Results

Through the development of designing the modular hardtop, there were several evolutional processes that influenced the design and what materials will be used. One design aspect that evolved through the budget cost calculations was the decision of whether to use E-Glass Fiberglass, S-Glass Fiberglass, or Carbon Fiber for the fabric material. Based on several iterations, the decision to use E-Glass Fiberglass deemed to be an adequate material option to use based on material properties and cost of the material. The cost of using E-Glass is significantly less than the other two options. A few aspects of the design that choosing this option effects are the weight of the panels and the thickness of the layup. Weighing the pros and cons of the material, the decision to use E-Glass seems like a logical choice. Another aspect that evolved was the decision on how to translate a load from the top panels to the vehicle. To incorporate another method of design and simplicity, structural square tubing was chosen to support a load that would be placed on the top panels. Choosing this option allows the side panels to incorporate insulation foam as the core material. Having this option will in turn assist in reducing the heat loss through the panels.

Through the project risk analysis process, this project seems like it will produce a product that will succeed in performing with the function requirements set. Through the documentation of this project, time management, budgeting and organizational skills were brought into perspective. By creating a Gant chart, time management became possible. Setting a timetable to complete tasks and comparing these values to the time that was spent completing the tasks gave insight on how individuals can overestimate how efficient one can be. Through the budgeting process, the cost of various materials became a factor that altered the design decisions. Through this process, addressing issues that come up in any design parameters were brought to attention. By organizing the document is this manner, the ability to communicate with others on the intensions of this project were made possible. The next phase in this project is to create test samples of the materials chosen for the construction of the panels and test for performance. With these values, an individual will then be able to conclude that the product will work and is ready to be construction or a different option will be needed.

There were a few issues that came up while making the first few panels.

Due to the size of the layup of the top panels, a good vacuum could not be made to get a mold of the shell. To eliminate this issue, a wet layup was made, and foam cutouts were placed on the contours to ensure the panels took the shape of the mold. This method provided a solution to the problem, but using this method made the top shells not as aesthetically pleasing as they could have been. While this did not affect the structural integrity of the panels, it revealed a practice bagging run over the layup surface, was a good idea.

Another issue addressed in the construction of the top front panel, was the mounting of an attach point to the Jeep. Instead of designing a new structure to support attachment points, a soft top header bar could be used as an effective alternative. This appeared to be the perfect solution to simplify the design. The header bar is completely made of plastic. The problem with that, is the epoxy resin does not adhere well to plastic. The solution to this problem was to layup fiberglass on the header bar. This will ensure that the epoxy will then adhere to the shell of the panel, the foam core, and the interior layup.

One modification made to the design, was changing the rear window from an original window to a window made of Lexan. Changing from a glass window to one made of Lexan adds another step to the project. That process includes cutting the Lexan with a jigsaw in order to get the right shape. Although this added a step, the Lexan also eliminated the need for adding hinges to the rear window. The design of the rear panel was still kept the same for the sake of having the ability of changing the rear window to an original window in the future but, in the meantime, using a window made of Lexan decreased the budget by roughly $240. 

To simplify the process of making the cores for the side panels the original idea of using an insulation foam board was changed to using an expanding polyurethane foam. This required only having to cut the excess foam off. By using expanding foam, time was saved in having to shape the foam from a board.

In order to eliminate the rough finishes on the panels, Bondo was used to smooth out the finish. This is a time-consuming process of adding Bondo and sanding it down multiple times to achieve the desired finish.

The last issue with the panels was the alignment of the panels. Getting a mold off the original hardtop was a great idea to get a shell of the parts needed. The problem was that all the shells were not completed before a panel was completed. This brought up issues in that there were spots with alignment issues. To fix these issues, the foam cores had to be adjusted before the interior of panels were layed up. This added a significant amount of time to the project.

Overall, the design of the hardtop performed well and met the projects success criteria. As the project progressed, the project was modified in quite a few ways. Some of the design modifications that were made were the use of a soft top header bar, the decision of welding on nuts in the side frame(s) and adjusting the seams where the panels came together on the top panels.

By applying a previously designed part to be used, the time to design a bracket for the front hinges to be attached to was eliminated. A soft bar header bar provided a product that was easy to implement into the top front panel and provided an attachment point that would line up perfectly with the font of the jeep.

One method used to optimize the strength of the side panels so that they could handle the load requirement was by welding the nuts onto the frame made for the side panels. By doing so, the foam core structure would make the side panels even stronger. Welding nuts onto the frame eliminated the need to make an access to both sides of the frame. While the strength of the square tubing is designed to handle the 200 lb load that would be applied to the roof of the hardtop, the steel frame does little to support a side load if someone were to step on the panel in storage. By using a foam core on the side panels, the panels become as strong as the other panels and they would be able to handle a 200 lb side load.

To simplify the seam where the top front and top rear panel met, the seam was modified from having an overlapping section of a 1/2" on both panels to having one panel having a 1/8" thick protruding section and the other section having a 3/4" section that overlapped on top. This gave the ability to create a section with just fiberglass. By doing so, the panels would have a 1/8" gap that would be perfect for a rubber seal. This made the process of creating an overlapping section easier and was perfect for creating a water-tight seal.

One project modification that was made was welding on nuts onto the side panel frame for the bolts that secured the hardtop to the roof panels and the vehicle. The thought was that, by welding on the nuts, the design of the panels would be simplified, and the panels will not scratch the vehicle when the panels are getting installed. The issue that came up was that this made putting in the bolts hard. The area in the Jeep where the bolts had to go through gave little room to work with. This made locating the nuts a nuisance. To eliminate this issue, the decision was to use studs. That would allow the individual installing the panels to only need to install the nuts. While the studs could potentially scratch the paint on the vehicle, the realization that being careful took care of that issue. The time saved installing the panels was worth the risk. If another hardtop were to be made, welding in bolts would be done instead of welding on the nuts.

Another project modification that would simplify the cost and the ease of construction would be using pink insulation foam instead of the high-density polyurethane foam that was used on the construction of the top panels. The problem with the high-density polyurethane foam was that it is delicate to work with because it crumbles easily. The polyurethane foam has great structural properties, but after seeing another student using pink insulation foam for a different project, his test results indicated that the foam would have been structurally sound for the top panels. The reason the high-density foam was used was that testing has been done by the manufacturer to ensure its material properties. There was concern that the insulation foam properties could have anomalies in the uniformity of its density. For this project, making test samples and testing them to failure could have been done to ensure the pink foam would work. That would have made starting the panels easier, since the pink insulation can be found in any hardware store.

By testing for the requirements, a few small issues were brought to light. One issue during the waterproof test was that there was a leak in the rear top corners of the side panels. This indicated that a seal in the corners was necessary. The assumption that the panels did not need a seal in the corners were made initially. This mistake was easily fixed with some seal material. The next issue was that, when adapting the original windows to the side panels, the windows only had an 1/8” clearance between the window and the panels. This made for a tight fix. With this tight fit, the windows needed more caulk to ensure a good adhesion between the panel and the window. Even though the windows fit, the realization that the measurements should have been checked earlier was made. This would have decreased the cost of the project by $18. The last issue that came to light was that a few of the bolts had slight alignment issues that increased the time to assemble the panels. While a time requirement was not made, this issue could affect whether someone would want to assemble/disassemble the panels themselves. Overall, the hardtop performed well and fulfilled the requirements.