As 3D printer hobbyists, we love PLA. It’s considerably strong, provides excellent surface quality, and most importantly, is freaking easy to use. However, PLA is probably not the jack of all trades. The low glass transition and the melting point of PLA are relatively low. This feature alone adds severe limits to this popular filament material.
Here, we will see different methods to protect PLA from heat and know more about its properties. Yet, if you’re short of time, In a nutshell:
There are three ways to protect PLA from heat
- Annealing the printed part
- Using PLA filament brands designed to withstand higher temperatures. For example, Tough PLA from MatterHackers
- Changing The design’s geometry so that it won’t easily deform
These three are the best way to protect your PLA printed part from the heat though there is more to know about details and how to do the job without ruining the print. So, let’s dive right into it!
What Is Annealing?
Annealing is the process of heating a material like plastic or metal and letting it slowly cool down so that its structure changes for the better. This way, the material becomes more pliant and less brittle. Note that the temperature’s value is vital because it directly affects the output’s physical properties.
The most common way of getting great results is to heat the plastic to a specific spot below the melting point and higher than its crystallization temperature. After reaching this point, the object should be maintained at this temperature for a while. The next step is to let it naturally cool down and get the ambient temperature.
Now, let’s get into “why do we do this?” The answer is related to the material’s internal structure. Once an object becomes deformed, independent of the substance, its crystalline or amorphous structure changes in specific ways, it’s better to know the metals’ annealing process to learn its mechanism.
When metal goes into a forming or casting process, some small crystalline structures named grains change their shapes. If the metal quickly cools down after casting, the grains become small and make the object hard and brittle. The hardness is a useful feature though the brittleness can cause cracks between the grains. These cracks start to grow and form a big visible gap along the junction lines of grains.
However, annealing metals is the opposite. The process starts with heating it below its melting point and letting it slowly cool down. This way, the grains have enough time to combine and create bigger grains than the original ones. As expected, the metal will have features opposite the previous scenario. It becomes softer and more malleable.
Even though annealing is more common for metals, a similar process exists for plastics. The technology behind annealing plastics isn’t new. This technology has been used for years in the production of injection-molded plastic products. Annealing can considerably increase the heat resistance of plastics. It also reduces residual stresses inside the plastic part, makes them more robust, and weakens the print warpage.
Annealing for 3D printed parts has the same mechanism. The extrusion process of the FDM 3D printer starts with melting the filament inside a hot end and sinking from its tip. After this, the melted filament’s temperature quickly changes near the ambient air. Hence, the hot filament soon cools down to room temperature. This way, it doesn’t have enough time to cool evenly, and internal stresses are induced in the printed object.
Annealing is one of the best ways to reduce internal stress and protect the print from heat.
How To Anneal And Protect PLA From Heat
As mentioned before, the overall process is similar to annealing metals. All you need is to heat PLA (or any other filament material) near its glass transition temperature but lower than its melting point. There are mainly two different methods to do this:
Annealing PLA In An Oven
First of all, it’s necessary to know the glass transition temperature of PLA is around 60o C (140o F), and it melts at 170o C (338o F). Hence, the basic concept here is to heat the print above 60o C that’s the glass transition temperature of PLA. On the other hand, it should be considerably below 170o C to avoid melting. You can find the step by step approach in how to do this using an oven is described in the following:
- The first step is to heat the oven to around 70 or 80o C and let it remain at this temperature for an hour. This way, the inside temperature reaches the desired temperature, passes its initial overshoot, and creates a uniform temperature profile. It’s also much better to use electric ovens because gas-powered ovens can melt the print by overheating its top surfaces.
- Once the oven reached the final temperature and one hour passed, it’s time to put the printed object into the oven. To do so, first turn off the stove, then place the item on an oven-safe surface and put it inside. You can also set the print in a vessel or similar containers to avoid excess heat. Note that oven thermostats usually have 3% to 10% errors, so it would be best to double-check the oven’s temperature using an accurate thermometer. No one wants to ruin a print.
- The only remaining work is to let the print slowly cool down in the oven without opening the oven’s door. This way, gradual cooling will restructure the plastic and relief its internal stresses. After it reached near ambient temperature, you can take the annealed printed object.
Annealing PLA In Hot Water
In this method, you can use hot water instead of an oven to provide 70o C for the print and let it slowly cool down. This solution doesn’t need anything special though it can’t provide a uniform temperature around the object. It may induce some warps in part. The following steps to use hot water are:
- Heat a container full of water to 80o it would be best to use a big one because bigger ones lose temperature much slower.
- Put the printed object in a plastic bag and submerge it into the hot water. Make it stay on the bottom and let it cool down to ambient temperature.
- Once the water is thoroughly cooled, you can take the print.
Important Notes About Annealing
Before annealing your prints, note that this process can shrink or expand the part in some directions. Based on the geometry, the PLA printed materials tend to shrink along the X and Y axis and expand along The Z-axis. The exact amount of expansion or contraction may vary between one to five percent. So it’s good to consider these changes insider your design.
Also, you can first create a sample and anneal it to see the exact results, then use the outputs to modify your final design.
Using Heat Resistant PLA
Some particular PLA brands provide filaments with high-temperature resistance.
- High-Temperature PLA(HTPLA) from Protopasta can reach an excellent heat deflection of up to 88° C. This filament is perfect for any print that can face moderately high temperatures. Having only white color is the only disadvantage of HTPLA, though you should paint it to get different colors.
- 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.
Using An Alternative
PLA is not the only filament option. Nowadays, even cheap desktop 3D printers do a perfect job of printing PETG or even ABS with some tweaks. So, here are some PLA alternatives for high-temperature environments.
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 ideal 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|
|Print Speed||50 – 90 mm/s|
|Bed Temperature||90 – 110o C|
|Cooling Fan||Not Required|
|Build Surface||PET Sheets, Blue tape with glue, Kapton tape|
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.
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||Glass bed with hairspray, Blue Painter tape|
There Will Always Be A Limit!
We have seen several ways to protect PLA from heat; however, the question is, “Can I expect PLA to work in every situation?”. Every material has its pros and cons so we should select a material based on ower projects.
In conclusion, PLA has many excellent properties that make it a material of choice. Yet, Some situations need something different.
Heat Is Not The Only Problem?
If you’re thinking about using PLA for outdoor use, you should know that heat isn’t the only problem. UV lights can also affect PLA filaments and drastically change their properties. Putting PLA under sunlight makes it more 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. You can see some examples in the video below.
Painting can protect the print from UV somewhat, though it won’t entirely solve the problem. So if you want to use a 3D printed part for outdoor purposes, you have the option to use specific PLA filaments like HTPLA then anneal and paint them.