Drilling of thick composite materials using a step gundrill

The assembly of aeronautical parts requires the machining of composite materials. Drilling is the most important process in the assembly. When drilling composite materials, a number of defects are generating. A solution, to reduce these defects, is to drill using a step gundrill. In this paper, drilling of thick composite plates using a step gundrill is studied. Delamination, which is considered the major drilling defect, is analytically modelled at the hole exit. The critical thrust force at delamination is then found dividing the plate under the tool into several zones corresponding to the tool active part. These results are experimentally validated. The Optimal cutting conditions at delamination are finally determined using a cutting force model. This model uses the same zones decomposition as the analytical critical thrust force model. The results of this paper can be extended to other tools to find the optimal cutting conditions corresponding for delamination-free drilling. (C) 2017 Elsevier Ltd. All rights reserved.