Note: Descriptions are shown in the official language in which they were submitted.
Background of the Invention
1. Field of the Invention
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This invention relates to a novel machine tool cutter
and particularly to a broaching tool in which the cutting
surfaces are at a positive rake angle to the work cut.
2. Description of the Prior Art
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The typical broaching tool is in the form of an
elongated body having a plurality of spaced annular ribs
generally transverse to the longitudinal axis of the body.
10 A series of titanium carbide teeth are braised onto side
walls of these ribs in a position perpendicular to the
longitudinal body axis. Each of these teeth has a curved
upper cutting edge and normally engages the work cut on the
work piece at a negative rake angle.
The usual designs have placed tremendous stresses on
the tool and the cutter teeth as well as on the work piece
being broached. There have been various attempts in the
past to develop new designs which will decrease the load
on individual cutters, such as the tooth design shown in
20 U.S. Patent 3,849,852, issued November 26, 1974. That
design in theory decreases the load because the individual -
tooth takes a narrow deep cut rather than a wide shallow
cut.
U.S. Patent 1,945,535, issued February 6, 1934, des-
cribes a broaching tool having cutters with a positive
rake angle and a specially designed chip relief groove.
The cutter at a positive rake angle will in theory take a
cleaner cut and leave a smoother surface behind the cut
by rolling the chip formed into the chip relief groove,
30 thereby reducing fracturing off of small particles and
serving to reduce generation of heat in the work and in the
tool.
As a tool cutter is forced through a work piece, high
friction is generated between the tool face and the com-
pressed material adjacent the tool face. With the high
temperature and high specific pressure present, a layer of
material clings to the tool face to form what is known as
a built-up edge. This built-up edge is, -therefore, forced
through the work by the cutter face and does the actual
fracturing or cutting. The chip body shears away from
this built-up edge and passes off above.
As the built-up edge becomes larger and larger, it
becomes more and more unstable until fragments thereof are
torn off. The built-up edge is, therefore, continually
varying in size and attacking the area of fracture or
shear with a varying area which causes roughness. Further-
more, as the built-up edge increases in size, the chip
being formed and following upwardly of the tool face is
subjected to a band of increasing curvature which would
remain at a substantially constant value if the built-up
edge can be kept at a reduced size.
Such problems were recognized by the inventors in U.S.
Patent 2,392,481, issued January 18, 1946, but they con-
tinued to work on the size and shape of the chip relief
grooves much in the manner as was done by the inventor in
U.S. Patent 1,945,535.
None of these prior designs was able to solve the
problem of the immense pressures and built-up edge which
caused the cutting edge to quickly wear and frequently
break wlth the resultant rough work piece surface behind
the cut.
; In Proulx et al U.S. Patent 3,946,472, issued March 30,1976,
there is described a broaching tool in which the cutter
teeth are in the snape of buttons or discs. This had the
unique feature of being able to make use of the angular
position of the discs so as to form a smoothly curving
contoured surface. This represented a very significant
advance in the art in being able to greatly reduce the
power required per unit volume of chip removed. The
result was less wear on the individual cutters, less breakage
of cutters and less damage to the work piece being machined.
It is, therefore, the object of the present invention
to provide an improved configuration of tool cutter which
can take advantage of the benefits of U.S. Patent 3,946,472
while providing a positive ral~e angle between the cutter
face and the work cut.
Summary of the Invention
In accordance with the present invention there is pro-
vided a novel metal cutting tool comprising an elongated
tool body having an elongated tool face portion. A plurality
of recesses or pockets are formed ln the tool face, each
having a flat bottom face inclined inwardly and rearwardly
to the longitudinal axis of the tool body. Cylindrical
cutter discs are mounted in the recesses with an end face
of each cutter resting on a recess flat bottom face. Each
cutter disc has a ~enerally cylindrical edge face with a
generally concave cutter portion forming an acute angle
with an adjacent end face of the disc. The magnitude of
this acute angle and the degree of inclination of the
recess flat bottom face are such as to provide a positive
rake angle of 1-25, preferably 5-20, between the cutting
portion of the cutter disc and the work cut.
The tool face can be arcuate or it can be flat. The
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arcuate face typically forms an arc of at least 45 and
usually at least 90. For a typical half-round broach,
the arc will be in excess of 180 and it may even form
a full cylindrical broach.
The angle of the cutter discs with respect to the
longitudinal axis of the tool body will normally be
varied within the range of about 1-15. ~n angle of about
10-15 is particul~arly preferred.
The cutter discs themselves are preferably quite
small, typically having a diameter of about 0.4 to 1.0
inch. The thickness of each cutter disc is preferably
in the range of about 0.15 to 0.4 inch.
The cutter discs are preferably arranged in rows
transverse to the longitudinal axis of the tool bodyA These
rows can be perpendicular to the longitudinal axis or they
can define helical paths. The discs of each row are stag-
gered laterally with respect to the discs of the next ad-
jacent row whereby paths of successive cutter discs partially
overlap. For the arcuate tool faces, the rows of cutter
discs are preferably of increasing diameter in a rearward
direction so as to produce a progressively larger hole
as the broach is moved through the work piece or the work
piece over the broach.
When the cutter discs are arranged in helical paths,
these normally define an angle of about 5 to 95 with res-
pect to the longitudinal axis of the tool body and a typical
tool has a helical angle in the order of about 15 to 45.
The helical configuration has been found to be particularly
advantageous in providing an exceptionally low impact load
between the cutter discs and the work piece. In other words,
with the helical configuration some of the discs will always
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be under load and this overcomes any tendency of impact
as successive rows of cutter discs come into engayement
with the work piece. This greatly decreases the tendency
of damage to the cutting tool as well as possible breakage
of the work piece being broached.
By setting the series of small cylindrical cutting
discs at a small angle with respect to the longitudinal
axis of the tool body, the cutting edges of these cutter
discs form small arcs of a much larger circle than the
diameter of the discs themselves. This, combined with the
overlapping of the successive cutters due to the staggered
arrangement of cutters in successive rows, results in a
smooth finished surface having very shallow grooving which
is easily removed by a finishing tool. This is true whether
these cutter discs are being used for planing a flat surface
or for broaching a round hole.
An important feature of the present invention is the
shape of the indexable cutter inserts. As mentioned above,
- these are preferably of a quite small diameter and are used
in large numbers. For instance, a half-round helical broach
for cutting a hole two inches in diameter will use 99
cutter discs each 1/2 inch in diameter.
- Each disc is of a generally annular configuration with
a countersink axial hole through which a screw passes to
hold the cutter disc in position in a tool face recess.
Each disc is preferably symmetrical, defining a cutting
edge at both the top and bottom, but it is equally possible
to have a design which is not symmetrical.
The cylindrical edge face of each disc can assume a
- 30 wide variety of profiles, with a simple concave arc of a
circle being the most convenient. It is, however, immaterial
whether the profile is in the form of flat or curved lines,
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provided the angle between the cylindrical face and the
adjacent encl face of a disc forms an acute angle which,
together with the degree of inclination of a disc with
respect to the longitudinal axis of a tool body provides
a positive rake angle of 1-25 between the cutter face
and the work cut.
Certain preferred embodiments of the present invention
will now be illustrated by the attached drawings in which:
Figure 1 is a side elevatlon of one embodiment of a
novel broaching tool;
Figure 2 is a top plan view of the broaching tool shown
in Figure l;
Figure 3 is a eross seetion through row 1 of the tool
of Figure l;
Figure 4 is a cross section through row 2 of the tool
of Figure l;
Figure 5 is an exploded detail view of a eutting dise and
soeket;
Figure 6 shows a transverse section through a eutter
aeeording to the invention together with a work pieee on
whieh it is funetioning; and
Figures 7a to 7i show different eonfigurations of
eutter dises aeeording to the invention.
The partieular broaeh illustrated in the drawings is
known as a half-round broaeh. This partieular one has been
illustrated sinee it is generally the most eomplex form
of tool and the size, spaeings, ete. of the eutter dises
apply equally to a flat broaeh as to the eonfiguration
illustrated.
Looking now at the drawings, the deviee ineludes an
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elongated tool holder body portion 20 having a bottom
spline 21 extending along the len~th thereof for retaining
the tool in a tool holder (not shown). The tool is held
rigidly in place in the holder by the mounting screws 22.
A series of cutter discs 24 are mounted in sockets 25
in the cylindrical surface. Each of these sockets have
a flat bottom face 26 which is inclined at a small angle(b)
of typically about 12 to 15 to the longitudinal axis of
the body portion 20 and the socket also has a semi-circular
abutment wall 27 shaped to mate with the corresponding por-
tion of a cutter disc. Extending into the body portion 20
through face 26 is a tapped hole 32.
One preferred form of cutting disc is shown at 24 and
this has a concave cylindrical wall 29 and bevelled end
faces 28. A hole 31 is formed axially through the insert
with a conical countersink 30. The cutting disc is typically
made from high speed steel, although any other suitable
material can be used. It is held in position by means of
a threaded screw 33 having a conical head portion which
mates with the countersink of the cutting disc and the
head of the screw includes a socket 34 for receiving a wrench.
When the cutting disc has been placed in position in the
socket 25 and the screw tightened, the insert is pressed
firmly against the abutment wall 27. Thus, when the
broach is in operation, the forces on the cutting inserts
are fully carried by the abutment walls 27 rather than by
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the screws themselves.
With this arrangement, it will be seen that only about
1/4 of the cutting edge of the cutter discs is used at one
time. This means that as the portion in use becomes dulled,
the screw 33 can be loosened and the cutter discs can then
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be rotated sufficiently to present fresh cutting edge
portions, after which the screws are again tightelled. The
result is that as many as four cutting edge portions may be
available on one face of a cutter disc. Furthermore, if
the discs are symmetrical, they may be reversed so that
another four cutting edge portions may be available on the
reverse face. In this way, as many as eiaht fresh cutting
edge portions may be obtainable from a single cutting disc.
In Figure 1, eight helical rows of cutting discs are
shown and these are indicated as rows 1 to 8. Figure 3
shows the positioning of the cutter discs for what are
designated as rows 1, 3, 5 and 7 in Figure 1 while Figure 4
is a cross section showing the position of the cutter discs
for the rows designated as 2, 4, 6, and 8 in Figure 1.
Particularly from Figures 3 and 4, it becomes evident that
the successive rows of cutting inserts are positioned in a
circumferentially staggered manner. Thus, the axis of the
cutting inserts of row 2 are positioned midway between the
axis of the inserts of row 1 while the inserts of row 3
are in alignment with the inserts of row 1. The diameter
typically is increased by an amount of about 0.004 inch
from one row to the next following row. However, it is
also possible to have two or more adjacent rows of the same
diameter followed by two or more rows of increased equal
diameter. It is also sometimes desirable to have the last
cutting insert of one row at the same elevation as the first
cutting insert of the next following row. Moreover, when the
inserts are mounted on a flat broach, they may all be
positioned identically on the tool body and the entire
tool body can be tilted slightly to increase the cut from
one row of inserts to the next.
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Looking now at l;`igure 6, the bevelled end face 28
of cutter disc 24 provides a clearance angle with respect
to the work cut 35 of about 1-3. Because the cutter discs
of this invention are of a relatively small diameter, the
effect of the positive rake angle is not simply that of
lifting the chip 36 away from the work cut 35 but because
the surface 29 is both inclined vertically away from the
cutting edge and at the same time is circular in cross
section, the chip 36 tends to lift and at the same time
fracture or shear so as to spread to each side of a disc
in a plowing action. This is highly effective in preventing
the build up of a compressed mass between the cutting edge
and the work plece so that a smooth clean cut is formed.
Turning now to Figure 7, a variety of different con-
figurations of the cutter discs are shown with Figure 7a
representing the disc shown in Figure 5. As aan be seen
from Figure 7a, the end faces 28 are bevelled at an angle
c. This angle c is typically in the range of 12 - 15.
The angle d is the angle between axes of the disc and a
-20 tangent to the cutting face and this is typically in the
range of 35 - 45. Thus, in a typical preferred embodiment
; angle d is 39, angle c is 11, angle b is 12~ and rake angle
a is 15. Such a cutter disc has a diameter of 0.5 inch, a
thickness of 0.1875 inch and the edge face is an arc of radius
0.125 inch.
Figure 7b shows a generally similar symmetrical cutter
disc to that of Figure 7a with the arcuate edge face 29 being
replaced by a pair of inwardly inclined faces 40 meeting at
the center point. Figure 7c again is a symmetrical design -
having a central cylindrical edge portion 41 and inclined
faces 42 providing the required positive rake angle for the
- cutting edge.
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Figure 7d is a non-symmetrical design having a lower
cylindrical edge portion 43 and an upper inclined edge 44
forming the positive rake cutting edge. While the design
of Figure 7d is not reversible, it has the advantage that
the abutment face 27 of the tool recess 25 can be o'
cylindrical configuration rather than being machined to mate
with the shapes of Figures 7a to 7c. Figure 7e, like Figure
7d, again has a lower cylindrical edge face 45 which merges
into an upper concave arcuate face 46 forming the positive
rake cutting face.
Figure 7f is a non-symmetrical design in which the
edge face is formed primarily of an arcuate face of large
diameter merging into an arcuate face of smaller diameter
at the upper corners. There is no bevel on the end face.
These provide a sharper cutting edge with a steeper rake
angle than, for instance, the design of Figure 7a.
Figure 7g shows a symmetrical configuration which is
generally similar to Figure 7c without end bevels. The side
edges have a central cylindrical portion 48 merging into upper
and lower arcuate portions 50 forming the positive rake angle
cutting faces. Figure 7h also represents a symmetrical
design, without end bevels, in this case with the side edge
of the cutter disc being divided into a pair of equal arcuate
concave faces 51 joined at a central point 52.
Figure 7i is a non-symmetrical configuration generally
along the lines of Figure 7e with a lower cylindrical
portion 53, but without the end bevel. The cutting portion
is formed in a pro~ection 54 and comprises an arcuate concave
face 55.
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