Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-01-27
2002-06-25
Picard, Leo P. (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S175000, C700S193000, C451S005000, C451S011000
Reexamination Certificate
active
06411861
ABSTRACT:
FIELD OF INVENTION
This invention concerns methods and apparatus for grinding of workpieces to form components which include both concentric and eccentric cylindrical regions. Such a component is an internal combustion engine crankshaft which includes both concentric journal bearing regions and eccentric crankpins. The invention is applicable to any such workpiece which is to be ground to size and finish, and such workpieces will be referred to herein as composite workpieces.
BACKGROUND TO THE INVENTION
Historically workpieces of this nature have been ground on two grinding machines. A first grinding machine has been used to grind the concentric cylindrical sections and a second grinding machine has been used to grind the eccentric cylindrical sections.
In the first grinding machine the workpiece is rotated about its primary axis and each of the concentric sections are ground by moving a grinding wheel into a grinding position and removing material from the workpiece to produce a concentric cylindrical region thereon, in a conventional manner.
In the second grinding machine, two approaches have been adopted. In one approach the workpiece has been rotated about the axis of each eccentric region in turn, and conventional cylindrical grinding is employed to remove material so as to produce a cylindrical bearing surface at each eccentric region, just as if the element were a concentric cylindrical region of an overall workpiece. In the second approach, the workpiece has been rotated about its primary axis so that the eccentric regions precess eccentrically around the primary axis of rotation, as for example do the crankpins of a crankshaft when the latter is mounted in and is rotated in an engine. In this second approach the grinding wheel has been aligned with an eccentric region and then been advanced and retracted under computer control in synchronism with the precession of the eccentric region so that the grinding wheel remains in contact therewith at all times. The region is thereby ground at all positions of its precession. As each eccentric region is ground to size, the grinding wheel is withdrawn and the workpiece or grinding wheel is repositioned axially so that another eccentric region is aligned with the grinding wheel, ready for a similar grinding operation at the new location.
A process requiring two grinding machines involves considerable down-time as components are moved from one machine to another.
During any grinding operation, but particularly noticeable when grinding regions of an elongate workpiece (such as a crankshaft) which is supported for grinding at its ends, unwanted eccentricity may be introduced into the workpiece due to forces acting on the workpiece during the grinding process. This eccentricity which is termed runout tends to be more noticeable in concentrically ground cylindrical regions of the workpiece. It often appears as a consequence of stress relieving the workpiece, after grinding, and any eccentricity introduced into concentrically ground journal bearing regions a crankshaft will introduce undesirable wear in the component when mounted and rotated in use.
It is one object of the invention to reduce the machining time required to machine composite workpieces containing both concentric and eccentric regions, such as crankshafts which contain concentric Journal bearing regions and eccentric crankpins.
It is a subsidiary object of the invention to reduce unwanted eccentricity of concentrically ground cylindrical regions of a composite workpiece such as concentric cylindrical bearing regions.
It is a further object to provide a method and apparatus which will not only reduce machining time of composite workpieces but also allows eccentricity correction to be applied to both concentrically and eccentrically ground cylindrical workpiece regions such as the joined bearing regions and the workpiece of an engine crankshaft.
SUMMARY OF THE INVENTION
(a) Composite Workpiece Grinding in Accordance With the Invention
A method of grinding a composite workpiece to form a component having concentric and eccentric cylindrical regions, comprises, mounting the workpiece in a computer controlled grinding machine having a grinding wheel the advance and withdrawal of which is controllable by a program entered ito the machine controlling computer, loading a wheelfeed controlling program into the computer, positioning the grinding wheel relative to the workpiece, or the workpiece relative to the grinding wheel, so that the wheel is aligned with a first selected region of the workpiece, advancing the grinding wheel towards the selected region so as to grind the surface thereof, controlling the wheel feed so as to maintain grinding contact between the grinding wheel and the workpiece so as either to grind a concentric cylindrical region thereon or to grind an eccentric cylindrical region thereon as required, information about each selected region of the workpiece being stored in the computer memory which is addressed as appropriate so that the wheel feed can be controlled appropriately depending on whether a selected workpiece region is to be ground as a concentric or an eccentric cylindrical region.
The invention allows a workpiece having both concentric and eccentric cylindrical regions thereon to be ground on a single grinding machine without demounting the workpiece from the machine. This enables a workpiece to be left in place between centres whilst different regions therealong are ground to form cylindrical surfaces some of which are concentric with the primary axis of rotation of the workpiece, and others of which are eccentric relative thereto.
The invention is of particular application to the grinding of crankshafts which have journal bearing regions which have to be ground as cylindrical surfaces concentric with the primary axis of rotation of the crankshaft and crankpins which have to be ground as cylindrical surfaces eccentric to the primary axis of rotation.
(b) Correction For Process Induced Eccentricity
During the grinding of any workpiece, stresses and strains introduced by the grinding process particularly in unsupported regions of the workpiece, can cause a cylindrical region which is being ground to become eccentric relative to the primary workpiece axis. Whilst these eccentricities may be of minor consequence in the case of a significantly eccentric region such as a crankpin of a crankshaft, minor eccentricities in what should be concentric cylindrical surface such as a journal bearing surface of a crankshaft, will result in friction and wear in an engine in which such a crankshaft is mounted.
The invention allows for this problem to be overcome in that the control system can be programmed so as to not only distinguish between concentric and eccentric regions of a workpiece to enable the wheel feed to be controlled accordingly (so as to grind a cylindrical surface concentric with the primary axis of the workpiece or a cylindrical surface which is eccentric thereto), (ie whose axis is spaced from but parallel to the said primary axis) but is also capable of being controlled so as to introduce small advance and retract movements in the wheel feed whilst the grinding wheel is engaged in grinding a concentric cylindrical workpiece region, so as to introduce into the ground region an eccentricity in the cylindrical surface which is equal and opposite to any eccentricity which the grinding process per se introduces into the ground region, so that the two cancel out.
The invention also provides for the control system as aforesaid to be programmed to adjust the wheel feed program instructions or control signals when grinding eccentric cylindrical surfaces, so as to introduce an additional eccentricity which is equal and opposite to any stress induced eccentricity introduced into the eccentric cylindrical surface by the grinding process.
This technique of eccentricity compensation therefore may be extended to include not only the grinding of concentric cylindrical workpiece surfaces but also the grinding of eccentric cylindrical workpiece surfaces.
(c) Se
Clewes Stuart
Pickles John David
Lee Mann Smith McWilliams Sweeney & Ohlson
Picard Leo P.
Rodriguez Paul
Unova U.K. Ltd.
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