Sept
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25, 2016 -
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Polycarbonate Windshield Forming
This is U of T's Blue Sky Solar Car Team. This page documents some key points in their composite process explained by Sean Doughty, their Chief Engineer.
Mounting to composite panels
When they want to mount to composite panels (CF - honeycomb core - CF) using fasteners, they will cut out an area of their core material and replace it with a metal plate. Holes are then drilled through the entire piece after it has cured to achieve the desired mounting points. This is ideally designed as part of the panel itself and implemented during the initial layup of the panel, however they are also able to add an arbitrary mounting point to an existing panel by cutting out one side and removing the core, inserting the metal, and laying up CF over top (weaker than doing it during the initial manufacturing of the panel).
This technique was developed with help from their team alumni after they ran into issues with their suspension ripping out of their car during races. Sean explains that attaching fasteners directly to composite panels with a honeycomb core will crush the panel, compromising its structural integrity.
Unibody structure
The main aerobody for U of T's most recent car was constructed using many separate MDF molds with interior faces soaked in epoxy resin. The external walls of their aerobody are extremely thin (~3 mm) as the majority of the structural strength for their car comes from a composite chassis formed with intersecting composite bulkheads. These bulkheads use thicker honeycomb core material similar to that used for MSXI's monocoque.method for forming a polycarbonate canopy without heat:
Prototyping labs with vacuum forming technology will also be able to help you. However, if you don't have either of these types of companies nearby, but have access to a negative canopy mold, carbon fibre/epoxy, and 1/8" polycarbonate, I can tell you a method that Blue Sky used on the past 4 vehicles that works very well and easy to do.
EDIT: Non-thermoforming method (no heat)
- Plan out where your windshield will be in CAD (you need 1 -1.5 inch of extra bonding surface all along the edge of windshield.
- Cut 2 copies of polycarbonate windshield screen (including the bonding surface)
- Hot glue one copy of the polycarbonate windshield screen to the surface of the mold (You're going to throw this one out) and put mold release over the polycarbonate in the mold.
- Layup over the polycarbonate onto the mold. (Creating a lip that the real good windshield will sit on.)
- Pop it and cut out the holes for the windshield screen (I suggest you make sure you leave some material that connects the bottom half of the carbon to the top half of carbon to ensure shape doesn't deform)
- Put the good polycarbonate windshield into the mold and put even layer of epoxy onto the bonding area to fix it (you can put vacuum on it while it's curing, but make sure you put flashbreaker tape along the edges of the bonding surface so you don't get epoxy all over your canopy)
Sept 10, 2016 - Dynamometer testing trip
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Azure and MSXI demonstrate the importance of having a sustainable team cycle that balances the development of new vehicles and current members with the bring up and integration of new members, all while keeping a healthy budget. Interestingly, at the time of this writing (Sept 11, 2016) U of T is in an extremely similar financial position as our team.
Sept 4, 2016 - Minghao's visit
On September 4, 2016, Minghao visited U of T's Blue Sky Solar Car Team. This page documents some key points in their composite process explained by Sean Doughty, their Chief Engineer.
Mounting to composite panels
When they want to mount to composite panels (CF - honeycomb core - CF) using fasteners, they will cut out an area of their core material and replace it with a metal plate. Holes are then drilled through the entire piece after it has cured to achieve the desired mounting points. This is ideally designed as part of the panel itself and implemented during the initial layup of the panel, however they are also able to add an arbitrary mounting point to an existing panel by cutting out one side and removing the core, inserting the metal, and laying up CF over top (weaker than doing it during the initial manufacturing of the panel).
This technique was developed with help from their team alumni after they ran into issues with their suspension ripping out of their car during races. Sean explains that attaching fasteners directly to composite panels with a honeycomb core will crush the panel, compromising its structural integrity.
Unibody structure
The main aerobody for U of T's most recent car was constructed using many separate MDF molds with interior faces soaked in epoxy resin. The external walls of their aerobody are extremely thin (~3 mm) as the majority of the structural strength for their car comes from a composite chassis formed with intersecting composite bulkheads. These bulkheads use thicker honeycomb core material similar to that used for MSXI's monocoque.