Polygonal cutting insert

A polygonal indexable cutting insert has a chip breaker with a backwall arranged in a sinuous path with the portion approaching the corner having a shallower slope than the main portion.

BACKGROUND OF THE INVENTION 
The present invention relates to disposable cutting inserts which may be 
detachably mounted on a tool holder for cutting a work piece. Cutting 
inserts of this type are generally made of cemented metal carbide and are 
formed by pressing and sintering techniques. 
In the type of cutting inserts referred to herein, it is desirable to have 
an indexable insert which presents a positive rake cutting edge to the 
working piece. 
U.S. Pat. No. 3,885,281 to Stambler describes an insert having both 
longitudinally curved and transversally curved channels along the side 
edges of the insert which meeting at the corners of the insert. Also each 
corner of the insert, V-shaped shallow grooves are depressed into the 
merging portions of the deeper longitudinal channels to provide chip 
control for shallow depth cuts. 
U.S. Pat. No. 3,786,541 to Lundgren relates to a cutting insert having chip 
breakers in two stages wherein the cutting edge and the associated chip 
breaker describe a curve of a particular description. 
U.S. Pat. No. 3,786,540 describes an insert having chip control groove 
extending along a side surface. The width of the groove describes a 
compound curve such that the width varies along the length of the side. 
U.S. Pat. No. 3,399,442 to Jones describes an insert having chip control 
groove along the entire outer edge comprising an inner and outer region. 
The outer region is concave in cross-section. 
U.S. Pat. No. 4,335,984 to Zweekly describes an insert having a plurality 
of breaking depressions in the chip breaker surface adjacent to the 
cutting corner. 
U.S. Pat. No. 4,273,480 describes a succession of chip control recesses 
formed on the cutting face at the outer periphery along the cutting edge. 
The chip control recesses are generally spherical and may intersect or 
contact each other as well as the cutting edge. 
U.S. Pat. No. 4,215,957 discloses depressions which are generally 
rectangular with inner corners spaced from the cutting edge. 
SUMMARY OF THE INVENTION 
As the workpiece is cut, the chip which is removed flows over the cutting 
edge and downwardly and inwardly along a descending wall portion. The chip 
next encounters a floor and then an ascending wall which directs the chip 
upwardly and outwardly. Chip breakers of the prior art include a variety 
of strategically located islands, bumps, and angles in a variety of 
configurations which tend to radial deform the flowing chip. This 
deformation tends to cause breakage of the chip. Heretofore, chip breakers 
have not concentrated on being oriented to the cutting edge in such a way 
so as to present an advantageous angle with the cutting edge to deflect 
the chip in an axial direction or a direction parallel with the cutting 
edge actually performing the cutting. In the present invention, the chip 
breaker angle with the cutting edge results an efficient chip-breaking 
action so as to provide chip control of the chip in an axial direction. 
More specifically, due to the configuration of the chip breaker, the chip 
tends to deflect in an axial direction toward the center. 
U.S. patent application Ser. No. 081,266 now U.S. Pat. No. 4,787,784 as 
referred to above relates an insert having a backwall surface extending in 
a sinuous path. More specifically, a polygonal indexable cutting insert 
comprises a pair of substantially parallel spaced-apart faces and 
peripheral side surfaces normal to said parallel faces. The faces on the 
side surfaces are joined to form corners. The pair of cutting edges extend 
away from each corner substantially within the plane of a respective face. 
Each cutting edge extends between a corner and its respective adjacent 
corners. A floor surface is substantially parallel to a respective face 
surface and spaced downwardly toward the center of the insert therefrom. A 
ramp surface extends downwardly from a respective cutting edge to the 
floor surface to form a positive rake insert. A backwall surface is spaced 
rearwardly of the cutting edge and extends upwardly from a respective 
floor surface to a respective face surface. The backwall surface extends 
in a sinuous path from a corner of the insert to a position intermediate 
the corners in a manner tending to deflect chips in a direction parallel 
to the cutting edge and toward the center of the insert. 
The present invention is an improvement of the aforementioned application 
and includes a backwall of reduced slope at the corners for enhancing nose 
stability by reducing uncontrolled deterioration of the corners during 
cutting. 
It is an object of the present invention to obviate one or more 
disadvantages of the prior art. 
Other and further objects of the present invention will be apparent to one 
of ordinary skill in the art from reading of the detailed specification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIG. 1, the cutting insert 15 has substantially parallel faces 
17,19 with peripheral side surfaces 21-24 normal to the parallel faces 
17,19. The faces 17,19 are joined with side surfaces 21-24 to form eight 
corners at the junctions. One corner 25 is at the juncture of face 17 and 
side surfaces 21 and 24. The remaining corners are similarly formed. A 
pair of cutting edges 27,29 extend away from corner 25 substantially 
within the plane of a face 17. Cutting edge 27 extends from corner 25 to 
an adjacent corner 26. Similarly, each of the respective cutting edges 
extend between adjacent corners. 
For purposes of the following discussion, inwardly or the inward direction 
is toward the center of the insert while outwardly or the outward 
direction is in a direction away from the center of the insert. With 
reference to chip flow over a cutting edge, the radial direction is 
generally perpendicular to the cutting edge while the axial direction is 
parallel to the cutting edge. 
Continuing with a discussion of FIGS. 1 and 2, the insert 15 is provided 
with a pair of floor surfaces 33,35. Each floor surface 33,35 is spaced 
inwardly from the respective face surfaces 17,19. The chip breaker, as 
shown in FIG. 2 and in detail in FIG. 3, includes a respective ramp 
surface 37 which extends downwardly from a respective cutting edge 21 to 
the floor surface 33 and a backwall 41 which slopes upwardly from the 
floor surface 33 to the face surface 17. Each cutting edge has associated 
therewith a similarly formed chip breaker. 
As illustrated in FIG. 1, the ramp surface 37 extends inwardly a 
predetermined distance from a respective cutting edge 27,29 and forms a 
land of uniform width extending entirely around the periphery of the 
insert 15. Typically, each ramp surface includes very small flatland 
portion 45 extending inwardly therefrom so as to strengthen the cutting 
edge. In FIG. 4, flatland portion 45 is shown at a 5 degree angle with the 
face surface 17. Preferably, the ramp surface 37 extends downwardly from 
the cutting edge at an angle of 15 to about 25 degrees, and more 
preferably at an angle of about 20.degree. as shown in FIG. 4 at B. 
Preferably, the ramp surface 37 extends downwardly a suitable distance 
respective face surface 17 to the floor surface 33. The floor surface 33 
should be sufficiently deep so as to change the direction of chip flow. 
The directional change enhances the tendency of the chip to break. 
The backwall surface 41 extends intermediate to respective floor surface 33 
and a respective face surface 17. As shown in FIG. 1, the backwall surface 
41 forms a sinuous path along a direction parallel to the cutting edge. A 
chip flowing over the cutting edge 27 down the ramp surface 37 and along 
the floor surface 33 encounters the backwall surface 41. At the junction 
of the floor surface 33 and backwall surface 41, a flowing chip encounters 
a backwall 41 which functions to deflect the chip in an outward direction 
away from the floor surface 33 and toward the parallel face 17. Due to the 
sinuous shape of the backwall 41, the chip tends to flow and be guided in 
the direction parallel to the cutting edge 27 and away from each of the 
corners 25,26. More specifically, the backwall extends from a position 
closely adjacent a corner to the intermediate position in such a manner 
that chips tend to be deflected toward inwardly along a direction parallel 
to the cutting edge. The tendency of chips to flow in a direction parallel 
with the cutting edge toward the center of the insert is achieved by 
having the backwall have a leg extending at an acute angle with the 
cutting edge. As chips flow over the cutting edge, they tend to be 
deflected toward the center of the insert. 
The sinuous backwall 41 forms a wave pattern undulating toward and away 
from the ramp surface 37. Starting at a point closely adjacent corner 26, 
the backwall 41 undulates toward the center of the insert and then 
outwardly toward the ramp surface 37 before undulating toward the center. 
Progressing from corner 26 to 25 in a direction parallel to the cutting 
edge 21, FIG. 1 shows an embodiment utilizing four undulations one of 
which is illustrated at 51. The backwall 41 includes at least two 
undulations positioned between each corner, preferably from 3 to 5 
undulations, and more preferably 4 undulations. The embodiment illustrated 
in FIG. 1 shows four undulations while the embodiment shown in FIG. 5 
illustrates five undulations. 
Undulation 51 is representative of the undulations forming the backwall 41. 
Undulation 51 includes an inner portion 53 and an outer portion 55. A pair 
of leg portions 57,59 connect the inner portion of undulation 51 to a 
respective outer portion 55. Progressing in a direction parallel to the 
cutting edge 21 from corner 26 to the center of the insert as represented 
by center line 63, the respective legs of the respective undulations are 
alternately longer and then shorter than the next adjacent leg. For 
example, leg 59 is longer than adjacent leg 51 which in turn is shorter 
than adjacent leg 61 and which in turn is longer than the next leg. 
As illustrated in FIG. 1 and in FIG. 5, the inner portions of the 
undulations such as shown at 53 are curved or arcuate while the outer 
portions adjacent the cutting edge 21 as shown at 55 are flat sections. 
The respective outer portions adjacent the respective corners are 
illustrated as curved sections. The purpose of the abrupt flat section 
closely adjacent the cutting edge is to impart an immediate change of 
direction to a chip. 
In operation, the chip breaker of the present invention tends to influence 
the flow of the chip in both a radial and axial direction. The greater 
distance a chip travels before striking a backwall, the greater the radial 
curve while the shorter the distance the tighter the radial curve. Due to 
this effect, the undulations tend to enhance the tendency of chips to be 
directed toward the center of the insert. 
FIG. 5 illustrates an embodiment utilizing five undulations 61 between 
corners 63 and 65. The inner portion 67 of the backwall 69 is directly 
adjacent the ramp surface 71 at one position adjacent the corner 65. 
Although both FIGS. 5 and 1 illustrate an indexable insert having four 
sides, it is contemplated that triangular inserts may be included within 
the scope of the present invention together with other variations apparent 
to one of ordinary skill in the art. 
FIG. 6 illustrates an embodiment of the present invention wherein the slope 
of the backwall at respective corners is modified. Although a 
triangularly-shaped cutting insert is shown at 71 in FIG. 6, the following 
description applies to other polygonal inserts typically used for cutting. 
The insert 71 includes a sinuous backwall 73 which undulates toward the 
center of the insert and then outwardly toward the ramp surface 75 before 
undulating toward the center. Preferably, the main portion of the backwall 
77 intermediate the corners slopes upwardly from the floor 79 to the face 
81 at a substantially constant angle. Preferably, the angle which is shown 
as angle C in FIG. 4 is relatively steep, an angle of from about 30 to 
about 40 degrees and more preferably at an angle of about 35 degrees. 
The following description of modified corner 83 applies to the remaining 
corners of the polygonal. Corner 83 is bisected by center line 85. At the 
corner 83, the main portion of the backwall 73 forms a pair of 
complementary backwall portions 85, 87 which extend on opposite sides of 
the bisector or center line 85 toward corner 83. The complementary 
backwall portions 85, 87 preferably have the predetermined uniform slope 
as hereinbefore discussed. The bridging backwall portion 89 which joins 
and extends intermediate the complementary backwall portions 85, 87 
extends outwardly closely adjacent the ramp surface 75. 
A substantial portion of the bridging backwall portion 89 slopes upwardly 
from the floor 79 at a gradual angle of from about 5 to about 12 degrees. 
This angle which is shown in FIG. 7 as angle D is relatively shallow. Most 
preferably, angle D is about 8 degrees. In FIG. 7, the bridging or 
modified backwall portion 89 includes a first section 93 and second 
section 95 which have a slope corresponding to the main portion of the 
backwall 77. The first section 93 forms a juncture between the gradual 
sloping portion of the bridging portion 89 and the floor 79. The second 
section 95 forms a juncture between the gradual sloping portion of the 
bridging portion 89 and the face surface 81. 
It has been found that reducing the slope of the backwall 73 at the corner 
results in enhanced nose stability by reducing uncontrolled deterioration 
of the corners during cutting.