The increasing demands in the field of machining lead to the intensified use of ultra-hard cutting materials such as polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PcBN).
In addition to grinding and laser machining, brushing is used for PcBN to give the tools their final contour. All processes have in common a high thermal or mechanical load on the tool cutting edge zone, which, among other things, influence the residual stress state near the surface. In the highly loaded area of the cutting edge, residual stress measurement with established methods, e.g. XRD , is not possible due to the strong curvature and the small measuring area. Residual stresses can be determined, however, by a strain-dependent peak shift in the Raman spectrum of diamond and boron nitride.

PcBN tools were ground and brushed and PCD tools were exclusively ground and the stress-dependent peak shift in the Raman spectrum was converted into absolute residual stress values by means of a conversion factor determined under bending load.
Depending on the process parameters of the preparation processes mentioned above, trending dependencies could be identified. In particular, the brushing process that follows the grinding process in PcBN preparation provides the rounding, and shows a reduction of previously high compressive residual stresses with increasing brushing speed. Furthermore, the thermal load during PCD grinding reduces the compressive residual stresses with increasing cutting speed. The combined load in the cutting edge area is determined by a superposition of load stresses occurring in the cutting process and previously induced residual stresses.  

The investigations were able to show that the final preparation of tools made of PcBN and PCD can influence the residual stress state in the cutting edge area. By this, it is possible to adjust the residual stress state in a targeted manner and thus there is the potential to positively influence the tool service life.