1. Core Definition and Working Principle
Silicone vacuum casting, also known as vacuum injection molding, is a mainstream steel‑mold‑free small‑batch replication technology in the rapid prototyping industry.
It works by taking a high‑precision prototype produced via SLA 3D printing or CNC machining as the master model to create a flexible silicone mold. Under vacuum negative pressure, PU polyurethane resin is poured into the mold cavity. After degassing and curing, plastic parts identical to the prototype are replicated rapidly.
Compared with traditional steel‑mold injection molding, vacuum casting removes air thoroughly in a vacuum environment, resulting in bubble‑free parts with high detail reproduction. Thanks to the flexibility of silicone molds, parts with undercuts, deep grooves and complex curved surfaces can be demolded smoothly without complicated core‑pulling mechanisms, making it ideal for new‑product verification and small‑batch production.
2. Complete Process of Silicone Vacuum Casting
Step 1: Fabricate High‑Precision Master Model
The original part is made by SLA stereolithography 3D printing or CNC precision carving to ensure accurate dimensions, smooth surfaces and intact structures. The precision of the master model directly determines the quality of cast parts. Wall thickness and draft angles are optimized in advance to avoid shrinkage, deformation and incomplete filling in later stages.
Step 2: Pre‑Treat Master Model and Build Mold Frame
The master model is polished, cleaned and coated with release agent evenly. It is then fixed inside a mold frame with well‑designed gates, runners and vents to guarantee complete filling and adequate air exhaust during pouring.
Step 3: Pour and Cure Silicone Mold
Mold silicone is mixed with curing agent, stirred and degassed in a vacuum chamber before being poured to fully wrap the master model. A second vacuum treatment is carried out, followed by thermal curing in an oven to form an integrated flexible silicone mold.
Step 4: Split Mold, Remove Master Model and Trim Mold
After full curing, the silicone mold is cut open along the parting line to take out the original master model. Flash and residues inside the cavity are cleaned, and minor defects are repaired to finish the reusable silicone mold.
Step 5: Vacuum Pouring and Molding
PU resin with suitable hardness, toughness and transparency is selected according to product requirements. The resin and curing agent are mixed, stirred and degassed, then injected into the silicone mold at a steady rate in a vacuum environment to achieve full filling without air holes.
Step 6: Thermal Curing and Demolding
The mold is placed in a temperature‑controlled chamber for full curing. Once the material is completely set, the flexible mold is opened to take out the finished part, and the silicone mold can be reused multiple times.
Step 7: Post‑Processing and Finishing
Sprues and runners are trimmed, edges are sanded. Additional surface treatments such as painting, sandblasting, screen printing and coloring can be applied to achieve a finish comparable to injection‑molded parts.
3. Core Advantages
Low cost: No expensive steel mold is required. Silicone molds cost far less than injection molds, significantly cutting investment in R&D and small‑batch trial production.
- Short lead time: Small‑batch finished parts can be completed within 1 to 3 days from the master model, much faster than traditional injection molding for rapid sample delivery.
High detail reproduction: Vacuum forming produces dense parts with minimal bubbles, accurately replicating fine textures, thin walls and complex curved surfaces.
Strong demolding capability: Flexible silicone allows direct demolding of parts with undercuts and irregular shapes without complex core‑pulling structures.
- Flexible material options: PU resin can simulate the properties of ABS, TPU, PC, nylon and other plastics. Hardness, softness, transparency and color can all be customized as needed.
