Polygonal rotor shaft with formed end cap

Abstract

A method of manufacturing a hollow polygonal shaft which is at least partially non-circular in cross-section includes a cold forming process where a cylindrical preform blank is inserted into a die cavity where a force is applied by a punch. The die cavity defines a polygonal cross-section transverse to a central axis that is at least partially non-circular and a circular end cap portion for a completed shaft. The punch includes an outer surface that defines an internal shape of the completed shaft.

Description

POLYGONAL ROTOR SHAFT WITH FORMED END CAPCROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Application Serial No. 63 / 655,149 filed on June 3, 2024.TECHNICAL FIELD

[0002] The present disclosure is directed toward a process of cold forming a polygonal rotor shaft with an integrally formed end cap.BACKGROUND

[0003] A shaft for use in automotive or machine applications is typically cylindrical and symmetric about a central axis. End caps may be attached the rotor shaft by welding or other attachment processes. Although less common, higher RPM applications may utilize a polygonal shaped shaft that includes non-circular portions. A polygonal shaped shaft includes a closed shape with flat portions at least an outer surface. A polygonal shaped shaft may provide increased torque transfer capacities, better stability, and simplify assembly.

[0004] Polygonal shafts are commonly formed utilizing radial forging techniques. Shafts are typically completed by attachment of end caps by a welding process. As demand for polygonal shaped shafts increases, improved manufacturing processes become more important and beneficial.SUMMARY

[0005] A method of manufacturing a hollow polygonal shaft which is at least partially non-circular in cross-section according to an exemplary embodiment of this disclosure includes, among other possible things the steps of inserting a cylindrical preform blank into a die cavity where the die cavity includes an inner wall that defines a polygonal cross-section transverse to a central axis that is at least partially non-circular and a circular end cap portion. The method further includes application of a force along the central axis against the cylindrical preform blank with a punch that forces material of the preform blank into a space between the inner walls of the die cavity and an outer surface of the punch to define a polygonal outer surface of the completed shaft.

[0006] In a further embodiment of the foregoing method, the end cap portion comprises a closed end of the completed polygonal shaft.

[0007] In a further embodiment of any of the foregoing methods, the end cap cross-section comprises at least two different cylindrical outer diameters.

[0008] In a further embodiment of any of the foregoing methods, the punch includes an outer surface configured to define an inner cross-sectional shape of the completed shaft, wherein the outer surface of the punch comprises a polygonal shape in cross-section that is at least partially non-circular for forming an inner profile of the completed shaft.

[0009] In a further embodiment of any of the foregoing methods, the punch includes an outer surface configured to define an inner cross-sectional shape of the completed shaft, wherein the outer surface of the punch comprises a cylindrical shape in cross-section for forming an inner profile of the completed shaft.

[0010] In a further embodiment of any of the foregoing methods, the cylindrical preform blank comprises a solid cylinder.

[0011] In a further embodiment of any of the foregoing methods, the cylindrical preform blank includes an outer diameter that is less than or equal to a maximum diameter superimposed within the polygonal cross-section within the die cavity.

[0012] In a further embodiment of any of the foregoing methods, the cylindrical preform blank comprises a hollow cylinder.

[0013] In a further embodiment of any of the foregoing methods, the preform blank further comprises an end portion with an opening.

[0014] In a further embodiment of any of the foregoing methods, the inner wall of the die cavity comprises at least two flat sides for defining at least two flat sides of the outer surface of the completed 1 shaft.

[0015] In a further embodiment of any of the foregoing methods, the inner wall of the die cavity comprises three flat sides for defining at least two flat sides of the outer surface of the completed polygonal shaft.

[0016] In a further embodiment of any of the foregoing methods, the applied force is between 200 and 300 tons and is applied along the central axis.

[0017] A cold forming assembly for forming a polygonal shaft with an integral end cap according to another exemplary embodiment of this disclosure includes, among otherpossible things, a die including a die cavity comprising an inner wall that defines a polygonal cross-section transverse to a central axis that is at least partially non-circular and a circular end cap portion, and a punch comprising an outer surface that defines an inner cross-sectional shape of a completed shaft, wherein the die and the punch are configured for operation in a press.

[0018] In a further embodiment of the foregoing cold forming assembly, the outer surface of the punch comprises a lead-in portion configured to force material of a preform blank radially outward into the inner wall of the die cavity in response to movement of the punch along the central axis.

[0019] In a further embodiment of any of the foregoing cold forming assemblies, the inner wall of the die cavity comprises at least two flat sides for defining at least two flat sides of the outer surface of the completed polygonal shaft.

[0020] In a further embodiment of any of the foregoing cold forming assemblies, the outer shape of the punch comprises a polygonal shape in cross-section to form a polygonal inner cross-sectional shape of the completed polygonal shaft.

[0021] In a further embodiment of any of the foregoing cold forming assemblies, the outer shape comprises a cylindrical shape in cross-section to form a circular inner cross- sectional shape of the completed polygonal shaft.

[0022] A polygonal shaft assembly according to another exemplary embodiment of this disclosure includes, among other possible things, a first part comprising a shaft portion and an end portion disposed along a central axis, the shaft portion including a polygonal shaped outer surface in cross-section transverse to the central axis and the end cap portion having a cylindrical cross-section.

[0023] In a further embodiment of the foregoing shaft assembly, a wall thickness between the polygonal outer surface and an inner surface varies circumferentially about the central axis.

[0024] In a further embodiment of any of the foregoing shaft assemblies, both the polygonal shaped inner surface and the polygonal shaped outer surface comprise at least two flat sides.

[0025] Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particularcombinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples.

[0026] These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a side view of an example polygonal shaft assembly.

[0028] Figure 2 is a perspective view of a portion of the example polygonal shaft assembly.

[0029] Figure 3 is a side view of a portion of the polygonal shaft assembly including a polygonal shaft portion with an integral end cap portion.

[0030] Figure 4 is a cross-section of a portion of an example the polygonal shaft embodiment.

[0031] Figure 5 is a cross-section of a portion of another example polygonal shaft embodiment.

[0032] Figure 6 is a schematic cross-sectional view of an example die and punch embodiment for forming a polygonal shaft.

[0033] Figure 7 is a schematic cross-sectional view of another example die and punch embodiment for forming a polygonal shaft.

[0034] Figure 8 is side view of an example preform blank.

[0035] Figure 9 is a top view of the example preform blank.

[0036] Figure 10 is a cross-sectional view of an example die cavity along a central axis.

[0037] Figure 11 is a cross-sectional view of the example die cavity transverse to the central axis.

[0038] Figure 12 is a cross-sectional view of the example die cavity transvers to the central axis within a portion for forming an end cap.

[0039] Figure 13 is a cross-sectional view of the preform blank placed within the die cavity prior to processing.

[0040] Figure 14 is a cross-sectional view of a punch at an initial position of an example cold working process.

[0041] Figure 15 is a cross-sectional view of a punch at an intermediate position of an example cold working process.

[0042] Figure 16 is a cross-sectional view of a punch at final position of an example cold working process.

[0043] Figure 17 is a side view of example hollow preform blank embodiment.

[0044] Figure 18 is a top view of the example hollow preform blank embodiment.

[0045] Figure 19 is a cross-sectional view of a punch at an initial position of an example cold working process.

[0046] Figure 20 is a cross-sectional view of a punch at an intermediate position of an example cold working process.

[0047] Figure 21 is a cross-sectional view of a punch at final position of an example cold working process.DETAILED DESCRIPTION

[0048] Referring to Figures 1, 2 and 3, an example shaft assembly 20 is schematically shown and includes a first part 22 with a polygonal shaft portion 24 and end portion 26. The shaft portion 24 and the end portion 26 are formed in a single cold forming process as a one piece integral part.

[0049] An end cap 28 is attached to an end 34 distal from the end portion 26 to provide a completed shaft assembly 20. The end cap 28 may be attached by a weld 36 to the first part 22. The weld 36 may be provided utilizing known welding processes appropriate for the materials and processing.

[0050] The term “polygonal” as used throughout this disclosure is used to refer to a closed shape having flat portions and curved portions in cross-section. The example shaft portion 24 includes a polygonal shape and the end portion 26 includes a circular cross-section without any flat portions. Accordingly, the example shaft portion 24 is shaped such that it is not entirely circular in cross-section. In one disclosed example, the shaft portion 24 includes an outer surface 30 with flat portions 32 between rounded portions 35. The example shaft portion 24 is generally triangularly shaped and includes three flat portions 32. Although a triangular shaped shaft is shown by way of example, other shapes, number, and arrangementsof flat portions 32 could be utilized and remain with the scope and contemplation of this disclosure.

[0051] Referring to Figure 4, with continued reference to Figures 1-3, the shaft portion 24 includes a hollow interior space 38 bounded by an inner surface 46. The inner surface 46 of the example shaft portion 24 shown in Figure 4 is formed to have a polygonal shape that corresponds with the shape of the outer surface. In this example, the inner shape is polygonal with flat portions 37 that correspond with the flat portions 32 of the outer surface 30. The example embodiment shown in Figure 4 has an inner shape with three flat portions 37 between curved portions 39 in locations that correspond with the features of the outer shaft shape. However, other shapes and numbers of flat portions may also be utilized.

[0052] The interior surface 46 is part of a wall 40 that may have a uniform or variable thickness. In the example embodiment shown in Figure 4, the wall 40 includes a substantially uniform wall thickness about the central axis. A first wall thickness 42 is substantially the same as a second wall thickness 44 at a different peripheral location. The first wall thickness 42 and the second wall thickness 44 are the same within known and understood manufacturing tolerances for a cold forming process. Such tolerances are dependent on material, process parameters and other known process dependent parameters and factors.

[0053] Referring to Figure 5 with continued reference to Figures 1-3, another example cross-section embodiment is shown and includes a circular hollow interior space 38’ bounded by an interior surface 46’. The interior surface 46’ is part of a wall 40’ with a thickness that varies about the central axis A. In one example embodiment, a first wall thickness 42’ is greater than a second wall thickness 44’. The first wall thickness 42’ corresponds with the rounded portion 35 of the outer shape. The second wall thickness 44’ corresponds with one flat portions 32 of the outer shape.

[0054] The disclosed example shaft portion embodiments are formed with a cold forming process where a cylindrical preform blank is inserted into a die cavity that defines an outer shape of a completed shaft. A punch applies force on the preform blank along a central axis to cause material to flow into a space against the inner wall of the die cavity. The outer surfaces of the completed shaft are therefore formed by the inner wall of the die cavity and the inner features of the shaft are formed by an outer surface of the punch.

[0055] Referring to Figure 6, the die 54 includes the die cavity 56 and a punch 64 includes an outer surface 66. Material from the preform die blank is forced into a space 74 defined between the die cavity 56 and the outer surface 66 of the punch 64. The space 74 is sized and shaped to provide the final cold formed shape of the shaft and end portion. In the example shown in Figure 6, the inner and outer shape are the same polygonal shape with a substantially uniform wall thickness.

[0056] Referring to Figure 7, in another example embodiment, a die 54’ includes a die cavity 56’ and punch 64’ with an outer surface 66’. The example punch 64’ includes an outer surface 66’ and a circular cross-sectional shape. Material forced into the space 74’ provides a non-uniform wall thickness about the central axis. The space 74’ is sized and shaped to provide the final formed shape of the shaft and end portion. In this example, the wall thickness is greater in the curved portions and thinner in the flat portions of the polygonal outer shape.

[0057] Referring to Figures 8 and 9, an example preform blank 48 is schematically shown and includes a height 52 and a diameter 50. The example preform blank 48 is solid cylindrical part. The preform blank 48 may be formed as a hot forging, cold formed, or press formed from bar stock. The preform blank 48 may also be cut from a bar stock. It should be appreciated that the preform blank may be formed utilizing other processes and remain within the contemplation and scope of this disclosure.

[0058] The material may be treated in an annealing process to improve ductility and reduce hardness to make the material more workable. The specific process is dependent on the specific material utilized for the preform blank 48. The height 52 and diameter 50 are dependent on the desired size and shape of the completed shaft.

[0059] Referring to Figures 10, 11 and 12 with continued reference to Figures 8 and 9, a die 54 and die cavity 56 are schematically shown. Figure 11 is a cross-section of a non-circular portion of the die cavity 56. Figure 12 is a cross-section through a portion of the die cavity 56 that defines the outer shape of the cylindrical end portion. Inner wall 62 of the die cavity 56 within the end portion is circular and stepped to provide the desired outer shape of the end portion in a completed shaft portion 22 (Figure 1). The end portion may have other sizes and configurations other than the stepped configuration shown. The inner wall 58 of theexample die cavity 56 includes flat portions 60 that form the flats 30 in the completed shaft portion 22.

[0060] The outer diameter 50 of the preform blank 48 is sized to fit within a circle superimposed within the die cavity 56 as is schematically shown by the dashed lines in Figure 11. As is shown in Figure 11, the diameter 50 of the preform blank 48 is sized to fit within the non-circular portion of the die cavity 56. The example diameter 50 is larger than any diameter of the end portion.

[0061] Referring to Figure 13, an initial step of forming the shaft portion 22 includes inserting the preform blank 48 into the die cavity 56. The example preform blank 48 seats atop the walls 62 that form the end portion.

[0062] Referring to Figures 14, 15, and 16 with continued reference to Figure 13, the die 54 is supported in a press (not shown) that moves a punch 64 into the die cavity 56 and against the preform blank 48. The punch 64 includes an outer surface 66 that has a shape that defines the inner cross-sectional shape of a completed shaft portion 22. The outer surface 66 includes a shaft portion 68 and a lead-in portion 70. The shaft portion 68 includes a shape that will define the inner shape of a completed shaft portion 22. The lead-in portion 70 includes a ramped surface that provides for moving material of the preform blank 48 outward into contact with the inner wall 58 of the die cavity 56 in response to the application of force.

[0063] A cold forming process according to a disclosed example embodiment includes the initial step of inserting the cylindrical preform blank 48 within the die cavity 56 as is shown in Figure 13. The punch 64 is brought into contact with the preform blank 48 under force within a press. The amount of force utilized is determined based on various process factors that include, among other things, material composition, completed shaft size and shape. In one example embodiment, a press capable of applying a force to the preform blank 48 of between 200 and 400 tons may be utilized. Other size and capacity of the press may be utilized depending on specific shaft configuration. The punch 64 is advanced along a central axis A against and into the preform blank 48. Initially, the lead-in portion 70 engages the preform blank 48 and begins moving material radially outward while also forcing the preform blank 48 downward into the die 54.

[0064] Figure 15 illustrates an intermediate position where the punch 64 has forced the preform blank 48 into the end portion of the die cavity 56. A portion of thepreform blank 48 has begun forming a wall 72 by flowing into a space 74 between the punch 64 and the die cavity 56. The lead-in portion 70 continues into the preform blank 48 to further push material downward and radially outward.

[0065] Figure 16 illustrates a final position where the punch 64 has moved along the central axis to complete the entire stroke and the wall 72 has extended further upward within the space 74 and material has filled the end portion of the die cavity 56 as indicated at 76. The cold forming process is complete once the punch 64 has completely pushed the preform blank 48 into the die cavity 56 and filled the space 76 between the outer surface 66 of the punch 64 and the wall 58 of the die cavity 56.

[0066] The punch 64 is subsequently retracted and the formed part removed. Potions of the completed part may remain as formed and require no additional processing. Other portions may require some secondary operations. For example, the wall of the open end of the completed part may be machined to provide a uniform surface for attachment of another end cap.

[0067] Referring to Figures 17 and 18, a hollow preform blank 80 is shown and includes a partially formed end portion 84 at an end of a hollow shaft portion 82. The shaft portion 82 includes a circular hollow inner space 96. The inner space 96 is bounded by a walls having a thickness 94. A circular end hole 92 extends through the end portion 84. The example preform blank 80 is of a total height 86. The end portion 84 includes an end length 88. The dimensions of the preform blank 80 provide material in locations to enable formation in the cold forming process.

[0068] Referring to Figure 19, an example cold forming process embodiment begins with a punch 102 entering the hollow inner space 96 of the preform blank 80 to force it into a die cavity 100 of a die 98. The example preform blank 80, punch 102 and die cavity 100 are shown in a cut-away view to illustrate how the punch 102 seats within the preform blank 80. The example punch 102 includes forward end 106 that seats within the preform blank 80 and is shaped to conform to the inner size and shape of the inner space 96 of the preform blank 80. The outer diameter 90 (Figure 18) is larger than the die cavity 100 and therefore the die 98 includes a chamfered lead-in portion 114. The lead-in portion 114 aids in the initial alignment and entry of the preform blank 80 into the die cavity 100.

[0069] Figure 20 shows an intermediate position of the punch 102 and preform blank 80 within the die cavity 100. The punch 102 includes the outer surface 104 that forms internal shape of the completed part. The space between the die cavity 100 and the punch 102 is smaller than the original wall thickness 94 of the preform blank 80. Accordingly, as the preform blank 80 is pushed into the die cavity 100, the preform blank’s original wall thickness is thinned and lengthened. In Figure 20, the wall thickness 94 of the preform blank 80 still outside of the die cavity 100 as indicated at 108 is thicker than the formed wall thickness within the die cavity 100 as shown at 110.

[0070] Referring to Figure 21, movement of the punch 102 into the die cavity 100 proceeds until the end portion is fully formed by reaching the bottom of the die cavity 100 as shown at 112. The wall 110 is completed and thinned as compared to the original wall thickness of the preform blank 80. The punch 102 and completed shaft removed from the die 98 to provide a completed shaft portion with an integral end cap. In this example embodiment, the integral end portion 112 includes the hole 92. Once the part is removed, most of the end shape is a final formed condition with only minimal secondary processing and machining necessary. In one example embodiment, the only secondary processing required is to machine surfaces at an open end to facilitate welding of second end cap to complete both ends of the shaft.

[0071] Accordingly, polygonal shafts of this disclosure are formed substantially complete with an integral end cap having a shape different than the shaft portion. In disclosed example embodiments, the end cap is round and the shaft portion is a polygonal shape with non-circular portions. The example disclosed cold working process provides for the formation of a polygonal shaft with a cylindrical end cap that has improved mechanical strength properties in an as formed condition.

[0072] Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the scope and content of this disclosure.

Claims

CLAIMSWhat is claimed is:

1. A method of manufacturing a hollow polygonal shaft which is at least partially noncircular in cross-section comprising the steps of: inserting a cylindrical preform blank into a die cavity, wherein the die cavity comprises an inner wall that defines a polygonal cross-section transverse to a central axis that is at least partially non-circular and a circular end cap portion; and applying a force along the central axis against the cylindrical preform blank with a punch, wherein the application of force moves material of the preform blank into a space between the inner walls of the die cavity and an outer surface of the punch to define a polygonal outer surface of the completed shaft.

2. The method of manufacturing as recited in claim 1, wherein the end cap portion comprises a closed end of the completed polygonal shaft.

3. The method of manufacturing as recited in claim 2, wherein the end cap cross-section comprises at least two different cylindrical outer diameters.

4. The method of manufacturing as recited in claim 1, wherein the punch includes an outer surface configured to define an inner cross-sectional shape of the completed shaft, wherein the outer surface of the punch comprises a polygonal shape in cross-section that is at least partially non-circular for forming an inner profile of the completed shaft.

5. The method of manufacturing as recited in claim 1, wherein the punch includes an outer surface configured to define an inner cross-sectional shape of the completed shaft, wherein the outer surface of the punch comprises a cylindrical shape in cross-section for forming an inner profile of the completed shaft.

6. The method of manufacturing as recited in claim 1, wherein the cylindrical preform blank comprises a solid cylinder.

7. The method of manufacturing as recited in claim 6, wherein the cylindrical preform blank includes an outer diameter that is less than or equal to a maximum diameter superimposed within the polygonal cross-section within the die cavity.

8. The method of manufacturing as recited in claim 1, wherein the cylindrical preform blank comprises a hollow cylinder.

9. The method as recited in claim 8, wherein the preform blank further comprises an end portion with an opening.

10. The method as recited in claim 1, wherein the inner wall of the die cavity comprises at least two flat sides for defining at least two flat sides of the outer surface of the completed 1 shaft.

11. The method as recited in claim 1, wherein the inner wall of the die cavity comprises three flat sides for defining at least two flat sides of the outer surface of the completed polygonal shaft.

12. The method as recited in claim 1, wherein the applied force is between 200 and 300 tons and is applied along the central axis.

13. A cold forming assembly for forming a polygonal shaft with an integral end cap, the fold forming assembly comprising: a die including a die cavity comprising an inner wall that defines a polygonal crosssection transverse to a central axis that is at least partially non-circular and a circular end cap portion; and a punch comprising an outer surface that defines an inner cross-sectional shape of a completed shaft, wherein the die and the punch are configured for operation in a press.

14. The cold forming assembly as recited in claim 13, wherein the outer surface of the punch comprises a lead-in portion configured to force material of a preform blank radially outward into the inner wall of the die cavity in response to movement of the punch along the central axis.

15. The cold forming assembly as recited in claim 14, wherein the inner wall of the die cavity comprises at least two flat sides for defining at least two flat sides of the outer surface of the completed polygonal shaft.

16. The cold forming assembly as recited in claim 15, wherein the outer shape of the punch comprises a polygonal shape in cross-section to form a polygonal inner cross-sectional shape of the completed polygonal shaft.

17. The cold forming assembly as recited in claim 15, wherein the outer shape comprises a cylindrical shape in cross-section to form a circular inner cross-sectional shape of the completed polygonal shaft.

18. A polygonal shaft assembly comprising: a first part comprising a shaft portion and an end portion disposed along a central axis, the shaft portion including a polygonal shaped outer surface in cross-section transverse to the central axis and the end cap portion having a cylindrical cross-section.

19. The polygonal shaft assembly as recited in claim 18, where a wall thickness between the polygonal outer surface and an inner surface varies circumferentially about the central axis.

20. The polygonal shaft assembly as recited in claim 19, wherein both the polygonal shaped inner surface and the polygonal shaped outer surface comprise at least two flat sides.

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