Polyurethane vacuum casting is a low-cost, traditional molding process for making rigid or rubber-like plastic parts. It is commonly used for small production runs or parts for market testing prototypes, personalized products, and custom medical devices, to name a few.
The thing with polyurethane vacuum casting is that it doesn’t require expensive rigid metal molds but rather used silicone molds to create effective quantities of castings. Not to mention, it makes it easy to add color to castings before and after the manufacturing process. It can also cast products such as clear electronic housings and presentation boxes using transparent materials.
During the polyurethane vacuum casting process, the master mold is placed inside a sealed box, covered with liquid silicone, and cured. After the silicone has solidified, the manufacturer cuts it in half to release the master mold. At this juncture, the casting polyurethane mold is ready for use.
So, how does polyurethane vacuum casting work? Well, polyurethane casting tech is similar to traditional injection molding, requiring molds with cavities shaped like components. But while injection molds are metal, polyurethane vacuum casting uses soft silicone molds.
You’ll then have to build the mold cartridge around the master model before encapsulating it in liquid silicone to form the mold tool and cure it for an average of 18-24 hours. The mold is then cut into two different halves with a very sharp cutting tool so that the two halves fit together better. The main pattern is then removed.
The remaining cavity is then used to cast the end-use part. Keep in mind any features that may be fatigued by multiple casting should be replaced with pins. Once the tool is created, the resin of your choice is injected into the cavity of the mold tool to form the part.
The resin must be allowed to cool before the finished part is removed from the tool. Any excess material flash or gait needs to be removed. This is caused by leakage between the mold’s two surfaces and the resin’s entry point into the mold.
To make a polyurethane casting, you will first have to create a master pattern using 3D CAD software, convert it to an STL file, slice it into layers using 3D printing software, and then 3D print using stereolithography (SLA) or PolyJet to provide the pattern for the silicone molding process.
