Surface integrity optimization in milling of aluminum 1100: effects of supercritical CO₂ + MQL and emulsion cooling with various milling strategies

Abstract Aluminum alloys, widely utilized for their superior thermal and electrical conductivity, excellent corrosion resistance, and high machinability, often encounter critical challenges during milling, particularly the formation of built-up edges (BUE) and surface integrity degradation. Effective cooling and lubrication strategies are essential to mitigate thermal effects, reduce tool wear, and improve surface quality. While supercritical CO₂ (scCO₂) combined with minimum quantity lubrication (MQL) has shown promise as a cooling and lubrication method in the milling of materials like titanium and Inconel, its effectiveness in aluminum milling remains unexplored. This study investigates the effects of different process fluids and milling strategies on the surface integrity of aluminum alloys. Three cooling methods—dry, emulsion, scCO₂ combined with MQL—were assessed across four milling strategies: unidirectional, bidirectional, contour, and trochoidal milling. Surface topography, roughness, and waviness were analyzed to evaluate milled surface quality. Additionally, variations in feed rate and cutting speed were explored to understand their influence on surface integrity. The results indicate that scCO₂ + MQL improves surface roughness by up to 15% and waviness by 35% compared to emulsion cooling, particularly when combined with trochoidal milling, which exhibited the best surface integrity. However, the extended machining time associated with trochoidal milling limits its practicality, making unidirectional milling a viable alternative for balancing surface quality and productivity. Adjustments in feed rate and cutting speed also influenced surface integrity, with lower feed rates and higher cutting speeds generally yielding better surface roughness. Overall, the findings show the potential of sustainable process fluids, particularly scCO₂ + MQL, for enhancing aluminum milling processes in precision manufacturing applications.