Rotary cutting tool having multiple helical cutting edges with differing helix angles

A rotary cutting tool is disclosed including a substantially cylindrical main body having a shank portion at one end and a point at an opposite end. Five flutes are formed in an outer surface of the main body. Each of the flutes extends continuously from the point to the shank portion, and defines a helical cutting edge having a helix angle between about 32 degrees and approximately 34 degrees with respect to an axis of the main body. At least 2 of the flutes define helical cutting edges having different helix angles.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to rotary cutting tools and end mills, and more particularly to helically fluted end mills having variable helical angles for improved performance characteristics.

2. Description of Related Art

Rotary cutting tools are used for various machining operations on workpieces. An end mill cutter or “end mill” is a type of rotary cutting tool. Machine operations often carried out using an end mill cutter include the forming of slots, keyways, and pockets. During typical use of an end mill cutter, a milling machine rotatably drives the end mill cutter about its longitudinal axis, and various cutting edges of the end mill cutter are used to remove material from a workpiece.

Over time, the cutting edges of an end mill cutter become dull due to physical contact between the end mill cutter and workpieces. As the cutting edges become dull, internal stresses generated within the end mill cutter during use increase. Harmonic vibrations constitute major sources of internal stresses in end mill cutters. It is common for end mill cutters to break during use due to the internal stresses. One way of extending the operation life of a end mill cutter is to reduce the amplitudes of harmonic vibrations generated within the tool during use.

It would thus be beneficial to have an end mill cutter wherein amplitudes of harmonic vibrations generated within the tool during use are reduced. The operational life of such an end mill cutter would expectedly be extended significantly.

The state of the art includes the following:

Flynn, et al, U.S. 2003/0118411 A1, teaches an end mill that include a flute having a helix which varies along the length of the tool. The end mill may include varying numbers of flutes, whether odd or even; helix change(s) within a flute or between flutes; or indexing between cutting edges or flutes. A ‘slow’ or ‘high’ helix may be used at the end or starting point of the tool, depending upon the application. A slow helix at the end or starting point is desirable for a strong corner in ramping and plunging into the material. When a higher helix is used at the end transitioning to a smaller helix at the shank, the corner is also protected because of the helix change. The high helix at the tip may be needed for shearing action in a given material.

Risen, Jr., U.S. Pat. No. 6,652,203 B1, teaches a precision drill bit that includes at least one cutting flute extends along the length of the bit and exhibits a helix angle of about 38.degree. at the tip. The helix angle decreases to an angle of about 15.degree. at the end of the flute run-out. The helix angle changes progressively and substantially linearly over a number of segments along the length of the drill bit.

Ito, U.S. 2003/0185640 A1, teaches a dual rake twist drill bit for drilling holes in articles made of abrasive materials (fiberglass-filled printed circuit boards, which relatively quickly dull bits). The bit includes spiraled flutes with cutting lips and inclined to the axis of the bit at a relatively small helix angle or rake in the range of about 3 degrees to 10 degrees. A longer rear portion which the flutes and cutting lips have a larger rake of about 33 degrees. The dual rake bit has substantially greater wear resistance than single rake bits. In a modification of the dual rake bit, the central web portion has a front longitudinal portion which is relatively acutely tapered, and a rear portion which is relatively modestly tapered, the dual tapered construction increasing resistance of the bit to breaking.

Noland, U.S. 2004/0120777 A1, teaches a rotary cutting tool that includes a plurality of axial flutes extends from an end surface to a fluted cutting end and combines with a plurality of cutting edges. The cutting edges are unequally spaced along the circumference of the end surface lying in a plane perpendicular to the longitudinal axis of rotation. In addition, all cutting edges are of a different helix from one another and the cutting edge geometries vary from one another to create a different sound pattern that reduces resonant harmonic vibrations.

Walrath, U.S. 2004/0057803 A1 and U.S. 2004/0258490, teach a rotary end-mill having a deferential flute construction with all individual flutes being unequally spaced about the circumference of the cylindrical tool body at different helix angles. The cutting edge of these flutes also face in the direction of tool rotation.

All of the above-described references are hereby incorporated by reference in full.

SUMMARY OF THE INVENTION

A rotary cutting tool is disclosed including a substantially cylindrical main body having a shank portion at one end and a point at an opposite end. Five flutes are formed in an outer surface of the main body. Each of the flutes extends continuously from the point to the shank portion, and defines a helical cutting edge having a helix angle between about 32 degrees and approximately 34 degrees with respect to an axis of the main body. At least 2 of the flutes define helical cutting edges having different helix angles.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a side elevation view of one embodiment of a rotary cutting tool10including a substantially cylindrical main body12having a shank portion14at one end and a point16at an opposite end. In the embodiment ofFIG. 1, the rotary cutting tool10is an end milling cutter or “end mill,” and has 5 flutes formed in an outer surface of the main body12. Each of the 5 flutes extends continuously from the point16to the shank portion14, and defines a helical cutting edge about an outer surface of the main body12. The rotary cutting tool10thus has 5 helical cutting edges about the outer surface of the main body12.

Four of the 5 flutes of the rotary cutting tool10are visible inFIG. 1and labeled18A–18D. The flute18A defines a helical cutting edge20A about the outer surface of the main body12. The flute18B defines a helical cutting edge20B about the outer surface of the main body12. Similarly, the flute18C defines a helical cutting edge20C about the outer surface of the main body12, and the flute18D defines a helical cutting edge20D about the outer surface of the main body12. Herein below, the 5 helical cutting edges will be referred collectively to as “the helical cutting edges20.”

Each of the helical cutting edges20has a helix angle with respect to an axis22of the substantially cylindrical main body12and a tangent line of the helical cutting edges20. In general, the helix angles of the helical cutting edges20are between about 32 degrees and approximately 34 degrees with respect to the axis22, and at least 2 of the helical cutting edges20have different helix angles. For example, in one embodiment, the helix angle of a first of the helical cutting edges20is about 34 degrees, the helix angle of a second of the helical cutting edges20adjacent the first is approximately 33 degrees, the helix angle of a third of the helical cutting edges20adjacent the second is about 32 degrees, the helix angle of a fourth of the helical cutting edges20adjacent the third is approximately 33 degrees, and the helix angle of the fifth of the helical cutting edges20adjacent the fourth is about 34 degrees.

For purposes of this application, the term “about X degrees” shall be defined to mean X+/−0.5 degrees. In the most preferred embodiment, these terms shall include X+/−0.3 degrees.

While the preferred embodiment includes flutes that have a constant helical angles along the length of the flute, in some embodiments this angle may be varied along the length of the flute. To the extent that such variation is made by one skilled in the art to significantly copy the above-described geometries and without impeding the performance of the tool, such variation should be considered equivalent to the embodiment described and within the scope of the invention, as claimed.

Varying the helix angles of helical cutting edges20has been found to substantially extend the operational life of the rotary cutting tool10. It is believed that these helix angles serve to reduce amplitudes of harmonic vibrations generated within the rotary cutting tool10during use, thereby substantially extending the operational life of the rotary cutting tool10.

As indicated inFIG. 1, the helical cutting edge20B has a helix angle “H1” with respect to an axis22of the substantially cylindrical main body12. The helical cutting edge20C has a helix angle “H2” with respect to the axis22, and the helical cutting edge20D has a helix angle “H3” with respect to the axis22. In the embodiment described above, and where the helical cutting edge20B is the first of the helical cutting edges20, the helix angle H1is about 34 degrees, the helix angle H2is approximately 33 degrees, and the helix angle H3is about 32 degrees.

FIG. 2is an end view of the rotary cutting tool10ofFIG. 1illustrating features of the point16of the main body12. As shown inFIG. 2, the rotary cutting tool10has 5 flat cutting edges at the point16. Each of the 5 flutes of the rotary cutting tool10extends continuously from a different one of the 5 flat cutting edges to the shank portion14of the main body12.

InFIG. 2, the 5 flat cutting edges are labeled30A–30E, and have corresponding leading edges32A–32E. In general, the flat cutting edges30A–30E are arranged about the point16such that an angle between about 70 degrees and approximately 74 degrees exists between a leading edge of one of the flat cutting edges30A–30E and a leading edge of an adjacent one of the flat cutting edges30A–30E.

In one embodiment, at least two different angles exist between the leading edges32A–32E of adjacent ones of the flat cutting edges30A–30E. More specifically, a first angle exists between the leading edge of a first one of the flat cutting edges30A–30E and an adjacent second one of the flat cutting edges30A–30E, and a second angle exists between the leading edge of the second one of the flat cutting edges30A–30E and an adjacent third one of the flat cutting edges30A–30E, wherein the first angle and the second angle are different.

InFIG. 2, an angle “A1” exists between the leading edge32A of the flat cutting edge30A and the leading edge32B of the adjacent flat cutting edge30B. An angle “A2” exists between the leading edge32B of the flat cutting edge30B and the leading edge32C of the adjacent flat cutting edge30C, and an angle “A3” exists between the leading edge32C of the flat cutting edge30C and the leading edge32D of the adjacent flat cutting edge30D. An angle “A4” exists between the leading edge32D of the flat cutting edge30D and the leading edge32E of the adjacent flat cutting edge30E, and an angle “A5” exists between the leading edge32E of the flat cutting edge30E and the leading edge32A of the adjacent flat cutting edge30A. In one particular embodiment, the angle A1is about 73 degrees, the angle A2is approximately 70 degrees, the angle A3is about 74 degrees, the angle A4is approximately 72 degrees, and the angle A5is about 71 degrees.

The rotary cutting tool10ofFIGS. 1–2is preferably made from at least one metal. Suitable metals and metal alloys include steel (including high speed steel and stainless steel), cast iron, carbide (an alloy including cobalt and tungsten), and titanium. A portion of the rotary cutting tool10including the 5 flat cutting edges30A–30E, and the 5 helical cutting edges (including the helical cutting edges20A–20D), is preferably coated with a wear reducing material. Suitable wear reducing materials include titanium nitride (TiN), titanium aluminum nitride (TiAlN), titanium carbonitride (TiCN), zirconium nitride (ZrN), and aluminum titanium nitride (AlTiN).

Four separate tests were conducted over a 4-month period to compare the operational effectiveness of the rotary cutting tool10ofFIGS. 1–2to other commonly used and commercially available end mill cutters. In each of these tests, the operational life of the rotary cutting tool10exceeded the operational lives of the other end mill cutters. It is believed that the helix angles used in the rotary cutting tool10and described above reduced amplitudes of harmonic vibrations generated within the rotary cutting tool10during use, thereby substantially extending the operational life of the rotary cutting tool10. In each test, the greater operational life of the rotary cutting tool10represented a significant savings in both operating time and operating cost.