Patent Publication Number: US-2012039677-A1

Title: Contour end mill

Description:
BACKGROUND OF THE INVENTION 
     End mills are widely used in milling operations due to their versatile range of application and due to the moderate cost of the tool. End mills are often of cylindrical shape, and are generally available up to about 80 mm diameter. Many end mills have flat ends; however other shapes such as conical and rounded ends are also used. Typically, an end mill has two (2) to ten (10) teeth, depending on diameter, size and whether configured for rough cutting or finishing. The teeth are usually spiral shaped, but can be straight and parallel to the longitudinal axis. Common materials used in the construction of end mills are high speed steel, solid carbide, cermets or ceramic, or combinations thereof. 
     Ball nose end mills are often used in difficult operations where demands are very high in terms of surface finish. In these applications, no unevenness and notches whatsoever may be tolerated that later may be able to cause failure, while simultaneous high productivity and predictable long tool life are highly desired. Further, the tool may not be exchanged during the machining operation which could result in worse precision of the manufactured part as the tool wears. 
       FIGS. 11(   a ) and ( b ) illustrate a typical cutting operation using a convention ball nose end mill using a predetermined step over width. As seen, the conventional ball nose end mill produces a somewhat rough finish in the form of sinusoidal scallops having a relatively large depth. In addition, the conventional ball nose end mill produces chips with relatively large thickness. This rough finish is unacceptable for operations that demand a smooth, even finish. 
     SUMMARY OF THE INVENTION 
     The problem of rough finish and relatively large chip thickness associated with conventional end mills is solved by a contour end mill with a major radius that is greater than one-half of the cutting diameter. 
     In one aspect, a contour end mill comprises a shank portion; and a cutting portion defining a cutting diameter, a corner radius and a major radius, wherein the the major radius that is greater than one-half of the cutting diameter. 
     In another aspect, a contour end mill comprises a shank portion; and a cutting portion defining a cutting diameter, a corner radius and a major radius. The cutting portion further includes a plurality of flutes defining a core diameter, a radial rake angle, a rake check point, a radial primary angle, a radial secondary angle, a primary relief, a secondary relief, a helical axial rake gash, a heel relief, and a cutting edge formed at an intersection between the helical axial rake gash and the primary relief, wherein the the major radius that is greater than one-half of the cutting diameter, and wherein the corner radius is less than one-half of the cutting diameter. 
     In another aspect, a method of end milling a workpiece using a contour end mill comprises performing a cutting operation with the major radius of the cutting portion; and performing a cutting operation with the corner radius of the cutting portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While various embodiments of the invention are illustrated, the particular embodiments shown should not be construed to limit the claims. It is anticipated that various changes and modifications may be made without departing from the scope of this invention. 
         FIG. 1  is a plan side view of an exemplary embodiment of a contour end mill of the invention; 
         FIG. 2  is cross-sectional view of the end mill taken along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is an enlarged cutaway view of the end mill of  FIG. 1 ; 
         FIG. 4  is a plan end view of the end mill of  FIG. 1 ; 
         FIG. 5  is a side view of a two-fluted contour end mill according to an embodiment of the invention; 
         FIG. 6  is an enlarged side view of the cutting portion of the end mill of  FIG. 5 ; 
         FIG. 7  is another enlarged side view of the cutting portion of the end mill of  FIG. 6  rotated ninety (90) degrees; 
         FIG. 8  is an end isometric view of the end mill of  FIG. 5 ; 
         FIG. 9  is a plan view of a cutting operation using the end mill of the invention; 
         FIGS. 10(   a ) and ( b ) are plan views of a cutting operation showing improved finish a reduced chip thickness using the end mill of the invention; and 
         FIGS. 11(   a ) and ( b ) are plan view of a cutting operation showing unacceptable finish and increased chip thickness using a conventional end mill. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Below are illustrations and explanations for a version of combination end milling drilling/push drilling cutting tool and a method for machining a workpiece. However, it is noted that combination cutting tool and machining method may be configured to suit the specific application and is not limited only to the example in the illustrations. 
     Referring to  FIGS. 1-4 , wherein like reference characters represent like elements, a contour end mill is generally shown at  10  according to an embodiment of the invention. In general, the end mill  10  has a shank portion  12  and a cutting portion  14 . The shank portion  12  defines a shank diameter  16 , and the cutting portion  14  defines a cutting diameter  18 . In some embodiments, the shank diameter  16  is substantially equal to the cutting diameter  18 . In other embodiments, the shank diameter  16  may be slightly larger or smaller than the cutting diameter  18 . The end mill  10  has an overall length  20  and a length of cut  22 . The cutting portion  14  includes a corner radius  24  and a major radius  26 . The end mill  10  has a central, longitudinal axis  28 . 
     Referring now to  FIG. 2 , the cutting portion  14  of the end mill  10  includes two flutes  30  defining a core diameter  32 , a radial rake angle  34 , a rake check point  36 , a radial primary angle  38  and a radial secondary angle  40 . In one embodiment, the radial rake angle  34  is approximately +4 degrees, the radial primary angle  38  is approximately +9 degrees, and the radial secondary angle  40  is approximately +20 degrees. 
     Referring now to  FIG. 3 , the cutting portion  14  of the end mill  10  includes an axial rake angle  42 , an axial primary angle  44  and an axial secondary angle  46 . In one embodiment, the axial rake angle is approximately +4 degrees, the axial primary angle  44  is approximately +9 degrees, and the axial secondary angle  40  is approximately +20 degrees. 
     Referring now to  FIG. 4 , the cutting portion  14  of the end mill  10  includes a primary relief  48 , a secondary relief  50 , a helical axial rake gash  52 , and a heel relief  54 . A center web  56  has a non-zero thickness. In one embodiment, for example, the thickness of the center web  56  is approximately 0.006 inches (0.152 mm). The helical axial rake gash  52  is offset from the central, longitudinal axis  28  by a distance  58  to allow the axial rake to be substantially aligned with the central, longitudinal axis  28  of the end mill  10 . In one embodiment, the distance  58  is approximately 0.006 inches (0.152 mm). The thickness of the center web  56  and the offset distance  58  is for illustrative purposes only, and the invention can be practiced with any desirable thickness and offset distance. A cutting edge  60  is formed at the intersection between the helical axial rake gash  52  and the primary relief  48 . In the illustrated embodiment, the end mill  10  has two (2) cutting edges  60 . However, it will be appreciated that the invention can be practiced with any desirable number of cutting edges  60 , for example, more than two (2) cutting edges, and the like. 
     As seen in  FIGS. 5-8 , the helical axial rake gash  52  is formed at a gash angle  62  with respect to the central, longitudinal axis  28  of the end mill  10 . In one embodiment, the gash angle  62  is approximately forty-five (45) degrees. It is noted that the end mill  10  also includes a bottom gash  64  between the helical axial rake gash  52  and the heel relief  54  for the adjacent flute  30  (not visible in  FIG. 5 ). In one embodiment, the angle of the bottom gash  64  is approximately 110 degrees. In addition, the end mill  10  includes a radial and axial release  66 . 
     In the invention, the corner radius  24  and the major radius  26  are defined as a function of the cutting diameter  18 . For example, the corner radius  24  is less than one-half of the cutting diameter  18 . For example, in the illustrated embodiment, the corner radius  24  is approximately 0.18 times the cutting diameter  18 . 
     In one aspect of the invention, the major radius  26  is greater than one-half of the cutting diameter  18  of the end mill  10 . For example, in the illustrated embodiment, the major radius  26  is 0.85 times the cutting diameter  18 . However, it will be appreciated that the major radius  26  can be any value greater than 0.50 times the cutting diameter  18 . For example, the major radius  26  can be 0.51 times the cutting diameter  18 , 0.52 times the cutting diameter  26 , . . . , 0.99 times the cutting diameter  26 , as well as values in thousandths in between. 
     As shown in  FIGS. 9(   a )-( f ), the end mill  10  of the invention provides superior cutting performance as compared to conventional end mills. The superior cutting performance is achieved by the use of both the corner radius  24  and the major radius  26  of the end mill  10  during the cutting operation. As shown in FIGS. (a), (b), (d) and (e), the major radius  26  is performing the cutting operation of the workpiece  70 . However, in FIGS. (c) and (f), the corner radius  24  is performing the cutting operation of the workpiece  70 . Because both the corner radius  24  and the major radius  26  of the end mill  10  can be used during the cutting operation, the end mill  10  of the invention can provide superior cutting performance on the most complicated three-dimensional workpieces. By contrast, conventional end mills are incapable of performing the same type of cutting operation on such complicated three-dimensional workpieces. 
     As shown in  FIGS. 10(   a ) and ( b ), the major radius  26  being larger than more than one-half of the cutting diameter  18  provides several distinct advantages as compared to the conventional ball nose end mill shown in  FIGS. 11(   a ) and ( b ). As shown in  FIG. 10(   a ), the end mill  10  of the invention provides a much smoother finish with the same step over width as compared to the conventional ball nose end mill. As a result, the user spends less time finishing the workpiece. Alternatively, the user can increase the step over width, which will dramatically reduce cycle time. As shown in  FIG. 10(   b ), the end mill  10  of the invention at the same feed rate produces chips having a thickness that is much less than the thickness of the chip produced by the conventional ball nose end mill shown in  FIG. 11(   b ). Alternatively, the user can substantially increase the feed rate of the workpiece, which will dramatically reduce cycle time. 
     As described above, the end mill  10  of the invention offers many distinct advantages when compared to conventional ball nose end mills. 
     The patents and publications referred to herein are hereby incorporated by reference. 
     Having described presently preferred embodiments the invention may be otherwise embodied within the scope of the appended claims.