Note: Descriptions are shown in the official language in which they were submitted.
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INTERFITTING ON-EDGE INSERTS
FOR MILLING CUTTERS
This invention relates to a form of on-edge
cutting insert for milling tools which is adapted for
cooperation with like inserts to provide a continuous
effective cutting edge along a single chip gullet.
Heretofore, in milling cutters designed to
produce cuts which exceed the length of the cutting edge
of a single insert, the necessary length of cut has been
accomplished with one or more auxiliary inserts
associated with a trailing chip gullet, either
effectively to extend the length of the cut made by a
single preceding insert, or to fill the gap or gaps
between adjacent but spaced inserts of the preceding
chip gullet. That arrangement, which has been
conventional practice in a variety of milling cutters,
including, for example, end mills, gear gashers, slot
mills, etc., obviously requires two chip gullets for a
single effective cutting edge, a space requirement which
has a limiting effect on the attainable metal removal
rate of the tool.
In the context of end mills, for example, the
necessary pairing of a leading and a trailing insert is
- a limitation upon the tool designer, particularly in the
smaller diameter end mills where the aforementioned
limitations require either 2, 4, or 6 chip gullets in
the tool for half that number of effective cutting edges.
The insert of this invention is formed for
interfitting cooperation with contiguous like inserts
along a given chip gullet in a manner such as to provide
a continuous effective cutting edge. In the end milling
context, this frees the designer from the restraints
imposed by the necessity of pairing chip gullets for a
single effective cutting edge, permitting the use of odd
numbers of chip gullets each with its own continuous
effective cutting edge. In all mentioned forms of
milling cutters, i.e., end mills, slotting mills of
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substantial face width, or gear gashing cutters cutting
to depth exceeding the length of cutting edge of a
single insert, the design capability made possible by -
the interfitting inserts of this invention, and the
resulting continuous effective cutting edge associated
with each individual chip gullet, permit design for
higher feed rates and thus higher metal removal rates
than their conventional counterparts wherever adequate
spindle power is available and the stability of the work
set-up will permit.
In brief, the on-edge indexable inserts of the
invention are generally parallelepiped in preferred form
with two major faces which serve alternately and
respectively as seating and clearance faces, two opposed
minor edge faces each providing two cutting edges at
their intersections with the two major faces, and two
remaining opposed minor edge faces which are recessed so
that the sideward projections of the cutting edges
defined by those recesses may be placed one behind the
other in an interfitted array of like inserts circum-
ferentially offset from one another along a single chip
gullet.
The invention, and its application to milling
` cutters of the kind heretofore identified, is explained
in the follow:ing specification in conjunction with the
accompanying drawings, in which:
FIG. 1 is a side elevation of a right-handed
end mill which employs the cutting inserts of the
invention to provide a continuous effective cutting edge
with positive axial rake along each flute or chip gullet
of the tool;
FIG. 2 is an end view of the end mill of FIG. l;
FIG. 3 is a developed view of the array of
inserts employed in the end mill of FIGS. 1 and 2,
illustrating the echeloned array of the inserts of the
invention as they constitute the five continuous
effective cutting edges of that end mill;
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FIG. 4 is a plan view of the insert of the
invention;
FIG. 5 is an edge view of the same, facing the
cutting edges thereof;
FIG. 6 is a side edge view of the insert,
facing the recess which permits the interfitting of the
inserts;
FIG. 7 is an enlarged fragmentary view of two
inserts of the invention disposed contiguously in offset
interfitting relation, also illustrated in FIGS. 1 and 3;
FIG. 8 is a sectional view taken along the line
8-8 of FIG. 7, showing an insert secured in its pocket
milled in the body of the tool;
FIG. 9 is a rear view of a single insert as
mounted in the tool, illustrating the inclination of the
insert for purposes to be described;
FIG. 10 is a plan view of one form of insert
suitable for use as the bottoming insert of each chip
gullet;
FIGS. 11 and 12 are, respectively, top and side
edge views of the insert of FIG. 10;
FIG. 13 is an elevational view of an end mill
equipped with a modified form of the insert of this
invention; and
FIG. 14 is an end view of such insert projected
from FIG. 13.
Referring initially to FIGS. 4 to 6, inclusive,
Eor a detailed description of the insert of this
invention in preferred form, the insert 20 is a block
essentially in the form of a rectangular parallelepiped
with certain modifications of form to adapt it to its
purpose. In particular, the two opposed side edge faces
22 of the insert are recessed midway thereof at 24 so
that the ends of the opposed front and rear edge faces
26 project sidewardly as wing-like extensions 28.
The front and rear edge faces 26 of the
j six-sided insert are the rake faces of the insert. Each
I
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provides two cutting edges 30 at the intersection of
each such edge face with the two major faces 32 of the
insert, thus providing four cutting edges to which the~
insert of the invention may be indexed by rotation of
the insert about an axis perpendicular to its major
faces 32, and also by turning the insert over to expose
the opposite major face thereof. As is otherwise
conventional, the insert is formed with a central cored
hole 34 for an insert retaining screw 36 (FIG. 8), the
hole being countersunk from both ends to accommodate the
head of the retaining screw at either major face of the
insert.
Referring particularly to FIG. 5, the insert is
preferably chamfered along the intersections 38 of both
side edge faces 22 with the major faces 32 to avoid the
chipping of the ends of the cutting edges 28 which might
otherwise occur at a sharp corner. In addition, and
depending upon the material to be cut, it may further be
desirable to groove the front and rear edge faces 26 of
the insert, as at 40, parallel to the cutting edges 30,
in order to provide positive radial rake in a given
cutting context.
Referring to the fragmentary enlargement of
FIG. 7, and also the FIGS. 1 to 3, inclusive, for
illustration of the interfitting relationship of
contiguous inserts 20 to provide a continuous effective
cutting edge, it will be seen that the insert pockets 42
for adjacent inserts are milled in the body 44 of the
tool and so dimensioned relative to the inserts that
adjacent inserts interfit, i.e., so that the sidewardly
extending wing-like projections 28 of the cutting edge
30 of one insert are received within the recesses 24 of
the next adjacent inserts along a single chip gullet 46
to provide a continuous cutting path, notwithstanding
the angular separation and resulting sequential action
of adjacent inserts.
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The degree of axial rake for a given cutting
application may vary from tool to tool, but given the
necessity for continuity in the effective cutting edge,
i.e., of the cutting paths of the inserts 20 along a
single flute 46, it is necessary, by a combination of
the mutual placement of the sideward projections 28 of
the cutting edges 30 of one insert into the recesses 24
of the other, and the axial rake angle of the adjacent
inserts, to eliminate gaps between the cutting paths
swept by adjacent individual inserts. This may be seen
from FIG. 7, in which a line 48 drawn from the end of
the cutting edge 30 of the lower insert through the
adjacent end of the cutting edge 30' of t~e upper insert
emplaced within the recess of the first, determines the
minimum axial rake angle necessary for continuity. It
may be appreciated from FIG. 7 that the deeper the
insertion of the cutting edge of one insert into the
recess of the next, and the more rearward the position
of the inserted cutting edge within the recess, the
smaller the rake angle required for continuity.
In the particular cutter 44 chosen to
illustrate the invention, the helix angle of the chip
gullet or flute 46 is somewhat greater than the axial
` rake angle of the cutting edges of the insert, but, as
can be appreciated from the laid-out view of FIG. 3, the
helical orientation of the chip gullets is necessitated
by the illustrated echeloned relation of the interfitted
inserts irrespective of the rake angle thereof.
The rear or trailing edge view of a mounted
insert, FIG. 9, illustrates somewhat exaggeratedly the
tipping of the insert to the "spotting angle" ~, which
is necessary to position the opposite ends of the
axially-raked cutting edge 30 of any given insert at the
same radial distance from the rotational axis of the
tool. That is, when an insert is rotated in its own
plane to impart axial rake to its cutting edge, the
trailing edge being radially depressed for clearance
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behind the cutting edge, the ends of the cutting edge
become disposed at different swing radii and require a
tipping of the clearance face out of parallelism to the
rotational axis of the tool to restore the ends of the
cutting edge to the same swing radius.
In the context of an end mill cutting with
positive axial rake, as illustrated in FIGS. 1, 2,
and 3, the upper edge of the insert is tipped outwardly
to position the parallel major faces at the compensating
spotting angle ~ from a plane parallel to the axis of
the tool in order to position the ends of the active
cutting edge equidistantly from the rotational axis. In
the relatively short length of the cutting edge of each
insert compared to the swing radius, the hyperbolic
deviation of the cutting path from linear is negligible.
Differing from the insert of the invention is
the specially formed single-edge, non-indexable
bottoming insert 50 at the tip of the tool 44 where the
clearance requirements for cutting in that position
dictate a different form. Referring in particular to
FIGS. 10 to 12, inclusive, it will be seen that the tip
insert 50 is provided at its upper end with a sidewardly
projecting extension 52 of the rake face 54, similar to
that provided in each of the inserts 20 mounted above it
along the chip flute 46, omitting the similar sideward
extension at the rear of the insert as unnecessary and
without function in that position.
The edge face 56 of the tip insert is disposed
at an acute angle to the rake face 54 in order to
provide necessary clearance behind the rake face 54 at
the bottom of the cut. As illustrated in FIGS. 10
to 12, the cutting edge 58 is shown terminating in a
radius to provide a corresponding radius at the bottom
of the cut, but it will be understood that that radius
may be reduced, at least, to a small chamfer for the
sake of preventing chipping at the end of the long
straight cutting edge.
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The form of the tip insert may be further
simplified as indicated by the broken lines in FIG. 10
by eliminating the sidewardly projecting ear 52 as such~l
and simply tapering the upper edge face of the insert as
it recedes from the rake face 54, and, in that manner,
provide the necessary clearance to receive the sideward
projection 28 of the next adjacent insert 20 in defilade
behind the rake face 54 of the tip insert.
For those end milling applications which will
tolerate nega.ive axial rake, e.g., edge milling or
contouring of plates or slabs or other operations where
chip clearing is not defeated by negative axial rake,
the specially formed tip insert may be eliminated. This
may be appreciated viewing FIG. 3 upside down, as though
the developed view of a left-handed cutter with negative
axial rake.
The form of the insert illustrated in FIGS. 1
to 9, inclusive, is preferred for its provision of four
indexable cutting edges at each insert position. It
will be appreciated however, from the foregoing
description, that whereas those four indexable cutting
edges result from the rectangularity of the generally
parallelepiped preferred form, the interfitting of
contiguous inserts can be achieved equally in skewed
form of parallelepiped, i.e., one in which the major
faces of the insert are parallelogram in form rather
than rectangular, broadly speaking. In that type of
insert, the opposed and parallel rake faces likewise
provide two cutting edges, for a total of four, but only
two of the four edges are usable at any insert position,
as the skewed form necessarily results in the creation
of "rights" and "lefts." Except in the cases of the
less numerous slotting mills and gear gashers, in which
"lefts" and "rights" are readily usable in a single
cutter, this reduces the utility of the insert.
For some end mill applications, however, for
example, end mills of small diameter, a skewed insert
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may be preferable because of the front-to-back
dimensional limitations imposed by the small swing
radius. Illustrated in FIGS. 13 and 14 are skewed
inserts 60 in accordance with the invention, modified
for use in a small end mill 62 of, say, one-inch
diameter. For this special application, in which only
two cutting edges would he usable at each insert
position in any event, the grooving of the cutting face
to provide two distinct rake faces is eliminated and the
entire cutting face 64 simply ground to the desired
radial rake angle. Moreover, inasmuch as the skewed
form of the insert inherently provides clearance behind
the bottom of the rake face in the tip position, no
special form of insert is required in that position, the
lS skewed form with two cutting edges being adequate to the
task.
Where a radius is desired at the bottom of the
cut, it may be provided in the manner of Johnson Patent
No. 4,411,564, i.e., by providing a radius at the
2G intersection of the major and edge clearance faces which
diminishes from the acute angle corner to the obtuse
angle corner of the insert so that the cutting edge of
the insert is merely slightly chamfered at the obtuse
` angle corner, and thus does not break the continuity of
the effective cutting edge at the junction between the
tip insert and the next adjacent insert.
As earlier indicated, the advantages of the
invention are the continuous and uninterrupted cutting
path provided by an assembly of its individual cutting
inserts 20 or 60 positioned along a single chip gullet,
notwithstanding the division of the cutting edge into
multiple cutting inserts. The benefit of this result is
the elimination of the necessity to pair chip gullets in
order to provide a continuous effective cutting path.
In the context of end mills, this renders their design
more flexible by permitting the use of a single flute as
well as odd numbers of flutes, but the more important
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benefit in all applicable milling cutters is the
increased metal removal rates of which these tools are
capable, and the speeding of production where the
necessary spindle power is available and the work set-up
provides adequate stability for its use.
The features of the invention believed new and
patentable are set forth in the following claims.
