Processing of post-industrial unidirectional prepreg tapes using SMC equipment

Abstract

The aerospace industry has an issue of disposing of waste, unused carbon fiber unidirectional prepreg tapes. This paper explores producing chips using sheet-molding compounding equipment (SMC) for conversion into products via compression molding, which are stronger than traditional glass-reinforced SMC parts due to the carbon fiber and high strength epoxy resin. Without a means to convert the continuous tape prepreg into chips, it will not be possible to convert the prepreg into a useful product and provide a way to reduce flow to the landfill and produce less expensive, lighter, and stronger parts for the transportation industry. The cure state of the epoxy resin in the prepreg tapes, which is affected by the amount of time the material has spent stored at elevated or room temperatures, significantly changes the ability of the material to be chopped into short fiber chips. In addition, equipment-related factors affect the material’s ability to be chopped by the SMC equipment. This paper accounts for each of these factors and uses statistical methods to design experiments to investigate the impact each of these material-related and equipment-related factors on the success of the cutting portion of the process. The level of cure, as defined by endothermic peak, glass-transition temperature (Tg), or heat of reaction/degree of cure, has the greatest impact on the cutting process. For material with a moderate level of cure, the sharpness of the blades in the cutting roller also has a major impact on the success of the process. The cutting pressure, roller speed, and tape tension also have an impact on the success of the process, but impact of these factors lessens for feedstock prepreg with a sufficiently high level of cure. An optimal setup was determined, and general rules of thumb for selecting material and equipment settings were established.