Countersink depth control in aeronautical structural components drilling processes by machining forces analysis

In the era of digitalization, Industry 4.0 is spreading across the aeronautical sector with the purpose of improving and optimizing its production systems by means of process monitoring with sensors and processing the large amount of generated data. In the aircraft assembly process, mechanical joints play a fundamental role and are critical points from a structural perspective. The countersink is one of the key elements of the joint, especially when located on the outer skin of the aircraft because of aerodynamic reasons. This paper proposes a countersink depth parameter quality control system performing data analysis techniques for industrial automatic drilling processes of carbon fiber reinforced polymer (CFRP) aircraft structural components. The proposed system intends to determine the countersink depth of the hole in real time and in a non-intrusive way by processing the signals of machining forces, axial force, and torque, recorded during the operation. The followed methodology is based on a series of experimental tests with force monitoring to develop the new system. Finally, the achieved results are validated using a high-performance contact measurement equipment. The validation is successful and shows the great potential of the new method. The industrial implementation of this system would mean an important progress within the process, allowing real-time hole inspection instead of the traditional periodic inspection systems.