Coolant delivery system for grinding tools

An abrasive grinding wheel having an annular grinding face depending from a substantially circular body includes a tubular inner wall which defines an axial bore configured to convey coolant in a downstream direction therethrough. The inner wall is coupled to a concave body portion terminating at an inner periphery of the annular grinding face. A flange having an outer periphery disposed, in representative embodiments, within about 20 mm of the inner periphery of the grinding face, is superposed with the concave body portion, to define a fluid flow passage between the flange and the concave body portion. The fluid flow passage is in fluid communication with the axial bore and with the grinding face, so that during operable rotation of the grinding wheel, coolant flowing downstream through the bore is conveyed radially outward into the fluid flow passage for delivery to the grinding face.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to abrasive tools, and more particularly to grinding wheels and methods adapted to replace milling operations used for the removal of large quantities of material from the surface of workpieces.

2. Background Information

Components intended for complex, precision assemblies such as automobiles and other industrial products must often be manufactured to stringent quality standards, including tight dimensional tolerances and surface finish requirements. Some of the tightest standards are associated with the manufacture of vehicular components. In the initial finishing step, these components are generally machined by common processes such as fly cutting or high speed milling using milling heads having hardened ceramic inserts, such as silicon nitride, tungsten carbide or polycrystalline diamond (PCD). To help insure that the finished surface is adequately smooth and flat following machining, a multi-step approach is often used, which includes a rough pass and one or more finish passes with precision grinding tools. With new high speed machining centers, coolant is supplied at relatively high pressure and low volume through the spindle (through an axial bore) to the center of the cutting head. Because machine cutting processes are very slow, compared to grinding processes, the nature of the coolant delivery system is not critical to the effectiveness of the cutting operation.

These milling processes have been used to make vehicular engines, transmission components, pump housings, solenoid valves, power steering components and bearing and mating faces for use in automobiles and other vehicles, appliances, machines and other manufactured items. In general, machine tool cutting processes (also known as “machining” or “milling”) have been used in any application or operation where the workpiece must have a precision flat, parallel surface. In nearly all of these applications and operations, the milling process must be followed by a grinding process to reduce surface roughness to a finer level than one can achieve with a milling process.

In many operations, the workpieces have had to be further processed, such as with a cup-type face grinding wheel on a conventional grinding machine, to meet these standards. Disadvantageously, this extra grinding step, including the extra tool change and set up, tends to increase the time and expense of workpiece fabrication.

One attempt to reduce the number of discrete fabrication steps has involved equipping the milling machines with grinding wheels in lieu of milling cutters to carry out a surface grinding step in lieu of a face milling step. In this manner, it was anticipated that both the rough and finish milling operations could be eliminated in favor of one or more grinding operations, to therefore eliminate the need for extra tool changes, multiple tool setups, etc. A drawback of this approach, however, is that the relatively high pressure, centrally (i.e., spindle) fed coolant flow provided by the milling machines tends to be incompatible with grinding wheels, which typically rely on lower pressure, peripherally fed coolant flow.

A need therefore exists for an improved tool and/or method for effecting grinding operations using conventional spindle-cooled milling machines.

SUMMARY OF THE INVENTION

In one aspect of the invention, an abrasive grinding tool includes a grinding wheel having an annular grinding face depending from a substantially circular body configured for being operably engaged by a machine spindle for rotation about a central axis. The body has a tubular inner wall defining an axial bore configured to convey coolant in a downstream direction therethrough from a proximal end to a distal end. The inner wall is coupled to a concave body portion terminating at an inner periphery of the annular grinding face. A flange having an outer periphery disposed within about 20 mm of the inner periphery of the grinding face, is disposed within the concave body portion, in superposed orientation therewith, to define a fluid flow passage between the flange and the concave body portion. The fluid flow passage is in fluid communication with the axial bore and with the grinding face, so that during operable rotation of the grinding wheel, coolant flowing downstream through the bore is conveyed radially outward into the fluid flow passage for delivery to the grinding face.

In another aspect of the invention, a method for grinding a workpiece to form a flat surface, includes providing an abrasive face grinding wheel having an annular grinding face depending from a substantially circular body, the body configured for being operably engaged by a machine tool spindle, and having a tubular inner wall defining an axial bore configured to convey coolant in a downstream direction therethrough. The inner wall is coupled to a concave body portion terminating at an inner periphery of the annular grinding face. A flange having a periphery disposed within about 20 mm of the inner periphery of the grinding face is superposed within the concave body portion, so that the flange and the concave body portion define a fluid flow passage therebetween, in fluid communication with the axial bore and with the grinding face. The method further includes orienting the central axis at a predetermined angle α relative to the workpiece, rotating the grinding wheel about the central axis, and delivering coolant flow downstream through the bore, for conveyance radially outward through the fluid flow passage for delivery to the grinding face in a substantially laminar flow. The grinding wheel is then translated towards the workpiece along a tool path parallel thereto, so that the grinding face engages and removes material from the workpiece.

In yet another aspect of the invention, a grinding system includes an abrasive face grinding wheel having an annular grinding face depending from a substantially circular body. The body is configured for being operably engaged by a machine tool spindle for rotation about a central axis, and has a tubular inner wall defining an axial bore configured to convey coolant in a downstream direction therethrough. The inner wall extends to a concave body portion that terminates at an inner periphery of the annular grinding face. A flange is superposed within the concave body portion to define a fluid flow passage therebetween. A plurality of channels located within the grinding face extends radially inward of the periphery of the flange, in fluid communication with the grinding face and with the fluid flow passage. During operable rotation of the grinding wheel, coolant flowing downstream through the bore is conveyed radially outward into the fluid flow passage and into the channels for delivery to the grinding face.

In still another aspect of the invention, a method for grinding a workpiece to form a flat surface, includes providing an abrasive face grinding wheel having an annular grinding face depending from a substantially circular body. The body is configured for being operably engaged by a machine tool spindle for rotation about a central axis, and includes a tubular inner wall defining an axial bore configured to convey coolant in a downstream direction therethrough from a proximal end to a distal end thereof. The inner wall is coupled to a concave body portion terminating at an inner periphery of the annular grinding face. A flange is disposed within the concave body portion, in superposed orientation therewith, so that the flange and the concave body portion define a fluid flow passage therebetween, the fluid flow passage being in fluid communication with the axial bore and with the grinding face. The flange has an outer periphery disposed sufficiently close to an inner periphery of the grinding face to maintain laminar coolant flow at a point of grinding. The method further includes orienting the central axis at a predetermined angle α relative to the workpiece, and rotating the grinding wheel about the central axis. Coolant flow is delivered downstream through the bore, for conveyance radially outward through the fluid flow passage for delivery of laminar coolant flow to the point of grinding. The grinding wheel is translated towards the workpiece along a tool path parallel thereto, so that the grinding face engages and removes material from the workpiece.

The above and other features and advantages of this invention will be more readily apparent from a reading of the following detailed description of various aspects of the invention taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An aspect of the invention was the realization that when grinding wheels were used on many conventional milling machines, much of the coolant fed axially through the spindle thereof either failed to reach, or inconsistently reached, the grinding zone of the wheel. While not wishing to be tied to a particular theory, it was hypothesized that the relatively large workpiece contact area of the grinding wheels as compared to milling cutters, in combination with the turbulence and entrained air of the high pressure, axially fed coolant flow, and/or the relatively low volume of this flow, effectively inhibited the ability of the coolant to migrate radially outward through the grinding zone, resulting in coolant deprivation.

Embodiments of the subject invention thus include an improved apparatus and method for machining flat a workpiece (FIG. 1) using a grinding wheel fitted onto a conventional milling machine of the type having an axial (spindle) coolant feed. These embodiments include a grinding wheel10(FIG. 1) having an annular grinding element or face12(FIGS. 2A,2B) disposed concentrically with the wheel on a body16(FIG. 1), and having an axial bore40to convey coolant therethrough. A flange52disposed within a concave portion48of body16, serves to direct coolant radially outward from the bore40for delivery to the grinding face12in a relatively evenly distributed, substantially laminar flow. In particular embodiments, a series of channels34(FIG. 3) may also extend from the face12into concave body portion48to facilitate this flow. As will be discussed in greater detail below, this improved coolant flow has generated significant improvements in tool life relative to conventional approaches.

In a particular embodiment, face12includes a single layer of abrasive18(FIG. 4) bonded (e.g., electroplated or brazed) onto body16. Alternatively, face12may include abrasive segments made from a bond matrix (e.g., vitrified bond) containing conventional abrasive grain or superabrasive grain (e.g., diamond or cubic boron nitride (CBN)). Still further, grinding face12may include metal matrix composite (MMC) segments. Grinding face12may be fabricated as a single, annular component, or alternatively, may comprise a series of segments disposed in radially spaced relation to one another in a conventional manner.

During a representative operation, grinding wheel10(FIG. 1) is oriented with its axis of rotation19at a predetermined angle α (e.g., typically 0 to 2 degrees) relative to workpiece8. The wheel is then translated along a tool path26parallel to the workpiece so that grinding face12engages the workpiece to remove material and to apply the requisite surface finish thereto.

Throughout this disclosure, the term “axial” when used in connection with a portion of a grinding wheel, refers to a direction substantially parallel to axis of rotation19as shown inFIG. 1. The term “downstream” refers to the direction of coolant fluid flow through the tool to the grinding face of embodiments of the present invention. The term “transverse” refers to a direction relative to a component described herein, which is orthogonal to the downstream direction of coolant fluid flow therethrough. The term “laminar” or “laminar flow” is used in its conventional fluid mechanics sense, to refer to the streamline (non-turbulent) flow of a viscous, incompressible fluid in which fluid particles travel along well-defined separate lines.

Referring now to the Figures in detail, as shown inFIG. 1, in various embodiments, wheel10may be fabricated as an industry standard face grinding wheel, such as a Type6, or flat cup wheel, having an annular grinding face12depending from a body16. Thus, as shown, grinding wheel10is utilized in a conventional face grinding manner, in which its axis of rotation19is oriented at a predetermined angle α to surface8. While maintaining angle α constant, the wheel is translated or moved along tool path26to engage and machine workpiece9to a predetermined height32. In a particular embodiment, angle α is approximately 88 or 89 degrees as shown. Alternatively, wheel10may be used in any number of operating modes, such as conventional multiple pass, orbital path, etc. Also, angle α may be 90 degrees (not shown) to orient grinding face12parallel to surface8, in which diametrically opposed portions of grinding face12may contact the workpiece simultaneously.

Turning now toFIGS. 2A-2B, embodiments of grinding wheel10are provided with a conventional collar46of the type used to facilitate engagement with a spindle of a milling machine11(FIG. 1). Collar46is fastened to, or integrally formed with, an end of body16opposite that of grinding face12. As also shown, body16includes a tubular inner wall which defines an axial bore40configured to convey coolant in a downstream direction therethrough from a similarly disposed bore within collar46. At a downstream end of the bore40, the inner wall of body16extends radially outward and downstream to define a concave body portion48which terminates at an inner periphery, e.g., inner diameter (ID)50of annular grinding face12.

A flange52is sized and shaped for receipt within concave body portion48, while defining a predetermined space or gap therebetween, which serves as a fluid flow passage49. Flange52is further sized and shaped so that it does not protrude axially (e.g., in the downstream direction) beyond the plane of grinding face12as shown. The flange52is typically provided with an outer diameter (OD) which is less than, but within about 40 mm, of ID50of grinding face12, to provide a gap58of about 20 mm or less. In various embodiments, the gap58is 10 mm or less, while in other embodiments, the flange periphery is sized to provide a gap58of 5 mm or less.

Flange52may be secured within concave body portion48in any convenient manner, such as by mechanically fastening the flange to the body as shown. However, nominally any other approach familiar to those skilled in the art may be used. For example, the flange and body portion may be fabricated unitarily, e.g., as a one-piece component by molding or casting, and/or with the fluid flow passage49being machined therein, e.g., as one or more discrete pathways. Alternatively, rather than fastening it to the body, flange52may be fastened directly to the grinding machine, e.g., to a conventional tool adapter, or to the spindle of the grinding machine such as by the use of a rod passing through bore40.

The fluid flow passage49is configured so that during operational rotation of the grinding wheel about axis19, coolant flowing downstream through bore40is conveyed radially outward through the passage, to the grinding face in a substantially laminar flow. This laminar flow may be accomplished, at least in part, by configuring the flange to be at least as close to concave body portion48at a radially outer portion, as it is at a radially inner portion thereof.

For example, as best shown inFIG. 2B, a particular embodiment of grinding wheel10includes a concave body portion48having a frusto-conical wall54disposed at an acute angle β to central axis19. Flange52also includes a frusto-conical wall (56,56′), which is superposed with wall54of body portion48. In some embodiments, the wall (shown in phantom at56′) may be disposed parallel to wall54. In other embodiments, however, wall56is disposed at an acute angle γ to central axis19, which is larger than angle β. Thus, in this latter configuration flange52is disposed progressively closer to body portion48in the downstream direction (e.g., towards the periphery of the flange). Controlling the size of fluid flow passage49in this manner has been shown to reduce turbulence and entrained air within the coolant flow, to improve tool life. While not wishing to be tied to any particular theory, as mentioned hereinabove, it is believed that this relative reduction in turbulence and entrained air, (and concomitant increase in laminar flow) increases density and improves pressure distribution of the coolant flow to more evenly distribute the coolant into and through the grinding zone. In particular embodiments, the smallest cross-sectional area of passage49transverse to the downstream flow direction, (e.g., as defined by the gap58between body portion48and flange52) may range from about 75 percent to about 300 percent of the smallest transverse cross-sectional area of axial bore40. This percentage will tend to be lower for smaller wheel diameters, and higher for larger diameters, such as shown in the exemplary values in the following Tables IA & IB.

As best shown inFIG. 2B, in a representative embodiment, this smallest cross-sectional area of passage49is provided by gap58located at the periphery of flange52, adjacent the inner diameter (ID) of annular grinding face12. However, this smallest cross-sectional area may be disposed upstream of peripheral gap58in some embodiments. Regardless of the particular location of this smallest cross-sectional area, controlling the size of passage49in this manner tends to promote collection or compression of the coolant to further dissipate turbulence and entrained air, and enhance the uniformity of density and pressure distribution, prior to exiting passage49, for improved coolant delivery to the grinding zone.

As also shown, passage49includes a medial transition portion59disposed between bore40and gap58. This medial portion59may be configured with substantially any geometry, including the substantially circular configuration shown in cross-section. Alternatively, as shown inFIG. 2C, this portion may take the form of one or more discrete pathways extending through body16(e.g., as shown in phantom at59′) or which simply extend continuously between body16and flange52′, along either curved or nominally straight trajectories from bore40to gap58as shown at59″.

In various embodiments, medial portions59,59′,59″ may be provided with a collective transverse cross-sectional area which is larger than that of bore40(and optionally, that of gap58). It is believed that this relatively larger medial portion enables the coolant to momentarily collect, to further facilitate the dissipation of turbulence and entrained air, prior to exiting passage49via gap58.

As another option, embodiments of the present invention may be provided with channels34, such as shown in phantom inFIGS. 2A and 2B, and inFIG. 3. Although channels34may be used without flange52, in particular embodiments they are used with the flange as shown, to further enhance coolant flow. As best shown inFIGS. 2A and 2B, channels34extend along, or define, a notional frusto-conical surface disposed at an acute angle to axis19. The channels provide fluid communication between grinding face12and fluid flow passage49. In various embodiments, this fluid communication is accomplished by extending channels34from a location radially inward of ID50of face12(and inward of the periphery51of flange52,FIGS. 2B,3), to a location radially outward of the flange. In particular embodiments, the channels34extend completely through grinding face12to the outer diameter (OD)62thereof. In particular embodiments, the total cross-sectional area of channels34may be within a range of 50 to 150 percent that of the inlet area (e.g., cross-section of bore40). Exemplary dimensions of channels34, for a wheel having a 10 mm diameter bore40, is shown in the following Table II.

As shown inFIG. 3, channels34may be disposed in either a clockwise or counterclockwise orientation, depending on the desired direction of rotation of grinding wheel10. For example, a set of channels34, denoted as34a, may be spaced circumferentially along grinding face12, extending radially outward in a substantially clockwise spiral pattern. This clockwise orientation may be optimal for wheels rotated counterclockwise during operation. Similarly, the channels (or a second set of channels34bas shown) may spiral in the opposite direction (i.e., counterclockwise), for use when wheel10is operated with a clockwise rotation.

Although exemplary dimensions are provided herein for both gap58(between body portion48and flange52) and channels34, it should be recognized that gap58may be reduced in size to as small as zero, i.e., so that the flange and the grinding face are nominally coterminous. In such a configuration, substantially all of the coolant may flow to the grinding face through channels34.

As best shown inFIG. 4, grinding face12may include a single layer18of abrasive bonded to a face of body16. Substantially any single layer of abrasive may be used in combination with a wide range of bond materials. For example, layer18may include diamond abrasive and/or CBN (cubic boron nitride) bonded in a braze to body16. Alternatively, the single layer of abrasive may be electroplated onto body16. In such single layer abrasive wheels, the (axial) height of the abrasive should be kept nearly uniform to minimize wheel “runout” (i.e., to minimize any tendency for the grinding face to wobble or otherwise run out of true during operation). The wheel may be finished to substantially reduce any runout by conventional grinding or machining to eliminate protruding grains and/or by using shim stock beneath individual segments as will be discussed hereinafter.

Advantageously, wheels comprising a metallic substrate (body)16onto which single layer of abrasive18is applied, generally do not require conventional truing or dressing and thus may be desired in many applications. In addition, however, many other types of abrasive articles may be used in the grinding wheel10, provided they are compatible with the particular coolant used. These abrasive articles may be in the form of a continuous rim with channels34, or in the form of abrasive segments. For example, conventional vitrified bond matrix containing abrasive or superabrasive grain may be used, provided it has sufficient strength and tool life to grind metallic components. A wheel utilizing conventional MMC (metal matrix composite) segments may also be used.

In this regard, substantially any abrasive grain may be used in the abrasive articles of this invention. Conventional abrasives may include, but are not limited to, fused, sintered and sol gel alumina grains, silica, silicon carbide, zirconia-alumina, garnet, and emery grains in grit sizes ranging from about 0.5 to about 5000 microns, preferably from about 2 to about 300 microns. Superabrasive grains, including but not limited to diamond and cubic boron nitride (CBN), with or without a metal coating, having substantially similar grit sizes as the conventional grains, may also be used.

Substantially any type of bond material commonly used in the fabrication of bonded abrasive articles may be used as a matrix or bond material in the abrasive article of this invention. For example, metallic, organic, resinous, or vitrified bond (together with appropriate curing agents if necessary) may be used.

Materials useful in a metal bond (e.g., as a braze or electroplating material with a single layer of abrasive) include, but are not limited to, copper, and zinc alloys (e.g., bronze, brass), cobalt, iron, nickel, silver, aluminum, indium, antimony, titanium, zirconium, chromium, tungsten, and their alloys, and mixtures thereof. A mixture of copper and tin in amounts satisfactory to form a bronze alloy is a generally desirable metal bond matrix composition in many applications. This bond material may be used with titanium or titanium hydride, chromium, or other known superabrasive reactive material capable of forming a carbide or nitride chemical linkage between the grain and the bond at the surface of the superabrasive grain under the selected sintering conditions to strengthen the grain/bond posts. Stronger grain/bond interactions generally reduce grain ‘pullout’ which tends to damage the workpiece and shorten tool life. Substantially any abrasive grain may be used in the abrasive articles of this invention.

As discussed hereinabove, it was discovered that in single layer abrasive wheels, a plurality of radially extending slots or channels34facilitate coolant flow. In the embodiment shown, the channels are formed in substrate16prior to application of the single abrasive layer18. Thereafter, abrasive layer18may be applied to the substrate as described hereinabove. Alternatively, however, slots34may be formed by masking the substrate, as with a protective tape material, followed by application of a paste comprising the brazing components, and then removing the mask. The masked area will then be free of abrasive to effectively form the slots34.

As shown inFIG. 4, grinding face12is preferably provided with a radius or chamfer36to help provide a smooth engagement of grinding wheel10with the workpiece and avoid scratching, particularly when wheel10is operated at an angle α as shown. As also shown, grinding face12is desirably formed integrally with body16, to thus enable manufacture using as few discrete parts as possible. Flange52may also be fabricated integrally with body16, though in desired embodiments, flange52is fabricated as a separate component removably fastened to body16, such as with threaded fasteners as shown. Such removable construction enables flange52to be used repeatedly in multiple grinding wheels. This construction also enables the flange to be removed, if necessary, for cleaning. In desired embodiments, body16and flange52are fabricated from steel (e.g., heat treated 4340 steel), but may be fabricated from substantially any other material having sufficient structural integrity, such as aluminum, titanium, alloys thereof, and reinforced or high molecular weight plastics.

In some applications, it may be desirable to fabricate grinding face ring12as a detachable (e.g., disposable) and/or multi-part assembly, such as in two semicircular, 180 degree portions, four 90 degree portions, such as demarked by phantom lines35inFIG. 3, or some other configuration in order to prevent or ameliorate the accumulation of stresses that may occur during high rotational speed testing. Grinding face12may thus be fabricated as a segmented wheel, utilizing either a single layer of abrasive on a segmented metallic substrate, or utilizing a porous bond matrix such as vitrified bonded abrasive segments. The segments may be fastened to body16in any suitable manner such as brazing, welding or mechanical fastening. Spacing between each segment may serve to form slots34. An example of a mechanically fastened detachable grinding face ring112(either one-piece or segmented), including an abrasive layer18′, is shown inFIG. 2D.

Wheels10fabricated according to the subject invention advantageously enable workpieces to be “machined” and precision ground in one or two passes, an improvement over prior art operations requiring two to four finishing steps. Moreover, wheel performance in a particular application may be further enhanced by adjusting various wheel parameters. Parameters such as the abrasive grit size utilized in layer18may be chosen by balancing desired surface finish with wheel life. Smaller grit sizes tend to produce fewer burrs and surface defects, but tend to promote shorter wheel life. For example, superabrasive (e.g., diamond, CBN) grit sizes of about 1 to 1181 microns, may be used, with grit sizes of about 1 to 252 microns used for precision applications. In other applications, superabrasive grit sizes in a range of 381 to about 1015 microns may be used. For conventional abrasives (i.e., non-superabrasive), grit sizes of about 3 to 710 microns may be desired. Particular embodiments may use conventional grit sizes of about 142 to 266 microns.

The following illustrative examples are intended to demonstrate certain aspects of the present invention, but are not intended to be limiting. All of the wheels in the Examples were Type 6A2 cup shaped wheels as shown inFIG. 1, with a 10.8 cm outer diameter. They were all tested by grinding an iron workpiece under conditions shown in the following Table III, and produced results summarized in the following Table IV. The results were achieved using a single grinding process, in lieu of the two-step milling/grinding process of the prior art.

TABLE IVResultsExample 1: (ComparativeAchieved 400-500 parts per wheelGrinding Wheels)in a one-step grinding processExample 2: (Invention I)Achieved 800-900 parts per wheelCoolant Flange closest tofor a 60 to 125 percent improvementbody at Flange outer diameterin tool life relative to Example Igrinding wheel in a one-stepgrinding processExample 3: (Invention II)Achieved 2200-2300 parts per wheelCoolant Flange and Channelsfor a 340 to 475 percent improvementextending through face, pastin tool life relative to Example IFlange outer diametergrinding wheel in a one-stepgrinding process

Comparative Wheels—Conventional Type 6A2 cup face grinding wheels, were fabricated from heat treated 4340 steel, substantially as shown inFIGS. 2A,2B, and4, without channels34extending into grinding face12. The outer diameter62of the wheels was 114.3 mm, the inner diameter50of face12was 74.8 mm. The wheels had a flange with a periphery located further than approximately 20 mm from the inner diameter50of the grinding face. The wheel face12was provided with a single layer18of electroplated CBN (Cubic Boron Nitride) grain.

Invention Wheels I—Grinding wheels were substantially similar to the wheels of Example I, while also including flanges52each having a periphery located 20 mm or less from the inner diameter of the grinding face. These wheels did not include channels34extending radially outward of flange periphery51. These wheels were provided with converging walls54and56as shown inFIG. 2A, disposed at an angle of 3 degrees to one another (β=55 degrees, γ=58 degrees) to form a gap58of about 0.5 mm between inner diameter50of face12and the periphery51of the flange. The outer diameter62of the wheels was 114.3 mm, the inner diameter50of face12was 74.8 mm, and the outer diameter of the flanges was 73.8 to provide the 0.5 mm gap58. The transverse cross-sectional area of annular gap58(about 117 mm2), was about 149 percent that of bore40(about 79 mm2). This configuration was observed to improve the laminarity of flow and yield significant grinding performance improvements (see Table IV) relative to that of Example 1.

Invention Wheels II were substantially similar (including flanges52) to wheels of Example 2, but were equipped with X-shaped slots or channels34as shown and described with respect toFIG. 3, extending into the grinding face from a point radially inward of the outer diameter of the flange52. The channels were 2.5 mm wide and up to 2 mm deep. The diameter60of axial bore40was 10 mm. These wheels yielded further significant grinding performance improvements as per Table IV.

The foregoing description is intended primarily for purposes of illustration. Although the invention has been shown and described with respect to an exemplary embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention.