Experimental Studies on the Cutting Characteristics of Hybrid CFRP/Ti Stacks

Abstract

Owing to their enhanced mechanical properties and improved structural functions, the use of hybrid CFRP/Ti stacks (a sandwich of one CFRP laminate and one Ti alloy) has experienced an increasing trend in modern aerospace industry. The emergence of such composite-to-metal alliances, however, poses a series of new challenges to the manufacturing sectors for high-quality finishing of the material-made components. The key machining problems usually arise from the disparate natures of the stacked constituents (CFRP laminate and Ti alloy) and their respective poor machinability. To study the fundamental cutting characteristics of the bi-material assembly, this paper presents an experimental study concerning the machinability evaluation of the hybrid CFRP/Ti stacks. An orthogonal cutting configuration (OCC) derived from the real manufacturing operation was adopted to finalize the CFRP/Ti cutting comprehension by using the polycrystalline diamond (PCD) tipped tools. The cutting trials were performed under the reasonable cutting sequence strategy of CFRP -> Ti as pointed out by most experimental studies. The key cutting responses including cutting forces, machined surface quality and tool wear mechanisms were precisely addressed versus the utilized cutting conditions. The experimental results highlight that a parametric combination of high cutting speeds and low feed rates often facilitates the reduction of cutting forces and induced damage extents. The basic damage modes promoted on the machined CFRP/Ti surfaces are observed to be fiber pullout, resin loss, surface cavity, deformation of feed marks and re-deposited materials. Moreover, the key wear mechanisms governing the PCD tool cutting are confirmed to be crater wear and flank wear, while the tool failure mode is edge chipping. To ensure the excellent machined surface quality, a stringent control of tool wear should be implemented when cutting hybrid CFRP/Ti stacks.