Surface Integrity Aspects of Machinability Testing of Fe—C—Cu Powder Metallurgy Components

Abstract

The surface condition produced by turning and boring secondary machining operations on Fe–C–Cu compacts has been examined by profilometric analysis. It was found that edge frittering, which may lead to component rejection, can be minimised by decreasing the feedrate or by changing tool nose radius or plan approach angle, as appropriate. Flank wear is the dominant tool wear mechanism and is promoted by the abrasive conditions existing when machining any PM component. The best results were obtained with low copper, low carbon additions, whereas increased flank wear and poor surface finish occur with high copper, high carbon compositions. Tool edge rounding produces surfaces characterised by high levels of plastic deformation and (in some cases) smearing of the surface, which should lead to compact rejection even though the metrological conditions are fulfilled. A new accelerated machinability test, a hybrid of the rapid facing and degraded tool tests, has been developed; the ISO P grades are found to be a better starting point for machinability trials than the K. grades recommended elsewhere. It is suggested that either R _a, together with the amplitude distribution function and its correlation length, or the FRG DIN 4776 standard based on the Abbott–Firestone curve be used to assess the surface texture produced by secondary machining of PM components. PM/0520