Speed, cost, and approximation to the final part design (including material properties and dimensions) are key criteria when selecting a fabrication method for making a silicone prototype. For silicone parts, there are actually more options than there are for thermoplastics, which makes the product development process for silicone products a little more challenging. Available processes for making silicone prototypes include: RTV (room temperature vulcanization) molding, selective laser sintering (SLA) and fused deposition modeling (FDM), transfer press molding using high consistency rubber (HCR) materials, and injection molding solutions. As we discuss these options, please keep in mind the majority of new silicone products are manufactured from LSR (liquid silicone rubber), injection molded in a durometer range of 30-70 Shore A.

A Review of 4 Methods

RTV Molding – Industrial RTV silicone formulations are widely available—some can even be found at the corner hardware store. Making parts out of these materials requires a mold, which can be made of almost any metal or plastic material. Although by definition RTVs will cure at ambient temperatures, albeit over hours, ovens are often used to accelerate the curing of the material.

  • Pros: The use of RTV is attractive because of the low capital equipment requirements and the availability of raw materials. RTVs can be a very close approximation to their LSR relatives. It is common that well equipped R&D labs have the ability to manufacture tools from plastic and/or soft metal materials in-house. Once the mold is made, making parts is a simple fill-and-wait process. A skilled technician can make the first part within a day.
  • Cons: RTV molding is a slow process with cure times extending from 20 minutes to hours. Production rates and cost per piece are both largely determined by the processing time.

HCR – Transfer molding is used to make parts out of HCR, and is a simple manufacturing process 3D printing in silicone is now an option for prototypes an HCR (“gum stock”) material into a heated cavity to cure and form a part. HCR is a natural fit for transfer molding since gum stock is much more viscous than LSR.

  • Pros: Simple tools.  Little or no process development.
  • Cons: Complex geometries may not be possible. Longer cycle times than LSR.

LSR – Production equivalent injection molding press and production grade materials are molded in soft metal tooling.

  • Pros: Tooling can be made quickly and the production of parts is fast. The resulting prototypes are very close approximations of production parts.
  • Cons: Can result in a higher cost per part for small runs of parts, since the initial tool cost can’t be amortized over a large number of parts.

Silicone Rapid Prototyping Comparison

Method Description Speed Cost Approximation to production
RTV Material is injected by hand at very low pressure; material cures at room temperature; many mold material choices Tooling needs to be machined (or 3D printed) – days to weeks
1-25 parts – Multiple days
25+ parts – Multiple days/weeks due to very long cure times		 $1,500 to $2,500 Medium – Durometer and dimensional attributes are close, but manufacturing process can be much different
SLA/FDM (“3D printing”) The part is formed layer by layer from raw material No tooling required
1-25 parts – 1-2 days
25+ parts – Multiple days		 $20-$50 each Low – Parts will have shape similar to finished part, but many limitations on material likeness. Typically a “cloudy” finish.
HCR Transfer molding; mold materials limited to metals Machined tools – fast
1-25 parts – 1-2 days
25+ parts – Multiple days		 $2,500 +
$20/part		 Medium – Parts will be silicone and durometer will be accurate, but manufacturing process can be different
LSR Injection molding; mold materials limited to metals Tooling and parts
3-7 days		 $2,500
$10/part		 High – Parts will be silicone, durometer will be accurate, manufacturing process is the same as production in most cases