Shell Layup

Laying out the Kevlar on the shell.

Within the last couple of months, CalSol started the cool process that is shell construction and we are happy to report that we have finished the layups for Impulse’s top and bottom shells !   For the past few weeks members have been out to the station essentially every day working to make this a reality.  Let’s describe the process that went into making it so.

The first step was securing the materials needed for the layup.  This was made possible by donations from our many generous sponsors.   Our molds were constructed by our platinum sponsor, Kreysler & Associates.   They machined the  female shape of the car into EPS foam, saving us an entire step of the shell construction process.  Carbon fiber composes the outside layer of the composite “sandwich.”  Discounted carbon fiber was donated by Hexcel.  Nomex honeycomb forms the inner layer providing a lightweight structural component.  Our honeycomb was donated by Aircraft Spruce.   Duratec, which is sprayed on top of the molds to provide a smooth surface, was donated by RevChem Composites, as well as Polyester EZ Sand Primer.

Applying epoxy to the Kevlar

The foam molds were sanded down to prepare for the Duratec coating.   After getting some of our members fitted with respirators, we began spraying the molds with Duratec Styroshield.  The surface was then coated again with Duratec EZ sand.   Any pits and defects were filled with Bondo and then sanded and polished to obtain a nice smooth surface for the shell.   After this PVA release was applied and release wax.   Once this was completed, it was time for the layup to begin.

Our team had done smaller practice layups on smaller parts to attempt to perfect the process, since the layup would have to be done in one go.

All pieces were carefully cut and measured.  Then we broke into three groups.   One would mix epoxy, one would spread the epoxy on the carbon fiber and the remaining group would smoothly lay the fabric on the molds and remove all bubbles.   We used kevlar for the top layer on our top shell to provide additional strength and resistance against electrical conductivity, but the rest uses a carbon fiber, honeycomb, carbon fiber sandwich.

Once the layup is complete, we lay down the release fabric to prevent sticking and breather fabrics to allow air to be removed properly.   The vacuum bag is then sealed and after the vacuum pumps are started the team enjoys a few minutes of silence searching for leaks.   The shell is left in vacuum until the next day allowing the team a few hours of sleep before coming back out to remove the shells from the molds.

After removing the bottom shell, we check out what it will look like when it is assembled.

Although the layups for the top and bottom shells are both complete, a lot of work still remains to inspect and touch up the shells, add the reinforcing panels, cut the fairings, complete the work on the canopy and get the car painted.    But our members are spending many hours out there, sometimes past midnight, completing these tasks.  8 weeks ago we set a goal to display the car at Cal Day and we are working our hardest to meet the goal.  We’ll see you then.