December 20, 2012
Winter Break Update 5
by Wesley Ford
Yesterday was our last day of work at VAIL before the final members of our team fly or drive home for the winter holidays. We had a solid 25+ hours at the shop with all hands on deck to manufacture our carbon fiber top shell. We started the day with sealing our molds with Freekote and trimming our second door to size. We placed the door back in the molds to give us a top shell that would mate perfectly with the team’s doors. This year our team ordered molds with scribe lines scored into the mold surface. These scribe lines leave lines on our carbon parts that we can use as cutting templates. This allows us to cut every part from our molds to the exact same size enabling us to replace parts like our doors and fairings with ease.
After we cut and sanded our door we experimented with laying a silicone strip around the perimeter of the door. This would later recess the lip of the carbon of our door allowing us to add foam in our door seal later down the road. Once our door was in place and covered in release film we began to lay down our new SurfaceMaster from Cytec on our Christensen Fiberglass Tooling molds. This year we have had a lot of success with placing foaming adhesive in regions where we are concerned about voids forming in our carbon parts, so we laid strips of foaming adhesive around our array inset and array wiring inset. We topped that with carbon pre-preg twill from Amber Composites, some reinforcement carbon, and a layer of film adhesive from Tencate.
Next, we cut normal hexagonal core and over-expanded core from Amber Composites to cover our top shell surface. Then we laid a mirroring stack of film adhesive, reinforcing carbons strips, and twill on top of our core. We brought our entire carbon sandwich up and over our mold flange with the intention of cutting off the excess material later. Amber Composites’s over-expanded core did a great job of bending to our sub 1/4″ radius fillet of our molds. Next came peel-ply, release film, and breather.
We only had twelve people working on the car today, but we still had everything bagged around midnight. When we pulled vacuum we had a small leak after spending a lot of time searching for the leak, so we unfortunately had to re-bag the stack before baking. Eventually we got the car in the oven and set up our online oven monitoring setup.
Then the entire team stuck around through the night to wait for the molds to bake. Apparently it is much easier to pull all-nighters for solar car when there are no looming p-sets or exams. We watched Apollo 13, and decided to set up a mission control room for our oven bake in the seminar space of VAIL.
Shortly after sunrise our bake cycle finished and we started to ramp down the temperature of our molds. Once the molds cooled we brought the stack out of the oven and de-molded the top shell. The top shell came off the molds with no stuck points but with tens of thousands of volts of static electricity much to dismay of our CS team. With the molds off the car we popped the door of of the top shell and inspected our work.
Over the course of this last week we managed to manufacture our first set of fairings, two doors, and a top shell. We also had significant progress with bringing up some of our new boards, coding much of the functionality of BMS, CADDing our chassis design, laying out our battery pack and much more. Having people staying around for winter break was a huge benefit for the team, so I really appreciate Sam, Rachel, Nathan, Wyles, Ian, Max, Michael, Guillermo, DC, Harry, Chris, Susan, Greg, Bryant, and all of the team alumni who came to help out!
PS: If you’re new to the team and you want to get involved in one of our next composite parties before we finish up our carbon fiber work come to our team meeting at 7:30pm on January 7th or at noon on Saturday January 12th for more info and to sign up for the next layup session.