Effect of a Ti alloy layer on CFRP hole quality during helical milling of CFRP/Ti laminate

During the helical milling of carbon fibre reinforced polymer (CFRP)/Ti laminated structures, there are inevitable influences between the CFRP and Ti. This paper investigated the effect of Ti on hole quality in CFRP during the helical milling of a CFRP/Ti laminate. Cutting force and heat, as well as the surface and subsurface qualifies of holes in CFRP, were observed with and without the presence of a Ti base layer. A subsurface damage assessment method is also proposed. The results show that Ti had slight influences on cutting force and surface quality, and significant influences on cutting temperature and subsurface quality. The cutting of Ti generates a great deal of heat, thus significantly increasing the temperature at the outlets of CFRP holes. Due to this high temperature, the rigidity and adhesive properties of the CFRP resin base decline, which causes serious subsurface damage to the fibre layers close to the hole outlets. Subsurface damage was evaluated by the proposed assessment method (maximum damage depth = 54.7 mu m). Additionally, the fibre cutting angle greatly influences the depth of subsurface damage. Hence, CFRP hole quality is significantly influenced by the cutting of adjacent Ti layers during the helical milling of CFRP/Ti laminates. Subsurface damage is the best factor for assessing CFRP processing quality.