Drilling of Aramid and Carbon Fiber Polymer Composites

Drilling tests were conducted on aramid and carbon fiber-reinforced composite laminates using an instrumented machining center. Machining parameters for the damage-free drilling of these materials were established together with semi-empirical relationships between drilling forces and cutting parameters. The drilling force responses as a function of various feed rates and drill sizes were characterized to define the key process stages taking place during a drilling cycle. Using a previously established delamination-based criterion for initiating damage during drilling, the critical feed rate for damage-free drilling was established for the two composite material types: aramid and carbon fiber-reinforced polymer laminates. Independent measurements of the opening-mode delamination crack energy release rates were conducted on both materials to determine the critical thrust force for damage initiation. This study establishes the key process stages exhibited by carbon and aramid fiber composites during drilling, the critical threshold feed rates to avoid damage, and machining relations that can be utilized for the design of intelligent controllers for efficient drilling of composite laminates.