Getting in focus

This week, we made many changes to our design for manufacturing and design-related reasons. We finished machining 3 of the 4 molds for injection molding, created a plan for the design of our magnetic photo piece, printed on plastic and successfully thermoformed the camera lens, and tested injection molding for two of our pieces (including checking the snap fit on the pegs). Things seem to be in good shape! Check out our progress sheet here. 

Machining

At this point, machining hurdles are somewhat expected — but it seemed like we ran into many this week! The CAM for the camera front pieces (both top and bottom) proved difficult for two main reasons:

(1) For the camera bottom piece, it was nearly impossible to generate a tool path that successfully removed enough material for the snap fit of our very small magnet. After trying horizontals, pencils, and several other finishing paths, we finally found the settings to sufficiently clean up the magnet hole (with a scallop, followed by a horizontal).

(2) The top piece itself was very small and non-circular, so designing the CAM to get as sharp corners as possible without taking hours was a challenge. 

Ultimately, we were able to tackle both of these issues! For the top piece (right), we faced our first set of very long tool paths, but ended with a smooth finished scallop and extremely tight corners, as desired. We ran into a major issue with tool offsets, which unfortunately set us back a little — the offsets were over an inch off in the mill for multiple tools, and therefore we ruined a nearly-completed cavity mold and 2 attempts at the core mold before correctly diagnosing the problem. Overall, however, once we realized was wrong, we finished the difficult mold. 


Our next major task is the photo mold. For this, we want to:

• Position 3-5 photos on the same mold to speed up our manufacturing rate. Ideally, we will have 5, but we need to research a bit more into injection molding parameters to make sure this is feasible and that all 5 photos will pack correctly.
• Insert a metal key into the photo, and design the mold with a magnet for registration to correctly locate the key. This week, we decided on the type of key we would use (pictured right). Essentially, once the part is completed, the plastic will rush around most of the key (since it is raised) and only two small circles will be visible. We'll need to order the smaller diameter magnets to be inserted into our mold as well as the keys themselves. 

• Since the front of the camera is actually distant from the photo (compared to the body), we decided to move the magnet location onto the body itself. Since we're already adding ribs to the body molds to prevent the previously noticed heat sink, we decided to also create an indentation to press fit the magnets into the body itself for better alignment with the photo. A picture of the final rib orientation is shown below. Though we originally opted for more visually appealing rib styles, they were extremely difficult to machine given the spacing and size of the feature, and in the few instances when possible, had a lengthy machining time of multiple hours. Therefore we chose to have the much simpler press fit and rails combo. Since this is an internal feature, we chose to simplify the geometry as much as was practical. 

In light of these changes, we'll need to tweak the molds slightly. We'll simply need to take slightly more off of the bottom front mold (to remove the magnet indentation), but we'll need to re-do the body core mold in order to create the ribs. The CAD and CAM for this is finished, so we're hoping to machine and have these done early in the week. We're currently working on the CAD and CAM for the photo molds.

Thermoforming

We also successfully printed on plastic and thermoformed the dome that will serve as our camera lens! We learned how to set up the Miyaki printer as well as the file on Adobe Illustrator. At the moment, we've included a center dot and vertical stripes to the left of the lens circle to continue testing some of the registration. We are iterating currently so that we don't have to worry as much about lining up the printed stripes manually. Instead, we're extending the vertical stripes above the lens circle since lining it up in the thermoform machine can be a bit difficult. We also decided that we are fine with the stripes being a few degrees off of vertical since it is a tiny and barely noticeably feature — more important to us is having clearly defining stripes (rather than a concentric pattern) that will identify our camera as a polaroid. 

Injection Molding & Assembling! 

After completing the camera bottom molds, we were able to test injection molding for it as well! We started to injection mold on Monday. We hadn't made the holes in the core mold small enough for a press fit, so we used lock tight to press the dowel pins in — which worked! Here are some pictures of our injection molded piece snapping into our body. The snap fit feels snug. We tested it by dropping it on a (carpeted) floor, and the components stayed together. This week we'll also do some measurements to understanding shrinkage and identify how well the parts are fitting into our tolerances. 

         

  

For injection molding, we are still learning and experimenting with shot size, cooling time, and packing pressures. Currently, we've started the process by adjusting the shot size until we're happy. Then we plan to move on and adjust the other parameters. To keep track of the parameters we test, we've created a google document of the test runs we complete. We hope to use this in the upcoming week to catalog our injection molding attempts and have a clear picture of how to optimize the settings!

We're pretty excited that the pegs fit, and we're really excited to see our designs come to life.