The influence of the machining strategy on milling of polyetheretherketone (PEEK)

Polyetheretherketone is a thermoelastic biopolymer that has good properties for use in medical implants. The paper presents the results of experimental research on the influence of some machining conditions (feed per tooth and cutting strategy) on the size of the temperature in the milling area, the size of the components of the cutting force, the roughness of the machined surface, the hardness of the surface layer resulting from the milling application. The working feeds had values in two ranges (0.0167–0.025 mm/tooth and, respectively, 0.05–0.15 mm/tooth). Different zig, zig-zag, and follow periphery machining strategies were applied to evaluate their effects on the values of some milling parameters of interest and, respectively, on the quality and integrity of the surface resulting from milling. The experimental research was carried out using modern research equipment, such as the confocal microscope and an interferometer, for the observation and analysis of the surface texture. It was found that a movement of the tool along a zig-zag type strategy leads to smoother surfaces compared to those obtained by zig-zag and follow periphery strategies. Higher cutting feeds (0.05–0.15 mm/tooth) determine lower values of the roughness parameter Sa. When feed values are in the range of 0.05–0.15 mm/tooth, the cutting temperature reaches values of 160–183 °C. In accordance with the higher temperature values, an increase in the hardness of the superficial layer resulting from milling is also observed. A consequence of the temperature increase in the cutting zone was a reduction in the sizes of the components of the cutting force, the material becoming more ductile and easier to cut.