Online adaptive measurement and adjustment for flexible part during high precision drilling process

Abstract

Shape of flexible part is easy to be out of tolerances due to deformations in the clamping and machining process. These deformations are generated randomly and hard to be predicted. Surface normal drilling and countersinking of flexible part is commonly necessary in aircraft assembly process. An online high precision surface normal measurement and cutter orientation compensation method is developed for adaptively drilling of flexible part in this paper. During the process of normal measurement and adjustment, the distance from tool nose to drilling point is accurately measured and adjusted synchronously, which is critical for countersinking. To accurately measure the current normal of the deformed workpiece, two 2D laser displacement sensors are applied to measure the surface profiles of the workpiece and sample two sets of geometrical points each time. Two crossed spatial curves are respectively fitted by the two sets of geometrical points, and the surface normal at the intersection point of the crossed curves is computed. After the deviation between the measured normal and tool orientation is calculated, an online compensation method is used to eliminate the deviation and meet the perpendicularity requirement of the cutter axis to the workpiece surface, and the distance from tool nose to drilling point is measured and adjusted to the setting value synchronously. The compensation method is based on the kinematic transformation of a five-axis machine tool and is implemented by NC compensation. Simulations and experiments are conducted to validate the feasibility and effectiveness of the online adaptive measurement and adjustment method.