WO2007092775A2

WO2007092775A2 - Self-centering broach

Info

Publication number: WO2007092775A2
Application number: PCT/US2007/061547
Authority: WO
Inventors: Richard Van Werden
Original assignee: Wright Coating Company
Priority date: 2006-02-02
Filing date: 2007-02-02
Publication date: 2007-08-16
Also published as: WO2007092775A3

Abstract

A self centering broach for broaching a profile on a coated workpiece comprises a centering portion and a cutting portion. The centering portion comprises multiple segments of indexing teeth that align the broach with the workpiece. The cutting position comprises multiple segments of cutting teeth that cut a profile into the coating on the workpiece. The workpiece can be a female splined shaft having a low friction coating.

Description

SELF-CENTERING BROACH

BACKGROUND OF THE INVENTION CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. utility application Serial No. 60/743,213, filed February 2, 2006, which is incorporated herein in its entirety.

Field of the Invention

This invention relates generally to a broach for shaping a coating on an internally splined workpiece.

Description of the Related Art

Slip joint assemblies are commonly used in drive line systems to transmit torque between components of the system. A slip joint assembly generally includes two slidably connected tubular members, a male splined shaft and a female splined shaft. The male splined shaft has a number of splines positioned around the exterior of the shaft that extend radially outwardly from the shaft. These splines mesh with splines on an internal bore of the female shaft such that the male shaft is received by the female shaft in a telescoping manner. The intermeshing splines provide a non-rotatable connection and allow torque to be applied from one shaft to the other. For a non-rotatable connection, the splines on the male splined shaft must complement the splines on the female splined shaft within a small dimensional tolerance. However, the shafts must still be able to slide relative to one another.

Low friction coatings are often applied to one or both of the male and female splined shafts to facilitate sliding between the shafts. This coating must be taken into account when determining the dimensions of the shafts to ensure a complementary fit between the splines of the shafts within an acceptable small dimensional tolerance. Many coating methods do not produce the dimensional tolerance needed for slip joints. Consequently, additional shaping or machining processes are necessary to produce the desired dimensional tolerance.

Broaching is one such process that can be used to shape the internal coating of a female splined shaft. A broach typically comprises an elongated member with surface features such as teeth that shape the internal bore of a hollow shaft as the broach is pulled or pushed through the internal bore. But using a broach to shape a thin coating in a splined bore with a very narrow range of acceptable tolerances requires considerable accuracy in keeping the broach centered in the bore. If the center axis of the broach is not coincident with the center axis of the female splined shaft, the resulting coating on the internal bore will not have a uniform thickness, and more than likely, will be outside of acceptable tolerances. The results can include a premature failure of the coating. A broach is needed that will consistently produce a shaped coating on an internal bore with uniform thickness.

SUMMARY OF THE INVENTION

A self-centering broach for broaching a coating profile on a coated workpiece comprises a centering portion and a cutting portion. The centering portion comprises at least two segments of centering teeth that align the broach with the workpiece. The cutting portion comprises multiple segments of cutting teeth that cut a profile into the coating on the workpiece. If the workpiece is provided with keyway, a guide key can be provided on the broach to align with the keyway.

According to one aspect of the invention, three indexing teeth are provided on each segment of the centering portion, positioned to align with corresponding centering splines on the work piece. The indexing teeth on each segment progressively increase in height away from a front shank on the broach. The height of centering teeth on the last segment is at a maximum so that the indexing teeth will substantially remove the coating within the centering splines on the workpiece. Preferably, at least two separated segments of indexing teeth at maximum height are provided in order to ensure more accurate centering.

According to another aspect of the invention, multiple cutting teeth corresponding to internal splines on the workpiece are provided on each segment of the cutting portion. The cutting teeth on each segment progressively increase in height along the broaching direction. The height of cutting teeth on the last segment is such that the cutting teeth will remove the coating on the workpiece to a predetermined thickness.

According to yet another aspect of the invention, a method is provided for broaching a splined shaft having a low friction coating, using a broach heretofore described. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 is a schematic illustration of a workpiece comprising a female splined shaft for broaching according to the present invention.

Fig. 2 is a cross-sectional view taken along line 2-2 of Fig. 1.

Fig. 3 is an enlarged view of section 3 of Fig. 2.

Fig. 4 is a schematic illustration of a broach according to the present invention.

Fig. 5 is a cross-sectional view taken along line 5-5 of Fig. 4.

Fig. 6 is a cross-sectional view taken along line 6-6 of Fig. 4.

Fig. 7 is a schematic illustration of centering teeth on the broach from Fig. 4.

Fig. 8 is a schematic illustration of a second embodiment of a broach according to the present invention.

Fig. 9 is a cross-sectional view taken along line 9-9 of Fig. 8. Fig. 10 is a cross-sectional view taken along line 10-10 of Fig. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, and in particular to Figs. 1 and 2, a workpiece to be acted on according to the present invention comprises a female splined shaft 10 having an internal bore 12 at one end that is adapted to receive a male splined shaft (not shown) to form a conventional slip joint. An extension 14 on the female splined shaft provides a yoke for connection to a universal joint (not shown), as is well known in the art. A plurality of female splines 16 is provided circumferentially around the inside of the bore 12 and extends the length of the bore. The female splines 16 are adapted to mesh with male splines on the male shaft. This embodiment, a keyway 18 is further positioned on the inside of the bore 12 and extends the length of the bore. Three of the splines 16 are designated as centering splines 16a, which will be explained below. The female splined shaft 10 is preferably made of metal. Referring to Fig. 3, a coating 20 is applied to the surface of the internal bore, including the female splines 16 and the keyway 18, using any suitable method. The coating 20 can be a low friction coating which facilitates sliding movement between the splines of the male and female splined shafts. A suitable material will include, for example, nylon. The coating 20 is typically applied to ensure that the internal bore 12 is completely covered, but the coating is generally not uniform in thickness, and normally not within acceptable tolerances. In most cases, the coating thickness is uniformly greater than the tolerances required between the male and female splined shafts. To remove the necessary material and leave a reduced friction surface within acceptable tolerances, a broach and broaching process according to the invention is provided.

Referring to Fig. 4, a self-centering broach 22 according to the present invention is used to shape the coating 20 to the desired tolerance. In this embodiment, the broach 22 comprises a front shank 24, a guide key 26, centering portion 28, a cutting portion 30, a trailing portion 31, and a rear shank 32. The front and rear shanks 24, 32 are alternately enagaged by a broaching machine during a broaching operation, in which the broach 22 is pulled and/or pushed through the female splined shaft 10 in a broaching direction defined by the arrow. The guide key 26 is adapted to fit within the keyway 18 of the female splined shaft 10 to initially position the broach 22 so that the broach 22 is generally in proper alignment about its longitudinal axis relative to the internal bore 12. In this way, splines on the centering portion 28, the cutting portion 30, and the trailing portion 31 align with the female splines 16.

Referring additionally to Fig. 5, the centering portion 28 comprises a plurality of centering tooth segments 34, each separated from another by a relief section 35. Each centering tooth segment 34 comprises at least three indexing teeth 36 that are spaced equidistantly from each about the circumference of the centering tooth segment 34. The number of indexing teeth 36 on each tooth segment 34 is equivalent to the number of female centering splines 16a that may be on the workpiece, but preferably no less than three. The number of centering tooth segments 34 in this embodiment is four, although it is within the scope of the invention to have any number of centering tooth segments more than one. The centering teeth are thus adapted to align with the female centering splines 16a. Referring to Fig. 7, the indexing teeth 36 on the first three centering tooth segments 34 have heights hi, h.₂, and hs, respectively. The heights hi, h2, and hi progressively increase in successive tooth segments 34 from the front shank 24, such that each centering tooth segment 34 will remove more of the coating 20 in the female centering splines 16a as the broach is urged through the female splined shaft 10. The third and fourth tooth segments 34 preferably have the same height h$ and are dimensioned such that the indexing teeth 36 will remove the coating 20 in the female centering splines 16a down to the base metal of the female splined shaft 10, but will not cut into the base metal or change the profile of the of the female centering splines 16a. At this point, the broach will be centered within the internal bore and ready to shape the other splines 16. Preferably, at least two centering tooth segments 34 will be dimensioned to remove the coating 20 down to the base metal of the female splined shaft 10 in order to minimize pitching, i.e., movement of the broach 22 about an axis perpendicular to the longitudinal axis of the female splined shaft 10. In other words, the height h.₃ will be equal on two of the centering tooth segments 34.

The cutting portion 30 comprises a plurality of cutting tooth segments 38, where each cutting tooth segment 38 comprises a number of cutting teeth 40 spaced equidistantly about the circumference of the cutting tooth segment 38. The number of cutting tooth segments 38 in this embodiment is sixteen grouped into four groups, each group separated by a relief section 41 of narrower diameter, although it is within the scope of the invention to have any number of cutting tooth segments 38. The number of cutting teeth 40 corresponds to the number of splines 16 on the female splined shaft 10 of the workpiece, and each cutting tooth 40 further has a shape and placement corresponding to a respective spline 16. Like the indexing teeth 36, the cutting teeth 40 have a profile similar to that illustrated in Fig. 7, and progressively increase in height h_x away from the front shank 24, such that the cutting teeth 40 will successively remove more of the coating 20. Preferably, the cutting teeth 40 on the last four cutting tooth segments 38 to advance have the same height and are dimensioned such that the cutting teeth 40 will remove the coating 20 to the final desired thickness and within the required tolerance for the female splined shaft 10. Notably, the tolerance height h_t will be less than the height h.₃ of the indexing teeth 36.

If the length of the workpiece or the length of the broach is such that insufficient stability against pitching is provided by the two adjacent centering tooth segments 34 with tooth height A₃, then one or more additional centering tooth segments with tooth height /2₃ can be inserted between or among the cutting tooth segments. For example, centering tooth segments 34 can be provided in a form to clamp onto the relief sections 41.

The trailing portion 31 can have at least one centering segment 42 having the same cross section as the centering tooth segments 34, i.e., having at least three indexing teeth (not shown) of height h.3, dimensioned and located to correspondent to the female centering splines 16a in the workpiece. The trailing portion 31 will thus assist in keeping the broach 22 centered and inhibit pitching of the broach during a broaching operation.

In operation, the front shank 24 is held by a puller (not shown) of a broaching machine, which pulls the broach 22 through the internal bore 12 of the female splined shaft 10 in the broaching direction, thereby broaching a desired coating profile. Initially, the guide key 26 is aligned with the key way 18 to generally position the broach 22 relative to the internal bore 12. As the broach 22 is advanced, the first centering tooth segment 34 begins to remove the coating 20 from the centering splines 16a. The next two centering teeth segments 34 remove more coating 20 from the centering splines 16a until the coating 20 is removed completely from the centering splines 16a, and the last centering segment stabilizes the broach 22 against pitching. After the centering portion 28 has passed, the broach 22 is fully aligned with the female splined shaft 10. As the broach 22 is further advanced, the first cutting teeth segments 38 begin to remove the coating 20 from the non-centering splines 16. More of the coating 20 is removed as the more of the cutting tooth segments 38 are advanced through the internal bore 12. The last four cutting tooth segments remove the coating 20 to the final desired thickness. After the broaching operation, the broach 22 is completely pulled through the female splined shaft 10, or alternatively, the rear shank 32 can be seized by a rear shank holder (not shown) to return the broach 22 to its initial position before the broaching operation. The trailing portion 31 provides additional stabilization of the broach 22 against pitching.

Fig. 8 illustrates another embodiment of a broach 122 according to the invention having essentially the same elements of the broach 22 of the first embodiment, with a slightly different arrangement. Here, the broach 122 has a front shank 124, a guide key 26 and six centering segments 134 in a centering portion 128. Each centering segment 134 has indexing teeth identical to those of the first embodiment and as shown in Fig. 7. Here, however, the height of the indexing teeth 136 on the final three centering tooth segments 134 away from the front shank 124 is the same. As well, instead of separate groupings, cutting teeth segments 138 are successively disposed, each having cutting teeth 140 with increasing heights h_x, and the last three segments having cutting teeth with the tolerance height h_t.

While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit. For example, a workpiece may not necessarily have a keyway. In such case, a guide key is not necessary on the broach and it is enough to have at least two centering tooth segments with indexing teeth of height A₅, spaced far enough apart to effectively inhibit pitching of the broach within a splined shaft during a broaching operation.

Claims

CLAIMSWhat is claimed is:

1. A self-centering broach (22, 122) for broaching a coating profile on a coated workpiece comprising a splined shaft (10) with a keyway (18) and splines (16), at least three of which are designated to be centering splines (16a), characterized by

a front shank (24, 124),

a centering portion (28, 128) having at least two segments (34, 134) of three spaced indexing teeth (36, 136) that are adapted to align with the centering splines (16a), and

a cutting portion (30, 130) having multiple segments (38, 138) of cutting teeth (40, 140) positioned to align with the splines,

whereby when the broach (22, 122) is urged through the splined shaft (10), it will be automatically centered and it will broach a coating profile on the coated workpiece to a predetermined tolerance.

2. The self-centering broach of claim 1 further comprising a trailing portion (31, 131) having at least two centering segments (42, 142) adapted to stabilize the broach (22, 122) within a splined shaft (10).

3. The self-centering broach of claims 1 or 2 further comprising relief portions (35, 135) between the centering segments (42, 142).

4. The self-centering broach of any of claims 1-3 characterized by the centering portion having four segments.

5. The self-centering broach of any of claims 1-4 wherein the indexing teeth (36, 136) on two adjacent centering segments furthest from the front shank (24) have the same tooth height, dimensioned to remove substantially all coating at the base of the centering splines (16a).

6. The self-centering broach of any of claims 1-5 wherein at least some indexing teeth (36, 136) increase in height the further they are from the front shank (24).

7. The self-centering broach of any of claims 1-6 wherein at least some cutting teeth (40, 140) increase in height the further they are from the front shank (24).

8. The self-centering broach of any of claims 1-7 wherein the cutting teeth (40, 140) on two adjacent cutting segments (38, 138) furthest from the front shank (24) have the same tooth height, dimensioned to remove coating to a predetermined tolerance.

9. The self-centering broach of any of claims 1-8 further characterized by a guide key (26) adapted to mate with a keyway (18) in the workpiece.

10. A method of broaching a coating profile on a coated workpiece comprising a splined shaft (10) with splines (16), at least three of which are designated to be centering splines (16a), characterized by the steps of:

providing a broach (22, 122) according to any of claims 1-8; and

urging the broach (22, 122) through the splined shaft (10).

11. The method of claim 10 wherein if the workpiece has a keyway (18), the method is further characterized by the step of

aligning a guide key (26, 126) on the broach with the keyway (18).