Patent Application
20140007638
The present disclosure relates generally to the forming of a part having an internal helical spline. More particularly, the present disclosure relates to the removal from a mandrel of a part that was formed on the mandrel and having at least one internal helical spline.
There if a long history and developed knowledge of the use of flow forming and related processing for making parts including, cylinders and forming cylinders having internal splines typically formed along the length of the cylinder and perpendicular to the base of the mandrel. Forming and processing to form a variety of such objects, including housings, has been developed and improved over the years.
In general, flow forming offers precision, economy, and flexibility over many other methods of metal forming. The flow forming process typically involves a cylindrical work piece referred to as a “pre-form” or “blank” which can be fitted over a mandrel. In flow forming, the mandrel is a tool on which the preform can be extruded to create an internal mirror shape of the external shape of this tool. In the machine tool, both the pre-form and the mandrel are fixtured and made to rotate while a forming tool applies compression forces to the outside diameter of the pre-form. Typically, the forming tool can include three equally spaced, hydraulically-driven, CNC-controlled rollers or formers. The rollers or formers are successively applied to the pre-form to make a pre-calculated amount of wall reduction during each pass of the roller over the pre-form to form the material toward the mandrel. The material of the preform is compressed above its yield strength, and is plastically deformed onto the mandrel. The desired geometry of the work piece is achieved when the outer diameter and the wall of the preform are decreased and the available material volume is forced to flow longitudinally over the mandrel.
The finished work piece, (i.e., final part) exhibits dimensionally accurate and consistent geometry on the inside of the final part. Subsequent operations can provide the final part a variety of dimensions as desired. The existing flow forming process works well with final parts designed to function as in a clutch housing application since the splines on the inside of the housing holds clutch packs that travel axially in the clutch housing to operate the clutch. Designs such as the clutch housing having straight splines allow for removal of the final part from the mandrel with relative ease since the axis of ejection is coincident to the direction of travel of the mandrel and mandrel adaptor. Generally, it is known to eject a final part including an axially-aligned, straight spline, from the mandrel using a stripper plate. The final part is ejected by moving the mandrel toward a stripper plate which an end of the final part engages while the mandrel continues to be withdrawn from the final part. However, such a process and design has been found to work very poorly when the mandrel is designed to form a axially-offset spline, such as a helical spline, on the pre-form. In these designs, it has been attempted to eject the final part including the helical spline using the same stripper plate and then rotating the mandrel, such as by rotating the main spindle during the stripping process. Such attempts to remove a final part including helical splines have not met with success.
In one failed attempt, part ejection was believed possible by considering the dimensional accuracy of the helical splines of the final part coupled with the traditional final part ejection technique (or system) as well as final part ejection using a rotation of the central ejector counter the direction to that of the main spindle rotation.
Alternatives do exist for making a final part having a helical spline. Such alternatives including processes using traditional broaching and hobbing methods which are multistep, expensive and time consuming processes. These broaching and hobbing techniques generally require a two-part pre-form that is first formed and machined and then the two parts are combined together or integrated into the final part, such as by welding. The current annulus gear vs. the proposed. One such part is generally known wherein the final part is produced using a two-piece construction. A helical ring is broached by a helical broach in each of the two pieces and then they are welded by a laser welder to a pre-machine piece. These generally known techniques were used to form splines in parts for a very long time and flow forming replaced these techniques for parts having straight, axially aligned splines. But the current use of these generally known techniques or systems for final parts having helical splines significantly increases the final and overall costs and inefficiency in creating such a final product. Accordingly, there has long been a need for a technique or system (apparatus and process) to reduce the costs and inefficiencies associated with the broaching and hobbing processes and for forming final parts having a helical spline where the costs and efficiencies are closer to those of using a flow forming technique.
In addition, despite many varied attempts, the flow forming process fails to protect the integrity of the final part and in particular, the dimensional integrity of the helical splines. The traditional broaching and hobbing techniques remain in use but are costly and inefficient. Accordingly, there long remains a significant need for a solution to providing an apparatus and process for stripping a final part having a helical spline from a mandrel while maintaining the integrity of the final part in all aspects.
The present invention is directed to a novel technique and apparatus of system (tool and process) for a flow formed final part including helical splines that can be automatically stripped from the tool while maintaining the integrity of the final part. The technique's essential concept outlines a flow forming process for forming a final part having splines where the equally spaced grooves form a generally helix shape about a central axis, typically defined by a central axis of a shaft of the part.
The sides of the helical splines can be parallel—where the sides of the equally spaced grooves of the spline are parallel in both directions (i.e., radial and axial)—or may be involute—where the sides of the equally spaced grooves of the spline are involute (or evolvent), for example, wherein a curve is obtained from another given curve by attaching an imaginary taut string to the given curve and tracing its free end as it is wound onto that given curve such as for an involute gear.
The helical splines of the final part have significant advantages such as being able to minimize stress concentrations for a stationary joint application under high load. Another benefit of the product is that helical splines can allow for rotary and linear motion between the parts. Helical splines can ultimately reduce damage and backlash of engaging components. Flow forming the helical splines allows building a final part having one-piece construction including flow formed helical splines.
This method proved to be cost effective and efficient because the current manufacturing process requires a broach method, which is more expensive then the new system and process which solely implements a flow forming technique for the one-piece, final part including a helical spline. The process in accordance with the present invention requires fewer steps including due to the lack of either the broaching and hobbing processes and by implementing flow forming. In addition, the one-piece design used in producing the product in accordance with the present invention significantly contributes to the overall efficiency in manufacturing.
Further, the present technique will work for obtaining a final product having a far greater variety of material properties. The present technique has been proven successful with many part designs and materials including relatively lower carbon metals (including, for example, SAE 1008, SAE 1010 SAE 1012) and have been developed and proven using progressively higher carbon steels (including, for example, SAE 1026, SAE 1030 SAE 1035). The present technique has been tested and proven successful for final part ejection from the flow forming tool (mandrel) while still maintaining dimensional accuracy and integrity of the helical splines of the final part.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
Referring to
A flow-forming machine, generally show at 10, is provided with a stripper plate 12 for removing the final part 4 having the helical splines therein from the mandrel 14 and a thrust bearing 16 is located between the stripper plate 12 and the final part 4 during stripping of the final part 4 from the mandrel 14 to allow relative motion between the stripper plate 12 and the final part 4 to successfully strip the final part 4 from the mandrel 14 without damage and while maintaining the integrity of the helical splines of the final part 4. An ejector driver 32 is axially moveable and rotatable (i.e., illustrative arrows in
To flow form the usable final part 4 having the helical splines therein, a plurality of rollers, generally shown at 18, engage the workpiece or pre-form 2 loaded on the mandrel 14. Most preferably, at least three rollers 18 are used. The workpiece 2 is loaded on the mandrel 14 in a generally known and standard form and is secured in place between the mandrel 14 and a tailstock assembly, generally shown at 20. The workpiece 2 is positioned using the inner diameter 22 of the central portion of the workpiece 2 as shown in
The tailstock assembly 20 and the plurality of rollers 18 are retractable. The tailstock assembly 20 provides support of a tailstock head 30 connected to the tailstock assembly 20. When not in a retracted position, the tailstock head 30 engages and secures the workpiece 2 in position on the mandrel 12 and the ejector driver head 24 (see
If the pre-form or workpiece 2 is to be rotated during forming, which is commonly the preferred approach to flow forming the pre-form, then the tailstock assembly 20 and the mandrel adaptor 28 are rotated in unison for simultaneously rotating the mandrel 14 and the pre-form 2. The plurality of rollers 18, flow forming rotatable pressure rollers 18, deform the pre-form 2 by using tremendous predetermined pressure to force the material against the mandrel 14, simultaneously axially lengthening and radially thinning the pre-form or work piece 2 toward the final part 4. The desired geometry of the workpiece is achieved when the outer diameter and the wall of the pre-form are decreased and the available material volume is forced to flow over the mandrel by one or more passes of the roller 18. (i.e., the final part 4) as best shown in
Once the final part 4 is completely flow formed on the mandrel 14, the rollers 18 are cleared and moved to a safe retracted position such that the rollers 18 are free of the final part 4, as best shown in
As should be appreciated, the tolerances of the tooling (i.e., mandrel 14) are transferred to the final part 4 during the flow forming process as is intended. However, since the final part 4 is intended to require very close tolerances, including for the helical splines, the final part 4 acquires a substantial interference fit with the mandrel 14 during the flow forming process and requires a relatively significant amount of force to remove the final part 4 from the mandrel 14. Since the helical splines match those of the mandrel 14, the interference fit is further complicated by the complicated geometry due to the helical splines. Typically, a force of approximately about 150 bar (2175 psi) is required to eject the final part 4 from the mandrel 14.
The stripper plate 12 is provided about the final part 4 and the mandrel adaptor (or spindle) 28 for creating a stop against which the final part 4 engages as the ejector driver 32 is moved or withdrawn to strip off or remove the final part 4 from the mandrel 14. Since there is a helical spline in the final part 4, the ejector driver 32 and the mandrel 14 are rotated in a direction opposite of the helical spline while the final part 4 engages the stripper plate 12 to “unthread” the final part 4 from the mandrel 14.
As shown in the Figures, the present process and system includes the thrust bearing 16 located proximal an opening 34 in the stripper plate 12. The thrust bearing 16 has a first side 36 coupled to the stripper plate 12 and a second side 38 for engaging a surface of the final part 4 during the stripping process, e.g., terminal end of the final part 4. The outer surface 40 of the second side 38 for engaging the final part 4 has a relatively roughened design for limiting and/or preventing relative movement between the second side 38 and the final part 4 during stripping of the final part 4 form the mandrel 14. The thrust bearing 16 allows the relative movement of the stripper plate 12 and the final part 4 during the stripping process which works to avoid and prevent certain movements of the final part 4 that cause damage to the helical splines. Further, it has been determined that the thrust bearing 16 may also be used.
The ejector driver 32 has a matching form feature 23 for engaging the inner diameter of the pre-form and final part to impart a rotational force in addition to axial force during removal. Because the stripper plate 12 is equipped with the thrust bearing 16 to allow the workpiece to rotate freely during the removal process from the mandrel 14, deformation of the spline or gear teeth is avoided. Damage is prevented because the helical splines of the final part 4 and the mandrel 14 completely control the relative movement and rotation of the two parts during the stripping process. Whereas, without the thrust bearing 16, the relative movement of the two pieces was attempted to be controlled by controlling the rotation of the mandrel 14 using the mandrel adaptor 28. It is contemplated that it is possible to strip a helically splined part without rotation of the ejector driver 32 and mandrel 14. Notwithstanding, with the thrust bearing 16 allowing relative movement of the stripper plate 12 and the final part 4 during the stripping process, it is now possible to rotate the mandrel 14 via the ejector driver 32 in either a clockwise or a counter-clockwise direction to strip the final part 4 with helical splines and the rotation of the ejector driver 32.
The sides of the helical splines 102 can be parallel—where the sides of the equally spaced grooves 104 of the spline are parallel in both directions (i.e., radial and axial)—or may be involute—where the sides of the equally spaced grooves 104 of the spline are involute (or evolvent), for example, wherein a curve is obtained from another given curve by attaching an imaginary taut string to the given curve and tracing its free end as it is wound onto that given curve such as for an involute gear.
The helical splines 102 of the final part 100 have significant advantages such as being able to minimize stress concentrations for a stationary joint application under high load. Another benefit of the product is that helical splines can allow for rotary and linear motion between the parts. Helical splines 102 can ultimately reduce damage and backlash of engaging components, and flow forming the helical splines 102 allows building a final part 100 having one-piece construction including flow formed helical splines 102.
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
The instant application claims priority to U.S. Provisional Patent Application Ser. No. 61/668,271, filed Jul. 5, 2012. The entire disclosure of the above application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61668271 | Jul 2012 | US |
