CA2261063C - Improvements relating to grinding methods and apparatus - Google Patents
Improvements relating to grinding methods and apparatus Download PDFInfo
- Publication number
- CA2261063C CA2261063C CA002261063A CA2261063A CA2261063C CA 2261063 C CA2261063 C CA 2261063C CA 002261063 A CA002261063 A CA 002261063A CA 2261063 A CA2261063 A CA 2261063A CA 2261063 C CA2261063 C CA 2261063C
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- Prior art keywords
- grinding
- wheel
- workpiece
- plunge
- region
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B5/00—Machines or devices designed for grinding surfaces of revolution on work, including those which also grind adjacent plane surfaces; Accessories therefor
- B24B5/02—Machines or devices designed for grinding surfaces of revolution on work, including those which also grind adjacent plane surfaces; Accessories therefor involving centres or chucks for holding work
- B24B5/04—Machines or devices designed for grinding surfaces of revolution on work, including those which also grind adjacent plane surfaces; Accessories therefor involving centres or chucks for holding work for grinding cylindrical surfaces externally
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B1/00—Processes of grinding or polishing; Use of auxiliary equipment in connection with such processes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B17/00—Special adaptations of machines or devices for grinding controlled by patterns, drawings, magnetic tapes or the like; Accessories therefor
- B24B17/10—Special adaptations of machines or devices for grinding controlled by patterns, drawings, magnetic tapes or the like; Accessories therefor involving electrical transmission means only, e.g. controlled by magnetic tape
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B27/00—Other grinding machines or devices
- B24B27/0076—Other grinding machines or devices grinding machines comprising two or more grinding tools
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B5/00—Machines or devices designed for grinding surfaces of revolution on work, including those which also grind adjacent plane surfaces; Accessories therefor
- B24B5/01—Machines or devices designed for grinding surfaces of revolution on work, including those which also grind adjacent plane surfaces; Accessories therefor for combined grinding of surfaces of revolution and of adjacent plane surfaces on work
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B5/00—Machines or devices designed for grinding surfaces of revolution on work, including those which also grind adjacent plane surfaces; Accessories therefor
- B24B5/36—Single-purpose machines or devices
- B24B5/42—Single-purpose machines or devices for grinding crankshafts or crankpins
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B51/00—Arrangements for automatic control of a series of individual steps in grinding a workpiece
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Grinding Of Cylindrical And Plane Surfaces (AREA)
- Constituent Portions Of Griding Lathes, Driving, Sensing And Control (AREA)
Abstract
The time to grind a workpiece can be reduced by selecting a grinding wheel whose width is not substantially greater than wheel strength considerations require, and which may therefore be less than the axial length of the region to be ground providing a work rest or work steady to increase the workpiece stiffness if required, and performing a succession of plunge grinding steps so as to grind the whole of the said axial region. Typically the grinding wheel is an electroplated CBN wheel, and the width of the grinding wheel selected is the narrowest permissible given the desired feed rate and motive power available. A grinding machine is disclosed comprising a wheelhead having mounted thereon a grinding wheel whose width is not substantially greater than that dictated by structural and strength requirements, programmable indexing 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 a region of the workpiece to be ground, the axial extent of which is greater than the width of the wheel, and wheel feed means and control means by which the feed rate is controlled, whereby the wheel feed rate is similarly programmable to enable a feed rate to be achieved which is 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.
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.
Description
Improvements relating to grinding methods and apparatus 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 (i.e. the time from the initial engagement of the wheel and the workpiece to final disengagement after the region has been ground 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 In accordance with one aspect of the present invention there is provided 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, la mounted on a wheelhead, comprising the steps of programming wheelhead and 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 data stores associated with the control system relating to maximum instantaneous and RMS power of the wheel spindle drive motor, and controlling the wheelfeed rate by the control system to enable a feed rat a 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.
In accordance with another aspect of the present invention there is provided a grinding machine comprising a single wheelhead having mounted thereon a grinding wheel whose width is not substantially greater than that dictated by structural and strength requirements, programmable indexing 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 a region of the workpiece to be ground, the axial extent of which is greater that the width of the wheel, wheelfeed means, control means by which the feed rate is controlled, and wherein the wheelfeed rate is programmable to enable a feed rate to be 1b selected dependent on the peak and RMS power capabilities of the wheel drive, 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.
In accordance with yet another aspect of the present invention there is provided a grinding machine comprising two narrow grinding wheels mounted on separate shafts for independent movement towards and away from a workpiece, for plunge grinding axially separated regions of a cylindrical portion of the workpiece, and means for adjusting each wheel in an axial direction, whereby the machine can grind a range of axial lengths up to a length not exceeding the sum of the two wheel widths.
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 workpieceT
stiffness and performing a succession of two or mare 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 ca~ 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 Dositions of the wheelhead and workpiece to be adjus4ed 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 cf the wheel, programming a computer based machine control system to generate control signals for controlling the rate of wheel feed during grinding dependent on feedback signals during grinding, and entering data into dat stores associated with the control system relating ~o maximum instantaneous and RMS power o. the wheel spin-dl a drive motor, and controlling the wheel feed rate by tre control system to enable a feed rate to be achieved limited only by the peak ar_d 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 cr 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 perfo~-_ned usi r_g the same wheel.
The invention also lies in methods as aforesaid wherein the plunge grinds are performed usir_g 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 capabili ty 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 anothe-_- aspect therefore of the invention, a method of grinding ~ r=gio-: 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 centraliv over the unground sections.
Where two additional plunge grinds 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 uniTorm 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 wav.
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 substar_tially 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 reaicr. to be grownd, at least ona of she additional plunge grinds required to grind the =whole of the said region is performed by a second grin-ding wheel also selected as aforesaid.
S
This said further aspect of the invention is of particularT
application to the grinding of workpiece regions which have an annular shoulder at at least one end, and which require one or more annular prcfiles 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 using 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 raauired, for example one at each end of the said regicn, 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 f i rst and second wheels, grinding the further material by one or :ore plunge grinds using one or more plain grinding ;wheels. By "plain" is meant a cylindrical grinding wheel which is rotated about an axis which is coaxial with the axis of the cyiindrica? grinding surface and the latter when viewed tangentially appears flat and plain (ie it possesses the same diameter across the whole width of the cylindrical grinding surf ace).
A particularly preferred aspect o. the invention is one in which two undercuts are to be formed adjacent two annular shoulder at opposite ends of a c~rlindrical region and according to this aspect of the inventicn a first grinding caheel having an appropriate formed grinding surface is engaged with one end of the said region so as to grind the undercut and surface grind part of the acjacent cylindrical surface and a second grinding wheel is employed to grind the other undercut and the remainder of the cylindrical surface between the two undercuts.
The two wheels may have the same or different widths but in either event the total width expressed as the sum of the two widths, should be not less than the total width between the shoulders.
Preferably the sum of the two wheel widths is just greater than the axial spacing between the two shoulders.
where the workpiece compri ses a crankshaft and the region being ground is a crankpin, typical dimensions are such that the cycle time can be significantly reduced by using two such wheels, since the axial extent of the pin regions of the cranks is such that the sum of the widths of two relatively narrow wheels will still be greater than the axial extent of the pin.
Where full optimisation recxuires narrower wheels to be used (and such wheels are still strong enough to be used), this can result in an axial region being left in the middle of the pin, which then has to be removed by plunge grinding using one or more plain grinding wheels, bu~ the overall cycle time may still be significantly less than. that if a single formed wheel is used albeit at reduced feed rates to accommodate the power capabilities of the given grinding machine.
It may be advantageous to use one or more minimum width grinding wheels and multiple plunge grinds to grind the whole of the cylindrical surface between the shoulders as a first operation and to use a single wide profiled grinding wheel to grind the two undercuts as a second operation, the diameter of the wide grinding wheel being such that its surface between the two annular profiles which will grind the undercuts, makes no contact with the ground surf ace be tween the undercoats ( or is merely used to polish the grc and surface during spark-out as the grinding of the t4TC undercuts is completed and this intermediate cylindrical sun=ace just makes grazing contact with the previously ground surf ace between the two undercuts.
In the first said operation the width of the material being ground is limited by the minimum width of the grinding wheel but the cycle time can be optimised using multiple plunge grinds with high metal removal rates without exceeding the power capability of the grindi~ g machine. During the second operation in which the ur_dercuts are ground, the actual width of grinding raheel which is in contact with the workpiece is limited to the width of the two undercuts, the rest of the wheel merely serving as a structural support for these two narrow annular profiles around the wheel. As a consequence, since the intermediate region of the profiled wheel is not performing any grinding, the affective width of the wheel is now the sum cT the widths of the tcvo annular profiles producing the undercuts and again high metal removal rates can be achieved without overloading the power capabilities of the machine.
Where two or more grinding wheels are required to plunge grind and finish a given region, the wheels may be introduced one after the other into the region, or may be located at different positions along a grinding machine bed and the workpiece is indexed so as to present the region to each of the different wheels at different times. The indexing is preferably controlled so as to present appropriate parts of each region to appropriate grinding wheels.
It is often desirable to enable a single grinding machine to be modified so as to grind difT~rent worknieces. In the case of cranksharts, different crankshafts will typically have different diameters and axial Lengths of crankpins and where methods according to the invention are employed, the use of a single prof ~ led wheel to produce two undercuts, one at each end of each crankpin, will require a different formed wheel to be substituted to allow different crankshafts to be grcund.
According to a further preferred aspect of the invention, two profiled grinding wheels may be used in place of a single profiled wheel, each of which includes a cylindrical surface (which may or may not be used in the grinding process to remove metal) and an annular region of greater diameter (referred to as an annular profile), which is intended to engage the ground cylindrical surface and form the undercut therein. By selecting the narrowest possible width wheels and mounting the wheels on a common shaft, so all the benefits of the aforementioned method can be achieved and alteration of the axial spacing betwean the undercuts is achieved by simply altering the spacing beyweer_ the two wheels mounted on the shaft .
In an alternative and preferred arrangement, the wheels are mounted on separate shafts (which may or may not be driven by the same motor), and one or both of the two shafts are adjustable in position so that the axial spacing between the two wheels can be altered, thereby adjusting the distance between the two undercsts to be formed by the two wheels.
Where the wheels are mounted on separate shafts, these may be positioned such as to enable both wheels to simultaneously plunge grind the two undercuts, but it may be more advantageous to locate the two wheels on different wheelheads and index the workpiece ( or the whee l head assembly ) so as to grind with first one and then the other of the two profiled grinding wheels.
where only two grinding wheels are to be employed, and a range of adjustment of the spacing between annular profiles is to be optimised provided for and ideally made as large as possible, it is probable that both of the wheels should have the same width. The minimum spacing between the two profiles is then equal to the width of one Y~hesl and the ma~:imum spacing is eaual to the sum of t':e widths of the two wheels, ie a range of 2:1.
The invention also lies in apparatus for performing the T
aforementioned methods.
In one embodiment, a grinding machine includes a single wheelhead having mounted thereon a grinding wheel whose width is not substantially greater than that dictated by structural and strength requirements, and programmable indexing means is provided to enable the relative positions of the wheelhead and workpieca to be adjusted in a sequenca of steps to achieve a sequence of plunge grinds; which may or may not overlap, to enable a region of the workpiece to be ground, the axial extent of which is greater than the width of the wheel, and the wheelfeed means is controlled by feed rate control means, wherein the wheel feed rate is programmable to enable the feed rate to be i ncreased up to the maximum permitted given the peak and RMS power capabilities of the wheel spindle drive, 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.
The grinding machine aforesaid may further comprise means for gauging the diameter of the workpiece during, or after, grinding and mear_s for gEnerating an electrical signal indicative of the diameter fo= supply to the computer based control system.
The invention also provides a machine as aforesaid when programmed so as to achieve the said optimal cycle time.
The wheelfeed programming capability preferably includes adjustable but essentially preset parameters such as maximum motor poorer ar_d RMS motor cc~ner, end other parameters such as grinding wheel materi~i, workpiece material and workpiece condition (is currer_~ wheel diameter) can be inserted by the operator.
Workpiece condition can be r~~antained and the process further optimised by sensing the wheel diameter (which reduces as the wheel becomes worn), and adjusting not only wheelfeed but also wheelfeed rate to take acccunt of the increasingly smaller diameter as the wheel becomes worn. The invention envisages a machine as aforesaid when fitted with wheel diameter sensing means and feedback control means for adjusting the wheel feed are wheel feed rate accordingly.
Since rate of cooling achieved by coolant may also be an important factor, a signal may also be generated for and means provided, responsive thereto for controlling the coolant fluid pump so that the latter is operated at an appropriate level as called for by the exnect2d material removal rate. Where the overall power for a machine is governed by the combination of coolant Tluid pump and wheelhead power, the computation of the wheelfeed rate preferably includes taking into account the power required for the coolant pump.
In another embodiment of the invention, the grinding machine includes two narrow gr i nding wheels mounted on a single spindle for simultaneous engagement with a workpiece to perform plunge grinds at accurately spaced apart positions on a workpiece.
According to a further aspect of the invention the grinding machine includes two narrow wheels mounted on separate spindles, each of which is mounted for independent movement towards and away from a workpiece.
The two wheels may be mounted at a fixed spacing relative to each other, o~ may be adjustable in position so that the spacing between the wheels (peas ured generally parallel to the workpiecJ axis) can be adjusted.
Adjustment of the axial spacing may be during set-up to allow for different axially spaced regions of a workpiece to be addressed or may b~ such as to permit traverse grinding, and/or ' ndexi ng, to permi t a secuance of plunge grinds to grind a surface.
The invention also lies in apparatus for grinding comprising a first grinding wheel having a profiled grinding surface, wheel dressing means associated therewith for dressing the grinding wheel as required to maintain the profile thereon, means for advancing and retracting the first grinding wheel towards and away from a workpiece so as to fo?~n an annular profile in the grinding surface and optionally to sur=ace grind at least an adjacent region of the ~eorkpiece surface, a second grinding wheel mounted independently of the first grinding wheel and adapted to be brought into engagement with the workpiec~ to grind an adjacent region of the workpiece surface within which the profile has beer_ formed by one or more plunge grinds.
The second grinding wheel may also include wheel dressing means.
Where a second profile l s to be formed in the workpiece surface a fixed distance from the first profile and the distance between the profiles is no greater than the combined widths of the two wheels, the szcond grinding wheel may also include a profiled grinding surf ace so as to form the second desired annular profile in the workpiece surface during grinding thereof by the second grinding wheel. 3y providing for independent movement of the two grinding wheels, so first one and then the other may be brought into grinding contact with the workpiece so that the full machine power is available for each of the two plunge grinding steps, thus enabling a high rate of material removal to be achieved.
Where tha axial extent of the workpiece surface which is to be ground is greater than ti:e sum of the two grinding wheel widths, the second grinding wn~el may be indexed so as to perform a sequence of plunge grinds assuming that it is not profiled. Where the second wheel is also profiled, the two extreme plunge grinds may be performed leaving an intermediate region to be removed by a third plain grinding wheel which may be operated so as to perform a single plunge grind or a sequence of plunge grinds so as to remove the said intermediate region.
Wherever possible the width of each grinding wheel is selected so as to be as close as possible to the minimum permitted given strength and rigidity considerations and wheel feed is adjusted so as to therebv optimise the tower available within the machine for grinding and obtain the maximum rate of material removal for the power and grinding medium available.
The invention will now be desc=ibed, by way of example, with reference to the accompanying drawings, in which:
Figure 1 shows a conventional plunge grind using a wide wheel;
Figure 2 shows how a sequer_ce of plunge grinds using a narrow wheel can remove material over the same axial extent as the wider wheel and under some circumstances obtain a faster grinding time;
Figure 3 shows a conventional twin profiled grinding wheel for grinding a workpiece in a plunge grind mode as shown;
Figure a shows has two narrower profiled grinding wheels can be used in accordance with the invention to grind the same region as the twin profiled wheel of Figure 3, and ur_der some circumstances achieve a higher grinding speed;
Figures5~, and C show how three different grinding wheels B
each to al 1 oc~ opti:ra ~ material removal plunge sel per ected given fixed power capability of the machine, can be used a to grind similar greater a region to tha=
shown in Figure but of axial than is possible using two profiled grinding extent wheels such in~Figure as Figure 6 is a perspective view of a computer controlled grinding machine fitted with two independently controllable narrow gauge grinding wheels; and Figure 7 is a control system functionality listing showing the data inputs and programme decisi ons required to achieve optimal material removal per plunge grind.
Detailed description of drawings Figure 1 shows a conventional plunge grinding technique. Here a grinding wheel IO is shown aligned with the region 12 of a workpiece 14 which has beer_ ground by plunging the wheel 10 into the workpiece 14 in she direction of the arrow 16 by a distance equal to the change in radius as between the larger diameter 14 and the smaller diameter 12.
If the axial distance between the shoulders at opposite ends of the reduced diameter region 12 is L, then it has hitherto generally been assumed that the minimum time for grinding is obtained by selecting a single grinding wheel of width L and performing a single plunge grind.
If unlimited power and infinite workpiece stiffness workpiece and machine supports etc can b~ assumed, then this co nventional approach would produce the mir~=mum grinding time. However it has been discovered that increasing the wheel width requires disproportionately greater increases in power to match the material removable capabilities of narrower wheels using the same grinding material, an d if unlimited power is not available, and in particular iT the RMS power requirement is significantly limited, the feed rate achievable, (ie the rate at which the wheel 10 is advanced ir_ the direction of arrow 16 ) reduces significantly as the ~r::eel width increases. Whilst a greater axial length of wo rkoiece is addressed by a wider wheel, the volume of ~:aterial removed per second can in fact 1~
be less than if the same power is available to drive a narrowerT
wheel.
Figure 2 illustrates the principle of the invention. Here the grinding wheel 10 is replaced by a narrower grinding wheel 18 the thickness of which is approximately one third that of the wheel 10. A single plunge grind of the wheel 18 will produce a reduced diameter section 20 which if the feed in the direction of arrow 22 in Figure 2 is the same as the distance through which wheel 10 i s moved, wi 11 result in the same final diameter for the region 20 Gs is the diameter of region 12.
In accordance with the i nvention, the wheel 18 is now retracted in the opposite direction of arrow 22 and either the wheel or the workpiece indexed (or both) so as to present another region of the workpiece 14 for grinding, after which a second plunge grind is performed so as to remove one or other of the regions denoted in dotted outlir_e at 2~ and 26.
Subsequent indexing allows the remaining region to be removed by a third plunge grind.
In order to obtain more uniform wheel wear, regions such as 26 are preferably plunge ground before region such as 24, so that each of the flat surfaces of the wheel 18 is subjected to the same number of interactions with unground material as is the other.
In order to ensure full removal of material, the actual thickness of the wheel 18 should be just greater than one third of the distance L.
By aligr_ing the left hard edge of the wheel 18 with the left hand end position of ~he region 20 which is to be ground, the first plunge grind twill remove just over one third of the distance L. By then aligning the right hand edge of the wheel 18 a distance L from the shoulder formed by the first plunge grind, a second plunge grind will remove material from the opposite end of the region 20 over a distance equal to just over one third of the length L measured from the right hand shoulder. This leaves an annular upstand in the middle which is somewhat less than one third L in axial extent and is equidistant from each of the two shoulders at opposite ends of the region 20. This annulus of unwanted material can then be removed by a single plunge grind by centering it and the wheel 18 and performing the third plunge grind.
If one of the ends of the region 20 is to be formed with an annular profile such as an undercut, then a second wheel (not shown) may be used to perform the plunge grind in the region in which the undercut is required, but the other region or regions in which an undercut is not required can be removed using a plain grindir_g wheel such as that shown at 18 in Figure 2.
Where two undercuts are required such as at opposite ends of a crankpin such as shown in Figure 3, it has been cor_ventional to employ a twin profiled grinding wheel such as shown at 28 in Figure 3. A wheel dressing device (not shown) is provided to produce and regularly maintain/reinstate the external peripheral profile oz the wheel 28, and a single plunge grind will result in a ground region in the workpiece 14 made up of a cylindrical pin surface 30 having a diameter less than the diameter of the adjoining regions of the workpiece 14, with two undercuts 32 and 3~, one at each end between the reduced diameter pin 30 and the shoulders 36 and 38. With use, the profile 40 and 42 on the gri~ding wheel 28 w:~ich produce the undercuts 32 and 34 become =corn and it is necessary in practice to frequently re-shape the wheel 28 so as to ensure that the correct depth of undercut is achieved.
Figure 4 shows how the region 30 of Figure 3 can be ground in accordance with the invention using two narrower grinding wheels 44 and 46 each cor_taining an edge profile 48 and 50 respectively for grinding an undercut. The method involves plunge grinding using the first grinding wheel 44 so as to grind the first half of a reduced diameter section 54 of the workpiece 52, with an undercut 56. The wheel 44 is then withdrawn and by appropriate relative movement, the second wheel 46 is aligned with the other part of the region to be ground. Using a second plunge grind, the region shown in dotted outline is now ground so as to complete the grinding of the region 54, with a second undercut at 58 . The wi dth of each of the two grinding wheels 44 and 46 (including the profiled region 48 and 50 in each case), is just a little in excess of 500 of the axial distance between the two shoulders or cheeks left after grinding, namely 50 ar_d 62. By ensuring that the sum of the two wheel widths is just greater than this dimension, there is little risk of any unground material being left after the second plunge grind by the wheel 46.
In f act the two wheels 44 and 46 can be used to grind any region similar to 54 in which the distar_ce between the two shoulders 60 and 62 can be anything between the width of the wider of the two wheels 44 and 46 up to the sum of the widths of the two grinding wheels. In this regard it will be seen that overlapping the two plain sections of the grinding wheels should not produce any additional unwanted grinding provided the two grinding wheels are advanced by the appropriate amount in each case.
If a general purpose machine is to be provided the twc grinding wheels 44 and 46 should both be of the same width since this will give the greatest range of dimensions between shoulders 60 and 62.
Using two such wheels as l n 5'=gure 4 may not allow ultimate optimisation of the grinding process, but where the same grinding material is utilised in the two wheels as is used on the single wheel of ~igura .:, the workpiece is of similar material, the same reduction in diameter and same axial extent 1i of the workpiece is to be ground, a significant saving in cycle time has been obtained using two wheels to grind, as in Figure 4, instead of a single wheel 28 as in Figure 3, when using the same grinding machine and operating the latter at its maximum peak/and RMS power capability during each grinding process.
What has been found is that the narrower the wheel such as 44 and 46, the higher is the rate at which the wheel car. be fed forward during the plunge grind mode. If the axial length of the region to be ground is such that half the axial length produces a relatively thick grinding wheel an advantage may be gained by adopting a method and technique such as shown in Figure 5. This permits the narrowest possible wheels to be utilised taking into consid~ratior- rigidity and wheel strength as well as power capability. For simplicity the same reference numerals have been used to describe the grinding wheels described in relation. to Figure 4 and the workpiece is likewise identified by reference numeral 52.
In the Figure 5 arrangement, a plunge grind using wheel 44 forms the shoulder 60 and the first region 54 with an undercut 56. Retraction and indexing (see Figure 5B) allows the second grinding wheel 46 to plunge gr~.rd the second shoulder 62, and a second part of the reduced diameter region 54 which in Figure 5B is denoted by 55. '"he edge profile on wheel 46 produces the second undercut 58. ''='he difference between the Figure 4 and Figure 5 arrangements is that after the second plunge grind there exists an annulzr region 64 between the two regions 54 and 55, the outside dl ameter cf which is commensurate with that of the wo=kpiece 52.
If no further undercuts are required, neither of the wheels 44 and 46 can be used to remove this regior_.
To this end a third grinding .rheel 66 is provided and after appropriate indexing (see rFigure 5(c)) to bring the workpiece region 6~ into registry with the third wheel 66 (either by moving the workpiece relative to the wheel or the wheel relative to the workpiece, or both) , the unwanted region 64 can be removed by plunge grinding using the third wheel 66. If the width of the latter is large enough a single plunge grind suitably located relative to the workpiece will remove the annulus of unwanted material 64. If as shown, the region 64 is of greater axial extent than the thickness of the wheel 66, two or more plunge grinds will be required. To even out wear on the wheel 66, the latter is preferably introduced in a given sequence which may have to be changed frcm one workpiece to the next. Thus for example the wheel 55 may be introduced at the left hand end of the region 64 first of all, and then the right hand end and then if any ~:aterial still remains to be removed, it can be brought in cer_trallv.
If the axial length o-~ the region 64 is excessive, so that four or five or even more plunge grinds are required, these are preferably arranged so that an equal number involve one side and an equal number the other side of the wheel 66 so as to create a uniform wear pattern.
The invention is of particular application to grinding using CBN electroplated wheels. The grinding capability of such wheels has not been taken fuel advantage of hitherto. The wheel manufacturers specify a maximum material removal rate and it has been found that rarely is this rate achieved during grinding. In particular the motor power, particularly the RMS
power of the motor driving the grinding wheel, limits the rate at which the wheel can be advanced and material removed. The RMS power capability of a motor is a measure of the continuous power requirements for the whole cycle and if the motor RMS
power specification is exceeded the motor will overheat.
Fcr electroplated wheels, the aheei specification is referred to in terms of specific metal ramoval rate (SMRR) and this is defined as the volume of meal removed per second, per millimetre wheat width, ar_c~ for-:es the basis for grinding power calculations. wheel manufacturers suggest that the maximum SMRR for electroplate CBN wheels is 360mm3/mm.s when grinding cast iron and using neat oil as a coolant. However it is often the case that motor power limitations have limited wheel feed rates so that actually grinding is in the range 30 to 66mm3/mm.s. By incorporating the techniques proposed by the invention, much higher grinding rates than the 30 to 60 rate quoted above can be achieved which enables feed times to be greatly reduced. By reducing the width of the wheel, more plunges are required but the additional time required for indexing to present the wheel to different regions of, or different wheels to the workpiece, can be more than offset by the much shorter grinding times required for each plunge grind step.
As one example let us consider a four cylinder crankshaft in which the pins have to be ground from 50mm to 40mm, and the pins are each 23mm wide. A work speed of 30rpm has been assumed. The motor power specification is assumed to be 50 kilowatts maximum peak power and 30 kilowatts maximum RMS
power.
Using a 23mr~ wide wheel, ar_d a single plunge method, the specific metal removal rate can be found to be 36. 9mm3/mm. s (from a graph of SMRR vs specific power). Grinding time for the four pins is therefore 4xI?~ which equals 56 seconds. The time with the spindle running/coolant on is 5.1 seconds.
However .o remain withir. the RMS power requirements of the motor, the feed rate has been reduced dramatically and the cycle tree has to be ar least X31.2 seconds.
Using two 12mm wide wheels and two separate plunge grinds the specific metal removal rate for each wheel of 110 . 7 mm3/mm. s is permissible (from the same graph or SMRR vs specific power).
The total grinding time 's now 4 x 2 x 6 which equals 48 seconds and the time with the spindle running and coolant is 10.1 seconds.
However ir_ view of the lower RMS power requirements, the feed rate can be increased and the cycle time is now reduced to 63.3 seconds for the same maximum RMS power requirement.
It will be seen therefore that the cycle time has been approximately halved using a two-plunge method and the majority of the time saving can be attributed to the reduction in RMS
power requirement sincs the higher feed rate during each plunge disproportionately coripensates for the need to perform two plunges, and there no increase in cycle time to accommodate the lower RMS power capability.
Figure 6 shows a grind? ng machine 68 having t~no gri nding wheels 70, 72 driven by motors 7s, 76 and mounted on wheelheads 78, 80 for movement towards and away from a workpiece 82 along linear tracks 8Q, 86 under the control of wheelfeed drive motors 88, 90. The workpiece is mounted between centres in a tailstock 92 and a headstock 94 which also houses a motor (not shown) for rotating the workpiece 82 via a chuck 96, the workpiece shown is a crankshaft of an internal combustion engine and includes offset crankpins such as 98 which are to be ground to size, each of which constitutes a cylindrical workpiece for grinding.
A computer 100 running a programme to be described, controls the operation of the machine and inter alia moves the wheelheads 78, 80 towards and array from the workpiece 82 as the workpiecs rotates, so as to maintain contact between the wheel and the crankpin being grcund, as the latter rotates circularly around the axis of t~:e workpiece centres.
A gauge, not shown, may be carried by the wheelhead assembly for in-process gauging the diameter oz the crankpin as it is ground.
At 102 is mounted a hydraulically or pneumatically operated T
worksteady having a base 104 and movable cantilever arm 106 adapted at the right hand end as shown to engage a cylindrical journal bearing region of the crankshaft workpiece 82.
Controlling signals for advancing and retracting 106 are derived from the comz~uter 100.
At 108 and 110 are mounted two :vheel diameter sensing gauges, signals from which are supplied back to the computer 100.
In Figure 7 the workpiece is described diagrammatically at 110, mounted between footstock 112 and headstock 114 which is driven by workdrive motor 115. uhe workpiece is engaged by a grinding wheel 118 carried by a wheelhead 120 which is moved towards and away from the workpiece 110 by feed motor 122. The grinding wheel is rotated by a spindly drive motor 124.
Input data which is entered by an operator is shown on the left hand side of the diagram.
The grinding wheel cuttir_g speed in revs/seconds is entered and stored at 126.
Grinding wheel spindle drive motor mechanism power capability is entered and stored (as a constant parameter) at 128.
Grinding wheel spindle drive motor maximum RMS power limit is entered and stored at 130. Again this will tend to be a constant parameter for the machine.
The maximum wheelfeed to be attempted per workpiece revolution, during grinding and exnress~d as a o of the theoretical maximum, is entered and stored at 132.
Details of the coolara composition are entered and stored at 134.
Details of the material from which the grinding wheel is composed are entered and stored at 136.
Details of the workt~iece material are entered and stored at 138.
The workpiece cutting speed in min/sec is entered and stored at 140 .
From 134, 136 and 138 the specific material rate during grinding in cubic mm per m-s, is computed by programme step 142 and the removal rats is supplied to programme step 144 to compute the theoretical grinding wheel feed in mm per workpiece revolution.
Step 146 adjusts this to a lesser value depending on the %
figure from 132 and using the rotational speed of the workpiece ( in revs/second) from programme step 148 the grinding wheel feed rate is computed in step ISO.
Control unit 152 serves to generate a control signal for motor 122 from the feed rate from 150.
The computed rotational speed from 148 is supplied to control unit I54 to generate a control signal for motor 146.
The grinding wheel cutting speed signal in rev/sec from 126 is converted by control unit 156 to a control signal for controlling the spindle drive motor 124, and a torque sensor (not shown) operates a feedback signal which is supplied together with the desired cutting speed in revs/second from 126, programme step IS8 which computes the power required to achieve the speed of cutting and the RMS power being consumed.
The instantaneous and F.MS power values are compared with the stored values in 128 and 130 by programme steps 160, 162 and if either is exceeded a further reduction in feed rate per revolution is effected by programme step 146. This in turn reduces the wheelfeed rate demand from 150 which reduces the demand made on motor 122, thereby reducing the wheelhead feed rate.
The control signal for motor 15'-= is obtained from the data in 140 and the workpiece radius obtained by gauging. Where this radius information is obtained by in process gauging, it is supplied along path 164 to programme step 148 together with the workpiece cutting speed informaticn from ? 40, to modify the rotational speed control signal to be computed by stay 48. In this way workpiece rotational speed is adjusted to accommodate the changing diameter of the workpiece and the latter is ground.
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 (i.e. the time from the initial engagement of the wheel and the workpiece to final disengagement after the region has been ground 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 In accordance with one aspect of the present invention there is provided 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, la mounted on a wheelhead, comprising the steps of programming wheelhead and 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 data stores associated with the control system relating to maximum instantaneous and RMS power of the wheel spindle drive motor, and controlling the wheelfeed rate by the control system to enable a feed rat a 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.
In accordance with another aspect of the present invention there is provided a grinding machine comprising a single wheelhead having mounted thereon a grinding wheel whose width is not substantially greater than that dictated by structural and strength requirements, programmable indexing 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 a region of the workpiece to be ground, the axial extent of which is greater that the width of the wheel, wheelfeed means, control means by which the feed rate is controlled, and wherein the wheelfeed rate is programmable to enable a feed rate to be 1b selected dependent on the peak and RMS power capabilities of the wheel drive, 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.
In accordance with yet another aspect of the present invention there is provided a grinding machine comprising two narrow grinding wheels mounted on separate shafts for independent movement towards and away from a workpiece, for plunge grinding axially separated regions of a cylindrical portion of the workpiece, and means for adjusting each wheel in an axial direction, whereby the machine can grind a range of axial lengths up to a length not exceeding the sum of the two wheel widths.
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 workpieceT
stiffness and performing a succession of two or mare 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 ca~ 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 Dositions of the wheelhead and workpiece to be adjus4ed 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 cf the wheel, programming a computer based machine control system to generate control signals for controlling the rate of wheel feed during grinding dependent on feedback signals during grinding, and entering data into dat stores associated with the control system relating ~o maximum instantaneous and RMS power o. the wheel spin-dl a drive motor, and controlling the wheel feed rate by tre control system to enable a feed rate to be achieved limited only by the peak ar_d 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 cr 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 perfo~-_ned usi r_g the same wheel.
The invention also lies in methods as aforesaid wherein the plunge grinds are performed usir_g 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 capabili ty 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 anothe-_- aspect therefore of the invention, a method of grinding ~ r=gio-: 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 centraliv over the unground sections.
Where two additional plunge grinds 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 uniTorm 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 wav.
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 substar_tially 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 reaicr. to be grownd, at least ona of she additional plunge grinds required to grind the =whole of the said region is performed by a second grin-ding wheel also selected as aforesaid.
S
This said further aspect of the invention is of particularT
application to the grinding of workpiece regions which have an annular shoulder at at least one end, and which require one or more annular prcfiles 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 using 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 raauired, for example one at each end of the said regicn, 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 f i rst and second wheels, grinding the further material by one or :ore plunge grinds using one or more plain grinding ;wheels. By "plain" is meant a cylindrical grinding wheel which is rotated about an axis which is coaxial with the axis of the cyiindrica? grinding surface and the latter when viewed tangentially appears flat and plain (ie it possesses the same diameter across the whole width of the cylindrical grinding surf ace).
A particularly preferred aspect o. the invention is one in which two undercuts are to be formed adjacent two annular shoulder at opposite ends of a c~rlindrical region and according to this aspect of the inventicn a first grinding caheel having an appropriate formed grinding surface is engaged with one end of the said region so as to grind the undercut and surface grind part of the acjacent cylindrical surface and a second grinding wheel is employed to grind the other undercut and the remainder of the cylindrical surface between the two undercuts.
The two wheels may have the same or different widths but in either event the total width expressed as the sum of the two widths, should be not less than the total width between the shoulders.
Preferably the sum of the two wheel widths is just greater than the axial spacing between the two shoulders.
where the workpiece compri ses a crankshaft and the region being ground is a crankpin, typical dimensions are such that the cycle time can be significantly reduced by using two such wheels, since the axial extent of the pin regions of the cranks is such that the sum of the widths of two relatively narrow wheels will still be greater than the axial extent of the pin.
Where full optimisation recxuires narrower wheels to be used (and such wheels are still strong enough to be used), this can result in an axial region being left in the middle of the pin, which then has to be removed by plunge grinding using one or more plain grinding wheels, bu~ the overall cycle time may still be significantly less than. that if a single formed wheel is used albeit at reduced feed rates to accommodate the power capabilities of the given grinding machine.
It may be advantageous to use one or more minimum width grinding wheels and multiple plunge grinds to grind the whole of the cylindrical surface between the shoulders as a first operation and to use a single wide profiled grinding wheel to grind the two undercuts as a second operation, the diameter of the wide grinding wheel being such that its surface between the two annular profiles which will grind the undercuts, makes no contact with the ground surf ace be tween the undercoats ( or is merely used to polish the grc and surface during spark-out as the grinding of the t4TC undercuts is completed and this intermediate cylindrical sun=ace just makes grazing contact with the previously ground surf ace between the two undercuts.
In the first said operation the width of the material being ground is limited by the minimum width of the grinding wheel but the cycle time can be optimised using multiple plunge grinds with high metal removal rates without exceeding the power capability of the grindi~ g machine. During the second operation in which the ur_dercuts are ground, the actual width of grinding raheel which is in contact with the workpiece is limited to the width of the two undercuts, the rest of the wheel merely serving as a structural support for these two narrow annular profiles around the wheel. As a consequence, since the intermediate region of the profiled wheel is not performing any grinding, the affective width of the wheel is now the sum cT the widths of the tcvo annular profiles producing the undercuts and again high metal removal rates can be achieved without overloading the power capabilities of the machine.
Where two or more grinding wheels are required to plunge grind and finish a given region, the wheels may be introduced one after the other into the region, or may be located at different positions along a grinding machine bed and the workpiece is indexed so as to present the region to each of the different wheels at different times. The indexing is preferably controlled so as to present appropriate parts of each region to appropriate grinding wheels.
It is often desirable to enable a single grinding machine to be modified so as to grind difT~rent worknieces. In the case of cranksharts, different crankshafts will typically have different diameters and axial Lengths of crankpins and where methods according to the invention are employed, the use of a single prof ~ led wheel to produce two undercuts, one at each end of each crankpin, will require a different formed wheel to be substituted to allow different crankshafts to be grcund.
According to a further preferred aspect of the invention, two profiled grinding wheels may be used in place of a single profiled wheel, each of which includes a cylindrical surface (which may or may not be used in the grinding process to remove metal) and an annular region of greater diameter (referred to as an annular profile), which is intended to engage the ground cylindrical surface and form the undercut therein. By selecting the narrowest possible width wheels and mounting the wheels on a common shaft, so all the benefits of the aforementioned method can be achieved and alteration of the axial spacing betwean the undercuts is achieved by simply altering the spacing beyweer_ the two wheels mounted on the shaft .
In an alternative and preferred arrangement, the wheels are mounted on separate shafts (which may or may not be driven by the same motor), and one or both of the two shafts are adjustable in position so that the axial spacing between the two wheels can be altered, thereby adjusting the distance between the two undercsts to be formed by the two wheels.
Where the wheels are mounted on separate shafts, these may be positioned such as to enable both wheels to simultaneously plunge grind the two undercuts, but it may be more advantageous to locate the two wheels on different wheelheads and index the workpiece ( or the whee l head assembly ) so as to grind with first one and then the other of the two profiled grinding wheels.
where only two grinding wheels are to be employed, and a range of adjustment of the spacing between annular profiles is to be optimised provided for and ideally made as large as possible, it is probable that both of the wheels should have the same width. The minimum spacing between the two profiles is then equal to the width of one Y~hesl and the ma~:imum spacing is eaual to the sum of t':e widths of the two wheels, ie a range of 2:1.
The invention also lies in apparatus for performing the T
aforementioned methods.
In one embodiment, a grinding machine includes a single wheelhead having mounted thereon a grinding wheel whose width is not substantially greater than that dictated by structural and strength requirements, and programmable indexing means is provided to enable the relative positions of the wheelhead and workpieca to be adjusted in a sequenca of steps to achieve a sequence of plunge grinds; which may or may not overlap, to enable a region of the workpiece to be ground, the axial extent of which is greater than the width of the wheel, and the wheelfeed means is controlled by feed rate control means, wherein the wheel feed rate is programmable to enable the feed rate to be i ncreased up to the maximum permitted given the peak and RMS power capabilities of the wheel spindle drive, 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.
The grinding machine aforesaid may further comprise means for gauging the diameter of the workpiece during, or after, grinding and mear_s for gEnerating an electrical signal indicative of the diameter fo= supply to the computer based control system.
The invention also provides a machine as aforesaid when programmed so as to achieve the said optimal cycle time.
The wheelfeed programming capability preferably includes adjustable but essentially preset parameters such as maximum motor poorer ar_d RMS motor cc~ner, end other parameters such as grinding wheel materi~i, workpiece material and workpiece condition (is currer_~ wheel diameter) can be inserted by the operator.
Workpiece condition can be r~~antained and the process further optimised by sensing the wheel diameter (which reduces as the wheel becomes worn), and adjusting not only wheelfeed but also wheelfeed rate to take acccunt of the increasingly smaller diameter as the wheel becomes worn. The invention envisages a machine as aforesaid when fitted with wheel diameter sensing means and feedback control means for adjusting the wheel feed are wheel feed rate accordingly.
Since rate of cooling achieved by coolant may also be an important factor, a signal may also be generated for and means provided, responsive thereto for controlling the coolant fluid pump so that the latter is operated at an appropriate level as called for by the exnect2d material removal rate. Where the overall power for a machine is governed by the combination of coolant Tluid pump and wheelhead power, the computation of the wheelfeed rate preferably includes taking into account the power required for the coolant pump.
In another embodiment of the invention, the grinding machine includes two narrow gr i nding wheels mounted on a single spindle for simultaneous engagement with a workpiece to perform plunge grinds at accurately spaced apart positions on a workpiece.
According to a further aspect of the invention the grinding machine includes two narrow wheels mounted on separate spindles, each of which is mounted for independent movement towards and away from a workpiece.
The two wheels may be mounted at a fixed spacing relative to each other, o~ may be adjustable in position so that the spacing between the wheels (peas ured generally parallel to the workpiecJ axis) can be adjusted.
Adjustment of the axial spacing may be during set-up to allow for different axially spaced regions of a workpiece to be addressed or may b~ such as to permit traverse grinding, and/or ' ndexi ng, to permi t a secuance of plunge grinds to grind a surface.
The invention also lies in apparatus for grinding comprising a first grinding wheel having a profiled grinding surface, wheel dressing means associated therewith for dressing the grinding wheel as required to maintain the profile thereon, means for advancing and retracting the first grinding wheel towards and away from a workpiece so as to fo?~n an annular profile in the grinding surface and optionally to sur=ace grind at least an adjacent region of the ~eorkpiece surface, a second grinding wheel mounted independently of the first grinding wheel and adapted to be brought into engagement with the workpiec~ to grind an adjacent region of the workpiece surface within which the profile has beer_ formed by one or more plunge grinds.
The second grinding wheel may also include wheel dressing means.
Where a second profile l s to be formed in the workpiece surface a fixed distance from the first profile and the distance between the profiles is no greater than the combined widths of the two wheels, the szcond grinding wheel may also include a profiled grinding surf ace so as to form the second desired annular profile in the workpiece surface during grinding thereof by the second grinding wheel. 3y providing for independent movement of the two grinding wheels, so first one and then the other may be brought into grinding contact with the workpiece so that the full machine power is available for each of the two plunge grinding steps, thus enabling a high rate of material removal to be achieved.
Where tha axial extent of the workpiece surface which is to be ground is greater than ti:e sum of the two grinding wheel widths, the second grinding wn~el may be indexed so as to perform a sequence of plunge grinds assuming that it is not profiled. Where the second wheel is also profiled, the two extreme plunge grinds may be performed leaving an intermediate region to be removed by a third plain grinding wheel which may be operated so as to perform a single plunge grind or a sequence of plunge grinds so as to remove the said intermediate region.
Wherever possible the width of each grinding wheel is selected so as to be as close as possible to the minimum permitted given strength and rigidity considerations and wheel feed is adjusted so as to therebv optimise the tower available within the machine for grinding and obtain the maximum rate of material removal for the power and grinding medium available.
The invention will now be desc=ibed, by way of example, with reference to the accompanying drawings, in which:
Figure 1 shows a conventional plunge grind using a wide wheel;
Figure 2 shows how a sequer_ce of plunge grinds using a narrow wheel can remove material over the same axial extent as the wider wheel and under some circumstances obtain a faster grinding time;
Figure 3 shows a conventional twin profiled grinding wheel for grinding a workpiece in a plunge grind mode as shown;
Figure a shows has two narrower profiled grinding wheels can be used in accordance with the invention to grind the same region as the twin profiled wheel of Figure 3, and ur_der some circumstances achieve a higher grinding speed;
Figures5~, and C show how three different grinding wheels B
each to al 1 oc~ opti:ra ~ material removal plunge sel per ected given fixed power capability of the machine, can be used a to grind similar greater a region to tha=
shown in Figure but of axial than is possible using two profiled grinding extent wheels such in~Figure as Figure 6 is a perspective view of a computer controlled grinding machine fitted with two independently controllable narrow gauge grinding wheels; and Figure 7 is a control system functionality listing showing the data inputs and programme decisi ons required to achieve optimal material removal per plunge grind.
Detailed description of drawings Figure 1 shows a conventional plunge grinding technique. Here a grinding wheel IO is shown aligned with the region 12 of a workpiece 14 which has beer_ ground by plunging the wheel 10 into the workpiece 14 in she direction of the arrow 16 by a distance equal to the change in radius as between the larger diameter 14 and the smaller diameter 12.
If the axial distance between the shoulders at opposite ends of the reduced diameter region 12 is L, then it has hitherto generally been assumed that the minimum time for grinding is obtained by selecting a single grinding wheel of width L and performing a single plunge grind.
If unlimited power and infinite workpiece stiffness workpiece and machine supports etc can b~ assumed, then this co nventional approach would produce the mir~=mum grinding time. However it has been discovered that increasing the wheel width requires disproportionately greater increases in power to match the material removable capabilities of narrower wheels using the same grinding material, an d if unlimited power is not available, and in particular iT the RMS power requirement is significantly limited, the feed rate achievable, (ie the rate at which the wheel 10 is advanced ir_ the direction of arrow 16 ) reduces significantly as the ~r::eel width increases. Whilst a greater axial length of wo rkoiece is addressed by a wider wheel, the volume of ~:aterial removed per second can in fact 1~
be less than if the same power is available to drive a narrowerT
wheel.
Figure 2 illustrates the principle of the invention. Here the grinding wheel 10 is replaced by a narrower grinding wheel 18 the thickness of which is approximately one third that of the wheel 10. A single plunge grind of the wheel 18 will produce a reduced diameter section 20 which if the feed in the direction of arrow 22 in Figure 2 is the same as the distance through which wheel 10 i s moved, wi 11 result in the same final diameter for the region 20 Gs is the diameter of region 12.
In accordance with the i nvention, the wheel 18 is now retracted in the opposite direction of arrow 22 and either the wheel or the workpiece indexed (or both) so as to present another region of the workpiece 14 for grinding, after which a second plunge grind is performed so as to remove one or other of the regions denoted in dotted outlir_e at 2~ and 26.
Subsequent indexing allows the remaining region to be removed by a third plunge grind.
In order to obtain more uniform wheel wear, regions such as 26 are preferably plunge ground before region such as 24, so that each of the flat surfaces of the wheel 18 is subjected to the same number of interactions with unground material as is the other.
In order to ensure full removal of material, the actual thickness of the wheel 18 should be just greater than one third of the distance L.
By aligr_ing the left hard edge of the wheel 18 with the left hand end position of ~he region 20 which is to be ground, the first plunge grind twill remove just over one third of the distance L. By then aligning the right hand edge of the wheel 18 a distance L from the shoulder formed by the first plunge grind, a second plunge grind will remove material from the opposite end of the region 20 over a distance equal to just over one third of the length L measured from the right hand shoulder. This leaves an annular upstand in the middle which is somewhat less than one third L in axial extent and is equidistant from each of the two shoulders at opposite ends of the region 20. This annulus of unwanted material can then be removed by a single plunge grind by centering it and the wheel 18 and performing the third plunge grind.
If one of the ends of the region 20 is to be formed with an annular profile such as an undercut, then a second wheel (not shown) may be used to perform the plunge grind in the region in which the undercut is required, but the other region or regions in which an undercut is not required can be removed using a plain grindir_g wheel such as that shown at 18 in Figure 2.
Where two undercuts are required such as at opposite ends of a crankpin such as shown in Figure 3, it has been cor_ventional to employ a twin profiled grinding wheel such as shown at 28 in Figure 3. A wheel dressing device (not shown) is provided to produce and regularly maintain/reinstate the external peripheral profile oz the wheel 28, and a single plunge grind will result in a ground region in the workpiece 14 made up of a cylindrical pin surface 30 having a diameter less than the diameter of the adjoining regions of the workpiece 14, with two undercuts 32 and 3~, one at each end between the reduced diameter pin 30 and the shoulders 36 and 38. With use, the profile 40 and 42 on the gri~ding wheel 28 w:~ich produce the undercuts 32 and 34 become =corn and it is necessary in practice to frequently re-shape the wheel 28 so as to ensure that the correct depth of undercut is achieved.
Figure 4 shows how the region 30 of Figure 3 can be ground in accordance with the invention using two narrower grinding wheels 44 and 46 each cor_taining an edge profile 48 and 50 respectively for grinding an undercut. The method involves plunge grinding using the first grinding wheel 44 so as to grind the first half of a reduced diameter section 54 of the workpiece 52, with an undercut 56. The wheel 44 is then withdrawn and by appropriate relative movement, the second wheel 46 is aligned with the other part of the region to be ground. Using a second plunge grind, the region shown in dotted outline is now ground so as to complete the grinding of the region 54, with a second undercut at 58 . The wi dth of each of the two grinding wheels 44 and 46 (including the profiled region 48 and 50 in each case), is just a little in excess of 500 of the axial distance between the two shoulders or cheeks left after grinding, namely 50 ar_d 62. By ensuring that the sum of the two wheel widths is just greater than this dimension, there is little risk of any unground material being left after the second plunge grind by the wheel 46.
In f act the two wheels 44 and 46 can be used to grind any region similar to 54 in which the distar_ce between the two shoulders 60 and 62 can be anything between the width of the wider of the two wheels 44 and 46 up to the sum of the widths of the two grinding wheels. In this regard it will be seen that overlapping the two plain sections of the grinding wheels should not produce any additional unwanted grinding provided the two grinding wheels are advanced by the appropriate amount in each case.
If a general purpose machine is to be provided the twc grinding wheels 44 and 46 should both be of the same width since this will give the greatest range of dimensions between shoulders 60 and 62.
Using two such wheels as l n 5'=gure 4 may not allow ultimate optimisation of the grinding process, but where the same grinding material is utilised in the two wheels as is used on the single wheel of ~igura .:, the workpiece is of similar material, the same reduction in diameter and same axial extent 1i of the workpiece is to be ground, a significant saving in cycle time has been obtained using two wheels to grind, as in Figure 4, instead of a single wheel 28 as in Figure 3, when using the same grinding machine and operating the latter at its maximum peak/and RMS power capability during each grinding process.
What has been found is that the narrower the wheel such as 44 and 46, the higher is the rate at which the wheel car. be fed forward during the plunge grind mode. If the axial length of the region to be ground is such that half the axial length produces a relatively thick grinding wheel an advantage may be gained by adopting a method and technique such as shown in Figure 5. This permits the narrowest possible wheels to be utilised taking into consid~ratior- rigidity and wheel strength as well as power capability. For simplicity the same reference numerals have been used to describe the grinding wheels described in relation. to Figure 4 and the workpiece is likewise identified by reference numeral 52.
In the Figure 5 arrangement, a plunge grind using wheel 44 forms the shoulder 60 and the first region 54 with an undercut 56. Retraction and indexing (see Figure 5B) allows the second grinding wheel 46 to plunge gr~.rd the second shoulder 62, and a second part of the reduced diameter region 54 which in Figure 5B is denoted by 55. '"he edge profile on wheel 46 produces the second undercut 58. ''='he difference between the Figure 4 and Figure 5 arrangements is that after the second plunge grind there exists an annulzr region 64 between the two regions 54 and 55, the outside dl ameter cf which is commensurate with that of the wo=kpiece 52.
If no further undercuts are required, neither of the wheels 44 and 46 can be used to remove this regior_.
To this end a third grinding .rheel 66 is provided and after appropriate indexing (see rFigure 5(c)) to bring the workpiece region 6~ into registry with the third wheel 66 (either by moving the workpiece relative to the wheel or the wheel relative to the workpiece, or both) , the unwanted region 64 can be removed by plunge grinding using the third wheel 66. If the width of the latter is large enough a single plunge grind suitably located relative to the workpiece will remove the annulus of unwanted material 64. If as shown, the region 64 is of greater axial extent than the thickness of the wheel 66, two or more plunge grinds will be required. To even out wear on the wheel 66, the latter is preferably introduced in a given sequence which may have to be changed frcm one workpiece to the next. Thus for example the wheel 55 may be introduced at the left hand end of the region 64 first of all, and then the right hand end and then if any ~:aterial still remains to be removed, it can be brought in cer_trallv.
If the axial length o-~ the region 64 is excessive, so that four or five or even more plunge grinds are required, these are preferably arranged so that an equal number involve one side and an equal number the other side of the wheel 66 so as to create a uniform wear pattern.
The invention is of particular application to grinding using CBN electroplated wheels. The grinding capability of such wheels has not been taken fuel advantage of hitherto. The wheel manufacturers specify a maximum material removal rate and it has been found that rarely is this rate achieved during grinding. In particular the motor power, particularly the RMS
power of the motor driving the grinding wheel, limits the rate at which the wheel can be advanced and material removed. The RMS power capability of a motor is a measure of the continuous power requirements for the whole cycle and if the motor RMS
power specification is exceeded the motor will overheat.
Fcr electroplated wheels, the aheei specification is referred to in terms of specific metal ramoval rate (SMRR) and this is defined as the volume of meal removed per second, per millimetre wheat width, ar_c~ for-:es the basis for grinding power calculations. wheel manufacturers suggest that the maximum SMRR for electroplate CBN wheels is 360mm3/mm.s when grinding cast iron and using neat oil as a coolant. However it is often the case that motor power limitations have limited wheel feed rates so that actually grinding is in the range 30 to 66mm3/mm.s. By incorporating the techniques proposed by the invention, much higher grinding rates than the 30 to 60 rate quoted above can be achieved which enables feed times to be greatly reduced. By reducing the width of the wheel, more plunges are required but the additional time required for indexing to present the wheel to different regions of, or different wheels to the workpiece, can be more than offset by the much shorter grinding times required for each plunge grind step.
As one example let us consider a four cylinder crankshaft in which the pins have to be ground from 50mm to 40mm, and the pins are each 23mm wide. A work speed of 30rpm has been assumed. The motor power specification is assumed to be 50 kilowatts maximum peak power and 30 kilowatts maximum RMS
power.
Using a 23mr~ wide wheel, ar_d a single plunge method, the specific metal removal rate can be found to be 36. 9mm3/mm. s (from a graph of SMRR vs specific power). Grinding time for the four pins is therefore 4xI?~ which equals 56 seconds. The time with the spindle running/coolant on is 5.1 seconds.
However .o remain withir. the RMS power requirements of the motor, the feed rate has been reduced dramatically and the cycle tree has to be ar least X31.2 seconds.
Using two 12mm wide wheels and two separate plunge grinds the specific metal removal rate for each wheel of 110 . 7 mm3/mm. s is permissible (from the same graph or SMRR vs specific power).
The total grinding time 's now 4 x 2 x 6 which equals 48 seconds and the time with the spindle running and coolant is 10.1 seconds.
However ir_ view of the lower RMS power requirements, the feed rate can be increased and the cycle time is now reduced to 63.3 seconds for the same maximum RMS power requirement.
It will be seen therefore that the cycle time has been approximately halved using a two-plunge method and the majority of the time saving can be attributed to the reduction in RMS
power requirement sincs the higher feed rate during each plunge disproportionately coripensates for the need to perform two plunges, and there no increase in cycle time to accommodate the lower RMS power capability.
Figure 6 shows a grind? ng machine 68 having t~no gri nding wheels 70, 72 driven by motors 7s, 76 and mounted on wheelheads 78, 80 for movement towards and away from a workpiece 82 along linear tracks 8Q, 86 under the control of wheelfeed drive motors 88, 90. The workpiece is mounted between centres in a tailstock 92 and a headstock 94 which also houses a motor (not shown) for rotating the workpiece 82 via a chuck 96, the workpiece shown is a crankshaft of an internal combustion engine and includes offset crankpins such as 98 which are to be ground to size, each of which constitutes a cylindrical workpiece for grinding.
A computer 100 running a programme to be described, controls the operation of the machine and inter alia moves the wheelheads 78, 80 towards and array from the workpiece 82 as the workpiecs rotates, so as to maintain contact between the wheel and the crankpin being grcund, as the latter rotates circularly around the axis of t~:e workpiece centres.
A gauge, not shown, may be carried by the wheelhead assembly for in-process gauging the diameter oz the crankpin as it is ground.
At 102 is mounted a hydraulically or pneumatically operated T
worksteady having a base 104 and movable cantilever arm 106 adapted at the right hand end as shown to engage a cylindrical journal bearing region of the crankshaft workpiece 82.
Controlling signals for advancing and retracting 106 are derived from the comz~uter 100.
At 108 and 110 are mounted two :vheel diameter sensing gauges, signals from which are supplied back to the computer 100.
In Figure 7 the workpiece is described diagrammatically at 110, mounted between footstock 112 and headstock 114 which is driven by workdrive motor 115. uhe workpiece is engaged by a grinding wheel 118 carried by a wheelhead 120 which is moved towards and away from the workpiece 110 by feed motor 122. The grinding wheel is rotated by a spindly drive motor 124.
Input data which is entered by an operator is shown on the left hand side of the diagram.
The grinding wheel cuttir_g speed in revs/seconds is entered and stored at 126.
Grinding wheel spindle drive motor mechanism power capability is entered and stored (as a constant parameter) at 128.
Grinding wheel spindle drive motor maximum RMS power limit is entered and stored at 130. Again this will tend to be a constant parameter for the machine.
The maximum wheelfeed to be attempted per workpiece revolution, during grinding and exnress~d as a o of the theoretical maximum, is entered and stored at 132.
Details of the coolara composition are entered and stored at 134.
Details of the material from which the grinding wheel is composed are entered and stored at 136.
Details of the workt~iece material are entered and stored at 138.
The workpiece cutting speed in min/sec is entered and stored at 140 .
From 134, 136 and 138 the specific material rate during grinding in cubic mm per m-s, is computed by programme step 142 and the removal rats is supplied to programme step 144 to compute the theoretical grinding wheel feed in mm per workpiece revolution.
Step 146 adjusts this to a lesser value depending on the %
figure from 132 and using the rotational speed of the workpiece ( in revs/second) from programme step 148 the grinding wheel feed rate is computed in step ISO.
Control unit 152 serves to generate a control signal for motor 122 from the feed rate from 150.
The computed rotational speed from 148 is supplied to control unit I54 to generate a control signal for motor 146.
The grinding wheel cutting speed signal in rev/sec from 126 is converted by control unit 156 to a control signal for controlling the spindle drive motor 124, and a torque sensor (not shown) operates a feedback signal which is supplied together with the desired cutting speed in revs/second from 126, programme step IS8 which computes the power required to achieve the speed of cutting and the RMS power being consumed.
The instantaneous and F.MS power values are compared with the stored values in 128 and 130 by programme steps 160, 162 and if either is exceeded a further reduction in feed rate per revolution is effected by programme step 146. This in turn reduces the wheelfeed rate demand from 150 which reduces the demand made on motor 122, thereby reducing the wheelhead feed rate.
The control signal for motor 15'-= is obtained from the data in 140 and the workpiece radius obtained by gauging. Where this radius information is obtained by in process gauging, it is supplied along path 164 to programme step 148 together with the workpiece cutting speed informaticn from ? 40, to modify the rotational speed control signal to be computed by stay 48. In this way workpiece rotational speed is adjusted to accommodate the changing diameter of the workpiece and the latter is ground.
Claims (10)
1. A method of grinding an axial region of a workpiece using a grinding wheel whose width is just greater than that dictated by structural and strength requirements, mounted on a wheelhead, comprising the steps of programming wheelhead and 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 data stores associated with the control system relating to maximum instantaneous and RMS power of the wheel spindle drive motor, and controlling the wheelfeed 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.
2. A method as claimed in claim 1, wherein the wheelfeed programming includes the steps of inputting parameters such as grinding wheel material, workpiece material, workpiece cutting speed, coolant composition, grinding wheelfeed per workpiece revolution limit, maximum instantaneous and RMS wheel spindle drive motor power, and grinding wheel cutting speed.
3. A method of grinding as claimed in claim 1 or claim 2, wherein the workpiece regions are to have an annular shoulder at at least one end, adjacent which is to be ground an annular profile, in the surface of the said region.
4. A method as claimed in claim 3, wherein two profiles are to be generated, one at each end of the said region and the grinding is performed firstly by plunge grinding one end using a first narrow formed wheel, secondly by plunge grinding the other end using a narrow formed wheel, and any further material remaining to be ground between the sections which have been ground by the first and second plunge grinds is removed by one or more plunge grinds using at least one plain grinding wheel.
5. A method as claimed in claim 3, by which two undercuts are formed adjacent two annular shoulders at opposite ends of a cylindrical region, wherein a first grinding wheel having an appropriate formed grinding surface is engaged with one end of the said region so as to grind one undercut and surface grind part of the adjacent cylindrical surface, and a second appropriate formed grinding wheel is engaged with the other end to grind the other undercut and the remainder of the cylindrical surface between the two undercuts.
6. A method as claimed in any one of claims 1 to 5, wherein the workpiece comprises a crankshaft and the region to be ground is a crankpin thereof.
7. A method as claimed in claim 3, wherein one or more minimum width grinding wheels perform a plurality of plunge grinds to grind a cylindrical surface between two shoulders in a first operation, and a profiled grinding wheel is employed to grind two undercuts as a second operation, the width of the profiled grinding wheel being not greater than the axial distance between the two shoulders and the diameter of the profiled grinding wheel being such that its surface between the two annular profiles which serve to grind the undercuts, makes no contact with the ground surface between the undercuts.
8. A method as claimed in claim 3, wherein during a first operation the width of material being ground is limited by the width of the grinding wheel but the cycle time is optimised using multiple plunge grinds with high metal removal rates, and during a second operation undercuts are ground and the actual width of grinding wheel which is in contact with the workpiece is limited to the widths of the two annular grinding profiles which form the two undercuts, the rest of the wheel serving as a structural support for the two annular profiles, whereby the effective width of the wheel during the grinding of the undercuts is the sum of the widths of the two annular profiles producing the undercuts, whereby high metal removal rates are achieved, without overloading the power capability of the machine.
9. A grinding machine comprising a single wheelhead having mounted thereon a grinding wheel whose width is just greater than that dictated by structural and strength requirements, programmable indexing 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 a region of the workpiece to be ground, the axial extent of which is greater that the width of the wheel, wheelfeed means, control means by which the feed rate is controlled, and wherein the wheelfeed rate is programmable to enable a feed rate to be selected dependent on the peak and RMS
power capabilities of the wheel drive, 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.
power capabilities of the wheel drive, 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.
10. A machine as claimed in claim 9, wherein the machine is fitted with wheel diameter sensing means and feedback control means for adjusting the wheelfeed and wheelfeed rate accordingly.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GBGB9615511.4A GB9615511D0 (en) | 1996-07-24 | 1996-07-24 | Improvements relating to grinding methods and apparatus |
| GB9615511.4 | 1996-07-24 | ||
| PCT/GB1997/001993 WO1998003303A1 (en) | 1996-07-24 | 1997-07-23 | Improvements relating to grinding methods and apparatus |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2261063A1 CA2261063A1 (en) | 1998-01-29 |
| CA2261063C true CA2261063C (en) | 2006-07-18 |
Family
ID=36694094
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002261063A Expired - Fee Related CA2261063C (en) | 1996-07-24 | 1997-07-23 | Improvements relating to grinding methods and apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2261063C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114473811B (en) * | 2022-01-24 | 2023-12-01 | 重庆松杰科技有限公司 | Shifting fork groove polishing device |
-
1997
- 1997-07-23 CA CA002261063A patent/CA2261063C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2261063A1 (en) | 1998-01-29 |
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