distortion problem

[thestig]

hi all. ive been fabricating aluminium trays to go back to back on steel frames but been having problems getting a smooth finish. the ally is 2.5mm thick and ive been tig welding them on about 70-75 amps then dressing the welds with a 4.5 inch 60 grain flapdisc then a 120 grain disc and smothing off with a palm sander first with p80 paper then p360 wet and dry. they look good until they come out of the spray room. they have a rippling effect where i tacked the top in place before doing the full run. any sugestions would be appreciated.

 

[Hitch]

Thats quite a lot of weld on 2.5mm sheet...The first thing i'd try would be weld a bit at a time, rather than going for the full run.
Get the two part edges to fit as close as possible before you attempt to tack.


Its difficult to see the ripple in the pics.

You could try using a sander with a larger pad, that would even some out a bit. DA sanders are pretty good. You could use a light coat of paint to show any ripples as you sand, a bit of carfull dressing and a bit more sander work should sort it out.

 

[thestig]

yeah i tried tacking with about 5 inch gaps then one inch runs between them and carried on doing this til it was fully welded. i ended up with more smaller ripples! like you say mate, more time on the sanding should do it. the ripples are difficult to see unless the lights are shining on it.

 

[Weldingartisan]

As it only appears to be signage, how about car body filler and a DA sander? Could be a lot quicker than sequence welding/cooling. W/A

 

[Hitch]

Just had another thought, no idea if it would work or not..

Maybe someone with a bit more ally experience than me might have an idea, how about preheating the edges slightly prior to tacking....

 

[thestig]

good idea. maybe preheating before each run?

 

[Paul.]

You need to keep the heat down, not put more in, a close fitting copper chill behind the tacks to draw the heat away from the sheet would help, or jig it up so that minimal tacking is needed, when welding I'd turn the current up a bit, weld downhill and move faster, its cleaned off so appearance isn't important,

 

[Hitch]

Ignore that idea then!

The thinking was to add a little bit of heat, so when you tack up, it doesnt change in such a small area, resulting in more ripples, but shallower andeasier to sand out.

I guess not.

 

[Paul.]

A wet cloth to quench the tacks and limit the spread of the heat will help as well

 

[thestig]

cheers for the advice, look at the similar threads section at the bottom of this page paul, cooling welds minimising distortion. il try your cooling method first and let you know.