I finally got around to experimenting with electroforming a combustion
chamber. Attached is a picture of my first experimental results. The
results were as good as I could expect.
All told, it cost me about $300 of equipment, not counting a power
supply which I already had and a 3D printer for printing the PLA
mandrel. It could probably be done for a bit cheaper.
I 3D printed a PLA mandrel. I then primer painted it, sanded for
several cycles until I had a nice smooth surface. I used a commercially
available conductive paint based on nickel to make the mandrel
conductive.
I placed the painted mandrel in the solution and almost immediately
started seeing plating.
The process used was the acid copper based on copper sulfate and
sulfuric acid (with a commercial brightner). I kept the current rather
low (about 0.04 Amps/sqin) and let it run for about 10 hours to get
about 0.0025 inch thick plating.
Of course, I have a lot more work to establish the mechanical
properties of the results.
I'm currently working on making cooling channels into the chamber. It
has required a small CNC based rotary axis to plot the channel pattern
onto the plated mandrel. I'll be working on this chamber over the next
few weeks.
I think that this is a very promising technique for making combustion
chambers and tankage for small upper stages. It is actually quite cheap
and can be replicated easily.
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