Goal: Mold and cast a snap-fit electronics case Software: Fusion 360, Mods (computes machine routes)Hardware: Roland SRM20 (milling)Materials: Machineable wax, silicone, resinPrior Experience: NoneNew Methods:
Mold design, mold milling, casting, injection
makes for a pretty picture, but it doesn't snap-fit Details:
Testing molding and casting as an alternative to 3D printing for producing snap-fit electronics cases
Step 1: CAD model of the electronics case (designed previously)
Step 2: CAD model your silicone mold (a negative of the case)
The process will depend on your particular design
In this example, the case has a top and bottom half
Producing 1 half requires 2 molds sandwiched together, designed here as follows:
Parameterize a buffer defining the thickness of your silicone walls (as depicted: 6mm)
Sketch a rectangle that outlines the case shape
Enlarge the rectangle to encompass the buffer
Starting from a buffer's distance below the model...
Extrude the rectangle to a midpoint on the model
Use "Combine" method to cut the 3D model's shape out of the extruded block
Trim and delete extra pieces as necessary
Do the same for the other half, but start from a buffers distance above the model, extruding to the same midpoint
It is good practice to add registration points--the bumps/divets in the corners--to help align the top/bottom molds
In this case, I added them, but they were too small to make with the milling bit that used
After doing this for both case halves (4 molds total)...
Step 3: CAD model the wax block (a negative of the silicone molds)
Model a block of the same dimensions as the physical wax block
Equally space the silicone molds along the block
Use "Combine" method to cut the molds out of the wax block
Step 4: Mill your wax block (see pcb milling for more general details on the process)
Use Mods to calculate the milling routes
In this case, I'm using the Roland SRM-20 with a 1/8" end mill
Milling the wax block requires two passes...
A low-res pass to remove large amounts of material
A high-res pass to smooth the surfaces and add high res features: mods program "mill 3D stl"
For low-res, I used mods program "mill 2.5D stl" (stepover between adjacent passes set to 0.5 the bit's diameter)
For high-res, I used mods program "mill 3D stl" with 'yz' pass only (stepover set to 0.125 the bit's diameter)
Step 5: Pour the silicone!
For silcone product, I used "OOMOO 25" by Smooth-On
Whatever your product of choice: note safety information and follow instructions
After your mold has finished curing, remove it carefully
If you did't model holes for pouring/injecting your resin...
A standard fabric hole puncher will do the trick so long as your resin is thin enough
Assuming your silicone molds are in good order...
Step 6: Pour the resin!
For resin product, I used "ONYX FAST" by Smooth-On
Whatever your product of choice: note safety information and follow instructions
In this case, I used a fume hood and gloves for protection, because urethane can be dangerous for both airborne and skin contact
To inject, I used a large plastic syringe and pressed it into one of the holes until resin pushed out of the other two
This was messy--not an elegant moment
Didn't get on film, as it was difficult to coordinate with the safety precautions involved (gloves, fume hood, etc)
Notes from experience with the process and final result:
The final case does not snap together like my 3D printed snap-fit electronics case
Poor fit is primarily due to rounded edges produced by the mill bit, which could be overcome
Tuning the process might be worth it in some situations, as the resulting plastic of a quality that feels more professional than 3D prints
However, I would not recomzmend casting and molding for small scale, basic electronics case production
The process is longer, more complicated, involves more safety hazards, and has more opportunities for error
Files: [next week] 