Abstract:
Methods of depositing hardfacing material portions of earth-boring tools may involve supporting at least a portion of an earth-boring tool in a holder of a workpiece positioner, the holder being movable in at least a third plane. A location of a surface of the at least a portion of the earth-boring tool may be determined utilizing at least one sensor. The workpiece positioner, the sensor, and a torch positioner comprising a hardfacing torch movable in at least a first plane perpendicular to the third plane and a second plane parallel to the third plane may be controlled utilizing a programmable control system to cause the torch positioner to oscillate the hardfacing torch in the second plane while selectively causing the workpiece positioner to move the holder in the third plane and causing the torch to deposit hardfacing material on the surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/903,310, filed May 28, 2013, which is a divisional of U.S. patent application Ser. No. 12/257,219, filed Oct. 23, 2008, now U.S. Pat. No. 8,450,637, issued May 28, 2013, the disclosure of each of which is incorporated herein in its entirety by this reference. The subject matter of this application is related to the subject matter of U.S. patent application Ser. No. 12/341,595, filed Dec. 22, 2008; U.S. patent application Ser. No. 12/603,734, filed Oct. 22, 2009, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/109,427, filed Oct. 29, 2008; U.S. patent application Ser. No. 12/562,797, filed Sep. 18, 2009, now U.S. Pat. No. 8,698,038, issued Apr. 15, 2014; and U.S. patent application Ser. No. 12/651,113, filed Dec. 31, 2009, now U.S. Pat. No. 8,471,182, issued Jun. 25, 2013; the disclosure of each of which is incorporated herein in its entirety by this reference. 
     
    
     FIELD 
       [0002]    The present invention relates to a system and method for the application of hardfacing to portions of a drill bit using robotic apparatus. 
       BACKGROUND 
       [0003]    In the exploration of oil, gas, and geothermal energy, wells or boreholes in the earth are created in drilling operations using various types of drill bits. These operations typically employ rotary and percussion drilling techniques. In rotary drilling, the borehole is created by rotating a drill string having a drill bit secured to its lower end. As the drill bit drills the well bore, segments of drill pipe are added to the top of the drill string. While drilling, a drilling fluid is continually pumped into the drilling string from surface pumping equipment. The drilling fluid is transported through the center of the hollow drill string and through the drill bit. The drilling fluid exits the drill bit through one or more nozzles in the drill bit. The drilling fluid then returns to the surface by traveling up the annular space between the well bore and the outside of the drill string. The drilling fluid transports cuttings out of the well bore as well as cooling and lubricating the drill bit. 
         [0004]    The type of drill bit used to drill the well will depend largely on the hardness of the formation being drilled. One type of rotary rock drill is a drag bit. Early designs for a drag bit included hardfacing applied to various portions of the bit. Currently, designs for drag bits have extremely hard cutting elements, such as natural or synthetic diamonds, mounted to a bit body. As the drag bit is rotated, the cutting elements form the bottom and sides of the well bore. 
         [0005]    Another typical type of rotary drill bit is the tri-cone roller drill bit that has roller cones mounted on the body of the drill bit, which rotate as the drill bit is rotated. Cutting elements, or teeth, protrude from the roller cones. The angles at which the roller cones are mounted on the bit body determine the amount of “cut,” or “bite” of the bit with respect to the well bore. As the roller cones of the drill bit roll on the bottom of the hole being drilled, the teeth or carbide inserts apply a high compressive and shear loading to the formation causing fracturing of the formation into debris. The cutting action of roller cones comprises a combination of crushing, chipping and scraping. The cuttings from a roller cone drill bit typically comprise a mixture of chips and fine particles. 
         [0006]    Yet another type of rotary drill bit is a hybrid drill bit that has a combination of hard cutting elements, such as natural or synthetic diamonds and roller cones mounted on the body of the drill bit. 
         [0007]    There are two general types of roller cone drill bits; TCI bits and steel-tooth bits. “TCI” is an abbreviation for Tungsten Carbide Insert. TCI roller cone drill bits have roller cones having a plurality of tungsten carbide or similar inserts of high hardness that protrude from the surface of the roller cone. Numerous styles of TCI drill bits are designed for various types of formations, in which the shape, number and protrusion of the tungsten carbide inserts on the roller cones of the drill bit will vary, along with roller cone angles on the drill bit. 
         [0008]    Steel-tooth roller cone drill bits are also referred to as milled-tooth bits because the steel teeth of the roller cones are fanned by a milling machine. However, in larger bits, it is also known to cast the steel teeth and, therefore, “steel-tooth” is a better reference. A steel-tooth roller cone drill bit uses roller cones, with each cone having an integral body of hardened steel with teeth formed on the periphery. There are numerous styles of steel-tooth roller cone drill bits designed for formations of varying hardness in which the shape, number and protrusion of the teeth will vary, along with roller cone angles on the drill bit. 
         [0009]    The cost efficiency of a drill bit is determined by the drilling life of the drill bit and the rate at which the drill bit penetrates the earth. Under normal drilling conditions, the teeth of the steel-tooth roller cone drill bits are subject to continuous impact and wear because of their engagement with the rock being drilled. As the teeth are worn away, the penetration rate of the drill bit decreases causing the cost of drilling to increase. 
         [0010]    To increase the cost efficiency of a steel-tooth roller cone drill bit or a hybrid drill bit having steel-tooth roller cones, it is necessary to increase the wear resistance of the steel teeth. To accomplish this, it is known to deposit one or more layers of a wear-resistant material or “hardfacing” to the exposed surfaces of the steel teeth. Fusion hardfacing refers to a group of techniques that apply (fuse) a wear-resistant alloy (hardfacing) to a substrate metal. Common hardfacing techniques include arc welding and gas torch welding, among other welding processes. 
         [0011]    Conventional welding techniques used to apply hardfacing to steel-tooth roller cone drill bits include oxyacetylene welding (OAW) and atomic hydrogen welding (AHW). Currently, manual welding is typically used in the commercial production of roller cone rock bits. Roller cones are mounted on a positioning table while a welding torch and welding rod are used to manually apply hardfacing to portions of each tooth of each roller cone by a welder moving from tooth to tooth and cone to cone from various positions. 
         [0012]    Conventional hardfacing materials used to add wear resistance to the steel teeth of a roller cone drill bit include tungsten carbide particles in a metal matrix, typically cobalt or a mixture of cobalt and other similar metals. Many different compositions of hardfacing material have been employed in the rock bit field to achieve wear-resistance, durability and ease of application. Typically, these hardfacing materials are supplied in the form of a welding rod, but can be found in powder form for use with other types of torches. 
         [0013]    The physical indicators for the quality of a hardfacing application include uniformity, thickness, coverage, porosity, and other metallurgical properties. Typically, the skill of the individual applying hardfacing determines the quality of the hardfacing. The quality of hardfacing varies between drill bits as well as between the roller cones of a drill bit, and individual teeth of a roller cone. Limited availability of qualified welders has aggravated the problem because the application of hardfacing is extremely tedious, repetitive, skill-dependent, time-consuming, and expensive. The application of hardfacing to roller cones is considered the most tedious and skill-dependent operation in the manufacture of a steel-toothed roller cone drill bit. The consistency of the application of hardfacing to a drill bit by a skilled welder varies over different portions of the drill bit. 
         [0014]    To summarize, manually applying hardfacing to a roller cone involves the continuous angular manipulation of a torch over the roller cone, the roller cone held substantially stationary, but being rotated on a positioning table. After hardfacing is manually applied to a surface of each tooth of the roller cone using a torch and welding rod containing the hardfacing material, the positioning table and cutter are indexed to a new angle and position to permit application of hardfacing to a surface of the next tooth of the roller cone until all the cutters have been rotated 360 degrees. At that time, the angle of the table and cutter is adjusted for the application of hardfacing to another tooth surface or row of teeth of the roller cone. 
         [0015]    When attempts to utilize robotics to automate the welding process were made, the same configuration was used having a robotic arm to replace the human operator&#39;s arm and its varied movements, while leaving the roller cone on a positioning table. The positioning table is capable of automatic indexing between teeth and rows of teeth of a roller cone. 
         [0016]    This configuration and procedure would be expected to provide the recognized benefits of manual hardfacing for a number of reasons. First, manual and automatic torches are much lighter and easier to continuously manipulate than the heavy steel cutters with teeth protruding in all directions. Second, the roller cone must be electrically grounded, and this can be done easily through the stationary positioning table. Third, gravity maintains the heavy roller cone in position on the positioning table. Fourth, highly angled (relative to vertical) manipulation of the torch allows access to confined spaces between teeth of the roller cone and is suited to the highly articulated movement of a robotic arm. 
         [0017]    U.S. Pat. No. 6,392,190 provides a description of the use of a robotic arm in hardfacing of roller cones, in which the torch is held by a robotic arm and the roller cones are moved on a positioning table. A manual welder is replaced with a robotic arm for holding the torch. The robotic arm and a positioning table are combined to have more than five movable axes in the system for applying hardfacing. However, U.S. Pat. No. 6,392,190 does not describe details of solutions to the numerous obstacles in automating the hardfacing of roller cones using robotic arms and positioners. 
         [0018]    One factor limiting use of robotic hardfacing has been the unsatisfactory appearance of the final product when applied using robotically held torches over stationary cutters. Another factor limiting use of robotic hardfacing to rolling cutters is the commercial unavailability of a material that directly compares to conventional Oxygen Acetylene Welding (OAW) welding rod materials that can be applied with commercially available Plasma Transferred Arc (PTA) torches. 
         [0019]    Another factor limiting use of robotic hardfacing is the inability to properly identify and locate individual roller cone designs within a robotic hardfacing system. The roller cones of each size of drill bit and style of drill bit are substantially different, and initiating the wrong program could cause a collision of the torch and part, resulting in catastrophic failure and loss. Another factor limiting use of robotic hardfacing is the inability to correct the critical positioning between the torch and roller cone in response to manufacturing variations of the cutter, wear of the torch, and buildup of hardfacing. 
         [0020]    Still another factor limiting use of robotic hardfacing has been the inability to properly access many of the areas on the complex surface of a roller cone that require hardfacing with commercially available Plasma Transferred Arc (PTA) torches large enough to permit application of the required material. A small form factor (profile) is required to access the roots of the teeth of a roller cone that are close together. However, most conventional PTA torches require large powder ports to accommodate the flow of the medium-to-large mesh powder required for good wear resistance. Torches with smaller nozzles have smaller powder ports that prohibit proper flow of the desired powders. 
         [0021]    Another factor limiting use of robotic hardfacing is the complexity of programming a control system to coordinate the critical paths and application sequences needed to apply the hardfacing. For example, undisclosed in the prior art, the known torch operating parameters, materials, application sequences, and procedures used for decades in manual hardfacing operations have proven to be mostly irrelevant to robotic hardfacing of roller cones. A related factor limiting use of robotic hardfacing is the cost and limitation of resources. A significant investment and commitment of machine time are required to create tests, evaluate results, modify equipment, and incrementally adjust the several operating parameters, and then integrate the variations into production part programs. These and several other obstacles have, until now, limited or prevented any commercial practice of automated hardfacing of roller cones. 
         [0022]    Therefore, there is a need to develop a system and method for applying hardfacing to roller cones consistent with the highest material and application quality standards obtainable by manual welding. There is also a need to develop a system that identifies parts, selects the proper program, and provides programmed correction in response to manufacturing variations of the roller cones, wear of the torch, and buildup of hardfacing. There is also a need to develop a PTA torch design capable of accessing more of the areas on a roller cone&#39;s cutter that require hardfacing. There is also a need to develop a hardfacing material, the performance of which will compare favorably to conventional Oxygen Acetylene Welding (OAW) materials and flow properly through the PTA torch design. 
       BRIEF SUMMARY 
       [0023]    A system and method for the application of hardfacing to surfaces of drill bits is disclosed. 
         [0024]    In some embodiments, methods for depositing hardfacing material on portions of drill bits comprise providing a vertically oriented plasma transfer arc torch secured to a positioner having controllable movement in a substantially vertical plane. A rolling cutter is secured to a chuck mounted on an articulated arm of a robot. A surface of a tooth of the rolling cutter is positioned in a substantially perpendicular relationship beneath the torch. The torch is oscillated along a substantially horizontal axis. The rolling cutter is moved with the articulated arm of the robot in a plane beneath the oscillating torch. A hardfacing material is deposited on the tooth of the rolling cutter. 
         [0025]    In other embodiments, methods for depositing hardfacing material on portions of drill bits comprise providing a vertically oriented plasma transfer arc torch secured to a positioner having controllable movement in a substantially vertical plane. A cutter is secured to a chuck mounted on an articulated arm of a robot. A surface of a tooth of the cutter is positioned in a substantially perpendicular relationship beneath the torch. A first waveform target path is provided and the torch is oscillated along a substantially horizontal axis. The cutter is moved with the articulated arm of the robot beneath the midpoint of the oscillating torch path so as to impose a second torch waveform onto the first waveform target path to create a hardfacing pattern on a tooth. 
         [0026]    In still other embodiments, methods for depositing hardfacing material on the teeth of rolling cutters of rock bits, wherein the rolling cutter has protruding teeth on a plurality of rows, comprise providing a vertically oriented plasma transfer arc torch, secured to a positioner in a substantially vertical plane. The rolling cutter is secured to a chuck mounted on an articulated arm of a robot and a surface of a tooth of the rolling cutter is positioned in a substantially horizontal plane beneath the torch. A bead of hardfacing material is deposited on the tooth of the rolling cutter while moving the rolling cutter with the articulated arm of the robot. 
         [0027]    In yet other embodiments, methods for hardfacing portions of drill bits comprise providing a portion of a drill bit having thin and thick portions and providing a plasma transfer arc torch secured to a positioner having program controllable motion. One of a portion of the drill bit and the drill bit is secured to a chuck mounted on an articulated arm of a robot having programmable controlled motion. A weld path is begun at the thin portion of the drill bit and hardfacing is deposited in a path directed towards the thick portion of the drill bit. Torch amperage is increased in proportion to a weld area as the torch path moves towards the thick portion of the drill bit. 
         [0028]    In other embodiments, methods for hardfacing rock bits comprise providing a drill bit and providing indexing indicium on the drill bit. A positioning sensor is indexed to the indicium on the drill bit to determine the location of the drill bit. A torch location is calibrated to the drill bit based indexed drill bit location. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0029]    The objects and features of the invention will become more readily understood from the following detailed description and appended claims when read in conjunction with the accompanying drawings in which like numerals represent like elements. 
           [0030]    The drawings constitute a part of this specification and include exemplary embodiments of the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown as exaggerated or enlarged to facilitate an understanding of the invention. 
           [0031]      FIG. 1  is a side view of a steel-tooth drill bit. 
           [0032]      FIG. 1A  is a side elevational view of an earth-boring drill bit according to an embodiment of the present invention. 
           [0033]      FIG. 1B  is a side elevational view of a drag bit type earth-boring drill bit according to an embodiment of the present invention. 
           [0034]      FIG. 2  is an isometric view of a typical steel-tooth cutter such as might be used on the steel-tooth drill bit of  FIG. 1 . 
           [0035]      FIG. 2A  is a partial sectional view of an embodiment of a rotatable cutter assembly, including a cone, of the present invention that may be used with the earth-boring drill bit shown in  FIG. 1A . 
           [0036]      FIG. 2B  is a sectional view of another embodiment of a rotatable cone of the present invention that may be used with the earth-boring drill bit shown in  FIG. 1A . 
           [0037]      FIG. 3  is an isometric view of a typical steel-tooth such as might be located on the steel-tooth cutter of  FIG. 2 . 
           [0038]      FIG. 4  is an isometric view of the steel-tooth of  FIG. 3  after hardfacing has been applied. 
           [0039]      FIG. 5  is a schematic of a preferred embodiment of a robotic welding system of the present invention for a cone. 
           [0040]      FIG. 5A  is a schematic of another embodiment of the robotic welding system of the present invention for a drag type drill bit. 
           [0041]      FIG. 6  is an isometric view of a robot manipulating a cutter to be hardfaced. 
           [0042]      FIG. 7  is an isometric view of a cutter positioned beneath a torch in preparation for the application of hardfacing. 
           [0043]      FIG. 8  is an isometric view of a chuck of a preferred type to be attached to an end of a robot. 
           [0044]      FIG. 9  is an isometric view of a jaw for a three jaw chuck specially profiled to include a journal land and a race land for gripping a rolling cutter. 
           [0045]      FIG. 10  is a schematic side view of a positioner and a torch. 
           [0046]      FIG. 11  is a schematic cross-section of the torch shown in  FIG. 10 . 
           [0047]      FIG. 12  is a cross-section of a torch configured in accordance with a preferred embodiment. 
           [0048]      FIG. 13  is an isometric view illustrating a robot manipulating a rolling cutter into position in preparation of the application of hardfacing to outer ends of the teeth. 
           [0049]      FIG. 13A  is an isometric view illustrating a robot manipulating a torch and a robot manipulating a rolling cutter into position in preparation of the application of hardfacing to the outer ends of the teeth. 
           [0050]      FIG. 14  is a side view illustrating a torch applying hardfacing to the outer end of a tooth on an outer row of the cutter. 
           [0051]      FIG. 15  is a side view illustrating the torch applying hardfacing to a leading flank of a tooth on the outer row of the cutter. 
           [0052]      FIG. 16  is an isometric view illustrating a robot manipulating a rolling cutter into position in preparation of the application of hardfacing to the inner end of a tooth on the cutter. 
           [0053]      FIG. 17  is a bottom view of a typical steel-tooth such as might be located on the steel-tooth cutter of  FIG. 2 , illustrating a substantially trapezoidal waveform target path for hardfacing in accordance with a preferred embodiment of the present invention. 
           [0054]      FIG. 18  is a schematic representation of oscillation of the torch on an axis of an oscillation “AO” having an oscillation midpoint “OM” in accordance with a preferred embodiment of the present invention. 
           [0055]      FIG. 19  is a schematic representation of a substantially triangular waveform torch path for hardfacing in accordance with a preferred embodiment of the present invention. 
           [0056]      FIG. 20  is a schematic representation of a waveform created by oscillation of a cutter relative to an intersection of a target path and oscillation midpoint “OM” in accordance with a preferred embodiment of the present invention. 
           [0057]      FIG. 21  is a schematic representation of a modified waveform of hardfacing created in accordance with the preferred embodiment of  FIG. 20 . 
           [0058]      FIG. 22  is a schematic representation of a generally rectangular shaped waveform created by oscillation of a cutter relative to an intersection of a target path and oscillation midpoint “OM” in accordance with a preferred embodiment of the present invention. 
           [0059]      FIG. 23  is a schematic representation of a modified waveform of hardfacing created in accordance with the preferred embodiment of  FIG. 22 . 
           [0060]      FIG. 24  is a schematic representation of a “shingle” pattern of hardfacing applied to a tooth of a cutter, in accordance with a preferred embodiment of the present invention. 
           [0061]      FIG. 25  is a schematic representation of a “herringbone” pattern of hardfacing applied to a tooth of a cutter, in accordance with a preferred embodiment of the present invention. 
           [0062]      FIG. 26A  is a cross-section of the cone illustrated in  FIG. 2A  having hardfacing thereon. 
           [0063]      FIG. 26B  is a cross-section of the cone illustrated in  FIG. 2B  having hardfacing thereon. 
           [0064]      FIG. 27  is a side elevational view of a drag type earth-boring drill bit according to an embodiment of the present invention having hardfacing applied to portions thereof. 
       
    
    
     DETAILED DESCRIPTION 
       [0065]    The system and method of the present invention have an opposite configuration and method of operation to that of manual hardfacing and prior automated hardfacing systems. In the present system and method a robotic system is used, having a plasma transfer arc torch secured in a substantially vertical position to a torch positioner in a downward orientation. The torch positioner is program-controllable in a vertical plane. Shielding, plasma, and transport gases are supplied to the torch through electrically controllable flow valves. Rather than use a torch positioner, a robotic arm can be used having a transfer arc torch secured thereto in a substantially vertical position in a downward orientation. For handling a roller cone, a robot having program controllable movement of an articulated arm is used. A chuck adapter is attached to the arm of the robot. A three jaw chuck is attached to the chuck adapter. The chuck is capable of securely holding a roller cone in an inverted position. 
         [0066]    A first position sensor is positioned for determining the proximity of the torch to a surface of the roller cone. A second position sensor may be positioned for determining the location, orientation, or identification of the roller cone. A programmable control system is electrically connected to the torch, the torch positioner or robotic arm having the torch mounted thereon, the robot, shielding, plasma, and transport gas flow valves, and the position sensors programmed for operation of each. The robot is programmed to position a surface of a cutter below the torch prior to the application of welding material to the roller cone. 
         [0067]    In this configuration, the torch is oscillated in a horizontal path. The roller cone is manipulated such that a programmed target path for each tooth surface is followed beneath the path midpoint (or equivalent indicator) of the oscillating torch. The movement of the roller cone beneath the torch generates a waveform pattern of hardfacing. In a preferred embodiment, the target path is a type of waveform path as well. Imposing the torch waveform onto the target path waveform generates a high-quality and efficient hardfaced coating on the roller cone. In another preferred embodiment, the roller cone is oscillated in relation to the torch as it follows the target path. This embodiment provides the ability to generate unique and desirable hardfacing patterns on the surface of the cutter, while maintaining symmetry and coverage. 
         [0068]    An advantage of the system and method of the present invention is that it automates the hardfacing application of roller cones or any other desired portion of a drill bit, which increases the consistency and quality of the applied hardfacing, and thus the reliability, performance, and cost efficiency of the roller cone and the drill bit. Another advantage of the system and method of present invention is that it reduces manufacturing cost and reliance on skilled laborers. Another advantage of the system and method of the present invention is that by decreasing production time, product inventory levels can be reduced. Another advantage of the system and method of the present invention is that it facilitates the automated collection of welding data, from which further process controls and process design improvements can be made. 
         [0069]    Another advantage of the system and method of the present invention is that utilization of the robotic arm to manipulate the roller cone and a robotic arm having the torch mounted thereon improves the opportunity to integrate sensors for providing feedback. Another advantage of the system and method of the present invention is that utilization of the robotic arm to manipulate the roller cone provides the necessary surface-to-torch angularity for access, without disrupting the flow of the powder due to changes in the angle of the torch. 
         [0070]    As referred to hereinabove, the “system and method of the present invention” refers to one or more embodiments of the invention, which may or may not be claimed, and such references are not intended to limit the language of the claims, or to be used to construe the claims. The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
         [0071]      FIG. 1  is a side view of a steel-tooth roller cone drill bit  1 . The drill bit  1  has a plurality of roller cones  10 .  FIG. 2  is an isometric view of a typical steel-tooth roller cone  10  such as might be used on the drill bit of  FIG. 1 . Steel-tooth roller cone  10  has a plurality of rows of teeth  20 . In  FIG. 2 , roller cone  10  has an inner row of teeth  12 , an intermediate row of teeth  14 , and an outer row of teeth  16 . Each of rows of teeth  12 ,  14 , and  16  has one or more teeth  20  therein. 
         [0072]      FIG. 1A  is a side elevational view of an earth-boring drill bit  510  according to another embodiment of the present invention. The earth-boring drill bit  510  includes a bit body  512  and a plurality of rotatable cutter assemblies  514 . The bit body  512  may include a plurality of integrally formed bit legs  516 , and threads  518  may be formed on the upper end of the bit body  512  for connection to a drill string (not shown). The bit body  512  may have nozzles  520  for discharging drilling fluid into a borehole, which may be returned along with cuttings up to the surface during a drilling operation. Each of the rotatable cutter assemblies  514  include a cone  522  comprising a particle-matrix composite material and a plurality of cutting elements, such as the cutting inserts  524  shown. Each cone  522  may include a conical gage surface  526 . Additionally, each cone  522  may have a unique configuration of cutting inserts  524  or cutting elements, such that the cones  522  may rotate in close proximity to one another without mechanical interference. 
         [0073]      FIG. 1B  illustrates a drill bit  610  incorporating a plurality of nozzle assemblies  630  therein. The drill bit  610  is configured as a fixed-cutter rotary full bore drill bit, also known in the art as a “drag bit.” The drill bit  610  includes a crown or bit body  611  composed of steel body or sintered tungsten carbide body coupled to a support  619 . The support  619  includes a shank  613  and a crossover component (not shown) coupled to the shank  613  in this embodiment of the invention by using a submerged arc weld process to form a weld joint therebetween. The crossover component (not shown), which is manufactured from a tubular steel material, is coupled to the bit body  611  by pulsed MIG process to form a weld joint therebetween in order to allow the complex tungsten carbide material, when used, to be securely retained to the shank  613 . It is recognized that the support  619 , particularly for other materials used to form a bit body, may be made from a unitary material piece or multiple pieces of material in a configuration differing from the shank  613  being coupled to the crossover by weld joints as presented. The shank  613  of the drill bit  610  includes conventional male threads  612  configured to API (American Petroleum Institute) standards and adapted for connection to a component of a drill string, not shown. The face  614  of the bit body  611  has mounted thereon a plurality of cutting elements  616 , each comprising a polycrystalline diamond (PCD) table  618  formed on a cemented tungsten carbide substrate. The cutting elements  616 , conventionally secured in respective cutter pockets  621  by brazing, for example, are positioned to cut a subterranean formation being drilled when the drill bit  610  is rotated under weight-on-bit (WOB) in a borehole. The bit body  611  may include gage trimmers  623  including the aforementioned PCD tables  618  configured with a flat edge aligned parallel to the rotational axis (not shown) of the drill bit  610  to trim and hold the gage diameter of the borehole, and gage pads  622  on the gage which contact the walls of the borehole to maintain the hole diameter and stabilize the drill bit  610  in the hole. 
         [0074]    During drilling, drilling fluid is discharged through nozzle assemblies  630  located in sleeve ports  628  in fluid communication with the face  614  of bit body  611  for cooling the PCD tables  618  of cutting elements  616  and removing formation cuttings from the face  614  of drill bit  610  into passages  615  and junk slots  617 . 
         [0075]    In  FIG. 2 , as shown by the dashed lines, an interior of roller cone  10  of drill bit  1  of  FIG. 1  includes a cylindrical journal race  40  and a semi-torus shaped ball race  42 . Journal race  40  and ball race  42  are internal bearing surfaces that are machined finish after hardfacing  38  (see  FIG. 4 ) has been applied to teeth  20 .  FIG. 2A  is a cross-sectional view illustrating one of the rotatable cutter assemblies  514  of the earth-boring drill bit  510  shown in  FIG. 1A . As shown, each bit leg  516  may include a bearing pin  528 . The cone  522  may be supported by the bearing pin  528 , and the cone  522  may be rotatable about the bearing pin  528 . Each cone  522  may have a central cone cavity  530  that may be cylindrical and may form a journal bearing surface adjacent the bearing pin  528 . The cone cavity  530  may have a flat thrust shoulder  532  for absorbing thrust imposed by the drill string (not shown) on the cone  522 . As illustrated in this example, the cone  522  may be retained on the bearing pin  528  by a plurality of locking balls  534  located in mating grooves formed in the surfaces of the cone cavity  530  and the bearing pin  528 . Additionally, a seal assembly  536  may seal bearing spaces between the cone cavity  530  and the bearing pin  528 . The seal assembly  536  may be a metal face seal assembly, as shown, or may be a different type of seal assembly, such as an elastomer seal assembly. Lubricant may be supplied to the bearing spaces between the cone cavity  530  and the bearing pin  528  by lubricant passages  538 . The lubricant passages  538  may lead to a reservoir that includes a pressure compensator  540  ( FIG. 1A ). 
         [0076]    As previously mentioned, the cone  522  may comprise a sintered particle-matrix composite material that comprises a plurality of hard particles dispersed through a matrix material. In some embodiments, the cone  522  may be predominantly comprised of the particle-matrix composite material. 
         [0077]      FIG. 2B  is a cross section of a cone  522  formed after assembling the various green components to form a structure sintered to a desired final density to form the fully sintered structure shown in  FIG. 2B . During the sintering process of the cone  522 , including the apertures  562  or other features, the cutting inserts  524  or other cutting elements, and bearing structures  568  may undergo shrinkage and densification. Furthermore, the cutting inserts  524  and the bearing structures  568  may become fused and secured to the cone  522  to provide a substantially unitary cutter assembly  514  (see FIB.  2 A). 
         [0078]    After the cutter assembly  514 ′ has been sintered to a desired final density, various features of the cutter assembly  514 ′ may be machined and polished, as necessary or desired. For example, bearing surfaces on the bearing structures  568  may be polished. Polishing the bearing surfaces of the bearing structures  568  may provide a relatively smoother surface finish and may reduce friction at the interface between the bearing structures  568  and the bearing pin  528  ( FIG. 2A ). Furthermore, the sealing edge  572  of the bearing structures  568  also may be machined and/or polished to provide a shape and surface finish suitable for sealing against a metal or elastomer seal, or for sealing against a sealing surface located on the bit body  512  ( FIG. 1A ). 
         [0079]    The cutting inserts  524 , lands  523 , and bearing structures  568  may be formed from particle-matrix composite materials. The material composition of each of the cutting inserts  524 , lands  523 , bearing structures  568 , and cone  522  may be separately and individually selected to exhibit physical and/or chemical properties tailored to the operating conditions to be experienced by each of the respective components. By way of example, the composition of the cutting inserts  524  and the lands  523  may be selected so as to form cutting inserts  524  comprising a particle-matrix composite material that exhibits a different hardness, wear resistance, and/or toughness different from that exhibited by the particle-matrix composite material of the cone  522 . 
         [0080]    The cutting inserts  524  and lands  523  may be formed from a variety of particle-matrix composite material compositions. The particular composition of any particular cutting insert  524  and lands  523  may be selected to exhibit one or more physical and/or chemical properties tailored for a particular earth formation to be drilled using the drill bit  510  ( FIG. 1A ). Additionally, cutting inserts  524  and lands  523  having different material compositions may be used on a single cone  522 . 
         [0081]    By way of example, in some embodiments of the present invention, the cutting inserts  524  and the lands  523  may comprise a particle-matrix composite material that includes a plurality of hard particles that are harder than a plurality of hard particles of the particle-matrix composite material of the cone  522 . The concentration of the hard particles in the particle-matrix composite material of the cutting inserts  524  and the lands  523  may be greater than a concentration of hard particles in a particle-matrix composite material of the cone  522 . 
         [0082]      FIG. 3  is an isometric view of a steel-tooth  20  located on steel-tooth roller cone  10  of  FIG. 2 . Tooth  20  has an included tooth angle of  0  degrees formed at a vertex  36 . Tooth  20  has a leading flank  22  and an opposite trailing flank  24 . Leading flank  22  and trailing flank  24  are joined at crest  26 , which is the top of tooth  20 . A generally triangular outer end  28  is formed between leading flank  22 , trailing flank  24 , and crest  26 . On the opposite side of tooth  20 , a generally triangular inner end  30  is formed between leading flank  22 , trailing flank  24 , and crest  26 . A base  32  broadly defines the bottom of tooth  20  and the intersection of tooth  20  with roller cone  10 . Various alternatively shaped teeth on roller cone  10  may be used, such as teeth having T-shaped crests. Tooth  20  represents a common shape for a tooth, but the system and method of the present invention may be used on any shape of tooth. 
         [0083]    To prevent early wear and failure of drill bit  1  (see  FIG. 1 ), it is necessary to apply an extremely wear-resistant material, or hardfacing  38 , to surfaces  22 ,  24 ,  26 ,  28 , and  30  of tooth  20 .  FIG. 4  is an isometric view of a typical steel-tooth  20  such having hardfacing  38  applied to surfaces  22 ,  24 ,  26 ,  28 , and  30 , as shown in  FIG. 3 . 
         [0084]      FIGS. 5 and 5A  are schematic illustrations of the system of the present invention. Seen in  FIG. 5  is an industrial robot  100  having a stationary base  102  and an articulated arm  104 . Articulated arm  104  has a distal end  106 . Robot  100  has a plurality of axes of rotation  108  about which controllable movement permits wide-range positioning of distal end  106  relative to base  102 . Robot  100  has six or more independently controllable axes of movement between base  102  and the distal end  106  of arm  104 .  FIG. 5A  illustrates a drill bit  610  attached to the articulated arm  104 , although drill bit  610  or drill bit  1  (see  FIG. 1 ) or portions of any drill bit may be attached to articulated arm  104  for the application of hardfacing to portions thereof. 
         [0085]    Robot  100  has a handling capacity of at least 125 kg, and articulated arm  104  has a wrist torque rating of at least 750 nm. Examples of industrial robots that are commercially available include models IRB 6600/IRB 6500, which are available from ABB Robotics, Inc., 125 Brown Road, Auburn Hills, Mich., USA, 48326-1507. 
         [0086]    An adapter  110  is attached to distal end  106 . Adapter  110  has a ground connector  112  (see  FIG. 7 ) for attachment to an electrical ground cable  114 . A chuck  120  is attached to adapter  110 . Chuck  120  securely grips roller cone  10  at journal bearing surface  40  (see  FIG. 2 ) and/or ball race  42  (see  FIG. 2 ), as shown in greater detail in  FIGS. 8 and 9 . 
         [0087]    A heat sink, or thermal barrier, is provided between roller cone  10  and adapter  110  to prevent heat from causing premature failure of the rotating axis at distal end  106  of articulated arm  104 . The thermal barrier is an insulating spacer (not shown) located between roller cone  10  and distal end  106  of robot  100 . Alternatively, roller cone  10  may be gripped in a manner that provides an air space between roller cone  10  and distal end  106  of robot  100  to dissipate heat. 
         [0088]    A robot controller  130  is electrically connected to robot  100  for programmed manipulation of robot  100 , including movement of articulated arm  104 . An operator pendant  137  may be provided as electrically connected to robot controller  130  for convenient operator interface with robot  100 . A sensor controller  140  is electrically connected to robot controller  130 . Sensor controller  140  may also be electrically connected to a programmable logic controller  150 . 
         [0089]    A plurality of sensors  142  are electrically connected to sensor controller  140 . Sensors  142  include a camera  144  and/or a contact probe  146 . Alternatively, sensors  142  include a suitable laser proximity indicator  148  (illustrated as an arrow). Other types of sensors  142  may also be used. Sensors  142  provide interactive information to robot controller  130 , such as the distance between a tooth  20  on roller cone  10  and torch  300 . 
         [0090]    A programmable logic controller  150  is electrically connected to robot controller  130 . Programmable logic controller (PLC)  150  provides instructions to auxiliary controllable devices that operate in coordinated and programmed sequence with robot  100 . 
         [0091]    A powder dosage system  160  is provided for dispensing hardfacing powder to the system. A driver  162  is electrically connected to PLC  150  for dispensing the powder at a predetermined, desired rate. 
         [0092]    A pilot arc power source  170  and a main arc power source  172  are electrically connected to PLC  150 . A cooling unit  174  is electrically connected to PLC  150 . In a preferred embodiment, a data-recording device  195  is electrically connected to PLC  150 . 
         [0093]    A gas dispensing system  180  is provided. A transport gas source  182  supplies transport gas through a flow controller  184  to carry or transport hardfacing welding powder to torch  300 . Flow controller  184  is electrically connected to PLC  150 , which controls the operation of flow controller  184  and the flow and flow rate of the transport gas. A plasma gas source  186  supplies gas for plasma formation through a flow controller  188 . Flow controller  188  is electrically connected to PLC  150 , which controls the operation of flow controller  188  and the flow and flow rate of the plasma gas. Similarly, a shielding gas source  190  supplies shielding gas through a flow controller  192 . Flow controller  192  is electrically connected to PLC  150 , which controls the operation of flow controller  192  and the flow and flow rate of the shielding gas. It is known to utilize a single gas source for more than one purpose, e.g., plasma, shielding, and transport. Thus, different, multiple flow controllers connected in a series alignment can control the flow and flow rate of gas from a single gas source. 
         [0094]    The torch  300  comprises a plasma transferred arc (PTA) torch, that receives hardfacing welding powder from powder dosage system  160 , and plasma, transport, and shielding gases from their respective supplies and controllers in gas dispensing system  180 . Torch  300  is secured to a positioner or positioning table  200 , which grips and manipulates torch  300 . In a preferred embodiment, positioner  200  is capable of programmed positioning of torch  300  in a substantially vertical plane. A positioner  200  has a vertical drive  202  and a horizontal drive  204 . Drives  202  and  204  may be toothed belts, ball screws, a toothed rack, pneumatic, or other means. If desired, an industrial robot  100  having six independently controllable axes of movement between base  102  and distal end  106  of arm  104  as described herein may be used as the positioner  200  having the torch  300  mounted thereon. 
         [0095]      FIGS. 6 and 7  are isometric views of robot  100  shown manipulating roller cone  10  secured to adapter  110  on distal end  106  of articulated arm  104  of robot  100 . As illustrated in  FIG. 6  and in  FIGS. 13-16 , the several axes of rotation  108  provide sufficient degrees of freedom to permit vertical, horizontal, inverted, and rotated positioning of any tooth  20  of roller cone  10  directly beneath torch  300 . As illustrated in  FIG. 7 , roller cone  10  is positioned beneath torch  300  in preparation for the application of hardfacing  38  (see  FIG. 4 ). 
         [0096]    Adapter  110  is aligned by indicator with articulated arm  104 . Adapter  110  is aligned to run substantially true with a programmable axis of movement of robot  100 . A chuck  120  is attached to adapter  110  and indicator aligned to within 0.005 inch of true center rotation. Roller cone  10  is held by chuck  120  and also centered by indicator alignment. Roller cone  10  has grooves that permit location and calibration of the end of torch  300 . Electrode  304  (see  FIG. 11 ) of torch  300  is then used to align roller cone  10  about the z-axis of rotation of roller cone  10  by robot  100 . 
         [0097]    As illustrated in  FIG. 7 , electrical ground cable  114  is electrically connected to adapter  110  by ground connector  112 , a rotatable sleeve connector. Alternatively, ground connector  112  is a brush connector. Ground cable  114  is supported by a tool balancer (not shown) to keep it away from the heat of roller cone  10  and the welding arc during hardfacing operations. Chuck  120  is attached to adapter  110 . Roller cone  10  is held by chuck  120 . 
         [0098]    As roller cones  10  are manipulated vertically, horizontally, inverted, and rotated beneath torch  300 , highly secure attachment of roller cone  10  to robot  100  is required for safety and accuracy of the hardfacing operation. Precision alignment of roller cones  10  in relation to chuck  120  is also necessary to produce a quality hardfacing and to avoid material waste. 
         [0099]      FIG. 8  is an isometric view of chuck  120 , a three jaw chuck, having adjustable jaws  122  for gripping a hollow interior of a roller cone  10 . Jaws  122  are specially profiled to include a cylindrical segment shaped journal land  124 , which contacts journal race  40  on roller cone  10 , providing highly secure attachment of roller cone  10  on chuck  120  of robot  100 . A seal relief  128  is provided to accommodate a seal supporting surface on roller cone  10 . 
         [0100]    Illustrated in  FIG. 9 , a jaw  122  of chuck  120  is specially profiled to include a semi-torus shaped race land  126  above journal land  124 . In this configuration, journal land  124  fits in alignment with journal race  40  (see  FIG. 2 ) and race land  126  fits in alignment with ball race  42  ( FIG. 2 ), providing precise alignment against the centerline of ball race  42  and secure attachment of roller cone  10  on chuck  120  of robot  100 . Seal relief  128  may be provided to accommodate a seal supporting surface on roller cone  10 . 
         [0101]      FIG. 10  is a schematic side view of positioner  200  and torch  300 . As illustrated, positioner  200  has a clamp  206  for holding torch  300  in a secure and substantially vertical orientation. Vertical drive  202  provides controlled movement of torch  300  along the z-axis. Drive  203  connected to PLC  150  ( FIG. 5 ) rotates the torch  300  of positioner  200  about the z-axis of the support  201 . Drive  205  connected to the PLC  150  rotates torch  300  of positioner  200  about the z-axis of support  207 . Drive  209  connected to the PLC  150  rotates torch  300  of positioner  200  about the y-axis of clamp  206 . Horizontal drive  204  provides controlled movement of torch  300  along the y-axis. In combination, drives  202  and  204  provide controlled movement of torch  300  on a vertical plane. Drives  202  and  204  are electrically connected to PLC  150 . 
         [0102]    Drive  204  oscillates torch  300  along the horizontal y-axis in response to PLC  150  for programmed application of a wide-path bead of hardfacing  38  on the surface of teeth  20  of roller cone  10  (see  FIG. 2 ). Drive  202  moves torch  300  along the vertical z-axis in real-time response to measured changes in the voltage or current between torch  300  and roller cone  10 . These occasional real-time distance adjustments maintain the proper energy level of the transferred arc between torch  300  and roller cone  10 . 
         [0103]    Gas dispensing system  180  is connected by piping or tubing to torch  300  for the delivery of transport gas, plasma gas and shielding gas. Hardfacing powder is delivered to torch  300  within the stream of flowing transport gas which receives the hardfacing powder from powder dosage system  160  (see  FIGS. 5 and 5A ). Torch  300  is electrically connected to pilot arc power source  170  and main arc power source  172 . 
         [0104]      FIG. 11  is a schematic cross-section of torch  300 . Torch  300  has a nozzle  302  that comprises a Plasma Transferred Arc (PTA) torch. A non-burning tungsten electrode (cathode)  304  is centered in nozzle  302  and a nozzle annulus  306  is formed between nozzle  302  and electrode  304 . Nozzle annulus  306  is connected to plasma gas source  186  ( FIG. 5 ) to allow the flow of plasma between nozzle  302  and electrode  304 . A restricted orifice  314  accelerates the flow of plasma gas exiting nozzle  302 . In this embodiment, nozzle annulus  306  is connected to powder dosage system  160  (not shown), which supplies hardfacing powder carried by transport gas to nozzle annulus  306 . 
         [0105]    Electrode  304  is electrically insulated from nozzle  302 . A pilot arc circuit  330  is electrically connected to pilot arc power source  170  ( FIG. 5 ), and electrically connects nozzle  302  to electrode  304 . A main arc circuit  332  is electrically connected to main arc power source  172  ( FIG. 5 ), and electrically connects electrode  304  to the anode work piece, roller cone  10 . An insulator separates pilot arc circuit  330  and main arc circuit  332 . A cooling channel  316  is provided in nozzle  302  for connection to a pair of conduits  176 ,  178  that circulate cooling fluid from cooling unit  174  ( FIGS. 5 and 5A ). 
         [0106]    A gas cup  320  surrounds nozzle  302 . Nozzle  302  is electrically insulated from gas cup  320 . A cup annulus  322  is formed between gas cup  320  and nozzle  302 . Cup annulus  322  is connected to shielding gas source  190  (see  FIG. 5 ) to allow the flow of shielding gas between gas cup  320  and nozzle  302 . 
         [0107]    A small, non-transferred pilot arc burns between non-melting (non-consumable) tungsten electrode  304  (cathode) and nozzle  302  (anode). A transferred arc burns between electrode  304  (cathode) and roller cone  10  (anode). Electrode  304  is the negative pole and roller cone  10  is the positive pole. Pilot arc circuit  330  is ignited to reduce the resistance to an arc jumping between roller cone  10  and electrode  304  when voltage is applied to main arc circuit  332 . A ceramic insulator separates circuits  330  and  332 . 
         [0108]    Plasma Transferred Arc (PTA) welding is similar to Tungsten Inert Gas (TIG) welding. Torch  300  is supplied with plasma gas, shielding gas, and transport gas, as well as hardfacing powder. Plasma gas from plasma gas source  186  (see  FIG. 5 ) is delivered through nozzle  302  to electrode  304 . The plasma gas exits nozzle  302  through orifice  314 . When amperage from main arc circuit  332  is applied to electrode  304 , the jet created from exiting plasma gas turns into plasma. Plasma gas source  186  is comprised of 99.9% argon. 
         [0109]    Shielding gas from shielding gas source  190  (see  FIG. 5 ) is delivered to cup annulus  322 . As the shielding gas exits cup annulus  322  it is directed toward the work piece, roller cone  10 . The shielding gas forms a cylindrical curtain surrounding the plasma column, and shields the generated weld puddle from oxygen and other chemically active gases in the air. Shielding gas source  190  is 95% argon and 5% hydrogen. 
         [0110]    Transport gas source  182  is connected to powder dosage system  160 , as shown in  FIGS. 5 and 5A . Powder dosage system  160  meters hardfacing powder through a conduit connected to nozzle  302  at the proper rate for deposit. The transport gas from transport gas source  182  carries the metered powder to nozzle  302  and to the weld deposit on roller cone  10 . 
         [0111]      FIG. 12  is a cross-section of torch  300  wherein gas cup  320  of torch  300  has a diameter of less than 0.640 inch and a length of less than 4.40 inches. Nozzle  302  (anode) of torch  300  is made of copper and is liquid cooled. One such torch that is commercially available is the Eutectic E52 torch available from Castolin Eutectic Group, Gutenbergstrasse 10, 65830 Kriftel, Germany. 
         [0112]    Gas cup  320  is modified from commercially available gas cups for use with torch  300  in that gas cup  320  extends beyond nozzle  302  by no more than approximately 0.020 inch. As such, gas cup  320  has an overall length of approximately 4.375 inches. As seen in the embodiment, transport gas and powder are delivered through a transport gas port  324  in nozzle  302 . An insulating material is attached to the exterior of gas cup  320  of the torch  300  for helping to prevent short-circuiting and damage to torch  300 . 
         [0113]    The shielding of gas cup  320  described above is specially designed to improve shield gas coverage of the melt puddle for reducing the porosity thereof. This permits changing the orientation of gas cup  320  to nozzle (anode)  302  and reduction of shielding gas flow velocity. This combination significantly reduces porosity that results from attempts to use presently available commercial equipment to robotically apply hardfacing  38  to steel-tooth roller cones  10 . 
       Operation 
       [0114]    Some of the problems encountered in the development of robotic hardfacing included interference between the torch and teeth on the roller cone, short circuiting the torch, inconsistent powder flow, unsustainable plasma column, unstable puddle, heat buildup when using conventional welding parameters, overheated weld deposits, inconsistent weld deposits, miss-shaping of teeth, and other issues. As a result, extensive experimentation was required to reduce the present invention to practice. 
         [0115]    As described herein, the system and method of the present invention begins with inverting what has been the conventional practice of roller cones. That is, the practice of maintaining roller cone  10  generally stationary and moving torch  300  all over it at various angles as necessary. Fundamental to the system and method of the present invention, torch  300  is preferably held substantially vertical, although it may be held at any angle or attitude desired through the use of a positioner  200  or robotic arm  100 , while roller cone  10  is held by chuck  120  of robotic arm  104  and manipulated beneath torch  300 . If torch  300  is robotically manipulated by positioner  200  or robotic arm  104  in varying and high angular positions relative to vertical, hardfacing powder in torch  300  will flow unevenly and cause torch  300  to become plugged. In addition to plugging torch  300 , even flow of hardfacing powder is critical to obtaining a consistent quality bead of hardfacing material on roller cone  10 . Thus, deviation from a substantially vertical orientation is avoided. Although, if plugging of torch  300  is not a problem with the particular hardfacing being used, the torch  300  may be oriented at any desired position. 
         [0116]    As the terms are used in this specification and claims, the words “generally” and “substantially” are used as descriptors of approximation, and not words of magnitude. Thus, they are to be interpreted as meaning “largely but not necessarily entirely.” 
         [0117]    Accordingly, a roller cone  10  is secured to distal end  106  of robot arm  104  by chuck  120  and adapter  110 . Roller cone  10  is grounded by ground cable  114  which is attached to adapter  110  at ground connector  112 . Providing an electrical ground source near distal end  106  of robot arm  104  of robot  100  is necessary, since using robot  100  in the role-reversed manner of the present invention (holding the anode work piece) would otherwise result in destruction of the robot  100  by arc welding the rotating components of the movable axes together. 
         [0118]    Robot arm  104  moves in response to program control from robot controller  130  and/or PLC  150 . As stated, torch  300  is mounted to positioner  200  having two controllable axes in a substantially vertical plane. As previously mentioned, a physical indicator, such as a notch or groove, may be formed on roller cone  10  to be engaged by torch  300  to ensure proper initial orientation between torch  300 , robot arm  104 , and roller cone  10 . Additionally, at least one position indicator is electrically connected to PLC  150  for determining location and orientation of roller cone  10  to be hardfaced relative to robot  100 . 
         [0119]    After initial orientation and positioning, transfer, plasma and shielding gases are supplied to torch  300  by their respective sources  182 ,  186 ,  190 , through their respective controllers  184 ,  188 ,  192 . 
         [0120]    Torch  300  is ignited by provision of current from pilot arc power source  170  and main arc power source  172 . Igniting pilot arc circuit  330  reduces the resistance to an arc jumping between roller cone  10  and electrode  304  when voltage is applied to main arc circuit  332 . 
         [0121]    Flow of hardfacing powder is provided by powder dosage system  160  dispensing controlled amounts of hardfacing powder into a conduit of flowing transport gas from transport gas source  182 , having a flow rate controlled by flow controller  184 . Then relative movement, primarily of roller cone  10  relative to torch  300 , as described above and below is obtained by movement of robot arm  104  and positioner  200 , permitting automated application of hardfacing  38  to the various selected surfaces of roller cone  10  in response to programming from robot controller  130  and PLC  150 . 
         [0122]    An imaging sensor  142  may be provided for identifying specific roller cones  10  and/or parts of roller cones  10  to be hardfaced. A laser sensor  142  ( FIG. 5 ) may also provided for determining proximity of torch  300  to roller cone  10  and tooth  20 , and/or to measure thickness of applied hardfacing  38 . Positioning and other programming parameters are correctable based on sensor  142  data acquisition and processing. 
         [0123]    Robot controller  130  is primarily responsible for control of robot arm  104 , while PLC  150  and data recording device  195  provide sensor  142  data collection and processing, data analysis and process adjustment, adjustments in robot  100  movement, torch  300  oscillation, and torch  300  operation, including power, gas flow rates and material feed rates. 
         [0124]      FIGS. 13 ,  13 A, and  14  illustrate robot  100  manipulating roller cone  10  into position to apply hardfacing material to outer end  28  (see  FIG. 3 ) of teeth  20  (see  FIGS. 2-4 ) on outer row  16  of roller cone  10  (see  FIG. 2 ).  FIG. 15  illustrates torch  300  in position to apply hardfacing to leading flank  22  or trailing flank  24  (see  FIG. 3 ) of tooth  20  (see  FIGS. 2-4 ) on outer row  16  (see  FIG. 16 ) of roller cone  10  (see  FIG. 2 ).  FIG. 16  is an isometric view illustrating robot  100  manipulating roller cone  10  (see  FIG. 2 ) into position in preparation for application of hardfacing  38  (see  FIG. 4 ) to inner end  30  (see  FIG. 3 ) of tooth  20  (see  FIGS. 2-4 ). 
         [0125]    As can be seen in  FIG. 6  and in  FIGS. 13-16 , several axes of rotation  108  of robot arm  100  provide sufficient degrees of freedom to permit vertical, horizontal, inverted, and rotated positioning of roller cone  10  beneath torch  300 , allowing torch  300  to access the various surfaces of roller cone  10  while maintaining torch  300  in a substantially vertical position. In addition to providing a system and apparatus that addresses the realities of automated application of hardfacing to the complex surfaces of roller cones, the present invention provides a system and method or pattern of application of the hardfacing material to the cutters that is adapted to take advantage of the precisely controlled relative movement between torch  300  and roller cone  10  made possible by the apparatus of the present invention. These patterns will be described with reference to  FIGS. 17 through 25  below. 
         [0126]    The above-described system and method of the present invention has resolved these issues and enabled development of the method of applying hardfacing of the present invention. The present invention includes a hardfacing pattern created by superimposing a first waveform path onto a second waveform path. 
         [0127]      FIG. 17  is a bottom view of a typical steel-tooth  20 , such as might be located on roller cone  10 , illustrating a first waveform target path  50  defined in accordance with the present invention. Tooth  20  has an actual or approximate included angle θ. Vertex  36  of included angle θ lies on centerline  34  of tooth  20 . Centerline  34  extends through crest  26  and base  32 . 
         [0128]    As illustrated, target path  50  traverses one surface of tooth  20 . By way of example, outer end surface  28  is shown, but applies to any and all surfaces of tooth  20 . Target path  50  has numerous features. Target path  50  may begin with a strike path  52  located near crest  26 . The various surfaces of teeth  20  are preferably welded from nearest crest  26  toward base  32 , when possible, to control heat buildup. 
         [0129]    Thereafter, target path  50  traverses the surface of tooth  20  in parallel paths while progressing in the direction of base  32 . Target path  50  is comprised of traversing paths  54 , which cross centerline  34 , are alternating in direction, and generally parallel to crest  26 . 
         [0130]    Step paths  56  connect traversing paths  54  to form a continuous target path  50 . Step paths  56  are not reversing, but progressing in the direction of base  32 . Step paths  56  are preferably generally parallel to the sides of the surface being hardfaced. As such, step paths  56  are disposed at an angle of approximately  0 / 2  to centerline  34 . Taken together, traversing paths  54  and step paths  56  form target path  50  as a stationary, generally trapezoidal waveform about centerline  34 , having an increasing amplitude in the direction of base  32 . 
         [0131]    The amperage of torch  300  is applied in proportion to the length of traversing path  54 . This permits generation of a good quality bead definition in hardfacing  38 . This is obtained by starting at the lowest amperage on traversing path  54  nearest to crest  26  of tooth  20 , and increasing the amperage in proportion to the length of traversing path  54  where hardfacing  38  is being applied. 
         [0132]    Alternatively, amperage and powder flow are increased as hardfacing  38  is applied to crest  26 . This results in increased height of the automatically welded crests  26  to their total design height. The programmed traversing paths  54  for flanks  22  and  24 , inner surface  30  and outer surface  28  (see  FIG. 3 ) are also modified such that to overlap crests  26  sufficiently to create the desired profile and to provide sufficient support to crests  26 . 
         [0133]    The program sequence welds the surface of a datum tooth, then offsets around the roller cone axis the amount needed to align with the next tooth surface. Also, teeth are welded from the tip to the root to enhance heat transfer from the tooth and prevent heat buildup. Welding is alternated between rows of teeth on the roller cone to reduce heat buildup. 
         [0134]      FIG. 18  is a schematic representation of the oscillation of torch  300 . In this illustration, x-y defines a horizontal plane. Torch  300  is movable in the z-y vertical plane perpendicular to the x-y plane. The y-axis is the axis of oscillation (“AO”). Torch  300  is oscillated along the AO. The oscillation midpoint is identified as OM. Oscillation of torch  300  is controlled by instructions from programmable logic controller  150  provided to horizontal drive  204  of positioner  200  (see  FIG. 5 ). Torch  300  has a variable linear velocity along its axis of oscillation AO depending upon the characteristics of the roller cone material and the hardfacing being applied. 
         [0135]      FIG. 19  is a schematic representation of a second waveform torch path  60  formed in accordance with the present invention. Hardfacing is applied to a tooth  20  by oscillating torch  300  while moving roller cone  10  on target path  50  beneath torch  300 . In this manner, hardfacing is applied by superimposing the waveform of torch path  60  onto the waveform of target path  50 . By superimposing torch path  60  onto target path  50 , a superior hardfacing pattern is created. More specifically, the superimposed waveform generates a uniform and continuous hardfacing bead, is properly defined, and efficiently covers the entire surface of tooth  20  with the desired thickness of material and without excessive heat buildup. 
         [0136]    As used throughout herein, the terms “waveform,” “trapezoidal waveform” and “triangular waveform” are not intended to be construed or interpreted by any resource other than the drawings and description provided herein. More specifically, they are used only as descriptors of the general path shapes to which they have been applied herein. 
         [0137]    As seen in  FIG. 19 , torch path  60  has an amplitude Λ. It is preferred to have a Λ between 3 mm and 5 mm. It is more preferred to have a Λ is about 4 mm. Traversing path  54  (see  FIG. 17 ) is positioned in approximate perpendicular relationship to the axis of torch  300  oscillation, at the oscillation midpoint (OM). The waveform of torch path  60  is formed by oscillating torch  300  while moving roller cone  10  along traversing path  54  (see  FIG. 17 ) beneath the OM of torch  300 . Thus, traversing path  54  of target path  50  (see  FIG. 17 ) becomes the axis about which the generally triangular waveform of torch path  60  oscillates. 
         [0138]    The torch path  60  has a velocity of propagation V t  of between 1.2 mm and 2.5 mm per second at the intersection of traversing path  54  and OM of torch  300 . Roller cone  10  is positioned and moved by instructions from robot controller  130  provided to robot  100 . Robot  100  moves roller cone  10  to align target path  50  directly beneath the OM. Roller cone  10  is moved such that the OM progresses along target path  50  at a linear velocity (target path speed) of between 1 mm and 2.5 mm per second. 
         [0139]    As illustrated, a momentary dwell period  68  is programmed to elapse between peaks of oscillation of torch  300 , wherein dwell period  68  helps prevent generally triangular waveform of torch path  60  from being a true triangular waveform. Preferably, dwell period  68  is between about 0.1 to 0.4 seconds. 
         [0140]      FIG. 20  is a schematic representation of the secondary oscillation  80  of traversing path  54  (see  FIGS. 17 ,  21 , and  23 ) modifying torch path  60  (see  FIG. 19 ). Traversing path  54  is oscillated as a function of the location of oscillation midpoint OM on target path  50  (see  FIG. 17 ). Secondary oscillation  80  is created by gradually articulating roller cone  10  between step paths  56  as oscillation midpoint OM of oscillating torch  300  passes over traversing path  54 . Each traversing path  54  constitutes ½λ of a wave length of secondary oscillation  80 . Since traversing paths  54  are of different lengths, the wavelength of secondary oscillation  80  expands as the hardfacing application progresses towards base  32  of tooth  20 . For example, where a l  represents a first traversing path  54  and α 2  represents the next traversing path  54 , α 1 &lt;α 2 . 
         [0141]      FIG. 21  is a bottom view of steel-tooth  20  illustrating traversing paths  54  connected by step paths  56  to form first waveform target path  50 . Second waveform torch path  60  is superimposed on target path  50 . When secondary oscillation  80  is imparted on traversing path  54 , an accordion-like alteration of second waveform torch path  60  results. 
         [0142]    Referring to  FIG. 20  and  FIG. 21 , a maximum articulation angle of about |θ/2| of roller cone  10  occurs at each step path  56 . In an optional embodiment, as oscillation midpoint OM of torch  300  progresses on each step path  56 , secondary oscillation  80  is dwelled. This can be done optionally based on prior path (hardfacing) coverage of step path  56 . Point  90  in  FIG. 20  schematically represents the dwell periods. 
         [0143]    As roller cone  10  moves along traversing path  54 , roller cone  10  is gradually articulated by robot  100  until axis of oscillation AO (see  FIG. 18 ) is substantially perpendicular to traversing path  54  at tooth  20  centerline  34 . This occurs schematically at point  88  on  FIG. 20 . As roller cone  10  continues to move along traversing path  54 , roller cone  10  is gradually articulated by robot  100  until step path  56  is again parallel to axis of oscillation AO. This occurs when oscillation midpoint OM arrives at a subsequent step path  56 . At that point, maximum articulation of θ/2 has been imparted to roller cone  10 . Oscillation is dwelled at point  90  until oscillation midpoint OM arrives at subsequent traversing path  54 . Roller cone  10  is then gradually articulated back by robot  100  until traversing path  54  is again perpendicular to axis of oscillation AO at tooth centerline  34 . This occurs at point  92  in  FIG. 20 . 
         [0144]    Secondary oscillation of roller cone  10  continues until subsequent step path  56  is parallel to axis of oscillation AO, when oscillation midpoint OM arrives at subsequent step path  56 . At that point, a maximum articulation of −θ/2 has been imparted to roller cone  10 . Oscillation is again dwelled at point  90  until oscillation midpoint OM arrives at subsequent traversing path  54 . 
         [0145]    Robot  100  rotates roller cone  10  a maximum of angle θ/2 at the intersection of traversing path  54  and step path  56 , such that step path  56  and the approaching edge of tooth  20  are oriented generally parallel to axis of oscillation AO of torch  300 . The waveform of torch path  60  is thus substantially modified as torch  300  approaches each step path  56 . The application result is a very efficient and tough “shingle” pattern  39  of hardfacing  38  near tooth  20  centerline  34 .  FIG. 24  is a schematic representation of “shingle” pattern  39 . 
         [0146]    Optionally, oscillation of roller cone  10  may be dwelled when oscillation midpoint OM is near centerline  34  of tooth  20  to obtain a more uniform bead deposition across the width of tooth  20 . In the preferred embodiment, step paths  56  are slightly offset from the edge of tooth  20  by a distance d. 
         [0147]    The path speed of step path  56  may be higher than the path speed of traversing path  54 , such that the amount of hardfacing deposited is controlled to provide the desired edge protection for tooth  20 . It is preferred to have the length of step path  56  is greater than height Λ, and less than 2Λ. Preferably, step path  56  is approximately 5 mm. Thus, hardfacing deposited on two adjacent traversing paths  54  will overlap. Preferably, the length of overlap is about 3 mm. Generating this overlap creates a smooth surface with no crack-like defects. 
         [0148]    Roller cone  10  may be preheated to prevent heat induced stress. When necessary, portions of the welds can be interrupted during processing to minimize and control heat buildup. Preferably, crests  26  are formed in three interrupted passes, in which the interruption provides cooling and shape stabilization of the applied material from the previous pass. 
         [0149]      FIG. 22  is a schematic representation of another embodiment of the system and method of the present invention wherein secondary oscillation  80  of traversing path  54  (see  FIGS. 17 ,  21 , and  23 ) again modifies torch path  60  (see  FIG. 19 ). However, in this embodiment, secondary oscillation  80  is created by relatively sudden and complete articulation of roller cone  10  at step paths  56  as oscillation midpoint OM of oscillating torch  300  reaches, or nearly reaches, step path  56  (see  FIGS. 17 ,  21 , and  23 ). Each traversing path  54  (see  FIGS. 17 ,  21 , and  23 ) constitutes ½λ of a wavelength of secondary oscillation  80 . Since traversing paths  54  (see  FIGS. 17 ,  21 , and  23 ) are of different lengths, the wavelength of secondary oscillation  80  expands as the hardfacing application progresses towards base  32  of tooth  20 . For example, where α 1  represents a first traversing path  54  (see  FIGS. 17 ,  21 , and  23 ) and α 2  represents the next traversing path  54 , α 1 &lt;α 2 . 
         [0150]      FIG. 23  is a bottom view of steel-tooth  20  illustrating traversing paths  54  connected by step paths  56  (see  FIGS. 17 ,  21 , and  23 ) to form first waveform target path  50  (see  FIG. 17 ). Second waveform torch path  60  (see  FIG. 19 ) is superimposed on target path  50  (see  FIG. 17 ). When secondary oscillation  80  is imparted on traversing paths  54  (see  FIGS. 17 ,  21 , and  23 ), a herringbone pattern of hardfacing  38  is produced on the surface of tooth  20 . 
         [0151]    Referring to  FIG. 22  and  FIG. 23 , a maximum articulation angle of about |θ/2| of roller cone  10  occurs at each step path  56  (as measured from the centerline  34  of tooth  20 ). In this embodiment, as oscillation midpoint OM of torch  300  progresses on each step path  56 , secondary oscillation  80  is dwelled. The dwell periods are schematically represented by the high and low points of secondary oscillation  80  in  FIG. 22 . 
         [0152]    As roller cone  10  moves along traversing path  54 , it is not again articulated by robot  100  until oscillation midpoint OM of torch  300  nears or reaches the subsequent step path  56 . This occurs schematically at point  96  on  FIG. 22 . At this point, roller cone  10  is articulated by robot  100  an angular amount θ, aligning subsequent step path  56  substantially parallel to axis of oscillation AO. 
         [0153]    A traversing row  54 A will comprise the centerline of a series of parallel columns of hardfacing  38  inclined at an angle to centerline  34  of tooth  20 . As illustrated, the angle is approximately θ/2. Additionally, traversing row  54 A will have an adjacent traversing row  54 B comprising the centerline of a series of parallel columns of hardfacing  38 , inclined at an angle to centerline  34  of tooth  20 , where the angle is approximately −(θ/2). Still, the hardfacing  38  of traversing row  54 A and the hardfacing of traversing row  54 B will overlap. The application result is a very efficient and tough “herringbone” pattern  41  of hardfacing  38  near tooth  20  centerline  34 .  FIG. 25  is a schematic representation of “herringbone” pattern  41 . 
         [0154]    As an alternative, a scooped tooth  20  configuration is obtained by welding crest  26  in two passes. The first pass adds height. When the second pass is made without pausing, hardfacing  38  applied to crest  26  adds width and laps over to the desired side. 
         [0155]      FIGS. 26A and 26B  illustrate hardfacing  38  applied using the systems and methods described herein to the cutter assemblies  514  and cones  522  illustrated in  FIGS. 2A  to provide protection to portions of cones of sintered materials using inserts  524  as teeth or cutters. 
         [0156]      FIG. 27  illustrates hardfacing  38  applied using the systems and methods described herein to a drill bit  610 , although hardfacing may be applied to any type drill bit or portions thereof as described herein. 
         [0157]    It will be readily apparent to those skilled in the art that the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. 
         [0158]    Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.