Analysis of machining green compacts of a sinter-hardenable powder metallurgy steel: A perspective of material removal mechanism

Green machining (machining green/un-sintered powder compacts) has prospects in dealing with poor machinability of sinter-hardened powder metallurgy (PM) steels. However, it has the limitation of resulting in a poor-quality machined surface and exit-edge (the edge from where the cutting tool leaves the workpiece) than that of counterparts machined post-sinter-hardening. The feasibility of overcoming the limitation using machining parameters is a scarcely explored area. Investigating this area through understanding the material removal mechanism constitutes the motivation of the present study. The study analyses the turning of green and sinter-hardened compacts prepared from FLC-4608 (Metal Powder Industries Federation denomination, Standard 35) steel powder-premix. Results indicated that, in green machining, a lower feed rate regulates the attribute of powder particles' plucking in the material removal mechanism and improves machined surface quality. Increased cutting velocity and feed rate were found to reduce the size of exit-edge damage (exit-edge-breakout) and improve edge quality. It was determined that these quality improvements could not feasibly achieve the machined surface and exit-edge quality comparable to a compact machined post-sinter-hardening. Nevertheless, green machining has significance in producing sinter-hardened PM components due to its advantages over machining sinter-hardened compacts, i.e., lower Fc (cutting force component in the cutting velocity direction) and favourable chip morphology, as identified in this investigation. The present study is potentially helpful to PM industries for green machining considerations in the manufacturing process flow.