How steel donuts are made?

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Hey guys, i was looking for exhaust headers pics, and i found this steel donuts for making tight radius exhaust runners, and i was just wondering how are they made.i guess they are made from two halves welded together because many of the websites that sell this donuts says "the inner seam requires finish welding after cut" but anyway i was wondering if there is some picture of the process.i made a simulation of what i think is the process for making one of this donuts XDif anyone have any real picture would be greatis just curiosity anyway.
Reply:this is really interesting, I have nothing to add but I will be watching this topic
Reply:Top example looks to be the easiest to stamp, weld and finish. Kinda hard to finish weld the inside of either one though. Just my noob 2 cents worth.
Reply:I suspect the parts are spun in two halves and then welded.  Look at this: http://www.hialeahmetalspinning.com/cover.html
Reply:looks like something somebody stole from area-51, OMG, the aliens lknow how to weld. i know thats where these exotic metals are coming from. i just knew it. the air-force are kidding anybody. especially us welders.
Reply:Here's a It is fascinating.
Reply:I want to learn how to do that... so bad.
Reply:wonderful, but in the case of donuts, i think the halves are made by metal press, or stamp.
Reply:Originally Posted by kommodorewonderful, but in the case of donuts, i think the halves are made by metal press, or stamp.
Reply:I also would imagine spinning, keeping material thickness uniform with stamping would be a nightmare and prolly involve multiple tools,Matt
Reply:Love that "how its made" metal spinning video.  I looked into what it would take to get a part (lightweight auto racing wheel rim halves...) fabricated from a local metal spinning shop, but it turns out that the tooling cost to make the center backing piece ("mandrel" maybe it was called) were pretty high, needing a fairly large production run to to justify it.  They did say they can make the form out of hardwood rather than metal, for a small production run, if the material to be formed is soft enough.  Anyhow pretty cool stuff.  Was really neat to see the video.I do still wonder about some of the details regarding how the steel donuts are made.  Can they spin .065" wall thickness stainless steel?  You can buy donuts in that material, it seems like it would take a lot of force to spin to me.  Are they really making them by welding two halves togeter?  There is an absence of visual weld seam around where the two pieces would be joined.  It would be interesting to see the inside of the donut, to see if there is any evidence of a weld joint around the OD.The neat thing about using steel donuts for fabricating automotive exhaust components is, you can get a really tight bend radius.  Centerline radius equal to tubing diameter is the common dimension of a metal donuts.  Usually for mandrel bent tubing, the centerline radius is larger than the diameter of the tubing.Last edited by jakeru; 10-30-2010 at 01:57 PM.
Reply:I also believe they are spun in two equal halfs then welded. I used some once, and the ID was not welded (as is the one in the bottom picture). Nice quality, and the thickness seemed very uniform. They can be purchased through Jegs or Summit Racing.