Indian Patents
Title of Invention

A MILLING CUTTER
Abstract The invention relates to a milling cutter assembly (20) comprising a cutting insert holder (22), a cutting insert (24) and a clamping screw (26), the cutting insert holder (22) comprising a clamping portion (30) connected to a body portion (28);the clamping portion (30) comprising: a lower clamping jaw (34) having a lower peripheral surface (46) and an upper clamping surface (50); an upper clamping jaw (32) resiliently connected to the lower clamping jaw (34), the upper clamping jaw (42) having a lower clamping surface (42) and an upper peripheral surface (38); a through bore (44) passing through the upper and lower clamping jaws, the through bore being threaded in one of the upper or lower clamping jaws; an insert receiving slot (36) defined between the upper and lower clamping surfaces (50,42); the cutting insert (24) comprising: an insert upper clamping surface (64) bounded by an upper edge (70) an insert lower clamping surface (66) bounded by a lower edge (72); a peripheral side surface (68) between the insert upper clamping surface (64) and the insert lower clamping surface (60); at least one cutting edge associated with the peripheral side surface; at least one through hole (118) passing through the cutting insert (24) between the insert upper and lower clamping surfaces; wherein: in a front view of the cutting tool assembly, the upper the lower clamping surfaces (50,42) of the lower and upper clamping jaws (34,32), respectively, are partially convex, and the insert lower and upper clamping surfaces (66,64) are concave; the cutting insert (24) is retained in the insert receiving slot (36) in a retained position by means of the clamping screw (26) which passes through the through bore (44) in the upper and lower clamping jaws of the cutting insert holder and through the at least one through hole (118) in the cutting insert (24) and is screwed into the threaded through bore in one of the upper or lower clamping jaws; the lower clamping surface (42) of the upper clamping jaw (32) engages the insert upper clamping surface (64) at at least one upper region of contact and the upper clamping surface (50) of the lower clamping jaw (34) engages the insert lower surface (66) at at least one lower region of contact; characterized in that: the inert upper clamping surface (64) conforms with a first cylindrical surface having a first radius of curvature, r1, and a first cylinder axis; the insert lower clamping surface (66) conforms with a second cylindrical surface having a second radius of curvature,r2, and a second cylinder axis; the upper clamping surface (50) of the lower clamping jaw (34) partially conforms with a third cylindrical surface having a third radius of curvature, R2, and a third cylindrical axis; the lower clamping surface (42) of the upper clamping jaw (32) partially conforms with a fourth cylindrical surface having a fourth radius of curvature, R1 and a fourth cylinder axis; the fourth radius of curvature, R1, is greater than the first radius of curvature, r1, the third radius of curvature, R2, is greater than the second radius of curvature, r2.
Full Text FIELD OF THE INVENTION
This invention relates generally to milling cutters and more
particularly to a ball nose end mill having a single replaceable cutting insert
retained between clamping jaws, for use in high precision milling operations.
BACKGROUND OF THE INVENTION
Milling cutters are commonly used for profile and cavity milling in
the auto, aircraft, die and mold industries. In order to achieve high accuracy
and good surface quality in the work products produced by the milling cutters
to which the present invention relates, the cutting insert should be retained in
the milling cutter with a high degree of locational precision.
A problem with prior art. milling cutters utilizing replaceable
cutting inserts is that the latter are either flat plate-like or generally prismatic
in shape and are clamped between two clamping jaws having clamping
surfaces with geometries complementary to those of the surfaces of the
cutting insert being clamped, i.e., flat or prismatic, respectively. The cutting
insert is secured in position by means of a clamping screw that passes through
through bores in the clamping jaws and in the cutting insert. Due to
manufacturing tolerances it is difficult to ensure that the cutting insert is on a
true centerline when retained in the milling cutter. Such manufacturing
tolerances include, for example, the diameter of the clamping screw, the
diameter of the through bores and the location of the through bores. That is.
for cutting tools such as end mills having a single replaceable cutting insert
retained between clamping jaws the radial location of two diametrically
opposite cutting edges of the cutting insert can be ascertained only to within
the total manufacturing tolerances. This being the case, the points on the
cutting edges of the cutting insert will not necessarily lie precisely on a flight
circle concentric with the axis of rotation of the milling cutter. For milling
cutters having flat plate-like cutting inserts, manufacturing tolerances of the
clamping screw and the through bore in the milling cutter and in the cutting
insert are the main contributing factors to the radial location imprecision of
the cutting insert. The radial location precision can be improved by using
inserts that have generally prismatic abutting surfaces clamped in clamping
jaws having complementary shaped clamping surfaces. However, even in this
case radial location imprecision of the cutting insert will exist The main
contribution to the radial location imprecision coming from geometrical
factors such as the tolerance of manufacture of the angle between adjacent
surfaces comprising the prismatic abutting surfaces.
In EP 0 417 862 B1 a cutting tool assembly is described which I
ensures effective clamping of a cutting insert in an insert holder so that the
cutting insert is effectively retained against displacement under cutting forces,
and so that the relative position of the cutting insert with respect to the cutting
insert holder is maintained substantially invariant, both during cutting
operations and also when inserts have to be replaced. In the embodiment
shown in Fig. 3 of '862, effective retention of the cutting insert is obtained
between ribs of the clamping jaws of the cutting insert holder and the cutting
insert along discrete axially directed locations which are symmetrically
disposed with respect to, and spaced from, a longitudinally directed median
plane. In the embodiment shown in Fig. 4 of '862, instead of effective
retention along discrete axially directed locations, the retention is along
narrow axially directed intennediate curved portions.
In both the embodiments described in '862 the ribs of the
clamping jaws are formed with a clamping surface of substantially circular
cross-sectional shape and the clamping contact between the clamping surfaces
of the clamping jaws and the cutting insert is designed to take place along
predetermined axial locations by forming the clamping surfaces of the cutting
insert with side curved portions having a larger radius of curvature than that
of the clamping surface of the clamping jaw and a central curved portion have
a smaller radius of curvature than that of the clamping surface of the
clamping jaw.
It should be noted that in both embodiments described in EP '862
the clamping surfaces of the cutting insert are of a non-uniform cross section
and that in both embodiments the side portions of the clamping surfaces of
the cutting inserts do not abut the clamping surfaces of the clamping jaws. A
disadvantage of such a clamping arrangement is that it cannot be applied to
cutting tool assemblies such as end mills comprising a single replaceable
cutting insert retained between a pair of clamping jaws. The cutting inserts of
such cutting tool assemblies have a width, measured between the side cutting
edges, which is much greater than their thickness, measured between the
clamping surfaces of the cutting insert, and the clamping arrangement
described in EP '862 would not provide adequate support for the side cutting
edges of the cutting insert-
It is therefore an object of the present invention to overcome the
aforementioned disadvantage and to provide a milling cutter that will ensure
accurate radial location of replaceable cutting inserts when clamped in the
milling cutter whilst providing adequate support for the side cutting edges of
the cutting insert.
It is a further object of the present invention to provide an
indexable cutting insert for such a milling cutter.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a
cutting tool assembly (20) comprising a cutting insert holder (22), a cutting
insert (24) and a clamping screw (26), the cutting insert holder (22)
comprising a clamping portion (30) connected to a body portion (28);
the clamping portion (30) comprising:
a lower clamping jaw (34) having a lower peripheral surface (46) and
an upper clamping surface (SO);
an upper clamping jaw (32) resiliently connected to the lower
clamping jaw (34), the upper clamping jaw (32) having a lower clamping
surface (42) and an upper peripheral surface (38);
a through bore (44) passing through the upper and lower clamping
jaws, the through bore being threaded in one of the upper or lower clamping
jaws;
an insert receiving slot (36) defined between the upper and lower
clamping surfaces (50,42);
the cutting insert (24) comprising:
an insert upper clamping surface (64) bounded by an upper edge (70);
an insert lower clamping surface (66) bounded by a lower edge (72);
a peripheral side surface (68) between the insert upper clamping
surface (64) and the insert lower clamping surface (60);
at least one cutting edge associated with the peripheral side surface;
at least one through hole (118) passing through the cutting insert (24)
between the insert upper and lower clamping surfaces;
wherein:
the insert upper clamping surface (64) conforms with a portion of a
first cylindrical surface having a first radius of curvature, r1, and a first
cylinder axis;
the insert lower clamping surface (66) conforms with a portion of a
second cylindrical surface having a second radius of curvature, r2. and a
second cylinder axis;
the upper clamping surface (50) of the lower clamping jaw (34) at
least partially conforms with a portion of a third cylindrical surface having a
third radius of curvature, RZ and a third cylinder axis;
the lower clamping surface (42) of the upper clamping jaw (32) at
least partially conforms with a portion of a fourth cylindrical surface having
a fourth radius of curvature, R1, and a fourth cylinder axis;
in a front view of the cutting tool assembly, the upper and lower
clamping surfaces (50, 42) of the lower and upper clamping jaws (34, 32),
respectively, are at least partially convex, and the insert lower and upper
clamping surfaces (66, 64) are concave;
the cutting insert (24) is retained in the insert receiving slot (36) in a
retained position by means of the clamping screw (26) which passes through
the through bore (44) in the upper and lower clamping jaws of the cutting
insert holder and through the at least one through hole (118) in the cutting
insert (24) and is screwed into the threaded through bore in one of the upper
or lower clamping jaws;
the lower clamping surface (42) of the upper clamping jaw (32)
engages the insert upper clamping surface (64) at at least one upper region
of contact (64') and the upper clamping surface (50) of the lower clamping
jaw (34) engages the insert lower surface (66) at at least one lower region of
contact (66');
characterized in that:
the at least one upper region of contact comprises at least two outer
regions (64') of the insert upper clamping surface (64) and the at least one
lower region of contact comprises at least two outer regions (66') of the
insert lower clamping surface (66).
Preferably, the cutting insert holder (22) has an axis of rotation
(A) and the cutting insert (24) has a longitudinal axis of rotational symmetry
(B) and a center (128) through which the longitudinal axis of rotational
symmetry (B) passes, the longitudinal axis of rotational symmetry (B)
constituting an axis of rotation of the cutting insert about which the cutting
insert has 180° rotational symmetry.
In accordance with a specific application, the first radius of
curvature and the second radius of curvature are equal in magnitude, r1=r2,
defining a radius of curvature, r, of the cutting insert clamping surfaces, and
the third radius of curvature and the fourth radius of curvature are equal in
magnitude, R1=R2, defining a radius of curvature, R, of the clamping jaws'
clamping surfaces.
In accordance with the present invention, the radius of curvature,
R, of the clamping jaws' clamping surfaces is greater than the radius of
curvature, r, of the cutting insert clamping surfaces.
In accordance with one specific application, r=16 mm and R =
16.2 mm.
In accordance with the present invention, the cutting insert has a
width, W, which is greater than a thickness, T, where the width and
thickness are measured in a front view of the cutting insert as, respectively,
the distance between opposing portions of the peripheral side surface, and a
maximum distance between the insert upper and lower clamping surfaces.
Generally, W/T lies in the range 2.5 to 4.0.
In accordance with a specific application, W/T is equal to 3.3.
Further in accordance with the present invention, the cutting
insert has a width, W, which is greater than a thickness, t, where the width
and thickness are measured in a front view of the cutting insert as,
respectively, the distance between opposing portions of the peripheral side
surface, and a minimum distance between the insert upper and lower
clamping surfaces.
Generally, W/t lies in the range 4.0 to 6.0.
In accordance with a specific application, W/t is equal to 5.3.
Yet further in accordance with a specific application the radius of
curvature, r, of the cutting insert clamping surfaces is approximately equal
to W, and the radius of curvature, R, of the clamping jaw's clamping
surfaces is approximately equal to W,
Generally, the insert receiving slot (36) has a forward end (36')
for receiving a cutting insert and a rear end (36") at which the upper
clamping jaw is resiliency connected to the lower clamping jaw.
Preferably, the rear end (36") of the insert receiving slot (36) is
provided with at least one insert axial location surface (56, 58) transverse to
the axis of rotation (A) of the cutting insert holder (22).
Still further preferably, the rear end (36") of the insert receiving
slot (36) is provided with at least one generally cylindrical groove (60, 62)
transverse to the axis of rotation (A) of the cutting insert holder (22) and
adjacent the at least one insert axial location surface (56, 58).
Still yet further preferably, the cutting insert (24) has two end
portions (24', 24") adjacent the axis of rotation (B) of the cutting insert (24),
at least one of the two end portions (24', 24") being provided with axial
abutment surfaces (88a, 88b, 90a, 90b) transverse to the axis of rotation (B) of
the cutting insert (24).
Preferably, the axial abutment surfaces (88a, 88b, 90a, 90b) are
ground.
In accordance with a first specific application, the at least one
through hole (118) in the cutting insert (100) is implemented as a circular
bore (102) having a bore axis (104) located substantially at the center of the
cutting insert in a top view of the cutting insert, the bore axis being
perpendicular to the axis of rotation (B) of the cutting insert.
In accordance with a second specific application, the at least one
through hole (118) in the cutting insert (106) is implemented as two circular
bores (108, 110), each circular bore having a bore axis (112, 114) and a bore
diameter (D1, D2), the bore diameter of each circular bore being substantially
equal in magnitude (D1=D2=D), each bore axis being located at substantially
the same distance (X1=X2=X) from the center (116) of the cutting insert
(106) in a top view of the cutting insert, the bore axes being perpendicular to
the axis of rotation (B) of the cutting insert (106) and the distance (2X)
between the two bore axes (112, 114) being greater than the bore diameter
(D).
In accordance with a third specific application of the present
invention, the at least one through hole (118) is implemented by two
intersecting circular bores (120, 122), each circular bore having a bore axis
(124, 126) and a bore diameter (D1, D2), the bore diameter of each circular
bore being substantially equal in magnitude (D1=D2=D). each bore axis
being located at substantially the same distance from the center (128) of the
cutting insert (24) in a top view of the cutting insert, each bore axis being
perpendicular to the axis of rotation (B) of the cutting insert and the distance
(Y) between the two bore axes being less man the bore diameter (D).
In accordance with the second specific application of the present
invention, the cutting insert (106) is retained in the insert receiving slot (36)
in a retained position by means of a clamping screw (26) which passes
through the through bore in the upper and lower clamping jaws of the
cutting insert holder and through the circular bore in the cutting insert
closest the forward end (36') of the insert receiving slot (36) and is screwed
into the threaded through bore (52) in one of the upper or lower clamping
jaws.
In accordance with the third specific application of the present
invention, the cutting insert (24) is retained in the insert receiving slot (36)
in a retained position by means of a clamping screw (26) which passes
through the through bore in the upper and lower clamping jaws of the
cutting insert holder and through the circular bore (120) in the cutting insert
(24) closest the forward end (36') of the insert receiving slot (36) and is
screwed into the threaded through bore (52) in one of the upper or lower
clamping jaws.
In accordance with a specific application of the invention, the
peripheral side surface (68) of the cutting insert (24, 100, 106) is provided
with two diametrically opposite pairs of cutting edges (74a, 74b; 76a, 76b)
so that when the cutting insert is retained in the insert receiving slot, one
pair of cutting edges (74a, 74b) is located closer to the forward end (36') of
the insert receiving slot (36) and constitutes a pair of operative cutting edges
and the other pair of cutting edges (76a, 76b) is located closer to the rear
end (36") of the insert receiving slot and constitutes a pair of inoperative
cutting edges.
Preferably, the peripheral side surface is provided with two
diametrically opposite notches (78', 78") which are located on a first
transverse axis of rotational symmetry (T1) and which separate between the
diametrically opposite sets of cutting edges (74a, 74b; 76a, 76b), the first
transverse axis of rotational symmetry (T1) passing through the peripheral
side surface (68) and perpendicular to the longitudinal axis of rotational
symmetry (B), the cutting insert having 180° rotational symmetry about the
first transverse axis of rotational symmetry (T1).
Typically, each pair of cutting edges (74a, 74b; 76a, 76b)
comprises one cutting edge (74b; 76b) which extends from a region close to
where the longitudinal axis of rotational symmetry (B) passes through the
peripheral side surface (68) upwards towards a notch whilst the other
cutting edge (74a; 76a) extends from the same region close to where the
longitudinal axis of rotational symmetry passes through the peripheral side
surface downwards towards the diametrically opposite notch.
Generally, each cutting edge is provided with a relief surface
(80) and a rake surface (82).
There is further provided in accordance with the present
invention, a cutting insert (24) having a longitudinal axis of rotation (B) and
a center (128) through which the longitudinal axis (B) passes, the
longitudinal axis (B) constituting an axis of rotation of the cutting insert, the
cutting insert (24) comprising:
an insert upper clamping surface (64) bounded by an upper edge (70);
an insert lower clamping surface (66) bounded by a lower edge (72);
a peripheral side surface (68) between the insert upper clamping
surface (64) and the insert lower clamping surface (60);
at least one cutting edge associated with the peripheral side surface;
at least one through hole (118) passing through the cutting insert (24)
between the insert upper and lower clamping surfaces;
wherein:
the insert upper clamping surface (64) conforms with a portion of a
first cylindrical surface having a first radius of curvature, r1, and a first
cylinder axis;
the insert lower clamping surface (66) conforms with a portion of a
second cylindrical surface having a second radius of curvature, r2, and a
second cylinder axis.
In accordance with a specific application, the first radius of
curvature and the second radius of curvature are equal in magnitude, r1=r2,
defining a radius of curvature, r, of the cutting insert clamping surfaces.
Further in accordance with a specific application, longitudinal
axis (B) constitutes an axis of rotational symmetry of the cutting insert
about which the cutting insert has 180° rotational symmetry.
In accordance with the present invention, the cutting insert has a
width, W, which is greater than a thickness, T, where the width and
thickness are measured in a front view of the cutting insert as, respectively,
the distance between opposing portions of the peripheral side surface, and a
maximum distance between the insert upper and lower clamping surfaces.
Generally, W/T lies in the range 2.5 to 4.0.
In accordance with a specific application W/T is equal to 3.3.
Further in accordance with the present invention, the cutting
insert has a width, W, which is greater than a thickness, t. where the width
and thickness are measured in an end view of the cutting insert as,
respectively, the distance between opposing portions of the peripheral side
surface, and a minimum distance between the insert upper and lower
clamping surfaces.
Generally, W/t lies in the range 4.0 to 6.0.
In accordance with a specific application, W/t is equal to 5.3.
Still yet further preferably, the cutting insert (24) has two end
portions (24', 24") adjacent the axis of rotation (B) of the cutting insert (24),
at least one of the two end portions (24', 24") being provided with axial
abutment surfaces (88a. 88b, 90a, 90b) transverse to the axis of rotation (B) of
the cutting insert (24).
Preferably, the axial abutment surfaces (88a, 88b, 90a, 90b) are
ground.
In accordance with a first specific application, the at least one
through hole (118) in the cutting insert (100) is implemented as a circular
bore (102) having a bore axis (104) located substantially at the center of the
cutting insert in a top view of the cutting insert, the bore axis being
perpendicular to the axis of rotation (B) of the cutting insert.
In accordance with a second specific application, the at least one
through hole (118) in the cutting insert (106) is implemented as two circular
bores (108, 110), each circular bore having a bore axis (112, 114) and a bore
diameter (D1, D2), the bore diameter of each circular bore being substantially
equal in magnitude (D1=D2=D), each bore axis being located at substantially
the same distance (X1=X2=X) from the center (116) of the cutting insert
(106) in a top view of the cutting insert, the bore axes being perpendicular to
the axis of rotation (B) of the cutting insert (106) and the distance (2X)
between the two bore axes (112, 114) being greater than the bore diameter
(D).
In accordance with a third specific application of the present
invention, the at least one through hole (118) is implemented by two
intersecting circular bores (120, 122), each circular bore having a bore axis
(124, 126) and a bore diameter (D1, D2), the bore diameter of each circular
bore being substantially equal in magnitude (D1=D2=D), each bore axis
being located at substantially the same distance from the center (128) of the
cutting insert (24) in a top view of the cutting insert, the bore axes being
perpendicular to the axis of rotation (B) of the cutting insert and the distance
(Y) between the two bore axes being less than the bore diameter (D).
There is yet further provided in accordance with the present
invention, a cutting insert holder (22) having an axis of rotation A and
comprising a clamping portion (30) connected to a body portion (28);
the clamping portion (30) comprising:
a lower clamping jaw (34) having a lower peripheral surface (46) and
an upper clamping surface (50);
an upper clamping jaw (32) resiliency connected to the lower
clamping jaw (34), the upper clamping jaw (32) having a lower clamping
surface (42) and an upper peripheral surface (38);
a through bore (44) passing through the upper and lower clamping
jaws, the through bore being threaded in one of the upper or lower clamping
jaws; and
an insert receiving slot (36) defined between the upper and lower
clamping surfaces (50, 42);
wherein:
the upper clamping surface (50) of the lower clamping jaw (34) at
least partially conforms with a portion of a third cylindrical surface having a
third radius of curvature, R2, and a third cylinder axis;
the lower clamping surface (42) of the upper clamping jaw (32) at
least partially conforms with a portion of a fourth cylindrical surface having
a fourth radius of curvature, R1, and a fourth cylinder axis; and
in a from view of the cutting tool assembly, the upper and lower
clamping surfaces (50, 42) of the lower and upper clamping jaws (34. 32),
respectively, are at least partially convex.
In accordance with a specific application, the third radius of
curvature and the fourth radius of curvature are equal in magnitude. R1=R2.
defining a radius of curvature, R, of the clamping jaws' clamping surfaces.
Generally, the insert receiving slot (36) has a forward end (36')
for receiving a cutting insert and a rear end (36") at which the upper
clamping jaw is resiliently connected to the lower clamping jaw.
Preferably, the rear end (36") of the insert receiving slot (36) is
provided with at least one insert axial location surface (56, 58) transverse to
the axis of rotation (A) of the cutting insert holder (22).
Still further preferably, the rear end (36") of the insert receiving
slot (36) is provided with at least one generally cylindrical groove (60, 62)
transverse to the axis of rotation (A) of the cutting insert holder (22) and
adjacent the at least one insert axial location surface (56,58).
In accordance with one embodiment, the lower clamping surface
(42) of the upper clamping jaw (32) is divided into three regions, two
substantially identical outer regions (42') having a first radius of curvature
and a central region (42") having a second radius of curvature and the
upper clamping surface (50) of the lower clamping jaw (34) is divided into
three regions, two substantially identical outer regions (50') having a first
radius of curvature and a central region (50") having a second radius of
curvature.
Preferably, the second radius of curvature is larger than the first
radius of curvature.
There is still yet further provided in accordance with the present
invention, a clamping screw (26) having a screw axis C and comprising:
an upper portion (140);
a central portion (142); and
a lower portion (144);
the upper portion (140) comprises an upper cylindrical portion (146) and an
upper frusto-conical portion (148), the upper frusto-conical portion (148)
tapers downwardly and inwardly from the upper cylindrical portion (146)
towards the central portion (142), the clamping screw upper portion (140) is
provided with a socket (149), for receiving a wrench for tightening or
loosening the clamping screw (26), the clamping screw central portion (142)
has a central cylindrical portion (150) connected at its upper end to the upper
frusto-conical portion (148) and at its lower end to a central frusto-conical
portion (152), the central frusto-conical portion (152) tapers downwardly and
inwardly from the upper end thereof to the lower end thereof, at the lower
end thereof the central frusto-conical portion (152) is connected, via a narrow
neck portion (154), to the clamping screw lower portion (144), the clamping
screw lower portion (144) comprises a threaded portion (156) of the clamping
screw (26), the central frusto-conical portion (152) tapers at an angle 9 to the
BRIEF DESCRIPTION OF THR DRAWINGS
For a better understanding the invention will now be described, by
way of example only, with reference to the accompanying drawings in which:
Fig. 1 is a perspective view of a cutting tool assembly according to the
present invention;
Fig. 2 is an exploded view of the cutting tool assembly of Fig. 1;
Fig. 3a is a bottom perspective view of the cutting insert holder shown
in Fig. 2 with the lower clamping jaw removed for the purpose of
clarification;
Fig. 3b is a top perspective view of the cutting insert holder shown in
Fig. 2 with the upper clamping jaw removed for the purpose of clarification;
Fig. 4a is similar to Fig. 3a but for a cutting insert holder with the
lower clamping surface of the upper clamping jaw divided into three
regions:
Fig. 4b is similar to Fig. 3b but for a cutting insert holder with the
upper clamping surface of the lower clamping jaw divided into three
regions;
Fig. 5a is a front view of the cutting insert holder according to the
present invention;
Fig. 5b is similar to Fig 5a but for a cutting insert holder with the
clamping surfaces of the clamping jaws divided into three regions;
Fig. 6 is a front view of the cutting insert according to the present
invention;
Fig. 7 is an enlarged view of the cutting insert shown in Fig. 2;
Fig. 8 is a top view of the cutting insert shown in Fig. 7;
Fig. 9 is a top view of a cutting insert in accordance with the present
invention with one circular through bore;
Fig. 10 is a top view of a cutting insert in accordance with the present
invention with two non-overlapping circular through bores;
Fig. 11 is a side view of a clamping screw used for clamping a cutting
insert in a cutting insert holder in accordance with the present invention;
Fig. 12 is a side cross sectional view, in a longitudinal median plane,
of the cutting tool assembly of Fig. 1 showing the clamping screw in an
initial position before engaging the upper clamping jaw of the cutting insert
holder;
Fig. 13 is a side cross sectional view, in a longitudinal median plane,
of the cutting tool assembly of Fig. 1 showing the clamping screw in an
initial position engaging the upper clamping jaw of the cutting insert holder
but prior to applying force to the clamping jaws;
Fig. 14 is a front view of the cutting tool assembly showing the
location of the insert clamping surfaces relative to the clamping surfaces of
the clamping jaws for both Figs. 12 and 13;
Fig. 15 is a side cross sectional view, in a longitudinal median plane,
of the cutting tool assembly of Fig. 1 showing the clamping jaws engaging
rotational symmetry about each of these axes. In this embodiment the lower
clamping surface 66 is identical in form to the upper clampins surface 64
and the lower edge 72 is identical in form to the upper edge 70.
In Fig. 6. three dimensions. W. T and t defining the basic linear-
dimensions of the cutting insert in an end view are shown. The width. W.
of the cutting insert is defined as the distance oerween opposing portions of
the peripheral side surface. The maximum thickness. T. of the cutting insert
is defined as the maximum distance between the insert upper and lower
clamping surfaces as measured in an end view. The minimum thickness, to
of the cutting insert is defined as the minimum distance between the insert
upper and lower clamping surfaces as measured in an end view.
Generally, W/T lies in the range 2.5 to 4 0 and W/t lies in the
range 4.0 to 6.0. In accordance with a specific application. W/T is equal to
3.3 and W/t is equal to 5.3.
In accordance with a preferred, embodiment of the present
invention, the radii of curvature Rl. R2 of the lower and upper clamping
surfaces of the clamping jaws are substantially equal in magnitude.
R1=R2=R, defining a single value for the radius of curvature R for each of
the clamping surfaces of the clamping jaws. The cylinder axes of the lower
and upper clamping surfaces of the clamping jaws are parallel and lie in the
vertical median plane of the cutting insert, when the cutting insert is
retained in the cutting insert holder.
In accordance with the present invention the radius of curvature
of the clamping jaw's clamping surfaces R is greater than the radius of
curvature r of the cutting insert clamping surfaces. That is. for the general
case, the value of Rl is greater than the value of rl and the value of R2 is
greater than the value of r2. In accordance with a preferred embodiment
R1=R2=R and r1=r2=r and the value of R is greater than the value of r.
Symbolically, this can be expressed as R=r-d. where d is a positive
lumber.
In accordance with one specific application, r = 16 mm and R =
16.2 mm.
The cutting insert 24 is provided with two axial abutment surfaces
88a. 88b at its; front end 24' and two axial abutment surfaces 90a. 90b at it
rear end 24". The axial abutment surfaces are transverse to the axis of
rotation B of the cutting insert. When the cutting insert 24 is retained in the
insert retaining slot 36. as shown in Fig. 1. the upper rear abutment surface
90b abuts the upper insert axial location surface 58. and the lower rear
abutment surface 9()a (not seen in the figures') abuts the lower insert axial
location surface 56. thereby fixing the axial location of the cutting insert in
the cutting insert holder. The axial abutment surfaces 88a. 88b; 90a, 90b are
preferably ground in order to increase the accuracy of the axial location of the
cutting insert in the cutting insert holder.
Attention is now drawn to Figs. 7 to 10. In order to securely
clamp the cutting insert in the cutting insert holder the cutting insert is
provided with at least one through hole passing through the cutting insert
between the insert upper and lower clamping surfaces. In general, a cutting
insert for clamping in the insert holder shown in Fig. 1 will have either one
or two through holes.. Gepending on the length of the cutting insert The
reason for this being that the through bore 44 in the upper clamping jaw 32
and the associated threaded bore 52 in the lower clamping jaw 34 are
preferably located as close as possible to the front end of the cutting insert
Holder in order to ensure that the front end portions of the clamping jaws
close tightly on the retained cutting insert.
Figs. 8 to 10 show cutting inserts of different lengths. The
length of a cutting insert in accordance with the present invention is
measured along the axis of rotation B from one end of the cutting insert to
the other. For example, in Fig. 8. the length of the cutting insert 24 is
measured alone the axis B from its front end 24' to us rear end 24"
Typically, in accordance with the present invention, insert lengths can vary
from very short, having a length of approximately 0.5W to very long.
having a length of approximately 2W. The cutting insert 100 shown in Fig.
9 is relatively short, and is provided with a single through hole, namely a
circular bore 102 having a bore axis 104 located substantially at the center of
the cutting insert in a top view of the cutting insert. The bore axis 104 is
perpendicular to the axis of rotation B of the cutting insert and lies in a
vertical longitudinal median plane of the cutting insert. The cutting insert
100 is provided with two axial abutment surfaces 88a, 88b at its front end
100' and two axial abutment surfaces 90a. 90b at it rear end 100" (only one
front axial abutment surface 88b and one rear axial abutment surface 90b are
seen in Fig. 9. However, the arrangement of the abutment surfaces is the same
as that of the abutment surfaces for the medium length cutting insert 24
shown in the perspective view in Fig. 1). The axial abutment surfaces are
transverse to the axis of rotation B of the cutting insert. The cutting insert
106 shown in Fig. 10 is relatively long and is provided with two circular
bores, a forward circular bore 108 and. a rear circular bore 110 having bore
axes 112 and 114. respectively. The bore diameter D1. D2 of each of the two
circular bores are of substantially equal magnitude D1=D2=D and each bore
axis is located at substantially the same distance X1=X2= X from the center
of the cutting insert 116 in a top view of the cutting insert. The distance
between the two bore axes X+X=2X is greater than a bore diameter D. The
bore axes 112. 114 are perpendicular to the axis of rotation B of the cutting
insert and lie in a vertical, longitudinal median plane of the cutting insert.
The cutting insert 24 shown in Figs. 7 and 8 is of an intermediate
length its length being typically of the order of 1.5W, and is provided with a
single through hole 118 formed from two intersecting circular bores, a
forward circular bore 120 and a rear circular bore 122 havine bore axes 124
and 126. respectively. The bore diameter of the forward circular bore 120 is
substantially equal in magnitude to the bore diameter of the rear circular bore
122 and. in a top view of the cutting insert 24. each bore axis is located at
substantially the same distance from the center 128 of the cutting insert 24.
The distance between the two bore axes is less than a bore diameter and
therefore the two bores overlap. The bore axes 124, 126 are perpendicular to
the axis of rotation B of the cutting insert and lie in a vertical longitudinal
median plane of the cutting insert.
The two dotted lines in Fig. 7 divide the insert upper clamping
surface 64 into three regions, two substantially identical outer regions
64' separated by a central region 64". This division into three regions :;s not
a physical division, since all portions of the insert upper clamping surface
64 lie on the same concave surface. However. when the cutting insert is
clamped in the cutting insert holder 22 of the embodiment shown in Figs.
4a, 4b and 5b (as will be described in greater detail below, with respect to
Fig. 18), the outer regions 42' of the lower clamping surface 42 of the upper
clamping jaw 32 abut the insert upper clamping surface 64 along the outer
regions 64' thereof. Hence, the outer regions 64' of the insert upper
clamping surface 64 are regions that correspond to the outer regions 42' of
the lower clamping surface 42 of the upper clamping jaw 32. Similarly, the
insert lower clamping surface 66 is divided into three regions, two
substantially identical outer regions 66' separated by a central region 66".
The two outer regions 66' correspond to the two outer regions 50' of the
upper clamping surface 50 of the lower clamping jaw 34.
It should be noted that the outer regions 64' of the insert upper
clamping surface 64 extend to the upper edge 70 thereof. Similarly, the
outer regions 66' of the insert lower clamping surface 66 extend to the
upper edge 72 thereof. In a similar manner, the clamping surfaces of the
cutting inserts 100. 106 shown in Figs. 9 and 10 are divided into three
regions.
Attention is now drawn to Fig. 11. The clamping screw 26 of the
present invention has a screw axis C and comprises generally three portions:
an upper portion 140. a central portion 142 and a lower portion 144. The
upper portion 140 comprises an upper cylindrical portion 146 and an upper
frusto-conical portion 148. The upper frusto-conical portion 148 tapers
downwardly and inwardly from the upper cylindrical portion 146 toward the
central portion 142. The clamping screw upper portion 140 is provided with a
socket 149 such as a Torx or hexagonal socket, for receiving a wrench for
tightening or loosening the clamping screw 26. The clamping screw central
portion 142 has a central cylindrical portion 150 connected at its upper end to
he upper frusto-conical portion 148 and at its loner end to a central frusto-
conical portion 152. The central frusto-conical portion 152 tapers
downwardly and inwardly from its upper end. where it is connected to the
central cylindrical portion 150. to its lower end where it is connected. is a
arrow neck portion 154, to the clamping screw lower portion 144. The
clamping screw lower portion 144 comprises a threaded portion 156 of the
clamping screw 26. The central frusto-conical portion 152 tapers at an angle
8 to the screw axis C. This angle will be referred to herein as the angle of
toper of the central frusto-conical portion 152.
Attention is now drawn to Figs. 12 to 16. illustrating the
principle stages involved in clamping the cutting insert in the cutting insert
holder 22. For illustrative purposes the cutting insert holder 22 shown in
Figs. 12 to 16 is in accordarce with the first embodiment wherein, in an end
view of the cutting insert, holder 22 the lower clamping surface 42 of the
upper clamping jaw 32 and the upper clamping surface 50 of the lower
clamping jaw 34 and are both uniformly convex. The cutting insert shown
in these figures is a cutting insert 100 with a single circular through bore
102. Furthermore, for simplicity of illustration the case R1=R2=R and
r1=r2=r is considered. The gaps between the curing insert 100 and the
cutting insert holder 22. between the camping screw 26 and the cutting
insert holder 22. and between the camping screw 26 and the cutting insert
100 are not to scale and have been exaggerated for illustrative purposes.
Figs. 12 and 14 show the initial arrangement after the cutting
insert 100 has been placed in the insert receiving slot 36 and the clamping
screw 26 has been positioned in the cutting insert holder 22. so that, it passes
through the bore 44 in the upper clamping jaw 32. through the through bore
102 in the cutting insert 100 and is received in the threaded bore 52 in the
lower clamping jaw 34. In this position, due to the fact that R=r+o. the
insert lower clamping surface 66 rests on the upper clamping surface 50 of
the lower clamping jaw 34 with the outer regions 66' of the insert lower
clamping surface 66 engaging the upper clamping surface 50 of the iower
clamping jaw 34 and with a maximum clearance d between the central
region 66" of the insert lower clamping surface 66 and the central region
50" of the upper clamping surface 50 of the lower clamping jaw 34. in
accordance with a specific application the clearance d is typically of the
order of 0.005 mm to 0.02 mm. There is also a clearance h between the
insert upper clamping surface 64 and the lower clamping surface 42 of the
upper clamping jaw 32.
The through bore 44 in the upper clamping jaw 32 and the
threaded bore 52 in the lower clamping jaw 34 have a common longitudinal
bore axis E. The screw axis C coincides with the longitudinal bore axis E
and makes an angle ø with a normal N to the axis of rotation A of the
cutting insert holder 22. The angle ø is chosen to be equal to the angle of
taper ? of the central frusto-conical portion 152. With this choice of the
angle ø, the rearmost generator 153" (i.e.. rearmost longitudinally directed
straight line on the central frusto-conical portion 152) of the central frusto-
conical portion 152 is parallel to the normal N to the axis of rotation A.
Fig. 13 shows the situation after the clamping screw 26 has been
tightened until the upper frusto-conical portion 148 of the clamping screw
26 engages a corresponding frusto-conicai bore 158 that constitutes part of
the through bore 44 in the upper clamping jaw 32. It is pointed out that due
to the fact that the rearmost generator 153" of the central frusto-conical
portion 152 is parallel to the normal N. that as the clamping screw 26 is
tightened the rearmost generator of the central frusto-conicai portion 152
moves parallel to itself and therefore :s always parallel to the normal N to
the axis of rotation A. In a non-binding example, for the position shown in
Fig. 13, the clearance h between the insert upper clamping surface 64 and
the lower clamping surface 42 of the upper clamping jaw 32 is
approximately 0.1 mm. There is a clearance x. of approximately 0.035 mm.,
between the rearmost generator 153" of the central frusto-conicai portion
152 and the rear portion 102' of the circular bore 102 of the cutting insert
100.
Fig. 15 shows the situation after further tightening of the
clamping screw 26. During the tightening of the clamping screw 26 the
clearance h between the insert upper clamping surface 64 and the lower-
clamping surface 42 of the upper clamping jaw 32 is gradually reduced and
a force is exerted by the clamping jaws on the insert clamping surfaces
causing the cutting insert 100 to become longitudinally aligned in the
cutting insert holder 22 so that the longitudinal axis of rotational symmetry
B of the cutting insert becomes aligned with the axis of rotation A of the
cutting insert holder 22. In passing from the situation shown in Fig. 13 to
that shown in Fig. 15. the clamping screw 26 has moved a vertical distance
of approximately 0.1 mm and a corresponding horizontal distance of 0.005
mm. reducing the clearance x between the rearmost generator 153" of the
central frusto-conicai portion 152 and the rear portion 102" of the circular
bore 102 of the cutting insert 100 to approximately 0.03 mm
As the clamping screw 26 is further tightened, the rearmost
insert 24. The forward circular bore 120 is engaged by the clampine screw
26 at the two rear side portions of the central frusto-conical portion 152
corresponding to the rear side portions 120" of the forward circular bore
120. Each of the two rear side portions of the central frusto-conical pertion
152 is located in a region of a portion of a rear side generator 153' of the
central frusto-conical portion 152 of the clamping screw 26. A rear side
generator 153' is shown in Fig. 11 by a dashed line. In Fig. 11. only one of
the two rear side generators 153' is seen, the other one being on the side of
the central frusto-conical portion 152 not seen in the figure, parallel to and
"directly behind" the rear side generator 153' that is seen. In order to
increase the areas of engagement between the tw o rear side portions of the
central frusto-conical portion of the clamping screw and the two the rear
side portions 120" of the forward circular bore 120. the design of the
through hole 118 can be suitably altered in the regions of the two the rear
side portions 120", as will be apparent to a person skilled in the art.
Fig. 18 shows the situation after the final tightening of the
clamping screw 26, for a cutting tool assembly having a cutting insert
holder 22 with the clamping surfaces of the clamping jaws divided into
three regions (as shown in Fig. 5b), in accordance with a preferred
embodiment of the present invention. As can be seen, the regions of
abutment between the upper surface of the cutting insert and the lower
clamping surface of the upper clamping jaw 32 is restricted to the outer
regions 64' of the clamping surfaces of the cutting insert and the
corresponding outer regions 42' of the lower clamping surface of the upper
clamping jaw 32. Since the central region 42" of the lower clamping
surface 42 has a larger radius of curvature than that of the outer regions
12'. a clearance is formed between the central region 42" of the lower
damping surface 42 and the central region 64' of the insert upper clamping
surface 64. Therefore, in accordance with the embodiment of the outline
insert holder with the clamping surfaces of the clamping jaws divided into
three regions, the central region 42" of the lower clamping surface 42
becomes a clearance surface and does not engage the central resion 64" of
the insert upper clamping surface 64. Similarly, the regions of abutment
between the insert lower clamping surface 66 and the upper clamping
surface 50 of the lower clamping jaw 34 are restricted to the outer regions
66' of the insert lower clamping surface 66 and the corresponding outer
regions 50' of the upper clamping surface 50 of the lower clamping jaw 34.
Therefore, in accordance with the embodiment of the cutting insert holder
with the clamping surfaces of the clamping jaws divided into three regions.
the central region 50" of the upper clamping surface 50 becomes a
clearance surface and does not engage the central region 66" of the insert
lower clamping surface 66. This arrangement assures that the clamping
forces applied by the clamping jaws of the cutting insert holder on the
clamping surfaces of the cutting insert are applied to the outer (or. side)
regions of the clamping surfaces, thereby giving support to the cutting edges
extending along the sides of the cutting insert from the front of the cutting
insert to the rear of the cutting insert-
It should be noted, that in accordance with the present invention,
the insert upper clamping surface 64 engages the lower clamping surface 42
of the upper clamping jaw 32 and the insert lower clamping surface 66
engages the upper clamping surface 50 of the lower clamping jaw 34.
Furthermore, in accordance with the preferred embodiment of the present
invention, the central region 42" of the lower clamping surface 42 does not
engage the central region 64" of the insert upper clamping surface 64 and
the central region 50" of the upper clamping surface 50 does not engage the
central region 66" of the insert lower clamping surface 66. hence only the
outer regions 64', 66' of the cutting insert engage the clamping surfaces 42.
50 of the clamping jaws. This is in complete contrast with the situation in
EP 0 417 862 B1. wherein the side portions numbered 16a. 16b and 16' a.
16' b therein) of the cutting insert described therein do not engase the
clamping surfaces of the clamping jaws.
In Fig. 18 two angles al and a 2 are defined relative to the center
of curvature O of the lower clamping surface 42 of the upper clamping jaw
32. The angles oil and a.2 are defined in a plane perpendicular to the axis
of rotation A of the cutting insert holder 22 Hence, the dashed lines and
the points O. P1 and P2 are all located in the same plane perpendicular to
the axis of rotation A The angle al defines the angular location of the
innermost point of contact P1 between an outer region 42'of the lower
clamping surface 42 of the upper damping jaw 32 and the insert upper
clamping surface 64. The angle a2 defines the angular location of the
outermost point of contact P2 between an outer region 42'of the lower
clamping surface 42 of the upper clamping jaw 32 and the insert upper
clamping surface 64. Since a2 is greater than al, and since the clamping
force on the cutting insert is applied in a direction parallel to the
longitudinal vertical median plane M of the cutting insert, which coincides
with a longitudinal vertical median plane of the cutting tool assembly when
the cutting insert is retained in the cutting insert holder, the condition for
sliding contact between the insert upper clamping surface 64 and the lower
damping surface 42 of the upper clamping jaw 32 is that al be greater than
the angle of friction. In accordance with a specific application the cutting
nsert holder 22 is made of steel and the cutting insert 24. 100, 106 is made
of cemented carbide. In accordance with this specific application al should
be greater than 10°. Preferably, a2 is approximately 30°.
Although the present invention has been described to a certain
degree of particularity of should be understood that various alterations and
nodifications can be made without departing from the spirit or scope of the
invention as hereinafter claimed. In particular, the invention has been
demonstrated with respect to a ball nose end mill having a sinele replaceable
cutting insert retained between the clamping jaws of the ball nose end mill. It
will be appreciated that the invention does not relate to a specific type of
milling cutter but relates to any milling cutter having a single replaceable
cutting insert retained between the clamping jaws of the milling cutter.
provided that the clamping surfaces of the clamping jaws are at least
partially convex and the insert clamping surfaces are concave and that the
radius of curvature of the clamping surfaces of the damping jaws is larger
than the radius of curvature of the insert clamping surfaces.
the insert clamping surfaces nut prior to the final tightening of the clamping
screw:
Fig. 16 is a side cross sectional view in a longitudinal median plane,
of the cutting tool assembly of Fig 1 showing the axial abutment surfaces at
the rear of the cutting insert engaging the insert axial location surfaces at the
rear of the insert receiving slot, after the final tightening of the clamping
screw;
Fig. 17 is a front view of the cutting tool assembly in accordance with
Fig. 16; and
Fig. 18 is a front view of the amine tool assembly having a cutting
insert holder with the clamping surfaces of the clamping jaws divided into
three regions, showing the situation after the final tightening of the
clamping screw.
DETAILED DESCRIPTION OF THE INVENTION
Attention is first drawn to Figs. 1. 2. 3a. 3b and 5a. As shown, a
cutting tool assembly 20 comprises a cutting insert holder 22 having an axis
of rotation A. a cutting insert 24 and a clamping screw 26 for securing the
cutting insert in the cutting insert holder. The cutting insert holder 22
comprises an elongated cylindrical body portion 28 and a clamping portion
30 in a front portion thereof. The clamping portion 30 consists of an upper
damping jaw 32 separated from a lower clamping jaw 34 by an insert
receiving slot 36. The upper clamping jaw 32 has an upper peripheral
surface 38 having a chip evacuation recess 40 in a front portion thereof, a
lower clamping surface 42 and a through bore 44 transverse to the axis of
rotation A. The lower clamping jaw 34 has a lower peripheral surface 46
having a chip evacuation recess 48 in a front portion thereof, an upper
clampins surface 50 and a threaded bore 52 transverse to the axis oi rotation
A and aligned with the through bore 44 in the upper clamping jaw The
terms "upper", "lower", "forward" and "rear" are used herein with reference
to the orientation of the cutting insert holder 22 and the cutting insert 24 as
shown in Figs. 1 and 2. Hence, the cutting insert 24 has a forward end
24' and a rear end 24" Similarly, the insert receiving slot 36 has a forward
end 36' and a rear end 36".
The upper clamping jaw is resiliently connected to the lower
clamping jaw at the rear end of the insert receiving slot via a slot 54
transverse to the axis of rotation A. Adjacent the slot 54 are two insert axial
location surfaces transverse to the axis of rotation A. a lower insert axial
location surface 56 and an upper insert axial location surface 58. A lower
generally cylindrical groove 60. transverse to the axis of rotation A. is located
between the lower insert axial location surface 56 and the upper clamping
surface 50 of the lower clamping jaw 34. An upper generally cylindrical
groove 62. transverse to the axis of rotation A. is located between the upper
insert axial location surface 58 and the lower clamping surface 42 of the
upper clamping jaw 32.
In accordance with a first embodiment of the cutting insert
holder 22. the lower clamping surface 42 of the upper clamping jaw 32
conforms with a portion of a cylindrical surface having a radius of curvature
R1 and a cylinder axis generally parallel to the axis of rotation A. so that in
an end view of the cutting insert holder 22 the lower clamping surface of
the upper clamping jaw is convex (see Figs. 3a and 5a). The upper
clamping surface 50 of the lower clamping jaw 34 conforms with a portion
of a cylindrical surface having a radius of curvature R2 and a cylinder axis
generally parallel to the axis of rotation A. so that in an end view of the
cutting insert holder 22 the upper clamping surface of the lower clamping
jaw is convex (see Figs. 3b and 5a). Generally, the radii of curvature Rl.
R2 cf the lower and upper clamping surfaces 42. 50 do not have to be
identical.
Figs. 4a. 4b and 5b show a second embodiment of the cutting
insert holder 22. In accordance with this embodiment, which is a preferred
embodiment of the present invention, the lower clamping surface 42 of the
upper clamping jaw 32 is divided into tnree regions, two substantially
identical outer regions 42' on either side of a central region 42" The terra
-substantially identical" in this context is used to indicate that the two outer
regions 42' are identical to within manufacturing tolerances. Each of the
two outer regions conforms with a portion of a common cylindrical surface
having a radius of curvature Rl and a cylinder axis generally parallel to the
axis of rotation A. whereas the central region 42" is either planar. or
:onforms with a portion of a cylindrical surface having a radius of curvature
Rl' larger than the radius of curvature Rl of the outer regions 42'.
Therefore, in accordance with this embodiment., the lower clamping surface
42 of the upper clamping jaw 32 at least partially conforms with a portion of
a cylindrical surface. Similarly, the upper clamping surface 50 of the lower
clamping jaw 34 can be formed to at least partially conform with a portion
cf a cylindrical surface by dividing it into three regions, two substantially
identical outer regions 50'on either side of a central region 50". Each of
the two outer regions 50' conforms with a portion of a common cylindrical
surface having a radius of curvature R2 and a cylinder axis generally
parallel to the axis of rotation A. whereas the central region 50" is either
planar. or conforms with a portion of a cylindrical surface having a radius of
curvature R2' larger than the radius of curvature R2 of the outer regions
50' .
Attention is now drawn to Prigs. 6 to 8. The cutting insert24
comprises an insert upper clamping surface 64. an insert lower clamping
surface 66 and a peripheral side surface 68 between the insert upper
clamping surface and the insert lower clamping surface. The insert upper
damping surface 64 intersects the peripheral side surface 68 at an upper
edge 70 and the insert lower clamping surface 66 intersects the peripheral
side surface 68 at a lower edge 72. The upper edge 70 constitutes a
peripheral boundary of the insert upper clamping surface 64. similarly the
lower edge 72 constitutes a peripheral boundary of the insert lower
clamping surface 66. The cutting insert 24 has a longitudinal axis of rotation
B. In accordance with a preferred embodiment. the axis of rotation B.
constitues an axis of rotational symmetry of the cuuing insert about which
the cutting insert has 180° rotational symmetry and the lower edge 72 is
equivalent in form to the upper edge 70. due to the 180° rotational symmetry
of the cutting insert about the axis of rotational .symmetry B.
The cutting inserr 24 is indexable and therefore the perpheral
side surface 68 of the cutting insert is provided with two diametrically
opposite pairs of cutting edges, a front pair of cuttins edges 74a, 74b and a
rear pair of cutting edges 76a. 76b. When the cutting insert 24 is retained in
the insert receiving slot 36. the from pair of cutting edges 74a. 74b is
located closer to the from end of the insert receiving pocket and constitute a
pair of operative cutting edges and the rear pair of cutting edges 76a. 76b is
located closer to the rear end of the insert receiving pocket and constitute a
pair of inoperative cutting edges
The cutting insert has a first transverse axis T1 passing through
the peripheral side surface 68 and perpendicular to the longitudinal axis of
rotation B. The cutting insert has a second transverse axis T2 perpendicular
to the longitudinal axis of rotation B and to the first transverse axis T1. the
cutting insert haying 180° rotational symmetry about the second transverse
axis of rotational symmetry T2.
The peripheral side surface is provided with two diametrically
opposite notches 78'. 78" which are located on the first transverse axis Tand which separate between the diametrically opposite pairs of cutting
edges, mat is. between the front pair 74a. 74b and the rear pair of cutting
edges 76a. 76b
For the front pair of cutting edges, cutting edge 74a extends from
a region close to where the longitudinal axis of rotational symmetry B
passes through the peripheral side surface 68 downwards and rearwards
towards the notch 78' whilst the other cutting edge 74b extends from the
same region close to where the longitudinal axis of rotational symmetn' B
passes through the peripheral side surface 68 upwards and rearwards
towards the diametrically opposite notch 78" Due to the symmetrical
nature of the cutting insert, the rear pair of cutting edges are identical to the
front pair of cutting edges. Each cutting edge is provided with a relief
surface 80 and a rake surface 82.
The insert upper clamping surface 64 conforms with a portion of
a cylindrical surface having a radius of curvature r1 and a cylinder axis
generally parallel to the longitudinal axis of rotational symmetry B.
Similarly, the insert lower clamping surface 66 conforms with a portion of a
cylindrical surface having a radius of curvature r2 and a cylinder axis
generally parallel to the longitudinal axis of rotational symmetry B. Hence.
in an end view of the cutting insert 24 the insert's upper and lower clamping
surfaces are concave (see Fig. 6). Generally, the radii of curvature r1, r2 of
the insert upper and lower clamping; surfaces do not have to be identical.
In accordance with a preferred embodiment of the present
invention, the radii of curvature rl, r2 of the insert upper and lower
clamping surfaces are substantially equal in magnitude. r1=r2=r. defining a
single value r for the radius of curvature for each of the cutting insert
clamping surfaces. The cylinder axis of the lower clamping surface is
parallel to the cylinder axis of the upper clamping surface and both the
cylinder axes lie in a vertical longitudinal median plane of the cutting insert
which includes the axes T2 and 13. In accordance with this preferred
embodiment, the longitudinal axis (if rotation B and the first transverse axis
T1 are axes of rotational symmetry. The cutting insert 24 having 180º
WE CLAIM:
1. A milling cutter assembly (20) comprising a cutting insert holder (22), a
cutting insert (24) and a clamping screw (26), the cutting insert holder (22)
comprising a clamping portion (30) connected to a body portion (28);
the clamping portion (30) comprising;
a lower clamping jaw (34) having a lower peripheral surface (46) and an
upper clamping surface (50);
an upper clamping jaw (32) resiliently connected to the lower clamping jaw
(34), the upper clamping jaw (42) having a lower clamping surface (42) and
an upper peripheral surface (38);
a through bore (44) passing through the upper and lower clamping jaws, the
through bore being threaded in one of the upper or lower clamping jaws;
an insert receiving slot (36) defined between the upper and lower clamping
surfaces (50,42);
the cutting insert (24) comprising:
an insert upper clamping surface (64) bounded by an upper edge (70)
an insert lower clamping surface (66) bounded by a lower edge (72);
a peripheral side surface (68) between the insert upper clamping surface
(64) and the insert lower clamping surface (60);
at least one cutting edge associated with the peripheral side surface;
at least one through hole (118) passing through the cutting insert (24)
between the insert upper and lower clamping surfaces;
wherein:
in a front view of the cutting tool assembly, the upper the lower clamping
surfaces (50,42) of the lower and upper clamping jaws (34,32), respectively,
are partially convex, and the insert lower and upper clamping surfaces
(66,64) are concave;
the cutting insert (24) is retained in the insert receiving slot (36) in a
retained position by means of the clamping screw (26) which passes through
the through bore (44) in the upper and iower damping jaws of the cutting
insert holder and through the at least one through hole (118) in the cutting
insert (24) and is screwed into the threaded through bore in one of the
upper or lower clamping jaws;
the lower clamping surface (42) of the upper clamping jaw (32) engages the
insert upper clamping surface (64) at at least one upper region of contact
and the upper clamping surface (50) of the lower clamping jaw (34) engages
the insert lower surface (66) at at least one lower region of contact;
characterized in that:
the insert upper clamping surface (64) conforms with a first cylindrical
surface having a first radius of curvature, r1, and a first cylinder axis;
the insert lower clamping surface (66) conforms with a second cylindrical
surface having a second radius of curvature r2, and a second cylinder axis;
the upper damping surface (50) of the lower damping jaw (34) partially
conforms with a third cylindrical surface having a third radius of curvature,
R2, and a third cylinder axis;
the lower clamping surface (42) of the upper clamping jaw (32) partially
conforms with a fourth cylindrical surface having a fourth radius of
curvature, Rl and a fourth cylinder axis;
the fourth radius of curvature, R1, is greater than the first radius of
curvature, r1, the third radius of curvature, R2, is greater than the second
radius of curvature, r2.
2. The cutting tool assembly (20) as claimed in claim 1, wherein the cutting
insert holder (22) has an axis of rotation (A) and the cutting insert (24) has a
longitudinal axis of rotational symmetry (B) and a center (128) through
which the longitudinal axis of rotational symmetry (B) passes, the
longitudinal axis of rotational symmetry (B) constituting an axis of rotation of
the cutting insert about which the cutting insert has 180° of rotational
symmetry.
3. The cutting too! assembly (20) as claimed in claim 2, wherein the first radius
of curvature and the second radius of curvature are equal in magnitude,
rl=r2, defining a radius of curvature, r, of the cutting insert clamping
surfaces, and the third radius of curvature and fourth radius of Curvature are
equal in magnitude, R1=R2, defining a radius of curvature, R, of the
clamping jaw's clamping surfaces.
4. The cutting tool assembly (20) as claimed in claim 3, wherein the at least
one upper region of contact comprises at least outer regions (64') of the
insert upper clamping surface (64) and the at least one lower region of
contact comprises at least two outer regions (660 of the insert lower
clamping surface (66).
5. The cutting tool assembly (20) as claimed in claim 4, wherein r=16mm and
R=16.2mm.
6. The cutting tool assembly (20) as claimed in claim 4, wherein the cutting
insert has a width, W, which is greater than a thickness, T, where the width
and the thickness are measured in a front view of the cutting insert as,
respectively, the distance between opposing portions of the peripheral side
surface, and a maximum distance between the insert upper and lower
clamping surfaces.
7. The cutting tool assembly (20) as claimed in claim 6, wherein W/T lies in the
range 2.5 to 4.0.
8. The cutting tool assembly (20) as claimed in claim 6, wherein W/T is equal
to 3,3,
9. The cutting tool assembly (20) as claimed in claim 6, wherein the cutting
insert has a width, W, which is greater than a thickness, t, where the width
and thickness are measured in a front view of the cutting insert as,
respectively, the distance between opposing portions of the peripheral side
surface, and a minimum distance the insert upper and lower clamping
surfaces.
10.The cutting tool assembly (20) as claimed in claim 9, wherein W/T lies in the
range 4.0 to 6.0.
11.The cutting tool assembly (20) as claimed in claim 9, wherein W/t is equal to
5.3.
12. The cutting tool assembly (20) as claimed in claim 2, wherein the radius of
curvature, r, of the cutting insert clamping surfaces is approximately equal to
W, and the radius of curvature, R, of the clamping jaw's clamping surfaces is
approximately equal to W.
13.The cutting tool assembly (20) as claimed in claim 2, wherein the insert
receiving slot (36) has a forward end (36*) for receiving a cutting insert and
rear end (36") at which the upper clamping jaw is resiliently connected to
the lower clamping jaw clamping jaw.
14.The cutting tool assembly (20) as claimed in claim 13, wherein the rear end
(36') of the insert receiving slot (36) is provided with at least one insert axial
location surface (56,58) transverse to the axis of rotation (A) of the cutting
insert holder (22).
15.The cutting tool assembly (20) as claimed in claim 14, wherein the rear end
(36') of the insert receiving slot (36) is provided with at least one generally
cylindrical groove (60,62) transverse to the axis of rotation (A)
of the cutting insert holder (22) and adjacent the at least one insert axial
location surface (56,58).
16.The cutting tool assembly (20) as claimed in claimed 2, wherein the cutting
insert (24) has two end portions (24',24') adjacent the axis of rotation (B) of
the cutting insert (24), at least one of the two end portions (24', 24') being
provided with axial abutment surfaces (88a, 88b, 90a, 90b) transverse to the
axis of rotation (B) of the cutting insert (24).
17.The cutting tool assembly (20) as claimed in claim 16, wherein the axial
abutment surfaces (88a, 88b, 90a, 90b) are ground.
18. The cutting tool assembly (20) as claimed in claim 2, wherein the at least
one through hole (118) in the cutting insert (100) is implemented as a
circular bore (102) having a bore axis (104) located substantially at the
center of the cutting insert in a top view of the cutting insert, the bore axis
being perpendicular to the axis of rotation (B) of the cutting insert.
19.The cutting tool assembly (20) as claimed in claim 2, wherein, the at least
one through hole (118) in the cutting insert (106) is implemented as two
circular bores (108,110), each circular bore having a bore axis (112,114) and
a bore diameter (D1,D2), the bore diameter of each circular bore being
substantially equal in magnitude (D1=D2=D), each bore axis being located
at substantially the same distance (X1=X2-X) from the center (116) of the
cutting insert (106) in a top view of the cutting insert, each bore axis being
perpendicular to the axis of rotation (B) of the cutting insert (106) and the
distance (2X) between the two bore axes (112,114) being greater than the
bore diameter (D).
20.The cutting tool assembly (20) as claimed in claim 2, wherein the at least
one through hole (118) is implemented by two intersecting circular bores
(120,122), each circular bore having a bore axis (124,126) and a bore
diameter (D1,02), the bore diameter of each circular bore being substantially
equal in magnitude (D1=D2=D), each bore axis being
located at substantially the same distance from the center (128) of the
cutting insert (24) in a top view of the cutting insert, each bore axis being
perpendicular to the axis of rotation (B) of the cutting insert and the
distance (Y) between the two bore axes being less than the bore diameter
(D).
21.The cutting tool assembly (20) as claimed in claim 19, wherein the cutting
insert (106) is retained in the insert receiving slot (36) in a retained position
by means of a clamping screw (26) which passes through the through bore
in the upper and lower clamping jaws of the cutting insert holder and
through the circular bore in the cutting insert closest the forward end (360 of
the insert receiving slot (36) and is screwed into the threaded through bore
(52) in one of the upper or lower clamping jaws.
22.The cutting tool assembly (20) as claimed in claim 20, wherein the cutting
insert (24) is retained in the insert receiving slot (36) in a retained position
by means of a clamping screw (26) which passes through the through bore
in the upper and lower clamping jaws of the cutting insert holder and
through the circular bore (120) in the cutting insert (24) closest the forward
end (36') of the insert receiving slot (36) and is screwed into the threaded
through bore (52) in one of the upper or lower clamping jaws.
23.The cutting tool assembly (20) as claimed in claim 2, wherein, the peripheral
side surface (68) of the cutting insert (24, 100, 106) is provided with two
diametrically opposite pairs of cutting edges (74a, 74b; 76a, 76b) so that
when the cutting insert is retained in the insert receiving slot,
one pair of cutting edges (74a, 74b) is located closer to the forward end
(360 of the insert receiving slot (36) and constitutes a pair of operative
cutting edges and the other pair of cutting edges (76a,76b) is located closer
to the rear end (36") of the insert receiving slot and constitutes a pair of
inoperative cutting edges.
24.The cutting tool assembly (20) as claimed in claim 23, wherein the peripheral
side surface is provided with two diametrically opposite notches (78',78")
which are located on a first transverse axis of rotational symmetry (T1) and
which separate between the diametrically opposite sets of cutting edges
(74a,74b;76a,76b), the first transverse axis of rotational symmetry (T1)
passing through the peripheral side surface (68) and perpendicular to the
longitudinal axis of rotational symmetry (B), the cutting insert having 180°
rotational symmetry about the first transverse axis of rotational symmetry
(T1).
25.The cutting tool assembly (20) as claimed in claim 24, wherein each pair of
cutting edges (74a,74b;76a,76b) comprises one cutting edge (74b; 76b)
which extends from a region close to where the longitudinal axis of rotational
symmetry (B) passes through the peripheral side surface (68) upwards
towards a notch whilst the other cutting edge (74a;76a) extends from the
same region close to where the longitudinal axis of rotational symmetry
passes through the peripheral side surface downwards towards the
diametrically opposite notch.
26.The cutting tool assembly (20) as claimed in claim 25, wherein each cutting
edge is provided with a relief surface (80) and a rake surface (82).
27.A cutting insert (24) having a longitudinal axis of rotational symmetry (B)
and a center (128) through which the longitudinal axis of rotational
symmetry (B) passes, the longitudinal axis of rotational symmetry (B)
constituting an axis of rotation of the cutting insert about which the
cutting insert (24) has 180° rotational symmetry, the cutting insert (24)
comprising:
an insert upper clamping surface (64) bounded by an upper edge (70);
an insert lower clamping surface (66) bounded by a lower edge (72); a
peripheral side surface (68) between the insert upper clamping surface (64)
and the insert lower clamping surface (60);
at least one cutting edge associated with the peripheral side surface;
at least one through hole (118) passing through the cutting insert (24)
between the insert upper and iower ciamping surfaces;
Wherein:
the insert upper clamping surface (64) conforms with a first cylindrical
surface having a first radius of curvature, rl, and a first cylinder axis;
the insert tower cfamping surface (66) conforms with a second cylindrical
surface having a second radius of curvature, r2, and a second cylinder axis.
28.The cutting insert as claimed in claim 27, wherein the first radius of
curvature and the second radius of curvature are equal in magnitude, r1=r2,
defining a radius of curvature, r, of the cutting insert clamping surfaces.
29.The cutting insert as claimed in claim 27, wherein the cutting insert has a
width, W, which is greater than a thickness, T, where the width and
thickness are measured in a front view of the cutting insert as, respectively,
the distance between opposing portions of the peripheral side surface, and a
maximum distance between the insert upper and lower clamping surfaces.
30.The cutting insert as claimed in claim 29, wherein W/T lies in the range 2.5
to 4.0.
31.The cutting insert as claimed in claim 29, wherein w/t is equal to 3.3.
32.The cutting insert as claimed in claim 27, wherein the cutting insert has a
width, W, which is greater than a thickness, t, where the width and thickness
are measured in an end view of the cutting insert as, respectively, the
distance between opposing portions of the peripheral side surface, and a
minimum distance between the insert upper and lower clamping surfaces.
33.The cutting insert as claimed in claim 32, wherein W/t lies in the range 4.0 to
6.0.
34.The cutting insert as claimed in claim 32, wherein W/t is equal to 5.
35.The cutting insert as claimed in claim 27, wherein the cutting insert (24) has
two end portions (24',24') adjacent the axis of rotation (B) of the cutting
insert (24), at least one of the two end portions (24',24") being provided
with axial abutment surfaces (88a,88b,90a,90b) transverse to the axis of
rotation (B) of the cutting insert (24).
36.The cutting insert as claimed in claim 35, wherein the axial abutment
surfaces (88a,88b,90a,90b) are ground.
37.The cutting insert as claimed in claim 27, wherein the at least one through
hole (118) in the cutting insert (100) is implemented as a circular bore (102)
having a bore axis (104) located substantially at the center of the cutting
insert in a top view of the cutting insert, the bore axis being perpendicular to
the axis of rotation (B) of the cutting insert.
38.The cutting insert as claimed in claim 27, wherein the at least one through
hole (118) in the cutting insert (106) is implemented as two circular bores
(108,110), each circular bore having a bore axis (112,114) and a bore
diameter (D1,D2), the bore diameter of each circular bore being substantially
equal in magnitude (D1=D2=D), each bore axis being located at
substantially the same distance (X1=X2=X) from the center
(116) of the cutting insert (106) in a top view of the cutting insert, the bore
axes being perpendicular to the axis of rotation (B) of the cutting insert (106)
and the distance (2X) between the two bore axes (112,114) being greater
than the bore diameter (D).
39.The cutting insert as claimed in claim 27, wherein the at least one through
hole (118) is implemented by two intersecting circular bores (120, 122),
each circular bore having a bore axis (124,126) and a bore diameter
(D1,D2), the bore diameter of each circular bore being substantially equal in
magnitude (D1=D2=D), each bore axis being located at substantially the
same distance from the center (128) of the cutting insert (24) in a top view
of the cutting insert, the bore axes being perpendicular to the axis of
rotation (B) of the cutting insert and the distance (Y) between the two bore
axes being less than the bore diameter (D),
40.A cutting insert holder (22) having an axis of rotation A and comprising a
clamping portion (30) connected to a body portion (28);
the clamping portion (30) comprising:
a lower clamping jaw (34) having a lower peripheral surface (46)
and an upper clamping surface (50);
an upper clamping jaw (32) resiliently connected to the lower clamping
jaw (34), the upper clamping jaw (32) having a lower clamping surface
(42) and an upper peripheral surface (38);
a through bore (44) passing through the upper and lower clamping jaws,
the through bore being threaded in one of the upper or lower clamping
jaws; and
an insert receiving slot receiving slot (36) defined between the upper and
lower clamping surfaces (50,42); wherein:
the upper clamping surface (50) of the lower damping jaw (34) partially
conforms with a portion of a third cylindrical surface having a third radius
of curvature, R2, and a third cylinder axis;
the lower clamping surface (42) of the upper clamping jaw (32) partially
conforms with a portion of a fourth cylindrical surface having a fourth
radius of curvature, R1, and a fourth cylinder axis; and
In a front view of the cutting insert holder, the upper and lower clamping
surfaces (50,42) of the lower and upper clamping jaws (34,32),
respectively, are partially convex;
the lower clamping surface (42) of the upper clamping jaw (32) is divided
into three regions, two substantially identical outer regions (42') having a
first radius of curvature and a central region (42") having a second radius
of curvature and the upper clamping surface (50) of the lower clamping
jaw (34) is divided into three regions, two subtantially identical outer
regions (50') having a first radius of curvature and a central region (50')
having a second radius of curvature.
41.A cutting insert holder as claimed in claim 40, wherein the third radius of
curvature and the fourth radius of curvature and fourth radius of curvature
are equal in magnitude, R1=R2, defining a radius of curvature, R, of the
clamping jaws' damping surfaces.
42. A cutting insert holder as claimed in claim 40, wherein the insert receiving
slot (36) has a forward end (360 for receiving a cutting insert and a rear end
(36") at which the upper clamping jaw is resiiiently connected to the lower
clamping jaw.
43.A cutting insert holder as claimed in claim 42, wherein the rear end (36") of
the insert receiving slot (36) is provided with at least one insert axial location
surface (56,58) transverse to the axis of rotation (A) of the cutting insert
holder (22).
44.A cutting insert holder as claimed in claim 43, wherein the rear end (36") of
the insert receiving slot (36) is provided with at least one generally
cylindrical groove (60,62) transverse to the axis of rotation (A) of the cutting
insert holder (22) and adjacent the at least one insert axial location surface
(56,58).
45.A cutting insert holder as claimed in claim 45, wherein the second radius of
curvature is larger than the first radius of curvature.
The invention relates to a milling cutter assembly (20) comprising a cutting insert
holder (22), a cutting insert (24) and a clamping screw (26), the cutting insert
holder (22) comprising a clamping portion (30) connected to a body portion
(28);the clamping portion (30) comprising: a lower clamping jaw (34) having a
lower peripheral surface (46) and an upper clamping surface (50); an upper
clamping jaw (32) resiliently connected to the lower clamping jaw (34), the
upper clamping jaw (42) having a lower clamping surface (42) and an upper
peripheral surface (38); a through bore (44) passing through the upper and
lower clamping jaws, the through bore being threaded in one of the upper or
lower clamping jaws; an insert receiving slot (36) defined between the upper and
lower clamping surfaces (50,42); the cutting insert (24) comprising: an insert
upper clamping surface (64) bounded by an upper edge (70) an insert lower
clamping surface (66) bounded by a lower edge (72); a peripheral side surface
(68) between the insert upper clamping surface (64) and the insert lower
clamping surface (60); at least one cutting edge associated with the peripheral
side surface; at least one through hole (118) passing through the cutting insert
(24) between the insert upper and lower clamping surfaces; wherein: in a front
view of the cutting tool assembly, the upper the lower clamping surfaces (50,42)
of the lower and upper clamping jaws (34,32), respectively, are partially convex,
and the insert lower and upper clamping surfaces (66,64) are concave; the
cutting insert (24) is retained in the insert receiving slot (36) in a retained
position by means of the clamping screw (26) which passes through the through
bore (44) in the upper and lower clamping jaws of the cutting insert holder and
through the at least one through hole (118) in the cutting insert (24) and is
screwed into the threaded through bore in one of the upper or lower clamping
jaws; the lower clamping surface (42) of the upper clamping jaw (32) engages
the insert upper clamping surface (64) at at least one upper region of contact
and the upper clamping surface (50) of the lower clamping jaw (34) engages the
insert lower surface (66) at at least one lower region of contact; characterized in
that: the inert upper clamping surface (64) conforms with a first cylindrical
surface having a first radius of curvature, r1, and a first cylinder axis; the insert
lower clamping surface (66) conforms with a second cylindrical surface having a
second radius of curvature,r2, and a second cylinder axis; the upper clamping
surface (50) of the lower clamping jaw (34) partially conforms with a third
cylindrical surface having a third radius of curvature, R2, and a third cylindrical
axis; the lower clamping surface (42) of the upper clamping jaw (32) partially
conforms with a fourth cylindrical surface having a fourth radius of curvature, R1
and a fourth cylinder axis; the fourth radius of curvature, R1, is greater than the
first radius of curvature, r1, the third radius of curvature, R2, is greater than the
second radius of curvature, r2.

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Patent Number 225251
Indian Patent Application Number IN/PCT/2002/00411/KOL
PG Journal Number 45/2008
Publication Date 07-Nov-2008
Grant Date 05-Nov-2008
Date of Filing 27-Mar-2002
Name of Patentee ISCAR LTD.
Applicant Address P.O. BOX 11, 24959 TEFEN
Inventors:
# Inventor's Name Inventor's Address
1 SATRAN AMIR 6, MORAN STREET, 25147 KFAR VRADIM
2 AGRANOVSKY DINA 5 STEINMETZ STREET APT. 2, 22405 NAHARIYA
PCT International Classification Number B23C 5/10
PCT International Application Number PCT/IL2000/00557
PCT International Filing date 2000-09-12
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 132261 1999-10-07 Israel