Abrading – Abrading process – Roll – roller – shaft – ball – or piston abrading
Reexamination Certificate
2001-04-17
2001-10-23
Hail, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Roll, roller, shaft, ball, or piston abrading
C451S051000, C451S177000, C451S242000, C451S397000, C451S407000
Reexamination Certificate
active
06306018
ABSTRACT:
FIELD OF INVENTION
This invention concerns grinding methods and machines particularly techniques and modifications by which grinding efficiency can be improved.
BACKGROUND TO THE INVENTION
Removal of metal from a workpiece to define a ground region of a given axial length and diameter can be achieved by plunge grinding using a wheel whose width is equal to the axial length of the region to be ground, or by using a narrower wheel and progressively removing the material from the workpiece by axially traversing the workpiece relative to the wheel (or vice versa), or by using the narrow wheel and performing a series of adjacent slightly overlapping plunge grinds.
All other things being equal, and providing unlimited power is available, overall cycle time (ie the time from the initial engagement of the wheel and the workpiece to final disengagement after the region has been found to size), will be least where a single wheel and single plunge is involved, although the need to regularly dress the wheel will increase the total machining time for a batch of workpieces to something in excess of the theoretical overall time.
SUMMARY OF THE INVENTION
According to one aspect of the present invention a method of optimising the grinding of a workpiece comprises the step of selecting a grinding wheel whose width is no larger than wheel strength considerations require and which may therefore be less than the axial length of the region of the ground providing a work rest or work steady if required to increase the workpiece stiffness and performing a succession of two or more plunge grinding steps so as to grind the whole of the said region.
In general it has been found that with conventional electroplated CBN grinding wheels, grinding efficiency increases as grinding wheel thickness is reduced, and structural strength of the wheel and/or workpiece stiffness will normally prevent a truly optimum solution to be obtained. However, in terms of cycle time, surprisingly, the feed rates which can be achieved within a given motive power capability when using the narrowest permissible wheel and multiple plunge grinds with axial indexing, can still be significantly less than the cycle time when using a single wheel of sufficient width to permit the whole axial extent of the region to be ground with a single plunge grind.
The invention also lies in a method of grinding an axial region of a workpiece using a grinding wheel whose width is not substantially greater than that dictated by structural and strength requirements, mounted on a wheelhead, comprising the steps of programming wheelhead and/or workpiece indexing drive means to enable the relative positions of the wheelhead and workpiece to be adjusted in a sequence of steps to achieve a sequence of plunge grinds, which may or may not overlap, to enable the said axial region of the workpiece to be ground, the axial extent of the said axial region being greater than the width of the wheel, programming a computer based machine control system to generate control signals for controlling the rate of wheelfeed during grinding dependent on feedback signals during grinding, and entering data into dat stores associated with the control system relating to maximum instantaneous and RMS power of the wheel spindle drive motor, and controlling the wheel feed rate by the control system to enable a feed rate to be achieved limited only by the peak and RMS power capabilities of the wheel spindle drive motor, so that the rate of material removal is as high as is compatible with the power capabilities of the machine during each plunge, thereby optimising the total cycle time for grinding, wherein the feedback signals enable each of the instantaneous, and RMS, wheel spindle motor power, to be calculated as grinding progresses.
The invention also lies in a method as aforesaid wherein the wheelfeed programming includes the steps of inputting parameters such as grinding wheel material, workpiece material, workpiece cutting speed, coolant composition, grinding wheel feed per workpiece revolution limit, maximum instantaneous and RMS wheel spindle drive motor power, and grinding wheel cutting speed.
The method may include the step of gauging the diameter of the workpiece during or after grinding. Information relating to the diameter may be supplied to a controlling computer and the workpiece speed of rotation may be adjusted in dependent on the gauged diameter.
The invention also lies in methods as aforesaid wherein the plunge grinds are performed using the same wheel.
The invention also lies in methods as aforesaid wherein the plunge grinds are performed using two or more wheels.
The invention generally envisages that each wheel is used in turn so that only one wheel is engaging the workpiece at any time but where power capability exists, two or more of the wheels may be engaged simultaneously.
The invention is of particular application in the grinding of workpiece regions which contain annular shoulders at one or both ends of the region, with or without an undercut or radius adjacent one, or both, shoulders.
According to another aspect therefore of the invention, a method of grinding a region between or to form shoulders comprises the step of plunge grinding adjacent one of the shoulders using a wheel whose width is less than the axial distance required there-between, indexing and plunge grinding adjacent the other shoulders with the same grinding wheel, and thereafter removing any unground material remaining between the two shoulders by performing one or more plunge grind steps with appropriate indexing.
Where a single additional plunge grind is needed to remove unground material, the indexing preferably registers the wheel centrally over the unground sections.
Where two additional plunge grids are required to remove the unground material, the indexing preferably registers the wheel so as to remove approximately equal widths of the unground material during each of the two additional plunge grinds so that uniform wheel wear can be achieved by alternating which of the two parts of the unground region is ground first by the additional plunge grinds, as between one workpiece and the next, when a succession of similar workpieces are to be ground in this way.
Where three (or more) additional plunge grinds are required, the indexing is preferably such as to present the wheel to the workpiece so that unground material makes contact with one side of the wheel substantially the same number of times in the sequence of additional plunge grinds as the other side of the wheel is presented with unground material.
According to a further aspect of the invention in a method of grinding a workpiece with a grinding wheel, selected as aforesaid and whose width is less than the axial extent of the region to be ground, at least one of the additional plunge grinds required to grind the whole of the said region is performed by a second grinding wheel also selected as aforesaid.
This said further aspect of the inventing is of particular application to the grinding of workpiece regions which have an annular shoulder at least one end, and which require one or more annular profiles such as undercuts or grooves or annular radial protrusions, to be ground in the surface of a region using appropriately formed wheel profiles.
Where a single such annular profile is to be formed it is preferably generated suing a narrow formed grinding wheel (selected as aforesaid) which grinds the annular profile and adjacent parts of said region, and the remainder of the region is ground using one or more additional grinding wheels by an appropriate number of plunge grinds.
Where two such profiles are required, for example one at each end of the said region, the grinding may be performed by plunge grinding one end using a first narrow formed wheel (selected as aforesaid), plunge grinding the other end using a second narrow formed wheel (also selected as aforesaid) and if any further material remains to be ground between those sections which have been ground by the first and second wheels, grinding the further material by on
Coverdale Stephen Roger
Laycock Michael
Hail III Joseph J.
Lee Mann Smith McWilliams Sweeney & Ohlson
McDonald Shantese
Unova U.K. Limited
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