Method of machining a workpiece using a ceramic cutting insert including alumina and boron carbide

1. A method of machining a workpiece comprising the steps of:

providing a workpiece;

providing a ceramic cutting insert formed from the consolidation of a starting powder mixture and having a rake surface and a flank surface wherein the rake surface and the flank surface intersect to form a cutting edge and the ceramic cutting insert having a substrate that comprises between about 15 volume percent and about 35 volume percent of a boron carbide phase and at least about 50 volume percent alumina, the substrate further contains the residue from one or more sintering aids present in the starting powder mixture in an amount between about 0.5 volume percent and about 5 volume percent of the starting powder mixture and being selected from the group comprising yttrium oxide, ytterbium oxide, yttrium aluminum garnet, lanthanum oxide, chromium oxide, and other rare earth oxides, and has a fracture toughness (K IC , 18.5 Kg Load E&C) greater than or equal to about 4.5 MPa·m 0.5 ;

causing relative rotational movement between the workpiece and the ceramic cutting insert wherein the surface speed of the relative rotational movement is equal to or greater than about 457 surface meters per minute; and

bringing the ceramic cutting insert and the workpiece into contact with each other so as to remove material from the workpiece.

2. The method of claim 1 wherein the surface speed of the relative rotational movement is equal to or greater than about 610 surface meters per minute.

3. The method of claim 1 wherein the workpiece material is cast iron.

4. The method of claim 1 wherein the workpiece material is ductile cast iron.

5. The method of claim 1 wherein the substrate has a coating thereon.

6. A method of machining a workpiece comprising the steps of:

providing a workpiece;

providing a ceramic cutting insert having a rake surface and a flank surface wherein the rake surface and the flank surface intersect to form a cutting edge and the ceramic cutting insert having a substrate that has a fracture toughness (K IC , 18.5 Kg Load E&C) greater than or equal to about 4.5 MPa·m 0.5 , and wherein the substrate being formed from a starting powder mixture comprising between about 15 volume percent and about 50 volume percent of a boron carbide irregular-shaped phase and at least about 50 volume percent alumina, and the starting powder mixture further comprising an effective amount to achieve full densification of a metal component including one or more of aluminum, magnesium and zinc;

causing relative rotational movement between the workpiece and the ceramic cutting insert wherein the surface speed of the relative rotational movement is equal to or greater than about 457 surface meters per minute; and

bringing the ceramic cutting insert and the workpiece into contact with each other so as to remove material from the workpiece.

7. The method of machining of claim 6 wherein the substrate further includes ytterbium boride.

8. The method of machining of claim 6 wherein the metal component comprises aluminum.

9. The method of machining of claim 6 wherein the metal component comprises magnesium.

10. The method of machining of claim 6 wherein the metal component comprises zinc.

11. The method of machining of claim 6 wherein the starting powder mixture further comprising a reduction component containing carbon.

12. The method of machining of claim 6 wherein the starting powder mixture contains between about 15 volume percent and about 35 volume percent boron carbide, and at least about 50 volume percent alumina.

13. The method of machining of claim 6 wherein the starting powder mixture contains between about 20 volume percent and about 30 volume percent boron carbide, and at least about 50 volume percent alumina.

14. The method of machining of claim 6 wherein the effective amount of the metal component is equal to an amount between about 0.01 volume percent and about 5.0 volume percent of the starting powder mixture.

15. The method of machining of claim 6 wherein the substrate further contains the residue from one or more sintering aids selected from the group comprising yttrium oxide, ytterbium oxide, yttrium aluminum garnet, lanthanum oxide, chromium oxide, and other rare earth oxides.