Prediction of cutting forces and delamination during carbon fiber reinforced plastics (CFRP) machining

Abstract

Carbon Fiber Reinforced Plastic (CFRP) has been widely used in various industrial areas due to its corrosion resistance, stiffness and high strength-to-weight ratio. However, the machining process of CFRP composite material is complex compared to that of metals. The reason is the unique properties of CFRP composite, such as anisotropy and inhomogeneous characteristics. Therefore, many defects, such as uncut fiber, delamination and tool wear, occur in the process of CFRP machining. To prevent defects in CFRP machining, we discuss important factors, cutting mechanism and chip formation. Based on these, numerical models are suggested for cutting forces and damage prediction. It will help optimize machinability and productivity of CFRP machining. In this study, we developed numerical solutions to predict cutting forces along the fiber orientation in each machining condition in CFRP orthogonal cutting. There are preliminary force prediction model and force prediction model according to varying fiber orientation. The first one is from Bhatnagar’s CFRP force prediction model. This model is proved with CFRP orthogonal cutting in each fiber orientation. This model shows that cutting force and thrust force are increased as increasing feed rate similar to the experimental results. High feed rate can increase the depth of cut in machining. This developed model is more accurate than Bhatnagar’s model in wider area in the condition of high feed rate. The reason is that epoxy region contained in preliminary force prediction model rises in wider area. The other model is modified force prediction model for varying fiber orientation. This model was expanded from Zhang’s CFRP force model. Zhang commented this cutting mechanism can be applied only in fiber orientation below 90°. He proved this in low speed CFRP cutting experiments. We did CFRP orthogonal cutting in high cutting speed over 80m/min. We applied similar cutting mechanism into modified model along all the fiber orientation from 0° to 180°. Force prediction model for all the fiber orientations has similar tendency as the experimental results. The prediction credibility is from 50% to 98.5%. Errors can be generated by many factors in CFRP machining. From this modified force prediction model for varying fiber orientation, damage prediction model can be suggested referring to Jahromi’s damage prediction model. It is based on energy balance in each fiber material. This damage prediction model has similar curve tendency as experimental results. It shows no defect along the fiber orientation from 0° to 90°. However, in the range of fiber orientation from 90° to 180°, it starts making defects inside UD CFRP workpiece because of fiber crush. It is verified by CT X-ray internal inspection. We need to consider poor machinability in the range of fiber orientation over 90°. In conclusion, this process will help optimize machinability in CFRP machining.