Liquid Impregnation Process

in Composite Lightweight Construction

The liquid impregnation process is a group of manufacturing techniques where dry fibres are impregnated with a liquid matrix (e.g., epoxy, polyester, or vinyl ester resin). These processes are particularly efficient for manufacturing large and complex components with a high fibre volume fraction.

How the Liquid Impregnation Processes work

Basically, liquid impregnation processes take place in two steps:

  • Placing the dry fibres: The dry fibres (fabric, UD tapes, or rovings) are placed in a tool. The fibre orientation is optimized according to the desired load direction.
  • Resin impregnation and curing: The liquid resin is injected into or drawn into the dry fibres under vacuum. The curing occurs at room temperature or elevated temperatures (for thermally activated resins).

Depending on the method, different Liquid Impregnation Processes are distinguished:

1. Resin Transfer Molding (RTM): Closed tool, Resin is injected under pressure

  • Good reproducibility, suitable for medium to high production volumes

2. Vacuum Assisted Resin Transfer Molding (VARTM): Open tool half covered with vacuum film, Resin is drawn into the dry fibres under vacuum

  • Low investment cost, but longer process times

3. Infusionsverfahren (Resin Infusion, LRI): Fibres lie in a closed vacuum system, Resin is slowly drawn into the fibres by capillary forces

  • Lower porosity, suitable for large surface components

4. Wet Lay-up (Hand Laminating): Resin is manually applied to the dry fibres

  • Simple, but harder to reproduce and higher material loss

Advantages of the Liquid Impregnation Processes

  • High fibre volume fraction possible: good mechanical properties
  • Flexible component size: particularly suitable for large structures
  • Low tooling costs (especially for infusion processes): ideal for small series
  • Low emissions (closed processes like RTM): more environmentally friendly than open processes
  • High automation potential (RTM and VARTM): Mass production possible

Applications of Liquid Impregnation Processes

  • Wind energy: Rotor blades for wind turbines (LRI & Infusion)
  • Automotive industry: Structural components for lightweight concepts (RTM)
  • Aerospace: Wings, fairings, interior components (VARTM & RTM)
  • Boat and shipbuilding: Hulls, decks, superstructures (Infusion & Hand Laminating)
  • Sports equipment: Kayaks, surfboards, bicycle frames (RTM & Hand Laminating)

The main advantages of fibre-reinforced lightweight construction at a glance

<p class="text-xl"><span class="font-bold">High strength with low weight</span></p><p class="text-lg">Maximum performance with minimal material usage, ideal for lightweight construction applications. </p>

High strength with low weight

Maximum performance with minimal material usage, ideal for lightweight construction applications.

<p class="text-xl"><span class="font-bold">Customizable properties</span></p><p class="text-lg">The targeted combination of fibers and matrix materials allows mechanical, thermal, and chemical properties to be precisely tailored to specific requirements. </p>

Customizable properties

The targeted combination of fibers and matrix materials allows mechanical, thermal, and chemical properties to be precisely tailored to specific requirements.

<p class="text-xl"><span class="font-bold">Corrosion-Resistance</span></p><p class="text-lg">Excellent resistance to environmental influences and chemicals, which extends the lifespan of components. </p>

Corrosion-Resistance

Excellent resistance to environmental influences and chemicals, which extends the lifespan of components.

<p class="text-xl"><span class="font-bold">Design freedom</span></p><p class="text-lg"><span class="font-bold"><span class="font-normal">Enables the realization of complex geometries and innovative constructions that would be difficult to achieve with traditional materials. </span> <br></span></p><p></p>

Design freedom

Enables the realization of complex geometries and innovative constructions that would be difficult to achieve with traditional materials.