GB2283696A - Matrix diamond drag bit with pcd cylindrical cutters - Google Patents

Abstract

A drag bit mold fabricated from high temperature resisting material is machined to accept cylindrically shaped polycrystalline diamond (PCD) cutters having tungsten carbide bodies. Each of the multiple cutter pockets in the mold is formed by two ball mill cuts. The first 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 42 creates a surrounding pocket 46 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. <IMAGE>

Description

MATRIX DIAMOND DRAG BIT WITH PCD CYLINDRICAL CUTTERS This invention relates to diamond drag bits for drilling earthen formations having polycrystalline diamond inserts imbedded in the cutting face of the bit.

More particularly, this invention relates to matrix type diamond drag bits fabricated by a powder metallurgy process wherein cutter pockets and relief pockets are formed in a female mold to accept and support cylindrically shaped polycrystalline diamond inserts subsequently brazed in place in the pre-formed pockets.

U.S. Patent No. 5,056,382 entitled MATRIX DIAMOND DRAG BIT WITH PCD CYLINDRICAL CUTTERS provides a milled relief pocket adjacent the cutter pocket that is vectored at a different angle than the angle of the cutters oriented in the face of the matrix bit. The relief pocket provides maximum compression support for the base of the PCD cylindrical cutter and increased cylindrical wall support while relieving the cutter back rake surface.

While the foregoing patent is an important advance in the state of the art it was determined in some drilling circumstances that the wide raised support platform surrounding the diamond cylindrical cutter limited insert penetration, i.e. the insert support platform inhibited penetration of the cutter in the rock formation.

It is desirable to provide back and side support for cylindrical type diamond inserts embedded in a matrix type drag bit yet allow the full depth of penetration of each insert as it works in the borehole. Preferably, there is back rake clearance for each cylindrically shaped PCD insert brazed in the cutting face of the matrix drag bit.

There is, therefore, provided a process of forming a matrix type diamond drag bit cutter head having a multiplicity of cylindrically shaped polycrystalline diamond inserts strategically positioned and metallurgically secured to a drag bit face. A female mold of heat resistant material, such as graphite is milled with a rotary ball mill forming a multiplicity of first cylindrically shaped insert channels or pockets the diameter of which is about the same diameter as each of the cylindrical cutters. The pockets are formed in a direction of rotation of the drag bit and at an angle to an earthen formation to be drilled such that a negative rake angle is established with respect to a cutting face of the cylindrically shaped polycrystalline diamond inserts.

A second channel is milled in the mold substantially aligned and superimposed over the first channel, at the same or a lesser angle than the first channel. The second ball end mill used for this channel is somewhat larger in diameter than the mill used to form the insert pocket and is positioned substantially above the axis of the first ball end mill such that it forms a shallow and narrow arcuate groove around the insert channel. The depth of the second cylindrically shaped channel or pocket is much less than the depth of the first cylindrically shaped channel. This provides a small arcuate fillet of matrix material around each of the subsequently secured inserts for ensuring the integrity of each insert without forming a penetration limiting platform around each insert as is taught in the prior art.

The process of forming a matrix drag bit body is as follows: A heat resistant cylindrically shaped stud is placed into each of the first cylindrically shaped insert pockets. The female mold is then filled with a matrix material in powder form. The mold and matrix material is then heated in a furnace for infiltrating a binder into the matrix material, thereby forming the diamond insert retaining cutter head.

The heat resistant studs are removed from the first cylindrically shaped insert pockets. The cylindrically shaped polycrystalline diamond inserts are then metallurgically bonded into each of the first insert pockets. The inserts have additional back and side support provided by the matrix filled second channel surrounding each insert.

An advantage then of the present invention over the prior art is the ability to provide side and back support for a cylindrical PCD diamond insert while assuring maximum penetration of each insert as it works in a borehole. Each insert is adequately supported by the fillet surrounding the insert to withstand compressive and shear forces under downhole drilling conditions.

Moreover, the angled double pocket mold design provides each insert with back rake clearance as well as superior support, thereby minimizing heat build up and assuring insert integrity as the diamond matrix drag bit works in a borehole.

Embodiments of the invention are described below with reference to the accompanying drawings, in which: FIGURE 1 is a perspective view of a matrix type diamond drag bit; FIGURE 2 is a semi-schematic partial cross section of a female mold illustrating a milling cutter pass forming a first pocket for a cylindrically shaped diamond insert in the female mold; FIGURE 3 is a semi-schematic partial cross section of a female mold illustrating a second milling cutter pass at a different angle than the first milling cutter pass forming a second pocket surrounding the first insert pocket in the female mold; FIGURE 4 is a semi-schematic partial cross section of a female mold with a heat resistant insert blank positioned in the first insert pocket; FIGURE 5 taken through 5-5 of Figure 4 illustrates the face of the insert blank and the surrounding second pocket;; FIGURE 6, a prior art illustration, is a partially broken away perspective view of a polycrystalline diamond insert brazed into a first insert pocket, the raised surrounding matrix material filling in a second, superimposed pocket to back up and strengthen an insert secured within the drag bit cutter head; and FIGURE 7, an illustration of the present invention, is a partially broken away perspective view of one of the polycrystalline diamond inserts brazed into the first insert pocket, the raised surrounding matrix material filling in the second, superimposed pocket to back up and strengthen the multiple inserts secured within the drag bit cutter head.

FIGURE 1 is a perspective view of a matrix type diamond drag bit generally designated as 10. Drag bit consists of a drag bit body 12 having oppositely opposed tool grooves 13 formed therein to facilitate removal of the bit from a drill string (not shown). At the upper end of body 12 is a threaded pin end 14. At the opposite end is the cutter head generally designated as 18. The cutter head is comprised of a matrix type body or head 15 that is cast in a female mold 40 (see Figs. 2, 3, 4 and 5). The mold generally is fabricated from, for example, a graphite material that is easily machinable and withstands extremely high heat during the casting process.

A multiplicity of cylindrical type diamond inserts generally designated as 26 are contained within ribs 16 which project substantially longitudinally along the head 15. Each insert, for example, has a body 28 fabricated from, for example, tungsten carbide, a base end 29 and a cutting end 27. The cutting end 27 comprises, for example, a polycrystalline diamond layer sintered to the tungsten carbide body. Each of the cavities surrounding the inserts is formed in the female mold 40 and is an important aspect of the present invention.

One or more nozzles 11 are formed by the matrix head 15. Drilling "mud" or fluid is directed down through the pin end and out through the nozzles during operation of the bit in a borehole. An inner cavity (not shown) is formed within the bit body 12 and is open to both the pin end 14 and the nozzles 11.

Each of the protruding ribs extending from the matrix head has a gage bearing surface 20 that, for example, may be embedded with natural diamonds to help maintain the gage or diameter of the borehole as the bit is rotated in an earthen formation.

Turning now to FIGURE 2 the partially cutaway illustration shows the female mold 40 with a groove or pocket 42 milled within the bottom 41 of the female mold 40. A ball mill 43 substantially the same diameter as the insert 26, is passed into the graphite mold bottom at an angle 44, thereby forming the insert pocket 42. The angle may be between 15 degrees and 25 degrees. The preferred angle is 20 degrees. The angle determines the degree of negative rake angle of the cutting face of each of the inserts with respect to a borehole bottom. The ball mill cutter 43 passes down a line at the angle 44 to the face of the mold a distance sufficient to form a pocket support for an insert stud body blank 49 (Fig. 4).

Referring now to FIGURE 3, the graphite mold bottom 40 is subsequently subjected to a second ball mill pass. The ball mill 47 is superimposed over the cavity 42 formed by the first pass of the smaller ball mill 43. The ball mill 47 is, for example, somewhat larger in diameter and is directed along a different or shallower angle 48 than the angle 44 of the insert pocket cavity formed by first ball mill 43. The second ball mill may be from 25% to 60% greater in diameter than first ball mill with the preferred size being 50% greater.

The prior art shows the second ball end mill to be about 180% greater than the first mill which produces a very wide cutter penetration limiting shoulder (154 in Fig. 6) surrounding each insert 126 (Fig. 6). This formation interference drastically reduces drilling rates in some formations. The angle 48 may be between 3 degrees and 12 degrees. The preferred angle is 5 degrees. The non-parallel angulation between the insert pocket 42 and the surrounding pocket 46 assures adequate insert backup support while providing insert back rake clearance 51 (see Fig. 4). The second end mill 47 is passed over the insert pocket forming a second narrow shallower groove 46 around the cavity 42.

The second end mill pass of the second ball mill forming the insert securing fillet 56 is only slightly larger than the first end mill pass of the first ball end mill forming the insert pocket to minimize the size of the fillet 56 subsequently formed, thus assuring that the fillet will not interfere with the depth of penetration of each of the PCD cutters as the drag bit works in the borehole.

Again, the angles 44 and 48 differ to provide both clearance for the right angle cutting face of the insert and adequate support for the base and sidewalls of body of the insert.

FIGURE 4 shows the completed cavities (insert pocket 42 and the insert support pocket 46). A heat resisting substitute insert blank 49 is then secured within the complementary insert pocket 42. The blank is preferably glued within the pocket.

There are a multiplicity of insert pockets and their attendant insert support cavities in the matrix ribs protruding from the matrix body.

The heat resisting blank is glued into position in its insert pocket prior to pouring of the matrix powder material into the female mold, thus filling all of the voids surrounding the stud blank prior to firing of the powdered matrix material within a furnace for a predetermined length of time.

The preferred matrix material is a powder metal such as crushed tungsten carbide which may be either W2C or WC. The female mold 40 is typically formed of graphite but may be fabricated from other suitable refractory material. The mold is vibrated to compact the tungsten carbide material around each of the insert blanks and to fill all the voids with the powdered material.

A braze material comprised of a combination selected from the group consisting of copper, nickel, manganese and zinc or tin is melted and subsequently is infiltrated through the tungsten carbide mass to form the matrix drag bit cutter head 14. This process is well known in the prior art.

FIGURE 5 is a view looking directly into the face of the substitute insert or blank 49 showing the sidewall cavities 46 surrounding the insert. The depth of the cavity 46 determines the amount of side support for each of the inserts. This drawing also illustrates the narrow groove 46 around the insert that will subsequently be filled with matrix material to provide side support for the insert, but will not act as a penetration limiter to inhibit drilling rates.

FIGURE 6, a prior art illustration, shows one of the polycrystalline diamond inserts 126 brazed into pocket 142 formed into the completed cutter head 115 after the matrix material 122 is fired. Shown is the massive matrix shoulder 154 that is formed around the diamond cutter insert which provides more than adequate shear and compressive strength for the cutter, but acts as a cutter penetration inhibitor, thus drastically slowing the drilling rate when drilling many types of rock formations.

Finally, with respect to FIGURE 7, a view is shown of one of the polycrystalline inserts brazed into the pocket in the completed cutter head after the matrix material is fired.

After the firing of the mold in a furnace following the processes just described, the tungsten carbide cutter head is removed from the female mold. Each of the dummy inserts 49 is then removed from its cavity leaving a insert shaped cavity for insertion of a cylindrically shaped polycrystalline diamond cutter into the pocket formed by the dummy insert 49. The PCD inserts are then brazed into position at joint 32, thus firmly securing the body of each of the inserts in the pockets 42 and 46 formed in the female mold through the use of the aforementioned process of two non-parallel mill passes.

The braze material used to braze the insert bodies into the respective cavities is essentially a combination of copper, silver, zinc and cadmium. The temperature of the brazing process, of course, is such that it will not destroy the polycrystalline diamond faces of the diamond insert blanks during the brazing process.

The result is a raised fillet 56 in the cutter head 14 that comes up the sidewall of the tungsten carbide body and almost completely surrounds the end of the tungsten carbide body of the diamond insert. The raised fillet 56 thus provides very strong resistance to compressive forces while firmly securing the sides of the insert body during operation of the drag bit in a borehole. As can be seen, each of the multiplicity of inserts is angled with respect to a borehole bottom such that a negative rake angle is established. This negative rake angle of course is established by the first mill pass of ball mill 43 in the female mold.

It will be apparent that any angle may be used, whether it be a negative rake angle, zero rake angle or positive rake angle without departing from the scope of this invention.

Fluid passage grooves 17 are formed between the ribs 15 and cutter head 14 to permit passage of detritus up through the grooves in the bit to the platform of the drill rig.

Typically, after the tungsten carbide cutter head 14 is formed in the female mold, it then is welded to a steel body 12 completing the assembly of the rock bit 10 as shown in FIGURE 1. The body is easily welded to the head after each of the tungsten carbide polycrystalline faced diamond inserts are brazed into their respective insert cavities thus completing the construction of the matrix type drag bit.

It will of course be realized that various modifications can be made in the design and operation of the present invention without departing from the spirit thereof. Thus, while the principal preferred construction and mode of operation of the invention have been explained in what is now considered to represent its best embodiments, it should be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically illustrated and described.

Claims (13)

1. A process of forming a matrix type diamond drag bit cutter head having a multiplicity of cylindrically 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 the mold, the channels each being formed in a direction of rotation of the drag bit and at an angle such that a negative rake angle is established with respect to a cutting face of the cylindrically shaped polycrystalline diamond insert;; milling a second non-parallel channel substantially axially aligned with and superimposed over the first channel but at a shallower angle and at a depth less than the depth of the first cylindrically shaped channel, the second non-parallel channel being milled by a milling cutter larger than the milling cutter used to form the first cylindrically shaped insert channels, the second, larger channel providing a small arcuate pocket surrounding the first channel; securing a heat resistant cylindrically shaped stud in each of the first cylindrically shaped insert channels; inserting a matrix material in powder form in the female mold; heating the matrix material in the mold in a furnace thereby forming the cutter head and providing a matrix filled fillet type support for a cylindrically shaped insert without insert penetration limitations;; removing the heat resistant studs from the first cylindrically shaped insert channels; and metallurgically bonding cylindrically shaped polycrystalline diamond inserts into each of the first insert channels, the inserts having additional support provided by the small matrix filled arcuate second channel at a different angle and a lesser depth surrounding the insert.

2. The process as set forth in Claim 1 wherein the angle of the first channel is between 15 degrees and 25 degrees.

3. The process as set forth in Claim 2 wherein the angle of the first channel is 20 degrees.

4. The process as set forth in any one of the preceding claims wherein the angle of the second channel superimposed over the first insert channel is between 3 degrees and 12 degrees.

5. The process as set forth in any one of the preceding claims wherein the angle of the second channel is 5 degrees.

6. The process as set forth in any one of the preceding claims wherein the curvature of the second channel is 25 to 60 percent greater in diameter than the curvature of the first channel.

7. The process as set forth in any one of the preceding claims wherein the heat resistant cylindrically shaped insert is secured into the first channel by gluing.

8. The process as set forth in any one of the preceding claims wherein the polycrystalline diamond inserts are metallurgically bonded into the insert channel by brazing.

9. The process as set forth in any one of the preceding claims wherein the first and second non-parallel channels are each formed by a ball end milling cutter, the ball end milling cutter forming the first cylindrically shaped channel being smaller than the ball end milling cutter forming the second non-parallel channel.

10. The process as set forth in any one of the preceding claims wherein the second ball end milling cutter is 50 percent greater in diameter than the first ball end milling cutter.

11. The process as set forth in any one of the preceding claims wherein the angle of the first channel is between 15 degrees and 25 degrees, the angle of the second channel superimposed over the first insert channel is between 3 degrees and 12 degrees, and the first and second non-parallel channels are each formed by a ball end milling cutter, the ball end milling cutter forming the first cylindrically shaped channel being 25 to 60 percent greater in diameter than the ball end milling cutter forming the second non-parallel channel.

12. A process for forming a matrix type diamond drag bit cutter head substantially as described herein.

13. A matrix type diamond drag bit when made by a process according to any one of Claims 1-12.