Urethane Casting 101: RTV Molding in 3D Printing

Moving from prototype to production doesn't need to happen all at once. It is often advantageous to perform additional fit and function testing in-between stages of development. Doing so can help to verify that the final product will perform exactly as intended. Urethane casting and RTV molding can help fill this gap, offering an affordable way to trial components before production. Cast urethane components closely resemble their production-quality counterparts in form, color, and texture, but they are more cost-effective to produce in low volumes.

At Advanced Prototype Molding (APM), we include urethane molding in our broad array of rapid prototyping services to help customers take their designs from concept to full-scale production. Urethane casting complements our other prototyping and production services, which also include injection molding, 3D printing, rotational molding, CNC machining, and stamping. Our expert team can help you determine where urethane casting fits into your individualized production process. 

What is Urethane Casting?

Urethane casting is the process of molding urethane polymers into rigid or flexible components. Once set, urethane closely mimics the properties of production-quality polymers, making it an ideal material for advanced prototyping. We typically employ room-temperature vulcanization (RTV) molding to cast urethane components, which involves pouring urethane into a silicone mold. These silicone molds can range from simple to highly complex, so they facilitate the production of virtually any desired part geometry.

Urethane Casting Process

The urethane casting process resembles plastic injection molding in many ways, but there are key distinctions. For instance, urethane casting via RTV molding uses a flexible silicone mold rather than hard plastic tooling. These silicone molds are affordable and easy to produce, making them ideal for prototyping and its potential for frequent design changes. 

The urethane casting process involves the following key steps:

1: Produce a master pattern. The first step in urethane casting is to create a precise 3D model of the component. This pattern will be used to create the initial silicone mold, and it will be kept as a reference in case the mold needs to be replaced. Silicone molds wear out more quickly than hard plastic ones, but the master pattern allows for easy replacements. This pattern may be 3D-printed, or it might be formed using CNC machining or another technique. What matters most is that it accurately represent the geometry of the final product.

2: Create the silicone mold. With a master pattern, creating a silicone mold is as simple as encasing that model in silicone. Once hardened, a technician slices the silicone in half and sets aside the pattern. The mold is now ready for casting.

3: Prepare the urethane. Urethane comes in two liquid phases that must be combined prior to molding. Different types of urethane suit different projects, depending on the desired rigidity.

4: Pour urethane into the mold. As in plastic injection molding, the next step is to fill the cavity with the liquid polymer.

5: Fill the voids. Simply pouring urethane into the mold is typically not sufficient to fill all the empty spaces in the mold. Applying a combination of heat and vacuum pressure to the mold can help remove all excess air and ensure that the urethane fully conforms to the cavities in the silicone.

6: Remove the component. The urethane will slowly set inside the mold, at which point the two halves can be separated and the hardened plastic removed.

7: Repeat. The process continues until all desired models are hardened. At this point, any desired finishing processes can take place.

Urethane Casting Advantages & Benefits

Urethane casting is an excellent choice for prototyping in many respects, and it can also be used for some production runs. Its advantages include:

• Low start-up costs. Injection molding requires a steep initial investment to create the steel molds used in casting. By contrast, silicone mold creation is fast and cost-effective, even when accounting for silicone's lower durability.
• Cost-effectiveness. Polyurethane is highly affordable, especially compared to some production materials. In combination with cheaper molds and faster prototyping, the cost advantage makes urethane casting a cost-effective option.
• Speed. Urethane casting is quick, thanks to the ease of creating the molds and the speed with which polyurethane cures. Choosing urethane casting can shorten an otherwise lengthy prototyping process, especially when working with multiple components.
• Precision: Despite its simplicity, silicone molding creates highly complex molds that capture the master pattern's intricate details. The vacuuming process ensures that all of these details are eventually captured and reflected in the urethane prototypes.
• Variety: Polyurethane describes several different polymers with different physical properties. Urethane casts, as a result, may be rigid, flexible, or rubber-like, mimicking the properties of the final product. Color matching is also possible by adding dyes to clear polyurethane. These options make urethane casting a feasible option for a vast array of prototyped components.
• Flexibility: Although most urethane casts are used in prototyping, the process can also be used for low- to mid-sized production runs. Urethane offers excellent chemical resistance at a low price, so it is not always relegated to the prototyping phase.

Urethane Casting Applications & Industries

Urethane casting is popular due to its flexibility and affordability, and its applications are not limited to a single industry. Many sectors have uses for urethane molds and prototypes, such as:

• Aerospace
• Automation
• Automotive
• Consumer products
• Dental and medical
• Electronics
• Industrial production
• Military and defense
• Robotics

Specific applications include almost any product that can be tested using rigid, flexible, or elastic polymers. Some examples include:

• Aerospace panels
• Bellows
• Boots
• Bumpers
• Cosmetic tools
• Covers for electronic, medical, and dental products
• Fans
• Industrial pipes, tanks, and fittings
• Lenses
• Toys

The experts at APM can help determine whether urethane casting is an appropriate choice for your project.

Urethane Casting & RTV Molding from Advanced Prototype Molding

Urethane casting provides an ideal combination of accuracy and affordability, making it a highly accessible option for prototyping. At Advanced Prototype Molding, we rely on RTV molding and urethane casting services to quickly craft prototypes, fit and function testing parts, and even final production components. We draw on more than 40 years of experience to guide clients through the production process, beginning with a free design consultation and ending with a product or prototype in-hand. 

To learn more about how APM's decades of experience can benefit your project, contact us or request a quote today.