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Why vacuum bag a 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.

Items Needed for a Carbon Fiber Vacuum Infusion Layup

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.

• 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.

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:

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Process:

1. Construct and prepare the mold for a lay-up. For more information check out https://uwarg-docs.atlassian.net/wiki/x/DoDDm.

2. Apply the release agent (need to go into specifics) you are using to the mold.

   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.

3. 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.

4. Place the first sheet of carbon into the mold. Have help!

   1. This sheet is visible on the outside, so 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.

5. Place the remaining sheets of fabric, keep in mind orientation if a pattern is being followed. Trim excess as needed.

6. 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.

7. 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)

8. 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, other sources mention breather material is not needed Vacuum Infusion.

9. Place vacuum inlets and outlets, including spiral tubing according to plan from step 9.

10. Enclose the lay-up in a vacuum bag. There are many methods that can be used. Some common ones are shown below.

    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.

11. Place resin lines onto the inlets and outlets.

    1. Include a line clamp on the outlet line.

12. Set up the resin trap and vacuum pump.

    1. Check for leaks now. With vacuum infusion, there is unlimited time to search for leaks. Ensure there are zero. (Will add more details of how to tell if there is a leak)

13. Now catalyze the resin and set up the inlet bucket.

14. Watch the flow of the resin and time how fast it infuses. Marking on the bag can help learn about the process for future infusions and whether to change viscosities of resin.

15. 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.

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