Gear manufacturing methods

Abstract

This invention provides a gear manufacturing method capable of producing high-precision gears in a short time. A method for manufacturing a gear (10) involves rotating a workpiece (W) around a first axis (A1), rotating a plurality of cutting edges (24a) arranged in a ring around a second axis (A2) located at a torsional position relative to the first axis (A1) around the second axis (A2), and moving the workpiece (W) and the plurality of cutting edges (24a) 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), while forming helical tooth grooves on the outer circumferential surface of the workpiece (W) using the plurality of cutting edges (24a). In a cross-section perpendicular to the first axis (A1), the contour line (O) of the cutting edge (24a) is... E The target contour lines (O) of the gear (10) and gear (10) G Rolling circle of rolling contact (C) F The diameter (D) F ) tooth height center circle (C C The diameter (D) C )big.

Description

Technical Field

[0001] This invention relates to a method for manufacturing gears. Background Technology

[0002] Conventionally, rolling forming methods are known as a method for manufacturing gears. For example, Patent Document 1 discloses a method for manufacturing gears using rolling forming, which involves pressing a mold with a predetermined tooth profile onto a cylindrical workpiece to form teeth.

[0003] [Existing technical documents]

[0004] [Patent Literature]

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-628

[0006] However, in the method described in Patent Document 1, the tooth grooves are gradually deepened by repeatedly pressing the mold onto the workpiece, thus making the gear manufacturing time-consuming. Summary of the Invention

[0007] The present invention was made in view of the above-mentioned actual situation, and one of its objectives is to provide a manufacturing method for producing high-precision gears in a short time.

[0008] The gear manufacturing method of the present invention involves rotating a workpiece about a first axis, rotating a ring-shaped tool or a tool having a plurality of cutting edges arranged in a ring around the second axis about a second axis that is in a torsional position relative to the first axis about the second axis, and moving the workpiece and the tool relative to each other at a speed synchronized with the rotational speed of the workpiece in a direction parallel to the first axis, while bringing the inner circumferential side of the tool into contact with the outer circumferential surface of the workpiece. The relative movement of the tool and the workpiece removes material from the contacted portion of the workpiece, thereby forming a helical tooth on the outer circumferential surface of the workpiece.

[0009] In a cross-section perpendicular to the first axis, the tool's contour line contacts the contour line of the formed helical teeth, i.e., the target contour line, while simultaneously rolling in non-slip contact relative to the target contour line at a predetermined point, and sliding and rotating relative to the target contour line at other points. This allows the workpiece to rotate around the first axis, and the workpiece and the tool to move relative to each other in a direction parallel to the first axis at a speed synchronized with the workpiece's rotational speed.

[0010] In a cross-section perpendicular to the first axis, the diameter of the first circle (centered on the first axis and passing through the specified point) is larger than the diameter of the second circle (centered on the first axis and passing through the center of the tooth height of the target contour line).

[0011] When the second axis is projected onto a plane that contains the first axis and is parallel to the second axis, the first axis and the projected second axis are set to be different axes.

[0012] According to the present invention, gears can be manufactured in one pass (the relative movement of the workpiece and the tool in a direction parallel to the first axis is considered one pass). Therefore, the time required to manufacture gears can be shortened.

[0013] The following structure is applicable, wherein the angle θ between the first axis and the projected second axis is determined by the number N of the helical teeth formed on the workpiece, the spacing P of the helical teeth formed on the workpiece in the direction parallel to the first axis, and the circumference L1 of the first circle.

[0014] In this case, the following structure can be applied, namely, the angle θ between the first axis and the projected second axis is represented by the following mathematical expression (1):

[0015] θ = tan -1 ((N×P) / L1) Mathematical expression (1)

[0016] N: The number of the spiral teeth formed on the workpiece.

[0017] P: The spacing of the helical teeth formed on the workpiece in a direction parallel to the first axis.

[0018] L1: Circumference of the first circle.

[0019] In this structure, the angle θ between the first axis and the projected second axis is defined based on the diameter of the first circle of the manufactured gear. Furthermore, since the diameter of the first circle is larger than the diameter of the second circle, this angle θ can be reduced compared to cases where the diameter of the first circle is less than or equal to the diameter of the second circle. Moreover, by reducing this angle θ, interference between the support portion supporting the workpiece and the tool or the support portion supporting the tool can be reduced when the workpiece and the tool move relative to each other along the rotational centerline of the workpiece. Therefore, the length of the portion where tooth grooves cannot be formed on the workpiece can be shortened. Additionally, by reducing the angle θ, the incomplete portions of the formed helical groove shape (i.e., the shape of the gear tooth groove) (parts that are not the target shape, in other words, not the designed shape) can be shortened.

[0020] The following structure is applicable, that is, regarding the tool,

[0021] In a cross-section cut along a plane containing the second axis, it has a pointed shape whose dimensions gradually decrease as it approaches the second axis and is parallel to the second axis.

[0022] In a cross-section cut along a plane containing the second axis, the angle of inclination of the two ends of the tool in the direction parallel to the second axis relative to a straight line perpendicular to the second axis, i.e., the tool pressure angle, is greater than the tool pressure angle when the diameter of the first circle is the same as the diameter of the second circle.

[0023] With this structure, the angle θ between the first axis and the projected second axis can be made smaller than the angle specified based on the diameter of the second circle of the manufactured gear. Therefore, the gear can be manufactured while suppressing the increase of the angle θ. Furthermore, with this structure, the angle θ can be reduced simply by increasing the tool pressure angle.

[0024] The tool is capable of having the following structure: a first portion having a predetermined tool pressure angle; and a second portion located on a side closer to the second axis than the first portion and having a tool pressure angle smaller than the predetermined tool pressure angle.

[0025] Additionally, the following structure is applicable: the tool comprises: a first portion whose tool pressure angle gradually increases as it approaches the second axis; and a second portion located on a side closer to the second axis than the first portion, wherein the tool pressure angle gradually increases as it approaches the second axis, and the tool pressure angle at the end of the second portion on the side away from the second axis is smaller than the tool pressure angle at the end of the first portion on the side closer to the second axis.

[0026] Based on these structures, compared to using a tool without a second part, the distance between the tooth surfaces near the root of the gear teeth can be increased. Therefore, the angle θ can be made smaller.

[0027] The tool can be adapted to rotate at a speed that is asynchronous with the rotational speed of the workpiece centered on the first axis and the relative movement speed of the workpiece and the tool in the direction of the first axis.

[0028] With this structure, the tool's rotational speed can be increased without being limited by the relative movement speed, thus increasing the cutting speed. Therefore, gears with low surface roughness can be manufactured. Furthermore, by increasing the cutting speed, the amount of material processed per unit time can be increased, thereby reducing the gear manufacturing time.

[0029] The structure is applicable to the following: a whirlwind cutting process is performed on the outer peripheral surface of the workpiece by using a tool having a plurality of cutting edges arranged in a ring around the second axis to cut the outer peripheral surface of the workpiece, thereby forming the spiral teeth on the outer peripheral surface of the workpiece.

[0030] Based on this structure, the manufacturing method of the present invention can be implemented using existing known devices capable of performing cyclone cutting (spiral rotation). Therefore, it does not lead to an increase in equipment costs.

[0031] It can be used for the following structures, namely, the manufactured gears are helical gears.

[0032] The lead angle of a helical gear (=90°-(helix angle (°))) is larger than that of a fastening thread, therefore, the angle θ must be increased compared to the case of manufacturing a fastening thread. Therefore, according to this structure, the angle θ can be reduced when manufacturing a helical gear.

[0033] It can be used for the following structures, namely, the number of teeth of the manufactured gear is any one of 1 to 6.

[0034] The fewer the number of teeth, the greater the ratio of the dimension from the center of the tooth height to the tooth tip to the diameter of the gear's base circle. Furthermore, as this ratio increases, the rate of decrease in angle θ relative to the increase in the diameter of the first circle (in other words, relative to the increase in the dimensional difference between the diameters of the first and second circles) becomes greater. Therefore, with this structure, it is possible to make the angle θ smaller.

[0035] The structure is applicable to gears with a helix angle of 30° or more and 60° or less.

[0036] The smaller the helix angle, the larger the lead angle of the helical gear. However, according to this structure, when manufacturing a helical gear with a large lead angle, it is possible to reduce the angle θ. Attached Figure Description

[0037] Figure 1A This is a three-dimensional diagram showing an example of a manufactured gear.

[0038] Figure 1B This is a cross-sectional view showing an example of a manufactured gear.

[0039] Figure 2A This is a perspective view showing an example of the structure of a gear manufacturing apparatus.

[0040] Figure 2B This is a top view showing an example of the structure of a gear manufacturing device.

[0041] Figure 3 It is a diagram showing the positional relationship between the workpiece and the cutting edge.

[0042] Figure 4 It is a diagram showing the movement trajectory of the cutting edge relative to the workpiece.

[0043] Figure 5 This is a side view showing an example of a manufactured gear.

[0044] Figure 6 It is a cross-sectional view showing the shape of the cutting edge.

[0045] Figure 7 This is a perspective view showing an example of the structure of a gear manufacturing apparatus.

[0046] Figure 8 It is a cross-sectional view showing the shape of the cutting edge involved in the first variation.

[0047] Figure 9 This is a cross-sectional view showing the shape of the cutting edge involved in the second variation.

[0048] Explanation of reference numerals in the attached figures

[0049] 10… Gear, 11… Gear teeth, 20a… First device, C C …tooth height center circle, C F …rolling circle Detailed Implementation

[0050] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, a method for manufacturing a gear 10 using a cylindrical or tubular component made of metal as the initial material (workpiece W) is shown. The gear 10 manufactured by the gear manufacturing method of this embodiment is a helical gear with one to six teeth 11 (hereinafter referred to as the number of teeth) and a helix angle of 30° or more and 60° or less. Figure 1A and Figure 1B This diagram shows an example of a gear 10 manufactured by the gear manufacturing method of this embodiment. Furthermore, Figure 1A This is a 3D view of gear 10. Figure 1B This is a cross-sectional view of gear 10 cut along a plane perpendicular to the axis. Figure 1A and Figure 1B The image shows a helical gear with two teeth and a helix angle of 45°.

[0051] In this embodiment, the circle C passing through the center of the tooth height of gear 10 is... C Noted as "tooth height center circle C" C The center circle of the tooth height C C This is an example of the second circle of the present invention. Tooth height center circle C C diameter D C For: Tooth height center circle C C diameter D C =((tooth root circle C)B diameter D B )+(Tooth tip circle C T diameter D T )) / 2. Furthermore, the center circle C of the tooth height. C It is actually a cylinder extending along the axis of gear 10.

[0052] Figure 2A and Figure 2B This is a schematic diagram illustrating a structural example of the main components of the first apparatus 20a capable of implementing the gear manufacturing method according to this embodiment. Furthermore, Figure 2A This is a three-dimensional view of the first device 20a. Figure 2B This is a top view of the first device 20a. The first device 20a can be equipped with a device capable of performing whirling machining. For example... Figure 2A As shown, the first device 20a includes a chuck 21, a center 22, a tailstock 23, a cutting edge 24a, and a tool holder 25a (whirling head). The chuck 21 is configured to support (hold) one end of a workpiece W, which is a cylindrical or tubular component, along its axial direction. The center 22 and tailstock 23 are configured to support the opposite ends of the workpiece W along its 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 mount (support) multiple cutting edges 24a. The cutting edges 24a and the tool holder 25a on which the cutting edges 24a are mounted are examples of the "tool having multiple cutting edges arranged in a ring" of the present invention. The first device 20a also includes a rotary power source (not shown), and the chuck 21 and the tool holder 25a are each configured to be rotatable by the rotary power source. Furthermore, the rotation center line A1 of the chuck 21 (i.e., the rotation center line (axis) of the workpiece W supported on the chuck 21) is denoted as the first axis A1, and the rotation center line A2 of the tool holder 25a (i.e., the rotation center line of the "tool having multiple cutting edges arranged in a ring") is denoted as the second axis A2. The first axis A1 and the second axis A2 are in a torsional position. That is, the first axis A1 and the second axis A2 are not parallel and do not intersect. In other words, when the second axis A2 is projected onto the plane in a direction perpendicular to the "plane containing the first axis A1 and parallel to the second axis A2", the first axis A1 and the projected second axis A2 are set as different axes. Moreover, the first axis A1 and the projected second axis A2 are at a predetermined angle θ (refer to...). Figure 2B The axes A1 and A2 are inclined to each other. The angle θ (where the smaller of the angles formed by 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.

[0053] The tool holder 25a is configured to have an annular shape centered on the second axis A2, and the workpiece W can be inserted through its inner circumference. On the tool holder 25a, a plurality of cutting edges 24a are mounted in a ring-like arrangement centered on the second axis A2 (in other words, along the circumference of a circle centered on the second axis A2). In this embodiment, the plurality of cutting edges 24a are arranged radially centered on the second axis A2 and at equal intervals in the circumferential direction.

[0054] The workpiece W is positioned relative to the tool holder 25a such that it is inserted into the inner circumference of the tool holder 25a. The cutting edge 24a is configured such that, when mounted on the tool holder 25a, it can cut the outer peripheral surface of the workpiece W inserted into the inner circumference of the tool holder 25a (removing material from the contact area of ​​the workpiece W). The shape of the cutting edge 24a will be described later. Furthermore, in Figure 2A The diagram shows a structure with six cutting edges 24a, but the number of cutting edges 24a is not limited.

[0055] The first device 20a is configured such that, when the workpiece W is supported by the chuck 21 and the tailstock 23 (center 22), it can 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). Furthermore, the first device 20a can be configured such that the chuck 21, center 22, and tailstock 23 can move linearly in a direction parallel to the first axis A1; it can also be configured such that the tool holder 25a can move linearly in a direction parallel to the first axis A1; or it can be configured such that both the chuck 21, center 22, tailstock 23, and tool holder 25a can move linearly in a direction parallel to the first axis A1. Additionally, the first device 20a is configured to set the rotational speed of the chuck 21 and the rotational speed of the tool holder 25a asynchronously (i.e., independently).

[0056] Figure 3 This diagram illustrates 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 from 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 tilt angle θ, the trajectory T of the tips of the multiple cutting edges 24a (i.e., the portions closest to the second axis A2) is as follows when the tool holder 25a rotates about the second axis A2: T When viewed in a direction parallel to the first axis A1, it becomes an ellipse. Furthermore, as... Figure 3 As shown, the trajectory T T The ellipse is eccentric relative to the first axis A1 along its major axis.

[0057] Here, the operation of the first device 20a in manufacturing the gear 10 will be described. With the workpiece W supported by the chuck 21 and tailstock 23, the workpiece W is rotated about the first axis A1. Meanwhile, with multiple cutting edges 24a mounted on the tool holder 25a, the tool holder 25a is rotated about the second axis A2. Furthermore, the rotational speed of the workpiece W and the rotational speed of the tool holder 25a may be asynchronous. Then, the workpiece W and the tool holder 25a 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. Specifically, the relative speed between 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 in the manufactured gear 10) × (distance between adjacent teeth 11 in the direction of the first axis A1)" per revolution of the workpiece W.

[0058] Furthermore, by bringing the tip of the rotating cutting edge 24a into contact with the outer peripheral surface of the workpiece W, material from the workpiece W at the contact point is removed. Since the first axis A1 and the second axis A2 are in a torsional position, tooth grooves 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 peripheral surface of the workpiece W. Then, by moving the workpiece W and the tool holder 25a relative to each other at a speed synchronized with the rotational speed of the workpiece W in a direction parallel to the first axis A1, helical tooth grooves are formed on the outer peripheral surface of the workpiece W, resulting in helical teeth 11 on the outer peripheral surface of the workpiece W. Thus, a helical gear is manufactured.

[0059] Thus, in the gear 10 manufacturing method according to this embodiment, the tooth groove (spiral groove) is formed by intermittent machining using multiple rotating cutting edges 24a. With such a structure, less heat is generated during machining compared to continuous machining using a single cutting edge. Therefore, a high-precision gear 10 can be manufactured. Furthermore, according to this embodiment, the gear 10 can be manufactured in one pass (one pass is defined as the relative movement of 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, since the material (workpiece) is not extruded as in the case of manufacturing gears by roll forming, additional machining (specifically, machining to remove the extruded material) is not required.

[0060] Figure 4 It represents the outline O of the cutting edge 24a within a cross section perpendicular to the first axis A1, with the workpiece W fixed. E The movement trajectory T U (That is, the contour line O of the cutting edge 24a relative to the workpiece W) E The movement trajectory T UThe diagram shows the contour line O of the cutting edge 24a with the workpiece W fixed. E The target contour line O of the tooth 11 of gear 10 is on one side. G (Referring to the design outline of the teeth 11 of the manufactured gear 10) in contact, while relative to the workpiece W at a straight line parallel to the first axis A1 (in Figure 4 The cutting edge 24a rotates around a straight line perpendicular to the paper plane, moving within that cross section. The trajectory T of the cutting edge 24a within this cross section is shown. U It is an incycloid curve.

[0061] When the contour line O of the cutting edge 24a E When moving within this cross section, there exists the contour line O of the cutting edge 24a. E The target contour line O relative to tooth 11 G The point R of non-slip rolling contact. Conversely, the contour line O of the cutting edge 24a. E One side is aligned with the target contour line O G Contact side at the target contour line O G The specified point R is relative to the target contour line O. G Non-slip rolling contact, outside a specified point R relative to the target contour line O G It slides and rotates simultaneously. Hereinafter, the circle centered on the first axis A1 and passing through the point R of rolling contact within the plane perpendicular to the first axis A1 will be denoted as "rolling circle C". F The rolling circle C F This is an example of the first circle of the present invention.

[0062] In cyclone cutting, the axis tilt angle θ is based on the rolling circle C. F diameter D F Therefore, in this embodiment, the axis tilt angle θ is also based on the rolling circle C. F diameter D F The axial tilt angle θ is defined 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 the direction parallel to the first axis, and the circumference L1 of the first circle. Specifically, the axial tilt angle θ is defined by the following mathematical formula (1).

[0063] θ = tan -1 ((N×P) / L1) Mathematical expression (1)

[0064] N: The number of tooth grooves formed in workpiece W (= the number of teeth in the manufactured gear 10),

[0065] P: The spacing formed in the tooth grooves of workpiece W in a direction parallel to the first axis A1.

[0066] L1: Rolling circle C F diameter D F ×π (= Rolling circle C) F (circumference).

[0067] Furthermore, the tool holder 25a, chuck 21, tip 22, and tailstock 23 can move relative to each other in a direction parallel to the first axis A1 within a range where they do not contact each other. And, as... Figure 2B As shown, the first axis A1 and the second axis A2 are set as different axes, inclined at an axis tilt angle θ. Therefore, even when the tool holder 25a is closest to the chuck 21 within a range where the outer periphery S2 of the tool holder 25a does not contact the chuck 21, the actual position S1 where the cutting edge 24a cuts the workpiece W (the center of the tool holder 25a) is located at a distance M1 from the chuck 21. That is, a tooth groove cannot be formed in the workpiece W within the range from the position S1 where the cutting edge 24a contacts the workpiece to the distance M1. The same applies to the center point 22 and the tailstock 23. Moreover, from Figure 2B It can be seen that as the axial tilt angle θ increases, the distance M1 also increases. Therefore, as the axial tilt angle θ increases, the portion on the workpiece W where the tooth groove cannot be formed becomes longer. Furthermore, as the axial tilt angle θ increases, the portion at the end of the tooth 11 within the range where the tooth groove is formed becomes incomplete in shape (the target contour line O of the tooth 11 cannot be obtained). G The portion where tooth 11 cannot be part of the design shape becomes longer. In particular, as in this embodiment, when manufacturing helical gears with a helix angle of 30° or more and 60° or less, the axial tilt angle θ must be increased compared to manufacturing general external threads for fastening, thus easily leading to the problems described above.

[0068] In this embodiment, the rolling circle C F diameter D F Let the center circle of the tooth height be C. C diameter D C Large and at the tooth tip circle C T diameter D T The following. Therefore, with the rolling circle C F diameter D F Center circle of tooth height C C diameter D C Compared to the following structures, the axial tilt angle θ can be reduced. Specifically, as follows: Figure 5 As shown, the helix angle of gear 10 decreases from the tooth root towards the tooth tip. Furthermore, Figure 5 This is a side view of gear 10. Figure 5 In the middle, β B β represents the helix angle at the tooth root. T β represents the helix angle at the tooth tip. F Indicates the center circle of the tooth height CF The helix angle at that point. Furthermore, the rolling circle C of the gear 10 (helical gear) manufactured by the above method... F The helix angle β F The following relationship exists.

[0069] Helix angle β F (°)=90(°)-(axis tilt angle θ(°))

[0070] Therefore, if the rolling circle C is increased F diameter D F Then the rolling circle C F diameter D F helix angle β at the location F The value of increases, thus reducing the value of the axis tilt angle θ.

[0071] Furthermore, by reducing the axis tilt angle θ, the aforementioned distance M1 can be reduced. That is, when the workpiece W and the cutting edge 24a move relative to each other in a direction parallel to the first axis A1, interference between the chuck 21, center 22, and tailstock 23, which serve as supports for the workpiece W, and the cutting edge 24a and the tool holder 25a, which serves as a support for the cutting edge 24a, can be reduced. Therefore, the length of the portion where tooth grooves cannot be formed on the workpiece W can be shortened. In addition, by reducing the axis tilt angle θ, the portion of the formed gear 10 with an incomplete tooth groove shape (the portion that is not the target shape, in other words, the portion that is not the design shape) can be shortened.

[0072] In particular, since the lead angle of the helical gear (=90°-(helix angle of gear 10 (°))) is larger than that of the lead angle of a general fastening thread, the axis tilt angle θ must be increased compared to the case of manufacturing a fastening thread. However, according to this embodiment, the axis tilt angle θ can be reduced when manufacturing the helical gear.

[0073] Furthermore, the fewer the number of teeth, the greater the ratio of the dimension from the center of the tooth height to the tooth tip to the diameter of the base circle or root circle of gear 10. And, as this ratio increases, the dimension relative to the rolling circle C... F diameter D F With the center circle C of the tooth height C diameter D C The increase in the dimensional difference between them (i.e., the rolling circle C) F diameter D F The rate of reduction of the axial tilt angle θ increases with the increase of the number of teeth. Therefore, the fewer the number of teeth, for example, when the number of teeth is any one of 1 to 6 as in this embodiment, the greater the effect of reducing the axial tilt angle θ.

[0074] In this embodiment, by setting the shape of the cutting edge 24a to the shape described below, the rolling circle C is made F diameter DF Greater than the center circle C of the tooth height C diameter D C . Figure 6 This is a cross-sectional view showing the cutting edge 24a being cut along a plane including the second axis A2, with the cutting edge 24a mounted on the tool holder 25a. Additionally, in Figure 6 In the middle, the first axis A1, the tooth root circle C B and tooth tip circle C T Tiltd relative to the paper surface. For example... Figure 6 As shown, the cross-sectional shape of the cutting edge 24a, which cuts along a plane containing the second axis A2, has a slender shape whose width (the dimension in the direction parallel to the second axis A2) decreases as it approaches the second axis A2. In other words, it enters the tooth tip circle C during machining. T The inner part ( Figure 6 Medium tooth 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 as the upper base, the side farther from the second axis A2 as the lower base, and the sides on both sides of the second axis A2 as hypotenuses. The sides on both sides of the second axis A2 (corresponding to the hypotenuses of the trapezoid) are curves (surfaces) that bulge outwards along the second axis A2. The surface corresponding to the upper base of the trapezoid is designated as the top surface 241, and the surface corresponding to the hypotenuse is designated as the side surface 242.

[0075] In this plane, the angle between the tangent to the side surface 242 at the intersection of the straight line Q perpendicular to the second axis A2 and the side surface 242 is the tool pressure angle α. In this embodiment, the tool pressure angle α of the cutting edge 24a when manufacturing a specified helical gear is "compared to" the angle at the rolling circle C. F diameter D F With the center circle C of the tooth height C diameter D C The tool pressure angle α of the cutting edge is greater than that of the aforementioned helical gear when manufacturing a helical gear (helical gear of the same shape and size) using the same apparatus under the same conditions. Furthermore, in this embodiment, since the side surface 242 of the cutting edge 24a is a curved surface bulging outwards, the tool pressure angle α gradually (smoothly) increases as it approaches the second axis A2. Therefore, more precisely, the tool pressure angle α at a specified distance from the top surface 241 (in a direction perpendicular to the second axis A2) of the cutting edge 24a when manufacturing the specified helical gear in this embodiment is greater than that at the rolling circle C. F diameter D F With the center circle C of the tooth height C diameter D CThe tool pressure angle α is the largest value at the position where the cutting edge is at the same specified distance in the height direction from the top surface when manufacturing a helical gear (helical gear of the same shape and size) that is the same as the helical gear specified above under the same conditions and using the same equipment. In addition, the specific value of the tool pressure angle α is specified according to the shape and size of the teeth 11 of the manufactured gear 10, and is not limited.

[0076] Furthermore, while there is no specific upper limit to the tool pressure angle α, it is actually limited by the axis inclination angle θ and the shape and size of the teeth 11 of the manufactured gear 10. Specifically, from Figure 6 It can be seen that 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 needs to be the tooth root circle C. B diameter D B Half of the cutting edge 24a. Furthermore, the radius dimension X2 of the circle centered on the second axis A2 of the side surface 242 of the cutting edge 24a (the height of the trapezoid mentioned above) needs to be greater than or equal to the tooth height of the manufactured gear 10. On the other hand, when the tool pressure angle α increases, the width B1 of the tip face 241 of the cutting edge 24a decreases. When the width B1 is 0, the cross-sectional shape of the cutting edge 24a is not approximately trapezoidal but approximately triangular. When the tool pressure angle α further increases, the dimension X2 of the side surface 242 of the cutting edge 24a decreases. Therefore, when the cross-sectional shape of the cutting edge 24a is approximately triangular, the dimension X2 of the cutting edge 24a used for manufacturing the gear 10 cannot be guaranteed. Therefore, the maximum value of the tool pressure angle α can be described as "the maximum value within the range where the dimension X2 of the cutting edge 24a (the dimension in the direction perpendicular to the second axis A2) remains unchanged" or "the maximum value within the range where the cross-sectional shape of the cutting edge 24a can maintain an approximately trapezoidal shape without changing the dimension X2."

[0077] Based on this structure, the rolling circle C can be made F Located at the center circle C of the tooth height C The outer side. Therefore, with the rolling circle C F diameter D F C is the center circle of the tooth height. C Compared to cases with diameters smaller than 1, the axial tilt angle θ decreases, thus reducing the... Figure 2B The distance M1 shown is used. Therefore, the area where tooth grooves cannot be formed on the workpiece W can be shortened. Furthermore, by reducing the axial tilt angle θ, the portion of the tooth 11 at the end of the area where the tooth groove cannot be formed (where the target contour line O of tooth 11 cannot be obtained) can be shortened. G (Partially). Furthermore, it increases the range of relative movement between the tool holder 25a and the chuck 21, center 22, and tailstock 23. Therefore, it allows for an increase in the axial dimension of the manufactured gear 10.

[0078] Furthermore, based on this structure, the axis tilt angle θ can be reduced simply by increasing the tool pressure angle α.

[0079] Furthermore, in the gear manufacturing method according to this embodiment, the rotational speed of the tool holder 25a is not limited by the rotational speed of the workpiece W. That is, the rotational speed of the tool holder 25a and the rotational speed of the workpiece W can be made asynchronous. Therefore, regardless of the rotational speed of the workpiece W, the rotational speed of the tool holder 25a, i.e., the cutting speed, can be increased. Moreover, since 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 relative movement speed of 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 cutting surface can be smoothed (the surface roughness of the machined surface can be reduced).

[0080] Furthermore, according to this embodiment, the first device 20a can utilize existing known devices capable of performing cyclone cutting (spiral rotation). Therefore, according to this embodiment, no increase in equipment cost is resulted.

[0081] Next, a second device 20b, which is a modified example of an apparatus capable of carrying out the gear manufacturing method according to the embodiments of the present invention, will be described. The second device 20b is an apparatus that applies a ring-shaped tool. Figure 7 This is a schematic diagram showing the structure of the second device 20b. Furthermore, structural elements common to the first device 20a are indicated using the same reference numerals as those for the first device 20a, and their descriptions are omitted.

[0082] like Figure 7 As shown, the second device 20b is configured to manufacture the gear 10 using a ring-shaped tool. A ring-shaped grinding stone 24b is used with the ring-shaped tool. The ring-shaped grinding stone 24b is configured to insert a workpiece W through its inner circumference and to grind the outer circumference of the workpiece W from its inner circumference. Furthermore, the tool holder 25b is configured to mount the ring-shaped grinding stone 24b so that its axis (centerline) aligns with the second axis A2. Additionally, the cross-sectional shape of the ring-shaped grinding stone 24b cut along a plane including the second axis A2 can be the same as the cross-sectional shape of the cutting edge 24a used with the first device 20a. Furthermore, the operation of the second device 20b is the same as that of the first device 20a. Moreover, the manufacturing method using the second device 20b achieves the same effects as the manufacturing method using the first device 20a.

[0083] Next, a variation of the shape of the cutting edge 24a and the annular grinding stone 24b will be described. Figure 8This is a diagram showing the shape of the cutting edge 24a and the annular grinding stone 24b involved in the first modified example. Figure 9 This is a diagram showing the shapes of the cutting edge 24a and the annular grinding stone 24b involved in the second variation. Additionally, Figure 8 and Figure 9 These are cross-sectional views showing the cutting edge 24a and the annular grinding stone 24b cut along a plane containing the second axis A2. If a gear has a small diameter and few teeth, and its tooth profile is standard (e.g., an involute gear), when it meshes with other gears, the portion near the tooth tip of one of the other gears may sometimes interfere with the portion near the tooth root of the gear. Therefore, to avoid such interference, the inter-tooth surface distance near the tooth root of a small-diameter gear with few teeth is sometimes larger than that in the case of a standard tooth profile. Figure 8 The shape involved in the first variation example shown and Figure 9 The second variation shown involves a shape that allows 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 profile.

[0084] like Figure 8 As shown, the cutting edge 24a and the annular grinding stone 24b involved in the first modified example have a first portion 243 and a second portion 244 located on the top side of the first portion 243 (the side closer to the second axis A2 than the first portion 243 when mounted in the tool holder). Both the first portion 243 and the second portion 244 have a pointed shape whose width decreases as they approach the second axis A2. In addition, the outline of the side surface 245 of the first portion 243 in a cross-section cut along the plane containing the second axis A2 is a straight line, and its tool pressure angle α1 is fixed. Similarly, the outline of the side surface 246 of the second portion 244 in a cross-section cut along the plane containing the second axis A2 is also a straight line, and its tool pressure angle α2 is fixed. 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. When this is the structure, the width of the top surface 241 is larger compared to the structure without the second portion 244. Therefore, compared with a structure that uses a cutting edge 24a without the second part 244 and an annular grinding stone 24b, the distance between tooth surfaces near the tooth root can be increased.

[0085] like Figure 9As shown, the cutting edge 24a and the annular grinding stone 24b involved in the second modification also have a first portion 243 and a second portion 244 located on the top side of the first portion 243. The first portion 243 has a pointed shape whose width decreases as it approaches the second axis A2. Furthermore, the side surface 245 of the first portion 243 is a curved surface in which the tool pressure angle α1 smoothly (continuously) increases as it approaches the second axis A2. Similarly, the second portion 244 also has a pointed shape whose width decreases as it approaches the second axis A2. Furthermore, the side surface 246 of the second portion 244 is also a curved surface in which the tool pressure angle α2 smoothly (continuously) increases 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. When this structure is used, the same effect as the first modification can be achieved.

[0086] Alternatively, one of the tool pressure angles α1 of the first part 243 and α2 of the second part 244 may be fixed, while the other may smoothly (continuously) increase as it approaches the second axis A2. Whether the tool pressure angles α1 of the first part 243 and α2 of the second part 244 are fixed respectively, and the specific tool pressure angles α1 and α2, are appropriately selected according to the tooth profile of the manufactured gear 11.

[0087] The embodiments and modifications of the present invention have been described above, but the technical scope of the present invention is not limited to the above embodiments and modifications. The present invention can be modified without departing from its spirit, and these modifications are also included within the technical scope of the present invention.

[0088] For example, in the above embodiment, an example of manufacturing a helical gear with two teeth and a helix angle of 45° is shown, but the number of teeth and helix angle of the manufactured gear 10 are not limited to the above embodiment. In addition, the shape of the teeth 11 of the manufactured gear 10 is not limited.

Claims

1. A method for manufacturing a gear, comprising rotating a workpiece about a first axis, rotating a ring-shaped tool or a tool having a plurality of cutting edges arranged in a ring about the second axis about the second axis, and rotating the workpiece and the tool relative to each other at a speed synchronized with the rotational speed of the workpiece in a direction parallel to the first axis, while bringing the inner circumferential side of the tool into contact with the outer circumferential surface of the workpiece, removing material from the contacted portion of the workpiece by the relative movement of the tool and the workpiece, thereby forming a helical tooth on the outer circumferential surface of the workpiece, wherein... In a cross-section perpendicular to the first axis, the tool's contour line contacts the contour line of the formed helical teeth, i.e., the target contour line, while simultaneously rolling in non-slip contact relative to the target contour line at a predetermined point, and sliding and rotating relative to the target contour line at other points. This allows the workpiece to rotate around the first axis, and the workpiece and the tool to move relative to each other in a direction parallel to the first axis at a speed synchronized with the workpiece's rotational speed. In a cross-section perpendicular to the first axis, the diameter of the first circle (centered on the first axis and passing through the specified point) is larger than the diameter of the second circle (centered on the first axis and passing through the center of the tooth height of the target contour line). When the second axis is projected onto a plane that contains the first axis and is parallel to the second axis, the first axis and the projected second axis are set to be different axes.

2. The method for manufacturing a gear according to claim 1, wherein, The angle θ between the first axis and the projected second axis is determined by the number N of the helical teeth formed on the workpiece, the spacing P of the helical teeth formed on the workpiece in the direction parallel to the first axis, and the circumference L1 of the first circle.

3. The method for manufacturing a gear according to claim 2, wherein, The angle θ between the first axis and the projected second axis is expressed by the following mathematical formula (1): θ = tan -1 ((N×P) / L1) Mathematical expression (1) N: The number of the spiral teeth formed on the workpiece. P: The spacing between the helical teeth formed on the workpiece in a direction parallel to the first axis. L1: Circumference of the first circle.

4. A method for manufacturing a gear according to any one of claims 1 to 3, wherein, Regarding the aforementioned tool In a cross-section cut along a plane containing the second axis, it has a pointed shape whose dimensions gradually decrease as it approaches the second axis and is parallel to the second axis. In a cross-section cut along a plane containing the second axis, the angle of inclination of the two ends of the tool in the direction parallel to the second axis relative to a straight line perpendicular to the second axis, i.e., the tool pressure angle, is greater than the tool pressure angle when the diameter of the first circle is the same as the diameter of the second circle.

5. The method for manufacturing a gear according to claim 4, wherein, The tool has the following features: The first part has a specified tool pressure angle; and The second part is located on the side closer to the second axis than the first part, and has a tool pressure angle smaller than the specified tool pressure angle.

6. The method for manufacturing a gear according to claim 4, wherein, The tool has the following features: The first part, its tool pressure angle gradually increases as it approaches the second axis; and The second part is located closer to the second axis than the first part, and the tool pressure angle gradually increases as it gets closer to the second axis. The tool pressure angle at the end of the second portion on the side away from the second axis is smaller than the tool pressure angle at the end of the first portion on the side closer to the second axis.

7. A method for manufacturing a gear according to any one of claims 1 to 3, wherein, The tool rotates at a speed that is out of sync with the rotational speed of the workpiece centered on the first axis and the speed of the relative movement of the workpiece and the tool in the direction of the first axis.

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

9. The method for manufacturing a gear according to claim 8, wherein, The number of teeth in the manufactured gear is any one from 1 to 6.

10. The method for manufacturing a gear according to claim 8, wherein, The helix angle of the manufactured gear is 30° or more and 60° or less.

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