Effects of cryogenic carbon-dioxide-assisted milling on the machining performance of wood–plastic composites

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Wood–plastic composites (WPCs) are eco-friendly materials widely used in both indoor and outdoor applications. However, conventional dry milling often results in built-up edge (BUE) formation on the tool rake face, leading to elevated cutting forces and unstable machining. By contrast, cryogenic CO2 milling promotes chip breakage and significantly lowers cutting forces, resulting in improved machining performance. In this study, dry and cryogenic CO2 milling of WPCs was compared by measuring cutting temperature, cutting forces, chip morphology, and surface roughness as functions of cutting speed and cutting depth. Experimental results indicate that increasing the cutting speed raises the cutting zone temperature but reduces the cutting forces and surface roughness. Under the same conditions, chips become more deformable. Conversely, increasing cutting depth elevates cutting temperature, increases cutting forces, worsens surface roughness, and produces wider chips. Most notably, cryogenic CO2 milling leads to enhanced chip segmentation and a significant reduction in the axial cutting force (Fz). This reduction in Fz lowers the resultant total cutting force, yielding a superior surface finish compared to dry milling. Thus, cryogenic CO2 milling achieves lower cutting forces and enhanced surface quality, demonstrating its feasibility and advantages for industrial WPCs machining.