Material Preparation:

1. Before you start, determine what is the total mass of silicone you would need, then mix about 10-15% more than the minimum required amount. An easy way to do this is by filling the molds with water and measuring the water volume

(The specific gravity of silicone is 1.07, thus for every 100g of water, you need 107g of Silicone to fill the same volume.)

2. Add 2-3% Slo-Jo to Part B and mix thoroughly. Note that this typically means just a few drops of Slo-Jo!

3. Add an equal amount of Part A and mix thoroughly

4. Put mixture into the vacuum chamber and degas until all bubbles are gone.

Bubbles are the main enemy, leading to weakness, tears, and leaks.

Ensure that your mold is 3D printed with 100% infill to minimize the air trapped in the material during the printing process.

Air trapped in the 3D printed material will expand and escape through the walls when the mold is under vacuum. This could lead to formation of new air-bubbles in the silicone during degassing. 100% infill helps prevent this problem.

But even with 100% infill, some air would still be trapped in the structure. Thus, another precautionary measure you can do is to print your structure such that the air is more likely to escape through the tap rather than through the sides when placed under vacuum. This can be achieved by adjusting the advanced settings in your 3D printer's slicer software and making the top more porous than the walls.

Use a vacuum chamber for degassing after each of the following steps:

After mixing parts A and B.

After pouring just enough silicone to cover the mold surface.

After filling the mold.

Variable vacuum leads to faster bubble extraction than constant vacuum.

Use the pressure relief valve to oscillate between max vacuum to low vacuum several times.

Bubbles are much more likely to form at corners and edges than elsewhere in the mold

Fillet all interior corners and edges of your mold

Always use Slo-Jo, even if you don't need the extra working time it provides.

Lowers the viscosity of the silicone

Reduced bubble formation.

Bubbles can escape more easily.

Allows more time for trapped bubbles to escape.

Surface tension causes uneven surfaces and leads to poor actuator behavior. 

Overfill the mold and put a transparent acrylic cover (and weight on top) to achieve smooth, even surface.

Overfilling helps ensure you don't trap any bubbles while putting the cover. 

Lower-durometer actuators can operate at much lower pressures, but also apply lower forces. 

Jamming chambers are great in this case for add stiffness to the actuators.

Use Sil-Poxy to seal the supply tube to the actuator.

Only use silicone tube and never a vinyl tube, or it will start leaking eventually.

Ecoflex / DragonSkin do not provide as strong seals as Sil-Poxy.

TechBond (tbbonding.com) also works as an  adhesive for silicone materials.

However, the bond is quite rigid, and the product is quite toxic while working with it.

​

​