Abstract:
A reactive foil is used to assemble the components of rock bit cutters and to affix cutting elements to rock bit bodies. A small pulse of localized energy ignites the foil in a fraction of second to deliver the necessary amount of heat energy to flow solder or braze and form a strong, true metallic joint. The reaction in the foil may be activated using optical, electrical, or thermal sources.

Description:
[0001]    This non-provisional patent application claims priority to and the benefit of U.S. Provisional Patent App. No. 60/994,983, filed Sep. 24, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates in general to fabricating earth boring bits and, in particular, to an improved system, method, and apparatus for brazing together the components of cutters for fixed cutter bits. 
         [0004]    2. Description of the Related Art 
         [0005]    Rotary drill bits are commonly used for drilling bore holes or wells in earth formations. One type of rotary drill bit is the fixed cutter bit or drag bit, which typically includes a plurality of cutting elements secured to a face region of a bit body. Generally, the cutting elements of a fixed cutter type drill bit have either a disk shape or a substantially cylindrical shape. A hard, super-abrasive material, such as mutually bonded particles of polycrystalline diamond, may be provided on a substantially circular end surface of each cutting element to provide a cutting surface. Such cutting elements are often referred to as “polycrystalline diamond compact” (PDC) cutters. 
         [0006]    Typically, the cutting elements are fabricated separately from the bit body and secured within pockets formed in the outer surface of the bit body. A bonding material such as an adhesive or, more typically, a braze alloy may be used to secured the cutting elements to the bit body. The fixed cutter drill bit may be placed in a bore hole such that the cutting elements are adjacent the earth formation to be drilled. As the drill bit is rotated, the cutting elements scrape across and shear away the surface of the underlying formation. 
         [0007]    The bit body includes wings or blades, which are separated by junk slots. Internal fluid passageways extend between the face of the bit body and a longitudinal bore, which extends through the steel shank and partially through the bit body. A plurality of PDC cutters are provided on the face of the bit body. The PDC cutters may be provided along the blades within pockets formed in the face of the bit body. 
         [0008]    The PDC cutters may be bonded to the bit body after the bit body has been cast by, for example, brazing, mechanical affixation, or adhesive affixation. Alternatively, the PDC cutters may be provided within mold and bonded to the bit body during infiltration or furnacing of the bit body if thermally stable synthetic diamonds, or natural diamonds, are employed. However, the high temperature ranges used to fabricate the bits can change the properties of the metals and other materials used. Thus, an improved system for joining the cutting elements to fixed cutter bits that overcomes the limitations of conventional processes would be desirable. 
       SUMMARY OF THE INVENTION 
       [0009]    Embodiments of a system, method, and apparatus for assembling rock bit compacts with a reactive exothermic foil are disclosed. A small pulse of localized energy ignites the foil in a fraction of second to deliver the necessary amount of heat energy to flow solder or braze (e.g., Ag—Cu) and form a strong, true metallurgical joint. The reaction in the foil may be activated using optical, electrical, or thermal sources. 
         [0010]    An effective bond may be formed between the substrate or extension of a rock bit cutter and its cutting element (e.g., tungsten carbide tip) using these techniques. The invention eliminates the need for a standard furnace, torch, or laser weld. Bonds between similar or dissimilar materials (e.g., ceramics to metals) may be formed in almost any environment (e.g., in ambient conditions), and are resistant to corrosion and degradation. The bonds exert low stress on the constituent parts, expose them to minimal thermal demands, and can be produced in a flux free environment. In addition, the invention may be used to join cutting elements to the bit body. 
         [0011]    The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    So that the manner in which the features and advantages of the present invention, which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings which form a part of this specification. It is to be noted, however, that the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
           [0013]      FIG. 1  is an isometric view of one embodiment of an earth boring bit constructed in accordance with the invention; 
           [0014]      FIG. 2  is a side view of one embodiment of a cutting element constructed in accordance with the invention; 
           [0015]      FIG. 3  is an exploded isometric view of one embodiment of a cutting element and is constructed in accordance with the invention; 
           [0016]      FIGS. 4A-C  are schematic sectional views of various embodiments of joint and material configurations for drill bit cutter assembly techniques and are constructed in accordance with the invention; and 
           [0017]      FIG. 5  is a high level flow diagram of one embodiment of a method in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Embodiments of a system, method and apparatus for reactively brazing together the components of rock bit cutters are disclosed. The invention utilizes technology disclosed in U.S. Patent Application Nos. 2004/0149373, published on Aug. 5, 2004; 2004/0247931, published on Dec. 9, 2004; 2005/0003228, published on Jan. 6, 2005; and 2006/0219759, published on Oct. 5, 2006, all of which are incorporated herein by reference. 
         [0019]    Referring to  FIG. 1 , one embodiment of a fixed cutter rotary drill bit  11  is shown. Bit  11  has a rotational axis  12  and a threaded end  13  for connection into a drill string. A cutting end  15  at a generally opposite end of the bit  11  is provided with a plurality of hard cutting elements  17  (e.g., polycrystalline diamond cutters, etc.) arranged about cutting end  15  to effect efficient removal or cutting of formation material as bit  11  is rotated in a borehole. 
         [0020]    The cutting elements  17  typically are secured in a pocket provided on cutting end  15  such that they engage formation material. As illustrated, cutting element  17  may comprise a frustoconical cutting element  21  having a beveled edge. Cutting element  17  acts somewhat like a plow that generally directs a high percentage of the material of the formation up the flat face. 
         [0021]    The arrangement of cutting elements  17  on bit  11  is configured in an overall cutting profile about bit axis  12 . Starting at axis  12  and moving toward the outer diameter of bit  11 , the profile includes a cone  27 , a nose  25 , a shoulder  31 , and a gauge pad or surface  33 . The gauge surface  33  essentially defines the flat, outer diameter portion of bit  11  that extends from cutting end  15  and is proximal to and contacts the sidewall of the borehole during drilling operation of bit  11 . A plurality of channels or junk slots  35  extend from cutting end  15  through gauge surface  33  to provide a clearance area for the removal of cuttings and chips formed by cutting elements  17 . 
         [0022]    As suggested above, a plurality of cutting elements  17  are provided on gauge surface  33 . Cutting elements  17  on gauge surface  33  provide the ability to actively cut formation material at the sidewall of the borehole to provide dynamic stability and improved gauge-holding ability in earth boring bits of the fixed cutter variety. The cutting elements  17  on gauge surface  33  may be ground flat at the outer diameter of bit  11  for some applications. Bit  11  is illustrated as a polycrystalline diamond cutter (PDC) bit, but cutting elements  17  are equally useful in other fixed cutter or drag bits that include a gauge surface for engagement with the sidewall of the borehole. Examples include impregnated and natural diamond bits. 
         [0023]    As shown in  FIGS. 2 and 3 , each cutting element  17  has a cylindrical base  19  with an axis  20  and a PDC cutter  21  affixed thereto. The cutting element  17  also is provided with a substrate extension  23  that may be formed from the same material as base  19 . The substrate extension  23  is secured to the base  19  opposite the PDC cutter  21 . 
         [0024]    A new set of materials and techniques may be used to braze and/or solder the components of the cutting element and replace the conventional brazing processes that are typically employed. The components having desired physical properties (e.g., toughness, wear resistance, etc.), and be secured together with a reactive exothermic brazing technology. This technique eliminates: (1) the need for conventional brazing; (2) inconsistencies in cutter placement during conventional brazing; (3) brazing defects such as porosity; and (4) heat-affected zones and undesired phase changes due to traditional brazing processes. In addition, this technique allows experimentation and development of cutters that utilize virtually unlimited material selection to obtain unsurpassed bit life. 
         [0025]    The various cutter components may be formed to design requirements and reactively brazed together. This technique is much more precise (e.g., within tolerances of approximately 0.010 inches) than conventional torch brazing techniques (e.g., within tolerances of approximately 0.030 inches) and does not degrade the parent material to produce a higher performing rock bit. 
         [0026]    In one embodiment ( FIG. 3 ), the base  19  and substrate extension  23  are joined with a reactive foil  41  and braze alloy that is located between the components. Physical pressure (e.g., on the order of 700 psi) is applied to the parts and a small, localized energy pulse or other ignition source flows the metallic foil  41  in milliseconds to produce a strong metallic joint that results in a very strong, completed braze that is cool to the touch in less than one second. This process only heats the immediate surface of the materials being joined and does not degrade any heat treatment or change any properties of the parts. The braze and/or solder material may comprise, for example, Ag—Cu, Ni—Al, Al—Si, Zn—Al, etc. The reaction in the foil may be activated with a small pulse of localized energy that can be applied using optical, electrical, or thermal sources, such as electrical pulse, spark, hot filament, laser beam, etc. Such techniques reduce processing time, eliminate brazing material and equipment, and provide a safer operation for personnel. 
         [0027]    The reactive brazing process is quicker than conventional techniques and lends itself to high volume production since the cutters may be readily assembled with the reactive foil. Activation of the film is accomplished as described herein using a small pulse of localized energy that occurs in milliseconds. This technique only heats the surface of the elements without destroying the steel heat treatment of the adjacent material. 
         [0028]    As described above, the feature and component may comprise many different elements of a bit. The flowable material may comprise an alloy material containing, for example, Ag, Cu, Al, Ni, Au, Zn, Sn, or Ti. 
         [0029]    Referring now to  FIG. 4A , the flowable material may comprise a first braze alloy foil  51   a  located adjacent to a first component  53   a  (e.g., base  19 ), a second braze alloy foil  55   a  located adjacent to a second component  57   a  (e.g., substrate extension  23 ), and the reactive material  59   a  (e.g., reactive foil) may be located between the first and second braze alloy foils  51   a ,  55   a.    
         [0030]    Alternatively ( FIG. 4B ), the first and second components  53   b ,  57   b  may be coated with a braze or solder alloy material  52   b ,  56   b , respectively, before assembly with reactive material  59   b.    
         [0031]    In another alternate embodiment ( FIG. 4C ), separate braze alloy foils  51   c ,  55   c , may be positioned adjacent the respective coatings  52   c ,  56   c  on components  53   c ,  57   c  prior to assembly with reactive material  59   c . Alternatively, two or more layers of reactive material and braze alloy foils may be used in combination. The different coatings may comprise the same materials or different materials depending on the application. Similarly, the coatings and braze alloy foils may comprise the same or different materials. The method may further comprise preheating the component and the feature and applying a compressive load between the rock bit body and the component before assembly. 
         [0032]    Referring now to  FIG. 5 , one embodiment of the invention includes a method of joining the cutting components of a rock bit. The method begins as indicated, and comprises providing a cutter having a base and a cutting end, and a substrate extension (step  501 ); positioning a reactive material on the substrate extension (step  503 ); placing the cutter on the substrate extension such that the reactive material is located between the base and the substrate extension (step  505 ); providing a flowable material between the base and the substrate extension (step  507 ); delivering a pulse of energy to the reactive material to ignite the reactive material and flow the flowable material to join the base to the substrate extension (step  509 ); before ending as indicated. Other embodiments of the methods may utilize steps and techniques as described herein. 
         [0033]    For example, one alternate embodiment of the method joins a cutter to a fixed cutter bit by providing a rock bit body having a fixed blade with a pocket formed therein; positioning a reactive foil in the pocket; placing a cutter in the pocket such that the reactive foil is located between the fixed blade and the cutter; providing a reflowable alloy between the fixed blade and the cutter; and delivering a pulse of energy to the reactive foil to ignite the reactive foil and reflow the reflowable alloy to join the cutter to the fixed blade in less than one second. 
         [0034]    While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.