The CAD files and ROS software and Matlab plot data is available here
Materials: Translucent Sorta Clear 18 Silicone Rubber (Part A & Part B), Techsil Clear Silicone Gel, colorant (HP Printer Ink), reflective tape
Equipment: 3D Printer, Vacuum Pump, UV Machine
Tools: Digital Scale, Tweezers, Normal Tape, Bolts, Disposable Cups (translucent and plastic)
Safety Precautions: Do not smell the products especially colorant. Always check if the equipment has any malfunctioning. Wear disposable gloves. Do not apply too much heat (>45C) in the UV machine as 3D printed parts can get deformed.
Tips: The cups are reusable after the silicone inside is dried: put it in the UV oven with the molds for faster drying. Then just remove the silicone easily. Make only the needed amount of silicone in every step as it will be solidified until the next step, which means it will be wasted. Pour the silicone mix in circles of a spiral to avoid bubbles’ reoccurrence
- 3D printing molds
(i) Design mold parts and draw their 3D models in SolidWorks™ or some other CAD tool according to the specification.
(ii) Print the mold parts in a 3D printer. For this sensor printer with better precision is used as size parameters are tiny.
- Making the silicone sensor
(i) Black base layer. Mix 10A:1B amount of Sorta Clear 18 in a cup. The needed mass is somewhere around 3-7 g depending on the material of the cup used. Add black colorant and mix well. Get rid of the air bubbles in the mixed mass using a Vacuum Pump. After checking for any bubbles left, pour the degassed mix into the base mold, make sure to clean edges, if the mix is spilled. Now the mold is put in the UV oven at a temperature of 35-45 C˚: it is leveled nicely, so that silicone will be spread evenly. After 15 mins, take it out if it is completely solidified/dry, otherwise, leave for more.
(ii) Pattern layer. First, we stick reflective tape on the black base layer. The diameter should be the same as the inner wall mold’s internal diameter, which is less than the base. Because the tape should not be in between the base and protective layer, otherwise, the sensor will be easily torn apart as the tape unsticks. Fix the pattern mold on top of the reflective tape layer
using bolts. Make a little amount of Sorta Clear 18 silicone mix as in part (i) but this time use red color. Do not forget to remove bubbles. Pour the red silicone and put it in the oven. Remove the pattern mold and stick tape on the red pattern to keep it clean from the yellow silicone. Once taped, fix the empty pattern mold and pour yellow parts. Send to the oven.
(iii) Techsil Layer. Take off the empty pattern mold. Then, remove the tapes on the red parts carefully. Fix the inner wall mold and the 2mm internal ring. Mix equal A & B parts of Techsil and remove the air bubbles. Pour the Techsil mix, so that it does not exceed the base of the internal ring. Remove the internal ring. Put it in the oven.
(iv) Transparent top Layer. Pour transparent Sorta Clear 18 mix until the inner wall mold is full but do does not exceed the mold height. Send it to the oven.
(v) Black Protective layer. Remove the inner wall mold. Put some tape on the top transparent layer. Fix the outer wall mold. Prepare Sorta Clear 18 mix with a black colorant added. Pour the mix into the gap between the silicone layers and outer wall mold. Put it in the oven. Then, take off the outer wall mold and check if the black protective layer completely covered the sides. Unstick the tape carefully.