Can you put PLA parts in your car (in the sun)?

Question

I'm in the process of building my own head unit / stereo prototype for a car, which will have a 3D-printed enclosure.

My concern is that cars can get quite hot in the sun, and even more so if you live in hot climates. Some estimations put the interior of cars getting up to 50-60 °C, sometimes even in only 20 °C weather due to the 'greenhouse' effect created in the car. I live in a fairly temperate climate, but the summers can still get up to 20-29 °C (80-85 °F), and my car might get up to 60 °C/150 °F on a hot day.

The part won't be exposed directly to the sun, but will obviously be exposed to heat both from the interior of the car when in the sun, and potentially from the engine radiating heat through the firewall, though the latter factor will differ from car to car.

Should I be concerned using PLA for my part? If not, what material, if any, would be better suited for these possible temperatures (other than metal)?

Answer 1

No, PLA cannot be used in cars standing in the sun. Temperatures can locally get over 50 °C (122 °F).

I have printed sun visor hinge pins from PLA for a car (not exposed to direct sunlight either), but after one day in the sun (it usually doesn't get over 29 °C or about 85 ˚F here too) the pin deformed (only printed it for form fitting). The actual pin was eventually printed in PETG, and even with PETG the part deformed a little when it got really hot in the car.

Your part might not get that hot as it is lower in the car, but you could best print parts in Nylon (Polyamide, PA), ABS or any other high temperature resistant Co-Polymer (e.g. made from Amphora HT5300), there are lots to choose from nowadays.

If it is a non load bearing component that is not stressed (e.g. a cover or a bushing) it could be printed in PLA, but I would not take a change and would print it directly in a more temperature resistant material.

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Downloading some of the technical data sheets from various filaments will give you for PLA:

Not suitable for long term outdoor usage or applications where the printed part is exposed to temperatures higher than 50 °C (122 °F).

similar for Nylon:

Not suitable for applications where the printed part is exposed to temperatures higher than 80 °C (176 °F).

To complete the overview, generally, materials should not be exposed prolonged periods of time above (give or take):

• 70 °C (158 °F) for basic Co-Polymers
• 85 °C (185 °F) for ABS
• 100 °C (212 °F) for enhanced Co-Polymers and ASA
• 105 °C (221 °F) for Polypropylene (PP)
• 110 °C (230 °F) for Polycarbonate (PC)

Answer 2

If you put PLA parts in a sealed plastic bag (or two to keep it dry) and simmer in water (212 °F or 100 °C), the part "anneals". The time taken varies with the part shape, but for small parts should be about 15-30 minutes. You can simmer longer if unsure, but it provides no additional benefit once the part is annealed. When you remove and cool the annealed part, it will feel harder and more compact. You may also notice a slight hazing or color change.

Annealed parts become a bit more resistant to heat warp. The annealing process shrinks and hardens your part (I've annealed gears) so you need to account for the shrinkage by making the unannealed part slightly larger. I do this for stepper mounts or gears as needed. Putting your part in the passenger compartment of a car can work depending on your climate. My daughter-in-law has a camera mount on her dashboard showing significant warp, but she still uses it.

Here's more information and I'm sure you can find more...

Answer 3

The sun will rot most, if not all plastics, with PLA, ABS and PETG rotting to varying degrees and at differing rates. So, if even part of your enclosure, such as the edges, are visible, they will invariably be exposed to the sun at some point (although maybe not sufficiently enough) which will make them brittle.

However, as you say, your main concern here is not direct sunlight, but heat. As this informative article, Using PLA for Long-Term Outdoor Applications, suggests:

PLA is great as the warping is less than with ABS.

Interestingly, it also notes (again related to sunlight, not a concern in your case):

As a side note, PLA is referenced as considerably UV resistant.

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Similar Questions

Whilst your question is not a duplicate, as such, there are already a number of questions (and answers) on this topic, that I remember having seen and being relevant.

Whilst I have quoted some of the relevant parts below, it might also be worth taking a look at the other posts on these links:

• PLA use outdoors?

Keep in mind that PLA has a much lower temperature point, where is starts getting flexible. I once had PLA-printed parts in my car in the summer for 3 hours and when I came back, they where bent.

I don't know about the weather conditions in your local environment, but if you experience hot temperatures and your sign is hanging in direct sunlight, I would suggest to make sure you secure the letters against bending (e.g. cover them with a coat of epoxy or something like this).

• PLA continuous operative temperature

The property you're looking for in the thermoplastic (which will determine the continuous operating temperature) is glass transition temperature. This is the point at which the plastic begins to flow, and becomes deformable as EvilTeach described. PLA reaches this state at around 60 °C, whereas ABS is around 105°C, just suiting your specifications. To go a bit further, polycarbonate offers a glass transition temperature of around 150 °C, and Ultem at 217 °C.

• ABS or PLA for structural printed parts?

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.

... 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.

• 3d printing for outdoor use: what types of filament are most weather resistant?

PLA also will slowly melt in direct sunlight. I have seen this one firsthand, having left a print on my windowsill and watching it slowly morph with the weight of objects on top of it.

Also related, temperature wise, although not strictly in-car related (although that is where you would most likely find a travel mug), is the most informative answer by Ryan Carlyle, which makes mention of annealing as suggested by OyaMist Aeroponics's answer:

• Travel Mug Woes

It is possible to anneal PLA to survive higher temperatures, as this increases the crystallinity of the polymer and thus makes it more heat-stable. However, that is highly experimental and results will vary considerably with filament provider, color/pigment, and annealing process used.

• Which is more durable to sunlight/weather - PLA, ABS or PETG

PLA would be a non-starter for outdoor use as it's biodegradable and can breakdown in sunlight. Albeit slowly, but won't be useful for long term project.

Answer 4

Just minutes ago, I took a PLA part from my car that is parked in the sun, it is warped and bloated. It was wrapped in a towel, not in direct sunlight. The temperature in the car was near 60°C. I would not recommend using PLA on parts that may be left in a vehicle.

Answer 5

Just for completeness sake, one can print a casting mould and then cast UV resilient resins from the mould.

The mould would be made of PLA. Because it is quite brittle, you would need to make a multi-part mould if you want it to be re-usable. Otherwise, if you are using something heat-resistant then you can melt or break the mould once you are done.