Apparatus for forming spline and method for forming spline

Abstract

To form a spline on a workpiece made of a material having high hardness without causing problems such as cracking.SOLUTION: An apparatus for forming a spline comprises a die, a punch accommodated in a hole of the die, a shaping space between an inner peripheral surface of the hole of the die and an outer peripheral surface of the punch, and a drive mechanism that presses a tubular workpiece into the shaping space. A plurality of rows of first engraving parts extending in an axial direction and arranged adjacent to each other in a circumferential direction are provided on the inner peripheral surface of the hole of the die and / or on the outer peripheral surface of the punch. In the apparatus, a plurality of rows of second engraving parts that extend in the axial direction and have top surfaces lower than the top surfaces of the first engraving parts are provided between the adjacent first engraving parts such that the range of the top surfaces of the second engraving parts in the axial direction at least partially overlaps with the range of the top surfaces of the first engraving parts. Preferably, the apparatus is configured such that, when the workpiece is pressed, the top surfaces of the second engraving parts and the top surfaces of the first engraving parts contact the workpiece simultaneously, or the top surfaces of the second engraving parts contact the workpiece earlier than the top surfaces of the first engraving parts.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a spline forming device and a spline forming method. [Background technology]

[0002] In the technical field, it is known to extrude splines (engagement projections and recesses) into the inner circumferential surface of a hole of a rotating body and / or the outer circumferential surface of a shaft, for example, for the purpose of fitting the rotating body and a shaft. The extrusion process involves pressing teeth and lands provided on a processing member (e.g., a punch, mandrel, or die) against the surface of a workpiece (workpiece) while the two are moved relative to one another. The engraving process causes plastic flow of the material constituting the workpiece, forming recesses in the surface of the workpiece. For example, a spline can be engraved into the inner circumferential surface of a hole of a rotating body by inserting a punch or mandrel provided with multiple teeth and lands on its outer circumferential surface into the hole of the rotating body. Alternatively, a spline can be engraved into the outer circumferential surface of a shaft by inserting the shaft into a hole in a die provided with multiple teeth and lands on its inner circumferential surface.

[0003] As a specific example of such technology, for example, Japanese Patent No. 3150045 (Patent Document 1) discloses a method for simultaneously forming (shaping) splines on the inner and outer peripheral surfaces of a ring-shaped workpiece. In this method, multiple teeth and lands are provided on both the inner peripheral surface of a hole formed in a die 5 and the outer peripheral surface of a mandrel 11. Furthermore, the outer peripheral surface of the die 5 is restrained by a die holder 2, which prevents deformation of the die 5 (expansion outward in the radial direction) due to reaction forces during processing.

[0004] As another specific example, Japanese Patent Laid-Open Publication No. 11-254083 (Patent Document 2) discloses a method for forming a helical gear using a die 13 having a plurality of teeth and lands obliquely provided on the inner peripheral surface of a hole. In this method, the outer peripheral surface of the die 13 is constrained by a wedge-shaped clamp 12 press-fitted into the center of a die holder 11, thereby preventing deformation of the die 13 (expansion outward in the radial direction) due to reaction forces during processing.

[0005] While the above-mentioned conventional spline forming (engraving) methods are effective for engraving splines into workpieces made of ordinary materials (i.e., materials with relatively low hardness), they pose problems when engraving splines into workpieces made of materials with high hardness (i.e., materials that are hard, brittle, and have low deformability). Specifically, when the workpiece slides against the general surface, which is the bottom surface of the valleys (grooves) between adjacent teeth and lands on the surface of the workpiece, frictional forces resulting from contact and friction between the two act on the surface of the workpiece. If this frictional force becomes excessive, defects such as cracks may occur at the tips of the spline teeth engraved into the workpiece. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3150045 [Patent Document 2] Japanese Patent Application Publication No. 11-254083 Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, there is a need in the art for a technique that can form splines without problems such as cracking, even when cutting into a workpiece made of a material having high hardness. [Means for solving the problem]

[0008] In view of the above problems, the inventor conducted extensive research and discovered that the above problems can be solved by providing second engraved portions lower than the first engraved portions between the first engraved portions on the inner surface of the die hole and / or the outer surface of the punch, on which multiple first engraved portions for forming splines in the workpiece are provided.

[0009] Specifically, the spline forming device of the present invention (hereinafter sometimes referred to as the "device of the present invention") comprises a die in which a hole is formed, a punch housed in the hole of the die, a shaping space which is a cylindrical space between the inner surface of the hole of the die and the outer surface of the punch, and a drive mechanism which is a mechanism configured to be able to push a cylindrical workpiece into the shaping space from one side in the axial direction, that is, the upstream side.

[0010] The shaping surface, which is either or both of the inner peripheral surface of the die hole and the outer peripheral surface of the punch, is provided with a first notched portion, which is a plurality of convex portions extending over a predetermined range in the axial direction, protruding toward the shaping space, and adjacent to each other in the circumferential direction.

[0011] The first notched portion includes a first land portion, a first tooth portion, and a first relief portion. The first land portion is a portion that extends over a predetermined range in the axial direction and has a first top surface that is a top surface parallel to the axial direction. The first tooth portion is a portion that is adjacent to the upstream side of the first land portion and includes a first introduction surface that is a surface that continuously connects the first top surface and the shaping surface. The first relief portion is a portion that is adjacent to the downstream side, that is the side opposite the upstream side of the first land portion, and includes a first relief surface that is a surface that continuously connects the first top surface and the shaping surface.

[0012] In the device of the present invention, second notched portions are further provided between adjacent first notched portions, which extend over a predetermined range in the axial direction, protrude toward the shaping space, and are multiple convex portions adjacent in the circumferential direction. Therefore, on the shaping surface of the device of the present invention, the first notched portions and the second notched portions are provided alternately in the circumferential direction.

[0013] The second notched portion includes a second land portion, a second tooth portion, and a second relief portion. The second land portion is a portion that extends over a predetermined range in the axial direction and has a second top surface that is lower than the first top surface parallel to the axial direction. The second tooth portion is a portion that is adjacent to the upstream side of the second land portion and includes a second introduction surface that is a surface that continuously connects the second top surface and the shaping surface. The second relief portion is a portion that is adjacent to the downstream side of the second land portion and includes a second relief surface that is a surface that continuously connects the second top surface and the shaping surface.

[0014] Furthermore, the range in which the first top surface extends and the range in which the second top surface extends at least partially overlap in the axial direction. Preferably, the second tip, which is the upstream end of the second top surface, is located at the same position as the first tip, which is the upstream end of the first top surface, or is located upstream of the first tip, in the axial direction.

[0015] As mentioned at the beginning of this specification, the present invention relates not only to a device for forming splines, but also to a method for forming splines.

[0016] The spline forming method according to the present invention (hereinafter sometimes referred to as the "method of the present invention") is a method for forming splines on the inner and / or outer peripheral surfaces of a cylindrical workpiece using the spline forming device according to the present invention (device of the present invention) described above. The method of the present invention includes a first step of setting the workpiece in the drive mechanism, and a second step of pushing the workpiece into the shaping space from the upstream side using the drive mechanism while the shaping space and the workpiece are coaxial. In the method of the present invention, the position and shape of the spline tooth bottom are determined by the first apex surface, and the position and shape of the spline tooth tip are determined by the second apex surface. [Effects of the Invention]

[0017] During the process of forming splines on the surface of a workpiece by forcing the workpiece into the forming space, which is the cylindrical space between the inner circumferential surface of the die hole and the outer circumferential surface of the punch, the material constituting the portion of the workpiece where the first engraved portions sink plastically flows into the valley-shaped portions between the first engraved portions. In spline forming methods using a conventional spline forming device that does not include a second engraved portion, as described above, the material that plastically flows into the valley-shaped portions between the first engraved portions contacts the general surface, which is the bottom surface of the valley-shaped portions, and becomes the tips of the splines formed on the surface of the workpiece. Therefore, during subsequent forcing of the workpiece, the tips of the splines formed on the surface of the workpiece and the general surface constantly slide against each other, and the frictional force acting between them can lead to defects such as cracks at the tips of the splines. This problem is particularly pronounced when forming splines on a workpiece made of a highly hard material.

[0018] On the other hand, in the device of the present invention, a plurality of second cut portions extending in the axial direction and having second top surfaces lower than the first top surfaces of the first cut portions are provided between adjacent first cut portions. Furthermore, the range of the first top surfaces of the first cut portions and the range of the second top surfaces of the second cut portions at least partially overlap in the axial direction. Therefore, in a spline forming method using the device of the present invention (the method of the present invention), when the workpiece is pressed into the shaping space, the second top surfaces of the second cut portions and the first top surfaces of the first cut portions contact the workpiece simultaneously, or the second top surfaces of the second cut portions contact the workpiece earlier than the first top surfaces of the first cut portions. As a result, the material that plastically flows into the valley-shaped portions between the first cut portions contacts the second top surfaces of the second cut portions provided between the first cut portions, rather than the shaping surface corresponding to the general surface, and becomes the tip of the spline formed on the surface of the workpiece.

[0019] As described above, the second top surface is the top surface of the second engraved portion, which is a convex portion that protrudes from the shaping surface toward the shaping space. Therefore, as the workpiece is pushed into the shaping space, after the spline tips formed on the surface of the workpiece pass the second top surface, the spline tips face the shaping surface with a gap between them, ensuring a clearance between them. As a result, excessive friction between the spline tips and the shaping surface is avoided, reducing the occurrence of defects such as cracks at the spline tips. In other words, according to the present invention, splines can be formed without problems such as cracks, even when shaping a workpiece made of a highly hard material.

[0020] Other objects, other features and attendant advantages of the present invention will be readily apparent from the following description of the embodiments of the present invention which will be given with reference to the drawings. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic side view showing an example of the configuration of a punch provided in a spline forming device (first device) according to a first embodiment of the present invention. FIG. [Figure 2] FIG. 2 is a schematic enlarged view of the portion surrounded by the thick dashed line in FIG. [Figure 3] 1. FIG. 4 is a schematic enlarged view of the portion surrounded by the thick dashed line in FIG. 1, in which the second engraved portion, which is omitted in FIG. 2, is not omitted. [Figure 4] 3. FIG. 4 is a schematic diagram in which the shape of the bottom of the valley-like portion between the first notched portions illustrated in FIG. 2 is added by a dashed line to FIG. [Figure 5] This is a schematic diagram showing the difference between the two by superimposing the cross-sectional shape of the first engraved portion taken along a plane that includes the axis AX and passes through the center of the first top surface, which is the top surface of the first engraved portion, on the cross-sectional shape of the second engraved portion taken along a plane that includes the axis AX and passes through the center of the second top surface, which is the top surface of the second engraved portion. [Figure 6] 10A to 10C are schematic cross-sectional views illustrating a process in which splines are formed on the inner peripheral surface of a cylindrical workpiece by pushing the workpiece into a shaping space using a first device. [Figure 7] This is a schematic cross-sectional view of a punch and a workpiece taken along a plane perpendicular to the axis and passing through the first and second top surfaces when splines are formed on the inner surface of the workpiece by the first and second notches provided on the outer surface (shaping surface) of the punch. [Figure 8] This is a schematic cross-sectional view of the die and workpiece taken along a plane perpendicular to the axis and passing through the first and second top surfaces when splines are formed on the outer surface of a cylindrical workpiece by first and second notches provided on the inner surface (shaping surface) of a hole formed in the die. [Figure 9] This is a schematic cross-sectional view of the die and workpiece taken along a plane perpendicular to the axis and passing through the first and second top surfaces when splines are formed on the outer surface of a cylindrical workpiece by first and second notches provided on the inner surface (shaping surface) of a hole formed in the die.

[0022] [Figure 10] 10A to 10C are schematic cross-sectional views illustrating the process of forming splines on the inner surface of a cylindrical workpiece by pushing the workpiece into a shaping space using a spline forming device (second device) according to a second embodiment of the present invention. [Figure 11] 10 is a schematic cross-sectional view showing an example of a change in pressing force acting on a workpiece by a first notched portion as the spline forming process in the second device progresses. FIG. [Figure 12] FIG. 10 is a schematic cross-sectional view showing an example of a first region in which an annular bulge is provided in a second device according to a more preferred embodiment. [Figure 13] 10 is a flowchart showing an example of the flow of each step included in a spline forming method (third method) according to a third embodiment of the present invention. [Figure 14] 1 is a photograph substituted for a drawing showing the appearance of a punch as a processing member provided in the conventional device and the device of the embodiment used in Example 1. [Figure 15] 10 is a photograph in place of a drawing for comparing the properties of splines formed on the surface of a workpiece using a conventional device and an example device in Example 1. [Figure 16] 10 is a photograph, substituted for a drawing, showing the appearance of splines formed as a result of tests 1 to 4 performed in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0023] First Embodiment A spline forming device according to a first embodiment of the present invention (hereinafter, may be referred to as a "first device") will be described below with reference to the drawings.

[0024] The first device includes a die having a hole formed therein, a punch housed in the hole of the die, a shaping space which is a cylindrical space between the inner surface of the hole of the die and the outer surface of the punch, and a drive mechanism which is a mechanism configured to be able to push a cylindrical workpiece into the shaping space from one side in the axial direction, that is, the upstream side.

[0025] The components of the apparatus of the present invention, including the die, punch, and drive mechanism, are made of materials with properties (e.g., mechanical strength and durability) that can withstand processing conditions such as the load acting on the components during the spline formation process. The drive mechanism can be appropriately selected from various drive mechanisms known in the art depending on the properties (e.g., mechanical strength and hardness) of the material that constitutes the workpiece. Typically, a press, such as a hydraulic press, is used as the drive mechanism.

[0026] In this specification, "pushing the workpiece into the shaping space from the upstream side" does not necessarily refer only to literally pushing the workpiece from the upstream side into the shaping space defined by the fixed die and punch by the drive mechanism, but is not particularly limited as long as the processed portion of the workpiece can reach the inside of the shaping space through the upstream opening of the shaping space. For example, the workpiece may be fixed, and the upstream openings of the die and punch that define the shaping space may be moved toward the fixed workpiece by the drive mechanism to allow the processed portion of the workpiece to reach the inside of the shaping space.

[0027] The shaping surface, which is either or both of the inner peripheral surface of the die hole and the outer peripheral surface of the punch, is provided with a first notched portion, which is a plurality of convex portions extending over a predetermined range in the axial direction, protruding toward the shaping space, and adjacent to each other in the circumferential direction.

[0028] That is, the shaping surface, which is the surface on which the first engraved portion for forming the spline in the workpiece is provided, may be either the inner peripheral surface of the die hole or the outer peripheral surface of the punch, or both. In other words, either the die or the punch, or both, can be used as the processing member for forming the spline in the workpiece. When only the inner peripheral surface of the die hole is the shaping surface, the spline is formed on the outer peripheral surface of the cylindrical workpiece. When only the outer peripheral surface of the punch is the shaping surface, the spline is formed on the inner peripheral surface of the cylindrical workpiece. When both the inner peripheral surface of the die hole and the outer peripheral surface of the punch are shaping surfaces, the spline is formed on both the outer peripheral surface and the inner peripheral surface of the cylindrical workpiece.

[0029] The first notched portion includes a first land portion, a first tooth portion, and a first relief portion. The first land portion is a portion that extends over a predetermined range in the axial direction and has a first top surface that is a top surface parallel to the axial direction. The first tooth portion is a portion that is adjacent to the upstream side of the first land portion and includes a first introduction surface that is a surface that continuously connects the first top surface and the shaping surface. The first relief portion is a portion that is adjacent to the downstream side, that is the side opposite the upstream side of the first land portion, and includes a first relief surface that is a surface that continuously connects the first top surface and the shaping surface.

[0030] The position (e.g., depth, etc.) and shape (e.g., width, etc.) of the tooth bottom of the spline formed in the workpiece are determined by the position (e.g., height, etc.) and shape (e.g., width, etc.) of the first top face. Therefore, the position and shape of the first top face are set according to the position and shape of the tooth bottom of the spline to be formed in the workpiece. Furthermore, the shape (e.g., inclination, roundness, etc.) of the side face connecting the tooth bottom to the tooth tip of the spline formed in the workpiece is determined by the shapes (e.g., inclination, roundness, etc.) of the faces adjacent to both sides of the first top face in the circumferential direction.

[0031] The first tooth portion is the portion that first comes into contact with the workpiece when the first engraved portion sinks into the processed portion of the workpiece by pushing the workpiece into the shaping space with the drive mechanism, and a spline begins to be formed on the surface of the workpiece. As described above, the first tooth portion is provided with a first introduction surface that continuously connects the first top surface and the shaping surface, so that a spline having a tooth bottom corresponding to the first top surface can be smoothly engraved. The configuration of the first tooth portion including the first introduction surface (e.g., the shape of the first tooth portion including the first introduction surface) can be appropriately designed depending on, for example, the properties (e.g., mechanical strength, hardness, etc.) of the material that constitutes the workpiece and the shape of the spline to be formed on the workpiece.

[0032] The first relief portion is a portion that faces the spline tooth bottom formed on the surface of the workpiece as described above when the spline tooth bottom moves downstream from the first crest surface as the workpiece is pushed further downstream. As described above, the first relief surface of the first relief portion is a surface that continuously connects the first crest surface and the shaping surface, and downstream of the first crest surface, the spline tooth bottom is not in contact with either the first notched portion or the shaping surface. This reduces the processing load associated with forming the spline.

[0033] Furthermore, by providing the first tooth portion and the first relief portion on the upstream and downstream sides of the first land portion, respectively, the area of ​​the bottom surface of the first notched portion (the surface connecting with the shaping surface) is increased, thereby reducing problems such as damage to the first notched portion due to the processing load associated with forming the spline. The configuration of the first notched portion including the first relief surface (e.g., the shape of the first notched portion including the first relief surface) can also be appropriately designed depending on, for example, the properties (e.g., mechanical strength, hardness, etc.) of the material constituting the workpiece and the shape of the spline to be formed in the workpiece. Furthermore, the material constituting the first notched portion (and / or the die and / or punch as the processing member having the first notched portion) can also be appropriately selected depending on, for example, the properties (e.g., mechanical strength, hardness, etc.) of the material constituting the workpiece and the shape of the spline to be formed in the workpiece.

[0034] As described above, when a spline is formed on the surface of a workpiece by forcing the workpiece into the shaping space, the material constituting the portion of the workpiece where the first indentations are recessed plastically flows into the valley-shaped portions between the first indentations. In a spline forming method using a conventional spline forming device equipped only with the first indentations, the material plastically flowing into the valley-shaped portions between the first indentations contacts the general surface (the portion of the shaping surface where the first indentations are not provided), which is the bottom of the valley-shaped portion, and becomes the tip of the spline formed on the surface of the workpiece. Therefore, when the workpiece is subsequently pushed into the workpiece, the tip of the spline formed on the surface of the workpiece and the general surface slide against each other. The frictional force acting between the two can lead to defects such as cracks at the tip of the spline. This problem is particularly pronounced when cutting splines into a workpiece made of a highly hard material.

[0035] Therefore, in the first device, second notched portions are further provided between adjacent first notched portions, which extend over a predetermined range in the axial direction, protrude toward the shaping space, and are multiple convex portions adjacent in the circumferential direction. Therefore, on the shaping surface of the first device, the first notched portions and the second notched portions are provided alternately in the circumferential direction.

[0036] As mentioned above, the shaping surface on which the first engraved portions are provided may be either the inner peripheral surface of the die hole or the outer peripheral surface of the punch, or both. When only the inner peripheral surface of the die hole is the shaping surface, the second engraved portions are provided between the first engraved portions provided on the inner peripheral surface of the die hole as the shaping surface. When only the outer peripheral surface of the punch is the shaping surface, the second engraved portions are provided between the first engraved portions provided on the outer peripheral surface of the punch as the shaping surface. When both the inner peripheral surface of the die hole and the outer peripheral surface of the punch are shaping surfaces, the second engraved portions are provided between the first engraved portions provided on both the inner peripheral surface of the die hole as the shaping surface and the outer peripheral surface of the punch. However, when both the inner peripheral surface of the die hole and the outer peripheral surface of the punch are shaping surfaces, the second engraved portions may be provided only between the first engraved portions provided on either the inner peripheral surface of the die hole as the shaping surface or the outer peripheral surface of the punch as the shaping surface.

[0037] The second notched portion includes a second land portion, a second tooth portion, and a second relief portion. The second land portion is a portion that extends over a predetermined range in the axial direction and has a second top surface that is lower than the first top surface parallel to the axial direction. The second tooth portion is a portion that is adjacent to the upstream side of the second land portion and includes a second introduction surface that is a surface that continuously connects the second top surface and the shaping surface. The second relief portion is a portion that is adjacent to the downstream side of the second land portion and includes a second relief surface that is a surface that continuously connects the second top surface and the shaping surface.

[0038] The position (e.g., height, etc.) and shape (e.g., width, etc.) of the tip of the spline formed in the workpiece are determined by the position (e.g., height, etc.) and shape (e.g., width, etc.) of the second top surface. Therefore, the position and shape of the second top surface are set according to the position and shape of the tip of the spline to be formed in the workpiece. Furthermore, the shape (e.g., inclination, roundness, etc.) of the side surface connecting the tip to the root of the spline formed in the workpiece is determined by the shape (e.g., inclination, roundness, etc.) of the surfaces adjacent to both sides of the second top surface in the circumferential direction. Note that this "surface adjacent to both sides of the second top surface in the circumferential direction" is a surface interposed between the first top surface included in the first notched portion and the second top surface included in the second notched portion in the circumferential direction, and is the same surface as the "surface adjacent to both sides of the first top surface in the circumferential direction" described above.

[0039] The second tooth portion is the first part that comes into contact with the workpiece when the first notched portion sinks into the workpiece surface by the drive mechanism, and a spline begins to form on the workpiece surface. The second tooth portion is provided with a second introduction surface that continuously connects the second top surface and the shaping surface, allowing the material to be smoothly introduced to the second top surface and form the tip of the spline. The configuration of the second tooth portion, including the second introduction surface (e.g., the shape of the second tooth portion, including the second introduction surface) can also be appropriately designed depending on, for example, the properties (e.g., mechanical strength, hardness, etc.) of the material that constitutes the workpiece and the shape of the spline to be formed on the workpiece.

[0040] The second relief portion is a portion that faces the tip of the spline tooth formed on the surface of the workpiece as described above when the tip of the spline tooth moves downstream from the second crest surface as the workpiece is pushed further downstream. As described above, the second relief surface of the second relief portion is a surface that continuously connects the second crest surface and the shaping surface, and downstream of the second crest surface, the tip of the spline tooth is not in contact with either the second notched portion or the shaping surface. This reduces the processing load associated with forming the spline.

[0041] Furthermore, similar to the first notched portion, by providing the second tooth portion and the second relief portion on the upstream and downstream sides of the second land portion, respectively, the area of ​​the bottom surface (the surface connecting with the shaping surface) of the second notched portion is increased, thereby reducing problems such as damage to the second notched portion due to the processing load associated with forming the spline. The configuration of the second relief portion including the second relief surface (e.g., the shape of the second relief portion including the second relief surface) can also be appropriately designed depending on, for example, the properties (e.g., mechanical strength, hardness, etc.) of the material constituting the workpiece and the shape of the spline to be formed in the workpiece. Furthermore, the material constituting the second notched portion (and / or the die and / or punch as the processing member having the second notched portion) can also be appropriately selected depending on, for example, the properties (e.g., mechanical strength, hardness, etc.) of the material constituting the workpiece and the shape of the spline to be formed in the workpiece.

[0042] As described above, the position and shape of the tooth bottom of the spline formed in the workpiece are determined by the position and shape of the first top surface, which is the top surface of the first notched portion, and the position and shape of the tooth tip of the spline formed in the workpiece are determined by the position and shape of the second top surface, which is the top surface of the second notched portion. For this to happen, the material that makes up the part of the workpiece where the first notched portion sinks must plastically flow into the valley-shaped part between the first notched portions and come into contact with the second top surface to form the tooth tip of the spline.

[0043] Therefore, in the first device, the range over which the first top surface, which is the top surface of the first notched portion, extends at least partially overlaps in the axial direction with the range over which the second top surface, which is the top surface of the second notched portion, extends. In this axial portion where the range over which the first top surface extends overlaps with the range over which the second top surface extends, material constituting the portion of the workpiece that plastically flows into the valley-like portion between the first notched portions as a result of the first notched portions sinking in can come into contact with the second top surface. Therefore, in splines formed on the inner and / or outer peripheral surfaces of a cylindrical workpiece using the first device, the position and shape of the spline tooth bottoms are determined by the first top surfaces, and the position and shape of the spline tooth tips are determined by the second top surfaces.

[0044] To reliably achieve the above-mentioned effect, it is preferable to appropriately design the shapes of the first indented portions (e.g., the cross-sectional shape of the first indented portions and the height of the first indented portions) and the second indented portions (e.g., the height and width of the second indented portions) according to the shape of the workpiece so that the material constituting the portion of the workpiece that plastically flows into the valley-like portions between the first indented portions as a result of the sinking of the first indented portions can reliably contact the second indented portions. Such a design can be determined appropriately, for example, based on the results of preliminary experiments conducted by variously changing the relationship between the shapes of the first indented portions and the shape of the workpiece and / or simulation analysis using the finite element method. Such preliminary experiments will be described in detail later in the explanation of the examples.

[0045] As described above, the material constituting the portion of the workpiece where the first notched portions sink plastically flows toward the valley-shaped portion between the first notched portions. However, if the second crest surface, which determines the position and shape of the spline tooth tip, is located downstream in the axial direction from the first crest surface, which determines the position and shape of the spline tooth bottom, the second notched portion does not exist at the bottom of the valley-shaped portion between the first notched portions into which the material flows. Therefore, the material flows toward the shaping surface that is farther (deeper) than the second crest surface.

[0046] In the above case, when a sufficient amount of material flows in to fill the valleys between the first indentations, the spline tooth tips are formed by the shaping surfaces that form the bottom surfaces of the valleys between the first indentations. Then, as the drive mechanism further pushes the workpiece into the shaping space, the spline tooth tips pass through the second entry surfaces of the second indentations and contact the second apex surfaces, ultimately determining the position and shape of the spline tooth tips by the second apex surfaces. However, after the spline tooth tips are once formed by the shaping surfaces that form the bottom surfaces of the valleys between the first indentations, the spline tooth tips are re-machined by the second indentations, and the position and shape of the spline tooth tips are determined by the second apex surfaces. However, the processing load tends to be excessive in this process. This is especially true when significant work hardening occurs at the spline tooth tips once formed by the shaping surfaces.

[0047] On the other hand, if the amount of material flowing into the valleys between the first notched portions is insufficient to fill those portions, the material will not be able to fully reach the shaped surface that forms the bottom of the valleys between the first notched portions, which could result in defects such as cracks occurring at the tips of the spline teeth.

[0048] Therefore, in a more preferred embodiment of the first device, the second tip, which is the upstream end of the second top surface, is located at the same position as or further upstream than the first tip, which is the upstream end of the first top surface, in the axial direction. This allows the material constituting the portion of the workpiece that plastically flows into the valley-shaped portion between the first notched portions as a result of the first notched portions sinking to reliably contact the second top surface. This reduces the above-mentioned problem, which is a concern when the second top surface, which determines the position and shape of the spline tooth tip, is located axially downstream of the first top surface, which determines the position and shape of the spline tooth bottom. As a result, with the first device according to a more preferred embodiment, the positions and shapes of the spline tooth bottom and tooth tip can be reliably determined by the first top surface and the second top surface, respectively, in splines formed on the inner and / or outer peripheral surfaces of a cylindrical workpiece.

[0049] FIG. 1 is a schematic side view showing an example of the configuration of a punch provided in the first device. The punch 100 shown in FIG. 1 has a first engraved portion 10 on its outer peripheral surface 101. The first engraved portion 10 extends over a predetermined range in the direction of the axis AX and protrudes toward a cylindrical shaping space (i.e., toward the outside in the radial direction), which is a cylindrical space between the inner peripheral surface of a hole formed in a die (not shown) and the outer peripheral surface 101 of the punch 100. The first engraved portion 10 is a plurality of adjacent protrusions in the circumferential direction. Hereinafter, a punch having engraved portions for forming splines on its outer peripheral surface may be referred to as a "spline punch." That is, the outer peripheral surface 101 of the punch 100 shown in FIG. 1 is configured as a shaping surface 102 on which the first engraved portion 10 for forming splines is provided on the inner peripheral surface of a cylindrical workpiece (not shown).

[0050] Figure 2 is a schematic enlarged view of the portion surrounded by the thick dashed line in Figure 1. Note that the second engraving portion is omitted from Figures 1 and 2 in order to clearly illustrate the configuration of the first engraving portion 10. That is, although the punch 100 illustrated in Figures 1 and 2 is depicted as having the same configuration as a spline punch according to the prior art that does not have a second engraving portion, in reality, the punch 100 provided in the first device has a second engraving portion in addition to the first engraving portion 10.

[0051] As illustrated in Fig. 2, the first notched portion 10 includes a first land portion 11, a first tooth portion 12, and a first relief portion 13. The first land portion 11 extends over a predetermined range in the direction of the axis AX and has a first top surface 11a that is a top surface parallel to the direction of the axis AX. The first tooth portion 12 is adjacent to the upstream side of the first land portion 11 and includes a first introduction surface 12a that is a surface that continuously connects the first top surface 11a and the shaping surface 102. The first relief portion 13 is adjacent to the downstream side, opposite the upstream side, of the first land portion 11 and includes a first relief surface 13a that is a surface that continuously connects the first top surface 11a and the shaping surface 102.

[0052] As described above, the punch 100 provided in the first device further includes second engraved portions, which are multiple circumferentially adjacent protrusions extending over a predetermined range in the direction of the axis AX and protruding toward the shaping space. FIG. 3 is also a schematic enlarged view of the area surrounded by the thick dashed line in FIG. 1. However, FIG. 3 does not omit the second engraved portions 20, which were omitted in FIG. 2. Furthermore, FIG. 4 is a schematic view in which the shape of the bottom of the valley-like portion between the first engraved portions 10 is added to FIG. 3 with dashed lines to clearly illustrate the difference in the shape of the bottom of the valley-like portion between the first engraved portions 10 with and without the second engraved portions 20. Note that in FIGS. 3 and 4, the reference numerals that should be assigned to the first engraved portions 10 are omitted to clearly illustrate the configuration of the second engraved portions 20. However, in the following description, the reference numerals shown in Figure 1 or 2 will also be used, so please refer to these drawings as needed. The same applies to Figure 5 and subsequent figures that will be referred to later.

[0053] As illustrated in Figures 3 and 4, the second notched portion 20 includes a second land portion 21, a second tooth portion 22, and a second relief portion 23. The second land portion 21 extends over a predetermined range in the direction of the axis AX shown in Figure 1 and has a second top surface 21a that is lower than the first top surface 11a parallel to the direction of the axis AX. The second tooth portion 22 is adjacent to the upstream side of the second land portion 21 and includes a second introduction surface 22a that is a surface that continuously connects the second top surface 21a and the shaping surface 102. The second relief portion 23 is adjacent to the downstream side of the second land portion 21 and includes a second relief surface 23a that is a surface that continuously connects the second top surface 21a and the shaping surface 102.

[0054] 5 is a schematic diagram illustrating the difference between the cross-sectional shape of the first engraved portion 10 taken along a plane including the axis AX and passing through the center of the first top surface 11a, which is the top surface of the first engraved portion 10, shown in FIG. 1, and the cross-sectional shape of the second engraved portion 20 taken along a plane including the axis AX and passing through the center of the second top surface 21a, which is the top surface of the second engraved portion 20. As illustrated in FIG. 5, in the punch 100 provided in the first device, the range over which the first top surface 10a, which is the top surface of the first engraved portion 10, extends at least partially in the direction of the axis AX, and the range over which the second top surface 21a, which is the top surface of the second engraved portion 20, extends. Furthermore, in the direction of the axis AX, the second tip, which is the upstream end of the second top surface 21a, is located upstream of the first tip, which is the upstream end of the first top surface 11a. In other words, the punch 100 illustrated in Figures 1 to 5 satisfies the requirements that must be met by the first top surface, which is the top surface of the first engraved portion provided on the processing member provided in the first device in the more preferred embodiment described above, and the second top surface, which is the top surface of the second engraved portion.

[0055] As described above, the first device includes a die having a hole formed therein, a punch accommodated in the hole of the die, a shaping space that is a cylindrical space between the inner peripheral surface of the hole of the die and the outer peripheral surface of the punch, and a drive mechanism that is a mechanism configured to be able to push a cylindrical workpiece into the shaping space from one axially upstream side. By pushing the cylindrical workpiece into the shaping space using the first device having such a configuration, splines can be formed on the inner peripheral surface of the workpiece.

[0056] FIG. 6 is a schematic cross-sectional view illustrating the process of forming splines on the inner circumferential surface of a cylindrical workpiece by forcing the workpiece into a shaping space, which is a cylindrical space between the inner circumferential surface of a die hole and the outer circumferential surface of a punch, using a first device 1. The left side of the axis AX in the drawing shows a state in which a cylindrical workpiece 400 is set on a plunger 300 connected to a drive mechanism (not shown). The workpiece 400 illustrated in FIG. 6 includes, in order from the base end to the tip end (from top to bottom in the drawing), a first portion having a predetermined first outer diameter and a predetermined first inner diameter; a second portion having a second outer diameter and a first inner diameter that are smaller than the first outer diameter; and a third portion having a second inner diameter that is smaller than the second outer diameter and the first inner diameter. In other words, the workpiece 400 is a type of so-called "differential thickness pipe."

[0057] On the other hand, the view to the right of the axis AX in the drawing shows a state in which the workpiece 400 is coaxial with the shaping space, which is a cylindrical space between the inner circumferential surface of the hole of the die 200 and the outer circumferential surface of the punch 100, and the workpiece is being pushed into the shaping space from the upstream side (upper side in the drawing) by the plunger 300 (see the black arrow). Through this process, a spline is formed on the inner circumferential surface of the third portion, which is a thick-walled portion formed at the tip of the workpiece 400. In the example shown in FIG. 6, the die 200 is composed of an inner die 201 and an outer die 202. However, the die provided in the first device does not necessarily have to be composed of multiple members as described above, and may be composed of a single, integrally formed member.

[0058] During the above process, material constituting the portion of the inner circumferential surface of the workpiece 400 where the first engraved portions 10 are recessed plastically flows into the valley-shaped portions between the first engraved portions 10. In a spline forming method using a conventional spline forming device that does not include the second engraved portions 20, as described above, the material plastically flowing into the valley-shaped portions between the first engraved portions 10 contacts the general surface, which is the bottom of the valley-shaped portion, and becomes the tips of the splines formed on the surface of the workpiece 400. Therefore, when the workpiece 400 is subsequently pressed into the workpiece 400, the tips of the splines formed on the surface of the workpiece 400 and the general surface constantly slide against each other. The frictional force acting between the two can lead to defects such as cracks at the tips of the splines. This problem is particularly pronounced when cutting splines into a workpiece made of a highly hard material.

[0059] Meanwhile, in the first device, a plurality of second engraved portions 20 extending in the direction of the axis AX and having second top surfaces 21a lower than the first top surfaces 11a of the first engraved portions 10 are provided between adjacent first engraved portions 10. Furthermore, in the direction of the axis AX, the ranges of the first top surfaces 11a of the first engraved portions 10 and the second top surfaces 21a of the second engraved portions 20 at least partially overlap. Therefore, when the workpiece 400 is pressed into the shaping space, the second top surfaces 21a and the first top surface 11a come into contact with the workpiece 400 simultaneously, or the second top surface 21a comes into contact with the workpiece 400 earlier than the first top surface 11a. As a result, the material plastically flows into the valley-shaped portion between the first engraved portions 10 and comes into contact with the second top surface 21a of the second engraved portion 20 provided between the first engraved portions 10, rather than the shaping surface 102 corresponding to the general surface, and becomes the tip of the spline tooth formed on the surface of the workpiece 400.

[0060] As described above, the second top surface 21a is the top surface of the second engraved portion 20, which is a convex portion that protrudes from the shaping surface 102 toward the shaping space. Therefore, as the workpiece 400 is pressed into the shaping space, after the tips of the splines formed on the surface of the workpiece 400 pass the second top surface 21a, the tips of the splines face the shaping surface 102 with a gap between them, ensuring a clearance between them. As a result, excessive friction between the tips of the splines and the shaping surface 102 is avoided, reducing the occurrence of defects such as cracks at the tips of the splines. In other words, the first device allows splines to be formed without problems such as cracks, even when shaping a workpiece made of a highly hard material.

[0061] In the above, as illustrated in Figures 1 to 6, the first device has been described, which has a configuration in which the first engraved portion 10 and the second engraved portion 20 are provided on the outer peripheral surface 101 of the punch 100 as the shaping surface 102. That is, in the first device illustrated above, as illustrated in Figure 7, splines are formed on the inner peripheral surface of the workpiece 400 by the first engraved portion 10 and the second engraved portion 20 provided on the outer peripheral surface 101 (shaping surface 102) of the punch 100. However, as mentioned above, the shaping surface is either or both of the inner peripheral surface of the hole formed in the die and the outer peripheral surface of the punch accommodated in the hole.

[0062] Therefore, depending on the location where the spline is to be formed in the workpiece, the first engraved portion and the second engraved portion may be provided only on the inner peripheral surface of the hole formed in the die, or only on the outer peripheral surface of the punch accommodated in the hole formed in the die, or may be provided on both the inner peripheral surface of the hole formed in the die and the outer peripheral surface of the punch accommodated in the hole. For example, as illustrated in Figure 8, a spline can be formed on the outer peripheral surface of a cylindrical workpiece 400 by a first engraved portion 10 and a second engraved portion 20 provided on the inner peripheral surface (shaping surface) of a hole formed in a die 200.

[0063] 8 illustrates an example in which splines are formed on the outer peripheral surface of a cylindrical workpiece 400. However, when splines are formed only on the outer peripheral surface of the workpiece by first and second engraved portions provided on the inner peripheral surface (shaping surface) of a hole formed in a die in this way, the shape of the workpiece does not necessarily have to be limited to a hollow cylinder, and may be a solid columnar shape (e.g., a circular column) as illustrated in Fig. 9. In this case, the shaping space into which the workpiece is pressed is the hole formed in the die itself, so no punch is required.

[0064] 7 indicate the radius of the inner peripheral surface of the cylindrical workpiece 400, the radius of the tip circle defined by the first top surface 11a of the first notched portion 10, and the radius of the root circle defined by the second top surface 21a of the second notched portion 20, respectively. These will be described in detail later in the explanation of the embodiments.

[0065] Second Embodiment A spline forming device according to a second embodiment of the present invention (hereinafter, may be referred to as a "second device") will be described below with reference to the drawings.

[0066] As described in the description of the first device, the second top surface is the top surface of the second notched portion, which is a convex portion that protrudes from the shaping surface toward the shaping space. Therefore, as the workpiece is pushed into the shaping space, the spline tooth tips formed on the surface of the workpiece pass the second top surface, and then the spline tooth tips face the shaping surface with a gap between them, ensuring a clearance between them. As a result, excessive friction between the spline tooth tips and the shaping surface is avoided, reducing the occurrence of defects such as cracks at the spline tooth tips.

[0067] However, when only one of the inner peripheral surface of the die hole or the outer peripheral surface of the punch is the shaping surface (i.e., when splines are formed on only one of the outer peripheral surface or the inner peripheral surface of a cylindrical workpiece), the surface of the workpiece on which the splines are not formed (hereinafter, this may be referred to as the "non-machined surface") and the other of the inner peripheral surface of the die hole or the outer peripheral surface of the punch that is not the shaping surface (hereinafter, this may be referred to as the "non-shaping surface") are constantly sliding against each other during the spline formation process. If the frictional force caused by contact and friction between the non-machined surface and the non-shaping surface is excessive, the processing load may become excessive, or defects such as so-called "biting" between the non-machined surface and the non-shaping surface may occur.

[0068] However, if an attempt is made to alleviate the above problem by increasing the clearance between the non-machined surface and the non-shaped surface, the workpiece may be deformed so that the non-machined surface approaches the non-shaped surface during the spline formation process, which may make it difficult to form the spline with the desired dimensional accuracy.

[0069] Therefore, the second device is the above-mentioned first device, and in the second device, the shaping surface is either the inner peripheral surface of the die hole or the outer peripheral surface of the punch, and an annular bulge is provided on the non-shaping surface, which is the surface of the inner peripheral surface of the die hole or the outer peripheral surface of the punch that is not the shaping surface. The annular bulge is an annular convex portion that protrudes around the entire circumference toward the shaping space in a first region that is a region radially opposite to the region where the first top surface of the first notched portion is provided, at least in the axial direction.

[0070] FIG. 10 is a schematic cross-sectional view illustrating the process of forming splines on the inner circumferential surface of a cylindrical workpiece by forcing the workpiece into the shaping space using the second device 2. Similar to FIG. 6 referred to in the description of the first device, FIG. 10(a) shows a state in which a cylindrical workpiece 400 is set on a pusher 300 connected to a drive mechanism (not shown) to the left of the axis AX. Meanwhile, to the right of the axis AX, the workpiece is being pushed into the shaping space, which is a cylindrical space between the inner circumferential surface of the hole of the die 200 and the outer circumferential surface of the punch 100, from the upstream side (upper side in the drawing) by the pusher 300, with the workpiece 400 coaxial with the shaping space (see the black arrow). FIG. 10(b) is a schematic enlarged view of the portion surrounded by the thick dashed line in FIG. 10(a). Furthermore, FIG. 10(c) is a schematic enlarged view of the portion surrounded by the thick dashed line in FIG. 10(b).

[0071] In the second device illustrated in FIG. 10, as illustrated in (a) and (b) of FIG. 10, the outer peripheral surface of the punch 100 is provided with a first engraved portion 10 and a second engraved portion 20 (not shown). That is, the outer peripheral surface of the punch 100 is a shaping surface. On the other hand, the inner peripheral surface of the hole of the die 200 is not provided with either the first engraved portion 10 or the second engraved portion 20 (not shown). That is, the inner peripheral surface of the hole of the die 200 is not a shaping surface but a non-shaping surface. The portion surrounded by the thick dashed line in (b) of FIG. 10 is a region that is radially opposite the region where the first top surface 11a of the first engraved portion 10 is provided, at least in the direction of the axis AX (see the portion sandwiched between two thin dashed lines), i.e., a portion that includes the first region.

[0072] As shown in (c) of Fig. 10, the above-mentioned portion has an annular bulge 210. The annular bulge 210 is an annular convex portion that protrudes around the entire circumference toward the shaping space in a first region that is a region radially opposite to the region where the first top surface 11a of the first notched portion 10 is provided, at least in the direction of the axis AX. Therefore, the inner diameter of the annular bulge 210 is smaller than the inner diameter of the non-shaping surface (the inner peripheral surface of the hole of the inner die 201 in the example shown in Fig. 10).

[0073] On the other hand, the size of the inner diameter of the annular bulge portion 210 relative to the outer diameter of the non-machined surface (the outer peripheral surface of the workpiece 400 in the example shown in FIG. 10 ) is determined so as to reduce the above problem. Specifically, the size of the inner diameter of the annular bulge portion 210 is determined so that the clearance between the annular bulge portion 210 and the non-machined surface is smaller than the clearance between the non-shaping surface and the non-machined surface. As long as it is possible to satisfactorily form a spline in the workpiece using the second device, the clearance between the annular bulge portion 210 and the non-machined surface may be zero, or the inner diameter of the annular bulge portion 210 may be smaller than the outer diameter of the non-machined surface, and the workpiece 400 may be forced into the shaping space by press-fitting.

[0074] The protrusion amount and inner diameter of the annular bulge 210 from the non-shape surface are determined so as to achieve a clearance between the non-machined surface and the non-shape surface that can alleviate the problem of the workpiece being deformed so that the non-machined surface approaches the non-shape surface during the spline formation process, making it difficult to form the spline with the desired dimensional accuracy. Typically, the protrusion amount of the annular bulge 210 is an extremely small value, for example, on the order of several tens of μm. The specific magnitudes of the protrusion amount and inner diameter of the annular bulge 210 can be determined as appropriate, for example, based on the results of preliminary experiments in which the protrusion amount of the annular bulge 210 from the non-shape surface is varied and / or simulation analysis using the finite element method.

[0075] In the second device, since there is little or no clearance between the non-machined surface and the non-shaping surface in the first region where the annular bulge 210 is provided as described above, it is possible to reduce the risk that the workpiece will deform so that the non-machined surface approaches the non-shaping surface during the spline formation process, making it difficult to form the spline with the desired dimensional accuracy. Therefore, the inner diameter of the non-shaping surface other than the first region where the annular bulge 210 is provided (in the example shown in Figure 10, the inner peripheral surface of the hole of the inner die 201) can be set sufficiently larger than the outer diameter of the non-machined surface (in the example shown in Figure 10, the outer peripheral surface of the workpiece 400).

[0076] As described above, the second device has an annular protrusion (annular bulge) that protrudes around the entire circumference toward the shaping space in a region (first region) that is radially opposite the region where the first top surface of the first notched portion is provided in the axial direction. This mitigates the problem of the workpiece deforming so that the non-machined surface of the workpiece approaches the non-shaping surface during the spline formation process, and allows only the annular bulge to slide against the non-machined surface of the workpiece, rather than the entire non-shaping surface. Therefore, the second device can form splines with the desired dimensional accuracy while avoiding excessive friction between the non-machined surface of the workpiece and the non-shaping surface, thereby reducing the risk of excessive processing loads or defects such as so-called "bite" between the non-machined surface and the non-shaping surface.

[0077] However, the pressing force acting on the workpiece by the first notched portion during the spline formation process does not act only toward the region radially opposite the region where the first top surface of the first notched portion is provided in the axial direction (i.e., the region where the normal to the first top surface intersects with the non-shape-imparting surface). Specifically, the pressing force acts not only toward the region where the normal to the first top surface intersects with the non-shape-imparting surface, but also toward the region where the normal to the first introduction surface intersects with the non-shape-imparting surface. Therefore, in a more preferred embodiment of the second device, the first region is a region that includes the region where the normal to the first introduction surface intersects with the non-shape-imparting surface and the region where the normal to the first top surface intersects with the non-shape-imparting surface.

[0078] FIG. 11 is a schematic cross-sectional view showing an example of the change in the pressing force acting on the workpiece by the first notched portion as the spline formation process in the second device 2 progresses. As shown by the black arrow in FIG. 11(a), the workpiece 400, which has been pushed into the shaping space, begins to contact the first entry surface 12a of the first tooth portion 12 located upstream of the first notched portion 10 provided on the shaping surface (the outer peripheral surface of the punch 100 in the example shown in FIG. 11). Then, a pressing force begins to act on the workpiece 400 in the normal direction of the first entry surface 12a (see the arrow drawn by the thick dashed line). As the workpiece 400 is further pushed into the shaping space, the leading edge of the workpiece 400 begins to contact the first top surface 11a of the first land portion 11 of the first notched portion 10, as shown in FIG. 11(b). Then, in addition to the pressing force in the normal direction of the first introduction surface 12a described above, a pressing force in the normal direction of the first top surface 11a also begins to act on the workpiece 400 (see the arrows drawn by thick dashed lines). When the workpiece 400 is then further pressed into the shaping space, as shown in (c) of Figure 11, pressing forces in the normal direction of the first introduction surface 12a and the normal direction of the first top surface 11a continue to act on the workpiece 400 (see the arrows drawn by thick dashed lines).

[0079] Therefore, from the viewpoint of alleviating the problem of the workpiece 400 being deformed so that the non-machined surface (the outer peripheral surface of the workpiece 400 in the example shown in FIG. 11) approaches the non-shaping surface (the inner peripheral surface of the inner die 201 in the example shown in FIG. 11) during the spline formation process, it is preferable to provide the above-mentioned annular bulge 210 not only in the region where the normal to the first top surface 11a intersects with the non-shaping surface, but also in the region where the normal to the first introduction surface 12a intersects with the non-shaping surface. In other words, it is preferable to define the region including the region where the normal to the first introduction surface 12a intersects with the non-shaping surface and the region where the normal to the first top surface 11a intersects with the non-shaping surface as the first region.

[0080] 12 is a schematic cross-sectional view showing an example of a first region R210 in the second device according to a more preferred embodiment. As shown in FIG. 12, the first region R210 includes both a region R12a where the normal to the first introduction surface 12a intersects with the non-shaping surface and a region R11a where the normal to the first top surface 11a intersects with the non-shaping surface. By providing the annular bulge 210 in the first region R210, it is possible to reduce not only deformation of the workpiece 400 caused by a pressing force acting in a direction toward the region R11a where the normal to the first top surface 11a intersects with the non-shaping surface, but also deformation of the workpiece 400 caused by a pressing force acting in a direction toward the region R12a where the normal to the first introduction surface 12a intersects with the non-shaping surface.

[0081] Therefore, according to the second device, which is a more preferred embodiment, it is possible to more reliably form splines with the desired dimensional accuracy while avoiding excessive frictional forces acting between the non-machined surface and the non-shaping surface of the workpiece, thereby reducing the risk of excessive machining loads or defects such as so-called "biting" between the non-machined surface and the non-shaping surface.

[0082] 12, a single region including both the region R12a where the normal to the first introduction surface 12a intersects with the non-shaping surface and the region R11a where the normal to the first top surface 11a intersects with the non-shaping surface is defined as the first region R210, and one annular bulge 210 (not shown) is provided in the first region R210. However, the number of first regions R210 and annular bulge 210 is not necessarily limited to one. For example, two first regions R210 may be set, one in each of the region R12a where the normal to the first introduction surface 12a intersects with the non-shaping surface and the region R11a where the normal to the first top surface 11a intersects with the non-shaping surface, and one in each of the region R210, for a total of two annular bulge 210.

[0083] In the above description of the second device, as illustrated in FIGS. 10 to 12 , the first engraved portion 10 and the second engraved portion 20 are provided on the outer peripheral surface 101 of the punch 100 as the shaping surface 102. However, as described above, the shaping surface is either or both of the inner peripheral surface of the hole formed in the die 200 and the outer peripheral surface of the punch 100 accommodated in the hole. Therefore, like the first engraved portion 10 and the second engraved portion 20 in the first device, the first engraved portion 10 and the second engraved portion 20 in the second device may be provided only on the inner peripheral surface of the hole formed in the die 200 or only on the outer peripheral surface of the punch 100 accommodated in the hole formed in the die 200, depending on the location where the spline is to be formed in the workpiece 100. In the former case, a portion of the outer peripheral surface of the punch 100 becomes the first region R210, and the annular bulge 210 is provided there. In the latter case, a part of the inner peripheral surface of the hole formed in the die 200 becomes the first region R210, and the annular bulge 210 is provided there.

[0084] Third Embodiment As described above, the present invention relates not only to a spline forming device but also to a spline forming method. Hereinafter, a spline forming method according to a third embodiment of the present invention (hereinafter, sometimes referred to as the "third method") will be described with reference to the drawings.

[0085] The third method is a spline forming method in which splines are formed on the inner and / or outer peripheral surfaces of a cylindrical workpiece using a spline forming device (the device of the present invention) according to the present invention, including the first and second devices described above. The configuration of the device of the present invention has already been described in detail in the explanations of the first and second embodiments of the present invention, so a detailed explanation will be omitted here.

[0086] Fig. 13 is a flowchart showing an example of the flow of each step included in the third method. As illustrated in Fig. 13, the third method includes a first step (step S01) of setting a workpiece in a drive mechanism, and a second step (step S02) of pushing the workpiece into the shaping space from the upstream side by the drive mechanism while the shaping space and the workpiece are coaxial.

[0087] In the first process executed in step S01, a workpiece is set in a drive mechanism provided in the device of the present invention. For example, as illustrated in Fig. 6 referred to in the description of the first device and Fig. 10 referred to in the description of the second device, the workpiece may be set in the drive mechanism via a plunger 300 connected to a drive mechanism (not shown).

[0088] In the second process performed in step S02, the workpiece is pushed into the shaping space from the upstream side by the drive mechanism while the shaping space and the workpiece are coaxial. In the second process, the workpiece may literally be pushed from the upstream side by the drive mechanism into the shaping space defined by the fixed die and punch. Alternatively, as described above, for example, the workpiece may be fixed, and the upstream openings of the die and punch that define the shaping space may be moved toward the fixed workpiece by the drive mechanism, so that the processed portion of the workpiece reaches the inside of the shaping space.

[0089] The changes in the positional relationship between the die and punch and the workpiece as the second step progresses, and the formation of splines in the workpiece, have already been described in detail with reference to Figures 6, 10 and 11 in the explanation of the first and second devices, so further explanation will be omitted here.

[0090] In a third method for forming splines on the inner and / or outer peripheral surfaces of a cylindrical workpiece using the device of the present invention, the position and shape of the spline tooth root are determined by the first crest surface, and the position and shape of the spline tooth tip are determined by the second crest surface. Therefore, according to the third method, splines can be formed without problems such as cracking, even when cutting splines into a workpiece made of a highly hard material.

[0091] Furthermore, according to the third method using the second device in which an annular bulge is provided in the first region, which is a predetermined region on the non-shaping surface, it is possible to reduce the risk of the workpiece being deformed so that the non-machined surface of the workpiece approaches the non-shaping surface during the spline formation process, making it difficult to form the spline with the desired dimensional accuracy, while avoiding excessive frictional force acting between the non-machined surface and the non-shaping surface of the workpiece, thereby reducing the risk of excessive processing load or defects such as so-called "sticking" between the non-machined surface and the non-shaping surface. [Example]

[0092] Examples of the present invention, including the first to third embodiments described above, will be described below with reference to the drawings. However, the examples described below are merely illustrative and do not limit the scope of the present invention.

[0093] In this example, the properties of splines actually formed using a spline forming device according to conventional technology (hereinafter sometimes referred to as the "conventional device") that includes a punch as a processing member in which no second engraving portions are provided between first engraving portions, and a spline forming device according to an example of the present invention (hereinafter sometimes referred to as the "example device") that includes a punch as a processing member in which second engraving portions are provided between first engraving portions, were compared.

[0094] Figure 14 is a photograph showing the appearance of a punch as a processing member provided in the conventional device and the device of the embodiment used in this example. Figure 14(a) is a photograph of the punch provided in the conventional device, which has a configuration similar to the punch without the second engraved portion shown in Figure 2. On the other hand, Figure 14(b) is a photograph of the punch provided in the device of the embodiment, which has a configuration similar to the punch without the second engraved portion shown in Figure 3.

[0095] Using these conventional devices and the device of the embodiment, splines were formed on the inner peripheral surface of a cylindrical workpiece made of stainless steel having a Vickers hardness of approximately 230 HV by performing the first step (step S01) and the second step (step S02) as described with reference to the flowchart of Fig. 13 for the third method. The changes in the positional relationship between the die and punch and the workpiece as the second step progresses and the formation of splines in the workpiece are the same as those shown in Fig. 6, which was referred to in the description of the first device.

[0096] FIG. 15 is a set of photographs comparing the properties of splines formed on the surface of a workpiece using a conventional device and the device of the embodiment. (a) of FIG. 15 is a photograph of a spline formed using the conventional device, and (b) of FIG. 15 is a photograph of a spline formed using the device of the embodiment. As is clear from (a) of FIG. 15, numerous cracks have occurred at the tips of the splines formed using the conventional device, resulting in poor spline formation. This is because the conventional device does not have second indentations between the first indentations. When the workpiece is pressed into the forming space, the material constituting the workpiece plastically flows into the valley-shaped portions between the first indentations and contacts the general surface, which is the bottom surface of the valley-shaped portions, to form the tips of the splines. However, when the workpiece is subsequently pressed into the forming space, the tips and the general surface constantly slide against each other, resulting in frictional forces acting between them, causing numerous cracks at the tips of the splines.

[0097] 15(b), no cracks were observed at the tips of the splines formed using the apparatus of the embodiment, and the splines were well formed. This is because, in the apparatus of the embodiment, second engraved portions are provided between the first engraved portions, and the material constituting the workpiece that plastically flows into the valley-like portions between the first engraved portions when the workpiece is pressed into the shaping space comes into contact with the second apex surface of the second engraved portion rather than the shaping surface corresponding to the general surface, becoming the tips of the splines formed on the surface of the workpiece. After the tips pass the second apex surface during subsequent pressing of the workpiece, the tips face the shaping surface with a gap between them, ensuring a clearance between them. As a result, excessive frictional force is prevented from acting between the tips of the splines and the shaping surface, and cracks are prevented from occurring at the tips of the splines.

[0098] As described above, it has been confirmed that the spline forming device and method according to the embodiment of the present invention can form splines satisfactorily without problems such as cracks, even when carving splines into a workpiece made of a highly hard material. [Example]

[0099] Next, in this embodiment, "Rw," "Ra," and "Rf" shown in Fig. 7, which were referred to in the description of the first device, will be described in detail below. As described above, "Rw," "Ra," and "Rf" shown in Fig. 7 represent the radius of the inner peripheral surface of the cylindrical workpiece 400, the radius of the tip circle defined by the first top surface 11a of the first notched portion 10, and the radius of the root circle defined by the second top surface 21a of the second notched portion 20, respectively.

[0100] In forming a spline, the relationship between the first and second notched portions provided on a punch or die as a processing member and the inner or outer diameter of the cylindrical workpiece is determined in consideration of the volume of material (thickness) constituting the workpiece that plastically flows toward the tip and root sides of the spline formed as the workpiece is pressed into the shaping space. In forming a typical spline according to the prior art, the inner diameter (input diameter) of the workpiece is determined to be approximately halfway between the tip diameter (diameter of the tip circle) of the shaping member defined by the first apex surface of the first notched portion and the root diameter (diameter of the root circle) of the shaping member defined by the second apex surface of the second notched portion, as shown in Figure 7, for example.

[0101] However, when forming a spline in a workpiece made of a material with high hardness, since the workpiece is hard, brittle, and has low deformability, it has been found that if the workpiece input diameter is set to a size approximately halfway between the tooth tip diameter and tooth root diameter defined by the first top surface of the first notched portion and the second top surface of the second notched portion provided on the punch as the shaping member as described above, a spline with the desired shape cannot be obtained, and cracks will occur in the spline.

[0102] Therefore, in this example, the diameter Da (= 2 × Ra) of the tip circle defined by the first apex surface of the first notched portion and the diameter Df (= 2 × Rf) of the root circle defined by the second apex surface of the second notched portion were fixed at 24.1 mm and 21.5 mm, respectively, and the inner diameter of the cylindrical workpiece was changed in various ways as listed in the following Table 1, and splines were formed using the example apparatus in the same manner as in Example 1. Also, a photograph, substituted for a drawing, showing the appearance of the splines formed as a result of Tests 1 to 4 listed in Table 1 is shown in Fig. 16.

[0103] [Table 1]

[0104] As shown in Table 1, in Test 1, the diameter Df of the root circle was 21.5 mm, while the inner diameter of the workpiece was 21.3 mm, which corresponds to so-called "full boring," in which the inner peripheral surface of the workpiece was treated over the entire circumference by the first and second notched portions provided on the outer peripheral surface of the punch. Therefore, the relationship between the tip and root diameters of the workpiece and the inner diameter of the workpiece in Test 1 is significantly different from the relationship between the tip and root diameters of the workpiece and the inner diameter of the workpiece in forming a general spline according to the above-mentioned prior art, but the properties of the resulting spline were good, as shown in Figure 16(a).

[0105] In Tests 2 and 3, the inner diameters of the workpiece were 21.6 mm and 21.7 mm, respectively, and there were clearances of 0.05 mm and 0.1 mm, respectively, between the tooth root of the workpiece defined by the second top surface of the second notched portion on the outer peripheral surface of the punch and the inner peripheral surface of the workpiece. The relationship between the tooth tip diameter and tooth root diameter of the workpiece and the inner diameter of the workpiece in these tests was also different from the relationship between the tooth tip diameter and tooth root diameter of the workpiece and the inner diameter of the workpiece in the formation of a general spline according to the prior art described above, but the properties of the resulting splines were good, as shown in Figures 16(b) and 16(c), respectively.

[0106] However, in Test 4, in which the inner diameter of the workpiece was 22.0 mm and there was a clearance of 0.25 mm between the tooth bottom of the workpiece defined by the second apex surface of the second notched portion on the outer peripheral surface of the punch and the inner peripheral surface of the workpiece, large cracks were observed in the resulting spline, as shown in Figure 16(d). This is thought to be because the tooth tip as the workpiece defined by the first apex surface of the first notched portion on the outer peripheral surface of the punch did not penetrate deeply into the inner peripheral surface of the workpiece, making it impossible to stably form the spline.

[0107] As described above, this embodiment has shown that when engraving splines into a workpiece made of a material having high hardness (i.e., hard, brittle, and low deformability), it is necessary to appropriately set the relationship between the tip diameter and root diameter of the workpiece and the inner diameter of the workpiece in accordance with the hardness of the material and the shape of the spline to be formed.

[0108] The specific relationship between the tip and root diameters of the workpiece and the inner diameter of the workpiece, which allows for the formation of a good spline, can be determined appropriately based on, for example, the results of preliminary experiments in which the relationship between the tip and root diameters of the workpiece and the inner diameter of the workpiece is changed in various ways, as in this embodiment, and / or the results of simulation analysis using the finite element method.

[0109] For the purpose of explaining the present invention, several embodiments and examples having specific configurations have been described above, sometimes with reference to the accompanying drawings. However, the scope of the present invention should not be construed as being limited to these exemplary embodiments and examples, and it goes without saying that appropriate modifications can be made within the scope of the claims and the matters described in the specification. [Explanation of symbols]

[0110] 1, 2...Spline forming device 10…1st engraving part 11...First Land Section 11a...first top surface 12...1st tooth part 12a…1st introduction page 13...First relief section 13a...First relief face 20…Second engraving part 21...Second Land Section 21a…Second top surface 22…Second tooth part 22a...Second entrance 23...Second relief section 23a...Second relief face 100...Punch 200...dice 201...Inner die 202...Outer die 210...Annular bulge 300...Pusher 400...Work R11a: Region where the normal to the first top surface 11a intersects with the non-shape-imparting surface R12a: Region where the normal to the first introduction surface 12a intersects with the non-shape surface R210: First region including region R11a and region R12a Rw: Radius of the inner surface of the cylindrical workpiece 400 Ra: radius of the tip circle defined by the first top surface 11a of the first notched portion 10 Rf: Radius of the root circle defined by the second top surface 21a of the second notched portion 20 Dw: Radius of the inner surface of the cylindrical workpiece 400 Da: radius of the tip circle defined by the first top surface 11a of the first notched portion 10 Df: Radius of the root circle defined by the second top surface 21a of the second notched portion 20

Claims

1. The die has a hole formed therein, a punch accommodated in the hole, a shaping space which is a cylindrical space between the inner peripheral surface of the hole and the outer peripheral surface of the punch, and a drive mechanism which is a mechanism configured to be able to push a cylindrical workpiece into the shaping space from one side in the axial direction, that is, the upstream side. The shaping surface, which is either one or both of the inner circumferential surface and the outer circumferential surface, is provided with a first notched portion, which is a plurality of convex portions extending over a predetermined range in the axial direction, protruding toward the shaping space, and adjacent to each other in the circumferential direction; The first notched portion includes: a first land portion which is a portion extending over a predetermined range in the axial direction and having a first top surface which is a top surface parallel to the axial direction; a first tooth portion which is a portion adjacent to the upstream side of the first land portion and including a first introduction surface which is a surface that continuously connects the first top surface and the shaping surface; and a first relief portion which is a portion adjacent to the downstream side, which is the side opposite the upstream side of the first land portion, and including a first relief surface which is a surface that continuously connects the first top surface and the shaping surface. A spline forming device, Between adjacent first notched portions, second notched portions are further provided, which are a plurality of convex portions extending over a predetermined range in the axial direction, protruding toward the shaping space, and adjacent in the circumferential direction, The second notched portion includes: a second land portion which is a portion extending over a predetermined range in the axial direction and having a second top surface which is a top surface parallel to the axial direction and lower than the first top surface; a second tooth portion which is a portion adjacent to the upstream side of the second land portion and including a second introduction surface which is a surface that continuously connects the second top surface and the shaping surface; and a second relief portion which is a portion adjacent to the downstream side of the second land portion and including a second relief surface which is a surface that continuously connects the second top surface and the shaping surface, an extending range of the first top surface and an extending range of the second top surface at least partially overlap with each other in the axial direction; Spline forming device.

2. The spline forming device according to claim 1, In the axial direction, a second tip which is an end portion on the upstream side of the second top surface is located at the same position as a first tip which is an end portion on the upstream side of the first top surface, or is located upstream of the first tip. Spline forming device.

3. The spline forming device according to claim 1 or 2, The shaping surface is either one of the inner circumferential surface and the outer circumferential surface, The non-shaping surface, which is the surface of the inner peripheral surface and the outer peripheral surface that is not the shaping surface, is provided with an annular bulge portion, which is an annular convex portion that protrudes around the entire circumference toward the shaping space, at least in the first region, which is a region radially opposite to the region where the first top surface is provided in the axial direction. Spline forming device.

4. The spline forming device according to claim 3, The first region is a region where a normal to the first introduction surface and a normal to the first top surface intersect with the non-shaping surface, Spline forming device.

5. A spline forming method for forming splines on an inner peripheral surface and / or an outer peripheral surface of the cylindrical workpiece using the spline forming device according to claim 1 or 2, comprising: a first step of setting the workpiece in the drive mechanism; a second step of pushing the workpiece into the shaping space from the upstream side by the drive mechanism while the shaping space and the workpiece are coaxial; Including, the position and shape of the tooth bottom of the spline are determined by the first top surface, and the position and shape of the tooth tip of the spline are determined by the second top surface; How the spline is formed.

6. 6. A method for forming a spline according to claim 5, comprising: The spline forming device according to claim 3 is used to form splines on either the inner peripheral surface or the outer peripheral surface of the cylindrical workpiece. How the spline is formed.

7. 7. A method for forming a spline according to claim 6, comprising: The spline forming device according to claim 4 is used to form splines on either the inner peripheral surface or the outer peripheral surface of the cylindrical workpiece. How the spline is formed.

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