What Material To Make A Mold For Silicone?

Silicone molding is a popular method for creating flexible and durable molds. It is used to replicate objects accurately and repeatedly for a wide range of applications. Some of the key applications of silicone molds include:

Medical devices – Silicone is biocompatible and can be used to create molds for devices like artificial body parts, hearing aids, dental retainers, and surgical tools. Its durability allows items to be sterilized after molding (https://www.newtopcustomsilicone.com/markets/silicone-medical-parts/).

Food products – Silicone molds are perfect for baking as they withstand high temperatures. They are also FDA-approved and can be used for candy, chocolate, ice cubes and more. Silicone enables easy mold release so food keeps its shape.

Consumer goods – Silicone molds are used to manufacture household items like cookware, baby products, sporting goods and more. The material is flexible, non-stick and heat resistant.

Prototyping – Silicone allows quick and inexpensive prototype production. It can rapidly replicate 3D printed or CNC machined masters.

This article will provide a comprehensive overview of materials used to create silicone molds, steps for mold making, curing and demolding processes.

Materials for Silicone Molds

There are several common materials used to make molds for casting silicone. Each material has its own advantages and disadvantages.

Plastic

Plastic like ABS or PLA can be 3D printed into a mold shape. Plastic is easy to work with and modify. It can capture very fine details if printed at a high resolution. However, the surface may have print lines that transfer to the silicone casting. Plastic can also warp or deform if the silicone cures at a high temperature. Some plastics like HDPE can withstand higher temperatures.

Wood

Wood is an inexpensive option for one-off molds. It is easy to carve and shape, but may require sealing to prevent moisture absorption. Wood grain and pores will show up on silicone castings. Wood also has limited re-use as silicone sticks to wood.

Metal

Metals like aluminum can be machined or cast into mold shapes. Metal conducts heat well, allowing even silicone curing. The mold surface is also smooth. However, metal molds take more time and skill to fabricate. The material cost is higher too.

Plaster

Plaster can be shaped by hand or molded around an object. It is good for organic shapes. Plaster is prone to absorbing moisture though, which can inhibit silicone curing. The surface may also crack after repeated castings. So plaster has a limited life expectancy.

Plastics

Plastics are commonly used materials for creating silicone molds due to their smooth, non-porous finish and durability. The most popular types of plastics used for silicone molds are polyurethane, epoxy resin, and ABS plastic according to Tap Plastics.

Polyurethane plastic is a versatile material that can be cast into rigid molds or coatings. It is durable, heat resistant, and releases well from silicone. Epoxy resin is another rigid plastic good for mold making. It can be tinted and cast into detailed molds. ABS plastic sheets are also smooth, non-porous, and economical. ABS can be easily cut, formed, and machined into custom mold frames and boxes.

When selecting a plastic, consider heat resistance, durability, cost, ease of fabrication, and mold release. Properly preparing the surface and using release agents also helps create quality silicone molds from plastic masters according to ProMed Molding.

Wood

Wood is a popular material choice for making silicone molds. Wood is inexpensive, easy to work with using common woodworking tools, and can create detailed molds. There are several types of wood well-suited for silicone mold making:

Birch – Birch plywood is an excellent choice for silicone molds. It’s smooth, uniform, and free of defects. Birch has a fine, even grain that allows for intricate mold details. It machines and sands easily. Birch plywood is available at most hardware stores.

Poplar – Poplar is an affordable hardwood that has a smooth face, especially after sanding. It’s softer than other hardwoods, which makes it relatively easy to carve and shape. Poplar takes detail well while still being durable enough for mold making.

Maple – Hard maple is dense, strong, and machines smoothly. It can capture great detail, essential for mold making. Hard maple is resistant to wear and has a nonporous surface. It is more expensive than other wood species but makes high quality, long lasting molds.

Metals

Metals can be a good option for making silicone molds. The most commonly used metals are aluminum, steel, and tin.

Aluminum is lightweight, affordable, and easy to work with. It can be cut, drilled, and formed into a variety of shapes. Aluminum molds allow for quick heat transfer to help cure castings faster. A downside is that aluminum can react with some casting materials like concrete.

Steel is strong, rigid, and holds fine details well. It withstands high temperatures and resists warping. However, steel is heavier and more difficult to fabricate compared to other metals. Rust-resistant tool steel or stainless steel are good options.

Tin is soft and melts at low temperatures, making it easy to melt and pour casts. The downside is tin deforms easily compared to other metals. Tin alloys like pewter increase hardness. Tin molds should be used for limited runs with plastics or waxes.

When using metal molds, applying mold release agents is critical for easy demolding of castings. Smooth non-porous metals like aluminum tooling plate work best. Metals can withstand the heat of platinum cure silicones for multiple runs before wearing out (Source: https://www.reddit.com/r/MetalCasting/comments/16xcig5/question_about_silicone_molding_or_similar/).

Plaster

Plaster is a popular material choice for silicone molds due to its smooth finish and ability to capture excellent detail. The main properties that make plaster ideal for silicone molds include:

• Smooth, non-porous surface – Plaster creates a uniform surface for silicone to imprint. Its low porosity helps prevent air bubbles.
• Detail capture – Plaster picks up very fine details, resulting in intricate molds.
• Quick drying time – Regular plaster sets in 30-60 minutes, allowing for quick mold making.
• Rigidity when dry – Once set, plaster holds its shape well under silicone.
• Available and inexpensive – Plaster is readily available at art and hardware stores for low cost.

Some types of plaster recommended for silicone mold making are Activa ArtPlaster (https://www.amazon.com/Activa-5-Pound-Easy-Plaster-White/dp/B001E0HO6S) and Hydrocal White Gypsum Cement (https://www.amazon.com/Dentistry-Resealable-Railroads-Capital-Ceramics/dp/B00TSOPMEI). They provide an optimal starting point before applying silicone.

3D Printed Molds

3D printed molds offer several advantages for creating silicone molds. With 3D printing, molds can be custom designed and iterated quickly using CAD software. Complex geometries like undercuts are easy to produce with 3D printing that would be difficult or impossible to create using traditional mold making methods.

3D printed molds are useful for lower volume production or rapid prototyping of silicone parts. They allow rapid design iteration since a new mold can be printed quickly after design changes. The smooth surface finish of resin 3D printed parts allows for easy mold release. 3D printing is also an affordable option for mold making compared to CNC machining metal or plastic.

Materials like stereolithography (SLA) and PolyJet photopolymers offer high accuracy and good heat resistance properties for silicone molding. According to Proto3000, high temperature resins like Accura Xtreme can withstand the temperature of platinum cure silicones. PolyJet materials also produce smooth finishes ideal for mold making.

Choosing a Material

When selecting a material for making a silicone mold, there are several factors to consider:

Cost – Some materials like wood, MDF, and certain plastics can be inexpensive options. Metals and plaster are more costly.

Rigidity – The material needs to be rigid enough to hold its shape under the pressure of poured silicone. Wood, MDF, and metals are rigid while plastics and plaster can be prone to flexing.

Porosity – The surface must be non-porous so the silicone does not seep into the material. Metals, plastics, and some treated woods are non-porous. Plaster and bare wood are porous.

Release – The silicone must be able to release cleanly from the surface after curing. Non-stick coatings or releases may be required for some materials. Wood and metals often need a release agent.

Detail resolution – The mold material must be able to hold fine details precisely for the mold. Rigid materials like metals and plastics capture more detail versus more porous plaster or flexible rubber.

Reuse – More durable materials like metal or plastic can allow the mold pattern to be reused many times. Materials like plaster or wood may only permit a few uses before degrading.

Compatibility – Ensure the mold material does not inhibit silicone curing. Some materials like sulfur-based clays can cause cure inhibition.

Ease of use – Working properties like cuttability, formability, complexity of prep-work, and more should factor into material selection.

With consideration for these factors, common choices are wood, MDF, plastic, 3D printed parts, and metal. Porous materials like plaster often require special surface treatment to be suitable.[1]

Making the Mold

Making a silicone mold involves a step-by-step process to ensure you end up with a high-quality mold.

First, prepare the master model that you want to make the mold from. Make sure the model is clean and free of any residue. Apply a release agent like vaseline to the model to help separate it from the silicone later.

Next, prepare the silicone. Mix the two parts of the silicone compound together as directed. Add colorants if desired. Ensure you mix thoroughly so the silicone cures evenly. Pour the silicone over the master model carefully to fully cover it.

Allow the silicone to cure fully, which can take 16-24 hours. Carefully peel the cured silicone off the master model. You may need to use a knife or other tool to separate detailed areas. Try to avoid ripping or tearing the mold.

Clean and trim excess silicone from the mold if needed. Your flexible silicone mold is now ready to use for casting resin, wax, plaster, concrete, chocolate, soap and more. Apply a release agent to the inside of the mold before each use.

Take care not to tear or puncture your silicone mold, as they can last for many castings if handled with care. Store unused molds away from heat and sunlight to prevent warping.

Curing and Using

To get the best results from a silicone mold, it’s important to allow it to fully cure before use. Silicone cures via a chemical reaction, and colder temperatures will slow the curing process. Ideal curing temperature is around 72°F/22°C. At this temperature, most silicone molds will be ready to use in 24 hours. Trying to demold or use the silicone mold too soon could damage the mold and lead to defects in castings [1].

Once fully cured, gently flex the mold to break the seal before carefully demolding cast pieces. Avoid tearing or distorting the silicone. With proper care, silicone molds can be used for dozens or even hundreds of castings. Make sure cast materials are compatible with silicone to prevent degredation. Check manufacturer instructions for full details on curing times, demolding, and usage limits. Properly cured and demold silicone molds will provide reliable performance and consistent cast results.