Abstract:
Ceramic forming polymers are used to form a tailorable bonding matrix for abrasive grit such as diamond, diamond-like carbon, cubic boron nitride, boron carbide and/or silicon carbide. The ceramic forming polymer is unique in that it can be heated to convert it to a ceramic material at a low enough temperature to prevent damage to the abrasive grits. The ceramic forming polymer may also contain controlled amounts of silicon, carbon, oxygen, and other elements to optimize the properties of the abrasive. A toughening media such as additional ceramic forming polymer, metal and/or polymer resin can be infused into a model of the abrasive tool to permit further tailoring of the abrasive tool to meet widely varying demands of machining both very hard materials as well as softer but more abrasive materials.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field  
           [0002]    The present invention relates generally to abrasives, and, more particularly, to a ceramic bonded abrasive tool, composition and method for making the same.  
           [0003]    2. Related Art  
           [0004]    Abrasive tooling parts formed of an abrasive grit held by a bonding material are commonly used to conduct a variety of machining operations (e.g., cutting, boring, grinding) on a workpiece. Where a workpiece is made of a hard or abrasive material itself, abrasive tooling typically includes high hardness abrasives such as carbide and/or superabrasives such as diamond, diamond-like carbon, or cubic boron nitride (CBN) are used. Unfortunately, there are few bonding materials that can match the properties of the high hardness abrasives. A typical result of use of these abrasives is significant pull-out of the abrasive material and/or accumulation of the bonding material on the workpiece.  
           [0005]    One obstacle to providing sufficient abrasive-to-bonding material adherence is that most bonding processes must be restricted to temperatures below 950° C. due to oxidation or other damage to the abrasive material. Hence, many materials that could conceivably be adequate bonding materials are inapplicable due to their required high processing temperatures. One process and material that has been considered is reaction bonding with metallic silicon or other reactive metals. Unfortunately, this process results in damage to the abrasive material.  
           [0006]    Currently, most processes for bonding abrasives fall into two categories. First, metallic brazes or active metal bonding such as disclosed in U.S. Pat. No. 5,874,175 to Li. Second, resin bonding such as disclosed in U.S. Pat. No. 5,651,729 to Benguerel. Unfortunately, both techniques still result in very hard abrasives bonded to a weak bonding material. In nearly all cases, the cutting rate is limited by both the low temperature capability of the bonding material and its low strength. As a result, the maximum advantage of abrasives and especially superabrasives cannot be realized.  
           [0007]    Another problem relative to abrasive parts is that the bonding material must be tailored to optimize material removal rate. That is, the bonding material must allow the abrasive material grains to fracture or pull out after they become worn to expose new cutting surfaces. This type of behavior is governed by the material of the workpiece. None of the above bonding materials and techniques can be adapted very easily for different workpiece materials.  
           [0008]    In view of the foregoing, there is a need in the art for an improved bonding material for abrasives and the related abrasive parts.  
         SUMMARY OF THE INVENTION  
         [0009]    Ceramic forming polymers are used to form a tailorable bonding matrix for abrasive grit such as diamond, diamond like carbon, cubic boron nitride, boron carbide and/or silicon carbide. The ceramic forming polymer is unique in that it can be heated to convert it to a ceramic material at a low enough temperature to prevent damage to the abrasive grits. The ceramic forming polymer may also contain controlled amounts of silicon, carbon, oxygen, and other elements to optimize the properties of the abrasive tool. A toughening media such as additional ceramic forming polymer, metal and/or polymer resin can be infused into a model of the abrasive tool to permit further tailoring of the abrasive tool to meet widely varying demands of machining both very hard materials as well as softer but more abrasive materials.  
           [0010]    In a first aspect of the invention is directed to an abrasive tooling material comprising: a bonding material having abrasive grit bonded therein, the bonding material formed from a ceramic forming polymer.  
           [0011]    A second aspect of the invention is directed to a method of manufacturing an abrasive tool, the method comprising the steps of: mixing an abrasive grit with a ceramic forming polymer to form a mixture; forming the mixture into a model having a desired shape for the abrasive tool; and curing the ceramic forming polymer to form the abrasive tool.  
           [0012]    A third aspect of the invention includes a composition for use in making an abrasive tool, the composition comprising: a mixture of abrasive grit and a ceramic forming polymer.  
           [0013]    A fourth aspect of the invention is directed to an abrasive tool comprising: an abrasive grit bonded in a bonding material comprised of a ceramic.  
           [0014]    The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The preferred embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein:  
         [0016]    FIGS.  1 A-B show a flow diagram illustrating a method of manufacture;  
         [0017]    [0017]FIG. 2 shows a partial cross-sectional view of an abrasive according to a first embodiment; and  
         [0018]    [0018]FIG. 3 shows a partial cross-sectional view of an abrasive according to a second embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    I. Method:  
         [0020]    Turning to FIGS.  1 A-B, a process of manufacturing an abrasive tool will be described in greater detail. For purposes of this disclosure, the term “abrasive tool” shall mean any flex abrasive or superabrasive material, object, tool or apparatus.  
         [0021]    In step S 1 , an abrasive grit is mixed with a ceramic forming polymer to form a mixture using, for example, a mechanical mixing system. In one preferred embodiment, the mixing step includes mixing until all of the abrasive grit is coated with a thin layer of ceramic forming polymer. The ceramic forming polymer is similar to that disclosed in U.S. Pat. No. 5,153,295 to Whitmarsh et al., which is hereby incorporated by reference. The ceramic forming polymer may include at least one of: a polycarbosilane, a polysilazane, a polysilane, a silicon oxycarbide precursor and a silicon oxynitride precursor and may also include other elements to control bonding with the abrasive grit, bonding material hardness, and bonding material toughness. For instance, the ceramic forming polymer may include at least one of: carbon, oxygen, nitrogen, silicon, titanium, zirconium, tungsten, molybdenum, niobium, nickel, iron, manganese, cobalt and copper. The ratios of polymer to grit varies depending on the density of the abrasive and the grit size. In one embodiment, ceramic forming polymer makes up at least 3% of the mass of the mixture, and no more than 25% of the mass of the mixture. In a more preferred embodiment, ceramic forming polymer makes up at least 5% and no more than 15% of the mass of the mixture.  
         [0022]    Abrasive grit may include any grit material. In one preferred embodiment, abrasive grit includes at least one of: diamond, diamond-like carbon, polycrystalline diamond, cubic-boron nitride, boron carbide and silicon carbide. Abrasive grit may have a grit size ranging from less than one (1) micrometer up to no more than 250 micrometers. Abrasive grit within a particular abrasive may be uniform in grit size or may vary in grit size.  
         [0023]    In step S 2 , the mixture is formed into a model having substantially the desired shape for the abrasive tool, i.e., a shape that approximates the ultimate tool shape. The term “model,” as used herein, shall denote an intermediate form of the ultimately constructed abrasive tool. The particular application of forming may include any well known method. For instance, the step of forming may include at least one of the following steps: uniaxial pressing, cold isostatic pressing, hot isostatic pressing, hot pressing, reaction bonding or reactive sintering using the ceramic forming polymer. Where pressing is used, the mixture may be pressed into a mold to form the model. Pressure is in the range of at least approximately 1,500 pounds per square inch and no more than approximately 3,000 pounds per square inch. In one preferred embodiment, the pressure is approximately 2,000 pounds per square inch, and may be held for approximately five minutes.  
         [0024]    Next, in steps S 3 -S 4  the model, i.e., the ceramic forming polymer, is cured to form the ceramic, which includes abrasive grit bonded therein. In steps S 3 -S 4 , the model is heated in an inert gas (step S 3 ), and then allowed to cool in the inert gas until it reaches approximately 100° C. (step S 4 ). In one embodiment, the heating temperature may be raised between one to three degrees Celsius per minute on the way to a maximum temperature. A maximum temperature of the heating step can be any temperature allowed by the abrasive grit used. In one embodiment, the maximum temperature falls within the range of at least approximately 600° C., and no more than approximately 1200° C. The maximum temperature may be held an appropriate amount of time to assure proper material curing and/or infusion, e.g., approximately thirty minutes for the ceramic forming polymer. The inert gas may be any of the well-known inert gases such as nitrogen, argon and helium. After curing is complete, the model is in the form of a porous ceramic web having abrasive grit bonded therein.  
         [0025]    At step S 5 , a toughening media is infused into the model, which provides additional toughening of the model and tailoring of the model to particular applications. The step of infusing occurs at least once, and may occur numerous times. Each infusing step is referred to as a cycle. The toughening media may take four general forms: ceramic, metal, polymer resin, or a combination of the preceding. In other words, the toughening media is at least one of a ceramic, a metal and a polymer resin. The type of infusion varies depending on the type of toughening media used.  
         [0026]    A. Ceramic:  
         [0027]    Turning to FIG. 1B, when the toughening media is a ceramic, in one preferred embodiment, the step of infusing includes, at step S 6 C, placing the model into a sealable container. The container has a shape that is a substantially form fitting to the model. That is, the container encloses the model but does not contact the model. For instance, approximately one (1) millimeter may be provided between an interior surface of the container and the exterior surface of the model. The container is constructed of a material that can withstand high temperatures such as steel or graphite.  
         [0028]    At step S 7 C, the model is exposed in the container to a vacuum. The vacuum is of sufficient strength to evacuate air from the container and the pores in the porous ceramic web. In one embodiment, the vacuum is less than 10 −3  atmospheres.  
         [0029]    In step S 8 C, the model is immersed in a ceramic forming polymer (liquid form) in the container while the model is exposed to the vacuum. The vacuum may be held for approximately thirty minutes after the immersion of the model. As the vacuum is applied, the ceramic forming polymer (liquid form) is infused into the porous ceramic web of the model.  
         [0030]    In step S 8 D, the model is heated again (second heating) in an inert gas. This heating step may be substantially similar to the heating step described above.  
         [0031]    In terms of the makeup of the ceramic forming polymer, the toughening media version can be identical to that originally used to create the porous ceramic web or a variant thereof. If a variant is used, the ceramic porous web and toughening media may include the same base makeup but have different additives, e.g., a polycarbosilane with copper in one instance and a polycarbosilane with nickel in another instance. Similarly, the ceramic porous web and toughening media may have different ceramic forming polymers, e.g., a polysilazane in one instance and a polycarbosilane in another instance. As one with skill in the art will recognize, a variety of makeups are possible to accommodate different application requirements.  
         [0032]    It should be recognized that a variety of different processes are available for implementing the infusion of the liquid ceramic forming polymer. Hence, the present invention should not be limited to the above described embodiment.  
         [0033]    B. Metal:  
         [0034]    As shown in FIG. 1B as step S 6 M, in the case of a metal toughening media, the process proceeds by heating the model in an inert gas while the model is exposed to a metal. Exposure to the metal may be according to any well known process that allows infusion of the metal into the model. For example, placing the model on a pad of metal particles during the heating step will cause the molten metal to wick into the model. Vapor deposition of a metal vapor onto the abrasive/ceramic media could also be used. Any known bonding or brazing metal used to bond an abrasive grit to a substrate may be used. The metal may be reactive or non-reactive with the ceramic. Exemplary non-reactive metals include: nickel, copper, silver, gold, platinum, palladium. Exemplary reactive metals include: titanium, tungsten, molybdenum, niobium, iron, manganese, cobalt, zirconium.  
         [0035]    C. Polymer Resin:  
         [0036]    As also shown in FIG. 1B as step S 6 P, when the toughening media is a polymer resin, the infusing step includes applying pressure to the model to infuse the polymer resin into the model. During the pressure step, the model may be heated (if necessary) to a temperature sufficient to melt the polymer resin. In one embodiment, this temperature may be at least approximately 100° C. and no more than approximately 400° C. Any known high temperature polymer used for bonding abrasive grit to a substrate may be used. Examples include: a polyimide resin, a phenolic resin and polyamide/polyimide copolymers. Use of a polymer resin toughening media would most likely be a final stage process.  
         [0037]    D. Combination:  
         [0038]    Returning to FIG. 1A, the infusing step may be repeated a number of times, i.e., a number of cycles. Subsequent processing makes the model harder and harder by filling in the porous ceramic web around the abrasive grit. In one embodiment, the infusion step is repeated in the range of at least four cycles, and no more than twelve cycles. Certain aspects of the infusion step may change from cycle to cycle to accommodate tailoring of the abrasive tool. For instance, the toughening media may change from one cycle to the next cycle. In one embodiment, the toughening media is a ceramic forming polymer for at least one cycle and at least one of a metal and a polymer resin for at least one other subsequent cycle. It is in this way that the toughening media may include a combination of ceramic, metal and polymer resin. That is, different toughening media can be infused at different cycles such that, for instance, ceramic forming polymer is infused in the first two cycles, and metal is infused into the abrasive during subsequent cycles. In this way, a broad range of abrasive characteristics can be customized for a particular application.  
         [0039]    In between certain cycles, the model may also be machined depending on the hardness and friability of the matrix that is desired. The model can be cut or machined to close tolerances to near-net-shape. In this way, the abrasive tool can be formed to make high tolerance grinding tools or bits and then hardened by subsequent cycles.  
         [0040]    The invention also includes a composition for use in making an abrasive tool, the composition comprising: a mixture of abrasive grit and a ceramic forming polymer.  
         [0041]    II. Apparatus:  
         [0042]    Referring to FIG. 2, the invention also includes an abrasive tool  10  created according to the above-described method. Abrasive tool  10  in accordance with the invention includes a bonding material  12  having an abrasive grit  14  bonded therein. Bonding material  12  is formed of a ceramic  16  created from a ceramic forming polymer. The ceramic forming polymer may include at least one of: a polycarbosilane, a polysilazane, a polysilane, a silicon oxycarbide precursor and a silicon oxynitride precursor. Furthermore, the ceramic forming polymer may include other elements to control bonding with abrasive grit  14 , bonding material hardness, and bonding material toughness. For instance, ceramic forming polymer may include at least one of: carbon, oxygen, nitrogen, silicon, titanium, zirconium, tungsten, molybdenum, niobium, nickel, iron, manganese, cobalt and copper.  
         [0043]    Abrasive tool  10  may be formed into a variety of now known or later developed shapes. For instance, abrasive tool  10  may be in the form of: a cutting tool, a grinding tool, a sanding tool, a boring tool, a machining tool, a drilling tool, a lapping bit, or a nozzle.  
         [0044]    Turning to FIG. 3, an alternative embodiment of the abrasive tool is illustrated. Abrasive tool  110 , includes an abrasive grit  114  bonded in a bonding material  112 . Bonding material  112  is formed, at least in part, of a ceramic  116  created from a ceramic forming polymer, as described above. In this case, the ceramic forming polymer forms a porous ceramic web  118  into which a toughening media  120  is infused. Toughening media  120  includes at least one of a ceramic, a metal and a polymer resin, as described above.  
         [0045]    The above described abrasive tool  10 ,  110  provides an abrasive tool having reduced abrasive grit pull out and capable of withstanding the high forces that the super hardness abrasives experience. In addition, bonding material  12 ,  112  have the advantage that their processing temperatures are not so high as to harm the abrasive grit. For instance, processing can take place at less than 950° C.  
         [0046]    Abrasive tool  10 ,  110  can be tailored to optimize bonding material removal rate. Hence, they allow adaptation for different workpiece materials. For instance, a ceramic-metal abrasive tool may find application relative to very hard workpieces; a ceramic-polymer abrasive tool may find application relative to an intermediate hardness workpieces; and a full ceramic abrasive tool may find application relative to very abrasive, but not very hard workpieces such as fiberglass or graphite composites. In terms of very hard workpieces, the polymer may be designed to have extra carbon and/or oxygen which would convert to a softer or more friable ceramic. This would allow the worn down grits to be removed from the matrix as it fractures, to expose fresh sharp grit to continue the cutting/grinding. The process for making the component would still be the same as described previously.  
         [0047]    In view of the foregoing, a wide variety of abrasive tools can be created that are tailored for particular applications by adjusting the ceramic forming polymer used to create the initial porous ceramic web and adjusting the type and makeup of the toughening media. Any combination of ceramic, resin and metal can be used to adjust the hardness, toughness, and friability of the abrasive tool. Adjusting the carbon, oxygen, silicon, or adding other elements including reactive metals to the ceramic forming polymer can be used to control both the bonding material/abrasive grit bond as well as control the abrasive toughness and hardness. Exemplary cutting bits have been made and shown to cut solid silicon carbide. The bits also have been shown to be tough enough to withstand clamping into the tool holder and the machining shock loads on a manual lathe.  
         [0048]    While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.