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The simple post-processing techniques presented in this guide are an excellent way for professionals to create low-cost silicone molds, threaded inserts for enclosures, vacuum formed parts, and more.
Silicone molding is a powerful production method that, when combined with 3D printing, can allow you to make several copies of one product. You can also create a product in a material that is not supported by your 3D printer.
In this How To, we will show you some of the best practices associated with creating silicone molds around 3D printed parts.
Working time will vary depending on a number of factors. Creating a mold around our 3D printed part took us about 1.5 hours. Casting into our mold took about 15 minutes.
3D printed mold box, hardware, vents & keys (read on for more info).
Master (the print you are molding)
Resin and dye
Hot glue or cyanoacrylate glue
Rubber bands, tape, or straps
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Step 1: Choose a file to cast a mold around
Obtain a file that you would like to either make several of, or create in a material not supported by your printer.
We chose the cap to a perfume bottle to understand what the process would look like for a product development team attempting to produce several concept models of a prototype.
Step 2: Create a Mold Box
The next step is to create your mold box. This is the structure that will hold the silicone in place around your part when pouring. Your master will need to be suspended in this structure.
You can create mold boxes from:
Foam core board
We chose to design and print ours as this method has a few benefits. Designing and 3D printing mold boxes allows you to:
Print in pour holes and vents
Easily calculate the volume of our mold
Create boxes that perfectly fit the parts you plan to create a mold of
Re-use mold boxes to create multiple molds
While 3D printing your mold box isn’t necessary, it provides you with a reusable customizable mold box that the other methods cannot produce.
Step 3: Prepare and Print
Because the silicone molding process is not very demanding on the 3D printed mold box or master, you can select standard print settings.
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Step 4: Suspend Master in
Mold Box and Prepare
3D printed mold box, 3D printed master, Cyanoacrylate glue, Mold release spray, Vents & Keys
A: Spray your mold box, master, vents, and keys with mold release.
B: Choose points across model to glue vents
C: With our 3D printed mold box we were able to glue our master directly onto the pour hole during preparation.
D: Spray again with mold release for good measure
You can suspend your master using popsicle sticks, skewers, or 3D printed rods glued to the surface of the master in an inconspicuous place. The holes left in their place after your mold has cured will aid in resin flow through the mold.
Step 5: Open Bottles of Silicone (Parts A and B) and Stir Thoroughly
Supplies Used: Silicone (Part A & B), Mixing Sticks
As silicone comes in two parts, it needs to be mixed both individually and once combined with its hardener.
Mix slowly using separate mixing sticks.
Step 6: Measure
Supplies Used: Measuring cups
A: Determine the volume of silicone needed to fill your mold
B: Measure desired amount of silicone and hardener separately in two measuring cups.
We calculated our mold volume by filling our 3D printed mold box with water and pouring the water into a measuring cup to find exact volume.
For two part molds like the one shown, you only need to mix enough silicone to fill half of the volume of your mold.
Step 7: Mix Silicone
Once you have measured each part, combine the two parts into one mixing cup and stir slowly with a mixing tool.
Be cautious not to stir in air bubbles. Be sure to scrape the sides of the cup to mix in all material.
Once your parts are thoroughly mixed the curing process will begin.
Read instructions on your silicone for “pot-life”. This is how long you have to work with the silicone before it cures.
Step 8: Pour into Mold Part One
Supplies Used: Mixed silicone, prepared mold box and master
Pour silicone into the first half of your mold box.
When pouring, pour slowly into one corner of the mold box and allow the silicone to run to other parts of the mold box as it fills.
Stop when the silicone reaches the top of the first half of your mold box.
Once you have poured your silicone place small keys into the silicone. These will create negative spaces and allow the mold halves to fit together once poured. We will remove them before pouring the second half of our mold.
Step 9: Let Cure
Depending on what type of silicone you are using it can take anywhere from 75 minutes to overnight to cure.
Temperature and humidity will affect curing times, so we recommend this process be done in a room temperature environment.
Step 10: Attach and Prepare Mold Part Two
Supplies Used: Mold box part two, hardware (nuts & bolts)
Once our mold has set, we will prepare to pour the second half of our mold.
A: Remove the keys you inserted in step 9.
B: Attach and secure second half of mold box.
C: Spray with mold release
Step 11: Pour into Mold Part Two
Next, repeat steps 5-9 and create the second half of your mold using the methods mentioned above.
Step 12: Let Cure
Step 13: Breakdown Mold and Remove
Supplies Used: Pliers or Ex-Acto knife
Once both halves of your mold have cured you are ready to remove them from the mold box and begin using them to recreate parts.
A. Remove the hardware
B: Remove the mold from the mold box and open.
C: Remove the master and vents.
Step 14: Reassemble and Prepare Mold
Supplies Used: Cured mold, mold release spray, rubber bands
Next, you will need to reassemble your mold.
A: Ensure that all parts of your mold are correctly aligned, and plug any holes created by vents.
B: Secure mold pieces using rubber bands, straps, or tape.
Another great application for 3D printing would be to design and print a box to hold the mold together when pouring resin, or modify the mold box we used to serve the same purpose.
If your vents leave holes in areas where resin can spill out during the pour, they will need to be plugged.
Step 15: Measure Resin and Add Dye
Supplies Used: Resin (Part A & B), measuring cups, measuring sticks, dye.
Just as with silicone you will need to measure each part of the mixture taking into account the volume needed to create a part.
If you have made several molds, you can mix a larger quantity of resin and pour several molds at once.
Add dye to the part of the resin mixture specified in the instructions.
Step 16: Mix Resin
Combine both parts of the resin mixture and mix thoroughly being sure not to stir in air bubbles.
Resins typically have a shorter “pot-life” than silicone meaning they will cure faster.
Step 17: Pour Resin
Once mixed, pour immediately into the opening of your mold using a funnel.
Pour slowly as not to overfill and spill resin.
Any resin that remains in the mixing cup will harden, but can typically be removed afterwards.
Step 18: Let Cure
Once poured, allow the resin to cure for the appropriate amount of time.
Step 19: Open and Remove
Supplies Used: Pliers
Once your resin has cured, you can open the mold and remove your cast part.
Any resin that escaped through seams or voids and cured is called “flash”. Flash will need to be removed from the part through post processing.
Below, you can see that we were able to recreate our perfume bottle cap in several different colors and opacities using silicone molding.
Visit one of our other applications pages for tips on how to take your print even further.
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Last but not least, remember to share your work with us on Thingiverse and social media @MakerBot.
We can’t wait to see what you make!
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