Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2001-02-20
2002-11-26
Eley, Timothy V. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S242000, C451S049000, C451S062000, C451S178000
Reexamination Certificate
active
06485353
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns methods and apparatus for grinding workpieces which are composed of concentric in-line cylindrical regions and intermediate non-axial non-circular or eccentric regions. Examples of such workpieces are camshafts and crankshafts of internal combustion engines and such workpieces are referred to herein as composite workpieces.
BACKGROUND OF THE INVENTION
Because of the different techniques used for grinding in-line and off-axis regions of workpieces, it has hitherto been commonplace to grind the cylindrical region of a composite workpiece on one grinding machine and to transfer the workpiece to another grinding machine for grinding the non-axial regions such as cam lobes or crankpins.
With the trend towards lightweight engine components, camshafts and crankshafts have become less stiff and more prone to distortion as a result of grinding forces exerted on the workpiece by the grinding wheel particularly when high metal removal rates are desired. To this end it has been proposed to resist grinding forces exerted by the grinding wheel by means of so-called worksteadies or workrests which engage diametrically opposite regions of the workpiece without inhibiting rotation, to resist the bending moment created by the grinding wheel forces exerted on the workpiece.
In general the workrests have been applied against the journal bearing regions of the workpieces, i.e., the cylindrical co-axial regions of the workpiece which are normally intermediate non-circular or off-axis components, such as the cam lobes and crankpins of the exemplary workpieces.
It is an object of the present invention to provide a single machine for grinding composite workpieces.
It is a further object of the invention to improve the rigidity of the mounting for a workrest as incorporated in such a machine.
SUMMARY OF THE INVENTION
According to one aspect of the present invention in a grinding machine comprising a stationary support structure, a wheelhead assembly slidable relative to the said structure in a direction perpendicular to a workpiece axis, headstock and footstock means mounted on the structure and defining the workpiece axis, rotating a workpiece mounted therebetween, at least one workrest slidably adjustable along at least one rigid elongate member or rail which extends generally parallel to the workpiece axis, and programmable computer based control means for controlling the movement of the wheelhead, the rotation of the workpiece, and engagement and disengagement of the workrest with a cylindrical region of the workpiece, wherein means is provided for fixing the workrest at a specific axial location along the length of the said elongate rail so that the workrest aligns with a cylindrical region of the workpiece.
During grinding, swarf, coolant and grinding medium particles will be present in the environment around the interface between the grinding wheel and the workpiece, and in order to prevent any such material from reaching the sliding surface of the elongate rail on which the workrest slides, and for axially positioning the workrest along the rail, cover means is provided on opposite sides of the workrest to keep any such unwanted material away from the surface of the elongate support rail therebelow, and prevent lateral movement of the workrest from its selected position.
The workrest and the cover means preferably form a linear bearing with the rail.
Preferably the rail is made up of two spaced apart parallel rails.
According to a preferred feature of the invention, each of the covers forming the cover means is rigid and structural and either adjustable in length or available in different lengths to enable differently sized gaps measured parallel to the axis of the workpiece to be covered by the covers, depending on the desired position of the workrest.
The covers may be clamped in an axial sense so as to clamp between them the workrest and position the latter along the workpiece axis.
Where the sealing between the workrest and the cover means is insufficiently reliable to prevent the Penetration of fine particle material and fluid, telescoping covers may be provided below the rigid cover means which are sealed at least to the opposite sides of the workrest and either extend sufficiently far axially along the length of the elongate rail to prevent the ingress of unwanted particulate or fluid material, or are sealed at their opposite ends to end faces of support members between which the elongate rail extends, thereby forming a sealed enclosure within which the elongate rail is protected. The telescoping nature of the inner covers enables the workrest to be moved axially for adjusting its position along the rail relative to the workpiece.
The telescoping inner covers may be in the form of bellows which can extend or contract to accommodate axial movement of the workrest along the elongate rail.
The rigid covers are conveniently in the form of spacers and may be tubular so as to wholly encompass the elongate member, or C-shaped in cross-section to permit their insertion over and removal from the elongate rail as required.
Typically a plurality of cover spacers are provided which fit between, the workrest and appropriate. surfaces extending perpendicularly to the elongate workrest support rail, so that when fitted between the said surfaces and the workrest, the latter is held rigidly and fixedly at a single axial position along the support rail and therefore in axial fixed relationship to the workpiece axis, so that the workrest will always align with a similar region of each workpiece which is mounted between the headstock and tailstock centres on the said workpiece axis.
Typically the alignment is such as to correspond with a cylindrical region of the workpiece near the mid-position of the length of the workpiece measured between the two centres.
The invention is not limited to a single workrest but envisages the mounting of two or more workrests along the said elongate support rail for positioning against other cylindrical regions of a composite workpiece as aforesaid, such that as the said other cylindrical regions are ground they can be engaged by a workrest to resist sideways deformation of the workpiece as the grinding wheel is forced against diametrically opposite regions of the workpiece to grind the particular regions thereof.
Where a composite workpiece includes for example three spaced apart cylindrical regions which are to form the inner surfaces of journal bearings, three workrests are typically provided and in this event four rigid covers are provided each of an axial extent sufficient to just space the two outer workrests accurately relative to the central workrest, and the two outer workrests from fixed end faces at opposite ends of the elongate support rail on which the workrests slide.
Alternatively three such rigid covers may be provided for spacing the first of the workrests accurately relative to the headstock end of the workpiece, the second workrest relative to the said first workrest, and the third workrest relative to the second middle workrest, and clamping means is provided to retain the third workrest axially in position along the elongate rail and to maintain the assembly of spacing covers and workrests between a face of the headstock (or a fixture at the headstock end of the elongate rail), and the said clamping means.
In addition or alternatively to the spacing achieved by means of the said rigid covers, the workrests may include clamping means, grub screws, wing nuts or other devices for securing each workrest at a desired position along the length of the elongate rail. However the spacing achieved by individual accurately machined spacers each forming a cover for providing at least partial protection for the elongate rail, may be preferred, since this does not involve the need for individual clamping or tightening mechanisms which could damage the surface of the rail.
Preferably axial force is applied to the horizontal stack of workrest(s) and spacers by means of a thrust member acting through the tailstock so as to
Laycock Michael
Locker Ian David
Eley Timothy V.
Grant Alvin J
Lee Mann Smith McWilliams Sweeney & Ohlson
UNOVA U.K. Limited
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