The research and technical tasks have been divided into three parts as following:
1. Thermoplastic resin photopolymerization at room temperature
A photo-polymerizable thermoplastic resin with properties suitable for AM was crucial for the aims of the project. Various combinations of resins and photoinitiators were investigated and modified to achieve the desired chemical and physical properties. The effect of photo-polymerization parameters such as the light wavelength, exposure distance, and time on polymerization kinetics, resin flowability, and solidification time were examined and adjusted for the RLDM process. The cure reaction kinetics were monitored by the exothermic reaction during UV polymerization and relevant kinetics models were employed to describe the reactions for different formulations. The rheological behaviour of resins was also assessed for different processing scenarios and relevant models were developed to predict the resin flowability.
2. Nozzle design and printer adaptation for RLDM Process
In the second part of the research, a 3D printer setup was designed and manufactured adopting the RLDM process requirements. Two different nozzles were constructed, one dedicated for pure polymer printing and the other one for fibre-reinforced printing. The latter accommodated an in-nozzle impregnation chamber where resin can thoroughly wet the fibres for an enhanced bonding between fibres and matrix. A photocuring system was manufactured capable of curing the resin at different light wavelengths, intensities, and exposure distance. Additionally, a resin dispensing system and custom G-codes were developed to account for the RLDM process.
3. Processing–microstructure–properties correlation
The constituent material properties, processing condition, and microstructure of printed parts are of great importance for the fabrication of robust and durable composite parts. Within this section, extensive experimental procedures were applied to maximize the mechanical performance of the printed parts by tuning the process and microstructure. For this, polymerization kinetics and processing parameters of the resin were optimized to augment the interphase quality between deposited layers and to reduce the void formation during the printing process. The mechanical and physical properties of resultant specimens were assessed and linked to the processing steps and also morphological observation on the internal structure of the parts. The microscopic images of the cross-section for pure resin and carbon-fibre-reinforced parts showed no void content and high-quality bonding between the deposited layers as well as between matrix and fibres in the final products. The optimized printed specimens demonstrate a mechanical performance comparable to conventional counterparts.
The dissemination was implemented in the form of a patent application, two master thesis, presentations in industrial and academic settings, and social media announcements. Additionally, several manuscripts are under preparation for publication in scientific and technical journals.
