Metal cutting tool

A metal cutting tool having a metal cutting tip such as a replaceable insert, having top and bottom faces and a plurality of peripheral faces and a rake face forming part of the top face. A cutting edge is formed at the intersection of the top face and one of the peripheral faces. Chip forming means is formed on the top face and comprises, in lateral sectional view, successive portions of which at least one is relatively recessed with respect to a preceding or succeeding portion. A through-going bore is formed in the insert and extends from one of the bottom and peripheral faces to the relatively recessed portion in a direction towards the cutting edge.

FIELD OF THE INVENTION 
This invention relates to a metal cutting tool of the kind having a metal 
cutting tip which is either an integral part of the tool or which is a 
metal cutting insert which is releasably retained in an insert holder for 
use in parting, grooving, turning or milling operations. 
BACKGROUND OF THE INVENTION 
With such metal cutting tools, the tip cutting edge becomes rapidly worn 
and must be frequently reset or, where the tip is a replaceable insert, 
the latter must therefore be frequently replaced. The degree of wear of 
the cutting edge is directly related to the degree of heating of the 
cutting edge during the cutting operation, and it is therefore known to 
provide means for cooling the cutting tip during the cutting operation. 
Such known means involve spraying the cutting tip or the cutting insert 
and/or the insert holder with a suitable cooling liquid and/or arranging 
for the generated heat to be thermally dissipated. (See, e.g. DE 3004166 
and DE 3429842.) 
Another well-known problem in the use of metal cutting tools for metal 
cutting operations of the kind indicated above resides in the effective 
and safe removal of the metal cutting chips formed during the cutting 
operation. Various means are employed so as to ensure the effective and 
safe removal of these chips, such means generally involving the provision 
of the metal cutting tip with suitable chip forming means which ensure 
that the chips are effectively compacted and break away in relatively 
short lengths. Furthermore, when the cutting tool is used in cut-off or 
grooving operations, it must be ensured that the chip does not become 
lodged within the cut-off slot and so the chip forming means are usually 
so designed as to ensure that the chip is narrowed in its lateral extent, 
thereby preventing the chip from becoming lodged in the slot. 
BRIEF SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a new and improved 
metal cutting tool as well as a replaceable metal cutting insert for use 
with such a metal cutting tool so as to facilitate the use of the flow of 
a cooling fluid, on the one hand to limit wear of the cutting edge, and on 
the other hand to ensure effective removal of metal cutting chips. 
According to one aspect of the present invention there is provided a metal 
cutting tool having a metal cutting tip having top and bottom faces and a 
plurality of peripheral faces and a rake face forming part of the top 
face; a cutting edge formed at the intersection of the top face and one of 
the peripheral faces; chip forming means formed on said top face and 
comprising, in lateral sectional view, successive portions of which at 
least one is relatively recessed with respect to a preceding or succeeding 
portion and a through-going bore formed in said insert and extending from 
one of said bottom and peripheral faces to said relatively recessed 
portion in a direction towards said cutting edge. 
According to another aspect of the present invention there is provided a 
metal cutting tool comprising a metal cutting insert, and an insert holder 
for releasably retaining said insert, said insert having top and bottom 
faces and a plurality of peripheral faces and a rake face forming part of 
the top face; a cutting edge formed at the intersection of the top face 
and one of the peripheral faces; chip forming means formed on said top 
face and comprising, in lateral sectional view, successive portions of 
which at least one is relatively recessed with respect to a preceding or 
succeeding portion and a through-going bore formed in said insert and 
extending from one of said bottom and peripheral faces to said relatively 
recessed portion in a direction towards said cutting edge, said insert 
holder being formed with a through-going bore, one end of which is adapted 
to be coupled to a cooling fluid supply source and the opposite end of 
which communicates with said insert bore. 
The invention also relates to metal cutting inserts for use with such a 
metal cutting tool. 
With a metal cutting tool in accordance with the invention, the cooling 
stream directed through the insert bore strikes the chip in the region 
thereof close to the cutting edge where the chip is still hot and 
relatively malleable. By directing the chip away from the insert, the 
effective length of contact of chip and the insert is reduced, thereby 
reducing heat which arises from the frictional contact of the chip with 
the insert. Furthermore, the effect of the cooling jet on the chip is, on 
the one hand, to influence and fix any deformation and narrowing of the 
chip caused by the chip forming means and also to render the chip more 
brittle and therefore readier to break and, on the other hand, to deflect 
the chip away from the insert and the workpiece. Thus, the cooling stream 
tends to assist in the effective removal of the compacted and readily 
broken chip lengths from the insert and the workpiece. At the same time, 
the cooling fluid serves to effect cooling of the insert, particularly in 
the region of the cutting edge thereof, and in this way effectively 
reduces the wear on the cutting edge. 
It will be realised that by virtue of the cooling of the chip and the 
insert, metallurgical phase changes occur in the chip and the workpiece. 
The particular construction of the cutting insert and the fact that the 
outlet of the insert bore is located in a relatively recessed portion of 
the chip forming means ensures that the chip, during its formation, does 
not effectively block the bore outlet but that there is rather formed a 
recess between the insert and the chip, which recess becomes filled with 
the cooling fluid, thereby contributing to the chip evacuation and to the 
cooling effect of the fluid.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
As seen in FIGS. 1 and 2 of the drawings, a metal cutting tool comprises a 
metal cutting insert 1 and an insert holder 2. Both the insert and the 
insert holder are, for example, of the kind disclosed in our U.S. Pat. No. 
4,558,974 to which reference can be made for further particulars. As seen 
in FIG. 2, the insert 1 comprises an upper face 3 and a bottom face 4, a 
front peripheral (relief) face 5, a rear peripheral face 6 and side 
peripheral faces 7. The top face 3 consists of a leading rake surface 8 of 
a leading insert portion and a trailing keying surface 9 of a trailing 
wedge-shaped portion 9a, the surface 9 sloping towards the bottom face 4 
which is also formed with a keying structure. 
A cutting edge 10 is formed at the intersection of the front relief face 5 
and the leading rake surface 8 and is provided with a substantially planar 
land surface 11. 
The rake surface 8 is provided with chip forming means 8a comprising a pair 
of elevated side ridges 12a and 12b which present rearwardly sloping chip 
deflecting surfaces 13a and 13b. Intermediate the ridges 12a and 12b is a 
relatively recessed central portion 12c. Thus the chip forming means 8a 
comprises, in lateral sectional view, successive portions 12a, 12c and 12b 
with the portion 12c being recessed with respect to the portions 12a and 
12b. 
Extending through the insert 1 is a through-going bore 15 which extends, in 
a direction towards the cutting edge 10, from a bore inlet 15a located in 
the bottom face 4 to a bore outlet 15b located in the recessed portion 12c 
of the rake face 8. 
As can be seen from FIG. 1, when the insert 1 is retainably wedge clamped 
in a corresponding wedge-shaped slot formed in an insert holder 2, the 
insert bore 15 communicates with a corresponding bore 16 formed in the 
insert holder 2 and the bore 16 communicates with a source of cooling 
fluid (not shown). 
The mode of use and functioning of the cutting tool just described with 
reference to FIGS. 1 and 2 of the drawings will now be considered with 
reference to FIGS. 3, 4 and 5 of the drawings. 
As seen in FIG. 3, when the metal cutting tool in accordance with the 
invention is used in a parting operation on a workpiece 17, the metal 
cutting chip 18, immediately after shearing is diverted upwardly by 
passing over the planar land surface 11 and the chip deflecting surfaces 
13a and 13b. At the same time, a stream of cooling fluid 19 passes through 
the insert bore 15, effectively fills and expands within the cavity formed 
by the recessed portion 12c and strikes the undersurface of the central 
portion of the chip 18. 
The action of the cooling fluid stream is essentially two-fold. On the one 
hand, it effectively cools the insert, especially in the region of the 
cutting edge thereof, thereby reducing the wear of the cutting edge and 
thus prolonging its effective working life. On the other hand, the stream 
contributes to the effective upward deflection of the chip 18 away from 
the cutting tool and the workpiece 17. Furthermore, the cooling fluid 
stream 19, by striking the central underportion of the chip 18, results in 
the differential cooling of this central underportion with respect to the 
upper portion of the chip 18 and this combines with the chip forming means 
to deform the chip 18. 
Thus, as can be seen in FIG. 4 of the drawings, the chip 18 immediately 
after shearing extends uniformly and flatly over the land surface 11 of 
the insert 1. However, when the chip has progressed over the recessed 
portion 12c it is struck by the cooling fluid stream 19. The combined 
effect of the chip former means 8a and the cooling stream results in the 
chip 18 being deformed downwardly as is clearly shown in FIG. 5 of the 
drawings. The thus deformed chip 18 narrows beyond the lateral dimension 
thereof in the initial stage as shown in FIG. 4 of the drawings. This 
narrowed, deformed chip 18 readily clears the slot formed in the workpiece 
in a parting-off operation. The cooling of the chip leads to its ready 
curling with a substantially increased curling radius and it readily coils 
into a compact shape and breaks off in compact masses. The breaking off of 
the chip 18 is facilitated by the differential cooling thereof by the jet, 
which renders the chip 18 much more brittle. 
In the embodiment schematically shown in FIG. 6 of the drawings, the rake 
face of the insert is provided, in addition to side ridges 21a, 21b, also 
with a central ridge 21c, the side ridges 21a, 21b defining with the 
central ridge 21c a pair of recessed portions 22a, 22b, each recessed 
portion 22a, 22b including the outlet 23a, 23b of a separate insert bore. 
In the embodiment shown in FIG. 7 of the drawings, the rake face of the 
insert is provided with a pair of central ridges 24a, 24b which, together 
with the side ridges 24c, 24d, define three successive recessed portions 
25a, 25b, 25c, each including an outlet 26a, 26b, 26c of a distinct insert 
bore. 
In all cases, however, the outlet of the or each insert bore is formed in a 
recessed portion of the rake face and in this way it is ensured that the 
chip cannot effectively seal the outlet of the insert bore so as to 
prevent the effective discharge of the cooling fluid. On the contrary, the 
cooling fluid spreads throughout the recess and therefore effective 
cooling and lubrication is achieved. 
Whilst in the embodiments described and illustrated above the insert bore 
and the outlets thereof are of circular cross-sectional shape, other 
cross-sectional shapes for the bore can effectively be used, a suitable 
cross-sectional shape being an effectively elliptical shape. 
The transverse extent of the bore outlet (or where a plurality of bore 
outlets are involved, the sum of the bore outlets) should be within the 
range of 5-50% (preferably 10-40%) of the overall lateral extent of the 
insert. 
The lateral dimensions of the base must be sufficiently low to ensure that 
the cooling stream strikes the chip with sufficiently high pressure but 
not so low as to reduce the flow rate to below that required for effective 
insert cooling and chip deformation. 
The cooling stream enters each bore at a pressure which can be between 
atmospheric pressure and 20 atm. A preferred pressure range is 6-16 atm. 
Whilst, as indicated above, the insert bore or bores should be directed 
towards the cutting edge, the angle of direction of the insert bore or 
bores with respect to the plane of the rake face can lie between 
5.degree.-85.degree. with respect to a plane which passes through the 
cutting edge and the rotational axis of the workpiece. Preferably the 
angle lies between 60.degree.-80.degree. and, as is the case in the 
embodiment shown in the drawings, the bore extends from the bottomface of 
the insert. The possibility, however, also exists for the bore to extend 
from a rear peripheral face of the insert. 
The or each recessed portion of the rake face can be constituted 
effectively by a flared outlet or mouth of the or each bore. 
FIG. 8 is a graph showing the relative wear of a GFN-3 IC20 insert when 
used in forming a groove in an INCONEL 718 steel bar. The figure shows the 
differing wear behaviour of the same type of insert used under the same 
conditions, on the one hand when the cutting tool is subjected to 
conventional cooling from an overhead cooling liquid source directed on to 
the rake face and, on the other hand when the cutting tool is subjected to 
cooling in accordance with the present invention with a fluid flow 
pressure of 16 atm. As can be readily seen from the figure, the wear 
experienced when the insert is cooled in accordance with the present 
invention is very significantly less than that when the insert is 
subjected to cooling under standard cooling conditions and, in 
consequence, the effective working lifetime of inserts in accordance with 
the present invention is very significantly greater than that of 
conventionally cooled inserts. 
Whilst the invention has been specifically described as applied to a 
parting or cut-off tool or the kind wherein the insert is wedge clamped in 
a correspondingly wedge-shaped slot formed in an insert holder, the 
invention is equally applicable to other forms of cutting tools wherein 
the cutting insert is releasably retained in the insert holder by other 
means and where the tool is designed also for other types of cutting 
operations, such as turning or milling. 
Thus, for example, and as described in our U.S. Pat. No. 4,992,008, the 
insert can be formed, in addition to a front cutting edge for use in 
parting or grooving, also with side cutting edges, for use in laterally 
directed turning operations. Such an insert can be provided, in accordance 
with the present invention, with a plurality of through-going bores so 
that one or more recessed portions respectively associated with the 
cutting edges are respectively formed with one or more bores. 
Whilst the invention has been specifically described by way of example in 
connection with a metal cutting tool wherein the cutting tool is 
constituted by a cutting tip which consists of a replaceable insert, the 
invention is equally applicable where the cutting tip forms an integral 
part of, e.g. is brazed to, the cutting tool.