tig welding tubing, fitting face perpendicular to tubing

[Spike2000]

looking for some existing fixturing or ideas on how to hold a very tight tolerance on butt welding a 4" fitting to 4" o.d. tubing with a perpendicular tolerance of .015"
we are tig welding and our current tolerance is .032" on this dimension, thank you in advance

 

[mfgenggear]

OP
Is this only one or or high volume.


Buy a tool cast plate large enough to hold assembly.
Buy soft angle plate.
Draw out the birds eye view of the layout
Obtain dimensions to assemble and weld
Assembly. Generally due to weld shrink and slight distortion it's generally best to fitup and weld inner assembly and cut and fit up flanges last. All angle flanges must be secure to the cast plate , socket head bolts or equivalent.
Mill out angle flanges with cradles to hold assembly during fitting and welding.
Drill out holes to bolt flanges when welding.
Angle flanges must be precision machined.
Faces perpendicular and square.

 

[Spike2000]

Thank you for the response, 2-3 pcs for prototype then production run quantities...100's of pcs

 

[EdStainless]

Are you using automated orbital welding?
If you are doing this by hand are you using a rotator to control the speed?
Are you welding in sections as opposed to 'all the way around in one shot?
If you really want to hold 0.015" your original fit will need to be <0.005" out.

 

[Spike2000]

semi auto welding, one shot
less than <.005" out....yikes

thank you

 

[mfgenggear]

OP
Actually welding fixture is for tacking , then weld .
It's critical to work from inside, then do the flanges last while it is restrained. Cut to fit up then tack. Then weld. While restrain.

 

[TugboatEng]

It may also be possible to weld it to a looser tolerance, then attach it to a fixture that holds it to the correct dimensions, and anneal/normalize it while in the fixture. I know of this process being used for cro-mo tube structures in aircraft.

 

[EdStainless]

Are you allowed to weld over tacks?
When I was doing high purity work we couldn't.

 

[mfgenggear]

It may also be possible to weld it to a looser tolerance, then attach it to a fixture that holds it to the correct dimensions, and anneal/normalize it while in the fixture. I know of this process being used for cro-mo tube structures in aircraft.

turbo
any time there is heat treat involved on finish parts is makes it worst.

 

[mfgenggear]

Are you allowed to weld over tacks?
When I was doing high purity work we couldn't.

ed
don't remember the specs but we had no issues as long as it passes NDT.

 

[TugboatEng]

To be more clear, the part gets attached to a fixture that holds it under stress in the correct position. It gets normalized in the fixture which leaves it with the correct dimensions. I know of a case where this technique was used on a radial airplane engine mount.

 

[dtimberlake]

Once upon a time we were asked to reface some used floating clutch disks from some vintage Ferrari. Maybe .2" thick or maybe less.
They were worn, and sort-of flat.
Each time .005" or so was gently wet ground off one face, the disk would distort to a new shape, so we stopped.

The owner took the disks off to some heat treater. Maybe BodyCote.
He brought the discs back pretty flat, and stress free, so it took very little grinding to re-surface the faces flat and parallel.
I still recall the owner saying the shop clamping the discs between two thick steel plates and tossing them in the oven.

Certainly "free range" heat treating, like welding = distortion.

And then there is heat straightening.

https://www.fhwa.dot.gov/bridge/steel/heat_guide.pdf

 

[TugboatEng]

I believe that is the company that did the radial engine mount.

 

[mfgenggear]

Once upon a time we were asked to reface some used floating clutch disks from some vintage Ferrari. Maybe .2" thick or maybe less.
They were worn, and sort-of flat.
Each time .005" or so was gently wet ground off one face, the disk would distort to a new shape, so we stopped.

The owner took the disks off to some heat treater. Maybe BodyCote.
He brought the discs back pretty flat, and stress free, so it took very little grinding to re-surface the faces flat and parallel.
I still recall the owner saying the shop clamping the discs between two thick steel plates and tossing them in the oven.

Certainly "free range" heat treating, like welding = distortion.

And then there is heat straightening.

https://www.fhwa.dot.gov/bridge/steel/heat_guide.pdf

It hard to say what they did. But generally reheat treating finished parts is a no go. However stress relieving is if the temperature is 50 degrees below the tempering temperature.

The reason the parts were warping because it was stress relieving causing it to warp.
And there must of been grain structure change.
Typically thick and thin sections heat unevenly.
Causing distortion. That is why Mar temper or Mar quench is used. The quenchen is higher temper generally above 400 degrees f.

 

[Tmoose]

The sliding surfaces of clutch components ( also brake rotors and even brake drums) can suffer severe localized heating and frictional wear.

https://www.v6z24.com/attachments/89-3400-z24-034-jpg.36543/

The late, great J. O. Almen wrote a wonderful article for Metal Progress in 1943 entitled "PEENED SURFACES IMPROVE ENDURANCE OF MACHINE PARTS" .

"Internal Stresses of the wrong kind are perhaps the most insidious of all fatigue hazards because we can seldom know their magnitude, or
the pattern in which they are distributed within the material, or even whether they are alike for all commercially identical machine parts. Internal
stresses may be the result of operating conditions such as occur in brake drums, clutch plates or other friction surfaces where the instantaneous
temperature in a thin layer is so great that the surface layer is stressed by thermal expansion beyond its yield point in compression. When the
source of heat is removed from such a part the heated surface layer is quenched by the adjacent cool metal and, under thermal contraction, it is
so severely stressed in tension that fractures occur. This is, of course, the same thing that happens in grinding unless great care is used."