Note: Descriptions are shown in the official language in which they were submitted.
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MILLING CUTTING INSERT
The present invention relates to a milling cutting
insert of a preferably square basic shape, with depressed
parallel lands, which cutting insert is suited for the
milling of right-angled corners. Usually, such inserts are
made of coated or uncoated cemented carbide, but
occasionally also certain ceramic materials may be used.
Often cutting tools with indexable cutting inserts
for the milling of right-angled corners in a workpiece have
had cutting inserts of a rhombic or triangular shape. They
have only two or three cutting edges but for a long time
they were considered to be the only ones which make it
possible to cut right-angular corners with sufficient side
clearance. When a conventional right-angled indexable
cutting insert is used for milling or turning of an internal
side surface, it cannot be positioned with a radial or axial
angle without its lower inner corner trailing on the
generated surface. Hence, when cutting an inner 90° shoulder
it has been common practice to use either an insert with an
acute angle between the main cutting edge and the secondary
cutting edge or the parallel land, respectively, or also
right-angled cutting inserts inserted into the tool body
with a negative radial angle and a positive axial angle.
In US-A-4 632 607 an indexable cutting insert is
disclosed with a square basic shape for the milling of
right-angled corners, which insert comprises four main
cutting edges, thus realizing a substantially improved
cutting economy. This is achieved by the fact that each main
cutting edge has an appurtenant secondary cutting edge which
is arranged outside the square basic shape upon a
protrusion that sticks out in a direction mainly parallel
to the appurtenant main cutting edge. This cutting
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insert works satisfactorily at a total cutting depth less
than the length of the main cutting edge. However, if one
intends to arrive at a total cutting depth that exceeds the
length of the main cutting edge by performing several runs,
then a protrusion will cause an undesired groove in the
workpiece.
In US-A-5 199 827 a further indexable cutting
insert for milling is disclosed having a square basic shape.
The insert is intended to be inclined axially positively and
radially negatively in the milling cutter body. Sufficient
axial clearance is obtained by inclining the insert radially
negatively. Each flank surface is shaped with a planar relief
surface, whose width increases in a direction towards one of
the corners of the insert. Sufficient radial clearance
between the parallel land and the main cutting edge is
intended to be obtained by the angle between the parallel
land and the adjacent main cutting edge of about 0 to 2°.
However, since the relatively short parallel land has to
support considerable stress, it may become worn, whereby also
the main cutting edge comes into contact with the generated
surface on the workpiece, resulting in decreased surface
smoothness, increased heat production and increased cutting
forces.
Thus, a primary object of the present invention
is to provide a milling cutting insert with an improved
clearance axially.
Another object of the present invention is to
design a milling cutting insert which removes the
inconvenience connected with the cutting insert as
disclosed in US-A-4 632 607.
These and further objects have been achieved
in a surprising way by shaping a milling cutting insert
with the features set out hereafter.
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For illustrative but non-limiting purposes, the invention
will now be further described under reference to the appended
drawings. These are herewith presented:
Figure 1 shows a plan view of milling cutting
insert.
Figure 1A shows an amplification of a corner
section of the cutting insert of fig 1.
Figure 2 shows a vertical section of the cutting
insert according to fig 1.
Figure 3 shows the cross-section A-A in fig 1.
Figure 4 illustrates the functional positioning of
the cutting insert relative to a workpiece.
Figure 5 illustrates the functional positioning
of a cutting insert according to the invention.
Figure 5A shows an amplification of a corner
section of the cutting insert according to fig 5.
Figure 6 shows a modified embodiment of an insert
corner, seen obliquely from underneath.
Figure 7 shows a modified corner portion straight
from above, in the same way as in fig lA.
Figure 8 shows the modified corner portion
according to fig 6, straight from above, as in fig 6.
Figure 9 shows a modified corner portion straight
from above, in the same way as in fig IA.
Figure 10 shows a perspective view obliquely from
above of another embodiment of the invention.
Figure 11 shows another perspective view of the
cutting insert according to fig 10.
A cutting insert according to the invention is generally
designated by reference numeral 1. Generally, it has an upper side 2
and a substantially planar lower side 3. According to the
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illustrated embodiment, said upper and lower sides are
connected by four side surfaces 4 of substantially the same
size and shape, since the cutting insert preferentially has a
square basic shape. However, it may also have another basic
shape, e.g., rectangular or triangular. The square basic
shape is preferred since it is the only one that makes
possible four operative main cutting edges, which of course
is the most advantageous for the cutting economy.
The upper surface 2 and the side surfaces 4 meet
along break lines which form main cutting edges 5. At the
corner, this main cutting edge transposes into a corner
cutting edge 6, which usually is rounded, but which also may
comprise one or several substantially straight chamfers. On
the upper side a primary land 7 adjoins to the main cutting
edge and the corner cutting edge. To this primary land are
adjoined chip surfaces 8 and 9, respectively. The transition
between chip surfaces 8 and 9 in an insert corner takes place
via an inclined transposition surface 10. Since the corner end
of chip surface 8 is situated higher than the corner chip
surface 9, the transposition surface 10 inclines from chip
surface 9 upwardly towards chip surface 8. The chip surfaces
8 and 9 and the transposition surfaces 10 are inwardly
delimited by a substantially planar part upper surface 11,
which is substantially parallel with bottom surface 3. In the
middle of part upper surface 11 is provided a through center
aperture 21 for introducing a suitable fastening device, such
as a locking screw, a clamp, a locking pin, etc.
The cutting insert has a positive geometry, i.e., the
flank surfaces 4 are arranged in planes that form an obtuse
angle to the plane of the bottom surface 3 and an acute angle to
the upper plane that is defined by the main cutting edges 5.
Preferably, the parts of the flank surfaces 4 adjacent to the main
cutting edges are shaped as planar or helically twisted primary
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relief surfaces 12, which at their lower limits join the secondary
relief surfaces 13 via a break line. However, alternatively, the
primary relief surface 12 may be disposed of, the relief surface
~ 13 coinciding with flank surface 4. Corresponding primary and
5 secondary relief surfaces 14 and 15, respectively, are provided
below the corner cutting edge 6.
The essential feature of the present invention is the
configuration of the parallel land or parallel land cutting edge,
which is the cutting edge of the cutting insert that generates the
surface. In the figures, this cutting edge is designated by 16,
16A, 16' or 16" and is depressed in relation to the main cutting
edge and possibly also to the corner cutting edge, the latter
being shown in for instance fig 2 and 6. Vertically, this level
difference may be between 0,05 and 0,5 mm, preferably between 0,1
and 0,4 mm. The parallel land cutting edge is provided upon a
projection 17 protruding from the center of the cutting insert,
which projection continues into the secondary relief surface 19,
preferably via a break line 18 or a radius surface. This relief
surface 19 is either planar or slightly curved and is delimited
towards the secondary relief surfaces 4 and 15 by break lines 20
or smooth radius transitions. Alternatively, the relief surface 19
may lie in the same plane as the secondary relief surface 13, in
which case the break line 20 between these is dropped.
Equally to the other relief, surfaces, the secondary
relief surface 19 below the parallel land is positive and has an
~ angle oc to the extension of the bottom surface. Suitably, this
angle is between 50 and 80°, preferably between 60 and 77°. The
angle i3 of the projection 17 to the bottom surface may be equally
large as oc, whereby the relief surface of the projection coincides
with the relief surface 19, or preferably somewhat smaller,
suitably between 50 and 75° and preferably between 53 and 7_0°,
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provided that f~ ~ a. The difference between a and f3 can suitably
be between 4 and 20°, preferably between 6 and 15°.
The parallel land cutting edge 16 is the break line along
the upper front edge of projection 17. According to fig 1 to 9, ~
this front edge is depressed relative to the main cutting edge and
the corner cutting edge by a depression or a depressed recess 22.
Like the rest of the cutting insert, this recess is preferably
pressed before the sintering, but it can also be ground. Suitably,
the recess can have a cross-section with the shape of a rectangle,
a circle segment, a frustrum of a circle segment, or a trapezoid.
As may be most clearly seen in the cross-section A-A in
fig 3, the recess 22 may be negatively angled relative to the
bottom surface 3. However, the inclination of the recess may be
varied within relatively wide limits, for instance between +20 and
-20°, preferably between +5 and -10°.
By the depressed and protruding position of the parallel
land relative to the other operative cutting edges, a number of
hitherto unattained advantages have been achieved, as may be best
seen in fig 4. By positioning the milling cutting insert
functionally in the milling cutter body, so that it assumes a
positive axial inclination, the lower, surface-generating
parallel land cutting edge 16A is tipped forwards. For instance,
if there is a level difference of about 0,2 mm between the main
cutting edge and the wiper edge, a tipping forwards of the wiper
edge 16A can be effected by a positive axial inclination, so that
it protrudes by about a further 0,07 mm in comparison with the
cutting insert disclosed in US-A-5 199 827. This contributes to
further clearance between the generated surface and the main
cutting edge 5A, which may be seen in the wedge-shaped play in fig
4 between said cutting edge 5A and the workpiece 25.
Correspondingly, the parallel land cutting edge 16B can be tipped
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inwards by a negative radial inclination of the cutting insert, so
that this parallel land cutting edge does not come into contact
with the vertical surface of the workpiece, thereby not causing
any groove in the latter. Contrary to this, the main cutting edge
5B is in engagement along its whole length, this also being the
purpose.
Within the framework of the invention, the parallel land
cutting edge 16 can have a plurality of embodiments. Thus, it can
be substantially straight and have a radius continuation 23 to the
corner cutting edge 6, as may be seen in fig 6 and 8, the radius
continuation being formed as a depressed curve. Further, the
parallel land cutting edge can be straight and have a
substantially straight chamfer continuation 24 to the corner
radius, in accordance with fig 7. Furthermore, the parallel land
cutting edge may be slightly curved or rounded, as illustrated by
the cutting edge 16' in fig 9.
Moreover, the parallel land cutting edge can be shaped
according to fig 10 and 11. Equally to the embodiments according
to fig 1 to 8, there is first a relatively sharp transition 26
between the main cutting edge 5 and the parallel land 16".
However, contrary to the previously described embodiments, there
is a stepless and continuous transition to the corner cutting edge
6", which is also depressed in comparison with the main cutting
edges 5. From a lowermost point adjacent to the parallel land
cutting edge 16", the corner cutting edge 6" rises in a direction
towards the next main cutting edge. Also a portion of this main
cutting edge 5 slopes somewhat, namely the portion 5". Thus, the
upward slope vertically starts at the parallel land cutting edge
16", then it goes continuously and substantially uniformly along
the corner cutting edge 6" and does not terminate till the
transition between cutting edges 5" and 5. Suitably, the cutting
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edge portion 5" is ~3 mm. The parallel land cutting edge is
suitably ~ 2 mm.
By this construction with a depressed corner cutting
edge, the cutting insert has become even more easy-cutting (lower
cutting forces), it generates very smooth surfaces and does not
cause any creation of grains. Further, the corner cutting edge has
obtained between 1 and 2° larger clearance in comparison with the
embodiments according to fig 1 to 9.
