Pla and heat resistance

[glipr]

Hi , Im designing a front splitter for my car, and I know that abs is probably the best alternative for it due to impact and heat resistance. But I have better results with pla , do you guys think that there is a way to protect a pla print from heat , like an epoxy layer or covering with carbon fiber . Any input will be appreciated. Ive attached part of a test print, I have to print in parts due to the size.

[Tim]

Polycarbonate such as the eSUN ePC will have the best heat and impact resistance. However, for any outdoor use, your main concern is likely to be UV resistance. I'm not sure what filaments are good at UV resistance---I would expect that nylon is high on the list---but I know that PLA is very poor and degrades rapidly under UV exposure.

I would tend to recommend PETg; it has good temperature resistance and good impact resistance, but I don't know much about its UV resistance. Maybe somebody else more knowledgeable about it can chime in.

[jimc]

well i will assume since its going on your car that it will be primed and painted. you wont want to leave it raw plastic no matter what you use. pla would be out of the question for this application. petg or esun epc would be the ticket here. abs will work also if you can print the parts without warping. epc will warp a little as well. petg will be similar to pla. there is no coating you can put on pla to make it withstand heat. pla is pla and it will get soft no matter what.

[ednisley]

impact and heat resistance

Park your car facing into the sun, let it sit for an hour, then measure the surface temperature along the front with an IR thermometer. I think you'll find it's pretty close to 100 °C, which means all the common plastics used in 3D printing will become surprisingly soft and bendy.

• PLA has a glass transition temperature around 60 °C. Somewhere around here, there's a picture of a very relaxed Mendel-style printer that spent a sunny afternoon in a car.
• ABS transitions around 100 °C, well below the temperature of parking-lot asphalt a few inches below a splitter, so it will have the consistency of limp rubber and probably flutter under aerodynamic pressure.
• PETG transitions around 90 °C: somewhat worse than ABS. The key advantage of PETG is lower shrinkage, so you can print parts with better dimensional stability.
• PC (polycarbonate) has a glass transition temperature around 150 °C, which should be just barely good enough for structural automotive use. The wizards around here can give you pointers on printing PC, but AFAICT if you dislike ABS, you'll hate PC.

As a simple test, set a fresh cup of coffee / tea on your sample part(s) and watch what happens.

The accumulation of knowledge in the "Filaments that Work" thread should be useful:
viewtopic.php?f=11&t=1951

[Tim]

PC (polycarbonate) has a glass transition temperature around 150 °C, which should be just barely good enough for structural automotive use. The wizards around here can give you pointers on printing PC, but AFAICT if you dislike ABS, you'll hate PC.

eSUN ePC warps considerably less than ABS, surprisingly enough, because most PC filaments warp like crazy. However, whatever eSUN put into their polycarbonate to make it warp less also makes the printing temperature lower than other PC filaments, and so I presume that it also has a lower glass transition temperature. But that's just a guess.

As a simple test, set a fresh cup of coffee / tea on your sample part(s) and watch what happens.

I performed this test by accident a long time ago, and it is probably the main reason I rarely print with PLA anymore. It is a very effective test.