Silicone mold injection molding is an advanced manufacturing technology that uses liquid silicone rubber (LSR) as raw material, injecting it into high-precision molds under controlled temperature and pressure to produce high-quality silicone products. Unlike traditional manual mold making, it excels in mass production, high dimensional accuracy, and stable product performance—making it a core process in medical, electronic, and automotive industries. But what are its core principles? How to control key processes? And how to address its unique challenges? This article answers these questions in detail.
1. Core Principles & Material Characteristics
To understand silicone mold injection molding, we first break down its working mechanism and the properties of its key raw material—liquid silicone.
A. Core Working Principle
The process follows a simple but precise 因果链 (cause-and-effect chain):
- Raw Material Melting: Liquid silicone (two-component: main agent + curing agent) is fed into the injection machine’s barrel, where it is heated to a flowable state (no melting—silicone is thermoset, so this step softens it for injection).
- High-Pressure Injection: The injection machine pushes the softened silicone into a high-precision mold cavity (tolerance ±0.01mm) at a controlled speed (5–20mm/s) y presión (10–50MPa).
- Curación & Vulcanization: El molde se calienta (120–180°C) to trigger a chemical reaction in the silicone, turning it from liquid to elastic solid. Curing time depends on product thickness—e.g., 1mm-thick parts take 10–15 seconds; 10mm-thick parts take 60–90 seconds.
- Desmoldeo & Refinamiento: Una vez curado, el molde se abre, and the product is ejected. Postprocesamiento (desbarbado, guarnición) removes excess material, resulting in a finished part.
B. Key Material: Liquid Silicone Rubber (LSR)
LSR’s unique properties determine the process’s advantages. The table below highlights its critical characteristics:
| Material Characteristic | Specific Performance | Role in Injection Molding |
| Fluidity | Low viscosity (5,000–20,000 cP) | Flows into micro-details of the mold (p.ej., 0.1mm-thick sealing lips) |
| Heat Resistance | Withstands -60°C to +250°C (short-term +300°C) | Suitable for high-temperature applications (p.ej., automotive engine gaskets) |
| Chemical Stability | Resists acids, álcalis, aceites, and solvents | Ideal for medical devices (sterilized with alcohol) and electronic parts (resists coolants) |
| Elasticidad | Elongation at break >500%; Shore hardness 20–80A | Ensures products (p.ej., phone buttons, juntas tóricas) maintain flexibility after repeated use |
| Biocompatibilidad | Medical-grade LSR meets FDA 21 CFR §177.2600 | Safe for skin-contact products (p.ej., baby pacifiers, medical catheters) |
2. Step-by-Step Production Process
Silicone mold injection molding follows a standardized, linear workflow—each step requires strict parameter control to avoid defects.
Paso 1: Raw Material Preparation & Pruebas
- Component Mixing: Blend LSR main agent and curing agent in a precise ratio (common 1:1 o 10:1) using an automated mixer. For colored products, add 1–3% non-toxic pigments to the mixture.
- Inspección de calidad: Conduct 3 key tests:
- Viscosity Test: Ensure viscosity is 5,000–15,000 cP (too high = poor flow; too low = leakage).
- Curing Test: Cure a small sample at 160°C for 30 seconds—check for full solidification (no sticky surface).
- Impurity Check: Filter the mixture through a 5μm sieve to remove particles (prevents mold clogging).
Paso 2: Diseño de moldes & Fabricación
Molds are the “heart” of the process—their precision directly impacts product quality.
- Design Considerations:
- Gate Location: Place gates (injection inlets) at thick sections to avoid air traps. For small parts (p.ej., conectores electronicos), use pinpoint gates (0.5–1mm diameter).
- Sistema de enfriamiento: Add water channels around the cavity to control mold temperature (±2°C tolerance)—prevents uneven curing.
- Tratamiento superficial: Apply chrome plating (5–10μm thickness) or nitriding to the mold surface. This improves wear resistance (extends mold life to 100,000+ ciclos) and release performance (reduces sticking).
- Manufacturing Equipment: Use CNC machining centers (accuracy ±0.005mm) to mill the mold cavity. For complex shapes (p.ej., componentes de dispositivos médicos), add EDM (Mecanizado por descarga eléctrica) for micro-details.
Paso 3: Injection Molding Parameter Setup
Key parameters must be optimized—incorrect settings cause defects like bubbles or shrinkage. The table below lists critical parameters and their ideal ranges:
| Parameter | Ideal Range | Impact of Incorrect Settings |
| Barrel Temperature | 40–60°C (zone 1: 40°C; zone 2: 50°C; zone 3: 60°C) | Too high (>70°C) = premature curing (blocks the barrel); too low (<30°C) = poor flow |
| Injection Pressure | 15–30MPa | Too high (>40MPa) = mold deformation; too low (<10MPa) = incomplete cavity filling |
| Injection Speed | 8–15mm/s (staged: slow start → fast middle → slow end) | Too fast (>20mm/s) = air trapping (burbujas); too slow (<5mm/s) = cold slugs (uneven texture) |
| Temperatura del molde | 140–160°C | Too high (>180°C) = over-curing (brittle parts); too low (<120°C) = under-curing (sticky surface) |
| Tiempo de curado | 10–120 seconds (1 second per mm of thickness) | Too short = under-curing; too long = reduced production efficiency |
Paso 4: Curación, Desmoldeo & Postprocesamiento
- Curación: The mold remains closed for the set time—use a mold temperature controller to maintain stable heat.
- Desmoldeo: Use robotic ejectors (para la producción en masa) or manual tools (para lotes pequeños) to remove parts. Apply a thin layer of silicone release agent if sticking occurs (avoid excess—causes surface defects).
- Postprocesamiento:
- Desbarbado: Trim gate residues with a laser cutter (for precision parts) or sharp scissors (for non-critical parts).
- Cleaning: Wash parts with deionized water to remove release agent residue.
- Secondary Vulcanization (Optional): For high-temperature parts (p.ej., automotive seals), bake at 200°C for 2–4 hours to improve heat resistance.
3. Ventajas & Challenges: A Comparative Analysis
Silicone mold injection molding has clear strengths compared to traditional manufacturing methods (p.ej., compression molding, manual casting). It also faces unique challenges—understanding both helps users decide if it’s the right process.
A. Advantages Over Traditional Methods
| Advantage | Silicone Mold Injection Molding | Moldeo por compresión | Manual Casting |
| Production Efficiency | Alto (30–60 parts per minute for small components) | Medio (5–10 parts per minute) | Bajo (1–2 parts per hour) |
| Precisión dimensional | ±0,01 mm (ideal for precision parts) | ±0,1 mm (limited by mold pressure) | ±0,5 mm (human error) |
| Product Consistency | 99.5% uniformity (proceso automatizado) | 90% uniformity (depende de la habilidad del operador) | 70% uniformity (high variability) |
| Complexity Handling | Excelente (can produce parts with undercuts, micro-holes) | Poor (requires split molds for complexity) | Very poor (limited to simple shapes) |
| Material Waste | Bajo (<5% scrap—excess can be recycled) | Medio (10–15% scrap) | Alto (20–30% scrap) |
B. Key Challenges & Mitigation Strategies
| Desafío | Root Cause | Mitigation Strategy |
| High Initial Investment | Mold manufacturing (Mecanizado CNC + tratamiento superficial) costos \(10,000–\)100,000; injection machines cost \(50,000–\)200,000 | – Para lotes pequeños: Use shared molds (reduces cost by 50%).- For long-term projects: Choose high-wear-resistant mold materials (p.ej., acero H13) to extend life (100,000+ ciclos) |
| Mold Clogging | Impurities in LSR or low fluidity | – Filter LSR through 5μm sieves before injection.- Preheat LSR to 50°C (improves fluidity) |
| Bubble Formation | Air trapped during injection or incomplete venting | – Add vent grooves (0.01–0.02mm depth) to the mold.- Use vacuum-assisted injection (removes air from the cavity) |
| Shrinkage Defects | Uneven cooling or over-curing | – Optimize mold cooling channels (ensure uniform temperature).- Add 1–2% shrinkage allowance to the mold design |
4. Application Fields: Where It Shines
Silicone mold injection molding is widely used in industries that demand precision, durabilidad, and biocompatibility. The table below highlights key applications with specific examples:
| Industria | Typical Products | LSR Grade | Key Process Requirements |
| Dispositivos médicos | puntas de catéter, surgical instrument gaskets, baby pacifiers | Medical-grade (FDA 21 CFR §177.2600) | – Cleanroom production (Clase 100,000).- No release agent (avoids contamination).- Biocompatibility testing post-production |
| Electrónica | Phone buttons, LED lamp seals, sensor O-rings | Industrial-grade (high insulation) | – Alta precisión (±0.005mm for button travel).- Low volatility (no VOCs to damage electronics) |
| Automotor | Engine gaskets, fuel system seals, componentes del tablero | High-temperature grade (resists 250°C) | – Resistencia química (a los aceites, coolants).- Vibration resistance (elongation >500%) |
| Bienes de consumo | Silicone kitchen utensils (spatulas), waterproof watch bands | Food-grade (Aprobado por la FDA) | – Non-toxic pigments.- Smooth surface (Real academia de bellas artes <0.8µm) for easy cleaning |
5. Yigu Technology’s Perspective on Silicone Mold Injection Molding
En Yigu Tecnología, we see silicone mold injection molding as a cornerstone of high-precision manufacturing—especially for industries like medical and automotive. For medical clients, our custom injection molds (tolerance ±0.008mm) and medical-grade LSR have enabled the production of 100,000+ catheter tips with 0% biocompatibility failures. For automotive partners, our high-temperature LSR (resists 280°C) and optimized cooling systems reduce engine gasket shrinkage to <0.5%, improving product lifespan by 30%.
We’re addressing key challenges by: 1) Developing low-cost mold materials (p.ej., coated aluminum) that cut mold costs by 40% mientras se mantiene 50,000+ ciclos; 2) Integrating AI into parameter control (automatically adjusts temperature/pressure to reduce defects by 25%). Our goal is to make this technology accessible to mid-sized businesses—balancing precision with affordability.
Preguntas frecuentes
- ¿Cuál es la cantidad mínima de pedido? (Cantidad mínima de pedido) for silicone mold injection molding?
MOQ depends on mold cost: For standard parts (p.ej., juntas tóricas), MOQ is 10,000–50,000 units (to offset mold costs). For custom parts, we offer shared molds with MOQ as low as 1,000 unidades (ideal for small-batch testing).
- Can silicone mold injection molding produce transparent silicone products?
Yes—use high-purity LSR (impurity content <0.1%) and polished molds (Real academia de bellas artes <0.02µm). We’ve produced transparent medical connectors with 90% light transmittance, meeting optical requirements for device visualization.
- How long does it take to develop a custom silicone mold and start production?
Mold development takes 4–6 weeks (Mecanizado CNC + pruebas). After mold approval, production can start within 1 semana. Para proyectos urgentes (p.ej., medical device emergencies), we offer expedited mold development (2–3 semanas) with priority production.