For the CWRUBotix MATE ROV competition team, our underwater drone has cameras that are critical to piloting and sometimes are used for computer vision tasks. 

We place the cameras at the center of a custom-made dome lens for the light to hit perpendicular to the surface and distort as little as possible. This lens is made using vacuum forming, where a heated plastic sheet is pulled onto a form via vacuum.

The previous vacuum form mold was 3D printed PLA that would melt after a few uses, required laborious manual sanding, had poor mold release. Lenses used to be difficult to make, require extensive post-processing, and had significant distortions. 

Process

I worked to address the mold issues within budget and timeline constraints:

• switched to higher temperature-resistant PETG filament used

• borrowed surface finish and accuracy from polished ball bearing for near-perfect dome quality

• used wax mold-release to protect the part and mold

• printed process reminders and documented process to ensure process repeatability

Results

The new mold design has allowed significantly improved optical quality and has continued to produce lenses without failure so far.