Method and Device for Forging Bevel Gear

Abstract

A method and a device for forging a bevel gear. The device includes a punch, a work positioning and holding die positioning and holding a work placed on the placing surface of a lower die, and an outer burr removing die removing outer burrs produced on the outer peripheral surfaces of the teeth of the work. In the state of the work positioned and held at a prescribed position by the work positioning and holding die, the inner burrs and the outer burrs of the work are simultaneously removed by the integrated lowering operation of the punch and the outer burr removing die.

Description

TECHNICAL FIELD

The present invention relates to a method and apparatus (device) for forging a bevel gear, for incorporation into the differential of an automobile, for example.

BACKGROUND ART

Heretofore, there have been known methods of manufacturing bevel gears for use in automobile power transmitting connectors, e.g., differentials, as well as dies for manufacturing such bevel gears (see, for example, Patent Document 1).

A bevel gear has conventionally been manufactured by the process described below, as shown in FIGS. 12A through 12D.

A cylindrical stock 1 (see FIG. 12A) is forged in a single forging cycle or in a plurality of forging cycles so as to produce a preform 4 (see FIG. 12B). The preform 4 has preliminary teeth 2, each of which includes a preliminary tooth tip surface 2a that is progressively larger in diameter in one direction along its axis, and a preliminary tooth end surface 2b contiguous to the preliminary tooth tip surface 2a. The preform 4 also has a preliminary main body 3, which includes a preliminary circumferential conical surface 3a contiguous to the preliminary tooth end surface 2b, and which is progressively smaller in diameter in one direction along its axis.

Then, the preform 4 is pierced to produce an intermediate form 6 (see FIG. 12C), having a through hole 5 defined therein along its central axis. Finally, the intermediate form 6 is sized into a bevel gear 7 (see FIG. 12D,) wherein the teeth thereof are finished to acquire desired dimensions.

While the bevel gear is manufactured according to the above process, the teeth of the intermediate form 6 are sized so as to increase their accuracy, for thereby producing the bevel gear 7 having desired teeth. However, when the teeth are sized, due to the flowing material being forged, outer burrs are formed along the tooth profile of the tooth end surfaces.

According to Patent Document 1, since the outer burrs that occur along the tooth profile of the tooth end surface are inclined to the axis of the bevel gear, and are produced within regions where the tooth profile is of a complex shape including an involute curve, it is difficult to remove such outer burrs using a press, and hence the outer burrs must be removed by a manual process (machining process) performed by the worker. According to Patent Document 1, the process of removing the outer burrs is time-consuming and lowers productivity.

Patent Document 2 discloses a forging press for forging a flange part having a shaft, and also discloses a technical concept in which both outer burrs and inner burrs of a roughly formed part are simultaneously cut off by a cutting blade and an upper punch of the forging press.

However, if such a technical concept, in which both outer burrs and inner burrs of a roughly formed part are simultaneously cut off as disclosed by Patent Document 2, were to be applied to forging a bevel gear, then since the outer burrs that occur along the tooth profile of the tooth end surface are inclined with respect to the axis of the bevel gear, and further are produced within regions where the tooth profile is of a complex shape including an involute curve, it is necessary to remove the outer burrs along the tooth profile of the tooth end surface using a deburring process, which is performed at the same time as the piercing process, after the workpiece, as the intermediate form of the bevel gear, has been positioned in place.

In other words, when a bevel gear is forged, in order to remove outer burrs occurring along the tooth profile of the tooth end surface, it is necessary to position and hold the workpiece in place, while removing the outer burrs without causing damage to the tooth profile of the workpiece that has been positioned and held. In contrast, the outer burrs disclosed in Patent Document 2 are of a simple ring shape that can easily be removed.

Patent Document 1: Japanese Laid-Open Patent Publication No. 9-85385; and

Patent Document 2: Japanese Laid-Open Patent Publication No. 2000-117628.

DISCLOSURE OF THE INVENTION

A general object of the present invention is to provide a method and apparatus for forging a bevel gear by means of a shortened manufacturing process, which increases productivity by simultaneously piercing and deburring a workpiece while the workpiece is being appropriately positioned and held in place.

According to the present invention, a forging stock is forged in a single forging cycle or in a plurality of forging cycles in order to produce an intermediate form. The intermediate form is mounted as a workpiece on a mount die of a lower die. The workpiece is positioned and held in a predetermined position by a positioning and holding die, which is fitted over a punch for displacement in unison with the punch.

While the intermediate form is positioned and held by the positioning and holding die, the intermediate form is pierced by the punch in order to remove an inner burr thereof, and simultaneously, outer burrs of the intermediate form also are removed by an outer deburring die, which is fitted over the positioning and holding die for displacement in unison with the punch.

The intermediate form is positioned when engaging fingers provided on an end of the positioning and holding die engage within valleys located between the teeth of the intermediate form.

According to the present invention, when the punch, the workpiece positioning and holding die, and the outer deburring die are displaced in unison with each other, the workpiece positioning and holding die, which projects a predetermined distance from the punch and the outer deburring die toward the lower die, contacts the workpiece mounted on the lower die, thereby holding the workpiece while it is positioned in the predetermined position.

With the workpiece positioned and held by the workpiece positioning and holding die, the punch and the outer deburring die are displaced in unison with each other, so as to simultaneously remove both the inner burr and the outer burrs of the workpiece.

According to the present invention, furthermore, a forging stock is forged in a single forging cycle or in a plurality of forging cycles in order to produce an intermediate form. The intermediate form is mounted as a workpiece on a mount die of a lower die. After circumferential positional errors of the workpiece have been corrected by a positioning and deburring die, which is fitted over a punch for displacement in unison with the punch, the workpiece is pressed against the lower die by a workpiece pressing die, which positions and holds the workpiece in a predetermined position.

While the intermediate form is positioned and held by the workpiece pressing die, the intermediate form is pierced by the punch in order to remove an inner burr thereof, and simultaneously, outer burrs of the intermediate form also are removed by the positioning and deburring die, which is fitted over the workpiece pressing die for displacement in unison with the punch.

The intermediate form is positioned when engaging protrusions on the positioning and deburring die engage within valleys located between the teeth of the intermediate form.

According to the present invention, when the punch, the workpiece pressing die, and the positioning and deburring die are displaced in unison with each other, the positioning and deburring die, which projects a predetermined distance from the punch and the workpiece pressing die toward the lower die, contacts the workpiece mounted on the lower die, thereby holding the workpiece while it is positioned in the predetermined position.

After the workpiece has been positioned and held by the positioning and deburring die, and while the workpiece is positioned and held in the predetermined position by the workpiece pressing die, the punch and the outer deburring die are displaced in unison with each other, so as to simultaneously remove both the inner burr and the outer burrs of the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1D are views showing a process of manufacturing a bevel gear according to an embodiment of the present invention;

FIG. 2 is a vertical cross-sectional view taken along the axial direction of a forming apparatus according to the embodiment of the present invention;

FIG. 3 is a vertical cross-sectional view showing the manner in which engaging fingers of a workpiece positioning and holding die of the forming apparatus shown in FIG. 2 are placed within valleys located between teeth of a workpiece;

FIG. 4 is a vertical cross-sectional view showing the manner in which the workpiece is positioned and held by the workpiece positioning and holding die of the forming apparatus shown in FIG. 2;

FIG. 5 is a vertical cross-sectional view showing the manner in which inner burrs of the workpiece are removed by a punch of the forming apparatus shown in FIG. 2, and in which outer burrs of the workpiece are removed by an outer burr cut-off die;

FIG. 6 is a bottom view of the workpiece positioning and holding die and the outer burr cut-off die of the forming apparatus shown in FIG. 2;

FIG. 7 is a vertical cross-sectional view taken along an axial direction of a forming apparatus, according to another embodiment of the present invention;

FIG. 8 is a vertical cross-sectional view showing the manner in which engaging fingers of a workpiece positioning and holding die of the forming apparatus shown in FIG. 7 are placed within valleys located between teeth of a workpiece;

FIG. 9 is a vertical cross-sectional view showing the manner in which the workpiece is positioned and held by the workpiece positioning and holding die of the forming apparatus shown in FIG. 7;

FIG. 10 is a vertical cross-sectional view showing the manner in which inner burrs of the workpiece are removed by a punch of the forming apparatus shown in FIG. 7, and in which outer burrs of the workpiece are removed by an outer burr cut-off die;

FIG. 11 is a bottom view of the workpiece positioning and holding die and the outer burr cut-off die of the forming apparatus shown in FIG. 7; and

FIGS. 12A through 12D are views showing a conventional process for manufacturing a bevel gear.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIGS. 2 through 5, reference numeral 10 denotes a forming apparatus according to an embodiment of the present invention. The forming apparatus 10 is used in a forging process for forging a bevel gear 12 (see FIG. 1D) as a result of forming a stock successively with a plurality of dies. The forming apparatus also is used to pierce (bore) and deburr the workpiece in a final process.

The forming apparatus 10 has a back plate (base) 16 fixedly mounted on a base plate, not shown, by a die holder 14, a hollow cylindrical lower die 18 disposed for displacement in a circumferential direction about an axis of the back plate 16 and in vertical directions along the axis of the back plate 16, and a first helical spring (spring member) 20 interposed between the back plate 16 and the lower die 18 for floatingly supporting the lower die 18 with respect to the fixed back plate 16 under spring forces.

The back plate 16 and the lower die 18 have a drop hole 24 defined vertically therethrough, which allows a cut-off inner burr 22 (see FIGS. 1D and 5), to be described below, to drop therethrough. The back plate 16 has an annular step 26 formed on an outer circumferential surface thereof, which is engaged by an end of the first helical spring 20.

The lower die 18 has a mount surface 30 on its upper end for mounting a workpiece 28 thereon. The mount surface 30 is complementary in shape to the bottom surface of the workpiece 28. The lower die 18 also has, on its lower end, an annular flange 34 having an end face engaged by the other end of the first helical spring 20, wherein the annular flange 34 is slidably displaceable vertically along an annular boss 32 of the back plate 16.

An annular surface 36 formed on an inner wall of the annular flange 34 of the lower die 18 performs a stop function by abutting against an upper surface 37 of the annular boss 32 of the back plate 16, thereby limiting further downward displacement of the lower die 18 (see FIG. 5).

Since the mount surface 30 of the lower die 18 is complementary in shape to the bottom surface of the bevel gear 12 to be manufactured, which is free of a tooth profile surface, an intermediate form can easily be mounted on the mount surface 30.

The forming apparatus 10 also has a piercing punch 38 mounted on the ram of a press, not shown, and vertically movable for piercing a central portion of the workpiece 28, a workpiece positioning and holding die 40 fitted over the punch 38 and vertically displaceable along the punch 38, and an outer deburring die 42 fitted over the workpiece positioning and holding die 40. The punch 38 and the outer deburring die 42 are integrally formed with each other and are fixed to the ram of the non-illustrated press for displacement in unison with each other.

The outer deburring die 42 houses in a hollow space thereof a second helical spring 44, having stronger spring forces than the first helical spring 20, and having a coil diameter that is greater than that of the first helical spring 20. The workpiece positioning and holding die 40 is pressed vertically downward by the second helical spring 44.

The workpiece positioning and holding die 40 has a larger-diameter portion 46 on an outer circumferential surface thereof. The workpiece positioning and holding die 40 is prevented from being removed out of the outer deburring die 42 by the larger-diameter portion 46, when it is engaged by a tapered surface 48 that extends radially inwardly from an inner wall surface of the outer deburring die 42.

The workpiece positioning and holding die 40 is displaceable independently of the punch 38 and the outer deburring die 42. The workpiece positioning and holding die 40 is lifted when it overcomes the spring forces of the second helical spring 44.

The workpiece positioning and holding die 40 has a smaller-diameter portion 50 on an inner wall surface thereof, providing a clearance between the workpiece positioning and holding die 40 and the outer circumferential surface of the punch 38 that extends centrally through the workpiece positioning and holding die 40.

The workpiece positioning and holding die 40 has a plurality of engaging fingers 52 formed on a lower end thereof, which project vertically downward a predetermined distance from the lower end face of the outer deburring die 42. Each of the engaging fingers 52 is of a substantially triangular cross-sectional shape having a slanted surface 54, wherein the number of engaging fingers 52 corresponds to the number of valleys 56 located between the teeth of the workpiece 28 (see FIG. 6). When the engaging fingers 52 enter along the valleys 56 located between the teeth of the workpiece 28, and the slanted surfaces 54 of the engaging fingers 52 come into contact with the valleys 56, the workpiece 28 is positioned in a predetermined position.

The workpiece positioning and holding die 40 has a pressing holder 58 disposed on a lower end thereof near the engaging fingers 52, wherein the pressing holder 58 comprises a hook-shaped step contiguous to the slanted surfaces 54. When the pressing holder 58 engages the upper surface of the workpiece 28 and presses the workpiece 28 against the lower die 18, the workpiece 28 is held while being positioned in place in the predetermined position.

The outer deburring die 42 has, on a portion thereof near the engaging fingers 52, a plurality of cutting edges 62 for cutting off outer burrs 60 produced between the teeth of the workpiece 28, wherein the cutting edges 62 have substantially the same inside diameter as the outside diameter A (see FIG. 2) of the workpiece 28 at a position between the teeth.

The forming apparatus 10 according to the embodiment of the present invention is basically constructed as described above. Operations and advantages of the forming apparatus 10 shall be described below.

First, the cylindrical billet 64 shown in FIG. 1A is forged into a preform 68 having a bevel 66, as shown in FIG. 1B, using a first forging die, not shown. Then, using a second forging die, not shown, the preform 68 is forged into an intermediate form 72 having teeth 70, as shown in FIG. 1C. The intermediate form 72 has thin outer burrs 60 that extend continuously along the outer circumference thereof between the teeth 70.

The forming apparatus 10 according to the present embodiment simultaneously pierces the intermediate form 72 and removes the outer burrs from the intermediate form 72, which makes up the workpiece 28. It shall be assumed that in an initial position, as shown in FIG. 2, the punch 38, the workpiece positioning and holding die 40, and the outer deburring die 42 are suspended in an upper position, which is spaced a predetermined distance from the lower die 18.

First, the intermediate form 72, which makes up the workpiece 28, is placed on the mount surface 30 of the lower die 18 (see FIG. 2). At this time, the bottom surface of the workpiece 28, which is free of any teeth, may simply be placed on the mount surface 30 of the lower die 18, which is shaped complementarily to the shape of the bottom surface of the workpiece 28. The workpiece 28 does not need to be positioned exactly.

Then, the ram of the non-illustrated press is actuated in order to lower the punch 38. The workpiece positioning and holding die 40, and the outer deburring die 42 are lowered in unison from the initial position until the engaging fingers 52 of the workpiece positioning and holding die 40, which project vertically downward by predetermined distances from the punch 38 and the outer deburring die 42, are positioned within the respective valleys 56 located between the teeth.

The workpiece 28 is simply placed on the mount surface 30 of the lower die 18, and the lower die 18 is floatingly supported on the back plate 16 under spring forces of the first helical spring 20. Therefore, the lower die 18 is angularly movable in the circumferential direction thereof.

Consequently, when the engaging fingers 52 of the workpiece positioning and holding die 40 enter into the valleys 56 and engage with the wall surfaces of the valleys 56, any circumferential positional errors of the workpiece 28 are corrected and the workpiece 28 is positioned in a predetermined position. Since the lower die 18 on which the workpiece 28 is placed is angularly movable in the circumferential direction, the workpiece 28 is easily positioned when the engaging fingers 52 simply enter into the valleys 56.

Then, as shown in FIG. 4, upon further downward movement of the punch 38, the workpiece positioning and holding die 40, and the outer deburring die 42 in unison, the engaging fingers 52 of the workpiece positioning and holding die 40 abut against the wall surfaces of the valleys 56 of the workpiece 28, and the hook-shaped pressing holder 58 abuts against the upper surface of the workpiece 28 and lowers the workpiece 28 against the lower die 18. Thus, the workpiece 28 is held while it is being positioned.

When the punch 38, the workpiece positioning and holding die 40, and the outer deburring die 42 are further lowered in unison, the lower die 18 with the workpiece 28 positioned and held thereon is slightly displaced downwardly in opposition to the spring forces of the first helical spring 20. At this time, the annular surface 36 formed on the inner wall of the annular flange 34 of the lower die 18 performs a stop function by abutting against the upper surface 37 of the annular boss 32 of the back plate 16, thereby limiting downward displacement of the lower die 18. As a result, the workpiece positioning and holding die 40, which presses the workpiece 28 against the lower die 18, is prevented from being lowered, and the workpiece 28 is held as it is positioned in the predetermined position.

Then, the punch 38 and the outer deburring die 42, except for the workpiece positioning and holding die 40, are further lowered in unison with each other, in opposition to the spring forces of the second helical spring 44. As shown in FIG. 5, the inner burr 22 at the center of the workpiece 28 is removed by the punch 38, while thin outer burrs 60 that extend along the outer circumference of the workpiece 28 between the teeth thereof are cut off by the cutting edges 62 of the outer deburring die 42.

Stated otherwise, while the workpiece 28 is held, while being positioned in the predetermined position between the lower die 18 and the workpiece positioning and holding die 40 under spring forces (pushing forces) of the second helical spring 44, only the punch 38 and the outer deburring die 42 are lowered in unison with each other, thereby simultaneously removing both the inner burr 22 and the outer burrs 60 from the workpiece 28.

As a result, the bevel gear 12 shown in FIG. 1D is manufactured.

According to the present embodiment, while the workpiece 28 is positioned and held against positional displacement by the workpiece positioning and holding die 40 disposed radially between the punch 38 and the outer deburring die 42, the inner burr 22 and the outer burrs 60 are both simultaneously removed by the punch 38 and the outer deburring die 42, respectively. Therefore, the process for manufacturing the bevel gear 12 is simplified, resulting in increased production efficiency and reduced production costs.

A forming apparatus 100 according to another embodiment of the present invention is shown in FIGS. 7 through 10. Parts of the forming apparatus 100 that are identical to those of the forming apparatus 10 shown in FIG. 2 are denoted using identical reference characters, and shall not be described in detail below.

The forming apparatus 100 according to the other embodiment has a piercing punch 38 mounted on the ram of a press, not shown, and vertically movable for piercing a central portion of a workpiece 28, a workpiece pressing die 140 fitted over the punch 38 and vertically displaceable along the punch 38, and a positioning and deburring die 142 fitted over the workpiece pressing die 140. The punch 38 and the positioning and deburring die 142 are integrally formed with each other and are fixed to the ram of the non-illustrated press for displacement in unison with each other.

The positioning and deburring die 142 houses within a hollow space thereof a second helical spring 44 having stronger spring forces than a first helical spring 20 that acts on a lower die 18, and which has a coil diameter greater than that of the first helical spring 20. The workpiece pressing die 140 is pressed vertically downward by the second helical spring 44.

The workpiece pressing die 140 is prevented from being removed out of the positioning and deburring die 142 by a larger-diameter portion 46 on the outer circumferential surface of the workpiece pressing die 140, when it is engaged by a tapered surface 48 that extends radially inwardly from an inner wall surface of the positioning and deburring die 142.

The workpiece pressing die 140 is displaceable independently of the punch 38 and the positioning and deburring die 142. The workpiece pressing die 140 is lifted when it overcomes the spring forces of the second helical spring 44.

The workpiece pressing die 140 has a smaller-diameter portion 50 formed on the inner wall surface thereof, providing a clearance between the workpiece pressing die 140 and the outer circumferential surface of the punch 38 that extends centrally through the workpiece pressing die 140.

The workpiece pressing die 140 has a pressing holder 158 on a lower end thereof, which abuts against the upper surface of the workpiece 28. The pressing holder 158 comprises a flat surface. When the pressing holder 158 presses the workpiece 28 against the lower die 18, the workpiece 28 is held while it is positioned in place in a predetermined position.

The positioning and deburring die 142 has a plurality of engaging protrusions 152 formed on the lower end thereof, which project vertically downward a predetermined distance from the lower end face (the pressing holder 158) of the workpiece pressing die 140. As shown in FIG. 11, each of the engaging protrusions 152 is of a substantially triangular cross-sectional shape having slanted surfaces 154. The number of engaging protrusions 152 corresponds to the number of valleys 56 that are formed between the teeth of the workpiece 28. When the engaging protrusions 152 enter along the valleys 56 located between the teeth of the workpiece 28, and the slanted surfaces 154 of the engaging protrusions 152 come into contact with the valleys 56, circumferential positional errors of the workpiece 28 are corrected, and the workpiece 28 is positioned in a predetermined position.

The positioning and deburring die 142 includes, on a portion thereof near to the engaging protrusions 152, a plurality of cutting edges 162 for cutting off outer burrs 60 that are produced between the teeth of the workpiece 28, wherein the cutting edges 162 have substantially the same inside diameter as the outside diameter A (see FIG. 11) of the workpiece 28 at a position between the teeth.

The forming apparatus 100 according to the other embodiment of the present invention is basically constructed as described above. Operations and advantages of the forming apparatus 100 shall be described below. It shall be assumed that in an initial position, as shown in FIG. 7, the punch 38, the workpiece pressing die 140, and the positioning and deburring die 142 are suspended in an upper position, which is spaced a predetermined distance from the lower die 18.

First, the intermediate form 72, which makes up the workpiece 28, is placed on the mount surface 30 of the lower die 18 (see FIG. 7). At this time, the bottom surface of the workpiece 28, which is free of any teeth, may simply be placed on the mount surface 30 of the lower die 18, which is shaped complementarily to the shape of the bottom surface of the workpiece 28. The workpiece 28 does not need to be positioned exactly.

Then, the ram of the non-illustrated press is actuated in order to lower the punch 38. The workpiece pressing die 140, and the positioning and deburring die 142 are lowered in unison from the initial position until the engaging protrusions 152 of the positioning and deburring die 142, which project vertically downward by predetermined distances from the punch 38 and the workpiece pressing die 140 and are disposed in an outermost circumferential position, are positioned within the respective valleys 56 located between the teeth, as shown in FIG. 8.

The workpiece 28 is simply placed on the mount surface 30 of the lower die 18, and the lower die 18 is floatingly supported on the back plate 16 under spring forces of the first helical spring 20. Therefore, the lower die 18 is angularly movable in the circumferential direction thereof.

Consequently, when the engaging protrusions 152 of the positioning and deburring die 142 enter into the valleys 56 located between the teeth of the workpiece 28 and engage with the wall surfaces of the valleys 56, any circumferential positional errors of the workpiece 28 are corrected and the workpiece 28 is positioned in a predetermined position. Since the lower die 18 on which the workpiece 28 is placed is angularly movable in the circumferential direction, the workpiece 28 is easily positioned when the engaging protrusions 152 simply enter into the valleys 56.

Then, as shown in FIG. 9, upon further downward movement of the punch 38, the workpiece pressing die 140, and the positioning and deburring die 142 in unison, the pressing holder 158 of the workpiece pressing die 140 abuts against the upper surface of the workpiece 28 and presses the workpiece 28 against the lower die 18, thereby holding the workpiece 28 while it is being positioned.

When the punch 38, the workpiece pressing die 140, and the positioning and deburring die 142 are further lowered in unison, the lower die 18 with the workpiece 28 positioned and held thereon is slightly displaced downwardly in opposition to the spring forces of the first helical spring 20. At this time, the annular surface 36 formed on the inner wall of the annular flange 34 of the lower die 18 performs a stop function by abutting against the upper surface 37 of the annular boss 32 of the back plate 16, thereby limiting downward displacement of the lower die 18. As a result, the workpiece pressing die 140, which presses the workpiece 28 against the lower die 18, is prevented from being lowered, and the workpiece 28 is held as it is positioned in the predetermined position.

Then, the punch 38 and the positioning and deburring die 142, except for the workpiece pressing die 140, are further lowered in unison with each other, in opposition to the spring forces of the second helical spring 44. As shown in FIG. 10, the inner burr 22 at the center of the workpiece 28 is removed by the punch 38, while the thin outer burrs 60 that extend along the outer circumference of the workpiece 28 between the teeth thereof are cut off by the cutting edges 162 of the positioning and deburring die 142.

Stated otherwise, while the workpiece 28 is held and positioned in the predetermined position between the lower die 18 and the workpiece pressing die 140, under spring forces (pushing forces) produced by the second helical spring 44, only the punch 38 and the positioning and deburring die 142 are lowered in unison with each other, for thereby simultaneously removing the inner burr 22 and the outer burrs 60 from the workpiece 28.

According to the other embodiment, after circumferential positional errors of the workpiece 28 have been corrected and the workpiece 28 is positioned in a predetermined position, and further while the workpiece 28 is positioned and held against positional displacement by the workpiece pressing die 140 that is disposed radially between the punch 38 and the positioning and deburring die 142, the inner burr 22 and the outer burrs 60 are simultaneously removed by the punch 38 and the positioning and deburring die 142, respectively. Therefore, the process of manufacturing the bevel gear 12 is simplified for enabling increased production efficiency, while also reducing production costs.

According to the other embodiment, furthermore, as a result of using the positioning and deburring die 142, wherein slanted surfaces 154 of the engaging protrusions 152, which act to correct circumferential positional errors of the workpiece 28, and cutting edges 162 for cutting off the outer burrs 60 between the teeth are disposed contiguously, the workpiece 28 is accurately positioned while the outer burrs 60 are cut off from the workpiece continuously and smoothly.

Claims

1. An apparatus for forging a bevel gear, comprising: a lower die having a mount surface for mounting a workpiece thereon, said lower die being mounted on a base for rotation in a circumferential direction;a punch mounted for vertical movement with respect to said lower die, for piercing a central portion of said workpiece in order to remove an inner burr thereof;a workpiece positioning and holding die fitted over said punch for displacement in unison with the punch, for pressing the workpiece that is mounted on said mount surface of said lower die against said lower die, for thereby positioning and holding the workpiece; andan outer deburring die fitted over said workpiece positioning and holding die and displaceable in unison with said punch, for removing outer burrs produced between teeth of said workpiece along an outer circumference of said workpiece,wherein while said workpiece is positioned in a predetermined position and held in said position by said workpiece positioning and holding die, the inner burr and the outer burrs of said workpiece are simultaneously removed by movement of said punch and said outer deburring die in unison with each other.

2. The apparatus according to claim 1, further comprising a spring member by which said lower die is floatingly supported on said base.

3. The apparatus according to claim 1, wherein said workpiece positioning and holding die comprises engaging fingers for positioning said workpiece in circumferential directions thereof, by entering along and engaging within valleys located between the teeth of said workpiece, and a pressing holder that abuts against an upper surface of said workpiece and presses said workpiece against the lower die to thereby hold said workpiece.

4. The apparatus according to claim 1, wherein said lower die includes an annular flange having an end face that is engaged by an end of said spring member, and which is slidably displaceable vertically along an annular boss of said base.

5. An apparatus for forging a bevel gear, comprising: a lower die having a mount surface for mounting a workpiece thereon, said lower die being mounted on a base for rotation in a circumferential direction;a punch mounted for vertical movement with respect to said lower die, for piercing a central portion of said workpiece in order to remove an inner burr thereof;a workpiece pressing die fitted over said punch for displacement in unison with said punch, for pressing the workpiece that is mounted on said mount surface of said lower die against said lower die, for thereby holding the workpiece; anda positioning and deburring die fitted over said workpiece pressing die and displaceable in unison with said punch, for correcting circumferential positional errors of said workpiece and positioning said workpiece, and for removing outer burrs produced between teeth of said workpiece along an outer circumference of said workpiece,wherein while said workpiece positioned in a predetermined position is held in said position by said workpiece pressing die, the inner burr and the outer burrs of said workpiece are simultaneously removed by movement of said punch and said positioning and deburring die in unison with each other.

6. The apparatus according to claim 5, further comprising a spring member by which said lower die is floatingly supported on said base.

7. The apparatus according to claim 5, wherein said positioning and deburring die comprises engaging protrusions for positioning said workpiece in circumferential directions thereof by entering along and engaging within valleys located between the teeth of said workpiece, and cutting edges for removing the outer burrs produced between the teeth of said workpiece along the outer circumference of said workpiece.

8. The apparatus according to claim 7, wherein said engaging protrusions project vertically downward a predetermined distance from a lower end face of said workpiece pressing die.

9. A method of forging a bevel gear, comprising the steps of: forging a forging stock in a single forging cycle or in a plurality of forging cycles, to thereby produce an intermediate form having teeth;placing said intermediate form on a mount surface of a lower die, and positioning and holding said intermediate form in a predetermining position with a positioning and holding die, which is fitted over a punch, for displacement in unison with said punch; andwhile said intermediate form is positioned and held by said positioning and holding die, simultaneously piercing said intermediate form in order to remove an inner burr thereof with said punch, and removing outer burrs of said intermediate form with an outer deburring die, which is fitted over said positioning and holding die, for displacement in unison with said punch.

10. The method according to claim 9, wherein said intermediate form is positioned when engaging fingers disposed on an end of said positioning and holding die engage within valleys located between the teeth of said intermediate form.

11. A method of forging a bevel gear, comprising the steps of: forging a forging stock in a single forging cycle or in a plurality of forging cycles, to thereby produce an intermediate form having teeth;placing said intermediate form on a mount surface of a lower die, correcting circumferential positional errors of said intermediate form, and positioning said intermediate form with a positioning and deburring die, which is fitted over a punch, for displacement in unison with the punch, and thereafter, positioning and holding said intermediate form in a predetermined position with a workpiece pressing die that is fitted in said positioning and deburring die; andwhile said intermediate form is positioned and held by said workpiece pressing die, simultaneously piercing said intermediate form in order to remove an inner burr thereof with said punch, and removing outer burrs of said intermediate form with said positioning and deburring die, which is displaced in unison with the punch.

12. The method according to claim 11, wherein said intermediate form is positioned when engaging protrusions disposed on said positioning and deburring die engage within valleys located between the teeth of said intermediate form.