Method of manufacturing gear

Abstract

To provide a method for manufacturing a gear capable of shortening an incompletely machined part.SOLUTION: Rotating a rod-shaped workpiece W about a first axis A1, and rotating a cutter 20 provided with a cutting edge 201 on an outer peripheral portion about a second axis A1 at a twisted position with respect to the first axis A2; The method includes forming the spiral grooves 301 on the outer peripheral surface of the workpiece W by the cutting edges 201 of the tools 20 while relatively moving the workpiece W and the tools 20 in a direction parallel to the first axis A1 at a speed synchronized with a rotation speed of the workpiece W, wherein a diameter DF of a rolling circle CF where a contour line OE of the tools 20 and a target contour line of the gears 30 or an extension line OG of the target contour line are in rolling contact with each other is equal to or larger than a diameter DT of an addendum circle CT in a cross section perpendicular to the first axis A1.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a gear. [Background technology]

[0002] Conventionally, whirling has been known as a method for manufacturing gears and screws, as disclosed in Patent Document 1. Whirling is a machining method for forming spiral grooves such as tooth grooves and screw grooves on the outer periphery of a rod-shaped workpiece by cutting the outer periphery of the workpiece with the inner periphery of an annular whirling cutter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2011 / 078365 Summary of the Invention

[0004] (Problem to be solved by the invention) However, whirling produces portions at both ends of the workpiece where the tooth grooves or thread grooves are not formed, and portions where the formed tooth grooves or thread grooves are incomplete (hereinafter, sometimes referred to as "incompletely machined portions"). Specifically, because the axis of the whirling cutter is not parallel to the axis of the workpiece but is inclined (see FIG. 1 of Patent Document 1), when the whirling cutter approaches the chuck or center (tailstock), the outer periphery of the whirling cutter interferes with the chuck or center. As a result, the machining point (the point where the whirling cutter contacts the workpiece) cannot be brought close to the chuck or center, and both ends of the workpiece (more specifically, the portions near the portion gripped by the chuck and the portion near the portion supported by the center) cannot be machined. As a result, these portions of the workpiece cannot be machined, and the incompletely machined portions described above occur.

[0005] The tilt angle of the whirling cutter's axis relative to the workpiece's axis is affected by the lead angle of the grooves (tooth grooves or screw grooves) to be formed in the workpiece. The larger the lead angle, the larger the tilt angle, which results in a longer imperfectly machined area. Therefore, the larger the lead angle of the gear or screw being manufactured, the longer the imperfectly machined area, resulting in greater waste of workpiece.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and one of its objects is to shorten the length of imperfectly machined portions that occur at both ends of a workpiece in a gear manufacturing method in which a gear is manufactured by forming spiral tooth grooves (or, alternatively, forming protruding teeth) in a rod-shaped workpiece.

[0007] (Means for solving the problem) The method for manufacturing a gear of the present invention includes the steps of: A method for manufacturing a gear, comprising the steps of: rotating a rod-shaped workpiece about a first axis; rotating a tool having cutting edges on an outer periphery about a second axis that is twisted relative to the first axis; and moving the workpiece and the tool relatively in a direction parallel to the first axis at a speed synchronized with the rotational speed of the workpiece, while bringing the cutting edges of the tool into contact with the outer periphery of the workpiece; and removing material of the workpiece at the contacting points by the relative movement between the tool and the workpiece, thereby forming spiral tooth grooves on the outer periphery of the workpiece, rotating the workpiece about the first axis and relatively moving the workpiece and the tool in a direction parallel to the first axis at a speed synchronized with the rotational speed of the workpiece so that, in a plane perpendicular to the first axis, a contour line of a cutting edge of the tool comes into rolling contact without slipping with a target contour line, which is a contour line of the spiral tooth groove to be formed, at a predetermined point on the target contour line or an extension line of the target contour line, and rotates while sliding with respect to the target contour line or the extension line at points other than the predetermined point; In a plane perpendicular to the first axis, the diameter of a first circle, which is a circle centered on the first axis and passing through the specified point, is between 1 and 1.5 times the diameter of a second circle, which is a tip circle of a gear manufactured from the contour line of the workpiece and centered on the first axis.

[0008] According to the present invention, the angle (axis inclination angle) between the first axis and the second axis projected onto a plane that includes the first axis and is parallel to the second axis can be reduced. Therefore, when the tool is moved in a direction parallel to the first axis, interference between the member that holds the end of the workpiece and the outer periphery of the tool can be prevented or suppressed. Therefore, during gear manufacturing, the distance between the tool and the member that holds the end of the workpiece can be reduced, thereby shortening the portions where no tooth grooves are formed and the incompletely machined portions. [Brief explanation of the drawings]

[0009] [Figure 1A] FIG. 1A is a perspective view showing an example of a gear to be manufactured. [Figure 1B] FIG. 1B is a cross-sectional view showing an example of a gear to be manufactured. [Figure 2A] FIG. 2A is a perspective view showing an example of the configuration of a gear manufacturing apparatus. [Figure 2B] FIG. 2B is a top view showing an example of the configuration of a gear manufacturing apparatus. [Figure 3] FIG. 3 is a diagram showing the movement trajectory of the cutting edge relative to the workpiece. [Figure 4] FIG. 4 is a side view showing an example of a gear to be manufactured. [Figure 5A] FIG. 5A is a schematic diagram showing the shape of a cutting edge of a conventional tool. [Figure 5B] FIG. 5B is a schematic diagram showing the shape of the cutting edge of the tool according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Hereinafter, a gear manufacturing method may be simply referred to as a manufacturing method. In this embodiment, a manufacturing method for a gear 30 is described using a rod-shaped workpiece W made of metal as a starting material. In this embodiment, an example is shown in which the workpiece W is a round bar-shaped (or cylindrical) member, but the workpiece W may be any rod-shaped member and is not limited to a round bar-shaped member. The workpiece W may also be a solid bar-shaped member or a hollow bar-shaped member. However, it is preferable that the workpiece W be a columnar or cylindrical member whose outer diameter is the same as the tip circle of the gear to be manufactured.

[0011] 1A and 1B are diagrams showing an example of a gear 30 manufactured by the manufacturing method according to this embodiment. FIG. 1A is a perspective view of the gear 30, and FIG. 1B is a cross-sectional view of the gear 30 cut along a plane perpendicular to the axial direction. The gear 30 manufactured by the manufacturing method according to this embodiment is a helical gear having a module of 0.3 to 2.0, the number of teeth 302 (hereinafter referred to as the number of teeth) of 1 to 4, and a helix angle of 30° to 60°. FIGS. 1A and 1B show a helical gear with two teeth and a helix angle of 45°. Also, in FIG. 1B, a circle C B indicates the root circle, and circle C C indicates the tooth height center circle, and circle C T indicates the tip circle. Tip circle C T is an example of the second circle of the present invention. In this embodiment, the outer peripheral surface of the workpiece W (the contour line as viewed in the axial direction) is formed on the tooth tip (tooth tip circle C T ) In other words, the outer diameter of the workpiece W and the tip circle C T The diameters are the same.

[0012] 2A and 2B are schematic diagrams illustrating an example of the configuration of essential parts of an apparatus 10 capable of implementing the manufacturing method according to this embodiment. FIG. 2A is a perspective view of the essential parts of the apparatus 10, and FIG. 2B is a top view of the essential parts of the apparatus 10. A gear cutting machine, such as a gear splitter, capable of manufacturing a gear 30 using a single cutter as the tool 20 can be applied to the apparatus 10. The single cutter as the tool 20 has a substantially circular disk shape and is provided with multiple cutting edges 201 arranged circumferentially on its outer periphery. The shape of the cutting edges 201 of the tool 20 will be described later. As shown in FIG. 2A, the apparatus 10 includes a chuck 11, a center 12, a tailstock 13, and a tool holder 14 that holds the tool 20. The chuck 11 is configured to support (grasp) one axial end of the workpiece W, which is a columnar or cylindrical member. The center 12 and the tailstock 13 are configured to support the end of the workpiece W opposite the one axial end. The tool holder 14 is configured to hold a tool 20 .

[0013] The apparatus 10 further includes a rotational power source (not shown). The apparatus 10 is configured to rotate the chuck 11 and the tool holder 14 using the rotational power source. The rotational center line A1 of the chuck 11 (which can also be referred to as the rotational center line (axial line) of the workpiece W supported by the chuck 11) is referred to as the first axis line A1, and the rotational center line A2 of the tool holder 14 (which can also be referred to as the rotational center line of the tool 20) is referred to as the second axis line A2. The first axis line A1 and the second axis line A2 are skewed. That is, the first axis line A1 and the second axis line A2 are not parallel to each other and do not intersect. Therefore, when the second axis line A2 is projected onto a "plane including the first axis line A1 and parallel to the second axis line A2" in a direction perpendicular to this plane, the first axis line A1 and the projected second axis line A2 extend in different directions. That is, as shown in Figure 2B, in this plane, the first axis A1 and the projected second axis A2 are inclined to each other at a predetermined angle θ that is not 0°. This predetermined angle θ (where the smaller angle between the first axis A1 and the second axis A2) is referred to as the axis inclination angle θ. This plane may also be referred to as a projection plane.

[0014] The device 10 is configured so that, with the workpiece W held in the chuck 11, the workpiece W and the tool holder 14 can be moved relatively in a direction parallel to the first axis A1 at a speed synchronized with the rotational speed of the chuck 11 (i.e., the rotational speed of the workpiece W). Note that the device 10 may be configured so that the chuck 11, the center 12, and the tailstock 13 are linearly movable in a direction parallel to the first axis A1, or so that the tool holder 14 is linearly movable in a direction parallel to the first axis A1, or so that both the chuck 11, the center 12, and the tailstock 13 and the tool holder 14 are linearly movable in a direction parallel to the first axis A1.

[0015] The device 10 is configured so that, with the workpiece W held in the chuck 11, the outer peripheral surface of the workpiece W can be cut by the cutting edge 201 (the outer peripheral portion of the tool 20) of the tool 20 held in the tool holder 14. Since the first axis A1 and the projected second axis A2 are in a torsional relationship, tooth grooves 301 are formed on the outer peripheral surface of the workpiece W, which are inclined at an angle corresponding to the magnitude of the axis inclination angle θ with respect to the direction perpendicular to the axis of the workpiece W (i.e., the first axis A1).

[0016] Here, the operation of the apparatus 10 when manufacturing the gear 30 will be described. With the workpiece W supported by the chuck 11 and tailstock 13, the workpiece W is rotated about the first axis A1. As shown in FIG. 2B , the position of the tool 20 is adjusted so that the center of the tool 20 on the projection plane is aligned with the first axis A1. After that, with the tool 20 attached to the tool holder 14, the tool holder 14 is rotated about the second axis A2. The workpiece W and the tool holder 14 (tool 20) are then moved relative to each other in a direction parallel to the first axis A1 at a speed synchronized with the rotational speed of the workpiece W. Specifically, the relative speed between the workpiece W and the tool holder 14 is the speed at which the workpiece W and the tool holder 14 move relative to each other over a distance equal to the number of teeth of the gear 30 to be manufactured multiplied by the distance between adjacent teeth 302 in the direction of the first axis A1 (or the distance between tooth spaces 301) per rotation of the workpiece W.

[0017] Then, by bringing the cutting edges 201 (the outer periphery of the tool 20) of the rotating tool 20 into contact with the outer periphery of the workpiece W, material of the workpiece W is removed at the contact points. As a result, tooth grooves 301 extending in a direction inclined relative to the first axis A1 at an angle corresponding to the axis inclination angle θ are formed on the outer periphery of the workpiece W. Then, the workpiece W and the tool holder 14 are moved relative to each other in a direction parallel to the first axis A1 at a speed synchronized with the rotational speed of the workpiece W, thereby forming spiral tooth grooves 301 on the outer periphery of the workpiece W, and as a result, spiral teeth 302 (spiral protrusions) are formed on the outer periphery of the workpiece W. In this way, a helical gear is manufactured.

[0018] The tool 20 attached to the tool holder 14 and the chuck 11 can move relatively in a direction parallel to the first axis A1 without coming into contact with each other. As shown in FIG. 2B , the projected second axis A2 is inclined at an axis inclination angle θ with respect to the first axis A1 on the projection plane. Therefore, even if the tool holder 14 is moved closest to the chuck 11 without bringing the outer periphery S2 of the tool 20 into contact with the chuck 11, the position S1 where the cutting edge 201 of the tool 20 actually cuts the workpiece W is located a distance M1 away from the chuck 11. In other words, the tooth groove 301 cannot be formed in the workpiece W within the distance M1 from the position S1 where the cutting edge 201 of the tool 20 comes into contact.

[0019] As is clear from FIG. 2B, as the axis inclination angle θ increases, the distance M1 also increases. Therefore, as the axis inclination angle θ increases, the portion of the workpiece W where the tooth space 301 cannot be formed becomes longer. Furthermore, as the axis inclination angle θ increases, the incompletely machined portion (the portion where the shape of the tooth 302 is incomplete at the end of the range where the tooth space 301 is formed) becomes longer. GIn particular, when manufacturing a helical gear with a helix angle of 30° or more and 60° or less, as in this embodiment, the axis inclination angle θ must be larger than when manufacturing a general male thread for fastening, which makes the above-mentioned problems more likely to occur. Therefore, in this embodiment, the axis inclination angle θ is reduced by the following configuration.

[0020] FIG. 3 shows a contour line O of the cutting edge 201 in a cross section perpendicular to the first axis A1 when the workpiece W is assumed to be fixed. E The movement trajectory T U (That is, the contour line O of the cutting edge 201 of the tool 20 relative to the workpiece W E The movement trajectory T U ) is a schematic diagram showing the cutting edge 201 of the tool 20 when the workpiece W is assumed to be fixed. E is the target contour O of the tooth 302 of the gear 30. G While in contact with the target contour line O (which refers to the design contour line of the teeth 302 of the gear 30 to be manufactured) or its extension, the target contour line O moves within this cross section while rotating around a straight line parallel to the first axis A1 (a straight line perpendicular to the paper surface in FIG. 3) relative to the workpiece W. G If is an involute curve, its extension is also an involute curve. G " refers to the target contour line and its extension line. Note that the movement trajectory T of the cutting edge 201 in this cross section U is a hypocycloid curve.

[0021] Contour line O of cutting edge 201 of tool 20 E When moving within this cross section, the contour line O of the cutting edge 201 E The target contour line O of the tooth 302 is G In other words, there is a point R where the cutting edge 201 makes rolling contact with the contour line O E is the target contour O G While touching the target contour O G At a given point R on the target contour line O GIt makes rolling contact with the target contour line O without slipping and at a predetermined point R. G Hereinafter, the circle that passes through the point R of rolling contact with the first axis A1 as its center in the plane perpendicular to the first axis A1 will be referred to as the "rolling circle C" F " Rolling circle C F is sometimes called the "reference circle" when machining using a single cutter or a whirling cutter. This rolling circle C F is an example of the first circle of the present invention.

[0022] In a manufacturing method using a disc-shaped tool 20 having a cutting edge 201 on the outer periphery, such as a single cutter, the axis inclination angle θ is F Diameter D F Therefore, in this embodiment, the axis inclination angle θ is determined based on the rolling circle C F Diameter D F Specifically, the axis inclination angle θ is determined based on the number N of the spiral teeth 302 formed on the workpiece W, the spacing P of the spiral tooth grooves 301 (or teeth 302 (i.e., spiral protrusions)) formed on the workpiece W in the direction parallel to the first axis A1, and the rolling circle C F More specifically, the axis inclination angle θ is defined by the following equation (3): θ=tan -1 ((N×P) / L1) Formula (3) N: Number of tooth grooves 301 formed in the workpiece W (= number of teeth of the gear 30 to be manufactured) P: Spacing of tooth spaces 301 formed in the workpiece W in a direction parallel to the first axis A1 L1: Rolling circle C F Diameter D F × Pi (= rolling circle C F perimeter of

[0023] As is clear from the above formula (3), the axis inclination angle θ is F Diameter D FIn conventional whirling and single cutter machining, the rolling circle C F Diameter D F is the tip circle C T Diameter D T More specifically, the rolling circle C F Diameter D F is the rolling circle C F In contrast, in this embodiment, the rolling circle C F Diameter D F and addendum circle C T Diameter D T This makes the rolling circle C F Diameter D F is the tip circle C T Diameter D T In comparison with the conventional configuration in which the axial inclination angle θ is less than 1.0 times the angle θ, the axial inclination angle θ can be made smaller.

[0024] FIG. 4 is a side view showing an example of a gear 30 to be manufactured, and is a diagram showing a schematic diagram of the helix angle of the gear 30. The helix angle is the angle between the axial direction of the gear 30 (the direction parallel to the first axis A1) and the extension direction of the tooth grooves 301 or teeth 302. In FIG. 4, β B is the helix angle at the tooth root, and β C indicates the helix angle at the center of the tooth, and β T indicates the helix angle at the tooth tip, and β F is the rolling circle C F As is clear from FIG. 4, the helix angle at each portion of the gear 30 decreases from the tooth root to the tooth tip. The rolling circle C of the manufactured gear 30 is F Twist angle β in F teeth, (Twist angle β F (°))+(Axis inclination angle θ(°))=90(°) Therefore, the rolling circle C F Diameter D F If you increase the rolling circle C FTwist angle β at the position F Since the value of becomes larger, the value of the axis inclination angle θ becomes smaller.

[0025] 2B can be reduced by reducing the axis inclination angle θ. That is, interference between the chuck 11 and the tool 20 can be reduced when the workpiece W and the tool 20 are moved relatively in a direction parallel to the first axis A1. Therefore, the length of the portion of the workpiece W where the tooth grooves 301 cannot be formed can be reduced. Furthermore, by reducing the axis inclination angle θ, the length of the incompletely machined portion (the portion that does not have the desired shape, in other words, the designed shape) where the shape of the teeth 302 (tooth grooves 301) of the gear 30 to be formed is incomplete can be reduced.

[0026] In particular, the lead angle of a helical gear (= 90 (°) - (helix angle (°) of gear 30)) is larger than the lead angle of a typical fastening screw, so the axis inclination angle θ must be larger than when manufacturing a fastening screw. According to this embodiment, the axis inclination angle θ can be made smaller when manufacturing a helical gear.

[0027] On the other hand, rolling circle C F Diameter D F If the error is large, the gear accuracy of the formed gear 30, particularly at the tooth root, may decrease for the following reason. The tooth profile error specified in JIS B1702:1998, for example, is used as an index of gear accuracy. Specifically, the surface shape of the tooth grooves 301 (which can also be referred to as the surface shape of the teeth 302) is a transcription of the shape of the side of the cutting edge 201 of the tool 20 (in other words, the contour shape of the rake face 202 of the tool 20). Therefore, when viewed in a direction perpendicular to the projection plane (viewed in a direction perpendicular to the paper in FIG. 4 ), the gear accuracy can be maximized when the extension direction of the tooth grooves 301 and the extension direction of the path of the cutting edge 201 of the tool 20 (i.e., the straight line T perpendicular to the second axis A2) are parallel. Conversely, the gear accuracy decreases as the difference in angle between the extension direction of the tooth grooves 301 and the extension direction of the path of the cutting edge 201 of the tool 20 increases. As mentioned above, the helix angle of the gear 30 is smallest at the tooth root, so the rolling circle C FTwist angle β in F (the angle between the line T perpendicular to the second axis and the first axis A1 on the projection plane) and the helix angle β at the tooth root B The difference angle η between the rolling circle C F Twist angle β in F and the helix angle of the part other than the tooth bottom. Therefore, the gear accuracy at the tooth bottom is F Root circle C of B As the distance from the center increases, the gear accuracy is more likely to decrease compared to other parts.

[0028] In the past, in order to prevent such a problem, as described above, the rolling circle C F Rolling circle C passes through the center of the tooth or its vicinity. F Diameter D F With this configuration, the rolling circle C F Twist angle β in F and helix angle β at the tooth root B The difference angle η between the rolling circle C F Twist angle β in F and helix angle β at the tooth tip T This reduces the angle of difference between the axial inclination angle θ and the rake face 202 of the cutting edge 201. This results in a closer profile between the cutting edge 201 (in other words, the shape of the cutting edge 201 when viewed in a direction perpendicular to the rake face 202 of the cutting edge 201) and the cross-sectional shape of the tooth groove 301 (the cross-sectional shape cut by a plane perpendicular to the extension direction of the tooth groove 301 at the center of the tooth depth). This prevents or suppresses a decrease in gear accuracy. However, with such a conventional configuration, the axis inclination angle θ cannot be reduced, resulting in a longer incompletely machined portion.

[0029] In this embodiment, the rolling circle C F Diameter D F tooth tip circle C T Diameter D TThis configuration makes it possible to prevent or suppress a decrease in gear accuracy. In other words, it is possible to reduce the axis inclination angle θ (shorten the imperfectly machined portion) while preventing or suppressing a decrease in gear accuracy. In other words, it is possible to achieve both a reduction in the imperfectly machined portion and prevention or suppression of a decrease in gear accuracy.

[0030] As shown in Figure 4, the rolling circle C F Twist angle β in F is the helix angle β at the tooth tip T (The helix angle β at the tooth bottom B or helix angle β at the center of the tooth C (It can be said that this is the case), and the helix angle β at the tooth height center C It is preferable that the magnitude of the angle is equal to or less than +25°. This relationship can also be expressed by the following formulas (1) and (2). 90° - (axis inclination angle θ (°)) ≥ (helix angle at tooth tip β T (°)) Formula (1) 90 (°) - (axis inclination angle θ (°)) ≦ (helix angle β at the center of the tooth depth of the tooth groove 301 to be formed) C (°))+25(°) Formula (2)

[0031] As mentioned above, rolling circle C F Twist angle β in F (=90(°)-axis inclination angle θ(°)) and the helix angle β of the tooth space 301 at the tooth bottom B As the difference angle η between the rolling circle C and the rolling circle C increases, the gear accuracy at the tooth bottom decreases. F Twist angle β in F By defining as above, it is possible to prevent or suppress the deterioration of gear accuracy at the tooth bottom. In this case, the rolling circle C F Diameter D F The lower limit of "tooth tip circle C T Diameter D T 1.0 times" and "Rolling circle C F Twist angle β in F The helix angle β at the center of the tooth depth of the tooth space 301C The larger value of the diameter that makes the same angle as the rolling circle C is applied. F Diameter D F The upper limit of "tooth tip circle C T Diameter D T 1.5 times" and "Rolling circle C F Twist angle β in F is the helix angle β at the center of the tooth C +25°" or "diameter that results in the same angle as +25°", whichever is smaller.

[0032] Furthermore, in this embodiment, the cross-sectional shape of the cutting edge 201 of the tool 20 is configured as follows to prevent or suppress a decrease in gear accuracy. FIG. 5A is a schematic diagram showing the shape of the cutting edge 201 of the conventional tool 90, and FIG. 5B is a schematic diagram showing the shape of the cutting edge 201 of the tool 20 according to this embodiment. Both FIGS. 5A and 5B are cross-sectional views of the cutting edge 201 taken along a plane including the second axis A2 with the tools 20 and 90 attached to the tool holder 14. As shown in FIGS. 5A and 5B, the cross-sectional shape of the cutting edge 201 taken along a plane including the second axis A2 has a tapered shape in which the width (dimension in a direction parallel to the second axis A2) decreases toward the outer periphery (as the distance from the second axis A2 increases) for both the conventional tool 90 and the tool 20 of this embodiment.

[0033] When manufacturing helical gears with the same specifications, the width of the cutting edge 201 of the tool 20 of this embodiment (more specifically, the width of the cutting edge 201 at a position at the same distance from the second axis A2 in a plane including the second axis A2) is smaller than the width of the cutting edge 201 of the conventional tool 90. Furthermore, when manufacturing helical gears with the same specifications, comparing the tool pressure angles (more specifically, the tool pressure angles at a position at the same distance from the second axis A2) between the tool 20 of this embodiment and the conventional tool 90, the tool pressure angle α1 of the tool 20 of this embodiment is smaller than the tool pressure angle α2 of the conventional tool 90. Note that the tool pressure angles α1 and α2 are the angles formed by the line Q and the tangent to the contour line of the cutting edge 201 at the intersection of the line Q perpendicular to the second axis A2 and the contour line of the cutting edge 201 in a plane including the second axis A2. Furthermore, the conventional tool 90 has a rolling circle C F Diameter D F is the tip circle C T Diameter D T If it is less than 1.0 times the tooth height center circle C C Diameter D C The upper and lower limits of the tool pressure angle α1 are not particularly limited, but are actually determined by the axis inclination angle θ and the shape and dimensions of the teeth 302 of the gear 30 to be manufactured.

[0034] With this configuration, it is possible to prevent or suppress a decrease in the gear precision of the manufactured gear 30.

[0035] The fewer the number of teeth on gear 30, the smaller the rolling circle C F Diameter D F Therefore, the fewer the number of teeth, for example, when the number of teeth is one to four as in this embodiment, the easier it is to reduce the axis inclination angle θ.

[0036] Furthermore, the smaller the number of teeth and the smaller the module, the smaller the pitch circle diameter of the gear 30. The smaller the pitch circle diameter, the smaller the rolling circle C F Diameter D FTherefore, when the module is in a small range, for example, when the module is in a range of 0.3 to 2.0 as in this embodiment, the axis inclination angle θ can be easily reduced.

[0037] Furthermore, according to this embodiment, compared to a method of manufacturing the gear 30 by whirling, it is possible to improve gear accuracy at the tooth root (reduce tooth profile error). That is, in whirling, the workpiece W is cut on the inner periphery of a circular tool (wirling cutter), so the workpiece W and the cutting edge 201 come into contact over a certain length. Therefore, even when a "specific point (machining point)" is machined with the cutting edge 201 of the tool 20, machining is performed over a certain range before and after the specific point (machining point). Therefore, "unwanted machining" is performed over a certain range before and after the specific point, resulting in reduced machining accuracy (gear accuracy). In contrast, according to this embodiment, the workpiece W is cut with the cutting edge 201 provided on the outer periphery of the circular tool 20, so the contact length between the cutting edge 201 and the workpiece W can be shortened. Therefore, the range where "unwanted machining" is performed can be reduced, thereby improving gear accuracy.

[0038] <Summary of the embodiment> (1) The manufacturing method of the gear 30 according to this embodiment is as follows: A method for manufacturing a gear (30) comprising the steps of: rotating a rod-shaped workpiece (W) about a first axis (A1); rotating a tool (20) having a cutting edge (201) on an outer periphery about a second axis (A2) that is twisted relative to the first axis (A1); and moving the workpiece (W) and the tool (20) relatively in a direction parallel to the first axis (A1) at a speed synchronized with the rotation speed of the workpiece (W), while bringing the cutting edge (201) of the tool (20) into contact with the outer periphery of the workpiece (W); and removing material of the workpiece (W) at the contacting portion by the relative movement between the tool (20) and the workpiece (W), thereby forming a spiral tooth groove (301) on the outer periphery of the workpiece (W), In a plane perpendicular to the first axis A1, the contour line of the cutting edge 201 of the tool 20 coincides with the target contour line O, which is the contour line of the spiral tooth groove 301 to be formed. G or the target contour line O G At a predetermined point R on the extension line of the target contour line O G Alternatively, the target contour line O may be in rolling contact with the extension line without sliding, and may be in contact with the target contour line O at points other than the predetermined point R. G Alternatively, the workpiece W is rotated about the first axis A1 so as to rotate while sliding relative to the extension line, and the workpiece W and the tool 20 are moved relative to each other in a direction parallel to the first axis A1 at a speed synchronized with the rotation speed of the workpiece W, In a plane perpendicular to the first axis A1, a first circle (rolling circle C) is a circle that has the first axis A1 as its center and passes through the predetermined point R. F ) diameter D F is the addendum circle C of the gear manufactured from the workpiece W, centered on the first axis A1. T The second circle (tooth tip circle C T ) diameter D T It is between 1 and 1.5 times the original value.

[0039] According to this embodiment, it is possible to reduce the axis inclination angle θ, which is the angle between the first axis A1 and the second axis A2 projected onto a plane that includes the first axis A1 and is parallel to the second axis. Therefore, when the tool 20 is moved in a direction parallel to the first axis A1, interference between the tool 20 and the member (chuck 11) that holds the end of the workpiece W can be prevented or suppressed, so that the tool 20 can be moved near the end of the workpiece W (near the member that holds the workpiece W). Therefore, it is possible to shorten the incompletely machined portion.

[0040] (2) In the manufacturing method of the gear 30 according to this embodiment, The magnitude of the axis inclination angle θ, which is the angle between the first axis A1 and the second axis A2 projected onto a plane that includes the first axis A1 and is parallel to the second axis A2, satisfies the following formulas (1) and (2). 90 (°) - (axis inclination angle θ (°)) ≧ (helix angle (°) at the tip of the tooth groove 301 to be formed) Formula (1) 90 (°) - (axis inclination angle θ (°)) ≦ (helix angle (°) at the center of the tooth depth of the tooth groove 301 to be formed) + 25 (°) Formula (2)

[0041] With this configuration, the imperfectly machined portion can be shortened, and a decrease in the precision of the manufactured gear 30 can be prevented or suppressed. F Twist angle β in F is the helix angle β at the tooth tip T (The helix angle β at the tooth bottom B or helix angle β at the center of the tooth C (It can be said that this is the case), and the helix angle β at the tooth height center C It can also be said that the magnitude is less than or equal to +25°.

[0042] (3) In the manufacturing method of the gear 30 according to this embodiment, The gear 30 to be manufactured has one to four teeth.

[0043] The fewer the number of teeth of the gear 30 to be manufactured, the shorter the first circle (rolling circle C F ) diameter D F Therefore, the effect of reducing the axis inclination angle θ increases as the number of teeth decreases, specifically, when the number of teeth is one to four as in this embodiment.

[0044] (4) The module of the gear 30 to be manufactured is 0.3 or more and 2.0 or less. A manufacturing method of the gear 30.

[0045] The smaller the module, the smaller the pitch diameter of the gear. And the smaller the pitch diameter, the smaller the rolling circle C F Diameter D FTherefore, when the module is in a small range, specifically, when the module is in a range of 0.3 or more and 2.0 or less as in this embodiment, the effect of reducing the axis inclination angle θ is increased.

[0046] (5) In the manufacturing method of the gear 30 according to this embodiment, The tool 20 is a single cutter.

[0047] According to this configuration, in the manufacturing method of the gear 30 using a single cutter, the incompletely machined portion can be shortened.

[0048] Although the embodiments and modifications of the present invention have been described above, the technical scope of the present invention is not limited to the above-described embodiments and modifications. The present invention can be modified within the scope of the spirit thereof, and such modifications are also included within the technical scope of the present invention.

[0049] For example, in the above embodiment, an example was shown in which a helical gear with two teeth and a 45° helix angle was manufactured, but the number of teeth and helix angle of the gear 30 to be manufactured are not limited to those in the above embodiment. Furthermore, the shape of the teeth 302 of the gear 30 to be manufactured is not limited either.

[0050] Furthermore, in the present embodiment, a configuration in which a single cutter is used as the tool 20 has been shown, but the tool 20 is not limited to a single cutter. For example, a hob cutter may be used as the tool. [Explanation of symbols]

[0051] 10...Apparatus capable of carrying out the gear manufacturing method according to this embodiment, 20...Tool (single cutter), 201...Cutting edge of the tool, 30...Gear manufactured by the gear manufacturing method according to this embodiment, 301...Gear tooth groove, 302...Gear tooth, W...Workpiece, A1...First axis, A2...Second axis

Claims

1. A method for manufacturing a gear, comprising: rotating a rod-shaped workpiece about a first axis; rotating a tool having cutting edges on an outer periphery about a second axis that is twisted relative to the first axis; and moving the workpiece and the tool relatively in a direction parallel to the first axis at a speed synchronized with the rotational speed of the workpiece, while bringing the cutting edges of the tool into contact with the outer periphery of the workpiece; and removing material of the workpiece at the contacting points by the relative movement between the tool and the workpiece, thereby forming spiral tooth grooves on the outer periphery of the workpiece, rotating the workpiece about the first axis and relatively moving the workpiece and the tool in a direction parallel to the first axis at a speed synchronized with the rotational speed of the workpiece so that, in a plane perpendicular to the first axis, a contour line of a cutting edge of the tool comes into rolling contact without slipping with a target contour line, which is a contour line of the spiral tooth groove to be formed, at a predetermined point on the target contour line or an extension line of the target contour line, and rotates while sliding with respect to the target contour line or the extension line at points other than the predetermined point; In a plane perpendicular to the first axis, a first circle having a center on the first axis and passing through the predetermined point has a diameter that is 1 to 1.5 times the diameter of a second circle having a center on the first axis and being a tip circle of a gear manufactured from the workpiece. Gear manufacturing method.

2. 2. A method for manufacturing a gear according to claim 1, comprising the steps of: The magnitude of an axis inclination angle, which is an angle between the first axis and the second axis projected onto a plane that includes the first axis and is parallel to the second axis, satisfies the following formulas (1) and (2): Gear manufacturing method. 90 (°) - (axis inclination angle (°)) ≧ (helix angle at tooth tip (°)) Formula (1) 90 (°) - (axis inclination angle (°)) ≦ (helix angle at the center of the tooth height (°)) + 25 (°) Formula (2)

3. 3. The method for manufacturing a gear according to claim 2, The number of teeth of the gear to be manufactured is any one of 1 to 4. Gear manufacturing method.

4. 4. A method for manufacturing a gear according to claim 3, comprising the steps of: The module of the gear to be manufactured is 0.3 or more and 2.0 or less. Gear manufacturing method.

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