Silicone Casting

Agenda

1. What is silicone casting?
2. Why is it useful?
3. Tips & tricks
4. Applications in BBA
5. Other types of casting
6. Casting in the world around us
7. Chocolate!

Has anyone done any casting or mold making?

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What is silicone casting?

master (desired part) + mold (negative)

+ resin (positive)

= part (duplicate of master)

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Why silicone casting?

The utility of silicone casting

• Duplicate a complicated part without selling your soul to CAD�
• Easily prototype and make multiples �
• Change the stiffness of your desired part�
• Fun!
• Chocolate and candy molds, toys, etc.

Silicone casting applications

• Medical simulation
• Orthotics + prosthetics
• Lifecasting (mask making)
• Industrial
• Candle making
• Food and desserts
• Architectural restoration�

See more of what’s possible here

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Process

Part 1: Selecting the master part

• 2D vs 3D
• Time
• Material �
• Level of detail (resolution)
• Material
• 3D printing vs. machining vs. purchased part�
• Resources
• grabCAD
• Objects around you

Part 2: Choosing + preparing the mold

• Material
• Smooth-On is your go-to in BBA
• Check the box for properties
• Cure time, elastic modulus, etc.�
• Final application
• Food-safe
• Toddler-safe�
• Preparation
• For Smooth-On, usually involves mixing Part A with Part B
• Check whether mix ratios are by volume or by weight

Part 3: Choosing + pouring the resin

• Material
• Check compatibility with mold material (same material won’t release, some will degrade mold)
• Working times
• Final application
• Stiffness
• Color
• Texture
• Preparation
• Be sure your mold is fully cured! Check cure and post-cure instructions

Part 4: De-molding + finishing

• De-molding
• Peel away mold VERY slowly and carefully
• Avoid using sharp tools to extract your part to preserve quality of mold
• Use non-abrasive liquids to de-mold if necessary�
• Finishing
• Depends on final applications
• If you aren’t happy with your part and can’t figure out what went wrong in your process, ask a TA!�

Casting tips & tricks

• Mold making
• Keep it as simple as possible (flat boxes and taped parts work)
• Check the 3D print time (can be in excess of 24 hours!)
• Smoothness of mold = smoothness of part
• Material properties
• Try changing the ratios of Part A to Part B to get your desired stiffness
• Finishing
• Use mold release when appropriate (box should indicate this)
• Avoid using sharp tools to extract part
• 3D parts
• Suspend your part in the box using toothpicks, popsicle sticks, or rod
• Working and curing times
• Always check the box! Working times can be as low as 1 minute!
• Some parts may need to post-cure at a different temperature

Useful links

• 3D printed master parts + 2-part molds
• https://www.makerbot.com/professionals/post-processing/silicone-molding-1/
• Applications
• https://www.reynoldsam.com/application/
• Tutorials
• https://www.smooth-on.com/tutorials/
• Simple and fast molds (food-safe too)
• https://www.smooth-on.com/tutorials/making-food-molds-silicone-putty-fast-easy-fun/
• Free 3D CAD models!!!
• https://grabcad.com/library
• Resin info
• https://www.smooth-on.com/product-line/urethane-resin-accessories/\
• https://www.smooth-on.com/product-line/smooth-cast/
• https://www.smooth-on.com/tutorials/casting-quickies-smooth-cast-325-colormatch-urethane-resin/�

Casting applications in BBA

Dream Toy applications

• Replicate parts of a toy or a full model�
• CAD to create original parts�
• Rapid prototyping of materials of different stiffness
• Pour multiple resins into your mold

Beyond BBA

Other types of casting

• Die casting
• Part-part consistency
• Minimal post-processing
• High tooling cost�
• Investment casting
• Good for complex shape and thin walls�
• Sand casting
• Least expensive in small batches
• Can cast large parts
• Need large tolerances
• Rough surface finish

Casting in the world around us

Questions?

And now...chocolate!