Triangular-shaped indexable cutting insert having recessed side surfaces and rotary cutting tool
An indexable cutting insert has opposing upper and lower end surfaces, and a peripheral surface including three side surfaces circumferentially alternating with three corner surfaces. The three side surfaces define an imaginary triangle and an imaginary hexagon. Each corner surface intersects the upper end surface to form an upper corner peripheral edge having a primary cutting edge. In a top view, each triangle side traverses two upper corner peripheral edges, imaginary lines tangential to the end points of each primary cutting edge are either collinear or form an obtuse angle greater than 175 degrees, each primary cutting edge has a primary length greater than half the hexagon side length, and at least one triangle side traverses each primary cutting edge. The insert is removably secured in a rotary cutting tool such that one of the upper corner peripheral edges contains an axially forwardmost point of the insert's upper peripheral edge.
1. An indexable triangular-shaped cutting insert ( 20 , 120 ) comprising:
opposing upper and lower surfaces ( 22 , 24 ) with a peripheral surface ( 26 ) extending therebetween and a central axis (A 1 ) extending therethrough,
the lower surface ( 24 ) having a downward facing planar base surface ( 36 ) defined by a first horizontal plane (PH 1 ) perpendicular to the central axis (A 1 ),
the peripheral surface ( 26 ) intersecting the upper surface ( 22 ) to form a continuous upper peripheral edge ( 30 ), and having three side surfaces ( 32 ) circumferentially alternating with three corner surfaces ( 34 ),
each corner surface ( 34 ) intersecting the upper surface ( 22 ) to form an upper corner peripheral edge ( 38 ), and each upper corner peripheral edge ( 38 ) having a primary cutting edge ( 40 ) extending from a first end point (N 1 ) to a second end point (N 2 ),
wherein in a cross-section taken in a second horizontal plane (PH 2 ) perpendicular to the central axis (A 1 ) and intersecting the three side surfaces ( 32 ), the three side surfaces ( 32 ) define three sides of a first imaginary triangle (T 1 ) and three non-adjacent sides of a first imaginary hexagon (H 1 ), and
wherein in a top view of the cutting insert ( 20 , 120 ):
each side of the first imaginary triangle (T 1 ) traverses two upper corner peripheral edges ( 38 ),
first and second imaginary straight lines (L 1 , L 2 ) tangential to each primary cutting edge ( 40 ) at its first and second end points (N 1 , N 2 ), respectively, are either collinear or form an obtuse primary bend angle (α 1 ) of greater than 175 degrees,
each primary cutting edge ( 40 ) has a primary length (LP) between its first and second end points (N 1 , N 2 ) greater than half the hexagon side length (LH) of the first imaginary hexagon (H 1 ), and
at least one side of the first imaginary triangle (T 1 ) traverses each primary cutting edge ( 40 ).
2. The cutting insert ( 20 , 120 ) according to claim 1 , wherein in the top view of the cutting insert ( 20 , 120 ):
the first imaginary triangle's three corners are located outside the upper peripheral edge ( 30 ).
3. The cutting insert ( 20 , 120 ) according to claim 1 , wherein in the top view of the cutting insert ( 20 ):
the first imaginary hexagon's six corners are located inside the upper peripheral edge ( 30 ).
4. The cutting insert ( 20 , 120 ) according to claim 1 , wherein:
the first imaginary triangle (T 1 ) has three imaginary first bisector lines (LB 1 ), each imaginary first bisector line (LB 1 ) containing one of the first imaginary triangle's three corners and bisecting its non-adjacent side, and
wherein in the top view of the cutting insert ( 20 , 120 ):
each imaginary first bisector line (LB 1 ) intersects one of the upper corner peripheral edges ( 38 ), and
each upper corner peripheral edge ( 38 ) does not exhibit mirror symmetry about its associated imaginary first bisector line (LB 1 ).
5. The cutting insert ( 20 , 120 ) according to claim 1 , wherein:
each primary cutting edge ( 40 ) slopes downwardly from its first end point (N 1 ) to its second end point (N 2 ).
6. The cutting insert ( 20 , 120 ) according to claim 1 , wherein:
the primary length (LP) is greater than two-thirds of the hexagon side length (LH).
7. The cutting insert ( 20 , 120 ) according to claim 1 , wherein in the top view of the cutting insert ( 20 , 120 ):
each upper corner peripheral edge ( 38 ) is traversed only once by the same side of the first imaginary triangle (T 1 ).
8. The cutting insert ( 20 , 120 ) according to claim 1 , wherein:
the upper surface ( 22 ) includes a rake surface ( 42 ) adjacent each primary cutting edge ( 40 ) and a chip deflection surface ( 44 ) between each rake surface ( 42 ) and a central top surface ( 46 ).
9. The cutting insert ( 20 , 120 ) according to claim 8 , wherein:
a central bore ( 28 ) coaxial with the central axis (A 1 ) intersects the upper and lower surfaces ( 22 , 24 ), and
the top surface ( 46 ) entirely surrounds the central bore ( 28 ).
10. The cutting insert ( 20 , 120 ) according to claim 8 , wherein in the top view of the cutting insert ( 20 , 120 ):
each chip deflection surface ( 44 ) is at least partially located inside the first imaginary hexagon (H 1 ).
11. The cutting insert ( 20 , 120 ) according to claim 8 , wherein:
the top surface ( 46 ) is planar and defined by a third horizontal plane (PH 3 ) perpendicular to the central axis (A 1 ).
12. The cutting insert ( 20 , 120 ) according to claim 11 , wherein:
no portion of the cutting insert ( 20 , 120 ) is located upward of the third horizontal plane (PH 3 ).
13. The cutting insert ( 20 , 120 ) according to claim 8 , wherein in a cross-section taken in a first vertical plane (PV 1 ) containing the central axis (A 1 ) and a mid-point (N 3 ) of one of the primary cutting edges ( 40 ):
the rake surface ( 42 ) slopes downwardly away from the primary cutting edge ( 40 ), and
the chip deflection surface ( 44 ) slopes upwardly towards the top surface ( 46 ).
14. The cutting insert ( 20 , 120 ) according to claim 13 , wherein in the cross-section taken in the first vertical plane (PV 1 ):
a fourth imaginary straight line (L 4 ) perpendicular to the central axis (A 1 ) intersects the rake surface ( 42 ) and the chip deflection surface ( 44 ) at first and second intersections points (I 1 , I 2 ), respectively,
a fifth imaginary straight line (L 5 ) tangential to the rake surface ( 42 ) at the first intersection point (I 1 ) forms an acute rake surface angle (β 1 ) with the fourth imaginary straight line (L 4 ),
a sixth imaginary straight line (L 6 ) tangential to the chip deflection surface ( 44 ) at the second intersection point (I 1 ) forms an acute deflection surface angle (β 2 ) with the fourth imaginary straight line (L 4 ), and
the deflection surface angle (β 2 ) is greater than the rake surface angle (β 1 ).
15. The cutting insert ( 20 , 120 ) according to claim 14 , wherein:
the deflection surface angle (β 2 ) is at least 5 degrees greater than the rake surface angle (β 1 ).
16. The cutting insert ( 20 , 120 ) according to claim 1 , wherein:
each upper corner peripheral edge ( 38 ) includes a ramping cutting edge ( 48 ) and a curved corner cutting edge ( 50 ), and
each curved corner cutting edge ( 50 ) extends between the first end point (N 1 ) of its associated primary cutting edge ( 40 ) and its associated ramping cutting edge ( 48 ).
17. The cutting insert ( 20 , 120 ) according to claim 16 , wherein in the top view of the cutting insert ( 20 , 120 ):
a seventh imaginary straight line (L 7 ) tangential to each ramping cutting edge ( 48 ) forms an acute ramp angle (ψ 1 ) with its associated first imaginary straight line (L 1 ), and
the acute ramp angle (ψ 1 ) is greater than 45 degrees.
18. A rotary cutting tool ( 60 ) rotatable about a tool axis (AT) defining a forward-rearward direction (DF, DR), and comprising:
a cutting body ( 62 ) having at least one insert receiving pocket ( 64 ); and
at least one cutting insert ( 20 , 120 ) in accordance with claim 1 removably secured in the insert receiving pocket ( 64 ).
19. The rotary cutting tool ( 60 ) according to claim 18 , wherein:
each insert receiving pocket ( 64 ) opens out at a forward end surface ( 66 ) of the cutting body ( 62 ), and
only one of the three upper corner peripheral edges ( 38 ) of the at least one cutting insert ( 20 , 120 ) serves as an operative upper corner peripheral edge ( 38 ′), containing an axially forwardmost point (NA) of its associated upper peripheral edge ( 30 ).
20. The rotary cutting tool ( 60 ) according to claim 19 , wherein:
each upper corner peripheral edge ( 38 ) includes a ramping cutting edge ( 48 ) and a curved corner cutting edge ( 50 ),
the ramping cutting edge ( 48 ) is spaced apart from its associated primary cutting edge ( 40 ) by the curved corner cutting edge ( 50 ), and
the axially forwardmost point (NA) is located on the curved corner cutting edge ( 50 ) of the operative upper corner peripheral edge ( 38 ′).
21. The rotary cutting tool ( 60 ) according to claim 20 , wherein:
the primary cutting edge ( 40 ) and the ramping cutting edge ( 48 ) of the operative upper corner peripheral edge ( 38 ′) diverge in the rearward direction (DR).
22. The rotary cutting tool ( 60 ) according to claim 19 , wherein:
each insert receiving pocket ( 64 ) has a seat surface ( 68 ) and first and second pocket walls ( 70 , 72 ) transverse to the seat surface ( 68 ), the first and second pocket walls ( 70 , 72 ) forming an external pocket angle (σ 1 ) in a front view of the insert receiving pocket ( 64 ), and
the insert's lower surface ( 24 ) has three lower abutment recesses ( 56 ) circumferentially spaced around the base surface ( 36 ), each lower abutment recess ( 56 ) including a radially outward facing lower abutment surface ( 58 ),
and wherein:
the insert's base surface ( 36 ) makes contact with the seat surface ( 68 ),
only one of the insert's three side surfaces ( 32 ) is an operative side surface ( 32 ′), making contact with the first pocket wall ( 70 ), and
only one of the insert's three lower abutment surfaces ( 58 ) is an operative lower abutment surface ( 58 ′), making contact with the second pocket wall ( 72 ).
23. The rotary cutting tool ( 60 ) according to claim 19 , wherein:
the pocket angle (σ 1 ) is greater than 60 degrees and less than or equal to 90 degrees.
24. The rotary cutting tool ( 60 ) according to claim 19 , wherein:
a first vertical plane (PV 1 ) containing the central axis (A 1 ) and a mid-point (N 3 ) of the primary cutting edge ( 40 ) of the operative upper corner peripheral edge ( 38 ′) intersects the first pocket wall ( 70 ).