WO2011059945A1

WO2011059945A1 - Compensating workholding equipment

Info

Publication number: WO2011059945A1
Application number: PCT/US2010/055934
Authority: WO
Inventors: Brian J. Baldeck; Kevin M. Spindler
Original assignee: The Gleason Works
Priority date: 2009-11-10
Filing date: 2010-11-09
Publication date: 2011-05-19

Abstract

Workholding equipment for a machine tool, in particular an arbor chuck (2), having a plurality of internal elements comprising a wobble washer (26) and at least one of a floating nut (24) and flat washer (28) which counteract workpiece misalignment. In arbor chucks, the wobble washer and floating nut counteract misaligned pulling forces due at least in part to the lead angle of threads (15) on an expander (14) of the arbor chuck.

Description

COMPENSATING WORKHOLDING EQUIPMENT

Field of the Invention

[0001] The present invention is directed to a workholding apparatus for machine tools. In particular, the workholding apparatus includes elements that counteract misaligned pulling forces during clamping thereby resulting in forces only along the direction of the pulling force.

Background of the Invention

[0002] In metalworking operations where a workpiece is machined, equipment of some type is necessary to hold the workpiece in position in a machine tool so the machining process can be successfully carried out. This type of equipment is known as "workholding" equipment. In the production of toothed articles, such as gears, workholding equipment may be generally categorized as arbor chucks. Examples of arbor chucks for gripping pinion shanks can be found in U.S. Patents Nos. 3,083,976 to Stark and 3,244,427 to Taschl. An example of an arbor chuck for a ring gear can be found in U.S. Patent No. 3,735,994 to Jaehn. An arbor chuck for expanding into contact with the bore of a pinion can be found in U.S. Patent No. 3,517,939 to Jaehn.

[0003] Many styles of workholding equipment, especially relating to the manufacture of gears, operate in a manner wherein an expander element, usually in the general form of a rod, cooperates with a collet element via complementary tapered surfaces on the expander and collet, to expand or contract the collet such that it grips a workpiece thereby holding the workpiece in position on a machine tool so that one or more machining operations can be carried out. It is common for one end of the expander to comprise the aforementioned tapered surfaces and for the other end to comprise threads which engage with threads on a draw rod, or a connector associated the draw rod, of the machine tool. When clamping (i.e. chucking) a workpiece, the draw rod pulls back (i.e. in a direction away from the workpiece, thereby pulling the expander back and effecting a sliding of the expander's tapered surface relative to the tapered surface of the collet. The relative sliding motion expands or contracts the collet to grip a

workpiece. It can be understood that opposite direction movement of the draw rod effects the release of a workpiece from the gripping force of the collet.

[0004] In chucking of some workpieces on conventional workholding equipment, a shift in the position of the workpiece away from its properly clamped axial position has been noted. In gear manufacture, a deviation of 0.0005 inch (0.0127 mm), for example, may be sufficient to result in a misaligned clamped workpiece that when machined, results in out-of-tolerance radial and/or axial runout on the workpiece.

[0005] The inventors have discovered that during the pulling back of the draw rod, the threaded connection between the expander and draw rod introduces a misalignment of the pulling forces away from the direction of the force being applied. The cause is believed to be due to the angle of the threads (lead angle) of the draw rod (or

connector) and the expander. During pull back of the draw rod, the angled threads direct a portion of the pulling forces away from the applied direction (i.e. in-line with the draw rod) resulting in a shifting or skewing of arbor chuck components, such as the expander, and the workpiece out of axial alignment on the workholding equipment. The angle of the threads creates an angle of distortion through which the pulling force can translate in a direction different than the applied direction.

[0006] The force exerted on the workholding equipment during a chucking cycle needs to be in line with the direction of the force being applied. The inventors have discovered means to counteract the misalignment of forces thereby reducing or eliminating arbor chuck and workpiece distortion.

Summary of the Invention

[0007] The present invention provides workholding equipment for a machine tool, in particular an arbor chuck for a gear manufacturing machine, having a plurality of internal elements comprising a wobble washer and floating nut and/or washer which counteract workpiece misalignment. In arbor chucks, the wobble washer and floating nut counteract misaligned pulling forces due at least in part to the lead angle of threads on the expander of the arbor chuck.

Brief Description of the Drawings

[0008] Figure 1 is a cross-sectional view of the inventive arbor chuck.

[0009] Figure 2 is an exploded view of the internal components of the connector assembly of the inventive arbor chuck.

[0010] Figure 3 is a cross-sectional view of a tailstock assembly including a wobble washer and flat washer of the present invention.

Detailed Description of the Preferred Embodiment

[0011] Before any features and at least one construction of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other constructions and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purposes of description and should not be regarded as limiting.

[0012] The use of "including", "having" and "comprising" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Although references may be made below to directions such as upper, lower, upward, downward, rearward, bottom, top, front, rear, etc., in describing the drawings, the references are made relative to the drawings (as normally viewed) for convenience.

[0013] Figure 1 shows an arbor chuck 2 for holding a workpiece 4 such as a cylindrical gear (e.g. spur or helical gear) in position about a work axis W on a gear manufacturing machine. Arbor chuck 2 is removably secured in a spindle 6 of the machine via an arbor base 8 which is usually a separate component from the arbor chuck or the machine spindle. Arbor chuck 2 comprises backing ring 10, collet 12 and expander 14. A first end of the expander 14 includes a tapered surface 16 which engages a

complementary tapered surface 18 of collet 12 in a sliding manner such that movement of the expander 14 in a direction toward the machine spindle 6 (i.e. to the left in Figure 1 ) results in the radial expansion of collet 12 into engagement with the workpiece 4 thereby gripping and securing the workpiece for machining. This motion is known as the "pull back" motion. The expander 14 is pulled back by the action of a machine draw rod 20 via a connector 22 which is discussed in detail below. It can be seen that movement of the expander 14 in the direction away from the spindle 6 (i.e. to the right in Figure 1 ), known as the "release" motion, results in the contraction of the collet 12 thereby releasing the grip on workpiece 4 which can then be removed from the machine and a subsequent workpiece can be loaded for the next machining cycle. [0014] With conventional arbor chucks, as discussed above, distortion of the arbor components can occur causing radial and axial runout of the work piece being held by the arbor chuck. The main cause of the force being transmitted in other directions than the applied direction is the influence of the threads on the expander in the arbor design. As mentioned, the lead of the threads on the end of the expander can create an angle of distortion through which the force can translate in a different direction other than the applied direction. The present invention provides an inventive manner by which an expander is secured in a connector of an arbor chuck thereby diminishing or eliminating the distortion of forces and arbor components experienced with the prior art arbor chucks.

[0015] The arbor chuck 2 of the present invention includes a connector 22 that comprises a floating nut 24, to which a threaded end 15 of an expander 14 is attached, and a wobble washer 26. The connector may further include a washer 28, preferably having ground, flat and parallel surfaces, positioned between the floating nut 24 and the wobble washer 26. A retaining cover 30 is included on the connector 22 and is fastened thereto by a plurality of screws 32 (two are shown). The connector 22 preferably further includes a plunger 34 and spring 36. Preferably, spring 36 is preloaded during assembly of the connector 22. Expander 14 extends through retaining cover 30, wobble washer 26, washer 28 (if included) and into threaded engagement with floating nut 24 via threads 15. Floating nut 24 preferably further includes a slot 25 extending along at least a portion of its axial length. During assembly, a means such as a pin or set screw (not shown) is inserted through the connector 22 and into slot 25 so as to prevent rotation of the floating nut 24 when the expander 14 is threaded into or removed from the floating nut 24.

[0016] Wobble washer 26, as best seen in Figure 2, comprises two radiused projections 38 (e.g. 0.050 inch (1 .27 mm) in height) on one side thereof and two radiused projections 40 (one shown) on the other side thereof. Preferably, the projections (e.g. 38) are arranged 180 degrees apart from one another on a side with the projections on one side (e.g. 38) being offset 90 degrees with respect to the projections on the other side (e.g. 40) of the wobble washer 26. The wobble washer 26 and floating nut 24 of the invention cancel out the influence of the lead angle of the threads 15. The wobble washer 26 allows realignment of the applied forces to create forces purely along the direction of the pulling force or action (i.e. the direction of draw rod motion). The floating nut 24 of the invention compensates for any misalignment in arbor assembly 2 to aid with realignment of the applied forces.

[0017] During the chucking sequence, a pulling force is applied by the machine draw rod 20 to the connector 22. The retaining cover 30 of the connector assembly is pulled against the wobble washer 26 which in turn is pulled against the flat and parallel ground washer 28 which then contacts the floating nut 24. The whole connector assembly moves back creating the pulling force on the expander 14 via threads 15. During this action, wobble washer 26 and floating nut 24 align the pulling force to cancel out the influence of the thread pitch or lead angle of threads 15 which reduces or eliminates deflection in the arbor chuck 2.

[0018] During de-chucking of the arbor chuck 2, the connector 22 is moved forward by the draw rod 20 in the machine. As the connector 22 moves forward, the pulling force is removed from the connector assembly. As a result, the wobble washer 26, flat washer 28 and nut 24 are free to relax or float. As the connector 22 is moved forward, pressure is applied by the spring loaded plunger 34 to the end 15 of the expander 14 to ensure de-chucking of the part 4 being held by the arbor chuck 2.

[0019] While the present invention has been discussed with reference to an arbor chuck that expands into the bore of a workpiece for gripping, the present invention is not limited thereto. The invention is also applicable to other types of arbor chucks including those that grip the shaft of a workpiece or those that grip a workpiece via its outer diameter or peripheral surface. The present invention is also not limited to arbor chucks for cylindrical gears but equally contemplates arbor chucks for other types of gears such as bevel ring gears and pinions (including hypoid gears) and crown gears.

[0020] Additionally, the present invention is also applicable to workholding tailstock assemblies utilized with apparatus such as arbor chucks for example. Tailstock assemblies assist in holding a workpiece in place and are usually mounted opposite the primary workholding apparatus. In Figure 1 , for example, a tailstock assembly would be advanced along axis W toward the outer end surface of workpiece 4 (opposite the end surface contacted by backing ring 10) and brought into contact with the outer end surface of workpiece 4 for additional workpiece support during a machining process. While a tailstock assembly has no expander, the presence of the inventive wobble washer with an adjacent flat washer in the tailstock assembly reduces or eliminates any distortion forces on the workpiece resulting from tail stock misalignment with respect to the workpiece and/or the end surfaces of a workpiece being out of parallel with respect to one another.

[0021] An example of such a tailstock assembly is shown in Figure 3. The assembly 41 comprises tailstock center 42 and rocker plate 44. Flat washer 28 is held in position via one or more screws 52. Wobble washer 26 sets on rocker plate 44 and both are held in position by screw 46, washer 48 and spring 50. Wobble washer 26 and flat washer 28 are protected against process fluids, swarf, etc. by cover 54 and a seal 56 such as an O-ring. A dowel pin 58 extends into a bore in tailstock center 42 to prevent rotation of tailstock center 42 relative to rocker plate 44. Tailstock assembly 41 is removably secured to a tailstock spindle (not shown) via a plurality of screws 58 (one shown). Upon removal of screws 58, tailstock assembly 41 may be loosened, if necessary, from the tailstock spindle via an ejector screw 62. Given that different workpieces have different geometries, a workpiece-specific clamp ring (not shown) is attached to the end face of rocker plate 44 by a plurality of screws 60 (one shown). [0022] While the invention has been described with reference to preferred embodiments it is to be understood that the invention is not limited to the particulars thereof. The present invention is intended to include modifications which would be apparent to those skilled in the art to which the subject matter pertains without deviating from the spirit and scope of the appended claims.

Claims

CLAIMS What is claimed is:

1 . Workholding equipment for a machine tool, said workholding equipment having an axis of rotation and comprising:

at least one of a floating nut and a flat washer;

a wobble washer, said wobble washer having a first side and a second side, said first side having two radiused projections located thereon, said second side having two radiused projections located thereon, wherein the radiused projections on said first side are offset with respect to the radiused projections on said second side;

wherein said first side or said second side of said wobble washer is located adjacent to said at least one of a floating nut and a flat washer.

2. The workholding equipment of claim 1 wherein said flat washer is positioned between said floating nut and said wobble washer.

3. The workholding equipment of claim 1 further including an expander extending through said wobble washer and having a first end being in threaded engagement with said floating nut.

4. The workholding equipment of claim 1 further comprising a draw rod connector with said floating nut and said wobble washer being positioned within said connector.

5. The workholding equipment of claim 4 wherein said connector includes a retaining cover positioned over said floating nut and said wobble washer.

6. The workholding equipment of claim 1 wherein on said first side said radiused projections are spaced 180 degrees apart.

7. The workholding equipment of claim 1 wherein on said second side said radiused projections are spaced 180 degrees apart.

8. The workholding equipment of claim 1 wherein said offset is ninety degrees.