Background and Brief Description of Invention

Various forms of workholding devices have been designed for use with gear cutting machines. Generally, these devices are referred to as arbors and include some means for gripping a workpiece through a tight contact with a bore of the workpiece. Typically, arbors have included sleeves or fingers for contacting the bore of a workpiece together with means for expanding the sleeve or fingers into tight engagement with the workpiece while it is being worked by a machine. Representative U.S. patents showing various forms of arbor designs and machanis s for actuating the arbors are shown in U.S. patents 308,639; 1,337,313; 2,935,329; 3,420,537; 3,517,939; 3,583,714; 4 121,847; and 4,198,066.

In gear cutting machinery, very high forces are applied to a workpiece by the cutting action of the machine. These forces are transmitted to the arbor which is holding the workpiece, and as a result of this transmittal of force, there is a tendency for the arbor to deflect or twist relative to the cutting tools of the machine. This problem is especially acute with relatively small arbors which are designed to secure small spur and helical gear workpieces. Movement of an arbor and the workpiece contained thereon can affect the precision with which a workpiece can be formed into a gear or other shaped article of manufacture. In addition, there is a danger of slippage of the workpiece relative to the arbor as the cutting forces increase and as the workpiece heats up from the cutting action. Thus, it is very important to provide for a gripping arrangement which can be

actuated into extremely tight engagement with a workpiece and which resists deflection of the forces applied thereto. In addition, the arbor which has these characteristics should be easily disengaged from the workpiece upon completion of a cutting operation.

Up to this time it has been a common practice to hold small diameter parts with arbors which are hydraulically actuated. For example, a known design of arbor provides a thin-walled sleeve which is expanded with hydraulic pressure (from grease or other heavy lubricant) to tightly engage the bore of a small workpiece. Arbors of this design have a relatively limited range of tolerances that can be accomodated on their expandable sleeves, and thus, it is not always possible to obtain a secure engagement of the arbor with a workpiece.

In accordance with the present invention an arbor is provided with means for mechanically expanding a sleeve into tight engagement with a bore formed through a workpiece. Mechanical expansion is accomplished with a tapered rod manufactured from an extremely rigid material such as high strength tungsten carbide. The tapered rod functions to not only expand the cylindrical sleeve into contact with the workpiece but also to provide increased rigidity and stiffness to the arbor to prevent unwanted bending and twisting deflections while the workpiece is being processed by the machine. Use of a high strength carbide material for a part of the assembly creates a special problem of how to anchor the carbide part into the arbor. This problem is solved with a novel press fitting of the carbide rod into the assembly.

In addition, the invention provides for an optional lubrication system which offers control of friction between the tapered rod and its associated cylindrical sleeve. In its preferred form, the lubrication system delivers small quantities of oil to the contact surfaces between the rod and the sleeve so that friction is reduced during initial actuation of the rod to a clamping position relative to a workpiece. When clamping is completed, lubrication is no longer required, and friction between the rod and the sleeve is automatically increased through an evaporation or dissipation of lubricant resulting from a heating up of the workpiece during a cutting operation. Thus, as the cutting forces increase and as the workpiece becomes warmer, the lubricant is evaporated more and more to the point where friction is considerably increased between the rod and the sleeve to thereby assure a stable relationship between the rod and the sleeve. This prevents any unwanted further movement of the rod into the sleeve, in a clamping direction, and thereby prevents any unwanted slight movement of the workpiece along the axis of the arbor. As a result of this arrangement, there is achieved a more rigid and tighter gripping of a workpiece with no unwanted movement of the workpiece relative to the arbor or to the cutting tools of the machine.

As a result of the improved arbor assembly of this invention, it is possible to hold a relatively - small diameter workpiece in a precise position with reference only to its bore and without a need for a reference surface at one end of the workpiece for seating the workpiece against a part of the arbor assembly.

These and other features and advantages of the invention will become apparent in the detailed discussion which follows, and in that discussion reference will be made to the accompanying drawings as briefly described below.

Brief Description of Drawings

Figure 1 is an elevational view of the arbor assembly of the present invention, shown partly in cross section;

Figure 2 is a cross-sectional view of Figure 1 as seen on line 2-2 thereon;

Figure 3 is an isometric view of a bifurcated sleeve component associated with the arbor assembly of this invention.

Detailed Description of Invention

Referring to Figures 1 and 2, the workholding device of this invention is illustrated with reference to a type of device which includes a rod 10 which is tapered at its free end and mounted for axial movement within a cylindrical sleeve 12 such that the cylindrical sleeve 12 can be expanded into contact with a workpiece 14 when the workpiece is placed on the cylindrical sleeve and the tapered rod is moved along its axis in a first direction relative to the cylindrical sleeve 12. The taper of the rod 10 is very slight and is in a direction that provides for a slightly smaller diameter for the free end of the rod as compared to an intermediate portion 16 of the rod. Thus, as the tapered rod 10 is moved in an upward direction as viewed in Figure 1, there is an advancement of an ever

OMPI

increasing larger diameter portion of the rod into the cylindrical sleeve 12. The cylindrical sleeve 12 comprise a very thin extension of a major component 18 of the assem and the thin walls of the cylindrical sleeve are slightly thicker in their outer ends (towards the top of Figure 1) as compared with their lower ends (at the base of the workpiece of Figure 1) . These basic constructions and relationships are well known in the art and it is known that such assemblies provide for an actual expansion or deformation of cylindrical sleeves as associated tapered rods are moved very slightly into clamping positions relative to workpieces carried thereon. In the Figure 1 illustration, the workpiece 14 is in the form of a spur gear which has been mounted over the cylindrical sleeve 12 of the workholding assembly.

The arbor assembly is provided with a dechucking mechanism for moving the rod 10 in a second direction along its axis (downwardly in the Figure 1 view) so as to disengage the tapered rod from its gripping relationship with the cylindrical sleeve 12 and a workpiece carried thereon. A base portion 20- of the rod 10 is tapered so as to be tightly engaged by a sleeve 22, which is a part of the dechucking mechanism,- when the sleeve 22 is drawn downwardly (in the Figure 1 view) to dechuck a part from the arbor. The dechucking mechanism also includes a known draw rod 24 having a threaded end portion 26 secured within a threaded bore of the sleeve 22. Threaded inserts 28 and 30 are also screwed into the threaded bore of sleeve 22 so as to press the tapered base portion 20 of the rod 10 into snug engagement with a mating surface formed through the end of sleeve 22. Thus, the carbide rod 10 can be anchored into the assembly without a need for boring or drilling the very hard material of the rod itself.

Although it is known to provide for deformation of a thin walled cylindrical sleeve member associated with an arbor assembly designed for small workpieces, one of the features of the present invention is to provide for a wide range of expansion characteristics of the cylindrical sleeve portion 12 of the assembly. This is accomplished by providing for a bifurcated structure, as shown in Figure 3.- in which the cylindrical sleeve 12 is essentially divided into two separate working parts which can be spread away from each other as the tapered rod 10 is advanced in its first direction of movement for clamping a workpiece. This provides for a much greater expansion possibility for the cylindrical sleeve member 12 than would be available with an unbifurcated construction in which expansion would be dependent solely upon the elastic characteristics of the sleeve material itself. In the present case, the sleeve material can be expanded both through its inherent characteristics of elasticity and through the interuptions in its integrity provided by slots 32 which form the bifurcated design of the cylindrical sleeve. Additional slots may be provided if desired.

The tapered rod of this invention is formed from an extremely strong and rigid material so as to prevent any bending or twisting deflections of the rod when a workpiece is mounted thereon and work is being performed on the workpiece. It has been found that the portion of the tapered rod 10 which is inserted into the workpiece can be made from a high strength tungsten carbide (designated as grade 2A5 carbide) having a Young's

Modulus of Elasticity of ninety-two million pounds per square inch, a Modulus of Rigidity of thirty-eight million pounds per square inch and a hardness approximately equal to 92 Rockwell (A) . This provides for an extremely

rigid and stiff support for the workpiece after the workpiece has been brought into a fully clamped condition relative to the cylindrical sleeve.

Figure 1 also illustrates an optional lubricating system which serves to inject small quantities of lubricant into a channel 34 formed into the housing. Lubricant is supplied from any known source under pressure (with a suitable pump) and is periodically pumped through a check valve assembly 36 so that metered small quantities (for example, three drops at a time) are injected into the channel 34 and ultimately into a space between the tapered rod 10 and an inner surface of the cylindrical sleeve 12. The channel 34 is formed in portions of the housing of the assembly and is in open communication with other openings in the assembly so as to lead to the very narrow space between the tapered rod 10 and the cylindrical sleeve 12. Each time a machining cycle is started, a small quantity of lubricant is injected into the arbor and onto the surfaces of the tapered rod 10 and the cylindrical sleeve 12 so as to permit easier advancement of the tapered rod 10 to its fully advanced position relative to the cylindrical sleeve 12. By lubricating these surfaces during the clamping operation, it is possible to advance the tapered rod 10 to its maximum position for expanding the sleeve 12 tightly against the bore of a workpiece 14, thereby assuring a very tight gripping action on the workpiece. Since the lubrication system provides for only a small metered quantity of lubricant at the beginning of each cycle, and thereafter discontinues any further flow of lubricant until a subsequent cycle, there is assured a film of lubrication between the tapered rod 10 and the cylindrical sleeve 12 only during the initial clamping action of the arbor.

Thereafter, as the machine begins a work cycle on the workpiece 14, the workpiece warms up and eventually becomes hot enough to evaporate the film of lubricant between the tapered rod 10 and the cylindrical sleeve 12. This results in an effective increase in friction between those two members as the machining cycle progresses and as the workpiece tends to heat up and expand. By increasing friction between the tapered rod and the cylindrical sleeve during the work cycle, there is no tendency for the tapered rod to advance any further in its first direction of movement relative to the sleeve so as to cause any unwanted deflection of the workpiece itself resulting from such movement. Thus, there is provided a very tight engagement of the workpiece which maintains itself in a precision relationship with the arbor throughout a cutting cycle. In addition, the lubrication system can be used to purge the assembly of any particles or contaminants resulting from the work process.

Figure 2 illustrates assembly features of the workholding device of this invention, including a projecting element 36 which is fitted into a groove formed in the sleeve 22 so as to resist any rotational movement of that component and the tapered rod 10 carried thereby. This further stiffens the relationship between the tapered rod 10 and the cylindrical sleeve member 12 to assure a rigid and precise relationship during a cutting operation.

Although the invention has been described with reference to a single embodiment thereof, it can be appreciated that variations will become apparent to those skilled in this art. All such variations are

intended to be included within the scope of the invention as defined in the claims which follow.