ABS or PLA for structural printed parts?

Question

TL;DR

Is ABS a better material to use for structural parts of a 3D printer, as opposed to PLA?

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I have been looking at various suppliers of printed parts for a Wilson II, on eBay.

One supplier supplies all of the parts printed in ABS, whereas another supplier provides the structural parts, which form part of the frame, in PLA, and the remaining (non-structural) parts in ABS. The second supplier states the following:

This kit is printed in two materials, the structural parts are printed on high-quality PLA to provide the necessary rigidity, and the others in premium ABS.

MJRice, who developed the printer, also supplies the printed parts, which are made of PLA.

Is PLA really a better choice for structural components? A quick google lead me to ABS or PLA: Which 3D printing filament should you use?

ABS is going to give your projects better structural integrity and will be more suited to mechanical use given the material can better withstand the elements, but it will also require specific types of printers and printing surfaces. On the flip side, PLA will give you more precise prints and better aesthetic quality, as well as more flexibility with printing conditions if you can do without the strength and resilience of ABS.

Another link, What's stronger? PLA or ABS?, also implies that ABS is stronger than PLA:

The strongest ABS is stronger than the strongest PLA

and

ABS is much less brittle than PLA

although warpage could be an issue...

I choose ABS for it's strength over PLA. I would love to avoid the warpage/shrinkage problems of ABS.

Heat seems to affect PLA more than ABS (obviously, due to the lower melting point),

FWIW, I know a guy who had a reprap using PLA-printed parts. He was taking his machine around to do demos and he left it in the car mid-day once. It melted the parts enough that prints were coming out very poorly even after his best effort at recalibrating the machine.

and as I am in Thailand, my room gets up to 50°C some days (it is unbearable), I wonder if that would be cause for concern?

So, from the above nuggets of information, wouldn't ABS be a better choice? I am surely missing something, as both the second supplier, and MJRice, use PLA.

Answer 1

To answer the main question "Is ABS better for structural parts of a 3D printer as opposed to PLA".

The answer, unfortunately is it depends.

ABS has lower yield and ultimate strengths compared to PLA. This means that at room temperatures, ABS is weaker than PLA. However the difference between yield and ultimate for ABS is much larger than PLA, meaning that ABS parts will deform, noticeably so before breaking. This can be a good thing. If your ABS part is highly loaded, you may want to be able to inspect it for overloading. The plastic deformation that occurs in ABS may be sufficient for you to identify, and modify your parts before a catastrophic failure. With PLA though since the two strengths are quite close, your part would more than likely fail completely without any warning or deformation before it. So in terms of strength, it's a design consideration. Would you rather have a slightly weaker part that shows signs of load failure, or is a catastrophic failure acceptable. There are use cases where either may be better.

As Ecnerwal pointed out, PLA has a lower Tg (glass transition temperature) compared to ABS. If your printed parts are going on a 3D printer and aren't sufficiently isolated from the hot parts (print bed or extruder) then you may end up having some localized deformation. That being said, the extruder is generally pretty localized and likely won't cause you too many issues assuming you're using any of the already available 3D printer designs out there, same for the print bed. However by the sounds of it your 'room' temperature is a fair bit higher than here in North America, by a factor of almost 2! This could cause you some issues if you're printing parts in the high heat with PLA. Your best option would be ABS, but even with it's higher Tg (roughly 90C if I remember correctly) you may still run into issues.

The warping and shrinkage issues mentioned in the question seem to be more about parts being built by a 3D printer. Once the parts are built warpage and shrinkage are essentially a non-issue unless you've heated parts back to within their melting temperatures.

Depending on where you're getting your plastic parts, there may be a third option. By the sounds of it you're looking at building your own printer. You may be able to get the STL files of the printed parts you need and then have someone print them for you in a stronger material such as Nylon.

Assuming alternative materials aren't an option I would personally suggest going with ABS for your use case. My reasoning is purely due to the potential operating temperatures. While 50C is below the Tg for PLA it's getting very close.

Answer 2

To answer your question, ABS is better than PLA for parts however I wouldn't use ABS for that, I would use PETG for structural parts.

PETG is more durable than ABS or PLA. PETG is more flexible than PLA and it not brittle like ABS. What makes PETG so good is the G! G stands for Glycol, this is added to prevent the material from crystallizing when over heated. While some companies say it is "Food Grade" you really need to be careful as note every factory produce it the same.

When I started printing I only used ABS, I thought it was better because it was stronger than PLA, so I just put up with the smell of ABS.

It wasn't until I bought my second printer that I found out about PETG. They guy that makes my printer used to work in the plastics industry, so he gave me some info on the filaments on the market.

Now I use PLA and PETG. PLA for testing and playing with different models and PETG for anything I want to last or will be used in hot environments (like in the car).

Printing with PETG is very easy, a lot easier than ABS. It sticks to the bed very well (I still use Glue stick though) and no smell. Temp depends on your printer. I use an ExtraBot, I run the Extruder at 220°C and the glass bed at 80°C

There are a lot of write ups on PETG, many different settings/temps they recommend. Honestly, watch while you print. Start off at 220°C and if you see bubbles, drop the temp in increments, if you see it not sticking to the bed or the nozzle is clogging up, increase the temp.

Answer 3

50°C is hot for you. PLA's glass transition temperature is 65°C. A car in the mid-day sun can get very hot indeed.

As to the question of "stronger" - if the part is designed to be strong enough for its use in PLA, it will be no better in "stronger" ABS. If the PLA part will be "more precise" and "less warped" - that may well make it better for its use. Other than a widespread community dedication to self-replication, (or mostly self-replicating with some metal parts) there's plenty of arguments for making most printer parts out of machined metal, for that matter - much stronger than ABS or PLA.

Brittleness likewise might matter if you were planning to drop the printer; but should not matter in use if the part is designed for the forces it will see in the material it's designed for. Looking at older technology, many machine tools are made of cast iron, which is quite brittle, rather than steel, which can be less brittle depending on how it's processed. If the part is designed for the job and used/handled in a reasonable way, "brittle" is not an inherently bad thing, and a thin steel part that flexes is a worse thing than a thick cast iron part that flexes less.

As for

withstand the elements

that appears to be a reference to outdoor use where PLA will break down - but if you are not leaving your printer out in the rain (which will be bad for many other parts unless you do a lot of engineering to protect them) that should be of little concern.

Answer 4

Actually, Both PLA and ABS could use for structural parts. PLA has high strength and is brittleness. ABS has better thermal resistance and durable. PLA and ABS are the main types of 3D printing material, each has cons and pros.

If you want to choose which type, you need to know the detailed application.