CT technology is widely used in the 3D printing industry, especially in laser powder bed fusion processes for metals. In these applications, CT is used to improve understanding of the technology and, more importantly, to inspect finished parts for internal voids or cracks. Breaking new ground, a research team recently used CT scanning to examine the hot end of a desktop 3D printer.
The research team focused their study on a Bondtech LGX extruder paired with an E3D V6 hot end and a Duet board, all placed near a CT scanner. For optimal CT scanning, the original heating block was replaced with a special aluminum version. A load cell was used to measure the force required for extrusion through the die. Using 360° CT scans, the team observed the material during extrusion. The filament used was HIPS, a somewhat unconventional choice, and was infused with tungsten to act as a contrast agent. Several experiments were carried out at different printing temperatures – 220 °C, 240 °C and 260 °C.
The study examined aspects such as wall sliding effects, material flow and the force required for extrusion. Key findings indicate that increasing the speed of filament extrusion increases the melt zone within the die. However, higher speeds also mean that the filament has less time to heat and melt. Additionally, at higher extrusion speeds, the filament is more likely to bend as it enters the print head.
Upon closer inspection, the team found that the filament remained stationary on the nozzle wall and reached its maximum speed in the center of the nozzle. They also noted that higher extrusion speeds could generate greater forces, potentially leading to extrusion problems. As a solution, the team suggests developing nozzles with longer barrels, particularly for high-speed printing applications. In the future, they want to delve deeper into the inner workings of the print head and examine the melting behavior of the filament.
The insightful article was written by Julian Kattinger, Mike Kornely, Julian Ehrler, Christian Bonnet and Marc Kreutzbruck from the Institute for Plastics Technology at the University of Stuttgart. This is truly necessary work and highlights the need to refocus the industry. We should spend a lot less time on features, movement speed and software and a lot more time understanding and focusing on the intricacies of what’s going on inside the nozzle. Such an in-depth look at actual melting could tell us a lot about nozzle design and nozzle settings. Perhaps a certain pattern on the cylinder could improve the melting behavior of 3D printers. Perhaps a new, longer barrel could print much faster and more accurately. Maybe we could also test which designs and materials could be optimal. We’re a strange industry that pays a lot of attention to motion control. We tinker with belts, pulleys, calibration and chassis components to make better printers. But positioning the nozzle to coherently extrude the material is the part of the equation that many other companies in other industries also use. Meanwhile, in the remarkably similarly named material extrusion process, this extrusion part is the only thing that makes us unique. The extrusion itself is the crucial step. And here it depends on where the filament melts and how, at what temperature and pressure. Subsequently, the drop and the actual deposition are also very important, as is the way in which that drop becomes a trace and how that trace connects to the underlying layer. We would appreciate further research that allows us to observe the printer’s printing process.
A comprehensive analysis of the actual melting process could revolutionize nozzle design and optimal settings. For example, introducing a specific pattern on the cylinder could improve melting behavior in 3D printers. A redesigned, longer cylinder could potentially result in faster, more accurate printing. Additionally, rigorous testing could help determine the best designs and materials for such innovations.
As an industry, we seem to be fixated on motion control and invest significant effort in optimizing belts, pulleys, calibration and chassis components to improve our printers. However, it should be borne in mind that many other industries also deal with the precise positioning of nozzles or similar components. What sets us apart is the material extrusion process – more precisely, the actual extrusion. This step is crucial, and this is where the details really matter: how the filament melts, what temperatures and pressures are at play, and how the subsequent waste and deposition occurs. The way in which this deposited material bonds to the underlying layer is also crucial.
I’m curious whether the addition of a contrast agent in this experiment might have affected the results. If we can take variables like this into account, the insights gained from studies like this could be invaluable. Focusing on elements such as wall slip effects and the interaction between printing parameters and actual results could significantly improve our precision in 3D printing. I’m really looking forward to further research in this direction!
