Application of ultra-thin fluorine-content lubricating films to reduce tool/workpiece adhesive interaction during thread-cutting operations

This paper considers the application of lubricious fluorine-organic-based surface-active substances such as perfluorpolyether (PFPE) films for thread-cutting operations. The coefficient of friction of samples prepared both with and without the lubricating film was studied over a range of temperatures from 20 to 550°C, to test the potential for this film to reduce tool/workpiece adhesive interaction. An 18% reduction in the coefficient of friction was observed at temperatures as high as 400–450°C for this film. This temperature is within the typical range of thread-tapping operations. To explore this potential application further, the PFPE films were applied on the surface of thread-cutting taps made of high-speed steel. Cutting tool life was also investigated for regular, spiral point, and spiral tap designs, both with and without the PFPE films. The surface morphology of the worn-cutting tools was studied using an SEM and the shape as well as the micro-structure of the chips was also investigated in detail. Overall it was shown that the application of the PFPE film improved the cutting tool life by a factor of two, decreased the average cutting torque by 8% and produced tightly curled chips.