Drilling carbon fiber reinforced plastics and titanium (CFRP/Ti) stacks is one of the most important activities in aircraft assembly. It is favorable to use different drilling parameters for each layer due to their dissimilar machining properties. However, large aircraft parts with changing profiles lead to variation of thickness along the profiles, which makes it challenging to adapt the cutting parameters for different materials being drilled. This paper proposes a force sensorless method based on cutting force observer for monitoring the thrust force and identifying the drilling material during the drilling process. The cutting force observer, which is the combination of an adaptive disturbance observer and friction force model, is used to estimate the thrust force. An in-process algorithm is developed to monitor the variation of the thrust force for detecting the stack interface between the CFRP and titanium materials. Robotic orbital drilling experiments have been conducted on CFRP/Ti stacks. The estimate error of the cutting force observer was less than 13%, and the stack interface was detected in 0.25 s (or 0.05 mm) before or after the tool transited it. The results show that the proposed method can successfully detect the CFRP/Ti stack interface for the cutting parameters adaptation.
Flexible and conformal positioning of the skin is of great significance for the efficient and low deformation assembly of aircraft panels. As the main conformal positioning part of the skin, the fixture positioning surface is complicated to design when taking into account the flexible positioning. In this study, taking the low deformation and flexible clamping of the skin under complex stress conditions as the target, a fixture positioning profile design method is proposed to predict the deformation of the skin and provide moderate support for the skin based on thin plate theory (TPT). In the face of complex stress and boundary conditions of the skin, the differential method is used to solve the stress and deformation of the skin under different support conditions, which is correctly verified by finite element simulation. The proposed method reveals the influence of the fixture positioning profile on the deflection of the aircraft skin under concentrated load (drilling force), which provides a good design theoretical basis for the fixture design for the low deformation flexible clamping of the skin.
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