Liquid silicone rubber (LSR) injection molding is widely used in medical devices, automotive electronics, baby products, and precision sealing components due to its excellent biocompatibility, high-temperature resistance, stability, and flexibility. As a key tool for LSR molding, the mold design directly determines product quality, production efficiency, service life, and dimensional accuracy. Compared with conventional plastic molds, LSR molds have extremely strict requirements for sealing, venting, cooling, dosing, and demolding. Below are the key design points for liquid silicone rubber injection molds to support stable mass production and high-quality molding.
The first key point is precision sealing structure design. LSR materials are low-viscosity fluids before curing and easily penetrate into small gaps during injection, leading to flashing and difficulty in demolding. Therefore, the entire mold cavity, parting surface, slider inserts, and ejector pins must adopt zero-clearance or micro-sealing structures. In general, the matching clearance of the cavity and core should be controlled below 0.005 mm to prevent material leakage. For side core-pulling structures, sealing rings or elastic pressure plates should be used to assist compression. In addition, the feed inlet and nozzle connection area must adopt a self-sealing structure to avoid material backflow and overflow during injection.
Effective sealing not only improves product surface quality but also reduces cleaning and maintenance costs during mass production.
The third key point is balanced and stable cooling system design. LSR needs to be cured under a certain temperature, usually between 110°C and 150°C. Uniform temperature control directly affects curing speed, shrinkage rate, and dimensional stability. Therefore, the cooling system of LSR molds should adopt a “uniform distribution, independent circulation” design. The water channel should be as close as possible to the cavity surface while ensuring mold strength, and the distance should be kept consistent to avoid local overheating or under-curing. For multi-cavity molds, it is recommended to use a separate water circuit for each cavity to achieve consistent temperature control. In addition, temperature sensors can be installed in the mold to realize real-time monitoring and closed-loop control, ensuring temperature fluctuations within ±2°C, which is crucial for precision silicone products.
The fourth key point is glue feeding and runner system design. Since LSR is supplied by a two-component mixing machine, the runner system must avoid dead corners and material retention to prevent premature curing and contamination. Hot runner systems are preferred for LSR molds to reduce material waste and improve filling stability. If using a cold runner, the runner should be short, thick, and smooth, with a rounded transition to reduce flow resistance. The gate size is also critical: for precision parts, a point gate or needle gate with a diameter of 0.6–1.2 mm is suitable; for large-area products, a film gate or edge gate can be used to ensure stable filling. The gate position should be selected to avoid affecting appearance and function, and to facilitate post-processing.
The fifth key point is demolding and ejection system design. After curing, LSR products are flexible and easy to deform or tear during ejection. Therefore, the ejection force must be uniform, and sharp corners should be avoided. Commonly used ejection methods include ejector pins, ejector sleeves, stripper plates, and air ejectors. For thin-walled, soft, or precision products, air ejection is the best choice because it can achieve non-destructive demolding. The surface roughness of the cavity is also critical; mirror-polished surface (Ra ≤ 0.025 μm) can reduce adhesion and make demolding smoother. In addition, the demolding angle should be appropriately increased, generally 3°–5° or higher, to avoid pulling and damaging the product during ejection.
The sixth key point is material selection and service life design. LSR molds need to withstand long-term heating, frequent switching, and chemical corrosion; thus, mold materials must have high hardness, corrosion resistance, and stability. Commonly used materials include pre-hardened mold steel, stainless steel (such as SUS420, S136), and high-speed tool steel. The cavity surface is usually heat-treated and mirror-polished to improve service life and surface quality. For molds with sliders or inserts, wear-resistant guide posts and wear blocks should be used to maintain long-term movement accuracy. A scientifically designed LSR mold can normally achieve millions of molding cycles under stable maintenance.
The seventh key point is compliance and compatibility design for special industries. Especially for medical-grade LSR products, molds need to meet cleanliness, traceability, and non-pollution requirements. The mold should be easy to clean and disinfect, avoid dead corners that can accumulate dirt, and use non-toxic and rust-proof materials. In addition, medical molds need to be equipped with a complete record system to facilitate production process monitoring and quality traceability. For food-grade and baby products, molds must also meet food-grade safety standards to ensure that products do not produce harmful substances during use.
In summary, liquid silicone rubber injection mold design is a comprehensive system that requires balanced consideration of sealing, venting, temperature control, runner, ejection, material selection, and service life. A high-quality LSR mold can achieve stable production, high yield, high precision, and long life, providing strong support for medical, automotive, consumer, and industrial products. With the increasing demand for high-performance silicone products, LSR mold design will continue to develop toward higher precision, intelligence, and integration, becoming a key competitiveness in the field of precision molding.
March. 30, 2026
February. 25, 2026
