Ultra-high molecular weight polyethylene (UHMWPE) is an engineering material with excellent properties. However, UHMWPE shows inferior machinability due to its high plasticity, and poor surface quality after micro-milling processing is often observed, which affects the machining accuracy and wear resistance. Consequently, optimizing the cutting process by selecting proper cutting parameters, could directly determine the processing quality and service life of UHMWPE. In the present work, the mechanisms of cutting parameters on surface quality and chip formation during UHMWPE machining were investigated by using the molecular dynamics simulation method. By increasing the cutting depth, the resultant surface could be more fluctuated on the machined UHMWPE, which indicates increased surface roughness and poor surface quality. At the cutting edge (r_c=38 nm), the polyethylene chains underwent plastic flow as the tool moves (v_c=3.16×10^-6 m/s) and elongated gradually. At the same time, since polyethylene chains entangled with each other in amorphous UHMWPE, the plastic flow of these chains could lead to the movement of polyethylene chains at the flank face of cutting tool, resulting in loosely distributed polyethylene chains and random voids. Meanwhile, polyethylene chains accumulate at the rake face of the linearly moved cutting tool, tumbling and curling gradually until forming chips. On the other hand, in the cutting process conducted by the cutting tool with a short length of cutting edge (L_c=143nm), polyethylene chains underwent plastic flow at the tool nose and their separation from the unmachined surface is inadequate. This will cause the movement of surrounding molecular chains towards the side cutting edge and the resultant accumulation at the tool nose. Eventually, as the accumulated clusters grow up to a certain extent, they could detach from the tool nose and remain at the edge of the machined surface by forming burrs. This will result in uneven surfaces, worsening the surface quality. By analyzing the cutting process of UHMWPE at the molecular level, our results could provide important theoretical insights and practical guidance for the evaluating and controlling the surface quality.

UHMWPE; cutting process; surface quality; chip flow; molecular dynamics simulation