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The nozzle: the unsung hero of 3D printing

31 March, 2020

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.

Generally, 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 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 cause a print to fail, which translates into downtime, but, luckily, it can be prevented.

Technologies such as Needle Valves, for example, seal against the inside surface of each nozzle to block off the flow of filament when required, eliminating the issue of stringing and greatly reducing feed problems. This technology also improves overall print speed in dual material prints, with material changes taking just 0.4 seconds.

How are nozzles integrated or changed?

Depending on the manufacturer of your 3D printer, there are different options in terms of how the nozzle is replaced. Modern 3D printers use a swappable print head system meaning that the nozzle is an integral part of the print head so, to change nozzle type and diameter, the entire head needs changing.

The main benefit here is that all components within the head are calibrated and standardised. The electronics will also automatically update the printer and software ensuring the best settings are always used for that specific head, reducing setup time to a minimum.

Several other manufacturers use interchangeable heads or cartridges. These also automatically feed the hot end and nozzle diameters back to the printer and software, ensuring the best settings and print quality. These systems are plug and play and can be very easy to use but do come at a price premium.

The other option on many 3D printers is to manually swap the nozzles from the heater block. Your printer's manual will show if this is possible, but, typically, great care must be taken including heating and gripping the delicate and very hot parts to avoid breakages. Once you've screwed in the new diameter nozzle, you then need to update the settings within the printer software. This process involves highlighting the new nozzle diameter and adjusting a host of settings while running tests to reduce stringing and blobbing with the new configuration.

What nozzle should I select for each filament type?

We’ve seen how the nozzle diameter dictates the surface finish or detail and speed, but there's more to consider. Most materials will print through a standard brass or copper nozzle, but there are specialist options also available for different materials.

Brass is the most common material as it is very thermally conductive. This means it transfers heat efficiently from the heater block to the nozzle to ensure a smooth flow of molten filament. The downside is that brass is a very soft metal, so a few too many knocks into the build platform or use of abrasive materials and the nozzle will start to wear affecting the quality of your prints.

Copper is another popular choice. These nozzles are often Nickel plated and can sustain higher temperatures than the brass equivalent. They also have the benefit that the Nickle plating helps prevent materials such as PEEK and PEI from sticking.

Stainless steel is a less common option, but it's hardwearing, meaning it’s far less likely to become damaged. Another benefit of stainless steel is that materials are far less likely to stick, so less maintenance is required.

The next level up is hardened steel, which is abrasion resistant, which makes it ideal for abrasive filaments such as carbon and metal fill. Hardened steel is generally regarded as an excellent all-round nozzle and, although more expensive than brass and copper, it will outlast the others.

The next level up is the Olsson Ruby; this nozzle is made from brass except for the tip which features a small ruby with the hole through it. These heads are completely abrasion resistant and are ideal if you print with plenty of carbon fill but do come with a hefty price tag.

Choosing the right nozzle

There's plenty of choice out there when it comes to nozzles; ultimately, your decision should be based on what material you're using and then the level of detail required and the time available to create the print.

For example, let’s say you've designed a camera dolly and need to print an enclosure for some electronics. ColorFabb nGen or TitanX ABS are both suitable materials, but you haven't finalised the design yet, so you just want a print to check proof of concept. Selecting a sizeable 0.8mm nozzle for a fast print speed is ideal for checking the concept works. Once you've checked the design, you can then print with at a higher detail using a smaller 0.3mm-diameter nozzle.

If you need to print parts that require the strength or rigidity of a composite material, such as a camera mount, then, once again, select the material and then the appropriate head. PETG CarbonFill is a good option with the SingleX head for Robox printers or an Olsson Ruby nozzle for other printers.

By matching material, nozzle type and diameter to what you're printing, you can achieve the best balance of detail and surface finish or speed. Correctly matching all elements is relatively easy and will make a significant difference to the quality of your prints and the longevity of your 3D printer.

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