Note: Descriptions are shown in the official language in which they were submitted.
~Q8;~497
BACKG~OUND OF THE INVENTION
1. Field of the invention
This invention relates to a novel broaching
tool of the type typically used to produce a round hole
or a semi-circular hole.
2. Description of the prior art
Broaching is a machining process whereby one or
more cutters with a series of teeth are pushed or drawn
entirely across a workpiece and is analogous to single-
stroke filing. Broaching is typically carried out onmanually-operated presses, on pull-screw machines or on
hydraulically actuated broaching machines or presses.
The broach has teeth which increase in height towards
one end and is typically held in the screw socket of a
broaching machine screw or ram by a taper cotter. Usually
the first few teeth on the broach are low to permit the
small end of the tool to pass through a hole in the work-
piece, while the intermediate teeth re ve most of the metal
and the last few teeth finish the surface to size.
The typical broaching tool presently in use is
in the form of an elongated body having a plurality of
spaced annular ribs generally transverse to the longitudinal
body of the axis. A series of titanium carbide teeth are
, brazed onto ~ide walls of these ribs in a position per-
pendicular to the longitudinal body axis. Each of these
teeth has a curved upper cutting edge. Of course, when
these cutter teeth become worn, it becomes a very expensive
proposition to remove the worn teeth and then braze new
cutter teeth into position against the ribs. Also,
because each cutting edge engages the workpiece at sub-
stantially 90, it will be appreciated that immense stresses
-- 2 --
. ~
1082497
are placed on the tool and the cutter teeth particularly
when broaching metals.
In Applicants U.S. Patent 3,946,472, issued
March 30, 1976, there is described a broaching tool in
which cutter teeth in the shape of buttons or discs have
been successfully used for the broaching of concave sur-
faces. This had the unique feature of being able to make
use of the angular positioning of the discs so as to form
a smoothly curving contoured surface. Although this re-
presented a great improvement over the previous broachingtools, it did have some problems. Thus, for most broaching
tools it was necessary to provide chip relief gaps between
the rows of cutter discs so that chips formed would be
dispersed easily and not become jammed between cutter
discs thereby creating difficulties. Moreover, because the
cutter discs were arranged in parallel rows, very heavy
instantaneous loads were placed on the tool as each row
came into engagement with the workpiece.
It is , therefore, the object of the present
invention to provide an improved configuration of broaching
tool for the broaching of concave surfaces in which the
chip dispersal is simplified and the tool is provided
with a substantially uniform loading during operation.
SUMMARY OF THE INVENTION
In accordance with the present invention there
is provided a novel broaching tool comprising an elongated
tool body having an arcuate face of at least 45. A
, plurality of recesses are formed in this arcuate face,
each recess having a flat bottom face inclined inwardly
and rearwardly within 1-15 of coincidence with the
longitudinal axis of the body and an arcuate abutment wall
-- 3 --
108'~497
perpendicular to and rearwardly surrounding the flat
bottom face. The recesses are arranged in helical paths
of an increasing diameter in a rearward direction about
the tool body arcuate face to form a series of spaced
helical rows. The recesses of each row are staggered
circumferentially with respect to the recesses of the
next adjacent row whereby paths of successive recesses
partially overlap. Cylindrical cutting discs are mounted
in the recesses, each disc having an end face providing a
cutting edge disposed about the periphery of the end face
and being rotatably indexable about its longitudinal axis
to bring successive portions into cutting position.
The arcuate face 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 helical path normally
defines an angle of about 5 to 95 with respect to the
longitudinal axis of the body and a typical tool has a
helical angle in the order of about 15 to 45.
The helical paths are of increasing diameter in
a rearward direction so as to produce a progressively
larger hole as the broach is moved through the workpiece
or the workpiece over the broach. This diameter difference
is normally quite small and may typically be in the order
of 0.004 ~nch between rows.
The angle of the cutter discs with respect to
- the longitudinal axis of the body can be varied within the
range of about 1-15. By setting the series of small
round cutting discs at a small angle with respect to the
longitudinal axis of the body, the cutting edges of the
-- 4 --
108Z497
cutter discs thereby 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 staggering arrangement of cutters in successive
rows,results in the depth of grooves formed in the finished
surface being very small. Normally, the discs are
arranged to broach a hole having a radius at least three
times the radius of the individual cutter discs.
Certain preferred embodiments of the present
invention will now be illustrated by the attached drawings
in which:
Figure 1 is a side elevation of one embodiment
of the novel broaching tool;
Figure 2 is a top plan view of the broaching
tool shown in Figure l;
Figure 3 is a cross section through row 1 of
the tool of Figure l;
Figure 4 is a cross section through row 2 of
the tool of Figure l; and
Figure 5 is an exploded detailed view of a
cutting disc and socket.
The particular broach illustrated in the
- drawings is known as a half-round broach. It has an
elongated tool holder body portion 20 having a bottom
-- spline 21 extending along the length thereof for retaining
the tool in a tool holder. The tool is held rigidly in
place in the holder by the mounting screws 22.
At the lower edges of the cylindrical surface
are provided a series of pockets 23 and these serve as
;, 30 interlocks with adjacent flat broaches which may be used
1, in conjunction with the half-round broach.
_ 5 _
-.
108~497
A series of cutter discs 24 are mounted in
sockets 25 in the cylindrical surface. Each of these
sockets has a flat bottom face 26 which is inclined at a
small angle of typically about 11 to the longitudinal
axis of the body portion 20 and the socket also has a
semi-circular abutment wall 27 which is perpendicular
to the bottom face 26. Extending into the body portion
20 through face 26 is a tapped h~le 32.
Each cutting disc 24 has a cylindrical wall
29 and end faces 28. A hole 31 is formed axially through
the insert with a conical countersink 30. The cutting
disc is typically made from tungsten carbide. It is held
in position by means of a threaded screw 33 which has a
conical head portion which mates with the countersink and
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 the screws themselves.
With this arrangement, it will be seen that only
about one-quarter of the cutting edge of the cutter discs
is in use at one time. This means that as the portion
~ in use becomes dulled, the screws 33 can be loosened and
the cutter discs can then be rotated sufficiently to present
fresh cutting edge portions, after which the screws are
again tightened. The result is that as many as four
cutting edge portions may be available on one face of a
cutter disc. Furthermore, it is possible to make the
discs reversible so that another four cutting edge portions
-- 6 --
108'~497
may be available on the reverse face. In this way as many
as eight fresh cutting edge portions may be obtainable
from a single cutting disc.
A typical cutter disc may have a diameter in
the range of about 3/8 inch to about 1 inch and these are
used in cutting holes having a diameter of at least 1
inch.
In Figure 1 eight helical rows of cutting discs
are shown and these are indicated as rows one to eight.
1~) 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 axes of the cutting inserts of row 2 are positioned
midway between the axes 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 re
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.
One of the advantages of this helical con-
figuration is that specific chip gaps are not necessary
since the spacing between cutting discs in the helical
configuration is increased thereby permitting easier
7 --
108;~497
flow of chips between cutters. The second and most im-
portant advantage of the helical configuration is that
during operation some of the discs will always be under
load. This overcomes any tendency of impact as successive
rows of cutting discs come into engagement with the work-
piece. This feature will be evident from Figures 1 and 2
so that each cuttinq disc of each row comes into engage-
ment with the workpiece successively and during engagement
with the last cutting disc of one row, the workpiece is
already coming into engagement with the first cutting
disc of the next row. This greatly decreases the
tendency of damage to the broach as well as possible
breakage of the workpiece being broached from impact.
While the above preferred embodiment illustrates
a screw connection for mounting the cutting inserts in
the sockets, it will be readily apparent to those skilled
in the art that many other kinds of mounting means are
possible. Thus, wedging pins, etc. can be used.
It will also be apparent to those skilled in
the art that although a half-round broach is illustrated,
, similar types of broaches forming arcs of less than a
semi-circle or as much as a full circle are within the
scope of the present invention.
-- 8 --
