Patent Publication Number: US-6669747-B2

Title: Grinding wheel with titanium aluminum nitride and hard lubricant coatings

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to grinding wheels and more particularly to an improved super abrasive grinding wheel having titanium aluminum nitride and hard lubricant coatings. 
     The performance of grinding wheels is a slowly but constantly evolving technology. Because of the pervasive use of grinding in numerous manufacturing processes, there has been a constant incentive to increase grinding wheel performance the primary criteria of which is enhanced service life. A significant increase in service life over conventional aluminum oxide grinding wheels was achieved by the incorporation of the first super abrasive, diamond, as diamond fragments or particles into the grinding wheel or on the peripheral surface of the grinding wheel. Grinding wheels utilizing diamond, however, were not successfully used with steels and other ferrous alloys because of the tendency of diamond to react with and be absorbed into such materials at the temperatures and pressures existing at the grinding wheel/material interface. This shortcoming has significantly reduced the utilization of such grinding wheels when grinding ferrous materials. 
     More recently, a manmade super abrasive, cubic boron nitride (cBN), has not only provided improved service life but also functioned with a wider variety of materials, particularly steels, hardened steels, stainless steels, and nickel and cobalt based super alloys. Cubic boron nitride grinding wheels typically perform better than diamond materials with steel and other ferrous alloys. 
     Cubic boron nitride grinding wheels typically comprise a metal wheel or core with a periphery onto which the cubic boron nitride particles or fragments are secured by electroplating, electroless plating or brazing. 
     U.S. Pat. No. 5,139,537 discloses the coating of such grinding wheels with titanium nitride. Such a coating is said to greatly strengthen the adherence of the cBN particles to the grinding wheel. 
     As noted above, however, due to the evolutionary improvements in grinding wheel technology, further performance enhancements are anticipated and the present invention as directed to a grinding wheel having improved performance characteristics. 
     BRIEF SUMMARY OF THE INVENTION 
     A grinding wheel according to the present invention includes cubic boron nitride (cBN) or other abrasive particles such as diamond secured to a substrate by an electroplated, electroless plated or brazed layer of nickel, chrome or nickel or chrome based alloy, a first antioxidation layer of, for example, vapor deposited titanium aluminum nitride (TiAIN) and a second hard lubricant layer of, for example, vapor deposited molybdenum disulfide (MoS 2 ), diamond graphite, tungsten carbide carbon, carbon nitride, titanium carbide carbon or titanium carbon nitride. The hard lubricant layer acts as a release agent and lubricant which reduces clogging of the wheel by lowering adhesion and facilitating the release of ground material from the wheel thereby providing improved grinding performance. 
     Thus it is an object of the present invention to provide a grinding wheel having grinding media coated with a first antioxidation layer and a second hard lubricant layer. 
     It is a further object of the present invention to provide a grinding wheel having grinding media covered with a first layer of vapor deposited titanium aluminum nitride and a second layer of a vapor deposited hard lubricant such as molybdenum disulfide, diamond graphite, tungsten carbide carbon, carbon nitride, titanium carbide carbon or titanium carbon nitride. 
     It is a still further object of the present invention to provide a grinding wheel having cubic boron nitride abrasive particles coated by layers of titanium aluminum nitride and molybdenum disulfide, diamond graphite, tungsten carbide carbon, carbon nitride, titanium carbide carbon or titanium carbon nitride. 
     It is a still further object of the present invention to provide a grinding wheel having electroplated, electroless plated or brazed nickel, chrome or nickel or chrome based alloys securing cubic boron nitride abrasive particles which are coated by a first antioxidizing layer of titanium aluminum nitride and a second hard lubricant layer of molybdenum disulfide, diamond graphite or tungsten carbide carbon, carbon nitride, titanium carbide carbon or titanium carbon nitride. 
     Further objects and advantages of the present invention will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a grinding wheel according to the present invention; 
     FIG. 2 is schematic representation of an electroplating apparatus which may be utilized during the manufacture of a grinding wheel according to the present invention; 
     FIG. 3 is a fragmentary, sectional view of a grinding wheel according to the present invention taken along line  3 — 3  of FIG. 1; 
     FIG. 4 is a schematic representation of a physical vapor deposition chamber which may be utilized during the manufacture of a grinding wheel according to the present invention; 
     FIG. 5 is a schematic representation of a magnetron sputtering physical vapor deposition chamber which may be utilized during the manufacture of a grinding wheel according to the present invention; 
     FIG. 6 is a greatly enlarged, fragmentary, sectional view of abrasive particles secured to a grinding wheel surface according to the present invention; 
     FIG. 7 is a greatly enlarged, fragmentary, sectional view of a grinding wheel having abrasive particles and a titanium aluminum nitride layer according to the present invention; and 
     FIG. 8 is a greatly enlarged, fragmentary, sectional view of a grinding wheel having abrasive particles, a titanium aluminum nitride layer and a hard lubricant layer according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
     Referring now to FIGS. 1 and 3, a grinding wheel according to the present invention is illustrated and generally designated by the reference number  10 . A typical grinding wheel  10  is circular and defines a diameter of, for example, 1 to 24 inches (2.54 cm to 61 cm) and defines a width, typically on a smaller scale of 0.5 to 6 inches (1.27 cm to 15.2 cm). Larger or smaller grinding wheels  10  are, of course, wholly suitable for use with the present invention. Although illustrated as having a flat outer peripheral surface  12 , more frequently, commercial and industrial grinding wheels will define a particular profile having larger diameter regions and smaller diameter regions merging with oblique, stepped, flat or curved regions which create corresponding shapes in a workpiece. The flat outer peripheral surface  12  is presented solely for purposes of illustration and explanation. 
     The grinding wheel  10  typically includes a centrally disposed bore  14  through which an arbor (not illustrated) may be disposed and upon which the grinding wheel  10  may be mounted. As illustrated in FIG. 3, the grinding wheel  10  typically includes a circumferential clocking or indicating ring or groove  18  generally proximate to the outer peripheral surface  12  which is utilized to center the grinding wheel  10  on the arbor. Centering of the grinding wheel  10  utilizing the clocking groove  18  enhances the concentricity achieved on the arbor when the grinding wheel  10  is rotated due to the proximity of the clocking groove  18  to the outer peripheral surface  12 . 
     Referring now to FIGS. 2 and 6, manufacture of the grinding wheel  10  according to the present invention comprises three distinct steps after the blank for the grinding wheel  10  has been manufactured. The blank for the grinding wheel  10  may be solid metal, for example, steel, or a metal composite which is machined to its final shape. The grinding wheel  10  may also be net formed powdered metal or a formed and sintered part. FIG. 2 schematically illustrates an electroplating machine  20  wherein the grinding wheel  10  is placed horizontally on a rotatable circular platform  22  attached to a rotating spindle  24  which is driven through any convenient means by a motor such as an electric motor  26 . Adjacent the periphery of the grinding wheel  10  is an electrode  30  of, for example, nickel or other metal alloy having similar electrical and physical characteristics, which is supplied with a direct current electrical charge from an external source (not illustrated). The grinding wheel  10  and the nickel electrode  30  are oppositely charged. 
     The grinding wheel  10 , the platform  22 , the spindle  24  and the nickel electrode  30  are disposed within an electroplating tank  32  which is filled with a suitable electroplating liquid  34 . Positioned to provide a controlled flow of abrasive particles such as cubic boron nitride (cBN) particles  36  or other abrasive particles such as diamond particles, is a nozzle  38 . FIG. 6 illustrates, in a greatly enlarged view, that operated for a sufficient time, the nickel or other material migrates from the electrode  30  to the outer peripheral surface  12  of the grinding wheel  10  to form a layer of electroplated nickel  30 A and secures a plurality of cubic boron nitride or other abrasive particles  36  to the surface  12  to provide an abrasive or grinding surface on the grinding wheel  10 . This process and its parameters are well known in the art, obviating the need to describe operating conditions and cycle times. It should be understood that other processes for attaching the abrasive particles such as electroless plating and brazing are also suitable and within the scope of this invention. 
     Referring now to FIGS. 4 and 7, a physical vapor deposition chamber  40  is illustrated. The grinding wheel  10 , with its outer peripheral surface  12  now including a plurality of abrasive particles  36  such as cubic boron nitride particles adhered by, for example, electroplated nickel  30 A, is placed upon a rotatable platform  42  which is rotated by a spindle  44  and suitable mechanical equipment (not illustrated) external to the deposition chamber  40 . Also disposed within the interior of the physical vapor deposition chamber  40  are one or preferably two target cathodes  46  which are electrically charged by a common source of electricity. The target cathodes  46  are preferably an alloy of between 50 and 55% aluminum (Al) with a remainder of titanium (Ti). It will be appreciated that the spindle  44  and platform  42  are conductive to create a path for electrical energy through the grinding wheel  10  within the deposition chamber  40 . The inlet of a vacuum pump  48  is in communication with the interior of the deposition chamber  40  and is utilized to draw down a deep vacuum, on the order of 10 −5  to 10 −6  torr. A controllable source  52  of nitrogen or other reactive gas is also provided. 
     The temperature of the grinding wheel  10  within the deposition chamber  40  is then raised to between 550° F. (290° C.) and 950° F. (510° C.) and an arc is struck first without the reactive gas to clean the surface of the previously deposited nickel  30 A and abrasive particles  36  and then in the presence of nitrogen to achieve, through the process of arc evaporation, a coating or layer of titanium aluminum nitride or other antioxidizing material on the order of less than 1.0 micron to 5.0 microns and preferably about 1.0 to 2.0 microns. Typically, the platform  42 , spindle  44  and thus the grinding wheel  10  are rotated at a speed of about 5 r.p.m. The vapor deposition process may take three to four hours or more or less depending on the desired coating or layer thickness and other process variables. FIG. 7 shows a greatly enlarged view of a portion of the exterior surface  12  of the grinding wheel  10  in cross-section which now includes an oxidation inhibiting layer  46 A of titanium aluminum nitride. Known antioxidizing metals, alloys and materials may also be utilized for the layer  46 A as will be readily appreciated. 
     Referring now to FIGS. 5 and 8, a final step in the manufacturing process includes a second coating or layer applying step which preferably utilizes magnetron sputtering. As such, a vapor deposition chamber  60  is also utilized wherein a rotating platform  62  is supported upon a spindle  64  for rotation, again at speeds on the order of 5 r.p.m. One or preferably a pair of targets  66  of a hard lubricant such as molybdenum disulfide, diamond graphite, tungsten carbide carbon, carbon nitride or titanium carbon nitride are arranged proximate to and on opposite sides of the grinding wheel  10  and are electrically charged. Preferably as well, magnets  68  are utilized to focus and enhance the ion and electron flow between the targets  66  and the surface  12  of the grinding wheel  10 . A vacuum pump  74  is utilized to evacuate the interior of the deposition chamber  60 , again to a deep vacuum on the order of 10 −5  to 10 −6  torr. A gas supply of an inert gas such as argon replaces the atmosphere within the deposition chamber  60  as those familiar with conventional magnetron sputtering techniques will acknowledge. A coating or layer  66 A of preferably less than about 3 microns of molybdenum disulfide or other hard lubricant as delineated above and more preferably, a coating or layer  66 A of about 1 micron of molybdenum disulfide or other hard lubricant is deposited on top of the layer  46 A of titanium aluminum nitride. FIG. 8 schematically illustrates on a greatly enlarged scale the final product wherein a magnetron sputtered coating or layer  66 A of molybdenum disulfide or other hard lubricant overcoats the layer  46 A of titanium aluminum nitride on the cubic boron nitride particles  36  secured by electroplated nickel  30 A on the peripheral surface  12  of the grinding wheel  10 . 
     Improved grinding wheel performance has been achieved by a double coating with a layer of antioxidizing titanium aluminum nitride and a layer of a hard lubricant such as molybdenum disulfide over abrasive material such as cubic boron nitride. Use of abrasive materials, particularly diamond, is expected to provide similar results. While the mechanism of the improvement is not fully understood, it is believed that the hard lubricant such as molybdenum disulfide, diamond graphite, tungsten carbide carbon, carbon nitride or tungsten carbide carbon acts as a lubricant and that such action tends to reduce clogging of the grinding wheel by reducing adherence and facilitating the release of ground material, thereby improving both grinding accuracy and wheel life. 
     The foregoing disclosure is the best mode devised by the inventor for practicing this invention. It is apparent, however, that products incorporating modifications and variations will be obvious to one skilled in the art of abrasives and grinding wheels. Inasmuch as the foregoing disclosure is intended to enable one skilled in the pertinent art to practice the instant invention, it should not be construed to be limited thereby but should be construed to include such aforementioned obvious variations and be limited only by the spirit and scope of the following claims.