Tool and method for finishing an outside diameter surface of a cylindrical workpiece

Abstract

A tool for finishing an outside diameter surface of a cylindrical workpiece. The tool includes a rotatable substantially cylindrical member having an inner work-engaging surface adapted for finishing the O.D. surface of the cylindrical workpiece. The inner work-engaging surface includes abrasive particles thereon and defines a bore to receive the workpiece. The substantially cylindrical member includes at least one longitudinal split permitting radial expansion and contraction of at least part of the cylindrical portion for workpiece O.D. finish adjustment. The tool includes a rotable shaft, a plurality of spring loaded work-engaging elements adapted for finishing the O.D. surface of the workpiece. The work engaging elements have abrasive inserts. The plateaued O.D. surface has peaks that are 3-10 times smaller than the valleys.

Description

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a tool for finishing and/or plateauing an outside diameter surface of a cylindrical workpiece by means of a size-adjustable cylindrical bore having abrasive particles for finishing the workpiece, a method of plateauing an O.D. surface and a workpiece with a plateaued O.D. surface.

[0004] 2. Background Art

[0005] There is considerable prior art relating to the honing, deburring, lapping, finishing, and superfinishing of bores by means of various tooling structures. However, there is no known prior art which addresses problems associated with the accurate finishing of an outside diameter (O.D.) surface of a cylindrical workpiece for close tolerancing. For example, a pulley hub for a timing belt may require close tolerancing on its O.D. surface, and may require accurate concentricity of the O.D. surface with respect to the central axis of the hub. This close tolerancing may not be achieved with existing prior art turning or lathing operations.

[0006] Accordingly, there remains a need in the art for inexpensive machine tools for finishing O.D. surfaces of cylindrical workpieces in a manner in which precise tolerancing can be achieved and concentricity with respect to a central axis of the workpiece can be achieved.

SUMMARY OF THE INVENTION

[0007] The present invention overcomes the above-referenced shortcomings of prior art O.D. surface finishing operations by providing a tool for plateauing the O.D. surface of a cylindrical workpiece which includes an adjustable interior bore having abrasive particles thereon for accurately finishing the cylindrical workpiece.

[0008] As used herein, the term “finishing” is used to refer to lapping, deburring, polishing, or machining or other operations in which substantially improved surface characteristics are achieved.

[0009] Preferably, the tool comprises a rotatable substantially cylindrical member (or “cylindrical portion”) having an inner work-engaging surface adapted for finishing the O.D. surface of the cylindrical workpiece. The inner work-engaging surface includes abrasive particles thereon and defines a bore to receive the workpiece. The substantially cylindrical member includes at least one longitudinal split permitting radial expansion and contraction of at least part of the cylindrical portion for workpiece O.D. finish adjustment.

[0010] An adjustment nut is threaded onto the substantially cylindrical member. The adjustment nut and substantially cylindrical member include at least one tapered adjustment surface therebetween which is operative as a cam to facilitate the expansion and contraction as the adjustment nut is rotated with respect to the substantially cylindrical member.

[0011] In one embodiment, the tapered adjustment surface is formed on an outside surface of the substantially cylindrical member. The adjustment nut includes at least one preload ring made of a compliant material engaged with the tapered adjustment surface to provide an adjustable compressive force on the substantially cylindrical member as the adjustment nut is rotated with respect to the substantially cylindrical member. This embodiment is particularly used for superfinishing the O.D. surface.

[0012] In another embodiment, the substantially cylindrical member comprises a tapered outer surface and the adjustment nut comprises a tapered portion slidably engageable with the tapered outer surface as the nut is rotated with respect to the substantially cylindrical member to provide an adjustable compressive force on the substantially cylindrical member as a result of interference-type engagement between the tapered portion of the nut and the tapered outer surface of the substantially cylindrical member. This structure is more rigid than the above-described embodiment, and is used primarily for rough-cutting, as opposed to superfinishing.

[0013] Accordingly, an object of the invention is to provide a tool for accurately finishing an O.D. surface of a cylindrical workpiece.

[0014] Another object of the invention is to provide a tool for accurately finishing an O.D. surface of a cylindrical workpiece which includes a cylindrical member defining a bore bordered by abrasive particles to receive and finish the workpiece.

[0015] The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 shows a longitudinal cross-sectional view of a plateauing tool and workpiece in accordance with a first embodiment of the invention;

[0017] FIG. 2 shows a longitudinal cross-sectional view of an adjustment nut corresponding with the embodiment of FIG. 1;

[0018] FIG. 3 shows an end view of the adjustment nut of FIG. 2;

[0019] FIG. 4 shows a longitudinal cross-sectional view of a shank and substantially cylindrical portion of the tool of FIG. 1;

[0020] FIG. 5 shows an end view of the shank and substantially cylindrical portion shown in FIG. 4;

[0021] FIG. 6 shows a longitudinal cross-sectional view of a plateauing tool and workpiece in accordance with an alternative embodiment of the invention;

[0022] FIG. 6A shows a longitudinal cross-sectional view of a plateauing tool and workpiece in accordance with an alternative embodiment of the invention;

[0023] FIG. 7 shows a longitudinal cross-sectional view of a plateauing tool and workpiece in accordance with an alternative embodiment of the invention;

[0024] FIG. 8 shows a cross-sectional view of an alternative embodiment of a plateauing tool.

[0025] FIG. 8 a shows a longitudinal cross-section along A-A of the plateauing tool shown in FIG. 8.

[0026] FIG. 8 b shows a longitudinal cross-sectional view of a plateauing tool and workpiece in accordance with an alternative embodiment of the invention;

[0027] FIG. 8 c shows a longitudinal cross-sectional view of a plateauing tool and workpiece in accordance with an alternative embodiment of the invention;

[0028] FIG. 9 a shows a graphical illustration of surface roughness for an unfinished surface showing an equal distribution of peak height and valley depth;

[0029] FIG. 9 b shows a graphical illustration of a material ratio curve corresponding with FIG. 9a;

[0030] FIG. 10 shows a graphical illustration of a plateaued surface having an unequal distribution of peak height and valley depth;

[0031] FIG. 10 b shows a graphical illustration of a material ratio curve corresponding with FIG. 10a;

[0032] FIG. 11 shows a schematic perspective view of a common surface corresponding with FIGS. 9a and 9b; and

[0033] FIG. 12 shows a schematic perspective view of a plateaued surface corresponding with FIGS. 10a and 10b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0034] Referring to FIGS. 1-5, an O.D. finishing tool 10 is shown in accordance with a first embodiment of the invention for plateauing an outside diameter (O.D.) surface 12 of a cylindrical workpiece 14. The primary function of plateauing is to remove the “peaks” of a surface finish.

[0035] The finishing tool 10 comprises a body 16, which includes a shank portion 18, with a substantially cylindrical portion (or “member”) 20 extending from the shank portion 18.

[0036] The substantially cylindrical portion 20 includes an inner work-engaging surface 22 with abrasive particles 24 thereon for finishing the O.D. surface 12 of the workpiece 14. Preferably, the abrasive particles 24 are diamond chips.

[0037] The inner work-engaging surface 22 defines a bore 26 to receive the workpiece 14, and includes a plurality of longitudinally extending splits 28, which are shown in FIGS. 4 and 5. The longitudinally extending splits 28 are configured to permit radial expansion and contraction of at least part of the cylindrical portion 20 for workpiece O.D. finish adjustment.

[0038] The inner work-engaging surface 22 includes a curved lead-in edge 30 to facilitate insertion of the workpiece 14 into the bore 26.

[0039] In the embodiment shown in FIG. 1, the substantially cylindrical portion 20 includes a tapered outside surface 32 which extends approximately the length of the work-engaging surface 22 along the length of the cylindrical portion 20.

[0040] An adjustment nut 34 is threadedly engaged with the substantially cylindrical portion 20 along the threads 36. Accordingly, the adjustment nut 34 is rotatably adjustable with respect to the substantially cylindrical portion 20 as a result of this threaded engagement 36. As shown in FIG. 3, the adjustment nut 34 also includes wrench flats 38 and a set screw hole 40 for receiving a set screw to secure the adjustment nut 34 in the desired position with respect to the substantially cylindrical portion 20 when adjusted.

[0041] As shown in FIG. 2, the adjustment nut 34 also includes grooves 42, 44 for receiving the O-rings 46, 48 (or any compressible or spring material), which are preload rings made of a compliant material operative to engage with the tapered outside surface 32 of the substantially cylindrical portion 20 to provide an adjustable compressive force on the substantially cylindrical member 20 to vary the diameter of the bore 26 for finish adjustment of the O.D. surface 12 of the workpiece 14.

[0042] This embodiment is particularly applicable to superfinishing operations because the O-rings 46, 48 are sufficiently compliant to allow very small adjustments.

[0043] By example, in order to improve the finish of the bore 26, the adjustment nut 34 is rotated with respect to the cylindrical portion 20, which causes the O-rings 46, 48 to slide to the right (as viewed in FIG. 1) along the tapered outside surface 32, thereby compressing the O-rings 46, 48 against the tapered outside surface 32, which provides a compressive force to reduce the width of the splits 28, thereby improving the bore 26 to ultimately reduce the O.D. of the workpiece 14 and plateau the surface as the abrasive particles 26 are rotated against the O.D. surface 12.

[0044] An alternative embodiment of the invention is shown in FIG. 6. As shown, the O.D. finish tool 110 is configured for plateauing an O.D. surface 112 of a cylindrical workpiece 114. The O.D. finishing tool 110 includes a body 116 having a shank portion 118 and a substantially cylindrical portion 120. The substantially cylindrical portion 120 includes an inner work-engaging surface 122 having abrasive particles 124 thereon.

[0045] The inner work-engaging surface 122 forms a bore 126 to receive the workpiece 114. The substantially cylindrical portion 120 includes one or more longitudinally extending splits 128 to enable selective radial expansion and contraction of at least part of the cylindrical portion 120 for adjustment of the bore 126 to finish the O.D. surface 112 of the workpiece 114.

[0046] The substantially cylindrical member (portion) 120 includes a tapered outer surface 132.

[0047] An adjustment nut 134 is threadedly engaged with the substantially cylindrical portion 120 at the threaded portion 136. The adjustment nut 134 includes a set screw hole 140 for holding the adjustment nut 134 in a desired rotational position with respect to the substantially cylindrical portion 120.

[0048] The adjustment nut 134 also includes a tapered portion 142 which is slidably engaged with the tapered outer surface 132 of the substantially cylindrical portion 120 as the nut is rotated with respect to the substantially cylindrical portion 120 to expand or contract the inner work-engaging surface 122 for workpiece O.D. finish adjustment.

[0049] Accordingly, as a result of the interference-type engagement between the tapered outer surface 132 of the substantially cylindrical portion 120 and the tapered portion 142 of the adjustment nut 134, relative sliding engagement of the surfaces 132, 142 causes finish adjustment of the inner work-engaging surface 122 as a result of the adjustable compressive forces applied to the substantially cylindrical member 120 by the tapered portion 142 of the adjustment nut 134. Compressing the O-rings 152, 154 against the outside surface provides a compressive force that reduces the width of splits 128.

[0050] The tool 110 also includes a coolant aperture 146 formed in a sleeve 148 in communication with the bore 126 for carrying coolant to the bore 126 for cooling the workpiece 114. Alternatively, coolant may be delivered through the distal end of the shank portion 118 as shown in FIG. 6A.

[0051] The flushing also removes the surface particles generated by the plateauing process, thereby providing a clean and predictable plateauing value.

[0052] The present invention recognizes that various other means may be provided for providing adjustable compressive forces on a substantially cylindrical portion of a tool for adjustment of an internal bore thereof within the scope of the present invention. Once the means for adjusting the compressive force applied to the substantially cylindrical portion has been appropriately adjusted, the workpiece is inserted into the bore, and the tool is rotated with respect to the workpiece to finish the O.D. surface.

[0053] In an alternative embodiment, the adjustment nut is not threaded to the cylindrical portion, but rather slides axially along the cylindrical portion. A handle 150 may be provided for manually sliding the nut. This configuration enables quick disengagement of the O.D. finishing tool and eliminates the helical tool marks for applications such as seal surfaces.

[0054] FIGS. 8 and 8 a show an alternative embodiment of an O.D. finishing tool 210. The finishing tool 210 comprises cylindrical arbor 214 having a channel 216 at a back end and a plurality of finishing elements 218 mounted at a front end, an outer sleeve assembly 220 slidable along the arbor 214 and along the finishing elements 218, and a drawbar 222 that is slidably mounted in the channel. The drawbar 222 is operatively connected to a cross pin 224.

[0055] The outer sleeve assembly 220 comprises a cylindrical sleeve 226, cross pin 224, and a plurality of adjustable elements 228. Preferably, the tool has three adjustable elements.

[0056] Each adjustable element 228 comprises a shoulder screw 230 with a spring 232 around it and an external rocker arm 234 operatively connected to the spring 232. The external rocker arm 234 has a roller 236 at its distal end. The roller 236 slides along an outer surface of a cooperating internal lever 238.

[0057] Each finishing element 218 comprises an internal lever 238 mounted at the front end of the arbor 214. The internal rocker arm pivots about a pin 248. Preferably, the outer surface 240 of the internal lever 238 is concave. As the roller 236 slides forward it moves ahead of the pivot pin 248 and pushes on the front end of the internal lever 238. The arm 238 pivots and the work engaging surface 250 is pushed into contact with and engages the workpiece. As the roller slides back, it moves behind the pivot pin 248 and pushes on the back end of the internal lever 238 which pivots and causes the front end to lift up and to disengage the workpiece 242. At the front end of the internal lever 238 is an abrasive surface 244 for engaging and finishing the workpiece 242. Preferably, the abrasive surface 244 is a diamond pad. Preferably, there is a plastic pad 254 that serves as a bumper when the work engaging element is retracted.

[0058] The cylindrical workpiece 242 is placed at the mouth of the tool 210. When drawbar 222 is pushed toward the tool 210, abrasive surfaces 244 on the finishing elements 218 engage the workpiece 242. As the drawbar 218 is pulled away from the tool 210, it pulls on the cross pin 220 which pulls the outer sleeve assembly 220 back. The spring loaded adjustable element 228 moves back, the roller 236 of the external rocker arm 234 moves behind the pivot point of the internal lever 238 and the front end of the internal lever 238 lifts up. As the drawbar 218 is pushed toward the tool 210, the cross pin 220 pushes the outer sleeve assembly 220 forward. The spring loaded adjustable elements 228 move forward and the rollers 236 of the external rocker arms 234 move ahead of the pivot point pushing the front end of the internal rocker arm down 238. The abrasive surfaces 244 engage the work piece 242.

[0059] The tool 210 is then rotated finishing the O.D. surface 246 of the workpiece. The arbor 214 is connected to a rotable spindle 256. The spindle 256 is rotated which rotates the tool 210 causing the abrasive surface 244 to rotate against the workpiece 242. The outer-diameter of the workpiece 242 is plateaued by the tool 210.

[0060] To cool the tool, coolant could be pumped through the channel 216 in the spindle as shown in FIG. 8b, pumped through a sleeve 258 in communication with the channel 216 as shown in FIG. 8c, or even pumped through the cylindrical workpiece.

[0061] These O.D. surface finishing tools are operative to “plateau” the surface of the workpiece to generate an Rpk value which is 3-10 times smaller than Rvk, thereby producing bearing ratios in excess of 40%, as these terms are described in commonly owned U.S. Pat. No. 6,139,414, which is hereby incorporated by reference in its entirety.

[0062] FIGS. 9-12 provide schematic illustrations of surfaces before and after the plateauing operation. A plateau tool may be applied to a common surface, as shown in FIGS. 8a, 8b, and 10 which has been previously machined where the peaks and valleys (Rvk, Rpk) are substantially equal. The plateauing tool removes only a prescribed amount of peaks to generate a predictable Rpk value without changing the size or geometry of the workpiece (i.e. the roughness average Ra remains the same). With the peaks removed and the valleys still intact to contain oil, this is the ideal condition for many applications.

[0063] As shown in FIGS. 9a and 9b, as well as FIG. 11, a common surface will have a roughness with an equal distribution of peak height and valley depth.

[0064] As shown in FIGS. 10a, 10b, and 12, the surface has been plateaued, thereby removing the peaks, and providing a much flatter material ratio curve and generating a Rpk which is 3-10 times smaller than Rvk, thereby producing bearing ratios in excess of 40%. Comparing FIGS. 11 and 12, the peaks P of FIG. 11 have been removed to form the plateaued surface S of FIG. 12, while the roughness average (Ra) remains at 2.4 micrometers, Rpk is reduced from 2.6 to 0.9 micrometers, Rk is reduced from 8.2 to 1.9 micrometers, and Rvk is increased from 2.6 to 9.8 micrometers by the plateauing process.

[0065] While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.

Claims

1. A tool for finishing an outside diameter surface of a cylindrical workpiece, comprising: a shank portion; a substantially cylindrical portion extending from said shank portion, said substantially cylindrical portion comprising: an inner work engaging surface adapted for plateauing the outside diameter surface of the workpiece, said inner work engaging surface defines a bore to receive the workpiece, and said inner work engaging surface is plated with abrasive particles; and at least one longitudinal split permitting radial contraction and expansion of at least part of the inner work engaging surface; and an adjustment nut mounted on the substantially cylindrical portion to controllably adjust the radius of the inner work engaging surface; wherein said inner work engaging surface is rotatable against the outer diameter surface of the workpiece.

2. The tool of claim 1, wherein at least one of an outside surface of said substantially cylindrical portion and an inner surface of said adjustment nut is tapered.

3. The tool of claim 2 wherein the outside surface of said substantially cylindrical portion is tapered and has a threaded portion; the adjustment nut is threadedly engaged with the threaded portion; and a set screw holds the adjustment nut in a desired position.

4. The tool of claim 3 wherein the adjustment nut has a tapered inner surface.

5. The tool of claim 3 further comprising an O-ring between said outside surface of the substantially cylindrical portion and the tapered inner surface of the adjustment nut.

6. The tool of claim 2 wherein the outside surface of said substantially cylindrical portion is tapered and the adjustment nut is slidable in an axial direction along the outside surface of the substantially cylindrical portion.

7. The tool of claim 6 wherein the adjustment nut is provided with a handle for manually sliding said adjustment nut.

8. The tool of claim 6 wherein the adjustment nut has a tapered inner surface.

9. The tool of claim 8 further comprising an O-ring between said outside surface of said cylindrical portion and tapered inner surface the adjustment nut.

10. The tool of claim 1 wherein the adjustment nut is threaded onto the substantially cylindrical portion, said adjustment nut and substantially cylindrical portion include at least one tapered adjustment surface therebetween to facilitate said expansion and contraction as the adjustment nut is rotated; and wherein said tapered adjustment surface is formed on an outside surface of the substantially cylindrical portion and said adjustment nut includes at least one elastic O-ring engaged with the tapered adjustment surface to provide an adjustable compressive force on the substantially cylindrical portion as the adjustment nut is slid axially with respect to the substantially cylindrical portion.

11. A tool of claim 1 wherein the substantially cylindrical portion comprises a tapered outer surface which engages a tapered portion of the adjustment nut which slides axially along the substantially cylindrical portion in a manner to adjust compressive forces to adjust an interference fit between the tapered portion of the substantially cylindrical portion and the tapered outer surface of the adjustment nut.

12. The tool of claim 11, wherein said adjustment nut is provided with a handle for manually sliding said adjustment nut.

13. The tool of claim 1, further comprising a coolant aperature in communication with said bore for carrying coolant to the bore.

14. The tool of claim 13, wherein said coolant aperature is located at the distal end of said shank portion.

15. The tool of claim 13, wherein said coolant aperature is formed in a sleeve wherein said sleeve is in communication with the bore.

16. The tool of claim 13 wherein the substantially cylindrical portion includes a tapered outer surface; the adjustment nut is threaded onto the substantially cylindrical portion and includes a tapered portion slidably engageable with said tapered outer surface as the nut is rotated with respect to the substantially cylindrical portion to expand or contract the inner work-engaging surface; and the coolant aperture formed in a sleeve and said sleeve is communication with said bore.

17. The product manufactured by the tool of claim 1.

18. The product of claim 17, said product comprising a cylindrical body having an outside diameter surface machined by said tool, said outside diameter surface with a bearing ratio of at least 40% as a result of being machined by said tool.

19. The product of claim 17, said product having an outside diameter surface having peaks and valleys, the peaks being 3-10 times smaller than the valleys as a result of the product being machined by said tool.

20. The product of claim 17, said product comprising a cylindrical body having an average roughness before being machined by said tool and wherein the average roughness of the outside diameter surface remains the same after being machined by said tool.

21. A method for finishing an outside diameter surface of a workpiece comprising the steps of: obtaining a cylindrical workpiece; inserting the workpiece into the bore of the tool of claim 1;radially expanding or contracting the inner work engaging surface of the tool; rotating the cylindrical portion to plateau the workpiece; and removing the workpiece from the tool.

22. The method of claim 24 further comprising the step of rotating the adjustment nut to expand or contract the inner work engaging surface.

23. The method of claim 22 further comprising the step of sliding the adjustment nut axially to expand or contract the inner work engaging surface.

24. The method for finishing of claim 21 further comprising the step of providing coolant to the bore.

25. The method for finishing of claim 24 further comprising the step of flushing surface particles.

26. The method of claim 21, wherein the workpiece is removed when a prescribed amount of peaks have been removed.

27. A tool for finishing an outer diameter surface of a workpiece comprising: a cylindrical arbor having a channel for housing a drawbar; a plurality of work engaging elements; said work engaging elements each comprising an internal rocker arm pivotable about a pivot point and a work engaging surface having an abrasive surface at a distal end; an outer sleeve assembly slidable along the arbor and the work engaging elements for engaging and disengaging the workpiece from the tool; and a drawbar; wherein moving the drawbar causes the outer sleeve to slide relative to the arbor and the work engaging elements.

28. The tool of claim 27 wherein the outer sleeve assembly comprises a plurality of external rocker arms each cooperating with one work engaging element, said external rocker arms each having a roller at a distal end, said roller moves along a concave outer surface of the cooperating inner rocker arm, and the work engaging surface engages the workpiece as the roller moves ahead of the pivot point and disengages the workpiece as the roller moves behind the pivot point.

29. The tool of claim 28 having three work engaging elements and three cooperating external rocker arms.

30. The tool of claim 28 wherein the external rocker arms are spring loaded.

31. The tool of claim 28 wherein the work engaging surfaces are independent of each other.

32. The product manufactured by the tool of claim 27.

33. The product of claim 32, said product comprising a cylindrical body having an outside diameter surface machined by said tool, said outside diameter surface with a bearing ratio of at least 40% as a result of being machined by said tool.

34. The product of claim 17, said product having an outside diameter surface having peaks and valleys, the peaks being 3-10 times smaller than the valleys as a result of the product being machined by said tool.