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Can we print an aircraft at room temperature?

Periodic Reporting for period 1 - Print2fly (Can we print an aircraft at room temperature?)

Okres sprawozdawczy: 2019-06-01 do 2021-05-31

With rising environmental concerns and fuel costs, we urgently need to reduce the weight of commercial aircraft to enhance fuel efficiency. Within the Print2fly project, the capabilities of additive manufacturing (AM) are combined with room temperature polymerization chemistry to fabricate thermoplastic composites with significant weight reduction and high recyclability.
The adaption of aerospace-grade thermoplastics for conventional AM processes is extremely challenging, considering the complications associated with their high processing temperatures and melt viscosity. Within Print2fly an extrusion-based AM method named Reactive Liquid Deposition Modelling (RLDM) is developed to fabricate reliable and high-performance continuous fibre reinforced thermoplastic composites at room temperature. The RLDM technology replaces the conventional melt processing with photopolymerization of a liquid resin with tailored flow-ability and polymerization kinetics. The RLDM demonstrated promises to fabri-cate defect-free and first-time right parts by eliminating interface defects and voids. The RLDM technology extends the applicability of AM for printing large structures with customized design, reduced cost, and lower environmental impact.

Following objectives were followed during the project:
1- To adapt thermoplastic resin chemistry for the RDLM process and tune the photopolymerization kinetics
2- To correlate interphase microstructure to bonding strength and its relation to macro-mechanical proper-ties
3- To validate and demonstrate AM of fibre reinforced parts through the RDLM process
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.
For the first time, photo-polymerization of a printable and recyclable thermoplastic resin with high mechanical-physical properties was realized for AM applications. The dilemma of polymerization kinetics, viscosity evolution, and printability of the resin were addressed as an essential element for producing high-quality composites by AM. The results of Print2fly contribute to the state of the art by introducing a new printing method named RLDM, probing the interphase formation mechanisms, and uncovering the process-microstructure-properties relations. RLDM proved to have a high capability for fibre-reinforced composite printing through full impregnation of fibres with liquid resin, stronger layer bonding, and lower inter/intra-filament porosity, therefore, parts with higher reliability while being recyclable.
Void-free cross-section of the (a) unreinforced and (b) fibre-reinforced parts produced by RLDM proc
Nozzle designed for fibre- reinforced printing in RLDM process.
RLDM uses UV light to replace melt processing in thermoplastic printing.