Towards tool-less thermoplastic CFRP manufacturing processes using a cooperating robot system

Abstract

Fiber-reinforced thermoplastics have gained popularity in the aerospace industry due to their light weight, formability, weldability, chemical resistance, and recyclability. In this paper we present a production chain consisting of in-situ consolidated Automated Fiber Placement (AFP) and a continuous ultrasonic welding process that enables component manufacturing without complex molds. The AFP process is an additive manufacturing method for producing CFRP composites. We introduce a system that allows both AFP and ultrasonic welding to be performed without fixtures. A second robot serves as a counter-holder in both cases. For AFP, an end-effector with a roller was developed to move synchronously with the AFP head, enabling tape deposition for flat or curved free-form surfaces. For ultrasonic welding, a solid end-effector was designed to act as an anvil. A steel strip is fed over a copper block, and the component is guided between the two end-effectors during the welding process. Our work demonstrates that both AFP and welding processes can be successfully carried out using a dual-robot process without fixtures. An important technology enabler has been the development of a fast model-based elastic calibration method to characterize the structural behaviour of the robots. The method conciliates requirements of minimal invasiveness, for seamless deployment in industrial settings, together with a high degree of coherence with the spectrum of action of the multirobot platform in production. Once calibrated, the kinetostatic models are exploited in a control scheme to correct the deviations of the force-cooperating robots in real-time. This enables the robots to follow their intended trajectories accurately in the case of both processes. This approach demonstrates the possibility of cost-effective production of complex geometries. The results have successfully demonstrated the feasibility in principle. By eliminating molds, this method reduces production costs and increases flexibility, making it an attractive solution for fiber-reinforced thermoplastics.