Spline Rolling Tool, and Process of Manufacturing ...

TECHNICAL FIELD

• The present invention relates to a spline rolling tool, and more particularly to such a spline rolling tool in which strength of forming teeth is so assured that durability of the forming teeth is improved and which can be manufactured at a low cost. The present invention also relates to a process of manufacturing the spline rolling tool.

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BACKGROUND ART

• Splines are a plurality of tooth-shaped keys provided in an outer circumferential surface of a shaft member, and are to be fitted into a member so that power (rotational force) can be transmitted through the mated members. In general, the splines are formed in an outer circumferential surface of a workpiece by a rolling operation using a rolling tool. Each of the splines can be easily broken at a longitudinal end portion of its root (at its ramped end portion). Therefore, there is a need for obtaining a torsional strength of such an easily breakable portion of the root (see Patent Document 1).

• In view of the above need, the applicant of the present application invented a spline 100 as shown in FIG. 8 (which is not publicly known at the time of filing of the present application). As shown in FIG. 8, a shoulder 101 a is provided in a ramped end portion of this spline 100, so that a root diameter defined by a root 101 of the spline 100 is changed in a direction of axis O (horizontal direction as seen in FIG. 8) of a shaft member. The provision of the shoulder 101 a assures a strength of the ramped end portion, namely, makes it possible to improve the torsional strength.

• In a rolling tool used for rolling the spline 100, one of widthwise end portions of each of its forming teeth is subjected to a crest removing operation (see FIG. 2), for permitting the shoulder 101 a to be provided in the root 101 when the spline 100 is formed by the rolling tool. Patent Document 1: JP-H11-290978A (see paragraph [0004] etc.)

DISCLOSURE OF INVENTION Object to be Solved by the Invention

• However, in this case, with each of the forming teeth being subjected to the crest removing operation for providing an incomplete toothed region, a periphery of the incomplete toothed region is defined by a sharp edge, by which each of the forming teeth (incomplete toothed region) is easily chipped or otherwise damaged. Further, since an angular portion is provided in the spline 100, a stress is easily concentrated in the angular portion. Consequently, there is a problem that durabilities of the rolling tool and the splined shaft are deteriorated.

• For example, JP-H09-308935 discloses a spline rolling tool in which a side surface of each tooth (forming tooth) is chamfered for making it possible to prevent deterioration of strength due to stress concentration. However, the chamfering is conventionally made by a handwork operation carried out by a skilled worker, thereby problematically causing increase in time required for the handwork operation and accordingly considerable increase in cost for manufacturing the tool. Further, since the chamfering is made by the handwork operation, there is problem that a sufficient accuracy can not be obtained due to variation with respect to shape of the chamfered portion and surface roughness in the chamfered portion.

• On the other hand, the periphery of the incomplete toothed region could be chamfered by a machining operation using a technique, as disclosed in Patent Document 1, which is for moving a grinding wheel along a predetermined path. However, it would be necessary to extremely accurately control feed movement of the grinding wheel through three controllable feed axes, in order to machine an entirety of the periphery of the incomplete toothed region having a stepped portion, such that the entirety of the periphery of the incomplete toothed region is round-chamfered. The necessity of the extremely accurate control of the feed movement of the grinding wheel leads to an increase in cost required for the control of the feed movement. Further, since such a machining operation with the extremely accurate control has to be made for each one of the forming teeth in the toothed forming face, the required operation time is extremely increased, resulting in, after all, considerable increase in cost for manufacturing the tool.

• The present invention was developed for solving the above-described problem, and has an object to provide a spline rolling tool in which strength of forming teeth is so assured that durability of the forming teeth is improved and which can be manufactured at a low cost, and also a process of manufacturing the spline rolling tool.

Measures for Achieving the Object

• For achieving the object, claim 1 defines a spline rolling tool having a toothed forming face provided with a plurality of forming teeth that are to bite into an outer circumferential surface of a workpiece so as to roll splines in the outer circumferential surface of the workpiece, the spline rolling tool being characterized in that: each of the forming teeth has an incomplete toothed region which is located in one of widthwise end portions thereof and which is formed by a crest removing operation, and a chamfered edge which defines a periphery of the incomplete toothed region and which is formed by a chamfering operation; the incomplete toothed region has a curved surface portion located in a widthwise end portion thereof and having an arcuate cross-section, a flat surface portion contiguous to the curved surface portion and substantially parallel to a crest of each of the forming teeth, and a slant surface portion contiguous to the flat surface portion and inclined upwardly toward the other of the widthwise end portions of each of the forming teeth; and the chamfered edge is formed in the periphery of the incomplete toothed region to have a rounded cross-section, by rotating a wire brush having a plurality of bristles to which abrasive grains adhere and parallelly moving the wire brush in a single direction, such that the chamfered edge has a surface roughness of not larger than about 3.2 μm.

• Claim 2 defines a process of manufacturing a spline rolling tool having a toothed forming face provided with a plurality of forming teeth that are to bite into an outer circumferential surface of a workpiece so as to roll splines in the outer circumferential surface of the workpiece, each of the forming teeth having an incomplete toothed region which is located in one of widthwise end portions thereof and which is formed by a crest removing operation, and a chamfered edge which defines a periphery of the incomplete toothed region and which is formed by a chamfering operation, the process being characterized by including: a teeth forming step of forming the forming teeth in the toothed forming face of the spline rolling tool, by using a grinding wheel; a crest removing step of subjecting the forming teeth formed in the teeth forming step, to a crest removing operation using a grinding wheel for forming the incomplete toothed region having a curved surface portion located in a widthwise end portion thereof and having an arcuate cross-section, a flat surface portion contiguous to the curved surface portion and substantially parallel to a crest of each of the forming teeth, and a slant surface portion contiguous to the flat surface portion and inclined upwardly toward the other of the widthwise end portions of each of the forming teeth; and a chamfering step of subjecting the incomplete toothed region formed in the crest removing step, to a chamfering operation using a wire brush having a plurality of bristles to which abrasive grains adhere, so as to form the chamfered edge in the periphery of the incomplete toothed region such that the chamfered edge has a rounded cross-section and a surface roughness of not larger than about 3.2 μm, wherein the chamfering step is implemented by rotating and parallelly moving the wire brush in a single direction.

• According to claim 3, in the process defined in claim 2, the direction is a direction that is substantially perpendicular to a width direction of each of the forming teeth.

EFFECTS OF THE INVENTION

• In the spline rolling tool defined in claim 1, since the incomplete toothed region having the curved surface portion, the flat surface portion and the slant surface portion is located in the one of the widthwise end portions of each of the forming teeth, roots of the respective splines can be formed such that a root diameter defined by the roots of the respective splines is changed in an axial direction of the workpiece, and a shoulder having a large diameter can be provided in a ramped end portion of each of the splines. That is, there is an effect that it is possible to roll the splines in each of which a torsional strength of the ramped end portion is improved.

• In this case, where the incomplete toothed region is provided in each of the forming teeth, the periphery of the incomplete toothed region would be defined by a sharp edge whereby durabilities of the forming teeth and splines could be reduced. However, in the spline rolling tool of the present invention, the periphery of the incomplete toothed region is subjected to the chamfering operation, so that the chamfered edge is formed in the periphery of the incomplete toothed region to have a rounded cross-section and the surface roughness of not larger than about 3.2 μm. Therefore, there is an effect that it is possible to restrain each of the forming teeth from being chipped or otherwise damaged and accordingly to improve the durability of the spline rolling tool per se.

• On the other hand, when the splines are rolled in the workpiece, it is possible to restrain formation of an angular portion in the ramped end portion of each of the splines and accordingly to improve a surface smoothness of the ramped end portion. Therefore, there is an effect that the splines each having a high strength can be rolled in the workpiece. Consequently, the durability of each of the splines can be improved.

• Further, the chamfered edge is formed by rotating the wire brush having the plurality of bristles to which abrasive grains adhere and parallelly moving the wire brush in the direction. Therefore, even in a case where the incomplete toothed region has the curved surface portion, the flat surface portion and the slant surface portion so as to have a complicated shape as a whole, as in the present invention, it is possible to cause the bristles to be flexed to follow the complicated shape of the incomplete toothed region, and accordingly to highly efficiently and accurately form the chamfered edge having the rounded cross-section and the surface roughness of not larger than about 3.2 μm in the periphery of the incomplete toothed region.

• Consequently, it is possible to uniformly form the chamfered edge having the rounded cross-section, and accordingly to avoid the problem of increase in variation with respect to shape of the chamfered portion and surface roughness in the chamfered portion, which problem has been encountered in a conventional product requiring a handwork operation to form the chamfered portion therein. Therefore, there is an effect that it is possible to restrain chipping or other damage of each of the forming teeth and also to roll the splines each having a high strength, restraining formation of an angular portion in the ramped end portion of each of the splines.

• Further, it is possible to improve accuracy in shape of each of the forming teeth, avoiding the problem of reduction in a non-chamfered portion of each of the forming teeth, which problem has been encountered in a conventional product in which each of the forming teeth has been likely to be chamfered too much in the chamfering operation. Therefore, there is also an effect that it is possible to roll the splines each having a high accuracy, and accordingly to improve accuracy in fitting of each of the splines.

• Further, since the chamfered edge is formed by parallelly moving the wire brush in the single direction, the chamfered edge can be formed in an extremely short length of time. That is, it is not necessary to carry out a complicated operation such as a machining operation with use of a numerically controlled machine tool in which a grinding wheel is fed through a three controllable axes of the machine tool so as to be moved along the periphery of the incomplete toothed region of each of the multiplicity of forming teeth provided in the toothed forming face. Thus, the chamfered edges can be formed in the multiplicity of forming teeth at a time. Consequently, it is possible to simplify the chamfering step and accordingly to reduce a time required to carry out the chamfering operation, thereby leading to reduction in the machining cost. Therefore, there is an effect that is it possible to reduce cost required for the entirety of the spline rolling tool as a product.

• In the spline-rolling-tool manufacturing process defined in claim 2, since the crest removing step is implemented to form the incomplete toothed region having the curved surface portion, the flat surface portion and the slant surface portion in the one of the widthwise end portions of each of the forming teeth, there is an effect that it is possible to manufacture the spline rolling tool capable of rolling the splines in each of which a root diameter defined by roots of the respective splines is changed in an axial direction of the workpiece. That is, by using the spline rolling tool, it is possible to roll the splines in each of which a shoulder having a large diameter is provided in a ramped end portion of the spline so that a torsional strength of the ramped end portion is improved.

• In this case, where the forming teeth are subjected to the crest removing operation performed by the grinding wheel in the crest removing step, the periphery of the incomplete toothed region would be defined by a sharp edge whereby durabilities of the forming teeth and splines could be reduced. However, in the spline-rolling-tool manufacturing process of the present invention, the chamfering step is implemented whereby the chamfered edge is formed in the periphery of the incomplete toothed region to have a rounded cross-section and the surface roughness of not larger than about 3.2 μm. Therefore, there is an effect that it is possible to restrain each of the forming teeth from being chipped or otherwise damaged and accordingly to manufacture the spline rolling tool whose durability is improved.

• On the other hand, when the splines are rolled in the workpiece by using the spline rolling tool having the above-described chamfered edge in the periphery of the incomplete toothed region, it is possible to restrain formation of an angular portion in the ramped end portion of each of the splines and also to improve a surface smoothness of the ramped end portion. Therefore, in the spline-rolling-tool manufacturing process of the present invention, there is an effect that it is possible to manufacture the spline rolling tool capable of rolling the splines each having a high strength in the workpiece.

• Further, in the chamfering step, the incomplete toothed region formed in the crest removing step is subjected to the chamfering operation using the wire brush having the plurality of bristles to which the abrasive grains adhere, whereby the chamfered edge is formed in the periphery of the incomplete toothed region such that the chamfered edge has the rounded cross section and the surface roughness of not larger than about 3.2 μm.

• Therefore, even in a case where the incomplete toothed region has the curved surface portion, the flat surface portion and the slant surface portion so as to have a complicated shape as a whole, as in the present invention, it is possible to cause the bristles to be flexed to follow the complicated shape of the incomplete toothed region, and accordingly to highly efficiently and accurately form the chamfered edge having the rounded cross-section and the surface roughness of not larger than about 3.2 μm in the periphery of the incomplete toothed region.

• Consequently, it is possible to uniformly form the chamfered edge having the rounded cross-section, and accordingly to avoid the problem of increase in variation with respect to shape of the chamfered portion and surface roughness in the chamfered portion, which problem has been encountered in a conventional manufacturing process requiring a handwork operation to form the chamfered portion therein. Therefore, there is an effect that it is possible to restrain chipping or other damage of each of the forming teeth and accordingly to improve durability of the spline rolling tool.

• Further, by using this spline rolling tool, it is possible to restrain formation of an angular portion in the ramped end portion of each of the splines and also to improve a surface smoothness of a rolled surface of the workpiece. Therefore, there is an effect that the splines each having a high strength can be rolled in the workpiece.

• Further, in a conventional manufacturing process, there has been a problem of reduction in a non-chamfered portion of each of the forming teeth, since each of the forming teeth has been likely to be chamfered too much in the chamfering operation. However, in the manufacturing process of the present invention in which the wire brush is caused to cut an angular portion of each of the forming teeth having a relatively low rigidity, there is an effect that it is possible to assuredly obtain a non-chamfered portion of each of the forming teeth. Therefore, since accuracy in the shape of each of the forming teeth can be improved, there is an effect that it is possible to roll the splines each having a high accuracy, and accordingly to improve accuracy in fitting of each of the splines.

• Further, since the chamfering step is performed by rotating and parallelly moving the wire brush in the single direction, the chamfered edge can be formed in an extremely short length of time. That is, it is not necessary to carry out a complicated operation such as a machining operation with use of a numerically controlled machine tool in which a grinding wheel is fed through a three controllable axes of the machine tool so as to be moved along the periphery of the incomplete toothed region of each of the multiplicity of forming teeth provided in the toothed forming face. Thus, the chamfered edges can be formed in the multiplicity of forming teeth at one time. Consequently, it is possible to simplify the chamfering step and accordingly to reduce a time required to carry out the chamfering operation, thereby leading to reduction in the machining cost. Therefore, there is an effect that is it possible to reduce cost required for manufacturing the spline rolling tool.

• In the spline-rolling-tool manufacturing process defined in claim 3, in addition to the effects provided by the spline-rolling-tool manufacturing process defined in claim 2, there is an effect that it is possible to cause each of the bristles of the wire brush to be appropriately brought into contact with the periphery of the incomplete toothed region and accordingly to highly efficiently and reliably carry out the chamfering operation even in a case where the incomplete toothed region has the curved surface portion, the flat surface portion and the slant surface portion so as to have a complicated shape as a whole, as in the present invention, since the wire brush is moved in the direction (the single direction) that is substantially perpendicular to the width direction of each of the forming teeth.

BRIEF DESCRIPTION OF DRAWINGS

• FIG. 1 A set of views showing a spline rolling tool according to an embodiment of the present invention, wherein views (a) and (b) are upper and side views of the spline rolling tool, respectively.

• FIG. 2 View (a) is a cross sectional view of the spline rolling tool, taken along line IIa-IIa of view (a) of FIG. 1, while view (b) is a side view of the spline rolling tool, as seen from a direction of arrow IIb of view (a) of FIG. 2.

• FIG. 3 A perspective view of forming teeth that are ground to be formed in a teeth forming step.

• FIG. 4 A perspective view of the forming teeth in each of which an incomplete toothed region is formed by a crest removing operation in a crest removing step.

• FIG. 5 A perspective view of the forming teeth in each of which a chamfering edge is formed by a chamfering operation in a chamfering step.

• FIG. 6 A bottom view of a wire brush.

• FIG. 7 A schematic view schematically showing the chamfering operation performed on the forming tooth by the wire brush.

• FIG. 8 A cross sectional view of a spline having a shoulder.

EXPLANATION OF REFERENCE SIGNS
• 1 spline rolling tool
• 11 toothed 1 forming face
• 12 forming teeth
• 30 incomplete toothed region
• 30 a curved surface portion
• 30 b flat surface portion
• 30 c inclined surface portion
• 40 chamfered edge
• 70 wire brush
• 72 a bristle
• 100 spline
• L single direction
BEST MODE FOR CARRYING OUT THE INVENTION

• Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a set of views for explaining a spline rolling tool 1 according to an embodiment of the present invention, wherein views (a) and (b) are upper and side views of the spline rolling tool 1, respectively. It is noted that incomplete toothed regions 30 and chamfered edges 40 are not shown in FIG. 1.

• Referring first to FIG. 1, there will be described a whole construction of the spline rolling tool 1. The spline rolling tool 1 is a tool that is to be used for causing plastic deformation in an outer circumferential surface of a workpiece provided by a cylindrical material so as to roll splines 100 (see FIG. 8) in each of which a shoulder 101 a is provided in a ramped end portion of a root 101 of this spline 100.

• In FIG. 1, one of a pair of spline rolling tools 1 that are to be fixed to a rolling apparatus (not shown) is shown, while the other of the spline rolling tools 1 that is to be parallelly moved relative to the one of the spline rolling tools 1 is not shown.

• The spline rolling tool 1 has a generally elongated, rectangular-parallelepiped body, as shown in FIG. 1, which is made of alloy tool steel, high speed tool steel or other metallic material that is suitable for a rolling work. In an upper surface (which is located in a top side of a drawing sheet of view (a) of FIG. 1 and which is located in an upper side in view (b) of FIG. 1), a toothed forming face 11 is provided to roll the splines 100 (see FIG. 8) in the outer circumferential surface of the workpiece.

• The toothed forming face 11 has a biting portion 11 a, a finishing portion 11 b and a relief portion 11 c, as shown in FIG. 1, which are arranged in this order of description as seen in a direction from a rolling initiation or leading end (right end in FIG. 1) of the spline rolling tool 1 toward a trailing end (left end in FIG. 1).

• The biting portion 11 a is used as a so-called biting portion in which the toothed forming surface 11 is to be caused to bite into an outer circumferential surface of the workpiece. As shown in view (b) of FIG. 1, this biting portion 11 a is formed to be upwardly inclined with an inclination angle k1 as it extends from the leading end (right end in FIG. 1) of the spline rolling tool 1 to the finishing portion 11 b in a leftward direction (as seen in FIG. 1).

• The finishing portion 11 b is a portion serving for finishing the splines 100 (see FIG. 8) that are rolled in the workpiece by the biting portion 11 a. As shown in view (b) of FIG. 1, the finishing portion 11 b is formed to be substantially parallel with a supported surface (lower surface as seen in view (b) of FIG. 1) of the spline rolling tool 1.

• The relief portion 11 c is used as a so-called relief portion serving for releasing the workpiece from the toothed forming surface 11. As shown in view (b) of FIG. 1, this relief portion 11 c is formed to be downwardly inclined with an inclination angle k2 as it extends from a terminal end of the finishing portion 11 b to the trailing end (left end in FIG. 1) of the spline rolling tool 1 in leftward direction (as seen in FIG. 1).

• In the toothed forming surface 11 constituted by the leading end portion 11 a, the finishing portion 11 b and the relief portion 11 c, there are formed a plurality of tooth profiles (hereinafter referred to as “forming teeth”) 12. The plurality of forming teeth 12 are formed to be successively arranged in a rolling feed direction (longitudinal direction of the rectangular-parallelepiped body of the spline rolling tool 1 corresponding to a horizontal direction as seen in FIG. 1) at a constant pitch that is dependent upon an outer circumferential dimension of the workpiece. Each of the forming teeth 12 is arranged to extend in a direction (vertical direction as seen in view (a) of FIG. 1) that is substantially perpendicular to the rolling feed direction. The workpiece is rolled and moved relative to the toothed forming surface 11 from the leading end toward the trailing end, whereby the splines 100 (see FIG. 8) are rolled in the outer circumferential surface of the workpiece.

• Referring next to FIG. 2, there will be described a construction of each of the forming teeth 12 in detail. View (a) of FIG. 2 shows a cross sectional view of the spline rolling tool 1, taken along line IIa-IIa of view (a) of FIG. 1, while view (b) of FIG. 2 shows a side view of the spline rolling tool, as seen from a direction of arrow IIb of view (a) of FIG. 2. It is noted that view (a) of FIG. 2 corresponds to a cross sectional view taken along a tooth root line 12 b of each of the forming teeth 12.

• As descried above, each of the forming teeth 12 is a portion that is to bite into the outer circumferential surface of the workpiece, so as to plastically deform the outer circumferential surface of the workpiece, for thereby rolling the splines 100. As shown in FIG. 2, each of the forming teeth 12 includes an incomplete toothed region 30 which is located in an end portion (right end in FIG. 2) as viewed in a width direction of the forming tooth 12 (horizontal direction in view (a) of FIG. 2) and which is formed by a crest removing operation. Each of the forming teeth 12 further includes a chamfered edge 40 which defines a periphery of an incomplete-toothed region surface in the incomplete toothed region 30 and which is formed by a chamfering operation.

• The incomplete toothed region 30 is a region in which a height of the tooth is relatively low, so that the shoulder 101 a can be formed in the root 101 of the spline 100 (see FIG. 8). As shown in FIG. 2, in the incomplete toothed region 30, a crest of each forming tooth 12 is removed such that an upper end of each forming tooth 12 is defined by the incomplete-toothed region surface that is constituted principally by a curved surface portion 30 a, a flat surface portion 30 b and an inclined surface portion 30 c.

• As shown in FIG. 2, the curved surface portion 30 a is located in an end portion (right end in view (a) of FIG. 2) as viewed in a width direction of the forming tooth 12 (horizontal direction in view (a) of FIG. 2), and is formed to have an arcuate cross-section. The flat surface portion 30 b is contiguous to the curved surface portion 30 a, and is formed to be substantially parallel to the crest of the forming tooth 12. The slant surface portion 30 c is contiguous to the flat surface portion 30 b, and is formed to be inclined upwardly as it extends from the flat surface portion 30 b to another end portion (left end in view (b) of FIG. 2) as viewed in the width direction of the forming tooth 12.

• Where the splines are rolled in the workpiece by this spline rolling tool 1, each of the splines can be formed such that a root diameter defined by the roots of the respective is changed in a direction of an axis of the workpiece and such that a shoulder having a large diameter is provided in a ramped end portion of each of the splines (see FIG. 8). Consequently, it is possible to roll the splines in each of which a torsional strength of the ramped end portion is improved.

• Where the forming teeth 12 are subjected to the crest removing operation to be formed with the respective incomplete toothed regions 30, the periphery of each incomplete toothed region 30 would be defined by a sharp edge whereby durabilities of the forming teeth 12 and splines could be reduced. In view of this, in the spline rolling tool 1 of the present invention, the periphery of each incomplete toothed region 30 is subjected to a chamfering operation, as described below, whereby the chamfered edge 40 is formed in the periphery of each incomplete toothed region 30.

• Owing to the formation of the chamfered edge 40, it is possible to restrain chipping or other damage of each of the forming teeth 12 and accordingly to improve durability of the spline rolling tool 1. Further, by using this spline rolling tool 1, it is possible to restrain formation of an angular portion in the ramped end portion of each of the splines, so that the splines each having a high strength can be rolled in the workpiece.

• The chamfered edge 40 is formed in the periphery of the incomplete-toothed region surface of the incomplete toothed region 30 to have a rounded cross-section (see FIG. 5), by a wire brush 70 (see FIG. 6) having a plurality of bristles 72 a to which abrasive grains adhere, as described below.

• Further, the chamfered edge 40 is formed to have a surface roughness of not larger than about 3.2 μm. Therefore, by using this spline rolling tool 1, it is possible to improve a surface smoothness of the ramped end portion of each of the splines, so that the splines each having a high strength can be rolled in the workpiece. Consequently, the durability of each of the splines can be improved.

• Referring next to FIGS. 3-5, there will be described a process of manufacturing the spline rolling tool 1. FIG. 3 is a perspective view of the forming teeth 12 that have been ground to be formed in a teeth forming step. FIG. 4 is a perspective view of the forming teeth 12 in each of which the incomplete toothed region 30 that has been formed by a crest removing operation in a crest removing step. FIG. 5 is a perspective view of the forming teeth 12 in each of which the chamfering edge 40 has been formed by a chamfering operation in a chamfering step.

• For manufacturing the spline rolling tool 1, a die material made of a metallic material such as alloy tool steel and high-speed tool steel is first cut to have a substantially rectangular parallelepiped shape, and is then subjected to a heat treatment. Then, the forming teeth 12 are formed in a surface of the die material that has been subjected to the heat treatment, by a grinding operation using a grinding wheel (teeth forming step).

• That is, in the teeth forming step, by rotating the grinding wheel having a disk shape while parallelly moving the grinding wheel in a direction of arrow W shown in FIG. 3 (width direction of the spline rolling tool 1, i.e., vertical direction in view (a) of FIG. 1), the multiplicity of forming teeth 12 are formed in the toothed forming face 11 (see FIG. 1), as shown in FIG. 3.

• The grinding wheel used in the teeth forming step has a cross section that is configured to correspond to a cross sectional shape of one or two forming teeth 12 (one or two grooves between the forming teeth 12) (i.e., shape defined by arcuate portions of teeth roots and crests, and straight line portions connecting the arcuate portions). In common case, one or two forming teeth 12 (one or two grooves between the forming teeth 12) are formed by one stroke movement of the grinding wheel in the direction of arrow W.

• In the present embodiment, a total of 243 forming teeth 12 (188 forming teeth in the leading portion 11 a, 43 forming teeth in the finishing portion 11 b, and 12 forming teeth in the relief portion 11 c) are formed. Each forming tooth 12 has a height of about 0.975 mm as a maximum value. A pitch between the forming teeth 12 (as measured in the rolling direction) is about 2.503 mm.

• After the teeth forming step, the crest removing step is implemented to carry out a crest removing operation on the forming teeth 12. In the crest removing step, as in the teeth forming step, a grinding wheel having a disk shape is rotated and parallelly moved in a direction of arrow L shown in FIG. 4 (direction substantially perpendicular to the width direction of each forming tooth 12, i.e., direction substantially perpendicular to the vertical direction in view (a) of FIG. 1), for thereby carrying out the crest removing operation in the end portion as viewed in the width direction of the forming tooth 12, so as to form the incomplete toothed regions 30 in the respective forming teeth 12, as shown in FIG. 4.

• The grinding wheel used in the crest removing step has a cross section that is configured to correspond to a shape of a cross section of each forming tooth 12 in the incomplete toothed region 30 (i.e., a shape of a cross section created by a plane cutting each forming tooth 12 in the incomplete toothed region 30 and parallel to the width direction of the forming tooth 12). In common case, the plurality of forming teeth 12 are successively subjected to the crest removing operation, by one stroke movement of the grinding wheel in the direction of arrow L, so as to form the incomplete toothed region 30 (in which the upper end of each forming tooth 12 is defined by the incomplete-toothed region surface that includes the curved surface portion 30 a, the flat surface portion 30 b and the inclined surface portion 30 c) in each forming tooth 12, as shown in FIG. 4.

• In the present embodiment, an amount of removal of an upper portion of each forming tooth 12 (i.e., a distance between the crest of each forming tooth 12 and the flat surface portion 30 b) is about 0.238 mm. A radius of curvature of the curved surface portion 30 a is about 5.5 mm. An inclination angle of the inclined surface portion 30 c (i.e., an angle defined between the flat surface portion 30 b and an extension of the inclined surface portion 30 c) is about 12°. A length of the incomplete toothed region 30 (as measured in the widthwise direction of each forming tooth 12) is about 7.5 mm.

• Where the forming teeth 30 are subjected to the crest removing operation in the crest removing step, the periphery of the incomplete-toothed region surface of the incomplete toothed region 30 would be provided by a sharp edge, and burrs could be left in the periphery, whereby the forming teeth 12 could be easily chipped or otherwise damaged. Further, an angular portion could be formed in each of the splines 100 that are rolled by such forming teeth 12, so that each spline 100 could suffer from a stress concentrated at the angular portion.

• For avoiding such a problem, after the crest removing operation in the crest removing step, the chamfering step is implemented to carry out the chamfering operation on the forming teeth 12. The chamfering operation is carried out by using the wire brush 70. Referring now to FIGS. 6 and 7, there will be described a construction of the wire brush 70 in detail.

• FIG. 6 is a bottom view of the wire brush 70. In FIG. 6, only some of a multiplicity of bristle clusters 72 is illustrated by solid lines, while the other bristle clusters 72 are schematically illustrated by two-dot chain lines.

• As shown in FIG. 6, the wire brush 70 is constituted to have the multiplicity of bristle clusters 72 disposed on a bottom surface of a substrate member 71. In the present embodiment, the substrate member 71 is provided by a disk-shaped body made of aluminum alloy and having a diameter of about 150 mm. The bristle clusters 72 are arranged in two lines extending along respective two virtual circles that are coaxial with an axis of the disk-shaped substrate member 71. The bristle clusters 72 arranged in a radially inner one of the two lines are disposed in a total of 20 portions that are circumferentially spaced apart from each other by an angular pitch of about 18°. The bristle clusters 72 arranged in a radially outer one of the two lines are disposed in a total of 30 portions that are circumferentially spaced apart from each other by an angular pitch of about 18°.

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• Each of the bristle clusters 72 consists of total of 30 bristles 72 a that are densely located within a virtual circle having a diameter of about 10 mm. Each of the bristles 72 a is provided by a line-shaped resin material such as nylon, to which abrasive grains adhere (or which contain the abrasive grains). Each of the bristles 72 a has a diameter of about 1 mm, and a length (i.e., dimension of its projection from the bottom surface of the substrate member 71) of about 13 mm. The abrasive grains are provided by GC (Green Carbon Random) as grain material, and has a grain size of #120.

• FIG. 7 is a schematic view schematically showing the chamfering operation performed on the forming teeth 12 by the wire brush 70. The wire brush 70 is rotated about the axis of the disk-shaped substrate member 71, and is moved in the direction indicated by arrow L shown in FIG. 7. In this instance, the bristles 72 a are moved while being flexed to have an arcuate shape, as shown in FIG. 7, so as to follow the complicated shape of the incomplete-toothed region surface of the incomplete toothed region 30. Therefore, the periphery of the incomplete-toothed region surface of the incomplete toothed region 30 can be chamfered to have an arcuate cross sectional shape that is constant over an entirety of the periphery of the incomplete-toothed region surface of the incomplete toothed region 30′.

• If the chamfering is performed by a handwork operation as conventionally practiced, the forming teeth 12 could be chamfered too much, thereby resulting in problematic reduction in a non-chamfered portion of each of the forming teeth 12. In the present invention, however, since it is possible to cause the bristles 72 of the wire brush 70 to cut an angular portion of each of the forming teeth 12 having a relatively low rigidity, it is possible to assuredly obtain the non-chamfered portion of each of the forming teeth 12. Consequently, it is possible to improve accuracy in fitting of each of the splines that is rolled in the workpiece.

• Referring back to FIG. 5, the chamfering operation is described. In the chamfering operation, the wire brush 70 constructed as described above is parallelly moved in the direction indicated by arrow L shown in FIG. 5 (the same direction as the direction of arrow L in FIG. 4) while being rotated, whereby the chamfering operation is performed on the forming teeth 12 by the abrasive grains adhering to the bristles 72 a of the wire brush 70. Thus, the chamfered edge 40 is formed in the periphery of the incomplete-toothed region surface of the incomplete toothed region 30, as shown in FIG. 5.

• In the chamfering operation, the plurality of forming teeth 12 (the peripheries of the incomplete-toothed region surface of the incomplete toothed regions 30) are successively subjected to the crest removing operation, by one stroke movement of the wire brush 70 in the direction of arrow L, thereby making it possible to complete the chamfering step in an extremely short length of time.

• That is, the chamfering operation can be performed successively on the multiplicity of forming teeth 12 provided in the toothed forming face 11, without having to carry out a complicated operation such as a machining operation with use of a numerically controlled machine tool in which a grinding wheel is fed through a three controllable axes of the machine tool so as to be moved along the periphery of the incomplete-toothed region surface of the incomplete toothed region 30 of every one of the multiplicity of forming teeth 12 of the toothed forming face 11. Consequently, it is possible to simplify the chamfering step and accordingly to remarkably reduce a time required to carry out the chamfering operation, thereby leading to reduction in the machining cost and consequent reduction in cost for manufacturing the spline rolling tool 1.

• Further, since the direction (direction of arrow L) of the parallel movement of the wire brush 70 is substantially perpendicular to the width direction of each of the forming teeth 12, it is possible to cause each of the bristles 72 a of the wire brush 70 to be appropriately brought into contact with the periphery of the incomplete-toothed region surface of the incomplete toothed region 30 and accordingly to highly efficiently and reliably carry out the chamfering operation, even in a case where the incomplete-toothed region surface of the incomplete toothed region 30 has the curved surface portion 30 a, the flat surface portion 30 b and the slant surface portion 30 c so as to have a complicated shape as a whole, as in the present invention.

• Further, since the direction (direction of arrow L) of the parallel movement of the wire brush 70 coincides with the direction (direction of arrow L) of the movement of the grinding wheel for the crest removing operation performed on the forming teeth 12, it is possible to suitably removed burrs by the bristles 72 a of the wire brush 70, if the burrs are left in the peripheries of the incomplete-toothed region surfaces of the respective incomplete toothed regions 30 after the crest removing operation.

• If the wire brush 70 were parallelly moved in a direction (direction of the width of each forming tooth 12) substantially perpendicular to the direction of arrow L, a direction of displacement of each of the bristles 72 a as a result of rotation of the wire brush 70 would be substantially perpendicular to the width direction of each forming tooth 12, so that the burrs removed by the bristles 72 a would be slid, together with the bristles 72 a, on the incomplete-toothed region surfaces and the chamfered edges 40 in the incomplete toothed regions 30, thereby damaging the surfaces of the incomplete-toothed region surfaces and the chamfered edges 40.

• On the other hand, where the wire brush 70 is parallelly moved in the direction of arrow L, the direction of displacement of each of the bristles 72 a as a result of rotation of the wire brush 70 coincides with the width direction of each forming tooth 12, thereby making it possible to cause the bristles 72 a to carry the removed burrs away from the forming teeth 12. Thus, the chamfering operation can be performed to form the chamfered edges 40, without the incomplete-toothed region surfaces and the chamfered edges 40 being damaged by the removed burrs.

• The wire brush 70 is fixed in a height position permitting distal ends of the respective bristles 72 a to be aligned with lower ends of the respective incomplete-toothed region surfaces of the curved surface portion 30 a, and is parallelly moved in the direction of arrow L shown in FIG. 5 while being fixedly held in such a height position. In the present embodiment, while the wire brush 70 is held in the height position, the distal ends of the respective bristles 72 a are positioned to be lower than the crests of the forming teeth 12, by about 5.738 mm that corresponds to a sum of about 0.238 mm as the amount of removal of the upper portions of the respective forming teeth 12 and about 5.5 mm as the radius of curvature of the curved surface portions 30 a.

• While the present invention has been described based on the embodiment, it is to be easily imagined that the present invention is not at all limited to the details of the above-described embodiment but may be subjected to various improvements and modifications within a range that is not deviated from the gist of the invention.

• For example, numerical values described above in the description of the embodiment are merely examples, and the numerical values may be changed as needed.

• Further, the present invention is not limited to the above-described embodiment in which the crest removing operation is performed on only the one widthwise end portion of each forming tooth 12. That is, the crest removing operation may be performed on widthwise opposite end portions of each forming tooth 12.

External Spline Machining