Tribo-functional effects of double-crossed helix on surface finish, cutting friction and tool wear mechanisms during the milling process of natural fiber composites

Tribological mechanisms that control the machining of natural fiber reinforced plastic (NFRP) composites are different from those of synthetic fiber composites in terms of cutting forces, tool wear, and surface finish. The aim of this paper is to investigate the cutting performances of NFRP composites using improved milling tool geometry with double-crossed helix (DCH). Cutting edges are coated with PVD-TiAlN thin coating thickness to ensure low cutting edge radius. Milling experiments are performed on unidirectional flax fibers reinforced polypropylene composites with CNC machine varying the tool kinematics. The in-situ cutting forces are acquired to evaluate the tribological performances of machining NFRP with DCH tool. The machined surfaces are rated by Scanning Electron Microscope (SEM) and peripheral surface defects are rated using an optical microscope. Moreover, the tool wear is evaluated at the cutting tool edge by SEM observations after accelerated wear tests. Results show that the improved milling tool overcomes the disadvantages and limitations of known NFRP machining in terms of surface finish. The functional design of the DCH generates a specific tool wear behavior where the wear mechanisms differ at each cutting helix orientation.