this is part 3 and the final video in this series, I am tig welding aluminum again on an aluminum intake manifold project.
What is backstep welding?
Is it better to use a small cup to reach tight joints or is it better to use a big cup and extend the electrode?
Watch the video and find out.
I got a question asking if I would show exactly how the cold bead works followed by a penetration pass.
First of all, its best to take the time to get a good fit up with no gap.
secondly, its not a perfect world.
Ever had someone bring you a part to weld where they did all the prep work?
Sometimes you just have to deal with some gaps.
So I tried to show a technique for dealing with gaps in aluminum.
I learned a long time ago that if you seal gaps in aluminum sheet metal with a very small cold beads...and then let the part cool...that you can go back over it using enough heat to fully penetrate without any issues.
Its hard to get even smooth penetration on the back side of aluminum when there is a gap...even if you use an argon purge. (and I was not purging this part)
But having that cold bead there to conduct heat evenly between the 2 parts being welded allows heat to flow evenly and allows for pretty smooth penetration.
Of course the best practice is to take care not to have gaps in the first place.
But like I mentioned earlier...sometimes someone brings you a part to be welded that will have some gaps either because the cuts are not accurate, or maybe they even tacked welded the part for you.
You either have to just say no and turn down the work, or cut the part back apart and improve the fit...
or make a judgement call and go ahead and weld the thing.
In the backstep welding technique, Bead segments progress in one direction but the overall direction of weld progression is in the opposite direction....the general progression of welding may be from left to right, but each bead segment is deposited from right to left.
Backstep welding can help prevent distortion.
but on certain alloys like aluminum, care must be taken on each stop to make sure complete penetration is obtained.
Also...a bit of extra filler metal should be added while tapering amperage to avoid crater cracks.