Manipulation of coating and subsurface properties in reconditioning of WC–Co carbide cutting tools

The physical properties in the surface layer of WC–Co cemented carbide tools have a significant influence on the tool wear behavior. In gear hobbing with carbide tools, the phenomenon that the tool life decreases with increasing number of reconditioning cycles has been identified. A significant correlation between residual stress in subsurface and tool life is shown as well as a steady decrease of residual compressive stress from cycle to cycle. This decrease can be linked to the thermal load of the cemented carbide substrate during the PVD coating process. h micro blasting, the residual stress can be readjusted and tool lives improved. Besides these successes, disappointments have also been encountered. Since many parameters can and must be adjusted in the micro blasting process, blasting is likely to have no or even a negative effect if the set of parameters is not set properly. In order to get a better understanding of the aerosol micro blasting technology, fundamental studies on the influence of blasting parameters on the energy content of the aerosol have been conducted. In these studies, several phenomena have been identified. Finally, blasting of coated tools has also been applied successfully with regard to tool life increase. h micro blasting compressive residual stress and increased hardness can be established in the cemented carbide substrate and the coating. Blasting of carbide tools prior to coating can improve the substrate properties through better clasping of the tungsten carbide grains. Moreover, blasting of the coating can improve its residual stress with regard to fatigue strength quality and cutting performance of the coated tool.