Silicone Molding, An Ultra-Clean Approach

FMI has experience designing manufacturing processes to accommodate all types of silicone molding.

We can advise your team on which type of molding best suits your particular part, and design the best production process to insure the highest quality and repeatability.

Call (847) 350-1535 or Contact FMI for more information.

 

Medical Molding

Silicone elastomers are typically molded through three main methods:

• Liquid injection molding (LIM)
• Transfer molding
• Compression molding

The LIM process, often chosen for high-volume applications, employs lower pressures and higher temperatures than the other molding methods — 250 to 2000 psi injection pressure and temperatures of 245° to 485°F.

By contrast, transfer and compression molding processes typically operate at pressures of 2000 to 8000 psi and temperatures of 200° to 370°F.

When designing for the molding process FMI helps you take into account the material shrinkage rate, which can range from 2% to 4% depending on the type of silicone.

During the molding process, the three variables that must be controlled are time, temperature, and pressure. The temperature must be high enough to minimize cure times, yet low enough to prevent material scorching. The selected pressure level must allow for complete mold filling while permitting the escape of air. The process must also be optimized to prevent voids and flash.

FMI has mastered the precise timing of all these functions, critical for the production of consistently high-quality, fully cured parts.

 

Liquid Injection Molding

Liquid Injection Molding (LIM) of silicone rubber offers many advantages over the other molding processes.

In the LIM process, pumping systems deliver the two-part liquid silicone (catalyst and crosslinker) directly into a mixer, which is then injected directly into the mold cavity in a completely closed process.

Because our system is closed, contamination and particulates are easily avoided. Additionally, LIM minimizes human interaction, which can improve process variation.

Because of these advantages, the LIM process is inherently clean and fast.

LIM is typically best suited for high volume production; however, FMI has developed numerous techniques for manufacturing low to medium volume production runs of silicone components while still taking advantage of the LIM process.

 

Transfer and Compression Molding

Transfer and compression molding of silicone are both widely accepted methods and are heavily used for medical products.

Unlike the LIM process, transfer and compression molding are more labor intensive and require the premixing of materials on a two-roll mill. Also, because these processes must be operated at lower temperatures, operating cycles are longer.

Given the slower curing times, it is not uncommon to see large molds with 100 cavities or more for diaphragms, bottle closures, O-ring seals, and other applications.

In transfer molding, a hydraulic ram displaces rubber through the gates and sprues into the cavities. Compression molding differs from Transfer in that the rubber is physically placed into the cavities, and it is the closing action of the mold that completes the fill.

 

Micro-molding

Smaller and more complex part geometries present unique challenges for the manufacturer.

FMI has extensive experience with the micro molding of silicone medical components. We have the ability to hold tolerances in the micron range, and can mold parts with even the most complex features. This includes insert molding and overmolding of silicone to metal and various substrates.

 

ISO Classifications

FMI exclusively molds silicone rubber for the medical device and health care industries. Specializing in silicone components for long-term implantable devices, FMI also molds parts for short-term implantable and disposable applications.

Our dedicated clean room facility provides unparalleled cleanliness and quality allowing us to manufacture from ISO class 5 to ISO class 7.

We utilize state of the art environmental controls and quality systems to ensure that your components are manufactured and delivered to you in pristine condition.

The chart below shows the various ISO classes and the requirements for each.

 

Class maximum particles/m³ ≥0.1 µm ≥0.2 µm ≥0.3 µm ≥0.5 µm ≥5 µm ≥5 µm FED STD 209E equivalent ISO 1 10 2           ISO 2 100 24 10 4       ISO 3 1,000 237 102 35 8   Class 1 ISO 4 10,000 2,370 1,020 352 83   Class 10 ISO 5 100,000 23,700 10,200 3,520 832 29 Class 100 ISO 6 1,000,000 237,000 102,000 35,200 8,320 293 Class 1000 ISO 7       352,000 83,200 2,930 Class 10,000 ISO 8       3,520,000 832,000 29,300 Class 100,000 ISO 9       35,200,000 8,320,000 293,000 Room air

 

Get To Market More Quickly And Cost Effectively

FMI has extensive experience with ultra clean silicone medical products. Let FMI create turnkey solutions for your medical device components.

Call (847) 350-1535 or Contact FMI to discuss your next medical silicone project.