Week 4

The third print began yesterday for the phone case and was retrieved this morning. Frustratingly, the filament was loaded incorrectly, resulting in a print fail. Utilizing a printer outside the Innovation Studio is being considered, as the group will be more responsible for the success of its print and have liberty to adjust print settings. The print did, however, produce enough of the amplifying portion of the case to provide valuable insight to the internal structure of the case. The shape of the internal horn starts at the width of the default phone speaker, then tapers around the bend before opening wide at the throat. This is consistent with research performed, which suggests that compressing the cross section then widening it amplifies sound greater than just widening it. Testing has been delayed, as a complete case is necessary for sound amplification tests. The result of the failed print is shown below.

Third print (face)

Third print (rear)

CAD designing for the dock has begun. Since the function of the dock is dependent on the use of the case, printing will not begin for the dock until a functioning case is produced. The first CAD model for the dock is shown below. It features simple circular extrusions rather than elaborate horns, as the latter would have a high degree of printing difficulty.

Dock CAD model

Research continues in order to find mathematical models that justify the horn shape for the amplification of sound, but the relationship is not explained in a simple equation. Research has shown that the relationship uses many complex equations and concepts with long derivations and gross approximations (i.e. only 1-dimensional motion is considered). Research will continue to try to justify the model and provide objective evidence to contribute to the design process.

Week 3

The first print for the phone case began yesterday and was retrieved this morning. The print failed, interrupted while making the phone-bearing portion of the case, with many factors possibly responsible for this outcome. The case may have been set to print too thinly, resulting in the "spider webbing" effect that interrupted the print. This also could have been caused by an excessive overhang on the edge of the case, or the lack of support braces in the print. However, the printing technician indicated that the printer used has a reputation for spider webbing, and a higher quality printer may be able to complete the exact same print. Much of the case was completed before the failure, however, including the entire inside of the case that contains the amplifying horn. The print was cut in half to analyze the inside. Some complications inside the case were expected; because the concept of the horn requires an unobstructed pathway for sound waves, braces were omitted from the design. However, printing a hollow object without braces very often results in sagging; since the plastic is laid at melting temperature, the top portion of a print often caves in if no support is provided. Surprisingly, the hollow inside of the case was found to be perfectly smooth. This reveals that an essential component of the case design, the unimpeded hollow center, will not be as great a manufacturing obstacle as expected. The images below show the first print attempt, and the spider webbing that occurred at failure, as well as the inside of the case after being cut in half.

First print (rear)

First print (face)

Spider web that occurred during face manufacture

Inside view of hollow portion, no sagging evident

The CAD model of the case was redesigned with chamfered edges to increase the chances of a successful print. Only the top "half" of the case, which caused the failure in the first print, was printed in the second trial to save printer plastic. The second model printed successfully, but is too small for the phone. However, the alterations made at the edges of the case proved to result in a successful print, so the model will likely just need to be enlarged to fit the phone. Once the phone-holding portion of the case is perfected, it will be able to be combined with the sound-amplifying portion, and sound amplification tests will be performed. The next case design is expected to be complete and printed by Tuesday. If the case fits, another prototype will be printed with the sound-amplifying portion, and sound enhancement tests will begin immediately. The images below show the second print. Note the difference in the shapes of the edges in the first and second print; the images above show straight edges that likely contributed to printer failure, while the edges in the images below are rounded and easier for the printer to create.

Second print (rear)

Second print (angled face)

Second print (angled face)

Week 2

After examining existing phone case amplifiers on the market, Week 1 models of the case were modified. Most models featured a design in which the sound from the iPhone speaker was channeled through a funnel of increasing girth before opening to release the sound, as in Figure 1. 

Source: https://images-na.ssl-images-amazon.com/images/I/71-oe7QD9eL._SL1500_.jpg

Figure 1

Existing market product

Though no mathematical equation has been found to explain the relationship between shape and sound intensity, it became clear that a funneling "horn" shape was an accepted model for sound magnification. Further research will be conducted to find mathematical evidence to support this theory and optimize the space. An equation was found, however, to explain a material's ability to transfer sound. The speed of sound, c, through a material can be expressed with Hook's Law as the square root of the quotient of bulk modulus elasticity, E, and density, ρ, in the following equation:

c = (E/ρ)^1/2

Thus, by maximizing bulk modulus elasticity (a material's ability to withstand volume change under pressure) and minimizing density, a greater sound projection can be achieved. Materials research conducted revealed that aluminum is a quintessential material for sound transfer, as it has a high E/ρ ratio. Since the phone case will be 3D printed, an aluminum-infused PLA was found online that would be compatible with the printers in the innovation studio. A roll with enough PLA to easily print a case and dock can be purchased for 30 dollars. This material would be ideal for the case and dock, but special clearances will have to be obtained to use it in the lab's printers. Also, aluminum's low specific heat may be problematic, as the phone may easily overheat in its case. A rigid metal would also likely be a poor shock absorber, endangering the phone in the event of a drop. The construction of a case made of multiple materials will be considered for improved shock absorbance and heat transfer.

CAD for the case has begun. The first printed model of the phone case is expected by Monday, April 16. A 2D CAD drawing of the phone case is shown in Figure 2.

Figure 2

2D CAD drawing

Week 1

In the first week of class, groups formed and chose a design topic. A hybrid topic incorporating elements of the 3D printing and speaker stand amplifier was chosen. This topic was selected in part due to the CAD experience of some group members, as well as the availability of materials. The objective of the design is to manufacture a phone case fitted to a standard iPhone 7/8 that will amplify the sound from the factory speaker. A separate dock will also be designed, in which the phone and case can be placed to further amplify the sound. The case will be designed to fit comfortably in the hand and pocket of the user. Materials research will be performed to determine what materials are feasible in the construction of the case. Ideally, a frame will be manufactured using a 3D printer, and the case will be filled in with a shock/heat resistant material. Research will also be performed to ensure the case does not trap heat, causing overheating. The material and shape of the case will be manipulated to avoid this issue. Notebook sketches were made depicting possible designs of the case, featuring a channel that begins at the speaker of the phone and widens as it runs the partial length of the phone. Figures 1 and 2 show first drafts of the case and dock, respectively.

                  Figure 1                                                                                           Figure 2

Current case concept

Current dock concept