Matrix diamond drag bit with PCD cylindrical cutters

Abstract

A drag bit mold fabricated from high temperature resisting material is machined to accept cylindrically shaped polycrystalline diamond cutters (PCD) having tungsten carbide bodies. Each of the multiple PCD matrix pockets in the mold is formed by two independent non-parallel end mill passes. The first end mill cut defines the PCD cutter position in the cutting face of the matrix diamond drag bit. The second end mill cut superimposed over the first end mill pocket creates a surrounding pocket which fills with powder metallurgy matrix material to provide support for the cylindrical cutter. The second end mill is only slightly larger than the first end mill to minimize the size of the insert securing fillet subsequently formed thus assuring that the fillet will not interfere with the depth of penetration of each of the PCD cutters.

What is claimed is: 
     
       1. A process of forming a matrix type diamond drag bit cutter head having a multiplicity of cylindricall.y shaped polycrystalline diamond inserts strategically positioned and metallurgically secured to a drag bit face comprising the steps of: forming a female mold of heat resisting material,   milling a multiplicity of first cylindrically shaped insert channels in said mold, said channels being formed in a direction of rotation of said drag bit and at an angle to an earthen formation such that a negative rake angle is established with respect to a cutting face of said cylindrically shaped polycrystalline diamond insert,   milling a second non-parallel channel substantially axially aligned with and superimposed over said first channel but at a shallower angle and at a depth less than the depth of said first cylindrically shaped channel, said second non-parallel channel being milled by a milling cutter slightly larger than the milling cutter used to form said first cylindrically shaped insert channels, said second, slightly larger channel provides a relatively small pocket surrounding said first channel thus providing a matrix filled fillet type support for said cylindrically shaped insert, said fillet support secures said insert without insert penetration limitations,   securing a heat resistant cylindrically shaped stud in each of said first cylindrically shaped insert channels,   inserting said matrix material in powder form in said female mold,   heating said matrix material in said mold in a furnace thereby forming said cutter head,   removing said heat resistant studs from said first cylindrically shaped insert channels; and   bonding metallurgically, said cylindrically shaped polycrystalline diamond inserts into each of said first insert channels, said inserts having additional support provided by the relatively small matrix filled second channel at a different angle and a lesser depth surrounding said insert.   
     
     
       2. The process as set forth in claim 1 wherein the angle of said first channel is between 25 degrees and 15 degrees. 
     
     
       3. The process as set forth in claim 2 wherein the angle is 20 degrees. 
     
     
       4. The process as set forth in claim 1 wherein the angle of said second channel superimposed over said first insert channel is between 12 degrees and 3 degrees. 
     
     
       5. The process as set forth in claim 4 wherein the angle is 5 degrees. 
     
     
       6. The process as set forth in claim 1 wherein said heat resistant cylindrically shaped insert is secured into said first channel by gluing. 
     
     
       7. The process as set forth in claim 1 wherein said polycrystalline diamond inserts are metallurgically bonded into said insert channel by brazing. 
     
     
       8. The process as set forth in claim 1 wherein said first and second non-parallel channels are formed by a ball end mill cutter, the ball end mill forming said first cylindrically shaped channels is slightly smaller than said ball end mill forming said second non-parallel channel. 
     
     
       9. The process as set forth in claim 8 wherein said second ball end mill is 25 to 60 percent greater in diameter than said first ball end mill. 
     
     
       10. The process as set forth in claim 9 wherein said second ball end mill is 50 percent greater in diameter than said first ball end mill.