Fast forming of multistacked UD prepreg using a high‐pressure process

In this article, the opportunities of fast forming of multistacked UD prepreg when using high‐pressure forming were examined in an experimental study. Forming is often considered a bottleneck in manufacturing of composite aircraft parts and speeding up the process is, therefore, of great interest. A Quintus Flexform fluid cell press was used to create pressure of 100 to 400 bars. In the study, different lay‐up sequences and thicknesses were tested for manufacturing of c‐shaped coupons. Tests were performed at different temperatures and some of the samples were sandwiched with mild steel sheets referred to as a steel sheet dummy. A case study was also performed on a double‐curved spar geometry. It was found that forming at a relatively high overall pressure level combined with an elevated temperature, created squeeze flow‐related wrinkle formations, and radius thinning. With high pressure forming, material compression/compaction mechanisms showed to have great influence on the forming result. This differs to low pressure vacuum forming, where intraply shear, interply shear, and ply bending are the dominant forming mechanisms. The steel sheet dummy minimized the squeeze flow related wrinkle in the web and flanges. Instead the forming temperature was found to exert the greatest influence on radius thinning. When forming at room temperature, radius thinning was almost eliminated and instead bending‐related wrinkles in the flange below the radii appeared. POLYM. COMPOS., 40:3550–3561, 2019. © 2019 Society of Plastics Engineers