Note: Descriptions are shown in the official language in which they were submitted.
CA 0220~866 1997-0~-22
WO g6/23614 PCT/US95/16386
PL~JNGB AND F-ACE ~(TT.T.TNG ~ SK
~ITH u~.lv~K8AL l~ s~. 8EAT~3
FIELD OF THE lN V~;N~l~loN
This invention generally relates to a milling
cutter capable of plunge, ramp, and face milling
operations for rapidly removing large amounts of
materials from a workpiece, and is specifically concerned
with such a cutter having seats capable of receiving and
securing inserts having differently dimensioned and~0 differently ch~p~ upper and lower cutting edges.
BACKGROUND OF T~IE INVENTION
Milling cutters for machining structural
components are well known in the prior art. However,
such structural components as those used, for example, in
aircraft are usually thin in cross-section and have deep
pockets. Such parts are generally machined from a large,
solid block of a strong, lightweight metal such as
titanium. Often, more material is removed from the block
of metal than remains in the fin;~he~ workpiece. The
most common method for ma~-h;n;ng such structural
components is to use a drill in combination with a
milling cutter. The drill is used to form access holes
of a predetermined depth equal to the depth of the pocket
to be formed. The milling cutter is then lowered into
the access hole and moved back and forth over the
workpiece in the same plane until the entire cross-
sectional area of the pocket being formed has been
traversed. The cutter is then lowered further into the
access hole and the process is repeated as many times as
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n~c~ccAry to form a pocket of the desired depth. Such a
prior art t~hnique is, of course, very time consuming.
Two separate ma~h;ning operations are required for every
pocket (i.e., drilling and milling). Since the depth of
cut which conventional milling cutters are capable of
making is usually small in relation to the depth of the
pocket being formed, many passes over the workpiece are
required to achieve the desired pocket depth.
While there are milling cutters capable of
performing both plunge and face milling operations, such
cutters are not without their limitations. For example,
when the same milling cutter is used to perform both
plunge and face milling operations, the cutting inserts
mounted in the cutter head are simultaneously subjected
to large axial, radial and tangential forces. In order
to prevent the inserts in the cutter head from axial,
radial, or tangential movement during the cutting
operation, the seats in such prior art cutters are
complementary in shape to the inserts that they receive
so that their upper and side edges securely engage and
mate with the transverse edge and side edge of the
inserts, respectively. Such an arrangement, however,
allows the milling head to accommodate only one
particular shape of cutting inserts. Hence, a dif~erent
milling cutter must be used whenever a differently shaped
cut is desired, such as when corners of a smaller or
larger radius between the sidewalls and floor of the cut
are required.
Clearly, what is needed is a milling cutter
capable of effectively cutting deep pockets in a
workpiece in both the vertical and transverse direction
in order to obviate the need for separate drilling and
milling operations in the workpiece. Ideally, the same
cutter head would be able to accommodate inserts having
different chApes so that the same milling cutter could be
used to make differently chAre~ cuts in the workpiece,
such as differently-radiused corners between the
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sidewalls and the floor of the cut. The insert seats
should be designed for positively securing the inserts
against axial, radial, or tangential movement during the
cutting operation, which could create an unsatisfactorily
rough cut and cause undue wear on the cutting edges of
the inserts. The milling cutter and inserts should be
designed so that the cutter is capable of making a deep
vertical cut in relation to its size. Additionally, a
positive rake angle should be maintained on the cutting
edges for both vertical and lateral cutting of the
workpiece both to reduce the power necessary to machine
the workpiece, and to maximize the life of the cutting
edges of the inserts.
SU~IARY OF THE INVENTION
Generally speaking, the invention is a milling
cutter for cutting a workpiece with cutting inserts
having a variety of different shapes that overcomes or at
least ameliorates all the aforementioned shortcomings
associated with the prior art. The milling cutter
comprises a plurality of cutting inserts, the transverse
edges being of different shapes for different inserts,
and an annular cutter body having a plurality of recessed
insert seats for securably receiving the inserts. The
insert seats each include a side shoulder for securably
engaging one of the side edges of the inserts, and a top
shoulder that is spaced apart from the transverse edges
of all of the inserts for allowing the insert seats to
receive inserts having transverse edges of different
shapes. The cutter further comprises a support means for
preventing relative movement between the cutting inserts
and the seats along the side and transverse insert edges
and the side and top shoulders of the recess. The
support means includes a projecting element formed on
either the back face of the cutting insert or the bottom
wall of the insert seat, and a recess formed on the other
of the back face or bottom wall for receiving the
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projecting element. The inserts may be secured in their
respective seats by means of screws.
The side edges of each of the inserts are
preferably straight in order to impart a smooth finish to
a sidewall of a workpiece. Additionally, the side edges
of each insert are preferably parallel so that the
inserts cut smooth sidewalls along both the inner and the
outer diameters of the annular cutter body. Each of the
inserts is preferably elongated along its side edges in
order to increase the depth of the cut made in a
workpiece by the transverse edges of the inserts. Each
of the side and transverse cutting edges may be formed by
an acute angle between the front face and side surfaces
of the inserts to impart a positive radial rake angle to
the cutting edges.
The support means of the cutter and insert may
include an elongated, rail-like projecting element and a
complementarily-ch~p~ recess, both of which may be
substantially parallel to the insert side edges and
recess side shoulder for preventing transverse relative
movement between the insert and the cutter body. The
projecting element is preferably formed on the back face
of the cutting insert, while the recess is formed on the
bottom wall of the seat for two reasons. First,~it is
easier to fabricate a projection, rather than a recess on
the back face of the insert. Secondly, such a projection
(unlike a recess) will not structurally weaken the
insert. The support means preferably also includes a
second elongated projection and complementary recess that
is oriented substantially parallel to the insert
transverse edges and the recess top shoulder for
preventing relative movement along the sides of the
insert and the cutter body. The first and second
elongated projections and their complementary rececs~s
may traverse one another, and are preferably orthogonally
disposed with respect to each other.
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A screw that secures each of the inserts
includes a head and a threaded shank, and each-of the
inserts includes a bore for receiving the shank and a
counter-bore for receiving the screw head. Preferably,
the counter-bore of each of the inserts forms a pilot
surface that engages the screw head in a manner than
securely seats the second projection of the support means
against the surface of-the second complementary recess.
The space between the top shoulder of the
insert recesses and the transverse edges of the inserts
allows the insert seats to receive and secure inserts
having virtually any shape of transverse edge. Hence the
same milling head can make cuts having corners of
different radii, if desired. Moreover, the pressure
applied by the pilot surface of the screw, in combination
with the complementary interfitting between the first and
second transversely disposed projections and recesses,
both secures and supports the inserts against movement
and their respective insert seats in any direction.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure l is a side view of the plunge and face
milling cutter of the present invention;
Figure 2 is a top view of the milling cutter
of Figure l;
Figure 3 is a side view of the milling cutter
with a mounting lug portion shown in section;
Figure 4 is a partial side view of the milling
cutter of Figure l shown without cutting inserts to show
the insert seats;
Figure 5 is a perspective view of both an
insert seat and the back face of an insert, illustrating
how the inserts fit into their respective seats;
Figure 6A is an enlarged front view of the
portion of the milling cutter circled in Figure 3;
Figure 6B is a cross-sectional side view of
the insert and insert seat shown in Figure 6A along the
line 6B-6B;
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--6--
Figure 7A is an enlarged front view of the
portion of the milling cutter circled in Figure 3 with a
differently Ch~pe~ insert;
Figure 7B is a cross-sectional side view of
the insert and insert seat shown in Figure 7A along the
line 7B-7B;
Figure 8A is a plan view of the cutting insert
shown in Figure 6A;
Figure 8B is a side elevation of the insert
shown in Figure 8A;
Figure 8C is a bottom view of the cutting
insert shown in Figure 8A;
Figure 9A is a plan view of an alternate
cutting insert for use in the milling cutter of Figure l;
Figure 9B is a side elevation of the insert
shown in Figure 9A;
Figure 9C is a bottom view of the insert shown
in Figure 9A;
Figure 10A is a plan view of the insert shown
in Figure 7A;
Figure lOB is a side elevational view of the
insert of Figure lOA;
Figure 10C is a bottom view of the insert of
Figure 10A;
Figures llA through llD are side sectional
views of a workpiece at various stages of milling using
the present invention, and
Figures 12A through 12D are top plan views of
the same workpiece at various stages of the milling using
the present invention.
DETAILED DESCRIPTION OF THE SEVERAL FIGURES
Referring now-to Figures 1, 2, and 3, a plunge
and face milling cutter according to the present
invention is shown therein and indicated generally by the
numeral 10. The milling cutter comprises a cutter body
12 which is mounted on an adapter 14 (shown in Figure 3).
The adapter 14 has a tapered shank 16 which may be
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-7-
inserted into the spindle of a milling machine (not
shown). The cutter body 12 is generally cylindrical in
shape and includes a forward end 18 formed with a central
cavity 20. In the embodiment shown, six tool mounting
lugs 22 are formed on the outer periphery of the cutter
body 12. The tool mounting lugs 22 are equally spaced
about the axis of the cutter body 12. As best seen in
Figure 2, chip gullets 23 are provided between the tool
mounting lugs 22 to facilitate the expulsion of metal
chips during a cutting operation. Each tool mounting lug
22 includes a tool mounting region 24 which faces in the
direction of rotation of the cutter body 12.
With reference now to Figure 4, an insert seat
26 for receiving an insert 36 is formed in the tool
mounting region 24 of each lug 22. Each insert seat 26
includes a bottom wall 28, a side shoulder 30, and a top
shoulder 31 as shown. As is best seen in Figure 5, the
bottom wall 28 of each seat 26 includes a longitudinally
oriented slot or recess 32 for receiving a complementary-
shaped rail 50 that protrudes from the back surface of
each of the inserts 36 and is oriented along a
longitll~;n~l axis 50a, as will be described in more
detail hereinafter. Each insert seat 26 includes a
threaded base 35 for receiving an insert mounting ~screw.
As is best seen in Figures 6A, 6B, 7A, and 7B, the top
shoulder 31 of each insert seat 26 is spaced apart from
the top edge of any insert 36 mounted in the seat 26.
Such spacing advantageously allows the insert seat 26 to
accommodate inserts 36 having differently shaped end
portions. Such spacing further creates a clearance
cavity 33 that prevents any portion of the upper edge of
the insert 36 from coming into contact with the top
shoulder 31 of the seat 26. This is an important
structural feature, as such contact during the operation
of the milling cutter could cause the upper edge of the
insert to chip. The clearance cavity 33 has an enlarged
portion 34 to insure that the cavity 33 can accommodate
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inserts having corners with small radii, such as the
insert shown in Figure 7A.
With reference now to Figures 5 and 6A through
7B, each insert 36 includes front and back parallel faces
38 and 40, respectively; sidewalls 41a, 41b, and upper
and lower walls 42a, 42b. The sidewalls 41a, 41b and
upper and lower walls 42a, 42b are not orthogonal with
respect to the front and back faces 38 and 40, but
instead form an acute angle with the front face 38 and
an obtuse angle with the back face 40. Sidewalls 41a,
41b form an acute angle with front and back faces 38 and
40 in a manner similar to that of upper and lower walls
42a, 42b with faces 38 and 40, as shown in Figures 6B and
7B. Such an oblique geometry creates side cutting edges
43a, 43b and transverse cutting edges 44a, 44b having a
positive rake angle where the walls 41a, 41b, 42a, and
42b intersect with the front face 38. Such positive rake
angles reduce the amount of vibration generated during a
cutting operation, as well as the amount of power
necessary to drive the milling cutter. The cutting
inserts 36 also have an elongated shape in order to
provide a relatively deep cut in proportion to their
overall size, and are, of course, indexable.
The inserts may have corners of different
radii in order to provide cuts having different radii.
For example, the insert shown in Figures 6A and 6B and 8A
through 8C has two broadly curved end portions for the
formation of a corner having a large radius between the
side and upper and lower cutting edges 43a, 43b and 44a,
44b. Figures 9A through 9C show an alternate design for
a cutting insert 36. This embodiment of the cutting
insert 36 is generally rectangular in shape and includes
relatively straight transverse cutting edges 44a and 44b,
and straight side cutting edges 43a and 43b. As shown in
Figure 9A, a small radius 45b is formed at each corner
where the upper and lower cutting edges 44a and 44b meet
the side cutting edges 43a and 43b. A third design for
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_g_
the cutting insert 36 is illustrated in Figures 7A, 7B,
and lOA through lOC. In this embodiment, the cutting
insert 36 is again generally rectangular in form and
includes relatively straight upper and lower cutting
edges 44a and 44b and straight side cutting edges 43a and
43b. As with the previous embodiment, all four corners
are radiused. Unlike the previous embodiment, however,
the radii at the four corners are not equal. Instead,
two diagonally opposed corners include a large radius
indicated at 45a, while the other two diagonally opposed
corners include a small radius indicated at 45b.
In all cases, the cutting insert 36 is mounted
in the insert seat 26 in such a manner that the straight
side cutting edges 43a and 43b are both presented in a
radially orthogonal orientation, and one of the
transverse cutting edges 44a, 44b is presented in a
downward direction, making it possible to smoothly finish
both inner and outer sidewall surfaces of a cavity formed
in a workpiece, as well as the floor of the cut. The
cutting insert 36 is secured in the insert seat by means
of a locking screw 53 as best seen in Figures 6A through
7B. More particularly, a threaded hole 35 is formed in
the bottom wall 28 of the insert seat 26 to threadably
engage the shank 54 of the locking screw 53. The~shank
54 of the locking screw 53 passes through a clearance
hole 46 formed in the center of the cutting insert 36.
The clearance hole 46 includes a tapered counter-bore 48
which is engaged by a corresponding tapered surface on
the head 56 of the locking screw 53. One side 49 of the
counter-bore 48 acts as a pilot surface such that, upon
the tightening of the locking screw 53, the engagement of
the head 56 of the locking screw 53 against the pilot
surface of the tapered counter-bore 48 not only presses
the cutting insert 36 downwardly and inwardly against the
bottom 28 and the sidewall 30 of the insert seat,
respectively, but also properly aligns the insert 36
within the seat 26.
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--10--
The milling cutter 10 of the present inventio~
is particularly designed for plunge and face type-milling
operations where the milling cutter is first fed axially
into the workpiece to a predetermined depth and then fed
alternately in a direction perpendicular to the axis of
rotation of the milling cutter 10. When the lateral
fee~in~ of the milling cutter begins, the cutting inserts
36 will cut on their radially outward edges during 180
degrees of travel and on their radially inward edges
during the next 180 degrees of travel. The cutting
forces acting on the inserts 36 tend to push them
inwardly or outwardly in the radial direction.
Additionally, there is a tendency for the cutting inserts
36 to rotate about the axis of the locking screw 53 which
can cause brinelling where the inserts rub against the
sidewall 30 of the insert seat 26.
To secure the inserts against these forces,
the milling cutter 10 of the present invention provides
means for improved lateral and rotational support for the
cutting insert 36. Such improved lateral and rotational
support is achieved by an integrally formed rail 50
formed on the back face 40 of each cutting insert 36
which is received in a similarly shaped slot 32 formed in
the bottom wall 28 of its respective insert seat 26, as
is best seen in Figure 5. The rail 50 extends along the
longitll~;nAl axis of each cutting insert 36. Additional
support is provided by transverse shoulders 51a, 51b
located on the upper and lower ends of the back face 40
of the insert 36. As seen in Figures 6B and 7B, one of
these shoulders 51a, 51b is received in a complementary-
shaped recess 52 located just below the top shoulder 31
of each insert seat 26. Preferably, the shoulders 51a,
51b are orthogonally disposed with respect to the rail
50.
Alternatively, the rail 50 could be formed on
the bottom 28 of the insert seat 26 with the slot 32
being formed in the back face 40 of the cutting insert
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36. In the embodiment shown, the rail 50 has a generally
rectangular cross-section. It will be appreciated,
however, that other configurations, such as V-shaped
rails, may be used. Similarly, the shoulders 51a, 51b
can be replaced with either rails or grooves, as can the
recess 52 of the insert seats 26.
Referring now to Figures llA through llD and
Figures 12A through 12D, a method for using the milling
cutter 10 of the present invention is illustrated. More
particularly, these figures illustrate how the milling
cutter 10 of the present invention can be used to mill a
cavity (shown in dotted lines) in a workpiece. The
milling cutter 10 is first fed axially into the workpiece
A to a predetermined depth Dl as shown in Figure llA.
During axial feeding of the milling cutter 10, an annular
groove B is formed in workpiece A as shown in Figure 12A.
A core C of mater-ial is left inside the annular groove B.
After feeding the milling cutter 10 to the predetermined
depth Dl, the milling cutter 10 is fed laterally as shown
in Figure llB. As the milling cutter 10 is moved
laterally, the inserts 36 will cut on the radially
outward directed edges of the insert 36 for 180 degrees
of travel and will cut on the radially inward directed
edges of the insert 36 for the next 180 degrees of
travel. After traveling laterally a distance equal to
the diameter of the milling 10, the entire core C will be
removed. The milling cutter 10 will continue to move
laterally until a groove of the desired length is made,
as shown in Figures llC and 12C. The -milling cutter 10
is then fed axially into the workpiece A to a
predetermined depth D2 as shown in Figures llD and 12D.
The milling cutter 10 is then -moved back towards its
original starting point in a direction perpendicular to
the axis of the milling cutter. The sequence can be
repeated as many times as necess~ry to mill a cavity of
any predetermined depth. The cutter 10 can also be moved
back and forth in both the x and y dimensions to form a
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cavity wider than the diameter of the cutter 10. Also,
the cutter 10 can be simultaneously moved axially and
laterally to form an incline or ramp in the workpiece.
During the axial feeding of the milling cutter
10, there is a potential problem with the formation of
long continuous chips. This situation is undesirable
since a continuous chip tends to wrap around the spindle
of the milling machine. It is far more desirable to
break the chip into small segments so that the chips can
be carried away by the coolant. In order to break the
chip into small segments, the milling cutter 10 is fed
intermittently into the workpiece. In other words, the
milling cutter 10 is instantaneously paused at a
predetermined interval during axial feeding of the cutter
into the workpiece. Such intermittent axial feeding may
not be required when the chip formed is discontinuous.
Based on the foregoing, it is apparent that
the milling cutter 10 of the present invention can be
used to rapidly remove material from a large workpiece in
a single operation. The milling cutter 10, due to the
shape and increased stability of the insert, can make
greater depths of cut than conventional milling cutters
requiring fewer passes to mill a cavity of a
predetermined size and depth. Further, the improved
stability of the insert prevents the insert from being
dislodged or rotated when cutting on both the inner and
outer edge of the insert.
The present invention may, of course, be
carried out in other specific ways than those herein set
forth without departing from the spirit and essential
characteristics of the invention. The present
embodiments are, therefore, to be considered in all
respects as illustrative and not restrictive and all
changes coming within the meaning and equivalency range
of the appended claims are intended to be embraced
therein.
