Optimising forming quality through friction characterisation for a high-volume Double Diaphragm Forming process using bindered-dry fibre tapes
Topic(s) : Manufacturing
Co-authors :
Nils WIDMAIER (AUSTRALIA), Racim RADJEF (AUSTRALIA), Peter MIDDENDORF , Bronwyn FOXAbstract :
The composite industry is experiencing a surge in production rate, revealing the need for high-volume manufacturing solutions. This increased demand has driven the development of new dry-fibre based production processes. Combining unidirectional dry-fibre tape materials with an automated, two-dimensional layup and subsequent forming step combines the advantages of each production process. This allows for near/net shape preforms with minimal waste and load-path optimised laminates for optimal material usage. Double Diaphragm Forming is a forming process that experiences increasing interest as a forming process for these preforms. Compared to conventional forming methods, Double Diaphragm Forming offers advantages such as reduced tooling costs, the capability to process near-net shapes, and the benefit of multi-layer forming to optimise cycle times.
The preform is positioned automatically between two diaphragms and secured by creating a vacuum between them. This vacuum application induces multi-axial in-plane tension on the preform. The tension level can be precisely controlled by adjusting the vacuum level, and the forming process is accomplished by applying a vacuum between the lower diaphragm and the tool surface. The two main process parameters are normal pressure (vacuum level) on the preform and forming temperature, both of which can significantly influence the friction characteristics of the tape material, which can influence forming quality. Research has shown that the appearance of wrinkle type and bridging defects changes with different levels of normal pressures on the preform with a balance necessary between in-plane tension on the preform to minimise forming defects and a reduction in frictional forces. Therefore, it is necessary to understand the connection between dry unidirectional tapes, process parameters and forming quality. This paper presents an experimental analysis of friction characteristics of dry-fibre tape material under double diaphragm forming conditions. Focus is placed on tape-tape interactions and the interface between the tape and auxiliary materials used to separate the preform from the reusable silicone-based diaphragms. The influence of local weld spots (used for layer fixation during layup) on the friction behaviour is also analysed.
Results show that forming temperature is the most influential parameter on tape characteristics, significantly influencing the binder material. Inter-ply sliding can lead to binder abrasion and accumulation depending on the process parameters and must be considered. The insights on tape characteristics and the forming process have been successfully transferred to a research benchmark geometry and an industry part. Results reveal that a trade-off must be made between wrinkle-type and bridging defects to gapping and tape movement while further considering binder presence.
The preform is positioned automatically between two diaphragms and secured by creating a vacuum between them. This vacuum application induces multi-axial in-plane tension on the preform. The tension level can be precisely controlled by adjusting the vacuum level, and the forming process is accomplished by applying a vacuum between the lower diaphragm and the tool surface. The two main process parameters are normal pressure (vacuum level) on the preform and forming temperature, both of which can significantly influence the friction characteristics of the tape material, which can influence forming quality. Research has shown that the appearance of wrinkle type and bridging defects changes with different levels of normal pressures on the preform with a balance necessary between in-plane tension on the preform to minimise forming defects and a reduction in frictional forces. Therefore, it is necessary to understand the connection between dry unidirectional tapes, process parameters and forming quality. This paper presents an experimental analysis of friction characteristics of dry-fibre tape material under double diaphragm forming conditions. Focus is placed on tape-tape interactions and the interface between the tape and auxiliary materials used to separate the preform from the reusable silicone-based diaphragms. The influence of local weld spots (used for layer fixation during layup) on the friction behaviour is also analysed.
Results show that forming temperature is the most influential parameter on tape characteristics, significantly influencing the binder material. Inter-ply sliding can lead to binder abrasion and accumulation depending on the process parameters and must be considered. The insights on tape characteristics and the forming process have been successfully transferred to a research benchmark geometry and an industry part. Results reveal that a trade-off must be made between wrinkle-type and bridging defects to gapping and tape movement while further considering binder presence.