Title:
ENHANCED NON-PLANAR DRILL INSERT
Kind Code:
A1


Abstract:
A cutting element, or insert, is provided for use with drills used in the drilling and boring of subterranean formations. This new insert has improved wear characteristics while maximizing the manufacturability and cost effectiveness of the insert. This invention accomplishes these objectives by employing a superabrasive diamond layer of increased depth and by making use of diamond layer surface shape that is generally convex.



Inventors:
Jensen, Kenneth M. (OREM, UT, US)
Application Number:
08/980471
Publication Date:
06/28/2001
Filing Date:
11/28/1997
Assignee:
JENSEN KENNETH M.
Primary Class:
Other Classes:
175/420.1
International Classes:
E21B10/56; E21B10/567; E21B10/573; (IPC1-7): E21B10/36
View Patent Images:
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Primary Examiner:
KRECK, JANINE MUIR
Attorney, Agent or Firm:
LLOYD W SADLER (SALT LAKE CITY, UT, US)
Claims:

I claim:



1. A cutting element insert for use on a bit for drilling subterranean formations, comprising: (A) a substrate having a top surface; and (B) a layer of superabrasive material, having an interface surface, bonded to said top surface of said substrate and an external contact surface, wherein said layer of superabrasive material completely covers said top surface of said substrate and wherein said external contact surface is of a generally hemispherical shape.

2. A cutting element insert as recited in claim 1, wherein said substrate is a carbide selected from the group consisting of tungsten carbide, niobium carbide, zirconium carbide, hafnium carbide, vanadium carbide, tantalum carbide, and titanium carbide.

3. A cutting element insert as recited in claim 1, wherein said layer of superabrasive material is composed of polycrystalline diamond.

4. A cutting element insert as recited in claim 1, wherein said layer of superabrasive material further comprises: a cutting surface and a center axis.

5. A cutting element insert as recited in claim 1, wherein said layer of superabrasive material is between 0.040 inches and 2.0 inches in thickness.

6. A cutting element insert as recited in claim 1, wherein said substrate is composed of cemented tungsten carbide.

7. A cutting element insert as recited in claim 1, wherein said layer of superabrasive material is bonded to said substrate by ultra-high pressure sintering.

8. A cutting element insert as recited in claim 1, wherein said layer of superabrasive material is bonded to said substrate by pressing.

9. A cutting element insert as recited in claim 1, wherein said layer of superabrasive material is bonded to said substrate by brazing.

10. A cutting element insert as recited in claim 1, wherein said layer of superabrasive material is composed of cubic boron nitride.

11. A cutting element insert for use on a bit for drilling subterranean formations, comprising: (A) a substrate having a top surface; and (B) a layer of superabrasive material, having an interface surface, bonded to said top surface of said substrate and an external contact surface, wherein said layer of superabrasive material completely covers said top surface of said substrate and wherein said external contact surface is of a generally conical shape.

12. A cutting element insert as recited in claim 11, wherein said substrate is a carbide selected from the group consisting of tungsten carbide, niobium carbide, zirconium carbide, hafnium carbide, vanadium carbide, tantalum carbide, and titanium carbide.

13. A cutting element insert as recited in claim 11, wherein said layer of superabrasive material is composed of polycrystalline diamond.

14. A cutting element insert as recited in claim 11, wherein said layer of superabrsive material further comprises: a cutting surface and a center axis.

15. A cutting element insert as recited in claim 11, wherein said layer of superabrasive material is between 0.040 inches and 2.0 inches in thickness.

16. A cutting element insert as recited in claim 11, wherein said substrate is composed of cemented tungsten carbide.

17. A cutting element insert as recited in claim 11, wherein said layer of superabrasive material is bonded to said substrate by sintering.

18. A cutting element insert as recited in claim 11, wherein said layer of superabrasive material is bonded to said substrate by pressing.

19. A cutting element insert as recited in claim 11, wherein said layer of superabrasive material is bonded to said substrate by brazing.

20. A cutting element insert as recited in claim 11, wherein said layer of superabrasive material is composed of cubic boron nitride.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to devices for drilling and boring through subterranean formations. More specifically, this invention relates to polycrystalline diamond compacts (“PDCs”), also known as cutting elements or diamond inserts, which are intended to be installed as the cutting element of a drill bit to be used for boring through rock in any application, such as oil, gas, mining, and/or geothermal exploration, requiring drilling through geological formations. Still more specifically, this invention relates to polycrystalline diamond inserts which have a surface topography formed integral to an otherwise spherical, conical, or other uniform geometric shape, to increase stress at the insert/rock interface, thereby inducing the rock to fail while requiring the expenditure of less overall energy and introducing little, if any, additional internal stresses to the insert.

[0003] 2. Description of Related Art

[0004] Three types of drill bits are most commonly used for penetrating geologic formations. These are: (1) percussion bits; (2) rolling cone bits, also referred to as rock bits; and (3) drag bits, or fixed cutter rotary bits. Each type of bits may employ polycrystalline diamond inserts as the primary cutting device.

[0005] In addition to the drill bits discussed above, polycrystalline diamond inserts may also be used with other down hole tools, including but not limited to: reamers, stabilizers, and tool joints. Similar devices used in the mining industry may also use this invention.

[0006] Percussion bits penetrate through subterranean geologic formations by an extremely rapid series of impacts. The impacts may be combined with a simultaneous rotations of the bit. An exemplary percussion bit is shown in FIG. 1b. The reader is directed to the following list of related art patents for further discussion of percussion bits.

[0007] Rolling cone bits currently make up the largest number of bits used in drilling geologic formations. Rolling cone bits have as their primary advantage the ability to penetrate hard geologic formations while being generally available at a relatively low cost. Typically, rolling cone bits operate by rotating three cones, each oriented substantially transverse to the bits axis and in a triangular arrangement, with the narrow end of each cone facing a point in the direct center of the bit. An exemplary rolling cone bit is shown in FIG. 1a.

[0008] A rolling cone bit cuts through rock by the crushing and scraping action of the abrasive inserts embedded in the surface of the rotating cone. These abrasive inserts are generally composed of cemented tungsten carbide, but may also include polycrystalline diamond coated cemented tungsten carbide, where increased wear performance is required.

[0009] The primary application of this PDC invention is currently believed to be in connection with percussion and rolling cone bits, although alternative embodiments of this invention may find application in connection with other drilling tools.

[0010] A third type of bit is the drag bit, also known as the fixed cutter bit. An example of a drag bit is shown in FIG. 2. The drag bit is designed to be rotated about its longitudinal axis. Most drag bits employ PDCs which are brazed into the cutting blade of the bit. The PDCs then shear the rock as the bit is rotated about its longitudinal axis.

[0011] While it is expected that this invention will find primary application in percussion and rolling cone bits, some use in drag bits may also be feasible.

[0012] A polycrystalline diamond compact (“PDC”), or cutting element, is typically fabricated by placing a cemented tungsten carbide substrate into a refactory metal container (“can”) with a layer of diamond crystal powder placed into the can adjacent to one face of the substrate. The can is then covered. A number of such can assemblies are loaded into a high pressure cell made from a soft ductile solid material such as pyrophyllite or talc. The loaded high pressure cell is then placed in an ultra-high pressure press. The entire assembly is compressed under ultra-high pressure and temperature conditions. This causes the metal binder from the cemented carbide substrate to become liquid and to “sweep” from the substrate face through the diamond grains and to act as a reactive liquid phase to promote the sintering of the diamond grains. The sintering of the diamond grains causes the formation of a polycrystalline diamond structure. As a result the diamond grains become mutually bonded to form a diamond mass over the substrate face. The metal binder may remain in the diamond layer within the pores of the polycrystalline structure or, alternatively, it may be removed via acid leeching and optionally replaced by another material forming so-called thermally stable diamond (“TSD”). Variations of this general process exist and are described in the related art. This detail is provided so the reader may become familiar with the concept of sintering a diamond layer onto a substrate to form a PDC insert. For more information concerning this process, the reader is directed to U.S. Pat. No. 3,745,623, issued to Wentorf Jr. et al., on Jul. 7, 1973.

[0013] Existing PDCs often exhibit durability problems in cutting through tough geologic formations, where the diamond working surface may experience high but transient stress loads. Under such conditions, existing PDCs have a general tendency to crack, spall, and break. Similarly, existing PDCs are relatively weak when placed under high loads from a variety of angles. These problems of existing PDCs are further exacerbated by the dynamic nature of both normal and torsional loading during the drilling process, during which the bit face moves into and out of contact with the uncut material forming the bottom of the well bore.

[0014] For optimal performance, the interface between the diamond layer and the tungsten carbide substrate must be capable of sustaining the high residual stresses that arise from thermal expansion and bulk modulus mismatches between the two materials. These differences create high residual stress at the interface as the materials are cooled from the high temperature and pressure process. Residual stress can be deleterious to the life of the PDC cutting elements, or inserts, during drilling operations, when high tensile stresses in the substrate or diamond layer may cause fracture, spalling, or complete delamination of the diamond layer from the substrate.

[0015] Typical prior PDCs have a relatively thin diamond layer, generally between 0.020 and 0.040 inches in thickness. The cylinder of carbide to which the diamond layer is attached is generally at least three times thicker than the diamond layer.

[0016] Diamond is used as a drilling material primarily because of its extreme hardness and abrasion resistance. However, diamond also has a major drawback. Diamond, as a cutting material, has very poor toughness, that is, it is very brittle. Therefore, anything that further contributes to reducing the toughness of the diamond, substantially degrades its durability.

[0017] A number of other approaches and applications of PDCs are well established in related art. The applicant includes the following references to related art patents for the reader's general familiarization with this technology.

[0018] U.S. Pat. No. 4,109,737 describes a rotary drill bit for rock drilling comprising a plurality of cutting elements mounted by interference-fit in recesses in the crown of the drill bit.

[0019] U.S. Pat. No. 4,604,106 reveals a composite polycrystalline diamond compact comprising at least one layer of diamond crystals and precemented carbide pieces which have been pressed under sufficient heat and pressure to create a composite polycrystalline material wherein polycrystalline diamond and the precemented carbide pieces are interspersed in one another.

[0020] U.S. Pat. No. 4,694,918 describes an insert that has a tungsten carbide body and at least two layers at the protruding drilling portion of the insert. The outermost layer contains polycrystalline diamond and the remaining layers adjacent to the polycrystalline diamond layer are transition layers containing a composite of diamond crystals and precemented tungsten carbide, the composite having a higher diamond crystal content adjacent to the polycrystalline diamond layer and a higher precemented tungsten carbide content adjacent to the tungsten carbide layer.

[0021] U.S. Pat. No. 4,858,707 describes a diamond insert for a rotary drag bit consists of an insert stud body that forms a first base end and a second cutter end.

[0022] U.S. Pat. No. 4,997,049 describes a tool insert having a cemented carbide substrate with a recess formed in one end of the substrate and having abrasive compacts located in the recesses and bonded to the substrate.

[0023] U.S. Pat. No. 5,154,245 relates to a rock bit insert of cemented carbide for percussive or rotary crushing rock drilling. The button insert is provided with one or more bodies of polycrystalline diamond in the surface produced by high pressure and high temperature in the diamond stable area. Each diamond body is completely surrounded by cemented carbide except the top surface.

[0024] U.S. Pat. No. 5,217,081 relates to a rock bit insert of cemented carbide provided with one or more bodies or layers of diamond and/or cubic boron nitride produced at high pressure and high temperature in the diamond or cubic boron nitride stable area. The body of cemented carbide has a multi-structure containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase and having a low content of cobalt in the surface and a higher content of cobalt next to the eta-phase zone.

[0025] U.S. Pat. No. 5,264,283 relates to buttons, inserts and bodies that comprise cemented carbide provided with bodies and/or layers of CVD- or PVD-fabricated diamond and then high pressure/high temperature treated in the diamond stable area.

[0026] U.S. Pat. No. 5,304,342 describes a sintered product useful for abrasion- and impact-resistant tools and the like, comprising an iron-group metal binder and refractory metal carbide particles.

[0027] U.S. Pat. No. 5,335,738 relates to a button of cemented carbide. The button is provided with a layer of diamond produced at high pressure and high temperature in the diamond stable area. The cemented carbide has a multi-phase structure having a core that contains eta-phase surrounded by a surface zone of cemented carbide free of eta-phase.

[0028] U.S. Pat. No. 5,370,195 describes a drill bit having a means for connecting the bit to a drill string and a plurality of inserts at the other end for crushing the rock to be drilled, where the inserts have a cemented tungsten carbide body partially embedded in the drill bit and at least two layers at the protruding drilling portion of the insert. The outermost layer contains polycrystalline diamond and particles of carbide or carbonitride.

[0029] U.S. Pat. No. 5,379,854 discloses a cutting element which has a metal carbide stud with a plurality of ridges formed in a reduced or full diameter hemispherical outer end portion of said metal carbide stud. The ridges extend outwardly beyond the outer end portion of the metal carbide stud. A layer of polycrystalline material, resistant to corrosive and abrasive materials, is disposed over the ridges and the outer end portion of the metal carbide stud to form a hemispherical cap.

[0030] U.S. Pat. No. 5,544,713 discloses a cutting element with a metal carbide stud that has a conic tip formed with a reduced diameter hemispherical outer tip end portion of said metal carbide stud. A corrosive and abrasive resistant polycrystalline material layer is also disposed over the outer end portion of the metal carbide stud to form a cap, and an alternate conic form has a flat tip face. A chisel insert has a transecting edge and opposing flat faces, which chisel insert is also covered with a polycrystalline diamond compact layer.

[0031] U.S. Pat. No. 5,624,068 describes buttons, inserts and bodies for rock drilling, rock cutting, metal cutting and wear part applications, where the buttons or inserts or bodies comprise cemented carbide provided with bodies and/or layers of CVD- or PVD-fabricated diamond and then HP/HT treated in a diamond stable area.

[0032] Each of the aforementioned patents and elements of related art is hereby incorporated by referenced in its entirety for the material disclosed therein.

SUMMARY OF THE INVENTION

[0033] In drill bits which are used to bore through subterranean geologic formations, it is desirable to provide an insert which has increased durability. This invention provides this increased durability by increasing the diamond layer thickness to decrease the spalling failure of the diamond layer from the non-planar upper surface of the insert and to reduce the residual stresses within the insert, thereby permitting the insert to withstand greater service loads.

[0034] Therefore, it is an object of this invention to improve cutter durability by increasing the thickness of the diamond layer.

[0035] It is a further object of this invention to improve cutter durability by providing a diamond layer which provides full cutter surface coverage.

[0036] It is a further object of this invention to provide a cutter with improved ability to resist spalling failure of the diamond layer.

[0037] It is a further object of this invention to provide a cutter which is capable of withstanding greater service loads.

[0038] These and other objectives, features and advantages of this invention, which will be readily apparent to those of ordinary skill in the art upon review of the following drawings, specification, and claims, are achieved by the invention as described in this application.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1a depicts an exemplary related art roller cone earth boring bit.

[0040] FIG. 1b depicts an exemplary related art percussion bit.

[0041] FIG. 2 depicts an exemplary related art drag or fixed cutter bit.

[0042] FIG. 3 depicts a preferred embodiment of the invention showing a full diamond cap.

[0043] FIG. 4 depicts a preferred embodiment of the invention showing an increased diamond layer thickness.

[0044] FIG. 5 depicts a preferred embodiment of the invention showing an increased diamond layer thickness in the center of the insert.

[0045] FIG. 6 depicts a preferred embodiment of the invention showing an increased diamond layer thickness in the periphery of the insert.

[0046] FIG. 7 depicts a preferred embodiment of the invention showing a full diamond cap on a generally conically shaped insert.

[0047] FIG. 8 depicts a preferred embodiment of the invention showing an increased diamond layer thickness on a generally conically shaped insert.

[0048] FIG. 9 depicts a preferred embodiment of the invention showing an increased diamond layer thickness in the center of a generally conically shaped insert.

[0049] FIG. 10 depicts a preferred embodiment of the invention showing an increased diamond layer thickness in the periphery of a generally conically shaped insert.

DETAILED DESCRIPTION OF THE INVENTION

[0050] This invention is intended for use in cutting tools, most typically roller cone bits, as shown in FIG. 1a, and percussion bits, as shown in FIG. 1b. The typical rolling cone bit 101 includes three rotating cones 102, 103, 104. Each rotating cone 102, 103, 104 has a plurality of cutting teeth 107. Each insert (also known as a drill insert, compact or PDC) is pressed into the drill bit such that the diamond surface is exposed outside the bit. FIG. 1b shows a standard percussion bit 109 with cemented carbide button drill inserts 108, for percussion rock drilling. The diamond coated inserts of this invention can be substituted for the carbide button inserts 108 shown in FIG. 1b.

[0051] FIG. 2 depicts the top view of an example of a typical drag bit 201. A number of inserts, which also could be of the type described in this invention are shown 201a-t arranged in rows emanating in a generally radial fashion from the approximate center 205 of the bit. It is expected by the inventor that the inserts of this invention could be used on rolling cone, percussion and drag bits of virtually any configuration.

[0052] In each embodiment of this invention the insert is composed of essentially two materials: polycrystalline diamond, which covers the cutting surface of the insert; and tungsten carbide. The tungsten carbide region is the area of the insert that is brazed or pressed into the bit body, while the polycrystalline diamond region is the area of the insert that comes in contact with the geologic formation during the drilling operation. In the present invention, the quantity of diamond in the polycrystalline diamond layer is significantly greater than used in prior art inserts. The present invention also has a non-linear, hemispherical or conical shape and is designed to cover the entire cutting surface of the insert. In some embodiments of the invention the polycrystalline diamond layer interfaces with the tungsten carbide region using a generally flat interface, a generally convex interface, an extension of diamond into the tungsten carbide region, and/or an extension of the tungsten carbide into the diamond region. Each interface has its own advantages and applications. Although the interfaces between the diamond region and the substrate regions are shown as generally smooth, it would also be possible to include in the interface a variety of mechanical modifications (e.g., ridges, undulations or dimples, or chemical modifications to enhance both the adhesion between the regions, as well as the transfer of stress between the diamond region and the substrate region. The polycrystalline diamond regions of the present invention are thicker than typically used because a thicker diamond layer provides a greater insert life. As the drill is operated the diamond region of the insert comes into direct physical contact with hard rock. The polycrystalline diamond regions of the various embodiments of the present invention are all essentially symmetrical around the center axis of the insert. This symmetry permits the installation of the insert without regard to the bit face.

[0053] The inserts, as described in this invention, although typically constructed with polycrystalline diamond on a tungsten carbide substrate, can, alternatively, use other materials, such as cubic boron nitride or some other superabrasive material in place of the polycrystalline diamond. Similarly, titanium carbide, tantalum carbide, vandium carbide, niobium carbide, hafnium carbide, or zirconium carbide can be used in place of the tungsten carbide for the substrate. Such superabrasive materials and substrate materials suitable for use in inserts are well known in the art.

[0054] Typically, the inserts of this invention are formed by sintering the diamond layer under high temperature and high pressure conditions to the substrate, using a metal binder or reactive liquid phase such as cobalt. The substrate may be brazed or otherwise joined to an attachment member such as a stud or to a cylindrical backing element to enhance its affixation to the bit face. The cutting element may be mounted to a drill bit either by press-fitting or otherwise locking the insert into a receptacle on a steel-body drag bit, percussion bit or roller cone bit, or by brazing the insert substrate (with or without cylindrical backing) directly into a preformed pocket, socket or other receptacle on the face of a bit body, as on a matrix-type bit.

[0055] An insert, as described in this invention, is preferably fabricated by placing a preformed cemented carbide substrate into a container or cartridge with a layer of diamond crystals or grains loaded into the cartridge adjacent to one face of the substrate. A number of such cartridges are then loaded into an ultra-high pressure press simultaneously. Next, the substrates and adjacent diamond crystal layers are subjected to ultra-high temperature and ultra-high pressure conditions. Such ultra-high pressure and ultra-high temperature conditions cause the metal binder from the substrate body to become liquid and to sweep from the region behind the substrate face next to the diamond layer, through the diamond grains and then to act as a reactive liquid phase to promote a sintering of the diamond grains thereby forming the polycrystalline diamond structure. As a result, the diamond grains become mutually bonded together forming a diamond mass over the substrate face. This diamond mass is also bonded to the substrate face. Alternatively, the diamond layer may be formed as above, but separately from the substrate, and may be subsequently bonded to the substrate material by brazing with a tungsten or titanium-base braze. Yet another alternative method is to deposit the diamond layer on the substrate by chemical vapor deposition (CVD) processing. The metal binder may remain in the diamond layer within the pores existing between the diamond grains or may be removed and optionally replaced by another material, as known in the art, to form a so-called thermally stable diamond. Where the binder is removed by leaching a diamond table is formed with silicon, or alternatively another material having a coefficient of thermal expansion similar to that of diamond. Variations of this general process exist in the art, but this detail is provided so that the reader will understand the concept of sintering a diamond layer onto a substrate on order to form a cutter or insert.

[0056] In a case of the present invention, the desired surface shape of the diamond layer is achieved by utilizing preformed cans. Alternatively, the surface shape can be formed by grinding or even through the use of etching, EOM, EDG, etc.

[0057] Eight examples of the inventive insert design are now described. Further modifications may be made without departing from the essential nature of the invention and such modifications should be considered to fall within the scope of this patent.

[0058] FIG. 3 depicts the top 301 and section 302 view of a single preferred embodiment of the invention. It can be seen that inserts of this invention are generally cylindrical in shape, with a generally hemispherical diamond surface 306, the apex of which is at the center axis 307 of the insert. This diamond insert is composed of a layer of polycrystalline diamond 303 bonded to a tungsten carbide substrate 304. The polycrystalline diamond layer 303 serves as the cutting surface. The interface region 305 is shown where the polycrystalline diamond layer 303 is joined to the substrate 304. In this embodiment of the invention the interface region 305 is essentially flat. Alternatively, the interface region can have an irregular geometry imposed on it.

[0059] FIG. 4 depicts the top 401 and section 402 view of a second embodiment of the invention. Again, the insert is generally cylindrical in shape, with a generally hemispherical diamond surface 406. Alternatively, the apex of the hemisphere could be offset from the center of the insert. This diamond insert is composed of a layer of polycrystalline diamond 403 bonded to a tungsten carbide substrate 404. The polycrystalline diamond layer 403 serves as the cutting surface. The interface region 405 is shown where the polycrystalline diamond layer 403 is joined to the substrate 404. In this embodiment of the invention the interface region 405 is curved with the apex 407 of the curve at the center axis 408 of the insert. Alternatively, the interface region 405 may be positioned such that the diamond layer is relatively thinner or relatively thicker.

[0060] FIG. 5 depicts the top 501 and the section 502 view of another embodiment of the invention. Again, the insert is generally cylindrical in shape, with a generally hemispherical diamond surface 506. This diamond insert is composed of a layer of polycrystalline diamond 503 bonded to a tungsten carbide substrate 504. The polycrystalline diamond layer 503 serves as the cutting surface. The interface region 505 is shown as the region where the polycrystalline diamond layer 503 is joined to the substrate 504. In this embodiment of the invention the interface region 505 includes a trough 507 in the substrate 504 in which the diamond layer 503 extends. This trough 507 intersects and runs perpendicular to the center axis 508 of the insert. Alternatively, the trough 507 can be revolved about the center axis 508 of the insert.

[0061] FIG. 6 depicts the top 601 and the section 602 view of another embodiment of the invention. Again, the insert is generally cylindrical in shape, with a generally hemispherical diamond surface 606. This diamond insert is composed of a layer of polycrystalline diamond 603 bonded to a tungsten carbide substrate 604. The polycrystalline diamond layer 603 serves as the cutting surface. The interface region 605 is shown as where the polycrystalline diamond layer 603 is joined to the substrate 604. In this embodiment of the invention, the interface region 605 includes a protrusion 607 of the substrate 604 into the polycrystalline diamond 603 layer. This protrusion 607 intersects and runs perpendicular to the center axis 608 of the insert. Alternatively, the protrusion 607 can be revolved about the center axis 608 of the insert.

[0062] FIG. 7 depicts the section 701 view of an alternative embodiment of the invention. In this embodiment the insert has a generally conic shaped polycrystalline diamond region 702 bonded to a cylinder which is the tungsten carbide substrate 703. The polycrystalline diamond region 702 serves as the cutting surface. The interface region 704 is shown where the polycrystalline diamond region 702 is joined to the substrate 703. In this embodiment of the invention the interface region 704 is generally flat. Alternatively, the interface region 704 may have irregularities imposed upon it. The apex of the cone 705 is formed along the center axis 706 of the insert.

[0063] FIG. 8 depicts the section 801 view of an alternative embodiment of the invention. In this embodiment the insert has a generally conic shaped polycrystalline diamond region 802 bonded to a generally conic shaped tungsten carbide substrate region 803. The polycrystalline diamond region 802 serves as the cutting surface. The interface region 804 is shown where the polycrystalline diamond region 802 is joined to the substrate 803. In this embodiment of the invention, the interface region 804 is of a generally conical shape. The apex of both the diamond region cone 805 and the interface region cone 806 is formed along the center axis 807 of the insert.

[0064] FIG. 9 depicts the section 901 view of an alternative embodiment of the invention. In this embodiment, the insert also has a generally conic shaped polycrystalline diamond region 902 bonded to a generally cylindrically shaped tungsten carbide substrate region 903. The polycrystalline diamond region 902 serves as the cutting surface. The interface region 904 is shown as the area where the polycrystalline diamond region 902 is joined to the substrate 903. In this embodiment of the invention, the interface region 904 includes a trough 905 in the substrate 903 in which the diamond region 902 extends. This trough 905 intersects and runs perpendicular to the center axis 906 of the insert. Alternatively, the trough 905 can be revolved about the center axis 906 of the insert.

[0065] FIG. 10 depicts the section 1001 view of an alternative embodiment of the invention. In this embodiment, the insert also has a generally conic shaped polycrystalline diamond region 1002 bonded to a generally cylindrically shaped tungsten carbide substrate region 1003. The polycrystalline diamond region 1002 serves as the cutting surface. The interface region 1004 is shown where the polycrystalline diamond region 1002 is joined to the substrate 1003. In this embodiment of the invention, the interface region 1004 includes a protrusion 1005 of the substrate 1003 into the polycrystalline diamond 1002 layer. This protrusion 1005 intersects and runs perpendicular to the center axis 1006 of the insert. Alternatively, the protrusion 1005 can be revolved about the center axis 1006 of the insert.

[0066] Alternative embodiments of the invention employing a combination of one or more of the features of the foregoing inserts should be considered within the scope of this invention.

[0067] The described embodiments are to be considered in all respects only as illustrative of the current best mode of the invention known to the inventor at the time of filing the patent application, and not as restrictive. Although several of the embodiments shown here include a trough or protrusion in the interface region, interface region geometry is not intended to be limited to a single trough or protrusion or to a particular interface region shape. The scope of this invention is, therefore, indicated by the appended claims rather than by the foregoing description. All devices which come within the meaning and range of equivalency of the claims are to be embraced as within the scope of this patent.