Silicone vacuum casting is a high-precision manufacturing process used to replicate complex parts—from electronic device shells to art prototypes—by eliminating air bubbles via vacuum pressure. O sucesso deste processo depende inteiramente da seleção dos materiais certos, que incluem moldes de silicone, protótipos básicos, agentes auxiliares, e resinas de fundição. This article breaks down each material category with clear comparisons, technical specs, e aplicações do mundo real, helping you optimize vacuum casting for accuracy, durabilidade, e custo-benefício.
1. Core Silicone Mold Materials: The Foundation of Casting
Silicone is the heart of vacuum casting molds—its flexibility and detail-retaining ability ensure replicas match the original prototype. Materials are categorized by curing mechanism and performance, each suited to specific needs.
| Silicone Type | Key Characteristics | Curing Parameters | Aplicações ideais |
| Condensation Silicone | – Releases small molecules (ethanol/acetic acid) during curing.- Baixo custo (30–50% cheaper than additive silicone).- Moderate shrinkage (2–3%), which may blur fine details.- Shore A hardness: 20–40 (macio, desmoldagem fácil). | – Mixing ratio: 100:2–5 (silicone:curing agent).- Tempo de cura: 4–8 horas (20°C–25°C).- No vacuum needed for mixing (but vacuum casting still requires bubble removal). | Simple parts with low precision demands: handicrafts, toy prototypes, and non-critical decorative items (por exemplo, plastic plant pots). |
| Additive (Platinum-Cure) Silicone | – No small molecule release during curing.- Ultra-low shrinkage (0.1–0,5%)—critical for high-precision parts.- Alta durabilidade (reusable 40–60 cycles, contra. 20–30 for condensation).- Shore A hardness: 30–60 (versatile for soft/hard parts). | – Mixing ratio: 1:1 (by volume/weight—easy to measure).- Tempo de cura: 2–4 horas (20°C–25°C; 1 hour at 50°C–60°C).- Requires vacuum defoaming (1–2 minutes at -0.1MPa) to avoid internal bubbles. | High-precision components: electronic device shells (TV remote casings), medical device parts (syringe nozzles), and automotive interior trim (botões do painel). |
| High-Temperature Resistant Silicone | – Withstands post-casting heat (200°C–300°C) for heat-curing resins.- Retains flexibility and shape at extreme temperatures.- Low shrinkage (0.3–0,8%) and high tear resistance. | – Mixing ratio: 100:5 (silicone:curing agent).- Tempo de cura: 6–10 hours (20°C–25°C; 2–3 hours at 80°C).- Must be cured in a temperature-controlled oven to activate heat resistance. | High-heat casting scenarios: metal alloy replicas (low-melting tin-lead alloys), thermoset resin parts (epoxy cured at 120°C), and aerospace component prototypes. |
| Transparent Silicone | – High light transmittance (85–95% after curing)—lets you monitor casting material flow.- Available in both condensation and additive types (additive preferred for precision).- Similar mechanical properties to non-transparent counterparts. | – Same curing parameters as matching non-transparent silicone (por exemplo, 1:1 ratio for additive transparent).- Requires extra care to avoid dust (which reduces transparency). | Componentes ópticos: light diffusers, transparent device housings (por exemplo, LED lamp covers), and prototypes where internal casting defects need visual inspection. |
2. Base Prototype Materials: The “Original Model”
The prototype (or master model) defines the shape of the final replica. It must be durable enough to withstand silicone pouring and compatible with silicone (no chemical reactions).
| Prototype Material | Key Traits | Compatibility with Silicone | Ideal para |
| 3D-Printed Resins (SLA/DLP) | – Alta precisão (±0,05 mm) for complex details.- Superfície lisa (Ra 0,8–1,6μm) reduces sanding time.- Available in rigid or flexible variants. | Excelente (no reaction with silicone). Use a light release agent (silicone oil) for easy demolding. | Rapid prototyping of intricate parts: jewelry patterns, electronic connector prototypes, and TV interface panels. |
| CNC-Machined Metals (Aluminum/Brass) | – Ultra-durable (reusable for 100+ mold makings).- High surface finish (Ra 0.4–0.8μm) for mirror-like replicas.- Resistente ao calor (suitable for high-temperature silicone). | Bom. Use petroleum jelly or specialized metal release spray to prevent silicone sticking. | Industrial-grade masters: automotive part prototypes (caixas de engrenagens), mold inserts for repeated use, and high-wear components. |
| CNC-Machined Resins/Wax | – Lower cost than metal.- Fácil de usinar (faster turnaround than metal).- Wax is ideal for low-temperature casting (melts away if needed). | Very good. Wax requires petroleum jelly (alcohol dissolves wax); resin uses standard release agents. | Art prototypes: sculptural replicas, custom candle molds, and low-volume decorative parts (por exemplo, ceramic vase masters). |
| Existing Finished Parts | – No need to design a new prototype (economiza tempo).- Must be clean and undamaged (scratches transfer to the mold). | Depends on the part material: plastic/metal works; rubber may react with condensation silicone. | Reverse-engineering projects: copying legacy parts (old TV knobs), replacement components for out-of-production equipment, and competitor product analysis. |
3. Auxiliary Materials: Ensure Process Smoothness & Mold Performance
These materials enhance mold durability, prevent defects, and optimize casting results—they’re often overlooked but critical for success.
| Auxiliary Material | Propósito | Usage Tips |
| Agentes desmoldantes | Create a barrier between silicone and the prototype/replica to avoid sticking. | – Petroleum Jelly: For wax prototypes (baixo custo, easy to apply).- Silicone Oil (100–500 cSt): For plastic/metal prototypes (no residue, won’t blur details).- Specialized Spray: For silicone-on-silicone casting (prevents chemical bonding).- Apply a thin, even layer—thick coats distort details. |
| Materiais de Reforço | Boost mold strength and wear resistance (prevents tearing during demolding). | – Fiberglass Cloth: Lay 1–2 layers over the silicone surface (after pouring, before curing) for large molds (por exemplo, TV back cover molds).- Silicone Fillers (Silica Powder): Mix 5–10% into silicone to increase hardness (Shore A +5–10) for high-wear parts. |
| Curing Agents/Catalysts | Control silicone curing speed and final properties. | – Condensation Catalysts: Use 2–5% (more = faster cure, but may reduce flexibility).- Platinum Catalysts: 1:1 ratio (fixed—cannot adjust cure speed without changing temperature).- Store in cool, dry places (heat deactivates platinum catalysts). |
| Sealants/Tapes | Prevent silicone leakage from the mold frame during pouring. | – Acrylic Sealant: For permanent frame seals (wood/metal frames).- Masking Tape: For temporary seals (plastic frames, easy to remove).- Apply 2–3 layers along frame edges to fill gaps. |
4. Casting Materials: The “Replica” Materials
After the silicone mold is made, these materials are poured (under vacuum) to create the final part. They’re chosen based on strength, flexibilidade, and end-use.
| Casting Material | Propriedades principais | Vacuum Casting Parameters | Aplicativos |
| Poliuretano (PU) Resina | – Fast curing (1–2 hours at 20°C–25°C; 30 minutes at 60°C).- Baixo custo ($20–40 per kg).- Versátil: rígido (Shore D 60–80) ou flexível (Shore A 30–50).- Boa resistência ao impacto (10–15 kJ/m²). | – Pressão de vácuo: -0.095 para -0.1MPa (removes bubbles).- Pouring temperature: 25°C–30°C (too hot = flash curing). | Small-batch functional parts: TV remote buttons, phone case replicas, and toy components. |
| Resina Epóxi | – Alta resistência (resistência à tracção: 50–80 MPa, contra. PU’s 30–50 MPa).- Resistente ao calor (120°C–180°C after curing).- Low shrinkage (0.5–1%)—good for structural parts. | – Pressão de vácuo: -0.1MPa (hold for 2–3 minutes to remove deep bubbles).- Tempo de cura: 4–6 horas (20°C–25°C; 1–2 hours at 80°C). | Componentes estruturais: suportes automotivos, electronic device housings (laptop bases), and medical tool handles. |
| Low-Melting Alloys (Tin-Lead/Bismuth) | – Ponto de fusão: 183°C–250°C (compatible with high-temperature silicone).- Metallic finish (no painting needed).- High density (feels like real metal). | – Pressão de vácuo: -0.1MPa (critical—metal bubbles cause cracks).- Pouring temperature: 20°C–30°C above melting point (avoids premature solidification). | Metal replicas: ferragens decorativas (maçanetas), scale model parts (miniature car bodies), and jewelry (metal pendants). |
| Gypsum/Plaster | – Ultra-low cost ($5–10 per kg).- Easy to color (mix pigments before pouring).- Frágil (low impact resistance—not for functional parts). | – Pressão de vácuo: -0.08 para -0.09MPa (too high = sucks out fine particles).- Tempo de cura: 24–48 horas (air-dry; no oven needed). | Art/teaching models: sculptural replicas, modelos anatômicos (skull casts), and classroom demonstrations. |
5. Yigu Technology’s Perspective on Silicone Vacuum Casting Materials
Na tecnologia Yigu, we’ve found that material mismatches cause 70% of vacuum casting failures—e.g., using condensation silicone for high-precision TV prototypes or low-temperature silicone for metal casting. Our key advice is: prioritize silicone type based on precision and end-use. For clients making electronic device shells (por exemplo, smartwatch casings), we always recommend additive silicone—it eliminates shrinkage-related defects, salvando 30% in rework costs. For budget-sensitive projects (por exemplo, réplicas de artesanato), condensation silicone works but requires extra sanding to fix detail blurring. We also emphasize testing material compatibility: a client once used a rubber prototype with condensation silicone, causing the rubber to degrade—switching to a 3D-printed resin prototype solved the issue. Finalmente, don’t skip reinforcement for large molds: fiberglass-clad silicone molds last 2x longer than unreinforced ones, critical for small-batch production (50+ réplicas).
6. Perguntas frequentes: Common Questions About Silicone Vacuum Casting Materials
Q1: Can I use condensation silicone for high-precision parts (por exemplo, electronic connectors with 0.1mm slots)?
A1: No—condensation silicone’s 2–3% shrinkage will close 0.1mm slots or blur fine details. Use additive silicone instead (0.1–0.5% shrinkage) to retain precision. Por exemplo, a 0.1mm slot cast with additive silicone will remain 0.095–0.1mm, while condensation silicone will reduce it to 0.07–0.08mm (too small for connectors).
Q2: What casting material should I use for a functional TV remote prototype that needs to withstand drops?
A2: Use rigid polyurethane (PU) resina (Shore D 70–80) or epoxy resin. PU resin offers better impact resistance (15 kJ/m² versus. epoxy’s 10 kj/), making it ideal for drop-prone parts. Test by dropping the replica from 1m onto a hard surface—PU resin should not crack, while gypsum/plaster will shatter immediately.
Q3: Why does my high-temperature silicone mold still deform when casting low-melting alloy?
A3: This usually stems from two issues: (1) The silicone wasn’t fully cured (insufficient oven time at 80°C—re-cure for 2 extra hours). (2) The alloy pouring temperature is too high (exceeding the silicone’s service limit—keep it 20°C–30°C above the alloy’s melting point, not higher). Por exemplo, a 200°C silicone mold will deform if poured with 300°C alloy—lower the temperature to 270°C (for a 250°C melting point alloy).