What filament to use for outdoor high humidity, temperature, and payload?

Question

I wanted to build a 4-wheel ground robot vehicle with a payload of 25 kg for outdoor use, but I wanted to make the frame/chassis using a 3D printer. The outside temperature ranges between 30 °C-35 °C and the humidity is 70-90%. I think the vehicle would be outside for 4 hours at a time. The dimensions of the vehicle would be about 1.0 m x 0.8 m x 0.8 m (LxWxH). From other stack exchange questions and some reading online, my choices have come down to ASA, PC, and Nylon. It's important that the printed part doesn't deform outside. I think I'm leaning towards Nylon for tensile strength, toughness, and heat deflection, but I don't know how the Nylon printed part will hold in high humidity.

Has anyone had experience with Nylon in the outdoor conditions I mentioned? Was it difficult to print a large surface area Nylon part (I'm thinking of printing with the filament directly coming out of an active dryer)? Which bed surface were you using? Would you recommend any other filaments?

Answer 1

The application doesn't look to be demanding at all from a material point of view. Operation below 40 °C and 70-90% RH is not that special.

Once taken out PLA for creep, most rigid filaments would work. Nylon deform under constant stress, so screws may get loose over time.

PETG, ABS, ABS+ (TitanX/niceABS are about as easy to print as PLA), ASA, ...

For ease of print, PETG or ABS+ should be fine, but ABS will deform more before breaking, while PETG tends to shatter when it breaks.

Answer 2

My first choice for this would be PET. Not PETG, which is a mess of blobbing, stringing, warping, creep under load, etc., but real PET, also known as BPET (bottle PET) or HTPET (high temperature PET, because it needs high temperatures to print and has high HDT)

Unlike ASA, PC, and nylon, PET is easy to print. It does not need a heated chamber or even a heated bed (although it does a little better with the bed a little above room temperature, at 30-45°C) and you don't have to fight with warping or compensate for significant part shrinkage.

The HTPET I use is rated for high HDT, 87°C as-is, and 100°C annealed. You can probably arrange for it to self-anneal during the printing process with the right settings; I'm planning to experiment with this at some point. To give you an idea how readily it anneals, the smokestack of a Benchy tends to anneal while printing it just from the accumulation of heat in a small area.

It needs high print temperatures. 275°C is about the minimum. The manufacturer of the HTPET I used recommends 285°C for high speed, but I've found flow increases all the way up to around 320°C if you want to go faster.

It is somewhat hard to find PET filament, despite it being fairly easy to make your own from recycling bottles. I would not really recommend that for your project because it's hard to get perfect flow to simultaneously ensure precision and part strength. There are at least a few manufacturers selling it in the US and probably elsewhere though.