Near-zero degree cross-axis angle gear cutter and gear cutting method using such tool

Abstract

A gear cutter tool (308) is provided for cutting internal teeth into a workpiece (312) to form a gear. The gear cutter tool is configured to rotate about a longitudinal gear cutter axis of rotation (354). The workpiece is configured to rotate about a workpiece axis of rotation (374). The gear cutter tool includes a gear cutter having a plurality of cutting teeth (332). Each cutting tooth of the plurality of cutting teeth has a tooth flank (341) defining a cross-axis tooth angle (350) between the tooth flank and a line (352) intersecting the longitudinal gear cutter axis of rotation. The cross-axis tooth angle is between 1 and 15 degrees. The cross-axis tooth angle (372) of the gear cutter tool, defined between the longitudinal gear cutter axis of rotation and the workpiece axis of rotation, is substantially close to 0 degrees.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Patent Application No. 63 / 091,675, filed October 14, 2020, the disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates generally to gear cutters for forming teeth on the inner diameter of a workpiece, and associated coolant delivery assemblies. [Background technology]

[0003] Gear manufacturers utilize a variety of machining processes and corresponding tooling to manufacture gears. Exemplary processes can include hobbing, shaping, milling, shear cutting, and grinding. The process selected by a gear manufacturer can depend on the type of gear being machined and the tolerances to which the gear is produced. Other considerations when selecting a method can include the size of the gear, the configuration of the interior section or flange, the quantity of gears being manufactured, as well as the gear-to-pinion ratio and cost.

[0004] Teeth adjacent to other part features are currently limited to manufacturing methods such as forming or rack rolling. For internal teeth, forming or broaching are traditional manufacturing methods, but each process is limited to the part type. In other words, broaching must have a completely unobstructed part layout so the tool can pass completely through the part. Gear forming allows teeth to be cut against interference surfaces, but is inherently slow in terms of machine cycles and flexibility.

[0005] Gear skiving is a recent development in gear manufacturing that reduces traditional gear forming cycle times by up to 80%. Traditional skiving is very fast, but is limited by cutter clearance and part configuration. Summary of the Invention

[0006] A gear cutter tool is provided for cutting internal teeth into a workpiece to form a gear. The gear cutter tool is configured to rotate about a longitudinal gear cutter axis of rotation. The workpiece is configured to rotate about the workpiece axis of rotation. The gear cutter tool includes a gear cutter having a plurality of cutting teeth. Each cutting tooth of the plurality of cutting teeth has a tooth surface defining a cross-axis tooth angle between the tooth surface and a line intersecting the longitudinal gear cutter axis of rotation. The cross-axis tooth angle is between 1 and 15 degrees. The cross-axis tool angle of the gear cutter tool defined between the longitudinal gear cutter axis of rotation and the workpiece axis of rotation is substantially close to 0 degrees.

[0007] According to additional features, the cross-axis tool angle is 1 to 6 degrees. In other features, the cross-axis tool angle is 1 to 5 degrees. In other features, the cross-axis tool angle is 1 to 4 degrees. In still other features, the cross-axis tool angle is 3 degrees. In still other features, the cross-axis tool angle is 2 degrees. In still other features, the cross-axis tool angle is 1 degree. In some configurations, the longitudinal gear cutting axis is transverse to the workpiece. The cross-axis tooth angle can be 10 to 15 degrees. In other configurations, the cross-axis tooth angle can be 1 to 10 degrees.

[0008] A method for cutting internal teeth into a workpiece to form a gear using a gear cutter tool includes providing a gear cutter having a plurality of cutting teeth. Each cutting tooth of the plurality of cutting teeth has a tooth surface defining a cross-axis tooth angle between the tooth surface and a line intersecting a longitudinal gear cutter rotation axis. The cross-axis tooth angle is between 1 and 15 degrees. The workpiece is rotated about a workpiece axis. The gear cutter tool is rotated about a longitudinal gear cutting axis. The workpiece axis and the longitudinal gear cutter axis define a cross-axis tool angle therebetween. The workpiece is cut with the plurality of teeth. The cross-axis tool angle is substantially close to 0 degrees.

[0009] According to additional features, the cross-axis tool angle is between 1 and 6 degrees. In other features, the cross-axis tool angle is between 1 and 5 degrees. In other features, the cross-axis tool angle is between 1 and 4 degrees. In still other features, the cross-axis tool angle is 3 degrees. In still other features, the cross-axis tool angle is 2 degrees. In still other features, the cross-axis tool angle is 1 degree. The cross-axis tooth angle can be between 10 and 15 degrees. In other configurations, the cross-axis tooth angle can be between 1 and 10 degrees. [Brief explanation of the drawings]

[0010] The present disclosure will become more fully understood from the detailed description and the accompanying drawings.

[0011] [Figure 1A] FIG. 1 is a schematic perspective view of an exemplary prior art gear cutter system including a gear cutter configured to cut an internal gear in a blank orientation. [Figure 1B] FIG. 1B is a schematic perspective view of the system of FIG. 1A showing the cutter that produced the precision internal gear in its final orientation. [Figure 2] 1B is a schematic end view of the system of FIG. 1A showing the center distance between the axis of rotation of the cutter and the axis of rotation of the internal gear. [Figure 3] 1B is a schematic side view of the cutter and internal gear of FIG. 1A, illustrating the cross axis angle between the rotation axis of the cutter and the rotation axis of the internal gear. [Figure 4] FIG. 1 is a schematic side view of a prior art gear cutter. [Figure 5] FIG. 1 is a side schematic view of a gear cutter according to an example of the present disclosure. [Figure 6] FIG. 1 is a schematic diagram of a proposed tooth flank superimposed on a conventional tooth tip flank. [Figure 7] FIG. 7 is a schematic side-by-side view comparing the gear cutters of FIGS. 5 and 6. [Figure 8A] FIG. 1 is a cross-sectional view of a conventional gear. [Figure 8B] FIG. 1 is a cross-sectional view of a conventional gear cutter shown at a 6 degree cross-axis angle, showing interference with the workpiece. [Figure 9A] FIG. 1 is a cross-sectional view of a conventional gear. [Figure 9B] FIG. 1 is a cross-sectional view of a gear cutter constructed in accordance with the present disclosure and shown with a cross axis angle substantially near 0 degrees, indicating no interference with the workpiece. DETAILED DESCRIPTION OF THE INVENTION

[0012] An exemplary involute gear cutter system (hereinafter "system") includes a computer numerically controlled (CNC) machine tool and a modified tooth ratio gear cutter (hereinafter "cutter") configured to cut a gear in a blank orientation to remove shavings from the gear in multiple passes to produce a precision gear in a final orientation. The CNC machine tool includes a chuck and an active sub-spindle, i.e., a CNC-controlled, controlled rotational movement. The cutter can be mounted on the spindle, and the blank gear can be mounted in the chuck. More specifically, the cutter can have multiple cutting teeth, each of which can have a pair of cutting edges configured to cut the gear in the blank orientation to provide a gear in a final orientation.

[0013] In its final orientation, the gear has an involute tooth profile including a plurality of cutting teeth and a plurality of valleys therebetween. The cutting tip may be configured to cut the gear in the blank orientation, such that the gear in its final orientation includes spaced-apart active contour sections and an operating pitch diameter. The cutter can thus apply a unidirectional or nearly constant force along the gear surface to improve precision in machining gears, for example, within a 0.0010-inch tolerance, without the need for special cutting tools or cutting systems.

[0014] 1A-3, an exemplary prior art system 100 includes, in part, a computer numerically controlled (CNC) machine tool 102 having a chuck 104 and a spindle 106. The system 100 further includes a cutter 108 mounted on the spindle 106, the spindle configured to rotate the cutter 108 about a cutting axis 110 to cut a gear 114 in a blank orientation (FIG. 1A) and produce a gear 112 in a final orientation (FIG. 1B). This form of cutter 108 is an external gear configured to cut the internal gear 112 in the blank orientation to produce the internal gear 114 in the final orientation. The internal gear 114 in the final orientation has a plurality of cutting teeth 116. The teeth 116 have an involute tooth profile 118 that includes an active contour section 120, which is a portion of each tooth flank configured to contact an opposing tooth of a mating gear.

[0015] The blank-oriented gear 112 is mounted in the chuck 104, which is configured to rotate the gear 112 about a cutting axis 122 (FIG. 1A), such that the cutting axis 122 and the cutting axis 110 are spaced apart by a center distance CD. W In addition, the cutting axis 122 and the cutting axis 110 are disposed at a cross axis angle α relative to one another when the gear 114 is in its final orientation. As used herein, the term "cross axis" is the angle that defines the difference between two axes of rotation of the gear workpiece and the cutting tool.

[0016] The system 100 may further include a flushing device 124 configured to deliver fluid to the gear 112 to remove shavings, chips, or dust from the gear 112 as the spindle 106 rotates the cutter 108 to cut the gear 112 in multiple passes. The fluid may also remove heat from the system 100. In one example, the flushing device 124 is a fluid line 126 in communication with a reservoir 128 to supply water, nitrogen gas, or another fluid to the external gear 112. In its final orientation, the gear 114 has an involute tooth profile including multiple cutting teeth 116 and multiple valleys therebetween. The involute tooth profile 118 includes an active contour section 120, and the operating pitch diameter is spaced apart from the active contour section when the gear 114 is in its final orientation. Further description of prior art skiving tools can be found in commonly owned U.S. patents. See US Pat. No. 10,016,827, the contents of which are expressly incorporated herein by reference.

[0017] The present disclosure enables skiving of teeth previously impossible with current methods due to its ability to precisely cut the workpiece while eliminating certain cutter / workpiece interferences. Conventional skiving methods consist of a rotary gear cutter mounted on an axis that is not the same as the axis of the workpiece. Conventional skiving methods are limited by workpiece clearance when holding the cutting tool at its rotational cross-axis angle. The gear cutter's cross-axis angle creates cutting motions that generate chips. A larger cross-axis angle allows for more cutting motion and increased chip formation. The desired cross-axis angle for conventional systems is typically 20 degrees, but can also be lower, such as 15 or 12 degrees. With these design parameters, tool clearance must be considered, limiting the application of the skiving process.

[0018] As described in detail herein, the present disclosure allows the workpiece axis and the tool axis to be the same or essentially the same (within a range of substantially 1 to 6 degrees), completely eliminating or significantly reducing the cross axis angle. Smaller cross axis angles are desirable in situations where small clearance exists between the cutter and the workpiece geometry. The proposed disclosure enables very small cross axis tool angles by adding local flank angle modifications that provide better cutting action while still allowing very small operational cross axis angles. In this regard, minimizing or eliminating the cross axis angle of the tool eliminates interference points. Minimizing or eliminating the cross axis angle allows the tool to reach areas previously not possible.

[0019] Conventional gear skive tools are manufactured with a helix angle equal to the cross axis angle of the skive machine. This state-of-the-art technology is readily available commercially. Chip formation occurs when the cutter's cross axis angle swipes across the workpiece teeth, shearing away material. The cross axis angle generates this cutting action and is made possible by the cross axis action of the machine (gear cutter). The present disclosure moves the cross angle from the macro-level of the workpiece and machine axes to the micro-level, local to each tooth on the gear cutter itself. This allows the cutter to be held at a cross axis angle of nearly 0 degrees while still providing the cross axis necessary for chip formation by utilizing the local cross axis angle on each tooth of the cutter. As used herein, nearly 0 or substantially zero refers to angles between 1 and 6 degrees. The advantage of this is that the tool can approach interference locations on the workpiece that were previously impossible. In this regard, the present disclosure opens skive machining to more types of workpieces, shoulder workpieces, and applications where clearance is a challenge. Additionally, the present disclosure opens up the skiving process to machines that do not have cross axes between the workpiece and cutting tool axes. Machine tool costs can be significantly reduced by utilizing standard machine tools versus custom skiving machines.

[0020] Referring now to FIG. 4, a gear cutter or cutting tool constructed in accordance with one prior art example is shown and generally identified by reference numeral 208. The gear cutter 208 includes a plurality of teeth 232. Each tooth 232 defines a tooth flank 241 having a tooth flank angle 242 relative to a workpiece 212. A cross axis angle 250 is defined between a longitudinal rotation axis 252 of the gear cutter 208 and a transverse axis 254 (also referred to herein as the rotation axis of the workpiece 212) passing through the workpiece 212. The cross axis angle 250 of the gear cutter 208 creates a small clearance distance at a particular location 258 of the workpiece 212. The maximum cross axis angle depends on the workpiece geometry and clearance. As shown in FIG. 4, the tooth flank angle 242 is parallel to the face of the workpiece 212. The workpiece 212 is cut at 270 by the teeth 232. During cutting, both the gear cutter 208 and the workpiece 212 are rotating (the gear cutter 208 about its longitudinal cutting axis 282, and the workpiece 212 about its rotation axis 254), but at different revolutions per minute (RPM).

[0021] 5 and 6, a gear cutter tool constructed in accordance with one example of the present disclosure is shown and generally identified by reference numeral 308. The gear cutter 308 has a plurality of teeth 332. Each tooth 332 defines a tooth flank 341. Each tooth 332 has a cross-axis tooth angle 350 that is localized to each tooth 332, rather than the entire cutter 308. The cross-axis angle 350 is not zero and is defined as the angle between the tooth flank 341 and a line 352 that intersects the longitudinal axis (or axis of rotation) 354 of the gear cutter 308. The present disclosure demonstrates that by providing a tooth angle 350 between 1 and 15 degrees, the gear cutter tool 308 can be positioned at an improved angle (relative to the workpiece) to reach areas of the workpiece that were previously not possible.

[0022] By creating a local cross-axis tooth angle 350 at each tooth 332, the cross-axis tool angle 372 defined between the longitudinal axis 354 of the gear cutter 308 and the axis of rotation 374 of the workpiece 312 can be significantly reduced to near 0 degrees. Again, it has been shown that angles of 1 to 6 degrees can be used to achieve improved cutting success and tool reach. In this regard, the longitudinal axis 354 of the gear cutter 308 can be positioned in or near a parallel relationship with the axis of rotation 374 of the workpiece 312. Rather than having to tilt the entire gear cutter 308 (see prior art, FIG. 4), each tooth flank 341 has its own local cross-axis angle 350. Thus, skiving can be successfully performed up to the shoulder of the workpiece 312. Furthermore, the path of the cutting tool 308 can penetrate further into areas of the workpiece 312 previously limited by the part geometry. The workpiece 312 is cut at 370 (the internal spline of the workpiece, FIG. 5) by the teeth 332. During cutting, both the gear cutter 308 and the workpiece 312 are rotating (the gear cutter 308 about its longitudinal cutting axis 372 and the workpiece 312 about its rotation axis 374), but at different RPMs.

[0023] FIG. 7 shows a comparison of a prior art gear cutter 208 and workpiece 212 with a gear cutter 308 and workpiece 312 according to the present disclosure. It will be appreciated that in FIG. 7, the cross-axis tool angle 372 is more precisely depicted as being between 1 and 6 degrees (which is more difficult to see compared to the exaggerated depiction of the same angle in FIG. 5). Notably, additional clearance 380 is provided for the gear cutter 308 before it interferes with the workpiece 312. FIG. 8A is a cross-sectional view of a conventional gear 412. FIG. 8B shows the conventional gear cutter 408 shown at a 6-degree cross-axis angle, indicating interference at 434 with the workpiece 412 as the gear cutter 408 advances along the feed axis 438. As shown, the interference 434 between the gear cutter 408 and the workpiece 412 makes skiving impossible. FIG. 9A shows a cross-sectional view of a conventional gear 512. FIG. 9B is a cross-sectional view of a gear cutter 308 configured in accordance with the present disclosure, shown with a cross axis angle substantially close to 0 degrees as the gear cutter 308 advances along the feed axis 538, indicating that it does not interfere with the workpiece.

[0024] In conventional skiving machines, the machine must have the capability to provide a cross axis. In this regard, instead of simply a horizontal milling machine, the skiving machine must also provide the user with the capability to provide a 5-axis table or other tilt axis to achieve the desired cross axis. The present disclosure eliminates this requirement so that the end result can be achieved with much less expensive equipment that does not provide an additional adjustment axis.

[0025] The examples in the foregoing description are provided for purposes of illustration and explanation. They are not intended to be comprehensive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular example, but, where applicable, may be interchangeable and used in selected examples even if not specifically shown or described. The same may be modified in many ways. Such modifications should not be considered a departure from the present disclosure, and all such modifications are intended to be included within the scope of the present disclosure.

Claims

1. 1. A gear cutter tool for cutting internal teeth into a workpiece to form a gear, the gear cutter tool being configured to rotate about a longitudinal gear cutter axis of rotation and the workpiece being configured to rotate about a workpiece axis of rotation, the gear cutter tool comprising: a gear cutter having a plurality of cutting teeth, each cutting tooth of said plurality of cutting teeth having a tooth surface defining a cross axis tooth angle between said tooth surface and a line perpendicular to said longitudinal gear cutter axis of rotation, said cross axis tooth angle being between 1 and 15 degrees, and a cross axis tool angle of said gear cutter tool defined between said longitudinal gear cutter axis of rotation and said workpiece axis of rotation being between 1 and 4 degrees; A gear cutter tool comprising:

2. The gear cutter tool of claim 1 , wherein the cross-axis tool angle is 3 degrees.

3. The gear cutter tool of claim 1 , wherein the cross-axis tool angle is 2 degrees.

4. The gear cutter tool of claim 1 , wherein the cross-axis tool angle is 1 degree.

5. The gear cutter tool of claim 1 , wherein the longitudinal gear cutter axis of rotation is transverse to the workpiece.

6. The gear cutter tool of claim 1 , wherein the cross axis tooth angle is between 10 and 15 degrees.

7. The gear cutter tool according to claim 6, wherein the cross axis tooth angle is between 1 and 10 degrees.

8. 1. A method of cutting internal teeth into a workpiece to form a gear using a gear cutter tool, the method comprising: providing a gear cutter having a plurality of cutting teeth, each cutting tooth of said plurality of cutting teeth having a tooth surface defining a cross-axis tooth angle between said tooth surface and a line perpendicular to a longitudinal gear cutter rotation axis, said cross-axis tooth angle being between 1 and 15 degrees; Rotating the workpiece about a workpiece axis; rotating the gear cutter tool about a longitudinal gear cutter axis of rotation, the work axis and the longitudinal gear cutter axis of rotation defining a cross-axis tool angle therebetween; cutting the workpiece using the plurality of cutting teeth, wherein the cross-axis tool angle is between 1 and 4 degrees; A method comprising:

9. The method of claim 8 , wherein the cross-axis tool angle is 3 degrees.

10. The method of claim 8 , wherein the cross-axis tool angle is 2 degrees.

11. The method of claim 8 , wherein the cross-axis tool angle is 1 degree.

12. The method of claim 8, wherein the cross axis tooth angle is between 10 and 15 degrees.

13. The method of claim 8, wherein the cross axis tooth angle is between 1 and 10 degrees.

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