Aerospace Liquid Silicone Rubber Injection Molding

Q: What are Benefits of Liquid Silicone Rubber Injection Molding in Aerospace?

Highly automated manufacturing, Short cycle times, Cost-effective, Precision, Limitless design possibilities, Durability, Customizable

Liquid silicone rubber (LSR) is a versatile elastomer that can be injection molded for various uses. It is durable, highly flexible and elastic, and resistant to harsh chemicals and temperatures. It is available in a range of durometer/Shore A hardnesses and maintains flexibility to -60ºF. Because it also has a low compression set, LSR is often used for seals, gaskets, and cushioning pads.

Elastomer Technologies, Inc. (ETI) specializes in injection molding of liquid silicone rubber for the aerospace sector. Learn about the benefits of LSR material, our molding process, and some of the many aerospace applications that rely on injection molded LSR parts.

Benefits of Liquid Silicone Rubber Injection Molding in Aerospace

LSR is a highly flexible, elastic, and durable material. It is well-suited to injection molding for several reasons, including:

Highly automated manufacturing. CNC injection molding machines and presses increase throughput.
Short cycle times. LSR requires a short time under pressure in the mold, between 30 seconds and 2 minutes, so more parts can be made with a smaller number of molds.
Cost-effective. Fast cycle times and precision injection mean high production rates and less money spent on labor and de-flashing.
Precision. Using fewer molds limits variation between parts for consistent dimensions, tight tolerances, and higher quality.
Limitless design possibilities. LSR has excellent flow and fills mold cavities completely, allowing for intricate, thin, and complex parts.
Durability. LSR stays flexible in temperatures as low as -60ºF, resists harsh chemicals, and has a low compression set, for a long service life.
Customizable. LSR is naturally transparent and smooth but can be colored with pigments or molded with textures and surface finishes.

LSR Injection Molding Process for Aerospace Components

Injection molding is a highly automated process that is efficient and consistent. Basic steps include:

A computerized CAD model of the part is created, noting dimensions, tolerances, and other critical design features.
In many cases, prototypes are created to fine-tune the shot size, molding time, amount of flashing produced, and finished part dimensions.
Tooling and mold components are machined with CNC equipment to meet part requirements, mold cavities, gates, cooling channels, and guiding elements. If necessary, these components are polished or further machined to produce desired part surface finishes.
The two liquid components that combine to form LSR (part A and part B) are mixed and pumped into an injection machine, then the machine injects a measured volume of LSR (i.e., a shot) into the preheated mold. The mold is clamped shut while the material vulcanizes and solidifies.
In most cases, finished parts are ejected from the molds with an automated actuator; however, depending on part features and design, manual removal may be required.
Any accumulated flashing on the part’s edges is removed, either by manual trimming or cryogenic de-flashing.

Injection Molding Process

Injection molding is a highly automated process that is efficient and consistent. Basic steps include:

1 Gather the Design Elements

Gather the Design Elements

A computerized CAD model of the part is created, noting dimensions, tolerances, and other critical design features.

2 Create a Prototype

Create a Prototype

Prototypes are frequently developed to optimize various parameters such as shot size, molding time, the amount of flashing, and the final part dimensions.

3 Develop the Mold Components and Tools

Develop the Mold Components and Tools

Tooling and mold components are machined with CNC equipment to meet part requirements, mold cavities, gates, cooling channels, and guiding elements.

If necessary, these components are polished or further machined to produce desired part surface finishes.

4 Prepare the Liquid Silicone Rubber

Prepare the Liquid Silicone Rubber

The two liquid components that combine to form Liquid Silicone Rubber (LSR) are mixed together and pumped into an injection machine.

5 Inject the Liquid Into the Mold

Inject the Liquid Into the Mold

A precise volume of LSR (a shot) is injected into the preheated mold and then clamped shut, allowing the material to vulcanize and solidify.

6 Properly Remove the Finished Product

Properly Remove the Finished Product

Eject the finished part from the mold using an automated actuator.

However, manual removal may be necessary depending on the part’s features and design.

7 Inspect and Test the Completed Part

Inspect and Test the Completed Part

Post-removal, parts are inspected for dimensional accuracy, material consistency, flashing, and color.

Testing and QC processes are conducted using Coordinate Measuring Machines (CMMs), computer-aided and manual visual inspection, and thermal imaging to ensure final products meet customer requirements.

Quality Control and Compliance Standards

In manufacturing, quality is cumulative; therefore, ETI incorporates several quality control measures throughout the injection molding process.

Prior to full production, CAD modeling and prototyping provide valuable insight into part manufacturability, needed shot volume, and potential design challenges.

Critical properties like elasticity and flexibility are tested based on ASTM D412 testing protocols. In addition, completed parts are inspected for dimensional accuracy, material consistency, flashing, color, and other characteristics. Coordinate measuring machines (CMMs) and computer-aided vision inspection, as well as manual inspection and thermal imaging can all be used to ensure finished parts meet customer requirements.

ETI is ISO 9001:2015 and ISO 1438:2016 certified and committed to quality management and production practices.

Liquid Silicone Rubber Injection Molding Aerospace Applications

LSR injection molding is commonly used for gaskets, seals, and padding in these and other aerospace applications:

Custom silicone keypads for control systems, monitoring equipment, and cockpit instrumentation

Overlays and seals for avionics, navigation, communications, and flight control equipment

Cockpit gaskets and seals

Cabin and cargo hold compartment gaskets and anti-vibration padding

Engine and turbine gaskets

Wing and tail hydraulics seals

Keypads, overlays, sealing rings, and padding for defense communications systems

Liquid Silicone Rubber Injection Molding for Aerospace by Elastomer Technologies

At ETI, we use LSR and high-consistency silicone rubber (HCR) for injection molding and have decades of experience with prototyping, and low- and high-volume production. Our capabilities include:

Lights-out, automation-driven molding processes for high speed without sacrificing precision

Cold deck systems for efficient material delivery and minimal waste

Prototyping and pilot production programs

ISO Class 8 clean room molding capabilities

State-of-the-art 50- and 100-ton presses