Pressure-washer Hydroforming Pt2 | Aluminium Nose Cone

Belly Tank Lakester project Ep35. Attempting to make a nosecone by hydroforming welded aluminium barrel shape (see previous episode).
Previous episode, welding up the approximate shape needed:
• Hydroforming a nosecon...
Outcome:
It partly worked. It is a little bit more rounded off than before. First 2 attempts limited by leaks and on the 3rd attempt we just went for it and the metal in the centre eventually ruptured next to my seam weld.
Materials:
If you want to see the parts and fittings I used to make this all go together I have discussed these from 08:00 onwards.
Analysis:
The way steel stretches versus aluminium is discussed in the video. Steel stretches until it reaches a limit point above which a lot more force has to be applied to stretch it further (until it eventually breaks). This limit point is not there for aluminium, once it starts to stretch it will continue to until it eventually breaks. In practice this means the weakest area, in my case next to the weld, perhaps due to it being heat annealed by nearby welding, will stretch first while other areas have not started to stretch yet, and then fail at that point.
My options now - comments invited.
1) It is slightly more rounded off than it was originally so now I cut it into upper and lower nosecone sections, smooth down the welds and English wheel it to finish off the shaping.
2) I patch the ruptured area, anneal the whole thing using a blowtorch to make the metal softer and have one more try at hydroforming it. It may still just blow at the point wherever the metal is softest but may be worth trying even so.
It was an interesting experiment anyway!

[@ConnorHolland]

Thank you for sharing your results, I would have expected to see more movement before rupturing, but I am used to 1mm mild steel. I imagine that aluminium gets brittle after welding, so annealing the whole thing before another attempt would be worth trying. I find this project particularly interesting as I love the design of open wheel cars, and hope that one day I can make my own electric version with a fully inflated metal body

[@XenonJohnD]

I did think of making my whole belly tank using hydroforming but I chickened out! The amount of water would have been 600 gallons - ish and it probably would have crumpled under its own weight when the pressure was released, before water was drained out. You could dig out a half-tank shape in the garden and line it with sand to stop that happing maybe.

[@ConnorHolland]

@@XenonJohnD For this project I think the English wheel is better for precision and control, to match a specific template or drawing. For a fully hydroformed car it would be good to do some scale models beforehand, make the body first and adapt all the other components to fit the result. Digging a trench is a good idea, as the water would likely weigh a ton or more and you don't want that rolling around!

[@stephengent9974]

I think the stepped inflation was work hardening the welds, so eventually the metal split

[@runcycleskixc]

Would annealing aluminum work? Or using a different Al alloy? Or both?

[@XenonJohnD]

I did try annealing it on a later attempt. I think it is to do with the fact that once it starts to stretch it keeps going whereas with steel it stretches so far then reaches a limit after which a lot more force is required to stretch it further, after which it then ruptures. This gives the other areas more time to catch up. With aluminium I think once one area starts to go then that will become the weakest point very quickly in terms of the point of rupture.

[@runcycleskixc]

@@XenonJohnD Thank you! It sounds like Aluminium (at least this kind) is more brittle than steel. There might be more malleable Al alloys, but they also might be less corrosion-resistant.