University of Twente Student Theses


Design and realization of composite molds for a solar car

Labee, R. (2015) Design and realization of composite molds for a solar car.

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Abstract:For the 2013 edition of the World Solar Challenge, Solar Team Twente designed a brand new solar car. In my role as a structural designer I was partly responsible for the internal structure of the car as well as the production of the body parts. The quality of the car's aerodynamic shape is mainly determined by the quality of the molds. During this report the design and production of the molds are outlined. In this way an overview is given of which design choices are made, how the process is simulated and how the theory worked out in practice during tests and production. Several options for the production of the molds have been investigated. The choice for vacuum infusion was not only based on its technical capabilities. In a project like this, but also in most actual designs, the financial aspect plays a role. Also the availability of facilities and knowledge is important. When setting up the criteria of the molds, the problem came across that it is very hard for an unexperienced team to specify certain requirements in measurable values. For example, the surface quality has to be very high. Of course a surface roughness can be specified, but then the problem arises of how rough is good enough and even more complex is how to chase after this required roughness during design. For this specific requirement we had to trust on the former team members and the professionals who helped us. For the selection of materials, a lot of discussion took place. Which materials would result in the best mold? Every specialist seemed to have a different opinion. In the end a laminate was chosen that had specific layers for stiffness (glass fibers and core material) and specific layers for anti-print through. The latter layers had the job to make the surface of the mold as smooth as possible. The company PolyWorx helped us with the simulation of the laminate in combination with our geometry. With these simulations the optimum injection strategy has been found. This strategy minimized the risk of air inclusions and other problems. Different aspects were collected from the simulations. Not only the optimal locations for injection and venting points were determined, but also the time and amount of resin needed. Different tests have been carried out in order to test the performance of the laminate and a few variations, as well as to verify the simulations. Some improvements had to be made afterwards, but all problems encountered during the tests have been solved before the actual production started. During production, which took place at Fokker Aerostructures, molds were made from total different scale in comparison with the tests. These larger scales brought some trouble. The exothermic reaction of the resin occurred faster than accounted for, which caused an air inclusion during the first injection. Also the first post-cure cycle revealed some weaknesses in the process. Although these problems cost a lot of time and energy, in the end also these troubles were solved. After about 2 months of testing and producing, all molds were approved for the next step in our project: the production of the actual car.
Item Type:Internship Report (Bachelor)
Fokker Aerostructures, Nederland
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering BSc (56966)
Keywords:Composite, Molds, Design cycle
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