Abstract:
A thermally conductive sand shell molding system allows for controlling heat flow in a molten metal infiltrate powdered metal drill bit molding system to differentially cool the mold system to control differential shrinking and accompanying stress concentrations.

Description:
This application claims priority from U.S. Provisional Patent application Ser. No. 61/294,897 filed on Jan. 14, 2010, and is hereby incorporated by reference for all it contains. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Disclosed herein is a rotary earth boring drill bit and the method of manufacture of such a bit, and in particular, a rotary fixed cutter drill bit suitable for use in drilling boreholes into the earth for oil and/or gas exploration and production. 
     Earth boring drill bits are well known and used for drilling through earthen formations for mineral exploration and extraction, and in particular hydrocarbons. One particular type of earth boring drill bit has an infiltrated metal matrix body. This type of drill bit may be manufactured by packing a mould that has a negative pattern of the bit form with metal powder, such as tungsten carbide powder, around a metal (typically steel) blank. This assembly is then infiltrated with a molten binding alloy in a high temperature furnace process. 
     For each design of a drill bit, a mould must be built for forming the body of the bit. Then the blank may typically be suspended in the mould, as the metal powders are added. The assembly is then typically furnaced until the mass reaches a fairly uniform temperature of greater than about 1900 F in its center, which causes the metal binder to melt. Upon cooling, the metal binder solidifies, fusing the assembly into a sold mass. Upon cooling, the metal pin section may be threaded for attachment to a drill string. 
     Conventionally, a bit mould may be fabricated by machining hard graphite material, or pressing soft mud (Graphite/clay) material in a graphite pot using a pattern. Another method for manufacturing a bit mould is to employ direct layered manufacture techniques. In the operation, the layered manufacturing equipment sinters or otherwise secures a first layer of particles of mould material together, disposes a second layer of particles over the first layer, sinters particles in selected regions of the second layer together and to the first layer, and repeats this process to fabricate subsequent layers until the mould has been formed from the mould material particles. 
     Other known methods for manufacturing fixed cutter drill bits include machining the bit bodies from steel (or other metallic) blanks. Rather than a matrix type bit body with impregnated diamond grains, a solid metallic bit body may be machined from one of more blocks of metal, preferably steel, and a series of cutting elements may be mounted upon the bit&#39;s body. As described above, such cutting elements may take the form of polycrystalline diamond compact cutters in which a table of polycrystalline diamond is bonded to a substrate of less hard material, for example tungsten carbide, which, in turn, is mounted upon the steel bit body. 
     2. Description of the Related Art 
     Known layered manufacture techniques for making sand moulds include inject glue printing technology and laser sintering technology. The printing technique selectively dispenses the resin in the layered sand material. The activator contained in the sand hardens the binder and realizes the object one layer at a time from bottom to top. In the laser sintering process, the laser selectively sinters coated sand material by scanning cross-sections generated from a CAD file on the surface of a process platform. After each cross-section is scanned, the platform is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed. 
     U.S. Pat. No. 6,353,771 and GB Patent application 231545 claim a method to use a layering device to build a mould for a drill bit using solid and conventional sand moulds. The present invention is drawn to a thin wall, hollow and fill type of mould with high thermal conductive material sand mould. This type of sand mould increases heating rates during infiltration process and direction solidification during cooling reducing the propensity for casting defects such a macro and micro porosity and blank-matrix disbond. The high thermal conductive sand mould shell essentially permits the fabrication of matrix bit body with a casting quality that is superior to convention printed sand molds. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention relates to method for manufacturing a highly thermal conductive sand mould shell or sand mould components which are used to form matrix drill bits. A 3-dimensional solid model of the mould or mould components are designed using a computer aided design (CAD) system. A layering device divides the solid model in thin cross-section layers revealing a cross-sectional area. Layered manufacturing equipment is used to trace a layer area of mould material such as sand with the same thickness as that of a corresponding divided layer, and sinters or otherwise secures the mould material layer area. The layered manufacturing device proceeds to build the mould shell or mould component layer by layer. 
     The present invention employs layering manufacturing techniques to fabricate a novel hollow mould shell or a hollow mould component which is different than solid sand moulds or components. The hollow area is filled with graphite composites or other high conductive materials. The mould surface in contact with the hard matrix powder may be coated with a ceramic based slurry to improve as-cast surface finish. The thickness of the mould shell is minimized to reduce the sand thermal barrier of the shell. Minimum thickness is dependent on sand shell preform strength for a given type of resin coated sand and mould sizes. In addition, cooling conductors  112  that have even higher thermal conductivity than the mould shell may be selectively used to further move heat selectively out of the mould. This sand mould shell or component will be then placed in a graphite mould pot for manufacturing a matrix bit. 
     The present invention discloses a drill bit having: 
     a) A hollow sand shell instead of solid sand mould components; 
     b) Hollow sand printed shell filled with highly conductive materials; 
     c) Improved heading rate during infiltration and improved axial direction cooling rates during cooling 
     d) Improved as-cast quality of a matrix bit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cut-away view of a drill rig drilling a borehole into the earth with a drill rig. 
         FIG. 2  is a side view of a typical fixed cutter-type drill bit which may be made by the method of the present invention. 
         FIG. 3  is a top view of the typical fixed cutter-type drill bit of  FIG. 2 . 
         FIGS. 4 and 5  are cutaway perspective views of mould systems of the prior art 
         FIGS. 6-12  are several cutaway perspective views of the mould systems of present invention. 
         FIGS. 13 and 14  are perspective views of the highly conductive material filling the internal ‘crows foot’ sand stalk used for forming flushing fluid passages through the body of the drill bit, and also for the face of the drill bit. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a drill string  2  suspended by a derrick  4  for directionally drilling a borehole  6  into the earth for minerals exploration and recovery, and in particular petroleum. A bottom-hole assembly (BHA)  8  is located at the bottom of the borehole  6 . In directional drilling, the BHA  8  may have a downhole steerable drilling system  9  and may comprise a drill bit  10  having a leading face  12  and a gauge region  14 . 
     As the drill bit  10  rotates downhole, it cuts into the earth allowing the drill string  2  to advance, forming the borehole  6 . For the purpose of understanding how these systems may be operated, for the type of steerable drilling system  9  illustrated in  FIG. 1 , the drill bit  10  may be carried by a drive shaft  16  which passes through a housing  18 . Within the housing  18 , the drive shaft  16  contains a bend such that the output part of the drive shaft  16  is not coaxial with the housing  18 , but rather is angled thereto. This is just one of many types and configurations of bottom hole assemblies, however, and is shown only for illustration. The drill bit mould system of the present invention is not limited only to these types of drilling systems, and the invention contemplates that the new mould system may be used for many, varied drilling systems such as coiled tubing, as well as many other drilling and bottom hole assemblies that are well known in the industry. 
     The drill bit  10  may take a range of forms. In the present invention the drill bit  10  comprises a matrix-type bit body  11  into which cutting elements, for example polycrystalline or single crystal diamond grains are embedded or impregnated, the diamond material serving to abrade the formation material upon rotation of the drill bit  10 . These infiltrated bodies may be made in any one of a number of types of moulds. The present invention is drawn to a particular manner of manufacture of these moulds and the method of manufacture of drill bits made with this new infiltrated type of moulding. 
     In the present invention, the matrix bit body  11  may be shaped to include a series of upstanding blades upon which the cutters are mounted, channels being formed between the blades. In such an arrangement, the bit body  11  may be arranged to include nozzles to allow drilling fluid to be supplied to the channels between the blades for the purposes of cooling and cleaning of the cutters and to carry away from the drill bit material abraded, gouged or otherwise removed from the formation during drilling. 
     The drill bit  10  has a central axis of rotation  12  and a bit body  14  having a leading face  16 , an end face  18 , a gauge region  20 , and a shank  22  for connection to a drill string. A plurality of blades  26  are upstanding from the leading face  16  of the bit body and extend outwardly away from the central axis of rotation  12  of the bit  10 . Each blade  26  terminates in a gauge pad  28  having a gauge surface  29  which faces a wall  30  of the borehole  6 . 
     A number of cutters  34  are mounted on the blades  26  at the end face  18  of the bit  10  in both a cone region  36  and a shoulder region  38  of the end face  18 . 
     Each of the cutters  34  partially protrude from their respective blade  26  and are spaced apart along the blade  26 , typically in a given manner to produce a particular type of cutting pattern. Many such patterns exist which may be suitable for use on the drill bit  10  fabricated in accordance with the teachings provided herein. 
     A cutter  34  typically includes a preform cutting element that is mounted on a carrier in the form of a stud which is secured within a socket in the blade  26 . Typically, each preform cutting element is a curvilinear shaped, preferably circular tablet of polycrystalline diamond compact (PDC) or other suitable superhard material bonded to a substrate of tungsten carbide, so that the rear surface of the tungsten carbide substrate may be brazed into a suitably oriented surface on the stud which may also be formed from tungsten carbide. 
     While the leading face  16  of the drill bit  10  is responsible for cutting the underground formation, the gauge region  20  is generally responsible for stabilizing the drill bit  10  within the borehole  6 . The gauge region  20  typically includes extensions of the blades  26  which create channels  52  through which drilling fluid may flow upwardly within the borehole  6  to carry away the cuttings produced by the leading face  16 . To facilitate stabilization of the bit without performing a cutting action, the gauge pads  28  are arranged such that the gauge surfaces  29  thereof are devoid of cutters. Although not included in the illustrated embodiment, the gauge surfaces  29  may be provided with means to improve the wear resistance thereof, for example wear resistant inserts or a coating of hard facing material. Such means do not result in the gauge surfaces performing a cutting action but rather simply improve the wear resistance of these parts of the drill bit. 
     Within the bit body  14  is passaging (not shown) which allows pressurized drilling fluid to be received from the drill string and communicate with one or more orifices  54  located on or adjacent to the leading face  16 . These orifices  54  accelerate the drilling fluid in a predetermined direction. The surfaces of the bit body  14  are susceptible to erosive and abrasive wear during the drilling process. A high velocity drilling fluid cleans and cools the cutters  34  and flows along the channels  52 , washing the earth cuttings away from the end face  18 . The orifices  54  may be formed directly in the bit body  14 , or may be incorporated into a replaceable nozzle. 
       FIGS. 4 and 5  show a typical prior art sand mould shells  80 ,  90 . A 3-dimensional solid model of the mould components are designed using a computer aided design (CAD) system. A layering device such as a selective laser sintering system or an ink printing system may be utilized to fabricate these sand mould components based on the solid models. Bit features such as cutter sockets  100 , blade faces  102  and nozzle ports  104  may be formed in the mould material  106 . 
       FIG. 6  shows various negative form of features  100 ,  102 ,  104  which may be formed in a solid cylindrical body  106  of the mould by conventional machine methods. 
       FIG. 7  shows another sample of a hollow component  108  in the form of a Crowfoot Sand Stalk  108   a , which is one of the mould components in a mould assembly of the present invention. The same methodology as described above may be used to fabricate other hollow sand components similar to  108 . These sand components may also preferably be also hollow as shown in  FIGS. 6 and 7 . Furthermore other various configurations of hollow components ( 108 ,  108   a ,  108   b ,  108   c ) may be provided, as shown for example in  FIGS. 10-12 . 
     The hollow volumes may be filled with graphite  110  composites or other highly thermal conductive materials as shown in  FIGS. 13 and 14  through an access hole  114 , or other suitable method. 
     These sand printed mould or components may have thin walls and are filled with highly thermal conductive materials in the hollow area so that their thermal conductivities are higher than those of solid sand components. These thermal conductive materials may have different thermal conductivities to help the heat to be selectively moved. In this case, additional cooling conductors  112  (in  FIGS. 6 &amp; 12 ) can be located within the walls of the mould to provide selective additional cooling in selected areas. Their thermal conductivities may be adjusted in relation to that of the adjacent thin walls. The sand mould or component fabricated using the methodology disclosed herein will improve heating rate during infiltration and axial direction cooling rate during cooling and solidification of the casting. 
     The differential cooling provided to the drill bit disclosed herein helps minimize cracking and aids in reducing or eliminating cracking problems that has been known to occur in prior art processes. In additions, this will also improve as-cast physical properties of a matrix bit, such as strength, ductility and impact resistance. 
     Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.