December/January 2019

| TECHNOLOGIES | G enerally, large-diameter nozzles are used for fast printing while the smaller ones are better suited for high detail. But nozzles also vary depending on the specialist materials they are needed for. In this article, we’re going to set out the different nozzle choices; the diameters and when to use them, the different integrations in 3D printers and what types of nozzles to go for when printing specialist materials. But let’s start by defining what a nozzle is. What is a 3D print nozzle and how does it work? A nozzle is an integral part of a 3D printer’s hot end and the most common diameter found on most FFF 3D printers is 0.4mm. This generally offers a good balance in terms of detail and speed. The process starts as the filament is pulled from a reel by the extruder, a stepper motor that is synchronised with the three axes of movement, X, Y and Z. The filament is pushed toward the hot end either directly (Direct Drive) or via a flexible tube (Bowden System). The hot end is a complex component that heats and extrudes the filament from the printer onto the build platform. It is made up of three sections: heat bridge, heater block and nozzle. The filament travels through a www.smartmachinesandfactories.com December/January 2020 | 37 | path that precisely sized for the filament diameter to ensure an optimised surface finish. Before reaching the heat bridge, both filament and feed path are actively cooled to keep the polymer solid and maintain control. As it enters the heat bridge, the filament transitions from solid to liquid and is pushed through the heater block toward the nozzle. It is then pushed out of the nozzle, where it adheres to the build plate or previously-extruded material. How can nozzles affect detail and speed? A nozzle’s diameter, which normally ranges from 0.25mm to 0.8mm, dictates a print’s detail and maximum flow speed. A small diameter will print high-detail objects, but the print time will be slow. By contrast, a large- diameter hole will print quickly, but detail such as small features and sharp corners will be limited. Heads featuring two different size nozzles offer the best balance in terms of surface quality and speed, combining 0.3mm and 0.8mm- diameter nozzles in a single print. The flow of material, which is controlled by the extruder pushing or pulling the filament, can also affect speed as a result of ‘stringing’. This is a common issue, especially with larger-diameter nozzles, that is due to molten material dripping. Stringing can The nozzle: the unsung hero of 3D printing The basic concept of Fused Filament Fabrication (FFF) 3D printing is simple: three- dimensional shapes are built up layer-by-layer. In some ways, it’s much like using an icing bag to pipe a cake. There is, of course, far more to 3D printing, but, essentially, like icing, the detail, style and speed of a print are all at the mercy of the nozzle you choose. Chris Elsworthy, MD and Lead Mechanical Engineer, CEL-UK, reports.