Vacuum infusion process

Resin infusion is a refined process for producing high-performance, non-porous composite materials, even for larger or more complex products. This process is well-suited for the manufacture of fiberglass reinforced plastic parts, such as engine covers and boat hulls. It is also suitable for smaller, intricate items that would be nearly impossible to achieve perfectly using open mold build-up.

Resin Vacuum Infusion Process

This article provides a detailed introduction to the entire vacuum bag infusion process, from the mold to the final polished product, along with the equipment and materials used.

What is resin infusion?

First, the reinforcement, or "dry" fabric (without any resin mix), is laid on top of the mold. Vacuum-assist materials (such as release cloth, mesh, or vacuum bag) are then applied, and finally, a vacuum pump is used to draw the vacuum. Once all the air has been removed from the vacuum bag and the composite material is completely flattened under atmospheric pressure, liquid resin (mixed with curing agent) can be directed through a hose into the reinforcement, flowing through the entire structure under vacuum. Once the resin is completely infused into the reinforcement, the supply is cut off (using a hose clamp), and the resin remains to cure (still under vacuum).

When performed correctly, resin infusion produces FRP parts with satisfactory strength and appearance. Compared to traditional wet lay-up processes, it avoids excess resin and unstable performance. It also eliminates voids (dead corners around reinforcement placement) and small bubbles in the part. The quality of resin infusion, and therefore the strength of the part, is achieved through prepreg.

Preparation – Materials and Equipment You Will Need

The key to successful resin infusion is preparing the correct vacuum equipment and auxiliary materials in advance. While this isn't part of the process itself, most infusion failures or issues are caused by using incorrect materials or equipment.

Mold

The mold's edges should have a sufficiently large flange to secure the vacuum auxiliary materials. The mold's surface quality determines the surface quality of your product. If using a composite mold, epoxy or vinyl mold coat is the preferred surface material; however, other molds, such as glass, steel, or aluminum, are also acceptable.

Equipment

Vacuum pump: Able to achieve a vacuum level exceeding 99.99%.

Silicone nipple: Placed inside the vacuum bag, this connects the resin feed line to the vacuum pump.

Resin collector: If you only use the infusion process once or twice, you can use a breathable felt instead of a resin collector to collect small amounts of resin; however, for long-term use, it's best to invest in a professional resin collector.

Vacuum bag accessories

Vacuum bag film

Vacuum sealing tape (also known as sealing tape or putty strips)

diversion network

Release cloth

Breathing felt (if you don't have a resin collector)

Spiral hose

PVC vacuum tube

Paper tape or pressure-sensitive tape

Materials

Release agent (wax, PVA, or chemical release agent)

Reinforcement, such as infusion mat, chopped strand mat, or fiberglass cloth

Vacuum infusion resin