Drilling of uni-directional carbon fibre reinforced plastics with diamond tools: experiment and finite element study

Carbon fibre reinforced plastics (CFRP) are increasingly being used in aerospace, automobile and sporting goods due to its high strength to weight ratios, high resistance to corrosion and low thermal expansion coefficient. One of the most extensively used processes in assembling CFRP components is drilling operation. Different challenges are faced when drilling CFRP, among which Peel-up and Push-out are two distinguishable delamination mechanisms associated with drilling of composite laminates, due to the extremely abrasive nature of the fibres. It is economically signicant to have composite components free of delamination and a long drill life. Owing to the ultra-hardness and superior wear resistance of diamond, polycrystalline diamond (PCD) tools are being used widely as one of the main solutions for drilling CFRP. In addition to the well known fact that diamond is the hardest material ever found or made, PCD has outstanding properties such as high thermal conductivity, low coefficient of friction and low thermal expansion. All of these properties are critical in drilling CFRP. In addition to cost, there is lots of time wasted when investigating the drilling process experimentally due to the large number of parameters included such as tool types, material type and machining conditions. One of the advantages of utilizing Finite Element Method (FEM) is obtaining mechanical results and thermal behaviour of the drilling tool and workpiece used without investing lots of time and money with the experimental work. Hence manufacturing time and costs are reduced dramatically especially when the input values for the FEM are accurate. In this research, a new 3D nite element model was developed in ANSYS-Explicit by implementing the ply-based modeling technology to simulate the drilling of unidirectional CFRP using PCD twist drill and a special diamond coated double point angle drill tool without using a back-up plate, and also for predicting the thrust force and torque at planned feed rate and speed combinations. The ply-based modeling technology was used to model the laminates and to validate if the meso-scale approach used in this research would be the ideal solution to characterize the drilling induced damage. Hole quality has been investigated through delamination factors in this research experimentally and by finite element analysis, as they are calculated and compared to study the effect of operating parameters for twist drill and double point angle drill on the drilling induced damage. The delamination factor Fd and the adjusted delamination factor Fda have been used in the research, a new approach to measure the equivalent adjusted delamination factor Feda was developed, all of these delamination factors have been compared. Results show that the Feda obtained is suitable to estimate the drilling induced damages, and feed rate is regarded as one of the parameters highly affect the drilling induced damage indicated from the experimental and simulation derived results. Experimental drilling validation process was implemented by utilizing a CNC machining centre, force-torque dynamometer and charge amplier to measure drill torque and forces. While a Philips XL30 scanning electron microscopy (SEM) and a Leica optical microscope were used in obtaining the images of the delaminated vicinity of entrance of the holes drilled, software "Image J" was utilized to process the image of delaminated areas