The principle of liquid silicone micro-precision injection molding technology

Liquid silicone micro-precision injection molding technology is a high-end manufacturing process that combines traditional injection molding with the properties of liquid silicone materials. It is specifically designed for producing silicone parts with minute dimensions, intricate structures, and stringent requirements.

Liquid Silicone Injection Molding
I. Overview of Core Principles

The core principle of liquid silicone micro-precision injection molding is as follows: Two components (component A and component B) of liquid silicone are precisely metered and mixed uniformly at low temperature. Then, through a precision injection system, it is injected into a preheated, high-precision mold cavity under low pressure. Within the mold, the silicone undergoes a rapid vulcanization (cross-linking) reaction due to heating, transforming from a liquid to a solid elastomer, thus obtaining the final product.

Its biggest difference from traditional thermoplastic injection molding is that the material is liquid, not solid, and the curing process is a chemical cross-linking reaction rather than a physical cooling phase change.

II. Key Components and Principles of the Technical System

A complete LSR micro-precision injection molding system mainly includes the following key components:

1. Feeding and Metering System

Principle: LSR materials are stored and transported separately as two components, A (base polymer + catalyst) and B (base polymer + crosslinking agent), typically in drums or via a pumping system. This is to prevent pre-crosslinking before they enter the machine.

Precision Metering: High-precision gear metering pumps or plunger pumps are used to deliver components A and B in a very precise ratio (typically 1:1). Metering accuracy directly determines the chemical stability and physical properties of the final product.

2. Dynamic Mixing System

Principle: The precisely metered components A and B are fed into a static mixer.

Static Mixer: Its interior consists of a series of special spiral elements that continuously cut, divide, and recombine the liquid flow, achieving thorough and uniform mixing of components A and B without any moving parts. The length and internal structure design of the mixer ensure complete mixing.

3. Precision Injection Molding Unit

Principle: A uniformly mixed liquid silicone rubber is delivered to the injection cylinder. A precision screw or plunger pushes the rubber material from the front of the barrel into the mold at a low temperature (usually maintained by a water cooling system, such as 20-30°C).

Key Points:

Low Temperature: Prevents premature vulcanization of the rubber material within the barrel.

Low Injection Pressure: Due to the low viscosity and excellent flowability of LSR, the injection pressure is typically much lower than that used in plastic injection molding. This helps protect the intricate mold structure and inserts such as chips.

Precision Control: Precise closed-loop control of injection speed, pressure, and holding pressure processes ensures the integrity and stability of filling micro-cavities.

4. High-Temperature Mold System

Principle: The mold is crucial for molding; it is heated to the vulcanization temperature (typically 150°C - 200°C).

Heating Method: Uniform heating is typically achieved using built-in heating rods or a hot oil/hot water circulation system.

Microstructure Design: The mold cavity and runner system are precision-machined (e.g., mirror polishing, micro-electrode electrical discharge machining), achieving dimensional accuracy down to the micrometer level. Cold runner systems are widely used to prevent the resin from solidifying within the runners, reducing waste.

Ventilation Design: Due to the high fluidity of LSR and the potential for gas generation during curing, precise venting channels are crucial to prevent trapped gas from causing material shortages or scorching in the product.

5. Curing and Ejection

Principle: When the mixed LSR is injected into the hot mold, the cross-linking reaction is triggered and proceeds rapidly. Within the set vulcanization time, the liquid silicone completely transforms into a solid elastomer.

Demolding: After molding, the mold opens, and the tiny finished product is ejected through a precise ejector system (or using compressed air). Due to the elasticity of silicone, even complex structures are easy to demold.

III. Process Flow Steps

Integrating the above systems, the process flow is as follows:

1. Material Preparation and Metering: Components A and B are precisely drawn from the material tank at low temperatures using metering pumps.

2. Mixing: Components A and B are thoroughly mixed in a static mixer to form a homogeneous injection compound.

3. Injection: In a cooled injection unit, a screw/plunger injects a measured amount of the mixed compound into the preheated mold cavity at low speed and low pressure.

4. Filling and Holding Pressure: The compound rapidly fills the entire cavity, including the microstructure. A brief holding pressure phase ensures that the volume difference caused by cross-linking shrinkage is compensated.

5. Vulcanization: The compound is held in the high-temperature mold for a period of time to complete the cross-linking and curing reaction.

6. Mold Opening and Ejection: The mold opens, and the molded micro-precision silicone parts are ejected.

7. Process Repetition: The entire cycle is automatically repeated, with the compound remaining liquid in the cold runner for the next injection cycle.

IV. Technical Features and Advantages

Extremely high dimensional accuracy and repeatability: Benefiting from precise metering, injection control, and a stable vulcanization process.

Superior Detail Replication Capability: Low-viscosity LSR can perfectly replicate micron-level structures on molds.

High Efficiency and Automation: Short cycle time enables 24/7 fully automated production.

Clean and Pollution-Free: LSR itself is a medical-grade material, with no byproducts in the process, making it suitable for demanding fields such as medical and optical applications.

Strong Integration Capability with Inserts: Easily overmolded onto microelectronic components (such as sensor chips) and metal parts.

V. Typical Application Areas

Medical Devices: Microcatheters, valves, seals, drug delivery components, implantable device assemblies.

Microelectronics and Optoelectronics: Camera module sealing, optical lens encapsulation, connector sealing sleeves, MEMS sensor encapsulation.

Automotive Electronics: Sealing and protection for various microsensors.

Consumer Electronics: Waterproof seals for smart wearable devices, microacoustic components (such as speaker diaphragms).

In summary, liquid silicone micro-precision injection molding technology is an advanced manufacturing technology that perfectly presents the excellent properties of liquid silicone on a microscale by precisely controlling materials, temperature, pressure and time. It is one of the core processes for the production of modern high-precision and high-reliability micro products.