The urethane casting method is a low-volume, mid-range production method. Compared with other methods with low costs but limited scalability, injection molding successfully bridges the gap. The method makes it possible to quickly and inexpensively create parts with high-quality, detailed features and a similar cosmetic appearance.
It is primarily designed for situations where aluminum or steel-hard tooling is prohibitive, such as injection-molded parts. UC is also known as room temperature vulcanization (RTV), where the silicone mold is cured in ambient conditions.
How does urethane Casting work?
Four key steps make up the UC process:
- A 3-D CAD pattern is created, converted to an STL file, sliced into layers using 3D printing software, then 3D printed using stereolithography (SLA) or PolyJet to produce the silicone mold. In post-processing, place tape on the flat surfaces of the master pattern so that the rubber casting part can be removed cleanly.
- The master pattern is placed inside a mold box (like a flask used in metal casting), which is then covered in liquid silicone and cured for about 18-24 hours.
- With a very sharp cutting implement, the mold is then cut into distinct halves so that the two halves fit together more efficiently. It is then removed from the mold. Once the part is cast, the mold cavities are removed. The replacement of dowels with casting components that are likely to fatigue over time is a good idea.
- Having created your mold tool, you inject the resin into the voids in the tool to create your parts. The resin must cure the finished product from the tool, typically in a heated vacuum chamber. Once the resin has cured, any excess material must be removed. It is caused by leaking resin between mold surfaces and an entry point for the resin to enter the mold.
Tips for Using Urethane
A variety of factors can influence the properties of urethane. Keep these in mind when designing your final parts:
- Moisture reacts with urethane as soon as it comes into contact with it. Urethane can be ruined by water even in the air, which would be a big hassle after you’ve just bought two large jugs. Keep the caps on your urethane once you’ve poured it. You’ll extend its lifespan and improve its performance.
- Urethane undergoes an exothermic reaction as it cures, causing heat to be generated. The result is that thicker areas will cure faster than thinner ones due to the concentration of urethane. Remember that one area is ready does not mean the whole part is, so ensure that everything dries thoroughly. Mold can also be damaged by the exothermic reaction, which evaporates heat.
- When your resin solidifies, it will shrink. When making a urethane mold, you’ll need to account for shrinkage of around 0.15%.
- Depending on the base color – Urethane has a white base color. Other colors include black, transparent, and colored. When you tint, the base color you choose will influence the final color. For example, if you choose a white base with a red tint, it’s likely to come out pink.
- If you have difficulty matching the color of urethane, don’t worry too much about tint. Paint your parts instead. If your paint chips and reveals the urethane underneath, we still advise tinting your parts to a similar color.
Before using urethane, always read the advice and guidance from your brand. It will ensure your urethane lasts for its full pot life, and you get the best finish.
