Assessment of machining forces and surface integrity in face milling of CW50/PEEK under different thermal and cutting conditions

This study investigates how thermal and cutting conditions affect machining force ( F U ) and workpiece surface finish during face milling of CW50/PEEK with a polycrystalline diamond tool. Four thermal conditions were evaluated across different cutting conditions using a 3-factor, 3-level Box-Behnken Design. Results showed that F U was lowest under dry machining (DRY) due to matrix thermal softening and highest with cooled compressed air (CCA). Surface roughness analysis indicated R a values below 1.0 µm, with most values ranging from 0.4 to 0.8 µm. DRY produced the lowest roughness values, whereas CCA resulted in the highest. Analysis of variance showed that axial depth of cut significantly affected F U under DRY and heated compressed air (HCA) and even significantly influenced R a under DRY and regular compressed air (RCA). Conversely, feed per tooth was significant for F U under DRY and RCA, whereas the interaction between cutting speed and feed per tooth was significant for Ra only under DRY. Finally, scanning electron microscopy analysis revealed surface failures such as smearing, matrix debris, and fiber exposure, which varied with thermal condition. Overall, the results show that thermal condition plays a decisive role in face milling CW50/PEEK, influencing both machining force and workpiece surface finish.