Here
is a concise overview of the Vacuum Casting process in Rapid
Prototyping Service, including its procedure, required equipment, and
key characteristics.
Process Steps:
Master Pattern Creation: A high-quality master model (positive) is produced, typically using SLA (Stereolithography) or CNC Machining, to ensure excellent surface finish and dimensional accuracy.
Mold Making (Silicone Mold/Tooling):
The master pattern is placed in a casting box with gates and vents.
Liquid silicone rubber is poured over it and cured under vacuum to remove air bubbles.
The cured mold is then cut open, and the master pattern is removed, leaving a precise negative cavity.
Casting:
The two halves of the silicone mold are reassembled and placed in a vacuum casting machine.
Pre-measured polyurethane (PU) resin (often with properties mimicking final plastics like ABS, PP, or PC) is mixed and degassed under vacuum.
The resin is poured into the mold, which remains under vacuum to ensure complete cavity filling and avoid air entrapment.
Curing & Demolding: The filled mold is transferred to a heating chamber or oven to cure. Once hardened, the prototype part is removed from the mold.
Post-Processing: Parts undergo support removal, sanding, and optional painting or secondary machining.
Key Equipment:
Vacuum Casting Machine: The core equipment for degassing silicone and resin, and for the casting process itself.
Heating Chamber/Oven: For controlled curing of molds and cast parts.
Mold Making Frame/Casting Box: To contain the liquid silicone during mold creation.
SLA 3D Printer or CNC Machine: For producing the initial master pattern.
Characteristics:
Advantages:
High-Quality Surface Finish: Produces parts with excellent detail and smooth surfaces, often directly from the mold.
Material Versatility: A wide range of PU resins can simulate various engineering thermoplastics (rigid, flexible, transparent, high-temp).
Cost-Effective for Small Batches: Ideal for 10-50+ functional prototypes, pre-production, or bridge tooling runs, as one silicone mold can produce ~20-25 parts.
Fast Turnaround: Much quicker than injection molding for low volumes (days vs. weeks for tooling).
Limitations:
Limited Mold Life: Silicone molds degrade after ~20-30 uses, making the process unsuitable for mass production.
Part Size Constraints: Limited by chamber size of the vacuum casting machine (typically for parts under ~500x500mm).
Material Properties:
While close, PU resins are not 100% identical to the true
injection-molded thermoplastics in long-term performance or chemical
resistance.
In summary, Vacuum Casting is a bridge prototyping and low-volume production
technique that efficiently creates high-quality, functional parts from
silicone molds, filling the gap between one-off 3D printing and
high-volume injection molding.
