Improved compression molding technology for continuous fiber reinforced composite laminates: Part 2: AS-4/Polyimidesulfone prepreg system

OCLC Number: 61195669 Excerpt: ... INTRODUCTION Compression molding flat panels of fiber reinforced resin matrix composite laminates is the simplest form of a molding process which employes matched metal dies. In this process, individual prepreg plies are cut into the des_ensions from a fiat sheet of prepreg material. The number of prepreg plies is dictated by the desired final part thickness. These plies are stacked inside the cavity of the female mold and subjected to consolidation under heat and compression force. The prepreg plies can be oriefited during the stacking sequence to yield orthotropic, quasi-isotropic or isolxopic laminates as required for various applications. Despite the simplicity in tooling design, the compression molding of composite laminates is by no means a trivial process [ !-10 ]. Due to the extremely high viscosity of polyimide resin_sin their fully imi'dizeM state, th ¢ ! mpregnafion of resin into the fiber tows is frequently becomes ve_ difficult? it easier tO_impregnate material by the technique of soludon prepreg_ng_Pre_iymers _th a iowdegree0_midi_tionreaetion_e firSt dissolved in solvents and subsequently coated onto the fiber tows and drum wound to form the prepreg.During the moldingcyele, the resin matrix is further imidized under elevated temperature and consolidated by pressure [ 11-13 ]. In order to achieve fully consolidated, void-free composite parts with good mechanical properties, various molding parameters need to be understood and controlled. For the class of prepreg system investigated here, the volatile by-product escape mechanism and the bulk consolidation behavior are the two moi_ng parameters which require eXtra attentiom From a processing point of view, these two pararneters work..... against each other and some compromises have to be made. It is understood that full consolidation of the composite part requires pressure to squeeze out voids formed by the volatile by-products and to facilitate interply prepreg ...