Patent Publication Number: US-6986297-B2

Title: Method of manufacturing PDC cutters with chambers or passages

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 09/495,143, filed Jan. 31, 2000, now U.S. Pat. 6,655,234, issued Dec. 2, 2003. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to superabrasive inserts or compacts for abrasive cutting of rock and other hard materials. More particularly, the invention pertains to methods for manufacturing polycrystalline diamond compact (PDC) cutting elements with internal chambers or passages, such cutting elements being mountable on earth-boring drill bits and the like. 
     2. State of the Art 
     Drill bits for oil field drilling, mining and other uses typically comprise a metal body into which replaceable cutting elements are incorporated. Such cutting elements, also known in the art (depending on their intended use) as inserts, compacts, buttons, cutters and cutting tools, are typically manufactured by forming a hard abrasive layer on the tip of a sintered carbide substrate. As an example, polycrystalline diamond may be sintered onto the surface of a cemented carbide substrate under high temperature and pressure, typically about 1450–1600° C. and about 50–70 kilobar. During this process, a metal sintering aid such as cobalt may be premixed with the powdered diamond or swept from the substrate into the diamond to form a bonding matrix at the interface between the diamond and substrate. The process is conducted in a high-pressure press receptacle or cell and is commonly known as a high-temperature, high-pressure (HTHP) process. 
     During drilling operations, cutters are subjected to high temperatures and very high forces imparted upon the cutters in various directions, leading to rapid fracture, delamination, or spalling of the superabrasive table and the underlying substrate. 
     The introduction of drilling fluids at the cutting end, or face, of the drill bit has long been known as advantageous for cooling the drill bit and washing out formation chips and rock particles from the cutting area. The drilling fluids are typically passed through the tubular drill string and into the bit body itself, which has outlets for discharging the drilling fluid at its cutting end. However, such an arrangement is not always sufficient to maintain the cutting elements themselves at a desired reduced temperature for prolonging their life. 
     U.S. Pat. No. 5,435,403 of Tibbitts discloses cutting elements formed of a superabrasive material mounted on a substrate. Various interfacial configurations are taught. 
     U.S. Pat. Nos. 5,316,095 of Tibbitts and 5,590,729 of Cooley et al., both assigned to the assignee hereof, Baker Hughes Incorporated, and hereby incorporated by reference herein, disclose cutting elements which have internal chambers and/or passages within the substrates thereof. These chambers and passages serve for passing drilling fluid to directly cool the diamond tables as well as for flushing cutting-induced chips of formation or other drilling-produced solids from the cutting surfaces engaging the formation. The internal chambers and/or passages are formed either during the formation of the substrate, or by machining, drilling, or other procedures subsequent to the construction of the substrate but before attachment of the superabrasive table thereto. The superabrasive table and substrate are usually bonded together by using a known HTHP process. As shown in these references, many different variations in cutting element types, sizes, shapes, and passage configurations are possible. 
     While the internally cooled cutting element is conceptually advantageous from a longevity standpoint, its construction has been difficult and time consuming, with all too frequently occurring problems arising in the HTHP bonding process. A primary problem is that during the HTHP process for bonding of the superabrasive, typically a diamond containing, table to the substrate, the substrate material, typically a carbide such as tungsten carbide, can yield under pressure and be forced into preformed passage(s) in the substrate, thereby constricting or even wholly blocking the preformed passage(s). In some cases, the substrate may collapse and even break, ruining the cutting element. In addition, diamond particles also may be forced into the preformed passage(s), closing off some as well as decreasing the diamond table thickness and integrity. In order to maintain an open passage for the flow of drilling fluid, the intrusive material, e.g., very hard carbide or diamond material, must be mechanically removed. Effective removal is difficult and costly, if not impossible, and the resulting cutting element may not be as structurally strong as an element having had no carbide and/or diamond material in the internal passage or cavity. 
     Forming a non-linear or complex-shaped passage or cavity, or passages or cavities, in a suitable location in a substrate following bonding to a superabrasive table is very difficult, inasmuch as precise drilling/machining of the very hard carbide of the substrate in different directions is generally required, and the attached superabrasive table may block access for drilling the interior of the substrate in the required directions. 
     A satisfactory method is needed for fabricating cutting elements with internal substrate passages with a high degree of reproducibility and reliability while significantly reducing the cost of manufacture, inasmuch as the present manufacturing methods are inadequate in that regard. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a cutting element for a drill bit, in which the cutting element has internal cavities forming at least one passage therein. The present invention also provides a superabrasive cutting element with at least one internal passage enabling passage of drilling fluid therethrough and into the cutting area for cooling the cutting element and removing cuttings generated by the cutting surfaces of the cutting elements as the cutting elements engage a formation. Additionally, the present invention provides a superabrasive cutting element having at least one internal fluid flow passage with reduced frictional resistance with respect to fluid flow therein. 
     The present invention includes methods for forming a superabrasive cutting element with at least one internal passage of a consistently controllable shape and size. The present invention yet further includes methods for forming a superabrasive cutting element having an internal chamber adjacent a cutting table interface for passage of cooling fluid past the cutting table. The present invention yet still further includes methods for forming a superabrasive cutting element having at least one internal passage, the size and shape of which is maintained in a HTHP fabrication step. 
     The invention comprises a method for manufacturing a cutting element having a superabrasive layer, or table, bonded to a substrate having at least one internal cavity, or passage. The cavity may comprise, for example, a continuous hollow passage through which a cutting fluid may be introduced from the bit body or a stud thereof so as to exit proximate the table of the cutting element for cooling the table as well as the cutting element. 
     In the present invention, a substrate is first formed with an internal cavity, and prior to attaching or bonding a superhard table thereto, the cavity is packed with a substantially rigid, solid filler material which may readily be removed following HTHP bonding. The filler material prohibits or, at a minimum, resists encroachment of either the substrate or table material into the internal cavity during the HTHP process. 
     The present invention also contemplates fabrication of a drill bit including cutting elements formed to the present invention wherein the drill bit has at least one internal passage for communication with at least one passage or cavity formed in the cutting elements. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The following drawings illustrate various embodiments of the invention, not necessarily drawn to scale, wherein: 
         FIG. 1  is a perspective view of a drill bit incorporating a plurality of cutting elements with internal chambers or passages, as manufactured by a method of the invention; 
         FIG. 1A  is an enlarged perspective view of a cutting element with internal passages and manufactured in accordance with a method of the invention, mounted on the face of the bit of  FIG. 1 ; 
         FIG. 1B  is an enlarged perspective view of the cutting element of  FIG. 1A  after use in drilling a borehole; 
         FIG. 2  is a top elevation of another cutting element with internal passages; 
         FIGS. 3 and 3A  are, respectively, top and front elevation views of a cutting element with internal passages; 
         FIG. 4  is a side sectional view of a stud-type cutter employing a cutting element with an internal passage in a bit; 
         FIG. 5  is a side elevation view of a further prior art cutting element with an internal passage and mounted in a bit; 
         FIG. 6  is a side elevation of another cutting element with an internal passage and mounted in a bit; 
         FIG. 7  is a side elevation view of an additional cutting element with an internal passage and mounted in a bit; 
       FIG;  8  is a side elevation view of another cutting element with an internal passage and mounted in a bit; 
         FIGS. 9 ,  10  and  11  depict cutting elements with slots or grooves communicating with the rear of the substrates; 
         FIG. 12  is a cross-sectional side view of a cutting element with an internal passage and mounted in a bit; 
         FIG. 13  is a side view of a cutting element with internal channels and mounted in a bit; 
         FIG. 14  is a cross-sectional view of a cutting element with an internal chamber and mounted in a bit and shown engaging a subterranean formation; 
         FIG. 15  is a cross-sectional side view of a cutting element with an internal cavity and mounted in a bit; 
         FIG. 16  is a cross-sectional side view of a cutting element with an internal cavity and mounted in a bit; 
         FIG. 17  is a block diagram of the general steps of a process embodying the present invention for forming a cutting element with an internal cavity; 
         FIG. 18  is an isometric exploded side view of an exemplary cutting element during a manufacturing process of the invention; and 
         FIGS. 19A–H  are diagrammatic views illustrating steps embodying the present invention for fabricating the exemplary cutting element depicted in  FIG. 18  as taken along line  19 — 19 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred method of the invention and various exemplary drill bit cutting elements formed thereby are illustrated in the figures. 
     The preferred method includes fabricating a drill bit cutting element  20  typically having a polycrystalline diamond compact (PDC) layer to form a superabrasive, or diamond, cutting table  30  which is bonded to a substrate  34 . Substrate  34  is characterized in that it includes an internal cavity  46  such as a channel in which a liquid, e.g., drilling fluid or mud, is passed for circulating chips away from the region in which cutting is occurring and for cooling purposes. 
     In  FIG. 1  is shown an exemplary, but not limiting, drill bit  10  which incorporates at least one cutting element or drill bit cutter  20  of the invention. The illustrated drill bit  10  is known in the art as a fixed cutter, or drag, bit useful for drilling in earth formations and is particularly suitable for drilling oil, gas, and geothermal wells. Cutting elements  20  made with the present invention may be advantageously used in any of a wide variety of drill bits  10  configured to use cutting elements. Drill bit  10  includes a bit shank  12  having a pin end  14  for threaded connection to a tubular drill string, not shown, and also includes a body  16  having a bit face  18  on which cutting elements  20  may be secured. Bit  10  typically includes a series of nozzles  22  for directing drilling fluid, or mud, to the bit face  18  for circulating and removing chips or cuttings of the formation to the bit gage  24  and passage thereof through junk slots  26 , past the bit shank  12  and drill string to the surface. 
       FIGS. 1 through 16  show a wide variety of configurations of cutting elements  20  manufacturable by the method of the invention, but are not meant to comprise limitations thereof. 
     As depicted in  FIGS. 1A ,  1 B,  2 ,  3  and  3 A, an exemplary cutting element  20  formed by the method of the invention comprises a PDC cutting element including a diamond layer or superabrasive table  30  having a front face  32  and a rear face (not shown) bonded to a disc-shaped substrate  34  of similar configuration. Front face  32  is maintained on the bit face  18  by brazing to a bit body  16  or to a carrier element secured thereto, or by direct bonding during formation of the bit body  16  during fabrication of the bit  10 . Cutting element  20  is supported from the rear against impact by protrusion  36  on the bit body face  18  which, as shown, defines a socket or pocket  38  in which the cutting element is cradled. Alternatively, cutting element  20  may be mounted on a cylindrical or stud-type carrier element, the latter type being press-fit or mechanically secured to the bit body  16 , while both cylinders and studs may be braced therein. 
     Cutting elements  20  include peripheral cutting edges or formation contact zones  40  which engage the subterranean formation as the bit  10  is rotated and a longitudinal force is applied to the bit by way of the drill string. 
     As disclosed herein, cutting element  20  includes at least one cavity  46  which opens into one or more channels  42  shown with outlets  44 . Channels  42  are shown as formed at the table/substrate interface, either within the superabrasive table  30  or substrate  34 , or partially within both. While drilling a bore hole with a drill bit  10  of this construction, a drilling fluid, not shown, may be pumped through the cavity  46 , channels  42  and outlets  44  to cool and lubricate the cutting element  20  and to flush cuttings from the bore hole. 
       FIGS. 4 through 13  illustrate other cutting elements  20  having an internal cavity  46 . In general, outlets  44  lie at the periphery of and below superabrasive table  30 . However, as shown in  FIG. 8 , an aperture  50  may be formed in superabrasive table  30  of alternate cutting element  20 ′, serving as an outlet for drilling fluid. 
     In  FIG. 4  is shown a stud type cutter  60 , wherein substrate  34  of cutting element  20  is mounted on a stud  62  whose lower end  64  is secured in an aperture  66  in bit face  18 . Fluid from a plenum  68  may be passed through passage  70  to channels  42  and discharged from outlets  44  preferably adjacent superabrasive table  30 . 
     As shown in the embodiments of  FIGS. 5 and 6 , channels  42  optimally do not actually abut superabrasive table  30  but are nevertheless generally proximate thereto in a preferred embodiment. 
       FIGS. 8 through 14  depict other cutting elements  20 ′ having a variety of differently shaped cavities or channels  42  and  42 ′. 
       FIG. 14  shows a cutter  20 ′ mounted in a bit body  16  as cutter  20 ′ engages a subterranean formation  200 . 
     In  FIG. 11  is shown a cutting element  20 ′ having a substrate  34  with flow channels  42 ′ on the exterior surface thereof. Such exterior channels  42 ′ may be preformed in the substrate  34  and protected against distortion by the present invention. 
       FIGS. 15 and 16  illustrate cutting elements  910  with substrates  914  having cavities  950  which abut cutting tables  912  in dead-end fashion. In this embodiment, a fluid  956  may be directed into cavities  950  from plenums  954 . 
     The preferred method of the invention is outlined in  FIGS. 17 ,  18  and  19 , and illustrates the difficulties overcome by the present invention in manufacturing cavitied cutting elements  20 ,  910  of the previous  FIGS. 1 through 16 , as well as others not shown. 
     An exemplary cutting element  20  formed by the preferred method of the invention is shown in  FIG. 18 . It includes a superabrasive table  30  and substrate  34 . Substrate  34  is shown as having a generally longitudinally oriented internal cavity  46  passing through it and side channels  42  communicating with the cavity  46  for passing fluid therethrough and discharging fluid through outlets  44 . 
     Steps of the preferred method are illustrated in  FIG. 19  for constructing the exemplary substrate  34  shown in  FIG. 18 . 
     Substrate  34  of  FIG. 19A  is formed typically of tungsten carbide. The substrate  34  may be molded to include a cavity or cavities  46 , including channel(s)  42  each having an inlet  43  and outlet(s)  44  for passage of cutting fluid, not shown, to the cutting edge(s)  40  of the superabrasive table  30 . Optionally, exterior channels  42 ′ shown in  FIG. 11  may be formed in substrate  34  but are not used in this example. 
     In an alternative method, cavity or cavities  46  in substrate  34  are formed by, e.g., drilling and/or machining of a preformed substrate  34 . 
     As depicted in  FIG. 19B , substrate  34  with internal cavity  46  is placed in a cell or receptacle  80 , and a filler material  90  is packed into the cavity or cavities  46  (including channels  42 ) to fill the space preferably with a solid mass having relatively low compressibility. For example, a ram  82  may be used to pack the filler material  90  to the desired density. Excess filler material  90  is then removed, resulting in substrate  34  supported against collapse by compressed filler material  90 , as depicted in  FIG. 19C . Filler material  90  is shown as a crystalline salt, but may comprise other materials having the appropriate properties. As shown, the substrate  34  may be placed on a plate  86  within the cell  80 . 
     As illustrated in  FIG. 19D , a layer  84  of particulate diamond crystals is placed atop substrate  34 , and the loaded receptacle or cell  80  is subjected to a HTHP process schematically shown in  FIG. 17 . For example, a ram  88  may be used to compress the diamond layer  84  and substrate  34  at high temperature to form a superabrasive diamond layer or table  30  (shown in  FIG. 19E ) securely bonded to the upper surface  72  of substrate  34 . If desired, a metal catalyst, not shown, may be included to enhance the table formation and bonding strength. 
     The conditions of the HTHP process are typically carried out at about 50–70 kilobar of pressure and at temperatures typically of about 1450–1600° C., and for a time period sufficient to form the superabrasive table  30  and tenaciously and securely bond substrate  34  and superabrasive table  30  to each other. 
     As shown in  FIG. 19E , cutting element  20  may then be removed from cell  80 . 
     Filler material  90  is then removed from the cavity or cavities  46 , typically by dissolution, melting, mechanical removal, chemical removal, or other suitable means.  FIG. 19F  illustrates mechanical removal of filler material  90  by a drill, reamer, or other tool  74 .  FIG. 19G  illustrates removal of filler material  90  from cavities  46 , including channels  42 , with a water stream  76  introduced through tube  78 . The soluble filler material  90 , e.g., salt, is simply dissolved within the water and flows away. 
     In an alternative method, not illustrated, filler material  90  comprises a material which is solid at the HTHP conditions previously discussed, for example, but melts at a temperature preferably nearly equal to or less than at the HTHP condition when at atmospheric pressure, or when subjected to a vacuum. Thus, filler material  90  is then removed by melting. 
     Optional methods for removal of filler material  90  include merely scraping it from cavity  46  with a hand tool, or using an erosive, e.g., sand or grit, blast to erode it away. 
     The completed cutting element  20  is then ready for attachment to a stud (not shown) or directly to a drill bit  10  for use. 
     As can be appreciated, the preferred manufacturing process may be modified in a variety of ways, without departing from the scope of the present invention. 
     In one alternative, for example, cell  80  is filled in reverse order. Thus, diamond layer  84  is first formed in cell  80 . Substrate  34  is then inserted, upside-down. The cavities  46  are filled with filler material  90  and compacted, followed by the previously discussed HTHP process. Removal of filler material  90  may be according to any effective manner. This method is especially useful where cavity  46  does not extend fully to the upper (interfacial) surface  72  of the substrate  34 . Thus, cavity  46  is filled with filler material  90  from the mounting end  56  of the substrate  34 , i.e., opposite the interfacial surface  72 . 
     Where a substrate  34  is of irregular shape, and/or the cavity  46  passes one or more sides  58  of the substrate  34  without passing through interfacial surface  72  and mounting end  56 , cell  80  will be somewhat larger than the substrate  34 . Filler material  90  is packed into the cell  80  to both fill the cavity  46  as well as substantially surround substrate  34 , thereby leaving interfacial surface  72  exposed to superabrasive layer  84  of, e.g., diamond material. Thus, a cutting element  20  having any shape may be formed in accordance with the process of the present invention. 
     In another embodiment of the invention, superabrasive table  30  itself has one or more outlets  44  for passage of drilling fluid to the front face  32  of superabrasive table  30 . 
     In another alternative, the invention is combined with a layering method of making the drill bit  10 . Cutting element  20  may be designed to include multiple cavities  46  and channels  42 , possibly creating complex passages. With the design of complex passages in the cutting element  20 , more complex internal passages may be required in the drill bit body  16  and face  18  for connection with the corresponding passages in the cutting element  20 . U.S. Pat. No. 5,433,280 of Smith, assigned to the assignee hereof, Baker Hughes Incorporated, and hereby incorporated by reference herein, discloses a layering method for manufacturing a drill bit  10  which would be suitable for designing such complex passages. The method, as disclosed by Smith, is carried out by sequentially depositing thin layers of a material upon one another and then fusing them together. Thus, the outer shape of the bit as well as inner passages and structures are defined incrementally layer by layer. By using such a method for the manufacture of a drill bit  10  in conjunction with the invention described herein, more numerous and complex passageways could be designed in both the cutting elements and the bit to which they are mounted for greater efficiency with respect to heat transfer and fluid flow properties. 
     The preferred process illustrated in  FIGS. 19A–H  having simplified components is exemplary, or suggestive, of that used in a more complex manufacturing method embodying the present invention. At a production scale, for example, cells  80  may be configured to simultaneously form a plurality of cutting elements  20 , and other equipment differences may be used, including automation of the process. Any cell configuration which enables the preferred HTHP fabrication process of constructing a cutting element by incorporating a removable filler material  90  may be used. 
     The term “substantially incompressible” is used to denote that at the conditions encountered herein, the filler material will resist and/or prevent any substantial encroachment of the substrate material and/or table material into cavity  46 . In most cases, the term “substantially incompressible” implies that the extent of volume reduction due to being subjected to compressive forces will typically be less than about 15 percent (15%). 
     Removable filler material  90  may be any material which acts as a relatively rigid-body structural member during high-pressure sintering and is readily removed thereafter by dissolution, shaking out, digging out, melting, erosion, chemical transformation, or other process. Thus, applying or bonding superabrasive table  30  to substrate  34  under high temperature and high pressure (HTHP) is accomplished without significant collapse or distortion of the substrate material or table material into cavities  46 , or roughening of cavity walls  52 . 
     Removable filler material  90  is selected on the basis of a number of properties and characteristics, among which are the following exemplary characteristics: 
     Filler material  90  preferably forms a relatively rigid member, i.e., has limited compressibility at conditions at least up to and including the HTHP temperature and pressure. 
     Filler material  90  preferably is readily and easily removable following the HTHP process. 
     Filler material  90  may be granular, but preferably does not easily flow or migrate into the superabrasive table material, and preferably does not significantly flow or migrate into the filler material. If desired, a thin member comprising a layer of a generally non-penetrable material such as tungsten, or other refractory materials, may be inserted between the granular filler material  90 , such as crystalline diamond particles, forming superabrasive table  30 , to prevent diffusion therebetween. Of course, if the passage or passages formed in the substrate do not open onto the end thereof where the superabrasive table  30  is formed, this is not a concern. 
     Filler material  90  may be a salt such as halite or sodium chloride (NaCl), which material is readily packed into the voids or cavities  46  formed in substrate  34 , is highly soluble in water at ambient conditions, and is non-toxic and inexpensive. Although a small quantity of carbide and/or diamond particles may infiltrate the interstices of the salt, the particles will be subsequently washed out of the cavities  46  by water or other solvent  76 . 
     Filler material  90  may optionally comprise a natural volcanic material such as Pyrofolyte™ volcanic material commercially available from Ore and Metal Company, LTD., 6 Street, Andrews Road, Parktown, Johannesburg, South Africa. This material is relatively soft, and is readily mechanically removable from internal cavities  46  of a substrate  34 . 
     Alternatively, a substance such as boron nitride may be used as filler material  90 , which remains a solid at the high-temperature, high-pressure sintering conditions and is easily removed by mechanical means. 
     For the purposes described herein, methods of this invention for fabricating cutting elements having voids, cavities or passages therein are particularly suitable for use with the construction of any cutting element  20  having a superabrasive table  30  and a substrate  34  being attached or bonded together in a HTHP or equivalent process. The cavities  46  formed in such cutting elements  20  may have any purpose without departing from the invention. Thus, it will be appreciated that various additions, deletions, and modifications to the embodiments of the invention disclosed herein are possible without departing from the spirit and scope of the present invention as claimed.