Inductive Pre-Bonding of Stiffened Structural Components made ​​of CFRP

Abstract

Current aircraft models from different manufacturers have already structural components made of CFRP (fuselage and wing shell, rudder, flaps), which must be reinforced by special profiles. In the state of the art processes, these profiles are pre-bonded with conduction- and convection-based heating methods, which are time consuming and inefficient. At the Center for Lightweight Production Technology (ZLP) of the German Aerospace Centre in Stade a new method for pre-bonding was patented and the foundation for industrialization was laid by extensive research. By using inductive heating, the process time for the pre-bonding of stringers is reduced from 30 - 45 seconds to 3 - 5 seconds per adhesive point. In cooperation with Premium Aerotec GmbH the applicability to Airbus A350 fuselage panel manufacturing was investigated. A comparison to ultrasonic heating and the state of the art pre-bonding method as well as the development and testing of automation concepts were performed. While the technique reached the next phase on the way to series production several findings emerged, which may require further process adaptions. To control the temperature on the bottom side repeatable and independent from stringer type or side attempts to regulate the process were made. Based on optical temperature measurements on the stringer’s top surface, the induction generator power was adjusted using different algorithms. Then several experiments were performed to establish a relation between top and bottom side temperatures in fast processes. Thermographic analysis showed that hotspots occurred during the heating process of A350 stringers, which worsened the temperature homogeneity and shrunk the process window. The problem was considered to be related to the junctions between different plies and could be solved by using an alternative induction coil design. Additionally, this new coil design is supposed to increase overall temperature homogeneity and decrease material dependencies significantly. It makes the process much more controllable. This paper summarizes the methods used to confront inductive heating with ultrasonic and the state of the art technology. Furthermore the automation concepts and thoughts on quality assurance are presented. Finally it shares the insights and results of the performed experiments as well as the future focus of research.