General Composites Manufacturing Notes from Chassis 2025

EA 9340 Guidelines

For Adhering Skins to Core

Roughly 250g glue (not hardener) per 24 sqft of area is the minimum
More may be required if the skins have wrinkles in them
Weight is applied via rigid panel and physical weights (i.e. thick plywood + buckets of water)

For Fillets

Roughly 100g glue (not hardener) per 120 inches (one side) of fillet (0.35" radius)
5 shots of milled glass per 100g glue to thicken at minimum
Sand fillet area and tape off outside fillet area before gluing. Apply a thin film of glue on normal surface, but most of the strength comes from the fillet (promotes shear loading)

Vacuum Bagging

Vacuum is measured in "inches of Mercury" [inHg] on our gauges typically. Full vacuum is ~29 inHg. Decent vacuum for our purposes is ~15 inHg. Anything less than that should be avoided. From our experience, venturi pumps can pull a maximum of about 25 inHg.

General Use

All folds or creases create vacuum leaks, avoid at all costs
When there are vacuum leaks (there are always leaks), pumps have a radius in which they are effective, position pumps effectively so that the area under pressure is maximized
Put extra breather under frog puck, or else you will a falsely high reading (it suctions itself down onto the surface, decreasing its effective radius)
Try to vacuum bag on the mold surface at all times, especially for large layups
- Examples of what not to do:
  - Car 4 chassis layup 1 - vacuum bagged on a glass sheet, which encompassed the entire foam mold. Could not pull vacuum because the volume was too large
  - Car 4 flat panel layup 1 - placed polycarbonate sheet on top of cardboard and put duct tape on cardboard, then tried to vacuum bag cardboard/duct tape seam
- Examples of what to do:
  - Car 4 chassis layup 2 - vacuum bagged along the very edge of the molded surface, pulled ~10 and 20 inHg depending on which pump's gauge was checked

Testing the Bag

If a bag test is performed (recommended for large layups), it will not indicate useful results unless breather in the bag area during the test
Oversize the bag so that it can be cut inside the tacky tape line after testing and be reused for the actual layup