Gear machining method, gear device, and gear cutting tool

Abstract

To realize a technique which can suppress, when a gear is formed on at least one of outer peripheral surfaces of objects to be processed where two or more cylindrical outer peripheral surfaces arranged coaxially to an object shaft center with a clearance in a direction along the object shaft center are integrally formed, the clearance required for formation of the gear to be small.SOLUTION: A gear processing method comprises: an arrangement step arranging a gear cutting tool 20A in which a tool shaft center A1 is in a relation of twisted positions regarding an object shaft center A, and an axis crossing angle α is to be a difference between a second angle θ2 and a first angle θ1; and a processing step forming an object gear 12A on an object outer peripheral surface 11A in which the gear cutting tool 20A is synchronously rotated with an object 10 to be processed after the arrangement step, and the gear cutting tool 20A is relatively displaced regarding the object 10 to be processed along the object axis direction Z within the range where the gear cutting tool 20A does not contact with a non-target outer periphery surface 11B.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a gear cutting method, a gear device, and a gear cutting tool. [Background technology]

[0002] One example of a gear cutting method is disclosed in Japanese Patent Application Laid-Open Publication No. 2016-155175 (Patent Document 1). Hereinafter, in the description of the background art, reference numerals in parentheses refer to those in Patent Document 1. Patent Document 1 discloses a gear cutting method in which a cutting tool (42) and a workpiece (W) are synchronously rotated while the cutting tool (42) is fed in the direction of the rotation axis of the workpiece (W) to form a gear. As shown in FIGS. 4A and 4B of Patent Document 1, the rotation axis (L) of the cutting tool (42) is disposed so as to be inclined with respect to the rotation axis (Lw) of the workpiece (W). The helix angle (θ) of the gear formed on the workpiece (W) is determined according to the intersection angle (φ) between these two rotation axes (L, Lw) and the helix angle (β) of the tool blade (42a) of the cutting tool (42). Thus, Patent Document 1 discloses a gear cutting method using skiving. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-155175 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, a workpiece (hereinafter referred to as a "specific workpiece") integrally formed with two or more cylindrical outer peripheral surfaces aligned coaxially with a target axis and spaced apart in a direction along the target axis may be used to form a gear using a gear cutting method. For example, by using a specific workpiece integrally formed with two cylindrical outer peripheral surfaces of different diameters and forming gears on each of these two outer peripheral surfaces, it is possible to manufacture a stepped external gear (an example of a gear device) in which a small-diameter external gear and a large-diameter external gear are axially connected. When forming gears on the outer peripheral surfaces of a specific workpiece in this manner, it is desirable to minimize the size of the gap required for forming the gears in order to meet the demand for smaller gear devices that can be manufactured. However, Patent Document 1 does not mention using a specific workpiece as a target for forming a gear.

[0005] Therefore, when a gear is formed on at least one of the outer surfaces of a workpiece that has two or more cylindrical outer surfaces integrally formed and aligned coaxially with the symmetrical axis with a gap in the direction along the symmetrical axis, it is desirable to realize a technology that can reduce the size of the gap required for forming the gear. [Means for solving the problem]

[0006] A gear cutting method according to the present disclosure is a gear cutting method for forming a helical gear on at least one of two or more cylindrical outer peripheral surfaces of a workpiece integrally formed with the two or more cylindrical outer peripheral surfaces arranged coaxially with a symmetric axis and spaced apart in a direction along the symmetric axis, wherein one of the two or more outer peripheral surfaces is a symmetric outer peripheral surface and another is a non-symmetric outer peripheral surface, the helical gear formed on the symmetric outer peripheral surface is a target gear, and a plurality of helical cutting blades are formed on the symmetric outer peripheral surface of a tool with a helix angle of the tooth trace of the target gear set to a first angle, and the helix angle of the tooth flank of each of the plurality of cutting blades is a second angle that is greater than the first angle, The method includes an arrangement step of using a gear cutting tool configured to rotate around a tool axis center, which is the axis of the tool outer peripheral surface, and arranging the gear cutting tool so that the tool axis center is in a twisted positional relationship with respect to the symmetric axis center and so that the axis crossing angle between the symmetric axis center and the tool axis center is the difference between the second angle and the first angle; and a processing step of forming the target gear on the target outer peripheral surface by moving the gear cutting tool relative to the workpiece along a symmetric axis direction, which is a direction parallel to the symmetric axis center, while rotating the gear cutting tool and the workpiece synchronously after the arrangement step, within a range where the gear cutting tool does not come into contact with the non-symmetric outer peripheral surface.

[0007] According to this configuration, by sequentially performing the arrangement process and the machining process, a target gear having a tooth flank helix angle of a first angle can be appropriately formed using a gear cutting tool having a tooth flank helix angle of a second angle. Furthermore, according to this configuration, the second angle is set to be larger than the first angle. When the target gear is an external gear as in this configuration, the movement locus (motion) of the cutting blade relative to the target gear in the machining process tends to be a locus that moves relatively sharply in and out relative to the cutting direction of the target gear. However, by setting the second angle to be larger than the first angle, the movement locus can be made closer to a locus along the tooth flank direction while keeping the axis-crossing angle small. As a result, the amount of movement of the cutting blade in the tooth flank direction per unit rotation of the gear cutting tool can be ensured to be large, thereby improving machinability.

[0008] As described above, according to this configuration, even when a gear is formed on the outer peripheral surface of a workpiece (i.e., when the target gear is an external gear), it is possible to improve machinability while keeping the crossed-axis angle small. During the machining process, the gear cutting tool is moved relative to the workpiece within a range where the gear cutting tool does not come into contact with the non-target outer peripheral surface. By keeping the crossed-axis angle small in this manner, it is possible to keep the amount of protrusion of the gear cutting tool from the target outer peripheral surface toward the non-target outer peripheral surface during the machining process small. As a result, it is possible to keep small the gap required to properly perform the machining process (the gap between the target outer peripheral surface and the non-target outer peripheral surface in the symmetric axial direction). This makes it easy to form the target gear on the target outer peripheral surface even when the gap is small.

[0009] As described above, according to this configuration, when a gear is formed on at least one of the outer surfaces of a workpiece having two or more cylindrical outer surfaces integrally formed and arranged coaxially with the symmetrical axis and with a gap in a direction along the symmetrical axis, the size of the gap required for forming the gear can be kept small.

[0010] A gear cutting tool according to the present disclosure is a gear cutting tool for forming a helical gear on at least one of two or more cylindrical outer peripheral surfaces of a workpiece integrally formed with the two or more cylindrical outer peripheral surfaces arranged coaxially with a symmetric axis and spaced apart in a direction along the symmetric axis, wherein one of the two or more outer peripheral surfaces is a symmetric outer peripheral surface and another is a non-symmetric outer peripheral surface, the helical gear formed on the symmetric outer peripheral surface is a target gear, and a plurality of helical cutting blades are formed on the outer peripheral surface of the tool with the helix angle of the tooth trace of the target gear as a first angle, and the plurality of cutting blades the helix angle of each tooth flank is a second angle greater than the first angle, the tool is configured to rotate around a tool axis center that is the axis of the tool outer peripheral surface, the tool axis center is in a twisted positional relationship with the symmetric axis center, and the crossed axis angle between the symmetric axis center and the tool axis center is the difference between the second angle and the first angle, and while rotating synchronously with the workpiece, the tool is moved relative to the workpiece along a symmetric axis direction that is a direction parallel to the symmetric axis center within a range that does not contact the non-symmetric outer peripheral surface, thereby forming the symmetric gear on the symmetric outer peripheral surface.

[0011] This configuration makes it possible to appropriately realize a gear cutting tool for use in the gear cutting method according to the present disclosure. Therefore, with this configuration, when a gear is to be formed on at least one outer peripheral surface of a workpiece having two or more cylindrical outer peripheral surfaces that are integrally formed and coaxial with a symmetrical axis and aligned with a gap in a direction along the symmetrical axis, the size of the gap required for forming the gear can be kept small.

[0012] Further features and advantages of the technology according to the present disclosure will become apparent from the following description of the embodiments, which is given with reference to the drawings. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing an example of a gear device manufactured by a gear processing method. [Figure 2] Partial cross-sectional view showing an example of a gear cutting tool [Figure 3]FIG. 1 is a diagram showing the positional relationship between a gear cutting tool and a workpiece according to an embodiment; [Figure 4] FIG. 10 is a diagram showing the positional relationship between a gear cutting tool and a workpiece according to a comparative example. [Figure 5] An explanatory diagram of the cutting blade movement path during the processing [Figure 6] Flowchart showing the procedure of a gear cutting method according to an embodiment [Figure 7] FIG. 1 is a diagram showing an example of the positional relationship between a gear cutting tool and a workpiece; [Figure 8] FIG. 10 is a diagram showing another example of the positional relationship between the gear cutting tool and the workpiece; DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the technology according to the present disclosure will be described with reference to the drawings. The gear cutting method according to the present disclosure is a method for forming a helical gear 12 on at least one of two or more (i.e., at least two) cylindrical outer peripheral surfaces 11 of a workpiece 10 (see FIGS. 1 and 3 ), the outer peripheral surfaces 11 being integrally formed with each other and coaxially with a target axis A and aligned with a gap G in a direction along the target axis A. The helical gear 12 is formed by skiving. A first gear cutting tool 20A according to the present disclosure is a tool for forming the helical gear 12 on at least one of the two or more outer peripheral surfaces 11 of the workpiece 10. The first gear cutting tool 20A is a skiving cutter used for skiving. Although three or more (e.g., three) outer peripheral surfaces 11 may be integrally formed with the workpiece 10, in this embodiment, two outer peripheral surfaces 11 are integrally formed with the workpiece 10. The gear cutting method according to this embodiment is a method for forming helical gears 12 on both of the two outer peripheral surfaces 11 of the workpiece 10. In this specification, the term "helical gear" is used as a concept that includes splines with a twist angle.

[0015] Before the helical gears 12 are formed, two or more (two in this embodiment) outer peripheral surfaces 11 are flat cylindrical surfaces, but for convenience, Fig. 3 shows a simplified view of the tooth traces of the helical gears 12 on both of the two outer peripheral surfaces 11. Fig. 1 also shows a gear device 1 in which helical gears 12 are formed on both of the two outer peripheral surfaces 11 by a gear cutting method (i.e., the workpiece 10 in a state after the helical gears 12 have been formed). Figs. 1 and 3 illustrate a case in which helical gears 12 with the same twist direction are formed on the two outer peripheral surfaces 11, but helical gears 12 with opposite twist directions may also be formed on the two outer peripheral surfaces 11.

[0016] The gear cutting method is performed on the workpiece 10 in a state where two or more (two in this embodiment) outer peripheral surfaces 11 arranged with a gap G therebetween are integrated. In the workpiece 10 illustrated in Fig. 3, the two outer peripheral surfaces 11 arranged with a gap G therebetween are connected via a shaft portion 14, thereby integrating these two outer peripheral surfaces 11. For example, the workpiece 10 may be one in which two or more (two in this embodiment) outer peripheral surfaces 11 are integrally formed from a single member (a single member made of a common material).

[0017] Here, as shown in FIGS. 1 and 3, one of the two or more outer peripheral surfaces 11 (in this embodiment, one of the two outer peripheral surfaces 11) is designated as a first outer peripheral surface 11A, and another (in this embodiment, the other of the two outer peripheral surfaces 11) is designated as a second outer peripheral surface 11B. The helical gear 12 formed on the first outer peripheral surface 11A is designated as a first helical gear 12A, and the twist angle of a first tooth trace 13A, which is the tooth trace of the first helical gear 12A, is designated as a first angle θ1. The first angle θ1 is the inclination angle of the first tooth trace 13A with respect to the symmetric axis A (see FIG. 3). In this embodiment, the two outer peripheral surfaces 11 have different diameters. The one of the two outer peripheral surfaces 11 with a smaller diameter is designated as the first outer peripheral surface 11A, and the one with a larger diameter is designated as the second outer peripheral surface 11B.

[0018] In this embodiment, the first outer peripheral surface 11A corresponds to the "target outer peripheral surface," the second outer peripheral surface 11B corresponds to the "non-target outer peripheral surface," the first helical gear 12A corresponds to the "target gear," and the first tooth trace 13A corresponds to the "tooth trace of the target gear." That is, in this embodiment, of the two or more outer peripheral surfaces 11, the target outer peripheral surface is the first outer peripheral surface 11A, the non-target outer peripheral surface is the second outer peripheral surface 11B, the target gear is the first helical gear 12A, the helical gear 12 formed on the second outer peripheral surface 11B is the second helical gear 12B, and the twist angle of the second tooth trace 13B, which is the tooth trace of the second helical gear 12B, is the third angle θ3. The third angle θ3 is the inclination angle of the second tooth trace 13B with respect to the target axis A (see FIG. 3). The third angle θ3 may be the same as or different from the first angle θ1. In this embodiment, the second tooth trace 13B corresponds to the "tooth trace of the second helical gear."

[0019] In the gear cutting method, a first gear cutting tool 20A is used. In this embodiment, the gear cutting method also uses a second gear cutting tool 20B. The first gear cutting tool 20A and the second gear cutting tool 20B have the same basic structure as shown in FIG. 2, so these two gear cutting tools are shown without distinction in FIG. 2. The first gear cutting tool 20A and the second gear cutting tool 20B do not necessarily have to be separate tools, and the same tool may be used as both the first gear cutting tool 20A and the second gear cutting tool 20B.

[0020] As shown in FIG. 2, the first gear cutting tool 20A is configured to rotate about a first tool axis A1, which is the axis of a first tool outer peripheral surface 21A (the outer peripheral surface of the first gear cutting tool 20A). That is, the first gear cutting tool 20A is held by a gear cutting machine (not shown) so as to rotate about the first tool axis A1. A plurality of helical first cutting blades 22A are formed on the first tool outer peripheral surface 21A. The helix angle of each tooth flank 23 (blade surface) of the plurality of first cutting blades 22A is a second angle θ2, which is larger than the first angle θ1 (see FIG. 3). The second angle θ2 is the helix angle of the tooth flank 23 of the first cutting blade 22A with respect to the first tool axis A1 (see FIGS. 2 and 3). The helix angle of the tooth flank 23 can be referred to as the helix angle of the cutting edge or the helix angle of the tooth flank.

[0021] In this embodiment, the first cutting blade 22A corresponds to the "cutting blade," the first tool outer peripheral surface 21A corresponds to the "tool outer peripheral surface," the first tool axis center A1 corresponds to the "tool axis center," and the first gear cutting tool 20A corresponds to the "gear cutting tool." That is, in this embodiment, the gear cutting tool is the first gear cutting tool 20A, the cutting blade is the first cutting blade 22A, the tool outer peripheral surface is the first tool outer peripheral surface 21A, and the tool axis center is the first tool axis center A1.

[0022] The end face of the first cutting blade 22A on one axial side constitutes a rake face 24, and the end face of the first cutting blade 22A on the outer radial side constitutes a tooth tip face 25 (cutting edge face). The tooth tip face 25 constitutes a part of the tooth flank 23, and the twist angle of the tooth flank 23 of the first cutting blade 22A described above can be said to be the twist angle of the tooth tip face 25 constituting the tooth flank 23. In this embodiment, the tooth tip face 25 of the first cutting blade 22A is an outer circumferential relief face that is inclined radially outward toward the one axial side (the side where the rake face 24 is formed) so as to form an outer circumferential relief angle δ (front relief angle). In other words, the first tool outer circumferential face 21A (specifically, the circumscribed circle of the multiple first cutting blades 22A provided in the first gear cutting tool 20A) is formed in a truncated cone shape. Note that the axial and radial directions herein are axial and radial directions based on the first tool axis A1.

[0023] The second gear cutting tool 20B is configured to rotate about a second tool axis A2, which is the axis of the second tool outer peripheral surface 21B (the outer peripheral surface of the second gear cutting tool 20B). That is, the second gear cutting tool 20B is held by a gear machining device (not shown) so as to rotate about the second tool axis A2. A plurality of helical second cutting blades 22B are formed on the second tool outer peripheral surface 21B. The helix angle of the tooth flank 23 of each of the plurality of second cutting blades 22B is a fourth angle θ4, which is larger than the third angle θ3 (see FIG. 3). The fourth angle θ4 is the helix angle of the tooth flank 23 of the second cutting blade 22B with respect to the second tool axis A2 (see FIGS. 2 and 3). The fourth angle θ4 may be the same as or different from the second angle θ2.

[0024] The end face of the second cutting blade 22B on one axial side constitutes the rake face 24, and the end face of the second cutting blade 22B on the outer radial side constitutes the tooth tip face 25. The tooth tip face 25 constitutes a part of the tooth flank 23, and the twist angle of the tooth flank 23 of the second cutting blade 22B described above can be said to be the twist angle of the tooth tip face 25 constituting the tooth flank 23. In this embodiment, the tooth tip face 25 of the second cutting blade 22B is an outer circumferential relief face that is inclined radially outward toward the one axial side (the side on which the rake face 24 is formed) so as to form an outer circumferential relief angle δ. That is, the second tool outer circumferential face 21B (specifically, the circumscribed circle of the multiple second cutting blades 22B provided on the second gear cutting tool 20B) is formed in a truncated cone shape. Note that the axial and radial directions herein are axial and radial directions based on the second tool axis A2. The peripheral clearance angle δ of the second gear cutting tool 20B may be the same as or different from the peripheral clearance angle δ of the first gear cutting tool 20A.

[0025] As shown in Fig. 6, this gear cutting method involves a first arrangement step P1 and a first processing step P2. The gear cutting method according to this embodiment also involves a second arrangement step P3 and a second processing step P4. In this embodiment, the first arrangement step P1 corresponds to the "arrangement step", and the first processing step P2 corresponds to the "processing step".

[0026] 3, a direction parallel to the target axis A is defined as a target axis direction Z. The side along which the first gear cutting tool 20A moves relative to the workpiece 10 along the target axis direction Z in the first machining step P2 is defined as a target axis direction first side Z1, and the opposite side is defined as a target axis direction second side Z2. In this embodiment, the target axis direction first side Z1 is the side along the target axis direction Z that faces from the first outer peripheral surface 11A to the second outer peripheral surface 11B.

[0027] As shown in FIG. 3, the first arrangement step P1 is a step of arranging the first gear cutting tool 20A so that the first tool axis A1 is in a twisted positional relationship with the target axis A and the cross-axis angle α between the target axis A and the first tool axis A1 is the difference between the second angle θ2 and the first angle θ1. Here, the cross-axis angle between the two axes means that the two axes are not parallel and do not intersect at a single point (in other words, they do not have a common point). The cross-axis angle α is the angle at which the first tool axis A1 intersects with a plane that includes the machining position M (the position where the first cutting edge 22A cuts the first outer peripheral surface 11A) and the target axis A.

[0028] In the first placement step P1, the first gear cutting tool 20A is placed on the second side Z2 in the axial direction relative to the first outer peripheral surface 11A. Note that Fig. 3 shows a state in which, after the first placement step P1 is performed, the first gear cutting tool 20A is moved to the first side Z1 in the axial direction relative to the workpiece 10 by performing the first machining step P2. In addition, in the first placement step P1, the first gear cutting tool 20A is placed so that the first tool outer peripheral surface 21A is in circumscribing contact with the first outer peripheral surface 11A in the first machining step P2 (see Fig. 7). The position where the first tool outer peripheral surface 21A and the first outer peripheral surface 11A come into contact corresponds to the machining position M (machining point).

[0029] The first machining step P2 is a step performed after the first placement step P1, in which the first gear cutting tool 20A and the workpiece 10 are rotated synchronously while the first gear cutting tool 20A is moved relative to the workpiece 10 along the target axis direction Z within a range in which the first gear cutting tool 20A does not come into contact with the second outer peripheral surface 11B (see the outline arrow in FIG. 3 ), thereby forming a first helical gear 12A on the first outer peripheral surface 11A. In this embodiment, the position of the workpiece 10 in the target axis direction Z is fixed, and the first gear cutting tool 20A is moved along the target axis direction Z, thereby moving the first gear cutting tool 20A relative to the workpiece 10.

[0030] In this way, the first gear cutting tool 20A is a tool for forming a first helical gear 12A on the first outer peripheral surface 11A by rotating synchronously with the workpiece 10 while moving it along the symmetrical axis direction Z relative to the workpiece 10 within a range that does not contact the second outer peripheral surface 11B, while being positioned so that the first tool axis A1 is in a twisted positional relationship with the symmetrical axis A and the axis crossing angle α between the symmetrical axis A and the first tool axis A1 is the difference between the second angle θ2 and the first angle θ1.

[0031] FIG. 7 shows the positional relationship between the first gear cutting tool 20A and the workpiece 10 during the first machining step P2. The upper diagram shows the positional relationship when viewed in a direction parallel to the target axis A, and the lower diagram shows the positional relationship when viewed in a direction perpendicular to the target axis A. In the upper diagram of FIG. 7, the back side of the page is the target axis direction first side Z1, and the front side of the page is the target axis direction second side Z2. The first tool outer peripheral surface 21A shown in the upper diagram of FIG. 7 represents the bottom of the first tool outer peripheral surface 21A, which is formed in a truncated cone shape, and the first tool axis A1 shown in the upper diagram of FIG. 7 represents the intersection position of the first tool axis A1 with a plane including the bottom. The first gear cutting tool 20A indicated by the dashed line in FIG. 7 will be described later.

[0032] 7, the position where the first cutting blade 22A (see FIG. 2) cuts the first outer peripheral surface 11A is defined as the machining position M, a plane including the target axis A and arranged parallel to any plane including the first tool axis A1 is defined as the first surface S1, and a plane including the target axis A and perpendicular to the first surface S1 is defined as the second surface S2. In this embodiment, in the first arrangement step P1, the first gear cutting tool 20A is arranged so that the machining position M is located on the second surface S2.

[0033] Fig. 3 corresponds to a view of the first gear cutting tool 20A and the workpiece 10 shown in Fig. 7 as viewed from the left side in Fig. 7. Therefore, in Fig. 3, a plane that includes the symmetric axis A and is parallel to the paper surface is the first surface S1, and a plane that includes the symmetric axis A and is perpendicular to the paper surface is the second surface S2. In Fig. 3, the first tooth trace 13A is a simplified representation of the tooth trace of the portion of the first outer peripheral surface 11A on the near side of the paper surface (the left side portion in Fig. 7), and the second tooth trace 13B is a simplified representation of the tooth trace of the portion of the second outer peripheral surface 11B on the near side of the paper surface. In addition, in Figure 3, the first gear cutting tool 20A is positioned on the front side of the paper relative to the workpiece 10, and the tooth surface 23 (specifically, the tooth tip surface 25) of the first cutting blade 22A provided on the first gear cutting tool 20A is shown as a simplified representation of the tooth surface 23 of the portion of the first tool outer peripheral surface 21A that is positioned on the back side of the paper (the right side portion in Figure 7).

[0034] The second arrangement step P3 is a step of arranging the second gear cutting tool 20B so that the second tool axis A2 is in a twisted positional relationship with the target axis A and the cross-axis angle α between the target axis A and the second tool axis A2 is the difference between the fourth angle θ4 and the third angle θ3. In the second arrangement step P3, the second gear cutting tool 20B is arranged so that the second tool outer peripheral surface 21B is circumscribed on the second outer peripheral surface 11B in the second machining step P4. The cross-axis angle α in the second arrangement step P3 may be the same as or different from the cross-axis angle α in the first arrangement step P1.

[0035] Although not shown in the drawings, the position where the second cutting blade 22B cuts the second outer peripheral surface 11B is defined as the second machining position, a plane including the target axis A and arranged parallel to any plane including the second tool axis A2 is defined as the third plane, and a plane including the target axis A and perpendicular to the third plane is defined as the fourth plane. In this embodiment, in the second arrangement step P3, the second gear cutting tool 20B is arranged so that the second machining position is located on the fourth plane.

[0036] The second machining step P4 is a step performed after the second placement step P3, in which the second gear cutting tool 20B and the workpiece 10 are rotated synchronously while the second gear cutting tool 20B is moved along the target axis direction Z relative to the workpiece 10 within a range in which the second gear cutting tool 20B does not come into contact with the first outer peripheral surface 11A, thereby forming a second helical gear 12B on the second outer peripheral surface 11B. In this embodiment, the position of the workpiece 10 in the target axis direction Z is fixed, and the second gear cutting tool 20B is moved along the target axis direction Z to move the second gear cutting tool 20B relative to the workpiece 10.

[0037] In this way, the second gear cutting tool 20B is a tool for forming a second helical gear 12B on the second outer peripheral surface 11B by rotating synchronously with the workpiece 10 while moving it along the symmetrical axis direction Z relative to the workpiece 10 within a range that does not contact the first outer peripheral surface 11A, while being positioned so that the second tool axis A2 is in a twisted positional relationship with the symmetrical axis A and the axis crossing angle α between the symmetrical axis A and the second tool axis A2 is the difference between the fourth angle θ4 and the third angle θ3.

[0038] By sequentially performing the first arrangement step P1 and the first machining step P2 described above, it is possible to appropriately form a first helical gear 12A in which the helix angle of the tooth trace (first tooth trace 13A) is the first angle θ1 using a first gear cutting tool 20A in which the helix angle of the tooth flank 23 is the second angle θ2. Because the first helical gear 12A is an external gear, the movement locus (motion) of the first cutting blade 22A relative to the first helical gear 12A in the first machining step P2 tends to be a locus that moves in and out relatively sharply with respect to the cutting direction of the first helical gear 12A (in other words, a locus that is relatively inclined with respect to the tooth trace direction of the first helical gear 12A), as shown by the dashed line in FIG. 5 . In FIG. 5 , the position “0” in the tooth trace direction corresponds to the start position of cutting, and the locus extending to the right from this position represents the movement locus of the first cutting blade 22A during cutting.

[0039] When the movement locus of the first cutting blade 22A is a locus that moves in and out relatively steeply relative to the cutting direction of the first helical gear 12A, as shown by the dashed line in FIG. 5, the rake angle γ during cutting becomes large and negative. In addition, the cutting thickness (uncut thickness) increases, which tends to increase the cutting load (machining point load). In particular, when a typical skiving method is used in which the second angle θ2 is smaller than the first angle θ1, as in the comparative example shown in FIG. 4, the movement locus of the first cutting blade 22A tends to resemble the locus shown by the dashed line in FIG. 5. Although the comparative example shown in FIG. 4 is not an example of the technology disclosed herein, the same reference numerals as in FIG. 3 are used in FIG. 4 to facilitate comparison with the example of the technology disclosed herein (FIG. 3).

[0040] In the comparative example shown in Fig. 4, increasing the cross-axis angle α can be considered to bring the movement path of the first cutting blade 22A closer to a path along the tooth trace direction of the first helical gear 12A, as shown by the solid line in Fig. 5. By bringing the movement path of the first cutting blade 22A closer to a path along the tooth trace direction of the first helical gear 12A, the absolute value of the negative rake angle γ can be kept small, thereby improving workability. However, if the cross-axis angle α is increased, the amount of protrusion of the first gear cutting tool 20A from the first outer peripheral surface 11A toward the second outer peripheral surface 11B during the first machining step P2 increases, which tends to increase the gap G required to properly perform the first machining step P2.

[0041] In contrast, in the gear cutting method according to the present disclosure, as described above, the second angle θ2 is set to be greater than the first angle θ1. As shown in FIG. 3, the tooth trace of the first helical gear 12A (first tooth trace 13A) is inclined toward the front side in the rotation direction of the workpiece 10 (first rotation direction R1, see also FIG. 7) as it moves toward the first side Z1 in the axial direction of the target object. Here, the inclination angle of the tooth trace of the first helical gear 12A (first tooth trace 13A) with respect to the axial center A is referred to as the tooth trace inclination angle. The tooth flank 23 of the first cutting blade 22A is inclined toward the front side in the rotation direction of the first gear cutting tool 20A (second rotation direction R2, see also FIG. 7) as it moves toward the first side Z1 in the axial direction of the target object. The inclination angle of the tooth flank 23 of the first cutting blade 22A with respect to the first tool axis center A1 is greater than the tooth trace inclination angle. This makes it possible to appropriately realize a configuration in which the second angle θ2, which is the twist angle of the tooth flank 23 of the first cutting blade 22A provided on the first gear cutting tool 20A, is larger than the first angle θ1, which is the twist angle of the tooth trace (first gear trace 13A) of the first helical gear 12A. In this embodiment, the first rotational direction R1 corresponds to the "rotational direction of the workpiece," and the second rotational direction R2 corresponds to the "rotational direction of the gear cutting tool."

[0042] In the gear cutting method according to the present disclosure, by configuring the second angle θ2 to be greater than the first angle θ1 as described above, the axis-crossing angle α can be kept small, and the movement path of the first cutting blade 22A can be made closer to the path along the tooth trace direction of the first helical gear 12A, as shown by the solid line in Fig. 5, thereby improving machinability. That is, even when an external gear is formed on the outer peripheral surface 11 of the workpiece 10, it is possible to improve machinability while keeping the axis-crossing angle α small. Furthermore, by keeping the axis-crossing angle α small in this way, it is possible to keep the amount of protrusion of the first gear cutting tool 20A from the first outer peripheral surface 11A toward the second outer peripheral surface 11B during the first machining step P2. As a result, the gap G (the gap G in the symmetric axial direction Z between the first outer peripheral surface 11A and the second outer peripheral surface 11B) required to properly execute the first machining process P2 can be kept small, and even if the gap G is small, it is easy to form the first helical gear 12A on the first outer peripheral surface 11A.

[0043] Furthermore, in this embodiment, by sequentially performing the second arrangement step P3 and the second machining step P4 described above, the second helical gear 12B, whose tooth flank 23 has a helix angle of the third angle θ3, can be appropriately formed using the second gear cutting tool 20B, whose tooth flank 23 has a helix angle of the fourth angle θ4. In this embodiment, the fourth angle θ4 is set to be larger than the third angle θ3, thereby improving machinability, as in the case of forming the first helical gear 12A. Furthermore, as in the case of forming the first helical gear 12A, the crossed-axis angle α can be kept small, and therefore the amount of protrusion of the second gear cutting tool 20B from the second outer peripheral surface 11B toward the first outer peripheral surface 11A during the second machining step P4 can be kept small. Therefore, the gap G required for appropriately performing the second machining step P4 can be kept small. Even if the gap G is small, the second helical gear 12B can be easily formed relative to the second outer peripheral surface 11B.

[0044] The gear cutting method described above provides a gear device 1 having a helical gear 12 formed on at least one of two or more outer peripheral surfaces 11. In this embodiment, as shown in FIG. 1 as an example, a gear device 1 having a helical gear 12 formed on both of two outer peripheral surfaces 11 is provided. The gear cutting method according to the present disclosure makes it possible to reduce the gap G required to properly execute the first machining step P2 (in this embodiment, the gap G in the symmetric axial direction Z between the two outer peripheral surfaces 11). Therefore, a gear device 1 having a helical gear 12 formed on at least one of two or more outer peripheral surfaces 11 can be properly manufactured even when a workpiece 10 having a small gap G is used.

[0045] Other Embodiments Next, other embodiments of the technology according to the present disclosure will be described.

[0046] (1) In the above embodiment, the first gear cutting tool 20A is arranged in the first arrangement step P1 so that the machining position M is located on the second surface S2. However, the present disclosure is not limited to such an arrangement. One side of the direction orthogonal to the second surface S2 (orthogonal direction X) is defined as the first orthogonal direction side X1. Alternatively, the first gear cutting tool 20A may be arranged in the first arrangement step P1 so that the first tool axis A1 extends toward the orthogonal direction first side X1 as it extends toward the second axial direction side Z2, and the machining position M is located on the first orthogonal direction side X1 relative to the second surface S2. The dashed line in FIG. 7 shows an example of the position of the first gear cutting tool 20A, where the first tool axis A1 extends toward the orthogonal direction first side X1 as it extends toward the second axial direction side Z2, and the machining position M is located on the first orthogonal direction side X1 relative to the second surface S2. 7, the other side of the orthogonal direction X is designated as the second orthogonal side X2. Here, the orthogonal direction X corresponds to the "direction orthogonal to the second surface," and the first orthogonal side X1 corresponds to the "specific side."

[0047] When the first gear cutting tool 20A is positioned so that the machining position M is located on the second surface S2 as in the above embodiment, a first gear cutting tool 20A with a conical (frustum-shaped) first tool outer peripheral surface 21A, as shown in FIG. 2, must be used to ensure a desired clearance angle (during machining clearance angle β, see the lower diagram in FIG. 7) when forming the first helical gear 12A. In contrast, when the first gear cutting tool 20A is positioned so that the machining position M is located on the first side X1, which is perpendicular to the second surface S2, the machining clearance angle β can be ensured to be larger than the clearance angle of the first gear cutting tool 20A itself (peripheral clearance angle δ), as shown in FIG. 8. In other words, the peripheral clearance angle δ required to ensure a desired during machining clearance angle β when forming the first helical gear 12A can be made smaller than when the first gear cutting tool 20A is positioned so that the machining position M is located on the second surface S2. As a result, the shape of the first tool outer peripheral surface 21A can be made closer to a cylindrical shape, and it is also possible to make the shape of the first tool outer peripheral surface 21A cylindrical. Note that Fig. 8 shows the positional relationship between the first gear cutting tool 20A and the workpiece 10 when the first gear cutting tool 20A is placed at the position shown by the dashed line in Fig. 7. The lower view of Fig. 8 is taken from a different perspective than the lower view of Fig. 7 so that the machining position M can be seen.

[0048] As described above, when the first gear cutting tool 20A is positioned so that the machining position M is located on the first side X1 in the direction perpendicular to the second surface S2, the shape of the first tool outer peripheral surface 21A of the first gear cutting tool 20A can be made closer to a cylindrical shape. Therefore, when the first cutting edge 22A of the first gear cutting tool 20A is re-ground, the change in the tooth profile of the first helical gear 12A formed before and after regrinding can be minimized. This allows for a greater number of possible regrinding cycles, thereby extending the service life of the first gear cutting tool 20A.

[0049] Similarly, in the above embodiment, an example has been described in which the second gear cutting tool 20B is arranged in the second arrangement step P3 so that the machining position M is located on the fourth surface. However, the present disclosure is not limited to such a configuration, and a configuration may be adopted in which one side in a direction perpendicular to the fourth surface is defined as the second specific side, and the second gear cutting tool 20B is arranged in the second arrangement step P3 in an orientation that moves toward the second specific side as the second tool axis A2 moves toward the second side Z2 in the target axial direction, and the second machining position is located on the second specific side with respect to the fourth surface.

[0050] (2) In the above embodiment, the fourth angle θ4 is greater than the third angle θ3. However, the present disclosure is not limited to such a configuration, and the fourth angle θ4 may be smaller than the third angle θ3. For example, as in the above embodiment, when the first outer peripheral surface 11A has a smaller diameter than the second outer peripheral surface 11B, the fourth angle θ4 may be smaller than the third angle θ3.

[0051] (3) In the above embodiment, the gear cutting method has been described as an example of a method of forming helical gears 12 on both of the two outer peripheral surfaces 11 of the workpiece 10. However, the present disclosure is not limited to such a configuration, and the gear cutting method may also be a method of forming a helical gear 12 on only one of the two outer peripheral surfaces 11 of the workpiece 10. In this case, unlike the above embodiment, the gear cutting method performs the first arrangement step P1 and the first processing step P2, but does not perform the second arrangement step P3 and the second processing step P4. When forming a helical gear 12 on only one of the two outer peripheral surfaces 11 of the workpiece 10 in this way, for example, a configuration in which a spline is formed on the other outer peripheral surface 11, or a configuration in which a gear or the like is not formed on the other outer peripheral surface 11 (for example, a configuration in which the portion having the outer peripheral surface 11 functions as a flange), may be used. Furthermore, the gear cutting method may also be a method of forming helical gears 12 on some or all of three or more outer peripheral surfaces 11 of the workpiece 10.

[0052] (4) Note that the configurations disclosed in the above-described embodiments can be applied in combination with configurations disclosed in other embodiments (including combinations of embodiments described as other embodiments) as long as no contradictions arise. Regarding other configurations, the embodiments disclosed in this specification are merely examples in all respects. Therefore, various modifications can be made as appropriate within the scope of the present disclosure. [Explanation of symbols]

[0053] 10: workpiece, 11: outer peripheral surface, 11A: first outer peripheral surface (target outer peripheral surface), 11B: second outer peripheral surface (non-target outer peripheral surface), 12: helical gear, 12A: first helical gear (target gear), 12B: second helical gear, 13A: first tooth trace (tooth trace of target gear), 13B: second tooth trace (tooth trace of second helical gear), 20A: first gear cutting tool (gear cutting tool), 20B: second gear cutting tool, 21A: first tool outer peripheral surface (tool outer peripheral surface), 21B: second tool outer peripheral surface, 22A: first cutting blade (cutting blade), 22B: second cutting blade, 23: tooth surface, A: target axis, A1: first tool axis ( Tool axis center), A2: Second tool axis center, G: Gap, M: Machining position, P1: First placement process (Placement process), P2: First machining process (Machining process), P3: Second placement process, P4: Second machining process, R1: First rotation direction (Rotation direction of the workpiece), R2: Second rotation direction (Rotation direction of the gear cutting tool), S1: First surface, S2: Second surface, X: Orthogonal direction (Direction perpendicular to the second surface), X1: Orthogonal direction first side (Specific side), Z: Target axis direction, Z1: Target axis direction first side, Z2: Target axis direction second side, α: Crossed axes angle, θ1: First angle, θ2: Second angle, θ3: Third angle, θ4: Fourth angle

Claims

1. A gear cutting method for a workpiece having two or more cylindrical outer peripheral surfaces integrally formed thereon, the two or more outer peripheral surfaces being aligned coaxially with a symmetric axis with a gap therebetween in a direction along the symmetric axis, the method comprising: forming a helical gear on at least one of the two or more outer peripheral surfaces, one of the two or more outer peripheral surfaces is a target outer peripheral surface, and the other is a non-target outer peripheral surface; a helical gear formed on the target outer peripheral surface is a target gear; a helix angle of a tooth trace of the target gear is a first angle; a gear cutting tool having a plurality of helical cutting blades formed on an outer peripheral surface of the tool, each of the tooth surfaces of the plurality of cutting blades having a helix angle of a second angle greater than the first angle, and configured to rotate around a tool axis that is the axis of the outer peripheral surface of the tool; an arrangement step of arranging the gear cutting tool so that the tool axis center is in a torsional positional relationship with respect to the symmetric axis center and so that an axis-crossing angle between the symmetric axis center and the tool axis center is equal to a difference between the second angle and the first angle; a processing step of forming the target gear on the target outer peripheral surface by moving the gear cutting tool relative to the workpiece along a symmetric axis direction that is a direction parallel to the symmetric axis center while synchronously rotating the gear cutting tool and the workpiece, within a range where the gear cutting tool does not come into contact with the non-symmetric outer peripheral surface, after the placing step; a gear machining method, wherein the second angle is set so that the plurality of cutting blades do not come into contact with the portion of the workpiece that forms the asymmetric outer peripheral surface when the plurality of cutting blades have completed machining the end of the asymmetric outer peripheral surface on the asymmetric outer peripheral surface side in the machining step.

2. A gear machining method for a workpiece having two or more cylindrical outer peripheral surfaces integrally formed and arranged coaxially with a target axis with a gap in a direction along the target axis, the method comprising the steps of: forming a helical gear on at least one of the two or more outer peripheral surfaces; one of the two or more outer peripheral surfaces is a target outer peripheral surface, and the other is a non-target outer peripheral surface; a helical gear formed on the target outer peripheral surface is a target gear; a helix angle of a tooth trace of the target gear is a first angle; a gear cutting tool having a plurality of helical cutting blades formed on an outer peripheral surface of the tool, each of the tooth surfaces of the plurality of cutting blades having a helix angle of a second angle greater than the first angle, and configured to rotate around a tool axis that is the axis of the outer peripheral surface of the tool; an arrangement step of arranging the gear cutting tool so that the tool axis center is in a torsional positional relationship with respect to the symmetric axis center and so that an axis-crossing angle between the symmetric axis center and the tool axis center is equal to a difference between the second angle and the first angle; a machining step of forming the target gear on the target outer peripheral surface by moving the gear cutting tool relative to the workpiece along a symmetric axis direction that is parallel to the symmetric axis while synchronously rotating the gear cutting tool and the workpiece, within a range in which the gear cutting tool does not come into contact with the non-symmetric outer peripheral surface, among the two or more outer peripheral surfaces, the target outer peripheral surface being designated as a first outer peripheral surface, and the non-symmetric outer peripheral surface being designated as a second outer peripheral surface; the target gear is a first helical gear, the helical gear formed on the second outer peripheral surface is a second helical gear, and a helix angle of the tooth trace of the second helical gear is a third angle; The gear cutting tool is a first gear cutting tool, the cutting blade is a first cutting blade, the tool outer peripheral surface is a first tool outer peripheral surface, and the tool axis is a first tool axis, a second gear cutting tool having a plurality of helical second cutting blades formed on an outer peripheral surface of the second tool, the helix angle of each tooth surface of the plurality of second cutting blades being a fourth angle greater than the third angle, and configured to rotate around a second tool axis center which is the axis center of the outer peripheral surface of the second tool; a second arrangement step of arranging the second gear cutting tool so that the second tool axis center is in a twisted positional relationship with respect to the symmetric axis center and so that an axis-crossing angle between the symmetric axis center and the second tool axis center is a difference between the fourth angle and the third angle; a second machining step of forming the second helical gear on the second outer peripheral surface by moving the second gear cutting tool relative to the workpiece along the axial direction of the target object within a range where the second gear cutting tool does not come into contact with the first outer peripheral surface while rotating the second gear cutting tool and the workpiece synchronously after the second placement step.

3. A gear machining method for a workpiece having two or more cylindrical outer peripheral surfaces integrally formed thereon and arranged coaxially with a target axis with a gap in a direction along the target axis, the method comprising the steps of: forming a helical gear on at least one of the two or more outer peripheral surfaces; one of the two or more outer peripheral surfaces is a target outer peripheral surface, and the other is a non-target outer peripheral surface; a helical gear formed on the target outer peripheral surface is a target gear; a helix angle of a tooth trace of the target gear is a first angle; a gear cutting tool having a plurality of helical cutting blades formed on an outer peripheral surface of the tool, each of the tooth surfaces of the plurality of cutting blades having a helix angle of a second angle greater than the first angle, and configured to rotate around a tool axis that is the axis of the outer peripheral surface of the tool; an arrangement step of arranging the gear cutting tool so that the tool axis center is in a torsional positional relationship with respect to the symmetric axis center and so that an axis-crossing angle between the symmetric axis center and the tool axis center is equal to a difference between the second angle and the first angle; a machining step of forming the target gear on the target outer peripheral surface by moving the gear cutting tool relative to the workpiece along a target axis direction that is a direction parallel to the target axis center while synchronously rotating the gear cutting tool and the workpiece, within a range where the gear cutting tool does not come into contact with the non-target outer peripheral surface, and the position where the cutting blade cuts the target outer peripheral surface is defined as a machining position; a plane including the symmetric axis center and arranged parallel to any plane including the tool axis center is defined as a first plane; a plane including the symmetric axis center and perpendicular to the first plane is defined as a second plane; and one side in a direction perpendicular to the second plane is defined as a specific side; a side on which the gear cutting tool moves relative to the workpiece along the target axis direction in the machining step is defined as a first side in the target axis direction, and an opposite side is defined as a second side in the target axis direction, In the positioning step, the gear cutting tool is positioned in an orientation in which the tool axis center moves toward the specific side as it moves toward the second side in the target axis direction, and the machining position is located on the specific side with respect to the second surface.

4. A gear machining method for a workpiece having two or more cylindrical outer peripheral surfaces integrally formed thereon and arranged coaxially with a target axis with a gap in a direction along the target axis, the method comprising the steps of: forming a helical gear on at least one of the two or more outer peripheral surfaces; one of the two or more outer peripheral surfaces is a target outer peripheral surface, and the other is a non-target outer peripheral surface; a helical gear formed on the target outer peripheral surface is a target gear; a helix angle of a tooth trace of the target gear is a first angle; a gear cutting tool having a plurality of helical cutting blades formed on an outer peripheral surface of the tool, each of the tooth surfaces of the plurality of cutting blades having a helix angle of a second angle greater than the first angle, and configured to rotate around a tool axis that is the axis of the outer peripheral surface of the tool; an arrangement step of arranging the gear cutting tool so that the tool axis center is in a torsional positional relationship with respect to the symmetric axis center and so that an axis-crossing angle between the symmetric axis center and the tool axis center is equal to a difference between the second angle and the first angle; After the placing step, a machining step is carried out in which the gear cutting tool and the workpiece are rotated synchronously, while the gear cutting tool is moved relative to the workpiece along a symmetric axis direction that is a direction parallel to the symmetric axis center, within a range in which the gear cutting tool does not come into contact with the non-symmetric outer peripheral surface, thereby forming the target gear on the target outer peripheral surface, and the side on which the gear cutting tool moves relative to the workpiece along the symmetric axis direction in the machining step is defined as a first symmetric axis direction side, and the opposite side is defined as a second symmetric axis direction side, The tooth trace of the target gear is inclined in a direction toward the front side in the rotation direction of the workpiece as it moves toward the first side in the target axis direction, and the inclination angle of the tooth trace of the target gear with respect to the target axis center is defined as a tooth trace inclination angle, a tooth surface of the cutting blade that is inclined toward the front side in the rotation direction of the gear cutting tool as it approaches the first side in the target axis direction, and an inclination angle of the tooth surface of the cutting blade with respect to the tool axis center is greater than the tooth trace inclination angle.

5. A gear device having a helical gear formed on at least one of the two or more outer peripheral surfaces by the gear cutting method according to any one of claims 1 to 4.

6. A gear cutting tool for forming a helical gear on at least one of two or more cylindrical outer peripheral surfaces of a workpiece integrally formed with the two or more cylindrical outer peripheral surfaces arranged coaxially with a symmetrical axis and with a gap in a direction along the symmetrical axis, the gear cutting tool comprising: one of the two or more outer peripheral surfaces is a target outer peripheral surface, and the other is a non-target outer peripheral surface; a helical gear formed on the target outer peripheral surface is a target gear; a helix angle of a tooth trace of the target gear is a first angle; a plurality of helical cutting blades are formed on the outer peripheral surface of the tool, and the helix angle of the tooth surface of each of the plurality of cutting blades is a second angle that is larger than the first angle, and the tool is configured to rotate around a tool axis that is the axis of the outer peripheral surface of the tool; the second angle is set so that the plurality of cutting blades do not come into contact with a portion of the workpiece that forms the asymmetric outer peripheral surface when the cutting blades have completed processing of the end of the asymmetric outer peripheral surface on the asymmetric outer peripheral surface side, a gear cutting tool for forming the target gear on the target outer peripheral surface by rotating the tool synchronously with the workpiece while moving it relatively to the workpiece along a symmetric axis direction that is a direction parallel to the symmetric axis, within a range where it does not come into contact with the non-symmetric outer peripheral surface, while being positioned so that the tool axis center is in a torsional positional relationship with the symmetric axis center and so that an axis crossing angle between the symmetric axis center and the tool axis center is the difference between the second angle and the first angle.

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