Imported: 13 Feb '17 | Published: 11 Oct '16
USPTO - Utility Patents
A method for forming the cutting edge and adjacent contoured surface area of rotary cutting tools utilizing a laser to remove material from the cutting end of the tool to create a predetermined point-by-point geometry is disclosed. Relatively complex surface and edge geometries may be formed by directing a laser beam toward the cutting end of the tool at an angle having a component that is normal to the surface of the cutting end. The laser beam is directed in multiple passes across the surface of the cutting end to remove material and form the desired cutting edge and adjacent three-dimensional contoured surface geometry.
The present invention relates to the formation of rotary cutting tool edges, and more particularly relates to the use of a laser to provide three-dimensional surface shaping of such cutting edges.
The need in machining to have cutting edges with a hardness greater than the material being machined is well known. Throughout the evolution of tools this has progressed from stone, to bronze, to iron, to carbon steel, to high speed steel, and then to solid carbide. In recent decades this evolution has continued further with the introduction of ceramics (silicon nitride, aluminum oxide, etc.) and “superabrasive” materials such as polycrystalline diamond (PCD) and cubic boron nitride (CBN). Although these materials have greatly enhanced tool life in certain materials by increasing the hardness, wear resistance and resistance to deformation of cutting edges, they have been difficult to apply to a broader spectrum of tools. This has been due to the difficulty in machining these materials themselves, especially with PCD and CBN, as there is no material of greater hardness than PCD to machine them with.
The current processes used to shape these materials are electrical discharge machining (EDM), electrical discharge grinding (EDG), and grinding with wheels containing PCD as the abrasive. These processes all have drawbacks of various sorts, such as poor cutting edge quality (EDM and ECG) and large costs and processing times (grinding). There are also limitations to all of these in that freeform geometries cannot be defined point to point, but rather have to consist of ruled surfaces created by the surface generator (grinding wheel face, wire electrode, etc.).
Lasers have been used to cut various types of materials. For example, U.S. Pat. Nos. 4,481,016; 4,849,602; 5,643,523; and 7,189,032 disclose the use of a laser to cut through a plate of cutting tool material to form several separate cutting tool inserts from the single plate of material. Lasers have also been used to cut through cutting tip portions of cutting tool inserts, for example, as disclosed in U.S. Pat. Nos. 4,714,385; 5,178,645; and 7,322,776, and published U.S. Patent Application No. 2008/029415. In such laser cutting operations, the laser beam slices through the cutting tool insert material in a direction parallel with the plane of the flat surface that is formed by the cutting operation.
Lasers have also been used to roughen the surface of cutting tool inserts in order to improve adhesion of a subsequently applied layer of material, as disclosed in U.S. Pat. Nos. 5,722,803; 5,776,355; and 6,161,990, or to provide a textured surface that helps to hold the cutting tool insert in position when it is mechanically clamped into a cutting machine, as disclosed in U.S. Pat. No. 6,712,564.
Despite these prior methods, a need still exists for a way to efficiently form cutting edges in tools having relatively complex geometries, such as drills and other rotary cutting tools.
The present invention provides a method for forming the cutting edge and adjacent contoured surface area of rotary cutting tools utilizing a laser to remove material from the cutting end of the tool to create a predetermined point-by-point geometry. Relatively complex surface and edge geometries may be formed by directing a laser beam toward the cutting end of the tool at an angle having a component that is normal to the surface of the cutting end. The laser beam is directed in multiple passes across the surface of the cutting end to remove material and form the desired cutting edge and adjacent three-dimensional contoured surface geometry.
An aspect of the present invention is to provide a method of forming a cutting edge of a rotary cutting tool having a body and at least one flute formed in the body along at least a portion of a length of the body defining a cutting edge adjacent to a cutting end of the tool, the method comprising removing material from the cutting end of the tool with a directed laser beam to thereby form the cutting edge and a predetermined three dimensional contoured surface adjacent to the cutting edge.
Another aspect of the present invention is to provide a rotary cutting tool comprising a body, at least one flute formed in the body along at least a portion of a length of the body defining a cutting edge adjacent to a cutting end of the tool, and a contoured surface adjacent to the cutting edge, wherein the cutting edge and adjacent contoured surface are formed by a laser beam.
These and other aspects of the present invention will be more apparent from the following description.
The laser-shaping method of the present invention may be used to form cutting edges and surrounding contoured surfaces in rotary cutting tools. As used herein, the term “rotary cutting tool” means a rotating tool for chip removal machining. Examples of some types of rotary cutting tools that may be formed by the methods of the present invention include drills and drill bits, milling cutters, reamers, taps, step drills, indexable drills, counterbores, spotfacing tools, orbital tools and the like. The cutting edges of such tools may be made of very hard materials including carbides, cermets such as cemented tungsten carbides, ceramics such as cubic boron nitride or aluminum oxide, polycrystalline diamond and the like.
FIGS. 1-4 illustrate drills that may be fabricated in accordance with the present invention. However, it is understood that any other type of rotary cutting tool having similar types of cutting edge geometries are considered to be within the scope of the present invention. As shown in FIGS. 1 and 2, the drills 10 have body 12 and shank portions 14 aligned along a longitudinal axis of rotation A. The body comprises at least one flute 16A, 16B miming along at least a portion of the axial length of the body 12. In the embodiments shown in FIGS. 1 and 2, the drills include two helical flutes 16A and 16B. However, the rotary cutting tools may have any other suitable number of flutes, and may have any other known type of flute geometry.
In accordance with the present invention, the cutting edges of the rotary cutting tools 10 and their adjacent contoured surface areas are formed into the desired shape by laser irradiation which removes material from the cutting end of the tool 10 on a controlled point-by-point basis. In the embodiments shown in FIGS. 1-4, the drills 10 have substantially conical cutting tips 18 which define major cutting edges 20 in the regions where the helical flutes 16A and 16B intersect the tips 18. In addition, the drills 10 have minor cutting edges 22 in the regions where the helical flutes radially intersect the outer periphery of the generally cylindrical bodies. The major cutting edges 20 and/or minor cutting edges 22, as well as their adjacent contoured surfaces, may be formed with a laser beam in accordance with the present invention.
FIG. 5 illustrates a conventional grinding method for shaping the cutting end of a drill. A pre-machined rod 30 with helical flutes formed therein is machined with a grinding wheel 32 to form the desired shape 34 at the cutting end of the drill. While such a conventional grinding process may be suitable for certain types of drill materials, the grinding method may not be practical for drills made of very hard materials such as carbides, cermets, ceramics, PCD, CBN and combinations of such materials.
FIG. 6 illustrates the volume of material 36 that is removed from the cutting end of the drill during the grinding process illustrated in FIG. 5. In order to obtain the desired shape, a significant amount of material must be removed from the tip of the drill, as well as from the side peripheral surfaces of the drill body adjacent to the trailing edge of each helical flute. The removal of such large amounts of material from drills made of very hard materials may be difficult or impossible.
FIG. 7 illustrates the cutting end of a rotary cutting tool 40, indicating the region 42 that is subjected to laser treatment in accordance with an embodiment of the present invention. Another region away from the cutting tip may be machined in a conventional manner such as grinding. FIG. 8 is an exploded end view of the rotary cutting tool 40 shown in FIG. 7.
FIG. 9 is a partially schematic illustration of a laser shaping operation of the present invention in which the laser beam L is directed toward the surface S of a rotary cutting tool at an angle Θ measured from the shaped surface S of the tool. The angle Θ has a component CN that is normal to the shaped surface S of the tool, and a component Cp that is parallel to the shaped surface S of the tool. As the laser beam L moves across the surface S, the angle Θ typically changes due in part to the contour of the shaped surface S, while maintaining a component that is normal to the surface S. In one embodiment, the angle Θ has a nominal value of 90°±45°, for example, 90°±30°. In particular embodiments, the angle Θ may be 90°±10° or 90°±5°. The focal point of the laser may be controlled. For example, the focal point may be located at the surface of the workpiece, or may be located a selected distance above the surface −δ, or a selected distance below the surface +δ, as shown in FIG. 9.
FIG. 10 is a partially schematic illustration of a laser beam path across the surface of the cutting end of a rotary cutting tool in which the laser beam is directed in multiple parallel passes across the surface in which each adjacent pass is made in the same direction.
FIG. 11 is a partially schematic illustration of a laser beam path across the surface of the cutting end of a rotary cutting tool in which the laser beam is directed in multiple parallel passes across the surface in which each adjacent pass is made in opposite directions.
FIG. 12 illustrates a free-form laser beam pattern across the surface of the cutting end of a rotary cutting tool in accordance with another embodiment of the present invention.
As shown in FIGS. 10-12, the laser beam travels across the surface of the workpiece in various controlled patterns in order to remove or ablate the cutting tool material on a controlled point-by-point basis in order to form the cutting edges and surrounding surface areas.
FIG. 13 illustrates the relative positions of a laser 50 and the cutting end of a rotary cutting tool 10 during irradiation with a laser beam L in accordance with an embodiment of the present invention. In accordance with the present invention, the laser L ablates or evaporates material from the cutting tip portion of the drill 10 or other tool to create the desired geometry point-by-point. The creation of single or multiple edges in freeform design is possible with the method of the present invention. In accordance with an embodiment of the invention, after the cutting edge(s) and adjacent surfaces are created, the rest of the tool may be manufactured by grinding, milling, EDM/ECG, further laser evaporation, or a combination of such methods. The mounting method of a dissimilar cutting edge material (such as PCD in a solid carbide body) could be done by brazing, shrink-fitting, co-sintering, or by other known fastening methods.
The lasers used in accordance with the present invention may comprise, for example, conventional diode pumped solid state lasers such as Nd:YVO4 lasers, Nd:YAG lasers, and the like. The pulse frequency and power of the laser may be adjusted as desired. For example, pulse frequencies of from 100 to 10,000 kHz may be suitable, and powers of from 1 to 500 W may be suitable. The laser is located a suitable distance away from the surface of the workpiece, e.g., from 1 to 100 cm.
Relative movement of the laser beam and the cutting tool workpiece may be achieved by linear and/or rotary positioning of the tool, e.g., by moving a table or other fixture upon which the tool is mounted in multiple axes, such as 3, 4 or 5 axes of movement. Furthermore, the laser beam may be moved, e.g., by mirrors and/or by translational or rotational movement of the laser in multiple axes. The laser beam may travel across the surface of the workpiece at any desired speed, typically from 1 to 10,000 mm/second, for example, from 10 to 1,000 mm/second. The size of the laser spot on the workpiece may be controlled as desired, e.g., the diameter of the laser spot may typically be from 1 to 100 microns. A feedback system may be used to control the laser ablation process. Alternatively, an open loop system may be used, with workpiece detection done first followed by laser ablation.
In accordance with an embodiment of the present invention, the cutting edge and adjacent surface area of the workpiece may be detected in order to guide and control the laser beam. For example, the cutting edge of the rotary cutting tool workpiece may be detected by an optical device such as a laser source, or by backscattering of the laser. Mechanical locating devices may also be used. In addition to detection of the cutting edge, the system may detect the geometry of the adjacent surface as material is removed from the surface by the laser beam in order to monitor and control the laser shaping operation.
FIG. 14 schematically illustrates a laser beam control system 60 that may be used in accordance with an embodiment of the present invention. The laser beam L is directed from the laser 50 toward the surface S of the cutting tool 10 to create a plasma point P and a plasma region R during the ablation process. In the embodiment shown in FIG. 14, a single laser 50 is used. A detector 62 may be used to locate the three-dimensional position of the plasma point P in relation to the cutting tool 10. An output signal from the detector 62 may be fed to a controller 64, which, in turn, controls the laser 50. During the process, adaptive control of the laser beam may be accomplished by means of adjusting various parameters of the laser including the pulse frequency, laser power, pulse sequence, translational speed across the surface, pattern of movement, focal depth and the like. The detector 62 may include a laser source or other optical device conventionally used for surface measurements, such as those found in laser eye surgery or three-dimensional sheet metal laser welding.
After the laser irradiation process, the resultant shaped surface may be very smooth with a typical surface roughness of less than 0.5 micron Ra, for example, from 0.01 to 0.2 micron Ra. In certain embodiments, the surface roughness is less than 0.1 or 0.05 Ra.
In accordance with an embodiment of the present invention, the cutting edge formed by the laser beam has sufficient sharpness for the intended use of the rotary cutting tool, without the necessity of any additional honing or machining. The cutting edge formed by the laser beam may have an edge sharpness of less than 130 microns, for example, less than 100 or 50 microns. In certain embodiments, the edge sharpness may be less than 10 microns or even less than 1 micron.
When forming a rotary cutting tool such as drills, the relatively complex contoured surfaces formed by the laser beam may include concave portions, convex portions, and combinations thereof. For example, in the region of the flute, at least a portion of the shaped surface is concave. For a typical helical flute, the shaped surface is inwardly curved in a plane perpendicular to the axis of the drill, and is helical along the length of the drill. In contrast with the concave flute surface, the laser-shaped surface at the tip of the drill may be convex, with an outwardly curved surface corresponding to a conical segment. In the embodiments shown in FIGS. 1-4, 7 and 8, the laser-shaped cutting edges are in the form of straight lines at the intersections of the substantially conical tip and helical flutes.
Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.