Co-authors​ :

 Racim RADJEF (AUSTRALIA), Nils WIDMAIER (AUSTRALIA), Tuyen TRAN , Mostafa NIKZAD (AUSTRALIA), Boris EISENBART (AUSTRALIA) 

In recent years, integration of zero tack prepreg materials into advanced manufacturing has garnered attention for its advantages, including long out-of-freezer storage, increased automation potential and high-volume production potential when combined with snap cure epoxy systems. The absence of tackiness in such prepreg materials presents a distinctive advantage in ATL systems, as it eliminates the need for backing paper or concerns related to tape sticking and contamination on guide rollers. On the other hand, the absence of tack requires alternative ways of bonding. In the study presented in this paper, our primary objective was to investigate the intricate dynamics governing the cure kinetics of zero tack prepreg materials when subjected to ultrasonic spot welding—a prevalent technique employed in automated tape placement systems for creating tailored thermoplastics tape stacks, also known as blanks.

Specifically, the study sets out to explore whether ultrasonic spot welding induces partial curing of the epoxy resin within the zero tack prepreg and, subsequently, what the potential ramifications could be on the integrity of the fully cured composite part. Ascertaining the extent and nature of the cure in the spot-welded area is paramount to understanding the compatibility of this joining process in producing defect-free composite structures. A detailed comparison of results obtained from Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), and Dielectric Analysis (DEA) between uncured zero tack prepreg samples and those subjected to ultrasonic spot welding will provide comprehensive insights into changes in glass transition temperature (Tg), ion viscosity, and dielectric properties—parameters indicative of changes in the cure kinetics of the epoxy resin. Initial results of DSC measurements showed no significant change in Tg for the spot-welded samples. This analytical approach aims to elucidate whether ultrasonic spot welding introduces variations in the material's microstructure that may translate into internal defects in the final composite part. Furthermore, a microscopic analysis and CT scans of the weld spots within fully cured panels alongside mechanical tests will be conducted to gain further insight.

The outcomes of this investigation are crucial for determining the acceptability of ultrasonic spot welding as a viable technology for producing defect-free composite components. This research contributes valuable insights to the nuanced interplay between zero tack prepreg materials, ultrasonic spot welding, and the resulting microstructural characteristics, thereby advancing the understanding of optimal manufacturing practices in composite fabrication.