US20070157763A1

US20070157763A1 - Drill bit with cutter pockets formed by plunge edm

Info

Publication number: US20070157763A1
Application number: US11/620,092
Authority: US
Inventors: Thomas W. Oldham
Original assignee: Smith International Inc
Current assignee: Smith International Inc
Priority date: 2006-01-11
Filing date: 2007-01-05
Publication date: 2007-07-12
Also published as: GB0700400D0; GB2438840A; CA2573575A1

Abstract

The disclosure provides an improved method for manufacturing a drill bit. The method includes applying a hardfacing material to the drill bit, forming a cutter pocket within the drill bit with plunge EDM, and inserting a cutting element into the cutter pocket.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority, pursuant to 35 U.S.C. 119(e), to U.S. Application Ser. No. 60/757,971 filed on Jan. 11, 2006, which is herein incorporated by reference in its entirety.

BACKGROUND OF INVENTION

1. Field of the Invention
The present disclosure generally relates to drill bits used in the oil and gas industry. Specifically, the disclosure relates to an improved method of manufacturing earth-boring bits for drilling earth formations.
2. Background Art
Drill bits are used in the oil and gas industry to drill earth formations in the exploration for gas and oil. FIG. 1 shows a drilling rig 107, which incorporates a drill bit 101. The drill bit 101 is connected to the bottom of a drill string 103 to drill a wellbore 105. The drill string 103 is controlled by surface equipment configured to rotate the drill string 103, apply downward force to the drill bit 101 to penetrate the earth formation (referred to as weight on bit (“WOB”)), and supply drilling fluid to the drill bit 101 by pumping the fluid through a bore of the drill string 103. Because a variety of earth formations are penetrated in the pursuit of oil and gas, several different types and configurations of drill bits are used. These drill bits are usually grouped into two different categories, shear bits and roller cone bits.
Shear bits are drill bits that cut the earth's formation by primarily scraping the earth formation when drilling. The shear bit is fixed to the drill string, which is rotated so, as the drill string rotates, the bit also rotates to cut into the earth formation. The shear bit has a plurality of cutting elements arranged on the body of the drill bit such that the cutting elements scrape and shear the earth formation from the bottom and sides of the wellbore as the drill bit is rotated. Shear bits do not have any moving parts upon the bit itself, only the bit body moves from the rotation of the drill string.
Roller cone bits, in contrast, are drill bits having cones rotatably mounted onto journals. The roller cone bit typically has a bit body with at least one journal, in which a cone is mounted thereon and allowed to rotate. As the bit body is rotated by the drill string, the cones rotatably contact the earth's formation. A plurality of cutting elements are arranged on the roller cones to crush and scrape the earth's formation as the bit is rotated. Even though both types of drill bits are useful for drilling into earth formations, only shear bits will be discussed from this point forward.
Shear bits can be further grouped into two categories: steel body bits and matrix body bits. Matrix body bits are constructed using a powder metallurgy manufacturing process. A head mold of the desired bit head shape is constructed and filled with matrix powder and a binder. Next, the mold is placed in a furnace to allow the binder to melt and infiltrate the matrix powder. As the binder infiltrates the matrix powder, a solid metal casting is formed. The two general types of matrix body bits consist of bits that incorporate polycrystalline diamond compact (“PDC”) cutting elements, and bits that incorporate diamonds impregnated in the matrix powder to shear the formation.
In contrast, steel body bits typically have their heads machined from solid pieces of steel. Steel body bits are usually machined with the entire outer geometry of the drill bit formed, including the bit body, the bit blades, and even the cutter pockets for cutting elements of the drill bit. Upon completion of the machining, the remainder of the steel body bit is assembled with a bit shank. Usually shear bits use PDC cutting elements or some other type of wear resistant material disposed within the cutter pockets to shear the earth formation. The focus of the remaining discussion will be directed toward steel body bits.
FIG. 2 shows an example of a prior art steel body bit having a plurality of cutting elements. The drill bit 200 includes a bit body 201 and a plurality of blades 203 formed on the bit body 201. The blades 203 are separated by channels or gaps 211 that enable drilling fluid to flow between, both cleaning and cooling, the blades 203 and cutting elements 205. Cutting elements 205 are held in the blades 203 at predetermined angular orientations and radial locations with a desired back rake angle against a formation to be drilled. Nozzles 207 are typically formed in the drill bit body 201 and positioned in the gaps 211 so fluid can be pumped to discharge drilling fluid in selected directions and at selected rates of flow between the cutting blades 203 for lubricating and cooling the drill bit 200, the blades 203, and the cutting elements 205. The drilling fluid also cleans and removes the cuttings as the drill bit rotates and penetrates the earth formation. The drill bit body 201 includes a plurality of cutter pockets 209 that are sized and shaped to receive a corresponding plurality of cutting elements 205. The drill bit body 201 is machined with the cutter pockets 209 so the cutting elements 205 may be inserted and secured in the pockets 209 using methods such as brazing, adhesive, or interference fit.
When machining the steel body bit in the prior art, the outer geometry is formed with the bit body, the bit blades, the cutter pockets, and the gaps. Typically, a hardfacing material is then manually applied, such as by arc or gas welding, to the exterior surface of the steel body bit to protect the bit against erosion and abrasion. The hardfacing material may be applied to the entire outer geometry of the steel body bit, or may only be applied to the parts of the drill bit that contact the earth formation during drilling or that are impinged by the drilling fluid. The hardfacing material is typically applied prior to the cutting elements being inserted into the cutter pockets. Displacements or coverings may be used to fill the cutter pockets as to protect the cutter pockets during hardfacing. The hardfacing material usually includes one or more metal carbides, which bond to the steel body by a metal alloy (“binder alloy”). In effect, the carbide particles are suspended in a matrix of metal, forming a layer on the surface of the drill bit. The carbide particles give the hardfacing material hardness and wear resistance, while the matrix metal provides strength and fracture toughness to the hardfacing material.
When the hardfacing the machined steel body bit, the hardfacing material layer is typically applied with a small diametrical clearance around the cutter pockets. The small clearance is necessary to allow the cutting elements to be later inserted and secured within the cutter pockets. The hardfacing application process, though, is not very precise and the diametrical clearance around the cutter pockets may result in a significant gap between the cutting elements and the hardfacing material. The gap is then large enough to allow erosion of the braze material when securing the cutting element within the cutter pockets and eventually allow erosion of the steel beneath the hardfacing.
Further, close-fitting cutting elements usually only have thin sections of steel therebetween. Hardfacing these thin sections of steel is difficult because the sections may not have much surface area for applying the hardfacing material. Hardfacing large, simple geometry areas allows for the hardfacing material to be uniformly applied with good quality bonding to the bit body. The thin sections of steel have a more complicated geometry, which is more difficult to apply a uniform hardfacing layer with good quality bonding.
Furthermore, if displacements are used to protect the cutter pockets when applying the hardfacing material, the displacements may need to be broken out of the cutter pockets to then allow the cutting elements to be inserted within the pockets. When removing and breaking out the displacements, the hardfacing material may actually chip and crack. Such chipping and cracking would lead to further damage and reduced bit life when the steel body bit is used for drilling earth formations.
Thus, it would be desirable to obtain a better method for manufacturing drill bits to avoid such problems with current methods.

SUMMARY OF INVENTION

In one aspect, embodiments of the present disclosure relate to a method of manufacturing a drill bit that includes applying a hardfacing to the drill bit, forming a cutter pocket on the at least one blade with plunge EDM, and inserting a cutting element into the cutter pocket.
In another aspect, embodiments of the present disclosure relate to a method of manufacturing a drill bit that includes forming a bit body having at least one blade thereon, applying a hardfacing to at least a portion of the bit body, forming a cutter pocket on the at least one blade with plunge EDM, and inserting a cutting element into the cutter pocket
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a prior art drilling rig.

FIG. 2 shows a prior art steel body bit.

FIG. 3 shows a prior art plunge electrical discharge machining assembly.

FIG. 4 shows a flow chart illustrating a method of manufacturing a drill bit in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

In one aspect, the present disclosure provides an improved method for manufacturing steel body bits. Specifically, the embodiments of the present disclosure incorporate plunge electrical discharge machining (“EDM”) to form cutter pockets within a steel body bit.
Plunge EDM, sometimes referred to as sinker EDM or ram EDM, is a technique used to remove material from a workpiece, in which the workpiece is made from an electrically conductive material, such as metal. Plunge EDM removes material through erosive action resulting from electrical discharges. The electrical discharges occur when an electrical voltage is applied between the workpiece and a cutting electrode, in which the two are submerged in a dielectric fluid. The dielectric fluid is usually oil or de-ionized water located in a work tank. The cutting electrode, usually formed from graphite, is guided along a desired path very close to the workpiece, but not touching the workpiece. When the cutting electrode and the workpiece are in close proximity of each other along the desired path, material is melted and vaporized from both the workpiece and the electrode by the electrical discharges occurring. This leaves a small amount of a resultant material on the surfaces of the cutting electrode and the workpiece. The resultant material may be removed by continuously washing the dialectic fluid across the cutting electrode and the workpiece. The final result from each electrical discharge is a small crater on both the cutting electrode and the workpiece. Plunge EDM uses very rapidly occurring electrical discharges to remove substantial portions of material from the workpiece.
FIG. 3 shows an illustration of a basic plunge EDM assembly, which includes an electrode 301 and a workpiece 303 submerged in dielectric fluid 305. The electrode 301 is a blank-shape of a cavity 309 to be formed in the workpiece 303. When the electrode 301 is in close proximity of the workpiece 303, electrical discharges 307 occur, between the electrode 301 and the workpiece 303. The electrical discharges 307 remove material from the workpiece 303 to form the cavity 309. The cavity 309 formed is a negative shape of the electrode 301.
Generally, several electrodes may be used in conjunction with one another to remove material from a workpiece during plunge EDM to improve the process. A first electrode may be used in a “rough pass” to form the general shape of the cavity. Then, further electrodes may be used in subsequent passes to further define the cavity. The subsequent passes may provide a better finish upon the workpiece and/or may improve tolerances of the shaped surfaces formed in the workpiece by removing additional material.
FIG. 4 shows a flow chart illustrating a method of manufacturing a drill bit in accordance with an embodiment of the present disclosure. As a first step 410, a drill bit is machined from a solid piece of steel. The drill bit may be machined to include an outer geometry of the drill bit, in addition to inner hydraulic passageways of the drill bit. When machining the outer geometry of the drill bit, the bit blades may be formed, but the cutter pockets are not yet formed. In one embodiment, substantially all of the outer geometry, excluding the cutter pockets, is formed as a first step 410. After machining the drill bit, hardfacing material is applied 420 to the drill bit. The hardfacing material may be applied to the entire outer geometry of the drill bit, or may be only applied to parts of the drill bit which may contact the earth formation when drilling.
After applying the hardfacing material to the drill bit, cutter pockets are formed 430 at selected locations on the drill bit. The cutter pockets are formed 430 in the drill bit using plunge EDM. In a plunge EDM process, an electrode in the presence of a dielectric fluid and an electric voltage is used to form a cutter pocket in the drill bit. Plunge EDM may be used to form cutter pockets in a drill bit after hardfacing because plunge EDM only requires the drill bit be electrically conductive. The electrode may be graphite and may be machined in a desired shape of the cutter pocket. Additionally, the plunge EDM process may be controlled by an automated system, such as a computer numerical control (“CNC”) machine. Further, multiple passes may be used with multiple electrodes to improve the plunge EDM process when forming the cutter pockets. After the cutter pockets have been formed, cutting elements may be inserted 440 into the cutter pockets of the drill bit. Methods such as brazing, adhesion, or interference fit may be used to secure the cutting elements within the cutter pockets.
Alternatively, in another method of manufacturing a drill bit in accordance with an embodiment of the present disclosure, as a first step 410, at least a portion of a drill bit may be cast or forged. For example, the drill bit may be cast in a mold with steel such that the mold forms the outer geometry, including the bit blades, of the drill bit. When forming the outer geometry of the drill bit though, the cutter pockets are not yet formed. The cutter pockets will be formed 430 with plunge EDM following applying hardfacing material 420 to the drill bit. Those having ordinary skill in the art will appreciate that combinations of these or other methods of manufacturing a drill bit may be used without departing from the scope of the present invention.
Those of ordinary skill in the art will appreciate that a number of techniques may be used to apply the hardfacing material upon a drill bit. For example, hardfacing material may be applied manually to the drill bit by arc welding or gas welding. In such instances, a skilled worker may be required to apply the hardfacing material upon the drill bit.
In another technique, an automated system may be used to apply the hardfacing material upon a drill bit. For example, a CNC machine may use a laser to apply the hardfacing material upon the drill bit. The outer geometry of the drill bit in the present disclosure may be less complex as compared to prior art drill bits because cutter pockets are not yet formed during hardfacing. The use of an automated system could then be more feasible and enabled with the present disclosure because not as many inputs may be necessary for the automated system when used to apply hardfacing material upon the less complex outer geometry drill bit. Though certain techniques may be more advantageous than others for applying the hardfacing material upon the drill bit, the specific technique used to deposit the sealing metal is not a limitation on the scope of the present invention. Also, those having ordinary skill in the art will appreciate that combinations of these or other hardfacing techniques may be used without departing from the scope of the present invention.
Embodiments of the present disclosure may have one or more of the following advantages. As mentioned above, when applying hardfacing material to a drill bit in the present disclosure, the drill bit will not yet have cutter pockets formed, allowing the drill bit to have a less complex outer geometry during the hardfacing process. A less complex outer geometry may allow for a more consistent hardfacing layer be applied to the drill bit. For example, a CNC machine may be used to apply hardfacing material to the surface of the drill bit, allowing the depth of the hardfacing material be controlled more precisely. If cutter pockets were present, the machine may have to work around the cutter pockets, which may add more factors and inputs to increase the difficulty of hardfacing the drill bit. Similarly, a less complex outer geometry of the drill bit may allow for a more time efficient hardfacing layer be applied to the drill bit. The hardfacing process may not have to work around the cutter pockets, which may decrease the time necessary to apply hardfacing material to the drill bit.
Additionally, hardfacing of thin sections of steel between close-fitting cutting elements is improved. Because the cutter pockets are formed using plunge EDM after the hardfacing process, this allows for a more even, uniform depth of hardfacing material be applied to the drill bit. When the cutter pockets are then formed into the drill bit, the thin sections of steel between the close-fitting cutting elements on the drill bit will have the more uniform hardfacing material applied. Otherwise, if the hardfacing material was applied after the cutter pockets were formed, hardfacing the thin sections of steel between the close-fitting cutters may be more difficult because the sections may not have as much area to apply the hardfacing material upon.
Further, the need for displacements to protect the cutter pockets during hardfacing may be eliminated. Because the cutter pockets are formed after hardfacing of the drill bit, no protection may be needed for the cutter pockets when hardfacing. Therefore, this may avoid chipping and cracking the hardfacing material of the drill bit when the displacements are needed to be removed and broken out from the cutter pockets.
Furthermore, the use of plunge EDM may improve the tolerances of the cutter pockets formed. For example, plunge EDM may be more precise for removing material and forming cutter pockets than conventional methods, such as machining. This precision is particularly enhanced with the use of multiple passes of electrodes during the plunge EDM process. This improved precision may allow the cutter pockets to have a more secure fit with cutting elements.
In addition, heat is used when applying the hardfacing material upon the drill bit. The use of heat may deform and warp portions of the drill bit, including the cutter pockets on the drill bit. Plunge EDM avoids using heat after the cutter pockets are formed, and therefore allows the shape of the cutter pockets to be better preserved. This also improves the ability of the cutter pockets to have a secure fit with cutting elements.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

1. A method of manufacturing a drill bit, the method comprising:

applying a hardfacing to the drill bit having at least one blade;

forming a cutter pocket on the at least one blade with plunge EDM; and

inserting a cutting element into the cutter pocket.

2. The method of claim 1, further comprising machining the drill bit from steel.

3. The method of claim 1, wherein the hardfacing is applied to the drill bit by an automated system.

4. The method of claim 3, wherein the automated system is a CNC machine.

5. The method of claim 1, wherein the plunge EDM is controlled by an automated system.

6. The method of claim 5, wherein the automated system is a CNC machine.

7. The method of claim 1, wherein the cutting element is comprised of PDC.

8. The method of claim 1, wherein forming the cutter pocket with plunge EDM comprises at least one plunge EDM pass.

9. The method of claim 1, wherein forming the cutter pocket with plunge EDM comprises a plurality of plunge EDM passes.

10. The method of claim 1, wherein the plunge EDM comprises a plurality of electrodes.

11. The method of claim 1, wherein the forming the cutter pocket occurs after the applying the hardfacing.

12. A method of manufacturing a drill bit, the method comprising:

forming a bit body having at least one blade thereon;

applying a hardfacing to at least a portion of the bit body;

forming a cutter pocket on the at least one blade with plunge EDM; and

inserting a cutting element into the cutter pocket.

13. The method of claim 12, wherein forming the bit body comprises at least one of machining, casting, and forging.

14. The method of claim 12, wherein the hardfacing is applied to the drill bit by an automated system.

15. The method of claim 14, wherein the automated system is a CNC machine.

16. The method of claim 13, wherein the plunge EDM is controlled by an automated system.

17. The method of claim 16, wherein the automated system is a CNC machine.

18. A drill bit manufactured with the method of claim 1.