Usually, bubbles in your extruded filament are considered a bad sign, but it turns out that now you can buy filaments that are specially formulated for foam. [Stefan] from CNC Kitchen did some experiments with these bubbly filaments and the results were very interesting.
The filaments in question are VARIOSHORE TPU and LW-PLA, both from ColorFabb. Both filaments have a propellant added to the formulation that releases gas when the temperature rises. This causes bubbles to form, creating a cellular structure that reduces density and increases the flexibility of the printed part. This isn’t the first time foaming has been sold as a feature, but previously it was done in Polymaker’s Polywood filament for aesthetic purposes only.
Before subjecting the materials to his excellent testing procedures, [Stefan] First, the print settings are adjusted. This can be difficult due to foaming, which increases the effective volume of the plastic and requires careful adjustment of the extrusion rate. The foaming in the PLA filament reached its maximum foaming at 250 ° C, at which its density was 44% of the non-foamed filament.
When testing physical properties [Stefan] found that the tensile strength and stiffness of printed parts decrease with increasing foaming, but the impact resistance is improved. He concludes that the lightweight PLA may have some interesting applications due to its lower weight and increased impact resistance, with 3D printed RC airplanes being a great example of this. It should also be possible to change the intermediate layers to effectively sandwich the foamed layers between solid skins.
[Stefan]The videos are an excellent source for those looking to master the intricacies of 3D printing with a variety of materials. He has reinforced prints with carbon fiber, played with extrusion widths, and developed a sophisticated gradient fill technique.