Patent Grant
7384329
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.
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.
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 (
In a particular embodiment, face 12 includes a single layer of abrasive 18 (
During a representative operation, grinding wheel 10 (
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 rotation 19 as shown in
Referring now to the Figures in detail, as shown in
Turning now to
A flange 52 is sized and shaped for receipt within concave body portion 48, while defining a predetermined space or gap therebetween, which serves as a fluid flow passage 49. Flange 52 is further sized and shaped so that it does not protrude axially (e.g., in the downstream direction) beyond the plane of grinding face 12 as shown. The flange 52 is typically provided with an outer diameter (OD) which is less than, but within about 40 mm, of ID 50 of grinding face 12, to provide a gap 58 of about 20 mm or less. In various embodiments, the gap 58 is 10 mm or less, while in other embodiments, the flange periphery is sized to provide a gap 58 of 5 mm or less.
Flange 52 may be secured within concave body portion 48 in 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 passage 49 being machined therein, e.g., as one or more discrete pathways. Alternatively, rather than fastening it to the body, flange 52 may 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 bore 40.
The fluid flow passage 49 is configured so that during operational rotation of the grinding wheel about axis 19, coolant flowing downstream through bore 40 is 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 portion 48 at a radially outer portion, as it is at a radially inner portion thereof.
For example, as best shown in
As best shown in
As also shown, passage 49 includes a medial transition portion 59 disposed between bore 40 and gap 58. This medial portion 59 may be configured with substantially any geometry, including the substantially circular configuration shown in cross-section. Alternatively, as shown in
In various embodiments, medial portions 59, 59′, 59″ may be provided with a collective transverse cross-sectional area which is larger than that of bore 40 (and optionally, that of gap 58). 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 passage 49 via gap 58.
As another option, embodiments of the present invention may be provided with channels 34, such as shown in phantom in
As shown in
Although exemplary dimensions are provided herein for both gap 58 (between body portion 48 and flange 52) and channels 34, it should be recognized that gap 58 may 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 channels 34.
As best shown in
Advantageously, wheels comprising a metallic substrate (body) 16 onto which single layer of abrasive 18 is 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 wheel 10, provided they are compatible with the particular coolant used. These abrasive articles may be in the form of a continuous rim with channels 34, 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 channels 34 facilitate coolant flow. In the embodiment shown, the channels are formed in substrate 16 prior to application of the single abrasive layer 18. Thereafter, abrasive layer 18 may be applied to the substrate as described hereinabove. Alternatively, however, slots 34 may 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 slots 34.
As shown in
In some applications, it may be desirable to fabricate grinding face ring 12 as 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 lines 35 in
Wheels 10 fabricated 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 layer 18 may 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 in
Comparative Wheels—Conventional Type 6A2 cup face grinding wheels, were fabricated from heat treated 4340 steel, substantially as shown in
Invention Wheels I—Grinding wheels were substantially similar to the wheels of Example I, while also including flanges 52 each having a periphery located 20 mm or less from the inner diameter of the grinding face. These wheels did not include channels 34 extending radially outward of flange periphery 51. These wheels were provided with converging walls 54 and 56 as shown in
Invention Wheels II were substantially similar (including flanges 52) to wheels of Example 2, but were equipped with X-shaped slots or channels 34 as shown and described with respect to
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.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3345281 | Falls | Oct 1967 | A |
| 3683566 | Walters | Aug 1972 | A |
| 3780476 | Sipe | Dec 1973 | A |
| 4791760 | Noll | Dec 1988 | A |
| 4854087 | Riha | Aug 1989 | A |
| 5129190 | Kovach et al. | Jul 1992 | A |
| 5259148 | Wiand | Nov 1993 | A |
| 5345726 | Gach | Sep 1994 | A |
| 5582540 | Su et al. | Dec 1996 | A |
| 5738572 | Giebmanns | Apr 1998 | A |
| 5895317 | Timm | Apr 1999 | A |
| 5951378 | Miller et al. | Sep 1999 | A |
| 5964649 | Bergqvist et al. | Oct 1999 | A |
| 5993297 | Hyatt et al. | Nov 1999 | A |
| 5997597 | Hagan | Dec 1999 | A |
| 6224473 | Miller et al. | May 2001 | B1 |
| Number | Date | Country |
|---|---|---|
| 1 321 232 | Jun 2003 | DE |
| 0581 507 | Jul 1993 | EP |
| 119 522 4 | Apr 2002 | EP |
| 60167769 | Aug 1985 | JP |
| 6155293 | Jun 1994 | JP |
| 7276243 | Oct 1995 | JP |
| 10034542 | Feb 1998 | JP |
| 10193271 | Jul 1998 | JP |
| 11347912 | Dec 1999 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20070275636 A1 | Nov 2007 | US |
