Abstract:
The present invention relates to a system and method for automated or “robotic” application of hardfacing to the surface of a steel-toothed cutter of a standard earth-boring rock bit or a hybrid-type rock bit. In particular, the system incorporates a grounded adapter plate and chuck mounted to a robotic arm for grasping and manipulating a rock bit cutter, particularly a hybrid rock bit cutter, beneath an electrical or photonic energy welding source, such as a plasma arc welding torch manipulated by a positioner. In this configuration, the torch is positioned substantially vertically and oscillated along a horizontal axis as the cutter is manipulated relative along a target path for the distribution of hardfacing. Moving the cutter beneath the torch allows more areas of more teeth to be overlayed, and allows superior placement for operational feedback, such as automatic positioning and parameter correction. In the preferred embodiment, sensors provide data to the control system for identification, positioning, welding program selection, and welding program correction. The control system, aided by data from the sensors, manipulates the robotically held cutter while controlling the operation and oscillation of the torch. These systems and methods can be applied to hardfacing steel teeth of the rolling cutters of both standard tri-cone or di-cone type rolling cone bits, as well as to hybrid-type earth boring drill bits.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/141,668, filed Dec. 31, 2008, the contents of all of which are incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       REFERENCE TO APPENDIX 
       [0003]    Not applicable. 
       TECHNICAL FIELD OF THE INVENTION 
       [0004]    The present invention relates to a system and method for automated or “robotic” application of hardfacing to the surface of a steel-toothed cutter of a rock bit, particularly a hybrid-type earth boring rock bit. In particular, the system incorporates an adapter plate and chuck mounted to a robotic arm for manipulating a rock bit cutter under a plasma arc welding torch manipulated by a positioner. Sensors provide data to the control system for identification, positioning, welding program selection, and welding program correction. The control system, aided by data from the sensors, manipulates the robotically held cutter while controlling the operation and oscillation of the torch. 
       BACKGROUND OF THE INVENTION 
       [0005]    In the exploration of oil, gas, and geothermal energy, drilling operations are used to create boreholes, or wells, in the earth. These operations normally employ rotary and percussion drilling techniques. In rotary drilling, the borehole is created by rotating a tubular drill string with a drill bit secured to its lower end. As the drill bit deepens the hole, tubular segments 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 into the drill bit. The drilling fluid exits the drill bit at an increased velocity 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 borehole and the outside of the drill string. The drilling fluid carries rock cuttings out of the borehole and also serves to cool and lubricate the drill bit. 
         [0006]    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 drag bits included hard facing applied to steel cutting edges. Modern 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 hard cutting elements scrape against the bottom and sides of the borehole to cut away rock. 
         [0007]    Another type of rotary rock drill is the rolling cutter bit. These drill bits have rotatable cutters mounted on bearings on the body of the drill bit, which rotate as the drill bit is rotated. Cutting elements, or teeth, protrude from the cutters. The angles of the cutters and bearing pins on which they are mounted are aligned so that the cutters essentially roll on the bottom of the hole with controlled slippage. As the rolling cutter cutters roll on the bottom of the hole being drilled, the teeth or carbide inserts apply a high compressive load to the rock and fracture it. The cutting action of rolling cutter cutters is typically by a combination of crushing, chipping and scraping. The cuttings from a rolling cutter rock bit are typically a mixture of moderately large chips and fine particles. 
         [0008]    There are two general types of rolling cutter drill bits; TCI bits and steel-tooth bits. In the oilfield, TCI is a well-recognized abbreviation for Tungsten Carbide Insert. These bits have steel cutters with a plurality of tungsten carbide or similar inserts of high hardness that protrude from the surface of the cutter. There are numerous styles of TCI drill bits designed for various formation hardnesses, in which the shape, number and protrusion of the tungsten carbide inserts will vary, along with cutter and journal angles. 
         [0009]    Steel-tooth bits are also referred to as milled-tooth bits, since most bits have their steel teeth created in a milling machine. However, in larger bits, it is also known to cast the steel teeth and, therefore, “steel-tooth” is the better reference. The steel-tooth bit has cutters having an integral body of hardened steel with teeth formed on the periphery. There are numerous styles of steel-tooth drill bits designed for formations of varying hardness in which the shape, number and protrusion of the teeth will vary, along with cutter and journal angles. 
         [0010]    The cost efficiency of a drill bit is determined by the drilling life of the drill bit and, largely, the rate at which the drill bit penetrates the earth. Under normal drilling conditions, the teeth of the steel-tooth bits are subject to continuous impact and abrasive wear because of their engagement with the rock being drilled. As the teeth are worn away, the penetration rate of the drill bit is reduced, and the cost of drilling increases significantly. 
         [0011]    To increase the cost efficiency of a steel-tooth drill bit, it is necessary to increase the wear resistance of the steel teeth. To accomplish this, in some instances, it may be desirable 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 welding related techniques that apply a wear resistant alloy to a substrate metal. Common hardfacing techniques include arc welding and gas torch welding, among other welding processes. 
         [0012]    Conventional welding techniques used to apply hardfacing to steel-tooth drill bits include oxyacetylene welding (OAW) and atomic hydrogen welding (AHW). Currently, the only method known to be in use in the commercial production of rolling cutters for rock bits is manual welding. Cutters are mounted on a positioning table, and the welder holds a welding torch and welding rod while applying the hardfacing to the desired portions of the teeth on each cutter. The welder must manually move from tooth to tooth on the cutter while addressing the cutter from various angles during the course of this process. 
         [0013]    Conventional hardfacing materials used to add wear resistance to the steel teeth of a rotary rock bit includes tungsten carbide particles in a metal matrix, typically cobalt or a mixture of cobalt and other similar metals. Many different compositions and formulations 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. 
         [0014]    The quality of a hardfacing application has several physical indicators including uniformity, thickness, coverage, porosity, and other metallurgical properties. Historically, the individual skills of the welder have largely controlled the hardfacing quality. Hardfacing quality is known to vary between rock bits, and even between cutters on a rock bit, and teeth on a cutter. Limited availability of qualified welders has aggravated the problem. The manual application is extremely tedious, repetitive, skill-dependent, time-consuming, and expensive. Indeed, application of cutter hardfacing is considered the single most tedious and skill-dependent step in the manufacture of a steel-toothed rock bit. The consistency of even a skilled welder can vary during a work day. 
         [0015]    As stated, the prior-art means of applying hardfacing to a cutter involves continuous manual, angular manipulation of a torch over the cutter, with the cutter held substantially stationary, but rotating, on a positioning table. After hardfacing is applied to a surface of each tooth by a welder holding 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. This continues until all the cutters have been rotated 360 degrees. At that time, the angle of the table and cutter would be adjusted for application to another tooth surface or row of teeth on the cutter. 
         [0016]    When attempts to utilize robotics to automate the welding process were made, the same configuration was used, designating the robotic arm to replace the human operator&#39;s arm and his varied movements, while leaving the cutter on the positioning table. The positioning table was wired for automatic indexing between teeth and rows. 
         [0017]    This is the intuitive configuration and procedure, which 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 cutter must be electrically grounded, and this can be done easily through the stationary positioning table. Third, gravity maintains the heavy cutter in position on the positioning table. Fourth, highly angled (relative to vertical) manipulation of the torch allows access to confined spaces between teeth, a manipulation suited to the highly articulated movement of a robotic arm. 
         [0018]    U.S. Pat. No. 6,392,190 describes a concept of robotically hardfacing cutters on a drill bit, in which the torch is held by a robotic arm and the cutters are moved on a positioning table. In particular, this patent discloses “an automated hardfacing system useful for hardfacing roller cones. The automated system includes a robot with an arm, a positioner, and a controller which co-ordinates the alignment of the robot and the positioner. The robot holds a hardfacing torch and is capable of movement in three axes of movement. These axes are the x, y, and z axes of the Cartesian co-ordinate system. The positioner holds a roller cone and is capable of movement in at least two axes of movement. The movement includes tilting and rotation about a Cartesian axis. The hardfacing coating produced by the automated system has improved quality and consistency as compared to the one obtained by a manual process.” The disclosure of the &#39;190 patent illustrates the concept of replacing the typical “manual welder” used in hardfacing applications with a robot for holding the torch, and essentially describes the rather obvious expedient of more than five movable axes in the system. However, U.S. Pat. No. 6,392,190 fails to provide any specific teaching directed to the critical details of the numerous obstacles that must be overcome to actually reduce to practice the science of robotically automating the hardfacing of rolling cutters. Indeed, to date, it is not known to have successfully automated the production of the application of hardfacing to rolling cutters. 
         [0019]    One factor preventing commercial use of robotic hardfacing has been the unsatisfactory appearance of the final product when applied using robotically held torches over stationary cutters. Another factor preventing commercial 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. 
         [0020]    Another factor preventing commercial use of robotic hardfacing is the inability to properly identify and locate individual rolling cutter designs within a robotic hardfacing system. The cutters of each bit size and style are different, and initiating the wrong program could cause a collision of the torch and part, resulting in catastrophic failure and loss. Another factor preventing commercial use of robotic hardfacing is the inability to correct the critical positioning between the torch and part in response to manufacturing variations of the cutter, wear of the torch, and buildup of hardfacing. 
         [0021]    Still another factor preventing commercial use of robotic hardfacing has been the inability to properly access many of the areas on the complex surface of a rolling cutter 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 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. 
         [0022]    Another factor preventing commercial use of robotic hardfacing is the complexity of programming the control system to coordinate the critical paths and applications sequences needed to apply the hardfacing. For example, heretofore 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 rolling cutters. A related factor preventing commercial 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, prevented any commercial practice of automated hardfacing of rolling cutters anywhere in the world. 
         [0023]    Therefore, there is a need to develop a system and method for applying hardfacing to rolling cutters 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 cutter, 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 rolling cutter that require hardfacing. There is also a need to develop a hardfacing material which performance will compare favorably to conventional Oxygen Acetylene Welding (OAW) materials and flow properly through the PTA torch design. 
       SUMMARY OF THE INVENTION 
       [0024]    The present invention provides a novel and unique system for automating the application of hardfacing to the surface of steel-tooth cutters for earth boring drill bits, both rolling cone and hybrid-type earth boring drill bits. The present invention also provides a novel and unique method of automated application of hardfacing the surface of steel-tooth cutters for rotary drill bits, including hybrid-type drill bits as will be described herein. 
         [0025]    The present invention operates in a configuration opposite that of manual hardfacing techniques, and opposite to the specific teachings of the prior art. In a preferred embodiment of the present invention, a robotic cutter welding system is provided, 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. For handling a rolling cutter of either a standard rolling cone type drill bit or a hybrid-type earth boring drill bit, a robot having program controllable movement of an articulated arm is provided. 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 rock bit cutter in the inverted position. 
         [0026]    A first position sensor is positioned for determining the proximity of the torch to a surface of the rolling cutter. A second position sensor may be positioned for determining the location, orientation, or identification of the rolling cutter. A programmable control system is electrically connected to the torch, the torch positioner, the robot, shielding, plasma, and transport gas flow valves, and the position sensors for programmed 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 cutter. 
         [0027]    In this configuration, the torch is oscillated in a horizontal path. The cutter 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 cutter 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 cutter. In another preferred embodiment, the cutter 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. 
         [0028]    The primary advantage of the present invention is that it provides a system and method for automating the hardfacing application of rolling cutters, which increases the consistency and quality of the applied hardfacing, and thus the reliability, performance, and cost efficiency of the final product. Another advantage of the present invention is that it reduces manufacturing cost and reliance on skilled laborers. Another advantage of the present invention is that by decreasing production time, product inventory levels can be reduced. Another advantage 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. 
         [0029]    Another advantage of the present invention is that utilization of the robotic arm to manipulate the rolling cutter improves the opportunity to integrate sensors for providing feedback. Another advantage of the present invention is that utilization of the robotic arm to manipulate the rolling cutter 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. 
         [0030]    These aspects of the invention are not meant to be exclusive and other features, aspects, and other advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the appended claims and accompanying drawings. 
         [0031]    As referred to hereinabove, the “present invention” refers to one or more embodiments of the present 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 in a limiting manner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    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. 
           [0033]    The following figures form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these figures in combination with the detailed description of specific embodiments presented herein. 
           [0034]      FIG. 1  is a side view of an exemplary steel-tooth drill bit. 
           [0035]      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 . 
           [0036]      FIG. 3  is an isometric view of a typical steel-tooth such as might be located on the steel-tooth cutter of  FIG. 2 . 
           [0037]      FIG. 4  is an isometric view of the steel-tooth of  FIG. 3  after hardfacing has been applied. 
           [0038]      FIG. 5  is a schematic of a preferred embodiment of the robotic cutter welding system of the present invention. 
           [0039]      FIG. 6  is an isometric view of the robot manipulating a cutter to be hardfaced. 
           [0040]      FIG. 7  is an isometric view of a cutter positioned beneath the torch in preparation for the application of hardfacing. 
           [0041]      FIG. 8  is an isometric view of a chuck of the preferred type attached to the end of the robot. 
           [0042]      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. 
           [0043]      FIG. 10  is a schematic side view of positioner  200  and torch  300 . 
           [0044]      FIG. 11  is a schematic cross-section of torch  300 . 
           [0045]      FIG. 12  is a cross-section of a torch configured in accordance with a preferred embodiment. 
           [0046]      FIG. 13  is an isometric view illustrating the robot manipulating a rolling cutter into position in preparation of the application of hardfacing to the outer ends of the teeth. 
           [0047]      FIG. 14  is a side view illustrating torch  300  applying hardfacing to the outer end of a tooth on the outer row of the cutter. 
           [0048]      FIG. 15  is a side view illustrating torch  300  applying hardfacing to the leading flank of a tooth on the outer row of the cutter. 
           [0049]      FIG. 16  is an isometric view illustrating the robot manipulating a rolling cutter into position in preparation of the application of hardfacing to the inner end of a tooth on the cutter. 
           [0050]      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. 
           [0051]      FIG. 18  is a schematic representation of the oscillation of the torch on axis of oscillation ‘AO’ having an oscillation midpoint ‘OM’ in accordance with a preferred embodiment of the present invention. 
           [0052]      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. 
           [0053]      FIG. 20  is a schematic representation of a waveform created by oscillation of the cutter relative to the intersection of the target path and the oscillation midpoint ‘OM’ in accordance with a preferred embodiment of the present invention. 
           [0054]      FIG. 21  is a schematic representation of a modified waveform of hardfacing created in accordance with the preferred embodiment of  FIG. 20 . 
           [0055]      FIG. 22  is a schematic representation of a generally rectangular shaped waveform created by oscillation of the cutter relative to the intersection of the target path and the oscillation midpoint ‘OM’ in accordance with a preferred embodiment of the present invention. 
           [0056]      FIG. 23  is a schematic representation of a modified waveform of hardfacing created in accordance with the preferred embodiment of  FIG. 22 . 
           [0057]      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. 
           [0058]      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. 
           [0059]      FIG. 26  is a side elevational view of an exemplary hybrid-type earth boring drill bit in accordance with embodiments of the present invention. 
           [0060]      FIGS. 27 and 28  are side elevational views of exemplary rolling cutters of the type employed in the embodiment of the hybrid earth-boring drill bit of  FIG. 26 , having a hardfacing applied thereto in accordance with embodiments of the present invention. 
       
    
    
       [0061]    While the inventions disclosed herein are susceptible to various modifications and alternative forms, only a few specific embodiments have been shown by way of example in the drawings and are described in detail below. The figures and detailed descriptions of these specific embodiments are not intended to limit the breadth or scope of the inventive concepts or the appended claims in any manner. Rather, the figures and detailed written descriptions are provided to illustrate the inventive concepts to a person of ordinary skill in the art and to enable such person to make and use the inventive concepts. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0062]    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. 
         [0063]      FIG. 1  is a side view of an exemplary steel-tooth drill bit  1  in accordance with the present disclosure. While the bit  1  illustrated therein is of the typical roller-cone or ‘tricone’ type, the phrase “steel-tooth drill bit” as used herein is meant to include the roller cones of hybrid-type earth boring drill bits, as will be described in more detail with reference to  FIGS. 26-28 , below. Returning to the Figure, steel-tooth drill bit  1  has a plurality of rolling cutters, or cones  10 .  FIG. 2  is an isometric view of a typical steel-tooth cutter  10  such as might be used on the drill bit of  FIG. 1 . Steel-tooth cutter  10  typically has a plurality of rows. In  FIG. 2 , cutter  10  has an inner row  12 , an intermediate row  14 , and an outer row  16 . Each of rows  12 ,  14 , and  16  has one or more teeth  20 . When steel-tooth drill bit  1  is rotated at the bottom of a well bore, teeth  20  engage and remove the earthen formation. 
         [0064]    As shown by the hidden lines, the interior of cutter  10  includes a cylindrical journal race  40  and a semi-torus shaped ball race  42 . Journal race  40  and a ball race  42  are internal bearing surfaces that are finish machined after hardfacing  38  has been applied to teeth  20 . 
         [0065]      FIG. 3  is an isometric view of a typical steel tooth  20  such as might be located on steel-tooth cutter  10  of  FIG. 2 . Tooth  20  has an included tooth angle of θ 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 cutter  10 . It is well-known in the drilling industry to include various alternatively shaped teeth on cutter  10 , such as teeth having T-shaped crests. Tooth  20  is generally representative of the most common teeth used in the industry, and serves the purpose of illustrating the application of the present invention, but practice of the present invention is not limited to any particular shape of steel tooth. 
         [0066]    To prevent early wear and failure of drill bit  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 . 
         [0067]      FIG. 5  is a schematic illustration 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  108  about which controllable movement permits wide-range positioning of distal end  106  relative to base  102 . In the preferred embodiment, robot  100  has six independently controllable axes of movement between base  102  and the distal end  106  of arm  104 . 
         [0068]    In the preferred embodiment, 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. In the more preferred embodiment, robot  100  has six independently controllable axes of movement between base  102  and distal end  106  of arm  104 . 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. 
         [0069]    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 cutter  10  at journal bearing surface  40  and/or ball race  42 , as shown in greater detail in  FIGS. 8 and 9 . 
         [0070]    In a preferred embodiment, a heat sink, or thermal barrier, is provided between cutter  10  and adapter  110  to prevent heat from causing premature failure of the rotating axis at distal end  106  of articulated arm  104 . In a preferred embodiment, the thermal barrier is an insulating spacer  116  (not shown) located between cutter  10  and distal end  106  of robot  100 . In another preferred embodiment, cutter  10  is gripped in a manner that provides an air space between cutter  10  and distal end  106  of robot  100  to dissipate heat. 
         [0071]    In another preferred embodiment, chuck  120  or adapter  110  is water cooled by circulating water. Heat energy absorbed by the water is removed by a remotely located cooling unit (such as cooling unit  174 , shown in  FIG. 5 ). In another preferred embodiment, jaws  122  ( FIG. 8  and  FIG. 9 ) of chuck  120  are water cooled by circulating water. Heat energy absorbed by the water is removed by a remotely located cooling unit (such as cooling unit  174 , shown in  FIG. 5 ). 
         [0072]    A robot controller  130  is electrically connected to robot  100  for programmed manipulation of robot  100 , including movement of articulated arm  104 . In a preferred embodiment, 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 . 
         [0073]    A plurality of sensors  142  are electrically connected to sensor controller  140 . In a preferred embodiment, sensors  142  include a camera  144  and/or a contact probe  146 . In an alternative embodiment, sensors  142  include a laser proximity indicator  148  (not shown). 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 cutter  10  and torch  300 . 
         [0074]    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 . 
         [0075]    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. 
         [0076]    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 the preferred embodiment, a data-recording device  190  is electrically connected to PLC  150 . 
         [0077]    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 series alignment can control the flow and flow rate of gas from a single gas source. 
         [0078]    A torch  300  is provided. In the preferred embodiment, torch  300  is 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 supply system  180 . Torch  300  is secured to a positioner or positioning table  200 , which grips and manipulates torch  300 . In the preferred embodiment, positioner  200  is capable of programmed positioning of torch  300  in a substantially vertical plane. In this embodiment, 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. 
         [0079]      FIGS. 6 and 7  are isometric views of robot  100  shown manipulating cutter  10 . Cutter can be seen secured to adapter  110  on distal end  106  of articulated arm  104  of robot  100 . As can be seen 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 cutter  10  directly beneath torch  300 .  FIG. 7  is illustrated cutter  10  positioned beneath torch  300  in preparation for the application of hardfacing  38 . 
         [0080]    In the preferred embodiment, 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″ of true center rotation. Cutter  10  is held securely by chuck  120  and also centered by indicator alignment. In the preferred embodiment, cutter  10  has grooves that permit location and calibration of the end of torch  300 . Torch  300  electrode  304  is then used to align cutter  10  about the z-axis of rotation of cutter  10  by robot  100 . 
         [0081]    As seen in  FIG. 7 , electrical ground cable  114  is electrically connected to adapter  110  by ground connector  112  (see  FIG. 7 ). In a preferred embodiment, ground connector  112  is a rotatable sleeve connector. In another preferred embodiment, ground connector  112  is a brush connector. In another preferred embodiment, ground cable  114  is supported by a tool balancer (not shown) to keep it away from the heat of cutter  10  and the welding arc during hardfacing operations. Chuck  120  is attached to adapter  110 . Cutter  10  is held in place by chuck  120 . 
         [0082]    As the present invention necessitates manipulation of heavy cutters  10  in vertical, horizontal, inverted, and rotated positioning beneath torch  300 , highly secure attachment of cutter  10  to robot  100  is required for safety and accuracy of the hardfacing operation. Precision alignment of cutters  10  in relation to chuck  120  is also necessary to produce a quality hardfacing and to avoid material waste. 
         [0083]      FIG. 8  is an isometric view of chuck  120 . In the preferred embodiment, chuck  120  is a three-jaw chuck having adjustable jaws  122  for gripping a hollow interior of cutter  10 . In another preferred embodiment, jaws  122  are specially profiled to include a cylindrical segment shaped journal land  124  which contacts journal race  40  on cutter  10 , providing highly secure attachment of cutter  10  on chuck  120  of robot  100 . A seal relief  128  is provided to accommodate a seal supporting surface on cutter  10   
         [0084]    In a more preferred embodiment illustrated in  FIG. 9 , jaws  122  are 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  and race land  126  fits in alignment with ball race  42 , providing precise alignment against the centerline of ball race  42  and secure attachment of cutter  10  on chuck  120  of robot  100 . Seal relief  128  may be provided to accommodate a seal supporting surface on cutter  10 . 
         [0085]      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. 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 . 
         [0086]    In the preferred embodiment, 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 cutter  10 . Also in the preferred embodiment, 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 cutter  10 . These occasional real-time distance adjustments maintain the proper energy level of the transferred arc between torch  300  and cutter  10 . 
         [0087]    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 . Torch  300  is electrically connected to pilot arc power source  170  and main arc power source  172 . 
         [0088]      FIG. 11  is a schematic cross-section of torch  300 . In the preferred embodiment, torch  300  is a Plasma Transferred Arc (PTA) torch  300 . Torch  300  has a nozzle  302 . 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  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 , which supplies hardfacing powder carried by transport gas to nozzle annulus  306 . 
         [0089]    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 cathode  304  to the anode work piece, cutter  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  ( FIG. 5 ). 
         [0090]    A cup  320  surrounds nozzle  302 . Nozzle  302  is electrically insulated from cup  320 . A cup annulus  322  is formed between cup  320  and nozzle  302 . Cup annulus  322  is connected to shielding gas source  190  to allow the flow of shielding gas between cup  320  and nozzle  302 . 
         [0091]    In the preferred embodiment, 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 cutter  10  (anode). Electrode  304  is the negative pole and cutter  10  is the positive pole. Pilot arc circuit  330  is ignited to reduce the resistance to an arc jumping between cutter  10  and electrode  304  when voltage is applied to main arc circuit  332 . In the preferred embodiment, a ceramic insulator separates circuits  330  and  332 . 
         [0092]    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  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. In the preferred embodiment, plasma gas source  186  is comprised of 99.9% Argon. 
         [0093]    Shielding gas from shielding gas source  190  is delivered to cup annulus  322 . As the shielding gas exits cup annulus  322  it is directed towards the work piece, cutter  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. In the preferred embodiment, shielding gas source  190  is 95% Argon and 5% Hydrogen. 
         [0094]    Transport gas source  182  is connected to powder dosage system  160 . 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 cutter  10 . 
         [0095]      FIG. 12  is a cross-section of torch  300  configured in accordance with a preferred embodiment. In this preferred embodiment, gas cup  320  of torch  300  has a diameter of less than 0.640 inches and a length of less than 4.40 inches. In the preferred embodiment, 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. 
         [0096]    In the preferred embodiment, gas cup  320  is modified from commercially available gas cups for use with torch  300 . In a preferred embodiment, gas cup  320  extends beyond nozzle  302  by no more than approximately 0.062 inches. In an embodiment suited for use with the E52 torch, 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 port  324  in nozzle  302 . In the preferred embodiment, an insulating material is attached to the exterior of gas cup  320  of the torch  300 . This tends to prevent short-circuiting and damage to torch  300 . 
         [0097]    The preferred embodiment of shielding gas cup  320  described above is specially designed to improve shield gas coverage of the melt puddle and reduce porosity. This change 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 cutters  10 . 
       OPERATION OF THE INVENTION 
       [0098]    Some of the problems encountered in the development of robotic hardfacing included interference between the torch and teeth on the cutter, 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. 
         [0099]    As described above, the present invention begins with inverting what has been the conventional practice since hardfacing of cutters was introduced several decades ago: that is, the practice of maintaining cutter  10  generally stationary and moving torch  300  all over it at various angles as necessary. Fundamental to the present invention, torch  300  is held substantially vertical, while cutter  10  is held by chuck  120  of robotic arm  104  and manipulated beneath torch  300 . If torch  300  is robotically manipulated 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 cutter  10 . Thus, deviation from a substantially vertical orientation is avoided. 
         [0100]    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.” 
         [0101]    Accordingly, a rolling cutter  10  is secured to distal end  106  of robot arm  104  by chuck  120  and adapter  110 . Cutter  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  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 the destruction of robot  100  by arc welding the rotating components of the movable axes together. 
         [0102]    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 cutter  10  to be engaged by torch  300  to insure proper initial orientation between torch  300 , robot arm  100 , and cutter  10 . Additionally, at least one position indicator is electrically connected to PLC  150  for determining location and orientation of cutter  10  to be hardfaced relative to robot  100 . 
         [0103]    After initial orientation and positioning, transfer, plasma and shielding gas are supplied to torch  300  by their respective sources  182 ,  186 ,  190  through their respective controllers  184 ,  188 ,  192 . 
         [0104]    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 cutter  10  and electrode  304  when voltage is applied to main arc circuit  332 . 
         [0105]    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 cutter  10  relative to torch  300 , as described above and below is obtained by movement of robot arm  100  and positioner  200 , permitting automated application of hardfacing  38  to the various selected surfaces of cutter  10  in response to programming from robot controller  130  and PLC  150 . 
         [0106]    An imaging sensor  142  may be provided for identifying specific cutters  10  and (or) parts of cutters  10  to be hardfaced. A laser sensor  142  may also or alternatively be provided for determining proximity of torch  300  to cutter  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. 
         [0107]    Robot controller  130  is primarily responsible for control of robot arm  100 , while PLC  150  and data recorder  190  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. 
         [0108]      FIGS. 13 and 14  illustrate robot  100  manipulating rolling cutter  10  into position to apply hardfacing material to outer  28  of teeth  20  on outer row  16  of cutter  10 .  FIG. 15  is illustrates torch  300  in position to apply hardfacing to leading flank  22  or trailing flank  24  of tooth  20  on outer row  16  of cutter  10 .  FIG. 16  is an isometric view illustrating robot  100  manipulating rolling cutter  10  into position in preparation for application of hardfacing  38  to inner end  30  of tooth  20 . 
         [0109]    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 cutter  10  beneath torch  300 , allowing torch  300  to access the various surfaces of cutter  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 rolling cutters, the present invention provides a 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 cutter  10  made possible by the apparatus of the present invention. These patterns will be described with reference to  FIGS. 17 through 25  below. 
         [0110]    The above-described apparatus has resolved these issues and enabled development of the novel and unique method of applying hardfacing of the present invention. A preferred embodiment of the present invention includes a hardfacing pattern created by superimposing a first waveform path onto a second waveform path. 
         [0111]      FIG. 17  is a bottom view of typical steel-tooth  20  such as might be located on steel-tooth cutter  10 , illustrating a first waveform target path  50  defined in accordance with a preferred embodiment of 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 . 
         [0112]    In the preferred embodiment illustrated, target path  50  traverses one surface of tooth  20 . By way of example, outer end surface  28  is shown, but the embodiment illustrated applies to 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  towards base  32  when possible to control heat buildup. 
         [0113]    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 . 
         [0114]    Step paths  56  connect traversing paths  54  to form 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 θ/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 increasing amplitude in the direction of base  32 . 
         [0115]    In the preferred embodiment, 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 . In the preferred embodiment, this is obtained by starting at the lowest amperage on 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. 
         [0116]    In another preferred embodiment, 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. In a more preferred embodiment, the programmed traversing paths  54  for flanks  22  and  24 , inner surface  30  and outer surface  28  are also modified such that to overlap crests  26  sufficiently to create the desired profile and to provide sufficient support to crests  26 . 
         [0117]    In the preferred embodiment, the program sequence welds the surface of a datum tooth, then offsets around the cutter axis the amount needed to align with the next tooth surface. Also in the preferred embodiment, teeth are welded from the tip to the root to enhance heat transfer from the tooth and prevent heat buildup. In a more preferred embodiment, welding is alternated between rows of teeth on the cutter to further reduce heat buildup. 
         [0118]      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 . In the preferred embodiment, torch  300  has a linear velocity of between about 1 and 10 mm per second along its axis of oscillation AO. 
         [0119]      FIG. 19  is a schematic representation of a second waveform torch path  60  formed in accordance with a preferred embodiment of the present invention. In the preferred embodiment, hardfacing is applied to a tooth  20  by oscillating torch  300  while moving cutter  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. 
         [0120]    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. 
         [0121]    As seen in  FIG. 19 , torch path  60  has an amplitude Λ. In the preferred embodiment, Λ is between about 3 mm and 5 mm. In a more preferred embodiment, Λ is about 4 mm. Traversing path  54  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 cutter  10  along traversing path  54  beneath the OM of torch  300 . Thus, traversing path  54  of target path  50  becomes the axis about which the generally triangular waveform of torch path  60  oscillates. 
         [0122]    Cutter  10  is positioned and moved by instructions from robot controller  130  provided to robot  100 . In the preferred embodiment, robot  100  moves cutter  10  to align target path  50  directly beneath the OM. Also in the preferred embodiment, cutter  10  is moved such that the OM progresses along target path  50  at a linear velocity (target path speed) of between approximately 1 and 4 mm per second. 
         [0123]    In the preferred embodiment illustrated, a momentary dwell period  68  is programmed to elapse between peaks of oscillation of torch  300 . In this embodiment, dwell  68  prevents generally triangular waveform of torch path  60  from being a true triangular waveform. In the preferred embodiment, dwell  68  is between about 0.01 to 0.6 seconds. 
         [0124]      FIG. 20  is a schematic representation of another preferred embodiment. In this embodiment, a secondary oscillation  80  of traversing path  54  modifies torch path  60 . Traversing path  54  is oscillated as a function of the location of oscillation midpoint OM on target path  50 . Secondary oscillation  80  is created by gradually articulating cutter  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 α 1  represents a first traversing path  54  and α 2  represents the next traversing path  54 , α 1 &lt;α 2 . 
         [0125]      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. 
         [0126]    Referring to  FIG. 20  and  FIG. 21 , a maximum articulation angle of about |θ/2| of cutter  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. 
         [0127]    As cutter  10  moves along traversing path  54 , cutter  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 cutter  10  continues to move along traversing path  54 , cutter  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 subsequent step path  56 . At that point, maximum articulation of θ/2 has been imparted to cutter  10 . Oscillation is dwelled at  90  until oscillation midpoint OM arrives at subsequent traversing path  54 . Cutter  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 . 
         [0128]    Secondary oscillation of cutter  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 cutter  10 . Oscillation is again dwelled at  90  until oscillation midpoint OM arrives at subsequent traversing path  54 . 
         [0129]    In this embodiment, robot  100  rotates cutter  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. 25  is a schematic representation of ‘shingle’ pattern  39 . 
         [0130]    Optionally, oscillation of cutter  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. 
         [0131]    In the preferred embodiment, 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 . In the preferred embodiment, the length of step path  56  is greater than height Λ, and less than 2Λ. In a preferred embodiment, step path  56  is approximately 5 mm. Thus, in the preferred embodiment, hardfacing deposited on two adjacent traversing paths  54  will overlap. In the preferred embodiment, the length of overlap is about 3 mm. Generating this overlap creates a smooth surface with no crack-like defects. 
         [0132]    In another preferred embodiment, cutter  10  is preheated to prevent heat induced stress. When necessary, portions of the welds can be interrupted during processing to minimize and control heat buildup. In the preferred embodiment, 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. 
         [0133]      FIG. 22  is a schematic representation of an alternative preferred embodiment. In this embodiment, secondary oscillation  80  of traversing path  54  again modifies torch path  60 . However, in this embodiment, secondary oscillation  80  is created by relatively sudden and complete articulation of cutter  10  at step paths  56  as oscillation midpoint OM of oscillating torch  300  reaches, or nearly reaches, step path  56 . Each traversing path  54  constitutes ½λ of a wavelength 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 α 1  represents a first traversing path  54  and α 2  represents the next traversing path  54 , α 1 &lt;α 2 . 
         [0134]      FIG. 23  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 paths  54 , a herringbone pattern of hardfacing  38  is produced on the surface of tooth  20 . 
         [0135]    Referring to  FIG. 22  and  FIG. 23 , a maximum articulation angle of about |θ/2| of cutter  10  occurs at each step path  56  (as measured from the centerline  34  of tooth  20 ). In this preferred 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 waveform  80  in  FIG. 22 . 
         [0136]    As cutter  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, cutter  10  is articulated by robot  100  an angular amount θ, aligning subsequent step path  56  substantially parallel to axis of oscillation AO. 
         [0137]    In the preferred embodiment, a traversing path  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 . In the preferred embodiment, the angle is approximately θ/2. Additionally, in the preferred embodiment, 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 more preferred, the hardfacing  38  of traversing path  54 A and the hardfacing of traversing path  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 . 
         [0138]    Turning now to  FIGS. 26-28 , an embodiment of the present disclosure is described, wherein the automated hardfacing methods and systems described above may be applied to earth-boring drill bits of the hybrid-type, such as illustrated generally in  FIG. 26 . To date, the use of steel-tooth cutters in hybrid-type drill bits has been relatively untested. The modern hard-facing techniques described herein, in combination with modern steel tooth bit designs such as shown herein, can provide benefits to the drilling operation not readily achievable in the past. In particular, such hard-faced steel-tooth cutters as used in hybrid type earth boring drill bits can be advantageous when used to drill through particularly hard subterranean strata, and/or when used as DOC limiters. 
         [0139]    A general hybrid-type earth boring drill bit in accordance with aspects of the present disclosure is shown in  FIG. 26 . The hybrid earth boring drill bit  400  comprises a bit body  413  having a central longitudinal axis  415  that defines an axial center of the bit body  413 . In the illustrated embodiment, the bit body  413  is steel, but may also be formed of matrix material with steel reinforcements, or of a sintered carbide material. Bit body  413  includes a shank at the upper or trailing end thereof threaded or otherwise configured for attachment to a hollow drillstring (not shown), which rotates bit  400  and provides pressurized drilling fluid to the bit and the formation being drilled. As also shown in  FIG. 26 , a reference plane  450  is illustrated, located at the leading or distalmost axial end of the hybrid drill bit  400 . In accordance with aspects of the present disclosure, at least one of each of the rolling cutter elements  420  and the fixed cutting elements  430  extend in the axial direction at the reference plane  450  at a substantially equal dimension, but are radially offset from each other, as described in U.S. Patent Publication No. 2008/0264695, incorporated herein by reference to the extent that it is not inconsistent with the present invention as described and claimed. 
         [0140]    The radially outermost surface of the bit body  413  is known as the gage surface and corresponds to the gage or diameter of the borehole (shown in phantom in  FIG. 1 ) drilled by bit  400 . At least one (two are shown) bit leg  417  extends downwardly from the bit body  413  in the axial direction. The bit body  413  also has a plurality (e.g., also two shown) of fixed blades  419  that extend downwardly in the axial direction. The number of bit legs  417  and fixed blades  419  is at least one but may be more than two. In the illustrated embodiment, bit legs  417  (and the associated rolling cutters) are not directly opposite one another (are about 191 degrees apart measured in the direction of rotation of bit  400 ), nor are fixed blades  419  (which are about 169 degrees apart measured in the direction of rotation of bit  400 ). Other spacings and distributions of legs  417  and blades  419  may be appropriate. 
         [0141]    A rolling cutter  420  is mounted on a sealed journal bearing that is part of each bit leg  417 . According to the illustrated embodiment, the rotational axis of each rolling cutter  420  intersects the axial center  415  of the bit. Sealed or unsealed journal or rolling-element bearings may be employed as cutter bearings. Each of the rolling cutters  420  is formed and dimensioned such that the radially innermost ends of the rolling cutters  420  are radially spaced apart from the axial center  415  by a minimal radial distance of about 0.60 inch. As shown in particular in  FIGS. 27 and 28 , discussed in more detail below, the rolling cutters  420  of a hybrid type earth boring bit are typically not conical in configuration as is typical in conventional rolling cutter bits, but rather are generally in the shape of a flattened sphere, having two opposite substantially planar faces and an intermediate region with a curved radius. Further, the radially outermost surface of each rolling cutter  420  (typically called the gage cutter surface in conventional rolling cutter bits), as well as the bit legs  417 , are “off gage” or spaced inward from the outermost gage surface of bit body  413 . In the illustrated embodiment, rolling cutters  420  have no skew or angle and no offset, so that the axis of rotation of each rolling cutter  420  intersects the axial center (central axis)  415  of the bit body  413 . Alternatively, the rolling cutters  420  may be provided with skew angle and (or) offset to induce sliding of the rolling cutters  420  as they roll over the borehole bottom. 
         [0142]    At least one (a plurality are illustrated) rolling-cutter cutting inserts or cutting elements  422  are arranged on the rolling cutters  420  in generally circumferential rows thereabout such that each cutting element  422  is radially spaced apart from the axial center  415  by a minimal radial distance of about 0.30 inch. The minimal radial distances (not shown) may vary according to the application and bit size, and may vary from cone to cone, and/or cutting element to cutting element, an objective being to leave removal of formation material at the center of the borehole to the fixed-blade cutting elements  430  (rather than the rolling-cutter cutting elements  422 ). Rolling-cutter cutting elements  422  need not be arranged in rows, but instead could be “randomly” placed on each rolling cutter  420 . Moreover, the rolling-cutter cutting elements may take the form of one or more discs or “kerf-rings,” which would also fall within the meaning of the term rolling-cutter cutting elements. 
         [0143]    Tungsten carbide inserts, secured by interference fit into bores in the rolling cutter  420  can optionally be used, but as shown in the figures and in accordance with the embodiments of the present disclosure, milled- or steel-tooth cutters having hardfaced cutting elements  422  integrally formed with and protruding outwardly from the rolling cutter could be used in certain applications and the term “rolling-cutter cutting elements” as used herein encompasses such teeth. The inserts or cutting elements which are suitable for hard-facing in accordance with the methods of the instant disclosure may be chisel-shaped as shown, conical, round, or ovoid, or other shapes and combinations of shapes depending upon the application. In addition, in accordance with the present disclosure, the steel-tooth cutting elements  422  may be hardfaced using the automated processes described and detailed herein. Hardfaced rolling-cutter cutting elements  422  may also be formed of, or further coated with, superabrasive or super-hard materials such as polycrystalline diamond, cubic boron nitride, and the like, as appropriate, and depending on the application of the hybrid bit. 
         [0144]    In addition, a plurality of fixed or fixed-blade cutting elements  430  are arranged in a row and secured to each of the fixed blades  419  at the leading edges thereof (leading being defined in the direction of rotation of bit  400 ). Each of the fixed-blade cutting elements  430  can comprise a polycrystalline diamond layer or table on a rotationally leading face of a supporting substrate, the diamond layer or table providing a cutting face having a cutting edge at a periphery thereof for engaging the formation. At least a portion of at least one of the fixed cutting elements  430  is located near or at the axial center  415  of the bit body  413  of hybrid drill bit  400 , and thus is positioned to remove formation material at the axial center of the borehole (typically, the axial center of the bit will generally coincide with the center of the borehole being drilled, with some minimal variation due to lateral bit movement during drilling). In an exemplary 7⅞ inch bit as illustrated, the at least one of the fixed cutting elements  430  has its laterally innermost edge tangent to the axial center of the bit  400 . In any size bit, at least the innermost lateral edge of the fixed-blade cutting element  430  adjacent the axial center  415  of the bit should be within approximately 0.040 inches of the axial center  415  of the bit (and, thus, the center of the borehole being drilled). 
         [0145]    Fixed-blade cutting elements  430  radially outward of the innermost cutting element  430  are secured along portions of the leading edge of blade  419  at positions up to and including the radially outermost or gage surface of bit body  400 . In addition to fixed-blade cutting elements  430  including polycrystalline tables mounted on tungsten carbide substrates, such term as used herein encompasses thermally stable polycrystalline diamond (TSP) wafers or tables mounted on tungsten carbide substrates, and other, similar superabrasive or super-hard materials such as cubic boron nitride and diamond-like carbon. Fixed-blade cutting elements  430  may be brazed or otherwise secured in recesses or “pockets” on each blade  419  so that their peripheral or cutting edges on cutting faces are presented to the formation. 
         [0146]      FIGS. 27 and 28  illustrate each of the rolling cutters  420 , which are of different configuration from one another, and neither is generally conical, as is typical of rolling cutters used in rolling-cutter-type bits. Both cutters  420  shown in  FIGS. 27 and 28  comprise a plurality of steel tooth cutting elements  422 , which in accordance with embodiments of the present disclosure are hardfaced using standard manual techniques, or more preferably, using automated methods as described herein. Cutter  421  of  FIG. 27  may have four (or more) surfaces or lands on which cutting elements or inserts are located. A nose or innermost surface  423  may be covered with flat-topped, wear-resistant inserts or cutting elements. A second surface  425  is conical and of larger diameter than the first  421 , and has chisel-shaped, steel-tooth, hardfaced cutting elements  422  on it. A third surface  426  is conical and of smaller diameter than the second surface  425  and again has chisel-shaped inserts  422  which are hardfaced steel-tooth cutting elements. A fourth surface  424  is conical and of smaller diameter than the second  425  and third  426  surfaces, but is larger than the first  423 . Fourth surface  424  as illustrated has round-topped inserts or cutting elements that are intended primarily to resist wear. 
         [0147]    Cutter  420  of  FIG. 28  also has four surfaces or lands on which cutting elements are located. A nose or first surface  443  has flat-topped, wear-resistant cutting elements on it. A second surface  445  is conical and of larger diameter than the first surface  4433  and has a plurality of hardfaced, steel-tooth cutting elements  422  mounted therein or formed thereon. A third surface  447  is generally cylindrical and of larger diameter than second surface  445 . Again, hard-faced steel-tooth cutting elements  422  are extending outwardly from the third surface  447 . A fourth surface  449  is conical and of smaller diameter than third surface  447 . Round-topped wear-resistant inserts may be placed on fourth surface  449 . 
         [0148]    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. 
         [0149]    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.