Build, Test, Document
Table of Contents
Build, Test, and Integrate
Vacuum Forming Mold: Design 1
The final revision of the mold was created using a 22 inch by 22 inch block of maple laminated wood. The mold was CNC machined at an outside company to form a single component. The mold featured the same rib structure that was used revision two. The base thickness for the rib features were increased to 0.80 inches. The increase in thickness was necessary to create a 0.125 inch clearance for the rebar. The overall height of the outer rib pieces was decreased to 1.0625 inches and the inner rib pieces height was reduced to 0.5625 inches. The reduction in height was to accommodate the switch over from using quarter inch HDPE to sixteenth inch plastic. The reduction in height was to maintain a half inch difference between inner and outer rib features. Two wood blocks were removed from the mold and replaced with eight additional rib features. The rib features were less complicated to machine and vacuum form, and provided improved strength and stability compared to wooden tabs. The four corner wood blocks were retained to provide features to support the cover. The additional rib features had a base thickness of 0.65 inches. Draft angles for outer tabs were increased to fifteen degrees. The increased draft angles allowed for improved removal of the mold from a formed base. All other draft angles were increased to seven degrees to improve mold extraction and to allow for standardized tooling for machining the mold.
Unsuccessful Attempts (On-Campus):
Successful Attempt (At Faro Industries):
In order to improve processing times, assembly fixtures were created. The rebar support frames for the Vacloo required two fixtures, which required welding; therefore, they were made of steel. A 3/16 inch steel plate and 1/8 inch by 1.5 inch by 1.5 inch angle iron was used for the base and stops for each of the Vacloo assemblies. The stops were welded to the base plate. Process times are improved by clamping rebar to the stops and tack welding to avoid having to measure and square for each assembly produced. The fixture for assembling the Deckloo is made from a particle wood base and sections of 2 by 4’s to space the floor stringers at the correct location without having to measure. There are also perimeter stops to line the ends of the stringers and the deck pieces.
The Vacloo is primarily constructed from vacuum formed HDPE and steel rebar. The main structural support for the design comes from the rebar, which forms a grid similar to two pound signs (#) that rest on top of each other. The rebar extends beyond the edges of the plastic and digs into the ground after the design is installed on location, which helps to provide stability and prevent movement while in use. Additionally, during assembly the device is inset slightly into the ground so that the outer perimeter flange of the plastic and the rebar are covered by a thin layer of dirt. The HDPE sheet is vacuum formed to create recesses for the rebar to nest inside of, and to create ribbing to increase the load distribution. A second, flat, piece of HDPE rests on top of the vacuum formed section to provide a surface to stand on, aid with load distribution, and increase the strength of the device. There is also another smaller section of HDPE which serves to cover the opening of the squat hole in the device when not in use. The entire device weighs 14.5lbs when assembled and is designed to support 270lbs.
The Deckloo is constructed from plastic lumber boards made from 100% recycled HDPE. The design has thinner sections of HDPE which lay next to each other to form the top surface to stand on. This is supported by several thicker cross-member sections of HDPE under the top surface that run perpendicular to the top boards. The inspiration for the design was based on the standard design layout for most common household decks and patios. The design is slightly inset into the ground to provide stability and prevent movement while in use. Also, there is an additional piece of HDPE to cover the opening to the hole below while the device is not in use. The entire device weighs 17.4lbs when assembled and is designed to support 270lbs.
The test for Engineering Requirement S2, load supported, used a custom set of loading fixtures to simulate a person standing on the bases and followed ASTM E455. For each base there was a fixture to simulate the ground during the test, and there was a second fixture that held standardized gym free-weights which had two posts underneath to simulate the feet of a person standing on the base. The bases were both loaded to 572lbs without failure, using all of the weights that were brought to the testing site.
Test Plans & Test Results
For each ER, a test was developed that could be applied to any design prototype; there were 14 tests created in total. Each test was performed under the same conditions and compared to the respective engineering metrics. The test for ER S1 was a cost analysis based on the assumptions described previously. The test for ER S2 used a custom set of loading fixtures to simulate a person standing on the bases and followed ASTM E455. For each base there was a fixture to simulate the ground during the test, and there was a second fixture that held standardized gym free-weights which had two posts underneath to simulate the feet of a person standing on the base. The tests for ER S3 and S4were conducted using a tape measure. Material properties of the materials, as specified by the suppliers, were used to ensure that ER S5 was satisfied. The tests for ER S6 and S12 were conducted using dial calipers. The tests for ER S7 and S8 were conducted base on observation and a stop-watch during the installation process. The tests for ER S9 and S10 were conducted using a scale. The test for ER S11 was conducted using organic compost matter to soil the prototypes and a wet rag cleaning. An ideal durability test for ER S13 could not be conducted due to time constraints. Instead, analysis was conducted based on the aforementioned mechanical analysis of the designs for cycles to failure and weather degradation. The test for ER S14 was conducted using SimaPro software for the LCA.
The Deckloo passed all except for two tests and the Vacloo passed all but one test. ER S6 that required a maximum change in level of 6mm was not met for either design. The reason that this ER was failed was because of the need to have a knob to use for the lid. It was concluded with the customer that the handle did not present a significant tripping hazard because it was something the user will actively focus on when using the device. This is because they must physically grasp it to lift the lid to use the device. The customer accepted this failure because they felt the hygiene and usability the handle added were more important than the tripping hazard concern. For the Deckloo, ER S4, regarding the maximum squat hole diameter was also not met. This ER required a maximum squat hole diameter of 0.25m. It was concluded after a discussion with the customer that this was an acceptable outcome, because a hole compliant with the ER would result in a product that would be difficult to use or increased manufacturing difficulty and costs, a much more critical ER. The ER itself was based on a recommendation from the World Health Organization for the size of pit latrine holes intended to keep toddlers from falling into deep pits. This risk was less concerning to the customer because Arborloos have much shallower pits than traditional latrines.