Optimization of machining parameters of Nomex honeycomb core for the development of a mesoscale numerical model to predict deformation and failure in core structures

Abstract

Nomex ® Honeycomb core is the foundational building block for the manufacturing of aerospace composite components. Its usage requires machining honeycomb in complex aerodynamic profiles which is of prime importance because of the complexities of the geometry involved. Machining defects of honeycomb core may result in the failure of sandwich structures when subjected to impact failures or fatigue failures. The quality of Honeycomb Core (HC Core) is governed by the accuracy and precision of these cut profiles. The assessment of accuracy and precision is directly related to the forces induced in the cutting tool and the cutting efficiency. These two parameters form the basis of a multi objective function that this paper aims to optimize for the milling operation. Based on literature review spindle speed, feed rate and depth of cut are taken as the influencing parameters. Taguchi based array of Design of Experiments is used to construct the experiments followed by ANOVA analysis and correlation analysis. The results indicate that the most significant factor is the feed rate with percentage contribution of 72% for the cutting forces and depth of cut with percentage contribution of 85% in case of cutting efficiency. The two parameters are then optimized using Desirability Function Analysis (DFA) and Grey Relational Analysis (GRA). The results are validated by experimental runs and the error is within 5% of the statistical predictions, whereas the percentage improvement in cutting forces for optimum run as compared to worst experimental run is 47.8%. The percentage improvement in cutting efficiency likewise is 11%. Numerical model was built on ABAQUS to simulate the machining process and the simulation was run using 2D Hashin Criteria. Furthermore, the simulation of the Honeycomb core was done using Johnson Cook Criteria.