Rapid Manufacturing of Tailored Thermoplastic Composites by Automated Lay-up and Stamp Forming

Abstract

Lightweight aircraft design is key to reducing the cost and environmental impact of flying. The high specific stiffness and strength make fiber reinforced polymer composites an attractive material for aircraft design. With the growing demand for aircraft and the increasing use of composite materials, there is a need for cost-effective composite manufacturing processes. Thermoplastic composites are potentially ideal for automated high-rate low-cost manufacturing as they can be repeatedly melted, shaped and solidified in short cycle times, which allows for forming, fusion bonding and recycling. This thesis proposes a novel processing route for the manufacturing thermoplastic composite components. In this route, automated lay-up is used to manufacture flat blanks with tailored and near net-shape lay-ups, which improve the performance over weight ratio of the part and reduce production scrap. Shaping of the blank into the final part takes place during a short stamp forming step. The main challenge is to achieve a high consolidation quality at the end of this process cycle, which is required for good mechanical performance. Blank lay-up is performed at high rates in order to achieve short cycle times, which results in a low degree of consolidation compared to in-situ lay-up at lower rates. This means that most consolidation has to take place during stamp forming, where the available time for consolidation is also short. Void content is considered as one of the most important measures for consolidation quality in this thesis. The main objective is to develop an understanding of the physical mechanisms that govern the evolution of void content during stamp forming and of the interrelation between material properties, processing parameters and final consolidation quality. The work presented in this thesis shows that the final consolidation quality is a complex function of the entire processing chain, where each step has a critical function in the consolidation process. Material, design and processing guidelines are provided to support process development. Finally, the processing route is demonstrated on a tailored spar, which confirms that good consolidation can also be achieved in realistic parts. However, the need for an improved understanding of the forming and consolidation of more complex tailored parts was highlighted. Altogether, this thesis provides a fundamental basis for the further development of the rapid manufacturing route for lightweight tailored composite components.