The paper deals with the mechanical properties of components manufactured ("printed") by the Fused Filament Fabrication (FFF) process
The authors want to increase the adoption of the FFF process by optimizing the laser for energy output and strength of the filament bond
They tested two types of materials used for the FFF process, polylactic acid (PLA) and acrylic-butadiene-styrene copolymer (ABS); both of these types require different levels of energy to avoid creating fractures in the filament.
The paper then describes the process of creating specimens and test results of the experiments conducted.
The FFF process produces a layered structure, with the strength of the final product being determined by the thickness and quality of the "weld seam" between the filaments, this also represents the weak point of the component.
The FFF process at the moment has lower ‘weld seam’ strength compared to conventional manufacturing like injection moulding.
It takes a lot more heat than producing glass (about 100 degrees more) but the control of the cooling rate affects the strength of the final product,
Current FFF systems use a heated printing platform and ideally a closed, heated printing chamber. There are multiple options for applying heat but the paper points to directly applied thermal radiation through a laser.
There were 4 types of laser reviewed in the paper, Heat input laser, CO2 Laser, Neodymium-doped yttrium aluminium garnet laser (Nd:YAG laser), or a Diode laser
The experimental section of the paper focuses on the potential for further optimized interfilament bond strength in the production phase, in order to quantify the relevant physical parameters for best results.
A qualitative assessment of interfilament bonding was done by visual/optical analysis. Fracture surface images of the tensile strength of the specimens were recorded with a Germany stereo-microscope type SZX16
Mechanical tests were conducted with a universal tensile testing machine Z020 (ZwickRoell, Ulm, Germany). The measure of elasticity, the fracture rate defined as tensile strength and the elongation at break were evaluated.
The tests were continued with a rate of 5 mm/min until rupture
For PLA as a printing material, the printed test specimens showed increased stiffness over the smaller test specimen shapes but lower tensile strength and elongation at break.
Improved cohesion was only observed at every second interface of the filament layers. Only every second layer is melted as a result of the experimental setup.
The one-sided use of the laser source relative to the back-and-forth movement of the heated printhead ensures that the already deposited substrate layer ahead of the printhead is heated by the laser only when moving in the direction where the laser is focused.
On the way back, the laser focus happens to be in the wake of the filament deposits. This drawback could be resolved in future FFF equipment designs incorporating circumferential laser arrays positioned around the nozzle or by a single laser equipped with an adequate laser beam guiding system.
The set up of the laser was proved to effect the creation of interfilament bonds and have a corresponding increase in the mechanical properties.
However, you will need to adjust the laser ration source to the ration absorbance of the polymer or vice versa.
The paper highlights that its set up printing layout is very important with getting the test specimen strength close to the injection mould specimens but not better than them yet. More work to do
Printing temperature [◦C] PLA (polylactic acid) 210 ABS ( acrylic-butadiene-styrene copolymer) 260
Bed temperature [◦C] PLA 50 ABS 90
Material and process engineering aspects to improve the quality of the bonding layer in a laser-assisted fused filament fabrication process