Experimental and computational studies of fused deposition modelling for the fabrication of microstructure patterns
Abstract
Fused Deposition Modelling (FDM) is an additive manufacturing process used in 3D
printers for the fabrication of complex 3D objects by layer deposition of molten
thermoplastic filaments. The FDM technology has the potential to produce customised
micro/nano structured patterned surfaces with applications in medical, microfluidic, bio surfaces, etc. FDM is widely used due to its simplicity, low costs and high throughput.
However, high printing accuracy and micro-manufacturing are still challenging due to the
nature of the process. Even though progresses on numerical simulations of FDM have
been made, there is a lack of comprehensive research on swelling and solidification of
the filament and microstructures by considering the temperature dependant properties of
polymers.
This project aims to improve the accuracy of printed parts by controlling the polymer
swelling phenomena as well as developing a cost-effective manufacturing technique, in
terms of predicting the evolution of the extrusion process for the fabrication of
microstructures using commercial desktop 3D printers which utilise the FDM technology.
To achieve this, the temperature dependant rheological and thermal properties of
polylactic acid, within the boundary of printing conditions are first obtained and analysed
numerically. The mechanisms and the effects of operation and design parameters on the
dimensional accuracy of the extruded filaments are then investigated by numerical
simulations based on the Finite Element Method developed in COMSOL Multiphysics
software. Moreover, the free surface of the polymer is determined by applying force
balance and energy equations on the interface to obtain the filament swell and phase
change behaviours. Finally, the model is validated using theoretical results from the
literature and experimental measurements and further used to investigate the evolution of
the microstructures on the filament surfaces during the extrusion process.
From this study, it is identified that both printing process parameters, especially printing
speed, and polymer properties have a significant impact on the formation of extrudate
swell and the shape of the microstructures. The deformation of the polymer increases
with the rise in temperature as the viscosity is highly affected by temperature changes.
Through enhancing the solidification rate and injection rate, the accuracy of filaments and
microstructures can be improved. It is discovered that the swelling phenomena can be
reduced by as much as 21% through cooling the filament with water. Also, in terms of
the micromanufacturing with FDM, several microstructures with different shapes including rectangles, triangles and semi-circles are simulated. The hydraulic swell value
of unity is possible to achieve through adjusting the printing speed for each geometrical
shape. Swell value of 1 is obtained at to 45,50 and 70 mm/s printing speed for rectangles,
semi-circles and triangles respectively which can be used as a reference point for printing
microstructures.
This study helps to predict the shape of the filament and its microstructures using
temperature dependant polymer data through simulations. This eliminates the need for
time-consuming experimentations for the determination of surface topography of the
filaments.
To further improve this study, the effect of layer deposition on the surface topography
needs to be considered.