Silicone Textured Inflatable Squeeze Bulb

In this tutorial, we will describe the fabrication process for making an inflatable textured bulb from silicone. The fabrication process takes about 5 minutes and the silicone bulb will be inflatable about 15 minutes thereafter.

Working with silicone is a messy process. Expect for all the materials and equipment to end up with uncured silicone. It is recommended to have a dedicated space and dedicated equipment for silicone fabrication or a disposable work surface such as wax-treated butcher paper.

For this project, we will be fusing two layers of silicone together and using a separator to keep select areas from fusing. This will allow us to create an inflatable geometry. Note that the tutorial provides instructions for separators made from vinyl (for quick prototyping) or from PVA prints (water-dissolvable 3D prints that can be removed from the bladder).

You will need:

• 3D Prints
  • Mold 3D Model File (available here)
• Mixing Implements
  • Plastic/ Glass Weight Boat or Container
  • Glass Rod/ Metal Spoon (avoid wood - prohibits curing)
• Materials
  • Ecoflex-0050 or Ecoflex-0010 (Part A and B)
    • Alternatively, you can use your preferred silicone. We recommend silicone systems with pot times around 30 minutes. Silicone Pigment Dyes (optional)
• Equipment
  • Gram Scale
  • Timer (things get messy; have a dedicated timer)
  • Incubator or Heat Lamp (optional; required for speed curing)

If using a vinyl separator:

• Vinyl cutter & vinyl
• Iron

If using a PVA separator:

• PVA filament & PVA compatible 3D printer (e.g., Ultimaker 3)
• PVA Separator 3D Model File (available here)
• Syringe or pipette for injecting water

About 4 hours

1. Print your Mold: Using an ABS or PLA printer to 3D print the mold.
   1. You will need to generate g-code specific to your 3D printer.
   2. We recommend a 2.0 mm layer height with 100% infill. This process takes about 4 hours depending on your 3D printer.
      1. Make your own DIY molds. Don’t have a 3D printer? You can make your own molds with cardboard or other craft materials. Cover all the surfaces with box tape to create a silicone-friendly surface.
2. Prepare your Vinyl Separator: Cut out only the SEPARATOR layer in the svg file found here. We recommend cutting multiple copies should you run into an error later during fabrication. Remove the negative vinyl. Place the vinyl under a cloth and iron until flat using the lowest setting on your iron. This will prevent the curl of the vinyl roll from affecting the bladder fabrication process.
3. (or) Prepare your PVA Separator: Use a 3D printer configured with PVA filament to print the separator STL file available here. We recommend 0.2 mm layer height and 100% infill. This process takes about 20 minutes depending on your 3D printer.

The values provided are based on the Ecoflex 00-50 silicone system. If using a different silicone, adjust the amounts based on the manufacturer's instructions. Aim to prepare about 32 grams of silicone.

1. Have your scale, container, mixing implements, and both silicone parts (A&B) ready.
2. Place the container on the scale and tare the scale (make the scale read 0).
3. Pour silicone from the part A bottle slowly until you measure about 16 grams.
   1. It is important to hold and pour the material as close as possible to your container to avoid introducing unnecessary air bubbles.
4. Repeat step 3, instead of measuring an additional 16 grams of part B.
   1. If you over or under pour, just be sure to match the amount of part A and part B in the container. Example: If you pour 3.5 grams of Part A, pour 3.5 grams from part B for a total weight of 7 grams. It is okay to be off by +/- 1 grams.
   2. Be sure to close the lids of both part A and B bottles.
5. Use the mixer tool to gently mix and stir the material together for about 30-60 seconds. We use a metal spatula.

1. Reposition your workspace to only have the mold and silicone directly in front of you. Position yourself so that you can freely move around the top of the mold.
2. Hold the silicone mixture container above the mold and slowly pour the silicone starting from the far edges working yourself to the center of the mold.
   1. Cover half of the height of our mold up to the parting level (the ledge on the inside wall of the mold). You will have extra silicone left over. Keep for the next step.
3. Place the mold inside the incubator at 135 F degree (57 C) for 3 minutes to cure the base layer to a tacky state.

Notes

• Ecoflex-005 Silicone is a relatively viscous material (thick). It will not move around on its own. When pouring, make sure you slowly pour the silicone and ensure you are covering the full surface of the mold evenly.
• To avoid creating air bubbles, hold the silicone container close to the mold.
  • If your container is too big or too heavy to hold and carry for a certain amount of time, you can transfer using a spoon.
• To create a strong bond between both layers, we avoid letting the first layer cure completely. You can do this by following the guideline from the bottle label. If you do not have an incubator or heat lamp, allow the base layer to cure for about half the recommended cure time.

1. After the first cure is done, remove the mold from the incubator.
2. Hold the separator by the rectangular geometry with tweezers.
   1. Use another pair of tweezers to hold the opposite end.
   2. Position the separator above the mold and lower the rectangular geometry to the registration site.
      1. Use this to anchor and position the separator so that it sits at the center of the mold.
3. Following the pour and mix instruction, prepare another silicone mixture to pour the sealing layer.
   1. Place your mold in the incubator at 135 F degree (57 C) for 15 minutes to cure the bladder.
   2. If you are using the room temperature, just let the silicone sit for the full cure time.

   3. Remove the bladder from the incubator and gently demold by pulling on the neck of the bladder.

1. After the object has been fully cured, use a syringe to slowly inject water into the bladder.
2. Keep inserting water until all the PVA inside has been covered with a layer of water.
   1. Using a binder clip, pinch the bladder opening tight.
3. Wait for the PVA to dissolve. To speed up the process, you can:
   1. Placing the bladder back in the incubator.
   2. Inject the bladder with hot water.
   3. Massage and agitate the bladder contents.
4. Empty out the bladder to remove the dissolved PVA.

1. Insert a barded air tube connector to the bladder and connect to an air tube.
2. We like to inflate (and deflate) your bladders:
   1. Manually
      1. We use these inflation bulbs commonly used in blood pressure measurement cuffs.
      2. Alternatively, you can use syringes.
   2. Electronically -- We use these 3V air pumps.
   3. Programmatically -- We use this Arduino compatible system (Programmable Air) to inflate and deflate bladders.

In the case of air bubbles...

Bubble defects can create holes in your bladder. You can detect these defects during the inflation process; sometimes the bubbles are large enough to see. No worries :) Silicone can be used as glue to itself! Mix a bit more silicone as you did in earlier steps and patch up the offending holes with the new silicone. Fully cure before inflating again.

Not curing?

Certain materials do not prevent the silicone from properly curing, such as wood. We also found 3D printed resin to be an offending material. Unfortunately, we have not found a way of recovering from this error aside from restarting the process with only PLA/ABS plastic, glass, and metal mixing implements.