Practical 3D Printing: Filament Drying

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Filament Drying

08.35

00:00	In the previous module we covered a lengthy list of different thermoplastic materials used for FDM 3D printing but we're yet to discuss one important property that's common to a lot of materials that we're interested in.
00:12	Most filaments are naturally hydroscopic and if you haven't heard this term before you're probably not alone.
00:19	Hydroscopic means that materials absorb and hold moisture from their surroundings and this is something we want to avoid as much as possible.
00:27	The rate at which each material absorbs moisture is different but generally about 24 hours can be troublesome and 48 hours can be enough to completely ruin a print.
00:38	There's a few reasons for this.
00:40	One is that more moisture content causes the filament to swell, keeping in mind that 3D printers work on such tight tolerances and small layer heights.
00:49	It also means that when a filament flows through the nozzle the water content will boil causing bubbles in the printed material.
00:57	This not only leads to inaccuracies and imperfections in the print quality but can also jam the extruder, damage the filament or in bad cases permanently damage the printer.
01:08	Some other issues can also appear that look like what you'd see with excessive temperature settings with bubbles or blobs in the layers or stringing.
01:17	We can also see poor bed adhesion as well.
01:20	We need to be able to discern if moisture is actually the root cause of the issue before we go and adjust the temperature.
01:27	Additionally, and without diving too deep into the chemistry here, when the material is melted during printing something called hydrolysis occurs where the water makes its way into the polymer molecule breaking up the bonds and shortening the chains.
01:41	Chains are inherent to the polymer's properties.
01:44	So, this changes the properties of the filament and generally makes the finished parts soft, brittle and fragile.
01:50	Past this there are some other signs that our filament has absorbed too much moisture.
01:55	For example, unprinted filament is no longer smooth, or bubbles in the printed filament accompanied by popping sounds as these bubbles flow through the nozzle.
02:05	Another telltale sign is when the material continues to ooze out the nozzle after the extruder has stopped moving.
02:12	All of this sounds pretty bad and clearly something that we want to avoid.
02:16	So, how do we control and prevent it? Firstly, it should be mentioned that this is why filament is supplied in a sealed bag accompanied by dessicant.
02:25	The dessicant usually bends the filament and creates a stringing effect.
02:27	The A silica gel, like you'd sometimes find in packaged food, is also hydroscopic, but to a greater extent than the filament.
02:34	So, the idea here is that the desiccant will be sacrificial and absorb any moisture before the filament.
02:41	Clearly though, once we've opened the packaging to use the filament, this is of little use and it will start to absorb moisture.
02:48	On printers with enclosed filament material storage and feeding systems, like Bamboo Labs AMS for example, we can place desiccant bags in with the filament to help reduce the moisture.
02:59	In this case the Bamboo Lab machines are also able to measure the humidity in the AMS, warning us when there's too much moisture.
03:06	The desiccant bags need to be replaced periodically because as they take in moisture they become less effective.
03:13	Most printers will have the filament roll out in the open though, and while we can do our best to store the filaments in low humidity, the reality is that moisture absorption is inevitable.
03:24	Luckily though, all is not lost, and this is reversible through a process referred to as drying, and there's a few options here, so let's start with the most straight forward.
03:33	This would be to use a dedicated filament dryer, which is a special machine that's been developed specifically for this job.
03:40	These make it as simple as loading your spool of filament, setting your desired settings, and letting the dryer do the work.
03:47	The settings include the temperature and duration of the drying process.
03:51	Every material has different requirements here, which we'll get into in a moment.
03:56	The dryer heats the material usually to between 40 and 80 degrees celsius, or 100 to 180 degrees fahrenheit for around 4 to 8 hours.
04:05	Generally, though, the longer the better.
04:07	This is right under what's referred to as the glass transition temperature, which is still far under the melting point.
04:14	The heat resistance of the material is governed by this glass transition temperature.
04:19	This is important because we don't want to exceed it, and for this reason, it's best to wait till the dryer temperature has stabilized before loading the filament, as they'll often overshoot the target initially before settling back on it.
04:32	If you want to be extra careful, it can be worth having a thermometer to check the temperature, because it's still very possible for the surface of the filament to melt just enough that the spool will stick together, at which point it becomes useless.
04:46	However, done correctly, the heat will evaporate the moisture from the contents of the dryer, including the filament.
04:52	After drying is complete, the spool can be removed and fed into the printer, although some dedicated dryers will also have the capability to feed the filament into the printer while also drying it.
05:04	An alternative is of course the use of an oven, and in some cases this can work well.
05:09	Generally, though, ovens are designed to achieve much higher temperatures, and the temperature usually fluctuates significantly, running the risk of damaging the material or simply not drying it enough.
05:22	Food dehydrators, which are designed to operate at lower temperatures than conventional ovens, and tend to have better temperature stability in this lower range.
05:31	Just be sure to check that the dehydrator is capable of achieving that required temperature before purchasing, as this is a common drawback.
05:39	They're also usually considerably cheaper than dedicated filament dryers, and usually large enough to dry multiple spools at once.
05:47	The downside is that they're typically not plug and play, and require some basic modifications, such as removing the internal food trays first.
05:55	With more modifications, they can also be made to allow the filament to be fed directly into the printer.
06:01	The final alternative to mention is using the printer itself.
06:05	Some printers, particularly those with heated chambers, have a filament drying function, where they're able to heat the bed and the enclosure with the spool sitting in the print bed, which can achieve the same results.
06:17	Naturally, the downside here is that we can't print at the same time, and we're putting extra wear our printer for a job that could be done with cheaper equipment.
06:26	Again, post-drying, while the filament is not in use, it's ideally stored in sealed containers with desiccant, because even though it can be dried again, it's still best to minimise the moisture content in the first place.
06:38	Before wrapping up, let's discuss the requirement for drying different filaments.
06:43	The most important thing here is that we should follow each supplier's instructions, as even the same material from two different manufacturers could be significantly different.
06:52	The other thing to note is that some materials' drying recommendations can be stated as optional, due to the fact that they're less hydroscopic and or sensitive to the effects of moisture.
07:03	PLA is a prime example of this.
07:06	On the other hand, some materials should always be dried prior to printing, as they take on moisture very quickly and the effects of moisture can be detrimental to printing.
07:16	TPU or Nylon 6 Carbon Fibre being good examples of this.
07:20	Finally, it should be noted that some, like ABS for example, will give off unpleasant smells and fumes, so if you're using an oven or something that you also use to prepare food, then be sure to allow for enough time for ventilation after drying.
07:36	With that, let's summarise the main points from this module before moving on.
07:40	The thermoplastic filaments we use in FDM 3D printing are hydroscopic, meaning they absorb moisture from their environment.
07:48	This moisture is detrimental to the printing process, as well as the quality and mechanical properties of the finished part.
07:55	Ideally, we should avoid any moisture in the first place by storing our filament in sealed containers with desiccant, however some amount of moisture is inevitable, in which case we'll need to turn to drying the filament.
08:07	This can be done with dedicated dryers, conventional ovens, food dehydrators or even the printers themselves.
08:14	The main thing is to maintain consistent temperature for a certain amount of time.
08:19	It needs to be hot enough to evaporate, and this is a good thing, as it will evaporate the moisture out of the material, but not too hot to damage the spools.
08:25	Every material from every supplier will have different requirements, so be sure to always follow their instructions.