Vacuum Casting Services

The master mold is the physical representation of the CAD design and is typically CNC machined or printed in 3D plastic such as SLA/SLS.  The quality of cast polyurethane parts depends on the quality of the master model, and CNC machining is recommended when you need plastic parts that require tight tolerances, high gloss or even optical clarity.

In practice, for those parts with complex shapes and structures, we will also consider using SLA to make the master mold.

Xinyi Technology can apply texture or satin effect to the surface of the part to simulate the final mold texture of the product.  The silicone mold will replicate the details and texture of the original master, so the cast polyurethane part will be a replica of the master.

Casting molds are made of liquid silicone, also known as RTV molds. Silicone rubber has excellent chemical stability, self-release performance and flexibility, and has a very small shrinkage rate, which can accurately transfer the texture and pattern of the master mold to the casting mold. The steps of manufacturing casting mold are as follows:

• Put the tape on a flat place around the master mold to make it easier to cut the mold later, and this position will also become the splitting surface of the final silicone mold.
• The master model is hung in the casting box and plastic rods are placed to set the gates and vents.
• Liquid silicone is poured around the master mold and all air is removed, creating a vacuum chamber to keep the master mold free of air bubbles. The liquid material is then put into an oven for curing at 40°C. It generally takes 8-16 hours, depending on the volume of the mold.
• After the silicone rubber has cured, the mold box is cut open, the master mold is removed from the silicone, the mold is cut open and the master mold is removed, leaving a cavity with the exact same negative shape as the original.

Xinyi Technology operates under a standardized process to ensure accurate parts and consistent mechanical properties.     Rigorously trained vacuum casting machinists control all operations including: mixing, degassing, stirring, preheating, casting and demolding to create highly accurate replicas of the originals.     The manufacturing process of vacuum castings is as follows:

First put the silicone mold into the oven and preheat it to 60-70°C.     It is very important to choose a suitable release agent and use it correctly before closing the mold to avoid stickiness and surface defects.

Prepare the polyurethane resin before use by preheating it to around 40°C.     Mix the two-component casting resin in precise proportions, then thoroughly agitate and degas under vacuum for 50-60 seconds to avoid air pockets or bubbles The resin is poured under computer control into molds inside a vacuum chamber and cured again in an oven.     Average cure time: 1-3 hours for small parts, 3-6 hours for large parts.

Remove the cast part from the silicone mold after curing Repeat this vacuum casting process.

The tolerances of vacuum cast parts depend on the precision of the master pattern, the geometry and the type of casting material used. In general, expect a shrinkage rate of 0.15%. 

It is worth noting that the model needs to be able to withstand heating at 40°C.