Cutting tools and drill inserts with chip control geometry

Details Cutting tools and drill inserts with chip control geometry Cutting tools and drill inserts with chip control geometry

2000-01-28

2001-08-07

Howell, Daniel W. (Department: 3722)

Cutting by use of rotating axially moving tool

Tool or tool with support

Having peripherally spaced cutting edges

C407S116000, C408S223000, C408S233000, C408S713000

Reexamination Certificate

active

06270297

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
Not Applicable.
FEDERALLY SPONSORED RESEARCH
Not Applicable.
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
The present invention is directed toward material cutting tools and chip control geometry of the material cutting tools. More particularly, the present invention is directed to a cutting insert having chip control geometry for improved chip formation while removing material from metal work pieces. The chip control geometry of the cutting insert controls chip formation as material is removed from a work piece; thereby preventing chip jamming and damage to the cutting insert.
The chip control geometry of the present invention is useful in any application wherein it is desirable to control the formation and breakage of the chips of material removed from a work piece during cutting operations such as, for example, turning, boring, planing, shaping, drilling, and reaming. The chip control geometry of the present invention is particularly useful when incorporated on the cutting edge of a spade drill.
BACKGROUND OF THE INVENTION
Spade drills are rotary cutting tools having one or more cutting edges. A spade drill generally includes a spade drill insert secured in a holder, but may also be manufactured in one piece. Spade drills including a spade drill insert and a holder are most widely used for drilling holes having diameters of 1 to 6 inches. Spade drills may be used for drilling metal work pieces, as well as work pieces of other materials, such as wood and plastics. Spade drills and certain other cutting tools include chip control geometry adjacent to the cutting edge. This chip control geometry improves cutting performance during cutting operations that produce chips. The chips are formed during metal cutting by the process shown in FIG.
1
. The cutting edge
13
of the cutting tool
10
moves into the work piece
12
in the general direction of the arrow shown in the FIG.
1
. Chip
11
is formed from the work piece
12
leaving a thickness
18
. The relative motion between the cutting tool
10
and the work piece
12
during cutting compresses the work piece material in the area
14
in front of the cutting tool
10
and induces primary or shear deformation of the work piece which begins to form the chip
11
. The chip
11
then passes over the rake face
16
of the cutting tool
10
and undergoes secondary deformation due to the shearing and sliding of the chip
11
against the tool
10
. The chip
11
subsequently breaks away from the work piece
12
to complete chip formation.
The physical properties of the material to be cut and the parameters of the cutting operation, including feed rate, cutting speed, depth of cut, rake angle, tool nose radius, lead angle, primarily control chip formation. Chips may be formed in a variety of shapes, from long, continuous metal strips, which may be severely deformed or in the form of long curls, to small fragments. The properties of the material that influence chip formation include yield strength, shear strength under compressive loading, hardness, ductility, as well as other properties. For example, cutting highly ductile materials may involve extensive plastic deformation of the chips, resulting in long, continuous chips. Longer chips remain in contact with the tool face longer, causing frictional heat buildup and thermal stress on the cutting edge. Long continuous chips are also more difficult to discharge from the cut in the work piece, especially during cutting operations such as boring or drilling hobs.
Cutting parameters that influence chip formation include lead angle, cutting edge geometry, feed rate, cutting speed, and depth of cut. These parameters may be controlled by the machinist in order to influence chip formation. Chips may separate from the work piece in one of three basic ways: they break off by themselves; they break against the cutting tool; or they break against the work piece. Machinists attempt to balance the foregoing cutting parameters to produce chips that are short and self-breaking. Chips of that type are easily discharged during the cutting operation and do not damage either the work piece or the cutting tool.
Certain materials are more likely to form undesirable chip shapes during cutting. Stainless steel, for example, tends to produce continuous, long, curled chips that may cause chip jamming and increased power consumption. Accordingly, a machinist's control of the parameters affecting chip formation is a particular importance when cutting these materials.
As shown in
FIG. 2
, conventional two-piece spade drills generally comprise a holder
21
having a clamping slot
24
and a plate-shaped drilling insert
22
which may be secured in the clamping slot
24
. The spade drill insert
22
is secured against limbs
27
and
28
of the clamping slot
24
by means of at least one threaded pin
23
. The head of the threaded pin
23
may engage a beveled bore
25
of the spade drill insert
22
and is secured in a threaded bore
30
in a limb
27
or
28
of the holder
21
. The spade drill insert
22
may be provided with a centering slot
29
or a tab which meshes with a corresponding element of the holder
21
to ensure that the spade drill insert
22
is centered along the axis of rotation
26
of the holder
21
.
FIGS.
3
(
a
) and
3
(
b
) depict the conventional spade drill insert
22
of FIG.
2
. The spade drill insert
22
is generally plate-shaped and includes a pair of cutting edges
31
. The cutting edges
31
extend radially outward from the central axis
26
of the spade drill insert
22
and are separated by 180° about the central axis
26
. As noted above, two-piece spade drills are most widely used for drilling relatively large holes, in the range of 1 to 6 inches in diameter. One-piece spade drills, which combine the shank and the cutting edges together in one piece, are typically used for drilling holes of smaller diameters.
There are several advantages to using a spade drills instead of a conventional twist drill to provide a bore in a work piece. Spade drills have heavier cross-sections than comparable twist drills. The additional strength this provides is concentrated along a line from the cutting point to the shank of the spade drill and gives the spade drill greater resistance to end thrusts experienced during piercing of the work piece. The additional strength also gives the spade drill a greater ability to withstand the high torque experienced during rotational cutting of the work piece, and minimizes vibration, chipping of the cutting edges, and drill breakage. Additionally, standard twist drills are likely to wear into a forward taper, which also has the tendency to cause binding. The shorter cutting edges of spade drills, which incorporate a greater back taper, reduce the tendency to bind.
Once worn, the spade drill insert of a two-piece spade drill can be replaced while the holder remains on the machine tool without the necessity to reset stops, break down setups, or increase or decrease the length of a drilling setup. Spade drills also may be more easily preset for use on automatic and computer numerical control machine tools than conventional twist drills.
Spade drills, however, also have certain limitations. As with all material removal operations, chip breaking and chip formation control are significant factors in the efficiency of the cutting operation. As seen in FIGS.
3
(
a
) and
3
(
b
), a conventional spade drill has primary cutting edge
31
with its corresponding rake face
32
for primary material removal from the work piece. A conventional spade drill does not incorporate any chip control geometry on the rake face
32
. The conventional design typically produces chips that are as wide as the cutting edges and, therefore, makes chip length control difficult. The large chips may accumulate in the bore being formed and cause jamming of the cutting tool in the work piece, increasing power consumption and resulting in poor drilling tolerances and excessive wear of the cutting tool.
Attempts have been made

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