Planning
I had no idea what "composites" is before the class this week. I started to be curious about two things. One is how strong the composites are depending on materials. I wanted to evaluate the stiffness by making something functional. The other is how the characteristics vary among materials we use. I wanted to evaluate various textiles/fibers. For the first objective, I decided to make a laptop stand. I thought that so-called IKEA effect might lead me to a hard worker.
Designing the mold
I used AutoCAD to design the mold part. The design is pretty straight forward. I referred to the product specifications of 13-inch Mac Book Air to obtain the dimensions. I used UNIT command to set the unit as inch. I used FILLET command and input [R]adius parameter to have a curved shape. I just used combination of lines. It took less than 30 minutes to export the .dxf file.
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Milling the mold
I used two-dimensional path with the Shopbot. It was the third time and started to be familiar with Shopbot functionalities. I loaded the .dxf file and editted the path using VCurve software on the lab PC. I closed the path, copied the part 7 times as an 1x7 array, and set the profiling tool path. I changed the iteration of cuts from 8 (default) to 2 to save the time and worked well. I loaded the foam material on and attached to the platform using a glue gun. The glue cured quickly when we were trying to scatter on the surface of the 8 ft-long foam. We used a cloth tape to attach the one side of the foam to the platform to make sure that it do not move loosely. I used the 1/4 inch Ballpoint tool tip. To cut through the foam material which has the thickness of 50 mm, I had no other options.
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It did not cut through for some of the part but it was okay. I cut out all the parts using a knife. I trimmed the edges using a pair of scissors. The foam mold itself actually worked as a laptop stand. I glued seven parts into one using a glue gun again.
Preparing a bag and materials
I employed the method vacuum bagging this time. I created a bag with the plastic sheet using a sealant tape. I covered the mold with a plastic wrap as a peel-ply. To make the final product strong enough to hold the laptop, I first thought of combining two layers of burlap, a layer of a textile with a honey comb structure (which was used during the resin infusion tutorial), and another two layers of burlap. However, I ended up with four layers of burlap since one of the TA taught me that the honey comb textile itself does not contribute to the strength of the structure.
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Putting the layers together and Vaccuming
I used CCR Epoxy and CCF Fast hardner. I pushed the pump of the epoxy 5 times and the pump of the hardner for 2.5 times. I mixed them for several minutes in a plastic cup. I poured and spread the epoxy just like spreading butter on a slice of toast. I was not sure how much would be too much/enough. I piled four sheets of the burlap carefully. I put them on the mold. Then I put the pink bleeder sheet on it and resin absorbers on and around. I used a piece of sealant tape again to attach the vacuum hose to the bag.
I turned on the vacuum. After adjusting the hose position several times, the pump sucked the air up to around 28 inHg. However, when I crapmed the hose, the pressure could not been kept. I continued to run the pump for several hours.
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Opening the bag
The surrounding parts can be taken off easily. When I opened the bag 18 hours later, the surface was a kind of wet and sticky. I bended the shape at that point and the shape lasted after it completely cured. However, someone told me that it may cut some links between molecules if I bend too much. Here are pictures how it looks like.
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Now I can devote more time on desgining circuit board with Eagle... with less trouble on my back.