Characterisation of machinability of sintered steels during drilling operations

This study deals with the quantitative evaluation of the machinability of s intered steels during drilling operations. A characterisation technique usi ng scanning electron microscopy and image analysis was developed to charact erise quantitatively the amount of flank wear on drillbits. It was shown ex perimentally, using a drilling test bench, that the evolution of flank wear was proportional to the rate of variation of the thrust force as measured during drilling. Thus. the results show that the slope of the linear region measured on the curve of the thrust Force upsilon the amount of material r emoved is a more accurate criterion to characterise the machinability of PM products than the average thrust force, which is often suggested in the li terature. Furthermore, the effect of the technique used to add MnS to PM powders was investigated. Quantitative characterisation of machinability during drillin g operations showed that parts made with steel powders of the type FC-0208 + 0.5 wt-% MnS machine better when the manganese sulphide particles are pre alloyed rather than admired. Finally, machinability of parts made with two sinter hardening powders was characterised including a pre-alloyed MnS powd er. The results showed that the 'drillability' of this type of part is impr oved when they are in the presintered state rather than when they are in th e green state, i.e. unsintered. Moreover, parts made with the sinter harden ing powder pre-alloyed with manganese sulphide particles (MnS) showed super ior machinability characteristics.