Materials

Owned by Adam Marchand
Last updated: Jun 02, 2017 by Vu Julian Hoa-Chau Huynh (Unlicensed)Version comment

Process to be used for Aerobody Production: Vacuum Infusion Process

This process requires a lot of preparation and preplanning in order to be done properly.  The initial selection of materials to be used for the process is very important including molds, vacuum lines and the actual material to be infused with resin.  Some of the important aspects of the process that have to be accounted for are the amount of time required for the infusion to be completed in and the speed at which the resin and hardener will spread throughout the material.  This leads to the consideration of the viscosity of the resin, the permeability of the material and the additional flow media within the material to aid in the infusion process.

The viscosity of the resin is important, as it determines how much times is required for the infusion to be completed and how well and even it spreads throughout the material.  The recommended viscosity is at less than 400 centipoise, however higher viscosities can be used, but curing time must be a lot longer to allow for the spreading to occur.  Alternatively, additional time can be allowed instead to allow higher viscosity resins to be used.

The permeability of the material is also important, due to it also determining the efficiency at which the resin and hardener spreads through the material.  The currently selected type of material will be sufficient for this, as the weaved fibres allow for easy spreading of the resin.  However looser weaves are recommended for easier spreading.

The flow media to be used has to also be considered.  Even though infusion can be done without any flow media throughout the material, it will take much more time to properly spread the resin and hardener throughout the mold.

Fibreglass types:

Fibreglass is a type of composite material that can be used in order to form parts.  Even though fibreglass is generally made of the one material, glass, there are many specifications and types that change its material properties and the process by which a part can be created.

Fibreglass is designated by 3 / 4 letters.  The 1st letter defines the type of glass within the fibreglass, where E is Electrical and S is high-Strength.  The 2nd letter indicates the type of strand that the fireglass material is composed of, for instance Continuous.  The 3rd or both the 3rd and 4th letter indicate the thickness of the strands.

Additionally, fibreglass weave is separated into two types: the vertical is warp and the horizontal is called fill / woof / weft.



Resins + hardeners:

As mentioned before, the viscosity of the resin and hardener is important to consider for the Vacuum Infusion Process.  This means that either the resin has to be lower than 400 centipoise or the hardener used has to be have a higher curing time.

The pot life given for the resin is the amount of time it takes for the resin to double in viscosity.  Additionally, the work life is the amount of time that the resin remains workable and spreadable, after which the curing time is the time required for it to fully solidify.

The current resin that is to be used is the West System 105 Epoxy Resin (http://www.westsystem.com/wp-content/uploads/User-Manual-2015.pdf).  It has a viscosity of 1000 centipoise, very thick for the vacuum infusion process.  However this can be compensated for by the resin hardener used.  The most likely hardener to be used is the West System 209 Extra-Slow Cure Hardener.  This has the following characteristics:

  • Mix ratio: 3 parts resin - 1 part hardener
  • Pot life at 72°F / 22°C: 40-50min
  • Cure to solid state: (72°F / 22°C) 20-24 hours, (95°F / 35°C) 6-8 hours
  • Cure to working strength: (72°F / 22°C) 4-9 days

The temperature is a major factor to the curing time, with a reduction to ca. 1/3 of the curing time at 35°C.  It is probably most efficient to perform the infusion at 22°C, but after that is completed the curing should be completed at 35°C.


Flow Media:

Flow media is the medium that is additionally inserted into the material to help the vacuum infusion process by allowing the resin and hardener to spread through the material faster.  The flow media can be chosen to only aid in the infusion, but also can be chosen to also structurally function as core material to strengthen the material additionally.

The most probable flow media to be used is the FibreGlast Divinycell DIVINYMAT (http://www.fibreglast.com/product/DIVINYMAT_01024_A/Vacuum_Bagging_Vacuum_Infusion).  It functions as both flow media and as the structural core for the material itself.

Resin Feed + Vacuum Lines:

The vacuum lines will be used to initially create a vacuum within the mold and then will later direct the resin into the mold, infusing with the material.  It is recommended to wrap the resin feed lines with peel ply in order to allow for easy and smooth removal of the lines.  According to the guide, there are two possibilities: either spiral tubing or a filter jacket which has pores on the outside to allow for the resin to flow out. (http://www.fibreglast.com/product/EnkaFusion_Filter_Jacket_1400/Vacuum_Bagging_Vacuum_Infusion and http://www.fibreglast.com/product/Spiral_Tubing_1403/Vacuum_Bagging_Vacuum_Infusion)

The spiral tubing is better suited for being used as also a vacuum line, however has the tendency to straighten out when used..  To prevent this from occurring, sealant tape can be used to reinforce it at key locations to prevent changes in the structure.

Resin Trap:

The resin trap is an airtight container to be placed within the vacuum tubing circuit between the laminate and the pump to catch excess resin before it can enter and destroy the pump. http://www.fibreglast.com/product/Resin_Trap_01500_A/Vacuum_Bagging_Vacuum_Infusion

Additional Notes from Andy Phillips (Composite Creations)

  1. The estimated setup time for a ca. 4m^2 area of mold is 8 hours to prepare with the layup and vacuum.  Additionally, vacuum checkup must be performed.
  2. The recommended weave for the fibreglass to be used is 2x2 twirl.  This allows for complex curves and sharp ridges to be made from cut off strips from the roll.  Additionally, cutting the material at 45° will increase its flexibility by 25-30%.
  3. For the vacuum within the mold, the recommended pressure should be 27 - 29 inches of mercury.  To measure this, a vacuum gauge is to be used, which will cost ca. $25.
  4. The estimated time for the epoxy and hardener mixture to fully be absorbed into the material will take from 45 minutes to 1 hour.
  5. The recommended available resin is MGS 135 resin, which can be mixed with a hardener to give it a longer pot life.
  6. If the mold is not sealed properly, the envelope could crush and collapse onto the mold.
  7. The spiral wrapping (is this what he meant?) to be used as the resin feed line is recommended, as it offers much greater versatility compared to other methods.
  8. In order to ensure a good finish of the part i.e. a good paint job for the aerobody, an epoxy primer should be used in the mold instead of a gel coat.  This will reduce the weight exponentially and also allow for the painters to easily paint the car.
  9. The core material to be used should be DIAB - Divinycell H60, however it needs to be cut to fit to size and does not need to be everywhere in the mold.
  10. There should be 4 layers of fibreglass, however other numbers are possible dependent on the shape of the car.
  11. It is very feasible to include multiple complex components of the aerobody into one single mold.
  12. To add lips and tongues for the trunks and the doors, dimensional wax can be used.  They come in sheets of 1-6mm thick, and can  be molded using heat to fit the specifications.
  13. For the windshield, a company called ? can be contacted.

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