Chip breaking insert for metal cutting tools

The disclosure relates to an insert for a metal cutting tool having a chip breaking groove in the top face thereof of truncated conical lateral cross section defined by spaced angularly related straight side walls joined by a straight bottom portion extending parallel to the top face of the insert.

BACKGROUND OF THE INVENTION 
Form-sintered metal carbide inserts are often attached to the end of a 
cutting bar or other machine tool to maximize tool cutting speed and 
efficiency. Such inserts are generally of polygonal configuration to 
provide multiple, indexable, cutting edges at the sides and corners of the 
insert. Generally, the top face of the insert extends at substantially a 
right angle to the surface of the workpiece and is provided with a "chip 
breaker" in the form of a groove or other structural configuration. Chip 
breakers are important to the function of the machine tool as well as to 
personal safety of the machine operator in that if the turning forms long 
threads or continuous curls as opposed to being broken into chips, such 
threads or curls may become wound around the workpiece or become entangled 
in the machine tool creating substantial risk of personal injury and 
disturbance of the cutting operation. However, chip breaking under varying 
working conditions, for example, varying feed and cutting depth, requires 
careful attention to the combination of feed, cutting depth, and chip 
breaker configuration. 
As a chip breaker breaks the chip only within a certain limited range of 
cutting depth and feed, as defined by the shape and size of the chip 
breaker, it is necessary to provide inserts having different chip breaker 
configurations for different cutting depths and feeds. 
A special problem is presented with respect to effective chip breaking in 
finish cutting because both the cutting depth and the feed are relatively 
small. A conventional chip breaker chosen with regard to suitable shape 
and size for rough cutting is unacceptable when the workpiece is to be 
finished. At small cutting depth it is essential to decrease the rake 
angle in order to break the chip satisfactorily. Stated another way, it is 
important to have significant chip breaking capability at the nose of the 
insert since, at small cutting depths and feeds, the chip has to be 
sharply bent in order to break because of its small cross section. On the 
other hand, if the chip breaker is dimensioned for small chip thickness 
and cutting depth, the angles thereof will be too severe for chip breaking 
at larger chip thickness and cutting depth. 
The deformation or initial bend which the turning receives in the course of 
separation from the workpiece depends not merely upon its thickness but 
also upon rake angle. A decreasing rake angle means increasing initial 
bend but results in increasing cutting forces. Increasing the rake angle 
permits large cutting depths with relatively smaller cutting forces but 
decreased initial bend of the turning. 
Inserts having a chip breaker at the corner or nose thereof as well as a 
chip breaker groove alongside the cutting edge of the insert of varying 
depth and/or width, are well known. Specifically, chip breaking inserts 
having an initial flat cutting surface which is backed up by an arcuate 
chip breaking section are taught in the patents to Wirfelt Nos. 3,395,434; 
Stambler 3,885,281; Gehri 3,968,550 and Newcomer 3,381,349. The chip 
breaker disclosed in each of the aforesaid patents features an initial 
flat cutting surface which extends at substantially a right angle to the 
surface of the workpiece which blends into an arcuate chip breaker. The 
insert may be orientated at a positive or negative rake, if desired. 
Another chip breaking configuration is the "V" configuration as taught in 
the patents to Krugger Nos. 4,288,179; Seidel 4,056,872; Arnold 4,189,265; 
and Lundgren 3,866,282. 
While the inserts taught in each of the aforesaid patents can be utilized 
in a specific application, a need exists for an improved insert having an 
efficient chip breaker for finish cuts as well as cuts of greater depth 
and feed. 
SUMMARY OF THE INVENTION 
The insert of the instant invention features a chip breaking configuration 
on the nose thereof that, in transverse cross section, comprises a center 
flat disposed between angularly related side walls. The center flat is a 
segment of a right circular cylinder and the adjacent side walls are 
segments of opposed truncated cones. The center flat of the chip breaking 
groove initiates deflection of the turning, bending continuing and 
breaking occurring when the curl hits the opposite side of the chip 
breaker configuration. Less severe chip breakers are provided along the 
sides of the inserts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
As seen in FIG. 1 of the drawings, a cutting insert 20, in accordance with 
an exemplary constructed embodiment of the instant invention, is of 
triangular configuration, a central aperture 22 therein providing for 
attachment to a tool (not shown). As best seen in FIG. 4 of the drawings, 
the corners or "nose" portions 23 of the triangular configuration of the 
insert 20, are provided with a truncated, V-shaped chip breaking groove, 
opposite conical side walls 24 and 26 of which are connected by a 
cylindrical section 28. The aforesaid configuration is ground into the 
insert 20 by a grinding wheel 30 having truncated conical surfaces 32 and 
34 spaced apart by a cylindrical surface 36. The conical surfaces 32 and 
34 extend at an angle of from 12.degree.-25.degree. with respect to the 
central axis of the grinding wheel 30. In an exemplary constructed 
embodiment, the diameter of the grinding wheel 30 is 0.140 inches and the 
angles of the conical sections 32 and 34 are 20.degree. relative to the 
central axis thereof. 
As best seen by comparing FIGS. 7-10 of the drawings, the V-shaped groove 
at the nose 23 of the insert 20 is formed by a plunge grind in a direction 
parallel to the axis of the central aperture 22 of the insert 20. The 
plunge grind intercepts a top face 40 of the insert 20, the axis of 
rotation of the grinding wheel 30 being spaced from the tip 23 of the 
insert 20 to provide a rake angle desired for a specific application. By 
comparing FIGS. 7, 8 and 9, it should be apparent that the rake angle of 
the surface 28 of the insert 20 can be controlled by the spacing of the 
axis of rotation of the grinding wheel 30 from the arcuate tip 23 of the 
insert 20. For example, movement of the axis of rotation of the grinding 
wheel 30 toward the tip 23 as illustrated in FIG. 8, will result in a 
relatively lower rake angle than the angle of the section 28 in the 
inserts illustrated in FIGS. 7 and 9. Thus, rake angle of the center chip 
breaker section 28 can be controlled by the placement of the plunger grind 
on the insert 20. 
As best seen in FIGS. 1, 5 and 6, an intermediate chip breaker groove is 
formed by a grinding wheel 50 and comprises a conical surface 54 that 
intersects a side face 56 of the insert 20 to form a positive rake 
aracuate cutting edge therewith. The conical surface 54 extends at an 
angle of approximate 20.degree. to the top face 40 of the insert 20. A 
cylindrical intermediate chip breaker section 58 intersects the surface 54 
and also intersects a conical chip breaker section 59. The section 59 
extends at an angle of 45.degree. to the top face 40 of the insert 20. 
Thus, a turning flowing across the surface 54 is given an initial change 
in direction by the surface 58 and is thereafter curled and broken by the 
surface 59. The chip breaker configuration illustration in FIG. 6 has 
application to intermediate depths of cut and feed. As with the surfaces 
24, 26 and 28 of the nose chip breaker, the surfaces 54 and 59 are 
sections of a cone whereas the surface 58 is a section of a right circular 
cylinder. The aforesaid groove configuration is ground into the insert by 
a grinding wheel 50 having conical surfaces spaced apart by a cylindrical 
surface, complementary to the surfaces 54, 58 and 59. In an exemplary 
constructed embodiment the surfaces 54 and 59 extend at angles of 
20.degree. and 45.degree., respectively, with respect to the top face 40 
of the insert 20. 
As seen in FIG. 11, a modified insert 60 is of triangular configuration and 
comprises an arcuate tip 62 for finish cuts at rates similar to the insert 
20. The insert 60 is to be distinguished from the insert 20 in that side 
or high speed and depth cutting edges thereof are provided with modified 
chip breaker grooves spaced from the arcuate tip 62. As best seen in FIG. 
12, the chip breaker groove adjacent the nose 62 comprises an angular flat 
64 that intersects a side face 66 of the insert 60 to form a cutting edge 
therewith. The surface 64 extends at an angle of approximately 20.degree. 
to a top face 68 of the insert 60. A flat intermediate chip breaker 
section 70 intersects the surface 64 and blends into an arcuate chip 
breaker section 72. Thus, a turning flowing down the surface 64 is given 
an initial change in direction by the chip breaker surface 70 and 
thereafter is curled and broken by the arcuate surface 72. The chip braker 
configuration illustrated in FIG. 12 has application to intermediate 
depths and feeds. 
As best seen in FIG. 13 of the drawings, a chip breaker configuration at 
relatively greater spacing from the arcuate tip 62 comprises a surface 80 
that intersects the edge face 66 to form a cutting edge. An intermediate 
secion 82 is parallel to the top face 68 of the insert 60. An arcuate 
section 84 is provided on the opposite side of the center section 82 from 
the surface 80. The chip breaker configuration illustrated in FIG. 13 can 
be distinguished from the chip breaker groove of FIG. 12 in that it is 
adapted to break chips formed at relatively high rates of feed and depths 
of cut. 
As seen in FIG. 11, a workpiece 90 having an axis of rotation 92 is shown 
in operative association with the tool insert 60. The arcuate cutting tip 
62 of the insert 60 is utilized at relatively shallow depths of cut and 
light feeds, as shown by the dashed line 94. An intermediate cut indicated 
by the dashed line 96 is coextensive with the intermediate chip breaker 
configuration illustrated in FIG. 12. For greater depths of cut as 
indicated by the broken line 98 in FIG. 11, the chip breaker configuration 
illustrated in FIG. 13 is utilized. Thus, the insert 60 like the insert 20 
accommodates varying depths of cut and rates of feed. 
As seen in FIG. 14 of the drawings, the relatively long chip breaker 
configuration illustrated in FIG. 13 of the drawings, is achieved by a 
continuous grind along the cutting edge of the insert 60 as opposed to a 
plunge cut. Similarly, the intermediate chip breaker configuration 
illustrated in FIG. 12 is achieved by a continuous cut for a predetermined 
distance along the cutting edge of the insert 60. In contradistinction, 
the chip breaker configuration at the nose section 62 of the insert 60 
constitutes a plunge cut by the grinder 30 illustrated in FIG. 4. 
In summary, the insert of the instant invention features a fine cut chip 
breaker having a center flat between angularly related surfaces. Chip 
control is achieved over a wide range of cutting depths as opposed to 
known inserts which, in general, feature single purpose surfaces. 
More specifically, the insert of the instant invention has a special tip 
for shallow or finishing cuts at feed rates in range of 0.002" per 
revolution. The center flat controls initial turning deflection, 
deflection continuing when the turning hits the other side of the "V" 
section. A simple "V" without the center flat, as taught in the prior art, 
results in a chip that is too long before initial curl and also results in 
too sudden of a change at the opposite "V" section. 
The preferred angle of the side flats is 20.degree. with an acceptable 
range of 12.degree. to 25.degree.. The nose chip breaker is formed by a 
straight vertical plunge of a grinding wheel. The depth of the plunge cut 
should be sufficient to extend the contour of the cut to the insert tip 
with a tolerance allowable to 0.005 below the top surface of the insert. 
The diameter of the grinding wheel is preferably between 0.130" and 0.150" 
diameter. Width of the center flat is preferably 0.030", a range of 0.015" 
to 0.035" is acceptable in triangular, square, or diamond shaped inserts. 
The intermediate chip breaker is applicable to the 0.002" to 0.008" feed 
rate for all depths of cut. The center chip breaker configuration is used 
for high cutting speed over 0.008" feed rate, for example, 0.010" to 
0.020". 
While the preferred embodiment of the invention has been disclosed, it 
should be appreciated that the invention is susceptible of modification 
without departing from the scope of the following claims.