Thickness Control of Autoclave-Molded Composite Laminates

Abstract

Composite materials and especially those made from pre-impregnated (prepreg) material are widely used in the aerospace industry. To achieve the tight assembly dimensional tolerances required, manufacturers rely on additional manufacturing steps like shimming or machining, which generate extra waste, which are time-consuming and expensive. Prepreg sheets come naturally with fiber and resin volume content variability that leads manufacturers to guarantee cured ply thicknesses within a typical +/−5% margin of their nominal values. For thick laminates, this can equate to a thickness variability of as much as a few millimeter. To solve the issue, it is proposed to twin in situ laser measurements of the uncured prepreg thickness with numerical simulations of the laminate autoclave consolidation and cure process and to adjust the number of additional sacrificial plies in the laminate based on the model predictions. This reduces the need for expensive and time-consuming trial and error approaches, extra machining operations, and results in the production of a part with high accuracy dimensions. Data for IM7/8552 and IM7/977-3 are presented to demonstrate the potential of the method to reach an almost exact target thickness for flat panels.