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Rapid Sand Casting

What is Urethane Casting?

Urethane is a type of resin used to make a range of plastic items. Its end-use is highly versatile; you can create flexible things that are almost rubbery in texture and very rigid plastics.

Urethane casting’s in the manufacture of short-run, low-volume products such as movie props or bespoke models. It involves pouring the urethane into a mold and letting it cure – but we’ll talk more about the process later.

Urethane casting is a brilliant low-cost, high-quality way to create parts and whole models. It works well for detailed designs, too, creating a high standard finish quickly and without the high price tag of other methods.

Benefits of Urethane

Still not sure if the urethane casting process is the option for you? Let’s run through some of the benefits:

You can test out your design and ensure a market for it before going into mass production. It’s a working prototype that isn’t too expensive. Once your product switches to higher volumes, you can change to a different process.

It gives you low-volumes of high-quality, production-grade parts.

You can create very detailed models and have more freedom with your designs. This is ideal for bespoke props and models. You can even create internal, sharp corners, which can be trickier with other processes.

You can bring your product to the market quicker with short lead times.

It can cure a variety of finishes, from very rigid to incredibly flexible.

It’s available in tons of different texture, finishes, and tints can be added to change the color. This means you can tailor your casting to suit your end-use.

The shrinkage rate of 0.15% is much less than many other processes.

Urethane castings can be FDA-approved, essential if you’re making items for the food, medical, and pharmaceutical industries.

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Rapid Sand Casting

Rapid Sand Casting Process

Casting urethane can be tricky, so we recommend ordering a tester sample before big order. You'll be able to get to grips with the process, work out whether you like the resin, and avoid losing too much in failed attempts.

Most of us mess up a few times when trying a new resin, so don't worry if it doesn't go to plan!

The process starts with a silicone mold. A master model of the parts will be manufactured by 3D Printing or CNC Machining to create this mold. Then, pouring the silicone into a tool imprint, the parts will be shaped.

You then have to mix your urethane, which comes as two separate liquids. You should mix the parts in a 1:1 ratio or as directed on the brand instruction. As soon as you combine the two, a chemical reaction starts that turns them from liquid to solid – this is curing.

You may also hear curing being referred to as room temperature vulcanization. It may sound more advanced, but it is the same thing.

If you're adding a tint to your resin, remember to do it before combining the two liquids. It can take a while to mix the shade, so this will give you more time. If you add the tint to the combined resins, the urethane may start to set before you've thoroughly mixed it.

Once you've mixed the tint, you can combine parts A and B of your urethane. Stir this for between 10-20 seconds. You can then carefully pour it into your mold.

Leave your urethane for around 1 hour to cure – although you can follow the brand's guidance for timing. Remember always to read their safety information, too, and they can tell you more about pot life and pouring techniques.

Things to Remember When Using Urethane

Urethane can be affected by many factors. Remember these so that they don't affect your final parts:

Urethane hates moisture – As soon as urethane comes into contact with moisture, it reacts. Even the water in the air can ruin your urethane, which would be a pain after you've just bought

Two large jugs. So, always remember to put the caps back on your urethane as soon as you've poured it. It will help it to last longer and work better.

Urethane is exothermic – An exothermic reaction is when heat is created, which happens to urethane while it cures. Because of this, areas with a higher volume of concentrated urethane will heal faster than thinner areas. Just because one place is ready doesn't mean the whole part is, so be sure to leave it for long enough for everything to dry. The exothermic reaction will also evaporate heat from your mold, which can cause damage.

It will shrink – As your resin turns from liquid to solid, it'll shrink. With urethane casting, you expect shrinkage of around 0.15%, which you'll have to bear in mind when creating your mold.

Your tint will be affected by the base color – The base color of urethane is usually white. It can also be black, translucent, or colored. Remember that whatever base color you pick will affect your final color when you use a tint. So if you choose a white base and red paint, for example, it'll more likely come out pink.

You can paint urethane – Don't worry too much about tint if you're finding it too hard to color match. You can also paint your urethane parts. We are still advising tinting your parts to a similar color; this will help if your paint chips and reveals the urethane beneath.

Each urethane brand will be slightly different, so always read the advice and guidance from your brand before using it. It will help you get the best finish and make sure your urethane lasts for its entire pot life.

Why Make your 3D Priting at Unionfab?

  • Endless Options Choose from millions of possible combinations of materials, finishes, tolerances, markings, and certifications for your order.
  • Easy to Use Get your parts delivered right to your door without the hassle of sourcing, project management, logistics, or shipping.
  • Vetted Network We are ISO 9001:2015 certified and AS9100D compliant. Only the top shops that apply to become Suppliers make it through our qualification process.

Compare our 3D Printing Services

Service Lead Times Materials Tolerances Max Part Size
SLA 1 – 3 days Resin / Somos +/- 0.003 in. 800 x 800 x 550 mm
SLS 2 – 5 days PA12/ PA12GB +/- 0.002 in. 350 x 350 x 400 mm
MJF 2 – 5 days PA12/ PA12GB +/- 0.002 in. 380 x 280 x 380 mm
FDM 2 – 5 days PLA / ABS  +/- 0.003 in. 500 x 500 x 400 mm
Poly Jet 2 – 5 days Resin +/- 0.003 in. 490 x 390 x 200 mm