MACHINABILITY STUDY AND FEM ANALYSIS OF UD-CFRP COMPOSITE MTM 44-1 MATERIAL UNDER ORTHOGONAL CUTTING CONDITION

Several engineering applications in the aerospace, marine, military and automotive industries have introduced modern synthetic composites as a substitute to metals due to their high specific strength and stiffness. Furthermore, their high corrosion resistance and lightweight make the aerospace industry the largest beneficiary of these materials. While the advantages of using composite materials are well known designers have to face their limitations. Being relatively new materials further studies are still required to better understand their actual limits, related to the high materials cost and the manufacturing process complexity when compared to metals. The aim of this project was to analyse some of the machinability challenges set by Carbon Fibre Reinforced Polymer (CFRP) and provide a better understanding of the relationship between a number of process parameters and relative cutting forces generated during the machining process. A Finite Element Model (FEM) was created to predict cutting forces during orthogonal cutting of Unidirectional Carbon Fibre Reinforce Polymer (UD-CFRP) composite material. The material analysed was a MTM 44-1 low density toughened epoxy matrix system particularly suited for the production of both primary and secondary aircraft structures. The work-piece was considered as an Equivalent Orthotropic Homogeneous Material (EOHM) alongside with a failure mechanism model using the Chang-Chang criteria. Experimental tests were performed on a lathe machine tool in order to compare and validate simulation results. Polycrystalline diamond (PCD) inserts were used to carry out the tests. Work-pieces with a ring shape were used for experimental tests to obtain suitable data. The specimens were carefully designed and built at the Advance Manufacturing Research Centre (AMRC) based in Sheffield. Six different fibre orientations, two cutting speeds and four feed rates have been used to generate a full set of experimental data. The cutting force results highlighted a dependency between cutting parameters and fibre orientations of the CFRP specimens. The results have shown that fibre orientation is a key factor that governs failure mechanisms, chip formations, surface integrity and cutting forces. Both the experimental tests and the FEM analysis have confirmed the influence that the feed rate has on the cutting forces. Conversely, negligible effects were observed when increasing the cutting speed at the tested cutting conditions.