FIELD OF INVENTION
The invention relates in general to a cutting insert that may be detachably mounted on a tool holder for cutting a work piece  and in particular to a cutting insert for performing a turning operation on a work piece made of titanium and the like.

BACKGROUND OF THE INVENTION
In normal titanium turning  heat generation at the interface between the tool and the workpiece is a detrimental factor in tool life. The problem is to identify a geometry of the cutting edge that lowers temperatures during a machining operation.

SUMMARY OF THE INVENTION
The problem of excessive heat generation at the interface between the tool and the workpiece is solved by providing a cutting edge with an edge radius with a radius up to 0.02 mm and a rake face extending inwardly and downwardly at an angle of up to 12 degrees with respect to a plane parallel to the face to help in smooth movement of the chip.

In one aspect of the invention  a polygonal indexable cutting insert comprises a pair of faces and a plurality of peripheral side surfaces normal to said parallel faces  said faces and said side surfaces being joined to form rounded corners  each face having a rake face and a central plateau; a plurality of cutting edges formed at an intersection between said faces and plurality of side surfaces; and a plurality of chip breaking scallops positioned along the cutting edges  each scallop comprises a bottom surface formed by the rake face and an arcuate back wall joining said bottom surface and said central plateau to form a chip breaker  wherein said central plateau of each face includes a triangular-shaped area including an apex that lies along a bisector passing through a central axis and opposite rounded corners.

In another aspect of the invention  a polygonal indexable cutting insert comprises a pair of faces and a plurality of peripheral side surfaces normal to said parallel faces  said faces and said side surfaces being joined to form rounded corners  each face having a central plateau that includes a triangular-shaped area proximate each rounded corner; a plurality of cutting edges formed at an intersection between said faces and plurality of side surfaces  each cutting edge formed with an edge radius; a rake face extending inwardly and downwardly at an angle with respect to a plane that is parallel to the pair of faces; and a plurality of chip breaking scallops positioned along the cutting edges comprising a bottom surface formed by the rake face and an arcuate back wall joining said bottom surface and said central plateau to form a chip breaker  wherein a depth of the arcuate back wall of each scallop varies  thereby increasing side curl of the chips and formation of short helical chips.

In another aspect of the invention  a polygonal indexable cutting insert comprises a pair of faces and a plurality of peripheral side surfaces normal to said parallel faces  said faces and said side surfaces being joined to form rounded corners  each face having a central plateau that includes a triangular-shaped area proximate each rounded corner; a plurality of cutting edges formed at an intersection between said faces and plurality of side surfaces  each cutting edge formed with an edge radius; a rake face extending inwardly and downwardly at an angle with respect to a plane that is parallel to the pair of faces; a triangular-shaped area proximate the rounded corners  each triangular-shaped area including an apex that lies along a bisector passing through a central axis and opposite rounded corners; and a plurality of chip breaking scallops positioned along the cutting edges comprising a bottom surface formed by the rake face and an arcuate back wall joining said bottom surface and said central plateau to form a chip breaker  wherein the arcuate back wall of each scallop intersects the arcuate back wall of adjacent scallops at a point located at a distance from each cutting edge for providing a wedge effect that facilitates in dividing and breaking chips  and wherein a depth of the arcuate back wall of each scallop is smallest proximate the point and largest between adjacent points  thereby increasing side curl of the chips and formation of short helical chips.

BRIEF DESCRIPTION OF THE DRAWINGS
These and other features  aspects  and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings  wherein:

FIGURE 1 shows a perspective view of an indexable cutting insert with scallops according to an embodiment of the invention;

FIGURE 2 shows a top view of the indexable cutting insert of FIGURE. 1; and

FIGURE 3 shows a cross-sectional view of the cutting insert taken along line 3-3 of FIGURE. 2.

DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1  an indexable cutting insert 10 is shown according to an embodiment of the invention. In general  the cutting insert 10 is generally diamond in shape having substantially parallel faces 12  14 and peripheral side surfaces 16  18  20  22 that are substantially normal to the parallel faces 12  14. The cutting insert 10 also has four rounded corners 24  26  28  30 extending between the parallel faces 12  14. Because of the symmetry of the cutting insert 10  it will be appreciated that corners 24 and 28 are substantially identical to each other  and that corners 26 and 30 are substantially identical to each other.

A plurality of cutting edges 32  34  36  38 are formed at the intersection between the face 12 and the side surfaces 16  18  20  22. Similarly  a plurality of cutting edges 40  42  44  46 are formed at the intersection between the face 12 and the side surfaces 16  18  20  22 (cutting edges 42  44 are not visible in FIG. 1). In the illustrated embodiment  the cutting edges 32  36 are substantially parallel to each other  while the cutting edges 34  38 are substantially parallel to each other. It will be appreciated that a generally diamond-shaped cutting insert is illustrated  the principles of the invention described below can be applied to a cutting insert having any polygonal shape.

Referring now to FIGS. 2 and 3  the intersection between each rounded corner 24  26  28  30 and the parallel faces 12  14 is formed with an edge radius 48 having a radius  R. Similarly  the cutting edges 32  34  36  38 are formed with the edge radius 48. In one embodiment  the radius  R  is in a range between about 10 microns to about 20 microns (0.01-0.02 mm). In addition  each face 12  14 has a rake face 50  52  respectively  that extends entirely around the periphery of the cutting insert 10. As shown in FIG. 3  the rake face 50  52 extends inwardly and downwardly from both the rounded corners 24  26  28  30 and the cutting edges 40  42  44  46 to a bottom 54 at an angle 56 with respect to a plane 58 parallel to the face 12  14 (rake face 52 is not visible in FIGS. 2 and 3). In one embodiment  the angle 56 is in a range between about 10 degrees to about 12 degrees. An arcuate back wall 60 extends upwardly from the bottom 54 to a central  substantially planar plateau 62 of each face 12  14 of the cutting insert 10. A difference in elevation between the central plateau 62 and the edge radius 48 defines a height 64. In one embodiment  the height 64 is in a range between about 0.08 mm to about 0.12 mm. The downward sloping rake face 50  52 and upward sloping arcuate back wall 60 facilitate desired chip formation during a machining operation.

One aspect of the invention is that the central plateau 62 of each face 12  14 includes a triangular-shaped area  shown generally at 66  68  70  72  proximate each rounded corner 24  26  28  30  respectively  of the cutting insert 10. Although not shown in FIG. 2  it is understood that the face 14 is identical to the face 12. Each triangular-shaped area 66  68  70  72 includes an apex 66a  68a  70a  72a and a pair of side walls 66b  66c  68b  68c  70b  70c  72b  72c. In the illustrated embodiment  the apex 66a  68a  70a  72a of the triangular-shaped area lie on a bisector passing through opposite rounded corners and through a central axis 74 of the cutting insert 10. For example  the apex 68a  72a of the triangular-shaped areas 68  72 proximate the opposite rounded corners 26  30 lie on a bisector 71 passing through opposite rounded corners 26  30 and the central axis 74. Similarly  the apex 66a  70a of the triangular-shaped areas 66  70 proximate the opposite rounded corners 24  28 lie on a bisector 73 passing through opposite rounded corners 24  28 and the central axis 74.

It is noted that a distance 75 from the sides of each triangular-shaped area 66  68  70  72 to the cutting edge 32  34  36  38 increases from the apex 66a  68a  70a  72a. This varying distance produces the unexpected results that chips don’t get over squeezed  and heat generation due to rubbing action is minimized. In addition  streaming of chips is such that the contact stresses are not concentrated near the cutting edge  but get distributed more evenly as compared to conventional cutting inserts. In addition  As a result  the peak stress and notching is reduced during a machining operation  thereby preventing the cutting insert 10 from premature failure.

Another aspect of the invention is that the cutting insert 10 includes a plurality of scallops  shown generally at 76  formed at particular locations along each cutting edge 32  34  36  38 of the cutting insert 10. It is intended that the scallops 76 are similarly formed and the following description of a single scallop 76 is applicable to the formation of other scallops. The bottom surface of each scallop 76 is formed by the inward  downward sloping rake face 50  52. As shown in FIG. 3  the rake face 50  52 extends inwardly and downwardly from the cutting edges 40  42  44  46 to the bottom 54 at the angle 56 with respect to the plane 58 parallel to the face 12  14 (rake face 52 is not visible in FIGS. 2 and 3). In one embodiment  the angle 56 is in a range between about 10 degrees to about 12 degrees. In other words  the scallops 76 extend inwardly and downwardly with respect to each cutting edge 32  34  36  38.

Each scallop 76 has an arcuate back wall 78 joining the bottom surface to form a chip breaker. Similar to the triangular-shaped area 66  68  70  72  the arcuate back wall 78 of each scallop 76 extends upwardly from the bottom 54 to the central  substantially planar plateau 62 of each face 12  14 of the cutting insert 10. The difference in elevation between the central plateau 62 and the edge radius 48 defines the height 64 in a range between about 0.08 mm to about 0.12 mm. The inward  downward sloping rake face 50  52 and upward sloping arcuate back wall 78 facilitate desired chip formation during a machining operation.

In addition  the arcuate back wall 78 of each scallop 76 intersects the arcuate back wall 78 of adjacent scallops at a point 80 for providing a wedge effect that facilitates in dividing and breaking chips. It is noted that the point 80 at which the back wall 78 of each scallop 76 intersect one another is located at a distance 82 from each cutting edge 32  34  36  38. In addition  a bisector 77 passing through the point 80 is substantially perpendicular to its respective proximate cutting edge 32  34  36  38.

In the illustrated embodiment  the depth of the arcuate back wall 78 of each scallop 76 varies  thereby increasing side curl of the chips and formation of short helical chips. Specifically  the depth of the arcuate back wall 78 is smallest proximate the point 80 and is largest at a midway point between adjacent points 80. The varying depth provides the unexpected results that chips flow smoothly over the rake face 50  even at higher depth of cuts without exerting high pressures on the back wall 78. In addition  the varying depth of the back wall 78 helps in trapping any coolant  which aids in the removal of excess heat during a machining operation.

The form of a typical scallop 76 can be established on a master by a grinding wheel (not shown) as is known in the art. In one embodiment  the grinder includes a sixteen degree included angle conical form presented with its end surface at a twenty degree angle to the face 12  14 of the cutting insert 10 providing a positive rake scallop face 50  52 and a twenty-eight degree angle of the back wall 78 relative to the axis 74 of the cutting insert 10.

The documents  patents and patent applications referred to herein are hereby incorporated by reference.

While the invention has been specifically described in connection with certain specific embodiments thereof  it is to be understood that this is by way of illustration and not of limitation  and the scope of the appended claims should be construed as broadly as the prior art will permit.

PARTS LIST

10 cutting insert
12 face
14 face
16 side surface
18 side surface
20 side surface
22 side surface
24 rounded corner
26 rounded corner
28 rounded corner
30 rounded corner
32 cutting edge
34 cutting edge
36 cutting edge
38 cutting edge
40 cutting edge
42 cutting edge
44 cutting edge
46 cutting edge
48 edge radius
50 rake face
52 rake face
54 bottom
56 angle
58 plane
60 arcuate back wall
62 central plateau
64 height
66 triangular-shaped area
66a apex
66b side wall
66c side wall
68 triangular-shaped area
68a apex
68b side wall
68c side wall
70 triangular-shaped area
70a apex
70b side wall
70c side wall
71 bisector
72 triangular-shaped area
72a apex
72b side wall
72c side wall
73 bisector
74 central axis
76 scallop
78 arcuate back wall (scallop)
80 point

We Claim:

1. A polygonal indexable cutting insert (10)  comprising:
a pair of faces (12  14) and a plurality of peripheral side surfaces (16  18  20  22) normal to said parallel faces  said faces and said side surfaces being joined to form rounded corners (24  26  28  30)  each face having a rake face (50  52) and a central plateau (62);
a plurality of cutting edges (32  34  36  38) formed at an intersection between said faces and plurality of side surfaces; and
a plurality of chip breaking scallops (76) positioned along the cutting edges  each scallop comprises a bottom surface formed by the rake face (50  52) and an arcuate back wall (78) joining said bottom surface and said central plateau to form a chip breaker 
wherein said central plateau of each face includes a triangular-shaped area (66  68  70  72) proximate the rounded corners  each triangular-shaped area including an apex (66a  68a  70a  72a) that lies along a bisector (71  73) passing through a central axis (74) and opposite rounded corners.

2. The cutting insert according to Claim 1  wherein the rake face slopes inwardly and downwardly with respect to the cutting edges at an angle in a range between 10 degrees to 12 degrees.

3. The cutting insert according to Claim 1  wherein both the cutting edges and the rounded corners are formed with an edge radius having a radius  R  in a range between 0.01 mm to 0.02 mm.

4. The cutting insert according to Claim 3  wherein a difference in elevation between the central plateau and the edge radius defines a height (64) in a range between 0.08 mm to 0.12 mm.

5. The cutting insert according to Claim 1  wherein a depth of the arcuate back wall of each scallop varies  thereby increasing side curl of the chips and formation of short helical chips.

6. The cutting insert according to Claim 1  wherein the arcuate back wall of each scallop extends upwardly from a bottom (54) to the central plateau.

7. The cutting insert according to Claim 1  wherein the arcuate back wall of each scallop intersects the arcuate back wall of adjacent scallops at a point (80) for providing a wedge effect that facilitates in dividing and breaking chips.

8. The cutting insert according to Claim 7  wherein the point (80) at which the back wall of each scallop intersect one another is located at a distance (82) from each cutting edge (32  34  36  38).

9. A polygonal indexable cutting insert (10)  comprising:
a pair of faces (12  14) and a plurality of peripheral side surfaces (16  18  20  22) normal to said parallel faces  said faces and said side surfaces being joined to form rounded corners (24  26  28  30)  each face having a central plateau (62) that includes a triangular-shaped area (66  68  70  72) proximate each rounded corner;
a plurality of cutting edges (32  34  36  38) formed at an intersection between said faces and plurality of side surfaces  each cutting edge formed with an edge radius;
a rake face (50  52) extending inwardly and downwardly at an angle with respect to a plane (58) that is parallel to the pair of faces (12  14); and
a plurality of chip breaking scallops (76) positioned along the cutting edges comprising a bottom surface formed by the rake face (50  52) and an arcuate back wall (78) joining said bottom surface and said central plateau to form a chip breaker 
wherein a depth of the arcuate back wall (78) of each scallop (76) varies  thereby increasing side curl of the chips and formation of short helical chips.

10. The cutting insert according to Claim 9  wherein said central plateau of each face includes a triangular-shaped area (66  68  70  72) proximate the rounded corners  each triangular-shaped area including an apex (66a  68a  70a  72a) that lies along a bisector (71  73) passing through a central axis (74) and opposite rounded corners.
11. The cutting insert according to Claim 9  wherein the arcuate back wall extends upwardly from a bottom (54) to the central plateau (62).

12. The cutting insert according to Claim 9  wherein a difference in elevation between the central plateau and the edge radius defines a height (64) in a range between 0.08 mm to 0.12 mm.

13. The cutting insert according to Claim 9  wherein the arcuate back wall of each scallop intersects the arcuate back wall of adjacent scallops at a point (80) for providing a wedge effect that facilitates in dividing and breaking chips.

14. The cutting insert according to Claim 13  wherein the point at which the back wall of each scallop intersect one another is located at a distance (82) from each cutting edge (32  34  36  38).

15. The cutting insert according to Claim 9  wherein the depth of the arcuate back wall is smallest proximate the point and largest between adjacent points.

16. A polygonal indexable cutting insert (10)  comprising:
a pair of faces (12  14) and a plurality of peripheral side surfaces (16  18  20  22) normal to said parallel faces  said faces and said side surfaces being joined to form rounded corners (24  26  28  30)  each face having a central plateau (62) that includes a triangular-shaped area (66  68  70  72) proximate each rounded corner;
a plurality of cutting edges (32  34  36  38) formed at an intersection between said faces and plurality of side surfaces  each cutting edge formed with an edge radius;
a rake face (50  52) extending inwardly and downwardly at an angle with respect to a plane (58) that is parallel to the pair of faces (12  14);
a triangular-shaped area (66  68  70  72) proximate the rounded corners  each triangular-shaped area including an apex (66a  68a  70a  72a) that lies along a bisector (71  73) passing through a central axis (74) and opposite rounded corners; and
a plurality of chip breaking scallops (76) positioned along the cutting edges comprising a bottom surface formed by the rake face (50  52) and an arcuate back wall (78) joining said bottom surface and said central plateau to form a chip breaker 
wherein the arcuate back wall of each scallop intersects the arcuate back wall of adjacent scallops at a point (80) located at a distance (82) from each cutting edge for providing a wedge effect that facilitates in dividing and breaking chips  and
wherein a depth of the arcuate back wall of each scallop is smallest proximate the point and largest between adjacent points  thereby increasing side curl of the chips and formation of short helical chips.

17. The cutting insert according to Claim 16  wherein a difference in elevation between the central plateau and the edge radius defines a height (64) in a range between 0.08 mm to 0.12 mm.

18. The cutting insert according to Claim 16  wherein the edge radius has a radius  R  in a range between 0.01 mm to 0.02 mm.