Shenzhen Alu Rapid Prototype Precision Co., Ltd.
Industry News
A vacuum casting machine produces high-quality polyurethane or resin parts by casting liquid material into silicone molds under vacuum — eliminating air bubbles and porosity to achieve near-injection-molded quality.
Core Operating Principle
The machine removes air from both the mold cavity and the liquid resin simultaneously before and during casting, so the material fills every detail without trapped gas or voids.
Main Components
Component | Function |
Vacuum chamber | Sealed enclosure where casting takes place |
Vacuum pump | Pulls chamber down to 1–5 mbar |
Mixing head / cups | Holds and mixes two-part resin (Part A + Part B) |
Tilting/pouring mechanism | Controlled pour of mixed resin into mold |
Heating oven | Cures cast parts at 60–80°C |
Silicone mold | Flexible mold made from master pattern |
Control panel | Timer, vacuum level, pour sequence control |
Viewing window | Observe pour and bubble release in real time |
Step-by-Step Process
Stage 1 — Master Pattern Preparation
A master pattern (CNC machined, 3D printed, or hand-finished) is created to exact dimensions
Surface finish on master transfers directly to silicone mold — so master must be finished to desired final quality
Sprues, vents, and parting lines are planned at this stage
Stage 2 — Silicone Mold Making
Master pattern is suspended in a casting frame
Liquid silicone (two-part RTV) is poured around the master under vacuum to remove bubbles
Silicone cures at room temperature (8–16 hours) or in oven (2–4 hours)
Mold is cut open along parting line and master removed
Mold is oven-dried at 60–70°C to remove moisture before casting
Stage 3 — Resin Preparation
Two-part polyurethane resin is pre-heated to 35–40°C to reduce viscosity
Parts A and B are measured by weight (typically 1:1 or 100:50 ratio per supplier spec)
Placed in separate cups inside the vacuum chamber
Stage 4 — Vacuum Mixing and Pouring
This is the core machine operation:
Chamber sealed
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Vacuum pump activated → chamber reaches 1–5 mbar (takes 30–60 sec)
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Resin cups degassed individually under vacuum (bubbles rise and collapse)
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Parts A and B mixed together under vacuum (30–60 sec mixing)
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Mold tilted/positioned → resin poured slowly through sprue
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Vacuum maintained during pour → air in mold cavity evacuated as resin fills
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Chamber vented to atmosphere → atmospheric pressure pushes resin into fine details
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Mold removed from chamber
Stage 5 — Curing
Filled mold placed in oven at 60–80°C for 30–90 minutes
Part solidifies and develops full mechanical properties
Cure time depends on resin type and wall thickness
Stage 6 — Demolding and Finishing
Silicone mold peeled away (flexible mold allows undercuts)
Sprues and vents trimmed
Part inspected, sanded, primed, or painted as required
Silicone mold reused — typically 20–50 shots per mold before degradation
Vacuum Level and Its Effect
Vacuum Level | Effect |
1–5 mbar (high vacuum) | Removes virtually all dissolved gas and air — best quality |
10–50 mbar | Good for most resins, minor micro-porosity possible |
100+ mbar | Insufficient — visible bubbles and voids likely |
No vacuum (open cast) | Significant porosity, poor surface on fine details |
Types of Vacuum Casting Machines
Bench-top / Small Chamber
Chamber size: 300×300×300mm typical
For small parts, jewelry, dental, electronics enclosures
Cost: $3,000–$15,000
Vacuum pump: single-stage rotary vane
Mid-size Industrial
Chamber size: 600×600×600mm to 1000×800×600mm
For automotive trim, consumer products, medical housings
Automated mixing ratio and pour control
Cost: $15,000–$60,000
Large Format
Chamber size: 1200×900×800mm+
For large panels, bumpers, full enclosures
Programmable tilt and pour sequence
Cost: $60,000–$200,000+
Resin Materials Used
Resin Type | Properties | Simulates |
Rigid polyurethane | Hard, stiff, paintable | ABS, PC, PP |
Flexible polyurethane | Rubber-like, Shore A 40–90 | TPE, TPU, silicone |
Transparent resin | Optically clear | PC, PMMA, glass |
High-temp resin | HDT up to 130–200°C | PA, PBT, engineering plastics |
Filled resin | Glass or carbon filled | Reinforced engineering plastics |
Flame retardant | UL94 V-0 rated | FR-ABS, FR-PC |
Quality Achievable
Parameter | Vacuum Casting Result |
Surface finish | Ra 0.8–3.2μm (replicates master exactly) |
Dimensional accuracy | ±0.1–0.3% of nominal dimension |
Wall thickness | Down to 0.5–1.0mm |
Porosity | Near zero with proper process |
Color matching | RAL or Pantone matched pigments added to resin |
Overmolding | Two-shot possible with sequential casting |
Advantages vs. Limitations
Advantages:
Near-injection-molded surface quality without expensive hard tooling
Silicone molds made in 1–2 days vs. weeks for steel tooling
Handles complex geometry and undercuts easily
Wide range of simulated production materials
Cost-effective for 1–50 parts
Limitations:
Each mold limited to 20–50 shots before dimensional drift
Slower cycle time than injection molding (30–90 min per part)
Part size limited by chamber dimensions
Resin properties not identical to true injection-molded thermoplastics
UV stability of polyurethane parts varies — may yellow over time
Typical Applications
Automotive interior and exterior prototype parts
Consumer electronics housings for testing and trade shows
Medical device enclosures for regulatory submissions
Aerospace cabin component mockups
Architectural models and display pieces
Short-run production bridge parts (while waiting for production tooling)