Individual pressure angle correction for powerful skiving

Abstract

A power skiving method, wherein a rotation of a three-dimensional cutter relative to the tooth flank of a gear workpiece is performed to reposition the cutter relative to the gear workpiece, thereby achieving a reduction and / or increase in the pressure angle of the tooth flank. The method can be applied independently to the left and right sides of the tooth gap, or the rotations can be superimposed on each other to achieve a pressure angle correction on both tooth flanks of the tooth gap.

Description

Technical Field

[0001] The present invention relates to manufacturing gears by power skiving, and more particularly to a method of using the inclination of a cutter to provide independent pressure angle correction to the sides of a gear tooth. Background Art

[0002] Skiving of cylindrical gears (also called "hob stripping" or "power skiving") is a cutting process that has been around for many years and is primarily used to manufacture internal ring gears (see, for example, DE 243514). Like honing, power skiving exploits the relative sliding movement between two "cylindrical gears" whose axes are inclined. Power skiving cutters typically look similar to profile cutters with a helix angle (e.g., 20°) that is different from the helix angle of the cylindrical gear to be machined (e.g., US 2011 / 0268523). Other power skiving tools include rod-shaped or stick-shaped cutting blades arranged in the head of the cutter, as shown, for example, in US 2012 / 0282055 or US 9,956,627. Power skiving of internal or external cylindrical gears (spur and helical) can be performed on any of several commercially available computer controlled (CNC) multi-axis machines, such as those disclosed in US 6,712,566 or US 9,956,627, the disclosures of which are incorporated herein by reference.

[0003] Figure 1 The geometrical setup of the cutting cutter relative to the internal ring gear is shown. The upper left figure shows a front view of the generated gear system. The ring gear is oriented in the main coordinate system, where its axis of rotation is colinear with the Y axis. The cutter center (origin of Rw) is located outside the center of Y4 in the X4-Z4 plane with a radial distance vector Ex. The pitch circles of the cutter and the ring gear are in tangential contact at the lowest point of the pitch circle. A top view showing the tool tilt angle or shaft angle Σ is drawn below the front view. In the case of spur gears, the direction of the stroke motion is consistent with the Y axis. The relative speed required for the cutting motion is measured around Figure 1 The axis angle Σ of the X4 axis of the coordinate system shown is generated. In the case of helical gears, the inclination of the cutter can be selected independently of the helix angle. However, a helix angle of 20° or more makes it possible to match the axis angle Σ and use a simplified spur gear shaper cutter for the cutting operation. Also, in this case, the stroke movement is oriented in the Y direction, but the incremental rotation ω2 depending on the stroke feed must be added to ω1. The axis angle Σ can also be defined differently from the helix angle still requiring the same increment ω2, but the front orientation angle and the side relief angle of the tool must be calculated from the difference between the helix angle and the axis angle Σ.

[0004] Figure 1The side view on the right side of the figure shows a second possible tool tilt, which is called the tilt angle. This tool tilt angle can be used to increase the effective clearance angle between the blade and the slot, and it can also be used to eliminate interference between the back sides of long spur gear shaper cutters with minimum clearance angles.

[0005] It may be desirable to individually correct the pressure angle of the cutter during the development of the workpiece and / or during the skiving process used to manufacture the workpiece. In the case of large pressure angle variations, the profile of the cutting teeth of the skiving cutter is usually reworked. However, since the slot width of the workpiece must be maintained, reworking the profile is usually not possible. In most cases, the solution is to manufacture the disc cutter with a corrected profile. Summary of the invention

[0006] The invention comprises a method in which a rotation of a three-dimensional cutter relative to a tooth flank of a gear workpiece is performed to reposition the cutter relative to the gear workpiece so as to achieve a reduction and / or increase in the pressure angle of the tooth flank. The method can be applied independently to the left and right flanks of a tooth gap, or the rotations can be superimposed on each other to achieve a pressure angle correction on both tooth flanks of the tooth gap.

[0007] More specifically, the present invention includes a method for machining teeth of a gear workpiece by power skiving, wherein the method includes: providing a cutting tool having a plurality of cutting blades; rotating the cutting tool; rotating the gear workpiece; and engaging the cutting tool with the gear workpiece to machine teeth of the gear workpiece, each of the teeth having a left tooth flank and a right tooth flank. The method further includes moving the cutting tool relative to the gear workpiece so that the cutting tool is positioned about at least one of:

[0008] a) The contour symmetry line between the left and right tooth flanks of the gear workpiece tooth,

[0009] b) a profile tangent of at least one of the left tooth flank and the right tooth flank of the gear workpiece tooth,

[0010] c) an axis perpendicular to the line of symmetry of the profile between the left and right tooth flanks of the gear workpiece tooth, and

[0011] d) a profile normal of at least one of the left tooth flank and the right tooth flank of the gear workpiece tooth,

[0012] The cutting tool is thereby repositioned relative to the gear workpiece, thereby achieving a reduction and / or increase in the pressure angle of at least one of the left and right tooth flanks of the gear workpiece teeth. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Shown are a front, side and top view of a power skiving arrangement between a workpiece and a cutter.

[0014] FIG. 2( a ) shows a three-dimensional view of a simplified gear slot with a cutting blade rotated through an angle γ to achieve a reduction in the pressure angle.

[0015] FIG. 2( b ) shows a front view of FIG. 2( a ) where the pressure angle reduction is caused by the rotation angle γ.

[0016] FIG. 2( c ) is a top view of FIG. 2( a ), showing the geometric relationship between the correction rotation γ and the pressure angle reduction Δα.

[0017] FIG. 3( a ) shows a three-dimensional view of a simplified gear slot with a cutting blade rotated by an angle γ about a profile tangent to the left side face to achieve a single-side correction that reduces the pressure angle on the right side face.

[0018] FIG. 3( b ) illustrates a simplified gear groove showing both left and right side face profile tangent lines with an angle γ correction rotation about each tangent line.

[0019] FIG. 4( a ) shows a three-dimensional view of a simplified gear slot with a cutting blade rotated by an angle about a line perpendicular to the line of symmetry of the profile.

[0020] FIG. 4( b ) is a front view of FIG. 4( a ), which shows that due to the rotation angle This causes the pressure angle to increase.

[0021] FIG. 4( c ) is a side view of FIG. 4( a ) showing the rotation of This results in a reduction of the profile depth h to h*.

[0022] FIG5( a ) shows a three-dimensional view of a simplified gear slot with a cutting blade rotated by an angle θ about a profile normal tangent to the left side face. To achieve single-side correction by increasing the pressure angle on the right side.

[0023] FIG. 5( b ) is a front view of FIG. 5( a ) showing the increase in the pressure angle on the right side.

[0024] FIG. 5( c ) shows a simplified gear slot showing the angles around each normal. Corrects both the left and right face normals for rotation. DETAILED DESCRIPTION

[0025] The terms "invention," "described invention," and "present invention" as used in this specification are intended to refer broadly to all subject matter of this specification and any patent claims below. Statements containing these terms should not be construed as limiting the subject matter described herein or limiting the meaning or scope of any patent claim below. In addition, this specification does not seek to describe or limit the subject matter covered by any claim to any particular part, paragraph, statement, or figure of this application. The subject matter should be understood by reference to the entire specification, all drawings, and any claims attached. The present invention can use other configurations and can be practiced or implemented in various ways. Furthermore, it should be understood that the words and terms used herein are for descriptive purposes and should not be considered limiting.

[0026] The use of "including," "having," and "comprising" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of letters to identify elements of a method or process is for identification only and is not meant to imply that the elements should be performed in a specific order.

[0027] Although reference may be made hereinafter to directions such as upper, lower, upward, downward, rearward, bottom, top, front, rear, etc., when describing the drawings, such references are made relative to the drawings (as normally viewed) for convenience. These directions are not intended to be taken literally or to limit the invention in any way. Additionally, terms such as "first," "second," "third," etc., are used herein for descriptive purposes and are not intended to indicate or imply importance or significance.

[0028] The invention will now be discussed in detail with reference to the accompanying drawings which illustrate the invention by way of example only.

[0029] The method of the present invention comprises positioning (i.e., rotating) a three-dimensional cutting machine about at least one of the following: a profile symmetry line, a side profile tangent line, a side profile normal line, and / or an axis perpendicular to a profile symmetry line relative to a left tooth side surface and / or a right tooth side surface of a gear workpiece, so as to reposition the cutting machine relative to the gear workpiece, thereby reducing and / or increasing the pressure angle of the tooth side surface of the gear workpiece by the cutting process. The process is suitable for manufacturing (e.g., soft cutting or rough cutting) teeth from a gear workpiece blank and for finishing processes (e.g., hard cutting or hard tooth surface finishing) of pre-(rough) cut and hardened gear teeth. Therefore, the gear workpiece should be understood to include a gear blank (initially formed teeth) and a pre-cut gear (finished teeth).

[0030] FIG. 2( a) shows a simplified trapezoidal blade profile with cutting edges on both sides of the trapezoid. Between the tool tooth and the work gear tooth groove (formed between adjacent workpiece teeth) is a virtual rack profile with a trapezoidal profile with straight edges. The simplified blade is located in a trapezoidal channel, which represents a reference profile also referred to as a rack profile. The three-dimensional view in FIG. 2( a) shows that the blade profile is rotated around a profile symmetry line between the left and right tooth flanks, which is shown as a vertical axis. The rotation angle is marked as γ in the front view FIG. 2( b) at the lower left. A top view of the blade and the trapezoidal channel is shown in FIG. 2( c) at the lower right. Figure 2(b) and 2(c) Both bottom views contain sufficient graphical information to deduce the rotation angle γ about the vertical axis required for the tooth flanks (internal or external) of workpieces such as spur and helical gears to achieve a desired pressure angle reduction Δα.

[0031] Equation (1) shows the relationship between the correction Δα and the rotation γ:

[0032]

[0033] exist Figure 3(a) and 3(b) A preferred embodiment for reducing the pressure angle of the workpiece is shown in FIG. The three-dimensional view of the blade profile and the trapezoidal channel in FIG. 3( a) shows that the blade profile is rotated around a profile tangent to the left side face. Since the tangent between the trapezoidal channel and the blade profile is the same, the rotation γ will not affect the pressure angle on the left side face, but for a given rotation angle γ, the pressure angle on the right side face is reduced by about a factor of two compared to the principle shown in FIG. 2( a). The rotation around the profile tangent causes a slight deformation of the involutes on the left and right side face profiles. The deformation is caused by the fact that the blade profile is not equal to a straight reference profile, but is also an involute generated from a reference profile similar to the working gear profile. However, any such deformation is negligible. Due to the effect of the pressure angle correction on the right side face, only a very small correction rotation angle is required, which makes any side effects on the left and right sides (e.g., auxiliary slot width changes) practically negligible in most cases. However, if slot width correction is required, the original slot width can be reestablished by a small number of deeper cuts.

[0034] As can be seen from the right side face profile tangent in Figure 3(b), if the blade cutting edge profile at the right side face is rotated about a profile tangent to the right side face, a similar correction can also be applied to correct the left side face. Rotating about the profile tangent will slightly deform the involutes above and below the profile reference height of the right side face, but the pressure angle of the right side face will remain constant. The deformation is caused by the fact that the blade profile is not equal to the straight reference profile, but is also an involute generated from a reference profile similar to the working gear profile. Due to the effect of the pressure angle correction (reduction) of the present invention on the left side face of the gear tooth, only a very small correction rotation angle is required, which makes any side effects on the left and right sides (e.g., auxiliary slot width changes) negligible. However, as mentioned above, if slot width correction is required, the original slot width can be reestablished by a small number of deeper cuts.

[0035] It is worth noting that Figures 2(a) to (c) and Figure 3(a) and 3(b) The correction principle presented in is only applicable to pressure angle reduction. Even if the rotation angle γ is opposite, the pressure angle reduction will still occur. It will be clear from looking at the correction method of Figures 2(a) to (c) about the reverse rotation that the reverse rotation about the profile tangent will also reduce the pressure angle of the right and / or left side face.

[0036] The present invention further includes achieving a pressure angle reduction (same or different) on both the right and left flanks of the workpiece using the same or different amounts of corrections with respect to both the left and right flank profile tangents as shown in FIG3( b). The combined correction with respect to both the left and right flank profile tangents effectively produces a correction defined with respect to a line located between the left and right flank profile tangents.

[0037] In order to increase the pressure angle, a blade profile rotation around an axis perpendicular to the profile symmetry line can be used. This principle of rotating the blade profile is shown in a three-dimensional view in Figure 4 (a). Figure 4 (b) shows a front view of the trapezoidal channel of Figure 4 (a), and Figure 4 (c) shows a side view of the trapezoidal channel of Figure 4 (a). Figure 4(b) and 4(c) Contains the information used to derive the rotation angle about the horizontal axis required to achieve the desired pressure angle increase Δα Equations (2) and (3) are related to Figures 4(a) to (c) and solved for the rotation angle The relationship between the correction Δα and

[0038]

[0039] b=h·tanα

[0040]

[0041]

[0042]

[0043] Figure 5(a) , 5(b) Another preferred embodiment for increasing the pressure angle is shown in Figures 5(c). The three-dimensional view of the blade profile and the trapezoidal channel in Figure 5(a) shows that the blade profile is rotated around the profile perpendicular to the left side of the tooth. Since the normal between the trapezoidal channel and the blade profile is the same, the rotation The pressure angle on the left flank will not be affected, but for a given rotation angle γ, the pressure angle on the right flank will increase by about a factor of two compared to the principle shown in FIG4( a). Rotation about the profile normal will result in a slight but negligible deformation of the involutes on the left and right flank profiles. The deformation is caused by the fact that the insert profile is not equal to a straight reference profile, but is also an involute generated from a reference profile similar to the working gear profile.

[0044] Since the pressure angle correction (increase) of the present invention affects only one of the two flanks of the gear tooth, only a very small correction rotation angle is required, which makes any side effects on the right flank (eg tooth depth change) negligible.

[0045] As can be understood from the right side normal in Figure 5(c), if the blade cutting edge profile at the right side is rotated around the profile normal of the right side, a similar correction can also be applied to correct the left side. Since the pressure angle correction (increase) of the present invention only affects one of the two sides of the gear tooth, only a very small correction rotation angle is required, which makes any side effects on the left side (e.g., tooth depth change) negligible.

[0046] Figure 5(a) and 5(b) The correction of the present invention shown in FIG. 4 independently provides an increase in the pressure angle of the right or left face. However, this correction cannot reduce the pressure angle by simply reversing the profile normal rotation. It will be clear from observing the correction method of FIG. 4 with respect to the reverse rotation that reversing the profile normal rotation will also increase the pressure angle of the right and / or left face.

[0047] The present invention further comprises achieving a pressure angle increase (same or different) on both the right and left tooth flanks of the workpiece using the same or different amount of corrections about both the left and right side normals as shown in Figure 5(c). The combined correction about both the left and right side normals effectively results in a correction defined about a line located in the three-dimensional space of the workpiece tooth groove.

[0048] The present invention further encompasses the above with respect to, for example Figure 3(a) , 3(b) , 5(a), 5(b) and 5(c) to allow independent pressure angle corrections to be achieved on two types of flanks of a gear. For example, a combination of two inventive corrections can simultaneously cause an increase in the pressure angle on the left flank of a gear and a decrease in the pressure angle on the right flank of the same gear by superimposing the two corrections. The combined correction of the flank tangent and the flank normal effectively causes a correction defined about a line located in the three-dimensional space of the workpiece tooth groove.

[0049] The inventors have found a correlation between the amplification of the correction effect and the difference between the tool axis inclination and the helix angle. In the case of a zero degree helix angle (spur gears) and a tool axis inclination angle of 20° relative to the working gear axis, the correction effect is amplified by a factor of about 100. In the case of a 20° helix angle (helical gears) and a tool axis inclination of also 20° relative to the working gear axis, the correction effect is not amplified. In this case, the cutter rotates in the normal plane of the working gear.

[0050] Preferably, the cutter rotation plane is the same as the normal plane of the working gear. In those cases where the cutter has a rotation plane that deviates from the normal plane of the working gear, the correction is amplified according to the sine of the difference angle according to the relationship in equation (5). A further adjustment for the internal workpiece according to the pitch ratio between the workpiece and the cutter is represented by equation (6).

[0051]

[0052]

[0053] in:

[0054] Δα eff …Effective pressure angle changes

[0055] Δα…Theoretically calculated pressure angle change

[0056] Σ…The inclination between the cutting machine and the working axis

[0057] VZ…Spiral direction mark. Right spiral → VZ = +1, left spiral → VZ = -1

[0058] VZPS...cut above the center → VZPS = +1, cut below the center → VZPS = -1

[0059] F red …reduction factor found empirically based on positive working gear and Σ = 20°

[0060] F int …For internal workpieces, based on the pitch diameter of the cutting machine to

[0061] Adjustment factor of working pitch diameter = 60%

[0062] Z…Number of teeth on the workpiece

[0063] Z cut …Theoretical number of teeth of the cutting machine

[0064] Although the present invention has been described with reference to preferred embodiments, it should be understood that the invention is not limited to the details thereof. The invention is intended to encompass modifications that will be obvious to one skilled in the art to which the subject matter pertains without departing from the spirit and scope of the appended claims.

Claims

1. A method for machining teeth of a gear workpiece by power skiving, the method being performed on a computer-controlled multi-axis gear machining machine, the method comprising: providing a cutting tool having a plurality of cutting blades, rotating the cutting tool, rotating the gear workpiece, engaging the cutting tool with the gear workpiece to machine the teeth of the gear workpiece, the teeth each having a left tooth flank and a right tooth flank, wherein the left tooth flank and the right tooth flank are machined simultaneously by the cutting tool, Moving the cutting tool relative to the gear workpiece so that the cutting tool is positioned about at least one of: a) a contour symmetry line between the left tooth flank and the right tooth flank of the gear workpiece tooth, b) a contour tangent of at least one of the left tooth flank and the right tooth flank of the gear workpiece tooth, c) an axis perpendicular to the profile symmetry line between the left tooth flank and the right tooth flank of the gear workpiece tooth, and d) a profile normal of at least one of the left tooth flank and the right tooth flank of the gear workpiece tooth, The cutting tool is thereby repositioned relative to the gear workpiece, thereby achieving a reduction and / or an increase in the pressure angle of at least one of the left and right tooth flanks of the gear workpiece teeth. 2 . The method according to claim 1 , wherein the gear workpiece is a spur gear workpiece or a helical gear workpiece. The method according to claim 1 , wherein the gear workpiece is a gear blank. The method of claim 1 , wherein the gear workpiece is a pre-cut gear including teeth. 5 . The method of claim 1 , wherein the left flank is located on a gear tooth, the right flank is located on an adjacent gear tooth, and wherein a tooth gap is defined between the gear tooth and the adjacent gear tooth. The method of claim 1 , wherein the teeth are internal gear teeth or external gear teeth.

7. The method of claim 1, wherein the amount by which the pressure angle is reduced and / or increased can be the same or different for the left and right flanks.

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