Diamond grain size effects in sustainable free-abrasive precision machining with green MEX 316L tools

This study investigates the sustainability and machining performance of green, as-printed material-extrusion (MEX) 316 L stainless-steel tools for free-abrasive precision finishing. Unlike conventional diamond tools that require energy-intensive sintering and post-processing, the MEX tools are fabricated in a single step and used directly, offering a low-energy, low-waste alternative for precision machining. Four diamond pastes (10–60 μm) were evaluated to examine how grain size influences the material removal rate (MRR), surface integrity, tool wear, and the underlying three-body abrasion mechanisms. The characteristic interlayer gaps of the printed 316 L structure (up to 80 μm) acted as self-regulating micro-reservoirs, selectively retaining only the 10–35 μm fraction and enabling a controlled transition from rolling-dominated abrasion (fine grains) to ploughing and micro-cutting (coarse grains). MRR increased with grain size (0.50–1.35 mm 3 /min across the 0.1–0.3 mm depth range) but saturated beyond ~50 μm, while medium-fine grains (SD 28/20) exhibited the highest load sensitivity (103.5% increase from 0.1 to 0.3 mm depth). Surface roughness increased with grain size (Sa = 0.33–0.87 μm), accompanied by systematic changes in skewness and kurtosis that reflected evolving abrasion modes. Tool wear remained moderate (maximum diameter reduction of 3.38% and a tool wear rate (TWR) of 10.54 mm 3 /min) despite the tools being in the green, unsintered state. Overall, the results demonstrate that MEX-316 L tools function as topographical filters that reduce abrasive consumption, eliminate post-processing, and support sustainable precision finishing of hardened steel. This work highlights the potential of MEX-based metal tools as a green, flexible alternative to conventional fixed-abrasive systems.