Cutters – for shaping – Rotary cutting tool – Face or end mill
Reexamination Certificate
1999-12-14
2003-01-28
Tsai, Henry (Department: 3722)
Cutters, for shaping
Rotary cutting tool
Face or end mill
C407S118000, C407S119000, C408S223000
Reexamination Certificate
active
06511265
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
FEDERALLY SPONSORED RESEARCH
Not Applicable
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
The present invention is generally directed to tools and tool blanks having a composite construction including regions of differing composition and/or microstucture. The present invention is more particularly directed to cemented carbide rotary tools and tool blanks for rotary tools having a composite construction. In addition, the present invention is directed to a method for producing rotary tools and rotary tool blanks having a composite construction. The method of the present invention finds general application in the production of rotary tools and may be applied in, for example, the production of cemented carbide rotary tools used in material removal operations such as drilling, reaming, countersinking, counterboring, and end milling.
DESCRIPTION OF THE INVENTION BACKGROUND
Cemented carbide rotary tools (i.e., tools driven to rotate).are commonly employed in machining operations such as, for example, drilling, reaming, countersinking, counterboring, end milling, and tapping. Such tools are conventionally of a solid monolithic construction. The manufacturing process for such tools involves consolidating metallurgical powder (comprised of particulate ceramic and binder metal) to form a compact. The compact is then sintered to form a cylindrical tool blank having a solid monolithic construction. As used herein, monolithic construction means that the tools are composed of a material, such as, for example, a cemented carbide material, having substantially the same characteristics at any working volume within the tool. Subsequent to sintering, the tool blank is appropriately machined to form the cutting edge and other features of the particular geometry of the rotary tool. Rotary tools include, for example, drills, end mills, reamers, and taps.
Rotary tools composed of cemented carbides are adapted to many industrial applications, including the cutting and shaping of materials of construction such as metals, wood, and plastics. Cemented carbide tools are industrially important because of the combination of tensile strength, wear resistance, and toughness that is characteristic of these materials. Cemented carbides materials comprise at least two phases: at least one hard ceramic component and a softer matrix of metallic binder. The hard ceramic component may be, for example, carbides of elements within groups IVB through VIB of the periodic table. A common example is tungsten carbide. The binder may be a metal or metal alloy, typically cobalt, nickel, iron or alloys of these metals. The binder “cements” the ceramic component within a matrix interconnected in three dimensions. Cemented carbides may be fabricated by consolidating a metallurgical powder blend of at least one powdered ceramic component and at least one powdered binder.
The physical and chemical properties of cemented carbide materials depend in part on the individual components of the metallurgical powders used to produce the material. The properties of the cemented carbide materials are determined by, for example, the chemical composition of the ceramic component, the particle size of the ceramic component, the chemical composition of the binder, and the ratio of binder to ceramic component. By varying the components of the metallurgical powder, rotary tools such as drills and end mills can be produced with unique properties matched to specific applications.
The monolithic construction of rotary tools inherently limits their performance and range of application. As an example,
FIG. 1
depicts side and end views of a twist drill
10
having a typical design used for creating and finishing holes in construction materials such as wood, metals, and plastics. The twist drill
10
includes a chisel edge
11
, which makes the initial cut into the workpiece. The cutting tip
14
of the drill
10
follows the chisel edge
11
and removes most of the material as the hole is being drilled. The outer periphery
16
of the cutting tip
14
finishes the hole. During the cutting process, cutting speeds vary significantly from the center of the drill to the drill's outer periphery. This phenomenon is shown in
FIG. 2
, which graphically compares cutting speeds at an inner (D
1
), outer (D
3
), and intermediate (D
2
) diameter on the cutting tip of a typical twist drill. In FIG.
2
(
b
), the outer diameter (D
3
) is 1.00 inch and diameters D
1
and D
2
are 0.25 and 0.50 inch, respectively. FIG.
2
(
a
) shows the cutting speeds at the three different diameters when the twist drill operates at 200 revolutions per minute. As illustrated in FIGS.
2
(
a
) and (
b
), the cutting speeds measured at various points on the cutting edges of rotary tools will increase with the distance from the axis of rotation of the tools.
Because of these variations in cutting speed, drills and other rotary tools having a monolithic construction will not experience uniform wear and/or chipping and cracking of the tool's cutting edges at different points ranging from the center to the outside edge of the tool's cutting surface. Also, in drilling casehardened materials, the chisel edge is typically used to penetrate the case, while the remainder of the drill body removes material from the casehardened material's softer core. Therefore, the chisel edge of conventional drills of monolithic construction used in that application will wear at a much faster rate than the remainder of the cutting edge, resulting in a relatively short service life for such drills. In both instances, because of the monolithic construction of conventional cemented carbide drills, frequent regrinding of the cutting edge is necessary, thus placing a significant limitation on the service life of the bit. Frequent regrinding and tool changes also result in excessive downtime for the machine tool that is being used.
Other rotary tool types of a monolithic construction suffer from similar deficiencies. For example, specially designed drill bits often are used for performing multiple operations simultaneously. Examples of such drills include step drills and subland drills. Step drills are produced by grinding one or more steps on the diameter of the drill. Such drills are used for drilling holes of multiple diameters. Subland drills may be used to perform multiple operations such as drilling, countersinking, and/or counterboring. As with regular twist drills, the service life of step and subland drills of a conventional monolithic cemented carbide construction may be severely limited because of the vast differences in cutting speeds experienced at the drills' different diameters.
The limitations of monolithic rotary tools are also exemplified in end mills. In general, end milling is considered an inefficient metal removal technique because the end of the cutter is not supported, and the length-to-diameter ratio of end mills is usually large (usually greater than 2: 1). This causes excessive bending of the end mill and places a severe limitation on the depths of cut and feed rates that can be employed.
In order to address the problems associated with rotary tools of a monolithic construction, attempts have been made to produce rotary tools having different properties at different locations. For example, cemented carbide drills having a decarburized surface are described in U.S. Pat. Nos. 5,609,447 and 5,628,837. In the methods disclosed in those patents, carbide drills of a monolithic cemented carbide construction are heated to between 600-1100° C. in a protective environment. This method of producing hardened drills has major limitations. First, the hardened surface layer of the drills is extremely thin and may wear away fairly quickly to expose the underlying softer cemented carbide material. Second, once the drills are redressed, the hardened surface layer is completely lost. Third, the decarburization step, an additional processing step, significantly increases the cost of the finished drill.
Thus, t
Keller Bruce A.
Mirchandani Prakash K.
ATI Properties Inc.
Tsai Henry
Viccaro Patrick J.
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