Green machining of powder-metallurgy-steels (PMS): An overview

Abstract

Though powder metallurgy route of product fabrication receives recognition for near-net-shape abilities, economic constraints often demand involvement of minimal machining in the process. To overcome difficulties associated with machining of sintered/sinter-hardened steels, concept of machining their un-sintered (green) and partially sintered (pre-sintered) counter-parts have been explored since last twenty-five to thirty years. ‘Green machining’ defines machining of green state powder compacts, and this communication describes the first report that reviews green machining of powder metallurgy steels. Schematic and theoretical models have been introduced in this review, to illustrate the phenomenal consequences commonly observed during green machining practices. The report focuses on the previous attempts on green machinability improvements, which are broadly classified herewith as - [I] through dealing with strength of the green compact, and [II] through dealing with the cutting conditions. Besides this, the description considers aggregate studies on green machining and machining post sintering/sinter-hardening. Such studies not only discuss analogies and differences between the machining avenues, but also signify effects of green machining on mechanical behavior of sintered/sinter-hardened steels. Further, the report briefly introduces machining of pre-sintered compacts, as well. As and when entailed, the issues involved in green machining are discussed and future scope for advancements are suggested.