WO1998033615A1

WO1998033615A1 - Cutting inserts

Info

Publication number: WO1998033615A1
Application number: PCT/IL1997/000374
Authority: WO
Inventors: Benjamin Betman
Original assignee: Iscar Ltd.
Priority date: 1997-02-03
Filing date: 1997-11-17
Publication date: 1998-08-06
Also published as: ZA9711040B; AR011380A1; JP3050537U; IL120137A0; AU4963597A; DE29800958U1

Abstract

A cutting insert (22) has an upper rake surface, peripheral flank surfaces, a base, and a central axis of rotational symmetry, the intersection between the upper rake surface and the peripheral flank surfaces forming at least one cutting edge. The peripheral flank surfaces of the cutting insert include a first flank surface portion (28) bounded in part by the cutting edge and in part by a lower boundary, the first flank surface portion having a primary positive relief angle, and a second flank surface portion (30) extending from the lower boundary towards the base, the second flank surface portion having a relief angle no greater than about zero. The positive relief angle is typically less than about 30°, and preferably between about 4° and about 20°. Optionally, the peripheral flank surfaces may further include a third flank surface portion (40) extending from adjacent to the second flank surface portion towards the base, the third flank surface portion having a secondary positive relief angle.

Description

CUTTING INSERTS

FIELD AND BACKGROUND OF THE INVENTTON

The present invention relates to indexable cutting inserts for cutting

operations and, in particular, it concerns the geometry of peripheral relief

surfaces of such inserts. The present invention also relates to cutting tool

holders and assemblies employing inserts of this type.

It is known to employ tools fitted with replaceable cutting inserts of

various shapes to cut metals. In order to prevent the insert from rubbing against

the workpiece, referred to as "heal-dragging", which causes unnecessary wear

and heating, it is necessary to provide a clearance angle between the relief

surface of the insert behind the cutting edge and the surface being machined.

As is schematically illustrated in Figures 1 and 2, conventional cutting

inserts may be broadly classified into two types: negative inserts, in which

radial and axial clearance angles α_R and α_A (only α_R being shown) depend on

^"double tilting" of the insert with respect to the surfaces being cut; and positive

inserts, in which the intrinsic geometry of the insert with built-in positive relief

angles provides sufficient clearance angles, thereby allowing an option of

mounting the cutting insert rake face normally to the surfaces being cut.

Figure 1 shows schematically a cutting tool assembly employing a

negative insert 10 mounted in a tool holder 12 to cut a rotating workpiece 14.

Insert 10 is termed "negative'^" since its intrinsic relief angle is no greater than 0°. This necessitates negative angling of the insert mounting surfaces of tool

holder 12 so as to generate the required clearance angles α_R and α_A (only α_R

being shown).

Also shown in Figure 1 are the typical in-plane components of the

cutting forces, in which F_τ represents the tangential component of the cutting

forces, i.e., the cutting force generated in the primary cutting direction

corresponding to the primary direction of relative motion between insert 10 and

workpiece 14, and F_R represents the radial component of the cutting forces,

which takes on a significant magnitude primarily during plunge grooving or

similar procedures. Under almost all machining conditions, tangential force F_τ

is much greater than either radial force F_R or axial force F_A (not shown).

As a result of the orientation of the abutment surfaces of tool holder 12,

the closest part of tool holder 12 available to react against tangential force F_τ is

displaced laterally by a distance d_t from the line of action of tangential force

F_τ. This displacement results in a large bending moment acting on the insert

corner causing significant bending stress which is additive to the transverse

shear stress (combined via, for example, Tresca's failure hypothesis), wherein

both stresses are directly proportional to F_τ. Practically speaking, two

independent measures can be employed in order to reduce the combined stress:

1) providing a chip forming groove in the rake face behind the cutting edge and

2) sloping the main cutting edge from the cutting corner to the base of the

insert. These measures render the simple rake angle (definition provided below) less negative and produce an acute cutting edge wedge angle, all of which

contributes to reducing F_τ.

An obvious advantage of negative inserts is the simple orthogonal

geometry of the base and lateral abutment surfaces of the insert receiving

pocket of the tool holder. Another advantage of negative inserts derives from

the fact that the insert is naturally restrained by the up-right rear abutment

surfaces of the insert receiving pocket against up-ending due to the

aforementioned bending moment.

Figure 2 shows schematically a cutting tool assembly employing a

positive insert 16 mounted in a tool holder 18 to cut a rotating workpiece 14.

Insert 10 is termed "positive" since its intrinsic relief angles are positive,

thereby providing sufficient clearance angles α_R and α_A when positioned in a

tool holder with a base abutment surface perpendicular to the primary cutting

direction. In the case of a positive insert, the rear abutment surfaces of the insert

receiving pocket must be correspondingly outwardly sloped.

Also shown in Figure 2 are the typical in-plane components of the

cutting forces. Here, the closest part of tool holder 18 available to react against

tangential force F_τ is displaced laterally by distance d₂ from the line of action

of tangential force F_τ. For a hypothetical situation where the clearance angle

and the height of the insert is the same as for the negative insert shown in

Figure 1, naturally d₂ = dj. Such a case actually exist wherein a relief angle of

a positive insert equals the tilt angle of a negative insert tool holder, at about 6°. Thus, it would appear that the stress problem is shared by positive inserts. In

fact, the positive rake angles of positive inserts tend to ameliorate the cutting

forces. However, a different problem is created by the resultant bending

moment which tends to up-end the insert. Since the outwardly sloped rear

abutment surfaces of the insert receiving pocket is ineffective at resisting this

up-ending moment, a heavy burden is placed on the clamping mechanism. As a

result, the more convenient clamping techniques such as bottom lever clamping

are typically insufficient, and clamping from the top of the insert, for example,

by means of screw clamping (as shown), becomes necessary.

Reference will now be made to two particular patent publications,

namely, European Patent Publication 160,278 A2 and UK Patent Publication

2.156,254 A. In order not to confuse the reader, it should be pointed out that

these references do not constitute particularly relevant background to the

present invention. However, they are cited here because of a superficial

similarity they bear to the present invention, and for the purpose of setting out

the clear differences between the structures described therein and that of the

present invention.

Referring first to the European publication, this relates to controlling the

axial run-out of a cutting insert for a face milling cutter by grinding a relief

flank surface of the insert. Reference is made to a "conventional insert" in

which the periphery of the insert includes a standard positive-type relief surface

adjacent to the cutting edge, and a "rearward portion ... offset inwardly throughout the entire periphery thereof to provide a clearance portion". This

clearance portion allows a grinding operation to be performed exclusively on

the forward relief surfaces, thereby saving time and labor. However, the

offsetting of the rearward flank surface generates an unnecessary overhang of

the cutting edge, thereby reducing the structural support to the cutting edge

compared with a corresponding standard positive insert.

Turning now to the UK publication, this relates to a milling cutter in

which the inserts are placed tangentially or "on-edge", as opposed to being

radially placed in the conventional manner. The insert is attached by the use of

a screw passing through a hole in the relief flank surface. Unlike in

conventionally placed inserts, here the radial rake angle is determined by the

design of the peripheral edge surfaces. Adjoining a pair of opposite cutting

edges are composite rake surfaces having two surface portions of which a first,

adjacent the base surface, is normal to the base surface and a second, adjacent

to the cutting edge, has a positive rake angle. The superficial similarity of this

insert structure to those of the present invention is solely to the extent that the

eye may be mislead by a view of the cross-section of the insert to interpret the

composite rake surfaces as relief surfaces and vice-versa. However, on further

consideration, it will be abundantly clear to anyone ordinarily skilled in the art

that neither the conceptual considerations nor the structural features of the rake

surface of the aforementioned UK publication bear any relation to the relief

flank surface structures of the present invention. There is therefore a need for a geometry of relief flank surface which

provides sufficient cutting edge clearance to allow the insert to be mounted

with zero radial and axial rakes, while providing improved structural integrity

and support for the cutting edge. It would also be advantageous to have a

cutting tool assembly which allows the insert to be mounted with zero radial

and axial rakes, while simultaneously allowing use of an insert receiving pocket

with simple orthogonal definition of abutment surfaces, as well as facilitating

the use of bottom lever clamping.

SUMMARY OF THE INVENTION

The present invention is a cutting insert structure in which the peripheral

flank surfaces provide sufficient cutting edge clearance to allow the insert to be

mounted with zero radial and axial rake, while providing improved structural

integrity and support for the cutting edge.

According to the teachings of the present invention there is provided, a

cutting insert having an upper rake surface, peripheral flank surfaces, a base,

and a central axis of rotational symmetry, the intersection between the upper

rake surface and the peripheral flank surfaces forming at least one cutting edge,

the cutting insert being characterized in that the peripheral flank surfaces

include: (a) a first flank surface portion bounded in part by the cutting edge and

in part by a lower boundary, the first flank surface portion having a primary

positive relief angle; and (b) a second flank surface portion extending from the lower boundary towards the base, the second flank surface portion having a

relief angle no greater than about zero.

According to a further feature of the present invention, the positive relief

angle is less than about 30°.

According to a further feature of the present invention, the positive relief

angle is between about 4° and about 20°.

According to a further feature of the present invention, the second flank

surface portion has a relief angle substantially equal to zero.

According to a further feature of the present invention, the upper rake

surface is formed with at least one feature for chip control.

According to a further feature of the present invention, the peripheral

flank surfaces further include a third flank surface portion extending from

adjacent to the second flank surface portion towards the base, the third flank

surface portion having a secondary positive relief angle.

According to a further feature of the present invention, the secondary

positive relief angle is greater than about 10°.

According to a further feature of the present invention, the cutting insert

is symmetrical under rotations of 360°/n where n is at least 3.

According to a further feature of the present invention, the first flank

portion is shaped such that a cross-section of the cutting insert taken

perpendicular to the central axis proximal to the at least one cutting edge

exhibits n corners where n is at least 3, each of the corners being formed between two substantially straight lines, wherein the internal angle between the

substantially straight lines is less than (180° - 3607«).

According to a further feature of the present invention, there is provided

a cutting tool assembly comprising: (a) the cutting insert described above; and

(b) a tool holder having at least one insert receiving pocket for receiving the

cutting insert, the insert receiving pocket having a base abutment surface, and a

first rear abutment surface perpendicular to the base abutment surface.

According to a further feature of the present invention, the insert

receiving pocket further includes a second rear abutment surface perpendicular

to the base abutment surface and forming an open angle of less than about 120°

with the first rear abutment surface.

According to a further feature of the present invention, the second rear

abutment surface forms an open angle of not more than about 90° with the first

rear abutment surface.

According to a further feature of the present invention, the second rear

abutment surface forms an open angle of less than 90° with the first rear

abutment surface.

There is also provided according to the teachings of the present

invention, a tool holder for receiving a cutting insert having an upper flank

surface portion with a positive relief angle adjacent to a cutting edge, and a

lower flank surface portion with a zero relief angle, the tool holder comprising:

(a) at least one reference feature for defining a plane corresponding to a plane of zero axial and radial rake when the tool holder is in use; and (b) at least one

insert receiving pocket, the insert receiving pocket having a base abutment

surface substantially parallel to the plane, and a first rear abutment surface

perpendicular to the base abutment surface for abutting the lower flank surface

portion of the insert.

According to a further feature of the present invention, the insert

receiving pocket further includes a second rear abutment surface perpendicular

to the base abutment surface and forming an open angle of less than about 120°

with the first rear abutment surface.

According to a further feature of the present invention, the second rear

abutment surface forms an open angle of not more than about 90° with the first

rear abutment surface.

According to a further feature of the present invention, the second rear

abutment surface forms an open angle of less than 90° with the first rear

abutment surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with

reference to the accompanying drawings, wherein:

FIG. 1 is a schematic side cross-sectional view of a conventional cutting

tool including a negative cutting insert being used to cut a rotating workpiece; FIG. 2 is a schematic side cross-sectional view of a conventional cutting

tool including a positive cutting insert being used to cut a rotating workpiece;

FIG. 3 is a schematic side cross-sectional view of a first preferred

embodiment of a cutting tool assembly, constructed and operative according to

the teachings of the present invention, being used to cut a rotating workpiece;

FIG. 4 is an isometric view of a cutting insert of the assembly of

Figure 3;

FIG. 5 is a schematic side cross-sectional view of a second preferred

embodiment of a cutting tool assembly, constructed and operative according to

the teachings of the present invention, illustrating additional features for cutting

an internal surface of rotating workpiece;

FIG. 6 is an isometric view of a cutting insert of the assembly of

Figure 5;

FIG. 7A is an isometric view of a cutting insert for use in a third

preferred embodiment of a cutting tool assembly, constructed and operative

according to the teachings of the present invention;

FIG. 7B is a top view of the cutting insert of Figure 7 A;

FIG. 7C is a partial cross-sectional view taken along the line A-A of

Figure 7B;

FIG. 7D is a side view of the cutting insert of Figure 7A; FIG. 8 A is a side view of the third preferred embodiment of a cutting

tool assembly, constructed and operative according to the teachings of the

present invention, in which the insert of Figure 7 A is mounted in a tool holder;

FIG. 8B is a front view of the cutting tool assembly of Figure 8A;

FIG. 8C is a top view of the cutting tool assembly of Figure 8A;

FIG. 9A is a side view of the tool holder of Figure 8A;

FIG. 9B is a front view of the tool holder of Figure 8 A; and

FIG. 9C is a top view of the tool holder of Figure 8 A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a cutting insert structure in which the peripheral

mounted with zero radial and axial rake, while providing improved structural

integrity and support for the cutting edge. The invention also provides a tool

holder for use with such an insert structure which has an insert pocket

presenting zero axial and radial rake while having a simple orthogonal

definition for its abutment surfaces.

The principles and operation of cutting inserts according to the present

invention may be better understood with reference to the drawings and the

accompanying description.

Before proceeding with a detailed description of the preferred

embodiments of the present invention, it will be helpful to define certain terminology which will be employed herein in the specification and claims to

refer to various angles. In this regard, it should be noted that, wherever

reference is made to an angle between a line and a plane, the angle concerned is

hereby defined to be the angle between the line and its own orthogonal

projection on to the plane, unless specified otherwise.

Firstly, with respect to the intrinsic geometry of an insert considered

independent of a specific cutting tool arrangement, reference is made to a

central axis of rotational symmetry about which the entire insert, including its

one or more cutting edges, exhibits rø-fold rotational symmetry where n is at

least two. For convenience of reference, the central axis of rotational symmetry

of an insert will be termed "the central axis" of the insert.

The "relief angle" α of a part of a flank surface of an insert is then

defined as the angle between the central axis and the plane of the flank surface.

In the case of a non-planar flank surface (as is always the case for a circular

insert), the relief angle is evaluated using a plane defined by the local

inclination of the flank surface at a given point. The sign of the relief angle is

defined to be positive for a surface which becomes more distant from the

central axis in an upwards direction from the base towards the upper surface of

the insert.

When referring to inclination of surfaces of a cutting insert mounted in a

tool holder, tool-rake and clearance angles are defined relative to axial and

radial directions defined by the relative motion of the tool and the workpiece. Specifically, the axial direction is defined to be parallel to a primary axis of

rotation, either of the workpiece or of a rotary cutting tool (for example, used in

milling or drilling). The radial direction connects between that axis and the

surface in question. Thus, the radial and axial tool-rake angles γ_R and γ_A of an

upper rake surface are defined as the angles between the rake surface and the

aforementioned radial and axial directions, respectively. With respect to

clearance angles, the radial clearance angle α_R of a part of a flank surface

oriented in the axial direction is defined as the angle between a line mutually

perpendicular to both the radial and axial directions and (a radial projection of

that line on to) the part of the flank surface. Similarly, the axial clearance angle

α_A of a part of a flank surface oriented in the radial direction is defined as the

angle between a line mutually perpendicular to both the radial and axial

directions and (an axial projection of that line on to) the part of the flank

surface.

In a further issue of terminology, it should be noted that the rake angle

referred to in the context of the present description is that of the overall

disposition of the upper surface of a cutting insert, independent of the detailed

geometrical form adjacent to the cutting edge. Thus, as a result of the rotational

symmetry of the cutting inserts in question, the plane of the rake surface is

defined to be perpendicular to the central axis. As a further result of the same

symmetry, it follows that the predominant plane of the base of the cutting

insert, and hence the inclination of a base abutment surface of a tool holder, are also parallel to the rake surface. The axial and radial rake angles are thus a

direct indication of the inclination of a base abutment surface of a tool holder in

two directions.

Turning now to the drawings, Figure 3 illustrates schematically a first

embodiment of a cutting tool assembly, generally designated 20, constructed

and operative according to the teachings of the present invention, which

employs a cutting insert 22 mounted in a tool holder 24 to cut a rotating

workpiece 26.

Cutting insert 22 is shown separately in more detail in Figure 4.

Generally speaking, the relief flank surface of cutting insert 22 has a relatively

small first flank portion 28, adjacent to the cutting edge, which has a positive

relief angle, and a second flank portion 30, further removed from the cutting

edge, which has a non-positive relief angle. First flank portion 28 ensures that

there is sufficient clearance under the cutting edge when cutting insert 22 is

mounted with zero axial and radial inclination, so long as the flank wear is

within acceptable limits. Once sufficient clearance has been guaranteed, second

flank portion 30 serves to provide the maximum possible support to the cutting

edge.

Comparing Figure 3 with the prior art cutting tools of Figures 1 and 2, it

will be noted that the closest part of tool holder 24 available to react against

tangential force F_τ is displaced laterally by a distance d₃ from the line of action

of tangential force F_τ. For the same clearance angles α_R and α_A (not shown), this displacement is much smaller than the displacements dj and d₂ of the

respective prior art cutting tools, thereby greatly reducing the bending moment

on the insert, and the resultant stress and up-ending moment.

The non-positive relief angle of second flank portion 30 also provides

considerable advantages for clamping of cutting insert 22 in tool holder 24. The

resulting up-right rear abutment surfaces of the insert receiving pocket provide

effective restraining action against considerable up-ending moments. This

allows use of the highly convenient bottom lever clamping to clamp insert 22.

Furthermore, in a preferred embodiment in which second flank portion 30 has a

relief angle substantially equal to 0°, the rear abutment surfaces and the base of

the insert receiving pocket are mutually perpendicular, thereby facilitating

production, and improving precision, of the tool holder.

It should be noted that, although the present invention is illustrated by

way of example in the context of an insert with 90° rotational symmetry, it may

equally be applied to cutting inserts and corresponding tools with other

symmetry. In general terms, cutting inserts of the present invention are

symmetrical under rotations of 360°/n where n preferably has a value of at least

3. and typically at least four. Also within the scope of the present invention are

inserts with circular symmetry (n→∞).

Figure 5 illustrates a second embodiment of a cutting tool assembly,

generally designated 32, constructed and operative according to the teachings

of the present invention, which is especially advantageous for cutting an internal surface of rotating workpiece 38. Generally speaking, cutting tool

assembly 32, which includes a cutting insert 34 mounted in a tool holder 36, is

similar to cutting tool assembly 20, and equivalent features are labeled

similarly. In addition, cutting insert 34 features a third relief flank portion 40,

located below second relief flank portion 30, which has a positive relief angle.

Third relief flank portion 40 provides additional clearance to accommodate the

internal curvature of workpiece 38. At the same time, third relief flank portion

40 allows the use of a large fillet radius at the intersection between the base and

each of the rear abutment surfaces which tends to reduce stress concentrations.

Cutting insert 34 is shown separately in more detail in Figure 6.

Turning now to Figures 7A-7D, these show a third preferred

embodiment of a cutting insert, generally designated 50, constructed and

operative according to the teachings of the present invention. Generally

speaking, cutting insert 50 is similar to cutting insert 34, described above, but is

formed with recessed side edges. This embodiment is especially advantageous

for cutting relatively shallow square shoulders.

Thus, cutting insert 50 features an upper rake surface 52, peripheral

flank surfaces 54, a base 56, and a central axis of rotational symmetry 58

(Figure 7D). The intersection between upper rake surface 52 and peripheral

flank surfaces 54 forms a cutting edge 60. Upper rake surface 52 is preferably

formed with at least one feature for chip control, exemplified here by chip-

breaking groove 53. Peripheral flank surfaces 54 include a first flank surface portion 62,

bounded in part by cutting edge 60 and in part by a lower boundary 64.

Peripheral flank surfaces 54 include a second flank surface portion 66,

extending from lower boundary 64 towards base 56. A third flank surface

portion 68 is provided around a part of the periphery of cutting insert 50,

extending from adjacent to second flank surface portion 66 towards base 56.

As shown in Figure 7C, first flank surface portion 62 has a primary

positive relief angle α. Relief angle α is preferably less than about 30°, and

typically between about 4° and about 20°. Second flank surface portion 66 has

a relief angle no greater than about zero, and typically substantially equal to

zero. Third flank surface portion 68 has a secondary positive relief angle β

which is typically greater than about 10°.

As mentioned above, cutting insert 50 preferably features recessed side

edges especially advantageous for cutting relatively shallow square shoulders.

Specifically, first flank portion 62 is preferably shaped such that a cross-section

of cutting insert 50 taken perpendicular to central axis 58 close to cutting edge

60 exhibits four outwardly extending corners 70, each being formed between

two approximately straight lines 72 and 74. Lines 72 and 74 lie inside a virtual

line 76 between adjacent corners 70 such that the sides are termed "recessed".

The result of this structure is that the angle formed between lines 72 and 74 at

each corner is less than 90°. This provides clearance for the inoperative cutting edges of cutting insert 50 during cutting of shallow square shoulders during a

range of cutting operations including, but not limited to, longitudinal turning.

As mentioned earlier, the present invention may be applied to a range of

geometries with different rotational symmetry. Thus, in more general terms,

cutting insert 50 may be considered to have n corners where n is at least 3, each

of the corners being formed between two substantially straight lines. In this

general case, the internal angle between the lines at each corner is less than

( 180° - 360%).

It should be noted that reference is made to a cross-section through first

flank portion 62 rather than the shape of cutting edge 60, itself. Typically, the

geometry of cutting edge 60 and first flank portion 62 are similar such that this

distinction is not critical. The distinction is made, however, to accommodate

cases in which the cutting edge is serrated or otherwise irregular.

Turning now to Figures 8A-8C, these show a cutting tool assembly,

generally designated 80, constructed and operative according to the teachings

of the present invention, in which cutting insert 50 is mounted within a tool

holder 82. Tool holder 82 is shown separately in Figures 9A-9C.

As best seen in Figures 9A-9C, tool holder 82 features an insert

receiving pocket 84 formed with a plurality of abutment surfaces for receiving

cutting insert 50. Specifically, insert receiving pocket 84 has a base abutment

surface 86, and a number of rear abutment surfaces 88, 90, 92 and 94, each of

which is orthogonal to base abutment surface 86. The upper extreme of each rear abutment surface is provided with an inclined recess surface 96 to

accommodate the positive relief flank portion of cutting insert 50. A bottom

lever recess 98 is provided in base abutment surface 86 to receive a lever for

lever clamping.

It should be noted that the present invention provides significant

advantages when applied to cutting tools with a wide range of axial and radial

tool-rake angles. For any given tool-rake angles, the orthogonal abutment

surfaces provide a simpler and higher precision structure, and better restraint

against up-ending, than a similarly positioned conventional positive insert.

Simultaneously, the present invention provides greater clearance angles than a

similarly positioned conventional negative insert.

In addition to these general advantages, certain preferred embodiments

of the present invention exploit this unique combination of features to

simultaneously employ orthogonal abutment surfaces together with zero axial

and radial tool-rake angles. Thus, in this case, base abutment surface 86 is

parallel to a plane of zero axial and radial tool-rake as defined by reference

features such as the upper surface of the shank of tool holder 82. It should be

appreciated that this combination of features is impossible with conventional

insert geometries since positive inserts require non-orthogonal abutment

surfaces and negative inserts require negative axial and radial rake angles to

provide the clearance angles. The geometry of rear abutment surfaces 88, 90, 92 and 94 is

complementary to the surfaces of second flank surface portion 66 along two

adjacent recessed sides. In order to provide effective restraint against a range of

cutting forces which may arise, the rear abutment surfaces preferably include at

least two non-parallel surfaces which form between them an open angle of less

than about 120°. Preferably, for effective restraint of rotational moments, at

least two of the surfaces form between them an open angle of not more than

about 90°. In the embodiment illustrated, it should be noted that rear abutment

surfaces 90 and 92 form between them an angle of less than 90°, thereby

providing particularly secure restraint.

It will be appreciated that the above descriptions are intended only to

serve as examples, and that many other embodiments are possible within the

spirit and the scope of the present invention.

Claims

WHAT IS CLAIMED IS:

1. A cutting insert having an upper rake surface, peripheral flank

surfaces, a base, and a central axis of rotational symmetry, the intersection

between the upper rake surface and the peripheral flank surfaces forming at

least one cutting edge, the cutting insert being characterized in that the

peripheral flank surfaces include:

(a) a first flank surface portion bounded in part by the cutting edge

and in part by a lower boundary, said first flank surface portion

having a primary positive relief angle; and

(b) a second flank surface portion extending from said lower

boundary towards the base, said second flank surface portion

having a relief angle no greater than about zero.

2. The cutting insert of claim 1 , wherein said positive relief angle is

less than about 30°.

3. The cutting insert of claim 1, wherein said positive relief angle is

between about 4° and about 20°.

4. The cutting insert of claim 1, wherein said second flank surface

portion has a relief angle substantially equal to zero.

5. The cutting insert of claim 1, wherein the upper rake surface is

formed with at least one feature for chip control.

6. The cutting insert of claim 1, wherein the peripheral flank

surfaces further include a third flank surface portion extending from adjacent to

said second flank surface portion towards the base, said third flank surface

portion having a secondary positive relief angle.

7. The cutting insert of claim 6, wherein said secondary positive

relief angle is greater than about 10°.

8. The cutting insert of claim 1, wherein the cutting insert is

symmetrical under rotations of 360° In where n is at least 3.

9. The cutting insert of claim 1, wherein said first flank portion is

shaped such that a cross-section of the cutting insert taken perpendicular to the

central axis proximal to the at least one cutting edge exhibits n corners where n

is at least 3, each of said corners being formed between two substantially

straight lines, wherein the internal angle between said substantially straight

lines is less than (180° - 360 «).

10. A cutting tool assembly comprising:

(a) the cutting insert of claim 1 ; and (b) a tool holder having at least one insert receiving pocket for

receiving said cutting insert, said insert receiving pocket having a

base abutment surface, and a first rear abutment surface

perpendicular to said base abutment surface.

11. The cutting tool assembly of claim 10. wherein said insert

receiving pocket further includes a second rear abutment surface peφendicular

to said base abutment surface and forming an open angle of less than about

120° with said first rear abutment surface.

12. The cutting tool assembly of claim 1 1, wherein said second rear

abutment surface forms an open angle of not more than about 90° with said first

rear abutment surface.

13. The cutting tool assembly of claim 1 1, wherein said second rear

abutment surface forms an open angle of less than 90° with said first rear

abutment surface.

14. A tool holder for receiving a cutting insert having an upper flank

surface portion with a positive relief angle adjacent to a cutting edge, and a

lower flank surface portion with a zero relief angle, the tool holder comprising: (a) at least one reference feature for defining a plane corresponding

to a plane of zero axial and radial rake when the tool holder is in

use; and

(b) at least one insert receiving pocket, said insert receiving pocket

having a base abutment surface substantially parallel to said

plane, and a first rear abutment surface perpendicular to said base

abutment surface for abutting the lower flank surface portion of

the insert.

15. The tool holder of claim 14, wherein said insert receiving pocket

further includes a second rear abutment surface perpendicular to said base

abutment surface and forming an open angle of less than about 120° with said

first rear abutment surface.

16. The tool holder of claim 15, wherein said second rear abutment

surface forms an open angle of not more than about 90° with said first rear

abutment surface.

17. The tool holder of claim 15, wherein said second rear abutment surface forms an open angle of less than 90° with said first rear abutment surface. AMENDED CLAIMS

[received by the International Bureau on 28 June 1998 (28.06.98) ; original claims 1 -17 replaced by new claims 1 - 19 (4 pages ) ]

1. A cutting insert having an upper rake surface, peripheral flank surfaces, a base, and a central axis of rotational symmetry, the intersection between the upper rake surface and the peripheral flank surfaces forming at least one cutting edge, the cutting insert being characterized in that the peripheral flank surfaces include:

(a) a first flank surface portion bounded in part by the cutting edge and in part by a lower boundary, said first flank surface portion having a primary positive relief angle; and

(b) a second flank surface portion extending from said lower boundary to adjacent to the base, said second flank surface portion having a relief angle no greater than about zero.

2. The cutting insert of claim 1. wherein said positive relief angle is less than about 30°.

3. The cutting insert of claim 1. wherein said positive relief angle is between about 4° and about 20°.

4. The cutting insert of claim 1, wherein said second flank surface portion has a relief angle substantially equal to zero.

5. The cutting insert of claim 1. wherein the upper rake surface is formed with at least one feature for chip control.

6. The cutting insert of claim 1, wherein the cutting insert is symmetrical under rotations of 360% where n is at least 3.

7. The cutting insert of claim 1. wherein said first flank portion is shaped such that a cross-section of the cutting insert taken perpendicular to the central axis proximal to the at least one cutting edge exhibits n corners where n is at least 3, each of said corners being formed between two substantially straight lines, wherein the internal angle between said substantially straight lines is less than (180° - 360°/«).

8. A cutting tool assembly comprising:

(a) a cutting insert having an upper rake surface, peripheral flank surfaces, a base, and a central axis of rotational symmetry, the intersection between the upper rake surface and the peripheral flank surfaces forming at least one cutting edge, the peripheral flank surfaces including:

(i) a first flank surface portion bounded in part by the cutting edge and in part by a lower boundary, said first flank surface portion having a primary positive relief angle; and

(ii) a second flank surface portion extending from said lower boundary towards the base, said second flank surface portion having a relief angle no greater than about zero; and

(b) a tool holder having at least one insert receiving pocket for receiving said cutting insert, said insert receiving pocket having a base abutment surface configured for abutting the base of said cutting insert and first and second rear abutment surfaces configured for abutting corresponding parts of said second flank surface portion of said cutting insert.

9. The cutting tool assembly of claim 8, wherein said second rear abutment surface forming an open angle of less than about 120° with said first rear abutment surface.

10. The cutting tool assembly of claim 9. wherein said first and second rear abutment surfaces are peφendicular to said base abutment surface.

11. The cutting tool assembly of claim 9. wherein said second rear abutment surface forms an open angle of not more than about 90° with said first rear abutment surface.

12. The cutting tool assembly of claim 9, wherein said second rear abutment surface forms an open angle of less than 90° with said first rear abutment surface.

13. A tool holder for receiving a cutting insert having an upper flank surface portion with a positive relief angle adjacent to a cutting edge, and a lower flank surface portion with a zero relief angle, the tool holder comprising:

(a) at least one reference feature for defining a plane corresponding to a plane of zero axial and radial rake when the tool holder is in use; and

(b) at least one insert receiving pocket, said insert receiving pocket having a base abutment surface substantially parallel to said plane, and first and second rear abutment surfaces perpendicular to said base abutment surface for abutting the lower flank surface portion of the insert.

14. The tool holder of claim 13. wherein said second rear abutment surface forms an open angle of less than about 120° with said first rear abutment surface.

15. The tool holder of claim 14. wherein said second rear abutment surface forms an open angle of not more than about 90° with said first rear abutment surface.

16. The tool holder of claim 14. wherein said second rear abutment surface forms an open angle of less than 90° with said first rear abutment surface.

17. A cutting insert having an upper rake surface, peripheral flank surfaces, a base, and a central axis of rotational symmetry, the intersection between the upper rake surface and the peripheral flank surfaces forming at least one cutting edge, the cutting insert being characterized in that the peripheral flank surfaces include:

(a) a first flank surface portion bounded in part by the cutting edge and in part by a lower boundary, said first flank surface portion having a positive relief angle; and

(b) a second flank surface portion extending from said lower boundary towards the base, said second flank surface portion being configured to provide abutment surfaces for restraining the cutting insert within a pocket, said abutment surfaces being peφendicular to the base of the insert.

18. The cutting insert of claim 17. wherein the peripheral flank surfaces further include a third flank surface portion extending from adjacent to said second flank surface portion towards the base, said third flank surface portion having a secondary positive relief angle.

19. The cutting insert of claim 17. wherein the cutting edge is formed with a number of corners, the peripheral flank surfaces further including a number of isolated third flank surface portions extending from adjacent to said second flank surface portion towards the base around parts of the periphery of the cutting insert adjacent to said corners, said third flank surface portions having a secondary positive relief angle.