Molding and Casting 101: Intro to Urethane and Silicone Casting

Posted on Oct 10, 2018 by Cullen Hikene

3Diligent CEO, Cullen Hilkene, and director of sales, Anna Villano, sat down for a quick discussion about molding and casting in polyurethane and silicone. Among the topics discussed in the vlog, Molding and Casting 101: Intro to Urethane and Silicone Casting, are:

  • What is casting?
  • What kind of material properties are achievable?
  • Why use casting?
  • What quantities are appropriate?
  • What are the drawbacks of casting?

Watch the videos below or read the transcripts and when you’re done, learn more about 3Diligent’s urethane casting and silicone casting services.

Intro to Molding and Casting

Cullen: Hey everybody it’s Cullen with 3Diligent along with Anna Villano, our director of sales. Today we are coming to you to talk about a topic, our different production processes…we have a wide range of them at 3Diligent and wanted to have a quick informal chat about some of the programs that we worked on utilizing urethane casting, some of its advantages, some of its drawbacks, one of the key processes we use to support our customers from prototype to production. So with that as a baseline, Anna, you wanna give everybody an idea of what urethane casting is?

What is Molding and Casting?

Anna: So basically urethane casting is taking your product, your image, creating a silicone mold, and then producing multiple castings off of that one mold.

Cullen: Got it. So commonly what we’ll be doing is printing a master pattern part, creating a silicone mold around it, taking that part out, and that creates basically negative space that you can fill in with polyurethane casting materials.

Anna: Now another note is that we are not only talking about hard rigid plastic. You can use cast urethanes and do rubber. So you can cast in different shore durometers where you can go with soft rubber or a very hard stiff rubber.

Cullen: Yeah, that’s spot on. Frankly, a very close cousin of urethane casting is silicone casting. Where commonly we will print molds and then in turn cast silicone within those molds in a very similar process. So as Anna alludes to there is a wide range of material options and material characteristics that can be delivered to you through the process and it’s one we commonly leverage when it’s the right one to give you the best value and meet the needs of your program.

What Are Urethane Casting Material Properties?

Anna: It somewhat simulates injection molding properties but it’s a two-part material. It gets you what you need.

Cullen: When we talk about cast urethanes having properties similar to injection molding, there are fire retardant materials, materials with high heat resistance, medical materials, a full gamut of urethane options available to you to address just about any issue save for a few things on the far ends of the spectrum, in terms of thermoplastics.

Anna: Absolutely. It will get you to that next step before going into injection molding.

Why Use Molding and Casting?

Cullen: We talked about some of the pros and advantages of this technology, one of them being that there is such a good range of polyurethane options, materials that can simulate injection molded materials.  But why simulate instead of going to straight to injection molding? Why do people use urethane casting?

Anna: Well there are a number of reasons.  Sometimes designers want to test out their designs in plastic to see how the product works at first.  So they can put their assemblies together and see how the product works. Sometimes their injection mold tooling won’t be ready in time but they need to be out in the market. So they’ll come to us, they’ll ask us for urethane cast parts, we’ll get them the parts, they’ll assemble their tools and they’ll use them for the time being until the injection molds are ready and the true plastics are off the tools.

Cullen: So that’s a great use case for where urethane castings can come into play.  If you are looking to get a few products into the market as you’re waiting for tooling, if you want to gauge interest in the market, that’s another option, and if you have low overall volumes on an annual basis, it can be an appropriate technology to utilize, so that’s exactly what we do.

What Quantities Are Best for Molding and Casting?

Cullen: Now when we talk about quantities and the fact is these are relatively smaller quantities what kind of a range are we talking about?

Anna: You can typically get around 100 parts per mold, and that depends on the geometry and the complexity of the part

Cullen: Yeah exactly. So as we talk about inputs to driving costs here, typically you’re printing out a pattern and creating a silicone mold of that pattern and then going through the manual process of pouring the urethane into the mold and waiting for that to cure.  All of that takes a bit of time and obviously it requires a bit of manual effort and with that expense. So as a result, it tends to be the sweet spot for urethane casting starts around five units and goes up to a few hundred units. Typically when you get into the thousands it makes sense to transition to injection molding, although based on the particular needs you have for a program, that can vary.   

What are the Drawbacks to Molding and Casting?

Cullen: Now the last thing we might want to mention, are there any drawbacks to the technology when we’re talking about pulling in urethane?

Anna: The materials will last for a while but they are not generally going to be for long term use. [They’re typically best] if you’re trying to get something out there. If you’re going to need them for several years, they should be okay though.

Cullen: Urethanes are commonly used for longer-term applications, as the characteristics they can have are quite extensive, but because you are working with a two-part process and experiencing the ongoing interlinking of the polymer chain, what ends up happening over time is that you can see the overall properties deteriorate, which is true for many polymers but thermoplastics may not see that as much. So that’s one thing to be aware of, we’re living in the world of polyurethanes. So you can get a good range of materials, but for higher quantities and certain material properties, it may not be a fit.

Molding and Casting 101: Intro to Molding and Casting Wrapup

Cullen: So any other closing thoughts before we wrap it up on urethane casting or casting more broadly?

Anna: No I think we covered it all pretty well.

Cullen: I think we did.  So pay us a visit at, submit an RFQ through the platform.  If Urethane Casting is right for you or you want to get pricing for it, just specify that in the process field and we’ll look forward to getting you a quote and some fantastic parts soon.  So thanks a bunch and we’ll talk to you soon!

Anna: Bye!

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