Advanced Technologies for Discrete-Parts Manufacturing

Modern airframes require thousands of drilled holes in difficult materials such as graphite-epoxy composites, titanium, or layered metal-composite assemblies. Drill life and hole quality are often limited when drilling composites due to heat buildup. Drilling composite/metallic stackups often requires costly interlayer deburring due to rapid drill wear. Trial-and-error approaches to improving drilling processes do not yield optimum results due to cost and time limitations. In this project, analytical and numerical methods for designing composite and composite-metal stackup drilling processes, which will permit rapid investigation of a broader range of conditions, will be developed and validated. A finite element program specifically written for machining will be used with brittle fracture constitutive descriptions appropriate for composites. In Phase I, the feasibility of the approach will be established by developing a first stage, homogeneous constitutive description of fiber-epoxy composite, suitable for calculating bulk temperatures and stresses and for evaluating drill wear. Algorithms for assessing drill life based on computed temperatures and stresses will be developed and validated against drill life tests. A pilot process at an airframe plant will be used for further validation; a 100 percent increase in drill life will be targeted for this application application.