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I just came across this sculpture and am really interested in knowing how it could even be done?

I thought that they put 2 hemispheres together but there isn’t any weld lines- is there any other methods that could make it please?

Source:https://www.davidharber.co.uk/sculpture/mantle.htm

enter image description here

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  • $\begingroup$ why don't you simply ask the artist? $\endgroup$
    – jsotola
    Nov 19, 2023 at 6:50

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On the video on David Harber - mantle at 15 s in you can see this internal shot.

enter image description here

It appears to me that 1, 2 and 3 are continuous connections but 4 is overlapped and indicates an extremely neat weld.

If I had to come up with a method of manufacture I would be looking at draw forming hemispherical sheets from flat stock - either mechanically or by fluid - and laser or water cutting the hemispheres. It might make sense to make the full sphere in more than two pieces to avoid having to cut too close to the "equator" and to allow some overlap.

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It looks like you've already received a pretty solid answer on how this specific ball was made (and I agree that it looks like it was welded).

For what it's worth, there are a few cases of hollow steel balls being made without welding though. One is used to make hollow ball bearings that are hollow to reduce mass. There have been hollow ball bearings for quite a while, but conventionally they've been made as two hemispheres, welded together, then the outside polished so there was no visible weld mark.

I have, however, read about a more recent method that's especially useful for small bearings (that are hard to weld together) or bearings with really thin walls to keep mass to a bare minimum.

Caveat: I read about this a while ago, and I'm going from memory, so I may get a few of the details wrong.

In this method they start with a plastic ball approximately the intended interior diameter (seems like some kind of polystyrene, but I don't remember for sure). They spray metal powder around the outside to a little more than the desired thickness.

Then they heat it enough that that 1) the metal just starts to sinter (enough to stay one piece, anyway), and 2) the polystyrene evaporates and dissipates through the still porous layer of metal powder.

When the polystyrene is gone, they heat the metal up more (and I think put it under pressure in a mold) to fully sinter the metal so it's a single, solid piece of metal. As I recall, they were using these are ball bearings, so after the metal was sintered, they polished them about like you would normal ball bearings (with the proviso that the ones with thinner walls can't withstand a lot of pressure).

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