Shahriar Bakrani Balani recently presented a thesis, ‘Additive manufacturing of the high-performance thermoplastics: Experimental study and numerical simulation of the Fused Filament Fabrication,’ to Institut National Polytechnique de Toulouse. Delving further into the science of materials and 3D printing, Balani offers a comprehensive definition of FFF 3D printing along with focusing on the importance of process parameters and materials.
Starting from the beginning of 3D printing with Chuck Hull and the first SLA printer, Balani gives a full history of the technology—along with explaining the basics of its evolution, and how it works. Balani outlines the three different AM groups (liquid-based, solid-based, and powder-based) and all the resulting processes possible.
Three different additive manufacturing groups according to Hernandez et al. [14]
“When this Ph.D. thesis started in 2015, none of the machines was suitable to print high-performance thermoplastics such as PEEK (polyetheretherketone). Indeed, PEEK is a high-performance semicrystalline thermoplastic with a melting temperature above 340 °C and a higher viscosity compared to other conventional polymers which are typically used in FDM (FFF) process,” explained Balani. “A high viscosity combined with a high melting temperature increases the difficulties to process this kind of material. Because of these properties, the use of PEEK as raw material for 3D printing is limited.
“However, in June 2015, INDMATEC launched the PEEK 3D Printer as the first FDM 3D Printer for high-temperature polymers. This new 3D printer, which features a build volume of 155 x 155 x 155 mm, is equipped with a hotend that reaches up to 420 °C. It can 3D print objects out of PEEK. The evolution of the FFF (FDM) printers from 1990 until now shows that their ability to print a broader range of polymers with higher precision increases while their price is reduced.”
Levels of analysis for FFF prototypes
Noting that there have not been many studies regarding the use of high-performance polymers, Balani cites only several previous sources concerned with printing orientation, temperatures regarding PEEK, and influences such as tensile, flexural, and impact strength.
Different raster orientations were examined, along with relation to mechanical properties. Other studies focused on basics like print speed, temperature, layer thickness—and ultimately, how environmental temperature influenced PEEK tensile strength. Other studies have been related to surface roughness and possible surface treatments.
For PEEK, several studies have been performed regarding FFF, beginning with medical use and experimentation with temperature and filament diameter—leaving the researchers to note that nozzle and printing platform temperature were critical to suitable tensile strength. Other studies examined the impact of thermal conditions on mechanical properties, as well as crystallization.
“The next step is to print PEEK samples under controlled environment at different temperatures and printing parameters to be mechanically tested. Furthermore, the determination of the temperature and the heat field by using infrared thermography would be necessary to validate the heat transfer predicted by our numerical model,” the researcher concluded. “Hereby, we have studied the mechanism of interdiffusion of the macromolecular chains and the relaxation at temperature above the melting temperature.
“However, the interdiffusion starts below the melting temperature at slow rate, so, determining the relaxation times at lower temperature could help to optimize the printing speed. Also, the influence of the printing conditions on the welding (bonding) strength of a few filaments is a step towards the improvement of the bonding strength. For that, a specific mechanical test would be developed to quantify the inter-filament adhesion. Lastly, when the use of the FFF process will be mastered for high-performance thermoplastics, polymeric based composites could be used as well. Bio-sourced composites, long carbon and glass fiber composites, and metal/polymer blends materials could be used as raw materials to reach new properties. For all these materials, the FFF process requires a fine control of the material properties during the deposition to ensure the best quality of the 3D printed parts.”
Sequence of the works done in this study in order to determine the crystallization kinetics in the FFF process
PEEK has been used for a wide range of applications, with numerous studies surrounding the material—from use with small medical implants to discs coated with antibacterial agents, and the use of composites.
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[Source / Images: ‘Additive manufacturing of the high-performance thermoplastics: Experimental study and numerical simulation of the Fused Filament Fabrication’]