Formation mechanism of tearing defects in machining Nomex honeycomb core

Abstract

Nomex honeycomb core has been widely applied in aerospace industries due to its superior strength and rigidity. However, the machining defects of honeycomb core can deteriorate the bonding strength between honeycomb core and connective face sheet. This paper investigates the tearing defects formatted in milling process of Nomex honeycomb core. Firstly, a cutting force model is proposed to predict the milling forces under various tool entrance angles. Then, finite element simulation for machining honeycomb wall is conducted to reveal the formation mechanism of tearing defects. The accuracy of the model is verified by a group of experiments under different entrance angles and the relative error is below 25% in 1-direction and 20% in 2-direction. It is found that the formation of tearing defects is closely related to the deformation of honeycomb wall and the component of cutting force in direction parallel to wall. The tool entrance angle can be thus optimized based on the reduction of tearing defects. The optimized entrance angle of double wall is among 40° and 70°.