Sequential and Multi-Pass Machining Effects on Surface Integrity and Functional Performance: A Critical Evidence Synthesis

Surface integrity in machining is conventionally characterised under a single-pass assumption, yet components are roughed, semi-finished and finished through sequences of passes, each inheriting the mechanical and thermal state left by the previous one. This review develops the position that sequential/multi-pass machining is a path-dependent process and synthesises 75 verified references (27 examining sequential/multi-pass machining directly), retrieved through a structured but non-systematic search, across residual stress, hardness, microstructure/white layer and roughness. It introduces a typology of four sequential-machining forms: repeated passes of one operation, roughing-to-finishing sequences, sequential different operations and rapid repeated engagement. Two contributions follow. First, two multi-attribute studies, which differ in material, process and pass range, suggest that residual-stress stabilisation with pass number, reported in several studies, may not be accompanied by stabilisation of hardness and roughness; this is an exploratory hypothesis, not an established trend. Second, a four-tier evidence ladder separates directly measured functional performance from single-pass extrapolation; only five studies reach the top tier, each for a different material–process system, and most performance claims rest on single-pass extrapolation. Screening limitations are reported explicitly, and staged research priorities are proposed to close the functional performance evidence gap.