JP7600869B2 - Gear Machining Method - Google Patents

Description

The present invention relates to a gear machining method.

Trochoidal interference is known to be one of the causes of damage to gears. Trochoidal interference is a phenomenon in which the tips of the teeth of a driven gear bite into the root of the teeth of a driving gear at the beginning of meshing due to deformation of the teeth caused by the load when the gears are driven or errors during assembly. To avoid this type of interference, it is known to perform semi-topping, in which the tips of the teeth in the entire tooth trace direction (tooth width direction) are chamfered.

Patent Document 1 also describes that in addition to semi-topping, the following tooth surface modifications are performed during gear skiving to adjust the meshing state of the gear teeth. Examples of such tooth surface modifications include crowning modification, bias modification, helix angle modification, pressure angle modification, and tooth profile roundness modification.

JP 2021-11011 A

When semi-topping is applied, the amount of tooth addendum available for meshing is reduced, and the meshing ratio is reduced. For this reason, large semi-topping cannot be applied. If the semi-topping is made small, the trochoidal interference cannot be sufficiently reduced.

In addition, in gears with a helix angle, such as helical gears, the line where the drive gear and driven gear make contact simultaneously when meshing is inclined relative to the tooth trace direction. Therefore, by applying semi-topping to the entire area of the tooth tip in the tooth trace direction, the meshing ratio decreases even in areas other than the early stage of meshing (middle and late stages of meshing). The decrease in meshing ratio increases the surface pressure.

Therefore, it is necessary to modify the tooth surface so as to avoid trochoidal interference in the early stages of meshing while not decreasing the contact ratio except in the early stages of meshing. It is not easy to improve the contact ratio while avoiding trochoidal interference in the early stages of meshing simply by applying crowning modification or bias modification.

The present invention has been made in view of this background, and aims to provide a gear cutting method that can improve the meshing ratio at times other than the initial stage of meshing while avoiding trochoid interference at the initial stage of meshing.

One aspect of the present invention is
A gear machining method for machining a gear tooth surface on a workpiece, comprising the steps of:
a tooth flank corner processing step of performing a gear skiving process with bias modification applied to a reference processing condition to perform a process of cutting off at least one of a tooth flank corner portion, which is a tooth tip and an end portion in a tooth trace direction, or a tooth base and an end portion in a tooth trace direction, with respect to a predetermined tooth flank shape;
a reference tooth flank machining step which is carried out before or after the tooth flank corner machining step, and which machines a portion other than the tooth flank corner into the predetermined tooth flank shape by performing gear machining under the reference machining conditions;
The present invention relates to a gear machining method comprising the steps of:

Bias modification is a modification method that changes the tooth flank shape before modification to a twisted surface shape. In other words, bias modification is a modification method that changes the tooth profile shape so that the pressure angle gradually changes as you move in the tooth trace direction. Therefore, when bias modification is applied and the entire tooth flank is machined, one pair of the four corners that make up the tooth flank will be cut off relatively deeply, and the remaining pair of corners will be cut off relatively shallowly.

Therefore, in the tooth flank angle processing step, a bias modification is applied to process the tooth flank angle, which is at least one of the tooth tip and end in the tooth trace direction, or the tooth base and end in the tooth trace direction. On the other hand, in the reference tooth flank processing step, a specified tooth flank shape is processed according to reference processing conditions. In other words, on the tooth flank of the gear after processing is completed, the tooth flank angle is the part that was processed in the tooth flank angle processing step, and the part other than the tooth flank angle is the part that was processed in the reference tooth flank processing step.

In this way, multiple machining processes are used, including a machining process with bias modification applied to the standard machining conditions, and a machining process under the standard machining conditions. Therefore, only the tooth flank corners can be machined deeper than other parts. Gears machined in this way can improve the meshing ratio except at the beginning of meshing while avoiding trochoid interference at the beginning of meshing.

FIG. 1 is a diagram illustrating an example of a gear machining device. 1 is a view of the workpiece and tool viewed from a direction perpendicular to the rotation axis of the workpiece in the XZ plane, with the dashed line showing the tool indicating the position after gear machining has been performed on the workpiece. 1 is a view of the workpiece and the tool as viewed from the Y direction, and the dashed line showing the tool indicates the position after gear machining has been performed on the workpiece. This shows the meshing portion between the drive gear and the driven gear where trochoid interference occurs. In a gear having a helix angle, the teeth of the driven gear are shown, and the line that simultaneously contacts the drive gear during meshing is shown by a dashed line, and the white arrow indicates the direction of movement of the contact line as meshing progresses. FIG. 4 is a diagram illustrating a pressure angle. FIG. 13 is a diagram illustrating bias correction. This is a coordinate system that represents the specified tooth flank shape of a gear on a plane of the tooth profile direction (radial direction) and the tooth trace direction (tooth width direction) on the vertical axis H0, and shows a permuted coordinate system in which the vertical axis represents the amount of deviation (modification amount) from the specified tooth flank shape. 1 shows the target shape of one tooth of the driven gear. 1 shows a diagram of a target shape of one tooth of a driven gear expressed in a permuted coordinate system. FIG. 11 is a diagram in which the permuted coordinate system shown in FIG. 10 is flipped 180°, and shows the tooth flank angle portion to be modified on the near side. 1 is a flowchart showing a gear machining method. In a permuted coordinate system, the tooth flank shape after the reference rough machining process two cycles before the finish machining process is shown. In a permuted coordinate system, the tooth flank shape after the rough machining process one cycle before the finish machining process is shown. This is a view of the tooth flank shape after the rough modification process, as viewed from the tooth profile direction (radial direction) of a permuted coordinate system. The oblique lines indicate the surface that is visible on the near side. This is a diagram showing the tooth flank shape after the rough modification process, as viewed from the tooth trace direction (tooth width direction) of a permuted coordinate system. The oblique lines indicate the surface that is visible on the near side. The tooth flank shape after the finishing process is shown in a permuted coordinate system. This is a view of the tooth flank shape after the finishing process, as viewed from the tooth profile direction (radial direction) of a permuted coordinate system. The oblique lines indicate the surface that is visible on the near side. This is a diagram showing the tooth flank shape after the finish machining process, as viewed from the tooth trace direction (tooth width direction) of a permuted coordinate system. The oblique lines indicate the surface that is visible on the near side. 1 shows a calculation diagram for determining machining conditions in a rough machining process in a permuted coordinate system. 10 is a flowchart showing another example of a gear machining method. 1 shows the target shape of one tooth of the drive gear. 1 shows a diagram of the target shape of one tooth of a drive gear in a permuted coordinate system.

(1. Configuration of gear machining device 1)
The gear machining device 1 will be described with reference to Fig. 1. The gear machining device 1 is a device that generates a tooth profile on the workpiece W by using the gear skiving cutter T by moving the gear skiving cutter T and the workpiece W relatively while rotating them.

In this embodiment, the gear machining device 1 is a general-purpose machine tool, for example, a machining center. The machining center is configured to be tool-replaceable, and can perform machining according to the attached tool. For example, in addition to the gear skiving cutter T, replaceable gear machining tools include a hob cutter and a shaper cutter. By replacing with a hob cutter or a shaper cutter, the gear machining device 1 becomes a device that processes a tooth profile on the workpiece W by hobbing or shaping.

In addition, examples of replaceable tools other than those for gear cutting include end mills, milling tools, drills, turning tools, threading tools, grinding tools, etc. Note that the tool exchange device and the tool magazine for storing tools are not shown in FIG. 1.

In this embodiment, the machining center serving as the gear machining device 1 is basically a horizontal machining center. However, the gear machining device 1 can also be configured in other ways, such as a vertical machining center.

As shown in FIG. 1, the gear machining device 1 has, for example, three mutually orthogonal linear axes (X-axis, Y-axis, Z-axis) as drive axes. Here, the direction of the rotation axis of the gear skiving cutter T (equal to the rotation axis of the tool spindle) is defined as the Z-axis direction, and the two axes perpendicular to the Z-axis direction are defined as the X-axis and Y-axis. In FIG. 1, the horizontal direction is the X-axis direction, and the vertical direction is the Y-axis direction.

The gear processing device 1 further has one rotation axis (B axis) as a drive axis for changing the relative position between the gear skiving cutter T and the workpiece W. In this embodiment, the B axis is a rotation axis whose center of rotation is the Y axis direction. The gear processing device 1 also has a Ct axis as a rotation axis for rotating the gear skiving cutter T, and a Cw axis as a rotation axis for rotating the workpiece W.

In the gear processing device 1, the configuration for moving the gear skiving cutter T and the workpiece W relative to each other can be selected as appropriate. For example, the gear processing device 1 may be configured to have an A-axis with the X-axis direction as the center of rotation instead of the B-axis. In the following, an example is given of the gear processing device 1 in which the gear skiving cutter T can move linearly in the Y-axis and Z-axis directions, the workpiece W can move linearly in the X-axis direction, and the workpiece W can rotate about the B-axis.

The gear machining device 1 comprises a bed 10, a workpiece holding device 20, a tool holding device 30, and a control device 40. The bed 10 is installed on an installation surface and formed into a shape corresponding to the shape of the workpiece holding device 20, the shape of the tool holding device 30, and the movement mechanisms thereof. In this embodiment, the bed 10 is, for example, rectangular. An X-axis guide rail 11 and a Z-axis guide rail 12 are formed on the upper surface of the bed 10.

The workpiece holding device 20 allows the workpiece W to move linearly in the X-axis direction relative to the bed 10, and to rotate about the B-axis and Cw-axis. The workpiece holding device 20 mainly comprises an X-axis moving table 21, a B-axis rotating table 22, and a workpiece spindle device 23.

The X-axis moving table 21 is driven by a driving device such as a linear motor or a ball screw mechanism (not shown) and moves in the X-axis direction while being guided by the X-axis guide rail 11 of the bed 10. The B-axis rotating table 22 is placed on the upper surface of the X-axis moving table 21 and moves in the X-axis direction together with the X-axis moving table 21. The B-axis rotating table 22 is also provided so as to be rotatable on the B-axis relative to the X-axis moving table 21. A rotating motor (not shown) is housed in the B-axis rotating table 22, and the B-axis rotating table 22 can be rotated on the B-axis by driving the rotating motor.

The workpiece spindle device 23 is provided on the B-axis rotating table 22 and rotates about the B-axis together with the B-axis rotating table 22. The workpiece spindle device 23 supports the workpiece W. A rotary motor (not shown) is housed in the workpiece spindle device 23, and the workpiece spindle device 23 can rotate the workpiece W about the Cw axis by driving the rotary motor. In this way, the workpiece holding device 20 can move the workpiece W in the X-axis direction relative to the bed 10 and rotate it about the B axis and the Cw axis.

The tool holding device 30 mainly comprises a column 31, a saddle 32, and a tool spindle device 3. The column 31 is driven by a driving device such as a linear motor or a ball screw mechanism (not shown) and moves in the Z-axis direction while being guided by the Z-axis guide rail 12 of the bed 10. A Y-axis guide rail 31a is formed on the surface (left surface in FIG. 1) that extends in the vertical direction of the column 31. The saddle 32 is driven by a driving device such as a linear motor or a ball screw mechanism (not shown) and moves in the Y-axis direction while being guided by the Y-axis guide rail 31a of the column 31.

The tool spindle device 33 is mounted on the saddle 32 and moves integrally with the saddle 32 in the Y-axis direction. The tool spindle device 33 supports the gear skiving cutter T. A rotary motor (not shown) is housed in the tool spindle device 33, and the tool spindle device 33 is capable of rotating the gear skiving cutter T on the Ct axis by driving the rotary motor. In this way, the tool holding device 30 holds the gear skiving cutter T so that it can move in the Y-axis and Z-axis directions relative to the bed 10 and can rotate on the Ct axis.

The control device 40 is equipped with a calculation device and a storage device, and controls each drive device by executing the machining program.

(2. Explanation of gear skiving)
The state in which a tooth profile is generated on a workpiece W by the gear skiving cutter T will be described with reference to Figs. 2 and 3.

In gear skiving, the rotation axis At of the gear skiving cutter T is set at an intersection angle θ with an axis parallel to the rotation axis Aw of the workpiece W. The rotation axis At of the gear skiving cutter T and the rotation axis Aw of the workpiece W are also parallel to the X-Z plane. The center-to-center distance between the rotation axis At of the gear skiving cutter T and the rotation axis Aw of the workpiece W, i.e., the distance in the Y-axis direction, is Da (hereinafter referred to as the "axis distance").

The workpiece W is rotated around the rotation axis Aw (Cw axis), and the gear skiving cutter T is rotated around the rotation axis At (Ct axis). The gear skiving cutter T is moved relative to the workpiece W in the direction of the rotation axis Aw of the workpiece W while synchronizing the rotation of the workpiece W and the gear skiving cutter T, thereby generating a gear tooth profile on the workpiece W. In gear skiving, each tooth groove portion of the workpiece W is machined only once by the gear skiving cutter T while the workpiece W rotates once.

(3. Explanation of Trochoidal Interference)
Trochoidal interference will be described with reference to Fig. 4. As shown in Fig. 4, the driving gear G1 and the driven gear G2 are in mesh with each other to transmit power. At the beginning of the meshing between the driving gear G1 and the driven gear G2, the tip of the driven gear G2 bites into the root of the driving gear at the portion Pa. This phenomenon is called trochoidal interference.

Also, referring to Figure 5, we will explain the change over time in the contact line between the drive gear G1 and the tooth flank of the driven gear G2 when the drive gear G1 and the driven gear G2 are gears with a helix angle. As shown by the dashed line in Figure 5, the contact line (meshing line) between the drive gear G1 and the tooth flank of the driven gear G2 is inclined with respect to the tooth trace direction. In detail, first, the tooth flank corner D, which is the tooth tip and one end in the tooth trace direction on the tooth flank of the driven gear G2, meshes, and then the contact line (meshing line) moves toward the tooth flank corner B, which is the tooth base and the other end in the tooth trace direction.

In other words, in gears with a helix angle, trochoid interference can occur at tooth flank corner D of driven gear G2. In drive gear G1, it can occur at a tooth flank corner (not shown) that corresponds to tooth flank corner D of driven gear G2 and is the tooth root and end in the tooth trace direction. Gears with a helix angle include, for example, helical gears, double helical gears, and spiral bevel gears.

(4. Tooth Surface Modification Method)
The pressure angle will be described with reference to Fig. 6. The pressure angle δ is the angle between a radial line passing through a certain point on the tooth flank of a gear G and a tangent to the tooth profile. In Fig. 6, the tooth flank is an involute tooth flank, and the pressure angle δ indicates the pressure angle at a reference pitch point of the involute tooth flank. Pressure angle modification, which is one of the tooth flank modification methods, is a method of modifying the pressure angle δ. For example, pressure angle modification means modification of the pressure angle δ at the center of the tooth trace direction of the gear G.

As one of the tooth surface modification methods, bias modification will be described with reference to FIG. 7. Bias modification is a method of continuously changing the pressure angle in the tooth trace direction to give the tooth surface a twist. For example, at the other end in the tooth trace direction (other end in the tooth width direction) which is the left front side of FIG. 7, the tooth surface angle A at the tooth tip is moved to the outside of the tooth surface (right side of FIG. 7), while the tooth surface angle B at the tooth base is moved to the inside of the tooth surface (left side of FIG. 7), so the pressure angle is modified. On the other hand, at one end in the tooth trace direction (one end in the tooth width direction) which is the right rear side of FIG. 7, the tooth surface angle D at the tooth tip is moved to the inside of the tooth surface (left side of FIG. 7), while the tooth surface angle C at the tooth base is moved to the outside of the tooth surface (right side of FIG. 7).

In Figure 7, the portion where the modification amount of the pressure angle, which changes continuously in bias modification, is 0 is the center in the tooth trace direction. However, the portion where the modification amount of the pressure angle, which changes continuously in bias modification, is 0 can also be located at a position shifted from the center in the tooth trace direction.

For example, if the modification amount of the pressure angle δ at the center of the tooth trace direction is set to 0, the modification amount of the pressure angle at one end of the tooth trace direction and the modification amount of the pressure angle at the other end of the tooth trace direction will be positive and negative, but the absolute values will be the same. However, if a modification amount of the pressure angle δ is applied to the center of the tooth trace direction, the modification amount of the pressure angle at one end of the tooth trace direction and the modification amount of the pressure angle at the other end of the tooth trace direction will be positive and negative, but the absolute values will not be the same.

Bias modification and pressure angle modification can be achieved by changing the intersecting angle θ, the axis distance Da, the position in the X-axis direction, the rotation axis Ct of the gear skiving cutter T, the rotation axis Cw of the workpiece W, etc. This is a well-known technology, for example, from JP 2021-11011 A. The same applies to tooth surface modification methods other than bias modification and pressure angle modification, such as crowning modification.

(5. Explanation of Permuted Coordinate System)
A permuted coordinate system as a coordinate system for easily grasping the tooth flank shape of a gear will be described with reference to Fig. 8. As shown on the left side of Fig. 8, the predetermined tooth flank shape of a gear G is, for example, an involute tooth flank shape or a shape obtained by applying a modification process such as crowning to an involute tooth flank. Since the predetermined tooth flank shape such as an involute tooth flank shape is a three-dimensional curved surface, it is not possible to visually grasp the amount of tooth flank modification.

Therefore, in order to visually grasp the tooth flank shape of the gear G, particularly the amount of tooth flank modification, a permuted coordinate system as shown on the right side of FIG. 8 is used. The permuted coordinate system is a coordinate system that represents the specified tooth flank shape of the gear G on a plane of the tooth profile direction (radial direction) and the tooth trace direction (tooth width direction) at the reference value H0 on the vertical axis. The vertical axis in the permuted coordinate system indicates the deviation amount (modification amount) from the specified tooth flank shape. A value larger than the reference value H0 indicates a deviation value in the shallower direction, and a value smaller than the reference value H0 indicates a deviation value in the deeper direction. When the tooth flank of the gear G has a specified tooth flank shape, the four tooth flank corners A, B, C, and D on the tooth flank shown on the left side of FIG. 8 are located at the corners of a rectangle on a plane whose vertical axis is the reference value H0, as shown on the right side of FIG. 8.

(6. Target Tooth Flank Shape of Driven Gear G2)
The target tooth flank shape of the driven gear G2 will be described with reference to Fig. 9 to Fig. 11. Fig. 9 shows the target tooth flank shape of the driven gear G2 in an actual three-dimensional coordinate system, and Fig. 10 and Fig. 11 show the tooth flank of the driven gear G2 in a permuted coordinate system.

The target tooth flank shape of the driven gear G2 is a shape for reducing the above-mentioned trochoid interference. Specifically, as shown in FIG. 9, the target tooth flank shape of the driven gear G2 is a shape in which the tooth flank corner D, which is the tooth tip and one end in the tooth trace direction, is cut away, and the area other than the tooth flank corner D is expressed by a specified tooth flank shape.

For example, if the specified tooth flank shape is an involute shape, the portions other than the tooth flank corner D are formed in an involute shape. On the other hand, the tooth flank corner D is cut away from the involute shape, which is the specified tooth flank shape. In other words, only the tooth flank corner D is formed into a shape that has been chamfered from the specified tooth flank shape. As shown in Figure 9, the tooth flank corner D is triangular. Note that the tooth flank corner D is not a flat surface, but rather a curved surface that is slightly convex.

Here, the specified tooth flank shape is not limited to an involute shape, but can also be a shape in which a specified tooth flank modification has been applied to an involute shape. For example, the specified tooth flank shape can be a shape in which a tooth flank modification such as crowning has been applied to an involute shape.

As shown in Figures 10 and 11, in the permuted coordinate system, the areas other than tooth flank corner D are represented by a plane whose vertical axis is the reference value H0, since they have a predetermined tooth flank shape. In other words, the areas other than tooth flank corner D are formed on a plane that passes through corner points A0, B0, and C0 corresponding to the tooth flank corners A, B, and C, respectively.

The tooth flank corner D has a shape that is cut away like a chamfer from the specified tooth flank shape. Therefore, the vertical axis of the tooth flank corner D indicates a value smaller than the reference value H0. The corner point D1 of the tooth flank corner D indicates the smallest value on the vertical axis. As shown in Figures 10 and 11, the tooth flank corner D has a shape with a triangular outline and is shown as a slightly curved surface. Note that since the tooth flank corner D is located at the back in Figure 10, Figure 11 is shown in a permuted coordinate system rotated so that the tooth flank corner D is located at the front.

(7. Gear Machining Method)
A gear machining method for machining the tooth surface of a gear G on a workpiece W by gear skiving will be described with reference to Fig. 12 to Fig. 19. Here, the case of machining the tooth surface of a driven gear G2 will be described.

The gear machining method is performed by the control device 40 (shown in FIG. 1) constituting the gear machining device 1 executing a machining program, which causes each drive device constituting the gear machining device 1 to operate. In this embodiment, the cutting from the material shape of the workpiece W to the finishing tooth surface of the driven gear G2 is performed in multiple steps.

First, the control device 40 performs a standard rough machining process ST1 in which gear skiving is performed under standard machining conditions. The standard machining conditions are machining conditions for machining the tooth flank of the gear G into a predetermined standard rough tooth flank shape. The predetermined standard rough tooth flank shape is, for example, an involute shape. In other words, in the standard rough machining process ST1, rough machining is performed on the entire tooth flank, so that the tooth flank is machined into a predetermined standard rough tooth flank shape, for example, an involute shape.

The specified reference rough tooth flank shape corresponds to the specified tooth flank shape in the target tooth flank shape of the driven gear G2 described above. However, because the cutting depth of the two is different, the specified reference rough tooth flank shape and the specified tooth flank shape in the target tooth flank shape do not match.

After the standard rough machining process ST1 is performed, the tooth surface of the driven gear G2 is machined in a permuted coordinate system as shown in FIG. 13. Since the entire tooth surface is formed into a predetermined standard rough tooth surface shape, in the permuted coordinate system, it is represented by a plane whose vertical axis is the reference value H2. In other words, in the permuted coordinate system, the tooth surface of the driven gear G2 after the standard rough machining process ST1 is performed is formed into a plane passing through the corner points A2, B2, C2, and D2 corresponding to the tooth surface corner portions A, B, C, and D.

Next, as shown in FIG. 12, the control device 40 judges whether the currently performed reference rough machining process ST1 is two cycles before the finish machining process (judgment process ST2). If it is not two cycles before the finish machining process (ST2: No), the control device 40 applies a cutting amount and performs the reference rough machining process ST1 again until it reaches two cycles before the finish machining process.

When the performed reference rough machining process ST1 reaches two cycles before the finish machining process (ST2: Yes), the control device 40 performs the modification rough machining process ST3 in which gear skiving is performed under modification rough machining conditions. The modification rough machining conditions are machining conditions in which at least bias modification is applied to the reference machining conditions as shown in FIG. 7. In this embodiment, the modification rough machining conditions are machining conditions in which bias modification is applied to the reference machining conditions as shown in FIG. 7, and pressure angle modification is applied at the center in the tooth trace direction as shown in FIG. 6. The pressure angle modification amount is δ.

After the modification rough machining process ST3 is performed, the tooth surface of the driven gear G2 is machined in the permuted coordinate system as shown in Figures 14 to 16. The reference value H1 in the modification rough machining process ST3 is a value obtained by adding a predetermined rough cutting depth Db to the reference value H2 in the immediately preceding reference rough machining process ST1. In other words, if machined under the reference machining conditions, the tooth surface will be machined to a plane that has the reference value H1 in the permuted coordinate system. The tentative reference machining conditions here are machining conditions in which a cutting depth is added to the reference machining conditions in the reference rough machining process ST1, and are machining conditions that machine the tooth surface into a tooth surface shape (virtual reference tooth surface shape) that corresponds to a predetermined reference rough tooth surface shape.

However, in the rough modification process ST3, at least a bias modification is applied to the reference machining conditions, and a pressure angle modification is also applied. Therefore, the tooth flank machined in the rough modification process ST3 has a surface shape that deviates from the plane passing through the reference value H1 (the virtual reference tooth flank shape in the rough modification process ST3).

In this embodiment, a predetermined rough cutting depth Db is set so that the corner point C1 corresponding to the tooth flank corner C coincides with the reference value H1. Therefore, the corner point C1 corresponding to the tooth flank corner C coincides with the corner point C10 located on the virtual reference tooth flank shape. The tooth flank corners B and D are machined to be deeply cut away from the virtual reference tooth flank shape. Therefore, the corner points B1 and D1 corresponding to the tooth flank corners B and D are located in the negative direction (downward in Figure 14) of the corner points B10 and D10 located on the virtual reference tooth flank shape.

In addition, in this embodiment, the corner point A1 corresponding to the tooth flank corner portion A is also set to coincide with the reference value H1. Therefore, the corner point A1 corresponding to the tooth flank corner portion A coincides with the corner point A10 located on the virtual reference tooth flank shape. However, the corner point A1 corresponding to the tooth flank corner portion A may be set so as not to coincide with the reference value H1.

By carrying out the rough modification process ST3 as described above, the entire tooth surface of the driven gear G2 is machined. In detail, in the rough modification process ST3, machining is performed to at least a predetermined rough cutting depth Db.

Here, in the rough modification process ST3, as shown in FIG. 14, the pressure angle modification amount at the center in the tooth trace direction is set to δ. This allows the absolute value of the pressure angle at one end in the tooth trace direction to be different from the absolute value of the pressure angle at the other end in the tooth trace direction. In particular, the corner point D1 corresponding to the tooth flank corner portion D can be cut deeper than the corner point B1 corresponding to the tooth flank corner portion B.

More specifically, the distance (modification amount) between corner point D1 corresponding to tooth flank corner D and corner point D10 located on the virtual reference tooth flank shape is set to a value larger than a predetermined finishing cut-in amount Dc, which will be described later. On the other hand, the distance (modification amount) between corner point B1 corresponding to tooth flank corner B and corner point B10 located on the virtual reference tooth flank shape is set to a value smaller than a predetermined finishing cut-in amount Dc, which will be described later. In this way, the rough modification process ST3 is called the tooth flank corner processing process because it is a process in which the tooth flank corner D is cut off to a larger extent than other parts.

Then, as shown in FIG. 12, the control device 40 performs the finishing process ST4 (reference tooth surface machining process) following the rough correction process ST3 (tooth surface corner machining process). The finishing process ST4 performs gear skiving under reference machining conditions.

After the finishing process ST4 is performed, the tooth surface of the driven gear G2 is machined in the permuted coordinate system as shown in Figures 17 to 19. The reference value H0 in the finishing process ST4 is a value obtained by adding a predetermined finishing cut-in amount Dc to the reference value H1 in the previously performed rough correction process ST3. In other words, in the finishing process ST4, the tooth surface is machined to a plane that has the reference value H0 in the permuted coordinate system. The reference machining conditions here are machining conditions in which a cut-in amount is added to the reference machining conditions in the reference rough machining process ST1, and are machining conditions for machining the tooth surface into a predetermined tooth surface shape (finished tooth surface shape).

However, as described above, in the rough modification process ST3, the distance (modification amount) between the corner point D1 corresponding to the tooth flank corner D and the corner point D10 located on the virtual reference tooth flank shape is set to a value greater than a predetermined finishing cut-in amount Dc described below. In other words, the tooth flank corner D is located at a position deeper than the position corresponding to the finishing cut-in amount Dc. On the other hand, the parts other than the tooth flank corner D are located at a position shallower than the position corresponding to the finishing cut-in amount Dc.

Therefore, in the finishing process ST4, the areas other than the tooth flank corner D are machined into the specified tooth flank shape. On the other hand, in the finishing process ST4, the tooth flank corner D is not machined. In other words, the tooth flank corner D remains as the surface machined in the rough correction process ST3.

(8. Method for determining machining conditions in rough machining process ST3)
A method of determining the machining conditions in the rough trimming step ST3 will be described with reference to FIGS. 11, 14, 17, and 20. FIG.

As shown in Figures 14 and 17, the corner point C1 corresponding to the tooth flank corner C in the rough modification process ST3 coincides with the reference value H1. The tooth flank machined in the rough modification process ST3 is located on the plane that is the reference value H1 or at a position deeper than the plane that is the reference value H1 in the permuted coordinate system.

As shown in Figures 14 and 17, the rough modification process ST3 applies a bias modification, so the tooth surface is twisted over the entire length S3 in the tooth trace direction. As shown in Figure 14, the length from one end face in the tooth trace direction to the position P1 in the tooth trace direction where the pressure angle modification amount becomes 0 is defined as S2. Here, because the pressure angle modification is applied at the center in the tooth trace direction, the position where the pressure angle modification amount becomes 0 is located at a position shifted from the center in the tooth trace direction. In this embodiment, the length S2 is longer than half the entire length in the tooth trace direction.

As shown in FIG. 17, the distance (modification amount) between the corner point D1 corresponding to the tooth flank corner D and the corner point D10 located on the virtual reference tooth flank shape is set to a value greater than the predetermined finishing cut-in amount Dc in the finishing process ST4. Therefore, in the finishing process ST4, the area other than the tooth flank corner D is machined, and the tooth flank corner D remains as a triangular chamfer. The length in the tooth profile direction in the modification area of the tooth flank corner D is R1, and the length in the tooth trace direction in the modification area of the tooth flank corner D is S1.

The tooth flank shape in the rough modification process ST3 is a very complex three-dimensional shape because bias modification has been applied. However, if this complex three-dimensional shape is used, it is not easy to design the tooth flank shape. Therefore, as shown in Figure 20, the range (S2) from one end in the tooth trace direction to the position where the pressure angle modification amount is 0, and the range (R2) of the entire length in the tooth profile direction, is defined as a virtual shape as shown below.

A reference plane is generated that passes through the corner point C1 corresponding to the tooth flank corner C to be machined in the rough modification process ST3. The reference plane is a plane that passes through points C1, P2, P3, and P4 and has the same vertical axis value. Point P2 coincides with point D10 shown in Figure 14. Point P3 has a different value from point P1 shown in Figures 14 and 17. However, point P3 may also coincide with point P1.

Next, a triangular plane with points C1, P3, and D1 as vertices is generated. This triangular plane is the shaded area in FIG. 20. In other words, this triangular plane is a plane including the tooth flank corner D, and is a truncated triangular plane in which the vertex P2 of the tooth part consisting of three surfaces, the tooth flank of the driven gear G2 (upper surface in FIG. 20), the tooth end surface on one side of the tooth trace direction (left front surface in FIG. 20), and the tooth tip surface (right front surface in FIG. 20), is cut off. In other words, the tooth flank corner D included in a part of the shaded area is approximated as a truncated triangular plane in which the vertex P2 of the tooth part consisting of three surfaces, the tooth flank of the driven gear G2 (upper surface in FIG. 20), the tooth end surface on one side of the tooth trace direction (left front surface in FIG. 20), and the tooth tip surface (right front surface in FIG. 20), is cut off.

The amount of pressure angle modification at one end of the tooth in the tooth trace direction is defined as α. The distance between corner point C0 corresponding to tooth flank corner C in the finishing process ST4 and corner point C1 corresponding to tooth flank corner C in the rough modification process ST3 is defined as β. In other words, the distance β is equal to the predetermined finishing depth of cut Dc in the finishing process ST4. Furthermore, in the final shape of the tooth flank, the maximum modification amount in the tooth thickness direction at tooth flank corner D is defined as γ.

The pressure angle modification amount α at one tooth end face in the tooth trace direction is determined so as to satisfy the formulas (1), (2), and (3).
α=β+γ... (1)
α/R2=γ/R1... (2)
α/S2=γ/S1... (3)
α: Pressure angle modification amount at tooth end face β: Distance in tooth thickness direction between the end point on the truncated triangular plane opposite the tooth flank corner in the tooth profile direction and the specified tooth flank shape γ: Maximum modification amount in tooth thickness direction at tooth flank corner R1: Length in tooth profile direction in the modification area of the tooth flank corner R2: Evaluation range in tooth profile direction (distance between the tooth tip and tooth bottom side tooth profile reference surface)
S1: Length in the tooth trace direction in the modification region of the tooth flank angle S2: Length from the tooth end face to the position in the tooth trace direction where the pressure angle modification amount becomes 0

Here, the predetermined finishing cut-in amount β in the finishing machining process ST4 is determined in the range of "0 < β < maximum modification amount of α". The maximum modification amount of α is the maximum modification amount that can be applied to the tooth flank corner portion D in the rough modification machining process ST3.

(9. Effects of gear processing method)
As described above, the tooth flank corner D is machined in the rough modification process ST3, and the portions other than the tooth flank corner D are machined in the finish processing process ST4. The bias modification in the rough modification process ST3 is a modification method that changes the tooth flank shape before modification to a twisted surface shape. In other words, the bias modification is a modification method that changes the tooth profile shape so that the pressure angle gradually changes as the tooth proceeds in the tooth trace direction. Therefore, when the entire tooth flank is machined by applying the bias modification, one pair of corners among the four corners that make up the tooth flank is cut off relatively deeply, and the remaining pair of corners is cut off relatively shallowly.

Therefore, in the rough modification process ST3 (tooth flank corner processing process), bias modification is applied to machine the tooth flank corner D located at the tip of the driven gear G2 and at one end in the tooth trace direction deeply. On the other hand, in the finish processing process ST4 (reference tooth flank processing process), a specified tooth flank shape is processed according to reference processing conditions. In other words, on the tooth flank of the driven gear G2 after processing is completed, the tooth flank corner D is the part machined in the rough modification process ST3, and the parts other than the tooth flank corner D are the parts machined in the finish processing process.

In this way, multiple machining steps are used, including a machining step in which bias adjustment is applied to the standard machining conditions, and a machining step under the standard machining conditions. Therefore, in the driven gear G2, only the tooth flank corner portion D can be machined deeper than other portions. The driven gear G2 machined in this way can improve the meshing ratio except for the initial meshing period while avoiding trochoid interference in the initial meshing period.

The finishing process ST4 is also implemented as a process following the rough modification process ST3. As a result, the rough modification process ST3 processes the tooth flank corner D and also processes areas other than the tooth flank corner D. The finishing process is implemented after the rough modification process ST3, and processes areas other than the tooth flank corner D in the rough modification process ST3. In other words, the rough modification process ST3 functions as one of the normal rough processing processes, and there is no need to add a special processing process to process the tooth flank corner D.

Here, the drive gear G1 and the driven gear G2 are gears with a helix angle. When the driven gear G2 is the subject of processing, the rough correction process ST3 processes the tooth flank corner D, which is the tooth tip and one end in the tooth trace direction of the driven gear G2. In particular, for gears with a helix angle, it is possible to avoid trochoid interference at the tooth flank corner D of the driven gear G2 and improve the meshing ratio except at the initial stage of meshing.

In the rough modification process ST3, in order to apply bias modification, if tooth flank corner D is machined deeper than the reference value H1, there is a possibility that the diagonally located tooth flank corner B will also be machined deeper than the reference value H1.

However, in the rough modification process ST3, bias modification is applied to the reference processing conditions, and pressure angle modification is applied to the center of the tooth trace direction. In this way, the amount of modification is relatively large at the tooth flank corner D, which is the tooth tip and one end in the tooth trace direction of the driven gear G2, and the amount of modification is relatively small at the tooth flank corner B, which is the tooth base and the other end in the tooth trace direction.

In other words, the tooth flank corner D, which is the tooth tip and one end in the tooth trace direction of the driven gear G2 machined in the rough modification process ST3, is a portion that is not machined in the finish processing process ST4. On the other hand, the tooth flank corner B, which is the tooth base and the other end in the tooth trace direction of the driven gear G2 machined in the rough modification process ST3, is a portion that is machined in the finish processing process ST4.

In this way, the rough modification process ST3 not only performs bias modification, but also applies pressure angle modification at the center of the tooth trace direction, so that the final tooth flank shape is a surface machined only at the tooth flank corner D in the rough modification process ST3, and the other areas are surfaces machined in the finish processing process ST4. Therefore, in a gear with a helix angle, trochoid interference at the tooth flank corner D of the driven gear G2 can be avoided, and the meshing rate can be improved except at the initial stage of meshing.

In addition, the standard rough machining process ST1, the rough correction machining process ST3, and the finishing machining process ST4 all use gear skiving to machine the tooth surfaces. This means that gears can be machined without changing tools. It is also possible to machine the gears in a series of machining operations.

(10. Other Examples of Gear Machining Methods)
Another example of the gear machining method will be described with reference to Fig. 21. In the above, the finishing process ST4 is performed after the rough modification process ST3 (tooth flank corner machining process). In this example, the finishing process ST13 is performed before the tooth flank corner machining process ST14.

The control device 40 performs the reference rough machining process ST11. The reference rough machining process ST11 is the same as the reference rough machining process ST1 described above. Next, the control device 40 judges whether the reference rough machining process ST11 performed this time is one cycle before the finish machining process (judgment process ST12). If it is not one cycle before the finish machining process (ST12: No), the control device 40 performs the reference rough machining process ST11 again until it reaches one cycle before the finish machining process.

When the standard rough machining process ST11 that has been performed reaches one cycle before the finish machining process (ST12: Yes), the control device 40 performs the finish machining process ST13. The finish machining process ST13 is performed under the same machining conditions as the finish machining process ST4 in the above embodiment. In other words, in the finish machining process ST13, the entire tooth surface is machined, and the tooth surface is formed into a predetermined tooth surface shape.

Next, the tooth flank corner machining process ST14 is carried out. The tooth flank corner machining process ST14 is carried out under the same machining conditions as the rough correction machining process ST3 described above. In other words, the tooth flank corner machining process ST14 machines the tooth flank corner D. However, the tooth flank corner machining process ST14 does not machine any areas other than the tooth flank corner D.

In this way, even if the finishing process ST13 is performed as a process preceding the tooth flank corner processing process ST14, it is possible to form a shape in which only the tooth flank corner D is ultimately cut away. As a result, trochoid interference at the tooth flank corner D of the driven gear G2 can be avoided, and the meshing rate can be improved except at the beginning of meshing.

(11. Target Tooth Flank Shape of Drive Gear G1)
The above description is for the driven gear G2. The same can be applied to the drive gear G1. However, the portion where trochoid interference occurs is the tooth tip in the driven gear G2, whereas it is the tooth base in the drive gear G1. Therefore, a shape equivalent to the tooth flank corner D of the tooth flank of the driven gear G2 is formed on the tooth base side of the tooth flank of the drive gear G1.

The target tooth flank shape of the drive gear G1 in this case will be described with reference to Figures 22 and 23. Figure 22 shows the target tooth flank shape of the drive gear G1 in an actual three-dimensional coordinate system, and Figure 23 shows the tooth flank of the drive gear G1 in a permuted coordinate system.

The target tooth flank shape of the drive gear G1 is a shape in which the tooth flank corner b, which is the tooth root and one end in the tooth trace direction, is cut away to reduce the above-mentioned trochoidal interference, and the parts other than the tooth flank corner b are expressed by a specified tooth flank shape. In Figures 22 and 23, the tooth flank of the drive gear G1 has tooth flank corners a, b, c, and d, and the corner points corresponding to the tooth flank corners a, b, c, and d are a0, b1, c0, and d0, respectively.

The gear machining method for the driven gear G2 described above can be applied to the machining method for the tooth surface of the driving gear G1. Specifically, the gear machining method shown in FIG. 12 and the gear machining method shown in FIG. 21 can be applied.

As for the method of determining the machining conditions in the tooth flank corner machining steps ST3 and ST14, in the driven gear G2, the tooth flank corner D is approximated as a truncated triangular plane with the apex of the tooth portion consisting of the three surfaces of the tooth flank, tooth end surface, and tooth tip surface cut off. In the drive gear G1, the tooth flank corner b can be approximated as a truncated triangular plane with the apex of the tooth portion consisting of the three surfaces of the tooth flank, tooth end surface, and tooth profile reference surface on the bottom side cut off. The tooth profile reference surface is a virtual surface that corresponds to the back surface of the tooth tip surface in the tooth portion.

In this way, trochoidal interference can be reduced by machining the drive gear G1 to have the tooth flank corner b cut off to a specified tooth flank shape. In addition, by machining both the drive gear G1 and the driven gear G2 as described above, trochoidal interference can be reduced more reliably.

(12. Other)
In the above embodiment, the standard rough machining process ST1, the rough modification process ST3, and the finishing process ST4 are all performed by performing gear skiving to machine the tooth surface. In addition, for example, the standard rough machining process ST1 and the rough modification process ST3 may apply gear skiving, and the finishing process ST4 may apply other gear machining methods such as hobbing with a hob cutter or shaping with a shaper cutter. Also, the standard rough machining process ST1 may apply hobbing or shaping, and the rough modification process ST3 and the finishing process ST4 may apply gear skiving. Also, a heat treatment process such as quenching may be performed after the rough modification process ST3, and the finishing process ST4 may be performed after the heat treatment process.

In addition, in the rough modification process ST3 and the tooth flank corner processing process ST14, bias modification was applied to the entire tooth flank. Alternatively, bias modification can be applied only to the portion including tooth flank corners D and b in the tooth trace direction, and the remaining portions in the tooth trace direction (portions close to tooth flank corners A and B, and portions close to tooth flank corners c and d) can be processed without bias modification. In other words, halfway through the tooth trace direction during one processing feed operation, a state in which bias modification is applied and a state in which bias modification is not applied are switched.

For example, in the case of driven gear G2, when machining is started from tooth flank corners A and B in the tooth trace direction, bias modification is not applied at first, and bias modification is applied from halfway in the tooth trace direction until machining reaches tooth flank corners C and D. In addition, in the case of driven gear G2, when machining is started from tooth flank corners C and D in the tooth trace direction, bias modification is applied at first, and machining is continued until tooth flank corners A and B without bias modification from halfway in the tooth trace direction.

For example, in the case of the drive gear G1, when machining is started from the tooth flank corners c and d in the tooth trace direction, bias modification is not applied at first, and bias modification is applied from halfway in the tooth trace direction until machining reaches the tooth flank corners a and b. Also, in the case of the drive gear G1, when machining is started from the tooth flank corners a and b in the tooth trace direction, bias modification is applied at first, and machining is continued from halfway in the tooth trace direction until machining reaches the tooth flank corners c and d without bias modification.

W Workpiece G, G1, G2 Gear ST3, ST14 Tooth flank corner machining process ST4, ST13 Reference tooth flank machining process D, b Tooth flank angle

Claims (7)

A gear machining method for machining a gear tooth surface on a workpiece, comprising the steps of:
a tooth flank corner processing step of performing a gear skiving process with bias modification applied to a reference processing condition to perform a process of cutting off at least one of a tooth flank corner portion, which is a tooth tip and an end portion in a tooth trace direction, or a tooth base and an end portion in a tooth trace direction, with respect to a predetermined tooth flank shape;
a reference tooth flank machining step which is carried out before or after the tooth flank corner machining step, and which machines a portion other than the tooth flank corner into the predetermined tooth flank shape by performing gear machining under the reference machining conditions;
A gear machining method comprising: The tooth flank corner processing step processes the tooth flank corner and also processes a portion other than the tooth flank corner,
2. The gear machining method according to claim 1, wherein the reference tooth flank machining step is performed after the tooth flank corner machining step, as a finish machining step for machining a portion other than the tooth flank corner in the tooth flank corner machining step. The gear machining method according to claim 1 or 2, wherein the reference tooth surface machining step performs gear skiving under the reference machining conditions to machine the areas other than the tooth surface corners into the specified tooth surface shape. The gear to be machined is a driven gear having a helix angle,
4. The gear machining method according to claim 1, wherein the tooth flank corner machining step machines a tooth flank corner that is a tooth tip and one end in a tooth trace direction of the driven gear. The gear machining method according to claim 4, wherein the tooth flank angle machining process applies the bias modification to the reference machining conditions and also applies pressure angle modification at the center in the tooth trace direction to relatively increase the amount of modification at the tooth tip and one end in the tooth trace direction and relatively decrease the amount of modification at the tooth base and the other end in the tooth trace direction, thereby machining the tooth tip and one end in the tooth trace direction of the driven gear. The gear to be machined is a drive gear having a helix angle,
4. The gear machining method according to claim 1, wherein the tooth flank corner machining step machines a tooth flank corner that is at a root and one end in a tooth trace direction of the drive gear. The gear machining method according to claim 6, wherein the tooth flank angle machining process applies the bias modification to the reference machining conditions and also applies pressure angle modification at the center in the tooth trace direction to relatively increase the amount of modification at the tooth base and one end in the tooth trace direction and relatively decrease the amount of modification at the tooth tip and the other end in the tooth trace direction, thereby machining the tooth base and one end in the tooth trace direction of the drive gear.

Images