Metal tools and implements – making – Blank or process – Drill
Reexamination Certificate
1998-08-17
2001-04-03
Watts, Douglas D. (Department: 3724)
Metal tools and implements, making
Blank or process
Drill
C419S005000, C419S028000
Reexamination Certificate
active
06209420
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method of fabricating rotary bits and components thereof for drilling subterranean formations. Particularly, the inventive method relates to manufacturing a “green” bit body or bit body component from particulate matter, machining the “green” bit body to define various structures and features, and binding the particles to one another. The method may be employed to fabricate an entire bit body, or bit body components which may be subsequently assembled with other components to form the bit body.
2. State of the Art
A typical rotary drill bit includes a bit body secured to a steel shank having a threaded pin connection for attaching the bit body to a drill string and a crown comprising that part of the bit fitted with cutting structures for cutting into an earth formation. Generally, if the bit is a fixed-cutter or so-called “drag” bit, the cutting structures include a series of cutting elements formed, at least in part, of a super abrasive material, such as natural diamond or polycrystalline diamond. The bit body is generally formed of steel or a matrix of hard particulate material such as tungsten carbide (WC) infiltrated with a binder, generally of copper alloy.
In the case of steel body bits, the bit body is typically machined from round stock to the desired shape, although cast bits are known in the art. Internal passages for delivery of drilling fluid to the bit face and topographical features defined at precise locations on the bit face may be machined into the bit body using a computer-controlled five-axis machine tool. Hardfacing for resisting abrasion during drilling is usually applied to the bit face and to other critical areas of the bit exterior, and cutting elements are secured to the bit face, generally by inserting the proximal ends of studs on which the cutting elements are mounted into apertures bored in the bit face. The end of the bit body opposite the face is then threaded, made up and welded to the bit shank.
In the case of a matrix-type bit body, it is conventional to employ a preformed, so-called bit “blank” of steel or other suitable material within the bit body matrix for attachment of the bit body to a hardened American Petroleum Institute (API) thread connection. The blank may be merely cylindrically tubular, or may be fairly complex in configuration and include protrusions corresponding to blades, wings or other features on and extending from the bit face. Other preform elements or displacements, comprised of cast resin-coated sand or, in some instances, tungsten carbide particles in a binder, may be employed to define internal passages for delivery of drilling fluid to the bit face, as well as cutting element sockets, ridges, lands, nozzle displacements, junk slots and other external topographic features of the bit. The blank and other displacements are placed at appropriate locations and orientations in the mold used to cast the bit body. The blank is bonded to the matrix upon cooling of the bit body after infiltration of the tungsten carbide particles with the binder in a furnace, and the other displacements are removed once the matrix has cooled. The upper end of the blank is then threaded, made up with a matingly hardened, threaded shank, and the two welded together. The cutting elements (typically diamond, and most often a synthetic polycrystalline diamond compact or PDC) may be bonded to the bit face during furnacing of the bit body if thermally stable PDC's, commonly termed TSP's (Thermally Stable Products), are employed, or may be subsequently bonded thereto, usually by brazing or mechanical affixation.
As may be readily appreciated from the foregoing description, the process of fabricating a matrix-type drill bit is a somewhat costly, complex multi-step process requiring separate fabrication of an intermediate product (the mold) before the end product (the bit) can be cast. Moreover, the blanks, molds, and any preforms employed must be individually designed and fabricated.
The mold used to cast a matrix body is typically machined from a cylindrical graphite element. For many years, bit molds were machined to a general bit profile, and the individual bit face topography defined in reverse in the mold by skilled technicians employing a profile mold and wielding dental-type drills and other fine sculpting tools. In more recent years, many details may be machined in a mold using a computer controlled five-axis machine tool. In some cases, the mold fabrication process has been made faster and less costly by use of rubber displacements duplicating in fine detail the topography of an entire bit profile and face, which displacements are then used to cast a ceramic bit mold of appropriate interior configuration, which is then used to contain the blank and matrix particles to cast a bit body.
While matrix-type bits may offer significant advantages over prior art steel body bits in terms of abrasion- and erosion-resistance, and while recent advances in matrix technology have markedly increased the toughness and ductility of matrix bodies, in many cases, the higher cost of a matrix-type bit and the longer time to fabricate same may result in the customer choosing a cheaper steel body bit with a faster delivery time. In either case, the customer must choose between a tough but less abrasion-resistant bit and a more expensive, highly abrasion- and erosion-resistant bit with reduced toughness.
One method that is not so time-consuming and costly as traditional matrix-type fabrication techniques is layered-manufacturing as disclosed in U.S. Pat. No. 5,433,280, assigned to the assignee of the present invention and incorporated herein for all purposes by this reference. The '280 patent discloses a method of fabricating a drill bit body or bit component in a series of sequentially superimposed layers or slices. As disclosed, a drill bit is designed as a three-dimensional “solid” model using a computer-aided design (CAD) program, which allows the designer to size, configure and place all internal and external features of the bit, such as (by way of example) internal fluid passages and bit blank voids, and external cutter receptacles, rakes and locations, as well as the height, thickness, profile and orientation of lands and ridges on the bit face and the orientation, depth and profile of waterways on the bit face and junk slots on the bit gage. The CAD program then provides an “.STL” file (i.e., a file which represents the surface of the bit body), which may later be transformed into a solid model and numerically “sliced” into a large number of thin, planar layers by known processes employing known computer programs.
After the mathematical slicing or layering is performed, a horizontal platen is provided on which a granular or particulate material such as a tungsten carbide coated with a laser-reactive bonding agent such as a polymer, a resin, and/or a low melting point metal such as Wood's metal or a lead alloy, or tungsten carbide intermixed with such a laser-reactive bonding agent is deposited in a thin, uniform layer. A finely focused laser, a focused light source such as from an incandescent or discharge type of lamp, or other energy beam, programmed to follow the configuration of the exposed section or layer of the bit body, is directed on the powder layer to melt the bonding agent and bond the metal particles together in the areas of the layer represented as solid portions of the bit in the model. Another layer of powder is then substantially uniformly deposited over the first, now-bonded layer, after which the metal particles of the second layer are bonded to each other and simultaneously to the first layer by the laser. The process continues until all layers or slices of the bit, as represented by the solid model, have been deposited and bonded, resulting in a mass of bonded-particulate material comprising a bit body which faithfully depicts the computer model in every dimensional respect. In areas of each layer which are not to form
Butcher Trent N.
Findley Sidney L.
Smith Redd H.
Baker Hughes Incorporated
Trask & Britt
Watts Douglas D.
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