Hole diameter variation compensation by integrating computation geometry for helical milling of stacked aerostructure

Abstract

The stack-ups of composite and metal are used in aircraft manufacturing to produce modern high-performance aircraft, which makes fastener-hole-making more difficult. Helical milling is an advanced machining process to improve the quality of hole-making. This paper seeks to control the hole diameter error and guarantee fastener-hole fitting performance. The setup of automated helical milling for assembling composite/metal aerostructures is first presented. Meanwhile, the helical milling procedure in aircraft wing manufacturing is discussed. Based on the designed helical milling end-effector, a length-gauge-based feedback control mechanism of the orbital eccentricity is designed to reduce the diameter error of an intended fastener hole. For accurate measurement, a least-squares method is used to find the calibration parameters of the length gauge. Then the mathematical model of hole diameter variation extraction based on B-spline curve construction is given for further variation compensation. After that, the feedback control system of the radial feed mechanism is established. Besides, the modeling and compensation system of the hole diameter variation is developed and used. In helical milling of CFRP/Ti stacks in an aircraft assembly, fastener holes tend to achieve the target diameter of 7.9400 mm without extending the range of hole entrance and exit diameters.