Positive -> Negative -> Positive
Mold Making in Kenya
The bulk of our success in constructing the pilots relied on the team’s ability to make the molds for precasting the concrete forms. The team first split up: Joel, being fluent in swahili, navigated the Gikomba marketplace daily to make quick mock-ups of the molds for testing; Ani scoured the industrial district for fabricators to establish contracts for the roll-out; and Ella went to the University to recruit local talent; in doing so she wandered into the FabLab.
Though not widely advertised, the facility located within the University of Nairobi Mechanical Engineering Building functions as a state of art, stand-alone technology park. Setup in affiliation with the FabLab at MIT, it is equipped with a large bed CNC routing machine, laser cutter, 3D scanner/printer, teleconferencing capabilities, and more. This level of modernity is a rare find in a city of people that take pride in their resourcefulness, but that is another discussion all together.
When Ella first met Kamau Gachigi, Director of the FabLab. He explained that by sponsoring local projects the FabLab hoped to enable innovation and prepare projects and/or businesses to be competitive in the world marketplace. After describing our project Kamau was extremely accommodating; recommending material sources, recruiting help, and contacting student operators. Which is how Ella met teammate Tom Odoyo. Tom was irreplaceable, putting his own windmill project on hold to become part of the Sanergy team throughout the summer.
The CNC Router provided us a means to fabricate a highly accurate form of the floor plate out of fiber board that we used as a plug from which we created our mold for casting. Being that the floor plate was the interface between the walls of the superstructure and access to the containers in the substructure it required a level of precision that was not likely to be found using make-shift methods.
Having already modeled the floor plate in 3D we split the form into stratus layers, the thickness of our MDF board, which we later laminated together to get our 3 foot wide by 5 foot long and 6 inch tall floor plate. Splitting time at the machine, working late into the night and through the inevitable hick-ups we were able to route out a floor and corner piece in just over a week.
Unclear as to the best method to use the (positive) plug to form our (negative) mold we looked into the commonly used rammed sand and aluminum cast and also casting it straight into concrete, but decided on having a fiberglass mold made for a heightened level of accuracy. For this step, we contracted the services of experienced folks at Specialised Fibreglass. With their help, the mold was further developed to incorporate tapered edges so it would easily release each cast.
The other molds consisting of 5 walls, 4 corners, 4 foundation posts, and a roof ring were made from steel.