How to Make 3D Prints More Heat-Resistant (PLA) – Annealing

It’s actually possible to increase the heat resistance of your 3D prints using a technique called annealing. It does have a process that can be quite tricky, but when it’s done right, it can provide good results. This article will answer how to make 3D prints more heat-resistant.

To make 3D prints more heat-resistant, you can put them through a heating process called annealing. This is where you apply a constant level of heat to a model using an oven or boiling water for a period of time, then let it cool down. This process changes the internal structure of the model to improve heat-resistance.

Keep on reading for more information about making 3D prints more heat-resistant.

How to Make PLA More Heat-Resistant – Annealing

Annealing is a process where you apply heat to a material to improve its heat resistance and durability. PLA prints can be annealed by placing them in a heat source at temperatures between 60-110°C

The PLA goes through a process called crystallization. The crystallization temperature refers to the temperature at which the structure of the material begins to become crystalline.

There are various means to anneal a PLA-based model. They include the following:

  • Baking in an Oven
  • Placing in Hot Water
  • Bake on 3D Printer Heated Bed

Baking in an Oven

Some people use toaster ovens, or electric ovens which is usually better than a gas oven because they have better uniform heat dissipation around your 3D models.

It’s also important to use a thermometer to ensure that the temperature of your oven actually matches what temperature you set.

You can make use of the following steps to ensure to anneal your PLA model:

  • Heat your electric oven to about 110°C.
  • Place your prints in the oven for about an hour.
  • Allow the model to sit in the oven for about an hour then switch it off.
  • Leave the model to cool in the oven gradually

This process of gradual cooling is what helps restructure the properties of the model and help relieve internal stresses built up during heating.

Here’s a detailed video showcasing how to heat your model in an oven.

One user who baked their PLA in an oven at 120°C, then a second at 90°C said they both warped really badly.

Another user said it’s better to use something like a cheap convection toaster oven hooked up to a PID temperature controller.

This would prevent a lot of warping by using forced convection for the heat, then setting your model on an insulating material, while protecting the oven’s heating elements to prevent thermal radiation from affecting your part.

People do wonder whether it’s safe to anneal PLA in the same oven you cook with, and there isn’t too much information on this. Some users say it’s better to be on the safe side since plastics can give off toxins before it gets too hot.

You wouldn’t want the residuals of these gases on the inside of the oven you cook food with. It’s a better idea to get a dedicated toaster oven or something similar to anneal your PLA with if you choose this method.

Some users say they anneal in the oven but they have the model in tightly wrapped foil to reduce exposure risk.

Placing in Hot Water

You can also anneal your PLA model in hot water by doing the following steps:

  • Heat water in a relatively big bowl to boiling point
  • Place the printed model into a plastic bag and put it into the hot water.
  • Leave for 2-5 minutes
  • Remove the model from the hot water and place it in a bowl of cold water
  • Dry off with desiccant or paper towels

People have different methods of annealing with boiling water, but this method seems to work pretty well.

Here’s a video to highlight this process and show a comparison of baking vs boiling PLA parts.

Some people recommended that you can use glycerol instead of water since it works even better due to being hygroscopic so it doesn’t need to dry.

In the video above, he compared annealing through baking with boiling and found that boiling it keeps the part more dimensionally accurate. Another cool thing is that it’s easier to anneal irregularly shaped parts through boiling rather than with an oven.

One user successfully annealed some motor mounts for RC airplanes in boiling water, but they did shrink a little bit. There were screw holes in that part but they were still usable by force-fitting them.

Bake on 3D Printer Heated Bed

In a similar way to annealing your 3D prints in an oven, some people recommend even doing it on your 3D printer’s heated bed. You simply heat the temperature up to around 80-110°C, place a cardboard box over the model and let it bake for around 30-60 minutes.

One user even implemented G-Code to improve the process by starting at an 80°C heated bed, letting it bake for 30 minutes, then letting it gradually cool down and bake for shorter times.

Here’s the G-Code they used:

M84 ;steppers off
M117 Warming up
M190 R80
M0 S1800 Bake @ 80C 30min
M117 Cooling 80 -> 75
M190 R75
M0 S600 Bake @ 75C 10min
M117 Cooling 75 -> 70
M190 R70
M0 S600 Bake @ 70C 10min
M117 Cooling 70 -> 65
M190 R65
M0 S300 Bake @ 65C 5min
M117 Cooling 65 -> 60
M190 R60
M0 S300 Bake @ 60C 5min
M117 Cooling 60 -> 55
M190 R55
M0 S300 Bake @ 55C 5min
M140 S0 ; Bed off
M117 Done

Best PLA Annealing Temperature (Oven)

The best temperatures to successfully anneal PLA models in an oven falls between 60-170°C, with a good value usually being around 90-120°C. This is above the glass transition temperature and below the melting temperature of PLA.

The structure of PLA materials is said to be amorphous, meaning the molecular structure of the material is disorganized. To make the material somewhat organized (crystalline) you would need to heat it above the glass transition temperature.

If you heat the material very close to the melting temperature or above, the structure of the material collapses and even after cooling, cannot return to its original structure.

Therefore, you shouldn’t stray too far from the glass transition temperature for optimal annealing.

The best temperatures for annealing PLA do vary based on how your PLA was manufactured and what types of fillers it has. One user said you usually only need to hit temperatures of around 85-90°C, while cheaper PLAs might need higher temperatures for longer.

A good PLA+ filament should only need a few minutes at 90°C to crystallize. He said he has even done it using the heated bed on his 3D printer by putting a box over the part to retain the heat.

How to Anneal PLA Without Warping

To anneal PLA without warping, many users suggest tightly packing your model in a bowl of sand before putting it in the oven to bake. You should also let the model cool down while in the sand. You can also use the boiling method with the model in a plastic bag and quenching it in cool water afterwards.

You should make sure there is sand at the bottom of the model as well, at around 2 inches if possible.

Here’s a great video by MatterHackers showing you how to do this process. You can also use salt instead of sand since it easily dissolves in water and is more accessible.

One user who did this method said it worked great for annealing his PLA without warping, even at a temperature of 100°C. He set the oven to run for an hour and let the print sit there to cool down and it came out great.

Another user who annealed PLA at 80°C said he could heat objects to around 73°C without them getting flexible. The PLA models didn’t change texture and had similar strength between layers.

One person described their experience of using fine salt instead of sand put a layer of it in his Pyrex dish, set his 3D print in, along with a Bluetooth thermometer and added more salt until the dish was full.

He then put it in the oven at 170°F (76°C) and waited until the thermometer hit 160°F (71°C), then turned the oven off and let it cool overnight with the part still packed in the salt.

The results of doing this eliminated his delamination (layer splitting) issues, along with almost no warping and a uniform shrinkage rate across the X, Y & Z axis of just 0.5%.

What is the Heat Resistance of PETG?

PETG has a heat resistance of about 70°C, unlike PLA which has a heat resistance of 60°C. These temperatures are known as their glass transition temperature. ABS and ASA have a heat resistance of around 95°C.

Here’s a video showing a heat resistance test of PETG amidst other filament types.

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