Injection Molding Urethane Casting

Five surprising benefits of urethane casting

By March 22, 2021
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Urethane casting is a useful manufacturing method that involves creating a silicone mold from a master pattern, which is essentially a replica of the final part. The mold is then filled with a shot of urethane casting resin and allowed to cure. Once the part has cooled, it can be ejected and the mold refilled. This allows for high-quality parts to be created quickly and cost-effectively, especially when used to produce parts in relatively low volumes.

It’s unfortunate that many product teams are not familiar with the process or aware that it can be a viable manufacturing method — in fact, many who are familiar with urethane casting only see the process as a bridge tooling method on the path to producing end-use parts via injection molding. In any case, teams often overlook the breadth of advantages and value propositions that urethane casting offers as an end-use manufacturing method. Here are five benefits of urethane casting:

1. Reduced tooling and part costs

Urethane-cast parts are typically more cost-effective to produce on a per-unit basis than those made through additive manufacturing methods, as order volume increases.

During prototyping, additive processes may require multiple build cycles to create a higher number of parts, which adds to the overall cost of production. Urethane casting, on the other hand, can be used to rapidly fabricate prototypes, avoiding the need for additional — and costly — build cycles.

The cast urethane molding process also uses silicone, which makes it far more affordable than the hard tooling needed to create the durable metal molds used in injection molding. Silicone molds can be fabricated in as little as 24 hours for hundreds or thousands of dollars (depending on the size and design of the given  mold), whereas aluminum and steel mold tooling may require weeks and tens of thousands of dollars to finish.

2. Increased design flexibility

Urethane casting is highly flexible with regard to part material; product development teams have hundreds of different materials in all sorts of colors and durometers to choose from. And in contrast to the many rigid thermoplastics and thermosets used in manufacturing, silicone urethane casting resins are softer and more flexible, which makes the molds more forgiving.

For instance, draft angles (which must be incorporated into mold design to allow parts to be ejected without damage) are no longer necessary with molds made from elastomeric materials like silicone. This allows designers to incorporate features into parts that would otherwise be impossible to achieve without expensive slides and actions, including undercuts and overmolds.

Furthermore, design changes can be easily incorporated into mold designs based on the results of prototype testing or consumer feedback without the expense of hard tooling. Because silicone molds have a lifetime of 25-30 shots, modifications can be easily integrated between molds at a minimal expense. This does create the need for additional molds as production volume increases, but, as mentioned, silicone molds can be produced at a fraction of the cost of hard molds.

3. Impressive speed of production

Silicone molds are much faster to produce than hard tools, with some molds being ready to use within 24 hours of being poured. Thanks to this speed, urethane casting is ideal for producing parts in lower volumes that would not justify the significant investment of a metal injection mold.

The process can also be used as a bridge to production if parts are needed immediately, enabling product teams to begin fabricating first-run parts while the hard tools are finalized. The majority of cast urethane parts can be shipped to market within two to four weeks, giving savvy manufacturers a valuable competitive edge.

cast urethane parts
Urethane casting is ideal for producing parts in lower volumes that would not justify the significant investment of a metal injection mold.

4. High precision and quality

Urethane casting enables manufacturers to create high quality parts in a variety of shapes, sizes, and materials — all with good tolerances. Typical tolerances are +/- .020″ per inch for cast urethane parts, though tolerances are still dependent on part geometry and other factors.

Deviances to normal tolerances may be caused by the thermal interaction between the liquid shot and the silicone mold. In general, teams should anticipate a material shrinkage rate of +0.15%, meaning the volume of the part will increase.

Further, it’s worth noting that many polyurethane casting resins are capable of providing chemical and physical properties comparable or superior to production-grade plastics. In contrast to additive technologies, which are limited in some material and structural ways, urethane casting allows for the rapid production of strong, high-quality end-use parts made of a wide variety of materials.

5. Excellent surface finish

Much like injection-molded parts, cast urethane parts offer excellent surface finish, and can be customized to include colors, surface textures, or post-production processes like painting. These options guarantee that parts will remain aesthetically pleasing even if they should be damaged or scratched during use. Urethane can be used to create parts featuring mechanical properties comparable to materials ranging from rigid plastic to rubber-like elastomer. Many materials are available in a breadth of translucencies, as well.

Discover efficient, affordable part production

When it comes down to urethane casting vs. injection molding, additive manufacturing, or any other process, there are a few key factors to consider. If a large number of prototypes is needed quickly, urethane casting’s speed and design flexibility make it a very compelling option. At the same time, if order volumes are huge, then urethane casting is an excellent way to beat competitors to the market until production tooling is ready.

The speed and affordability of urethane casting make it an exceptionally useful means of production that offers a range of benefits to product teams of all kinds. Partnering with an experienced manufacturing team is the best way to ensure you’re taking advantage of all the value-adds of urethane casting and optimizing your product development process.

Fast Radius is a cutting-edge on-demand digital manufacturing platform reimagining what’s possible in modern manufacturing. Our design and production capabilities are backed by decades of experience, and we specialize in doing the previously undoable — usually faster and more efficiently than our customers expect. Contact us today to get started.

Visit our learning center to read more about when to use urethane casting, common cast urethane materials, and much more.

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