I got to tour the Getzen/Edwards plant at Elkhorn Wi while picking up my new trombone. The plant produces Trombones and Trumpets. If you are ever in the neighborhood, I encourage you to schedule a visit to sample their horns and see the plant. These instruments are very much hand crafted.
She assembles all trombone slides
Tapered dies for various tubing
As I recall, what they do is rough bend tubing bends and then use these wooden dies with hydraulically driven balls to expand the bends to final diameter.
All of these instruments start from a roll of brass.
The character and alloy of the brass I suspect are trade secrets.
There are two ways to form a trombone bell. One is to make a ring and then roll it out over a die. This is the easier method, however the metal gets thinner and thinner as the diameter gets larger which affects the performance of the bell. Getzen makes both types.
Edwards/Getzen does it the hard way, by forming it from flat sheet, brazing it into a tube and rolling and forming into a bell. Here are some of the patterns they use for bells.
Then a craftsman hammers it into a tube with a seam that can be brazed.
Once the bell is assembled, it is formed over a rotary mandrel.
Assembled bell sections awaiting buffing and lacquering.
Buffing and final assembly.
Completed bells ready for shipment.
There were two appreciations that I had. First was the sheer amount of high quality hand labor needed to build one of these instruments.
The second was the almost infinite number of ways they can color the sound. Degrees of freedom range from the metal, taper, flame tempering, tube radius, resonant mass etc.
Here is their website, https://www.edwards-instruments.com/