Cutters – for shaping – Rotary cutting tool – Face or end mill
Utility Patent
1999-05-11
2001-01-02
Tsai, Henry W.H. (Department: 3722)
Cutters, for shaping
Rotary cutting tool
Face or end mill
C407S057000, C407S063000, C408S230000
Utility Patent
active
06168355
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
In general, the present invention relates to machining of a workpiece. More particularly, the present invention relates to end-mill tools for milling a workpiece and a related method.
2. Background of the Invention
Rotary cutting end-mill tools are used for various machining operations on workpieces. Such machine operations are generically referred to as milling operations and include the forming of slots, keyways, pockets, and the like. Several considerations related to end-mill tool design include time for completing a machining operation, amount of material removed in a cut, quality of the cut, and wear on the tool itself during the milling operation.
End-mill tools are formed from materials such as tungsten carbide, high speed steel, ceramic, and other advanced materials and coatings and typically include a “shank” portion, a “body” portion and a “point”. The shank portion is located towards one end of the end-mill tool and is generally cylindrical (but may be tapered) for engagement by a spindle of a milling machine. In use, the milling machine rotatably drives the end-mill tool about its longitudinal axis. The body portion of the end-mill tool is located between the shank and the point. The point is formed at an opposite end of the tool from the shank portion, and typically includes one or more cutting edges.
To manufacture an end-mill tool, a grinder is typically used to grind a flute face and a corresponding cutting edge on the body of the end-mill tool. The grind (grinding operation) typically starts from a position adjacent an end of the body portion and continues to a point at or near the interface of the body portion and the shank portion, commonly referred to as a “flute runnout.” The grind forms a desired helical flute face and/or helical cutting edge. Prior art end-mills typically have continuous helical flutes with continuous cutting edges helically extending from the inception location to the point (or vice-versa). The flutes function primarily for chip removal, in a manner similar to the helical flutes found on an ordinary drill bit.
An end-mill tool representative of the end-mill tools of the prior art is illustrated in
FIGS. 1A and 1B
and identified with reference numeral
100
. The tool
100
has been formed of cylindrical rod stock which has been ground to form distinctive portions. At one end of the tool
100
is a shank portion
102
, suitable for chucking to the spindle of a milling machine (not shown) for rotating and advancing the tool
100
. At an other end of the tool
100
is a point
104
which is provided with flat cutting edges
114
and
116
. Between the shank portion
102
and the point
104
is a body portion
106
which is helically ground to have a number of flutes
110
and
112
. A “boundary” between the body portion
106
and the shank portion
102
is designated
108
in the drawing.
In the embodiment illustrated, the formation of flutes in the body portion
106
generally involves the grinding of two channels, or flutes
110
and
112
, which form two diametrically-opposed positions at the point
104
towards the shank portion
102
. The grinding is discontinued at the boundary
108
of the body portion
106
and the shank portion
102
. It will be appreciated that the direction of the grind could, of course, be reversed. In a known variation referred to as a four-flute end-mill, four flutes wind helically around the body portion of the tool terminating in four cutting edges. The flutes, similar to flutes
110
and
112
, are formed at a helix angle which “winds” around the cylindrical body portion.
Generally, the location of the flat cutting edges
114
and
116
is determined by the location of the flutes
110
and
112
at the point
104
of the tool
100
. The end-mill tool
100
illustrated in
FIG. 1A
has two cutting edges
114
and
116
at the point
104
. The number and location of the cutting edges
114
and
116
is determined by the flutes
110
and
112
.
FIG. 1B
shows the cutting edges
114
and
116
of the tool
100
in greater detail.
It is known in the art to form flutes at a low helix angle or a high helix angle. A “low helix” (or low helical flute) is a flute that helically “winds” around a cylinder at an angle of no more than 40° (forty degrees). A “high helix” (or high helical flute) is a flute that helically winds around a cylinder at an angle of greater than 40° Low helix angle flutes are typically employed for rough cutting while high helix angle flutes are employed for finish cutting.
Returning to
FIG. 1A
, the tool
100
is illustrated to include two cutting edges
120
and
122
. Each of the cutting edges
120
and
122
is helical and follows one of the flutes
110
and
112
helically around the body portion
106
. A notable feature of these cutting edges
120
and
122
is that they are “continuous”—in other words they helically extend continuously from the point
104
to the shank
102
. These cutting edges
120
and
122
function to remove material in the linear direction of travel of the end-mill
100
(e.g., from right-to-left, as viewed in
FIG. 1A
) during a machining operation when the end-mill is “buried”into a workpiece. Material removed from the workpiece will tend to be in the form of an elongated helical (curlicue) chip, and will be guided away from the workpiece by the channels formed by the flutes
110
and
112
. In a known variation, four flutes have four cutting edges that wind helically around the body portion in a continuous manner. Material removed from the workpiece will chip and fall away from the piece through the channels formed by the four flutes.
By way of further definition, the edges
114
and
116
at the point
104
of the tool
100
can be considered to be “flat”cutting edges, and the cutting edges
120
and
122
along the body
106
of the tool
100
can be considered to be “helical”cutting edges.
The following U.S. Pat. Nos. are further instructive of the prior art: 4,610,581; 5,049,009; 4,721,421; and 4,963,059. These patents are incorporated by reference as if fully set forth herein.
Numerous variations of the grind (e.g., flute angle) have been attempted for end-mill tool design. Prior advancements relating to material removal and feed rate of end-mill cutters have been accomplished by (1) varying the spiral lead angle; (2) increasing the depth of the flutes in the body portion of the end-mill, (3) changing the radial rake; (4) changing the clearance angles of the cutting edges; and (5) forming chip splitting grooves in the flutes.
While such variations have proven successful in various applications, they are also associated with disadvantages and limitations. For example, such variations may weaken the core diameter of the end-mill cutter, thereby weakening the tool. Additionally, such noted variations are not suitable for a particular applications (e.g., regarding milling time, rough cut, finish cut, etc.). Furthermore, known end-mills are not efficient for both rough cutting and finish cutting.
It is often advantageous when performing an end-mill machining operation to provide a multiplicity of cutting edges at the point of the tool to increase the life of the tool. The corners formed along the outside-diameter of the tool point tend to dull with use. This is so because this is the only area where a 90° angle exists making the corners much weaker than the flat areas along the outside diameter of the tool. Thus, it is a further advantage to provide multiple cutting edges at the point of the tool to reduce the chip load on each corner of the cutting edge. Dull corners at the point of the tool are generally anathema to tools. To the end of reducing wear and increasing longevity of the tool, it is known to use a four fluted tool. However, each additional flute creates additional chips while eliminating chip room, causing chip backing. Generally, the end-mill of the present invention provides for increased tool life and strength without sacrificing chip removal space.
SUMMARY OF THE INVENTION
It is
Gifford Krass Groh Sprinkle Anderson & Citkowski PC
Tsai Henry W.H.
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