Material Stiffness and Cutting Parameters for Honeycomb Aluminum Sandwich Panel: a Comparison with Bulk Material

Abstract

Abstract Aluminum sandwich panel provides a high-strength, light-weight structural material for use in aircraft and aerospace applications such as cabin bulkheads, rotor blades, and luggage and cargo unit load devices. This unique material also has application in many other industries such as machine tool enclosures, museum exhibits, marine craft bulkheads, and hurricane panels for storm survivability. This material, consisting of aluminum face sheets surrounding an aluminum honeycomb core, offers very high rigidity in a low density material. Machining this material is quite challenging due to variable cutting conditions in the low density, low lateral stiffness honeycomb core. Machining often requires a significant amount of post-processing in the form of manual removal of the partially released core walls (flags) along machined edges. The purpose of this work is to reduce the flagging created in the machining of this material. The first step to improving the cutting conditions is to better understand the causes that impact them. In this pursuit, a series of experiments was conducted to measure, quantify, and study the cutting forces during the machining of aluminum sandwich panel. A force dynamometer was used to measure forces during slot milling in bulk aluminum generating cutting coefficients for the force model. Cutting results in bulk aluminum showed generally good agreement with the model with over-predictions ranging from 5 to 20% depending on the feed rate. A series of cutting tests was then conducted on the aluminum sandwich panel in order to decouple the machining forces for the face sheets, the honeycomb core, and combinations of face sheets and core. The data revealed vibration in the honeycomb material that were significantly worse for shallower depths of cut involving the top face sheet and the upper portion of the honeycomb structure despite efforts at stiffening the fixture. The data showed force spikes that correlate with specific engagement conditions in the honeycomb structure. Peak forces were measured as high as 400N though it is not entirely clear whether these peak values are representative of actual peak forces or a combination of peak force with harmonic vibration. The resulting cut walls showed signs of tearing, rubbing, and remaining cell walls indicating that for much of the cut, ideal shearing of the material did not occur. The research highlights the need for further study of the actual mechanism of cell wall removal in this complex cutting environment.