This Instructable is about casting a Silicone Gasket in 3D printed PLA mold on an Ultimaker (See video here). It shows how the mold is modeled in Autodesk Fusion 360 then 3D printed in 4 snap together parts. It is injection cast using a syringe to force direct the silicone into the molds. The Silicone gaskets are one of the parts in a product mock up I am fabricating.
You will need the following for this project:
3D software to create the data for your mold, I used Autodesk Fusion 360
3D printer to print the molds, or access to one, I used an Ultimaker
X-acto Knife to clean up and trim the 3D printed parts
Silicone, I used GI-1040 from Silicone Inc. I got mine form Innovative Polymers
-Digital cooking scale for accurate mixing of the Silicone set to grams
-Protective latex gloves to keep your body from getting sticky and absorbing harmful materials
-Wax paper or Aluminum foil to keep silicone off your work surface
-Kitchen Timer so you know how long you have to work your silicone
-An good well lit place to work
-60ml syringe to inject your silicone into your 3D printed mold
Optional: Vacuum Tank/Chamber, and a heated tank/vessel to speed up the curing of the silicone
Colorant, a pigment of some sort to make your parts a specific color other than the stock silicone color
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Step 1: Model Your Mold in CAD and 3D Print the Mold
I had a pretty good idea about the diameter and section that my gasket had to have and was able to model it quickly in Fusion 360. From there is was a matter of making a mold of the gasket that could be assembled and disassembled easily once the silicone was set.
I chose to make a main master race (See the video here) that has three rings that fit inside of it to form the silicone with the type of section I needed for my purpose. The rings snap into the main race, the space that is left inside will get filled with silicone to make the gasket. One of the images shows a rendering with the the three rings inside of a clear race to illustrate the concept a bit better. The video shows the assembly and disassembly too.
I made a total of four molds so that I could try out some variations to see what worked best.
I made the .stl files for each mold and their corresponding rings and printed them on the Ultimaker 3D printer. They are made with about .01-.02mm offset between the parts in the horizontal dimension so that they fit together with minimal clean up. This is important or you will be spending a lot of time making 3D printed the parts fit together instead of making gaskets.
Step 2: Mix Your Siicone and De-Gas It If You Have a Vacumm Tank
Now it's time to mix up your silicone. I used GI-1040. I got it from Innovative Polymers. They are my local distributor for the Silicone Inc.
Put on your gloves and get out your scale and mix up what you need. I mixed up about 30g. See the Video for more detail. Make sure you put down some wax paper or aluminum foil on your work surface to protect it. Use a digital kitchen scale set to metric grams (don't waste your time with standard ounces). Mix the appropriate amount of silicone and catalyst based on your manufacturers recommendation. You can add a colorant at this point if you want your gasket to be a different color than the standard color.
Use a good mixing stick with square edges so you can mix the stuff at the bottom corner of the cup. Mix thoroughly and mix some more. Most good silicone's have a a fairly long pot life, so take your time and mix it well.
If you have a vacuum tank to de-Gas your material, you will want to place it in the tank for about 20 minutes to remove the air that you just mixed into the silicone when you added the catalyst.
Next, we will work on getting the silicone into the mold....
Step 3: Load the Silicone in Your Syringe and Inject It Into Your 3D Printed Mold
The Silicone is now ready to be put into the mold. Since it's to thick to pour in to the mold we will inject it with a syringe. See the video to get a better idea of how this is done.
I used a 60ml syringe. It has a big opening so it's relatively easy to pour the Silicone into the syringe and then add the plunger. I used my vacuum tank to remove any air trapped in the syringe, before I inject the material into the mold.
I place the syringe tip on the mold and gently inject the material into the mold cavity. I walk the syringe around the circular opening of the mold to fill it completely.
Once the silicone is in the mold it's just a matter of waiting until the mixture cures so you can DE-mold.
Step 4: Let the Silicone Cure and Then Remove the Gasket Form the Mold
I let the silicone cure over night. This silicone has about a 16 hour cure time. I added some heat to cure it over night to speed up the cure time to about 12 hours in my heat tank. See the video for a bit more detail on my heated pressure tank and my set up.
The next morning I removed the mold with the cured silicone and began the process of dissembling the mold to get the gasket I just made.
First I trim of the excess overflow silicone from the top of the mold with an X-acto blade, you can use a scalpel here as well if you have one. I then use a dental pick to hook and remove the rings form inside the race and reveal the finished gasket.
Step 5: Instantly Test Your Gasket and See How It Works!
As soon as you De-mold the silicone you can try it out on your application. See the video to see me test the gasket out and observe it's functionality. Works excellent for the mock up that I am making for this product.
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About Me: I am an Industrial Designer living in Southfield MI USA. I have a home-based Product Design Studio called “Botzen Design”and have been designing consumer products for 25+ years ranging from sunglasses for Bauch & Lomb, Traps eyewear, entry level luxury vehicles for Ford, wireless charging PowerMat for Homedics, to magnetic toys for Guidecraft. I specializes in tabletop and handheld products, ranging from WiFi routers to cosmetic products to Bluetooth devices and everything in between, I also teach Industrial Design at Wayne State University and CCS (College for Creative Studies) Follow me on Twitter @botzendesign or G+and Facebook and Subscribe to my Youtube channel Here. If you need a consumer product designed or high quality Urethane parts made, feel free to contact me through my website. You can check out my previous Instructable here about how to make your own Home made silent shop compressor from a refrigerator motor, and a glow in the dark vehicle antenna.
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