Composites Vacuum Infusion [IN PROGRESS]

Why do an infusion layup?

While wet layups can be sufficient for simple geometries, the vacuum infusion process allows for more complex geometries to be made with an ideal resin to fabric ratio. A vacuum infusion also allows for unlimited set up time as the mold and fabric is prepared before the epoxy and hardener are mixed.

All composites work should take place in the composites room and using appropriate PPE

Items Needed for a Carbon Fiber Vacuum Infusion Layup

Carbon Fiber	Epoxy	Hardener	Release Agent
Sealant Tape	Vacuum Bag	Acetone	Peel Ply
Infusion Mesh	Breather	CF Shears	T-Fittings
Spiral Tubing	Vacuum Hose	Duct Tape	Resin Bucket
3M Super77 Spray Adhesive	Popsicle Sticks	Line Clamps	Vacuum Pump

Specifics at the bottom of page.

Vocabulary and Notes:

Vacuum Pump: Many different types of vacuum pumps that are available. They range in ability and cost.

Dry (oil-less) Rotary Vane Pump:
- Oil-free which leads to less possibility of a mess.
- Creates a high vacuum and good for high volume.
- Loud as there is no oil.
- Can run for a long time and be regulated down on strength.
- Not as strong as oil-lubricated rotary pumps.
Oil-Lubricated Rotary Pump:
- Best option for lay-ups.
- Can reach a higher vacuum than the other options.
- Lots of maintenance.
- Not the best after all the air is pulled out of an infusion.
- What is at University of Waterloo in the Composites Room
Diaphragm Pumps:
- Use a flexible diaphragm rather than a piston.
- Quieter than the other types.
- However, a tradeoff is it is not as high of a vacuum.
Piston Pumps:
- Long lasting and simple.
- Can be a compressor or vacuum
- Not as strong as rotary pumps.
Venturi:

Carbon Fiber Fabric:

Release Agents: the material placed on the mold to ensure a layup can be removed

The most common that WARG uses is wax (Need to find which kind)
PVA (Poly vinvyl alcohol): water-based alcohol that creates a surface between the mold and the part. This affects finish quality and should be used sparingly on complex molds. PVA is good at not allowing two chemically incompatible materials from binding.
The release agent can also come from how the mold is prepared, such as semi-permanents. This is discussed on the https://uwarg-docs.atlassian.net/wiki/x/DoDDm page more.

Peel Ply:

Infusion Mesh:

Spiral Tubing:

Tubing:

PVC: cheap and not recommended as it kinks easily

Poly:

Nylon: disposable and not the best for the job, but cheap to buy and easy to use with barbed fittings
Permanent: better quality and can be used with quick connects
- In the long run better to look into

Process:

Construct and prepare the mold (if needed) for a lay-up. For more information check out https://uwarg-docs.atlassian.net/wiki/x/DoDDm.
Apply the release agent (need to go into specifics).
1. WARG commonly uses wax. Another release agent should only be used if discussed as a mech team.
2. For wax, apply 5 layers waiting 5-10 minutes between layers for it to dry and develop a slight haze. Buff off and apply the next layer.
Cut carbon fiber fabric to correct size for the mold, add about 1”-2” extra on each side.
1. Easiest method to get a straight cut is to pull on fiber out and follow the gap that is created with CF shears.
Place the first sheet of carbon into the mold. Have help!
1. If this sheet will be visible, keep that in mind.
2. Choose the sheet that looks the cleanest and has fibers orientated the correct direction.
3. Use a small amount of 3M Super77 spray adhesive to stick the piece of fabric into place, ensuring there are no air gaps between the mold and the fabric.
4. Trim the excess fabric that is not in contact with the mold. Make sure no stray fibers end up in the layup.
Place the remaining sheets of fabric, keep in mind orientation if a pattern is being followed. Trim excess as needed.
1. (Need to go into depth about orientation of fabric)
Place peel ply over top of the carbon fiber, using many pieces if needed for complicated shapes.
1. Duct tape can be used to stick the peel ply down. Do not stick duct tape to carbon fiber directly.
Plan the path for the resin to flow. This is one of the most important steps and needs to be thought out. (Will include examples after we do it ourselves. Will find some online diagrams too)
If the part is large, use an infusion mesh to help the resin spread quickly and evenly.
1. Duct tape can once again be used to secure this; however, stop 2-3 inches before the resin outlet.
2. UWFE suggests placing breather material around sharp edges on the mold to absorb excess resin and prevent the bag from ripping.
Place vacuum inlets and outlets, including spiral tubing according to plan from step 9.
Enclose the lay-up in a vacuum bag. There are many methods that can be used. Common ones can be found online.
1. Place sealant tape along the surface you choose to close the bag onto (can be a mold, the bag itself, or a table). Leave the tape that is facing outwards covered.
2. Include pleats around complex surfaces to allow extra bag material to wrap around the shape.
3. Only peel off the outer side of tape when approaching that area with the bag.
Place tubes onto the inlets and outlets, clamping off the inlet tube.
Set up the resin trap and vacuum pump.
Turn on the pump until a complete vacuum is pulled, then clamp the outlet line and turn off the vacuum. Wait 10-20 minutes and unclamp the line, looking at the vacuum gauge for any movement.
1. No movement means there are no leaks. Continue!
2. If the gauge moves, then find the leaks and don’t continue until you are sure there are no leaks.
Now catalyze the resin and set up the inlet bucket.
After the part is fully infused, aerated resin will enter the outlet tube. Let it reach close to the resin trap and then clamp off the line and turn off the vacuum at this point. Allow the inlet to draw in resin for another 1-2 minutes, then clamp the inlet off too.
After the part is fully cured, unwrap it and remove all disposable items (spiral tubing, peel ply, infusion mesh). Remove the part from the mold/surface being careful with the edges.

It is highly recommended everyone interested in composite layups reads the resources used to help create this introduction document. As WARG is beginning with vacuum infusion, there is a lot to learn and add to this knowledge base.