Vacuum-Assisted Resin Transfer (VARTM)

VARTM infuses resin through dry fiber preforms under vacuum, producing large, high-fiber composite laminates with low tooling pressure and good surface finish.

Overview

Vacuum-Assisted Resin Transfer (VARTM) pulls liquid resin through a dry fiber stack inside a sealed vacuum bag on a rigid tool. Vacuum compacts the laminate and drives flow through distribution media, enabling large composite structures without high-pressure injection equipment.

Choose VARTM for medium-volume composite parts where size, weight, and fiber volume matter more than tight machined tolerances—common for marine, wind, and industrial structures. It handles complex cores (foam/honeycomb) and integrated stiffeners well, and tooling costs are typically lower than matched-metal processes.

Tradeoffs: dimensional control depends on tooling, bagging quality, and cure shrink; expect secondary trimming and drilling. Resin flow path design is critical—thick sections, tight radii, and inserts can create dry spots or race-tracking. Cycle time is driven by layup, bagging, infusion, and cure, and variability increases if vacuum integrity and material handling aren’t tightly controlled.

Common Materials

  • Epoxy
  • Vinyl ester
  • Polyester
  • E-glass
  • Carbon fiber
  • Aramid (Kevlar)

Tolerances

±0.030" to ±0.060" (trimmed features typically ±0.010" to ±0.020")

Applications

  • Wind turbine blades and spar caps
  • Boat hulls and decks
  • Composite sandwich panels with foam core
  • Vehicle body panels and fairings
  • Large industrial covers and enclosures
  • Aerospace secondary structures (radomes, access panels)

When to Choose Vacuum-Assisted Resin Transfer (VARTM)

VARTM fits large or moderately complex composite parts where low tooling pressure, good laminate quality, and scalable part size drive the decision. It’s a good match for low-to-medium production where layup labor is acceptable and post-trim is planned into the process.

vs Resin Transfer Molding

Choose VARTM when your part is too large for practical closed-mold injection pressures or when you want lower-cost tooling and simpler equipment. VARTM tolerates bigger, flatter tools and sandwich construction, but typically gives less consistent thickness and dimensional control than matched-mold RTM.

vs Prepreg Layup with Autoclave

Choose VARTM when part size or cost rules out autoclave processing and you can accept more variability in void content and thickness. Autoclave prepreg wins on highest structural performance and repeatability; VARTM wins on tool/capital cost and large structures.

vs Prepreg Out-of-Autoclave (OOA)

Choose VARTM when you need thicker laminates or large panels without freezer storage, prepreg tack management, and strict OOA cure cycles. OOA prepreg can offer better process control and cleaner layup, while VARTM is often more flexible on material sourcing and cost for big parts.

vs Hand Lay-Up

Choose VARTM when you need higher fiber volume fraction, better laminate consistency, and lower styrene/odor exposure for open resins. Hand lay-up is simpler for very low volume and quick prototypes, but it’s harder to control resin content and voids on structural parts.

vs Compression Molding (Composites)

Choose VARTM when part size is large, geometry is not suited to a matched tool, or capital for presses and heated steel tooling isn’t justified. Compression molding is better for high-rate production with tight repeatability; VARTM is better for large, lower-volume structures.

Design Considerations

  • Provide defined resin inlet and vacuum outlet locations and keep flow paths short; long, thin flow distances increase dry-spot risk
  • Avoid abrupt thickness changes; taper ply drops and core transitions to maintain predictable resin flow and reduce print-through
  • Design flanges wide enough for reliable bag seals and leak checks; narrow sealing lands drive rework and scrap
  • Plan secondary trim and drill features with realistic trim allowance and datums; molded edges rarely hold tight tolerances
  • Minimize tight inside radii and deep pockets unless you can prove venting and wet-out; these areas trap air and slow infusion
  • Specify insert and core details early (perforations, resin dams, potting) so the shop can prevent resin starvation and race-tracking