Tooling, Consumables, and Infusion Stack Setup

What Is an Infusion Stack?

Vacuum infusion (also called vacuum-assisted resin transfer molding, or VARTM) pulls liquid resin through dry reinforcement using atmospheric pressure and a sealed vacuum bag. The resin inlet and vacuum outlet are both inside the bag, and every layer between the mold surface and the bag film has a specific job. Understanding that job is why the order of layers matters — a stack installed out of sequence will produce voids, bonding failures, or an unacceptable surface finish.

The term infusion stack refers to the complete assembly of consumable layers placed on top of the mold laminate before the bag is sealed. You will install this stack before any resin is introduced.

Layer-by-Layer Breakdown

1. Release Coat (Mold Preparation)

Before any consumable touches the mold, the mold surface must carry a fully cured release agent — typically a wax, semi-permanent release, or a combination of both. Without adequate release, the cured laminate bonds permanently to the mold. On the demonstration mold used in class, this step is already completed: the aluminum surface has been waxed and buffed. Never skip verifying that the mold is properly released before the stack goes down.

2. Peel Ply

Peel ply is a tightly woven nylon or polyester fabric placed directly on top of the laminate (or, in a demonstration setup, directly on the mold surface representing the laminate face). Because it does not bond chemically to most thermoset resins, it peels away after cure and leaves a textured, bondable surface ready for secondary lamination or fairing. In an infusion stack it also acts as a controlled resin break between the laminate and the flow media above it.

3. Reinforcement

The structural layers — typically fiberglass woven roving, biaxial stitched fabric, or chopped strand mat — are placed according to the laminate schedule card. Each ply must be oriented as specified. Dry reinforcement in a VARTM process carries no resin until infusion begins, so handling is clean but fabric edges must be managed carefully to prevent fraying into the flow path.

4. Flow Media

Flow media (also called distribution media or infusion mesh) is an open-weave biaxial mesh placed above the reinforcement. Its high permeability lets resin travel quickly across the surface and then bleed downward through the laminate thickness. Correct placement of the flow media is the primary tool you have for controlling infusion speed and uniformity. Flow media is a consumable — it is removed with the rest of the bag after cure.

5. Spiral Wrap Feed Lines

Spiral wrap tubing is a flexible, ribbed plastic conduit threaded onto the supply (resin inlet) and vacuum (outlet) lines where they pass through or under the bag. The ribs prevent the tubing from collapsing under vacuum and create a high-flow channel. Resin inlet lines are typically positioned on one edge or at the center; the vacuum line is positioned at the opposite side. Placement follows the laminate schedule card or the resin manufacturer's technical data sheet (TDS).

6. Vacuum Bag Film

Vacuum bag film is a thin, flexible nylon or polyethylene film that drapes over the entire stack and is sealed to the mold flange. The film must overlap corners without bridging — a bridged corner creates a void that air leaks through or that the laminate cannot fill with resin. Press the film into corners gently and pleat excess film rather than stretching it.

7. Sealant (Tacky) Tape

Tacky tape is a soft, pressure-sensitive mastic tape applied to the mold flange before the bag film is laid down. When the bag film is pressed onto the tape, it forms the airtight perimeter seal. Continuity of this seal is critical: any gap, fold, or missed section is a leak point. Run the tape in one continuous piece around the perimeter whenever possible, and butt-join ends cleanly if a second piece is needed.

Connecting the Vacuum System

Once the bag is sealed, connect the vacuum pump through a vacuum gauge and a catch pot (resin trap). The catch pot prevents liquid resin from entering the pump during infusion. Draw the system down to the vacuum level specified in the resin manufacturer's TDS — do not assume a standard value because different resin systems have different requirements. After reaching target vacuum, isolate the pump by closing the valve and monitor the gauge for three minutes. A drop beyond the allowable rate stated in the TDS indicates a leak; find and fix it before infusing resin.

Safety

• PPE required throughout: safety glasses, nitrile gloves, and where resin vapors are present, a respirator rated for organic vapors (NIOSH-approved).
• Tacky tape contains solvents; keep away from ignition sources and ensure adequate ventilation.
• Vacuum pumps generate heat. Do not block the exhaust or leave the pump unattended for extended periods.
• Do not use damaged bag film or cracked sealant tape — a bag failure during infusion releases resin quickly and creates a slip and inhalation hazard.
• Dispose of resin-contaminated consumables as directed by your facility's hazardous-waste procedures.

The Six-Point Checklist

Your instructor will use the following six checkpoints to sign off your stack:

1. Layer sequence is correct per the laminate schedule card.

2. Sealant tape is continuous with no gaps around the full perimeter.

3. Resin supply and vacuum lines are positioned as specified.

4. Vacuum gauge is correctly connected between the pump and the bag.

5. Target vacuum (per resin TDS) is achieved.

6. Vacuum holds within the allowable drop rate for three minutes after pump isolation.

All six must be correct before you advance to a live infusion.