Influence of abrasive passes on surface roughness evolution of selected engineering materials under fixed AFM conditions

Abstract

This study investigates surface roughness evolution during abrasive flow machining (AFM) of four commonly used engineering materials mild steel, brass, copper, and aluminium under a fixed experimental window comprising a single abrasive size (65 μm SiC), constant abrasive concentration (50 wt%), and constant extrusion pressure. Surface roughness parameters Ra, Rz, and Rmax were measured after 0, 3, 6, 9, 12, and 15 passes to evaluate material-dependent finishing behaviour. The results reveal that surface roughness decreases progressively with increasing number of passes for all materials, with softer materials such as aluminium and copper exhibiting faster initial improvement compared to harder materials such as mild steel and brass. A plateauing trend beyond approximately 12 passes indicates diminishing returns, attributed to reduced asperity height, abrasive wear, and increased elastic smearing of the polymer-based medium. Taguchi signal-to-noise ratio analysis, applied using Ra as the primary industrial roughness indicator, identifies the number of passes as the dominant control factor, while material type plays a secondary role. Measurement uncertainty and repeatability were quantified in accordance with metrological practice, confirming that observed trends exceed instrument-related variability. While the findings provide material-specific guidance for pass selection in AFM process planning, the conclusions are limited to the selected abrasive size, concentration, pressure, and laboratory-scale geometry. Future work should incorporate broader parameter ranges, material removal rate quantification, and flow-field modelling to enhance industrial generalizability.