Mechanics of chip formation in Ultra-High Molecular Weight Polyethylene (UHMWPE)

Ultra-High Molecular Weight Polyethylene (UHMWPE) is widely used in medical and food applications but remains challenging to machine due to unstable chip formation, poor chip control, burr generation, and surface distortion. Chip formation mechanics in two grades of UHMWPE (medical-grade GUR 1050 and food-compliant PE1000) is investigated using a bespoke in situ orthogonal cutting rig and direct observation via high-speed imaging synchronised with force measurement. The influence of the uncut chip thickness on chip morphology and deformation behaviour was systematically examined. A gradually increasing uncut chip thickness revealed a sequence of rubbing, ploughing, mixed ploughing-shearing and shear-dominated continuous chip formation, with the crossover of the cutting and thrust forces marking the transition. The polymer grade had a profound effect on the formation of the chip within the primary and secondary deformation zones as well as the chip curvature: at similar uncut chip thickness the cutting forces of the two grades were comparable, whereas the thrust force of the medical grade was up to about 60% lower and its chip–tool contact length longer. With increasing uncut chip thickness, separation at the tool tip changed from shear to tearing ahead of the tool. The proposed methodology provides a robust platform for optimising cutting-edge geometries for improving chip control and reducing reliance on CO₂ cooling strategies, and for linking machining-induced surface deformation to the fatigue performance of UHMWPE components