A hybrid model to analyze stress distributions at the tool and workpiece interface during drilling of thick CFRP laminates

Abstract

Drilling is employed as a machining method to meet the demands for producing functional CFRP structures without compromising their unique and desirable material properties. Because of its temperature-dependent properties and drillinduced damages, drilling CFRP remains an ambitious task. This study proposes an analytical drilling model coupled with a finite element-based thermal model to predict the characteristic time point-based thrust force and torque generated during the drilling operation. A better understanding of pressure and tangential stress distribution along the drilling cutting edge is necessary to select process parameters better. The drill margin region, which directly affects the hole wall quality, has also been included in the analysis. Drilling experiments were conducted to measure thrust force, torque, and temperature for five different configurations of feeds and spindle speeds. The workpiece FE model utilizes a Gaussian distributed ring-type heat flux, and the tool uses characteristic time point-based step functions as heat fluxes to emulate the drill’s progress through the CFRP laminate. The finite element-based thermal models have been considered to evaluate the heat partition during the drilling operation and estimate the subsequent temperature profiles on the drill tip and hole wall surface, respectively. The hybrid analytical and computational model has been used to analyze the variation of peak pressure and tangential stress distributions on the tip of the drill as well as the thermomechanical response of CFRP based on experimental measurements of thrust force, torque, and temperature and investigation of the condition of the holes for various drilling configurations.