Copyrighted Materials Copyright 2009 DEStech Publications Retrieved from www.knovel.con CHAPTER7 Liquid Composite Molding 1.INTRODUCTION The last three chapters have presented a few processes for the manu- facturing of composite structures. These have advantages and disadvan- tages. The hand-lay-up on open molds provides flexibility and versatility in terms of different configurations; However it does not provide good quality of the part due to the lack of control of compaction and the entrap- ment of air during the laying-up process. In addition, this process suffers from the evaporation of styrene into the atmosphere, which is an environ- mental concern. For the autoclave molding process, even though it also uses laying-up either by hand or by tape laying machine, the environmental concern is not critical because prepreg tapes are used and the evaporation of volatiles is not serious. The quality of the parts is very good due to the fact that the impregnation of the fibers is done off-line. The use of vac- uum, pressure and temperature control also gives parts of good quality. However the autoclave molding process has disadvantages as follows: . Since prepregs have to be used, the cost is high compared to cases where dry fibers are used. . The prepregs have a shelf life, which imposes time constraint on their usage. This also can produce waste if the prepregs are not used during their shelf lives. . Since laying up is required, the component cannot have fiber orientations other than in-plane. Having fibers along the thickness 247CHAPTER 7 1. INTRODUCTION The last three chapters have presented a few processes for the manu￾facturing of composite structures. These have advantages and disadvan￾tages. The hand-lay-up on open molds provides flexibility and versatility in terms of different configurations; However it does not provide good quality of the part due to the lack of control of compaction and the entrap￾ment of air during the laying-up process. In addition, this process suffers from the evaporation of styrene into the atmosphere, which is an environ￾mental concern. For the autoclave molding process, even though it also uses laying-up either by hand or by tape laying machine, the environmental concern is not critical because prepreg tapes are used and the evaporation of volatiles is not serious. The quality of the parts is very good due to the fact that the impregnation of the fibers is done off-line. The use of vac￾uum, pressure and temperature control also gives parts of good quality. However the autoclave molding process has disadvantages as follows: • Since prepregs have to be used, the cost is high compared to cases where dry fibers are used. • The prepregs have a shelf life, which imposes time constraint on their usage. This also can produce waste if the prepregs are not used during their shelf lives. • Since laying up is required, the component cannot have fiber orientations other than in-plane. Having fibers along the thickness 247