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CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 10/229,192 filed on Aug. 27, 2002. The disclosures of the above application is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   present invention relates to earth boring drill bits. Specifically, this invention relates to a method of producing/manufacturing earth boring bits with integral carbide studs for downhole drilling through rock and other material. 
   BACKGROUND OF THE INVENTION 
   Rotary drill bits used in earth drilling are generally comprised of a cast, forged or machined material of significant hardness, to keep wear to the drill bit head to a minimum. To further enhance the effect of the drill, drill bit heads often utilize a plurality of hardened studs of tungsten carbide or other hard material mounted in a configuration on the head of the drill bit to increase the durability and efficiency of the bit. Conventionally, these studs are mounted in their seats upon the head of the drill bit by brazing or cementing them to the drill bit, which is economically inefficient, time consuming, and often results in the loss of studs during vigorous drilling. Furthermore, it is often necessary for the bits to be heavily machined after casting or forging prior to the attachment thereto of any carbide studs, requiring additional labor and costs. 
   U.S. Pat. No. 4,607,712 to inventor Larsson teaches a rock drill bit with studded inserts positioned within drilled holes, following the casting of the drill bit. This additional step of requiring the bit to be machined prior to the attachment of the studs requires significant amounts of resources and time. 
   U.S. Pat. No. 4,181,187 to inventor Lumen, teaches a method of attaching inserts to a rock drill bit using a press to force the hardened metal inserts into pre-bored holes in the rock drill bit head. Exemplifying the obstacle of extra tooling of the drill bit head following the casting, the present invention overcomes this by providing a cast drill bit head with hardened stud inserts already attached to the drill bit head during the casting process. 
   U.S. Pat. No. 4,499,795 to inventor Radtke teaches another method of drill bit manufacture wherein soft iron or steel plugs are embodied in the mold. After casting, the plugs are subsequently drilled out and cutting studs are inserted in their place. This extra machining significantly increases production time and cost to the drill bit. That will allow the final side to come 
   U.S. Pat. No. 4,014,395 to inventor Pearson discloses a rock drill bit assembly wherein the hardened drill inserts are maintained in pre-drilled apertures in the head of the drill bit by tapered sleeves that are pressed into place around the studs. The addition of the sleeves increases production costs as well as the possibility of the incidental release of the studded insert due to the vibrations caused by the earth drilling process. 
   The present invention overcomes these problems, by providing a method of manufacturing a downhole drill bit with pre-cast carbide studs, creating a time and cost efficient alternative to the traditional methods of manufacturing requiring post-casting attachment of the carbide studs, followed by subsequent machining prior to use of the drill bit. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide for a downhole drill bit for earth boring, implementing a plurality of hardened carbide studs in the drill bit head which can be manufactured easily and economically. 
   A more specific object of the present invention is to provide a means for manufacturing a downhole drill bit for earth boring from Austempered ductile iron, or iron hardened by other means, utilizing a lost-foam casting process. 
   It is a further object of the present invention to provide for a means of casting a downhole drill bit head so as to attach a plurality of hardened carbide studs to the head of the drill bit during the casting process. 
   It is a more specific object of the present invention to provide a copper plating to the carbide studs prior to being set into the foam tooling thereby protecting the carbide itself during the subsequent Austemper heat treatment process. 
   It is another object of the present invention to embody a plurality of steel water tubes set into the foam tooling providing for appropriate flow of cooling liquid to the drill bit head without the need for post-casting machining of these passageways. 
   The foregoing objects are accomplished in the preferred embodiment of the present invention by providing a downhole drill bit implementing hardened carbide studs and method of manufacturing the same. The drill bit, cast from ductile iron, is formed by the lost-foam process. This process consists of making a foam pattern, generally out of polystyrene, having the exact geometry of the desired finished metal part. After a short stabilization period, the pattern is dipped into a solution containing a suspended refractory. The refractory material coats the exterior surface of the foam, leaving a thin, heat-resistant, semi-permeable coating, that is subsequently dried. When the drying is complete, the foam is suspended in a container that is agitated while sand is poured in and around the foam pattern, filling all voids in the coated pattern. The sand provides mechanical support to the thin coating. 
   Molten metal, preferably ductile iron, is then poured into the mold where the molten metal subsequently vaporizes the foam and replaces its volume. The solidified metal is formed into a nearly exact replica of the pattern which is subsequently heat treaded, preferably by the Austempering process, for application. 
   In this specific application of the lost foam casting process, a plurality of hardened carbide studs are partially inserted into the foam tooling in a predetermined pattern that maximizes efficiency of the drill, prior to the molten metal being poured into the mold. The carbide studs are plated in copper or some other suitable material prior to being set in the foam tooling to prevent degradation of the carbide material that would otherwise result from the subsequent heat treatment process. The carbide studs can be of various shapes and sizes. The studs are “blown” into the foam molds and have the necessary undercut(s) to secure them into the solidified metal and expose the appropriate cutting surface. 
   Not only are the carbide studs more easily attached to the drill bit head by this invention in not requiring subsequent machining of the drill bit head prior to attachment thereto of the carbide studs, but also the studs are held more securely than those implemented by alternative means, and thus the drilling head and the bits last longer and are more durable for severe drilling applications. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a partial perspective view of the downhole drill bit of the present invention. 
       FIG. 2  is cross-sectional side view of the downhole drill bit of the present invention showing the steel tube water supply means. 
       FIG. 3  is a top view of one embodiment of the downhole drill bit of the present invention. 
       FIG. 4  is a top view of an alternative embodiment of the downhole drill bit of the present invention. 
       FIG. 5  shows a top view of a third embodiment of the downhole drill bit of the present invention. 
       FIG. 6  shows a cross sectional close-up view of a typical carbide stud of the present invention attached to the drill bit head. 
       FIG. 7  shows a cross-sectional close-up view of an alternative embodiment of the carbide stud of the present invention. 
       FIG. 8  shows a cross sectional side view of a carbide stud, covered by a copper plating or other suitable material. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   Referring to the drawings by numeral, and more specifically to  FIG. 1 , the preferred embodiment of the present invention is shown generally numbered as  10 . This drill bit comprises a generally cylindrically shaped cast iron body  12  for attaching to a down hole drilling apparatus of a conventional drill string. The body  12  is formed of cast iron or any suitable alloy, especially a high temperature alloy which will provide for greater strength and endurance. The bit body  12  has an upper grinding portion  14  and a lower shaft portion  16  which subsequently attaches to a drilling apparatus by conventional means. 
   Both the upper portion  14  and the lower portion  16  are separated by an annular groove  18 , have a plurality of longitudinal recesses  20  within the surface of the bit, created by the mold within which the bit  10  is formed. These recesses  20  allow for material and debris that has been drilled out by the upper grinding portion  14  of the drill bit  10  to be displaced and conveyed away from the specific area of drilling, preventing the clogging of the hole with recently created debris. The recesses  20  may further provide for leading edge  21  that shaves and shapes the walls of the hole as the drill bit  10  progresses through the rock. 
   The upper portion  14  has a tapered section  22  providing a transition between the cylindrical sides of the drill bit and the grinding face  24  of the upper portion  14 . Both the tapered section  22  and the grinding face  24  have a plurality of semi-spherical, carbide studs  30  embedded within the bit body  12 , projecting outward for abrasively grinding the rock or other material through which the drill bit  10  is being used. 
   Referring now to  FIG. 2 , a partial cross-sectional view of the upper grinding portion  14  of the drill bit  10  is shown. A plurality of steel tubes  26  having an inner channel  27  are positioned within the drill bit body  12 , terminating in an aperture through the grinding face  24  of the upper portion  14 . These channels  27  provide for the movement of cooling fluid to the face  24  of the drill bit  10 , preventing over-heating of the drill bit due to excessive friction. The steel tubes  26  are cast in the metal body  12  of the drill bit  10  simultaneously with the carbide studs  30  during the casting process. 
     FIGS. 3 ,  4  and  5 , show frontal views of the upper grinding portion of the drill bit  10 . The orientation of the carbide studs  30  and the steel cooling tubes  26  as shown can be arranged in a variety of patterns depending of the desired use or application. These illustrations in no way intend to exhaust the possible arrangements of these elements and are intended to be covered by the present invention. 
   In this particular invention as previously pointed out, the arrangement as well as the method of assembly and retention of the carbide studs  30  is especially important to the operation of the drill bit  10 . The drill bit  10 , designed to cut through rock or other hard material is subject to substantial vibration and stress. Therefore the carbide studs  30  need to be retained within the drill bit  10  in a manner which would prevent dislodgement from the various vibrations and stresses involved in the drilling process. 
   Specifically referring to  FIGS. 6 and 7 , cross sectional views are shown of the typical carbide studs of the present invention as partially embedded in the drill bit body  12 . Each typical carbide stud  30 , comprising a generally hour-glass shape, has a semispherical grinding surface  32 , a mounting end  33 , and a narrower body portion  34  extending within the cast bit body  12 . The narrower stud portion  34  provides for a retaining means to engage with the casting iron of the bit body  12 , maintaining the stud  30  partially within the bit body  12  so as to expose the grinding surface  32  once the casting iron has cooled. 
     FIGS. 6 and 7  illustrate different embodiments of the carbide studs  30  and do not exhaust the possibilities of other carbide stud designs which are intended to be covered within the scope of this invention. The studs  30  as mentioned previously, are cast into the drill bit body  12  during the casting process, whereas molten iron flows around the narrow portion  34  of each stud  30  and solidifies, holding the stud  30  in position 
   The casting process used in forming the drill bit is the lost-foam process. This process consists of first making a foam pattern, generally out of polystyrene, having the geometry of the desired finished metal part. After a short stabilization period, the pattern is dipped into a liquid solution containing a suspended refractory. The refractory material coats the exterior surface of the foam tooling  38  leaving a thin, heat-resistant, semi-permeable coating that is subsequently dried. When the drying is complete, the foam pattern  38  is suspended in a special container that is agitated while sand is poured in and around the foam pattern, filling all voids in the coated pattern. The sand provides mechanical support to the thin coating. 
   Molten metal, in this case, ductile iron, is then poured into the mold where the molten metal subsequently vaporizes the foam pattern  38 . The solidified metal replaces the volume of the foam and leaves a nearly exact replica of the pattern. It is subsequently heat treated, preferably by Austempering, to harden the newly cast part for application. 
   In this specific application of the lost foam casting process for creating the drill bit  10  of the present invention, the plurality of carbide studs  30  are partially inserted into the foam tooling  38  so as to maintain the semispherical grinding portion exposed to the refractory coat and the sand. The studs  30  are arranged in a predetermined orientation that maximizes efficiency of the drill prior to the molten metal being poured into the foam pattern. Referring now specifically to  FIG. 8 , an individual carbide stud  30  partially mounted within the drill bit body  12  is shown. The carbide studs are plated in a thin layer of copper  40  or other suitable material prior to being set in the foam tooling  38  to protect the carbide and prevent degradation of the stud  30  that would otherwise result from the subsequent Austempering or other heat treatment process. 
   The casting process provides for efficient integration of the carbide studs  30  into the bit body  12 , thereby preventing their incidental release during use of the drill bit  10  due to the annular recess  33  around each individual stud  30  engaging with the metal used to create the bit body  12 . During use of the drill bit  10 , the copper plating or other suitable material  40  rapidly wears off from the abrasion with the rock material, revealing the carbide grinding surfaces  32  which are significantly resistant to wear. 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Summary:
A down hole rock drill bit and method of manufacture of the same comprising a cast metal drill bit body having a plurality of hardened carbide studs partially cast in the drill bit body. The drill bit is cast by means of a foam pattern replicating the drill bit, typically made from polystyrene within which a plurality of carbide studs are partially inserted into the grinding surface of the foam drill bit model. The model is then subsequently supported within a vessel of sand and molten metal is poured over the foam, vaporizing it and taking the exact form of the foam pattern and permanently retaining the carbide studs within the metal drill bit.