Advancing Additive

Fused Filament Fabrication (FFF) is the most common additive technique to create a 3D solid object out of stock material. An FFF printer extrudes a thermoplastic through a nozzle to build a 3D object in successive layers of extruded lines.

The nozzle diameter has a direct relationship with the XY-resolution of a 3D print. Nozzle diameters are usually chosen depending on the scale of the printed pieces. The smallest printable feature size from a certain nozzle diameter is that exact diameter.

Demonstrating this relationship is Figure A, using a 0.25 mm we are able to achieve a corner radius of 0.125 mm. On the other hand, the 0.6 mm nozzle will yield a minimum corner radius of 0.3 mm. Therefore, to represent a 90-degree sharp corner, the 0.25 mm nozzle will yield a better accuracy in comparison to a 0.6 mm nozzle.

Build time, Z-resolution, and nozzle diameter are directly related to each other. First, Z-resolution is a function of layer height. Second, build time is related to layer height, as shown by the thicker layers that give a faster print time but poorer approximation of a curve at the right in Figure B. Each nozzle diameter has a corresponding maximum layer height. Larger nozzles can print thicker layers and thereby reduce build time.

We expect a variable-nozzle system to improve the trade-off between print speed and resolution. The system will use a small nozzle diameter for the detailed features and a large nozzle diameter for features that don’t require high resolution. This system will reduce the print time significantly, which matters because the cost of an additively manufactured object is driven by its build time.

While metal AM has the potential to revolutionize the way we make metal parts, it is not yet ready for mass manufacturing because of the challenges in assuring part quality. Issues such as porosity, warping, residual thermal stresses, and layer separation cause parts to have anisotropic, degraded, or unreliable mechanical properties such as tensile strength, fracture toughness, or fatigue life.

One solution is to monitor the print quality "in-situ", meaning during the printing process, which will save time and money compared to the current examination that is "ex-situ", or after the part has been fabricated.

Furthermore, putting this sensing capability into the process opens up new opportunities in closed loop feedback control of the metal AM process, which can further tackle quality issues. Such a system could detect an anomalous event during the printing process and take either of two actions: stop the print if it is irrecoverably out of tolerance or modify the printing instructions to bring the print back within tolerance. We expect to improve the printing process and save otherwise wasted time and materials with this in-situ and closed-loop approach.