Study on the design and cutting performance of stepped bi-directional milling cutters for hole making of CFRP

During hole making of carbon fiber reinforced plastic (CFRP) by helical milling, the tool wear is a main factor in machined surface damage, being unable to guarantee machining quality and accuracy, and restricting the improvement of hole making efficiency. In order to prolong the service life of cutters, this paper has carried out the research into the design, manufacture, and cutting performance of stepped bi-directional milling cutters, combining with hole making of CFRP by bi-directional helical milling. By the method of differential geometry, the geometric model of the profile shape and the mathematical model of the helical edge are established of the stepped bi-directional milling cutter. Additionally, based on the transformation matrix between grinding wheel and workpiece coordinates of any point, the track equation of grinding wheel is derived from grinding the side edge helical groove of the stepped bi-directional milling cutter. What is more, the grinding process and accuracy are measured about the designed stepped bi-directional milling cutter. The experiment of CFRP holes made by bi-directional helical milling is designed, and the experimental results show that the axial cutting force of stepped bi-directional milling cutters is smaller and fluctuates more gently than that of symmetrical bi-directional milling cutters in the backward milling. Especially, the former has better distributed and slower flank wear on the backward cutting edge, and better machining quality than the latter.