configured so that the outside diameter thereof is equal to the inside diameter of the blind hole 34 in an aimed product (fuel injection nozzle), and a tip end portion 12a thereof has a conical shape to form a female tapered portion 34a at the tip end of the blind hole 34 of aimed product.

As shown in FIG. 14(b), the material 31 is pushed in to a position at which the material 31 abuts on a stopper 13 by using the mandrel 12, and the outside surface of the material 31 is struck by the swaging dies 8 as described above to perform swaging operation. The inside diameter of the recess 32 is decreased to the outside diameter of the mandrel 12 by this swaging operation with the undercut 33 being left.

With decreasing diameter, a material in the corner portion of the bottom of the material 31 also moves to the inside as indicated by the arrow marks so as to wrap the tip end portion 12a of the mandrel, by which the female tapered portion 34a is formed as shown in FIG. 14(c). At this time, since the corner portion forms the chamfered portion 32a, a shortage of material does not occur when the material moves.

The machining method for the material is not limited to plunge machining in which a tool is moved in the radial direction as shown in the figure, and infeed machining in which the material is moved in the axial direction may be performed. Also, the turning can be omitted by forming the tip end portion of the swaging die into a predetermined shape in advance.

Fourth Invention

Next, an example of a fourth invention will be explained. The fourth invention is an improvement on the first invention; specifically, in the first invention, the large-diameter recess is formed in the material by forging (forward extrusion or backward extrusion), and after the undercut has been formed at the inner periphery of the recess, the mandrel having a diameter equal to the diameter of the inner peripheral portion of an aimed member is inserted into the recess, and then the material is swaged from the outside. Thereafter, the nozzle shape is formed, for example, by grinding the outside surface.

The method of the first invention is very effective in forming a fuel injection nozzle etc. However, when the forming ratio is high, the material flows in the opening direction along the lengthwise direction at the time of swaging operation. As a result, in some products, a deficient thickness may be produced at the inner periphery of the bottom portion of the recess as shown in FIG. 15.

Accordingly, in the fourth invention, a rod-shaped material 41 shown in FIG. 16(a) is prepared by cutting a billet. As this rod-shaped material, SCM415 etc. are suitable. Subsequently, as shown in FIG. 16(b), a recess 42 is formed in the rod-shaped material 41 by cold forging (forward extrusion or backward extrusion). This recess 42 is a portion that forms the inner peripheral portion of product subsequently. The recess 42 is formed so as to have a diameter larger than that of the inner peripheral portion of product and have a diameter so large that the recess 42 can be machined satisfactorily (not smaller than 10 mm).

In the case where forward extrusion is performed as the cold forging operation as shown in FIG. 17, an excess thickness portion 41a is provided at the outer periphery of the rod-shaped material 41 in a predetermined length range from the bottom of the recess 42. This excess thickness portion 41a compensates the flow of material at the time of swaging operation, described later. The preferred range (L) is 2d ≦L≦4d, where d is mandrel diameter (nozzle inside diameter) at the time of swaging operation.

Also, in the case where backward extrusion is performed as the cold forging operation as shown in FIG. 18, an excess thickness portion 41b is provided at the inner periphery of the recess 42 in a predetermined length range from the bottom thereof. For this excess thickness portion 41b as well, the preferred range is 2d≦L≦4d.

An excess thickness is produced from a position of a clearance between the mandrel and the prepared hole from the bottom. Therefore, if the range of the excess thickness portion is narrower than two times the mandrel diameter (d), the material may run short in the portion above the production position. Also, if the range exceeds four times, the material flows into the undercut, which may deform the shape of the undercut. For this reason, the range was set at two to four times of d. Also, the volume of the excess thickness portion is determined from a preliminary test so as to be larger than the volume of a deficient thickness portion produced.

In this example, an example in which the excess thickness portion is formed simultaneously with the cold forging operation has been shown. However, the excess thickness portion may be formed apart from the formation of the recess 42.

After the rod-shaped material 41 has been cold forged as described above, as shown in FIG. 16(c), an undercut 43 is formed in the recess 42, and successively, as shown in FIG. 16(d), the recess 42 is formed into a blind hole 44 having an inside diameter of 2 to 4 mm by cold swaging. Further, the outer peripheral surface is machined by turning to obtain a product (fuel injection nozzle) shown in FIG. 15(e).

The swaging device is the same as the device used in the first invention. Specifically, as shown in FIG. 2, the swaging device has an inside rotor 5 and an outside rotor 6. In the inside rotor 5, through holes 7 extending in the radial direction are formed at 90° intervals, and a swaging die 8 and a striker 9 are slidably fitted in each of the through holes 7 in the named order from the inside. On the other hand, in the outside rotor 6, twelve pins 10 are rotatably held at equal intervals in the circumferential direction.

In the above-described swaging device, when the inside rotor 5 is turned clockwise and the outside rotor 6 is turned counterclockwise, the swaging die 8 and the striker 9 that are held in the inside rotor 5 are urged to the outside in the radial direction by a centrifugal force. Since the outside rotor 6 turns on the outside and a part of each of the pins 10 held in the outside rotor 6 projects to the inside from the outside rotor 6, the pin 10 pushes the striker 9 inward in the radial direction each time the pin 10 passes through the outer end portion of the striker 9. Accordingly, the swaging die 8 is also pushed inward in the radial direction to strike the surface of the material set in the center of the four swaging dies 8 at a rate of several thousand cycles per minute to perform swaging operation.

In order to form the material 41 formed with the recess 42 and the undercut 43 by using the above-described swaging device, first, as shown in FIG. 19(a), the material 41 is gripped by a damper 11, and a mandrel 12 is inserted into the recess 42 of the material 41. This mandrel 12 is configured so as to have an outside diameter equal to the inside diameter of the blind hole in an aimed product (fuel injection nozzle).

As shown in FIG. 19(b), the material 41 is pushed in to a position at which the material 41 abuts on a stopper 13 by using the mandrel 12, and the outside surface of the material 41 is struck by the swaging dies 8 as described above to perform swaging operation. The inside diameter of the recess 42 is decreased to the outside diameter of the mandrel 12 by this swaging operation with the undercut 43 being left. At this time, since the material of the material 41 moves in the opening direction along the axial direction, the material runs short near the bottom of the recess 42. However, this shortage is compensated by the excess thickness portion 41a or 41b.

The machining method for the material is not limited to plunge machining in which a tool is moved in the radial direction as shown in the figure, and infeed machining in which the material is moved in the axial direction may be performed.

Thereafter, the external shape of product (fuel injection nozzle) is formed by turning. However, the turning can be omitted by forming the tip end of the swaging die 8 into a predetermined shape.

Fifth Invention

A fifth invention relates to a valve guide and a method of forming the valve guide. Specifically, first, a rod-shaped material 51 consisting of an Al-base composite material shown in FIG. 20(a) is prepared by cutting a billet. The Al-base composite material is an alloy consisting mainly of A1203 to which SiC etc. are added. This Al-base composite material has an elongation percentage of 2 to 5%. The elongation percentage allowing a cold swaging operation, described later, is about 10%. However, the swaging operation can be performed even on a material having an elongation percentage of 2 to 5% by decreasing the feed of die.

Subsequently, as shown in FIG. 20(b), a recess 52 is formed in the rod-shaped material 51 by cold forging (forward extrusion or backward extrusion). This recess 52 is a portion that forms an inner peripheral portion for slidingly guiding a valve stem subsequently. The recess 52 is formed so as to have a diameter larger than that of the inner peripheral portion of valve guide and have a diameter so large that the recess 52 can be machined satisfactorily (not smaller than 10 mm).

After the recess 52 has been formed by cold forging, as shown in FIG. 20(c), the recess 52 is formed into a small-diameter hole 53 (the same diameter as that of the valve stem) by cold swaging.

In the above-described swaging operation, the bottom portion of the recess 52 is left because the bottom portion is gripped by a mandrel and a stopper of a swaging device. Therefore, as shown in FIG. 20(d), the bottom portion is cut to form a cylindrical shape. Subsequently, by machining the outer peripheral portion, a valve guide W having a flange 54 is obtained as shown in FIG. 20(e).

The outer peripheral portion can be formed by cutting simultaneously with the swaging operation. In this case, the cutting operation can be omitted by contriving the shape of swaging die.

For the above-described swaging operation, the swaging device used in the first invention is used. Specifically, as shown in FIG. 2, the swaging device has an inside rotor 5 and an outside rotor 6. In the inside rotor 5, through holes 7 extending in the radial direction are formed at 90° intervals, and a swaging die 8 and a striker 9 are slidably fitted in each of the through holes 7 in the named order from the inside. On the other hand, in the outside rotor 6, twelve pins 10 are rotatably held at equal intervals in the circumferential direction.

In the above-described swaging device, when the inside rotor 5 is turned clockwise and the outside rotor 6 is turned counterclockwise, the swaging die 8 and the striker 9 that are held in the inside rotor 5 are urged to the outside in the radial direction by a centrifugal force. Since the outside rotor 6 turns on the outside and a part of each of the pins 10 held in the outside rotor 6 projects to the inside from the outside rotor 6, the pin 10 pushes the striker 9 inward in the radial direction each time the pin 10 passes through the outer end portion of the striker 9. Accordingly, the swaging die 8 is also pushed inward in the radial direction to strike the surface of the material set in the center of the four swaging dies 8 at a rate of several thousand cycles per minute to perform swaging operation.

In order to form the material 51 formed with the recess 52 by using the above-described swaging device, first, as shown in FIG. 22(a), the material 51 is gripped by a damper 11, and the mandrel 12 is inserted into the recess 52 of the material 51. This mandrel 12 is configured so as to have an outside diameter equal to the inside diameter of a guide hole in the valve guide, namely, the diameter of the valve stem.

As shown in FIG. 22(b), the material 51 is pushed in to a position at which the material 51 abuts on the stopper 13 by using the mandrel 12, and the outside surface of the material 51 is struck by the swaging dies 8 as described above to perform swaging operation. The inside diameter of the recess 52 is decreased to the outside diameter of the mandrel 12 by this swaging operation.

The conventional valve guide has no problem of lubricity because it is formed of a sintered product of oil-bearing alloy or formed of cast iron. However, in the case where the Al-base composite material is used as the material for the valve guide and is swaged as in the present invention, the lubricity may become insufficient.

An example for solving this problem is shown in FIG. 23. FIG. 23(a) shows a state in which the recess 52 is formed by cold forging the rod-shaped material 51 and a groove 52a is formed in the inner peripheral surface of the recess 52 by post-machining. After this material 51 has been swaged, the groove 52a does not disappear and remains as a groove 53a in the inner peripheral surface of the small-diameter hole 57, the groove 53a serving as an oil groove.

Sixth Invention

A sixth invention relates to a method of forming a tubular member such as a valve guide. Specifically, first, a rod-shaped material 61 consisting of an Al-base composite material shown in FIG. 24(a) is prepared by cutting a billet. The Al-base composite material is an alloy consisting mainly of Al₂O₃ to which SiC etc. are added. This Al-base composite material has an elongation percentage of 2 to 5%. The elongation percentage allowing a cold swaging operation, described later, is about 10%. However, the swaging operation can be performed even on a material having an elongation percentage of 2 to 5% by decreasing the feed of die.

Subsequently, as shown in FIG. 24(b), an inside-diameter hole 62 is formed in the rod-shaped material 61 by cold forging (forward extrusion or backward extrusion), and this material is used as an intermediate material 63. Next, as shown in FIG. 24(c), the inner peripheral surface of the inside-diameter hole 62 is metal plated to form a metallic deposit 64 consisting of iron (Fe) or nickel—silicon carbide (Ni—SiC). The size of the inside-diameter hole 62 is set at a size allowing metal plating, concretely, at 10 to 15 mm.

Thereafter, as shown in FIG. 24(d), the inside-diameter hole 62 is formed into a small-diameter hole 65 having the same diameter as that of the valve stem by cold swaging.

The material having been swaged as described above is cut to a predetermined length, and further, by machining the outer peripheral portion, a valve guide W having a flange 66 is obtained as shown in FIG. 24(e).

The outer peripheral portion can be formed by cutting simultaneously with the swaging operation. In this case, the cutting operation can be omitted by contriving the shape of swaging die.

For the above-described swaging operation, the swaging device used in the first invention is used. Specifically, as shown in FIG. 2, the swaging device has an inside rotor 5 and an outside rotor 6. In the inside rotor 5, through holes 7 extending in the radial direction are formed at 90° intervals, and a swaging die 8 and a striker 9 are slidably fitted in each of the through holes 7 in the named order from the inside. On the other hand, in the outside rotor 6, twelve pins 10 are rotatably held at equal intervals in the circumferential direction.

In the above-described swaging device, when the inside rotor 5 is turned clockwise and the outside rotor 6 is turned counterclockwise, the swaging die 8 and the striker 9 that are held in the inside rotor 5 are urged to the outside in the radial direction by a centrifugal force. Since the outside rotor 6 turns on the outside and a part of each of the pins 10 held in the outside rotor 6 projects to the inside from the outside rotor 6, the pin 10 pushes the striker 9 inward in the radial direction each time the pin 10 passes through the outer end portion of the striker 9. Accordingly, the swaging die 8 is also pushed inward in the radial direction to strike the surface of the material set in the center of the four swaging dies 8 at a rate of several thousand cycles per minute to perform swaging operation.

Claims

1: A method of forming a member having an inside-diameter portion with a small diameter, comprising the steps of forming a large-diameter recess in a material;machining the recess; andswaging the material from an outside by inserting a mandrel having a diameter equal to a diameter of an inner peripheral portion of an aimed member.

2: A method of forming a member, including a method of providing an undercut in an inner peripheral portion of the member, comprising the steps of: forming a recess having a diameter larger than that of the inner peripheral portion of the member in a material;forming an undercut at an inner periphery of the recess;inserting a mandrel having a diameter equal to a diameter of an inner peripheral portion of an aimed member into the recess of the material having been formed with the undercut; andswaging, from an outside, the material into which the mandrel has been inserted so that an inside diameter of the recess of the material is decreased to an outside diameter of the mandrel with the undercut left.

3: The method of forming a member according to claim 2, wherein the member is a fuel injection nozzle.

4: A method of forming a member having an undercut, comprising the steps of forming a recess having a diameter larger than the diameter of an inner peripheral portion of the member in a material;forming the undercut at an inner periphery of the recess;inserting a mandrel having a diameter equal to a diameter of an inner peripheral portion of an aimed member and having a conical tip end portion into the recess of the material having been formed with the undercut; andswaging, from an outside, the material into which the mandrel has been inserted, by which an inside diameter of the recess of the material is decreased to an outside diameter of the mandrel with the undercut left, and at the same time, a tip end portion of the inner peripheral portion of the aimed member is formed into a female taper shape following the tip end portion of the mandrel.

5: The method of forming a member having an undercut according to claim 4, that wherein a positioning hole into which the mandrel tip end portion is inserted is formed in a center of the large-diameter recess, and a depth of the positioning hole is equal to or shallower than a length of the mandrel tip end portion and an opening angle thereof is equal to or larger than an angle of the mandrel tip end portion.

6: The method of forming a member having an undercut according to claim 5, wherein the positioning hole is formed by forging at the same time that the recess is formed.

7: The method of forming a member having an undercut according to claim 4, wherein the member is a fuel injection nozzle.

8: A method of forming a member having an undercut, comprising the steps of: forming a recess having a diameter larger than the diameter of an inner peripheral portion of the member in a material;forming the undercut at an inner periphery of the recess;inserting a mandrel having a diameter equal to a diameter of an inner peripheral portion of an aimed member into the recess of the material having been formed with the undercut; andswaging, from an outside, the material into which the mandrel has been inserted so that an inside diameter of the recess of the material is decreased to an outside diameter of the mandrel with the undercut left, wherein a chamfered portion is formed in a bottom portion of the recess of the material before the swaging operation, and a formation region of the chamfered portion is within an outside region that provides a clearance with a tip end of the mandrel abutted on the bottom portion of the recess.

9: The method of forming a member having an undercut according to claim 8, wherein the formation region of the chamfered portion is 35 to 100% of a clearance between the mandrel and the inner periphery of the recess.

10: The method of forming a member having an undercut according to claim 8 or 9, claim 8, wherein the member is a fuel injection nozzle.

11: A method of forming a member having an undercut, comprising the steps of: forming a recess having a diameter larger than the diameter of an inner peripheral portion of the member in a material;forming the undercut at an inner periphery of the recess;inserting a mandrel having a diameter equal to a diameter of an inner peripheral portion of an aimed member into the recess of the material having been formed with the undercut; andswaging, from an outside, the material into which the mandrel has been inserted so that an inside diameter of the recess of the material is decreased to an outside diameter of the mandrel with the undercut left, wherein an excess thickness portion is provided in a predetermined length range from a bottom of the recess at the inner or an outer periphery of the recess of the material before the swaging operation.

12: The method of forming a member having an undercut according to claim 11, wherein the excess thickness portion is formed by forging at the same time that the recess is formed.

13: The method of forming a member having an undercut according to claim 11, wherein the member is a fuel injection nozzle.

14: A valve guide for slidingly guiding a valve stem, wherein the valve guide is formed of an Al-base composite material, and an oil groove is formed in an inner peripheral surface of the valve guide.

15: A method of forming a valve guide for slidingly guiding a valve stem, comprising the steps of: forming a recess having a diameter larger than the diameter of an inner peripheral portion into which the valve stem is inserted in a valve material; andswaging, from an outside, the material into which a mandrel has been inserted so that an inside diameter of the recess of the material is decreased to an outside diameter of the mandrel by inserting the mandrel having almost a same diameter as the diameter of the valve stem into the large-diameter recess.

16: The method of forming a valve guide according to claim 15, wherein a groove remaining as an oil groove after swaging operation is formed in advance in an inner peripheral surface of the large-diameter recess.

17: The method of forming a valve guide according to claim 15, wherein the material is an Al-base composite material.

18: A method of forming a tubular member formed with a small-diameter hole along the axial direction, comprising the steps of; obtaining an intermediate material such that a diameter of an inside-diameter hole has a dimension allowing metal plating;forming a metallic deposit in the inside-diameter hole of the intermediate material; andswaging, from an outside diameter side, the intermediate material into which a mandrel has been inserted so that the diameter of the inside-diameter hole of the intermediate material is decreased to an outside diameter of the mandrel by inserting the mandrel having a diameter corresponding to the diameter of the small-diameter hole of an aimed tubular member into the inside-diameter hole of the intermediate material formed with the metallic deposit.

19: The method of forming a tubular member according to claim 18, wherein a material for the tubular member is an aluminum alloy or an aluminum-base composite material, and a material for the metallic deposit a highly wear resistant material such as iron (Fe) or nickel—silicon carbide (Ni—SiC).