Gear manufacturing method

Abstract

To provide a gear production method capable of producing a gear with high accuracy at short time.SOLUTION: A workpiece W is rotated around a first axis line A1, and a plurality of cutting edge 24a which is annularly arranged with a second axis line A2 which is at a twisted position to the first axis line A1 as a center, is rotated around the second axis line A2, and the workpiece W and the plurality of cutting edges 24a are moved relatively at a speed synchronized with a rotation speed of the workpiece W in a direction being parallel to the first axis line A1, and a spiral tooth groove is formed on the peripheral face of the workpiece W by the plurality of cutting edges 24a. In the production method of the gear 10, in a cross section which is at a right angle to the first axis line A1, a diameter DF of a rolling circle CF where a contour line OE of the cutting edge 24a and a target contour line OG of the gear 10 contact in rolling contact, is greater than a diameter DC of a tooth depth center circle CC.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for manufacturing gears.

Background Art

[0002] Conventionally, as a method for manufacturing gears, a forging method is known. For example, Patent Document 1 discloses a method for manufacturing a gear by pressing a die in which a predetermined tooth profile is formed against a cylindrical workpiece to form teeth.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] (Problems to be Solved by the Invention) However, in the method described in Patent Document 1, since the tooth groove is gradually deepened by repeatedly pressing the die against the workpiece, it takes time to manufacture the gear.

[0005] The present invention has been made in view of the above circumstances, and one of its objects is to provide a manufacturing method capable of manufacturing gears with high precision in a short time.

[0006] (Means for Solving the Problems) The present invention provides a method for manufacturing a gear, which involves rotating a workpiece around a first axis, rotating an annular tool or a tool having multiple cutting edges arranged in an annular shape around the second axis, which is positioned twisted to the first axis, around the second axis, and moving the workpiece and the tool relative to each other in a direction parallel to the first axis at a speed synchronized with the rotational speed of the workpiece, while bringing the inner circumference of the tool into contact with the outer surface of the workpiece, and removing the material of the workpiece at the contact point through the relative movement between the tool and the workpiece, thereby forming helical teeth on the outer surface of the workpiece. In a cross section perpendicular to the first axis, the workpiece is rotated about the first axis and the workpiece and the tool are moved relative to each other in a direction parallel to the first axis at a speed synchronized with the rotational speed of the workpiece, such that the tool's contour line is in contact with the target contour line, which is the contour line of the helical teeth on which the tool's contour line is formed, and the tool rolls and makes contact with the target contour line without slipping at a predetermined point on the target contour line, and rotates while slipping with respect to the target contour line at other points. In a cross-section perpendicular to the first axis, the diameter of the first circle, which is a circle centered on the first axis and passing through a predetermined point, is greater than the diameter of the second circle, which is a circle centered on the first axis and passing through the center of the tooth height of the target contour line. This is a method for manufacturing a gear, wherein the second axis is set such that when the second axis is projected onto a plane that includes the first axis and is parallel to the second axis, the projected second axis is different from the first axis.

[0007] According to the present invention, gears can be manufactured in a single pass (meaning a single relative movement between the workpiece and the tool in a direction parallel to the first axis). Therefore, the time required for gear manufacturing can be reduced.

[0008] An applicable configuration is one in which the angle θ between the first axis and the projected second axis is determined by the number of teeth N of the helical teeth formed on the workpiece, the spacing P of the helical teeth formed on the workpiece in a direction parallel to the first axis, and the circumference L1 of the first circle.

[0009] In this case, the angle θ between the first axis and the projected second axis is the gear manufacturing method shown in the following formula (1), and this configuration can be applied. θ = tan -1 ((N×P) / L1) Formula (1) N:: Number of teeth of the helical teeth formed on the workpiece. P: The distance between the helical teeth formed on the workpiece in a direction parallel to the first axis. L1: Circumference of the first circle

[0010] In this configuration, the angle θ between the first axis and the projected second axis is determined based on the diameter of the first circle of the gear being manufactured. Since the diameter of the first circle is larger than the diameter of the second circle, this angle θ can be made smaller compared to the case where the diameter of the first circle is less than or equal to the diameter of the second circle. By making this angle θ smaller, interference between the support part that supports the workpiece and the tool or the support part that supports the tool can be reduced when the workpiece and the tool are moved relative to each other in the direction of the rotational centerline of the workpiece. Therefore, the length of the portion of the workpiece where the tooth groove cannot be formed can be shortened. Furthermore, by making the angle θ smaller, the portion where the shape of the formed helical groove (i.e., the shape of the gear tooth groove) is incomplete (the portion that is not the target shape, in other words, the design shape) can be shortened.

[0011] The aforementioned tool is In a cross-section obtained by cutting through a plane containing the second axis, the shape is tapered, with the dimension in the direction parallel to the second axis gradually decreasing as it approaches the second axis. In a cross-section cut by a plane containing the second axis, the tool pressure angle, which is the angle of inclination of the ends of the tool in a direction parallel to the second axis with respect to a straight line perpendicular to the second axis, is greater than the tool pressure angle when the diameter of the first circle is the same as the diameter of the second circle. This configuration can be applied.

[0012] With this configuration, the angle θ between the first axis and the projected second axis can be made smaller than the angle determined based on the diameter of the second circle of the gear being manufactured. Therefore, gears can be manufactured while suppressing an increase in the angle θ. Furthermore, with this configuration, the angle θ can be reduced simply by increasing the tool pressure angle.

[0013] The tool has a first portion which is a predetermined tool pressure angle, A second portion is located closer to the second axis than the first portion and has a tool pressure angle smaller than the predetermined tool pressure angle, Equipped with, This configuration can be applied.

[0014] Furthermore, the tool has a first portion in which the tool pressure angle gradually increases as it approaches the second axis, A second portion is located closer to the second axis than the first portion, and the tool pressure angle gradually increases as it approaches the second axis, Equipped with, The tool pressure angle at the end of the second portion that is farther from the second axis is smaller than the tool pressure angle at the end of the first portion that is closer to the second axis. This configuration can be applied.

[0015] With these configurations, the distance between tooth surfaces near the tooth roots of the gear teeth can be increased compared to when using a tool without the second part. Therefore, the angle θ can be made smaller.

[0016] The tool is rotated at a speed asynchronous to the rotational speed of the workpiece around the first axis and the speed of the relative movement between the workpiece and the tool in the direction of the first axis. This configuration can be applied.

[0017] With this configuration, the rotational speed of the tool can be increased without being restricted by the relative movement speed, thus increasing the cutting speed. This makes it possible to manufacture gears with a low surface roughness. Furthermore, increasing the cutting speed allows for a larger amount of material to be removed per unit time, thus shortening the gear manufacturing time.

[0018] The spiral teeth are formed on the outer surface of the workpiece by whirring, which involves cutting the outer surface of the workpiece with a tool having a plurality of cutting edges arranged in a ring shape around the second axis. This configuration can be applied.

[0019] With this configuration, the gear manufacturing method of the present invention can be carried out using equipment capable of performing conventionally known whirling (thread whirling). Therefore, it does not lead to an increase in equipment costs.

[0020] The gears being manufactured are helical gears. This configuration can be applied.

[0021] The lead angle of the helical gear (=90° - (helix angle (°))) is larger than the lead angle of the fastening screw, so the angle θ must be larger compared to when manufacturing the fastening screw. Therefore, with this configuration, the angle θ can be reduced when manufacturing the helical gear.

[0022] The configuration in which the number of teeth of the manufactured gear is one to six can be applied.

[0023] The fewer teeth there are, the larger the ratio of the tooth height from the center to the tip to the diameter of the base circle of the gear. And as this ratio increases, the rate of decrease in the angle θ with respect to the increase in the diameter of the first circle (in other words, with respect to the increase in the dimensional difference between the diameter of the first circle and the diameter of the second circle) becomes larger. For this reason, with this configuration, the angle θ can be made smaller.

[0024] The configuration in which the helix angle of the manufactured gear is 30° or more and 60° or less can be applied.

[0025] The smaller the helix angle, the larger the lead angle of the helical gear. However, with this configuration, when manufacturing a helical gear with a large lead angle, the angle θ can be reduced. [Brief explanation of the drawing]

[0026] [Figure 1A] Figure 1A is a perspective view showing an example of a gear being manufactured. [Figure 1B] Figure 1B is a cross-sectional view showing an example of a gear being manufactured. [Figure 2A] Figure 2A is a perspective view showing an example of the configuration of a gear manufacturing apparatus. [Figure 2B] Figure 2B is a top view showing an example of the configuration of a gear manufacturing apparatus. [Figure 3] Figure 3 shows the positional relationship between the workpiece and the cutting edge. [Figure 4] Figure 4 shows the movement trajectory of the cutting edge relative to the workpiece. [Figure 5] Figure 5 is a side view showing an example of a gear being manufactured. [Figure 6] Figure 6 is a cross-sectional view showing the shape of the cutting edge. [Figure 7] Figure 7 is a perspective view showing an example of the configuration of a gear manufacturing apparatus. [Figure 8] Figure 8 is a cross-sectional view showing the shape of the cutting edge according to the first modified example. [Figure 9] Figure 9 is a cross-sectional view showing the shape of the cutting edge according to the second modified example.

Best Mode for Carrying Out the Invention

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, a method for manufacturing a gear 10 using a columnar member or a cylindrical member made of metal as a starting material (work W) is shown. The gear 10 manufactured by the gear manufacturing method according to this embodiment is a helical gear having 1 to 6 teeth (hereinafter referred to as the number of teeth) and a twist angle of 30° or more and 60° or less. FIGS. 1A and 1B are diagrams showing an example of the gear 10 manufactured by the gear manufacturing method according to this embodiment. Note that FIG. 1A is a perspective view of the gear 10, and FIG. 1B is a cross-sectional view of the gear 10 cut along a plane perpendicular to the axial direction. In FIGS. 1A and 1B, a helical gear having 2 teeth and a twist angle of 45° is shown.

[0028] In this embodiment, a circle C passing through the center of the tooth thickness of the gear 10 C is denoted as "tooth thickness center circle C C ". This tooth thickness center circle C C is an example of the second circle of the present invention. The diameter D C of the tooth thickness center circle C C is the diameter D C of the tooth thickness center circle C C = ((the diameter D B of the root circle C B ) + (the diameter D T of the tip circle C T )) / 2 That is. Note that the tooth thickness center circle C C is actually a cylinder extending in the axial direction of the gear 10.

[0029] Figures 2A and 2B are schematic diagrams showing an example of the configuration of the main parts of a first apparatus 20a capable of carrying out the gear manufacturing method according to this embodiment. Figure 2A is a perspective view of the first apparatus 20a, and Figure 2B is a top view of the first apparatus 20a. The first apparatus 20a can be an apparatus capable of whirring. As shown in Figure 2A, the first apparatus 20a comprises a chuck 21, a center 22, a tailstock 23, a cutting edge 24a, and a tool holder 25a (wirling head). The chuck 21 is configured to support (grip) one end of a workpiece W, which is a cylindrical or cylindrical member, in the axial direction. The center 22 and tailstock 23 are configured to support the opposite end of the workpiece W in the axial direction. The cutting edge 24a is configured to cut the outer circumferential surface of the workpiece W. The tool holder 25a is configured to be able to mount (support) a plurality of cutting edges 24a. The cutting edge 24a and the tool holder 25a to which the cutting edge 24a is attached are examples of the "tool having a plurality of cutting edges arranged in an annular manner" of the present invention. The first device 20a is further equipped with a rotational power source not shown, and the chuck 21 and the tool holder 25a are configured to be rotatable by the rotational power source. The rotational centerline A1 of the chuck 21 (i.e., the rotational centerline (axis) of the workpiece W supported by the chuck 21) is denoted as the first axis A1, and the rotational centerline A2 of the tool holder 25a (i.e., the rotational centerline of the "tool having a plurality of cutting edges arranged in an annular manner") is denoted as the second axis A2. The first axis A1 and the second axis A2 are in a twisted position. That is, the first axis A1 and the second axis A2 are not parallel and do not intersect. In other words, the second axis A2 is set such that when it is projected onto a plane that includes the first axis A1 and is parallel to the second axis A2, in a direction perpendicular to this plane, the first axis A1 and the projected second axis A2 become different axes. The first axis A1 and the projected second axis A2 are inclined toward each other at a predetermined angle θ (see Figure 2B). This predetermined angle θ (where the smaller of the angles made between the first axis A1 and the second axis A2) is denoted as the axis inclination angle θ. When the axis inclination angle θ is 0°, the first axis A1 and the second axis A2 are parallel.

[0030] The tool holder 25a has an annular shape centered on the second axis A2, and is configured to allow the workpiece W to be inserted through its inner circumference. Multiple cutting edges 24a are mounted on the tool holder 25a in an annular shape (in other words, in the circumferential direction of a circle centered on the second axis A2) around the second axis A2. In this embodiment, the multiple cutting edges 24a are arranged radially around the second axis A2 and at equal intervals in the circumferential direction.

[0031] The workpiece W is positioned relative to the tool holder 25a so as to pass through the inner circumference of the tool holder 25a. The cutting edge 24a, while attached to the tool holder 25a, is configured to cut the outer surface of the workpiece W that is inserted through the inner circumference of the tool holder 25a (to remove the material from the workpiece W at the point of contact). The shape of the cutting edge 24a will be described later. In Figure 2A, a configuration with six cutting edges 24a is shown, but the number of cutting edges 24a is not limited.

[0032] The first device 20a is configured to move the workpiece W and the tool holder 25a relative to each other in a direction parallel to the first axis A1 at a speed synchronized with the rotational speed of the chuck 21 (i.e., the rotational speed of the workpiece W), while the workpiece W is supported by the chuck 21 and the tailstock 23 (center 22). The first device 20a may be configured so that the chuck 21, center 22 and tailstock 23 are linearly movable in a direction parallel to the first axis A1, the tool holder 25a is linearly movable in a direction parallel to the first axis A1, or both the chuck 21, center 22 and tailstock 23 and the tool holder 25a are linearly movable in a direction parallel to the first axis A1. Furthermore, the first device 20a is configured so that the rotational speed of the chuck 21 and the rotational speed of the tool holder 25a can be set asynchronously (i.e., independently of each other).

[0033] Figure 3 shows the positional relationship between the workpiece W and the cutting edge 24a, and is a view of the workpiece W and the cutting edge 24a in the direction of the first axis A1. Since the first axis A1 and the second axis A2 are inclined relative to each other at a predetermined axial inclination angle θ, when the tool holder 25a rotates around the second axis A2, the trajectory T of the tips of the multiple cutting edges 24a (i.e., the part closest to the second axis A2) is shown. T In a view parallel to the first axis A1, it becomes an ellipse. And, as shown in Figure 3, this trajectory T T The ellipse (i.e., the first axis A1) is eccentric in the direction of the major axis of the ellipse.

[0034] Here, the operation of the first apparatus 20a for manufacturing the gear 10 will be described. With the workpiece W supported by the chuck 21 and tailstock 23, the workpiece W is rotated around the first axis A1. Also, with multiple cutting edges 24a attached to the tool holder 25a, the tool holder 25a is rotated around the second axis A2. Note that the rotational speed of the workpiece W and the rotational speed of the tool holder 25a do not need to be asynchronous. The workpiece W and the tool holder 25a 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 of the workpiece W and the tool holder 25a is the speed at which the workpiece W and the tool holder 25a move relative to each other by a distance of "(number of teeth of the gear 10 to be manufactured) × (distance between adjacent teeth 11 in the direction of the first axis A1)" for each rotation of the workpiece W.

[0035] Then, by bringing the tip of the rotating cutting edge 24a into contact with the outer circumferential surface of the workpiece W, the material of the workpiece W at the point of contact is removed. Since the first axis A1 and the second axis A2 are in a twisted position, tooth grooves are formed on the outer circumferential surface of the workpiece W, extending in a direction that is angle-inclined with respect to the first axis A1 according to the axial inclination angle θ. Then, by moving the workpiece W and the tool holder 25a 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, helical tooth grooves are formed on the outer circumferential surface of the workpiece W, and as a result, helical teeth 11 are formed on the outer circumferential surface of the workpiece W. This manufactures a helical gear.

[0036] As described above, in the method for manufacturing the gear 10 according to this embodiment, tooth grooves (helical grooves) are formed by intermittent machining with a plurality of rotating cutting edges 24a. With this configuration, the amount of heat generated during machining is reduced compared to continuous machining with a single cutting edge. Therefore, it becomes possible to manufacture high-precision gears 10. Furthermore, according to this embodiment, the gear 10 can be manufactured in one pass (meaning that there is one relative movement between the workpiece and the tool in a direction parallel to the first axis). Therefore, the time required to manufacture the gear 10 can be shortened. Moreover, according to this embodiment, the material (workpiece) is not extruded as when manufacturing gears by rolling, so additional machining (specifically, machining to remove the extruded material) is unnecessary.

[0037] Figure 4 shows the contour line of the cutting edge 24a in a cross section perpendicular to the first axis A1 when the workpiece W is fixed. E Movement trajectory T U (That is, the contour line of the cutting edge 24a relative to the workpiece W) E Movement trajectory T U This figure shows the contour line of the cutting edge 24a when the workpiece W is fixed. E This is the target contour line O of the teeth 11 of gear 10. G While in contact with the design contour of the teeth 11 of the gear 10 to be manufactured, the cutting edge 24a moves within this cross-section, rotating around a straight line parallel to the first axis A1 relative to the workpiece W (a straight line perpendicular to the plane of the paper in Figure 4). The movement trajectory T of the cutting edge 24a within this cross-section. U This is a hypocycloid curve.

[0038] Outline O of the cutting edge 24a E As it moves within this cross-section, the contour line O of the cutting edge 24a E This is the target contour line O of tooth 11. G There exists a point R where it rolls and makes contact without slipping. Conversely, the contour line O of the cutting edge 24a E This is the target contour line O G While in contact with the target contour O G At a predetermined point R, the target contour line O GIt rolls and makes contact with the target contour line O without slipping, except at a predetermined point R. G It rotates while sliding relative to the first axis A1. Hereafter, in a plane perpendicular to the first axis A1, the circle that passes through the point R where this rolling contact occurs, centered on the first axis A1, is called the "rolling circle C". F " is written. This rolling circle C F This is an example of the first circle of the present invention.

[0039] In the whirling process, the axial inclination angle θ is the rolling circle C. F Diameter D F It is defined based on this. Therefore, in this embodiment as well, the axial inclination angle θ is the rolling circle C F Diameter D F It is defined based on the following. In this case, the axial inclination angle θ is determined by the number of teeth N of the helical teeth formed on the workpiece W, the spacing P of the helical teeth formed on the workpiece W in a direction parallel to the first axis, and the circumference L1 of the first circle. Specifically, the axial inclination angle θ is defined by the following formula (1). θ = tan -1 ((N×P) / L1) Formula (1) N: Number of tooth grooves formed on the workpiece W (= number of teeth on the 10 gears to be manufactured) P: The spacing of the tooth groove formed in the workpiece W in a direction parallel to the first axis A1. L1: Rolling circle C F Diameter D F × Pi (π = rolling circle C) F (Circumference)

[0040] Incidentally, the tool holder 25a, the chuck 21, the center 22, and the tailstock 23 can move relative to each other in a direction parallel to the first axis A1, as long as they do not come into contact with each other. As shown in Figure 2B, the first axis A1 and the second axis A2 are set to be different axes and are inclined at an axis inclination angle θ. Therefore, even when the tool holder 25a is brought as close to the chuck 21 as possible, as long as the outer circumference S2 of the tool holder 25a does not come into contact with the chuck 21, the position S1 (the center of the tool holder 25a) where the cutting edge 24a actually cuts the workpiece W is at a distance M1 from the chuck 21. In other words, tooth grooves cannot be formed in the area within a distance M1 from the position S1 where the cutting edge 24a contacts the workpiece W. The same applies to the center 22 and the tailstock 23. As is clear from Figure 2B, as the axial inclination angle θ increases, the distance M1 also increases, so as the axial inclination angle θ increases, the portion of the workpiece W where tooth grooves cannot be formed becomes longer. Also, as the axial inclination angle θ increases, the shape of the tooth 11 at the end of the area where tooth grooves are formed becomes incomplete (target contour line O of tooth 11). G The portion where the desired shape cannot be obtained (i.e., the portion where the tooth 11 does not conform to the design shape) becomes longer. In particular, when manufacturing a helical gear with a helix angle of 30° to 60°, as in this embodiment, the axial inclination angle θ must be larger compared to when manufacturing a general fastening male screw, which makes the above-mentioned problems more likely to occur.

[0041] In this embodiment, the rolling circle C F Diameter D F The tooth height center circle C C Diameter D C Larger, tooth tip circle C T Diameter D T The following applies. This results in the rolling circle C. F Diameter D F The tooth height is center circle C C Diameter D C Compared to the following configuration, the axial inclination angle θ can be reduced. Specifically, as is clear from Figure 5, the helix angle of gear 10 decreases from the tooth root to the tooth tip. Note that Figure 5 is a side view of gear 10, and in Figure 5, β Bβ indicates the torsional angle at the root of the tooth, T β indicates the twist angle at the tooth tip, F The tooth height is center circle C F This shows the twist angle. And the rolling circle C of gear 10 (helical gear) manufactured by the method described above. F Torsion angle β F teeth, Twist angle β F (°)=90(°)-(Axis inclination angle θ(°)) This relationship exists. Therefore, the rolling circle C F Diameter D F If you increase the size, the rolling circle C F Diameter D F Torsion angle β F Since the value of becomes larger, the value of the axis inclination angle θ can be reduced.

[0042] Furthermore, by reducing the axial inclination angle θ, the distance M1 can be reduced. That is, when the workpiece W and the cutting edge 24a are moved relative to each other in a direction parallel to the first axis A1, interference between the support parts that support the workpiece W, namely the chuck 21, center 22, and tailstock 23, and the cutting edge 24a and the tool holder 25a that supports the cutting edge 24a can be reduced. Therefore, the length of the portion of the workpiece W where a tooth groove cannot be formed can be shortened. In addition, by reducing the axial inclination angle θ, the portion of the gear 10 where the tooth groove shape is incomplete (the portion that is not the target shape, or in other words, the shape according to the design) can be shortened.

[0043] In particular, the lead angle of a helical gear (=90° - (helix angle of gear 10 (°))) is larger than that of a typical fastening screw. Therefore, the axial inclination angle θ must be larger compared to when manufacturing a fastening screw. However, according to this embodiment, the axial inclination angle θ can be reduced when manufacturing a helical gear.

[0044] Furthermore, the fewer teeth a gear has, the larger the ratio of the tooth height from the center to the tip to the diameter of the base circle and root circle of gear 10. And as this ratio increases, the rolling circle C F Diameter D Fand tooth height center circle C C Diameter D C Increase in the dimensional difference (i.e., the rolling circle C) F Diameter D F The rate of decrease in the axial inclination angle θ with respect to the increase in ( ) becomes larger. For this reason, the fewer the number of teeth, for example, when the number of teeth is 1 to 6 as in this embodiment, the greater the effect of reducing the axial inclination angle θ.

[0045] In this embodiment, by making the shape of the cutting edge 24a the shape described below, the rolling circle C F Diameter D F The tooth height center circle C C Diameter D C To make it larger. Figure 6 is a cross-sectional view of the cutting edge 24a cut by a plane containing the second axis A2, with the cutting edge 24a attached to the tool holder 25a. Note that in Figure 6, the first axis A1 and the root circle C B , and the tip circle C T It is inclined with respect to the plane of the paper. As shown in Figure 6, the cross-sectional shape of the cutting edge 24a cut by a plane containing the second axis A2 has a tapered shape in which the width (dimension in the direction parallel to the second axis A2) decreases as it approaches the second axis A2. In other words, the tooth tip circle C during machining T The part that extends inward (in Figure 6, the tip circle C) T The portion closer to the first axis A1 and the second axis A2 has a roughly trapezoidal shape, with the side closer to the second axis A2 being the top base, the side further from the second axis A2 being the bottom base, and the sides on both sides in the axial direction of the second axis A2 being the hypotenuses. However, the sides on both sides in the axial direction of the second axis A2 (the sides corresponding to the hypotenuses of the trapezoid) are curves (curved surfaces) that bulge outward in the axial direction of the second axis A2. The surface corresponding to the top base of the trapezoid is denoted as the tip surface 241, and the surface corresponding to the hypotenuses of the trapezoid is denoted as the side surface 242.

[0046] In this plane, the angle between the tangent to the side surface 242 and the line Q perpendicular to the second axis A2 at the intersection of the side surface 242 and the line Q is the tool pressure angle α. In this embodiment, the tool pressure angle α of the cutting edge 24a when manufacturing a predetermined helical gear is "rolling circle C FDiameter D F The tooth height is center circle C C Diameter D C In the case where it is the same as the predetermined helical gear, the tool pressure angle of the cutting edge when manufacturing a helical gear identical to the predetermined helical gear (a helical gear of the same shape and size) using the same apparatus is a value greater than the tool pressure angle of the cutting edge. In this embodiment, since the side surface 242 of the cutting edge 24a is a curved surface that bulges outward, the tool pressure angle α gradually (smoothly) increases as it approaches the second axis A2. For this reason, more precisely, in this embodiment, the tool pressure angle α at a predetermined distance in the height direction (direction perpendicular to the second axis A2) from the tip surface 241 of the cutting edge 24a when manufacturing a predetermined helical gear is a value greater than the tool pressure angle of the cutting edge C F Diameter D F The tooth height is center circle C C Diameter D C It is a value greater than the tool pressure angle at the same position as the predetermined distance in the height direction from the tip surface of the cutting edge when manufacturing a helical gear identical to the predetermined helical gear (a helical gear of the same shape and size) using the same apparatus, in the case where it is the same as the predetermined helical gear. Note that the specific value of the tool pressure angle α is determined according to the shape and dimensions of the teeth 11 of the gear 10 to be manufactured, and is not limited to that value.

[0047] While there is no particular upper limit to the tool pressure angle α, in practice it is restricted by the axial inclination angle θ and the shape and dimensions of the teeth 11 of the gear 10 being manufactured. Specifically, as is clear from Figure 6, when the cutting edge 24a is closest to the first axis A1, the distance X1 from the first axis A1 to the tip of the cutting edge 24a is equal to the root circle C B Diameter D BIt must be 1 / 2 of this. Also, the radial dimension X2 (the height of the said trapezoid) of the circle centered on the second axis A2 of the side surface 242 of the cutting edge 24a needs to be higher than the tooth width of the gear 10 to be manufactured. On the other hand, when increasing the tool pressure angle α, the width B1 of the tip surface 241 of the cutting edge 24a becomes smaller. When the width B1 becomes 0, the cross-sectional shape of the cutting edge 24a becomes a substantially triangular shape instead of a substantially trapezoidal shape. Furthermore, when continuously increasing the tool pressure angle α, the dimension X2 of the side surface 242 of the cutting edge 24a becomes smaller. For this reason, when the cross-sectional shape of the cutting edge 24a becomes a substantially triangular shape, it becomes impossible to secure the dimension X2 of the cutting edge 24a for manufacturing the gear 10. Therefore, the maximum value of the tool pressure angle α can be said to be "the maximum value within the range where the dimension X2 (the dimension in the direction perpendicular to the second axis A2) of the cutting edge 24a does not change" or "the maximum value within the range where the cross-sectional shape of the cutting edge 24a can maintain a substantially trapezoidal shape without the dimension X2 changing".

[0048] According to such a configuration, the rolling circle C F can be positioned outside the tooth width center circle C C . For this reason, compared with the case where the diameter D F of the rolling circle C F is less than or equal to the diameter of the tooth width center circle C C , the axis inclination angle θ becomes smaller, so that the distance M1 shown in Fig. 2B can be reduced. Therefore, the range where the tooth groove cannot be formed in the workpiece W can be shortened. Also, by reducing the axis inclination angle θ, the incomplete part (the part where the target contour line O G of the tooth 11 cannot be obtained) of the shape of the tooth 11 at the end of the range where the tooth groove is formed can be shortened. Also, the range in which relative movement is possible between the tool holder 25a and the chuck 21, the center 22, and the center pressing base 23 can be increased. For this reason, the axial dimension of the gear 10 to be manufactured can be increased.

[0049] Also, according to such a configuration, by simply increasing the tool pressure angle α, the axis inclination angle θ can be reduced.

[0050] Furthermore, in the gear manufacturing method according to this embodiment, the rotational speed of the tool holder 25a is not restricted by the rotational speed of the workpiece W. That is, the rotational speed of the tool holder 25a can be made asynchronous with the rotational speed of the workpiece W. Therefore, the rotational speed of the tool holder 25a, i.e., the cutting speed, can be increased regardless of the rotational speed of the workpiece W. And because the cutting speed can be increased, the gear 10 can be manufactured by moving the workpiece W and the tool holder 25a relative to each other only once. In addition, by increasing the cutting speed, the speed of relative movement between the workpiece W and the tool holder 25a can be increased. Therefore, the time required to manufacture the gear 10 can be shortened. Furthermore, by increasing the cutting speed, the cut surface can be made smoother (the surface roughness can be reduced).

[0051] Furthermore, according to this embodiment, the first apparatus 20a can be a conventionally known apparatus capable of performing thread waring. Therefore, this embodiment does not lead to an increase in equipment costs.

[0052] Next, a second apparatus 20b, which is a modified example of an apparatus capable of carrying out a gear manufacturing method according to an embodiment of the present invention, will be described. The second apparatus 20b is an apparatus to which an annular tool is applied. Figure 7 is a schematic diagram showing the configuration of the second apparatus 20b. Components common to the first apparatus 20a are denoted by the same reference numerals as in the first apparatus 20a, and their descriptions are omitted.

[0053] As shown in Figure 7, the second apparatus 20b is configured to manufacture the gear 10 using an annular tool. An annular grinding wheel 24b is used as the annular tool. The annular grinding wheel 24b is configured to allow a workpiece W to be inserted through its inner circumference and to grind the outer circumference of the workpiece W on its inner circumference. The tool holder 25b is configured to mount the annular grinding wheel 24b so that its axis (centerline) coincides with the second axis A2. The cross-sectional shape of the annular grinding wheel 24b when cut by a plane containing the second axis A2 may be the same as the cross-sectional shape of the cutting edge 24a used in the first apparatus 20a. The operation of the second apparatus 20b is also the same as that of the first apparatus 20a. The manufacturing method using the second apparatus 20b can achieve the same effects as the manufacturing method using the first apparatus 20a.

[0054] Next, modifications of the shapes of the cutting edge 24a and the annular grinding wheel 24b will be described. Figure 8 shows the shapes of the cutting edge 24a and the annular grinding wheel 24b according to the first modification, and Figure 9 shows the shapes of the cutting edge 24a and the annular grinding wheel 24b according to the second modification. Figures 8 and 9 are both cross-sectional views obtained by cutting the cutting edge 24a and the annular grinding wheel 24b through a plane containing the second axis A2. When a gear has a small diameter and a small number of teeth, and the tooth profile is of a standard shape (for example, an involute gear), when the gear meshes with other gears, the portion of the tooth tip of the other gear's teeth may interfere with the portion of the tooth root of the gear's teeth. For this reason, in order to prevent such interference, the inter-tooth surface distance near the tooth root of a small-diameter, small-tooth gear may be made larger than the inter-tooth surface distance in the case of a standard tooth profile. The shapes related to the first modified example shown in Figure 8 and the shapes related to the second modified example shown in Figure 9 are shapes that allow the inter-tooth surface distance near the tooth root to be larger than the inter-tooth surface distance in the case of a standard tooth shape.

[0055] As shown in Figure 8, the cutting edge 24a and annular grinding wheel 24b according to the first modified example have a first portion 243 and a second portion 244 located on the tip side of the first portion 243 (closer to the second axis A2 than the first portion 243 when mounted on the tool holder). Both the first portion 243 and the second portion 244 have a tapered shape, with their width decreasing as they approach the second axis A2. Furthermore, the contour line of the side surface 245 of the first portion 243 in a cross-section cut by a plane containing the second axis A2 is straight, and its tool pressure angle α1 is constant. Similarly, the contour line of the side surface 246 of the second portion 244 in a cross-section cut by a plane containing the second axis A2 is also straight, and its tool pressure angle α2 is constant. However, the tool pressure angle α2 (absolute value) of the second portion 244 is smaller than the tool pressure angle α1 (absolute value) of the first portion 243. With this configuration, the width of the tip surface 241 is larger compared to a configuration without the second portion 244. Therefore, the inter-tooth surface distance near the tooth root can be increased compared to a configuration using a cutting edge 24a without the second portion 244 and an annular grinding wheel 24b.

[0056] As shown in Figure 9, the cutting edge 24a and annular grinding wheel 24b in the second modified example also have a first portion 243 and a second portion 244 located on the tip side of the first portion 243. The first portion 243 has a tapered shape, with its width decreasing as it approaches the second axis A2. The side surface 245 of the first portion 243 is a curved surface in which the tool pressure angle α1 increases smoothly (continuously) as it approaches the second axis A2. Similarly, the second portion 244 also has a tapered shape, with its width decreasing as it approaches the second axis A2. The side surface 246 of the second portion 244 is also a curved surface in which the tool pressure angle α2 increases smoothly (continuously) as it approaches the second axis A2. However, the tool pressure angle α2 at the position of the second portion 244 furthest from the second axis is smaller than the tool pressure angle α1 at the position of the first portion 243 closest to the second axis. With this configuration, the same effects as the first modified example can be achieved.

[0057] Furthermore, the shape may be such that one of the tool pressure angles α1 of the first part 243 and α2 of the second part 244 is constant, while the other increases smoothly (continuously) as it approaches the second axis A2. Whether or not the tool pressure angles α1 of the first part 243 and α2 of the second part 244 are constant, and the specific tool pressure angles α1 and α2, are appropriately selected according to the tooth profile of the gear 11 to be manufactured.

[0058] Although embodiments and modifications of the present invention have been described above, the technical scope of the present invention is not limited by the embodiments and modifications described above. The present invention can be modified without departing from its spirit, and such modifications are also included within the technical scope of the present invention.

[0059] For example, the above embodiment shows an example of manufacturing a helical gear with 2 teeth and a helix angle of 45°, but the number of teeth and helix angle of the gear 10 to be manufactured are not limited to the above embodiment. Also, the shape of the teeth 11 of the gear 10 to be manufactured is not limited. [Explanation of Symbols]

[0060] 10...gear, 11...gear teeth, 20a...first device, C C ...tooth height center circle, C F ...rolling circle

Claims

1. A method for manufacturing a gear, comprising: rotating a workpiece about a first axis; rotating an annular tool or a tool having multiple cutting edges arranged in a ring around the second axis, which is in a twisted position with respect to the first axis, about the second axis; and moving the workpiece and the tool relative to each other in a direction parallel to the first axis at a speed synchronized with the rotational speed of the workpiece, while bringing the inner circumference of the tool into contact with the outer surface of the workpiece, and removing the material of the workpiece at the contact point through the relative movement between the tool and the workpiece, thereby forming helical teeth on the outer surface of the workpiece; In a cross section perpendicular to the first axis, the workpiece is rotated about the first axis and the workpiece and the tool are moved relative to each other in a direction parallel to the first axis at a speed synchronized with the rotational speed of the workpiece, such that the tool's contour line is in contact with the target contour line, which is the contour line of the helical teeth on which the tool's contour line is formed, and the tool rolls and makes contact with the target contour line without slipping at a predetermined point on the target contour line, and rotates while slipping with respect to the target contour line at other points. In a cross-section perpendicular to the first axis, the diameter of the first circle, which is a circle centered on the first axis and passing through a predetermined point, is greater than the diameter of the second circle, which is a circle centered on the first axis and passing through the center of the tooth height of the target contour line. A method for manufacturing a gear, wherein the second axis is set such that when the second axis is projected onto a plane that includes the first axis and is parallel to the second axis, the projected second axis is different from the first axis.

2. A method for manufacturing a gear according to claim 1, wherein the angle θ between the first axis and the projected second axis is the number of teeth N of the helical teeth formed on the workpiece, the spacing P of the helical teeth formed on the workpiece in a direction parallel to the first axis, and the circumference L of the first circle. １ A method for manufacturing gears, determined by the following:

3. A method for manufacturing a gear according to claim 2, wherein the angle θ between the first axis and the projected second axis is represented by the following formula (1). θ=tan －１ ((N×P) / L) １ ) Equation (1) N:: The number of teeth of the helical teeth formed on the workpiece. P: The spacing between the helical teeth formed on the workpiece in a direction parallel to the first axis. L １ : The circumference of the first circle

4. A method for manufacturing a gear according to any one of claims 1 to 3, The aforementioned tool is In a cross-section obtained by cutting through a plane containing the second axis, the shape is tapered, with the dimension in the direction parallel to the second axis gradually decreasing as it approaches the second axis. In a cross-section cut by a plane containing the second axis, the tool pressure angle, which is the angle of inclination of the ends of the tool in a direction parallel to the second axis with respect to a straight line perpendicular to the second axis, is greater than the tool pressure angle when the diameter of the first circle is the same as the diameter of the second circle. A method for manufacturing gears.

5. A method for manufacturing a gear according to claim 4, The tool has a first portion which is a predetermined tool pressure angle, A second portion is located closer to the second axis than the first portion and has a tool pressure angle smaller than the predetermined tool pressure angle, Equipped with, A method for manufacturing gears.

6. A method for manufacturing a gear according to claim 4, The tool has a first portion in which the tool pressure angle gradually increases as it approaches the second axis, A second portion is located closer to the second axis than the first portion, and the tool pressure angle gradually increases as it approaches the second axis, Equipped with, The tool pressure angle at the end of the second portion that is farther from the second axis is smaller than the tool pressure angle at the end of the first portion that is closer to the second axis. A method for manufacturing gears.

7. A method for manufacturing a gear according to any one of claims 1 to 3, The tool is rotated at a speed asynchronous to the rotational speed of the workpiece around the first axis and the speed of the relative movement between the workpiece and the tool in the direction of the first axis. A method for manufacturing gears.

8. A method for manufacturing a gear according to any one of claims 1 to 3, The gears being manufactured are helical gears. A method for manufacturing gears.

9. A method for manufacturing a gear according to claim 8, The number of teeth on the gear to be manufactured is one to six. A method for manufacturing gears.

10. A method for manufacturing a gear according to claim 8, The helix angle of the gear manufactured is between 30° and 60°. A method for manufacturing gears.

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