Optimisation of process parameters for the orbital and conventional drilling of uni-directional carbon fibre-reinforced polymers (UD-CFRP)

The machining behaviour of carbon fibre-reinforced polymer (CFRP) is not a very extensively researched topic. With respect to this material, it must be noted that it is difficult to find its analogy in traditional metal machining because of its non-homogenous and anisotropic features. With the help of the latest technology, it is possible to machine good-quality holes using expensive and special cutting tools, but for the purpose of developing cheaper alternative technologies (like helical milling with a solid carbide tool) additional research and investigation are necessary in order to evaluate such possible technologies. In this study, the machinability of a hand-laminated uni-directional CFRP is investigated in the case of using a special diamond coated twist drill and a solid carbide end mill (helical milling) with a view to analysing and optimising referent machining parameters. Relying on the data obtained during the experiments, axial cutting force, delamination effect and surface roughness are analysed and modelled using analysis of variance (ANOVA) and response surface methodology (RSM) techniques. It was found that the solid carbide end mill with optimal cutting conditions is able to produce better-quality holes than the special diamond coated twist drill, as long the tool wear does not appear. It is also concluded that the average ratio of Rz to Ra is higher than in the case of homogeneous materials because of the uncut fibres, of the matrix and of the micro-crackings.