Process design space for optimal surface integrity in finish hard milling of tool steel

Hard milling has the potential to replace finish grinding in manufacturing dies and molds. A significant impediment for wide-spread application of hard milling is the lack of understanding and control on the surface integrity of machined surface and subsurface. In this study, a Taguchi design-of-experiment based dry finish milling of AISI H13 tool steel (50 ± 1 HRc) with (Ti, Al) N/TiN coated cutting tools was conducted to investigate the process-induced surface integrity. The mechanism of surface integrity in hard milling was investigated to understand the effects of mechanical/thermal loads on surface microstructure and properties. The microstructure, microhardness and residual stresses were characterized. Phase transformation was not observed under the process parameters, while the increased microhardness and high compressive residual stresses obtained are beneficial for improving fatigue properties and wear resistance of the machined components. Finally, the process design space for the desired surface properties has been established via the microhardness and residual stress maps.