How to make your 3D prints stronger?
FDM style printers can produce some very strong and rugged prints for a wide range of applications, however if your prints are subjected to stress or weathering for long periods of time, then it is not uncommon for your filament to denature causing de-lamination and in turn weaken and cause failure of that vital functional print.
For example, last winter a friend of mine made a replacement hinge for his garden gate as a way to save some money, the part looked the business and it seemed that it would last for many years to come.
Fast forward three months of rain and cold snaps, the combination of water and repeat freezing caused his hinge to fracture and his gate is now hanging off!
Its worth pointing out that you could purchase carbon fibre blended filament that is incredibly strong but comes at a price as some retailers are selling carbon fibre blend at around £8.95 just for 10 meters of filament. If you are going to do that then whats stopping you from buying a new gate hinge right?
So how can I make my print stronger without having to buy expensive specialist filament?
Annealing is process used in metallurgy to heat-treat metal to give it stronger properties, the same principles apply to 3D printing. By heating and slow cooling your prints will eliminate internal stresses and gives your prints improved properties.
Plastics are known as poor conductors of heat, when extruded out of your printer the plastic will cool unevenly. This uneven cooling creates stress points within the structure of your print, by heating you print to the point past glass transition temperature but keeping it below its melting temperature allows the plastic to uniformly soften, this slow cooling will reduce the stress points.
We can recreate this process by heating your oven at home, once your oven has reached the desired temperature we can turn it off and place your prints on a suitable baking tray in the centre of the oven and close the door. leave the oven for an hour to cool but don’t open the door again until the oven is cold.
Each time you repeat this process it will further reduce stress points creating a less brittle and stronger model, but don’t over do it more than three times as your print may lose its shape or some fine detail.
What temperature should I set my oven?
We need to achieve a temperature sweet spot, you may find that you have to experiment a little for different however for our experiment we are going to use Rigid.ink Black PLA.
A simple google search tells me the following.
PLA – Polylactic acid
Glass transition temperature 60-65C
melting temperature 173-178C
Annealing temperature 110C approx.
ABS – Acrylonitrile Butadiene Styrene
Glass transition temperature 105-108C
melting temperature 215-240C
Annealing temperature 100C approx
You want to set the annealing temperature of your oven and leave it for 30-45 minutes to ensure the heat in the oven is evenly distributed, once you have done this place your print on to a baking tray with a layer of tin foil under your print and place it into the oven and switch it off.
We will leave the model in the oven for an hour to ensure the cooling has completed.
1st attempt of the annealing process
As you can see the statue doesn’t look like it has changed much, but does feel different to the touch, almost more solid in feel.
One issue I had come across was my oven is an electric fan oven, when switched off the fan is left running to aid cooling. I am not sure if this has effected the final outcome of the annealing as the model might not have enough exposure to the heat. I have decided to repeat this experiment but this time unplug my oven rather than switch it off.
2nd attempt of the annealing process
The second attempt still looks the same with a slightly noticeable loss of shine, the model its self has held up well with no deformity or any sign of shrinkage. If I scratch my nail against the grain the noise is different, the original model feels and sounds hollow in comparison to the 2nd attempt at annealing.
I am quite pleased with the outcome of this after the second attempt of annealing. The model feels more solid and less tacky and plastic like compared to the print before hand with minimal or no loss of detail on the model its self. I would recommend anyone to give it a try, you may need to experiment a little to find the perfect sweet spot for your filament manufacturer.
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Why not show us your annealed prints? what would you have done differently? Comment below and share with your friends.