A PLA part in a car

Will PLA melt in a car? ways to avoid it

PLA is probably the most common filament in the 3D printing world. It’s cheap, easy to print, quite resistant, and biodegradable. There are numerous PLA manufacturers with various PLA types and different characteristics in the world.

Yet, most PLA filaments have a common problem: the low glass transition temperature of 55 to 60° C. 

So this question comes to the minds of many users:

Will PLA melt in a car?

Most PLA filaments start to deform at 40-45o C. On a sunny day, depending on the outdoor temperature, A car cabin may heat up to 60o C. So in most cases, PLA prints will melt in a car.

However, you can increase the glass transition temperature by annealing the part. Also, there are specific PLA filaments that are designed to withstand higher temperatures.

Another threat to PLA prints in a car is UV light; it can cause it to color and make it more brittle.

Obviously, based on the PLA filament manufacturer and the car temperature, you can expect different results. 

Let’s get into details about what you can do to prevent your piece from melting under the sun and some alternative options.

What is annealing, and how it affects the glass transition temperature?

First of all, let’s discuss what annealing is and how it can help us.
Annealing is the heat treatment of an object; the process alters materials’ structure by heating and then cooling slowly.

This process was first used in metallurgy to increase the ductility of metals. Now the base concept of annealing has been adopted to use for plastics.

Annealing metal is similar to PLA annealing

The process of shaping a metal object often causes crystalline structures, named grains, to deform. The arrangement of these grains can be modified by the heating and cooling speed of the material. When they are heated, they will return to their natural shape, and by adjusting the cooling rate, the grain sizes can be altered.

Fast cooling can produce smaller grains, causing the material to become more rigid but brittle. On the other hand, when the metal is cooled slowly, it becomes softer and more ductile.

Even though annealing is similar for plastics, the final results are a little different. As you know, the standard FDM 3D printers first heat the filament and fuse it, and then the filament cools down at room temperature. This fast cooling process can add stress to the object, shrinkage in different points, and unstabilizing the plastic’s molecular structure.

Annealing 3D prints involve reheating the part to around its glass transition temperature, keeping it around that temperature for a while, and then slowly cooling it down.

This simple method doesn’t need anything more than an oven in your kitchen, making prints much more substantial and durable.

How to Anneal PLA prints?

First of all, you need an electric oven and a vessel or oven-safe container. Don’t use gas-fire ones, they cause your print to melt or warp due to uneven heating.

electric oven used in annealing

Heat your oven around 55 to 60° C and let it sit for an hour. One hour is a proper time for the oven to reach a stable temperature so that the print can heat up uniformly.

Oven thermistor usually has a 5% error; you can check the actual temperature with an accurate thermometer.

After one hour, put your PLA print on the container and place it in the oven. Now turn off the oven and leave the part until it cools down to ambient temperature.

This process also takes around one hour. Do not open the lid during this time. Once the oven returns to ambient temperature, you can remove the object.

Another option is to put your print into a sealed bag and put it in hot water. This process may cause warpage due to its uneven heating and cooling nature, so it is recommended to use the oven.

Annealing a 3D printed object can change its dimensions by about 3 to 5%. This change often occurs as shrinkage along the x and y-axis and a decent amount of elongation along the z-axis. However, it may differ according to the object’s shape. You can consider these dimension changes in your design and control the situation.

Annealing can affect every PLA filament from different manufacturers, improving their glass transition temperatures.

Other PLA options

  1. A few manufacturers make High-Temperature PLA(HTPLA), which can reach an excellent heat deflection of up to 88° C. These filaments are perfect for any print that can face moderately high temperatures. Having only white color is the only disadvantage of HTPLA, so you should paint it to get different colors. 
  2. Another option is the Tough PLA series from MatterHackers. They come in various colors and can withstand high temperatures up to 85o C. However, it would be best if you annealed them too.

How UV affects PLA and how to handle it

Another problem while using PLA in a car is the UV lights from the sun. It may become brittle after a while, but it will keep its shape and strength as long as it’s not under heavy loads of pressure. So you can still use PLA outdoor in the sun for aesthetic pieces.

Sun exposure can also cause the color of pigments in PLA to shift. The resulting color can vary based on the exposure time, base color, filament quality, etc.

Painting can protect the print from UV to some extent, though it won’t entirely solve the problem.

So if you want to use a 3D printed part in your car and outdoors, you have the option to use specific PLA filaments like HTPLA then anneal and paint them.

Another wise solution is to use other filament materials. for example, you can use ASA or PETG.

PLA alternatives for outdoor use

1.ASA

ASA has similar properties to ABS. However, it’s ten times more UV resistant than ABS. The high temperature, wear, UV, and impact resistance of ASA combined with its high glass transition temperature make it a perfect filament material for outdoor usage.

You can find the minimum requirements to print with ASA filaments in the below table:

ASA printer settings and hardware requirements
Extruder Temperature 240 – 260o C
Bed Temperature 90 – 110o C
Print Speed 50 – 90 mm/s
Cooling Fan Not Required
Build Surface Kapton tape, PET Sheets, Blue tape with glue

 

As you see, printing ASA is not so hard. You can do it with a desktop 3D printer that has a heated bed. However, trying new filaments may prove challenging and requires patience.

2.PETG

PETG is similar to PLA but has a higher glass transition temperature of up to 80o C. So in most cases, PETG doesn’t melt in a car. However, UV light can affect PETG, too, so you may consider painting it.

Printing PETG is easy, and a heated bed is not necessary. You can find recommended printer settings and requirements for it in the table below:

PETG printer settings and hardware requirements
Extruder Temperature 220 – 245o C
Bed Temperature 70 – 75o C
Print Speed 60 – 100 mm/s
Cooling Fan Not Required
Recommended Build Surface Blue Painter tape, Glass bed with hairspray

 

Conclusion

PLA is the most common filament in the 3D printing industry. However, it’s not the right filament choice for outdoor usage. PLA usually melts in a car or any high-temperature circumstances. However, you can make it more durable by annealing it. Some varieties of PLA are specifically designed to withstand high temperatures.

You can always use other filaments that are more suitable for outdoor use. It’s up to you to either enforce PLA or use an alternative.