Gear grinding method

Abstract

A gear grinding method is provided in which a workpiece (W) which is a gear is ground with a threaded grindstone (11) as a processing tool, while the workpiece and the grindstone are being synchronously rotated. The method includes a first processing step (S1) for conducting first processing wherein the threaded grindstone is moved in a radial direction (X) of the workpiece while the intersection angle (Σ) between the threaded grindstone and the workpiece is being changed on the basis of the distance (WL) between the threaded grindstone and the workpiece, thereby grinding the workpiece. The first processing is conducted with respect to a plurality of positions along the axial direction of the workpiece while the axial-direction position of the workpiece is being successively changed.

Description

Gear grinding method

[0001] The present invention relates to a gear grinding method.

[0002] Conventionally, a gear to be machined and a threaded grinding wheel of a machining tool are rotated synchronously to grind the gear using the threaded grinding wheel. For example, in the configuration disclosed in Patent Document 1, a barrel-shaped threaded grinding wheel is used, and the axis-crossing angle between the threaded grinding wheel and the gear is increased as the radius change of the threaded grinding wheel increases, thereby increasing the sliding speed between the threaded grinding wheel and the gear, improving the cutting quality of the threaded grinding wheel, and aiming to improve machining accuracy and extend the tool life.

[0003] Furthermore, the configuration disclosed in Patent Document 2 aims to reduce the processing load and uneven wear and improve processing accuracy by using a threaded grinding wheel formed in a barrel shape that gradually becomes smaller from the axial middle portion toward both axial ends in accordance with the amount of allowance to be removed from the internal gear by the threaded grinding wheel.

[0004] In addition, the configuration disclosed in Patent Document 3 uses a threaded grinding wheel whose tooth tip outer shape is perpendicular to the axial direction, and grinds the workpiece radially multiple times with the grinding wheel positioned at a first grinding width in the axial direction of the workpiece. The grinding wheel is then removed from the workpiece and moved to a second grinding width in the axial direction of the workpiece, and grinds the workpiece radially multiple times. The grinding wheel is then moved from the other end of the tooth width along the tooth surface to remove the finishing allowance and the remaining grinding allowance between the first and second grinding widths in a single grinding run. In this configuration, grinding while moving in the axial direction requires grinding at a relatively low speed to maintain accuracy, but by performing this process in a single run, grinding time is shortened while maintaining accuracy.

[0005] In addition, the configuration disclosed in Patent Document 4 uses a grinding wheel with a conical tooth tip so that the tip of the grinding wheel does not come into contact with the workpiece when grinding the workpiece, thereby preventing the tip of the grinding wheel from grinding the workpiece and preventing localized wear of the tip of the grinding wheel.

[0006] Japanese Patent Application Laid-Open No. 2010-158749 Japanese Patent Application Laid-Open No. 4875602 Japanese Patent Application Laid-Open No. 59-219116 Japanese Patent Application Laid-Open No. 2021-13989

[0007] However, in the configuration disclosed in Patent Document 1, when the threaded grinding wheel is moved in the axial direction of the gear, the end of the threaded grinding wheel cuts into the gear in the radial direction while grinding it away, which results in a locally large cutting depth at the end of the threaded grinding wheel, resulting in so-called "uneven contact."This causes uneven wear at the end of the threaded grinding wheel, shortening the life of the threaded grinding wheel.

[0008] Furthermore, the configuration disclosed in Patent Document 1 uses a threaded grinding wheel whose tooth tips are offset relative to the axial direction of the grinding wheel. Therefore, when the threaded grinding wheel and the gear are ground at a predetermined crossing angle, the tip of the threaded grinding wheel is offset from the central axis of the gear. Therefore, when the threaded grinding wheel is brought closer to the gear in the radial direction during grinding, the tip of the threaded grinding wheel exceeds the target shape of the gear and interferes with the gear. As a result, the gear's machining accuracy is reduced.

[0009] Furthermore, in the configuration disclosed in Patent Document 2, the diameter of the end of the threaded grinding wheel is further reduced, but if the grinding allowance is large, uneven contact occurs at the end of the threaded grinding wheel even if the grinding allowance is smaller than the amount of reduction in the diameter of the end of the threaded grinding wheel, resulting in uneven wear of the threaded grinding wheel.

[0010] Furthermore, the configuration disclosed in Patent Document 3 uses a threaded grinding wheel in which the outer shape of the tooth tip is parallel to the axial direction of the grinding wheel, and therefore does not suffer from the problem of grinding beyond the target shape at the tip of the threaded grinding wheel, which occurs in the configuration disclosed in Patent Document 1. However, with a threaded grinding wheel in which the outer shape of the tooth tip is parallel to the axial direction, grinding in the axial direction of a gear with high precision requires operation at a relatively low speed, resulting in poor grinding efficiency.

[0011] In addition, the configuration disclosed in Patent Document 4 uses a grinding wheel with a conical tooth tip, so that the tip of the grinding wheel does not come into contact with the workpiece when grinding the workpiece, which narrows the area of ​​the grinding wheel that actually contributes to the grinding process, resulting in reduced grinding efficiency. Even if the tip of the grinding wheel is prevented from coming into contact with the workpiece, the portion of the grinding wheel tooth surface that comes into contact with the gear, which essentially corresponds to the tip of the grinding wheel in Patent Document 1, exceeds the target shape of the gear and interferes with the gear, resulting in reduced gear machining accuracy.

[0012] The present disclosure has been made in consideration of the above circumstances, and aims to provide a gear grinding method that can prevent the occurrence of partial contact in the threaded grinding wheel, thereby extending the life of the threaded grinding wheel and improving processing accuracy and grinding efficiency.

[0013] One aspect of the present disclosure is a gear grinding method in which a workpiece, which is a gear, and a threaded grinding wheel, which is a processing tool, are rotated synchronously while grinding the workpiece with the threaded grinding wheel, the gear grinding method including a first processing step in which the threaded grinding wheel is moved in the radial direction of the workpiece while changing the crossing angle between the threaded grinding wheel and the workpiece based on the distance between the workpiece and the threaded grinding wheel, thereby grinding the workpiece at a plurality of axial positions by sequentially changing the axial position of the workpiece.

[0014] According to the gear grinding method of this embodiment, the workpiece is ground by performing a first grinding process in which the axial position of the workpiece is sequentially changed and the threaded grinding wheel is moved radially at a plurality of axial positions. In this grinding method, the first grinding process is a plunge grinding process in which the threaded grinding wheel is moved radially of the workpiece, making uneven contact relatively unlikely. This prevents uneven contact, thereby preventing uneven wear at the end of the threaded grinding wheel and extending the life of the threaded grinding wheel.

[0015] Furthermore, in the first processing step, the threaded grinding wheel is used to grind the workpiece by moving the threaded grinding wheel in the radial direction of the workpiece while changing the crossing angle between the threaded grinding wheel and the workpiece based on the distance between the threaded grinding wheel and the workpiece, thereby reducing interference between the tip of the threaded grinding wheel and the workpiece. This prevents the workpiece from being cut beyond the target shape, improving the processing accuracy of the workpiece. Furthermore, since the grinding can be performed with the tip of the threaded grinding wheel involved in the grinding process while the crossing angle between the threaded grinding wheel and the workpiece is maintained, the grinding efficiency can be improved.

[0016] As described above, according to the above-described aspect, it is possible to provide a gear grinding method that can prevent the occurrence of partial contact in the threaded grinding wheel, thereby extending the life of the threaded grinding wheel and improving the processing accuracy and grinding efficiency.

[0017] FIG. 1 is a conceptual diagram showing the configuration of a threaded grinding wheel and a gear used in the gear grinding method of the first embodiment. FIG. 2 is an axial cross-sectional view of the threaded grinding wheel of the first embodiment. FIG. 3(a) is a conceptual diagram illustrating a meshing line, and FIG. 3(b) is a cross-sectional view of the threaded grinding wheel and workpiece of the first embodiment, taken along the workpiece rotation axis. FIG. 4 is a flow diagram of the gear grinding method of the first embodiment. FIG. 5 is a conceptual diagram illustrating a first processing step in the gear grinding method of the first embodiment. FIG. 6 is another conceptual diagram illustrating the first processing step in the gear grinding method of the first embodiment. FIG. 7 is a conceptual diagram illustrating a comparative example in which interference occurs between the workpiece and the threaded grinding wheel. FIG. 8 is another conceptual diagram illustrating the first processing step in the gear grinding method of the first embodiment. FIG. 9 is a conceptual diagram illustrating a second processing step in the gear grinding method of the first embodiment. FIG. 10 is another conceptual diagram illustrating the second processing step in the gear grinding method of the first embodiment. FIG. 11 is a conceptual diagram illustrating a conventional gear grinding method as a comparative example. FIG. 12 is a diagram showing test results of the gear grinding methods of the first embodiment and the comparative example in the confirmation test.

[0018] (Embodiment 1) 1. Workpiece The workpiece W to be ground by the gear grinding method of this embodiment 1 is a gear, and may be either an internal gear or an external gear. In this embodiment 1, an internal gear having a tooth surface on the inner peripheral surface of the workpiece W is used, as shown in FIG.

[0019] 2. Configuration of Gear Grinding Apparatus In the gear grinding method of the first embodiment, a gear, or workpiece W, is machined using a gear grinding apparatus. The apparatus is selected appropriately depending on the shape of the gear to be machined. In the first embodiment, since the workpiece W is an internal gear, an internal gear generating grinding machine (not shown) is used as the gear grinding apparatus 1. The gear grinding apparatus has a threaded grinding wheel 11, which is a machining tool, as shown in FIG. 1. The workpiece W is mounted on the gear grinding apparatus (not shown) so that it can rotate around a workpiece rotation axis C1 R1 that is parallel to the vertical direction (Z-axis direction). A predetermined tooth profile is formed in advance in the workpiece W, as shown in FIG. 1, and the axial direction of the workpiece W is parallel to the Z-axis direction.

[0020] The gear grinding apparatus also supports a grinding wheel arbor 12 rotatably about a grinding wheel rotation axis B1 R2. The grinding wheel arbor 12 is movable in a direction that adjusts the distance between the workpiece rotation axis C1 and the grinding wheel rotation axis B1 (hereinafter referred to as the X-axis direction), a direction perpendicular to the grinding wheel rotation axis B1 (hereinafter referred to as the Y-axis direction), and a Z-axis direction. A threaded grinding wheel 11 for grinding the workpiece W is attached to the tip of the grinding wheel arbor 12. Therefore, by moving the grinding wheel arbor 12 in the X-axis, Y-axis, and Z-axis directions and rotating it about the grinding wheel rotation axis B1, the threaded grinding wheel 11 moves and rotates together with the grinding wheel arbor 12.

[0021] The grinding wheel rotation axis B1 of the grinding wheel arbor 12 is inclined with respect to the workpiece rotation axis C1, and the two intersect at a crossing angle Σ. During grinding, the threaded grinding wheel 11 rotates around the grinding wheel rotation axis B1, which intersects with the workpiece rotation axis C1 of the workpiece W at the crossing angle Σ. As will be described later, the crossing angle Σ is configured to be changeable, and is configured to be changed in accordance with the distance in the X-axis direction between the threaded grinding wheel 11 and the workpiece W during the first processing.

[0022] When the object to be machined is an external gear, grinding of the external gear is possible by attaching a grinding wheel gear for external tooth grinding to the tip of the grinding wheel arbor 12 instead of the threaded grinding wheel 11.

[0023] 2 , when the threaded grinding wheel 11 is rotated about the wheel rotation axis B1 of the threaded grinding wheel 11, the rotation locus 11a of the outer peripheral surface of the threaded grinding wheel 11 (i.e., the outer shape of the tooth tips of the threaded grinding wheel 11) changes in the direction of the wheel rotation axis B1. The rotation locus 11a of the outer peripheral surface of the threaded grinding wheel 11 is determined based on the meshing line between the threaded grinding wheel 11 and the workpiece W, i.e., the machining area.

[0024] As shown in Fig. 3(a) , the meshing line ML in the case of an internal gear can be represented by a partial line segment of an imaginary ellipse VR1 formed by a cross section of the inner peripheral surface of the workpiece W at a certain plane PN, and as shown in Fig. 3(b) , the rotation locus 11a of the outer peripheral surface of the threaded grinding wheel 11 is a curved surface including the meshing line ML. In this embodiment, one end of the meshing line ML in the workpiece W is located on a first end 111, which is one axial end of the threaded grinding wheel 11, and the other end of the meshing line ML is located on a second end 112, which is the other axial end of the threaded grinding wheel 11. Note that one and the other ends of the meshing line ML do not necessarily have to be located on the first end 111 and the second end 112 of the threaded grinding wheel 11; if the width of the threaded grinding wheel 11 is wide, one and the other ends of the meshing line ML may not be located on the first end 111 and the second end 112. 3(b), the grinding wheel rotation axis B1 of the threaded grinding wheel 11 is inclined with respect to the meshing line ML. Note that the tooth trace of the workpiece W is inclined with respect to the axial direction Z of the workpiece W as shown in FIG. 1, but in FIG. 3(b), for convenience, the tooth trace of the workpiece W is shown as extending parallel to the axial direction Z.

[0025] In the first embodiment, in the rotation locus 11a of the outer peripheral surface of the threaded grinding wheel 11, the diameter D1 of the rotation locus of the outer peripheral surface at a first end 111, which is one axial end of the threaded grinding wheel 11, is smaller than the diameter D2 of the rotation locus of the outer peripheral surface at a second end 112, which is the other axial end. In the rotation locus 11a of the outer peripheral surface of the threaded grinding wheel 11, at least the rotation locus of the outer peripheral surface at the second end 112 has the largest diameter D2. As shown in Fig. 1 , the grinding wheel rotation axis B1 of the threaded grinding wheel 11 is inclined with respect to the workpiece rotation axis C1 of the workpiece W, forming an intersecting angle Σ. Therefore, as shown in Fig. 3(b), when viewed from the X-axis direction where the first machining is performed, a virtual line F2 that passes through the center of the first end 111 and is parallel to the workpiece rotation axis C1 is offset, as indicated by arrow d1, from a virtual line F1 that overlaps with the workpiece rotation axis C1 of the threaded grinding wheel 11 and passes through the center of a central position 113 in the width direction of the threaded grinding wheel 11.

[0026] In the first embodiment, the diameter of the threaded grinding wheel 11 decreases from the second end 112 to the first end 111. This gives the threaded grinding wheel 11 a cup shape. Note that the threaded grinding wheel 11 may have a region between the first end 111 and the second end 112 where the diameter of the rotation locus does not change.

[0027] 4. Gear Grinding Method The gear grinding method of this embodiment will be described in detail using the flow diagram shown in Fig. 4 and the diagrams illustrating the grinding states in Figs. 5 to 11. First, as shown in Fig. 4, the gear grinding method of this embodiment includes a first machining step S1 and a second machining step S2. As will be described later, in the first machining step, a first machining operation is performed multiple times using the threaded grinding wheel 11, and in the second machining step S2, a second machining operation is performed using the threaded grinding wheel 11. Note that, although the tooth trace of the workpiece W is inclined with respect to the axial direction Z of the workpiece W as shown in Fig. 1, in Figs. 5 and 9, for convenience, the tooth trace of the workpiece W is shown as extending parallel to the axial direction Z.

[0028] 4-1. First Machining Step S1 In the first machining step S1, in step S11 shown in Fig. 4, the threaded grinding wheel 11 is moved to a first axial position. The first axial position is not limited to a specific position, but may be a position near an end of the workpiece W in the axial direction Z. In this embodiment, as shown in Fig. 5, the first axial position is a position near the upper end Wc, which is one end of the workpiece W in the axial direction Z, and where the arrow P1 is located.

[0029] Next, in step S12 shown in Fig. 4, the threaded grinding wheel 11 is moved in the radial direction X toward the inner peripheral surface of the workpiece W while changing the crossing angle Σ based on the distance WL between the workpiece W and the threaded grinding wheel 11, thereby starting the first machining process. The distance WL between the workpiece W and the threaded grinding wheel 11 shown in Fig. 6(a) is the difference between the state where the threaded grinding wheel 11 contacts the inner peripheral surface of the workpiece W and the threaded grinding wheel 11, resulting in a zero depth of cut (a state where the workpiece W has the final finish shape that is the target for machining). The crossing angle Σ shown in Fig. 6(b) is changed within a range from an initial value Σ0 to a target value Σ1. The correspondence relationship between the distance WL and the crossing angle Σ can be, for example, the relationship indicated by OK in Table 1 below, when the initial value Σ0 of the crossing angle Σ is 32° and the target value Σ1 is 35°, and the initial value of the distance WL is 6 mm.

[0030]

[0031] Based on the relationship shown in Table 1, in the first machining, as the distance WL decreases from the initial value of 6 mm, the crossing angle Σ is changed from the initial value Σ0 = 32° to the target value Σ1 = 35° while the threaded grinding wheel 11 is moved in the radial direction X toward the inner peripheral surface of the workpiece W. Note that in Figures 6(a) and 6(b), the state in which the crossing angle Σ is at the initial value Σ0 is indicated by a solid line, and the state in which it is at the target value Σ1 is indicated by a dashed line.

[0032] In the portion of Table 1 where the relationship between the distance WL and the crossing angle Σ is NG, as shown in the comparative example in Fig. 7, the vicinity of the first end 111 of the threaded grinding wheel 11 interferes with the gear on the inner peripheral surface of the workpiece W at the portion indicated by the arrow G, cutting the workpiece W beyond the target shape, thereby reducing the machining accuracy. Also, although not shown, a similar phenomenon occurs at the second end 112 of the threaded grinding wheel 11.

[0033] In the first machining operation, the target value Σ1 of the crossing angle Σ can be set based on the helix angle of the workpiece W and the helix angle of the threaded grinding wheel 11. The initial value Σ0 of the crossing angle Σ is not limited, but can be set appropriately based on the target value Σ1 of the crossing angle Σ, the tooth height, number of teeth, pitch, and width of the threaded grinding wheel 11 of the workpiece W, etc. Similarly, the initial value of the distance WL is not limited, but can be set appropriately based on the target value Σ1 of the crossing angle Σ, the tooth height, number of teeth, pitch, and width of the threaded grinding wheel 11 of the workpiece W, etc.

[0034] In this embodiment 1, in step S12 shown in FIG. 4, the first machining operation is started by moving the threaded grinding wheel 11 in the radial direction X toward the inner surface of the workpiece W as indicated by the arrow P1 in FIG. 5 while changing the crossing angle Σ shown in FIG. 6(b) from the initial value Σ0 to the target value Σ1 based on the distance WL shown in FIG. 6(a).

[0035] Then, in step S13 shown in FIG. 4 , the threaded grinding wheel 11 is moved in the radial direction X to cut a predetermined depth of cut at the position indicated by arrow P1. The amount of movement of the threaded grinding wheel 11 in the radial direction X in the first processing in step S13 is not limited, but as shown in FIG. 8 , it can be until the outermost part of the threaded grinding wheel 11 in the radial direction X of the gear to be formed on the workpiece W (the tip 11b in the radial direction X of the rotation locus 11a) reaches the target shape Wa of the gear to be formed on the workpiece W at the axial position where the first processing is performed. The amount of movement of the threaded grinding wheel 11 in the radial direction X in the first processing corresponds to the depth of cut of the workpiece W in the first processing. The depth of cut of the workpiece W in the first processing can be within a range of several tens of μm to several hundreds of μm. Note that the first processing is also called plunge processing because it involves grinding the workpiece W in the radial direction X.

[0036] After moving a predetermined amount in step S13, in step S14, the threaded grinding wheel 11 is moved in the radial direction X of the workpiece W so as to move away from the inner peripheral surface of the workpiece W, i.e., in the opposite direction to the arrow P1 in Fig. 5, while returning the crossing angle Σ from the target value Σ1 to the initial value Σ0. Then, in step S15 shown in Fig. 4, it is determined whether or not a preset end position of the first machining has been reached. The end position of the first machining is not limited, but in this embodiment, the end position of the first machining is a position in the axial direction Z near the lower end Wd on the opposite side from the start position of the first machining in the axial direction Z, where the arrow Pe in Fig. 5 is located.

[0037] If it is determined in step S15 shown in FIG. 4 that the threaded grinding wheel 11 has not reached the end position of the first machining, the process proceeds to No in step S14, and in step S16, the threaded grinding wheel 11 is moved to the next axial position. In this embodiment, the threaded grinding wheel 11 is moved from the first machining position indicated by arrow P1 to the second machining position indicated by arrow P2, which is the next axial position. Thereafter, steps S12 to S15 are performed again. Therefore, the first machining is repeatedly performed while changing the axial position until the threaded grinding wheel 11 reaches the end position Pe of the first machining. In this embodiment, the first machining is repeatedly performed in the order of the first machining position indicated by arrow P1 in FIG. 5, the second machining position indicated by arrow P2, the third machining position indicated by arrow P3, ... and the end position indicated by arrow Pe.

[0038] Then, in step S15 shown in Figure 4, when it is determined that the threaded grinding wheel 11 has reached the preset end position Pe of the first processing, proceed to Yes in step S15 and end the first processing step S1.

[0039] The intervals between the machining positions in the first machining step S1, i.e., the pitch of the machining positions, which is the distance between adjacent arrows P1 to Pe, is not limited and can be set appropriately based on the shape of the threaded grinding wheel 11 and the shape of the workpiece W. For example, the pitch of the machining positions can be at least smaller than the pitch of the multiple teeth provided on the threaded grinding wheel 11. In this embodiment, the pitch L of the machining positions is set to be equal, as shown in FIG.

[0040] As shown in FIG. 8 , at the end of the first machining step S1, an uncut region Wb is formed, which is the difference between the shape of the workpiece W at the end of the first machining step S1 and the target shape Wa. In this embodiment, the first machining is performed by setting the pitch of the machining position in the first machining step S1 so that the uncut region Wb at the end of the first machining step S1 is large enough not to contact the first end 111 of the threaded grinding wheel 11 shown in FIG. 2 during the second machining in the second machining step S2 described later. In this embodiment, as shown in FIG. 8 , the workpiece W is ground in the first machining step S1, forming the uncut region Wb in a substantially fan-shaped form. More specifically, the uncut region Wb has a shape in which multiple substantially fan-shaped forms are arranged at predetermined intervals in the axial direction Z in a cross section parallel to the tooth trace direction (in this embodiment, the direction coincident with the axial direction Z). The size H1 of the uncut region Wb in the radial direction X can be 10 μm or less.

[0041] In this embodiment, in the first machining step S1, as shown in Figure 8, the first machining at each axial position is performed by grinding until the tip 11b reaches the target shape Wa in one machining operation. However, this is not limited to this, and the cutting depth of the first machining at each axial position may be reduced, and the first machining at each axial position may be performed in multiple steps.

[0042] 4-2. Second Machining Step S2 After the first machining step S1 is completed, the second machining step S2 is performed. In the second machining step S2, in step S21 shown in FIG. 4, the threaded grinding wheel 11 is moved to the start position of the second machining. The start position of the second machining is not limited, but in this embodiment, it is set to the position of the lower end Wd of the workpiece W, as shown by arrow P21 in FIG. 9. The start position of the second machining may also be set to the position of the upper end We of the workpiece W.

[0043] Next, in step S22 shown in Fig. 4, the threaded grinding wheel 11 is moved in the axial direction Z of the workpiece W to start the second machining. In this embodiment, the second machining removes the uncut area Wb left at the end of the first machining step S1 by moving the threaded grinding wheel 11 in the axial direction Z, as shown by arrow P22 in Fig. 9. The uncut area Wb removed in the second machining step S2 is sufficiently smaller than the amount of material removed from the workpiece W in the first machining step.

[0044] In this embodiment, the second machining is completed in one grinding operation by performing the second machining so that the outermost portion of the threaded grinding wheel 11 (the tip 11b in the radial direction X of the rotation locus 11a) coincides with the target shape Wa, as shown in Fig. 10. Note that the second machining is also called traverse machining because it involves grinding the workpiece W in the axial direction Z.

[0045] Then, in step S23, when the threaded grinding wheel 11 reaches the end position of the second machining, the second machining step S2 is completed and the flow ends. The end position of the second machining is not limited, but in this embodiment, it is set to the upper end Wc of the workpiece W, opposite the lower end Wd of the workpiece W, which is the start position. Note that if the start position of the second machining is set to the upper end Wc, the end position can be set to the lower end Wd of the workpiece W.

[0046] In this embodiment, in the second processing step S2, the second processing is performed by a single grinding process from the start position Wd to the end position Wc, but this is not limited to this, and the second processing may be performed by dividing it into multiple grinding processes.

[0047] 5. Confirmation Test Next, a simulation test was conducted to measure the abrasive grain load on one tooth surface of the threaded grinding wheel 11 when the workpiece W was ground using the gear grinding method of this embodiment with the threaded grinding wheel 11, and when the workpiece W was ground using a conventional gear grinding method as a comparative example. In the comparative example, plunge grinding was performed in a single location, in which the threaded grinding wheel 11 was used to grind the workpiece W in the radial direction X at approximately the center of the axial direction Z of the workpiece W, as shown by arrow P91 in Fig. 11 , and then traverse grinding was performed, in which the threaded grinding wheel 11 was moved upward and downward in the axial direction Z to perform grinding, as shown by arrow P92 in Fig. 11 .

[0048] As shown in FIG. 12( a), in the second processing (traverse processing), the abrasive grain load on the tooth surface of the threaded grinding wheel 11 was relatively small overall, and there were no areas on the threaded grinding wheel 11 where the abrasive grain load was locally high, and no uneven contact occurred.

[0049] On the other hand, in the conventional gear grinding method shown in FIG. 12(b), which is a comparative example, during traverse grinding, a portion Q where the abrasive grain load is locally high occurs on the tooth surface at the end of the threaded grinding wheel 11, resulting in uneven contact of the threaded grinding wheel 11.

[0050] From the above, it was confirmed through the confirmation test that in the conventional gear grinding method, which is the comparative example, uneven contact occurs on the threaded grinding wheel 11, resulting in a shortened lifespan due to uneven wear, whereas in this embodiment, uneven contact does not occur on the threaded grinding wheel 11, thereby achieving the effect of improving lifespan.

[0051] 6. Effects According to the gear grinding method of this embodiment, the axial position of the workpiece W constituting the gear is sequentially changed to perform a first grinding process in which the threaded grinding wheel 11 is moved in the radial direction X of the workpiece W at a plurality of axial positions to grind the workpiece W, and then a second grinding process is performed in which the threaded grinding wheel 11 is moved in the axial direction Z of the workpiece W to grind the workpiece W into a target shape. In this grinding method, the first grinding process is a plunge grinding process in which the threaded grinding wheel 11 is moved in the radial direction X of the workpiece W to grind the workpiece W, so that uneven contact is relatively unlikely to occur. This makes it possible to prevent uneven contact, thereby preventing uneven wear on the threaded grinding wheel 11 and extending the life of the threaded grinding wheel.

[0052] Furthermore, in the first processing, the threaded grinding wheel 11 is used to grind the workpiece W by moving the threaded grinding wheel 11 in the radial direction X of the workpiece W while changing the crossing angle Σ between the threaded grinding wheel 11 and the workpiece W based on the distance WL between the threaded grinding wheel 11 and the workpiece W, thereby reducing interference between the axial ends 111, 112 of the threaded grinding wheel 11 and the workpiece W. This makes it possible to prevent the workpiece W from being cut beyond the target shape, thereby improving the processing accuracy of the workpiece W. Furthermore, since the grinding can be performed by involving the axial ends 111, 112 of the threaded grinding wheel 11 in the grinding process while the threaded grinding wheel 11 and the workpiece W have the crossing angle Σ, grinding efficiency can be improved.

[0053] In this embodiment, in the first machining step S1, the workpiece is ground as the first machining while changing the intersection angle Σ from the initial value Σ0 to a preset target value Σ1 so as to prevent the workpiece W from being cut to a depth exceeding the target shape. This makes it possible to reliably prevent the workpiece W from being cut to a depth exceeding the target shape, thereby further improving machining accuracy.

[0054] In this embodiment, the grinding wheel rotation axis B1 of the threaded grinding wheel 11 is inclined with respect to the meshing line ML between the workpiece W and the threaded grinding wheel 11. This improves the grinding efficiency of the workpiece W.

[0055] In this embodiment, one end of the meshing line ML of the workpiece W is located on a first end 111, which is one axial end of the threaded grinding wheel 11, and the other end of the meshing line ML is located on a second end 112, which is the other axial end of the threaded grinding wheel 11. This further improves the grinding efficiency of the workpiece W.

[0056] In this embodiment, in the first machining step S1, as the first machining, the threaded grinding wheel 11 is moved in the radial direction X of the workpiece W toward the inner circumferential surface, which is the portion to be machined, of the workpiece W while changing the crossing angle Σ from the initial value Σ0 until it reaches the target value Σ1, and then the threaded grinding wheel 11 is moved in the radial direction X of the workpiece W so as to move away from the inner circumferential surface, which is the portion to be machined of the workpiece W, while returning the crossing angle Σ from the target value Σ1 to the initial value Σ0, performing a grinding process. This prevents the threaded grinding wheel 11 from cutting beyond the target shape both when cutting into the workpiece W with the threaded grinding wheel and when the threaded grinding wheel is moved away from the workpiece W after cutting, thereby further improving machining accuracy.

[0057] Furthermore, in this embodiment, the first machining step is followed by a second machining step in which the workpiece W is ground by moving the threaded grinding wheel 11 in the axial direction Z of the workpiece W, thereby machining the workpiece W into a target shape. This second machining is a traverse machining in which the threaded grinding wheel 11 is moved in the axial direction Z of the workpiece W to grind the workpiece W, and thus uneven contact is likely to occur. Furthermore, by performing the first machining step, which is less likely to cause uneven contact, before the second machining step, which is prone to uneven contact, it is possible to reduce the amount of cutting in the radial direction X in the second machining step, since it is only necessary to remove the remaining uncut portion Wb from the first machining step during the second machining step. As a result, the occurrence of uneven contact can be suppressed overall. In particular, reducing the amount of cutting in the radial direction X in the second machining step can prevent the occurrence of uneven contact that previously occurred at the end of the threaded grinding wheel 11. This prevents uneven wear on the threaded grinding wheel 11 and extends the life of the threaded grinding wheel.

[0058] Furthermore, in this embodiment, the first machining in the first machining step S1 is performed so that the uncut area Wb, which is the difference between the shape of the workpiece W at the end of the first machining step S1 and the target shape, is of a size that will not abut against the axial end 111 of the threaded grinding wheel 11 during the second machining in the second machining step S2. This reliably prevents uneven contact of the threaded grinding wheel 11 during the second machining, prevents uneven wear of the threaded grinding wheel 11, and extends the life of the threaded grinding wheel 11.

[0059] Furthermore, in this embodiment, the cross-sectional shape of the uncut region Wb in the first machining step S1, which is parallel to the tooth trace direction (in this embodiment, the direction coincident with the axial direction Z), is a shape in which a plurality of approximately fan-shaped shapes are arranged at predetermined intervals in the axial direction Z. By forming the uncut region Wb in this shape in the first machining step S1, the size H1 of the uncut region Wb can be made relatively small. This prevents uneven contact of the threaded grinding wheel 11 in the second machining, prevents uneven wear of the threaded grinding wheel 11, and extends the life of the threaded grinding wheel 11.

[0060] Furthermore, in this embodiment, in the first machining step S1, the threaded grinding wheel 11 is moved in one direction in the axial direction Z to change its axial position to perform the first machining, and in the second machining step S2, the threaded grinding wheel 11 is moved in the other direction in the axial direction Z to perform the second machining. This makes it possible to shorten the distance over which the threaded grinding wheel 11 is moved to the start position of the second machining step S2 when transitioning from the first machining step S1 to the second machining step S2, thereby improving work efficiency.

[0061] The direction in which the axial position is changed in the first machining step S1 and the direction in which the threaded grinding wheel 11 is moved in the second machining step S2 may be the same. In this case, the effect of improving the work efficiency described above is not achieved, but other effects can be achieved.

[0062] Furthermore, in this embodiment, when the threaded grinding wheel 11 is rotated about the grinding wheel rotation axis B1 of the threaded grinding wheel 11, the rotation locus 11a of the outer peripheral surface of the first end 111, which is one axial end of the threaded grinding wheel 11, is smaller in diameter than the rotation locus 11a of the outer peripheral surface of the second end 112, which is the other axial end, and at least the rotation locus of the outer peripheral surface of the second end 112 has the largest diameter among the rotation loci 11a of the outer peripheral surface of the threaded grinding wheel 11. This makes it possible to suppress uneven contact at the end of the threaded grinding wheel 11, prevent uneven wear of the threaded grinding wheel 11, and extend the life of the threaded grinding wheel 11, compared to when the rotation locus 11a of the threaded grinding wheel 11 is cylindrical.

[0063] In this embodiment, the amount of workpiece W removed in the first machining step S1 is greater than the amount of workpiece W removed in the second machining step S2. This reduces the amount of workpiece W removed in the second machining step S2, further preventing uneven contact during the second machining.

[0064] In this embodiment, in the first machining step S1, the first machining is performed at each of a plurality of axial positions where the first machining is performed until the outermost portion 11b of the threaded grinding wheel 11 in the radial direction X of the workpiece W reaches the target shape Wa. Then, in the second machining step S2, an uncut region Wb, which is the difference between the shape of the workpiece W at the end of the first machining step S1 and the target shape, is removed. This reduces the amount of material that needs to be removed in the second machining step S2, further preventing uneven contact during the second machining.

[0065] As described above, according to the above-described embodiment, it is possible to provide a gear grinding method that can prevent the occurrence of partial contact in the threaded grinding wheel 11, thereby extending the life of the threaded grinding wheel 11 and improving the processing accuracy and grinding efficiency.

[0066] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A gear grinding method in which a workpiece, which is a gear, and a threaded grinding wheel, which is a processing tool, are rotated synchronously with each other and the workpiece is ground by the threaded grinding wheel, a first machining step in which a first machining operation is performed at a plurality of axial positions by sequentially changing the axial position of the workpiece, in which the threaded grinding wheel is moved in a radial direction of the workpiece while changing an intersecting angle between the threaded grinding wheel and the workpiece based on a distance between the threaded grinding wheel and the workpiece; a second machining step of machining the workpiece into a target shape by a second machining step of grinding the workpiece by moving the threaded grinding wheel in the axial direction of the workpiece after the first machining step.

2. 2. The gear grinding method according to claim 1, wherein in the first machining step, the workpiece is ground as the first machining while changing the intersecting angle from an initial value to a preset target value so as not to generate a cutting depth in the workpiece that exceeds a target shape.

3. 3. The gear grinding method according to claim 1, wherein a grinding wheel rotation axis of the threaded grinding wheel is inclined with respect to a meshing line between the workpiece and the threaded grinding wheel.

4. 4. The gear grinding method according to claim 3, wherein one end of the meshing line of the workpiece is located on one axial end of the threaded grinding wheel, and the other end of the meshing line of the workpiece is located on the other axial end of the threaded grinding wheel.

5. 3. The gear grinding method according to claim 1, wherein the first machining step comprises: moving the threaded grinding wheel radially toward the machined portion of the workpiece to a predetermined cutting depth while changing the intersecting angle from an initial value until it reaches a target value; and then performing grinding by moving the threaded grinding wheel radially away from the machined portion of the workpiece while returning the intersecting angle from the target value to the initial value.

6. 3. The gear grinding method according to claim 1, wherein the first machining step is performed so that an uncut area, which is the difference between the shape of the workpiece at the end of the first machining step and the target shape, is of a size that does not abut against an axial end of the threaded grinding wheel in the second machining step.

7. 7. The gear grinding method according to claim 6, wherein a cross-sectional shape of the uncut area in the first machining step parallel to a tooth trace direction of the workpiece is a shape in which a plurality of approximately fan-shaped shapes are arranged at predetermined intervals in an axial direction of the workpiece.

8. In the first machining step, the threaded grinding wheel is moved in one direction in the axial direction of the workpiece to change the axial position thereof, and the first machining is performed; 3. The gear grinding method according to claim 1, wherein in the second machining step, the second machining is performed by moving the threaded grinding wheel in another direction in the axial direction of the workpiece.

9. 3. The gear grinding method according to claim 1, wherein, when the threaded grinding wheel is rotated on a grinding wheel rotation shaft, a rotation locus of an outer peripheral surface of a first end, which is one axial end of the threaded grinding wheel, has a smaller diameter than a rotation locus of an outer peripheral surface of a second end, which is the other axial end, and at least the rotation locus of the outer peripheral surface of the second end has a maximum diameter among the rotation loci of the outer peripheral surfaces of the threaded grinding wheel.

10. 3. The gear grinding method according to claim 1, wherein the amount of material removed from the workpiece in the first machining step is greater than the amount of material removed from the workpiece in the second machining step.

11. In the first machining step, the first machining is performed at each of the plurality of axial positions where the first machining is performed until an outermost portion of the threaded grinding wheel in a radial direction of the workpiece reaches the target shape; 3. The gear grinding method according to claim 1, wherein the second machining step removes an uncut area that is a difference between the shape of the gear at the end of the first machining step and the target shape.

12. (delete)