Qualitätsregelkreis zur Kompensation fertigungsbedingter Steifigkeitsschwankungen in FVK-Strukturbauteilen

• Quality control loop for the compensation of process-induced stiffness fluctuations for structural composite parts

Stender, Sebastian; Hopmann, Christian (Thesis advisor); Brecher, Christian (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2021

Abstract

The combination of the direct preforming processes 3D Fiber Spraying and Automated Fiber Placement is a promising way to significantly reduce the amount of precious fibers used in the production of textile-based preforms. This can save up to 50 % of the manufacturing costs of components made from fiber-reinforced plastics. However, production fluctuations of the 3D Fiber Spraying process lead to wide tolerances of the mechanical component behavior. The feed-forward quality control loop presented in this thesis is intended to detect the fiber areal weight and fiber orientation fluctuations of the 3D Fiber Spraying process and to compensate them by adjusting the layup parameters in the subsequent Fiber Placement process. In addition, in the subsequent HD-RTM process, the resin mass is tailored to the individual preform by the control system to guarantee a complete impregnation of the fibers. The presented investigations aim to determine the tolerance band widths of torsional, bending and tensile stiffness after intervention of the quality control loop and to compare them with known tolerances of the 3D Fiber Spraying process. FEM simulations and experimental investigations show that very small tolerances for torsional and tensile stiffness of 3.4 % and 2.2 % respectively will be achieved by the compensation measures, if the production fluctuation data is fed to the algorithm. However, due to the different sensitivities of the load cases to the layup parameters of the Fiber Placement, the bending stiffness exceeds the target value by up to 34 %.In contrast, if the process fluctuations are not known, but must be determined by the quality control loop itself, an intervention of the compensation algorithm will only result in a reduction of the stiffness tolerances when the fiber areal weight of the Fiber Spraying process fluctuates by more than 45%. This can be attributed in particular to the indirect determination of the fiber areal weight via a correlation with the preform height and the superficial measurement of the fiber orientation with a camera system. The calculation of the material properties of the long fiber preforms for the control model is subjected to only small tolerances. With a direct determination of the fiber areal weight by means of an X-ray scanner and the volumetric fiber orientation distribution by means of an eddy current device, the quality control loop could already be used for fiber areal weight fluctuations of the Fiber Spraying process of >11.4 % and thus, within technically relevant production fluctuation limits.